GB2294096A

GB2294096A - Fuel-injection pump

Info

Publication number: GB2294096A
Application number: GB9520868A
Authority: GB
Inventors: Siegfried Haberland
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1994-10-14
Filing date: 1995-10-12
Publication date: 1996-04-17
Anticipated expiration: 2015-10-12
Also published as: FR2725757A1; JPH08177669A; DE4436733A1; GB9520868D0; GB2294096B; FR2725757B1

Description

- 1 DESCRIPTION FUEL-INJECTION PUMP

2294096 The invention proceeds from a fuel-injection pump of the distributor type according to the pre-characterizing clause of Patent Claim 1. Such a fuel- injection pump is known, for example, from DE-A-3,439,497. The annular slide of this known pump lies freely in the spill space and is subjected to pressure waves which occur in this spill space as a result of the drive movement of the pump piston. In particular, the cam disc executes a constantly reciprocating movement in the axial direction is of the pump piston and at the same time generates pressure surges which act axially on the annular slide. The result of this is that the annular slide can be displaced axially on the pump piston within the movement play which the governor possesses. This play exists, on the one hand, at the connection point between the actuator and annular slide and, on the other hand, also in the remaining parts of the governor. It is unimportant whether this governor is designed as a mechanical speed governor or is an electromechanically driven speed governor. On account of these pressure waves, the annular slide may also execute non- systematic movements, that is to say movements which differ from feed stroke to feed stroke of the pump piston, which can lead to injection- quantity dispersions. Furthermore, the connecting part between the actuator and annular slide is also subjected to considerable mechanical load, particularly by the pressure waves which are triggered by the cam disc.

In contrast to this, the advantage of the device according to the invention, having the characterizing is features of Patent Claim 1, is that the annular slide is protected f rom pressure waves occurring in the spill space. Nevertheless, sufficiently open cross-sections remain between the space enclosed in the pot-shaped part and the spill space, on the one hand not to impede the movement of the annular slide hydraulically and, on the other hand, to transfer the fuel spilled per pump-piston feed stroke into the spill space without reaction on the annular slide.

Advantageous possibilities of fixing the potshaped part within the injection-pump housing by utilizing already existing components are afforded according to the subclaims.

An exemplary embodiment of the invention is represented in the drawing and is explained in more detail in the following descriptions. Figure 1 shows in section a fuel-injection pump according to the prior art, Figure 2 shows in section the detail of construction of the fuel-injection pump which is essential to the invention, and Figure 3 shows a section through the exemplary embodiment according to the invention, as shown in Figure 2, along the line III-III.

Figure 1 shows a part section through a distributor fuel-injection pump of the reciprocating type. Inserted f ixedly in the housing 1 of this pump is a cylinder bush 2 receiving a pump cylinder 3, in which a pump piston 4 limits a pump working space 5. The pump piston is driven in a reciprocating and, at the same time, rotating manner. It projects at its end facing away from the pump working space 5 into a spill space 7 and there rests with a foot 8 on the end face of a cam disc 9. The foot 8 is coupled rotationally to the cam disc in a way not shown further and is held axially on the cam disc 9-by a plurality of springs 10. The springs 10 are supported via a spring plate 11 on one end wall 12 of the 1 3 housing surrounding the spill space 7 and, on the other hand, load a spring bridge 14 which is supported on a shoulder 15, facing the pump working space, on the foot 8 of the pump piston. The pretensioned spring thus presses via the pump piston onto the cam disc which is, in turn, thereby held axially on rollers 17 which are mounted within a roller ring 18. On the same side as the rollers 17, the cam disc 9 has a cam track 19, over which it runs in the event of a rotating drive via the rollers 17 and at the same time executes a reciprocating stroke movement in addition to its rotational movement. The drive of the cam disc takes place via a coupling 20 from a drive shaft 21 synchronously with the speed of the associated internal-combustion engine.

The spring plate 11 has a guide bolt 23 passing through it or is integrally part of the latter. The guide bolt is inserted, on the far side of the spring plate 11, into the housing 1 of the fuel-injection pump, extends coaxially relative to the compression spring 10 and engages at its free end 24 into a recess 25 of the spring bridge and thus secures the spring bridge against rotation and consequently keeps the compression spring in its position axis-parallel to the pump-piston axis.

