Evaluation method of durability performance of tire

Abstract

To provide an evaluation method of durability performance of a tire, capable of rapidly and accurately evaluating durability performance of a heavy load duty tire incorporating an RFID tag.SOLUTION: An evaluation method for evaluating durability performance of a heavy load duty tire having a tread and incorporating an RFID tag includes reclaiming the tread worn by travel when a period from start of use to reach of a use limit is set as a period of service so as to define a second period of service after reclamation in addition to a first period of service before reclamation. The evaluation method includes a processing step S2 and a travel step S4. In the processing step S2, heat deterioration processing is performed for a test tire T so as to generate on the test tire T, a change of a state corresponding to a change of a state of the tire in the first period of service.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the durability performance of a tire, and more particularly to a method for evaluating the durability performance of a heavy-duty tire having an RFID tag built therein. [Background technology]

[0002] It has been proposed to embed an RFID (Radio Frequency Identification) tag in a tire in order to manage data such as tire manufacturing management, customer information, driving history, etc. Various studies have been conducted on the technology of embedding an RFID tag in a tire (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-046057 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a method for evaluating the durability of a tire, which can quickly and accurately evaluate the durability of a heavy-duty tire having an RFID tag built in. [Means for solving the problem]

[0005] The method for evaluating the durability performance of a tire according to the present invention is a method for evaluating the durability performance of a heavy-duty tire with an RFID tag built in, which has a tread and, when a usage period is defined as a period from the start of use to the end of use, a second usage period after retreading is set in addition to a first usage period before retreading by retreading the tread worn by running. This evaluation method includes a processing step of performing a heat deterioration treatment on a test tire with an RFID tag built in, and a running step of performing a running test on the test tire that has been subjected to the processing step. The test tire is a tire that has no running history. In the processing step, the heat deterioration treatment is performed on the test tire so that a state change equivalent to the state change of the tire in the first usage period occurs in the test tire.

[0006] In another aspect, a method for evaluating durability performance of a tire according to one embodiment of the present invention is a method for evaluating durability performance of a heavy-duty tire with an RFID tag built in, which has a tread and, when a usage period is defined as a period from the start of use to the reaching of a usage limit, sets a first usage period before retreading and a second usage period after retreading by retreading the tread worn by running. This evaluation method includes a running step of conducting a running test on a test tire with the RFID tag built in. The test tire is the tire that has passed the first usage period, or the tire whose tread has been retreaded after the first usage period has passed. Effect of the Invention

[0007] According to the present invention, a method for evaluating the durability of a tire can be obtained, which can quickly and accurately evaluate the durability of a heavy-duty tire having an RFID tag built in. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a heavy duty tire. [Diagram 2] FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 2 is an enlarged cross-sectional view showing a portion of the tread. [Diagram 5] FIG. 2 is a cross-sectional view showing a part of a retread tire obtained by retreading the tire of FIG. 1. [Figure 6] 1A to 1C are diagrams illustrating a method for manufacturing a retread tire. [Figure 7] FIG. 2 is a schematic side view showing an overview of a running test device. [Figure 8] FIG. 8 is a schematic front view of the running test device of FIG. 7. [Figure 9] FIG. 1 is a flow diagram of a method for evaluating tire durability performance according to one embodiment of the present invention. [Figure 10] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state.

[0010] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0011] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0012] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0013] In the present invention, the complex modulus E* of an element made of crosslinked rubber among elements constituting a tire is measured using a viscoelasticity spectrometer in accordance with the provisions of JIS K 6394. The measurement conditions are as follows. Initial distortion = 10% Dynamic distortion = ±1% Frequency = 10Hz Mode = Decompression mode Temperature=70℃ In this measurement, a test piece (length 40 mm x width 4 mm x thickness 1 mm) is sampled from the tire. The length direction of the test piece is aligned with the circumferential direction of the tire. If it is not possible to sample a test piece from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the complex modulus E* is represented by the complex modulus E* at 70°C.

[0014] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0015] [Foundations underlying the present invention] Tire treads wear down as the tires are driven. In some cases, heavy-duty tires fitted to trucks and buses have their worn tread retreaded and reused. As parts other than the tread are not retreaded, the tires are used as is even after retreading. When reusing tires as retreaded tires, it is necessary to understand their durability performance after retreading.

[0016] Toward the creation of a recycling-oriented business society, the recycling and reuse of tires is being considered as a way to make effective use of resources. As part of this consideration, the adoption of the aforementioned RFID tags is being promoted in order to identify individual tires and grasp their history information.

[0017] RFID tags are foreign objects to tires, and there is a risk that damage may occur originating from the RFID tag or that the RFID tag itself may be destroyed. Therefore, when applying RFID tags to retreaded tires, it is necessary to understand the impact of the RFID tag on durability performance not only in the first period of use before retreading, but also in the second period of use after retreading.

[0018] In actual vehicle driving tests, where test tires are actually mounted on vehicles and evaluated, it takes a considerable amount of time to obtain results. It is difficult to obtain reproducible results because the state of tire deterioration is affected by the weather. In drum driving tests, where test tires are run on a drum, it is possible to run the test tires until they need to be retreaded, but it is not possible to reflect the thermal deterioration that occurs in tires when running on an actual vehicle on the test tires.

[0019] Therefore, the inventors have conducted intensive research into technology that can quickly and accurately evaluate the durability performance of heavy-duty tires equipped with RFID tags, in particular the durability performance during the second period of use after retreading, and have completed the present invention, which is described below.

