JPH04293671A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To provide the rear wheel steering device of a vehicle capable of improving the traveling stability by providing a control switching means stopping the feedback control of the steering angle of rear wheels by a yaw rate feedback control means when the turning state detected by a turning state detecting means is sharper than the preset turning state. CONSTITUTION:In the sharp turning state with large lateral acceleration, the control of the steering angle of rear wheels 3 is switched by a control switching means 33 from the control by a yaw rate feedback control means 30 to the control by a sideslip angle control means 31 controlling the steering angle of the rear wheels 3 in the in-phase direction as the estimated sideslip angle is increased. In the sharp turning state with high lateral acceleration, the rear wheels 3 are surely prevented from being steered in the reverse-phase direction to front wheels to decrease the in-phase quantity. The traveling stability can be improved in the sharp turning state with high lateral acceleration.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a vehicle, and more particularly to a rear wheel steering system for a vehicle.

0002

BACKGROUND OF THE INVENTION A rear wheel steering device for a vehicle is known that steers the rear wheels at a predetermined steering ratio with respect to the steering angle of the front wheels corresponding to the steering angle of the steering wheel, depending on the vehicle speed. In such a vehicle's rear wheel steering system, it is possible to obtain steering performance that matches the driver's intention regardless of the vehicle speed, but in a transient state immediately after the driver operates the steering wheel, the front and rear wheels are often in phase, and therefore there is a problem in that the initial turning performance in a transient state is not good.

[0003] In order to solve this problem, Japanese Unexamined Patent Publication No. 1-2
Publication No. 62268 proposes a rear wheel steering device for a vehicle that calculates a target yaw rate based on a steering wheel steering angle and performs feedback control of the steering angle of the rear wheels so that the measured yaw rate becomes equal to the target yaw rate.

0004

[Problems to be Solved by the Invention] However, vehicles are generally designed to understeer in driving conditions with high lateral acceleration in order to improve running stability. In the device, when the vehicle enters a sharp turn with high lateral acceleration, the turning radius increases and the yaw rate decreases.
When the steering angle of the rear wheels is feedback-controlled so that the measured yaw rate becomes the target yaw rate, the rear wheels are steered in the opposite phase direction to the front wheels to compensate for the decrease in yaw rate, and the in-phase amount increases. There was a problem in that the running stability was easily reduced, and when some kind of disturbance was applied to the vehicle, the running stability was significantly reduced.

[0005]

OBJECTS OF THE INVENTION The present invention includes a turning state detecting means for physically detecting the turning state of a vehicle, and a rear wheel control system that detects the turning state of a vehicle so that an actual yaw rate based on a detection value detected by the turning state detecting means becomes a target yaw rate. Provided is a rear wheel steering device for a vehicle, which is equipped with a yaw rate feedback control means for feedback controlling the steering angle of the vehicle, and is capable of improving driving stability even in a sharp turning state with high lateral acceleration. The purpose is to

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to perform feedback control on the steering angle of the rear wheels by the yaw rate feedback control means when the turning state detected by the turning state detection means is steeper than a predetermined turning state. This is achieved by providing a control switching means for stopping the operation.

In a preferred embodiment of the present invention, the invention further includes sideslip angle estimating means for estimating a sideslip angle of the vehicle, and a steering angle of the rear wheels is adjusted as the sideslip angle estimated by the sideslip angle estimation means increases. The steering angle of the rear wheels is controlled by the yaw rate feedback control means when the turning state detected by the turning state detection means is less steep than a predetermined turning state. , when the turning state detected by the turning state detection means is a steeper turning state than a predetermined turning state, the steering angle of the rear wheels is adjusted so that the steering angle of the rear wheels is controlled by the sideslip angle control means. A control switching means is provided for switching the control means to be controlled.

[0008]

According to the present invention, when the turning radius becomes large in a sharp turning state with large lateral acceleration, feedback control of the rear wheel steering angle is stopped so that the measured yaw rate becomes the target yaw rate. Therefore, to compensate for the decrease in yaw rate, the rear wheels are steered in the opposite phase direction relative to the front wheels, and the in-phase amount does not decrease. Therefore, even in sharp turns with high lateral acceleration, It becomes possible to perform stable driving.

