GB1034264A - New or improved trailer coupling - Google Patents

Abstract

1,034,264. Overrun brakes for trailer vehicles; shock-absorbers. B. & B. TRAILER Ltd. Aug. 10, 1964 [Aug. 10, 1963], No. 31680/63. Headings F2E and F2S. ]Also in Division B7] A trailer coupling of the kind adapted to operate the trailer brake as a result of relative movement between two portions connected respectively to the tractor and trailer on overrunning of the former by the latter, includes a piston-and-cylinder type damper unit in which the piston has a valve assembly which is preloaded to provide an initial resistance to flow past the piston in at least one direction, another valve being provided on the piston or in the cylinder where the latter communicates with a reservoir for providing an initial resistance to flow of fluid in the other direction past the piston or in a corresponding direction with respect to the reservoir In one embodiment, the damper unit 53, Fig 1 (Complete), is arranged between a resilient mounting 11 on a bracket 47a, upstanding from a stop sleeve 47 on a shaft 43 of a tractor connector portion 40, and a mounting 10 on a sleeve 45, surrounding the shaft 43, of a trailer attachment portion 44 which includes a brake-operating lever 48 pivoted at 50 for actuation by the end 43a of shaft 43 to actuate the trailer brakes via a cable 49. The damper unit thus extends when the coupling is compressed and moves a piston assembly. 16, Fig. 1 (Provisional), not shown, secured to a rod 13 attached to the mounting 10, relative to a structure comprising an inner cylinder 15 and an outer cylinder 12, which forms a reservoir for hydraulic fluid. A dustprotector 14 surrounding the outer cylinder is secured to the mounting 10 together with the rod 13. Extension of the damper is prevented for small overrunning forces produced by the trailer, since fluid trapped in the left-hand chamber of the cylinder cannot move past the piston until the force acting on an annular valve plate 23, via passages 21 in the piston, is sufficient to overcome prestressed spring 26. Thereafter, the plate valve 23 lifts and exerts a fairly constant resistance on fluid flow, additional fluid needed to supply the space to the right of the piston being provided by the reservoir via a lightly loaded diaphragm valve 28 covering holes 29 of a compensating valve assembly 17. During acceleration of the tractor the damper unit is compressed and fluid can flow easily past the piston via a lightly loaded valve and spring 18, 19, but fluid can only return to the reservoir via a sleeve valve 25, apertured at 27 and loaded by a spring 26 designed to give progressively increasing resistance to fluid flow with increasing speed of damper compression, so that the brake will only release slowly. The reservoir may be pressurized by an air cylinder. The alternative embodiment of Figs. 2 and 3 (Complete), not shown, performs similarly but uses a simplified construction whereby a compressed-air chamber D is formed at one end of a damper cylinder 112 and communicates pressure via a floating piston 170 to hydraulic chambers B and C separated by piston assembly 116 which is secured to rod 113 attached to mounting 110. The damper is assembled with mounting 110 attached to bracket 147a of stop sleeve 147 on shaft 143 of tractor connector portion 140, and mounting 111 on the pivot 150 of the brake-operating lever 148, so that the damper is compressed when the coupling is compressed, the shaft 143 being extended to position its end 143a for engagement with the lever 148. The piston assembly 116 comprises a valve structure for restricting flow past the piston in both directions and formed by Belleville washers 169 which are trapped between a seating 167 engaging their inner peripheries and a peripheral flange of the piston engaging their outer peripheries, so as to be prestressed. As a result they offer an initial resistance to flow in both directions through piston apertures 166 and calibrated apertures 166a in a setting ring 166 secured to the piston, the inner or outer peripheries lifting from the seating or piston flange respectively when the respective extension or compression force on the damper exceeds a predetermined value. The resistance to extension rises more steeply than the resistance to compression. The air chamber D renders the unit self-extending at a slow rate. In both embodiments a hand lever is provided on the trailer attachment portion for manual operation of the brake-operating lever.