[0020] [Overview of the embodiment of the present invention] [Configuration 1] One embodiment of the present invention relates to a method for evaluating the durability performance of a heavy-duty tire having an RFID tag built in, which has a tread and, when the usage period is defined as the period from the start of use to the reaching of its usage limit, by retreading the tread that has worn down through driving, a second usage period after retreading is set in addition to a first usage period before retreading, and the method includes a processing step of performing a thermal degradation treatment on a test tire having an RFID tag built in, and a running step of conducting a running test on the test tire that has been subjected to the processing step, wherein the test tire is a tire that has no running history, and in the processing step, the thermal degradation treatment is performed on the test tire so that a change in condition occurs in the test tire that is equivalent to the change in condition of the tire during the first usage period.

[0021] According to the tire durability evaluation method thus established, the durability of heavy-duty tires incorporating RFID tags can be evaluated quickly and accurately.

[0022] [Configuration 2] Preferably, the method for evaluating durability performance of a tire described in the above-mentioned [Configuration 1] further includes a confirmation step of confirming whether the data written in the RFID tag of the test tire that has been subjected to the running step can be read.

[0023] [Configuration 3] Preferably, in the method for evaluating durability performance of a tire described in the above-mentioned [Configuration 1] or [Configuration 2], the change in state of the test tire in the treatment step is represented by a heat aging resistance index of the tread represented by the following formula (1), and the heat aging resistance index of the tread is 14 or more and 60 or less. Heat aging resistance index = | (complex modulus of elasticity E* of tread after heat aging treatment - complex modulus of elasticity E* of tread before heat aging treatment) | / complex modulus of elasticity E* of tread before heat aging treatment × 100 Formula (1)

[0024] [Configuration 4] Preferably, in the method for evaluating durability performance of a tire described in any one of the above-mentioned [Configuration 1] to [Configuration 3], the running speed of the test tire in the running test is 10 km / h or more and 40 km / h or less, the load applied to the test tire is 200% or more and 300% or less of the normal load, and the internal pressure of the test tire is 100% or more and 130% or less of the normal internal pressure.

[0025] [Configuration 5] Preferably, in the method for evaluating durability performance of a tire according to any one of [Configuration 1] to [Configuration 4] above, the running time of the test tire set in the running test is 250 hours or more and 600 hours or less.

[0026] [Configuration 6] In another aspect, one embodiment of the present invention relates to a method for evaluating the durability performance of a tire, which has a tread and has an RFID tag built in, and where the usage period is the period from the start of use to the reaching of the usage limit, by retreading the tread that has worn down through driving, a first usage period before retreading and a second usage period after retreading are set, the method including a running step of conducting a running test on a test tire having the RFID tag built in, and the test tire is a tire that has passed the first usage period, or a tire whose tread has been retreaded after the first usage period has passed.

[0027] According to the tire durability evaluation method thus established, the durability of heavy-duty tires incorporating RFID tags can be evaluated quickly and accurately.

[0028] [Configuration 7] Preferably, the method for evaluating tire durability performance described in the above-mentioned [Configuration 6] further includes a confirmation step of confirming whether the data written in the RFID tag can be read for the test tire that has been subjected to the running step.

[0029] [Configuration 8] Preferably, in the method for evaluating durability performance of a tire described in the above-mentioned [Configuration 6] or [Configuration 7], the running speed of the test tire in the running test is 10 km / h or more and 40 km / h or less, the load applied to the test tire is 200% or more and 300% or less of the normal load, and the internal pressure of the test tire is 100% or more and 130% or less of the normal internal pressure.

[0030] [Configuration 9] Preferably, in the method for evaluating durability performance of a tire according to any one of [Configuration 6] to [Configuration 8] above, the running time of the test tire set in the running test is 250 hours or more and 600 hours or less.

[0031] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0032] A "method for evaluating tire durability performance" (hereinafter referred to as the "evaluation method") according to one embodiment of the present invention is a method for evaluating the durability performance of a heavy-duty tire equipped with an RFID tag, in which a second usage period after retreading is set in addition to a first usage period before retreading by retreading the tread worn down by driving.

[0033] The first usage period is the period from the start of use until the tread wears down and the tire reaches its usage limit. The usage limit of a tire means a state in which the tread has worn down to the point where the wear indicator makes contact with the road surface, or a state in which uneven wear has progressed to the point where further use is difficult. The first usage period is also called the first life of a tire. A tire in the first usage period is also called a first-life tire.

[0034] The second use period is the period from when the tread is retreaded and use resumes until the tread wears again and the tire reaches its use limit. The second use period is also called the second tire life. A tire in the second use period is also called a second-life tire. A tire in the second use period is also called a retreaded tire because the tread has been retreaded.

[0035] [Heavy-duty tires with built-in RFID] FIG 1 shows an example of a tire 2 that is a target of an evaluation method according to one embodiment of the present invention. This tire 2 is an example of a first-life tire. This tire 2 is mounted on vehicles such as trucks and buses. This tire 2 has an RFID tag 30 built in. This tire 2 is a heavy-duty tire with an RFID tag built in.

[0036] FIG. 1 shows a portion of a cross section (hereinafter, meridian cross section) of the tire 2 taken along a plane including the rotation axis of the tire 2. The direction indicated by the double-headed arrow AD in FIG. 1 is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double-headed arrow RD is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. The dashed dotted line CL extending in the radial direction in FIG. 1 represents the equatorial plane of the tire 2.

