| 摘要 |
PURPOSE: To simplify the circumference of a housing so as to improve fitting property to a vehicle, and dispense with special sensors and control devices so as to simplify the construction and decrease the cost. CONSTITUTION: A plunger 14 capable of being interlocked with an input shaft 16 through a guide member 15 is arranged in a valve body 9 extended from a power piston 5 to the rear of a housing 1, and when movement of the valve body 9 is small, valve mechanisms 23, 24, 25 are interlocked with movement of the plunger 14 so as to introduce the atmosphere into a working pressure chamber 7 through an atmospheric passage 20, meanwhile, an opening/closing valve 36 connected to a high pressure air generating source 34 is provided on a casing 32 surrounding the valve body 9. Consequently when the valve body 9 is moved exceeding a prescribed value, the poppet 39 of the opening/ closing valve 36 is operated by the step difference part 41 on the outer circumference of the valve body 9, high pressure air is introduced into the working pressure chamber 7, and thrust is generated on the power piston 5 in two stages according to pressure difference against a negative pressure chamber 6. |
