Abstract: A motor vehicle transmission unit provided with an automatic variable ratio transmission mechanism and a supplementary fixed ratio transmission mechanism which transmits torque from an input shaft to an output shaft of the unit in conditions of low speed and high torque. A free wheel clutch allows the variable ratio transmission mechanism to take over the drive when the speed increases, this being accomplished by means of an automatic speed sensitive clutch which engages when the speed of the output shaft reaches a predetermined threshold valve. A torque converter or other progressive coupling device links the input shaft of the unit, via an isolating friction clutch, to the fixed ratio transmission mechanism.

Abstract: A motor vehicle engine is arranged to drive the vehicle wheels through a mechanical transmission, an hydraulic system including a variable-output, reversible, hydraulic pump, a variable-output hydraulic motor usable reversibly as a pump and a two-speed gear box. The outlet and inlet of the pump are reversibly connected by delivery and return conduits respectively, through a distributor, to the inlet and outlet of the motor and an hydraulic accumulator is connected through a closable valve to the delivery conduit, the operation of the system being controlled by a microcomputer so that when the vehicle decelerates at a rate greater than that due to natural resistance, kinetic energy which is normally lost in the engine is stored in the accumulator and can subsequently be reused to drive the vehicle wheels, the engine being cut out or maintained at minimum power.