JP2963237B2 - 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 rear wheel steering device for a vehicle, and more particularly, to turning state detecting means for physically detecting a turning state of a vehicle, and detecting the turning state detecting means. Feedback control so that the measured yaw rate based on the detected value becomes the target yaw rate,
The present invention relates to a rear wheel steering device of a vehicle including a yaw rate feedback control means for controlling a steering angle of a rear wheel.

[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, since the rear wheel steering device of such a vehicle is generally designed to be understeered, when the vehicle turns sharply, the turning radius increases and the yaw rate decreases. Therefore, when the yaw rate feedback control is executed, the rear wheels are turned in the opposite phase to compensate for the decrease in the yaw rate. There was a problem of instability.

[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. The present invention provides a rear wheel steering device for a vehicle that includes a yaw rate feedback control unit that controls a steering angle of a rear wheel and that can improve running stability even in a sharp turning state. The purpose is to do so.

[0006]

According to the first aspect of the present invention, it is an object of the present invention to provide a slip angle estimating means for estimating a slip angle of a vehicle, and to increase the slip angle estimated by the slip angle estimating means. When the turning state detected by the turning state detecting means is a gentle turning state less than a predetermined turning state, the yaw rate feedback control means controls the rear wheel steering by the side slip angle controlling means for controlling the steering angle of the wheels in the same phase direction. Angle control is performed, and in a sharp turning state exceeding a predetermined turning state, the side slip angle control means controls the rear wheel steering angle so that the rear wheel steering angle is controlled. Switching control switching means, the control switching means, even in a traveling state in which the rear wheel steering angle should be controlled by the side slip angle control means,
The rear wheel steering angle calculated by the side slip angle control means,
This is achieved by a configuration in which the control means for controlling the steering angle of the rear wheels is not switched to the side slip angle control means until the rear wheel steering angle calculated by the yaw rate feedback control means is equal to or larger than the rear wheel steering angle.

[0007] According to the second aspect of the present invention, it is an object of the present invention to provide a slip angle estimating means for estimating a slip angle of a vehicle, and to increase the slip angle estimated by the slip angle estimating means, to increase the rear wheel angle. A side slip angle control unit that controls a steering angle in the same phase direction; and a turning state detected by the turning state detecting unit, in a gentle turning state that is less than a predetermined turning state, the yaw rate feedback control unit controls the rear wheel steering angle. The control is executed, and in a sharp turning state exceeding a predetermined turning state, the control for switching the control means for controlling the steering angle of the rear wheel by the side slip angle control means so that the control of the rear wheel steering angle is executed. Switching means,
When the control switching means switches the control means for controlling the steering angle of the rear wheels from the yaw rate feedback control means to the skid angle control means, the control means calculates the yaw rate feedback control means at the time of the switching. This is achieved by using the value of the rear wheel steering angle thus set as an initial value to control the steering angle of the rear wheels in the in-phase direction with the increase in the estimated side slip angle.

In a preferred embodiment of the present invention, the vehicle further includes a vehicle speed detecting means for detecting a vehicle speed, and a lateral acceleration detecting means for detecting a lateral acceleration applied to the vehicle in a lateral direction. When the control means for controlling the angle is switched from the yaw rate feedback control means to the side slip angle control means, the vehicle speed detected by the vehicle speed detection means is equal to or less than a predetermined value, and the lateral acceleration detected by the lateral acceleration detection means is In a traveling state equal to or less than a predetermined value, the side slip angle control means is configured to hold the value of the rear wheel steering angle at the value of the rear wheel steering angle calculated by the yaw rate feedback control means at the time of switching. .

In a further preferred aspect of the present invention, the apparatus further comprises 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 wherein the control switching means comprises The control means for controlling the steering angle of the rear wheel is switched to the fuzzy control means when a turning state which is steeper than the turning state is exceeded.

