JP6852309B2 - Pneumatic tire test method - Google Patents

Description

The present invention relates to a method for testing a pneumatic tire.

Tires have been evaluated for various performances. This performance evaluation is useful for improving and developing tires. JP-A-2006-170693 and JP-A-2008-203145 disclose test methods for evaluating the durability of tires. In these test methods, the durability is evaluated using a tire filled with a gas having a predetermined oxygen concentration. Further, Japanese Patent Application Laid-Open No. 2001-59800 discloses a device for measuring the gas concentration filled in a tire.

JP-A-2006-170693 JP-A-2008-203145 JP 2001-59800

Tires are filled with gas before use. The filled gas increases the internal pressure of the tire. The internal pressure of this tire causes dimensional growth of the tire. The magnitude of this dimensional growth varies from tire to tire even in tires having the same structure. Due to this dimensional growth, the internal pressure of the tire decreases. This decrease in the internal pressure of the tire causes variation from tire to tire. This variation in the internal pressure of the tire causes variation in the evaluation result of the tire test. This decrease in internal pressure reduces the evaluation accuracy of the pneumatic tire test.

An object of the present invention is to provide a tire test method for improving the evaluation accuracy of a tire test.

The test method for a pneumatic tire according to the present invention includes a gas filling step in which a tire assembly in which a tire is incorporated in a rim is filled with gas and the internal pressure of the tire assembly is set to the test internal pressure, and the above test internal pressure. An internal pressure stabilizing step in which the tire assembly is stored for a predetermined storage time, an internal pressure inspection step in which the internal pressure of the tire assembly is measured after the internal pressure stabilizing step, and a tire assembly after the internal pressure inspection step. It is provided with an internal pressure adjusting step in which the internal pressure of the tire is adjusted to the test internal pressure, and a test step in which the tire assembly adjusted to the test internal pressure is tested.

Preferably, the storage time in the internal pressure stabilizing step is 1 hour or more.

Preferably, the gas filled in the gas filling step contains at least one of oxygen, nitrogen and water components. In the internal pressure inspection step, the concentration of the component of the tire assembly is measured. In the internal pressure adjusting step, the concentration of the component measured in the internal pressure inspection step is adjusted to the concentration of the test conditions.

Preferably, the test step includes a thermal deterioration step in which the tire assembly after the internal pressure adjusting step is left in an atmosphere higher than room temperature for a predetermined standing period.

Preferably, the test step includes a running step in which the tire assembly is run after the internal pressure adjusting step.

Preferably, the test step includes a thermal deterioration step in which the tire assembly after the internal pressure adjusting step is left in an atmosphere higher than room temperature for a predetermined period of time, a gas replacement step, and the tire assembly is run. It has a running process. In the gas replacement step, the gas filled in the tire assembly is replaced after the thermal deterioration step. In the traveling process, the tire assembly after the gas replacement process is traveled.

Preferably, the test method comprises an evaluation step. The tire comprises a tread and a belt located radially inside the tread. It is provided with a tread surface on which the tread touches the road surface and a groove formed on the tread surface in the shoulder region of the tread and extending in the circumferential direction. The belt includes an inner layer and an outer layer laminated on the radial outer side of the inner layer. In the evaluation step, the tire of the tire assembly after the test step is evaluated, and delamination between the inner layer and the outer layer is evaluated inside the groove in the radial direction.

Preferably, in the thermal deterioration step, the atmospheric temperature is 50 ° C. or higher and 100 ° C. or lower, the leaving period is 1 week or longer and 9 weeks or shorter, and the oxygen concentration of the gas filled in the tire assembly is 50% or higher. is there.

Preferably, in the traveling process, the normal internal pressure of the tire is P (kPa), the internal pressure of the traveling test is Pr (kPa), the regular load of the tire is F (kN), and the test load is Fr (kN). , The total load index FI obtained by the following mathematical formula (1) is 1.05 or more and 1.30 or less.

The test method for a pneumatic tire according to the present invention includes an internal pressure stabilizing step, an internal pressure inspection step, and an internal pressure adjusting step. In the internal pressure adjusting step after the internal pressure inspection step, the internal pressure of the tire is readjusted to the test internal pressure. In this test method, the variation in the internal pressure of the tire is suppressed in the test process. The tire test internal pressure is adjusted with high precision. This test method can improve the evaluation accuracy of the tire test.

FIG. 1 is a cross-sectional view showing a part of a tire assembly used in the test method of the present invention. FIG. 2 is a flowchart of the test method of the present invention. FIG. 3 is a flowchart of the test process of FIG. FIG. 4 is an explanatory view showing the testing machine used in the traveling process of FIG. 2 together with the tire assembly. FIG. 5 is a graph showing the relationship between the elapsed time and the change in the internal pressure of the tire.

