| 摘要 |
PROBLEM TO BE SOLVED: To effectively effect the braking even when a brake step-in force is small in an emergency by providing a boosting means to boost the brake hydraulic pressure, and operating the boosting means based on the difference between the value on the step-in quantity of a brake pedal and the value on the brake hydraulic pressure. SOLUTION: When a brake pedal is operated, a vacuum valve 22 is closed by the leftward movement of an input rod 16, the communication of a negative pressure chamber 6 with an atmospheric pressure chamber 8 is disconnected to open the atmospheric valve 24, a power piston 10 is moved by the differential pressure between the negative pressure chamber 6 and the atmospheric pressure chamber 8, and the hydraulic pressure of a brake cylinder is increased. When the brake pedal step-in force is small in an emergency brake operation, an assist valve 36 is opened by the output of a detecting means to detect the condition. The atmosphere is introduced from an atmosphere introduction pipe 34 into the atmosphere pressure chamber 8 all at once, the differential pressure is rapidly generated between the negative pressure chamber and the atmospheric pressure chamber 8, and the brake hydraulic pressure is rapidly increased to obtain a large braking force. |
