GB2281357A

GB2281357A - Fuel pumping apparatus

Info

Publication number: GB2281357A
Application number: GB9317616A
Authority: GB
Inventors: Peter Alban George Collingborn
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-08-24
Filing date: 1993-08-24
Publication date: 1995-03-01
Also published as: GB9317616D0

Abstract

A fuel pumping apparatus of the rotary distributor type includes a cam actuated pumping plunger (15) housed in a bore (14). The apparatus includes a fuel pressure actuated spill valve having a valve member (30) coupled to an actuating piston (27). The fuel pressure to actuate the piston and open the spill valve is derived from the bore (14) and is controlled by a control valve formed by an inclined groove (36) on the distributor member and a port (35) in the surrounding body. The distributor member is axially movable to determine the position during the inward movement of the pumping plunger (15), at which the spill valve operates to spill fuel from the bore. <IMAGE>

Description

FUEL PUMPING APPARATUS This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine, the apparatus being of the kind comprising a rotary distributor member housed within a body, the distributor member defining a delivery channel for registration in turn with a plurality of outlet ports formed in the body, passage means in the distributor member connecting said delivery channel with a bore in which is mounted a pumping plunger, cam means for imparting inward movement to said pumping plunger in timed relationship with the associated engine whereby fuel is supplied to said outlet ports in turn during successive inward movements of the pumping plunger, means for supplying fuel to said bore to effect outward movement of the pumping plunger, a spill valve including a valve member operable by an actuating piston and a control valve operable to apply fluid under pressure to said actuating piston to open said spill valve, said spill valve when open allowing fuel under pressure to escape from said bore during the inward movement of the plunger thereby to terminate delivery of fuel through an outlet port.

An example of such an apparatus is seen GB-A-2253445 in which the control valve is an electrically operated on/off valve which controls the application of fuel under pressure to the actuator piston. The fuel under pressure is derived from the bore and is therefore the fuel pressure which is developed during delivery of fuel to the associated engine. The control valve has to be designed to withstand the high pressures which are developed in the use of the apparatus and furthermore, the operation of the valve has to be precisely timed. Another form of the apparatus is disclosed in EP-A-0500231 in which the control valve is in the form of a shuttle which controls the application of fuel under pressure derived from the bore, to the actuator piston.The shuttle is axially movable in a cylinder by fluid displaced by an auxiliary plunger which is operated in timed relationship with the associated engine. The shuttle is also angularly movable in its cylinder to determine the instant during its axial movement, when fuel pressure is applied to the actuator piston. The angular setting of the shuttle can be determined by an electromagnetic actuator under the control of an electronic control system. The hydraulic circuit of the apparatus is complex and an additional plunger is required.

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

According to the invention in an apparatus of the kind specified the distributor member is also axially movable and the distributor member and the surrounding body define said control valve, one of said components defining an inclined slot or slots and the other component defining a port or ports, the communication of a slot with a port taking place during the inward movement of the pumping plunger and the instant at which communication is established during rotation of the distributor member depending upon the axial position thereof.

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 sectional side elevation of part of the apparatus; and Figure 2 is an external view of part of the apparatus seen in Figure 1.

Referring to the drawings the apparatus comprises a rotary distributor member 10 which is housed within a body 11 and opening into the bore in which the distributor member is located is a plurality of equi-angularly spaced outlet ports 12 which are connected to outlets 13 respectively.

The outlets in use are connected to the injection nozzles of the associated engine.

A portion of the distributor member extends from the bore in the body in which it is located and is provided in the particular example with a pair of transversely extending bores 14 which are disposed at right angles to each other and mounted in each bore is a pair of pumping plungers 15.

The space 16 which is defined intermediate the pumping plungers constitutes the pumping chamber of the high pressure pump and this is connected by way of a passage 17 formed in the distributor member with a delivery channel in the form of a slot 18 which is formed on the periphery of the distributor member. The slot is positioned to register in turn with the outlet ports 12 during successive inward movements of the pumping plungers 15.

The outer ends of the plungers are engaged by cam followers which include rollers 19 which engage with the internal peripheral surface of an annular cam ring 20 which is mounted within the body and is permitted limited angular movement therein about the axis of a rotation of the distributor member. The cam followers are conveniently mounted within slots formed in a hollow extension of a drive shaft 21 which is rotatably mounted within the body. The distributor member is coupled to the drive shaft so as to rotate therewith and formed on the internal peripheral surface of the cam ring 20 is a plurality of cam lobes which impart inward movement to the plungers as the drive shaft and distributor member rotate.

In order to effect outward movement of the pumping plungers fuel is supplied to the space 16 and the fuel flow takes place through a plurality of inlet ports 22 which open onto the periphery of the distributor member and which are alternately spaced with the outlet ports 12. The inlet ports 22 are connected to a source of fuel under pressure conveniently in the form of a vane type pump which is mounted about the drive shaft.

The connection between the distributor member and the drive shaft is such as to permit relative axial movement there between and the distributor member is biased towards the right as seen in the drawings, by means of a coiled compression spring 23 which is interposed between the drive shaft and a cap 24 mounted in screw thread engagement with a hollow extension 25 of the distributor member.

