GB2206382A - Fuel injection pumping apparatus - Google Patents

Abstract

A fuel injection pumping apparatus for supplying fuel to an internal combustion engine includes a rotary distrbutor member (11) housed in a housing 9. The distributor member includes a bore (14) in which is mounted a pair of pumping plungers (15) which are movable inwardly by cam lobes formed on a cam ring (17) located in the housing. One of the plungers and the bore defines a spill path through which fuel can escape from the bore when the plunger reaches a predetermined position during its inward movement. The concentricity of the cam ring (17) with the axis of rotation of the distributor member (11) can be assured by adjusting screws threaded into the housing, (9) into engagement with respective pressure pads (46) which support the cam ring (17) in the housing (9). <IMAGE>

Description

"FUEL INJECTION PUMPING APPARATUS" This invention relates to a rotary distributor type fuel inject ion pumping apparatus of the kind having a rotary distributor member rotatably mounted in a housing, a tranverse bore formed in the distributor member, at least one pumping plunger located in the bore, a cam ring surrounding the distributor member, the cam ring being provided with inwardly directed cam lobes for imparting inward movement to the plunger as the distributor member rotates, means for feeding fuel to the bore to effect outward movement of the plunger, distribution means defined by the distributor member and the housing to direct fuel displaced from the bore to a plurality of outlets in turn, and the plunger and the bore defining a spill path which is opened at a predetermined position of the plunger in the bore during the inward movement of the plunger, to terminate the delivery of fuel through an outlet.

With such an apparatus a problem arises if the cam ring is eccentrically disposed relative to the distributor member. This can cause the volume of fuel delivered at each outlet to vary even though the same quantity of fuel is supplied to the bore at each filling period thereof. The discrepancy in the delivery of fuel through the outlets will result in unequal volumes of fuel being supplied to the cylinders of the associated engine leading to irregularity in the operation of the engine and the possible emission of smoke in the engine exhaust.

The above effect can be minimised by arranging that it is the relative position of a pair of opposed plungers which determines the instant at which the spill path is opened. This however increases the difficulty of manufacturing the plungers and 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 the cam ring is supported about its peripheral surface in the housing by at least three angularly spaced support pads, means being provided to adjust the radial position of the pads whereby the axis of the cam ring can be adjusted to coincide with the axis of the distributor member.

An example of a fuel injection pumping 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 the apparatus, Figure 2 is a view to an enlarged scale of part of the apparatus seen in Figure 1, Figures 3 and 4 are part sectional cross sections of part of the apparatus seen in Figure 1, and Figure 5 is a view similar to Figure 2 showing a modification.

Referring to the drawings the apparatus comprises a two part housing 9, 10 the part 9 being provided with an open end in which is located the part 10 and the part 10 having a close fitting relationship with the wall of the bore defined in the part 9 of the housing.

Formed within the part 10 of the housing is a bore in which is mounted a rotary cylindrical distributor member 11 which is coupled to a drive shaft 12 which is located in the part 9 of the housing and which is adapted to be driven in timed relationship with an engine with which the apparatus is associated. Formed in the distributor member is a transversely extending bore 14 in which is mounted a pair of reciprocable pumping plungers 15 which are arranged to be moved inwardly as the distributor member rotates, through the intermediary of a pair of rollers 16 respectively, by cam lobes formed on the internal peripheral surface of an annular cam ring 17 which is mounted for angular movement within the part 9 of the housing. The apparatus may have a further bore or bores together with the plungers.

Formed in the distributor member is a longitudinally extending passage 18 which at one end is in communication with the bore 14 and which at its other end communicates with a radially disposed delivery passage 19. The passage 19 is arranged to register in turn with a plurality of equi-angularly spaced outlet ports 20 which are formed in the part 10 of the housing and which in use are connected by pipe lines respectively to the injection nozzles of the associated engine. The registration of the passage 19 with an outlet 20 takes place during the whole time the plungers 15 are being moved inwardly so that liquid fuel in the bore 14 will be displaced by way of an outlet 20 to a combustion chamber of the associated engine.

