GB2239058A

GB2239058A - Fuel pumping apparatus

Info

Publication number: GB2239058A
Application number: GB8926481A
Authority: GB
Inventors: Peter Alban George Collingborn
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1989-11-23
Filing date: 1989-11-23
Publication date: 1991-06-19
Also published as: GB8926481D0

Abstract

A fuel pumping apparatus of the rotary distributor type includes a cam actuated fixed stroke plunger 13 and an auxiliary plunger 33. A spill valve 26 is provided and which is opened to allow the fuel delivered by the plunger 13 during its inward movement to flow to a drain. The spill valve is actuated by fluid pressure developed during inward movement of the auxiliary plunger. The instant at which the spill valve is opened is determined by varying the extent of the allowed outward movement of the auxiliary plunger using an adjustable stop ring 35. <IMAGE>

Description

FUEL PUMPING APPARATUS This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a rotary distributor member adapted to be driven in timed relationship with an associated engine, a pumping plunger mounted in a bore in the distributor member, cam means for imparting inward movement to the pumping plunger as the distributor member rotates, a delivery passage in the distributor member, said delivery passage communicating with the bore and opening onto the periphery of the distributor member at a position to register with a plurality of delivery ports in turn during successive inward movements of the pumping plunger, means for supplying fuel to the bore in the intervals between the inward movement of the plunger to effect maximum outward movement of the plunger and valve means operable during the inward movement of the plunger to terminate delivery of fuel through said delivery passage thereby to control the quantity of fuel which is supplied to the associated engine.

The object of the present invention is to provide an apparatus of the kind specified in a simple and convenient form.

According to the invention said valve means comprises a valve member shaped for cooperation with a seating to prevent escape of fuel from said bore, resilient means biasing the valve member into contact with the seating, a surface on the valve member or on a part coupled thereto against which fluid under pressure can act to lift the valve member from the seating, an auxiliary plunger slidable in a further bore in the distributor member, said surface being exposed to the pressure of fluid in said further bore, said auxiliary plunger being moveable inwardly by said cam means and adjustable stop means for limiting the extent of outward movement of the further plunger whereby the instant during the inward movement of the pumping plunger at which said auxiliary plunger is moved inwardly to generate a fluid pressure to lift the valve member from the seating, can be controlled.

An example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional side elevation of the apparatus, and Figure 2 is a view to an enlarged scale of part of the apparatus which is seen in Figure 1.

Referring to the drawings the apparatus comprises a rotary cylindrical distributor member 10 which is mounted in a surrounding body part 11. Formed in the distributor member is a transversely extending bore 12 in which is mounted a pair of pumping plungers 13. At their outer ends the plungers are engaged by cam followers each of which comprises a shoe engaging with the outer end of the plunger and a roller supported in the shoe. The rollers engage the internal peripheral surface of an annular cam ring 14 which has formed on its internal surface, a plurality of pairs of cam lobes.

The bore 12 communicates by way of a passage 15 formed in the distributor member, with a delivery passage 16 which extends to the periphery of the distributor member and which is positioned to register in turn with a plurality of outlet ports 17 formed in the body part and which in use, are connected to the injection nozzles of the associated engine respectively. The communication of the delivery passage with an outlet port is arranged to occur during the whole time the plungers 13 are moved inwardly by the leading flanks of the cam lobes.

Also formed in the distributor member is an inlet passage 18 which during the time when the plungers are allowed outward movement by the cam lobes and when the delivery passage 16 is out of register with an outlet 17, registers with a plurality of inlet ports 19 formed in the body part 11 and which communicate with the outlet of a low pressure fuel supply pump 20. In operation, as the distributor member rotates the delivery passage 16 will be brought into register with an outlet 17 and during the inward movement of the plungers 13 fuel will be delivered to the associated engine.As the distributor member further rotates the delivery passage 16 will move out of register with an outlet 17 and the inlet passage 18 will move into register with an inlet port 19 so that fuel is now supplied to the bore 12 to effect outward movement of the plungers such outward movement being limited either by the profile of the cam ring or by special stop surfaces.

The distributor member is coupled to a drive shaft 21 which is journalled within the body part 11 and the drive shaft has a cup shaped portion 22 which is best seen in Figure 2. The cam followers associated with the plungers 13 are located in slots 23 formed in the wall of the cup shaped portion so that the cam followers are driven by the drive shaft 21, the distributor member being non-rotatably coupled to the drive shaft by means not shown. The cup shaped portion of the drive shaft has a cylindrical extension 24 of reduced diameter and the purpose of this extension will be discussed later in the description.

In order to control the quantity of fuel which is supplied to the associated engine there is provided valve means 25 and this comprises a valve member 26 which at one end is coupled to a piston member 27 which is slidable within a cylinder 28 formed in the distributor member. The other end of the valve member 26 is formed as a guide 29 which is slidable within a bore 30 extending within the distributor member and traversing the bore 12 which contains the pumping plungers. At its end adjacent the piston, a seating is defined about the bore 30 and the valve member is shaped for cooperation with this seating. The valve member is biased into contact with the seating by means of a coiled compression spring 31 which is engaged with the aforesaid piston.

The bore 30 extends into a further transverse bore 32 in which is slidably mounted a pair of auxiliary plungers 33. In addition the bore 32 intermediate the plungers 33 communicates with a passage 34 extending to the periphery of the distributor member and positioned to register in turn with the inlet ports 19, such communication taking place when an inlet passage 18 is in register with an inlet port.

