WO1992004539A1

WO1992004539A1 - Fuel pumping apparatus

Info

Publication number: WO1992004539A1
Application number: PCT/GB1991/001356
Authority: WO
Inventors: Ronald Phillips
Original assignee: Lucas Industries Public Limited Company
Priority date: 1990-09-01
Filing date: 1991-08-09
Publication date: 1992-03-19
Also published as: AU8394391A; GB9019098D0

Abstract

A rotary distributor fuel pumping apparatus includes a distributor member (12) defining a pair of bores (13) in which are slidable pumping plungers (14). The outer ends of the plungers are engaged by cam followers (27, 28) which engage cam lobes to urge the plungers inwardly as the distributor member is rotated. The fuel displaced from the bores is supplied to an outlet port (17) and a spill valve (22) is provided to control the amount of fuel supplied. The bores are completely filled with fuel and in order to control the initial rate of fuel delivery at least one plunger is moved inwardly before the others. In one arrangement the cam follower of that plunger is housed in an inclined slot (26) and the other cam followers housed in straight slots in a part (23) surrounding the distributor member and the cam followers are movable axially in the slots so that the one cam follower moves angularly relative to the others and therefore is moved inwardly in advance of the others.

Description

FUEL PUMPING APPARATUS

This invention relates to a fuel pumping apparatus for supplying fuel to a compression ignition engine and of the kind comprising a distributor member rotatable in timed relationship with an associated engine, a pair of radially disposed plungers slidably mounted in the distributor member, the inner ends of the plungers defining at least in part, a pumping chamber, a delivery passage communicating with the pumping chamber and positioned to register in turn with a plurality of outlets during successive inward movements of the plungers, means for feeding fuel to the pumping chamber to effect outward movement of the plungers to their maximum extent, a plurality of pairs of cam lobes carried on a cam ring, for imparting inward movement to the plungers as the distributor member rotates, a drive shaft, an annular member driven by the drive shaft and surrounding the portion of the distributor member in which the plungers are located, a pair of slots formed in the annular member and cam followers slidable in said slots respectively, said cam followers being engagable with the cam lobes to impart inward movement to the pumping plungers.

Such apparatus is well known in the art and is usually arranged so that both plungers are moved inwardly at the same time to achieve a given rate of delivery of fuel. A reduced initial rate of fuel delivery is beneficial to the operation of certain types of engine and it is known from GB-A-2091349, GB-A-2090343 and GB-A-2086490 for example, to arrange for one plunger to be moved inwardly before the other plunger in order to reduce the initial rate of fuel delivery. This is achieved in the examples of apparatus shown in the aforesaid specifications, by allowing one plunger to move further outwardly than the other plunger. The object of the invention is to provide an apparatus of the kind specified in a simple and convenient form.

According to the invention, in an apparatus of the kind specified the angular relationship about the axis of rotation of the distributor member, between one of said cam followers and the other cam follower or between one of each pair of cam lobes and the other of said pair of cam lobes is adjustable so that one plunger will be moved inwardly at a different instant to the other.

Examples of fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in whic :-

Figure 1 is a part sectional side elevation of one example of the apparatus,

Figure 2 is a perspective view to an enlarged scale of part of the apparatus seen in Figure 1,

Figure 3 is a view similar to Figure 1 showing another example of the apparatus,

Figure 4 is a perspective view of part of the apparatus seen in Figure 3, and

Figure 5 shows an alternative form of cam for incorporation in the apparatus shown in Figure 3.

Referring to Figures 1 and 2 of the drawings the apparatus comprises a body part 10 in which is located a fixed sleeve 11. Rotatable within the sleeve is a distributor member 12 which extends at one end beyond the sleeve and is of enlarged diameter. Formed in the enlarged portion of the distributor member is a pair of transverse bores 13. The bores in the case of an apparatus for supplying fuel to a four cylinder engine as illustrated, extend at right angles to each other and located within each bore is a pair of pumping plungers 14. The inner portions of the plungers together with the bores define a pumping chamber from which extends a longitudinal passage 15. Extending from the passage 15 is a delivery passage 16 which is arranged to register in turn with outlet ports 17 which in use, are connected to the injection nozzles respectively of the associated engine. The passage 15 also communicates with in the particular example, four radially disposed passages 18 which extend to the periphery of the distributor member. For communication with the passages 18 there is formed in the sleeve and body a spill port 19 and a fuel supply port 20 the latter being connected to the outlet of a low pressure fuel supply pump 21. The spill port 19 communicates with an electromagnetically controlled spill valve 22.

Surrounding the enlarged portion of the distributor member is an annular member 23 which is coupled to a drive shaft 24. The drive shaft and member 23 are supported in appropriate bearings and in use, are driven in timed relationship with the associated engine. The distributor member is coupled to the annular member so as to be driven thereby.