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

FIG. 1 shows a part of a tire assembly 2 used in a test method according to an embodiment of the present invention. The tire assembly 2 includes a tire 4 as a pneumatic tire and a rim 6 as a regular rim. The tire 4 is assembled to the rim 6. In FIG. 1, the vertical direction is the radial direction of the tire 4, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The regular rim here means a rim defined in the standard on which the tire 4 depends. The "standard rim" in the JATTA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

The tire 4 has a substantially symmetrical shape centered on the alternate long and short dash line CL in FIG. The alternate long and short dash line CL represents the equatorial plane of the tire 4. The straight line BL represents the bead baseline. This bead baseline is a line that defines the rim diameter of the rim 6. The tire 4 is a heavy-duty tire mounted on a truck, a bus, or the like.

The tire 4 includes a tread 8, a pair of sidewalls 10, a pair of clinches 12, a pair of beads 14, a carcass 16, a belt 18, an inner liner 20, a pair of cushion layers 22, and a pair of chafers 24. This tire 4 is a tubeless type. The tire 4 may be a tube type provided with a tube as long as it is a tire filled with air.

The tread 8 is made of crosslinked rubber. The tread 8 has a shape that is convex outward in the radial direction. The tread 8 includes a tread surface 26. The tread surface 26 is in contact with the road surface. A groove 28 is carved on the tread surface 26.

The double-headed arrow C in FIG. 1 represents the center region of the tread 8. The double-headed arrow S represents the shoulder area of the tread 8. The tread 8 includes a center region C and a pair of shoulder regions S. The center region S is located at the center of the tread 8 in the axial direction across the equatorial plane. Each shoulder region S is located outside the center region C in the axial direction. In the tire 4, for example, the center region C is a region of 25% of the width of the tread surface 26, and the pair of shoulder regions S are regions of 37.5% of the width of the tread surface 26, respectively.

In the tread 8, the groove 28c is formed in the center region C, and the groove 28s is formed in the shoulder region S. The groove 28c and the groove 28s extend in the circumferential direction. The groove 28c and the groove 28s circle the tread surface 26 in the circumferential direction. The groove 28c and the groove 28s are referred to as a main groove. A tread pattern is formed by the grooves 28c and 28s and other grooves (not shown).

Each sidewall 10 extends substantially inward in the radial direction from the end of the tread 8. The sidewall 10 is made of crosslinked rubber. Each clinch 12 is located approximately inside the sidewall 10 in the radial direction. The clinch 12 is located outside the bead 14 and the carcass 16 in the axial direction. The clinch 12 is made of crosslinked rubber having excellent wear resistance. The clinch 12 comes into contact with the flange 6f of the rim 6.

Each bead 14 is located axially inside the clinch 12. The bead 14 includes a core 30 and an apex 32. The core 30 is ring-shaped and includes a wound non-stretchable wire. A typical material for wire is steel. The apex 32 extends radially outward from the core 30. The apex 32 includes a first apex 32a and a second apex 32b. The first apex 32a is made of a high hardness crosslinked rubber. The second apex 32b is located on the outer side in the axial direction and the outer side in the radial direction with respect to the first apex 32a. The second apex 32b is softer than the first apex 32a.

The carcass 16 is composed of a carcass ply 34. The carcass ply 34 spans between the beads 14 on both sides and runs along the inside of the tread 8 and sidewall 10. The carcass ply 34 is folded around the core 30. The carcass ply 34 is composed of a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle each code makes with respect to the equatorial plane is 75 ° to 90 °. In other words, the carcass 16 has a radial structure. The material of the cord is steel and may be organic fiber. The carcass 16 may be formed from two or more carcass plies. The carcass 16 may have a so-called bias structure instead of the radial structure.

The belt 18 is located inside the tread 8 in the radial direction. The belt 18 is laminated with the carcass 16. The belt 18 extends from the vicinity of one end of the tread surface 26 to the vicinity of the other end in the axial direction. The belt 18 reinforces the carcass 16. The belt 18 includes a first layer 18a, a second layer 18b, a third layer 18c, and a fourth layer 18d. From the inside to the outside in the radial direction, the first layer 18a, the second layer 18b, the third layer 18c, and the fourth layer 18d are laminated in this order.

Although not shown, each of the first layer 18a, the second layer 18b, the third layer 18c and the fourth layer 18d consists of a large number of parallel cords and topping rubbers. Each cord is made of steel with a plating layer. This code is tilted with respect to the equatorial plane. The direction of inclination of the cord of the first layer 18a with respect to the equatorial plane is the same as the direction of inclination of the cord of the second layer 18b with respect to the equatorial plane. The direction of inclination of the cord of the second layer 18b with respect to the equatorial plane is opposite to the direction of inclination of the cord of the third layer 18c with respect to the equatorial plane. The direction of inclination of the cord of the third layer 18c with respect to the equatorial plane is the same as the direction of inclination of the cord of the fourth layer 18d with respect to the equatorial plane. In each layer, the absolute value of the angle that the cord makes with respect to the equatorial plane is 15 ° to 70 °. In this belt 18, the cords of the first layer 18a and the second layer 18b and the cords of the third layer 18c and the fourth layer 18d extend so as to intersect with each other. The belt 18 may have a plurality of layers of two or more layers.