Furthermore, there is arranged on the part of the pump piston 4 projecting from the pump cylinder 3 an annular slide 27 which is displaceable and rotatable by means of its inner bore 28 on the cylindrical surface with a sealing fit. At the same time, the position of the annular slide is determined by an actuator 29 which engages via a head 30 into a corresponding recess 31 in the cylindrical surface of the essentially circularcylindrical annular slide. The actuator 29 belongs to a governor which can be a conventional mechanical, a hydraulic or even an electromagnetically driven governor.

This is not shown in more detail here.

The annular slide controls a relief duct 32 which, starting from the end face 33 located on the same side as the pump working space, extends coaxially in the pump piston and then merges into a radial bore 34 which opens out on the cylindrical surface 35 of the pump piston in the working region of the annular slide 27. There leads off from the longitudinal bore of the relief duct 32 a transverse bore 37, of which the mouth on the cylindrical surface of the pump piston serves as a distributor orifice and which, in the course of the rotation of the pump piston, comes successively, during its individual feed strokes, in each case into connection with one of a plurality of injection conduits 39 distri- buted uniformly on the circumference of the pump cylinder 3. These lead to injection valves, not shown further, on the associated internalcombustion engine. The pump piston executes its suction stroke under the effect of compression springs 10, of which only one was described above and of which also only one is shown in the drawing. The compression springs are preferably arranged distributed at equal angular intervals around the pump piston, in such a way that it is possible for the actuator 29 to have access to the annular slide and a loading of the cam disc which is free of tilting moment is achieved.

During the suction stroke of the pump piston 4, as a result of a corresponding rotation of the pump piston, one of a plurality of suction grooves 41 starting on the end face 33 of the pump piston is connected to a suction conduit 42 which opens into the pump cylinder in the region of these and which is itself supplied with fuel from the spill space 7. The supply of the spill space conventionally takes place by means of a pilot feed pump not shown further here. After the filling of the pump working space or the end of the suction stroke, the pump piston has rotated to such an extent that the connection between the suction grooves 41 and suction conduit 42 is broken, so that, as a result, the pump piston can execute a feed stroke, and the pump working space can be put under pressure. This takes place as soon as the transverse bore 37 is closed by the annular slide, and only until the transverse bore 37 emerges from the annular slide again. In the intermediate region, fuel feed takes place under high pressure in each case to an injection conduit controlled by the distributor orifice.

After the opening of the transverse bore, the pump working space is relieved for the remaining stroke to be executed by the pump piston and injection is consequently interrupted.

The control of injection depends essentially on the position of the annular slide which can influence both the injection quantity and the start of injection. An exact setting by means of the governor mentioned therefore follows. However, if the annular slide is exposed to pulsating, uncontrollable forces, it can also execute, over and above the set movement, additional movements which adversely influence the injectionquantity control result. Quantity dispersions in the case of different feed strokes then occur disadvantageously, such that, on account of the differing quantity introduced, the associated internal - combur, t ion engine runs out of true and, overall, fuel consumption and emissions may rise.

In an embodiment according to the invention, therefore, according to Figure 2 the annular slide is screened off from pressure waves which occur in the spill space and which run through this. For this purpose, there is provided a pot-shaped part 44 which has a cylindrical surface 45 surrounding the annular slide spaciously according to its possible axial displacement and which has a bottom 46 located opposite the lower end face of the annular slide, with a central recess 47, through which the pump piston can be guided. On this end face confronting the end wall 12 of the housing, the potshaped part has two radially projecting tabs 48 which are located diametrically opposite one another according to the arrangement of the compression springs 10 within the spill space 7. These tabs form a flange which comes to bear on the spring plates 11 of the compression springs 10 and which is held on these in each case by the pretensioned compression springs, the flange in each case having a passage orifice 49 for the passage of the guide bolt 23.

The diameter of the pot-shaped part is coordinated with the diameter of the annular slide and, in the exemplary embodiment, is also essentially identical to the diameter of the cylinder bush 2. It is essential that, in the installed state, the pot-shaped part encloses, between its bottom 46 and the end wall 12 or the end face of the cylinder bush 2, a space 50 which is uncoupled from the spill space 7 by means of overflow cross-sections. The axially running pressure waves, which are generated during the axial movement of the cam disc 9 and which would otherwise have struck the annular slide 27, are now intercepted by the pot-shaped part. Also other reflecting pressure waves, which could act from other sides on the slide, particularly to influence its axial position, are reliably kept away by means of this pot-shaped part. The overflow cross-sections, for example at the location of the central recess between the piston and the edge of the recess and in the region of the end wall 12, are made sufficiently large to transfer the fuel quantity spilled into the space 50 into the control space 7 at the end of the effective feed stroke of the pump piston. Furthermore, as inferred from the section according to Figure 3, there is provided in the cylindrical surface 35 a slot-shaped recess 51, through which the actuator 29 can engage with its head 30, for the axial displacement of the annular slide on the pump piston. At this location too, overflow cross-sections which have an uncoupling effect are available.

