GB2194002A - Fuel pump - Google Patents

Abstract

A fuel pump of the rotary distributor type for supplying fuel to a compression ignition engine includes a rotary distributor member 14 defining a bore 23 in which are located pumping plungers 24 operable by cam followers defined by shoes 31 and respective rollers 32. The followers are located by a cage including end cheeks 37 and are mounted in slots 36 in a drive shaft 16. The followers are biased by a spring 38 in one direction and are moved in the opposite direction by an annular piston 39, the drive shaft and shoes defining stop surfaces whereby the amount the plungers can move outwardly depends on the axial setting of the cage. <IMAGE>

Description

SPECIFICATION Fuel pump This invention relates to a rotary distributor type fuel injection pump of the kind comprising a body part defining a bore in which is journalled a rotary cylindrical distributor member, a drive shaft coupled to the distributor member, a transverse drilling formed in the distributor member, a pumping plunger located in the drilling, passage means in the distributor member and body part for allowing fuel to flow to the drilling during the filling periods of the pump and from the drilling during inward movement of the plunger, to a plurality of outlets in turn, the outlets in use being connected to injection nozzles respectively of an associated engine, a follower located at the outer end of the plunger, an annular cam ring mounted about the distributor member and having cam lobes formed on the internal peripheral surface for engagement by the follower to impart inward pumping movement to the plunger as the distributor member rotates and means for controlling the amount of fuel delivered during inward movement of the plunger.

In a known form of such a pump the distributor member is axially movable within the bore in the body part and the cam follower is axially fixed relative to the distributor member.

The means for controlling the amount of fuel delivered includes a setting arrangement whereby the axial position of the distributor member can be adjusted and the cam follower is provided with shaped stop surfaces which co-operate with complementary stop surfaces formed on the drive shaft to limit the extent of outward movement of the plunger during the filling periods.

In this form of pump the distributor member has to be longer than in the usual form of distributor pump, to ensure that there is adequate support for the distributor member throughout its range of axial movement and that the sealing lands defined by the distributor member between the various ports conveying fuel and the low pressure zones, are adequate. This results in the volume of fuel in the distributor member commonly known as the dead volume, being higher than in the more usual form of pump. In addition, the fact that the distributor member is axially movable means that it is no longer possible to use simple ports in the distributor member and in the bore, to allow fuel flow to the drilling and from the drilling to the outlets. It is necessary to form either the distributor member or the body part, with axially extending grooves.The grooves themselves increase the so-called dead volume of fuel but in addition they increase the possibility of fuel leakage.

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

According to the invention in a pump of the kind specified the distributor member is axially fixed within said bore and the cam follower is axially movable relative to the distributor member, the pump further including an annular piston surrounding the distributor member and axially movable relative thereto, means coupling said piston to the follower whereby axial movement of the piston in one direction will cause axial movement of the follower in said one direction against the action of resilient means and means for controlling the application of fluid under pressure to said piston.

Examples of fuel injection pump 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 one example of a pump, and Figure 2 is a view of a further example of pump.

Referring to Figure 1 of the drawings the pump comprises a multipart body 10, 11 and 12, the parts being secured together during assembly, by bolts not shown. The body part 10 mounts a sleeve 13 in which is journalled a rotary cylindrical distributor member 14. The distributor member extends from the sleeve into a space 15 defined by the body part 11.

The body part 12 carries a drive shaft 16 which in use is adapted to be driven in timed relationship with the associated engine. The drive shaft has an enlarged head 17 which is located in the space 15 and which surrounds a portion of the distributor member within the space 15.

The distributor member is provided with a stepped peripheral surface and one of the steps locates against the end of the sleeve 13. At the opposite end of the sleeve is located the rotor of a low pressure fuel supply pump 18, the rotor being secured to the distributor member so that the latter is held against axial movement relative to the sleeve and the body. The low pressure pump 18 is conveniently of the vane type and the body is provided with a fuel inlet which communicates with the inlet of the low pressure pump and which in use is connected by way of a filter to a source of fuel supply. The outlet of the pump 18 is supplied by way of a control valve 19, to a circumferential groove 20 which is formed in the outer peripheral surface of the sleeve.The output pressure of the low pressure pump is controlled by a valve 21 which is located in the body part 12 and also formed in the body part 12 is a vent outlet 22 through which surplus fuel collecting in the space 15 can be returned to the source of fuel supply.

Formed in the portion of the distributor member, which is in the space 15, is a transverse drilling 23 in which is located a pair of pumping plungers 24. The portion of the drilling intermediate the plungers is connected by way of an axial passage 25 in the distributor member, to an outwardly extending delivery passage 26 and the delivery passage is arranged to register in turn with outlet ports 27 formed in the sleeve and extending to outlets 28 on the exterior of the body part 10.

The outlets 28 are connected in use to the injection nozzles of the associated engine respectively.

The passage 25 is also connected to an inlet passage 29 formed in the distributor member and positioned to register in turn with inlet ports 30 which extend inwardly from the groove 20.

Each plunger has associated therewith a follower comprising a shoe 31 and a roller 32.

The rollers engage with the internal peripheral surface of an annular cam ring 33 which is mounted for limited angular movement in the body part 11. The position of the cam ring can be varied in known manner by means of a fluid pressure operable piston 34 which is coupled to the ring by means of peg 35. The cam ring on its internal peripheral surface is provided with pairs of cam lobes which are engaged by the rollers 32 as the distributor member rotates, to impart inward movement to the plungers 24.

