JP2962025B2 - Body slip angle estimation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for estimating a side slip angle of a vehicle at the center of gravity of a vehicle, and more particularly to a technique for improving the accuracy of the estimation.

[0002]

2. Description of the Related Art There is a demand for appropriately controlling the maneuverability and stability of a vehicle in relation to the actual amount of motion of the vehicle, and one of the amounts of motion is the vehicle body slip angle at the center of gravity of the vehicle. I do. Generally, it is relatively difficult to directly obtain the vehicle body side slip angle itself, and therefore, a parameter related thereto is detected and then obtained indirectly.

An example of a technique for indirectly obtaining a vehicle body slip angle is described in Japanese Patent Application Laid-Open No. Sho 62-105776. This is related to the side slip motion of the vehicle. Β ′ = G _y / V−γ where β ′: Time derivative of the vehicle side slip angle β G _y : Lateral acceleration at the center of gravity of the vehicle V: Vehicle speed γ which is the running speed of the vehicle : Yaw rate Based on the fact that the equation of motion holds, the vehicle body side slip angle β is estimated by integrating the values on the right side of the equation.

[0004]

This conventional vehicle body slip angle estimating technique (hereinafter simply referred to as "prior art") specifically, detects a lateral acceleration detection value based on an output signal from a lateral acceleration sensor from a vehicle speed sensor. The vehicle body slip angle β is successively estimated by integrating the value obtained by subtracting the detected value of the yaw rate γ based on the output signal from the yaw rate sensor from the value divided by the detected value of the vehicle speed V based on the output signal of the vehicle with respect to time. is there.

[0005] However, an output signal from a sensor mounted on the vehicle usually drifts due to a temperature change or the like. Therefore, when adopting this conventional technology,
An error generated in the detected value based on the drift is also integrated to estimate the vehicle body slip angle β, and there is a problem that the estimation accuracy cannot be sufficiently improved.

[0006] The present invention has been made to solve this problem.

[0007]

SUMMARY OF THE INVENTION In order to solve this problem, the gist of the present invention is to provide a device for estimating a vehicle body slip angle at the center of gravity of a vehicle, comprising: (a) a lateral acceleration sensor for detecting a lateral acceleration generated in the vehicle body; (B) a vehicle speed sensor that detects a vehicle speed that is the traveling speed of the vehicle body, (c) a yaw rate sensor that detects a yaw rate generated on the vehicle body, and (d) a vehicle body slip angle β at the vehicle center of gravity connected to them. a vehicle slip angle estimating means for sequentially estimating acquires the current value of a variable by dividing the yawing moment YM generated around the vehicle center of gravity in the yaw inertia moment I _Z of the vehicle YM / I _Z, The vehicle body side slip angle β and the yaw rate γ assumed for the plane movement of the vehicle including the vehicle side slip movement and the yawing movement are set as state variables, respectively. The rate G _y and the G _y / V is a variable divided by the vehicle speed V, the from YM / I _Z respectively input variables and variables obtained by subtracting the previous estimated value of the vehicle slip angle beta, soluble to output variable yaw rate γ Using an observer in the observed linear constant coefficient system, the current values of the lateral acceleration G _y , the vehicle speed V and the yaw rate γ based on the output signals from the lateral acceleration sensor, the vehicle speed sensor and the yaw rate sensor, and the obtained YM / I _Z Of the vehicle body slip angle β based on the current value of
And that for estimating the current value.

[0008] Here, the definitive "vehicle slip angle estimating means" may employ various things modes of obtaining the current value of YM / I _Z. For example, a method of obtaining the current value of YM / I _Z by the yaw inertia moment I _Z to obtain the current value of the yawing moment YM under the assumption that it is invariant, for each wheel of the vehicle wheel slip It is also possible to adopt a device that acquires the current value of the yawing moment YM based on the angle α, the cornering power C (constant) of each wheel, the rotational force T generated on each wheel, and the like.

When the lateral acceleration sensor is mounted on the vehicle body so as to coincide with the center of gravity of the vehicle, the "lateral body slip angle estimating means" uses the lateral acceleration detected by the lateral acceleration sensor at the center of gravity of the vehicle as it is. Lateral acceleration G
_If the lateral acceleration sensor does not match the center of gravity of the vehicle, the lateral acceleration detected by the lateral acceleration sensor is used as the relative positional relationship between the lateral acceleration sensor and the center of gravity of the vehicle. it can be made to obtain the lateral acceleration G _y of the vehicle center of gravity by correcting by the time differential value of the yaw rate γ and.

[0010]

In the vehicle body slip angle estimating apparatus according to the present invention, for example, YM / I _Z is a variable obtained by dividing the yawing moment YM generated around the vehicle center of gravity by the yaw inertia moment I _Z of the vehicle as described above. Is obtained.

Except for the transient vehicle motion when the vehicle is suddenly accelerated or decelerated or when the steering wheel is quickly operated, the change in the vehicle speed V and the rolling motion of the vehicle can be ignored. As described above, when it is possible to pay attention only to the motion in which the vehicle travels in the horizontal plane at a constant speed without the rolling motion, that is, only the plane motion of the vehicle, it is only necessary to consider only two of the sideslip motion and the yawing motion of the vehicle. In this case, the following two equations of motion generally hold.

MV (β ′ + γ) = CF (1) Equation (1) relating to the side slipping motion, and I _Z γ ′ = YM (2) Equation (2) relating to the yawing motion: One is established. Where: m: inertial mass of the vehicle V: vehicle speed β: body slip angle at the center of gravity of the vehicle (left is positive,
The right direction is negative) β ': The vehicle side slip angle differential which is the time differential value of the vehicle side slip angle β γ: The yaw rate (positive in the counterclockwise direction and negative in the clockwise direction) γ': The yaw rate differential which is the time differential value of the yaw rate γ CF: a front wheel cornering force F _f generated based on the operation of its slip angle alpha _f and the vehicle engine and braking to the front wheels of the vehicle, to the operation of the engine and brake and its slip angle alpha _r on the rear wheel sum I _Z of the wheel cornering force F _r after generated based: yaw moment of inertia of the vehicle YM: yawing moment generated around the vehicle center of gravity based on the front wheel cornering force F _f and the rear wheel cornering force F _r

In the vehicle body slip angle estimating apparatus according to the present invention, the cornering force CF is not directly detected, but when V (β '+ γ) in the above equation (1) matches the lateral acceleration G _y at the vehicle center of gravity. That is, V (β ′ + γ) = G _y (3) The relation is indirectly detected by using the relationship expressed by the equation (3).

Therefore, equation (1) can be transformed into equation (1) 'of β' = G _y / V-γ (1) ', and equation (2) can be expressed as γ' = YM / I _Z .. (2) ′.

Since the lateral acceleration G _y , the vehicle speed V, the yaw rate γ, and the YM / I _Z can be detected among the physical quantities in the equations (1) ′ and (2) ′, the apparatus for detecting the vehicle body slip angle according to the present invention is provided. In formulas (1) ′ and
(2) The vehicle body slip angle β is momentarily estimated from 'and the detectable physical quantity. With respect to the plane motion of the vehicle described by equations (1) 'and (2)', an observable linear constant coefficient system (also called a linear time-invariant system) is assumed, which contains the undetectable body slip angle β as a state variable. Further, the vehicle body slip angle β is estimated by assuming an observer therewith.

In order to assume a linear constant coefficient system for the plane motion of the vehicle, it is conceivable to introduce, for example, the following input variables, output variables and state variables. First input variable u ₁ (t): G _y / V Second input variable u ₂ (t): YM / I _Z Output variable y (t): γ First state variable x ₁ (t): β Second state variable x ₂ (t): γ However, these input variables, output variables and state variables cannot form an observable linear constant coefficient system. Hereinafter, the reason will be described.

When such input variables, output variables and state variables are introduced, a state equation (4) expressed in the following matrix form is derived.

[0018]

(Equation 1)

Further, an output equation (5) expressed in the following matrix form is derived.

[0020]

(Equation 2)

On the other hand, in order for the linear constant coefficient system to be observable, the rank of the observable matrix U ₀ must be equal to the dimension n of the state variable.
(This time, 2) must match. The observable matrix U ₀ is represented using a system matrix A and an output matrix C, which will be described later, and when the value of the dimension n is 2,

[0022]

(Equation 3)

## EQU2 ## In the above state equation (4) and output equation (5),

[0024]

(Equation 4)

Since C = [0 1], after all,

[0026]

(Equation 5)

Since the rank is 1 and is not 2 which is the dimension n, the present linear constant coefficient system is not observable.

Therefore, in the vehicle body slip angle estimating apparatus according to the present invention, the vehicle body slip angle β has a characteristic that changes relatively slowly with time, and the current estimated value β _{(i) of the} vehicle body slip angle β Using the fact that the difference between the estimated value and the previous estimated value β _(i-1) can be regarded as almost 0,
Introduce the following input, output, and state variables. First input variable u ₁ (t): G _y / V Second input variable u ₂ (t): YM / I _Z -β _(i-1) Output variable y (t): γ First state variable x ₁ (t): β _(i) Second state variable x ₂ (t): γ Accordingly, the following state equation (6) is derived.

