Vehicle and method for controlling vehicle

1. A vehicle comprising:

a power steering; and

a controller configured to:

adjust an amount of an assistance in a steering to be provided by the power steering, wherein the amount of the assistance is adjusted in accordance with a change in a state quantity related to an ease of the steering, wherein the state quantity is frequency-related data related to a steering input by a driver of the vehicle;

control a control amount of a driving force on a wheel of the vehicle in accordance with the change in the state quantity;

calculate a target yaw rate of the vehicle based on a vehicle model that defines a relationship between the target yaw rate of the vehicle and a vehicle speed and a steering wheel angle with a target stability factor, wherein the target stability factor is a parameter, related to a turning performance of the vehicle, determined from specifications of the vehicle,

wherein the target stability factor comprises a first stability factor, a second stability factor greater than the first stability factor, and a third stability factor calculated with linear interpolation between the first stability factor and the second stability factor;

vary the turning performance of the vehicle by:

when an absolute value of the frequency-related data is smaller than or equal to a first threshold value, setting the first stability factor as the target stability factor,

when the absolute value of the frequency-related data is greater than or equal to a second threshold value, setting the second stability factor as the target stability factor, and

when the absolute value of the frequency-related data is greater than the first threshold value and smaller than the second threshold value, setting the third stability factor as the target stability factor;

compare the frequency-related data with a threshold value;

determine whether the target stability factor should be corrected or not, based on a result of the comparison of the frequency-related data with the threshold value;

correct the target stability factor based on the determination that the target stability factor should be corrected; and

control the vehicle based on the target yaw rate.

2. The vehicle according to claim 1 ,

wherein the frequency-related data is obtained, by subjecting one of a steering wheel torque and an amount of a steering operation of the driver to a frequency analysis, from a change in one of a first rate of change in the steering wheel torque caused by the driver and a second rate of change in the amount of the steering operation by the driver.

3. The vehicle according to claim 1 ,

wherein the controller is further configured to cause the amount of the assistance to decrease as high-frequency components included in the frequency-related data increase.

4. The vehicle according to claim 1 ,

wherein the controller is further configured to cause the target yaw rate to increase as a value of the target stability factor decreases.

5. The vehicle according to claim 4 ,

wherein the controller is further configured to:

acquire, as a yaw rate generated by the vehicle, a feedback yaw rate to be compared with the target yaw rate;

calculate a control target yaw moment based on a first difference between the target yaw rate and the feedback yaw rate;

calculate the control target yaw moment by adding up a steady-state damping control yaw moment and a transient inertia compensation yaw moment, wherein each of the steady-state damping control yaw moment and the transient inertia compensation yaw moment is calculated based on the first difference; and

correct at least one of the steady-state damping control yaw moment and the transient inertia compensation yaw moment based on the frequency-related data.

6. The vehicle according to claim 5 ,

wherein the controller is further configured to:

acquire a first yaw rate obtained from the vehicle model and a second yaw rate obtained from a yaw rate sensor; and

calculate the feedback yaw rate, based on the first yaw rate and the second yaw rate, with an increased distribution of the first yaw rate when a second difference between the first yaw rate and the second yaw rate is small and an increased distribution of the second yaw rate when the second difference is large.

7. The vehicle according to claim 5 ,

wherein the controller is further configured to cause a value of the transient inertia compensation yaw moment to decrease as high-frequency components included in the frequency-related data increase.

8. The vehicle according to claim 1 ,

wherein the controller is further configured to:

acquire, as a yaw rate generated by the vehicle, a feedback yaw rate to be compared with the target yaw rate;

calculate a control target yaw moment based on a first difference between the target yaw rate and the feedback yaw rate;

calculate the control target yaw moment by adding up a steady-state damping control yaw moment and a transient inertia compensation yaw moment, wherein each of the steady-state damping control yaw moment and the transient inertia compensation yaw moment is calculated based on the first difference; and

correct at least one of the steady-state damping control yaw moment and the transient inertia compensation yaw moment based on the frequency-related data.

9. The vehicle according to claim 8 ,

wherein the controller is further configured to cause a value of the transient inertia compensation yaw moment to decrease as high-frequency components included in the frequency-related data increase.

10. The vehicle according to claim 9 ,

wherein the controller is further configured to cause a value of the transient inertia compensation yaw moment to decrease as high-frequency components included in the frequency-related data increase.

11. The vehicle according to claim 8 ,

wherein the controller is further configured to:

acquire a first yaw rate obtained from the vehicle model and a second yaw rate obtained from a yaw rate sensor; and

calculate the feedback yaw rate, based on the first yaw rate and the second yaw rate, with an increased distribution of the first yaw rate when a second difference between the first yaw rate and the second yaw rate is small and an increased distribution of the second yaw rate when the second difference is large.

