JP6775752B2 - 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 side surface", Japan Society of Mechanical Engineers, M & M2017 Strength of Materials Conference Number OS0303, p187-191

Therefore, what the present invention seeks to solve in view of the above situation is a road surface friction coefficient estimation technique capable of more stably measuring the deformation of the tire and accurately estimating the friction coefficient of the traveling road surface from the deformation. Is in the point of providing.

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 affect the load and frictional force acting on the tire at all rotation angles (α). On the other hand, we found that it deformed 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, etc., but the rotation angle α is controlled. There are problems that it is necessary and that the result varies depending on the rotation angle α to be selected.

This time, the present inventor focused on the average value, the maximum value, and the minimum value of the strain per rotation of the tire. This is because it is considered that if these values can be used, it is not necessary to control the rotation angle α, the practicality is enhanced, and the variation can be suppressed to be small by using the average value. As a result of further diligent studies, the average value of strain on the tire side surface, especially in the intermediate direction, has a linear relationship with the frictional force in the tire circumferential direction, and the position of the tire sidewall portion near the bead portion is located. The minimum value of the radial strain is linearly related to the vertical load, and the maximum value of the radial strain at the position of the central region overhanging to the side of the tire sidewall is the friction in the tire circumferential direction. They have found that they have a linear relationship with force and vertical load, respectively, and have completed the present invention.

That is, the present invention includes the following inventions.
[1] Average value of measured strains in the intermediate direction between the circumferential direction and the radial direction during tire rotation (ε _{A_1 (ave)} ) at a predetermined position in the region _RA near the bead portion of the sidewall portion of the tire. or, at a predetermined position in the central region R _B which protrudes most side of the sidewall portion of the tire, the intermediate direction of the measuring strain average value between the circumferential direction and the radial direction in the tire rotation (epsilon _{B_1 ( ave))} ) and the minimum value of the measured strain in the radial direction during tire rotation (ε _{A_2 (min)} ) at a predetermined position in the region R _A of the same tire, or the region R of the same tire. _The step of calculating the maximum value (ε _{B_2 (max)} ) of the measured strain in the radial direction during tire rotation at a predetermined position of _B , and the average value of the calculated intermediate strain (ε _{A_1 (ave)} or ε _{B_1 ). (ave)} ) is substituted into the following equation (1) to obtain the frictional force ( _FY ) in the tire circumferential direction during tire rotation, and the calculated minimum value of radial strain (ε _{A_2 (min)} ). or substituted into the following equation (2), or the calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the friction force and (F _Y) are substituted into the following equation (3), It is provided with a step of obtaining a vertical load W when the tire rotates and a step of obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). A characteristic method for estimating the road surface friction coefficient.

[2] The average value per rotation of the measured strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation at a predetermined position in the region _RA near the bead portion of the tire sidewall portion (ε _{A_1). (ave))} ) and the minimum value (ε _{A_2 (min)} ) of the measured strain in the radial direction during tire rotation per tire rotation are calculated.
Substituting the calculated mean value of intermediate strain (ε _{A_1 (ave)} ) into the above equation (1), the frictional force ( _FY ) in the tire circumferential direction during tire rotation is obtained.
The method for estimating the road surface friction coefficient according to [1], wherein the calculated minimum value of radial strain (ε _{A_2 (min)} ) is substituted into the above equation (2) to obtain the vertical load W during tire rotation.

[3] Strain that can measure strain in at least two directions, that is, the strain in the intermediate direction between the circumferential direction and the radial direction and the strain in the radial direction at a predetermined position in the region _RA of the tire. The method for estimating a road surface friction coefficient according to [2], wherein a gauge is provided.

[4] at a predetermined position in the central region R _B which protrudes most side of the sidewall portion of the tire, measuring the strain of the mean value of the intermediate direction between the circumferential direction and the radial direction in the tire rotation (epsilon _{B_1 ( ave))} ) and the maximum value (ε _{B_2 (max)} ) of the measured strain in the radial direction during tire rotation are calculated, and the average value (ε _{B_1 (ave)} ) of the calculated intermediate strain is calculated by the above equation (1). by substituting determined friction force in the tire circumferential direction when the tire rotates (F _Y), the calculated radial distortion maximum value _{(ε B_2 (max))} and the tire circumferential direction of the friction force and (F _Y) The method for estimating a road surface friction coefficient according to claim 1, wherein the vertical load W at the time of tire rotation is obtained by substituting into the above equation (3).

[5] in place of the region R _B of the tire, the strain of the intermediate direction between the circumferential direction and the radial direction during the tire rotation, and of the strain in the radial direction, the strain can be measured strain of at least two directions The method for estimating a road surface friction coefficient according to [4], wherein a gauge is provided.

