JPH06329040A - Steering system for vehicle - Google Patents

Abstract

PURPOSE:To secure the stability of a vehicle by judging the state of rear wheel steering control exceeding a range of guaranteeing the stability of the vehicle in an early stage so as to switch the steering control to the other control system in the case of performing this steering control of rear wheels, for instance, in order to make the actual yaw rate of the vehicle the target value at the time of steering front wheels. CONSTITUTION:The motor 28 of a rear wheel steering system steers rear wheels, and this motor 28 is controlled by a first control means 45 so that the actual yaw rate of a vehicle becomes the target yaw rate. The control means 45 is constituted of Hinfinity control composed of a state feedback control means 46, for instance, and a control gain computing means 47 for setting the control gain of the state feedback control to '1' or less on a frequency axis. A judging means 49 judges the state of exceeding the guarantee range of the control means 45 when a phase delay at the specified frequency in the phase delay characteristic of the frequency transfer function of the actual yaw rate in relation to the steering of a steering wheel exceeds the specified value, and a control switching means 50 switches the control of the motor 28 to a map control means 48.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system and, more particularly, to forcibly steer the rear wheels or the front wheels in response to a steering wheel steering of a driver to enhance drivability and stability of the vehicle. It is related to the improvement of the thing

[0002]

2. Description of the Related Art Conventionally, as a steering device for a vehicle of this type, when a driver operates a steering wheel, a steering angle ratio of rear wheels corresponding to a steering angle of front wheels, that is, a steering ratio is determined according to a vehicle speed. It is known that the rear wheels are steered in accordance with the steering ratio based on the steering ratio. With this, while it is possible to obtain steering performance that matches the driver's intention, in the initial state immediately after the driver operates the steering wheel, the front wheels and the rear wheels are often in phase, so There was a pity that the turning ability of the vehicle in the initial state was low.

Therefore, conventionally, for example, Japanese Unexamined Patent Publication No. 1-262 has been proposed.
In the system disclosed in Japanese Patent No. 268, the control target yaw rate of the vehicle is calculated based on the steering wheel steering amount of the driver, the yaw rate of the vehicle is measured, and the deviation between the measured yaw rate and the control target value is calculated. By performing feedback control of the steering angle of the rear wheels with a corresponding feedback control amount, the yaw rate is quickly generated even in the initial state immediately after the steering wheel is operated, and the turning ability of the vehicle in the initial state is enhanced. But,
This conventional feedback control is a one-input one-output control system that controls the rear wheels by calculating the feedback control amount of the rear wheel steering angle based only on the deviation between the measured yaw rate value and the control target value. For example, when the sideslip angle of the vehicle has a large value, control hunting is more likely to occur than when it has a small value. Therefore, it is necessary to always set the control gain to a small value so that control hunting does not easily occur.
In that case, the quick response to the control target yaw rate value deteriorates, and the actual yaw rate cannot be accurately controlled to the control target value, and there is a limit in improving the steady-state characteristic.

[0004]

Therefore, the applicant of the present invention is
Previously, for example, in the specification and drawings of Japanese Patent Application No. 4-237437, etc., it has been proposed to employ state feedback control of measured yaw rate instead of the above feedback control. This yaw rate state feedback control measures the yaw rate of the vehicle and estimates multiple state variables of the vehicle, such as the sideslip angle of the vehicle, the cornering force of the front and rear wheels, etc., based on the state equation and the output equation of the vehicle. The movement state of the vehicle is grasped by using these state variables, and, for example, the rear wheel steering angle is optimally controlled so that the actual yaw rate of the vehicle becomes the control target value using these state variables.
Since this control system is a multi-variable one-output control system, the rear wheels can be steered by a feedback control amount that matches the motion state of the vehicle, and the turning performance of the vehicle at the time of steering wheel operation can be improved. It is possible to improve both the quick response property and the steady-state characteristic.

Further, the present applicant has noticed that the above-mentioned state feedback control has the following drawbacks, and invented that H∞ control is applied in order to solve the drawbacks. That is, in the state feedback control, when estimating the sideslip angle of the vehicle, the cornering force, etc., the vehicle speed and the cornering power of the wheels are calculated as constants, but these are actually variables, and the latter cornering power is It changes according to the friction coefficient of the road surface and the tire air pressure. Therefore, under the preset motion characteristics of the vehicle, it is possible to improve the quick response and steady-state characteristics of the control, but as shown in FIG. 20, the motion characteristics of the vehicle are changed according to changes in the vehicle speed, the friction coefficient of the road surface, and the like. If a large change occurs, an error occurs in the estimation of the sideslip angle of the vehicle, which causes a deviation in the optimum control, which reduces the quick response to the target yaw rate, and the stability of the vehicle cannot be guaranteed.

Therefore, for example, H∞ control for improving the stability of the control system by satisfying that the loop transfer function of the control system is "1" or less over all frequency regions (see, for example, "Measurement of Society" And Control ”, Vol. 29, No. 2 (February 1990), pp. 111 to 119), to improve stability against vehicle characteristic variations, that is, robust stability. Conceivable. The H∞ control for steering the front wheels or the rear wheels requires steady-state characteristics and speed response of the vehicle in a low frequency range of, for example, 1 Hz or less as a steering wheel steering frequency, and in a high frequency range of more than 1 Hz, when the characteristics of the vehicle change. Since stability is required and these requirements are different in the frequency domain, it is considered as a mixed sensitivity problem as disclosed in the journal of the academic society, and the control gain of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the front wheels or the rear wheels is considered. Two types of characteristics are set: a performance target index that gives the vehicle quick response and steady-state characteristics, and a performance target index that gives the stability when the characteristics of the vehicle have a complementary sensitivity function relationship with the performance target index. The control gain is determined on the frequency axis by emphasizing the former in the low frequency range and the latter in the high frequency range. Therefore, if the H∞ control is used, even if there is a characteristic variation of the vehicle, if the variation is within the set allowable range, it is possible to constantly control all of the vehicle speed response, steady performance, and stability. .

However, in both the conventional yaw rate feedback control and the yaw rate state feedback control and H∞ control proposed by the applicant, the vehicle is operated in a driving region in which the cornering force of the wheel with respect to the sideslip angle of the wheel is linear. Although stable control is possible, it is difficult to reliably and stably control the vehicle in a nonlinear driving range.

The present invention has been made in view of the above points, and an object of the present invention is to provide the conventional yaw rate feedback control, state feedback control, and H control.
In the case of ∞ control, etc., if the characteristics of the vehicle fluctuate beyond the range where the control guarantees the stability of the vehicle, the situation beyond this stability guarantee range is judged early and the steering angle of the front wheels or the rear wheels is An object of the present invention is to provide a vehicle steering system capable of ensuring vehicle stability by stabilizing a control system.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 is a steering apparatus for a vehicle, for example, as shown in FIG. 1, steering front wheels or rear wheels separately from a steering wheel. Steering means 20 and yaw rate detection means 3 for detecting the actual yaw rate generated in the vehicle.
6, and the control amount is calculated based on the deviation between the actual yaw rate and the target yaw rate detected by the detection means 36,
It is premised that a first control means 45 for feedback-controlling the steering means 20 so as to match the actual yaw rate with the target yaw rate by the control amount is provided. Further, the determination means 49 for determining when the control by the first control means 45 exceeds the range for ensuring the stability of the vehicle, and the steering wheel steering so that the stability of the vehicle is essentially ensured. The steering means 2 with a control amount according to
Second control means 48 for controlling 0 and the determination means 49
When the control by the first control means 45 exceeds the range in which the stability of the vehicle is guaranteed, the steering control of the front wheels or the rear wheels is changed from the control by the first control means 45 to the second control. A control switching means 50 for switching to control by the control means 48 is provided.