[0037] The tire 2 is mounted on a rim R. The inside of the tire 2 is filled with air, for example, and the internal pressure is adjusted. Although not described in detail, the rim R is a regular rim.

[0038] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of chafers 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a pair of cushion layers 16 , an inner liner 18 , and a tag member 20 .

[0039] Each sidewall 6 is continuous with an edge of the tread 4. The sidewalls 6 are located axially outward of the carcass 12. The sidewalls 6 are made of crosslinked rubber.

[0040] The position indicated by the symbol PW is the position where the tire 2 in a normal state has the maximum width. The maximum width position PW is also the axial outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the maximum width position PW is determined based on a virtual outer surface obtained by assuming that there is no decoration.

[0041] Each chafer 8 is located radially inside the sidewall 6. The chafers 8 contact the rim R. The chafers 8 are made of crosslinked rubber.

[0042] Each bead 10 is located axially inside the chafer 8. The beads 10 are located radially inside the sidewall 6. The bead 10 includes a core 22 and an apex 24. Although not shown, the core 22 includes a steel wire wound in the circumferential direction. The apex 24 is located radially outside the core 22. The apex 24 is tapered. The apex 24 is made of hard crosslinked rubber.

[0043] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of chafers 8. The carcass 12 bridges between a pair of beads 10, that is, a first bead 10 and a second bead 10. The carcass 12 includes at least one carcass ply 26. The carcass 12 of the tire 2 is made up of one carcass ply 26. The carcass ply 26 is turned up from the axially inner side to the axially outer side at each bead 10. The end of the turned up carcass ply 26 is located radially inner side of the outer end of the chafer 8. Although not shown, the carcass ply 26 includes a number of carcass cords arranged in parallel. These carcass cords intersect with the equator plane. The carcass 12 has a radial structure. The carcass cord of this tire 2 is a steel cord.

[0044] The belt 14 is located radially inside the tread 4. The belt 14 is laminated on the carcass 12. The belt 14 includes a plurality of belt plies 28 laminated in the radial direction. The belt 14 of the tire 2 includes four belt plies 28. The four belt plies 28 are a first belt ply 28A, a second belt ply 28B, a third belt ply 28C, and a fourth belt ply 28D, which are arranged in this order in the radial direction. The first belt ply 28A is located at the innermost position in the radial direction. The second belt ply 28B has the widest width, and the fourth belt ply 28D has the narrowest width.

[0045] Although not shown, each belt ply 28 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cords are steel cords.

[0046] Each cushioning layer 16 is located at an end of the belt 14, between the belt 14 and the carcass 12. The cushioning layer 16 is made of a soft crosslinked rubber.

[0047] The inner liner 18 is positioned inside the carcass 12. The inner liner 18 constitutes the inner surface of the tire 2. The inner liner 18 is made of crosslinked rubber with excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0048] The tag member 20 is located radially inward of the maximum width position PW of the tire 2. The tag member 20 is located radially outward of the end of the turned-up carcass ply 26. The tag member 20 is located between the bead 10 and the chafer 8.

[0049] Fig. 2 is a plan view of the tag member 20. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. The tag member 20 is plate-shaped. The tag member 20 is disposed so that the length direction of the tag member 20 is aligned with the circumferential direction of the tire 2.

[0050] The tag member 20 includes an RFID tag 30. The RFID tag 30 is located at the center of the tag member 20. In Fig. 3, the RFID tag 30 is shown by a solid line for convenience of explanation, but is entirely covered with a protective body 32. The tag member 20 is composed of the protective body 32 and the RFID tag 30 wrapped in the protective body 32. The protective body 32 is a cross-linked product of a rubber composition.

[0051] Although not described in detail, the RFID tag 30 is a small and lightweight electronic component consisting of a semiconductor chip 34 that integrates a transmitting / receiving circuit, a control circuit, a memory, etc., and an antenna 36. When the RFID tag 30 receives an interrogation radio wave, it uses the received signal as electrical energy and transmits the various data stored in the memory as a response radio wave. This RFID tag 30 is a type of passive radio frequency identification transponder.

[0052] The tag member 20 is a plate-shaped member in which the RFID tag 30 is covered with crosslinked rubber. From the viewpoints of reducing the risk of damage to the RFID tag 30 and creating a good communication environment, the thickness of the tag member 20 in the tire 2 is preferably 1.0 mm or more and 2.5 mm or less. The length TL of the tag member 20 before being embedded in the tire 2 is 60 mm or more and 80 mm or less. The width TW is 10 mm or more and 20 mm or less.

[0053] The RFID tag 30 is located radially inward of the maximum width position PW of the tire 2. The RFID tag 30 is located radially outward of the end of the turned-up carcass ply 26. The RFID tag 30 is located between the bead 10 and the chafer 8. In this tire 2, the position of the RFID tag 30 is not limited to the position shown in Fig. 1. The position of the RFID tag 30 is determined taking into consideration the effect on durability performance of the tire 2 and the communication environment. The RFID tag 30 may be disposed between the sidewall 6 and the bead 10. The RFID tag 30 may be disposed radially outward of the maximum width position PW of the tire 2. The RFID tag 30 may be disposed between the sidewall 6 and the carcass 12. An evaluation method, described below, determines whether the location of the RFID tag 30 is optimal.

