JP2021060270A - Tire testing method - Google Patents

Abstract

To provide a tire testing method by which the growth potential of a groove crack can be evaluated with high accuracy.SOLUTION: A tire testing method includes: a processing step ST101 of shaping scalpel cuts on the groove bottom of a main groove that is formed in the tread part of a pneumatic tire; a test step ST102 of bringing a circumferential area of the pneumatic tire where no scalpel cuts are shaped into contact with the ground and applying a load to the pneumatic tire in the vertical direction to test it while the pneumatic tire is exposed to ozone under an atmosphere adjusted to a prescribed temperature; and an evaluation step ST103 of evaluating the growth potential of cracks from the growth potential in the longitudinal direction of scalpel cuts after the test step ST102.SELECTED DRAWING: Figure 2

Description

The present invention relates to a tire test method.

With pneumatic tires, cracks may occur at the bottom of the groove formed in the tread portion due to distortion during vehicle running, deterioration over time, and the like. The cracks generated at the bottom of the groove are so-called groove cracks, and various methods have been conventionally proposed as test methods for evaluating the degree of occurrence of groove cracks.

For example, in the test methods described in Patent Documents 1 and 2, after the tire to be tested is left in an ozone atmosphere for a predetermined period of time, a running test is performed using the rotating drum while pressing the tire against the rotating drum and applying a load to the tire. By doing so, the groove cracks in the market are reproduced and evaluated. Further, in the test method described in Patent Document 3, the tire to be tested is subjected to a running test with a rotating drum in a state where a load is applied to the tire by injecting ozone into the tire in the market. The groove crack is reproduced and evaluated.

Japanese Unexamined Patent Publication No. 2006-84290 Japanese Unexamined Patent Publication No. 2014-100977 Japanese Unexamined Patent Publication No. 2008-26228

Since all the conventional test methods evaluate the presence or absence of groove cracks, the growth status of groove cracks may differ greatly between the tested tire and the actual tire, resulting in poor market reproducibility. Sometimes it was enough. Therefore, a test method for evaluating the growth potential (growth degree) of groove cracks is being sought.

The present invention has been made in view of the above, and an object of the present invention is to provide a tire test method capable of evaluating the growth potential of groove cracks with high accuracy.

In order to solve the above-mentioned problems and achieve the object, the tire test method according to the present invention includes a pre-process for making a notch in the groove bottom of the groove formed in the tread portion of a pneumatic tire, and a predetermined temperature. In a conditioned atmosphere, with the pneumatic tire exposed to ozone, the region where the notch is not processed in the circumferential direction of the pneumatic tire is grounded, and a vertical load is applied to the pneumatic tire. It is characterized by including an intermediate step for testing, and a post-step for evaluating crack growth potential from the growth rate of the cut in the longitudinal direction after the intermediate step.

In the tire test method, in the intermediate step, the notch is preferably located in a region where the central angle is at least 55 ° or more and 85 ° or less on both sides in the circumferential direction from the center of the contact patch of the pneumatic tire. ..

Further, in the tire test method, in the previous step, the notch to be machined extends along the circumferential direction of the pneumatic tire, and the length of the notch in the longitudinal direction is in the range of 2 mm or more and 8 mm or less. The depth of the cut is preferably in the range of 0.1 mm or more and 3.0 mm or less.

Further, in the tire test method, in the previous step, the notch is processed into the groove bottom of the groove portion on the shoulder portion side of the pneumatic tire, and the groove width is widened from the groove wall of the groove portion on the shoulder portion side. It is preferable to process within the range of 50% or less.

Further, in the tire test method, when a plurality of the cuts are machined in one groove extending in the circumferential direction of the pneumatic tire in the previous step, the plurality of cuts are made in the groove bottom of the one groove. It is preferable that the tires are provided at positions shifted in the circumferential direction of the pneumatic tire and in the width direction of the groove.

Further, in the tire test method, in the post-process, when the growth rate of the notch in the longitudinal direction is equal to or less than a predetermined threshold value, the load applied to the pneumatic tire may be increased and the intermediate process may be executed again. preferable.

Further, in the tire test method, in the intermediate step, the load applied to the pneumatic tire is preferably in the range of 40% or more and 100% or less of the maximum load capacity of the pneumatic tire.

Further, in the tire test method, in the intermediate step, the concentration of ozone that exposes the pneumatic tire is preferably in the range of 50 pphm or more and 250 pphm or less.

Further, in the tire test method, in the intermediate step, the temperature of the atmosphere is preferably in the range of 30 ° C. or higher and 70 ° C. or lower.

Further, in the tire test method, in the intermediate step, the internal pressure of the pneumatic tire is preferably in the range of 60% or more and 100% or less of the maximum air pressure of the pneumatic tire.

Further, in the tire test method, in the intermediate step, it is preferable to reduce the internal pressure with the lapse of time for applying a load to the pneumatic tire.

Further, in the tire test method, in the intermediate step, it is preferable to change the temperature of the atmosphere while continuing to apply the load to the pneumatic tire.

The tire test method according to the present invention can evaluate the growth potential of groove cracks with high accuracy. Therefore, the market reproducibility for groove cracks can be improved.

FIG. 1 is a meridional cross-sectional view showing an example of a pneumatic tire used in the tire test method according to the present embodiment. FIG. 2 is a flowchart showing the procedure of the tire test method according to the present embodiment. FIG. 3 is a partially enlarged plan view showing a main groove in which a female cut is machined. FIG. 4 is a partially enlarged cross-sectional view showing a main groove in which a female cut is processed. FIG. 5 is a schematic view showing the positional relationship between the region where the female cut is processed and the ground contact surface in the tire circumferential direction. FIG. 6 is a partially enlarged cross-sectional view showing a processed region of the female cut processed in the shoulder main groove. FIG. 7 is a diagram showing an example of the positional relationship of a plurality of female cuts machined in the main groove. FIG. 8 is a diagram showing an example of the positional relationship of a plurality of female cuts machined in the main groove. FIG. 9 is a configuration diagram showing an example of a tire test device used in the test process. FIG. 10 is a view taken along the line AA of FIG. FIG. 11 is a flowchart showing the procedure of the test process. FIG. 12 is a flowchart showing the procedure of the evaluation process. FIG. 13 is a chart showing the evaluation results of the tire test method.

Hereinafter, embodiments of the tire test method according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. In addition, the components in the following embodiments include those that can be easily conceived by those skilled in the art, or those that are substantially the same.

The tire test method according to the present embodiment focuses on the degree of growth (whether or not it is easy to grow) of groove cracks (hereinafter, simply referred to as cracks) that may occur in the grooves of pneumatic tires in the market. In this tire test method, by reproducing the usage state of the pneumatic tire in the market, the growth state of cracks due to static factors for the pneumatic tire such as a long-term stop of the vehicle is reproduced and evaluated. First, a pneumatic tire used in the tire test method according to the present embodiment will be described.

