TECHNICAL FIELD 
       [0001]    The present invention relates to a drive device which drives a fuel injection device of an internal combustion engine. 
       BACKGROUND ART 
       [0002]    Generally, in order to promptly switch a valve closed state to a valve opened state, a drive circuit of an electromagnetic fuel injection device performs a control of applying a high voltage from a high voltage source to a coil in response to an output of an injection pulse to rapidly raise a current of the coil. Next, a control is performed in which a needle is separated from a valve seat to move toward a fixed core and the applied voltage is changed to a low voltage so that a constant current is supplied to the coil. When the supply of the current to the coil is stopped after the needle collides with the core, the valve opening operation of the needle is delayed and hence a controllable injection amount is limited. Thus, a control is required in which the supply of the current to the coil is stopped before the needle collides with the fixed core and a valve body is controlled in a so-called half-lift condition in which the needle and the valve body move according to a parabolic motion. 
         [0003]    As a control method in the condition in which the valve body is driven in a half-lift state, a method disclosed in PTL 1 is particularly known. PTL 1 discloses a method of calculating an integrated value of a drive current flowing in a coil driving a fuel injection valve and calculating an inductance of the driving coil in consideration of a direct current superposition characteristic of the driving coil based on the integrated value. Accordingly, since the inductance is calculated with high accuracy, a lift amount can be highly accurately estimated by estimating the lift amount of the valve body based on the inductance. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: JP 2013-108422 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    When the injection pulse is input, the drive device for the fuel injection device first applies the voltage of the high voltage source to the coil to quickly raise the current and rapidly generates a magnetic flux in the magnetic circuit. If a boost voltage VH is applied until the valve body reaches the fixed core, a magnetic attraction force acting on the needle increases and thus the gradient of the displacement amount of the valve body increases. As a result, in the half-lift condition which is an operation in which the valve body does not contact the fixed core, the gradients of the injection pulse width and the injection amount increase and the injection amount change amount increases with respect to a change in injection pulse width. Accordingly, there is a case in which the accuracy of the injection amount is degraded due to the limitation of the control resolution of the drive device. Further, when the magnetic attraction force acting on the needle is large, the needle collides with the fixed core in a condition in which the speed of the valve body is high. For this reason, the needle bounds due to a repelling force caused by the collision of the needle and thus the valve body also bounds. As a result, since a relation between the injection pulse and the injection amount is not linear in a range in which the valve body bounds, there is a case in which the control accuracy of the injection amount is degraded and the PN (Particulate Number) increases. 
         [0006]    An object of the invention is to improve accuracy of an injection amount in a half-lift state by stabilizing a behavior of a valve body in the half-lift state and decreasing gradients of an injection pulse width and an injection amount and to ensure continuity of an injection amount in a range in which a needle in the half-lift state collides with a fixed core by reducing abound of the valve body caused by the collision of the needle with the fixed core. 
       Solution to Problem 
       [0007]    In order to solve the above-described problems, a drive device of the invention controls a valve body so that the valve body reaches a height position lower than a maximum height position by decreasing a driving current flowing to a coil from a maximum current to a first drive current lower than the maximum current before the valve body reaches the maximum height position. 
       Advantageous Effects of Invention 
       [0008]    According to the invention, it is possible to provide a drive device capable of reducing a controllable minimum injection amount by stabilizing a behavior of a valve body and decreasing gradients of an injection pulse width and an injection amount even when the valve body is controlled at a position lower than a maximum height position. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram showing a case where a fuel injection device, a pressure sensor, a drive device, and an ECU (Engine Control Unit) according to a first embodiment are mounted on an in-cylinder direct injection engine. 
           [0010]      FIG. 2  is a longitudinal cross-sectional view of the fuel injection device according to the first embodiment of the invention and is a diagram showing a configuration of a drive circuit and an engine control unit (ECU) connected to the fuel injection device. 
           [0011]      FIG. 3  is a diagram showing an enlarged cross-sectional view of a structure of a driving unit of the fuel injection device according to the first embodiment of the invention. 
           [0012]      FIG. 4  is a diagram showing a relation of a general injection pulse for driving the fuel injection device, a drive voltage and a drive current supplied to the fuel injection device, and a valve body displacement amount in time. 
           [0013]      FIG. 5  is a diagram showing a detail of the ECU (Engine Control Unit) and the drive device of the fuel injection device according to the first embodiment of the invention. 
           [0014]      FIG. 6  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a timing of a switching element of the fuel injection device, a voltage across coils, and a behavior of a valve body and a needle in time according to the first embodiment of the invention. 
           [0015]      FIG. 7  is a diagram showing a relation of an injection pulse and an injection amount according to the first embodiment. 
           [0016]      FIG. 8  is a diagram showing a relation of an injection pulse, a drive current supplied to a fuel injection device, a timing of a switching element of the fuel injection device, a voltage across terminals of a coil, and a behavior of a valve body and a needle in time according to a second embodiment. 
           [0017]      FIG. 9  is a diagram showing an enlarged cross-sectional view of a structure of a driving unit of a fuel injection device according to a third embodiment of the invention. 
           [0018]      FIG. 10  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a timing of a switching element of the fuel injection device, a voltage across terminals of a coil, and a behavior of a valve body and a needle in time according to the third embodiment of the invention. 
           [0019]      FIG. 11  is an enlarged cross-sectional view showing a structure of a driving unit of a fuel injection device according to a fourth embodiment of the invention. 
           [0020]      FIG. 12  is a diagram showing a relation of a voltage across terminals, a drive current, a first order differential value of the current, a second order differential value of the current, and a valve body displacement amount in time in three fuel injection devices having different valve opening start and completion timings in a condition in which the valve body according to the fourth embodiment of the invention reaches a maximum opening degree. 
           [0021]      FIG. 13  is a diagram showing a relation of an injection pulse, a drive current supplied to a fuel injection device, a timing of a switching element of the fuel injection device, a voltage across terminals of a coil, and a behavior of a valve body and a needle in time according to a fifth embodiment of the invention. 
           [0022]      FIG. 14  is a diagram showing a relation of an injection pulse, a drive current supplied to a fuel injection device, a voltage across terminals of a coil, and a behavior of a valve body and a needle in time according to a sixth embodiment of the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0023]    Hereinafter, embodiments of the invention will be described with reference to the drawings. 
       First Embodiment 
       [0024]    Hereinafter, a fuel injection system including a fuel injection device and a drive device according to the invention will be described with reference to  FIGS. 1 to 7 . 
         [0025]    First, a configuration of the fuel injection system will be described with reference to  FIG. 1 . Fuel injection devices  101 A to  101 D are respectively installed in cylinders so that fuel is directly sprayed from injection holes to a combustion chamber  107 . The fuel is pressurized by a fuel pump  106 , is sent to a fuel pipe  105 , and is delivered to the fuel injection devices  101 A to  101 D. An ejection amount from the fuel pump  106  is controlled so that a fuel pressure becomes a predetermined pressure as a target value based on information obtained by a pressure sensor  102 . 
         [0026]    The injection of the fuel from the fuel injection devices  101 A to  101 D is controlled by a width of an injection pulse sent from an engine control unit (ECU)  104 . The injection pulse is input to a drive circuit  103  of the fuel injection device. Then, the drive circuit  103  determines a drive current waveform based on an instruction from the ECU  104  and supplies a drive current waveform to the fuel injection devices  101 A to  101 D based on the injection pulse. Additionally, the drive circuit  103  is mounted as a component or a substrate integrated with the ECU  104  and an integrated device thereof is referred to as a drive device  150 . 
         [0027]      FIG. 2  is a longitudinal cross-sectional view of the fuel injection device and is a diagram showing an example of a configuration of the ECU  104  and the drive circuit  103  for driving the fuel injection device. Additionally, in  FIG. 2 , the same reference numerals will be given to the same components as those of  FIG. 1  and the description thereof will be omitted. The ECU  104  receives a signal indicating an engine state from various sensors and calculates an injection pulse width or an injection timing for controlling an injection amount from the fuel injection device in response to an operation condition of an internal combustion engine. The injection pulse which is output from the ECU  104  is input to the drive circuit  103  of the fuel injection device via a signal line  110 . The drive circuit  103  supplies a current by controlling a voltage applied to a solenoid  205 . The ECU  109  communicates with the drive circuit  103  via a communication line  111  and can change a setting value of a driving time or a drive current generated by the drive circuit  103  based on an operation condition or a pressure of fuel supplied to the fuel injection device. 
         [0028]    Next, a configuration and an operation of the fuel injection device will be described with reference to a longitudinal cross-sectional view of the fuel injection device of  FIG. 2  and an enlarged cross-sectional view in the vicinity of a needle  202  and a valve body  214  of  FIG. 3 . The fuel injection device shown in  FIGS. 2 and 3  is a normally closed electromagnetic fuel injection device. Here, in a state where a current is not supplied to the solenoid (the coil)  205 , the valve body  214  is urged in the valve closing direction by a first spring  210  so that the valve body  214  contacts a valve seat  218  to close the valve. 
         [0029]    An upper end surface  302 A of the needle  202  is provided with a concave portion  302 C which is formed to be directed toward the lower end surface  302 B. A lower surface side of an intermediate member  220  provided inside the concave portion  302 C is provided with a concave portion  333 A which is directed upward. The concave portion  333 A has a diameter (an inner diameter) and a depth in which a stepped portion  329  of a head portion  214 A is received therein. That is, the diameter (the inner diameter) of the concave portion  333 A is larger than the diameter (the outer diameter) of the stepped portion  329  and the depth dimension of the concave portion  333 A is larger than the dimension between the upper end surface and the lower end surface of the stepped portion  329 . The bottom portion of the concave portion  333 A is provided with a penetration hole  333 B in which a protrusion portion  131  of the head portion  214 A penetrates. A third spring  234  is held between the intermediate member  220  and a cap  232  and an upper end surface  320 C of the intermediate member  220  forms a spring seat which contacts one end portion of the third spring  234 . The third spring  234  urges the needle  202  from a fixed core  207  in the valve closing direction. 
         [0030]    The upper end portion of the cap  232  located above the intermediate member  220  is provided with a flange portion  332 A which protrudes in the radial direction and a spring seat which contacts the other end portion of the third spring  234  is formed at the lower end surface of the flange portion  332 A. A cylindrical portion  332 C is formed downward from the lower end surface of the flange portion  332 A of the cap  232  and the upper portion of the valve body  214  is fixed to the cylindrical portion  332 C by press-inserting. 
         [0031]    Since the cap  232  and the intermediate member  220  respectively form the spring seat of the third spring  234 , the diameter (the inner diameter) of the penetration hole  333 B of the intermediate member  220  is smaller than the diameter (the outer diameter) of the flange portion  332 A of the cap  232 . 
         [0032]    The cap  232  receives an urging force of the first spring  210  from above and receives an urging force (a set load) of the third spring  234  from below. The urging force of the first spring  210  is larger than the urging force of the third spring  234 , so that the cap  232  is pressed against the protrusion portion  331  of the valve body  214  by an urging force corresponding to a difference between the urging force of the first spring  210  and the urging force of the third spring  234 . Since no force is applied to the cap  232  in a direction in which the cap is separated from the protrusion portion  331 , the cap  232  can be sufficiently fixed to the protrusion portion  331  by press-inserting instead of welding. 
         [0033]    The state shown in  FIG. 2  is a state where the valve body  214  receives the urging force of the first spring  210  and a magnetic attraction force is not applied to the needle  202 . In this state, the intermediate member  220  receives the urging force of the third spring  234  and a bottom surface  333 E of the concave portion  333 A contacts the upper end surface of the stepped portion  329  of the valve body  214 . That is, the size (the dimension) of the gap G 3  between the bottom surface  333 E of the concave portion  333 A and the upper end surface of the stepped portion  329  is zero. 
         [0034]    Meanwhile, the needle  202  receives an urging force of a zero spring (a second spring)  212  to be urged toward the fixed core  207 . For this reason, the needle  202  contacts the lower end surface of the intermediate member  220 . Since the urging force of the second spring  212  is smaller than the urging force of the third spring  234 , the needle  202  cannot press back the intermediate member  220  urged by the third spring  234  and the movement in the upward direction (the valve opening direction) is suppressed by the intermediate member  220  and the third spring  234 . 
         [0035]    Since the depth dimension of the concave portion  333 A of the intermediate member  220  is larger than the dimension between the upper end surface and the lower end surface of the stepped portion  329 , the needle  202  does not contact the lower end surface of the stepped portion of the valve body  214  and the gap G 2  between the needle  202  and the lower end surface of the stepped portion of the valve body  214  has a size (a dimension) D 2  in the state shown in  FIG. 3 . The gap G 2  is smaller than the size (the dimension) D 1  of the gap G 1  between the upper end surface (a facing surface of the fixed core  107 )  202 A of the needle  202  and the lower end surface (a facing surface of the needle  202 )  207 B of the fixed core  107  (D 2 &lt;D 1 ). As described herein, the intermediate member  220  is a member that forms the gap G 2  having a size D 2  between the needle  202  and the lower end surface of the stepped portion  329 . 
         [0036]    When the lower end surface of the intermediate member (the gap forming member)  220  contacts the needle  202  while the intermediate member is positioned to the upper end surface (the reference position) of the stepped portion  329  of the valve body  214 , the gap D 2  is formed between the lower end surface of the stepped portion  329  of the engagement portion of the valve body  214  and the bottom surface  302 D of the concave portion which is the engagement portion of the needle  202 . The third spring  234  urges the intermediate member  233  in the valve closing direction so that the intermediate member contacts the upper end surface (the reference position) of the stepped portion  329 . The intermediate member  233  is positioned to the upper end surface (the reference position) of the stepped portion  329  when the bottom surface  333 E of the concave portion contacts the upper end surface (the reference position) of the stepped portion  329 . Among the first spring  210 , the second spring  212 , and the third spring  234 , the spring force (the urging force) of the first spring  210  is the largest, the spring force (the urging force) of the third spring  234  is secondly large, and the spring force (the urging force) of the second spring  212  is the smallest. 
