fig1 is a structural view showing a schematic structure of a first embodiment . in an internal combustion engine 1 , each cylinder is provided with two intake valves 2 and two exhaust valves 3 . in fig1 one of the intake valves 2 and one of the exhaust valves 3 alone are illustrated . an intake passage 4 is connected to the intake valve 2 of the internal combustion engine , and a throttle valve 5 serving to regulate the intake air flow is disposed in the intake passage 4 . further , upstream of the intake passage 4 are provided an intake measuring device and an air cleaner which are not shown . an air - assist fuel injection valve 6 is disposed between the throttle valve 5 and the intake valve 2 in the intake passage 4 . the air - assist fuel injection valve 6 comprises a fuel injection nozzle through which the fuel is injected and an assist air jet nozzle through which assist air is jetted toward the fuel injected from the fuel injection nozzle . further , the air - assist fuel injection valve 6 is fixed in the intake passage 4 so as to make the fuel injection nozzle thereof point at the intake valve 2 . the air - assist fuel injection valve 6 is supplied with the fuel from a fuel tank which is not shown , which fuel is pressurized by a fuel pump and regulated at a fixed pressure by a pressure regulating valve , while a control pulse generated by a control unit which is not shown and having a pulse duration corresponding to the amount of fuel to be injected to sent to the air - assist fuel injection valve 6 . in addition , the assist air is introduced to the air - assist fuel injection valve 6 through an assist air passage 7 communicated with the intake passage 4 upstream of the throttle valve 5 . fig2 is a sectional view showing the structure of the air - assist fuel injection valve 6 . the air - assist fuel injection valve 6 comprises a fuel valve section 600 . a popular fuel injection valve is used as this fuel valve section 600 . the fuel valve section 600 has a valve housing 602 which is formed with a fuel injection nozzle 601 at the tip end thereof . a valve needle 603 serving to open and close the fuel injection nozzle 601 is received in the valve housing 602 . the valve housing 602 is fixed to a housing 604 . a magnet coil 605 is disposed in the housing 604 and energized by a control circuit which is not shown through a connector 606 . the valve needle 603 is provided with an armature 607 so that the valve needle 603 is moved by the electromagnetic force produced due to energization of the magnet coil 605 . a stator 608 is fixed to the housing 604 and the fuel is supplied to the upper end portion , in this drawing , of the stator 608 from the fuel pump which is not shown . as the magnet coil 605 is energized and , hence , the valve needle 603 is moved , the fuel injection nozzle 601 is opened so that the fuel is allowed to pass through the inside of the stator 608 , the inside of the armature 607 and , further , between the valve needle 603 and the valve housing 602 until it is injected from the fuel injection nozzle 601 . the fuel valve section 600 is inserted in a case 610 which serves to form assist air passage . the case 610 is equipped with a pipe 611 so that the assist air is introduced from the assist air passage 7 into the case 610 through the pipe 611 . within the case 610 , a sleeve 620 and a socket 630 are disposed at the tip end portion of the valve housing 602 of the fuel valve section 600 . by inserting and fixing the fuel valve section 600 in the case 610 , the sleeve 620 and the socket 630 are fixedly held between the fuel valve section 600 and the case 610 . the sleeve 620 is formed with two fuel passages 621 and 622 through which the fuel injected from the fuel injection nozzle 601 is made to pass . a partition wall 623 is formed between these two fuel passages 621 , 622 so as to divide into two parts the fuel injected from the fuel injection nozzle 601 . each of the two fuel passages 621 , 622 is conical in shape so that the sectional area thereof is reduced as going toward the downstream of the spray of the fuel . further , the sleeve 620 is formed with two assist air passages 624 and 625 through which the assist air is made to pass . the upstream ends of the assist air passages 624 , 625 are opened into the interior space of the case 610 , while the downstream ends of the assist air passages 624 , 625 are opened into the downstream parts of the fuel passages 621 , 622 of the sleeve 620 , respectively . the axis of the assist air passage 624 crosses the axis of the fuel passage 621 , while the axis of the assist air passage 625 crosses the axis of the fuel passage 622 . further , the axes of the two assist air passages 624 , 625 cross each other at a point