Tire performance evaluation method and tire performance evaluation device

Abstract

To provide a technique capable of objectively and accurately evaluating performance of a tire which varies depending on environment.SOLUTION: A tire performance evaluating method 100 includes: an obtaining step S1 of performing a braking test of an evaluation target tire on a wet road surface and obtaining μ-s-data specifying a relationship between slip ratio s and a frictional coefficient μ; and a specifying step S2 of specifying a tread front-rear rigidity Cx of an evaluation target tire, a maximum static frictional coefficient μ s of a tread rubber, and a sliding frictional coefficient μ d based on the μ-s-data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating tire performance. [Background technology]

[0002] BACKGROUND ART Various methods for evaluating tire performance have been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-090440 Summary of the Invention [Problem to be solved by the invention]

[0004] However, tire performance varies depending on the environment, such as the road surface and its temperature, making it difficult to objectively and accurately evaluate tire performance.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a technique that can objectively and accurately evaluate tire performance that varies depending on the environment. [Means for solving the problem]

[0006] The present invention provides a method for evaluating tire performance, comprising: an acquisition step of performing a braking test on the evaluation target tire on a wet road surface to acquire μ-s data that identifies the relationship between the slip ratio s and the friction coefficient μ; and a specifying step of specifying the tread front-rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tire to be evaluated based on the μ-s data. [Effects of the Invention]

[0007] The tire performance evaluation method of the present invention has the above-mentioned configuration, and therefore can objectively and accurately evaluate tire performance that varies depending on the environment. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a flowchart showing the procedure of a tire performance evaluation method according to one embodiment of the present invention. [Figure 2] 1 is a block diagram showing a schematic configuration of a tire performance evaluation device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram illustrating a configuration of an acquisition unit in FIG. 2. [Figure 4] 2 is a graph showing an example of μ-s data acquired in the acquisition step of FIG. 1. [Figure 5] FIG. 2 is a diagram schematically illustrating the contact patch of the evaluation target tire during sudden braking. [Figure 6] 1 is a graph showing a curve obtained by approximating the contact pressure distribution on the tire equator with an n-th order parabola. [Figure 7] 1 is a graph showing the relationship between the theoretical friction coefficient μ′ on the left side of equation (1) and the first and second terms on the right side, and the slip ratio s. [Figure 8] 1 is a graph showing the transition of the theoretical friction coefficient μ′ when the tread front-rear rigidity Cx in equations (1) and (2) is varied. [Figure 9] 10 is a graph showing the transition of the theoretical coefficient of friction μ′ when the maximum static coefficient of friction μs of the tread rubber in equation (2) is varied. [Figure 10] 1 is a graph showing the transition of the theoretical coefficient of friction μ′ when the coefficient of sliding friction μd of the tread rubber in formula (1) is varied. [Figure 11] 3 is a flowchart showing the detailed procedure of the fitting step in FIG. 2. [Figure 12] 12 is a graph showing a theoretical friction coefficient μ′ fitted to the actually measured friction coefficient μ in the provisional determination step S21 of FIG. 11. [Figure 13]13 is a graph showing a theoretical friction coefficient μ′ after completion of the provisional determination step S21 in FIG. 12. [Figure 14] 12 is a graph showing a theoretical friction coefficient μ′ fitted to the actually measured friction coefficient μ in the provisional determination step S22 of FIG. 11. [Figure 15] 15 is a graph showing a theoretical friction coefficient μ′ after completion of the provisional determination step S22 in FIG. 14. [Figure 16] 12 is a graph showing a theoretical friction coefficient μ′ fitted to the actually measured friction coefficient μ in fitting step S23 of FIG. 11. [Figure 17] 17 is a graph showing an enlarged view of a part of FIG. 16. [Figure 18] 17 is a graph showing the theoretical friction coefficient μ′ after completion of fitting step S23 in FIG. 16. [Figure 19] 12 is a graph showing a theoretical friction coefficient μ′ when the deviation Δs of the first slip ratio s1 is corrected in the correction step S25 of FIG. 11. [Figure 20] 20 is a graph showing the theoretical friction coefficient μ′ after completion of the correction step S25 in FIG. 19. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described with reference to the drawings. 1 is a flowchart showing the steps of a tire performance evaluation method 100 according to this embodiment. The tire performance evaluation method 100 includes an acquisition step S1 for acquiring μ-s data of a tire to be evaluated, a specification step S2 for specifying the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd of the tire to be evaluated, and an evaluation step S3 for evaluating the performance of the tire to be evaluated. The evaluation step S3 may be a step independent of the tire performance evaluation method 100. In this case, the tire performance evaluation method 100 is composed of the acquisition step S1 and the specification step S2.

