JP5228799B2 - Vehicle ground contact surface friction state estimation apparatus and method - Google Patents

Description

  The present invention relates to an apparatus and a method for estimating a friction state of a wheel ground contact surface or a road surface grip state of a wheel, or a margin for a friction limit.

Conventionally, as this type of technology, the horizontal axis corresponds to the slip ratio of the wheel and the vertical axis corresponds to the actual wheel slip ratio and the road friction coefficient in a two-dimensional map corresponding to the road friction coefficient. And the evening-ear friction state is estimated from the slope of a straight line passing through the plotted point and the origin (see Patent Document 1). The braking / driving force of the wheel is controlled based on the estimated tire friction state.
JP 2006-34012 A

However, in the conventional technique of Patent Document 1, since the friction limit of the tire cannot be grasped, the margin to the tire friction limit is not known.
The subject of this invention is estimating the margin with respect to the friction limit of a tire more appropriately.

  In order to solve the above-described problem, in the present invention, the input unit sets an input which is a ratio of the self-aligning torque of the wheel and the slip degree of the wheel on the ground contact surface. The output unit determines an output which is a grip characteristic parameter indicating the grip characteristic of the wheel based on the input set by the input unit.

  According to the present invention, if the self-aligning torque of the wheel and the slip degree of the wheel are known, the grip characteristic parameter indicating the grip characteristic of the wheel can be acquired based on the ratio. Since the tire friction state can be appropriately estimated even when the wheel grip force is in the limit region based on the grip characteristic parameter indicating the grip characteristic of the wheel, a margin with respect to the friction limit of the tire can be appropriately estimated.

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 angle and wheel lateral force FIG. 1 shows a tire characteristic curve. This tire characteristic curve shows a general relationship established between the wheel slip angle βt and the wheel lateral force Fy. For example, by tuning the 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. In this embodiment, the lateral force corresponds to the wheel force acting on the wheel on the ground contact surface, and the slip angle 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 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, 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. When the slip angle βt (absolute value) increases to some extent, the relationship between the slip angle βt and the lateral force Fy becomes a non-linear relationship. Therefore, the tire characteristic curve has a linear portion and a non-linear portion.

  Such a transition from the linear relationship to the non-linear relationship is obvious when attention is paid to the inclination (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 the change amount of the slip angle βt and the change amount of the lateral force Fy, that is, a partial differential coefficient related to the slip angle βt of the lateral force Fy. . The inclination of the tangent line of the tire characteristic curve shown in this way is the tire at the intersection (intersection indicated by a circle in FIG. 1) with any straight line a, b, c,... Intersecting the tire characteristic curve. It can also be seen as the slope of the tangent line of the characteristic curve. If the position on the tire characteristic curve, that is, the slip angle βt and the lateral force Fy are known, the friction state of the tire can be estimated. For example, as shown in FIG. 1, if the tire characteristic curve is at a position x0 close to the linear region even in the non-linear region, it can be estimated that the tire friction state is in a stable state. If the friction state of the tire is stable, it can be estimated that, for example, the tire is at a level where it can exhibit its ability. 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.2 (a) shows the characteristic curve of the tire of various road surface micro | micron | mu. 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. 2A, the tire characteristic curve shows a qualitatively similar tendency 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, 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 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 the tire characteristic curves of various road surfaces μ and arbitrary straight lines a, b, c passing through the origin. As shown in FIG. 3, as in the case of FIG. 1, tangent slopes are obtained at intersections of arbitrary straight lines a, b, and c with respect to tire characteristic curves of various road surface 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. With respect to the tire characteristic curves on various road surfaces μ, tangent slopes are obtained at the intersections with the straight line b. With respect to tire characteristic curves on various road surfaces μ, tangent slopes are obtained at intersections with the straight line c. As a result, it is possible to obtain a result in which the slopes of the tangents on the tire characteristic curve 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 slopes of tangents on the tire characteristic curves of various road surfaces μ obtained at intersections with the same straight line c are the same. That is, the ratio (Fy1 / βt1) of the lateral force Fy1 and the slip angle βt1 to obtain the intersection point x1 on the tire characteristic curve where the road surface μ is μ = 0.2, and the characteristics of the tire where the road surface μ is μ = 0.5 Ratio (Fy2 / βt2) of the lateral force Fy2 and the slip angle βt2 to obtain the intersection point x2 on the curve, and the lateral force Fy3 and slip to obtain the intersection point x3 on the tire characteristic curve where the road surface μ is μ = 1.0 The ratio (Fy3 / βt3) to the angle βt3 is the same value. And the inclination of the tangent at each intersection x1, x2, x3 obtained on the tire characteristic curve of each road surface μ is the same.

  FIG. 5 shows the ratio (Fy / βt) between the lateral force Fy and the slip angle βt indicating the intersection of an arbitrary straight line and the tire characteristic curve, and the slope of the tangent line on the tire characteristic curve at the intersection (∂Fy). / ∂βt). As shown in FIG. 5, in any road surface μ (for example, μ = 0.2, 0.5, 1.0), the ratio of the lateral force Fy to the slip angle βt (Fy / βt) and the tire are thus obtained. The slope of the tangent line on the characteristic curve shows a certain relationship. Therefore, the characteristic curve shown in FIG. 5 is established even on road surfaces having different road surface μ, such as dry asphalt road surfaces and frozen road surfaces. That is, the tire characteristic curve shown in FIG. 5 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. It is out. In the tire characteristic curve, the inclination is not affected by the road surface μ. That is, there is a feature that the slope can be specified without obtaining or estimating the road surface state information. Here, it can be said that the characteristic curve of FIG. 5 shows the characteristic curve of the tire as in FIG. However, in distinction from FIG. 1, the characteristic curve of FIG. 5 can also be called, for example, a grip characteristic curve.

  The characteristic curve shown in FIG. 5 has a negative tangent slope (corresponding to the grip characteristic parameter) on the tire characteristic curve in a region where the ratio (Fy / βt) of the lateral force Fy to the slip angle βt is small (small ratio region). Value. In this region, as the ratio (Fy / βt) increases, the slope of the tangent on the tire characteristic curve once decreases and then increases. Here, the slope of the tangent line on the tire characteristic curve being a negative value indicates that the partial differential coefficient related to the slip angle of the lateral force is a negative value.

  Further, in a region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is large (large ratio region), the slope of the tangent line on the tire characteristic curve becomes a positive value. In this region, as the ratio (Fy / βt) increases, the slope of the tangent line on the tire characteristic curve increases. In the region where the ratio (Fy / βt) between the lateral force Fy and the slip angle βt is large, the characteristic curve in FIG. 5 is in the form of a monotonically increasing function. Here, the inclination of the tangent line on the tire characteristic curve being positive indicates that the partial differential coefficient related to the slip angle of the lateral force is positive. Further, the maximum inclination of the tangent on the tire characteristic curve indicates that the inclination of the tangent is in the linear region of the tire characteristic curve. In the linear region, the slope of the tangent on the tire characteristic curve is always a constant value regardless of the ratio between the lateral force Fy and the slip angle βt.

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

  As described above, the inventor of the present application has the tangential slope of the tire characteristic curve of each road surface μ at the intersection of any one straight line passing through the origin of the tire characteristic curve and the tire characteristic curve. I found the same point. Accordingly, the inventor of the present application has a characteristic curve (grip characteristic curve) that has a relationship between the ratio of the lateral force Fy and the slip angle βt (Fy / βt) and the slope of the tangent on the tire characteristic curve regardless of the road surface μ. ) Was obtained (FIG. 5). Thus, if the lateral force Fy and the slip angle βt are known, it is possible to obtain information on the friction state of the tire based on the characteristic curve (grip characteristic curve) without requiring information on the road surface μ. A procedure for obtaining information on the friction state of the tire will be described with reference to FIG.

  First, the lateral force Fy and the slip angle βt are detected. Then, by using the characteristic curve shown in FIG. 6A (the same characteristic curve as in FIG. 5), on the tire characteristic curve corresponding to the detected lateral force Fy and slip angle βt (corresponding to Fy / βt). The slope of the tangent line can be specified. For example, as shown in FIG. 6A, tangent slopes Id1, Id2, Id3, Id4, and Id5 on the tire characteristic curve are obtained. From the slope of the tangent on the tire characteristic curve, the position on the tire characteristic curve of a certain road surface μ can be identified as shown in FIG. For example, the positions xid1, xid2, xid3, xid4, xid5 corresponding to the tangential slopes Id1, Id2, Id3, Id4, Id5 on the tire characteristic curve can be specified. Here, the position on the tire characteristic curve indicates the frictional state of the tire and the tire performance on the road surface μ where the tire characteristic curve is established. For this reason, as shown in FIG. 6B, the position on the tire characteristic curve can be specified, so that the tire friction state and the tire performance (for example, on the road surface μ where the tire characteristic curve is established) Grip ability). For example, when the slope of the tangent on the tire characteristic curve is negative or near zero (for example, Id4 or Id5), the lateral force of the tire is determined based on the position on the tire characteristic curve (for example, xid4 or xid5) that can be specified from the slope. Is in the limit region.

As long as the lateral force Fy and the slip angle βt are known by the above procedure, the frictional state of the tire on the road surface μ where the lateral force Fy and the slip angle βt are obtained by using the characteristic curve (grip characteristic curve). You can know the tire capacity.
FIG. 7 further shows the relationship with the friction circle. FIG. 7A shows the relationship between the ratio (Fy / βt) between the lateral force Fy and the slip angle βt and the slope of the tangent on the tire characteristic curve (similar to FIG. 5). FIG. 7B shows a tire characteristic curve. FIG. 7C shows a friction circle. In these relationships, first, the tangent slope Id on the tire characteristic curve corresponding to the lateral force Fy and the slip angle βt (corresponding to Fy / βt) is obtained (FIG. 7A). Thereby, the position on the characteristic curve of a tire can be specified (Drawing 7 (b)). Furthermore, the relative value of the lateral force in the friction circle can be known. That is, it is possible to know the margin M for the lateral force that the tire can tolerate. In addition, the slope of the tangent line on the tire characteristic curve itself indicates the change rate of the lateral force Fy with respect to the change of the slip angle βt. Therefore, it can be said that the value on the vertical axis of the characteristic curve shown in FIG. 7A (the slope of the tangent on the tire characteristic curve) indicates the change rate of the vehicle behavior.

  Further, the relationship between the ratio (Fy / βt) between the lateral force Fy and the slip angle βt when the wheel load is changed and the slope of the tangent on the tire characteristic curve is obtained. The relationship is obtained by the same procedure as described above. FIG. 8 shows the relationship. Here, the wheel load is changed by multiplying the initial wheel load value Fz (the wheel load value when there is no fluctuation) by 0.6, 0.8, 1.2,. In the case of 1.0 times, it becomes the initial value Fz of the wheel load. As shown in FIG. 8, when the wheel load of the tire decreases, the slope of the tangent line on the tire characteristic curve obtained with each wheel load decreases. At this time, the maximum value of the tangent slope (value in the linear region) on the tire characteristic curve obtained with each wheel load moves on a straight line passing through the origin of the characteristic diagram shown in FIG. Furthermore, the characteristic curves showing the relationship between the ratio of the lateral force Fy and the slip angle βt (Fy / βt) and the slope of the tangent on the tire characteristic curve are different in size while maintaining the shape. In other words, they are similar and have different sizes. The inventor of the present application has also discovered such a relationship with the wheel load.