The shoes 31 are located in slots 36 formed in the enlarged portion 17 of the drive shaft and the distributor member is coupled to the drive shaft so as to be driven thereby by any convenient form of connection. In one example the connection comprises a tongue on the end of the distributor member and which is located within a slot formed in the drive shaft and in another example, the end of the distributor member is shaped to define a splined spigot upon which is mounted a bush having a pair of wings which locate in the slots 36. The shoes and rollers are accommodated within a cage which defines end cheeks 37 engaging the opposite ends of the shoes and rollers and the cage is biased towards the sleeve 13 by means of a coiled compression spring 38. The end checks are interconnected by webs (not shown) which slide on the distributor member.The cage is moved in the opposite direction by means of a fluid pressure operable piston 39 which is slidably mounted about the projecting portion of the distributor member and movement of the piston is transmitted to the cage and therefore the shoes and rollers, by means of an annular push piece 40 which also surrounds the distributor member. The push piece may be formed as part of the piston.

The piston on its inner and outer peripheral surfaces is provided with seal rings and the outer peripheral surface of the piston co-operates with a cylindrical surface defined on an extension of the body part 10. There is thus defined on the side of the piston remote from the shoes, a chamber 41 into which fuel under pressure can be admitted from the low pressure pump 18 under the control of a valve 42. In this manner the pressure within the chamber 41 can be controlled and therefore by varying the pressure the axial setting of the shoes and rollers relative to the distributor member can be adjusted.

The internal peripheral surface of the enlarged portion 17 of the drive shaft, flares outwardly away from the main body of the drive shaft and the shoes 31 are provided with stop surfaces complementary to the aforesaid flared surface.

In the position shown in the drawings, the plungers 24 are in their innermost positions so that the surfaces on the shoes and the flared surface on the enlarged portion of the drive shaft, are separated. In addition, it will be noted that the inlet passage 29 is in communication with an inlet port 30 so that fuel can flow to the drilling 23 to force the plungers outwardly as the distributor member rotates and as the rollers move down the trailing faces of the cam lobes. The extent of outward movement allowed to the plungers is limited by the abutment of the stop surfaces of the shoes and the flared surface and the extent of outward movement is determined by the axial position of the shoes which as previously described, can be varied by altering the pressure within the chamber 41.During continued rotation of the distributor member the passage 29 moves out of register with a port 30 and the delivery passage 26 moves into register with an outlet port 27. When such registration is established the plungers 24 are moved inwardly by the action of the cam lobes and fuel is delivered to an outlet 28.

The valve 42 conveniently is electromagnetically controlled and the supply of current to the valve operator is controlled by a control circuit which is supplied with a feedback signal indicative of the axial position of the shoes, by means of a transducer 43 which has an input member 44 coupled to the piston 39 by means of a pivotal lever 45. In this manner the control circuit is provided with a signal representing the amount of fuel which is supplied to each outlet in turn. The control system will receive desired engine operating parameters and it can also be arranged to receive a signal indicative of the angular position of the cam ring 33 by means of a further transducer 47 which is coupled to the cam ring in a manner similar to the piston 34.

The pump shown in Figure 2 is basically the same as that shown in Figure 1 and Figure 2 shows the distributor member 14 provided with the aforesaid spigot which is referenced 50 and upon which is mounted the bush 50A which carries the wings 50B. In the pump shown in Figure 2 the low pressure pump is mounted within a body part 51 which corresponds to the body part 12 of the pump seen in Figure 1. The rotor of the low pressure pump 52 is coupled to the drive shaft. The distributor member 14 in the example of Figure 2 is restrained against axial movement by means of a wavy spring 53 which is positioned intermediate the drive shaft and the distributor member and the spring which biases the shoes 31 and rollers 32 against the fluid pressure applied to the piston 39 is a conical spring 54 located between the cage and the wings 50B. Moreover, in this arrangement the piston 39 acts directly upon the adjacent end cheek 37 of the cage.

Claims (3)

1. A rotary distributor type fuel injection pump comprising a body part defining a bore in which is journalled a rotary cylindrical distributor member, a drive shaft coupled to the distributor member, a transverse drilling formed in the distributor member, a pumping plunger located in the drilling, passage means in the distributor member and body part for allowing fuel to flow to the drilling during the filling periods of the pump and from the drilling during inward movement of the plunger, to a plurality of outlets in turn, the outlets in use being connected to injection nozzles respectively of an associated engine, a follower located at the outer end of the plunger, an annular cam ring mounted about the distributor member and having cam lobes formed on the internal peripheral surface for engagement by the follower to impart inward pumping movement to the plunger as the distributor member rotates, means for controlling the amount of fuel delivered during inward movement of the plunger, said distributor member being axially fixed in said bore and the cam follower being axially movable relative to the distributor member, the pump further including an annular piston surrounding the distributor member and axially movable relative thereto, means coupling said piston to the follower whereby axial movement of the piston in one direction will cause axial movement of the follower in said one direction against the action of resilient means and means for controlling the application of fluid under pressure to said piston.

2. A pump according to Claim 1 in which said cam follower is accommodated within a cage slidable on the distributor member, said cage including end cheeks engaging the opposite ends of the follower, said resilient means acting on one of said end cheeks and said piston acting on the other of said cheeks.

3. A rotary distributor type fuel injection pump comprising the combination and arrangement of parts substantially as hereinbefore defined with reference to the accompanying drawings.