JP2010195325A - Device and method for estimating tread friction state of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately obtain a value of an estimation object to a tread friction factor. <P>SOLUTION: In the device for estimating a tread friction state of a vehicle, a road surface friction factor &mu;<SB>1</SB>differed from a reference road surface friction factor and a slip angle &beta;t<SB>1</SB>on a road surface with the road surface friction factor &mu;<SB>1</SB>differed from the reference road surface friction factor are taken as inputs, and a slip angle &beta;t<SB>0</SB>on a reference road surface is obtained by multiplying the input slip angle &beta;t<SB>1</SB>by a value (&mu;<SB>0</SB>/&mu;<SB>1</SB>) obtained by dividing the reference road surface friction factor &mu;<SB>0</SB>by the road surface friction factor &mu;<SB>1</SB>. According to a tire model obtained by modeling tire characteristics established in a correlation between a tire force and a slippage obtained on the reference road surface with the reference road surface friction factor, a lateral force Fy<SB>0</SB>on the reference road surface corresponding to the slip angle &beta;t<SB>0</SB>on the reference road surface obtained by the multiplication is obtained, and a lateral force Fy<SB>1</SB>on the road surface with the road friction factor &mu;<SB>1</SB>is obtained by multiplying the obtained lateral force Fy<SB>0</SB>on the reference road surface by a value obtained by dividing the road surface friction factor &mu;<SB>1</SB>by the reference road surface friction factor &mu;<SB>0</SB>. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a technique for estimating a friction state of a wheel contact surface or a road surface grip state of a wheel.

  As a conventional technology, the road friction coefficient estimator has a plurality of tire models with different road friction coefficients, and the tire model to be used is switched according to the estimated road friction coefficient, and the vehicle behavior using the selected tire model Some of them (mainly vehicle speed) are estimated.

Japanese Examined Patent Publication No. 6-78736

However, since a plurality of tire models are switched in accordance with a change in the road surface friction coefficient, the estimation accuracy of values to be estimated such as vehicle behavior obtained from the tire models is lowered. This can be said that the estimation accuracy of the value of the estimation target corresponding to the road surface friction coefficient is low.
An object of the present invention is to obtain a value to be estimated with high accuracy with respect to a road surface friction coefficient.

In order to solve the above-mentioned problem, the present invention is either a first input value which is a road surface friction coefficient input and set by the first input means, and a tire force or a slip degree which is set by the second input means. Based on the second input value, the output means outputs either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the first input means from the tire model.
Here, the tire model is a model of tire characteristics established by the correlation between the tire force obtained on the reference road surface of the reference road friction coefficient and the slip degree, and the tire force and the slip degree on the reference road surface are modeled. If the ratio between the tire force and the slip degree on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient is the same, the road surface with a road surface friction coefficient different from the tire force on the reference road surface and the reference road surface friction coefficient The ratio between the tire force at the road or the slip ratio on the reference road surface and the slip ratio on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient is the reference road friction coefficient and the reference road surface friction coefficient. It has a characteristic indicating a ratio with different road surface friction coefficients.

  Further, the output means multiplies the second input value input and set by the second input means by the value obtained by dividing the reference road friction coefficient by the first input value set and input by the first input means. Either the force or the slip degree is obtained, and the tire force or the slip degree on the reference road surface corresponding to either the tire force or the slip degree on the reference road surface obtained by multiplication according to the tire model is obtained. The first input is obtained by multiplying either the tire force or the slip degree on the obtained reference road surface by the value obtained by dividing the first input value set by the first input means by the reference road surface friction coefficient. Either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the means is obtained.

According to the present invention, based on either the road surface friction coefficient, the tire force or the slip degree on the road surface of the road surface friction coefficient, and the sole tire model, the tire force or slip on the road surface of the road surface friction coefficient. One of the degrees can be estimated.
Thereby, it is possible to obtain the tire force and the slip degree to be estimated with high accuracy with respect to the road surface friction coefficient.

FIG. 6 is a characteristic diagram showing a tire characteristic curve (Fx-λ characteristic curve) established between a wheel slip ratio λ and a wheel braking / driving force Fx, which is used for explaining a presupposed technology. It is a figure used in order to explain a premise technique, and is a characteristic view showing a tire characteristic curve (Fx-λ characteristic curve) and a friction circle of each road surface μ. It is the figure used in order to explain the premise technology, and shows the inclination of the tangent at the intersection of the tire characteristic curve (Fx-λ characteristic curve) of each road surface μ and the straight line passing through the origin of the tire characteristic curve FIG. It is the figure used in order to explain the premise technology, and shows the inclination of the tangent at the intersection of the tire characteristic curve (Fx-λ characteristic curve) of each road surface μ and the straight line passing through the origin of the tire characteristic curve It is another characteristic view. It is the figure used in order to explain the technology which is the premise, the ratio of braking / driving force Fx, the ratio of slip ratios λ, or the ratio of line lengths and road surface μ obtained for tire characteristic curves with different road surface μ It is a characteristic view which shows that the ratio of becomes equal. FIG. 5 is a characteristic diagram showing the relationship between braking / driving force Fx and slip ratio λ obtained on road surfaces with different road surface μ, which is used to explain the underlying technology. It is a figure used in order to explain the technology used as a premise, and is a characteristic view showing the relation between braking / driving force Fx and slip ratio λ obtained on road surfaces with different road surface μ for studless tires. It is the figure used in order to explain the premise technology, the ratio (Fx / λ) of braking / driving force Fx and slip ratio λ of arbitrary point of tire characteristic curve (Fx-λ characteristic curve), this arbitrary point FIG. 6 is a characteristic diagram composed of a set of plot points with a slope (μ gradient) of a tangent line of a tire characteristic curve in FIG. FIG. 9 is a characteristic diagram showing a characteristic curve (grip characteristic curve) obtained from the plotted points in FIG. 8, which is used to explain the underlying technology. It is a diagram used to describe the the base technology, based on the slip ratio lambda ₁ detected, shows a reference to obtain the longitudinal force Fx ₁ in constituting the tire characteristic curve of the reference road surface. Based on the detected slip ratio lambda _1, it is a diagram illustrating a procedure of obtaining a longitudinal force Fx ₁ with reference to the tire characteristic curve of the reference road surface. FIG. 5 is a characteristic diagram showing a tire characteristic curve (Fy-βt characteristic curve) established between a wheel slip angle βt and a wheel lateral force Fy. It is a figure used in order to explain a premise technique, and is a characteristic figure showing a tire characteristic curve (Fy-βt characteristic curve) and a friction circle of each road surface μ. It is the figure used in order to explain the premise technology, and shows the inclination of the tangent at the intersection of the tire characteristic curve (Fy-βt characteristic curve) of each road surface μ and the straight line passing through the origin of the tire characteristic curve FIG. It is the figure used in order to explain the premise technology, and shows the inclination of the tangent at the intersection of the tire characteristic curve (Fy-βt characteristic curve) of each road surface μ and the straight line passing through the origin of the tire characteristic curve It is another characteristic view. It is the figure used in order to explain the technology which is the premise, the ratio of the side forces Fy which are obtained about the tire characteristic curve where road surface μ differs, the ratio of slip ratio λ or the ratio of line length and road surface μ It is a characteristic view which shows that ratio becomes equal. It is the figure used in order to explain the premise technology, the ratio (Fy / βt) of lateral force Fy and slip angle βt of the arbitrary point of the tire characteristic curve (Fy-βt characteristic curve) and the arbitrary point It is a characteristic view which shows the relationship (grip characteristic curve) with the inclination (micro gradient) of the tangent of the tire characteristic curve. Based on the slip angle [beta] t ₁ detected is a diagram showing a configuration for obtaining a lateral force Fy ₁ with reference to the tire characteristic curve of the reference road surface. Based on the slip angle [beta] t ₁ detected is a diagram illustrating a procedure for obtaining a lateral force Fy ₁ with reference to the tire characteristic curve of the reference road surface. It is a figure showing the schematic structure of the vehicles of this embodiment. It is a block diagram which shows the structure of a vehicle behavior control command calculating part. It is the figure used in order to explain the dynamic model (linear two-wheel model) of vehicles. It is a flowchart which shows the process sequence of a vehicle behavior control command calculating part. It is a flowchart which shows the process sequence of the tire lateral force estimation by a vehicle behavior control command calculating part. Based on the lateral force Fy ₁ detected is a diagram showing a configuration of obtaining the slip angle [beta] t ₁ with reference to the tire characteristic curve of the reference road surface. Based on the lateral force Fy ₁ detected is a diagram illustrating a procedure for obtaining the slip angle [beta] t ₁ with reference to the tire characteristic curve of the reference road surface. Based on the detected longitudinal force Fx _1, a diagram illustrating a configuration for obtaining a slip ratio lambda ₁ with reference to the tire characteristic curve of the reference road surface. Based on the detected longitudinal force Fx _1, a diagram illustrating a procedure for obtaining a slip ratio lambda ₁ with reference to the tire characteristic curve of the reference road surface.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Technology that is the premise of the embodiment)
First, a technique that is a premise of the present embodiment will be described.
(1) Relationship between wheel slip ratio and wheel braking / driving force FIG. 1 shows a tire characteristic curve. This tire characteristic curve shows a general correlation established between the slip ratio λ of the drive wheel and the braking / driving force (or longitudinal force) Fx of the drive wheel. For example, a tire characteristic curve is obtained from a tire model such as MagicFormula. Here, the braking / driving force Fx is a force acting on the ground from the tire. The braking / driving force Fx corresponds to the wheel force acting on the wheel on the ground contact surface. The slip ratio λ of the wheel corresponds to the slip degree of the wheel.