         [0037]    In the valve body  214 , since the diameter of the penetration hole  128  formed in the needle  202  is smaller than the diameter of the stepped portion  329 , the lower end surface of the stepped portion  329  of the valve body  214  engages with the needle  202  so that the needle  202  and the valve body  114  move together during a valve opening operation in which the valve closed state is switched to the valve opened state or a valve closing operation in which the valve opened state is switched to the valve closed state. However, when a force of moving the valve body  114  upward, that is, a force of moving the needle  202  downward is independently exerted, the valve body  114  and the needle  202  can be moved in different directions. The operations of the needle  202  and the valve body  214  will be described in detail later. 
         [0038]    In the embodiment, the movement of the needle  202  in the vertical direction (the valve opening/closing direction) is guided in such a manner that the outer peripheral surface contacts the inner peripheral surface of the nozzle holder  201 . Further, the movement of the valve body  214  in the vertical direction (the valve opening/closing direction) is guided in such a manner that the outer peripheral surface contacts the inner peripheral surface of the penetration hole of the needle  202 . The front end portion of the valve body  214  is guided by the guide hole of the guide member  215  and is guided by the guide member  215 , the nozzle holder  201 , and the penetration hole of the needle  202  to move straightly in a reciprocating manner. 
         [0039]    Additionally, in the embodiment, a case in which the upper end surface  302 A of the needle  202  contacts the lower end surface  307 B of the fixed core  207  has been described, but a case may be employed in which a protrusion portion is provided in any one of the upper end surface  302 A of the needle  202  and the lower end surface  307 B of the fixed core  207  or both the upper end surface  302 A of the needle  202  and the lower end surface  307 B of the fixed core  207  and the end surface of the protrusion portion contact any protrusion portion. In this case, the above-described gap G 1  becomes a gap between a contact portion near the needle  202  and a contact portion near the fixed core  207 . 
         [0040]    In  FIG. 2 , the fixed core  207  is press-inserted into an inner peripheral portion of a large-diameter cylindrical portion  240  of the nozzle holder  201  and is welded at the press-inserting contact position. The fixed core  207  is a component which exhibits a magnetic attraction force in the needle  202  to attract the needle  202  in the valve opening direction. A gap formed between external air and the inside of the large-diameter cylindrical portion  23  of the nozzle holder  201  is sealed by the welding of the fixed core  207 . A penetration hole having a diameter slightly larger than the diameter of the intermediate member  233  is provided as a fuel passage at the center of the fixed core  207 . The cap  232  and the head portion of the valve body  214  are inserted through the inner periphery of the lower end portion of the penetration hole in a non-contact state. 
         [0041]    The lower end of the spring  210  for setting an initial load contacts a spring receiving surface formed on the upper end surface of the cap  232  provided at a head portion  241  of the valve body  214  and the other end of the spring  210  is received by an adjustment pin  224  press-inserted into the penetration hole of the fixed core  207  so that the spring  210  is fixed between the cap  232  and the adjustment pin  224 . When the fixed position of the adjustment pin  224  is adjusted, an initial load in which the spring  210  presses the valve body  214  against the valve seat  218  can be adjusted. 
         [0042]    In a state where the initial load of the spring  210  is adjusted, the lower end surface of the fixed core  207  faces the upper end surface of the needle  202  with the magnetic attraction gap G 1  of about 40 to 100 micron formed therebetween. Further, in the drawings, the dimensions are displayed while the ratios are not taken into consideration. 
         [0043]    The large-diameter cylindrical portion  240  of the nozzle holder  201  is inserted through a penetration hole formed at the center of a bottom portion of a housing  203 . A portion of the outer peripheral wall of the housing  203  forms an outer peripheral yoke portion which faces the outer peripheral surface of the large-diameter cylindrical portion  240  in the nozzle holder  201 . The coil  205  includes an annular bobbin  204  which includes a groove having a U-shaped cross-section and opened outward in the radial direction and a copper wire which is wound in the groove. A rigid conductor  209  is fixed to a winding start portion and a winding end portion of the coil  205 . A magnetic passage is formed in an annular shape at a portion of the fixed core  207 , the needle  202 , the large-diameter cylindrical portion  240  of the nozzle holder  201 , and the housing (the outer peripheral yoke portion)  203  to surround the coil  205 . 
         [0044]    The fuel is supplied from the fuel pipe installed at the upstream of the fuel injection device and flows to the front end of the valve body  214  through a first fuel passage hole  231 . The fuel is sealed by the valve seat  218  and the seat portion formed at the end portion near the valve seat  218  in the valve body  214 . When the valve is closed, a differential pressure is generated between the upper and lower portions of the valve body  214  by the fuel pressure and the valve body  214  is pressed in the valve closing direction by a force obtained by multiplying the fuel pressure by the pressure receiving area of the seat inner diameter at the valve seat position. In the valve closed state, the gap G 2  is formed between the needle  202  and the contact surface of the valve body  214  with respect to the needle  202  through the intermediate member  220 . Since the gap G 2  is provided, the needle  202  is disposed to have a gap with respect to the valve body  214  in the axial direction while the valve body  214  sits on the valve seat  218 . 
         [0045]    When a current is supplied to the solenoid  205 , a magnetic flux passes between the fixed core  207  and the needle  202  due to a magnetic field generated by a magnetic circuit and a magnetic attraction force is applied to the needle  202 . At a timing in which the magnetic attraction force which acts on the needle  202  exceeds the load generated by the third spring  234 , the needle  202  starts to be displaced in the direction of the fixed core  207 . At this time, since the valve body  214  and the valve seat  218  contact each other, the movement of the needle  202  is performed in a state without the flow of the fuel and is an idling movement independently from the valve body  214  that receives the differential pressure by the fuel pressure. Accordingly, the needle can move at a high speed without the influence of the pressure of the fuel and the like. 
         [0046]    Further, there is a need to strongly set the load of the first spring  214  in order to suppress the injection of the fuel even when a combustion pressure inside an engine cylinder increases. That is, since the load of the first spring  214  does not act on the valve body  214  in the valve closed state, the valve body  214  can move at a high speed. 
         [0047]    When the displacement amount of the needle  202  reaches the size of the gap G 2 , the needle  202  transmits a force to the valve body  214  through a contact surface  302 E so that the valve body  214  is pulled up in the valve opening direction. At this time, since the needle  202  moves idly and collies with the valve body  214  while having kinetic energy, the valve body  214  receives the kinetic energy of the needle  202  and starts to be displaced at a high speed in the valve opening direction. A differential pressure which is generated by the pressure of the fuel is applied to the valve body  214  and the differential pressure acting on the valve body  214  is generated by a decrease in pressure of the front end portion of the valve body  214  according a decrease in pressure generated by a decrease in static pressure caused by a Bernoulli effect after the flow rate of the fuel at the seat portion increases in a range having a small passage cross-sectional area in the vicinity of the seat portion of the valve body  214 . Since the differential pressure is largely influenced by the passage cross-sectional area of the seat portion, the differential pressure increases in a condition in which the displacement amount of the valve body  214  is small and the differential pressure decreases in a condition in which the displacement amount is large. 
         [0048]    Thus, since the valve body  214  is opened by a collision in accordance with the idle movement of the needle  202  at a timing in which the valve body  214  starts to open the valve from the valve closed state so that the displacement is small, the differential pressure increases, and the valve opening operation is difficult, the valve opening operation can be performed even in a state where a higher fuel pressure is exhibited. Alternatively, it is possible to set the first spring  210  to a stronger force in the fuel pressure range necessary for the operation. Since the first spring  210  is set to a stronger force, a time necessary for the valve closing operation to be described later can become short and thus a minute injection amount can be effectively controlled. 
         [0049]    After the valve body  214  starts the valve opening operation, the needle  202  collides with the fixed core  207 . At the time in which the needle  202  collides with the fixed core  207 , the needle  202  bounds backward, but the needle  202  is attracted and stopped by the fixed core  207  due to the magnetic attraction force acting on the needle  202 . At this time, since a force which is exerted in the direction of the fixed core  207  by the first spring  212  is applied to the needle  202 , the rebounding displacement amount can be decreased and a time taken until the rebounding is stabilized can become short. Since the rebounding operation is small, a time in which a gap between the needle  202  and the fixed core  207  increases becomes short and thus a stable operation can be performed even in a smaller injection pulse width. 
         [0050]    The needle  202  and the valve body  214  having used to perform the valve opening operation in this way are stopped in the valve opened state. In the valve opened state, a gap is formed between the valve body  214  and the valve seat  218  and the fuel is injected. The fuel flows in the downstream direction while passing through the center hole formed in the fixed core  207 , the fuel passage hole formed in the needle  202 , and the fuel passage hole formed in the guide member  215 . When the supply of the current to the solenoid  205  is stopped, a magnetic flux generated in the magnetic circuit disappears and a magnetic attraction force also disappears. Since the magnetic attraction force acting on the needle  202  disappears, the valve body  214  is pressed back to a closed position in which the valve body contacts the valve seat  218  due to a force generated by the fuel pressure and the load of the first spring  210 . 
         [0051]    Next, a configuration of the drive device of the fuel injection device according to the embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a diagram specifically showing the ECU  104  and the drive circuit  103  of the fuel injection device. 
         [0052]    The CPU  501  is built in, for example, the ECU  104  and calculates an injection timing or an injection pulse width for controlling an injection amount from the fuel injection device in response to an operation condition of an internal combustion engine by receiving signals indicating an engine state from various sensors described above including a pressure sensor which is attached to an upstream fuel pipe of the fuel injection device, an A/F sensor which measures the amount of air flowing into an engine cylinder, an oxygen sensor which detects an oxygen concentration of an exhaust gas discharged from an engine cylinder, and a crank angle sensor. Further, the CPU  501  calculates an appropriate injection timing or an appropriate injection pulse width Ti (that is, an injection amount) in response to the operation condition of the internal combustion engine and outputs the injection pulse width Ti to a driving IC  502  of the fuel injection device via a communication line  504 . Next, the supply of the current to switching elements  505 ,  506 , and  507  is switched by the driving IC  502  so that a drive current is supplied to a fuel injection device  540 . 
         [0053]    A switching element  805  is connected between a high voltage source which is higher in voltage than a voltage source VB input to the drive circuit and a high voltage side terminal of the fuel injection device  540 . The switching elements  505 ,  506 , and  507  are configured as, for example, FETs or transistors and the supply of the current to the fuel injection device  540  can be switched. A boost voltage VH which is an initial voltage value of the high voltage source is, for example 60 V and is generated when a battery voltage is raised by a boost circuit  514 . There is known a method in which the boost circuit  514  includes, for example, a DC/DC converter or the like or a coil  530 , a transistor  531 , a diode  532 , and a capacitor  533 . In the case of the latter boost circuit  514 , when the transistor  531  is turned on, a battery voltage VB flows toward a ground potential  534 , but when the transistor  531  is turned off, a high voltage generated in the coil  530  flows through the diode  532  so that electric charge is accumulated in the capacitor  533 . The transistor is repeatedly turned on and off until the voltage becomes the boost voltage VH so that the voltage of the capacitor  533  increases. The transistor  531  is connected to the IC  502  or the CPU  501  and the boost voltage VH output from the boost circuit  519  is detected by the IC  502  or the CPU  501 . 
         [0054]    Further, a diode  535  is provided between a power supply side terminal  590  of the solenoid  205  and the switching element  505  so that a current flows from the second voltage source toward the solenoid  205  and the installation potential  515  and a diode  511  is also provided between the power supply side terminal  590  of the solenoid  205  and the switching element  507  so that a current flows from the battery voltage source toward the solenoid  205  and the installation potential  515 . While the current flows in the switching element  508 , the current cannot flow from the ground potential  515  toward the solenoid  205 , the battery voltage source, and the second voltage source. Further, the ECU  104  is provided with a register and a memory which are used to memorize numerical data necessary for the control of the engine when calculating the injection pulse width or the like. 
         [0055]    Further, the switching element  507  is connected between the low voltage source and the high voltage terminal of the fuel injection device. The low voltage source VB is, for example, a battery voltage and a voltage value is about 12 to 14 V. The switching element  506  is connected between the low voltage side terminal of the fuel injection device  540  and the ground potential  515 . The driving IC  502  detects a value of a current flowing in the fuel injection device  540  by current detecting resistances  508 ,  512 , and  513  and generates a desired drive current by switching the supply of the current to the switching elements  505 ,  506 , and  507  based on the detected current value. The diodes  509  and  510  are provided to rapidly reduce the current supplied to the solenoid  205  by applying a reverse voltage to the solenoid  205  of the fuel injection device. The CPU  501  communicates with the driving IC  502  via a communication line  503  and can change a drive current generated by the driving IC  502  based on the operation condition or the pressure of the fuel supplied to the fuel injection device  540 . Further, both ends of the resistances  508 ,  512 , and  513  are connected to an A/D converter of the IC  502  and the voltage applied to both ends of the resistances  508 ,  512 , and  513  is detected by the IC  502 . 
         [0056]    Next, a relation ( FIG. 4 ) of the injection pulse output from the ECU  104 , the drive voltage of both ends of the terminal of the solenoid  205  of the fuel injection device, the drive current (the excitation current), and the displacement amount (the behavior of the valve body) of the valve body  214  of the fuel injection device and a relation ( FIG. 7 ) of the injection pulse and the fuel injection amount according to the embodiment will be described. 
         [0057]    When an injection pulse is input to the drive circuit  103 , the drive circuit  103  starts the supply of the current to the solenoid  205  by applying the high voltage  401  to the solenoid  205  from the high voltage source of which the voltage is raised to be higher than the battery voltage through the switching elements  505  and  506 . When the current value reaches a maximum drive current I peak  (hereinafter, referred to as a peak current value) set in the ECU  104  in advance, the application of the high voltage  401  is stopped. 
