GB2103728A - Fuel injection pumping apparatus - Google Patents

Abstract

A fuel injection pumping apparatus of the rotary distributor type has a drive shaft 14 carried by a bearing 20 in the housing of the apparatus. The drive shaft carries an enlarged portion 14A which is supported about a spigot portion 17 defined in the housing. The cam ring for imparting inward movement to the pair of pumping plungers 30 has internal cam lobes arranged in opposed pairs, one of each pair being arranged to impart inward movement to one plunger before the other. The other plunger is held against movement by a stop surface on the enlarged portion 14A and this applies a side thrust to the drive shaft. The aforesaid ones of each pair of cam lobes are arranged adjacent each other and are positioned so that the thrust acts on the drive shaft in the same direction as any side thrust imparted upon the drive shaft due to its driving connection with the associated engine. <IMAGE>

Description

SPECIFICATION Fuel injection pumping apparatus This invention relates to a liquid fuel injection pumping apparatus of the kind comprising a rotary distributor member housed within a body, a transverse bore formed in the distributor member and a pair of pumping plungers therein, passage means for conveying fuel from said bore to a plurality of outlet ports in turn during successive inward movements of the plungers, further passage means for conveying fuel to the bore to effect outward movement of the plungers, a drive shaft mounted within the housing and extending to the exterior of the housing, driving means carried by the drive shaft and arranged in use to be driven by an associated engine, means coupling the drive shaft to the distributor member, a cam ring surrounding the distributor member, said cam ring defining pairs of cam lobes which act as the distributor member rotates, to impart inward movement to the plungers and stop means carried by the drive shaft for limiting the outward movement of the plungers and thereby the amount of fuel delivered to the associated engine.

Such an apparatus is described in published British Specification 2037365A. In this case the stop means is defined by surfaces which are inclined to the axis of rotation of the distributor member and which are defined upon the internal surface of a cup-shaped member carried by the drive shaft, The distributor member is axially movable and the aforesaid surfaces co-operate with complementary surfaces defined upon shoes which carry rollers for engagement with the cam lobes, the plungers engaging with the shoes.

Other forms of apparatus are known in which the distributor member is axially fixed but in which the stops are carried by a collar slidable upon the drive shaft.

It is possible with such an apparatus to modify the profile of one lobe of each pair of lobes to provide for an initial delivery of fuel at a reduced rate. For example, if the leading flank of one cam lobe lies slightly in advance of the leading flank of the other lobe of the pair then the plunger which is to be actuated by the one lobe will start to move inwardly before the other plunger. The initial delivery of fuel will therefore be effected by one plunger only. During the inward movement of the one plunger the other plunger is subjected to the pressure of fuel in the bore and the resulting thrust has to be resisted by the associated stop. This thrust is transmitted to the drive shaft as a side loading. When fuel is next delivered to the engine the thrust will be in a different direction.In the case of an apparatus having four plungers the thrust can be balanced but to provide four plungers when only two plungers are necessary to deliver the desired amount of fuel, is expensive.

The drive shaft of the apparatus may be subject to a side loading by the driving connection with the engine. For example, if a toothed belt is utilized to drive the apparatus with a pulley on the drive shaft, there will be side loading on the drive shaft due to the belt tension. This side loading whilst fluctuating during use of the apparatus will be of longer duration than the thrust imposed by the plunger. It is therefore not possible to balance the side loading on the shaft.

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 in an apparatus of the kind specified one of each pair of cam Icbes is modified to impart inward movement to one plunger before the other, said one cams being positioned adjacent each other on the internal surface of the cam ring at positions so that the thrust imparted to the drive shaft due to the fuel pressure in the bore acting upon the other plunger, acts upon the drive shaft in a direction to assist the thrust exerted upon the drive shaft by said drive means.

An example of an 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 an example of the apparatus; Figure 2 is a section of part of the apparatus seen in Figure 1 taken along a different radial plane; Figures 3 and 4 are sections through parts of the apparatus seen in Figures 1 and 2; Figure 5 is a section through part of the apparatus seen in Figure 1; Figure 6 is a section through another part of the apparatus seen in Figure 1; and Figure 7 is a diagram showing the profiles of the leading flanks of each lobe of a pair of cam lobes.

Referring to the drawings, the apparatus comprises a body part generally indicated at 10 and which conveniently is formed by a generally cup-shaped portion 11 , the open end of which is closed by a closure portion 1 2. The body portion 10 is provided with apertured lugs 1 3 whereby in use the apparatus can be secured to the engine with which it is associated.

