Anti-skid hydraulic braking systems for vehicles

Claim 1

An anti-skid hydraulic braking system for vehicles in which the supply of operating fluid from a supply (1) to a wheel brake (2) is modulated by a modulator assembly (3) in accordance with skid signals from skid sensing means (9), the modulator assembly comprising a housing (4) incorporating a normally open one-way valve (7) through which the operating fluid is supplied to the brake and which is movable into a closed position to isolate the supply from the brake when a skid signal is operative, an expander piston (17) operable in sequence with the one-way valve and movable between an advanced position in which the effective volume of an expansion chamber (16) leading to the brake is at a minimum when the one-way valve is open and a retracted position in which the effective volume of the chamber is increased to relieve the pressure applied to the brake following movement of the one-way valve into the closed position, a pump (8) operative to effect re-application of the brake following correction of the skid, and a flow-control regulator valve (6) for controlling the rate of brake re-application following correction of the skid with the one-way valve closed, characterised in that a cut-off valve (5) responsive to a skid signal is disposed between the expander chamber (16) and the brake (2), and the cut-off valve is operable independently of and separately from the expander piston (17), the cut-off valve (5) co-operating with the one-way valve (7) to hold the one-way valve in an open position when the cut-off valve is in a closed position with means (10) responsive to a skid signal inoperative.

Claim 7

A system as claimed in any preceding Claim characterised in that the expander piston (17) and a plunger (22) for the pump (8) both work in a common bore (18, 23) in the housing (4) and in the advanced position the expander piston co-operates with the plunger to hold the plunger out of co-operation with a drive mechanism for the pump whereby to disable the pump, movement of the expander piston into its retracted position enabling the plunger to co-operate with the drive mechanism whereby pumping of fluid takes place with fluid being withdrawn from the expander chamber through a first one-way valve (30) during an induction stroke and being pumped into a passage (31) between the supply of operating fluid (1) and the flow-control regulating valve (6) through a second one-way valve (32) during a power stroke.