         [0058]    When the switching element  506  is turned on during a period in which the peak current value I peak  changes to the current  403  and the supply of the current to the switching elements  505  and  507  is interrupted, a voltage of 0 V is applied to the solenoid  205  and the current flows along the fuel injection device  540 , the switching element  506 , the resistance  508 , the ground potential  515 , and the fuel injection device  540  so that the current gently decreases. Since the current gently decreases, the current supplied to the solenoid  205  is ensured. Thus, the needle  202  and the valve body  214  can stably perform the valve opening operation even when the pressure of the fuel supplied to the fuel injection device  540  increases. In addition, when the switching elements  505 ,  506 , and  507  are turned off during a period in which the peak current value I peak  changes to the current  403 , the current is supplied to the diode  509  and the diode  510  due to a counter electromotive force caused by the inductance of the fuel injection device  540 . Accordingly, the current returns to the voltage source VH and the current supplied to the fuel injection device  540  rapidly decreases from the peak current value I peak  as in the current  402 . As a result, since a time taken until the current reaches the current  403  becomes short, it is possible to effectively shorten a time in which the magnetic attraction force becomes constant after a predetermined delay time elapses from a timing in which the current reaches the current  403 . When the current value becomes smaller than a predetermined current value  404 , the drive circuit  103  supplies a current to the switching element  506  and makes a switching period for a control of keeping the predetermined current  403  by applying the battery voltage VB according to the supply of the current to the switching element  507 . 
         [0059]    When the pressure of the fuel supplied to the fuel injection device  540  increases, a fluid pressure acting on the valve body  214  increases and thus a time in which the opening degree of the valve body  214  reaches a target opening degree becomes longer. As a result, there is a case in which a timing reaching the target opening degree is late compared to a timing reaching the peak current I peak . When the drive current rapidly decreases, the magnetic attraction force acting on the needle  202  also rapidly decreases, the behavior of the valve body  214  becomes unstable. Thus, in some cases, the valve closing operation may start even in a current supply state. When a current is supplied to the switching element  506  while the peak current I peak  changes to the current  403  so that the current gently decreases, a decrease in magnetic attraction force can be suppressed and safety of the valve body  214  can be ensured at the high fuel pressure. Accordingly, it is possible to suppress a change in injection amount. 
         [0060]    The fuel injection device  540  is driven by such a supply current profile. Up to the peak current value I peak  from the application of the high voltage  401 , the needle  202  starts to be displaced at the timing t 41  and the valve body  214  starts to be displaced at the timing t 42 . Next, the opening degrees of the needle  202  and the valve body  214  reach the maximum opening degree (the maximum height position). Additionally, in the embodiment, the displacement amount in which the needle  202  contacts the fixed core  107  is set as the maximum height position of the needle. However, the invention is not particularly limited to a case where the valve body  214  moves in the vertical direction while the fuel injection device is mounted on the engine. Thus, the maximum height position of the needle  202  may be referred to as the maximum displacement position of the needle  202 . 
         [0061]    At the timing t 43  in which the needle  202  reaches the maximum height position, the needle  202  collides with the fixed core  207  and the needle  202  bounds against the individual core  207 . Since the valve body  214  is formed to be displaceable relative to the needle  202 , the valve body  214  is separated from the needle  202  and the displacement of the valve body  214  overshoots beyond the maximum height position. Next, the needle  202  is stopped at a predetermined maximum height position due to the magnetic attraction force generated by the holding current  403  and the force of the second spring  212  in the valve opening direction and the valve body  214  sits on the needle  202  to be stopped at the maximum height position, thereby forming the valve opened state. 
         [0062]    In the case of the fuel injection device including a movable valve in which the valve body  214  and the needle  202  are integrated with each other, the displacement amount of the valve body  214  does not become higher than the maximum height position and the valve body  214  and the needle  202  reaching the maximum height position have the same displacement amount. 
         [0063]    Next, an injection amount characteristic Q 701  obtained using a current waveform shown in  FIG. 4  will be described with reference to  FIG. 7 . When the injection pulse width Ti is not obtained for a predetermined time, the valve body  214  is not opened and the fuel is not injected in a condition that a force applied in the valve opening direction and obtained as the resultant force of the magnetic attraction force acting on the needle  202  and the load of the second spring  214  does not exceed the force in the valve closing direction corresponding to the load of the third spring  234  or the needle  202  cannot contact the valve body  214  while the magnetic attraction force necessary for sliding in the gap G 3  is not ensured even after the needle  202  starts to be displaced. 
         [0064]    Further, in the condition of, for example, the line  701  in which the injection pulse width Ti is short, the needle  202  collides with the valve body  214  and the valve body  214  is separated from the valve seat  218  to be lifted. However, since the valve is closed before the valve body  214  reaches a target lift position, the injection amount is small from a straight region  730  in which the injection pulse width and the injection amount have a linear relation to an alternate dotted-chain line  720 . 
         [0065]    Further, in the pulse width of the point  702 , the valve closing operation is started immediately after the valve body  214  reaches the maximum height position and the locus of the valve body  214  becomes parabolic. In this condition, since the kinetic energy of the valve body  214  in the valve opening direction is large and the magnetic attraction force acting on the needle  202  is large, the portion of the time necessary to close the valve is large and thus the injection amount is large in the one-dotted chain line  720 . A region  840  in which the valve body  214  does not contact the fixed core  207  and the locus of the valve body  214  becomes parabolic will be referred to as a half-lift region and a region  841  in which the valve body  214  contacts the fixed piece  207  will be referred to as a full-lift region. 
         [0066]    In the injection pulse width of the point  703 , since the valve closing operation is performed at a timing in which the bounding amount of the valve body  214  caused by the collision of the needle  202  with the fixed core  207  becomes maximal, a repelling force generated when the needle  202  collides with the fixed core  207  acts on the needle  202 . Accordingly, a valve closing delay time until the valve body  214  closes the valve after the injection pulse is turned off becomes small. As a result, the injection amount is small in the one-dotted chain line  720 . A point  704  indicates a state where the valve closing operation starts at the timing t 24  immediately after the bound of the valve body converges. Then, in the injection pulse width Ti larger than that of the point  704 , the fuel injection amount substantially linearly increases in response to an increase in injection pulse width Ti. In a region to the pulse width Ti indicated by the point  704  after the injection of the fuel starts, the valve body  214  does not reach the maximum height position or the bound of the valve body  214  is not stabilized even when the valve body  214  reaches the maximum height position. For this reason, the injection amount changes. In order to decrease the controllable minimum injection amount, there is a need to increase a region in which the fuel injection amount linearly increases in response to an increase in injection pulse width Ti or to suppress a change in injection amount in a non-linear region in which a relation between the injection amount and the injection pulse width Ti smaller than the injection pulse width Ti  704  is not linear. 
         [0067]    In the drive current waveform described in  FIG. 4 , the bound of the valve body  214  generated by the collision between the needle  202  and the fixed core  207  is large and the valve closing operation starts while the valve body  214  bounds. For that reason, non-linearity is generated in a region of the injection pulse width Ti which is short to the point  704  and this non-linearity causes the minimum injection amount deterioration. Thus, there is a need to reduce the bound of the valve body  214  caused after the valve body reaches the maximum height position in order to solve the non-linearity of the injection amount characteristic in a condition in which the valve body  214  reaches the target lift. Further, since there is a change in behavior of the valve body  114  due to tolerance, a timing in which the needle  102  and the fixed core  107  contact each other becomes different for each fuel injection device. Further, since there is a change in collision speed between the needle  102  and the fixed core  107 , the bound of the valve body  114  becomes different for each fuel injection device and each injection amount becomes uneven. 
         [0068]    Meanwhile, since the valve body  214  behaviors unstably so as not to contact the fixed core  207  corresponding to a stopper in a region in which a driving (hereinafter, referred to as a half-lift) for allowing the valve body  214  to reach the height position lower than the maximum height position is performed, there is a need to accurately control the magnetic attraction force acting on the needle  202  for determining a speed when the needle  202  collides with the valve body  214  and the magnetic attraction force acting on the needle  202  after the valve body  214  starts to open the valve in order to accurately control the injection amount. 
         [0069]    Next, the fuel injection device control method of the embodiment will be described with reference to  FIGS. 6 and 7 .  FIG. 6  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a voltage Vinj across terminals of the solenoid  205  and the switching elements  505 ,  506 , and  507  of the fuel injection device, and a behavior of the valve body  214  and the needle  202  in time. Additionally, a displacement amount  722  of the valve body  214  and a drive current  721  when using the current waveform of  FIG. 4  are indicated by a dashed line.  FIG. 7  is a diagram showing a relation between the injection pulse width and the injection amount when the fuel injection device  540  is controlled in the drive current waveform of  FIG. 6 . Additionally, in  FIG. 7 , an injection amount characteristic when the fuel injection device  540  is controlled at a drive current  610  is indicated by an injection amount Q 702 . 
         [0070]    First, when the injection pulse width Ti is input from the CPU  501  to the driving IC  502  via the communication line  504  at a timing t 61 , the switching element  505  and the switching element  506  are turned on, the boost voltage VH higher than the battery voltage VH is applied to the solenoid  205 , and the drive current is supplied to the fuel injection device  540  so that the current rapidly rises. When the current is supplied to the solenoid  205 , the magnetic attraction force is exerted between the needle  202  and the fixed core  207 . The needle  202  starts to be displaced at a timing in which a force in the valve opening direction corresponding to a resultant force of the magnetic attraction force and the load of the second spring  212  exceeds the load of the third spring  234  corresponding to the force in the valve closing direction. Next, after the needle  202  slides in the gap G 2  so that the needle  202  collides with the valve body  214 , the valve body  214  starts to be displaced so that the fuel is injected from the fuel injection device  540 . 
         [0071]    When the current reaches the peak current value I peak , the supply of the current to the switching element  505 , the switching element  506 , and the switching element  507  is stopped, the current is supplied to the diode  509  and the diode  510  due to the counter electromotive force caused by the inductance of the fuel injection device  540 , the current returns to the voltage source VH, and the current supplied to the fuel injection device  540  rapidly decreases from the peak current value I peak  as in the current  602 . Additionally, when the switching element  506  is turned on during a period in which the peak current value I peak  changes to the first drive current  610 , the current generated by the counter electromotive energy flows to the ground potential and the current gently decreases. 
         [0072]    Next, when the time reaches a timing t 63 , the supply of the current to the switching element  506  is resumed and the supply of the current to the switching element  507  is switched so that the current value of the first drive current  610  is held at the current value  604  or the vicinity thereof. Additionally, a period of controlling the first drive current  610  will be referred to as a first current hold period. 
         [0073]    Further, the supply of the current to the switching element  505  and the switching element  507  is stopped and the current is supplied to the switching element  506  at a timing t 64  immediately after or before the displacement amount of the valve body  214  reaches the maximum height position after the first drive current  610  is held for a predetermined time so that the current gently decreases as in a current  603 . Then, the supply of the current to the switching element  507  is switched again at a timing t 65  in which the current reaches a current  605  having a current value smaller than that of the first drive current  610  so that the current value of the second drive current  611  is held at the current value  605  or the vicinity thereof. Additionally, a period of controlling the second drive current  611  will be referred to as a second current hold period. 
         [0074]    Next, a relation between a current waveform  651  and the valve body  214  in a half-lift condition in which the valve body  214  is driven at a height position  650  lower than the maximum height position will be described. Additionally, the displacement of the valve body  214  when using the current waveform  651  is indicated by a one-dotted chain line (displacement  652 ). 
         [0075]    When the injection pulse Ti is stopped at a timing t 69  of the first drive current  610  after the valve body  214  starts to open the valve, the boost voltage VH is applied to the solenoid  205  in a negative direction so that the current decreases and reaches 0 A. When the supply of the current is stopped, the magnetic attraction force acting on the needle  202  decreases. Then, at a timing in which the force in the valve opening direction corresponding to the resultant force of the magnetic attraction force, the load of the second spring  212 , and the inertia force of the needle  202  is lower than the force in the valve closing direction of the differential pressure acting on the first spring  210  and the valve body  214 , the valve body  214  starts to close the valve from the height position  650  lower than the maximum height position. Then, at the timing t 67 , the valve body contacts the valve seat  218  to stop the injection of the fuel. 
         [0076]    In the current waveform  610  of the embodiment, the needle  202  slides in the valve opening direction to ensure the kinetic energy necessary for the valve opening operation so that the peak current I peek  is stopped at an early timing. Accordingly, it is possible to decrease the gradient of the displacement amount of the valve  214  until the valve body reaches the maximum height position from the start of the valve opening operation of the valve body  214 . That is, the CPU  501  of the ECU  104  of the embodiment controls the height position of the valve body  214  in the height position region (half-lift region) lower than the maximum height position by decreasing the drive current flowing to the solenoid  205  from the current I peak  to the first drive current  610  lower than the current I peak  before the valve body  214  reaches the maximum height position and changing the application time of the first drive current  610 . That is, a control is performed so that the height position of the valve body  214  in the half-lift region increases as the application time of the first drive current  610  increases. 
         [0077]    Alternatively, the CPU  501  controls the needle  202  so that the needle reaches the height position lower than the facing surface of the fixed piece  107  by decreasing the drive current flowing to the solenoid  205  from the maximum drive current I peak  to the first drive current  610  before the needle  202  collides with the fixed piece  107 . Then, the height position of the needle  202  at the height position region lower than the facing surface of the fixed piece  107  may be controlled in such a manner that the application time of the first drive current  610  changes. Further, the CPU  501  controls the needle  202  so that the needle collides with the fixed piece  107  by decreasing the current to the second drive current  611  lower than the first drive current  610 . In addition, a time in which the needle  202  contacts the fixed piece  107  is controlled in such a manner that the application time of the second drive current  611  changes. Further, a control is performed so that the needle  202  reaches the height position lower than the facing surface of the fixed piece  611  in such a manner that the current is decreased to the first drive current  610  and is interrupted. 