The inner liner 20 is located inside the carcass 16. The inner liner 20 is made of crosslinked rubber having excellent air shielding properties. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 4.

Each cushion layer 22 is laminated with the carcass 16 in the vicinity of the end of the belt 18. The cushion layer 22 is located between the carcass 16 and the belt 18 in the radial direction. The cushion layer 22 is made of soft crosslinked rubber. The cushion layer 22 absorbs the stress at the end of the belt 18.

The chafer 24 is located in the vicinity of the bead 14. When the tire 4 is incorporated into the rim 6, the chafer 24 comes into contact with the seat surface of the rim 6. This contact protects the vicinity of the bead 14. The chafer 24 is integrated with the clinch 12. The material of the cheffer 24 is the same as that of the clinch 12. The chafer 24 may be separate from the clinch 12. The chafer 24 may consist of a cloth and rubber impregnated in the cloth.

FIG. 2 shows a flowchart of a test method for the tire 4. This test method includes a visual inspection step, a gas filling step, an internal pressure stabilizing step, an internal pressure inspection step, an internal pressure adjusting step, a test step, and an evaluation step.

FIG. 3 shows a flowchart of this test process. This test step includes a thermal deterioration step, a gas replacement step, and a running step.

FIG. 4 shows the drum type tester 36 used in this traveling process together with the tire assembly 2. The testing machine 36 includes a tire support portion 38 and a drum support portion 40. The tire support 38 includes a load device 42 and a spindle 44. Although not shown, the tire support portion 38 includes a steering angle imparting mechanism, a camber angle imparting mechanism, and the like.

The load device 42 can move the spindle 44 in the vertical direction. The load device 42 may load the spindle 44 with a downward test load. The load device 42 makes it possible to control the magnitude of this test load. A tire assembly 2 is detachably attached to the tip of the spindle 44. The spindle 44 is rotatable around its axis as a rotation axis. The spindle 44 is rotatable in both the forward rotation direction and the reverse rotation direction.

The drum support portion 40 includes a drum 46 and a main body 48. The drum 46 has a cylindrical shape. The outer peripheral surface of the drum 46 forms a traveling surface 50. The tire assembly 2 travels on the traveling surface 50. The drum 46 is rotatable about its axis as a rotation axis. The drum 46 is rotatable in both the forward rotation direction and the reverse rotation direction.

The test method of the tire 4 according to the present invention will be described with reference to FIGS. 2 to 4. In the visual inspection step of FIG. 2, the appearance of the tire 4 is inspected. The surface of the tire 4 is visually inspected for any abnormalities such as scratches. The tire 4 confirmed to be normal is incorporated into the rim 6 to obtain the tire assembly 2.

In the gas filling step, the tire assembly 2 is filled with gas. The internal pressure of the tire assembly 2 is set to a predetermined test internal pressure Pb (kPa). For example, the test internal pressure Pb is made higher than the normal internal pressure P of the tire 4. For example, the test internal pressure Pb is 1.25 times the normal internal pressure P. This test internal pressure Pb is predetermined as a test condition for the thermal deterioration process.

The normal internal pressure P of this test method means the internal pressure defined in the standard on which the tire 4 depends. The "maximum air pressure" in the JATTA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are the normal internal pressure P.

In this gas filling step, for example, a mixed gas of oxygen and nitrogen is filled as a gas. In this mixed gas, oxygen and nitrogen are mixed at a predetermined concentration. In the mixed gas, for example, the oxygen concentration is 90% and the nitrogen concentration is 10%. In this test internal pressure Pb, the partial pressure of oxygen is Po (kPa) and the partial pressure of nitrogen is Pn (kPa). At this time, the partial pressure Po of oxygen is 0.9 times the internal pressure Pb of the test, and the partial pressure Pn of nitrogen is 0.1 times the internal pressure Pb of the test.

The oxygen concentration at this time is calculated by the following formula from the partial pressure Po of oxygen and the test internal pressure Pb which is the total pressure of the tire assembly 2.
Oxygen concentration (%) = (Po / Pb) · 100
Similarly, the nitrogen concentration is calculated by the following formula from the partial pressure Pn of nitrogen and the internal pressure Pb of the test.
Nitrogen concentration (%) = (Pn / Pb) · 100

This mixed gas may further contain water. For example, a heatable water tank (not shown) is prepared. The water in this water tank is heated to steam. The mixed gas may contain this water vapor. Water vapor may be mixed with the mixed gas at a predetermined concentration in the test step to obtain a predetermined water concentration. In this gas filling step, the mixed gas may be filled in the tire assembly 2. Further, in this gas filling step, the tire assembly 2 may be filled with a predetermined mass of water.

In the internal pressure stabilizing step, the tire assembly 2 filled with the mixed gas and brought to the test internal pressure Pb is stored at room temperature for a predetermined storage time. This room temperature is, for example, 25 ° C. This room temperature is generally 20 ° C. or higher and 30 ° C. or lower. This storage time is, for example, 2 hours.