At another point the longitudinal passage 18 is in communication with a plurality of radially disposed inlet passages 22 which are arranged to register in turn with an inlet 23 formed in the housing. The inlet port 23 communicates by way of a passage 24 with a control port 25 which in turn is in- communication with the outlet 26 of a low pressure fuel supply pump 27. The effective size of the control port 25 can be varied by varying the - angular setting of a throttle member 28 which has an axial groove formed therein.

The arrangement is such that when an inlet passage 22 registers with the inlet port 23, fuel will flow from the outlet 26 of the low pressure pump to the bore 14 to move the plungers 15 outwardly. The aforesaid registration takes place only during the time when the delivery passage 19 is out of register with an outlet 20 and during the time when the rollers 16 are clear of the cam lobes. By adjusting the angular setting of the throttle member 28 the rate at which fuel is supplied to the bore 14 can be controlled and hence also the amount of fuel delivered to the associated engine.

The low pressure pump 27 has a rotary component which is carried by the distributor member and it is provided with an inlet which is in communication with an inlet port 30 formed in a hollow part 37 which is secured to the housing of the apparatus. The inlet communicates with the inlet port 30 by way of a passage 29 also formed in the part 37 and the latter has mounted therein a tubular filter element 32 and a relief valve which includes a spring loaded element 33.

One end of the element 33 is exposed to the pressure of fuel at the outlet 26 and it controls the size of a spill port 34. The arrangement is such that the low pressure pump always delivers more fuel than is required to be delivered to the engine with the result that the output pressure of the low pressure pump is controlled in a manner which is dependent upon the speed of the engine and which increases as the speed thereof increases.

The angular setting of the throttle member 28 is conveniently controlled by a mechanical governor which includes weights 29A which are accommodated within a cage driven by the shaft 12. The weights act upon an axially movable flanged collar 30A which is mounted about the shaft 12 and the axial movement of the collar is resisted by a governor spring 31 which is mounted between one end of a pivotal lever 32A and a operator adjustable member 33A. The latter is connected to, for example, the throttle pedal of the vehicle of which the engine associated with the apparatus forms part.

The same end of the lever 32A is connected to an arm on the throttle member 28 by means of a tie rod 34A and the opposite end of the lever 32A is engaged with the collar 30A. The arrangement is such that as the speed of rotation of the engine increases, the weights 29A will move outwardly and will impart axial movement to the collar 30A against the action of the spring 31.

The pivotal movement of the lever 32 is transmitted to the throttle member in such a manner that the latter is moved angularly to reduce the amount of fuel which can be supplied to the engine. The opposite effect is obtained if the engine speed should decrease. If the operator adjustable member 33A is moved to vary the force exerted by the spring then as the aforesaid force is decreased, the throttle member will move angularly to reduce the amount of fuel supplied to the engine and vice versa. With this form of apparatus the timing of fuel delivery by the apparatus to the associated engine will vary as the quantity of fuel supplied is varied.

As the quantity of fuel increases the timing of the start of delivery of fuel will advance and vice versa.

In order to provide a control over the timing of fuel delivery, the cam 17 is angularly adjustable and is provided with a peg 35 which extends through an aperture in the housing. The peg is connected to a spring loaded piston not shown which is subject to the outlet pressure of the low pressure pump and it is arranged that as the speed of the associated engine increases, the piston is moved to advance the timing of delivery of fuel.

In conventional pumps of this type the termination of fuel delivery occurs when the inward movement of the plungers by the cam lobes ceases. This causes substantial stress of the rollers and also the crests of the cam lobes of the cam ring and it is known with this form of apparatus to open a spill path before the rollers reach the crests of the cam lobes so that the high pressure in the transverse bore is dissipated and the high stress of the rollers and cam lobes is avoided. In the example and as more clearly seen in Figure 2, the spill path is defined by a groove 38 formed on one of the plungers, the groove communicating by way of a passage 39 with the portion of the transverse bore 14 lying between the plungers.In addition in the wall of the bore is formed a port 40 which extends to the exterior of the distributor member and opens to form a seating 41 for a ball 42 which is spring loaded by means of a spring 43 into contact with the seating. When during the inward movement of the plunger the groove 38 communicates with the port 40, fuel is spilled from the transverse bore, the fuel lifting the ball 42 from its seating. The fuel flows into the interior of the housing and can then be returned to the inlet of the low pressure pump or the fuel supply tank. The extent of movement of the ball 42 away from its seating is limited by means of a stop peg 44, the stop peg and the spring 43 being located within a chamber 45 defined in the drive shaft. Each plunger may be provided with a groove 38 and the associated bore, a port 40.

