GB2138970A - Fuel pumping apparatus - Google Patents

Abstract

A fuel pumping apparatus for supplying fuel to an internal combustion engine is of the rotary distributor type and has an annular cam 18 which imparts inward movement to pumping plungers forming part of a high pressure pump. The cam is angularly adjustable to control the timing of fuel delivery by a piston 51. The apparatus includes a further annular cam (29, Figs. 1 & 2, not shown) which is controlled by a further piston to operate a spill valve (27) carried by the distributor member. The angular setting of the further cam controls the quantity of fuel delivered but angular movement of the cam 18 will also effect fuel quantity. A peg 55 coupled to the piston 51 is located within a central aperture 56 in a plate member 57 and at its edge the plate has a slot 58 in which is located a similar peg coupled to the further piston. The plate has projections 59, 60 which define cam surfaces engaged by cam followers 67 coupled to the sleeves 63, 64 respectively of a pair of servo valves 61 which control the application of fluid under pressure to the cylinder housing the pistons. <IMAGE>

Description

SPECIFICATION Fuel pumping apparatus This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a high pressure fuel injection pump for supplying fuel at high pressure to the engine in timed relationship therewith, the apparatus including first and second fluid pressure operable means for adjusting the timing of delivery of fuel and the quantity of fuel delivered by the injection pump respectively and valve means for controlling the application of fluid under pressure to said pressure operable means.

One example of an apparatus of the aforesaid kind is described in the specification of British Application 8235049. In this form of apparatus timing adjustment is achieved by moving a first cam ring which actuates the pumping plungers of the injection pump, angularly about the axis of rotation of a rotary part which carries the pumping plungers and quantity adjustment is achieved by moving a second cam ring angularly about the same axis, the second cam ring controlling the operation of a spill valve carried in said rotary part. The positions of the cam rings are determined by fluid pressure operable pistons.

In order to provide accurate control of the amount of fuel delivered by the apparatus and also the timing of fuel delivery it is necessary to have information regarding the actual positions of the first and second fluid pressure operable means and the parts moved thereby. This information can be utilized to ensure that the fluid pressure operable means and said parts adopt their correct positions.

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

According to the invention an apparatus of the kind specified comprises, a plate member, means pivotally connected to said plate member at spaced points in the plane of the plate member, said means being operatively connected to said first and second fluid pressure operable means so that when a change in the pressure applied to either or both of said fluid pressure operable means takes place the plate member will move in the aforesaid plane, a pair of cam surfaces on said plate member and followers engaging said cam surfaces respectively, said followers providing signals indicative of the positions of said first and second fluid pressure operable means.

An example of an apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure lisa part sectional side elevation of a portion of the apparatus, Figure 2 is an exploded view of the rotary parts of the apparatus, Figure 3 is a cross section taken on the line 3-3 of Figure 1, Figure 4 is a timing diagram of the pump, Figure 5 is a side elevation of a further portion of the apparatus, Figure 6 is a perspective view of part of the portion of the apparatus seen in Figure 5, Figure 7 is a view similar to Figure 5 showing a modification, and Figure 8 is a view taken at right angles to Figure 7.

Referring to Figures 1-3 of the drawings the apparatus comprises a body indicated at 10 and in which is journalled a rotary member in the form of a cylindrical distributor member 11. The distributor member has an enlarged portion generally indicated at 12 extending into a chamber defined in the body and is coupled by means not shown, to a rotary drive shaft 13 which is mounted within the body and which extends to the exterior thereof. The drive shaft 13 is coupled in use to a rotary part of the associated engine so that the distributor member is driven in timed relationship with the engine. The drive shaft carries a cup-chaped portion 14 which surrounds part of the enlarged portion of the distributor member and in which partthere is formed a transversely extending bore 15 in which is mounted a pair of pumping plungers 16.At the outer ends of the pumping plungers are located cam followers 17 respectively each of which comprises a shoe carrying a roller, the roller co-operating in use with a first annular cam ring 18 carried within the body. The cam followers are slidably mounted in slots 19 in the cup-shaped portion 14 so that the driving force required to drive the cam followers is transmitted directly from the drive shaft rather than through the distributor member. The plungers 16 form part of a high pressure pump.