[6] Strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation at a predetermined position in the region _RA near the bead portion of the sidewall portion of the tire, or the circumference of the tire during tire rotation. tire in means, and the predetermined position of said region R _a of the tire to measure the strain in the intermediate direction between the direction and the radial direction at a predetermined position in the central region R _B which protrudes most side of the sidewall portion strain in the radial direction during rotation, or the strain measurement device comprises means for measuring the strain in the radial direction during the tire rotation at a predetermined position of said region R _B of the tire, measured by the strain measurement device the intermediate Means for reading directional and radial strain data from internal or external storage means, the average value of intermediate strain at a given position in the measured region _RA (ε _{A_1 (ave)} ), _{Alternatively,} a means for calculating the average value (ε _{B_1 (ave)} ) of the strain in the intermediate direction at the predetermined position of the region R _B , the minimum value (ε) of the strain in the radial direction at the predetermined position of the measured region R _{A. A_2 (min)),} or the maximum value of strain in the radial direction at a predetermined position of the region _{R B (ε B_2 (max)} ) means for calculating said calculated intermediate direction strain average value (epsilon _{A_1 (ave )} or epsilon _{B_1} the _(ave)) is substituted into the following equation (1), the friction force in the tire circumferential direction at the time of tire rotation (F _Y) means for determining said calculated radial distortion minimum value (epsilon _{A_2 (} or substituting _min)) by the following formula (2), or the calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the frictional force (F _Y) and the following formula (3 ) To obtain the vertical load W when the tire rotates, and the means to obtain the estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). A road surface friction coefficient estimation system including a friction coefficient calculation device having the above.

[7] The strain measuring device is provided at a predetermined position in the region _RA of the tire, and at least the strain in the intermediate direction between the circumferential direction and the radial direction and the strain in the radial direction during tire rotation. A strain gauge capable of measuring strain in two directions, wherein the friction coefficient calculating device calculates an average value (ε _{A_1 (ave)} ) of strain in the intermediate direction at a predetermined position in the measured region _RA . _A means for calculating the minimum value (ε _{A_2 (min)} ) of the radial strain at a predetermined position of the measured region _RA , and the average value (ε _{A_1 (ave)} ) of the calculated intermediate strain. A means for obtaining the frictional force ( _FY ) in the tire circumferential direction when the tire rotates by substituting into the equation (1), and the calculated minimum value of the radial strain (ε _{A_2 (min)} ) is applied to the equation (2). By substituting, there is a means for obtaining the vertical load W at the time of tire rotation, and a means for obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). [6] The road surface friction coefficient estimation system according to the above.

[8] the strain measurement device is provided at a predetermined position of said region R _B of the tire, the strain of the intermediate direction between the circumferential direction and the radial direction during the tire rotation, and radial strain, at least A strain gauge that can measure strain in two directions.
Said friction coefficient calculation device, means for calculating an average value of the intermediate direction strain _{(ε B_1 (ave))} at a predetermined position of the measurement region R _B, at a predetermined position of the measurement region R _B A means for calculating the maximum value of the radial strain (ε _{B_2 (max)} ), the average value of the calculated intermediate strain (ε _{B_1 (ave)} ) is substituted into the above equation (1), and the tire is rotated. friction force in the tire circumferential direction (F _Y) means for determining said calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the frictional force (F _Y) and the formula (3) A means for obtaining the vertical load W when the tire rotates, and a means for obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). The road surface friction coefficient estimation system according to [6].

[9] A program that causes a computer to function as the friction coefficient calculation device according to any one of [6] to [8], and is a strain in the intermediate direction and a strain in the radial direction measured by the strain measuring device. the data, internal or means for reading from the external storage means, said average value of the strain in the intermediate direction at a predetermined position of the measurement area _{R a (ε A_1 (ave)} ), or a predetermined position of the region R _B Means for calculating the average value of the strain in the intermediate direction (ε _{B_1 (ave)} ), the minimum value of the strain in the radial direction (ε _{A_2 (min)} ) at a predetermined position of the measured region _RA , or the region. A means for calculating the maximum value of the radial strain (ε _{B_2 (max)} ) at a predetermined position of R _B , the average value of the calculated intermediate strain (ε _{A_1 (ave)} or ε _{B_1 (ave)} ). Substituting into the following formula (1), a means for obtaining the frictional force ( _FY ) in the tire circumferential direction during tire rotation, and the calculated minimum value of radial strain (ε _{A_2 (min)} ) are obtained in the following formula (2). or substituted or the calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the friction force and (F _Y) are substituted into the following equation (3), the event of a tire rotation Road surface friction for operating a computer as a means for obtaining a vertical load W and as a means for obtaining an estimated value (μ) of a road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). Coefficient estimation program.

According to the road surface friction coefficient estimation method, estimation system, and estimation program according to the present invention as described above, the average value of the measured strains in the intermediate direction of the region _RA or region R _B of the sidewall portion of the tire is used. , the frictional force in the tire circumferential direction (F _Y) can be obtained with variation without precision, further also using the maximum value of the radial direction of the measuring strain of minimum or region R _B of the strain measurement of the radial region R _a Therefore, the vertical load can be obtained stably without controlling the rotation angle, and the experimental constants are also stabilized. Therefore, the estimated value of the friction coefficient can be easily and stably obtained from these frictional forces and the vertical load with high accuracy. It is possible to provide a practical road surface friction coefficient estimation technique.

