JPH04342667A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To ensure the proper travel stability of a vehicle regardless of a difference in road state without any need of a large capacity computer by performing the fuzzy control of a rear wheel steering angle so as to maintain the change rate of an actual measurement value on the basis of a deviation between a target yaw rate and the actual measurement value, or the change rate of the deviation. CONSTITUTION:The yaw rate feedback control means 30 of a control unit 29 performs the feedback control of the motor 24 of a steering wheel steering device, so that an actual yaw rate detected with a yaw rate sensor 42 becomes equal to a yaw rate target value set with each detected signals from a speed sensor 40 and a steering angle sensor 41. In this case, a fuzzy control means 32 performs the fuzzy control of a rear wheel steering angle, so that the change rate of the actual measurement value nears zero. Also, when the absolute value of a deviation between the target value and actual measurement value exceeds the predetermined value, or the absolute value of the change rate of the deviation exceeds the predetermined value, the fuzzy control means 32 is selected by a control selector means 33. Furthermore, the deviation and change rate are set with a critical value setting means 35, according to the state of a road.

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 system for a vehicle, and more particularly to a rear wheel steering system for a vehicle.

0002

BACKGROUND OF THE INVENTION A rear wheel steering device for a vehicle is known that steers the rear wheels at a predetermined steering ratio with respect to the steering angle of the front wheels corresponding to the steering angle of the steering wheel, depending on the vehicle speed. In such a vehicle's rear wheel steering system, it is possible to obtain steering performance that matches the driver's intention regardless of the vehicle speed, but in a transient state immediately after the driver operates the steering wheel, the front and rear wheels are often in phase, and therefore there is a problem in that the initial turning performance in a transient state is not good.

[0003] In order to solve this problem, Japanese Unexamined Patent Publication No. 1-2
Publication 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 performs feedback control of the steering angle of the rear wheels so that the measured yaw rate becomes equal to the target yaw rate.

0004

[Problems to be Solved by the Invention] However, in such a rear wheel steering system of a vehicle, when driving on a road with a small coefficient of road friction, the lateral acceleration applied in the lateral direction of the vehicle when making a sharp turn is extremely high. If this occurs, there is a tendency for excessive oversteer to occur, and unless a large computer with extremely fast calculation speed is used, even if feedback control is attempted so that the actual yaw rate becomes the target yaw rate, it will not follow the changes in the vehicle's yaw rate. Due to yaw rate feedback control,
It is extremely difficult to control the steering angle of the rear wheels; however, it is extremely uneconomical to equip a vehicle with a computer that can control the steering angle of the rear wheels using yaw rate feedback control. However, there was a problem in that it was extremely difficult in terms of space.

[0005]

OBJECTS OF THE INVENTION The present invention provides turning state detection means for physically detecting the turning state of a vehicle, and feedback control so that the measured yaw rate based on the detection value detected by the turning state detection means becomes the target yaw rate. This makes it possible to improve driving stability even under different road conditions without requiring a large computer in a vehicle rear wheel steering system equipped with a yaw rate feedback control means for steering the rear wheels. The object of the present invention is to provide a rear wheel steering device for a vehicle.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide fuzzy control means for fuzzy controlling the steering angle of the rear wheels so that the rate of change of the measured yaw rate approaches zero, and to control the absolute value of the deviation between the target yaw rate and the measured yaw rate. When the predetermined deviation is exceeded 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 the predetermined rate of change, the control means for controlling the steering angle of the rear wheels is controlled by the fuzzy control. This is achieved by comprising a control switching means for switching the control to the other means, and a threshold value setting means for setting a predetermined deviation and/or a predetermined rate of change depending on the road surface condition.

In an embodiment of the present invention, the fuzzy control means, 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 in the measured yaw rate approaches zero. It is configured to fuzzy control the steering angle of the rear wheels. 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 rate of change to become smaller as the road surface friction coefficient becomes smaller.

In a second preferred embodiment of the present invention, the threshold value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. 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 as the road surface friction coefficient becomes smaller, the steering angle control amount of the rear wheels becomes larger. It is configured to correct.

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

[0010] In this specification, the critical value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the road surface friction coefficient becomes smaller.
If the predetermined deviation and/or predetermined rate of change are set to decrease linearly as the road friction coefficient decreases, the predetermined deviation and/or predetermined rate of change may be set to decrease non-linearly as the road friction coefficient decreases. When setting the road surface friction coefficient to increase, the predetermined deviation and/or predetermined change rate are constant within a certain range, and in other ranges, the predetermined deviation and/or predetermined rate of change decreases as the road surface friction coefficient becomes smaller. This includes cases in which the rate of change is set to increase linearly or nonlinearly.