Formed in the distributor member are a pair of longitudinally extending passages 20,21 both passages communicate with the bore 15 and the passages are disposed in side-by-side relationship.

The passage 21 at its end remote from the bore 15 communicates with a delivery passage 22 which is positioned to register in turn with outlets 23 formed in the body. The outlets in use, are connected possibly by way of delivery valves, to the injection nozzles respectively of the associated engine. The passage 20 extends beyond the passage 22 and communicates with a circumferential groove 24 formed in the periphery of the distributor member.

The groove 24 is in permanent communication with the outlet of a low pressure supply pump shown in block form at 25. In practice the rotary part of the low pressure pump will be connected to the distributor member 11 on the drive shaft so as to be driven thereby. The low pressure pump, as is well known in the art, will incorporate a relief valve so that the output pressure is controlled.

The passages 20 and 21 extend through a bore 26 formed in the distributor member, the axis of the bore 26 conveniently being at right angles to that of the bore 15. Slidable within the bore 26 is a control valve in the form of a cylindrical valve member 27 which at one end is contacted by a cam follower 28.

The cam follower includes a shoe which supports a roller arranged to co-operate with the internal peripheral surface of a second annular cam ring 29.

The cam follower 28 is located within a groove 30 defined between a first pair of projections 31,32 on the cup-shaped portion 14. The cup-shaped portion 14, as is clearly seen in Figure 2, defines a further pair of projections 33, 34. The enlarged portion of the distributor member in the region of the bore 26, is provided with a pair of flats which extend substantially parallel to the axis of the bore 26 and slidable on the flats is a stirrup member 36 having a pair of side limbs 37 which are connected by a curved portion 38. The portion 38 is provided with a central aperture in which is located the reduced end of the valve member 27.The side limbs at their other ends have outwardly turned portions 39 which are provided with central projections 40 which serve to locate the ends of a pair of coiled compression springs 41 the other ends of which are located by similar projections 42 defined on the projections 33, 34 respectively. The springs act to bias the valve member 27 downwardly as seen in the drawings so that the roller of the cam follower 28 contacts the internal surface of the cam ring 29.

The valve member 27 is provided with a groove 43 intermediate its ends and in the inoperative position of the valve member as shown in Figures 1 and 2, the groove 43 is aligned with the passage 21 so that flow of fuel can take place along the passage 21 from the bore 15 to the delivery passage 22.

The valve member 27 is moved to its operative position by the action of a lobe on the cam ring 29 and as it moves to the operative position the end wall 44 of the groove uncovers a spill port 45 constituted by the passage 20 at its point of entry from the bore 15 into the bore 26. At the same time the end wall 44 uncovers the remaining portion of the passage 20 and during continued movement of the valve member 27 to its operative position, the communication between the portions of the passage 20 will increase and the communication between the portions of the passage 21 will decrease.

Considering now the mode of operation of the apparatus so far described. As shown in Figure 1 the delivery passage 22 is in communication with an outlet 23 and the valve member 27 is in its operative position. This corresponds to inward movement of the pumping plungers 16 and fuel is being supplied to an outlet 23 and hence to the associated engine.

While the delivery passage 22 is in communication with an outlet, the valve member 27 will start to move inwardly and when the side wall or control edge 44 uncovers the port 45, fuel will be spilled to the low pressure pump 25. The supply of fuel through the outlet 23 will therefore cease and if the outlet 23 has a delivery valve, the latterwill close. It should be noted that before the spill port is uncovered, the area of the passage 21 is reduced by the valve member and this reduction in area can be used to control the rate at which fuel returns from the pipeline associated with the outlet receiving fuel.

