GB1467541A - Couplings for vehicles - Google Patents

Abstract

1467541 Vehicle towing assemblies R H ROBINSON 29 April 1975 17801/75 Heading B7T [Also in Division F2] A trailer towing assembly allowing, in use, damped longitudinal relative movement between a trailer and a towing vehicle, comprises a body assembly for mounting on the trailer, and a tow shaft provided at its forward end with a coupling element for coupling with a mating coupling element of the towing vehicle, the tow shaft being slidably mounted in the body assembly and arranged such that relative movement therebetween is damped by the flow of hydraulic fluid through a constriction formed between the tow shaft and the body assembly, a one-way valve being provided and the arrangement being such that the degree of damping is greater when, in use, the towing vehicle and trailer move away from one another than when the towing vehicle and trailer move towards one another. The trailer towing assembly 10 as embodied in Fig. 1, comprises a two shaft 13 provided at its forward end with a coupling socket and having pistons 12 slidably mounted in a body assembly formed by cylinder members 11 spaced by a plate 14. Rearward movement of the tow shaft 13 causes hydraulic fluid to flow through a one-way valve 40, through a by-pass passage 27, and through a constriction formed between a bore 18 of the plate 14 and stepped portions 23, 24, 25 of the tow shaft 13. The one-way valve 40 closes during forward movement of the tow shaft 13 so as to give a greater damping effect. The stepped portions 23, 24, 25 provide varying damping depending on the longitudinal position of the tow shaft relative to the body assembly. An adjustable bolt 32 mounted on an end portion 31 of the tow shaft 13 is arranged to operate the piston rod of a brake master cylinder, on trailer overrun, so as to actuate the trailer brakes. A locking device 33 is operable to prevent actuation of the trailer brakes during trailer reversal. In modifications of the embodiment of Fig. 1, the end portion 31 of the tow shaft may be constructed to function as an actuation piston of the trailer hydraulic overrun brake system, and the locking device 33 may be electromagnetically controlled. In the embodiment of Fig. 3, rearward movement of the tow shaft 21 relative to the body assembly 12 causes hydraulic fluid to flow into chamber portions 34, 35 through a one-way valve 38 and a two-way valve 39. During forward relative movement of the tow shaft 21 the one-way valve 38 closes to increase the damping effect. Operation of the trailer overrun brake system during trailer reversal can be prevented by closing a valve 50 which creates an "hydraulic lock" in a chamber 45. The stepped portions 31 of the tow shaft 21 of Fig. 3 may be replaced by a tapered shaft portion.