Noise reduction structure of electronic power steering apparatus

1. A noise reduction structure of an electronic power steering apparatus including a worm shaft rotated by a motor, a worm wheel engaged in the worm shaft and rotating a steering shaft, and a housing surrounding the worm shaft, the noise reduction structure comprising:

a cylindrical damper unit formed as an elastic member in an inner side of the cylindrical damper unit rotatably connected to the worm shaft and configured to absorb a shock transmitted to the worm shaft;

a rubber holder coupled to a semi-cylindrical damper holder formed on a side surface of the damper unit for making a close contact between the worm shaft and the worm wheel; and

a plug unit including a plug holder formed on a lower end of a side surface of the plug unit for coupling to the rubber holder, the plug unit fixed to the housing on an other side surface of the plug unit.

2. The noise reduction structure of claim 1 , wherein the damper holder includes a first groove and the plug holder includes a second groove, respectively for coupling with the rubber holder, which closely contacts and surrounds the grooves.

3. The noise reduction structure of claim 2 , wherein the rubber holder includes an upper hole and a lower hole formed in a figure eight-letter shape so that a first inner surface of the upper hole is in close contact with a first outer circumference of the first groove formed in the damper holder and a second inner surface of the lower hole is in close contact with a second outer circumference of the second groove formed in the plug holder.

4. The noise reduction structure of claim 3 , wherein a thickness between the upper hole and the lower hole is at least equal to or more than a clearance gap between the worm shaft and the worm wheel.

5. The noise reduction structure of claim 1 , wherein an upper end surface of the plug holder supports a lower end surface of the damper holder coupled with the rubber holder.

6. The noise reduction structure of claim 1 , wherein the rubber holder maintains a first shape thereof at a room temperature and contracts as a second shape with a decrease in ambient temperature, and the damper unit coupled with the contracted second shape of the rubber holder is pulled downward so that a clearance between the worm shaft and the worm wheel is decreased.

7. The noise reduction structure of claim 1 , wherein the rubber holder is formed by nitrile rubber material or hydrogenated nitrile butadiene rubber material.