In particular, the same area R _A or the frictional force with the measurement value of the intermediate direction strain and radial strain of R _B (F _Y), is possible to determine the vertical load (W) and estimated value of road surface friction coefficient (mu), Therefore, it is possible to measure the strain in only one region to improve the efficiency of the tire strain measurement, and it is possible to keep the cost low.

Further, when measuring strain in only one region, if a strain gauge capable of measuring strain in at least two directions of intermediate strain and radial strain is provided, the strain gauge is only provided in one place of the tire. It is possible to obtain all the measured strains required for estimating the road surface friction coefficient, to make the tire strain measurement more efficient, and to further reduce the cost.

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 view showing a region of a tire sidewall portion where a strain measuring device is provided, and (b) is an explanatory view showing a 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 1st Embodiment. The step diagram which shows the processing procedure of 2nd Embodiment. The perspective view which shows the experimental apparatus. Perspective view of the main part of the experimental device. (A) and (b) are graphs showing the relationship between the intermediate strain obtained from the strain gauge A and the rotation angle α. (A) and (b) are graphs showing the relationship between the radial strain obtained from the strain gauge A and the rotation angle α. (A) and (b) are graphs showing the relationship between the intermediate strain obtained from the strain gauge B and the rotation angle α. (A) and (b) are graphs showing the relationship between the radial strain obtained from the strain gauge B and the rotation angle α. (A) is a graph showing a graph showing the relationship between the average value and the F _Y intermediate direction strain, the relationship between (b) is likewise an average value and W. (A) is a graph showing the relationship between the maximum value / minimum value and F _Y radial strain graph showing the relationship between (b) is also the maximum value / minimum value and W. The graph which shows the result of the calculated value by the strain gauge A and the true value. The graph which shows the result of the calculated value by the strain gauge B and the true value.

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

In the present invention, as shown in FIG. 2A, the region _RA near the bead portion of the sidewall portion of the tire, or the central region R _B protruding most laterally of the sidewall portion in the intermediate direction at a predetermined position. And the strain in the radial direction is measured, and the estimated value of the road surface friction coefficient is obtained by using the average value of the measured strains in the intermediate direction and the minimum value or the maximum value of the strain in the radial direction. First, a first embodiment in which an estimated value of the road surface friction coefficient is obtained using only the measured strain of the region _RA will be described.

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.

The strain measuring device 11 measures at least the strain in the intermediate direction between the circumferential direction and the radial direction when the tire is rotating and the strain in the radial direction when the tire is rotating. In this embodiment, the side of the tire 9 is measured. At a predetermined position in the region _RA near the bead portion 90 of the wall portion 91, one strain gauge 4 having two or more axes capable of simultaneously measuring the strain in the intermediate direction and the strain in the radial direction in at least two directions is provided. Has been done.

In this embodiment, it suffices to measure each strain in the intermediate direction and the radial direction in the region _RA . Instead of providing a strain gauge having two or more axes as in this example, a strain gauge capable of measuring the strain in the intermediate direction, Strain gauges capable of measuring the strain in the radial direction may be provided at predetermined positions different from each other in the region _RA . As shown in FIG. 2B, the intermediate direction is preferably a direction inclined by 45 degrees from the circumferential direction toward the radial direction orthogonal to the circumferential direction, but is offset to the circumferential direction side or the radial direction side. It may be in the 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.

Further, such a strain measuring device 11 may be provided on either the left or right (front surface side, back surface side) sidewall portion of the tire, and the strain gauge 4 may be installed on the outer and inner surfaces of the sidewall portion. The form does not matter, such as bonding or embedding a strain gauge of the mold. A strain measuring device other than the strain gauge may be used.

On the tire side, a transmission unit (not shown) for wirelessly transmitting strain data detected by the strain gauge 4 to a receiver 5 on the vehicle side is provided, and the receiver 5 is provided at an appropriate position near the tire of the vehicle. 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. 2, 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 1, 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 area _RA 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. Unit 20, the measured strain reading processing unit 21 that reads the measured intermediate strain and radial strain data from the strain data storage unit 30, and the average value of the read intermediate strain (ε _{A_1 (ave). )} ) Is calculated, the intermediate direction average strain calculation processing unit 22 stored in the average strain data storage unit 31 and the minimum value (ε _{A_2 (min)} ) of the read radial strain are calculated, and the maximum or minimum strain is calculated. minimum distortion calculation processing unit 23 is stored in the data storage unit 32, the average value of the intermediate direction strain _{(ε A_1 (ave))} tire circumferential direction of the frictional force during tire rotation based on the (F _Y) determined, the frictional force data The frictional force calculation processing unit 24 stored in the storage unit 33 and the vertical load W during tire rotation are obtained based on the minimum value of radial strain (ε _{A_2 (min)} ), and the vertical load stored in the vertical load data storage unit 34. The estimated value (μ) of the road surface friction coefficient is obtained from the calculation processing unit 25 and the friction force ( _FY ) and the vertical load (W) in the tire circumferential direction stored in the storage means 3, and the friction coefficient data storage unit 35. It is provided with at least a strain coefficient calculation processing unit 26 stored in, and these functions are realized by the above program.