In the internal pressure inspection step, it is determined whether or not the elapsed time from the filling of the mixed gas is equal to or longer than the storage time in the internal pressure stabilizing step. Here, it is determined whether or not the elapsed time is 2 hours or more. When this elapsed time is 2 hours or more, the measured internal pressure Pb'(kPa) of the tire assembly 2 after the internal pressure stabilizing step is measured. The internal pressure of the tire assembly 2 set to the internal pressure Pb gradually changes with the elapsed time. There is a difference between the measured internal pressure Pb'and the test internal pressure Pb as the storage time of the internal pressure stabilizing step elapses.

In the internal pressure adjusting step, if the measured internal pressure Pb'is lower than the test internal pressure Pb, the tire assembly 2 is filled with the mixed gas. The internal pressure of the tire assembly 2 is readjusted to the test internal pressure Pb. On the other hand, if the measured internal pressure Pb'is higher than the test internal pressure Pb, the mixed gas is discharged from the tire assembly 2. The internal pressure of the tire assembly 2 is readjusted to the test internal pressure Pb. In this way, the internal pressure of the tire assembly 2 is readjusted to the test internal pressure Pb. For example, when the difference between the test internal pressure Pb and the measurement internal pressure Pb'is 1 (kPa) or more, the difference is adjusted to less than 1 (kPa). The tire assembly 2 whose test internal pressure is Pb in the internal pressure adjusting step is sent to the test step.

In the thermal deterioration step of FIG. 3, the tire assembly 2 adjusted to the test internal pressure Pb in the internal pressure adjusting step is left for a predetermined standing period in an atmosphere higher than room temperature. For example, the tire assembly 2 is left in an atmosphere of 60 ° C. for 5 weeks.

In the gas replacement step, the tire assembly 2 after this heat deterioration step is placed in an atmosphere of room temperature. The mixed gas is discharged from the tire assembly 2. Instead of this mixed gas, the tire assembly 2 is filled with air. The internal pressure of the tire assembly 2 is set to a predetermined test internal pressure Pr (kPa) of the running process. For example, this test internal pressure Pr is made higher than the normal internal pressure P of the tire 4. For example, this internal pressure Pr is 1.25 times the normal internal pressure P. This test step may further include the same steps as the internal pressure stabilizing step, the internal pressure inspection step, and the internal pressure adjusting step described above between the gas replacement step and the running step.

As shown in FIG. 4, in the traveling process, the tire assembly 2 having the test internal pressure Pr is set in the testing machine 36. The tread surface 26 of the tire 4 comes into contact with the running surface 50 of the drum 46.

The load device 42 loads the tire assembly 2 with a predetermined load Fr (kN). By this load Fr, the tire 4 is pressed against the traveling surface 50 of the drum 46. For example, this load Fr is 1.4 times the normal load. The drum 64 rotates. The tire 4 that touches the running surface 50 rotates. As a result, the tire 4 travels on the traveling surface 50. The running speed of the tire 4 is adjusted by the rotation speed of the drum 46. The tire 4 travels at a predetermined traveling speed. For example, this traveling speed is set to 80 (km / h).

In this traveling process, the appearance of the tire 4 is observed at predetermined time intervals. When the tire 4 is confirmed to be damaged, the traveling process ends. If no damage is confirmed on the tire 4, the traveling process is completed within a predetermined mileage.

In the evaluation process, the tire 4 after running is inspected for the presence or absence of delamination of the belt 18. This inspection is performed by visually confirming the appearance of the tire 4. This inspection may be performed by confirming a photograph taken by an X-ray inspection apparatus. In addition, the presence or absence of air confinement may be examined by inspection by sialography (determining the presence or absence of air confinement from the interference of sialo fringes as a vacuum). The disassembled portion of the tire 4 may be determined by comparing with the result of the inspection by this sialography. At this time, the traveling time of the traveling process until the delamination occurs is measured. It is judged that the longer the traveling time, the higher the durability against delamination.

In this evaluation step, the durability of delamination may be evaluated after traveling a predetermined distance. This predetermined distance may be determined based on the mileage of the actual vehicle on which the tire 4 is mounted. The tire 4 that has traveled this predetermined distance is evaluated for the presence or absence of delamination. Further, a plurality of test tires may be tested under the same conditions to relatively evaluate the durability of delamination. By evaluating this delamination, the effects of various improvements such as the change in the structure of the tire 4, the thickness of the inner liner 20, and the composition of the rubber composition can be confirmed with high accuracy. The knowledge obtained in this evaluation can be utilized in the development of the tire 4 having excellent durability for delamination.

FIG. 5 is a graph showing the relationship between the internal pressure of the tire assembly 2 and the time. The horizontal axis of FIG. 5 is the elapsed time T (min) since the tire is filled with air, and the vertical axis is the internal pressure Pm (kPa) of the tire assembly 2. The size of the tire 4 is "12R22.5" and the size of the rim 6 is "22.5x8.25". The tire assembly 2 was filled with air to bring the normal internal pressure P to 800 (kPa). The tire assembly 2 was left at room temperature. FIG. 5 shows the change in the internal pressure of the tire assembly 2.

