This invention relates to variable ratio frictional drive transmission systems including drive units or gears of the kind comprising basically two axially spaced torus discs or rotors, one serving as an input and the other an output, between which there is a set of circumferentially spaced drive rollers in frictional rolling contact with part toroidal surfaces on the discs, each roller being rotatably mounted in a bearing structure which can tilt about an axis at right angles to the axis of rotation of each roller so as to vary the distances from the gear axis at which the roller engages the two discs respectively, thus varying the drive ratio of the gear. The angle of tilt of the roller bearing structure as it controls the drive ratio of the gear, is called the ratio angle.
One way of changing the ratio angle is to tilt the roller bearing structure by bodily moving it tangentially with respect to the gear axis, and by allowing the rollers then to steer themselves towards a different ratio angle. This adjustment is achieved by arranging the rollers at an angle to a plane perpendicular to the gear axis so as to induce the required steering. This angle is called the caster angle. Such a drive gear will for convenience herein be described as being of the kind specified.
This invention is particularly concerned with gears in which the plane of each roller, normal to the axis of rotation of the roller and passing through the points of contact of the roller with the two opposed torus discs, contains the axis about which the roller tilts, being tangential to the torus centre circle (i.e. the locus of the centre of the circle revolved to generate the torus) as distinct from gears in which the same plane for each roller is closer to the main axis of rotation of the gear.
The apparatus may run at very high rotational speeds, perhaps up to 20,000 revolutions per minute, and thus operating conditions may be extremely arduous and power transmission requirements may be very high.
There are, moreover, certain practical limitations on the size of the transmission system. If the components are of large size the wear characteristics tend to be poor and power transmissions are therefore limited by the stength of the components.
It is the object of this invention to provide a variable speed transmission system in which power of relatively high order can be transmitted.
According to the present invention there is provided a variable speed transmission system of the kind specified comprising at least two variable ratio gears of the kind specified and having an input and an output respectively, the inputs and outputs of the gears being respectively coupled together to operate in parallel, there being a common hydraulic fluid supply to each of the variable ratio gears for controlling the ratio change means of the respective gears.
The invention will now be described by way of example, with reference to the accompanying drawings, in which: