JPH05208681A - Rear wheel steering angle control device - Google Patents

Abstract

PURPOSE:To properly control a rear wheel steering angle in a relation to not only the yaw rate but also the car body side slip angle by correcting a gain in accordance with the car body side slip angle, in a rear wheel steering angle control device for controlling the rear wheel steering angle in accordance with a product of the yaw rate and yaw rate feedback gain. CONSTITUTION:A front wheel steering angle sensor 30, rear wheel steering angle sensor 32, car speed sensor 34, yaw rate sensor 36 and cross acceleration sensors 40, 42 are connected to an input part, and a step motor 20 is connected to an output part, of a controller 50. Various programs including rear wheel steering angle control and car body side slip angle estimating routines and various maps or the like including a map for determining a target rear wheel steering angle are previously stored in a ROM of the controller 50. Thus based on not only an obtained yaw rate but also at least one of an obtained car body side slip angle and differentiation thereof, a rear wheel steering angle is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering angle control device for controlling a steering angle of rear wheels of a vehicle based on at least a yaw rate of a vehicle body.

[0002]

2. Description of the Related Art One type of rear wheel steering angle control device is a fluctuation of a vehicle that occurs when the vehicle receives a side wind, when the vehicle is braked, or when the vehicle is started or accelerated on a slippery road surface. There is a system in which (deflection) is detected as a yaw rate γ, and the steering angle of the rear wheels is controlled so as to cancel out such a vehicle fluctuation, that is, a rotation motion of the vehicle. This type of rear wheel steering angle control device is generally (a) a yaw rate acquisition unit that acquires the yaw rate generated in the vehicle body, and (b) at least a rear wheel steering angle control unit that controls the rear wheel steering angle based on the acquired yaw rate. And a wheel steering angle control means.

A conventional example of this rear wheel rudder angle control device is disclosed in Japanese Patent Laid-Open No. Hei 2
-220974 and Japanese Patent Laid-Open No. 3-112781.

In the above publication, δ _r = (K _V + K _Y γ) δ _f where δ _f : front wheel steering angle δ _r : rear wheel steering angle γ: yaw rate K _V : variable gain depending on vehicle speed V K _Y : A rear wheel steering angle control device (hereinafter referred to as the above-mentioned conventional device) that determines a target value of the rear wheel steering angle δ _r according to a formula of fixed gain multiplied by yaw rate γ is described.

On the other hand, in the later publication, δ _r = K _V δ _f + K _Y γV where δ _f : front wheel steering angle δ _r : rear wheel steering angle γ: yaw rate V: vehicle speed K _V : vehicle speed V Variable gain _KY : Fixed gain by which yaw rate γ is multiplied A rear wheel steering angle control device (hereinafter, referred to as a conventional device hereinafter) that determines a target value of a rear wheel steering angle δ _r is described.

[0006]

In the above conventional device, the larger the yaw rate γ, the larger the rear wheel steering angle δ _{r and} the running stability of the vehicle is improved. However, in the general running of the vehicle, However, based on the fact that the higher the vehicle speed V is, the stronger the improvement in running stability of the vehicle is strongly requested, in the later conventional device, not only when the yaw rate γ is large, but also when the vehicle speed V is large, δ _r is increased to improve running stability.

As described above, the latter conventional device is improved from the previous conventional device, and the rear wheel steering angle δ _r is controlled to be larger as the vehicle speed V is higher. However, there are times when running stability is strongly desired.

As a measure for realizing a sufficiently high running stability even when the vehicle speed V is low, for example, a measure for setting the value of the gain K _Y to a relatively large value in a later conventional device can be considered. However, when this measure is taken, for example, another problem as described below occurs. That is, when this measure is taken, the front wheel steering angle δ _f is input and the yaw rate γ
Both the frequency characteristics relating to the gain of the yaw rate response, which is the output, and the respective frequency characteristics relating to the gain and the phase angle of the vehicle body lateral velocity response, which are input the front wheel steering angle δ _f and output the vehicle lateral velocity v. This causes a problem that the tendency to deteriorate in the low frequency region and the steering response deteriorates becomes stronger.

In view of such circumstances, the present invention provides not only a yaw rate that is required for running stability but also a vehicle side slip angle at a vehicle center of gravity point and a vehicle side slip angle differential which is a time differential value thereof. By obtaining at least one of them, it is an object to satisfactorily suppress unplanned fluctuations of the vehicle without unduly reducing the steering response.

