Coupling structure of suspension

1. A coupling structure of a suspension, the coupling structure comprising:

an assist knuckle in which a strut is located;

a knuckle engaged with the assist knuckle, rotated independently from the assist knuckle, and configured to perform steering of a vehicle wheel;

a steering input portion fixed to a vehicle body and configured to apply a steering force to the knuckle during steering; and

a rotation transmission unit which is engaged with the knuckle and the steering input portion and has a length which is varied in a response to a wheel rebound of a vehicle,

wherein a lower arm is engaged with the vehicle body and an end portion of the assist knuckle, and

wherein one end portion of the lower arm and a lower end portion of the assist knuckle are coupled through an engagement unit which is configured to be prevented from being rotated about a central axis in a height direction of the assist knuckle and configured to absorb a front-rear movement and a left-right movement which are applied from the vehicle wheel.

2. The coupling structure of claim 1 , wherein the rotation transmission unit includes:

a first rod engaged with an output end portion of the steering input portion;

a second rod configured to pass through the assist knuckle to be engaged with the knuckle; and

a variable rod located between the first rod and the second rod and engaged to the first rod and the second rod.

3. The coupling structure of claim 2 , wherein the assist knuckle includes an upper end hole and the second rod is aligned to pass through the upper end hole of the assist knuckle to be engaged with an upper end portion of the knuckle.

4. The coupling structure of claim 2 , wherein the variable rod is rotatable in a first direction based on a first end portion of the variable rod engaged with the first rod.

5. The coupling structure of claim 4 , wherein the variable rod is rotatable in a second direction based on a second end portion of the variable rod engaged with the second rod.

6. The coupling structure of claim 5 , wherein the first direction is different from the second direction.

7. The coupling structure of claim 2 , wherein the variable rod includes:

a first variable rod engaged with the first rod; and

a second variable rod slidably engaged to the first variable rod and engaged with the second rod.

8. The coupling structure of claim 7 , wherein the second variable rod includes an insertion groove to allow the first variable rod to be inserted into the insertion groove.

9. The coupling structure of claim 8 , further including:

at least a protrusion located on an external side of the first variable rod; and

recesses formed in the insertion groove of the second rod to allow the at least a protrusion to be inserted into the recesses.

10. The coupling structure of claim 8 , wherein, when an external force is applied between the steering input portion and the knuckle, the first variable rod is configured to be variable in length along the insertion groove of the second variable rod.

11. The coupling structure of claim 8 , further including:

a lubrication layer located in a region in which the first variable rod and the second variable rod are adjacent to each other.

12. The coupling structure of claim 2 , wherein the variable rod is variable in length in a response to a change in trajectory of a center portion of the vehicle wheel according to the wheel rebound.

13. The coupling structure of claim 1 , wherein the engagement unit is a U-joint.