JP3044136B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forcible steering control of a rear wheel or a front wheel according to a steering state of a vehicle.
The present invention relates to an improvement in a vehicle steering system that enhances drivability and stability of a vehicle.

[0002]

2. Description of the Related Art Conventionally, a steering apparatus for a vehicle of this type determines a steering ratio of a rear wheel according to a vehicle speed with respect to a steering angle of a front wheel corresponding to a steering operation amount. It is known that the steering control of the rear wheels is known, but with this one, it is possible to obtain the steering performance that matches the driver's intention at any vehicle speed, but on the other hand, in the initial stage when the driver operates the steering. In this state, the front wheels and the rear wheels often have the same phase, and there is a regret that the turning performance of the vehicle in the initial state is low.

For this reason, conventionally, for example, Japanese Unexamined Patent Publication No.
In the device disclosed in Japanese Patent Publication No. 268, a control target yaw rate of a vehicle is calculated based on a steering amount of a driver, and a yaw rate of the vehicle is actually measured. The feedback control amount is calculated, and the steering angle of the rear wheel is feedback-controlled with the feedback control amount, thereby quickly generating a yaw rate even in the initial state of the steering operation, thereby improving the turning performance of the vehicle in this initial state. Is increasing.

[0004]

However, in the above-mentioned conventional feedback control, the feedback control amount is calculated only in accordance with the deviation between the actual measured value of the yaw rate and the control target value, and the rear wheels are steered. For this reason, there is also a limit in accurately controlling the actual yaw rate to the control target value.

Therefore, for example, it is conceivable to employ state feedback control instead of the above feedback control. In this state feedback control, in addition to the yaw rate, a plurality of state variables of the vehicle, for example, the sideslip angle of the wheel, the cornering force of the front wheel and the rear wheel, and the like are estimated to grasp the motion state of the vehicle. Since the control target is controlled using the plurality of state variables of the vehicle, if the steering angle of the front wheel or the rear wheel is feedback-controlled so that the yaw rate generated in the vehicle becomes the control target value, the vehicle is always controlled. Therefore, it is possible to control the vehicle optimally for drivability and stability, for example, by generating a target yaw rate and improving the turning performance of the vehicle at the time of steering operation.

In this case, the state feedback control uses a linear equation as a state equation, and a plurality of state quantities of the vehicle are estimated on the basis of the linear equation. When the dynamic characteristics of the vehicle change due to nonlinear motion that deviates from the linear equation,
The estimated plurality of state quantities deviate from the optimal values, and as a result, the control target yaw rate is not generated with high accuracy in the vehicle, and the vehicle becomes unstable.

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and an object of the present invention is to change the dynamic characteristic of a vehicle from a linear region to a non-linear region when the state feedback control is used for the front wheel or rear wheel steering control as described above. Another object of the present invention is to ensure the stability of the vehicle even when the vehicle shifts to the area.

[0008]

In order to achieve the above object, according to the present invention, apart from state feedback control,
Second using a second control law that is inherently stable in the nonlinear region
Is provided, and the second control law is used in a nonlinear region.

That is, a specific solution of the invention according to claim 1 is to provide, as shown in FIG. 1, a steering means 20 for steering a front wheel or a rear wheel separately from the steering, and to reduce the side slip angle of the wheel. Area discriminating means 34 for discriminating whether the cornering force of the wheel is in a linear area or a non-linear area that varies proportionally, and at least a front wheel or a rear wheel based on the actual yaw rate of the vehicle and the estimated side slip angle of the wheel. A state feedback control means for calculating a target control amount for steering and performing state feedback control of an actual yaw rate of the vehicle to a control target yaw rate; and a second state control means for stably controlling the front wheels or the rear wheels in the nonlinear region.
When the cornering force of the wheel is in the linear region, the steering unit 20 is controlled by the state feedback control unit 30 so that the cornering force of the wheel is in the non-linear region. At this time, a control switching means 32 for switching the steering control of the front wheels or the rear wheels so that the steering means 20 is controlled by the second control means 31 is provided.

According to the second aspect of the present invention, the area determining means of the first aspect of the present invention is specified, and the area determining means detects the steering speed of the front wheel. When the steering speed of the front wheels is equal to or higher than the set speed, it is determined that the vehicle is in the linear region when the speed is lower than the set speed, and is in the non-linear region when the steering speed of the front wheel is higher than the set speed.