downstream of the partition wall 623 . the socket 630 is formed with a conical passage 631 which serves to regulate the spray cone angle of the fuel . the air - assist fuel injection valve 6 shown in fig2 is fixed in the intake passage 4 of the internal combustion engine so that the axes of the two fuel passages 621 , 622 are directed respectively to the intake valves of the internal combustion engine and the two sprays of fuel injected through the two fuel passages 621 , 622 are directed respectively to the intake valves . fig3 and 4 are schematic views each showing the form of spraying of the fuel from the fuel injection valve to the intake valves of the internal combustion engine . the internal combustion engine is equipped with two intake valves 2a and 2b . the intake passage 4 is branched off into two intake ports 4a and 4b which are communicated with the two intake valves 2a and 2b , respectively . an intermediate wall 4c is formed between the two intake ports 4a , 4b . it is noted that , in fig3 and 4 , the form of spraying from the fuel injection valve 6 is shown as the hatched section and the spray cone angle is indicated by α or β . in this embodiment , when the throttle valve 5 is opened , the differential pressure of the assist air passage 7 is caused to disappear to cut the assist air , resulting in that the injection of the assist air from the assist air passages 624 , 625 is stopped . as the magnet coil 605 of the fuel valve section 600 is energized while the throttle valve 5 is being opened , the fuel is injected from the fuel injection nozzle 601 . the fuel injected from the fuel injection nozzle 601 is separated into the two fuel passages 621 , 622 . the fuel passed through the two fuel passages 621 , 622 becomes two sprays of fuel the spray cone angle of which is narrow as indicated by 60 in fig3 . these sprays of fuel each having the narrow spray cone angle α are made to pass through the passage 631 and then go toward the two intake valves 2a , 2b , respectively . in consequence , fuel adhesion to the inside of the intake passage 4 can be prevented when the engine is operated in the high rotational speed and high load condition , that is , when the throttle valve 5 is opened , so that it is possible to supply the fuel to the combustion chamber with reliability , resulting in that it is possible to improve the transient response characteristic of the engine , particularly the transient response characteristic obtained when heavy gasoline is used . as the throttle valve 5 is closed , the differential pressure arises in the assist air passage 7 so as to allow the assist air to be supplied into the case 610 , resulting in that the assist air is jetted through the assist air passages 624 , 625 . as the magnet coil 605 of the fuel valve section 600 is energized when the throttle valve 5 is closed , the fuel is injected from the fuel injection nozzle 601 . the fuel injected from the fuel injection nozzle 601 is separated into the two fuel passages 621 , 622 . since the assist air is introduced to the downstream parts of the fuel passages 621 , 622 , the fuel passed through the two fuel passages 621 , 622 collides with the assist air so as to be disposed . at this time , dispersion of the sprayed fuel is regulated by the passage 631 formed in the socket 630 , and however , it becomes a single spray of fuel having a wide spray cone angle β as shown in fig4 . in consequence , atomization of fuel can be promoted when the engine is operated in the low rotational speed and low load - condition , that is , when the throttle valve 5 is closed , so that it is possible to supply the mixture of high quality , with the result that it is possible to reduce the emission and the change of combustion as well as to improve the transient response characteristic . particularly in the case that , since a large quantity of fuel is injected when the temperature of the internal combustion engine is low , the magnet coil 605 is energized for a long time and the injection is started before the rising of air stream in the seat portions of the intake valves 2a , 2b , fuel adhesion to the intake pipe can be reduced and hence the fuel can be supplied to the combustion chamber with reliability owing to the large spray cone angle of the fuel and the promotion of the atomization . as described above , according to this embodiment , it is possible to inject the fuel in accordance with the operating condition of the internal combustion engine and reduce the fuel adhesion to the intake passage caused at the time of increasing the amount of fuel in the case that the fuel is injected toward the intake valves , resulting in that it is possible to reduce the emission and the change of combustion as well as to improve