GB2239057A

GB2239057A - Fuel pumping apparatus

Info

Publication number: GB2239057A
Application number: GB8926479A
Authority: GB
Inventors: Peter Alban George Collingborn; George Nicholas Felton
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: GB8926479D0

Abstract

A fuel pumping apparatus of the rotary distributor type has fixed stroke pumping plungers 15 operable through followers by cam lobes on a cam ring 17. A valve member 20 is provided which can be moved to an open position to spill fuel delivered during the inward movement of the pumping plungers and the valve member is operated by fluid under pressure developed by auxiliary plungers 24 operated by the cam lobes. The fluid displaced by the plungers 24 effects movement of a spring loaded shuttle 28 and an adjustable stop 32 is provided to halt the shuttle movement to allow sufficient fluid pressure to be developed. The stop is positioned by a cam profile 34 on a pivot lever 35 the position of which is determined by a governor mechanism. <IMAGE>

Description

FUEL PUMPING APPARATUS This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and comprising a rotary distributor member housed within a body part, the distributor member in use being driven in timed relationship with the associated engine, a bore formed in the distributor member and a pumping plunger mounted therein, cam means for imparting inward movement to the pumping plunger, means for supplying fuel expelled from the bore to a plurality of outlet ports in turn during successive inward movements of the pumping plunger, further means for filling the bore with fuel in the intervals between inward movements of the plunger and valve means operable to spill fuel from said bore during the inward movements of the plunger thereby to control the quantity of fuel which is delivered through said outlet ports.

The object of the 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 which is resiliently biased into contact with the seating to prevent flow of fuel through a spill port connected to said bore, a surface defined on the valve member or on a part connected thereto and against which fluid pressure can act to lift the valve member from the seating, an auxiliary plunger operable by said cam means and slidable in a further bore, the fluid pressure in said further bore acting on said surface, a shuttle slidable in a cylinder, resilient means biasing the shuttle towards one end of the cylinder and said one end of the cylinder communicating with said further bore so that the shuttle is exposed to the fluid pressure in said further bore, an axially movable stop member positioned to limit the movement of the shuttle so that the fluid pressure applied to said surface becomes sufficient to lift the valve member from the seating, an angularly adjustable lever and a cam profile defined on the lever for engagement by an end of said stop member whereby the axial setting of said stop member can be adjusted.

An example of the fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawing which is a sectional side elevation of the apparatus.

Referring to the drawing, the apparatus comprises a multi-part body 10 in which is mounted a rotary distributor member 11 which is coupled to a drive shaft 12 adapted in use to be driven in timed relationship with the associated engine. The drive shaft mounts the rotary part of a low pressure fuel supply pump generally indicated at 13.

Formed in the distributor member is a transversely extending bore 14 in which is mounted a pair of reciprocable plungers 15. At their outer ends the plungers engage cam followers 16 each comprising a shoe and a roller, the latter engaging with the internal peripheral surface of an annular cam ring which is adjustably mounted in the body of the apparatus. On the internal surface of the cam ring is formed a plurality of pairs of inwardly extending cam lobes which as the distributor member rotates, impart inward movement to the pumping plungers 15.

Extending axially within the distributor member is a central drilling 18 which extends through the bore 14 and defines a seating for engagement by a valve member 20 which extends within the drilling towards the opposite end thereof. The valve member is provided with a guide portion 19 which cooperates with the wall of the drilling. Intermediate the guide portion and the portion of the valve member which cooperates with the seating, the valve member is of reduced diameter to define an annular space which is connected to a delivery passage in known manner, and which extends to the periphery of the distributor member for communication in turn with a plurality of outlet ports 21 formed in the body which in use are connected to the injection nozzles of the associated engine respectively.Also communicating with the aforesaid annular space are a plurality of inlet passages which open onto the periphery of the distributor member for communication with inlet ports 22 formed in the body and communicating with the outlet of the low pressure pump 13.