  As shown in FIG. 1, in the tire characteristic curve, the relationship between the slip ratio λ and the braking / driving force Fx changes from linear (linear relationship) to non-linear (curve relationship) as the absolute value of the slip rate λ increases. That is, in the tire characteristic curve, when the slip ratio λ is within a predetermined range from zero, a linear relationship is established between the slip ratio λ and the braking / driving force Fx. In the tire characteristic curve, when the slip ratio λ (absolute value) increases to some extent (exceeding the predetermined range), the relationship between the slip ratio λ and the braking / driving force Fx becomes a non-linear relationship. Thus, the tire characteristic curve has a linear portion and a non-linear portion.

Such a transition between the slip ratio λ and the braking / driving force Fx or a transition from a linear relationship to a non-linear relationship is obvious when attention is paid to the slope of the tangent line of the tire characteristic curve. The slope of the tangent line of the tire characteristic curve here is a value indicated by a partial differential coefficient with respect to a ratio of a change amount of the slip ratio λ and a change amount of the braking / driving force Fx, that is, the slip ratio λ of the braking / driving force Fx. is there.
Here, as shown in FIG. 1, arbitrary straight lines a, b, c, d,... Passing through the origin of the tire characteristic curve are drawn. Then, the slope of the tangent line of the tire characteristic curve can be obtained at the intersections with arbitrary straight lines a, b, c, d,. The slope of the tangent line of the tire characteristic curve is different at each intersection. By paying attention to the inclination of the tangent line of the tire characteristic curve, it is possible to know the relationship between the slip ratio λ and the braking / driving force Fx or the state of transition from the linear relationship to the nonlinear relationship.

  Thereby, estimation of the friction state of the tire is also possible. For example, as shown in FIG. 1, if the tire characteristic curve is at a position x0 that is close to the linear region even in the non-linear region, it can be estimated that the tire friction state is in a stable state. If the friction state of the tire is in a stable state, it can be estimated that, for example, the tire is at a level at which the ability can be exhibited. Alternatively, it can be estimated that the vehicle is in a stable state.

  FIG. 2 shows tire characteristic curves and friction circles of various road surfaces μ. FIG. 2A shows tire characteristic curves of various road surfaces μ. 2 (b) to 2 (d) show the friction circle of each road surface μ. The road surface μ is, for example, 0.2, 0.5, or 1.0. As shown in FIG. 2 (a), the tire characteristic curve shows the same tendency qualitatively at each road surface μ. Further, as shown in FIGS. 2B to 2D, the friction circle becomes smaller as the road surface μ becomes smaller. That is, the braking / driving force that the tire can tolerate decreases as the road surface μ decreases. As described above, the tire characteristics are characteristics using the road surface friction coefficient (road surface μ) as a parameter. Therefore, as shown in FIG. 2, depending on the value of the road surface friction coefficient, the tire characteristic curve in the case of low friction, the tire characteristic curve in the case of medium friction, the tire characteristic curve in the case of high friction, etc. Can be obtained.

  FIG. 3 shows the relationship between tire characteristic curves of various road surfaces μ and arbitrary straight lines b, c, d passing through the origin of the tire characteristic curve. As shown in FIG. 3, as in FIG. 1, tangent slopes are obtained at intersections with arbitrary straight lines b, c, d for tire characteristic curves of various road surfaces μ. That is, for the tire characteristic curves on various road surfaces μ, tangent slopes are obtained at the intersections with the straight line b. For tire characteristic curves on various road surfaces μ, tangential slopes are obtained at intersections with the straight line c. With respect to tire characteristic curves on various road surfaces μ, tangent slopes are obtained at intersections with the straight line d. As a result, a result can be obtained in which the tangent slopes of the tire characteristic curves of various road surfaces μ obtained at the intersections with the same straight line are the same.

  For example, FIG. 4 focuses on the straight line c shown in FIG. As shown in FIG. 4, the inclination of the tangent line at the intersection with the straight line c is the same in the tire characteristic curves of various road surfaces μ. That is, the ratio (Fx1 / λ1) between the braking / driving force Fx1 and the slip ratio λ1 indicating the intersection x1 with the tire characteristic curve with the road surface μ of μ = 0.2 is obtained. Further, a ratio (Fx2 / λ2) between the braking / driving force Fx2 and the slip ratio λ2 indicating the intersection x2 with the tire characteristic curve with the road surface μ of μ = 0.5 is obtained. Further, a ratio (Fx3 / λ3) between the braking / driving force Fx3 and the slip ratio λ3 indicating the intersection point x3 with the tire characteristic curve where the road surface μ is μ = 1.0 is obtained. Each value thus obtained is the same value. And the inclination of the tangent in each of these intersection x1, x2, x3 becomes the same value.

  Thus, even if the road surface μ is different, the slope of the tangent line is the same for each tire characteristic curve at the value (λ, Fx) where the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same. Become. Further, regarding the values (λ, Fx) at which the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ is the same in each tire characteristic curve, the ratio between the braking / driving forces Fx obtained between the different tire characteristic curves. Alternatively, the ratio between the slip ratios λ is equal to the ratio of the road surface μ.

With reference to FIG. 5, it will be described that the ratio between the braking / driving forces Fx or the ratio between the slip ratios λ is equal to the ratio between the road surface μ for each tire characteristic curve having a different road surface μ. FIG. 5 shows tire characteristic curves obtained respectively on the road surface A (road surface μ = μ _A ) and the road surface B (road surface μ = μ _B ) having different road surfaces μ.
As shown in FIG. 5, the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same (λ, Fx) (values indicated by ■ and ● in the same figure), respectively. What is the ratio (a2 / b2) between the braking / driving force a2 and the braking / driving force b2 and the ratio (μ _A / μ _B ) between the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B? It becomes the same value.

Similarly, the ratio (a3 / b3) of the slip ratio a3 and the slip ratio b3, which are respectively obtained with values (λ, Fx) at which the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same. becomes the same value as the ratio of the road surface mu values mu _B of the road surface mu values mu _a and the road surface B of road surface _{a (μ a / μ B)} .
For this reason, the line length a1 obtained by connecting the value (λ, Fx) and the origin (0, 0) where the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same, and and the ratio of the line length b1 (a1 / b1), becomes the same value as the ratio of the road surface mu values mu _B of the road surface mu values mu _a and the road surface B of road surface _{a (μ a / μ B)} . This can be proved geometrically as follows.

The triangle that can be drawn using the tire characteristic curve of road surface A (triangle with sides a1, a2, and a3) and the triangle that can be drawn using the tire characteristic curve of road surface B (triangle with sides b1, b2, and b3) are similar. It becomes a triangle. From this, the ratio of a1 and b1, the ratio of a2 and b2, and the ratio of a3 and b3 are the same value (a1: b1 = a2: b2 = a3: b3). And the ratio (a2 / b2) of a2 and b2 regarding the braking / driving force Fx and the ratio (a3 / b3) of a3 and b3 regarding the slip ratio λ are the values of the road surface μ μ value μ _A and the road surface B. It becomes the same value as the ratio (μ _A / μ _B ) with the road surface μ value μ _B. Therefore, as described above, the ratio between the line length a1 and the line length b1 (a1 / b1) and the ratio between the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B (μ _A / μ _B ) Can be concluded to be the same value.
As described above, if the ratio between the braking / driving forces Fx, the ratio between the slip ratios λ, or the ratio between the line lengths can be known, the ratio of the road surface μ can be known.

  FIG. 6 shows the relationship between the braking / driving force Fx and the slip ratio λ obtained on road surfaces having different road surfaces μ. In FIG. 6, the vibration waveform indicates actual measurement values obtained on the Dry road, the Wet road, and the low μ road. A dotted line indicates a characteristic curve of a tire (normal tire) on each road surface. As shown in FIG. 6, the tire characteristic curve on each road surface with different road surface μ maintains the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ, but the braking / driving force Fx decreases as the road surface μ decreases. And the slip ratio λ becomes small.

FIG. 7 shows the relationship between the braking / driving force Fx and the slip ratio λ obtained on the road surface with different road surface μ for the studless tire. In FIG. 7, the vibration waveform indicates actual values obtained on the Dry road, the Wet road, and the low μ road. Moreover, a dotted line shows the tire characteristic curve in each road surface. A thick dotted line indicates a tire characteristic curve of a normal tire.
As shown in FIG. 7, the tire characteristic curve (thin dotted line) on each road surface with different road surface μ maintains the ratio (Fx / λ) of braking / driving force Fx and slip ratio λ, but the road surface μ is small. As it is, the braking / driving force Fx and the slip ratio λ are reduced. Furthermore, the ratio (Fx / λ) of the braking / driving force Fx and slip ratio λ of the tire characteristic curve (thick dotted line) of the normal tire, and the braking / driving force Fx and slip of the tire characteristic curve (thin dotted line) of the studless tire The ratio (Fx / λ) to the rate λ is the same value. That is, the tire characteristic curve of the normal tire and the tire characteristic curve of the studless tire have a similar shape. That is, even when the gripping force, the tire surface shape, and the like are different as in a studless tire, the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ of the tire characteristic curve of the normal tire is the same value.

