Anti-lock braking system

Claim 1

An anti-lock braking system (ABS) comprising a master cylinder (12) for supplying pressurized fluids a wheel brake (16) receiving pressurized fluid from the master cylinder and for restraining rotational movement of a wheel (14): a controller (18) cognizant of the rotational condition of the wheel and providing a signal when the rotational condition of the wheel is within preset parameters; an isolation valve (24) responsive to an activation signal given by the controller to prevent fluid communication between the master cylinder and the wheel brake: an actuator (28) having a bore (32) with a first fluid passage (42) in fluid communication with the wheel brake; a piston (44) slidably sealably mounted within the bore for providing a variable control volume in communication with the wheel brake and thereby modulating the pressure therein; a nut (46) operatively associated with the piston and slidably mounted within the bore in a non-rotative fashion; a power screw (48) projecting into the nut and threadedly engaged therewith in an efficient manner, the power screw having a fixed rotational axis with respect to the piston: and a reversible motor (50) for powering the power screw, the reversible motor being responsive to signals given by the controller: characterised by a sleeve (120) which is non-rotative and located between the power screw (48) and the reversible motor (50) in a fixed position, the sleeve having an inner diameter of a first value; a coil spring (130) having a free outer diameter of a second value generally equal to or greater than the first value, the coil spring being captured within the sleeve, and having a tang (132) on each end: a driver member (100) with a torsion transfer portion (152) projecting into the sleeve, the driver member having a rotational axis, the driver member having an angular position in correspondence with the angular position of the reversible motor, the driver member having first and second contact surfaces (104) for engagement with the tangs to cause the tangs to move inwardly to allow the coil spring to have sliding movement within the sleeve in both directions; a driven member (86) with an angular position in correspondence with the angular position of the power screw, the driven member having a rotational axis generally coterminous with the rotational axis of the driver member and the driven member having projecting into the sleeve a torsion transfer portion (182) for making contact with the torsion transfer portion (152) of the driver member for transferring torque from the driver member to the power screw, the driven member having at least one contact surface for making contact with the tang on the opposite side (138) of the tang to that contacted by the contact surface of the driver member to cause the coil spring to radially expand and lock within the sleeve to prevent torque from the power screw being transferred to the reversible motor when the piston is subjected to fluid pressure but the rotational condition of the wheel is outside the preset parameters.