GB703541A - Improvements in or relating to hydraulic servo-motors and control valves therefor - Google Patents

Abstract

703,541. Fluid-pressure servomotors. DAVY & UNITED ENGINEERING CO., Ltd., MARSHALL, A. F., and REES, H. A. July 6, 1949 [July 8, 1948], No. 18405/48. Class 135 A hydraulic servomotor comprises a doubleacting piston 22 movable in a cylinder 21, a control valve having co-operating rotary and reciprocating ported members 62, 60 to control the relative magnitude of hydraulic pressure on opposite sides of the piston, and resilient means such as the spring 28 arranged to exert an increasing reaction on the piston as it is moved in either direction from an intermediate position in its travel, the piston being moved an axial distance which is related to the arcuate movement of the rotary ported member. The members 62, 60 are formed as sleeves the inner of which is fixed to a tapered extension 41 of the piston rod 24. The outer sleeve 62 is formed with pairs of ports 65, 65 and 66, 66 connected by galleries 67 in a rotary valve body 64. The sleeve 60 has six ports 61 in the shape of a rhombus. The ports 65, 66 are in the shape of,a parallellogram. The piston rod 24 and its extension 41 have three axial passages 47, 48, 49 connected at one end by radical passages 50, 51, 52 to three adjacent ports 61. The passages 50, 51, 52 are connected to the diametrically opposite ports 61 by two U-shaped grooves 53, 55, Fig. 4, and an extension 51a of the passage 51. The axial passage 47 has a radial extension 57 permanently connected to an exhaust port 46 through grooves 43, 45 and a passage 44. The axial passage 49 is similarly connected with a source of hydraulic pressure through a radial passage 59a and a port 42. The third axial passage 48 is connected with the remote side of the piston 22 through an inclined passage 58. The piston 22 is normally centered by the spring 28 which surrounds a piston rod 23 of less diameter than the rod 24. The compression of the spring 28 between flanges 29, 31 is limited by a distance sleeve 30 loose on the rod 23. The spring 28 is confined by a flange 35 directed inwardly from a cage 34. A distance piece 33 moves with clearance in the flange 35. Fig. 3 shows the ports 61, 65, 66 in the neutral position of the valve. On rotation of the sleeve 62, each pair of ports 65, 65, and 66, 66 coincides with two of the ports 61 whereupon the piston 22 moves until the ports no longer coincide. As applied to the control of a variable delivery pump, the piston rod 23 is connected to a cross head 20 of the pump and the rotary valve body 64 is connected by a coupling adapter to an electric torque motor. The cross head 20 controls the eccentricity of a normally fixed disc round which the pump plungers rotate.