JP3027223B2 - 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, the vehicle tends to oversteer and tends to follow the yaw rate change of the vehicle, even if the actual yaw rate is feedback controlled so that it becomes the target yaw rate, unless a large-scale computer with a very fast calculation speed is used. 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. Thereby, in the rear wheel steering device having the yaw rate feedback control means for steering the rear wheels, the running stability can be improved even if the road surface conditions are different, without requiring a large-sized computer. It is an object of the present invention to provide a vehicle rear wheel steering device.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide 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, and the absolute value of the deviation between the target yaw rate and the measured yaw rate. The control means for controlling the steering angle of the rear wheel when the deviation exceeds a predetermined deviation and / or when the absolute value of the rate of change of the deviation between the target yaw rate and the actually measured yaw rate exceeds the predetermined rate of change; This is achieved by providing control switching means for switching to means, and critical value setting means for setting a predetermined deviation and / or a predetermined change rate according to road surface conditions.

[0007] In an embodiment of the present invention, the fuzzy controller controls the fuzzy control so that the rate of change of the measured yaw rate approaches zero based on a deviation between the target yaw rate and the measured yaw rate and / or a rate of change of the deviation. The steering angle of the rear wheels is configured to be fuzzy controlled. In a first preferred embodiment of the present invention, the critical value setting means is configured to set the predetermined deviation and / or the predetermined change rate to be smaller as the road surface friction coefficient becomes smaller.

[0008] In a second preferred embodiment of the present invention, the critical value setting means sets the predetermined deviation and / or the predetermined rate of change such that the lateral acceleration applied to the vehicle in the lateral direction decreases. It is configured as follows. In a first more preferred embodiment of the present invention, the critical value setting means further includes a membership function of the fuzzy control means such that the steering angle control amount of the rear wheels increases as the road surface friction coefficient decreases. Is corrected.

In a second more preferred embodiment of the present invention, the critical value setting means further controls the rear wheel steering angle control amount to increase as the lateral acceleration applied in the lateral direction of the vehicle decreases. , Is configured to correct the membership function of the fuzzy control means. In a third more preferred embodiment of the present invention,
A side slip angle estimating means for estimating a side slip angle of the vehicle, and a sideslip angle control means for controlling the steering angle of the rear wheels in the same phase direction with an increase in the sideslip angle estimated by the sideslip angle estimating means; In a state where the absolute value of the deviation from the measured yaw rate does not exceed a predetermined deviation, and / or in a state where the absolute value of the change rate of the deviation between the target yaw rate and the measured yaw rate does not exceed the predetermined change rate, The control switching means is configured to switch the control means such that the control of the rear wheel steering angle is performed by the sideslip angle control means when the sideslip angle estimated by the above exceeds the predetermined sideslip angle. I have.

In the present specification, it is defined that the critical value setting means sets the predetermined deviation and / or the predetermined change rate to be smaller as the road surface friction coefficient becomes smaller.
When the predetermined deviation and / or the predetermined change rate is set to decrease linearly as the road surface friction coefficient decreases, the predetermined deviation and / or the predetermined change rate nonlinearly increase as the road surface friction coefficient decreases. When the road surface friction coefficient is set to be large, the predetermined deviation and / or the predetermined change rate are constant within a certain range, and the predetermined deviation and / or predetermined value are reduced as the road surface friction coefficient decreases in other ranges. The case where the rate of change is set to increase linearly or nonlinearly is included.

In the present specification, the critical value setting means sets the predetermined deviation and / or the predetermined rate of change to be smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. When the predetermined deviation and / or the predetermined rate of change are set to decrease linearly as the value decreases, the predetermined deviation and / or the predetermined rate of change are set to increase nonlinearly as the lateral acceleration decreases. When the lateral acceleration is within a certain range, the predetermined deviation and / or the predetermined rate of change are constant, and in other ranges, the predetermined deviation and / or the predetermined rate of change linearly decrease as the lateral acceleration decreases. Alternatively, a case where the value is set to be non-linearly large is included.

