Abstract: A torque converter has a positive displacement pump (15,16) for charging and for circulating fluid for cooling purposes, which is driven at a speed equal to the difference in speed between the input and the output of the torque converter. The torque converter can be locked-up by stalling the pump flow by means of a valve (36).

Abstract: A constant mesh parallel shaft gearbox providing a plurality of ratios has its ratio controlled by having, in place of conventional synchronizer assemblies and dog clutches, rotary positive displacement pumps each having one element (4) connected to the gearbox shaft (2) and another (3) connected to a gear (1). With the pump recirculating fluid the gear (1) freewheels on the shaft (2), a valve ring (9) can prevent recirculation and hence lock the gear for rotation with the shaft. Unidirectional rotation of the gear on the shaft in each direction can be obtained passing pump flow through non-return valves 13 or 14. The invention is equally applicable to epicyclic gearboxes and where brake bands, for example, can be replaced by a rotary pump and valve in accordance with the invention.

Abstract: A transmission incorporating a continuously variable ratio unit connected to further gearing, such that a plurality of regimes are available with synchronous shifting between regimes, is controlled such that to avoid hunting between regimes when the transmission is running at or around the synchronous ratio, regime and ratio changing beyond the synchronous ratio is inhibited until the optimum ratio for the prevailing operating conditions differs from the synchronous by a predetermined value.