JP6775753B2 - Road friction coefficient estimation method, estimation system and estimation program - Google Patents

Description

The present invention relates to a technique for estimating a road surface friction coefficient suitable for automobile safety technology and automatic driving technology.

Estimating the coefficient of friction of the road surface is important for the further development of automobile safety technology represented by automatic braking systems and automatic driving technology that is expected to be put into practical use. At present, these technologies are based on measurement by wheel speed sensors, acceleration sensors, etc., which are relatively easy to measure (see, for example, Patent Documents 1 and 2), but these sensors accurately determine the coefficient of friction of the traveling road surface. It is difficult to grasp.

In addition, various studies have been conducted on "intelligent tires" that measure the coefficient of friction between a tire and a traveling road surface from deformations that occur in the tire (see, for example, Patent Documents 3 and 4). However, it has not yet become widespread because it is difficult to stably measure the deformation of the tire and it is difficult to accurately estimate the friction coefficient from the generated deformation.

Japanese Unexamined Patent Publication No. 2001-253334 Japanese Unexamined Patent Publication No. 2005-7792 JP-A-2002-36836 Japanese Unexamined Patent Publication No. 2005-345238

Tomohiko Sasano, Hiroshi Tachiya, Yoshihiro Higuchi, Daisei Ise, Masato Sato, Marino Fukuda, "Study on Measurement of Road Friction Coefficient by Strain Measurement of Tire Sides", Japan Society of Mechanical Engineers, M & M2017 Strength of Materials Conference, Lecture Number OS0303, p187-191

Therefore, what the present invention seeks to solve in view of the above situation is the estimation of the road surface friction coefficient, which enables more stable measurement of tire deformation and accurate estimation of the friction coefficient of the traveling road surface from the deformation. The point is to provide technology.

The present inventor has already proposed a method of measuring the strain generated on the side surface of a tire and estimating the friction coefficient from the result (see Non-Patent Document 1). That is, the present inventor provides a strain gauge of three axes (tire rotation direction, radial direction, and intermediate direction) on the side surface of the tire, and conducts an experiment in which a plurality of magnitudes of frictional force are applied under a constant vertical load. By conducting experiments in which vertical loads of multiple magnitudes are applied under a constant frictional force, the strains in all three axial directions are applied to the load and frictional force acting on the tire at all rotation angles (α). On the other hand, we found that it changes almost linearly, derived the following equation, selected arbitrary two rotation angles α using this equation, and combined the equations (5) that hold each of them together to create a frictional force F. , It was proposed to calculate the vertical load W and further to calculate the friction coefficient μ.

Since this method uses the measured strain on the side surface of the tire, stable results can be obtained, the accuracy is good, and it can be a robust friction coefficient measuring method that is resistant to the influence of disturbances, but the direction of the frictional force (tire). There are problems that the components in the circumferential direction and the width direction cannot be specified and that the formula becomes complicated.

As a result of diligent studies in view of the current situation, the present inventor has found that the frictional force in the tire width direction and the strain in the triaxial directions all change substantially linearly at all rotation angles (α), and the above equation (5) ) Is divided into two components, the tire circumferential direction and the width direction, and the following equation (6) is established. Furthermore, the deformation of the tire is similarly deformed on the front side and the back side (left and right). The present invention was completed by finding that the equation (6) can be simplified by using the measurement strains of the left and right symmetrical positions (the same rotation angle positions and the same radial positions corresponding to each other) on the front surface side and the back surface side. It came to be done.

That is, for formula (6), symmetrically _L A of the left and right tires, strain measurement in the rotation angle α of L _{A 'is} represented by the following formula (7), it is established respectively (8). Here, by considering that deformation of the tire is symmetrical, the coefficient of _{F Y} (and _{l A (α) l A '} (α)) is equal to the coefficients of W and _{(m A} (α) _{m a '(α))} is equal to the coefficients of _{F X (k a} (α) and -k _{a' (α))} is the absolute value is equal relationship opposite polarities. Therefore, the equation (9) is derived by adding both sides of the equations (7) and (8), and the equation (10) is derived by subtracting both sides of the equations (7) and (8), respectively.

Since Equation (9) is a two-way linear equations, symmetrical position _(L A, L _{A ')} any two of the rotation angle of the (alpha _1, alpha ₂₎ By using the strain measurement at, _{F Y} and W Can be sought. Further, Equation (10) because it is a one yuan of linear equations (function _{F X),} left-right symmetric positions _(L A, L _{A ')} any one of the rotation angle of the (alpha ₃₎ (alpha ₃ are alpha ₁ or the use of strain measurement in may be the same as α _2.), it is possible to obtain the F _X.