Further, in the present specification, correcting the membership function of the fuzzy control means means that the fuzzy control means has a single membership function, and the threshold value setting means determines the membership function of the fuzzy control means. Not only when correcting the part and / or the consequent part, the fuzzy control means has a plurality of membership functions of different antecedent parts and / or the consequent parts, and the critical value setting means is adapted to respond to the road surface condition. In addition, a case where a specific membership function is selected from among them is also included.

In this specification, correcting the membership function of the fuzzy control means so that the steering angle control amount of the rear wheels increases as the road surface friction coefficient decreases means that the road surface friction coefficient decreases. According to
When the membership function of the fuzzy control means is corrected so that the rear wheel steering angle control amount increases linearly, the rear wheel steering angle control amount increases nonlinearly as the road surface friction coefficient decreases. As described above, when correcting the membership function of the fuzzy control means, as the road surface friction coefficient is within a certain range, the steering angle control amount of the rear wheels is constant, and in other ranges, as the road surface friction coefficient becomes smaller, The case where the membership function of the fuzzy control means is corrected so that the steering angle control amount of the rear wheels increases linearly or nonlinearly is included.

Further, in this specification, correcting the membership function of the fuzzy control means so that the steering angle control amount of the rear wheels increases as the lateral acceleration applied to the vehicle in the lateral direction decreases. When correcting the membership function of the fuzzy control means so that the steering angle control amount of the rear wheel increases linearly as the acceleration decreases, the steering angle control amount of the rear wheel decreases as the lateral acceleration decreases. When the membership function of the fuzzy control means is corrected so that is increased nonlinearly, when the lateral acceleration is within a certain range, the steering angle control amount of the rear wheel is constant, and in other ranges, the lateral acceleration is small. As the case may be, the membership function of the fuzzy control means is corrected so that the steering angle control amount of the rear wheels increases linearly or nonlinearly. For free.

[0015]

According to the present invention, when the absolute value of the deviation between the target yaw rate and the actually measured yaw rate exceeds a predetermined deviation,
And / or when the absolute value of the rate of change of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined rate of change, the fuzzy control means controls the rear wheel steering angle so that the rate of change of the measured yaw rate approaches zero. Is fuzzy controlled, so even if an excessive oversteering tendency occurs, the absolute value of the rate of change of the yaw rate decreases, so it is possible to improve the running stability even in such an unstable running state In addition, since the predetermined deviation and / or the predetermined change rate are set by the critical value setting means according to the road surface condition, the running stability can be always improved even if the road surface condition is different.

According to the embodiment of the present invention, the fuzzy control means controls the rear wheels based on the deviation between the target yaw rate and the measured yaw rate and / or the rate of change of the deviation so that the rate of change of the measured yaw rate approaches zero. Since the steering angle is fuzzy controlled, the lateral acceleration increases while traveling on a road surface with a low coefficient of friction, and if the steering angle of the rear wheels is controlled by yaw rate feedback control, excessive oversteering tends to occur. It is possible to reliably prevent the occurrence of an excessive oversteering tendency in a sharp turning state in which there is a high risk of occurrence, and to improve running stability even in such a turning state.

According to a first preferred embodiment of the present invention, the critical value setting means is configured to set the predetermined deviation and / or the predetermined change rate to be smaller as the road surface friction coefficient becomes smaller. Therefore, when the vehicle turns while traveling on a road with a low coefficient of road surface friction, the measured yaw rate can be immediately converged to the target yaw rate, and therefore, it is possible to improve the running stability, When turning on a road with a large coefficient of road surface friction, the measured yaw rate can be made to gradually converge to the target yaw rate, so that vibrations can be prevented from occurring in the vehicle, and riding comfort and running stability can be reduced. It is possible to achieve both.

According to a second preferred embodiment of the present invention, the critical value setting means sets the predetermined deviation and / or the predetermined change rate as the lateral acceleration applied in the lateral direction of the vehicle decreases. Therefore, when the vehicle turns while traveling on a road with a low coefficient of road friction and a small lateral acceleration, the measured yaw rate can be immediately converged to the target yaw rate. On the other hand, when the vehicle turns while traveling on a road having a large coefficient of road surface friction and a large lateral acceleration, the measured yaw rate can be gradually made to converge to the target yaw rate. This makes it possible to achieve both riding comfort and running stability.

