GB2086490A - Liquid fuel injection pumping apparatus - Google Patents

Abstract

A liquid fuel injection pumping apparatus has a pair of plungers 63 housed within bores formed in a rotary distributor member 28. A cam ring has cam lobes positioned to effect inward movement of the plungers through rollers 62 and stop surfaces 64, 65 are provided to limit the extent of outward movement of the plungers to control the amount of fuel supplied by the apparatus. The stop surfaces have different radial positions so that one roller will project more than the other or others whereby the plunger associated with that roller will be moved inwardly before the other plunger or plungers. <IMAGE>

Description

SPECIFICATION Liquid fuel injection pumping apparatus This invention relates to a liquid fuel injection pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a rotary distributor member located in a housing, bores formed in the distributor member and a plunger in each bore, cam followers located at the outer ends of the plungers respectively for engagement with cam lobes formed upon the internal peripheral surface of an annular cam ring surrounding the distributor member, means for feeding fuel to the transverse bore to effect outward movement of the plungers and followers, passage means for conveying fuel from the bore to outlets in the housing and adjustable stop means for limiting the outward movement of the plungers during the time when fuel is supplied to the bore thereby to determine the amount of fuel supplied at each delivery stroke of the apparatus.

Such apparatus is well known in the art and it provides for a variable start of delivery of fuel depending upon the volume of fuel contained in the transverse bore at the end of the filling stroke. As is well known, the termination of fuel delivery is constant irrespective of the volume of fuel delivered.

The instant at which fuel delivery starts, advances with an increase in the quantity of fuel delivered. The leading flanks of the cam lobes are designed so that delivery of fuel takes place quickly and it is not possible to vary the shapes of the cam lobes to obtain a low initial rate of delivery over the full range of the fuel delivery volume. It may be possible to obtain a low initial rate of delivery at the maximum fuel volume only.

A low initial rate of fuel delivery is desired for many engines over the full range of fuel delivery volume and the object of the present invention is to provide a pump of the kind specified in which this desideratum is achieved.

According to the invention, in an apparatus of the kind specified the cam lobes and followers are so disposed that one of said followers, and hence the associated plunger, is moved inwardly to effect pumping of fuel before the other, the other of said followers being held by said stop means against outward movement.

In the accompanying drawings: Figure 1 is a sectional side elevation of one example of an apparatus to which the invention may be applied, Figure 2 and 3 are similar sectional diagrams showing two ways of modifying the apparatus of Figure 1, Figure 4 is a developed view of part of a further modified form of the apparatus and, Figure 5 is a section of another part of the apparatus shown in Figure 4.

With reference to Figure 1 of the drawings, the apparatus shown therein is of the kind disclosed in British Published specification 2037365 and it comprises a housing 10 which is formed in two parts 11, 12, the part 11 being provided with apertured lugs 13 whereby it may be secured to the associated engine.

The part 11 mounts a rotary drive shaft 14 which in use, is coupled to a drive member of the associated engine so that the shaft 14 rotates in synchronism with the engine. The drive shaft extends into a generally cylindrical chamber 15 and has an enlarged cup shaped portion 1 4A within the chamber.

The enlarged portion is provided with a pair of diametrically disposed slots 16 and it is also hollow.

The open end of the enlarged portion is located about a spigot portion 17 defined by the part 12 of the body. The remainder of the interior surface of the enlarged portion tapers for a purpose which will be described.

The drive shaft is also provided with a counter bore 18 and an oil seal 19 is provided at the outer end of the body part 11 for engagement with the drive shaft. The latter is supported by a sleeve bearing 20. The shaft is located against axial movement by thrust surfaces which engage with the end surfaces of the enlarged portion of the shaft. In one case the thrust surface is defined directly by the part 12 of the body whilst in the other case, the thrust surface is defined by an annular plate 21 which surrounds the drive shaft and which additionally 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 and it in turn carries vanes which co-operate with an eccentrically disposed surface on a stator ring 22B carried within the part 11 of the body.The low pressure pump has a fuel inlet 23 connected to a fuel inlet 23A in a housing secured to the body portion. The low pressure pump also has an outlet 24. A relief valve 25 is provided to ensure that the output pressure of the low pressure pump remains within desired limits.