That is, the present invention includes the following inventions.
[1] to one another corresponding pair of symmetrical positions of the left and right sidewall portions of the tire _{(L A,} L A _') a in strain each measurement in the same direction at the time of tire rotation _{(ε A, ε A')} , Measured strains (ε _A (α ₁ ), ε _A' (α ₁ ), ε _A (α ₂ ), ε _A' (α) at two different predetermined tire rotation angle positions (α ₁ , α ₂ ), respectively. ₂ )) is substituted into the following equations (1) and (2), respectively, and is the same as the process of obtaining the frictional force ( _FY ) in the tire circumferential direction during tire rotation and the vertical load (W) during tire rotation. wherein the position _{(L a, L} a _') in the respective measuring strain (ε _a, ε _a') a, respectively predetermined tire rotational angular position (alpha ₃₎ measurement strain when the (ε _a (α ₃ ), epsilon _{a '(the} alpha _3)), by substituting each of the following formula (3), the frictional force in the tire width direction at the time of tire rotation (F _X) a step of determining, said tire circumferential direction of the frictional force (F method of estimating the road surface friction coefficient, characterized in that it comprises a step of obtaining the estimated value of road surface friction coefficient from _Y) and the friction force of the tire width direction (F _X) and the vertical load (W).

[2] The method for estimating the road surface friction coefficient according to [1], wherein the tire rotation angle position (α ₃ ) is the same position as the tire rotation angle position (α ₁ ) or (α ₂ ).

[3] The road surface friction according to [1] or [2], wherein the tire rotation angle position (α ₁ , α ₂ ) is a position excluding a position within a predetermined front-rear angle range from the angle position directly below the road surface closest to the road surface. How to estimate the coefficient.

[4] The tire rotation angle positions (α ₁ , α ₂ ) are positions preferentially selected from those having a larger absolute value of the determinant of the following equation (4) [1] to [3]. ]. The method for estimating the road surface friction coefficient according to any one of.

_'In each strain each measurement in the same directions _{(ε A, ε A [5} ] the symmetrical position of the side wall portion of the tire _{(L A, L A)'} ) formed by providing a strain gauge capable of measuring [1 ] To [4], the method for estimating the road surface friction coefficient.

[6] a pair of symmetrical positions corresponding to each other of the side wall portions of the left and right tires _{(L A,} L A _') in, a the strain each in the same direction during tire rotation, at least two respective different predetermined tire rotation a strain measurement device comprises means for measuring the strain when the angular position, by said each distortion data measured by the strain measuring device, means for reading from the internal or external storage means, which is the measuring position (L _a , LA _' ), each measured strain (ε _A , ε _A' ) in the same direction during tire rotation, and measured at two different predetermined tire rotation angle positions (α ₁ , α ₂ ), respectively. Substitute the strains (ε _A (α ₁ ), ε _A' (α ₁ ), ε _A (α ₂ ), ε _A' (α ₂ )) into the following equations (1) and (2), respectively, and tire. means for obtaining the tire circumferential direction of the frictional force during rotation _{(F Y)} and vertical load at the time of tire rotation (W), also the location _{(L a, L} a _') in the strain each measurement (ε _a, ε _{a 'a),} each predetermined tire rotational angular position (alpha ₃₎ measurement strain when the (epsilon _a (alpha _3), epsilon _a' a (alpha _3)), by substituting each of the following formula (3), friction force in the tire width direction at the time of tire rotation (F _X) means for obtaining, as well as the frictional force of the tire circumferential direction (F _Y) and the friction force of the tire width direction (F _X) and the vertical load (W) A road surface friction coefficient estimation system including a friction coefficient calculation device having a means for obtaining an estimated value (μ) of the road surface friction coefficient from the above.

[7] The strain measurement device, the symmetrical positions _{(L A,} L A _') of the sidewall portion of the tire, each strain each measurement in the same directions (ε _A, ε _A' strain) to be measured gauge [6] The road surface friction coefficient estimation system according to [6].

[8] A program for causing a computer to function as the friction coefficient calculation device according to [6] or [7], and means for reading data of each strain measured by the strain measuring device from an internal or external storage means. the measured position _{(L a,} L a _') in the strain each measurement in the same direction at the time of tire rotation (ε _a, ε _a') a, each of the two different predetermined tire rotational angular position (alpha _1, alpha ₂₎ measurement strain when the _{(ε a (α 1),} ε a '(α 1), ε a (α 2), ε a' a (alpha _2)), the following equation (1), wherein (2) substituted respectively, the frictional force in the tire circumferential direction at the time of tire rotation (F _Y) and means for determining the vertical load (W) at the time of tire rotation, also the location (L _{a, L} a _') in the The measured strains (ε _A (α ₃ ), ε _A' (α ₃ )) at the predetermined tire rotation angle positions (α ₃ ) for each measured strain (ε _A , ε _A' ) are shown below. substituted respectively in equation (3), the frictional force in the tire width direction at the time of tire rotation (F _X) means for obtaining, as well as the tire circumferential direction of the frictional force (F _Y) and the friction force of the tire width direction (F A road surface friction coefficient estimation program for operating a computer as a means for obtaining an estimated value (μ) of the road surface friction coefficient from _X ) and the vertical load (W).

