SHAFT SUPPORT FOR AN INFINITELY-VARIABLE-RATIO TRANSMISSION

Abstract: The present invention provides an infinitely-variable-ratio transmission (30) in which the two input discs (38, 40) are mounted on an intermediate or auxiliary input shaft (36) which is splined to the main input shaft (32) for rotation therewith. The auxiliary input shaft (36) is mounted in bearings (42, 44) which are located in a cradle (46) which is itself mounted within the transmission housing (48). Flexing of the input shaft (32) is avoided as the load is taken by the cradle (46).

Description: SHAFT SUPPORT FOR AN INFINITELY- VARIABLE-RATIO TRANSMISSION The present invention relates to infinitely-variable-ratio transmission apparatus of the toroidal race rolling friction type, hereinafter referred to as a variator. In such apparatus there is employed a main shaft which takes drive from an engine e.g. an internal combustion engine to two input discs which are mounted on the shaft. Two output discs are mounted back to back between the input discs and are free to rotate relative to the shaft. In such an arrangement motion is transferred from the input discs to the output discs via a plurality of rollers positioned in toroidal cavities which are provided between the input discs and the output discs. The rollers are subjected to hydraulic forces so that they make contact with the faces of the respective input and output discs in order to transmit power from the input discs to the output discs. The power is transferred from the output discs via a chain or belt drive to a further transmission component such as an epicyclic gear box. The drive through the chain or belt exerts a transverse load onto the shaft and causes the shaft to flex. The degree of flexing is relatively small but has the potential of causing a significant effect on the position of the two output discs which can cause the load on some of the rollers to be increased i.e. a crushing effect will be applied, whilst the load on some of the remaining rollers will be decreased, thereby not allowing the drive to be transferred efficiently from the input to the output discs. It will be appreciated that the effect of shaft flexing is in effect a distortion of the toroidal cavities between the input and output discs. A solution to the above problem can be summarised as preventing or minimising flexing of the shaft by earthing or anchoring the output discs. The present invention seeks to provide a transmission apparatus in which the output discs are located on bearing means, and the bearing means are supported, so that the shaft is isolated from bending loads applied to the output discs. Accordingly the present invention provides a variator transmission apparatus comprising a housing, an input shaft, two input discs mounted on an auxiliary shaft for rotation therewith, an output disc assembly, the input discs and the output disc assembly defining between them two toroidal cavities, a plurality of rollers located in the cavities and the apparatus being subjected to an end load to maintain the rollers in contact with the respective discs and disc assembly in order to transmit drive, characterised in that the input shaft is arranged to drive the auxiliary shaft and the output disc assembly is supported from the housing. One of the input discs can be mounted for rotation with the input shaft and be provided with abutment means to limit axial movement, whilst the other one of the input discs is also mounted for rotation on the input shaft and be axially moveable thereon, under an applied load to maintain the rollers into contact with the respective surfaces of the input and output discs. The output disc assembly can be mounted on bearing means which are supported from the housing. The housing can comprise a transmission housing, or a cradle attached to the transmission housing. The present invention will now be more particularly described with reference to the accompanying drawings in which, Figure 1 shows a diagrammatic representation of a steplessly-variable-ratio transmission apparatus of the type to which the present invention can be applied; Figure 2 shows a diagrammatic view of one form of variator according to the present invention. Referring to Figure 1, there is shown an infinitely-variable-ratio transmission apparatus (a variator) which comprises an input shaft (10), two input discs (12, 14), two output discs (16, 18), two sets of rollers (20, 22) which are located in toroidal cavities (24, 26) which are formed between the input and output discs, and a chain or belt drive (28) which is mounted on the two output discs (16, 18). The two inputs discs (12, 14) are mounted for rotation with the shaft (10) e.g. by means of splined mountings, whilst the output discs (16, 18) are free to rotate relative to the shaft (10). Both of the input discs (12, 14) have limited axial movement and one of the discs e.g. disc 12 is prevented by an abutment (not shown) on the shaft (12) from moving too far to the left as shown in Figure 1. The other disc (14) is subjected to an end load operating towards the left as shown in Figure 1 e.g. by means of hydraulic pressure or the like so that the sets of rollers (20, 22) are forced into contact with the toroidal surfaces of the input and output discs, thereby allowing drive to be transmitted from a power source e.g. an internal combustion engine via the chain drive (28) to a further component of a vehicle transmission e.g. an epicyclic gearbox (not shown). It will be appreciated that the chain drive (28) exerts a bending load on the shaft (10) and therefore there is a distortion in the shape of the toroidal cavities (24, 26). It will thus be appreciated that the load on some of the rollers (20, 22) will be increased whilst the load on the remaining rollers can be decreased. The increase in load on some of the rollers may be unacceptable in that unduly high stresses are caused within the rollers, whilst the decrease in load on the remaining rollers is likely to reduce the efficiency of the drive between the input and output discs because slipping may occur between the input and output discs. In order to prevent or substantially reduce the effect of the distortion of the shapes of the toroidal cavities (24, 26) which can be produced by a bending load being applied to the shaft (10), the present invention proposes a design which restrains the output disc assembly, and isolates the input shaft from bending forces applied to the output disc assembly. Referring to Figure 2, a variator (30) comprises an input shaft (32) which receives power from, for example, an internal combustion engine, is arranged to drive by means of a splined coupling (34), an auxiliary input shaft (36). Mounted on the shaft (36) are two input discs (38, 40). Both discs (38, 40) are mounted so as to be rotatable with the auxiliary shaft (36) but the disc (40) is axially moveable with respect to the shaft (36) under an applied force, e.g. the application of the end load. The auxiliary shaft (36) is mounted in bearings (42, 44) which are located in a cradle (46), the cradle itself being mounted within a transmission housing (48). Two output discs (50, 52) are mounted in bearings (54), the bearings being supported by a web or radial struts or some such load bearing structure (56) in the cradle (46). Sets of rollers (58, 60) are located between the input and output discs (38, 50) and (40, 52) respectively. The surfaces of the input and output discs are shaped so as to create two toroidal cavities (62, 64) in which the sets of rollers (58, 60) are located. In operation an hydraulic load is applied to the input disc (40) which forces the sets of rollers into contact with the respective faces of the input and output discs and rotation of the input shaft (32) causes power to be transferred from the input discs (38. 40) to the output discs (50, 52). The drive from the output discs can then be taken by a chain or belt, for example, to another transmission element of a vehicle drive. The other transmission element can be an epicyclic gearbox. It will be appreciated that the load exerted by the drive from the output discs (50, 52) on the support structure (56) will not cause any flexing of the input shaft (32) nor the auxiliary shaft (36). Instead the load will be taken by the cradle (46). As both the input shaft (32) and the auxiliary shaft (36) are isolated from the load exerted by the drive from the output discs (50, 52) the toroidal cavities (62, 64) will not be distorted and the load on the rollers (58, 60) will not be affected by the load exerted by the drive from the output discs. In the above arrangement the bearings (42, 44) are bearings of the roller type which do not provide any axial location. This enables the auxiliary shaft (36) to float axially within limits enabling the input discs to move under hydraulic pressure applied to one of the discs so that the rollers (58, 60) make driving contact with the surfaces of the input and output discs. Also in the above arrangement it will be appreciated that the provision of the cradle (46) isolates the variator (30) from any distortion of the transmission casing (48). In the situation where there is unlikely to be any deflection of the transmission casing the cradle can be dispensed of. In such an arrangement the output discs (50, 52) are mounted with respect to the casing as also is the auxiliary shaft (36). In such an arrangement the bearings for the auxiliary shaft can be roller bearings. In a further arrangement (not shown) the roller bearings for the auxiliary shaft (36) can be dispensed with and replaced by plain bushes with clearance so that the bushes act as a steady only. It will be appreciated that in the embodiments of the invention described above i.e. with or without a cradle, with either roller bearings or plain bushes for the auxiliary shaft, the load applied to the variator (30) to the drive from the output discs (50, 52) does not apply a bending load to the input shaft (32) nor the auxiliary shaft (36). Therefore in all cases the shape of the toroidal cavities (62, 64) is not affected and the rollers (58, 60) remain in driving contact with the respective input and output discs in order to transmit drive without slippage.

