Brake Device for a unit of Drag to an articulated vehicle, such as a Highway tractor for Towing a Trailer

摘要

A braking system for the tractor unit of a tractor trailer vehicle in which the ratio of the pressure applied to the front brakes (11) to the pressure applied to the rear brakes (12) changes automatically when a trailer is connected to or disconnected from the tractor. The brake system includes two dual mode relay valves (71a, 71b) and feedback conduits (31a, 133a) which convey feedback pressures between the front and rear dual mode valves (71a, 71b) and between a trailer brake service conduit (133) and the front valve (71a). The brake system includes brake pressure proportioning apparatus (71b) which is operative to reduce brake pressures on the rear tractor brakes (12), during normal brake applications, when the tractor is operated bobtail but which can be overriden by a vehicle operator if conditions warrant. The pressure feedback and system hysteresis cooperate to produce balanced braking and the proper sequence of brake application under a variety of vehicle operating conditions.