Patent GB-781980-A (GB)
Title: Improvements in or relating to fluid-pressure-operated mechanisms
Inventor: HARDY WILLIAM GUY
IPC: B62D5/087
Filed: 1954-06-08
Abstract: 781,980. Vehicle power steering. ROLLROYCE, Ltd. May 26. 1955 [June 8, 1954; Seut. 8, 1954]. Nos. 16864/54 and 26073/54. Class 79(5) [Also in Group XXIX] A valve for a fluid pressure assisted vehicle steering gear, and of the kind providing a fluid pressure which varies in accordance with the extent of displacement of a valve element and in which the fluid pressure acts to provide a reaction against said displacement is adapted so that displacement of the valve element beyond a selected position results in relief of at least part of the fluid-pressure reaction. In the embodiment shown in Fig. 2 the steering column 11 has a splined connection 25a with a shaft 25 which carries a worm 26 and a valve member 27. The worm 26 meshes with a member connected to the drop arm 15 and is able to move the shaft 25 axially to operate the valve member 27 in response to the resistance to turning of the road wheels. Each end of the valve member carries a washer 45 which is urged by springs 46 against a shoulder 44 the springs bearing also against a member 47 which is retained by a circlip 48. The housing of the valve also has a number of bores which are paralled to the shaft 25 and each of which contains a pair of pistons 41 urged apart by a spring 42, the outer ends of the pistons normally engaging shoulders 43 which are spaced apart a distance equal to the spacing of the shoulders on the valve member against which the washers 45 abut. Hydraulic fluid under pressure is supplied by a pump to a connection 20 from which it passes to an annular groove 36 which communicates with the spaces between the pistons 41 and also, due to the central land of the valve member being of smaller axial width than the groove 36, with annular grooves 39, 40 which connect with passages 21, 22 leading to the hydraulic actuator. The grooves 39, 40 also communicate, in the central position of the valve, with annular grooves 37, 38 which lead to an exhaust passage 24. When the valve member 27 is displaced', say to the right, the pressure in the passage 21 is increased and that in the passage 22 decreased resulting in operation of the hydraulic actuator. Also, the pressure in the passage 20 and consequently between the pistons 41 will increase due to the greater restriction offered by the valve to the escape of liquid to the exhaust 24. Thus the left hand piston 41, which will be displaced from its abutment 43. will exert greater reaction on the valve member through the washer 45. springs 46. abutment 47 and circlip 48 as the pressure in the annular groove 36 increases until such a value is reached that the piston overcomes the force of the springs 46 and engages its abutment 43 whereupon the sole axial load applied to the valve member 27 is that provided by the springs 46. In a modification certain pistons 41 only are enabled to engage their abutments 43 upon increase of pressure in the grooves 36, the others being engaged by extensions on the members 47 so that they always apply reaction to the valve member when the latter is displaced. In another embodiment the pump pressure is effective through ports 92, Fig. 9, in the hollow interior of pistons 90 which apply the reaction to the valve member. Increasing pressure within the pistons 90 ultimately causes secondary pistons 95 to move inwardly against a loading spring 98 and engage abutments 99 in the pistons 90 thereby reducing the reaction which the latter apply to the valve member. Fig. 6 illustrates a further embodiment which is adapted for insertion in the drag link of the steering gear, one part of the drag link being connected to the valve member 50 whilst the other part is connected to the housing 118. Pressure liquid enters the housing at 20 and passes to a bore 51 in the valve member, the latter having radial passages 52 interconnecting the bore 51 with annular grooves 54. The connection 24 to the actuator communicates with an annular groove 57 whilst passages 21, 22 lead to exhaust. At each end of the valve member is a further set of radial passages 53 communicating with an annular chamber formed between a flange 59a, on a sleeve 60 which is slidable on a reduced part of the valve member and a further sleeve 64 which is slidable on the sleeve 60. Both sleeves are loaded by springs to engage with the abutments as shown. When the valve member is moved. say to the right. an abutment 58 is moved away from the flange of the left-hand sleeve 60 whilst the right-hand sleeve 60 is moved against its loading spring 61 and also against the pressure of liquid in the annular chamber. As the pressure increases the right-hand sleeve 64 is moved to the right against its spring 66 until it engages an abutment 67 on the sleeve 60 whereupon the hydraulic reaction on the valve member is removed. In a modification, the effective area of the sleeve 64 facing the annular chamber in which the pressure acts is less than that of the flange on the sleeve 60 so that when the sleeve 64 engages the abutment 67 the hydraulic reaction is reduced but not entirely removed.