(2) Relationship between Wheel Slip Angle and Wheel Self-Aligning Torque FIG. 9 shows a tire characteristic curve. This tire characteristic curve shows a relationship established between the wheel slip angle βt and the wheel self-aligning torque Mz. For example, by tuning the 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 self-aligning torque is a torque that returns the steering to the neutral position.

  As shown in FIG. 9, in the tire characteristic curve, the relationship between the slip angle βt and the self-aligning torque Mz changes from linear to non-linear as the absolute value of the slip angle βt increases. That is, when the slip angle βt is within a predetermined range from zero, a linear relationship is established between the slip angle βt and the self-aligning torque Mz. When the slip angle βt (absolute value) increases to some extent, the relationship between the slip angle βt and the self-aligning torque Mz becomes a non-linear relationship. Therefore, the tire characteristic curve has a linear portion and a non-linear portion.

  Such a transition from the linear relationship to the non-linear relationship is obvious when attention is paid to the inclination (gradient) of the tangent line of the tire characteristic curve. The slope of the tangent to the tire characteristic curve here is the ratio between the amount of change in the slip angle βt and the amount of change in the self-aligning torque Mz, that is, the partial differential coefficient related to the slip angle βt of the self-aligning torque Mz. Value. The inclination of the tangent line of the tire characteristic curve shown in this way is a tire at an intersection (intersection indicated by a circle in FIG. 9) with any straight line a, b, c,... Intersecting the tire characteristic curve. It can also be seen as the slope of the tangent line of the characteristic curve. If the position on the tire characteristic curve, that is, the slip angle βt and the self-aligning torque Mz are known, the friction state of the tire can be estimated. For example, as shown in FIG. 9, it can be estimated that the tire friction state is in a stable state if the tire is located at a position x0 close to the linear region even in the nonlinear region on the tire characteristic curve. If the friction state of the tire is stable, it can be estimated that, for example, the tire is at a level where it can exhibit its ability. Alternatively, it can be estimated that the vehicle is in a stable state.

  FIG. 10 shows the relationship between the tire characteristic curves of various road surfaces μ and arbitrary straight lines a, b, c passing through the origin. As shown in FIG. 10, as in FIG. 9, tangent slopes are obtained at intersections of arbitrary straight lines a, b, and c with respect to tire characteristic curves of various road surface 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. With respect to the tire characteristic curves on various road surfaces μ, tangent slopes are obtained at the intersections with the straight line b. With respect to tire characteristic curves on various road surfaces μ, tangent slopes are obtained at intersections with the straight line c. As a result, it is possible to obtain a result in which the slopes of the tangents on the tire characteristic curve of various road surfaces μ obtained at the intersections with the same straight line are the same.

  For example, in FIG. 11, attention is paid to the straight line c shown in FIG. As shown in FIG. 11, the slopes of the tangents on the tire characteristic curves of various road surfaces μ obtained at the intersections with the same straight line c are the same. That is, the ratio (Mz1 / βt1) of the self-aligning torque Mz1 and the slip angle βt1 for obtaining the intersection point x1 on the characteristic curve of a tire having a road surface μ of μ = 0.3, and a tire having a road surface μ of μ = 0.6. The ratio (Mz2 / βt2) of the self-aligning torque Mz2 and the slip angle βt2 to obtain the intersection point x2 on the characteristic curve of the tire, and the self to obtain the intersection point x3 on the tire characteristic curve where the road surface μ is μ = 1.0 The ratio (Mz3 / βt3) between the aligning torque Mz3 and the slip angle βt3 is the same value. And the inclination of the tangent at each intersection x1, x2, x3 obtained on the tire characteristic curve of each road surface μ is the same.

  FIG. 12 shows the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt indicating the intersection between an arbitrary straight line and the tire characteristic curve, and the slope of the tangent on the tire characteristic curve at the intersection ( The relationship with (∂Mz / ∂βt) is shown. As shown in FIG. 12, the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt is thus obtained for any road surface μ (for example, μ = 0.3, 0.6, 1.0). And the slope of the tangent line on the tire characteristic curve show a certain relationship. Therefore, the characteristic curve shown in FIG. 12 is established even when the road surface μ is different, such as a dry asphalt road surface or a frozen road surface. That is, the tire characteristic curve shown in FIG. 12 is 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. Contains. In the tire characteristic curve, the inclination is not affected by the road surface μ. That is, there is a feature that the inclination can be specified without obtaining or estimating road surface state information. Here, it can be said that the characteristic curve of FIG. 12 shows the characteristic curve of the tire as in FIG. However, in distinction from FIG. 1, the characteristic curve of FIG. 12 can also be called a grip characteristic curve, for example.

  The characteristic curve shown in FIG. 12 shows the slope of the tangent line on the tire characteristic curve (corresponding to the grip characteristic parameter) in a region where the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt is small (small ratio region). Is negative. In this region, as the ratio (Mz / βt) increases, the slope of the tangent on the tire characteristic curve once decreases and then increases. Here, the slope of the tangent line on the tire characteristic curve being a negative value indicates that the partial differential coefficient related to the slip angle of the lateral force is a negative value.

  Further, in a region where the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt is large (large ratio region), the slope of the tangent line on the tire characteristic curve becomes a positive value. In this region, as the ratio (Mz / βt) increases, the slope of the tangent line on the tire characteristic curve increases. In the region where the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt is large, the characteristic curve in FIG. 5 has a monotonically increasing function. Here, the inclination of the tangent line on the tire characteristic curve being positive indicates that the partial differential coefficient related to the slip angle of the lateral force is positive. Further, the maximum inclination of the tangent on the tire characteristic curve indicates that the inclination of the tangent is in the linear region of the tire characteristic curve. In the linear region, the slope of the tangent on the tire characteristic curve is always a constant value regardless of the ratio between the self-aligning torque Mz and the slip angle βt.

  The slope of the tangent on the tire characteristic curve that can be obtained in this manner is a grip characteristic parameter, a variable that represents the grip state of the tire, or a parameter that represents a saturation state of the force that the tire can exert in the lateral direction. Similarly to the case of the lateral force Fy, in the case of a positive value region, it is shown that a stronger self-aligning torque Mz can be generated by increasing the slip angle βt. On the other hand, in the zero or negative value region, even if the slip angle βt is increased, the self-aligning torque Mz does not increase and may decrease.

  As described above, the inventor of the present application has the tangential slope of the tire characteristic curve of each road surface μ at the intersection of any one straight line passing through the origin of the tire characteristic curve and the tire characteristic curve. I found the same point. Thereby, the inventor of the present application has a characteristic curve (grip) having a relationship between the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt and the slope of the tangent on the tire characteristic curve, regardless of the road surface μ. A result that can be expressed as a characteristic curve was obtained (FIG. 12). Thus, if the self-aligning torque Mz and the slip angle βt are known, it is possible to obtain information on the friction state of the tire based on the characteristic curve (grip characteristic curve) without requiring information on the road surface μ. . A procedure for obtaining information on the tire friction state will be described with reference to FIG.

  First, the self-aligning torque Mz and the slip angle βt are detected. Then, by using the characteristic curve shown in FIG. 13A (the same characteristic curve as in FIG. 12), the tire characteristics corresponding to the detected self-aligning torque Mz and slip angle βt (corresponding to Mz / βt). The slope of the tangent on the curve can be specified. For example, as shown in FIG. 13A, tangent slopes Id1, Id2, Id3, and Id4 on the tire characteristic curve are obtained. From the slope of the tangent on the tire characteristic curve, the position on the tire characteristic curve of a certain road surface μ can be specified as shown in FIG. For example, the positions xid1, xid2, xid3, xid4 corresponding to the tangential slopes Id1, Id2, Id3, Id4 on the tire characteristic curve can be specified. Here, the position on the tire characteristic curve indicates the frictional state of the tire and the tire performance on the road surface μ where the tire characteristic curve is established. For this reason, as shown in FIG. 13B, the position on the tire characteristic curve can be specified, so that the tire friction state and the tire performance (for example, on the road surface μ where the tire characteristic curve is established (for example, Grip ability). For example, if the slope of the tangent line on the tire characteristic curve is negative or near zero (for example, Id3 or Id4), the tire self-adjustment is based on the position on the tire characteristic curve (for example, xid3 or xid4) that can be identified from that. It can be seen that the lining torque is in the limit region.

If the self-aligning torque Mz and the slip angle βt are known by the above procedure, the characteristic curve (grip characteristic curve) is used to obtain the self-aligning torque Mz and the slip angle βt on the road surface μ. It is possible to know the tire friction state and the tire capacity.
Further, the relationship between the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt when the wheel load is changed and the slope of the tangent on the tire characteristic curve is obtained. The relationship is obtained by the same procedure as described above. FIG. 14 shows the relationship. Here, the wheel load is changed by multiplying the initial wheel load value Fz (the wheel load value when there is no fluctuation) by 0.6, 0.8, 1.2,. In the case of 1.0 times, it becomes the initial value Fz of the wheel load. As shown in FIG. 14, when the wheel load of the tire decreases, the slope of the tangent on the tire characteristic curve obtained with each wheel load decreases. At this time, the maximum value of the tangent slope (value in the linear region) on the tire characteristic curve obtained with each wheel load moves on a straight line passing through the origin of the characteristic diagram shown in FIG. Furthermore, the characteristic curve showing the relationship between the ratio of the self-aligning torque Mz and the slip angle βt (Mz / βt) and the slope of the tangent on the tire characteristic curve maintains its shape and differs in size. Become. In other words, they are similar and have different sizes. The inventor of the present application has also discovered such a relationship with the wheel load.

(3) Relationship Between Lateral Force of Wheel and Self-Aligning Torque of Wheel FIG. 15 shows a relationship between lateral force Fy and self-aligning torque Mz with respect to slip angle βt. For example, the relationship between the slip angle βt and the lateral force Fy is the relationship shown in FIG. Further, the relationship between the slip angle βt and the self-aligning torque Mz is the relationship shown in FIG. When FIG. 1 and FIG. 9 are superimposed, the result is as shown in FIG. As shown in FIG. 15, both the lateral force Fy and the self-aligning torque Mz show characteristics that change from an increasing tendency to a decreasing tendency with respect to an increase in the slip angle βt. At this time, the self-aligning torque Mz first changes from an increasing tendency to a decreasing tendency, and then the lateral force Fy changes from an increasing tendency to a decreasing tendency.

  FIG. 16 shows the relationship shown in FIG. 15 for various road surfaces μ. As described above, in the tire characteristic curve (also referred to as Fy-βt characteristic curve) of the slip angle βt and the lateral force Fy, on the tire characteristic curve of various road surfaces μ obtained at the intersections with the same straight line. It is possible to obtain a result in which the slope of the tangent line (μ gradient or lateral μ gradient, hereinafter also referred to as μ gradient) is the same. In addition, as described above, the tire characteristic curve (also referred to as the Mz-βt characteristic curve) with the slip angle βt and the self-aligning torque Mz also has various road surfaces obtained at the intersection with the same straight line as similar characteristics. It is possible to obtain a result in which the slope of tangent to the tire characteristic curve of μ (hereinafter also referred to as torque gradient) is the same. That is, in the Fy-βt characteristic curve and the Mz-βt characteristic curve, the positional relationship with respect to the βt axis is uniquely determined if there is no change in the road surface μ. Alternatively, when the road surface μ changes, both the Fy-βt characteristic curve and the Mz-βt characteristic curve are enlarged or reduced in proportion to the road surface μ (maintaining the aspect ratio). That is, the Fy-βt characteristic curve and the Mz-βt characteristic curve maintain a relative relationship regardless of the road surface μ change.