Further, according to the third aspect of the present invention, the area discriminating means is specified as another one, and the deviation between the actual yaw rate of the vehicle and the control target yaw rate is calculated. It is configured to determine that it is in a non-linear area when the deviation is equal to or greater than a set value.

In addition, according to the present invention, the area determining means calculates the speed of change of the deviation between the actual yaw rate of the vehicle and the control target yaw rate. And when the rate of change of the deviation is equal to or greater than a set value, it is determined to be in a non-linear area.

According to the present invention, the area discriminating means detects the actual yaw rate of the vehicle, and when the actual yaw rate is less than the set value, the area is in a linear area. When it is determined that it is in the non-linear region.

Further, in the invention according to claim 6, the area determining means 34 detects a lateral acceleration acting on the vehicle, and when the lateral acceleration is less than a set value, the area is in a linear area, and the lateral acceleration is not less than the set value. At this time, it is configured to be determined to be in the nonlinear region.

[0015]

According to the above-mentioned structure, according to the first aspect of the present invention,
In the linear region, the state feedback control means 30 is selected by the control switching means 32, and the steering angle of the front wheel or the rear wheel is state feedback controlled by the operation means 20, so that the yaw rate acting on the vehicle is always accurately adjusted to the control target value. Consistently, good vehicle motion characteristics are obtained as intended by the control.

On the other hand, in the non-linear region, the second control means 31 is selected by the control switching means 32 instead of the state feedback control means 30. As a result, the steering angle of the front wheel or the rear wheel is stably controlled based on the second control law of the second control means 31, so that the motion of the vehicle is stabilized.

According to the second aspect of the present invention, when the steering speed of the front wheels is slower than a set value, the driver may request that the vehicle be turned as desired. Since the steering angle of the front wheel or the rear wheel is controlled by the state feedback control means 30, the yaw rate generated in the vehicle is accurately controlled to the control target value, and the vehicle moves as desired by the driver. Meet the requirements of

On the other hand, when the steering speed of the front wheels is higher than the set value, the steering angle of the front wheels or the rear wheels is controlled by the second control means 31, so that the motion of the vehicle is stabilized.
In this case, although the yaw rate generated in the vehicle does not exactly match the target value as compared with the state feedback control, it is considered that the driver is mainly intended to change the direction of the vehicle, so there is no problem.

Further, according to the third and fourth aspects of the present invention, in addition to the quick steering operation by the driver, the deviation between the actual measured value of the yaw rate and the control target value becomes larger than the set value due to disturbance. In this case, although the state feedback control means 30 tends to become unstable due to a sudden change in the yaw rate deviation due to disturbance, the second control means 31 is replaced with the state feedback control means 30. The steering angle of the front or rear wheels is
And the vehicle motion is stabilized.

In addition, according to the fifth and sixth aspects of the present invention, since the linear region and the non-linear region are determined by using the yaw rate and the lateral acceleration of the vehicle, these regions can be accurately determined.

[0021]

As described above, according to the vehicle steering system of the first aspect of the present invention, the state feedback control is selected and used in the linear region, and the second state is controlled in the nonlinear region.
The control means is selected and used, realizing the desired vehicle motion characteristics by state feedback control, and improving the running performance of the vehicle, while the cornering force of the wheel shifts to the nonlinear region. The vehicle can be satisfactorily stabilized, and the stability of the vehicle can be improved.

According to the second aspect of the present invention, the linear region and the non-linear region of the cornering force of the wheel are determined based on the steering speed of the front wheel, so that the driver operates the steering wheel gently. In the area, the desired vehicle motion characteristics can be accurately realized to meet the demands of the driver, and when the driver quickly operates the steering and shifts to the non-linear area, the turning direction of the vehicle is stabilized. It can be carried out.

Further, according to the third and fourth aspects of the present invention, the linear region of the cornering force of the wheel is determined based on the deviation between the actual yaw rate of the vehicle and the control target value, and the rate of change of the deviation. , The non-linear region is discriminated, so that even when shifting to the non-linear region due to disturbance, the second
By using the control law, the motion of the vehicle can be stabilized.