Formed in the annular member 23 and as best seen in Figure 2, are four outwardly extending slots. Two of these slots extend axially and are referenced 25 and the other slots referenced 26 are inclined to the axis of rotation of the distributor member. The slots carry cam followers each of which comprises a shoe 27 and a roller 28. The shoes engage the outer ends of the plungers 14 and the rollers 28 project beyond the outer surface of the annular member 23 for engagement with pairs of cam lobes formed on the internal peripheral surface of an annular cam ring 29 mounted in the body of the apparatus and in the particular example, angularly adjustable to enable the timing of fuel delivery of the apparatus to be varied, by means of a piston cylinder combination 30. The cam followers are restrained against axial movement relative to the distributor member, by side plates 31 which are secured to the distributor member and which conveniently are formed with outwardly extending projections which locate in the slots 25 and 26 to transmit drive from the annular member to the distributor member.

In operation, and ignoring for the moment the inclined slots 26 and with the parts in the position shown in the drawing, the rollers are engaging the leading flanks of the cam lobes and the plungers are being moved inwardly so that fuel is displaced from the pumping chamber and flows to one of the outlet ports 17 by way of the delivery passage 16. One of the passages 18 is in communication with the spill port 19 and the filling port 20 is closed off. The amount of fuel which is displaced to the engine is controlled by means of the spill valve 22 which is opened after a predetermined but variable time after inward movement of the pumping plungers has taken place. The spill valve is under the control of an electronic control system not shown, which is responsive to various engine actual and desired operating parameters . With this type of apparatus delivery of fuel starts as soon as the plungers are moved inwardly and this can be determined by angular adjustment of the cam ring 29. Following complete inward movement of the pumping plungers, as the distributor member further rotates, the delivery passage 16 moves out of register with an outlet port 17 and the passage 18 which was in register with the spill port 19 is moved out of register therewith. A further passage 18 moves into register with the filling port 20 so that fuel from the pump 21 is supplied to the pumping chamber to effect outward movement of the plungers . The maximum outward movement of the plungers is determined in the particular example, by the engagement of the rollers with the base circle of the cam ring 29 although if desired, special stop plates may be provided for this purpose.

As described above all the plungers partake of inward movement under the action of the cam lobes, at the same time however, if the distributor member is moved axially, the cam followers which are located in the slots 26 will move angularly relative to the distributor member in a direction opposite to the direction of rotation of the distributor member. The practical effect of this is that the rollers associated with those cam followers will engage the leading flanks of the next cam lobes earlier than the other rollers so that the plungers associated therewith will start to move inwardly before the other plungers . Inward movement of two plungers with the other two plungers held against outward movement, will result in fuel being displaced from the pumping chamber but at a reduced rate which as stated, is beneficial to the operation of certain types of engine. It will be understood that the apparatus can be designed so that it is the plungers associated with the slots 25 which are moved inwardly first.

In the particular example a spring not shown is provided to bias the distributor member towards the right as shown in the drawing and the actual position of the distributor member is determined by controlling the pressure within a chamber 32 located at the end of the distributor member. For this purpose a pair of valves 33, 34 are provided the valve 34 when open, connecting the chamber 31 to the outlet of the low pressure pump 21 to move the distributor member towards the left against the action of the aforesaid spring and the valve 33 when open, allowing the distributor member to move towards the right under the action of the spring. The fuel expelled from the chamber 32 during movement of the distributor member under the action of the spring, flows to a drain. The valves are controlled by the aforesaid control system 22 so that the period in terms of degrees of rotation of the distributor member during which the fuel is delivered at the reduced rate can be controlled. It will be appreciated that the movement of the distributor member must not be so much as to prevent communication between the passages 16 and 18 in the distributor member and the ports 17, 19 and 20 in the body. In practice it may be necessary to provide longitudinal grooves in the distributor member at the outer ends of the passages 16 and 18.

As stated the apparatus as described is for supplying fuel to a four cylinder engine and for convenience, four pumping plungers are provided two of which are arranged to be moved inwardly before the others. It is possible for one only of the slots to be inclined if so desired and it is also possible for the pump to be provided with only two plungers .

