Tire testing methods

Abstract

Even if tire sizes differ, the exposure of tires to ozone should be kept uniform overall. [Solution] An indicator is attached to the tire to display the actual ozone exposure amount. An ozone target exposure amount and initial conditions are set. The tire is exposed to ozone in an atmosphere with a higher ozone concentration than the atmosphere. The actual ozone exposure amount received by the tire is measured. It is determined whether the actual ozone exposure amount has reached the ozone target exposure amount. It is then determined whether to continue or terminate the ozone exposure. If it is determined in the fourth step to continue the ozone exposure, the theoretical ozone exposure amount and the actual ozone exposure amount are compared. It is determined whether it is necessary to change the ozone exposure conditions. If it is determined that it is necessary to change the ozone exposure conditions, the ozone exposure conditions are changed using elements calculated from the actual ozone exposure amount, the theoretical ozone exposure amount, and the theoretical ozone exposure time. If it is determined to terminate the ozone exposure, the condition of the tire is evaluated.

Description

Technical Field

[0001] The present invention relates to a tire test method that can be carried out under a uniform ozone exposure condition regardless of tire size, tire usage conditions, or the environment around the tire.

Background Art

[0002] As tire durability tests for exposing tires to ozone, there are static ozone tests and dynamic tests using a rotating drum. For example, in a test chamber in which a tire test device for reproducing the usage state by applying a predetermined load to a tire is housed, ozone for accelerating the deterioration of the tire is supplied from an ozone supply device that generates ozone to the air whose temperature and humidity are adjusted by an air conditioner for adjusting the temperature and humidity in the test chamber, and the air and ozone are sent out in a mixed state. A tire durability test method is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the tire durability test method disclosed in Patent Document 1, it is said that the durability test of the tire can be carried out by accelerating the deterioration of the tire in the same manner as the deterioration phenomenon during actual tire use.

[0005] However, when conducting the durability test disclosed in Patent Document 1, differences in tire size, tire usage conditions (e.g., tire rotation speed), or the surrounding environment (e.g., airflow and temperature in the test chamber) may result in differences in the amount of ozone (amount of ozone contact per unit surface area of ​​the tire) when the tire surface is exposed to ozone. Therefore, it may be necessary to evaluate the condition of the tires (e.g., presence or absence of groove cracks) under conditions where the degree of tire exposure to ozone varies among multiple tires. However, such evaluations are based on the premise that uniform ozone exposure conditions cannot be achieved among the tires, and therefore comparisons between tires may not be appropriate.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a tire testing method that can evaluate the condition of a tire after creating a uniform ozone exposure condition for the tire, even when the tire size, tire usage conditions, or the environment surrounding the tire differ. [Means for solving the problem]

[0007] The tire testing method of the present invention is A tire testing method for evaluating tire durability by accelerating tire degradation under an ozone atmosphere, An indicator that displays the actual amount of ozone exposure is attached to the aforementioned tire. (a) A first step of setting the target ozone exposure and initial conditions, (b) A second step in which the surrounding atmosphere of the tire is made into an atmosphere with a higher ozone concentration than the atmosphere, and the tire is exposed to ozone. (c) A third step of measuring the actual amount of ozone exposure received by the tire from the indicator, (d) A fourth step in which the actual ozone exposure amount is determined to have reached the target ozone exposure amount, and whether to continue or end the ozone exposure, (e) If it is determined in the fourth step to continue exposure to ozone, the fifth step involves comparing the theoretical ozone exposure amount with the actual ozone exposure amount to determine whether it is necessary to change the ozone exposure conditions, (f) If it is determined in the fifth step that it is necessary to change the ozone exposure conditions, the sixth step involves changing the ozone exposure conditions using elements calculated from the actual ozone exposure amount, the theoretical ozone exposure amount, and the theoretical ozone exposure time. (g) If it is determined in the fourth step to end the exposure to ozone, the seventh step is to evaluate the condition of the tires, It is characterized by including. [Effects of the Invention]

[0008] The tire testing method according to the present invention combines measuring the actual ozone exposure using an indicator with a feedback mechanism for the actual ozone exposure (including steps 4 to 6 described above). This allows for the creation of a uniform ozone exposure state for the tire, even when tire size, tire usage conditions, or the surrounding environment differ, and enables the evaluation of the tire's condition. As a result, such an evaluation is suitable for comparisons between tires. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows a conventional tire testing method, where (A) is a flowchart showing each step, and (B) is a graph showing the relationship between the target ozone exposure, the theoretical ozone exposure, and the actual ozone exposure within the theoretical ozone exposure time from start to finish. [Figure 2] Figure 2 shows an example of the tire testing method of the present invention, where (A) is a flowchart showing each step, and (B) is a graph showing the relationship between the target ozone exposure, the theoretical ozone exposure, and the actual ozone exposure within the theoretical ozone exposure time from start to finish. [Figure 3] Figure 3 is a graph showing examples of considering changes to ozone exposure conditions for each N divided time period, where (A) shows the case where N is 1, and (B) shows the case where N is 3. [Modes for carrying out the invention]

