Patent GB-371816-A (GB)
Title: Improvements in fuid controlled steering mechanism for self-propelled vehicles
IPC: B62D5/24
Filed: 1931-01-19
Abstract: 371,816. Motor vehicle steering-gear ; hydraulic apparatus. DAVIS, F. W., 124, Lexington Street, Waltham, Massachusetts, U.S.A. Jan. 19, 1931, No. 1801. [Class 79 (v).] Fluid-pressure steering-mechanism comprises a steering control member or shaft co-axial with the fluid control mechanism, a valve being threaded on said steering shaft so as to move axially thereof during rotation of the shaft and being connected with a movable member, either a piston or a cylinder, by a resilient centring means of predetermined stiffness in such manner that the valve is displaced to promote pressure differences in the opposed pressure chambers formed by the piston and cylinder to augment the steering when the resistance thereto exceeds a value determined by the stiffness of said centring means. In the construction shown the steering-shaft 31 is formed with a screw-thread 30 engaged by a nut 29 mounted in a piston 26 connected to the rocker shaft 13 by trunnion blocks 35 and arms 34. The nut and piston are prevented from rotating in the stationary cylinder 10 by means of keys sliding in keyways, but the nut can move axially through a very small distance in the piston, this movement being governed by spring washers 63, 64, Fig. 9. Thus, for hand actuation, when the shaft 31 is rotated by the steering wheel 12 the nut and piston move axially in the cylinder 10, the shaft 13 is rocked and the road wheels 17 are steered by the usual drop arm 14 and drag link 15. For power actuation a constantlydriven pump 18 supplies liquid through a pipe 19 to the cylinder 10, an outlet pipe 20 leading back to a tank 21 and the pump. A relief valve 25 is inserted in a byepass pipe 24. The nut acts as a distributing valve for the liquid, the small axial movement of the nut in the piston being used for this purpose. The piston is formed with four internal annular grooves 49 .. 52, the 'groove 50 being in permanent communication with the inlet pipe 19 through a port 55 and a longitudinal groove 56, while the grooves 49, 52 are in permanent communication with the outlet pipe 20 by means of ports 58, 59 and a longitudinal groove 48. The remaining groove 51 is in permanent communication with the left-hand chamber 28 of the cylinder 10, through radial passages 61, Fig. 15, and longitudinal grooves 62. The nut or valve 29 is formed with ports 53 in permanent communication with the interior space 270 of the nut and the right-hand chamber 27 of the cylinder through longitudinal passages (not shown). Grooves 54 are also formed in the nut to allow communication between the ring grooves 50, 51, 52. In the neutral position shown in Fig. 9 the inlet groove 50 overlaps the edges of the ports 53, 54, so that liquid can pass from the groove 50 to all the other grooves and out at the outlet pipe 20. Both ends. of the cylinder 10 are also open to pressure through the ports 53 and the groove 51, but these pressures balance each other. When the shaft 31 is turned so as to move the nut 29 to the right (say) the ports 53, and therefore the right-hand chamber 27, are cut off from the inlet groove 50 and are more fully opened to the exhaust groove 49, while the ports 54 and groove 51, and therefore the lefthand chamber 28, are cut off from the exhaust groove 52 and more fully opened to the inlet groove. Thus the piston is forced to the right to keep pace with the nut. If the spring washers 63, 64 which tend to keep the nut in a neutral position in the piston are very stiff normal .steering may be effected by hand, the nut only being moved in the piston to bring hydraulic power into action when the resistance to steering is very great. By using springs of different strengths the relative proportion of hand to power steering may be varied. as desired. In order to relieve the liquid pressure on the piston when it has reached the end of its stroke in either direction it is formed with ports 67, 68 which are in communication with its ends and when in the extreme, positions are also in communication with the outlet pipe. Air trapped in the cylinder chambers 27, 28 is allowed to escape into the outlet pipe when grooves 72, 74 in the piston register with the ends of small bores 71, 73 leading to the chambers, the grooves 73, 74 leading out of the groove 48 which is in permanent communication with the outlet pipe. If the pump is not working liquid can circulate freely through the system when the steering-gear is operated by hand ; the pump is preferably of the kind which permits this or else a byepass with a check valve is provided. In a modification the valve ports and grooves are so arranged that the inlet groove 50 is normally closed by the nut, so that liquid does not circulate continuously through the cylinder 10.