In addition, according to the present invention, the linear region and the nonlinear region of the cornering force of the wheel are determined based on the actual yaw rate of the vehicle and the lateral acceleration acting on the vehicle, respectively. It is possible to accurately determine whether the region is a linear region or a non-linear region.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a schematic plan view of a vehicle steering system according to the present invention, wherein 1 is a steering wheel, 2 is left and right front wheels, 3
Is a left and right rear wheel, 10 is a front wheel steering device that steers the left and right front wheels 2 and 2 by operating the steering 1, and 20 is a left and right rear wheel 3 according to steering of the front wheels 2 and 2 by the front wheel steering device 10. 3 is a rear wheel steering device as steering means for steering the third wheel.

The front wheel steering device 10 has a relay rod 11 arranged in the width direction of the vehicle body, and both ends of the rod 11 are tie rods 12, 12 and a knuckle arm 1, respectively.
It is connected to the left and right front wheels 2, 2 via 3, 13.
The relay rod 11 is provided with a rack and pinion mechanism 14 for moving the relay rod 11 right and left in conjunction with the operation of the steering wheel 1. In this configuration, the front wheels 2, 2 are steered.

On the other hand, the rear wheel steering device 20 has a relay rod 21 arranged in the width direction of the vehicle body in the same manner as described above, and both ends of the rod 21 are respectively connected via tie rods 22, 22 and knuckle arms 23, 23. And are connected to the left and right rear wheels 3,3. The relay rod 21 is provided with a centering spring 22 for urging the rod 21 to a neutral position, and a rack-and-pinion mechanism 23. The mechanism 23 includes a clutch 24, a speed reduction mechanism 25. ,
When the clutch 24 is engaged, the relay rod 21 is moved in the vehicle width direction via the rack-and-pinion mechanism 23 by rotating the motor 26 when the clutch 24 is engaged, so that the rear wheels 3 are moved to the motor 26. The steering is steered by an angle corresponding to the rotation amount.

The motor 26 is connected to the control unit 2
9 is driven and controlled. The control unit 29
As shown in FIG. 3, the steering angle of the rear wheel 3 is internally controlled by the motor 26 based on at least the actual yaw rate at which the state of the vehicle can be estimated and the side slip angle of the wheel (hereinafter referred to as LQG control). LQG control means 30 as state feedback control means, vehicle speed sensitive MAP control means 31 as second control means, and LQG control by LQG control means 30 and MAP control by vehicle speed sensitive MAP control means 31 are selectively performed. Control switching means 32 for switching. The vehicle speed sensitive MAP control means 31
Determines a target steering angle of the rear wheel 3 to be controlled based on a map stored in advance so that the control is stabilized according to the vehicle speed and the front wheel steering angle. The steering angle is controlled by the motor 26. Therefore, as shown in FIG. 5, in the cornering force characteristic with respect to the side slip angle β of the wheel, the control is stable even in a nonlinear region where the change in the cornering force is not proportional to the side slip angle β. It is.

The control unit 29 includes a lateral acceleration sensor 35 for detecting a lateral acceleration acting on the vehicle, a yaw rate sensor 36 for detecting a yaw rate acting on the vehicle, and a sensor for detecting a steering angle of the rear wheel 3. A wheel steering angle sensor 37, a front wheel steering angle sensor 38 for detecting the steering angle of the front wheel 2, and a vehicle speed sensor 39 for detecting the vehicle speed are input.

Next, the drive control of the motor 26 by the control unit 29 will be described with reference to the control flow of FIG. In FIG. 5, when the control timing for each set cycle is reached in step S1, the above-mentioned sensors 3 are set in step S2.
Vehicle speed Vs, front wheel steering angle Fs based on detection signals of 6 to 39
tg, the rear wheel steering angle Rstg, the yaw rate dψ / dt occurring in the vehicle, and the vehicle motion state quantity of the lateral acceleration Yg acting on the vehicle are measured.

In step S3, the control target yaw rate yrt of the vehicle is calculated based on the following equation.

[0033] Here, A is the stability factor, and L is the wheelbase of the vehicle. Thereafter, the front wheel steering speed df is calculated from the following equation based on the previous value and the current value of the front wheel steering angle Fstg detected by the front wheel steering angle sensor 38 in step S4.

Df = {Fstg (n) −Fstg (n−1)} * k (k is a proportionality constant) Then, in step S 5, the actually measured yaw rate dψ / dt detected by the yaw rate sensor 36 and the above calculated control A deviation en from the target yaw rate yrt is calculated, and a current value en (n) and a previous value en (n) of the deviation en are calculated.
-1), that is, the rate of change Δen of the yaw rate deviation
(= En (n) -en (n-1)) is calculated.