The extension 25 defines a cylinder 26 in which is mounted an actuator piston 27. The piston is biased towards one end wall of the cylinder by means of a pair of coiled compression springs 28 which are interposed between the piston and the cap 24. Formed in said end wall of the cylinder is a seating which is located about a spill passage 29 which opens into the space 16. Moreover for engagement with the seating there is provided on the piston 27, a valve member 30.

Formed within the piston 27 is a drilling 31 the inner end of which is in communication with the spill passage 29. Slidably mounted within the drilling is a plunger 32 which engages with the inner end face of the cap 24. The diameter of the drilling is slightly larger than the seat diameter of the valve member 30.

When the valve member 30 is in engagement with the seating a small space is provided between the piston 27 and the end wall of the cylinder and this space communicates by way of passages 33, with a circumferential groove 34 which is formed on the periphery of the distributor member.

The groove 34 by way of valve means to be described, can be brought into communication with the passage 17 during the inward movement of the pumping plungers. The valve means takes the form in the example illustrated, of a plurality of valve ports 35 which open onto the periphery of the distributor member and an inclined groove 36 which is formed on the distributor member and which communicates with the passage 17.

In operation, and starting from the positions of the various parts as shown in Figure 1, the plungers 15 have been moved outwardly their maximum extent by the fuel supplied by way of the inlet port 22. As the distributor member rotates, the slot 18 moves out of register with a port 22 and into register with an outlet port 12. As soon as this communication is established the plungers start to move inwardly as the rollers 19 engage the leading flanks of the cam lobes. The inward movement of the plungers displaces fuel along the passage 17 to the slot 18 and to an outlet port 12 so that fuel is supplied to one of the injection nozzles of the associated engine.During continued rotation of the distributor member the groove 36 moves into the register with a valve port 35 and as soon as this communication is established fuel at the high pressure within the space 16 is supplied by way of the passages 33 to the inner end of the cylinder 26. This fuel causes displacement of the piston 27 against the action of its springs and the valve member 30 is lifted from its seating so that fuel from the space 16 can flow directly into the inner end of the cylinder. This flow of fuel causes a rapid reduction in the pressure of fuel in the outlet 13 which is receiving fuel and the valve member in the nozzle receiving fuel closes quickly and no more fuel is supplied to the associated engine. The outlets 13 may be provided with the usual unloading or non-return delivery valves.

As the rollers roll over the crests of the cam lobes the slot 18 moves out of register with an outlet port 12 and into register with a supply port 22 in addition, the groove 36 moves out of register with the valve port 35.

The strength of the springs 28 is such that the piston 27 is returned towards the one end of the cylinder to allow the valve member to move into engagement with the seating. During the movement of the piston the fuel previously spilled into the one end of the cylinder is returned to the space 16 less some leakage which is provided to ensure that the valve member forms a proper seal with the seating. Further outward movement of the plungers is effected by fresh fuel which flows through one of the inlet ports 22 and the slot 18. The cycle is then repeated and fuel is supplied to the outlets 13 in turn.

The provision of the drilling 31 and the plunger 32 therein ensures that during delivery of fuel, the valve member is held in engagement with the seating not only by the springs but by a force which acts upon the piston due to the fuel pressure within the drilling.

The amount of fuel which is supplied to the associated engine before the groove 36 is brought into register with a valve port, depends upon the axial position of the distributor member. As previously mentioned the spring 23 biases the distributor member towards the right as seen in the drawing and the distributor member is moved in opposition to the force exerted by the spring 23 by fluid under pressure which is admitted into a space 37 formed in the body. The end surface of the distributor member is exposed to the pressure in this space and by varying the pressure using a suitable valve not shown, the axial position of the distributor member can be adjusted. The valve which controls the pressure is itself controlled by an electronic control system and a signal indicative of the axial position of the distributor member can be provided by a position sensor 38.

The inward movement of the plungers 15 starts as soon as the rollers engage the leading flanks of the cam lobes and in order to vary the timing of delivery of fuel to the associated engine the cam ring 20 as previously mentioned is angularly adjustable. The angular adjustment is effected in known manner by means of a fluid pressure operable piston 39. The control system has to take account of the angular setting of the cam ring because variation of the angular setting of the cam ring will for a given axial position of the distributor member, vary the amount of fuel which is delivered to the engine. For this purpose an angular position sensor 40 is provided which is responsive to the position of a peg 41 fixed to the cam ring.

It will be understood that the number of plungers 15, the disposition of the bore or bores 14, the spacing of the cam lobes, the number of outlet ports 12 and their disposition together with the number of ports 22 and 35 and their disposition, is chosen with a particular engine application in mind.

Claims

1. A fuel pumping apparatus of the kind specified in which the distributor member is also axially movable and the distributor member and the surrounding body define said control valve, one of said components defining an inclined slot or slots and the other component defining a port or ports, the communication of a slot with a port taking place during the inward movement of the pumping plunger and the instant at which communication is established during rotation of the distributor member depending upon the axial position of the distributor member within the surrounding body.

2. An apparatus according to Claim 1, in which the axial position of the distributor member is determined by fluid pressure applied to one end of the distributor member.