JP2009173112A - Vehicle status quantity estimating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate a transverse skid angle of a vehicle body and a wheel of an automobile with high precision regardless of a road surface state. <P>SOLUTION: A vehicle status quantity estimating apparatus is constituted of a vehicle movement detection means; a rear wheel lateral force arithmetic means, which calculates a rear wheel lateral force acting on a rear wheel from a yaw rate detected by a yaw rate detection means and lateral acceleration detected by a lateral acceleration detection means; a rear wheel lateral skid angle arithmetic means, which calculates a rear wheel lateral skid angle from the rear wheel lateral force and predetermined rear wheel tire characteristics; and a front wheel lateral skid angle conversion means, which converts the rear wheel lateral skid angle to a first front wheel lateral skid angle based on a two-wheel model of a vehicle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for estimating a side slip angle of a vehicle body and wheels of an automobile.

  In a conventional side slip angle estimation device, estimation is performed by calculation based on the lateral acceleration of the entire vehicle body. In this method, the accuracy decreases when the lateral force is saturated on either the front wheel or the rear wheel of the tire. Therefore, it is necessary to perform a limit running determination process or a correction process using a side slip angular velocity feedback. (See Patent Document 1)

JP-A-9-311042 (page 6)

  The reason why various correction processes are required in such a side slip angle estimation device is that the estimation accuracy of the side slip angle obtained from the calculation of the vehicle tire model is lowered in a situation called limit driving in the publication. is there. Therefore, a complicated correction process is required, and the amount of calculation becomes enormous. For this reason, there has been a problem that an expensive microcomputer is required.

The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a highly accurate estimate of the side slip angle of a front wheel or a vehicle body with an inexpensive microcomputer or similar product.

In order to achieve the above object, a vehicle state quantity estimating device of the present invention includes a steering angle detecting means for detecting a steering angle, a vehicle speed detecting means for detecting a vehicle speed, a yaw rate detecting means for detecting the yaw rate of the vehicle body, Vehicle acceleration detecting means including lateral acceleration detecting means for detecting lateral acceleration;
Rear wheel lateral force calculating means for calculating a rear wheel lateral force acting on a rear wheel from the yaw rate detected by the yaw rate detecting means and the lateral acceleration detected by the lateral acceleration detecting means;
A rear wheel side slip angle calculating means for calculating a rear wheel side slip angle based on the rear wheel lateral force and a predetermined rear wheel tire characteristic;
Front wheel side slip angle conversion means for converting the rear wheel side slip angle into a first front wheel side slip angle based on a two-wheel vehicle model;
It is what has.

Moreover, the vehicle state quantity estimating device of the present invention is
Vehicle motion detection means including steering angle detection means for detecting the steering angle, vehicle speed detection means for detecting the vehicle speed, yaw rate detection means for detecting the yaw rate of the vehicle body, and lateral acceleration detection means for detecting the lateral acceleration of the vehicle body When,
Front wheel lateral force calculating means for calculating a front wheel lateral force acting on a front wheel from the yaw rate detected by the yaw rate detecting means and the lateral acceleration detected by the lateral acceleration detecting means;
Front wheel side slip angle calculating means for calculating a second front wheel side slip angle based on the front wheel side force and predetermined front wheel tire characteristics;
The rear wheel lateral force calculating means and the rear wheel side slip angle calculating means;
The front wheel side slip angle conversion means;
Front wheel side slip angle collation for obtaining a front wheel side slip angle by comparing and collating the first front wheel side slip angle obtained by the front wheel side slip angle conversion means and the second front wheel side slip angle obtained by the front wheel side slip angle calculating means. Means,
It is what has.

  The vehicle state quantity estimation device of the present invention can determine the vehicle body and wheel side slip angles by selectively using only one of the front wheel tire characteristics and the rear wheel tire characteristics. For this reason, since it is not always necessary to use the characteristics of both the front and rear wheels of the tire, the conventional example (for example, Japanese Patent Application Laid-Open No. Hei 9) is used even in the situation where the estimation accuracy is lowered when the tire characteristics of either the front wheels or the rear wheels are used. No.-311042), the vehicle state quantity estimation accuracy is improved.