Turning now to the example shown in Figures 3 and 4, in this case, the distributor member 12 is axially fixed within the sleeve 11 and the slots in the annular member 23 all extend axially. The difference lies in the construction of the cam ring 29 and this will be seen to be formed in two sections 36, 37. Each section is of annular form and defines a pair of axially extending teeth 38 which locate within recesses 39 formed in the other section. The recesses and the teeth have inclined edges with the teeth being narrower than the recesses so that the two sections can move angularly relative to each other. Each section carries a pair of cam lobes 36A, 37A, so that as the two sections of the cam ring are moved angularly relative to each other the pairs of cam lobes will also be moved angularly. The practical effect of this is that one pair of plungers can be arranged to start to move inwardly before the other pair of plungers to give the reduced initial rate of fuel delivery. As shown in Figure 3 the section 36 of the cam ring is connected to the usual piston 30 for controlling the timing of fuel delivery and the section 37 will be driven by the reaction of the rollers with the cam lobes, in the direction of rotation of the distributor member. It is therefore the cam lobes 36A which are carried on the section 36 which will cause two of the plungers to be moved inwardly before the other two. The relative angular position of the sections can be determined by adjusting their relative axial position and in Figure 3 one way of achieving this is by means of a screw threaded and angularly adjustable stop ring 50 mounted in the housing of the apparatus, and the other way is by means of a piston 51 which is slidable within a cylinder to which fuel under pressure can be delivered from the source 21^' by means of a valve 39 or from which fuel can escape to a drain by means of a valve 40. The valves 39 and 40 would be controlled in the same way as the valves 33 and 34 of the arrangement shown in Figure 1.

An alternative cam construction is shown in Figure 5 in which the main section 41 of the cam ring is formed as two arcuate parts 42 each of which carries a cam lobe 42A and which are inter-connected by curved beams 43 each of which slidably supports one of a pair of segments 44 each having a cam lobe 44A. Each segment 44 defines arms 44B which extend circumferentially and locate on opposite sides of the respective beam 43 and each segment is provided with projections 45 which are engaged in recesses 46 formed in ring members 47 which are disposed on opposite sides of the parts 42. The segments 44 and the rings 47 form the other section of the cam ring. By moving the rings 47 angularly the cam lobes 44A on the segments 44 can be moved angularly relative to the cam lobes 42A on the parts 42 so that the same effect as is obtained with the cam construction as shown in Figures 3 and 4, is obtained.

Claims

1. A f el pumping apparatus for supplying fuel to a compression ignition engine comprising a distributor member (12) rotatable in timed relationship with an associated engine, a pair of radially disposed pumping plungers (14) slidably mounted in the distributor member, the inner ends of the plungers defining at least in part, a pumping chamber, a delivery passage (16) communicating with the pumping chamber and positioned to register in turn with a plurality of outlets (17) during successive inward movements of the plungers, means (18, 20) for feeding fuel to the pumping chamber to effect outward movement of the plungers to their maximum extent, a plurality of pairs of cam lobes carried on a cam ring, for imparting inward movement to the plungers (14) as the distributor member rotates, a drive shaft (24), an annular member (23) driven by the drive shaft and surrounding the portion of the distributor member (12) in which the plungers are located, a pair of slots (25, 26) formed in the annular member (23), and cam followers (27, 28) slidable in the slots respectively, said cam followers being engageable with the cam lobes to impart inward movement to the pumping plungers, characterised in that the angular relationship about the axis of rotation of the distributor member (12) between one of said cam followers (27, 28) and the other cam follower or between one cam lobe (36A, 42A) of each pair of cam lobes and the other cam lobe (37A, 44A) is adjustable so that one plunger (14) will be moved inwardly at a different instant to the other.

2. An apparatus according to Claim 1 characterised in that the one slot (26) formed in the annular member (23) is inclined to the axis of rotation of the distributor member and by the provision of means for moving the cam follower (27) in said one slot (26) axially thereby to vary its angular position relative to the other cam follower.

3. An apparatus according to Claim 2 characterised by side plates (31) located at the opposite ends of the cam followers (27), said side plates being secured to the distributor member, and means (33, 34) for varying the axial setting of the distributor member (12) relative to the annular member (23).

4. An apparatus according to Claim 1 characterised in that said cam ring (29) is formed in two sections (36, 37, 41, 44, 47) which are movable angularly relative to each other about the axis of rotation of the distributor member.

5. An apparatus according to Claim 4 characterised in that each section (36, 37) is of annular form and defines teeth (38) located in recesses (39) formed in the other section, said recesses and teeth having inclined co¬ operating edges which are urged into engagement by the reaction of the cam followers and the cam lobes to cause relative axial movement of the sections and therefore relative angular movement and means (50, 51) for adjusting the axial spacing of the sections.

6. An apparatus according to Claim 5 characterised in that said means (50) comprises an angularly adjustable stop ring which is in screw threaded engagement with the housing of the apparatus.

7. An apparatus according to Claim 5 characterised in that said means (51) comprises a piston housed within a cylinder and valve means (39, 40) for controlling the flow of liquid into and out of said cylinder.

8. An apparatus according to Claim 4 in which one section (41), the cam ring comprises a plurality of arcuate parts (42) each carrying a cam lobe (42A), a plurality of curved beams (43) interconnecting said arcuate parts, the other section of the cam ring comprising a plurality of segments (44) slidable on said beams (43) respectively, each segment carrying a cam lobe (44A) and at least one ring member (47) coupled to said segments (44) .