Evaluation method and evaluation device for tire performance

Abstract

To provide a performance evaluation method or the like enabling performance of a tire on a wet road surface to be accurately evaluated.MEANS FOR SOLVING THE PROBLEM: An evaluation method for tire performance includes: a braking step S1 of causing a vehicle to travel on a wet road surface and stopping the vehicle by suddenly braking the tire; a measurement step S2 of measuring speed and acceleration of the vehicle during the braking step S1 in time series; and a calculation step S3 of estimating hydroplaning occurrence probability of the tire during the braking step based on change in the time series of the acceleration of the vehicle measured in the measurement step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Various methods for evaluating tire performance on wet road surfaces have been proposed. For example, Patent Document 1 discloses a method for evaluating tire performance by estimating the hydroplaning convergence speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-184497 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the method disclosed in Patent Document 1 does not always reveal differences in performance between tires, and further improvement is desired.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a performance evaluation method and the like that can accurately evaluate tire performance on wet road surfaces. [Means for solving the problem]

[0006] The present invention provides a method for evaluating tire performance on wet roads, comprising the steps of: a braking step of running a vehicle equipped with the tire on the wet road surface and suddenly braking the tire to stop the vehicle; a measuring step of measuring the speed and acceleration of the vehicle in time series during the braking step; a calculation step of estimating a probability of hydroplaning of the tire during the braking step based on the time-series change in the acceleration of the vehicle measured in the measurement step; and an evaluation step of evaluating the tire performance based on the probability of hydroplaning occurrence. [Effects of the Invention]

[0007] The performance evaluation method of the present invention has the above-mentioned configuration, and therefore can accurately evaluate tire performance on a wet road surface. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an embodiment of a performance evaluation device of the present invention. [Figure 2] 1 is a graph showing the change in tire contact patch index with respect to vehicle speed. [Figure 3] FIG. 2 is a conceptual diagram showing changes in the speed and acceleration of a vehicle during braking. [Figure 4] 1 is a flowchart showing the procedure of a performance evaluation method of the present invention. [Figure 5] 5 is a flowchart showing details of the calculation process of FIG. 4. [Figure 6] 10 is a graph showing an example of a first acceleration function and a second acceleration function. [Figure 7] 10 is a graph showing modified examples of the first acceleration function and the second acceleration function. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will now be described with reference to the drawings. 1 is a schematic diagram showing the configuration of a performance evaluation device 1 of this embodiment. The performance evaluation device 1 is a device for evaluating the performance of a tire 2 on a wet road surface 100.

[0010] 1, the performance evaluation device 1 of this embodiment includes a measurement unit 3 and a calculation unit 4. The measurement unit 3 and calculation unit 4 of this embodiment are mounted on a vehicle 10 on which a tire 2 to be evaluated is mounted, but may also be installed outside the vehicle.

[0011] The measurement unit 3 measures the speed and acceleration of the vehicle 10 in time series when the vehicle 10 equipped with the tire 2 travels straight on a wet road surface 100 and stops the vehicle 10 by suddenly braking the tire 2. The measurement unit 3 of this embodiment has a speed sensor 31 and an acceleration sensor 32.

[0012] The wet road surface 100 refers to a road surface that is in a wet state and is covered with a water film of, for example, several millimeters. When a vehicle traveling at high speed passes over such a wet road surface 100, the tire 2 may float up due to the hydrodynamic pressure of the water, which is known as hydroplaning. The water depth on the wet road surface 100 is not particularly limited, but a water depth of 1 mm or more, at which hydroplaning is likely to occur, is used, for example.

[0013] Hydroplaning can be classified into complete hydroplaning, in which the tire is completely lifted off the road surface, and partial hydroplaning, in which the tire is only partially lifted off the road surface (for example, the leading edge of the tire's contact patch is partially lifted off the road surface, while the trailing edge is in contact with the road surface). While the following description focuses on a tire in a partial hydroplaning state, the present invention is also applicable to a tire in a complete hydroplaning state.