As shown in FIG. 5, the internal pressure of the tire assembly 2 decreases with the passage of time. The amount of decrease in the internal pressure is particularly large in the first 30 minutes. This amount of decrease gradually decreases as the elapsed time increases, such as 60 minutes (1 hour) and 90 minutes (1 hour and 30 minutes).

This decrease in the internal pressure of the tire assembly 4 is mainly due to the dimensional growth of the tire 4. The tire 4 whose main material is rubber grows in size due to internal pressure. The dimensional growth of the tire 4 increases the volume filled with air. As a result, the internal pressure of the tire assembly 2 is reduced. This amount of change in volume gradually decreases with the passage of time. As a result, the amount of decrease in internal pressure also gradually decreases as the elapsed time increases.

This test method includes an internal pressure stabilizing step, an internal pressure inspection step, and an internal pressure adjusting step after the gas filling step. The tire assembly 2 that has undergone this internal pressure adjusting step is tested in the test step. In this test step, the tire assembly 4 is set to the test internal pressure Pb with high accuracy. In this test method, the variation in the test internal pressure Pb of the tire assembly 4 is suppressed. The variation in the evaluation result due to the variation in the test internal pressure Pb is suppressed. This test method can evaluate the tire 4 with high accuracy.

The tire 4 is a heavy-duty tire mounted on a truck, a bus, or the like. The normal internal pressure P of the tire 4 is 800 (kPa). Generally, the normal internal pressure of a passenger car tire is about 200 (kPa). The regular internal pressure P of the tire 4 is higher than that of the passenger car tire. A tire 4 having a high normal internal pressure P tends to grow in size. Further, the outer diameter of the tire 4 is larger than that of the passenger car tire. The amount of change in volume due to the dimensional growth of the tire 4 is larger than that of the passenger car tire. Since the amount of change in volume is large, the amount of decrease in internal pressure is also large. This test method can particularly improve the evaluation accuracy of the test of a heavy-duty tire such as the tire 4.

As shown in FIG. 5, the internal pressure of the tire 4 gradually decreases with the passage of time. By lengthening the storage time in the internal pressure stabilizing process, the internal pressure of the tire assembly 2 in the test process can be controlled with high accuracy. From this point of view, this storage time is preferably 1 hour or more, more preferably 2 hours or more, and particularly preferably 3 hours or more. On the other hand, from the viewpoint of efficient testing, this storage time is preferably 7 hours or less.

In this test method, the durability of delamination of the belt 18 is evaluated. The delamination of the belt 18 is affected by the oxygen concentration and the water concentration of the filled gas. This is because the oxygen and moisture of the filled gas permeate the inside of the tire to promote delamination of the belt 18.

Specifically, due to the rotation of the tire 4, the deformed portion of the tire 4 moves in the circumferential direction. The tire 4 repeats periodic deformation. Shear strain occurs between each layer of the belt 18. In particular, a large shear strain occurs between the second layer 18b and the third layer 18c, which have different inclination directions of the cord. Further, as compared with the other parts of the tread 4, the rubber in the vicinity of the belt 18 is more likely to be deteriorated at the bottom of the groove 28s due to the influence of the permeation of oxygen in the atmosphere and the repeated deformation. Due to the shear strain of the belt 18 and the deterioration of the rubber at the bottom of the groove 28s, the belt 18 is slightly peeled off. This minute peeling grows due to repeated deformation of the tire 4 during running. Eventually, delamination occurs on the belt 18.

The filled gaseous oxygen affects the delamination of the belt 18. In the evaluation of delamination of the belt 18, the oxygen concentration affects the accuracy of the evaluation. From the viewpoint of improving the evaluation accuracy, the oxygen concentration is preferably measured in this internal pressure inspection step. The oxygen concentration is measured using a known gas concentration measuring device. For example, the oxygen concentration is measured with an oxygen concentration meter manufactured by Daiichi Thermal Research Institute. This oxygen concentration may be measured with a small amount of the filled gas extracted. In this internal pressure adjusting step, the oxygen concentration is preferably adjusted. For example, a mixed gas having a higher oxygen concentration than the filled gas and a mixed gas having a lower oxygen concentration are prepared. In the internal pressure adjusting step, the oxygen concentration can be adjusted by replacing a part of the filled gas with a mixed gas having a high oxygen concentration or a mixed gas having a low oxygen concentration. Further, the nitrogen concentration may be measured in the internal pressure inspection step. The nitrogen concentration may be adjusted in the internal pressure adjusting step. The nitrogen concentration is measured by a known gas concentration measuring device. Nitrogen concentration can be adjusted in the same way as oxygen concentration. Adjusting the concentration of an inert gas such as nitrogen contributes to further improvement of evaluation accuracy.

