JP3012348B2 - Vehicle rear wheel 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 vehicle rear wheel steering device, and more particularly to a vehicle rear wheel steering device.

[0002]

2. Description of the Related Art There is known a rear wheel steering device for steering a rear wheel at a predetermined steering ratio with respect to a front wheel steering angle corresponding to a steering wheel steering angle in accordance with a vehicle speed. In such a rear wheel steering device of a vehicle, it is possible to obtain steering performance that matches the driver's intention regardless of the vehicle speed. However, in a transient state immediately after the driver operates the steering wheel, the front wheel and the rear wheel Are often in phase with each other, so that there is a problem that the initial turning property in the transient state is not good.

To solve such a problem, Japanese Patent Laid-Open Publication No. 1-2
Japanese Patent Laid-Open 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 feedback-controls a steering angle of a rear wheel so that an actually measured yaw rate becomes equal to the target yaw rate.

[0004]

However, in general, a vehicle is designed so as to understeer in a running state in which a lateral acceleration applied in a lateral direction of the vehicle is high in order to enhance running stability. In such a vehicle rear wheel steering device, when the vehicle turns sharply with a high lateral acceleration, the turning radius increases, the yaw rate decreases, and the steering angle of the rear wheel is fed back so that the measured yaw rate becomes the target yaw rate. When the vehicle is controlled, the rear wheels are steered in the opposite phase to the front wheels to compensate for the decrease in yaw rate, and the in-phase amount is likely to decrease.When any disturbance is applied to the vehicle, the running stability is reduced. If the speed drops significantly and the vehicle turns extremely steeply with high lateral acceleration, causing a slip, etc., a large computer with a very high calculation speed should not be used. In the case of yaw rate feedback control, it is extremely difficult to follow the vehicle. On the other hand, it is uneconomical and extremely difficult to mount a large computer that can follow the vehicle in terms of space. There was a problem.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a turning state detecting means for physically detecting a turning state of a vehicle, and a rear wheel so that an actually measured yaw rate based on a detection value detected by the turning state detecting means becomes a target yaw rate. In a rear-wheel steering system provided with a yaw rate feedback control means for feedback-controlling the steering angle of a vehicle, when the lateral acceleration changes between zero or a very high running state, the driver may feel uncomfortable in any running state. It is an object of the present invention to provide a rear-wheel steering device of a vehicle that can improve running stability without giving the vehicle.

[0006]

The object of the present invention is to provide a second control means for controlling a steering angle of a rear wheel based on a control law different from that of the yaw rate feedback control means, and a turning state detected by the turning state detecting means. Control switching means for switching to control of the rear wheel steering angle by the second control means when the vehicle is turning sharper than a predetermined turning state, wherein the control switching means controls the rear wheel steering angle. When switching the means between the yaw rate feedback control means and the second control means, if the change in the steering amount of the rear wheel is larger than a predetermined limiter value, the control for executing the steering angle control of the rear wheel is performed. The means is achieved by regulating and controlling the steering amount of the rear wheel to be the limiter value.

In a preferred embodiment of the present invention, the limiter value is set to a larger value as the lateral acceleration detected by the turning state detecting means is higher. In another preferred embodiment of the present invention, the limiter value is set to a larger value as the road surface friction coefficient is smaller.

In another preferred embodiment of the present invention, a steering angle sensor for detecting a steering angle of the steering wheel is further provided, and as the rate of change of the steering angle detected by the steering angle sensor increases, the limiter value increases. It is configured to be set to. In a further preferred aspect of the present invention, the vehicle further comprises a sideslip angle estimating means for estimating a sideslip angle of the vehicle, and the second control means, with an increase in the sideslip angle estimated by the sideslip angle estimating means, The vehicle comprises a side slip angle control means for controlling the steering angle of the rear wheels in the same phase direction.

In another preferred embodiment of the present invention, the second control means is constituted by fuzzy control means for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the measured yaw rate is reduced. ing. In still another preferred embodiment of the present invention, the fuzzy control means reduces the rate of change of the measured yaw rate based on a deviation between the target yaw rate and the measured yaw rate and / or a rate of change of the deviation. The steering angle of the rear wheels is configured to be fuzzy controlled.

In still another preferred embodiment of the present invention, the vehicle further comprises a sideslip angle estimating means for estimating a sideslip angle of the vehicle, wherein the second control means controls the sideslip angle estimated by the sideslip angle estimating means. With the increase in the steering angle of the rear wheels in the same phase direction, and fuzzy control means for fuzzy controlling the steering angle of the rear wheels so that the rate of change of the measured yaw rate decreases. When the turning state detected by the turning state detecting means is abruptly in a first turning state exceeding a first predetermined turning state, the control switching means controls the rear wheel steering by the side slip angle control means. Angle control is performed, and in a more steep second turning state beyond the second predetermined turning state, the rear wheel steering angle is controlled by the fuzzy control means. As described above, the limiter value when switching the control means and the control means for controlling the rear wheels from the yaw rate feedback control means to the sideslip angle control means is a limiter when switching between other control means. It is configured to be set to a value smaller than the value.

[0011]

According to the present invention, the second control means for controlling the steering angle of the rear wheel based on a control law different from that of the yaw rate feedback control means, and the turning state detected by the turning state detecting means, When the vehicle is in a turning state that is steeper than the predetermined turning state, control switching means for switching to control of the rear wheel steering angle by the second control means is provided. As a result, the steering angle of the rear wheel, the measured yaw rate,
By performing feedback control to achieve 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 when the in-phase amount decreases, any disturbance is applied to the vehicle. In addition, it is possible to solve the conventional problem that the running stability is significantly reduced, and the control switching means controls the control means for controlling the steering angle of the rear wheel by the yaw rate feedback control means and the second control. If the change in the steering amount of the rear wheel is greater than a predetermined limiter value when switching between the control means and the control means, the control means for executing the steering angle control of the rear wheel sets the steering amount of the rear wheel to a predetermined limiter value. Therefore, the change of the rear wheel steering angle when switching the control means is limited to a predetermined limiter value or less, and therefore, by switching the control means, Steering angle of the wheel changes rapidly and large, as a result, the driver, to feel a sense of discomfort,
It is possible to reliably prevent it.

