JP3027221B2 - 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 such a rear-wheel steering device for a vehicle, when traveling on a road having a small coefficient of road surface friction, the vehicle makes a sharp turn and the lateral acceleration applied to the vehicle in the lateral direction is extremely high. In this state, excessive oversteering tends to occur, and unless a large-scale computer with a very fast calculation speed is used, the measured yaw rate follows the yaw rate change of the vehicle even if the feedback control is performed so as to become the target yaw rate. Can't do it, and with yaw rate feedback control,
It is extremely difficult to control the steering angle of the rear wheels, but it is extremely uneconomical to install a computer in the vehicle that can control the steering angle of the rear wheels by yaw rate feedback control. However, there is a problem that the space is extremely difficult.

[0005]

SUMMARY OF THE INVENTION The present invention provides a turning state detecting means for physically detecting a turning state of a vehicle, and a feedback control so that an actually measured yaw rate based on a detection value detected by the turning state detecting means becomes a target yaw rate. Therefore, in a rear wheel steering device of a vehicle including a yaw rate feedback control means for steering the rear wheels, a large turn computer can be used, even if the vehicle makes a sharp turn while traveling on a road with a small coefficient of road surface friction. It is another object of the present invention to provide a rear wheel steering device for a vehicle that can improve running stability.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for measuring an absolute value of a deviation between a target yaw rate and an actual yaw rate that exceeds a predetermined value while the actual yaw rate is increasing. This is achieved by providing a regulating means for regulating the steering angle of the rear wheel so that the steering amount of the rear wheel becomes maximum in the direction in which the measured yaw rate decreases.

In the embodiment of the present invention, in addition to the yaw rate feedback control means as the first control means, the second control for controlling the steering angle of the rear wheels based on a control law different from that of the first control means. Control switching means for switching the control means for controlling the steering angle of the rear wheel to the second control means when the turning state detected by the turning state detecting means is a steeper turning state than the predetermined turning state; When the measured yaw rate is increasing, the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and when the absolute value of the deviation exceeds the predetermined value, the rear yaw rate of the rear wheel is reduced. And a restricting means for restricting the steering angle of the rear wheels so as to maximize the steering amount.

In a preferred embodiment of the present invention, a steering angle sensor for detecting a steering angle of the steering wheel is further provided, and after the sign of the rate of change of the steering angle of the steering wheel detected by the steering angle sensor changes, While the measured yaw rate is increasing,
When the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and the absolute value of the deviation exceeds the predetermined value, the steering amount of the rear wheel is maximized in the direction in which the measured yaw rate decreases. In addition, the steering angle of the rear wheels is controlled.

In a further preferred first 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 an increase in the sideslip angle estimated by the sideslip angle estimating means. In addition, it is constituted by side slip angle control means for controlling the steering angle of the rear wheels in the same phase direction. In a further preferred second embodiment of the present invention, the second control means is constituted by fuzzy control means for fuzzy controlling the steering angle of the rear wheels so that the rate of change of the measured yaw rate approaches zero.

In a third preferred embodiment of the present invention, the second control means makes the rate of change of the measured yaw rate close to zero based on the deviation between the target yaw rate and the measured yaw rate and / or the rate of change of the deviation. As described above, it is constituted by fuzzy control means for fuzzy controlling the steering angle of the rear wheel. In a further preferred fourth embodiment 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. A side slip angle control means for controlling the steering angle of the rear wheels in the same phase direction, and a change rate of the actually measured yaw rate approaches zero.
Fuzzy control means for fuzzy controlling the steering angle of the rear wheel, wherein the control switching means determines that the turning state detected by the turning state detecting means is a sharp first turning state exceeding a first predetermined turning state. In the above, the control of the rear wheel steering angle is executed by the side slip angle control means, and in the second steeper turning state beyond the second predetermined turning state, the control of the rear wheel steering angle is performed by the fuzzy control means. Is executed to switch the control means.

In a fifth preferred embodiment of the present invention, when the absolute value of the deviation between the actually measured yaw rate and the target yaw rate starts decreasing, the regulating means releases the regulation of the steering angle of the rear wheels, The control switching means is configured to switch the control means for controlling the rear wheel steering angle to the yaw rate feedback control means as the first control means.

[0012]

According to the present invention, when the absolute value of the deviation between the target yaw rate and the actual yaw rate exceeds a predetermined value and the absolute value of the deviation exceeds the predetermined value while the actual yaw rate is increasing, the actual measurement is performed. The steering wheel is operated to control the steering angle of the rear wheel so that the amount of steering of the rear wheel is maximized in the direction in which the yaw rate becomes smaller, so the steering wheel is operated and the measured yaw rate begins to increase. , Before crossing its peak value,
When the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and the absolute value of the deviation exceeds the predetermined value, and there is a great possibility that an excessive oversteering tendency occurs, the steering angle of the rear wheels is extremely large. However, since the steering amount of the rear wheels is regulated in the direction in which the measured yaw rate becomes smaller, even when making a sharp turn while driving on a road with a low road friction coefficient, excessive oversteering tendency Is reliably prevented from occurring, and running stability can be improved.