According to the road surface friction coefficient estimation method, estimation system, and estimation program according to the present invention as described above, the friction force is determined by both the tire circumferential direction and the width direction while avoiding complicated equations and calculations. Since it can be obtained, the road surface friction coefficient can be obtained immediately and accurately not only when traveling straight but also when cornering, and a practical road surface friction coefficient estimation technique can be provided.

The schematic explanatory view which shows the whole structure of the road surface friction coefficient estimation system which concerns on this invention. (A) is an explanatory diagram showing the state of the positions of the rotation angles α ₁ and α ₂ of the strain measuring device provided at symmetrical positions on the left and right sidewalls of the tire, and (b) is an explanatory diagram showing the strain measuring direction. .. Similarly, a block configuration diagram showing a road surface friction coefficient estimation system. The step diagram which shows the processing procedure of this embodiment. The perspective view which shows the experimental apparatus. Perspective view of the main part of the experimental device. (A) is an explanatory diagram showing the position of the strain gauge, and (b) is an explanatory diagram showing the friction angle. Graph showing the strain and time variation of the load of the tire rotation angle α is 30deg obtained from strain gauges A1 and A2 at the time of changing the frictional force F _X of the tire width direction. (A) ~ (c) is a graph showing the tire rotational angular position alpha = 30 deg, the relationship between the strain gauge A1, strain and friction force in the tire width direction in each direction obtained by the A2 _{F X.} (A) ~ (c) is a graph showing the relationship between α strain and the tire rotational angular position in each direction obtained by the strain gauge A1 at the time of changing the frictional force F _Y in the tire circumferential direction. (A) ~ (c) is a graph showing the relationship between α strain and the tire rotational angular position in each direction obtained by the strain gauge A2 at the time of changing the frictional force F _Y in the tire circumferential direction. (A) to (c) are graphs showing the relationship between the strain in each direction obtained by the strain gauge A1 when the vertical load W is changed and the tire rotation angle position α. (A) to (c) are graphs showing the relationship between the strain in each direction obtained by the strain gauge A2 when the vertical load W is changed and the tire rotation angle position α. (A) ~ (c) is a graph showing the relationship between the tire rotational angle position alpha = 0, the strain gauge A1, strain in each direction obtained by A2 and the tire circumferential direction of the frictional force F _Y. (A) to (c) are graphs showing the relationship between the strain in each direction obtained by the strain gauges A1 and A2 and the vertical load W at the tire rotation angle position α = 0. The graph which shows the result of the measured value (calculated value) and the true value by the pair of strain gauges A1 and A1'. The graph which shows the result of the measured value (calculated value) and the true value by the pair of strain gauges A2 and A2'.

Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention includes a pair of symmetrical positions corresponding to each other of the left and right sidewall portions of the tire as shown in FIG. _{2 (a) (L A,} L A ') in, there in strain each measurement in the same direction during tire rotation Te, by using the strain each measurement when each of the two or more different predetermined tire rotational angle position, the frictional force in the tire circumferential direction (F _Y), friction force in the tire width direction (F _X), vertical load (W ) Is efficiently obtained, and an accurate estimated value of the road surface friction coefficient is quickly obtained in consideration of the frictional force in the tire width direction.

As shown in FIGS. 1 and 2A, the road surface friction coefficient estimation system S according to the present invention includes a strain measuring device 11 for measuring the strain of the sidewall portion of the tire 9 of the vehicle 10 and the measured strain. It is composed of a friction coefficient calculation device 1 for obtaining an estimated value of a road surface friction coefficient based on data, and a storage means 3 inside or outside the friction coefficient calculation device 1.

Symmetrical positions _{(L A,} L A _') to the strain measurement device is provided, respectively 11 is for measuring the strain at the tire rotation, as long as it can measure the strain in the same direction, specifically to the measurement The direction is not particularly limited, and may be set in any direction such as the tire circumferential direction, the radial direction, or the intermediate direction between them. Preferably, it is set to measure the strain in the intermediate direction with a small variation. Further, among the intermediate directions, as shown in FIG. 2B, a direction inclined by 45 degrees from the circumferential direction toward the radial direction orthogonal to the circumferential direction is more preferable, but the direction is offset to the circumferential direction side or the radial direction side. It may be in any direction. The angle of inclination from the circumferential direction to the radial direction is preferably an angle in the range of 30 to 60 degrees, and more preferably an angle in the range of 40 to 55 degrees.

As such a strain measuring device 11, a strain gauge 4 is preferably used, and the installation form thereof is not limited, such as adhering or embedding a foil type strain gauge on each outer surface or inner surface of the sidewall portion. .. However, it is preferable that the left and right have the same installation form. A strain measuring device other than the strain gauge may be used.