The calculation of the average value (ε _{A_1 (ave)} ) by the intermediate direction average strain calculation processing unit 22 may be the average value of each measured value per one rotation of the tire, or the average of each measured value per multiple rotations of two or more rotations. It may be a value. Further, the minimum value (ε _{A_2 (min)} ) calculated by the minimum strain calculation processing unit 23 may be the minimum value among the measured values per rotation of the tire, or the measured values in a predetermined range exceeding one rotation. The minimum value may be used. It can be dealt with by setting the data of the intermediate direction strain and the radial direction strain read by the measurement strain reading processing unit 21 according to the calculation method. However, even if the range of strain measurement values used is different, the average value of intermediate strain (ε _{A_1 (ave)} ) and the minimum value of radial strain (ε _{A_2 (min)} ) are calculated for each measured strain at the same timing. The road surface friction coefficient can be estimated accurately by calculating each using the data.

The frictional force ( _FY ) in the tire circumferential direction is calculated by the frictional force calculation processing unit 24 with the average value (ε _{A_1 (ave)} ) calculated by the intermediate direction average strain calculation processing unit 22 as i = A. Calculated by substituting into equation (1). Experimental constants The experimental constants l _{i_1 (ave)} and _{bi_1 (ave)} are experimentally determined in advance for each tire (for each tire type (brand, size)).

The calculation of the vertical load W by the vertical load calculation processing unit 25 is calculated by substituting the minimum value (ε _{A_2 (min)} ) calculated by the radial maximum or minimum strain calculation processing unit 23 into the following equation (2). To. Experimental constants The experimental constants m _{A_2 (min)} and b _{A_2 (min)} are also experimentally determined for each tire (for each tire type (brand, size)).

To calculate the estimated value (μ) of the road surface friction coefficient by the friction coefficient calculation processing unit 26, substitute the calculated friction force ( _FY ) and vertical load (W) in the tire circumferential direction into the following equation (4). Is calculated by.

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, the intermediate strain and the radial strain are detected by the strain gauge 4, and are transmitted from a transmitter (not shown) to the receiver 5 on the vehicle 10 side (S101). Strain detection is continuously detected at regular intervals. 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 the measurement data of the intermediate direction strain and the radial strain stored in the strain data storage unit 30 (S103), and the intermediate direction per predetermined rotation. The average value of strain (ε _{A_1 (ave)} ) and the minimum value of radial strain during the same rotation (ε _{A_2 (min)} ) are calculated, respectively, and the average strain data storage unit 31, the maximum or minimum strain data storage unit 32, respectively. It is stored in (S104, S105).

Next, the frictional force calculation processing unit 24 substitutes the calculated average value (ε _{A_1 (ave)} ) of the intermediate strain into the above equation (1), and the frictional force ( _FY ) in the tire circumferential direction. Is calculated and stored in the frictional force data storage unit 33 (S106). Further, the vertical load calculation processing unit 25 substitutes the calculated minimum value of the radial strain (ε _{A_2 (min)} ) into the above equation (2) to calculate the vertical load W, and the vertical load data. It is stored in the storage unit 34 (S107).

Then, the friction coefficient calculation processing unit 26 substitutes the calculated friction force ( _FY ) in the tire circumferential direction and the vertical load (W) into the above equation (4), and estimates the road surface friction coefficient (μ). ) Is calculated and stored in the friction coefficient data storage unit 35 (S108).

It will now be described a second embodiment for obtaining the estimated value of the road surface friction coefficient using a strain measurement area R _B.

The strain measuring device 11 of the present embodiment also measures at least the strain in the intermediate direction between the circumferential direction and the radial direction when the tire is rotating and the strain in the radial direction when the tire is rotating. gauge 4 strain at a predetermined position in the central region R _B which protrudes most side of the sidewall portion 91 of the tire 9 is provided one is. In the present embodiment, instead of providing the two or more axes strain gauge, the strain can be measured strain of the intermediate direction gauge, be provided with a strain gauge to measure the strain in the radial direction at different predetermined positions of the respective region R _B Good.

Measurements strain reception processor 20 of the processing unit 2 receives from the receiving device 5 the measured strain data area measured by the strain measuring device 11 R _B, stores it in the strain data storage unit 30 of the storage unit 3. The intermediate direction average strain calculation processing unit 22 calculates the average value (ε _{B_1 (ave)} ) of the read intermediate direction strain and stores it in the average strain data storage unit 31. The average value (ε _{B_1 (ave)} ) may be calculated by the average value of each measured value per one rotation of the tire or the average value of each measured value per multiple rotations of two or more rotations.

