[ 0030 ] fig1 shows a schematic view of a first embodiment in accordance with the present invention . a suction pipe 2 and a throttle valve 3 are provided in an engine 1 . a suction air enters into the throttle valve 3 via an air cleaner 6 , an air flow meter ( afm ) 5 , a compressor 13 b of a turbocharger 13 and an intercooler 4 , and is supplied to the engine 1 from the suction pipe 2 . an exhaust gas from the engine 1 is discharged to a passage 22 through two passages 21 , 21 a branched from the exhaust pipe 10 and disposed in parallel to each other . a turbine 13 a is arranged on the passage 21 , and a pre catalyst 11 is arranged on the passage 21 a . in this case , the pre catalyst 11 is structured such as to assist a main catalyst 15 . respective downstream sides of the pre catalyst 11 and the turbine 13 a communicate with a control valve 7 , are combined so as to enter to the passage 22 , and communicate with the main catalyst 15 . an angle signal of a crank angle sensor 19 in the engine and an air amount signal of the afm 5 are input to an engine control unit ( ecu ) 14 , and an ignition signal and drive signals for fuel injection valves 18 a , 18 b , 18 c and 18 d are output via an ignition apparatus 20 . further , a signal for controlling an actuator 7 a of the control valve 7 is output , and an exhaust gas pressure signal of the exhaust gas pressure sensor 8 and an idle switch ( sw ) signal for detecting a position of the throttle valve 3 are applied . since an upstream pressure of the turbocharger is applied to the pre catalyst by placing the control valve 7 downstream the pre catalyst , it is possible to set a temperature of the pre catalyst higher than that in the case of attaching the control valve upstream the pre catalyst . [ 0031 ] fig2 shows an operation of the control valve 7 in accordance with the first embodiment shown in fig1 . the control valve 7 is controlled to a closed position , a middle opening degree and an open position by the actuator 7 a . in the case of the closed position , a passage for the pre catalyst is closed ( a turbo side passage is opened ). in the case of the open position , a passage for the pre catalyst is opened ( the turbo side passage is closed ). in the case of the middle opening degree , the passages on both sides are opened , and the exhaust gas flows through both passages . a position in the case of the middle opening degree is changed on the basis of an exhaust gas amount and an exhaust gas pressure . [ 0032 ] fig3 is a control method of the control valve 7 in accordance with the first embodiment shown in fig1 . at first , a judgement of a cooling water temperature tw is executed . in the case that the relation tw ≧ a is no , the engine is under warming up , and the process is finished by opening the control valve 7 ( the exhaust gas is flowed only through the pre catalyst ). in the case that the relation tw ≧ a is yes , a judgement of an idle sw is executed . in the case that a condition of the idle sw on is yes , a time t that the sw is on is judged . in the case that the relation t ≧ t1 is yes , the process is finished by opening the control valve 7 . immediately after the engine returns to the idle state from a traveling state ( a load operation ), the main catalyst maintain an activation due to the remaining heat , and it is not necessary to immediately use the pre catalyst . in the case that the relation t ≧ t1 is no , the process is finished by closing the control valve 7 ( the exhaust gas is flowed only through the turbocharger 13 ). when the idle period becomes certainly long , an effect of the remaining heat of the main catalyst is lost , and it is necessary to use the pre catalyst . further , it is possible to reduce a frequency of use of the control valve 7 by using a timer in the manner mentioned above , and it is useful to improve a durability of the control valve . in the case that the condition of the idle sw on is no , a judgement of an exhaust gas pressure pe is executed . in the case that the relation pe ≧ p1 is no , the process is finished by closing the control valve 7 . in the case that the relation pe ≧ p1 is yes , the process is finished by opening the control valve 7 at a middle opening degree so that pe becomes p1 so as to control the exhaust gas pressure . [ 0033 ] fig4 shows a relation between a rotational number of the engine and an output torque . in the conventional engine with the turbocharger , a supercharge is started from a point close to one half of a maximum rotational number , and an output torque becomes larger than that of a natural air supply engine in an area having a great engine rotational number . on the contrary , in the engine in accordance with the present invention , weight saving is achieved by making the turbocharger compact and shifting the actuation range of the turbocharger to a low rotational number side . as a result , in the engine in accordance with the present invention , the output torque is increased from the low rotational number range of the engine . however , since the turbocharger is made compact and light , the exhaust gas pressure becomes too high in a high rotational number side ( near substantially one half of the maximum rotational number ) in which the exhaust gas amount of the engine is increased . accordingly , the passage ( the conventional waist gate valve ) for bypassing the turbocharger is opened earlier ( at the lower rotational number ) than the conventional engine with the turbocharger , and the output torque becomes smaller than that of the conventional apparatus on the high rotational number side . [ 0034 ] fig5 shows an effect of the present invention , and shows a relation between the engine rotational number and the output torque . an air amount in the low rotational number range is increased by additionally providing the turbocharger in accordance with the present invention , and it is possible to expand