[0011] In this specification, the critical value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. If the predetermined deviation and/or the predetermined rate of change are set to decrease linearly as the lateral acceleration decreases, the predetermined deviation and/or the predetermined rate of change are set to increase non-linearly 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, as the lateral acceleration becomes smaller, the predetermined deviation and/or the predetermined rate of change are linear. Alternatively, it includes a case where the value is set to increase non-linearly.

Furthermore, in this specification, correcting the membership function of the fuzzy control means means that the fuzzy control means has a single membership function, and the critical value setting means corrects the membership function of the membership function. In addition to correcting the antecedent and/or consequent, the fuzzy control means has a plurality of different membership functions for the antecedent and/or consequent, and the critical value setting means corrects the antecedent and/or consequent. This also includes the case where a specific membership function is selected from among them.

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 correcting the membership function of the fuzzy control means so that the rear wheel steering angle control amount increases linearly, as the road surface friction coefficient decreases, the rear wheel steering angle control amount increases nonlinearly. When correcting the membership function of the fuzzy control means, as shown in FIG. This includes 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.

Furthermore, 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 in the lateral direction of the vehicle decreases When correcting the membership function of the fuzzy control means so that the amount of steering angle control for the rear wheels increases linearly as the acceleration decreases, the amount of steering angle control for the rear wheels increases as the lateral acceleration decreases. If the membership function of the fuzzy control means is corrected so that the lateral acceleration increases nonlinearly, the amount of rear wheel steering angle control is constant within a certain range, and the lateral acceleration is small in other ranges. This includes 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.

[0015]

According to the present invention, when the absolute value of the deviation between the target yaw rate and the 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 steering angle of the rear wheels so that the rate of change of the measured yaw rate approaches zero. is controlled in a fuzzy manner, so even if an excessive oversteer tendency occurs, the absolute value of the rate of change in yaw rate decreases, making it possible to improve driving stability even in such unstable driving conditions. Furthermore, since the predetermined deviation and/or the predetermined rate of change are set by the critical value setting means according to the road surface conditions, driving stability can be constantly improved even if the road surface conditions vary.

According to an 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 in the measured yaw rate approaches zero. Since the steering angle is fuzzy controlled, lateral acceleration increases while driving on a road surface with a low coefficient of road friction, and when the rear wheel steering angle is controlled using yaw rate feedback control, there is a tendency for excessive oversteer. This system reliably prevents the occurrence of excessive oversteer tendency in sharp turning situations where there is a great danger of
Even in such a turning state, it is possible to improve running stability.

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 rate of change to become smaller as the road surface friction coefficient becomes smaller. Therefore, when the vehicle turns while driving on a road with a small coefficient of road friction, the measured yaw rate can be immediately converged to the target yaw rate, which makes it possible to improve driving stability. When turning while driving on a road with a high coefficient of road friction, the measured yaw rate can be gently converged to the target yaw rate, which prevents vibrations from occurring in the vehicle and improves ride comfort and driving stability. It becomes possible to achieve both.

According to a second preferred embodiment of the present invention, the threshold value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. Therefore, when turning while driving on a road with a low coefficient of road friction and low lateral acceleration, the measured yaw rate can be immediately converged to the target yaw rate, thus improving driving stability. On the other hand, it becomes possible to improve
When turning while driving on a road with a high coefficient of road friction and high lateral acceleration, the measured yaw rate can be gently converged to the target yaw rate, which prevents vibrations from occurring in the vehicle and improves ride comfort. This makes it possible to achieve both stability and driving stability.

According to the first more preferred embodiment of the present invention, the critical value setting means further includes a fuzzy control means so that the steering angle control amount of the rear wheels increases as the road surface friction coefficient becomes smaller. Since the vehicle is configured to correct the membership function of It is possible to improve driving stability, and on the other hand, when driving on roads with a high coefficient of road friction,
When turning, the measured yaw rate can be gradually converged to the target yaw rate, making it possible to more reliably prevent vibrations from occurring in the vehicle, making it possible to achieve both ride comfort and driving stability. .

According to a second more preferred embodiment of the present invention, the critical value setting means further controls the steering angle control amount of the rear wheels to increase as the lateral acceleration applied in the lateral direction of the vehicle decreases. Since it is configured to correct the membership function of the fuzzy control means, while driving on a road with a small road surface friction coefficient and a small lateral acceleration,
When turning, it is possible to converge the measured yaw rate to the target yaw rate more quickly, thereby improving driving stability. When turning while driving, the measured yaw rate can be gradually converged to the target yaw rate, which can more reliably prevent vibrations from occurring in the vehicle, achieving both ride comfort and driving stability. becomes possible.