         [0078]    In other words, when the fuel is injected in the first injection amount region, the CPU  501  of the embodiment controls the needle  202  so that the needle reaches the height position lower than the facing surface of the fixed piece  611  by decreasing the drive current flowing to the solenoid  205  from the maximum drive current I peak  to the first drive current  610  before the needle  202  collides with the fixed piece  611 . 
         [0079]    As a result, it is possible to decrease the gradients of the injection pulse Ti of the half-lift region  742  and the valve opening period of the valve body  214 . This corresponds to a case where the changed injection amount decreases in accordance with a change in injection pulse Ti. Since there is a limitation in the resolution of the injection pulse width controlled by the ECU  104 , it is possible to increase the control resolution of the injection amount and to improve the accuracy of the injection amount by decreasing the changed injection amount when the injection pulse width Ti changes. Since the accuracy of the injection amount is improved, the PN suppression effect is improved and the fuel can be appropriately injected in response to the engine rotation speed. As a result, it is possible to obtain an effect of improving drivability. 
         [0080]    In the case of the fuel injection device  540  having a mechanism in which the needle  202  slides and collides with the valve body  214  to open the valve, the timing of interrupting the peak current I peak  may be set to a timing before the valve body  214  starts to open the valve in a condition in which the needle  202  is accelerated to ensure the kinetic energy sufficient for the valve opening operation. As a result, it is possible to shorten the timing which changes to the first hold current period and to easily control the injection amount smaller than that of the half-lift region  742 . A detailed description of the effect will made below. 
         [0081]    Further, when the timing for stopping the peak current I peak  is set to a timing immediately after the valve body  214  starts to open the valve, the energy (the integrated value of the current waveform) supplied to the solenoid  205  until the valve body  214  starts to open the valve is large and thus the kinetic energy at the time when the needle  202  collides with the valve body  214  can be easily ensured. As a result, even when the fuel pressure supplied to the fuel injection device  540  is large, the valve body  214  can be controlled stably to the valve opened state. 
         [0082]    Further, in a cold start condition or a high-rotation/high-load condition in which knocking is likely to occur due to self ignition due to the high temperature and the high pressure of the unburned gas during the propagation of the flame in the engine cylinder, the necessity of the multi-stage injection is high and the smaller injection amount is required. Thus, in the above-described operation condition, a control of selecting the current waveform  621  may be performed by the ECU  104  in a condition in which the injection amount of the half-lift region  742  is not obtained by using the current waveform  610  of the first embodiment. When the fuel pressure supplied to the fuel injection device  540  increases, the displacement amount of the needle  202  does not change until the needle  202  collides with the valve body  214 . However, since the differential pressure acting on the valve body  214  increases, the gradient of the displacement amount of the valve body  214  decreases even when the needle  202  collides with the valve body  214  at the same speed. 
         [0083]    Thus, since the magnetic attraction force necessary for the valve opening operation increases, the current waveform selection control may be performed so that the peak current value I peak  increases, the current value  610  of the first hold current period increases, or both values are corrected in response to an increase in fuel pressure. Due to this selection control, it is possible to suppress a change in locus of the displacement of the valve body  214  until the valve body reaches the maximum height position even when the fuel pressure changes and thus stably control the displacement amount of the valve body  214 . As a result, since the accuracy of the injection amount can be improved, the PN suppression effect is improved. Further, when the number of fuel injections in the half-lift region  742  is large in the engine condition requiring the multi-stage injection, the PN suppression effect is easily obtained by the improvement in accuracy of the injection amount. By this effect, it is possible to decrease the gradients of the injection pulse and the injection amount in the half-lift region  742 . Since the sensitivity of the injection amount with respect to a change in injection pulse width is set to be small, it is possible to highly accurately control the injection amount even when the control resolution of the injection pulse generated by the ECU  104  is large. Since the gradient of the injection amount is set to be small, the half-lift region  740  in the case of using the conventional current waveform  621  becomes the half-lift region  742 . 
         [0084]    As described above, since the differential pressure acting on the valve body  214  is largely influenced by the passage cross-sectional area of the seat portion, the differential pressure increases in a condition in which the displacement amount of the valve body  214  is small and the differential pressure decreases in a condition in which the displacement amount is large. Thus, since the valve of the valve body  214  is opened by a collision in accordance with the idle movement of the needle  202  at a timing in which the valve body  214  starts to open the valve from the valve closed state so that the displacement is small, the differential pressure is large, and the valve opening operation is difficult, the valve opening operation can be performed even in a state where the high fuel pressure is exhibited. 
         [0085]    In the current waveform  621 , an undulation generated in the injection amount characteristic after the half-lift region  740  changes to the full-lift region  741  is generated when the needle  202  collides with the fixed core  207 . Thus, the current value may be decreased as in the current  603  in such a manner that the first hold current period is stopped before the valve body  214  reaches the maximum height position. Since the current value decreases, the speed of the needle  202  can be reduced or the acceleration thereof can be suppressed. Accordingly, it is possible to reduce the collision speed of the needle  202  at a timing in which the needle  202  collides with the fixed core  207 . Further, it is possible to reduce the bound of the valve body  214  in accordance with the suppression of the bound of the needle  202 . As a result, since it is possible to suppress an undulation generated in the injection amount characteristic after the half-lift region  742  changes to the full-lift region  743 , it is possible to accurately control the injection amount. 
         [0086]    When the injection pulse Ti is changed during the second current hold period in which the current becomes the second drive current  611 , it is possible to change a time in which the valve body  214  is located at the maximum height position. That is, when the fuel is injected in the second injection amount region in which the injection amount is larger than that of the first injection amount region, the CPU  501  of the embodiment controls the needle  202  so that the needle collides with the fixed piece  107  by decreasing the drive current flowing to the solenoid from the maximum drive current I peak  to the first drive current  610  before the needle  202  collides with the fixed piece  107  and then decreasing the second drive current  611 . When the injection pulse Ti is set to be long, a time in which the valve body is located at the maximum height position becomes long and a time (referred to as a valve closing delay time) in which the valve body  214  contacts the valve seat  218  after the stop of the injection pulse Ti changes. A range causing the bound of the valve body  214  is excluded from the full-lift region and the injection amount is determined in synchronization with the valve closing delay time. When the valve closing delay time increases, the injection amount increases. Thus, since a time in which the valve body  214  is located at the maximum height position is controlled when the application time of the second drive current  611  is changed, the injection amount can be accurately controlled. As a result, the PN suppression effect can be improved. 
         [0087]    Further, the current value  610  of the first current hold period may be set to be larger than the current value  611  of the second current hold period. In the valve opened state in which the valve body  214  performs the valve opening operation and is located at the maximum height position, it is easy to ensure the magnetic attraction force since a gap (a magnetic gap) between the needle  202  and the fixed core  207  is smaller than the valve closed state in which the valve body  214  contacts the valve seat  218  and the differential pressure acting on the valve body  214  is also small since the cross-sectional area of the seat portion of the valve body  214  is large. Thus, a current which is equal to or larger than the minimum current value  606  capable of keeping the valve body  214  in the valve opened state may be supplied to the solenoid  205 . Meanwhile, the needle  202  and the valve body  214  are displaced during the first current hold period  610 . 
         [0088]    Thus, the magnetic attraction force is not easily ensured since the gap (the magnetic gap) between the needle  202  and the fixed core  207  is larger than that of the valve opened state and the differential pressure acting on the valve body  214  also increases since the cross-sectional area of the seat portion of the valve body  214  is small. Thus, since the magnetic attraction force necessary to open the valve is larger than that of the valve opened state, there is a need to set the current value  610  of the first current hold period to be larger than the current value  611  of the second current hold period in order to ensure the safety of the valve body  214  in the half-lift region. In the half-lift region, since the displacement amount of the valve body  214  in the half-lift region  742  and the valve open period until the valve closing operation ends from the start of the valve opening operation of the valve body  214  can be accurately determined by the kinetic energy generated by the collision of the needle  202  with the valve body  214  and the magnetic attraction force generated by the current value  610  during the first hold current period, a minute injection amount can be accurately controlled. 
         [0089]    When the current is rapidly decreased from the peak current value I peak  as in the current  602  by applying the boost voltage VH to the solenoid  205  in the negative direction in a case where the peak current value I peak  changes to the current value  610  of the first hold current period, the current can reach the value of the first hold current period in a condition that the displacement amount of the valve body  214  is small in such a manner that the first hold current period is promptly selected while ensuring the kinetic energy after increasing the magnetic attraction force necessary to open the valve until a timing immediately before the start of the valve opening operation, that is, a timing in which the needle  202  collides with the valve body  214 . Accordingly, a range in which the displacement amount of the valve body  214  is controlled at the first drive current  610  can be expanded in a direction having a small displacement amount. As a result, since the range of the injection amount which can be controlled during the first hold current period in the half-lift region  742  can be expanded in a direction having a small displacement amount, there is an effect that a control up to a minute injection amount can be performed. 
         [0090]    Additionally, when the current is supplied to the switching element  506  during a period in which the peak current value I peak  changes to the first drive current  610  and the switching elements  505  and  507  are turned off, a voltage of about 0 V is applied to the solenoid  205  so that the current decreases gently. In this case, since the current value supplied to the solenoid  205  increases, the magnetic attraction force increases at a timing in which the displacement amount of the valve body  214  is small. Accordingly, there is an effect that the valve body  214  can stably perform the valve opening operation. Particularly when the fuel pressure supplied to the fuel injection device  540  is large, the differential pressure acting on the valve body  214  increases. For this reason, a current waveform of applying a voltage of 0 V to the solenoid  205  may be used. Further, since the current promptly decreases even when the application voltage to the solenoid  205  is 0 V when the inductance of the fuel injection device  540  is small, the current may be controlled by using the application of the voltage of 0 V. 
         [0091]    The application voltage obtained when the peak current value I peak  changes to the first drive current  610  may be changed in response to the specification of the fuel injection device  540  or the fuel pressure supplied to the fuel injection device  540 . 
         [0092]    Further, when the first hold current period changes to the second hold current period, a voltage of 0 V or less may be applied to the solenoid  205  to rapidly decrease the current value. When the supply of the current to the switching elements  505 ,  506 , and  507  is not allowed so that the boost voltage VH is applied to the solenoid  205  in the negative direction, a speed at which the current  603  decreases can be increased. Since an effect of decreasing the speed of the needle  202  is improved, it is possible to reduce the undulation of the injection amount characteristic caused by the bound of the valve body  214  and to improve the injection amount injection accuracy. 
         [0093]    When the injection pulse Ti is stopped during a transition period  630  from the first current hold period to the second current hold period, the current waveform supplied to the solenoid  205  does not change even when the injection pulse Ti changes. Thus, a dead zone in which the injection amount does not change may be generated even when the injection pulse Ti changes. In this case, the injection amount is the same in a condition that the injection pulse is stopped at a timing in which the transition period  630  starts, that is, the first current hold period ends and a condition that the injection pulse is stopped at a timing in which the transition period  630  ends, that is, the second current hold period starts. Thus, when the injection amount larger than the injection amount at a timing in which the first current hold period ends is injected, the injection amount can be continuously controlled in such a manner that the injection pulse width is set while skipping the dead zone. 
         [0094]    Further, when the supply of the current to the switching elements  505  and  507  is stopped and the current is supplied to the switching element  506  so that a voltage of about 0 V is applied to the solenoid  205 , the boost voltage VH is applied to the solenoid  205  in the negative direction after the injection pulse Ti is stopped even when the injection pulse Ti is stopped during the transition period  630 . Thus, it is possible to control the width of the current waveform application time of even when the application of the injection pulse Ti to the transition period  630  is stopped and to reduce the dead zone in which the injection amount does not change even when the injection pulse Ti changes. Accordingly, it is possible to ensure the continuity of the injection amount. As a result, since the injection amount can be appropriately changed in response to the rotation speed of the operation condition, drivability is improved. 
         [0095]    Further, since the fuel adhering to wall surfaces of a piston and a cylinder hardly evaporates while the engine is cooled, there is a tendency that unburned particles increase in a cold start condition. As means for suppressing the generation of unburned particles in a cold start condition, it is effective to adopt a method of simultaneously achieving a low-startup exhaust and an early catalyst activation due to the adhesion of the fuel to the piston or cylinder wall by dividing the fuel injection until a fast idle state in which the engine rotation speed is constant at the cold start of the engine. In this case, when the undulation of the injection amount characteristic occurs after the half-lift region  740  changes to the full-lift region  741  as in the conventional current waveform  621 , the injection amount cannot be continuously controlled and a range in which the fuel cannot be injected is generated. When it is desired to inject the fuel at a flow rate in which the undulation of the injection amount is generated, a method of injecting the fuel by changing the number of split injections of the fuel during one intake/exhaust stroke is also considered. However, when the number of split injections of the fuel increases during the cold start-up, an error occurs between the actual fuel injection amount and the target injection amount calculated by the ECU  104  at a timing of changing the number of split injections and thus a combustion becomes unstable. 
         [0000]    Accordingly, there is a tendency that PN increases. 
         [0096]    When the current waveform  610  of the first embodiment of the invention is used, it is possible to ensure the continuity of the injection amount until the half-lift region  742  changes to the full-lift region  743  and to suppress a change in the number of split injection in a condition that the accuracy of the injection amount is required. Thus, it is possible to improve the stability of the combustion and to suppress the PN. 
