GB2333809A

GB2333809A - Bearing mounting for swash plate.

Info

Publication number: GB2333809A
Application number: GB9801356A
Authority: GB
Inventors: Roderick Howell Spurry
Original assignee: Sauer Sundstrand Ltd; Sauer Sundstrand SpA
Current assignee: Sauer Danfoss Swindon Ltd; Sauer Sundstrand SpA
Priority date: 1998-01-23
Filing date: 1998-01-23
Publication date: 1999-08-04
Anticipated expiration: 2018-01-23
Also published as: GB2333809B; GB9801356D0

Abstract

A variable displacement axial piston pump has a swash plate 20, pivotally mounted by a pair of diametrically opposed trunnions 26 in a housing 2, with a variable angle of inclination to vary the displacement of pistons (16 Fig. 1) in a rotary cylinder block (12). The swash plate mounting comprises a bearing 24 for each trunnion 26, retained as a snap fit in an arcuate housing recess 4 of more than 180‹. The opening of each recess 4 faces towards the cylinder block (direction B). The bearings are fitted by local distortion of a small amount of over centre material which then retains the bearings, the load in direction. A being greater than B in use. The angle of inclination is varied by co-operation between a spring (34) and a fluid actuated piston (30).

Description

TITLE Trunnion Retention for Variable Displacement Axial Piston Pump DESCRIPTION Inventive Field: The invention relates to variable displacement axial piston pumps, and in particular to the means for retaining the trunnion bearings of the swash plate of such a pump within the pump housing.

Background Art: A typical variable displacement axial piston pump comprises a cylinder block rotatably mounted on a drive shaft. Disposed within the cylinder block is a plurality of cylinders. These cylinders are substantially parallel to and arranged at the same radial distance from the drive shaft. All of the cylinders open to one of the end faces of the cylinder block. A piston is inserted into each of these openings to reciprocate with the cylinder. A slipper is attached to the outer end of each piston.

As the drive shaft rotates, each slipper circumscribes a circular path about a swash plate. If the swash plate is inclined to the normal of the axial plane, the volume within each cylinder varies as the cylinder block rotates.

Consequently the flow of the working fluid within each cylinder fluctuates. Generally, high pressure and low pressure take-off ports are provided in the pump housing.

Each port is connected to and disconnected from each of the cylinders during a single rotation of the cylinder block.

Altering the angle of the swash plate varies the inclination of the plane on which the slippers rotate and therefore the displacement of the pump may be varied.

To vary the output flow from such a pump, it is necessary to change the inclination of the swash plate. This is generally achieved by two trunnions on the swash plate being received in two bearings within the pump housing to permit rotation of the plate about a trunnion axis.

Conventionally, these bearings have been retained in the housing of the pump by full diameter recesses machined therein or by retaining straps mounted thereon.

The cost of assembling the swash plate into the retention means along with the provision of retention means (full diameter recesses or retaining straps) represents a significant expense in the manufacture of variable displacement axial piston pumps.

The Invention The invention provides a variable displacement axial piston pump in which a swash plate, pivotally mounted by a pair of diametrically opposed mounting trunnions in a housing, has a variable angle of presentation to vary the displacement of one or more pistons in a rotary cylinder block and thereby to vary the pump flow, wherein the swash plate pivotal mounting comprises a bearing for each mounting trunnion, retained as a snap fit in an arcuate recess of more than 1800 in the housing, the opening of each arcuate recess facing towards the cylinder block.

It is preferred that the bearings are rolling element bearings, for example roller or ball bearings.

Alternatively, plain bushings may be used as bearings for the trunnions.

The snapping of the bearings into their arcuate recesses is accompanied by temporary distortion of the local material of the housing and/or bearings but once the swash plate is in position it will not move axially towards the cylinder block during assembly or in use.

Drawings Figure 1 illustrates a variable displacement axial piston pump which could be a prior art pump or a pump according to the invention, with the swash plate at maximum inclination; Figure 2 illustrates an axial section through a pump according to the invention, showing the swash plate and the drive shaft along the trunnion axis; Figure 3 is a section taken along the line P-P of Figure 2.

As shown in Figure 1, a typical variable displacement axial piston pump 1 comprises a cylinder block 12 rotatably mounted on and driven by a drive shaft 10.

Formed in the cylinder block 12 is a plurality of cylinders 14. These cylinders 14 are substantially parallel to and arranged at the same radial distance from the drive shaft 10. Each cylinder 14 houses a piston 16 which extends from an open end of the cylinder and terminates in a slipper 18.

On rotation of the drive shaft 10 each slipper 18 circumscribes a circular path around a swash plate 20 which is substantially circular in shape, has a central hole 22 through which the drive shaft 10 passes, and is formed with a pair of diametrically opposed mounting trunnions 26 (Fig. 2). The swash plate can rotate on its mounting trunnions about two bearings 24. The trunnion axis may be offset to drive line axis so as to ensure that the reactional forces imposed on the swash plate 20, resulting from the pumping action, move the swash plate to maximum possible inclination.

Altering the angle of the swash plate 20 varies the inclination of the plane on which the slippers 18 rotate and therefore the displacement of the pump 1 may be varied.

The angle of inclination of the swash plate 20 is controlled by a control piston 30. The control piston 30 is limited in the distance through which it can travel. If no pressure is applied to the control piston 30, the pump 1 remains at maximum angle. When the system controls require the pump flow to be reduced, pressure is applied to the control piston 30, which decreases the swash plate 20 inclination.

A compression spring 34 located on the opposing side of the swash plate 30 to the control piston 30 provides the necessary reactional support to move the swash plate 20 to full angle if no other forces are applied, for example when the system is initially started.

As illustrated in Figures 2 and 3, the trunnions 26 of the swash plate are supported by the bearings 24 retained in the pump housing 2. During development, the Applicant found that the vast majority of loads on the swash plate 20 are in the direction labelled A. It was therefore realized that no or little reactional support is required for forces in the B direction. A means sufficiently adequate for retaining the swash plate 20 in the housing 2 was thereby developed wherein retention is achieved by machining an annular recess 4 of slightly greater than 1800 into the pump housing 2 as shown in Figure 3. This recess 4 commences at point 7 and terminates at point 9.

The amount of over-centre material is just sufficient to enable the bearings 24 of the swash plate 20 to be snapped into position by temporary distortion of the local material while at the same time the retention is sufficient so that once in place the swash plate 20 will not move in the B direction during assembly or due to any transient loads in use.

Claims

CLAIMS 1. A variable displacement axial piston pump in which a swash plate, pivotally mounted by a pair of diametrically opposed mounting trunnions in a housing, has a variable angle of presentation to vary the displacement of one or more pistons in a rotary cylinder block and thereby to vary the pump outlet, wherein the swash plate pivotal mounting comprises a bearing for each mounting trunnion, retained as a snap fit in an arcuate recess of more than 1800 in the housing, the opening of each arcuate recess facing towards the cylinder block.
2. A variable displacement axial piston pump according to claim 1, wherein the bearings are rolling element bearings.
3. A variable displacement axial piston pump according to claim 1, wherein the bearings are plain bushings.
4. A variable displacement axial piston pump as hereinbefore described with reference to the drawings.