According to a third more preferred embodiment of the present invention, there is further provided a sideslip angle estimation means for estimating the sideslip angle of the vehicle, and an increase in the sideslip angle estimated by the sideslip angle estimation means. sideslip angle control means for controlling the steering angle in the same phase direction, and the absolute value of the deviation between the target yaw rate and the measured yaw rate does not exceed a predetermined deviation, and/or the deviation between the target yaw rate and the measured yaw rate changes. When the sideslip angle estimated by the sideslip angle estimating means exceeds the prescribed sideslip angle in a state where the absolute value of the ratio does not exceed the prescribed rate of change,
Since the control switching means is configured to switch the control means so that the rear wheel steering angle is controlled by the sideslip angle control means, the control switching means is configured to switch the control means so that the rear wheel steering angle is controlled by the sideslip angle control means. Driving stability can be significantly improved.

[0022]

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

In FIG. 1, a wheel steering system for a vehicle including a rear wheel steering system for a vehicle according to an embodiment of the present invention includes a steering wheel 1 and a front wheel steering system that steers left and right front wheels 2 by operating the steering wheel 1. It has a steering device 10 and a rear wheel steering device 20 that steers left and right rear wheels 3, 3 in accordance with the steering of the front wheels 2, 2 by the front wheel steering device 10. Front wheel steering device 10
is arranged in the width direction of the vehicle body, and its both ends are connected to the left and right front wheels 2, 2 via tie rods 11, 11 and knuckle arms 12, 12.
and a rack-and-pinion type steering gear mechanism 14 that moves the relay rod 13 left and right in conjunction with the operation of the handle 1. , the left and right front wheels 2, 2 are 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 connected to tie rods 21, 21.
and a relay rod 23 connected to the left and right rear wheels 3, 3 via knuckle arms 22, 22, a motor 24, and a deceleration mechanism 25 and a clutch 26.
A rack-and-pinion type steering gear mechanism 27 that is driven to move the relay rod 23 left and right, a centering spring 28 that biases the relay rod 23 to be held in the neutral position, and a centering spring 28 that is driven to move the relay rod 23 left and right, and It is equipped with a control unit 29 that controls the operation of the motor 24 according to the state, and controls the left and right rear wheels 3, 3 in a direction corresponding to the rotation direction of the motor 24 by an angle corresponding to the amount of rotation of the motor 24. It is designed to be steered.

FIG. 2 is a block diagram of a control unit 29 that controls the operation of the motor 24 and a running state detection system provided in the vehicle. In Figure 2,
The control unit 29 includes a yaw rate feedback control means 30, a sideslip angle control means 31, a fuzzy control means 32, a control switching means 33, a sideslip angle calculation means 34 for calculating an estimated value β of the sideslip angle, and a critical value setting means 35, a vehicle speed sensor 40 that detects the vehicle speed V, and a steering angle of the steering wheel 1, that is, the front wheels 2, 2.
Detection signals are inputted from a steering angle sensor 41 that detects the steering angle θf of the vehicle, a yaw rate sensor 42 that is a turning state detection means that detects the yaw rate Y of the vehicle, and a lateral acceleration sensor 43 that detects the lateral acceleration GL applied to the vehicle. There is.

The yaw rate feedback control means 30 calculates a target yaw rate Y0 based on the detection signal of the vehicle speed V inputted from the vehicle speed sensor 40 and the steering angle θf of the front wheels inputted from the steering angle sensor 41, and also calculates the target yaw rate Y0. The deviation E between the measured yaw rate Y(n) input from the yaw rate sensor 42 is calculated, and the feedback control amount Rb(n) of the yaw rate Y is calculated based on the I-PD control calculation formula stored in advance. Calculate,
When a control execution signal is input from the control switching means 33, a feedback control signal is output to the motor 24.

The control switching means 33 also determines the deviation E(
n), the rate of change ΔE(n) of the deviation E(n) is calculated, 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) respectively When the turning state exceeds the deviation E0 and the predetermined rate of change ΔE0, that is, when the turning state is extremely sharp, a control execution signal is output to the fuzzy control means 32 and the function critical value setting means 35, and the deviation E(n ) and the absolute value of the change rate ΔE(n) of the deviation E(n) are less than or equal to the predetermined deviation E0 and the predetermined change rate ΔE0, respectively, and the sideslip angle calculated by the sideslip angle calculating means 34 is Estimated value β(n)
A control execution signal is output to the sideslip angle control means 31 in a turning state in which the absolute value of β exceeds a predetermined value β0, that is, in a sharp turning state, and in other cases, that is, in a normal turning state. The yaw rate feedback control means 30 is configured to output a control execution signal to the yaw rate feedback control means 30.