the stratified area of the conventional natural air supply to the large output torque . as a result , a fuel consumption is improved . [ 0035 ] fig6 shows a second embodiment in accordance with the present invention . the passage 21 is communicated with the exhaust pipe 10 , and the control valve 7 is placed there . the passage 21 is connected to the turbine 13 a of the turbocharger . on the other side , a passage 23 is branched from the control valve 7 and is communicated with the pre catalyst 11 . when the control valve 7 is attached to the upstream of the pre catalyst 11 in the manner mentioned above , a heat insulating effect of the pre catalyst 11 at a time when the control valve 7 is closed is reduced , however , the same effects as that in fig1 are expected except the above effect . [ 0036 ] fig7 describes an operation of the control valve 7 in accordance with the second embodiment shown in fig6 . in the case that the control valve 7 is at the closed position , the passage 23 corresponding to the passage for the pre catalyst 11 is closed . in the case that the control valve 7 is at the open position , the passage 23 is inversely opened and the passage 21 is closed . a control method of the control valve 7 is the same as that in fig3 . [ 0037 ] fig8 and 9 show an example of a passage structure of the control valve 7 . the passage is formed in a t - shaped pipe shape in fig1 and 6 , however is formed in a y - shaped pipe shape in the present embodiment . fig8 shows a case of confluence of the flows and fig9 shows a case of separation of the flows . in both cases , the rotational angle of the control valve 7 can be made smaller than that of the t - shaped pipe . further , since a curve of an exhaust gas flow is the same in both passages , there is no difference between flow resistances caused by the passages . [ 0038 ] fig1 shows a third embodiment in accordance with the present invention , in which the control valve employs a control valve 17 having a two - position motion between “ open ” and “ close ”. accordingly , a waist gate valve 12 is placed so as to bypass the turbine 13 a . the control valve can be simplified by employing the two - position motion valve to the control valve . further , although the waist gate valve 12 is newly required , the similar structure has been conventionally provided in the turbocharger , so that a mechanical improvement is reduced . [ 0039 ] fig1 shows a motion of the control valve 17 in accordance with the third embodiment . the passage of the pre catalyst is opened ( the turbine 13 a is closed ) at the open position . the turbine 13 a side is opened ( the pre catalyst 11 side is closed ) at the closed position . [ 0040 ] fig1 shows a control flow chart of the control valve 17 in accordance with the third embodiment . at first , a cooling water temperature tw is judged . in the case that the relation tw ≧ a is no , the engine is under warming up , and the process is finished by opening the control valve 17 . in the case that the relation tw ≧ a is yes , a judgement of an idle sw is executed . in the case that a condition of the idle sw on is yes , a time t that the sw is on is judged . in the case that the relation t ≧ t1 is yes , the process is finished by opening the control valve 17 . in the case that the relation t ≧ t1 is no , the process is finished by closing the control valve 17 . in the case that the condition of the idle sw on is no , the process is finished by closing the control valve 17 . [ 0041 ] fig1 shows a structure of the waist gate valve 12 in accordance with the third embodiment . when a valve opening signal is input to an actuator 12 a , a valve 24 is opened in correspondence to a magnitude thereof , and the exhaust gas flows so as to bypass the turbine 13 a , thereby controlling the exhaust gas pressure . [ 0042 ] fig1 shows a control method of the waist gate valve 12 in accordance with the third embodiment . the waist gate valve 12 in accordance with the present invention controls the exhaust gas pressure to a predetermined value . at first , a judgement of an exhaust gas pressure pe is executed . in the case that the relation pe ≧ p1 is no , the process is finished by closing the waist gate valve 12 . in the case that the relation pe ≧ p1 is yes , the process is finished by controlling the exhaust gas pressure ( the middle opening degree ) by the waist gate valve 12 . [ 0043 ] fig1 shows a fourth embodiment in accordance with the present invention . this embodiment corresponds to an embodiment in which the pre catalyst 11 is positioned on the upstream side of the turbine 13 a in the structure in which the pre catalyst and the turbine 13 a are arranged in series and a passage 25 bypassing the turbine 13 a is placed . the control valve 7 is placed in a branch portion between the passage 21 and the passage 25 . [ 0044 ] fig1 is an operation view of the control valve 7 in accordance with the fourth embodiment . when the control valve 7 is at the open position , the exhaust gas flows only through the passage 25 . when the control valve 7 is at the closed position , the exhaust gas flows to the turbine 13 a side . in the case of executing the exhaust gas pressure control , the valve is at the middle opening degree , and the exhaust gas flows through both of the passages 21 and 25 . [ 0045 ] fig1 is a control flow chart of the control valve 7 shown in fig1 . at first , a judgement of a cooling water temperature tw is executed . in the case that the relation tw ≧ c ° c . is no , the process is finished by opening the control valve 7 . in the case that the relation tw ≧ c ° c . is yes , a judgement of an exhaust gas pressure pe is executed . in the case that the relation pe ≧ p1 is no , the process is finished by closing the control valve 7 . in the case that the relation pe ≧ p1 is yes , the exhaust gas pressure control is executed by the control valve 7 ( the middle opening degree ). [ 0046 ] fig1 shows a fifth embodiment in accordance with the present invention . this embodiment corresponds to an embodiment in which the pre catalyst 11 is positioned on the downstream side of the turbine 13 a in the structure in which the pre catalyst and the turbine 13 a are arranged in series and a passage 26 bypassing the turbine 13 a is placed . the control valve 7 makes the passage 26 and a passage 27 confluent . [ 0047 ] fig1 is an operation view of the control valve 7 in accordance with the fifth embodiment . the closed position of the control valve 7 corresponds to a state that the passage 26 is closed . the open position of the control valve 7 corresponds to a state that the turbine 13 a is closed . the middle opening degree corresponds to a state that the exhaust gas flows through both of the passages 27 and 26 and the exhaust gas pressure control is executed . the control flow is the same as that shown in fig1 . [ 0048 ] fig2 shows a sixth embodiment in accordance with the present invention in which for omitting the conventional main catalyst , a so - called manifold catalyst 28 having one catalyst placed at a position close to the engine is combined with the pre catalyst of which the capacity is increased . the main catalyst conventionally placed in the passage 22 is omitted . the mounting and the operation of the control valve 7 are the same as those in fig1 . further , in each of the embodiments shown in fig6 , 18 and 20 , in the same manner as that of the third embodiment shown in fig1 , it is possible to place the waist gate valve 12 , and the control valve can be replaced by the two - position motion valve . [ 0050 ] fig2 shows a fuel injection method at a time of starting and warming up of the engine . in the timing after finishing the warming - up executed in the normal operation , there is executed a so - called compression stroke injection of injecting the fuel at a rear half of the compression stroke , forming the mixture in a stratified state and igniting the mixture . however , at a time of starting and warming up , an early warming - up of the exhaust gas system including the pre catalyst for a short time is important in view of an improvement of an exhaust performance . the fuel is injected at a specific injection timing for warming up , and an engine warm up condition of stratified combustion is executed . that is , a first time fuel injection is executed at a rear half of the compression stroke in the same manner as the normal operation , and an ignition is executed . next , the engine proceeds on to an expansion stroke , however , a second time fuel injection which is substantially the same as the first time injection is executed at a rear half of the expansion stroke . since the fuel injected at the second time is hardly converted into work and is exhausted , the exhaust gas temperature is raised , and the fuel contributes to the temperature up of the exhaust system . when the present invention is combined with the two - time injection in the compression and the expansion strokes , the engine warm up time can be further reduced , and an exhaust gas purification effect can be improved . [ 0051 ] fig2 shows a relation between the a / f and the exhaust gas temperature . there is known a characteristic that an exhaust gas temperature achieves a maximum temperature on a little rich side in comparison with a theoretical air fuel ratio , and the temperature is reduced on either of a lean side or a rich side in comparison thereof . in the case that the exhaust gas amount is increased , the exhaust gas pressure becomes high and the exhaust gas bypasses the turbine , as in the embodiments in accordance with the present invention , there is a case that the pre catalyst is exposed to the high temperature exhaust gas and a durability of the catalyst is reduced . in the case mentioned above , there is employed a method of shifting the air fuel ratio of the mixture supplied to the engine to a rich side and reducing the exhaust gas temperature . in accordance with the present invention , these methods are also effective means . [ 0052 ] fig2 shows a seventh embodiment in accordance with the present invention in which a bypass passage 29 always bypassing a part of the exhaust gas is added to the control valve 7 . with the structure , the exhaust gas always flows through the pre catalyst , and an activation is kept . in the seventh embodiment shown in fig2 , there is shown a case that the control valve 7 is placed in a confluent portion downstream of the pre catalyst 11 and the turbine 13 a . in the case of placing the control valve 7 in the branch portion upstream of both of them , the present embodiment is also effective . it is effective for raising the temperature of the pre catalyst and keeping the activation to attach the bypass passage 29 to the pre catalyst side . [ 0053 ] fig2 is an eighth embodiment in accordance with the present invention in which a hole 30 is pierced to the control valve 7 and a part of the exhaust gas is always bypassed . when piercing the hole 30 in the control valve 7 , a part of the exhaust gas flows to the turbine 13 a even in the case of closing the turbine 13 a , so that the exhaust performance at a time of starting is reduced in some degree . however , since a preliminary rotation is previously given to the turbine , a response at a time of starting the turbine is improved . in this embodiment , the same effect can be obtained even when placing in the junction portion shown in fig2 . in accordance with the present invention , since it is possible to prevent the exhaust gas from being cooled by the turbocharger at a time of starting the engine , an early warm up of the main catalyst can be executed , the exhaust gas is purified and an amount of air in the stratified area is increased , so that the stratified area expands to the high output side and the fuel consumption is improved .