[0010]

In order to solve this problem, the gist of the present invention is (a) a yaw rate acquiring means for acquiring a yaw rate generated in a vehicle body, and (b) a vehicle based on at least the acquired yaw rate. In a rear wheel steering angle control device including a rear wheel steering angle control means for controlling the steering angle of the rear wheels,
(c) At least one of a vehicle side slip angle acquisition means for acquiring the vehicle side slip angle at the vehicle center of gravity point and a vehicle side slip angle differential acquisition means for acquiring a vehicle side slip angle differential which is the time derivative of the vehicle side slip angle is provided, and The rear wheel steering angle control means controls the rear wheel steering angle based not only on the acquired yaw rate but also on at least one of the acquired vehicle body side slip angle and vehicle body side slip angle differential.

The "vehicle body side slip angle acquisition means" here can adopt various modes. For example,
One mode thereof includes two Doppler velocity sensors that are respectively attached to the vehicle body in the front-rear direction and the lateral direction and that detect the ground velocity by utilizing the Doppler effect of waves, and the two Doppler velocity sensors detected by them. Is a Doppler effect utilization type that acquires the vehicle body side slip angle β based on the vehicle speed to ground, that is, the longitudinal speed u and the lateral speed v.

[0012] Another aspect is to use an observer to lay down the vehicle body.
It is an observer-based type that sequentially estimates the slip angle β and
The yawing moment YM generated around the center of gravity is
Vehicle yaw moment of inertia I _Z The variable YM divided by
/ I _Z The current value of
The planar motion of a vehicle consisting of motion and yawing motion
The assumed vehicle side slip angle β and yaw rate γ
The lateral acceleration G at the vehicle center of gravity is used as the state variable. _y To
Variable G divided by vehicle speed V _y / V and YM / I _Z From
The value obtained by subtracting the previous estimated value of the vehicle body slip angle β
Linear with each input variable and yaw rate γ as output variable
The constant coefficient system is installed in the corresponding observer.
Output from each of the lateral acceleration sensor and vehicle speed sensor
Lateral acceleration G based on signal _y And vehicle speed V and yaw rate
The current value of the yaw rate γ acquired by the acquisition means and
Acquired YM / I _Z Of the vehicle body side slip angle β
By using the previously estimated value and the vehicle side slip angle β
This time the value is estimated. In addition, in detail of this aspect
This will be described in Examples.

Further, the "vehicle body side slip angle differential acquisition means" of the present invention can also adopt various aspects. For example, one mode thereof is an equation of motion that holds for the lateral slip motion of the vehicle, that is, mV (β ′ + γ) = mG _y (1) where m: inertia mass of the vehicle V: vehicle speed β: vehicle center of gravity Vehicle side slip angle at point (left direction is positive,
Rightward is negative) β ': Vehicle side slip angle derivative G _y : Lateral acceleration at vehicle center of gravity (negative in left direction, positive in right direction) It is a type that uses the side-slip motion equation to be acquired. Specifically, this embodiment is a modification of the above formula (1), that is, β ′ = G _y / V−γ (2) Lateral acceleration G _y detected by the acceleration sensor, V detected by the vehicle speed sensor, and yaw rate γ acquired by the yaw rate acquisition means.
By substituting each of these, the vehicle body sideslip angle derivative β ′ is obtained.

The "rear wheel steering angle control means" in the present invention can also adopt various aspects. For example, in one mode thereof, the target value of the rear wheel steering angle δ _r is determined using an arithmetic expression including a product term of the yaw rate gain K _Y and the yaw rate γ, and the yaw rate gain K _{Y is set} to the vehicle body side slip angle β.
And at least one of the vehicle side slip angle differential β ′ (hereinafter,
It is simply changed depending on the vehicle side slip angle β, etc.).

In another embodiment, the yaw rate γ acquired by the yaw rate acquisition means is changed according to the vehicle body side slip angle β and the like, and the rear wheel steering angle δ _{r is} changed by using the changed yaw rate γ.
The target value of is determined.

Yet another embodiment is a gain (for example, a motion state variable) in a variable term in an arithmetic expression for determining the target value of the rear wheel steering angle δ _r and including a motion state variable other than the yaw rate γ. As a result, the gain in the term including the front wheel steering angle δ _f ) is changed according to the vehicle side slip angle β and the like.

In still another embodiment, the value of a constant term in an arithmetic expression for determining the target value of the rear wheel steering angle δ _r , which does not include a motion state variable such as yaw rate γ, is used as the vehicle body slip angle β etc. It changes according to.

