JP2010195327A - Device and method for estimating tread friction state of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for estimating a road surface μ before the occurrence of slip. <P>SOLUTION: The device for estimating a tread friction state of a vehicle detects a resultant force composed of a braking force and a lateral force of a wheel, and a slippage of the wheel (steps S21 and S22); and calculates a road surface friction factor of a current road surface based on a distance obtained by projecting, in a three-dimensional space having the braking force, lateral force and slippage of the wheel as coordinate axes, the magnitude of a current tire force to a line extending from an origin where the braking force, lateral force and slippage are zero to the detected current slippage in the direction of the detected current tire force (steps S23 and S24). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for estimating a ground contact surface grip characteristic of a vehicle wheel.

  As a travel control device, there is a device that measures the rotational speed of driving wheels, estimates the road surface μ from the maximum value of the rotational angular acceleration, and performs optimal torque control so that slip does not occur on the driving wheels (for example, Patent Document 1). reference).

Japanese Examined Patent Publication No. 6-78736

However, in this apparatus, since the road surface μ is estimated from the rotational speed of the drive wheel, the road surface μ cannot be determined unless slip actually occurs in the drive wheel. This causes a loss of braking / driving force due to the slip, and may spin or drift out while the vehicle is turning.
An object of the present invention is to estimate the road surface μ of the traveling road surface before slip occurs.

In order to solve the above problems, the present invention calculates a road surface friction coefficient of a current road surface based on a current tire force, a current slip degree, and a tire characteristic correlation map.
The tire characteristic correlation map is a model of tire characteristics representing a three-dimensional curved surface established by the correlation between the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel obtained on the reference road surface of the reference road surface friction coefficient. The ratio of the resultant force between the braking / driving force and lateral force on the reference road surface and the slip ratio and the resultant force and the slip force on the road surface with a road surface friction coefficient different from the reference road friction coefficient If the ratio is the same, the ratio of the resultant force of braking / driving force and lateral force on the reference road surface to the resultant force of braking / driving force and lateral force on the road surface with a road surface friction coefficient different from the reference road friction coefficient, Alternatively, the ratio between the slip degree on the reference road surface and the slip degree on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient is the ratio between the reference road surface friction coefficient and the road surface friction coefficient different from the reference road surface friction coefficient. It has the characteristics shown.

  The present invention uses a tire characteristic correlation map having such characteristics to use the braking force, lateral force, and lateral force in a three-dimensional space with wheel braking / driving force, wheel lateral force, and wheel slip degree as coordinate axes. Distance obtained by projecting the current tire force magnitude on a straight line extending from the origin where the slip degree is zero to the current tire force direction detected in the detection step and to the current slip degree detected in the detection step Then, the road surface friction coefficient of the current road surface is calculated based on the ratio of the distance between the intersection point intersecting the tire characteristic correlation map by extending the straight line and the origin point.

  Here, in a three-dimensional space with the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes, the ratio of the resultant force of the braking / driving force and the lateral force on the reference road surface to the slip degree and the reference When the ratio of the resultant force of the braking / driving force and lateral force on the road surface with a road surface friction coefficient different from the road surface friction coefficient and the slip ratio is the same, the resultant force of the braking / driving force and lateral force on the reference road surface, The ratio of the braking / driving force and lateral 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 road surface friction coefficient different from the reference road surface friction coefficient A ratio obtained by projecting the magnitude of the current tire force on a straight line extending from the origin of the three-dimensional space to the detected current tire force direction and to the detected current slip degree; , Extending the straight line and intersecting with the tire characteristic correlation map And the ratio of the distance between the origin is consistent viewed geometrically.

  Therefore, the distance obtained by projecting the magnitude of the current tire force on the straight line extending from the origin of the three-dimensional space to the detected current slip direction in the direction of the detected current tire force, and the straight line extended. Thus, the road surface friction coefficient of the current road surface can be calculated from the ratio of the intersection between the tire characteristic correlation map and the distance between the origin and the reference road surface friction coefficient.

According to the present invention, the road surface friction coefficient of the current road surface can be calculated by detecting the direction and magnitude of the tire force of the wheel and the slip degree.
As a result, the road surface friction coefficient of the current road surface can be estimated before slip occurs.

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. It is a figure used in order to explain a premise technique, and is a figure showing a procedure which calculates road surface μ based on a ratio of line lengths obtained from braking / driving force Fx and slip rate λ. 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, ratio (Fx / λ) of braking / driving force Fx and slip ratio λ of the arbitrary point of the tire characteristic curve (Fx-λ characteristic curve) and the 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. 10 is a characteristic diagram showing a characteristic curve (grip characteristic curve) obtained from the plotted points in FIG. 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, ratio of the lateral forces Fy which are obtained about the tire characteristic curve where road surface μ differs, ratio of slip angle βt or ratio of line length and road surface μ It is a characteristic view which shows that ratio becomes equal. It is a figure used in order to explain the technology used as a premise, and is a figure which shows the procedure which calculates road surface (micro | micron | mu) based on ratio of the line length obtained from lateral force Fy and slip angle (beta) t. It is the figure used in order to explain the technology which is the premise, the ratio of tire force F which is obtained about the tire characteristic curve where road surface μ differs, ratio of slip degree S or 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 a premise technique, and is a ratio (Fy / βt) of lateral force Fy and slip angle βt of an arbitrary point of a 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. It is the figure used in order to explain the premise technology, the characteristic which expressed the friction circle on the orthogonal coordinate plane which expresses braking / driving force (front / rear force) Fx on the 1st axis and lateral force Fy on the 2nd axis FIG. FIG. 5 is a diagram used to explain the procedure for displaying the relationship between braking / driving force Fx and slip rate λ in a three-dimensional coordinate system in the premise technology, and shows the relationship between braking / driving force Fx and slip rate λ FIG. It is a figure used in order to demonstrate the procedure which displays the relationship between lateral force Fy and slip angle (beta) t in a three-dimensional coordinate system in a premise technique, and is a characteristic view which shows the relationship between lateral force Fy and slip angle (beta) t. is there. FIG. 5 is a diagram used to explain the procedure for displaying the relationship between wheel force (braking / driving force Fx, lateral force Fy) and slip degree (slip rate λ, slip angle βt) in a three-dimensional coordinate system in the underlying technology. FIG. 5 is a characteristic diagram showing the relationship between wheel force (braking / driving force Fx, lateral force Fy) and slip degree (slip rate λ, slip angle βt) on a three-dimensional curved surface. It is the figure used in order to demonstrate the technique used as a premise. (A) is a characteristic diagram showing an intersection line between a three-dimensional curved surface representing the relationship between the slip degree and the wheel force, a vector of the resultant force F of the braking / driving force Fx and the lateral force Fy, and a plane including the Z axis. . (B) is a characteristic diagram showing a tire characteristic curve (FZ characteristic curve) showing a relationship between the resultant force F and the slip degree Z generated due to the resultant force F. FIG. It is the figure used in order to demonstrate the technique used as a premise. (A) is a characteristic view showing a difference in size of a tire friction circle in a three-dimensional coordinate system. (B) is a characteristic diagram for showing a change in the tire characteristic curve (FZ characteristic curve) due to the difference in the magnitude of the maximum frictional force that determines the size of the friction circle. It is the figure used in order to demonstrate the technique used as a premise. (A) shows that the slope at the intersection of the tire characteristic curve and a straight line passing through the origin 0 (a point where both the slip degree and the wheel force are 0) has a constant value regardless of the magnitude of the maximum frictional force. It is a characteristic view of the three-dimensional coordinate system shown. (B) is a characteristic diagram of a two-dimensional coordinate system showing that the slope at the intersection of the tire characteristic curve and a straight line passing through the origin 0 is a constant value regardless of the magnitude of the maximum frictional force. It is the figure used in order to explain the technology which becomes the premise, for each tire characteristic curve (FZ characteristic curve) where road surface μ differs, ratio of resultant force F or ratio of slip degree Z and the road surface μ It is a characteristic view which shows that ratio becomes equal. It is a figure used in order to explain the technology used as a premise, and is a figure which shows the procedure which calculates road surface (micro | micron | mu) based on ratio of the line length obtained from resultant force F and slip degree S. FIG. It is the figure used in order to explain the technology used as a premise, the ratio (F / Z) of the resultant force F and the slip degree Z of the arbitrary point of a tire characteristic curve (FZ characteristic curve), and the arbitrary point FIG. 5 is a characteristic diagram showing a relationship (grip characteristic curve) with a tangential slope (μ gradient) of a tire characteristic curve. It is a figure showing a schematic structure of a vehicle of an embodiment. It is a block diagram which shows the structure of a vehicle running state estimation apparatus. It is a block diagram which shows the structure of a vehicle body slip angle estimation part. It is the figure used in order to explain the field force which acts on the body during turning. It is the figure used in order to explain the field force which acts on the body during turning. It is the characteristic view used in order to demonstrate the control map for setting a compensation gain. It is the figure used in order to explain the linear two-wheel model of vehicles. It is a figure which shows 3D characteristic map. It is the figure used in order to demonstrate the procedure which calculates road surface micro | micron | mu with reference to a 3D characteristic map. It is the flowchart used for description of operation | movement.

