tire

Abstract

We offer Tire 2, which achieves improved durability in environments where loads even higher than those previously anticipated are applied. [Solution] The tire 2 is equipped with a tread 4. The tire 2 is mounted on a regular rim, the internal pressure of the tire 2 is adjusted to 290 kPa, and no load is applied to the tire 2, which is the standard state of the tire 2. In the standard state of the tire 2, the ratio CD / CW of the radial distance CD from the equator Eq of the tire 2 to the ground contact reference end PC to the axial distance CW from the equator Eq of the tire 2 to the ground contact reference end PC is 0.040 or more and 0.092 or less. The thickness TA of the tread 4 at the equator Eq is 6.0 mm or more and 8.0 mm or less.

Description

Technical Field

[0001] The present invention relates to a tire. More specifically, the present invention relates to a tire mounted on a passenger car.

Background Art

[0002] In a tire, deformation and restoration are repeated. The tire contacts the road surface at the tread. The shape of the tread surface (also called the tread surface profile) affects the performance of the tire. The tread surface profile is adjusted according to the performance required for the tire. For example, Patent Document 1 shown below proposes adjusting the camber amount at the tread edge in addition to the ratio of the widths of the shoulder land portion and the middle land portion in order to suppress side slip on ice and snow and improve the wear resistance of the shoulder land portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tire capable of achieving improved durability in an environment where a load higher than the load assumed so far acts.

Means for Solving the Problems

[0005] The tire according to the present invention comprises a pair of beads, a carcass spanning between the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt. The tire's reference state is when the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire. The reference contact end is the position on the outer surface of the tire that corresponds to the axial outer end of the tire's contact surface, obtained by applying a longitudinal load to the tire in the reference state and bringing the tire into contact with a plane. The longitudinal load is the maximum load capacity represented by the load index of a HIGH LOAD CAPACITY type tire, as defined in the ETRTO 2024 standard manual, which has the same dimensional and structural characteristics as the tire's nominal size. In the tire in the aforementioned standard state, the ratio CD / CW of the radial distance CD from the tire's equator to the ground contact reference end to the axial distance CW from the tire's equator to the ground contact reference end is 0.040 or more and 0.092 or less. The thickness TA of the tread at the equator is 6.0 mm or more and 8.0 mm or less. [Effects of the Invention]

[0006] According to the present invention, a tire can be obtained that can achieve improved durability in environments where loads higher than those previously assumed are applied. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view showing a part of a tire relating to one embodiment of the present invention. [Figure 2] This is an explanatory diagram illustrating the structure of the carcass and belt. [Figure 3] This is a perspective view showing a portion of the band strip used to form the band. [Figure 4] This is a cross-sectional view showing the outline of the outer surface of the tread. [Figure 5]This is a cross-sectional view showing a portion of the tread. [Figure 6] This is a cross-sectional view showing a portion of the tread area in the center region. [Figure 7] This is a cross-sectional view showing a portion of the tread area in the shoulder region. [Figure 8] This is a cross-sectional view showing the configuration of the belt and band in the center region. [Figure 9] This is a cross-section of a belt cord. [Figure 10] This is a cross-sectional view showing a first modified example of a belt cord. [Figure 11] This is a cross-sectional view showing a second modified example of the belt cord. [Modes for carrying out the invention]

[0008] The present invention will be described in detail below, with reference to drawings as appropriate, based on preferred embodiments.

[0009] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0010] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is called the standard state. The state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire is called the reference state.

[0011] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under standard conditions. The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured with the tire mounted on the regular rim are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in the tire mounted on the regular rim. Incidentally, the structure of the tire that cannot be confirmed with the tire mounted on the regular rim is confirmed on the aforementioned cut surface.

[0012] The regular rim means the rim defined 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 regular rims.

[0013] The regular internal pressure means the internal pressure defined in the standard on which the tire is based. The "Maximum Air Pressure" in the JATMA 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 regular internal pressures.