Moisture affects the delamination of the belt 18. In the evaluation of delamination of the belt 18, the water concentration of the filled gas affects the accuracy of the evaluation. From the viewpoint of improving the evaluation accuracy, the water concentration is preferably measured in the internal pressure inspection step. Moisture concentration is measured using a known moisture meter. For example, the water concentration is measured with a moisture meter manufactured by Michel Japan. In this internal pressure adjusting step, the water concentration is preferably adjusted. For example, a mixed gas having a higher water concentration than the filled gas and a mixed gas having a lower water concentration are prepared. In the internal pressure adjusting step, the water concentration can be adjusted by replacing a part of the filled gas with a mixed gas having a high water concentration or a mixed gas having a low water concentration.

Here, the delamination of the belt 18 is illustrated, but the evaluation accuracy can be improved by adjusting the oxygen concentration, the nitrogen concentration and the water concentration in the thermal deterioration test and the running durability test of other tires.

Further, for example, in the evaluation of durability or thermal deterioration due to repeated deformation of the tread 8 of the tire 4, the tire assembly 2 may be filled with nitrogen. By using nitrogen, deterioration of the inside of the tire 4 due to oxygen and moisture is suppressed. Thereby, the durability of the tread 8 of the tire 4 can be evaluated by eliminating the influence of oxygen and moisture. In such an evaluation, the nitrogen concentration particularly affects the accuracy of the evaluation. From this point of view, the nitrogen concentration may be measured in the internal pressure inspection step. The nitrogen concentration may be adjusted in the internal pressure adjusting step.

In this gas filling step and the internal pressure adjusting step, the test internal pressure Pb is set to be equal to or higher than the normal internal pressure P of the tire 4. The high internal pressure Pb promotes the penetration of oxygen and moisture into the tire 4. The high internal pressure Pb promotes the occurrence of delamination of the belt 18. From the viewpoint of promoting delamination of the belt 18, the test internal pressure Pb is preferably 1.0 times or more, more preferably 1.2 times or more the normal internal pressure P. On the other hand, in the tire 4 in which the test pressure Pb is too high, delamination of the belt 18 proceeds rapidly. In the subsequent running process, the tire 4 deteriorates rapidly. Sudden deterioration of the tire 4 lowers the evaluation accuracy of the durability of the tire 4. From this point of view, the test internal pressure Pb is preferably 1.4 times or less of the normal internal pressure P, and more preferably 1.3 times or less.

In the evaluation of delamination of the belt 18, the atmospheric temperature in the thermal deterioration step is made higher than room temperature at room temperature, thereby promoting the occurrence and progress of this delamination. From the viewpoint of promoting this peeling, the atmospheric temperature in the thermal deterioration step is preferably 50 ° C. or higher, more preferably 55 ° C. or higher. On the other hand, if this temperature is too high, the rubber deteriorates rapidly. Rapid deterioration reduces the accuracy of delamination evaluation of the belt 18. From this point of view, this temperature is preferably 100 ° C. or lower, more preferably 95 ° C. or lower.

In this heat deterioration step, oxygen, moisture, and the like are sufficiently permeated into the tire 4 to promote the occurrence and progress of peeling of the belt 18. From the viewpoint of promoting this peeling, the leaving period of the heat deterioration step is preferably 1 week or longer, more preferably 2 weeks or longer, and particularly preferably 3 weeks or longer. On the other hand, if this leaving period is made longer than necessary, efficient test evaluation cannot be performed. From this viewpoint, the leaving period is preferably 9 weeks or less, more preferably 8 weeks or less, and particularly preferably 7 weeks or less.

Further, from the viewpoint of permeating oxygen into the tire 4 to promote peeling of the belt 18, the oxygen concentration is preferably 50% or more, more preferably 60% or more. This oxygen concentration is 100% or less.

This test step includes a thermal degradation step. In the thermal deterioration step, the tire assembly 2 is left for a predetermined period of time in an atmosphere higher than room temperature. The thermal deterioration step accelerates the deterioration of the tire 4. By providing this thermal deterioration process, the time required for this traveling process can be shortened. By providing this thermal deterioration step, evaluation can be performed in a short time.

This test process includes a running process. By providing this traveling process, the reproducibility of the phenomenon that occurs in the traveling tire 4 is excellent. Since this test step includes a running step, the evaluation of delamination of the belt 8 is facilitated.

In this traveling process, the test internal pressure Pr is higher than the normal internal pressure P of the tire 4. The tire 4 having a high test internal pressure Pr is harder than the state in which the gas is filled with the normal internal pressure P. With the hard tire 4, the impact when the tread surface 26 touches the traveling surface 50 is large. In the hard tire 4, the occurrence of delamination of the belt 18 is promoted. From the viewpoint of promoting this peeling, the test internal pressure Pr is preferably 1.1 times or more, more preferably 1.2 times or more the normal internal pressure P. On the other hand, in the tire 4 in which the test pressure Pr is too high, delamination of the belt 18 proceeds rapidly. In the traveling process, the tire 4 deteriorates rapidly. Sudden deterioration of the tire 4 causes damage to the tire 4 other than delamination of the belt 18. The evaluation accuracy of this delamination is reduced. From this viewpoint, the test internal pressure Pr is preferably 2.1 times or less of the normal internal pressure P, and more preferably 2.0 times or less.