[0010]

According to the first aspect of the present invention, in a sharp turning state exceeding a predetermined turning state, the side slip angle control means increases the slip angle estimated by the slip angle estimating means to increase the rear wheel. Since the rudder angle is controlled in the same phase direction, an excessively reversed phase state is prevented from occurring, and it is possible to improve running stability. Over and over,
When the rear of the vehicle body is swung sideways and excessive oversteer occurs, the yaw rate becomes extremely high. Therefore, the value of the rear wheel steering angle calculated by the yaw rate feedback control means is calculated by the side slip angle control means. May be larger than the value of the rear wheel steering angle, and in such a case, the side slip angle control unit determines that the vehicle is in a running state in which the control of the rear wheel steering angle is to be executed. When the control is switched to the control of the rear wheel steering angle, the in-phase amount is reduced, and the yaw motion is further accelerated and the running state may become unstable. Even if the control of the rear wheel steering angle is to be executed by the side slip angle control unit, the control switching unit sets the rear wheel steering angle calculated by the side slip angle control unit to the yaw rate. Fed back to a higher wheel steering angle after being calculated by the control means, the control means for controlling the rear wheel steering angle, do not switched to the side slip angle control means,
By switching to the side slip angle control means, the running stability can be improved without reducing the in-phase amount.

According to the second aspect of the present invention, in a sharp turning state exceeding a predetermined turning state, the side slip angle control means increases the slip angle estimated by the slip angle estimating means, thereby increasing the rear wheel steering angle. Is controlled in the same phase direction, so that an excessively reversed phase state is prevented from occurring, it is possible to improve running stability, and furthermore, when turning, sudden acceleration or braking is applied. Then, if the rear of the vehicle body is shaken sideways and excessive oversteer occurs, the yaw rate becomes extremely high,
The value of the rear wheel steering angle calculated by the yaw rate feedback control means may be larger than the value of the rear wheel steering angle calculated by the side slip angle control means.
When the vehicle is switched to the control of the rear wheel steering angle by the side slip angle control means just because the vehicle is in a running state in which the control of the rear wheel steering angle should be executed by the side slip angle control means, the in-phase amount decreases conversely. Further, the yaw motion may be accelerated and the running state may become unstable.
The side slip angle control means controls the rear wheel steering angle in the in-phase direction with the value of the rear wheel steering angle calculated by the yaw rate feedback control means as an initial value at the time of switching, with an increase in the estimated side slip angle. , By switching to the sideslip angle control means,
The in-phase amount does not decrease, and the running stability can be improved.

According to a preferred embodiment of the present invention, a sudden acceleration or a braking operation is performed at the time of turning, so that the rear portion of the vehicle body is swung laterally, excessive oversteer occurs, and the yaw rate is extremely high. In a state where the vehicle speed is equal to or less than a predetermined value and the lateral acceleration is equal to or less than a predetermined value,
That is, when the vehicle is traveling on a road surface having a high coefficient of road friction at a low speed and the control of the rear wheel steering angle by the side slip angle control means is performed, loosening the accelerator pedal increases the grip force of the tire. If the steering wheel is not excessively steered temporarily and the steering wheel is not sharply turned, the running state may become unstable. However, in this embodiment, the rear wheel calculated by the yaw rate feedback control means is used. Since the value of the rear wheel steering angle is held at the value of the steering angle, it is possible to prevent the occurrence of an excessive understeer state temporarily and improve the running stability. Become.

According to a further preferred embodiment of the present invention, fuzzy control means for fuzzy controlling the steering angle of the rear wheel is provided so that the rate of change of the actually measured yaw rate approaches zero, and the control switching means includes: Since the control means for controlling the steering angle of the rear wheels is switched to the fuzzy control means when the vehicle turns over a steeper turning state than the predetermined turning state, when an excessive oversteer state occurs. In addition, it is possible to prevent a decrease in running stability.

[0014]

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

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

On the other hand, the rear wheel steering device 20 is 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
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
When the control execution signal is input from the
And outputs a feedback control signal.

Further, 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 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 ΔE0, 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 ΔE0, 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. Output an execution signal, and when the control signal is input from the sideslip angle control means 31 to the control suspension signal; and
In other cases, that is, in a normal turning state, a control execution signal is output to the yaw rate feedback control means 30.

