GB1311206A - Hydraulic cylinder with pressure control - Google Patents

Abstract

1311206 Hydraulic pressure actuators CESSNA AIRCRAFT CO 21 April 1970 [28 April 1969] 18927/70 Heading F1D The speed of a hydraulic operated single-stroke double-acting piston 12, Fig. 1 is controlled by varying an orifice 30 in a flow discharge duct 27, 28, 39 by means of a restrictor spool valve 42 subjected at one end by discharge pressure in the contracting end 15 of the cylinder 11 and transmitted through a duct 34 and subjected at the other end to a biassing spring 48 and supply pressure acting on a spool 46 which by means of a pin 43 holds restrictor valve spool 42 fully open until at a predetermined decrease in inlet pressure at 33, spring 48 is over-ridden and valve 42 restricts the exhaust flow. Such inlet pressure decrease at 33 may occur due to a sudden increase of an external load-assisting retraction of the piston resulting in increase in velocity thereof and cavitation in the expanding end of the cylinder accompanied by a pressure increase on the contracting side. Cushioning at the end of the stroke is effected by entry of a piston projection 38 into discharge duct 27 which thus increases pressure in duct 34 and results in partial closing of restrictor valve 42. The upward return stroke is initiated by switching a distributing valve 19 to apply inlet pressure to duct 29 and past a check valve 36 to a by-pass 35 and duct 34. A similar valve construction may be provided at the other end of the cylinder. In a modification cushioning near the end of the stroke is effected when a spring-biassed hollow plunger 85, Fig. 4 carried by the piston 95 seats at 91 against the exhaust duct 28 whereon fluid at the head end of the actuator cylinder passes along a tapered notch 99, through apertures 88 into the interior of plunger 85 and thence through an orifice 92 into exhaust duct 28 and through the throttle valve (not shown) as described with reference to Fig. 1. In this embodiment the bypass 35 and check valve 36 and dispensed with. In a further modification two double acting piston and cylinder actuators are arranged in tandem.