Prior to describing the embodiment, tire characteristics and tire saturation will be described below. In the following, the side slip angle is distinguished by referring to the side slip angle at the center of gravity of the vehicle as the vehicle body side slip angle and the side slip angle of the tire as the tire side slip angle. Further, among the tire side slip angles, the front wheel side slip angle is particularly called a front wheel side slip angle, and the rear wheel side slip angle is called a rear wheel side slip angle.
As shown in FIG. 1, there is usually a relationship in which the lateral force increases as the tire side slip angle increases. By using the correspondence relationship (tire characteristics) between the tire side slip angle and the side force, the tire side slip angle can be obtained from the side force. The gradient at the origin of the tire characteristics is called cornering power.
In this tire characteristic, as the tire side slip angle increases, the increase in the lateral force decreases, and the increase stops or decreases (saturation of the tire). This degree is hereinafter referred to as the saturation degree. At this time, the characteristic approximated by the cornering power decreases the accuracy of obtaining the tire side slip angle from the lateral force due to the actual tire characteristic and the above approximate characteristic.
In addition, it goes without saying that the accuracy for obtaining the tire slip angle decreases with the approximate characteristics, but even if the correct tire characteristics are used, the accuracy with which the tire slip angle is obtained decreases when the degree of saturation is large. This will be described next with reference to FIG.

In FIG. 2, it is considered that the tire side slip angle is obtained in a situation where a certain error is included in the lateral force. First, when the degree of saturation is small, the error remains relatively small even if the tire side slip angle is obtained from the lateral force using the tire characteristics as shown in the figure. On the other hand, in a situation in which the degree of saturation is large, if the same amount of error is present in the lateral force as in the previous case, the tire side slip angle is a large error.
Therefore, if there is a slight error in the lateral force, when the degree of saturation is large compared to the case where the degree of saturation is small, the error becomes large when calculating the tire side slip angle.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1
FIG. 3 is a configuration diagram illustrating the vehicle state quantity estimating device according to the first embodiment of the present invention. In FIG. 3, the vehicle motion detection means 1 detects the lateral acceleration, yaw rate, vehicle speed, and steering angle of the vehicle (generally, particularly the steering angle of the front wheels; the same applies hereinafter). Of these, the rear wheel lateral force calculating means 2 calculates the rear wheel lateral force based on the lateral acceleration and the yaw rate. Based on the calculated rear wheel lateral force, the rear wheel side slip angle calculating means 3 having a predetermined tire model calculates the rear wheel side slip angle. Based on the rear wheel side slip angle, the yaw rate, the vehicle speed, and the rudder angle, the front wheel side slip angle conversion means 4 obtains a first front wheel side slip angle.

Further, as shown in FIG. 4, the vehicle motion detection means 1 in FIG. 3 includes a lateral acceleration detection means 101 that detects the lateral acceleration of the vehicle, a yaw rate detection means 102 that detects the yaw rate of the vehicle, and a vehicle speed detection that detects the vehicle speed. It comprises means 103 and rudder angle detection means 104 for detecting the rudder angle.

Next, the operation of this apparatus will be described with reference to FIG. First, the lateral force acting on the rear wheel is calculated by the rear wheel lateral force calculating means based on the vehicle momentum detected by the vehicle motion detecting means 1 (S101). Next, a rear wheel side slip angle is calculated from the rear wheel side force using a rear wheel tire characteristic (S102), and the rear wheel side slip angle is converted into a first front wheel side slip angle by a front wheel side slip angle conversion means ( S103).

The details will be described below.
First, the operation of the rear wheel lateral force calculating means 2 in FIG. 3 will be described.
Since the following formula (2-1) is known as a vehicle two-wheel model when handling the motion of the vehicle, this formula is used here.