FIG. 1 is a meridional cross-sectional view showing an example of a pneumatic tire used in the tire test method according to the present embodiment. In the following description of the pneumatic tire 100, the tire radial direction means a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 100. Further, the tire circumferential direction means a circumferential direction with the rotation axis as the central axis. Further, the tire width direction means a direction parallel to the rotation axis. The tire equatorial plane CL is a plane that is orthogonal to the rotation axis of the pneumatic tire 100 and passes through the center of the tire width of the pneumatic tire 100. The tire equatorial line is a line on the tire equatorial plane CL along the tire circumferential direction of the pneumatic tire 100. The tire meridional cross section is a cross section when the tire is cut on a plane including the tire rotation axis.

As shown in FIG. 1, the pneumatic tire 100 according to the present embodiment includes a tread portion 101, shoulder portions 102 located on both sides of the tread portion 101 in the tire width direction, and sidewalls sequentially continuous from each shoulder portion 102. A unit 103 and a bead unit 104 are provided. Further, the pneumatic tire 100 includes a carcass layer 105 and a belt layer 106.

The tread portion 101 is made of a rubber material (tread rubber) and is exposed on the outermost side of the pneumatic tire 100 in the tire radial direction, and the outer peripheral surface thereof serves as the contour of the pneumatic tire 100. The outer peripheral surface of the tread portion 101 is a surface that can come into contact with the road surface mainly during traveling, and is configured as the tread surface 110.

On the tread surface 110 of the tread portion 101, main grooves (grooves) 111 extending in the tire circumferential direction are formed side by side in the tire width direction, and lug grooves (grooves: not shown) extending in the tire width direction are formed in the tire. They are formed side by side in the circumferential direction. A tread pattern is formed on the tread surface 110 by the grooves such as the main groove 111 and the lug groove. In the example of FIG. 1, four main grooves 111 are formed, and two center main grooves 112 provided adjacent to the center in the tire width direction so as to sandwich the tire equatorial plane CL, and each center main groove. The 112 has shoulder main grooves 113 provided on the outer side in the tire width direction (shoulder portion 102 side), respectively. In the following description, when it is not necessary to distinguish between the center main groove 112 and the shoulder main groove 113, it is simply referred to as the main groove 111.

In the tire test method according to the present embodiment, a female cut (cut) having a predetermined length is previously processed in the groove bottom of the main groove 111 of the pneumatic tire 100, and crack growth using this female cut as a base point (also referred to as a starting point). Reproduce and evaluate the situation. FIG. 2 is a flowchart showing the procedure of the tire test method according to the present embodiment. In the tire test method according to the present embodiment, as shown in FIG. 2, the processing step (pre-process) ST101 for processing the female cut on the pneumatic tire 100 and the usage state of the pneumatic tire 100 on which the female cut is processed are displayed. It is configured to include a test step (intermediate step) ST102 for reproducing and testing, and an evaluation step (post-process) ST103 for evaluating crack growth from the amount of change in the length of the female cut after the test.

Next, the processing process will be described. FIG. 3 is a partially enlarged plan view showing a main groove in which a female cut is machined. FIG. 4 is a partially enlarged cross-sectional view showing a main groove in which a female cut is processed. In the processing step ST101, for example, using a tool (not shown) such as a scalpel (cutting tool), as shown in FIGS. 3 and 4, the groove bottom 111A of the main groove 111 formed of a rubber material (tread rubber) is used. A processing operation for processing a female cut (cut) 120 specified to a predetermined length and a predetermined depth is performed. In the present embodiment, the operator (operator) processes the female cut 120 one by one using a female, but the present invention is not limited to this. For example, these female cuts 120 may be processed by a processing apparatus provided with a female, or may be processed by irradiating the groove bottom 111A of the main groove 111 with a laser beam.

As shown in FIG. 3, the processed female cut 120 extends along the extending direction of the main groove 111 (extending direction of the reference line 115). Since the main groove 111 extends along the tire circumferential direction as described above, the longitudinal direction (machining direction) of the female cut 120 also extends along the tire circumferential direction. Here, the extending direction of the female cut 120 is not only the one that completely coincides with the tire circumferential direction, but also rotates at a predetermined angle α or less on both sides with respect to the reference line 115 extending in the tire circumferential direction as shown in FIG. Includes within the specified range. The range of the predetermined angle α is, for example, ± 5 °, but more preferably ± 2 °. In this case, the angle in the clockwise direction with respect to the reference line 115 is + (plus), and the angle in the counterclockwise direction is − (minus). In this configuration, since the female cut 120 extends along the tire circumferential direction, the stress applied to the pneumatic tire 100 is efficiently transmitted to the female cut 120. Therefore, it is possible to approach the degree of crack growth in the usage environment starting from the female cut 120.

Further, as shown in FIG. 3, the female cut 120 is defined in a range in which the length L in the longitudinal direction is 2 mm or more and 8 mm or less. If the length L of the female cut 120 is less than 2 mm, crack growth from the female cut 120 as a base point is unlikely to occur, and there is a problem that the crack growth property cannot be evaluated with high accuracy. Further, when the length L of the female cut 120 is longer than 8 mm, the strain from the female cut 120 becomes large and cracks are likely to grow, so that the crack growth property cannot be evaluated with high accuracy. The length L of the female cut 120 is more preferably 4 mm or more and 6 mm or less, and all the female cuts 120 are set to the same length (6 mm).

On the other hand, as shown in FIG. 4, the depth D of the female cut 120 is defined in the range of 0.1 mm or more and 3.0 mm or less. If the depth D of the female cut 120 is less than 0.1 mm, crack growth from the female cut 120 as a base point is unlikely to occur, and there is a problem that the crack growth property cannot be evaluated with high accuracy. Further, when the depth D of the female cut 120 is deeper than 3.0 mm, the strain from the female cut 120 becomes large and cracks are likely to grow, and there is a possibility that the cracks reach other members such as the belt layer 106. There is a problem that the crack growth property cannot be evaluated with high accuracy. The depth D of the female cut 120 is more preferably 0.5 mm or more and 1.5 mm or less, and all the female cuts 120 are set to the same depth (1.5 mm).

In the present embodiment, by setting the length L and the depth D of the female cut 120 to be processed within the above ranges, it is possible to approach the degree of crack growth in the usage environment, and the crack growth potential is evaluated with high accuracy. It becomes possible to do.

In the tire test method according to the present embodiment, as described above, the female cut 120 is processed in advance in the main groove 111, and the female cut 120 grows into cracks due to static factors for the pneumatic tire such as a long-term stop of the vehicle. Is reproduced and evaluated. It is preferable that the female cut 120 is provided in a region off the ground contact surface of the pneumatic tire 100 so that the female cut 120 is sufficiently distorted due to the deformation of the pneumatic tire 100 due to the load. FIG. 5 is a schematic view showing the positional relationship between the region where the female cut is processed and the ground contact surface in the tire circumferential direction.

