Method for reducing vibration caused by gear backlash in drive system for hybrid vehicle

1. A method for reducing vibration caused by gear backlash in a drive system for a hybrid vehicle, the method comprising:

a first step of determining whether an effective torque command, which is a value obtained by subtracting a drag torque from a motor torque command, enters or leaves a null torque zone of a gear backlash mechanism; and

in response to determining that the effective torque command enters or leaves the null torque zone, implementing a second step of initializing a control time and performing a control to restrict the effective torque to have a parabolic or exponential torque to reduce an amplitude of vibration and prevent deterioration of torque response.

2. The method of claim 1 , wherein the first step determines whether the effective torque command enters or leaves the null torque zone of the gear backlash mechanism by calculating whether the motor torque command (driver request torque) T in is greater than a sum (T dead /2+T drag ) of a half of the null torque zone T dead and the drag torque T drag and whether a T in value of the previous sample time T in — old is smaller than or equal to the sum (T dead /2+T drag ) of the half of the null torque zone T dead and the drag torque T drag ; or by calculating whether the motor torque command (driver request torque) T in is smaller than a sum (−T dead /2+T drag ) of the other half of the null torque zone T dead and the drag torque T drag and whether the T in value of the previous sample time T in — old is greater than or equal to the sum (−T dead /2+T drag ) of the other half of the null torque zone T dead and the drag torque T drag .

3. The method of claim 1 , wherein in the second step, when the effective torque leaves the null torque zone, a final motor torque command value T out is subjected to a parabolic torque restriction control in which the effective torque increases in the form of a parabolic curve by [T out =(T in −T drag )*t 2 /t max 2 +T drag ].

4. The method of claim 1 , wherein in the second step, when the effective torque enters the null torque zone, the effective torque has a curve in the form of 1−exp(−αt) using an exponential function and is converged to the drag torque.

5. The method of claim 1 , further comprising the step of determining whether the parabolic torque restriction control is performed and, if the effective torque command value exists in the null torque zone, stopping the parabolic torque restriction control to determine the final motor torque command T out as the drag torque T drag .

6. The method of claim 1 , further comprising the step of stopping the parabolic torque restriction control to determine the final motor torque command T out as the motor torque T in , if the effective torque command value leaves the null torque zone and thus the control time elapses.

7. A method for reducing vibration caused by gear backlash in a drive system for a hybrid vehicle, the method comprising:

a first step of determining whether an effective torque command enters or leaves a null torque zone of a gear backlash mechanism; and

in response to determining that the effective torque command enters or leaves the null torque zone, implementing a second step of initializing a control time and performing a control to restrict the effective torque to have a parabolic or exponential torque that reduces an amplitude of vibration and prevents deterioration of torque response.

8. The method for reducing vibration caused by gear backlash in a drive system for a hybrid vehicle of claim 7 , wherein the effective torque command is a value obtained by subtracting a drag torque from a motor torque command.

9. The method for reducing vibration caused by gear backlash in a drive system for a hybrid vehicle of claim 7 , wherein the second step is performed if it is determined that the effective torque command enters or leaves the null torque zone.

10. The method of claim 7 , wherein the first step determines whether the effective torque command enters or leaves the null torque zone of the gear backlash mechanism by calculating whether the motor torque command (driver request torque) T in is greater than a sum (T dead /2+T drag ) of a half of the null torque zone T dead and the drag torque T drag and whether a T in value of the previous sample time T in — old is smaller than or equal to the sum (T dead /2+T drag ) of the half of the null torque zone T dead and the drag torque T drag .

11. The method of claim 7 , wherein the first step determines whether the effective torque command enters or leaves the null torque zone of the gear backlash mechanism by calculating whether the motor torque command (driver request torque) T in is smaller than a sum (−T dead /2+T drag ) of the other half of the null torque zone T dead and the drag torque T drag and whether the T in value of the previous sample time T in — old is greater than or equal to the sum (−T dead /2+T drag ) of the other half of the null torque zone T dead and the drag torque T drag .