DUO-SERVOMOTOR VALVE MEANS

1,242,174. Servo-motor control valves. BENDIX CORP. 17 Feb., 1969 [6 March, 1968], No. 8403/69. Heading F2F. A control valve 18 of the type comprising in a housing 68, 70 a servovalve means for controlling fluid pressure actuation of at least one servomotor, includes a first movable piston 88 sealingly arranged in a stepped bore of the housing to define therein a first fluid control chamber 144 connected to a first inlet control port 52, which piston is operatively connected to the servovalve means for actuating the same in response to fluid pressure in the chamber 144, and a second movable piston means 92, 90 sealingly arranged in the first control chamber to divide the chamber into a second fluid control chamber 146 connected to a second inlet control port 54, which second piston is responsive to the fluid pressure differential between the first and second control chambers so as to engage the first piston for biasing same to actuate the servovalve in the event of failure of fluid pressure in the first control chamber, the servomotor control valve being characterized in that the second piston means is of a differential design with the effective area thereof subjected to a fluid pressure in the first control chamber being larger than the area subjected to the fluid pressure in the second control chamber. As shown, a pedal-operated master cylinder 10 creates separate fluid pressures in conduits 14, 16 leading to the control valve 18 having an atmospheric inlet 20 communicating with an air cleaner, and a vacuum inlet 22 branching via conduits 26, 28 and 30 to the engine intake manifold and vacuum chambers within a housing 32 of a servomotor. The valve 18 is provided also with a control discharge port connected by conduit 36 to the central chamber of the housing 32, the servomotor being so constructed as to have two diaphragms internally thereof dividing each half of the housing into a vacuum chamber and a control chamber. Slave hydraulic cylinders 40, 42 develop pressures in conduits 44, 46 connected to wheel brake cylinders 48, 50. The control valve comprises two members 68, 70 between which is secured a diaphragm 76, the member 78 including a port 78 for connection to the vacuum conduit 22, hydraulic inlet ports 52, 54 and hydraulic discharge ports 56, 58, and the member 68 having an atmospheric air inlet 80. Working in the bore 86 of the housing 70 are pistons 88, 90 of different diameter and therebetween a floating piston 90, piston 80 receiving the stem