In this example, the tire side is provided with a transmission unit (not shown) that wirelessly transmits each strain data detected by the left and right strain gauges 4 to the reception device 5 on the vehicle side, and the reception device 5 is close to the tire of the vehicle. It is installed in the right place. The strain data received by the receiving device 5 is transmitted to the friction coefficient calculating device 1 that calculates the road surface friction coefficient, which is also provided at an appropriate position of the vehicle, and is stored in the storage means 3 inside and outside the device. It may be configured to be transmitted to another device and stored in the storage means 3 through the device.

As shown in FIG. 3, the friction coefficient calculation device 1 is a computer including an arithmetic processing unit 2 and a storage means 3. The arithmetic processing unit 2 is mainly composed of a CPU such as a microprocessor, and each data is input from the receiving device 5 and the storage means 3 through the input / output unit and the bus line. The storage means 3 is composed of storage memories such as RAM and ROM, hard disks inside and outside the device 2, and stores programs and processing data that define procedures for various processing operations in the arithmetic processing device 2.

The arithmetic processing device 2 functionally receives the measured strain data of the symmetrical positions measured by the strain measuring device 11 from the receiving device 5, and stores the measured strain data in the strain data storage unit 30 of the storage means 3. The measurement strain reading processing unit 21 that reads the measured strain data at the time of the measured two different predetermined tire rotation angle positions from the strain data storage unit 30, and the two different predetermined tire rotation angle positions that have been read. Based on the measured strain at the time of, the frictional force ( _FY ) in the tire circumferential direction during tire rotation and the vertical load (W) during tire rotation are obtained, and the circumferential frictional force stored in the peripheral friction force / vertical load data storage unit 31. -The friction in the tire width direction during tire rotation based on the measured strain at one of the two different predetermined tire rotation angle positions read by the vertical load calculation processing unit 22 and the measured strain at one of the angle positions. force (F _X) and determined, and the width frictional force calculation processing unit 23 to be stored in the width friction data storage unit 32, the frictional force in the tire circumferential direction stored in the storage unit 3 (F _Y) and vertical load (W ) and estimated value of road surface friction coefficient (mu) determined from the tire width direction frictional force (F _X), comprising at least a friction coefficient calculation processing unit 24 to be stored in the coefficient of friction data storage unit 33, these functions the program It will be realized.

Calculated in the tire circumferential direction of the frictional force by the circumferential friction-vertical load calculation unit 22 (F _Y) and vertical load (W), the read symmetrical positions _{(L A,} L A _') strain each measurement of (epsilon _{a, ε a '2} different predetermined tire rotational angular position) (α _1, α ₂₎ measured strain when the _{(ε a (α 1),} ε a' (α 1), ε a (α 2) , Ε _A' (α ₂ )) is substituted into the following equations (1) and (2), respectively, and calculated by simultaneous. Experimental constants of l _{A + A'} (α ₁ ), m _{A + A'} (α ₁ ), b _{A + A'} (α ₁ ), l _{A + A'} (α ₂ ), m _{A + A'} (α ₂ ), b _{A + A'} (α ₂ ) Is determined in advance by experiment for each tire (for each tire type (brand, size)).

The tire rotation angle position (α ₁ , α ₂ ) is preferably a position excluding a position within a predetermined front-rear angle range from the angle position directly below the road surface. This is because the tire is significantly deformed within a predetermined angle range in the front-rear direction from the angle position directly below the tire, so that the linearity with the load is lower than in other ranges. Specifically, it is preferable to exclude the angular position within the range of 30 deg before and after the selection.

Further, it is preferable that the tire rotation angle positions (α ₁ , α ₂ ) are preferentially selected from those in which the absolute value of the determinant of the following equation (4) becomes large. This is because the solution becomes unstable when the determinant shown in the equation (4) approaches zero, and conversely, the larger the value of the determinant, the higher the accuracy.

Friction force in the tire width direction by the width frictional force calculation processing unit 23 calculates the (F _X) is measured when the two different predetermined tire rotational angle position read strain _{(ε A (α 1),} ε A '( Measured strain at one of the angular positions of α ₁ ), ε _A (α ₂ ), ε _A' (α ₂ )) ((ε _A (α ₁ ), ε _A' (α ₁ ))) Or, by changing (ε _A (α ₂ ), ε _A' (α ₂ ))) to (ε _A (α ₃ ), ε _A' (α ₃ )) and substituting this into the following equation (3), respectively. It is calculated.

However, the rotation angle position α ₃ may be set to a third angle position different from α ₁ and α ₂ . That is, for the rotational angle position alpha _3, the results of pre-calibration experiments, for each rotation angle alpha, and calculates the correlation coefficient of the strain _{(ε A (α) -ε A} '(α)) and F _X, its It is preferable to preferentially select the one having a large absolute value in order to improve the accuracy. _{k A-A '(α 3} ), b A-A' experimental constants (alpha ₃₎ is also determined in advance by experiment for each tire (each type of tire (brand, size)).

