| 摘要 |
PURPOSE:To maintain the airtightness in a vacuum passage by fixing a sealing member that forms the vacuum passage, to the recessed part of a power piston, when the power piston is moved following the movement of air, and by fitting the sealing member to the outer periphery of a passage tube airtight. CONSTITUTION:A changeover valve 40 is switched by a controller 41 so as to generate brake oil pressure by a traction control and so on, and the part from the changeover valve 40 of a vacuum passage 22 communicated with a negative pressure source 4 to a vacuum valve 32 is communicated with outside air 44. Since the vacuum valve 32 is closed, the air is flowed into a first working pressure chamber 11 through a by-pass 42, and is further flowed into a second working pressure chamber 13 through a working pressure passage 12. The balance of pressure is thereby lost, and a power piston 18 is moved to the side of a second constant pressure chamber 6, and the vacuum valve 32 is thus opened. Since the power piston 18 is moved while a sealing member 25 fixed to an opening part 29 of a recessed part 24 is fitted to the outer periphery of a passage tube 23 airtight, the loss of airtightness in the vacuum passage 22 is prevented. |
