Electric power steering apparatus for vehicle and method of assembling the same

1. An electric power steering apparatus comprising:

a boss having a coupling hole formed at one end thereof and an insertion hole formed at the other end in a shape extending in a spoke-like pattern in a radial direction from a center thereof, a driving shaft of a motor being inserted into the coupling hole;

an elastic member having vanes extending in the spoke-like pattern in the radial direction from a center thereof to be inserted into and engaged in the insertion hole, the elastic member being closed at one axial end and formed with a fastening hole at the other axial end in a shape extending in a spoke-like pattern from the center thereof, and a radial length of the vanes being set to be shorter than that of the portions extending in the spoke-like pattern in the insertion hole such that a first predetermined clearance space is formed between each of the vanes and an inner wall of the insertion hole in the radial direction at each of the portions extending in the spoke-like pattern in the insertion hole in the portions extending in the spoke-like pattern in the insertion hole; and

a worm shaft having coupling portions at one end of an outer circumferential surface thereof, the coupling portions extending in the spoke-like pattern in a radial direction to be inserted into and engaged in the fastening hole,

wherein the elastic member further includes a connection portion interconnecting adjacent vanes so that a second predetermined clearance space is formed between the connection portion and an inner circumferential surface of the insertion hole.

2. The electric power steering apparatus of claim 1 , wherein the opposite side surfaces of each of the vanes of the elastic member in the circumferential direction are in close contact with the inner circumferential surface of the insertion hole.

3. The electric power steering apparatus of claim 1 , wherein bumps are formed around a peripheral edge of the one axial end surface of the elastic member to come in contact with a peripheral surface of the insertion hole of the boss.

4. The electric power steering apparatus of claim 2 , bumps are formed around a peripheral edge of the one axial end surface of the elastic member to come in contact with a peripheral surface of the insertion hole of the boss.

5. The electric power steering apparatus of claim 1 , wherein a protrusion is formed in the axial direction on the one end of the worm shaft to center the worm shaft when the worm shaft is inserted into the fastening hole of the elastic member.

6. The electric power steering apparatus of claim 2 , wherein a protrusion is formed in the axial direction on the one end of the worm shaft to center the worm shaft when the worm shaft is inserted into the fastening hole of the elastic member.

7. The electric power steering apparatus of claim 3 , wherein a protrusion is formed in the axial direction on the one end of the worm shaft to center the worm shaft when the worm shaft is inserted into the fastening hole of the elastic member.

8. The electric power steering apparatus of claim 4 , wherein a protrusion is formed in the axial direction on the one end of the worm shaft to center the worm shaft when the worm shaft is inserted into the fastening hole of the elastic member.

9. A method of assembling an electric power steering apparatus for a vehicle, the method comprising:

coupling a boss and an elastic member with each other, wherein the boss has a coupling hole formed at one end thereof and an insertion hole formed at the other end in a shape extending in a spoke-like pattern in a radial direction from a center thereof, a driving shaft of a motor being inserted into the coupling hole, and the elastic member has vanes extending in the spoke-like pattern in the radial direction from a center thereof, the elastic member being closed at one axial end and formed with a fastening hole at the other axial end in a shape extending in a spoke-like pattern from the center thereof, and a radial length of the vanes being set to be shorter than that of the portions extending in the spoke-like pattern in the insertion hole such that a first predetermined clearance space is formed between each of the vanes and an inner wall of the insertion hole in the radial direction at each of the portions extending in the spoke-like pattern in the insertion hole in the portions extending in the spoke-like pattern in the insertion hole;

coupling the boss coupled with the elastic member to the driving shaft of the motor; and

coupling a worm shaft to the elastic member, wherein the worm shaft has, at one end of an outer circumferential surface thereof, coupling portions extending in the spoke-like pattern in a radial direction to be inserted into and engaged in the fastening hole, and a protrusion formed in the axial direction on the one end of the worm shaft,

wherein the elastic member further includes a connection portion interconnecting adjacent vanes so that a second predetermined clearance space is formed between the connection portion and an inner circumferential surface of the insertion hole.

10. A method of assembling an electric power steering apparatus for a vehicle, the method comprising:

coupling a driving shaft and a boss with each other, wherein the boss has a coupling hole formed at one end thereof and an insertion hole formed at the other end in a shape extending in a spoke-like pattern in a radial direction from a center thereof, the driving shaft of the motor being inserted into the coupling hole;

coupling the boss and an elastic member with each other, wherein the elastic member has vanes extending in the spoke-like pattern in the radial direction from a center thereof, the elastic member being closed at one axial end and formed with a fastening hole at the other axial end in a shape extending in a spoke-like pattern from the center thereof, and a radial length of the vanes being set to be shorter than that of the portions extending in the spoke-like pattern in the insertion hole such that a first predetermined clearance space is formed between each of the vanes and an inner wall of the insertion hole in the radial direction at each of the portions extending in the spoke-like pattern in the insertion hole in the portions extending in the spoke-like pattern in the insertion hole; and

coupling a worm shaft to the elastic member, wherein the worm shaft has, at one end of an outer circumferential surface thereof, coupling portions extending in the spoke-like pattern in a radial direction to be inserted into and engaged in the fastening hole, and a protrusion formed in the axial direction on the one end of the worm shaft,

wherein the elastic member further includes a connection portion interconnecting adjacent vanes so that a second predetermined clearance space is formed between the connection portion and an inner circumferential surface of the insertion hole.

11. The method of claim 9 wherein, when coupling the elastic member and the worm shaft, the worm shaft is laid under the motor, the centers of the protrusion of the worm shaft and the fastening hole of elastic member are aligned with a coaxial line, and then the worm shaft is rotated such that the coupling portion of the worm shaft can be inserted into the fastening hole of the elastic member by the weight of the motor to be engaged in the fastening hole of the elastic member.

12. The method of claim 10 , wherein, when coupling the elastic member and the worm shaft, the worm shaft is laid under the motor, the centers of the protrusion of the worm shaft and the fastening hole of elastic member are aligned with a coaxial line, and then the worm shaft is rotated such that the coupling portion of the worm shaft can be inserted into the fastening hole of the elastic member by the weight of the motor to be engaged in the fastening hole of the elastic member.