GB820704A - Improvements in or relating to hydraulic motors - Google Patents

Abstract

820,704. Hydraulic control systems. CURTISS-WRIGHT CORPORATION. March 24, 1958 [March 25, 1957], No. 9412/58. Class 69(2). A control system for one or more reciprocating motors is such that the pressure of the hydraulic fluid supply can vary over a wide range without adversely affecting the operation of the motors. The motors are supplied through a throttle valve from a main hydraulic system, and a reversing valve which is actuated by the rise in motor-operating pressure at the end of each stroke, is restrained from actuation until the motor-operating pressure has risen to near the pressure then existing in the main system. Motors 17, 18 for actuating aircraft windscreen wipers are supplied with liquid from the aircraft hydraulic system via a line 2, an adjustable throttle valve, a line 7 and a reversing valve 16 alternately to motor lines 11, 14, the exhaust side being open via a valve chamber 20 to a line 15. Reversing valve 16 is actuated, through a quick-throw arrangement, by a piston 10 subject to the pressures in the motor lines 11, 14. Balancing pistons 24, 25 are provided in chambers on opposite sides of the piston 10 and are urged inwardly by the pressure in the aircraft system applied via a shut-off valve and a line 3, the inner faces of the pistons being subject to the pressure in the associated end of the cylinder of piston 10. Operation.-When a manually operable stem 33 of a master control and metering valve 1 is raised, the first operation is to admit liquid past valve seating surfaces 31<SP>1</SP> to the line 3 to move pistons 24, 25 inwards to centralize the valve actuator piston 10. Further opening movement of stem 33 permits a floating plug 31 to engage a shoulder 32<SP>1</SP> and further upward movement opens a bore in the plug to give throttled flow to the line 7. As shown, liquid is supplied to the line 11 to move the motor pistons to the right, the piston 10 being prevented by piston 25 from moving the quickthrow mechanism past dead centre. When the motor pistons are arrested the pressure in line 11 rises, and when it almost equals the then existing supply system pressure it is sufficient to move the piston 10 to the right to reverse valve 16 and initiate another stroke. By slowly closing the master control valve 1 the wipers can be parked at either end of the stroke. The quick-throw mechanism is described in U.S.A. Specification 2,451,449.