JP3320882B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system, and more particularly, to a vehicle steering system in which a rear wheel or a front wheel is forcibly steered in response to a steering wheel operation of a driver to enhance drivability and stability of the vehicle. Related to the improvement of what was done.

[0002]

2. Description of the Related Art Conventionally, as a steering apparatus for a vehicle of this type, a ratio of a steering angle of a rear wheel corresponding to a steering angle of a front wheel when a driver operates a steering wheel, that is, a steering ratio is determined according to a vehicle speed. 2. Description of the Related Art There is a known steering control system in which a rear wheel is steered by a steering ratio in accordance with front wheel steering. In this case, 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 often have the same phase, Unfortunately, the turning performance of the vehicle in the initial state was low.

For this reason, conventionally, for example, Japanese Unexamined Patent Publication No.
In the device disclosed in Japanese Patent Publication 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 actually measured, and the deviation between the measured value of the yaw rate and the control target value is calculated. By performing feedback control of the steering angle of the rear wheels with the corresponding feedback control amount, the yaw rate is quickly generated even in the initial state immediately after the steering wheel operation, thereby improving the turning performance of the vehicle in the initial state. But,
This conventional feedback control is a one-input, one-output control system that calculates the feedback control amount of the rear wheel steering angle only in accordance with the deviation between the actual measured value of the yaw rate and the control target value, and controls the rear wheels by steering. For example, when the side slip angle of the vehicle is a large value, control hunting is more likely to occur than when the vehicle has a small value. For this reason, it is necessary to always set the control gain to a small value so that control hunting hardly occurs.
In this case, the responsiveness to the control target yaw rate value is deteriorated, and the actual yaw rate cannot be accurately controlled to the control target value, and there is a limit in improving the steady-state characteristics.

[0004]

Therefore, the present applicant has
Previously, for example, in the specification and drawings such as Japanese Patent Application No. 4-23737, it has been proposed to employ state feedback control of actually measured yaw rate instead of the above-mentioned feedback control. This state feedback control of the yaw rate not only measures the yaw rate of the vehicle but also estimates a plurality of state variables of the vehicle, for example, the sideslip angle of the vehicle, the cornering forces of the front and rear wheels, etc. based on the state equation and the output equation of the vehicle. The motion state of the vehicle is grasped by using the above-mentioned 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.
Since this control system is a multivariable one-output control system, it is possible to control the steering of rear wheels and the like with a feedback control amount matching the motion state of the vehicle, and to improve the turning performance of the vehicle at the time of steering wheel operation. It is possible to improve both the responsiveness and the steady-state characteristics.

Further, the present applicant has noticed the following disadvantages in the above-mentioned state feedback control, and has invented the application of the H た め control in order to solve these disadvantages. That is, in the state feedback control, the vehicle speed and the cornering power of the wheel are calculated as constants when estimating the side slip angle and the cornering force of the vehicle, but these are actually variables, and the latter is the variable. It changes according to the coefficient of friction of the road surface and the air pressure of the tire. Accordingly, under the preset vehicle motion characteristics, the control responsiveness and the steady-state characteristics can be improved. However, as shown in FIG. 20, the vehicle motion characteristics are changed according to changes in vehicle speed, road surface friction coefficient, and the like. If a large change occurs, an error occurs in the estimation of the side slip angle of the vehicle and the like, and a deviation occurs in the optimal control. As a result, the responsiveness to the target yaw rate is reduced and the stability of the vehicle is not guaranteed.

[0006] Therefore, for example, H 図 る control (for example, “Measurement Journal”, which is intended to improve the stability of a control system by satisfying that the loop transfer function of the control system is “1” or less over all frequency ranges). And Control, Vol. 29, No. 2 (February 1990), pp. 111-119) to improve stability against vehicle characteristic fluctuations, that is, to improve robust stability. Conceivable. In the H∞ control for the front wheel or rear wheel steering, the steady-state characteristics and the quick response of the vehicle are required in a low frequency range of, for example, 1 Hz or less as the steering wheel steering frequency, and in a high frequency range exceeding 1 Hz, when the characteristic of the vehicle fluctuates. Since stability is required and these requirements differ in the frequency domain, it is considered as a mixed sensitivity problem as disclosed in the journal of the 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 wheel or the rear wheel is controlled. Two types of characteristics are set: a performance target index that gives the vehicle responsiveness and steady-state characteristics, and a performance target index that gives stability when the characteristics of the vehicle have a complementary sensitivity function. The control gain is determined on the frequency axis with emphasis on 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 change in the characteristics of the vehicle, if the change is within the set allowable range, all of the speed responsiveness, the steady performance and the stability of the vehicle can always be satisfactorily controlled. .

However, in the conventional yaw rate feedback control and the yaw rate state feedback control and the H∞ control proposed by the present applicant, the vehicle is operated in an operating region where the cornering force of the wheel with respect to the side slip angle of the wheel is linear. Although stable control is possible, it is difficult to reliably and stably control the vehicle in a non-linear driving range.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a conventional yaw rate feedback control, state feedback control, and H
∞ In control and the like, if the characteristics of the vehicle fluctuate beyond the range in which the control guarantees the stability of the vehicle, the situation exceeding the stability assurance range is determined early, and the steering angle of the front wheels or the rear wheels is determined. It is an object of the present invention to provide a vehicle steering device capable of guaranteeing vehicle stability by stabilizing a control system.