In the example of FIG. 5, in the pneumatic tire 100, a part of the tread portion 101 is grounded to the grounding plate 131 as a grounding surface 110A. In this case, since the ground contact surface 110A of the pneumatic tire 100 in contact with the ground contact plate 131 is greatly deformed by the ground contact, the region where the female cut 120 is not processed becomes the ground contact surface 110A. Here, it is assumed that the ground plane 110A includes not only the region of the tread portion 101 that directly contacts the ground plate 131 but also the region of the main groove 111 provided in this region. Generally, in the groove bottom 111A of the main groove 111 of the ground plane 110A, compressive strain is generated in the direction in which the groove is closed, so that cracks tend to be less likely to occur. Therefore, it is preferable to remove the ground plane 110A and process the female cut 120 at a position where tensile strain occurs in the direction in which the groove opens.

As shown in FIG. 5, the female cut 120 is provided within a range of predetermined angles β on both sides in the tire circumferential direction from the center of the ground contact surface 110A of the pneumatic tire 100. Specifically, the predetermined angle β is set to at least 55 ° or more and 85 ° or less, respectively, with the center of the ground plane 110A as a reference (0 °). That is, in the range where the central angle is smaller than 55 °, the strain with respect to the female cut 120 is small, and in the range where the central angle is larger than 85 °, the load applied to the pneumatic tire 100 is not sufficient. , There is a risk that cracks starting from the female cut 120 will not grow sufficiently. On the other hand, according to the configuration in which the central angles are 55 ° or more and 85 ° or less, respectively, the degree of crack growth based on the female cut 120 when the vehicle is stopped for a long period of time can be approached, so that the crack growth potential can be improved. It is possible to evaluate with high accuracy. Further, the predetermined angles β are preferably 60 ° or more and 80 ° or less, respectively. According to this configuration, it is possible to approach the degree of crack growth with respect to the female cut 120 as the base point when the vehicle is stopped for a long period of time, so that the crack growth potential can be evaluated with high accuracy.

Further, the position where the female cut 120 is processed is not only within the range of the predetermined angle β described above, but also, for example, when the pneumatic tire 100 is grounded, the position is horizontal from the center O of the pneumatic tire 100 toward the tread surface 110. It may be provided on the reference line 116 extending in each direction, or may be provided on the reference line 117 extending vertically upward from the center O toward the tread surface 110. In this case, 4 to 8 female cuts 120 can be processed in the circumferential direction of the pneumatic tire 100. Further, the processing position of the female cut 120 is not only the one that completely coincides with the above-mentioned reference lines 116 and 117, but also within the region rotated by a predetermined angle (for example, ± 2 °) on both sides with respect to these reference lines 116 and 117. It should be.

Further, in the processing step ST101 described above, it is preferable that the female cut 120 is provided at least in the shoulder main groove 113 of the pneumatic tire 100. FIG. 6 is a partially enlarged cross-sectional view showing a processed region of the female cut processed in the shoulder main groove. Generally, in the pneumatic tire 100, the strain of the shoulder portion 102 tends to be larger than that of the tread portion 101. Therefore, by processing the female cut 120 into the groove bottom 113A of the shoulder main groove 113, it is possible to create an environment in which cracks due to the strain of the pneumatic tire 100 are likely to grow.

Specifically, as shown in FIG. 6, the female cut 120 is the groove bottom 113A of the shoulder main groove 113, and is 50% (1 / 2W) or less of the groove width W from the groove wall 113B on the shoulder portion 102 side. It is processed within the range. According to this configuration, by processing the female cut 120 into the groove bottom 113A of the shoulder main groove 113 having a large strain, the degree of crack growth in the usage environment can be approached, and the crack growth potential can be evaluated with high accuracy. .. The position where the female cut 120 is processed is within a range of 20% or more and 40% or less (1 / 5W or more and 2 / 5W or less) of the groove width W from the groove wall 113B so as to include the groove bottom 113A on the shoulder portion 102 side. Is preferable.

Further, in the above-mentioned processing step ST101, when a plurality of female cuts 120 are machined in any one of the main grooves 111, the plurality of female cuts 120 are provided so as not to overlap each other in the same main groove 111. It has become. 7 and 8 are views showing an example of the positional relationship of a plurality of female cuts machined in the main groove. FIG. 7 shows a state in which three female cuts 120 are machined in the main groove 111, and FIG. 8 shows a state in which two female cuts 120 are machined in the main groove 111. As described above, since each main groove 111 is provided with 0 to 3 female cuts 120, there is a situation in which a plurality of female cuts 120 are processed in the main groove 111.

At this time, the plurality of female cuts 120 are provided at positions shifted in the tire circumferential direction in the groove bottom 111A of the same main groove 111 and in the width direction (tire radial direction) of the main groove 111, and overlap each other. It is designed not to be done. For example, when a plurality of female cuts 120 are provided side by side in the width direction of the main groove 111, stress is dispersed and applied to each female cut 120 at a portion where the female cuts 120 overlap each other. Therefore, there is a problem that the growth of cracks starting from each female cut 120 is suppressed, and it is difficult to accurately evaluate the growth potential of cracks. Further, for example, when a plurality of female cuts 120 are processed on an extension line in the tire circumferential direction, cracks grown in the longitudinal direction of the female cuts 120 may be continuous (connected), and the crack growth potential is accurately evaluated. There is a problem that it is difficult.

In the present embodiment, since the plurality of female cuts 120 are provided at positions shifted in the tire circumferential direction and the width direction of the main groove 111 in the groove bottom 111A of the same main groove 111, the above-mentioned problem occurs. It can be prevented, and the growth potential of cracks growing from the female cut 120 as a base point can be evaluated with high accuracy.

Next, the test process will be described. The test step ST102 is a step of performing a load-load test on the pneumatic tire 100 on which the female cut 120 has been processed, which reproduces the usage state of the tire 100, which is mounted on a vehicle that has been stopped for a long period of time without running. In this embodiment, the test step ST102 is performed using the following tire test apparatus 1. FIG. 9 is a configuration diagram showing an example of a tire test device used in the test process. FIG. 10 is a view taken along the line AA of FIG. 9 and 10 schematically show the overall configuration of the tire test device 1. In the following description, the vertical direction of the tire test device 1 in the normal use state will be described as the vertical direction in the tire test device 1, and the horizontal direction of the tire test device 1 in the normal use state will be referred to as the tire test device 1. Also in 1, it will be described as the horizontal direction.

