A fuel supply device of an engine

Abstract: A fuel supply device comprising a nozzle opening (24) for injecting fuel and pressurized air. The opening operation of the nozzle opening is electromagnetically controlled by a needle (23). The nozzle (37) of a fuel injector (36) is arranged in a nozzle chamber (32). The nozzle chamber (32) has an air inlet (33) and an air outlet (35) separately formed from and spaced from the air inlet (33). The air inlet (33) is connected to a pressurized air source (34), and the air outlet (35) is connected to the nozzle opening (24).

Description: The present invention relates to a fuel supply device of an engine according to the preamble of claim 1. According to the document JP-A-61 104 154 there is disclosed a generic fuel supply device, wherein the opening and closing operation of a nozzle opening is controlled by a needle to inject a fuel by pressurized air. A pressurized air passage extending from the nozzle opening along the needle is formed around the needle, thereby forming a needle insertion bore. A pressurized air outflow passage extends from a pressurized fuel source to one end of the needle insertion bore located opposite to the nozzle opening. By means of this arrangement fuel is injected from a fuel injector and air is introduced from a pressurized air source along the pressurized air outflow passage toward the needle and the needle opens the nozzle opening, whereby the fuel thus introduced in the needle insertion bore is injected from the nozzle opening together with the pressurized air. However, the pressurized air introduced from the pressurized air outflow passage into the needle insertion bore substantially flows in such a manner that fuel accumulates on the inner wall of the deep portion of the needle insertion near the connecting portion with the pressurized air outflow passage. An object of the present invention is to provide a fuel supply device capable of injecting the entire fuel, injected by means of the fuel injector, from the nozzle opening of the fuel supply device. This object is achieved by the combination of the features defined in claims 1 and 6, respectively. Preferable embodiments of the invention are defined in the subclaims. In the following the invention is further illustrated by embodiments with reference to the enclosed drawings. In the drawings: Fig. 1 is a partly cross-sectional side view of a fuel supply device; Fig. 2 is a bottom view of the inner wall of the cylinder head of a two-stroke engine; Fig. 3 is a cross-sectional side view of the two-stroke engine; Fig. 4 is an enlarged cross-sectional side view of a portion of the fuel supply device according to the invention; Fig. 5 is a side view of the needle, looking along the arrow VII in Fig. 4; and Fig. 6 is a partly cross-sectional side view of another embodiment of the fuel supply device. Referring to Figs. 2 and 3, reference numeral 1 designates a cylinder block, 2 a piston, 3 a cylinder head, and 4 a combustion chamber; 5 designates a pair of intake valves, 6 intake ports, 7 a pair of exhaust valves, 8 exhaust ports; and 9 designates a spark plug. Masking walls 10, each masking the valve opening formed between the valve seat and the peripheral portion of the intake valve 5, which is located on the exhaust valve side, for the entire time for which the intake valve 5 is open, are formed on the inner wall of the cylinder head 3. Consequently, when the intake valves 5 open, fresh air flows into the combustion chamber 4 from the valve opening which is located at a position opposite to the exhaust valves 7, as illustrated by the arrow A in Fig. 3. A fuel supply device 20 is arranged on the inner wall of the cylinder head 3 between the intake valves 5. The fuel supply device 20 in Fig. 1 does not show the invention, but only illustrates features which are present in an embodiment of the invention shown in Figs. 4 and 5. Referring to Fig. 1, a straight needle insertion bore 22 is formed in the housing 21 of the fuel supply device 20, and a needle 23 having a diameter smaller than that of the needle insertion bore 22 is inserted into the needle insertion bore 22. A nozzle opening 24 is formed at one end of the needle insertion bore 22, and the opening and closing operation of the nozzle opening 24 is carried out by the valve head 25 formed on the tip of the needle 23. In the fuel supply device illustrated in Fig. 1, the nozzle opening 24 is arranged in the combustion chamber 4. A spring retainer 26 is mounted on the needle 23, and a compression spring 27 is inserted between the spring retainer 26 and the housing 21. The nozzle opening 24 is normally closed by the valve head 25 of the needle 23 due to the spring force of the compression spring 27. A movable core 28 continuously abuts against the end portion of the needle 23, which is positioned opposite to the valve head 25, due