GB2250784A

GB2250784A - Radial piston motor.

Info

Publication number: GB2250784A
Application number: GB9124981A
Authority: GB
Inventors: Peter Wusthof; Sinclair Cunningham
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1990-11-24
Filing date: 1991-11-25
Publication date: 1992-06-17
Anticipated expiration: 2011-11-25
Also published as: JP3205019B2; GB2250784B; ITMI912953A1; DE4037455C1; ITMI912953A0; GB9124981D0; FR2669682A1; JPH05157043A; IT1254760B; FR2669682B1

Description

22507,34 - 1 RADIAL PISTON MOTOR The invention relates to a radial piston

motor. It is known from German Offenlegungsschriften 32 16 007 or 35 31 632 to provide a radial piston motor comprising an annular cam plate, a cylinder block rotatable relative to the cam plate and having a plurality of radial bores, a plurality of pistons displaceably mounted in the bores and provided with bearing members which engage the cam plate. These are characterised by compact and economical construction and by their high pressure resistance. In such motors the pistons take over the displacing and sealing functions and the rollers transmit the forces for generating torque from the cam plate to the pistons. The maximum piston diameter in these known motors is determined by the number of pistons, the piston stroke and the radius of the rotor and consequently the torque of the motor is also determined by these factors.

The aim of the invention is to improve the known radial piston motors of the kind described above so that their torque can be increased whilst maintaining the same size of construction.

According to the present invention, there is provided a radial piston motor comprising an annular cam plate, a cylinder block rotatable relative to the cam plate and having a plurality of radial bores, a plurality of pistons displaceably mounted in the bores and provided with bearing members for engaging the cam plate, wherein each piston is provided with a guide pin disposed radially inwardly thereof, the guide pin having a diameter smaller than that of the piston, and there being an annular bore space in the cylinder block defined by the piston in conjunction with the guide pin 2 and arranged to receive operating medium so as to be subject to the pressure thereof.

By the provision of a guide pin, the length of the piston can be shortened and consequently its diameter can be increased without reducing the spacing from the neighbouring piston bores. The strength of the cylinder block is thus unaffected. In a preferred form of the invention, a sealing element is provided on the piston in the vicinity of the rollers, which seals off the cylinder space formed by the annular bore space to the outside. The sealing element may additionally be provided substantially at the end of the piston adjacent the guide pin.

Preferably, the longitudinal extent of the guide pin is slightly greater than the operating stroke of the piston and is in a favoured design about 17-22% greater.

The ratio of diameters of the guide pin to piston is, in a preferred design between 0.5 and 0.8.

In a preferred embodiment, the guide pin and piston together form a kind of stepped piston, the annular bore space defined by the piston and guide pin and the guide pin bore space of which can be acted upon by the same pressure of operating medium through a recess. Such a recess may be provided in the cylinder block. Alternatively, the bore space defined by the guide pin is connectible, via a recess and an annular groove in the guide pin, to the annular bore space defined by the piston and guide pin such that an operating medium can be supplied to the bore space defined by the guide pin and to the annular bore space defined by the piston and guide pin through a valve either jointly or separately.

The bearing members comprise, in preferred embodiments, cylindrical rollers having axes extending parallel to the axis of rotation of the cylinder block.

Compared with the prior art, a preferred design of the radial piston motor results in an increase of about 44% in the surface area of the piston with guide pin

3 which can be acted upon by the pressure and consequently a correspondingly greater torque. As a result of the larger diameter of the pistons and the guide pins disposed radially inwardly thereof, improved guiding of the pistons is achieved at the same time, so that when the torque is transmitted from the cam plate to the rotor any tilting of the short pistons is effectively prevented and hence the torque is transmitted substantially without any losses.

In a known radial piston motor according to German Offenlegungsschrift 20 04 350 the operating piston has an extension of larger diameter which accommodates the support ball which is intended solely for improving the guiding of the operating piston. The annular space defined by the extension communicates with the housing space via a lubricating gap between the guide bore and the piston-shaped extension. There is no intention of acting upon the annular space with the pressure of the operating medium in order to increase the torque. ' The invention is hereinafter described more fully by reference to an embodiment given by way of example. In the drawings:

Fig. 1 shows an axial longitudinal section through a radial piston motor according to the invention, Fig. 2 shows a section on the line II in Fig. 1 and Fig. 3 shows another connection of the guide pin bore spaces and annular spaces acted upon by pressure.

