Electric servo assisted brake system

The system has an electric brake booster (100) comprising a master cylinder piston (121) controlled by an electric motor (160). A spiral spring (146) is coaxially mounted with a drive shaft (143) carrying a spur pinion (142) engaged with a toothed rack (141) and a worm wheel (145) engaged with a screw (162) carried by an output shaft (161) of the motor. Ends of the spring are supported on the shaft and a complex brake booster housing (110), respectively, to exert return torque on an actuating piston (140) by the shaft and the pinion for pushing back the piston to rest position.