[0018]

In the rear wheel steering angle control device according to the present invention, the yaw rate γ is acquired by the yaw rate acquisition means, and the vehicle body side slip angle β and the vehicle body side slip angle are acquired by at least one of the vehicle body side slip angle acquisition means and the vehicle body side slip angle differential acquisition means. At least one of the angle differential β ′ is acquired, and the rear wheel steering angle control means controls the rear wheel steering angle δ _r based on the yaw rate γ and at least one of the vehicle body side slip angle β and the vehicle body side slip angle differential β ′. To be done. The rear wheel steering angle control means controls the rear wheel steering angle δ _r as the absolute value of at least one of the vehicle body side slip angle β and the vehicle body side slip angle differential β'becomes larger, and controls it in the same phase as the front wheel steering angle. It is desirable that the vehicle sway is satisfactorily suppressed without unduly lowering the steering response.

[0019]

As described above, according to the present invention, the strength required for running stability is considered not only as the yaw rate γ but also as at least one of the vehicle body side slip angle β and the vehicle body side slip angle differential β ′. As a result, the rear wheel steering angle δ _r is controlled, so that the running stability can be improved without lowering the steering stability more than necessary.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A rear wheel steering angle control system according to some embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 2, the rear wheel steering angle control device according to the embodiment of the present invention is a front wheel steering mechanism for changing the steering angle δ _f of the left and right front wheels 12 according to the steering angle of the steering wheel 10. 16 and a step motor 20 as a drive source
Therefore, the vehicle is provided with a rear wheel steering mechanism 26 that changes the steering angle δ _r of the left and right rear wheels 22.

As shown in FIG. 1, this rear wheel steering angle control device includes a front wheel steering angle sensor 30 for detecting a front wheel steering angle δ _f , a rear wheel steering angle sensor 32 for detecting a rear wheel steering angle δ _r , and a vehicle speed. A vehicle speed sensor 34 for detecting V, a yaw rate sensor 36 for detecting yaw rate γ, and two lateral accelerations G _y1 , G described later.
Two lateral acceleration sensors 40, 42 for respectively detecting _y2
Is equipped with. Those sensors 30, 32, 34, 36,
40 and 42 are connected to the input part of the controller 50, and the step motor 20 is connected to the output part thereof.

The front wheel steering angle sensor 30 and the rear wheel steering angle sensor 32 detect the steering angles δ _f and δ _r , respectively, with the counterclockwise direction being positive and the clockwise direction being negative. The yaw rate sensor 36 detects the yaw rate γ with the counterclockwise direction being positive and the clockwise direction being negative. One lateral acceleration sensor 40
Is located at the center of gravity of the vehicle and detects the lateral acceleration G _y1 at the center of gravity of the vehicle with the left direction as negative and the right direction as positive. The other lateral acceleration sensor 42 is arranged at a position distant from the center of gravity of the vehicle straight ahead of the vehicle by a distance s, and the lateral acceleration G _y2 there is negative in the left direction,
The right direction is detected as positive.

The controller 50 includes a CPU (not shown),
The computer mainly includes a ROM, a RAM, and a bus. In the ROM, a rear wheel steering angle control routine represented by the flowchart of FIG. 1 and a vehicle body side slip angle estimation routine represented by the flowchart of FIG. 3 are started. And various maps including the maps for determining the target rear wheel steering angle represented by the graphs of FIGS. 4, 5 and 6 are stored in advance.

The vehicle body slip angle estimation routine of FIG.
From the lateral accelerations G _y1 , G _y2 and the distance s, the yaw moment YM generated around the center of gravity of the vehicle is divided by the yaw inertia moment I _Z of the vehicle, and the current value of YM / I _Z (that is, It is possible to obtain the current value of the yaw rate differential γ ′, which is the time differential value of the yaw rate γ. Specifically, the current value of YM / I _Z is set to ΔG _y / s
To get as. Here, ΔG _y is (G _y1
-Gy2 ).

Further, this vehicle body side slip angle estimating routine is also capable of successively estimating the vehicle body side slip angle β. Hereinafter, a method for estimating the vehicle body side slip angle β will be described in detail.