the transient response characteristic of the internal combustion engine . next , description will be given of a second embodiment of the present invention with reference to fig5 and 6 . fig5 is a structural view showing a schematic structure of the second embodiment . the assist air passage 7 is provided with a control valve 8 which serves to open and close this passage . the control valve 8 serves to open and close the assist air passage 7 in accordance with a signal from the control unit 9 . the control unit 9 receives a signal from an operating condition detecting means 10 which serves to detect the operating condition of the internal combustion engine 1 and serves to control the control valve 8 in accordance with this operating condition . in this embodiment , it is designed that the operating condition detecting means 10 detects the low temperature condition of the internal combustion engine 1 from the cooling water temperature of the internal combustion engine . the second embodiment has the same construction as that of the first embodiment except the above - described control valve 8 disposed in the assist air passage 7 . fig6 is a flow chart showing the operation of the control unit 9 of the second embodiment . at step 101 , the cooling water temperature is received from the operating condition detecting means 10 as the operating condition of the internal combustion engine . at step 102 , it is judged whether or not the cooling water temperature is the temperature representative of the low temperature condition of the internal combustion engine . if it is judged to be in the low temperature condition , the operation proceeds to the next step as indicated by an arrow mark yes . while if it is judged not to be in the low temperature condition , the operation proceeds to the next step as indicated by an arrow mark no . at step 103 , the control valve 8 is opened , while at step 104 , the control valve 8 is closed . according to this embodiment , only when the internal combustion engine is in the low temperature condition , the assist air is supplied and the atomization of the fuel is promoted . it is therefore possible to reduce the emission and the change of combustion as well as to improve the transient response characteristic of the internal combustion engine . although the supply of the assist air is interrupted in accordance with the cooling water temperature of the engine in the above second embodiment , it is possible to interrupt the supply of the assist air in accordance with the operating condition of the internal combustion engine such as the gear changing operation of the transmission , for example . further , it is also possible that , by linking to a variable intake device which varies the intake valve operating timing of the internal combustion engine , the assist air is supplied only in the case that the timing at which the intake valve is opened is delayed so as to cause the fuel injection to start before the intake valve is opened , thereby promoting the atomization of the fuel . next , a third embodiment of the present invention will be described . although the aforesaid first embodiment employs the air - assist fuel injection valve of the structure of fig2 the third embodiment employs an air - assist fuel injection valve shown in fig7 to 19 in place of the air - assist fuel injection valve of fig2 . it is noted that the air - assist fuel injection valve of this embodiment is fixed in the intake passage of the internal combustion engine in the same manner as the first embodiment . as shown in fig7 an electromagnetic type fuel injection valve 701 is fitted in a delivery pipe 702 which serves to supply the fuel to the cylinders of the internal combustion engine . a housing 703 of the fuel injection valve 701 is formed in the shape of a stepped cylinder and a magnet coil 705 wound on a spool 704 is disposed in the large diameter portion of the housing 703 . a cylindrical iron core 706 extends through the spool 704 from above and an adjusting pipe 707 is disposed within the iron core 706 so as to be axially slidable . a nozzle body 710 is lap fixed in the small diameter portion of the housing 703 through a spacer 709 and an injection nozzle 712 is formed in a downward projected end surface of the nozzle body 710 . a needle valve 714 is disposed in the nozzle body 710 from above so as to be slidable . a pintle 716 is formed at the tip end of the needle valve 714 , which pintle 716 penetrates through the injection nozzle 712 leaving a gap from the inner peripheral wall of the latter and projects out from the injection nozzle 712 . on the other hand , a stopper 718 is formed substantially in the middle of the needle valve 714 so as to be opposite to the spacer 709 . further , a movable core 720 is provided at the top end of the needle valve 714 so as to be opposite to and connected with the iron core 706 . the movable core 720 is biased downward by a coiled spring 722 disposed between the iron core 706 and the adjusting pipe 707 . a split sleeve 724 is provided at the end portion of the body 710 in which the injection nozzle 712 is formed in such a manner that it covers the end portion of the body 710 . the sleeve 724 comprises an inner sleeve nozzle 730 and an outer cover nozzle 731 as shown in fig8 and 9 . the sleeve nozzle 730 and the cover nozzle 731 constituting the sleeve 724 are made of 6 -- 6 nylon ( containing 30 wt % glass ), polyacetals , pps or the like . the inner sleeve nozzle 730 has two fuel passages 732 and 733 . the fuel passages 732 and 733 are each conical in shape so that the sectional area thereof is reduced as going toward the downstream of the spray of the fuel . the inner sleeve nozzle 730 is formed in the outer peripheral wall thereof with semicircular grooved portions 734 , 735 , 736 , 737 , 738 and 739 each of which serves to form an air passage . the grooved portion 734 serving to form the air passage can have the cross section of rectangular shape shown in fig1 , for example , in place of the cross section of circular arc shape shown in fig1 . the inner sleeve nozzle 730 has a tapered surface 730a and an annular stepped portion 730b . the outer cover nozzle 731 has six holes 744 , 745 , 746 , 747 , 748 and 749 , for example , these holes each penetrating from the inside wall to the outside wall and serving to form an air induction port . it is sufficient for each of the holes 746 to 749 to have a passage area which is not smaller than the passage area surrounded by the grooved portion 734 , 735 , 736 , 737 , 738 or 739 and the inside wall of the cover nozzle 731 . further , the cover nozzle 731 is formed at the tip end thereof with a diffuser portion 750 which serves to guide the spray of the fuel stirred and atomized by the assist air and regulate the same within the desired spray cone angle as well as a chamfered portion 751 which is to be used for positioning in the automatic assembling process . gaps g1 and g2 shown in fig1 are designed to have a clearance of about 0 . 1 to 0 . 3 mm . this makes it possible to prevent other parts than the stepped portion 730 from being melted and welded at the time of the ultrasonic welding which is to be described later , thereby preventing the assist air passage from being clogged due to generation of unnecessary fins . fig8 to 11 are illustrations showing the structure of the sleeve nozzle 730 after the welding . namely , fig8 is a side view of the sleeve nozzle 730 , fig9 is a view as viewed from an arrow mark direction a of fig8 fig1 is a sectional view taken along the line i - o - i of fig9 and fig1 is a view as viewed from an arrow mark direction b of fig1 . further , fig1 to 14 are illustrations showing the shape of the sleeve nozzle 730 before it is welded , in which fig1 is a side view , fig1 is a view as viewed from an arrow mark direction c of fig1 , and fig1 is a sectional view taken along the line ii - o - ii of fig1 . moreover , fig1 is a sectional view taken along the line iii -- iii of fig1 . in addition , fig1 to 19 are illustrations showing the shape of the cover nozzle 731 before it is welded , in which fig1 is a side view , fig1 is a view as viewed from an arrow mark direction d of fig1 , and fig1 is a sectional view taken along the line iv - o - iv of fig1 . it is noted here that fig1 to 14 illustrate the stepped portion 730b and the guide portion 752 , the stepped portion 730b being shown for a longer distance in the axial direction as compared with fig8 to 11 . this axial elongated portion of the stepped portion 730b is the portion which is to be melted at the time of the ultrasonic welding which is to be described later . on the other hand , the guide portion 752 is formed to have an outside diameter which is substantially equal to an inside diameter of the cylindrical surface 731a of the cover nozzle 731 shown in fig1 , which guide portion forms a guide surface by means of which the sleeve nozzle 730 is inserted into the cover nozzle 731 with the stepped portion 730b thereof being melted in the welding process , so that a fixed gap is maintained between the cover nozzle 731 and the sleeve nozzle 730 . within the delivery pipe 702 , the passage of the fuel taken from the fuel intake port is formed between a first o ring 758 and a second o ring 759 . the air induced through an air passage 702a and a passage 702b formed in the delivery pipe 702 is radially sealed between the second o ring 759 and a third o ring 760 . next , description will be given of the