JP2013130442A - Tire testing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a testing method with which durability of treads of a tire can be evaluated efficiently.SOLUTION: A testing method of a pneumatic tire 4 includes a preprocessing step for obtaining a test tire by promoting deterioration of the tire 4, and a durability travel step for performing durability travel using the test tire. The preprocessing step includes a tire assembly preparation step for preparing a tire assembly 2 by integrating the tire 4 into a rim 6, and a test tire preparation step for obtaining a test tire by filling the tire assembly 2 with inert gas and then leaving the tire assembly 2 in the atmosphere of 70°C or higher and 90°C or lower for ten days or longer.

Description

  The present invention relates to a tire testing method. More specifically, the present invention relates to a test method for evaluating crack growth of a tread of a tire.

  The tire is configured by combining rubber members such as a tread, a sidewall, a bead, a carcass, a belt, and a band.

  The tread of the tire has a shape protruding outward in the radial direction. The tread has a tread surface. This tread surface is installed on the road surface. Grooves are generally carved on the tread surface. A tread pattern is formed by this groove. The tread transmits driving force and braking force to the road surface. The durability of the tread is important in evaluating the durability of the tire.

  If the tire is used for a long time, cracks may occur in the groove of the tread. This crack impairs the performance of the tire. In order to prevent the occurrence of cracks, improvements have been made from various viewpoints such as the composition of the rubber composition for the tread, the groove shape, the tire profile, and the thickness of the tread. This improvement can improve the durability of the tread.

  This improved tire is evaluated for tread durability. In normal use, tire deterioration is caused by long-term use. In normal use, it takes time to evaluate the durability of the tread. The tread cannot be improved efficiently by evaluation by normal use.

  Document 1 proposes a test method for evaluating the durability of a tire by deteriorating the tire in advance. In this test method, a tire assembly in which a tire is incorporated in a rim is prepared. This tire is filled with high oxygen air and water. The tire is left in a predetermined temperature and humidity atmosphere for a predetermined period. Thus, the durability of the tire is evaluated using the deteriorated tire.

  The durability evaluation test of Document 1 is a relatively short running test, and the durability of the tire can be evaluated. Thereby, durability of a tire can be evaluated efficiently in a short time.

JP 2006-337100 A

  In the evaluation method of Literature 1, the inside and outside of the tire are deteriorated. This evaluation method corrodes and degrades the internal structural material of the tire, for example, the metal cord of the belt ply. In this evaluation method, structural damage to the tire can occur before cracks occur in the tread. This structural damage can cause the tire to become unworkable. This evaluation method may not be able to efficiently evaluate the durability of the tread.

  An object of the present invention is to provide a test method capable of efficiently evaluating the durability of a tire tread.

The test method for a pneumatic tire according to the present invention includes a pretreatment process for accelerating the deterioration of the pneumatic tire to obtain a test tire, and an endurance travel process in which endurance travel is performed using the test tire.
This pretreatment step is
A tire assembly preparation step in which a tire assembly in which a pneumatic tire is incorporated in a rim is prepared;
A test tire preparation step in which after the tire assembly is filled with an inert gas, the tire assembly is left in an atmosphere of 70 ° C. or higher and 90 ° C. or lower for 10 days or more to obtain a test tire. .

  Preferably, the test tire is caused to travel in the durability traveling process. In this running, the test tire is filled with air at a standard maximum pressure P-60 (unit kPa) or more and a standard maximum pressure P (unit kPa) or less. The room temperature is set to 20 ° C. or higher and 40 ° C. or lower. The load is set to a standard maximum load F (unit kN) or more and 1.5 · F (unit kN) or less. The traveling speed is set to 60 km / h or more and 85 km / h or less.

  In the test method for a pneumatic tire according to the present invention, the tire tread is deteriorated while the internal deterioration of the test tire is suppressed. This test method can efficiently test the durability of the tire.