According to a preferred embodiment of the present invention, the higher the lateral acceleration detected by the turning state detecting means, the larger the limiter value is set. Therefore, the lateral acceleration is high and the driver feels uncomfortable. In unstable driving conditions where driving stability should be more important than not,
Control of the rear wheel steering angle based on the switched control means or control similar thereto is performed, so that it is possible to improve running stability.

According to another preferred embodiment of the present invention,
Since the limiter value is set to a larger value as the road surface friction coefficient is smaller, the road surface friction coefficient is smaller, and in an unstable driving state where driving stability should be more important than whether or not the driver feels uncomfortable, Control of the rear wheel steering angle based on the switched control means or control similar thereto is performed, so that it is possible to improve running stability.

According to another preferred embodiment of the invention,
In addition, a steering angle sensor that detects the steering angle of the steering wheel is provided, and as the rate of change of the steering angle detected by the steering angle sensor is larger, the limiter value is set to a larger value. In unstable driving conditions where driving stability is more important than feeling or not,
Control of the rear wheel steering angle based on the switched control means or control similar thereto is performed, so that it is possible to improve running stability.

According to a further preferred aspect of the present invention, the vehicle further comprises a sideslip angle estimating means for estimating the sideslip angle of the vehicle, and the second control means controls the increase in the sideslip angle estimated by the sideslip angle estimating means. In addition, since the vehicle is constituted by the side slip angle control means for controlling the steering angle of the rear wheels in the same phase direction, the vehicle turns sharply with a high lateral acceleration and the turning radius of the vehicle increases, so that the steering angle of the rear wheels is reduced. When the yaw rate feedback control is performed so that the measured yaw rate is equal to the target yaw rate,
Conventionally, the rear wheels are steered in the opposite phase to the front wheels to compensate for the decrease in yaw rate, and the in-phase amount is reduced.When any disturbance is applied to the vehicle, the running stability of the vehicle is significantly reduced. Problem can be surely solved.

According to still another preferred embodiment of the present invention, the second control means is constituted by fuzzy control means for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the measured yaw rate is reduced. Therefore, when the vehicle is traveling on a road surface with a low coefficient of friction, the lateral acceleration increases, and when the steering angle of the rear wheels is controlled by the yaw rate feedback control, in a sharp turning state where there is a high risk of spinning,
It is possible to reliably prevent the occurrence of spin and improve running stability even in such a turning state.

According to still another preferred embodiment of the present invention, the vehicle further comprises a sideslip angle estimating means for estimating a sideslip angle of the vehicle, and the second control means controls the slip angle estimated by the sideslip angle estimating means. With the increase, a side slip angle control means for controlling the steering angle of the rear wheels in the same phase direction,
Fuzzy control means for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the measured yaw rate is reduced, and the control switching means determines that the turning state detected by the turning state detecting means is a first predetermined turning. Steep 1st beyond state
In the turning state of, by the side slip angle control means,
The control means controls the rear wheel steering angle such that the control of the rear wheel steering angle is executed by the fuzzy control means in a more rapid second turning state beyond the second predetermined turning state. In the case of a sharp turning state where the lateral acceleration is high, the turning radius increases and the yaw rate decreases, the steering angle of the rear wheels is controlled in the same phase direction, and the lateral acceleration further increases In a steeper turning state where spin is likely to occur, the steering angle of the rear wheel is controlled so that the rate of change of the measured yaw rate is reduced, so that it is possible to improve running stability in any running state And furthermore, a control means for controlling the rear wheels,
Since the limiter value at the time of switching from the yaw rate feedback control means to the side slip angle control means is set to a value smaller than the limiter value at the time of switching between other control means, the driver particularly feels discomfort. When switching from easy yaw rate feedback control to side slip angle control, it is possible to reliably prevent the driver from feeling uncomfortable.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail 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.

Referring to FIG. 1, a vehicle wheel steering system including a vehicle rear wheel steering system according to an embodiment of the present invention includes a steering wheel 1 and front wheels for turning left and right front wheels 2 and 2 by operating the steering wheel 1. The vehicle includes a steering device 10 and a rear wheel steering device 20 that steers left and right rear wheels 3, 3 in accordance with steering of the front wheels 2, 2 by the front wheel steering device 10. Front wheel steering device 10
Are arranged in the width direction of the vehicle body, and both ends of the relay rods 13 connected to the left and right front wheels 2, via tie rods 11, 11 and knuckle arms 12, 12.
And a rack-and-pinion type steering gear mechanism 14 for moving the relay rod 13 right and left in conjunction with the operation of the handle 1, and in the operation direction of the handle 1 by an angle corresponding to the operation amount. , Left and right front wheels 2, 2
Is to be steered.

On the other hand, the rear wheel steering device 20 is disposed in the width direction of the vehicle body, and both ends thereof are tie rods 21, 21.
And a relay rod 23 connected to the left and right rear wheels 3, 3 via knuckle arms 22, 22, and a motor 24.
And the motor 24, the speed reduction mechanism 25 and the clutch 2
6, a rack and pinion type steering gear mechanism 27 that is driven to move the relay rod 23 to the left and right, a centering spring 28 that urges the relay rod 23 to be held at the neutral position, and a vehicle A control unit 29 for controlling the operation of the motor 24 in accordance with the running state is provided, and the left and right rear wheels 3, 3 are moved in directions corresponding to the rotation direction of the motor 24 by angles corresponding to the amount of rotation of the motor 24. Only to steer.