[0009]

In order to achieve the above object, the invention according to claim 1 or 2 is directed to a steering apparatus for a vehicle, in which, as shown in FIG. 1, a front wheel or a rear wheel is separately provided from a steering wheel. The control amount is calculated based on the deviation between the actual yaw rate detected by the detection means 36 and the target yaw rate, the yaw rate detection means 36 detecting the actual yaw rate generated in the vehicle, It is assumed that a first control unit 45 that performs feedback control of the steering unit 20 so that the actual yaw rate matches the target yaw rate according to the control amount is provided. Further, a determining means 49 for determining when the control by the first control means 45 is out of a range in which the stability of the vehicle is guaranteed, and a steering wheel steering so that the stability of the vehicle is essentially guaranteed. The second control means 48 for controlling the steering means 20 with a control amount according to the above, and the output of the determination means 49, the control of the first control means 45 exceeding the range which guarantees the stability of the vehicle In this case, a control switching means 50 for switching the steering control of the front wheels or the rear wheels from the control by the first control means 45 to the control by the second control means 48 is provided.

Further, according to the invention of claim 1 ,
The first control means 45 performs H∞ control. That is, the first control means 45 controls the actual yaw rate of the vehicle to the control target yaw rate based on at least the actual yaw rate of the vehicle and the output equation based on the state equation of the vehicle that uses the estimated yaw rate and the estimated side slip angle as the state quantity of the vehicle. State feedback control means for controlling the steering means 20 so as to perform the control, and a performance target index for providing stability when the characteristic of the vehicle fluctuates as a control gain characteristic of a frequency transfer function of a yaw rate change of the vehicle with respect to the steering of the front wheel or the rear wheel. And calculating a control gain of the state feedback control means on the basis of two types of performance target indices that give the responsiveness and steady-state characteristics of the vehicle, and a state equation and an output equation of the vehicle that input the steering angle of the front wheel or the rear wheel. Control gain calculating means.

Further, according to the first aspect of the present invention,
The determination means 49 has a performance in which the frequency component of the control gain of the yaw rate change of the vehicle with respect to the steering of the front wheel or the rear wheel at the time of steering control of the front wheel or the rear wheel by the first control means 45 provides stability when the characteristic of the vehicle fluctuates. This is to judge when the control by the first control means 45 exceeds the range in which the stability of the vehicle is guaranteed due to exceeding the target index.

In the invention according to claim 2 , the determination means 4
9 is that the control by the first control means 45 is stable because the amount of phase delay at a predetermined frequency of the actual yaw rate of the vehicle during the steering control of the front wheel or the rear wheel by the first control means 45 exceeds a predetermined value. This is to determine when the value exceeds the range in which the performance is guaranteed.

The inventions according to claims 3 and 4 are all contracted.
According to the invention described in claim 2 , the predetermined value which is the threshold value for determining the amount of phase delay by the determination means 49 is appropriately changed. That is, the predetermined value is changed according to the vehicle speed in the invention described in claim 3 , and is changed according to the side slip angle of the vehicle in the invention described in claim 4 .

[0014]

According to the above construction, according to the first aspect of the present invention, the actual yaw rate and the target yaw rate are controlled by the control means 45 within a range in which the stability of the vehicle is guaranteed by the control of the first control means 45. The control amount is calculated based on the deviation of the front wheel or the rear wheel is controlled by the control amount so that the actual yaw rate matches the target yaw rate.
Good stability of the vehicle is ensured even if the characteristics of the vehicle slightly fluctuate. On the other hand, if the stability of the steering control of the front wheels or the rear wheels by the first control means 45 is exceeded and the control system enters a nonlinear region and becomes unstable, 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 unit 45 to the control by the second control unit 48 such as a map control, a fuzzy control, or a control based on a neural network, in which the control system is inherently stable, the dynamic characteristics of the vehicle are normally changed. Even if it fluctuates greatly beyond the width, the stability of the vehicle is well ensured. In particular, when the control is switched to the control based on the neural network, even if the vehicle's kinetic characteristics greatly fluctuate beyond the normal fluctuation range, the vehicle stability is almost equivalent to the case where a skilled driver operates by steering wheel operation. Is secured.

[0015] According to the first aspect of the invention, the first
In the range in which the control by the control means 45 guarantees the stability of the vehicle, the steering control of the front wheel or the rear wheel by the control means 45 is performed by H∞ control, and the control gain of the control means 45 determines the stability when the characteristic of the vehicle fluctuates. Since it is set within a range determined by two types of the performance target index to be given and the performance target index to give the responsiveness and the steady-state characteristics of the vehicle, all of the stability, the responsiveness and the steady-state characteristics of the vehicle are properly secured. .

Furthermore, according to the first aspect of the present invention, the range limits vicinity of the control by the first control means 45 to ensure stability of the vehicle, the control of the yaw rate change of the vehicle to the steering of the front wheels or the rear wheels Focusing on the fact that the frequency component of the gain has exceeded the performance target index that provides stability when the characteristics of the vehicle fluctuate, the frequency component is detected by the determination means 49, and the fact that the stability component has exceeded the guaranteed range is early. And is accurately determined.

According to the second aspect of the present invention, in the vicinity of the limit of the range in which the control by the first control means 45 guarantees the stability of the vehicle, the actual yaw rate of the vehicle with respect to the steering of the front wheels or the rear wheels is set. 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 quickly and accurately determined that the stability is out of the guaranteed range. Here, according to the third and fourth aspects of the present invention, even if the first control means 45 is near the limit of the range in which the stability of the vehicle is guaranteed, if the vehicle speed at that time is high, the stability assurance range The amount of phase lag corresponding to the limit value also increases, and if the side slip angle of the wheel or vehicle at that time is large, the amount of phase lag is reduced, but the set value as a criterion value of the stability guarantee range is determined. Since the vehicle speed is changed according to the vehicle speed, the wheels, or the sideslip angle of the vehicle, the situation that exceeds the guaranteed range of the stability of the vehicle can be more accurately determined.

[0018]

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

FIG. 2 shows a schematic structure of a steering apparatus for a vehicle according to a first embodiment of the present invention, wherein 1 is a steering wheel, 2 is left and right front wheels, 3 is left and right rear wheels, and 10 is a steering wheel. A front wheel steering device 20 for steering left and right front wheels 2 and 2 by operation, and a rear wheel steering device 20 as steering means for steering left and right rear wheels 3 and 3 in accordance with steering of the front wheels 2 and 2 by the front wheel steering device 10. It is.

