GB1443799A - Valve assembly - Google Patents

Abstract

1443799 Hydrostatic transmissions; valves KLOCKNER - HUMBOLDT - DEUTZ AG 10 Oct 1973 [11 Oct 1972] 47340/73 Headings F2W and F2V A pressure relief valve assembly for limiting- hydrostatic braking in a hydrostatic transmission comprising a pump 2 and a motor 5 comprises a valve member 10 spring loaded towards a seating 11, the face 12 of the valve member having respective coaxial surfaces loaded by the pressures in the lines 3 and 4 between pump and motor, the chamber 16 enclosing the spring 9 being pressurized by the higher pressure line 3 or 4 through a shuttle valve 13 and a throttle 14, and the pressure in chamber 9 being relievable through an escape valve 18. The valve 18 is electrically controlled from a current source 25 through a switch 26 operated by a direction selector lever and through one of two pressure operated switches 28, 30, these being actuated by return line pressure when this is sufficiently high (the switch 28 being in use in forward, position I of switch 26 when line 3 is return, and similarly for switch 30, actuated by pressure in line 4 in reverse, position II). On actuation of a pressure switch due to pump 2 being driven by motor 5 the electric circuit is closed, the valve 18 opened and the return line pressure is limited by a pressure regulating valve 21 which, by opening at a preset pressure to limit pressure in chamber 16 allows the valve member 10 to be lifted off its seat 11 by pressure on its face 12 and so by-pass fluid between lines 3 and 4. The valve 21 is adjustable to vary the preset pressure and so the hydrostatic braking possible. The transmission may be used on a motor vehicle.