The radial minimum or maximum strain calculation processing unit 23 calculates the maximum value (ε _{B_2 (max)} ) of the read radial strain and stores it in the maximum or minimum strain data storage unit 32. The maximum value (ε _{B_2 (max)} ) may be calculated by the maximum value of each measured value per rotation of the tire or the maximum value of each measured value in a predetermined range exceeding one rotation. It can be dealt with by setting the data of the intermediate direction strain and the radial direction strain read by the measurement strain reading processing unit 21 according to the calculation method. However, even if the range of strain measurement values used is different, the average value of intermediate strain (ε _{B_1 (ave)} ) and the maximum value of radial strain (ε _{B_2 (max)} ) are calculated for each measured strain at the same timing. The road surface friction coefficient can be estimated accurately by calculating each using the data.

Frictional force calculation processing unit 24, the average value of the intermediate direction strain _{(ε B_1 (ave))} tire circumferential direction of the frictional force during tire rotation based on the (F _Y) value is stored into the frictional force data storage unit 33. Calculation of the frictional force (F _Y) is calculated by substituting the average value calculated in the intermediate direction average strain calculation unit 22 (epsilon _{B_1 (ave)),} the i = B and the above formula (1) To.

Vertical load calculation unit 25, based on the radial distortion maximum value _{(ε B_2 (max))} and the calculated frictional force (F _Y), determine the vertical load W during tire rotation, vertical load data storage unit Store in 34. For the calculation of the vertical load W, the minimum value (ε _{B_2 (max)} ) calculated by the radial maximum or minimum strain calculation processing unit 23 and the above-calculated frictional force ( _FY ) are calculated by the following equation (3). Calculated by substituting. The experimental constants of l _{B_2 (max)} , m _{B_2 (max)} , and b _{A_2 (max)} are also experimentally determined for each tire (for each tire type (brand, size)).

To calculate the estimated value (μ) of the road surface friction coefficient by the friction coefficient calculation processing unit 26, substitute the calculated friction force ( _FY ) and vertical load (W) in the tire circumferential direction into the above equation (4). Is calculated by.

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

First, the intermediate strain and the radial strain are detected by the strain gauge 4 and transmitted from a transmitting device (not shown) to the receiving device 5 on the vehicle 10 side (S201). Strain detection is continuously detected at regular intervals. 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 (S202).

Next, the measurement strain reading processing unit 21 of the arithmetic processing device 2 reads the measurement data of the intermediate direction strain and the radial strain stored in the strain data storage unit 30 (S203), and the intermediate direction per predetermined rotation. The average value of strain (ε _{B_1 (ave)} ) and the maximum value of radial strain during the same rotation (ε _{B_2 (max)} ) are calculated, respectively, and the average strain data storage unit 31, the maximum or minimum strain data storage unit 32, respectively. It is stored in (S204, S205).

Then, the frictional force calculation processing unit 24, the calculated intermediate direction strain average value (epsilon _{B_1 (ave))} are substituted in equation (1) described above, the friction force in the tire circumferential direction (F _Y) Is calculated and stored in the frictional force data storage unit 33 (S206). Further, the vertical load calculation processing unit 25 substitutes the calculated maximum value of the radial strain (ε _{B_2 (max)} ) into the above equation (3) to calculate the vertical load W, and the vertical load data. It is stored in the storage unit 34 (S207).

Then, the friction coefficient calculation processing unit 26 substitutes the calculated friction force ( _FY ) in the tire circumferential direction and the vertical load (W) into the above equation (4), and estimates the road surface friction coefficient (μ). ) Is calculated and stored in the friction coefficient data storage unit 35 (S208).

Other configurations, processing procedures, and modifications are basically the same as those in the above-described first embodiment, and description thereof will be omitted.

Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and for example, intermediate strain and radial strain are not detected in the same regions _RA and R _B. Detection in different regions _RA / R _B , specifically, intermediate strain is detected by a strain gauge provided at a predetermined position in region R _B , and the average value of intermediate strain from the measured strain ( calculates epsilon _{B_1} the _(ave)), together with obtaining the F _Y from equation (1), with the strain gauge provided at a predetermined position in the region R _a detects the radial strain, surveying the constant strain from the radial strain of The minimum value (ε _{A_2 (min)} ) is calculated, the W is obtained from the equation (2), and the road surface friction coefficient μ is calculated from these _FY and W, or conversely, a predetermined position in the region _RA. detecting an intermediate direction strain in the strain gauge provided, calculates surveying constant strain average value of the intermediate direction strain from a (epsilon _{A_1 (ave)),} together with obtaining the F _Y from equation (1), the region R _B The radial strain is detected by a strain gauge provided at a predetermined position, the maximum value of the radial strain (ε _{B_2 (max)} ) is calculated from the measured strain, and the W is obtained from the equation (3). Of course, it can be carried out in various forms without departing from the gist of the present invention, such as calculating the road surface friction coefficient μ from _Y and W.