The front wheel steering device 10 has a relay rod 11 arranged in the width direction of the vehicle body, and both ends of the rod 11 are tie rods 12, 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 for moving the relay rod 11 right and left in conjunction with the operation of the steering wheel 1 is disposed on the relay rod 11. When the steering wheel 1 is operated, the rack and pinion mechanism 14 is moved left and right by an angle corresponding to the operation amount. The front wheels 2 are steered.

On the other hand, the rear wheel steering device 20 has a relay rod 21 disposed in the vehicle width direction in the same manner as described above, and both ends of the rod 21 are respectively connected via tie rods 22, 22 and knuckle arms 23, 23. And are connected to the left and right rear wheels 3,3. On the relay rod 21, a centering spring 24 for urging the rod 21 to a neutral position is disposed, and a rack & pinion mechanism 25 is disposed.
The mechanism 25 is associated with a clutch 26, a speed reduction mechanism 27, and a motor 28. 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 rotation of the motor 28. Thus, the rear wheels 3, 3 are configured to be steered by an angle corresponding to the rotation amount of the motor 28.

The operation of the motor 28 is controlled by a control unit 29. The control unit 2
9 includes a first control means 45 for performing H∞ control therein as shown in FIG. The control means 45 includes:
The motor 28 performs state feedback control of the actual yaw rate of the vehicle to the control target yaw rate in accordance with the control flow of FIG. Feedback control means 47 for controlling the steering angle of the rear wheel 3 by using the control gain calculation means for calculating the control gains of the state equation and output equation of the state feedback control means 47 based on the control gain calculation flow shown in FIG. 47.

The control unit 29 includes:
As shown in FIG. 21, the driving condition of the vehicle is changed to the vehicle side slip angle β.
Map as second control means for steering-controlling the rear wheel 3 based on a map stored in advance so that the control system essentially maintains stability when the vehicle enters a nonlinear region of the cornering force of the wheel with respect to A control unit 48, a determination unit 49 for determining that the first control unit 45 has exceeded a range in which the stability of the vehicle is guaranteed, and a steering control of the rear wheel 3 based on an output of the determination unit 49. 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, 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 yaw rate sensor for the rear wheel 3. A rear wheel steering angle sensor 38 for detecting a steering angle, a front wheel steering angle sensor 38 for detecting a steering angle of the front wheel 2, and these four sensors 3
The detection signals 5 to 38 are input to the state feedback control means 47. A vehicle speed sensor 39 detects a vehicle speed, and a road surface friction coefficient sensor 40 detects a friction coefficient μ of a road surface below the vehicle.
Is input to the control gain calculating 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 supplied 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 with reference to the control flow of FIG.

In FIG. 4, at step S1, for example, 20
After waiting for the control timing for each set cycle such as msec, in step S2, each of the sensors 36-39 is set.
, The front wheel steering angle Fstg, the rear wheel steering angle Rstg, and the actual yaw rate y generated in the vehicle.
r and the lateral motion Yg acting on the vehicle are measured.

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 the actual yaw rate yr signal pair of the vehicle as the identification signal, identification is performed in step S4. In this identification, first, a cross spectrum Sfy of the yaw rate yr with respect to the front wheel steering angle Fstg is calculated, and the front wheel steering angle Fstg is calculated.
The power spectrum Sff of stg is calculated, and then the frequency transfer function H (ω) is calculated based on the following equation.

[0028]

(Equation 1)

Subsequently, in step S5, the frequency transfer function H
The phase delay angle φ (1) at the set frequency of (ω) (steering wheel steering frequency, for example, 1 Hz) is calculated from the phase characteristic phase (H (ω)), and step S6 is performed.
Then, the phase delay angle φ (1) is compared with a predetermined value (for example, 30 deg) as a reference value as to whether or not the stability of the vehicle is guaranteed by the first control means 45. And
If it is within the guaranteed range of φ (1) ≦ 30 deg, while the rear wheel 3 is H∞ controlled in step S7, φ (1)> 3
If it exceeds the guaranteed range of 0 deg, the map of the rear wheel 3 is 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.
rt is set, and a yaw rate deviation en between the target yaw rate yrt and the actual yaw rate yr is calculated.

[0031]

(Equation 2)

Where A is a stability factor and L is
Is the wheelbase of the vehicle.

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

[0034]

(Equation 3)

Here, Xh is a state quantity corresponding to a plurality of state quantities of the vehicle (hereinafter, "state quantity" in the present specification means this), and the state quantity of the vehicle is, for example, a skid of the vehicle. The angle, the steering angle of the rear wheel or its changing speed, the cornering force of the front wheel and the rear wheel, or the yaw rate acting on the vehicle. These are estimated by the above two equations.

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

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

In FIG. 5, first, in step S11, a performance target index W3 for providing stability when the characteristic of the vehicle fluctuates as a control gain characteristic of a frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheel 3 is changed. Is changed according to the vehicle speed Vsp. This change is performed by determining the correction coefficient Wn to a large value in accordance with the increase in the vehicle speed Vsp, as shown in step S11.

Thereafter, in step S12, a performance target index W3 for providing stability when the characteristics of the vehicle fluctuates is determined based on the following quadratic expression of the Laplace variable s.

[0040]

(Equation 4)

Where a and c are constants. Based on the above equation, as shown in FIG. 18, the performance target index W3 for providing stability when the characteristics of the vehicle fluctuates is changed to the low frequency side when the correction coefficient Wn is large, and the performance coefficient Wn is small for the correction coefficient Wn. When the value is a value, it is changed to the high frequency side.

Subsequently, at step S13, a performance target index W1 (provided that the vehicle has quick response and steady-state characteristics as control gain characteristics of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheel 3) is shown in FIG. , Reciprocal) are specified as fixed values based on the following cubic expression of the Laplace variable s.

