GB1477586A - Control valve for the pressure medium in power assisted steering systems - Google Patents

Abstract

1477586 Power assisted steering systems ZAHNRADFABRIK FRIEDRICHSHAFEN AG 22 Jan 1975 [23 Jan 1974] 2778/75 Heading B7H A power assisted steering gear control valve includes fixed reaction pistons and pressure relief valves which act to equalize the pressure in the reaction chambers when a predetermined working pressure is reached, for example during parking, thus reducing the reactive feel. The valve piston 2 or 502 is slidably received in a cylinder 19 defined in a piston of a servo-motor (16) (Fig. 1, not shown) and is actuable by a pin 20 connected to the steering wheel. The reaction pistons 23, 24 or 323, 324 or 523, 524 are fixed relative to the cylinder. In one embodiment, Fig. 2, the pressure relief valves 27, 28 comprise ball valves 33, 34 received within the reaction pistons in bores 25, 26. Working pressure in chambers 3 and 4 passes via throttle bores 41, 42 and 35, 36 in the cylinder and reaction pistons to the reaction chambers 39, 40 and bores 25, 26. On deflection of the piston valve control edges 43, 46 open and edges 45, 44 close thus pressurizing reaction chamber 39 and exhausting chamber 40 via bore 42, edge 46, cylinder groove 48 and return conduits 50, 7. When the working pressure reaches a predetermined value fluid in bore 26 lifts the ball valve 34 and working pressure passes into the reaction chamber 40 thus equalizing the pressure with that in chamber 39. In a further embodiment, Fig. 3, the ball valves are replaced by pistons 55, 56 having flow control surfaces 57, 58 mounted in bores 53, 54 in the reaction pistons. The pressure in chambers 3 and 4 is communicated to bores 53, 54 via throttle passages 51, 52. In another embodiment, Fig. 5, the reaction chambers 539, 540 are formed between the reaction pistons 523, 524 and the pressure relief valves. Throttle bores 63, 64 and 65, 66 in the cylinder respectively connect the reaction chambers and the discharge side of the pressure relief valves. On deflection of the piston valve one chamber 539 is connected via bore 63 to chamber 3 whilst the other, 540, is connected via bore 64 to exhaust. When pressure in chamber 539 reaches a certain value pressure relief valve 527 opens and pressure fluid spills via bore 65 to exhaust. The provision of the throttle supply bores helps to reduce vibration of the valve piston.