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. Side slip angle control amount Rβ (n)
Is determined to be equal to or greater than the feedback control amount Rb (n) of the yaw rate Y input from the yaw rate feedback control means 30, and the side slip angle control amount Rβ (n) is less than the feedback control amount Rb (n) of the yaw rate Y. In the case of, a control hold signal is output to the control switching means 33,
When the side slip angle control amount Rβ (n) is equal to or larger than the yaw rate Y feedback control amount Rb (n), a side slip angle control signal is output to the motor 24.

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 the membership function stored in advance and the correction signal input from the function correction means 35, for example, the measured yaw rate Y (n) is set so that the rate of change ΔY (n) of the measured yaw rate Y (n) approaches zero. ) Is calculated, and the fuzzy control amount Rf (n) is calculated so that the absolute value of the change rate ΔY (n) decreases, and the fuzzy control signal is
4 is output.

The side slip angle calculating means 34 is provided with the 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.
Force C. 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 The lateral acceleration GL (n) applied to the vehicle detected by the lateral acceleration sensor 43 is input to the control unit 29.

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), the target yaw rate Y0 (n) at the control timing is calculated according to the following equation. Y0 (n) = V (n) / {1 + A · V (n) ² } × θf (n) / L where A is a stability factor and L Is the length of the wheel base.

Next, the yaw rate feedback control means 30 calculates the target yaw rate Y0 calculated in this way.
A 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 deviation E (n) of the yaw rate Y (n) calculated in this way.
Is output to the control switching means 33. The control switching means 33 determines which of the yaw rate feedback control means 30, the side slip angle control means 31, and the fuzzy control means 32 should control the steering angle θr (n) of the rear wheels 3, 3. First, the change rate ΔE (n) of the deviation E (n) is calculated, and the absolute value of the difference E (n) is larger than a predetermined value E0, and the change rate ΔE (n) of the deviation E (n) is calculated.
It is determined whether or not the absolute value of (n) is larger than a predetermined value ΔE0.

When the determination result is YES, that is, when the absolute value of the deviation E (n) is larger than the predetermined value E0,
When the absolute value of the change rate ΔE (n) is larger than the predetermined value ΔE0, the vehicle is in a state corresponding to the region S3 in FIG. 4, the vehicle is in a very sharp turning state, and excessive oversteer is occurring. Because it is in an unstable running state that it is recognized that it is changing direction suddenly,
When the steering angle θr (n) of the rear wheels 3 and 3 is controlled by the yaw rate feedback control so that the vehicle runs stably, the yaw rate change of the vehicle is performed unless a large computer having a very high calculation speed is used. It is extremely difficult to follow this, and on the other hand, mounting such a large computer in a vehicle is uneconomical and extremely difficult in terms of space. In such a turning state, the control switching means 33 controls the rear wheels 3, 3 based on fuzzy logic.
Is determined to be a turning state in which fuzzy control is to be performed for the steering angle θr (n), and a control execution signal is output to the fuzzy control means 32.

When the control execution signal is input from the control switching means 33, the fuzzy control means 32 determines the rate of change ΔY (Y) of the yaw rate Y (n) based on the detection signal of the yaw rate Y 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 change rate ΔE (n), the change rate ΔY (n) of the yaw rate Y (n) approaches zero according to the following equation. Thus, the fuzzy control amount Rf (n) is calculated,
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 ΔE0, the control switching unit 33 sets the absolute value of the estimated value β (n) of the sideslip angle input from the sideslip angle calculation unit 34. Is larger than a predetermined value β0.

As a result, when the absolute value of the estimated value of the sideslip angle β (n) is equal to or smaller than the predetermined value β0, the cornering force C.C. 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.