According to the embodiment of the present invention, in addition to the yaw rate feedback control means as the first control means,
A second control unit that controls the steering angle of the rear wheel based on a control law different from the first control unit; and a turning state detected by the turning state detection unit is a turning state that is steeper than a predetermined turning state. Control switching means for switching the control means for controlling the steering angle of the rear wheel to the second control means; and while the measured yaw rate is increasing, the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and When the absolute value of the deviation exceeds a predetermined value, there is provided a regulating means for regulating the steering angle of the rear wheel so that the steering amount of the rear wheel is maximized in the direction in which the measured yaw rate becomes smaller. Further, as a result of a sharp turning state in which the lateral acceleration is high, the turning radius increases, and the yaw rate decreases, as a result, the steering angle of the rear wheel is feedback-controlled so that the actually measured yaw rate becomes the target yaw rate. To compensate for the drop, the problem that the rear wheels are steered in the opposite phase to the front wheels to reduce the in-phase amount and reduce the running stability when any disturbance is applied to the vehicle can be solved. Will be possible.

According to a preferred embodiment of the present invention, after the sign of the rate of change of the steering wheel steering angle detected by the steering angle sensor changes, while the measured yaw rate is increasing,
When the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and the absolute value of the deviation exceeds the predetermined value, the steering amount of the rear wheel is maximized in the direction in which the measured yaw rate decreases. In addition, since the steering angle of the rear wheels is regulated, the target yaw rate and the measured yaw rate can be determined even when the steering wheel is not turned back, for example, when entering a road with a significantly different road surface friction coefficient. The absolute value of the deviation exceeds the predetermined value, and the absolute value of the deviation exceeds the predetermined value. As a result, the steering wheel is accidentally turned back, and the deviation between the target yaw rate and the measured yaw rate continues to increase rapidly. Judging that this is a phenomenon, in a running state in which there is little possibility that an excessive oversteering tendency will occur, the steering angle of the rear wheel is increased in the direction in which the measured yaw rate is reduced. This ensures that running stability is not adversely affected, and the steering wheel is turned back.When the measured yaw rate exceeds its peak and begins to decrease, the rear wheels It is possible to surely prevent the running stability from being lowered by being steered in the opposite phase.

According to a first 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 increases the sideslip angle estimated by the sideslip angle estimating means. As a result, 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 is further turned into a sharp turning state in which the lateral acceleration is high, the turning radius is increased, and the yaw rate is reduced. By performing feedback control on the steering angle of the rear wheel so that the measured yaw rate becomes the target yaw rate, the rear wheel is steered in the opposite phase to the front wheel to compensate for the decrease in yaw rate, and the amount of in-phase is reduced. However, when some disturbance is applied to the vehicle, the problem that running stability decreases
It is possible to solve the problem reliably.

According to a further preferred second 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 such that the rate of change of the measured yaw rate approaches zero. Since it has been
If the lateral acceleration increases while traveling on a road surface with a low coefficient of road surface friction and the steering angle of the rear wheels is controlled by the yaw rate feedback control, an excessive It is possible to reliably prevent the occurrence of an oversteer tendency and to improve running stability even in such a turning state.

According to a further preferred third embodiment of the present invention, the second control means determines a difference between the target yaw rate and the actually measured yaw rate and / or a rate of change of the difference.
Fuzzy control means for fuzzy controlling the steering angle of the rear wheels so that the rate of change of the measured yaw rate approaches zero, further increases the lateral acceleration while traveling on a road surface with a low road surface friction coefficient, 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 an excessive oversteering tendency, the occurrence of an excessive oversteering tendency is reliably prevented, and even in such a turning state. This makes it possible to improve running stability.

According to a fourth 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 increases the sideslip angle estimated by the sideslip angle estimating means. Along with this, it is constituted by a side slip angle control means for controlling the steering angle of the rear wheel in the same phase direction and a fuzzy control means for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the measured yaw rate approaches zero.
When the turning state detected by the turning state detecting means is more than the first predetermined turning state, the control switching means controls the rear wheel steering angle by the sideslip angle control means. Then, in the second turning state which is steeper than the second predetermined turning state, the control means is switched by the fuzzy control means so that the control of the rear wheel steering angle is executed. Therefore, even in the case of a sharp turning state in which the lateral acceleration is high, the turning radius becomes large and the yaw rate is reduced, and also in the case of a sharp turning state in which the lateral acceleration is further high and an excessive oversteering tendency is likely to occur. This makes it possible to improve running stability.