In this traveling process, a load Fr in the radial direction is applied to the tire 4 and pressed against the traveling surface 50. By loading this load Fr, a large load is applied to the tread 8. Due to this load Fr, delamination of the belt 18 is likely to occur. From this viewpoint, the load Fr is preferably 1.1 times or more, more preferably 1.2 times or more, and particularly preferably 1.3 times or more the normal load F. On the other hand, when a large load Fr is applied to the tire 4, the distortion of the ground contact portion of the tread 8 becomes large. Due to this large distortion, the heat generated by the tire 4 increases. This increase in heat generation causes damage other than delamination of the belt 18. This hinders the evaluation of delamination. From this viewpoint, the load Fr is preferably 2.0 times or less of the normal load F, more preferably 1.9 times or less, and particularly preferably 1.8 times or less.

In the present specification, the normal load F means the load defined in the standard on which the tire 4 depends. The "maximum load capacity" in the JATTA standard, the "maximum value" in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads F.

By increasing the traveling speed of the tire 4 in this traveling process, delamination of the belt 18 is promoted. By promoting this delamination, test evaluation can be performed efficiently. From this point of view, the traveling speed of the test tire is preferably 60 km / h or more, and more preferably 70 km / h or more. On the other hand, if the traveling speed is too high, the heat generated by the tire 4 becomes large. This increase in heat generation causes damage other than delamination of the belt 18. This hinders the evaluation of delamination. From this point of view, the traveling speed is preferably 100 km / h or less, and more preferably 90 km / h or less.

This test step includes a gas replacement step between the thermal deterioration step and the running step. In this gas replacement step, the gas that accelerates the deterioration of the tire 4 is replaced with normal air. As a result, the tire 4 is prevented from being rapidly deteriorated in the traveling process. This method is provided with a gas replacement step, so that the evaluation accuracy of the tire 4 is improved. The gas replaced in this gas replacement step is not limited to air. This gas may be, for example, a mixed gas containing nitrogen or oxygen as a main component.

In this traveling process, the total load index FI can be obtained from the regular internal pressure P, the traveling test internal pressure Pr, the regular load F, and the test load Fr by the following mathematical formula (1).

In the tire 4 in which the total load index FI is too small, damage other than delamination of the belt 18 occurs. The occurrence of damage other than this peeling hinders the evaluation of delamination of the belt 18. On the other hand, even if the tire 4 has an excessively large total load index FI, damage other than delamination of the belt 18 occurs. From the viewpoint of appropriately evaluating the delamination of the belt 18, the total load index FI is preferably 1.05 or more. From the same viewpoint, this total load index FI is preferably 1.30 or less.

This test step is not limited to the delamination test. This test step includes a thermal deterioration step and a running step, but may consist of either step. This test step may consist of a thermal deterioration step. Deterioration of the tire 4 may be evaluated by this thermal deterioration step. By managing the internal pressure of the tire assembly 2 in this thermal deterioration step with high accuracy, the evaluation accuracy of the thermal deterioration of the tire 4 can be improved. Further, by controlling the oxygen concentration, nitrogen concentration, water concentration and the like of the gas filled in the tire assembly with high accuracy, the evaluation accuracy of thermal deterioration of the tire 4 can be improved.

Similarly, the test process may consist of a running process. The running durability of the tire 4 may be evaluated by this running process. By managing the internal pressure of the tire assembly 2 in this traveling process with high accuracy, the evaluation accuracy of the traveling durability of the tire 4 can be improved. By managing the oxygen concentration, nitrogen concentration, water concentration, and the like of the gas filled in the tire assembly 2 with high accuracy, the evaluation accuracy of the running durability of the tire 4 can be improved.

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

[Heat deterioration test]
Test tires were prepared. This tire had the structure shown in FIG. This tire size was "12R22.5 152 / 149L SP391 T / L". The normal internal pressure of this tire was 800 kPa. This tire is a heavy-duty tire mounted on trucks and buses. This tire was assembled on a regular rim "22.5x8.25" to form a tire assembly. Five tire assemblies were prepared.

These five tire assemblies were subjected to a thermal deterioration test. This thermal deterioration test includes a gas filling step, an internal pressure stabilizing step, an internal pressure inspection step, an internal pressure adjusting step, a thermal deterioration step, and an evaluation step of the test method shown in FIG. This thermal deterioration test does not include a gas replacement process and a running process.

In this gas filling step, a mixed gas was prepared. This mixed gas had an oxygen concentration of 95% and a nitrogen concentration of 5%. This mixed gas was filled in the tire assembly at an internal pressure of 800 kPa. In the internal pressure stabilization step, the tire assembly was stored at room temperature of 25 ° C. for 1 hour. In the internal pressure inspection process, the internal pressure of the tire assembly after the internal pressure stabilization process was measured. In the internal pressure adjusting step, the tire assembly was filled with the mixed gas, and the internal pressure was readjusted to 800 kPa. Then, in the heat deterioration step, the tire assembly was put into a dry heat oven. The tire assembly was thermally degraded at 80 ° C. for 4 weeks.