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. And if the friction state of a tire is in a stable state, for example, it can be estimated that the tire is at a level at which its 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) at which the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same. Become.
The ratio of the braking / driving force Fx obtained between the different tire characteristic curves with respect to the values (λ, Fx) at which the ratio (Fx / λ) of the braking / driving force Fx and the slip ratio λ is the same in each tire characteristic curve. Alternatively, the ratio between the slip ratios λ is equal to the ratio of the road surface μ.

The relationship between the ratio of braking / driving forces Fx or the ratio of slip ratios λ and the ratio of the road surface μ will be described with reference to FIG. 5 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, as an example, a calculation procedure for calculating the road surface μ of the traveling road surface based on the line length. Here, based on the longitudinal force Fxb and slip ratio λb obtained in some road surface B, with reference to the tire characteristic curve of the road surface mu values mu _A known road A, road mu values mu of a road surface B An example of calculating _B will be shown.
As shown in FIG. 6, first, in step S1 and step S2, braking / driving force Fxb and slip ratio λb on a certain road surface B are detected. Next, in step S3 the origin (0, 0) and the measured point of the tire characteristic curve of the road surface A of road surface mu values mu _A ([lambda] b, Fxb) and the straight line is the value of the point of intersection with the tire characteristic curve passing through ([lambda] a , Fxa).

Subsequently, in step S4, a road surface μ value μ _B of a certain traveling road surface B is calculated (estimated). That is, a straight line length b1 (= √ (λb ² + Fxb ² )) connecting the actual measurement point (λb, Fxb) and the origin of the tire characteristic curve on the road surface A is obtained. Further, the straight line length a1 (= √ (λa ² + Fxa ² )) connecting the intersection value (λa, Fxa) of the tire characteristic curve on the road surface A specified in step S3 and the origin of the tire characteristic curve is obtained. . Further, the ratio (b1 / a1) between the line length b1 and the line length a1 is calculated. Then, its calculated ratio (b2 / b1), multiplying the road surface mu values mu _A of road surface A, to obtain the multiplied value as the road surface mu value mu _B of road surface _{B (μ B = μ A ·} b1 / a1).

  FIG. 7 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. 7, the vibration waveform indicates actual 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. 7, 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. 8 shows the relationship between the braking / driving force Fx and the slip ratio λ obtained on the road surfaces having different road surfaces μ for the studless tire. In FIG. 8, 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. 8, 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. 9 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 that arbitrary point (∂ braking / driving force / ∂ slip ratio). ). In FIG. 9, the values obtained for each road surface μ (for example, μ = 0.2, 0.5, 1.0) are plotted. As shown in FIG. 9, 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. 10 shows a characteristic curve obtained based on the plotted points in FIG. As shown in FIG. 10, in this characteristic curve, the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio 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. As described above, the characteristic curve shown in FIG. 10 is a tire characteristic curve as in FIG. Differentiating from FIG. 1, the characteristic curve of FIG. 10 can also be called a grip characteristic curve, for example.

  As shown in FIG. 10, 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 has 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. 10, in the region (large ratio region) where the ratio (Fx / λ) between the braking / driving force Fx and the slip ratio λ is large, 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 to the tire characteristic curve that can be obtained in this way (μ slope, hereinafter also referred to as Cp value) is a grip characteristic parameter, a variable that represents the grip state of the tire, or saturation of the force that the tire can exert in the lateral direction. It becomes a parameter indicating the state.
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.

Thus, it can be known from the slope of the tangent to the tire characteristic curve that the grip force of the tire is in the limit region. Thereby, for example, even when the wheel grip force is in the limit region, it is possible to appropriately estimate the margin of the tire grip force with respect to the friction limit.
A grip characteristic curve (FIG. 10) 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. 10). 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.

(2) Relationship between wheel slip angle and wheel lateral force FIG. 11 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. 11, 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. 11, arbitrary straight lines a, b, c,... Passing through the origin of the tire characteristic curve are drawn. Then, the tangent slope of the tire characteristic curve can be obtained at the intersections (intersections indicated by circles in FIG. 11) 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. 11, if the tire characteristic curve is at a position x0 that is 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. 12 shows tire characteristic curves and friction circles of various road surfaces μ. FIG. 12A shows tire characteristic curves of various road surfaces μ. 12 (b) to 12 (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. 12 (a), the tire characteristic curve shows the same tendency qualitatively at each road surface μ. Further, as shown in FIGS. 12B to 12D, 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. 12, 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 according to the value of the road surface friction coefficient. it can.

  FIG. 13 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. 13, as in FIG. 11, 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. 14, attention is paid to the straight line c shown in FIG. As shown in FIG. 14, 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 (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. .
Then, 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.

The relationship between the ratio of the lateral forces Fy or the ratio of the slip angles βt and the ratio of the road surface μ will be described with reference to FIG. 15 for each tire characteristic curve having a different road surface μ. FIG. 15 shows tire characteristic curves obtained 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. 15, the values (βt, Fy) in which the ratio (Fy / βt) between the lateral force Fy and the slip angle βt are the same (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. 16 shows, as an example, a calculation procedure for calculating the road surface μ of the traveling road surface based on the line length. Here, based on the lateral force Fyb and the slip angle βtb obtained on a certain road surface B, a road surface μ value μ _B of a certain road surface B is referred to with reference to a known tire characteristic curve of the road surface μ value μ _A of the road surface A. An example of calculating is shown.
As shown in FIG. 16, first, in step S11 and step S12, the lateral force Fyb and the slip angle βtb on a certain road surface B are detected. Then In step S13, the origin (0, 0) and the measured point of the tire characteristic curve of the road surface A of road surface mu values μ _A (βtb, Fyb) and the straight line is the value of the point of intersection with the tire characteristic curve passing through (Betata , Fya).

Subsequently, in step S14, a road surface μ value μ _B of a certain traveling road surface B is calculated (estimated). That is, a straight line length b1 (= √ (βtb ² + Fyb ² )) connecting the actual measurement point (βtb, Fyb) and the origin of the tire characteristic curve on the road surface A is obtained. Further, a straight line length a1 (= √ (βta ² + Fya ² )) connecting the intersection value (βta, Fya) of the tire characteristic curve on the road surface A specified in step S13 and the origin of the tire characteristic curve is obtained. . Further, the ratio (b1 / a1) between the line length b1 and the line length a1 is calculated. Then, its calculated ratio (b2 / b1), multiplying the road surface mu values mu _A of road surface A, to obtain the multiplied value as the road surface mu value mu _B of road surface _{B (μ B = μ A ·} b1 / a1).

In FIG. 17, the horizontal axis represents the slip degree S, and the vertical axis represents the tire force F.
Here, the braking / driving force Fx and the lateral force Fy can be considered as a conceptual tire force (wheel force) F including these values, and the slip ratio λ and the slip angle βt are conceptualized as a slip degree S of the concept including these values. it can. Further, for example, the resultant force of the braking / driving force Fx and the lateral force Fy can be considered as the tire force F.

Thus, since the braking / driving force Fx and the lateral force Fy can be considered as the tire force F, and the slip ratio λ and the slip angle βt can be considered as the slip degree S, the tire force F and the slip degree S are also shown in FIGS. The relationship as shown in FIG. 15 can be obtained.
Therefore, as shown in FIG. 17, for each tire characteristic curve having a different road surface μ, the ratio of tire forces F (a2 / b2), the ratio of slip degrees S (a3 / b3), or the ratio of line lengths (a1 / and b1), the ratio of the road surface μ (μ _a / μ _B) and are equal.

  FIG. 18 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 tangential slope (∂Fy / ∂βt) of the tire characteristic curve at the arbitrary point. Indicates. As shown in FIG. 18, the ratio (Fy / βt) between the lateral force Fy and the slip angle βt and the tangent line of the tire characteristic curve at any road surface μ (for example, μ = 0.2, 0.5, 1.0). 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, the characteristic curve shown in FIG. 18 is a tire characteristic curve like FIG. Differentiating from FIG. 11, the characteristic curve of FIG. 18 can also be called a grip characteristic curve, for example.