This control of the return flow when either no delivery valve is employed or where the delivery valve is of the unloading type, can help to minimise the risk of secondary injection of fuel taking place due to reflected pressure waves generated by closure of the valve member in the fuel injection nozzle.

When the inward movement of the plungers 16 has ceased, they can commence their outward movement under the action of fuel under pressure supplied by the low pressure pump 25 and the valve member remains in its operative position for a length of time sufficient to allow the complete filling of the bore 15. It should be noted that filling of the bore 15 can take place while the delivery passage 22 is still in register with an outlet 23 and this means that the pressure in the column of fuel between the bore 15 and the pipeline or between the bore 15 and the delivery valve, will be reduced to that of the output pressure of the pump 25. This ensures that the pressures within the passages in the pump is equal at the start of every period of fuel delivery.As the distributor member continues to rotate the cam lobe on the cam ring 29 will allow the valve member to move to the position in which it is shown, under the action of the springs 41. Flow through the passage 20 is thereby prevented and the pump is ready for the next delivery of fuel, it being appreciated that the delivery passage 22 will be moving towards the next outlet 23.

It is arranged that the valve member 27 is moved to cause spilling of fuel before the crests of the cam lobes on the cam ring 18 are reached. The fuel pressure in the bore 15 is therefore substantially reduced before the rollers of the cam followers 17 move over the crests of the cam lobes. There is therefore a substantial reduction in the stress imparted to the cam lobes and therefore the cam ring 18 and the cam lobes can be made from a cheaper material as compared with the type of pump in which pumping occurs over the crests of the cam lobes.

During delivery of fuel through an outlet 23 the pressure in the passage 20 will act on the valve member 27 and create a side thrust which might hinder the operation of the valve member. The side thrust can be substantially balanced by providing a balancing recess in the valve member on the opposite side of the valve member to the port 45 and connecting the recess to the groove 43 by means of a drilling the valve member. The valve member for the balancing recess to be effective, must not be allowed to rotate.

Turning now to Figure 4 this shows in the upper part of the Figure, the profile of the lobes on the cam ring 18. It will be seen that the lobes are symmetrical about their axes and in the particular example the axes are angularly spaced by 45" since the pump is intended to supply fuel to an eight cylinder engine.

Above the profile of the cam lobes, two periods A and B are indicated, both periods represent the time during which the delivery passage 22 is open to an outlet 23. The length of the period is of course determined by the diameters of the passage 22 and the ports 23. Period A shows the period relative to the cam lobes, when the cam ring 18 is moved to the retarded position whereas period B shows the situation when the cam ring is moved to the advanced position, the direction of movement of the followers relative to the cam lobes being indicated by the arrow C.

Turning now to the lower portion of the Figure, two curves 46 and 47 are indicated and these are related to the movement of the valve member 27 between its two extreme positions under the action of the lobes on the cam ring 29. The curve 46 represents the effect of the valve on the flow through the passage 20 and the curve 47 the flow through the passage 21. In the case of the curve 46 the lower portion of the curve represents the situation when the parts of the passage 20 are out of communication with each other due to the fact that the valve member 27 is in the so-called inoperative position and with the valve in this position the portions of the passage 21 are in communication with each other.

Considering the upper one of the two lower diagrams it will be seen that the valve member is moved by a cam lobe and intially the movement starts to restrict the communication between the parts of the passage 21. However, this restriction is not sufficient to cause any restriction to the flow of fuel and at a point indicated at 48, the spill port 45 is opened. The effect of opening the spill port is to lower the pressure in the bore 15 to below that which is necessary to maintain fuel flow to the injection nozzle. Injection of fuel to the associated engine therefore ceases at the point 48 and it will be noted that in the upper diagram this is approximately two thirds the way up the leading flank of the cam lobe on the cam ring 18. The valve member continues to move under the action of the lobe on the cam ring 29 and the spill port is progressively opened.At the same time the communication between the parts of the passage 21 is progressively closed and it will be noted that there is a step in the curve 47, this step corresponding to a reduced portion 48A on the valve member 27. The purpose of this reduced portion is to control the rate at which fuel flows from the pipeline thereby, as previously mentioned, reducing the possibility of secondary injection due to reflected pressure waves. It is possible to extend the reduced portion of the valve member so that the passage 22 remains in restricted communication with the bore 15 throughout the filling period.