[0029]

(Equation 6)

Further, the following output equation (7) is derived.

[0031]

(Equation 7)

In equation (6), the system matrix A is

[0033]

(Equation 8)

Thus, the observable matrix U _{0 of} this time is

[0035]

(Equation 9)

## EQU2 ## This observable matrix U
_Since the rank of ₀ is 2 and is equal to 2 which is the dimension n of the state variable, the linear constant coefficient systems described by the equations (6) and (7) are observable.

In short, in the vehicle body slip angle estimating apparatus according to the present invention, the vehicle body slip angle β and the yaw rate γ are set as state variables for the vehicle plane movement including the vehicle skid movement and the yawing movement, and the vehicle center of gravity is set. the lateral acceleration G _y is the G _y / V is a variable divided by the vehicle speed V, the from YM / I _Z respectively input variables and variables obtained by subtracting the previous estimated value of the vehicle body slip angle β at the point, the output variable yaw rate γ An observable linear constant coefficient system is assumed, and an observer is used in the linear constant coefficient system to obtain the current values of the lateral acceleration G _y , the vehicle speed V and the yaw rate γ, and the obtained YM / I _Z
And the current value of is the previous estimate of the vehicle body slip angle β β _(i-1) between the present value of the vehicle slip angle beta, based on the beta _(i) is estimated.

The observer estimates the current value β _(i) of the vehicle body slip angle β without directly integrating the lateral acceleration G _y and the yaw rate γ. Therefore, as described above, even if a drift occurs in the lateral acceleration _Gy or the like, an error based on the drift is not integrated, and the vehicle body side slip angle β
Does not need to be reduced due to the drift.

By the way, since values detected by various sensors usually include noise, it is impossible to accurately estimate the vehicle body slip angle β by integrating such detected values. On the other hand, in the vehicle body slip angle estimating device according to the present invention, the use of the observer allows the vehicle body slip angle β to be estimated without integrating such a detected value. The detection value is less affected by noise.

[0040]

As described above, according to the present invention, the vehicle body slip angle β can be estimated without integrating values detected by various sensors. The effect is obtained that the influence of drift or the like is not so much affected.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A rear wheel steering angle control device including a vehicle body slip angle estimation device according to an embodiment of the present invention will be described in detail with reference to the drawings.

This rear wheel steering angle control device is provided in a vehicle which is a four-wheel drive type vehicle that transmits the output of the engine to the left and right front wheels and the left and right rear wheels via an automatic transmission, as shown in FIG. to a front wheel steering mechanism 16 for changing the steering angle [delta] _f of the left and right front wheels 12 in accordance with the steering angle of the steering wheel 10, to vary the steering angle [delta] _r of the left and right rear wheels 22 by a step motor 20 as a driving source And a rear wheel steering mechanism 26.

[0043] The rear wheel steering angle control apparatus further includes, as shown in the figure, the front wheel steering angle sensor 3 for detecting a front wheel steering angle [delta] _f
0, wheel steering angle sensor 32 after detecting the rear wheel steering angle [delta] _r, the vehicle speed sensor 34 for detecting the vehicle speed V is a vehicle speed, lateral acceleration in the yaw rate sensor 36, and the vehicle center of gravity detecting a yaw rate gamma G A lateral acceleration sensor 40 for detecting _y is provided. These sensors 30, 32, 34,
Reference numerals 36 and 40 are connected to an input section of a controller 50, and the output section thereof is connected to the step motor 20.

[0044] and detects each front wheel steering angle sensor 30 and the rear wheel steering angle sensor 32, the counterclockwise steering angle [delta] _f, the [delta] _r positive, clockwise steering angle [delta] _f, as a negative the [delta] _r . The yaw rate sensor 36 detects the counterclockwise yaw rate γ as positive and the clockwise yaw rate γ as negative. The lateral acceleration sensor 40, located on the center-of-gravity point of the vehicle, and detects the lateral acceleration G _y of the vehicle center of gravity negative leftward, rightward as positive.

The controller 50 includes a CPU (not shown),
The computer mainly includes a ROM, a RAM, and a bus. The ROM includes a vehicle body slip angle estimation routine shown in the flowchart of FIG.
Various programs including a rear wheel steering angle control routine represented by the flowchart of FIG. 4, various maps including a map for determining a target rear wheel steering angle represented by the graphs of FIGS. 4, 5, and 6, and the like. Is stored in advance.