According to a fifth preferred embodiment of the present invention, when the absolute value of the deviation between the actually measured yaw rate and the target yaw rate starts decreasing, the regulating means releases the regulation of the steering angle of the rear wheels. Since the control switching means is configured to switch the control means for controlling the rear wheel steering angle to the yaw rate feedback control means as the first control means, it is apparent that the control will be shifted to the yaw rate feedback control soon. Nevertheless, the regulating means continues the control to steer the rear wheels at a steering speed smaller than the steering speed of the rear wheels calculated by the first control means or the second control means, or The steering angle control of the rear wheels is executed by the second control means. As a result, at the time of shifting to the yaw rate feedback control, the steering angle of the rear wheels is largely steered and the running stability is improved. To be impaired, it is possible to effectively prevent.

[0020]

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, 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 arranged 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, a sideslip angle calculation unit 34 for calculating an estimated value β of the sideslip angle, and a steering angle regulation. Means 35, a vehicle speed sensor 40 for detecting the vehicle speed V, a steering angle of the steering wheel 1, that is, a steering angle sensor 41 for detecting the steering angle θf of the front wheels 2, 2, and a turning state for detecting the yaw rate Y of the vehicle. Detection signals are input from a yaw rate sensor 42 which is a detecting means and a lateral acceleration sensor 43 which detects a lateral acceleration GL applied to the vehicle.

Yaw rate feedback control means 30
Calculates the target yaw rate Y0 based on the detection signal of the vehicle speed V input from the vehicle speed sensor 40 and the steering angle θf of the front wheel input from the steering angle sensor 41, and inputs the target yaw rate Y0 and the yaw rate sensor 42. A deviation E from the actually measured yaw rate Y (n) is calculated, and a feedback control amount Rb (n) of the yaw rate Y is calculated based on a previously stored formula for I-PD control. And the control switching means 33
Then, when the control execution signal is input, a feedback control signal is output to the steering angle regulating means 35.

Further, the control switching means 33 provides a deviation E between the target yaw rate Y0 (n) inputted from the yaw rate feedback control means 30 and the actually measured yaw rate Y (n).
Based on (n), the change rate ΔE (n) of the deviation E (n) is calculated, and the absolute value of the deviation E (n) and the absolute value of the change rate ΔE (n) of the deviation E (n) are In the turning state exceeding the predetermined value E0 and the predetermined value ΔE1, that is,
In a very steep turning state, the fuzzy control means 32
And the absolute value of the deviation E (n) and the absolute value of the rate of change ΔE (n) of the deviation E (n) are equal to or less than the predetermined value E0 and the predetermined value ΔE1, respectively, and
In a turning state in which the absolute value of the estimated value β (n) of the sideslip angle calculated by the sideslip angle calculating means 34 exceeds a predetermined value β0, that is, in a sharp turning state, control is performed by the sideslip angle control means 31. Outputs an execution signal, otherwise
That is, the control execution signal is output to the yaw rate feedback control means 30 in the normal turning state.

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. A side slip angle control signal is output to the steering angle restricting means 35. Also, 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, and when a control execution signal is input from the control switching means 33, based on a previously stored calculation formula. And measured yaw rate Y
The absolute value of the change rate ΔY (n) of the actually measured yaw rate Y (n) is calculated so that the change rate ΔY (n) of (n) approaches zero, and the fuzzy calculation is performed so that the absolute value decreases. By calculating the control amount Rf (n), the fuzzy control signal is calculated as
Output to the steering angle regulating means 35.

The side slip angle calculating means 34 includes a vehicle speed sensor 4
0, the vehicle speed V (n) detected by the yaw rate sensor 42, the measured yaw rate Y (n) detected by the yaw rate sensor 42, and the lateral acceleration sensor 4
Based on the lateral acceleration GL (n) detected in Step 3, an estimated value of the side slip angle β (n) is calculated according to the following equation, and is output to the control switching means 33. 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.