FIG. 1 is a cross-sectional view showing a tire assembly used in the test method of the present invention.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view showing a part of a tire assembly 2 used in a tire testing method according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. In the tire assembly 2, a tire 4 as a pneumatic tire is assembled to a rim 6. The tire 4 has a substantially bilaterally symmetric shape with a one-dot chain line CL in FIG. 1 as the center. This alternate long and short dash line CL represents the equator plane of the tire 4. The tire 4 includes a tread 8, a sidewall 10, a bead 12, a carcass 14, a belt 16, a band 18, an inner liner 20, and a chafer 22. The tire 4 is a tubeless type. The tire 4 is used for evaluating crack growth of the tread 8.

  The tread 8 of the tire 4 is made of a crosslinked rubber. The tread 8 has a shape protruding outward in the radial direction. The tread 8 includes a tread surface 24. The tread surface 24 is in contact with the road surface. A groove 26 is carved in the tread surface 24. The groove 26 forms a tread pattern.

  The sidewall 10 extends substantially inward in the radial direction from the end of the tread 8. The sidewall 10 is made of a crosslinked rubber. The sidewall 10 absorbs an impact from the road surface by bending. Further, the sidewall 10 prevents the carcass 14 from being damaged.

  The bead 12 is located substantially inward of the sidewall 10 in the radial direction. The bead 12 includes a core 28 and an apex 30 that extends radially outward from the core 28. The core 28 has a ring shape. The core 28 includes a plurality of non-stretchable wires (typically steel wires). The apex 30 is tapered outward in the radial direction. The apex 30 is made of a highly hard crosslinked rubber.

  The carcass 14 includes a first ply 32a and a second ply 32b. The first ply 32 a and the second ply 32 b are bridged between the beads 12 on both sides, and extend along the inside of the tread 8 and the sidewall 10.

  In the tire 2, the first ply 32 a and the second ply 32 b are folded around the core 28. The first ply 32a and the second ply 32b may not be folded around the core 28. The ply 32 that is folded around the core 28 can contribute to the rigidity of the sidewall 10. Since the folded ply 32 can suppress the deformation in the side wall 10 portion, the distortion generated in the tire 2 in the running state tends to concentrate on the tread 8 portion. From the viewpoint that the tread 8 of the tire 2 in the running state can be appropriately deformed, it is preferable that at least one of the first ply 32 a and the second ply 32 b is folded around the core 28.

  Although not shown, the first ply 32a and the second ply 32b are composed of a large number of cords arranged in parallel and a topping rubber. The first ply 32a and the second ply 32b are composed of a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, this carcass has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers. The carcass 14 may be formed from a single ply. Here, the tire structure is described by taking the tire 4 as a so-called radial tire as an example, but a so-called bias tire may be used.

  The belt 16 is located on the inner side in the radial direction of the tread 8. The belt 16 is laminated with the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 includes an inner layer 34 and an outer layer 36. Each of the inner layer 34 and the outer layer 36 is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the inner layer 34 with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 36 with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The belt 16 may include three or more layers.

  The band 18 is located on the radially outer side of the belt 16. In the axial direction, the width of the band 18 is larger than the width of the belt 16. Although not shown, the band 18 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 16 is restrained by this cord, lifting of the belt 16 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 16 and the band 18 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 16. A reinforcing layer may be formed only from the band 18.

  The inner liner 20 is joined to the inner peripheral surface of the carcass 14. The inner liner 20 is made of a crosslinked rubber. The inner liner 20 is made of rubber having excellent air shielding properties. The inner liner 20 plays a role of maintaining the internal pressure of the tire 2.

  The chafer 22 is located in the vicinity of the bead 12. When the tire 4 is incorporated in the rim 6, the chafer 22 comes into contact with the rim 6. By this contact, the vicinity of the bead 12 is protected. The chafer 22 is usually made of cloth and rubber impregnated in the cloth. A chafer 22 made of a single rubber may be used.

  The rim 6 is a regular rim of the tire 4. The regular rim means a rim defined in a standard on which the tire depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims.

  A test method for the pneumatic tire 4 using the tire assembly 2 will be described. This test method includes a pretreatment process and an endurance running process after the pretreatment process.

  The pretreatment process includes a tire assembly preparation process and a test tire preparation process after the tire assembly preparation process.