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

Yaw rate feedback control means 30
Calculates the target yaw rate Y0 (n) based on the detection signal of the vehicle speed V (n) input from the vehicle speed sensor 40 and the steering angle θf (n) of the front wheels 2 and 2 input from the steering angle sensor 41. , The target yaw rate Y0 (n), and the actually measured yaw rate Y input from the yaw rate sensor 42.
A deviation E (n) from (n) is calculated, and the yaw rate Y (Y) is calculated based on a previously stored I-PD control formula.
, And outputs the feedback control amount Rb (n) to the control switching means 33. From the control switching means 33, a control execution signal is input, and the control means for controlling the steering angles of the rear wheels 3, 3 From the yaw rate feedback control means 30 to the fuzzy control means 32, from the sideslip angle control means 31 to the fuzzy control means 32, from the sideslip angle control means 31 to the yaw rate feedback control means 30, from the fuzzy control means 32 to the yaw rate feedback control means 3.
0, from the fuzzy control means 32 to the sideslip angle control means 3
1, when the first switching signal output from the control switching means 33 is input, the steering amount θ of the rear wheels 3, 3 at the control timing is input.
r (n) is set to θr (n) = Rb (n), and the steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr (n−
It is determined whether or not the absolute value of the difference from 1) is larger than the limiter value θrL1 (n) (n).
The steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr (n−n) of the rear wheels 3, 3 at the previous control timing are output to the motor 24 as they are. 1)
Is greater than the limiter value θrL1 (n), if the difference is positive, then θr (n) = θr (n−1) + θrL1 (n), and the difference is negative. In this case, a feedback control signal is output to the motor 24 as θr (n) = θr (n−1) −θrL1 (n), and only the control execution signal is input from the control switching unit 33. When the switching signal is not input, the steering amount θ of the rear wheels 3 at the control timing is
r (n) is the feedback control amount Rb of the yaw rate Y
As (n), it is configured to output a feedback signal to the motor 24.

Further, the control switching means 33 determines the rate of change ΔE (n) of the deviation E (n) based on the deviation E (n) between the target yaw rate Y0 and the actually measured yaw rate Y (n) input from the yaw rate feedback control means 30. n), and the deviation E (n) and the rate of change ΔE (n) of the deviation E (n) are respectively determined by the predetermined deviation E0 and the rate of change ΔE of the predetermined deviation.
In a turning state exceeding 0, that is, in a very 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 of the deviation E (n) are output.
(N) is equal to or less than a predetermined deviation E0 and a predetermined change rate ΔE0 of the deviation, respectively, and the absolute value of the estimated value β (n) of the sideslip angle calculated by the sideslip angle calculation means 34 is a predetermined value. The turning state exceeding β0, that is,
A control execution signal is output to the sideslip angle control means 31 during a sharp turning state, and in other cases, that is, during a normal turning state, the yaw rate feedback control means 30 is output.
And a control means for controlling the steering angle of the rear wheels 3, 3 at the control timing, from the yaw rate feedback control means 30 to the fuzzy control means 32 and from the sideslip angle control means 31 to the fuzzy control means. 32, when the side slip angle control unit 31 switches to the yaw rate feedback control unit 30, from the fuzzy control unit 32 to the yaw rate feedback control unit 30, and from the fuzzy control unit 32 to the side slip angle control unit 31, the first switching signal is output. Are output to the yaw rate feedback control means 30, the sideslip angle control means 31, and the fuzzy control means 32, respectively.
, The first switching signal is output to the sideslip angle control means 31.

When a control execution signal is input from the control switching means 33, the sideslip angle control means 31 calculates a sideslip angle control amount Rβ (n) based on a previously stored formula. The steering amount θr (n) of the rear wheels 3 at the control timing is set to θr (n) = Rβ (n), and when the first switching signal is input together with the control execution signal, Steering amount θr of wheels 3
The absolute value of the difference between (n) and the steering amount θr (n−1) of the rear wheels 3 at the previous control timing is the limiter value θrL.
It is determined whether or not it is greater than 1 (n). If not, the steering amount θr (n) of the rear wheels 3, 3 is output to the motor 24 as it is as a side slip angle control signal. When the absolute value of the difference between the steering amounts θr (n) of the rear wheels 3 and 3 and the steering amounts θr (n−1) of the rear wheels 3 and 3 at the previous control timing is larger than the limiter value θrL1 (n), When the difference is positive, θr (n) = θr (n−1) + θrL1 (n), and when the difference is negative, θr (n) = θr (n−1) −θrL1 (n) Output a side slip angle control signal to the motor 24,
On the other hand, when the control execution signal and the second switching signal are input from the control switching means 33, the rear wheels 3,
The absolute value of the difference between the steering amount θr (n) of the rear wheel 3 and the steering amount θr (n−1) of the rear wheels 3 and 3 at the previous control timing is
It is determined whether or not the limiter value θrL2 (n), which is a value smaller than the limiter value θrL1 (n), is larger than the limiter value θrL2 (n).
As it is, it is output to the motor 24 as a side slip angle control signal, while the steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr (n−n) of the rear wheels 3, 3 at the previous control timing are output.
When the absolute value of the difference from 1) is larger than the limiter value θrL2 (n), if the difference is positive, θr (n) = θr (n−1) + θrL2 (n), and the difference is In the case of a negative value, it is configured to output a side slip angle control signal to the motor 24 as θr (n) = θr (n−1) −θrL2 (n).

The fuzzy control means 32 calculates the rate of change ΔY (n) of the yaw rate Y (n) detected by the yaw rate sensor 42. When a control execution signal is input from the control switching means 33, The fuzzy control amount Rf is determined based on a calculation formula stored in advance such that the rate of change ΔY (n) of the actually measured yaw rate Y (n) decreases.
(N) is calculated, the steering amount θr (n) of the rear wheels 3 at the control timing is set as θr (n) = Rf (n), and the first switching signal is input together with the control execution signal. In this case, the absolute value of the difference between the steering amount θr (n) of the rear wheels 3, 3 at the control timing and the steering amount θr (n-1) of the rear wheels 3, 3 at the previous control timing is further determined. It is determined whether or not the limiter value θrL1 (n) is larger than the limit value.
(N) is directly output to the motor 24 as a fuzzy control signal, while the steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr of the rear wheels 3, 3 at the previous control timing are output.
The absolute value of the difference from (n-1) is the limiter value θrL1 (n)
When the difference is larger, when the difference is positive, θr (n) = θr (n−1) + θrL1 (n), and when the difference is negative, θr (n) = θr (n−1) ) -ΘrL1 (n), and outputs a side slip angle control signal to the motor 24.

The slip angle calculating means 34 is provided with a vehicle speed sensor 4.
Based on the detected vehicle speed V of 0, the measured yaw rate Y detected by the yaw rate sensor 42, and the lateral acceleration GL detected by the lateral acceleration sensor 43, an estimated value β of the sideslip angle is calculated according to the following equation, and the control switching means 33 Output to β (n) = 9.8 × {GL (n) / V (n)} × {Y (n) / 57} + β (n−1) where ( (n) indicates the value at the current control timing, and (n-1) indicates the value at the previous control timing.