Then, in steps S6 to S10, it is selected whether the steering angle of the rear wheel 3 is controlled by LQG or the vehicle speed sensitive MAP control. That is, in step S6, the magnitude of the absolute value | Δen | of the change speed of the calculated yaw rate deviation is determined, and the change speed | Δen | of the yaw rate deviation is set to the set value Δ.
Enlarged more than eno (| Δen | ≧ Δeno)
In the case of YES, as shown in FIG. 5, it is determined that the linear region in which the cornering force of the wheel with respect to the side slip angle β of the wheel is in a substantially proportional relationship has shifted to the nonlinear region in which the proportional relationship is broken, and step S15 is performed. The program proceeds to S16, in which the vehicle speed sensitive MAP control is selected. In step S7, the magnitude of the absolute value | en | of the yaw rate deviation is determined, and if the yaw rate deviation | en | expands beyond the set value en1 (| en | ≧ en1), the linear region of FIG. , The vehicle speed sensitive MAP control is selected, and in step S8, the absolute value of the front wheel steering speed |
The magnitude of df | is determined, and when the front wheel steering speed | df | is faster than the set value dfo (df ≧ dfo), it is determined that a transition has been made from the linear region to the nonlinear region, and the vehicle speed sensitive MAP is determined.
Select control. In addition, in step S9, the magnitude of the measured yaw rate dψ / dt is determined, and the measured yaw rate dψ / dt is determined.
When ψ / dt is greater than or equal to a set value α (dψ / dt ≧ α), it is determined that the operation has shifted from the linear region to the non-linear region, and the vehicle speed response MA
Select P control. In step S10, the magnitude of the lateral acceleration Yg of the vehicle is determined, and when the lateral acceleration Yg is a sharp turn at or above the set value Ygo (Yg ≧ Ygo), the vehicle speed sensitive MAP control is selected. On the other hand, the above steps S6 to S
If all of the determinations at 10 are NO, it is determined that the cornering force of the wheel is in the linear region of FIG. 5, and the process proceeds to steps S11 to S14 to select the LQG control.

When LQG control is selected as a result of the above determination, first, in step S11, a plurality of state quantities of the vehicle are calculated and estimated by an observer (state observer).
Here, four types of vehicle state quantities are estimated: the sideslip angle β of the wheels, the changing speed dRstg / dt of the steering angle of the rear wheels, the cornering force Cff of the front wheels, and the cornering force Cfr of the rear wheels. This estimation is performed by calculation based on the following state equation, with the estimated state quantity of the vehicle being xob.

Dxob / dt = Aob * xob + Bob
* Y + Job * RFB (n-1) Here, Aob, Bob, and Job are observer gains, RFB is an LQG control amount, and y is a measured yaw rate d / dt and an LQG control amount RFB value.

Subsequently, the estimated observation amount yob of the vehicle as an output is calculated based on the following output equation. Here, as the estimated observation amount, the output of the above-mentioned four types of estimated state quantities include the steering angle Rstg of the rear wheel, and the yaw rate dψ acting on the vehicle.
Compute 6 types by adding / dt. However, the steering angle Rs of the rear wheel
For tg and yaw rate dψ / dt, actual measured values are used.

Yob = Cob * xob + Dob * y Here, Cob and Dob are observer gains.

Thereafter, in step S12, the LQG control amount RFB is calculated. In this calculation, first, the measured yaw rate d
偏差 / dt and the control target yaw rate yrt (dψ / dt)
dt−yrt) is calculated by the equation Sig (n) = Sig (n−1) + (dψ / dt−yr)
After the calculation based on t), the LQG control amount RFB is calculated by the following equation using the integral value Sig and the estimated observation amount yob as follows: RFB = −F * yob−F1 * Sig. Here, F and F1 are control gains.

When the LQG control amount RFB is obtained as described above, the control amount R for the motor 26 is set to the LQG control amount RFB in step S13 (R = RFB), and in step S14, this control amount R Thus, the drive of the motor 26 is controlled and the left and right rear wheels 3 and 3 are steered.

On the other hand, if the vehicle speed sensitive MAP control is selected, a proportional constant r on a map corresponding to the vehicle speed Vs shown in the step is calculated in step S15, and the calculated proportional constant r is added to the front wheel steering angle. Fstg is multiplied to obtain a MAP control amount RMAP. Then, in step S16, the control amount R to the motor 26 is set to the MAP control amount RMAP (R = RMAP), and in step S14, the control amount R
The drive control of the motor 26 is then performed to steer the left and right rear wheels 3 and 3.

