GB1578131A

GB1578131A - Fuel supply systems for engines

Info

Publication number: GB1578131A
Application number: GB1990676A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1976-05-14
Filing date: 1976-05-14
Publication date: 1980-11-05
Also published as: FR2351272B1; JPS538420A; DE2721628A1; IT1074534B; FR2351272A1

Description

(54) FUEL SUPPLY SYSTEMS FOR ENGINES (71) We, LUCAS INDUSTRIES HMI- TED, a British Company of Great King Street, Birmingham Bl9 2XP do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to an internal combustion engine fuel system, the system comprising an injection nozzle including a resiliently loaded valve operable by fuel under pressure to allow the fuel to flow through an outlet orifice, and the system also including a fuel pump for delivering fuel under pressure to the injection nozzle.

When such a system is utilised to supply fuel to a compression ignition engine it is advantageous for the operation of the engine, to supply a small volume of fuel to the engine, in advance of the remaining volume of fuel and the object of the present invention is to provide a fuel system of the kind specified in a form in which this desideratum is achieved.

According to the invention, a fuel system of the kind specified comprises a pilot pump means separate from the fuel pump for actuating the pilot pump, the outlet of said pilot pump being connected to the nozzle so that fuel under pressure delivered by the pilot pump can act upon the resiliently loaded valve to allow fuel delivered by the pilot pump to flow to the outlet orifice, the system including a non-return valve through which the fuel flowing from the fuel pump flows to act upon the resiliently loaded valve, the arrangement being such that the pilot pump can be actuated in advance of the fuel pump to provide the pilot quantity of fuel in advance of the main quantity of fuel delivered by the fuel pump.

Examples of fuel systems in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows in diagrammatic outline, one example of the system, Figure 2 shows a portion of another example of the system and Figure 3 shows a modification of the system of Figure 1.

Referring to Figure 1 of the drawings, the fuel system comprises an injection pump 10 having a plurality of outlets 11 for connection to respective fuel injection nozzles ob the associated engine. One such nozzle is indicated at 12 and it comprises a housing 13 having a valve member 14 slideable therein. The valve member is urged into contact with a seating 15 by means of a coiled compression spring 16 and a fuel supply passage 17 is provided, and through which fuel under pressure can act upon the valve member to lift same against the action of the spring thereby to allow fuel flow through an outlet orifice 18. When the supply of fuel under pressure through the passage 17 ceases then the valve member 14 moves into contact with the seating 15.One outlet of the injection pump is connected to the passage 17 by way of a non-return valve 19, the valve 19 being spring-loaded and opening to permit the flow of fuel between the injection pump and the passage 17.

In order to provide a pilot quantity of fuel a pilot pump generally indicated at 20 is provided and conveniently it is housed in assembly with the nozzle. The pilot pump comprises a piston 21 located within a cylinder communicating with the passage 17 and the piston 21 is spring-loaded in a direction away from the end of the cylinder communicating with the passage 17. For actuating the piston 21 an actuator 22 is provided and in the particular example, this comprises a plurality of piezoelectric crystals. The crystals can be energized by means of an electronic control unit 23 which receives an engine crankshaft position signal from a rotary part of the engine.The injection pump 10 is of course driven in timed relationship with the engine and the arrangement is such that the control unit 23 activates the stack of crystals which then move the piston 21 in a direction to discharge fuel from the cylinder, the pressure of the discharged fuel acting on the valve member 14 to lift same from its seating thereby to allow fuel flow through the outlet 18. The crystal unit remains energised even when the piston 21 has reached the end of its stroke, and it is then arranged that the in jection pump supplies a quantity of fuel which flows past the non-return- valve 19 to maintain the valve member 14 open or to lift the valve member 14 from its seating to allow the fuel to flow through the outlet 18.

Towards the end of the discharge stroke of the pump 10 the stack of crystals is de-energised to permit the piston 21 to return to the position in which it is shown. During this movement, fuel is drawn into the cylinder 21, this fuel coming from the pump 10.

It can be arranged that the stack of crystals is de-energised at a precise moment in relation to the discharge of fuel by the pump 10 in such a manner that the piston 21 absorbs the final quantity of fuel pumped by the pump 10. This has the beneficial effect of reducing the pressure in the passage 17 thereby allowing the valve member 14 to close quickly. It will be appreciated that the non-return valve 19 is provided to prevent the pilot pump discharging fuel towards the fuel pump 10 as might occur if the valve 19 were not provided.

It will be understood that the stack of piezoelectric crystals may be replaced by some other form of actuating device for instance, a solenoid and armature, a mechanical drive from the engine or some form of pressure intensifier which may be actuated by the engine cylinder pressure or by a pneumatic source.