FIGS. 3 and 4 show the limiter value θrL1.
6 is a graph showing a relationship between (n) and θrL2 (n), lateral acceleration GL, and steering wheel angle, that is, steering angle θf of front wheels 2 and 2, and road surface friction coefficient μ. In FIG.
A curve A indicated by a solid line indicates a limiter value θrL1 (n) and a lateral acceleration G when traveling on a road having a large road surface friction coefficient μ.
A curve B showing a relationship with L by a broken line is a limiter value θrL1 when traveling on a road having a small road surface friction coefficient μ.
(N) and the lateral acceleration GL, respectively, and a curve C indicated by a dashed line indicates a limiter value θrL2 (n) when traveling on a road having a large road surface friction coefficient μ. , Curve A. As shown in FIG. 3, the limiter values θrL1 (n) and θrL2 (n) are set to increase as the lateral acceleration GL increases, and the lower the road friction coefficient μ, the lower the lateral acceleration. GL is set to be a small value and a large value. As described above, the limiter value θrL1 (n) is set to increase as the lateral acceleration GL increases. When the lateral acceleration GL is large, it is recognized that the vehicle is in an unstable traveling state. This is because driving stability should be more important than discomfort,
The lower the road surface friction coefficient μ, the smaller the lateral acceleration GL is set to be a larger value. Also, when traveling on a road with a lower road surface friction coefficient μ, the lateral acceleration GL is set to be larger.
This is based on the reason that even if L is a small value, it is recognized that the vehicle is in an unstable running state, and therefore, the running stability should be more important than the sense of incongruity. Furthermore, the reason why the limiter value θrL2 (n) is set to a value smaller than the limiter value θrL1 (n) is that the driver tends to feel uncomfortable especially in a running state where the yaw rate feedback control is shifted to the sideslip angle control. That's why.

In FIG. 4, a curve a indicated by a solid line represents a relationship between the limiter value θrL1 (n) and the absolute value of the rate of change Δθf of the steering angle θf when traveling on a road having a large road surface friction coefficient μ. A curve b indicated by a broken line indicates a relationship between the limiter value θrL1 (n) and the absolute value of the rate of change Δθf of the steering angle θf when the vehicle is traveling on a road with a small road surface friction coefficient μ. A curve c indicated by a dashed line is a limiter value θrL when the vehicle is traveling on a road having a large road surface friction coefficient μ.
2 (n) and the absolute value of the rate of change Δθf of the steering angle θf, which corresponds to the curve a. As shown in FIG. 3, as the limiter values θrL1 (n) and θrL2 (n) increase as the absolute value of the rate of change Δθf of the steering angle θf increases,
The absolute value of the change rate Δθf of the steering angle θf is set to be a small value and a large value as the road surface friction coefficient μ is lower. As described above, the limiter value θrL1 (n) is set to increase as the absolute value of the change rate Δθf of the steering angle θf increases, when the absolute value of the change rate Δθf of the steering angle θf is large. This is because it is recognized that the vehicle is in an unstable traveling state, and therefore, it is necessary to prioritize traveling stability over uncomfortable feeling. In addition, the lower the road surface friction coefficient μ, the lower the change rate Δθf of the steering angle θf. The absolute value is set to be a small value and is set to be a large value, even when the absolute value of the rate of change Δθf of the steering angle θf is small when traveling on a road having a low road friction coefficient μ, This is based on the reason that it is recognized that the vehicle is in an unstable running state, and therefore, the running stability should be more important than the sense of discomfort. Further, the reason why the limiter value θrL2 (n) is set to a value smaller than the limiter value θrL1 (n) is that the driver is likely to feel a sense of discomfort especially in a running state in which the yaw rate feedback control is shifted to the sideslip angle control. That's why.

FIGS. 5, 6 and 7 are flowcharts of the steering angle control of the rear wheels 3, 3 executed by the control unit 29 constructed as described above.
Is the cornering force C. of tires. F. 6 is a graph showing the relationship between the slip angle and the slip angle. 5, 6 and 7, first, the vehicle speed V detected by the vehicle speed sensor 40 is shown.
(N), the steering angle θ of the front wheels 2, 2 detected by the steering angle sensor 41
f (n), the yaw rate Y (n) of the vehicle detected by the yaw rate sensor 42 and the lateral acceleration GL (n) applied to the vehicle detected by the lateral acceleration sensor 43 are input to the control unit 29.

Yaw rate feedback control means 30
Are the vehicle speed V (n) input from the vehicle speed sensor 40 and the steering angle θf of the front wheels 2, 2 input from the steering angle sensor 41.
Based on (n), the target yaw rate Y0 (n) at the control timing is calculated according to the following equation. Y0 (n) = V (n) / {1 + A · V (n) ² } × θf (n) / L where A is a 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 calculated in this manner.
The deviation E (n) between (n) and the actually measured yaw rate Y (n) input from the yaw rate sensor 42 is calculated according to the following equation: E (n) = Y0 (n) −Y (n) Further, a feedback control amount Rb (n) of the yaw rate Y (n) at the control timing is calculated according to the following I-PD control calculation formula.

Rb (n) = Rb (n−1) − [KI × E (n) −FP × {Y (n) −Y (n−1)} − FD × ΔY (n) −2 × Y (N-1) + Y (n-2)] where KI is an integral constant, FP is a proportional constant, FD is a differential constant, and Rb (n-1) is the last time. Is the feedback control amount at the control timing, Y (n-1) is the measured yaw rate at the previous control timing, and Y (n-2) is
The measured yaw rate at the control timing two times before is shown, respectively.

The feedback control amount Rb (n) and the deviation E (n) of the yaw rate Y (n) calculated in this way.
Is output to the control switching means 33 and the control switching means 3
3 calculates a change rate ΔE (n) of the deviation E (n), and the deviation E (n) is larger than a predetermined deviation E0, and the change rate ΔE (n) is larger than a predetermined change rate ΔE0. It is determined whether or not.