The tire test device 1 includes a test room 10, an air conditioner 20, an ozone supply device 30, and a load mechanism device 40. The test room 10 is a room for forming a space separated from the outside air when testing the pneumatic tire 100. The air conditioner 20 can adjust the temperature inside the test chamber 10 to a predetermined temperature. The air conditioner 20 is installed outside the test chamber 10, and the temperature inside the test chamber 10 can be adjusted through a vent 22 communicating with the inside of the test chamber 10. Further, a temperature sensor 25 capable of detecting the temperature of the surrounding atmosphere is arranged inside the test chamber 10, and the air conditioner 20 is electrically connected to the temperature sensor 25. The air conditioner 20 can acquire the temperature detected by the temperature sensor 25, and by comparing the temperature set by the operation unit with the temperature in the test chamber 10 acquired from the temperature sensor 25. , The operation is performed so that the temperature in the test chamber 10 approaches the temperature set by the operation unit.

The ozone supply device 30 generates ozone, and the generated ozone can be supplied to the inside of the test chamber 10. The ozone supply device 30 is installed outside the test chamber 10, and ozone can be supplied to the inside of the test chamber 10 through a vent 32 communicating with the inside of the test chamber 10. Further, inside the test chamber 10, an ozone concentration sensor 35 capable of detecting the ozone concentration in the surrounding atmosphere is arranged, and the ozone supply device 30 is electrically connected to the ozone concentration sensor 35. .. The ozone supply device 30 can acquire the ozone concentration detected by the ozone concentration sensor 35, and the ozone concentration set by the operation unit and the ozone concentration in the test room 10 acquired from the ozone concentration sensor 35. By comparing with the ozone concentration, the operation is performed so that the ozone concentration in the test chamber 10 approaches the ozone concentration set by the operation unit.

The load mechanism device 40 is installed inside the test chamber 10, and can load the pneumatic tire 100 in the test chamber 10 in a direction orthogonal to the tire width direction of the pneumatic tire 100. It has become.

In the present embodiment, the load mechanism device 40 uses a flat spot generator 41 that can easily apply a load to the pneumatic tire 100. The flat spot generator 41 has a ground surface plate 42, a support column 44, and a connecting member 47. The ground contact patch 42 has a contact patch 43 that contacts the ground contact patch 110A, which is a part of the tread surface 110 of the pneumatic tire 100 to be tested. The ground surface plate 42 is formed, for example, in the shape of a rectangular plate, and the contact surface 43 is a flat surface formed by one surface of the ground surface plate 42 in the thickness direction. The ground surface plate 42 is arranged with the contact surface 43 facing upward. The support column 44 has a rod-like shape and is a columnar member erected on the ground surface plate 42. In the present embodiment, the support column 44 is formed of a solid structure having a circular cross section, and its length is longer than the outer diameter of the pneumatic tire 100 to be tested. A screw thread (not shown) is formed on one end side of the support column 44, and a fixing member 45 gripped by a tool when the support column 44 is attached to the ground surface plate 42 is fixed in the vicinity of the screw thread. There is. At the position where the support column 44 is attached on the grounding surface plate 42, a screw hole (not shown) penetrating the grounding surface plate 42 in the thickness direction of the grounding surface plate 42 is formed.

The support column 44 extends to the contact surface 43 side of the ground surface plate 42 by screwing the screw thread formed on one end side into the screw hole formed on the ground surface plate 42 from the contact surface 43 side. It is installed in a direction in which the presence direction is substantially perpendicular to the contact surface 43. As a result, the support column 44 is erected on the ground surface plate 42. Further, two columns 44 are erected with respect to the ground surface plate 42, and the two columns 44 are arranged at intervals wider than the width in the tire width direction of the pneumatic tire 100 to be tested.

The connecting member 47 is a member that supports the pneumatic tire 100 on the ground surface plate 42. The connecting member 47 can support the pneumatic tire 100 by being connected to both the rim wheel 130 mounted on the pneumatic tire 100 and the support column 44 erected on the ground surface plate 42. ing.

Specifically, the connecting member 47 is a cylindrical member, and has a connecting portion 48 connected to the rim wheel 130 at a position near the center in the longitudinal direction. The connecting portion 48 is formed in a flange shape and is provided on the connecting member 47, and is a position of the rim wheel 130 corresponding to a mounting hole (not shown) through which a bolt is passed when the rim wheel 130 is mounted on a vehicle. An insertion hole (not shown) is formed in the rim. As a result, the connecting portion 48 aligns the mounting holes formed in the rim wheel 130 with the positions of the insertion holes formed in the connecting portion 48, and allows the bolts 49 to communicate with both holes so that the bolts 49 and the nuts ( By screwing with (not shown), it is possible to connect to the rim wheel 130.

Further, the connecting member 47 is formed with a through hole that penetrates the connecting member 47 in the radial direction of the connecting member 47 that is formed in a cylindrical shape, and the support column 44 can be passed through the through hole. There is. The connecting member 47 allows any of the two columns 44 erected on the ground surface plate 42 to pass through the through holes, that is, the connecting member 47 has two through holes at two positions. , It is formed at intervals of two columns 44 erected on the ground surface plate 42. As a result, the connecting member 47 can move relative to the support column 44 in the extending direction of the support column 44. That is, the connecting member 47 can move in the vertical direction along the support column 44, and the distance from the contact surface 43 can be changed. By moving the connecting member 47 in the vertical direction along the support column 44, the flat spot generator 41 can apply a load in the direction along the support column 44, that is, in the vertical direction, to the pneumatic tire 100. It has become.

On the other hand, a screw thread is formed on the support column 44 in a predetermined range including a region where the distance from the contact surface 43 is at least as large as the radius of the pneumatic tire 100. Therefore, the connecting member 47 is a restraining member 46 such as a nut screwed into the thread at a position above the connecting member 47 in the screw thread formed on the support column 44 with the support column 44 passed through the through hole. By screwing, the upward movement of the connecting member 47 can be restricted. As the restraint member 46, for example, by using a wing nut, the restraint member 46 can be easily rotated without using a tool, and a position for restricting the movement of the connecting member 47 can be determined.

Next, the procedure of the test process using the tire test apparatus 1 will be described. FIG. 11 is a flowchart showing the procedure of the test process. When performing the test process, the pneumatic tire 100 is rim-assembled on the rim wheel 130 and adjusted to a predetermined internal pressure (step ST1). The internal pressure of the pneumatic tire 100 in this case shall be within the range of 60% or more and 100% or less of the maximum air pressure of the pneumatic tire 100. The internal pressure of the pneumatic tire 100 is preferably in the range of 80% or more and 100% or less of the maximum air pressure of the pneumatic tire 100. The maximum air pressure referred to here is the "maximum air pressure" specified by JATTA, the maximum value described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or "INFLATION PRESSURES" specified by ETRTO.