The vehicle body slip angle estimation routine shown in FIG. 1 is capable of estimating the yawing moment YM generated around the vehicle center of gravity according to the following equation (8). _{YM = a f F f -a r} F r ··· (8) However, a _f: front wheel axle and the distance between the vehicle center of gravity (constant) a _r: rear wheel axle and the distance between the vehicle center of gravity (constant) F _f : Total cornering force generated on left and right front wheels 12 (hereinafter simply referred to as front wheel cornering force) F _r : Total cornering force generated on right and left rear wheels 22 (hereinafter simply referred to as rear wheel cornering force) Note that front wheel cornering force F _f is defined by −α _f C _f (1−h _f T _f ), while the rear wheel cornering force F _r is defined by −α _r C _r (1−h _r T _r ). Here, C _f : the total cornering power of the left and right front wheels 12 (hereinafter simply referred to as front wheel cornering power; constant) C _r : the total cornering power of the left and right rear wheels 22 (hereinafter simply referred to as rear wheel cornering power. Constant) α _f : Wheel slip angle of the left and right front wheels 12 α _r : Wheel slip angle of the left and right rear wheels 22 T _f : Total torque generated in the left and right front wheels 12 based on the operation of the engine and the front wheel brake (hereinafter simply referred to as front wheel torque) T _r : total rotational force generated on the left and right rear wheels 22 based on the operation of the engine and the rear wheel brake (hereinafter, simply referred to as rear wheel rotational force) _hf : front wheel cornering power C by front wheel rotational force _Tf
reduction factor _f (constant) h _r: rear wheel rotational force T _r rear wheel cornering power by C
Reduction factor of _r (constant)

The front wheel slip angle α _f is defined by β + a _f γ / V−δ _f , while the rear wheel slip angle α _r is defined by β−a _r γ / V−δ _r .

The reduction coefficient h _f is defined by δ _f / (α _f C _f ), while the reduction coefficient h _r is defined by δ _r / (α _r C _r ).

In the present embodiment, there is a respective constant wheel cornering power C _f also the rear wheel cornering power C _r also decreases the coefficient h _f, h _r as the plane motion of the vehicle is in the linear region. However, the front wheel and rear wheel slip angles α _f , α _r are obtained by the calculations using the above-described respective definition expressions. Specifically, for the front wheel slip angle α _f , β is defined as a previously estimated value β _(i−1) described later in a definition equation thereof, that is, an equation of β + a _f γ / V−δ _f , and γ, V and [delta] _f is obtained by being a value detected by various sensors, respectively, whereas, for the rear wheel slip angle alpha _r, its definition formula, i.e., the _{β-a r γ / V-} δ r becomes formula , beta is the previous estimate of below _{β (i-1), γ} , V and [delta] _r is obtained by being a value detected by various sensors, respectively. The front wheel and rear wheel rotational forces T _f and _Tr are also obtained by calculation as follows.

That is, the front wheel rotational force _Tf is obtained by subtracting the braking force applied to the front wheels 12 by the front wheel brake of the vehicle from the front wheel driving force transmitted from the automatic transmission (hereinafter simply referred to as transmission) of the vehicle to the front wheels 12. The driving force of the front wheels is obtained as follows: the opening degree of the throttle valve of the engine (hereinafter simply referred to as the throttle opening degree) θ, the engine speed _Ne , the transmission gear ratio R, and the output from the transmission to the front wheels 12. The front wheel braking force is obtained based on the allocated ratio and the like, while the front wheel braking force is obtained based on the wheel cylinder pressure of the front wheel brake and the like. The rear wheel rotational force _Tr is obtained in the same manner. Specifically, the rear wheel driving force transmitted from the transmission to the rear wheels 22 is obtained by subtracting the rear wheel braking force applied to the rear wheels 22 by the rear wheel brake of the vehicle. The throttle opening θ, the engine speed N _e , the transmission gear ratio R, and the output from the transmission are distributed based on the ratio of the rear wheels 22 and the like. Is obtained based on the wheel cylinder pressure of the vehicle.

Therefore, the front wheel cornering force F
_f and the rear wheel cornering force _Fr are determined,
Expression for the yawing motion of the vehicle (2) is, after _{all, γ '= (a f F} f -a r F r) / I becomes _Z · · · (9) made to be deformed into the equation (9). In this equation, since the yaw moment of inertia I _Z is treated as a constant, after all,
_{(A f F f -a r F} r) / it current value of _Z i.e. the yaw rate differentiation gamma 'can be said to be detectable physical quantity.

