Patent GB-855579-A (GB)
Title: Improvements in or relating to servo-steering devices for motor vehicles
IPC: B62D5/06
Filed: 1958-07-24
Abstract: 855,579. Power-steering. ZAHNRADFABRIK FRIEDRICHSHAFEN A.G. July 24, 1958 [July 24, 1957], No. 23928/58. Class 79(5). A servo-steering system for motor vehicles comprises a valve having a control member movable in relation to a stationary housing part and at least one pair of opposed reaction pistons which are moved by said control member relatively to each other or to the control member and which are subjected to the pressure medium which is under the working pressure at any given time and is characterized in that a pre-stressed spring is inserted between the control member and at least one reaction piston of each pair, the pre-stressing of the spring corresponding to a predetermined maximum working pressure and in that each pair of reaction pistons is held between two fixed stops, with the interpositioning of a chamber filled by a pressure medium. As shown in Fig. 1, a steering system comprises a fluid supply 2, pump 3, the control valve and a working cylinder 26, the supply of fluid to which through lines 22 or 23 is determined by movement of a control member 14 of the valve actuated by a connection from its part 12 to a lever transmission operated by an axially slidable worm or steering spindle, not shown. Within the member 14 in appropriate recesses are disposed bolts 38 and 39 bearing against the valve housing 40 and an abutment 42 respectively and a pair of reaction pistons 33 and 34 kept apart by a spring 36. The bolts 38 and 39 are surrounded by springs 44 and 45 respectively, bearing against fixed check plates 46 and 47 and check plates 50 and 51. Prestressing of the springs 44 and 45 may be varied by using check plates of different thicknesses. On movement of the control member 14 to the left, control slots 16 and 18 are closed and the pressure fluid passes through the passage 9, line 23 into the cylinder chamber 21, and also from the annular passage 5 into the reaction chamber 31 between the pistons. The movement of the member 14 to the left produces a relative movement between it and the bolt 38 which is transmitted to the reaction piston 33 providing a resistance perceptible at the steering wheel. A further increase in pressure in the chamber 31 forces the bolts 38 and 39, through the pistons 33 and 34, against the cover 40 and abutment 42 and no further back pressure is experienced. In a modification, Fig. 2, a steering shaft having two parts 60 (carrying the steering worm) and 62 and rocker bolts 61 displacing a valve control member 64 axially in response to reaction from the steering worm 60, is provided, in appropriate recesses, within the outer valve portion 75, with two pairs of reaction pistons 76, 79 and 77, 80 enclosing reaction chambers 104, 105 and bolts 86 and 85 which are surrounded by springs 82 and 83, bearing at one end against the collars 89 and 90 of the bolts and at the other against pins 92 and 93, held in the valve bush, through washers 95 and 96. By using washers of different thicknesses, pre-stressing of the springs may be varied. The reaction pistons bear against the bolts 85 and 86 on the one hand and against plates 106 and 81 attached to the valve control member 64. On rotation of the steering wheel in one direction or the other, displacement of the control member 64 occurs and fluid is admitted to one or other of the chambers 104 or 105 opposing the motion of the control member providing a resistance perceptible at the steering wheel. The reaction pistons may be given different diameters to correspond with the different diameters in the working cylinder 26. The extension of the reaction pistons is limited when the bolts bear against the collar of the control member and against the plate 84. In a further modification, Fig. 3, wherein the steering shaft has two parts, one of which 181 carries the steering worm, axial movement of which operates a valve control member 133 through rocker bolts 182, 182<SP>1</SP>, a pair of reaction pistons 131, 132 are provided bearing against a disc 135 and a spring loaded bolt 137 which bears against a bush 136. On travel of the control member 133 to the left the body 134 is displaced and on its travel to the right the disc 135 is displaced. Compression springs, not shown, separate the members 134, 135. The pressure fluid is admitted to the chamber 161 through the passage 169, recess 190 and bore 189 and initially the fluid pressure operates the piston 131 to oppose the movement of the control member. The extension of the reaction pistons is limited when the bolt 137 bears against the bush 136 and the piston 131 against the plate 135. Specification 855,578 is referred to.