[0054] The tread 4 is located radially outside the carcass 12. The tread 4 is located radially outside the tire 2 and extends in the circumferential direction. The outer peripheral surface of the tread 4 is a tread surface 38. The tire 2 comes into contact with the road surface at the tread surface 38. The tread 4 has the tread surface 38 that comes into contact with the road surface.

[0055] 1, the symbol TE indicates an end of the tread surface 38. The axial distance from one end TE of the tread surface 38 to the other end TE is the width of the tread surface 38.

[0056] The tread 4 includes a cap portion 40 and a base portion 42. The cap portion 40 comes into contact with the road surface. The cap portion 40 includes a tread surface 38. The cap portion 40 is made of crosslinked rubber that takes into consideration wear resistance and grip performance. The base portion 42 is located radially inside the cap portion 40. The base portion 42 is entirely covered by the cap portion 40. The base portion 42 is made of cross-linked rubber that is designed to generate low heat. The base portion 42 is not intended to be exposed and to come into contact with the road surface.

[0057] A plurality of circumferential grooves 44 aligned in the axial direction are formed in the tread 4. Each of the circumferential grooves 44 extends continuously in the circumferential direction. Four circumferential grooves 44 are formed in the tread 4 of this tire 2.

[0058] 4 shows a cross section of the circumferential groove 44. This cross section of the circumferential groove 44 is a cross section of a middle circumferential groove, which will be described later. The circumferential groove 44 has a pair of wall surfaces 44W including a groove mouth 44M, and a bottom surface 44B including a groove bottom 44T. The groove width of the circumferential groove 44 is represented by the distance between the pair of wall surfaces 44W, that is, the first wall surface 44W and the second wall surface 44W, that is, the wall surface distance.

[0059] 4, the length indicated by the double arrow WG is the groove width at the groove mouth 44M of the circumferential groove 44. The groove width WG of the circumferential groove 44 is represented by the shortest distance between a pair of edges 44E that define the groove mouth 44M. The length indicated by the double-headed arrow DG is the groove depth of the circumferential groove 44. The groove depth DG of the circumferential groove 44 is represented by the shortest distance from the line segment connecting the left and right edges 44E to the groove bottom 44T. When a protrusion such as a weighing indicator is provided at the bottom of the groove, the groove depth is expressed as the groove depth at a position where the protrusion is not provided, or the groove depth obtained assuming that the protrusion is not provided. The position, groove width, and groove depth of the circumferential groove 44 are determined appropriately according to the specifications of the tire 2. In the case of a heavy-duty tire, from the viewpoint of contributing to drainage and traction performance, the groove width WG of the circumferential groove 44 is set in the range of 1 to 10% of the width WT of the tread surface 38. The groove depth DG of the circumferential groove 44 is set in the range of 13 to 25 mm.

[0060] The tread 4 of the tire 2 has four circumferential grooves 44. Of the four circumferential grooves 44, the two circumferential grooves 44 located on the outermost sides in the axial direction are shoulder circumferential grooves 44s. The circumferential grooves 44 located axially inward of the shoulder circumferential grooves 44s are middle circumferential grooves 44m.

[0061] As shown in FIG. 1, a groove bottom 44mT of the middle circumferential groove 44m of the tire 2 is provided with a protrusion 46. As described above, the tread 4 wears. The circumferential grooves 44 become shallower, and the tread 4 eventually loses its function. Therefore, the tread 4 is retreaded or replaced with a new tire 2 before the tread 4 loses its function. The protrusions 46 are members that indicate the timing to retread the tread 4 or to replace the tire 2 with a new one. When the protrusions 46 are exposed and in contact with the road surface, this indicates that the tire 2 has reached its limit of use. The protrusions 46 are also called wear indicators.

[0062] 4, the length indicated by the double-headed arrow HW is the height of the protrusion 46. The height of the protrusion 46 is set in the range of 1.6 to 2.0 mm.

[0063] As mentioned above, the tread wears out. In the case of heavy duty tires, if the tire is a first-life tire, the tread is retreaded. If the tire is a second-life tire, i.e. a retreaded tire, the tire is replaced with a new tire. The tire 2 shown in Figure 1 is a first-life tire. When the tread 4 wears down and the condition of the tire 2 reaches its limit of use, the tread 4 is retreaded.

[0064] [Retreaded tires and their manufacturing method] Fig. 5 shows an example of a retread tire 52 that is the subject of the evaluation method of the present invention. This tire 52 is obtained by retreading the tread 4 of the tire 2 shown in Fig. 1. This tire 52 is also called a second-life tire. 5 shows a portion of a meridian cross section of a retread tire 52. The tire 52 includes a base tire 54 and a tread 56. Other than the tread 56 of the tire 52, that is, the base tire 54, has the same configuration as the configuration of the portion corresponding to the base tire 54 in the tire 2 shown in FIG. Since the RFID tag 30 is already embedded in the base tire 54, this tire 52 is also a heavy-duty tire having an RFID tag 30 embedded therein, like the tire 2 described above.

[0065] FIG. 6 is a diagram illustrating a manufacturing method for a retread tire 52. When retreading a tread 4, the tread 4 is scraped off, for example, by buffing. As a result, a base tire 54 having a molding surface 58 is formed, as shown in FIG. 6. A new tread 56 is attached to this molding surface 58. Since this manufacturing method is a remolding type manufacturing method, the unvulcanized tread 56 molded in a sheet shape is attached to the base tire 54. The tread 56 is pressurized and heated by a mold (not shown), and a tire 52 is obtained in which the tread 56 and the base tire 54 are integrated. The tread 4 may be retreaded by a pre-cure manufacturing method. In this case, a tread 56 prepared in advance as a vulcanization molded product is attached to the molding surface 58 via an adhesive. By performing vulcanization adhesion in a vulcanizer (not shown), a tire 52 in which the tread 56 and the base tire 54 are integrated is obtained.