Therefore, in the control flow of FIG.
Steps S4 to S10 constitute a region discriminating means 34 for discriminating whether the cornering force of the wheel is in a linear region or a nonlinear region in which the cornering force of the wheel changes proportionally with respect to the side slip angle β of the wheel.

Therefore, in the above embodiment, the steering speed | df | of the front wheel is slower than the set value dfo (| df).
When | <dfo), the cornering force of the wheel is in the linear region, and the steering angle of the rear wheels 3, 3 is LQG controlled by the LQG control means 30. In this case, since the dynamic characteristic of the vehicle satisfies the above-mentioned state equation, the state quantity xob of the vehicle and the observation amount yob of the vehicle by the observer are accurately estimated, and therefore, the yaw rate of the vehicle is accurately controlled to the control target value yrt. As a result, the intended vehicle motion characteristics are obtained, and the driving performance of the vehicle is improved.

On the other hand, when the steering speed | df | of the front wheels is higher than the set value dfo and is faster (| df | ≧ dfo),
The sideslip angle of the wheel is in the non-linear region of FIG. in this case,
In the LQG control, the dynamic characteristics of the vehicle do not satisfy the above state equation, and an error easily occurs in the vehicle state quantity xob or the like by the observer. Therefore, the control becomes unstable, and the vehicle motion becomes unstable. is there. However, in this non-linear region, the control switching means 32 selects the vehicle speed sensitive MAP control by the second control means 31 which is inherently stable in this non-linear region, and the steering angles of the rear wheels 3, 3 are changed to the vehicle speed Vs and the vehicle speed Vs. Since the vehicle is controlled by the control amount RMAP corresponding to the front wheel steering angle Fstg, the running stability of the vehicle is sufficiently secured. Moreover,
When the steering speed df of the front wheels is lower than the set value dfo and is slow, it is a case where the driver requests to accurately guide the vehicle in a desired direction. In this case, the L of the rear wheels 3 is set as described above.
Since the yaw rate generated in the vehicle by the QG control accurately matches the control target value yrt, the vehicle changes direction as requested by the driver, and the driving performance of the vehicle can be further improved.

On the other hand, the steering speed df of the front wheels is set to the set value dfo.
If the speed is faster than the above, the speed-sensitive MA
Since the yaw rate of the vehicle is generated stably by the P control, the stability of the vehicle is improved. In this case, the generated yaw rate does not match the control target value yrt more accurately than in the case of the LQG control, but there is no problem because the driver does not require much accuracy of the turning angle of the vehicle. .

Further, the selection switching between the LQG control and the vehicle speed sensitive MAP control is performed by changing the yaw rate deviation changing speed | Δen |
When the deviation en between the actually measured yaw rate and the control target value suddenly increases due to disturbance, L
In the QG control, the control amount RFB greatly changes and the steering angle of the rear wheel 3 also greatly changes. However, since the steering angle of the rear wheel 3 is controlled independently of the disturbance by selecting the vehicle speed sensitive MAP control, the stability of the vehicle is improved. Good performance is ensured.

In addition, the above LQG control and vehicle speed sensitive MAP
The selection switching between the control and the control, that is, the discrimination between the linear region and the non-linear region in FIG.
Since the determination is performed based on n, the measured yaw rate d 横 / dt, and the lateral acceleration Yg acting on the vehicle, the area can be determined accurately and quickly.

FIG. 6 shows another embodiment. In the above-mentioned embodiment, the rear wheels 3, 3 are controlled by the rear wheel steering device 20 instead of the front wheels 2, 2, and the front wheels 2, 2 are electrically controlled separately from the steering. This is applied to a steering control.

That is, in the steering system shown in FIG.
The rear wheel steering device 20 shown in FIG. 1 is not provided, and the rack and
A pinion mechanism 40 and a motor 41 for driving the mechanism 40
And the drive of the motor 41 is controlled by the control unit 29. Other configurations are the same as those of the above-described embodiment. However, in the present embodiment, when the rear wheels are steered and the rear wheels are steered in the opposite phase to the front wheels, the front wheels are steered. Steering control to increase the angle,
In the above embodiment, when the steering control of the rear wheels is performed in the same phase, in the present embodiment, the steering control may be performed to reduce the steering angle of the front wheels.