According to a first more preferred embodiment of the present invention, the critical value setting means further includes a fuzzy control means such that the steering angle control amount of the rear wheels increases as the road surface friction coefficient decreases. Is configured so as to correct the membership function, the measured yaw rate can be made to converge more quickly to the target yaw rate when the vehicle turns while traveling on a road with a small coefficient of road surface friction. On the other hand, when the vehicle turns while traveling on a road with a large coefficient of road surface friction, the measured yaw rate can be gradually converged to the target yaw rate, so that vibration occurs in the vehicle. Can be more reliably prevented, and it is possible to achieve both riding comfort and running stability.

According to a second more preferred embodiment of the present invention, the critical value setting means further controls the rear wheel steering angle control amount to increase as the lateral acceleration applied in the lateral direction of the vehicle decreases. In addition, since it is configured to correct the membership function of the fuzzy control means, while traveling on a road having a small road surface friction coefficient and a small lateral acceleration,
When the vehicle turns, the measured yaw rate can be made to converge more quickly to the target yaw rate, so that the running stability can be improved.
When the vehicle turns while traveling on a road having a large coefficient of road friction and a large lateral acceleration, the measured yaw rate can be gradually converged to the target yaw rate, so that the occurrence of vibration in the vehicle can be more reliably prevented. Thus, it is possible to achieve both riding comfort and running stability.

According to a third more 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 the rear wheels are increased with an increase in the side slip angle estimated by the side slip angle estimating means. A state in which the absolute value of the deviation between the target yaw rate and the measured yaw rate does not exceed a predetermined deviation, and / or a change in the deviation between the target yaw rate and the measured yaw rate. In a state where the absolute value of the rate does not exceed the predetermined change rate, when the sideslip angle estimated by the sideslip angle estimation means exceeds the predetermined sideslip angle,
The control switching unit is configured to switch the control unit so that the control of the rear wheel steering angle is performed by the side slip angle control unit. Driving stability can be greatly improved.

[0022]

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 running state detecting 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 that calculates an estimated value β of the sideslip angle, and a critical value setting. Means 35 for detecting the vehicle speed V, the steering angle of the steering wheel 1, that is, the front wheels 2, 2
Detection signals from a steering angle sensor 41 for detecting the steering angle θf of the vehicle, a yaw rate sensor 42 as turning state detecting means for detecting a yaw rate Y of the vehicle, and a lateral acceleration sensor 43 for detecting a lateral acceleration GL applied to the vehicle. I have.

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 a turning state exceeding the predetermined deviation E0 and the predetermined change rate ΔE0, that is, in a very steep turning state, a control execution signal is output to the fuzzy control means 32 and the function critical value setting means 35, and the deviation E ( The absolute value of n) and the absolute value of the change rate ΔE (n) of the deviation E (n) are equal to or smaller than the predetermined deviation E0 and the predetermined change rate ΔE0, respectively, and the sideslip angle calculated by the sideslip angle calculation means 34. Estimate β
A turning state in which the absolute value of (n) exceeds a predetermined value β0,
That is, a control execution signal is output to the side slip angle control means 31 during a sharp turning state, and a control execution signal is output to the yaw rate feedback control means 30 in other cases, that is, during a normal turning state. Is configured.

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, the membership function stored in advance and the Based on the setting signal input from the function critical value setting means 35, the change rate ΔY (n) of the actually measured yaw rate Y (n) approaches, for example, the change rate ΔY of the actually measured yaw rate Y (n).
The absolute value of (n) is calculated, and the fuzzy control amount Rf (n) is calculated so that the absolute value decreases, and a fuzzy control signal is output to the steering angle regulating means 35.

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.

