System and method for determining backlash in driving system of vehicle

1. A system for determining backlash in a driving system of a vehicle, comprising:

a motor speed sensor configured to detect a motor speed;

a wheel speed sensor configured to detect a wheel speed;

a speed difference determination unit, of a controller, configured to receive the detected motor speed and wheel speed and to determine a rotational speed difference of the driving system, occurring between a motor and a driving wheel, from the motor speed and the wheel speed;

a torsion speed determination unit, of the controller, configured to receive the determined rotational speed difference of the driving system and to determine a reference torsion speed for backlash determination of the driving system based on the rotational speed difference of the driving system and a motor torque command generated during driving of the vehicle; and

a backlash determination unit, of the controller, configured to receive the determined rotational speed difference of the driving system and the determined reference torsion speed, to determine a backlash speed that corresponds to a difference between the rotational speed difference of the driving system and the reference torsion speed, and to determine whether backlash in the driving system occurs using the determined backlash speed;

wherein the torsion speed determination unit is further configured to:

determine a spring stiffness of the driving system through an arithmetic operation process using equations using the determined rotational speed difference of the driving system and the motor torque command; and

determine the reference torsion speed from the spring stiffness of the driving system and the motor torque command.

2. The system of claim 1 , wherein the speed difference determination unit is configured to:

determine an equivalent wheel speed, which is a wheel speed equivalent to that of the motor, from the detected wheel speed using a gear ratio between the motor and the driving wheel; and

determine a difference between the detected motor speed and the determined equivalent wheel speed as the rotational speed difference of the driving system.

3. The system of claim 1 , wherein the torsion speed determination unit is configured to determine a value, acquired by multiplying the spring stiffness of the driving system by the motor torque command, as the reference torsion speed.

4. The system of claim 1 , wherein the backlash determination unit is configured to determine a filtered value of a difference between the rotational speed difference of the driving system and the reference torsion speed, as the backlash speed.

5. The system of claim 4 , wherein the filtered value is acquired through high-pass filtering.

6. The system of claim 1 , wherein the backlash determination unit is configured to determine whether the backlash occurs by comparing the determined backlash speed to a predetermined backlash determination threshold.

7. The system of claim 6 , wherein the backlash determination unit is configured to generate a backlash flag indicating whether the backlash occurs based on a result of the determination.

8. The system of claim 1 , wherein the torsion speed determination unit is configured to determine a spring stiffness of the driving system through an arithmetic operation process using an Equation E1 using the rotational speed difference of the driving system and the motor torque command:

{circumflex over ({dot over (k)})} spr =deadzone( K u ×(1−Flag backlash )×(ω d −{circumflex over (k)} spr ×{dot over (T)} cmd )),   E1:

wherein K u indicates a predetermined update gain, Flag backlash indicates a backlash flag value, which is a result of determination in an earlier determination cycle, ω d indicates the rotational speed difference of the driving system, {circumflex over (k)} spr indicates the spring stiffness of the driving system, T cmd indicates the motor torque command, deadzone(x) indicates a deadzone function, and {dot over ( )} indicates a differential value.

9. The system of claim 1 , wherein the torsion speed determination unit is configured to determine a spring stiffness of the driving system through an arithmetic operation process using an Equation E2 using the rotational speed difference of the driving system and the motor torque command:

{tilde over ({dot over (k)})} spr =deadzone( K u ×(1−Flag backlash )×(ω d −( k spr +{tilde over (k)} spr )× {dot over (T)} cmd )),   E2:

wherein K u indicates a predetermined update gain, Flag backlash indicates a backlash flag value, which is a result of determination in an earlier determination cycle, ω d indicates the rotational speed difference of the driving system, k spr +{tilde over (k)} spr indicates the spring stiffness of the driving system, k spr is a predetermined constant, {tilde over (k)} spr indicates a change in the spring stiffness which is acquired at each determination so as to be updated, T cmd indicates the motor torque command, deadzone(x) indicates a deadzone function, and {dot over ( )} indicates a differential value.

10. A method for determining backlash in a driving system of a vehicle, comprising:

detecting, by a motor speed sensor, a motor speed;

detecting, by a wheel speed sensor, a wheel speed;

determining, by a controller, a rotational speed difference of the driving system occurring between a motor and a driving wheel from the detected motor speed and the detected wheel speed;

determining, by the controller, a reference torsion speed for backlash determination of the driving system based on the determined rotational speed difference of the driving system and a motor torque command generated during driving of the vehicle;

determining, by the controller, a backlash speed that corresponds to a difference between the determined rotational speed difference of the driving system and the determined reference torsion speed;

determining, by the controller, whether backlash in the driving system occurs using the determined backlash speed;

determining, by the controller, a spring stiffness of the driving system through an arithmetic operation process using equations using the determined rotational speed difference of the driving system and the motor torque command; and

determining, by the controller, the reference torsion speed from the spring stiffness of the driving system and the motor torque command.

11. The method of claim 10 , wherein the controller is configured to:

determine an equivalent wheel speed, which is a wheel speed equivalent to the motor, from the detected wheel speed using a gear ratio between the motor and the driving wheel; and

determine a difference between the detected motor speed and the determined equivalent wheel speed as the rotational speed difference of the driving system.

12. The method of claim 10 , wherein the controller is configured to determine a value, acquired by multiplying the spring stiffness of the driving system by the motor torque command, as the reference torsion speed.

13. The method of claim 10 , wherein the controller is configured to determine a filtered value of a difference between the rotational speed difference of the driving system and the reference torsion speed, as the backlash speed.

14. The method of claim 13 , wherein the filtered value is acquired through high-pass filtering.

15. The method of claim 10 , wherein the controller is configured to determine whether the backlash occurs by comparing the determined backlash speed to a predetermined backlash determination threshold.

16. The method of claim 15 , wherein the controller is configured to generate a backlash flag indicating whether the backlash occurs based on a result of the determination.

17. The method of claim 16 , wherein the controller is configured to determine a spring stiffness of the driving system through an arithmetic operation process using an Equation E1 using the rotational speed difference of the driving system and the motor torque command:

{circumflex over ({dot over (k)})} spr =deadzone( K u ×(1−Flag backlash )×(ω d −{circumflex over (k)} spr ×{dot over (T)} cmd )),   E1:

wherein K u indicates a predetermined update gain, Flag backlash indicates a backlash flag value, which is a result of determination in an earlier determination cycle, ω d indicates the rotational speed difference of the driving system, {circumflex over (k)} spr indicates the spring stiffness of the driving system, T cmd indicates the motor torque command, deadzone(x) indicates a deadzone function, and {dot over ( )} indicates a differential value.

18. The method of claim 16 , wherein the controller is configured to determine a spring stiffness of the driving system through an arithmetic operation process using an Equation E2 using the rotational speed difference of the driving system and the motor torque command:

{tilde over ({dot over (k)})} spr =deadzone( K u ×(1−Flag backlash )×(ω d −( k spr +{tilde over (k)} spr )× {dot over (T)} cmd )),   E2:

wherein K u indicates a predetermined update gain, Flag backlash indicates a backlash flag value, which is a result of determination in an earlier determination cycle, ω d indicates the rotational speed difference of the driving system, k spr +{tilde over (k)} spr indicates the spring stiffness of the driving system, k spr is a predetermined constant, {tilde over (k)} spr indicates a change in the spring stiffness which is acquired at each determination so as to be updated, T cmd indicates the motor torque command, deadzone(x) indicates a deadzone function, and {dot over ( )} indicates a differential value.