In Fig. 1, reference numeral 1 denotes one half of the housing and reference numeral 2 the other half of the housing. The cam plate 3 is mounted between the two halves of the housing. The two halves are Joined together by means of the fixing screws 4 to form a solid unit. A shaft 5 is mounted in the housing half 1 by means of the ball bearings 6, 7. The end 8 of the shaft at the housing space end is constructed as a spline shaft and carries the rotor 10 via a corresponding recess 9. The rotor 10 is constructed as a cylinder - 4 block and has bores 11 and 18 uniformly distributed over its circumference (Fig. 2), serving to receive the pistons 12 with their guide pins 16. The pistons 12 are provided, in their radially outer area, with a recess 12d for receiving a bearing cup 13 for the cylindrical rollers 14. The cylindrical rollers 14 are supported on the cam path 17 of the cam plate 3. In the radially lower area of the piston, the latter has a piston ring 20, in an encircling groove 12c, to act as a sealing element. The bores 18 are constructed of such a length that the guide pins will still safely guide the piston even in its extended position. The guide pins are slightly longer than the piston stroke. The diameters of the bores 11 and 18 are such that, viewed in the direction of the rotor, the walls of the bores remaining between the bores will withstand the operating pressures which occur.

The guide pin bore spaces 19 formed by the bores 18 are connected, via radial recesses 27 in the rotor 10, to the annular spaces 15 formed by the bores 1- the pistons 12 and guide pins 16. The guide pin bore spaces 19 and annular spaces 15 are in turn operatively connected, via axially extending bores 21 in the rotor 10, to control bores 22, 23, which also extend axially, of a fixed control sleeve 24 accommodated in the housing half 2. The control sleeve 24 delimits encircling control spaces 25, 26 which communicate, by means of connections (not shown in detail), via a control valve, to the source of pressure medium or to the tank. Depending on the position of the guide pin bore spaces 19 or annular spaces 15 relative to the control bores 22, 23 the latter are connected either to the source of pressure medium or to the tank and in this way torque is generated on the rotor 10 which transmits it outwards via the spline connection to the drive shaft or driven shaft 5.

Fig. 3 shows a different construction of the - connection of the guide pin bore spaces 19 to the annular spaces 15, compared with Fig. 1. The guide pin bore spaces 19 are connected to the annular spaces 15 by means of axially extending recesses 28 in the centre of the guide pins 16 and by means of radially extending recesses 29 and encircling annular grooves 30 at the end of the guide pins towards the piston.

If the operating medium is supplied to the piston spaces and annular spaces through separate control channels and control spaces, the piston and annular spaces can be controlled separately by means of a control valve and in this way the torque can be graduated, by having the pressure medium act either on the annular spaces alone or on the piston spaces alone or on both together.

Claims

Claims 1. A radial piston motor comprising an annular cam plate, a

cylinder block rotatable relative to the cam plate and having a plurality of radial bores, a plurality of pistons displaceably mounted in the bores and provided with bearing members for engaging the cam plate, wherein each piston is provided with a guide pin disposed radially inwardly thereof, the guide pin having a diameter smaller than that of the piston, and there being an annular bore space in the cylinder block defined by the piston in conjunction with the guide pin and arranged to receive operating medium so as to be subject to the pressure thereof.
2. A radial piston motor as claimed in claim 1, wherein a sealing element is provided on the piston in the vicinity of the rollers, which seals off the cylinder space formed by the annular bore space to the outside.

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3. A radial piston motor as claimed in claim 2, wherein the sealing element is provided substantially at the end of the piston adjacent the guide pin.

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4. A radial piston motor as claimed in any of claims to 3, wherein the longitudinal extent of the guide pin is slightly greater than the operating stroke of the piston.
5. A radial piston motor as claimed in claim 4, wherein the longitudinal extent of the guide pin is about 17 to 22% greater than the operating stroke of the piston.

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6. A radial piston motor as claimed in any preceding claim, wherein the ratio of the diameters of the guide pin to piston is between 0.5 and 0.8.

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7 7. A radial piston motor as claimed in any of claims 1 to 6, wherein a bore space defined by the guide pin and the bore space defined by the piston in conjunction with the guide pin are arranged to receive operating medium so as to be subject to the same pressure thereof.
8. A radial piston motor as claimed in claim 7, wherein the bore space defined by the guide pin is connected, by means of a recess in the cylinder block, to the annular bore space defined by the piston and guide pin.
9. A radial piston motor as claimed in any of claims 1 to 6, wherein a bore space defined by the guide pin is connectible, via a recess and an annular groove in the guide pin, to the annular bore space defined by the piston and guide pin.
10. A radial piston motor as claimed in claim 9, wherein the operating medium can be supplied to the bore space defined by the guide pin and to the annular bore space defined by the piston and guide pin through a valve either jointly or separately.
11. A radial piston motor as claimed in any preceding claim, wherein the bearing members comprise cylindrical rollers having axes extending parallel to the axis of rotation of the cylinder block.
12. A radial piston motor substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
13. A radial piston motor substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.