JPH04356280A - Vehicle rear wheel steering device - Google Patents

Abstract

PURPOSE:To enable the running stability of a vehicle to be secured even if the tendency of excessive oversteering arises by performing fuzzy control of the steering angle of rear wheels in case of a sudden turn of the rear wheels by which transverse acceleration exceeds a predetermined value, so that the rate of change of actually measured yaw rates approximates zero. CONSTITUTION:A control unit 29 which controls the steering of right and left rear wheels by means of control of the drive of the motor 24 of a rear wheel steering device is provided with a yaw rate feedback control means 30 which performs feedback control of the motor 24 by means of the deviation between an actually measured yaw rate based on values detected by a turning state detection means and a target yaw rate. Also a fuzzy control means 32 is provided which performs fuzzy control of the rear wheels so that the rate of change of the actually measured yaw rate approximates zero. The fuzzy control means 32 is switched by a control switching means 33 and actuated when a turning state detected is judged to be a sudden one; the membership function of the fuzzy control means 32 is corrected by a function correction means 35 on the basis of the condition of a road surface.

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 It is an object of the present invention 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 a turning state detected by the turning state detecting means to a predetermined value. control switching means for switching the control means for controlling the steering angle of the rear wheels to the fuzzy control means when the turning state is steeper than the turning state; and a membership function of the fuzzy control means for correcting the membership function of the fuzzy control means according to the road surface condition. This is achieved by providing a correction means.

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 preferred embodiment of the present invention, the steering angle of the rear wheels is further controlled in the same phase direction as the sideslip angle estimating means estimates the sideslip angle of the vehicle and the sideslip angle estimated by the sideslip angle estimation means increases. and a sideslip angle control means, in which the control switching means causes the sideslip angle control means to:
The control means controls the rear wheel steering angle so that the fuzzy control means controls the rear wheel steering angle in a second turning state that is even steeper than the second predetermined turning state. It is configured to switch.

In a further preferred embodiment of the present invention, the correction means corrects 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. It is composed of In another preferred embodiment of the present invention, the correcting means uses a membership function of the fuzzy control means such that the steering angle control amount of the rear wheels increases as the lateral acceleration applied in the lateral direction of the vehicle decreases. It is configured to correct.

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 correction means corrects the antecedent and/or In addition to correcting the consequent part, the fuzzy control means has a plurality of different membership functions for the antecedent part and/or the consequent part, and the correction means can select a specific one from among them according to the road surface condition. It also includes the case of selecting the membership function of .

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.

0012

According to the present invention, in an extremely sharp turning state where the lateral acceleration exceeds a predetermined value, the steering angle of the rear wheels is adjusted by the fuzzy control means so that the rate of change of the measured yaw rate approaches zero. Fuzzy control reduces the rate of change in yaw rate even if excessive oversteer tends to occur, making it possible to improve driving stability even in such unstable driving conditions. Since the membership function of the fuzzy control means is corrected by the correction 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. It is possible to reliably prevent an excessive oversteer tendency from occurring in a sharp turning state where there is a great risk of occurrence of oversteer, and to improve running stability even in such a turning state.

According to a preferred embodiment of the present invention, the sideslip angle estimation means estimates the sideslip angle of the vehicle, and as the sideslip angle estimated by the sideslip angle estimation means increases, the steering angles of the rear wheels are set in the same phase direction. and a sideslip angle control means for controlling the sideslip angle control means, wherein the control switching means controls the sideslip angle control means in a sudden first turning state in which the turning state detected by the turning state detection means exceeds a first predetermined turning state. The rear wheel steering angle is controlled by the fuzzy control means in a second turning state that is even steeper than the second predetermined turning state, and the rear wheel steering angle is controlled by the fuzzy control means. Since it is configured to switch the control means,
Furthermore, running stability can be significantly improved from running states with low lateral acceleration to running states with high lateral acceleration.

