GB1035686A - Improvements in or relating to power-assisted steering systems, particularly for motor vehicles - Google Patents

Abstract

1,035,686. Power assisted steering. ZAHNRADFABRIK FRIEDRICHSHAFEN A.G. July 4, 1963 [July 7, 1962], No. 26566/63. Heading B7H. In a power assisted steering system, means are provided for disconnecting the servo assistance at an adjustably predetermined position. The steering mechanism may comprise a worm and nut wherein the nut, 38, Fig. 1, is formed as the servo piston working in a cylinder comprised of the steering housing 36, and is also formed with a rack 40 co-operating with an axially adjustable bevelled pinion 42 mounted on a shaft 45 to which is connected a link 46 of the steering mechanism. A limited amount of axial play is allowed in the steering shaft 2 whereby a control valve 10, concentric therewith, is operated to direct pressure fluid to one side or the other of the power piston from a pump 20 and to connect the other to a reservoir 30. The shaft 45 carries a toothed disc 50, Fig. 3, which cooperates with a toothed segment 51 which is pivoted at 56 and is pivotally connected by means of rods 58 and 59 to a pair of spools 62, <SP>6</SP>3 which operate in valve cylinders 65 and 66. The cylinder 65 is formed with a groove 76 connected through a conduit 81 to chamber 34 of the servo-cylinder and the spool 63 is hollow forming a permanent connection between the servo-cylinder space 35 and the upper part 83 of the cylinder 66. Grooves 71 and 72 in the cylinders 65 and 66 are connected together by the passage 78 and to the reservoir by a passage 79. A groove 87 in the spool 62 is connected via a slot 89 with the cylinder space 90. Edges 85 and 88 are control edges of the spools 63 and 62, the arrangement being that when there is servo pressure in the cylinder space 35, the shaft 45 is rotated so that the spool 63 moves downwardly and the spool 62 moves upwardly. When the edge 85 registers with the groove 72, the cylinder space 35 is connected to reservoir through the centre of spool 63 and further steering effort must be manual. When the steering motion is in the opposite sense, spool 63 moves upwardly and 62 downwardly until the edge 88 registers with groove 76, whereby the cylinder space 34 is connected to reservoir through passage 81, grooves 77, 87, 71 and passage 79. The cylinders 65 and 66 have threaded ends 69 and 70, whereby they are secured in the housing 36 at any position of adjustment, locking nuts 67 and 68 being provided. In a modification, Fig. 5 (not shown), the toothed sector 51 and wheel 50 are replaced by connecting rods (100 and 101). In another modification, Fig. 6, the shaft 45 has a toothed segment 155 which engages a toothed rack 154 formed on a rod 150, the ends 160, 161 of which form control edges by means of which, in a steering action in one direction or the other, either the grooves 167 and 168 or grooves 170 or 171 are interconnected, whereby the cylinder space 35 or 34 is connected to reservoir at a predetermined angle of steer, the grooves 167 and 168 and 170 and 171 being formed in valve cylinders 156 and 157, respectively. These cylinders are adjustably mounted in the housing 36 by means of threaded portions 162 and 163 and are secured by lock nuts 165 and 166. In a development of this modification, Fig. 8, control edges 212, 213 of a valve spool co-operate with a valve cylinder 210 to short circuit the pressure cylinder space 34 or 35 to reservoir at a predetermined position, the cylinder 10 being adjustably mounted in the housing 36. The valve spool is connected by a push rod 205 to a U-shaped member 203 which is also connected to a guide rod 204 and is reciprocated in unison with the movements of shaft 45 by means of a crank bolt 200 which engages the U member 203. In a further embodiment, Fig. 11, the valve members for short circuiting the pressure fluid from chambers 34 or 35 are provided by a cylindrical member 254 adjustably mounted in the housing 36 and the shaped end of a rod 252 which is reciprocated in unison with movements of shaft 45 by means of teeth 251 which engage a toothed segment 250 fixed to shaft 45.