GB629884A - Improvements in hydraulic control systems - Google Patents

Abstract

629,884. Fluid-pressure servomotors. MILES AIRCRAFT, Ltd., and HEAL, L. C. Aug. 10, 1944, No. 15287. [Class 135] In a fluid-pressure operated apparatus having a piston or ram mounted for relative sliding movement in a cylinder, means for locking the piston and cylinder together comprise spaced locking rings associated with the piston and a valve for admitting operating fluid under pressure between the rings to cause them to grip the cylinder wall. As shown, the piston 3 has two sealing. rings 10a, 10b of synthetic rubber or the like engaging the cylinder 1. The space 11 between the rings is connected by passages 12a, 12b with the pressure inlet ports 6a, 6b of a control valve 4 movable within the piston 3 on either side of a neutral position to an extent permitted by annular buffers 9a, 9b of synthetic rubber or the like. Pressure fluid is admitted to the two sides of the piston through ports 5a, 5b placed in communication with the ports 6a, 6b respectively or with a common exhaust port 8 according to the direction of movement of the valve 4. The passages 12a, 12b and hence the space 11 are respectively connected with ports 13a, 13b and exhaust passages 14 when the valve 4 moves away from its neutral position thus releasing the sealing rings from pressure. The pistonrod is in two relatively movable parts, one 2a carrying the control valve and being connected to the pilot's control column and the other 2b carrying the piston 3 and being connected to the controlled member, for example an aircraft control surface. An auxiliary valve 15 with closure heads 16, 18 adapted to co-operate with seats 17, 19 is urged by a spring 20 to seat the head 18 and unseat the head 16 but is normally prevented from doing so by the fluid pressure supply which passes 'through the part 2a into passages 7 and hence to the ports 6a, 6b. When the supply pressure falls or fails, the valve head 16 opens to place passages 7 and 14 in communication so that on movement of the control valve 4 fluid can pass freely from one side of the piston to the other without hindering manual actuation of the piston. A non-return valve is provided in the pressure inlet and exhaust. The valve centring means and the connections for the fluid pressure supply and exhaust may be as described in Specification 629,086.