According to a further preferred embodiment of the present invention, the correction means corrects 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. With this configuration, when the vehicle turns while driving on a road with a low coefficient of road friction, the measured yaw rate can immediately converge to the target yaw rate, thus improving driving stability. On the other hand, when turning while driving on a road with a large coefficient of road friction, the measured yaw rate can be gradually converged to the target yaw rate.
It is possible to prevent vibrations from occurring in the vehicle, and it is possible to achieve both ride comfort and running stability.

According to another preferred embodiment of the present invention, the correction means includes a member of the fuzzy control means such that the smaller the lateral acceleration applied in the lateral direction of the vehicle, the larger the steering angle control amount of the rear wheels. Since the vehicle is configured to correct the ship function, when the vehicle turns while driving on a road with a low coefficient of road friction and low lateral acceleration, it is possible to immediately converge the measured yaw rate to the target yaw rate. This makes it possible to improve driving stability, and on the other hand, when turning while driving on a road with a high coefficient of road friction and high lateral acceleration, the measured yaw rate can be gradually converged to the target yaw rate, so the vehicle It is possible to prevent vibrations from occurring in the vehicle, making it possible to achieve both ride comfort and running stability.

[0017]

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 function correction means. 35, a vehicle speed sensor 40 that detects the vehicle speed V, a steering angle sensor 41 that detects the steering angle of the steering wheel 1, that is, the steering angle θf of the front wheels 2, 2, and a turning state detector that detects the yaw rate Y of the vehicle. Detection signals from a yaw rate sensor 42 and a lateral acceleration sensor 43 that detects lateral acceleration GL applied to the vehicle are input.

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 detects 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 value E0 and the predetermined value 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 correction means 35, and the deviation E
Absolute value of (n) and rate of change of deviation E(n) ΔE(n)
The absolute values of are the predetermined value E0 and the predetermined value ΔE0, respectively.
In a turning state in which the estimated value β(n) of the sideslip angle calculated by the sideslip angle calculating means 34 is below and the absolute value of the estimated sideslip angle β(n) exceeds the predetermined value β0, that is, in a sharp turning state, the sideslip It is configured to output a control execution signal to the angle control means 31, and output a control execution signal to the yaw rate feedback control means 30 in other cases, that is, in a normal turning state.

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) 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 pre-stored membership function and function correction means 3
Based on the correction signal input from 5, for example, the absolute value of the rate of change ΔY(n) of the measured yaw rate Y(n) is adjusted so that the rate of change ΔY(n) of the measured yaw rate Y(n) approaches zero. The fuzzy control amount Rf(n) is calculated and the fuzzy control signal is output to the steering angle regulating means 35 so that its absolute value decreases.

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 is output 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 function correction means 35 is the control switching means 33
When a control execution signal is input from the lateral acceleration sensor 4
Based on the lateral acceleration GL(n) input from 3, a correction value for correcting the membership function of the fuzzy control means 32 is calculated according to a map or table stored in advance, and the correction signal is sent to the fuzzy control means. Output to 32.

FIGS. 3 and 4 show the rear wheel 3, which is executed by the control unit 29 configured as described above.
FIG. 5 is a flowchart of the steering angle control of No. 3. 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 Y of the vehicle detected by the yaw rate sensor 42. (n) and the lateral acceleration GL (
n) 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 a steering angle θf of the front wheels inputted from the steering angle sensor 41.
Based on (n), 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 30 calculates the target yaw rate Y0(n
) and the measured yaw rate Y(n) input from the yaw rate sensor 42, the deviation E(n) is calculated 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. Control switching means 3
3, in order to determine which of the yaw rate feedback control means 30, sideslip angle control means 31, or fuzzy control means 32 should control the steering angle θr(n) of the rear wheels 3, 3, the deviation is first determined. The rate of change ΔE(n) of E(n) is calculated, and the absolute value of the deviation E(n) is larger than the predetermined value E0, and the rate of change ΔE(
It is determined whether the absolute value of n) is larger than a predetermined value ΔE0.