It will be noted that filling ofthe bore 15 can occur as soon as the followers have moved over the crests of the cam lobes. The duration of the filling period in terms of degrees, depending upon the position of the cam ring 29. The upper diagram shows the setting of the cam ring to obtain maximum fuel and it will be observed that the filling period is between 20 and 25 . The filling period is determined by the interval in terms of degrees, between the axis or crest of the cam lobe and the closure of the spill port 45. The lower diagram represents zero fuel since it will be observed that the spill port opens at the point 49 which corresponds to the initial portion of the cam lobe. There is therefore no displacement of the plungers while the spill port is closed and hence all the fuel contained in the bore will be spilled.It should be noted that as the quantity of fuel delivered to the engine reduces, so also does the filling period.

It must be remembered however that the bore 15 must be completely filled with fuel each time the plungers are allowed to move outwardly but even when the cam ring 29 is set for zero fuel, the filling period is of the order of 15o. In the case of a pump for supplying fuel to a six cylinder engine the filling period at the maximum fuel setting is about 40 and in the case of a pump for supplying fuel to a four cylinder engine, about 70 .

It will be appreciated that if the cam ring 18 is moved without movement of the cam ring 29, the amount of fuel delivery will vary. If therefore it is required to maintain the quantity of fuel delivery through an outlet constant while altering the timing of fuel delivery it is necessary to move both cam rings.

Turning now to Figures 5 and 6, there is shown in FigureS, the cam ring 18 i.e. the cam which actuates the pumping plungers 16. The cam is provided with an aperture in which is located one end of a peg 50 which is located in a transverse drilling in a fluid pressure operable piston 51 housed within a cylinder 52. The piston is biased by a spring 53 and the end of the cylinder remote from the spring has a passage 54 communicating therewith. The other end of the peg defines a head 55 which is located within a central aperture 56 formed in a plate member 57. The cylinder 52 is tangentially disposed relative to the cam and the plate member is disposed in a plane parallel to that of the axis of the piston and is movable in that plane.

As seen in Figure 6, the plate member defines a slot 58 in which is located the head of a further peg carried by a further spring loaded piston not shown which is coupled to the cam ring 29. The plate member 57 has on its upper surface, a pair of projections 59, 60, the upper surfaces of which define cam forms or surfaces. The projections are diametrically disposed relative to the aperture 56 and lie generally on the line of movement of the piston 51.

As shown in Figure 5, a valve assembly 61 is associated with the plate member, the valve assembly including a housing 62 having formed therein a pair of spaced drillings in which are located a pair of sleeve members 63, 64. The sleeve members are slidable in the drillings and the axes of the drillings and the sleeve members are disposed normal to the plane of the plate member. The sleeve members accommodate slidable servo valve members 65, 66 respectively and the lower ends of the bores in the sleeve members 63, 64 are closed by plugs 67 each having a follower for engagement respectively with the cam forms on the projections 59,60.

The servo valve members 65, 66 are biased towards the plugs by coiled compression springs respectively and the portions of the bores in the sleeve members intermediate the valve members and the plugs can be supplied with control pressures respectively by passage means not shown. Each servo valve member is provided with a groove to which is supplied fuel under pressure from the low pressure supply pump 25. Moreover each sleeve member defines a control port which opens into the bore of the sleeve member at a position so that it is controlled by a land on the associated valve member. The control port 68 in the sleeve member 63 communicates with the passage 54, the control port 69 of the sleeve member 64 communicating with the cylinder containing the piston coupled to the cam ring 29.