[0010] 2 shows a schematic configuration of the tire performance evaluation device 1 of this embodiment. The tire performance evaluation method 100 is executed by the tire performance evaluation device 1.

[0011] The tire performance evaluation device 1 includes an acquisition unit 10 that executes an acquisition step S1, an identification unit 21 that executes an identification step S2, and an evaluation unit 22 that executes an evaluation step S3, and is configured to be mountable on a vehicle. A computer device 20 is applied to the identification unit 21 and the evaluation unit 22 of this embodiment.

[0012] The computer device 20 includes, for example, a CPU (Central Processing Unit) that executes various types of arithmetic processing, information processing, etc., and a memory that stores programs that control the operation of the CPU and various types of information. The identification unit 21 and the evaluation unit 22 of this embodiment are configured by a single computer device 20. The identification unit 21 and the evaluation unit 22 may each be configured by separate computer devices 20.

[0013] The evaluation unit 22 may be configured independent of the tire performance evaluation device 1. In this case, the tire performance evaluation device 1 is configured by the acquisition unit 10 and the identification unit 21, and the evaluation step S3 may also be executed by, for example, an engineer. The engineer refers to the identified tread front-rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tread rubber, and evaluates the performance of the tire to be evaluated based on past knowledge and experience.

[0014] 3 shows the configuration of the acquisition unit 10. The acquisition unit 10 includes a water sprinkler unit 11, encoders 12 and 17, a braking device 13, a load cell 14, a calculation processing unit 15, and a memory unit 16. Each component of the acquisition unit 10 is mounted, for example, on a vehicle (not shown) on which a tire T1 to be evaluated is mounted.

[0015] The water sprinkler 11 sprinkles water W onto the road surface to recreate a wet road surface under specific conditions. The amount of water W sprinkled is controlled by, for example, the calculation processor 15 so that the wet road surface has a predetermined water depth.

[0016] The encoder 12 is provided near the rotation axis of the evaluation target tire T1, and outputs an electric signal for detecting the rotation angular velocity ω1 of the evaluation target tire T1 to the calculation processing unit 15. For example, a rotary encoder is used as the encoder 12.

[0017] The braking device 13 is provided near the rotation axis of the evaluation target tire T1 and applies a braking force to the evaluation target tire T1. As the braking device 13, for example, a device having the same configuration as a braking device mounted on a vehicle is applied.

[0018] The load cell 14 is provided near the rotation axis of the evaluation target tire T1 and detects the force applied to the evaluation target tire T1. The load cell 14 outputs, to the calculation processing unit 15, electric signals for detecting the vertical force (load Fz) and the longitudinal force (braking force Fx) applied to the evaluation target tire T1.

[0019] The calculation processing unit 15 has, for example, a CPU that executes various calculation processes, information processing, etc., and a memory that stores programs that control the operation of the CPU and various information. The calculation processing unit 15 calculates the rotational angular velocity ω1 of the evaluation target tire T1 based on the electrical signal input from the encoder 12. The calculation processing unit 15 also calculates the velocity V1 of the tread portion of the evaluation target tire T1 from the dynamic load radius R1 and the rotational angular velocity ω1 of the evaluation target tire T1.

[0020] Furthermore, the calculation processing unit 15 calculates the load Fz and braking force Fx applied to the evaluation target tire T1 based on the electrical signal input from the load cell 14. The calculation processing unit 15 feedback-controls a load device (not shown) that applies a load to the evaluation target tire T1 and the braking device 13 based on the load Fz and braking force Fx obtained by the calculation.

[0021] The storage unit 16 stores various data such as the rotational angular velocity ω1 calculated by the arithmetic processing unit 15. For example, the storage unit 16 may be configured to store data input to the arithmetic processing unit 15 from the encoders 12, 17, and the load cell 14. The storage unit 16 may also be configured to store data calculated using the above data.

[0022] The encoder 17 is provided near the rotation axis of the speed detection tire T2 and outputs an electrical signal for detecting the rotational angular velocity ω2 of the speed detection tire T2 to the calculation processing unit 15. The speed detection tire T2 is a tire for detecting the speed of the vehicle, and is not subjected to braking force or driving force, but rotates as the vehicle travels. For example, a rotary encoder is used as the encoder 17.

[0023] The calculation processing unit 15 calculates the rotational angular velocity ω2 of the speed detection tire T2 based on the electrical signal input from the encoder 17. The calculation processing unit 15 also calculates the speed V2 of the vehicle (road surface) from the dynamic load radius R2 and the rotational angular velocity ω2 of the speed detection tire T2.

[0024] Furthermore, the calculation processing unit 15 calculates the slip ratio s during braking based on the tread speed V1 of the evaluation target tire T1 and the vehicle speed V2. The slip ratio s is calculated by taking the ratio (V2-V1) / V2 of the slip speed V2-V1 to the vehicle speed V2. The calculated slip ratio s is stored in the memory unit 16.