Except for transient vehicle movements that occur when the vehicle is suddenly accelerated or decelerated or the steering wheel 10 is quickly operated, changes in the vehicle speed V and rolling movements of the vehicle can be ignored. In this way, when it is possible to focus only on the motion of the vehicle traveling at a constant speed in the horizontal plane without rolling motion, that is, the planar motion of the vehicle,
It is only necessary to consider the two sideslip motions of the vehicle and the yawing motion. In this case, the following two motion equations generally hold. MV (β ′ + γ) = mG _y1 (3) for the lateral slip motion (3) and I _Z γ ′ = YM (4) for the yawing motion (4) are satisfied. is there. However, m: inertial mass of the vehicle V: vehicle speed β: vehicle side slip angle at the center of gravity of the vehicle (positive in the left direction,
Rightward is negative) β ′: Vehicle side slip angle derivative that is the time derivative of vehicle body slip angle β γ: Yaw rate (counterclockwise is positive, clockwise is negative) γ ′: Yaw rate derivative that is the time derivative of yaw rate γ G _y1 : lateral acceleration at the center of gravity of the vehicle (negative in the left direction, positive in the right direction) I _Z : yaw moment of inertia of the vehicle YM: yawing moment generated around the center of gravity of the vehicle

The above formula (3) can be transformed into a formula (5) such that β '= _Gy1 / V-γ (5). Further, as described above, since the current value of YM / I _Z is obtained as ΔG _y / s, the above formula (4) is expressed by the following formula (6): γ ′ = ΔG _y / s (6) It can be transformed into

Of the physical quantities in these equations (5) and (6), lateral acceleration G _y1 , vehicle speed V, yaw rate γ and ΔG
_{Since y} / s can be detected, in the present embodiment, the vehicle body side slip angle β is estimated from moment to moment based on these two equations and the detectable physical quantity. Regarding the plane motion of the vehicle described by these two equations, an observable linear constant coefficient system (also called a linear time-invariant system) that includes the undetectable vehicle body slip angle β as a state variable is assumed. Therefore, the vehicle body side slip angle β is estimated.

In order to assume a linear constant coefficient system that is observable with respect to the plane motion of the vehicle, it is possible to introduce the following input variables, output variables and state variables, for example. First input variable u ₁ (t): G _y1 / V Second input variable u ₂ (t): ΔG _y / s Output variable y (t): γ First state variable x ₁ (t): β Second state variable x ₂ (t): γ However, an observable linear constant coefficient system cannot be constructed with those input variables, output variables and state variables. The reason for this will be described below.

When such input variables, output variables and state variables are introduced, the state equation (7) expressed in the following matrix form is derived.

[0032]

[Equation 1]

Furthermore, the output equation (8) expressed in the following matrix form is also derived.

[0034]

[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 is the dimension n of the state variable.
It is necessary to match (2 this time). The observable matrix U ₀ is expressed using a system matrix A and an output matrix C described later, and when the value of the dimension n is 2,

[0036]

[Equation 3]

It is represented by

The above equation of state (7) and output equation
In (8),

[0039]

[Equation 4]

Since C = [0 1],

[0041]

[Equation 5]

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

Therefore, in the present embodiment, the vehicle body side slip angle β has a characteristic that it changes relatively slowly with the passage of time, and the present estimated value β _{(i) of the} vehicle body side slip angle β is obtained.
By utilizing the fact that the difference between the previous estimated value β _(i-1) can be regarded as almost 0, the following input variables, output variables and state variables are newly introduced. First input variable u ₁ (t): G _y1 / V Second input variable u ₂ (t): ΔG _y / s-β _(i-1) Output variable y (t): γ First state variable x ₁ (t): β _(i) Second state variable x ₂ (t): γ Therefore, the following state equation (9) is derived.

[0044]

[Equation 6]

Furthermore, the following output equation (10) is also derived.

[0046]

[Equation 7]

In equation (9), the system matrix A is

[0048]

[Equation 8]

Since the observable matrix U _{0 of} this time is represented by

[0050]

[Equation 9]

Will be represented by This observable matrix U
_Since the rank of ₀ is 2, which is equal to 2, which is the dimension n of the state variable, the linear constant coefficient system described by the equations (9) and (10) is observable.

The observable linear constant coefficient system obtained as described above has a two-dimensional state variable, but one of them, γ, can be detected and the other, β.
Only _(i) is undetectable. Therefore, this time, instead of estimating all two state variables, only the vehicle body side slip angle β is estimated, and the dimension of the observer is reduced to form the minimum dimension observer.