Estimate the road surface friction coefficient by the friction coefficient calculation unit 24 (mu) the calculation of the frictional force of the calculated tire circumferential direction (F _Y) and vertical load (W) and the tire width direction frictional force (F _X) Is calculated by substituting into the following equation (11).

Hereinafter, the processing procedure by the road surface friction coefficient estimation system S of the present embodiment will be described with reference to FIG.

First, symmetric position L _A, strain in the same direction by the respective strain gauges 4 L A _'is detected, it is transmitted from a not-shown transmitting device to the receiving device 5 of the vehicle 10 side (S101). The measured strain received by the receiving device 5 is stored in the strain data storage unit 30 of the storage means 3 by the measurement strain receiving processing unit 20 of the arithmetic processing device 2 of the friction coefficient calculation device 1 (S102). For this measured strain data, the rotation angle data obtained by a sensor (not shown) that detects the rotation angle of the tire is received directly or from another processing device, and is combined with the rotation angle data in the strain data storage unit 30. It is preferable that the memory is managed.

Next, the measurement strain reading processing unit 21 of the arithmetic processing device 2 reads each strain data when the _two rotation angles α ₁ and α ₂ are among the measured strain data stored in the strain data storage unit 30 ( S103).

Next, the peripheral friction force / vertical load calculation processing unit 22 substitutes each measured strain at the two different predetermined tire rotation angle positions read into the above equations (1) and (2) to rotate the tire. The frictional force ( _FY ) in the tire circumferential direction and the vertical load (W) during tire rotation are obtained and stored in the peripheral frictional force / vertical load data storage unit 31 (S104).

Next, the width friction force calculation processing unit 23 applies the measured strain at one of the two different predetermined tire rotation angle positions read to the above equation (3). assignment, and the frictional force in the tire width direction when the tire rotates (F _X) value is stored into the width frictional force data storage unit 32 (S105).

Then, the friction coefficient calculation processing unit 24, and a frictional force of the calculated tire circumferential direction (F _Y) and vertical load (W) and the tire width direction frictional force (F _X) are substituted into the formula (11) , The estimated value (μ) of the road surface friction coefficient is calculated and stored in the friction coefficient data storage unit 33 (S106).

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Hereinafter, using the experimental apparatus shown in FIG. 5, the verification of the equations (1) to (3) of the present invention and the comparison between the calculated value (estimated value) and the true value (actual measurement value) of the road surface friction coefficient μ will be compared. The result of the test will be described.

(experimental method)
The experimental device 7 is shown in FIGS. 5 and 6. The tire 9 used in the experiment was a DSX-2 155 / 80R13 79Q manufactured by Dunlop. As shown in FIG. 7A, a total of four 3-axis strain gauges (KFG-2-120-D17-23 L3M2S manufactured by Kyowa Electric Co., Ltd.) are installed on the front side surface of the tire 9 and on the back surface side. I pasted it. Strain gauge surface side, the position of 15mm in a radial direction from the portion in contact with the wheel 8 (the position _L A1 serving as the region _{R 1} of FIG. 2), the 55mm position (region _{R 2} of FIG. 2 position It was attached to _LA2 ), respectively, and the strain gauge A1 and the strain gauge A2 were used from the side closest to the wheel 8. The back surface side of the strain gauge, symmetrical position with the surface side L _{A1 ',} L _A2' strain respectively gauges A1 ', A2' was affixed.

That is, there are two pairs of strain gauges at symmetrical positions (the first pair consisting of strain gauges A1 and A1'provided with the first symmetrical positions _LA1 and _LA1', respectively, and the second symmetrical positions _LA2 and L. _A2'A second pair of strain gauges A2 and A2', respectively) is provided. Region R _1, a region, a region R ₂ near the bead portion of the sidewall portion of the tire, and a central region which protrudes most side of the sidewall portion of the tire. The triaxial strain gauge simultaneously detects intermediate strain, radial strain, and circumferential strain.

The experimental device 7 can apply a vertical load W by driving the force plate 73 in the Z-axis direction and pressing it against the tread surface of the tire 9. The drive in the Z-axis direction has a pair of screw feed mechanisms that horizontally move the front and rear legs 71 composed of the links of the support base 72 supporting the force plate 73 in the direction toward or away from each other by the same amount. It is realized by the parallel type load unit 70.

In this state, by rotating the tire driving unit 74 and a drive motor for the tire 9 is driven to rotate the shaft tire fixed shaft, it is possible to load a frictional force F _Y in the tire circumferential direction. Further, by driving the force plate 73 in the X-axis direction, it can be loaded with frictional force F _X in the width direction of the tire 9. The drive in the X-axis direction is realized by moving the legs 71 in the same direction in the front-rear direction by the same amount by the parallel load unit 70. By adjusting the magnitude of F _X and F _Y, it is a frictional force F is these force can be acted in any direction. In the present specification, as shown in FIG. 7B, the angle θ formed by the frictional force F with the frictional force _FY component is defined as the “friction angle” θ.

