| 摘要 |
PURPOSE:To obtain a good braking effect of a brake by constituting a negative pressure type servo unit such that a projection is provided at least at one of a valve plunger and an abutting surface of a reaction plate so as to enable a rapid rise of hydraulic pressure in a master cylinder. CONSTITUTION:Upon treadling down a brake pedal for braking, a valve operating rod 14 connected with the brake pedal is pushed in a direction A against the urging of a spring 16. A valve body 10 and a valve plunger 15 are thereupon moved leftwardly in an integral relationship with a movable end portion of the valve body 10 kept contacted with the valve plunger 15 as shown in the drawing due to the urging of a spring 17 (that is, in a closed position of an air valve 18). When the movable end of the valve body 10 is seated on a shoulder 4b, then a vacuum valve 11 is closed. If the pedal is thereafter treadled down further, the air valve 18 is opened to allow atmospheric air to be introduced into a variable pressure chamber 8 so that a power piston 4 is moved leftwardly. A projection 15a is provided on an end face of the valve plunger 15 which is contacted with a reaction plate 20 by the leftward movement of the power piston 4. |
