Rack-driven steering apparatus and rack-driven auxiliary power steering apparatus including the same

1. A rack-driven steering apparatus comprising:

a first gear provided at a lower end of a steering shaft; and

a ball nut having one end provided with a second gear engaged with the first gear and having a screw groove on an inner periphery surface thereof to transmit a steering force of the steering shaft to a rack bar,

wherein the rack bar is coupled to an inner side of the ball nut and has a second screw groove corresponding to the first screw groove on an outer peripheral surface thereof to be slid during rotation of the ball nut, and

the second gear extends from an end face of the ball nut so that at least a portion of the second gear overlaps the end face in an axial direction of the ball nut.

2. The rack-driven steering apparatus as claimed in claim 1 , wherein an outer peripheral surface of the first gear, a diameter of which is expanded, is formed at a lower end of the steering shaft to be inclined toward the steering shaft and gear teeth are formed on the inclined outer peripheral surface of the first gear.

3. The rack-driven steering apparatus as claimed in claim 2 , wherein the first gear is separately formed to be coupled to the steering shaft.

4. The rack-driven steering apparatus as claimed in claim 2 , wherein the first gear is integrally formed with the steering shaft.

5. The rack-driven steering apparatus as claimed in claim 3 or 4 , wherein the gear teeth of the first gear are formed in a linear form in a center axis direction thereof or in a spiral form inclined at a predetermined angle with respect to the center axis.

6. The rack-driven steering apparatus as claimed in claim 1 , wherein the second gear is formed at one end of the ball nut to be inclined toward a center axis thereof or gear teeth are formed at the inclined end.

7. The rack-driven steering apparatus as claimed in claim 6 , wherein the second gear is separately formed to be coupled to one end of the ball nut.

8. The rack-driven steering apparatus as claimed in claim 6 , wherein the second gear is integrally formed with the ball nut.

9. The rack-driven steering apparatus as claimed in claim 7 or 8 , wherein the gear teeth of the second gear are formed in a linear form in a center axis direction thereof or in a spiral form inclined at a predetermined angle with respect to the center axis.

10. A rack-driven auxiliary power steering apparatus comprising:

a first gear provided at a lower end of a steering shaft;

a ball nut having one end provided with a second gear engaged with the first gear and having a first screw groove on an inner peripheral surface thereof to transmit a steering force of the steering shaft to a rack bar;

a rack bar coupled to an inner side of the ball nut and having a second screw groove corresponding to the first screw groove on an outer peripheral surface thereof to be slid during rotation of the ball nut;

a motor for generating an auxiliary steering force; and

a nut pulley coupled to an outer peripheral surface of the ball nut such that the ball nut is rotated by a driving force of a belt driven by the motor, to transmit the auxiliary steering force.

11. The rack-driven auxiliary power steering apparatus as claimed in claim 10 , further comprising:

a torque sensor for outputting an electric signal proportional to a steering torque when a driver manipulates a steering wheel; and

an electronic control unit (ECU) for generating an auxiliary steering force control signal based on the electric signal transferred from the torque sensor and transmitting the auxiliary steering force control signal to the motor.