[0014] The sudden braking mentioned above refers to braking strong enough to cause partial hydroplaning of the tire 2. When the tire 2 is in a partial hydroplaning state, the speed of the vehicle 10 gradually decreases due to the grip of the contact area, after which the hydroplaning subsides and the grip state is restored.

[0015] The measurement unit 3 measures the speed and acceleration of the vehicle 10 in time series from before braking begins until the vehicle 10 comes to a stop. Therefore, the speed and acceleration measured by the measurement unit 3 include the speed and acceleration of the vehicle 10 in a partial hydroplaning state and the speed and acceleration of the vehicle 10 after it has regained grip.

[0016] The speed sensor 31 detects the speed of the vehicle during braking in time series. The speed sensor of this embodiment receives signals transmitted from GPS (Global Positioning System) satellites to identify the position of the vehicle 10 at each time and acquire the speed. The speed sensor 31 is not limited to a GPS-based sensor, as long as it can accurately detect the vehicle speed even when the tires 2 are locked due to sudden braking.

[0017] The acceleration sensor 32 detects the acceleration of the vehicle 10 during braking in a time series. The acceleration sensor 32 detects acceleration by a mechanical, optical, or electromagnetic (capacitive, etc.) method. Since acceleration is calculated from speed and speed is calculated from acceleration, either the speed sensor 31 or the acceleration sensor 32 may be configured to measure the speed and acceleration in a time series.

[0018] The speed detected by the speed sensor 31 and the acceleration detected by the acceleration sensor 32 are input to the calculation unit 4 as electrical signals.

[0019] The calculation unit 4 is a computer device that processes the electrical signals input from the speed sensor 31 and the acceleration sensor 32 to estimate the probability of hydroplaning (described later) of the tire 2. The calculation unit 4 of this embodiment estimates the probability of hydroplaning of the tire 2 based on the time-series change in acceleration input from the acceleration sensor 32. The calculation unit 4 has, for example, a CPU 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.

[0020] Figure 2 shows the reduction in contact area due to hydroplaning, along with the footprint at speeds of 100km / h, 80km / h, 60km / h, and 0km / h.

[0021] In the figure, the hatched area A1 is the contact area, and the white area A2 is the area where hydroplaning is occurring. Area A2 is an area that is raised above the road surface, so it does not contribute to grip. The total contact area of ​​tire 2 is the sum A1 + A2 of contact area A1 and area A2 where hydroplaning is occurring.

[0022] The graph in Figure 2 shows the change in contact area index with speed. The contact area index is an index of the contact area at each speed, with the contact area at a speed of 0 km / h being 100%. At high speeds, hydroplaning occurs in area A2 ahead of the direction of travel, and the contact area index decreases. As the speed decreases, area A2 where hydroplaning is occurring becomes smaller, and the contact area index increases.

[0023] The probability of hydroplaning occurring is the proportion of area A2 where hydroplaning is occurring to the total contact area of ​​tire 2. The total contact area of ​​tire 2 is the area where tire 2 is in contact with the road surface without a film of water between tire 2 and the road surface when hydroplaning is not occurring at all (for example, when the vehicle is stopped or on a dry road surface or an extremely shallow road surface). Even on a wet road surface 100, it can be said that hydroplaning is almost not occurring in the extremely low speed range just before the vehicle comes to a stop, so the contact area of ​​tire 2 that is in a gripping state in such an extremely low speed range may be applied approximately as the total contact area.

[0024] The probability of hydroplaning can be thought of as the size of the area in a hydroplaning state within the total contact patch. The probability of hydroplaning occurring when the tire is completely lifted off the road surface and in a complete hydroplaning state is 100%. When the entire contact patch of tire 2 is in contact with the road and no hydroplaning is occurring (when the contact patch index in Figure 2 is 100%), the probability of hydroplaning occurring is 0%.

[0025] It is desirable to keep the probability of hydroplaning low even for a tire 2 that is experiencing hydroplaning. A tire 2 with a low probability of hydroplaning has a large contact area A1 that remains in contact with the road surface without lifting off, and the grip in the contact area A1 contributes to vehicle control, such as braking and cornering.