[0025] The friction coefficient μ during braking when no lateral force is generated is calculated by the calculation processing unit 15 using the ratio Fx / Fz of the braking force Fx and the load Fz.

[0026] In the acquisition step S1, the above operations are performed by the acquisition unit 10 to acquire the slip ratio s and friction coefficient μ of the evaluation target tire T1 during braking on a wet road surface. It is generally known that the friction coefficient μ of a tire varies depending on the slip ratio s. In the acquisition step S1, the friction coefficient μ corresponding to each slip ratio s is calculated to acquire μ-s data that specifies the relationship between the slip ratio s and the friction coefficient μ, and the slip ratio s and the friction coefficient μ are stored in association with each other in the memory unit 16.

[0027] FIG. 4 shows the relationship between the slip ratio s and the friction coefficient μ obtained in the obtaining step S1. As shown in the figure, the friction coefficient μ rises sharply as the slip ratio s is increased. In this friction coefficient μ rise region, as the slip ratio s increases from 0, the relationship between the slip ratio s and the friction coefficient μ can be approximated as linear (i.e., the slope of the μ-s curve is constant). Then, as the slip ratio s increases further, the slope of the μ-s curve becomes gentler, and the friction coefficient μ peaks and then gradually declines.

[0028] In the identification step S2, the identification unit 21 identifies the front-rear tread stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd of the evaluation target tire T1 based on the μ-s data shown in Fig. 4. Of the identified front-rear tread stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd, the front-rear tread stiffness Cx depends on the specifications of the evaluation target tire T1 (tread pattern, tread rubber compounding and structure, etc.), while the maximum static friction coefficient μs of the tread rubber and the sliding friction coefficient μd are affected by the compatibility between the specifications of the evaluation target tire T1 and the road surface.

[0029] In the evaluation step S3, the evaluation unit 22 evaluates the performance of the evaluation target tire T1 based on the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd.

[0030] The evaluation unit 22 relatively compares, for example, the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd of the tread rubber of a plurality of evaluation target tires T1 having different tread patterns, tread rubber compounding and structures, etc. This makes it possible to objectively and accurately evaluate the performance of each evaluation target tire T1.

[0031] Furthermore, by relatively comparing the tread front / rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd of the tread rubber determined based on μ-s data acquired under a plurality of water depth conditions for the above-mentioned plurality of specifications of the evaluation target tires T1, it becomes possible to estimate the compatibility between the specifications of each evaluation target tire T1 and the water depth, and it becomes possible to objectively and accurately evaluate the performance of each evaluation target tire T1.

[0032] Furthermore, by relatively comparing the tread front / rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tread rubber, which are determined based on μ-s data obtained by bringing the above-mentioned multiple specifications of the evaluation target tire T1 to a test course with different road surfaces, it becomes possible to estimate the compatibility between the specifications of each evaluation target tire T1 and each road surface, and it becomes possible to objectively and accurately evaluate the performance of each evaluation target tire T1.

[0033] Once the target values ​​for the longitudinal tread stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd are obtained through the above evaluation, the tire design elements are developed to achieve those targets. More specifically, by using simulation technology such as CAE (Computer Aided Engineering), the tread pattern, tread rubber hardness, and belt structure can be optimized to bring the longitudinal tread stiffness Cx closer to the target value.

[0034] In addition, by optimizing the hardness of the tread rubber according to the roughness of the road surface, the maximum static friction coefficient μs of the tread rubber can be brought closer to the target value. Furthermore, by optimizing the hardness and viscosity of the tread rubber according to the roughness of the road surface, the sliding friction coefficient μd of the tread rubber can be brought closer to the target value.

[0035] Fig. 5 shows a schematic diagram of the contact patch Tc of the tire T1 under evaluation during sudden braking. The contact patch Tc includes an adhesive region Tc1 where no slippage occurs between the tire and the road surface, and a slippage region Tc2 where slippage occurs between the tire and the road surface.

[0036] The adhesive region Tc1 occurs mainly on the contact-entry side (step-in side) of the contact patch Tc, while the slip region Tc2 occurs mainly on the contact-exit side (take-off side) of the contact patch Tc. The distribution of the adhesive region Tc1 and the slip region Tc2 depends on the slip ratio s. When the slip ratio s is 0, most of the contact patch Tc becomes the adhesive region Tc1. As the slip ratio s increases, the slip region Tc2 occurs on the take-off side of the contact patch Tc and increases. When the slip ratio s is s1 or greater, the entire contact patch Tc becomes the slip region Tc2.