[0066] The outer peripheral surface of the tread 56 is the tread surface 60. The tread 56 is formed with four circumferential grooves 62 aligned in the axial direction. The four circumferential grooves 62 have the same configuration as the circumferential groove 44 of the tire 2 shown in FIG. 1. Of the four circumferential grooves 62, the two circumferential grooves 62 located on the outermost sides in the axial direction are shoulder circumferential grooves 62s. The circumferential grooves 62 located axially inside the shoulder circumferential grooves 62s are middle circumferential grooves 62m. A groove bottom 62mT of the middle circumferential groove 62m is provided with a protrusion 64 serving as a wear indicator.

[0067] [Running test equipment] A running test device 102 (hereinafter, device 102) used in the evaluation method described below will now be described. Figures 7 and 8 show the device 102. Figure 7 is a side view of the device 102. Figure 8 is a front view of the device 102. Figures 7 and 8 show an overview of the device 102. The apparatus 102 is an apparatus for conducting a running test of a test tire T. The apparatus 102 includes a drum 104, a driving unit 106, and a ground contact unit 108.

[0068] The drum 104 has a road surface 110 and a central axis 112. The road surface 110 is the portion on which the test tire T rolls. In this device 102, the outer peripheral surface of the drum 104 is the road surface 110. The central axis 112 supports the drum 104. The drum 104 rotates as the central axis 112 rotates. The test tire T rolls on the road surface 110 as the drum 104 rotates. 8, the direction indicated by the arrow Drd is the rotation direction of the drum 104. The direction indicated by the arrow Trd is the rotation direction of the test tire T.

[0069] The drive unit 106 drives and rotates the drum 104. The drive unit 106 rotatably supports a central shaft 112 of the drum 104. Although not shown, the drive unit 106 includes a motor. The motor drives and rotates the central shaft 112 of the drum 104. The rotation speed of the motor is controlled to adjust the rotation speed of the drum 104. This adjusts the running speed of the test tire T rolling on the road surface 110.

[0070] The ground contact unit 108 supports the test tire T. The ground contact unit 108 can move the test tire T toward the road surface 110 of the drum 104 and bring the test tire T into contact with the road surface 110. This applies a load to the test tire T. The state in which a load is applied to the test tire T is also called a loaded state. The ground contact unit 108 can also pull the test tire T, which has been in contact with the road surface 110, away from the road surface 110. This removes the load that was applied to the test tire T. The state in which no load is applied to the test tire T is also called an unloaded state. The ground contact unit 108 includes a tire axle 114 and a support 116 .

[0071] One end of the tire shaft 114 is supported by a support portion 116. The tire shaft 114 is supported so that its axis is parallel to the axis of the central axis 112 of the drum 104. A test tire T mounted on a rim R is rotatably attached to the other end of the tire shaft 114. The test tire T is set in the device 102 so that the axis of the test tire T is located within an imaginary plane including the axis of the drum 104.

[0072] The support portion 116 supports the tire shaft 114. The support portion 116 has a moving mechanism (not shown) capable of moving the tire shaft 114 in the radial direction of the drum 104. The support portion 116 brings the tire shaft 114 closer to the drum 104, thereby pressing the test tire T against the road surface 110. This puts the test tire T in a loaded state. The magnitude of the load applied to the test tire T is adjusted by controlling the amount of movement of the tire shaft 114. The support portion 116 moves the tire axis 114 away from the drum 104, thereby separating the test tire T from the road surface 110. This places the test tire T in an unloaded state.

[0073] The support portion 116 has an angle adjustment mechanism (not shown). The angle adjustment mechanism can adjust the angle that the tire axis 114 forms with respect to the central axis 112 of the drum 104. Although not described in detail, the device 102 can adjust the slip angle and camber angle of the test tire T by tilting the tire axis 114 with respect to the central axis 112 of the drum 104.

[0074] Although not shown, the device 102 includes a control unit. The control unit is connected to each of the driving unit 106 and the grounding unit 108 via a communication cable. The control unit is composed of, for example, a programmable sequencer, a microcomputer, a personal computer, or other control device. The control unit controls the operations of the driving unit 106 and the grounding unit 108.

[0075] [Method of evaluating tire durability] The present invention relates to a method for evaluating the durability of a tire. As described above, the method is for evaluating the durability of a heavy-duty tire having an RFID tag built therein. Fig. 9 is a flow diagram of the evaluation method. Fig. 9 shows an example of the flow of the evaluation method. This evaluation method includes a preparation step S1, a treatment step S2, a rehabilitation step S3, a traveling step S4, and a confirmation step S5.

[0076] The preparation step S1 is a step of preparing a test tire T. In this preparation step S1, a test tire T having an RFID tag built-in is prepared. The RFID tag built-in in the test tire T is, for example, the RFID tag 30 described with reference to Figs. 2 and 3. There are no particular limitations on the RFID tag built-in in the test tire T as long as it is an RFID tag used for the same purpose as the RFID tag 30.