A 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). Where 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 formula: ω (t) '= A'ω (t) + KY (t) + B'U (t) X (t) = Dω (t) + HY (t) A minimum dimensional observer can be constructed. However, a time differential value A ′: (n−r) × (n of a variable ω (t) ′: ω (t) that is converted from ω (t): X (t) and has a lower dimension than X (t). −r) dimensional matrix K: (n−r) × r dimensional matrix B ′: (n−r) × m dimensional matrix D: n × (n−r) dimensional matrix H: n × r dimensional matrix Matrix The general method of constructing the minimum dimensional observer is explained below, but this is described in detail in the document "Introduction to System Control Theory (Jikkyo Shuppan Co., Ltd., issued January 20, 1991)". , Here is a brief description.

To determine each element in each matrix, first,
Determine an n × n dimensional matrix S. This matrix S is

[0056]

[Equation 10]

## EQU1 ## where C is the above-mentioned output matrix, but W is an appropriate (n-r) .times.n-dimensional matrix in which the value of the determinant of the matrix S is not zero. next,

[0058]

[Equation 11]

The matrices A ₁₁ , A ₁₂ , A ₂₁ and A _{22 in}
Each of the

[0060]

[Equation 12]

Determine each of the matrices B ₁ and B ₂ in. Subsequently, a matrix L of (n−r) × r dimensions is introduced as a design parameter, and the matrix A ′ is further defined by the formula A ′ = A ₂₂ −LA ₁₂ . Then, each element of the matrix L is determined so 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

[0062]

[Equation 13]

[0063]

[Equation 14]

It is determined so that the following equation holds.

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

[0066]

[Equation 15]

[0067]

[Equation 16]

C = [0 1]. At this time, if W = [1 0], the requirement that the value of the determinant of the matrix S is not 0 can be satisfied. Since the matrix L is a matrix consisting of one element this time, the eigenvalue of the matrix A ′ is represented by −L, and it is assumed that this corresponds to −p which is the pole of the minimum dimension observer this time. Then, L = p. Note that the matrix A'in order for the observer to be established.
Since it is also necessary to be a stable matrix, the value of −p, which is the pole of the observer, is made negative, and the value of p is made positive in the end. Therefore, the matrices A ', K, B', D and H are as follows this time. A ′ = − p K = −p ² −1 B ′ = [1 −p]

[0069]

[Equation 17]

[0070]

[Equation 18]

Since ω is one-dimensional this time and the vehicle body sideslip angle β which is the _first state variable x ₁ (t) is converted, the equation of the minimum dimensional observer at this time is

[0072]

[Formula 19]

Equation (11)

Β _(i) = ω + pγ (12), which is an equation (12).

Therefore, first, according to the above equation (11), p, γ, G _y1 / V, Δ which are known or detectable physical quantities.
Ω is estimated from G _y / s and β _(i-1) , and then β _(i) is estimated from the ω and known or detectable physical quantities p and γ according to the following equation (12). ..

However, since the equation (11) describes a continuous time system, the present value β _(i) of the vehicle body sideslip angle β is estimated by converting this into a discrete time.

By the way, as described above, the linear constant coefficient system is generally expressed by the state equation (13) of X (t) ′ = EX (t) + FU (t) (13) Is generally U
Supposing that the sampling period of (t) is represented by dt, X (t) _(i) = E'X (t) _(i-1) + F'U (t) _(i) ... (14) The rule that it is converted to (14) is already known. Since this rule is also described in the above-mentioned document "Introduction to System Control Theory", detailed description will be omitted. However, X (t): State vector X (t) ': Time derivative of state vector U (t): Input vector E: System matrix F: Input matrix X (t) _(i) : X (t) this time 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: identity matrix

The equation (11) is converted according to this rule. First, when the configuration of the equation (13) is aligned with the equation (11), X (t) '= EX (t) + F ₁ U ₁ (t ) + F ₂ U ₂ (t) + F ₃ U ₃ (t) ・ ・ ・ (15) becomes the expression (15), and as a result, the correspondence between each element in this expression (15) and each element in the expression (11) The relationship 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 _y1 / V U ₃ (t) = ΔG _y / s−β _(i-1) . Further, 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 Further, since E ⁻¹ = 1 / (− p), the formula (11) is as follows: ω _(i) = e ₁ ω _(i-1) + e ₂ γ _(i) + e ₃ G _{y1 (i) / V (i) + e 4} (ΔG y (i) / s + β (i-1)) is converted to (16) becomes equation (16).