Hereinafter, using the experimental apparatus shown in FIG. 6, the verification of the equations (1) to (3) of the present invention, and the calculated values (estimated values) for the friction force _FY , the vertical load W, and the road surface friction coefficient μ are true. The result of comparison with the value (measured value) will be described.

(experimental method)
The experimental device 7 is shown in FIGS. 6 and 7. The tire 9 used in the experiment was a DSX-2 155 / 80R13 79Q manufactured by Dunlop. As shown in FIG. 1, two 3-axis strain gauges (KFG-2-120-D17-23 L3M2S manufactured by Kyowa Electric Co., Ltd.) were attached to the front side surface of the tire 9. The strain gauges are located at a position 15 mm (inside the area R _A in FIG. 2) and 55 mm (inside the area R _B in FIG. 2) in the radial direction from the portion of the front side surface of the tire in contact with the wheel. They were attached to each of them, and strain gauge A and strain gauge B were used from the side closest to the wheel. As for the strain in each axial direction of the strain gauge (A / B), the intermediate strain is ε _{i_1} , the radial strain is ε _{i_2} , and the circumferential strain is ε _{i_3} (i = A, B).

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 72, which consist of the links of the support base 72 supporting the force plate 73, by the same amount in the direction toward or away from each other. 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 72 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.

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. 7, X-axis direction, Y axis direction, Z It is measured by load cells 761, 762, and 763 on the support base 72 side that supports from the axial direction.

As shown in FIG. 6, 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. This time, the above strain was acquired for one tire rotation (-180 to 180 deg), and the measured values of the strain at a plurality of tire rotation angles were used.

(Verification of equations (1) to (3))
Relationship F _Y and W acting on the ground surface and the strain generated in the tire side, an experiment was conducted to vary respectively the F _Y and W to be applied to the tire. Experiments changing the F _Y, as shown in Table 1, the W and 2500N, different rubber sheet having a friction surface coefficient of friction, textured acrylic sheet, the three stages of F _Y by three road PTFE plate It was allowed to act. Also, experiments varying the W, as shown in Table 2, in the friction surfaces of the (3 road), F _Y adjusts each vertical load so as to 1150N, was allowed to act W of three stages ..

Other main experimental conditions, the friction angle _{θ 90deg (F X = 0)} , the friction distance 2200 mm (1 turn of the tire), the friction velocity 30 mm / s, the air pressure of the tires was 200 kPa.

The relationship between the rotational angle α intermediate direction and strain resulting from the strain gauges A, a comparison of the case where F _Y has changed in FIG. 8 (a), shows a comparison of the case where W is changed in Figure 8 (b). Further, the relation between the strain radial obtained from strain gauge A rotation angle alpha, the comparison of the case where F _Y has changed in FIG. 9 (a), a comparison of the case where W is changed in FIG. 9 (b) Shown.

Further, the relation between the strain intermediate direction obtained from the strain gauges B rotation angle alpha, the comparison of the case where F _Y is changed in FIG. 10 (a), a comparison of the case where W is changed in FIG. 10 (b) Shown. Further, the relation between the strain radial obtained from strain gauge B rotation angle alpha, the comparison of the case where F _Y has changed in FIG. 11 (a), a comparison of the case where W is changed in FIG. 11 (b) Shown.

From the results of the F _Y course experiments and W course experiments, intermediate directions Strain of each strain gauge A / B, alpha = averaged in a range of -180~ + 180 [deg] (ε A_1 (ave), ε B_1 (ave ₎ ), The relationship with _FY and W was sought. From FIG. 12 (a), (b), for any of the strain gauge (A / B), the intermediate direction strain is not dependent on W, and is in the F _Y linear relationship, the above formula (1) is It turns out that it holds. The experimental constants l _{i_1 (ave)} and _{bi_1 (ave)} are obtained from the graph obtained in this experiment by using the least squares method.

Moreover, was determined from the results of the F _Y course experiments and W course experiments, the maximum and minimum values of the radial strain, the relationship between F _Y in FIG. 13 (a), the relationship between the W in FIG. 13 (b) Shown. As shown in FIG. 13, the minimum value of the radial strain of the strain gauge A is for the W changes linearly does not change with respect to F _Y. As described above, it can be seen that the above equation (2) holds for the strain gauge A. The experimental constants m _{A_2 (min)} and b _{A_2 (min)} are obtained from the graph obtained in this way by using the least squares method.

Similarly, from FIG. 13, the maximum value of the radial strain of the gauge B changes linearly with respect to both _FY and W. Therefore, it can be seen that the equation (3) holds as the relational expression between the strain value and the load. The experimental constants l _{B_2 (max)} , m _{B_2 (max)} , and b _{A_2 (max)} are obtained from the graph obtained in this experiment by using the least squares method.

Then, the road surface friction coefficient, when using the gauge A, the F _Y from equation (1), respectively obtained the W from equation (2) can be determined by dividing the F _Y at W, using a gauge B case, first, seek F _Y from equation (1), determine the W from further obtained F _Y of formula (3), obtained by dividing the F _Y at W.