In operation, when a control pressure increases the respective servo valve member will move against the action of its spring to uncover the associated control port to the groove in the valve member Fuel under pressure is therefore supplied to the cylinder of the associated piston and the piston moves against the action of its spring. In so doing the plate member 57 pivots about the peg carried by the other piston. The cam form on the associated projection causes movement of the associated sleeve member in the direction to reclose the control port. A follow up servo action in therefore provided.

The control pressures in the example are generated at a remote point from the apparatus and are supplied thereto by way of a pair of pipes. The pressures can however be generated within the apparatus.

The cam form on the projection 59 is shaped so that there is no movement of the sleeve member 63 as the plate member moves angularly about the head 55 with the head 55 fixed but that as the head 55 moves due to movement of the piston 51 the follow up servo action is obtained. The cam form on the projection 60 is shaped so that as the plate member moves angularly about the head 55 due to a fuel quantity change the follow up servo action will be obtained. As the plate moves due to movement of the piston 51 with the head in the slot 58 fixed, movement will be imparted to the sleeve 64.

If therefore the control pressure applied to the valve member 64 is altered to achieve a timing variation the port 68 will be uncovered by the land either to allow fuel to enter the cylinder 52 or to allow fuel to escape from the cylinder. The piston 51 will therefore move and the plate will pivot about the head in the slot 58. As a result the sleeve 63 will be moved and the port 68 reclosed. The described follow up servo action is obtained. The control pressure applied to the valve member 66 may remain constant indicating that the quantity of fuel supplied is to remain the same. However, during angular movement of the plate about the head in the slot 58, the cam surface will impart movement to the sleeve 64 and this will uncoverthe port 69 to allow fuel to enter or leave the cylinder of the piston which determines the setting of the cam ring 29.As a result the plate member will tend to pivot about the head 55 causing movement of the sleeve 64 which will be returned to its original position with the port 69 closed. The practical effect therefore is that the timing of delivery of the fuel is altered but the quantity of fuel supplied remains the same. In practice both movements will take place at the same time.

If a change in the amount of fuel delivered is required without a timing change the sleeve 64 will be moved to provide the follow up servo action but the sleeve 63 will remain fixed.

It will of course be understood that the quantity of fuel delivered and the timing may require to be changed and in this event both valve members will move due to the change in the respective control pressures.

In a modification (not shown) electromagnetically operated valves are utilized to control the pressures applied to the pistons respectively. The flow of current in the valves is controlled by an electronic control system. Feedback signals are supplied to the control system by a pair of transducers the moving components of which engage the cam forms on the projections 59,60. The shapes of the cam forms are as described. Within the control systems desired fuel quantity and timing signals are produced and these are compared with the signals provided by the respective transducers. The error signals obtained as a result of the comparisons determine the currents flowing in the respective valves and the effect obtained is as described above.

Turning now to Figures 7 and 8 the valve assembly 75 is in many respects similar to the assembly 61 and identical reference numbers are used for the parts which have the same function. In this example the servo valve members 65, 66 instead of being subjected to control pressures which are adjusted to represent the required timing and fueling, are subjected to the same control pressure which is provided by a regulator 76. The pressure developed by the regulator varies as the square of the speed at which the apparatus is driven and conveniently the liquid is fuel which is derived from the outlet of the low pressure pump 25. The position of the servo valve member 65 will therefore vary in accordance with the speed.