         [0097]    Further, when the interruption timing of the peak current I peak  is set to be earlier than the start of the valve opening operation of the valve body  214 , it is possible to control a collision speed at which the needle  202  collides with the valve body  214  and to control the kinetic energy given from the needle  202  to the valve body  214 . As a result, it is possible to control the gradient of the valve displacement amount after the valve body  214  starts to open the valve by changing a timing t 62  in which the peak current I peak  is interrupted. Specifically, when the timing t 62  of interrupting the peak current I peak  is set to be earlier, a speed at which the needle  202  collides with the valve body  214  decreases and the kinetic energy given to the valve body  214  decreases. For this reason, the gradient of the valve displacement amount decreases and the gradient of the injection amount characteristic in the half-lift region decreases. As a result, since the injection amount can be accurately controlled, the PN suppression effect is improved. 
         [0098]    Further, since the differential pressure acting on the valve body  214  increases when the fuel pressure supplied to the fuel injection device  540  is large, the gradient of the displacement amount of the valve body  214  decreases after the valve body  214  starts to open the valve. Thus, the magnetic attraction force necessary until the valve body  214  reaches the maximum height position increases when the fuel pressure increases and the magnetic attraction force necessary until the valve body  214  reaches the maximum height position decreases when the fuel pressure decreases. Thus, the first drive current  610  may be determined in response to the fuel pressure. 
         [0099]    When the fuel pressure increases to a set value or more, the first drive current  610  or the application time is increased to ensure the magnetic attraction force necessary for the valve opening operation and to improve the stability of the behavior of the valve body  214 . As a result, since it is possible to accurately control the maximum height position and the valve open period in which the valve body  214  opens the valve, it is possible to improve the accuracy of the injection amount. When the fuel pressure decreases to a set value or less, the first drive current  610  or the application time is decreased to improve the accuracy of the injection amount. 
         [0100]    Accordingly, even when the fuel pressure changes in the half-lift region, it is possible to suppress a change in gradient of the valve body displacement amount until the valve body  214  reaches the height position lower than the maximum height position from the start of the valve opening operation and to improve a behavior of the stability of the valve body  214 . 
         [0101]    Since the differential pressure acting on the valve body  214  increases when the fuel pressure increases, the valve closing delay time until the valve body  214  closes the valve after the stop of the injection pulse Ti is shortened. Since the differential pressure is influenced after the valve body  214  starts to open the valve, the behavior of the valve body  214  is largely influenced after the valve body reaches the height position  650  lower than the maximum height position. When the fuel pressure increases, the first drive current  610  is increased to increase the valve closing delay time. Accordingly, it is possible to remove an influence on the valve body  214  due to an increase in differential pressure in accordance with an increase in fuel pressure. As a result, since it is possible to suppress a change in height position  650  lower than the maximum height position and a change in valve open time of the valve body  214  in accordance with an increase in fuel pressure, it is possible to perform a stable operation with respect to a change in fuel pressure. 
         [0102]    Q 710  of  FIG. 7  indicates the injection amount characteristic when the first drive current is corrected in a condition that the fuel pressure increases. Even when the valve open period of the valve body  214  and the height position  650  lower than the maximum height position are the same, the flow rate of the fuel flowing in an injection hole  219  increases when the fuel pressure changes and thus the injection amount also increases. Generally, in a hole like the injection hole  219 , the injection amount is proportional to √ of the fuel pressure. When a change in valve open period of the valve body  214  is suppressed in a case where the fuel pressure increases, it is possible to accurately calculate a change in injection amount by the ECU  104  and to improve the accuracy of the injection amount. As a result, since it is possible to control the minute injection amount, it is possible to suppress the PN by increasing the number of multi-stage injections. 
         [0103]    Further, since the differential pressure acting on the valve body  214  increases when the fuel pressure increases, the magnetic attraction force necessary for keeping the valve body  214  in the valve opened state changes. Thus, the second drive current  611  may be determined in response to the fuel pressure. Specifically, when the fuel pressure increases, the second drive current  611  may be increased to increase the magnetic attraction force. 
         [0104]    Further, since the differential pressure acting on the valve body  214  increases, the valve closing delay time is shortened. Since the second drive current  611  is increased to increase the valve closing delay time, it is possible to obtain an effect of suppressing a decrease in valve closing delay time in accordance with an increase in differential pressure. As a result, since it is possible to suppress a change in valve open period and a change in valve closing delay time of the valve body  214  in accordance with an increase in fuel pressure and to suppress a change in injection amount, it is possible to improve the PN suppression effect. Additionally, since it is possible to improve the accuracy of the flow rate in the half-lift region and the full-lift region by the corrections of the first drive current and the second drive current, it is possible to obtain an effect of improving the accuracy of the injection amount in a target region by a single correction thereof. 
         [0105]    Further, the differential pressure acting on the valve body  214  in accordance with an increase in fuel pressure is large in the half-lift condition in which the valve body  214  does not reach the maximum height position compared to a case where the valve body  214  reaches the maximum height position. Regarding the differential pressure, the cross-sectional area of the seat portion decreases when the valve body  214  has a small displacement amount and an influence of a decrease in static pressure increases in accordance with an increase in flow rate of the fuel flowing in the seat portion. Thus, in the case of the corrections of the first drive current  610  and the second drive current  611  when the fuel pressure increases, the corrections may be performed so that an increase in current of the first drive current  610  is larger than an increase in current of the second drive current  611 . When the current value  611  of the second drive current  611  is set to be smaller than that of the first drive current  610 , the current supplied to the solenoid  205  can be suppressed and thus a merit of suppressing power consumption is obtained. 
         [0106]    Further, since it is possible to suppress the heating of the solenoid  205  in accordance with a decrease in current value, it is possible to suppress a change in temperature in accordance with the heating of the solenoid  205  and to suppress a change in resistance value of the solenoid  205 . Since the current supplied to the solenoid  205  is dependent on the resistance value of the solenoid  205  compared to the Ohm&#39;s law, it is possible to suppress a change in current by suppressing a change in resistance value. Accordingly, an effect of improving the accuracy of the injection amount is improved. Additionally, the fuel pressure can be detected in such a manner that a signal of the pressure sensor  102  attached to the fuel pipe  105  is detected by the ECU  104 . 
         [0107]    Further, in order to suppress the air-fuel ratio variation for each cylinder, there is a case in which the injection pulse is corrected for each cylinder by the A/F sensor. Since the sensitivity given to the injection amount of the injection pulse is small, it is possible to obtain an effect of preventing an erroneous correction for the correction calculated by the A/F sensor and thus to accurately control the injection amount. 
         [0108]    Further, the injection amount may be controlled by controlling the injection pulse width of the first hold current period in a condition that the valve body  214  is driven in the half-lift state. Since the current value is kept at a constant value in the first hold current period  610 , it is possible to accurately control the magnetic attraction force regardless of the influence of a change in battery voltage VB. 
         [0109]    Further, the first drive current  610  may be stopped before the valve body  214  reaches the maximum height position. When the first drive current  610  is stopped, the magnetic attraction force acting on the needle  202  decreases and thus a speed reduction effect can be obtained. Since the valve body  214  decreases in speed before reaching the maximum height position due to this effect, it is possible to reduce the bound of the valve body  214  caused when the needle  202  collides with the fixed core  207 . As a result, it is possible to ensure the continuity of the flow rate when the half-lift region changes to the full-lift region. When the undulation of the injection amount is caused by the bound of the valve body  214  in a section in which the half-lift region changes to the full-lift region, there is a case in which the combustion of the engine becomes unstable. When the control method of the first embodiment is used, it is possible to accurately control the injection amount from the minute flow rate to the large flow rate and thus to obtain an effect of improving the combustion robustness of the engine. 
         [0110]    In the current waveform  621 , in a case where the fuel in one intake/exhaust stroke is divided and injected (split injection), when the number of split injections is large and the interval between the injections is small, the boost voltage VH does not return to the initial value and the fuel is injected in a condition that the boost voltage VH is small. In the current waveform  610  of the embodiment, since the application period of the boost voltage VH is short compared to the current waveform  621 , there is an effect that a decrease in boost voltage VH can be suppressed. Since it is possible to accurately control the displacement amount of the valve body  214 , it is possible to improve the accuracy of the injection amount in the split injection. As a result, since it is possible to improve the homogeneity of the air-fuel mixture for each injection, it is possible to suppress the PN. Further, since the application time of the boost voltage VH is shortened, it is possible to suppress the heating of the boost circuit  514  and the power consumption of the ECU  104  and thus to suppress the heating of the coil  205 . 
         [0111]    Next, when the injection pulse in the second drive current  611  is turned off, the supply of the current to the switching elements  505 ,  506 , and  507  is stopped. When the supply of the current to the switching elements  506  and  507  is stopped, the current cannot flow to the ground potential (GND). For this reason, the voltage of the voltage source side terminal increases due to the counter electromotive force generated by the inductance of the fuel injection device  540  and charge returns from the ground potential (GND) to the high voltage source via the diode  509 , the fuel injection device  540 , and the diode  510  so that the charge is accumulated in the capacitor  533 . 
       Second Embodiment 
       [0112]    Hereinafter, a current control method of a fuel injection device according to a second embodiment will be described with reference to  FIG. 8 .  FIG. 8  is a diagram showing a relation of the injection pulse, the drive current supplied to the fuel injection device, a voltage Vinj between terminals of the solenoid  205  and the switching elements  505 ,  506 , and  507  of the fuel injection device  540 , and a behavior of the valve body  214  and the needle  202  in time according to the second embodiment of the invention. In the drawing, the first drive current  610  when using the current waveform of  FIG. 6  is indicated by a dotted line. Additionally, the same reference numerals are given to the same components as those of  FIG. 6 . Further, the drive device of the second embodiment is the same as that of the first embodiment. A difference from the current waveform of the first embodiment is that a current value  701  of the first hold current period is higher than the current value  604 , the boost voltage VH is applied to the solenoid  205  to reach the current  701  after the peak current I peak  is stopped, and the boost voltage VH is applied to the solenoid  205  in the negative direction during a transition period from the first hold current period to the second hold current period. 
         [0113]    In the current waveform  710  of the second embodiment, the supply of the current to the switching elements  505 ,  506 , and  507  is stopped after reaching the peak current I peak  and the boost voltage VH is applied to the solenoid  205  in the negative direction to rapidly decrease the current value as in the current  802 . Additionally, a period  830  of applying the boost voltage VH in the negative direction may be set as a time in the CPU  501  or the IC  501  in advance or may be set as a timing in which the current value is lower than a threshold value. When the boost voltage VH in the negative direction is set by time, the time resolution is higher than that of the current value and the application time of the boost voltage VH can be accurately controlled. Accordingly, the accuracy of the time in which the current reaches the first drive current is improved. As a result, it is possible to accurately determine a minimum range in which the injection amount can be controlled in the half-lift state. Further, when the application time of the boost voltage VH in the negative direction is set to a timing in which the current value is lower than the threshold value after reaching the peak current value I peak , it is possible to keep the current value at a constant value at a timing t 83  even when the resistance value of the solenoid  205  changes or the voltage value of the boost voltage VH changes. Accordingly, it is possible to suppress a decrease in magnetic attraction force caused by a decrease in current value. Additionally, the application time of the boost voltage VH in the negative direction may be a combination of the above-described time setting method and the method of setting the threshold value of the current. Specifically, the period  830  in which the boost voltage VH is applied in the negative direction after the current reaches the peak current value I peak  may be set by time and the boost voltage VH is applied so that the current value reaches a current  801  at a timing in which the current is lower than the threshold value set by the CPU  501  or the IC  502  after the elapse of the period  830 . As a result, since it is possible to finely set the time resolution and to keep the current value even when the battery voltage VB or the resistance value of the solenoid  205  changes, it is possible to improve the accuracy of the injection amount. 
         [0114]    At the timing t 83  in which the period  830  ends, the current is supplied to the switching elements  505  and  506  and the boost voltage VH is applied to the solenoid  205  so that the current reaches the current  801 . When the boost voltage VH is applied so that the current value reaches the current  801 , the current value reliably reach the current  801  regardless of a change in battery voltage VB. Further, since the current value supplied to the solenoid  205  by the boost voltage VH is larger than that of the battery voltage VB according to the Ohm&#39;s law, it is possible to shorten a time from the timing t 83  to the first drive current  801  and to expand a control range in a direction in which the displacement amount of the valve body  214  is small. Thus, the minute injection amount can be controlled. As a result, since a required injection amount can be realized even in a case where an injection having a small split ratio is extremely required in the compression stroke as in the case where the split ratio of the injection amount is 9:1 in the intake stroke and the compression stroke in the condition of the multi-stage injection, it is possible to improve the homogeneity of the air-fuel mixture or to realize the weak stratified charge combustion which locally forms a lean air-fuel mixture around an ignition plug. Accordingly, it is possible to achieve both low fuel consumption and PN suppression. 
         [0115]    When the current value reaches the current  801 , the supply of the current to the switching element  505  is stopped and the current is supplied to the switching elements  506  and  507  so that the battery voltage VB is applied to the solenoid  205 . Generally, on the assumption that the number of windings of the solenoid  205  is N and the magnetic flux generated in the magnetic circuit is φ, the voltage V between the terminals of the fuel injection device  540  is expressed by the term of −Ndφ/dt of the induced electromotive force and the product of the resistance R of the solenoid  205  caused by the Ohm&#39;s law and the current i flowing through the solenoid  205  as shown in Formula (1). 
