Patent GB-628925-A (GB)
Title: Improvements in or relating to fluid pressure systems
IPC: F16H61/46
Filed: 1947-08-05
Abstract: 628,925. Fluid-pressure servomotor-control systems. MANLY CORPORATION. Aug. 5, 1947, No. 21199. Convention date, Feb. 17, 1940. [Class 135] [Also in Group XXVI] A hydraulic motor B, of the outwardlysliding vane type described in Specification 627,924, is supplied with pressure fluid by a variable-delivery pump A, and has means in the supply line to provide a differential pressure drop to (a) determine the speed of operation of the motor, (b) maintain the determined speed substantially constant, and (c) supply the higher of the two differential pressures to the inner ends of the vanes. A modified arrangement has means to cater for variation in the viscosity of the fluid. The higher-pressure fluid is led through a pipe 45 to press the vanes of motor B outwards and the lesser-pressure fluid, which drives the motor, passes from a restriction 70. The high and low pressures act through pipes 72, 73 upon a piston 60. An increase in the pressure in pipe 42 forces the piston 60 to the left, allows fluid to pass up a pipe 54, force a piston 50 to the right and decrease the quantity of fluid delivered by the pump A. To compensate for changes in viscosity of the fluid, Fig. 2 includes an extra pump 83 supplying high-pressure fluid to an end 79 of a cylinder 75, and lower-pressure fluid through a restriction 86 to an end 80 of the cylinder or to drain 47. Since the same type of fluid flows through both restrictions 86, 70, any change in the pressure drop across the restriction 86 affects the pressures in the ends 79, 80. A decrease in viscosity of the fluid decreases the pressure drop across restriction 70 tending to move a valve 60 towards the left, and the effect of the restriction 86 is to counter-balance this and move the valve towards the right. To prevent leakage of fluid from the valve bore 561 into the ends 79, 80, grooves 87, 88 are provided. Fig. 5 shows a modification having a cylinder 95 in place of the restriction 70. A balanced piston 90 controls the flow from the supply pipe 42 by way of inlet and outlet ports 97, 98. The position of the piston 90 may be altered by a lever 101 which acts on a pin 100. The lever may be clamped in position by a friction grip 105. At its other end, the lever has a slot 106 for slidable connection with a fulcrum block which is rotatable on a pin 107. The restriction 86 causes a difference in pressures in pipes 81, 82 and the consequent movement of the piston 111 to the right upon decrease in viscosity causes the lever 101 to rock about its pivot 103 and move the pistion valve 90 downwards and reducing the opening of the metering orifice so that the output of the pump A remains substantially constant despite varia. tions in viscosity. Fig. 3 shows a constant capacity pump supplying the motor B through a pipe 42 and a regulating valve 121 through a pipe 421. Movement of the valve piston 118 towards the right, through movement of the piston 50, progressively opens a port 122 and allows fluid to escape from port 122 to a drain 591. V-shaped notches are provided on the piston-head 120. As the port 122 opens, less fluid flows through the restriction 70 in the pipe 42. Fig. 4 shows another arrangement having a constant-capacity pump A and a variable byepass valve 135 in the pipe 42 which is controlled by pressures in the pipes 42, 45 and 73. The valve 135 is moved responsive to the pressure across the restriction 70 to hold the speed of the motor B substantially constant. The speed of the motor is regulated by varying the size of the restriction 70. The metering arrangement of Fig. 5 may be substituted for the restriction 70.