[0026] Fig. 3 is a conceptual diagram showing the transition of the speed and acceleration of the vehicle 10 during sudden braking. In the figure, the horizontal axis represents time (elapsed time), the right vertical axis represents speed, and the left vertical axis represents acceleration (the same applies to Figs. 6 and 7 below). Note that acceleration is represented by deceleration (negative acceleration).

[0027] When sudden braking is applied to the vehicle 10, after a free-running period, deceleration rises suddenly and hydroplaning occurs, but as the probability of hydroplaning decreases, deceleration gradually increases. Then, as hydroplaning converges, the vehicle regains a grip state that generates a certain deceleration G. In the grip state after the hydroplaning convergence point, the contact patch index is 100% and the probability of hydroplaning is 0% (see Figure 2).

[0028] It is generally difficult to measure the contact area of ​​a tire 2 while it is running on a road surface and calculate the contact area index, but in the present invention, the calculation unit 4 estimates the probability of hydroplaning occurring based on time-series changes in the acceleration of the vehicle measured by the measurement unit 3. This makes it possible for the performance evaluation device 1 to accurately and precisely evaluate the performance of a tire 2 on a wet road surface 100, compared to, for example, devices that evaluate performance by simply measuring braking distance or devices such as those in Patent Document 1 that evaluate performance based on the hydroplaning convergence speed.

[0029] 4 shows a flowchart illustrating the procedure of the performance evaluation method of the present invention. This performance evaluation method is a method for evaluating the performance of a tire 2 on a wet road surface 100. The performance evaluation method includes a braking step S1, a measurement step S2, and a calculation step S3.

[0030] The braking step S1 is a step in which the vehicle 10 equipped with the tire 2 is driven on a wet road surface 100 and the tire 2 is suddenly braked to stop the vehicle. In the braking step S1, hydroplaning that occurs immediately after the sudden braking subsides as the speed decreases, and the vehicle 10 stops after recovery of the grip state.

[0031] In the measurement step S2, the speed and acceleration of the vehicle 10 during the braking step S1, i.e., from the start of sudden braking until the vehicle comes to a stop, are measured in time series by the calculation unit 4. As already mentioned, the speed and acceleration measured in the measurement step S2 include the speed and acceleration of the vehicle 10 when it is in a complete hydroplaning state or a partial hydroplaning state, and the speed and acceleration of the vehicle 10 when it has regained grip.

[0032] The calculation step S3 is a step of estimating the probability of hydroplaning occurring for tire 2 during the braking step S1. In the calculation step S3, the probability of hydroplaning occurring for tire 2 during the braking step S1 is estimated based on the time-series change in the acceleration of vehicle 10 measured in the measurement step S2.

[0033] In the present invention, the probability of hydroplaning occurrence is estimated in calculation step S3. As a result, compared to, for example, a method of evaluating performance by simply measuring the braking distance or a method of evaluating performance based on the hydroplaning convergence speed as in Patent Document 1, this performance evaluation method makes it possible to accurately and precisely evaluate the performance of the tire 2 on a wet road surface 100.

[0034] The performance evaluation method further includes an evaluation step S4 in which the performance of the tire 2 is evaluated. In the evaluation step S4, the calculation unit 4 evaluates the performance of the tire 2 based on the probability of hydroplaning. For example, among multiple types of tires 2, a tire with a low probability of hydroplaning is evaluated as a tire with relatively high wet performance (drainage performance). In addition, by comparing the probability of hydroplaning estimated in the calculation step S3 with a predetermined threshold value, it is possible to absolutely evaluate the performance of the tire 2. This type of evaluation is particularly effective in developing a tread pattern with excellent drainage performance.

[0035] 5 shows details of the calculation step S3. The calculation step S3 includes a first calculation step S31 for calculating a first acceleration function and a second calculation step S32 for calculating a second acceleration function.