ただし、ａ_ｙ:横加速度、γ：ヨーレイト（ｄ／ｄｔは時間微分を示し、ｄ／ｄｔ・γはヨー角加速度）、ｍ：車両質量、Ｆ_ｆ：前輪横力（左右輪の和）、Ｆ_ｒ：後輪横力（左右輪の和）、Ｉ：車両ヨー慣性モーメント、Ｌ_ｍ：車両重心位置から前輪車軸までの距離、Ｌ_ｒ：車両重心位置から後輪車軸までの距離である。

However, _ay : Lateral acceleration, γ: Yaw rate (d / dt indicates time differentiation, d / dt · γ is yaw angular acceleration), m: Vehicle mass, _Ff : Front wheel lateral force (sum of left and right wheels), F _r : rear wheel lateral force (sum of left and right wheels), I: vehicle yaw moment of inertia, L _m : distance from vehicle center of gravity position to front wheel axle, L _r : distance from vehicle center of gravity position to rear wheel axle.

Here, the vehicle mass m and the vehicle yaw inertia moment I are preset known values, and the lateral acceleration _ay and the yaw angular acceleration d / dt · γ are obtained by the values of the detection means or their derivatives, respectively. with things, by the equation (2-1) from the following equation (2-2), the front wheel lateral force _{F f} and Kowayokoryoku _{F r} is obtained.

このような関係を利用して、後輪横力演算手段２は後輪横力を演算する。なお、ここで横加速度については、センサオフセット補正などを目的としてハイパスフィルタに通してもよく、また、車両ヨー角加速度を得るに際して、ノイズ低減等を目的として微分演算をハイパスフィルタによって代用してもよい。

Using such a relationship, the rear wheel lateral force calculating means 2 calculates the rear wheel lateral force. Here, the lateral acceleration may be passed through a high-pass filter for the purpose of sensor offset correction or the like, and when obtaining vehicle yaw angular acceleration, a differential operation may be substituted by a high-pass filter for the purpose of noise reduction or the like. Good.

Next, the rear wheel side slip angle calculating means 3 will be described. The rear wheel side slip angle calculating means 3 uses the relationship between the tire side slip angle and the side force shown in FIG. 1 to obtain the corresponding rear wheel side slip angle from the value of the rear wheel side force as indicated by an arrow in the figure.
In particular, in the first embodiment, the tire characteristics indicated by the curve in FIG. 1 are approximated by the inclination (cornering power) at the origin indicated by the broken line. By approximating in this way and dividing the rear wheel lateral force by the cornering power, the rear wheel side slip angle is obtained.

ここで、α_ｆは前輪横すべり角、Ｃ_ｆは前輪コーナリングパワー、α_ｒは後輪横すべり角、Ｃ_ｒは後輪コーナリングパワーである。なお付記すれば、必ずしもコーナリングパワーで近似する必要はなく、精度向上のため、より詳細なタイヤモデル（図１の曲線）によって後輪横すべり角を求めてもよい。

Here, α _f is a front wheel side slip angle, C _f is a front wheel cornering power, α _r is a rear wheel side slip angle, and C _r is a rear wheel cornering power. Note that it is not always necessary to approximate with the cornering power, and the rear wheel side slip angle may be obtained by a more detailed tire model (curve in FIG. 1) in order to improve accuracy.

  Next, the front wheel side slip angle conversion means 4 will be described. The front wheel side slip angle conversion means 4 converts the rear wheel side slip angle into a front wheel side slip angle using the following known relationship.

ここで、α_ｆは前輪横すべり角、Ｖは車速、δは舵角、Ｌはホイールベース（前輪車軸から後輪車軸までの距離であり、Ｌ＝Ｌ_ｆ＋Ｌ_ｒである）を示す。

Here, α _f is the front wheel side slip angle, V is the vehicle speed, δ is the rudder angle, and L is the wheel base (the distance from the front wheel axle to the rear wheel axle, L = L _f + L _r ).

