Patent GB-1409773-A (GB)
Title: Assisted steering control with automatic return especially for automobile vehicles
IPC: B62D5/08
Filed: 1973-06-20
Abstract: 1409773 Power assisted steering SOC ANON FRANCAISE DU FERODO 20 June 1973 [22 June 1972] 29244/73 Heading B7H A power assisted steering system which will automatically restore the steered wheels 14 of the vehicle to the straight line position when the steering wheel 11 is released includes a distribution device 21 which controls the flow of pressure fluid from a pump 21<SP>1</SP> to a servomotor 19, the distribution device 21 comprising a first element 50 which is urged into a mean position by a centring spring 57 and which can be moved to either of its two extreme positions by detector means (not shown) responsive to movement of the steering column 10, and a second element 35 which is controlled by an operating member 38 responsive to movement of the steered wheels 14, the second element 35 constituting a reversing device capable of ensuring a reversal of the direction of actuation of the servomotor 19 after the first element has returned to its mean position. As described, the servomotor 19 consists of a differential jack having a large chamber 29 of twice the area of a small chamber 28. The pump 21<SP>1</SP> is connected by line 30 to the small chamber 28 and to the distributer 21 which in turn is connected by line 31 to reservoir 22 and by line 32 to the large chamber 29. The distributer 21 has a fixed casing 33, a tubular jacket 35 (which constitutes the second element) and a valve spool 50 (which constitutes the first element). The jacket 35 is fixed to an operating member 38 having a boss 39 projecting through an aperture in the casing 33, movement of the operating member 38 being limited by the boss 39 engaging walls 42, 43 of the aperture. A ball catch 60 fixed to the rack 12 engages a recess 62 in the boss 39. The valve spool 50 is urged into a mean position as shown in Figs. 2 and 3A by a centring spring 57 and can be moved to either of its extreme positions by detector means (not shown) responsive to movement of the steering column 10. The arrangement operates as follows:-in neutral position of the steering wheel (Figs. 2, 3A) the output of pump 211 flows to the reservoir 22 through two gaps 30E, 31E, each of which causes an equal pressure drop so that the pressure in chamber 28 is twice that in chamber 29 thus resulting in no movement of the jack 19. When the steering wheel 11 is turned, e.g. to move the rack 12 to the right as shown in Figs. 1, 2, the valve spool 50 is moved to the right to the position shown in Fig. 3B. This causes the output of pump 211 to be supplied to chamber 28 and connects chamber 29 to the reservoir 22 so that the jack 19 causes the rack 12 to move to the right. This movement of the rack 12 causes the boss 39 to move into engagement with face 43, thus moving the jacket 35 to the right to the position shown in Fig. 3C, the direction in which the jack 19 acts remaining unchanged. When the steering effort applied to the steering wheel 11 is removed the spring 57 returns valve spool 50 to its central position, the jacket 35 remaining in its extreme position as shown in Fig. 3D. The output of pump 21<SP>1</SP> is then applied to both ends of the jack 19 thus reversing the direction of action of the jack 19 which returns the wheels 14 to their straight line position. When the straight line position is reached the ball catch 60 moves the jacket 35 back to its central position, thus returning the distributer 21 to its neutral position as shown in Figs. 2, 3A. In a modification (not shown) the casing 33 is reduced to abutments which limit the movement of the jacket 35, the lines 30, 31, 32 being attached directly to the jacket 35. The invention may also be applied to a system having a symmetrical jack.