[0010] <Various aspects of the present invention> The present invention includes the following embodiments. [Aspect 1] The tire testing method of the present invention is A tire testing method for evaluating tire durability by accelerating tire degradation under an ozone atmosphere, An indicator that displays the actual amount of ozone exposure is attached to the aforementioned tire. (a) A first step of setting the target ozone exposure and initial conditions, (b) A second step in which the surrounding atmosphere of the tire is made into an atmosphere with a higher ozone concentration than the atmosphere, and the tire is exposed to ozone. (c) A third step of measuring the actual amount of ozone exposure received by the tire from the indicator, (d) A fourth step in which the actual ozone exposure amount is determined to have reached the target ozone exposure amount, and whether to continue or end the ozone exposure, (e) If it is determined in the fourth step to continue exposure to ozone, the fifth step involves comparing the theoretical ozone exposure amount with the actual ozone exposure amount to determine whether it is necessary to change the ozone exposure conditions, (f) If it is determined in the fifth step that it is necessary to change the ozone exposure conditions, the sixth step involves changing the ozone exposure conditions using elements calculated from the actual ozone exposure amount, the theoretical ozone exposure amount, and the theoretical ozone exposure time. (g) If it is determined in the fourth step to end the exposure to ozone, the seventh step is to evaluate the condition of the tires, A tire testing method characterized by including [a certain element]. [Aspect 2] The tire testing method according to Embodiment 1, wherein in the third step, the actual ozone exposure is measured at intervals divided by N (where N is a natural number of 1 or more) with respect to the theoretical ozone exposure time determined from the target ozone exposure and the initial conditions. [Aspect 3] In the third step, the ozone actual exposure amount is quantified by a dye, ultraviolet absorbance, or resistance change in the test method of the tire according to Embodiment 1 or 2. [Embodiment 4] In the fourth step, If the ozone actual exposure amount measured in the third step immediately preceding among the third steps performed so far is 90% or more of the ozone target exposure amount of 3, or if it exceeds the ozone target exposure amount, the tire exposure to ozone shall be terminated. If the ozone actual exposure amount measured in the third step immediately preceding among the third steps performed so far is less than 90% of the ozone target exposure amount, proceed to the fifth step. The test method of the tire according to any one of Embodiments 1 to 3. [Embodiment 5] In the fifth step, If the ozone actual exposure amount measured in the third step immediately preceding among the third steps performed so far is 90% or more of the ozone target exposure amount, proceed to the second step. If the ozone actual exposure amount measured in the third step immediately preceding among the third steps performed so far is less than 90% of the ozone target exposure amount, proceed to the sixth step. The test method of the tire according to any one of Embodiments 1 to 4. [Embodiment 6] In the sixth step, change to the ozone exposure conditions calculated from the ozone actual exposure amount measured in the third step immediately preceding among the third steps performed so far, the ozone theoretical exposure amount, and the ozone theoretical exposure time. The test method of the tire according to any one of Embodiments 1 to 5. [Embodiment 7] Set the concentration of the ozone to 30 pphm or more and 250 pphm or less. The test method of the tire according to any one of Embodiments 1 to 6. [Embodiment 8] Before the second step, clean the main groove bottom of the tire. The test method of the tire according to any one of Embodiments 1 to 7.

[0011] [Definition] In the following explanation, the circumferential direction of the tire refers to the direction around the tire's axis of rotation.

[0012] Similarly, in the following explanation, "regular rim" refers to the "applicable rim" as defined by JATMA, the "Design Rim" as defined by TRA, or the "Measuring Rim" as defined by ETRTO.

[0013] Similarly, in the following explanation, "normal internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO. Furthermore, "normal load" refers to the "maximum load capacity" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "LOAD CAPACITY" specified by ETRTO.

[0014] <Conventional testing method> Figure 1 shows a conventional tire testing method, where (A) is a flowchart showing each step, and (B) is a graph showing the relationship between the target ozone exposure, the theoretical ozone exposure, and the actual ozone exposure within the theoretical ozone exposure time from start to finish.

[0015] As shown in Figures 1(A) and 1(B), conventional tire testing methods involved leaving the tire in a test chamber with a constant concentration of ozone for a certain period of time, or rotating the tire (exposure to ozone in Figure 1(A)), and then observing the condition of the tire (for example, groove cracks (GC)) (GC observation in Figure 1(A)).

[0016] However, when conventional ozone exposure, as shown in Figure 1(B), is performed on tires of different sizes, for example, the amount of ozone contact per unit surface area of ​​the tire is not uniform among the tires. As a result, various situations can occur where the actual ozone exposure amount approaches or deviates from the target ozone exposure amount for multiple tires after exposure, leading to differences in ozone exposure conditions among tires.