However, ω _(i) : current estimated value of ω ω _(i-1) : previous estimated value of ω γ _(i) : current sampled value of yaw rate γ G _{y1 (i)} : current lateral acceleration G _y1 Sampling value ΔG _{y (i)} : G _{y1 (i)} −G _{y2 (i)} G _{y2 (i)} : Lateral acceleration G _y2 current sampling value V _(i) : Vehicle speed V current sampling value

In this equation, e ₁ , e ₂ , e ₃ and e ₄ are all constants. Specifically, e ₁ : e ^-pdt e ₂ : (e ^-pdt -1) (p _{^{2 +1) / p e 3 :-(}} e -pdt -1) / p e 4: the ^e-PDT -1.

Therefore, in equation (16), ω _(i-1) , γ _(i) ,
By substituting the values of G _{y1 (i)} , V _(i) , ΔG _{y (i)} and β _(i-1) , the value of ω _(i) can be obtained, and this value and the value of γ _(i) can be obtained. The value of β _(i) can be obtained by substituting it into the formula β _(i) = ω _(i) + pγ _(i) , which is a formula corresponding to the above formula (12). Note that the formula
In (16), when V _(i) = 0, ω _(i) cannot be calculated. Therefore, at this time, ω _{(i) is set} to 0 and β _(i)
Will also be 0.

Against the background of the details described above, the vehicle body slip angle estimation routine of FIG. 3 is executed every time the sampling cycle dt elapses. In each execution of this routine, first, in step S1 (hereinafter, simply referred to as S1; the same applies to other steps), the present execution of this routine is performed for the first time after the power of the controller 50 is turned on. It is determined whether or not there is. Since this is the case this time, the determination is YES, and the value of ω is 0 and the value of β is pγ in S2. p is a scheduled 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. If this is not the case this time, the determination is NO, and in S4, ω, γ, V are added to the equation (equation shown in FIG. 3 and hereinafter referred to as an arithmetic expression) corresponding to the equation (16). , G _y1 , G _y2, and β are respectively substituted (however, this time, ω and β are equal to the above-described initial values), so that the current value of ω is updated. Note that in this equation, e ₁ , e ₂ ,
e ₃ , e ₄ and s are constants. Then, 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 the current β value is updated in S6.
RA is the current estimated value of the vehicle body slip angle β.
Stored in M. Thus, one execution of this routine is completed.

On the other hand, when the vehicle speed V is 0, the determination in S3 is YES, the current value of ω and the current value of β are both 0 in S7, and then in S6,
The current value of β, that is, 0 is stored in the RAM as the current estimated value of the vehicle body side slip angle β.

When each of the second and subsequent executions of this routine is executed, the determination of S1 is NO and the execution of S2 is skipped, but the vehicle speed V is not 0 and the determination of S3 is NO, and S4 is executed. When executed, in S4, the respective values of ω and β acquired in the previous execution of this routine, that is, the respective current values of ω and β, and γ, V, G _y1 and G _y2. The current value of ω is updated by substituting the current value of ω and the current value of ω into the arithmetic expression, and the current value of ω and p and γ are updated in S5.
The current value of β is updated by calculating the sum of the product of and.

The vehicle body sideslip angle estimating routine of FIG. 3 has been described in detail above. Next, the rear wheel steering angle control routine of FIG. 1 will be described in detail.

The rear wheel steering angle control routine in FIG. 1 is a program for determining the target value of the rear wheel steering angle δ _r according to the equation δ _r = Kδ _f + λγ, and controlling the step motor 20 so that the target value is realized. Is. In this equation, K is the steering angle gain,
It is determined according to the vehicle speed V according to the map of FIG. Further, λ is a yaw rate feedback gain, and the first partial gain λ ₁ determined according to the vehicle speed V according to the graph of FIG. 5 and the vehicle body side slip angle β according to the graph of FIG.
It is determined as the sum with the second partial gain λ ₂ determined according to the absolute value of. The graphs of FIGS. 4 to 6 have characteristics for making the actual value of the vehicle body side slip angle β as close to 0 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. 1 is also repeatedly executed. It should be noted that the vehicle body slip angle estimation routine of FIG. 3 is designed to be executed only once in the rear wheel steering angle control routine of FIG. 1, and in the end, these routines are executed in synchronization with each other. It is like this.