As a result, when YES, that is, when the deviation E (n) is larger than the predetermined deviation E0 and the change rate ΔE (n) is larger than the predetermined change rate ΔE0,
The vehicle is in a state corresponding to the area S3 in FIG.
The vehicle is in a very sharp turn, spins,
Since it is recognized that the direction is suddenly changed and the vehicle is in an extremely unstable traveling state, the vehicle travels stably at the steering angle θr (n) of the rear wheels 3 and 3 by the yaw rate feedback control. In such a control, it is extremely difficult to follow the change in the yaw rate of the vehicle unless a large computer having a very high calculation speed is used, and it is extremely difficult. Since the mounting is uneconomical and extremely difficult in terms of space, in this embodiment, in this turning state, the control switching means 33 controls the steering of the rear wheels 3, 3 based on fuzzy theory. It is determined that the angle θr (n) is in a turning state in which fuzzy control is to be performed, and a control execution signal is output to the fuzzy control means 32 and the control switching means 33 Further, at the previous control timing, the fuzzy control means 32 determines whether or not the steering angle control of the rear wheels 3, 3 has been performed.

As a result, when the result is YES, that is, when it is determined that the fuzzy control has been executed even at the previous control timing, the control switching means 33 outputs only the control execution signal to the fuzzy control means 32. On the other hand, when it is determined that the control by the yaw rate feedback control means 30 or the sideslip angle control means 31 has been executed at the previous control timing, the control switching means 33 causes the fuzzy control means 32 to
A first switching signal is output in addition to the control execution signal.

When the fuzzy control means 32 receives the control execution signal from the control switching means 33, the rate of change ΔY (n) of the yaw rate Y (n) is based on the detection signal of the yaw rate Y input from the yaw rate sensor 42. ), And based on the membership function which is a function of the deviation E (n) and the change rate ΔE (n), the change rate ΔY (n) of the yaw rate Y (n) is reduced according to the following equation. Then, the fuzzy control amount Rf (n) is calculated, and Rf (n) = f (E (n), ΔE (n))... Quantity θr
(N) is set as θr (n) = Rf (n), and when only the control execution signal is input, it is output to the motor 24 as a fuzzy control signal as it is.

On the other hand, when receiving the first switching signal in addition to the control execution signal from the control switching means 33, the fuzzy control means 32 further controls the steering amount θr (n) of the rear wheels 3, 3 at the control timing. ) And the steering amount θr (n−1) of the rear wheels 3 at the previous control timing are determined to be greater than or equal to the limiter value θrL1 (n). Steering amount θr of wheels 3
(N) is directly output to the motor 24 as a fuzzy control signal, while the steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr of the rear wheels 3, 3 at the previous control timing are output.
The absolute value of the difference from (n-1) is the limiter value θrL1 (n)
If it is larger, the steering amount θr (n) of the rear wheels 3, 3 and the steering amount θr of the rear wheels 3, 3 at the previous control timing
When the difference from (n−1) is positive, θr (n) = θr (n−1) + θrL1 (n), and when the difference is negative, θr (n) = θr (n− 1) Output a fuzzy control signal to the motor 24 as -θrL1 (n).
Here, the maps shown in FIGS. 3 and 4 are stored in the control switching means 33 in advance, and the control switching means 33 determines the vehicle speed V (n), the steering angle θf of the front wheels 2 and 2.
(N), measured yaw rate Y (n) and lateral acceleration GL
Based on (n), the limiter value θrL1 (n) is determined according to the maps shown in FIGS.

On the other hand, the deviation E (n) is not larger than the predetermined deviation E0 or the rate of change ΔE (n)
Is smaller than the predetermined change rate ΔE0, the control switching unit 33 sets the absolute value of the estimated value β (n) of the sideslip angle input from the sideslip angle calculation unit 34 to the predetermined value β0.
It is determined whether it is greater than. When the determination result is YES, that is, when the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0, the region S in FIG.
2 and the lateral acceleration GL
(N) is a sharp turning state, a large tire slip occurs, the turning radius of the vehicle increases, and the yaw rate Y (n) decreases.
In the case where the steering angle θr (n) of the front wheels 3 and 3 is controlled by the yaw rate feedback control, the rear wheels 3 and 3 rotate the steering angles θf
In contrast to (n), the vehicle is steered in the opposite phase, and the running stability may be significantly reduced. On the other hand, the direction of the vehicle changes rapidly as the fuzzy control must be performed. Since the vehicle is not in such an unstable traveling state, the control switching means 33 determines that the vehicle is in a turning state in which the sideslip angle control should be executed, and outputs a control execution signal to the sideslip angle control means 31 and the control switching means. Further, at the previous control timing, the side slip angle control means 31 determines whether or not the steering angle control of the rear wheels 3, 3 has been performed. It is determined whether or not the yaw rate feedback control means 30 has controlled the steering angles of the rear wheels 3,3.

As a result, when it is determined that the control by the skid angle control means 31 has been executed even at the previous control timing, the control switching means 33 outputs only the control execution signal to the skid angle control means 31. On the other hand, at the previous control timing, when it is determined that the control has been executed by the control means other than the sideslip angle control means 31, the control by the yaw rate feedback control means 30 is further performed at the previous control timing. To determine if it was running, and as a result
At the previous control timing, the fuzzy control means 32
When it is determined that the control has been executed,
The switching signal is supplied to the yaw rate feedback control means 30.
Is determined to have been executed, the control switching means 33 outputs the second switching signal to the sideslip angle control means 31 together with the control execution signal.

When the control execution signal is received from the control switching means 33, the sideslip angle control means 31 calculates the sideslip angle control amount Rβ (n) according to the following equation: Rβ (n) = k × β (n) ······························· θr
If (n) is set as θr (n) = Rf (n) and only the control execution signal is input, the control signal is output to the motor 24 as it is as a side slip angle control signal. Here, k is a control constant and has a positive value. Therefore, the side slip angle control amount Rβ (n) increases as the sideslip angle β (n) increases, and the sideslip angle β (n) Is larger, the rear wheels 3, 3 are steered in the same phase direction as the front wheels 2, 2, so that the amount of in-phase increases, so that the turning radius of the vehicle is larger and the yaw rate Y
In the running state where (n) is reduced, the rear wheels 3, 3 are steered in a direction opposite to the steering angle θf (n) of the front wheels 2, 2, and the running stability is greatly reduced. Is reliably prevented.

