Arrangement for steering-power limitation in hydraulic servo-steering systems

Claim 1

An arrangement for limiting the steering power in hydraulic servo-steering systems for vehicles having steerable wheels and a steering wheel, a servo-motor (4) having a cylinder (24), a piston (26) and a piston rod (25) defining larger (28) and smaller (27) working areas, the smaller working area (27) being continuously connected with a pressure source (1), the servo-motor (4) being operatively connected with the steerable wheels, a comparator means (3, 3o) being operatively connected with the steering wheel and provided for the relay of a steering sensation to the steering wheel, the comparator means (3, 3o) including an activator means (33, 34; 11), a first reaction chamber (17) of a larger effective reaction area (F 2 ) and a second reaction chamber (42) of a smaller effective reaction area (F 1 ) continuously connected with the pressure source (1) and a three way, three position control valve portion (7, 31) controlling a pressure medium flow from the pressure source (1) to the larger working area (28) of the servomotor (4) or from said larger working area (28) to a return flow (T 1 , 16), said larger working area (28) of the servo-motor (4) being connected by a restrictor (19) with the first reaction chamber (17), the smaller working area (27) of the servo-motor (4) 41 and the pressure source (1) being connected with the first reaction chamber (17) by a pressure release valve (23), said pressure release valve (23) opening during the reduction of a predetermined lower pressure in the first reaction chamber (17) or during the exceeding of a predetermined pressure difference between the smaller working area (27) and the first reaction chamber (17), and the first reaction chamber (17) being connected with 51 and exhaust passage via a pressure limitation valve (21), with said pressure limitation valve (21) preventing the exceeding of a predetermined upper pressure of the first reaction chamber (17).