In each execution of the rear wheel steering angle control routine of FIG. 1, first, in S101, the front wheel steering angle δ _f , the yaw rate γ, the lateral accelerations G _y1 , G _y2 and the vehicle speed V are _fetched from various sensors, Then, in S102, the vehicle speed V
The value of the steering angle gain K corresponding to is using the map of FIG.
The value of the first partial gain λ ₁ corresponding to the vehicle speed V is determined using the map in FIG. 5, and in S103, the value in FIG.
The vehicle body slip angle estimation routine is executed to estimate the current value of the vehicle body slip angle β. Then, in S104, the value of the second partial gain λ ₂ corresponding to the absolute value of the current value of the vehicle body side slip angle β is determined using the map of FIG. 6, and further, the first partial gain λ ₁ and its second value. The sum of the partial gain λ ₂ and the yaw rate feedback gain λ is determined as the current value. Subsequently, in S105, the sum of the product of the steering angle gain K and the front wheel steering angle δ _f and the product of the yaw rate feedback gain λ and the yaw rate γ is determined as the current target value of the rear wheel steering angle δ _r , and S106. At, the drive signal is output to the step motor 20 so that the current target value is realized. Thus, one execution of this routine is completed.

As is clear from the above description, in this embodiment, the yaw rate sensor 36 constitutes one aspect of the "yaw rate acquisition means" of the present invention, and the vehicle body sideslip angle estimating routine of the controller 50 shown in FIG. The part to be executed constitutes an observer utilization type which is one mode of the "vehicle body side slip angle acquisition means" of the present invention in cooperation with the vehicle speed sensor 34 and the lateral acceleration sensors 40 and 42. The part that executes the wheel steering angle control routine is the front wheel steering angle sensor 30 and the vehicle speed sensor 3.
4 forms one aspect of the "rear wheel steering angle control means" in the present invention.

A rear wheel steering angle control device according to another embodiment will be described. As shown in FIG. 7, this rear wheel steering angle control device has substantially the same configuration as the rear wheel steering angle control device of FIG. 2, and the front wheel steering mechanism 16, the rear wheel steering mechanism 26, and the front wheel steering angle are described above. It is configured to include a sensor 30, a rear wheel steering angle sensor 32, a vehicle speed sensor 34, and a yaw rate sensor 36. The rear wheel steering angle control device further includes a lateral acceleration sensor 70 for detecting a lateral acceleration G _y at the center of gravity of the vehicle and a controller 8.
It is also configured to include 0 and.

The controller 80 is the controller 5
Like 0, it is mainly composed of computers,
The rear wheel steering angle δ _r is controlled by controlling the step motor 20 based on output signals from various sensors. Therefore, in the ROM thereof, various programs including the rear wheel steering angle control routine represented by the flowchart of FIG. 8 and the vehicle body side slip angle differential estimation routine represented by the flowchart of FIG. 9, FIG. Various maps including the map for determining the target rear wheel steering angle represented by the graph of FIG. 10 are stored in advance.

The vehicle side slip angle differential estimation routine of FIG. 9 is an equation corresponding to the above equation (5), using equation (17) of β ′ = G _y / V−γ (17) It is a program for estimating the vehicle body side slip angle differential β ', and is executed every time a certain minute time elapses.

At each execution of this routine, first, S
In 201, it is determined whether the vehicle speed V is 0,
If so, in S202, the vehicle body side slip angle differential β '
The current value of 0 is set to 0, but otherwise, in S203, the vehicle speed V detected by the vehicle speed sensor 34 and the yaw rate γ detected by the yaw rate sensor 36 are added to the respective terms on the right side of the equation (17). The vehicle body lateral slip angle differential β ′ is calculated by substituting the lateral acceleration G _y detected by the lateral acceleration sensor 70. In either case, thereafter, in S204, the vehicle body sideslip angle derivative β ′ acquired in S202 or S203 is stored in the RAM as its current estimated value. Thus, one execution of this routine is completed.

On the other hand, the rear wheel steering angle control routine of FIG. 8 is similar to the rear wheel steering angle control routine of FIG. 1, δ _r = Kδ _f + λ
It is a program that determines the target value of the rear wheel steering angle δ _r according to the expression γ and controls the step motor 20 so that the target value is realized. However, the yaw rate feedback gain lambda, the first and partial gain lambda ₁ that is determined according to the vehicle speed V according to the graph of FIG. 5, is determined in accordance with the absolute value of the vehicle slip angle differential beta 'according to the graph of FIG. 10 It is determined as the sum of the two partial gains λ ₂ .

The routine of FIG. 8 is different from the routine of FIG. 1 only in the method of determining the yaw rate feedback gain λ, and is otherwise the same, and therefore will be briefly described.