[0031] When the judgment result is YES, that is, when the absolute value of the deviation E(n) is larger than the predetermined value E0, and when the absolute value of the rate of change ΔE(n) is larger than the predetermined value ΔE0, , the vehicle is in a state corresponding to region S3 in FIG. 5, and the vehicle is in an extremely sharp turning state, with an excessive tendency to oversteer and an unstable state in which the direction is suddenly changed. Therefore, when controlling the steering angle θr(n) of the rear wheels 3, 3 using yaw rate feedback control so that the vehicle runs stably, a large computer with extremely fast calculation speed is used. It is extremely difficult to follow changes in the vehicle's yaw rate unless there is a computer installed in the vehicle.On the other hand, it is not only uneconomical to install such a large computer on the vehicle, but also extremely difficult in terms of space. Therefore, in this embodiment, in such a turning state, the control switching means 33 switches the rear wheels 3,
The steering angle θr(n) of No. 3 is determined to be a turning state that should be fuzzy controlled, and a control execution signal is output to the fuzzy control means 32 and the function correction means 35.

The function correction means 35 is the control switching means 33
, when the control execution signal is input, the correction coefficient C is calculated based on the lateral acceleration GL(n) input from the lateral acceleration sensor 43 according to the map stored in advance.
is calculated, and a correction signal is output to the fuzzy control means 32. In this embodiment, as shown in FIG. 3, the correction coefficient C is set to a value equal to 1 when the lateral acceleration GL(n) is equal to or greater than the predetermined value GLo;
o, it increases linearly and the lateral acceleration GL(n) reaches 0.
It is set to be Co when .

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 correction signal input from the function correction means 35, the yaw rate Y is calculated according to the following formula (■).
The fuzzy control amount Rf(n) is calculated so that the rate of change ΔY(n) of (n) approaches zero, and the fuzzy control signal is
Output to the motor 24.

Rf(n)=C×f(E(n),
ΔE(n))・・・・・・■ Here, as is clear from FIG. 3, when the lateral acceleration GL(n) is less than the predetermined value GLo, the correction coefficient Acceleration GL(n
) is set to a larger value, so
When the lateral acceleration GL(n) is less than the predetermined value GLo, the smaller the lateral acceleration GL(n) is, the more the rear wheels 3, 3 are steered. In driving conditions where n) is small, the measured yaw rate Y
(n) quickly converges to the target yaw rate Y0(n). Therefore, in driving conditions where emphasis should be placed on driving stability, excessive oversteer tendency is prevented from occurring and driving stability is sufficiently maintained. On the other hand, when driving on a road with a high coefficient of road friction, the lateral acceleration GL (
In a driving state where n) is large, if the rear wheels 3 are steered so that the measured yaw rate Y(n) quickly converges to the target yaw rate Y0(n), vibrations occur in the vehicle.
Although the ride comfort deteriorates, in this embodiment, when the lateral acceleration GL(n) is greater than or equal to the predetermined value GLo, the correction coefficient C is 1.
Therefore, the convergence speed of the measured yaw rate Y(n) to the target yaw rate Y0(n) is small, and therefore, in such a driving state, it is possible to achieve both ride comfort and driving stability.

