GB692838A - Improvements in or relating to hydraulic systems for controlling double acting hydraulic motors - Google Patents

Abstract

692,838. Hydraulic machines. BENDIX AVIATION CORPORATION. July 16, 1951 [Sept. 25, 1950], No. 16863/51. Class 69(ii) A hydraulic system for controlling a doubleacting motor wherein the stroke of its piston in one direction is limited to a predetermined value comprises a control unit 10, having a valve member 25 actuated by a piston 27 slidable in a cylin-. der 23 communicating at one end through a passage 33 with a gear pump 34 connected by a shaft 36 to a gear motor 21. The motor 21 communicates through a passage 22 with the other end of the cylinder 23 and is driven by liquid exhausted from the left-hand end of the cylinder 12 of the doubleacting motor when the valve 25 is open. To move the piston 12a of the double-acting motor outwards, a control cock 13 is positioned to connect the unit 10 to a pressure liquid supply pump 16 and the right-hand end of the cylinder 12 to a tank 118. Pressure liquid, the pressure of which is insufficient to rotate either the pump 34 or the motor 21, is then supplied through non-return check valves 38, 40 to opposite ends of the cylinder 23. The valve 38 is lightly loaded opening first to cause rightward movement of the piston 27 and opening of the valve 25 until arrested by an adjustable stop member 29. Pressure then builds up in the cylinder 23 and the passage 33 when the more heavily loaded check valve 40 opens to pass pressure liquid through the now open valve 25 to the cylinder 12 and move the piston 12a outwards to the full extent of its stroke. To move the piston 12a inwards, the cock 13 is positioned to connect the unit 10 to the tank and the righthand end of the cylinder 12 to the pump 16. The check valves 38, 40 now close and liquid exhausted from the left of the piston 12a passes through the valve 25 to drive the motor 21 and with it the pump 34. The pump 34 then withdraws liquid from the cylinder 23 which permits movement of the valve 25 towards closure. On closure of the valve 25 the piston 12a stops, the stop position being determined by the stop 29 which determines the volume of liquid admitted to and hence withdrawn from the cylinder 23. The operator may if he desires limit the outward movement of the piston 12a by manipulation of the cock 13 which will also effect the final position of the piston on its inward stroke, e.g. assuming no adjustment is made to stop 29, the piston 12a will move farther to the left on its inward stroke. A spring 28 may be fitted to assist closure of the valve 25 and a non-return check valve 45 fitted in the outlet from the motor 21. In a modification, the outlet flow from the pump 34 instead of being led direct to the tank 118 through the cock 13 is led to the back of another piston connected to the valve 25 to assist its closure in lieu of the spring 28. A passage connects the opposite sides of this other piston and a check valve in the passage permits expulsion of liquid from the back thereof during its rightward movement.