In each execution of the rear wheel steering angle control routine of FIG. 8, first, in S301, the front wheel steering angle δ _f , yaw rate γ, lateral acceleration G _y and vehicle speed V are fetched from various sensors, and then S302 The value of the steering angle gain K corresponding to the vehicle speed V is calculated by using the map of FIG.
The value of the first partial gain λ ₁ corresponding to is determined using the map of FIG. 5, and in S303, the vehicle side slip angle differential estimation routine of FIG. 9 is executed to estimate the current value of the vehicle side slip angle differential β ′. To be done. Then, in S304, the value of the second partial gain λ ₂ corresponding to the absolute value of the current value of the vehicle body side slip angle differential β ′ is determined using the map of FIG. 10, and the first partial gain λ ₁ and The sum of the second partial gain λ ₂ is determined as the current value of the yaw rate feedback gain λ. Subsequently, in S305, the sum of the product of the steering angle gain K and the front wheel steering angle δ _f and the product of the yaw rate feedback gain λ and the yaw rate γ is determined as the current target value of the rear wheel steering angle δ _r , and S306 At, the drive signal is output to the step motor 20 so that the current target value is realized. Thus, one execution of this routine is completed.

As is clear from the above description, in the present embodiment, the yaw rate sensor 36 constitutes one aspect of the "yaw rate acquisition means" of the present invention, and the vehicle body side slip angle differential estimation routine of FIG. Is a vehicle speed sensor 34, a yaw rate sensor 3
6 and the lateral acceleration sensor 70, a lateral slip motion equation utilization type which is one mode of the "vehicle side slip angle differential estimation means" of the present invention is configured, and the rear wheel steering angle control routine of FIG. The portion to be executed cooperates with the front wheel steering angle sensor 30 and the vehicle speed sensor 34 and constitutes one mode of the "rear wheel steering angle control means" in the present invention.

In each of the above-described two embodiments, the yaw rate γ is obtained by the yaw rate sensor 36. For example, the wheel speeds of the left and right front wheels 12 which are idle wheels are detected. It is also possible to use two wheel speed sensors and obtain the yaw rate γ by using the difference between the two wheel speeds.

In each of the two embodiments, the rear wheel steering angle δ _r is controlled by using only one of the vehicle body side slip angle β and the vehicle body side slip angle differential β ′, not both of them. However, it is also possible to control the rear wheel steering angle δ _r using both the vehicle body side slip angle β and the vehicle body side slip angle differential β ′. For example, in the above-mentioned embodiment, the yaw rate feedback gain λ is variable λ ₁ according to the vehicle speed V, λ ₂ is variable according to the vehicle body side slip angle β, and λ ₃ is variable according to the vehicle body side slip angle differential β ′. It is also possible to control the rear wheel steering angle δ _r by calculating the sum of and.

Although some embodiments of the present invention have been described above in detail with reference to the drawings, various modifications other than these will 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 implemented in an improved mode.

[Brief description of drawings]

FIG. 1 is a flowchart showing a rear wheel steering angle control routine used by a rear wheel steering angle control device according to an embodiment of the present invention.

FIG. 2 is a system diagram showing a rear wheel steering angle control device.

FIG. 3 is a flowchart showing a vehicle body sideslip angle estimation 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.

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

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

FIG. 7 is a system diagram showing a rear wheel steering angle control device according to another embodiment of the present invention.

FIG. 8 is a flowchart showing a rear wheel steering angle control routine used by a rear wheel steering angle control device.

FIG. 9 is a flowchart showing a vehicle body sideslip angle differential estimation routine used by a rear wheel steering angle control device.

10 is a graph showing a relationship between an absolute value of a vehicle body sideslip angle derivative β ′ used in a rear wheel steering angle control routine of FIG. 8 and a second partial gain λ ₂ .

[Explanation of symbols]

 34 vehicle speed sensor 36 yaw rate sensor 40, 42, 70 lateral acceleration sensor 50, 80 controller

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Claims (1)

[Claims] 1. A rear wheel steering angle control including yaw rate acquisition means for acquiring a yaw rate generated in a vehicle body, and at least rear wheel steering angle control means for controlling a steering angle of a rear wheel of the vehicle based on the acquired yaw rate. The apparatus is provided with at least one of a vehicle body slip angle acquiring means for acquiring a vehicle body slip angle at a vehicle center of gravity point and a vehicle body slip angle differential acquiring means for acquiring a vehicle body slip angle differential which is a time derivative value of the vehicle body slip angle, and The rear wheel steering angle control means controls the rear wheel steering angle based not only on the acquired yaw rate but also on at least one of the acquired vehicle body side slip angle and vehicle body side slip angle differential. Rear wheel steering angle control device characterized by.