GB2269210A

GB2269210A - Fuel injection pumps for internal combustion engines

Info

Publication number: GB2269210A
Application number: GB9315776A
Authority: GB
Inventors: Heinz Popp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-07-31
Filing date: 1993-07-30
Publication date: 1994-02-02
Anticipated expiration: 2013-07-30
Also published as: GB9315776D0; DE4225363A1; GB2269210B; JPH06159191A

Abstract

In a fuel injection pump having a pump piston (7) reciprocable in a cylindrical bore (5) by a cam acting on a roller tappet (15) of the piston to deliver fuel from a working chamber (11), the roller tappet (15) is guided in a housing bore (29) in a way which ensures that its angular position relative to the cam does not alter. To this end the pin (17) rotatably mounting the tappet roller (19) has a head piece (25) which is guided in a longitudinal groove (27) of circular segmental cross-section which is provided in the housing (1). The head piece (25) is of prismatic construction in an axial direction with a circular segmental cross section in the radial plane which is complementary with the groove (27). <IMAGE>

Description

2269210

DESCRIPTION FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES

The invention relates to fuel injection pumps for internal combustion engines.

In a fuel injection pump known from DE-OS39 10 794 Al, a separate fuel injection device is associated with each cylinder of the internal combustion engine to be supplied'. Each injection pump comprises a pump piston which is guided in a cylinder liner. The piston defines in the cylinder liner a pump working chamber which is connected to the injection point into the combustion chamber of the internal combustion engine. The piston is driven axially against the force of a return spring by a cam drive by way of a roller tappet. In the known fuel injection pump, in order reliably to fix the angular position of the roller tappet relative to the cam drive, a radially fitting pin is inserted into the housing of the internal combustion engine in such a way that it projects into the region of the bore guiding the roller tappet in the housing and engages a longitudinal groove in he roller tappet.

In the known fuel injection pump, the fixing of the angular position of the roller tappet has the disadvantage that the disposing of the fitting pin in the housing of the internal combustion engine requires -2an additional component, thus resulting in additional production and machining requirements on the housing in addition to the increased costs.

Moreover. constructions are already known from the general prior art of fuel injection pumps in which the roller tappet is secured against turning by guiding the roller pin, carrying the roller and disposed at right angles to the axis of the roller tappet, in an axial groove in the housing surrounding the roller tappet.

However, in fuel injection pumps which are inserted directly into the housing of the internal combustion engine and where the guide bore for the roller tappet in the housing of the internal combustion engine is not pre-machined during the manufacture of the housing, there is the disadvantage that a longitudinal groove serving as a means for preventing turning may only be produced in several working operations and by clamping the housing several times in addition to producing the guide bore of the roller tappet.

In accordance with the present invention there is provided a fuel injection pump for internal combustion engines, having a pump piston which is guided in a cylindrical bore of a cylinder liner inserted into a housing the pump piston defining a pump working -3chamber in the cylinder liner and being movable axially against a restoring force by a cam drive by way of a roller tappet which is guided in the housing and rolls on a track of a cam of the cam drive by means of a roller guided on a roller pin disposed at right angles to the axis of the roller tappet, wherein the roller tappet is fixed in its angular position relative to the cam of the cam drive by way of a grooved guide, and the means for fixing the roller tappet in its angular position is formed by a head piece of the roller pin, which head piece extends out of the roller tappet and has a circular segmental cross section in a sectional plane at right angles to the axis of the roller tappet and engages a longitudinal groove in the housing which groove extends parallel to the axis of the roller tappet and has a cross section corresponding to the cross section of the head piece. This has the advantage that the longitudinal groove in the guide bore of the roller tappet and serving as a means for fixing the angular position of the roller tappet may be produced in the housing together with the guide bore in only two working operations and by clamping the housing only once. The shape of the head piece, extending into the longitudinal groove, of the roller pin at the same time makes it possible to guide the roller pin in the longitudinal groove in a -4virtually play-free manner, so that the advantage of simple manufacture can be combined with the reliable fixing of the roller tappet in its angular position.

Preferably. the head piece extends in the form of a prism in the axial direction of the roller tappet beyond the diameter of the roller pin, wherein an axial boundary, facing the pump working chamber, of the head piece is a horizontal surface, and an axial boundary remote from the pump working chamber has an oblique surface which slopes relative to the axis of the roller tappet and by which the wall thickness of the head piece of the roller pin tapers in an axial direction towards the cam drive. The bevelled lower end face of the end of the roller pin which extends into the longitudinal groove and which, is of prismatic construction, makes it possible to insert the preassembled roller tappet into the guide bore in a simple manner and at the same time to insert the head piece of the roller pin extending out of the roller tappet into the longitudinal groove of the guide bore.

Preferably the centre point of the circle forming the circular segment lies in the surface of the bore which guides the roller tappet in the housing.

By way of example only a specific embodiment of the present invention will now be described with -5reference to the accompanying drawings, in which:Figure 1 is a cross sectional view through the fuel injection pump constructed in accordance with the invention in which the arrangement of the roller tappet and the manner in which it is fixed in its angularposition in the guide bore in the housing of an internal combustion engine are shown; Figure 2 is an end elevation of an enlarged portion of Figure 1 showing the fixing of the roller tappet in its angular position: and Figure 3 is a cross sectional view through the housing of the internal combustion engine on a level with the roller tappet guide of Figure 1.

