Patent GB-764204-A (GB)
Title: Improved control valve for power steering mechanism for motor vehicles
IPC: F15B9/12
Filed: 1954-12-15
Abstract: 764,204. Vehicle power steering. GENERAL MOTORS CORPORATION. Dec. 15, 1954 [Jan. 11, 1954], No. 36338/54. Class 79(5). [Also in Group XXIX] In a control valve 24 for a fluid-pressure power steering mechanism for motor vehicles a pair of spring-pressed plunger valves 144 abut, in the neutral position, shoulders in a ported casing 76 and a slidable spool valve 78, the plunger valves 144 being disposed in bores 145 in communication with an inlet passage and exhaust passages of the valve, and one of the plunger valves being displaced by the spool to connect the inlet passage to an exhaust passage on excessive relative displacement of the spool and casing. As shown in Fig. 1 the steering mechanism comprises a steering column 12 carrying a worm 38 on which is mounted by balls a nut 30 having rack teeth 32 which mesh with teeth on a sector 34, other teeth on the sector meshing teeth on a rack 44 connected at 37 to a rod 46, and the rack 44 being adjusted relative to the sector 34 by a screw 50. A piston 19 on the rod 46 is arranged in a cylinder 18 which is supplied with pressurised liquid through a pump 20 from a reservoir 22. A relief valve 142 is arranged in the output conduit 90 of the pump 20 to divert the fluid through a conduit 140 to an exhaust conduit 92. The valve 24 controls liquid flow to and from the cylinder 18 and is actuated by manual rotation of the column 12. The valve comprises annular chambers 84, 86, 88 in the casing 76, the chamber 84 being connected to the output conduit 90 and the chambers 86, 88 being connected to the cylinder 18 on opposite sides of the piston 19 and to the exhaust conduit 92. A shoulder 106 on the column 12 forms a stop for one race of a ball thrust bearing 108, the other race 110 bearing against the spool 98. A similar bearing 109 is arranged at the other end of the spool 98, the race 102 of which is engaged by a nut 100 on the column 12. The spool 98 moves axially with the column but is free to rotate thereon, axial movement being limited by abutment of races 110, 112 against end faces of a casing 76. The spool 98 is normally centred by five springs 118, one of which is shown in Fig. 4, each spring acting on plungers 120 abutting the races 110, 112, and the springs and plungers being housed in bores in the casing 76 and bores opening into the chamber 84. With the spool 98 centred fluid from the pump 20 issues from chamber 84 and is divided by a central land 122 on the spool into two streams equalizing the pressures on both sides of the piston 19 and returning to the reservoir 22 through the conduit 92. The plungers 144 and a light spring 146 are disposed in the bore 145, each plunger having lands 150, 152. With the spool 98 centred the plungers 144 abut shoulders 154 on easing parts 78, 82 and the races 110, 112, the chambers 84, 86, 88 being connected with the bore 145 by ports 158, 156 and the lands 152 sealing the chamber 84 from the outlet chambers 86, 88. When the hand wheel 36 is moved with a pressure above the centring force of the springs 118 (i.e. three pounds at the steering wheel), for example, for a right hand turn, the spool 98 is moved to the left thereby pressurizing the right hand end of the cylinder 18. When a steering effort greater than a predetermined amount is applied to the steering wheel or when the piston 19 reaches its limit position and steering effort is still applied, the race 112 moves the right hand plunger 144 as shown in Fig. 6 to connect the chambers 84, 88 to relieve pressure. Movement of the plunger 144 is said to be less noisy than operation of the relief valve 142.