procedure for manufacturing the above - described embodiment . the cover nozzle 731 and the sleeve nozzle 730 are formed by means of the injection molding . the both nozzles are unified by being welded to each other as the sleeve nozzle 730 is inserted into the cover nozzle 731 . the sleeve nozzle 730 is inserted from an opening 731c of the cover nozzle 731 . on the occasion of the welding , as shown in fig1 , the sleeve nozzle 730 is inserted into the cover nozzle 731 , the cover nozzle 731 and the sleeve nozzle 730 are pressed against each other so that the stepped portion 730b and the stepped portion 731b are subjected to the ultrasonic pressure , thereby melting the stepped portion 730b by ultrasonic vibrations . fins produced by ultrasonic waves are received in a fin receiver 753 so as to avoid exerting bad influence on the o ring 760 shown in fig7 . in the course of press - fitting the sleeve nozzle 730 while melting the stepped portion 730b by the ultrasonic waves , when the tapered surface 730a is brought into contact with the cover nozzle 731 , application of the ultrasonic vibrations is brought to an end . in the welding process described above , in case of press - fitting the sleeve nozzle 730 while melting the stepped portion 730b , the gaps g1 and g2 are maintained due to the guide portion 752 as shown in fig1 , thereby preventing generation of fins caused due to unnecessary melting and welding . in fig7 the sleeve nozzle 730 is assembled to the fuel injection valve 701 in such a manner that the sleeve nozzle 730 is press - fitted on the outer periphery of the nozzle body 710 of the fuel injection valve 701 and , in order to prevent come - off , a grooved portion 710a and a projection 730c are fastened to each other by means of snap - fitting . in this case , the relative position of the nozzle body 710 and the sleeve nozzle 730 in the direction of rotation is decided as well . according to the above - described embodiment , the fuel taken from the fuel intake port is passed through the regulating portion and then injected through the injection nozzle 712 . the injected fuel is divided into two directions by the fuel passages 732 , 733 of the sleeve nozzle 730 and , thereafter , atomized at once due to air jets issued from the grooves 734 , 735 , 736 , 737 , 738 and 739 . further , according to the above - described embodiment , since the supply of the assist air is interrupted , it is possible to obtain two spraying patterns , that is , fuel injection with high directivity and spray of well atomized fuel . particularly , by directing the two fuel passages 732 , 733 formed in the sleeve nozzle 730 toward the intake valves of the internal combustion engine , respectively , when the assist air is out off , the fuel passing through the fuel passages 732 , 733 can be supplied to the intake valves with high directivity . this makes it possible to reduce the amount of fuel adhered to the wall surface of the intake pipe and hence to supply the required amount of fuel to the combustion chamber of the internal combustion engine with accuracy . further , in the above - described embodiment , the outlets of the assist air passages formed between the cover nozzle 731 and the sleeve nozzle 730 are so arranged as to cross the streams of fuel injected from the fuel passages 732 , 733 at the outlets of the two fuel passages 732 , 733 and , moreover , they are distributed substantially uniformly around the two fuel passages 732 , 722 , as shown in fig9 and 10 in detail . for this reason , it is possible to make the fuel injected from the two fuel passages 732 , 733 collide against the assist air effectively when the assist air is supplied , thereby making it possible to obtain the spray of fuel in which the fuel is atomized satisfactorily and stirred as if it is a single stream of sprayed fuel . in consequence , mixing with the air taken into the internal combustion engine can be assured favorably and the fuel can be taken into the combustion chamber with reliability by being carried by the flow of intake air even when the amount of intake air is small , so that the required amount of fuel can be supplied to the combustion chamber of the internal combustion engine as being held in the state suitable to obtain a good combustion . further , in the foregoing description , the number of fuel passages has been described as being two since the number of intake valves is two , and however , it is possible to easily design the number of fuel passages to be even one or more than three as occasion demands . incidentally , the supply of the assist air can be interrupted in accordance with the load of the internal combustion engine or the like . for example , it is possible to supply the assist air at the