The critical value setting means 35 includes the lateral acceleration sensor 4
3, a predetermined deviation E0 and a predetermined change rate ΔE0 are calculated based on the lateral acceleration GL (n) inputted from the third embodiment according to a map or a table stored in advance, and a setting signal is output to the control switching means 33. . FIG.
4 is a flowchart of steering angle control of the rear wheels 3 and 3 executed by the control unit 29 configured as described above, and FIG. 5 is a flowchart of tire cornering force C.R. F. 6 is a graph showing the relationship between the slip angle and the slip angle.

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 and 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. Next, based on the lateral acceleration GL (n) input from the lateral acceleration sensor 43, the critical value setting means 35 calculates a predetermined deviation E0 and a predetermined change rate ΔE0 according to a map, a table, or the like stored in advance. Is output to the control switching means 33.

FIG. 6 shows an example of a map for calculating the predetermined deviation E0 and the predetermined change rate ΔE0 stored in the critical value setting means 35. As shown in FIG. The map is determined such that the calculated predetermined deviation E0 and predetermined change rate ΔE0 decrease linearly as (n) decreases. The control switching means 33 includes the yaw rate feedback control means 3
0, sideslip angle control means 31 or fuzzy control means 3
2, the steering angle θr of the rear wheels 3, 3
In order to determine whether (n) should be controlled, first, the deviation E
The change rate ΔE (n) of (n) is calculated, and the critical value setting means 3
5 and the predetermined change rate ΔE0
, It is determined whether the absolute value of the deviation E (n) is larger than the predetermined deviation E0 and whether the absolute value of the change rate ΔE (n) of the deviation E (n) is larger than the predetermined change rate ΔE0. .

When the determination result is YES, that is, when the absolute value of the deviation E (n) is larger than the predetermined deviation E0 and the absolute value of the change rate ΔE (n) is equal to the predetermined change rate Δ
When it is larger than E0, the vehicle moves to the region S3 in FIG.
The vehicle is in a very sharp turning state, and has an excessive oversteering tendency, and is in an unstable running state in which it is recognized that the direction is suddenly changed, so that the yaw rate feedback is performed. When the steering angle θr (n) of the rear wheels 3, 3 is controlled by the control so that the vehicle runs stably, it follows the yaw rate change of the vehicle unless a large-scale computer having a very high calculation speed is used. It is extremely difficult to mount such a large computer on a vehicle, and it is uneconomical and extremely difficult in terms of space. In such a turning state, the control switching means 33 determines that the steering angle θr (n) of the rear wheels 3, 3 is a turning state in which fuzzy control is to be performed based on fuzzy theory. Then, the fuzzy control means 32
Outputs a control execution signal.

When the control execution signal is input from the control switching means 33, the fuzzy control means 32 determines the rate of change ΔY () 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 the absolute value and deviation E of the deviation E (n) between the measured yaw rate Y (n) and the target yaw rate Y0 (n).
A judgment is made in the antecedent part as to whether the absolute value of the change rate ΔE (n) of (n) is large, and a function of the deviation E (n) and the change rate ΔE (n) is determined according to the judgment. Based on the membership function and the setting signal input from the function critical value setting means 35, the fuzzy control amount Rf () is calculated according to the following equation so that the rate of change ΔY (n) of the yaw rate Y (n) approaches zero. n) and outputs a fuzzy control signal to the motor 24.

