GB2187257A - Roller type friction drive assembly with hydraulic axial loading - Google Patents

Abstract

A roller type friction drive assembly includes at least one set of angularly spaced tapered rollers 4 for the transmission of torque between relatively rotatable members 2 and 7 each engageable by all the rollers of the set. Means 17, 19 and 24 are provided for communicating hydraulic pressure in common to each roller to urge each roller axially into engagement with the surfaces of the relatively rotatable members 2 and 7. <IMAGE>

Description

SPECIFICATION Roller drive assembly with hydraulic axial loading The present invention relates to roller drive assemblies and is concerned with the hydraulic positioning of rollers in a set of rollers which work between relatively rotatable members and more particularly to the equalisation of axial end loads of the rollers in such a set.

In a set of rollers which provide for the transmission of torque between relatively rotatable members, such as a sun and an annulus, the axial end load of the whole rolling assembly should be shared substantially equally between the rollers so that they may each provide their share of transmitted torque.

Where there are two or three rollers per set, the arrangement is potentially load equalising, but where there are four or more rollers per set the torque can be equalised only by means of deflections of the engagement surfaces or the supports. Nevertheless the present invention has utility in any roller set and although it will be described in relation to an assembly arranged according to the prior copending British Patent Application No.

8600331, the present invention is intended to have a more general utility.

Broadly speaking, the present invention utilises the conical shape of roller engagement faces to equalise axial loads by means of hydraulic pressure acting on each roller, preferably employing a common stationary reaction member which is torsionally fixed to a casing for the assembly. In particular, according to the invention, a roller drive assembly includes a set of angularly spaced tapered rollers for the transmission of torque between relatively rotatable members having mutually inclined engagement surfaces each engageable by all the rollers in the set and means for communicating hydraulic pressure in common to each roller to urge the rollers into engagement with the said surfaces.

Preferably, the means for communicating hydraulic pressure comprises, for each roller, an annular cylinder having as one wall a portion of the respective roller. Thus if each roller has the same pressure in its cylinder, which is preferably similarly sized for all the rollers, the axial forces will be the same for all the rollers and the radial loading on which torque sharing depends will also be the same. Accordingly, all the rollers in a set are preferably fed by hydraulic pressure which may be supplied by way of a transfer through roller reaction pins on a stationary reaction member. This pressure may be provided by a fixed displacement pump.Where there are two sets of rollers, for example each set engaging a respective central bevelled roller and a respective bevelled surface on an annulus which is common to the two sets, the bevelling being in opposite senses, the pressure to each set of rollers may be the same but largely indpendent of the other, for example by means of an orifice feed to each set of rollers from a relatively high pressure source.

Preferably, for each roller, there is a thrust bearing for supporting the respective roller against axial loading in the absence of the said hydraulic pressure. Such thrust bearings will support the rollers at zero rotary speed of the assembly but in normal operation the rol lers will be adjusted to an axial position where the load on the roller is taken wholly hydrauli cally and the thrust bearings will be unloaded.

The axial positioning of the rollers may be controlled by a pressure release port openable by means of predetermined axial movement of one roller in a set. Provided that the arrangement is such that all the rollers take the same pressure, they will lead to assume positions where their axial loads are equal.

There follows a description of the invention by way of example only with reference to the accompanying drawings, which illustrates a roller drive assembly incorporating an embodiment of the present invention.

In the assembly shown in Fig. 1, a shaft 1 carries a sun roller 2. Mechanical end load on the sun 2 is provided by torque sensitive means 3. In frictional engagement with the sun 2 are all the rollers 4 in a set of rollers, of which only one is shown, spaced apart annularly around the sun 2. Each of the rollers 4 is bevelled and engages the bevelled surface 6 of an annulus 7 which is fixed to an end disc 8 mounted for rotation with a shaft 9 coaxial with the shaft 1. One each of the shafts 1 and 9 constitutes an input and output shaft respectively.