  FIG. 8 shows the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ at an arbitrary point of the tire characteristic curve, and the slope of the tangent line of the tire characteristic curve at the arbitrary point (∂ braking / driving force / ∂ slip ratio). ). In FIG. 8, the values obtained at each road surface μ (for example, μ = 0.2, 0.5, 1.0) are plotted. As shown in FIG. 8, regardless of the road surface μ, the ratio of the braking / driving force Fx to the slip ratio λ (Fx / λ) and the slope of the tangent line of the tire characteristic curve show a constant relationship.

FIG. 9 shows a characteristic curve obtained based on the plotted points in FIG. As shown in FIG. 9, in this characteristic curve, the ratio of the braking / driving force Fx to the slip ratio λ (Fx / λ) and the slope of the tangent line of the tire characteristic curve are always constant regardless of the road surface μ. It will be shown.
That is, this characteristic curve is established even on a road surface having a different road surface μ, such as a dry asphalt road surface or a frozen road surface. Alternatively, it can be said that the characteristic curve includes a high friction tire characteristic curve for a high friction road surface having a high friction coefficient and a low friction tire characteristic curve for a low friction road surface having a low friction coefficient lower than the high friction coefficient. Thus, it can be said that the characteristic curve shown in FIG. 9 shows the tire characteristic curve, as in FIG. However, in distinction from FIG. 1, the characteristic curve of FIG. 9 can also be called, for example, a grip characteristic curve.

  As shown in FIG. 9, in the region where the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ is small (small ratio region), the tangent slope of the tire characteristic curve is a negative value. In this region, as the ratio (Fx / λ) increases, the tangential slope of the tire characteristic curve once decreases and then increases. Here, the slope of the tangent line of the tire characteristic curve being a negative value indicates that the partial differential coefficient relating to the slip ratio of the braking / driving force is a negative value.

  Further, as shown in FIG. 9, in a region where the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ is large (large ratio region), the slope of the tangent line of the grip characteristic curve becomes a positive value. In this region, as the ratio (Fx / λ) increases, the tangential slope of the tire characteristic curve increases. That is, in the region where the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ is large, the grip characteristic curve has a monotonically increasing function.

  Here, the slope of the tangent line of the tire characteristic curve being a positive value indicates that the partial differential coefficient relating to the slip ratio of the braking / driving force is a positive value. In addition, the maximum inclination of the tangent line of the tire characteristic curve indicates that the inclination of the tangent line is in the linear region of the tire characteristic curve. In the linear region, the slope of the tangent line of the tire characteristic curve always shows a constant value regardless of the ratio between the braking / driving force Fx and the slip ratio λ.

  The slope of the tangent line of the tire characteristic curve that can be obtained in this manner is a grip characteristic parameter, a variable that represents the grip state of the tire, or a parameter that represents a saturation state of the force that the tire can exert in the lateral direction. Specifically, when the slope of the tangent line of the tire characteristic curve is a positive value, it indicates that a larger braking / driving force Fx can be generated by increasing the slip ratio λ. When the slope of the tangent line of the tire characteristic curve is zero or a negative value, it indicates that the braking / driving force Fx does not increase even if the slip ratio λ is increased and may decrease.

A grip characteristic curve (FIG. 9) can be obtained by performing partial differential calculation on the tire characteristic curve (FIG. 1) and drawing continuously.
As described above, the inventor of the present application has the same tangential slope at the intersection of any one straight line passing through the origin of the tire characteristic curve and the tire characteristic curve for the tire characteristic curve of each road surface μ. I found a spot. That is, with respect to the tire characteristic curve of each road surface μ, a point was found where the slope of the tangent line was the same at the value (λ, Fx) where the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ was the same.

  Thereby, the inventor of the present application has a characteristic curve (grip characteristic curve) having a relationship between the ratio of the braking / driving force Fx and the slip ratio λ (Fx / λ) and the slope of the tangent line of the tire characteristic curve regardless of the road surface μ. The result which can be expressed as was obtained (FIG. 9). By using this result, if the braking / driving force Fx and the slip ratio λ are known, based on the characteristic curve (grip characteristic curve), the information on the frictional state of the tire can be obtained without requiring information on the road surface μ. Obtainable.

Further, the inventor of the present application uses a tire characteristic curve with different road surface μ, and the braking / driving forces Fx between the braking / driving forces Fx at values (λ, Fx) at which the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same. It has been found that the ratio, the ratio between the slip ratios λ or the ratio between the line lengths becomes equal to the ratio of the road surface μ.
Thereby, if the ratio between the braking / driving forces Fx, the ratio between the slip ratios λ, or the ratio between the line lengths is known, the ratio of the road surface μ can be known. In the present embodiment, this relationship is applied to detect or estimate the road surface μ of the traveling road surface, thereby detecting or estimating the braking / driving force Fx and the slip ratio λ on the traveling road surface.

The braking / driving force Fx and the slip ratio λ on the traveling road surface can be detected or estimated by detecting or estimating the road surface μ of the traveling road surface based on the following principle.
By the, relationship similar triangles between the tire characteristic curve of the road surface mu values mu _A and (lambda _A, Fx _A) the tire characteristic curve of the road surface mu values _{μ B (λ B, Fx B} ), the following (1) The relationship like the formula is established.
Fx _A : Fx _B = λ _A : λ _B = μ _A : μ _B (1)

In the equation (1), when attention is paid to the relationship between the slip ratio λ and the road surface μ, the following equation (2) is established.
λ _A = λ _B · (μ _A / μ _B ) (2)
The (2) as a slip ratio lambda _A is unknown in the road surface of the road surface mu values mu _A according to formula slip ratio lambda _B in road of the road surface mu values mu _B, and the road surface mu values mu _A, mu _B if is known, it is possible to obtain the slip ratio lambda _a in road of the road surface mu values mu _a.
Then, knowing the tire characteristic curve of the road surface of the road surface mu values mu _A (with reference to the tire characteristic curve of the road surface of the road surface mu values mu _A), the longitudinal force Fx corresponding to the slip ratio lambda _A so obtained _A can be obtained.

Then, in the equation (1), this time, by paying attention to the relationship between the braking / driving force Fx and the road surface μ, the road surface of the road surface μ value μ _{B according to} the following equation (3) based on the braking / driving force Fx _A: It can be calculated longitudinal force Fx _B in.
Fx _B = Fx _A · (μ _B / μ _A ) (3)
Thus, if the tire characteristic curve becomes the road mu values and reference (tire characteristic curve of the road surface of the road surface mu values mu _A in this case) is known, the braking-driving force from the known slip ratio lambda (detected or estimated slip ratio lambda) Fx can be obtained. Further, on the contrary, the slip ratio λ can be obtained from the known braking / driving force Fx by the same principle.

A more specific description will be given with reference to FIGS. 10 and 11. FIG. 10 is a configuration for realizing the above-described principle.
As shown in FIG. 10, the detected slip ratio λ ₁ is input to the μ ₀ / μ ₁ multiplier 1 (procedure (1) in FIG. 11). mu _{0 /} mu ₁ multiplication unit road mu values mu ₁ is set to the road surface mu values mu ₁ and described below mu _{1 /} mu ₀ multiplication unit 3 is set to 1, the road surface of the traveled road surface that has detected the slip ratio lambda ₁ The μ value (for example, 0.6). The road surface μ value μ ₁ is a detected value or an estimated value. The μ ₀ / μ ₁ multiplier ₁ multiplies the slip ratio λ ₁ by (μ ₀ / μ ₁ ) (corresponding to the equation (2)). Then, mu ₀ / mu ₁ multiplication unit 1 outputs the operation result _{(λ 1 · μ 0 / μ} 1) to the tire characteristic estimating section 2.

The tire characteristic estimation unit 2 has a tire characteristic curve having a road surface μ value μ ₀ . The tire characteristic curve with the road surface μ value μ _{0 is} the tire characteristic curve of the reference road surface. For example, the road surface μ value μ ₀ is 1.0 assuming that the reference road surface is a Dry road surface. Moreover, the tire characteristic estimation part 2 has the tire characteristic curve of the reference | standard road surface like FIG. 11 as a map. In this case, the map is a two-dimensional map including continuous line segments each having the tire force and the slip degree obtained on the reference road surface as coordinate axes.

