GB2199902A - Fuel injection pump - Google Patents

Abstract

In a distributor-type fuel injection pump for internal combustion engines with a distributor rotor (6) which is mounted in the pump housing and has at least one pump plunger (9) arranged in a radial bore (7) in the rotor, the aim is to prevent high delivery rates and associated high combustion noise at the start of delivery when a large quantity of fuel is being delivered. According to the invention the radial bore (7) has in the region of maximum stroke of the plunger (9) at least one spill port (28) which is uncovered by a control edge (29) on the pump plunger (9) at the start of the delivery stroke when the plunger exceeds a predetermined stroke level (S1). With smaller delivery quantities the outward suction stroke of the plunger is insufficient to uncover the spill port(s) (28). <IMAGE>

Description

FUEL INJECTION PUMP The invention relates to a distributor-type fuel injection pump for internal combustion engines, with an engine-driven distributor rotor mounted in the pump housing, and having at least one pump plunger arranged in a radial bore in the rotor, the end of the plunger opposite the working chamber of the pump co-operating with a cam ring around the rotor.

A fuel injection pump of the kind -stated in the introduction is known from DE-PS 22 61 988. A distributor rotor is rotatably mounted in a pump housing and driven through its end portion from the engine which in its turn is- fed by the injection pump.

The distributor rotor has a bore extending diametrally through it, in which is present a pair of reciprocating pump plungers which define the working chamber of the pump. The outer ends of the pump plungers engage tappet shoes carrying rollers which are guided in radial slots in the rotor. These rollers co-operate with a circular cam ring on the inner periphery of which there are a number of cams. The working chamber of the pump between the plungers communicates with a passage extending longitudinally within the rotor.

This passage has radial bores which, according to the angle of rotation of the rotor, are connected during the delivery stroke to the delivery pipe leading to the injection nozzles, or during the intake stroke, to the fuel supply pipe having a metering device. A drawback in injection pumps of this kind is that with large injection quantities the injection rate rises excessively at the beginning of the delivery, causing an increase in the noise generated by the combustion.

It is the aim of the invention to overcome the drawbacks of the orthodox fuel injection pumps and in particular to ensure that with large injection quantities the injection rate at the beginning of the delivery is kept small and the combustion noise is correspondingly reduced.

This problem is solved according to the invention in that the radial bore has in the region of the maximum stroke of the pump plunger at least one spill port of which the outlet leading from the working chamber is uncovered by a control edge arranged on the pump plunger when a predetermined stroke is exceeded.

By the provision of a spill port in the region of the maximum stroke of the pump plunger, a part of the fuel is bled off at the beginning of the stroke (in the presence of large fuel delivery quantities) so that high injection rates or an increase in the injection rate at the beginning of the injection process are prevented. When only a small amount of fuel is delivered to the working chamber by the metering device the control edge of the pump plunger does not reach the predetermined minimum stroke necessary for bleeding off the fuel, and so the delivery with small delivery quantities is not affected at all by the control device. With low deliveries, in which the mean injection rate and thereby the combustion noise is small, the spill port accordingly remains closed during the whole of the delivery stroke.

Only in the case of large fuel delivery quantities, when the pump plungers exceed a predetermined stroke level during the suction stroke, is the port uncovered by the control edge of the pump plunger in accordance with the predetermined quantity of fuel to be delivered.

In a further development of the invention it is provided that a number of spill ports are provided, associated with a pump plunger, arranged offset or staggered, in the direction of the stroke, in relation to the control edge of the pump plunger. By the provision of several such ports which are closed off in turn by the control edge it is possible to match the injection rate at the beginning of the delivery stroke still more closely to the requirements of the engine.

In an alternative arrangement giving the same result it is possible to provide several spill ports at the same axial level and to provide the pump plunger with an inclined control edge.

If the quantities to be spilled are to rise linearly with the stroke of the pump plunger it is provided in one embodiment of the invention that the port of the spill passage has a rectangular cross-section of which the longer side, if present, is parallel to the axis of the plunger.