[0077] In this evaluation method, an unrunning tire and a running tire are evaluated. In this preparation step S1, an unrunning tire and a running tire are prepared as a test tire T. An undriven tire is a tire that has no history of being driven. An undriven tire is a tire that has no traces of wear due to driving. An example of an undriven tire is a new tire, for example, a new tire such as tire 2 shown in FIG. 1. If the tire has no history of being driven, a tire that has been stored after manufacture is also an undriven tire. If the tire has no history of being driven, a tire in which worn tread has been reproduced by buffing the tread is also an undriven tire. A running tire is a tire that has a running history. The running tires targeted by this evaluation method are, in particular, tires that have passed the first usage period and tires whose tread has been retreaded after the first usage period. The tire 2 shown in FIG. 1 in which the tread 4 has worn down and reached its usage limit is a running tire. The retreaded tire 52 shown in FIG. 5 is a running tire because the base tire 54 has passed the first usage period, even though there is no sign of wear on the retreaded tread 56.

[0078] As shown in FIG. 9, when a tire with no running history, that is, an unrunning tire, is prepared as a test tire T in a preparation step S1, a processing step S2 is performed. In this evaluation method, the treatment step S2 is a step of subjecting the test tire T to a heat deterioration treatment.

[0079] The thermal degradation treatment is carried out, for example, in a treatment chamber 152 shown in Fig. 10. This treatment chamber 152 is an air-circulating oven whose internal temperature can be adjusted. A table 154 is provided inside the treatment chamber 152. The test tire T to be subjected to the thermal degradation treatment is placed on this table 154.

[0080] In the treatment step S2, the test tire T is mounted on the rim R. The inside of the test tire T is filled with gas. The test tire T is placed in a temperature-controlled treatment chamber 152. The test tire T is heated. This causes the test tire T to undergo a thermal degradation treatment. In this treatment step S2, the test tire T undergoes a thermal degradation treatment so that a state change corresponding to the state change of the tire 2 during the first usage period occurs in the test tire T. If an undriven tire is prepared as the test tire T, a running step S4 is performed on the test tire T after the treatment step S2. The state change of the test tire T is controlled by adjusting the gas filled inside the test tire T, the heating temperature, and the heating time.

[0081] The tread of test tire T that has been subjected to processing step S2 may be buffed until a wear indicator (protruding portion 46 of tire 2 shown in FIG. 1) is exposed. In this case, a test tire T that reproduces a tire after the first period of use is obtained. The tread of test tire T that has been subjected to processing step S2 may be buffed until a wear indicator is exposed, and then the tread may be retreaded. In this case, a test tire T that reproduces a tire with a retreaded tread after the first period of use is obtained.

[0082] When a running tire is prepared as a test tire T in the preparation step S1, the processing step S2 is not performed on the test tire T. This is because the running tire is a tire that has passed the first usage period.

[0083] When a running tire is prepared as a test tire T in the preparation step S1, as shown in FIG. 9, the running step S4 is performed on the test tire T without going through the retreading step S3, or the retreading step S3 is performed on the test tire T and then the running step S4 is performed.

[0084] In the retreading process S3, the tread of a tire that has reached its service limit is retreaded. In this retreading process S3, the tread is retreaded in the manner described in the "Manufacturing method of retreaded tires" above.

[0085] The running step S4 is a step of conducting a running test on the test tire T. In this evaluation method, the running step S4 is conducted on the test tire T based on an unrunning tire that has been subjected to the processing step S2, the test tire T based on a running tire that has not been subjected to the retreading step S3, and the test tire T based on a running tire that has been subjected to the retreading step S3. In the running step S4, for example, the above-mentioned running test device 102 is used.

[0086] In the running step S4, the test tire T is mounted on a rim R. As described above, the rim R is a regular rim. This rim R may be an allowable rim in the JATMA standard, or may be a test rim corresponding to an applicable rim in the JATMA standard. When the test tire T is mounted on the rim R, air is filled inside the test tire T. This adjusts the internal pressure of the test tire T. After adjusting the internal pressure, the rim R with the test tire T mounted thereon is attached to the tire axis 114 of the ground contact unit 108. The test tire T is pressed against the road surface 110, and a load is applied to the test tire T. The load applied to the test tire T is adjusted by adjusting the distance between the tire axis 114 and the road surface 110. In this evaluation method, the slip angle and camber angle are usually set to 0 degrees. The slip angle and camber angle may be adjusted to angles other than 0 degrees.

[0087] When the test tire T has been set on the device 102, the drive unit 106 is driven to rotate the drum 104. This starts the running of the test tire T. The running speed of the test tire is controlled based on a preset speed profile. The running test may be performed while keeping the running speed constant, or while increasing the running speed stepwise. The running test may be performed while increasing the load applied to the test tire T stepwise. In this evaluation method, a running test is performed until the running time reaches a preset running time or the test tire T breaks down.

[0088] The predetermined running time means a running time obtained by converting the distance that the retreaded tire can be run from when it resumes use (running) until it reaches its usage limit (hereinafter referred to as the running distance in the second usage period) into time based on the speed profile of the test tire performed in the running test. In the running step S4, a time period that can guarantee that the tire can withstand running in the second usage period (hereinafter, a time period that can guarantee running in the second usage period) is set as a running time in the running test.

[0089] This evaluation method may further include a confirmation step S5. The confirmation step S5 is a step of confirming whether the data written in the RFID tag of the test tire T that has been subjected to the running step S4 can be read. In this confirmation step S5, it is confirmed whether the RFID tag has been damaged during the running test.