From the above relationship, as shown in FIG. 16, from the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt on the Mz-βt characteristic curve of a certain road surface μ, Fy of the corresponding road surface μ is obtained. The slope of the tangent line (μ gradient) on the −βt characteristic curve can be specified.
FIG. 17 shows the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt, and the tangential slope (上 の Fy / ∂βt, μ gradient) on the tire characteristic curve (Fy-βt characteristic curve). The relationship is shown. FIG. 17 has the same characteristics as FIG. 5 except that the horizontal axis is different. That is, as shown in FIG. 17, on each road surface μ, the ratio of the self-aligning torque Mz to the slip angle βt (Mz / βt) and the slope of the tangent line on the tire characteristic curve (Fy-βt characteristic curve) ( (μ gradient) and a certain relationship. That is, the tire characteristic curve shown in FIG. 17 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. Contains. In the tire characteristic curve, the inclination is not affected by the road surface μ. That is, there is a feature that the inclination can be specified without obtaining or estimating road surface state information. Here, the characteristic curve of FIG. 17 can also be called a grip characteristic curve, for example.

  The characteristic curve shown in FIG. 17 shows the slope of the tangent line on the tire characteristic curve (grip characteristic parameter) in a region (small ratio region) where the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt is small. Is equivalent to a negative value. In this region, as the ratio (Mz / βt) increases, the slope of the tangent on the tire characteristic curve once decreases and then increases. Here, the slope of the tangent line on the tire characteristic curve being a negative value indicates that the partial differential coefficient related to the slip angle of the lateral force is a negative value. Further, in a region where the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt is large (large ratio region), the slope of the tangent line on the tire characteristic curve becomes a positive value. In this region, as the ratio (Mz / βt) increases, the slope of the tangent line on the tire characteristic curve increases. In the region where the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt is large, the characteristic curve in FIG. 17 has a monotonically increasing function.

The μ gradient obtained in this way can be used as dynamic cornering power, and is a very important parameter for estimating vehicle characteristics and predicting the limit of vehicle behavior.
Further, the relationship between the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt when the wheel load is changed and the slope of the tangent on the tire characteristic curve (Fy-βt characteristic curve) is obtained. Yes. The relationship is obtained by the same procedure as described above. FIG. 18 shows the relationship. Here, the wheel load is changed by multiplying the initial wheel load value Fz (the wheel load value when there is no fluctuation) by 0.6, 0.8, 1.2,. In the case of 1.0 times, it becomes the initial value Fz of the wheel load. As shown in FIG. 18, when the wheel load of the tire decreases, the slope of the tangent line on the tire characteristic curve obtained with each wheel load decreases. At this time, the maximum value of the tangent slope on the tire characteristic curve obtained at each wheel load (value in the linear region) moves on a straight line passing through the origin of the characteristic diagram shown in FIG. Furthermore, the characteristic curve showing the relationship between the ratio of the self-aligning torque Mz and the slip angle βt (Mz / βt) and the slope of the tangent on the tire characteristic curve maintains its shape and differs in size. Become. In other words, they are similar and have different sizes.

(Embodiment)
Next, an embodiment realized by adopting the above technique will be described.
(First embodiment)
(Constitution)
FIG. 19 shows a schematic configuration of the vehicle according to the first embodiment. As shown in FIG. 19, the vehicle includes a steering angle sensor 21, a yaw rate sensor 22, a lateral acceleration sensor 23, a longitudinal acceleration sensor 24, a wheel speed sensor 25, an EPS ECU (Electric Power Steering Electronic Control Unit) 26, a steering torque sensor 35, a brake. An ECU 36, an EPS (Electric Power Steering) motor 27, and a vehicle running state estimation device 28 are provided. The vehicle running state estimation device 28 realizes a vehicle contact surface friction state estimation device according to the present invention.

The steering angle sensor 21 detects the rotation angle of the steering shaft 30 that rotates integrally with the steering wheel 29. The steering angle sensor 21 outputs the detection result (steering angle) to the vehicle running state estimation device 28. The yaw rate sensor 22 detects the yaw rate of the vehicle. The yaw rate sensor 22 outputs the detection result to the vehicle running state estimation device 28. The lateral acceleration sensor 23 detects the lateral acceleration of the vehicle. The lateral acceleration sensor 23 outputs the detection result to the vehicle running state estimation device 28. The longitudinal acceleration sensor 24 detects the longitudinal acceleration of the vehicle. The longitudinal acceleration sensor 24 outputs the detection result to the vehicle running state estimation device 28. The wheel speed sensor 25 detects the wheel speeds of the wheels 31 _{FL to} 31 _RR provided on the vehicle body. The wheel speed sensor 25 outputs the detection result to the vehicle running state estimation device 28.

  The EPS ECU 26 outputs a steering assist command to the EPS motor 27 based on the steering angle detected by the steering angle sensor 21. The steering assist command here is a command signal for performing steering force assist. The EPS ECU 26 outputs a steering assist command to the EPS motor 27 based on the command value (unstable behavior suppression assist command) output by the vehicle running state estimation device 28. The steering assist command here is a command signal for suppressing the unstable behavior of the vehicle.

The steering torque sensor 35 detects a steering torque that is an input torque from the driver. The steering torque sensor 35 outputs the detected steering torque to the vehicle running state estimation device 28.
The EPS motor 27 applies rotational torque to the steering shaft 30 based on the steering assist command output from the EPS ECU 26. Thereby, the EPS motor 27 steers the left and right front wheels 31 _FL and 31 _FR via the rack and pinion mechanism (pinion 32 and rack 33) connected to the steering shaft 30, the tie rod 34 and the knuckle arm. Assist.

The brake ECU 36 controls the braking force of the wheels. The brake ECU 36 controls the braking force of the wheels based on the command value (unstable behavior suppression assist command) output from the vehicle running state estimation device 28.
The vehicle running state estimation device 28 estimates the running state of the vehicle based on the detection results of the steering angle sensor 21, the yaw rate sensor 22, the lateral acceleration sensor 23, the longitudinal acceleration sensor 24, the wheel speed sensor 25, and the steering torque sensor 35. . The vehicle running state estimation device 28 outputs a command value (unstable behavior suppression assist command) to the EPS ECU 26 and the brake ECU 36 based on the estimation result. The command value here is a command signal for controlling the EPS motor 27 and the braking force so as to suppress the unstable behavior of the vehicle.

  FIG. 20 shows the internal configuration of the vehicle running state estimation device 28. As shown in FIG. 20, the vehicle running state estimation device 28 includes a vehicle body speed calculation unit 41, a vehicle body slip angle estimation unit 42, a tire slip angle calculation unit 43, an EPS assist torque calculation unit 44, a self-aligning torque calculation unit 45, Self-aligning torque-slip angle ratio calculation unit (hereinafter referred to as Mz / βt calculation unit) 46, wheel load change calculation unit 47, torque gradient calculation unit 48, μ gradient calculation unit 49, and unstable behavior suppression assist command value A calculation unit 50 is provided.

The vehicle body speed calculation unit 41 estimates the vehicle body speed based on the wheel speed detected by the wheel speed sensor 25 and the longitudinal acceleration detected by the longitudinal acceleration sensor 24. The vehicle body speed calculation unit 41 outputs the estimation result to the vehicle body slip angle estimation unit 42 and the tire slip angle calculation unit 43. Specifically, the vehicle body speed calculation unit 41 calculates the average value of the wheel speeds of the driven wheels 31 _RL and 31 _RR or the average value of the wheel speeds of the wheels 31 _{FL to} 31 _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 slip angle estimating unit 42 detects the steering angle (tire steering angle δ) detected by the steering angle sensor 21, the yaw rate γ detected by the yaw rate sensor 22, the lateral acceleration detected by the lateral acceleration sensor 23, and the longitudinal acceleration sensor 24. The side slip angle (slip angle) of the vehicle is estimated based on the longitudinal acceleration and the vehicle body speed V calculated by the vehicle body speed calculation unit 41.
FIG. 21 shows a configuration example of the vehicle body slip angle estimation unit 42. As shown in FIG. 21, the vehicle body slip angle estimation unit 42 includes a linear two-input observer 61 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 61 is constructed based on the 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 shown in FIG. 21 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.

Then, based on this state equation, the yaw rate and the lateral acceleration are input, and a linear two-input observer 61 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 61 includes a β estimation compensator 63 that corrects the input of the integrator 62. Thereby, the linear two-input observer 61 can ensure estimation accuracy even in the limit region. In other words, by including the β estimation compensator 63, not only in the road surface condition assumed when designing the two-wheel model of the vehicle and in the linear region where the tire side slip angle does not become a nonlinear 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. 22 shows a turning vehicle running at a vehicle body side slip angle β. As shown in FIG. 22, the field force acting on the vehicle body, that is, the centrifugal force acting outward from the turning center is also generated in the direction shifted by the side slip angle β from the vehicle width direction. Therefore, the β estimation compensator 63 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 61.

Here, G _x is the longitudinal acceleration. Further, as shown in FIG. 23, the balance of force due to the 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 63 subtracts the target value β ₂ from the skid angle β estimated by the linear two-input observer 61. Further, the β estimation compensator 63 multiplies the subtraction result by the compensation gain K2 set by the control map of FIG. Then, the β estimation compensator 63 uses the multiplication result as an input of the integrator 62.
In the control map of FIG. 24, 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. 24, 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. 24, 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 21, the yaw rate γ detected by the yaw rate sensor 22, the vehicle body speed V calculated by the vehicle body speed calculation unit 41, and vehicle body slip angle estimation. Based on the 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).

The tire slip angle calculation unit 43 outputs the calculated front wheel slip angle β _f (βt) to the Mz / βt calculation unit 46. In the present embodiment, the configuration of the EPS unit of the front wheel steering vehicle, that is, the configuration in which the road surface μ (for example, the maximum road surface μ) is estimated using the steering angle sensor 21 and the steering torque sensor 35 is used. Therefore, only the slip angle β _f of the front wheel, which is a steered wheel, is necessary for estimating the road surface μ, and the rear wheel slip angle β _r is unnecessary.

Note that when the road surface μ (for example, the maximum road surface μ) is estimated separately for the front wheel and the rear wheel, the rear wheel slip angle β _r is also required. In that case, a self-aligning torque calculation unit or detection unit is required for the rear wheel. The basic concept of the method of estimating the road surface μ by combining the two front wheels described in this embodiment, the method of estimating the road surface μ separately for the front and rear wheels, and the method of estimating the road surface μ for each of the four wheels are as follows: Since it is the same, the description is abbreviate | omitted here.

The self-aligning torque calculator 45 calculates the self-aligning torque simultaneously with the calculation of the tire slip angle by the tire slip angle calculator 43 as described above. Therefore, the EPS assist torque calculator 44 calculates the steering assist torque. Specifically, the EPS assist torque calculator 44 calculates the assist torque T _EPS by the following equation (6).

Here, the EPS motor 27 generates a torque proportional to the current I. _Let the proportionality coefficient be _KMTR . Further, when the motor angle is theta _MTR, there is a torque loss due to friction and torque losses proportional to the angular acceleration and angular velocity about the motor angle theta _MTR, to correct these torque losses. At this time, gain corresponding to inertia is I _MTR , gain corresponding to viscosity (including counter electromotive force) is C _MTR , and friction is R _MTR, and these parameters are identified in advance.

