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1,133,892. Hydraulic control circuits. GENERAL PRECISION SYSTEMS Inc. Dec. 28, 1966 [Jan.14, 1966], No.57956/66. Heading F1P. The supply of working fluid and hence speed of a double-acting hydraulic piston 102, Fig. 7, is maintained constant against a varying reactor torque exerted by a rock shaft 20 driven by the piston 102, by controlling an adjustable orifice 276, 280, Fig. 13, in a by-pass 264, 262 connecting the delivery passage 76 of a constant flow electric motor driven supply pump 14 to a sealed pressurized return reservoir 36; said orifice being varied by a piston 246 held by a spring 252 in constant abutment with the free end of the rod 238 of a sensing piston 226 which assumes a position determined by the pressure difference between chambers 106, 108 either side the actuator piston 102. Pump delivery is connected to one or other chamber 108, 106 through feed passages 78, 80 of a four-way proportioning valve 89 having a spool 90 adjustably positioned by a plunger 91 controlled by a solenoid coil 92, through supply passages 82, 84; the return chamber being connected to reservoir 36 through a passage 88. In operation and during say downward stroke of piston 102 with valve urged towards the left, fluid from feed passage 80 is supplied to passage 84 and also to an end chamber 200 of a shuttle valve cylinder 186 thereby shifting the shuttle 192 to the right. Supply pressure is thus admitted to chamber 212 of valve 186 and also to chamber 228 of sensing cylinder; the other chamber 230 being connected to reservoir 36 through shuttle valve chamber 214, a passage 220 and exhaust passage 88 of valve 89. The solenoid coil 92 is variably energized by a potentiometer 174 and a feedback sensor 282 responsive to reactor forces on shaft 20. The potentiometer includes a rotor wiper 178 driven from the rod shaft 20 and associated with means not shown for indicating the angular position of the shaft relative to a fixed datum. During shut-down the fluid within the sealed reservoir 36 is maintained under pressure by a spring-biased inverted cup-shaped piston 38 in sliding sealing engagement with a cylinder housing 37 and when operating the pump 14 delivers to an accumulator chamber 138 to lift a piston 130 against a spring 146. The pump also delivers through a bore 166 Fig. 11 of piston 130 into a pilot chamber 164 thereby depressing a piston 162 integral with piston 38 thus assisting spring 154 to further pressurize reservoir fluid. Leakage is made up by admitting fluid through a fill port closed by a plug.
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