to the spring force of the compression spring 27, and a solenoid 30 and a stator 31 are arranged in the housing 21 to attract the movable core 28. When the solenoid 30 is energized, the movable core 28 moves toward the stator 31. At this time, since the needle 23 moves toward the nozzle opening 24 against the compression spring 27, the nozzle opening 24 is opened. A nozzle chamber 32 having a cylindrical shape is formed in the housing 21. The nozzle chamber 32 has an air inlet 32a and an air outlet 32b separately formed from and spaced from the air inlet 32a. The air inlet 32a is connected to a pressurized air source 34 via a pressurized air inflow passage 33, and the air outlet 32b is connected to the needle insertion bore 22 via a pressurized air outflow passage 35. The nozzle 37 of a fuel injector 36 is arranged in the nozzle chamber 32 at a position between the air inlet 32a and the air outlet 32b. As can be seen from Fig. 1, the pressurized air outlet passage 35 extends straight. The nozzle 37 of the fuel injector 36 is arranged on the axis of the pressurized air outlet passage 35, and fuel having a small spread angle is injected from the nozzle 37 along the axis of the pressurized air outflow passage 35. The pressurized air outlet passage 35 extends obliquely to the needle insertion bore 22 toward the nozzle opening 24 and is obliquely connected to the needle insertion bore 22 at an angle of 20 through 40 degrees with respect to the axis of the needle insertion bore 22. The needle insertion bore 22, the nozzle chamber 32, and the pressurized air outflow passage 35 are connected to the pressurized air source 34 via the pressurized air inflow passage 33 and thus filled with pressurized air. Fuel is injected into the pressurized air from the nozzle 37 along the axis of the pressurized air outflow passage 35. Since the pressurized air outflow passage 35 is obliquely connected to the needle insertion bore 22, a large part of the injected fuel reaches the interior of the needle insertion bore 22 around the needle 23 near the valve head 25. At this time, a part of the injected fuel is stuck to both the inner wall of the pressurized air outflow passage 35 and the inner wall of the nozzle chamber 32. When the solenoid 30 is energized, the needle 23 opens the nozzle opening 24. At this time, since the injected fuel is collected near the valve head 25, both the fuel and the pressurized air are injected together from the nozzle opening 24 into the combustion chamber 4 (Fig. 3) as soon as the needle 23 opens the nozzle opening 24. In addition, when the needle 23 opens the nozzle opening 24, pressurized air flows into the nozzle chamber 32 from the pressurized air inflow passage 33 and then flows toward the nozzle opening 24 via the pressurized air outflow passage 35. Consequently, the fuel stuck to the inner wall of the pressurized air outflow passage 35 and the inner wall of the nozzle chamber 32 is carried away by the pressurized air and then injected from the nozzle opening 24. Therefore, as soon as the needle 23 opens the nozzle opening 24, the entire injected fuel is injected from the nozzle opening 24 and, after the injection of the entire injected fuel is completed, only the pressurized air is injected from the nozzle opening 24. Then, the solenoid 30 is deenergized, and thus the needle 23 closes the nozzle opening 24. Consequently, only the pressurized air is injected from the nozzle opening 24 immediately before the needle 23 closes the nozzle opening 24. If fuel is still injected from the nozzle opening 24 immediately before the needle 23 closes the nozzle opening 24, when the flow area of the nozzle opening 24 becomes small due to the closing operation of the needle 23, and the velocity of the pressurized air flowing out from the nozzle opening 24 becomes low, the fuel is not atomized, and thus the liquid fuel is stuck to the wall around the nozzle opening 24. However, if the liquid fuel is stuck to the wall around the nozzle opening 24, carbon is accumulated on the wall around the nozzle opening 24 and affects the injecting operation. Nevertheless, in the fuel supply device illustrated in Fig. 1, since only the pressurized air is injected from the nozzle opening 24 immediately before the needle 23 closes the nozzle opening 24, the liquid fuel is not stuck to the wall around the nozzle opening 24, and therefore there is no danger that carbon will be accumulated on the wall around the nozzle opening 24. In the fuel supply device, an enlarged portion 38 closing the entire cross-section of the needle insertion bore 22 is integrally formed on the needle 23 at a position adjacent to the connecting portion between the pressurized air outflow passage 35 and the needle insertion bore 22 and opposite to the nozzle opening 24. By forming the enlarged portion 38 on the needle 23, when fuel is injected from