According to a second aspect of the present invention, the first control means 45, which is a subordinate element of the subordinate to the first aspect, performs H∞ control. That is, the first control means 45 is a vehicle state equation in which at least the actual yaw rate of the vehicle and the estimated sideslip angle are vehicle state quantities,
In addition, based on the output equation, the state feedback control means for controlling the steering means 20 so as to perform the state feedback control of the actual yaw rate of the vehicle to the control target yaw rate, and the frequency transfer function of the yaw rate change of the vehicle for the steering of the front wheels or the rear wheels. Two types of control gain characteristics, a performance target index that gives stability when the characteristics of the vehicle fluctuate, and a performance target index that gives vehicle speed response and steady-state characteristics, and the state of the vehicle that inputs the steering angle of the front or rear wheels. Control gain calculation means for calculating the control gain of the state feedback control means based on the equation and the output equation.

The inventions according to claims 3 to 5 are all dependent on the invention according to claim 1 or 2, and specifically show the contents of the judgment of the judging means 49 which is one component thereof. That is, in the third aspect of the invention, the determining means 49 determines that the frequency component of the control gain of the yaw rate change of the vehicle with respect to the steering of the front wheels or the rear wheels is the vehicle when the steering control of the front wheels or the rear wheels by the first control means 45 is performed. It is determined when the control by the first control means 45 exceeds the range that guarantees the stability of the vehicle by exceeding the performance target index that gives the stability when the characteristic changes. In the invention according to claim 4, the determination means 4 is provided.
9 indicates that when the front control or the rear wheel steering control by the first control means 45, the state quantity of the vehicle exceeds a predetermined value indicating the performance limit of the vehicle, the control by the first control means 45 stabilizes the vehicle. The judgment is made when the guaranteed range is exceeded.
Further, in the invention according to claim 5, the determination means 49 is provided.
Is the stability of the vehicle when the control by the first control means 45 exceeds the predetermined value because the phase delay amount at the predetermined frequency of the actual yaw rate of the vehicle during the steering control of the front wheels or the rear wheels by the first control means 45. The judgment is made when the value exceeds the guaranteed range.

The sixth and seventh aspects of the invention are both dependent on the fifth aspect of the invention, and appropriately change the predetermined value which is the determination threshold of the phase delay amount by the determination means 49. That is, the predetermined value is changed according to the vehicle speed in the invention described in claim 6, and is changed according to the side slip angle of the vehicle in the invention described in claim 7.

The inventions described in claims 8 to 10 are all subordinate to the invention described in claim 1 and are second constituent elements of the invention.
The control mode of the control means 48 of FIG. That is, the second
The control means 48 of the present invention performs control based on a preset map in the invention described in claim 8, and the fuzzy control in the invention described in claim 9.
In the invention described in 0, control based on a neural network is performed.

The eleventh aspect of the invention is dependent on the tenth aspect of the invention, and the vehicle speed, the steering wheel steering angle, and the actual yaw rate of the vehicle are controlled when the second control means 48 performs the control based on the neural network. It is input as the state quantity of the vehicle.

The twelfth aspect of the invention is dependent on the eleventh aspect of the invention, wherein the second control means 48 inputs the vehicle speed V in the form of 1 / V and 1 / V ^2. is there.

[0016]

With the above construction, according to the first aspect of the present invention, within the range where the stability of the vehicle is guaranteed by the control by the first control means 45, the control means 45 controls the actual yaw rate and the target yaw rate. The control amount based on the deviation of is calculated, and the steering of the front wheels or the rear wheels is controlled so that the actual yaw rate matches the target yaw rate by the control amount.
Good stability of the vehicle is ensured even if the characteristics of the vehicle fluctuate to some extent. On the other hand, when the stability control range of the steering control of the front wheels or the rear wheels by the first control means 45 is exceeded and the control system becomes unstable due to entering the nonlinear region, the steering control of the front wheels or the rear wheels is performed as described above. Since the control system is switched from the first control means 45 to the control by the second control means 48 such that the control system is essentially stable, such as map control, fuzzy control, or control based on a neural network, the motion characteristics of the vehicle normally fluctuate. Good vehicle stability is ensured even if there is a large variation over the width. In particular, when the control is switched to the control based on the neural network as in the invention described in claim 8, even if the motion characteristics of the vehicle largely fluctuate beyond the fluctuation range, a trained driver operates the steering wheel to cope with it. The stability of the vehicle is secured in the same manner as.

According to the second aspect of the invention, as long as the control by the first control means 45 guarantees the stability of the vehicle, the steering control of the front wheels or the rear wheels by the control means 45 is H.
It is performed by ∞ control, and its control gain is set within a range determined by two types: a performance target index that gives stability when the characteristics of the vehicle fluctuate, and a performance target index that gives vehicle responsiveness and steady-state characteristics. All of the stability, quick response and steady-state characteristics of the vehicle are well secured.

According to the third aspect of the invention, in the vicinity of the limit of the range where the control by the first control means 45 guarantees the stability of the vehicle, the control gain of the yaw rate change of the vehicle with respect to the steering of the front wheels or the rear wheels is set. Focusing on that the frequency component exceeded the performance target index that gives stability when the characteristics of the vehicle change,
By detecting the frequency component by the determination means 49, it is possible to quickly and accurately determine that the stability guarantee range has been exceeded.

According to the fourth aspect of the invention, in the vicinity of the limit of the range where the control by the first control means 45 guarantees the stability of the vehicle, the state variables such as the sideslip angle of the vehicle and the cornering force of the wheels are reduced. Focusing on the fact that the performance limit is exceeded, and the state quantity is detected by the determination means 49, it is early and accurately determined that the stability guarantee range has been exceeded.

According to the fifth aspect of the invention, in the vicinity of the limit of the range where the control by the first control means 45 guarantees the stability of the vehicle, at the set frequency of the actual yaw rate of the vehicle for steering the front wheels or the rear wheels. Paying attention to the fact that the phase delay amount becomes large, and by detecting the phase delay amount by the determination means 49, it is possible to accurately and early determine that the stability has been exceeded. Here, in the inventions according to claims 6 and 7, even if the first control means 45 is near the limit of the range for guaranteeing the stability of the vehicle, if the vehicle speed at that time is high, the stability range for the stability is ensured. The phase delay amount corresponding to the limit value also increases, and if the sideslip angle of the wheel or vehicle at that time is large, the phase delay amount decreases, but the set value as the determination reference value of the stability guaranteed range is Since the speed is changed according to the vehicle speed or the sideslip angle of the wheels or the vehicle, the situation in which the stability of the vehicle is beyond the guaranteed range is more accurately determined.

According to the eleventh aspect of the present invention, the vehicle speed, the steering wheel steering angle, and the actual yaw rate of the vehicle are used as the vehicle state quantity when performing the control based on the neural network in the second control means 48, and the front wheel or the rear wheel is used. Since the control amount for the steering angle is calculated, it becomes almost the same when a trained driver drives, and the stability of the vehicle is well secured.

According to the invention of claim 12, the second
Of the vehicle speed V to the control means 48 of 1 / V and 1 / V
Since it is performed in the form of ^{2, if} the control based on the neural network is designed based on the theoretical formula of the motion characteristics of the vehicle that normally steers only the front wheels, the control amount of the front wheel or rear wheel steering can be shortened for a short time. Can be calculated with.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a schematic structure of a vehicle steering system according to the first embodiment of the present invention. 1 is a steering wheel, 2 is front left and right wheels, 3 is left and right rear wheels, and 10 is the steering wheel 1. A front wheel steering device that steers the left and right front wheels 2 and 2 by an operation, and a rear wheel steering device 20 as a steering means that steers the left and right rear wheels 3 and 3 according to the steering of the front wheels 2 and 2 by the front wheel steering device 10. Is.

