GB2304829A

GB2304829A - Fuel-injection pump for internal combustion engines

Info

Publication number: GB2304829A
Application number: GB9616064A
Authority: GB
Inventors: Peter Traub; Kasim-Melih Hamutcu; Steffen Berns; Sieghart Maier; Karsten Schneider; Markus Egger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-09-02
Filing date: 1996-07-31
Publication date: 1997-03-26
Anticipated expiration: 2016-07-31
Also published as: DE29514106U1; JP3850928B2; GB2304829B; JPH09105369A; GB9616064D0

Description

DESCRIPTION FUEL-INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES Prior Art The invention relates to a fuel injection pump for internal combustion engines according to the generic type of claim 1. In such a fuel injection pump known from DE-OS 24 21 100 a pump piston is guided in a cylinder bore of a cylinder liner and is driven by a cam drive axially in a reciprocating manner. The pump piston thus defines with one of its end faces a pump working chamber in the cylinder liner, into which working chamber a controllable control bore issues which emerges from a low pressure chamber full of fuel, and from which working chamber a high pressure injection line leads which is connected at the other end to an injection valve protruding into the combustion chamber of the internal combustion engine to be supplied. In order to control the delivery quantity the pump piston comprises a control recess on its outer surface, which is constantly connected to the pump working chamber and is defined by an inclined control edge, of which the passage over the control bore in the wall of the cylinder bore determines the termination of delivery. Thus by means of a rotation of the pump piston the moment at which the inclined control edge passes over the control bore can be set, for which purpose the pump piston is connected to a control sleeve In a rotationally locked manner. On this control sleeve, pushed onto the pump piston, a radially extending lever arm is disposed which protrudes with a spherical head provided at its free end into a groove of a control rod which extends perpendicular to the axis of the pump piston and is displaceable from the outside. The formation of the control rod on the known fuel injection pump has the disadvantage that in particular at the site of force transfer between the control rod and the lever arm of the control sleeve an increased danger of fracture occurs as a result of component stresses and oscillation stresses.

Advantages of the Invention In contrast, the fuel injection pump for internal combustion engines in accordance with the invention with the characterising features of claim 1 has the advantage that by the provision of an undercut on the base of the groove of the control rod an increased durability against fractures in the control rod can be achieved. Thus this constructive feature for increasing the strength of the control rod has the advantage over a possible change in material, dimensions, or surface treatment or an additional heat treatment, that the new groove geometry in accordance with the invention has no cost implications as it can be integrated into the punching tool. The improved groove -geometry leads to a clear reduction in the component stresses at the control rod and therefore to increased security against a fracture in the control rod. The undercut on the groove base is advantageously formed as an increase in cross section with respect to the groove in the region of the groove sides, wherein the transition surfaces between the base of the groove and the groove sides are formed as curved surfaces, preferably ellipses and radii.

Further advantages and advantageous embodiments of the subject matter of the invention are given in the description, the drawing and the claims.

Drawing An embodiment of the fuel injection pump for internal combustion engines in accordance with the invention is illustrated in the drawing and explained in more detail in the following description. Figure 1 illustrates a known fuel injection pump with a control rod engaging at the control sleeve of the pump piston and Figure 2 illustrates an enlarged cross-sectional view of the control rod with the formation in accordance with the invention of the groove receiving the lever arm of the control sleeve.

Description of the embodiment In the fuel injection pump for internal combustion engines illustrated in Figure 1 a pump piston s is guided in a cylinder bore 1 of a cylinder liner 3, defines a pump working chamber 9 in the cylinder liner 3 with one of its end faces 7, and is driven axially in a reciprocating manner by a cam drive 11 engaging at the end remote from the pump working chamber. For the purpose of filling or relieving the pump working chamber 9 of fuel the wall of the cylinder liner 3 comprises a control bore 13 which issues from a fuel-filled low pressure chamber 15 surrounding the cylinder liner 3 into the pump working chamber 9. In addition, a high pressure injection line 17 leads from the pump working chamber 9, issues at an injection valve, not illustrated in more detail, protruding into the combustion chamber of the internal combustion engine to be supplied, and has a pressure valve 19 inserted in it which opens in the direction towards the injection valve.

In order to control the delivery quantity the pump piston 5 comprises a control recess 21 in its outer surface, which is continuously connected by means of a longitudinal groove 23 to the pump working chamber 9 and is defined in the direction towards the pump working chamber 9 by an inclined control edge 25, of which the passage over the control bore 13 determines the termination of delivery in a manner known from the prior art. Thus by means of a rotation of the pump piston 5 the moment at which the inclined control edge 25 passes over the control bore 13 can be set and therewith the termination of delivery and the delivery quantity. In order to rotate the pump piston 5 a control sleeve 27 is disposed thereon, with which the pump piston 5 is connected in a rotationally locked manner by a piston lug 29 which engages in a corresponding formation on the control sleeve 27. The control sleeve 27 comprises a radially extending lever arm 31 at the free end of which a spherically shaped headpiece 33 is disposed, with which the lever arm 31 protrudes into a groove 35 of a control rod 37 which is preferably formed as an angle profile, wherein the groove 35 is incorporated in the horizontal control rod profile part 39. This control rod 37 disposed perpendicular to the axis of the pump piston 5 is thus displaceable from the outside in its longitudinal direction and comprises a number of grooves 35 corresponding to the number of pump pistons 5 to be displaced, the grooves being disposed in series one after another.

For improved strength in the control rod 37 in particular in the region of the groove 35, the groove 35 comprises, as shown in the enlarged detail of Figure 2, an undercut 41 outside the bearing surface of the head piece 33 of the lever arm 31 in the region of the base of the groove. This undercut 41 is thus formed on the base of the groove by a widening of cross section in the groove 35, wherein a linear region 43 of the groove base first passes via an elliptical region 45, preferably a quarter ellipse into a first radius 47 adjoined by a second oppositely curved radius 49 which forms the transition to the groove sides. Thus the radii 47, 49 are optimally adapted to each other in that the stress at the transition between the groove base and groove sides of the groove 35 can be minimised.

Claims

1. Fuel injection pump for internal combustion engines, with a pump piston driven by a cam drive axially in a reciprocating manner and guided in a cylinder bore of a cylinder liner, which pump piston defines with one of its end faces a pump working chamber and is connected in a rotationally locked manner to a control sleeve which comprises a lever arm directed radially outwards which protrudes with a headpiece disposed at its free end into a groove of a control rod, characterised in that the groove on the control rod comprises an undercut in the region of the groove base outside the bearing surface of the lever arm.

2. Fuel injection pump according to claim 1, characterised in that the undercut of the groove is disposed outside the guide region of the head piece of the lever arm and is formed by an increase in the cross-section of the groove in the region of the groove base, wherein the transition surfaces between the groove sides and the groove base are formed as curved surfaces.

3. Fuel injection pump according to claim 2, characterised in that firstly an elliptical region adjoins a linear region of the base of the groove and passes by means of at least one radius into the cylindrical wall of the groove sides.

4. Fuel injection pump according to claim 3, characterised in that the transition from the elliptical region into the region of the grooves sides of the groove is formed by two oppositely curved radii adjacent to each other.

5. Fuel injection pump according to claim 3, characterised in that the elliptical transition region is formed as a quarter ellipse.

6. Fuel injection pump according to claim 1, characterised in that the headpiece of the lever arm protruding into the groove of the control rod is formed as a sphere.

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