The servo valve member 66 is arranged to act as an hydraulic two speed governor and for this purpose the valve member is biased by a pair of springs 80,81, the spring 80 being a preloaded spring located between the valve meinber and an abutment plate 82, slidable on a stem secured to the valve member and the spring 81 being located between the abutment plate and an adjustable abutment 83. The position of the abutment 83 can be preset by means of an adjuster 84 on the exterior of the apparatus and the position of the abutment plate 82 can be adjusted from the exterior of the housing by the engine operator, by way of a rotary shaft 85 coupled to a cranked plate 86.The spring 81 forms the idling control spring and is effective to control in conjunction with the servo valve member 66, the idling speed of the associated engine when the shaft 85 is set in the idling position with the plate 86 disengaged from the abutment plate. As the idling speed rises the servo valve member will move upwardly and the piston connected to the cam ring 29 will move to reduce the quantity of fuel delivered and vice versa. For normal operation of the engine the position of the abutment plate 82 and the valve member 66 is determined by the operator but the valve member will move against the action of the spring 80 to control the maximum speed of the engine irrespective of the setting of the abutment plate 82.

If it is desired to have some variation in timing of fuel delivery as the fuel quantity is changed, this can be achieved by suitable shaping of the cam surface on the projection 59.

The projections 59 and 60 may be formed by a sintering operation from a hard material such as tungsten carbide. This method of manufacture enables the desired profiles of the cam surfaces to be accurately constructed. The contact forces bearing in mind that the followers defined by the plugs should be as thin as possible, can be kept within acceptable limits.

Claims (14)

1. Afuel pumping apparatus for supplying fuel to an internal combustion engine, comprising a high pressure fuel injection pump for supplying fuel at a high pressure to the engine in timed relationship therewith, the apparatus including first and second fluid pressure operable means for adjusting the timing of delivery of fuel and the quantity of fuel delivered by the injection pump respectively, valve means for controlling the application of fluid under pressure to said pressure operable means, a plate member, means pivotally connected to said plate member at spaced points in the plane of the plate member, said means being operatively connected to said first and second fluid pressure operable means so that when a change in the pressure applied to either or both of said fluid pressure operable means takes place the plate memberwill move in the aforesaid plane, a pair of cam surfaces on said plate member and followers engaging said cam surfaces respectively, said followers providing signals indicative of the positions of said first and second fluid pressure operable means.

2. An apparatus according to Claim 1 including transducers connected to said followers respective ly, and a fluid pressure control system, said system being responsive to the signals provided by said transducers and acting to control the fluid pressures applied to said first and second fluid pressure operable means.

3. An apparatus according to Claim 2 in which said control system includes electromagnetically operable valves.

4. An apparatus according to Claim 1 including a pair of servo valves for regulating the pressures applied to said fluid pressure operable means re spectively, means for generating a control pressure or pressures which is applied to said servo valve, said followers being connected to said servo valves respectively to provide feedback signals theretc

5. An apparatus according to Claim 4 in whist said servo valves include resiliently loaded elem nts respectively responsive to said control pressure o.

pressures.

6. An apparatus according to Claim 5 in which said elements are servo valve elements mounted in axially movable sleeves respectively, said sleeves being coupled to said followers respectively.

7. An apparatus according to Claim 6 in which the control pressure is applied to both servo valve elements and varies according to the speed at which the apparatus is driven, and means for adjusting the resilient loading acting on the one servo valve element which is associated with the second fluid pressure operable means.

8. An apparatus according to Claim 7 in which the resilient loading acting on the one servo valve element includes an idle spring which controls the idling speed of the associated engine and a main spring which provides for control of the maximum speed of the associated engine.

9. An apparatus according to Claim 7 in which said main spring is a preloaded spring the control of engine speed intermediate the idle and maximum speeds being effected by an engine operator controlled member.

10. An apparatus according to Claim 1 in which said fluid pressure operable means comprises a pair of pistons respectively, each piston mounting a lateral peg, the peg mounted on the piston of the first means being located within a central aperture in the plate member and the other peg being mounted within a slot formed in the edge of the plate member.

11. An apparatus according to Claim 10 in which said cam surfaces are defined on projections on the surface of the plate member, said projections being located at diametrically opposed positions on said plate member.

12. An apparatus according to Claim 11 in which said projections are formed from hard material by a sintering operation.

13. An 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 Figures 1-6 of the accompanying drawings.

14. An 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 Figures 1-4 and 6-8 of the accompanying drawings.