Electric power-assisted steering apparatus and method of assembling the same

1. An electric power-assisted steering (EPAS) apparatus comprising:

a gear housing in which a nut coupler coupled to a ball nut through a bearing is formed and an accommodation portion is formed to be recessed from an internal circumferential surface of the nut coupler; and

a lock screw configured to have an external circumferential surface on which a screw portion is formed and coupled to the nut coupler and supports the bearing, and to have a loosening preventer formed to protrude toward the accommodation portion after the screw portion is coupled to the nut coupler.

2. The EPAS apparatus of claim 1 , wherein one or more accommodation portions are disposed in a circumferential direction on the internal circumferential surface of the nut coupler.

3. The EPAS apparatus of claim 1 , wherein the accommodation portion is disposed between a motor coupler and the nut coupler of the gear housing.

4. The EPAS apparatus of claim 1 , wherein an assembly portion formed to have a reduced external diameter in the screw portion is provided in a lower portion of the external circumferential surface of the lock screw.

5. The EPAS apparatus of claim 1 , wherein an insertion groove is formed to be recessed from an upper surface of the lock screw in a groove shape.

6. The EPAS apparatus of claim 5 , wherein a depth to which the insertion groove is recessed is formed to be larger than a distance between adjacent ridges of the screw portion.

7. The EPAS apparatus of claim 5 , wherein a thickness between the external circumferential surface of the lock screw and the insertion groove is formed to be smaller than a thickness between an internal circumferential surface of the lock screw and the insertion groove.

8. The EPAS apparatus of claim 5 , wherein a transformation portion, which is transformed when the lock screw protrudes toward the accommodation portion, is formed between the insertion groove and a valley of the screw portion.

9. The EPAS apparatus of claim 8 , wherein a transformation-inducing groove configured to facilitate transformation of the transformation portion is formed in the screw portion.

10. The EPAS apparatus of claim 9 , wherein the transformation-inducing groove is formed to be recessed and have a smaller diameter than a valley of the screw portion.

11. The EPAS apparatus of claim 5 , wherein, between an outer circumferential wall and an inner circumferential wall of the insertion groove facing each other, a support portion is formed to taper in the outer circumferential wall so that a width of the insertion groove increases going upward in the support portion.

12. The EPAS apparatus of claim 5 , wherein, between an outer circumferential wall and an inner circumferential wall of the insertion groove facing each other, the outer circumferential wall is diagonally formed so that a width of the insertion groove increases going upward.

13. The EPAS apparatus of claim 5 , wherein a plurality of dividing slits are formed at an upper end of the lock screw between the screw portion and the insertion groove of the lock screw.

14. The EPAS apparatus of claim 13 , wherein the plurality of dividing slits are formed to be spaced apart at identical intervals in a circumferential direction of the lock screw, and

the circumferential intervals between the plurality of dividing slits are formed to be smaller than half a circumferential width of the accommodation portion.

15. The EPAS apparatus of claim 13 , wherein at least one of portions of the lock screw divided in a circumferential direction by adjacent dividing slits is disposed in the accommodation portion.

16. The EPAS apparatus of claim 1 , wherein an auxiliary groove is formed to be recessed at a position away from the accommodation portion in the internal circumferential surface of the nut coupler, and a hanger portion is formed to protrude from the lock screw toward the auxiliary groove, so that loosening of the lock screw is prevented.

17. A method of assembling an electric power-assisted steering (EPAS) apparatus, the method comprising:

fixing a bearing, which supports rotation of a ball nut in a gear housing, in a shaft direction by fastening a lock screw to a nut coupler of the gear housing; and

forming an insertion groove in an upper surface of the lock screw, and fixing the lock screw in the gear housing by plastic deformation in which a caulking tool is inserted into the insertion groove to make the upper surface of the lock screw protrude outward.

18. The method of claim 17 , wherein the caulking tool is formed to have an end whose thickness is smaller than a width of the insertion groove and have a thickness gradually increasing going upward from the end such that the upper surface of the lock screw is subjected to plastic deformation while the caulking tool is inserted into the insertion groove.

19. The method of claim 17 , wherein a thickness between an external circumferential surface of the lock screw and the insertion groove is formed to be smaller than a thickness between an internal circumferential surface of the lock screw and the insertion groove, and

the caulking tool is gradually inserted into the insertion groove.

20. The method of claim 17 , wherein an accommodation portion is formed to be recessed from an internal circumferential surface of the nut coupler, and

the upper surface of the lock screw is made to protrude toward the accommodation portion by inserting the caulking tool into the insertion groove adjacent to the accommodation portion.