(Comparison experiment between calculated value and true value)
Strain gauges A, strain intermediate direction B, radial distortion, and using equation (1) to (3), to obtain the F _Y and W, further friction coefficient mu, as shown in Table 3, W = 2000 A slip simulation experiment was conducted using a rubber sheet having a different coefficient of friction, a patterned acrylic plate, a PTFE plate, an aluminum plate, a smooth acrylic plate, and a smooth acrylic plate coated with oil as a ground contact surface at 2500 N. As the experimental constants of the formulas (1) to (3), the values obtained from the graph at the time of the above verification were used.

The results of the calculated value and the true value by the strain gauge A are shown in FIG. 14, and the result of the calculated value and the true value by the strain gauge B is shown in FIG. From 14 and 15, any of F _Y and W in the gauge, it is found that can more accurately estimate the friction coefficient mu.

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 Intermediate direction average strain calculation processing Part 23 Radial maximum or minimum strain calculation processing unit 24 Friction force calculation processing unit 25 Vertical load calculation processing unit 26 Friction coefficient calculation processing unit 30 Strain data storage unit 31 Average strain data storage unit 32 Maximum or minimum strain data storage unit 33 Friction Force data storage unit 34 Vertical load data storage unit 35 Friction coefficient data storage unit 70 Parallel load unit 72 Support base 72 Legs 72 Support base 73 Force plate 74 Tire drive unit 75 Press block 90 Bead part 91 Side wall part 761-763 load cell R _A, R _B region S estimation system

Claims (9)