  In the tire assembly preparation process, the tire 4 is incorporated into the rim 6. A tire assembly 2 shown in FIG. 1 is prepared.

In the test tire preparation process, the tire assembly 2 is filled with nitrogen gas. The pressure of the filled nitrogen gas is preferably 0.8 to 1.2 times the standard maximum pressure P. The nitrogen gas here is a gas having a nitrogen concentration of 50% or more. This nitrogen concentration is obtained by the following equation (1).
Nitrogen concentration (%) = (Pn / Pt) · 100 (1)
Pt in this formula (1) is the total pressure of nitrogen gas to be filled, and Pn is the partial pressure of nitrogen with respect to this total pressure.

  The tire assembly 2 is allowed to stand for 10 days or more in an atmosphere at a temperature of 70 ° C. or higher and 90 ° C. or lower in a state filled with nitrogen gas. As a result, the tread 8 of the tire assembly 2 deteriorates. A test tire is thus obtained.

  Nitrogen gas is extracted from the test tire. Thereafter, the test tire is sent to the endurance running process.

  In the durability running process, the test tire is filled with air. At the standard maximum pressure P of the tire 4, the internal pressure of the test tire is preferably set to P-60 (unit kPa) or more and P (unit kPa) or less. This air pressure is measured in an atmosphere at a temperature of 25 ° C. before traveling. The room temperature for this durable running is preferably 20 ° C. or higher and 40 ° C. or lower. When the standard maximum load F of the tire 4 is applied, a load of F (unit kN) or more and 1.5 · F (unit kN) or less is preferably applied to the test tire. The test tire filled with air is allowed to run endurance with this load applied at this room temperature. The traveling speed is preferably 60 km / h or more and 85 km / h or less. In the durability running process, for example, a drum type tester is used.

  In this test method, the durability of the tread is evaluated. Here, the growth of the tread crack is evaluated by running a predetermined distance. This predetermined distance may be determined in consideration of the travel distance of the actual vehicle on which the tire is mounted. The growth of cracks is evaluated on the test tire that has traveled this predetermined distance. For example, the predetermined distance may be set to 7000 km for motorcycle tires, 20000 km for passenger cars, and 30000 km for small truck tires. Further, a plurality of test tires may be prepared, and the crack growth may be relatively evaluated. In the case of relative evaluation, the endurance running may be terminated when a relative difference is confirmed.

  By evaluating the growth properties of the cracks, effects of various improvements such as blending of the rubber composition, groove shape, tire profile, and tread thickness can be confirmed. The knowledge gained from this evaluation will be applied to the development of tires that can suppress the growth of cracks.

  In this test method, the tire assembly 2 is filled with nitrogen gas to obtain a test tire. By using nitrogen gas, which is an inert gas, deterioration inside the tire 4 is suppressed. Thereby, generation | occurrence | production of the structural damage of a test tire is suppressed in the durable driving | running | working process. In this test method, structural damage of the test tire is suppressed from occurring before the tread 8 cracks grow. This tire test method can efficiently evaluate the crack growth of the tread of the tire 4. Although nitrogen gas is illustrated here as long as it is an inert gas, argon gas, helium gas, or a mixed gas of a plurality of inert gases may be used. From the viewpoint of suppressing deterioration inside the tire 4, the concentration of the inert gas is preferably 50% or more, and more preferably 80% or more.

  In the pretreatment process, the tread 8 is deteriorated when the tire assembly 2 is left for 10 days or more in an atmosphere having a temperature of 70 ° C. or higher and 90 ° C. or lower. Since the tread 8 deteriorates, the occurrence and progress of cracks in the tread of the test tire are accelerated. Thereby, the growth property of the crack of a tread can be evaluated in a comparatively short time.

  From the viewpoint of advancing the deterioration of the tread 8, the temperature of the leaving atmosphere in the pretreatment process is set to 70 ° C. or higher. From this viewpoint, this temperature is preferably 75 ° C. or higher, and more preferably 80 ° C. or higher. On the other hand, if the deterioration of the tread 8 proceeds excessively, the generation and progress of cracks are accelerated too quickly in the durability traveling process. It becomes difficult to evaluate and improve the tread of the test tire during durability running. From this viewpoint, the temperature is set to 90 ° C. or less. From this viewpoint, this temperature is preferably 85 ° C. or lower, and more preferably 83 ° C. or lower.