[0037] Fig. 6 shows a curve obtained by approximating the contact pressure distribution on the tire equator CL (see Fig. 5) with an n-th order parabola (n is an even number equal to or greater than 2). By adjusting the order n according to the contact pressure distribution obtained by actually measuring the evaluation target tire T1, a theoretical mathematical model of the evaluation target tire T1 with an approximated contact pressure distribution can be obtained.

[0038] When the contact pressure distribution on the tire equator CL is approximated by an order n as shown in FIG. 6, the theoretical friction coefficient μ′ is expressed by the following formula (1).

number

number

[0039] Of the above parameters, the load Fz is applied with a target value of the feedback control in the acquisition step S1. A load Fz calculated based on an electrical signal input from the load cell 14, for example, the average value of the loads Fz applied to the evaluation target tire T1, may be applied. Furthermore, values ​​obtained by applying the load Fz to the evaluation target tire T1 and performing actual measurements are applied to the contact length L [m] and the contact width w [m] (see FIG. 5). Furthermore, the order n is applied with the order of the contact pressure distribution approximated based on FIG. 6.

[0040] As is clear from equation (1), the theoretical friction coefficient μ' is expressed as the sum of the first term relating to the shear resistance in the adhesion region Tc1 and the second term relating to the sliding friction in the slip region Tc2. In equation (1), the friction coefficient μ' on the left side and the first and second terms on the right side are functions with the slip ratio s as a variable.

[0041] Figure 7 shows the relationship between the theoretical friction coefficient μ' on the left-hand side of equation (1) and the first and second terms on the right-hand side, and the slip ratio s. In Figure 7, the first term on the right-hand side of equation (1) is represented by curve A, the second term on the right-hand side is represented by curve B, and the friction coefficient μ' on the left-hand side is represented by curve C. Curve C, which represents the friction coefficient μ', can be decomposed into the component of curve A related to the shear resistance in the adhesive region Tc1 and the component of curve B related to sliding friction in the sliding region Tc2.

[0042] As shown in Figure 7, the theoretical friction coefficient μ' in equation (1) also rises sharply as the slip ratio s is applied. In this region where the friction coefficient μ' rises, the relationship between the slip ratio s and the friction coefficient μ' can be approximated as linear as the slip ratio s increases from 0. Then, as the slip ratio s increases further, the slope of the μ'-s curve becomes gentler, and the friction coefficient μ' reaches a peak value and then gradually declines.

[0043] In FIG. 7, at the first slip ratio s1 where curve A relating to shear resistance becomes 0, the adhesion region Tc1 disappears and the entire contact patch Tc becomes the slip region Tc2.

[0044] In Figure 7, curves A and B change depending on the values ​​of the tread front-rear stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd. Therefore, curve C, which is the sum of curves A and B, also changes depending on the values ​​of the tread front-rear stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd. In other words, it can be understood that the theoretical friction coefficient μ' is a function whose variables are the tread front-rear stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd.

[0045] Figure 8 shows the theoretical friction coefficient μ' on the left-hand side and the first and second terms on the right-hand side when the maximum static friction coefficient μs and sliding friction coefficient μd of the tread rubber are fixed and the tread front-rear stiffness Cx is varied. When the tread front-rear stiffness Cx is a reference value, the friction coefficient μ', the first term, and the second term are represented by the solid curves A, B, and C, respectively, and when the tread front-rear stiffness Cx is the reference value + 20%, the friction coefficient μ', the first term, and the second term are represented by the dashed curves A1, B1, and C1.

[0046] As can be seen from Figure 8, as the tread front / rear stiffness Cx increases / decreases or fluctuates, the first slip ratio s1, at which the adhesive region Tc1 disappears and the entire contact patch Tc becomes the slip region Tc2, shifts, and accordingly, the slip ratio s, at which the theoretical friction coefficient μ' takes on its maximum value μmax, also shifts.

[0047] Figure 9 shows the theoretical friction coefficient μ' on the left-hand side and the first and second terms on the right-hand side when the maximum static friction coefficient μs of the tread rubber is varied while the tread front-rear stiffness Cx and the tread rubber's sliding friction coefficient μd are fixed. When the maximum static friction coefficient μs is a reference value, the friction coefficient μ', the first term, and the second term are represented by the solid curves A, B, and C, respectively, and when the maximum static friction coefficient μs is the reference value + 20%, the friction coefficient μ', the first term, and the second term are represented by the dashed curves A2, B2, and C2.

[0048] From Figure 9, it can be seen that as the maximum static friction coefficient μs increases, decreases, or fluctuates, the adhesion region Tc1 disappears and the first slip ratio s1, where the entire contact patch Tc enters the slip region Tc2, shifts. It can also be seen that as the maximum static friction coefficient μs increases, decreases, or fluctuates, the peak value of the first term related to the shear resistance in the adhesion region Tc1 fluctuates significantly. Accordingly, it can be seen that the slip ratio s, where the theoretical friction coefficient μ' reaches its maximum value μmax, shifts, and its peak value also fluctuates.

