GB709310A - Power steering booster - Google Patents

Abstract

709,310. Fluid-pressure servomotor-control systems. GARRISON, R. A. Jan. 7, 1952, No. 495/52. Class 135 Power-assisted steering gear, e.g. for a vehicle comprises a hydraulic piston and cylinder motor 11, Fig. 1, for moving the road wheels and controlled by a piston valve 10 actuated by relative movement between the plunger 53, Fig. 2, and sleeve 34 due to movement of the drag link 23 by the steering wheel through the drop arm 14. The valve comprises a block 32 having connections 36 ... 39 respectively from an engine driven pump 21, to the reservoir 22 and to opposite ends of the motor cylinder 42, and leading into annular grooves 46 ... 49. Groove 46 communicates via a bore 50 in the block with a groove 51, and groove 47 communicates via a similar bore with a groove 52. The sleeve 34 is fixed in the block by plates 30, 31 and slidable therein is the hollow plunger 53, which has lands 76, 77 disposed, with the valve in neutral position, centrally between and having negative lap with respect to sets of ports 78, 79 and 80, 81 respectively. Ports 78, 79 connect with groove 48 and connection 38, and ports 80, 81 with groove 49 and connection 39. Supply pressure enters the sleeve via connection 36, groove 46, bore 50 and groove 51, and also passes to the interior of plunger 53 through ports 90. With the valve in neutral position, supply pressure bleeds through ports 78, 81 to both ends of the cylinder, and passes through ports 79, 80 back to the reservoir connection 37. Relative movement between the plunger and sleeve joins one of connections 38, 39 to the supply and the other to exhaust. Pressure entering the plunger passes through ports 91 into chambers 92 to act against pistons 84, 85, which urge the plunger 53 to its neutral position. A sleeve 27, rigid with the block 32 and link 23, contains a plunger 57 carrying the steering arm ball joint 29 and urged to a central position by similar springs 64, 70. The springs act against spring seats 60, 65, respectively, the flanges 61, 68 of which are permitted slight lost motion. The plunger 53 is connected to the plunger 57 by a rod 55. Thus, when the drag link 23 is moved, and the resistance of the road wheels is sufficient to hold the steering arm 20 and its ball 29 stationary, one of springs 64, 70 will be compressed and the lost-motion of the associated flange 61, 68 taken up, causing the sleeve 34 to move along the plunger 53. Hydraulic fluid is supplied to the motor to move the wheels in the appropriate direction, and the movement of the road wheels is transmitted via the arm 20 to recentre the plunger 53. Pressure in the chambers 92 assist the springs 64, 70 in resisting relative displacement of the sleeve and plunger and provides feel at the steering wheel. If the fluid supply fails, the wheels are steerable directly, being subject to the slight lost-motion of flanges 61, 68.