| 摘要 |
PURPOSE:To stabilize the characteristic of the captioned device by providing a seal part which can introduce the air into a main body side at the time of the advance of an input shaft in the rear of a poppet valve and providing an orifice for connecting the main body side to the air when the input shaft is stopped midway while advancing. CONSTITUTION:A valve body 18 is surrounded by a bellows type boot 28 and a seal part is provided on its rear end side. The seal part is formed with a boot end part 28a which is airtightly slidingly brought into contact with an input shaft 20 and a large diameter part 20b and a small diameter part 20c formed on the input shaft 20, and an orifice 30 is formed on the large diameter part 20b. As a brake pedal is stepped in, the input shaft 20 is advanced and a poppet valve 23 and a plunger 19 are separated from each other while the boot end part 28a is positioned in the small diameter part 20c, and the air is introduced from the inside of the valve body 18 into a pressure changing chamber to boost up an output shaft 21. If the stepping is stopped in the midway, since the valve body 18 is advanced, the boot end part 28a is slidingly brought into contact with the large diameter part 20b and the air is gradually introduced into the pressure changing chamber via the orifice 30.
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