The body portion 11 mounts a rotary drive shaft 14 which in use is coupled to a drive member of the associated engine so that it is rotated in synchronism with the engine. The drive shaft 14 extends into a generally cylindrical chamber 1 5 defined by the two body portions and it has an enlarged cup-shaped portion 1 4A within the chamber. This enlarged portion is provided with a pair of diametrically disposed slots 16. The enlarged portion of the drive shaft is hollow and at its end remote from the smaller diameter portion of the shaft, is of right cylindrical form and locates about a spigot portion 1 7 defined by the body part 12. The remainder of the interior surface of the enlarged portion of the drive shaft tapers for a purpose which will be described.In addition, the drive shaft is provided with a counter bore 1 8. An oil seal 1 9 is provided at the outer end of the body portion for engagement with the drive shaft and the shaft is supported by a sleeve bearing 20, the shaft being given additional support by the spigot 1 7. The drive shaft is tapered on its exterior portion to receive a toothed sprocket or pulley (not shown), with which is engaged a chain or a toothed belt.

The shaft is located against axial movement by thrust surfaces one of which is defined by an annular plate 21 which surrounds the drive shaft and which also serves as an end closure for a low pressure fuel supply pump 22. The rotor 22A of the supply pump is carried by the drive shaft 14 and it carries vanes which co-operate with an eccentrically disposed surface on a stator ring 22B which is carried within the body portion 11. The low pressure pump has a fuel inlet 23 and fuel outlet 24. A relief valve 25 is provided to ensure that the output pressure of the pump remains within desired limits, the relief valve acting to permit fuel to flow from the outlet of the pump to the inlet.

Formed in the body portion 12 is a cylindrical bore 26 in which is a fixed sleeve 27. The sleeve 27 accommodates an angularly and axially movable distributor member 28 which projects into the chamber 1 5 and has an enlarged head portion lying within the chamber. Formed in the head portion is a transversely extending bore 29 in which is located a pair of pumping plungers 30.

The bore 29 communicates with a blind passage 31 formed in the distributor member and which at its end within the head portion is sealed by means of a plug. As is more clearly shown in Figures 2, 3 and 4, the passage 31 communicates with a pair of diametrically disposed longitudinal slots 32 formed in the periphery of the distributor member and communicating with the passage 31 by means of a single or a plurality of connecting passages. The passage 31 also communicates with a further longitudinal slot 33 formed in the periphery of the distributor member and this slot communicates in turn with a plurality of outlet ports 34 formed in the sleeve 27 and communicating with outlets 35 respectively in the body portion 1 2.

Each outlet 35 incorporates a conventional form of delivery valve 36. The slots 32 register in turn with diametrically disposed inlet ports 37 formed in the sleeve 27 and communicating with a circumferential groove 38 fromed in the periphery of the sleeve. The groove 38 communicates with the outlet 24 of the low pressure pump 22 by way of an on/off valve 39 conveniently controlled by an electromagnetic actuator 40. If desired a single slot 32 may be provided with the number of inlet ports being equal to the number of outlets.

Surrounding the head portion of the distributor member 28 is an annular cam ring 41 on the internal peripheral surface of which are formed pairs of diametrically disposed cam lobes. In the particular example three pairs of cam lobes are provided since the apparatus is intended to supply fuel to a six cylinder engine. The cam ring 41 is angularly movable about the axis of rotation of the distributor member by means of a fluid pressure operable device generally indicated at 42 and connected to the cam ring by way of a radially disposed peg 43. The device 42 conveniently includes a resiliently loaded piston housed within a cylinder to one end of which liquid under pressure can be supplied to act on the piston to urge the piston against the action of its resilient loading.

Positioned at the outer ends of the plungers are cam followers respectively each of which comprises a roller 44 carried in a shoe 45. The followers are retained axially relative to the distributor member by a pair of side plates 46, 47 which are secured to the side faces of the head portion of the distributor member. Conveniently the side plates are of annular form having outwardly extending tongues 48 (Figure 5) which locate in the slots 1 6 formed in the enlarged portion of the drive shaft, in Figure 5 the plate 46 only is seen. The plate act to transmit rotary motion to the distributor member from the drive shaft. The shoes 45 are also located within the aforesaid slots 1 6 and the rotary motion is transmitted to the shoes directly by the drive shaft.The circumferential side faces of the shoes are provided with circumferentially extending projections 49, the radially outer surfaces of which are tapered to co-operate with the tapered internal surface of the enlarged portion of the drive shaft 14.

In use when fuel is supplied to the bore 29 upon registration of a groove 32 with an inlet passage 37, the plungers 30 are moved outwardly by the fuel pressure and in so doing impart outward movement to the shoes 45 and the rollers 44. The outward movement is limited by the abutment of the tapered surfaces on the shoes and shaft and by moving the distributor member axially the extent of outward movement can be varied. Thus the amount of fuel supplied to the bore 29 can be controlled and this in turn determines the amount of fuel delivered through an outlet, when the plungers 30 are moved inwardly by a pair of cam lobes.

The axial position of the distributor member in the particular example, is varied hydraulically. It can however be varied mechanically if so desired.