[0017] Furthermore, when tires with different usage conditions (e.g., tire rotation speed) and surrounding environmental conditions (e.g., airflow and temperature in the test chamber) were subjected to the conventional ozone exposure method shown in Figure 1(B), the amount of ozone contact per unit surface area of ​​the tire was not uniform among the tires. As a result, various situations arose where the actual ozone exposure amount after ozone exposure approached or deviated from the target ozone exposure amount for multiple tires, leading to differences in ozone exposure conditions among the tires.

[0018] Thus, when multiple tires are sequentially exposed to conventional ozone under conditions with different tire sizes, usage conditions, or surrounding environmental factors, the ozone exposure levels may differ between tires. Evaluating groove cracks under such conditions is undesirable. This is because the evaluation results for groove cracks are obtained under conditions that do not guarantee the optimal prerequisites (uniform ozone exposure levels across tires), and consequently, it may not be meaningful to compare such evaluation results across tires.

[0019] <Inventor's insights> Therefore, the inventors reconsidered that creating a state in which the tire's exposure to ozone is generally uniform, even when tire size, tire usage conditions, or the surrounding environment differs (i.e., the amount of ozone contact per unit surface area of ​​the tire is generally the same across tires), is a necessary prerequisite for evaluating groove cracks occurring on the surface of tire grooves. Before evaluating groove cracks, the inventors diligently investigated how to achieve such a uniform state of ozone exposure for the tire.

[0020] As a result, the inventors have found that, assuming that an indicator capable of measuring the actual amount of ozone exposure is attached to the tire, in addition to conventional ozone exposure and GC observation, it is possible to achieve a uniform ozone exposure state across tires by employing an opportunity to feed back the actual amount of ozone exposure (an opportunity to interrupt ozone exposure midway, analyze whether the actual amount of ozone exposure at the point of interruption is a reasonable exposure, and, if necessary, change the ozone exposure conditions thereafter and restart ozone exposure). The tire test method of this embodiment, based on this finding, is described in detail below.

[0021] <Test Method of the Invention> Figure 2 shows an example of the tire testing method of the present invention (hereinafter sometimes referred to as "the tire testing method of this embodiment"), where (A) is a flowchart showing each step, and (B) is a graph showing the relationship between the target ozone exposure, the theoretical ozone exposure, and the actual ozone exposure within the ozone theoretical exposure time (time determined from the target ozone exposure and initial conditions) from start to finish. In this embodiment, all of the above ozone exposure amounts refer to the amount of ozone contact per unit surface area of ​​each tire, not the total amount of ozone that came into contact with each tire.

[0022] As shown in Figure 2(A), the tire testing method of this embodiment includes steps 1 through 7. It should be noted that the tire testing method of this embodiment is based on the premise that an indicator displaying the actual ozone exposure is attached to the tire. Here, the actual ozone exposure refers to the total amount of ozone that actually comes into contact with the tire.

[0023] Furthermore, the indicators used here are those that exhibit a color difference, a change in ultraviolet absorbance, or a change in resistance when exposed to ozone. Specifically, the difference in color, the difference in ultraviolet absorbance, or the difference in resistance before and after exposure to ozone is quantified to determine the actual amount of ozone exposure.

[0024] For example, if an indicator that quantifies color difference is used, when the indicator attached to the tire is exposed to ozone, at least a portion of the indicator will change color. By measuring the color difference before and after the change, the actual amount of ozone exposure can be visualized and further quantified.

[0025] Next, the tire testing method of this embodiment will be described in detail for each step.

[0026] ((a) 1st step) The first step is to set the target ozone exposure and initial conditions. Here, the target ozone exposure refers to the total amount of ozone that the tire should be in contact with at the end of the ozone exposure period. The initial conditions refer to the conditions related to various factors that affect the tire's ozone exposure state, such as the ozone concentration in the test chamber, the temperature of the test chamber, and the theoretical ozone exposure time.

[0027] The target ozone exposure and initial conditions should be set to the amount of ozone that can be expected when the tires are actually mounted on a vehicle and in use, as well as conditions such as temperature. It is important to set these quantities and conditions appropriately, as they will vary depending on the location and season.

[0028] For example, the initial ozone concentration in the test chamber is preferably 30 pphm or higher and 250 hm or lower. By setting the ozone concentration in the test chamber to 30 pphm or higher, the indicator can react accurately to the tire's exposure to ozone, and the supply of ozone to the test chamber can be stably maintained.

[0029] In contrast, by setting the ozone concentration in the test chamber to 250 pphm or less, groove cracks can be formed in the tire in a manner that is roughly correlated with natural degradation. Such a manner of groove crack formation is preferable as a prerequisite for evaluating the presence or absence of groove cracks.