The steering angle restricting means 35 controls the steering wheel 1 based on the steering angle θf (n) of the front wheels input from the steering angle sensor 41.
Is determined to have been turned back, and the measured yaw rate Y (n) is determined to be increasing, the target yaw rate Y0 (n) input from the yaw rate feedback control means 30 and the measured yaw rate Y (n) ) And E
A change rate ΔE (n) of the deviation E (n) is calculated based on (n), and the absolute value of the deviation E (n) exceeds a predetermined value E0.
Further, when the absolute value of the rate of change ΔE (n) of the deviation E (n) exceeds a predetermined value ΔE2 which is larger than the predetermined value ΔE1, the steering angle θr (n) of the rear wheels 3, 3 is measured by the measured yaw rate. Y
A rear wheel steering angle regulation signal for regulating the steering angle θr (n) of the rear wheels is output to the motor 24 so that the steering amount of the rear wheels 3 and 3 becomes maximum in the direction in which (n) decreases. , Measured yaw rate Y
When (n) has not increased, the measured yaw rate Y (n)
When the steering wheel 1 has not been turned back, the measured yaw rate Y (n) has increased and the steering wheel 1 has been turned back, but the absolute value of the deviation E (n) is equal to or smaller than a predetermined value E0. Or the measured yaw rate Y (n) is increasing, the steering wheel 1 is also turned back, and the deviation E (n)
Is greater than the predetermined value E0, but when the absolute value of the rate of change ΔE (n) of the deviation E (n) is equal to or smaller than the predetermined value ΔE2, the rear wheel steering angle restriction signal is generated at the previous control timing. Is not output, the yaw rate feedback control signal selected by the control switching means 33, the yaw rate feedback control signal, the sideslip angle control signal, or the fuzzy control signal input from the sideslip angle control means 31 or the fuzzy control means 32 is output. When the yaw rate Y (n) is no longer in the increased state, and the rear-wheel steering angle restriction signal is output at the previous control timing, the side slip angle is output. Control means 31 or fuzzy control means 3
2 is selected by the control switching means 33 and the yaw rate feedback control means 30 outputs the yaw rate feedback control signal to the motor 24 even if the sideslip angle control signal or the fuzzy control signal is input.

FIGS. 3 and 4 show the rear wheel 3, which is executed by the control unit 29 constructed as described above.
5 is a flowchart of the steering angle control of FIG. F. FIG. 6 is a graph showing the relationship between the target yaw rate Y0 (n), the measured yaw rate Y (n), the steering angle θf of the front wheels 2, 2, and time.

3 and 4, 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 yaw rate sensor 4
2 and the lateral acceleration GL (n) applied to the vehicle detected by the lateral acceleration sensor 43.
Is input to the control unit 29. The yaw rate feedback control means 30 detects the detection signal of the vehicle speed V (n) input from the vehicle speed sensor 40 and the steering angle sensor 4
The target yaw rate Y0 (n) at the control timing is calculated based on the steering angle θf (n) of the front wheels input from 1 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 a deviation E (n) between the target yaw rate Y0 (n) thus calculated and the actually measured yaw rate Y (n) input from the yaw rate sensor 42 according to the following equation. , E (n) = Y0 (n) -Y (n) Further, according to the following I-PD control calculation formula, the yaw rate Y ( The feedback control amount Rb (n) of n) is calculated.

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 deviation E
(N) is output to the steering angle regulating means 35. The steering angle restricting means 35 calculates the measured yaw rate Y (n) inputted from the yaw rate feedback control means 30 by the measured yaw rate Y (n-1) inputted at the previous control timing.
Greater or less, ie, the measured yaw rate Y (n)
Is increasing and has not yet reached its peak value Ymax.

If the result is YES, the steering angle sensor 4
The absolute value of the steering angle θf (n) of the front wheels 2 and 2 input from 1 is calculated based on the front wheels 2 and 2 input at the previous control timing.
It is determined whether the steering angle is smaller than the absolute value of the steering angle θf (n−1), that is, whether the steering wheel 1 is turned back. If the result is YES and it is determined that the steering wheel 1 has been turned back, the steering angle regulating means 35 further
Based on the deviation E (n) input from the yaw rate feedback control means 30, it is determined whether or not the absolute value of the deviation E (n) is larger than a predetermined value E0.

If the determination result is YES, the steering angle restricting means 35 calculates the rate of change ΔE (n) of the deviation E (n), and further calculates the rate of change ΔE (n) of the error E (n). Is determined whether or not the absolute value of is larger than a predetermined value ΔE2. As a result, in the case of YES, the steering wheel 1 is operated to one side,
Target yaw rate Y0 (n) and measured yaw rate Y
After (n) starts to increase, the steering wheel 1 is turned back, and the target yaw rate Y0 (n) starts to decrease, but the actually measured yaw rate Y (n) continues to increase due to the control delay, and Target yaw rate Y0 (n) and measured yaw rate Y
A traveling state in which the absolute value of the deviation E (n) of (n) exceeds a predetermined value E0 and the absolute value of the rate of change ΔE (n) of the deviation E (n) exceeds a predetermined value ΔE2; Target yaw rate Y
The absolute value of the deviation E (n) between 0 (n) and the actually measured yaw rate Y (n) sharply changes greatly, and it is recognized that the vehicle is in a traveling state in which there is a great risk of causing an excessive oversteering tendency. The running state at time t1 in FIG. 6 indicates such a state.

In such a running state, the rear wheels 3, 3 calculated by the yaw rate feedback control means 30, the skid angle control means 31 or the fuzzy control means 32 selected by the control switching means 33 according to the running state at that time. When the steering angle θr of the rear wheels 3 is controlled in accordance with the steering angle control amount Rb (n), Rβ (n) or R (n) f, the steering angle θr (n) of the rear wheels 3 6, and the measured yaw rate Y (n) changes as shown by a broken line in FIG. 6, and the steering angles θ of the front wheels 2, 2 and the rear wheels 3, 3, respectively.
Since the in-phase amount of f (n) and θr (n) is small, it is difficult to prevent the occurrence of excessive oversteering tendency, and it is inevitable that the running state becomes unstable.