  The self-aligning torque calculator 45 calculates self-aligning torque using the assist torque calculated by the EPS assist torque calculator 44, the input torque (steering torque) from the driver, and the steering angle information (steering angle). . Specifically, the self-aligning torque SAT is calculated by the following equation (7).

Here, T _STR is an input torque from the driver detected by the steering torque sensor 35. θ _STR is a steering angle detected by the steering angle sensor 21. According to this equation (7), the sum of the input torque T _STR and the assist torque T _EPS from the driver is the self-aligning torque SAT input from the road surface.
In this case as well, the torque loss due to the friction of the steering system is corrected in the same manner as the assist torque calculation in the EPS assist torque calculation unit 44. Specifically, there are torque loss proportional to the angular acceleration and angular velocity for the steering angle θ _STR and torque loss due to friction, and these torque losses are corrected. At this time, gain corresponding to inertia is set to I _STR , gain corresponding to viscosity is set to C _STR , friction is set to R _STR, and these parameters are also identified in advance. The self-aligning torque calculator 45 outputs the calculated self-aligning torque SAT (Mz) of the steered wheel (front wheel) to the Mz / βt calculator 46.

The Mz / βt calculation unit 46 is based on the self-aligning torque Mz and the slip angle βt based on the front wheel self-aligning torque Mz and the slip angle βt calculated by the self-aligning torque calculation unit 45 and the tire slip angle calculation unit 43. The ratio (Mz / βt) is calculated. The Mz / βt calculator 46 outputs the calculation result to the torque gradient calculator 48 and the μ gradient calculator 49.
Further, the wheel load change amount calculation unit 47 calculates the wheel load change amount of the wheel based on the lateral G and the longitudinal G detected by the lateral acceleration sensor 23 and the longitudinal acceleration sensor 24. Specifically, the wheel load change amount of the wheel corresponding to the lateral G and the front-rear G is calculated. The wheel load change amount calculation unit 47 outputs the calculation result to the torque gradient calculation unit 48 and the μ gradient calculation unit 49.

Based on the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt calculated by the Mz / βt calculation unit 46, the torque gradient calculation unit 48 determines the amount of change in the slip angle βt (β _f ) and the self-alignment. The ratio with the change amount of the lining torque Mz is estimated. That is, the torque gradient is estimated. Therefore, the torque gradient calculation unit 48 has the characteristic diagram shown in FIG. 12 as a torque gradient characteristic map. In this embodiment, a torque gradient characteristic map of the entire front wheel (total of two front wheels) is provided. For example, a torque gradient characteristic map is stored and held in a storage medium such as a memory. Thereby, the torque gradient calculation unit 48 refers to the torque gradient characteristic map and obtains a torque gradient corresponding to the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt as an estimated value.

  Further, the torque gradient calculation unit 48 corrects the torque gradient characteristic map based on the wheel load change amount calculated by the wheel load change amount calculation unit 47. As described with reference to FIG. 14, the characteristic curve indicating the relationship between the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt and the torque gradient changes according to the wheel load. Specifically, it becomes a similar characteristic curve having different sizes depending on the wheel load. For this reason, the torque gradient calculation unit 48 corrects the torque gradient characteristic map (map in FIG. 12) while maintaining the ratio between the horizontal axis (Mz / βt) and the vertical axis (torque gradient). For example, if the wheel load change amount calculated by the wheel load change amount calculation unit 47 decreases the initial value of the wheel load, a similar characteristic curve that is reduced according to the wheel load is corrected.

The torque gradient calculation unit 48 can also calculate the scale ratio of the torque gradient characteristic map according to the load change correction function, and can correct the scale ratio with the scale ratio. The load change correction function adds the wheel load (initial value) when there is no change to the wheel load change amount calculated by the wheel load change amount calculation unit 47, divides the added value by the initial value, and the divided value. Is a function for calculating the scale ratio of the torque gradient characteristic map from Thus, the torque gradient characteristic map is corrected by multiplying (doubling) the calculated scale ratio while maintaining the ratio between the horizontal axis (Mz / βt) and the vertical axis (torque gradient).
The torque gradient calculation unit 48 outputs the result (torque gradient or its correction value) obtained as described above to the unstable behavior suppression assist command value calculation unit 50.

Based on the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt calculated by the Mz / βt calculation unit 46, the μ gradient calculation unit 49 determines the amount of change in the slip angle βt (β _f ) and the tire lateral direction. The ratio of the force Fy (Fy _f ) to the amount of change is estimated. That is, the μ gradient is estimated. Therefore, the μ gradient calculation unit 49 has the characteristic diagram shown in FIG. 17 as a μ gradient characteristic map. In the present embodiment, there is a μ gradient characteristic map of the entire front wheel (total of two front wheels). For example, the μ gradient characteristic map is stored and held in a storage medium such as a memory. Thereby, the μ gradient calculation unit 49 refers to the μ gradient characteristic map and obtains the μ gradient corresponding to the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt as an estimated value.

  In addition, the μ gradient calculation unit 49 corrects the μ gradient characteristic map based on the wheel load change amount calculated by the wheel load change amount calculation unit 47. As described with reference to FIG. 18, the characteristic curve indicating the relationship between the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt and the μ gradient changes according to the wheel load. Specifically, it becomes a similar characteristic curve having different sizes depending on the wheel load. For this reason, the μ gradient calculation unit 49 corrects the μ gradient characteristic map (the map in FIG. 17) while maintaining the ratio between the horizontal axis (Mz / βt) and the vertical axis (μ gradient). For example, if the wheel load change amount calculated by the wheel load change amount calculation unit 47 decreases the initial value of the wheel load, a similar characteristic curve that is reduced according to the wheel load is corrected.

  Further, the μ gradient calculation unit 49 can calculate the scale ratio of the μ gradient characteristic map according to the load change correction function, and can correct the scale ratio by the scale ratio. The load change correction function adds the wheel load (initial value) when there is no change to the wheel load change amount calculated by the wheel load change amount calculation unit 47, divides the added value by the initial value, and the divided value. Is a function for calculating the scale ratio of the μ gradient characteristic map. Thus, the μ gradient characteristic map is corrected by multiplying (doubling) the calculated scale ratio while maintaining the ratio between the horizontal axis (Mz / βt) and the vertical axis (μ gradient).

The μ gradient calculation unit 49 outputs the result (μ gradient or its correction value) obtained as described above to the unstable behavior suppression assist command value calculation unit 50.
In addition, a turning traveling experiment is performed in advance, and a torque gradient characteristic map and a μ gradient characteristic map are created based on the data. Specifically, actual measurements of self-aligning torque, lateral force, and slip angle are performed by an actual vehicle turning experiment (accelerated circular turning with a constant turning radius is preferable). If direct measurement is not possible, other physical quantities can be measured. For example, when obtaining front and rear tire lateral force Fy _f, the Fy _r is the lateral acceleration G _y, by measuring the yaw rate gamma, this and may be simultaneous with the following equation (8) consisting of vehicle parameters (see FIG. 25).

  The unstable behavior suppression assist command value calculation unit 50 performs processing for suppressing the unstable behavior of the vehicle based on the μ gradient and torque gradient calculated (estimated) by the μ gradient calculation unit 49 and the torque gradient calculation unit 48. Therefore, based on the μ gradient and the torque gradient, the assist command value is output to the EPS ECU 26 and the brake ECU 36 when the vehicle behavior is likely to be unstable or when it is determined that the vehicle is unstable. In the present embodiment, an example in which the present invention is applied to the steered wheels of a front-wheel steered vehicle is shown, and therefore processing for preventing vehicle drift-out will be described based on the grip state of the front wheels. The vehicle drift-out here is a vehicle behavior when the grip state of the front wheel is saturated and the front wheel loses lateral force.

FIG. 26 shows a processing procedure of the unstable behavior suppression assist command value calculation unit 50. As shown in FIG. 26, first, in step S21, it is determined whether or not the torque gradient is a negative value. If the torque gradient is negative (torque gradient <0), the process proceeds to step S22. If the torque gradient is positive (torque gradient ≧ 0), the processing in FIG. 26 is terminated.
In step S22, it is determined whether or not the μ gradient is a negative value. If the μ gradient is a positive value (μ gradient ≧ 0), the process proceeds to step S23. If the μ gradient is negative (μ gradient <0), the process proceeds to step S24.

In step S23, a command value (unstable behavior suppression assist command) is output to EPS ECU 26. Here, a command value for adding a steering reaction force in a direction to suppress the increase in turning of the steering wheel 29 by the driver is output. Then, the processing in FIG.
In step S24, a command value (unstable behavior suppression assist command) is output to EPSECU 26. Here, a command value for adding a steering reaction force in a direction that prompts the driver to switch back the steering wheel 29 is output. Then, the process proceeds to step S25.

In step S25, it is determined whether braking is in progress. If braking is in progress, the process proceeds to step S26. If not braking, the processing of FIG. 26 is terminated.
In step S26, a command value (unstable behavior suppression assist command) is output to the brake ECU 36. Here, the command value is output so as to weaken the braking force of the μ gradient decreasing wheel which is the wheel having the decreased μ gradient. Then, the processing in FIG.

As described above, the unstable behavior suppression assist command value calculation unit 50 performs processing for suppressing the unstable behavior of the vehicle.
(Operation and action)
FIG. 27 shows an example of a calculation processing procedure in the vehicle body travel state estimation device 28. The vehicle body travel state estimation device 28 executes this calculation process while the vehicle is traveling.

First, the vehicle body running state estimation device 28 estimates the vehicle body speed based on the wheel speed detected by the wheel speed sensor 25 and the longitudinal acceleration detected by the longitudinal acceleration sensor 24 (step S11). The vehicle body travel state estimation device 28 then detects the steering angle detected by the steering angle sensor 21, the yaw rate detected by the yaw rate sensor 22, the lateral acceleration detected by the lateral acceleration sensor 23, the longitudinal acceleration detected by the longitudinal acceleration sensor 24, and the vehicle body speed. A slip angle β _f (wheel slip angle βt) is calculated based on the vehicle body speed calculated by the calculation unit 41 (step S12).

The vehicle body travel state estimation device 28 calculates an EPS assist torque (assist torque T _EPS ) based on the EPS current (current I), the motor rotation speed, and the like (step S13). Then, the vehicle body running state estimation device 28 calculates a self-aligning torque Mz based on the calculated EPS assist torque, steering angle, and steering torque (step S14). The vehicle body running state estimation device 28 calculates the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt based on the self-aligning torque Mz and the slip angle βt thus calculated (step S15). .

  Then, the vehicle body travel state estimation device 28 refers to the μ gradient characteristic map and calculates a μ gradient (lateral μ gradient) corresponding to the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt ( Step S16). Further, the vehicle body running state estimation device 28 calculates a torque gradient corresponding to the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt with reference to the torque gradient characteristic map (step S17).

