Hydraulic anti-skid systems for vehicle

A vehicle braking system comprising a fluid pressure-operable brake for braking a wheel, a supply of fluid under pressure for operating said brake, anti-skid sensing means for producing a skid signal, and a modulator assembly for modulating said supply of fluid to said brake in accordance with said skid signal from said anti-skid sensing means, wherein said anti-skid sensing means comprises a shaft adapted to be driven by said wheel, a flywheel assembly including relatively movable parts, all said parts being mounted on said shaft for rotation with respect to said shaft, drive means including a clutch and through which said flywheel assembly is driven from said shaft, camming means responsive to relative angular movement between said shaft and said flywheel assembly to produce said skid signal for operating said modulator assemby to reduce the pressure of fluid supplied to said brake when the deceleration of said shaft relative to said flywheel assembly exceeds a predetermined value, said skid signal comprising relative axial movement between said shaft and said flywheel assembly, common biassing means for biassing both said clutch and said camming means, a reaction means for transmitting thrust from said biassing means to said flywheel assembly, and means for positively driving said reaction means from said wheel at alltimes, said biassing means exerting a biassing force on said clutch and camming means to prevent said skid signal from being produced unless said flywheel assembly has generated sufficient torque to overrun said shaft by a predetermined amount and to maintain said skid signal by permitting said flywheel assembly to overrun said shaft against said clutch.