  Further, from the viewpoint of advancing the deterioration of the tread 8, the leaving period in the pretreatment process is set to 10 days or more. From this viewpoint, the standing period is preferably 12 days or more, and more preferably 14 days or more. On the other hand, if the occurrence and progress of cracks are too fast, it becomes difficult to evaluate the tread of the test tire. From this point of view, this leaving period is set to 21 days or less. From this viewpoint, the standing period is preferably 18 days or less, and more preferably 16 days or less.

  When this test tire is run, bending distortion repeatedly occurs at the groove bottom of the tread. When the internal pressure of the test tire is lowered, this bending strain is likely to occur. This bending strain contributes to crack growth. From this viewpoint, the air pressure of the test tire is preferably the standard maximum pressure P or less, and more preferably the standard maximum pressure P-30 kPa or less.

  On the other hand, if the internal pressure of the test tire becomes too low, the bending strain increases. When the bending strain increases, tread separation occurs and the vehicle cannot run. If the vehicle cannot run, the durability, particularly the growth of cracks in the tread, cannot be evaluated. From this viewpoint, the air pressure of the test tire is preferably P-60 (kPa) or more, and more preferably the standard maximum pressure P-50 kPa or more.

  The standard maximum pressure means an internal pressure defined in a standard on which the tire depends. “Maximum air pressure” in the JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and “INFLATION PRESSURE” in the ETRTO standard are the maximum pressures in this standard.

  When the room temperature is high, heat tends to accumulate inside the test tire during running. This heat accumulation makes the test tire more susceptible to tread separation. In this respect, the room temperature is preferably 40 ° C. or lower, and more preferably 30 ° C. or lower. On the other hand, if the room temperature is low, the growth of cracks is suppressed. If the room temperature is low, the durability running time will be long. Not suitable for efficient testing. In this respect, the room temperature is preferably 20 ° C. or higher, and more preferably 25 ° C. or higher.

  A radial load is applied to the test tire and pressed against the road surface. By applying this load, bending distortion is easily generated in the groove of the tread. Thereby, the crack of a groove | channel is made easy to grow. From this point of view, the load load is preferably not less than the standard maximum load F (unit kN), and more preferably not less than 1.1 times the standard maximum load F. On the other hand, when a large load is applied to the test tire, distortion of the ground contact portion of the tread increases. This large strain increases the heat generation of the test tire. This increase in heat generation tends to cause tread separation. When tread separation occurs, it interferes with the evaluation of crack growth. From this viewpoint, the load load is preferably 1.5 times or less of the standard maximum load F, and more preferably 1.4 times or less of the standard maximum load F.

  By increasing the running speed of the test tire, the growth of cracks in the tread is promoted. This accelerated crack growth allows efficient testing. From this viewpoint, the running speed of the test tire is preferably 60 km / h or more, and more preferably 65 km / h or more. On the other hand, if the running speed of the test tire is increased too much, the heat generation of the test tire increases. This increase in heat generation tends to cause tread separation. From this viewpoint, the traveling speed is preferably 85 km / h or less, and more preferably 80 km / h or less.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Prototype tire assembly]
Several prototype tires were prepared. The tire size was “150 / 70-14M / C66S”. The standard maximum pressure of this tire was 250 kPa. This tire is a scooter tire. This prototype tire was assembled to a rim to prepare a prototype tire assembly.

[Test tire]
A test tire was obtained from the prototype tire assembly by being pretreated in the pretreatment step according to the present invention. In this pretreatment process, the prototype tire assembly was filled with nitrogen gas having a nitrogen concentration of 90%. After filling with the nitrogen gas, the prototype tire assembly was left in a room at a room temperature of 80 ° C. for 14 days to obtain a test tire.