Next, the pneumatic tire 100 is mounted on the flat spot generator 41 (step ST2). When the pneumatic tire 100 is mounted on the flat spot generator 41, the connecting member 47 is connected to the rim wheel 130 mounted on the pneumatic tire 100, and the support column 44 is passed through the through hole formed in the connecting member 47. .. As a result, the direction of the pneumatic tire 100 with respect to the ground surface plate 42 is set so that the rotation axis of the pneumatic tire 100 is parallel to the contact surface 43 of the ground surface plate 42. In this state, by moving the connecting member 47 along the support column 44, the ground contact surface 110A of the tread portion 101 of the pneumatic tire 100, which faces the contact surface 43, is brought into contact with the contact surface 43. That is, with the ground contact surface 110A of the tread portion 101 of the pneumatic tire 100 in contact with the contact surface 43, the pneumatic tire 100 is placed on the ground surface plate 42, and the pneumatic tire is formed by the support column 44 and the connecting member 47. Support 100. As a result, the pneumatic tire 100 is mounted on the flat spot generator 41.

Further, when the pneumatic tire 100 is mounted on the flat spot generator 41, the area where the female cut 120 in the tire circumferential direction of the pneumatic tire 100 is not processed is defined as the ground contact surface 110A. Specifically, as shown in FIG. 5, female cuts 120 are arranged within a range at predetermined angles β (55 ° or more and 85 ° or less) on both sides in the tire circumferential direction from the center of the contact patch 110A of the pneumatic tire 100 and are in contact with each other. Adjust so that the female cut 120 is not placed in the ground 110A region. Here, the region of the contact patch 110A includes not only the contact patch 110A of the tread portion 101 that is in direct contact with the contact surface 43, but also the groove bottom 111A of the main groove 111 that is connected to the contact patch 110A in the tire width direction.

Next, a load is applied to the pneumatic tire 100 (step ST3). The load on the pneumatic tire 100 is applied by changing the distance between the connecting member 47 and the contact surface 43. That is, the rim mounted on the pneumatic tire 100 by moving the connecting member 47 connected to the rim wheel 130 in the vertical direction along the support column 44 to change the distance between the connecting member 47 and the contact surface 43. The wheel 130 is moved up and down.

On the other hand, in the pneumatic tire 100, since the ground contact surface 110A of the tread portion 101 is in contact with the contact surface 43, the relative positional relationship of the pneumatic tire 100 with respect to the contact surface 43 does not change. Therefore, a load in the direction of being crushed in the vertical direction by the rim wheel 130 and the contact surface 43 is applied from the rim wheel 130 to the portion of the pneumatic tire 100 located mainly below the rim wheel 130. The wheel. When a load is applied to the pneumatic tire 100, the restraint member 46 is rotated along the threads formed on the columns 44 to press the restraint member 46 from above the connecting member 47 and lower the connecting member 47. Move to. As a result, a downward load can be applied to the rim wheel 130 from the connecting member 47 in the vertical direction, and a load is applied to the pneumatic tire 100 from the rim wheel 130 to which the downward load is applied. .. That is, the flat spot generator 41 applies a load in the direction orthogonal to the tire width direction of the pneumatic tire 100 to the pneumatic tire 100 at the same position in the tire circumferential direction of the pneumatic tire 100.

Since the restraint member 46 that moves the connecting member 47 downward by rotating along the threads of the columns 44 is screwed with the threads of the columns 44, it is possible to maintain the position in the vertical direction with respect to the columns 44. it can. Therefore, the restraint member 46 can maintain the position of the connecting member 47 in the vertical direction in a state where the load is applied to the pneumatic tire 100, and the load is applied to the pneumatic tire 100. The state can be maintained. That is, the flat spot generator 41 on which the pneumatic tire 100 is mounted continuously applies a load to the pneumatic tire 100 at the same position in the tire circumferential direction. At that time, the magnitude of the load applied to the pneumatic tire 100 is, for example, a magnitude that is the same as the amount of deformation when the pneumatic tire 100 mounted on the vehicle is deformed by the weight of the vehicle. Load the load of. In the present embodiment, the load applied to the pneumatic tire 100 is within the range of 40% or more and 100% or less of the maximum load capacity of the pneumatic tire 100, and the load is within this range in one test. Is constant (for example, 60%).

Next, the temperature and ozone concentration of the atmosphere in the test chamber 10 are adjusted (step ST4). Of these, the temperature is adjusted by the air conditioner 20, and the ozone concentration is adjusted by the ozone supply device 30. That is, the temperature of the atmosphere in the test chamber 10 is adjusted to a predetermined temperature by inputting a predetermined temperature to the operation unit of the air conditioner 20 to operate the air conditioner 20. In the present embodiment, the temperature of the atmosphere in the test chamber 10 is within the range of 30 ° C. or higher and 70 ° C. or lower. Similarly, by inputting a predetermined ozone concentration to the operation unit of the ozone supply device 30 and operating the ozone supply device 30 to supply ozone into the test chamber 10, ozone in the atmosphere in the test chamber 10 is supplied. The concentration is adjusted to a predetermined concentration, and the pneumatic tire 100 is exposed to ozone. In the present embodiment, the concentration of ozone that exposes the pneumatic tire 100 is within the range of 50 pphm or more and 250 pphm or less.

The temperature of the atmosphere around the pneumatic tire 100 in the test chamber 10 is preferably in the range of 40 ° C. or higher and 60 ° C. or lower, and the concentration of ozone that exposes the pneumatic tire 100 in the test chamber 10 is high. , 120 pphm or more and 180 pphm or less is preferable. In this way, the temperature was adjusted by the air conditioner 20, and ozone was supplied from the ozone supply device 30 to adjust the ozone concentration, so that the pneumatic tire 100 was exposed to ozone in an atmosphere adjusted to a predetermined temperature. In this state, a load is applied to the pneumatic tire 100.

Next, it is determined whether or not the specified time has elapsed (step ST5). In this case, the specified time is for cracks that grow at the groove bottom 111A of the main groove 111 formed in the tread portion 101 of the pneumatic tire 100 when the pneumatic tire 100 is actually used, and ozone for the pneumatic tire 100. It is preset as a time that can be reproduced by continuing to apply a load in a state of being exposed to the tire. Specifically, the specified time is set in advance as a time during which a crack that grows from the female cut 120 at the groove bottom 111A of the main groove 111 of the pneumatic tire 100 can be reproduced when the vehicle is stopped for a long period of time. ing. The specified time is preferably set within the range of 8 hours or more and 40 hours or less. The pneumatic tire 100 is mounted on the flat spot generator 41, a load is applied, and the ozone concentration in the test chamber 10 is adjusted so that the pneumatic tire 100 is exposed to ozone and the test process is started. It is determined whether or not the elapsed time from has passed this specified time.

Whether or not the specified time has elapsed is determined by applying a load to the pneumatic tire 100 and the operator continuing to measure the elapsed time since the pneumatic tire 100 was exposed to ozone. The operator may determine whether or not the above has passed. Alternatively, the air conditioner 20 or the ozone supply device 30 is provided with a notification means (not shown) and a timer for notifying the operator of information by voice or display, and the elapsed time from the start of operation of these devices is set. The operator may be notified by the notification means whether or not the elapsed time has elapsed by measuring with a timer. Further, when a timer is provided in the air conditioner 20 or the ozone supply device 30, the operation of these devices may be stopped after the elapsed time elapses.