The front wheel steering apparatus 10 has a relay rod 11 arranged in the vehicle width direction, and both ends of the relay rod 11 are tie rods 12 and 12 and a knuckle arm 1, respectively.
It is connected to the left and right front wheels 2, 2 via 3, 13.
A rack and pinion mechanism 14 that moves the relay rod 11 left and right in conjunction with the operation of the steering wheel 1 is arranged on the relay rod 11, and when the steering wheel 1 is operated, the rack and pinion mechanism 14 is moved by an angle corresponding to the operation amount. It is configured to steer the front wheels 2, 2.

On the other hand, the rear wheel steering system 20 has a relay rod 21 arranged in the vehicle width direction as described above, and both ends of the rod 21 are respectively provided with tie rods 22, 22 and knuckle arms 23, 23. Is connected to the left and right rear wheels 3, 3. A centering spring 24 for urging the rod 21 to a neutral position is arranged on the relay rod 21, and a rack & pinion mechanism 25 is arranged on the relay rod 21.
A clutch 26, a speed reduction mechanism 27, and a motor 28 are associated with the mechanism 25, and when the clutch 26 is engaged, the relay rod 21 is moved in the vehicle width direction via the rack and pinion mechanism 25 by the rotational driving of the motor 28. The rear wheels 3 and 3 are steered by an angle corresponding to the rotation amount of the motor 28.

The operation of the motor 28 is controlled by the control unit 29. The control unit 2
As shown in FIG. 3, the 9 is provided with a first control means 45 for H∞ control inside. The control means 45 is
Based on at least the actual yaw rate of the vehicle and the estimated side slip angle of the vehicle as the vehicle state quantities and the output equation of the vehicle, the motor 28 is used to feedback the actual yaw rate of the vehicle to the control target yaw rate in accordance with the control flow of FIG. The state feedback control means 47 for controlling the steering angle of the rear wheels 3 and the control gain calculation means for calculating the control gains of the state equation and the output equation of the state feedback control means 47 based on the control gain calculation flow shown in FIG. It consists of 47 and.

Further, the control unit 29 is
As shown in FIG. 21, the driving condition of the vehicle is as shown in FIG.
A map as a second control means for steering-controlling the rear wheels 3 based on a map stored in advance so that the control system essentially maintains stability when entering the non-linear region of the cornering force of the wheel with respect to The control means 48, the determination means 49 for determining a situation in which the first control means 45 exceeds the range in which the stability of the vehicle is guaranteed, and the steering control of the rear wheel 3 based on the output of the determination means 49 are performed. A control switching means 50 for selectively switching between the first control means 45 and the map control means 48 is provided.

Further, in FIG. 3, reference numeral 35 is a lateral acceleration sensor for detecting a lateral acceleration acting on the vehicle, 36 is a yaw rate sensor as a yaw rate detecting means for detecting an actual yaw rate generated in the vehicle, and 37 is a rear wheel 3. A rear wheel steering angle sensor for detecting a steering angle, a front wheel steering angle sensor 38 for detecting a steering angle of the front wheels 2, and these four sensors 3
The detection signals of 5 to 38 are input to the state feedback control means 47. Further, 39 is a vehicle speed sensor that detects the vehicle speed, and 40 is a road surface friction coefficient sensor that detects the friction coefficient μ of the road surface below the vehicle.
The detection signal of is input to the control gain calculation means 46. Further, the detection signal of the front wheel steering angle sensor 38 is input to the map control means 48, and the yaw rate sensor 36 and the front wheel steering angle sensor 38 are input to the determination means 49.
And each detection signal of the vehicle speed sensor 39 is input.

Next, the control of the motor 28 by the control unit 29 will be described according to the control flow of FIG.

In FIG. 4, in step S1, for example, 20
After waiting for the control timing for each set cycle such as msec, in step S2, the sensors 36 to 39 are
The vehicle speed Vsp, the front wheel steering angle Fstg, the rear wheel steering angle Rstg, and the actual yaw rate y occurring in the vehicle based on the detection signal of
r and the amount of motion state of each vehicle of lateral acceleration Yg acting on the vehicle are measured.

Then, in step S3, in order to identify the transfer function of the yaw rate generated in the vehicle with respect to the front wheel steering,
After updating a large number (for example, 1024) of front wheel steering angles Fstg and signal pairs of the actual yaw rate yr of the vehicle as the identification signals, the identification is performed in step S4. This identification is performed by first calculating the cross spectrum Sfy of the yaw rate yr with respect to the front wheel steering angle Fstg and calculating the front wheel steering angle F
The power spectrum Sff of stg is calculated, and then the frequency transfer function H (ω) is calculated based on the following equation.

[0033]

[Equation 1] Then, in step S5, the set frequency of the frequency transfer function H (ω) (the steering wheel steering frequency is, for example, 1
Hz) and the phase delay angle φ (1)
e (H (ω)), and a predetermined value as a reference value for determining whether or not the phase delay angle φ (1) exceeds the guaranteed range of vehicle stability by the first control means 45 in step S6. (For example, 30 deg). And φ (1) ≦
If it is within the guarantee range of 30 deg, step S7
While the rear wheel 3 is controlled to H∞ in step S4, if the guaranteed range of φ (1)> 30 deg is exceeded, the rear wheel 3 is map-controlled in step S8.

The above H∞ control is performed as follows. That is, first, the target yaw rate y of the vehicle is calculated based on the following equation.
While setting rt, the yaw rate deviation en between the target yaw rate yrt and the actual yaw rate yr is calculated.

[0035]

[Equation 2] However, A is the stability factor and L is the wheel base of the vehicle.

After that, the steering amount r of the rear wheels 3 as the feedback control amount of the H∞ control is determined based on the following vehicle state equation (1) and output equation (2) in the H∞ control, and this control amount is determined. The steering control of the rear wheel 3 is performed by r.

[0037]

[Equation 3] However, Xh is a state quantity corresponding to a plurality of state quantities of the vehicle (hereinafter, “state quantity” in the description of the present specification means this), and the state quantity of the vehicle is, for example, a sideslip angle of the vehicle,
It is the steering angle of the rear wheels or the changing speed thereof, the cornering force of the front wheels and the rear wheels, or the yaw rate acting on the vehicle, and these are estimated by the above two equations.

The control gains Acl, Bcl, Ccl and Dcl of the vehicle state equation (1) and the output equation (2) are also used.
Is calculated and determined in advance based on the control gain determination flow shown in FIG.

Next, the control gain determination flow in the H∞ control shown in FIG. 5 will be described.

In FIG. 5, first, in step S11, in order to change the performance target index W3 which gives the stability when the characteristic of the vehicle changes as the control gain characteristic of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheels 3. The correction coefficient (weight) Wn is changed according to the vehicle speed Vsp. This change is made by determining the correction coefficient Wn to a large value according to the increase of the vehicle speed Vsp, as shown in step S11.

Then, in step S12, a performance target index W3 that gives the stability when the characteristics of the vehicle are changed is determined based on the following quadratic expression of the Laplace variable s.

[0042]

[Equation 4] However, a and c are constants. Based on the above equation, as shown in FIG. 18, the performance target index W3 that gives stability when the characteristic of the vehicle changes is changed to the low frequency side when the correction coefficient Wn is large, and the correction coefficient Wn is small. When it is a value, it is changed to the high frequency side.

Subsequently, in step S13, the performance target index W1 (however, shown in FIG. 18) which gives the vehicle speed response and steady-state characteristics as the control gain characteristics of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheels 3 is provided. , Reciprocal display) is designated as a fixed value based on the cubic expression of the Laplace variable s below.

[0044]

[Equation 5] However, d, e, f, g and h are constants.

Then, in step S14, the above two performance target indices W3 and W1 are converted into state equations, respectively, and the two state equations and the following vehicle state equation (3) and output equation (4) are expressed. Each of the control gains Acl ~ Dcl of the H ∞ control is obtained by synthesizing the person into one state equation, decomposing the synthesized state equation into two Riccati equations, and solving this equation as an eigenvalue problem by the Hamilton matrix. Ask for.