[0043]

(Equation 5)

Here, d, e, f, g and h are constants.

In step S14, the two performance target indices W3 and W1 are converted into state equations, and the two state equations and the vehicle state equation (3) and the output equation (4) shown below are converted. Are combined into one state equation, the combined state equation is decomposed into two Riccati equations, and this equation is solved as an eigenvalue problem using a Hamilton matrix, thereby obtaining each control gain Acl to Dcl of H∞ control. Ask for.

[0046]

(Equation 6)

In the 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, respectively, and Rstg is the steering angle of the rear wheel. , If 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 the yaw rate, m is the body mass, Vsp is the vehicle speed, and G
y is the lateral elastic modulus of the wheel, and Kyf and Kyr are the cornering powers of the front and rear wheels, respectively. Here, the actual vehicle speed detected by the vehicle speed sensor 39 is used as the vehicle speed Vsp.
Others are preset fixed values.

Thereafter, in step S15, the control gains Acl to Dcl are changed from a continuous control system to a digital control system by a bilinear conversion method, and the processing is terminated. The control gains Acl to Dcl may be determined not only by the above-described sequential calculation but also by a method of sequentially reading values stored in a map in advance according to the motion state of the vehicle.

Further, the map control in step S8 in FIG. 4 determines the rear wheel steering amount r in accordance with the following equation according to the front wheel steering angle Fstg as shown in the step.

[0050]

(Equation 7)

Is calculated by However, k is a proportional constant, and the proportional constant k is set to a large value according to 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 predetermined value V0. The control system is essentially stabilized in the region.

Therefore, step S7 of the control flow of FIG.
Based on the vehicle's state equation (1) and the output equation (2), 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, etc., are used as the vehicle state variables. State feedback control means 46 for controlling the rear wheel steering device 20 is provided so as to perform state feedback control of the actual yaw rate yr to the control target yaw rate yrt.

Further, according to the control gain determination flow of FIG. 5, a performance target index W3 for providing stability when the characteristic of the vehicle fluctuates as a control gain characteristic of the frequency transfer function of the yaw rate change of the vehicle with respect to the steering of the rear wheel 3, and the vehicle performance. A state equation (3) of a vehicle which receives two kinds of performance target indices W1 for providing quick response and steady-state characteristics and the steering angle Rstg of the rear wheel 3 as input.
A predetermined frequency (0.3 r in FIG. 18) at which the vehicle motion characteristic (control gain characteristic) has a loop transfer function of 0 db as shown by a solid line in FIG.
ad / sec) is located immediately below the performance target index W3 that provides the above stability, and in the low frequency range below a predetermined frequency (0.3 rad / sec), the performance target index that provides the above-mentioned steady-state characteristics. A control gain calculating 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. The control amount (rear wheel steering amount) r is calculated by the state feedback control means 46 and the control gain calculation means 47 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 actual yaw rate yr is determined by the control amount r.
Rear wheel steering system 2 so that the vehicle speed matches the target yaw rate yrt.
The first control means 45 for performing feedback control of 0 is configured.

Further, at step S8 of the control flow of FIG. 4, a vehicle speed-proportional coefficient characteristic map set in advance so that the stability of the vehicle is essentially guaranteed, and the front wheel steering angle Fst
A map control unit 48 is configured as a second control unit that calculates a control amount r corresponding to 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 same 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 is obtained.
determining means 4 for determining that the amount of phase delay φ (1) of r at a predetermined frequency (1HZ) exceeds a predetermined value (30 deg)
9 and the shift from step S6 to step S8 determines that the phase delay amount φ (1) of the frequency transfer function of the vehicle is a predetermined value (30d
For example, a control switching unit 50 is configured to switch the steering control of the rear wheel 3 from H∞ control to control by the map control unit 48 when it is determined that the vehicle speed exceeds the range (eg).

Therefore, in the first embodiment,
Within the guaranteed range of vehicle stability by H∞ control, the front wheels 2
Transfer function H of the yaw rate of the vehicle for the steering of the vehicle
Since the phase delay angle φ (1) of (ω) is less than the predetermined value (30 deg), the steering control of the rear wheel 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 immediately below the performance target index W3 for providing stability in a high frequency range exceeding a predetermined frequency (0.3 rad / sec).
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.
The control gain is small in the high frequency range exceeding 0.3 rad / sec, and the control gain is small in the low frequency range of 0.3 rad / sec or less, with respect to the motion characteristics of a normal vehicle in which the H∞ control is not performed. Is large. Therefore, in the high frequency range, the oscillation of the rear wheel steering control is reliably prevented by the small control gain, and the stability against the characteristic fluctuation of the vehicle is improved, and the robust stability is improved. The vehicle responds quickly with a large control gain in response to the steering wheel operation of the driver, and the vehicle generates a yaw rate with a very small deviation from the target yaw rate, thereby improving the responsiveness and steady-state characteristics. become.

On the other hand, as the motion of the vehicle approaches the limit of the guarantee 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
If the phase delay angle φ (1) of (ω) increases and the phase delay angle φ (1) exceeds a predetermined value 30 deg at the time when the value exceeds the guaranteed range, this is determined by the determination means 49, and immediately at that time, In addition, the steering control of the rear wheel 3 is reliably switched from the H∞ control to the map control by the control switching means 50. Since this map control is essentially formed in a control system that guarantees the stability of the vehicle, the vehicle can be stably controlled even in a non-linear region beyond the guaranteed range of the H∞ control.

