Patent GB-1200131-A (GB)
Title: Improvements in or relating to servo steering devices, particularly for motor vehicles
IPC: B62D5/097
Filed: 1968-01-12
Abstract: 1,200,131. Power steering. ZAHNRADFABRIK FRIEDRICHSHAFEN A.G. 12 Jan., 1968 [18 Jan., 1967], No. 1903/68. Heading B7H. A motor vehicle power steering device comprises a control pump 2 driven from the steering wheel, a servo pump 3 driven by the vehicle engine and a valve 1 operable in dependence in the direction of rotation of the steering wheel for controlling fluid supply to a servomotor 5 and is characterized in that the control valve includes a system for regulating the pressure in the servomotor proportional to the movement of the steering wheel and a valving arrangement to control the supply of pressure fluid to the servomotor, between which system and arrangement is provided a non- return valve which permits fluid flow only from the pressure regulating system to the valving arrangement whereby, in the event of the control valve jamming, a reverse movement of the steering wheel will free the valve. The valve comprises a casing 1, sleeve 10 and a rotary control member 12 normally centred by a pair of spring devices 27, 27<SP>1</SP>, Fig. 6. The casing 8 is provided with annular grooves and the sleeve 10 and control member 12 with circumferential grooves and radial passages. The steering shaft 60 is fast with an internally toothed annulus 61 with which meshes a gear 65 formed upon the end of a hollow shaft 64 swingably supported at the lower end of mem. ber 12 upon trunnions 66, 66<SP>1</SP>, the gear 65 being located by a bearing upon an eccentric 63 integral with a shaft 62 through which the steering shaft movement is transmitted to the control pump 2. The shaft 62 transmits movement from the steering shaft 60 direct to the pump 2 while the gears 61, 65 provide a step-up ratio for the member 12. When the control valve is in its neutral position, Fig. 5, pressure fluid from pump 3 enters groove 7 and flows through bores 9, 9<SP>1</SP> in sleeve 10 and thence past chamfered control edges 13, 14, 13<SP>1</SP>, 14' and thence through passages 15, 15<SP>1</SP>, 16, 16<SP>1</SP>, 17, 17<SP>1</SP>,  18,  18<SP>1</SP> ,  19, 19<SP>1</SP>, 20, 201 into the interior chamber 21 from where it returns to reservoir through passages 23 and 24. With a rotational movement of the steering wheel, for example in a clockwise direction as seen in Fig. 5, the flow passages 17, 17<SP>1</SP> are cut off and the spaces adjacent the chamfered grooves 14, 141 gradually reduce thereby causing a build up of pressure proportional to the steering movement. This raises a check valve 30 allowing fluid to flow through passages 31, 32 and 32<SP>1</SP> into longitudinal grooves 33, 33<SP>1</SP> in the valve sleeve 10, and thence through grooves (34) in the member 12 and further radial bores in the member 10 into an annular groove 35 and by way of duct 36 into an inlet chamber 38 for the control pump 2, the outlet chamber 39 of which leads by way of a passage 40 into a groove 41 from which through further bores and passages in the members 10 and 12 the fluid passes into the groove 45 and to the servomotor 47 through a passage 46. Return fluid from the motor 47 enters groove 50 and through bores and grooves in the sleeve 10 and control member 12 finally through grooves 17, 17<SP>1</SP>, bores 19, 19<SP>1</SP> and into the return central chamber 21. In the event of failure of the pump 3, the pump 2 acts as the power source, the flow pipe 6 is blocked by the pump 3 and fluid is drawn from the chamber 21 through ducts 23, 24, passages 55, 54 and 53 and past a non-return valve 31. By virtue of the non-return valve 30 allowing fluid to pass in one direction only from groove 7 to groove 31, should the control member 12 jam during a steering movement, a movement in the reverse direction will build up sufficient pressure to release the member. In a modification, Fig. 7, an engine driven pump 103 supplies fluid to a valve 101 comprising a sliding spool centred by springs 127, 127<SP>1</SP> and having grooves 121, 122, 1211, 122<SP>1</SP> which co-operate with grooves 11, 112, 113, 111<SP>1</SP>, 112<SP>1</SP>, 1131 in a sleeve. The spool further has radial passages 123, 123<SP>1</SP> and axial bores 124, 124<SP>1</SP> closed by non-return valves 130, 130<SP>1</SP>. In the neutral position, the pressure fluid flows through grooves 113, 121 and a passage 134 to groove 113<SP>1</SP> and through a passage 135 to the reservoir 104. A control pump 102 is actuated by the steering wheel and supplies pressure to one end of the valve spool, moving it, for example, to the left, as shown in Fig. 9. The pressure fluid now flows through groove 122 and passages 123, 124, past check valve 130, into a chamber 126 and thence through the control pump 102, through line 138 and into chamber 126<SP>1</SP>, from which it passes through line 149 into the servo cylinder 105. The fluid displaced from the latter passes through line 146 and by way of groove 121, line 134 and groove 113<SP>1</SP> back to reservoir. In the event of failure of the pump 103, the pump 102 acts as the power source. Chamfers 125 and 125<SP>1</SP> are provided on the valve spool and during the initial part of a steering movement allow short circuiting of the fluid to reservoir through passage 134. If the spool becomes jammed, a reverse movement on the steering wheel will cause it to unjam, the fluid acting from pump 102 upon the check valves 130, 130<SP>1</SP>.