On the other hand, the absolute value of the deviation E(n) is
not greater than a predetermined value E0, or the rate of change ΔE(n
) is not greater than the predetermined value ΔE0, the control switching means 33 determines whether the absolute value of the estimated side slip angle β(n) input from the sideslip angle calculating means 34 is greater than the predetermined value β0. Determine whether or not. The judgment result is YES
When S, that is, when the absolute value of the estimated side slip angle β(n) is larger than the predetermined value β0, it is recognized that the driving state corresponds to region S2 in FIG. 5, and the lateral acceleration GL(n) The steering angle θr of the rear wheels 3, 3 is (n) by yaw rate feedback control, the yaw rate Y(n)
In order to compensate for the decrease of , the control switching means 33 determines that the turning state is such that the vehicle is in a turning state where sideslip angle control should be executed, since the vehicle is not in an unstable running state where the direction of the vehicle is changing rapidly to the extent that fuzzy control is required. Then, a control execution signal is output 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, it 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)
) are larger than the predetermined values E0 and ΔE0, respectively, and the vehicle is in an unstable driving state region S3 in an extremely sharp turning state in which there is an excessive oversteer tendency that is recognized as changing direction rapidly. Then, the yaw rate Y(n
) so that the rate of change ΔY(n) approaches zero, the rear wheels 3,
Since the rudder angle θr of No. 3 is fuzzy controlled, it is possible to improve driving stability even in such extremely sharp turning conditions and unstable driving conditions without using an extremely large computer. Become. Further, a correction coefficient C is calculated by the function correction means 35 based on the value of the lateral acceleration GL(n) and outputted to the fuzzy control means 32.
is C when the lateral acceleration GL(n) is less than the predetermined value GLo.
>1 and the smaller the lateral acceleration GL(n),
Since the value is set to a large value, when the lateral acceleration GL(n) is less than the predetermined value GLo, the smaller the lateral acceleration GL(n), the more the rear wheels 3, 3 are steered, and the road surface has a low coefficient of 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), and therefore, this is a driving state where emphasis should be placed on such driving stability. In this case, it is possible to prevent the occurrence of an excessive oversteer tendency and sufficiently improve driving stability.On the other hand, when driving on a road with a high coefficient of road friction and a driving state where the lateral acceleration GL(n) is large, , the measured yaw rate Y(n) is the target yaw rate Y0
If the rear wheels 3, 3 are steered so as to quickly converge to value G
Lo Above, since the correction coefficient C is set to 1, the target yaw rate Y0(n) of the actual measured yaw rate Y(n)
The convergence speed to is small, and therefore, in such a running state, it is possible to achieve both ride comfort and running stability.

FIGS. 6 and 7 are flowcharts showing other embodiments of steering angle control of the rear wheels 3, 3 executed by the control unit 29. In FIGS. 6 and 7, the function correction means 35 calculates a correction coefficient C for correcting the consequent of the membership function of the fuzzy control means 32, and does not output a correction signal. Deviation E(
A correction signal is provided to determine how large the absolute value of n) and the absolute value of the change rate ΔE(n) of the deviation E(n) are, according to the lateral acceleration GL(n). This embodiment differs from the embodiments shown in FIGS. 3 and 4 only in that output is provided.

That is, the smaller the lateral acceleration GL(n) input from the lateral acceleration sensor 43, the more the fuzzy control means 32 adjusts the actually measured yaw rate Y(n).
) and the target yaw rate Y0(n), and the absolute value of the rate of change ΔE(n) of the deviation E(n) are:
Even if it is smaller, it is judged to be larger, and the deviation E(n) between the measured yaw rate Y(n) and the target yaw rate Y0(n) is calculated.
Even if the absolute value of the change rate ΔE(n) of the deviation E(n) is the same, the smaller the lateral acceleration GL(n) input from the lateral acceleration sensor 43, the larger the fuzzy control means 32. Fuzzy control means 32 so as to determine
The correction signal that corrects the antecedent part of the membership function of
It is output to the fuzzy control means 32.

Therefore, similarly to the embodiments shown in FIGS. 3 and 4, when the vehicle is traveling on a road with a low road surface friction coefficient and the lateral acceleration GL(n) is small, the measured yaw rate Y(n) is , quickly converges to the target yaw rate Y0(n), and therefore, in driving conditions where emphasis should be placed on driving stability, it is possible to prevent the occurrence of an excessive oversteer tendency and sufficiently improve driving stability. I can do it,
On the other hand, when driving on a road with a high coefficient of road friction, the lateral acceleration G
In a driving state where L(n) is large, the measured yaw rate Y(n
) convergence speed to the target yaw rate Y0(n) is small,
Therefore, in such running conditions, it is possible to achieve both ride comfort and running stability.