On the other hand, the control switching means 33
When receiving the first switching signal together with the control execution signal,
The sideslip angle control means 31 further calculates the difference between the steering amount θr (n) of the rear wheels 3, 3 at the control timing and the steering amount θr (n-1) of the rear wheels 3, 3 at the previous control timing. It is determined whether or not the absolute value is larger than the limiter value θrL1 (n). If not, the steering amount θr (n) of the rear wheels 3, 3 is directly used as the side slip angle control signal.
Output to the motor 24, and on the other hand, the steering amount θr of the rear wheels 3, 3.
The absolute value of the difference between (n) and the steering amount θr (n−1) of the rear wheels 3 at the previous control timing is the limiter value θrL.
When the difference is larger than 1 (n), when the difference is positive, θr (n) = θr (n−1) + θrL1 (n), and when the difference is negative, θr (n) = θr A side slip angle control signal is output to the motor 24 as (n−1) −θrL1 (n).

On the other hand, when receiving the second switching signal together with the control execution signal from the control switching means 33, the sideslip angle control means 31 further controls the steering amount θr (n) of the rear wheels 3, 3 at the control timing. ) And the absolute value of the difference between the steering amount θr (n−1) of the rear wheels 3 and 3 at the previous control timing is larger than the limiter value θrL2 (n) that is smaller than the limiter value θrL1 (n). If it is not large, the steering amount θr (n) of the rear wheels 3, 3 is output to the motor 24 as it is as a side slip angle control signal, while the steering amount θr ( n) and the steering amount θr (n−1) of the rear wheels 3 at the previous control timing
Is greater than the limiter value θrL2 (n), if the difference is positive, then θr (n) = θr (n−1) + θrL2 (n), and the difference is negative. In this case, a side slip angle control signal is output to the motor 24 as θr (n) = θr (n−1) −θrL2 (n). Here, the control switching means 33 includes the signals shown in FIGS.
Are stored in advance, and the control switching means 33 calculates the vehicle speed V (n), the steering angle θf of the front wheels 2 and 2,
(N), measured yaw rate Y (n) and lateral acceleration GL
Based on (n), the limiter value θrL2 (n) is determined according to the maps shown in FIGS.

On the other hand, the estimated value of the sideslip angle β
When the absolute value of (n) is equal to or smaller 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 a region S1 in which the vehicle and the sideslip angle are in a substantially proportional relationship, and it can be determined that the vehicle is in a stable running state. Therefore, the control switching means 33 sends a control execution signal to the yaw rate feedback control means 30. Is output, and it is determined whether or not the control by the yaw rate feedback control means 30 was executed at the previous control timing, and when NO, that is, at the previous control timing, the side slip angle control means 31 or the fuzzy When the control means 32 determines that the steering angle control of the rear wheels 3 has been executed, the control section 32 outputs a first switching signal to the yaw rate feedback control means 30 together with a control execution signal.

Yaw rate feedback control means 30
When only the control execution signal is received from the control switching means 33, the steering amount θr (n) of the rear wheels 3, 3 at the control timing is set as θr (n) = Rb (n), and the yaw rate feedback control is performed. A signal is output to the motor 24 to rotate the motor 24 and steer the rear wheels 3 and 3.

On the other hand, the control switching means 33
When receiving the first switching signal together with the control execution signal,
The yaw rate feedback control means 30 further controls the steering amount θr of the rear wheels 3 at the control timing.
The absolute value of the difference between (n) and the steering amount θr (n−1) of the rear wheels 3 at the previous control timing is the limiter value θrL.
It is determined whether or not it is greater than 1 (n). If not, the steering amount θr (n) of the rear wheels 3, 3 is output as it is to the motor 24 as a yaw rate feedback control signal. And the steering amount θr (n−n) of the rear wheels 3 and 3 at the previous control timing.
When the absolute value of the difference from 1) is larger than the limiter value θrL1 (n), when the difference is positive, θr (n) = θr (n−1) + θrL1 (n), and the difference is In the negative case, the yaw rate feedback control signal is output to the motor 24 as θr (n) = θr (n−1) −θrL1 (n), and the rear wheels 3, 3 are steered.

