Patent ID: 7861522

Claim:
An electrically driven brake booster, comprising: a cylindrical booster piston adapted to pressurize a pressure chamber in a master cylinder; an input piston slidably and liquid-tightly inserted through the booster piston with a seal portion sandwiched between the input piston and the booster piston, the input piston adapted to pressurize the pressure chamber in the master cylinder in response to an operation of a brake pedal; an electric motor; and a rotation-linear motion converting mechanism adapted to convert a rotation of the electric motor into a linear motion to provide a thrust force to the booster piston, wherein the thrust force provided to the booster piston is adjusted by controlling an operation of the electric motor according to an input to the input piston; and the electrically driven brake booster further comprises a discharge passage for discharging a brake fluid which leaks from the seal portion between the booster piston and the input piston so that the leaking brake fluid is prevented from entering portion(s) susceptible to corrosion by the brake fluid.