[0030] Furthermore, as an initial condition, the ozone concentration in the test chamber is more preferably 50 pphm to 230 hm, and more preferably 70 pphm to 210 hm.

[0031] ((b) 2nd step) The second step involves exposing the tire to ozone by creating an ozone concentration atmosphere (the atmosphere inside the test chamber) that is higher than that of the atmosphere. The reason for creating an ozone concentration atmosphere higher than that of the atmosphere is that simply exposing the tire to the atmosphere would require an enormous amount of time for the test. By increasing the rate of ozone exposure of the tire compared to when the tire is used in the market (i.e., the amount of ozone that the tire comes into contact with per unit time), the theoretical ozone exposure time is efficiently reduced, thereby shortening the overall test time of this embodiment.

[0032] Furthermore, when exposing the tires to ozone, the tires may be in a static state (for example, simply left in the test room) or in a dynamic state (for example, mounted on a drum-type tire braking and driving test machine and rotated).

[0033] Furthermore, if a considerable amount of time has passed since the tire on which the indicator is attached, from its manufacture through receipt, storage, and up to the time of testing, a layer containing deterioration inhibitors may rise to the surface of the main groove bottom, etc., potentially resulting in a layer with a different composition on the groove bottom surface compared to a new tire. For this reason, if multiple tires with varying amounts of time elapsed since their manufacture are simultaneously exposed to ozone, it is expected that the degree of groove cracking formed on the tires will be completely different, even if the actual amount of ozone exposure is the same. Therefore, it is preferable to clean the main groove bottom of the tire on which the indicator is attached before the second step described above. Here, the main groove refers to the groove in a plan view of the tire with normal internal pressure applied and no load (a state in which no normal load is applied), where the groove width is in the range of 3% to 11% of the contact width, and its direction of extension is not limited to the circumferential direction of the tire, but can be any direction.

[0034] As for the method of cleaning the bottom of the tire grooves, in addition to the method of wiping off the above-mentioned layer (a layer containing a deterioration inhibitor, etc.) formed at the bottom of the main groove using an organic solvent, any known method can be adopted, such as a method of removing unwanted deposits adhering to a predetermined area of ​​the tire surface by irradiating the area with plasma from an irradiation head (see Japanese Patent Publication No. 2020-203474), or a method of spraying a cleaning medium (such as steam) towards the area to be cleaned on the tire (see Japanese Patent Publication No. 2020-96997).

[0035] Furthermore, the second step (exposure to ozone) described above can be carried out at a constant ozone concentration throughout the entire theoretical ozone exposure time (Type 1), or it can be carried out by dividing the theoretical ozone exposure time and using different or a unified ozone concentration for each divided time period (Type 2). Here, a unified ozone concentration means that although the theoretical ozone exposure time is divided, the ozone concentration is the same for all time periods.

[0036] Regarding the second step (exposure to ozone), the aforementioned types 1 and 2 will be noted together in the explanations for the case where the third step (measurement of actual ozone exposure), which is linked to the second step and will be performed in one step, and the case where it is performed two or more times, respectively.

[0037] ((c) 3rd step) The third step involves measuring the actual ozone exposure received by the tire using an indicator. While the measurement of actual ozone exposure can be done in a single step, linked to the second step (ozone exposure), it is also possible to divide the predetermined theoretical ozone exposure time into multiple segments and measure the actual ozone exposure at each segment (after performing the second step (ozone exposure)).

[0038] First, if the actual ozone exposure is to be measured in a single step in the third step, the ozone theoretical exposure time, which is determined from the target ozone exposure, the ozone concentration in the test room, the temperature of the test room, etc., is not divided during the second step, but is instead exposed to ozone in a test room with a constant concentration for the entire duration (Type 1 described above). Then, in the third step, the actual ozone exposure received by the tire (the total amount of ozone that came into contact with the tire) is measured using an indicator.

[0039] In contrast, when measuring actual ozone exposure in two or more steps, the theoretical ozone exposure time is first divided into two or more segments (Type 2 described above). Then, ozone is brought into contact with the tire during the first segment (second step), and the total amount of ozone that came into contact during the first segment (actual ozone exposure) is measured using an indicator (third step). Subsequently, the fourth step (determination of whether to continue or end ozone exposure) and fifth step (determination of changing ozone exposure conditions) are carried out, and if necessary, the sixth step (change of ozone exposure conditions) is also implemented.

[0040] Next, ozone is brought into contact with the tire over the divided second time period (second step), and the total amount of ozone that has come into contact with the tire up to the second time period (i.e., both the first and second time periods) (actual ozone exposure) is measured using an indicator (third step). Subsequently, the fourth step (determination of whether to continue or end ozone exposure) and fifth step (determination of changing ozone exposure conditions) described later are carried out, and if necessary, the sixth step (change of ozone exposure conditions) described later is also performed.