FIG. 6 shows a block diagram of a control system in a vehicle steering system according to a second embodiment of the present invention. In the case of the second embodiment, the configuration of the control system differs from that of the first embodiment shown in FIG. 3 in that a fuzzy control unit 61 is provided as the second control unit instead of the map control unit 48. It is. The other configuration of the control system is the same as that of the first embodiment, and the same members are denoted by the same reference numerals and description thereof will be 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 a reference value (predetermined value) for judging that the vehicle stability has been exceeded in step Sx after step S5 in step Sx. The control switching phase angle φ1 is not fixed, but is changed to a large value in accordance with the increase of the vehicle speed Vsp. If φ (1)> φ1 in step S6, another alternative to the H∞ control is performed in step S8 ′. A fuzzy control is used as the control, a fuzzy control amount r of the rear wheel steering by the fuzzy control is calculated, and the motor 28 is driven and controlled by the control amount r to control the steering angle of the rear wheel 3.

The fuzzy control in step S8 'is a control system tuned exclusively for a nonlinear region so that the control system is essentially stable. Specifically, the yaw rate deviation en and the rate of change den are Based on the membership function, which is a function with / dt,

[0061]

(Equation 8)

Accordingly, the control amount r is calculated such that the rate of change of the actual yaw rate yr of the vehicle decreases while ensuring the stability of the vehicle in a favorable manner.

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

Therefore, in the second embodiment, when the driving condition of the vehicle is near the limit of the guaranteed range of the H∞ control, when the vehicle speed is high, the control responsiveness is lower than at the low vehicle speed. Although the amount of phase delay corresponding to the limit value of the guaranteed range is larger than that at the time of low vehicle speed, the predetermined value φ1 as a criterion value for control switching is changed to a larger value at higher vehicle speeds. The determination of a situation beyond the guaranteed range of stability is performed accurately and quickly. In addition, when the H 越 え control is out of the guaranteed range determined in this way, the steering control of the rear wheel 3 is switched from the H∞ control to the fuzzy control, and the fuzzy control is performed as shown in FIG. Since the control system is tuned to a control system that makes the vehicle essentially stable in the nonlinear region of the cornering force of the vehicle with respect to the estimated side slip angle β, the vehicle can be stably operated even in the nonlinear region exceeding the guaranteed range of the H∞ control. Can control.

FIG. 8 shows a block configuration of a control system in a vehicle steering system according to a third embodiment of the present invention. In the case of 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 instead of the map control means 48 as the second control means. 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
9 are input. The other configuration of the control system is the same as that of the first embodiment, and the same members are denoted by the same reference numerals and description thereof will be omitted.

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

Here, as shown in FIG. 10, the neural network comprises, for example, three layers, four input layers a, four intermediate layers b, and one output layer c. In 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 the three layers are given by the following equations, where x is the input.

[0068]

(Equation 9)

Further, the weights of the layers a to c are determined in advance by the vehicle speed, the steering angles of the front wheels and the rear wheels, the actual yaw rate, and the actual yaw rate when a highly skilled driver repeatedly travels beyond the stability limit of the vehicle. The skid angle at the center of gravity of the vehicle and the steering wheel operation of the skilled driver at that time are given as a teacher input and learned, and the learning result is incorporated as a control law and obtained.

The vehicle speed Vsp input to the neural network
However, the reciprocal 1 / Vsp and the squared reciprocal 1 / Vsp ² are in the form of a linear motion model of a normal two-wheel steering vehicle expressed by the following equation, and the term relating to the vehicle speed in the arithmetic equation is 1 / Vsp
And 1 / Vsp ² in order to match this arithmetic expression (vehicle speed is represented by V).

[0071]

(Equation 10)

In step S8 ″ of FIG. 9, the steering wheel operation of the skilled driver when the vehicle has run beyond the stability limit is learned in advance so that the stability of the vehicle is essentially guaranteed. A control amount r corresponding to the steering wheel steering is calculated based on the control law built in, and the second control method for controlling the motor 28 of the rear wheel steering device with the control amount r.
The neural network control means 62 as the control means of the above is configured.

Therefore, in the third embodiment,
Even if the phase lag characteristic of the frequency transfer function of the actual yaw rate of the vehicle changes according to the sideslip angle β at the center of gravity of the vehicle, the control switching phase angle (predetermined value) φ1 correspondingly changes the sideslip angle β.
Irrespective of the side slip angle β at the time when the vehicle operating condition exceeds the guarantee range of the H∞ control, the time point beyond the guarantee range can be accurately and quickly determined. .

Further, in a situation beyond the guaranteed range of the H 保証 control, the steering control of the rear wheel 3 is switched from the H∞ control to the control based on the neural network, and the control based on the neural network is changed to the side slip angle β of the wheel. Therefore, since the control system simulates the operation of a skilled driver in the nonlinear region of the cornering force of the vehicle, the vehicle can be stably controlled even in the nonlinear region exceeding the guaranteed range of the H∞ control.

In addition, the inputs to the neural network shown in FIG. 10 are the actual 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. In addition, since the actual yaw rate is input, it is possible to improve the steering response of the rear wheels to the front wheels and to improve the stability against disturbances such as crosswinds and road surfaces. Further, the vehicle speed Vsp, so are input in 1 / Vsp, 1 / Vsp ² forms adapted to the section on the vehicle speed arithmetic expression characteristics of two-wheel steering vehicle model,
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 modified example of the rear wheel steering control as a fourth embodiment of the present invention. In the case of the fourth embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
3 is substantially the same as that of the first embodiment shown in FIG. 3, and in the following description of the control flow, the member symbols shown in FIG. 2 and FIG. 3 are used.

In FIG. 11, after waiting for the control timing for each predetermined period at step S21, the process proceeds to step S22.
The vehicle speed Vsp based on the detection signals of the various sensors 35 to 39,
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
Measure the motion amount of each vehicle in g.

Subsequently, 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 wheels 3 as the feedback control amount of the H∞ control is performed. The control amount r is determined based on the vehicle state equation and the output equation in the H∞ control. The calculations in steps S23 and S24 are performed in the first embodiment by using H∞ in step S7 in FIG.
The control is the same as that described, and the equations for calculating the target yaw rate yrt and the yaw rate deviation en are described in "Equation 2", and the state equation and output equation of the vehicle are described in "Equation 3".