[0014] The regular load means the load defined in the standard on which the tire is based. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0015] In the present invention, the maximum mass that a tire is allowed to carry under specified conditions is the maximum load capacity, and the index representing the maximum load capacity is the load index (LI). Unless otherwise specified, the load index of the tire of the present invention uses the load index for HIGH LOAD CAPACITY type tires (hereinafter also referred to as HLC tires) defined in the ETRTO 2024 standard manual. That is, the load index of the tire of the present invention is represented by the load index of HIGH LOAD CAPACITY type tires defined in the ETRTO 2024 standard manual that have the same dimensional structure characteristics as the dimensional structure characteristics included in the tire designation of the tire.

[0016] In the present invention, for an element of a tire containing parallel cords, the number of cords contained per 50 mm width is represented as cord ends (unit: ends / 50 mm). Unless otherwise specified, the cord ends are obtained at the cut surface of the element obtained by cutting with a plane perpendicular to the length direction of the cord. For an element containing a helically wound cord, since it appears that a plurality of cords are parallel, the cord ends can be obtained in the same manner as for an element of a tire containing parallel cords.

[0017] In the present invention, among the elements constituting the tire, the complex elastic modulus and loss tangent of the element made of crosslinked rubber are measured using a viscoelastic spectrometer in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial strain = 10% Dynamic strain = ±1% Frequency = 10 Hz Mode = elongation mode Temperature = 30°C, 70°C In this measurement, the test specimen (40 mm long x 4 mm wide x 1 mm thick) is sampled from the tire. The length of the test specimen is aligned with the circumferential direction of the tire. If it is not possible to sample a test specimen from the tire, a test specimen is sampled from a sheet of cross-linked rubber (hereinafter also referred to as a rubber sheet) obtained by pressurizing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes.

[0018] In this invention, the tensile strength and elongation at break of the cross-linked rubber element among the components constituting the tire are measured using a tensile testing machine in a 23°C temperature atmosphere in accordance with the provisions of JIS K6251. In this measurement, a strip (150 mm long x 25 mm wide x 2 mm thick) is sampled from the tire, and this strip is used to prepare the No. 3 dumbbell test specimen. The strip is sampled with its length aligned with the circumference of the tire. If a strip cannot be sampled from the tire, the test specimen is prepared from the aforementioned rubber sheet.

[0019] In this invention, the cord strength of the steel cord is expressed as the breaking load measured using a tensile testing machine in accordance with the provisions of JIS G3510 under a temperature atmosphere of 23°C. The tensile speed to obtain the breaking load is set to 50 mm / min.

[0020] In this invention, the tread portion of a tire is the part of the tire that makes contact with the road surface. The bead portion is the part of the tire that is fitted onto the rim. The sidewall portion is the part of the tire that spans the space between the tread portion and the bead portion. The tire comprises the tread portion, a pair of bead portions, and a pair of sidewall portions. The central part of the tread is also called the crown. The edges of the tread are also called the shoulder. In the drawings of this specification, the tread portion is denoted by the symbol "T", the bead portion by the symbol "B", and the sidewall portion by the symbol "S".

[0021] [Practices that formed the basis of this invention] Due to environmental concerns, electric vehicles are becoming increasingly popular. Electric vehicles are equipped with batteries. Batteries that allow a vehicle to travel a distance of around 500 km are heavy. Electric vehicles tend to be heavier than conventional gasoline-powered vehicles. Therefore, the tires fitted to electric vehicles are subjected to a higher load than the tires fitted to gasoline-powered vehicles. In order to provide tires that can support high loads, the ETRTO standard has revised its load index, and the HIGH LOAD CAPACITY type (hereinafter referred to as HLC type) tire has been introduced as a new category. To qualify as an HLC-type tire, it is required that the tire be able to support a much higher load than conventional tires. As the load acting on the tire increases, the amount of tire deformation increases. It is necessary to consider not only mechanical fatigue due to strain, but also thermal fatigue due to heat generation. Therefore, in order to improve durability under environments where loads higher than those previously assumed are applied, the inventors diligently studied technologies that can suppress the strain caused by the load and suppress the heat accumulation caused by the strain, and have completed the invention described below.