When the control execution signal is input from the control switching means 33, the sideslip angle control means 31 calculates the sideslip angle control amount Rβ(n) based on a calculation formula stored in advance. A sideslip angle control signal is output to the steering angle regulating means 35. Further, the fuzzy control means 32 controls the yaw rate Y detected by the yaw rate sensor 42.
The rate of change ΔY(n) of (n) is calculated, and the control switching means 3
3, when the control execution signal is input, the rate of change ΔY(n ) approaches zero, for example, the rate of change ΔY(
n), a 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 sideslip angle calculating means 34 includes the vehicle speed sensor 4
0 detected vehicle speed V(n), measured yaw rate Y(n) detected by yaw rate sensor 42, and lateral acceleration sensor 4
Based on the detected lateral acceleration GL(n) of step 3, an estimated value β(n) of the sideslip angle is calculated according to the following equation (2) and outputted to the control switching means 33. β(n)=9.8×{GL(n)/V(n)}×{
Y(n)/57}
+β(n-1)・・・・・・
...■ Here, (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
Based on the lateral acceleration GL(n) input from 3, a predetermined deviation E0 and a predetermined rate of change ΔE0 are calculated according to a map or table stored in advance, and a setting signal is output to the control switching means 33. . 3 and 4 are flowcharts of the steering angle control of the rear wheels 3, 3 executed by the control unit 29 configured as described above, and FIG. F. It is a graph showing the relationship between the side slip angle and the sideslip 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, 2 detected by the steering angle sensor 41, and the yaw rate sensor 4
Yaw rate Y(n) of the vehicle detected by No. 2 and 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 receives a detection signal of the vehicle speed V(n) inputted from the vehicle speed sensor 40 and the steering angle sensor 4.
Based on the steering angle θf(n) of the front wheels input from 1, the target yaw rate Y0(n) at that control timing is calculated according to the following equation (2).

Y0(n)=V(n)/{1+A·V(n)2
}×θf(n)/L

.....■Here, A is the stability factor and L is the length of the wheel base. Next, the yaw rate feedback control means 3
0 is calculated by calculating the deviation E(n) between the target yaw rate Y0(n) thus calculated and the actual yaw rate Y(n) input from the yaw rate sensor 42 according to the following formula (■), E(n) =Y0(n)-Y(n)
・・・・・・・・・・・・・・・■Furthermore, according to the following I-PD control calculation formula■, calculate the feedback control amount Rb(n) of the yaw rate Y(n) at that control timing. .

Rb(n)=Rb(n-1) −[KI×E(n)−F
P×{Y(n)-Y(n-1)}
−FD×{Y(n)−2×Y(n−1
)+Y(n-2)]

・・・・・・・・・・・・■Here, KI is an integral constant, FP is a proportional constant, FD is a differential constant, and Rb(n-1)
represents the feedback control amount at the previous control timing, Y(n-1) represents the measured yaw rate at the previous control timing, and Y(n-2) represents the measured yaw rate at the control timing before the previous one.

The feedback control amount Rb(n) and deviation E(n) of the yaw rate Y(n) thus calculated are output to the control switching means 33. Next, the critical value setting means 35 calculates a predetermined deviation E0 and a predetermined rate of change ΔE0 based on the lateral acceleration GL(n) inputted from the lateral acceleration sensor 43, according to a map, table, etc. 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 rate of change ΔE0 stored in the critical value setting means 35, and as shown in FIG. The map is determined such that as (n) becomes smaller, the calculated predetermined deviation E0 and predetermined rate of change ΔE0 become smaller linearly. The control switching means 33 is the yaw rate feedback control means 3
0, sideslip angle control means 31 or fuzzy control means 3
The steering angle θr of the rear wheels 3, 3 is controlled by either control means of 2.
In order to determine whether to control the deviation E(n), first, the deviation E(
The rate of change ΔE(n) of n) is calculated, and the critical value setting means 35
Based on the predetermined deviation E0 and predetermined rate of change ΔE0 input from It is determined whether the rate of change is greater than a predetermined rate of change ΔE0.

[0036] When the determination result is YES, that is, the absolute value of the deviation E(n) is larger than the predetermined deviation E0,
And the absolute value of the rate of change ΔE(n) is equal to the predetermined rate of change ΔE0
When it is larger, the vehicle is in a state corresponding to region S3 in FIG. 5, and the vehicle is in an extremely sharp turning state, causing an excessive oversteer tendency and rapidly changing its direction. Since the driving condition is admittedly unstable, yaw rate feedback control
, 3 so that the vehicle runs stably, it is impossible to follow changes in the vehicle's yaw rate unless a large computer with extremely fast calculation speed is used. On the other hand, mounting such a large computer on a vehicle is both uneconomical and extremely difficult in terms of space, so in this embodiment, in such a turning state, Based on fuzzy theory, the control switching means 33 determines that the steering angle θr(n) of the rear wheels 3, 3 is in a turning state in which fuzzy control is required, and outputs a control execution signal to the fuzzy control means 32.