Rf (n) = f (E (n), ΔE (n)) As shown in FIG. 6, the predetermined deviation E0 and the predetermined change rate ΔE0 are Each is set so as to decrease linearly as the lateral acceleration GL (n) decreases, so that as the lateral acceleration GL (n) decreases, the measured yaw rate Y (n) and the target yaw rate Y0
The fuzzy operation is performed such that the absolute value of the deviation E (n) from the difference (n) and the absolute value of the change rate ΔE (n) of the deviation E (n) are small and the change rate of the actually measured yaw rate Y (n) is reduced. In a running state in which the rear wheels 3 and 3 are largely steered by the control means 32 and the road surface friction coefficient is low and the lateral acceleration GL (n) is small, the actually measured yaw rate Y (n) becomes equal to the target yaw rate. Y0 (n) quickly converges, and therefore, in a running state where such running stability is important,
The traveling stability can be sufficiently improved by preventing the oversteering tendency from being excessively large. On the other hand, when traveling on a road having a high road surface friction coefficient and the lateral acceleration GL (n) is large, When the rear wheels 3, 3 are steered by the fuzzy control means 32 so that the measured yaw rate Y (n) quickly converges to the target yaw rate Y0 (n),
Although vibration occurs in the vehicle and the riding comfort deteriorates, in the present embodiment, as the lateral acceleration GL (n) increases, the predetermined deviation E0 and the predetermined change rate ΔE0 are set to large values. The convergence speed of the yaw rate Y (n) to the target yaw rate Y0 (n) is low, and
In such a running state, it is possible to achieve both riding comfort and running stability.

On the other hand, the absolute value of the deviation E (n) is
Not greater than the predetermined deviation E0, or the rate of change ΔE
When the absolute value of (n) is not larger than the predetermined change rate ΔE0, the control switching unit 33 sets the sideslip angle calculation unit 34
It is determined whether or not the absolute value of the estimated value of the sideslip angle β (n) input from is larger than a predetermined value β0. When the determination result is YES, that is, the estimated value β of the sideslip angle
When the absolute value of (n) is larger than the predetermined value β0,
It is recognized that the vehicle is in a running state corresponding to the area S2, and 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 increases. Since the steering angle θr (n) of the rear wheels 3, 3 is controlled by the yaw rate feedback control because the Y (n) is reduced, the rear wheels are compensated for the reduction of the yaw rate Y (n). The steering wheels 3 and 3 may be steered in a direction opposite to the steering angle θf (n) of the front wheels 2 and 2 to reduce running stability.
The control switching means 33 determines that the vehicle is in a turning state in which the side slip angle control should be executed, since the vehicle is not in an unstable traveling state in which the direction of the vehicle is rapidly changing as much as the fuzzy control is required. , Side slip angle control means 31
And outputs a control execution signal.

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 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) 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)
When the absolute value of E (n) is larger than the predetermined deviation E0 and the predetermined change rate ΔE0, respectively, there is a possibility that an excessive oversteering tendency occurs in a very steep turning state in which the vehicle is recognized to be turning suddenly. In the unstable running state area S3 where the yaw rate Y (n) is large,
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 without using a very large computer. Even in the state, it is possible to improve running stability. In addition, the deviation E between the target yaw rate Y0 (n) and the actually measured yaw rate Y (n)
The absolute value of (n) and the rate of change ΔE (n) of the deviation E (n)
Are larger than a predetermined deviation E0 and a predetermined change rate ΔE0, respectively, a predetermined deviation E0 and a predetermined change rate ΔE0 at which fuzzy control is executed are determined by the lateral acceleration GL
As the lateral acceleration GL (n) becomes smaller, the absolute value of the deviation E (n) between the target yaw rate Y0 (n) and the actually measured yaw rate Y (n) becomes smaller as the lateral acceleration GL (n) becomes smaller. Change rate ΔE of value and deviation E (n)
When the absolute value of (n) is a small value, the steering angle control of the rear wheels 3, 3 by the fuzzy control means 32 is executed, and the rear wheels 3, 3 are largely turned, and the vehicle is traveling on a road having a low road surface friction coefficient. so,
In a running state where the lateral acceleration GL (n) is small, the actually measured yaw rate Y (n) quickly converges to the target yaw rate Y0 (n). And the running stability can be sufficiently improved. On the other hand, when the vehicle is running on a road having a high coefficient of road surface friction and the lateral acceleration GL (n) is large, the fuzzy control means 32 controls the measured yaw rate. When the rear wheels 3, 3 are steered so that Y (n) quickly converges to the target yaw rate Y0 (n),
Although vibration occurs in the vehicle and the riding comfort deteriorates, in the present embodiment, as the lateral acceleration GL (n) increases, the predetermined deviation E0 and the predetermined change rate ΔE0 are set to large values. The convergence speed of the yaw rate Y (n) to the target yaw rate Y0 (n) is low, and
In such a running state, it is possible to achieve both riding comfort and running stability.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention described in the appended claims, which are also included in the scope of the present invention. Needless to say, this is done. For example,
In the embodiment, as the lateral acceleration GL (n) decreases, the predetermined deviation E0 and the predetermined change rate ΔE0
Is set to decrease linearly, but as the lateral acceleration GL (n) decreases, the predetermined deviation E
0 and the predetermined change rate ΔE0 are set to be non-linearly small, the predetermined deviation E0 and / or the predetermined change rate ΔE0 is constant within a certain range, and the lateral acceleration is set in other ranges. As GL (n) decreases, predetermined deviation E0 and / or predetermined change rate ΔE0
May be set to increase linearly or nonlinearly.