  Then, the vehicle body travel state estimation device 28 performs the process of FIG. That is, if the torque gradient is a positive value (torque gradient ≧ 0), the processing of FIG. 27 is terminated (step S21). That is, the process ends without performing control or the like for applying the steering reaction force. Further, if the torque gradient is negative and the μ gradient is positive (torque gradient <0 and μ gradient ≧ 0), a steering reaction force is applied in a direction to suppress the increase of the steering wheel 29 by the driver. The command value to be output is output (step S21 → step S22 → step S23). If the torque gradient is a negative value and the μ gradient is a negative value (torque gradient <0 and μ gradient <0), a steering reaction force is applied in a direction that prompts the driver to switch back the steering wheel 29. A command value is output (step S21 → step S22 → step S24). At this time, if braking is in progress, a command value is output so as to weaken the braking force of the μ gradient lowering wheel (step S25 → step S26).

The vehicle behavior obtained by the above process will be described. This will be described with reference to FIG.
As described above, when the torque gradient is a negative value and the μ gradient is a positive value (torque gradient <0 and μ gradient ≧ 0), the steering reaction is suppressed in a direction that suppresses the increase of the steering wheel 29 by the driver. A command value for adding force is output (step S21 → step S22 → step S23). As shown in FIG. 28, when the torque gradient is a negative value and the μ gradient is a positive value, the attention area is controlled.

  The attention area is an area where the self-aligning torque is saturated (torque gradient is negative), but the lateral force is still before saturation (μ gradient is positive). In this attention area, the yaw rate can be increased by cutting the steering wheel. On the other hand, if the steering wheel is cut too carelessly, the lateral force Fy will be saturated. For this reason, as a control of the attention area, a command value is output to the EPS ECU 26 so as to assist the steering in a direction to suppress the steering wheel from being increased. For example, this is realized by adding a current of a predetermined value I1 (A) (hereinafter referred to as an addition assist current) to a normal assist current in a rectangular wave shape. Thus, in the attention area, it is possible to prevent the driver from turning the steering wheel too much due to a decrease in the steering reaction force. That is, for example, when the self-aligning torque is saturated and the steering reaction force is reduced, it is possible to prevent the steering wheel from lightening suddenly and a driver with low driving skill from turning the steering wheel too much.

  In the present embodiment, the torque gradient and μ gradient can be estimated quantitatively and continuously in real time. Therefore, the command value (addition assist current) can be set to a value proportional to the amount of decrease from the torque gradient or μ gradient in the stable state in a direction that suppresses additional steering. However, if the command value for canceling the self-aligning torque decrease is made smooth, there is a possibility that a skilled driver may misunderstand that the tire grip force has a margin. For this reason, it is possible to add an information function such as adding a vibration component to the command value (vibrating the assist current) or notifying the driver by sound or display (buzzer, lamp, etc.).

  Further, when the torque gradient is a negative value and the μ gradient is a negative value (torque gradient <0 and μ gradient <0), a steering reaction force is applied in a direction that prompts the driver to switch back the steering wheel 29. The command value is output (step S21 → step S22 → step S24). As shown in FIG. 28, when the torque gradient is a negative value and the μ gradient is a negative value, the saturation region is controlled.

  The saturation region is a region in which the lateral force (cornering force) cannot be increased even when the steering wheel is increased, but the lateral force is decreased when the steering wheel is increased. That is, this is a region where drift-out has occurred as a vehicle behavior. There are various possible causes for the occurrence of the saturated region (saturated state). For example, too much slip angle of the steering wheel (too much turning of the steering wheel) or excessive braking during turning may be mentioned.

  In this saturation region control, a command value for adding a steering reaction force in a direction that prompts the driver to switch back the steering wheel 29 is output. For example, this is realized by adding a command value (addition assist current) of a predetermined value I2 (A) (> I1) to the normal assist current in a rectangular wave shape. As a result, the driver is encouraged to switch back the steering wheel, and a gripping force or a lateral force can be secured. As a result, vehicle behavior such as suppression of drift-out can be shifted in the stabilization direction.

Further, when braking is applied in this saturation region, a command value is output so as to weaken the braking force of the μ gradient-decreasing wheel (step S25 → step S26). That is, the command value is output so as to weaken the braking force of the steering wheel in order to recover the grip of the steering wheel. Here, if the vehicle can control the braking force of the left and right wheels independently, the braking force of the outer turning wheel can be particularly weakened. Thereby, simultaneously with the recovery of the gripping force, it is possible to generate a turning moment due to a difference in braking force between the left and right wheels, thereby ensuring an appropriate turning behavior.
When the μ gradient is a positive value, normal assist control is performed as the stable region control. That is, the assist control is performed only with the normal assist current without adding the command value (addition assist current).

  As described above, by utilizing the fact that the torque gradient is saturated before the lateral force is saturated and the torque gradient starts to decrease, the self-aligning torque and the lateral force are monitored by monitoring the torque gradient and the μ gradient. Predicting saturation. That is, the decrease in torque gradient and μ gradient is used as a quantitative index indicating the state in which the lateral force of the front wheels approaches saturation. Then, EPS reaction force control (steering reaction force control) and brake control are performed in accordance with such a self-aligning torque and lateral force saturation state, and also whether or not braking is performed.

(Modification of the first embodiment)
(1) In the first embodiment, an electric current is applied in a direction in which the steering wheel is returned by the steering reaction force control. On the other hand, for the purpose of suppressing drift-out, the steering assist can be simply reduced to a state close to a manual handle. By reducing the steering assist in this way, the steering reaction force becomes heavier, and as a result, it is possible to suppress a steering operation in which the driver increases the steering wheel.

(2) In the first embodiment, when the grip characteristic parameters (torque gradient, μ gradient) as output variables are determined from the ratio (Mz / βt) of the self-aligning torque Mz as an input variable and the slip angle βt. The non-linear relationship between them is in the form of a characteristic map or characteristic diagram. On the other hand, such a non-linear relationship can be in the form of a mathematical expression. In addition, if possible, the relationship can be simplified to a linear relationship without using a non-linear relationship.

(3) In the first embodiment, a torque gradient characteristic map and μ gradient characteristic map of the entire front wheel (total of two front wheels) are provided. On the other hand, an individual torque gradient characteristic map and μ gradient characteristic map can be provided for each front wheel. In this case, an individual torque gradient characteristic map or μ gradient characteristic map is acquired for each front wheel by providing a configuration capable of detecting, measuring, or estimating the self-aligning torque and slip angle for each front wheel. For example, a configuration corresponding to a tire slip angle calculation unit 43, a self-aligning torque calculation unit 45, a self-aligning torque-slip angle ratio calculation unit 46, a torque gradient calculation unit 48, and a μ gradient calculation unit 49 (vehicle contact surface friction state) The configuration equivalent to the estimation device can be realized by providing the right wheel and the left wheel of the vehicle.

  Thus, by having a separate torque gradient characteristic map and μ gradient characteristic map for each front wheel, based on the detection results (estimation results) of the self-aligning torque Mz and the slip angle βt for each of the left and right wheels, A torque gradient and μ gradient for each of the left and right wheels can be obtained. Thereby, it is also possible to detect the left / right difference in the road surface condition including during traveling from the difference in torque gradient (or μ gradient) between the left and right wheels. Thereby, the difference in the grip characteristics of the left and right wheels can be detected. For example, a difference in road surface μ, that is, a split μ state can be detected. Furthermore, it is possible to detect vehicle behavior or vehicle characteristics resulting from the split μ state.

  In the first embodiment, the tire slip angle calculation unit 43, the self-aligning torque calculation unit 45, and the self-aligning torque-slip angle ratio calculation unit 46 return the wheel steering to the neutral position on the ground contact surface. An input unit for setting an input that is a ratio between a self-aligning torque that is a torque and a slip degree of the wheel is realized. In addition, the torque gradient calculation unit 48 and the μ gradient calculation unit 49 realize an output unit that determines an output that is a grip characteristic parameter indicating the grip characteristic of the wheel based on the input set by the input unit. That is, the tire slip angle calculation unit 43, the self-aligning torque calculation unit 45, the self-aligning torque-slip angle ratio calculation unit 46, the torque gradient calculation unit 48, and the μ gradient calculation unit 49 are the vehicle ground contact surface friction state estimation device. Realized.

  In the first embodiment, the torque gradient calculation unit 48 (torque gradient characteristic map) and the μ gradient calculation unit 49 (μ gradient characteristic map) do not use the friction coefficient of the ground, and the self-aligning torque and slip The grip characteristic parameter is determined only from the ratio to the degree. Alternatively, the torque gradient calculation unit 48 (torque gradient characteristic map) and the μ gradient calculation unit 49 (μ gradient characteristic map) do not use the friction coefficient of the ground, but only from the ratio of the self-aligning torque and the slip degree, the tire characteristics. It is configured to determine the slope of the curve. Alternatively, the torque gradient calculation unit 48 (torque gradient characteristic map) and the μ gradient calculation unit 49 (μ gradient characteristic map) calculate the grip characteristic parameter from the current value of the ratio between the self-aligning torque and the slip degree obtained by the input unit. The current value is determined, and the slope value of the high friction tire characteristic curve corresponding to the current value of the self-aligning torque and the current value of the slip degree, the current value of the self-aligning torque, and the current value of the slip degree The gradient value of the low friction tire characteristic curve is set to be the same as the current value of the grip characteristic parameter.

  In the first embodiment, the characteristic curve (FIG. 12) of the torque gradient characteristic map and the characteristic curve (FIG. 17) of the μ gradient characteristic map are characteristic curves representing tire characteristics depending on the road surface friction coefficient. Thereby, the torque gradient calculation unit 48 and the μ gradient calculation unit 49 are configured to determine the gradient of the tire characteristic curve only from the ratio of the self-aligning torque and the slip degree without using the road surface friction coefficient.

  In the first embodiment, in the characteristic curve (FIG. 12) of the torque gradient characteristic map and the characteristic curve (FIG. 17) of the μ gradient characteristic map, the grip characteristic parameters (torque gradient, μ gradient) are self-aligning. It becomes a function that increases as the ratio of torque to slip increases from the critical ratio value. The critical ratio value corresponds to a value at which the torque gradient becomes zero or the μ gradient becomes zero. In the characteristic curve of the torque gradient characteristic map (FIG. 12) and the characteristic curve of the μ gradient characteristic map (FIG. 17), the ratio between the self-aligning torque and the slip degree is large in a large ratio region larger than the critical ratio value. As the ratio increases, the grip characteristic parameter increases nonlinearly so that the ratio of the increase in the grip characteristic parameter to the increase in the ratio between the self-aligning torque and the slip ratio increases. When the ratio between the self-aligning torque and the slip degree is equal to the critical ratio value, the grip characteristic parameter is equal to the critical parameter value, and when the ratio between the self-aligning torque and the slip degree decreases from the critical ratio value, The grip characteristic parameter decreases from the critical parameter value, and the grip characteristic parameter increases from the critical parameter value when the ratio of the self-aligning torque and the slip degree increases from the critical ratio value.

  Moreover, in this 1st Embodiment, the unstable behavior suppression assist command value calculating part 50 has implement | achieved the control part. That is, the control of the saturation region by the unstable behavior suppression assist command value calculation unit 50 is performed in the grip characteristic parameter (saturation region) where the grip characteristic parameter (μ gradient) is equal to or less than the critical parameter value (μ gradient <0). Grip recovery control that increases the (μ gradient) above the critical parameter value is realized. In addition, the control of the attention area by the unstable behavior suppression assist command value calculation unit 50 is performed by a predetermined characteristic in which the grip characteristic parameter (μ gradient) is larger than the predetermined critical parameter value (μ gradient> 0) is larger than the critical parameter value. Grip reduction that prevents the grip characteristic parameter (μ gradient) from decreasing toward the critical parameter value in the marginal region (attention region) smaller than the first parameter threshold (corresponding μ gradient value when torque gradient <0). Preventive control is realized.