[0049] Figure 10 shows the theoretical friction coefficient μ' on the left-hand side and the first and second terms on the right-hand side when the sliding friction coefficient μd of the tread rubber is varied while the tread front-rear stiffness Cx and the maximum static friction coefficient μs of the tread rubber are fixed. When the sliding friction coefficient μd is a reference function with the slip ratio s as a variable, the friction coefficient μ', the first and second terms are represented by the solid curves A, B and C, and when the sliding friction coefficient μd is set to a uniform +20% increase from the reference function, the friction coefficient μ', the first and second terms are represented by the dashed curves A3, B3 and C3.

[0050] It can be seen from Figure 10 that the increase, decrease, and fluctuation of the sliding friction coefficient μd causes a large change in the slope of the second term related to sliding friction in the sliding region Tc2 until it reaches its peak. Accordingly, it can be seen that the maximum value μmax of the theoretical friction coefficient μ' and the drop in the friction coefficient μ' after the maximum value μmax also fluctuate.

[0051] 8 to 10, it can be seen that the μ'-s curve, which is the relationship between the theoretical friction coefficient μ' and the slip ratio s, can be freely modified to some extent by adjusting the tread front-rear stiffness Cx, the value of the maximum static friction coefficient μs of the tread rubber, and the function of the sliding friction coefficient μd. Then, by fitting the relationship between the theoretical friction coefficient μ' and the slip ratio s to the μ-s data, which are the actual measured values ​​of the evaluation target tire T1, it becomes possible to identify the tread front-rear stiffness Cx, the maximum static friction coefficient μs of the tread rubber, and the sliding friction coefficient μd of the evaluation target tire T1.

[0052] That is, the identification step S2 of this embodiment includes a fitting step S2' in which the relationship between the theoretical friction coefficient μ' and the slip ratio s expressed by equation (1) is fitted to the μ-s data, which are actual measured values ​​(see Figure 1).

[0053] By including the fitting step S2' in the specifying step S2, variables such as the tread front-rear stiffness Cx and the maximum static friction coefficient μs, and functions such as the sliding friction coefficient μd, which are included in the theoretical formula for the friction coefficient, are specified based on μ-s data obtained by actual measurements, thereby enabling the performance of the tire to be evaluated to be evaluated with high accuracy.

[0054] The relational expression between the theoretical friction coefficient μ' and the slip ratio s is not limited to Equation (1). For example, any expression that specifies the relationship between the theoretical friction coefficient μ' and the slip ratio s may include variables other than the tread front / rear stiffness Cx and the maximum static friction coefficient μs, and functions other than the sliding friction coefficient μd. Similar to the above-mentioned tread front / rear stiffness Cx, other variables that specify the relationship between the theoretical friction coefficient μ' and the slip ratio s are specified by fitting with μ-s data, which are actually measured values, and are used to evaluate the performance of the tire under evaluation.

[0055] 11 shows a more specific procedure of the fitting step S2'. The fitting step S2' includes provisional determination steps S21 and S22 for provisionally determining the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd in equation (1). The provisional determination steps S21 and S22 are performed using, for example, a macro function or a solver function included in spreadsheet software installed in the computer device 20.

[0056] Fig. 12 shows the theoretical friction coefficient μ' fitted to the measured friction coefficient μ in the provisional determination step S21. Fig. 13 shows the theoretical friction coefficient μ' after the completion of the provisional determination step S21. Note that Fig. 13 shows an enlarged region of the friction coefficient μ' where the slip ratio s is close to 0 (the same applies to Figs. 14 to 19 below).

[0057] In the tentative determination step S21, the determination unit 21 tentatively determines the sliding friction coefficient μd. The tentatively determined sliding friction coefficient μd is a function with the slip ratio s as a variable. Examples of functions with the slip ratio s as a variable include a linear function and a quadratic function. The determination unit 21 tentatively determines the sliding friction coefficient μd so that the theoretical friction coefficient μ' at a first slip ratio s1 or higher where the shear resistance is 0 is linearly approximated to the friction coefficient μ on the μ-s data acquired by actual measurement in the acquisition step S1.

[0058] In the linear approximation, the sliding friction coefficient μd is provisionally determined so that the theoretical friction coefficient μ' approximates the measured friction coefficient μ at both ends of the region where no shear resistance acts for the theoretical friction coefficient μ', i.e., at two points: slip ratio s (= s1) and slip ratio s (= 1) where shear resistance is zero. In other words, the provisional determination step S21 includes a first approximation step in which the theoretical friction coefficient μ' at a first slip ratio s1 or higher where shear resistance is zero is linearly approximated to the friction coefficient μ on the μ-s data acquired by actual measurement in the acquisition step S1. Here, various statistical methods, such as regression analysis, are applied to the linear approximation in the provisional determination step S21. The provisional determination step S21 is executed until the error due to the approximation is equal to or less than a predetermined threshold.