  As shown in FIG. 18, in the region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is small (small ratio region), the tangent slope of the tire characteristic curve becomes 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. 18, 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 tangential slope (μ slope) of the tire characteristic curve that can be obtained in this way is a grip characteristic parameter, a variable that represents the grip state of the tire, or a parameter that represents a saturated state of 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. Thus, it can be known from the slope of the tangent to the tire characteristic curve that the grip force of the tire is in the limit region. Thereby, for example, even when the wheel grip force is in the limit region, it is possible to appropriately estimate the margin of the tire grip force with respect to the friction limit.

A grip characteristic curve (FIG. 18) can be obtained by performing partial differential calculation on the tire characteristic curve (FIG. 11) 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. 18). 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.

(3) Relationship between the tire friction circle and the wheel force (tire force) of the wheel FIG. 19 shows the braking / driving force Fx based on the longitudinal grip force as the X axis and the lateral force Fy based on the lateral grip force as the Y axis. The tire friction circle is expressed on the orthogonal coordinate plane expressed above.
Here, the tire friction circle indicates a friction limit at which the tire can maintain a friction state on the contact surface.
That is, if the value of the resultant force of the braking / driving power Fx, the lateral force Fy, or the braking / driving power Fx and the lateral force Fy is within the tire friction circle, the friction limit is not reached. The state where the friction state is maintained is shown.

Moreover, when the value corresponds with a tire friction circle, the state which is exhibiting the maximum frictional force is shown. That is, the size of the tire friction circle is determined by the maximum value of the frictional force between the tire and the contact surface. That is, by plotting the maximum value of the resultant force between the braking / driving power Fx and the lateral force Fy in accordance with the direction of the resultant force, an elliptical tire friction circle can be drawn.
Further, when the external force applied to the tire on the tire contact surface is larger than the tire friction circle, the tire is not in a frictional state with the contact surface, that is, the relative displacement between the tire and the ground increases, so-called Indicates a slip state. This means that the relationship between the tire friction circle and the grip force in the front-rear direction and the lateral direction cannot exhibit the maximum grip force in the front-rear direction and the lateral direction simultaneously.

Based on the relationship between the tire friction circle and the wheel force, the maximum frictional force that can be exerted by the tire (friction limit) increases as the wheel force approaches the radius (outer periphery) of the tire friction circle. It can be identified when approaching. That is, the margin of the grip force of the tire with respect to the friction limit can be determined.
In the following description, the braking / driving power Fx, the lateral force Fy, and the resultant force of the braking / driving power Fx and the lateral force Fy are collectively referred to as wheel force or tire force.

(4) Relationship between wheel force, slip degree, and tire friction circle using three-dimensional coordinates Relationship between tire friction circle and wheel force as described above, and further, wheel force and wheel slip degree (slip ratio λ, Based on the relationship with the slip angle βt), the relationship between the wheel force of the wheel, the degree of slip, and the tire friction circle can be obtained using three-dimensional coordinates. A procedure for obtaining a characteristic curve of three-dimensional coordinates indicating the relationship will be described below.

(4-1) Relationship between Wheel Force and Slip Degree of Wheel Using Three-dimensional Coordinate FIG. 20 converts the relationship (two-dimensional coordinate system) between braking / driving force Fx and slip ratio λ into a three-dimensional coordinate system. Show the procedure. As shown in FIG. 20A (corresponding to the tire characteristic curve (Fx-λ characteristic curve) in FIG. 1), the slip ratio λ at which the braking / driving force Fx has the maximum value is defined as λpeak. That is, the braking / driving force Fx increases as the slip ratio λ increases, but when the slip ratio λ increases to some extent, the braking / driving force Fx saturates and thereafter decreases. A point (saturation point) at which the braking / driving force Fx is saturated is defined as λpeak.

  Next, as shown in FIG. 20B, after converting the axis of the slip ratio λ to a dimensionless value of λ / λpeak by λpeak, the value of λ / λpeak is changed to the origin (braking / braking) The axis of force Fx is moved to a value where λ / λpeak is 1. Then, as shown in FIG. 20C, the two-dimensional coordinate system of FIG. 20B is rotated by 90 degrees. Next, as shown in FIG. 20 (d), a relationship line (characteristic curve) between the braking / driving force Fx and λ / λpeak is represented on one quadrant of the three-dimensional coordinate system. In FIG. 20D, the axis of λ / λpeak is the Z axis. Z is the slip degree (slip degree S).

  FIG. 21 shows a procedure for converting the relationship (two-dimensional coordinate system) between the lateral force Fy and the slip angle βt into a three-dimensional coordinate system. The relationship between the lateral force Fy and the slip angle βt is also converted into a three-dimensional coordinate system in the same manner as the relationship between the braking / driving force Fx and the slip rate λ. That is, as shown in FIG. 21 (a) (corresponding to the tire characteristic curve (Fy-βt characteristic curve in FIG. 11)), the slip angle βt at which the lateral force Fy becomes the maximum value is defined as βtpeak. That is, the lateral force Fy increases as the slip angle βt increases. However, when the slip angle βt increases to some extent, the lateral force Fy saturates and thereafter decreases. A point (saturation point) of the slip angle βt at which the lateral force Fy is saturated is defined as βtpeak.

  Next, as shown in FIG. 21B, after converting the axis of the slip angle βt to a dimensionless value of βt / βtpeak by βtpeak, the value of βt / βtpeak is changed to the origin (lateral force) The axis of Fy is moved to a value of βt / βtpeak of 1). Then, as shown in FIG. 21 (c), the two-dimensional coordinate system of FIG. 21 (b) is rotated by 90 degrees. Next, as shown in FIG. 21 (d), the relationship line (characteristic curve) between the lateral force Fy and βt / βtpeak is expressed in one quadrant of the three-dimensional coordinate system. In FIG. 21D, the axis of βt / βtpeak is the Z axis.

  FIG. 22 shows the relationship between the braking / driving force Fx and λ / λpeak in FIG. 20D (characteristic curve, Fx-Z plane) and the lateral force Fy and βt / βtpeak in FIG. A three-dimensional curved surface obtained by interpolating between the relationship lines (characteristic curve, Fy-Z plane) is shown. The relationship line (characteristic curve) a between the braking / driving force Fx and λ / λpeak in FIG. 20D and the relationship line (characteristic curve) b between the lateral force Fy and βt / βtpeak in FIG. The three-dimensional curved surface of FIG. 22 is obtained by complementing the gap with each value on the Z axis by an ellipse, that is, equivalent to a tire friction circle. The three-dimensional curved surface of FIG. 22 forms a curved surface that exists between the Fx-Z plane including the Fx axis and the Z axis and the Fy-Z plane including the Fy axis and the Z axis.

In FIG. 22, the slip ratio λ and the slip angle βt, which are different units, are set to dimensionless values of λ / λpeak and βt / βtpeak, respectively, so that the slip ratio λ and the slip angle βt are expressed on the same coordinate axis Z-axis. is doing. As described above, the concept that collectively refers to the slip ratio λ and the slip angle βt is the slip degree (Z). For this reason, the Z-axis in FIG. 22 is an axis indicating the slip degree (λ / λpeak, βt / βtpeak).
Therefore, the three-dimensional curved surface represents the correlation between the slip degree and the wheel force (tire force). The three-dimensional curved surface is composed of a set of relational lines between the resultant force F of the braking / driving force Fx and the lateral force Fy and the slip degree Z generated due to the resultant force F.

  Here, the resultant force F corresponds to a force generated in the tire oblique direction using the braking / driving force Fx and the lateral force Fy as components. Therefore, if the braking / driving force Fx is zero, the resultant force F is the lateral force Fy itself, and if the lateral force Fy is zero, the resultant force F is the braking / driving force Fx itself. The slip degree Z caused by the resultant force F is a concept of a value obtained by combining the slip ratio λ and the slip angle βt, or a value having the slip ratio λ and the slip angle βt as components. Therefore, if the slip ratio λ is zero, the slip degree Z is the slick angle βt itself, and if the slip angle βt is zero, the slip degree Z is the slip ratio λ itself.

In FIG. 22, the three-dimensional curved surface representing the relationship between the slip degree and the wheel force is displayed only for a quarter of a quarter (quarter quadrant). However, in practice, a three-dimensional curved surface that represents the correlation between the slip degree and the wheel force exists for the entire circumference, and has a dome shape or a hemispherical shape.
FIG. 23 shows that FIG. 22 is composed of a set of relation lines (two-dimensional characteristic curves) between the resultant force F of the braking / driving force Fx and the lateral force Fy and the slip degree Z generated due to the resultant force F. It is a figure explaining this. The magnitude / direction of the resultant force F in the three-dimensional coordinate system is infinite due to different combinations of the scalar amount / direction of the braking / driving force Fx and the scalar amount / direction of the lateral force Fy. In this embodiment, the wheel force (F) may be in any direction 360 degrees around the Z axis, and corresponds to all directions in the illustrated embodiment. Thereby, in the three-dimensional coordinate system shown in FIG. 23A, the relationship between the resultant force F and the slip degree Z generated due to the resultant force F is expressed in a plane including the Z axis and the resultant force F. It can be said that it consists of a set of dimensional characteristics. That is, as shown in FIG. 23 (b), the relationship between the resultant force F and the slip degree Z generated due to the resultant force F can be obtained as a two-dimensional characteristic curve. That is, there are an infinite number of planes including the Z axis and the resultant force F around the Z axis according to the direction of the resultant force, and these infinite planes form an asheaf of planes around the Z axis. is doing. A two-dimensional characteristic curve as shown in FIG. 23B exists on each of the planes.