Therefore, in the present embodiment, the steering angle restricting means 35 controls the rear wheels 3, 3 so that the steering amount of the rear wheels 3, 3 becomes maximum in the direction in which the measured yaw rate Y (n) becomes smaller.
A rear wheel steering angle regulation signal that regulates the steering angle θr (n) of No. 3 is output to the motor 24. as a result,
In FIG. 6, the steering angle θr (n) of the rear wheels 3, 3 is regulated so as to suddenly become a large steering angle from the time t1, as indicated by the solid line, and the measured yaw rate Y (n) is also indicated by the solid line. It changes as shown by.

On the other hand, when the measured yaw rate Y (n) is not increasing, the measured yaw rate Y (n) is increasing, but when the steering wheel 1 is not turned back, the measured yaw rate Y (n) is Although the steering wheel 1 has been turned back, the steering wheel 1 is also turned back when the absolute value of the deviation E (n) is equal to or less than the predetermined value E0 or the measured yaw rate Y (n) has increased. Although the absolute value of the deviation E (n) also exceeds the predetermined value E0, the rate of change Δ
When the absolute value of E (n) is equal to or smaller than the predetermined value ΔE2 and the rear wheel steering angle restriction signal has not been output at the previous control timing, the steering angle restriction means 35 outputs the steering angle restriction signal. Instead, a yaw rate feedback control signal, a sideslip angle control signal, or a fuzzy control signal input from the yaw rate feedback control means 30, the sideslip angle control means 31, or the fuzzy control means 32 is sent to the motor 24 in accordance with the determination of the control switching means 33. Output.

On the other hand, at the previous control timing, a rear wheel steering angle restriction signal is output and the measured yaw rate Y
If (n) has not increased, the steering angle θr (n) of the rear wheels 3, 3 has been regulated by the steering angle regulating means 35 until the previous control timing, but the steering wheel 1 is turned back. As a result, it is recognized that the actually measured yaw rate Y (n) has reached its peak value and has started to decrease, that is, a running state corresponding to the time t2 in FIG. 6. Since this is considered to be a precursory phenomenon of returning to the running state in which the control by the yaw rate feedback control means 30 should be performed, it is possible to prevent the running state from becoming unstable when shifting to the yaw rate feedback control, and to improve the connection of the control. Therefore, the steering angle restricting means 35 is such that the control switching means 33 selects the sideslip angle control means 31 or the fuzzy control means 32 and outputs a side slip angle control signal or Even fuzzy control signal has not been inputted, without outputting these signals, the yaw rate feedback control means 30, by outputting the yaw rate feedback control signal, which is output to the motor 24.

When the measured yaw rate Y (n) does not increase, the measured yaw rate Y (n) increases, but when the steering wheel 1 is not turned back, the measured yaw rate Y (n) increases.
(N) has increased, and the steering wheel 1 has been turned back. However, when the absolute value of the deviation E (n) is equal to or less than the predetermined value E0, or when the measured yaw rate Y (n) has increased, the steering wheel 1 has increased. And the absolute value of the deviation E (n) is also set to a predetermined value E0.
When the absolute value of the rate of change ΔE (n) of the deviation E (n) is equal to or less than the predetermined value ΔE2 and the rear wheel steering angle restriction signal is not output at the previous control timing. The control switching means 33 controls the steering angle θr of the rear wheels 3, 3 by any of the yaw rate feedback control means 30, the sideslip angle control means 31 and the fuzzy control means 32.
In order to determine whether (n) should be controlled, first, the deviation E
The change rate ΔE (n) of (n) is calculated, and the absolute value of the deviation E (n) is larger than a predetermined value E0 smaller than the predetermined value E0,
Further, it is determined whether or not the absolute value of the change rate ΔE (n) of the deviation E (n) is larger than a predetermined value ΔE1 smaller than the predetermined value ΔE2.