According to a preferred embodiment of the present invention, in a sharp turning state with large lateral acceleration, the control switching means changes the control of the steering angle of the rear wheels to the estimated sideslip from the control by the yaw rate feedback control means. As the steering angle increases, control is switched to the side slip angle control means that controls the steering angle of the rear wheels in the same phase direction. Therefore, in a sharp turn with high lateral acceleration, the rear wheels are steered in the opposite phase direction from the front wheels. Therefore, a decrease in the in-phase amount is reliably prevented, and therefore, driving stability can be improved even in a sharp turning state with high lateral acceleration.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic plan view of a vehicle wheel steering device including a vehicle rear wheel steering device according to an embodiment of the present invention.

In FIG. 1, a wheel steering system for a vehicle including a rear wheel steering system for a vehicle according to an embodiment of the present invention includes a steering wheel 1 and a front wheel steering system that steers left and right front wheels 2 by operating the steering wheel 1. It has a steering device 10 and a rear wheel steering device 20 that steers left and right rear wheels 3, 3 in accordance with the steering of the front wheels 2, 2 by the front wheel steering device 10. Front wheel steering device 10
is arranged in the width direction of the vehicle body, and its both ends are connected to the left and right front wheels 2, 2 via tie rods 11, 11 and knuckle arms 12, 12.
and a rack-and-pinion type steering gear mechanism 14 that moves the relay rod 13 left and right in conjunction with the operation of the handle 1. , the left and right front wheels 2, 2 are steered.

On the other hand, the rear wheel steering device 20 is arranged in the width direction of the vehicle body, and both ends thereof are connected to tie rods 21, 21.
and a relay rod 23 connected to the left and right rear wheels 3, 3 via knuckle arms 22, 22, a motor 24, and a deceleration mechanism 25 and a clutch 26.
A rack-and-pinion type steering gear mechanism 27 that is driven to move the relay rod 23 left and right, a centering spring 28 that biases the relay rod 23 to be held in the neutral position, and a centering spring 28 that is driven to move the relay rod 23 left and right, and It is equipped with a control unit 29 that controls the operation of the motor 24 according to the state, and controls the left and right rear wheels 3, 3 in a direction corresponding to the rotation direction of the motor 24 by an angle corresponding to the amount of rotation of the motor 24. It is designed to be steered.

FIG. 2 is a block diagram of a control unit 29 that controls the operation of the motor 24 and a running state detection system provided in the vehicle. In Figure 2,
The control unit 29 includes a yaw rate feedback control means 30, a sideslip angle control means 31, a fuzzy control means 32, a control switching means 33, and a sideslip angle calculation means 34 for calculating an estimated value β of the sideslip angle, A vehicle speed sensor 40 that detects the vehicle speed V, a steering angle sensor 41 that detects the steering angle of the steering wheel 1, that is, the steering angle θf of the front wheels 2, 2, a yaw rate sensor 42 that is a turning state detection means that detects the yaw rate Y of the vehicle, and A detection signal from a lateral acceleration sensor 43 that detects lateral acceleration GL applied to the vehicle is input.

The yaw rate feedback control means 30 determines a target yaw rate based on the detection signal of the vehicle speed V(n) inputted from the vehicle speed sensor 40 and the steering angle θf(n) of the front wheels 2, 2 inputted from the steering angle sensor 41. In addition to calculating Y0(n), the target yaw rate Y0(n) and the measured yaw rate Y(n) input from the yaw rate sensor 42 are calculated.
Calculate the deviation E from the I-P stored in advance.
The feedback control amount Rb(n) of the yaw rate Y is calculated based on the calculation formula of the D control, and is output to the control switching means 33. When the control execution signal is input from the control switching means 33, the feedback control amount Rb(n) of the yaw rate Y is , outputs a feedback control signal.

The control switching means 33 also detects the deviation E(
n), calculate the rate of change ΔE(n) of the deviation E(n), and calculate the rate of change ΔE(n) of the deviation E(n) and the deviation E(n).
) exceeds a predetermined deviation E0 and a predetermined deviation change rate ΔE0, that is, in an extremely steep turning state, a control execution signal is output to the fuzzy control means 32, and the deviation E( n) and the rate of change ΔE(n) of the deviation E(n) are respectively less than or equal to the predetermined deviation E0 and the rate of change of the predetermined deviation ΔE0, and the sideslip angle is estimated by the sideslip angle calculating means 34. The value β (
In a turning state in which the absolute value of n) exceeds a predetermined value β0, that is, in a sharp turning state, the sideslip angle control means 3
1, and in other cases, that is,
The vehicle is configured to output a control execution signal to the yaw rate feedback control means 30 during a normal turning state.

