A BRAKING SYSTEM FOR A VEHICLE

摘要

A braking system for a vehicule, particularly a rear axle braking sytem for a towing vehicle, has a primary electronic braking circuit supplied with a source (S1) of primary braking pressure and a mechanical back-up braking circuit supplied with a source of back-up braking pressure (S2). A braking actuator (40) receives braking pressure and thereby brakes a wheel on a vehicle axle. During braking, a changeover valve (34) is normally actuated to apply the primary braking pressure to the braking actuator. In the event of electronic system failure the changeover valve (34) is not applied and instead applies the source of back-up braking pressure (S2) is supplied to the actuator. A regulating valve (V) is located in the back-up braking circuit between the source of back-up braking pressure (S2) and the changeover valve (34) and is operable as a function of axle loading and back-up braking pressure to control the supply of back-up braking pressure to the changeover valve. In this way, the application of additional braking pressure to a wheel on a vehicle axle can be limited if the loading on the axle is likely to result in vehicle instability under braking.