NEGATIVE PRESSURE BOOSTER

摘要

The invention relating to the field of a technique relating to a negative pressure booster (1) used for a brake booster device in a brake system of a vehicle where deceleration in normal braking operation is obtainable according to the amount of pedal stroke. The negative pressure booster (1) has vacuum valve opening means (21, 27d) for opening a vacuum valve (15) when a valve seat member (27) moves to a predetermined position. When a brake pedal is returned, the vacuum valve (15) is opened to release the pressure in a pressure change chamber, and this returns the valve seat member (27) and a valve body (4) to a normal position.