The concept behind the invention can be further developed in a particularly simple manner if, in a distributor rotor having several pump plungers, or with respective pump plungers arranged oppositely in pairs, spill ports are associated only with one of the plungers.

Finally, according to a further feature of the invention, it is provided that each pump plunger provided with a control edge has a projection directed towards the working chamber, of which the diameter is only slightly smaller than that of the radial bore in the rotor. By the provision of such projections pointing into the working chamber the dead space in the pump can be kept small in a simple manner.

The invention is further explained in the following in conjunction with some embodiments by way of example.

Figure 1 is a section through a fuel injection pump according to the invention, taken on the line I-I in Figure 2, Figure 2 is a partial section on the line II-II in Figure 1, Figure 3 and 4 show another embodiment by way of example, with the same sections as in Figures 1 and 2, Figure 5a is a detail from Figure 2, Figures 5b to 5d show different variants of the detail of Figure 5a; and Figure 6 is a stroke diagram of the pump plunger.

The fuel injection pump illustrated in Figs 1 and 2 has a distributor rotor 2 which is mounted for rotation in a bore 1' in the pump housing 1 and has an end portion 3 through which it is driven from the engine through a shaft 5 co-operating with a spigot 4.

Mounted in the end portion 3 of the rotor 2 which projects out of the housing 1 and which has a larger diameter than the portion 6 mounted in the bore 1' of the housing 1 there is a diametral bore 7 which is perpendicular to the axis 8 of the rotor 2. The bore 7 receives two opposed pump plungers 9 which, together with the bore 7 define a working chamber 10. Each pump plunger 9 has at that end of it which is furthest from the chamber 10 a shoe 12 guided in a radial slot 11 in the rotor 2 and carrying a roller 13. The rollers 13 co-operate with a circular cam ring 14 secured to a portion 15 of the housing. On the inner surface 16 of the ring 14 there are the cams 17 of which the contour is shown in Figure 2.It will be understood that it is possible within the scope of the invention to select a different number of cams or a different cam profile, and there could even just be a single plunger in a single radial bore.

Present in the portion 6 of the rotor and extending from the working chamber 10 there is an axial bore 18 which, at that end of it furthest from the chamber 10, communicates with a radial distributing bore 19. This distributing bore 19, according to the instantaneous angular position of the rotor 2, leads into one of a number of delivery bores 20 distributed around the periphery of the housing 1 and in their turn leading to the respective injection nozzles, not illustrated, of the engine.

The bore 1' of the pump housing has an annular groove 21 which is connected to the fuel supply passage 22. A bore 23 connected to this groove 21 leads to a metering device 24 which incorporates a rotary valve 25 with inclined edges 26 by means of which the necessary quantity of fuel is delivered through a further radial bore 33 in the distributor rotor 2 to the axial bore 18.

The working chamber 10 of the rotor 2 has at least one spill passage 27 of which the outlet port 28 is traversed in the region of the maximum stroke by the control edge 29 of the pump plunger 9 when it exceeds a predetermined stroke level S S1. When it reaches the stroke level S2 the whole of the cross section of the port 28 through which fuel can spill away into the low pressure region of the pump is uncovered. When the quantities of fuel to be injected are small the control edge 29 of the pump plunger 9 does not reach the stroke level S1 and the pump behaves in the normal manner.

With an increasing quantity of fuel delivered the pump plunger is lifted beyond the level S1 so that in the subsequent delivery stroke effected by the cam 17 a portion of the fuel at the beginning of the delivery is allowed to escape through the spill passage 27, with the result that the injection does not start suddenly and the generation of noise at high delivery quantities is reduced.

Here the control edge 29 is formed by a shoulder on the pump plunger 9 defining a projection 30 of slightly smaller diameter than the rest of the plunger and of the bore 7. It will be understood that it would alternatively be possible to form the end face of the plunger, facing the chamber 10, as the control edge, the shoulder then being omitted.

In the following embodiments by way of example the respective corresponding components have been given the same reference numerals.