The average value (ε _{A_1 (ave)} ) of the measured strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation at a predetermined position in the region _RA near the bead part of the tire sidewall, or at a predetermined position in the central region R _B which protrudes most side of the sidewall portion of the tire, the intermediate direction of the measuring strain average value between the circumferential direction and the radial direction in the tire rotation _{(ε B_1 (ave))} And the process of calculating
The minimum value of the measured strain in the radial direction during tire rotation (ε _{A_2 (min)} ) at a predetermined position in the region R _A of the tire, or the tire rotation at a predetermined position in the region R _B of the tire. The process of calculating the maximum value of the measured strain in the radial direction of time (ε _{B_2 (max)} ) and
The calculated intermediate direction strain average value of the (epsilon _{A_1 (ave)} or epsilon _{B_1 (ave))} is substituted into the following equation (1), a step of determining the friction force in the tire circumferential direction when the tire rotates (F _Y) ,
Substitute the calculated minimum value of radial strain (ε _{A_2 (min)} ) into the following equation (2), or the maximum value of the calculated radial strain (ε _{B_2 (max)} ) and the tire circumferential direction. The process of substituting the frictional force ( _FY ) into the following equation (3) to obtain the vertical load W during tire rotation, and
A step of obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W).
A method for estimating the coefficient of friction of the road surface, which comprises.
The average value per rotation of the measured strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation at a predetermined position in the region _RA near the bead portion of the tire sidewall portion (ε _{A_1 (ave)).} ), And the minimum value (ε _{A_2 (min)} ) of the measured strain in the radial direction during tire rotation per tire rotation is calculated.
Substituting the calculated mean value of intermediate strain (ε _{A_1 (ave)} ) into the above equation (1), the frictional force ( _FY ) in the tire circumferential direction during tire rotation is obtained.
The method for estimating the road surface friction coefficient according to claim 1, wherein the calculated minimum value of radial strain (ε _{A_2 (min)} ) is substituted into the above equation (2) to obtain the vertical load W during tire rotation. _A strain gauge capable of measuring strain in at least two directions, that is, the strain in the intermediate direction between the circumferential direction and the radial direction and the strain in the radial direction during tire rotation, is provided at a predetermined position in the region _RA of the tire. The method for estimating the road surface friction coefficient according to claim 2. At a predetermined position in the central region R _B which protrudes most side of the sidewall portion of the tire, the intermediate direction of the measuring strain average value between the circumferential direction and the radial direction in the tire rotation _{(ε B_1 (ave))} , And the maximum value of the measured strain in the radial direction when the tire rotates (ε _{B_2 (max)} ), respectively.
The calculated average value of the intermediate direction strain (epsilon _{B_1 (ave))} tire circumferential direction of the frictional force during to tire rotation substituted into the equation (1) to determine the (F _Y),
Calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the frictional force (F _Y) and the formula (3) are substituted into comprising seeking vertical load W during tire rotation claims Item 1. The method for estimating the road surface friction coefficient according to Item 1. In a predetermined position of said region R _B of the tire, the strain of the intermediate direction between the circumferential direction and the radial direction during the tire rotation, and of the strain in the radial direction, provided the strain gauge can measure the strain in at least two directions The method for estimating the road surface friction coefficient according to claim 4. Distortion in the intermediate direction between the circumferential direction and the radial direction during tire rotation at a predetermined position in the region _RA near the bead portion of the tire sidewall portion, or overhanging to the most lateral side of the tire sidewall portion. at a predetermined position in the central region R _B, means for measuring the strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation,
Further, the present invention has means for measuring the radial strain during tire rotation at a predetermined position in the region _RA of the tire, or the radial strain during tire rotation at a predetermined position in the region R _B of the same tire. Strain measuring device and
A means for reading the intermediate-direction strain and radial-direction strain data measured by the strain measuring device from an internal or external storage means.
The average value of the strain in the intermediate direction at the predetermined position of the measured region _RA (ε _{A_1 (ave)} ) or the average value of the strain in the intermediate direction at the predetermined position of the region R _B (ε _{B_1 (ave)).} ), A means to calculate
The measured radial strain minimum value of the predetermined position of the region _{R A (ε A_2 (min)} ), or the maximum value of strain in the radial direction at a predetermined position of the region R _{B (ε B_2 (max)} ), A means to calculate
Substituting the calculated intermediate direction strain average value of the (epsilon _{A_1 (ave)} or epsilon _{B_1 (ave))} to the following equation (1), means for calculating the frictional force in the tire circumferential direction when the tire rotates (F _Y) ,
Substitute the calculated minimum value of radial strain (ε _{A_2 (min)} ) into the following equation (2), or the maximum value of the calculated radial strain (ε _{B_2 (max)} ) and the tire circumference. A means of substituting the frictional force ( _FY ) in the direction into the following equation (3) to obtain the vertical load W during tire rotation.
In addition, a friction coefficient calculation device having a means for obtaining an estimated value (μ) of the road surface friction coefficient from the friction force ( _FY ) in the tire circumferential direction and the vertical load (W).
A system for estimating the coefficient of friction of the road surface.
The strain measuring device is provided at a predetermined position in the region _RA of the tire, and the strain in the intermediate direction between the circumferential direction and the radial direction during tire rotation and the strain in the radial direction are provided in at least two directions. A strain gauge that can measure strain
Said friction coefficient calculation device, means for calculating an average value of the intermediate direction strain _{(ε A_1 (ave))} at a predetermined position of the measurement region R _A, at a predetermined position of the measurement region R _A A means for calculating the minimum value of the radial strain (ε _{A_2 (min)} ), the average value of the calculated intermediate strain (ε _{A_1 (ave)} ) is substituted into the above equation (1), and the tire is rotated. A means for obtaining the frictional force ( _FY ) in the tire circumferential direction, the minimum value (ε _{A_2 (min)} ) of the calculated radial strain is substituted into the above equation (2) to obtain the vertical load W during tire rotation. The road surface friction coefficient estimation system according to claim 6, further comprising means and means for obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). The strain measurement device is provided at a predetermined position of said region R _B of the tire, the strain of the intermediate direction between the circumferential direction and the radial direction during the tire rotation, and of the strain in the radial direction, at least two directions A strain gauge that can measure strain
Said friction coefficient calculation device, means for calculating an average value of the intermediate direction strain _{(ε B_1 (ave))} at a predetermined position of the measurement region R _B, at a predetermined position of the measurement region R _B A means for calculating the maximum value of the radial strain (ε _{B_2 (max)} ), the average value of the calculated intermediate strain (ε _{B_1 (ave)} ) is substituted into the above equation (1), and the tire is rotated. friction force in the tire circumferential direction (F _Y) means for determining said calculated radial distortion maximum value (epsilon _{B_2 (max))} and the tire circumferential direction of the frictional force (F _Y) and the formula (3) A means for obtaining the vertical load W when the tire rotates, and a means for obtaining an estimated value (μ) of the road surface friction coefficient from the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W). The road surface friction coefficient estimation system according to claim 6. A program that causes a computer to function as the friction coefficient calculation device according to any one of claims 6 to 8.
A means for reading the intermediate-direction strain and radial-direction strain data measured by the strain measuring device from an internal or external storage means.
The average value of the strain in the intermediate direction at the predetermined position of the measured region _RA (ε _{A_1 (ave)} ) or the average value of the strain in the intermediate direction at the predetermined position of the region R _B (ε _{B_1 (ave)).} ), A means to calculate
The measured radial strain minimum value of the predetermined position of the region _{R A (ε A_2 (min)} ), or the maximum value of strain in the radial direction at a predetermined position of the region R _{B (ε B_2 (max)} ), A means to calculate
Substituting the calculated intermediate direction strain average value of the (epsilon _{A_1 (ave)} or epsilon _{B_1 (ave))} to the following equation (1), means for calculating the frictional force in the tire circumferential direction when the tire rotates (F _Y) ,
Substitute the calculated minimum value of radial strain (ε _{A_2 (min)} ) into the following equation (2), or the maximum value of the calculated radial strain (ε _{B_2 (max)} ) and the tire circumference. A means of substituting the frictional force ( _FY ) in the direction into the following equation (3) to obtain the vertical load W during tire rotation.
In addition, 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 the frictional force ( _FY ) in the tire circumferential direction and the vertical load (W).