ELECTRONIC DISC BRAKE

1 . An electronic disc brake which has a carrier fixed to a frame of a vehicle, a caliper housing installed on the carrier so as to be slidable, a pair of pad plates installed within the carrier so as to be forwardly and backwardly movable and disposed at both sides of a disc rotating together with a wheel of the vehicle, and a piston installed within a cylinder part provided on the caliper housing so as to be forwardly and backwardly movable and pressing one of the pair of pad plates toward the disc, the electronic disc brake comprising:

a spindle member passing through the rear wall of the caliper housing and rotated within the cylinder part;

a nut member screw-connected to the spindle member and moving forward and backward according to rotation of the spindle member to press the piston or to release pressing of the piston;

a motor installed on the outer surface of the caliper housing and generating driving force to rotate the spindle member; and

a cycloid reducer amplifying the driving force generated from the motor and transmitting the amplified driving force to the spindle member,

wherein the motor, the cycloid reducer and the spindle member are coaxially connected in series.

2 . The electronic disc brake according to claim 1 , wherein the motor is a thin motor.

3 . The electronic disc brake according to claim 1 , wherein the motor and the cycloid reducer are accommodated in a motor cover housing and are installed on the rear wall of the caliper housing.

4 . The electronic disc brake according to claim 1 , wherein the cycloid reducer includes:

an eccentric rotator connected to a rotary shaft of the motor and eccentrically transmitting rotation of the motor;

a cycloid gear provided with a plurality of through holes disposed in a radial direction from the center thereof and eccentrically rotated by the eccentric rotator, the eccentric rotator being installed at the center of the cycloid gear;

an internal gear engaged with the outer surface of the cycloid gear and revolving and rotating the cycloid gear by rotation of the rotary shaft; and

pins respectively inserted into the plurality of through holes and compensating for the eccentric center of the cycloid gear.

5 . The electronic disc brake according to claim 4 , wherein the internal gear is fixed to the motor so as not to be rotated.

6 . The electronic disc brake according to claim 4 , wherein bearings are installed between the cycloid gear and the eccentric rotator.

7 . The electronic disc brake according to claim 4 , further comprising an output shaft connected with the pins and transmitting rotating force to the spindle member, wherein the output shaft includes:

a shaft part screw-connected to the spindle member having passed through the rear wall of the caliper housing; and

a flange part protruded from the end of the shaft in the radial direction; and

insertion holes are formed on the flange part at positions corresponding to the plurality of through holes, and connected with the pins.

8 . The electronic disc brake according to claim 4 , wherein the spindle member includes:

a spindle shaft having a designated length and provided with a male screw part screw-connected to the nut member and formed on the outer circumferential surface of one end of the spindle shaft; and

a flange part protruded from the other end of the spindle shaft in the radial direction; and

insertion holes are formed on the flange part at positions corresponding to the plurality of through holes, and connected with the pins.