Ignoring for the moment the valve member, during inward movement of the pumping plungers 15 fuel is expelled from the bore 14 and will be delivered through the delivery passage to one of the outlet ports 21.

During continued rotation of the distributor member the distributor passage will move out of register with an outlet and the inlet ports will move into register with the inlet passages 22 so that fuel can flow to the bore 14 to urge the plungers 15 outwardly their maximum extent as determined by the profile of the cam ring or by stops (not shown).

The valve member 20 extends into an enlarged portion of the drilling which forms a cylinder for a piston 23 integral with the valve member, and formed in the distributor member is a further bore which accommodates a pair of auxiliary plungers 24. The pressure generated during inward movement of the auxiliary plungers is applied to the end surface of the piston 23 and when the pressure is sufficient, the piston will move to lift the valve member from the seating against the action of a spring 25 which normally biasses the valve member into contact with the seating. The auxiliary plungers 24 are operated by the cam followers 16 so that they move inwardly at the same time as the pumping plungers 15.

The inner portion of the bore containing the auxiliary plungers is in constant communication with a transfer port 26 which opens into the inner end of a cylinder 27. Slidable within the cylinder is a shuttle 28 and it is biased towards the aforesaid end of the cylinder by means of a coiled compression spring 29. The shuttle 28 is of cup-shaped form and the spring 29 is located against the internal base wall of the shuttle.

At its other end the spring 29 is in engagement with a cup-shaped abutment 30 which is secured within a housing 31 secured to the body of the apparatus.

Formed in the base wall of the cup-shaped abutment is an aperture through which extends an axially movable stop member 32 which is engageable by the shuttle to limit the extent of movement of the shuttle against the action of the spring 29. The stop member includes an enlarged portion 33 which is guided for movement by the internal surface of the abutment 30 and at its outer end it is profiled and is engageable with a cam profile 34 formed on a lever 35 which is pivotally mounted at 36 in a cover of the housing 31. Assuming for the moment that the lever 35 is in a fixed position then during inward movement of the plungers fuel will be displaced by the auxiliary plungers 24 and will flow by way of the transfer port 26 into the cylinder 27. Such flow of fuel will displace the shuttle 28 against the action of the spring 29 and will therefore prevent the pressure which is applied to the piston 23 rising to a value such that the piston will lift the valve member from the seating.

Movement of the shuttle continues until it engages the stop member 32 and when this occurs the pressure developed by the auxiliary plungers will rapidly increase and the piston will move against the action of the spring 25 and will lift the valve member from the seating. This permits fuel displaced by the pumping plungers 15 to flow into the cylinder containing the piston and the pressure of fuel delivered through the respective outlet will rapidly decrease so that no more fuel will be supplied to the associated engine. As the distributor member continues to rotate and the plungers are allowed outward movement by the cam lobes, the spring 25 will effect movement of the piston 23 and valve member so that the previously displaced fuel will now be returned to the bores containing the plungers. The shuttle will also return to the one end of the cylinder under the action of the spring 29.Any fuel which has been lost by leakage is made up by the fact that fuel can flow through auxiliary inlet ports 37 which open onto the periphery of the distributor member and which register with auxiliary inlet passages which communicate with the bore containing the auxiliary plungers 24. In order to permit the valve member to return quickly to the closed position the space beyond the guide portion 19 of the valve member is vented through a bleed orifice to the interior of the apparatus.

The enlarged portion 33 of the stop member is biased into light engagement with the cam profile 34 by means of a light spring 38 which is interposed between the portion 33 and the base wall of the abutment 30. The light spring minimises the adverse torque reaction and resistance to movement of the lever 35. Moreover, since the spring 29 does not engage the portion 33 of the stop member the lever 35 is not subject to the high force of the spring 29. The force of the spring 29 must be high enough to return the shuttle 29 against the pressure developed by the pump 13.