the nozzle 37 of the fuel injector 36, the enlarged portion 38 prevents the injected fuel from entering into the deep interior of the needle insertion bore 22, that is, entering into the needle insertion bore 22 located above the enlarged portion 38, and prevents the injected fuel from being stuck to the inner wall of the deep interior of the needle insertion bore 22. Consequently, the entire fuel injected from the nozzle 37 can be injected from the nozzle opening 24. In addition, when the needle 23 opens the nozzle opening 24, the enlarged portion 38 moves toward the nozzle opening 24. At this time, the fuel stuck onto the inner wall of the needle insertion bore 22 near the enlarged portion 38 is wiped off by the lower end face of the enlarged portion 38. Consequently, it is possible to prevent the fuel from accumulating on the inner wall of the needle insertion bore 22 near the enlarged portion 38. In addition, the enlarged portion 38 also serves to retain the needle 23 at a regular position in the needle insertion bore 22. Figure 3 illustrates the case where the fuel supply device 20 is used for a two-stroke engine, and the injection of fuel by the fuel supply device 20 is started a little while before the intake valves 5 close. When the engine is operating under a light load, since the velocity of the fresh air A flowing into the combustion chamber 4 is low, the fuel injected from the fuel supply device 20 is collected around the spark plug 9, and thus a good ignition can be obtained. When the engine is operating under a heavy load, since the velocity of the fresh air A flowing into the combustion chamber 4 is high, a strong loop scavenging operation is carried out. In addition, since the fuel injected from the fuel supply device 20 is carried downward along the inner wall of the combustion chamber 4 by the fresh air A flowing in a loop shape, a homogenous air-fuel mixture is formed in the combustion chamber 4. As a result, a high output power of the engine can be obtained. Figures 4 and 5 illustrate an embodiment of the fuel supply device according to the invention. In this embodiment, the enlarged portion 39 of the needle 23 is arranged to cover the opening of the pressurized air outflow passage 35, and a cutaway portion 39a is formed on the outer circumferential wall of the enlarged portion 41 at a position which faces the opening of the pressurized air outflow passage 35. In this embodiment since the fuel injected from the nozzle 37 (Fig. 1) impinges upon the surface of the cutaway portion 41a, which has a small surface area, the amount of fuel stuck to the wall around the opening of the pressurized air outflow passage 35 becomes small. Consequently, in this embodiment, there is an advantage that the amount of the injected fuel which reaches the needle insertion bore 22 near the valve head 25 can be increased. Figure 6 illustrates a further embodiment of the fuel supply device. In this embodiment, in addition to the air outlet 32b, another air outlet 32c is formed on the inner circumferential wall of the nozzle chamber 32 at a position opposite to the air inlet 32a with respect to the axis of the pressurized air outflow passage 35. This air outlet 32c is obliquely connected to the nozzle insertion bore 22 via a bypass passage 70 so that the distance between the nozzle opening 24 and the connecting portion of the pressurized air outlet passage 35 and the needle insertion bore 22 is approximately one half of the distance between the nozzle opening 24 and the connecting portion of the bypass passage 70 and the needle insertion bore 22. Also in this embodiment, fuel is injected from the nozzle 37 of the fuel injector 36 into the pressurized air outflow passage 35. At this time, a large part of the injected fuel is introduced into the needle insertion bore 22 near the valve head 25 of the needle 23, but a small part of the injected fuel flowing out from the pressurized air outflow passage 35 flows into the deep interior of the needle insertion bore 22. However, in this embodiment, when the needle 23 opens the nozzle opening 24, since the pressurized air is fed into the needle insertion bore 22 from both the pressurized air outflow passage 35 and the bypass passage 70, the fuel existing in the deep interior of the needle insertion bore 22 is carried away toward the nozzle opening 24 by the pressurized air fed into the needle insertion bore 22 from the bypass passage 70. As a result, this makes it possible to prevent the fuel from accumulating in the deep interior of the needle insertion bore 22. According to the present invention, since the entire fuel injected from the fuel injector is injected from the nozzle opening together with the pressurized air, there is no danger that the amount of fuel injected from the nozzle opening becomes irregular, and thus it is possible to obtain stable combustion.