As a result, when YES, that is, when the absolute value of the deviation E (n) is larger than the predetermined value E0 and the absolute value of the rate of change ΔE (n) is smaller than the predetermined value ΔE1 smaller than the predetermined value ΔE2 When it is large, it is recognized that the vehicle is in a state corresponding to the area S3 in FIG. 5, the vehicle is in a very sharp turning state, an excessive oversteering tendency occurs, and the direction is rapidly changed. Therefore, when the steering angle θr (n) of the rear wheels 3, 3 is controlled by the yaw rate feedback control so that the vehicle runs stably, a large calculation speed is extremely high. Without the use of a computer, it is very difficult to follow the yaw rate change of the vehicle,
On the other hand, mounting such a large computer on a vehicle is uneconomical,
Since it is extremely difficult, in the present embodiment, in such a turning state, the control switching means 33 assumes that the steering angle θr (n) of the rear wheels 3, 3 is a turning state in which fuzzy control should be performed based on fuzzy theory. Judge, fuzzy control means 32
And outputs a control execution signal. Here, the reason why the predetermined value ΔE1 is set to a value smaller than the predetermined value ΔE2 is that, by setting a certain membership function, an excessive oversteer tendency tends to occur on a road having a significantly different road surface friction coefficient. It is difficult to improve the running stability while preventing the vehicle from moving. Therefore, when the vehicle is suddenly and largely changed in direction while traveling on a road having a high coefficient of road surface friction, the steering angle restricting means is used. By 35, the occurrence of an excessive oversteer tendency is prevented, and while the vehicle is traveling on a road having a road surface friction coefficient of medium or less, the vehicle suddenly and greatly increases
This is because when the direction is changed, the fuzzy control means 32 prevents an excessive tendency to oversteer.

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) approaches zero according to the following equation. Next, the fuzzy control amount Rf (n) is calculated, and a fuzzy control signal is output to the motor 24.

Rf (n) = f (E (n), ΔE (n)) In contrast, the absolute value of the deviation E (n) is not larger than the predetermined value E0. Alternatively, when the absolute value of the change rate ΔE (n) is not larger than the predetermined value ΔE1, 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. Is larger than a predetermined value β0.

When the result of the determination is YES, that is,
When the absolute value of the estimated value of the side slip angle β (n) is larger than the predetermined value β0, it is recognized that the vehicle is in the running state corresponding to the area S2 in FIG. 5, and the vehicle is in a sharp turning state in which the lateral acceleration GL (n) is large. And a large tire slip occurs, the turning radius of the vehicle increases, and the yaw rate Y
(N) is reduced, the steering angle θr of the rear wheels 3, 3
When (n) is controlled by the yaw rate feedback control, in order to compensate for a decrease in the yaw rate Y (n), the rear wheels 3, 3 are moved with respect to the steering angle θf (n) of the front wheels 2, 2. The vehicle may be steered in the opposite phase and the running stability may be reduced. On the other hand, the vehicle is not in an unstable running state in which the direction of the vehicle is rapidly changing so that fuzzy control must be performed. Therefore, the control switching unit 33 determines that the vehicle is in the turning state in which the sideslip angle control should be executed, and outputs a control execution signal to the sideslip angle control unit 31.

When receiving the control execution signal 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.
Output to the motor 24. Rβ (n) = k × β (n) where k is a control constant and has a positive value, and therefore, the sideslip angle The control amount Rβ (n) has a larger value as the sideslip angle β (n) is larger, and the sideslip angle β
As (n) is larger, the rear wheels 3, 3 are steered in the same phase direction as the front wheels 2, 2 so that the in-phase amount increases, so that the turning radius of the vehicle is larger and the yaw rate Y (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 surely reduced. Is prevented.

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. Is output.

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

According to the present embodiment, in the area 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 Y0 determined based on the steering angle of the steering wheel 1. (N), the rear wheels 3, 3 are steered so that the rear wheels 3, 3 can be steered as desired, while the estimated value of the sideslip angle β (n) Is larger than the predetermined value β0, and in a sharp turning state where the lateral acceleration GL is large, in the running state area S2 where the turning radius of the vehicle is large and the yaw rate Y (n) is low, the estimated value of the side slip angle is obtained. As β (n) is larger, the rear wheels 3, 3 are in the same phase direction as the front wheels 2, 2,
Since the sideslip angle control is performed so that the in-phase amount increases, the rear wheels 3 and 4 are controlled based on the yaw rate feedback control.
, The steering angle θr of the rear wheels 3, 3
(N) is in a direction opposite to the steering angle θf (n) of the front wheels 2, 2, so that running stability is prevented from lowering, and running stability can be improved. The vehicle
The absolute value of the deviation E (n) between the target yaw rate Y0 (n) and the actually measured yaw rate Y (n) and the change rate Δ of the deviation E (n)
The absolute value of E (n) is a predetermined value E0 and ΔE, respectively.
In an unstable running state area S3, which is larger than 1 and in which the vehicle is remarkably turning, in an extremely sharp turning state, an excessive oversteering tendency is likely to occur, the yaw rate Y (n) Since the steering angle θr of the rear wheels 3, 3 is fuzzy controlled so that the rate of change ΔY (n) approaches zero, the vehicle is in such a very sharp turning state without using a very large computer, and Even in a stable running state, running stability can be improved. Then, while traveling on a road with a small road surface friction coefficient, the target yaw rate Y0 (n) and the measured yaw rate Y
The absolute value of the deviation E (n) from (n) is larger than a predetermined value E0, and the absolute value of the rate of change ΔE (n) of the deviation E (n) is a predetermined value larger than the predetermined value ΔE1. If the fuzzy control means 32 having a membership function set for a road which is larger and has a road surface friction coefficient of medium or less is difficult to prevent spinning, the steering angle restricting means 35 From time t1 to time t2, the steering angle θr (n) of the rear wheels 3, 3 is set such that the steering amount of the rear wheels 3, 3 is maximized in the direction in which the measured yaw rate Y (n) becomes smaller. Since the restriction is imposed, regardless of the road surface friction coefficient, it is possible to prevent the occurrence of an excessive tendency of oversteering and to improve the running stability. Furthermore, after starting the regulation of the steering angle θr (n) of the rear wheels 3, 3 by the steering angle regulating means 35, the actually measured yaw rate Y
When (n) does not increase any more, it is determined that this is a precursor phenomenon that shifts to the yaw rate feedback control, and the control is immediately switched to the yaw rate feedback control regardless of the determination of the control switching means 33. When shifting to the yaw rate feedback control, it is possible to prevent the running of the vehicle from becoming unstable, and to realize well-connected control.