The above control is executed at predetermined time intervals.
The rear wheels 3, 3 are steered. According to the present embodiment, in the region S1 where the running state of the vehicle is stable, the actually measured yaw rate Y (n) is determined by the yaw rate feedback control so that the target yaw rate Y determined based on the steering angle of the steering wheel 1.
Since the rear wheels 3, 3 are steered so as to be 0 (n),
It is possible to steer the rear wheels 3, 3 as desired, while the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0, and the vehicle is in a sharp turning state where the lateral acceleration GL is large. In the traveling state area S2 in which the turning radius of the vehicle is large and the yaw rate Y (n) is low, the rear wheels 3, 3 are connected to the front wheels 2, 2 as the estimated value β (n) of the sideslip angle increases. Since the sideslip angle control is performed in the in-phase direction so as to increase the amount of in-phase, the rear wheels 3, 3 are steered based on the yaw rate feedback control, so that the steering angle θr (n) of the rear wheels 3, 3 is obtained. However, the steering angle θf (n) of the front wheels 2 is opposite to the steering angle θf (n), so that the running stability is prevented from being lowered, and the running stability can be improved. Deviation E (n) between target yaw rate Y0 (n) and measured yaw rate Y (n) And the rate of change ΔE (n) of deviation E (n) is greater than predetermined values E0 and ΔE0,
In an extremely unstable running state area S3 where a spin is likely to occur in a very steep turning state in which the vehicle is recognized to be turning suddenly, the yaw rate Y
The rear wheels 3, so that the rate of change ΔY (n) of (n) decreases,
Since the steering angle θr of 3 is fuzzy controlled, it is possible to improve running stability even in such an extremely steep turning state and an extremely unstable running state without using a very large computer. become. Further, when the control means for controlling the steering angles of the rear wheels 3, 3 is different from the previous control timing, the steering amount of the rear wheels 3, 3 may change rapidly and greatly. In such a case, the driver may feel uncomfortable. However, in this embodiment, the control means for controlling the steering angles of the rear wheels 3 at the control timing is fuzzy from the yaw rate feedback control means 30. The control means 32, the side slip angle control means 31 to the fuzzy control means 32, the side slip angle control means 31 to the yaw rate feedback control means 30, the fuzzy control means 32 to the yaw rate feedback control means 30, and the fuzzy control means 32 to the side slip angle control. When the control is switched to the means 31, the change in the steering amount of the rear wheels 3, 3 at the control timing is The steering angle of the rear wheels 3, 3 is controlled so as to be equal to the emitter value θrL1 (n), and at the control timing, the control means for controlling the steering angle of the rear wheels 3, 3 comprises a yaw rate feedback control means. When the control is switched from 30 to the slip angle control means 31 and the control is directly performed by the slip angle control means 31, particularly,
When the driver easily gives a sense of discomfort, the change in the amount of steering of the rear wheels 3 at the control timing is limited to a limiter value θrL2 that is smaller than the limiter value θrL1 (n).
(N), the steering angles of the rear wheels 3, 3 are controlled, and the limiter values θrL1 (n) and θrL
2 (n) is set to be a large value in an unstable running state according to the maps shown in FIGS. 3 and 4, respectively, so that the running of the vehicle becomes unstable. It is possible to realize well-connected control while preventing the driver from feeling uncomfortable.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention described in the appended claims, which are also included in the scope of the present invention. Needless to say, this is done. For example,
In the embodiment, at the control timing,
The control means for controlling the steering angles of the rear wheels 3, 3 is provided by the fuzzy control means 32 from the yaw rate feedback control means 30.
Then, the sideslip angle control means 31 to the fuzzy control means 32
When the side slip angle control unit 31 is switched to the yaw rate feedback control unit 30, the fuzzy control unit 32 is switched to the yaw rate feedback control unit 30, and the fuzzy control unit 32 is switched to the side slip angle control unit 31, the rear wheel 3 is uniformly switched. 3 is used as the limiter value of the steering amount θr, a different limiter value may be used for each or only a part thereof, and FIGS. , Limiter value θrL
1 (n) and θrL2 (n) are merely examples of a graph showing the relationship between the lateral acceleration GL, the road surface friction coefficient μ, and the change rate Δθf of the steering angle θf of the front wheels 2 and 2, and these relationships are as follows.
The setting as shown in FIGS. 3 and 4 is not indispensable, and these relations can be set as desired.

Further, in the above embodiment, the limiter values θrL1 (n) and θrL1 (n) are determined based on the lateral acceleration GL, the road friction coefficient μ, and the rate of change Δθf of the steering angle θf of the front wheels 2, 2.
Although rL2 (n) is set, the limiter values θrL1 (n) and θrL2 (n) are set based on other operating conditions in addition to these or based on other operating conditions instead of some of them. n) may be set.

In the above embodiment, when the absolute value of the estimated value of the sideslip angle β becomes larger than the predetermined value β0,
From the yaw rate feedback control to the side slip angle control, in a running state where the estimated value β of the side slip angle is larger than the predetermined value β0, the steering angle θ of the rear wheels 3, 3 is increased.
The ratio between r and the steering angle θf of the front wheels 2 and 2 may be fixed. Alternatively, instead of the yaw rate feedback control up to that point, the control gain may be reduced and new yaw rate feedback control may be performed. You may.

Further, in the above embodiment, β0 is a constant value, but β0 may be changed according to the vehicle speed V, the lateral acceleration GL, and the like. FIG. 9 shows a flowchart for setting β0 based on the vehicle speed V and the lateral acceleration GL. In FIG. 9, β0 is determined by the side slip angle calculating means 34 based on the threshold value βt, the coefficient jv that is a function of the vehicle speed V, and the coefficient jg that is a function of the lateral acceleration GL, according to the following equation. It has become.

Β0 = jv × jg × βt That is, first, the coefficient jv is determined according to the value of the vehicle speed V. Here, when the vehicle speed V increases, the coefficient jv becomes:
It is set to converge to 1.0. This is because drivers are more likely to feel anxious at higher speeds,
This is because even if the estimated value β of the sideslip angle is a small value, it is possible to shift to the sideslip angle control. Then, the coefficient jg
Is determined by the value of the lateral acceleration GL. In FIG. 9, when the lateral acceleration GL increases, the coefficient jg becomes 1.
It is set to converge to zero. This is so that the vehicle can shift to the side slip angle control with a small value of the lateral acceleration GL while traveling on a road having a small road surface friction coefficient μ. Here, in FIG. 9, β0 is set by the vehicle speed V and the lateral acceleration GL. However, β0 may be set by adding other operation parameters, or β0 may be set by other operation parameters. You may make it set.

In the above-described embodiment, the yaw rate Y is detected by using the yaw rate sensor 42 as the turning state detecting means, but the yaw rate Y is detected based on the lateral acceleration GL detected by the lateral acceleration sensor 43 or the vehicle speed sensor 40. 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 vehicle.
3 without using 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
May be calculated based on.

Further, the formula for calculating the estimated value of the sideslip angle β and the formula for calculating the target yaw rate Y0 are merely examples, and the estimated value of the sideslip angle β is calculated by a Kalman filter method, an observer method, or the like. Alternatively, the target yaw rate Y0 may be calculated by another arithmetic expression. Further, the sensor for detecting the running state of the vehicle may be selected as needed in that case, and the vehicle speed sensor 4 used in the above embodiment may be selected.
0, another sensor can be used without using a part of the steering angle sensor 41, the yaw rate sensor 42, and the lateral acceleration sensor 43.

In the above embodiment, when the deviation E between the target yaw rate Y0 and the actually 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, 3, the steering control of the rear wheels 3, 3 by fuzzy control may be executed when any one of them is greater than a predetermined value. , The membership function of the fuzzy control is a function of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y and the rate of change ΔE of the deviation E, but the target yaw rate Y0
The membership function of the fuzzy control may be determined based on the measured yaw rate Y, and may be one of the deviation E and the change rate ΔE of the deviation E. Further, instead of the deviation E or the change rate ΔE of the deviation E, the lateral acceleration GL
Exceeds a predetermined value, the rear wheels 3 by fuzzy control,
The steering control of No. 3 may be executed.
The membership function of the fuzzy control is determined based on the lateral acceleration GL and / or its change rate, or the steering angle θf of the front wheels 2 and 2, the change speed of the steering angle θf, and the change rate of the change speed of the steering angle θf. You may do so.