In the first embodiment, the wheel load change amount calculation unit 47 realizes a wheel load detection unit that calculates the wheel load of the wheel. The correction of the characteristic map based on the wheel load change amount in the torque gradient calculation unit 48 and the μ gradient calculation unit 49 is a correction unit that corrects the relationship between the input and the output based on the wheel load obtained by the wheel load detection unit. It is realized by the function.
In the first embodiment, the characteristic curve of the torque gradient characteristic map (FIG. 12) and the characteristic curve of the μ gradient characteristic map (FIG. 17) are the first axis representing the ratio between the self-aligning torque and the slip degree. A grip characteristic curve in a plane coordinate system having a grip characteristic parameter and a second axis representing the grip characteristic parameter. The grip characteristic curve intersects the first axis at a crossover point, at which the self-aligning torque and the The ratio to the slip ratio is equal to the critical ratio value, the grip characteristic parameter is equal to the critical parameter value, the grip characteristic curve extends from the crossover point to the end point, and at the end point, the grip characteristic parameter is equal to the maximum parameter value. . The correction of the characteristic map based on the wheel load change amount in the torque gradient calculation unit 48 and the μ gradient calculation unit 49 is performed by setting the end point to the origin that is the intersection of the first axis and the second axis according to the change in the wheel load. It is possible to move on a straight line. Alternatively, the correction of the characteristic map based on the wheel load change amount in the torque gradient calculation unit 48 and the μ gradient calculation unit 49 forms a curve family that extends in a curved line along each other without intersecting each other in a region larger than the critical ratio value. As described above, the grip characteristic curve is corrected in accordance with the wheel load. Further, the correction of the characteristic map based on the wheel load change amount in the torque gradient calculation unit 48 and the μ gradient calculation unit 49 is based on the origin that is the intersection of the first axis and the second axis as the wheel load increases. The functional relationship is corrected so that the crossover point is moved in a direction away from the origin on a straight line passing through the crossing point and the crossover point is moved in a direction away from the origin on the first axis. Here, the coordinates at which the torque gradient and μ gradient are zero in the characteristic curve of the torque gradient characteristic map (FIG. 12) and the characteristic curve of the μ gradient characteristic map (FIG. 17) correspond to the crossover point. Further, the coordinates at which the torque gradient and the μ gradient are maximum in the characteristic curve of the torque gradient characteristic map (FIG. 12) and the characteristic curve of the μ gradient characteristic map (FIG. 17) correspond to the end points.

(Effect in the first embodiment)
(1) The input unit sets an input that is a ratio between the self-aligning torque of the wheel and the slip degree of the wheel on the ground contact surface. The output unit determines an output which is a grip characteristic parameter indicating the grip characteristic of the wheel based on the input set by the input unit. Therefore, if the self-aligning torque of the wheel and the slip degree of the wheel are known, a grip characteristic parameter indicating the grip characteristic of the wheel can be acquired based on the ratio.
Thereby, based on the grip characteristic parameter which shows the grip characteristic of a wheel, a tire friction state and a grip state can be estimated appropriately. And even when the grip force of the wheel is in the limit region, the tire friction state can be estimated more appropriately, so that the margin for the tire friction limit can be estimated appropriately.

  Therefore, unlike the method of estimating the tire friction state based on the actual lateral acceleration and yaw rate (conventional method), the tire friction state can be appropriately estimated even when the vehicle behavior changes suddenly. In addition, in the conventional method, when the slow behavior of the vehicle behavior change that occurs on the frozen road surface or the case of a four-wheel drift state is reached, the value of the lateral acceleration and the yaw rate is small. The accuracy of the detected values of acceleration and yaw rate deteriorated, and the estimation accuracy of the tire friction state was poor. On the other hand, in the present embodiment, even when the vehicle behavior change speed is slow, it is possible to estimate using a slip degree (for example, slip angle) having a value larger than that of the lateral acceleration or yaw rate. Can be estimated appropriately.

(2) The grip characteristic parameter is a change rate (μ gradient) of wheel force acting on the wheel with respect to the change amount of the slip degree. This utilizes the fact that the self-aligning torque, wheel force (for example, lateral force), and slip degree (for example, slip angle) are similarly affected by the road surface μ. From this ratio, the rate of change of the wheel force acting on the wheel with respect to the amount of change in the slip degree is obtained. That is, it is possible to obtain a lot of information from the ratio between the self-aligning torque and the slip degree. Thereby, for example, even if the wheel force cannot be obtained by a detection means such as a wheel force sensor, the change rate of the wheel force acting on the wheel with respect to the change amount of the slip degree can be obtained.

(3) The grip characteristic parameter is the rate of change (torque gradient) of the self-aligning torque with respect to the amount of change in the slip degree. Thereby, based on the rate of change of the self-aligning torque with respect to the amount of change in the slip degree (torque gradient), the margin for the tire friction state, the grip state, and the tire friction limit can be estimated more appropriately.
(4) The output unit outputs the rate of change of the wheel force with respect to the amount of change in the slip degree (μ gradient) and the rate of change of the self-aligning torque with respect to the amount of change in the slip degree (torque gradient) as the grip characteristic parameters. Yes. That is, the rate of change of the self-aligning torque (torque gradient) with respect to the amount of change in the slip degree is obtained from the ratio of the self-aligning torque and the degree of slip, and further, the rate of change in wheel force with respect to the amount of change in the slip degree μ gradient). Thus, by using a plurality of parameters (torque gradient, μ gradient) obtained from the ratio of the self-aligning torque and the slip degree, it is possible to appropriately estimate the margin for the tire friction state, the grip state, and the tire friction limit. .

(5) The slip degree is the slip angle of the wheel. Here, the information on the slip angle of the wheel is usually information that can be easily obtained in the vehicle. Thereby, the margin with respect to a tire friction state, a grip state, and a tire friction limit can be easily estimated.
(6) The output unit determines the grip characteristic parameter from the ratio between the self-aligning torque and the slip degree according to a predetermined non-linear relationship between the input variable represented by the input and the output variable represented by the output. It is configured to decide. The predetermined nonlinear relationship between the input variable and the output variable is in the form of a characteristic curve or a mathematical expression. By making the output unit simple in this way, it is possible to appropriately estimate the margin for the tire friction state, the grip state, and the tire friction limit.

(7) The grip characteristic parameter is a variable representing the grip state of the wheel. The output unit is configured to determine the grip characteristic parameter only from the ratio between the self-aligning torque and the slip degree without using the ground friction coefficient. In this way, a configuration that does not require the friction coefficient of the ground realizes a simple configuration that does not require a map for each friction coefficient of the ground, and the appropriate margin for the tire friction state, the grip state, and the tire friction limit. Can be estimated.

(8) The grip characteristic parameter represents the slope of the tire characteristic curve of the wheel force with respect to the slip degree, the slope of the tire characteristic curve of the self-aligning torque with respect to the slip degree, or these two slopes. The output unit is configured to determine the slope of the tire characteristic curve from only the ratio between the self-aligning torque and the slip degree without using the ground friction coefficient. In this way, a configuration that does not require the friction coefficient of the ground realizes a simple configuration that does not require a map for each friction coefficient of the ground, and the appropriate margin for the tire friction state, the grip state, and the tire friction limit. Can be estimated.

(9) The tire characteristic curve of the wheel force with respect to the slip degree or the tire characteristic curve of the self-aligning torque with respect to the slip degree has a high friction coefficient for a high friction road surface having a high friction coefficient and a low friction coefficient lower than the high friction coefficient. And a low friction tire characteristic curve for a low friction road surface. Further, the grip characteristic parameter represents at least one gradient of the high friction tire characteristic curve and the low friction tire characteristic curve. The input unit obtains the current value of the ratio between the self-aligning torque and the slip degree from the current value of the self-aligning torque and the current value of the slip degree. Also, the output unit determines the current value of the grip characteristic parameter from the current value of the ratio between the self-aligning torque and the slip degree obtained at the input unit, and corresponds to the current value of the self-aligning torque and the current value of the slip degree. The slope value of the high friction tire characteristic curve, the current value of the self-aligning torque, and the slope value of the low friction tire characteristic curve corresponding to the current value of the slip degree are the same and set equal to the current value of the grip characteristic parameter. It is configured to do. That is, ground friction such that the tire 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. A configuration that does not require a coefficient is realized. In addition, the tire characteristic curve is configured to obtain the current value of the grip characteristic parameter based on the current value of the self-aligning torque and the current value of the slip degree. As a result, a simple configuration such as not requiring a map for each friction coefficient of the ground is realized, and the margin for the tire friction state, the grip state, and the tire friction limit can be estimated appropriately.

(10) The tire characteristic curve is a characteristic curve representing tire characteristics depending on the road surface friction coefficient. The output unit is configured to determine the slope of the tire characteristic curve from only the ratio between the self-aligning torque and the slip degree without using the ground friction coefficient. In this way, a configuration that does not require the friction coefficient of the ground realizes a simple configuration that does not require a map for each friction coefficient of the ground, and the appropriate margin for the tire friction state, the grip state, and the tire friction limit. Can be estimated.

(11) The grip characteristic parameter is a function that increases when the ratio between the self-aligning torque and the slip ratio increases from the critical ratio value. By expressing the grip characteristic parameter as a function in this way, it is possible to appropriately estimate the margin for the tire friction state, the grip state, and the friction limit.
(12) When the ratio of the self-aligning torque and the slip degree increases in a large ratio region larger than the critical ratio value, the ratio of the increase in the grip characteristic parameter to the increase in the ratio of the self-aligning torque and the slip degree is increased. The grip characteristic parameter increases nonlinearly so as to increase. Thus, by expressing the grip characteristic parameter as having a predetermined characteristic, it is possible to appropriately estimate the margin with respect to the tire friction state, the grip state, and the tire friction limit.

(13) When the ratio between the self-aligning torque and the slip degree is equal to the critical ratio value, the grip characteristic parameter is equal to the critical parameter value. Further, when the ratio between the self-aligning torque and the slip degree decreases below the critical ratio value, the grip characteristic parameter decreases below the critical parameter value. When the ratio between the self-aligning torque and the slip degree increases above the critical ratio value, the grip characteristic parameter increases above the critical parameter value. As described above, the grip characteristic parameter is further clarified by the predetermined characteristic, so that the margin with respect to the tire friction state, the grip state, and the tire friction limit can be appropriately estimated.

(14) In the critical region where the grip characteristic parameter is equal to or less than the critical parameter value, the control unit performs grip recovery control for increasing the grip characteristic parameter from the critical parameter value. Further, the control unit decreases the grip characteristic parameter toward the critical parameter value in the marginal region where the grip characteristic parameter is larger than the predetermined critical parameter value but smaller than the predetermined first parameter threshold value larger than the critical parameter value. Grip reduction prevention control is performed to prevent this. Thereby, in the grip recovery control, it is possible to ensure the grip force by urging the driver to switch back the steering wheel. Furthermore, in the grip reduction prevention control, it is possible to prevent the driver from excessively turning the steering wheel and to prevent a decrease in grip force.