time of low load operation in which the amount of intake air is small while cut off at the time of high load operation in which the amount of intake air is large . with the structure of the above - described embodiment , in forming the assist air passage in the resinous sleeve 724 , the sleeve 724 is divided into two parts , that is , the inner cylindrical sleeve nozzle 730 and the outer cylindrical cover nozzle 731 , and the assist air passage is formed between them , and therefore , it becomes possible to form a plurality of assist air passages each having a complicated shape without difficulty . moreover , the induction ports of the assist air are formed as penetrating through the cover nozzle 731 from the outside wall to the inside wall , and the cover nozzle 731 is overlapped by the sleeve nozzle 730 at the portion thereof nearer to the fuel injection valve than ( or above ) these induction ports , and the cover nozzle 731 and the sleeve nozzle 730 are welded to each other at this overlapped portion , and therefore , it is possible to prevent generation of fins and clogging of the assist air passages which are expected to take place when the cover nozzle 731 and the sleeve nozzle 730 are welded to each other around the assist air passages formed below the induction ports . in addition , in order to form the gap between the cover nozzle 731 and the sleeve nozzle 730 except the above overlapped portion , when the cover nozzle 731 and the sleeve nozzle 730 are welded to each other at the above - described overlapped portion as the sleeve nozzle 730 is inserted into the cover nozzle 731 , the guide portion 752 is formed . therefore , it is possible to prevent the cover nozzle 731 and the sleeve nozzle 730 from being welded to each other around the assist air passages and hence to prevent the generation of fins and the clogging of the assist air passages . in the fourth embodiment , the assist air passages are formed in the cover nozzle 731 . each assist air passage 772 is formed by slotting the inner wall of the cover nozzle 731 . in the fifth embodiment , the cover sleeve 731 is formed on the outer peripheral wall thereof with a projection 774 and the delivery pipe 702 is formed with a groove so that the sleeve 730 and the fuel injection valve 701 are positioned relative to the delivery pipe 702 due to this projection 774 . in the sixth embodiment , the fuel feed passage is of the top feed type . in the sixth embodiment , the fuel is fed through a filter 776 and the inside of the adjusting pipe 707 . to the fuel injection valve 701 of this top feed type is assembled the same sleeve 724 as that of the third embodiment described before . in the embodiments described above , the assist air passage is wholly formed between the sleeve nozzle 730 and the cover nozzle 731 from the penetrating hole to the outlet thereof . however , part of the assist air passage may be formed as extending into the sleeve nozzle 730 and opened in the vicinity of the outlets of the fuel passages 732 , 733 formed in the sleeve nozzle 730 . in this case , the assist air passage extending into the sleeve nozzle 730 can be formed in such a manner that it is branched off from the assist air passage formed between the sleeve nozzle 730 and the cover nozzle 731 so as to extend toward the sleeve nozzle 730 . this makes it possible to reduce the length of the assist air passage formed in the sleeve nozzle 730 , thereby making it easy to form the assist air passage . further , the position of the outlet of the assist air passage can be set freely relative to the positions of the outlet of the fuel passage , and therefore , it becomes possible to obtain the desired atomizing form . as has been described above , according to the third to sixth embodiments of the fuel feed apparatus of the internal combustion engine , it goes without saying that the supply of the assist air makes it possible to obtain a favorable atomizing form and , in addition , it is possible to easily manufacture the split type sleeve that has a plurality of assist air passages of a complicated shape . since it is possible to easily form a plurality of complicated assist air passages by fitting and welding the inner member in and to the outer cylindrical member , high workability can be achieved in manufacturing and assembling the members , forming the assist air passages and the like operations . further , since the inner member is welded to the outer cylindrical member at the portion nearer to one of the openings of the outer member through which the inner member is inserted than the penetrating holes , clogging of the assist air passages , change of the passage area and the like problem can be prevented from taking place in the manufacturing process .