Electronic disc brake

1. An electronic disc brake comprising:

a disc configured to be rotated with a wheel;

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

an actuator including:

a piston disposed in the caliper housing and configured to press the pad plates to bring the pad plates into contact with the disc;

a spindle rotatably installed in the caliper housing to move the piston forward and backward;

a motor configured to rotate the spindle; and

a speed reduction apparatus configured to transmit a rotational force of the motor to the spindle,

wherein the speed reduction apparatus includes:

a power connecting unit connected to the motor;

a bracket disposed above the motor and configured to support the power connecting unit;

a speed reduction gear unit having gear teeth and configured to sequentially connect the power connecting unit and the spindle; and

a housing configured to accommodate the motor, and

wherein the housing includes a speed reduction gear installation portion therein having gear teeth to be engaged with the gear teeth of the speed reduction gear unit,

wherein the power connecting unit includes:

a slave helical gear disposed at a first end of the power connecting unit and engaged with a master helical gear of the motor;

a worm shaft gear connected to the speed reduction gear unit; and

a bearing disposed at a second end of the power connecting unit, the bearing configured to support the power connecting unit and to reduce vibration.

2. The electronic disc brake of claim 1 , wherein the speed reduction apparatus further includes: a cover configured to cover an upper portion of the housing; and

a first damper arranged between the bracket and the cover.

3. The electronic disc brake of claim 2 , wherein a second damper is interposed between a lower portion of the motor and the housing.

4. The electronic disc brake of claim 1 , wherein the housing further includes a motor accommodation portion on which the motor is seated,

wherein the speed reduction gear unit is disposed in the speed reduction gear installation portion, and

wherein the housing is parallel to the speed reduction gear installation portion.

5. The electronic disc brake of claim 4 , wherein the speed reduction gear unit includes:

a worm wheel gear engaged with the worm shaft gear;

a sun gear configured to be rotated with the worm wheel gear;

a plurality of planetary gears engaged with an outer side of the sun gear;

a ring gear configured to accommodate the planetary gears, as an internal gear; and

a carrier configured to rotatably support the planetary gears, installed to be rotated about the same shaft as the sun gear, and configured to output rotational power,

wherein the ring gear is disposed in the speed reduction gear installation portion to be engaged therewith.

6. The electronic disc brake of claim 4 , wherein gear teeth of at least one among the master helical gear, the slave helical gear, the worm shaft gear, the worm wheel gear, the planetary gear, or the ring gear are composed of a synthetic resin.

7. The electronic disc brake of claim 4 , wherein angles of gear teeth of the master helical gear and the slave helical gear are 30° to 43°.

8. The electronic disc brake of claim 4 , wherein angles of gear teeth of the worm shaft gear and the worm wheel gear are 30° to 43°.

9. The electronic disc brake of claim of claim 1 , wherein the motor comprises a power line configured to supply power, and

wherein the power line includes:

a connecting portion connected to a connector inside the housing; and

a bent portion configured to connect the connecting portion and the motor.

10. The electronic disc brake of claim 9 , wherein the connecting portion includes a contact portion in contact with the connector and having a rectangular plate shape, and allows a connection state to be maintainable when the motor vertically and transversely moves or rotates.

11. The electronic disc brake of claim 9 , wherein the bent portion protrudes from an upper side of the motor and has an “S” shape.