The lever 35 is angularly adjustable about the pivot 36 in order to vary the position of the stop and in the example the angular setting of the lever 35 is determined by a governor mechanism which includes a governor spring 39 coupled at one end to the lever 35 and at its other end to an operator adjustable member 40. In addition the lever 35 is coupled by way of a curved link 41 with a further link 42 which is engageable by the output member of a centrifugal weight mechanism which includes weights 43 mounted in a cage 44 which is coupled by gearing to the drive shaft 12. For a given setting of the operator adjustable control, as the speed of the associated engine increases, the lever 35 will be moved by the weights against the action of the spring 39 to reduce the allowed movement of the shuttle 28 and thereby the amount of fuel which is supplied to the associated engine.A governing action is therefore obtained.

A further lever 45 also pivotally mounted at 36, is provided for engagement by the enlarged portion 33 and as illustrated, the position of the further lever 45 is determined by a spring loaded piston 46 which is subject to the output pressure of the low pressure pump 13. As the pressure increases, the piston 46 will move against the action of its spring and will pivot the further lever 45 which also has a cam profile and the effect will be to provide what is known in the art as "torque control".

The further lever 45 can be actuated by for example a diaphragm responsive to the pressure of air supplied to the associated engine or it may simply form a maximum fuel stop. The lever 45 can be held in contact with the piston 46 by means of a light spring.

The lever 41 is curved to provide clearance for a shaped portion of the housing 31 in which is formed a cylinder 47 which accommodates a spring loaded piston which is also responsive to the outlet pressure of the low pressure pump and which is coupled to the cam ring 17 so that the angular setting of the cam ring depends upon the speed of the associated engine so that the timing of delivery of fuel by the apparatus is dependent upon the engine speed.

It will be noted that the line of action of the pivot 36 and the point of contact between the enlarged portion 33 of the stop member and the cam profile 34 is offset from the axis of movement of the stop member 32 and the enlarged portion 33 thereof. It is necessary to prevent angular movement of the enlarged portion 33 and this can be achieved by a peg and an axial slot. If desired the end surface of the enlarged portion 33 may be flat and a follower interposed between the enlarged portion and the cam profile 34. The follower can be guided for movement in a support secured to the cover of the housing 31.

Claims

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine and comprising a rotary distributor member housed within a body part, the distributor member in use being driven in timed relationship with the associated engine, a bore formed in the distributor member and a pumping plunger mounted therein, cam means for imparting inward movement to the pumping plunger, means for supplying fuel expelled from the bore to a plurality of outlet ports in turn during successive inward movements of the pumping plunger, further means for filling the bore with fuel in the intervals between inward movements of the plunger and valve means operable to spill fuel from said bore during the inward movements of the plunger thereby to control the quantity of fuel which is delivered through said outlet ports, said valve means comprising a valve member which is resiliently biased into contact with the seating to prevent flow of fuel through a spill port connected to said bore, a surface defined on the valve member or on a part connected thereto and against which fluid pressure can act to lift the valve member from the seating, an auxiliary plunger operable by said cam means and slidable in a further bore, the fluid pressure in said further bore acting on said surface, a shuttle slidable in a cylinder, resilient means biasing the shuttle towards one end of the cylinder and said one end of the cylinder communicating with said further bore so that the shuttle is exposed to the fluid pressure in said further bore, an axially movable stop member positioned to limit the movement of the shuttle so that the fluid pressure applied to said surface becomes sufficient to lift the valve member from the seating, adjustable means engagable with said stop member for adjusting the axial setting thereof and further resilient means biasing the stop member into engagement with said adjustable means.

2. An apparatus according to Claim 1 in which said adjustable means comprises an angularly adjustable lever and a cam profile defined on the lever for engagement by an end of said stop member.

3. An apparatus according to Claim 2 in which the line of action defined by the pivot of the lever and the point of contact of the cam surface with said end of the stop member is offset relative to the axis of movement of the stop 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 drawing.