W loaded on the tire, F _X, magnitude of F _Y are each pressing block 75 provided on the back surface side of the four corners of the force plate 73 as shown in FIG. 6, X-axis direction, Y axis direction, Z It is measured by load cells 761, 762, and 763 on the support base 72 side supported from the axial direction, whereby the friction force F and the friction angle θ are also obtained at the same time.

As shown in FIG. 5, the change in the position of the strain gauge with the rotation of the tire is represented by a clockwise rotation angle α from the position vertically below.

(Verification of equations (1) to (3))
F _x acting on the strain and the ground surface occurring in the tire _side, in order to verify the relationship of F _Y and W, [1] F _X only is varied, to confirm the relationship between strain and F _X experiment, [2] F _Y only varied, experiments to confirm the relationship between strain and F _Y, [3] W only is varied, experiments to confirm the relationship between strain is W, it was respectively. For the strain, the strain values of the strain gauges A1 and A2 on the surface side were used.

[1] was subjected to _{F X} and strain changes only experiment F _X to confirm the relationship _(F Y = 0N) is to experiment. First, the force plate 73 of the experimental apparatus shown in FIG. 5 is driven in the Z-axis direction by the action of W by, by driving the force plate 73 in the X-axis direction in this state, was allowed to act F _X. The tires were not rotated during the experiment in order to set _FY to 0. Therefore, only one result at one rotation angle α was obtained from one experiment.

In this experiment, three types of rotation angles of α = -30 deg, 0 deg, and 30 deg, that is, three patterns in which the gauge positions are different with respect to the friction surface were tested. The experimental conditions were common to each α. The experimental conditions are shown in Table 1. The target vertical load and 1360～1390N, smooth acrylic plate friction surface, an aluminum plate, changing the _{F X} by three kinds of PTFE (Teflon). Further, by setting the friction angle θ to 2 types of 0 deg and 180 deg, that is, by setting the drive of the force plate 73 in the X-axis direction to 2 types in the X-axis positive and negative directions, a total of 6 types of F for each α _X was allowed to act. The experiment was performed 3 times for each condition.

As an example of the experimental results, FIG. 8 shows a case where the rotation angle α is 30 deg, the friction surface is a PTFE plate, and the friction angle θ is 0 deg. In FIG. 8, t = 13 to 21s is a friction section (a section in which the force plate 73 and the tire 9 are in friction). First, a relatively stable waveform range (t = 15 to 17s in FIG. 8) is selected from the friction section. Next, the frictional force FX _and strain ε in the same range are averaged. This way, the relation of F _X and ε obtained, shows the results of alpha = 30 deg in FIG. From FIG. 9, the relationship of F _X and ε even distortion in either direction was confirmed to be approximately linear.

[2] The F _Y and experiments in which only the course experiment F _Y to confirm the relationship between the strain was performed using the same device. The experimental conditions are shown in Table 2. The W and 2500N, different rubber sheet having a friction surface coefficient of friction, textured acrylic plate, allowed to act three stages of F _Y by three road surface PTFE plate. Other main experimental conditions were a friction angle θ of 90 deg, a friction distance of 2200 mm (for one round of the tire), a friction speed of 30 mm / s, and a tire air pressure of 200 kPa.

The experimental results of the strain gauge A1 are shown in FIG. 10, and the experimental results of the strain gauge A2 are shown in FIG. The load shown in the legend is an average value of α = −180 to +180 deg. Figure 14 is a waveform distortion in FIGS. 10 and 11, in which the obtained relation and strain _{F Y} in alpha = 0 deg. Than 14, one of the strain gauges (A1, A2), any direction of strain (strain circumferential, radial strain, intermediate direction strain) even, the strain ε is changed linearly with respect to F _Y ..

[3] Experiment to confirm the relationship between W and strain An experiment to change only W was performed using the same device. The experimental conditions are shown in Table 3. Different rubber sheet having a friction surface coefficient of friction, textured acrylic plate, and 3 a road surface of the PTFE sheet, both _{F Y} is such that the 1150N, was changed W (adjustment). Other main experimental conditions were a friction angle θ of 90 deg, a friction distance of 2200 mm (for one round of the tire), a friction speed of 30 mm / s, and a tire air pressure of 200 kPa.

The experimental results of the strain gauge A1 are shown in FIG. 12, and the experimental results of the strain gauge A2 are shown in FIG. The load shown in the legend is an average value of α = −180 to +180 deg. FIG. 15 shows the relationship between W and strain at α = 0 deg from the strain waveforms of FIGS. 12 and 13. From FIG. 15, the strain ε changes linearly with respect to W in any strain gauge (A1, A2) and in any direction strain (circumferential strain, radial strain, intermediate strain). It is known that W changes linearly from the conventional equation (5).

