Method of controlling torque of drive system of electric vehicle

1 . A method of controlling torque of a drive system of a vehicle, the method comprising:

determining, by a controller, a required torque according to a vehicle driving state while the vehicle is driven, and determining, by the controller, a total torque command based on the determined required torque; and

performing, by the controller, a front wheel and rear wheel torque distribution process on the total torque command, so that a front wheel torque command and a rear wheel torque command following the total torque command are determined,

wherein the controller is configured to:

perform a backlash control for limiting a torque slope of the front wheel torque command while the front wheel torque command passes through a backlash band, which is a torque region where there is possibility that backlash occurs in a front wheel-side drive system; and

generate a braking torque command for generating a friction braking torque while the backlash control is performed,

wherein a maximum permissible change rate in the backlash band of the front wheel torque command is set in the controller; and

wherein, in the controller, the maximum permissible change rate in the backlash band of the front wheel torque command is set to a value not causing backlash impact in the front wheel-side drive system.

2 . The method of claim 1 , wherein the backlash band of the front wheel-side drive system is set to a torque range including 0 torque while bordering a lower limit threshold value, which is a negative (−) value, and an upper limit threshold value, which is a positive (+) value.

3 . The method of claim 1 ,

wherein in the controller, the rear wheel torque command is determined as a value greater than or equal to a minimum torque threshold value, which is a preset positive (+) torque value, and

wherein the minimum torque threshold value is set in the controller to a value greater than an upper limit threshold value of a backlash band, which is a torque region where there is possibility that backlash occurs in a rear wheel-side drive system.

4 . The method of claim 3 , wherein the controller is configured to:

compare the total torque command and the minimum torque threshold value, and determine the rear wheel torque command as the minimum torque threshold value when the total torque command is less than or equal to the minimum torque threshold value;

allow a sum of the rear wheel torque command, the front wheel torque command, and the braking torque command to follow the total torque command while the front wheel torque command passes through the backlash band; and

suspend generation of the braking torque command after the front wheel torque command passes through the backlash band, so that a sum of the rear wheel torque command and the front wheel torque command follows the total torque command.

5 . The method of claim 3 , wherein the backlash band of the rear wheel-side drive system is set to a torque range including 0 torque while bordering a lower limit threshold value, which is a negative (−) value, and an upper limit threshold value, which is a positive (+) value.

6 . The method of claim 3 , wherein, in response that an ON state of a backlash band evasion mode is selected and input by a driver, the controller is configured to:

perform the backlash control of the front wheel torque command;

generate a braking torque command for generating the friction braking torque; and

maintain the rear wheel torque command at a value equal to or greater than the minimum torque threshold value.

7 . The method of claim 1 , wherein the front wheel torque command is determined as a positive (+) torque value or a negative (−) torque value obtained by subtracting the rear wheel torque command and the braking torque command from the total torque command.

8 . The method of claim 1 , wherein the braking torque command is a braking torque command of a rear wheel friction braking device that applies the friction braking torque to rear wheels of the vehicle.

9 . The method of claim 3 ,

wherein a driving input value is an accelerator pedal input value, and

wherein in response that an accelerator pedal of the vehicle is disposed in a tip-out state while a driver depresses the accelerator pedal, the controller is configured to:

perform the backlash control of the front wheel torque command;

generate a braking torque command for generating the friction braking torque; and

maintain the rear wheel torque command at a value equal to or greater than the minimum torque threshold value.

10 . The method of claim 9 , wherein, in response that the accelerator pedal is disposed in the tip-out state from a depressed state, the controller is configured to switch the front wheel torque command from a positive (+) torque value to a negative (−) torque value so that the front wheel torque command passes through the backlash band.

11 . The method of claim 10 ,

wherein the controller is configured to limit the torque slope of the front wheel torque command to the maximum permissible change rate while performing the backlash control.

12 . The method of claim 9 , wherein, in response that the accelerator pedal tips in again after tipping out by the driver, and in response that a value of the front wheel torque command is a positive (+) value and a value of the total torque command is a positive (+) value, the controller is configured to perform an operation to set the braking torque command to 0 torque to suspend generation of the braking torque command, and allow the total torque command to be satisfied by a sum of the front wheel torque command and the rear wheel torque command.

13 . The method of claim 9 , wherein, in response that the accelerator pedal tips in again after tipping out by the driver, and in response that a value of the front wheel torque command is a positive (+) value and a value of the total torque command is a positive (+) value, the controller is configured to perform an operation to:

determine the rear wheel torque command as a value equal to or greater than the minimum torque threshold value, which is a preset positive (+) torque value; and

set the braking torque command to 0 torque to suspend generation of the braking torque command, and then allow the total torque command to be satisfied by a sum of the front wheel torque command and the rear wheel torque command when the front wheel torque command passes through the backlash band and becomes a negative (−) value.

14 . The method of claim 9 , wherein, in response that the accelerator pedal tips in again after tipping out by the driver, and in response that a value of the front wheel torque command is a negative (−) value and a value of the total torque command is a positive (+) value, the controller is configured to perform an operation to:

set the braking torque command to 0 torque to suspend generation of the braking torque command; and

allow the total torque command to be satisfied by a sum of the front wheel torque command and the rear wheel torque command.

15 . The method of claim 9 , wherein, in response that the accelerator pedal tips in again after tipping out by the driver, and in response that a value of the front wheel torque command is a negative (−) value and a value of the total torque command is a negative (−) value, the controller is configured to perform an operation to:

determine the rear wheel torque command as a value equal to or greater than the minimum torque threshold value, which is a preset positive (+) torque value; and

set the braking torque command to 0 torque to suspend generation of the braking torque command, and then allow the total torque command to be satisfied by a sum of the front wheel torque command and the rear wheel torque command.

16 . The method of claim 9 , wherein, in response that a brake pedal is applied while the front wheel torque command passes through the backlash band after tip-out of the accelerator pedal by the driver, the controller is configured to change the braking torque command at a negative (−) slope to additionally generate the friction braking torque so that a total braking torque corresponding to a brake pedal input value is allowed to be satisfied.

17 . The method of claim 16 , wherein the controller is configured to:

determine the rear wheel torque command as a value equal to or greater than the minimum torque threshold value, which is a preset positive (+) torque value, after tip-out of the accelerator pedal; and

change the braking torque command at a positive (+) slope to decrease the friction braking torque, and changes the front wheel torque command at a negative (−) slope to increase regenerative braking torque of front wheels in the vehicle when the front wheel torque command becomes negative (−) torque after passing through the backlash band.

18 . The method of claim 9 , wherein, in response that a brake pedal is applied by the driver when the front wheel torque command is a negative (−) torque value after passing through the backlash band after tip-out of the accelerator pedal, the controller is configured to:

determine the rear wheel torque command as the minimum torque threshold value, which is a preset positive (+) torque value; and

change the front wheel torque command at a negative (−) slope to satisfy total braking torque by a regenerative braking torque of front wheels of the vehicle.

19 . The method of claim 18 , wherein the controller is configured to generate the regenerative braking torque of the front wheels to satisfy the total braking torque and to generate a braking torque command to additionally generate friction braking torque at a same time.