JP3889469B2 - Vehicle steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle steering system that stabilizes the lateral behavior of a vehicle, and in particular, compensates for the friction coefficient between a tire and a road surface and the influence of lateral acceleration acting on the vehicle so that the vehicle body slip angle is minimized. The present invention relates to a vehicle steering apparatus including a feedforward compensator to be controlled.
[0002]
[Prior art]
The conventional vehicle steering system has a steady-state gain between the yaw rate and the calculated yaw rate on the dry road surface estimated by the “appliance estimation device for vehicle tire / road surface friction state” proposed in Japanese Patent Application No. 7-240810. The steady gain of the reference yaw rate is varied according to the ratio. When the coefficient of friction between the tire and the road surface is small, the reference yaw rate is also calculated to a small value, thereby stabilizing the lateral behavior of the vehicle. Controlled in direction.
[0003]
[Problems to be solved by the invention]
The conventional vehicle steering system is configured to change only the steady gain, and thus can cope with the steady state of the vehicle, but cannot deal with the friction coefficient between the tire and the road surface according to the transient state of the vehicle. There is a problem that the scope of application is limited.
[0004]
In addition, since the conventional vehicle steering apparatus does not consider the influence of lateral acceleration acting on the vehicle, there is a problem that the behavior of the vehicle changes due to the lateral acceleration and the steering feeling is lowered.
[0005]
SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a vehicle steering apparatus that stabilizes lateral behavior in a steady state and a transient state of a vehicle regardless of changes in road conditions. There is to do.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, a vehicle steering apparatus according to the present invention is a vehicle steering apparatus having a control unit including an adaptive feedforward compensation unit that compensates for a vehicle body slip angle to be minimized in a steady state and a transient state. And a control means for estimating a friction coefficient between the tire and the road surface based on a steering angle signal, a rear steering angle signal provided from the adaptive feedforward compensation means, and a yaw rate signal supplied from an actual vehicle. And a correction means for correcting the control amount of the adaptive feedforward compensation means according to the friction coefficient between the tire and the road surface estimated by the friction coefficient estimation means .
[0007]
Since the vehicle steering apparatus according to the present invention includes the correction means for correcting the control amount of the adaptive feedforward compensation means in accordance with the friction coefficient between the tire and the road surface, the vehicle steering angle in the steady state and the transient state is adjusted. The corresponding slip angle can be set to the minimum, and the lateral behavior of the vehicle can be stably controlled.
[0008]
The correction means according to the present invention is characterized in that the control amount of the adaptive feedforward compensation means is changed based on the lateral acceleration detected by the vehicle.
[0009]
Since the correction means according to the present invention changes the control amount of the adaptive feedforward compensation means based on the lateral acceleration detected by the vehicle, the effect of the lateral acceleration acting on the vehicle is compensated for and the behavior of the vehicle in the lateral direction is compensated. It can be controlled more stably.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
The present invention stabilizes the lateral behavior of the vehicle by compensating for the slip angle of the vehicle corresponding to the steady and transitional vehicle operating conditions regardless of changes in road conditions.
[0011]
FIG. 1 is a block diagram showing a main part of a vehicle steering system according to the present invention.
Note that the present embodiment is directed to a vehicle steering apparatus having four-wheel steering.
[0012]
In FIG. 1, a vehicle rear wheel steering device 1 forming a vehicle steering device in an actual vehicle 2 is composed of various calculation means, storage means, processing means, etc. based on a microprocessor, and includes a friction coefficient estimation means 4, adaptive The control means 3 including the type feedforward compensation means 5 and the correction means 6 is provided, and the rear steering angle δ _R of the vehicle is calculated and calculated based on the steering angle signal θ _H detected by the steering angle sensor 10 of the driver's steering wheel operation. by calculating and outputting a yaw rate γ on the basis of the rear steering angle signal [delta] _R and the steering angle signal theta _H, in which the lateral behavior of the vehicle is controlled by another control device so as to be stable.
The estimation of the rear rudder angle δ _R is performed based on the friction coefficient μ between the tire and the road surface.
[0013]
The actual vehicle 2 is constituted by an electronic control circuit or the like having a calculation function, and a digital steering angle signal θ obtained by A / D converting (not shown) an analog electric signal corresponding to the steering angle detected by the steering angle sensor 10. _H, and the adaptive feedforward compensation means 5 on the basis of the rear steering angle signal calculated [delta] _R (slip angle) calculates the yaw rate gamma, other electronic control of a vehicle without a yaw rate signal gamma friction coefficient estimating means 4 and shown It supplies to an apparatus (ECU).
[0014]
The adaptive feedforward compensation means 5 has a control amount calculation function and a parameter variable function, and basically sets the control amount so that the vehicle slip angle is kept at 0 in the steady state and the transient state of the vehicle.
[0015]
Further, the adaptive feedforward compensation means 5, after determining the feed forward control amount based on the steering angle signal theta _H, calculates rear steering angle (slip angle) [delta] _R, the actual vehicle rear steering angle signal [delta] _R 2 and friction coefficient estimating means 4.