  The margin to the friction limit for the resultant force F will be described on the three-dimensional coordinate system with reference to FIG. As an intersection line between the three-dimensional curved surface representing the relationship between the slip degree and the wheel force (Fx, Fy, F) and the plane including the vector of the resultant force F and the Z axis shown in FIG. The tire characteristic curve shown in b) can be obtained. The slope of the tangent line of the tire characteristic curve of FIG. 23 (b) obtained in this way indicates the margin to the tire friction limit. That is, when the slope of the tangent line of the tire characteristic curve in FIG. 23B approaches zero from a positive value, the tire approaches the friction limit. Therefore, if the inclination of the tangent line of the tire characteristic curve can be detected, it is possible to know the margin to the friction limit in the state before reaching the friction limit. Further, when the tangent slope of the tire characteristic curve in FIG. 23B becomes a negative value, the frictional force is saturated, that is, a so-called slip state. In this respect, if the slope of the tangent line of the tire characteristic curve can be detected, it can be said that the margin to the friction limit (friction force is saturated) can be known before the slip state is reached.

  FIG. 24 shows the relationship between the resultant force F when the size of the tire friction circle changes and the slip degree Z generated due to the resultant force F. As described above, the size of the tire friction circle is determined by the maximum value of the frictional force between the tire and the ground contact surface (hereinafter referred to as the maximum frictional force). That is, when the maximum value of the frictional force between the tire and the contact surface is reduced, the tire friction circle is also reduced. For this reason, the tire characteristic curve (tire friction circle) changes depending on the magnitude of the maximum frictional force, as shown in FIGS. 24 (a) and 24 (b), due to actual changes in the road surface μ. To come.

  FIG. 25 shows a tire characteristic curve (FZ characteristic curve) having different maximum frictional force, that is, road surface μ, and a straight line (a straight line indicated by a one-dot chain line) passing through the origin O (a point where both the slip degree and the wheel force are zero). Shows the relationship. As shown in FIGS. 25 (a) and 25 (b), the tire characteristic curves with different road surface μ have the same tangential slope (μ gradient) at the intersection with the straight line. That is, if the ratio (F / Z) between the resultant force F and the slip degree Z is the same for tire characteristic curves having different maximum frictional forces, the tangential slopes are the same.

Then, with respect to the values (Z, F) at which the ratio (F / Z) of the resultant force F and the slip degree Z is the same in each tire characteristic curve (FZ characteristic curve), the resultant forces F obtained with different tire characteristic curves Or the ratio between the slip degrees Z is equal to the ratio of the road surface μ. That is, if the ratio between the resultant forces F or the ratio between the slip degrees Z can be known, the ratio of the road surface μ can be known.
26, the relationship between the ratio of the resultant force F or the ratio of the slip degree Z and the ratio of the road surface μ will be described for each tire characteristic curve having a different road surface μ.

As shown in FIG. 26 (b) in which the relationship (two-dimensional tire characteristic curve) between a certain resultant force F and slip degree Z in FIG. 26 (a) is extracted, the ratio (F / Z) of the resultant force F and slip degree Z is shown. ) Are the same values (Z, F) (values indicated by ■ and ● in the figure), respectively, and the ratio (a2 / b2) between the lateral force a2 and the lateral force b2 and the road surface A It 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 (μ a / μ B)} .

Similarly, the ratio (a3 / b3) of the slip degree a3 and the slip degree b3 obtained at values (Z, F) at which the ratio (F / Z) of the resultant force F and the slip degree Z is the same, and the road surface becomes the same value as the ratio of the road surface mu values mu _B of a of road surface mu values mu _a and the road surface _{B (μ a / μ B)} .
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 (F / Z) between the resultant force F and the slip degree Z (F, Z). and the origin (0, 0) ratio and the a line length a1 and line length b1 obtained by connecting each (a1 / b1), a road surface a of road surface mu values mu _a and the road surface B road mu values of mu _B The ratio (μ _A / μ _B ) is the same value. 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 resultant force F and the ratio of a3 and b3 for the slip degree Z 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 ) and the same value. 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. 27 shows a calculation procedure for calculating the road surface μ of the traveling road surface based on the line length as an example. Here, based on the resultant force Fyb and slip degree Zb obtained on a certain road surface B, a road surface μ value μ _B of a certain road surface B is obtained by referring to a tire characteristic curve of a road surface μ value μ _A of a known road surface A. An example of calculation is shown.
As shown in FIG. 27, first, in step S21 and step S22, the resultant force Fb and slip degree Zb on a certain road surface B are detected. Subsequently, in step S23, the origin of the tire characteristic curve of the road surface A of road surface mu values mu _A (0,0) and the measured point (Zb, Fb) and a straight line, the value of the point of intersection with the tire characteristic curve passing through (Za , Fa).

Subsequently, in step S24, a road surface μ value μ _B of a certain traveling road surface _B is calculated (estimated). That is, a straight line length b1 (= √ (Zb ² + Fb ² )) connecting the actual measurement point (Zb, Fb) and the origin of the tire characteristic curve of the road surface A is obtained. Further, the straight line length a1 (= √ (Za ² + Fa ² )) connecting the intersection value (Za, Fa) of the tire characteristic curve on the road surface A specified in step S23 and the origin of the tire characteristic curve is obtained. . Further, the ratio (b1 / a1) between the line length b1 and the line length a1 is calculated. Then, its calculated ratio (b1 / a1), multiplying the road surface mu values mu _A of road surface A, to obtain the multiplied value as the road surface mu value mu _B of road surface _{B (μ B = μ A ·} b1 / a1).

(4-2) Relationship between wheel force and grip state (μ gradient) using three-dimensional coordinates Ratio of resultant force F to slip degree (F / Z) and slope of tangent to tire characteristic curve (μ gradient) ) With the maximum frictional force.
FIG. 28 shows the relationship between the ratio (F / Z) between the resultant force F and the slip degree Z and the tangent slope of the tire characteristic curve. As shown in FIG. 28, by arranging the relationship between the ratio (F / Z) of the resultant force F and the slip degree Z and the slope of the tangent to the tire characteristic curve, one characteristic (two-dimensional) that does not depend on the maximum frictional force is obtained. Characteristic curve). Therefore, characteristic data as shown in FIG. 28 is prepared in advance. For example, it is prepared as a characteristic map. If the resultant force F and the slip degree Z are known, the characteristic data can be used to know the value of the tangent slope of the tire characteristic curve, and the margin with respect to the friction limit can be determined. That is, the margin with respect to the friction limit can be determined without obtaining information on the maximum friction force (without estimating the maximum friction force).
As described above, the relationship between the wheel force of the wheel, the slip degree, and the tire friction circle can be obtained as the characteristics of the three-dimensional coordinate system. Furthermore, the relationship between the ratio (F / Z) between the resultant force F and the slip degree Z and the slope of the tangent to the tire characteristic curve (μ gradient) can be obtained as a characteristic of the two-dimensional coordinate system (μ gradient characteristic).

(Embodiment)
Next, an embodiment realized by adopting the above technique will be described.
(Constitution)
The present embodiment is a vehicle to which the present invention is applied. FIG. 29 shows a schematic configuration of the vehicle. As shown in FIG. 29, the vehicle includes a steering angle sensor 1, a yaw rate sensor 2, a lateral acceleration sensor 3, a longitudinal acceleration sensor 4, a wheel speed sensor 5, an EPS ECU (Electric Power Steering Electronic Control Unit) 6, and an EPS (Electric Power Steering). A motor 7 and a vehicle running state estimation device 8 are provided. Further, the vehicle has braking / driving motors 21 _{FL to} 21 _RR and braking / driving motor ECUs (Electronic Control Units) 22 directly connected to the wheels 11 _{FL to} 11 _RR .