[0041] Furthermore, this process is repeated, and ozone is brought into contact with the tire over the last divided time period (second step), and the total amount of ozone to which the tire has been exposed up to the last time period (actual ozone exposure) is measured using an indicator (third step).

[0042] Here, the ozone theoretical exposure time can be divided equally or unevenly. However, considering work efficiency, it is preferable to complete the second and third steps without dividing the time as much as possible. For this reason, it is desirable to avoid dividing the ozone theoretical exposure time too much in the first half and to expose the subject to a constant concentration of ozone for a long period of time in one time slot, while in the second half, to increase the frequency of divisions and fine-tune the actual ozone exposure amount to bring it closer to the target ozone exposure amount.

[0043] Furthermore, when dividing the exposure time, it is preferable that each time period be between 2 and 10 hours, and most preferably between 3 and 6 hours. By imposing such limitations, even when the total ozone exposure time is long (for example, one week), it is possible to achieve a formation pattern equivalent to that which occurs when the tire is actually used, while ensuring that the exposure time to a certain concentration of ozone is not too short, and allowing the tire surface to react efficiently with ozone.

[0044] Furthermore, if the number of divisions is too small, it is anticipated that a rapid change in ozone concentration will occur immediately after the division, which may result in a formation pattern different from that of groove cracks when the tire is actually used. For this reason, it is preferable to divide the ozone theoretical exposure time into three or more divisions.

[0045] Conversely, if the ozone exposure time is divided too many times, not only will work efficiency decrease, but each time period set by the division may also be too short, resulting in insufficient exposure time to a certain concentration of ozone. As a result, the tire surface may not react well to ozone, and the manner in which groove cracks are formed may differ from that of normal tire use. Specifically, groove cracks may not be formed to the extent expected. Therefore, it is preferable to divide the ozone theoretical exposure time into 10 or fewer divisions.

[0046] Based on the above findings, it is even more preferable that the number of divisions be between 4 and 9, and it is extremely preferable that the number of divisions be between 5 and 8.

[0047] Figure 3 is a graph showing examples of considering changes to ozone exposure conditions for each N divided time period, where (A) shows the case where N is 1, and (B) shows the case where N is 3.

[0048] In the example shown in Figure 3(A) (N=1), the ozone theoretical exposure time is divided into two equal parts. In the example shown in Figure 3(A), at the end of the first half of the ozone theoretical exposure time, the difference between the actual ozone exposure and the theoretical exposure is determined, and then the amount of ozone exposure for the second half is determined.

[0049] Here, the theoretical ozone exposure is the so-called ozone accumulated value (OA value), which is the product of the ozone concentration and the theoretical ozone exposure time. Furthermore, when dividing the theoretical ozone exposure time and determining the actual ozone exposure after the exposure for a predetermined time period, it is possible to change at least one of the ozone concentration or ozone exposure time in the test room, or the temperature in the test room. However, it is preferable not to change the temperature in the test room because the manner of tire deterioration due to ozone exposure differs significantly.

[0050] In contrast, in the example shown in Figure 3(B) (N=3), the ozone theoretical exposure time is divided into four parts, although not entirely evenly. This allows for more frequent changes in the amount of ozone contact with the tire, although it reduces work efficiency compared to the example shown in Figure 3(A). As a result, in the example shown in Figure 3(B), the difference in the actual ozone exposure per unit time before and after the division (i.e., the difference in the slope of the straight line representing the actual ozone exposure) can be made smaller than the difference in the example shown in Figure 3(A). Consequently, it is possible to achieve a configuration that is closer to the actual groove crack formation that occurs when the tire is used, without drastically changing the amount of ozone contact with the tire immediately after the division.

[0051] ((d) 4th step) The fourth step is to determine whether the actual ozone exposure has reached the target ozone exposure level, and then decide whether to continue or terminate the ozone exposure (of the tires).

[0052] In the fourth step, if the actual ozone exposure received by the tire (measured in the most recent third step) (the total amount of ozone that has come into contact with the tire up to that point) is less than 90% of the target ozone exposure, the process proceeds to the fifth step, which will be described later. In this case, the ozone exposure to the tire has not effectively ended.

[0053] Therefore, as described above, when the second step (exposure to ozone) and the third step (measurement of actual ozone exposure) are performed by dividing the theoretical ozone exposure time (in the case of type 2 above), at the time the third step is completed for all time periods except the last of the divided time periods, the actual ozone exposure received by the tire should normally be less than 90% of the target ozone exposure. Therefore, in the fourth step, it is decided to continue the ozone exposure.

[0054] In contrast, if the second step (exposure to ozone) and the third step (measurement of actual ozone exposure) are performed without dividing the ozone theoretical exposure time (as in Type 1 above), after the third step is completed, the fourth step determines whether the actual ozone exposure received by the tire is 90% or more of the ozone target exposure. If it is less than 90%, the decision is made to continue the ozone exposure.