When it was determined that the elapsed time measured as described above did not elapse the specified time (step ST5, No determination), the pneumatic tire 100 was exposed to ozone in an atmosphere adjusted to a predetermined temperature. In this state, the load is continuously applied to the pneumatic tire 100.

On the other hand, when it is determined that the elapsed time has elapsed (step ST5, Yes determination), the pneumatic tire 100 is removed from the flat spot generator 41 to end the test process. That is, in an atmosphere adjusted to a predetermined temperature, the elapsed time in a state where the pneumatic tire 100 is exposed to ozone and a load is applied to the pneumatic tire 100 elapses a predetermined predetermined elapsed time. Then, the test process is completed and the process proceeds to the evaluation process.

Next, the evaluation step ST103 will be described. FIG. 12 is a flowchart showing the procedure of the evaluation process. The evaluation step ST103 evaluates the degree of crack growth with respect to the female cut 120 as a base point from the amount of change in the female cut 120 in the longitudinal direction after the test step ST102. First, the length of the female cut 120 is measured after the test step ST102 (step ST21). Specifically, the lengths of the female cuts 120 processed in the tire circumferential direction in the longitudinal direction are measured, and the measurement results are recorded in association with the positions of the female cuts 120 in the tire circumferential direction. In the present embodiment, all the female cuts 120 processed in the tire circumferential direction as described above are set to have the same length and depth. Therefore, the degree of growth (ease of growth) of cracks that grow from the female cut 120 when the vehicle is stopped for a long period of time is evaluated from the length of the female cut 120 after the test step ST102 and the position of the female cut 120. it can.

Subsequently, the growth rate IM of each measured female cut 120 is calculated (step ST22). This growth rate IM is calculated using the following formula.

Growth rate IM (%) = (length TL after test-former length OL) / original length OL x 100

In this calculation formula, the post-test length TL is the length in the longitudinal direction of each female cut 120 measured in step ST21. The original length OL is the length in the longitudinal direction of each female cut 120 processed in the processing step ST101 at the time of processing. By calculating the growth rate IM of the female cut 120 based on the above calculation formula, the crack growth potential with the female cut 120 as a base point can be evaluated. Further, by associating the position of the female cut 120 with the position of the female cut 120 in the tire circumferential direction when the test step ST102 is performed, the position where the female cut 120 easily grows and the position where it does not easily grow can be known. Can be done.

Next, it is determined whether the calculated growth rate IM of the female cut 120 is equal to or higher than a predetermined threshold value (step S23). In this case, the female cut having the highest growth rate may be the target of discrimination, or the female cut at a specific position in the tire circumferential direction may be used. In this determination, when the growth rate IM of the female cut 120 is equal to or higher than a predetermined threshold value sufficient for evaluating the crack growth potential (step ST23; Yes), the crack growth potential is evaluated based on the growth rate IM (step). ST24). In this case, it is possible to evaluate the position where cracks are likely to grow in the tire circumferential direction, the relationship between the loaded load and the crack growth potential, and the like. In the present embodiment, by evaluating the crack growth potential based on the female cut 120, the evaluation can be performed closer to the actual crack risk as compared with the existing evaluation. Therefore, the crack risk that occurs when the pneumatic tire 100 is actually used can be reproduced with high accuracy, and as a result, the crack growth potential can be evaluated with high accuracy.

On the other hand, in the above determination, when the growth rate IM of the female cut 120 is not equal to or higher than a predetermined threshold value (step ST23; No), the load applied to the pneumatic tire 100 is increased and the test step ST102 described above is executed again. To end the evaluation process (step ST25). When the growth rate IM of the female cut 120 is not equal to or higher than a predetermined threshold value, that is, when the crack growth is not sufficient, the material of the pneumatic tire 100 is difficult to grow cracks, or the pneumatic tire 100 is loaded. The reason may be that the load was not sufficient. Therefore, the load loaded in the test step ST102 is set to an increase (for example, a value of 60% to 70% of the maximum load capacity of the pneumatic tire 100), and the test step ST102 is executed again. Thereby, by evaluating the growth rate IM of the female cut 120 again in the evaluation step ST103, the crack growth potential of the pneumatic tire 100 can be evaluated with high accuracy.

As described above, the tire test method according to the present embodiment includes the processing step ST101 for processing the female cut 120 on the groove bottom 111A of the main groove 111 formed in the tread portion 101 of the pneumatic tire 100, and the atmosphere adjusted to a predetermined temperature. Then, with the pneumatic tire 100 exposed to ozone, the region where the female cut 120 in the circumferential direction of the pneumatic tire is not processed is grounded, and a vertical load is applied to the pneumatic tire 100 for testing. The test step ST102 and the evaluation step ST103 for evaluating the crack growth property from the growth rate in the longitudinal direction of the female cut 120 after the test step ST102 are included. According to this configuration, the pre-processed female cut 120 serves as a base point, and cracks can be grown on the tire circumference due to distortion in a certain direction due to the applied load. Therefore, the actual pneumatic tire 100 mounted on the vehicle is actually used. A test for growing cracks can be performed by reproducing the usage mode. Specifically, by continuously applying a load to the same position of the pneumatic tire 100 in the tire circumferential direction, the pneumatic tire 100 is processed into a pneumatic tire 100 when the vehicle equipped with the pneumatic tire 100 is stopped for a long period of time. The effect on crack growth starting from the female cut 120 can be reproduced by the test.

The pneumatic tire 100 may be damaged not only when the vehicle is running but also when the vehicle is stopped. In particular, when the vehicle is stopped for a long period of time, a load in the same direction continuously acts on the same part of the pneumatic tire 100 for a long period of time, so that scratches caused by some cause grow as cracks. There is. When testing the damage and durability of the pneumatic tire 100, if the test is performed using a rotating drum, the change in the pneumatic tire 100 when the vehicle is running can be reproduced, but the vehicle The change in the pneumatic tire 100 when the vehicle is stopped for a long period of time is very difficult in the test using the rotating drum. On the other hand, in the present embodiment, since the load is applied to the same position in the tire circumferential direction of the pneumatic tire 100, it is possible to reproduce the change regarding the crack growth of the pneumatic tire 100 when the vehicle is stopped for a long period of time. ..

Further, when the test is performed while applying a load to the pneumatic tire 100, the deterioration of the pneumatic tire 100 can be accelerated because the test is performed while the pneumatic tire 100 is exposed to ozone. As a result, the change of the pneumatic tire 100 in a state where the vehicle equipped with the pneumatic tire 100 is stopped for a long period of time can be reproduced in a short time, and when the pneumatic tire 100 is actually used, it grows in the main groove 111. The cracks that occur can be reproduced in a short time. As a result, the market reproducibility for cracks can be improved.

