JP3040509B2 - 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, spin and the like are likely to occur, and unless a large-scale computer with a very fast calculation speed is used, it is not possible to follow the yaw rate change of the vehicle even if trying to feedback control the measured yaw rate to the target yaw rate. However, it is extremely difficult to steer the rear wheels by the yaw rate feedback control. However, it is extremely uneconomical to mount a computer capable of controlling the steering angle of the rear wheels by the yaw rate feedback control on the vehicle. In addition, there is a problem that space is extremely difficult.

[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 equipped with a yaw rate feedback control means for feedback-controlling the steering angle of a vehicle, even if lateral acceleration becomes extremely high and spin occurs, a large computer is not required and running stability can be improved. It is an object of the present invention to provide a rear wheel steering device for a vehicle that can improve the vehicle speed.

[0006]

The object of the present invention is to provide fuzzy control means for fuzzy controlling rear wheels so that the rate of change of the actually measured yaw rate is reduced, and that the turning state detected by the turning state detecting means is not less than a predetermined value. Achieved by providing control switching means for executing control by the fuzzy control means when the vehicle is in a sharp turning state, and performing control of the rear wheels by the yaw rate feedback control means in a turning state which is not sharper than a predetermined turning state. Is done.

In a preferred embodiment of the present invention, the fuzzy control means reduces the rate of change of the actually measured yaw rate based on a difference between the target yaw rate and the actually measured yaw rate and / or a rate of change of the difference. In addition, the rear wheels are configured to perform fuzzy control. In a further preferred aspect of the present invention, when the deviation between the target yaw rate and the actually measured yaw rate exceeds a predetermined value, and / or when a rate of change of the deviation exceeds a predetermined value. Then, the control of the rear wheels by the fuzzy control means is executed, and in other cases, the control of the rear wheels by the yaw rate feedback control means is executed.

[0008] In still another preferred embodiment of the present invention, there is further provided a side slip angle estimating means for estimating a side slip angle of the vehicle, and a rear wheel steering operation in accordance with an increase in the side slip angle estimated by the side slip angle estimating means. A side slip angle control unit for controlling the angle in the same phase direction, wherein the turning state detected by the turning state detection unit is a steep first turning state exceeding a first predetermined turning state; Is performed by the side slip angle control means, and the turning state detected by the turning state detecting means exceeds a second predetermined turning state which is steeper than the first predetermined turning state.
In the turning state, the control switching means is configured to switch the control means for controlling the steering angle of the rear wheel so that the control of the steering angle of the rear wheel is executed by the fuzzy control means. .

[0009]

According to the present invention, in a very sharp turning state in which the lateral acceleration exceeds a predetermined value, the steering angle of the rear wheels is reduced by the fuzzy control means so that the rate of change of the actually measured yaw rate is reduced. Since the fuzzy control is performed, even if the vehicle spins, the rate of change of the yaw rate decreases, so even in such an extremely unstable running state,
It is possible to improve running stability.

According to a preferred embodiment of the present invention, in a very sharp turning state in which the lateral acceleration exceeds a predetermined value, the fuzzy control means adjusts the steering angle of the rear wheel to the deviation between the target yaw rate and the actually measured yaw rate. And / or fuzzy control is performed on the basis of the rate of change of the deviation so that the rate of change of the actually measured yaw rate decreases. Therefore, even if the vehicle spins, the rate of change of the yaw rate decreases. Even in an unstable traveling state, traveling stability can be improved.

[0011] According to a further preferred aspect of the present invention, the control switching means is provided when the deviation between the target yaw rate and the actually measured yaw rate exceeds a predetermined value and / or the rate of change of the deviation exceeds a predetermined value. When the vehicle speed exceeds the threshold, the rear wheel is controlled by the fuzzy control unit. In other cases, the rear wheel is controlled by the yaw rate feedback control unit. Is reliably detected by the fuzzy control means so that the steering angle of the rear wheel is reduced based on the deviation between the target yaw rate and the actually measured yaw rate and / or the rate of change of the deviation, so that the rate of change of the actually measured yaw rate is reduced. Because the fuzzy control can be performed and the rate of change of the yaw rate decreases even if the vehicle spins, such an extremely unstable running state Oite also, it is possible to improve the running stability.

According to still another preferred embodiment of the present invention, when the turning state detected by the turning state detecting means is a steep first turning state exceeding the first predetermined turning state,
The control of the steering angle of the rear wheel is executed by the side slip angle control means, and the turning state detected by the turning state detecting means is:
In a second turning state exceeding a second predetermined turning state which is steeper than the first predetermined turning state, the control of the steering angle of the rear wheel is executed by the fuzzy control means.
From running conditions with low lateral acceleration to running conditions with high lateral acceleration,
Driving stability can be greatly improved.

[0013]

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, 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
Is the detection signal of the vehicle speed V (n) input from the vehicle speed sensor 40 and the steering angle θ of the front wheels input from the steering angle sensor 41
Based on f (n), a target yaw rate Y0 (n) is calculated, and a deviation E (n) between the target yaw rate Y0 (n) and the actually measured yaw rate Y (n) input from the yaw rate sensor 42 is calculated. , I-
The feedback control amount Rb (n) of the yaw rate Y (n) is calculated based on the PD control calculation formula, and is output to the control switching means 33. When a control execution signal is input from the control switching means 33, A feedback control signal is output to the motor 24.