Claims: CLAIMS 1. A variator transmission apparatus comprising a housing, an input shaft, two input discs mounted on an auxiliary shaft for rotation therewith, an output disc assembly, the input discs and the output disc assembly defining between them two toroidal cavities, a plurality of rollers located in the cavities and the apparatus being subjected to an end load to maintain the rollers in contact with the respective discs and disc assembly in order to transmit drive, characterised in that the input shaft is arranged to drive the auxiliary shaft and the output disc assembly is supported from the housing. 2. An apparatus as claimed in Claim 1 in which one of the input discs is mounted for rotation with the input shaft and includes abutment means to limit axial movement, whilst the other one of the input discs is also mounted for rotation on the input shaft and be axially moveable thereon under an applied load to maintain the rollers into contact with the respective surfaces of the input and output discs. 3. An apparatus as claimed in any one of Claims 1 to 4 in which the output disc assembly is mounted on bearing means which are supported from the housing. 4. An apparatus as claimed in any one of Claims 1 to 4 in which the housing comprises a transmission housing, or a cradle attached to the transmission housing.

Inventors: ROBINSON LESLIE KENDRICK, ROBINSON, LESLIE, KENDRICK
Applicants: ROBINSON LESLIE KENDRICK, TOROTRAK DEV LTD, ROBINSON, LESLIE, KENDRICK, TOROTRAK (DEVELOPMENT) LIMITED
Application year: 1998
Main classification: F16H15
IPC codes: F16H15