When the control execution signal is input from the control switching means 33, the sideslip angle control means 31 calculates the sideslip angle control amount Rβ(n) based on a calculation formula stored in advance. , outputs a sideslip angle control signal to the motor 24. Further, the fuzzy control means 32
The yaw rate Y detected by the yaw rate sensor 42 (
control switching means 33
, when the control execution signal is input, the measured yaw rate Y(n) is calculated based on the calculation formula stored in advance.
The fuzzy control amount Rf(n) is calculated so that the rate of change ΔY(n) of
Output to 4.

The sideslip angle calculating means 34 includes the vehicle speed sensor 4
0 detected vehicle speed V(n), measured yaw rate Y(n) detected by yaw rate sensor 42, and lateral acceleration sensor 4
Based on the detected lateral acceleration GL(n) of step 3, an estimated value β(n) of the sideslip angle is calculated according to the following equation (2) and outputted to the control switching means 33. β(n)=9.8×{GL(n)/V(n)}×{
Y(n)/57}
+β(n-1)・・・・・・
...■ Here, (n) indicates the value at the current control timing, and (n-1) indicates the value at the previous control timing.

FIG. 3 is a flow chart of the steering angle control of the rear wheels 3, 3 executed by the control unit 29 configured as described above, and FIG. F. It is a graph showing the relationship between the side slip angle and the sideslip angle. In FIG. 3, first, the vehicle speed V(n) detected by the vehicle speed sensor 40, the steering angle θf(n) of the front wheels 2, 2 detected by the steering angle sensor 41, and the vehicle yaw rate Y(n) detected by the yaw rate sensor 42. and lateral acceleration sensor 4
The detected lateral acceleration GL(n) applied to the vehicle in step 3 is input to the control unit 29.

The yaw rate feedback control means 30 uses the vehicle speed V(n) inputted from the vehicle speed sensor 40 and the steering angle θf(n) of the front wheels 2, 2 inputted from the steering angle sensor 41.
), the target yaw rate Y0(n) at that control timing is calculated according to the following equation (2). Y0(n)=V(n)/{1+A・V(n)2
}×θf(n)/L

.....■Here, A is the stability factor and L is the length of the wheel base.

Next, the yaw rate feedback control means 30 calculates the target yaw rate Y0(n
) and the measured yaw rate Y(n) input from the yaw rate sensor 42, the deviation E(n) is calculated according to the following formula (■): E(n) = Y0(n) - Y(n)
・・・・・・・・・・・・・・・■Furthermore, according to the following I-PD control calculation formula■, calculate the feedback control amount Rb(n) of the yaw rate Y(n) at that control timing. .

Rb(n)=Rb(n-1) −[KI×E(n)−F
P×{Y(n)-Y(n-1)}
−FD×{Y(n)−2×Y(n−1
)+Y(n-2)]

・・・・・・・・・・・・■Here, KI is an integral constant, FP is a proportional constant, FD is a differential constant, and Rb(n-1)
represents the feedback control amount at the previous control timing, Y(n-1) represents the measured yaw rate at the previous control timing, and Y(n-2) represents the measured yaw rate at the control timing before the previous one.

The feedback control amount Rb(n) and deviation E(n) of the yaw rate Y(n) thus calculated are output to the control switching means 33.
calculates the rate of change ΔE(n) of the deviation E(n), and calculates the change rate ΔE(n) of the deviation E(n).
(n) is larger than the predetermined deviation E0, and the rate of change Δ
It is determined whether E(n) is larger than a predetermined rate of change ΔE0.

As a result, when YES, that is, when the deviation E(n) is larger than the predetermined deviation E0, and when the rate of change ΔE(n) is larger than the predetermined rate of change ΔE0,
The vehicle is in a state corresponding to region S3 in FIG.
The vehicle is making a very sharp turn, causing a spin.
Since it is recognized that the vehicle is changing its direction suddenly and is in an extremely unstable running state, yaw rate feedback control allows the vehicle to run stably with the steering angle θr(n) of the rear wheels 3 and 3. It is extremely difficult to control the yaw rate of the vehicle unless you use a large computer with extremely fast calculation speed. Since it is uneconomical and extremely difficult to install the vehicle in terms of space, in this embodiment, in such a turning state, based on fuzzy theory,
In order to control the steering angle θr(n) of the rear wheels 3, 3, the control switching means 33 transfers the control execution signal to the fuzzy control means 3.
Output to 2.