In Figures 3 and 4 there is illustrated a distributor rotor of a fuel injection pump having two mutually perpendicular diametral bores 7 forming in effect four radial bores. Each of the bores 7 contains two pump plungers which co-operate with the cam ring 14 around the rotor 2 in the manner described above. The plungers 9 which are shown moving vertically as viewed in Figure 4 each have a control edge 29 of which the lower one as viewed in the drawing co-operates with a spill passage 27. It will be understood that it would also be possible within the scope of the invention to provide the horizontally lying plungers 9 with control edges as well ad to associate spill passages with one or both of these plungers.

The port 28 of the spill passage 27 is illustrated in detail in Fig. 5a, and it is shown in a section corresponding to Fig. 2 or 4. For greater clarity the plunger guided in the bore 7 has been omitted and has been indicatedPsimply by its central axis 31. The shoe guided in the radial slot 11 in the rotor 2 has also been omitted. The stroke level indicated at S1 defines the start of delivery for small delivery quantities, where no fuel is to be allowed to escape, and that shown at S2 defines the start of delivery for large delivery .quantities, in which case some of the fuel is allowed to escape at the start of injection.

Figs 5b to 5d show variants on the spill ports.

In particular in Fig. 5b are shown several ports 28, controlled simultaneously and distributed around the periphery of the bore 7. The passages 27 leading away from the spill ports could be directed to the outside radially or equally well parallel to one another.

As shown in Fig. Sc it is also possible to provide several spill passages 27 which are staggered or offset in the direction of the stroke, and thereby to increase the region between S1 and 82. 'However the same effect can also be achieved by the variant shown in Fig. 5b, if one provides the pump plunger with an inclined control edge.

In the embodiment shown in Fig. 5d the port 28' has a rectangular cross-section with its longer side 32 parallel to the axis 31 of the plunger. It will be understood that it is possible to provide spill ports of other cross-sections, for example square or triangular, to obtain other spill characteristics.

Figure 6 shows the stroke diagram of the pump plunger of an injection pump according to the invention. On the abscissa line of the right hand graph is the cam angle a, and on the common ordinate is shown the stroke H of the pump plunger, the end of delivery being indicated at D . From 2 to S e 2 1 the control edge of the plunger is moving past the spill port, the respective free surface of the outlet opening effective for allowing the escape of fuel being evident from the left hand diagram, on the abscissa of which is shown the effective area A of the spill port, and A shows the area reached when it is fully open.

m The curve shown in the left hand diagram arises for example when a spill port of the kind shown in Fig. 5a is used. The variants shown in Figs 5b to 5d produce correspondingly different shapes of curve, for example with the version shown in 5d there would be a linear relationship between the stroke and the surface area exposed.

Claims (6)

1. A distributor-type fuel injection pump for internal combustion engines with an engine-driven distributor rotor mounted in the pump housing and having at least one pump plunger arranged in a radial bore in the rotor, the end of the plunger which is opposite the working chamber of the pump co-operating with a cam ring around the rotor, in which the radial bore has at least one spill passage in the region of maximum stroke of the plunger, the outlet port from the working chamber to the passage being uncovered by a control edge on the plunger at the start of the delivery stroke when the plunger exceeds a predetermined stroke.

2. A fuel injection pump according to claim 1 in which several spill passage. are provided associated with a given plunger, of which the ports are offset or staggered in the direction of the stroke in relation to the control edge of the pump plunger.

3. A fuelinjection pump according to claim 1 or 2 in which the port of the spill passage has a rectangular cross-section of which the longer edge, if any, lies parallel to the axis of the plunger.

4. A fuel injection pump according to any one of claims 1 to 3 in which, in a distributor rotor having several plungers, or with respective plungers in opposed pairs, there is a spill passage or passages associated with only one of the plungers.

5. A fuel injection pump according to any one of claims 1 to 4 in which the or each plunger provided with a control edge has a projection which is directed into the working chamber and which has a diameter slightly smaller than that of the radial bore in the rotor.

6. A distributor-type injection pump for internal combustion engines, substantially as described with reference to the accompanying drawings.