588,145. Fluid-pressure servomotorcontrol systems. BENDIX-WESTING- HOUSE AUTOMOTIVE AIR BRAKE CO. Oct. 10, 1944, No. 19532. Convention date, Oct. 9, 1943. [Class 135] In fluid-pressure clutch-operating mechanism for motor vehicles which is under control of a speed responsive device, the fluid-pressure supplied to initiate the declutching operation as the speed falls to a predetermined idling value also operates a valve device to apply momentarily an additional fluid-pressure to effect more complete declutching and to avoid " drag " due to mechanical friction in the clutch parts resulting from the adjustment to give the desired controlled engaging operation of the clutch by the speed-responsive device. In the Figure, a speed responsive device 15, of the type described in Specification 520,59i, controls the supply of pressure-fluid from a reservoir 23 to a clutch disengaging motor 8, through conduits 24, 26, 27, 28 and 29 and double check valves 30, 31. The arrangement is such that at idling speed of the engine, sufficient fluid-pressure is supplied to the motor 8 to move the clutch lever 7 to just disengage the clutch, whilst on increase of engine speed the pressure is released to give a controlled engagement. A valve 32 also controls the application of full pressure fluid from the conduit 24 to the motor 8, through conduit 38 and the double-check valve 31, to effect complete declutching operations in accordance with the operation of the gear shaft mechanism 12, 14 and 11..This valve is of the type described in Specification 485,101. Owing to mechanical friction in the clutch mechanism the disengagement of the clutch at idling speed is not always complete when the mechanism is set for the desired controlled engagement and to overcome this a further valve device 40 is provided, having an inlet and exhaust valve member 48, 50, a valve actuating member 52 and a piston 62. Thus, when pressure is supplied by the speed responsive device to the motor 8 it also passes through conduit 28 to act on the piston 62 to move the actuating member 52 to close a conduit 61 from exhaust and open it to a pressure conduit 60, thus supplying full fluid-pressure through conduit 61 and check valve 30 to the motor 8 to effect complete disengagement of the clutch. In its movement the valve actuating member 52 comes up against a stop surface 70 and allows the piston 62 to move further owing to a spring detent connection 66 riding from a groove 65 onto the cylindrical surface 72 of the member 52. Thus, when the additional pressure supplied to motor 8 rises to a certain value it acts in the chamber 43 of valve device 40 to move member 52 back relative to its actuating piston 62, as allowed by a clearance space 73, to close inlet valve 48 again and shut off the additional supply of fluid pressure. Thus this additional pressure supply acts only momentarily and is then released by its own action, the clutch however remaining in complete disengagement owing to the frictional forces being first overcome and then assisting in preventing re-engagement. The piston 62 is reset by spring 64 on subsequent operation of the speed responsive device to re-engage the clutch by reducing the pressure acting in motor 8 and on the piston 62. Additional means ensuring a 'positive resetting of the piston 62 may be provided, comprising a valve device 76 of the kind described in Specification. 488,208, operated by a pedal 78, for controlling the throttle valve 5 of the engine through a servomotor 74. When this pedal 78 is depressed to speed up the engine pressure-fluid is supplied to servomotor 74 and also through a conduit 84 to a chamber 45 in the valve device 40, behind the piston 62, which latter is then returned to its original position.