Patent GB-603281-A (GB)
Title: Improvements relating to the power-operated or power-assisted steering of land vehicles
IPC: B62D5/04
Filed: 1945-12-21
Abstract: 603,281. Power steering. PRECISION DEVELOPMENTS CO., Ltd., and OLAH, G. Dec. 21, 1945, No. 34675. [Class 40 (i)] A power steering device for road vehicles comprises an input element such as a steering wheel controlled by the driver, an output element connected to the steered parts, a mechanical lost-motion connection between the two, a follow-up control utilizing the lostmotion coupling for the control of an electric servo-motor which produces at least part of the steering effort, the motor having a brake, the motor and brake being jointly controlled by a follow-up contact device arranged to uncouple the motor automatically on failure of the electric power. The servo-motor may also be uncoupled manually. As shown, the device comprises an input shaft 1, Fig. 1, controlled at its upper end by a steering wheel and having fixed to its lower end a crossshaped member 9, Fig. 3, and a gear wheel 7 resiliently connected to each other by a peg 40 and a pair of spring-loaded plungers 41. Aligned with shaft 1 is an output shaft 5 whose upper end carries a gear 6 which is connected with some play to the cross member 9 by pegs 12. Mounted to the side and parallel with the shaft 1 is a pair of shafts 27, 46 the former being geared to the output shaft by gears 28, 29 and the latter geared to the input shaft by gear 45. A servomotor 15 is mounted on the casing 3 the shaft 20 of which, Fig. 2, provides a gear 21 meshing with another gear 22 carried on a slidable shaft 23. Also mounted on shaft 23 is another gear 24 adapted to mesh with a gear 26 mounted on shaft 27. Manual and electrical means are provided to disconnect the motor from the shaft 27 by axially shifting the shaft 23 thereby disengaging the gears 24, 26. The means provided comprises a bell-crank lever 31 acting upon the collar 30 integral with gear 24 which bell-crank is operated either manually by a knob 38 or automatically by a spring 37 upon release of the solenoid 36 on current failure. The shafts 46, 27 carry permanently meshing contact gears 47, 48, 52, 53 in which some backlash exists. The gears are insulated from their respective shafts and gears 52, 53 are insulated from one another. The teeth of the contact gears 52, 53 are slightly offset circumferentially whereby the gears 48, 53 are in contact for one direction of rotation and gears 47, 52 for the reverse direction. The servomotor has two oppositely wound field coils and the circuit to one is completed when gears 48, 53 are in contact and the other for reverse drive when the gears 47, 52 are in contact. In operation the shaft 1 is rotated which causes the armature and appropriate field coil to be energized by the switch effect of one pair of contact gears, thereby causing the servomotor to rotate shaft 27 and shaft 5 in the same direction as input shaft 1. An automatic brake for the motor 15, Fig. 1, comprises friction members 72, 73 held in contact by solenoid winding 17 permanently connected to the power supply, winding 17 being neutralized by winding 18 or 19 to release the brake wherein the motor is running, windings 18 and 19 being connected in parallel with the motor field coils. In an alternative arrangement, winding 17 is dispensed with and a spring 71 normally keeps the friction members 72, 73 in contact, the spring 71 being overcome to release the brake when either of windings 18 or 19 are energized whilst the motor is running ; this arrangement has the advantage that the motor is braked on current failure. In the case of power failure the vehicle may be steered manually. Torque is then transmitted from the input shaft 1 to the output shaft 5 through the resilient coupling 9, 7, the latter pin 40 and spring loaded plungers 41 described above. As the member 9 is connected to the gear 6 on the output shaft 5, any high torque loads cause relative movements between the members 7 and 9 and so prevents straining of the contact gears. Specifications 556,287, 573,666, 594,257, 594,258 and 597,276 are referred to.