Motor driven power steering apparatus

1. A motor-driven power steering apparatus comprising:

an input shaft and an output shaft being coaxially connected via a torsion bar;

a drive gear connected to an electric motor, the drive gear being pivoted to a gear housing;

a driven gear engaging with the drive gear, the driven gear being fixed to an intermediate portion of the output shaft;

a torque detecting structure detecting a steering torque applied to the input shaft, the torque detecting structure being provided between the input shaft and the output shaft;

a spiral cable spirally wound around a same axis of the input shaft and the output shaft in an inner portion of the gear housing; and

one end portion of the spiral cable being connected to the torque detecting structure, another end portion of the spiral cable being connected to a torque detection result pickup portion, and driving of the electric motor being controlled on the basis of the steering torque which the torque detecting structure detects,

wherein a rotation preventing structure is installed in the gear housing which prevents the drive gear from rotating with respect to the gear housing.

2. The motor-driven power steering apparatus as claimed in claim 1 , wherein the rotation preventing structure is a rotation preventing arm, and

wherein the rotation preventing arm has a boss portion which is coupled to a serration provided in a gear shaft of the drive gear, and a locking portion which locks to a stopper provided in the gear housing.

3. The motor-driven power steering apparatus as claimed in claim 2 , wherein the boss portion of the rotation preventing arm is provided with an inner peripheral projection which is connected to at least a part of the serration provided in the gear shaft of the drive gear at a plurality of positions in a peripheral direction of an inner periphery of the boss portion, and

wherein the locking portion is provided with an outer peripheral projection which locks to the stopper provided in the gear housing.

4. The motor-driven power steering apparatus as claimed in claim 3 , wherein the boss portion of the rotation preventing arm has a cylindrical shape, a grip portion is radially protruded from a plurality of positions in a tube outer periphery in a base end side of the boss portion, and the locking portion is radially protruded from a plurality of positions of a tube outer periphery in a leading end side of the boss portion.

5. The motor-driven power steering apparatus as claimed in claim 4 , wherein in a state in which the rotation preventing arm is installed, the rotation preventing arm is accommodated in an inner portion of a cup-shaped portion to which the electric motor of the gear housing is attached.

6. The motor-driven power steering apparatus as claimed in claim 3 , wherein in a state in which the rotation preventing arm is installed, the rotation preventing arm is accommodated in an inner portion of a cup-shaped portion to which the electric motor of the gear housing is attached.

7. The motor-driven power steering apparatus as claimed in claim 3 , wherein the drive gear is a worm gear.

8. The motor-driven power steering apparatus as claimed in claim 2 , wherein the boss portion of the rotation preventing arm has a cylindrical shape, a grip portion is radially protruded from a plurality of positions in a tube outer periphery in a base end side of the boss portion, and the locking portion is radially protruded from a plurality of positions of a tube outer periphery in a leading end side of the boss portion.

9. The motor-driven power steering apparatus as claimed in claim 8 , wherein in a state in which the rotation preventing arm is installed, the rotation preventing arm is accommodated in an inner portion of a cup-shaped portion to which the electric motor of the gear housing is attached.

10. The motor-driven power steering apparatus as claimed in claim 8 , wherein the drive gear is a worm gear.

11. The motor-driven power steering apparatus as claimed in claim 2 , wherein the stopper is provided in the gear housing in such a manner that the locking portion of the rotation preventing arm which locks thereto is a tool engaging surface which is provided in an inner periphery of a nut threadably attached by a screw to the gear housing for retaining a bearing in the gear housing, and the bearing pivots the gear shaft of the drive gear to the gear housing.

12. The motor-driven power steering apparatus as claimed in claim 11 , wherein in a state in which the rotation preventing arm is installed, the rotation preventing arm is accommodated in an inner portion of a cup-shaped portion to which the electric motor of the gear housing is attached.

13. The motor-driven power steering apparatus as claimed in claim 2 , wherein the stopper is provided in the gear housing in such a manner that the locking portion of the rotation preventing arm which locks thereto is a locking convex portion which is provided in an inner surface of the gear housing and to which the locking portion of the rotation preventing arm is fitted.

14. The motor-driven power steering apparatus as claimed in claim 13 , wherein the boss portion of the rotation preventing arm has a cylindrical shape, a grip portion and the locking portion is protruded to an outer side in a radial direction from a tube outer peripheral in a base end side of the boss portion, and a concave portion provided in the locking portion is fitted to the locking convex portion.

15. The motor-driven power steering apparatus as claimed in claim 2 , wherein the stopper is provided in the gear housing in such a manner that the locking portion of the rotation preventing arm which locks thereto is a locking hole portion which is open to an inner surface of the gear housing, and into which the locking portion of the rotation preventing arm is locked.

16. The motor-driven power steering apparatus as claimed in claim 15 , wherein the boss portion of the rotation preventing arm has a cylindrical shape, a lever portion of the locking portion is protruded to an outer side in a radial direction from a tube outer periphery in a base end side of the boss portion, a locking pin is provided in a leading end of the lever portion, and the locking pin is locked to the locking hole portion.

17. The motor-driven power steering apparatus as claimed in claim 2 , wherein the stopper is provided in the gear housing in such a manner that the locking portion of the rotation preventing arm which locks thereto is a locking surface portion which is provided in an inner surface of the gear housing, and with which the locking portion of the rotation preventing arm is engaged.

18. The motor-driven power steering apparatus as claimed in claim 2 , wherein in a state in which the rotation preventing arm is installed, the rotation preventing arm is accommodated in an inner portion of a cup-shaped portion to which the electric motor of the gear housing is attached.

19. The motor-driven power steering apparatus as claimed in claim 2 , wherein the drive gear is a worm gear.

20. The motor-driven power steering apparatus as claimed in claim 1 , wherein the drive gear is a worm gear.