Patent GB-822644-A (GB)
Title: Hydraulic reaction control
IPC: B62D6/02
Filed: 1956-05-22
Abstract: 822,644. Vehicle power steering. BENDIX AVIATION CORPORATION. May 22, 1956 [June 7, 1955], No. 15816/56. Class 79(5) In a power assisted steering mechanism having first and second type pressure reaction areas to provide "feel" associated with the control valve, the two reaction areas of different types are provided for each direction of movement of the valve and subjected to forces due to variable pressures and both areas oppose movement of the valve from a neutral position, the forces increasing at one rate up to a predetermined value and at a lesser rate thereafter. As shown in Fig. 1 the invention is applied to vehicle steerable wheels 10 having steering arms 12 connected to track links 14, 16, the links being interconnected by a rod 18 having one end connected to an arm 20 pivoted to the vehicle frame 24 and having the other end connected to an arm 34 operatively controlled by a steering shaft 36. Power steering is effected by a jack 28 interconnecting the rod 18 and frame 24, a control valve 26 of the open centre type being interposed between 'the jack and a pump 30 and reservoir 32. The valve 26 comprises a valve casing 38 having ports 48, 50 connected to opposite ends of the jack, a port 58 connected to the reservoir 32 and a port 62 connected to the output of the pump 30. The casing 38 has a bore housing a spool 42 having grooves 44, 46, the spool being carried by a..bolt 106 connected by a member 110 to a sleeve 116 containing the ball end 122 of the arm 34. The ball 122 is engaged by members 118, 120, and a spring 124 and a member 126 are interposed between the member 110 and the members 118, 120. In order to prevent rotation of the bolt 106 on applying a retaining nut 128 the head 114 of the bolt carries a pin 134 engaging sockets 130, 132 in an extension 98 of the casing 38. Adjacent the ends of the spool 42 are packing members 68, 70. Reaction chambers 76, 80 and 78, 82 are defined between the members 68, 70 and the spool 42, and are subjected to hydraulic pressure resisting movement of the spool 42 by the steering shaft 36. The chambers 80, 82 are connected by passages 145, 147 in the spool 42 to the grooves 44, 46 so as to be subject continually to the pressures in the grooves. The chambers 76, 78 are connected by passages 164, 166 to a bore 148 in the casing 38. The bore houses valve elements 144, 146 urged apart by a spring 154. The bore 148 is connected by passages 160, 162 to the grooves 44, 46, the elements 144, 146 being adapted to disconnect the chambers 76, 78 from the grooves 44, 46 on an excess hydraulic pressure whereby the "feel" transmitted to the vehicle driver by means of the reaction chambers is continuous with increased steerable wheel resistance but the rate of increase of "feel" is not constant. The point of change of rate of increase (i.e. where the chambers 76, 78 are cut off) can be determined by suitable proportioning of the effective areas of the chambers 76, 78, 80, 82 which are shown as being equal. In another embodiment, Fig. 3, the control valve is of the non-open centre type, the casing 38a having ports 48a, 50a connected to opposite ends of the jack, an exhaust port 58a and pressure input ports 62a. A bore in the casing 38a houses a bolt 288 carrying sealing members 284, 286 and connected to the steering shaft operated arm (not shown). The bore houses a sleeve 242 having an aperture 244 registering with the port 58a, and springs 260, 162 abutting the ends of the sleeve 242 urge valve members 248, 250 on to seats 268, 170 formed on fixed members 264, 266. In operation, axial movement of the bolt 288 serves to move either valve member 258, 250 off its associated seat thereby connecting the associated ports 62a and 48a or 50a to pressurize one end of the jack. The valve is formed with reaction chambers 290, 292, 294, 296, the chambers 294, 296 being continually subject to hydraulic pressure and the chambers 290, 292 being subject to pressure up to a predetermined maximum. The chambers 290, 292 are connected by passages 165a to regulating valves 144a, 146a arranged in separate bore 310, 312 and having separate springs 314, 316, the valves 144a, 146a functioning in a similar manner to the valves 144, 146 in Fig. 1. Specification 812,827 is referred to.