Patent GB-154176-A (GB)
Title: Improvements in or relating to pneumatic cushioning or shock absorbing devices for vehicles
IPC: B60G17/044
Filed: 1920-08-27
Abstract: 154,176. Holmes, B. B. Nov. 14, 1919, [Convention date]. Pneumatic springs; fluid-friction vibrationdampers.-A pneumatic cushioning or shockabsorbing device primarily for use on vehicles, comprises a cushion space from which fluid is pumped more or less continuously into a reservoir at higher pressure; the energy for pumping the fluid is derived from variations in the load sustained by the device and means controlled by the relative positions of the parts are provided to regulate a back flow of fluid from the reservoir to the cushion space. As shown in Fig. 1, the device comprises a base casting 6 with a cylindrical bore 10 and having an upper cast member 12 screwed into its upper end, a flange 14 on the member 12 seating on the upper edge of the casting 6 and a felt washer in a channel 15 being fed with oil through a wick 16 from an oil chamber 11 provided with a filling cap 17. An inward tubular extension 18 at the top of the member 12 contains an inwardly-opening check valve 19 and has a closing cap 20 and dust cap 21. Sliding in the member 12 in an elongated piston 22 containing the reservoir 23 which is closed by a threaded thimble 24 with a conical flange 25. Held in place by annular flanges 26, 27, Fig. 3, on the thimble and the upper face 28 of the piston 22 are three flexible packing-rings 29, 32, 31 preferably of chrome-tanned leather or oilresisting rubber compound. The rings 29, 31 are cup-shaped with their free ends turned towards the cushion space 13, while the U-shaped ring 32 is expanded against the plane surfaces of the other rings by a series of Balleville washers 33 and outwards by pressure fluid admitted through a port 34 from the bottom of the reservoir 23. A certain amount of lubricating liquid. such as a heavy oil, is provided within the system to lubricate the parts and ensure tightsealing of all valves and packing, and some of the oil is forced from the bottom of the reservoir into the ring 32. The washers 33 may be stressed to the desired extent by screwing the thimble 24 within the piston. The thimble carries a downwardly projecting cylinder 35 extending into a cup 36 on the bottom of the reservoir and closed at its upper end by a plug 38 with an axial guideway for a tubular piston-rod 39 with a piston 42. This piston and the plug 38 are provided with cup packings permitting fluid to flow from the cushion space 13 to the reservoir 23 but checking return flow. Upward movement of the piston-rod is limited by a stop 43. A combined guide and dash-pot 44 is screwed on the upper end of the rod 39 and has a seat for a spring-controlled ball check-valve 46 which closes flow from the reservoir to the cushion space. The upper end of the member 44 is guided on the extension 18 and the fit is close enough to give a dash-pot action in the presence of oil. As shown, the casting 6 is secured to the rear spring horn 7 of a vehicle by a bolt 8 engaging the usual shackle-bolt eye and by an undercut lug 9 engaging the flange of the horn 7, while the piston 22 is connected by a link 51<1> to the leaf spring 54 of the vehicle. Initially sufficient oil is forced past the valve 19 and then air is pumped in until the pressure is preferably higher than that necessary to support the heaviest load to be borne. When the vehicle is in motion, the road shocks cause the piston 22 to move against the pressure in the cushion space and the member 44 to make contact with the head of the member 12, the impact being cushioned by the dash-pot action and the piston 42 being moved downwards in the cylinder 35, causing first oil and then air to be pumped from the space 13 into the reservoir. The reverse movement is caused by a spring 49 and is gradual. During ordinary oscillations of the vehicle, the valve 46 is unseated by the extension 18 but only for short periods, so that there is little flow of oil through the long passage in the piston-rod 39, the pump action having predominance. If the pressure in the space 13 is diminished unduly or the load is increased substantially, the continued unseating of the valve 46 allows oil to pass up the piston-rod, and as oil is admitted to the cup 36 only through a restricted port 3, the cylinder 35 and pistonrod are blown clear of oil and air is then vented into the cushion space from the reservoir. The oil from the rod 39 is sprayed through a lateral port in the member 44 against the wall of the outer cylinder and passes the flange 25 to the space above the packing. Any excess flows into the well of the thimble 24 and is gradually pumped through ports 40 by the pump 42, 35 into the reservoir. If load variations are slight, a modified form of the device may be used wherein the pumping and venting are dispensed with, a non-return valve being provided in the bottom of the thimble 24 which is made deeper to extend down into the reservoir. This form is suitable for use with the front springs of a vehicle, the pumping and venting form being used with the rear springs, but either form may be used with all the springs. Instead of the link 51', a plunger sliding in a bushed guideway in the casing 6 may be used, and a bolt may be used instead of the lug 9. The device may be mounted at the end of a quarter elliptic spring, the piston 22 being linked to a semi-elliptic spring below. Reference has been directed by the Comptroller to Specification 137,585.