Vehicle drive device

1. A vehicle drive device comprising:

a left electric motor connected to a left wheel of a vehicle;

a right electric motor connected to a right wheel of the vehicle; and

an electric motor controller that controls a torque of the left electric motor and a torque of the right electric motor,

wherein a generation of an excess slippage occurs above a predetermined amount of either the left wheel or the right wheel, the electric motor controller changes the torque of the electric motor connected to the wheel at which the excess slippage occurred by only a first change amount, and also changes the torque of the other electric motor connected to the other wheel by only a second change amount having a sign that is opposite the first change amount, the first change amount and the second change amount having absolute values that are approximately the same, and

wherein when shifting the torque of the left electric motor and the torque of the right electronic motor, a torque difference of the left electric motor and the right electric motor is changed and a total sum of torque of the left electric motor and the right electric motor does not change before and after the shift.

2. The vehicle drive device according to claim 1 , wherein the first change amount and second change amount are applied to a user requested torque.

3. The vehicle drive device according to claim 1 , wherein a yaw moment is reduced.

4. The vehicle drive device according to claim 1 , wherein the electric motor controller does not change the torque of the left and right electric motors when the excess slippage is below the predetermined amount.

5. The vehicle drive device according to claim 1 , wherein the left wheel is a rear left wheel and the right wheel is a rear right wheel.

6. A vehicle drive device comprising:

a first motor connected to a first wheel on a first side of a vehicle;

a second motor connected to a second wheel on a second side of the vehicle; and

a motor controller that controls a torque of the first motor and a torque of the second motor,

wherein when a generation of slippage at the first wheel is above a predetermined amount, the motor controller decreases an absolute value of the torque of the first motor connected to the first wheel, and increases an absolute value of the torque of the second motor connected to the second wheel, and

wherein when shifting the torque of the first motor and the torque of the second motor, a torque difference of the first motor and the second motor is changed and a total sum of torque of the first motor and the second motor does not change before and after the shift.

7. The vehicle drive device according to claim 6 , wherein the motor controller generates approximately same change amount values for the absolute value of the torque that is decreased and the absolute value of the torque that is increased.

8. The vehicle drive device according to claim 7 , wherein the change amount values are applied to a user requested torque.

9. The vehicle drive device according to claim 6 , wherein the motor controller does not change the torque of the first and second motors when the slippage is below the predetermined amount.

10. The vehicle drive device according to claim 6 , wherein when the slippage is an acceleration slippage above the predetermined amount and the first wheel is driving and the second wheel is braking, the motor controller decreases the absolute value of the torque of the first motor connected to the first wheel, and decreases the absolute value of the torque of the second motor connected to the second wheel.

11. The vehicle drive device according to claim 6 , wherein when the slippage is a deceleration slippage above the predetermined amount and the first wheel is driving and the second wheel is braking, the motor controller decreases the absolute value of the torque of the first motor connected to the first wheel, and decreases the absolute value of the torque of the second motor connected to the second wheel.

12. A method for controlling motor traction by a motor controller comprising:

calculating a slippage of a first wheel connected to a first motor and a second wheel connected to a second motor;

determining whether the slippage of the first wheel exceeds a predetermined amount;

changing a torque by a first amount in the first wheel when the slippage exceeds the predetermined amount in the first wheel;

changing a torque in the second wheel by a second amount having an opposite sign of the first amount; and

setting the first amount and the second amount to have approximately a same absolute value,

wherein when shifting the torque of the first motor and the torque of the second motor, a torque difference of the first motor and the second motor is changed and a total sum of torque of the first motor and the second motor does not change before and after the shift.

13. The method of claim 12 , wherein the first amount and second amount are applied to a user requested torque.

14. The method of claim 13 , further comprising

calculating a next slippage of the first wheel;

determining whether the next slippage exceeds the predetermined amount; and

reverting back to the user requested torque when the next slippage does not exceed the predetermined amount.

15. The method of claim 14 , further comprising adjusting the torque to the first wheel by a third amount when the next slippage exceeds the predetermined amount and then adjusting the torque to the second wheel by a fourth amount having an opposite sign to the third amount.

16. The method of claim 15 , further comprising setting the third amount and the fourth amount to have approximately a same absolute value.

17. The method of claim 12 , further comprising maintaining driving performance without unnecessary sense of deceleration to passengers.

18. The method of claim 12 , further comprising reducing a yaw moment.