[0036] FIG. 6 shows the first acceleration function a1 calculated in the first calculation step S31 and the second acceleration function a2 calculated in the second calculation step S32.

[0037] This example shows the changes in the speed detected by the speed sensor 31 and the acceleration detected by the acceleration sensor 32 when a vehicle 10 traveling on a wet road surface 100 at a predetermined speed (e.g., 100 km / h) is suddenly braked (the same applies to Figure 7).

[0038] The first acceleration function a1 is a function of acceleration and time at the beginning of vehicle braking, and the second acceleration function a2 is a function of acceleration and time at the end of vehicle braking.

[0039] The first acceleration function a1 is a function of acceleration and time within a predetermined first time T1 range at the beginning of vehicle braking. The first time T1 is defined as a predetermined time range immediately after hydroplaning occurs and the deceleration slope becomes gentler after sudden braking causes deceleration.

[0040] The first time T1 mainly includes the time when hydroplaning occurs, and is preferably set to be short so as not to include the time when hydroplaning subsides.

[0041] The first time T1 is preferably 10% or more of the total braking time TT. This allows an appropriate first acceleration function a1 to be acquired. The total braking time TT is defined as the time from when the deceleration of the vehicle 10 starts to increase and the speed of the vehicle 10 starts to decrease after the start of sudden braking until the vehicle 10 stops.

[0042] The first acceleration function a1 calculated in the first calculation step S31 is preferably a linear approximation line of the acceleration at the first time T1. In this case, the first acceleration function a1 is expressed, for example, by a1 = β1t + γ1 (β1 and γ1 are constants). This enables the calculation unit 4 to accurately derive the first acceleration function a1 in a short time. Note that the first acceleration function a1 may also be a quadratic approximation curve of the acceleration at the first time T1.

[0043] The first acceleration function a1 calculated in the first calculation step S31 may be a linear approximation of the moving average curve of the acceleration at the first time T1, etc. This allows the detection error of the acceleration sensor 32 to be rounded off, making it possible to derive the first acceleration function a1 accurately in a short time.

[0044] The second acceleration function a2 is a function of acceleration and time within a predetermined second time T2 range at the end of vehicle braking. The second time T2 is defined as a predetermined range of time just before the vehicle 10 comes to a stop. The second time T2 is set to be short so as not to include the time when hydroplaning ceases.

[0045] The second time T2 is preferably 10% or more of the total braking time TT, thereby obtaining an appropriate second acceleration function a2.

[0046] The second time T2 mainly includes the time when the vehicle is in a grip state after hydroplaning has subsided. The second acceleration function a2 is preferably a linear approximation of the acceleration at the second time T2. In this case, the second acceleration function a2 is expressed, for example, as a2 = β2t + γ2 (β2 and γ2 are constants). This allows the calculation unit 4 to accurately derive the second acceleration function a2 in a short period of time. Note that the second acceleration function a2 may also be a quadratic approximation curve of the acceleration at the second time T2.

[0047] The second acceleration function a2 calculated in the second calculation step S32 may be a linear approximation of the moving average curve of the acceleration at the second time T2, etc. This allows the detection error of the acceleration sensor 32 to be rounded off, making it possible to derive the second acceleration function a2 accurately in a short time.

[0048] In the grip state, the rate of change of the second acceleration function a2 is small, so it may be approximated as a substantially constant value. In this case, the second acceleration function a2 may be approximated as a constant value by the average value of the acceleration within the range of the second time T2.

[0049] In the calculation step S3, which includes the first calculation step S31 and the second calculation step S32, it is preferable to execute an estimation step S33 for estimating the probability of hydroplaning. In the estimation step S33, the probability of hydroplaning is estimated based on the ratio of the first acceleration function a1 to the second acceleration function a2.

[0050] In the estimation step S33, the average or median value of the first acceleration function a1 at the first time T1 may be used as the first acceleration function a1. Also, the average or median value of the second acceleration function a2 at the second time T2 may be used as the second acceleration function a2. This makes it possible to accurately estimate the probability of hydroplaning.