The tire characteristic estimation unit 2 obtains the slip ratio λ ₀ in the tire characteristic curve on the reference road surface based on the calculation result (λ ₁ · μ ₀ / μ ₁ ) (procedure (2) in FIG. 11).
Then, the tire characteristic estimation unit 2 obtains the braking / driving force Fx ₀ corresponding to the slip ratio λ ₀ from the tire characteristic curve of the reference road surface. Tire estimation unit 2 outputs the longitudinal force Fx ₀ so obtained to μ _{1 /} μ ₀ multiplication unit 3.
The μ ₁ / μ ₀ multiplication unit 3 multiplies the braking / driving force Fx ₀ by (μ ₁ / μ ₀ ), and outputs the braking / driving force Fx ₁ as the calculation result (procedures (3) and (4) in FIG. ), Corresponding to the expression (3)).
As described above, by having the tire characteristic curve data of the reference road surface, based on the detected value or estimated value of the road surface μ ₁ of a certain road surface and the detected value of the slip ratio λ _{1 on} the road surface, It can be detected or estimated longitudinal force Fx ₁ in the traveling road surface.

(2) Relationship between wheel slip angle and wheel lateral force FIG. 12 shows a tire characteristic curve. This tire characteristic curve shows a general correlation established between the wheel slip angle βt and the wheel lateral force Fy. For example, by tuning a tire model based on experimental data, an equivalent characteristic diagram (tire characteristic curve) for two wheels is obtained for each of the front and rear wheels. Here, for example, a tire model is constructed on the basis of a magic formula. The lateral force Fy is a value represented by a cornering force or a side force. Here, the lateral force Fy is a force acting on the ground from the tire. Further, the lateral force Fy corresponds to the wheel force acting on the wheel on the ground contact surface. The wheel slip angle βt corresponds to the slip degree of the wheel.

  As shown in FIG. 12, in the tire characteristic curve, the relationship between the slip angle βt and the lateral force Fy changes from linear to non-linear as the absolute value of the slip angle βt increases. That is, in the tire characteristic curve, when the slip angle βt is within a predetermined range from zero, a linear relationship is established between the slip angle βt and the lateral force Fy. In the tire characteristic curve, when the slip angle βt (absolute value) increases to some extent (exceeding the predetermined range), the relationship between the slip angle βt and the lateral force Fy becomes a non-linear relationship. Thus, the tire characteristic curve has a linear portion and a non-linear portion.

The transition from the relationship between the slip angle βt and the lateral force Fy or the linear relationship to the non-linear relationship is obvious when attention is paid to the slope (gradient) of the tangent line of the tire characteristic curve. The inclination of the tangent line of the tire characteristic curve here is a value represented by a ratio of a change amount of the slip angle βt and a change amount of the lateral force Fy, that is, a partial differential coefficient related to the slip angle βt of the lateral force Fy.
Here, as shown in FIG. 12, arbitrary straight lines a, b, c, d,... Passing through the origin of the tire characteristic curve are drawn. Then, the tangential slope of the tire characteristic curve can be obtained at the intersections (intersections indicated by circles in FIG. 12) with arbitrary straight lines a, b, c,... Intersecting the tire characteristic curve. The slope of the tangent line of the tire characteristic curve is different at each intersection. By paying attention to the inclination of the tangent line of the tire characteristic curve, it is possible to know the relationship between the slip angle βt and the lateral force Fy or the state of transition from the linear relationship to the non-linear relationship.

  Thereby, estimation of the friction state of the tire is also possible. For example, as shown in FIG. 12, if the tire characteristic curve is at a position x0 close to the linear region even in the nonlinear region, it can be estimated that the tire friction state is in a stable state. And if the friction state of a tire is a stable state, it can be estimated that a tire is in the level which can exhibit the capability, for example. Alternatively, it can be estimated that the vehicle is in a stable state.

  FIG. 13 shows tire characteristic curves and friction circles of various road surfaces μ. FIG. 13A shows tire characteristic curves of various road surfaces μ. FIGS. 13B to 13D show the friction circle of each road surface μ. The road surface μ is, for example, 0.2, 0.5, or 1.0. As shown in FIG. 13 (a), the tire characteristic curve shows the same tendency qualitatively at each road surface μ. Moreover, as shown in FIGS. 13B to 13D, the friction circle becomes smaller as the road surface μ becomes smaller. That is, as the road surface μ decreases, the lateral force that the tire can tolerate decreases. As described above, the tire characteristics are characteristics using the road surface friction coefficient (road surface μ) as a parameter. Therefore, as shown in FIG. 13, according to the value of the road surface friction coefficient, a tire characteristic curve in the case of low friction, a tire characteristic curve in the case of medium friction, a tire characteristic curve in the case of high friction, and the like can be obtained. it can.

  FIG. 14 shows the relationship between tire characteristic curves of various road surfaces μ and arbitrary straight lines a, b, c passing through the origin. As shown in FIG. 14, as in FIG. 12, tangent slopes are obtained at intersections with arbitrary straight lines a, b, c for tire characteristic curves of various road surfaces μ. That is, for the tire characteristic curves on various road surfaces μ, tangent slopes are obtained at the intersections with the straight line a. For tire characteristic curves on various road surfaces μ, tangent slopes are obtained at intersections with the straight line b. For tire characteristic curves on various road surfaces μ, tangential slopes are obtained at intersections with the straight line c. As a result, a result can be obtained in which the tangent slopes of the tire characteristic curves of various road surfaces μ obtained at the intersections with the same straight line are the same.

  For example, in FIG. 15, attention is paid to the straight line c shown in FIG. As shown in FIG. 15, the slope of the tangent line at the intersection with the straight line c is the same in the tire characteristic curves of various road surfaces μ. That is, the ratio (Fy1 / βt1) between the lateral force Fy1 and the slip angle βt1 indicating the intersection x1 with the tire characteristic curve with the road surface μ of μ = 0.2 is obtained. Further, a ratio (Fy2 / βt2) between the lateral force Fy2 and the slip angle βt2 indicating the intersection x2 with the tire characteristic curve with the road surface μ of μ = 0.5 is obtained. Further, a ratio (Fy3 / βt3) between the lateral force Fy3 and the slip angle βt3 indicating the intersection x3 with the tire characteristic curve with the road surface μ of μ = 1.0 is obtained. Each value thus obtained is the same value. And the inclination of the tangent line in each intersection x1, x2, x3 becomes the same value.

  Thus, even if the road surface μ is different, the slope of the tangent line is the same for each tire characteristic curve at the value (βt, Fy) where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is the same. . Further, regarding the values (βt, Fy) at which the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is the same in each tire characteristic curve, the ratio or slip angle between the lateral forces Fy obtained with different tire characteristic curves. The ratio between βt is equal to the ratio of the road surface μ. That is, if the ratio between the lateral forces Fy or the ratio between the slip angles βt can be known, the ratio of the road surface μ can be known.

With reference to FIG. 16, it will be described that the ratio of the lateral forces Fy or the ratio of the slip angles βt and the ratio of the road surface μ are equal for each tire characteristic curve having a different road surface μ. FIG. 16 shows tire characteristic curves obtained respectively on the road surface A (road surface μ = μ _A ) and the road surface B (road surface μ = μ _B ) having different road surfaces μ.
As shown in FIG. 16, the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is the same (βt, Fy) (values indicated by ■ and ● in the same figure), respectively. The ratio of the lateral force a2 and the lateral force b2 (a2 / b2) and the ratio (μ _A / μ _B ) between the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B are the same value. Become.
Similarly, the ratio (a3 / b3) between the slip ratio a3 and the slip ratio b3, which are respectively obtained with values (βt, Fy) at which the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is the same, The ratio (μ _A / μ _B ) between the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B is the same value.

Therefore, the tire characteristic curve obtained on the road surface A and the tire characteristic curve obtained on the road surface B have the same ratio (Fy / βt) between the lateral force Fy and the slip angle βt (βt, Fy). ) And the origin (0, 0), respectively, the ratio (a1 / b1) of the line length a1 and the line length b1, and the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B It becomes the same value as the ratio (μ _a / μ _B) of. This can be proved geometrically as follows.

A triangle (triangle with sides a1, a2 and a3) obtained using the tire characteristic curve of road surface A and a triangle (triangle with sides b1, b2 and b3) obtained using the tire characteristic curve of road surface B, and Becomes a similar triangle. From this, the ratio of a1 and b1, the ratio of a2 and b2, and the ratio of a3 and b3 are the same value (a1: b1 = a2: b2 = a3: b3). The ratio of a2 and b2 for the lateral force Fy and the ratio of a3 and b3 for the slip angle βt are the ratio of the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B (μ _A / Μ _B ). Therefore, as described above, the ratio between the line length a1 and the line length b1 (a1 / b1) and the ratio between the road surface μ value μ _A of the road surface _A and the road surface μ value μ _B of the road surface B (μ _A / μ _B ) Can be concluded to be the same value.

  FIG. 17 shows the relationship between the ratio (Fy / βt) between the lateral force Fy and the slip angle βt at an arbitrary point of the tire characteristic curve, and the slope of the tangent line of the tire characteristic curve at the arbitrary point (∂Fy / ∂βt). Indicates. As shown in FIG. 17, for each road surface μ (for example, μ = 0.2, 0.5, 1.0), the ratio (Fy / βt) between the lateral force Fy and the slip angle βt and the tangent line of the tire characteristic curve Shows a certain relationship with the slope.

