FUEL INJECTION NOZZLE

Abstract: In a fuel injection nozzle (10) having an outwardly opening poppet valve (22) that controls the delivery of fuel to an engine combustion chamber, an actuating piston (46) increases the difference between the injection pressure required to initiate opening (58) of the poppet valve and the injection pressure required to fully open (58,60) the poppet valve. The actuating piston effectively limits opening of the poppet valve during light load engine operation, thereby reducing the rate of injection during light load engine operation and thus enhancing the ability of the engine to operate with low noise, hydrocarbon and nitrogen oxide emissions.

Description: This invention relates to a fuel injection nozzle for delivering fuel to the combustion chamber of an internal combustion engine. In a fuel injection system for a direct injection engine, a pump supplies a measured amount of fuel to a fuel injection nozzle for delivery directly into the engine combustion chamber. US-A-4693424 describes a fuel injection nozzle having an outwardly opening poppet valve that controls delivery of fuel to the engine combustion chamber. That fuel injection nozzle allows the engine to operate with lower noise, hydrocarbon and nitrogen oxide emissions than engines with other nozzles. FR-A-2289756 discloses a fuel injection valve assembly in which a poppet valve with upper and lower sets of orifices discharge fuel sequentially to improve dosage mixture. During light load operation, for example during idling, only the lower set of orifices might be used. US-A-4750675 describes an improved fuel injection nozzle also having an outwardly opening poppet valve that controls delivery of fuel to the engine combustion chamber. That improved fuel injection nozzle includes a piston that dampens opening movement of the poppet valve, thereby reducing the initial rate of injection and thus enhancing the ability of the engine to operate with low noise, hydrocarbon and nitrogen oxide emissions. This invention provides a further improved fuel injection nozzle also having an outwardly opening poppet valve that controls the delivery of fuel to the engine combustion chamber. A fuel injection nozzle in accordance with the present invention is characterised over US-A-4750675 by the features specified in the characterising portion of claim 1. In the improved fuel injection nozzle provided by this invention, an actuating piston increases the difference between the injection pressure required to initiate opening of the poppet valve and the injection pressure required to fully open the poppet valve. The actuating piston effectively limits opening of the poppet valve during light load engine operation, thereby reducing the rate of injection during light load engine operation and thus enhancing the ability of the engine to operate with low noise, hydrocarbon and nitrogen oxide emissions. The present invention will now be described, by way of example, with reference to the following description and the accompanying drawings, in which:- Figure 1 is an axial sectional view of one embodiment of this improved fuel injection nozzle, showing the construction of the fuel injection nozzle; Figure 2 is a view similar to Figure 1, showing the position of the parts when the poppet valve is partially open; Figure 3 is a view similar to Figure 1, showing the position of the parts when the poppet valve is fully open; Figure 4 is a view similar to Figure 1, showing the position of the parts during closing movement of the poppet valve; and Figure 5 is an axial sectional view of another embodiment of this improved fuel injection nozzle. Referring first to Figures 1-4, a nozzle 10 has a body 12 adapted to be received in an engine cylinder head, and a holder 14 having a fitting 16 that receives fuel from an injection pump. Body 12 and holder 14 are threaded together at 18, and a gasket 20 seals the threaded connection. A poppet valve 22 is received in a bore 24 of body 12. Poppet valve 22 has a head 26 that engages a lower end 28 of body 12, and a stem 30 that extends into a chamber 32 formed between body 12 and holder 14. Within chamber 32, a spring 34 is compressed between a spring retainer 36 secured around the upper end of stem 30 and a stop member 38 that rests against the top 40 of body 12. Holder 14 has a fuel inlet passage 42 that opens into a piston bore 44. An actuating piston 46 is lapped fit in piston bore 44. The lower end 48 of actuating piston 46 is tapered or recessed to a face 50 that seals against the top 52 of stem 30. When the injection pump supplies fuel to fuel injection nozzle 10, the injection pressure of the fuel acts on an upper face 53 of actuating piston 46. Actuating piston 46 transfers the resulting opening force to stem 30 to displace poppet valve 22 against the bias of spring 34. Fuel then flows through fuel inlet passage 42, a passage 54 in actuating piston 46, and a passage 56 in stem 30 to lower and upper sets of orifices 58 and 60, and is discharged across a gap 62 (Figures 2-4) between head 26 and the lower end 28 of body 12. The area of the upper face 53 of actuating piston 46 and the characteristics of spring 34 are chosen so that, in response to the lower injection pressures of light load engine operation, poppet valve 22 is displaced only far enough to expose the lower set of orifices 58 below the lower end 28 of body 12. By using only the orifices 58 to deliver fuel to the engine combustion chamber during light load engine operation, the rate of injection is reduced and the ability of the engine to operate with low noise, hydrocarbon and nitrogen oxide emissions is enhanced. In response to the higher injection pressures of heavy load engine operation, poppet valve 22 is displaced until a shoulder 64 on stem 30 engages stop member 38. At that time, both sets of orifices 58 and 60 are exposed below the lower end 28 of body 12 to allow delivery of the fuel required for heavy load engine operation. It will be appreciated that the same fuel delivery characteristics could be achieved by employing a spring 34 having an increased spring rate. However, an increase in the spring rate would require an increase in the diameter or length of the fuel injection nozzle. The improved fuel injection nozzle provided by this invention does not require such an increase in length or diameter. An opening 66 through stop member 38 is eccentric to the axis of fuel injection nozzle 10, thereby allowing stop member 38 to be assembled around stem 30 and then, upon insertion into holder 14, to slide laterally under shoulder 64 to act as a stop for poppet valve 22. Toward the end of the injection event, the rate of fuel delivery falls off, and spring 34 raises poppet valve 22. Because the diameter of stem 30 is larger than the diameter of actuating piston 46, the pressure in chamber 32 will increase slightly above the pressure in fuel inlet passage 42. The resulting pressure difference causes actuating piston 46 to lift away from stem 30 as shown in Figure 4, venting the pressure in chamber 32 through the passage 54 in actuating piston 46 to the fuel inlet passage 42. When the injection pump again supplies fuel to fuel injection nozzle 10, the actuating piston 46 is pushed and seated against the top 52 of stem 30, as shown in Figure 1, and the cycle repeats. Referring now to Figure 5, a fuel injection nozzle 110 has a body 112 adapted to be received in an engine cylinder head, and a holder 114 having a fitting 116 that receives fuel from an injection pump. Body 112 and holder 114 are threaded together at 118, and a gasket 120 seals the threaded connection. A poppet valve 122 is received in a bore 124 of body 112. Poppet valve 122 has a head 126 that engages a lower end 128 of body 112, and a stem 130 that extends into a chamber 132 formed between body 112 and holder 114. Within chamber 132, a spring 134 is compressed between a spring retainer 136 secured around an upper end of stem 130 and a stop member 138 that rests against the top 140 of body 112. Holder 114 has a fuel inlet passage 142 that opens into a piston bore 144. An actuating piston 146 formed as an extension of stem 130 is received in piston bore 144. When the injection pump supplies fuel to fuel injection nozzle 110, the injection pressure of the fuel acts on an upper face 153 of actuating piston 146. Actuating piston 146 transfers the resulting opening force to stem 130 to displace poppet valve 122 against the bias of spring 134. Fuel then flows through fuel inlet passage 142, a passage 155 in actuating piston 146 and stem 130 to lower and upper sets of orifices 158 and 160, and is discharged across a gap between head 126 and the lower end 128 of body 112. The area of the upper face 153 of actuating piston 146 and the characteristics of spring 134 are chosen so that, in response to the lower injection pressures of light load engine operation, poppet valve 122 is displaced only far enough to expose the lower set of orifices 158 below the lower end 128 of body 112. By using only the orifices 158 to deliver fuel to the engine combustion chamber during light load engine operation, the rate of injection is reduced and the ability of the engine to operate with low noise, hydrocarbon and nitrogen oxide emissions is enhanced. In response to the higher injection pressures of heavy load engine operation, poppet valve 122 is displaced until a shoulder 164 on stem 130 engages stop member 138. At that time, both sets of orifices 158 and 160 are exposed below the lower end 128 of body 112 to allow delivery of the fuel required for heavy load engine operation. Any fuel leakage around actuating piston 146 enters chamber 132 and is vented through a passage 168. Toward the end of the injection event, the rate of fuel delivery falls off, and spring 134 raises poppet valve 122. Because the diameter of stem 130 is larger than the diameter of actuating piston 146, the volume in chamber 132 will decrease as the poppet valve 122 closes. Any fuel displaced from chamber 132 is vented through passage 168.