On the other hand, when the determination result is YES, that is, when the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0, it is determined that the vehicle is in the running state corresponding to the area S2 in FIG. It is recognized that the vehicle is in a sharp turning state in which the lateral acceleration GL (n) is large, a large tire slip occurs, the turning radius of the vehicle increases, and the yaw rate Y (n) decreases. Steering angle θ of rear wheels 3
r (n) is calculated by the yaw rate feedback control.
In the case of control, in order to compensate for the decrease in the yaw rate Y (n), 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 increased. However, the control switching means 33 is not in an unstable running state in which the direction of the vehicle is rapidly changing so that the vehicle must be subjected to the fuzzy control.
It is determined that the vehicle is in a turning state in which side slip angle control should be performed,
A control execution signal is output to the sideslip angle control means 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. 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) increases as the sideslip angle β (n) increases, and according to the sideslip angle control amount Rβ (n), the steering angle θr of the rear wheels 3, 3
By controlling (n), as the sideslip angle β (n) is larger, the rear wheels 3, 3 are steered in the same phase direction as the front wheels 2, 2 so that the amount of in-phase increases. In a running state in which the turning radius is large and the yaw rate Y (n) is reduced, the rear wheels 3, 3 are steered in the opposite phase to the steering angle θf (n) of the front wheels 2, 2. A decrease in running stability is reliably prevented.

However, when the rear of the vehicle body is shaken sideways due to rapid acceleration or braking during turning, and excessive oversteer occurs, the yaw rate Y (n) is extremely high. Therefore, the feedback control amount Rb (n) calculated by the yaw rate feedback control unit 30 may be larger than the sideslip angle control amount Rβ (n) calculated by the sideslip angle control unit 31, and in such a case, the sideslip may occur. When the vehicle is in the running state in which the control of the steering angle of the rear wheels 3 and 3 is to be executed by the angle control means 31 and the control is switched to the control of the rear wheel steering angle by the side slip angle control means 31, the in-phase amount becomes On the contrary, since the yaw motion is accelerated and the running state becomes unstable, the sideslip angle control means 31 further increases the sideslip angle control amount. beta (n) determines whether or not the feedback control amount Rb (n) or more.

As a result, in the case of YES, even if the mode is switched to the sideslip angle control, the amount of in-phase is reduced and there is no possibility that the yaw motion is accelerated. Is output to the motor 24. On the other hand, in the case of NO, when switching to the side slip angle control, the in-phase amount decreases, the yaw motion is accelerated, and the running state may become unstable.
The sideslip angle control unit 31 outputs a control suspension signal to the control switching unit 33 without outputting a sideslip angle control signal to the motor 24.

The control switching means 33 outputs a control execution signal to the yaw rate feedback control means 30 when receiving the control suspension signal from the side slip angle control means 31. When receiving the control execution signal from the control switching means 33, the yaw rate feedback control means 30 outputs a yaw rate feedback control signal to the motor 24, and according to the yaw rate feedback control amount Rb (n) calculated by the equation. , The motor 24 is rotated,
The rear wheels 3, 3 are steered.

The above control is executed at predetermined time intervals.
The rear wheels 3, 3 are steered. According to the present embodiment, in the region S1 where the running state of the vehicle is stable, the actually measured yaw rate Y (n) is determined by the yaw rate feedback control so that the target yaw rate Y determined based on the steering angle of the steering wheel 1.
Since the rear wheels 3, 3 are steered so as to be 0 (n),
The rear wheels 3, 3 can be steered as desired, while the turning radius of the vehicle in a sharp turning state in which the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0. Is large and the yaw rate Y (n) is low, the slip angle control means 31 causes the rear wheels 3, 3 to move toward the front wheels 2, 2 as the estimated slip angle β (n) increases. The sideslip angle control is performed in the same phase direction so that the in-phase amount increases. Therefore, by turning the rear wheels 3, 3 based on the yaw rate feedback control, the steering angle θr (n ) Is the steering angle θf of the front wheels 2, 2.
In contrast to (n), the running stability is prevented from lowering, and the running stability is prevented from lowering. As a result, the running yaw rate Y (n) and the target yaw rate Y0 (n) can be improved. The absolute value of the deviation E (n) and the deviation E
The absolute value of the rate of change ΔE (n) of (n) is larger than the predetermined values E0 and ΔE0, respectively, and the vehicle has an extremely overturning tendency that is excessively steered, which is recognized as rapidly changing direction. State, unstable running state area S
3, the steering angle θr of the rear wheels 3, 3 is fuzzy controlled so that the rate of change ΔY (n) of the yaw rate Y (n) approaches zero, so that the extremely large computer is not used. It is possible to improve running stability even in a sharp turning state and an unstable running state. Further, the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0, and the sideslip angle control means 31
The side slip angle control amount R
β (n) is the yaw rate feedback control amount Rb
(N) When it is less than, that is, when the vehicle suddenly accelerates during a turn or when braking is applied, the rear portion of the vehicle body is shaken sideways, excessive oversteer occurs, and the yaw rate becomes extremely high. In this state, the side slip angle control amount R
β (n) is the yaw rate feedback control amount Rb
Until the value becomes larger than (n), the control by the sideslip angle control means 31 is not performed, and the control by the yaw rate feedback control means 30 is performed.
By switching to the control by the side slip angle control means 31, the in-phase amount is further reduced, and it is possible to prevent the running state from becoming unstable due to the acceleration of the yaw movement.

