ELECTRIC BOOSTER

PROBLEM TO BE SOLVED: To keep a substantially constant relationship between the position of an input rod and a brake fluid pressure even with caliper rigidity changed, thereby improving a pedal feel. SOLUTION: An electric booster interposes, between an input piston 32 and a booster piston 31 both disposed in a relatively movable condition, a spring 60 retaining the both pistons at neutral positions of relative displacement, and moves the booster piston 31 by an electric motor 40 according to the movement of the input piston in response to a brake pedal to generate the brake fluid pressure in a master cylinder 10, wherein a preferred relationship between the position of the input piston 32 and the brake fluid pressure is set beforehand, a desired fluid pressure is calculated from the preferred relationship according to the position of the input piston 32, then the rotation of the electric motor 40 is controlled to obtain the desired fluid pressure. COPYRIGHT: (C)2009,JPO&INPIT