[0055] If the actual ozone exposure received by the tire is less than 90% of the target ozone exposure, then in step 7 (the step of evaluating the tire's condition), the actual ozone exposure will be too far removed from the target exposure, making it difficult to check for groove crack formation, for example. Therefore, there is a risk that the tire surface condition will be evaluated with varying degrees of ozone exposure across multiple tires, and thus the tires need to be further exposed to ozone.

[0056] For example, if the ozone theoretical exposure time is divided into four parts as shown in Figure 3(B), at times T1 to T3, the actual ozone exposure is less than 90% of the target ozone exposure, so the process proceeds to step 5, which will be described later.

[0057] In contrast, if the actual ozone exposure received by the tire is 90% or more of the target ozone exposure, the process proceeds to step 7, which will be described later. In this case, the tire's exposure to ozone has effectively ended.

[0058] If the actual ozone exposure received by the tire is 90% or more of the target ozone exposure, then in step 7, for example, when checking for groove crack formation, it is highly likely that the actual ozone exposure is close to or equal to the target ozone exposure. Therefore, since the degree of ozone exposure of the tires is likely to be uniform across multiple tires when evaluating the surface condition of the tires, there is no need to further expose the tires to ozone.

[0059] For example, if the ozone theoretical exposure time is divided into four parts as shown in Figure 3(B), at time T4, the actual ozone exposure is 90% or more of the target ozone exposure, so the process proceeds to step 7, which will be described later.

[0060] However, in the third step, if the actual ozone exposure exceeds 103% of the target ozone exposure, then in the seventh step (the step in which the tire condition is evaluated), the actual ozone exposure will be too far removed from the target ozone exposure when, for example, checking for groove crack formation. As a result, there is a risk that the tire surface condition will be evaluated with varying degrees of ozone exposure among multiple tires.

[0061] However, in this case, since it is not possible to reduce the actual ozone exposure once the tire has come into contact with ozone, such tires (tires with an actual ozone exposure exceeding 103% of the target ozone exposure) are judged to be removed from the test tires (tires subjected to step 7 (evaluation of the tire condition), which will be described later) in the fourth step.

[0062] Based on the above findings, it is even more preferable to proceed to step 5 described later if the actual ozone exposure received by the tire is less than 93% of the target ozone exposure, and it is extremely preferable to proceed to step 5 described later if it is less than 95%.

[0063] ((e) 5th step) Step 5 is a step in which, if it was determined in Step 4 to continue the ozone exposure of the tires, the theoretical ozone exposure amount is compared with the actual ozone exposure amount to determine whether it is necessary to change the ozone exposure conditions of the tires.

[0064] In step 5, if the actual ozone exposure amount received by the tire (measured in the most recent step 3) (the total amount of ozone that has come into contact with the tire up to that point) is less than 90% of the theoretical ozone exposure amount at that point, the process proceeds to step 6, which will be described later. In this case, the conditions for the tire's ozone exposure are effectively changed.

[0065] If the actual ozone exposure received by the tire (measured in the most recent third step) is less than 90% of the theoretical ozone exposure, then even if the ozone exposure conditions are the same as before, assuming that the second step (ozone exposure) is repeated, the actual ozone exposure cannot be efficiently brought closer to the theoretical ozone exposure, and the tire's ozone exposure time will be unnecessarily prolonged. Therefore, the ozone exposure conditions for the tire are reset to efficiently bring the actual ozone exposure closer to the theoretical ozone exposure before the actual ozone exposure reaches the target ozone exposure.

[0066] For example, if the ozone theoretical exposure time is divided into four parts as shown in Figure 3(B), at time T1, the actual ozone exposure is less than 90% of the theoretical ozone exposure, so the process proceeds to step 6, which will be described later.

[0067] In contrast, if the actual ozone exposure received by the tire (measured in the most recent third step) is 90% or more of the theoretical ozone exposure, the process proceeds to the second step (ozone exposure) described above. In this case, the conditions for the tire's ozone exposure are not substantially changed.

[0068] If the actual ozone exposure received by the tire (measured in the most recent third step) is 90% or more of the theoretical ozone exposure, then when repeating the second step (ozone exposure), even if the ozone dew conditions are the same as before, the actual ozone exposure can be efficiently brought closer to the target ozone exposure, and the subsequent ozone exposure time will not be unnecessarily prolonged. Therefore, there is no need to readjust the ozone exposure conditions for the tire, and the actual ozone exposure can be brought closer to the target ozone exposure early on.

[0069] For example, if the ozone theoretical exposure time is divided into four parts as shown in Figure 3(B), at time T2, the actual ozone exposure is 90% or more of the theoretical ozone exposure, so the process proceeds to the second step described later.

