GB1306712A - Steering mechanisms - Google Patents

Abstract

1306712 Power assisted steering A E BISHOP 27 Jan 1970 [3 Feb 1969] 3992/70 Heading B7H A power assisted steering assembly includes a variable ratio steering gear consisting of an hour-glass worm 25 connected to the steering shaft 11, and a worm follower 29 mounted on a cross-shaft 13 which is connected to the pitman arm (not shown) of the steering linkage. The cam track in the worm 25 is shaped to provide a high ratio in the on-centre, or straightahead, condition which decreases as the steering- wheel is turned. The follower 29 (Figs. 2, 13) is rotatably mounted on an axle 28 which is supported at one end by a surrounding ear formed on the cross-shaft 13. The other end of the axle 28 is mounted in a bush 28b which is seated in a semi-cylindrical recess formed in the crosa-shaft 13, the bush 28b being formed with a shoulder to provide axial thrust support. Tha follower 29 consists of a roller which is supported axially by bearings 28d, 28e and which is rotatably mounted on an eccentric sleeve (not shown) on the axle 28. The eccentric sleeve is connected to a worm-wheel 29d whicn can be rotated by worm 29e. Rotation of the worm 29e thus moves the follower 29 towards and away from the worm 25 so that the alignment of the worm 25 and follower 29 can be adjusted. Power is applied to the cross-shaft 13 (Fig. 3) by an hydraulic piston 41 and cylinder 40, the piston 41 being connected to a rack 42 which meshes with a gear segment 43 on the crossshaft 13. The gear teeth 42a, 43a have a varying ratio so that the torque supplied to the crossshaft 13 increases as the wheels are turned from their on-centre position. Ideally the torque supplied to the cross-shaft matches the torque required to turn the wheels when the vehicle is stationary. The supply of fluid to the cylinder 40 is controlled by a rotary steering valve 23 (Fig. 2) including a torsion bar coupling 26. (For Figures see next page)