[0046]

[Equation 6] In the vehicle state equation (3) and the output equation (4), β is the sideslip angle at the center of gravity of the vehicle, Cf and Cr are the cornering forces of the front and rear wheels, and Rst.
g is the steering angle of the rear wheels, lf and lr are the distances between the front and rear axles and the center of gravity of the vehicle, I is the moment of inertia of the vehicle with respect to yaw rate, m is the vehicle body mass, Vsp is the vehicle speed, Gy is the lateral elastic coefficient of the wheels, and Kyf And Kyr are the cornering powers of the front and rear wheels, respectively. Here, the vehicle speed Vsp is the vehicle speed sensor 39.
The actual vehicle speed detected by is used, and the others are fixed values set in advance.

After that, in step S15, the control gains Acl to Dcl are changed from the continuous control system to the digital control system by the bilinear conversion method, and the process ends. The control gains Acl to Dcl can be determined by a method of sequentially reading the values stored in the map in advance according to the motion state of the vehicle, in addition to the above-described sequential calculation.

Further, in the map control of step S8 of FIG. 4, as shown in the same step, the rear wheel steering amount r is calculated according to the following equation according to the front wheel steering angle Fstg.

[Equation 7] Calculate with. However, k is a proportional constant, and the proportional constant k is set to a large value in accordance with the vehicle speed up to a predetermined high vehicle speed value V0, and is gradually set to a small value at a vehicle speed exceeding the above predetermined value V0, resulting in non-linearity. It is designed to make the control system essentially stable in the area.

Therefore, step S7 in the control flow of FIG.
Thus, the actual yaw rate yr of the vehicle, the estimated sideslip angle β of the vehicle, and the cornering forces Cf, Cr of the front and rear wheels are used as the state quantities of the vehicle, based on the vehicle state equation (1) and the output equation (2). A state feedback control means 46 is configured to control the rear wheel steering device 20 so that the actual yaw rate yr is controlled by the state feedback control to the control target yaw rate yrt.

Further, according to the control gain determination flow of FIG. 5, as the control gain characteristic of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheels 3, the performance target index W3 that gives stability when the characteristic of the vehicle changes and the vehicle target index W3. A vehicle state equation (3) in which two types of performance target indexes W1 giving quick response and steady characteristics and the steering angle Rstg of the rear wheels 3 are input.
18 and the output equation (4), the vehicle motion characteristic (control gain characteristic) is a predetermined frequency (0.3 r in FIG. 18) at which the open loop transfer function becomes 0 db as shown by the solid line in FIG.
It is located immediately below the performance target index W3 that gives the above stability in a high frequency range exceeding ad / sec), and provides the above steady-state characteristics etc. in a low frequency range below a predetermined frequency (0.3 rad / sec). A control gain calculation means 47 for calculating the control gains Acl to Dcl of the state feedback control means 46 is arranged so as to be located immediately above W1. Then, the state feedback control means 46 and the control gain calculation means 47 calculate the control amount (rear wheel steering amount) r based on the deviation en between the actual yaw rate yr detected by the yaw rate sensor 36 and the target yaw rate yrt, The yaw rate yr is actually controlled by the controlled variable r.
The rear wheel steering device 2 so as to match the target yaw rate yrt.
A first control unit 45 that feedback-controls 0 is configured.

Further, in step S8 of the control flow of FIG. 4, a vehicle speed-proportional coefficient characteristic map preset so that the stability of the vehicle is essentially guaranteed, and the front wheel steering angle Fst.
A map control means 48 is configured as a second control means that calculates a control amount r according to the steering wheel steering based on g and controls the rear wheel steering device 20 with the control amount r.

In addition, steps S3 to S of the control flow
6, the actual yaw rate y of the vehicle with respect to the steering of the front wheels 2 during the steering control of the rear wheels 3 by the first control means 45.
Judgment means 4 for judging that the phase delay amount φ (1) at a predetermined frequency (1HZ) of r exceeds a predetermined value (30 deg).
9, and the determination means 49 causes the phase delay amount φ (1) of the frequency transfer function of the vehicle to be a predetermined value (30d by the shift from step S6 to step S8).
The control switching means 50 is configured to switch the steering control of the rear wheels 3 from the H ∞ control to the control by the map control means 48 when it is determined that the vehicle speed has exceeded Eg).

Therefore, in the first embodiment described above,
Within the guaranteed range of vehicle stability by H∞ control, the front wheels 2
Frequency transfer function H of yaw rate of vehicle for steering
Since the phase delay angle φ (1) of (ω) is less than the predetermined value (30 deg), the steering control of the rear wheels 3 is performed by the above H∞ control. As a result, the H ∞ control of the rear wheel 3
As shown by the solid line in FIG. 18, the motion characteristics of the vehicle are located just below the performance target index W3 which gives stability in a high frequency range exceeding a predetermined frequency (0.3 rad / sec), and is 0.
In the low frequency range of 3 rad / sec or less, since it is located immediately above the performance target index W1 that gives steady characteristics and the like, FIG.
In contrast to the normal vehicle motion characteristics in which H ∞ control is not performed, the control gain becomes a small value in the high frequency range exceeding 0.3 rad / sec, and the control gain in the low frequency range of 0.3 rad / sec or less. Is a big price. Therefore, in the above high frequency range, since the control gain is small, the oscillation of the rear wheel steering control is reliably prevented, the stability against vehicle characteristic variation is improved, the robust stability is improved, and the driving in the low frequency range is improved. The vehicle responds quickly with a large control gain in response to the operator's steering wheel operation, and the vehicle produces a yaw rate with a very small deviation from the target yaw rate, improving the quick response and steady-state characteristics. become.

On the other hand, as the vehicle motion approaches the limit of the guaranteed range of the vehicle stability by the H∞ control, the frequency transfer function H of the yaw rate of the vehicle with respect to the steering of the front wheels 2 is increased.
If the phase delay angle φ (1) of (ω) increases and the phase delay angle φ (1) exceeds the predetermined value 30 deg at the time when it exceeds the guaranteed range, this is determined by the determination means 49, and immediately at that time. Further, the steering control of the rear wheels 3 is surely switched by the control switching means 50 from the H∞ control to the map control. Since this map control is essentially formed in the control system that guarantees the stability of the vehicle, the vehicle can be stably controlled even in a non-linear region that exceeds the guaranteed range of the H∞ control.

FIG. 6 shows a block configuration of a control system in the vehicle steering system according to the second embodiment of the present invention. In the case of the second embodiment, the configuration of the control system is different from that of the first embodiment shown in FIG. 3 in that instead of the map control means 48, the fuzzy control means 61 is provided as the second control means. Is. The rest of the configuration of the control system is the same as that of the first embodiment, and the same members are designated by the same reference numerals and their description is omitted.

The control of the motor 28 by the control unit 29 of the control system is performed according to the control flow shown in FIG. This control flow is basically the same as the control flow of FIG. 4, except that the reference value (predetermined value) for determining that the vehicle stability guarantee range has been exceeded in step Sx after step S5. If the control switching phase angle φ1 is not fixed and the value is changed to a large value in accordance with the increase of the vehicle speed Vsp, and φ (1)> φ1 in step S6, the H∞ control is replaced with another in step S8 ′. Fuzzy control is used as the control, and a fuzzy control amount r for steering the rear wheels by the fuzzy control is calculated, and the motor 28 is drive-controlled by the control amount r to steer the steering angle of the rear wheel 3.

The fuzzy control in step S8 'is a control system tuned exclusively for the non-linear region so that the control system is essentially stable. Specifically, the yaw rate deviation en and its change rate den The following formula based on the membership function which is a function with / dt

[Equation 8] Therefore, the control amount r is calculated so that the change rate of the actual yaw rate yr of the vehicle decreases while ensuring good vehicle stability.