In the above embodiment, the lateral acceleration G
The predetermined deviation E0 and the predetermined change rate ΔE0 are set to be smaller as L (n) becomes smaller. In a running state where the road surface friction coefficient is small and the lateral acceleration GL (n) is small, the actually measured yaw rate Y (n) And target yaw rate Y0
The fuzzy control by the fuzzy control means 32 is executed with the absolute value of the difference E (n) from the difference (n) and the absolute value of the change rate ΔE (n) of the difference E (n) being small, and the measured yaw rate Y ( n) is controlled so as to quickly converge to the target yaw rate Y0 (n). On the other hand, in a running state where the road surface friction coefficient is large and the lateral acceleration GL (n) is large, the actually measured yaw rate Y (n) and the target yaw rate Absolute value of deviation E (n) from Y0 (n) and rate of change ΔE of deviation E (n)
If the absolute value of (n) does not become a large value, the fuzzy control by the fuzzy control means 32 is not executed, and the measured yaw rate Y (n) is controlled so as to gradually converge to the target yaw rate Y0 (n). In the running state where the road surface friction coefficient is small and the lateral acceleration GL (n) is small, the running stability is sufficiently improved, and in the running state where the road surface friction coefficient is large and the lateral acceleration GL (n) is large, the riding comfort is improved. Although the driving stability is compatible, the critical value setting means 35 further increases the steering angle control amount of the rear wheels 3, 3 as the lateral acceleration GL (n) decreases.
The membership function of the fuzzy control means 32 may be corrected. In this case, the lateral acceleration GL
The fuzzy control means 3 is controlled so that the steering angle control amount of the rear wheels 3, 3 increases linearly as (n) decreases.
2, the lateral acceleration GL is corrected.
Even if the membership function of the fuzzy control means 32 is corrected so that the steering angle control amount of the rear wheels 3 and 3 increases nonlinearly as (n) decreases, or the lateral acceleration GL (n) However, in a certain range, the steering angle control amounts of the rear wheels 3, 3 are constant, and in other ranges, the lateral acceleration GL
The membership function of the fuzzy control means 32 may be corrected such that the steering angle control amount of the rear wheels 3, 3 increases linearly or nonlinearly as (n) decreases. Is that the fuzzy control means 32 has a single membership function and the threshold value setting means 35
Even if the antecedent part and / or consequent part of the membership function is set, the fuzzy control means 32 has a plurality of membership functions having different antecedent parts and / or consequent parts, and 35 may select a specific membership function from among them according to the road surface condition.

Further, in the above embodiment, the predetermined deviation E0 and the predetermined change rate Δ are determined based on the lateral acceleration GL (n).
Although E0 is set to be small, the road surface friction coefficient is directly detected using a laser or the like, and the predetermined deviation E0 and the predetermined change rate ΔE0 are set to become smaller as the road surface friction coefficient becomes smaller. You may do so.

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,
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.

Β0 = 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. 7, 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 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 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 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 both 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, in the above-described embodiment, in the area S3 of FIG. 5, the rear wheels 3, 3 are controlled by fuzzy control.
Of the tire cornering force C. F. Fig. 5 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 traveling on a road with a small road 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.