[0059] Fig. 14 shows the theoretical friction coefficient μ' fitted to the measured friction coefficient μ in the provisional determination step S22. Fig. 15 shows the theoretical friction coefficient μ' after the provisional determination step S22 is completed.

[0060] In the tentative determination step S22, the specification unit 21 provisionally determines the tread front / rear stiffness Cx and the maximum static friction coefficient μs. The specification unit 21 provisionally determines the tread front / rear stiffness Cx and the maximum static friction coefficient μs so that the friction coefficient μ' and the maximum value μ'max of the friction coefficient μ' at a predetermined second slip ratio s2 approximate the friction coefficient μ on the μ-s data. In other words, the tentative determination step S22 includes a second approximation step in which the friction coefficient μ' and the maximum value μ'max of the friction coefficient μ' at the second slip ratio s2 approximate the friction coefficient μ on the μ-s data. Here, various statistical methods such as regression analysis are applied to the approximation in the tentative determination step S22.

[0061] The second slip ratio s2 described above is the upper limit of the slip ratio at which the relationship between the slip ratio s and the friction coefficient μ can be linearly approximated as the slip ratio s increases from 0. With current measurement accuracy, it is generally said that the relationship between the slip ratio s and the friction coefficient μ can be linearly approximated when the slip ratio s is in the range of 0 to 0.03. Therefore, the second slip ratio s2 is, for example, 0.03. The provisional determination step S22 is executed until the error due to the approximation falls below a predetermined threshold.

[0062] The relationship between the slip ratio s and the friction coefficient μ changes approximately linearly in the range of slip ratio s from 0 to the second slip ratio s2. Therefore, by completing the provisional determination step S22, in the region where the friction coefficient μ rises as the slip ratio s goes from 0 to the second slip ratio s2, the theoretical friction coefficient μ' is fitted to the friction coefficient μ on the μ-s data obtained by actual measurement (see FIG. 15).

[0063] The fitting step S2' includes a fitting step S23 in which the theoretical friction coefficient μ' is fitted to the actually measured friction coefficient μ in the transition region from the second slip ratio s2 to the maximum value μ'max. The fitting step S23 is performed using, for example, a macro function or a solver function included in spreadsheet software installed in the computer device 20.

[0064] Fig. 16 shows the theoretical friction coefficient μ' fitted to the measured friction coefficient μ in fitting step S23. Fig. 17 shows an enlarged view of the theoretical friction coefficient μ' from the second slip ratio s2 to the maximum value μ'max in Fig. 16. Fig. 18 shows the friction coefficient μ' after fitting step S23 is completed.

[0065] As shown in FIG. 17, in the fitting step S23, the specification unit 21 adjusts the tread front-rear stiffness Cx and the maximum static friction coefficient μs. The specification unit 21 adjusts the tread front-rear stiffness Cx and the maximum static friction coefficient μs so that the difference between the theoretical friction coefficient μ' and the friction coefficient μ based on the μ-s data obtained by actual measurement becomes small in the transition region from the second slip ratio s2 to the maximum value μ'max. In other words, the fitting step S23 includes a third approximation step in which the theoretical friction coefficient μ' in the transition region from the second slip ratio s2 to the maximum value μ'max is approximated to the friction coefficient μ based on the μ-s data. Various statistical methods, such as regression analysis, are applied to the fitting in the fitting step S23. The fitting step S23 is executed until the error due to the approximation becomes equal to or less than a predetermined threshold.

[0066] Upon completion of fitting step S23, the theoretical friction coefficient μ' is fitted to the friction coefficient μ on the μ-s data obtained by actual measurement in the region where the slip ratio s ranges from 0 to the maximum value μmax of the friction coefficient μ.

[0067] 8 and 9, as the tread front / rear stiffness Cx and the maximum static friction coefficient μs increase, decrease, or fluctuate, curves A, B, and C deform, and the value of the first slip ratio s1 at which the shear resistance becomes 0 also fluctuates. If the first slip ratio after performing fitting step S23 is s1', the deviation of the first slip ratio resulting from performing tentative determination step S22 and fitting step S23 is calculated as Δs = s1' - s1 (see FIG. 18).

[0068] Therefore, it is preferable that fitting step S2' includes a comparison step S24 in which the absolute value of deviation Δs of first slip ratio s1 is compared with a predetermined threshold value. If the absolute value of deviation Δs of first slip ratio s1 is equal to or less than the predetermined threshold value in comparison step S24 (Y in S24), fitting step S2' ends.