When the fuzzy control means 32 receives the control execution signal from the control switching means 33, the change rate ΔY(n) of the yaw rate Y(n) is determined based on the detection signal of the yaw rate Y inputted from the yaw rate sensor 42. ), and based on the membership function that is a function of deviation E(n) and rate of change ΔE(n), the rate of change ΔY(n) of yaw rate Y(n) decreases according to the following formula ■ The fuzzy control amount Rf(n) is calculated as follows, and a fuzzy control signal is output to the motor 24.

Rf(n)=f(E(n), ΔE
(n))・・・・・・・・・■On the other hand, the deviation E(
n) is not larger than the predetermined deviation E0, or when the rate of change ΔE(n) is not larger than the predetermined rate of change ΔE0, the control switching means 33 switches the sideslip angle calculation means 3
It is determined whether the absolute value of the estimated value β(n) of the sideslip angle inputted from step 4 is larger than a predetermined value β0.

[0026] When the determination result is YES, that is,
When the absolute value of the estimated side slip angle β(n) is larger than the predetermined value β0, it is recognized that the driving state corresponds to region S2 in FIG. 4, and a sharp turning state with a large lateral acceleration GL(n) Therefore, a large tire skid occurs, and the turning radius of the vehicle increases, causing the yaw rate Y to increase.
(n) is decreasing, the steering angle θr(n
) by yaw rate feedback control, in order to compensate for the decrease in yaw rate Y(n),
The rear wheels 3, 3 have a steering angle θf(n) of the front wheels 2, 2,
Unstable driving conditions where the vehicle is being steered in the opposite direction and driving stability may be significantly reduced, and the direction of the vehicle is changing rapidly enough to require fuzzy control. Therefore, the control switching means 33
Outputting a control execution signal to the sideslip angle control means 31,
The sideslip angle control means 31 is caused to execute sideslip angle control.

When the sideslip angle control means 31 receives the control execution signal from the control switching means 33, it calculates the sideslip angle control amount Rβ(n) according to the following equation (2).
Output to the motor 24. Rβ(n)=k×β(n)...
・・・・・・・・・・・・・・・■Here, k is a control constant and has a positive value. Therefore, the sideslip angle control amount Rβ(n) is equal to the sideslip angle β(n ) is larger,
The larger the side slip angle β(n) is, the more the rear wheels 3, 3 will be steered in the same phase direction as the front wheels 2, 2, and the amount of same phase will increase, so the turning radius of the vehicle will increase. is large and the yaw rate Y(n) is low, the rear wheels 3, 3 are steered in a direction opposite to the steering angle θf(n) of the front wheels 2, 2, which improves the running stability. This ensures that a significant decrease in

On the other hand, the estimated side slip angle β(n
) is less than the predetermined value β0, the cornering force C. in FIG. F. It is recognized that the vehicle is in a running state corresponding to the region S1 where the side slip angle and the side slip angle are in an almost proportional relationship, and it can be determined that the vehicle is in a stable running state.
The control switching means 33 outputs a control execution signal to the yaw rate feedback control means 30.

When the yaw rate feedback control means 30 receives the control execution signal from the control switching means 33, the yaw rate feedback control means 30 transfers the yaw rate feedback control signal to the motor 24.
The motor 24 is outputted to rotate the motor 24 and the rear wheels 3 are steered according to the yaw rate feedback control amount Rb(n) calculated by the equation (2). The above control is executed at predetermined time intervals, and the rear wheels 3, 3 are steered.