  That is, this characteristic curve is established even on a road surface having a different road surface μ, such as a dry asphalt road surface or a frozen road surface. Alternatively, it can be said that the characteristic curve includes a high friction tire characteristic curve for a high friction road surface having a high friction coefficient and a low friction tire characteristic curve for a low friction road surface having a low friction coefficient lower than the high friction coefficient. Here, it can be said that the characteristic curve shown in FIG. 17 shows a tire characteristic curve as in FIG. However, in distinction from FIG. 12, the characteristic curve of FIG. 17 can also be called, for example, a grip characteristic curve.

  As shown in FIG. 17, in the region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is small (small ratio region), the tangential slope of the tire characteristic curve is a negative value. In this region, as the ratio (Fy / βt) increases, the tangential slope of the tire characteristic curve once decreases and then increases. Here, the negative slope of the tangent of the tire characteristic curve indicates that the partial differential coefficient regarding the slip angle of the lateral force is a negative value.

  Further, as shown in FIG. 17, in the region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is large (large ratio region), the tangent slope of the tire characteristic curve becomes a positive value. In this region, as the ratio (Fy / βt) increases, the tangential slope of the tire characteristic curve increases. That is, in the region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is large, the grip characteristic curve has a monotonically increasing function.

  Here, the inclination of the tangent line of the tire characteristic curve being a positive value indicates that the partial differential coefficient regarding the slip angle of the lateral force is a positive value. In addition, the maximum inclination of the tangent line of the tire characteristic curve indicates that the inclination of the tangent line is in the linear region of the tire characteristic curve. In the linear region, the slope of the tangent line of the tire characteristic curve always shows a constant value regardless of the ratio between the lateral force Fy and the slip angle βt.

  The slope of the tangent line of the tire characteristic curve that can be obtained in this manner is a grip characteristic parameter, a variable that represents the grip state of the tire, or a parameter that represents a saturation state of the force that the tire can exert in the lateral direction. Specifically, when the slope of the tangent line of the tire characteristic curve is a positive value, it indicates that a stronger lateral force Fy (cornering force or the like) can be generated by increasing the slip angle βt. If the slope of the tangent line of the tire characteristic curve is zero or a negative value, it indicates that even if the slip angle βt is increased, the lateral force Fy (cornering force or the like) does not increase and may decrease.

A grip characteristic curve (FIG. 17) can be obtained by performing partial differential calculation on the tire characteristic curve (FIG. 12) and drawing continuously.
As described above, the inventor of the present application has the same tangential slope at the intersection of any one straight line passing through the origin of the tire characteristic curve and the tire characteristic curve for the tire characteristic curve of each road surface μ. I found a spot. That is, the tire characteristic curve of each road surface μ was found to have the same tangent slope at a value (βt, Fy) at which the ratio (Fy / βt) of the lateral force Fy to the slip angle βt is the same.

  Accordingly, the inventor of the present application uses a characteristic curve (grip characteristic curve) having a relationship between the ratio of the lateral force Fy and the slip angle βt (Fy / βt) and the slope of the tangent line of the tire characteristic curve regardless of the road surface μ. The result which can be expressed was obtained (FIG. 14). By using this result, if the lateral force Fy and the slip angle βt are known, information on the friction state of the tire is obtained based on the characteristic curve (grip characteristic curve) without requiring information on the road surface μ. be able to.

Further, the inventor of the present application is a tire characteristic curve with different road surface μ, and the ratio between the lateral forces Fy at the values (βt, Fy) where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is the same, It has been found that the ratio between the slip angles βt or the ratio between the line lengths becomes equal to the ratio of the road surface μ.
Thereby, if the ratio between the lateral forces Fy, the ratio between the slip angles βt, or the ratio between the line lengths is known, the ratio of the road surface μ can be known. In this embodiment, this relationship is applied to detect or estimate the road surface μ of the traveling road surface, thereby detecting or estimating the lateral force Fy and the slip angle βt on the traveling road surface.

The lateral force Fy and the slip angle βt on the traveling road surface can be detected or estimated by detecting or estimating the road surface μ of a certain traveling road surface according to the following principle (the slip ratio λ of the wheel and the wheel described above). This is similar to the relationship with the braking / driving force Fx.
_A similar triangle exists between the tire characteristic curve (lateral force Fy _A , slip angle βt _A ) of the road surface μ value μ _A and the tire characteristic curve (lateral force Fy _B , slip angle βt _B ) of the road surface μ value μ _B. Thus, the following relationship (4) is established.
Fy _A : Fy _B = βt _A : βt _B = μ _A : μ _B (4)

In the equation (4), when attention is paid to the relationship between the slip angle βt and the road surface μ, the following equation (5) is established.
_{βt A = βt B · (μ} A / μ B) ··· (5)
The (4) as a slip angle [beta] t _A is unknown in the road surface of the road surface mu values mu _A according to formula, slip angle [beta] t B in the road surface of the road surface mu values mu _B, and the road surface mu values mu _A, mu _B if is known, it is possible to obtain the slip angle [beta] t _a in the road of the road surface mu values mu _a.
Then, if the tire characteristic curve of the road surface μ value μ _A is known (refer to the tire characteristic curve of the road surface μ value μ _A road surface), the lateral force Fy _A corresponding to the slip angle βt _A thus obtained is obtained. Can be obtained.

Then, in the equation (4), this time, by paying attention to the relationship between the lateral force Fy and the road surface μ, the lateral force on the road surface of the road surface μ value μ _B is calculated by the following equation (6) based on the lateral force Fy _A. The force Fy _B can be calculated.
Fy _B = Fy _A · (μ _B / μ _A ) (6)
Thus, if the tire characteristic curve becomes the road mu values and reference (tire characteristic curve of the road surface of the road surface mu values mu _A in this case) is known, the lateral force from a known slip angle [beta] t (detected or estimated slip angle [beta] t) Fy Can be requested. Further, on the contrary, the slip angle βt can be obtained from the known lateral force Fy by the same principle.

A more specific description will be given with reference to FIGS. 18 and 19. FIG. 18 is a configuration for realizing the above-described principle.
As shown in FIG. 18, the detected slip angle βt ₁ is input to the μ ₀ / μ ₁ multiplier 1 (procedure (1) in FIG. 19). μ _{0 /} μ ₁ multiplication unit 11 road mu values mu ₁ is set to or below μ _{1 /} μ ₀ multiplication unit 13 road mu values mu ₁ is set to the road surface of the traveled road surface that has detected the slip angle [beta] t ₁ The μ value (for example, 0.6). The road surface μ value μ ₁ is a detected value or an estimated value. The μ ₀ / μ ₁ multiplier 11 multiplies the slip angle βt ₁ by (μ ₀ / μ ₁ ) (corresponding to the equation (5)). Then, the μ ₀ / μ ₁ multiplication unit 11 outputs the calculation result (βt ₁ · μ ₀ / μ ₁ ) to the tire characteristic estimation unit 12.

The tire characteristic estimation unit 12 has a tire characteristic curve having a road surface μ value μ ₀ . The tire characteristic curve with the road surface μ value μ _{0 is} the tire characteristic curve of the reference road surface. For example, the road surface μ value μ ₀ is 1.0 assuming that the reference road surface is a Dry road surface. Moreover, the tire characteristic estimation part 12 has a tire characteristic curve of the reference | standard road surface like FIG. 19 as a map. The tire characteristic estimation unit 12 obtains the slip angle βt ₀ in the tire characteristic curve on the reference road surface based on the calculation result (βt ₁ · μ ₀ / μ ₁ ) (procedure (2) in FIG. 19).

Then, the tire characteristic estimation unit 12 obtains the lateral force Fy ₀ corresponding to the slip ratio λ ₀ from the tire characteristic curve of the reference road surface. The tire characteristic estimation unit 12 outputs the lateral force Fy ₀ thus obtained to the μ ₁ / μ ₀ multiplication unit 13.
The μ ₁ / μ ₀ multiplier 13 multiplies the lateral force Fy ₀ by (μ ₁ / μ ₀ ), and outputs the lateral force Fy ₁ as the calculation result (procedures (3) and (4) in FIG. 19). (Corresponding to the equation (6)).
As described above, by having the tire characteristic curve data of the reference road surface, based on the detected value or estimated value of the road surface μ ₁ of a certain road surface and the detected value of the slip angle βt _{1 on} that road surface, The lateral force Fy ₁ on the traveling road surface can be detected or estimated.

(Embodiment)
Next, an embodiment realized by adopting the above technique will be described.
(Constitution)
FIG. 20 shows a schematic configuration of the vehicle of the embodiment. This vehicle has a configuration that controls VDC (Vehicle Dynamics Control) in a feed-forward manner. It is generally known that VDC is controlled by yaw rate feedback.
As shown in FIG. 20, the vehicle includes a steering angle sensor 21, a wheel speed sensor 22, a road surface μ estimation unit 23, a brake ECU (Electronic Control Unit or VDC control unit) 24, and a vehicle behavior control command calculation unit 25.