[0069] If the absolute value of the deviation Δs of the first slip ratio s1 is greater than the predetermined threshold value (N in S24), the following correction step S25 is executed.

[0070] That is, the fitting step S2' includes a correction step S25.

[0071] Fig. 19 shows the theoretical friction coefficient μ' corrected in the correction step S25, and Fig. 20 shows the friction coefficient μ' after the correction step S25 is completed.

[0072] In the correction step S25, the function of the sliding friction coefficient μd is finely corrected by the determination unit 21 so as to reduce the absolute value of the deviation amount Δs of the first slip ratio (Δs=s1′−s1). The correction step S25 is executed until the absolute value of the deviation amount Δs becomes equal to or less than a predetermined threshold value.

[0073] 11, after the correction step S25 is completed, the process returns to the tentative determination step S21, and the tentative determination steps S21, S22, and adjustment step S23 are executed again in sequence. The tentative determination steps S21, S22, adjustment step S23, comparison step S24, and correction step S25 are repeated until the deviation amount Δs of the first slip ratio s1 becomes equal to or less than a predetermined threshold value in the comparison step S24 (Y in S24). After the correction step S25 is completed, the process may return to the tentative determination step S22, and the tentative determination step S22 and adjustment step S23 are executed again in sequence.

[0074] The thresholds to be compared with the error due to approximation in the tentative determination steps S21 and S22 and fitting step S23 in the second cycle may be set to be smaller than the thresholds in the steps S21, S22, and S23 in the first cycle.

[0075] According to the fitting step S2', the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd are accurately determined, making it possible to evaluate the performance of each evaluation target tire T1 more objectively and accurately.

[0076] Although the tire performance evaluation method 100 of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above and can be modified and practiced in various aspects.

[0077] [Note] [Invention 1] A method for evaluating tire performance, comprising: an acquisition step of performing a braking test on the evaluation target tire on a wet road surface to acquire μ-s data that identifies the relationship between the slip ratio s and the friction coefficient μ; and a specifying step of specifying the tread front-rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tire to be evaluated based on the μ-s data. Tire performance evaluation method. [Invention 2] The tire performance evaluation method according to the first aspect of the present invention, wherein the identifying step includes a fitting step of fitting a theoretical relational expression, in which the friction coefficient μ' when the contact pressure distribution on the tire equator is approximated by an n-th order (n is an even number of 2 or more) parabola is expressed as the sum of a term relating to shear resistance in the adhesion region and a term relating to sliding friction in the slip region, to the μ-s data. [Invention 3] A tire performance evaluation method according to aspect 2, wherein the relational expression includes, as variables, the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd. [Invention 4] A tire performance evaluation method according to aspect 3, wherein the fitting step includes a provisional determination step of provisionally determining the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd in the relational expression. [Invention 5] The tire performance evaluation method according to present invention 4, wherein the provisional determination step includes a first approximation step of provisionally determining the sliding friction coefficient μd so that the friction coefficient μ' at a first slip ratio s1 or more at which the shear resistance in the relational expression becomes 0 is linearly approximated to μ on the μ-s data. [Invention 6] The tire performance evaluation method according to aspect 5, wherein the provisional determination step includes a second approximation step of provisionally determining the tread front-rear stiffness Cx and the maximum static friction coefficient μs so that the friction coefficient μ' and the maximum value of the friction coefficient μ' at a predetermined second slip ratio s2 approximate μ on the μ-s data. [Invention 7] A tire performance evaluation method according to present invention 6, wherein the second slip ratio s2 is an upper limit slip ratio at which the relationship between the slip ratio s and the friction coefficient μ' can be approximated as linear when the slip ratio s increases from 0. [Invention 8] 7. A tire performance evaluation method according to claim 6, wherein the fitting step further includes a fitting step of fitting the tread front-rear stiffness Cx and the maximum static friction coefficient μs. [Invention 9] The tire performance evaluation method according to claim 8, wherein the fitting step includes a third approximation step of fitting the tread front-rear stiffness Cx and the maximum static friction coefficient μs so that the friction coefficient μ' in a transition region from the friction coefficient μ' at the second slip ratio s2 to the maximum value approximates μ on the μ-s data. [Invention 10] A tire performance evaluation method according to present invention 9, wherein the fitting step further includes a correction step of finely correcting the sliding friction coefficient μd so as to reduce an absolute value of a deviation amount of the first slip ratio that occurs as a result of execution of the provisional determination step and the fitting step. [Invention 11] A tire performance evaluation method according to invention 10, wherein the provisional determination step and the fitting step are also performed after the correction step. [Invention 12] 12. A tire performance evaluation method according to claim 11, wherein the correction step is repeated until the absolute value of the deviation of the first slip ratio s1 from the μ-s data becomes equal to or less than a predetermined threshold value. [Invention 13] The tire performance evaluation method according to present invention 1, further comprising an evaluation step of evaluating the performance of the evaluation target tire based on the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd. [Invention 14] A device for evaluating tire performance, an acquisition unit that performs a braking test on the evaluation target tire on a wet road surface and acquires μ-s data that identifies the relationship between the slip ratio s and the friction coefficient μ; and a specifying unit that specifies the tread front-rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tire to be evaluated based on the μ-s data. Tire performance evaluation device. [Explanation of symbols]