The guide portion 29 defines a surface which is exposed to the pressure developed in the bore 32 during the inward movement of the auxiliary plungers and when the pressure is sufficient, the valve member will be moved axially against the action of its spring to allow fuel to flow from the bore 12 into the cylinder 28, such flow of fuel displacing the piston 27 and the valve member against the action of the spring 31.

The instant at which sufficient pressure is developed within the bore 32 is determined by controlling the extent of outward movement of the auxiliary plungers when the passage 34 is in communication with an inlet port 19. At their outer ends the plungers engage cam followers which are housed in slots 34 in an annular member 35 which is non-rotatably connected to the enlarged portion 22 of the drive shaft but which can be moved axially relative thereto. As shown in Figure 2 the annular member 35 is mounted about the extension 24. As also will be seen from Figure 2, the slots 34 define ramp surfaces 36 and the cam followers which are associated with the plungers 32 define complementary surfaces so that the extent of outward movement of the auxiliary plungers depends upon the relative axial setting of the annular member 35 and the cam followers.The cam followers are located in a fixed axial position either by biasing springs or by means of a retaining plate neither of which is shown. Two ways of adjusting the axial setting of the annular member 35 are illustrated in Figure 1, the first being a pivotal lever 37 which is engageable within a slot 38 formed in the annular member and the second method is by push rods 39 which extend through the drive shaft into engagement with the annular member. The lever 37 or the push rods 39 can be connected to a governor mechanism of any convenient type for example, a centrifugal weight mechanism. Where the push rods 39 are utilised to determine the setting of the annular member, the latter must be provided with a spring operable to maintain it in engagement with the push rods.

Considering now the operation of the apparatus and assuming that a filling stroke has just been completed.

As the distributor member rotates the plungers 13 will start to move inwardly and fuel will be supplied to the associated engine. After such movement has started a position will be reached at which the cam lobes engage the cam followers associated with the auxiliary plungers to effect inward movement to the plungers. Since the passage 34 during delivery of fuel is closed off, the pressure within the bore 32 will rapidly increase and this pressure acting on the guide portion 29 of the valve member will effect axial movement of the valve member against the action of its spring and in particular will lift the valve member from the seating to permit fuel to flow from the bore 12 into the cylinder.The flow of fuel from the bore 12 into the cylinder will displace the valve member against the action of the spring and the fuel will be stored in the cylinder and will be returned to the bore 12 as soon as inward movement of the plungers has ceased. In like manner the fuel which is displaced into the passage 30 by the auxiliary plungers will be returned to the bore. The fuel which has been delivered to the engine will be made up by fuel flowing from an inlet port 19 into the inlet passage 18 and any leakage of fuel which may have occurred from the bore 32 will be made up by fuel flowing from an inlet port 19 through the passage 34.

It is necessary to ensure that the working clearance between the bore 30 and the guide portion 29 is as small as possible to avoid leakage of fuel at high pressure from the bore 12 into the bore 32 and it may be desirable to provide a leakage path from the bore 32 the leakage path merely ensuring that pressure build up in the bore 32 does not occur before inward movement of the auxiliary plungers. It is also necessary to ensure that the valve member returns into engagement with its seating during the initial outward movement of the plungers and for this purpose leakage of fuel past the piston member 27 may be permitted and the spring 31 must exert sufficient force on the piston and valve member to move the latter against the pressure of fuel developed by the low pressure pump 20.

As shown the pressure developed by the auxiliary plungers acts upon the comparatively small end area of the guide portion 29. It is possible for the bore 30 to be connected to the inner end of the cylinder 28 so that the pressure developed upon inward movement of the auxiliary plungers, is applied to the piston 27.

In the particular example as the annular member 35 is moved to the left as shown in Figure 2 the extent of outward movement of the plungers will be reduced and therefore the quantity of fuel which is supplied to the associated engine will increase.

Claims

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine comprising a rotary distributor member adapted to be driven in timed relationship with an associated engine, a pumping plunger mounted in a bore in the distributor member, cam means for imparting inward movement to the pumping plunger as the distributor member rotates, a delivery passage in the distributor member, said delivery passage communicating with the bore and opening onto the periphery of the distributor member at a position to register with a plurality of outlet ports in turn during successive inward movements of the pumping plunger, means for supplying fuel to the bore in the intervals between the inward movement of the plunger to effect maximum outward movement of the plunger, valve means operable during the inward movement of the plunger to terminate delivery of fuel through said delivery passage thereby to control the quantity of fuel which is supplied to the associated engine, said valve means comprising a valve member shaped for cooperation with a seating to prevent escape of fuel from said bore, resilient means biasing the valve member into contact with the seating, a surface on the valve member or on a part coupled thereto against which fluid under pressure can act to lift the valve member from the seating, an auxiliary plunger slidable in a further bore in the distributor member, said surface being exposed to the pressure of fluid in said further bore, said auxiliary plunger being moveable inwardly by said cam means and adjustable stop means for limiting the extent of outward movement of the auxiliary plunger whereby the instant during the inward movement of the pumping plunger at which said auxiliary plunger is moved inwardly to generate a fluid pressure to lift the valve member from the seating, can be controlled.

2. An apparatus according to Claim 1 in which said stop means comprise an annular member rotatable with the distributor member, said annular member being axially movable relative to the distributor member and defining a ramp surface for engagement by a complementary ramp surface joined on a cam follower associated with the auxiliary plunger.

3. An apparatus according to Claim 2 in which said annular member is mounted upon a part of a drive shaft coupled to the distributor member.

4. A fuel pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.