In the first embodiment, as described above, the rear wheel side slip angle is obtained from the rear wheel side force and is converted into the front wheel side slip angle. As a result, when the degree of saturation of the front wheels is higher than the degree of saturation of the rear wheels, the estimation accuracy is improved as compared to obtaining the front wheel side slip angle directly from the front wheel lateral force.
That is, as described in the description of FIGS. 1 and 2 (see paragraphs 0009 and 0010), when the tire slip angle is determined from the lateral force, the accuracy decreases as the degree of saturation increases. Rather than directly obtaining the front wheel side slip angle, the accuracy of estimating the front wheel side slip angle is improved by obtaining the rear wheel side slip angle from the rear wheel having a low degree of saturation and converting it to the front wheel side slip angle.
For example, as a typical example when the degree of saturation of the front wheels is higher than the degree of saturation of the rear wheels, there is a situation called an understeer state, and according to this embodiment, the front wheel side slip angle can be estimated well even in such a situation. It becomes possible.

When a vehicle side slip angle is required (for example, when the present invention is applied to a vehicle side slip prevention device), vehicle side slip angle conversion means (not shown) is provided instead of the front wheel side slip angle conversion means. The rear wheel side slip angle may be converted into the vehicle body side slip angle by the following equation (2-5).

ここで、βは車体横すべり角である。
なお補記すれば、上記のように、式（２−５）で実施する場合においては、舵角は用いる必要がないゆえに、車両運動量検出手段１において舵角検出手段１０４は必須の構成要件ではない。このような場合においては、後輪の飽和度合いに比して前輪の飽和度合いが高い場合でも車体横すべり角を良好に推定することが可能となる。
以上、本実施の形態１に拠れば、アンダーステア状況でも前輪横すべり角および車体横すべり角、又は、前輪横すべり角あるいは車体横すべり角を良好に推定することができる。

Here, β is a vehicle body side slip angle.
In addition, since it is not necessary to use the steering angle in the case of carrying out with the formula (2-5) as described above, the steering angle detection unit 104 is not an essential component in the vehicle momentum detection unit 1 as described above. . In such a case, the vehicle body side slip angle can be estimated well even when the degree of saturation of the front wheels is higher than the degree of saturation of the rear wheels.
As described above, according to the first embodiment, the front wheel side slip angle and the vehicle body side slip angle, or the front wheel side slip angle or the vehicle body side slip angle can be well estimated even in an understeer situation.

Embodiment 2. FIG.
FIG. 5 is a configuration diagram illustrating a vehicle state quantity estimation device according to Embodiment 2 of the present invention.
In FIG. 5, the vehicle motion detection means 1, the rear wheel lateral force calculation means 2, the rear wheel side slip angle calculation means 3, and the front wheel side slip angle conversion means 4 are the same as those in the first embodiment. However, in the present embodiment, the front wheel side slip angle obtained by the front wheel side slip angle conversion means 4 is referred to as a first front wheel side slip angle. This is for distinguishing from a second front wheel side slip angle which will be described later.
Further, the front wheel lateral force calculation means 5 calculates the front wheel lateral force based on the lateral acceleration and yaw rate obtained by the vehicle motion detection means 1. A second front wheel side slip angle is obtained by the front wheel side force, the tire model, and the front wheel side slip angle calculating means 6. The front wheel side slip angle collating means 7 collates the first front wheel side slip angle obtained by the front wheel side slip angle converting means and the front wheel side slip angle obtained by the front wheel side slip angle calculating means, and compares the first front wheel side slip angle and the Select and output an appropriate front wheel side slip angle from the two front wheel side slip angles.

Next, the operation of this apparatus will be described with reference to FIG. First, based on the amount of vehicle motion such as lateral acceleration detected by the vehicle motion detection means 1, the lateral force acting on the front wheels and the lateral force acting on the rear wheels are respectively calculated by the front wheel lateral force calculation means 5 and the rear wheel lateral force calculation means 2. Calculate (step S201). Next, the front wheel side slip angle calculating means 6 calculates the second front wheel side slip angle from the front wheel side force using the front wheel tire characteristics, and the rear wheel side slip angle calculating means 3 calculates the rear wheel from the rear wheel side force. A rear wheel side slip angle is calculated using the tire characteristics (step S202). Further, a first front wheel side slip angle is calculated from the rear wheel side slip angle by the front wheel side slip angle conversion means (step S203). Next, the first front wheel side slip angle and the second front wheel side slip angle are compared and collated (step S204), and the first front wheel side slip angle and the second front wheel side slip angle are closer to the actual front wheel side slip angle. A front wheel side slip angle is selected (step S205 or step S206).

