Electric disc brake

An electric disc brake comprising:

• frictional pads to press a disc;
• a first carrier supporting the frictional pads;
• a caliper housing supported to the carrier such that the caliper housing is movable back and forth to press the frictional pads;
• and
• a pressing unit pressing the frictional pads,
• wherein the pressing unit comprises:
• a piston installed in the caliper housing such that the piston is movable back and forth to press one of the frictional pads;
• a spindle unit including a nut spindle member allowing the piston to move back and forth and a spindle member screwed with the nut spindle member;
• and
• a reduction unit coaxially coupled with the spindle unit, and a motor rotating the reduction unit forward and backward, and
• wherein the reduction unit comprises:
• a sun gear coupled with a shaft of the motor;
• a planet gear engaged with the sun gear;
• a second carrier coupled with the planet gear to rotate the spindle member;
• and
• an internal gear engaged with the planet gear,
• wherein the internal gear and planet gear are arranged such that in a first position the internal gear and planet gear are engaged to amplify a rotational force of the motor and in a second position the internal gear and planet gear are engaged to transfer the rotational force of the motor to the spindle member without a reduction gear ratio, and
• wherein the internal gear and planet gear shift from the second position to the first position after the spindle unit presses the piston.