Fluid pump assembly

Abstract

A fluid pump assembly comprising a driven cam and a reciprocating member reciprocal within a bore provided in a pump housing as the cam is driven, in use, to cause pressurisation of fluid within a pump chamber. The pump assembly further comprises an interface between the cam and the reciprocating member, for example in the form of bevelled surfaces of the cam and the reciprocating member, which serve to drive the reciprocating member (i) to translate in a first, axial direction within the bore and (ii) to rotate within the bore in a second, rotational direction. An optional feature of the fluid pump assembly is that the pump housing defines a bearing for the cam which is provided with a recess to define a region of weakness to allow the bearing to deflect, in use, thereby to provide an increased lubrication volume between the cam and the bearing. The reciprocating member may take the form of a tappet which cooperates with a pumping plunger to pressurise fluid within the pump chamber.

Description

TECHNICAL FIELD[0001]The invention relates to a fluid pump assembly and, in particular, but not exclusively, to a pump assembly for fuel. The pump assembly is suitable for use in a common rail fuel injection system for supplying high pressure fuel to a compression ignition (diesel) internal combustion engine. In particular, the invention has application in a pump assembly of the type in which an engine driven cam imparts reciprocating, pumping motion to a drive member.BACKGROUND TO THE INVENTION[0002]One known common rail fuel pump is of radial pump design and includes three pumping plungers arranged at equi-angularly spaced locations around an engine driven cam—such a pump is described in, for example, WO 2004 / 104409. In this pump, each plunger is mounted within a plunger bore provided in a pump head mounted to a main pump housing. As the cam is driven in use, the plungers are caused to reciprocate within their bores in a phased, cyclical manner. As the plungers reciprocate, each c...

AI Technical Summary

Benefits of technology

[0010]In one embodiment, the interface means includes a bevelled face of the reciprocating member and a correspondingly bevelled face of the cam which cooperate so as to cause axial and rotational motion of the reciprocating member as the cam rotates. As the reciprocating member rotates about its own axis within its bore, the constant relative velocity between the parts aids lubrication so as to reduce the effects of wear due to friction.

[0013]The cam may be provided with a low friction coating, for example a soft phosphate or PTFE coating, which deforms, in use, to the profile of the radial bearing. The profile of the coating on the cam being matched with the profile of the radial bearing provides good conditions for promotion of a hydrodynamic film.

[0014]The axial bearing may be provided with at least one recess to provide a volume for receiving lubricating fluid. The recess therefore provides for a supply of lubricating fluid to the axial bearing to aid lubrication between the rotating cam and the axial bearing.

[0016]In one particular embodiment, the axial bearing is provided with a region of weakness to allow the axial bearing to deflect, in use, thereby to create an increased volume for lubricating fluid between the axial bearing and the facing surface of the cam. Deflection of the axial bearing in this way opens up an enlarged gap between the cam and the axial bearing to encourage lubricating fluid to be drawn between the parts. Optionally, the region of weakness is defined by forming a recess in the bearing.

[0023]According to a third aspect of the invention, a fluid pump assembly comprises a driven cam and a reciprocating member reciprocal within a bore provided in a pump housing as the cam is driven, in use, so as to cause pressurisation of fluid within a pump chamber. The pump housing defines a bearing for the cam which is provided with a region of weakness to allow the bearing to deflect, in use, thereby to provide an increased lubrication volume between the cam and the bearing. Optionally, it is an axial bearing defined by the pump housing that is provided with the region of weakness. Such an arrangement provides the aforementioned advantages for lubrication between the rotating cam and the axial bearing.

Problems solved by technology

A fuel pump of radial pump design necessarily occupies a relatively high volume and, for some engine applications, this can be a disadvantage.

Furthermore, the tappets are prone to wear due to the side loads experienced as they reciprocate, in use, and there can be significant damage to the tappet face that cooperates with the cam rider due to inadequate lubrication.

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