When the control execution signal is input from the control switching means 33, the fuzzy control means 32 changes the rate of change ΔY( In addition to calculating the absolute value of the deviation E(n) between the measured yaw rate Y(n) and the target yaw rate Y0(n), the deviation E(
The antecedent determines how large or not the absolute value of the rate of change ΔE(n) of n) is, and according to that determination, the function of the deviation E(n) and the rate of change ΔE(n) Based on a certain membership function and a setting signal input from the function critical value setting means 35, the fuzzy control amount Rf( n) and outputs a fuzzy control signal to the motor 24.

Rf(n)=f(E(n), ΔE
(n))......■Here, as is clear from FIG. 6, the predetermined deviation E0 and the predetermined rate of change ΔE0 are linear Therefore, the smaller the lateral acceleration GL(n), the smaller the actual yaw rate Y(n).
) and the target yaw rate Y0(n), and the rate of change of the deviation E(n). When the absolute value of the change rate ΔE(n) of the deviation E(n) is small, the rate of change of the actual measured yaw rate Y(n) decreases. The rear wheels 3, 3 are largely steered by the fuzzy control means 32 so that the vehicle is traveling on a road with a low coefficient of road friction,
In a driving state where the lateral acceleration GL(n) is small, the measured yaw rate Y(n) quickly converges to the target yaw rate Y0(n). It is possible to prevent the tendency to steer and sufficiently improve driving stability.On the other hand, when driving on a road with a high coefficient of road friction and in a driving state where the lateral acceleration GL(n) is large, the actual yaw rate Y If the rear wheels 3, 3 are steered by the fuzzy control means 32 so that (n) quickly converges to the target yaw rate Y0(n), vibrations will occur in the vehicle and the ride comfort will deteriorate; In this example, the lateral acceleration GL(n)
As becomes larger, the predetermined deviation E0 and the predetermined rate of change ΔE0 are set to larger values, so the speed at which the measured yaw rate Y(n) converges to the target yaw rate Y0(n) becomes smaller. Therefore, in such a driving state, It becomes possible to achieve both ride comfort and running stability.

On the other hand, the absolute value of the deviation E(n) is
not larger than the predetermined deviation E0, or the rate of change ΔE(
When the absolute value of n) is not larger than the predetermined rate of change ΔE0, the control switching means 33 determines that the absolute value of the estimated side slip angle β(n) input from the sideslip angle calculating means 34 is
It is determined whether the value is larger than a predetermined value β0. When the judgment result is YES, that is, the estimated value β(n
) is larger than the predetermined value β0, it is recognized that the driving condition corresponds to region S2 in FIG. has occurred, the turning radius of the vehicle has increased, and the yaw rate Y(n) has decreased, so when controlling the steering angle θr(n) of the rear wheels 3, 3 using yaw rate feedback control, is, yaw rate Y
In order to compensate for the decrease in (n), the rear wheels 3, 3 are replaced by the front wheels 2, 2.
With respect to the steering angle θf(n), there is a risk that the vehicle will be steered in the opposite phase direction and the running stability will deteriorate.On the other hand, the direction of the vehicle may change rapidly enough that fuzzy control must be used. Therefore, the control switching means 33 determines that the turning state is such that sideslip angle control should be executed, and outputs a control execution signal to the sideslip angle control means 31.

When the sideslip angle control means 31 receives the control execution signal from the control switching means 33, it calculates the sideslip angle control amount Rβ(n) according to the following equation (2).
Output to the motor 24. Rβ(n)=k×β(n)...
・・・・・・・・・・・・・・・■Here, k is a control constant and has a positive value. Therefore, the sideslip angle control amount Rβ(n) is equal to the sideslip angle β(n ) is larger,
The larger the side slip angle β(n) is, the more the rear wheels 3, 3 will be steered in the same phase direction as the front wheels 2, 2, and the amount of same phase will increase, so the turning radius of the vehicle will increase. is large and the yaw rate Y(n) is low, the rear wheels 3, 3 are steered in a direction opposite to the steering angle θf(n) of the front wheels 2, 2, which improves the running stability. This ensures that a decrease in

On the other hand, the estimated side slip angle β(n
) is less 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 the region S1 where the side slip angle and the side slip angle are in an almost proportional relationship, and it can be determined that the vehicle is in a stable running state.
The control switching means 33 outputs a control execution signal to the yaw rate feedback control means 30.