Further, the vehicle body slip angle estimation routine successively estimates the vehicle body slip angle β, and specifically, an observable linear constant assumed for a plane motion of the vehicle including a vehicle slip motion and a yawing motion. Assuming an observer in the coefficient system, the current values of the lateral acceleration G _y , the vehicle speed V and the yaw rate γ, and the yawing moment Y
The current value of YM / I _Z obtained by dividing M by the yaw moment of inertia I _Z of the vehicle (= (a _f F _f −a
_r F _r ) / I _Z ) and the previous estimated value β of the vehicle body slip angle β
It is also possible to estimate the current value β _(i) of the vehicle body side slip angle β based on _(i-1) .

In the observable linear constant coefficient system, specifically, the following input variables, output variables and state variables are introduced, and a first input variable u ₁ (t): G _y / V second input variable _{u 2 (t): (a} f F f -a r F r) / I
_Z- β _(i-1) Output variable y (t): γ First state variable x ₁ (t): β _(i) Second state variable x ₂ (t): γ

[0054]

(Equation 10)

The state equation (10) becomes:

[0056]

[Equation 11]

This is described by the following output equation (11).

As is clear from the above description, this linear constant coefficient system has a two-dimensional state variable.
On the other hand, one γ can be detected, and only the other β _(i) cannot be detected.This time, instead of estimating all two state variables, only the vehicle body slip angle β is estimated, The dimension of the observer is reduced to form the minimum dimension observer.

Incidentally, the linear constant coefficient system is generally described by a state equation of X (t) '= AX (t) + BU (t) and an output equation of Y (t) = CX (t). X (t): n-dimensional state vector Y (t): r-dimensional output vector U (t): m-dimensional input vector A: n × n-dimensional system matrix B: n × m-dimensional input matrix C: r × n-dimensional output matrix

Then, this system is generally expressed by the following equation: ω (t) ′ = A′ω (t) + KY (t) + B′U (t) X (t) = Dω (t) + HY (t) Can be constructed. Where ω (t): a variable converted from X (t) and lower in dimension than X (t) ω (t) ′: time derivative of ω (t) A ′: (n−r) × (n -R) dimensional matrix K: (nr) × r dimensional matrix B ′: (nr) × m dimensional matrix D: nx (nr) dimensional matrix H: nxr dimensional matrix Matrix Hereinafter, a general construction method of the minimum-dimensional observer will be described. This is described in detail in the document "Introduction to System Control Theory (Jikkyo Shuppan Co., Ltd., published on January 20, 1991)". Here, a brief description will be given.

To determine each element in each matrix, first
An n × n-dimensional matrix S is determined. This matrix S is

[0062]

(Equation 12)

Where C is the output matrix described above, and W is an appropriate (n−r) × n-dimensional matrix that does not set the determinant of the matrix S to zero. next,

[0064]

(Equation 13)

The matrices A ₁₁ , A ₁₂ , A ₂₁ and A _{22 in}
Is determined, and further,

[0066]

[Equation 14]

Determine each of the matrices B ₁ and B ₂ in Subsequently, an (n−r) × r-dimensional matrix L is introduced as a design parameter, and a matrix A ′ is defined by the following equation: A ′ = A ₂₂ −LA ₁₂ . Then, each element of the matrix L is determined such that the eigenvalue of the matrix A 'becomes the pole (arbitrary value) of the observer. Thereafter, the matrix K, B ', each element in the D and _{H K = A'L + A 21 -LA} 11 B' = - LB 1 + B 2

[0068]

(Equation 15)

[0069]

(Equation 16)

The following equation is established.

The general configuration of the minimum-dimensional observer has been briefly described above, but the configuration in the present embodiment will be specifically described. As described above, in this embodiment,

[0072]

[Equation 17]

[0073]

(Equation 18)

C = [0 1]. At this time, if W = [1 0], the requirement that the determinant of the matrix S is not 0 can be satisfied. In this case, since the matrix L is a matrix composed of one element, the eigenvalue of the matrix A 'is represented by -L, and this time, it is assumed that it coincides with -p which is the pole of the minimum dimension observer this time. Then, L = p. In order for the observer to satisfy the condition, the matrix A 'needs to be a stable matrix. Therefore, the value of the pole -p of the observer is negative, and the value of p is eventually positive. Will be done.