[0078] 1: Tire performance evaluation device 10: Acquisition part 21: Specific part 100: Tire performance evaluation method CL: Tire equator Cx: Front and rear tread stiffness S1: Acquisition step S2: Specific step S21: Tentative decision step S21: Step S22: Step S22: Tentative decision step S23: Step S23: Adjustment step S25: Correction step S2': Fitting step S3: Evaluation step T1: Tire to be evaluated Tc1: Adhesion area Tc2: Slip region s: slip ratio s1: First slip ratio s2: Second slip ratio Δs: deviation amount μ: Friction coefficient μd: Coefficient of sliding friction μmax: Maximum value μs: Maximum static friction coefficient μ': coefficient of friction μ'max: Maximum value

Claims

1. A method for evaluating tire performance, comprising: an acquisition step of performing a braking test on the evaluation target tire on a wet road surface to acquire μ-s data that specifies the relationship between the slip ratio s and the friction coefficient μ; and a specifying step of specifying the tread front-rear stiffness Cx, the maximum static friction coefficient μs and the sliding friction coefficient μd of the tire to be evaluated based on the μ-s data. Tire performance evaluation method.

2. 2. The tire performance evaluation method according to claim 1, wherein the specifying step includes a fitting step of fitting a theoretical relational expression, in which the friction coefficient μ' when the contact pressure distribution on the tire equator is approximated by an n-th order (n is an even number of 2 or more) parabola is expressed as the sum of a term related to shear resistance in the adhesion region and a term related to sliding friction in the slip region, to the μ-s data.

3. 3. The tire performance evaluation method according to claim 2, wherein the relational expression includes, as variables, the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd.

4. 4. The tire performance evaluation method according to claim 3, wherein the fitting step includes a provisional determination step of provisionally determining the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd in the relational expression.

5. 5. The tire performance evaluation method according to claim 4, wherein the tentative determination step includes a first approximation step of tentatively determining the sliding friction coefficient μd so that the friction coefficient μ' at a first slip ratio s1 or more at which the shear resistance in the relational expression is 0 is linearly approximated to μ on the μ-s data.

6. 6. The tire performance evaluation method according to claim 5, wherein the tentative determination step includes a second approximation step of tentatively determining the tread front-rear stiffness Cx and the maximum static friction coefficient μs so that the friction coefficient μ' and a maximum value of the friction coefficient μ' at a predetermined second slip ratio s2 approximate μ on the μ-s data.

7. 7. The tire performance evaluation method according to claim 6, wherein the second slip ratio s2 is an upper limit slip ratio at which the relationship between the slip ratio s and the friction coefficient μ′ can be approximated as linear when the slip ratio s increases from 0.

8. 7. The tire performance evaluation method according to claim 6, wherein the fitting step further includes a fitting step of fitting the tread front-rear stiffness Cx and the maximum static friction coefficient μs.

9. 9. The tire performance evaluation method according to claim 8, wherein the fitting step includes a third approximation step of fitting the tread front-rear stiffness Cx and the maximum static friction coefficient μs so that the friction coefficient μ' in a transition region from the friction coefficient μ' at the second slip ratio s2 to the maximum value approximates μ on the μ-s data.

10. 10. The tire performance evaluation method according to claim 9, wherein the fitting step further includes a correction step of finely correcting the sliding friction coefficient μd so that an absolute value of a deviation amount of the first slip ratio s1 caused by execution of the tentative determination step and the fitting step is reduced.

11. The tire performance evaluation method according to claim 10, wherein the provisional determination step and the fitting step are also performed after the correction step.

12. 12. The tire performance evaluation method according to claim 11, wherein the correction step is repeated until the absolute value of the deviation of the first slip ratio s1 from the μ-s data becomes equal to or less than a predetermined threshold value.

13. 2. The tire performance evaluation method according to claim 1, further comprising an evaluation step of evaluating performance of the evaluation target tire based on the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd.

14. A device for evaluating tire performance, an acquisition unit that performs a braking test on the evaluation target tire on a wet road surface and acquires μ-s data that specifies the relationship between the slip ratio s and the friction coefficient μ; and a specifying unit that specifies the tread front-rear stiffness Cx, the maximum static friction coefficient μs, and the sliding friction coefficient μd of the tire to be evaluated based on the μ-s data. Tire performance evaluation device.

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