12. A vehicle comprising:

a power steering, and

a controller configured to:

adjust an amount of an assistance in a steering to be provided by the power steering, wherein the amount of the assistance is adjusted in accordance with a change in a state quantity related to an ease of the steering, wherein the state quantity is frequency-related data related to a steering input by a driver of the vehicle;

control a control amount of a driving force on a wheel of the vehicle in accordance with the change in the state quantity;

cause the amount of the assistance to decrease as high-frequency components included in the frequency-related data increase;

calculate a reference value of a front wheel steering angle and a steering wheel torque based on a steering model;

calculate the frequency-related data based on:

a result of a frequency analysis of at least one of the steering wheel torque and an amount of a steering operation by the driver, or

at least one of a change in a first rate of change in the steering wheel torque and a change in a second rate of change in the amount of the steering operation;

calculate a steering correction gain for correcting the reference value of the front wheel steering angle based on the frequency-related data;

multiply the reference value of the front wheel steering angle by the steering correction gain;

calculate a requested value of the front wheel steering angle based on the multiplication of the reference value of the front wheel steering angle by the steering correction gain; and

output the requested value of the front wheel steering angle to the power steering,

wherein the controller is further configured to calculate the frequency-related data based on a ratio between a first area obtained by a first integration of a waveform resulting from the frequency analysis, and a second area obtained by a second integration of a portion of the waveform over a range greater than or equal to a predetermined frequency range.

13. The vehicle according to claim 12 ,

wherein the frequency-related data is obtained, by subjecting one of the steering wheel torque and the amount of the steering operation of the driver to the frequency analysis, from the change in one of the first rate of change in the steering wheel torque caused by the driver and the second rate of change in the amount of the steering operation by the driver.

14. A method for controlling a vehicle, the method comprising:

adjusting an amount of an assistance in a steering to be provided by a power steering of the vehicle, wherein the amount of the assistance is adjusted in accordance with a change in a state quantity related to an ease of the steering, wherein the state quantity is frequency-related data related to a steering input by a driver of the vehicle;

controlling a control amount of a driving force on a wheel of the vehicle in accordance with the change in the state quantity,

wherein the controlling the control amount includes:

calculating a target yaw rate of the vehicle based on a vehicle model that defines a relationship between the target yaw rate of the vehicle and a vehicle speed and a steering wheel angle with a target stability factor, wherein the target stability factor is a parameter, related to a turning performance of the vehicle, determined from specifications of the vehicle,

wherein the target stability factor comprises a first stability factor, a second stability factor greater than the first stability factor, and a third stability factor calculated with linear interpolation between the first stability factor and the second stability factor;

varying the turning performance of the vehicle by:

when an absolute value of the frequency-related data is smaller than or equal to a first threshold value, setting the first stability factor as the target stability factor,

when the absolute value of the frequency-related data is greater than or equal to a second threshold value, setting the second stability factor as the target stability factor, and

when the absolute value of the frequency-related data is greater than the first threshold value and smaller than the second threshold value, setting the third stability factor as the target stability factor;

comparing the frequency-related data with a threshold value;

determining whether the target stability factor should be corrected or not, based on a result of the comparison of the frequency-related data with the threshold value; and

correcting the target stability factor based on the determination that the target stability factor should be corrected; and

controlling the vehicle based on the corrected target stability factor.

15. A method for controlling a vehicle, the method comprising:

adjusting an amount of an assistance in a steering to be provided by a power steering of the vehicle, wherein the amount of the assistance is adjusted in accordance with a change in a state quantity related to an ease of the steering;

controlling a control amount of a driving force on a wheel of the vehicle in accordance with the change in the state quantity,

wherein the state quantity is frequency-related data related to a steering input by a driver of the vehicle,

wherein, in the adjusting the amount of the assistance, the amount of the assistance is decreased as high-frequency components included in the frequency-related data increase, and

wherein the adjusting the amount of the assistance includes:

calculating a reference value of a front wheel steering angle and a steering wheel torque based on a steering model,

calculating the frequency-related data based on:

a frequency analysis of at least one of the steering wheel torque and an amount of a steering operation by the driver, or

at least one of a change in a first rate of change in the steering wheel torque and a change in a second rate of change in the amount of the steering operation;

calculating a steering correction gain for correcting the reference value of the front wheel steering angle based on the frequency-related data;

multiplying the reference value of the front wheel steering angle by the steering correction gain; and

calculating a requested value of the front wheel steering angle based on the multiplication of the reference value of the front wheel steering angle by the steering correction gain; and

outputting the requested value of the front wheel steering angle to the power steering; and

controlling the power steering of the vehicle based on the requested value of the front wheel steering angle,

wherein the frequency-related data is further calculated based on a ratio between a first area obtained by a first integration of a waveform resulting from the frequency analysis, and a second area obtained by a second integration of a portion of the waveform over a range greater than or equal to a predetermined frequency range.