Therefore, the matrices A ', K, B', D
And H this time are as follows. A ′ = − p K = −p ² −1 B ′ = [1−p]

[0076]

[Equation 19]

[0077]

(Equation 20)

In this case, ω is one-dimensional, and the vehicle state slip angle β, which is the _first state variable x ₁ (t), is converted.

[0079]

(Equation 21)

Equation (12)

[0081]

(Equation 22)

That is, β _(i) = ω + pγ (13) Therefore, first, the previous expression
According to (12), a known or detectable physical quantity p,
_{γ, G y / V, (} a f F f -a r F r) / I Z and β
ω is estimated from _(i-1) , and then, according to equation (13),
And β _(i) , that is, the current value of the vehicle body slip angle β, is estimated from the known or detectable physical quantities p and γ. However, since equation (12) describes a continuous-time system, ω is successively estimated by making this a discrete-time system.

As described above, the linear constant coefficient system is generally expressed by a state equation (14) as follows: X (t) '= EX (t) + FU (t) (14) , U (t) is represented by dt. X (t) _(i) = E'X (t) _(i-1) + F'U (t) _(i) (15) The rule that the expression is converted into Expression (15) is already known. Since this rule is also described in the above-mentioned document "Introduction to System Control Theory", detailed description is omitted. X (t): state vector X (t) ': time derivative of state vector U (t): input vector E: system matrix F: input matrix X (t) _(i) : this time of X (t) Estimated value X (t) _(i-1) : Previous estimated value of X (t) U (t) _(i) : ^Current detected value of U (t) E ': e ^Edt F': (e ^Edt -I) E ^-1 FI: unit matrix

Equation (12) is converted in accordance with this rule. First, when the construction of equation (14) is adjusted to equation (12), X (t) '= EX (t) + F ₁ U ₁ (t ) + F ₂ U ₂ (t) + F ₃ U ₃ (t) (16) As a result, the relationship between each element in this equation and each element in equation (12) is E = -p X (t) = ω (t) F 1 = -p 2 -1 F 2 = 1 F 3 = -p U 1 (t) = γ U 2 (t) = G y / V U 3 ( t) = become _{(a f F f -a r F} r) / I Z -β (i-1). F ₁ ′ = (e ^Edt −I) E ⁻¹ F ₁ F ₂ ′ = (e ^Edt −I) E ⁻¹ F ₂ F ₃ ′ = (e ^Edt −I) E ⁻¹ F ₃ , In addition, since E ⁻¹ = 1 / (− p), the equation (12) eventually becomes: ω _(i) = e ₁ ω _(i-1) + e ₂ γ _(i) + e ₃ G _{y (i)} is converted to _{/ V (i) + e 4} (((a f F f -a r F r) / I Z) (i) -β (i-1)) ··· (17) becomes equation (17) .

Where ω _(i) : the current estimated value of ω ω _(i-1) : the previous estimated value of ω γ _(i) : the current sampling value of the yaw rate γ G _{y (i)} : the current value of the lateral acceleration G _y sampled values V _(i): this sampling value of the vehicle speed _{V ((a f F f -a} r F r) / I Z) (i): ((a f F f
-A _r F _r ) / I _z )

In the equation (17), e ₁ , e ₂ , e ₃ and e
₄ is a both a constant, ^{_{specifically, e 1: e -pdt e 2}} : (e -pdt -1) (p 2 +1) / p e 3 :-( e -pdt -1) / p e ₄ : e ^−pdt −1

Therefore, the equation (17)_(i-1), Γ_(i),
G_{y (i)}, V_(i)And ((a_fF _f-A_rF_r) / I
_Z)_(i)Substituting each value of ω_(i)Can be obtained.
And γ_(i)Is a formula corresponding to the formula (13).
And β_(i)= Ω + pγ, then β_(i)Can be obtained. Note that the expression
In (17), V_(i)= 0 if = 0_(i)Operation becomes impossible
Therefore, at this time ω_(i)To 0 and β_(i)
Is also set to 0.

Against the background described above, the vehicle body slip angle estimation routine of FIG. 1 is executed every time the sampling period dt elapses. In each execution of this routine, first, in step S1 (hereinafter simply referred to as S1; the same applies to other steps), this execution of this routine is performed for the first time after the power of the controller 50 is turned on. It is determined whether there is. Since this is the case this time, the determination is YES, and the value of ω is set to 0 and the value of β is set to pγ in S2. p is a predetermined constant and γ is the current yaw rate. This step is a step for setting respective initial values of ω and β.

