Patent GB-669521-A (GB)
Title: Improvements in hydraulic devices for damping oscillations for spring suspensions of vehicles and the like
IPC: F16F9/48
Filed: 1948-08-18
Abstract: 669,521. Pressure relief valves. KATZ, M. Aug. 18, 1948 [Dec. 31, 1947], No. 21827/48. Class 135 [Also in Group XXXII] The piston of a hydraulic device for damping movement between bodies connected by springs, particularly for vehicle suspensions, is formed with two longitudinal ducts, each end of which opens freely into one of the two respective chambers formed by the cylinder on either side of the piston, and is connected with the other compartments by a valve, loaded by a resilient member which is augmented by a movable element or sleeve, the displacements of which are a function of the piston displacement on outward movement, the valve during the whole of the return piston movement being maintained in the position reached at the end of the outward stroke, due to the application against the element or sleeve, of the same hydraulic pressure which is applied in the respective cylinder chamber to the face of the valve. The device may be singleacting in which case one longitudinal duct, only, is provided. As applied to a double-acting shock absorber (Fig. 2), each end of the piston 6 is slidable in a corresponding cylinder chamber 12. Journalled in the piston 6 is a cylindrical member 7 in which is slidable the outer end of an arm 8 which is rigid with an operating shaft 9 journalled in the main casing (not shown). Journalled on the member 7 is a cam 26 rigid with a slotted arm 27 in which works a pin 28 carried by an arm 29: The latter is rotatable by sheathed cable means (not shown) so as to vary the angular setting of the cam 26 relative to the member 7. Each end of the piston 6 has a valve 21 which is urged on to a seating 19 by a spring.25 and is slidable within a sleeve 22 which forms an abutment for the spring 25. The sleeve 22 is slidable itself in a bore 22a in the piston 6 and has a projecting stem 24 which engages the cam 26 so that movement of the arm 8 varies the spring loading of the valve 21. The wall of the bore 22 has an upper recess 34 connected by a duct 34a with a central reservoir space 14 of the shock absorber, and a further lower recess 35. The latter is connected with a duct 13 which opens into the cylinder chamber 12 at one end and the valve chamber of the valve 21 at the other end (not shown) of the piston 6. A further duct 13<SP>1</SP> connects the left hand cylinder chamber 12 with the right hand valve chamber. The reservoir space 14 is connected with each cylinder chamber 12 by a respective non-return valve 17. The valve seating 19 may be screwed in or out of the piston head to vary the initial loading of the spring 25, by the engagement of a slot 33 with a projection on the inner end of a screw (not shown) mounted in the end of the cylinder and manually rotatable from the outside thereof. In operation of the construction of Fig. 2, on outward movement of the piston 6 from a normal central position, the effect of the cam 26 is such as to increase the loading of the valve spring 25 associated with the end of the piston which is receding from its corresponding cylinder end, and to maintain the loading of the other spring 25. Liquid thus flows freely through the valve 21 loaded by the latter spring and passes via the corresponding duct 13 (or 13r as the case may be) to the other cylinder chamber. At the commencement of the return movement, the first-mentioned valve spring 25 is loaded by an amount proportional to the outward piston travel. This loading is maintained by the action of liquid pressure in an annular space 36 on a flange 23 of the sleeve 22. The force due to this pressure is augmented by friction between the sleeve 22 and its bore 22a due to the difference in pressures in the recesses 34, 35. The annular area of the flange is substantially equal to the area of the aperture of the valve seat 21. The space 36 is connected via the recess 35 with the cylinder chamber 12 in which the corresponding end of the piston works. In a modification (Fig. 5) the sleeve 22 is loaded by springs 37, 38 which may be selected to provide a desired damping resistance of the valve 21 for a given degree of outward piston travel. This resistance may increase in relation to increased piston travel in a manner corresponding to the rate of the vehicle suspension springs. In the construction shown in Fig. 6, flow in respective directions through a piston 42 through ducts 69, 69<SP>1</SP> is controlled by valves 67, 67<SP>1</SP> loaded by springs 66, 66<SP>1</SP>. The latter are in abutment with respective sleeves 64, 64<SP>1</SP> which are slidable relative to the piston body and engage a rim 57 carried by a member 56. A rod 54 having helicoidal grooves or a large-pitch screw-thread engages corresponding grooves or threads internally formed in the member 56 which has a further threaded portion 58 which engages a corresponding thread in the hollow piston rod 43. Annular spaces formed behind flanges 65, 65<SP>1</SP> of the sleeves 64, 64<SP>1</SP> are connected respectively with the ducts 69<SP>1</SP>, 69. The flanges 65, 65<SP>1</SP> are each in the form of a narrowed lip which is slightly extensible so as to frictionally engage the wall of the bore in which it is slidable. Alternatively the flanges may be formed by detachable cup-shaped members of rubber or other material and may be provided with resilient packing segments. The cylinder 41 is connected with a reservoir space 63 by respective valves 50, 52 at the upper and lower ends of the cylinder. The valves 50, 52 are spring-urged to open and closed positions respectively when the shock absorber is inoperative. The seat of the valve 67<SP>1</SP> has slots 71<SP>1</SP> which may be engaged with a projection 72 for adjustment of the valve loading on relative rotation of the piston rod and cylinder. Similar provision may be made for adjustment of the valve 67. In operation of the construction of Fig. 6, on compression from the position shown, the helicoidal grooves on the member 54 cause rotation of the member 56. Due to its threaded engagement at 58 with the piston rod, the member 56 thus moves axially relative to the piston body to increase and decrease respectively the loads of the springs 66, 66<SP>1</SP>. Free flow thus occurs through the duct 69<SP>1</SP> and since little pressure is developed in the cylinder space above the piston, liquid passes to the reservoir through the valve 50. On rebound, the load on the spring 66 is maintained due to pressure acting on the flange 65 the effect of which is aided by friction between the flange and the bore in which it is slidable. Liquid passes freely from the reservoir through the valve 52. A similar action occurs for upward deflection from, and return to, the central position shown. The rod 54 may alternatively be replaced by a smooth rod of variable section which co-operates in the manner of a cam acting through levers &c. to vary the loading of the springs 66. The damping valves and associated loading mechanism may be disposed elsewhere than in the pistons.