The control switching means 33 provides a deviation E between the target yaw rate Y0 (n) input 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 deviation E (n) and the change rate ΔE (n) of the deviation E are calculated.
Output a control execution signal to the fuzzy control means 32 when the vehicle is in a turning state exceeding a predetermined deviation E0 and a predetermined change rate ΔE0 of the deviation, that is, in an extremely steep turning state, respectively, and outputs a deviation E (n ) And the rate of change ΔE (n) of the deviation E (n) are respectively equal to or smaller than the predetermined deviation E0 and the rate of change ΔE0 of the predetermined deviation, and the estimated value of the sideslip angle calculated by the sideslip angle calculating means 34. β
A turning state in which the absolute value of (n) exceeds a predetermined value β0,
That is, it is configured to output a control execution signal to the sideslip angle control means 31 during a sharp turning state, and to output a control execution signal to the yaw rate feedback control means 30 in other cases.

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 motor 24. When the control execution signal is input from the control switching means 33, the fuzzy control means 32 controls the yaw rate Y input from the yaw rate sensor 42.
The change rate ΔY (n) of the yaw rate Y (n) is calculated based on the detection signal of (n), and the change rate ΔY of the yaw rate Y (n) is calculated based on a calculation formula stored in advance.
The fuzzy control amount Rf (n) is set so that Y (n) decreases.
, And outputs a fuzzy control signal to the motor 24.

The slip angle calculating means 34 is provided with 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.

FIG. 3 is a flowchart of the steering angle control of the rear wheels 3, 3 executed by the control unit 29 configured as described above, and FIG. F. 6 is a graph showing the relationship between the slip angle and the slip angle. 3, first, the vehicle speed V (n) detected by the vehicle speed sensor 40, the steering angle θf (n) of the front wheels 2, 2 detected by the steering angle sensor 41, and the yaw rate Y (n) of the vehicle detected by the yaw rate sensor 42 And lateral acceleration sensor 4
The lateral acceleration GL (n) applied to the vehicle detected by No. 3 is input to the control unit 29.

Yaw rate feedback control means 30
Is based on the vehicle speed V (n) input from the vehicle speed sensor 40 and the steering angle θf (n) of the front wheels input from the steering angle sensor 41, according to the following equation, and the target yaw rate Y0 ( n) is calculated. 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 mounting is uneconomical and extremely difficult in terms of space, in this embodiment, based on fuzzy theory,
In order to control the steering angle θr (n) of the rear wheels 3, the control switching means 33 sends a control execution signal to the fuzzy control means 3.
Output to 2.

When the fuzzy control means 32 receives a control execution signal from the control switching means 33, the rate of change ΔY of the yaw rate Y (n) is based on the detection signal of the yaw rate Y (n) input from the yaw rate sensor 42. (N), and based on the membership function, which is a function of the deviation E (n) and the rate of change ΔE (n), the rate of change ΔY (n) of the yaw rate Y (n) decreases according to the following equation: Thus, 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 deviation E (n) is not larger than the predetermined deviation E0, or When the rate of change ΔE (n) is not greater than the predetermined rate of change ΔE0, the control switching means 33
Determines whether the absolute value of the estimated value of the sideslip angle β (n) input from the sideslip angle calculation means 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. 4, 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 significantly reduced, while the unstable running state in which the direction of the vehicle changes rapidly so that the fuzzy control must be performed. Therefore, the control switching means 33
Outputs a control execution signal to the sideslip angle control means 31 to cause the sideslip angle control means 31 to execute the sideslip angle control.

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 ), The rear wheels 3, 3 are steered in the opposite phase to the steering angle θf (n) of the front wheels 2, 2, and the running stability is greatly reduced. It is surely 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 by the yaw rate feedback control.
By turning the steering wheel 3, the steering angle θr of the rear wheels 3, 3 becomes
The steering angle θf (n) of the front wheels 2, 2 is in the opposite phase to the steering angle θf (n), so that the running stability is prevented from lowering, the running stability can be improved, and the target yaw rate Y0 ( n) and the deviation E (n) between the measured yaw rate Y (n)
And the rate of change ΔE (n) of the deviation E (n) are
In an extremely unstable running state area S3, which is larger than the predetermined value E0 and the predetermined value ΔE0, and is recognized as abruptly turning, and in which a spin is likely to occur, the actually measured yaw rate The steering angle θ of the rear wheels 3, 3 so that the rate of change ΔY (n) of Y (n) decreases.
Since r is fuzzy controlled, it is possible to improve running stability even in such an extremely unstable direction state without using a very large computer.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say, this is done. For example,
In the above embodiment, the steering angle of the rear wheels 3, 3 is controlled by the side slip angle control in the region S2 of FIG. 4, but the cornering force C.I. F. As shown in FIG. 4, the relationship between and the side slip angle varies depending on the road surface friction coefficient μ. Therefore, when traveling on a road with a small road surface friction coefficient μ, the range of the region S2 is extremely small, and The yaw rate feedback control is immediately performed without any side slip angle control,
If there is a transition to fuzzy control,
It is not always necessary to execute the sideslip angle control.