[0043] 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 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 described above, the correction coefficient C is calculated using the map shown in FIG. 3, but the method of setting the correction coefficient C using the map shown in FIG. 3 is only an example and is not limited to this. 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 without Even if you set the correction coefficient C,
As the lateral acceleration GL(n) decreases, the rear wheels 3,
The correction coefficient C may be set to correct the membership function of the fuzzy control means 32 so that the steering angle control amount of No. 3 increases nonlinearly.

In the embodiments shown in FIGS. 3 and 4, the consequent of the membership function of the fuzzy control means 32 is corrected using the correction coefficient C calculated by the function correction means 35, Further, in the embodiment shown in FIGS. 6 and 7, the function correction means 35 corrects the antecedent part of the membership function of the fuzzy control means 32, but the function correction means 35 corrects the lateral acceleration GL (n), a correction signal for correcting the antecedent part and the consequent part of the membership function of the fuzzy control means 32 may be output, or the fuzzy control means 32 may output the antecedent part and the consequent part of the membership function of the fuzzy control means 32 /Or it may have a plurality of membership functions with different consequents, and the function correction means 35 may select a specific membership function from among these depending on the lateral acceleration GL(n). .

Furthermore, in the embodiment described above, the antecedent and consequent parts of the membership function of the fuzzy control means 32 are corrected based on the lateral acceleration GL(n), but the road surface The friction coefficient may be directly detected and the antecedent and consequent parts of the membership function of the fuzzy control means 32 may be corrected based on the value of the road surface friction coefficient.

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. 8 shows a flowchart for setting β0 based on vehicle speed V and lateral acceleration GL. In FIG. 8, 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. 8, 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. 8, 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 above embodiment, 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.

[0050] Furthermore, the calculation formula for the estimated side slip angle β is
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. Further, instead of the deviation E or the rate of change ΔE of the deviation E, the steering angle control of the rear wheels 3, 3 may be performed using fuzzy control when the lateral acceleration GL(n) exceeds a predetermined value. , Furthermore, the membership function of the fuzzy control is the lateral acceleration GL(n) and/or its rate of change,
Alternatively, the determination may be made based on the steering angle θf of the front wheels 2, 2, the rate of change of the steering angle θf, and the rate of change of the rate of change of the steering angle θf.

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.

[0053]

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 drawings]

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

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

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

[Explanation 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 Deceleration 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 Function correction means 40 Vehicle speed sensor 41 Rudder angle sensor 42 Yaw rate sensor 43 Lateral acceleration sensor

Claims (5)

[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 of a vehicle, the control means fuzzy control means for controlling the steering angle of the rear wheels in a fuzzy manner so that the rate of change of the measured yaw rate approaches zero, and the turning state control switching means for switching the control means for controlling the steering angle of the rear wheels to the fuzzy control means when the turning state detected by the detection means is a turning state that is steeper than a predetermined turning state; A rear wheel steering device for a vehicle, comprising: a correction means for correcting the membership function of the fuzzy control means. 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. 2. 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. 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, wherein the control switching means detects a sudden first turning state in which the turning state detected by the turning state detecting means exceeds a first predetermined turning state.
In the turning state, the sideslip angle control means controls the rear wheel steering angle, and in the second turning state, which is even steeper than the second predetermined turning state, the fuzzy control means controls the rear wheel steering angle. 3. The rear wheel steering device for a vehicle according to claim 1, wherein the control means is configured to switch so that the control of the wheel steering angle is executed. 4. The correction means is configured to correct the 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. A rear wheel steering device for a vehicle according to any one of claims 1 to 3. 5. The correction means corrects 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. A rear wheel steering device for a vehicle according to any one of claims 1 to 3.