GB1099170A - Improvements in and relating to hydrostatic steering systems for motor vehicles - Google Patents

Abstract

1,099,170. Power-assisted steering mechanism. ZAHNRADFABRIK FRIEDRICHSHAFEN A.G. Oct. 6, 1966 [Oct. 7, 1965], No. 44708/66. Heading B7H. In power-assisted steering mechanism comprising a control valve 15, a servo pump 5, and a positive displacement pump 4 actuated by the steering shaft 1, a non-return valve 42 is disposed in the supply line 18 between the servo pump 5 and the valve 15. Movement of the steering shaft 1 as a result of road shocks causing pressure surges which open a pressure relief valve 41 is thereby prevented. The pump (Fig. 8, not shown) which is driven through an Oldham couplings or, as shown, is keyed to coupling member 3 driven from the shaft 1 through means permitting a limited degree of relative rotation. The valve 15 rotates with the coupling member 3 and is connected to the steering shaft 1 through a screwed coupling 17 which produces axial displacement of the valve 15 in response to relative rotation between the shaft 1 and member 3. When the valve 15 occupies a neutral position, fluid delivered by the servo pump 5 to a groove 19 returns through a passage 33, groove 34 and pipe 31 to a reservoir 32. Upon displacement of the valve 15, fluid from the groove 19 flows through slots 13 or 14, radial bores 38 or 39 and respective ones of axial bores 12 to the pump 4. Fluid leaving the pump 4 flows through the remaining bores 12, radial bores 38, 39 and slots 13, 14 to one of grooves 22, 27 communicating with the respective ends 24, 25 of a servo cylinder. The other groove 22, 27 is placed in communication with the reservoir through the interior of the valve 15. A valve 35 permits manual operation of the steering mechanism should the pressure supply from the servo pump 5 fail. Another embodiment (Fig. 5, not shown) employs a control valve displaced against spring loading by the pressure differential across the positive displacement pump.