         [0000]    
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       
                         - 
                         N 
                       
                        
                       
                         d 
                         dt 
                       
                     
                     + 
                     
                       R 
                       · 
                       i 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0116]    When the current value  801  of the first hold current period is larger than the current value  604  or in a condition that a change in magnetic flux in accordance with the valve opening operation of the needle  202  increases so that the induced electromotive force increases, there is a case in which the current flowing in the solenoid  205  decreases and does not reach the current  801  even when the battery voltage VB is applied to the solenoid  205  after reaching the first hold current period. In this case, in the first hold current period, the current switching control, that is, the switching of the supply of the current to the switching element  507  is not performed and the battery voltage VB is continuously applied to the solenoid  205 . When the needle  202  reaches the maximum height position, a change in induced electromotive force caused by the movement of the needle  202  in the valve opening direction disappears and thus the gradient of the current value changes as in the current  804 . Since the current value supplied to the solenoid  205  changes in accordance with a change in battery voltage VB when the injection amount in the half-lift region  742  is controlled while the battery voltage VB is continuously applied as in the current waveform  810 , the magnetic attraction force acting on the needle  202  changes. For example, when the current is supplied to an in-vehicle device connected to the battery voltage VB during the first hold current period, the voltage value of the battery voltage VB decreases, the current value supplied to the solenoid  205  decreases, and the magnetic attraction force decreases. As a result, when the injection pulse width in the first hold current period is stopped, the maximum displacement of the valve body  214  and the valve open period decrease and thus the injection amount decreases. 
         [0117]    The application time of the battery voltage VB after the timing t 83  or the supply of the current to the switching element  507  may be detected by the CPU  501  or the IC  502  and the target current value  801  of the first hold current period may be decreased when the battery voltage VB is continuously applied. The supply of the battery voltage VB may be normally performed by detecting a state where the current switching control of the first hold current period is not performed due to a decrease in battery voltage VB and changing the target current value  801  to perform the current switching control. As a result, since it is possible to keep the magnetic attraction force acting on the needle  202  even when the battery voltage VB changes, it is possible to accurately control the displacement amount of the valve body  214  in the half-lift region  742 . As a result, since it is possible to accurately control the minute injection amount in the half-lift region  742 , the homogeneity of the air-fuel mixture is improved and thus the PN can be suppressed. Specifically, the target current value  801  may be controlled to decrease when the battery voltage VB is continuously applied. 
         [0118]    Further, when the battery voltage VB is continuously applied from the time at which the current reaches the current  801  after the timing t 83 , the supply of the current to the switching element  507  is stopped, the current is supplied to the switching element  506 , and the switching of the supply of the current to the switching element  505  is performed to determine the application of the boost voltage VH. Since the boost voltage VH is not easily influenced by a change in battery voltage VB, it is possible to reliably perform the current value switching control in the first hold current period of keeping the current  801  and thus to stably operate the valve body  214  in the half-lift condition. Further, since the current flowing in the solenoid  205  depends on the application voltage V from Formula (1), it is possible to keep the current value of the first drive current even in a condition that the current value  801  is high or the induced electromotive force in accordance with the movement of the needle  202  is large by using the boost voltage VH of which the voltage value is higher than that of the battery voltage VB to generate the first drive current, it is possible to increase the magnetic attraction force necessary for the valve opening operation. As a result, since it is possible to ensure the stability of the valve body  214  in the half-lift condition, the homogeneity of the air-fuel mixture is improved in accordance with the improvement in accuracy of the injection amount and the PN can be reduced. Further, the boost voltage VH may be used to generate the first drive current in a condition that the fuel pressure is high. Since the fluid pressure acting on the valve body  214  increases in a condition that the fuel pressure is high, the needle  202  and the valve body  214  can reach the maximum opening degree and thus the accuracy of the injection amount can be improved. Meanwhile, in the battery voltage VB, the application time width during the current switching control is smaller than that of the boost voltage VH and a difference between the current value  801  of the first drive current and the lower limit of the current value is small. Thus, since a change in magnetic attraction force in accordance with the switching of the current decreases, it is possible to improve the accuracy of the magnetic attraction force acting on the needle  202 . As a result, since the accuracy of the injection amount is improved, the homogeneity of the air-fuel mixture is improved and the PN can be reduced. 
         [0119]    Further, when the battery voltage VB is continuously applied even when the target current  801  is small, the application of the boost voltage VH may be switched. As a result, in the case of the normal drive state, the number of times of using the boost voltage VH is decreased to suppress the power consumption or the heating of the boost circuit  514 . Further, when the battery voltage VB largely decreases unexpectedly, the valve open period and the displacement of the valve body  214  at the boost voltage VH are controlled to suppress the power consumption and the heating and to improve the robustness. 
         [0120]    Further, a combination of the boost voltage VH and the battery voltage VB may be used to generate the first drive current. Specifically, a current control is performed such that the battery voltage VVB is applied to gently decrease the current when the current value reaches the current  801  after the timing t 83  and the boost voltage VH is applied so that the current value reaches the current  801  again after a predetermined time elapses or when the current value becomes lower than a predetermined threshold value. When the current value is made to reliably reach the current  801  by the application of the battery voltage VH and the current is gently decreased by the application of the battery voltage VB, it is possible to increase the current switching width in the first drive current and to decrease the number of times of switching the voltage. As a result, since it is possible to decrease a change in magnetic attraction force, it is possible to improve the accuracy of the injection amount. 
         [0121]    Further, the second drive current may be generated by switching the application of the battery voltage VB after the first drive current changes to the second drive current before and after the needle  202  and the valve body  214  reach the maximum opening degree. Since the differential pressure acting on the valve body  214  decreases compared to the half-lift condition after the needle  202  reaches the maximum opening degree, the needle  202  and the valve body  214  can be kept in the valve opened state even when the battery voltage VB is selected from the application of the boost voltage VH. Further, since a range in which the boost voltage VH is used can be decreased by using the battery voltage VB for the second drive current even when the boost voltage VH is used for the first drive current, it is possible to suppress a decrease in boost voltage VH. As a result, since a decrease width of the boost voltage VH can be suppressed when the next injection is performed in the condition of the multi-stage injection, it is possible to suppress a change in injection amount for the first and second injections. Also, it is possible to improve the homogeneity of the air-fuel mixture and to suppress the PN. 
       Third Embodiment 
       [0122]    Hereinafter, a configuration and an operation of a fuel injection device of a third embodiment and a method of controlling the fuel injection device will be described with reference to  FIGS. 9 and 10 .  FIG. 9  is an enlarged cross-sectional view showing the vicinity of the needle  202  and the valve body  214  of the fuel injection device of the third embodiment. Additionally, in  FIG. 9 , the same reference numerals will be given to the same components as those of  FIGS. 2 and 3 .  FIG. 10  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a voltage Vinj between terminals of the solenoid  205  and the switching elements  505 ,  506 , and  507  of the fuel injection device, and a behavior of the valve body  214  and the needle  202  in time according to the third embodiment of the invention. Additionally, in  FIG. 10 , the same reference numerals will be given to the same components as those of  FIG. 6 . 
         [0123]    There is no difference in the fuel injection device between the first embodiment and the third embodiment, but there is a difference in that the third spring  234  and the intermediate member  220  are not provided and a gap between the contact portion near the needle  202  and the contact portion near the valve body  214  becomes zero while the valve body  214  and the valve seat  218  are in contact with each other. 
         [0124]    The fuel injection device shown in  FIG. 9  is a normally closed electromagnetic valve (an electromagnetic fuel injection device). Then, in a state where the current is not supplied to the solenoid  205 , the valve body  214  is urged in the valve closing direction by a spring  901  which is a first spring and the valve body  214  comes into close contact with the valve seat  218  to become the valve closed state. In the valve closed state, a force which is generated by the return spring  212  corresponding to the second spring and is applied in the valve opening direction acts on the needle  202 . At this time, since a force which is generated by the spring  910  and is applied to the valve body  214  is larger than a force generated by the return spring  212 , the end surface  302 E of the needle  202  contacts the valve body  214  so that the needle  202  is stopped. Further, the valve body  214  and the needle  202  are formed to be displaceable relatively and are enclosed in the nozzle holder  201 . Further, the nozzle holder  201  includes an end surface  303  which is the spring seat of the second spring  212 . A force which is generated by the spring  910  is adjusted at the time of assembly by the press-insertion amount of the spring retainer  224  which is fixed to the inner diameter of the fixed core  207 . 
         [0125]    When the valve body  214  is closed, a differential pressure is generated between the upper and lower portions of the valve body  214  by the fuel pressure and the valve body  214  is pressed in the valve closing direction by the differential pressure obtained by multiplying the fuel pressure by the pressure receiving area of the seat inner diameter at the valve seat position and the load of the spring  210 . When the current is supplied to the solenoid  205  in the valve closed state, a magnetic field is generated in the magnetic circuit, a magnetic flux passes between the fixed core  207  and the needle  202 , and a magnetic attraction force acts on the needle  202 . The valve body  214  starts to be displaced in the direction of the fixed core  207  along with the needle  202  at a timing in which the magnetic attraction force acting on the needle  202  exceeds the differential pressure and the load of the set spring  210 . 
         [0126]    After the valve body  214  starts the valve opening operation, the needle  202  moves to the position of the fixed core  207  and the needle  202  collides with the fixed core  207 . Although the needle  202  bounds back by the repelling force applied from the fixed core  207  after the needle  202  collides with the fixed core  207 , the needle  202  is suctioned to the fixed core  207  by the magnetic attraction force acting on the needle  202  to be stopped. At this time, since a force is applied to the needle  202  in the direction of the fixed core  207  due to the second spring  212 , it is possible to shorten a time until the rebounding converges. Since the rebounding operation is small, a time in which a gap between the needle  202  and the fixed core  207  is large is shortened and thus a stable operation can be performed even in the smaller injection pulse width. 
         [0127]    The needle  202  and the valve body  202  having finished the valve opening operation in this way are stopped in the valve opened state. In the valve opened state, a gap is formed between the valve body  202  and the valve seat  218  and the fuel is injected from the injection hole  219 . The fuel flows to the downstream direction while passing through the center hole provided in the fixed core  207  and the fuel passage hole provided in the needle  202 . 
         [0128]    When the supply of the current to the solenoid  205  is stopped, the magnetic flux generated in the magnetic circuit disappears and the magnetic attraction force also disappears. Since the magnetic attraction force acting on the needle  202  disappears, the needle  202  and the valve body  214  are pressed back to the valve closing position in which both members contact the valve seat  218  due to the differential pressure and the load of the spring  910 . 
         [0129]    Further, when the valve body  214  closes the valve from the valve opened state, the valve body  214  contacts the valve seat  218 , the needle  202  is separated from the valve body  214 , and the needle  202  to move in the valve closing direction. Then, the needle is returned to the initial position in the valve closed state by the return spring  212  after moving for a predetermined time. Since the needle  202  is separated from the valve body  214  at a timing in which the valve body  214  completes the valve opening operation, the mass of the movable member at the moment in which the valve body  214  collides with the valve seat  218  can be reduced by the mass of the needle  202 . For this reason, since the collision energy generated by the collision with the valve seat  218  can be decreased, it is possible to suppress the bound of the valve body  214  generated when the valve body  214  collides with the valve seat  218 . 
         [0130]    In the fuel injection device of the embodiment, the valve body  214  and the needle  202  cause a relative displacement for a short time in which the needle  202  collides with the fixed core  207  for the valve opening operation or the valve body  214  collides with the valve seat  218  for the valve closing operation. Accordingly, there is an effect that the bound of the needle  202  with respect to the fixed core  207  or the bound of the valve body  214  with respect to the valve seat  218  is suppressed. 
         [0131]    Next, a method of driving the fuel injection device of the third embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a voltage Vinj between terminals of the solenoid  205  and the switching elements  505 ,  506 , and  507  of the fuel injection device, and a behavior of the valve body  214  and the needle  202  in time according to the third embodiment of the invention. Additionally, in  FIG. 10 , the same reference numerals will be given to the same components as those of  FIG. 6 . A difference between  FIG. 10  and  FIG. 6  is that the peak current I peak  is stopped and the first hold current period is selected after the valve body  214  starts to open the valve. 
         [0132]    Next, a method of driving the valve body  214  of the invention will be described. First, when the injection pulse width Ti is transmitted from the CPU  501  to the driving IC  502  via the communication line  504  at a timing t 11 , the switching element  505  and the switching element  506  are turned on. Accordingly, the boost voltage VH higher than the battery voltage VH is applied to the solenoid  205  and the drive current is supplied to the fuel injection device to rapidly raise the current. When the current is supplied to the solenoid  205 , a magnetic attraction force is exhibited between the needle  202  and the fixed core  207 . At a timing in which a force in the valve opening direction corresponding to the resultant force of the magnetic attraction force and the load of the second spring  212  exceeds the load generated in the spring  910  corresponding to the first spring as a force in the valve closing direction, the needle  202  and the valve body  214  start to be displaced and the fuel is injected from the fuel injection device. 
         [0133]    A differential pressure which is generated by the pressure of the fuel is applied to the valve body  214  and the differential pressure acting on the valve body  214  is generated by a decrease in pressure of the front end portion of the valve body  214  according a decrease in pressure generated by a decrease in static pressure caused by a Bernoulli effect after the flow rate of the fuel at the seat portion increases in a range having a small passage cross-sectional area in the vicinity of the seat portion of the valve body  214 . Since the differential pressure is largely influenced by the passage cross-sectional area of the seat portion, the differential pressure increases in a condition in which the displacement amount of the valve body  214  is small and the differential pressure decreases in a condition in which the displacement amount is large. Thus, there is a need to increase the magnetic attraction force at a timing in which the valve body  214  starts to open the valve from the valve closed state so that the displacement is small, the differential pressure increases, and the valve opening operation is difficult in a configuration of the fuel injection device of the third embodiment in which the needle  202  does not collide with the valve body  214 . Since a timing t 13  at which the peak current value I peak  stops is set to be later than a timing t 12  at which the valve body  214  becomes the valve opened state, it is possible to ensure the magnetic attraction force at a timing in which the differential pressure increases and to improve the stability when the valve is opened. As a result, since it is possible to accurately control the injection period and the displacement amount of the valve body  214  in the half-lift region, the accuracy of the injection amount is improved and the PN suppression effect is improved. 