The steering angle sensor 1 detects the rotation angle of the steering shaft 10 that rotates integrally with the steering wheel 9. The steering angle sensor 1 outputs the detection result (steering angle) to the vehicle running state estimation device 8. The yaw rate sensor 2 detects the yaw rate of the vehicle. The yaw rate sensor 2 outputs the detection result to the vehicle running state estimation device 8. The lateral acceleration sensor 3 detects the lateral acceleration of the vehicle. The lateral acceleration sensor 3 outputs the detection result to the vehicle running state estimation device 8. The longitudinal acceleration sensor 4 detects the longitudinal acceleration of the vehicle. The longitudinal acceleration sensor 4 outputs the detection result to the vehicle running state estimation device 8. The wheel speed sensor 5 detects wheel speeds of the wheels 11 _{FL to} 11 _RR provided on the vehicle body. The wheel speed sensor 5 outputs the detection result to the vehicle running state estimation device 8.

  The EPS ECU 6 outputs a steering assist command to the EPS motor 7 based on the steering angle detected by the steering angle sensor 1. The steering assist command here is a command signal for performing steering force assist. Further, the EPS ECU 6 outputs a steering assist command to the EPS motor 7 based on the command value (unstable behavior suppression assist command) output by the vehicle running state estimation device 8. The steering assist command here is a command signal for suppressing the unstable behavior of the vehicle.

The EPS motor 7 applies rotational torque to the steering shaft 10 based on a steering assist command output from the EPS ECU 6. Thereby, the EPS motor 7 steers the left and right front wheels 11 _FL and 11 _FR via the rack and pinion mechanism (pinion 12 and rack 13) connected to the steering shaft 10, the tie rod 14 and the knuckle arm. Assist.
The braking / driving motor ECU 22 controls the braking / driving motors 21 _{FL to} 21 _RR based on driver inputs from the brake pedal 15 and the accelerator pedal 16 and information from the vehicle running state estimation device 8.

  The vehicle travel state estimation device 8 estimates the travel state of the vehicle based on the detection results of the steering angle sensor 1, the yaw rate sensor 2, the lateral acceleration sensor 3, the longitudinal acceleration sensor 4, and the wheel speed sensor 5. The vehicle running state estimation device 8 outputs a command value (unstable behavior suppression assist command) to the EPS ECU 6 and the braking / driving motor ECU 22 based on the estimation result. The command value here is a command signal for controlling the EPS motor 7 and the braking / driving force so as to suppress the unstable behavior of the vehicle.

FIG. 30 shows the configuration of the vehicle running state estimation device 8. As shown in FIG. 30, the vehicle running state estimation device 8 includes a vehicle body speed calculation unit 41, a vehicle body slip angle estimation unit 42, a tire slip angle calculation unit 43, a slip ratio calculation unit 44, and a road surface μ estimated value calculation unit 45. . The vehicle also has a tire force sensor 46.
The vehicle body speed calculation unit 41 estimates the vehicle body speed based on the wheel speed detected by the wheel speed sensor 5 and the longitudinal acceleration detected by the longitudinal acceleration sensor 4. Specifically, the vehicle body speed calculation unit 41 calculates the average value of the wheel speeds of the driven wheels 11 _RL and 11 _RR or the average value of the wheel speeds of the wheels 11 _{FL to} 11 _RR , and uses the calculated value as the vehicle body. This is the basic value of speed. The vehicle body speed calculation unit 41 corrects the basic value by the longitudinal acceleration. Specifically, correction is made from the basic value so as to eliminate the influence of errors caused by tire slipping during sudden acceleration and tire lock during sudden braking. The vehicle body speed calculation unit 41 uses the corrected value as the estimation result of the vehicle body speed. The vehicle body speed calculation unit 41 outputs the estimation result to the vehicle body slip angle estimation unit 42.

The vehicle body slip angle estimation unit 42 includes a steering angle detected by the steering angle sensor 1, a yaw rate detected by the yaw rate sensor 2, a lateral acceleration detected by the lateral acceleration sensor 3, a longitudinal acceleration detected by the longitudinal acceleration sensor 4, and a vehicle body speed calculation unit. Based on the vehicle body speed calculated by 41, the side slip angle (slip angle) of the vehicle is estimated.
FIG. 31 shows a configuration example of the vehicle body slip angle estimation unit 42. As shown in FIG. 31, the vehicle body slip angle estimation unit 42 includes a linear two-input observer 51 that estimates a vehicle state quantity (a vehicle side slip angle β, a slip angle β). As a result, the vehicle body slip angle estimation unit 42 estimates the side slip angle (slip angle) β of the vehicle. Here, a linear two-input observer 51 is constructed based on a two-wheel model of the vehicle. The two-wheel model of the vehicle can be expressed by the following equation (1) from the balance between the lateral force and moment of the vehicle.

  Here, A, B, C, and D are matrices determined by the linear two-wheel model of the vehicle. When the tire rudder angle is input u, and the yaw rate and lateral acceleration are output y, the state equation (output equation) of the equation (1) is as shown in the following equation (2).

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. G _y is the lateral acceleration. a ₁₁ , a ₁₂ , b ₁ are the elements of the matrices A and B.

Based on this state equation, the yaw rate and the lateral acceleration are input, and a linear two-input observer 51 is created as the observer gain K1. Here, the observer gain K1 is a value set so as to be less susceptible to modeling errors and perform stable estimation.
The linear two-input observer 51 includes a β estimation compensator 53 that corrects the input of the integrator 52. Thereby, the linear two-input observer 51 can ensure estimation accuracy even in the limit region. In other words, by including the β estimation compensator 53, not only in the road surface condition assumed at the time of designing the two-wheel model of the vehicle and in the linear region where the tire side slip angle does not become a non-linear characteristic, but also when the road surface μ changes or when the vehicle travels marginally. Even if it exists, the side slip angle β can be estimated with high accuracy.

FIG. 32 shows a turning vehicle running at a vehicle body side slip angle β. As shown in FIG. 32, the field force acting on the vehicle body, that is, the centrifugal force acting outward from the turning center is also generated in a direction shifted by the side slip angle β from the vehicle width direction. Therefore, the β estimation compensator 53 calculates a field force deviation β ₂ according to the following equation (3). This deviation β ₂ becomes a reference value (target value) G for correcting the vehicle slip angle β estimated by the linear two-input observer 51.

Here, G _x is the longitudinal acceleration. Also, as shown in FIG. 33, force balance due to speed change is also taken into consideration. Thereby, when only the thing by turning is extracted, the said (3) Formula can be represented as following (4) Formula.

Then, the β estimation compensator 53 subtracts the target value β ₂ from the sideslip angle β estimated by the linear two-input observer 51. Further, the β estimation compensator 53 multiplies the subtraction result by the compensation gain K2 set by the control map of FIG. Then, the β estimation compensator 53 uses the multiplication result as an input of the integrator 52.
In the control map of FIG. 34, when the absolute value (| G _y |) of the lateral acceleration G _y of the vehicle is equal to or smaller than the first threshold value, the compensation gain K2 is zero. Further, if the absolute value of lateral acceleration G _y of the vehicle is of the second or more threshold greater than the first threshold value, the compensation gain K2 is relatively large constant value. Further, when the absolute value of lateral acceleration G _y of the vehicle is between the first threshold and the second threshold value, the absolute value becomes larger in the lateral acceleration G _y, compensation gain K2 is increased.

Thus, in the control map of FIG. 34, when the absolute value of lateral acceleration G _y has a value close to zero or less the first threshold value, and the compensation gain K2 is zero. Thereby, since it is not necessary to correct | amend under the condition where the turning G does not generate | occur | produce like the time of straight running, it is trying not to correct by mistake. Further, in the control map of FIG. 34, when the absolute value of lateral acceleration G _y is greater than the first threshold value increases (e.g., becomes greater than 0.1 G), proportional to the absolute value of lateral acceleration G _y and gradually increases the feedback gain (compensation gain) K2, when the absolute value of lateral acceleration G _y is equal to or greater than the second threshold value (for example, equal to or greater than 0.5G), stabilizes the control of the compensation gain K2 Constant value. By doing so, the estimation accuracy of the side slip angle β is improved.

The tire slip angle calculation unit 43 estimates the steering angle (tire steering angle δ) detected by the steering angle sensor 1, the yaw rate γ detected by the yaw rate sensor 2, the vehicle speed V calculated by the vehicle speed calculation unit 41, and the vehicle slip angle estimation. Based on the vehicle side slip angle (vehicle slip angle) β calculated by the unit 42, the slip angles β _f and β _r (wheel slip angle βt) of the front and rear wheels are calculated according to the following equation (5).

Tire slip angle calculating section 43 outputs the calculated slip angle βt _f (β _f), and outputs [beta] t _r a (beta _r) of the road surface μ estimated value calculating section 45.
The slip ratio calculating unit 44 is based on the wheel speeds of the respective wheels 11 _{FL to} 11 _RR detected by the wheel speed sensor 5 and the vehicle body speed calculated by the vehicle body speed calculating unit 41 (front wheels 2 and rear wheels 2). The slip ratios λ _f and λ _r of the ring _segments are calculated. The slip ratio calculation unit 44 outputs the calculated slip ratios λ _f and λ _r to the road surface μ estimated value calculation unit 45.

