GB2238084A

GB2238084A - Fuel pumping apparatus

Info

Publication number: GB2238084A
Application number: GB8923486A
Authority: GB
Inventors: Peter Alban George Collingborn
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1989-10-18
Filing date: 1989-10-18
Publication date: 1991-05-22
Also published as: GB8923486D0

Abstract

A fuel pumping apparatus for an engine includes a cam actuated pumping plunger 15, a fluid pressure operable spill valve 20 operable to open a spill path from a bore containing the plunger 15, a cam actuated auxiliary plunger 24 located in a bore communicating with a cylinder 18 containing a shuttle 26, a stop 28 operable to limit the movement of the shuttle during inward movement of the plunger 15, and means for varying the initial position of the shuttle the pressure of fluid developed when the shuttle engages the stop acting to open the spill valve 20 to terminate delivery of fuel to the engine. The initial position of the shuttle 26 is determined by an angularly adjustable member 35 having a helical rib 34 with an axial length smaller than the diameter of a port 36 communicating with the cylinder 18. One side of the rib is connected to drain and the other to a low pressure pump whereby the rotary position of the rib controls the pressure in the cylinder 18 and hence the starting position of the shuttle. <IMAGE>

Description

FUEL PUMPING APPARATu 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, a 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, and means for varying the volume of fuel in said further bore and said one end of said cylinder prior to inward movement of the further plunger, whereby the extent of movement of the shuttle before it engages said stop can be varied.

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-pZrt 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 17 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. At the end of the drilling adjacent the bore 14 there is formed a seating for engagement by a valve member 20 which extends within the drilling and is provided with a guide portion 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 by way of passages (not shown), is connected to a delivery passage in the form of a groove 21A on the periphery of the distributor member and which communicates 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.The groove 21A can also communicate 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 groove 21A to one of the outlet ports 21. During continued rotation of the distributor member the groove 21A will move out of register with an outlet and into register with an 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 within an enlarged portion of the drilling which forms a cylinder. Slidable in the cylinder is a piston 23 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 guide portion of the valve member and when the pressure is sufficient, the valve member will be lifted from the seating against the action of a spring 25 which normally biases 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 drilling 18 forms a cylinder for a shuttle 26 which is biased towards the valve member by a spring 27.

The limit of the movement of the shuttle by the spring is determined by a stop which is in the form of a circlip let into a groove formed in the wall of the drilling.

The movement of the shuttle 26 against the action of the spring 27 is limited by an adjustable stop 28 slidable axially within a plug secured in the end of the passage 18. The stop is in the form of a rod the inner end of which is engaged by the shuttle and the outer end of which is engageable with a cam profile 30 formed on a member 31 movable in a transverse direction by a piston 32 which is subject to the outlet pressure of the low pressure pump 13 and is movable by the pressure against the action of a spring 33.

The volume of fuel in the space defined between the plungers 24 and the shuttle 26 can be controlled so that the location of the shuttle between the circlip and the stop 28 can be controlled. The volume of fuel is determined by a fluid potentiometer in conjunction with the spring 27. The fluid potentiometer is formed by a helical or like rib 34 formed on an angularly adjustable member 35. The member 35 is mounted within a cylinder in the wall of which is formed a port 36. The opposite ends of the cylinder which accommodates the member 35 are connected respectively to the outlet of the low pressure pump 13 and to a drain formed by the interior of the housing.The axial width of the rib 34 is slightly less than the diameter of the port 36 and the latter communicates with a supply port 37 opening onto the periphery of the distributor member at a position to register in turn with a plurality of supply passages 38 formed in the distributor member and communicating with the space between the plungers 24 and the shuttle 26.

The rib 34 forms with the port 36 two variable orifices the restriction offered by one orifice decreasing and the other increasing as the member 35 is moved in one direction and vice versa. The port 37 registers with a passage 38 during the time the plungers 24 can move outwardly and the volume of fuel which flows into the space defined between the plungers 24 and the shuttle 26 depends on a number of factors amongst which are the angular setting of the member 35, the output pressure of the low pressure pump 13, the area of the shuttle 26, the force exerted by the spring 27 and the time during which the port 37 is in register with a passage 38. The volume of fuel is fixed once the port 37 has moved out of register with a passage.Assuming that the plungers have been moved outwardly their maximum extent and the shuttle 26 has been moved away from the circlip then with the groove 21A in register with an outlet port 21, as the plungers 15 move inwardly fuel will be displaced to the associated engine in the manner described. As the plungers 15 move inwardly so also do the plungers 24 and the fuel displaced by the plungers 24 will cause movement of the shuttle towards the stop 28.