(15) At least two vehicle ground contact surface friction state estimating devices are provided on the right wheel and the left wheel of the vehicle. Thereby, a difference in grip characteristics between the left and right wheels can be detected.
(16) A grip characteristic parameter for the right wheel and a grip characteristic parameter for the left wheel are compared to detect a left-right difference in the road surface condition of the ground. As a result, for example, a difference in road surface μ, that is, a split μ state can be detected as the left-right difference in the road surface state.

(17) The wheel load detection unit determines the wheel load of the wheel, and the correction unit calculates the relationship between the input and output (torque gradient characteristic map, μ gradient characteristic map) based on the wheel load determined by the wheel load detection unit. It is corrected. Thereby, it is possible to obtain the grip characteristic parameter with high accuracy without being influenced by the wheel load.
(18) The relationship between the input and the output is a functional relationship that can be expressed as a grip characteristic curve in a planar coordinate system having a first axis that represents the ratio of the self-aligning torque and the slip ratio and a second axis that represents the grip characteristic parameter. It has become. The grip characteristic curve intersects the first axis at the crossover point, at which the ratio of the self-aligning torque to the slip degree is equal to the critical ratio value and the grip characteristic parameter is set to the critical parameter value. Are equal. Further, the grip characteristic curve extends from the crossover point to the end point, and at the end point, the grip characteristic parameter is equal to the maximum parameter value. And the correction | amendment part is moving the end point on the straight line which passes along the origin which is an intersection of a 1st axis | shaft and a 2nd axis | shaft according to the change of a wheel load. That is, correction is performed using a characteristic when the grip characteristic curve changes according to the wheel load (a characteristic that changes with a similar shape). Thereby, a grip characteristic parameter can be obtained with high accuracy.

(19) In a region larger than the critical ratio value, the correction unit corrects the grip characteristic curve according to the wheel load so as to form a curve group extending in a curved line along each other without intersecting each other. That is, correction is performed using a characteristic when the grip characteristic curve changes according to the wheel load (a characteristic that changes with a similar shape). Thereby, a grip characteristic parameter can be obtained with high accuracy.

(20) The correction unit moves the end point in a direction away from the origin on a straight line passing through the origin, which is the intersection of the first axis and the second axis, according to the increase in wheel load, and sets the crossover point to the first point. The functional relationship is corrected so that it moves in the direction away from the origin on the axis. That is, correction is performed using a characteristic when the grip characteristic curve changes according to the wheel load (a characteristic that changes with a similar shape). Thereby, a grip characteristic parameter can be obtained with high accuracy.

(21) The steering angle detection means detects the steering angle. The steering torque detection means detects the steering torque when the driver steers. Then, the self-aligning torque calculating means calculates the self-aligning torque based on the steering angle detected by the steering angle detecting means and the steering torque detected by the steering torque detecting means. Thereby, the self-aligning torque can be easily obtained.

(Second Embodiment)
(Constitution)
In the second embodiment, the vehicle body running state estimation device 28 specifies the vehicle behavior based on the μ gradient of the front and rear wheels, and performs assist control according to the specified vehicle behavior.
FIG. 29 shows the configuration of the vehicle body travel state estimation device 28 in the second embodiment. As shown in FIG. 29, the vehicle body travel state estimation device 28 includes a stability factor calculation unit 61 and a vehicle behavior estimation unit 62. Further, in the second embodiment, a configuration for detecting the μ gradient for each of the front and rear wheels is provided. Specifically, a configuration corresponding to a tire slip angle calculation unit 43, a self-aligning torque calculation unit 45, a self-aligning torque-slip angle ratio calculation unit 46, a torque gradient calculation unit 48, and a μ gradient calculation unit 49 (vehicle connection) The configuration corresponding to the ground friction state estimation device) is provided corresponding to the front wheel and the rear wheel of the vehicle.

FIG. 30 shows a processing procedure by the stability factor calculation unit 61 and the vehicle behavior estimation unit 62. The processing contents in the stability factor calculation unit 61 and the vehicle behavior estimation unit 62 will be described along this processing procedure.
As shown in FIG. 30, first, in step S31, the stability factor calculation unit 61 calculates a static margin SM. Specifically, the stability factor calculation unit 61 calculates the static margin SM according to the following formula (9) based on the front and rear wheel μ gradients K _f and K _r calculated (estimated) by the front and rear wheel μ gradient calculation unit 49. Is calculated.

The static margin SM is a value indicating the ease with which drift-out or spin occurs. Alternatively, the static margin SM is a value indicating the saturation state of the tire lateral force. For example, the static margin SM becomes small when the grip state of the front wheels 31 _FL and 31 _FR reaches the limit (the tire lateral force is saturated) and the μ gradient K _{f of the} front wheels becomes zero or a negative value. That is, the static margin SM is reduced when the lateral force does not increase even when the slip angle is increased on the front wheels (the lateral force is saturated) and drift-out is likely to occur. The stability factor calculation unit 61 outputs the static margin SM having such characteristics to the vehicle behavior estimation unit 62.

  Subsequently, in step S32 and subsequent steps, the vehicle behavior estimation unit 62 determines whether the turning characteristic is an understeer tendency, an oversteer tendency, or a neutral steer tendency based on the static margin SM calculated by the stability factor calculation unit 61. To do. Specifically, first, in step S32, the vehicle behavior estimation unit 62 determines whether or not the static margin SM is zero. Here, if the static margin SM is zero (SM = 0), the vehicle behavior estimation unit 62 proceeds to step S33. Further, when the static margin SM is not zero (SM ≠ 0), the vehicle behavior estimation unit 62 proceeds to step S34. Note that it is also possible to determine that the static margin SM is zero when the static margin SM is within a predetermined range including zero.

In step S34, it is determined whether or not the static margin SM is a positive value. Here, if the static margin SM is a positive value (SM> 0), the vehicle behavior estimation unit 62 proceeds to step S35. If not (SM <0), the vehicle behavior estimation unit 62 proceeds to step S36.
In step S33, the vehicle behavior estimation unit 62 determines that the turning characteristic of the vehicle has a neutral steer tendency. Moreover, in step S35, the vehicle behavior estimation part 62 determines with the turning characteristic of a vehicle having an understeer tendency. Furthermore, in step S36, the vehicle behavior estimation unit 62 determines that the turning characteristic of the vehicle has an oversteer tendency. The vehicle behavior estimation unit 62 outputs the determination result to the unstable behavior suppression assist command value calculation unit 50.

  The unstable behavior suppression assist command value calculation unit 50 outputs an unstable behavior suppression assist command to the EPS ECU 26 based on the determination result input from the vehicle behavior estimation unit 62. Specifically, the unstable behavior suppression assist command value calculation unit 50 outputs the unstable behavior suppression assist command to the EPS ECU 26 when the vehicle behavior estimation unit 62 determines that there is an understeer tendency (SM> 0). . The unstable behavior suppression assist command output here is a command signal for reducing the output of the EPS motor 27. Thereby, when it exists in an understeer tendency and drift-out is easy to occur, the steering force assist torque by the EPS motor 27 is reduced.

  Further, the unstable behavior suppression assist command value calculation unit 50 outputs an unstable behavior suppression assist command to the EPS ECU 26 when the vehicle behavior estimation unit 62 determines that there is an oversteer tendency (SM <0). The stable behavior suppression assist command output here prevents the output of the EPS motor 27 from being reduced. That is, the reduction of the steering force assist torque is suppressed. When a four-wheel drift state or spin behavior occurs, it is necessary to quickly apply counter steer (return steering). For this reason, it is difficult to apply counter-steer only by controlling to reduce the assist amount in accordance with the grip reduction of the front wheels. For this reason, by not reducing the steering force assist torque, it is possible to apply quick counter steer in a situation where there is an oversteer tendency and spin is likely to occur, and the vehicle behavior can be stabilized.

  Then, as in the first embodiment, the attention region (torque gradient <0 and μ gradient ≧ 0) and the saturation region (torque gradient <0 and μ gradient <0) are specified based on the μ gradient and torque gradient. Then, it is also possible to output a stable behavior suppression assist command corresponding to the region. Thereby, it is possible to prevent drift-out and to prevent the occurrence of spin, corresponding to the attention region and the saturation region.

(Effect in 2nd Embodiment)
(1) At least two vehicle ground contact surface friction state estimation devices are provided, and the two devices are provided on a front wheel and a rear wheel of the vehicle, respectively. Thereby, a difference in grip characteristics between the front and rear wheels can be detected.
(2) The variation in vehicle characteristics is estimated by comparing the grip characteristic parameters for the front wheels and the grip characteristic parameters for the rear wheels. As a result, for example, an oversteer tendency or an understeer tendency can be estimated as a change in vehicle characteristics.

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 diagram 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 about the tire characteristic curve (Fy-βt characteristic curve) of each road surface μ, the slope of the tangent at the intersection with 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 about the tire characteristic curve (Fy-βt characteristic curve) of each road surface μ, the slope of the tangent at the intersection with the straight line passing through the origin of the tire characteristic curve FIG. It is a figure used in order to explain a premise technique, and is a ratio (Fy / βt) of a lateral force Fy and a slip angle βt indicating an intersection of an arbitrary straight line and a tire characteristic curve (Fy-βt characteristic curve). FIG. 5 is a characteristic diagram showing a relationship (μ gradient characteristic map) with a slope (μ gradient) of a tangent on a characteristic curve of a tire at the intersection. It is the figure used in order to explain the premise technology, and is the figure used for explanation of the procedure which obtains the slope of the tangent on the tire characteristic curve (Fy-βt characteristic curve) from the lateral force Fy and the slip angle βt. is there. It is a figure used in order to explain a premise technique, and is a figure showing a relation between a characteristic curve (μ gradient characteristic map), a tire characteristic curve (Fy-βt characteristic curve), and a friction circle. It is the figure used in order to explain the premise technique, ratio (Fy / βt) of lateral force Fy and slip angle βt when changing wheel load and tire characteristic curve (Fy-βt characteristic curve) It is a characteristic view which shows the relationship with the inclination of an upper tangent. FIG. 6 is a characteristic diagram showing a tire characteristic curve (Mz-βt characteristic curve) established between a wheel slip angle βt and a wheel self-aligning torque Mz. is there. It is the figure used in order to explain the premise technology, about the tire characteristic curve (Mz-βt characteristic curve) of each road surface μ, the slope of the tangent at the intersection with 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 about the tire characteristic curve (Fy-βt characteristic curve) of each road surface μ, the slope of the tangent at the intersection with the straight line passing through the origin of the tire characteristic curve FIG. FIG. 5 is a diagram used for explaining a presupposed technique, and is a ratio of an aligning point between an arbitrary straight line and a tire characteristic curve (Mz-βt characteristic curve) to a self-aligning torque Mz and a slip angle βt (Mz / FIG. 6 is a characteristic diagram showing a relationship (torque gradient characteristic map) between βt) and a tangential slope (torque gradient) on a tire characteristic curve at the intersection. It is the figure used in order to explain a premise technique, and was used for explanation of the procedure which obtains the slope of the tangent on the tire characteristic curve (Mz-βt characteristic curve) from the self-aligning torque Mz and the slip angle βt. FIG. It is the figure used in order to explain the premise technology, ratio (Mz / βt) of self-aligning torque Mz and slip angle βt when changing wheel load and tire characteristic curve (Mz-βt characteristic) It is a characteristic view showing the relationship with the slope of the tangent on the (curve). FIG. 5 is a characteristic diagram showing the relationship between the lateral force Fy and the self-aligning torque Mz with respect to the slip angle βt. FIG. 16 is a characteristic diagram showing the relationship shown in FIG. 15 for various road surfaces μ, which is used for explaining a presupposed technology. It is the figure used in order to explain the premise technology, the ratio (Mz / βt) of the self-aligning torque Mz and the slip angle βt, and the slope of the tangent on the tire characteristic curve (Fy-βt characteristic curve) It is a characteristic view showing a relationship (μ gradient characteristic map) with (μ gradient). It is a figure used to explain the underlying technology, and the ratio (Mz / βt) between the self-aligning torque Mz and the slip angle βt when the wheel load is changed, and the tire characteristic curve (Fy-βt characteristic) It is a characteristic view showing the relationship with the slope of the tangent on the (curve). It is a figure showing the schematic structure of the vehicles which are the 1st embodiment of the present invention. It is a block diagram which shows the internal structure of a vehicle running condition estimation apparatus. It is a block diagram which shows the internal 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 flowchart which shows the process sequence of an unstable behavior suppression assist command value calculating part. It is a flowchart which shows an example of the arithmetic processing procedure in a vehicle body running state estimation apparatus. The figure used for explanation of the control in the safety region (torque gradient ≧ 0 and μ gradient ≧ 0), the attention region (torque gradient <0 and μ gradient ≧ 0) and the saturation region (torque gradient <0 and μ gradient <0). It is. It is a block diagram which shows the internal structure of the vehicle running condition estimation apparatus in 2nd Embodiment. It is a flowchart which shows the process sequence of the vehicle running condition estimation apparatus in 2nd Embodiment.