[0016]
Furthermore, the adaptive feedforward compensation means 5, to change the parameter on the basis of the correction value e corresponding to the friction coefficient mu _E provided by the correction means 6 corrects the feedforward control amount corrected rear steering angle signal δ _{R is provided} to the actual vehicle 2 and the friction coefficient estimating means 4.
[0017]
The correction means 6 has a calculation function for calculating a correction coefficient corresponding to the friction coefficient, calculates the correction coefficient e based on the (estimated) friction coefficient signal μ _E provided from the friction coefficient estimation means 4, and corrects the correction coefficient e. Is supplied to the control amount calculation means 5 so as to change the feedforward control amount in accordance with the change of the friction coefficient.
[0018]
The friction coefficient estimation means 4 has a calculation function for estimating the friction coefficient between the tire and the road surface. The steering angle signal θ _H , the rear steering angle signal δ _R provided from the adaptive feedforward compensation means 5, and the actual vehicle 2 Based on the supplied yaw rate signal γ, the (estimated) friction coefficient μ _E that compensates for the effects of the lateral acceleration y _G and the vehicle speed V is calculated from Equation 1, and the (estimated) friction coefficient signal μ _E is adaptive feedforward compensated. Supply to means 5.
[0019]
[Expression 1]
μ _E = {e _E + √ (e _E ² + 4k _E · y _G )} / 2
However, k _E is a constant [0020]
In Equation 1, the estimated value e _E is expressed by Equation 2.
[0021]
[Expression 2]
e _E = (A + 1−B) / (λ _E ⁻¹ · A + 1−B)
However, A = K _SPO · V ² , B = C _BO · V / l
K _SPO : Vehicle weight M, distance l from front / rear axis to acceleration center, and constant C _BO regarding cornering power K: feedback gain in steady state
Thus, since the vehicle steering apparatus according to the present invention includes the correction means for correcting the control amount of the adaptive feedforward compensation means in accordance with the coefficient of friction between the tire and the road surface, the vehicle in the steady state and the transient state is provided. By setting the slip angle corresponding to the steering angle to the minimum, the lateral behavior of the vehicle can be stably controlled.
[0023]
Next, correction means for correcting the influence of the lateral acceleration y _G acting on the vehicle will be described.
FIG. 2 is a block diagram showing the principal part of another embodiment of the correcting means according to the present invention.
[0024]
In FIG. 2, the correction means 11 includes a friction parameter setting means 7, an acceleration parameter setting means 8, and a correction value calculation means 9, and the correction coefficient e is calculated based on the (estimated) friction coefficient signal μ _E and the lateral acceleration signal y _G. calculated, the coefficient of friction between the tire supplying the correction coefficient e to control amount calculation means 5 road, and feedforward control amount so that the lateral acceleration compensation slip angle [delta] _R influence of is minimized acting on the vehicle To control.
[0025]
Friction parameter setting means 7, (estimated) Friction coefficient signal mu _E to shew parameters and operational functions, supplied from the coefficient of friction estimation unit 4 shown in FIG. 1 (estimated) friction parameter corresponding to the friction coefficient signals mu _E p _A is calculated and the friction parameter p _A is provided to the correction value calculation means 9.
[0026]
The acceleration parameter setting means 8 has a calculation function using the lateral acceleration signal y _G as a parameter, and is subjected to A / D conversion in the same manner as the lateral acceleration signal y _G acting on the vehicle (the steering angle signal θ _H shown in FIG. 1). The acceleration parameter p _B corresponding to the digital value) is calculated, and the acceleration parameter p _B is provided to the correction value calculation means 9.
[0027]
The correction value calculation means 9 calculates a correction coefficient e based on the friction parameter p _A provided from the friction parameter setting means 7 and the acceleration parameter p _B provided from the acceleration parameter setting means 8, and adapts the correction coefficient signal e. is supplied to the mold feedforward compensation means 5 performs control so as to correct the feed-forward control amount in response to changes in (estimated) friction coefficient signals mu _E and the lateral acceleration signal y _G.
[0028]
Thus, since the correction means according to the present invention changes the control amount of the adaptive feedforward compensation means based on the lateral acceleration detected by the vehicle, the effect of the lateral acceleration acting on the vehicle is compensated to compensate for the vehicle. The lateral behavior can be controlled more stably.
[0029]
(Estimated) The feedforward control amount C _f ^e (s) calculated based on the friction coefficient μ _E and the lateral acceleration y _G is shown in Equation 3.
[0030]
[Equation 3]
C _f ^e (s) = − K {c ₁ (s) + C ₀ (s)} / {c ₁ (s) +1}
Where C ₀ (s) and c ₁ (s) are parameters relating to the vehicle volume M, cornering power K, distance 1 from the axle to the center of acceleration, and vehicle speed V, with the correction coefficient e as a parameter, and s is a Laplace operator 0031
Further, the correction coefficient e is expressed by Equation 4 with respect to the estimated friction coefficient μ _E and the acceleration y _G.