In the following, further explanation will be given with respect to FIG.
The vehicle motion detection means 1, the rear wheel lateral force calculation means 2, the rear wheel side slip angle calculation means 3, and the front wheel side slip angle conversion means 4 in FIG. 5 are the same as those in the first embodiment and will not be described. . With respect to the front wheel lateral force calculating means 5 in FIG. 5, the front wheel lateral force is obtained by the equation (2-2). For the front wheel side slip angle calculating means 6, the front wheel side slip angle is obtained by the equation (2-3).

Next, the front wheel side slip angle matching means 7 in FIG. 5 will be described.
The front wheel side slip angle matching means 7 determines which of the front wheel saturation degree and the rear wheel saturation degree is higher, and if the front wheel saturation degree is higher, selects the first front wheel side slip angle. If not, the second front wheel side slip angle is selected. As this saturation degree determination method, for example, a method of comparing the magnitudes of the first front wheel side slip angle and the second front wheel side slip angle is used. The principle is described below.
8, 9 and 10 show the relationship between the lateral force and the tire slip angle when the degree of saturation is small, medium and large, respectively. In these figures, the true value of the tire side slip angle is represented by a, the lateral force generated at that time is represented by F, and the tire side slip angle obtained from this lateral force by the equation (2-3) is represented by b. When the degree of saturation is small (Fig. 8), a and b almost coincide with each other, but as the degree of saturation increases (Fig. 9 and Fig. 10), the difference between these a and b increases and Is smaller.
Therefore, if the degree of saturation of the rear wheel is large, the rear wheel side slip angle calculating unit 3 calculates the rear wheel side slip angle calculated by the equation (2-3) to be smaller than the true rear wheel side slip angle. . Therefore, the first rear wheel side slip angle converted by the front wheel side slip angle converting means 4 according to the equation (2-4) is also smaller than the true value.
Similarly, the second front wheel side slip angle calculated by the formula (2-4) in the front wheel side slip angle calculating means 6 is a value smaller than the true value as much as the degree of front wheel saturation is large.
Therefore, the magnitudes of the first front wheel side slip angle and the second front wheel side slip angle are compared, and if the first front wheel side slip angle is smaller, it is determined that the degree of saturation of the rear wheel is larger than the degree of saturation of the front wheel. it can.
For example, it is assumed that the situation of the front wheels is as shown in FIG. At this time, the true value of the front wheel side slip angle is a, and the second front wheel side slip angle is b. If the rear wheel saturation degree is higher than the front wheel saturation degree, the first front wheel side slip angle is located at d (smaller than b), and conversely if the rear wheel saturation degree is low, at c. (Larger than b).
According to this embodiment, in addition to being able to satisfactorily estimate the front-slip side slip angle even when the degree of saturation of the front wheels is high compared to the degree of saturation of the rear wheels, conversely, compared to the degree of saturation of the front wheels, Even when the degree of wheel saturation is high, the front wheel side slip angle can be estimated well.

As described in the first embodiment, when a vehicle side slip angle is required (for example, when the present invention is applied to a vehicle side slip prevention device), vehicle side slip angle conversion means (not shown) is provided. May be implemented.
At this time, the front wheel side slip angle output by the front wheel side slip angle collating means may be converted into a vehicle body side slip angle by the equation (2-5), or the front side or the rear wheel of the tire side with a low degree of saturation may be used. You may implement as converting into a vehicle body side slip angle conversion from a tire side slip angle.
In such a case, the front side slip angle can be estimated well even when the saturation degree of the front wheels is higher than the saturation degree of the rear wheels. Even when the degree of wheel saturation is high, the vehicle body slip angle can be estimated well.