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 above embodiment, the steering angle restricting means 35 turns the steering wheel 1 to the target yaw rate Y0 (n) and the measured yaw rate Y (n) after the steering wheel 1 is operated to one side, and then the steering wheel 1 is turned back. Although Y0 (n) has started to decrease, the measured yaw rate Y (n) continues to increase due to control delay, and the deviation E (n) between the target yaw rate Y0 (n) and the measured yaw rate Y (n). ) Exceeds a predetermined value E0, and the rate of change ΔE (n) of the deviation E (n).
Is greater than the predetermined value ΔE2, the steering angle of the rear wheels 3, 3 is set such that the steering amount of the rear wheels 3, 3 is maximized in the direction in which the measured yaw rate Y (n) decreases. θr (n) is restricted, and when the measured yaw rate Y (n) exceeds the peak value and does not increase thereafter, the control switching means 33
Even if a control execution signal is output to the sideslip angle control means 31 or the fuzzy control means 32, the control immediately shifts to the yaw rate feedback control, but when the control shifts from the sideslip angle control or the fuzzy control to the yaw rate feedback control, If the running state is unlikely to become unstable, the control means selected by the control switching means 33 executes the steering angle control of the rear wheels 3, 3 when the actually measured yaw rate Y (n) starts to decrease. It is not always necessary to forcibly shift to the yaw rate feedback control.

In the above embodiment, if the absolute value of the estimated value β of the sideslip angle 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. 7 shows a flowchart for setting β0 based on the vehicle speed V and the lateral acceleration GL. In FIG. 7, β0 is determined by the side slip angle calculating means 34 based on the threshold value βt, the coefficient jv which is a function of the vehicle speed V, and the coefficient jg which is a function of the lateral acceleration GL, according to the following equation. It has become.

Β 0 = jv × jg × βt That is, first, the coefficient jv is determined based on 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. 7, 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. 6, 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.

Further, in the above-described embodiment, the yaw rate Y is detected by using the yaw rate sensor 42 as a 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 by 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 calculation formula of the estimated value of the sideslip angle β and the calculation formula of the target yaw rate Y0 are merely examples, and the estimated value β of the sideslip angle 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, the steering angle restricting means 35 determines that the absolute value of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y exceeds a predetermined value E0. The condition for executing the regulation of the steering angle θr (n) is set, and the fuzzy control means 32
The condition for executing the control of the steering angle θr (n) of the rear wheels 3, 3 is that the change rate ΔE of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y exceeds a predetermined value ΔE1. , Fuzzy control means 32, rear wheels 3, 3
Of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y is a predetermined value ΔE2 that is larger than the predetermined value ΔE1.
May be used as a condition for executing the regulation of the steering angle θr (n) of the rear wheels 3 and 3 by the steering angle regulating means 35, and the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y That the absolute value of the rear wheel exceeds the predetermined value E1 by the steering angle restricting means 35.
As a condition for executing the regulation (n), the fuzzy control means 32 determines that the absolute value of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y exceeds a predetermined value E2 different from the predetermined value E1. , Rear wheel 3, steering angle θr (n)
May be set as a condition for executing the above control.

Further, in the above embodiment, the absolute value of the deviation E between the target yaw rate Y0 and the actually measured yaw rate Y and the absolute value of the rate of change ΔE of the deviation E are both the predetermined value E0
When ΔE1 is greater than ΔE1, the steering angle control of the rear wheels 3, 3 is performed by fuzzy control. When one of them is greater than a predetermined value, steering control of the rear wheels 3, 3 by fuzzy control is performed. May be executed, and
In the above embodiment, 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,
Based on the target yaw rate Y0 and the measured yaw rate Y,
The membership function of the fuzzy control may be determined, 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 rate of change ΔE of the deviation E, the steering control of the rear wheels 3, 3 by fuzzy control may be executed in a state where the lateral acceleration GL exceeds a predetermined value. 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.

