Abstract: A ratio selector mechanism for the selection of the operative ratio in an associated synchromesh vehicle transmission in which a fluid pressure operated actuator operates synchromesh units. The operating pressure of the actuator is varied either mechanically or electronically during selection of a given ratio in the associated transmission or dependent on the ratio being selected. A first actuator selects a shift rail, and a second actuator engages a gear. A valve member acts against a bias force which is varied based on the position of the first actuator to control the pressure in the second actuator.

Abstract: A clutch control system for the automatic control of a motor vehicle clutch (14) which connects an engine (10) with a gearbox (12) under the control of a driver-operated gear ratio selector member (24). The control system includes an electric control unit (36) which controls the level of clutch engagement in response to an engine speed error signal (E) derived from a comparison of current engine speed (Ve) and a reference speed signal (Vr) generated by the control unit. A sensing means (19a) is provided to detect a "foot-off" condition of an engine controlling accelerator pedal (19) and to provide and indication of the full range of movement of the accelerator pedal from the "foot-off" condition to the fully depressed position. The electronic control unit (36) responds to an accelerator pedal "foot-off" signal to ensure that the reference speed signal is above the engine idle signal by a predetermined amount to prevent creeping of the associated vehicle due to partial clutch engagement at engine idle.