In this evaluation step, the peeling between the carcass and the belt was evaluated in the tire assembly after the heat deterioration step. A test sample was taken from this tire. This sample was cut to a width of 25 mm, and the peeling drag (unit: N / 25 mm) at the interface between the carcass and the belt was measured. The peeling drag was measured at a speed of 50 (mm / sec) using a tensile tester manufactured by Intesco.

Table 1 shows the internal pressure measured in the internal pressure inspection process of each tire, the peeling drag measured in the evaluation process, the average value of the peeling drag, and the standard deviation of the tires E1 to E5. There is. In Table 1, the peeling drag, the average value of the peeling drag, and the standard deviation are shown as an index (%) with the average value of the peeling drag of the tires E1 to E5 as 100.

[Heat deterioration comparison test]
The peeling between the carcass and the belt of the five tires was evaluated in the same manner as the above-mentioned thermal deterioration test except that the internal pressure stabilizing step, the internal pressure inspection step and the internal pressure adjusting step were not provided. In this test, a thermal degradation step was performed immediately after the gas filling step. After that, the peeling drag was measured in the evaluation step. Table 1 shows the peeling drag measured in the evaluation process of each tire, the average value of the peeling drag, and the standard deviation of the tires C1 to C5. In Table 1, the peeling drag, the average value and the standard deviation of the peeling drag of the tires C1 to C5 are shown as an index (%) with the average value of the peeling drag of the tires E1 to E5 as 100.

As shown in Table 1, the variation in the peeling drag of the tires E1 to E5 is smaller than that of the tires C1 to C5. The average peeling drag of the tires E1 to E5 is larger than that of the tires C1 to C5 because the mixed gas (oxygen) is further filled in the internal pressure adjusting step.

As shown in Table 1, the test method according to the present invention has higher evaluation accuracy than the test method of the comparative example. From this evaluation result, the superiority of the present invention is clear.

[Delamination test]
Four types of tires were prepared. Both tires have the same belts as in FIG. All of these tire sizes were "12R22.5". These tires differ in the durability of delamination of the belt. The tire S4 also had the best durability for delamination of the belt in the actual vehicle. Tire S3 was superior to tires S2 and S1. Tire S2 was superior to tire S1.

[Example]
The delamination of the belt was evaluated by the test method shown in FIG. In the tires S1 to S3, delamination of the belt was confirmed. In tire S4, belt edge looseness, which is peeling at the end of the belt, was confirmed without belt delamination occurring. The mileage until the belt edge looseness was confirmed on the tire S4 was set to 100, and the mileage until the belt delamination was confirmed on the tires S1 to S3 was indexed. This index is shown in Table 2. The larger the value of this index, the longer the mileage. The larger the index, the more preferable the evaluation result.

[Comparison example]
The delamination of the belt was evaluated in the same manner as in the test method of the example except that the internal pressure stabilizing step, the internal pressure inspection step, and the internal pressure adjusting step were not provided. In this test as well, the belt delamination was confirmed in the tires S1 to S3. In tire S4, belt edge looseness, which is peeling at the end of the belt, was confirmed without belt delamination occurring. The mileage until the belt edge looseness was confirmed on the tire S4 was set to 100, and the mileage until the belt delamination was confirmed on the tires S1 to S3 was indexed. The index is shown in Table 2.

The evaluation results of the examples in Table 2 are in agreement with the evaluation of belt delamination in an actual vehicle. On the other hand, as for the evaluation results of the comparative examples, the evaluation results of the implementation and the evaluation results of the tires S2 and S3 were reversed.

A method for testing the durability of delamination of a belt has not been established so far. This test method can evaluate the durability of delamination of the belt efficiently and with high accuracy. From this evaluation result, the superiority of the present invention is clear.

Here, the test method for delamination of the belt has been mainly described, but the present invention is not limited to this. The test method according to the present invention can be applied to various tests in which an air-filled tire is used. The present invention can be applied to various pneumatic tire test methods.

2 ... Tire assembly 4 ... Tire 6 ... Rim 8 ... Tread 18 ... Band 20 ... Inner liner 26 ... Tread surface 28 ... Groove

Claims (1)

A gas filling process in which the tire assembly in which the tire is incorporated in the rim is filled with gas and the internal pressure of the tire assembly is set to the test internal pressure.
An internal pressure stabilization step in which the tire assembly subjected to the test internal pressure is stored for a predetermined storage time,
An internal pressure inspection step in which the internal pressure of the tire assembly after the internal pressure stabilization step is measured, and
An internal pressure adjusting step in which the internal pressure of the tire assembly after the internal pressure inspection step is adjusted to the test internal pressure, and
It is equipped with a test process in which the tire assembly adjusted to the test internal pressure is tested.
The storage time in the internal pressure stabilizing step is 1 hour.
The above test process
A thermal deterioration step in which the tire assembly after the internal pressure adjusting step is left in an atmosphere higher than room temperature for a predetermined period of time, and
Evaluation process in which the peeling drag at the interface between the carcass and belt of the tire is measured
A test method for pneumatic tires.

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