Subsequently, in S3, it is determined whether or not the vehicle speed V is zero. Assuming that it is not the case this time, a negative decision (NO) is obtained in S4, first, the front wheel, rear wheel cornering force F _f, the current value of F _r is calculated according to the equation. In this step, an expression corresponding to the expression (17) (the expression shown in FIG.
), Current values of ω, γ, G _y , V and β (however, this time, ω and β are equal to the above initial values) and current calculations of F _f and _Fr respectively The current value of ω is updated by substituting the value. Note that e ₁ , e ₂ , e ₃ ,
e ₄ , a _f , _ar and I _Z are constants, respectively. Thereafter, in S5, the current value of β is updated by calculating the sum of the current value of ω and the current value of pγ, and in S6
, The current value of β is stored in the RAM as the current estimated value of the vehicle side slip angle β. This completes one execution of this routine.

On the other hand, if the vehicle speed V is 0, the determination in S3 is YES, and in S7, the current value of ω and the current value of β are also set to 0, and thereafter, in S6,
The current value of β, that is, 0, is stored in the RAM as the current estimated value of the vehicle body slip angle β.

In each of the second and subsequent executions of this routine, the determination in S1 is NO and the execution of S2 is skipped. However, the vehicle speed V is not 0 and the determination in S3 is NO and S4 is executed. If executed, in S4, the respective values of ω and β obtained in the previous execution of this routine, that is, the current values of ω and β, and γ, G _y , V, F _f and the current value of omega by each and the current value is assigned to the arithmetic expression of F _r is updated, further, in S5, the current value of the omega, p
The current value of β is updated by calculating the sum of the product of the current value and the current value of the yaw rate γ.

[0092] On the other hand, wheel steering angle control routine after 3 determines a target value of the rear wheel steering angle [delta] _r in accordance with δ _r = Kδ _f + λγ made wherein control step motor 20 as it is implemented Is what you do. In this equation, K is a steering angle gain, which is determined according to the vehicle speed V according to the map of FIG. Λ is a yaw rate gain, and the second partial gain λ ₁ is determined according to the vehicle speed V according to the graph of FIG. 5 and the second partial gain λ ₁ is determined according to the absolute value of the vehicle body slip angle β according to the graph of FIG. It is determined as the sum of the partial gains lambda _2. In addition,
4 to 6 have characteristics to make the actual value of the vehicle body slip angle β approach 0 as much as possible regardless of whether the vehicle is in a steady state or a transient state.

The rear wheel steering angle control routine of FIG. 3 is also repeatedly executed. Note that the vehicle body slip angle estimation routine of FIG. 1 is executed only once in one execution of the rear wheel steering angle control routine of FIG. 3, and eventually these routines are executed in synchronization with each other. It has become.

[0094] The wheel steering angle at each time of execution of the control routine after 3, first, in S101, the front wheel steering angle [delta] _f from the various sensors, yaw rate gamma, lateral acceleration G _y and the vehicle speed V is taken, followed by, S102 , The value of the steering angle gain K corresponding to the vehicle speed V is calculated using the map shown in FIG.
The first portion gain lambda ₁ value corresponding to the determined respectively by using a map of Figure 5, in S103, the vehicle body slip angle is executing the vehicle body slip angle estimation routine of FIG. 1 beta
Is estimated. Thereafter, in S104, the value of the second partial gain λ ₂ corresponding to the absolute value of the current value of the vehicle body slip angle β is determined using the map of FIG. 6, and further, the first partial gain λ ₁ and its second the sum of the partial gains lambda ₂ is determined to the current value of the yaw rate gain lambda. Subsequently, in S105, the sum of the product of the product and the yaw rate gain λ and the yaw rate γ and the steering angle gain K and the front wheel steering angle [delta] _f is determined as the current target value of the rear wheel steering angle [delta] _r, in S106 A drive signal is output to the step motor 20 so that the current target value is realized. This completes one execution of this routine.

As is clear from the above description, in this embodiment, the vehicle body slip angle β is estimated by the observer without integrating the detection values from the various sensors, and the estimated value is used as the noise of the detection value. The effect that the influence of the drift or the like is not so large can be obtained, and the reliability of the estimated value, that is, the accuracy can be sufficiently improved.

Further, in this embodiment, the vehicle body slip angle β is estimated by the observer, and in this observer, the decay speed (convergence speed) of the estimation error of the vehicle body slip angle β is determined by the matrix L as a design parameter, that is, the observer. Can be arbitrarily set depending on the value of the pole (−p) of Therefore, an effect is obtained that the decay speed of the estimation error can be relatively freely and easily approximated to a desired value.