When the yaw rate feedback control means 30 receives the control execution signal from the control switching means 33, the yaw rate feedback control means 30 transfers the yaw rate feedback control signal to the motor 24.
The motor 24 is outputted to rotate the motor 24 and the rear wheels 3 are steered according to the yaw rate feedback control amount Rb(n) calculated by the equation (2). 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 condition of the vehicle is stable, the actual yaw rate Y(n) is changed to the target yaw rate Y0 determined based on the steering angle of the steering wheel 1 by the yaw rate feedback control. Since the rear wheels 3, 3 are steered so that (n), it becomes possible to steer the rear wheels 3, 3 as desired. In the driving state region S2, where the absolute value of is larger than the predetermined value β0, the lateral acceleration GL is large, the turning radius of the vehicle is large, and the yaw rate Y(n) is decreasing, the estimated value of the sideslip angle is The larger β(n) is, the more the rear wheels 3, 3 are in the same phase direction as the front wheels 2, 2, and the sideslip angle control is performed so that the in-phase amount increases. 3
By steering the rear wheels 3, 3, the steering angle θr(n)
is in the opposite phase direction with respect to the steering angle θf(n) of the front wheels 2, 2, which prevents the running stability from deteriorating and improves the running stability.Furthermore, the vehicle The absolute value of the deviation E(n) between the target yaw rate Y0(n) and the measured yaw rate Y(n) and the rate of change ΔE(n) of the deviation E(n)
) is larger than the predetermined deviation E0 and predetermined rate of change ΔE0, respectively, and there is a high possibility that an excessive oversteer tendency will occur in an extremely sharp turning condition in which the vehicle is recognized to be rapidly changing direction. In the stable running state region S3, 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 an extremely large computer is used. Without this, it is possible to improve running stability even in such extremely sharp turning conditions and unstable running conditions. In addition to this, the target yaw rate Y0(n
) and the measured yaw rate Y(n), and the absolute value of the rate of change ΔE(n) of the deviation E(n) is larger than the predetermined deviation E0 and the predetermined rate of change ΔE0, respectively. Since the predetermined deviation E0 and the predetermined rate of change ΔE0 at which the fuzzy control is executed are set to smaller values as the lateral acceleration GL(n) becomes smaller, the smaller the lateral acceleration GL(n) becomes, the lower the target yaw rate Y0 becomes. (n
) and the measured yaw rate Y(n), and the absolute value of the change rate ΔE(n) of the deviation E(n) is small, and the fuzzy control means 32 controls the rear wheels 3, 3. When the steering angle control is executed, the rear wheels 3, 3 are largely steered, and the vehicle is traveling on a road with a low coefficient of road friction, and the lateral acceleration GL(n) is small, the measured yaw rate Y(n) is In a driving state in which the target yaw rate Y0(n) is quickly converged and therefore driving stability should be emphasized,
The occurrence of spin can be prevented and running stability can be sufficiently improved. On the other hand, when the vehicle is running on a road with a high road surface friction coefficient and the lateral acceleration GL(n) is large, the fuzzy control means 32 , the measured yaw rate Y(n) is
When the rear wheels 3, 3 are steered so as to quickly converge to the target yaw rate Y0(n), vibrations occur in the vehicle,
Although the ride comfort deteriorates, in this embodiment, as the lateral acceleration GL(n) increases, the predetermined deviation E0 and the predetermined rate of change ΔE0 are set to larger values, so the target of the actual measured yaw rate Y(n) The convergence speed to the yaw rate Y0(n) is small, and therefore, in such a running state, it is possible to achieve both ride comfort and running stability.

[0044] The present invention is not limited to the above-mentioned examples, and various modifications can be made within the scope of the invention described in the claims, and these are also included within the scope of the present invention. Needless to say, this is something that will be done. for example,
In the embodiment, as the lateral acceleration GL(n) becomes smaller, the predetermined deviation E0 and the predetermined rate of change ΔE0
is set to decrease linearly, but as the lateral acceleration GL(n) decreases, the predetermined deviation E
Even if 0 and the predetermined rate of change ΔE0 are set to be nonlinearly small, the lateral acceleration remains constant within a certain range, and the lateral acceleration remains constant in other ranges. As GL(n) becomes smaller, the predetermined deviation E0 and/or the predetermined rate of change ΔE0
may be set so that it increases linearly or non-linearly.