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

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

In the above control flow, at step S27, the map control means as the second control means for the control system to perform essentially stable map control in a region where the change of the cornering force with respect to the side slip angle of the wheel is nonlinear. 48
Is configured. In step S25, a determining means 49 for determining when the state quantity Xh of the vehicle exceeds the predetermined value Xr is constituted. By the transition from step S25 to step S27, the determining means 49 determines that the state quantity Xh of the vehicle is Control switching means 50 is provided for switching the steering control of the rear wheel 3 from H∞ control to control by the map control means 48 when it is determined that the predetermined value Xr has been exceeded.

Therefore, in the fourth embodiment,
The steering control of the rear wheels 3 is performed by the H∞ control in the guaranteed range of the H∞ control in which the internal state quantities Xh such as the estimated sideslip angle β of the vehicle and the cornering forces Cf and Cr of the front and rear wheels are equal to or less than a predetermined value Xr. As shown in FIG. 18, the control gain of the rear wheel steering control is set to a large value in a low frequency range of 0.3 rad / sec or less in accordance with a performance target index W1 that gives the vehicle responsiveness and steady-state characteristics. In a high frequency range exceeding .3 rad / sec, the value is limited to a small value in accordance with a performance target index W3 for providing stability when the characteristics of the vehicle fluctuate, so that the vehicle responds quickly and responds to the vehicle in response to the driver's steering operation. Means that the yaw rate with a very small deviation from the target yaw rate is generated, and even if the motion characteristics of the vehicle fluctuate, the oscillation of the rear wheel steering control is reliably prevented, and the stability of the vehicle is secured well. Will be.

On the other hand, when the state quantity Xh of the vehicle is a predetermined value Xr
Over the guarantee range of the H∞ control, the rear wheel 3
Is switched from H∞ control to map control, and this map control is tuned to a control system that makes the vehicle essentially stable in the nonlinear region of the vehicle's cornering force with respect to the estimated side slip angle β of the vehicle. The stability of the vehicle can be ensured even in a non-linear region beyond the guaranteed range of the H∞ control.

FIG. 12 is a flowchart showing a modified example of the rear wheel steering control according to the fifth embodiment of the present invention. In the case of the fifth embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
Are substantially the same as those of the first embodiment shown in FIG. 6 and the second embodiment shown in FIG. 6, and in the following description of the control flow, the member codes shown in FIG. 2 and FIG.

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

As described in detail in the second embodiment, the fuzzy control in step S27 'is performed by setting the yaw rate deviation en set in advance so that the stability of the vehicle is essentially assured and the rate of change den / dt thereof. Control amount r according to the steering wheel steering based on the membership function which is a function of
And the motor 2 of the rear wheel steering system is calculated using the control amount r.
This step S27 'constitutes a fuzzy control means 61 as a second control means. The other steps are the same as those in the control flow of FIG. 11, and therefore, the same steps are denoted by the same reference characters and description thereof will be omitted.

Then, also in the fifth embodiment, H∞
In the non-linear region exceeding the guaranteed range of the control, the steering control of the rear wheels 3 is switched from the H∞ control to the fuzzy control. Since the control system is tuned to a stable control system, the stability of the vehicle can be ensured.

FIG. 13 is a flowchart showing a modified example of the rear wheel steering control according to the sixth embodiment of the present invention. In the case of the sixth embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
8 and the third embodiment shown in FIG. 8, and in the following description of the control flow, the member codes shown in FIGS. 2 and 8 will be used.

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

As described in detail in the third embodiment, the neural network control in step S27 ″ is performed by moving the vehicle 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 a control amount r corresponding to the steering wheel steering is calculated based on the built-in control law, and the motor 28 of the rear wheel steering device is controlled with the control amount r. The step S27 '' constitutes a neural network control means 62 as a second control means. still,
The other steps are the same as those in the control flow of FIG. 11, and therefore, the same steps are denoted by the same reference characters and description thereof will be omitted.

Then, also in the sixth embodiment, H∞
In the nonlinear region exceeding the guaranteed range of the control, the steering control of the rear wheel 3 is switched from H∞ control to the control based on the neural network. This fuzzy control is performed in the nonlinear region of the vehicle cornering force with respect to the estimated side slip angle β of the vehicle. Is tuned to a control system that essentially makes the vehicle stable, so that the stability of the vehicle can be ensured.

FIG. 14 is a flowchart showing a modification of the rear wheel steering control according to the seventh embodiment of the present invention. In the case of the seventh embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
3 is substantially the same as that of the first embodiment shown in FIG. 3, and in the following description of the control flow, the member symbols shown in FIG. 2 and FIG. 3 are used.

In FIG. 14, after waiting at step S31 for the control timing for each predetermined period, step S32 is executed.
The vehicle speed Vsp based on the detection signals of the various sensors 35 to 39,
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
Measure the motion amount of each vehicle in g.

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 wheels 3 as the feedback control amount of the H∞ control is performed. The control amount r is determined based on the vehicle state equation and the output equation in the H∞ control. The calculations in steps S33 and S34 are performed in the first embodiment by using H∞ in step S7 in FIG.
The control is the same as that described, and the equations for calculating the target yaw rate yrt and the yaw rate deviation en are described in "Equation 2", and the state equation and output equation of the vehicle are described in "Equation 3".

Subsequently, after calculating the power spectrum P of the yaw rate of the vehicle detected by the yaw rate sensor 36 in step S35, the noise intensity, that is, the component ratio Piz of 1 Hz or more with respect to the whole power spectrum P is calculated in step S36. It is calculated by the formula.