The steering angle sensor 21 detects the rotation angle of the steering shaft 32 that rotates integrally with the steering wheel 31. The steering angle sensor 21 outputs the detection result (steering angle) to the vehicle behavior control command calculation unit 25. The wheel speed sensor 22 detects the wheel speed of the wheels ₃₃ FL _{~ 33 RR} provided on the vehicle body. The wheel speed sensor 22 outputs the detection result (wheel speed signal) to the vehicle behavior control command calculation unit 25. The road surface μ estimation unit 23 estimates the current road surface μ value. The road surface μ estimation unit 23 outputs the estimation result (road surface μ value) to the vehicle behavior control command calculation unit 25. The vehicle behavior control command calculation unit 25 predicts the traveling state of the vehicle based on the input values from the steering angle sensor 21 and the like, and calculates a control command value. The vehicle behavior control command calculation unit 25 outputs the control command value to the brake ECU 24. Brake ECU24 outputs based on the control command value, an unstable behavior of the vehicle to suppress brake pressure command value to the brake actuator ₃₄ FL _{to 34C RR} of each wheel ₃₃ FL _{~ 33 RR.} Based on the brake pressure command value, the brake actuators 34 _{FL to} 34 _RR change the brake fluid pressure to the wheels 33 _{FL to} 33 _RR to generate a braking force.

  FIG. 21 shows a configuration of the vehicle behavior control command calculation unit 25. As shown in FIG. 21, the vehicle behavior control command calculation unit 25 includes a vehicle body speed calculation unit 41, a tire side slip angle (slip angle) estimation unit 42, a road surface change corresponding tire model 43, and an F / F (feed forward) vehicle model. 44, a linear vehicle model 45, a vehicle behavior deviation calculation unit 46, and a VDC_F / F command value calculation unit 47.

The vehicle body speed calculation unit 41 estimates the vehicle body speed based on the wheel speed detected by the wheel speed sensor 22. For example, the vehicle body speed is estimated based on the average value of the driven wheels or the average value of the four wheels. In addition, a vehicle body speed estimation observer can be configured by adding a longitudinal acceleration sensor. Thereby, the estimation accuracy can be increased. The vehicle body speed calculation unit 41 outputs the calculation result (vehicle body speed) to the tire skid angle estimation unit 42, the F / F vehicle model 44, and the linear vehicle model 45.
The tire side slip angle estimation unit 42 calculates the vehicle body speed calculated by the vehicle body speed calculation unit 41, the steering angle detected by the steering angle sensor 21, and the vehicle body side slip angle predicted value β calculated by the F / F vehicle model 44 as will be described later. Based on the predicted yaw rate value γ, the sideslip angles βt _f (β _f ) and βt _r (β _r ) of the front and rear wheels are calculated using the following equation (7).

Here, V is the vehicle speed. δ is a steering angle. For simplicity, the vehicle is a two-wheel model, and the left and right wheels have the same side slip angle and side force. Tire slip angle estimating section 42 outputs the calculated side slip angle (slip angle) [beta] t _f, the [beta] t _r to road surface changes corresponding tire model 43.
The road surface change corresponding tire model 43 calculates the lateral force of the front and rear wheels, which is the tire force. The road surface change compatible tire model 43 specifically has a configuration for detecting lateral force shown in FIG. Thus, the road surface changes corresponding tire model 43 calculates the slip angle [beta] t f of the front wheels and the rear wheels tire slip angle estimating section 42 calculates _the lateral force Fy f of the front wheels and the rear wheels from [beta] t _r, the Fy _r.

Here, a procedure for calculating the front wheel lateral force Fy _f from the front wheel slip angle βt _f will be described as a representative.
First, the road surface change correspondence tire model 43 inputs the front wheel slip angle βt _f calculated by the tire side slip angle estimation unit 42 to the μ ₀ / μ ₁ multiplication unit 11 (procedure (1) in FIG. 19). Further, the road surface changes corresponding tire model 43 sets the road surface mu values mu ₁ of μ _{0 /} μ ₁ multiplication unit 11, and μ _{1 /} μ ₀ multiplication unit 13 by the road surface mu values road surface mu estimating unit 23 estimates.

Thereby, in the road surface change corresponding tire model 43, the μ ₀ / μ ₁ multiplication unit 11 multiplies the slip angle βt _f by (μ ₀ / μ ₁ ). Then, the μ ₀ / μ ₁ multiplication unit 11 outputs the calculation result (βt _f · μ ₀ / μ ₁ ) to the tire characteristic estimation unit 12.
The tire characteristic estimation unit 12 obtains a slip angle βt ₀ in a tire characteristic curve of a reference road surface (for example, a road surface of μ ₀ = 1.0) based on the calculation result (βt _f · μ ₀ / μ ₁ ) ( Procedure (2) in FIG. Then, the tire characteristic estimation unit 12 obtains the lateral force Fy ₀ corresponding to the slip angle βt ₀ from the tire characteristic curve of the reference road surface. The tire characteristic estimation unit 12 outputs the lateral force Fy ₀ thus obtained to the μ ₁ / μ ₀ multiplication unit 13.

The μ ₁ / μ ₀ multiplier 13 multiplies the lateral force Fy ₀ by (μ ₁ / μ ₀ ) and outputs the calculation result (procedures (3) and (4) in FIG. 19). This calculation result is a lateral force Fy _f obtained on the traveling road surface of the road surface μ value estimated by the road surface μ estimation unit 23. That is, the calculation result is the lateral force Fy _f correlated with the front wheel slip angle βt _f calculated by the tire side slip angle estimating unit 42.

Performed also slip angle [beta] t _r of the rear wheels the aforementioned processing. As a result, the lateral force Fy _r of the rear wheels can also be calculated. Road changes corresponding tire model 43 outputs the lateral forces _Fy f of the calculated front and rear wheels, the Fy _r in F / F for the vehicle model 44.
F / F for the vehicle model 44, the lateral force of the front and rear wheels of the vehicle speed and the road surface changes corresponding tire model 43 vehicle speed calculating unit 41 has calculated is calculated Fy _f, based on Fy _r, calculates a vehicle behavior (vehicle Predict behavior). For example, the vehicle behavior is calculated from these using a dynamic model.

FIG. 22 shows an example of a dynamic model. In FIG. 22, m is the vehicle mass. I is the yaw moment of inertia. l _f is the distance between the vehicle center of gravity and the front axle. l _r is the distance between the vehicle center of gravity and the rear axle. β is a side slip angle (vehicle slip angle) of the vehicle. γ is the yaw rate. G _y is the lateral acceleration. For example, to detect the yaw rate γ and lateral acceleration G _y as required.

The F / F vehicle model 44 calculates the predicted value of the vehicle body slip angle and the predicted value of the yaw rate as the predicted vehicle behavior value using such a dynamic model. The F / F vehicle model 44 outputs the calculated vehicle body slip angle predicted value and yaw rate predicted value to the vehicle behavior deviation calculating unit 46 and the tire side slip angle estimating unit 42.
The linear vehicle model 45 calculates a reference yaw rate. Specifically, the linear vehicle model 45 calculates the reference yaw rate γ using the following equation (8) based on the vehicle body speed calculated by the vehicle body speed calculation unit 41 and the steering angle detected by the steering angle sensor 21.

Here, m is the vehicle mass. I is the yaw moment of inertia. l _f is the distance between the vehicle center of gravity and the front axle. l _r is the distance between the vehicle center of gravity and the rear axle. The cp _f is the front wheel cornering power (right and left wheels total). Cp _r is the rear wheel cornering power (the left and right wheels total value). V is the vehicle speed. β is the side slip angle of the vehicle. γ is the yaw rate.
The linear vehicle model 45 outputs the calculated reference yaw rate γ to the vehicle behavior deviation calculation unit 46.

  The vehicle behavior deviation calculation unit 46 calculates a difference between the yaw rate predicted value calculated by the F / F vehicle model 44 and the reference yaw rate calculated by the vehicle behavior deviation calculation unit 46. Here, the case where the difference is obtained is a case where there is a deviation between the yaw rate prediction value and the reference yaw rate. In such a case, it can be predicted that the yaw rate expected in the grip state cannot be generated (understeer state), or the yaw rate is generated more than necessary (oversteer state). For this reason, the vehicle behavior deviation calculator 46 outputs a control command value (feedforward VDC control command value) that cancels this deviation (difference). This control command value becomes a braking force command value (braking force difference command value) for causing the vehicle to generate a yaw moment so as to cancel out the deviation (difference).

FIG. 23 shows an example of the processing procedure of the vehicle behavior control command calculation unit 25 described above. As shown in FIG. 23, first, in step S1, the vehicle behavior control command calculation unit 25 acquires various data. Specifically, the steering angle detected by the steering angle sensor 21, the wheel speed detected by the wheel speed sensor 22, and the road surface μ value (estimated value) estimated by the road surface μ estimation unit 23 are acquired.
Subsequently, in step S2, the vehicle body speed calculation unit 41 estimates the vehicle body speed based on the wheel speed acquired in step S1.

Subsequently, in step S3, the tire side slip angle estimating unit 42 calculates the steering angle acquired in step S1, the vehicle body speed calculated in step S2, and the predicted vehicle side slip angle β and yaw rate predicted value calculated in step S4 described later. Based on γ, the sideslip angles βt _f (β _f ) and βt _r (β _f ) of the front and rear wheels are calculated.
Subsequently in step S10, the road surface changes corresponding tire model 43, is calculated sideslip angle [beta] t _f of the front and rear wheels calculated in the step S3, based on the [beta] t _r, the lateral force _Fy f of the front wheels and the rear wheels, the Fy _r (presume.