The tire force sensor 46 detects the tire forces of the front wheels 11 _FL and 11 _FR and the rear wheels 11 _RL and 11 _RR . The tire force is a force acting on the tire from the road surface. That is, the tire force is also a force input from the tire to the vehicle. Specifically, the tire force sensor 46 detects a tire force vector indicating the magnitude and direction of the tire force. The tire force vector referred to in the present embodiment is a vector having a force parallel to the contact surface generated between the tire and the road surface, that is, a braking / driving force and a lateral force as components. Therefore, the tire force vector referred to in the present embodiment does not include a force acting on the tire in a direction perpendicular to the road surface. For example, the tire force sensor 46 is a six-axis force sensor. Also includes a tire force sensor 46 to the respective wheels ₁₁ FL _{to 11 RR.}

The tire force sensor 46 outputs the detected tire forces F _f and F _r of the front and rear wheels to the road surface μ estimated value calculation unit 45. When each wheel 11 _{FL to} 11 _RR includes the tire force sensor 46 as in the present embodiment, the tire force sensor 46 outputs the average value of the front left and right wheels as the tire force F _f of the front wheel, and the rear left and right wheels. _Is output as the tire force F _r of the rear wheel.
Road μ estimated value calculating section 45, the slip angle [beta] t f of the front and rear wheels of tire slip angle calculating section 43 is _calculated, [beta] t _r, the slip ratio of the front and rear wheels slip rate calculating section 44 has calculated lambda _f, lambda _r, and the tire The road surface μ is estimated based on the tire forces F _f and F _r of the front and rear wheels detected by the force sensor 46.

  Therefore, the road surface μ estimated value calculation unit 45 includes the three-dimensional curved surface shown in FIG. 22 as a 3D characteristic map 45a as shown in FIG. In FIG. 36 (a), as a representation of the 3D characteristic map 45a, a three-dimensional curved surface representing the relationship between the slip degree and the wheel force is displayed only for 1/4 turn (1/4 quadrant). However, in practice, in the 3D characteristic map 45a, a three-dimensional curved surface representing the relationship between the slip degree and the wheel force exists for the entire circumference, and the 3D characteristic map 45a is dome-shaped or hemispherical. The tire grip state calculation unit 48 has such a 3D characteristic map 45a corresponding to each of the front and rear wheels. For example, the 3D characteristic map 45a is stored and held in a storage medium such as a memory.

  This 3D characteristic map 45a shows a correlation between the braking / driving force Fx and the slip degree Z (slip rate λ) as shown in FIG. 36 (b) in a plane including the braking / driving force Fx axis and the slip degree Z axis. The tire characteristic curve which shows a relationship is shown. Further, in the 3D characteristic map 45a, the correlation between the lateral force Fy and the slip degree Z (slip angle βt) is shown in FIG. 36C in a plane including the lateral force Fy axis and the slip degree Z axis. The tire characteristic curve which shows is shown. Further, as shown in FIG. 36 (d), the 3D characteristic map 45a is a composite value of the resultant force F and the slip degree Z (slip ratio λ and slip angle βt within a plane including the resultant force F and the slip degree Z axis. The tire characteristic curve which shows a correlation with this is shown.

  Here, a straight running test and a turning test are performed in advance on a certain reference road surface, and such a 3D characteristic map is created based on the data at that time. Specifically, an actual measurement of the braking / driving force-slip ratio characteristic curve is performed by a linear acceleration / acceleration experiment on an actual vehicle on the reference road surface. Further, actual measurement of a lateral force (cornering force) -tire slip angle characteristic curve is performed by a turning test using an actual vehicle on a reference road surface (accelerated circular turning with a constant turning radius is preferable). A 3D characteristic map is created based on the actual measurement result.

When direct measurement is not possible, other physical quantities can be measured and converted. Further, it is possible to obtain a 3D characteristic map not by a driving experiment but by calculation by simulation or the like.
The road surface μ estimated value calculation unit 45 estimates the road surface μ with reference to the 3D characteristic map 45a as described above. FIG. 37 shows a relationship for obtaining the road surface μ with reference to the 3D characteristic map 45a as a relationship between an input and an output with respect to the 3D characteristic map 45a.

First, the case of the front wheel will be described. As shown in FIG. 37, the road surface μ estimated value calculation unit 45 receives the front wheel tire force vector F _f and the slip degree Z (Z _f ) as inputs.
At this time, the road surface μ estimated value calculation unit 45 obtains the slip degree Z by combining and converting the slip ratio λ _f and the slip angle βt _f of the front wheels. Specifically, the road surface μ estimated value calculation unit 45 calculates the slip degree Z by the following equation (6).
Z = S / S _Peak = √ ((λ / λ _Peak ) ² + (βt / βt _Peak ) ² ) (6)

Here, λ _Peak is a slip ratio λ (λ _f ) at which the braking / driving force Fx (Fx _f ) is saturated on the reference road surface. βt _Peak is a slip angle βt (βt _f ) at which the lateral force Fy (Fy _f ) is saturated on the reference road surface. If the reference road surface is a dry road surface (μ = 1), λ _Peak and βt _Peak are values corresponding to the dry road surface. S / S _Peak is a composite value of the normalized value of the slip ratio λ (λ / λ _Peak ) and the normalized value of the slip angle βt (βt / βt _Peak ). Alternatively, S / S _Peak is a value having a normalized value of the slip ratio λ (λ / λ _Peak ) and a normalized value of the slip angle βt (βt / βt _Peak ) as components.

The slip degree Z is a value for evaluating the slip ratio and the slip angle at the same time while making the slip ratio and the slip angle having different dimensions the same dimension.
Then, the road surface μ estimated value calculation unit 45 refers to the 3D characteristic map 45a corresponding to the front wheel, and calculates the road surface μ based on the tire force vector F _f of the front wheel and the slip degree Z. Specifically, the road surface μ estimated value calculation unit 45 calculates the road surface μ according to the calculation procedure shown in FIG.

That is, the road surface μ estimated value calculation unit 45 calculates the values (Za, Fa of the points where a straight line passing through the origin (0, 0) and the actual measurement point (Zb, Fb) of the 3D characteristic map 45a intersects the 3D characteristic map 45a. ) Is specified (step S23).
Here, the actual measurement points (Zb, Fb) are specified by the slip degree Zb (actual slip degree Z) and the tire force vector Fb (F _f ) in the Fx-Fy-Z space where the 3D characteristic map 45a is shown. Coordinates (plot points). That is, the coordinates can be specified by the tire force vector Fb on the Fx-Fy plane and the Z-axis direction can be specified by the slip degree Zb.

Then, the road surface μ estimated value calculation unit 45 calculates the road surface μ of the current traveling road surface from which the actual measurement points are obtained (step S24).
That is, first, the road surface μ estimated value calculation unit 45 obtains a straight line length b (= √ (Zb ² + Fb ² )) connecting the actual measurement point (Zb, Fb) and the origin of the 3D characteristic map 45a. That is, from the origin where the braking force, lateral force and slip degree are zero in a three-dimensional space having the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes, the current detected tire force F _f A distance b obtained by projecting the magnitude of the current tire force F _f onto a straight line extending in the direction and up to the current detected slip degree Z is obtained.

In addition, a straight line length a (= √ (Za ² + Fa ² )) connecting the value (Za, Fa) of the intersection with the previously specified 3D characteristic map 45a and the origin of the 3D characteristic map 45a is obtained. That is, the straight line obtained from the distance b is extended to obtain the distance a between the intersection point intersecting the 3D characteristic map 45a and the origin.
Further, the ratio (b / a) between the line length b and the line length a is calculated. Then, the road surface μ estimated value calculation unit 45 multiplies the calculated ratio (b / a) by the road surface μ value μ _A of the road surface from which the 3D characteristic map 45a is obtained, and multiplies the multiplication value of the current traveling road surface. The road surface μ value is obtained as μ _B (μ _B = μ _A · b / a).

Through the above procedure, the road surface μ estimated value calculation unit 45 is based on the braking / driving force Fx _f , lateral force Fy _f and slip degree Z (Z _f ) of the front wheels, and the road surface μ of the current traveling road surface for the front wheels. Get. Then, the road surface μ estimated value calculation unit 45 obtains the road surface μ of the current traveling road surface for the rear wheels based on the tire force vector F _r and the slip degree Z (Z _r ) of the rear wheels by a similar procedure.