FIG. 5 is a block diagram showing another embodiment of the control unit 29 for controlling the operation of the motor 24 and a traveling state detecting system provided in the vehicle. FIGS. 9 is a flowchart showing another embodiment of the steering angle control of the rear wheels 3 executed. In the embodiment of FIGS. 5, 6 and 7, when the sideslip angle control means 31 receives a control execution signal from the switching control means 33, the vehicle speed sensor 40
From the vehicle speed V (n) input from the vehicle, the detection signal of the lateral acceleration GL (n) input from the lateral acceleration sensor 43, and the feedback control amount Rb (n) input from the yaw rate feedback control means 30. Is the side slip angle control amount Rβ (n) by a different arithmetic expression.
Is calculated, and a side slip angle control signal is output to the motor 24.

That is, as shown in FIG. 6, the absolute value of the deviation E (n) becomes
If it is not greater than 0 or the absolute value of the change rate ΔE (n) is not greater than the predetermined value ΔE0, the control switching means 33 outputs the estimated value of the sideslip angle β (n ) Is determined to be greater than or equal to a predetermined value β0.

As a result, when the absolute value of the estimated value of the sideslip angle β (n) is equal to or smaller than the predetermined value β0, the control switching means 33 controls the yaw rate feedback control means 30 to control the yaw rate feedback control means 30 in the same manner as in the above embodiment. An execution signal is output, and the motor 24 outputs a feedback control signal based on the yaw rate feedback control amount Rb (n). On the other hand, the absolute value of the estimated value of the sideslip angle β (n) is equal to the predetermined value β.
When it is determined that the value is greater than 0, the control switching means 33
Outputs a control execution signal to the sideslip angle control means 31.

When receiving the control execution signal from the control switching means 33, the sideslip angle control means 31 controls the steering angles θr (n-1) of the rear wheels 3, 3 and the front wheels 2, 2 at the previous control timing. Steering wheel angle ratio r of steering wheel θf (n-1)
(N-1) is calculated, and then it is determined whether or not the vehicle speed V (n) is higher than a predetermined vehicle speed V0. As a result, YES
In other words, when the vehicle speed V (n) is higher than the predetermined vehicle speed V0, the sideslip angle control means 31 places importance on the running stability and controls the previous control timing, that is, immediately before shifting to the sideslip angle control. The steering angle θr (n−1) of the rear wheels 3, 3 obtained from the rear wheel steering angle ratio r (n−1) is changed to the minimum steering angle θr of the rear wheels 3, 3 at the current control timing.
(N) and the estimated value of the sideslip angle β
When (n) further increases, the steering angle θr (n) of the rear wheels 3, 3 increases at the same time, that is, so that the in-phase amount increases. Rear wheel steering angle ratio r of rear wheels 3, 3 and front wheels 2, 2
(N) is calculated according to the following equation.