[0051] In the estimation step S33, it is desirable to estimate the probability of hydroplaning based on the ratio α1 / α2 of the average value α1 of the first acceleration function a1 to the average value α2 of the second acceleration function a2, which enables accurate and easy estimation of the probability of hydroplaning.

[0052] The estimation step S33 preferably includes a step of calculating the probability of hydroplaning occurring based on the following formula (1). Probability of hydroplaning = {(α2-α1) / α2} × 100 (1) This makes it possible to estimate the probability of hydroplaning occurring more accurately.

[0053] 7 shows a first acceleration function a1' and a second acceleration function a2', which are modifications of the first acceleration function a1 and the second acceleration function a2. Portions of the first acceleration function a1' and the second acceleration function a2' that are not described below are similar to the first acceleration function a1 and the second acceleration function a2 described above.

[0054] The first acceleration function a1' is a function of acceleration and time in a predetermined first speed range V1 at the beginning of vehicle braking. The first speed range V1 is defined as a predetermined range of time immediately after the deceleration rate increases due to sudden braking, hydroplaning occurs, and the deceleration rate becomes gentler.

[0055] The first speed range V1 includes the speed range where hydroplaning occurs. It is desirable that the first speed range V1 be set short so as not to include the speed range where hydroplaning converges.

[0056] More specifically, the first speed range V1 is preferably −5 to −15 km / h, which is the initial speed at the start of braking. For example, if the initial speed at the start of braking is 100 km / h, the first speed range V1 is preferably 95 to 85 km / h. This allows an appropriate first acceleration function a1′ to be obtained.

[0057] The first acceleration function a1' calculated in the first calculation step S31 is preferably a linear approximation line of the acceleration at the first time T1, etc. The first acceleration function a1' calculated in the first calculation step S31 may be a linear approximation line of the moving average curve of the acceleration at the first time T1, etc.

[0058] The second acceleration function a2' is a function of acceleration and time within a predetermined second speed range V2 at the end of vehicle braking. The second speed range V2 is defined as a predetermined speed range immediately before the vehicle 10 comes to a stop. The second speed range V2 is set short so as not to include the speed at which hydroplaning converges.

[0059] More specifically, the second speed range V2 is preferably 30 to 10 km / h, thereby obtaining an appropriate second acceleration function a2'.

[0060] The second speed region V2 mainly includes the time when the vehicle is in a grip state after hydroplaning has subsided. The second acceleration function a2' is preferably a linear approximation of the acceleration in the second speed region V2. The second acceleration function a2' calculated in the second calculation step S32 may also be a linear approximation of the moving average curve of the acceleration at the second time T2. In the grip state, the rate of change of the second acceleration function a2' is small, so it may be approximated to a substantially constant value.

[0061] In the estimation step S33, the probability of hydroplaning is estimated based on the ratio of the first acceleration function a1' to the second acceleration function a2'. In the estimation step S33, the average or median value of the first acceleration function a1' in the first speed range V1 may be applied as the first acceleration function a1'. Also, the average or median value of the second acceleration function a2' in the second speed range V2 may be applied as the second acceleration function a2'.

[0062] In the estimation step S33, it is desirable to estimate the probability of hydroplaning based on the ratio α1 / α2 of the average value α1 of the first acceleration function a1' to the average value α2 of the second acceleration function a2', which enables accurate and easy estimation of the probability of hydroplaning.

[0063] The estimation step S33 preferably includes a step of calculating the probability of hydroplaning occurring based on the following formula (1). Probability of hydroplaning = {(α2-α1) / α2} × 100 (1) This makes it possible to estimate the probability of hydroplaning occurring more accurately.

[0064] Although the performance evaluation device 1 and the performance evaluation method of the present invention have been described in detail above, the present invention is not limited to the specific embodiments described above and can be modified and implemented in various aspects.