[0090] In this evaluation method, the durability performance of the tire is evaluated based on the running time of the test tire T, whether or not the RFID tag is damaged, and whether or not there is any damage originating from the RFID tag. Specifically, after confirming that there is no damage to the RFID tag or any damage originating from the RFID tag, it is confirmed whether or not the running time exceeds the time set as the time that can guarantee running in the second usage period, and the durability performance of the tire is evaluated. RFID-embedded heavy-duty tires are required to have no damage to the RFID tag or any damage originating from the RFID tag, and to have a running time that exceeds the time set as the time that can guarantee running in the second usage period.

[0091] In this evaluation method, when a driven tire is used as the test tire T, a tire that has passed the first usage period or a tire whose tread has been retreaded after the first usage period is used. When an undriven tire is used as the test tire T, in the treatment step S2, a thermal degradation treatment is performed on the test tire T so that a state change corresponding to the state change of the tire during the first usage period occurs in the test tire T. The results obtained by this evaluation method reflect the first usage period. This evaluation method can efficiently obtain results that reflect the first usage period with high reproducibility. This evaluation method can quickly and accurately evaluate the durability performance of heavy-duty tires equipped with RFID tags.

[0092] As described above, in the treatment step S2, the thermal degradation treatment is performed on the test tire T so that a state change corresponding to the state change of a tire in the first usage period occurs in the test tire T. In this way, the thermal degradation treatment corresponding to the first life is performed on the test tire T.

[0093] Whether or not the first-life heat deterioration treatment has been performed on the test tire T can be confirmed using the heat aging resistance index of the tread. The heat aging resistance index is expressed by the following formula (1): Heat aging resistance index = | (complex modulus of elasticity E* of tread after heat aging treatment - complex modulus of elasticity E* of tread before heat aging treatment) | / complex modulus of elasticity E* of tread before heat aging treatment × 100 Formula (1)

[0094] In this evaluation method, the heat aging resistance index of the tread is preferably 14 or more and 60 or less. By performing a heat aging treatment on the test tire T so that the heat aging resistance index is in the range of 14 or more and 60 or less, heat aging equivalent to the heat aging of the tire during the first period of use is reproduced in the test tire T.

[0095] The range of the heat aging resistance index is set based on the complex modulus E* of the new tread of the tire to be evaluated and the complex modulus E* of the tread after the first period of use.

[0096] As described above, the state change of the test tire T is controlled by adjusting the gas filled inside the test tire T, the heating temperature, and the heating time. In other words, the heat aging resistance index of the tread of the test tire T is controlled by adjusting the gas filled inside the test tire T, the heating temperature, and the heating time.

[0097] In the treatment step S2, from the viewpoint of effectively reproducing the deterioration state of the tire after the first usage period has elapsed, it is preferable that the gas filled inside the test tire T contains oxygen. In this case, the oxygen concentration is preferably 70% or more, more preferably 90% or more. In particular, the oxygen concentration is preferably 100%.

[0098] The heating temperature in the thermal degradation treatment is preferably 60°C or higher and 80°C or lower. If the heating temperature is less than 60°C, the rubber encasing the RFID tag (the protective body 32 encasing the RFID tag 30 in the tag member 20 in the tire 2 in FIG. 1) cannot be sufficiently thermally deteriorated, and the adhesive strength of the rubber to the RFID tag cannot be reduced as desired. Therefore, the heating temperature is preferably 60°C or higher. If the heating temperature exceeds 80°C, the oil contained in the rubber will evaporate, and thermal degradation will proceed more rapidly than expected. Since the RFID tag will be exposed to high heat, there is a concern that the RFID tag may be damaged in unexpected ways. Therefore, it is preferable to keep the heating temperature below 80°C.

[0099] The heating time in the thermal deterioration treatment is preferably 14 days or more and 35 days or less. If the heating time is less than 14 days, the rubber encasing the RFID tag (the protective body 32 encasing the RFID tag 30 in the tag member 20 in the tire 2 in FIG. 1) cannot be sufficiently thermally deteriorated, and the adhesive strength of the rubber to the RFID tag cannot be reduced as desired. Therefore, the heating time is preferably 14 days or more. If the heating time exceeds 35 days, the oil contained in the rubber will evaporate, and thermal degradation will proceed more than expected. This will take a long time to evaluate, making it difficult to quickly evaluate durability performance. Therefore, it is preferable to keep the heating time to 35 days or less.

[0100] From the viewpoint of being able to quickly and accurately evaluate the durability performance of a heavy-duty tire incorporating an RFID tag, it is more preferable that in the processing step S2, the tire is heated while mounted on a rim and filled with a gas containing oxygen, the oxygen concentration inside the tire is 70% or more, the heating temperature of the tire is 60°C or more and 80°C or less, and the heating time of the tire is 14 days or more and 35 days or less.

[0101] As described above, in the running step S4, a running test is performed on the test tire T. In this running step S4, the running speed in the running test, the load applied to the test tire T, and the internal pressure of the test tire T are adjusted.

[0102] The running speed of the test tire T in the running test is preferably 10 km / h or more and 40 km / h or less. If the running speed is less than 10 km / h, the running test takes a long time, making it difficult to quickly evaluate the durability performance. Therefore, the running speed is preferably 10 km / h or more. If the running speed exceeds 40 km / h, heat generation is promoted in the tread portion of the test tire T. In heavy-duty tires, damage may occur in the tread portion before damage occurs in the bead portion or sidewall portion, where RFID tags tend to be located. Therefore, the running speed is preferably 40 km / h or less.