R (n) = r (n−1) + C1 × [β (n) −β0) On the other hand, when the vehicle speed V (n) is equal to or lower than the predetermined vehicle speed V0, the side slip angle control is performed. The means 31 further includes a lateral acceleration sensor 43
It is determined whether or not the absolute value of the lateral acceleration GL (n) input from is larger than a predetermined value GL0. As a result, YES
In the case of, it is recognized that the vehicle is traveling on a road surface with a high coefficient of road surface friction, so sudden acceleration or braking is applied when turning, the rear part of the vehicle body is shaken sideways, and excessive oversteer occurs When the yaw rate becomes extremely high and the rear wheel steering angle is controlled by the skid angle control means while traveling on a road surface having a high coefficient of road friction at a low speed, if the accelerator pedal is released, the tire grip will be reduced. The force increases, temporarily leading to excessive understeer,
If the steering wheel 1 is not sharply cut, the running state may become unstable.
The sideslip angle control means 31 sets the rear wheel steering angle ratio r (n) this time to the previous control timing, that is, the sideslip angle control, so that the traveling direction of the vehicle and the direction of the vehicle match as much as possible. Rear wheel steering angle ratio r (n-1) immediately before shifting
To keep it.

On the other hand, when the answer is NO, it is recognized that the vehicle is traveling on a road surface having a low coefficient of road surface friction. Therefore, importance must be placed on traveling stability.
With emphasis on running stability, the previous control timing, that is, the rear wheel steering angle ratio r (n) immediately before shifting to the sideslip angle control
-1) Steering angle θr (n-1) of rear wheels 3, 3 obtained from
As the minimum steering angle θr (n) of the rear wheels 3 at the current control timing, and when the estimated value β (n) of the sideslip angle further increases, the The rear wheel steering angle ratio r () of the rear wheels 3, 3 and the front wheels 2, 2 at the current control timing is set so that the steering angle θr (n) of the wheels 3, 3 increases, that is, the in-phase amount increases. n) is calculated according to the following equation.

R (n) = r (n−1) + C2 × [β (n) −β0) When the rear wheel steering angle ratio r (n) is calculated in this manner, the side slip angle control is performed. The means 31 calculates the steering angle θr (n) of the rear wheels 3, 3 according to the equation, and outputs a side slip angle control signal to the motor 24. θr (n) = θf (n) × r (n) The above control is executed at predetermined time intervals, and the rear wheels 3, 3 are steered.

According to this embodiment, in the region S1 where the running 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) In a traveling state area S2 where the absolute value of is sharply larger than the predetermined value β0, the turning radius of the vehicle is large, and the yaw rate Y (n) is reduced,
The estimated value β of the sideslip angle is obtained by the sideslip angle control means 31.
The larger the value of (n) is, the more the rear wheels 3, 3 are controlled in the same direction as the front wheels 2, 2 in such a manner that the side slip angle control is performed in such a manner that the in-phase amount increases.
By turning the rear wheels 3, 3, the steering angle θr (n) of the rear wheels 3, 3 becomes larger than the steering angle θf (n) of the front wheels 2, 2.
The running stability is improved by preventing the running stability from lowering in the opposite phase direction. Further, the deviation E (n) between the target yaw rate Y0 (n) and the actually measured yaw rate Y (n) can be improved. )) And the rate of change ΔE of the deviation E (n)
The absolute value of (n) is a predetermined value E0 and ΔE0, respectively.
In an unstable running state area S3 in a very steep turning state in which the vehicle is excessively steered, which is recognized as being sharply turning, the rate of change ΔY () of the yaw rate Y (n) Since the steering angle θr of the rear wheels 3, 3 is fuzzy controlled so that n) approaches zero, the vehicle is in such an extremely sharp turning state and unstable running state without using a very large computer. Also, it is possible to improve running stability. Also,
Even when the absolute value of the estimated value of the sideslip angle β (n) is larger than the predetermined value β0, and the control by the sideslip angle control means 31 is to be executed, the yaw rate feedback control amount Rb ( n) if
In other words, when the rear of the vehicle body is swung laterally, as in the case of sudden acceleration during turning or braking, excessive oversteer occurs and the yaw rate is extremely high, the previous control timing That is, the rear wheels 3, which are obtained from the rear wheel steering angle ratio r (n-1) in the yaw rate feedback control immediately before shifting to the side slip angle control,
3, the steering angle θr (n−1) is guaranteed as the minimum rear wheel steering angle, and the vehicle speed V (n) is higher than the predetermined vehicle speed V0.
Further, in a traveling state in which traveling stability is important where the vehicle speed V (n) is equal to or lower than the predetermined vehicle speed V0 and the lateral acceleration GL (n) is equal to or lower than the predetermined value GL0, the estimated side slip angle β ( As the steering angle θr (n) of the rear wheels 3 and 3 increases with the increase of n), that is, the in-phase amount increases so that the rear wheels 3 and 3
3 is steered, so if you suddenly accelerate during turning,
As if braking, the rear of the car was swung,
When excessive oversteer occurs and the yaw rate is extremely high and the system shifts to skid angle control, the in-phase amount decreases and the yaw motion is further accelerated.
It is possible to prevent the running state from becoming unstable, to improve the running stability, and to improve the vehicle speed V.
(N) is equal to or lower than the predetermined vehicle speed V0 and the lateral acceleration GL
In the traveling state where (n) is larger than the predetermined value GL0,
The steering angle θr (n) of the rear wheels 3, 3 is determined by the previous control timing, that is, the steering angle θr of the rear wheels 3, 3 in the yaw rate feedback control immediately before shifting to the side slip angle control.
Since (n-1) is maintained, when the accelerator pedal is released, the vehicle temporarily becomes in an excessive understeer state, and the running state becomes unstable unless the steering wheel 1 is kept turned. In addition, it is possible to effectively prevent this.