According to this embodiment, in the region S1 where the running condition of the vehicle is stable, the actual yaw rate Y(n) is changed to the target yaw rate Y0 determined based on the steering angle of the steering wheel 1 by the yaw rate feedback control. Since the rear wheels 3, 3 are steered so that (n), it becomes possible to steer the rear wheels 3, 3 as desired. In the driving state region S2, where the absolute value of is larger than the predetermined value β0, the lateral acceleration GL is large, the turning radius of the vehicle is large, and the yaw rate Y(n) is decreasing, the estimated value of the sideslip angle is The larger β(n) is, the more the rear wheels 3, 3 move in the same phase direction as the front wheels 2, 2.
Since sideslip angle control is performed so that the in-phase amount increases, rear wheel 3
, 3, the steering angle θr of the rear wheels 3, 3 is
(n) is in the opposite phase direction with respect to the steering angle θf(n) of the front wheels 2, 2, which prevents the running stability from decreasing and improves the running stability. The vehicle is
Deviation E(n) between target yaw rate Y0(n) and measured yaw rate Y(n) and rate of change ΔE(n) of deviation E(n)
is larger than the predetermined values E0 and ΔE0, and in an extremely sharp turning state in which the vehicle is recognized to be rapidly changing direction, and in an extremely unstable driving state region S3 where there is a high possibility that spin has occurred, the yaw rate Y Rate of change Δ of (n)
Since the steering angle θr of the rear wheels 3, 3 is fuzzy controlled so that Y(n) decreases, the steering angle θr of the rear wheels 3, 3 is controlled in a fuzzy manner, so that it is possible to avoid such extremely sharp turning conditions and extremely unstable conditions without using an extremely large computer. Even in running conditions, it is possible to improve running stability.

[0031] The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included within the scope of the present invention. Needless to say, this is something that will be done. for example,
In the embodiment described above, when the absolute value of the estimated value β of the sideslip angle becomes larger than the predetermined value β0, the yaw rate feedback control is shifted to the sideslip angle control, but the absolute value of the estimated value β of the sideslip angle is In a driving state that is larger than the predetermined value β0, the ratio of the steering angle θr of the rear wheels 3, 3 to the steering angle θf of the front wheels 2, 2 may be fixed, or,
Instead of the previous yaw rate feedback control, a new yaw rate feedback control may be performed by reducing the control gain.

Further, in the embodiment described above, β0 is a constant value, but β0 may be changed depending on the vehicle speed V, lateral acceleration GL, etc. FIG. 5 shows a flowchart for setting β0 based on vehicle speed V and lateral acceleration GL. In FIG. 5, β0 is determined by the sideslip angle calculating means 34 based on the threshold value βt, a coefficient jv that is a function of the vehicle speed V, and a coefficient jg that is a function of the lateral acceleration GL, according to the following formula (2). It looks like this.

β0=jv×jg×βt...
. . . ■ That is, first, the coefficient jv is determined based on the value of the vehicle speed V. Here, the coefficient jv
is set to converge to 1.0 as the vehicle speed V increases. This is to allow the driver to shift to sideslip angle control even if the estimated value β of the sideslip angle is a small value, since the driver tends to feel uneasy as the speed increases. The coefficient jg is then determined by the value of the lateral acceleration GL. In FIG. 5, the coefficient jg is set to converge to 1.0 as the lateral acceleration GL increases. This is to enable the vehicle to shift to sideslip angle control with a small lateral acceleration GL while driving on a road with a small road surface friction coefficient μ. Here, in FIG. 5, β0 is set by vehicle speed V and lateral acceleration GL, but even if β0 is set by adding other driving parameters, or by other driving parameters, β0 can be set by vehicle speed V and lateral acceleration GL. You may also set it.

Furthermore, in the embodiment described above, the yaw rate Y is detected using the yaw rate sensor 42 as a turning state detection means. The detected vehicle speed V and the front wheels 2, 2 detected by the steering angle sensor 41
The yaw rate Y may be calculated based on the steering angle θf of the lateral acceleration sensor 4, and the lateral acceleration GL may also be calculated based on the lateral acceleration sensor 4.
3, the vehicle speed V detected by the vehicle speed sensor 40
and the steering angle θf of the front wheels 2, 2 detected by the steering angle sensor 41
It may be calculated based on.

[0035] Furthermore, the calculation formula for the estimated side slip angle β is
The calculation formula (■) for the target yaw rate Y0 is only an example; the estimated side slip angle β can also be calculated by the Kalman filter method, the observer method, etc., and the target yaw rate Y0 can also be calculated by other methods. It may be calculated using the following arithmetic expression. Further, the sensor for detecting the running state of the vehicle may be selected depending on the necessity of the case, and the vehicle speed sensor 4 used in the embodiment described above may be selected.
, the steering angle sensor 41, the yaw rate sensor 42, and the lateral acceleration sensor 43 may be omitted, and other sensors may be used.