Formed in the part 12 of the body is a cylindrical bore 26 in which is fixed a sleeve 27. The sleeve 27 accomodates an anguiarly and axially movable distributor member 28 which projects into the chamber 15 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 reciprocable 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. The passage communicates with a pair of diametrically disposed longitudinal slots 32 formed in the periphery of the distributor member and also with a single longitudinal slot 33 also formed in the periphery of the distributor member.The slot 33 can communicate in turn with a plurality of outlet ports 34 formed in the sleeve and extending through the part 12 of the body. The ports 34 communicate with outlets 35 and with the injection nozzles respectively of the associated engine. The slots 32 register in turn with inlet ports 37 formed in the sleeve and which extend inwardly from a circumferential groove 38 which communicates with the outlet 24 of the low pressure pump by way of an on/off valve 39 and which is controlled by a solenoid device 40.

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 two pairs of cam lobes are provided since the apparatus is intended to supply fuel to a four 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 radially disposed peg 43.

Positioned atthe outer ends of the plungers are a pair of followers respectively each of which compris es 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. The side plates are of annular form and have outwardly extending portions which locate in the sloths 16 formed in the drive shaft. The circumferential side faces of the shoes are provided with circumferentially extending projections 49 the radial ly outer surfaces of which are tapered to co-operate with the tapered surface formed on the internal surface of the enlarged portion of the drive shaft.

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 of the plungers 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 34 when the piungers 30 are moved inwardly by a pir of the cam lobes.

The axial position of the distributor member is varied hydraulically and this is achieved by varying the pressure within a chamber 50 defined by the end of the bore 26 in the part 12 of the body. The end of the bore 26 is closed by a closure member and fuel under pressure is supplied to the chamber 50 by way of a restricted orifice 51 carried by the sleeve 27. The orifice 51 communicates with the outlet 24 of the pump and fuel is allowed to escape from the chamber 50 so that the pressure in the chamber can be controlled, by way of an electro-magnetically controlled valve 52. Moreover, the distributor member is biased by means of a coiled compression spring 53 located within the bore 18, the spring acting between the drive shaft and the distributor member and acting to urge the distributor member against the action of fuel under pressure in the chamber 50.

A transducer 54 is located within the chamber 50 and it includes a part rotatable with the distributor member. The transducer 54 provides an indication of the speed of rotation of the distributor member and it also provides a signal indicative of the axial setting of the distributor member. These signals together with others, are supplied to an electronic control system which controls the operation of the valve 52.

In the apparatus described, the rollers engage the cam lobes at the same time and hence the delivery of fuel starts at a high rate and is maintained at this rate until towards the end of the delivery of fuel. It is required to reduce the initial rate of fuel delivery and this can be achieved in a number of ways. In the description which follows, the apparatus is assumed to have four plungers which are housed in a pair of transverse bores, the axes of which intersect.

In Figure 2 the cam lobes 55 are disposed at right angles to each other and the axes of the bores are not at right angles, the bores being indicated by the rollers 56,5/. With this arrangement and with the direction of rotation as shown by the arrow, the rollers 57 will engage the cam lobes before the rollers 56. The initial delivery of fuel is therefore at a reduced rate and is effected by the plungers associated with the rollers 57. In this example the cam lobes must all be of the same shape. However, the pairs of plungers can be of differing diameter since it is always the plungers associated with the rollers 57 which cause the delivery of fuel and the other plungers which supply fuel at the end of the period of fuel delivery.It should be pointed out that when the plungers associated with the rollers 57 start to deliver fuel and therefore pressurize the fuel in the bores, the plungers associated with the rollers 56 are urged outwardly and are held by the inclined surfaces on the enlarged portion of the drive shaft.

At the end of fuel delivery all the rollers are urged into contact with the cam lobes.

In the arrangement shown in Figure 3 the plungers are represented by the rollers 58, are equiangularly spaced and the pairs of cam lobes are angularly displaced from 90 . In the example the cam lobes 60 always start the delivery of fuel whilst the cam lobes 59 are the ones which are responsible for the final fuel delivery. In this arrangement the plungers must be of the same diameter but the shapes of the cam lobes 59, 60 can be different for example, the leading flanks of the lobes 60 can be less steep than those of the lobes 59 to give a further reduced rate of initial fuel delivery.