[0070] However, if the actual ozone exposure amount received by the tire (measured in the most recent third step) (the total amount of ozone that has come into contact with the tire up to that point) exceeds 103% of the theoretical ozone exposure amount at that point, the process proceeds to the sixth step, which will be described later. In this case, too, the conditions for ozone exposure to the tire are substantially changed.

[0071] If the actual ozone exposure received by the tire (measured in the most recent third step) exceeds 103% of the theoretical ozone exposure, then assuming the second step (ozone exposure) is repeated with the same ozone exposure conditions, the actual ozone exposure will reach the theoretical ozone exposure considerably earlier than the end of the theoretical ozone exposure time. Consequently, there is a high probability that the actual ozone exposure at the end of the theoretical ozone exposure time will exceed 103% of the target ozone exposure. Therefore, the ozone exposure conditions for the tire are reset to efficiently bring the actual ozone exposure closer to the target ozone exposure at the end of the theoretical ozone exposure time.

[0072] For example, if the ozone theoretical exposure time is divided into four parts as shown in Figure 3(B), at time T3, the actual ozone exposure is more than 103% of the ozone theoretical exposure, so the process proceeds to step 6, which will be described later.

[0073] Based on the above findings, it is even more preferable to proceed to the sixth step described later if the actual ozone exposure received by the tire (measured in the most recent third step) is less than 93% of the theoretical ozone exposure, and it is extremely preferable to proceed to the sixth step described later if it is less than 95%.

[0074] ((f) 6th step) Step 6 is the process of changing the ozone exposure conditions using elements calculated from the actual ozone exposure amount, the theoretical ozone exposure amount, and the theoretical ozone exposure time, if it is determined in Step 5 above that a change in ozone exposure conditions is necessary.

[0075] Here, the elements calculated from the actual ozone exposure, the theoretical ozone exposure, and the theoretical ozone exposure time are the ozone concentration and the ozone exposure time, which are the elements for calculating the OA value mentioned above. If the actual ozone exposure received by the tire (measured in the most recent third step) is less than the theoretical ozone exposure at that time, the ozone exposure conditions are changed so as to increase at least one of the ozone concentration and the ozone exposure time, while if it is greater than the theoretical ozone exposure, the ozone exposure conditions are changed so as to decrease at least one of the ozone concentration and the ozone exposure time.

[0076] Thus, by changing the ozone exposure conditions, it is expected that the actual ozone exposure received by the tire, measured in the third step after the change, will approach the theoretical ozone exposure.

[0077] ((g) 7th step) Step 7 is a process in which the condition of the tires is evaluated if it is determined in Step 4 above that exposure to ozone should be terminated.

[0078] Here, "tire condition" refers to, for example, the surface condition of the tire. Furthermore, "evaluating the tire condition" means, for example, investigating what kind of cracks (groove cracks) are formed at the bottom of the tire's main grooves and evaluating the tire's durability performance based on the investigation results.

[0079] Groove cracks are evaluated, for example, by visually checking the longitudinal dimension of cracks formed at the bottom of the main groove (or the dimension connecting both ends if the crack is curved in a plan view), and by the number of cracks exceeding a certain dimension in the entire main groove.

[0080] The tire testing method of this embodiment, as described above, is based on the premise of measuring the actual ozone exposure using an indicator, and employs an opportunity to feed back the actual ozone exposure (the area enclosed by the dotted line in Figure 2(A), including the fourth to sixth steps described above), thereby continuously exposing the tire to ozone, including when the exposure conditions are changed, so that the actual ozone exposure has a certain relationship with the target ozone exposure and the theoretical ozone exposure. As a result, according to the tire testing method of this embodiment, even if the tire size, tire usage conditions, or the environment around the tire are different, the tire's ozone exposure state can be made generally uniform, and the condition of the tire (for example, groove cracks occurring on the groove surface) can be evaluated. [Examples]

[0081] The following describes an example of a tire testing method. For each test tire with tire size 215 / 55R17 94V, both the conventional tire test method and the inventive tire test method shown in Table 1 were performed. Note that the terms used in Table 1 are the same as those used in this embodiment, and their descriptions have been partially simplified.

[0082] Here, the conventional tire testing method is the testing method according to the flowchart shown in Figure 1(A), and the inventive tire testing method is the testing method according to the flowchart shown in Figure 2(A). Furthermore, as shown in Table 1, the ozone concentration used in the first time period in the inventive test method was the same as the ozone concentration used in the conventional test method.

[0083] Under these premises, in conventional tire testing methods, the ozone theoretical exposure time (24 hours) was not divided (and furthermore, no opportunity was given to provide feedback on the ozone exposure conditions) and ozone was continuously exposed at a constant concentration, after which the glue cracks formed at the bottom of the main grooves were evaluated.