FIG. 24 shows an example of the lateral force calculation process. First, in step S11, the μ ₀ / μ ₁ multiplication unit 11 multiplies the slip angle βt ₁ (βt _f , (βt _r ) by (μ ₀ / μ ₁ ), and then in step S12, the tire characteristic estimation unit 12 Obtains a reference slip angle βt ₀ in the tire characteristic curve of the reference road surface based on the value (βt ₁ · μ ₀ / μ ₁ ) calculated in step S11, and then obtains a reference lateral force Fy ₀ .
Subsequently, in step S13, the μ ₁ multiplication unit 13 multiplies the reference lateral force Fy ₀ obtained in step S12 by (μ ₁ / μ ₀ ), and the lateral force Fy ₁ (Fy _f , Fy on the current traveling road surface). _r ) is calculated.

In step S4 Subsequently, F / F for the vehicle model 44, the lateral force Fy f of the front and rear wheels calculated at step _S10, based on Fy _r, as the vehicle behavior prediction value, the predicted value and the yaw rate of the vehicle body slip angle Calculate the predicted value.
Subsequently, in step S5, the linear vehicle model 45 calculates a reference yaw rate γ.
Subsequently, in step S6, the vehicle behavior deviation calculation unit 46 calculates a difference between the yaw rate predicted value calculated in step S4 and the reference yaw rate calculated in step S5.

Subsequently, in step S7, the vehicle behavior deviation calculation unit 46 outputs a feedforward (F / F) VDC control command value based on the difference calculated in step S6. At this time, the VDC control command value is a braking force command value that causes the vehicle to generate a yaw moment so as to cancel the difference between the yaw rate predicted value and the reference yaw rate.
Here, when there is a difference (deviation) between the predicted yaw rate and the reference yaw rate, the yaw rate expected in the grip state cannot be generated (under steer state), or the yaw rate is generated more than necessary ( Oversteer state) can be predicted.

For this reason, the yaw moment is generated in such a direction that the braking / driving force difference between the left and right wheels is controlled by the VDC control command value to cancel the difference. This can prevent an understeer state or an oversteer state.
In a normal VDC, control is performed according to a deviation between a reference yaw rate calculated by a linear vehicle model and an actually measured yaw rate. However, since the vehicle behavior that may occur due to the steering input can be predicted before the vehicle behavior occurs as in this embodiment, more stable control can be realized. Another great advantage is that the logic is simple and only one map is needed.

(Modification of the embodiment)
(1) In this embodiment, the lateral force Fy is calculated (estimated) from the slip angle βt (FIGS. 18 and 19). On the other hand, the slip angle βt can be calculated (estimated) from the lateral force Fy. The calculation procedure will be described with reference to FIGS.
As shown in FIG. 25, the detected lateral force Fy ₁ is input to the μ ₀ / μ ₁ multiplier 61 (procedure (1) in FIG. 26). The μ ₀ / μ ₁ multiplier 61 multiplies the lateral force Fy ₁ by (μ ₀ / μ ₁ ). Then, the μ ₀ / μ ₁ multiplication unit 61 outputs the calculation result (Fy ₁ · μ ₀ / μ ₁ ) to the tire characteristic estimation unit 62.

The tire characteristic estimation unit 62 obtains the lateral force Fy ₀ on the tire characteristic curve on the reference road surface based on the calculation result (Fy ₁ · μ ₀ / μ ₁ ) (procedure (2) in FIG. 26). Then, the tire characteristic estimation unit 62 obtains the slip angle βt ₀ corresponding to the lateral force Fy ₀ from the tire characteristic curve of the reference road surface. The tire characteristic estimation unit 12 outputs the slip angle βt ₀ to the μ ₁ / μ ₀ multiplication unit 63.
The μ ₁ / μ ₀ multiplier 63 multiplies the slip angle βt ₀ by (μ ₁ / μ ₀ ) and outputs the calculation result (procedures (3) and (4) in FIG. 26). The calculation result of the μ ₁ / μ ₀ multiplication unit 63 corresponds to the slip angle βt ₁ obtained on the traveling road surface with the road surface μ value μ ₁ .
As described above, the slip angle βt can also be estimated from the lateral force Fy. By enabling such estimation, the slip angle βt can be estimated with high accuracy without using a GPS (Global Positioning System) or an optical sensor.

(2) The braking / driving force (front / rear force) Fx can also be calculated (estimated) from the slip ratio λ (previous FIGS. 10 and 11). Based on the braking / driving force Fx calculated as described above, braking / driving force control such as TCS (Traction Control System) control can be performed. In this case, since the braking / driving force Fx can be estimated, the braking / driving force Fx can be estimated with high accuracy without using detection means such as a sensor.

(3) The slip ratio λ can also be calculated (estimated) from the braking / driving force Fx. The calculation procedure will be described with reference to FIGS.
As shown in FIG. 27, the detected braking / driving force Fx ₁ is input to the μ ₀ / μ ₁ multiplier 71 (procedure (1) in FIG. 28). The μ ₀ / μ ₁ multiplier 71 multiplies the braking / driving force Fx ₁ by (μ ₀ / μ ₁ ). Then, the μ ₀ / μ ₁ multiplier 71 outputs the calculation result (Fx ₁ · μ ₁ / μ ₁ ) to the tire characteristic estimator 72.

The tire characteristic estimation unit 72 obtains the braking / driving force Fx ₀ in the tire characteristic curve on the reference road surface based on the calculation result (Fx ₁ · μ ₁ / μ ₁ ) (procedure (2) in FIG. 28). Then, the tire characteristic estimation unit 72 obtains the slip ratio λ ₀ corresponding to the braking / driving force Fx ₀ from the tire characteristic curve of the reference road surface. The tire characteristic estimation unit 72 outputs the slip ratio λ ₀ to the μ ₁ / μ ₀ multiplication unit 73.
The μ ₁ / μ ₀ multiplier 73 multiplies the slip ratio λ ₀ by (μ ₁ / μ ₀ ) and outputs the calculation result (procedures (3) and (4) in FIG. 28). The calculation result of the μ ₁ / μ ₀ multiplication unit 73 corresponds to the slip ratio λ ₁ obtained on the traveling road surface with the road surface μ value μ ₁ .
As described above, the slip ratio λ can also be estimated from the braking / driving force Fx. Since such estimation becomes possible, the slip ratio λ can be estimated with high accuracy without using a detection means such as a sensor.

(4) The road surface μ value μ ₀ of the reference road surface can be set to a value other than 1.0.
(5) The road surface μ estimated by the road surface μ estimation unit 23 can be estimated using the principle shown in FIG. That is, the detected value is obtained based on the ratio between the detected value (for example, detected braking / driving force Fx ₁ ) and the value corresponding to the detected value (for example, braking / driving force Fx ₀ ) on the reference road surface of the road surface μ value μ _0. The road surface μ value μ ₁ (= μ ₀ · Fx ₁ / Fx ₀ ) of the traveling road surface is estimated.

(6) The tire model of the reference road surface may be expressed by a mathematical expression (function expression) using the tire force and the slip degree obtained on the reference road surface of the reference road surface friction coefficient as variables.
In this embodiment, the road surface μ estimation unit 23 realizes a first input unit that sets a road surface friction coefficient between the tire and the road surface as a first input value. Further, the tire side slip angle estimating unit 42 realizes second input means for setting, as a second input value, either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the first input means. To do. Further, the road surface change corresponding tire model 43 (the tire characteristic estimation unit in FIG. 18 and the reference road surface tire characteristic curve map) is established by the correlation between the tire force obtained on the reference road surface of the reference road surface friction coefficient and the slip degree. Realize a tire model that models tire characteristics. Further, the tire model 43 corresponding to the road surface change (μ ₀ / μ ₁ multiplication unit, tire characteristic estimation unit and μ ₁ / μ ₀ multiplication unit in FIG. 18 and the like) has a first input value set by the first input means, And, based on the second input value input and set by the second input means, an output for outputting either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the first input means from the tire model. Realize the means. In this embodiment, the tire model has the same ratio of the tire force and the slip degree on the road surface having a road surface friction coefficient different from the ratio of the tire force and the slip degree on the reference road surface and the reference road surface friction coefficient. If so, the ratio of the tire force on the reference road surface to the tire force on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient, or the slip degree on the reference road surface and the reference road surface friction coefficient are different. The ratio of the road surface friction coefficient to the slip degree on the road surface has a characteristic indicating a ratio between the reference road surface friction coefficient and a road surface friction coefficient different from the reference road surface friction coefficient.

Here, the road surface friction coefficient different from the reference road surface friction coefficient is an arbitrary road surface friction coefficient other than the reference road surface friction coefficient.
In this embodiment, the output means divides the second input value set by the second input means by a value obtained by dividing the reference road friction coefficient by the first input value set by the first input means. Multiplying to obtain either the tire force or the slip degree on the reference road surface, and corresponding to either the tire force or the slip degree on the reference road surface obtained by the multiplication according to the tire model Either the tire force or the slip degree on the reference road surface is obtained, and the first input value input by the first input means is set to the other one of the obtained tire force or slip degree on the reference road surface. By multiplying the value divided by the reference road surface friction coefficient, either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the first input means is obtained.