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, β0 is a constant value,
0 may be changed according to the vehicle speed V, the lateral acceleration GL, and the like. FIG. 8 shows a flowchart for setting β0 based on the vehicle speed V and the lateral acceleration GL. In FIG. 8, 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. Has become.

Β0 = jv × jg × βt That is, first, the coefficient jv is determined by 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. 8, 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. 8, β0 is set by the vehicle speed V and the lateral acceleration GL. However, β0 may be set by adding other operation parameters, or β0 may be set by other operation parameters. You may make it set.

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

In the above embodiment, when the 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 larger than the predetermined values E0 and ΔE1, The steering angle control of the rear wheels 3 and 3 is executed by the control.
When it is larger than the predetermined value, the rear wheels 3 by fuzzy control,
3 may be executed, and in the above-described embodiment, the membership function of the fuzzy control is based on the deviation E0 between the target yaw rate Y0 and the actually measured yaw rate Y.
And the rate of change ΔE of the deviation E, the membership function of the fuzzy control may be determined based on the target yaw rate Y0 and the actually measured yaw rate Y, and the deviation E or the rate of change ΔE of the deviation E may be determined. One function may be used. Further, instead of the deviation E or the change rate ΔE of the deviation E, the steering angle control of the rear wheels 3, 3 by the fuzzy control may be executed in a state where the lateral acceleration GL (n) exceeds a predetermined value. Further, the membership function of the fuzzy control includes the lateral acceleration GL (n) and / or its rate of change, or the steering angle θf of the front wheels 2, the rate of change of the steering angle θf, and the rate of change of the steering angle θf. The determination may be made based on the change rate.

Further, in the above embodiment, the rear wheels 3, 3 are controlled by fuzzy control in the area S3 of FIG.
Of the tire cornering force C. F. Fig. 4 shows the relationship between
As shown in the figure, since it changes depending on the road surface friction coefficient μ, when traveling on a road other than a road having a small road surface friction coefficient μ, only the regions S1 and S2 exist, and the region S
3 does not exist, and therefore, it may not always be necessary to execute the fuzzy control. On the other hand, when the vehicle travels on a road with a small road surface friction coefficient μ, as shown in FIG. Is very small, and it is possible that the control immediately shifts to the fuzzy control without performing the skid angle control temporally.

Further, in the present invention, each means does not necessarily indicate a physical means, and when the function of one means is realized by two or more physical means, The invention also covers the case where the function of the means is realized by one physical means.