The control unit 23 may in addition to the engine crankshaft position signal, also receive signals representative of the engine speed and the load on the engine, so as to adjust the timing of the pilot quantity of fuel in a manner depending on the aforesaid engine parameters.

The arrangement shown in Figure 2 is substantially the same with the exception that the non-return valve is accommodated in the end of the cylinder which contains the piston. As shown the non-return valve comprises a flared valve head 24 which is mounted upon a fluted body 25 slidable within the cylinder which contains the piston. Moreover, a passageway shown in dotted outline extends between the opposite ends of the valve and it is through this passageway that the pilot quantity of fuel is supplied to the passage 17. The area of the valve head which is exposed to the pressure of fuel delivered by the fuel pump is sufficient to ensure that a force is produced on the valve member which can overcome the force exerted by the return spring 26, the purpose of which is to load the valve head onto a seating.

In the arrangement shown in Figure 3 the pilot pump 20 delivers the pilot quantity of fuel through one nozzle 30 and the fuel pump 10 delivers fuel to the same nozzle 30 by way of a non-return valve 32. In addition, a further nozzle 31 is provided and only fuel delivered by the fuel pump 10 can flow through this nozzle. The main quantity of fuel therefore flows to the engine through both nozzles and fuel is supplied to the pilot pump 20 during the delivery of fuel by the fuel pump 10. The valve members ot the two nozzles share a common return spring 33 by virtue of a balance beam 34. The lever ratio of the balance beam together with the diameters of the valve members can be chosen to provide the desired operating characteristics for the two nozzles.

Whilst the pilot pump has been shown to be in assembly with the nozzle body, this need not necessarily be the case. It is desirable, however, in view of the small quantity of fuel which constitutes the pilot injection that the pilot pump should be as close to the nozzle as possible.

WHAT WE CLAIM IS: 1. An internal combustion engine fuel system, comprising an injection nozzle including a resiliently loaded valve operable by fuel under pressure to allow the fuel to flow through an outlet orifice, a fuel pump for delivery of fuel under pressure to the injection nozzle, a pilot pump, means separate from the fuel pump for actuating the pilot pump, the outlet of said pilot pump being connected to the nozzle so that fuel under pressure delivered by the pilot pump can act upon the resiliently loaded valve to allow fuel delivered by the pilot pump to flow to the outlet orifice, the system including a non-return valve through which the fuel flowing from the fuel pump flows to act upon the resiliently loaded valve, the arrangement being such that the pilot pump can be actuated in advance of the fuel pump to provide the pilot quantity of fuel in advance of the main quantity of fuel delivered by the fuel pump.

2. A fuel system according to Claim 1 including a control unit for controlling the operation of the pilot pump, and means for supplying to said control unit an engine crankshaft position signal representation of the position of the engine.

3. A fuel system according to Claim 1 in which said pilot pump includes a piston movable within a cylinder, said actuating means when energised effecting movement of the piston in one direction to discharge fuel, the actuating means when de-energised allowing the piston to move in the other direction thereby allowing fuel to flow into the cylinder.

4. A fuel system according to Claim 3 in which said actuating means is de-energised before the end of delivery of fuel by the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

crystal unit remains energised even when the piston 21 has reached the end of its stroke, and it is then arranged that the in jection pump supplies a quantity of fuel which flows past the non-return- valve 19 to maintain the valve member 14 open or to lift the valve member 14 from its seating to allow the fuel to flow through the outlet 18.

Towards the end of the discharge stroke of the pump 10 the stack of crystals is de-energised to permit the piston 21 to return to the position in which it is shown. During this movement, fuel is drawn into the cylinder 21, this fuel coming from the pump 10.

It can be arranged that the stack of crystals is de-energised at a precise moment in relation to the discharge of fuel by the pump

10 in such a manner that the piston 21 absorbs the final quantity of fuel pumped by the pump 10. This has the beneficial effect of reducing the pressure in the passage 17 thereby allowing the valve member

14 to close quickly. It will be appreciated that the non-return valve 19 is provided to prevent the pilot pump discharging fuel towards the fuel pump 10 as might occur if the valve 19 were not provided.

It will be understood that the stack of piezoelectric crystals may be replaced by some other form of actuating device for instance, a solenoid and armature, a mechanical drive from the engine or some form of pressure intensifier which may be actuated by the engine cylinder pressure or by a pneumatic source.

The control unit 23 may in addition to the engine crankshaft position signal, also receive signals representative of the engine speed and the load on the engine, so as to adjust the timing of the pilot quantity of fuel in a manner depending on the aforesaid engine parameters.

