This invention relates to toroidal race rolling traction transmission units. Such units, as is well known, typically comprise two coaxial confronting discs defining a toroidal race and a plurality of rollers each engaging the discs to provide a variable transmission ratio between the discs in accordance with the attitude of the rollers with respect to the common axis of the discs. The discs are urged towards each other by a suitable end load in order to provide sufficient traction between the toroidal race of each disc and the rollers. By varying, usually in unison, the common attitude of the rollers with respect to the main, common axis of the input and output discs the transmission ratio may be changed. It is in practice necessary to change the attitude of the rollers by steering them in helical paths with respect to the discs. In a common form of construction, each roller is mounted in a carriage which has a rotary axis lying in a plane substantially normal to the main common axis of the discs. Each carriage may have its rotary axis defined by, at one end of the carriage, a sliding pivot such as a ball guide, and at the other end a spherical, ball joint comprising a race and a ball which may be connected to a rocker arm which is or can be pivoted in unison with corresponding rocker arms for the other carriages in order to achieve a change in the attitude of the rollers and accordingly a change in the transmission ratio between the input and output discs.

Toroidal race rolling traction units of the general type are described in GB 979062 and GB 1069874; an arrangement including rocker arms is described in GB 2107009.

In many designs of this general kind there is difficulty in providing sufficient working clearances around the ball socket of the carriage for the roller in order to provide full angular travel of the carriage during a ratio change and yet to keep sufficient material to support the ball on the rocker against severe impulse loading. It is also necessary though difficult to maintain proper clearances between the carriage and the rocker at extreme limits of the range of variation of the attitude of the rollers and accordingly the transmission ratios that they provide.

One aspect of the present invention is to provide an improved transmission unit including an improved ratio changing mediansim including rocker arms.

The present invention is based on the provision of a ball race which is disposed at an angle which is substantially less than ninety degrees though substantially more than zero degrees' with respect to* the rotary axis of the carriage. Another aspect of the invention is the provision of a ratio changing mechanism in which each carriage has a sliding pivot connection with one rocker arm and a spherical ball joint connection with another rocker arm, each rocker arm thereby supporting the opposite ends of two carriages, and the rocker arms being movable in unison to cause a change in the attitude of the rollers.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a view of part of a toroidal race rolling traction transmission unit showing the characteristic features of the present invention; and

Figure 2 is an explanatory diagram.

DETAILED DESCRIPTION

Figure 1 illustrates rollers 1 which are disposed between two confronting coaxial discs in a toroidal race rolling traction unit of the kind described in GB 2107009. The rollers 1 of the present embodiment correspond to the rollers 4 of the aforementioned GB 2107009. The main axis of the discs is identified at 2 in Figure 1. Each roller is mounted in a carriage 3 corresponding to the carriage 9 in the aforementioned specification.

Each carriage is disposed for bodily movement in a plane which is normal to the main axis 2 and is also capable of movement about an axis 4 defined between a sliding pivot 5 and a ball joint 6. The sliding pivot 5 comprises a cylindrical socket 7 in which is slidable a part spherical head 8 carried on an extension 9 of a rocker arm 10 which is pivoted at 11 and has a main stem 12 extending towards the centre of the assembly, generally towards the axis 2. In the present embodiment there are three balls and associated carriages and three rocker arms. Each rocker arm carries a part spherical ball head 13 on the opposite side of the main stem to the first ball head 8. The line between the centres of the two ball heads for any particular carriage defines the rotary axis of the carriage. The second ball head 13 is separated from the main stem 12 by a neck 14.

In this embodiment of the invention each roller 1 is mounted

by means of bearings 15 in its carriage 3 so that it can rotate about an axis generally directed towards the central axis of the assembly.

In earlier practice, as shown in GB-2107009, the ball race 16 for the ball joint 6 is disposed at an angle such that the axis thereof is at approximately ninety degrees to the rotary axis 4 of the respective carrier.

In the present embodiment however, the race is disposed obliquely, at an angle substantially more than zero degrees but substantially less than ninety degrees to the rotary axis of the carriage. Preferably the angle is between thirty degrees and sixty degrees from the angle shown in the aforementioned specification.

The fundamental purpose of the joints at each end of the carriage _ι are to take the torque reaction forces of the

*roller and to define the rotational axis of the carriage. The configuration now adopted allows a reduced rotation component of the carrier on the ball end and thus the facility of providing greater clearance between the carrier and the ball neck and between the carrier socket and the rocker arm. Furthermore, the line of action of the reaction forces of the roller on the ball 13 is resisted mainly by compression of metal in the rocker neck instead of shear at the weakest point under the ball. Moreover, full bearing contact may be provided between the ball and its race to keep the stresses on the ball quite low and reduce wear and play to negligible amounts.

Whatever radial play is present between the ball 13 and its race, the consequent movement of the carriage, which constitues a ratio change signal, is not multiplied by much because of an oblique angle of operation. In Figure 2 the relative axial play, bearing surface load and rotary

friction are indicated for axial, normal and oblique configurations of ball and race. If, for instance, the ball cage were at ninety degrees to the roller axial centre line the effect of such an angle would be to increase the axial carriage play for a given amount of radial ball race clearance by about five times, to increase the contact stress on the ball for a given carriage reaction load and thereby increase wear and to increase frictional resistance to the rotational movements of the carrier during ratio change. Keeping axial play small in torque reversals minimises the amount of ratio change between drive and overrun.