Patent GB-1160449-A (GB)
Title: Servo Valve Device for Power Steering Gear in Automobiles.
IPC: B62D5/08
Filed: 1966-09-01
Abstract: 1,160,449. Power-assisted steering. TOY ODA MACHINE WORKS Ltd. 1 Sept., 1966 [2 Sept., 1965; 2 April, 1966 , No. 39186/66. Heading B7H. A vehicle steering gear comprises a servomotor piston 7 slidable in a cylinder 3 and connected to the steerable wheels of a vehicle, a steering shaft comprising parts 25 and 11 interconnected by a resilient means 33, a main valve member 19 rotatable with said shaft part 11 and having a pair of control ports 28a (Fig. 4) and 28b (Fig. 3) on opposite sides connected respectively with the opposite ends of the cylinder 3 through ports 17 and 18, and a flap valve 25<SP>1</SP> which is rotatable with said shaft part 25 and controls the flow resistance of the ports 28a and 28b, increasing the resistance at one port while reducing it at the other port to adjust the relative flows to an exhaust port 16 and hence produce movement of the piston. In Fig. 1 the main valve member 19 includes two chambers 27, 28, the latter containing the flap valve 25<SP>1</SP> and pairs of ports 28a and 28b on opposite sides of its axis of rotation and the former communicating with a pressure pump 40 through a port 15 and containing a second flap valve which cooperates with two pairs of oppositely located distribution ports (27a) and 27b) (Fig. 2, not shown). In operation when the steering shaft part 25 is rotated clockwise, for example, the thin part 33a of the torsion bar resilient means 33 twists, before the wheels are turned through the recirculating ball steering gear interconnecting the shaft part 11 and the piston 7, permitting the flap valve 24<SP>1</SP> to close the distribution ports (27a) and direct pressure fluid only through passages 29b in valve member 19 and hence, as thicker portion 33b of the torsion bar twists moving flap valve 25<SP>1</SP>, round annular passage 23, port 18 and passage 38 to the righthand side of the piston 7, fluid from the left-hand side of the piston passing through the passage 37, the port 17, an annulus 22 and the ports 28 a  which are opened by the clockwise rotation of the flap valve 25<SP>1</SP>, to the chamber 28 and thence through the exhaust port 16 to a reservoir 41. A steering reaction is produced by the highpressure fluid in the closed ports 28b acting on the flap valve 25<SP>1</SP>. In a modification the torsion bar portion 33a is replaced by a transverse pin (46) (Fig. 6, not shown) between grooves in the end of the torsion bar 44 and in a spring-loaded seating (49) which is rotatable with the main valve member to provide an initial resistance to relative rotation of the valve members. In further modifications in which the torsion bar has a single reduced diameter portion and the flap valves rotate together, the distribution ports (27a), (27b) are engaged by resiliently mounted parts (50<SP>1</SP>) of the flap valve (50) (Fig. 8, not shown), the lower end of the flap valve (141<SP>1</SP>) is acted upon by opposed slidable plungers, each subject to the fluid pressure in the distribution port on the same side of the valve body to balance the forces on the flap valve (141<SP>1</SP>) to avoid a resultant steering reaction (Fig. 22, not shown), the effective radius of the distribution ports is made less than that of the control ports to provide a suitable steering reaction (Fig. 15, not shown) or the distribution ports (152a), (152b) are closable by mushroomheaded valves (151a), 151b) slidable in the ports and spring loaded against the flap valve (Fig. 22, not shown). In two further modifications having a torsion bar with two reduced diameter portions and two flap valves the control ports have axes in a single radial plane and communicate with the annuli (74), (75) connected to the servo cylinders through bores in the main valve body (64) (Figs. 9 to 13 and Fig. 14), the latter embodiment including two bores parallel to the valve axis each containing a pair of plungers (94), (95), which are held against the adjacent end faces of the flap valves by a spring (96) and the fluid input pressure acting between the plungers. In Fig. 15 (not shown) a single flap valve (102) and two pumps (114), (115) are provided and two pairs of ports (106a) and (106b) each of which controls the flow of pressure fluid from one pump to one end of the servo cylinder and from the same servo cylinder end to exhaust.