Hydraulic anti-lock braking systems for vehicles

Claim 1

An hydraulic anti-lock braking system for a vehicle comprising a brake on a wheel of the vehicle, an hydraulic master cylinder for supplying hydraulic fluid under pressure to said brake to apply said brake, modulator means for modulating the supply of pressure fluid from said master cylinder to said brake in accordance with the behaviour of said braked wheel, said modulator means comprising fluid storage means comprising an expansion chamber, a first control valve located between said master cylinder and said brake and movable between a first open position to provide communication between said master cylinder and said brake and a second closed position to isolate said brake from said master cylinder, a second control valve located between said brake and said expansion chamber and movable between a first closed position to isolate said brake from said expansion chamber and a second open position in which fluid in said brake is dumped to said expansion chamber, a motor, and a pump driven by said motor to produce an output which generates energy necessary to recover fluid in order to re-apply said brake automatically after said pressure fluid applied to said brake has first been released to said expansion chamber in response to movement of said second control valve into said second open position, said pump comprising a pump plunger movable in opposite first and second directions during an induction stroke and a power stroke respectively, means defining a pressure space in advance of said plunger, a one-way inlet valve through which fluid is adapted to be withdrawn from said expansion chamber into said pressure space upon movement of said plunger in said first direction, a first passage means defining a first connection between said pressure space and said brake, first flow-control means disposed in said first passage means through which fluid is pumped back to said brake, and a second passage means defining a second connection between said pressure space and said master cylinder, and second flow-control means disposed in said second passage means through which fluid is pumped back to said master cylinder, said first flow-control means including first pressure-responsive means responsive to pressure in said brake in opposition to flow from said pump to said brake, said second flow control means including second pressure-responsive means responsive to pressure in said master cylinder in opposition to flow from said pump to said master cylinder, and one of said pressure-responsive means exhibiting a greater resistance to flow than the other of said first pressure-responsive means, whereby fluid is returned by said pump to both said brake and said master cylinder.