Electric booster and method for manufacturing the same

An electric booster, which drives an electric motor in response to movement of an input member moving together with a brake pedal, assists a piston of a master cylinder through a rotation-linear motion converting mechanism, and generates a brake hydraulic pressure in the master cylinder, wherein:

• the electric motor comprises a stator including a coil, a hollow rotor in which the rotation-linear motion converting mechanism is fitted, and which rotates by applying a current to the stator, and an annular motor casing containing the stator and the rotor;
• an opening on one axial end side of the motor casing is formed on a front side to which the master cylinder is connected, and has a larger diameter than an outer diameter of the rotation-linear motion converting mechanism;
• the rotation-linear motion converting mechanism comprises a nut member fitted to the hollow rotor so as to be non-rotatable relative to the hollow rotor, and a hollow screw shaft engaged with the nut member and disposed so as to be non-rotatable relative to the motor casing while being axially movable;
• the input member includes a flange portion having a smaller diameter than an inner diameter of the hollow screw shaft;
• the motor casing includes a protrusion extending radially inwardly on another axial end side thereof so as to enable the small diameter flange portion to abut against the protrusion;
• and
• the input member is inserted through the opening on the one axial end side of the motor casing to be disposed in the hollow screw shaft, resulting in abutment of the small diameter flange portion against the protrusion, and this abutment functions to limit movement of the input member in a backward direction opposite from the master cylinder.

An electric booster, which drives an electric motor in response to a movement of an input member moving together with a brake pedal, assists a piston of a master cylinder through a rotation-linear motion converting mechanism, and generates a brake hydraulic pressure in the master cylinder, wherein:

• the electric motor comprises a stator including a coil, a hollow rotor in which the rotation-linear motion converting mechanism is fitted, and which rotates by applying a current to the stator, and an annular motor casing containing the stator and the rotor;
• an opening on one axial end side of the motor casing is formed on a front side to which the master cylinder is connected, and has a larger diameter than an outer diameter of the rotation-linear motion converting mechanism;
• the rotation-linear motion converting mechanism comprises a nut member fitted to the hollow rotor so as to be non-rotatable relative to the hollow rotor, and a screw shaft engaged with the nut member and disposed so as to be non-rotatable relative to the motor casing while being axially movable;
• and
• the screw shaft is inserted through the opening on the one axial end side of the motor casing so as to be disposed in the hollow rotor, resulting in abutment of a back end side of the screw shaft against another axial end side of the motor casing, and this abutment functions to limit a movement of the screw shaft in a backward direction opposite from the master cylinder.