Patent GB-621625-A (GB)
Title: Hydraulic shock absorber
IPC: F16F9/516
Filed: 1946-04-29
Abstract: 621,625. Hydraulic shock absorbers. FOCHT, N. S. April 29, 1946, No. 12855 [Class 108(iii)] A hydraulic shock-absorber of the kind described in Specifications 594,006, 594,007 and 621,630, comprising a piston reciprocable in a cylinder 10, Fig. 5, closed at its lower end by a head 14, has a port 22 providing communication between the lower end b of the cylinder and a liquid reservoir c, a metering pin 23 upwardly movable to close the port 22 and having a downwardly tapering portion for movement into the port to progressively decrease its area, the top of the pin 23 being exposed to pressure within the lower cylinder space b, yieldable means tending constantly to urge the pin 23 upwardly to close the port 22, and a dash-pot 36, 37 controlling downward movement of the pin 23. The dash-pot comprises a disc' 37 carried by the pin 23 and movable with limited clearance in a well 36 formed in the head 14. In a modified construction, Fig. 9 (not shown), the disc 37 has ports controlled by a flap valve. A bevelled portion 28 of the metering pin stem, is urged into contact with a constricted valve seat portion 26 of the port 22 under the static condition of the shock absorber by a spring 31 which may be supplemented by a further spring 32. Above the valve portion 28 of the pin 23 is a tapered metering portion 27. The spring 31 also controls a flap-valve 25 which allows oneway flow from the reservoir c to the lower cylinder space b. Excessive pressure in the space b may be relieved by a ball-valve 34 loaded by a blade-spring 35. In the construction of Fig. 9 (not shown) the ball-valve is replaced by a second tapered metering portion, disposed above the portion 27 on the pin 23, and which has a pressure-relieving action. Downward movement of the pin 23 is limited by an adjustable screw-plug 39, the position of which is looked by a similar second plug (not shown). A coiled compression-spring may be provided between the end of the pin 23 and the plug 39. The piston (Fig. 2) comprises a head 41 having an annular group of ports 65 and a skirt 11 carrying a valve seat ring 43 at its lower end on which is mounted a cup-shaped valve 46 having a central metering-orifice 58. A co-operating metering-rod 57 is in adjustable threaded engagement with a plunger 53 which is mounted for limited axial movement in a hollow end portion of the piston rod against the resistance of a coiled spring 62. The axial movement of the plunger 53 is limited by a U-shaped abutment 56 and is damped by liquid displaced through a clearance 66. Its lower axial movement is further damped by the dashpot action of a disc-ended portion 54 of the plunger 63, which has limited clearance in the hollow portion of the valve 45. Axial adjustment of the metering pin 67 is effected by the rotation of a rod 60 which extends to the outside of the shock-absorber at its upper end and has an extension 59 at its lower end which is in engagement with an upper stem of polygonal cross-section, of the metering pin 57. Operation.-On compression following normal conditions, entry of the piston-rod into the cylinder space a above the piston results in increased cylinder pressure which acts on the top surface of the metering pin 23 causing the valve portion 28 to open and permit displacement of liquid from space b to the reservoir c. Further movement of the metering pin 23 progressively reduces the area of the port 22. During this stage the valve 45 is raised against the action of a coiled spring 49 and flow from space b to space a occurs through ports 65 in the piston. The valve 45 carries the plunger 53 and metering pin 57 upwardly with it, but on rebound while the valve 45 seats instantly, the plunger 53 moves back slowly due to damping action through the clearance 66, and the metering pin 57 consequently provides progressively decreasing damping of the return flow through the orifice 58 in the valve 45. Final movement of the plunger 53 is still further damped when its disc portion 54 re-enters the valve 45. Under low-frequency vibrations applied to the shock absorber the deflection of valve 45 under compression is insufficient for it to be separated from the disc 54. During rebound, liquid returns from the reservoir to space b through the annular disc valve 25. Under extension from normal conditions as when a vehicle wheel enters a depression, pressure acting on the difference of areas x, y of the valve 45 also raises the valve 45 and liquid passes again from the reservoir c to the space b through the valve 25.