Explanation of symbols

21 Steering angle sensor, 22 Yaw rate sensor, 23 Lateral acceleration sensor, 24 Longitudinal acceleration sensor, 25 Wheel speed sensor, 26 EPS CPU, 27 EPS motor, 28 Vehicle body travel state estimation device (vehicle ground contact surface friction state estimation device), 29 Steering wheel , 30 Steering shaft, 31 _{FL to} 31 _RR wheel, 32 pinion, 33 rack, 34 tie rod, 35 steering torque sensor, 36 brake ECU, 41 vehicle body speed calculation unit, 42 vehicle body slip angle estimation unit, 43 tire slip angle calculation unit, 44 EPS assist torque calculation unit, 45 self-aligning torque calculation unit, 46 self-aligning torque-slip angle ratio calculation unit, 47 wheel load change calculation unit, 48 torque gradient calculation unit, 49 μ gradient calculation unit, 50 unstable Behavior suppression assist command value calculation unit, 1 stability factor calculation unit, 62 vehicle behavior estimating section

Claims (22)

In the vehicle ground contact surface friction state estimation device for estimating the ground contact surface grip characteristics of the vehicle wheel,
An input unit that sets an input that is a ratio of a self-aligning torque that is a torque that returns the steering of the wheel to a neutral position on the ground surface and a slip degree of the wheel;
Based on the input set in the input unit, an output unit that determines an output that is a grip characteristic parameter indicating a grip characteristic of the wheel;
Equipped with a,
The grip characteristic parameter is at least one of a change rate of wheel force acting on a wheel with respect to a change amount of the slip degree, and a change rate of the self-aligning torque with respect to the change amount of the slip degree,
On the basis of the size of the grip characteristic parameter, friction state or the wheels of the road surface gripping state of the wheel vertical plane, or vehicle ground plane friction state estimating apparatus characterized that you estimate margin for the friction limit. The output unit outputs, as the grip characteristic parameter, a change rate of wheel force with respect to a change amount of the slip degree and a change rate of the self-aligning torque with respect to the change amount of the slip degree. vehicle ground contact surface friction state estimating apparatus as claimed in 1. The slip degree, vehicle ground plane friction state estimating apparatus as claimed in claim 1 or 2, characterized in that the slip angle of the wheel. The output unit determines the grip based on a ratio between the self-aligning torque and the slip degree according to a predetermined non-linear relationship between an input variable represented by the input and an output variable represented by the output. it is configured to determine the characteristic parameters, the predetermined non-linear relationship between the input variables and output variables, any one of claim 1 to 3, characterized in that in the form of a characteristic curve or formula The vehicle ground contact surface friction state estimation device according to claim 1. The grip characteristic parameter is a variable representing a grip state of a wheel, and the output unit determines the grip characteristic parameter only from a ratio of the self-aligning torque and the slip degree without using a ground friction coefficient. vehicle ground contact surface friction state estimating apparatus as claimed in any one of claims 1-4, characterized in that it is configured. The grip characteristic parameter represents a slope of a tire characteristic curve of a wheel force with respect to the slip degree, a slope of a tire characteristic curve of the self-aligning torque with respect to the slip degree, or these two slopes. without using the friction coefficient, any one of claim 1 to 5, characterized in that only from the ratio between the slip degree and the self-aligning torque is configured to determine the gradient of the tire characteristic curve The vehicle ground contact surface friction state estimation device according to claim 1. The tire characteristic curve of the wheel force with respect to the slip degree or the tire characteristic curve of the self-aligning torque with respect to the slip degree is a high friction tire characteristic curve for a high friction road surface having a high friction coefficient and a low friction coefficient lower than the high friction coefficient. includes a low friction tire characteristic curve for a low friction road surface having the grip characteristic parameter, wherein the high friction tire characteristic curve and a low friction tire characteristic curve sac Chino represents at least one of the gradient, wherein the input unit, the A current value of a ratio of the self-aligning torque and the slip degree is obtained from a current value of the self-aligning torque and a current value of the slip degree, and the output unit is configured to calculate the self-aligning torque obtained from the input unit and A current value of the grip characteristic parameter is determined from a current value of the ratio to the slip degree, and the self-alarm is determined. The current value of the lining torque and the slope value of the high friction tire characteristic curve corresponding to the current value of the slip degree, the current value of the self-aligning torque, and the low friction tire characteristic curve corresponding to the current value of the slip degree 7. The vehicle ground contact surface friction state estimating device according to claim 6 , wherein the vehicle ground contact surface friction state estimating device is set to be equal to a current value of the grip characteristic parameter. The tire characteristic curve is a characteristic curve that represents a tire characteristic that depends on a road surface friction coefficient, and the output unit does not use a ground friction coefficient, but only from a ratio between the self-aligning torque and the slip degree. 8. The vehicle ground contact surface friction state estimation device according to claim 6 , wherein the vehicle characteristic contact surface friction state estimation device is configured to determine a slope of a tire characteristic curve. The said grip characteristic parameter is a function which increases when the ratio of the said self-aligning torque and the said slip degree increases from a critical ratio value, The any one of Claims 1-8 characterized by the above-mentioned. Vehicle ground contact surface friction state estimation device. When the ratio between the self-aligning torque and the slip degree increases in a large ratio region larger than the critical ratio value, the grip characteristic parameter increases with respect to the increase in the ratio between the self-aligning torque and the slip degree. 10. The vehicle ground contact surface friction state estimating device according to claim 9 , wherein the grip characteristic parameter increases nonlinearly so that the ratio increases. When the ratio between the self-aligning torque and the slip degree is equal to the critical ratio value, the grip characteristic parameter is equal to the critical parameter value, and the ratio between the self-aligning torque and the slip degree is calculated from the critical ratio value. When decreasing, the grip characteristic parameter decreases from the critical parameter value, and when the ratio of the self-aligning torque and the slip degree increases from the critical ratio value, the grip characteristic parameter increases from the critical parameter value. The vehicle ground contact surface friction state estimation device according to claim 9 or 10 , characterized in that In a critical region where the grip characteristic parameter is less than or equal to the critical parameter value, grip recovery control is performed to increase the grip characteristic parameter from the critical parameter value, and the grip characteristic parameter is greater than the predetermined critical parameter value. In a marginal region that is smaller than a predetermined first parameter threshold value that is greater than the critical parameter value, a control unit that performs grip reduction prevention control that prevents the grip characteristic parameter from decreasing toward the critical parameter value is provided. The vehicle ground contact surface friction state estimation device according to claim 11 , wherein A vehicle ground contact surface friction state estimation device comprising at least two devices according to any one of claims 1 to 12 and including the two devices on a right wheel and a left wheel of a vehicle. A vehicle ground contact surface friction state estimation device comprising at least two devices according to any one of claims 1 to 12 and including the two devices on a front wheel and a rear wheel of a vehicle, respectively. 14. The vehicle ground contact surface friction state according to claim 13 , wherein the right and left difference in the road surface condition of the ground is detected by comparing the grip characteristic parameter for the right wheel and the grip characteristic parameter for the left wheel. Estimating device. 15. The vehicle ground contact surface friction state estimation device according to claim 14 , wherein a variation in vehicle characteristics is estimated by comparing the grip characteristic parameter for the front wheel and the grip characteristic parameter for the rear wheel. The wheel load detection unit for determining the wheel load of the wheel, and a correction unit for correcting the relationship between the input and the output based on the wheel load determined by the wheel load detection unit. The vehicle ground contact surface friction state estimation device according to any one of 1 to 16 . The relationship between the input and output is a functional relationship that can be expressed as a grip characteristic curve in a plane coordinate system having a first axis that represents the ratio of the self-aligning torque and the slip degree and a second axis that represents the grip characteristic parameter. And the grip characteristic curve intersects the first axis at a crossover point, at which the ratio of the self-aligning torque and the slip degree is equal to a critical ratio value, and the grip characteristic The parameter is equal to the critical parameter value, the grip characteristic curve extends from the crossover point to the end point, and at the end point, the grip characteristic parameter is equal to the maximum parameter value, and the correction unit responds to a change in wheel load. The end point is moved on a straight line passing through the origin which is the intersection of the first axis and the second axis. Vehicle ground contact surface friction state estimating apparatus as claimed in claim 17, characterized in that. The correction unit corrects a grip characteristic curve according to a wheel load so as to form a curve group extending in a curved line along each other without intersecting each other in a region larger than the critical ratio value. The vehicle ground contact surface friction state estimation device according to claim 18 . The correction unit moves the end point in a direction away from the origin on a straight line passing through the origin, which is an intersection of the first axis and the second axis, according to an increase in wheel load, and sets the crossover point. The vehicle ground contact surface friction state estimation device according to claim 18 or 19 , wherein the functional relationship is corrected so as to move in a direction away from the origin on the first axis. Steering angle detection means for detecting the steering angle;
Steering torque detection means for detecting steering torque when the driver steers,
Self-aligning torque calculating means for calculating the self-aligning torque based on the steering angle detected by the steering angle detecting means and the steering torque detected by the steering torque detecting means;
The vehicle installation surface friction state estimation device according to any one of claims 1 to 20 , wherein the vehicle installation surface friction state estimation device is provided. In the vehicle ground contact surface friction state estimation method for estimating the ground contact surface grip characteristics of the vehicle wheel,
An input step for setting an input which is a ratio of a self-aligning torque of the wheel and a slip degree of the wheel on a ground surface;
Based on the input set in the input step, an output step for determining an output that is a grip characteristic parameter indicating a grip characteristic of the wheel;
I have a,
The grip characteristic parameter is at least one of a change rate of wheel force acting on a wheel with respect to a change amount of the slip degree, and a change rate of the self-aligning torque with respect to the change amount of the slip degree,
A vehicle ground contact surface friction state estimation method characterized by estimating a friction state of a wheel contact surface or a road surface grip state of a wheel or a margin with respect to a friction limit based on the magnitude of the grip characteristic parameter .

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