  In this embodiment, the road surface friction coefficient between the tire and the road surface is set as the first input value, and either the tire force or the slip degree on the road surface of the road surface friction coefficient is set as the second input value. An output step of outputting either the tire force or the slip degree on the road surface of the road surface friction coefficient from the tire model based on the input step and the first input value and the second input value input and set in the input step; The tire model models tire characteristics established by the correlation between the tire force obtained on the reference road surface of the reference road surface friction coefficient and the slip degree, and the tire force on the reference road surface If the ratio of the tire force and the slip degree on the road surface of the road surface friction coefficient different from the ratio of the slip degree and the reference road surface friction coefficient is the same, the tire force on the reference road surface and the reference road surface friction coefficient are The ratio of the road surface friction coefficient to the tire force on the road surface, or the ratio of the slip degree on the reference road surface to the slip degree on the road surface of a road surface friction coefficient different from the reference road surface friction coefficient is the reference road surface friction coefficient. And having a characteristic indicating a ratio of a road surface friction coefficient different from the reference road surface friction coefficient. In the output step, the input step inputs and sets the reference road surface friction coefficient to the second input value input and set in the input step. By multiplying the value divided by the first input value to obtain either one of the tire force or the slip degree on the reference road surface, according to the tire model, the tire force on the reference road surface obtained by the multiplication or One of the tire force and the slip degree on the reference road surface corresponding to one of the slip degrees is obtained, and the input step is obtained on the other of the obtained tire force and slip degree on the reference road surface. The vehicle ground contact surface is obtained by multiplying the first input value set in step 1 by the reference road surface friction coefficient to obtain either the tire force or the slip degree on the road surface of the road surface friction coefficient set in the input step. A friction state estimation method is realized.

(Effect of this embodiment)
(1) The first input means sets a road surface friction coefficient between the tire and the road surface as a first input value. The second input means sets either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set by the first input means as the second input value. Based on the first input value input and set by the first input means and the second input value input and set by the second input means, the road surface friction coefficient input and set by the first input means from the tire model is calculated on the road surface. Either the tire force or the slip degree is output by the output means.

  Here, the tire model is a model of tire characteristics established by the correlation between the tire force obtained on the reference road surface of the reference road surface friction coefficient and the slip degree. In addition, a tire model can be used on the reference road surface if the ratio of the tire force on the road surface and the slip ratio on the road surface is different from the ratio of the tire force on the road surface and the slip coefficient on the road surface. The tire force on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient, or the slip degree on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient. The ratio between the reference road surface friction coefficient and the road surface friction coefficient different from the reference road surface friction coefficient has a characteristic.

  The output means multiplies the second input value input and set by the second input means by the value obtained by dividing the reference road friction coefficient by the first input value input and set by the first input means. Either force or slip is obtained. Further, the output means obtains either the tire force or the slip degree on the reference road surface corresponding to either the tire force or the slip degree on the reference road surface obtained by multiplication according to the tire model. Further, the output means multiplies the value obtained by dividing the first input value input and set by the first input means by the reference road surface friction coefficient by either the tire force or the slip degree on the obtained reference road surface. One of the tire force and the slip degree on the road surface of the road surface friction coefficient input and set by one input means is obtained.

As a result, either the road surface friction coefficient, the tire force or the slip degree on the road surface of the road surface friction coefficient, and the tire force or the slip degree on the road surface of the road surface friction coefficient based on one tire model. Or the other can be estimated.
As a result, it is possible to obtain the tire force and the slip degree to be estimated with high accuracy with respect to the road surface friction coefficient.

(2) The tire model of the reference road surface is a two-dimensional map composed of continuous line segments each having the tire force and the slip degree obtained on the reference road surface as coordinate axes.
Thereby, a tire force and a slip degree can be estimated easily with high accuracy.
(3) The tire model of the reference road surface is expressed mathematically using the tire force and the slip degree obtained on the reference road surface as variables.
Thereby, a tire force and a slip degree can be estimated easily with high accuracy.

(4) The tire force is a lateral force of the tire, and the slip degree is a tire slip angle.
Thereby, the slip angle of the tire corresponding to the lateral force of the tire can be estimated with high accuracy.
(5) The tire force is the braking / driving force of the tire, and the slip degree is the tire slip rate.
Thereby, the slip degree of the tire corresponding to the braking / driving force of the tire can be estimated with high accuracy.
(6) Since the vehicle behavior that will occur due to the steering input can be predicted before the vehicle behavior occurs, more stable control can be realized. The logic is simple and only one map is required.

1,11,61,71 μ ₀ / μ ₁ multiplication unit, 2,12,62,72 tire characteristic estimating unit, 3,13,63,73 μ ₁ / μ ₀ multiplying unit, 23 road mu estimating unit, 42 tires Side slip angle estimation unit, 43 Tire model for road surface change

Claims (6)

First input means for setting a road surface friction coefficient between the tire and the road surface as a first input value;
Second input means for setting, as a second input value, either the tire force or the slip degree on the road surface of the road surface friction coefficient set by the first input means;
A tire model that models tire characteristics established by the correlation between the tire force obtained on the reference road surface of the reference road surface friction coefficient and the slip degree;
Based on the first input value input and set by the first input means and the second input value input and set by the second input means, the road surface of the road surface friction coefficient input and set by the first input means from the tire model. Output means for outputting either the tire force or the slip degree of
The tire model has the same reference road surface as long as the ratio of the tire force and slip degree on the road surface having a road surface friction coefficient different from the ratio of the tire force and slip degree on the reference road surface and the reference road surface friction coefficient is the same. The ratio of the tire force at the road surface and the tire force on the road surface having a road surface friction coefficient different from the reference road surface friction coefficient, or the slip degree on the reference road surface and the road surface coefficient of friction different from the reference road surface friction coefficient. The ratio of the slip degree has a characteristic indicating a ratio between a reference road friction coefficient and a road friction coefficient different from the reference road friction coefficient,
The output means includes
By multiplying the second input value set by the second input means by the value obtained by dividing the reference road friction coefficient by the first input value set by the first input means, the tire force or slip on the reference road surface is obtained. Get one of the degrees,
According to the tire model, obtaining either the tire force or the slip degree on the reference road surface corresponding to either the tire force or the slip degree on the reference road surface obtained by the multiplication,
The first input means is obtained by multiplying the other one of the obtained tire force or slip degree on the reference road surface by a value obtained by dividing the first input value set by the first input means by the reference road surface friction coefficient. A vehicle ground contact surface friction state estimation device characterized in that either the tire force or the slip degree on the road surface of the road surface friction coefficient input and set in step (2) is obtained.   2. The vehicle contact surface friction state estimation device according to claim 1, wherein the tire model is a two-dimensional map including continuous line segments each having a tire force and a slip degree obtained on the reference road surface as coordinate axes. .   The vehicle tire contact surface friction state estimation device according to claim 1, wherein the tire model is expressed mathematically by using a tire force and a slip degree obtained on the reference road surface as variables.   The vehicle tire contact surface friction state estimation device according to any one of claims 1 to 3, wherein the tire force is a tire lateral force, and the slip degree is a tire slip angle.   The vehicle tire contact surface friction state estimation device according to any one of claims 1 to 3, wherein the tire force is a braking / driving force of a tire, and the slip degree is a tire slip ratio. An input step for setting a road surface friction coefficient between the tire and the road surface as a first input value, and either a tire force or a slip degree on the road surface of the road surface friction coefficient as a second input value;
An output step of outputting either the tire force or the slip degree on the road surface of the road surface friction coefficient from the tire model based on the first input value and the second input value input and set in the input step. ,
The tire model is
This is a model of tire characteristics established by the correlation between the tire force obtained on the reference road surface of the reference road surface friction coefficient and the slip degree.
If the ratio of the tire force and the slip degree on the road surface of the road surface friction coefficient different from the ratio of the tire force and the slip degree on the reference road surface and the reference road surface friction coefficient is the same, the tire force on the reference road surface and The ratio of the road surface friction coefficient different from the reference road surface friction coefficient to the tire force on the road surface, or the ratio of the slip degree on the reference road surface to the slip degree on the road surface of the road surface friction coefficient different from the reference road surface friction coefficient. Has a characteristic indicating a ratio of a reference road friction coefficient and a road friction coefficient different from the reference road friction coefficient,
In the output step,
Either the tire force or the slip degree on the reference road surface is obtained by multiplying the second input value input and set in the input step by the value obtained by dividing the reference road friction coefficient by the first input value input and set in the input step. Get one,
According to the tire model, obtaining either the tire force or the slip degree on the reference road surface corresponding to either the tire force or the slip degree on the reference road surface obtained by the multiplication,
The obtained tire force or slip degree on the reference road surface is multiplied by a value obtained by dividing the first input value input and set in the input step by the reference road surface friction coefficient, and input and set in the input step. A vehicle ground contact surface friction state estimation method characterized by obtaining either the tire force or the slip degree on the road surface with a road surface friction coefficient.

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