- 7

Claims

1. Fuel-injection pump with a pump piston which encloses a pump working space in a pump cylinder and is driven in a reciprocating and, at the same time, rotating manner by a cam drive having a cam disc and which, on a part of the pump piston projecting out of the pump cylinder into a spill space and coupled there to the cam disc via a foot ofthe pump piston / has an annular slide which is displace able and rotatable on the cylindrical surface of the pump piston relative to the latter with a sealing fit and which is adjustable relative to the pump piston by means of an actuator -.engaging an the an.nular slide, of a governor controlling the injection quantity per feed stroke of the pump piston, in such a way that, in the event of a feed stroke of the pump piston reducing the volume of the working space a relief duct opening on the cylindrical surface of the pump piston via a radial bore and belonging to the pump working space is opened sooner or later by a control edge located on the annular slide J characterized in that there is provided in the spill space a pot-shaped constructional part having in its bottom a central recess, through which the part of the pump piston projecting into the spill space is guided, in such a way that the cylindrical surface of the pot-shaped part surrounds the annular slide circumferentially and with its bottom sur- rounds the annular slide from its side facing the cam drive and extends with its end edge to the pump housing surrounding the exit of the pump piston, thereby forming a space receiving the annular slide, between the pot-shaped part and the pump housing

2.

Fuel-injection pump according to Claim 1 ' characterized in that there is formed on the edge of the pot-shaped part at least one flange having a passage orifice for a fastening element via which the pot-shaped part is fastened to the pump housing

3. Fuel-injection pump according to Claim 2, charac terized in that there serve as fastening element at least two axial guide bolts which each have a spring plate which bears on the pump housing and on which comes to bear in each case a compression spring which is supported at the other end on a spring bridge supported on the foot of the pump piston and common to the compression springs, and the flange is clamped between the compression springs and the spring plates

4. Fuel-injection pump according to Claim 3, charac terized in that the pot-shaped part has as flanges, according to the number of compression springs present, at least two tabs which are located dia metrically opposite one another.

5. Fuel-injection pump according to Claims 1 to 4, characterized in that a passage orifice for leading the actuator through to the annular slide is provided in the cylindrical surface of the pot shaped part

6. Fuel injection system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Amendments to the claims have been filed as follows 1. Fuel-injection pump with a pump piston which encloses a pump working space in a pump cylinder and is driven in a reciprocating and, at the same time, rotating manner by a can drive having a cam disc and which, on a part of the pump piston projecting out of the pump cylinder into a spill space and coupled there to the cam disc via a foot of the pump piston. has an annular slide which is disiDlace able and rotatable on the cylindrical surface of the pump piston relative to the latter with a sealing fit and which is adjustable relative to the pump piston by means of an actuator -, engaging on theannular slide, of a governor controlling the injection quantity per feed stroke of the pump piston, in such a way that, in the event of a feed stroke of the pump piston reducing the volume of the working space a relief duct opening on the cylindrical surface of the pump piston via a radial bore and belonging to the pump working space is opened sooner or later by a control edge located on the annular slide I characterized in that there is provided in the spill space a pot-shaped constructional part having in its bottom a central recess, through which the part of the pump piston projecting into the spill space is guided, in such a way that the cylindrical surface of the pot-shaped part surrounds the annular slide circumferentially and with its bottom Sur rounds the annular slide from its side facing the ca-m drive and extends with its end edge to the pump housing surrounding the exit of the pump piston, thereby forming a space receiving the annular slide, between the pot-shaped part and the pump housing 2. Fuel-injection Pump according to Claim 1, characterized in that there is formed on the edge of the pot-shaped part at least one flange having a passage orifice for a fastening element via which the pot-shaped part is fastened to the pump housing 3. Fuel-injection pump according to Claim 2, charac terized in that there serve as fastening elements at least two axial guide bolts which each have a spring plate which bears on the pump housing and on which comes to bear in each case a compression spring which is supported at the other end on a spring bridge supported on the foot of the pump piston and common to the compression springs. and the flange is clamped between the compression springs and the spring plates 4. Fuel-injection pump according to Claim 3, charac terized in that the pot-shaped part has as flanges, according to the number of compression springs present, at least two tabs which are located diametrically opposite one another.