[0032]
[Expression 4]
e = e (y _E / μ _E ) ≈μ _E {1-k _E (y _E / μ _E ) ² }
Where k _E is a constant [0033]
The yaw rate characteristics of the present invention using the feedforward control amount C _f ^e (s) of Equation 3 and the conventional yaw rate characteristics are shown in FIGS.
[0034]
FIG. 3 is a yaw rate frequency characteristic diagram when the lateral acceleration is zero.
(A) The gain frequency characteristic of yaw rate is shown in the figure, and the phase frequency characteristic is shown in (b) figure.
The yaw rate gain and yaw rate phase are set with the lateral acceleration y _G = 0, the vehicle speed V = 30 m / s set to a constant value, and the friction coefficient μ _E as a parameter (0.2, 0.4). is there.
[0035]
The yaw rate characteristic (solid line display) of the present invention shows a stable characteristic with little change even when the frequency of the gain and phase changes compared to the conventional yaw rate characteristic (dotted line display).
[0036]
As apparent from the characteristics of FIG. 3, the vehicle steering apparatus of the present invention can suppress the fluctuation of the yaw rate even if the friction coefficient changes, so that the influence of the friction between the tire and the road surface is compensated for. The lateral behavior of can be kept stable.
[0037]
FIG. 4 is a yaw rate frequency characteristic diagram when the friction coefficient is constant.
(A) The gain frequency characteristic of yaw rate is shown in the figure, and the phase frequency characteristic is shown in (b) figure.
The yaw rate gain and yaw rate phase were set such that the friction coefficient μ _E = 0.8, the vehicle speed V = 30 m / s were set to constant values, and the lateral acceleration y _G was set as a parameter (0.6 _G , 0.8 _G ). Is.
[0038]
The yaw rate characteristic (displayed with a solid line) of the present invention shows a stable characteristic as the lateral acceleration y _G increases with respect to the conventional yaw rate characteristic (displayed with a broken line) with little change even if the gain and phase change in frequency. .
[0039]
As is apparent from the characteristics of FIG. 4, the vehicle steering apparatus of the present invention can suppress the fluctuation of the yaw rate even if the lateral acceleration increases, so that the influence of the lateral acceleration acting on the vehicle is compensated for. The lateral behavior of can be kept stable.
[0040]
In the present embodiment, the lateral acceleration y _G is detected by the lateral acceleration sensor, but the product of the vehicle speed V and the yaw rate γ may be calculated and approximated.
[0041]
In this embodiment, a vehicle steering apparatus having four-wheel steering is targeted, but the present invention can also be applied to other vehicles.
[0042]
【The invention's effect】
As described above, the vehicle steering apparatus according to the present invention includes the correction unit that corrects the control amount of the adaptive feedforward compensation unit in accordance with the friction coefficient between the tire and the road surface, and the vehicle in the steady state and the transient state. Since the slip angle corresponding to the steering angle can be set to the minimum and the lateral behavior of the vehicle can be stably controlled, a stable steering feeling can be obtained even on dry roads and slippery roads.
[0043]
Further, the correction means according to the present invention changes the control amount of the adaptive feedforward compensation means based on the lateral acceleration detected by the vehicle, compensates for the influence of the lateral acceleration acting on the vehicle, and acts in the lateral direction of the vehicle. Can be controlled more stably, and a stable steering feeling can be obtained even when a large lateral acceleration is applied.
[0044]
Therefore, it is possible to provide a vehicle steering apparatus capable of obtaining a stable steering feeling by compensating for the influence of the road surface condition and the lateral acceleration.
[Brief description of the drawings]
FIG. 1 is a block diagram of a main part of a steering system for a vehicle according to the present invention. FIG. 2 is a block diagram of a main part of another embodiment of a correcting means according to the present invention. Characteristic diagram [Fig. 4] Yaw rate frequency characteristic graph with constant friction coefficient [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Vehicle rear-wheel steering apparatus, 2 ... Real vehicle, 3 ... Control means, 4 ... Friction coefficient estimation means, 5 ... Adaptive feedforward compensation means, 6, 11 ... Correction means, 7 ... Friction parameter setting means, 8 ... acceleration parameter setting means, 9 ... correction value calculating means, 10 ... steering angle sensor.

Claims (2)

A vehicle steering apparatus having a control unit including an adaptive feedforward compensation unit that compensates so that a vehicle body slip angle in a steady state and a transient state is minimized.
The control means includes a friction coefficient estimating means for estimating a friction coefficient between a tire and a road surface based on a steering angle signal, a rear steering angle signal provided from the adaptive feedforward compensation means, and a yaw rate signal supplied from an actual vehicle; ,
The vehicle steering system is characterized in that a correction means for correcting the control amount of the adaptive feedforward compensation means in accordance with the friction coefficient between the said tire which is estimated by the friction coefficient estimation unit road.   2. The vehicle steering apparatus according to claim 1, wherein the correction unit changes a control amount of the adaptive feedforward compensation unit based on a lateral acceleration detected by the vehicle.

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