With this arrangement the delivery of fuel through an outlet is terminated before the rollers reach the crests of the cam lobes and therefore the stresses imposed on these two components are reduced. With this arrangement however it is essential to ensure that the cam ring 17 is concentric with the axis of rotation of the distributor member otherwise there will be a variation in the amount of fuel delivered at each outlet even though the quantity of fuel supplied to the transverse bore during the filling periods thereof is the same. This is because the point at which the spill path is opened is determined by the relative positions of the plunger or plungers within the transverse bore.

In order to be able to ensure that the cam ring is concentric it is proposed to provide an adjustment arrangement and one example of this arrangement is illustrated in Figure 3 and with reference to this figure there is interposed between the outer peripheral surface of the cam ring and the inner peripheral surface of the housing, three support pads 46 which in the example of Figure 3, are of elongated arcuate form, a small gap being left between adjacent pads. Each pad is provided with an adjustment means 47 which in the example comprises a screw 48 which is provided with a lock nut, the screw being located in a boss formed on the housing. By adjustment of the pads it is possible to ensure that the cam ring is concentric with the axis of rotation of the distributor member at the same time still permitting the cam ring to be moved angularly for the purpose of timing adjustment.It will be clear that at least three pads are required to enable the adjustment to be effected.

In the modification shown in Figure 4 the pads 49 are of reduced circumferential length but nevertheless function in the same manner as the pads 46. In the example of Figure 4 the main body portion of each pad is located within a recess defined in the internal surface of the housing.

Turning now to Figure 5, this illustrates a modification to the support for the spring 43 which biases the ball 42 into contact with its seating. In the arrangement shown in Figure 2 the spring will impose an end thrust cn the distributor member and this can be a disadvantage. In the modification of Figure 5 the end thrust on the distributor member is avoided by the provision of a generally cup-shaped member 50 which is in screw thread engagement with the distributor member. The base :wall of the cup-shaped member forms the abutment for the spring 43 and also carries the stop 44. Since the fuel will spill into the interior of the cup-shaped member, the latter is provided with apertures 51 to allow the fuel to escape.

Claims (5)

1. A rotary distributor type fuel injection pumping apparatus comprising a rotary distributor member rotatably mounted in a housing, a transverse bore formed in the distributor member, at least one pumping plunger located in the bore, a cam ring surrounding the distributor member, the cam ring being provided with inwardly directed cam lobes for imparting inward movement to the plunger as the distributor member rotates, means for feeding fuel to the bore to effect outward movement of the plunger, distribution means defined by the distributor member and the housing to direct fuel displaced from the bore tic a plurality of outlets in turn, the plunger and the bore defining a spill path which is opened at a predetermined position of the plunger in the bore during the inward movement of the plunger, to terminate the delivery of fuel through an outlet, said cam ring being supported about its outer peripheral surface in the housing, by at least three angularll spaced support pads, and means for adjusting the radial position of the pads whereby the axis of the cam ring can be adjusted to coincide with the axis of rotation of the distributor member.

2. An apparatus according to Claim 1 in which the means for adjusting the support pads comprises screws associated with the pads respectively, said screws being carried by the housing.

3. An apparatus according to Claim 2 in which each pad is located in a recess in the internal surface of the housing.

4. An apparatus according to Claim 2 in which the support pads extend about the cam ring, with gaps defined between the adjacent ends of a pair of rings.

5. A rotary distributor type fuel injection pumping apparatus substantially as hereinbefore described with reference to the accompanying drawings.