GB819479A - A pressure control device for a variable displacement pump - Google Patents

Abstract

819,479. Fluid-pressure servomotor control systems. UNITED AIRCRAFT CORPORATION. Oct. 18, 1955 [Oct. 19, 1954], No. 29678/55. Class 135. An hydraulic servomotor for varying the displacement of a variable displacement pump comprises a casing 20 housing a servomotor cylinder 30 within which slides a piston 28 having a hollow rod 26 slidably mounting a piston control valve 24 subjected on one end face to pump discharge pressure admitted to the casing through a port 22 against a spring 42 which abuts at one end an abutment 40 carried by the valve and at its other end an abutment 44 formed on a sleeve 46 which moves with the piston. On pump discharge pressure exceeding a value determined by the spring, the valve 24 moves leftwardly to connect the right side of the piston to pump pressure through a passage 34 and ports 38, 36 and the left side of the piston to drain through a passage 72, ports 74, 76 and axial bores 78, 80 in the valve and piston rod respectively so that the rod 26 follows-up the movement of the valve 24 and a yoke 64 connected to the piston moves to adjust the stroke varying mechanism of the pump, the compression of the spring 42 and the pump output pressure remaining constant. The sleeve 46 may if desired be omitted in which case the spring abuts a shoulder on the cylinder 30 and the compression of the spring is dependent upon the position of the piston so that the volumetric output of the pump would be reduced slowly before the maximum desired pump output pressure is reached. Specification 730,086 is referred to.