GB2064674A

GB2064674A - An Axial Piston Machine

Info

Publication number: GB2064674A
Application number: GB8037638A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-11-28
Filing date: 1980-11-24
Publication date: 1981-06-17
Also published as: GB2064674B; DE2947896A1; JPS5685579A

Abstract

An axial piston machine comprises a piston block 12 driven by a shaft 14 and in the axial bores 21 of which pistons 22 are sealingly slidingly guided. The ends of the pistons are urged by the force of springs 23 against a tilting yoke 29. The pivot point (C) of the tilting yoke is displaced - with respect to the axis of the shaft 14 - towards the upper dead centre and is displaced-with request to the plane A - A extending through the centres of the piston ball joints 26 - in an axial direction towards the piston block 12. This means that, due to the unequal lever arms, the piston forces acting on the tilting yoke produce an automatic tilting of the tilting yoke. It was previously necessary to provide a special spring for this purpose. The resetting of the tilting yoke 29 takes place, for example, through a pressure influenced piston 31. <IMAGE>

Description

SPECIFICATION An Axial Piston Machine The invention originates from an axial piston machine according to the preamable to the main claim. With such machines, it is necessary to provide a compression spring for tilting, that is to say for pivoting, the tilting yoke, which engages the tilting yoke as far as possible out of centre and so adjusts it that the pistons perform a stroke.

Normally, the return of the tilting yoke is produced by a pressure influenced piston or a rotary spindle against the force of the adjusting spring. Such a construction of an axial piston machine is complicated and therefore expensive.

Advantages of the Invention As opposed to this, the axial piston machine in accordance with the invention comprising the characterising features of the main claim has the advantage that it is simpler and cheaper, that is to say the adjusting spring can be omitted. Due to the displacement of the fulcrum, it is possible for the adjustment of the tilting yoke to take place automatically through the pistons or through the springs acting on them which are necessary in any event.

Drawing An embodiment of the invention is illustrated in the drawing and is described in detail in the following specification. Figure 1 shows a longitudinal section through an axial piston machine in a somewhat simplified representation, Figure 2 is a modification of the embodiment according to Figure 1.

Description of the Embodiments Apart from the inventive features, the axial piston machine according to Figures 1 and 2 is of conventional construction. A piston block 12 which engages a valve plate 13 is located in a housing 10 closed by a cover 11; the valve plate is fixed to the cover 11. The piston block 12 is driven by a central shaft 14 which is mounted on the one hand on a ball bearing 1 5 in the cover 11, and is mounted on the other hand in the lower part of the housing on axial and radial ball bearings 1 6, 1 7. The shaft 14 has external teeth 1 8 substantially in its centre and which engage in internal teeth 1 9 on the lower part of the piston block for driving the piston block.

A plurality of longitudinal bores 21 are formed in the piston block in which pistons 22 are sealingly slidingly guided. The pistons are made hollow and springs are arranged in their interior which are supported on the one hand by shoulders 24 in the piston bores 21 and on the other hand by the base 25 of the pistons. At their ends projecting out of the piston block, the pistons have ball joints 26 which are pivotally mounted in slide shoes 27. The pistons are forced through the slide shoes onto a supporting surface 28 of a tilting yoke 29 by the springs 23. The tilting yoke 29 is adjustable in one direction; the stroke of the pistons is determined by its angular position with respect to the axis of the shaft 14.

For tilting or adjusting the tilting yoke 29, it was previously usual to provide a strong compression spring which acted on the tilting yoke 29 as near as possible to its outer periphery.

A pressure influenced piston 31 which is sealingly slidingly guided on a pin 32 fixed to the cover 11, serves for resetting the tilting plate. In the pin 32, a bore 33 is provided into which controi oil is conveyed through a line (not shown) into the pressure chamber 34 of the piston 31 which then tilts the tilting yoke 29 towards its zero position.

With known axial piston machines, this takes place against the force of the above mentioned spring which acts on the tilting yoke substantially in an axial direction of the piston 31.

In accordance with the invention this spring is omitted. This is achieved by the fact that the rotary axis C of the tilting yoke takes up quite a special position. Two opposite cheeks 37, 38 are formed, in known manner, on the tilting yoke, of which only the cheek 37 is visible in Figure 1. A respective pin 39 or 40 is located on each cheek, which pins extend coaxially and are pivotaily arranged in a bearing (not shown) in the housing 10. What is now essential is that the axis C is displaced radially towards the right with respect to the axis of the shaft 1 4 by the amount e, that is to say in the direction in which the tilting yoke is pivoted towards the piston 31 or also in the direction towards the upper dead centre OT.The axis C is also displaced with respect to a pivotal support plane A-A for the pistons in an axial direction in relation to the shaft 14 towards the piston block by the amount f, that is to say a plane which extends through the centres of the ball joints 26 of the pistons 22 and as was previously normal through the pivotal axis M which is no longer present with this machine. The distance f is substantially greater than the distance e.

This means that, due to the springs acting on the pistons, the lever arm is longer with respect to the axis C on the side towards the lower dead centre UT than it is towards the other side, that is to say, in the tilting direction of the tilting yoke, there exists a greater tilting moment than on the opposite side. Due to the selected position of the rotary axis C, there is achieved on the one hand a complete adjustment of the tilting yoke without an additional spring up to the piston 31, but, on the other hand, the return moment into the socalled idling position (pivotal angle a: equals substantially zero degrees) is prevented from being too large.

The displacement of the tilting plate pivot point by the distances e and f can be so optimised that the adjustment moment at the tilting yoke with a maximal tilt angle is either zero or that a piedetermined surplus adjusting moment is achieved.

The method of operation of the axial piston machine will be discussed only briefly since this is generally known. Pressure medium is sucked through a duct 36, 37, 38 in the cover 11, in the valve plate 13 ana in the position block 12 and is exhausted at the upper dead centre through a similar duct 39 to 41. The tilting yoke 29 takes up a position inclined to a greater or lesser extent according to the position of the piston 32.

The embodiment according to Figure 2 differs from that according to Figure 1 simply by the fact that, in this case, the pistons-referenced 50are supported directly on the tilting yoke 52 through rounded ends 51. For this reason, the tilting yoke is made in two parts and consists of an upper portion 53 which the ends of the piston engage and a frame 54 against which the upper portion is supported through ball bearings 55 and 56. The plane A-A coincides with the ends 51 of the pistons. The displacement of the pivot C is the same as in the previous embodiment.

Claims

1. An axial piston machine comprising a piston block driven by a shaft and in which are arranged in substantially axially extending bores, pistons which are urged by spring force against a tilting yoke determining the stroke of the pistons and which is mounted in the housing of the axial piston machine for pivotal movement towards one side, in which the fulcrum of the tilting yoke is displaced both in a radial direction with reference to the axis of the shaft towards the side of the upper dead centre and in an axial direction towards the piston block.

2. A machine according to claim 1, in which the pistons are connected through hall joints to slide shoes bearing against the tilting yoke.

3. A machine according to claim 1, in which the pistons have rounded ends bearing against the tilting yoke.

4. A machine according to any preceding claim, in which the radial displacement is substantially less than the axial displacement.

5. An axial piston machine substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.