[0084] In contrast, the tire testing method of the invention divides the ozone theoretical exposure time (24 hours) into four parts (providing three opportunities to provide feedback on the ozone exposure conditions), and modifies the ozone exposure conditions through feedback all three times. After exposure to ozone, the glue cracks formed at the bottom of the main grooves were evaluated.

[0085] Table 1 shows the results of the conventional tire test method and the results of the inventive tire test method.

[0086] [Table 1]

[0087] According to Table 1, in conventional cases, the actual ozone exposure at the end of ozone exposure was 70% of the target ozone exposure.

[0088] In contrast, in the inventive example, the actual ozone exposure amounts immediately before the first, second, and third feedback of ozone exposure conditions were 70%, 86%, and 95% of the theoretical ozone exposure amount at that time, respectively.

[0089] Ultimately, while the actual ozone exposure in the conventional example was 70% of the target ozone exposure, the actual ozone exposure in the inventive example was 101% of the target ozone exposure.

[0090] Based on these results, regarding the number of groove cracks generated at the bottom of the main groove, the conventional example showed a smaller amount of groove crack formation (81) compared to the inventive example (baseline: 100).

[0091] From the above results, it can be seen that the tire testing method of the invention example, which falls within the technical scope of the present invention (i.e., a combination of measuring the actual ozone exposure amount using an indicator and a device for feeding back the actual ozone exposure amount), is able to achieve a superior ozone exposure state (a state in which the actual ozone exposure amount is closer to the target ozone exposure amount) compared to conventional tire testing methods that do not fall within the technical scope of the present invention.

[0092] Furthermore, since the amount of groove crack formation in conventional tire testing methods was significantly less than the amount actually observed in the market (an amount close to the amount observed in the inventive example), it was reaffirmed that it is important to properly control the actual ozone exposure in order to accurately evaluate the amount of groove cracks (relative to the amount actually observed in the market).

Claims

1. A tire testing method for evaluating tire durability by accelerating tire degradation under an ozone atmosphere, An indicator that displays the actual amount of ozone exposure is attached to the aforementioned tire. (a) A first step of setting the target ozone exposure amount and initial conditions, (b) A second step in which the surrounding atmosphere of the tire is made an ozone concentration atmosphere with a higher ozone concentration than the atmosphere, (c) A third step of measuring the actual amount of ozone exposure received by the tire from the indicator, (d) A fourth step in which the actual ozone exposure amount is determined to have reached the target ozone exposure amount, and whether to continue or terminate the ozone exposure, (e) If it is determined in the fourth step to continue exposure to ozone, a fifth step is to compare the theoretical ozone exposure amount with the actual ozone exposure amount and determine whether it is necessary to change the ozone exposure conditions, (f) If it is determined in the fifth step that it is necessary to change the ozone exposure conditions, the sixth step involves changing the ozone exposure conditions using elements calculated from the actual ozone exposure amount, the theoretical ozone exposure amount, and the theoretical ozone exposure time. (g) If it is determined in the fourth step that exposure to ozone should be terminated, a seventh step is performed in which the condition of the tires is evaluated, A tire testing method characterized by including [a certain element].

2. The tire testing method according to claim 1, wherein in the third step, the actual ozone exposure is measured at intervals divided by N (where N is a natural number of 1 or more) with respect to the theoretical ozone exposure time determined from the target ozone exposure and the initial conditions.

3. The tire testing method according to claim 1 or 2, wherein in the third step, the indicator quantifies the actual ozone exposure amount by means of a dye, ultraviolet absorption, or resistance change.

4. In the above fourth step, If the actual ozone exposure amount measured in the third step immediately preceding the third step performed up to that point is 90% or more of the target ozone exposure amount, or exceeds the target ozone exposure amount, the tire exposure to ozone shall be terminated. The tire testing method according to claim 1 or 2, wherein if the actual ozone exposure amount measured in the third step immediately preceding the third step performed up to that point is less than 90% of the target ozone exposure amount, the process proceeds to the fifth step.

5. In the fifth step described above, If the actual ozone exposure amount measured in the third step immediately preceding the third step that has been performed up to that point is 90% or more of the target ozone exposure amount, then proceed to the second step. The tire testing method according to claim 1 or 2, wherein if the actual ozone exposure amount measured in the third step immediately preceding the third step performed up to that point is less than 90% of the target ozone exposure amount, the process proceeds to the sixth step.

6. The tire testing method according to claim 1 or 2, wherein in the sixth step, the ozone exposure conditions are changed to those calculated from the actual ozone exposure amount measured in the immediately preceding third step, the theoretical ozone exposure amount, and the theoretical ozone exposure time, among the third steps performed up to that point.

7. The tire testing method according to claim 1 or 2, wherein the concentration of ozone is 30 ppm or more and 250 ppm or less.

8. The tire testing method according to claim 1 or 2, wherein the bottom of the main groove of the tire is cleaned before the second step.

Images