As described above, it was confirmed that the strain generated on the side surface of the tire and the load acting on the ground contact surface (F _x , _FY , W) have a linear relationship in any direction. From this, it can be seen that the above equations (6) to (10), and by extension, (1) to (3) hold. Experimental constants of equations (1) to (3) l _{A + A'} (α ₁ ), mA _{+ A'} (α ₁ ), b _{A + A'} (α ₁ ), l _{A + A'} (α ₂ ), mA _{+ A'} (α ₂ ) , B _{A + A'} (α ₂ ), k _A-A' (α ₃ ), b _A-A' (α ₃ ) are obtained from the graph obtained in this way by the method of least squares. However, when obtaining such an empirical constant, instead of the experimental friction surface as in this example a plurality prepared by changing the θ by changing the F _X and F _Y, even from one type of friction surface Experimental constants can be calibrated.

(Comparison experiment between calculated value and true value)
Of the measured strains of the strain gauges A1, A1', A2, and A2', the friction coefficient μ and the friction angle θ were obtained from the equations (1) to (3) using the intermediate direction measurement strain. Specifically, as shown in Table 4, smooth acrylic plates having different friction coefficients, PTFE (Teflon (registered trademark)) sheets, aluminum plates, and oil-coated smooth acrylic plates (oil-coated acrylic) are used as grounding surfaces. While changing the direction of the frictional force, that is, the friction angle θ, W was changed to 1500, 2000, 2500N, a slip simulation experiment was performed, and the strain was measured with strain gauges A1, A1', A2, and A2'.

Empirical constants of formula (1) to _{(3), F} X, F Y, using a value obtained from the measurement results of the obtained strain using the above tire by the device 7 the _W while varying. The direction of friction (friction angle θ) was 60, 90, 120, 240, 270, 300 deg, the friction distance was 2000 mm (about one round of the tire), the friction speed was 30 mm / s, and the tire air pressure was 200 kPa. .. Equation (1), by (2) _F Y, the angular position alpha ₁ measurement strain for calculating the W, alpha _2, and the angular position alpha ₃ of the measuring strain for calculating _{F X} by the formula (3) , Each α of the top 5 sets (No. 1 to No. 5) shown in Table 5 was used. The determinant is the above-mentioned equation (4). Also the correlation coefficient of the strain and the load is a correlation coefficient of the strain mentioned above _{(ε A (α) -ε A} '(α)) and F _X.

Strain gauges A1 and A1'No. 5 in Table 5. The measured values (calculated values) and the true values of the friction coefficient and the friction angle using each strain data at the angle position of 1 are shown in FIGS. 16 (a) and 16 (b). In addition, the strain gauges A2 and A2'No. Figures 17 (a) and 17 (b) show the measured values (calculated values) and true values of the friction coefficient and friction angle using each strain data at the angle position of 1. From FIG. 16 and 17, any of F _Y and W in the gauge, it is found that can more accurately estimate the friction coefficient mu.

In addition, from the results using the strain data of each of the five sets of angular positions in Table 5, the average squared error of the true value of the friction coefficient and the measured value and the average squared of the true value of the friction angle and the measured value are used using equation (13). The results of calculating the square error are shown in Table 6. As can be seen from Table 6, No. It can be seen that the friction coefficient and the friction angle can be calculated accurately even if the combination of the angle positions of 1 is not used.

1 Friction coefficient calculation device 2 Arithmetic processing device 3 Storage means 4 Strain gauge 5 Reception device 7 Experimental device 8 Wheels 9 Tires 10 Vehicles 11 Strain measurement device 20 Measurement strain reception processing unit 21 Measurement strain reading processing unit 22 Circumferential friction force / vertical load Calculation processing unit 23 Width friction force calculation processing unit 24 Friction coefficient calculation processing unit 30 Strain data storage unit 31 Circumferential friction force / vertical load data storage unit 32 Width friction force data storage unit 33 Friction coefficient data storage unit 70 Parallel load unit 71 legs 72 supporting stand 73 force plate 74 tire driving unit 75 press block 761,762,763 load cell A1, A1 ', A2, A2 ' strain gauge _{L A1, L A1 ', L} A2, L A2' symmetrical positions R _1, R ₂ region S estimation system

Claims (8)