(Operation)
This will be described with reference to FIG.
First, in the vehicle body travel state estimation device 8, the vehicle body speed calculation unit 41 calculates the vehicle body speed (step S31). In the vehicle body running state estimation device 8, the slip ratio calculation unit 44 calculates the slip ratios λ _f and λ _r for the front and rear wheels based on the vehicle body speed (step S32). Furthermore, the vehicle body travel state estimating device 8, the tire slip angle calculating section 43 of the respective front and rear wheels slip angle [beta] t _f, to calculate the [beta] t _r (step S33). On the other hand, the tire force sensor 46 detects the tire force vectors F _f and F _r of the front and rear wheels (step S34).

Then, the vehicle body travel state estimating device 8, the road surface μ estimated value calculating section 45, the slip ratio lambda _f of the front and rear _wheels, lambda _r, slip angle [beta] t f of the front and rear _wheels, [beta] t _r and the front and rear wheels of the tire force vector F _f, The road surface μ is estimated based on F _r . The vehicle body travel state estimation device 8 outputs the calculated road surface μ estimated value to the EPS ECU 6 and the braking / driving motor ECU 22.
The EPS ECU 6 controls the EPS motor 7 by a steering assist command based on the estimated road surface μ value. Specifically, the EPS ECU 6 performs control such that the output of the EPS motor 7 is reduced as the estimated road surface μ value decreases.

The braking / driving motor ECU 22 controls the braking / driving motors 21 _{FL to} 21 _RR based on the driving torque command value based on the estimated road surface μ value. Specifically, the braking / driving motor ECU 22 performs control to suppress the output of the driving force by decreasing the driving torque command value as the estimated road surface μ value decreases. Alternatively, the braking / driving motor ECU 22 performs control to suppress the output of the braking force by decreasing the braking torque command value as the estimated road surface μ value decreases.

(Modification of the embodiment)
(1) In this embodiment, the tire characteristic correlation map is expressed as a continuous three-dimensional curved surface, assuming that the tire characteristic correlation map exists in a three-dimensional space having the wheel braking / driving force, wheel lateral force, and wheel slip degree as coordinate axes. 3D characteristic map obtained. On the other hand, the 3D characteristic map (tire characteristic correlation map) may be expressed numerically with the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel as variables.

(2) In this embodiment, a dry road surface such as dry asphalt is assumed as a reference road surface for obtaining a 3D characteristic map, and the road surface μ value is set to μ = 1.0. However, it is not limited to this. For example, a 3D characteristic map can be created using a wet road surface or a frozen road surface as a reference road surface. If the reference road surface is a high road surface μ, there is an advantage that disturbances such as instrument noise can be relatively suppressed.

(3) In this embodiment, the braking / driving force Fx and the lateral force Fy are simultaneously swung in various directions, that is, the direction of the resultant force is swung in various directions to obtain a 3D characteristic map. On the other hand, a 2D characteristic map in the front-rear direction (braking / driving force Fx) and a 2D μ characteristic map in the lateral direction (lateral force Fy) are obtained separately, and the 3D characteristics are complemented between these 2D characteristic maps. You can also get a map. In this case, the 2D characteristic maps are complemented by elliptical approximation.

(4) In this embodiment, the turning behavior or lateral behavior of the vehicle is controlled by steering control (steering reaction force addition control). On the other hand, the vehicle behavior can also be controlled by turning control based on the braking / driving force difference between the left and right wheels such as VDC (Vehicle Dynamics Control). As a result, it is possible to realize vehicle behavior stabilization control (side slip prevention control) with even faster response.
(5) In this embodiment, a front wheel steering vehicle is taken as an example. On the other hand, it can also be set as a rear-wheel steering vehicle.

(6) In this embodiment, the road surface μ is calculated for each of the front and rear wheels. On the other hand, the road surface μ can be calculated for each of the left and right wheels (separately for four wheels). It is also possible to calculate a certain road surface μ for all the wheels.
(7) This embodiment includes an EPS ECU 6 that performs steering control based on the road surface μ, and a braking / driving motor ECU 22 that performs braking / driving force control based on the road surface μ. On the other hand, only one of EPSECU 6 and braking / driving motor ECU 22 can be provided. That is, only one of braking / driving force control and steering control can be performed based on the road surface μ.

  In this embodiment, a vehicle ground contact surface friction state estimation device for estimating the ground contact surface grip characteristics of the vehicle wheel is realized. Further, the tire force sensor 46 realizes tire force detection means for detecting the direction and magnitude of the wheel tire force including the braking / driving force and lateral force of the wheel as components. Further, the tire slip angle calculation unit 43 and the slip ratio calculation unit 44 realize a slip degree detection means for detecting the slip degree of the wheel. Further, the road surface μ estimated value calculation unit 47 and the 3D characteristic map 47a are a three-dimensional curved surface formed by the correlation between the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel obtained on the reference road surface of the reference road surface friction coefficient. The tire characteristic correlation map that models the tire characteristic that represents is realized. Further, the road surface μ estimated value calculating unit 47 calculates the current road surface based on the current tire force detected by the tire force detecting unit, the current slip degree detected by the slip degree detecting unit, and the tire characteristic correlation map. A road surface friction coefficient calculating means for calculating a road surface friction coefficient is realized.

Further, in this embodiment, the tire characteristic correlation map is obtained on the road surface having a road surface friction coefficient different from a ratio of a resultant force of the braking / driving force and lateral force on the reference road surface and a slip ratio and a reference road surface friction coefficient. If the ratio of the resultant force of the braking / driving force and the lateral force and the slip ratio is the same, the resultant force of the braking / driving force and the lateral force on the reference road surface is different from the reference road surface friction coefficient on the road surface. The ratio between the braking / driving force and the resultant force of the lateral force, or the ratio of the slip degree on the reference road surface and the slip degree on the road surface having a road surface friction coefficient different from the reference road surface friction coefficient is the reference road surface friction coefficient. In addition, it has a characteristic indicating a ratio of 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.

  Further, in this embodiment, the road surface friction coefficient calculating means has the braking force, lateral force, and slip degree in a three-dimensional space having the wheel braking / driving force, wheel lateral force, and wheel slip degree as coordinate axes. Projecting the magnitude of the current tire force onto a straight line extending from the zero origin to the current tire force direction detected by the tire force vector detecting means and to the current slip degree detected by the slip degree detecting means. The road surface friction coefficient of the current road surface is calculated based on the ratio between the obtained distance and the distance between the intersection and the origin that extends the straight line and intersects the tire characteristic correlation map.

  Further, in this embodiment, in the vehicle ground contact surface friction state estimation method for estimating the ground contact surface grip characteristic of the vehicle wheel, the wheel tire force vector including the wheel braking / driving force and lateral force as components, and the wheel Detection step for detecting the slip degree, and a road surface friction coefficient calculating step for calculating the road surface friction coefficient of the current road surface based on the current tire force vector detected in the detection step, the current slip degree and the tire characteristic correlation map The tire characteristic correlation map represents a three-dimensional curved surface established by the correlation of the braking / driving force of the wheel, the lateral force of the wheel and the slip degree of the wheel obtained on the reference road surface of the reference road surface friction coefficient. The tire characteristics are modeled, and the ratio of the resultant friction between the braking / driving force and lateral force on the reference road surface and the slip ratio is different from the reference road surface friction coefficient. If the ratio of the resultant force between the braking / driving force and the lateral force on the surface and the slip ratio is the same, the resultant force of the braking / driving force and the lateral force on the reference road surface is different from the reference road friction coefficient. The ratio of the resultant force of braking / driving force and lateral 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 having a road surface friction coefficient different from the reference road surface friction coefficient is the reference road surface. The road surface friction coefficient calculation step has a characteristic indicating a ratio between a friction coefficient and a road surface friction coefficient different from a reference road surface friction coefficient, and the road surface friction coefficient calculation step uses coordinate axes of the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel. In a three-dimensional space, a straight line extending from the origin where the braking force, lateral force and slip degree are zero to the current tire force direction detected in the detection step and to the current slip degree detected in the detection step. The size of the current tire force The road surface friction coefficient of the current road surface is calculated based on the ratio between the distance obtained by the shadow and the distance between the intersection and the origin of the tire characteristic correlation map by extending the straight line. A vehicle ground contact surface friction state estimation method is realized.

(Effect of embodiment)
(1) The ratio of the resultant force of the braking / driving force and the lateral force on the reference road surface to the slip degree and the reference road surface friction coefficient is different from the reference road surface friction coefficient. If the ratio of the resultant force and the slip ratio is the same, the resultant force between the braking / driving force and the lateral force on the reference road surface and the braking / driving force and the lateral force on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient are calculated. The ratio of the resultant force or the slip ratio on the reference road surface to the slip ratio on the road surface having a different road friction coefficient from the reference road friction coefficient is different from the reference road friction coefficient and the reference road friction coefficient. It has a characteristic indicating a ratio with a coefficient.