In the above embodiment, the steering angle θr (n) of the rear wheels 3, 3 is controlled by fuzzy control in the area S3 of FIG. 5, but the cornering force C.R. F. As shown in FIG. 5, the relationship between and the side slip angle changes depending on the road surface friction coefficient μ.
For example, when traveling on a road other than a road having a small road friction coefficient μ, only the regions S1 and S2 exist, and the region S3 does not exist. 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. 5, the area S2 in which the sideslip angle control is to be executed is extremely small, and the sideslip angle control is not performed temporally. Immediately, it may shift to fuzzy control.

[0058]

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 device provided with a yaw rate feedback control means for steering a rear wheel by feedback control, a sharp turn is performed while traveling on a road having a small coefficient of road surface friction without requiring a large computer. However, it is possible to provide a rear wheel steering device for a vehicle that can improve running stability.

[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 diagram showing a first half of a flowchart of a rear wheel steering angle control executed by a control unit.

FIG. 4 is a drawing showing a latter half of a flowchart of rear wheel steering angle control executed by the control unit.

FIG. 5 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. 6 is a graph showing a relationship between a target yaw rate, an actually measured yaw rate, a steering angle of a front wheel, and time.

FIG. 7 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 35 Steering angle regulating 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 133: 00 137: 00

Claims (9)

(57) [Claims] A turning state detecting means for physically detecting a turning state of a vehicle, and a feedback control 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 provided with a yaw rate feedback control unit that steers the vehicle, wherein the absolute value of a deviation between the target yaw rate and the actual yaw rate exceeds a predetermined value while the actual yaw rate is increasing,
And, when the absolute value of the rate of change of the deviation exceeds a predetermined value, regulating means for regulating the steering angle of the rear wheel so that the steering amount of the rear wheel is maximized in the direction in which the measured yaw rate is reduced. A rear wheel steering device for a vehicle, comprising: 2. In addition to the yaw rate feedback control means, a second control means for controlling a steering angle of a rear wheel based on a control law different from the yaw rate feedback control means, and a turning detected by the turning state detecting means. 2. The control device according to claim 1, further comprising: control switching means for switching control means for controlling a steering angle of a rear wheel to said second control means when the state is a steeper turning state than a predetermined turning state. A rear wheel steering device according to claim 1. 3. 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 sets the steering angle of the rear wheels in phase with the increase in the side slip angle estimated by the side slip angle estimating unit. The rear wheel steering device according to claim 2, wherein the control is performed in a direction. 4. The rear wheel of a vehicle according to claim 2, wherein the second control means performs fuzzy control of the steering angle of the rear wheel so that the rate of change of the actually measured yaw rate approaches zero. Steering gear. 5. The fuzzy control means performs fuzzy control of a steering angle of a rear wheel based on a deviation between the target yaw rate and the measured yaw rate such that a rate of change of the measured yaw rate approaches zero. The vehicle rear wheel steering device according to claim 4. 6. The fuzzy control means performs fuzzy control of a steering angle of a rear wheel based on a change rate of a deviation between the target yaw rate and the measured yaw rate so that the change rate of the measured yaw rate approaches zero. The vehicle rear wheel steering device according to claim 4, wherein the vehicle is configured as follows. 7. 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 sets a steering angle of a rear wheel in accordance with an increase in the side slip angle estimated by the side slip angle estimating unit. And the fuzzy control means for fuzzy controlling the steering angle of the rear wheel so that the rate of change of the actually measured yaw rate approaches zero, and the control switching means comprises: In a sharp turning state in which the turning state detected by the state detecting means exceeds the first predetermined turning state, control of a rear wheel steering angle is executed by the side slip angle control means, and the first predetermined turning is performed. The rear wheel steering angle is controlled by the fuzzy control means in a sharp turning state exceeding a second predetermined turning state which is steeper than a state. Rear wheel steering apparatus of the vehicle. 8. A control means for canceling the regulation of the steering angle of the rear wheel by the regulation means and controlling the rear wheel steering angle when the absolute value of the deviation between the measured yaw rate and the target yaw rate starts decreasing. 2. The rear wheel steering device according to claim 1, wherein the control unit switches to the yaw rate feedback control unit. 9. A steering angle sensor for detecting a steering angle of the steering wheel, wherein the regulating means increases the actually measured yaw rate after the sign of the rate of change of the steering angle of the steering wheel detected by the steering angle sensor changes. In the meantime, when the absolute value of the deviation between the target yaw rate and the actually measured yaw rate exceeds a predetermined value, and when the absolute value of the rate of change of the deviation exceeds a predetermined value, the measured yaw rate becomes smaller in the subsequent direction. The rear wheel steering device according to claim 1, wherein the steering angle of the rear wheel is regulated so that the steering amount of the wheel is maximized.