Hydraulic anti-lock braking systems for vehicles

Claim 1

A hydraulic anti-lock braking system for vehicles comprising a master cylinder for applying hydraulic fluid under pressure to a brake on a wheel to apply said brake, a modulator responsive to the behaviour of said braked wheel to modulate the supply of fluid from said master cylinder to said brake in an anti-lock mode, and a pump having an output which generates the energy necessary to recover fluid after the pressure applied to said brake had first been released to prevent said wheel from locking, wherein said modulator comprises means defining a control chamber, a solenoid-operated valve for determining the pressure in said control chamber, a poppet valve for controlling communication between said master cylinder and said brake in accordance with pressure in said control chamber, means defining an expansion chamber to which fluid is relieved from said brake in an anti-lock mode, a re-application valve for determining the rate of re-application of pressure to said brake upon recovery of said braked wheel, and a restricted connection between said master cylinder and said output from said pump, and wherein said poppet valve comprises a means defining a passage, a spool responsive to pressure in said control chamber for controlling the supply of fluid to the brake through said passage, a valve seating, and a valve head movable relative to said spool and which, in an open position, is normally spaced from said seating to provide unrestricted communication between said master cylinder and said brake, movement of said spool in a direction to open said passage to cause said head to co-operate with the seating to cut-off unrestricted communication between said master cylinder and said brake.