GB2115887A - Liquid fuel injection pumping apparatus - Google Patents

Abstract

A liquid fuel injection pumping apparatus has a rotary and axially movable distributor member 12 provided with bores 13 locating pumping plungers 14. Fuel can be supplied to the bores to effect outward movement and inward movement is effected by cam lobes on a cam ring 29. The extent of outward movement of the plungers is controlled by stop surfaces defined on cam followers 25, 26 which can co- operate with an inlined surface 22 on a part rotatable with the distributor member. The outward movement of one plunger while fuel is supplied to the bores can be limited or prevented by an adjustable stop member 34 having a stop surface engageable with the cam follower of that plunger. The stop surface declines in the direction of rotation of the distributor member whereby the one plunger can move outwardly while the other plunger or plungers move inwardly under the action of the leading flanks of the cam lobes. <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 and axially movable distributor member housed within a surrounding body, radial bores formed in the distributor member and pumping plungers therein, cam followers disposed at the outer ends of said plungers, an annular member surrounding the distributor member, said annular member being rotatable with the distributor member but being axially fixed within the surrounding body, slots formed in the annular member, said slots accommodating said cam followers, a cam ring mounted within the body, cam lobes formed on the inner surface of the cam ring whereby inward movement is imparted to the plungers as the distributor member rotates, means for feeding fuel to said bores to effect outward movement of the plungers, passage means through which fuel displaced by said plungers can flow to an outlet in the body, stop surfaces defined on said cam followers and said annular member, said stop surfaces acting to limit the outward movement of the plungers while fuel is supplied to said bores, and means for adjusting the axial setting of the distributor member thereby to vary the extent of outward movement of the plungers and hence the amount of fuel supplied through said outlet.

An apparatus of the aforesaid kind is described in British Published Specification 2037365. With the apparatus described in this specification the delivery of fuel by the plungers takes place at the same time and at a rate which depends upon the profile of the leading flanks of the cam lobes and the areas of the plungers. With some engines it is desirable that the initial flow of fuel to the engine should be at a reduced rate as compared with the main flow, and that the proportion of fuel which is supplied at the reduced rate as compared with the main flow, should be variable in accordance with an engine operating parameter for example engine speed.

The object of the present invention is to provide an apparatus of the kind specified in a form in which this desideratum can be achieved.

According to the invention an apparatus of the kind specified comprises an adjustable stop member mounted within the body, said stop member being positioned to limit or prevent outward movement of one of said plungers while fuel is supplied to said bores and having a control surface shaped to allow outward movement of said one plunger, the position of said control surface being angularly adjustable in relation to the cam ring whereby the extent of outward movement of the one plunger during inward movement of the other plunger or plungers by the cam lobes can be varied the arrangement being such that when the one plunger is moving outwardly fuel is supplied to the outlet at a reduced rate, the apparatus including means for positioning said stop member in accordance with said operating parameter.

An example of a fuel 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 developed view of a portion of the apparatus seen in Fig. 1 together with a graph indicating the quantity of fuel pumped against rotation of a component of the apparatus, and Figures 3 and 4 are views similar to Fig. 2 showing different settings of parts of the apparatus.

Referring to Fig. 1 of the drawings the pumping apparatus comprises a housing 10 in which is located a fixed sleeve 11. The sleeve 11 mounts a rotary distributor member 1 2 which is also axially movable. At its end which extends beyond the sleeve 11 the distributor member is formed with two transversely extending bores 1 3 only one of which is shown in Fig. 1, the axes of the bores being at 90 . Each bore 1 3 has a pair of pumping plungers 14 slidable therein and the spaces at the inner ends of the plungers communicate by way of a passage 15, with a delivery groove 1 6 formed in the periphery of the distributor member.