In the above-described 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 wheel 3, fuzzy control is executed. 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 the lateral acceleration GL and / or its change rate, or the steering angle θf and the steering angle θ.
f, the rate of change of the rate of change of the steering angle θf,
It may be determined.

Further, in the above-described embodiment, when the absolute value of the estimated value β of the sideslip angle becomes larger than the predetermined value β0, the control shifts from the yaw rate feedback control to the sideslip angle control. When the absolute value of the steering angle is larger than the predetermined value β0, the ratio between the steering angle θr of the rear wheels 3 and 3 and the steering angle θf of the front wheels 2 and 2 may be fixed, or the yaw rate up to that time may be fixed. Instead of the feedback control, a new yaw rate feedback control may be performed by reducing the control gain.

In the above embodiment, β0 is a constant value. However, β0 may be changed according to the vehicle speed V, the lateral acceleration GL, and the like. FIG. 5 shows a flowchart for setting β0 based on the vehicle speed V and the lateral acceleration GL. In the example of FIG. 5, 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 is supposed to be.

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. 5, 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. 5, β0 is set by the vehicle speed V and the lateral acceleration GL, but 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 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 detected by the steering angle sensor 41,
The yaw rate Y may be calculated on the basis of the steering angle θf of the second vehicle. The lateral acceleration GL may also be calculated without using the lateral acceleration sensor 43 and the vehicle speed V detected by the vehicle speed sensor 40 and the yaw rate Y of the steering angle sensor 41. The detected steering angle θ of the front wheels 2 and 2
You may make it calculate based on f.

The equation for calculating the estimated value of the sideslip angle β and the equation for calculating the target yaw rate Y0 are merely examples, and the estimated value of the sideslip angle β can be 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.

[0041]

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 of a vehicle including a yaw rate feedback control unit that feedback-controls a steering angle of a rear wheel, even if a lateral acceleration becomes extremely high and a spin occurs, the vehicle travels without a large computer. It is possible to provide a rear wheel steering device of a vehicle that can improve 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 flowchart of a rear wheel steering control executed by a control unit.

FIG. 4 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. 5 is a flowchart illustrating an example of a method of setting β0.

[Description of Signs] 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 sideslip angle control means 32 fuzzy control means 33 control switching means 34 sideslip angle calculation means 40 vehicle speed sensor 41 steering angle sensor 42 yaw rate sensor 43 lateral acceleration sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 13:00

Claims (6)

(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. In a rear-wheel steering device provided with a yaw rate feedback control means for performing feedback control, a fuzzy control means for fuzzy controlling a rear wheel and a turning state detection means for detecting rearward wheels so that a change rate of the actually measured yaw rate decreases. When the turning state is a sharp turning state equal to or more than a predetermined turning state, the control by the fuzzy control unit is executed, and in the turning state less than the predetermined turning state, the control by the rear wheel by the yaw rate feedback control unit is executed. A rear wheel steering device for a vehicle, comprising switching means. 2. The fuzzy control means is configured to perform fuzzy control of rear wheels based on a deviation between the target yaw rate and the measured yaw rate so that a rate of change of the measured yaw rate decreases. Claim 1
A rear wheel steering device according to claim 1. 3. The fuzzy control means is configured to perform fuzzy control on rear wheels based on a change rate of a deviation between the target yaw rate and the measured yaw rate so that a change rate of the measured yaw rate decreases. The vehicle rear wheel steering device according to claim 1, wherein: 4. The control switching means causes the fuzzy control means to execute control of a rear wheel when a deviation between the target yaw rate and the measured yaw rate exceeds a predetermined value, and in other cases, The rear wheel steering device according to claim 2, wherein the rear wheel control is performed by the yaw rate feedback control means. Wherein said control switching means, when the change rate of the deviation between the target yaw rate and the actual yaw rate exceeds a predetermined value, to execute the control of the rear wheels by the fuzzy control means, other 4. The rear wheel steering device according to claim 3 , wherein in the case of (1), the rear wheel control by the yaw rate feedback control means is executed. 6. A side slip angle estimating means for estimating a side slip angle of a vehicle, and a side slip angle control for controlling a steering angle of a rear wheel in the same phase with an increase in the side slip angle estimated by the side slip angle estimating means. A turning state detected by the turning state detecting means, in a steep first turning state exceeding a first predetermined turning state, control of a steering angle of a rear wheel is performed by the side slip angle control means. In the second turning state which is executed and the turning state detected by the turning state detecting means exceeds a second predetermined turning state which is steeper than the first predetermined turning state, the control of the steering angle of the rear wheel is performed. The control switching means is configured to switch control means for controlling a steering angle of a rear wheel so that the control means is executed by the fuzzy control means. Term A rear wheel steering device for a vehicle according to claim 1.