Liquid pressure operated braking system

Claim 1

A liquid pressure operated braking system for a vehicle having a clutch actuated by a clutch pedal via a clutch operating mechanism, comprising: at least two sub-systems, each sub-system being for the transmission of liquid pressure from a respective one of two sources of liquid pressure to a respective one of two groups of brake operating wheel cylinders; a valve assembly including a first valve fluidly disposed in one of the sub-systems and operatively coupled to the clutch operating mechanism for confining the liquid pressure applied to the associated one group of brake operating wheel cylinders to the one sub-system upon clutch disengagement when the vehicle is at a standstill on an up-hill road; the valve assembly also including a second valve fluidly disposed in the other sub-system, the second valve including a housing having a first port connected to the associated source of liquid pressure to the other sub-system, a second port connected to the associated one group of brake operating wheel cylinders to the other sub-system and a valve bore constantly communicating with said first port, the second valve also including a stepped piston, movably disposed in said housing, having a large pressure acting area exposed to liquid pressure acting in the associated one group of brake operating wheel cylinders to the one sub-system and a small pressure acting area exposed to liquid pressure acting in the associated one group of brake operating wheel cylinders to the other sub-system, said stepped piston being movable to a predetermined valve close position wherein said stepped piston closes said valve bore to prevent at least fluid flow communication from said second port to said first port.