Claims: A fuel supply device of an engine, comprising: nozzle opening (24) for injecting fuel and pressurized air, valve means (20) comprising a needle (23) arranged in a needle insertion bore (22) having a diameter larger than that of said needle for electro-magnetically controlling the opening operation of said nozzle opening (24) formed at a tip end of said needle insertion bore; a nozzle chamber (32) having an air inlet (32a) connected to a pressurized air source (34) and an air outlet (32b) separately formed from and spaced from said air inlet and connected to said needle insertion bore via a pressurized air outflow passage (35); and fuel injection means (36) arranged in said nozzle chamber for injecting fuel, characterized in that said needle (23) has an enlarged portion (39) formed thereon, said enlarged portion closing the entire cross section of the needle insertion bore and being slidably fitted into said needle insertion bore (22) at a position opposite to said nozzle opening (24) with respect to a connection portion of said pressurized air outflow passage (35) and said needle insertion bore, wherein said pressurized air outflow passage (35) is obliquely connected to said needle insertion bore (22), and said enlarged portion (39) has a cutaway portion (39a) connecting said pressurized air outflow passage (35) to said nozzle opening (24). A fuel supply device according to claim 1, characterized in that said valve means (20) further comprises a solenoid (30) actuating said needle (23) and a valve head (25) formed on said needle (23) to control the opening operation of said nozzle opening (24). A fuel supply device according to claim 1, characterized in that said nozzle chamber (32) has an inner circumferential wall circumferentially extending about an axis of said nozzle chamber (32) an said air inlet (32a) is formed on the circumferential wall of said nozzle chamber (32), said air outlet (32b) being formed on said axis of said nozzle chamber (32). A fuel supply device according to claim 3, characterized in that said fuel injection means (36) comprises a nozzle (37) arranged on said axis of said nozzle chamber (32) to inject fuel from said nozzle (37) along the axis of said nozzle chamber (32). A fuel supply device according to claim 4, characterized in that said air outlet (32b) is connected to said nozzle opening (24) via a pressurized air outflow passage (35) which extends straight on said axis of said nozzle chamber (32). A fuel supply device of an engine, comprising: a nozzle opening (24) for injecting fuel and pressurized air, valve means (20) comprising a needle (23) arranged in a needle insertion bore (22) having a diameter larger than that of said needle for electro-magnetically controlling the opening operation of said nozzle opening (24) formed at a tip end of said needle insertion bore; a nozzle chamber (32) having an air inlet (32a) connected to a pressurized air source (34) and an air outlet (32b) separately formed from and spaced from said air inlet and connected to said needle insertion bore via a pressurized air outflow passage (35); and fuel injection means (36) arranged in said nozzle chamber for injecting fuel, characterized in that said nozzle chamber (32) has another air outlet (32c) formed on the inner circumferential wall of said nozzle chamber and connected to said needle insertion bore (22) via a bypass passage (70) at a position opposite to said nozzle opening (24) with respect to a connecting portion of said pressurized air outflow passage (35) and said needle insertion bore (22), wherein said needle (23) has an enlarged portion formed thereon, said enlarged portion closing the entire cross-section of the needle insertion bore and being slidably fitted into said needle insertion bore (22) at a position opposite to said nozzle opening (24) with respect to the connection portion of said bypass passage (70) and said needle insertion bore, and said pressurized air outflow passage (35) is obliquely connected to said needle insertion bore (22). A fuel supply device according to claim 6, characterized in that said other air outlet (32c) is arranged at a position opposite to said air inlet (32a) with respect to said axis of said nozzle chamber (32).

Inventors: KUSHIBE TAKAHIRO, OHNO EISHI, SHIRABE NAOTAKA, TAKANO YUICHI, TATENO MANABU, KUSHIBE, TAKAHIRO, OHNO, EISHI, SHIRABE, NAOTAKA, TAKANO, YUICHI, TATENO, MANABU, SHIRABE, NAOTAKA 53-2, AZA MYOGAN
Applicants: DENSO CORP, TOYOTA MOTOR CO LTD, DENSO CORPORATION, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F02M69
IPC codes: F02M51, F02M61, F02M69, F02B75, F02M53, F02M67