Skid-sensing means for vehicle hydraulic anti-skid braking systems

Skid sensing means for vehicle hydraulic anti-skid braking systems comprising a brake for a wheel on a vehicle, a source of fluid under pressure for applying said brake hydraulically, a shaft driven from said wheel to be braked by said brake, a housing having a fluid chamber and a fluid-tight seal sealing said fluid chamber from atmosphere, a dump valve for relieving pressure applied to said brake and movable between an open position and a closed position, said dump valve being disposed within said fluid chamber, a flywheel assembly in said housing mounted on said shaft, a clutch through which said flywheel assembly is driven from said shaft, said flywheel assembly comprising a flywheel member, a reaction member, and a ball and ramp mechanism co-operating with said two members and so constructed and arranged that relative angular movement between said members which occurs when the deceleration of said braked wheel exceeds a predetermined value is accompanied by relative axial movement therebetween into an expanded condition in order to open said dump valve to relieve said pressure applied to said brake, said clutch being arranged to slip at a predetermined threshold torque so that said two members can continue to rotate together or "overrun", in said expanded condition with respect to said shaft to maintain said dump valve in said open condition, at least until said wheel has recovered a predetermined rotational speed, wherein said dump valve comprises a valve seating, and a valve member for engagement with said seating, and said flywheel assembly acts on said valve member through a lever assembly comprising a single member, a fixed pivot in said housing and about which said member is angularly movable in response to relative axial movement between said members of said flywheel assembly, and said single member is constituted by an elongate lever, and an arm rigid with said lever, said lever having a force receiving part spaced from said pivot and with which said flywheel co-operates, and said arm having a force transmitting part spaced from said lever and which projects into said fluid chamber in said housing through said fluid-tight seal and acts to co-operate directly with said valve member of said dump valve to urge said member away from said seating against a force due to fluid brake-pressure in said fluid chamber which acts normally to urge said valve member into engagement with said seating in said closed position of said dump valve.