Claims: A fuel injection nozzle (10,110) having a body (12,112) with an axial bore (24,124), a poppet valve (22,122) having a stem (30,130) received in the bore and a head (26,126) adapted to engage an end (28,128) of the body, a spring (34,134) biasing the stem to engage the head with the end of the body, and a holder (14,114) secured to the body, the holder having a fuel inlet passage (42,142), wherein the fuel inlet passage opens into a piston bore (44,144) formed in the holder, whereby fuel can flow through the fuel inlet passage and through passage means (56,155) in the stem to first and second sets of orifices (58,60,158,160) opening through the stem from the passage means to be discharged from the orifices across a gap (62) formed between the head and the end of the body, characterised in that an actuating piston (46,146) is received in the piston bore, the actuating piston having a face (53,153) exposed to the injection pressure of fuel in the fuel inlet passage, and passage means (54,155) for fuel flow from the fuel inlet passage to the passage means in the stem, the actuating piston being adapted to transfer the injection pressure to the stem to displace the poppet valve against the bias of the spring to allow fuel flow; in that the area of the face of the actuating piston and the characteristics of the spring are chosen so that, in response to the lower injection pressures of light load engine operation, the poppet valve is displaced only far enough to allow fuel to be discharged from the first set (58,158) of said orifices, and that, in response to the higher injection pressures of heavy load engine operation, the poppet valve is displaced far enough to allow fuel to be discharged from all said orifices, whereby the rate at which fuel is discharged during light load engine operation is lower than the rate at which fuel is discharged during heavy load operation. A fuel injection nozzle as claimed in claim 1, wherein the stem (30) extends into a chamber (32) formed between the body (12) and the holder (14), wherein the actuating piston (46) extends into the chamber and has another face (50) adapted to seal against an end (52) of the stem, and wherein the area of the face (52) of the actuating piston (46) exposed to said injection pressure is larger than the area of the face (50) of the actuating piston adapted to seal against the end (52) of the stem, whereby when the spring (34) moves the poppet valve (22) to reengage the head (26) with the end (28) of the body, the actuating piston lifts away from the end (52) of the stem and vents the pressure in the chamber through the passage means (56) in the actuating piston to the fuel inlet passage (42). A fuel injection nozzle as claimed in claim 1, wherein the stem (130) extends into a chamber (132) formed between the body (112) and the holder (114), wherein the actuating piston (146) is an extension of the stem (130), and wherein the fuel injection nozzle has a passage (168) opening from the chamber (132) whereby the pressure in the chamber is vented when the spring (134) moves the poppet valve (122) to reengage the head (126) with the end (128) of the body.

Inventors: SCZOMAK, DAVID PETER
Applicants: GENERAL MOTORS CORPORATION
Application year: 1989
Main classification: F02M61
IPC codes: F02M61