Electronic disc brake

1. An electronic disc brake comprising:

a disc configured to rotate with vehicle wheels;

a caliper housing configured to operate pad plates installed at both sides of the disc; and

an actuator having a piston provided inside the caliper housing to press the pad plates to adhere the pad plates to the disc, a spindle rotatably installed at the caliper housing to reciprocate the piston, an electric motor configured to rotate the spindle, and a decelerator configured to transmit a rotational force of the electric motor to the spindle, wherein:

the decelerator includes a power connection unit connected to the electric motor, planetary gear units configured to connect the power connection unit to the spindle, and a center pin configured to pass through the power connection unit and the planetary gear units;

the center pin is fitted into the power connection unit and the planetary gear units to be rotatable relative thereto; and

one end of the center pin is slidably and rotatably coupled to a housing cap of the decelerator.

2. The electronic disc brake of claim 1 , wherein:

the power connection unit includes a driving gear provided at a shaft of the electric motor and a driven gear connected to the planetary gear units;

the planetary gear units include a first planetary gear unit and a second planetary gear unit for multi-stage deceleration;

each of the first planetary gear unit and the second planetary gear unit includes a sun gear, a plurality of planetary gears engaged to an outer portion of the sun gear, a ring gear which is an internal gear configured to accommodate the planetary gears, and a carrier installed to rotatably support the planetary gears and coaxially rotate with the sun gear and configured to output a rotational power; and

the center pin is spaced apart from and slidably and rotatably provided at a central hole provided at central portions of the driven gear of the power connection unit and the sun gear and the carrier of each of the first and second planetary gear units.

3. The electronic disc brake of claim 2 , wherein:

the decelerator further includes the housing cap configured to surround the power connection unit and the planetary gear units;

the carrier of the second planetary gear unit includes an output shaft coupled to the spindle; and

both ends of the center pin are rotatably supported by the housing cap and the output shaft, respectively.

4. The electronic disc brake of claim 1 , wherein a grease is applied between the center pin and the decelerator through which the center pin passes.

5. The electronic disc brake of claim 1 , wherein an other end of the center pin is rotatably coupled to an output shaft coupled to the spindle.

6. The electronic disc brake of claim 5 , wherein the housing cap of the decelerator has a hole to which the one end of the center pin is rotatably coupled.

7. The electronic disc brake of claim 5 , wherein the output shaft has a recess which the other end of the center pin is rotatably coupled.