In step S8 ', steering wheel steering is performed based on the membership function which is a function of the yaw rate deviation en and the rate of change den / dt of the yaw rate preset so that the stability of the vehicle is essentially guaranteed. A fuzzy control means 61 is configured as a second control means for calculating a control amount r corresponding thereto and controlling the motor 28 of the rear wheel steering device with the control amount r.

Therefore, in the second embodiment, when the driving condition of the vehicle is near the limit of the guaranteed range of the H∞ control, the control response is lower when the vehicle speed is high than when the vehicle speed is low. However, the phase delay amount corresponding to the limit value of the above-mentioned guaranteed range increases more than that at low vehicle speed, but the predetermined value φ1 as the determination reference value for control switching is changed to a larger value at higher vehicle speed. Accurate and quick determination of situations that exceed the stability guarantee range. Moreover, in the situation where the H∞ control guaranteed range thus determined is exceeded, the steering control of the rear wheels 3 is switched from the H∞ control to the fuzzy control, and the fuzzy control of the vehicle is performed as shown in FIG. Since the control system is tuned to essentially stabilize the vehicle in the nonlinear region of the cornering force of the vehicle with respect to the estimated sideslip angle β, the vehicle is stabilized even in the nonlinear region that exceeds the guaranteed range of H∞ control. You can control.

FIG. 8 shows a block configuration of a control system in a vehicle steering system according to the third embodiment of the present invention. In the third embodiment, the configuration of the control system differs from that of the first embodiment shown in FIG. 3 in that a neural network control means 62 is provided as the second control means instead of the map control means 48. That is. The control means 62 includes a yaw rate sensor 36, a front wheel steering angle sensor 38 and a vehicle speed sensor 3.
Each detection signal 9 is input. The rest of the configuration of the control system is the same as that of the first embodiment, and the same members are designated by the same reference numerals and their description is omitted.

The control of the motor 28 by the control unit 29 of the control system is performed according to the control flow shown in FIG. In this control flow, the sideslip angle β of the center of gravity of the vehicle is determined in step Sy after step S5.
The control switching phase angle (predetermined value) φ1 is changed according to
The value is set to a smaller value when the side steer angle β increases and the understeer tendency increases with reference to deg, while it is set to a larger value when the side slip angle β decreases and the oversteer tendency decreases.
When φ (1)> φ1 in step S6, the steering control amount r of the rear wheels by the neural network is calculated in step S8 ″, and the rear wheels 3 are steered by the control amount r.

Here, the neural network is composed of, for example, three layers, as shown in FIG. 10, four input layers a, four intermediate layers b, and one output layer c. For each of the input layers a, the front wheel steering angle Fstg, the actual yaw rate yr, and the reciprocal of the vehicle speed 1
/ Vsp, the reciprocal 1 / Vsp ² of the square of the vehicle speed is input, the output layer c outputs the wheel steering amount r after the controlled variable. Also,
The output functions f1, f2, and f3 of each of the three layers are given by the following equations with the input as x.

[0063]

[Equation 9] Further, the weights of the layers a to c are, in advance, the vehicle speed, the steering angle of the front wheels and the rear wheels, the actual yaw rate, and the center of gravity of the vehicle when an extremely skilled driver repeatedly travels beyond the stability limit of the vehicle. The skid angle and the steering wheel operation of a skilled driver at that time are given as a teacher input for learning, and the learning result is incorporated as a control law.

Vehicle speed Vsp input to the neural network
Is in the form of its reciprocal 1 / Vsp and the square reciprocal 1 / Vsp ^2. The linear motion model of a normal two-wheel steering vehicle is expressed by the following equation, and the term relating to the vehicle speed in the equation is 1 / Vsp
And 1 / Vsp ² are used, and this is for matching with this arithmetic expression (vehicle speed is expressed by V).

[0065]

[Equation 10] In step S8 '' of FIG. 9, the stability of the vehicle is essentially guaranteed by learning the steering wheel operation of the skilled driver when the vehicle exceeds the limit of stability and incorporating it in advance. The neural network control means 62 as the second control means for calculating the control amount r according to the steering wheel steering based on the control law and controlling the motor 28 of the rear wheel steering device by the control amount r is configured. ing.

Therefore, in the third embodiment described above,
Even if the phase delay characteristic of the frequency transfer function of the actual yaw rate of the vehicle changes according to the sideslip angle β of the center of gravity of the vehicle, the control switching phase angle (predetermined value) φ1 also corresponds to the sideslip angle β.
Therefore, regardless of the skid angle β at the time when the driving condition of the vehicle exceeds the limit of the guaranteed range of the H∞ control, the time when the vehicle exceeds the guaranteed range can be accurately and quickly determined. .

Moreover, in a situation where the guaranteed range of the H ∞ control is exceeded, the steering control of the rear wheels 3 is switched from the H ∞ control to the control based on the neural network, and the control based on the neural network is controlled by the side slip angle β of the wheel. Since the control system imitates the operation of the skilled driver in the non-linear region of the cornering force of the vehicle, the vehicle can be stably controlled even in the non-linear region exceeding the guaranteed range of the H∞ control.

Moreover, the inputs to the neural network shown in FIG. 10 are actually the yaw rate yr, the front wheel steering angle Fstg and the vehicle speed Vsp, and these inputs can be measured relatively stably, so that the state quantity of the vehicle can be stabilized. Can be detected. Further, since the yaw rate is actually input, it is possible to improve the steering responsiveness of the rear wheels with respect to the steering of the front wheels and the stability with respect to a disturbance such as a side wind or a road surface. Further, since the vehicle speed Vsp is input in the form of 1 / Vsp, 1 / Vsp ² which is adapted to the term relating to the vehicle speed in the arithmetic expression of the characteristic of the two-wheel steering model of the vehicle,
The calculation speed of the rear wheel steering amount r based on the neural network can be increased.

FIG. 11 is a flow chart showing a modification of the steering control of the rear wheels as the fourth embodiment of the present invention. In the case of the fourth embodiment, the hardware structure of the vehicle steering system is as shown in FIG.
2 and FIG. 3 will be used in the following description of the control flow.

In FIG. 11, after waiting for the control timing for each predetermined cycle in step S21, step S22 is performed.
Based on the detection signals of the various sensors 35 to 39, the vehicle speed Vsp,
Front wheel steering angle Fstg, rear wheel steering angle Rstg, actual yaw rate yr occurring in the vehicle, and lateral acceleration Y acting on the vehicle.
The motion state quantity of each vehicle in g is measured.

Then, in step S23, the target yaw rate yrt of the vehicle and the yaw rate deviation en between the target yaw rate yrt and the actual yaw rate yr are calculated, and in step S24, the steering of the rear wheel 3 as the feedback control amount of the H∞ control is calculated. The control amount r is determined based on the vehicle state equation and the output equation in the H ∞ control. Incidentally, the calculation of steps S23 and S24 is carried out by H∞ of step S7 of FIG. 4 in the first embodiment.
The control yaw rate yrt and the yaw rate deviation en are described in "Equation 2", and the vehicle state equation and the output equation are described in "Equation 3".

Thereafter, in step S25, the vehicle state quantity Xh estimated from the vehicle state equation and the output equation is calculated.
For example, the estimated sideslip angle of the vehicle or the estimated cornering force of the wheels is compared with a limit value Xr for the instability of the vehicle (that is, a predetermined value indicating the performance limit of the vehicle). Then, the motor 28 is drive-controlled based on the feedback control amount r by the above H∞ control to steer-control the steering angle of the rear wheels 3.

On the other hand, in step S25, the estimated state quantity X of the vehicle
When Xh> Xr where h exceeds the predetermined value Xr, the steering wheel steering is performed based on the vehicle speed-proportional coefficient characteristic map and the front wheel steering angle Fstg which are preset so that the control system is essentially stable in step S27. Is calculated, and the rear wheel steering device 20 is controlled by the map control amount r in step S26.