In the arrangement described the variation is achieved by varying the pressure within a chamber 50 defined by the end of the bore 26 in the body portion 12. The end of the bore is closed by a closure member and fuel under pressure is supplied to the chamber 50 by way of a restricted orifice 51 which communicates with the outlet 24 of the pump 22. Fuel is allowed to escape from the chamber 50 so that the pressure therein can be controlled, by way of an electromagnetically controlled valve 52. The distributor member is biased by means of a coiled compression spring 53 which is housed within the blind bore 18 formed in the drive shaft 14. The spring acts between the drive shaft and the distributor member and urges the distributor member against the action of fuel under pressure In the chamber 50.

For a given axial setting of the distributor member and ignoring leakage, the amount of fuel delivered by the plungers will remain the same throughout the speed range of the associated engine and an indication of the axial setting of the distributor member is provided by a position transducer 54 which is carried on the end closure.

The signal provided by the transducer can be utilized also to provide a signal indicative of the speed of rotation of the distributor member as well as the signal indicative of the axial position and therefore the amount of fuel being delivered by the apparatus. In use, the signals are supplied to an electronic control system which is also provided with signals representing various engine operating parameters and the desired engine speed. The control system controls the operation of the valve 52 to ensure that the correct amount of fuel is supplied to the associated engine.

The cam lobes which effect inward movement of the plungers are indicated at 55 and 55A in Figure 6. It will be noted that a lobe 55A is disposed diametrically opposite a lobe 55 so as to form a pair of lobes which together impart inward movement to the plungers 30. In Figure 7 there is shown the profile of the leading flanks of the cam lobes with a roller indicated at 44 and the direction of movement of the rollers relative to the cam lobes being indicated by the arrow 56. It will be seen that the leading flank of one lobe is slightly in advance of the leading flanks of the lobes 55. The effect of this arrangement is that as the distributor member rotates after the plungers have been moved outwardly to their maximum extent, one plunger the roller of which is engaging with a lobe 55A will be moved inwardly in advance of the other plunger.As a result delivery of fuel to the engine will take piace at a reduced rate since only one plunger is moving. This has a beneficial effect upon the combustion of fuel by the engine. The other plunger is subject to the pressure of fuel in the bore 29 and this generates a force acting on the plunger which urges the shoe 45 into firm engagement with the surfaces on the enlarged portion 1 4A of the drive shaft. Side loading is therefore applied to the drive shaft which will tend to tilt the drive shaft about the spigot portion 17. The cam lobes 55A lie next to each other and it is arranged that the force which acts upon the cup-shaped member 1 4A assists the force due to the tension in the driving belt or chain which is engaged with the pulley or sprocket on the drive shaft exterior of the housing. The arrow 57 indicates the line of action of the force due to the tension in the belt or chain. By this arrangement the side loads acting on the drive shaft act in substantially the same direction so that there is little tendency for the axis of the drive shaft to move around by virtue of the fluctuating side load. The possibility of movement of the drive shaft influencing the delivery characteristics of the apparatus is therefore minimised.

In the case where the drive shaft is supported only by a bearing or split bearings disposed between the cup shaped member and the pulley or sprocket, the positions of the lobes 55 and 55A will have to be reversed to ensure that the forces due to the tension in the belt or chain and the force acting on the plunger which is held by the cup shaped member, are additive.

Claims (4)

1. A liquid fuel injection pumping apparatus comprising a rotary distributor member housed within a body, a transverse bore formed in the distributor member and a pair of pumping plungers therein, passage means for conveying fuel from said bore to a plurality of outlet ports in turn during successive inward movements of the plungers, further passage means for conveying fuel to the bore to effect outward movement of the plungers, a drive shaft mounted within the housing and extending to the exterior of the housing, driving means carried by the drive shaft and arranged in use to be driven by an associated engine, means coupling the drive shaft to the distributor member, a cam ring surrounding the distributor member, said cam ring defining pairs of cam lobes which act as the distributor member rotates, to impart inward movement to the plungers, stop means carried by the drive shaft for limiting the outward movement of the plungers and thereby the amount of fuel delivered to the associated engine, one of each pair of cam lobes being modifed to impart inward movement to one plunger before the other, said one cams being positioned adjacent each other on the internal surface of the cam ring at positions so that the thrust imparted to the drive shaft due to the fuel pressure in the bore acting upon the other plunger, acts upon the drive shaft in a direction to assist the thrust exerted upon the drive shaft by said drive means.

2. An apparatus according to claim 1, in which said drive shaft is supported by a bearing in said housing and carries an integral enlarged portion which is mounted about a spigot bearing in the housing, said drive shaft and said enlarged portion tilting about said spigot portion under the action of the thrust imparted to the drive shaft, the enlarged portion defining stop surfaces to limit the outward movement of the plungers, said stop surfaces being disposed between said bearings.

3. An apparatus according to claim 1, in which said drive shaft is supported by a bearing in the housing, said bearing or split bearings, said drive shaft tilting about said bearing.

4. A liquid fuel injection pumping apparatus comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.