Further, in the above embodiment, when the deviation E between the target yaw rate Y0 and the measured yaw rate Y and the rate of change ΔE of the deviation E are both larger than the predetermined values E0 and ΔE0, the rear wheels 3, However, when either one is greater than a predetermined value, the steering control of the rear wheels 3, 3 may be executed using fuzzy control. , the membership function of the fuzzy control is a function of the deviation E between the target yaw rate Y0 and the measured yaw rate Y and the rate of change ΔE of the deviation E.
The membership function of the fuzzy control may be determined based on the measured yaw rate Y, and may be a function of either the deviation E or the rate of change ΔE of the deviation E. Also, instead of the deviation E or the rate of change ΔE of the deviation E, the lateral acceleration GL
exceeds a predetermined value, rear wheel 3 is controlled by fuzzy control.
The steering control of 3 may be executed, and further,
The membership function of fuzzy control is lateral acceleration GL and/or its rate of change, steering angle θf, steering angle θ
Based on the rate of change of f and the rate of change of steering angle θf,
It may be decided.

Furthermore, in the above embodiment, in the region S3 of FIG. 4, the rear wheels 3, 3 are
The steering angle of the tires is controlled, but the cornering force of the tires C. F. As shown in Fig. 4, the relationship between the side slip angle and the sideslip angle changes depending on the road friction coefficient μ, so when driving on a road other than a road with a small road friction coefficient μ, only regions S1 and S2 exist. , region S3 does not exist, so it is not necessarily necessary to perform fuzzy control.

[0038]

According to the present invention, the turning state detecting means physically detects the turning state of the vehicle, and the actually measured yaw rate based on the detection value detected by the turning state detecting means is set to the target yaw rate. A rear wheel steering system for a vehicle equipped with a yaw rate feedback control means for feedback controlling the steering angle of the rear wheels, which can improve running stability even in a sharp turning state with high lateral acceleration. It becomes possible to provide the device.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of a vehicle including a vehicle suspension system according to a preferred embodiment of the present invention.

FIG. 2 is a block diagram of a control unit and a driving state detection system provided in the vehicle.

FIG. 3 is a flowchart of rear wheel steering control executed by a control unit.

FIG. 4 shows tire cornering force C.
F. It is a graph showing the relationship between the side slip angle and the sideslip angle.

FIG. 5 is a flowchart illustrating an example of a method for setting β0.

[Explanation of symbols]

1 Handlebar 2 Front wheel 3 Rear wheel 10 Front wheel steering device 11 Tie rod 11 12 Knuckle arm 13 Relay rod 14 Steering gear mechanism 20 Rear wheel steering device 21 Tie rod 22 Knuckle arm 23 Relay rod 24 Motor 25 Reduction mechanism 26 Clutch 27 Steering gear mechanism 28 Centering Spring 29 Control unit 30 Yaw rate feedback control means 31 Side slip angle control means 32 Fuzzy control means 33 Control switching means 34 Side slip angle calculation means 40 Vehicle speed sensor 41 Rudder angle sensor 42 Yaw rate sensor 43 Lateral acceleration sensor

Claims (2)

[Claims] 1. Turning state detection means for physically detecting the turning state of the vehicle; and controlling the steering angle of the rear wheels so that the measured yaw rate based on the detection value detected by the turning state detection means becomes the target yaw rate. In a vehicle rear wheel steering system comprising a yaw rate feedback control means for performing feedback control, when the turning state detected by the turning state detection means is a turning state that is steeper than a predetermined turning state, the yaw rate feedback control means A rear wheel steering device for a vehicle, comprising control switching means for stopping feedback control of steering angles of wheels. 2. Further, a sideslip angle estimating means for estimating a sideslip angle of the vehicle, and a sideslip angle for controlling the steering angle of the rear wheels in the same phase direction as the sideslip angle estimated by the sideslip angle estimation means increases. comprising a control means, in a turning state in which the turning state detected by the turning state detection means is less steep than a predetermined turning state, the steering angle of the rear wheels is controlled by the yaw rate feedback control means;
When the turning state detected by the turning state detection means is a steeper turning state than a predetermined turning state, the steering angle of the rear wheels is controlled such that the steering angle of the rear wheels is controlled by the sideslip angle control means. 2. The rear wheel steering system for a vehicle according to claim 1, further comprising control switching means for switching the control means.