GB836924A - Improvements in or relating to the operation of brakes on trailer vehicles - Google Patents

Abstract

836,924. Trailer vehicle brakes. HENRY, H. P. June 12, 1958 [June 3, 1957], No. 17605/57. Class 103 (1). In a trailer brake operating device comprising a liquid pressure master cylinder operable by relative approach movement of coupled tractor and trailer vehicles to apply brakes on the trailer vehicle, the master cylinder is arranged to serve also as a damping device for damping the relative approach of the vehicles. In the embodiment illustrated, the trailer brake operating device 10 is mounted on the forward end of a tow-bar 11 forming a part of a trailer vehicle. A rod 12 projecting forwardly from the body 13 of the device 10 carries at its front end one part of a trailer coupling, shown as a ball-and-socket coupling of which the socket 14 is mounted on the rod 12 and the ball 15 is mounted on a horizontal transverse bar forming part of a tractor vehicle. In operation, when the trailer vehicle tends to overrun the tractor vehicle, the master cylinder piston 32 moves rearwardly in the reduced portion 24 of the bore 18. Liquid is forced through the conduit 45 to apply the brakes and a disc valve 52 is provided in the master cylinder outlet to ensure that the flow of liquid from the master cylinder is retarded, and the master cylinder thus acts also as a dashpot to regulate the rate of relative approach movement of the vehicle. When the towing pull is restored, the rod 12 tends to move forwardly and the movement is damped by the movement of a piston 39 in a chamber 27, this piston forcing liquid from a chamber 27 into a reservoir 19 through a passage 42. Under the pressures generated by normal running, the pressure build up in the master cylinder is insufficient to open a valve 35 in the master cylinder piston 32, but if the tractor vehicle is backed towards the trailer, thus applying the brakes on the latter, a pressure is built up sufficient to open this valve and allow escape of liquid from the master cylinder through passages 31 and 43 to the reservoir. The piston 32 moves rearwardly until the pin 53 contacts the valve 35 and holds it away from its seat to release the trailer brakes and allow the vehicles to be backed together. Alternative embodiments are disclosed in the Complete and Provisional Specifications. Specification 714,400 is referred to.