[0096]

[Equation 11]

Thereafter, in step S37, it is determined whether or not the noise intensity Piz has exceeded a predetermined value Pi corresponding to a performance target index W3 for providing stability when the characteristics of the vehicle fluctuate.
i is within the guaranteed range of the H∞ control, the steering control of the rear wheel 3 is performed by the H∞ control in step S38, while if Piz> Pi and exceeds the guaranteed range of the H∞ control, step S39 is performed.
The control amount r corresponding to the steering wheel steering is calculated based on the vehicle speed-proportional coefficient characteristic map and the front wheel steering angle Fstg set in advance so that the control system becomes essentially stable, and the map control amount is calculated in step S38. The rear wheel steering device 20 is controlled by r.

In the above control flow, in step S39, the map control means as the second control means in which the control system performs essentially stable map control in a 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,
Judgment is made when the noise intensity Piz mixed in the actual yaw rate exceeds a predetermined value Pi corresponding to the performance target index W3 for providing stability when the characteristics of the vehicle fluctuates and thus exceeds the range in which the stability of the vehicle is guaranteed. When the determination means 49 determines that the vehicle is out of the guaranteed range of the stability of the vehicle by shifting from step S37 to step S39, the steering control of the rear wheel 3 is changed from the H∞ control to the map. Control switching means 5 for switching to control by control means 48
0 is configured.

Therefore, in the seventh embodiment,
The noise intensity Piz mixed into the yaw rate of the vehicle is a predetermined value P
i and below, in the guaranteed range of the H∞ control in which the motion state of the vehicle is less than the performance target index W3, the control gain of the rear wheel steering control is set to a low frequency of 0.3 rad / sec or less as shown in FIG. In the high frequency range exceeding 0.3 rad / sec, a small value is set along the performance target index W3 which provides stability when the characteristics of the vehicle fluctuates. Value, the vehicle responds quickly in response to the driver's steering operation, and the vehicle generates a yaw rate with a very small deviation from the target yaw rate. Oscillation of the wheel steering control is reliably prevented, and the stability of the vehicle is properly secured.

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 rear wheel 3 The steering control is switched from the H∞ control to the map control, and since this map control is a control system that simulates the operation of a skilled driver even in the nonlinear region of the cornering force of the vehicle with respect to the estimated side slip angle β of the vehicle shown in FIG. , H∞ control, the stability of the vehicle can be ensured even in a non-linear region exceeding the guaranteed range.

FIG. 15 is a flowchart showing a modification of the steering control of the rear wheels as an eighth embodiment of the present invention. In the case of the eighth embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
Are substantially the same as those of the first embodiment shown in FIG. 6 and the second embodiment shown in FIG. 6, and in the following description of the control flow, the member codes shown in FIG. 2 and FIG.

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 at the 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 for providing stability, step S39 '
The fuzzy control is used as another control instead of the H∞ control, and a 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. For steering control.

As described in detail in the second embodiment, the fuzzy control in step S39 'is performed by setting the yaw rate deviation en set in advance so that the stability of the vehicle is essentially assured and the rate of change den / dt thereof. Control amount r according to the steering wheel steering based on the membership function which is a function of
And the motor 2 of the rear wheel steering system is calculated using the control amount r.
The step S39 'constitutes a fuzzy control means 61 as a second control means. The other steps are the same as those of the control flow of FIG.

In the eighth embodiment, H 上 記
In the non-linear region exceeding the guaranteed range of the control, the steering control of the rear wheels 3 is switched from the H∞ control to the fuzzy control. Since the control system is tuned to a stable control system, the stability of the vehicle can be ensured.

FIG. 16 is a flowchart showing a modification of the rear wheel steering control according to the ninth embodiment of the present invention. In the case of the ninth embodiment, the hardware configuration of the vehicle steering system is the same as that shown in FIG.
8 and the third embodiment shown in FIG. 8, and in the following description of the control flow, the member codes shown in FIGS. 2 and 8 will be used.

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 is changed when the characteristic of the vehicle fluctuates. In a region exceeding a predetermined value Pi corresponding to the performance target index W3 for providing stability, step S39 ''
As another control instead of the H∞ control, a control based on a neural network is used, a control amount r of rear wheel steering by the neural network control is calculated, and the driving of the motor 28 is controlled by the control amount r to control the rear wheels. The steering angle of No. 3 is steered.

As described in detail in the third embodiment, the neural network control in step S39 ″ is performed by moving the vehicle 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 a control amount r corresponding to the steering wheel steering is calculated based on the built-in control law, and the motor 28 of the rear wheel steering device is controlled with the control amount r. The step S39 ″ constitutes the neural network control means 62 as the second control means. still,
The other steps are the same as those in the control flow of FIG. 14, and therefore, the same steps are denoted by the same reference characters and description thereof will be omitted.

Then, also in the ninth embodiment, H∞
In the nonlinear region exceeding the guaranteed range of the control, the steering control of the rear wheel 3 is switched from H∞ control to the control based on the neural network. This fuzzy control is performed in the nonlinear region of the vehicle cornering force with respect to the estimated side slip angle β of the vehicle. Is tuned to a control system that essentially makes the vehicle stable, so that the stability of the vehicle can be ensured.

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

That is, in the case of the tenth embodiment, the steering device does not include the rear wheel steering device 20 shown in FIG.
A pinion mechanism 71 and a motor 72 for driving the mechanism 71
And the operation of the motor 72 is controlled by the control unit 29. Other configurations of the steering device are the same as those of the above-described first embodiment. However, in view of steering the front wheels, in the case where the rear wheels are steered in the opposite phase to the front wheels in the rear wheels of the first embodiment, In this embodiment, the steering control is performed to increase the front wheel steering angle. In the first embodiment, when the rear wheels are controlled to have the same phase, in this embodiment, the steering control is performed to decrease the front wheel steering angle. Good.

In the above description, in the state feedback control of the rear wheel steering, the estimated slip amount of the vehicle, the steering angle of the rear wheel, the changing speed of the steering angle, the cornering force of the front wheel and the rear wheel are obtained as the estimated amount of the vehicle. , And the yaw rate acting on the vehicle, the state of the vehicle is accurately observed. However, to observe the state of the vehicle, it is sufficient to observe at least two types of the actual yaw rate of the vehicle and the sideslip angle of the vehicle.