In the above description, in the LQG control, there are six types of estimated observable amounts of the vehicle, namely, the sideslip angle β of the wheel, the changing speed dRstg / dt of the steering angle of the rear wheel, and the cornering force of the front wheel and the rear wheel. Cff, Cfr, the steering angle Rstg of the rear wheels, and the yaw rate dψ /
Although the state of the vehicle was accurately observed using dt, it is sufficient to observe the state of the vehicle at least by observing the actual yaw rate of the vehicle and the estimated sideslip angle of the wheel.

In the above description, the second control means 3
Although the vehicle speed sensitive MAP control was used as the control law in 1,
The second control law is only required to be able to stably control the rear wheels 3 and 3 in a nonlinear region where the cornering force does not change proportionally. For example, feed forward control other than MAP control, fuzzy control , Feedback control or the like may be used.

[Brief description of the drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention.

FIG. 2 is a diagram illustrating an overall configuration of a steering device that also steers a rear wheel of a vehicle.

FIG. 3 is a diagram showing a block configuration of steering control of a rear wheel.

FIG. 4 is a diagram showing a control flow of rear wheel steering control.

FIG. 5 is a diagram showing a cornering force characteristic with respect to a side slip angle of a wheel.

FIG. 6 is a diagram showing an overall configuration of a steering device for steering a front wheel as another embodiment.

[Explanation of symbols]

Reference Signs List 1 steering 3 rear wheel (wheel) 20 rear wheel steering device 26 motor 29 control unit 30 LQG control means (state feedback control means) 31 vehicle speed sensitive MAP control means (second control means) 32 control switching means 34 area discriminating means 35 Lateral acceleration sensor 36 Yaw rate sensor 37 Rear wheel steering angle sensor 38 Front wheel steering angle sensor 39 Vehicle speed sensor

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 117: 00 137: 00 (56) References JP-A-3-239673 (JP, A) JP-A-3-193558 (JP, A) JP-A-6-24251 (JP, A) JP-A-2-77360 (JP, A) JP-A-1-262268 (JP, A) JP-A-2-85073 (JP, A) JP-A-4 −293671 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 7/14

Claims (6)

(57) [Claims] A steering device for steering a front wheel or a rear wheel separately from a steering wheel, and whether the cornering force of the wheel is in a linear region or a nonlinear region in which a cornering force of the wheel changes proportionally to a side slip angle of the wheel. Calculating a target control amount for front-wheel or rear-wheel steering based on at least the actual yaw rate of the vehicle and the estimated sideslip angle of the wheels, and performing state feedback control of the actual yaw rate of the vehicle to the control target yaw rate. Feedback control means, second control means capable of stably controlling the front wheel or the rear wheel in the non-linear region, and the state feedback control when the cornering force of the wheel is in the linear region, receiving the output of the region discriminating means. Means for controlling the steering means so that the cornering force of the wheels is in a non-linear region. And a control switching means for switching the steering control of the front wheels or the rear wheels so that the steering means is controlled by the second control means. 2. The region determining means detects a steering speed of a front wheel, and determines that the steering wheel is in a linear region when the steering speed of the front wheel is lower than a set speed and is in a non-linear region when the steering speed of the front wheel is higher than the set speed. 2. The method according to claim 1, wherein
A steering device for a vehicle according to the above. 3. The area determining means calculates a deviation between the actual yaw rate of the vehicle and the control target yaw rate, and is in a linear area when the deviation is less than a set value, and is in a non-linear area when the deviation is not less than the set value. 2. The vehicle steering system according to claim 1, wherein the vehicle steering device is configured to determine: 4. An area determining means calculates a speed of change of a deviation between an actual yaw rate of the vehicle and a control target yaw rate, and when the speed of change of the deviation is less than a set value, the area is in a linear area. 2. The vehicle steering apparatus according to claim 1, wherein when the value is equal to or more than a set value, the vehicle is determined to be in a non-linear region. 5. The area determining means detects an actual yaw rate of the vehicle, and determines that the vehicle is in a linear area when the actual yaw rate is less than a set value, and is in a non-linear area when the actual yaw rate is equal to or more than the set value. The vehicle steering system according to claim 1, wherein: 6. The area determining means detects a lateral acceleration acting on the vehicle, and determines that the vehicle is in a linear area when the lateral acceleration is less than a set value and is in a non-linear area when the lateral acceleration is equal to or more than the set value. The vehicle steering apparatus according to claim 1, wherein