  Then, when viewed in a three-dimensional space with the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes, the ratio of the resultant force of the braking / driving force and lateral force on the reference road surface to the slip degree and the reference road surface When the ratio of the resultant force between the braking / driving force and the lateral force on the road surface having a different friction coefficient from the friction coefficient and the slip ratio is the same, the resultant force between the braking / driving force and the lateral force on the reference road surface and the reference The ratio of the resultant force of braking / driving force and lateral force on the road surface with a road surface friction coefficient different from the road surface friction coefficient, or the slip degree on the reference road surface, and the slip on the road surface with a road surface friction coefficient different from the reference road surface friction coefficient The distance obtained by projecting the magnitude of the current tire force on a straight line extending in the direction of the current tire force detected from the origin of the three-dimensional space and extending to the detected current slip degree; An intersection that extends a straight line and intersects with the tire characteristic correlation map The ratio of the distance between the points, match viewed geometrically.

Therefore, the distance obtained by projecting the magnitude of the current tire force on a straight line extending from the origin of the three-dimensional space to the detected current slip degree in the direction of the current tire force, and the straight line is extended. Thus, the road surface friction coefficient of the current road surface can be calculated from the ratio of the intersection between the tire characteristic correlation map and the distance between the origin and the reference road surface friction coefficient.
Thereby, the direction and magnitude | size of the tire force of a wheel and a slip degree are detected, and the road surface friction coefficient of the present road surface is computable.
As a result, the road surface friction coefficient of the current road surface can be estimated before slip occurs.

(2) The tire force detecting means detects a tire force vector.
Thereby, the direction and magnitude of the tire force can be detected simultaneously.
(3) The tire characteristic correlation map is expressed as a continuous three-dimensional curved surface as being present in a three-dimensional space having the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes. .
Thereby, the road surface friction coefficient of the current road surface can be easily estimated with high accuracy.

(4) The tire characteristic correlation map is expressed mathematically using the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel as variables.
Thereby, the road surface friction coefficient of the current road surface can be easily estimated with high accuracy.
(5) The slip degree is a value having the slip ratio of the wheel and the slip angle of the wheel as components.
Thereby, the road surface friction coefficient of the present road surface can be estimated corresponding to the slip ratio of the wheel and the slip angle of the wheel.
(6) The slip degree is a value obtained by combining dimensionless values of the wheel slip ratio and the wheel slip angle.
The road surface friction coefficient of the current road surface can be estimated based on the degree of slip that is generalized by making it dimensionless.

(7) A dimensionless value of the wheel slip ratio is obtained by dividing the wheel slip ratio by the wheel slip ratio at which the braking / driving force of the wheel is saturated on the reference road surface.
The road surface friction coefficient of the current road surface can be estimated based on the degree of slip that is generalized by making it dimensionless.
(8) A dimensionless value of the wheel slip angle is obtained by dividing the wheel slip angle by the wheel slip angle at which the lateral force of the wheel is saturated on the reference road surface.
The road surface friction coefficient of the current road surface can be estimated based on the degree of slip that is generalized by making it dimensionless.

  43 tire slip angle calculation unit, 44 slip ratio calculation unit, 45 road surface μ estimated value calculation unit, 45a 3D characteristic map, 46 tire force sensor

Claims (9)

In the vehicle ground contact surface friction state estimation device for estimating the ground contact surface grip characteristics of the vehicle wheel,
Tire force detecting means for detecting the direction and magnitude of the wheel tire force including the braking / driving force and lateral force of the wheel as components;
Slip degree detecting means for detecting the slip degree of the wheel;
A tire characteristic correlation map that models tire characteristics representing a three-dimensional curved surface formed by the correlation of wheel braking / driving force, wheel lateral force, and wheel slip degree obtained on the reference road surface of the reference road surface friction coefficient;
Road surface friction coefficient calculating means for calculating a road surface friction coefficient of the current road surface based on the current tire force detected by the tire force detecting means, the current slip degree detected by the slip degree detecting means, and a tire characteristic correlation map. And comprising
The tire characteristic correlation map includes a ratio of a resultant force between a braking / driving force and a lateral force on the reference road surface and a slip ratio, and a braking / driving force and a lateral force on a road surface having a road surface friction coefficient different from the reference road surface friction coefficient. If the ratio of the resultant force to the slip ratio is the same, the resultant force of the braking / driving force and lateral force on the reference road surface, and the braking / driving force and lateral force on the road surface having a road surface friction coefficient different from the reference road surface friction coefficient The ratio of the slip ratio on the road surface and the ratio of the slip degree on the reference road surface and the slip degree on the road surface having a different road friction coefficient from the reference road surface friction coefficient are the reference road friction coefficient and the reference road surface friction coefficient. It has the characteristic to show the ratio with different road friction coefficient,
The road surface friction coefficient calculating means is configured such that the tire from the origin where the braking force, lateral force, and slip degree are zero in a three-dimensional space with the wheel braking / driving force, wheel lateral force, and wheel slip degree as coordinate axes. A distance obtained by projecting the magnitude of the current tire force on a straight line extending in the direction of the current tire force detected by the force vector detecting means and extending to the current slip degree detected by the slip degree detecting means; The road contact surface friction state is calculated by calculating a road surface friction coefficient of the current road surface based on a ratio of a distance between the intersection point intersecting with the tire characteristic correlation map and the origin point Estimating device.   The vehicle tire contact surface friction state estimation device according to claim 1, wherein the tire force detection means detects a vector of the tire force.   The tire characteristic correlation map is expressed as a continuous three-dimensional curved surface as existing in a three-dimensional space having the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes. The vehicle ground contact surface friction state estimation device according to claim 1 or 2.   3. The vehicle ground contact surface according to claim 1, wherein the tire characteristic correlation map is expressed mathematically by using the braking / driving force of the wheel, the lateral force of the wheel, and the slip degree of the wheel as variables. Friction state estimation device.   The vehicle slip surface friction state estimation device according to any one of claims 1 to 4, wherein the slip degree is a value that includes a slip ratio of a wheel and a slip angle of the wheel.   The vehicle slip surface friction state estimation according to any one of claims 1 to 5, wherein the slip degree is a value having a dimensionless value of each of a wheel slip ratio and a wheel slip angle as a component. apparatus.   The dimensionless value of the slip ratio of the wheel is obtained by dividing the slip ratio of the wheel by the slip ratio of the wheel at which the braking / driving force of the wheel is saturated on the reference road surface. The vehicle ground contact surface friction state estimation apparatus as described.   The dimensionless value of the slip angle of the wheel is obtained by dividing the slip angle of the wheel by the slip angle of the wheel at which the lateral force of the wheel is saturated on the reference road surface. Vehicle ground contact surface friction state estimation device according to claim 1. In the vehicle ground contact surface friction state estimation method for estimating the ground contact surface grip characteristics of the vehicle wheel,
A detection step of detecting a wheel tire force vector including wheel braking / driving force and lateral force as components and a wheel slip degree;
A road surface friction coefficient calculating step for calculating a road surface friction coefficient of the current road surface based on the current tire force vector detected in the detection step, the current slip degree and the tire characteristic correlation map, and
The tire characteristic correlation map models a tire characteristic representing a three-dimensional curved surface formed by a correlation of wheel braking / driving force, wheel lateral force and wheel slip degree obtained on the reference road surface of the reference road surface friction coefficient. The ratio of the resultant force between the braking / driving force and lateral force on the reference road surface and the slip ratio, and the resultant force of the braking / driving force and the lateral force on the road surface having a road surface friction coefficient different from the reference road friction coefficient and slip If the ratio to the degree is the same, the resultant force of the braking / driving force and the lateral force on the reference road surface and the resultant force of the braking / driving force and the lateral force on the road surface having a road surface friction coefficient different from the reference road surface friction coefficient Or the ratio of the slip degree on the reference road surface to the slip degree on the road surface having a road surface friction coefficient different from the reference road surface friction coefficient is different from the reference road surface friction coefficient and the road surface friction coefficient. And a characteristic indicating the ratio of
The road surface friction coefficient calculating step is performed by detecting the braking force, lateral force and slip degree from a zero point in a three-dimensional space having the wheel braking / driving force, wheel lateral force and wheel slip degree as coordinate axes. A distance obtained by projecting the magnitude of the current tire force on a straight line extending in the direction of the current tire force detected in the step and extending to the current slip degree detected in the detection step; and A vehicle contact surface friction state estimation method, wherein a road surface friction coefficient of a current road surface is calculated based on a ratio between an intersection point intersecting with a tire characteristic correlation map and a distance between the origin.

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