Figure 1 shows a portion of an engine housing 1 of an internal combustion engine in the region of a fuel injection pump fitted into a stepped housing bore 2. This fuel injection pump comprises a pump body 3 which forms a cylinder liner and which has a blind cylindrical bore 5 in which is sealingly guided a pump piston 7 whose end face 9 defines a pump working chamber 11 in the cylindrical bore 5. The pump working chamber 11 is connected by way of a fuel line 12 to an injection point (not shown) in the combustion chamber of the internal combustion engine to be supplied. and by way of a control valve to a lowpressure chamber carrying fuel. A fuel injection pump -6comprising a pump body 3 and a pump piston 7 being associated with each cylinder of the internal combustion engine.

The pump piston 7 is driven against the force of a return spring 13 by a cam drive of the internal combustion engine. For this purpose. the end of the pump piston 7 remote from the pump working chamber is connected to a cylindrical roller tappet 15 which is of hollow cylindrical construction towards the side of the pump piston 7 and which forms a sliding apron 29 and which, by means of a roller 19 mounted on a roller pin 17 disposed in the roller tappet 15, runs on a cam of a camshaft (not shown) driven by the internal combustion engine. During its downward movement corresponding to the suction stroke. the pump piston 7 is held in abutment against the roller tappet 15 and the latter is held in abutment against the camshaft by the return spring 13, disposed between the pump body 3 and the roller tappet 15, by way of a spring abutment plate 21 whose periphery is guided on the inner wall of the sliding apron 29 and which overlaps a plunger 23 of the pump piston 7.

In order to reliably fix the roller tappet 15 in its angular position relative to the camshaft (not shown), a head piece 25, extending out of the roller tappet 15, of the roller pin 17 is guided in a -7longitudinal groove 27, extending parallel to the axis of the roller tappet, in the portion 29 of the housing bore 2 guiding the roller tappet 15. For this purpose, the head piece 25 of the roller pin 17 has a circular segmental cross section which lies in a radial section through the roller tappet 15 and by which the head piece is guided in the longitudinal groove 27 which also has a circular segmental cross section. The end faces of the head piece 25, extending out of the roller tappet 15, of the roller pin 17 extend beyond the diameter of the roller pin 17, wherein the upper end face 31 facing the pump working chamber 11 extends horizontally, while the lower end face 33 remote from the pump working chamber 11 is bevelled, and the wall thickness of the head piece 25 of the roller pin 17 tapers, at the side facing the longitudinal groove 27. from the centre axis of the head piece towards the lower surface 33 of the head piece, so that the head piece 25 has the shape of a prism. Figure 2 shows the angular position of the roller tappet 15 fixed by way of the head piece 25 of the roller pin 17 in an end elevation which is limited to showing the components material to the Invention. The outer surface, directed towards the housing bore portion 29. of the head piece 25 of the roller pin 17 slides in the longitudinal groove 27 of -8the housing bore portion 29, the head piece 25 being flattened relative to the remaining part of the roller pin 17.

The position and the contour of the longitudinal groove 27 in the housing bore portion 29 are shown in the cross section, shown in Figure 3, through the pump housing above the roller tappet 15. The centre point of the radius of the circle which forms the cross section of the longitudinal groove 27 lies in the surface of the housing bore portion 29 forming the roller tappet guide, whereby a maximum effective surface between the head piece 25 of the roller pin 17 and the longitudinal groove 27 is obtained. Furthermore, this arrangement makes inexpensive manufacture possible if the housing bore portion 29 is produced after the production of a bore of which a portion of the surface forms the longitudinal groove 27.

Claims

-gCLAIMS

1. A fuel injection pump for internal combustion engines, having a pump piston which is guided in a cylindrical bore of a cylinder liner inserted into a housing, the pump piston defining a pump working chamber in the cylinder liner and being, movable axially against a restoring force by a cam drive by way of a roller tappet which is guided in the housing and rolls on a track of a cam of the cam drive by means of a roller guided on a roller pin disposed at right angles to the axis of the roller tappet, wherein the roller tappet is fixed in its angular position relative to the cam of the cam drive by way of a grooved guide, and the means for fixing the roller tappet in its angular position is formed by a head piece of the roller pin, which head piece extends out of the roller tappet and has a circular segmental cross section in a sectional plane at right angles to the axis of the roller tappet and engages a longitudinal groove in the housing which groove extends parallel to the axis of the roller tappet and has a cross section corresponding to the cross section of the head piece.

2. A fuel injection pump as claimed in claim 1, wherein the head piece extends in the form of a prism in the axial direction of the roller tappet beyond the -10diameter of the roller pin, wherein an axial boundary, facing the pump working chamber. of the head piece is a horizontal surface, and an axial boundary remote from the pump working chamber has an oblique surface which slopes relative to the axis of the roller tappet and by which the wall thickness of the head piece of the roller pin tapers in an axial direction towards the cam drive.

3. A fuel injection pump as claimed in claims 1 and 2, wherein the centre point of the circle forming the circular segment lies in the surface of the bore which guides the roller tappet in the housing.

4. A fuel injection pump constructed and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

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