Formed in the sleeve 11 and extending into the body 10 are a plurality of equi-angularly spaced outlet passages 1 7 which are connected to outlets 1 8 in the body and which at their inner ends open onto the periphery of the distributor member. The delivery groove 1 6 registers with the outlets in turn during inward movement of the plungers 14 so that fuel displaced from the bores 1 3 flows to the outlets in turn. The outlets 1 8 are connected to the injection nozzles respectively of the associated engine.

Also mounted in the body 10 is a drive shaft 1 9 which in use, is coupled to a rotary part of the engine so as to be driven in timed relationship therewith. The drive shaft extends into a chamber 20 which also accommodates the projecting portion of the distributor member 12, and mounted on the drive shaft is an annular member 21 which has a flared internal surface 22. In addition, the member is provided with a plurality of slots 23 which correspond to the bores formed in the distributor member there therefore being four such slots. Each slot houses a cam follower which comprises a shoe 25 and a roller 26. The slots 23 are open ended and the rollers have an axial length such that they locate between a surface of the body which defines the chamber 20, and the end wall of the respective slot. The rollers are thus located against axial movement.The shoes however which define part spherical recesses accommodating the rollers, are of a reduced axial length and are located against axial movement relative to the distributor member, by means of a pair of side plates 27 carried by the distributor member.

The plates 27 are of generally annular form but carry projecting tongues which are located in slots in the member 21. The plates therefore serve as the drive coupling between the annular member 21 and the distributor member 1 2 but at the same time they permit relative axial movement of these two components.

The shoes 25 have main body portions as shown in Fig. 2, which project through the slots 23 but in addition, they define ledge portions 28 for engagement with the internal peripheral surface 22 of the annular member 21. Because the surface 22 is flared so also are the aforesaid surfaces. The surfaces defined on the ledges 28 together with the surface 22 constitute stop surfaces to limit the extent of outward movement of the shoes 25 and hence also the associated plungers 14.

Also provided is an annular cam ring 29 which as shown in Fig. 2, is provided with a plurality of cam lobes 30 each cam lobe comprising a leading flank 31 and a trailing flank 32. The cam ring is adjustably mounted within the body part and it is coupled to a fluid pressure operable piston 33 which is housed within a cylinder whereby the cam ring can be moved angularly for the purpose of adjusting the commencement of inward movement of the plungers.

The apparatus also includes a pair of stop plates 34, the stop plates 34 being of annular form and being positioned on opposite sides of the cam ring 29. The stop plates define control surfaces 35 which can operate to control the outward movement of two plungers only. Moreover, the stop plates are coupled to each other by a bridging member 36 which again is coupled to a piston 37 whereby the angular setting of the stop plates can be adjusted.

In order to supply fuel to the bores 1 3 ports 38 are provided in the sleeve 11, the ports 38 being alternately positioned with the ports 1 7. The ports 38 communicate with a source 39 of fuel under pressure.

In describing the operation of the apparatus it will first of all be assumed that the stop plates 34 are inoperative, this being the situation as shown in Fig. 2, the plungers 14 are moved inwardly as the rollers 26 engage the leading flanks of the cam lobes 30. During inward movement of the plungers fuel is displaced from the bores 1 3 and the displaced fuel flows to an outlet 1 8 by way of the passage 15, the delivery groove 1 6 and the appropriate outlet passage. When the rollers move over the crests of the cam lobes, the delivery groove 1 6 moves out of register with the outlet passage 1 7 and into register with an inlet passage 38.During the further angular movement of the distributor member, fuel flows into the bores 1 3 to effect outward movement of the plungers 14, the shoes 25 and the rollers 26. The extent of outward movement depends upon the axial position of the distributor member by virtue of the surfaces on the ledges 28 and the surface 22, outward movement of the plungers continues until the aforesaid surfaces engage and thereafter no further outward movement of the plungers can take place. The cycle is repeated and fuel is delivered to the next outlet passage 1 7 and hence another injection nozzle of the engine. As the distributor member 1 2 is moved towards the right as shown in Fig. 1, so the allowed outward movement of the plungers increases and therefore the greater the quantity of fuel which is supplied to the engine.Any convenient form of arrangement can be utilized for determining the axial position of the distributor member within the sleeve.