Further, in the above description, the first control means 4
5 that performs H∞ control, but performs LQG control (state feedback control) of the yaw rate of the vehicle,
Alternatively, it is needless to say that the present invention can be similarly applied to a system in which the steering angle of the rear wheels is feedback-controlled by a feedback control amount corresponding to the deviation between the actual yaw rate and its target value.

[0113]

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

[0114] In particular, according to the first aspect of the invention, since the steering control of the front or rear wheels according to the first control means is performed by H∞ control, stability of the vehicle at the time of characteristic variation of the vehicle, the speed This also has the effect that all of the responsiveness and the steady-state characteristics can be satisfactorily secured.

According to the first or second aspect of the present invention, it is possible to quickly and accurately detect that the control by the first control means has exceeded the range in which the stability of the vehicle is guaranteed. Can be more preferably secured.

According to the third and fourth aspects of the present invention, the first
Irrespective of the difference in the vehicle speed or the vehicle side slip angle at the time when the control means exceeds the range in which the stability of the vehicle is guaranteed, it is possible to more accurately determine the situation beyond the guaranteed range.

[Brief description of the drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention;

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 diagram of a control system in the steering device.

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

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

FIG. 6 is a diagram corresponding to FIG. 3, showing a second embodiment.

FIG. 7 is a diagram corresponding to FIG. 4;

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

FIG. 9 is a diagram corresponding to FIG. 4;

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 diagram corresponding to FIG. 2, showing a tenth embodiment.

FIG. 18 shows two types of performance target indices W1 used for H∞ control.
, W3.

FIG. 19 is a diagram illustrating gain characteristics of a frequency transfer function of a vehicle motion characteristic 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 vehicle motion characteristics for rear wheel steering changes when the road surface friction coefficient changes.

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

[Explanation of symbols]

Reference Signs List 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 network control means (Second control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 17:00 B62D 17:00 (56) References JP-A-4-362472 (JP, A) JP-A-4-201784 (JP) JP-A-4-356280 (JP, A) JP-A-4-138970 (JP, A) JP-A-4-339509 (JP, A) JP-A-3-61650 (JP, A) 5-69845 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00-6/06 B62D 7/14

Claims (4)

(57) [Claims] A front wheel or a rear wheel is referred to as a steering wheel.
Is a separate steering means and a yaw rate that detects the actual yaw rate generated in the vehicle
Detecting means, and the actual yaw rate and the target yaw detected by the detecting means.
A control amount is calculated based on the deviation from the rate, and the control amount is calculated.
Make the actual yaw rate more consistent with the target yaw rate
First control means for feedback-controlling the steering means
And the control by the first control means guarantees the stability of the vehicle.
Determination means for determining when the vehicle is out of range, and steering so that vehicle stability is essentially assured.
The above-mentioned steering means is controlled by a control amount corresponding to wheel steering.
Receiving the output of the second control means and the determination means and receiving the output of the first control means
When control exceeds the range that guarantees vehicle stability, the front wheels
Alternatively, the steering control of the rear wheels is changed from the control by the first control means.
Control switching means for switching to control by the second control means
With the door, the first control means, at least the vehicle actually Yorei
Vehicle state method using the vehicle and estimated sideslip angle as vehicle state variables
The actual yaw ray of the vehicle based on the equation and the output equation
Feedback control to the target yaw rate
Feedback control means for controlling the steering means as described above
Step and yaw ray of the vehicle with respect to the steering of the front or rear wheels
As a control gain characteristic of the frequency transfer function of
Target index and vehicle that provide stability when vehicle characteristics fluctuate
Two types of performance target indices that give the responsiveness and steady-state characteristics of
The equation of state of a vehicle with the steering angle of the front or rear wheels as input
State feedback control based on
From the control gain calculating means for calculating the control gain of the means.
The above-mentioned determination means is characterized in that the frequency component of the control gain of the yaw rate change of the vehicle with respect to the steering of the front wheel or the rear wheel at the time of the steering control of the front wheel or the rear wheel by the first control means gives the stability when the characteristic of the vehicle fluctuates. the vehicle steering system, characterized in that the control by the first control means by exceeding the target indicator is to determine if the result exceeds the range that ensures the stability of the vehicle. 2. A front wheel or a rear wheel is referred to as a steering wheel.
Is a separate steering means and a yaw rate that detects the actual yaw rate generated in the vehicle
Detecting means, and the actual yaw rate and the target yaw detected by the detecting means.
A control amount is calculated based on the deviation from the rate, and the control amount is calculated.
Make the actual yaw rate more consistent with the target yaw rate
First control means for feedback-controlling the steering means
And the control by the first control means guarantees the stability of the vehicle.
Determination means for determining when the vehicle is out of range, and steering so that vehicle stability is essentially assured.
The above-mentioned steering means is controlled by a control amount corresponding to wheel steering.
Receiving the output of the second control means and the determination means and receiving the output of the first control means
When control exceeds the range that guarantees vehicle stability, the front wheels
Alternatively, the steering control of the rear wheels is changed from the control by the first control means.
Control switching means for switching to control by the second control means
With the door, said determining means, the control by the first control means by a phase delay amount at a predetermined frequency of the actual yaw rate of the vehicle when the steering control of the front or rear wheel by the first control means exceeds a predetermined value A vehicle steering device for determining when the vehicle exceeds a range in which the stability of the vehicle is guaranteed. 3. The vehicle steering system according to claim 2 , wherein the predetermined value, which is a threshold value for determining the amount of phase delay by the determination means, is changed according to a vehicle speed. 4. The vehicle steering system according to claim 2 , wherein the predetermined value, which is a threshold value for determining the amount of phase delay by the determination means, is changed according to a side slip angle of the vehicle.