As is apparent from the above description, in this embodiment, the part of the controller 50 that executes the vehicle body slip angle estimation routine of FIG.
The yaw rate sensor 36 and the lateral acceleration sensor 40 cooperate with each other to constitute a vehicle body slip angle estimating apparatus according to the present invention, and the part of the controller 50 that executes the vehicle body slip angle estimating routine of FIG. Of the vehicle body slip angle estimating means.

It should be noted that, in this embodiment, the front wheel and rear wheel cornering powers C _f and C _r are assumed to be constants assuming that the plane motion of the vehicle is in the linear region. It is defined as a function using vehicle motion state quantities such as slip angles α _f and α _r as variables, and the relationship between the front wheel cornering power C _f and the front wheel slip angle α _f is defined as
The relationship between the rear wheel cornering power C _r and the rear wheel slip angle α _r can be obtained in advance and stored in a ROM or the like as a map or the like. regardless of whether a certain or non-linear region, also will be able to determine the rear wheel cornering force F _r also the front wheel cornering force F _f.

[0099] In addition, the present embodiment aims at estimating the vehicle side slip angle β used in a rear wheel steering angle control device which is an example of a vehicle motion control device for controlling the motion state of the vehicle. Although it is a side slip angle estimating apparatus, another vehicle motion control apparatus, that is, for example, distributes the driving torque of the engine to the front wheels 12 and the rear wheels 22 so that the traveling direction and the direction of the vehicle body match each other as much as possible. The present invention can also be implemented as a vehicle body slip angle estimating apparatus for the purpose of estimating a vehicle body slip angle β used in a drive torque distribution control device or the like for controlling a ratio to be controlled.

While the preferred embodiment of the present invention has been described in detail with reference to the drawings, various modifications and improvements may be made based on the knowledge of those skilled in the art without departing from the scope of the claims. The present invention can be carried out in the mode in which it is performed.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a vehicle body slip angle estimation routine used by a vehicle body slip angle estimation apparatus according to an embodiment of the present invention.

FIG. 2 is a system diagram showing a rear wheel steering angle control device including the vehicle body slip angle estimation device.

FIG. 3 is a flowchart showing a rear wheel steering angle control routine used by a rear wheel steering angle control device.

FIG. 4 is a graph showing a relationship between a vehicle speed V and a steering angle gain K used in a rear wheel steering angle control routine of FIG.

FIG. 5 is a graph showing a relationship between a vehicle speed V and a first partial gain λ ₁ used in a rear wheel steering angle control routine of FIG. 3;

6 is a graph showing a relationship between an absolute value of a vehicle body side slip angle β and a second partial gain λ ₂ used in the rear wheel steering angle control routine of FIG. 3;

[Explanation of symbols]

 34 vehicle speed sensor 36 yaw rate sensor 40 lateral acceleration sensor 50 controller

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B62D 6/00 B62D 101: 00 B62D 111: 00 B62D 137: 00

Claims (1)

(57) [Claims] 1. A lateral acceleration sensor for detecting a lateral acceleration generated in a vehicle body, a vehicle speed sensor for detecting a vehicle speed which is a running speed of the vehicle body, a yaw rate sensor for detecting a yaw rate generated in the vehicle body, and connected thereto. A vehicle slip angle estimating means for sequentially estimating a vehicle slip angle β at a vehicle center of gravity, wherein YM is a variable obtained by dividing a yawing moment YM generated around the vehicle center of gravity by a yaw inertia moment I _Z of the vehicle.
/ I _Z is obtained, and the vehicle body slip angle β and the yaw rate γ, which are assumed for the plane motion of the vehicle including the vehicle slip motion and the yawing motion, are set as state variables, respectively, and the lateral acceleration at the center of gravity of the vehicle is obtained. the G _y and each input variable and a variable obtained by subtracting the previous estimated value of the G _y / V is a variable divided by the vehicle speed V the YM / I _Z vehicle body slip angle from the beta, observable to output variable yaw rate γ The linear acceleration coefficient system uses an observer to calculate the current values of the lateral acceleration G _y , the vehicle speed V and the yaw rate γ based on the output signals from the lateral acceleration sensor, the vehicle speed sensor and the yaw rate sensor, and the obtained YM
A vehicle slip angle estimating apparatus characterized by including a device that estimates a current value of the vehicle body slip angle β based on a current value of / I _Z and a previous estimated value of the vehicle body slip angle β.