Automatic brake fluid pressure control device

A brake fluid pressure control device having an automatic brake function comprising:

• an antilock control means provided between a master cylinder and a wheel brake, said antilock control means comprising a wheel brake fluid pressure control valve for controlling the fluid pressure in the wheel brake, a first fluid reservoir for storing brake fluid discharged from the wheel brake through said control valve, and a pump for pumping and returning the fluid in said first fluid reservoir into a line connecting the master cylinder to said control valve,
• said brake fluid pressure control device further comprising a first valve means for connecting said master cylinder to an inlet port of said pump, a second valve means for checking fluid flow from said pump to said master cylinder, and a first relief valve for releasing brake fluid into said master cylinder when the fluid pressure in the line between said second valve means and said wheel brake fluid pressure control valve exceeds a predetermined value,
• said brake fluid pressure control device further comprises a normally open on-off valve provided between said master cylinder and said wheel brake fluid pressure control valve, and a fluid supply amplifier and a pressure-responsive valve provided parallel to each other between the discharge port of said pump and said wheel brake fluid pressure control valve,
• said fluid supply amplifier comprising an input chamber, an output chamber, an adjusting chamber, and a stepped piston having a first pressure-receiving surface facing said input chamber, a second pressure-receiving surface facing an adjusting chamber and receiving the pressure in the same direction as said first pressure-receiving surface, and a third pressure-receiving surface having an area equal to the sum of the areas of said first and second pressure-receiving surfaces and facing said output chamber, and a biasing means biasing said stepped piston toward said input chamber, said input chamber being connected to the discharge port of said pump, and said output chamber being connected to a line connecting said on-off valve to said wheel brake fluid pressure control valve,
• said brake fluid pressure control device further comprising a first check valve provided between said adjusting chamber and said master cylinder for allowing only fluid flow from said master cylinder toward said adjusting chamber, and a second check valve provided between said adjusting chamber and said output chamber for allowing only fluid flow from said adjusting chamber to said output chamber,
• said pressure-responsive valve receiving the fluid pressure from said output chamber in a valve opening direction and receiving the fluid pressure from said master cylinder and a spring force in a valve closing direction and adapted to open and connect the discharge port of said pump to said wheel brake fluid pressure control valve when the fluid pressure in said output chamber exceeds a predetermined value.