Vehicle turning control device

1. A vehicle turning control device for controlling a turning characteristic of a vehicle, the vehicle including braking/driving sources for independently controlling braking/driving torques applied to a plurality of wheels, a vehicle speed detection device for detecting a vehicle speed, and a steering angle detection device for detecting a steering angle, the vehicle turning control device comprising:

a memory; and

at least one processor coupled to the memory, the at least one processor including:

a target yaw rate calculation module configured to calculate a target yaw rate for the vehicle based on a yaw response characteristic, with respect to the vehicle speed detected by the vehicle speed detection device and the steering angle detected by the steering angle detection device;

a yaw moment calculation module configured to calculate the braking/driving torques developed at the plurality of wheels based on the target yaw rate calculated by the target yaw rate calculation module, so as to calculate a yaw moment predicted to act on the vehicle;

a yaw rate deviation-and/or-road surface friction calculation module including one or both of a yaw rate deviation calculation module configured to calculate a yaw rate deviation, from a difference between the target yaw rate and an actual yaw rate detected by a yaw rate detection device provided to the vehicle, and a road surface frictional coefficient calculation module configured to estimate a road surface frictional coefficient; and

a yaw response characteristic changing module configured to cause the yaw response characteristic used in the target yaw rate calculation module so as to approach a reference yaw response characteristic from a predetermined yaw response characteristic different from the reference yaw response characteristic, as the yaw rate deviation calculated by the yaw rate deviation calculation module increases or as the road surface frictional coefficient estimated by the road surface frictional coefficient calculation module decreases.

2. The vehicle turning control device as claimed in claim 1 , wherein

the yaw response characteristic changing module determines a control gain for the yaw response characteristic used in the target yaw rate calculation module, in accordance with one or both of the yaw rate deviation and the road surface frictional coefficient.

3. The vehicle turning control device as claimed in claim 1 , wherein

the yaw response characteristic changing module adjusts the yaw response characteristic used in the target yaw rate calculation module to the reference yaw response characteristic, when the road surface frictional coefficient is smaller than a road surface frictional coefficient threshold value or when the yaw rate deviation is greater than a yaw rate deviation threshold value.

4. The vehicle turning control device as claimed in claim 1 , wherein

the yaw response characteristic changing module is configured such that, when the yaw response characteristic used in the target yaw rate calculation module is changed from the reference yaw response characteristic to the predetermined yaw response characteristic, an amount of change in the yaw response characteristic per time is smaller than when the yaw response characteristic is changed from the predetermined yaw response characteristic to the reference yaw response characteristic.

5. The vehicle turning control device as claimed in claim 1 , wherein

the yaw response characteristic used in the target yaw rate calculation module is represented by a calculation expression of a second-order lag system of the target yaw rate relative to an actual steering angle, and the yaw response characteristic is changed by changing a gain of a natural frequency in a yaw direction and/or a gain of an attenuation coefficient in the yaw direction included in the calculation expression.

6. The vehicle turning control device as claimed in claim 1 , wherein

the road surface frictional coefficient calculation module estimates the road surface frictional coefficient from a magnitude of an actual lateral acceleration detected by a lateral acceleration detection device provided to the vehicle when a deviation between a target lateral acceleration and the actual lateral acceleration is greater than a predetermined value.

7. The vehicle turning control device as claimed in claim 1 , the at least one processor further comprises a vehicle attitude stabilization control device configured to perform control for stabilizing an attitude of the vehicle, wherein

the vehicle attitude stabilization control device uses the target yaw rate calculated by the target yaw rate calculation module, for the control for stabilizing the attitude of the vehicle.

8. The vehicle turning control device as claimed in claim 1 , wherein

the braking/driving sources are electric motors configured to drive the respective wheels.

9. A vehicle turning control device for controlling a turning characteristic of a vehicle, the vehicle including braking/driving sources for independently controlling braking/driving torques applied to a plurality of wheels, a vehicle speed detection device for detecting a vehicle speed, and a steering angle detection device for detecting a steering angle, the vehicle turning control device comprising:

a computer configured to:

calculate a target yaw rate for the vehicle based on a yaw response characteristic, with respect to the vehicle speed detected by the vehicle speed detection device and the steering angle detected by the steering angle detection device;

calculate the braking/driving torques developed at the plurality of wheels based on the calculated target yaw rate, so as to calculate a yaw moment predicted to act on the vehicle;

calculate a yaw rate deviation, from a difference between the target yaw rate and an actual yaw rate detected by a yaw rate detection device provided to the vehicle, and/or estimate a road surface frictional coefficient; and

cause the yaw response characteristic so as to approach a reference yaw response characteristic from a predetermined yaw response characteristic different from the reference yaw response characteristic, as the calculated yaw rate deviation increases or as the estimated road surface frictional coefficient decreases.

10. The vehicle turning control device as claimed in claim 9 , wherein

the computer is further configured to determine a control gain for the yaw response characteristic, in accordance with one or both of the yaw rate deviation and the road surface frictional coefficient.

11. The vehicle turning control device as claimed in claim 9 , wherein

the computer is further configured to adjust the yaw response characteristic to the reference yaw response characteristic, when the road surface frictional coefficient is smaller than a road surface frictional coefficient threshold value or when the yaw rate deviation is greater than a yaw rate deviation threshold value.

12. The vehicle turning control device as claimed in claim 9 , wherein

when the yaw response characteristic is changed from the reference yaw response characteristic to the predetermined yaw response characteristic, an amount of change in the yaw response characteristic per time is smaller than when the yaw response characteristic is changed from the predetermined yaw response characteristic to the reference yaw response characteristic.

13. The vehicle turning control device as claimed in claim 9 , wherein

the yaw response characteristic is represented by a calculation expression of a second-order lag system of the target yaw rate relative to an actual steering angle, and the yaw response characteristic is changed by changing a gain of a natural frequency in a yaw direction and/or a gain of an attenuation coefficient in the yaw direction included in the calculation expression.

14. The vehicle turning control device as claimed in claim 9 , wherein

the computer is further configured to estimate the road surface frictional coefficient from a magnitude of an actual lateral acceleration detected by a lateral acceleration detection device provided to the vehicle when a deviation between a target lateral acceleration and the actual lateral acceleration is greater than a predetermined value.

15. The vehicle turning control device as claimed in claim 9 , wherein the computer is further configured to perform control for stabilizing an attitude of the vehicle using the calculated target yaw rate.

16. The vehicle turning control device as claimed in claim 9 , wherein

the braking/driving sources are electric motors configured to drive the respective wheels.