GB810716A - Improvements relating to servo-operated or servo-assisted steering means in motor vehicles - Google Patents

Abstract

810,716. Vehicle power steering. DAIMLER-BENZ A. G. July 8, 1957 [July 18, 1956], No. 21593/57. Class 79(5). In a servo-steering system for a motor vehicle a centrifugal device driven in accordance with the vehicle speed provides increasing opposition to the movement of the servo slide valve as the vehicle speed increases so as to reduce the servo assistance. In one example the centrifugal device comprises a governor 36, Fig. 1, connected to the vehicle transmission and actuating a reducing valve 35 in a pipe 33 from an auxiliary pump 37 to obtain pressures which increase as the vehicle speed increases. The line 33 is connected to two points on a servo valve 10 and according to the movement of the valve slide 11 by rotation of the steering ball-nut 4 fluid passes through one or other of passages 32, 32<SP>1</SP> to actuate pistons 31, 31<SP>1</SP> in the ends of the slide 11 to resist the movement of the slide. The pressure in the line 33 may also be used to reduce the pressure in the supply line 23 from the main pump 24 at the higher vehicle speeds so that pressures in the servo cylinder 15, 16 are also reduced at higher speeds to reduce the servo assistance. The line 33 is connected by a pipe 41 to a differential regulator valve 39 which permits the pump 24 to blow-off through a return port 42 when higher pressures are reached in the pipe 33 at the higher vehicle speeds. In another embodiment a pressure which varies according to the vehicle speed is obtained from an auxiliary pump 84, Fig. 2, in combination with a double piston valve 85 having a revoluble casing connected to the vehicle transmission and carrying a weight which actuates the valve through centrifugal force. At low speeds the valve 85 permits the oil flow to return direct to the tank 50 but progressively shuts off as the speed increases to build up the delivery pressure in the line 83. In this example the pressure in the line 83 indirectly influences the pressures in spaces 77, 77<SP>1</SP> behind restoring pistons 78, 78<SP>1</SP> of a valve slide 46 through a system of piston manometer devices 63, 63<SP>1</SP>. Each device comprises a piston 64 balancing a reducing valve 69 through a weight-beam 67 pivoted on a movable fulcrum 70 attached to winging arms 71. Each piston 64 and valve 69 is connected to one end of the servo cylinder 60 through lines 62, 74 and supply reduced pressure line 75 connected to one of the restoring pistons 78 to provide a restoring bias according to the setting of the swinging arm 71. Movement of the swinging arms 71 is governed by a spring- loaded piston and cylinder 81, 82 connected to the variable pressure line 83 from the centrifugal valve 85.