Further, in the above embodiment, the rear wheels 3, 3 are controlled by fuzzy control in the area S3 of FIG.
The steering angle of the tire is controlled, but the cornering force C. F. As shown in FIG. 8, the relationship between and the side slip angle changes depending on the road surface friction coefficient μ. Therefore, when traveling on a road other than a road having a small road surface friction coefficient μ, only the regions S1 and S2 exist. , The region S3 does not exist, and therefore, it may not always be necessary to execute the fuzzy control. On the other hand, when traveling on a road with a small road surface friction coefficient μ, as shown in FIG.
The region S2 in which the sideslip angle control is to be executed is extremely small, and the control may immediately shift to the fuzzy control without performing the sideslip angle control.

[0056]

According to the present invention, the turning state detecting means for physically detecting the turning state of the vehicle and the measured yaw rate based on the detection value detected by the turning state detecting means are set to the target yaw rate. In a rear-wheel steering system for a vehicle including a yaw rate feedback control unit that feedback-controls a steering angle of a rear wheel, when a lateral acceleration changes between zero or an extremely high traveling state, the driver can perform the driving in any traveling state. It is possible to provide a rear wheel steering device of a vehicle that can improve running stability without giving a feeling of strangeness to the vehicle.

[Brief description of the drawings]

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

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

FIG. 3 is a graph showing limiter values θrL1 (n) and θrL2
It is a graph which shows the relationship between (n), a lateral acceleration GL, and a road surface friction coefficient μ.

FIG. 4 is a graph showing limiter values θrL1 (n) and θrL2
6 is a graph showing a relationship between (n) and an absolute value of a change rate Δθf of the steering angle θf of the front wheels.

FIG. 5 is a drawing showing the first half of a flowchart of rear wheel steering control executed by the control unit.

FIG. 6 is a drawing showing a part of the latter half of the flowchart of the rear wheel steering control executed by the control unit.

FIG. 7 is a drawing showing a part of the latter half of the flowchart of the rear wheel steering control executed by the control unit.

FIG. 8 is a diagram showing a tire cornering force C.I.
F. 6 is a graph showing the relationship between the slip angle and the slip angle.

FIG. 9 is a flowchart illustrating an example of a method of setting β0.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Handle 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 Steering angle sensor 42 Yaw rate sensor 43 Lateral acceleration sensor

Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 137: 00

Claims (9)

(57) [Claims] A turning state detecting means for physically detecting a turning state of a vehicle, and a steering angle of a rear wheel is adjusted so that an actually measured yaw rate based on a detection value detected by the turning state detecting means becomes a target yaw rate. A rear wheel steering device including a yaw rate feedback control unit that performs feedback control, a second control unit that controls a steering angle of a rear wheel based on a control rule different from that of the yaw rate feedback control unit, and the turning state detection. Control switching means for switching to control of the rear wheel steering angle by the second control means when the turning state detected by the means is a steeper turning state than a predetermined turning state, and controls the steering angle of the rear wheels. When the control means is switched between the yaw rate feedback control means and the second control means, a change in the steering amount of the rear wheel is
When the vehicle is larger than the predetermined limiter value, the control means for controlling the steering angle of the rear wheel is configured to regulate the steering amount of the rear wheel to the limiter value. Wheel steering device. 2. The rear wheel of a vehicle according to claim 1, wherein the limiter value is set to a larger value as the lateral acceleration detected by the turning state detecting means is higher. Steering gear. 3. The rear wheel steering device according to claim 1, wherein the limiter value is set to a larger value as the road surface friction coefficient is smaller. 4. A steering angle sensor for detecting a steering angle of the steering wheel, wherein the limiter value is set to a larger value as the rate of change of the steering angle detected by the steering angle sensor is larger. The rear wheel steering device according to any one of claims 1 to 3, wherein: 5. The vehicle according to claim 1, further comprising: a side slip angle estimating unit for estimating a side slip angle of the vehicle, wherein the second control unit controls the steering of the rear wheel in accordance with an increase in the side slip angle estimated by the side slip angle estimating unit. The rear wheel steering device according to any one of claims 1 to 4, further comprising a side slip angle control unit that controls the angle in the same phase direction. 6. The fuzzy control means according to claim 1, wherein said second control means comprises fuzzy control means for fuzzy controlling a steering angle of a rear wheel such that a rate of change of said actually measured yaw rate is reduced. The rear wheel steering device according to any one of claims 4 to 8. 7. The fuzzy control means is configured to perform fuzzy control of a steering angle of a rear wheel based on a deviation between the target yaw rate and a measured yaw rate so that a rate of change of the measured yaw rate is reduced. The vehicle rear wheel steering device according to claim 6, wherein: 8. The fuzzy control means is configured to perform fuzzy control of a steering angle of a rear wheel based on a change rate of a deviation between the target yaw rate and a measured yaw rate so that a change rate of the measured yaw rate is reduced. The vehicle rear wheel steering device according to claim 6, wherein 9. The vehicle according to claim 1, further comprising: a side slip angle estimating unit for estimating a side slip angle of the vehicle, wherein the second control unit controls the steering of the rear wheel with an increase in the side slip angle estimated by the side slip angle estimating unit. A side slip angle control unit for controlling the angle in the same phase direction; and a fuzzy control unit for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the measured yaw rate is reduced. The turning state detected by the state detecting means is the first turning state.
In the sharp first turning state beyond the predetermined turning state, the control of the rear wheel steering angle is executed by the side slip angle control means, and the steeper second turning state beyond the second predetermined turning state is performed.
In the turning state of, by the fuzzy control means,
The control means is switched so that the control of the rear wheel steering angle is executed, and the limiter value when the control means for controlling the rear wheels is switched from the yaw rate feedback control means to the sideslip angle control means is different from the limiter value. The rear wheel steering device according to any one of claims 1 to 4, wherein the value is set to a value smaller than a limiter value at the time of switching between the control means.