Anti-lock braking systems (ABS) for road vehicles to avoid premature engagement of the anti-lock braking system

An anti-skid braking system for multi-axled wheeled vehicles having fluid actuated brakes associated with the vehicle wheels, comprising speed sensors associated with the vehicle wheels a scanning control device responsive to speed signals from the speed sensors to actuate a pressure dump device to periodically release the fluid pressure applied to the brake of any wheel which is determined, by detection of a predetermined normal level of relative slip between that wheel and the road surface, to be about to lock, and to later re-apply the actuating pressure to that brake when the tendency of that wheel to lock has reduced, and control means which includes:

• (a) means for detecting when an anti-skid operation is in progress and for providing an inhibiting signal when an anti-skid operation is in progress;
• (b) means which, in the absence of said inhibiting signal, adjusts the magnitude of said predetermined level of relative slip to which said control device responds such as to reduce a slip detection sensitivity to a low level below said normal level of relative slip, at the first detection of an impending skid condition;
• (c) storage means for storing a signal representative of a predetermined time needed by an axle of the vehicle to move rapidly through its available deflection;
• (d) means which maintain the slip detection sensitivity at the low level for a period corresponding to said predetermined time needed by the axle to move rapidly through its available deflection;
• and
• (e) means to then restore the slip detection sensitivity to the level corresponding to said normal level of relative slip.