[0054]

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 means for steering a rear wheel by feedback control, a running stability can be improved even when road surface conditions are different without requiring a large-sized computer. It is possible to provide a rear wheel steering device for a vehicle that can perform the following.

[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 lateral acceleration and a predetermined deviation EO and a predetermined change rate ΔE0.

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 Critical value setting means 40 Vehicle speed sensor 41 Steering angle sensor 42 Yaw rate sensor 43 Lateral acceleration sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 133: 00 137: 00

Claims (11)

(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 yaw rate feedback control means for turning the vehicle, a fuzzy control means for fuzzy controlling a steering angle of a rear wheel so that a change rate of the measured yaw rate approaches zero, and the target yaw rate. When the absolute value of the deviation between the measured yaw rate and the measured yaw rate exceeds a predetermined deviation, control switching means for switching the control means for controlling the steering angle of the rear wheel to the fuzzy control means; and And a critical value setting means for setting the predetermined deviation. 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. A yaw rate feedback control means for turning the vehicle, a fuzzy control means for fuzzy controlling a steering angle of a rear wheel so that a change rate of the measured yaw rate approaches zero, and the target yaw rate. When the absolute value of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined deviation, and when the absolute value of the change rate of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined change rate. Control switching means for switching the control means for controlling the angle to the fuzzy control means; and the predetermined deviation and the predetermined deviation in accordance with running conditions including road surface conditions. And a critical value setting means for setting the predetermined rate of change. 3. The fuzzy control means is configured to perform fuzzy control of a steering angle of a rear wheel based on a deviation between the target yaw rate and the measured yaw rate so that a change rate of the measured yaw rate approaches zero. The rear wheel steering device according to claim 1 or 2, wherein: 4. The rear wheel steering device according to claim 1, wherein the critical value setting means sets the predetermined deviation so as to decrease as the road surface friction coefficient decreases. . 5. The rear wheel steering device according to claim 2, wherein the critical value setting unit sets the predetermined change rate to decrease as the road surface friction coefficient decreases. 6. The vehicle according to claim 1, wherein the critical value setting means sets the predetermined deviation so as to decrease as the lateral acceleration applied to the vehicle in the lateral direction decreases. Rear wheel steering device. 7. The method according to claim 2, wherein the critical value setting means sets the predetermined deviation and the predetermined rate of change to be smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. A rear wheel steering device for a vehicle according to claim 1. 8. The critical value setting means is further configured to set a membership function of the fuzzy control means such that a steering angle control amount of a rear wheel increases as a road surface friction coefficient decreases. The rear wheel steering device according to claim 4, wherein the rear wheel steering device is used. 9. The fuzzy control means according to claim 1, wherein said critical value setting means further adjusts a membership function of said fuzzy control means so that a steering angle control amount of a rear wheel increases as a lateral acceleration applied in a lateral direction of the vehicle decreases. The rear wheel steering device according to claim 6, wherein the rear wheel steering device is configured to be set. 10. 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 an in-phase direction with an increase in the side slip angle estimated by the side slip angle estimating means. Means in the state where the absolute value of the deviation between the target yaw rate and the actual measured yaw rate does not exceed a predetermined deviation, when the sideslip angle estimated by the sideslip angle estimating means exceeds the predetermined sideslip angle value. 2. The vehicle according to claim 1, wherein the control switching means switches control means such that control of a rear wheel steering angle is performed by the sideslip angle control means. Wheel steering device. 11. 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 an in-phase direction with an increase in the side slip angle estimated by the side slip angle estimating means. Means, wherein the absolute value of the deviation between the target yaw rate and the measured yaw rate does not exceed a predetermined deviation, and the absolute value of the change rate of the deviation between the target yaw rate and the measured yaw rate exceeds a predetermined change rate. When the sideslip angle estimated by the sideslip angle estimating means exceeds a predetermined sideslip angle value in a state where the rear wheel steering angle is not controlled, the control of the rear wheel steering angle is performed by the sideslip angle control means. The rear wheel steering device according to claim 2, wherein the switching means is configured to switch the control means.