In step S27 of the above control flow, the map control means as the second control means for performing the map control in which the control system is essentially stable in the region where the change of the cornering force with respect to the side slip angle of the wheel is nonlinear. 48
Is configured. Further, the step S25 constitutes the judging means 49 for judging when the state quantity Xh of the vehicle exceeds the predetermined value Xr. By the shift from step S25 to step S27, the state quantity Xh of the vehicle is judged by the judging means 49. A control switching unit 50 is configured to switch the steering control of the rear wheels 3 from the H∞ control to the control by the map control unit 48 when it is determined that the predetermined value Xr is exceeded.

Therefore, in the fourth embodiment,
In the guaranteed range of H∞ control in which the estimated side slip angle β of the vehicle and the internal state quantities Xh of the front and rear wheels cornering forces Cf, Cr, etc. are below a predetermined value Xr, the steering control of the rear wheels 3 is performed by the H∞ control, As shown in FIG. 18, the control gain of the rear wheel steering control is set to a large value in accordance with the performance target index W1 which gives the speed response and the steady characteristic of the vehicle in the low frequency range of 0.3 rad / sec or less, and is set to 0. In the high frequency range exceeding 0.3 rad / sec, the value is limited to a small value along the performance target index W3 that gives stability when the characteristics of the vehicle fluctuate, so the vehicle responds quickly in response to the steering operation of the driver and Produces a yaw rate with a very small deviation from the target yaw rate, and even if the dynamic characteristics of the vehicle fluctuate, the oscillation of the rear wheel steering control is reliably prevented and good vehicle stability is ensured. It will be.

On the other hand, the state quantity Xh of the vehicle is a predetermined value Xr.
If the H∞ control range is exceeded, the rear wheel 3
The steering control of is switched from the H ∞ control to the map control, and this map control is tuned to a control system that essentially stabilizes the vehicle in the nonlinear region of the cornering force of the vehicle with respect to the estimated sideslip angle β of the vehicle. It is possible to ensure the stability of the vehicle even in a non-linear region that exceeds the guaranteed range of the H∞ control.

FIG. 12 is a flowchart showing a modified example of the rear wheel steering control as the fifth embodiment of the present invention. In the case of the fifth embodiment, the hardware structure of the vehicle steering system is as shown in FIG.
1 and the second embodiment shown in FIG. 6, and in the following description of the control flow, the member reference numerals shown in FIGS. 2 and 6 are used.

The control flow of the fifth embodiment is basically the same as the control flow of FIG. 11, except that in the region where the internal state quantity Xh of the vehicle exceeds the predetermined value Xr in step S25, In S27 ′, fuzzy control is used as another control in place of the H∞ control, a fuzzy control amount r for steering the rear wheels by the fuzzy control is calculated, and the motor 28 is driven and controlled by the control amount r to control the rear wheel 3 The steering angle is controlled.

As described in detail in the second embodiment, the fuzzy control in step S27 'is performed with the yaw rate deviation en and its change rate den / dt that are preset so that the stability of the vehicle is essentially guaranteed. Based on the membership function, which is a function of
Is calculated, and the motor 2 of the rear wheel steering device is calculated with the control amount r.
8 is controlled, and the step S27 'constitutes the fuzzy control means 61 as the second control means. Since the other steps are the same as those in the control flow of FIG. 11, the same steps are designated by the same reference numerals and the description thereof will be omitted.

Also in the fifth embodiment, H∞
In the non-linear region beyond the control guarantee range, the steering control of the rear wheels 3 is switched from the H∞ control to the fuzzy control, and this fuzzy control essentially causes the vehicle to be in the non-linear region of the cornering force of the vehicle with respect to the estimated sideslip angle β of the vehicle. It is tuned to a control system that stabilizes the vehicle so that the stability of the vehicle can be ensured.

FIG. 13 is a flow chart showing a modified example of the steering control of the rear wheels as the sixth embodiment of the present invention. In the case of the sixth embodiment, the hardware structure of the vehicle steering system is as shown in FIG.
2 is substantially the same as that of the first embodiment shown in FIG. 8 and the third embodiment shown in FIG. 8, and the member reference numerals shown in FIGS. 2 and 8 are used in the following description of the control flow.

The control flow of the sixth embodiment is basically the same as the control flow of FIG. 11, except that in the region where the internal state quantity Xh of the vehicle exceeds a predetermined value Xr in step S25, In S27 '', a control based on a neural network is used as another control in place of the H∞ control, a fuzzy control amount r for rear wheel steering by the neural network control is calculated, and the motor 28 is controlled by the control amount r. Then, the steering angle of the rear wheel 3 is controlled.

As described in detail in the third embodiment, the neural network control in step S27 '' described above causes the vehicle to travel in advance beyond the stability limit so that the stability of the vehicle is essentially guaranteed. The steering wheel operation of the skilled driver at the time of learning is learned, and the control amount r corresponding to the steering wheel steering is calculated based on the incorporated control law, and the motor 28 of the rear wheel steering device is controlled by the control amount r. This step S27 ″ constitutes the neural network control means 62 as the second control means. still,
Since the others are the same as the control flow in FIG. 11, the same reference numerals are given to the same steps and the description thereof will be omitted.

Also in the sixth embodiment, H∞
In the non-linear region exceeding the control guarantee range, the steering control of the rear wheels 3 is switched from the H ∞ control to the control based on the neural network, and this fuzzy control is performed in the non-linear region of the vehicle cornering force with respect to the estimated skid angle β of the vehicle. Since it is tuned to a control system that essentially stabilizes the vehicle, it is possible to ensure the stability of the vehicle.

FIG. 14 is a flow chart showing a modified example of the steering control of the rear wheels as the seventh embodiment of the present invention. In the case of the seventh embodiment, the hardware configuration of the vehicle steering system is as shown in FIG.
2 and FIG. 3 will be used in the following description of the control flow.

In FIG. 14, after waiting for the control timing for each predetermined cycle in step S31, step S32 is performed.
Based on the detection signals of the various sensors 35 to 39, the vehicle speed Vsp,
Front wheel steering angle Fstg, rear wheel steering angle Rstg, actual yaw rate yr occurring in the vehicle, and lateral acceleration Y acting on the vehicle.
The motion state quantity of each vehicle in g is measured.

Subsequently, in step S33, the target yaw rate yrt of the vehicle and the yaw rate deviation en between the target yaw rate yrt and the actual yaw rate yr are calculated, and in step S34, the steering of the rear wheel 3 as the feedback control amount of the H∞ control is calculated. The control amount r is determined based on the vehicle state equation and the output equation in the H ∞ control. Incidentally, the calculation of steps S33 and S34 is carried out by H∞ of step S7 of FIG. 4 in the first embodiment.
The control yaw rate yrt and the yaw rate deviation en are described in "Equation 2", and the vehicle state equation and the output equation are described in "Equation 3".

Then, in step S35, the power spectrum P of the yaw rate of the vehicle detected by the yaw rate sensor 36 is calculated, and in step S36, the noise intensity, that is, the component ratio Piz of 1 Hz or more with respect to the entire power spectrum P is calculated as follows. Calculate by formula.

[0089]

[Equation 11] Then, in step S37, it is determined whether or not the noise intensity Piz exceeds a predetermined value Pi corresponding to the performance target index W3 that gives stability when the characteristics of the vehicle fluctuate, and within the guaranteed range of H∞ control of Piz≤Pi. Rear wheel 3 under H∞ control in step S38
On the other hand, when Piz> Pi is exceeded and the guaranteed range of the H∞ control is exceeded, the vehicle speed-proportional coefficient characteristic map preset in step S39 so that the control system is essentially stable, and The control amount r corresponding to the steering wheel steering is calculated based on the front wheel steering angle Fstg, and step S
At 38, the rear wheel steering device 20 is controlled by the map control amount r.