It is possible for the arrangements shown in Figures 2 and 3 to be applied to a two plunger apparatus, in Figure 2 the single transverse bore would in fact be two bores with their axes out of line by the desired amount. Moreover in both cases the final delivery of fuel will be affected because whilst the rollers associated with one pair of plungers are moving up to the crests of the cam lobes the other pair of rollers will be moving outwardly having already passed the crests of the cam lobes.

Turning now to Figures 4 and 5. In this arrangement the cam lobes 61 are equiangularly spaced as also are the plungers the latter being represented in Figure 4 by the rollers 62 and being shown at 63 in Figure 5. The difference lies in the radial dimensions of the tapered surfaces on the shoes and the enlarged portions of the drive shaft. In Figure 4, the rollers 62 are shown in the positions which they adopt at the end of the filling stroke whilst in Figure5 the rollers are shown in their innermost positions that is when the rollers are on the crests of the cam lobes.The rollers and plungers have the same innermost positions but due to the differing radial distances of the inclined surfaces 64,65 on the drive shaft, one pair of rollers 62, and hence the associated plungers at the end of the filling stroke are disposed further away from the axis of rotation of the distributor member than the other pair. As a result the one pair of rollers ie. those controlled by the surfaces 64, will engage the cam lobes before the other pair of rollers. The plungers controlled by the surfaces 64 will therefore deliver fuel before the plungers controlled by the surfaces 65. As a result the initial rate of fuel delivery is reduced. The inward movement of each plunger terminates at the same time and hence in this case the final delivery of fuel is not affected.Since one pair of plungers always starts the delivery of fuel it is possible for the pair of plungers to have differing diameters.

Moreover, the cam lobes have the same shape and size and the ramp angles of the tapered surfaces 64, 65 are the same. This means that the volume of fuel delivered at the low initial rate remains the same throughout the fuel range. In order to obtain variation of the volume of fuel delivered at the low initial rate the ramp angles of the surfaces 64 and 65 can be different.

It is possible to adapt the example shown in Figures 4 and 5 to a two plunger pump of the kind shown in Figure 1.

Another form of apparatus to which the invention can be applied has an axially fixed distributor member with the stop means being formed by a pair of rings positioned on the opposite sides of the enlarged portion of the distributor member and notable therewith. The shoes or the rollers are extended axially to engage with cam surfaces formed on the internal surfaces of the rings and the rings are angularly adjustable relative to the distributor member whereby the extent of outward movement of the plungers during the filling strokes can be varied.

Claims (7)

1. A liquid fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising a rotary distributor member located in a housing, bores formed in the distributor member and a plunger in each bore, cam followers located at the outer ends of the plungers respectively for engagement with cam lobes formed upon the internal peripheral surface of an annular cam ring surrounding the distributor member, means for feeding fuel to the transverse bore to effect outward movement of the plungers and followers, passage means for conveying fuel from the bore to outlets in the housing and adjustable stop means for limiting the outward movement of the plungers during the time when fuel is supplied to the bore thereby to determine the amount of fuel supplied at each delivery stroke of the apparatus, said cam lobes and followers being so disposed that one of the followers and hence the associated plunger, is moved inwardliy to effect pumping of fuel before the other, the other of said cam followers being held by said stop means against outward movement.

2. An apparatus according to Claim 1 in which said cam lobes are equiangularly spaced about the axis of rotation of the distributor member and said followers and the associated plungers are not equiangularly spaced.

3. An apparatus according to Claim 1 in which said followers and plungers are equiangularly spaced about the axis of rotation of the distributor member, and the cam lobes are not equiangularly spaced.

4. An apparatus according to Claim 1 including stop surfaces defined by said stop means for engagement with complementary surfaces defined by said followers, said stop means being axially adjustable relative to the followers to vary the extent of outward movement of the followers and plungers.

5. An apparatus according to Claim 4 in which said stop surfaces are defined on a part surrounding the distributor member, said part being rotatable with a drive shaft coupled to the distributor member, slots defined in said part to accommodate said cam followers, the internal surface of said part adjacent said slots being tapered and defining said stop surfaces, said cam followers having projecting portions which define complementary surfaces for engagement with said stop surfaces, the radial positions of said stop surfaces being different.

6. An apparatus according to Claim 5 in which the angles of inclination of the surfaces on the two followers and said part, are different.

7. A liquid fuel injection pumping apparatus for supplying fuel to an internal combustion engine and comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.