GB1415878A - Arrangement for limitting the - Google Patents

Abstract

1415878 Power-assisted steering mechanism K-H THOMAS [trading as LANGEN & CO] 21 Dec 1972 [23 Dec 1971] 59162/72 Heading B7H In an arrangement for limiting the manual steering effort in a power-assisted steering system including a control piston 9 exercising two-edge control over the supply of pressure fluid from a pump 1 to one chamber 27 of a servo-motor 22, the control piston 9 has a reaction face f subjected to the pressure in the servomotor chamber 26 directly connected to the pump 1 and acts through a tappet 11 on an actuating lever 13 pivotally displaceable relative to housing 6, and a reaction piston 10 having a reaction face f 1 subjected to the pressure in the chamber 27 acts on the lever 13 through a tappet 12 and a compression spring 30, movement of the reaction piston 10 in each direction being limited by a stop-ring 33 and end wall 34 so that when the pressure in the chamber 27 rises above or falls below respective prescribed limits the force transmitted to the lever 13 through the tappet 12 remains constant at the value determined by the corresponding compression of the spring 31. The required manual steering effort thus remains substantially constant when it has risen to a predetermined value in either direction. The housing 6 and lever 13 form respective parts of a linkage connecting a steering wheel to steerable road wheels. The areas of the faces F, F 1 of the servomotor piston 25 disposed in the chamber 26, 27 are in the ratio 1 : 2 and the areas of the reaction faces f,f 1 are in the same proportion. The faces of the servomotor piston may alternatively have equal areas, fluid being supplied to one chamber at a reduced pressure through a pressure changing device. In other embodiments, the reaction piston and control piston are coaxially arranged with a compression spring between them, a leaf-spring or tension bar spring replaces the coil spring shown, and the reaction piston acts through a tappet on a lever which acts on the actuating lever through a spring.