Hydraulic brake apparatus for a vehicle

A hydraulic brake apparatus for a vehicle comprising:

• a master cylinder having a cylinder body and a master piston slidably disposed therein for defining a pressure chamber ahead of said master piston and a power chamber behind said master piston, said master piston being moved forward in response to operation of a manually operated member to generate a brake pressure from said pressure chamber;
• a control piston slidably disposed in said cylinder body ahead of said master piston for defining said pressure chamber behind said control piston, said control piston being moved in response to movement of said master piston;
• an auxiliary pressure source for pressurizing brake fluid to generate a power pressure;
• and
• valve means having a regulator chamber defined ahead of said control piston and communicated with said auxiliary pressure source for introducing the power pressure into said regulator chamber to regulate the power pressure into a regulated pressure in response to movement of said control piston, said valve means supplying the regulated pressure into said power chamber to assist the operation of said manually operated member, and
• said control piston being provided with at least one sealing member for separating said regulator chamber from said pressure chamber with substantially equal pressure applied to one end of said sealing member and the other end of said sealing member.