In step S39 of the above control flow, the map control means as the second control means for performing the map control in which the control system is essentially stable in the region where the change of the cornering force with respect to the side slip angle of the wheel is nonlinear. 48
Is configured. Also, by steps S35 to S37,
When the noise intensity Piz mixed in the yaw rate exceeds the predetermined value Pi corresponding to the performance target index W3 which gives the stability when the characteristics of the vehicle fluctuate, it is determined that the stability of the vehicle exceeds the guaranteed range. The determination means 49 is configured, and when the determination means 49 determines that the stability of the vehicle has been exceeded by the transition from step S37 to step S39, the steering control of the rear wheels 3 is mapped from the H∞ control to the map. Control switching means 5 adapted to switch to control by the control means 48
0 is configured.

Therefore, in the seventh embodiment,
The noise intensity Piz mixed in the yaw rate of the vehicle is a predetermined value P
In the guaranteed range of the H∞ control in which the motion state of the vehicle is i or less and is less than the performance target index W3, the control gain of the rear wheel steering control is, as shown in FIG. 18, a low frequency of 0.3 rad / sec or less. In the range, it is set to a large value along the performance target index W1 that gives the vehicle speed response, etc., and in the high frequency range exceeding 0.3 rad / sec, it is set to a small value along the performance target index W3 that gives the stability when the characteristics of the vehicle change. Since the value is limited, the vehicle responds quickly in response to the driver's steering operation, and the yaw rate with a very small deviation from the target yaw rate occurs in the vehicle, and even if the characteristics of the vehicle fluctuate, Oscillation of the wheel steering control is reliably prevented, and good vehicle stability is ensured.

On the other hand, when the noise intensity Piz mixed in the yaw rate of the vehicle exceeds the predetermined value Pi and the motion state of the vehicle exceeds the performance target index W3 and is out of the guaranteed range of the H∞ control, The steering control is switched from the above H ∞ control to the map control, and this map control is a control system that imitates the operation of a skilled driver even in the nonlinear region of the cornering force of the vehicle with respect to the estimated sideslip angle β of the vehicle shown in FIG. , H ∞ control can ensure vehicle stability even in a non-linear region that exceeds the guaranteed range.

FIG. 15 is a flow chart showing a modified example of the steering control of the rear wheels as the eighth embodiment of the present invention. In the case of the eighth embodiment, the hardware configuration of the vehicle steering system is as shown in FIG.
1 and the second embodiment shown in FIG. 6, and in the following description of the control flow, the member reference numerals shown in FIGS. 2 and 6 are used.

The control flow of the eighth embodiment is basically the same as the control flow of FIG. 14, except that the noise intensity Piz mixed in the yaw rate of the vehicle in step S37 changes when the characteristic of the vehicle changes. In a region exceeding a predetermined value Pi corresponding to the performance target index W3 that gives stability, step S39 '
The fuzzy control is used as another control instead of the H∞ control, the control amount r of the rear wheel steering by the fuzzy control is calculated, and the motor 28 is drive-controlled by the control amount r to control the steering angle of the rear wheel 3. Steering control.

As described in detail in the second embodiment, the fuzzy control in step S39 'is performed with the yaw rate deviation en and its rate of change den / dt preset so that the stability of the vehicle is essentially guaranteed. Based on the membership function, which is a function of
Is calculated, and the motor 2 of the rear wheel steering device is calculated with the control amount r.
8 and the step S39 'constitutes a fuzzy control means 61 as a second control means. The other steps are the same as those in the control flow shown in FIG.

Also in the eighth embodiment, H∞
In the non-linear region beyond the control guarantee range, the steering control of the rear wheels 3 is switched from the H∞ control to the fuzzy control, and this fuzzy control essentially causes the vehicle to be in the non-linear region of the cornering force of the vehicle with respect to the estimated sideslip angle β of the vehicle. It is tuned to a control system that stabilizes the vehicle so that the stability of the vehicle can be ensured.

FIG. 16 is a flow chart showing a modification of the rear wheel steering control as the ninth embodiment of the present invention. In the case of the ninth embodiment, the hardware structure of the vehicle steering system is as shown in FIG.
2 is substantially the same as that of the first embodiment shown in FIG. 8 and the third embodiment shown in FIG. 8, and the member reference numerals shown in FIGS. 2 and 8 are used in the following description of the control flow.

The control flow of the sixth embodiment is basically the same as the control flow of FIG. 14, except that the noise intensity Piz mixed in the yaw rate of the vehicle in step S37 changes when the characteristic of the vehicle changes. In a region exceeding a predetermined value Pi corresponding to the performance target index W3 giving stability, step S39 ''
A control based on a neural network is used as another control in place of the H ∞ control, the control amount r of the rear wheel steering by the neural network control is calculated, and the motor 28 is driven and controlled by the control amount r. The steering angle of 3 is controlled.

As described in detail in the third embodiment, the neural network control in step S39 '' described above allows the vehicle to travel beyond the stability limit in advance so that the stability of the vehicle is essentially guaranteed. The steering wheel operation of the skilled driver at the time of learning is learned, and the control amount r corresponding to the steering wheel steering is calculated based on the incorporated control law, and the motor 28 of the rear wheel steering device is controlled by the control amount r. This step S39 ″ constitutes the neural network control means 62 as the second control means. still,
Others are the same as the control flow in FIG. 14, and therefore, the same reference numerals are given to the same steps and the description thereof will be omitted.

Also in the ninth embodiment, H∞
In the non-linear region exceeding the control guarantee range, the steering control of the rear wheels 3 is switched from the H ∞ control to the control based on the neural network, and this fuzzy control is performed in the non-linear region of the vehicle cornering force with respect to the estimated skid angle β of the vehicle. Since it is tuned to a control system that essentially stabilizes the vehicle, it is possible to ensure the stability of the vehicle.

FIG. 17 shows a vehicle steering system according to the tenth embodiment of the present invention. In the above-described first to ninth examples,
In each case, the rear wheels 3 and 3 are steered by using the rear wheel steering device 20, whereas in the tenth embodiment, the front wheels 2 and 2 are electrically steered separately from the steering wheel 1. It was done.

That is, in the case of the tenth embodiment, the steering system does not include the rear wheel steering system 20 shown in FIG. 2, but the rack and rack arranged on the relay rod 11 in parallel with the front wheel steering system 10.
Pinion mechanism 71 and motor 72 for driving the mechanism 71
Are provided, and the operation of the motor 72 is controlled by the control unit 29. The other configuration of the steering device is the same as that of the first embodiment described above, but in the case where the rear wheels are steered by the rear wheel steering of the first embodiment, the steering control is performed in a phase opposite to that of the front wheels because of steering the front wheels. In the present embodiment, steering control is performed to increase the steering angle of the front wheels, and in the case of steering control of the rear wheels to the same phase in the first embodiment, in this embodiment, steering control is performed to the side that decreases the steering angle of the front wheels. Good.

In the above explanation, in the state feedback control of the rear wheel steering, the vehicle side slip angle, the rear wheel steering angle, the changing speed of the steering angle, the cornering force of the front wheels and the rear wheels are estimated as the observed amount of the vehicle. , And the yaw rate acting on the vehicle was used to accurately observe the state of the vehicle. To observe the state of the vehicle, at least two types of the actual yaw rate of the vehicle and the sideslip angle of the vehicle should be observed.

In the above description, the first control means 4
5 is configured by H∞ control, but performs LQG control (state feedback control) of the vehicle yaw rate,
Alternatively, it is needless to say that the same can be applied to the one in which the steering angle of the rear wheel is feedback-controlled by the feedback control amount according to the deviation between the actual yaw rate and its target value.

[0105]

As described above, according to the vehicle steering system of the present invention, the dynamic characteristics of the vehicle exceed the range in which the steering control of the front wheels or the rear wheels by the first control means guarantees the stability of the vehicle. If it fluctuates, grasp the situation early,
Since the steering control of the front wheels or the rear wheels can be switched by the essentially stable second control means, the stability of the vehicle can be favorably ensured.