A pair of symmetrical positions _{(L A,} L A _') corresponding to each other of the side wall portions of the left and right tires of strain each measurement in the same direction at the time of tire rotation (ε _A, ε _A') A, two each Measured strains at different predetermined tire rotation angle positions (α ₁ , α ₂ ) (ε _A (α ₁ ), ε _A' (α ₁ ), ε _A (α ₂ ), ε _A' (α ₂ )) Is substituted into the following equations (1) and (2), respectively, to obtain the frictional force ( _FY ) in the tire circumferential direction during tire rotation and the vertical load (W) during tire rotation.
_'In the strain each measurement (ε _A, ε _A similarly the position _{(L A, L A)'} ) A, respectively predetermined tire rotational angular position (alpha ₃₎ Measurement strain when the (ε _A (α _3), epsilon _{a 'a} (alpha _3)), a step of substituting respectively the following formula (3), determine the frictional force in the tire width direction when the tire rotates _{(F X),}
A step of determining the estimated value of road surface friction coefficient from the frictional force of the tire circumferential direction (F _Y) frictional forces of the tire width direction (F _X) and the vertical load (W),
A method for estimating the coefficient of friction of the road surface, which comprises.


The method for estimating the road surface friction coefficient according to claim 1, wherein the tire rotation angle position (α ₃ ) is the same position as the tire rotation angle position (α ₁ ) or (α ₂ ). The method for estimating the road surface friction coefficient according to claim 1 or 2, wherein the tire rotation angle position (α ₁ , α ₂ ) is a position excluding a position within a predetermined angle range in the front-rear direction from the angle position directly below the road surface closest to the road surface. Any one of claims 1 to 3 where the tire rotation angle position (α ₁ , α ₂ ) is a position preferentially selected from those having a larger absolute value of the determinant of the following equation (4). The method for estimating the coefficient of friction of the road surface described in the section.
The symmetrical positions _{(L A,} L A _') of the sidewall portion of the tire, each strain each measurement in the same directions (ε _A, ε _A') formed by providing a strain gauge to measure the claims 1-4 The method for estimating the road surface friction coefficient according to any one of the above items. A pair of symmetrical positions corresponding to each other of the side wall portions of the left and right tires _{(L A,} L A _') in, a the strain each in the same direction during tire rotation, at least two different predetermined tire rotational angular position respectively A strain measuring device having a means for measuring the strain at the time,
A means for reading the data of each strain measured by the strain measuring device from an internal or external storage means,
The measured position _{(L A,} L A _') a in strain each measurement in the same direction at the time of tire rotation _{(ε A, ε A')} , each of the two different predetermined tire rotational angular position (alpha ₁ , Α ₂ ) measured strains (ε _A (α ₁ ), ε _A' (α ₁ ), ε _A (α ₂ ), ε _A' (α ₂ )) are expressed by the following equations (1) and (α ₂ ). Means for obtaining the frictional force ( _FY ) in the tire circumferential direction during tire rotation and the vertical load (W) during tire rotation by substituting into 2), respectively.
_'In the strain each measurement (ε _A, ε _A similarly the position _{(L A, L A)'} ) A, respectively predetermined tire rotational angular position (alpha ₃₎ Measurement strain when the (ε _A (α _3), epsilon _{a '(alpha 3)),} and assigns each of the following formula (3), means for calculating the frictional force in the tire width direction when the tire rotates _{(F X),}
And the friction coefficient comprises means for obtaining an estimated value of road surface friction coefficient (mu) from the friction force of the tire circumferential direction (F _Y) the frictional force in the tire width direction (F _X) and the vertical load (W) Calculator and
A system for estimating the coefficient of friction of the road surface.


The strain measurement device, the symmetrical positions _{(L A,} L A _') of the sidewall portion of the tire, each strain each measurement in the same directions (ε _A, ε _A' is a strain gauge) to be measured according to Item 6. The road surface friction coefficient estimation system according to Item 6. A program that causes a computer to function as the friction coefficient calculation device according to claim 6 or 7.
A means for reading the data of each strain measured by the strain measuring device from an internal or external storage means,
The measured position _{(L A,} L A _') a in strain each measurement in the same direction at the time of tire rotation _{(ε A, ε A')} , each of the two different predetermined tire rotational angular position (alpha ₁ , Α ₂ ) measured strains (ε _A (α ₁ ), ε _A' (α ₁ ), ε _A (α ₂ ), ε _A' (α ₂ )) are expressed by the following equations (1) and (α ₂ ). Means for obtaining the frictional force ( _FY ) in the tire circumferential direction during tire rotation and the vertical load (W) during tire rotation by substituting into 2), respectively.
_'In the strain each measurement (ε _A, ε _A similarly the position _{(L A, L A)'} ) A, respectively predetermined tire rotational angular position (alpha ₃₎ Measurement strain when the (ε _A (α _3), epsilon _{a '(alpha 3)),} and assigns each of the following formula (3), means for calculating the frictional force in the tire width direction when the tire rotates _{(F X),}
And the tire circumferential direction of the frictional force (F _Y) and the friction force in the tire width direction (F _X) and said computer function as means for obtaining a from the vertical load (W) estimated value of road surface friction coefficient (mu) A program for estimating the coefficient of friction of the road surface.