[0065] For example, by estimating the probability of hydroplaning on a wet road surface with multiple levels of water depth in the manner described above, it becomes possible to more accurately evaluate the performance of the tire 2. More specifically, by estimating the probability of hydroplaning on a wet road surface with a water film with a water depth of 1.0 mm or more and the probability of hydroplaning on a wet road surface with a water film with a water depth of 0.6 mm or less and calculating the difference between the two, it becomes possible to more accurately evaluate the performance of the tire 2 on a road surface that has deteriorated due to long-term use since the initial construction.

[0066] [Note] The present invention includes the following aspects.

[0067] [Invention 1] 1. A method for evaluating tire performance on wet roads, comprising: a braking step of running a vehicle equipped with the tire on the wet road surface and suddenly braking the tire to stop the vehicle; a measuring step of measuring the speed and acceleration of the vehicle in time series during the braking step; and a calculation step of estimating a probability of hydroplaning of the tire during the braking step based on the time-series change in the acceleration of the vehicle measured in the measurement step. Methods for evaluating tire performance. [Invention 2] The calculation step a first calculation step of calculating a first acceleration function which is a function of the acceleration and time at an initial stage of braking of the vehicle; a second calculation step of calculating a second acceleration function which is a function of the acceleration at the end of braking of the vehicle and time. [Invention 3] the first acceleration function is a function of the acceleration and time within a predetermined first time range at the beginning of braking of the vehicle, A tire performance evaluation method according to aspect 2, wherein the second acceleration function is a function of the acceleration and time within a predetermined second time range in the final stage of braking of the vehicle. [Invention 4] 4. The tire performance evaluation method according to claim 3, wherein the first time period is 10% or more of the total braking time. [Invention 5] 5. The tire performance evaluation method according to invention 3 or 4, wherein the second time period is 10% or more of the total braking time. [Invention 6] 6. The tire performance evaluation method according to any one of claims 3 to 5, wherein the first acceleration function is a linear approximation line of the acceleration within the first time range. [Invention 7] 7. A tire performance evaluation method according to any one of claims 3 to 6, wherein the second acceleration function is a linear approximation line of the acceleration within the second time range. [Invention 8] 8. The tire performance evaluation method according to any one of claims 3 to 7, wherein the second acceleration function is an average value of the acceleration within the second time range. [Invention 9] 9. A tire performance evaluation method according to any one of claims 3 to 8, wherein the calculation step includes an estimation step of estimating the probability of hydroplaning occurring based on a ratio of the first acceleration function to the second acceleration function. [Invention 10] the first acceleration function is a function of the acceleration in a predetermined first speed range at the initial stage of braking of the vehicle and time, A tire performance evaluation method according to aspect 2, wherein the second acceleration function is a function of the acceleration in a predetermined second speed range at the end of braking of the vehicle and time. [Invention 11] 11. The tire performance evaluation method according to claim 10, wherein the first speed range is an initial speed at the start of braking of −5 to −15 km / h. [Invention 12] 12. The tire performance evaluation method according to claim 10 or 11, wherein the second speed range is 30 to 10 km / h. [Invention 13] 13. A tire performance evaluation method according to any one of claims 2 to 12, wherein the calculation step estimates the probability of hydroplaning based on a ratio α1 / α2 of the average value α1 of the first acceleration function to the average value α2 of the second acceleration function. [Invention 14] 14. A tire performance evaluation method according to claim 13, wherein the calculation step includes a step of calculating the probability of hydroplaning occurrence based on the following formula (1): Probability of hydroplaning occurrence = {(α2-α1) / α2} × 100 (1) [Invention 15] 15. The tire performance evaluation method according to any one of claims 1 to 14, further comprising an evaluation step of evaluating the tire performance based on the probability of hydroplaning occurrence. [Invention 16] An apparatus for evaluating tire performance on a wet road surface, comprising: a vehicle equipped with the tire is driven on the wet road surface, and the tire is suddenly braked to stop the vehicle; a measurement unit that measures the speed and acceleration of the vehicle during braking in time series; a calculation unit that estimates a probability of hydroplaning of the tire based on the time-series change in the acceleration of the vehicle measured by the measurement unit, Tire performance evaluation device. [Explanation of symbols]