The arrangement shown in Figure 2 is substantially the same with the exception that the non-return valve is accommodated in the end of the cylinder which contains the piston. As shown the non-return valve comprises a flared valve head 24 which is mounted upon a fluted body 25 slidable within the cylinder which contains the piston. Moreover, a passageway shown in dotted outline extends between the opposite ends of the valve and it is through this passageway that the pilot quantity of fuel is supplied to the passage 17. The area of the valve head which is exposed to the pressure of fuel delivered by the fuel pump is sufficient to ensure that a force is produced on the valve member which can overcome the force exerted by the return spring 26, the purpose of which is to load the valve head onto a seating.

In the arrangement shown in Figure 3 the pilot pump 20 delivers the pilot quantity of fuel through one nozzle 30 and the fuel pump 10 delivers fuel to the same nozzle 30 by way of a non-return valve 32. In addition, a further nozzle 31 is provided and only fuel delivered by the fuel pump 10 can flow through this nozzle. The main quantity of fuel therefore flows to the engine through both nozzles and fuel is supplied to the pilot pump 20 during the delivery of fuel by the fuel pump 10. The valve members ot the two nozzles share a common return spring 33 by virtue of a balance beam 34. The lever ratio of the balance beam together with the diameters of the valve members can be chosen to provide the desired operating characteristics for the two nozzles.

Whilst the pilot pump has been shown to be in assembly with the nozzle body, this need not necessarily be the case. It is desirable, however, in view of the small quantity of fuel which constitutes the pilot injection that the pilot pump should be as close to the nozzle as possible.

WHAT WE CLAIM IS: 1. An internal combustion engine fuel system, comprising an injection nozzle including a resiliently loaded valve operable by fuel under pressure to allow the fuel to flow through an outlet orifice, a fuel pump for delivery of fuel under pressure to the injection nozzle, a pilot pump, means separate from the fuel pump for actuating the pilot pump, the outlet of said pilot pump being connected to the nozzle so that fuel under pressure delivered by the pilot pump can act upon the resiliently loaded valve to allow fuel delivered by the pilot pump to flow to the outlet orifice, the system including a non-return valve through which the fuel flowing from the fuel pump flows to act upon the resiliently loaded valve, the arrangement being such that the pilot pump can be actuated in advance of the fuel pump to provide the pilot quantity of fuel in advance of the main quantity of fuel delivered by the fuel pump.
2. A fuel system according to Claim 1 including a control unit for controlling the operation of the pilot pump, and means for supplying to said control unit an engine crankshaft position signal representation of the position of the engine.
3. A fuel system according to Claim 1 in which said pilot pump includes a piston movable within a cylinder, said actuating means when energised effecting movement of the piston in one direction to discharge fuel, the actuating means when de-energised allowing the piston to move in the other direction thereby allowing fuel to flow into the cylinder.
4. A fuel system according to Claim 3 in which said actuating means is de-energised before the end of delivery of fuel by the

fuel pump to allow the piston to absorb the final quantity of fuel supplied by the fuel pump.
5. A fuel system according to Claim 3 including resilient means acting on said piston to urge the piston in said other direction.
6. A fuel system according to Claim 3 in which said non-return valve comprises a valve member slidable in the cylinder, a passage through the valve member and through which fuel from the cylinder flows to the injection nozzle without operating the valve, a valve head at the end of the valve member removed from the piston, a seating defined at the end of the cylinder and with which the head co-operates, a space defined in the cylinder wall adjacent the head, passage means through which said space communicates with said fuel pump and a resilient means biassing the head into contact with the seating.
7. A fuel system according to Claim 3 including a further injection nozzle, said further injection nozzle being supplied with fuel only by said fuel pump, said first mentioned nozzle being supplied by said pilot pump and also receiving a proportion of the fuel supplied by said fuel pump.
8. A fuel system according to Claim 7 in which said nozzles are mounted in a common body, the two resiliently loaded valve members being disposed in spaced side by side relationship and slidable within separate bores, the bores and resiliently loaded valve members defining chambers to which fuel under pressure can be supplied to effect movement of the resiliently loaded valve members to allow fuel flow through the outlets, first passage means connecting said fuel pump to the one of said chambers associated with the further nozzle, second passage means connecting the cylinder of the pilot pump with the other of said chambers, resilient means biassing said resiliently loaded valve members to the closed position said resilient means acting on said members by way of a balance beam, whereby the closing force exerted by said resilient means is divided between the resiliently loaded valve members.
9. A fuel system according to Claim 8 in which said non-return valve is disposed in a passage interconnecting said chambers.
10. A fuel system according to any one of the preceding claims in which said actuating means comprises a stack of piezoelectric crystals.
11. An internal combustion engine fuel system comprising the combination and parts substantially as hereinbefore described with reference to the Figure 1 of the accompanying drawings.
12. An internal combustion engine fuel system comprising the combination and parts substantially as hereinbefore described with reference to Figure 1 as modified by Figure 2 of the accompanying drawings.
13. An internal combustion engine fuel system comprising the combination and parts substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.