[Tests 1 to 3]
The test tire was allowed to run endurance under the conditions of each test shown in Table 1 below. In the column of the load, when the standard maximum load F is assumed and the load Ft is applied, the magnification Ft / F is shown. The number of cracks generated at the bottom of the tread groove due to the durability running was counted. The number of cracks is described in the TGC number column. Moreover, the average value of the length of a crack was calculated | required for every test. This average value is described in the column of TGC length.

[Comparative tests 1 to 3]
The prototype tire assembly was run durability under the same test conditions as the test tire. Table 1 below shows the test conditions, the number of cracks, and the average value of the crack lengths.

  In Tests 1 to 3, compared with Comparative Tests 1 to 3, the crack growth at the groove bottom of the tread is large. From this result, the growth of cracks can be evaluated in a shorter time. From this test result, it is clear that the test method according to the present invention can more efficiently evaluate the durability of the tread.

[Tests 4 to 9]
Several test tires were prepared. The internal pressure of this test tire was set as shown in Table 2 below. Tests 4 to 9 were performed with other test conditions in common. Table 2 below shows the test conditions, the number of cracks generated at the groove bottom of the tread, and the average value of the crack lengths. In Test 8, when the running distance exceeded 5000 km, tread separation occurred and the running was impossible. Test 8 ends the test at 5000 km, and describes the number of cracks and the average value of the crack lengths at that time.

[Tests 10 to 15]
Several test tires were prepared. The load applied to the test tire was set as shown in Table 3 below. Tests 10 to 15 were performed with other test conditions in common. Table 3 below shows the test conditions, the number of cracks generated in the groove bottom of the tread, and the average value of the crack lengths. In Test 15, when the traveling distance exceeded 3500 km, tread separation occurred, and traveling was impossible. In test 15, the test was completed at 3500 km, and the number of cracks and the average value of the crack length at that time are described.

[Tests 16 to 20]
Several test tires were prepared. The running speed and room temperature of this test tire were set as shown in Table 4 below. Tests 16 to 20 were performed with other test conditions in common. The test conditions, the number of cracks generated at the groove bottom of the tread, and the average value of the crack length are shown in Table 4 below. In Tests 17 and 19, tread separation occurred before the traveling distance reached 7000 km, and traveling was impossible. The test is finished at a time before traveling becomes impossible, and the traveling distance, the number of cracks, and the average value of the crack length are described at that time.

  In the tests where the test tires were unable to run, all were due to tread separation. In these tests, there was no phenomenon that the vehicle could not run due to structural damage other than the tread. From the results shown in Tables 1 to 4, it is clear that the durability evaluation of the tire tread can be made efficient by combining the test tire and the test conditions.

  Furthermore, the difference in crack growth between tires having different specifications can be efficiently evaluated by combining the pretreated test tire with the durability running test conditions. From this evaluation result, the superiority of the present invention is clear.

  The present invention can be applied to various tire test methods.

2 ... Tire assembly 4 ... Tire 6 ... Rim 8 ... Tread 10 ... Side wall 12 ... Bead 14 ... Carcass 16 ... Belt 18 ... Band 20 .... Inner liner 22 ... Chafer 24 ... Tread surface 26 ... Groove 28 ... Core 30 ... Apex 32 (26a, 26b) ... Ply 34 ... Inner layer 36 ..Outer layer

Claims (2)

A pretreatment step of accelerating the deterioration of the pneumatic tire to obtain a test tire;
Including a durability running process in which durability running is performed using this test tire,
The pretreatment process includes a tire assembly preparation process in which a tire assembly in which a pneumatic tire is incorporated in a rim is prepared, and after the tire assembly is filled with an inert gas, the tire assembly is A test method for a pneumatic tire, including a test tire preparation step in which a test tire is obtained by being allowed to stand for 10 days or more in an atmosphere of ° C or higher and 90 ° C or lower.   In the durability running process, the test tire is filled with air at a standard maximum pressure P-60 (unit kPa) or more and a standard maximum pressure P (unit kPa) or less, and the room temperature is set to 20 ° C. or more and 40 ° C. or less. The load is set to the standard maximum load F (unit kN) or more and 1.5 · F (unit kN) or less, the running speed is set to 60 km / h or more and 85 km / h or less, and the test tire is run. The test method according to claim 1.

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