| 摘要 |
PURPOSE:To restrain the amount of brake hydraulic oil under pressure from increasing, by opening a first safety valve to establish a hydraulic circuit bypassing a valve mechanism which closing a second safety valve to inhibit brake hydraulic pressure from entering into a pressure reducing chamber. CONSTITUTION:When a hydraulic pump 9 in a hydraulic pressure source 11 fails and therefore the hydraulic pressure in the control chamber 19 of a pressure reducing means 5 extremely decreases, a valve mechanism 23 closes. However, since the hydraulic pressure in a hydraulic chamber 41 also decreases, a safety piston 40 is displaced so that a first safety valve 43 opens while a second safety valve 44 closes. When a brake pedal P is depressed in this condition, the hydraulic pressure for braking acts upon a wheel brake B through an inlet oil passage 26, an inlet hydraulic pressure chamber 22, a first oil passage 37, a first valve hole 49, an output hydraulic pressure chamber 42 and an output hydraulic pressure passage 48. At this time, since the output hydraulic pressure chamber 42 and the pressure reducing valve 20 are isolated, it is possible to prevent the supply amount of brake hydraulic oil under pressure from a master cylinder from increasing. |