[0053]

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 controls a steering angle of a rear wheel by feedback control, a rear wheel steering device of a vehicle that can improve running stability even in a sharp turning state. Can be provided.

[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 angle 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 block diagram showing another embodiment of the traveling state detection system provided in the control unit and the vehicle.

FIG. 6 is a drawing showing the first half of a flowchart showing another embodiment of the rear wheel steering angle control executed by the control unit.

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

FIG. 8 is a flowchart illustrating an example of a method of setting β0.

[Explanation of symbols]

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

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-77360 (JP, A) JP-A-63-192667 (JP, A) JP-A-3-57771 (JP, A) JP-A-3-7771 135873 (JP, A) JP-A-1-262268 (JP, A) JP-A-3-7675 (JP, A) JP-A-60-191876 (JP, A) JP-A-2-20476 (JP, A) JP-A-62-218281 (JP, A) JP-A-3-74280 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B62D 6/00

Claims (4)

(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. In a rear wheel steering device provided with a yaw rate feedback control means for controlling a steering angle of a vehicle, a side slip angle estimating means for estimating a side slip angle of the vehicle, and an increase in the side slip angle estimated by the side slip angle estimating means A side slip angle control unit that controls the steering angle of the rear wheels in the same phase direction; and a turning state detected by the turning state detecting unit, when the turning state is less than a predetermined turning state, the yaw rate feedback control unit performs rearward turning. The control of the wheel steering angle is executed, and in a sharp turning state exceeding a predetermined turning state, the side slip angle control means As the control of the rear wheel steering angle is executed,
Control switching means for switching control means for controlling the steering angle of the rear wheel, wherein the control switching means controls the side slip angle even in a running state in which the control of the rear wheel steering angle is to be performed by the side slip angle control means. Until the rear wheel steering angle calculated by the means is equal to or larger than the rear wheel steering angle calculated by the yaw rate feedback control means, the control means for controlling the steering angle of the rear wheel is not switched to the side slip angle control means. A rear wheel steering device for a vehicle, comprising: 2. 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. In a rear wheel steering device provided with a yaw rate feedback control means for controlling a steering angle of a vehicle, a side slip angle estimating means for estimating a side slip angle of the vehicle, and an increase in the side slip angle estimated by the side slip angle estimating means A side slip angle control unit that controls the steering angle of the rear wheels in the same phase direction; and a turning state detected by the turning state detecting unit, when the turning state is less than a predetermined turning state, the yaw rate feedback control unit performs rearward turning. The control of the wheel steering angle is executed, and in a sharp turning state exceeding a predetermined turning state, the side slip angle control means As the control of the rear wheel steering angle is executed,
Control switching means for switching control means for controlling the steering angle of the rear wheel, wherein the control switching means switches the control means for controlling the steering angle of the rear wheel from the yaw rate feedback control means to the side slip angle control means. At the time of switching, the side slip angle control unit sets the rear wheel steering angle calculated by the yaw rate feedback control unit as an initial value, and sets the rear wheel steering angle in phase with the increase in the estimated side slip angle. A rear-wheel steering device for a vehicle, which is configured to control in a direction. 3. A vehicle control apparatus comprising: vehicle speed detecting means for detecting a vehicle speed; and lateral acceleration detecting means for detecting a lateral acceleration applied to the vehicle in a lateral direction, wherein the control switching means includes a control means for controlling a steering angle of a rear wheel. When switching from the yaw rate feedback control means to the side slip angle control means, when the vehicle speed detected by the vehicle speed detection means is equal to or less than a predetermined value, and the lateral acceleration detected by the lateral acceleration detection means is less than or equal to a predetermined value, the traveling state. 3. The vehicle according to claim 2, wherein the side slip angle control unit holds the value of the rear wheel steering angle at the value of the rear wheel steering angle calculated by the yaw rate feedback control unit at the time of switching. Rear wheel steering device. 4. 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, wherein the control switching means changes the turning state more sharply than the predetermined turning state. 4. The rear wheel steering device according to claim 1, wherein the control means for controlling the steering angle of the rear wheel is switched to the fuzzy control means when the vehicle speed exceeds the threshold value.