To restrain the sharp reduction of vehicle braking force at the time of the failure of one side in two hydraulic systems.
The spring 28 of a relief valve 26 is installed between a valve element 27 and a control piston 31, for making the decompression quantity of the relief valve 26, installed in one side hydraulic system, variable. The control piston 31 is energized in a direction for increasing the force of the spring 28 by the master cylinder fluid pressure of the other side fluid pressure system and an added spring 32. Also, the control spring 31 is energized in a direction for reducing the force of the spring 28, by the fluid pressure of the wheel brakes 17 and 18 of one side fluid pressure system, and when the brake is operated, in a condition where one side fluid pressure system is normal, and the other side fluid pressure system is empty, the control piston 21 is made to be displaced in a direction for reducing the force of the spring 28.
ENOMOTO NAOYASU
ANDO MASAKI
KOIKE YASUHIRO
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