Furthermore, in the above embodiment, the lateral acceleration G
The predetermined deviation E0 and the predetermined rate of change ΔE0 are set to become smaller as L(n) becomes smaller, and in a driving state where the road surface friction coefficient is small and the lateral acceleration GL(n) is small, the actual yaw rate Y(n) and target yaw rate Y0 (
When the absolute value of the deviation E(n) from the actual yaw rate Y(n) and the absolute value of the change rate ΔE(n) of the deviation E(n) are small, the fuzzy control means 32 executes the fuzzy control to adjust the actual measured yaw rate Y(n). ) is controlled so that it quickly converges to the target yaw rate Y0(n). On the other hand, in a driving state where the road surface friction coefficient is large and the lateral acceleration GL(n) is large, the actual yaw rate Y(n) and the target yaw rate Y0 The absolute value of the deviation E(n) from (n) and the rate of change of the deviation E(n) ΔE(n
) unless the absolute value of In driving conditions where the friction coefficient is small and lateral acceleration GL(n) is small, driving stability is sufficiently improved, and in driving conditions where the road surface friction coefficient is large and lateral acceleration GL(n) is large, ride comfort and driving stability are improved. However, the critical value setting means 35 further controls the fuzzy control means 32 so that the steering angle control amount of the rear wheels 3, 3 increases as the lateral acceleration GL(n) decreases. The membership function may be corrected. In this case, 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, 3 increases linearly as the lateral acceleration GL(n) decreases, 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, 3 increases non-linearly as the lateral acceleration GL(n) decreases, or the lateral acceleration GL
(n), within a certain range, the steering angle control amount of the rear wheels 3, 3 is constant, and in other ranges, as the lateral acceleration GL(n) decreases, the steering angle control amount of the rear wheels 3, 3 is The membership function of the fuzzy control means 32 may be corrected so that the amount increases linearly or nonlinearly,
Furthermore, even if the fuzzy control means 32 has a single membership function and the critical value setting means 35 sets the antecedent part and/or the consequent part of the membership function, the fuzzy control means 32 may have a plurality of membership functions with different antecedent parts and/or consequent parts, and the critical value setting means 35 may select a specific membership function from among them depending on the road surface condition. good.

Furthermore, in the embodiment, the predetermined deviation E0 and the predetermined rate of change 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 as the road surface friction coefficient becomes smaller, the predetermined deviation E0 and the predetermined rate of change ΔE0 are set to become smaller. You can do it like this.

Further, in the above embodiment, when the absolute value of the estimated value β of the sideslip angle becomes larger than the predetermined value β0,
Yaw rate feedback control has shifted to sideslip angle control, but in a driving state where the absolute value of the estimated sideslip angle β is larger than the predetermined value β0, the steering angle θ of the rear wheels 3, 3 is changed.
The ratio between r and the steering angle θf of the front wheels 2, 2 may be fixed, or the control gain may be reduced to perform new yaw rate feedback control in place of the previous yaw rate feedback control. You can.

Further, in the embodiment described above, β0 is set to a constant value, but β0 may be changed depending on the vehicle speed V, lateral acceleration GL, etc. FIG. 7 shows a flowchart for setting β0 based on vehicle speed V and lateral acceleration GL. In FIG. 7, β0 is determined by the sideslip angle calculating means 34 based on the threshold value βt, a coefficient jv that is a function of the vehicle speed V, and a coefficient jg that is a function of the lateral acceleration GL, according to the following formula (2). It looks like this.

β0=jv×jg×βt...
. . . ■ That is, first, the coefficient jv is determined based on the value of the vehicle speed V. Here, the coefficient jv
is set to converge to 1.0 as the vehicle speed V increases. This is to allow the driver to shift to sideslip angle control even if the estimated value β of the sideslip angle is a small value, since the driver tends to feel uneasy as the speed increases. The coefficient jg is then determined by the value of the lateral acceleration GL. In FIG. 7, the coefficient jg is set to converge to 1.0 as the lateral acceleration GL increases. This is to enable the vehicle to shift to sideslip angle control with a small lateral acceleration GL while driving on a road with a small road surface friction coefficient μ. Here, in FIG. 7, β0 is set by vehicle speed V and lateral acceleration GL, but even if β0 is set in addition to other driving parameters, or β0 can be set by other driving parameters. You may also set it.

Further, in the embodiment described above, the yaw rate Y is detected using the yaw rate sensor 42 as a turning state detecting means. 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 lateral acceleration sensor 4, and the lateral acceleration GL may also be calculated based on the lateral acceleration sensor 4.
3, 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
It may be calculated based on.

[0051] Furthermore, the calculation formula for the estimated value β of sideslip angle ■
The calculation formula (■) for the target yaw rate Y0 is only an example; the estimated side slip angle β can also be calculated by the Kalman filter method, the observer method, etc., and the target yaw rate Y0 can also be calculated by other methods. It may be calculated using the following arithmetic expression. Further, the sensor for detecting the running state of the vehicle may be selected depending on the necessity of the case, and the vehicle speed sensor 4 used in the embodiment described above may be selected.
, the steering angle sensor 41, the yaw rate sensor 42, and the lateral acceleration sensor 43 may be omitted, and other sensors may be used.

