GB1477566A - Power steering system - Google Patents

Abstract

1477566 Vehicle power steering systems DAVID BROWN TRACTORS Ltd 16 Oct 1975 42541/75 Heading B7H A vehicle power steering system comprises: a power-driven pump 12 drawing oil from a main tank 10 sealed against ingress of foreign matter and discharging said oil through a delivery pipe 13 to a valve housing 14 secured to a steering-wheel-operated feedback-controlled metering valve means 21 capable of functioning as a manually-operated emergency steering pump; an hydraulic steering cylinder 22 connected to the metering valve means 21; a return pipe 15 from the valve housing 14 to the main tank 10; a hermetically sealed reserve tank 18 interposed in the return pipe 15; a spring-loaded relief valve 20 in the part of the return pipe 15 between the reserve tank 18 and the main tank 10; a spring-loaded non- return valve 30 in a delivery conduit 26 connecting the delivery pipe 13 and the metering means 21; and a non-return valve 32 in a conduit 31 connecting the delivery conduit 26 to a return conduit 27 which connects the metering means 21 to the return pipe 15. In normal operation of the system, the check valve 32 remains closed. Oil supplied by the pump 12 flows through valve 30 to the metering means 21 controlling oil flow to the chambers of steering cylinder 22. Oil returning from metering means 21 flows to the main tank 10 through the reserve tank 18 and the relief valve 20. In the event of failure of the pump 12 or fracture of the delivery pipe 13, the check valve 30 and the relief valve 20 close. Steering may then be effected by using the metering means 21 as a manually-operated steering pump. During such operation of the system, the valve 32 opens and the reserve tank 18 receives any excess displaced oil and provides any additional oil required. The illustrated steering system further comprises relief valves 33, 34 for protecting the system against shock loads on piston-rod 25. The main tank 10 has a relief valve 11, and a filter 16 is interposed in the return pipe 15. In a modification of the illustrated system, the double-acting steering cylinder 22 may be replaced by two singleacting steering cylinders.