         [0134]    When the current reaches the peak current value I peak , the supply of the current to the switching elements  505  and  507  is stopped and the current is supplied to the switching element  506  so that a voltage of about 0 V is applied to the solenoid  205 . Accordingly, the current gently decreases from the peak current value I peak  as in a current  1002 . In the current waveform  1001  of the embodiment, the valve body  214  and the needle  202  are displaced in the valve opening direction to ensure a necessary magnetic attraction force and the peak current I peak  is stopped at an early timing. Accordingly, it is possible to ensure the valve opening stability and to decrease the gradient of the displacement amount of the valve body  214 . Further, since the timing t 13  of stopping the peak current I peak  is set to a timing after the valve body  214  starts to open the valve, the magnetic attraction force generated by the needle  202  increases. Thus, even when the fuel pressure is large, the valve body  214  can be stably controlled until the valve opened state. As a result, since it is possible to control the displacement of the valve in the half-lift region while the displacement amount of the valve body  214  is stabilized, the accuracy of the injection amount is improved. 
         [0135]    In the fuel injection device of the third embodiment, the valve opening start timing of the valve body  214  is largely dependent on the fuel pressure supplied to the fuel injection device. Since the differential pressure acting on the valve body  214  increases when the fuel pressure increases, the valve opening start timing is delayed. Thus, since an influence of the fuel pressure on the displacement amount of the valve body  214  is large, an effect of improving the accuracy of the injection amount is improved when the control method described in the first and second embodiments is applied to the fuel injection device of the third embodiment and thus the PN can be suppressed. 
       Fourth Embodiment 
       [0136]    Hereinafter, a configuration and an operation of a fuel injection device of a fourth embodiment will be described with reference to  FIG. 11 .  FIG. 11  is an enlarged cross-sectional view showing the vicinity of the valve body  114  and the needle  202  of the fuel injection device of the fourth embodiment. Additionally, in  FIG. 11 , the same reference numerals will be given to the same components as those of  FIGS. 2 and 3 . 
         [0137]    A difference from the fuel injection device of the first embodiment shown in  FIG. 11  is that the third spring  234  and the intermediate member  320  are not provided and a stopper member  1151  and a thin plate member  1152  are provided. 
         [0138]    The stopper member  1151  is fixed to the valve body  214  by press-inserting or welding. Further, the thin plate member  1151  is weld-fixed to the needle  202  by a lower end surface  1153  of the needle  202 . The second spring  1150  is disposed between the stopper member and the thin plate member  1152  and urges the needle  202  in the valve closing direction. A gap G 5  is provided between the valve body  214  and the needle  202  and a value obtained by subtracting the gap G 5  from the gap G 6  between the needle  202  and the fixed core  207  becomes the maximum height position of the valve body  214 . Additionally, the thin plate member  1152  is provided with a plurality of fuel passage holes  1156  in the circumferential direction and the fuel which flows from the upstream side of the fuel injection device flows toward the downstream side while passing through the fuel passage hole  1155  and the fuel passage hole  1156  of the needle  202 . 
         [0139]    Next, an operation of the fuel injection device will be described. Additionally, the configuration of the drive circuit and the current generation means are the same as those of the first embodiment. When the current is supplied to the solenoid  205 , a magnetic attraction force acts on the needle  202 . The needle  202  starts to be displaced in the valve opening direction at a timing in which the magnetic attraction force exceeds the load of the second spring  1150 . When the needle  202  displaces the gap G 5 , the needle  202  collides with a lower end surface of a flange portion  1154  of the valve body  214  and the valve body  214  starts to open the valve so that the fuel is injected from the injection hole  219 . When the needle  202  displaces the gap G 6 , the needle  202  collides with the fixed core  207  and the needle  202  and the valve body  214  reach the maximum height position. An effect of opening the valve by the collision between the needle  202  and the valve body  214  is the same as that of the first embodiment, but since the third spring  234  and the intermediate member  320  are not provided in the configuration shown in the fourth embodiment, the number of components is small and the cost can be reduced. However, since the second spring  1150  urges the needle  202  in the valve closing direction instead of the valve opening direction in which the bound of the needle  202  is suppressed when the needle  202  collides with the fixed piece  207 , it is difficult to stabilize the bound with respect to the valve body  214 . Thus, since a relation between the injection amount and the injection pulse becomes non-linear in the full-lift region after the needle  202  reaches the valve opening position, a change in injection amount may occur. In the fuel injection device shown in  FIG. 11 , the boost voltage VH may be applied to the solenoid  205  in the negative direction before the needle  202  reaches the maximum height position after the current is supplied to the solenoid  205  to reach the first drive current. Asa result, the magnetic attraction force acting on the needle  202  rapidly decreases and the needle  202  is decelerated by the differential pressure acting on the valve body  214  and the first spring  210 . Accordingly, since a speed at which the needle  202  collides with the fixed core  207  decreases, the bound of the needle  202  can be suppressed. As a result, since the bound of the valve body  214  is reduced, it is possible to improve the accuracy of the injection amount after the valve body  214  reaches the maximum height position. Further, when a surface facing the fixed core  207  in the needle  202  is substantially flat, the fuel passage hole  1155  of the needle  202  is blocked by the fixed core  207  and a gap between the flange portion  1154  of the valve body  214  and the inner diameter of the fixed core  207  decreases, an effective cross-sectional area of the fuel passage cannot be easily ensured. In this case, a tapered surface  1160  may be provided in the inner diameter of the core  207  to ensure a fuel passage between the fixed core  207  and the valve body  214 . Further, the position of the fuel passage of the needle  202  in the radial direction may be located near the outer diameter in relation to the outer diameter of the flange portion  1154  of the valve body  214 . By this effect, it is possible to suppress the cross-sectional area of the fuel passage of the needle  202  from being decreased by the flange portion  1154 . Further, since it is possible to increase the contact area between the valve body  214  and the needle  202 , there is an effect of suppressing the collision load generated when the needle  202  collides with the valve body  214 . As a result, since it is possible to suppress the abrasion of the collision surface between the valve body  214  and the needle  202 , it is possible to suppress a change in injection amount and to improve the accuracy of the injection amount. Further, a longitudinal end portion  1161  of the tapered surface  1160  in a surface facing the needle in the fixed core  207  may be located near the inner diameter in relation to the outer diameter of the fuel passage hole  1155  of the needle  202 . When a gap between the needle  202  and the fixed core  207  decreases, the fuel pressure between the needle  202  and the fixed core  207  increases due to a squeeze effect and a differential pressure is generated in a direction in which the movement of the needle  202  is disturbed. Since the outer diameter of the fuel passage hole  1155  of the needle  202  is located at the outer diameter in relation to the longitudinal end portion  1161  of the tapered surface  1160 , an excluded flow amount between the needle  202  and the fixed core  207  in accordance with the movement of the needle  202  easily flows to the fuel passage hole  1155  of which the cross-sectional area of the fuel passage increases and thus there is an effect of reducing the differential pressure acting on the needle  202 . Further, when the gap between the valve body  214  and the fixed core  207  and the cross-sectional area of the fuel passage of the needle  202  are large, it is possible to suppress pressure loss generated when the fuel passes through the fuel passage. Accordingly, it is possible to decrease the vertical differential pressure between the valve body  214  and the needle  202  and to decrease the differential pressure acting on the valve body  214  and the needle  202 . As a result, when an influence of the non-linear differential pressure acting on the needle  202  is suppressed, the needle  202  and the valve body  214  behave stably and thus the accuracy of the injection amount can be improved. Further, since the differential pressure acting on the valve body  214  and the needle  202  increases in accordance with an increase in fuel pressure, it is possible to operate the needle  202  and the valve body  214  in a condition of a high fuel pressure by decreasing the differential pressure. Since the particle diameter of the fuel injected from the injection hole  219  can be decreased in accordance with an increase in fuel pressure, the homogeneity of the air-fuel mixture is improved and thus the PN can be suppressed. 
         [0140]    Further, the fuel injection device described in the fourth embodiment may be controlled by the current waveform control method described in the first, second, and third embodiments. 
       Fifth Embodiment 
       [0141]    Hereinafter, a control method and a detection method for a change in operation of a valve of the valve body  214  of the fuel injection device of each cylinder of the fifth embodiment will be described with reference to  FIGS. 12 and 13 .  FIG. 12  is a diagram showing a relation of a voltage Vinj between terminals, a drive current, a first order differential value of the current, a second order differential value of the current, and a valve body displacement amount in time of three fuel injection devices having different valve opening start and completion timings in a condition in which the valve body  214  of the embodiment of the invention reaches a maximum opening degree.  FIG. 13  is a diagram showing a relation of an injection pulse, a drive current supplied to the fuel injection device, a voltage Vinj between terminals of the solenoid  205 , and a behavior of the valve body  214  and the needle  202  in time according to the fifth embodiment of the invention. Additionally, in  FIG. 13 , the same reference numerals will be given to the same components as those of  FIG. 6 . Additionally, in the drawings, the displacement values of the valves of three fuel injection devices having different forces acting on the valve body  214  in the valve closing direction are denoted by a dashed line, a solid line, and a one-dotted chain line. 
         [0142]    First, a method of detecting a valve opening completion timing which is a timing in which the valve body  214  reaches the maximum height position (the maximum opening degree) will be described with reference to  FIG. 12 .  FIG. 12  is a diagram showing a relation of a voltage Vinj between terminals of the solenoid  205 , a drive current, a first order differential value of the current, a second order differential value of the current, and a displacement amount of the valve body  214  in time after the injection pulse is turned on. Additionally, the drive current, the first order differential value of the current, the second order differential value of the current, and the displacement amount of the valve body  214  of  FIG. 12  are shown as three profiles of the fuel injection devices having different valve body operation timings in accordance with a change in force acting on the needle  202  and the valve body  114  due to a tolerance. From  FIG. 12 , the boost voltage VH is first applied to the solenoid  205  to rapidly increase the current and increase the magnetic attraction force acting on the needle  202 . Next, the needle  202  collides with the valve body  214  so that the valve body  214  starts to open the valve. The peak current value I peak  or the peak current arrival time Tp and the voltage interruption period T 2  may be set so that the valve opening start timing of the valve body  214  of each of individuals  1 ,  2 , and  3  of the fuel injection devices of different cylinders comes before the timing t 123  in which the drive current reaches the peak current value I peak  and the voltage interruption period T 2  ends. Additionally, the voltage interruption period T 2  indicates a time in which the reverse voltage VH is applied in the negative direction after the end of the peak current I peak . Since a change in application voltage to the solenoid  205  is small in a condition that the battery voltage VB is continuously applied so that a predetermined voltage value  1201  is supplied, the needle  202  starts to be displaced from the valve closing position and then a change in magnetic resistance caused by a change in gap between the needle  202  and the fixed core  207  can be detected as a change in induced electromotive force. Since the gap between the needle  202  and the fixed core  207  decreases when the valve body  214  and the needle  202  start to be displaced, the number of the magnetic fluxes passing between the needle  202  and the fixed core  207  increases, the induced electromotive force increases, and the current supplied to the solenoid  205  gently decreases as in a line  1203 . Since a change in induced electromotive force in accordance with a change in gap is small at a timing in which the needle  202  reaches the fixed core  207 , that is, a timing (a valve opening completion timing) in which the valve body  214  reaches the maximum opening degree, the current value gently increases as in a line  1204 . The magnitude of the induced electromotive force is influenced by the current value other than the gap, but since a change in current is small in a condition that the valve lower than the boost voltage VH is applied as in the battery voltage VB, it is possible to easily detect a change in induced electromotive force in accordance to a change in gap in terms of the current. 
         [0143]    Regarding the individuals  1 ,  2 , and  3  of the cylinders of the above-described fuel injection devices, the timings t 113 , t 114 , and t 115  at which the first order differential value of the current becomes zero may be detected as the valve opening completion timing by performing a first order differentiation of the current in order to detect a timing in which the valve body  214  reaches the maximum opening degree as a point in which the drive current changes from a decrease state to an increase state. 
         [0144]    Further, in the configurations of the magnetic circuit and the drive unit in which the induced electromotive force generated by a change in gap is small, there is a case in which the current does not necessarily decrease in accordance with a change in gap. However, since the gradient of the current, that is, the differential value of the current changes at the valve opening completion timing, it is possible to detect the valve opening completion timing by detecting the maximum value of the second order differential value of the current detected by the drive device. Accordingly, it is possible to stably detect the valve opening completion timing regardless of the limitation of the magnetic circuit, the inductance, the resistance value, or the current. 
         [0145]    Even in the configuration of the movable valve in which the valve body  214  and the needle  202  are integrated with each other, the valve opening completion timing can be also detected by the same principle as that of the detection of the valve opening completion timing described in the structure in which the valve body  214  and the needle  202  are separated from each other. 
         [0146]    Additionally, the peak current value I peak  and the current interruption period T 2  may be adjusted so as not to reach a target current value  1210  set in the IC  502  in advance during a period in which the voltage value  1201  is supplied from the battery voltage source VB after the application of the boost voltage VH in the negative direction is stopped. Since the drive device is controlled so that the current  1210  becomes a constant value when the drive current reaches the target current value  1210  before the valve body  214  reaches the maximum opening degree by this effect, the first order differential value of the current repeatedly passes through a point  0 . Accordingly, it is possible to solve a problem in which a change in induced electromotive force cannot be detected by the differential value of the drive current. 
