GB663526A - Improvements relating to liquid operated servo mechanisms - Google Patents

Abstract

663,526. Fluid-pressure servomotor control systems. LUCAS, Ltd., J. April 6, 1949 [March 8, 1948], No. 7070/48. Class 135. A fluid pressure servomotor system comprises a piston 16 movable in a cylinder a under liquid pressure under the control of a valve d operated by an actuating member such as the diaphragm e, itself controlled by a number of normally-open control valves o, p, q arranged in series. The valves o, p, q are responsive to different controlling factors such as the speed of a pump, the rate of fluid delivery, temperature, blower delivery pressure or atmospheric pressure. Thus the valve o is actuated by a solenoid 7 controlled by a thermally or manually operated switch (not shown). The valve p is actuated by a capsule g responsive to blower or other pressure, and the valve q is actuated by a spring-loaded diaphragm 11 exposed through a port 13 to the discharge pressure of a pump and responsive therefore to the speed of the pump. The valves o, p, q are opened by springs 2, 3, 4 and have restricted by-passes x, y, z which may be separate channels as shown or may be provided in either of the valve closure surfaces. The final valve q has an exhaust outlet n. The diaphragm e is loaded by a spring f in a chamber g having a connection 20 to atmospheric or other pressure. The chamber below the diaphragm is supplied through a restriction h from the same source 22 as supplies the servocylinder a through a further restriction 19. A spring 17 maintains the piston 16 in its upper position until an outlet b is opened by the valve d. The piston 16 may control the output of a swashplate pump supplying liquid fuel to a furnace or the combustion chamber of an engine. Alternatively it may control a throttle valve. Fig. 2 shows a modification in which the by-pass passages x, y, z are dispensed with, since the valve d has a direct outlet n<SP>1</SP> to exhaust. In this case the control pressure acts in a chamber g above the valve and passes through the valves o, p, q to exhaust in the reverse order. In another modification, the valve d is formed as a piston and has a direct passage to exhaust. The valve d in this case controls two servopistons simultaneously. In a still further modification, the valve d is of spool form and controls the inlet and exhaust of pressure liquid to and from both ends of the servocylinder.