In particular, according to the second aspect of the invention, since the steering control of the front wheels or the rear wheels by the first control means is performed by the H∞ control, the stability and speed of the vehicle when the characteristic of the vehicle changes It also has the effect of ensuring good responsiveness and steady-state characteristics.

According to the invention described in claims 3 to 5, it is possible to detect early and accurately that the control by the first control means exceeds the range for guaranteeing the stability of the vehicle, and the stability of the vehicle is stabilized. It is possible to better secure the property.

According to the inventions of claims 6 and 7, the first
Regardless of the difference in the vehicle speed or the sideslip angle of the vehicle when the control means exceeds the range in which the stability of the vehicle is guaranteed, the situation beyond the guaranteed range can be more accurately determined.

According to the invention of claim 10, the second aspect
When the steering control of the front wheels or the rear wheels by the control means is performed by the control based on the neural network, and even if the motion characteristics of the vehicle largely fluctuate beyond the fluctuation range, a trained driver handles it by operating the steering wheel. Since the steering is carried out substantially in the same manner, the stability of the vehicle can be better ensured.

According to the eleventh aspect of the present invention, when the control based on the neural network is performed, the vehicle speed, the steering wheel steering angle, and the actual yaw rate of the vehicle are used as the vehicle state quantities to control the steering angle of the front wheels or the rear wheels. Since the amount is calculated, it becomes almost the same when a trained driver drives, and the stability of the vehicle can be better ensured.

According to the twelfth aspect of the invention, the input of the vehicle speed V in the control based on the neural network is 1
If the control based on the neural network is designed based on the theoretical equation of the motion characteristics of the vehicle that normally steers only the front wheels, the steering is performed in the form of / V and 1 / V ^2. The control amount can be calculated in a short time.

[Brief description of drawings]

FIG. 1 is a block diagram of the invention according to claim 1.

FIG. 2 is a schematic configuration diagram showing an overall configuration of a vehicle steering system according to a first embodiment of the present invention.

FIG. 3 is a block configuration diagram of a control system in the steering system.

FIG. 4 is a flowchart of steering control of rear wheels.

FIG. 5 is a flowchart for determining a control gain of H∞ control.

FIG. 6 is a view corresponding to FIG. 3 showing a second embodiment.

FIG. 7 is also a view corresponding to FIG.

FIG. 8 is a view corresponding to FIG. 3 showing a third embodiment.

FIG. 9 is a view equivalent to FIG.

FIG. 10 is a diagram showing a specific example of a neural network.

FIG. 11 is a view corresponding to FIG. 4 showing a fourth embodiment.

FIG. 12 is a view, corresponding to FIG. 4, showing a fifth embodiment.

FIG. 13 is a view corresponding to FIG. 4 showing a sixth embodiment.

FIG. 14 is a view, corresponding to FIG. 4, showing a seventh embodiment.

FIG. 15 is a view corresponding to FIG. 4 showing an eighth embodiment.

FIG. 16 is a view, corresponding to FIG. 4, showing a ninth embodiment.

FIG. 17 is a view, corresponding to FIG. 2, showing the tenth embodiment.

FIG. 18: Two performance target indexes W1 used for H∞ control
, W3.

FIG. 19 is a diagram showing a gain characteristic of a frequency transfer function of a motion characteristic of a vehicle with respect to rear wheel steering when H∞ control is not performed.

FIG. 20 is an explanatory diagram showing how the frequency transfer function of the motion characteristics of the vehicle with respect to the rear wheel steering changes when the friction coefficient of the road surface changes.

FIG. 21 is a diagram showing a cornering force characteristic of a wheel with respect to a sideslip angle of the wheel.

[Explanation of symbols]

1 Steering Wheel 2 Front Wheel 3 Rear Wheel 20 Rear Wheel Steering Device (Steering Means) 28 Motor 29 Control Unit 36 Yaw Rate Sensor (Yaw Rate Detection Means) 45 First Control Means 46 Control Gain Calculation Means 47 State Feedback Control Means 48 Map Control Means (Second Control Means) 49 Judging Means 50 Control Switching Means 61 Fuzzy Control Means (Second Control Means) 62 Neural Net Control Means (Second Control Means)

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B62D 137: 00

Claims (12)

[Claims] 1. Steering means for steering front wheels or rear wheels separately from a steering wheel, yaw rate detecting means for detecting an actual yaw rate generated in a vehicle, and actual yaw rate and target yaw rate detected by the detecting means. The control amount is calculated based on the deviation of the first yaw rate, and the first yaw rate is controlled so that the actual yaw rate matches the target yaw rate. The first control means controls the stability of the vehicle. And a second control means for controlling the steering means with a control amount according to the steering of the steering wheel so that the stability of the vehicle is essentially guaranteed. When the output of the determination means is received and the control by the first control means exceeds the range that guarantees the stability of the vehicle, steering of the front wheels or the rear wheels is performed. The vehicle steering system is characterized in that a control switching means for switching control from the control by the first control means to control by said second control means. 2. The first control means sets the actual yaw rate of the vehicle to a control target yaw rate based on at least an actual yaw rate of the vehicle and a vehicle state equation in which the estimated sideslip angle is a vehicle state quantity and an output equation. State feedback control means for controlling the steering means so as to perform feedback control, and a performance target that gives stability when the characteristics of the vehicle change as a control gain characteristic of the frequency transfer function of the yaw rate change of the vehicle with respect to steering of the front wheels or the rear wheels. The control gain of the above-mentioned state feedback control means is determined based on two kinds of indices, a performance target index that gives the vehicle speed response and steady-state characteristics, and a vehicle state equation and an output equation that inputs the steering angle of the front wheels or rear wheels. The vehicle steering system according to claim 1, further comprising a control gain calculation unit that calculates the control gain. 3. The stability of the determining means when the frequency component of the control gain of the yaw rate change of the vehicle with respect to the steering of the front wheels or the rear wheels during the steering control of the front wheels or the rear wheels by the first control means changes when the characteristics of the vehicle change. 3. The vehicle steering system according to claim 2, wherein it is determined when the control by the first control means exceeds a range in which the stability of the vehicle is guaranteed by exceeding the performance target index that gives the above. 4. The control means according to claim 1, wherein the determining means is controlled by the first control means when the state quantity of the vehicle exceeds a predetermined value indicating a performance limit of the vehicle during steering control of the front wheels or the rear wheels by the first control means. The vehicle steering system according to claim 1, wherein the steering system is for determining when the vehicle stability is exceeded. 5. The determination means is controlled by the first control means when the phase delay amount of the actual yaw rate of the vehicle at a predetermined frequency exceeds a predetermined value during steering control of the front wheels or the rear wheels by the first control means. 2. The vehicle steering system according to claim 1, wherein the control is for determining when the control exceeds a range that guarantees vehicle stability. 6. The vehicle steering system according to claim 5, wherein the predetermined value that is the threshold value for determining the phase delay amount by the determining means is changed according to the vehicle speed. 7. The vehicle steering system according to claim 5, wherein the predetermined value that is the threshold value for determining the phase delay amount by the determining means is changed according to the sideslip angle of the vehicle. 8. The vehicle steering system according to claim 1, wherein the second control means performs control based on a preset map. 9. The vehicle steering apparatus according to claim 1, wherein the second control means performs fuzzy control. 10. The vehicle steering system according to claim 1, wherein the second control means performs control based on a neural network. 11. The second control means inputs a vehicle speed, a steering wheel steering angle, and an actual yaw rate of the vehicle as state quantities of the vehicle when performing control based on a neural network. Vehicle steering system. 12. The vehicle steering system according to claim 11, wherein the second control means inputs the vehicle speed V in the form of 1 / V and 1 / V ² .