Further, in the test step ST102, the female cut 120 is processed into a region where the central angle is at least 55 ° or more and 85 ° or less on both sides in the tire circumferential direction from the center of the contact patch 110A of the pneumatic tire 100. It is possible to improve the market reproducibility regarding crack growth when the vehicle equipped with the pneumatic tire 100 is stopped for a long period of time. That is, within the range where the central angle is smaller than 55 °, the strain with respect to the female cut 120 becomes small and cracks are unlikely to grow, and the cracks with the female cut 120 as the base point may not grow sufficiently. Further, in the range where the central angle is larger than 85 °, the load applied to the pneumatic tire 100 when the vehicle is stopped for a long period of time is not sufficient, so that the crack starting from the female cut 120 may not grow sufficiently.

On the other hand, when the female cut 120 is machined in a region where the central angle is at least 55 ° or more and 85 ° or less on both sides in the tire circumferential direction from the center of the contact patch 110A of the pneumatic tire 100, the vehicle An appropriate load can be applied to the pneumatic tire 100 when the vehicle is stopped for a long period of time. Therefore, the market reproducibility for cracks can be improved more reliably.

Further, the female cut 120 to be processed extends along the tire circumferential direction of the pneumatic tire 100, and the length of the female cut 120 in the longitudinal direction is within the range of 2 mm or more and 8 mm or less, and the depth of the cut is Is in the range of 0.1 mm or more and 3.0 mm or less, so that damage that may occur in the main groove 111 of the pneumatic tire 100 can be reproduced in the market. Therefore, the crack growth starting from the female cut 120 can be reproduced in the market.

Further, the female cut 120 is processed into the groove bottom 113A of the shoulder main groove 113 on the shoulder portion 102 side of the pneumatic tire 100, and is within a range of 50% or less of the groove width from the groove wall 113B of the shoulder main groove 113. By processing the female cut 120 into the groove bottom 113A of the shoulder main groove 113, it is possible to create an environment in which cracks due to the strain of the pneumatic tire 100 are likely to grow. Therefore, it is possible to reproduce the cracks that grow in the shoulder main groove 113 when the pneumatic tire 100 is actually used. As a result, the market reproducibility for cracks can be improved.

Further, when a plurality of female cuts 120 are machined in one main groove 111 extending in the tire circumferential direction of the pneumatic tire 100, the plurality of female cuts 120 are formed in the tire circumferential direction at the groove bottom 111A of the single main groove 111. Further, since the main grooves 111 are provided at positions shifted in the width direction, the load on the pneumatic tire 100 can be concentrated on each female cut 120, thereby promoting the growth of cracks starting from the female cut 120. , The crack growth potential can be evaluated accurately. Further, it is possible to prevent the plurality of female cuts 120 from growing in the longitudinal direction and continuing (connecting) in the tire circumferential direction, and it is possible to accurately evaluate the growth potential of cracks.

Further, in the evaluation step ST103, when the growth rate of the female cut 120 in the longitudinal direction is equal to or less than a predetermined threshold value, the load applied to the pneumatic tire 100 is increased and the test step ST102 is executed again, so that the female cut 120 grows. The reason why the rate IM is not equal to or higher than a predetermined threshold can be selected because the material of the pneumatic tire 100 is difficult for cracks to grow, the load applied to the pneumatic tire 100 is not sufficient, and the like. ..

Further, since the concentration of ozone that exposes the pneumatic tire 100 is within the range of 50 pphm or more and 250 pphm or less, it is more efficient while ensuring the reproducibility of changes in the pneumatic tire 100 when the vehicle is stopped for a long period of time. It is possible to accelerate the deterioration and evaluate in a short time. That is, when the ozone concentration is 50 pphm, the ozone concentration is too low, so that even if the pneumatic tire 100 is exposed to ozone, deterioration may not easily occur. In this case, there is a possibility that the efficiency of the deterioration promotion evaluation, which evaluates in a short time by promoting the deterioration, tends to deteriorate. Further, when the ozone concentration exceeds 250 pphm, the ozone concentration is too high, so that the correlation with the natural deterioration of the pneumatic tire 100 during normal use is lowered, and the change of the pneumatic tire 100 during the test is the air. There is a risk that the tire 100 will easily deviate from the change when it is mounted on the vehicle and actually used.

On the other hand, when the concentration of ozone that exposes the pneumatic tire 100 is within the range of 50 pphm or more and 250 pphm or less, the reproducibility of the change of the pneumatic tire 100 when the vehicle is stopped for a long period of time is ensured. Deterioration promotion evaluation can be performed by efficiently promoting deterioration. As a result, the market reproducibility for cracks can be improved more reliably.

Further, since the temperature of the atmosphere in the test room 10 is within the range of 30 ° C. or higher and 70 ° C. or lower, it is more efficient while ensuring the reproducibility of changes in the pneumatic tire 100 when the vehicle is stopped for a long period of time. It is possible to accelerate the deterioration and evaluate in a short time. That is, when the temperature of the atmosphere in the test chamber 10 is less than 30 ° C., the temperature is too low, so that the ozone reactivity of the pneumatic tire 100 tends to decrease, and the efficiency of deterioration promotion evaluation tends to deteriorate. There is. Further, when the temperature of the atmosphere in the test chamber 10 exceeds 70 ° C., the temperature is too high, so that the heat aging phenomenon of the pneumatic tire 100 becomes remarkable, and the change of the pneumatic tire 100 at the time of the test is pneumatic. There is a risk that the tire 100 will easily deviate from the change when it is mounted on the vehicle and actually used.

On the other hand, when the temperature of the atmosphere in the test room 10 is within the range of 30 ° C. or higher and 70 ° C. or lower, the reproducibility of the change of the pneumatic tire 100 when the vehicle is stopped for a long period of time is ensured. Deterioration promotion evaluation can be performed by efficiently promoting deterioration. As a result, the market reproducibility for cracks can be improved more reliably.

Further, when the test is performed, the internal pressure of the pneumatic tire 100 is set within the range of 60% or more and 100% or less of the maximum air pressure, so that the test is performed closer to the actual use state of the pneumatic tire 100. It can be performed. As a result, the market reproducibility for cracks can be improved more reliably.

[Example]
FIG. 13 is a chart showing the evaluation results of the tire test method. Hereinafter, regarding the above-mentioned tire test method, an evaluation test conducted on the tire test method according to the present invention and the tire test method of a comparative example for comparison with the tire test method according to the present invention will be described.

In the evaluation test, a pneumatic tire 100 with a tire nominal size of 225 / 65R17 specified by JATTA was assembled on a JATTA standard rim wheel 130, and the inside of the test chamber 10 was in an ozone atmosphere with an ozone concentration of 150 pphm. The temperature was adjusted to 50 ° C.

