GB1154851A - Improvements in or relating to Power-Assisted Steering Systems, particularly for Motor Vehicles - Google Patents

Abstract

1,154,851. Power assisted steering. ZAHNRADFABRIK FRIEDRICHSHAFEN A.G. 5 July, 1966 [6 July, 1965], No. 30180/66. Heading B7H. In a control device for a power assisted steering mechanism, a casing 1 located within a groove 2 within a housing (not shown) is rotatable by the steering shaft acting through a torsion bar 3 and a pair of forks 5, 5<SP>1</SP>. A pair of control spool valves 8, 81 are slidable in bushes 11, 11<SP>1</SP> located within the casing and have control edges 12, 12<SP>1</SP> and 13, 13<SP>1</SP> which cooperate with control edges 15, 15<SP>1</SP> and 16, 16<SP>1</SP> formed in the bushes. The groove 2 is supplied with pressure fluid which, in the neutral position of the valves, Fig. 1, passes between the control edges 12<SP>1</SP>, 15<SP>1</SP> and 12, 15 into ducts 25, 25<SP>1</SP> and returns through ports 26, 26<SP>1</SP>, 21, 21<SP>1</SP> and grooves 24, 24<SP>1</SP> to spaces 10 and 10<SP>1</SP> which are connected to the fluid reservoir. With a clockwise steering movement, the valves 8 and 8<SP>1</SP> are displaced as shown in Fig. 2, and pressure fluid passing between the control edges 12<SP>1</SP> and 15<SP>1</SP> of valve 8<SP>1</SP> flows through duct 25<SP>1</SP> to one chamber 7 of the power assistance servomotor, to provide power assistance. Return fluid from the other chamber 7<SP>1</SP> of the servomotor is admitted through the port 211 and groove 24<SP>1</SP> to the space 10<SP>1</SP>. The control edges 12, 15; 13, 16 of valve 8 are closed. With an anti-clockwise steering movement, valves 8 and 81 are actuated conversely. At the lower part of each valve 8 and 8<SP>1</SP> is included a bush 31, 31<SP>1</SP> protruding from the end of the valve and enclosing a valve member 34, 34<SP>1</SP> slidable upon a stem 39, 39<SP>1</SP> and having an abutment face urged into contact with an abutment face on the bush by a spring 36, 36<SP>1</SP>. The protruding ends 31, 31<SP>1</SP> are enclosed within covers 38, 38<SP>1</SP> enclosing fluid spaces 43, 43<SP>1</SP> to which pressure fluid is admitted through passages 40, 45, 46 and 50. The upper faces 28, 28<SP>1</SP> of the valves 8 and 81 are smaller than the lower faces comprising the two parts 29, 29<SP>1</SP> and 30, 30<SP>1</SP>, but annular surfaces 17, 17<SP>1</SP> in the upper part become exposed to the pressure fluid in the upwardly displaced position of the valve. The combined surfaces 28, 17 (28<SP>1</SP>, 17<SP>1</SP>) may or may not be equal to the combined surfaces 29, 30 (29<SP>1</SP>, 30<SP>1</SP>) to give different " feel " characteristics. When they are equal, the fluid forces acting upon the upwardly displaced valve are balanced and there is a " feel " reaction force acting upon the other. Under heavy steering conditions, however, as when the vehicle is at rest, the fluid pressure will rise until in the chambers 43, 43<SP>1</SP>, it overcomes the force of the springs 36, 36<SP>1</SP>. With the upwardly displaced valve, however, say 8<SP>1</SP>, the fluid passages 42<SP>1</SP>, 45<SP>1</SP>, 46<SP>1</SP> are still in register because upward movement of the valve is limited by the head of stem 29<SP>1</SP>, so that this valve is still balanced by the fluid pressure, whereas in the other, the fluid in chamber 43 is cut off from passage 45 and opened into the interior of bush 31 and thence to exhaust through passage 52 (Fig. 3).