In this embodiment of the invention there is a second sun 2a and a second set of bevelled rollers 4a providing the transmission of torque between the sun and a second engagement surface 6a on the annulus 7, the bevelling of the second set of rollers being in a sense opposite to that of the bevelling of the first set. As will become apparent, the axial urging of the two sets of rollers should be in mutually opposite directions but for the sake of simplicity only the hydraulic arrangements for the first set of rollers will be described in detail.

Each roller 4 is mounted on and axially movable relative to a respective reaction pin 10, needle bearings 11 being disposed between the inner periphery of the roller 4 and the pin 10. The pins 10 are located tangentially but not radially in a fixed reaction member 12 which is torsionally fixed to casing member 13. Within the casing member 13 is a passageway 14 adapted to receive hydraulic pressure from a source to be described. The passageway 14 communicates by way of a transfer 1 5 with a passage 16 in the reaction member 12, the passage 16 communicating by means of a bore 17 in the leg 18 of the reaction member to an axially directed passageway 19 in the reaction pin. At the end of passageway 19 are bores 20 leading to an annular hydraulic pressure pad 21 which is in the form of an annular cylinder 22 which at one end has needle thrust bearings 23.Protruding into the cylinder is an annular end portion 25 attached to and rotating with the roller 24 and in this example an integral part of it.

The inner wall of the cylinder 22 is comparatively short and allows hydraulic pressure from the bores 20 to enter the space 24 defined within the cylinder. The outer wall of the cylinder is comparatively long and includes a relief port 26 which is uncovered when the roller 4 moves axially, relative to the cylinder 22, sufficient to move a piston ring seal 27 beyond the location of the port 26.

A fixed displacement pump 28, driven by the assembly, feeds a distributor 29 which has a pressure relief valve 30, shown schematically. From the distributor hydraulic pressure is conveyed by way of orifice 31 by means not shown to the passage 14 and thence to the cylinders for the rollers in the first set and also, separately, to similar cylinders for the rollers in the second set. Provision of orifices 31 prevents widely unequal pressures in the two pressure feed lines to the rollers.

In the absence of hydraulic pressure, as when the drive assembly is stationary, the roller 4 is forced back on to the needle thrust bearings 23. However, although torque may have to be transmitted at zero speed and, in the present embodiment, with zero hydraulic pressure, the duration of torque transmitting periods with the roller 4 in contact with the needle thrust bearings would be very short and the provision of reasonably small bearings is feasible for an adequate fatigue life.

In normal operation, the hydraulic pressure which is communicated in common to the cylinders for all the rollers in a set, forces each roller axially into engagement with the engagement surfaces 5 and 6 and the axial end load on the roller 4 is taken wholly hydraulically, the end face 25 of the roller being lifted off the thrust bearings 23, which are thereby unloaded.

In order to ensure equalisation of the axial loads on the rollers in the set, one of the rollers 4 has a cylinder 22 having the relief port 26, which is preferably omitted in respect of the other rollers. Thus the other rollers take the same pressure as the "positioning" roller and all have equal axial loads.

In the present embodiment, piston ring type rotary seals are employed for the roller 4 but other types of seal are possible.

Claims (6)

1. A roller drive assembly which includes at least one set of angularly spaced tapered rollers for the transmission of torque between relatively rotatable members having mutually inclined engagement surfaces each engageable by all the rollers of the said set and means for communicating hydraulic pressure in common to each roller to urge the rollers in respective axial directions into engagement with the said surfaces.

2. An assembly according to claim 1, further comprising thrust bearing means for supporting each respective roller against axial loading in the absence of the said pressure.

3. An assembly according to claim 1 or claim 2 in which the means for communicating hydraulic pressure comprises, for each roller, an annular cylinder having as one wall a portion rotating with the roller.

4. An assembly according to claim 3 in which the cylinder for one roller in a set includes means for limiting the axial movement caused by the said hydraulic pressure.

5. An assembly according to claim 4 in which the means for limiting comprises a pressure relief port openable by means of a predetermined movement of the said portion of the roller.

6. A roller drive assembly according to any foregoing claim, further comprising means driven by the drive system to provide the said hydraulic pressure.