When the shuttle engages the stop there will be a rapid increase in the pressure applied to the end surface of the guide portion of the valve member and as a result the valve member will be lifted from its seating and fuel displaced by the plungers will flow into the enlarged portion of the drilling but will be contained therein by the piston 23. There will be a rapid reduction in the pressure of fuel supplied through the outlet and the flow of fuel to the associated engine will cease.

As the distributor member further rotates the groove 21A will move out of register with the outlet 12 and into register with an inlet port 22 to allow fuel to flow into the bore 14. In the meantime the fuel stored under the piston 23 will be returned to the bore 14 and the valve members returned to its seating. In addition a passage 38 will move into register with the port 37 to re-establish the starting position of the shuttle.

In order to increase the amount of fuel supplied by the apparatus the starting position of the shuttle is moved further away from the stop 28 which requires adjustment of the member 35 to reduce the volume of fuel supplied to the space defined between the plungers 24 and the shuttle 26. The volume of fuel admitted to the space may be reduced to the extent that with the shuttle in contact with the circlip, the plungers 24 are not moved outwardly their maximum extent. This does not effect the operation of the apparatus except that the plungers 24 do not start to move inwardly at the same time as the plunger 15.

The angular setting of the member 35 is determined by a governor mechanism which in the example comprises a governor spring 40 which at one end is coupled to an operator adjustable member 41. At its other end the spring is coupled to one end of a curved link 42 which is also operatively connected to the member 35. At its other end the curved link 42 is pivotally connected to a further link 43 which is acted upon by a centrifugal weight mechanism including weights 44 mounted in a cage 45 which is driven from the drive shaft 12 through gearing. The weights under the action of centrifugal force move outwardly and impart axial movement to a collar 46 which engages the link 43.As the speed of the associated engine increases the member 35 will be moved angularly to reduce the travel of the shuttle 26 before it engages the stop 28 thereby to reduce the quantity of fuel supplied to the associated engine and vice versa.

If the operator moves the member 41 to increase the force exerted by the governor spring 40, the member 35 will be moved angularly to increase the travel of the shuttle before it engages the stop 28 thereby increasing the quantity of fuel supplied to the engine and vice versa.

The governor can be an "all speed" or a "two speed" governor.

The position of the stop 28 is determined by the transverse position of the member 31 and the shape of the cam profile 30. The member 31 therefore forms a maximum fuel stop and in the example its transverse position is determined by the piston 32 which is subject to the outlet pressure of the low pressure pump 13. This pressure is arranged by means of a suitable valve, to increase as the speed of the associated engine increases.

The shape of the cam profile 30 is such that with increasing engine speed the stop 28 is moved to reduce the travel of the shuttle thereby reducing the amount of fuel supplied to the associated engine and providing what is known in the art as "torque control".

It will be noted that the link 42 is curved to provide clearance around a housing in which is formed a cylinder 46. This cylinder contains a spring loaded piston which is coupled to the cam ring 17 and which is subjected to the outlet pressure of the low pressure pump 13. In this manner variation of the timing of delivery of fuel with engine speed is obtained.

Claims

1 A fuel pumping apparatus for supplying fuel to an internal combustion engine 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, 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, a 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, and means for varying the volume of fuel in said further bore and said one end of said cylinder prior to inward movement of the further plunger, whereby the extent of movement of the shuttle before it engages said stop can be varied.

2 An apparatus according to Claim 1 in which the means for varying the volume of fuel in said further bore comprises a fluid potentiometer including a member adjustable by a governor mechanism.

3 An apparatus according to Claim 1 or Claim 2 in which the position of said stop member is adjustable in accordance with the speed at which the apparatus is driven.

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.