Patent ID: 6959639

Claim:
A hydraulic booster brake system comprising: a power steering hydraulic circuit including a power steering booster provided on the downstream side of a hydraulic pump; a brake booster connected in parallel with the power steering booster on the downstream side of the hydraulic pump, said brake booster receiving a stipulated quantity of hydraulic fluid discharged from the hydraulic pump; a distributing mechanism connected to a discharge portion of the hydraulic pump, said distributing mechanism supplying the stipulated quantity of hydraulic fluid to the brake booster, and supplying a remaining portion of the quantity of the hydraulic fluid to the power steering booster; wherein the distributing mechanism is a flow priority valve including a spool valve supplying the hydraulic fluid in a total flow quantity of the hydraulic fluid discharged from the hydraulic pump to the brake booster by priority, the spool valve comprising a hollow cylinder which has a first port communicating with the discharge portion of the hydraulic pump, a second port communicating with the power steering booster, and a third port communicating with the brake booster; a spool which is accommodated in the cylinder while being pressed by an urging member so as to be capable of moving in an axial direction of the cylinder, and has a receiving port which receives a pressure of the hydraulic fluid flowing into the first port; a brake booster passage which includes an orifice through which the hydraulic fluid from the receiving port passes, and leads a stipulated flow quantity of the hydraulic fluid passing through the orifice to the third port; a power steering passage which leads the excessive hydraulic fluid which does not pass through the orifice to the second port via a space between the spool and the cylinder; a first choke portion which is formed to the brake booster passage and narrows the passage by using the spool which moves when a pressure of the power steering booster is increased; a second choke portion which is formed to the power steering passage and narrows the passage by using the spool which moves when a pressure of the brake booster is increased; a by-pass port which can be connected to a drain side of the power steering hydraulic circuit; and a gate portion which is formed between the spool and an inner surface of the cylinder, causes the second port and the by-pass port to communicate with each other when the spool is in an initial position, and disconnects the second port and the by-pass port when the spool moves in the axial direction.