  In the second embodiment, since it is not always necessary to use the characteristics of both the front and rear wheels of the tire at the same time as described above, a case where only one side of the front and rear wheels is saturated is a conventional example. The estimation accuracy is improved as compared with (for example, JP-A-9-311042). Therefore, for example, when the driver turns the steering angle more than necessary on a road surface with a low μ (friction coefficient) such as an ice board road, the front wheels are saturated and become understeered. Since the front-wheel side slip angle or the vehicle body side-slip angle is obtained from the tire characteristics of the rear wheels that are not, it is possible to easily obtain good estimation accuracy.

As described above, the vehicle state quantity estimating device according to the present invention has an effect that the front wheel side slip angle or the vehicle body side slip angle can be obtained with high accuracy by using the tire characteristics of the rear wheel which is not saturated in, for example, an understeer state. There is.

It is a figure which shows a general tire characteristic. It is a figure explaining that the precision which calculates | requires a tire side slip angle from side force will fall when side force is near saturation based on a general tire characteristic. It is a block diagram of the vehicle state quantity estimation apparatus by Embodiment 1 of this invention. It is a block diagram which shows an example of the vehicle motion detection means by Embodiment 1 of this invention. It is a block diagram of the vehicle state quantity estimation apparatus by Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the vehicle state quantity estimation apparatus by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the vehicle state quantity estimation apparatus by Embodiment 2 of this invention. It is a figure which shows an example of the tire characteristic in case a saturation degree is small. It is a figure which shows an example of the tire characteristic in case a saturation degree is medium. It is a figure which shows an example of the tire characteristic in case a saturation degree is large.

Explanation of symbols

1 vehicle motion detecting means, 2 rear wheel lateral force calculating means, 3 rear wheel side slip angle calculating means, 4 front wheel side slip angle converting means, 5 front wheel lateral force calculating means, 6 front wheel side slip angle calculating means, 7 front wheel side slip angle checking means, 101 lateral acceleration detection means, 102 yaw rate detection means, 103 vehicle speed detection means, 104 steering angle detection means.

Claims (3)

Vehicle motion detection means including steering angle detection means for detecting the steering angle, vehicle speed detection means for detecting the vehicle speed, yaw rate detection means for detecting the yaw rate of the vehicle body, and lateral acceleration detection means for detecting the lateral acceleration of the vehicle body When,
Rear wheel lateral force calculating means for calculating a rear wheel lateral force acting on a rear wheel from the yaw rate detected by the yaw rate detecting means and the lateral acceleration detected by the lateral acceleration detecting means;
A rear wheel side slip angle calculating means for calculating a rear wheel side slip angle based on the rear wheel lateral force and a predetermined rear wheel tire characteristic;
Front wheel side slip angle conversion means for converting the rear wheel side slip angle into a first front wheel side slip angle based on a two-wheel vehicle model;
A vehicle state quantity estimation device comprising: Vehicle motion detection means including steering angle detection means for detecting the steering angle, vehicle speed detection means for detecting the vehicle speed, yaw rate detection means for detecting the yaw rate of the vehicle body, and lateral acceleration detection means for detecting the lateral acceleration of the vehicle body When,
Front wheel lateral force calculating means for calculating a front wheel lateral force acting on a front wheel from the yaw rate detected by the yaw rate detecting means and the lateral acceleration detected by the lateral acceleration detecting means;
Front wheel side slip angle calculating means for calculating a second front wheel side slip angle based on the front wheel side force and predetermined front wheel tire characteristics;
The rear wheel lateral force calculating means and the rear wheel side slip angle calculating means;
The front wheel side slip angle conversion means;
Front wheel side slip angle collation for obtaining a front wheel side slip angle by comparing and collating the first front wheel side slip angle obtained by the front wheel side slip angle conversion means and the second front wheel side slip angle obtained by the front wheel side slip angle calculating means. Means,
A vehicle state quantity estimation device comprising: When the front wheel saturation degree is larger than the rear wheel saturation degree, the first front wheel side slip angle is set as the vehicle body or wheel side slip angle. When the front wheel saturation degree is smaller than the rear wheel saturation degree, 3. The vehicle state quantity estimating device according to claim 2, wherein the front wheel side slip angle is a side slip angle of a vehicle body or a wheel.

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