Patent ID: 8342617

Claim:
A hydraulic brake system comprising: an intake passage connecting a master cylinder to an intake side of a fluid pump; a discharge passage connecting a discharge side of the fluid pump to the master cylinder; a first passage branched from the discharge passage and connected to a wheel cylinder; a pressure reduction passage connected to a reservoir that reserves a pressure reduced brake fluid from the wheel cylinder; an outlet passage connecting the reservoir to the intake passage; and a gate-in valve that selectively opens and closes the intake passage in accordance with both a master cylinder pressure produced by the master cylinder and a pump intake side pressure produced in an intake side of the fluid pump; wherein the gate-in valve selectively opens and closes the intake passage in accordance with a pressure difference between the master cylinder pressure and the pump intake side pressure; wherein, when the master cylinder pressure is higher than a first given pressure and lower than a second given pressure, the gate-in valve takes a closed position when the pump intake side pressure is higher than a third given pressure but takes an open position when the pump intake side pressure is lower than the third given pressure; wherein the gate-in valve comprises: a valve seat provided in a part of the intake passage; a valve body that is movable onto the valve seat to close the intake passage when a certain pressure is produced by the master cylinder; a piston movable together with the valve body; a pin having one end fixed to the piston and the other end contactable with the valve body; and a biasing spring biasing the piston toward the valve body; and wherein the following inequality is satisfied by the brake system: Pm×S 1 >f 1 >Pm×S 2, wherein: Pm: the master cylinder pressure; S 1 : a sectional area of the piston; S 2 : a sectional area of the intake passage at the valve seat that is actually closed by the valve body; and f 1 : biasing force of the biasing spring.