[0103] The load applied to the test tire T in the running test is preferably 200% or more and 300% or less of the normal load. If the load applied to the test tire T is less than 200% of the normal load, the degree of distortion caused by repeated bending of the test tire T is small, the running test takes time, and it becomes difficult to quickly evaluate the durability performance. Therefore, the load applied to the test tire T is preferably 200% or more of the normal load. If the load applied to the test tire T exceeds 300% of the normal load, there is a risk that the test tire T will be damaged before mechanical fatigue is applied to the test tire T. In this case, the usage state of the test tire T will deviate from the usage state of the tire in the first usage period. Therefore, it is preferable that the load applied to the test tire T is 300% or less of the normal load.

[0104] In the running test, the internal pressure of the test tire T is preferably 100% or more and 130% or less of the normal internal pressure. If the internal pressure of the test tire T is less than 100% of the normal internal pressure, even if the test tire T is repeatedly flexed and distorted, there is a risk that damage will occur before the test tire T experiences mechanical fatigue. In this case, the tire usage conditions in the first usage period cannot be reproduced in the test tire T. For this reason, it is preferable that the internal pressure of the test tire T is 100% or more of the normal internal pressure. If the internal pressure of the test tire T exceeds 130% of the normal internal pressure, the rigidity of the test tire T increases, making it difficult to cause distortion in the test tire T. In this case, the tire usage condition in the first usage period cannot be reproduced in the test tire T. Therefore, it is preferable that the internal pressure of the test tire T is 130% or less of the normal internal pressure.

[0105] From the viewpoint of being able to quickly and accurately evaluate the durability performance of a heavy-duty tire incorporating an RFID tag, it is more preferable that in the running step S4, the running speed of the test tire T in the running test is 10 km / h or more and 40 km / h or less, the load applied to the test tire T is 200% or more and 300% or less of the normal load, and the internal pressure of the test tire T is 100% or more and 130% or less of the normal internal pressure. In this case, it is even more preferable to increase the load applied to the test tire T and the internal pressure of the test tire T in a stepwise manner.

[0106] In this evaluation method, from the viewpoint of accurately evaluating the durability performance, the running time of the test tire T set in the running test is preferably 250 hours or more. From the viewpoint of quickly evaluating the durability performance, the running time is preferably 600 hours or less.

[0107] As is clear from the above description, according to the present invention, a method for evaluating tire durability can be provided, which can quickly and accurately evaluate the durability of heavy-duty tires having built-in RFID tags. [Industrial Applicability]

[0108] The above-described method for evaluating the durability performance of a tire can be applied to various types of tires. [Explanation of symbols]

[0109] 2. Tires 4, 56... tread 6. Sidewall 8. Chafer 10 Bead 12. Carcass 14. Belt 20 Tag member 26···Carcass ply 30... RFID tags 32 Protective body 38, 60... Tread surface 44, 62...Circumferential groove 46, 64... Convex part 52 Retreaded tires 54··· units of tires 58...molding surface

Claims

1. having a tread, A method for evaluating durability performance of a heavy-duty tire incorporating an RFID tag, in which a period from the start of use to the end of use is defined as a usage period, and a second usage period after retreading is set in addition to a first usage period before retreading by retreading the tread worn by running, the method comprising: a treatment step of subjecting the test tire having the RFID tag therein to a thermal degradation treatment; a running step of performing a running test on the test tire that has been subjected to the processing step; Including, The test tire is a tire that has no running history, In the treatment step, the heat deterioration treatment is performed on the test tire so that a state change corresponding to a state change of the tire during the first period of use occurs in the test tire. A method for evaluating tire durability performance.

2. having a tread, A method for evaluating durability performance of a heavy-duty tire incorporating an RFID tag, in which a period from the start of use to the end of use is defined as a usage period, and a second usage period after retreading is set in addition to a first usage period before retreading by retreading the tread worn by running, the method comprising: A running step of performing a running test on the test tire having the RFID tag built therein. Including, The test tire is a tire after the first usage period has elapsed, or a tire whose tread has been retreaded after the first usage period has elapsed. A method for evaluating tire durability performance.

3. The method further includes a step of confirming whether the data written in the RFID tag of the test tire that has been subjected to the running step can be read. A method for evaluating durability performance of a tire according to claim 1 or 2.

4. The change in state of the test tire in the treatment step is represented by a heat aging resistance index of the tread represented by the following formula (1), The heat aging resistance index of the tread is 14 or more and 60 or less. The method for evaluating durability performance of a tire according to claim 1. Heat aging resistance index=|(complex modulus of elasticity E* of tread after heat aging treatment−complex modulus of elasticity E* of tread before heat aging treatment)| / complex modulus of elasticity E* of tread before heat aging treatment×100 Formula (1)

5. The running speed of the test tire in the running test is 10 km / h or more and 40 km / h or less, The load applied to the test tire is 200% or more and 300% or less of the normal load, The internal pressure of the test tire is 100% or more and 130% or less of the normal internal pressure. A method for evaluating durability performance of a tire according to claim 1 or 2.

6. The method for evaluating durability performance of a tire according to claim 5 , wherein a running time of the test tire set in the running test is 250 hours or more and 600 hours or less.

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