[0068] 1: Performance evaluation device 2: Tires 3: Measurement section 4: Calculation section 10: Vehicle 31: Speed ​​sensor 32: Acceleration sensor 100: Wet road surface S1: Braking process S2:Measurement process S3: Calculation process S4: Evaluation process S31: 1st calculation step S32: 2nd calculation process S33: Estimation process T1: First Hour T2: Second period V1: 1st speed range V2: 2nd speed range a1: First acceleration function a2: Second acceleration function

Claims

1. 1. A method for evaluating tire performance on wet roads, comprising: a braking step of running a vehicle equipped with the tire on the wet road surface and suddenly braking the tire to stop the vehicle; a measuring step of measuring the speed and acceleration of the vehicle in time series during the braking step; and a calculation step of estimating a probability of hydroplaning of the tire during the braking step based on the time-series change in the acceleration of the vehicle measured in the measurement step. Methods for evaluating tire performance.

2. The calculation step a first calculation step of calculating a first acceleration function which is a function of the acceleration and time at an initial stage of braking of the vehicle; The tire performance evaluation method according to claim 1 , further comprising a second calculation step of calculating a second acceleration function which is a function of the acceleration at the end of braking of the vehicle and time.

3. the first acceleration function is a function of the acceleration and time within a predetermined first time range at the initial stage of braking of the vehicle, 3. The tire performance evaluation method according to claim 2, wherein the second acceleration function is a function of the acceleration and time within a second predetermined time range in the final stage of braking of the vehicle.

4. The tire performance evaluation method according to claim 3 , wherein the first time period is equal to or greater than 10% of the total braking time.

5. The tire performance evaluation method according to claim 3 , wherein the second time period is 10% or more of the total braking time.

6. The tire performance evaluation method according to claim 3 , wherein the first acceleration function is a linear approximation of the acceleration within the first time range.

7. The tire performance evaluation method according to claim 3 , wherein the second acceleration function is a linear approximation of the acceleration within the second time range.

8. The tire performance evaluation method according to claim 3 , wherein the second acceleration function is an average value of the acceleration within the second time range.

9. 4. The tire performance evaluation method according to claim 3, wherein the calculation step includes an estimation step of estimating the probability of hydroplaning occurring based on a ratio of the first acceleration function to the second acceleration function.

10. the first acceleration function is a function of the acceleration in a predetermined first speed range at the initial stage of braking of the vehicle and time, 3. The tire performance evaluation method according to claim 2, wherein the second acceleration function is a function of the acceleration in a predetermined second speed range during a final stage of braking of the vehicle and time.

11. The tire performance evaluation method according to claim 10, wherein the first speed range is an initial speed at the start of braking of −5 to −15 km / h.

12. The tire performance evaluation method according to claim 10, wherein the second speed range is 30 to 10 km / h.

13. 3. The tire performance evaluation method according to claim 2, wherein the calculating step estimates the probability of hydroplaning based on a ratio α1 / α2 of the average value α1 of the first acceleration function to the average value α2 of the second acceleration function.

14. 14. The tire performance evaluation method according to claim 13, wherein the calculating step includes a step of calculating the probability of hydroplaning occurrence based on the following formula (1): Probability of hydroplaning occurrence = {(α2 - α1) / α2} × 100 (1)

15. The tire performance evaluation method according to claim 1 , further comprising an evaluation step of evaluating tire performance based on the probability of hydroplaning occurrence.

16. An apparatus for evaluating tire performance on a wet road surface, comprising: a vehicle equipped with the tire is driven on the wet road surface, and the tire is suddenly braked to stop the vehicle; a measurement unit that measures the speed and acceleration of the vehicle during braking in time series; a calculation unit that estimates a probability of hydroplaning of the tire based on the time-series change in the acceleration of the vehicle measured by the measurement unit, Tire performance evaluation device.

Images