         [0147]    Further, the switching elements  605 ,  606 , and  607  are controlled so that the application of the voltage or the boost voltage VH in the negative direction is stopped (so that a voltage of 0 V is applied) from a state where a constant voltage value  1202  is applied, the current value reaches the current  704  of  FIG. 7 , and then the application of the battery voltage VB is repeatedly switched to the current  703 . At time in which the current value  1210  is obtained after the injection pulse width Ti is turned on is different in accordance with a change in valve opening completion timing due to a change in fuel pressure and a difference in valve body  214 . The magnetic attraction force at the time of stopping the injection pulse width Ti is largely dependent on the value of the drive current when the injection pulse width Ti is turned off. When the drive current is large, the magnetic attraction force increases and the valve closing delay time increases. In contrast, when the drive current at the time of turning off the injection pulse width Ti is small, the suction force decreases and the valve closing delay time decreases. As described above, since it is desirable that the current value at the timing of turning off the injection pulse width Ti in a condition that the valve opening completion state is detected become the same current  703  in different individuals, the timing of applying the boost voltage VH in the negative direction from the constant voltage value  1102  or the timing of stopping the application of the voltage may be controlled by the time after the injection pulse width Ti is turned ON or the time after the peak current value I peak  is obtained. 
         [0148]    The current waveform may be switched so that the target current value  1210  becomes a small value and the application of the battery voltage VB is repeatedly switched during the first current hold period after the valve opening completion timing of the fuel injection device of each cylinder is detected. Further, in the current waveform of  FIG. 12  of the fifth embodiment of the invention, a correction of increasing the peak current value I peak  or shortening the voltage interruption time T 2  or a correction of increasing the peak current and shortening the voltage interruption time may be performed in order to increase the current value at the timing t 123 . 
         [0149]    When the battery voltage VB decreases due to the supply of the current to the in-vehicle device, the magnetic attraction force acting on the needle  202  decreases and thus the needle  202  and the valve body  214  may be displaced unstably. When the peak current I peak  is set to a large value, the kinetic energy obtained when the needle  202  collides with the valve body  214  can be increased and the magnetic attraction force acting on the needle  202  after the valve body  214  starts to open the valve can be increased. Accordingly, the stability of the displacement of the valve body  214  is improved and the accuracy of the injection amount can be improved. Since the magnetic attraction force acting on the needle  202  can be kept at a high value when the current value at the timing t 123  is large, the stability of the valve body  214  is further improved. 
         [0150]    Next, a method of correcting the second drive current from the valve opening completion timing detection information will be described with reference to  FIG. 13 . Regarding the displacement amount, the displacement of the valve body  214  is indicated as a displacement  1310 , a displacement  1311 , and a displacement  1312  in order in which a force acting on the valve body  214  in the valve closing direction is large. The force of the valve body  214  in the valve closing direction is the resultant force of the differential pressure acting on the valve body  214  and the first spring  210 . In a condition that the same current waveform  1320  is supplied to the fuel injection device of each cylinder, the force in the valve closing direction is large, the gradient of the displacement of the valve after the valve body  214  start to open the valve is small, and the timing in which the valve body  214  reaches the maximum opening degree is delayed. Regarding the displacement  1312 , since the timing of stopping the first drive current is late compared to the valve opening completion timing, the needle  202  and the valve body  214  cannot be decelerated in time and the bound of the valve body  214  increases. As a result, there is a case in which a relation between the injection pulse and the injection amount after the full-lift is non-linear and the injection amount cannot be continuously controlled. Regarding the displacement  1310 , since the timing of stopping the first drive current is fast compared to the valve opening completion timing, the magnetic attraction force acting on the needle  202  decreases and the speed of the needle  202  and the valve body  214  largely decreases. As a result, since it is not possible to ensure the magnetic attraction force necessary for the valve opening operation and the valve opening completion timing is delayed, the behavior of the valve body  214  may become unstable. 
         [0151]    In a case where each fuel injection device has a different valve opening completion timing, it is possible to ensure a stable behavior in a half-lift state of each individual by determining the timing of stopping the first drive current using the information of the valve opening completion timing detected for the fuel injection device of each cylinder. Accordingly, since the accuracy of the injection amount is improved, it is possible to improve the homogeneity of the air-fuel mixture and to suppress the PN. Further, since it is possible to appropriately adjust the injection amount with respect to a change in engine rotation speed by ensuring the continuity of the flow rate from the half-lift to the full-lift, it is possible to improve the drivability. Specifically, the current waveform may be set so that the timing t 134  of stopping the first drive current is fast in the individual  1310  in which the valve opening completion timing is slow and the timing t 134  of stopping the first drive current is slow in the individual  1312  in which the valve opening completion timing is fast. In  FIG. 13 , a voltage of about 0 V is applied to the solenoid  205  when the first drive current changes to the second drive current so that the current gently decreases as in the current  1303 , but the boost voltage VH in the negative direction may be applied so that the current fast changes to the second drive current  611 . Since the boost voltage VH in the negative direction is used when the first drive current changes to the second drive current, the bound of the valve body  214  can be reduced by decelerating the needle  202  in accordance with a decrease in magnetic attraction force immediately before the valve opening completion timing after a large magnetic attraction force is applied to the needle  202  before the valve opening completion timing to ensure the stability of the valve body  214 . As a result, it is possible to reduce the PN by improving the accuracy of the injection amount in the half-lift and to improve the drivability by ensuring the continuity of the flow rate after the full-lift. 
         [0152]    Regarding the voltage applied to the solenoid  205  when the first drive current changes to the second drive current, the setting of the current waveform may be changed so that the boost voltage VH in the negative direction is applied in a condition that the fuel pressure is low and a voltage of about 0 V is applied in a condition that the fuel pressure is high. Since the differential pressure acting on the valve body  214  is small in a condition that the fuel pressure is low, a time taken until the needle  202  and the valve body  214  are decelerated after the first drive current is stopped and the magnetic attraction force decreases is long. Further, since the differential pressure acting on the valve body  214  is small in a condition that the fuel pressure is high, a time taken until the needle  202  and the valve body  214  are decelerated after the first drive current is stopped and the magnetic attraction force decreases is short. Thus, since the application voltage at the time of stopping the first drive current is changed in response to the fuel pressure, the needle  202  can be decelerated at an appropriate timing and the bound of the valve body generated after the valve body  214  reaches the maximum opening degree can be reduced. As a result, since it is possible to continuously control the injection amount, the drivability is improved. 
         [0153]    Further, since the differential pressure acting on the valve body  214  increases when the fuel pressure increases, the valve opening completion timing is delayed. The valve opening completion timing for each fuel pressure in each fuel injection device may be detected by the ECU  104  and may be set in the CPU  501  in advance. Additionally, the valve opening completion timing may be acquired in at least two points having different pressures. When an approximate equation is obtained from the information of detecting the valve opening completion timing at a plurality of points and an interpolation is performed, it is possible to accurately calculate a change in valve opening completion timing even when the fuel pressure is changed. Specifically, the timing of stopping the first drive current may be delayed as the fuel pressure increases. The valve opening completion timing is dependent on the differential pressure acting on the valve body  214  and the needle  202  and the displacement profile of the needle  202  determining the valve opening start timing of the valve body  214 . Due to the influence of the tolerance of each fuel injection device, the sensitivities of the fuel pressure and the valve opening completion timing are different for each fuel injection device. In the control method of the fifth embodiment of the invention, a relation between the fuel pressure and the valve opening completion timing may be detected for the fuel injection device of each cylinder and the first drive current stop timing may be determined based on the detection information. As a result, since it is possible to improve the accuracy of the injection amount and the stability of the valve body  214  in the half-lift and to reduce the bound of the valve body  214  in the full-lift, it is possible to improve the drivability by ensuring the continuity of the flow rate. 
       Sixth Embodiment 
       [0154]    An injection control method of the split injection of the sixth embodiment of the invention will be described with reference to  FIG. 14 .  FIG. 14  is a diagram showing a relation of an injection pulse, a drive current supplied to a fuel injection device, a voltage Vinj between terminals of the solenoid  205 , and a behavior of the valve body  214  and the needle  202  in time according to the sixth embodiment of the invention. Additionally, in  FIG. 14 , the same reference numerals will be given to the same components as those of  FIG. 6 . Regarding the valve displacement amount of the drawing, in a case where the injection pulse is stopped at the first drive current and the valve body  214  is driven in the half-lift condition, the displacement amount of the valve body  214  is indicated by a one-dotted chain line and the displacement amount of the needle  202  is indicated by a dashed line. Then, the displacement amount of the valve body  214  driven in the full-lift condition is indicated by a solid line and the displacement amount of the needle  202  is indicated by a dotted line. Additionally, the configurations of the fuel injection device and the drive device of the sixth embodiment are the same as those of the first to fifth embodiments. 
         [0155]    From  FIG. 14 , in the current  1451  in which the injection pulse is stopped at the first drive current and which corresponds to the half-lift condition, the maximum height position  1450  of the valve body  214  is smaller than that of the full-lift condition. For this reason, the displacement amount of the valve body  214  until the valve body  214  closes the valve after the stop of the injection pulse is small. When the displacement amount of the valve body  214  is small, a period  1422  in which the valve body  214  reaches the maximum height position  1450  so that the speed of the valve body  214  becomes zero and then the valve body is accelerated again in the valve closing direction is short and thus a speed at which the valve body  214  contacts the valve seat  218  is small. The time in which the needle  202  is separated from the valve body  214  and is returned to the initial position after the valve body  214  closes the valve is influenced by the valve closing speed of the valve body  214  and thus the time in which the needle  202  reaches the initial position becomes long when the valve closing speed of the valve body  214  is high. Thus, compared to the full-lift condition, the period  1422  corresponding to the time until the needle  202  returns to the original position is short and the injection interval of the split injection can be decreased in the half-lift condition in which the maximum height position is small. 
         [0156]    In the control method of the sixth embodiment of the invention, the interval of the injection pulse may be set to be small after the first and second injections in the condition of the split injection in the half-lift condition compared to the case of the fuel injection in the full-lift condition. When the interval of the injection pulse in the half-lift condition is set to be small, a control of forming the air-fuel mixture is easily performed by the fuel injection. Then, when the air-fuel mixture having a locally high homogeneity is formed in the vicinity of the ignition plug, it is possible to reduce the fuel efficiency and to suppress the PN by the weak stratified charge combustion. Further, the split injection interval may be set by determining whether the injection amount is in the full-lift condition or the half-lift condition when the injection amount is calculated by the CPU  501 . As a result, since the split injection interval can be appropriately determined, the PN suppression effect is improved. 
         [0157]    In a condition of a cold start or a high-rotation/high-load, the necessity of the multi-stage injection is high and a minute injection amount is further obtained. Since an unburned gas increases in temperature and pressure during the propagation of the flame in the engine cylinder in the high-rotation/high-load condition, a knock is easily caused by the self-ignition before an ignition using the ignition plug attached into the cylinder. For this reason, the multi-stage injection is highly required and a further minute injection amount is obtained. When the multi-stage injection is performed in the compression stroke of the piston in order to suppress the knock, the split injection interval can be reduced by the fuel injection in the half-lift condition. Accordingly, the high-temperature air-fuel mixture is cooled by the intake cooling effect using the fuel injection at an appropriate timing and thus the knock suppression effect is improved. 
         [0158]    Further, the fuel injection may be divided in the half-lift condition during the compression stroke while the injection amount necessary for the combustion is ensured using the fuel injection in the full-lift condition during the intake stroke. Since the intake air flows large during the intake stroke, it is possible to form the uniform air-fuel mixture by injecting a large amount of the fuel. Further, the injection pulse in the full-lift condition may be adjusted so that the fuel injection is performed in the half-lift during the compression stroke by saving an injection amount necessary for one combustion cycle using the fuel injection in the full-lift condition. As a result, since it is possible to reliably inject the fuel in the half-lift condition during the compression stroke, the knock suppression effect can be improved. Further, since the rich air-fuel mixture is formed only in the vicinity of the ignition plug by the minute injection in the half-lift condition during the compression stroke, it is possible to obtain an effect of obtaining high fuel efficiency and reducing the PN by realizing the weak stratified charge combustion. 
         [0159]    Further, since the fuel injection amount is small in the half-lift condition, the flow rate of the fuel injected from the injection hole  219  is slow and the fuel spray arrival distance is small compared to the full-lift condition. The flow rate of the sprayed fuel is dependent on the passage cross-sectional area of the seat of the valve seat  218  and the valve body  214  and the flow rate of the fuel decreases as the maximum height position of the valve body  214  decreases. Since the piston moves to the top center during the compression stroke, a distance between the surface of the piston and the injection hole  219  of the fuel injection device becomes shorter as it becomes the late compression stroke. Accordingly, the sprayed fuel easily adheres to the piston and the PN increases. When the injection amount in the half-lift is set to be smaller, that is, the first drive current application time is set to be shorter as it becomes the late compression stroke, it is possible to suppress the knock and the PN. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           101 A to  101 D,  540  fuel injection device 
           103  drive circuit 
           104  engine control unit (ECU) 
           150  drive device 
           202  needle 
           205  solenoid 
           207  fixed core 
           210  first spring 
           212  zero spring (second spring) 
           234  third spring 
           214  valve body 
           218  valve seat 
           220  intermediate member 
           232  cap 
           501  CPU  501
The purpose of the present invention is to provide a drive device that improves the precision of injection quantities by stabilizing the behavior of a valve body  214  under the condition that a valve body reaches a height position lower than a maximum height position and making the injection pulse width and the injection quantity gradient small. The present invention is a drive device for a fuel injection device for use in an internal combustion engine, wherein: the fuel injection device is provided with a valve body  214  that can open and close a fuel passage, a needle  202  that activates an opening and closing valve by transmitting power between itself and the valve body  214 , and an electromagnet that comprises a solenoid  205  and a fixed core  207  provided as drive means for the needle  202 , and a cylindrical nozzle holder  201  disposed on the outer peripheral side of the needle  202 ; and the drive device  150  controls a drive current flowing to the coil so as to decrease from the maximum drive current to a first drive current  610  that is lower than the maximum drive current before the valve body  214  reaches the maximum height position so that the valve body  214  reaches a height position lower than the maximum height position.