There are two types of evaluation tests, an example which is an example of the tire test method according to the present invention and a comparative example which is a tire test method to be compared with the tire test method according to the present invention. This was done by comparing with the actual vehicle example that was installed and used in. An example of this actual vehicle is a pneumatic tire that has actually been cracked in the market.

Of these, in the comparative example, although the pneumatic tire 100 is exposed to ozone, the air pressure is 20% of the maximum air pressure, and no load is applied to the pneumatic tire 100. On the other hand, in the embodiment which is an example of the tire test method according to the present invention, a female cut 120 having a predetermined length is machined on the groove bottom 111A of the main groove 111 extending in the tire circumferential direction. Then, the pneumatic tire 100 was exposed to ozone, the air pressure was set to 90% of the maximum air pressure, and a load was applied to the pneumatic tire 100. In this embodiment, the load applied to the pneumatic tire 100 is 60% of the maximum load capacity of the pneumatic tire 100.

The evaluation method of the comparative example is an index in which the number of cracks finally generated after the completion of the test in the test process is counted, and the number of cracks is set to the reference value (100) by the number of cracks in the actual vehicle example described later. It was evaluated by expressing with. Specifically, the crack is expressed by an index in which the length of the crack is measured in each main groove 111, all the cracks having a length of 1 mm or more that can be visually confirmed are counted, and the number of cracks in the actual vehicle example described later is 100. It was evaluated by. This evaluation indicates that the larger the index, the larger the number of cracks, and the closer it is to 100, the closer the number of cracks generated to the actual vehicle example, and the better the market reproducibility of cracks. .. Here, the difference from the reference value of the actual vehicle example is indicated by “◯” for 0 to 10, “Δ” for 11 to 20, and “x” for 21 or more.

On the other hand, in the evaluation method of the example, the length of the female cut 120 (crack) finally grown after the completion of the test in the test process is measured, and the length of the female cut 120 after the test process and the processed female cut 120 are measured. The growth rate IM of the female cut 120 was calculated from the original length to evaluate the crack growth potential. This evaluation indicates that the higher the number, the higher the risk of cracks in the market (cracks are more likely to grow). Here, a growth rate IM of 90 or less is indicated as "low", 91-124 is indicated as "medium", and 124 or more is indicated as "high". In addition, the market reproducibility is indicated by "○", "△", and "×" based on the correlation between this crack risk and the actual vehicle example.

As a result of evaluating the tire test method, as shown in FIG. 13, the tire test method according to the example has a high female cut growth rate (crack risk), and the market reproduction of cracks in the actual vehicle example is higher than that in the comparative example. It turned out to be excellent in sex. That is, the tire test method according to the embodiment can improve the market reproducibility for crack growth.

The tire test method according to the above-described embodiment may be performed together with other tests. For example, before or after the tire test method according to the above-described embodiment, an exposure test is performed in which the internal pressure of the pneumatic tire 100 is set to a predetermined internal pressure and exposed to an outdoor shade for a long time with a predetermined load applied. You may. When the vehicle is parked outdoors for a long period of time, it may be parked in the shade for a long time. Therefore, by conducting an additional exposure test in the shade, the environment of the pneumatic tire 100 mounted on the vehicle that is stopped for a long period of time is reproduced. can do. As a result, crack growth can be reproduced with higher accuracy.

Alternatively, before or after the tire test method according to the above-described embodiment, a test may be performed in which ozone is not supplied and the pneumatic tire 100 is left in a high temperature atmosphere. By additionally performing a test in which the pneumatic tire 100 is left in a high temperature atmosphere, the effect of the rubber hardening due to the high temperature can be reproduced, and the pneumatic tire 100 used in the high temperature environment grows. Cracks can be reproduced with higher accuracy. As a result, the market reproducibility for crack growth can be improved more reliably.

100 Pneumatic tire 101 Tread part 102 Shoulder part 110 Tread surface 110A Ground surface 111 Main groove 111A Groove bottom 112 Center main groove 113 Shoulder main groove 113A Groove bottom 113B Groove wall 120 Female cut (cut)
ST101 Processing process ST102 Test process ST103 Evaluation process IM Growth rate

Claims (12)

The pre-process of making a notch in the groove bottom of the groove formed in the tread part of the pneumatic tire, and
In an atmosphere adjusted to a predetermined temperature, with the pneumatic tire exposed to ozone, the region where the notch is not processed in the circumferential direction of the pneumatic tire is grounded, and the direction perpendicular to the pneumatic tire. The intermediate process of loading and testing with the load of
A post-process for evaluating crack growth from the growth rate in the longitudinal direction of the notch after the intermediate process, and a post-process.
A tire test method comprising. The tire test method according to claim 1, wherein in the intermediate step, the notch is located in a region having a central angle of at least 55 ° or more and 85 ° or less on both sides in the circumferential direction from the center of the contact patch of the pneumatic tire. .. In the previous step, the notch to be machined extends along the circumferential direction of the pneumatic tire, the length of the notch in the longitudinal direction is within the range of 2 mm or more and 8 mm or less, and the depth of the notch is The tire test method according to claim 1 or 2, wherein the tire test method is in the range of 0.1 mm or more and 3.0 mm or less. In the previous step, the notch is processed into at least the groove bottom of the groove portion on the shoulder portion side of the pneumatic tire, and is processed within a range of 50% or less of the groove width from the groove wall of the groove portion on the shoulder portion side. The tire test method according to any one of claims 1 to 3. When a plurality of the cuts are machined in one groove extending in the circumferential direction of the pneumatic tire in the previous step.
The plurality of the cuts according to any one of claims 1 to 4, which are provided at positions shifted in the circumferential direction of the pneumatic tire and the width direction of the groove at the groove bottom of one groove. Tire test method. In the post-step, when the growth rate in the longitudinal direction of the cut is equal to or less than a predetermined threshold value,
The tire test method according to any one of claims 1 to 5, wherein the load applied to the pneumatic tire is increased and the intermediate step is executed again. The method according to any one of claims 1 to 6, wherein in the intermediate step, the load applied to the pneumatic tire is within a range of 40% or more and 100% or less of the maximum load capacity of the pneumatic tire. Tire test method. The tire test method according to any one of claims 1 to 7, wherein in the intermediate step, the concentration of ozone that exposes the pneumatic tire is in the range of 50 pphm or more and 250 pphm or less. The tire test method according to any one of claims 1 to 8, wherein in the intermediate step, the temperature of the atmosphere is in the range of 30 ° C. or higher and 70 ° C. or lower. The tire test method according to any one of claims 1 to 9, wherein in the intermediate step, the internal pressure of the pneumatic tire is in the range of 60% or more and 100% or less of the maximum air pressure of the pneumatic tire. The tire test method according to any one of claims 1 to 10, wherein in the intermediate step, the internal pressure is reduced with the lapse of time for applying a load to the pneumatic tire. The tire test method according to any one of claims 1 to 11, wherein in the intermediate step, the temperature of the atmosphere is changed while continuing to apply a load to the pneumatic tire.

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