As described the four plungers are delivering fuel at the same to the engine and hence the rate of fuel delivery is at a maximum. If now the stop plates 34 are moved angularly to a position such as is shown in Fig. 3, the extent of outward movement of one pair of plungers is limited not by the surfaces on the ledges 28 and the surface 22 but by contact of the rollers 26 with the control surfaces 35 on the stop plates. In this situation as the distributor member rotates whilst fuel will be displaced from the bore 1 3 by one pair of plungers, the other pair of plungers by the shape of the control surfaces 35, will be allowed outward movement.The declination of the control surfaces 35 is less than the inclination of the leading flanks 31 of the cam lobes and hence some fuel will flow to the delivery groove 1 6 and to the outlet passage which is in register therewith. The rate at which fuel is delivered is therefore reduced.

Considering again the situation shown in Fig.

3 a point will be reached at which the rollers 26 previously controlled by the control surfaces 35 encounter the leading flanks of the cam lobes and when this occurs all the plungers will be moving inwardly and hence the rate at which fuel is delivered will be the same as described with reference to Fig. 2. The graph which accompanies Fig. 3, shows the increase in the rate of fuel delivery which occurs when the rollers previously controlled by the stop plates, engage the cam lobes. In Fig. 4 it is arranged that the rollers 26 associated with one pair of plungers never engage the cam lobes and in this situation all the fuel which flows to the engine, flows at a reduced rate.

It is convenient to control the angular setting of the stop plates 34 in accordance with the speed and this may be achieved by subjecting the piston 37 to a pressure which varies in accordance with the speed. This can be obtained from the source 39 which may be a simple constant displacement pump the output pressure of which is controlled by a spring loaded relief valve.

Claims (5)

1. A liquid fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising a rotary and axially movable distributor member housed within a surrounding body, radial bores formed in the distributor member and pumping plungers therein, cam followers disposed at the outer ends of said plungers, an annular member surrounding the distributor member, said annular member being rotatable with the distributor member but being axially fixed within the surrounding body, slots formed in the annular member, said slots accommodating said cam followers, a cam ring mounted within the body, cam lobes formed on the inner surface of the cam ring whereby inward movement is imparted to the plungers as the distributor member rotates, means for feeding fuel to said bores to effect outward movement of the plungers, passage means through which fuel displaced by said plungers can flow to an outlet in the body, stop surfaces defined on said cam followers and said annular member, said stop surfaces acting to limit the outward movement of the plungers while fuel is supplied to said bores, means for adjusting the axial setting of the distributor member thereby to vary the extent of outward movement of the plungers and hence the amount of fuel supplied though said outlet, an adjustable stop member mounted within the body, said stop member being positioned to limit or prevent outward movement of one of said plungers while fuel is supplied to said bores and having a control surface shaped to allow outward movement of said one plunger, the position of said control surface being angularly adjustable in relation to the cam ring whereby the extent of outward movement of the one plunger during inward movement of the other plunger or plungers by the cam lobes can be varied, the arrangement being such that when the one plunger is moving outwardly fuel is supplied to the outlet at a reduced rate, the apparatus including means for positioning said stop member in accordance with said operating parameter.

2. An apparatus according to Claim 1 in which said stop member is of annular form and said control surface having a declination which is less than the leading flanks of said cam lobes.

3. An apparatus according to Claim 2 including a further stop member, said stop members being positioned to engage with the cam followers adjacent opposite ends thereof, said stop members being coupled together so as to be angularly movable together about the axis of rotation of the distributor member.

4. An apparatus according to Claim 3 including a fluid pressure operable piston coupled to said stop members, and means for applying to said piston a fluid pressure which varies in accordance with the speed of the apparatus.

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