Further, in the above embodiment, when the absolute value of the deviation E between the target yaw rate Y0 and the 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 fuzzy Although the steering angle control of the rear wheels 3 and 3 is performed by the control, one of the
When the value is larger than a predetermined value, the rear wheel 3 is controlled by fuzzy control.
Further, in the above embodiment, the membership function of the fuzzy control is determined by the deviation E between the target yaw rate Y0 and the measured yaw rate Y.
It is a function of the deviation E or the rate of change ΔE of the deviation E, but it is only necessary to determine the membership function of fuzzy control based on the target yaw rate Y0 and the measured yaw rate Y. It may be one of the functions.

Furthermore, in the above embodiment, in the region S3 of FIG. 5, the rear wheels 3, 3 are
The steering angle θr(n) of the tire is controlled, but the tire cornering force C. F. The relationship between and sideslip angle is shown in Figure 5.
As shown in , it changes depending on the road surface friction coefficient μ, so when driving on a road other than a road with a small road surface friction coefficient μ, only regions S1 and S2 exist, and region S3
Therefore, it may not be necessary to perform fuzzy control. On the other hand, when driving on a road with a small road friction coefficient μ, sideslip angle control may not be necessary, as shown in FIG. The region S2 to be executed is extremely small, and there is a possibility that the control immediately shifts to fuzzy control without performing sideslip angle control.

[0054]

According to the present invention, the turning state detecting means physically detects the turning state of the vehicle, and the actually measured yaw rate based on the detection value detected by the turning state detecting means is set to the target yaw rate. To improve running stability even under different road surface conditions without requiring a large-sized computer in a rear wheel steering device for a vehicle equipped with a yaw rate feedback control means for steering rear wheels by feedback control. It becomes possible to provide a rear wheel steering device for a vehicle that can perform

[Brief explanation of the drawing]

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

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

FIG. 3 is a drawing showing the first half of a flowchart of rear wheel steering angle control executed by a control unit.

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

FIG. 5 shows tire cornering force C.
F. It is a graph showing the relationship between the side slip angle and the sideslip angle.

FIG. 6 is a graph showing the relationship between lateral acceleration, predetermined deviation EO, and predetermined rate of change ΔE0.

FIG. 7 is a flowchart illustrating an example of a method for setting β0.

[Explanation of symbols]

1 Handlebar 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 Rudder angle sensor 42 Yaw rate sensor 43 Lateral acceleration sensor

Claims (7)

[Claims] 1. Turning state detection means for physically detecting the turning state of the vehicle, and feedback control for controlling the rear wheels so that the measured yaw rate based on the detection value detected by the turning state detection means becomes the target yaw rate. yaw rate feedback control means for steering the rear wheels; and fuzzy control means for fuzzy control of the steering angle of the rear wheels so that the rate of change 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, and/
or control switching means for switching the control means for controlling the steering angle of the rear wheels to the fuzzy control means 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; A rear wheel steering device for a vehicle, comprising: threshold value setting means for setting the predetermined deviation and/or the predetermined rate of change according to road surface conditions. 2. The fuzzy control means adjusts the steering angle of 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. 3. The rear wheel steering device for a vehicle according to claim 1, wherein the rear wheel steering device is configured to perform fuzzy control. 3. The critical value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the road surface friction coefficient becomes smaller. Rear wheel steering system for vehicles. 4. The threshold value setting means sets the predetermined deviation and/or the predetermined rate of change to become smaller as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller. 3. The rear wheel steering device for a vehicle according to 1 or 2. 5. The critical value setting means is further configured to set a membership function of the fuzzy control means so that as the road surface friction coefficient becomes smaller, the steering angle control amount of the rear wheels becomes larger. The rear wheel steering device for a vehicle according to claim 3, characterized in that: 6. The threshold value setting means further comprises: as the lateral acceleration applied in the lateral direction of the vehicle becomes smaller;
5. The rear wheel steering device for a vehicle according to claim 4, wherein a membership function of the fuzzy control means is set so that a steering angle control amount of the rear wheels becomes large. 7. A side slip angle estimating means for estimating a side slip angle of the vehicle; and side slip angle control for controlling steering angles of rear wheels in the same phase direction as the sideslip angle estimated by the side slip angle estimating means increases. means, the absolute value of the deviation between the target yaw rate and the measured yaw rate does not exceed a predetermined deviation, and/or the absolute value of the rate of change of the deviation between the target yaw rate and the measured yaw rate changes by a predetermined value. The sideslip angle estimated by the sideslip angle estimating means is
The control switching means is configured to switch the control means so that when the sideslip angle exceeds a predetermined sideslip angle value, the sideslip angle control means controls the rear wheel steering angle. A rear wheel steering device for a vehicle according to any one of claims 1 to 6.