[0022] [Summary of Embodiments of the Invention] The present invention relates to a tire comprising a pair of beads, a carcass spanning between the pair of beads, a tread located radially outside the carcass and in contact with the road surface, a belt located radially inside the tread and radially outside the carcass, and a band located radially between the tread and the belt, wherein the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire, which is the reference state of the tire, and the position on the outer surface of the tire corresponding to the axial outer end of the tire's contact surface, obtained by applying a longitudinal load to the tire in the reference state and bringing the tire into contact with a plane, is the contact reference end, and the longitudinal load has the same dimensional and structural characteristics as the tire nominal size, as defined in the ETRTO 2024 standard manual for high load capacity. The tire is a tire whose load index represents the maximum load capacity, and in the tire in the standard condition, the ratio CD / CW of the radial distance CD from the tire's equator to the ground contact reference end to the tire's axial distance CW from the tire's equator to the ground contact reference end is 0.040 or more and 0.092 or less, and the tread thickness TA at the equator is 6.0 mm or more and 8.0 mm or less.

[0023] The tire of the present invention can achieve improved durability in environments where loads higher than those previously assumed are applied. Although the mechanism by which this effect is achieved has not been clarified, it is presumed to be as follows.

[0024] In the tire of the present invention, the outer surface of the tread is configured to be flat when inflated. The amount of deformation of the tread when it makes contact with the road surface is reduced. The distortion that occurs in the tread due to the action of load is suppressed. Since the volume of the tread is reduced, the accumulation of heat in the tread due to the action of distortion is also suppressed. This tire can also suppress the rise in tread temperature due to driving. This tire can reduce not only mechanical fatigue due to distortion but also thermal fatigue due to heat generation. This tire can achieve improved durability in environments where loads higher than those previously anticipated are applied.

[0025] Preferably, the reference region is centered on the equator and has an axial width of 110% of the axial width of the contact surface, the center region is centered on the equator and has an axial width of 55% of the axial width of the contact surface, the shoulder region is the axial outer portion of the center region within the reference region, the band is formed by spirally winding a band strip, the band strip is a code array in which one or more band cords are arranged, the band comprises a full band covering the entire belt, and the ratio Es / Ec of the code ends Es of the full band in the shoulder region to the code ends Ec of the full band in the center region is 1.2 or more and 1.6 or less. In this case, the full band has a high code ends Es in the shoulder region. The full band in the shoulder region can contribute to reducing strain at the end of the belt. The full band has a low code ends Ec in the center region. The full band in the center region can contribute to reducing the weight of the band. Lightweight bands can contribute to reducing the centrifugal force generated in the tire during driving. In particular, since the ratio Es / Ec is set within the aforementioned range, the restraining force and centrifugal force are well balanced. These tire bands can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation.

[0026] Preferably, the tread comprises a plurality of rubber layers arranged radially, the outermost rubber layer in the radial direction being the cap layer, and the tensile strength TB, elongation at break EB, and loss tangent LTc at 30°C of the cap layer satisfy the following equation. 20000 ≤ TB × EB / LTc ≤ 100000 This increases the mechanical strength of the tread's cap layer and suppresses heat generation in the cap layer. This cap layer can effectively contribute to reducing both mechanical fatigue caused by strain and thermal fatigue caused by heat generation. In addition to having a ratio CD / CW of 0.040 to 0.092 and a tread thickness TA at the equator of 6.0 mm to 8.0 mm, the tensile strength TB of the cap layer, elongation at break EB, and loss tangent LTc at 30°C satisfy the aforementioned formula. Therefore, due to the synergistic effect of the shape and material aspects, strain generated in the cap layer in contact with the road surface is effectively suppressed, and the heat generated by this strain is effectively suppressed. In other words, from the viewpoint of reducing mechanical fatigue due to strain and thermal fatigue due to heat generation, it is preferable that the ratio CD / CW is 0.040 to 0.092, the tread thickness TA at the equator is 6.0 mm to 8.0 mm, and the tensile strength TB of the cap layer, elongation at break EB, and loss tangent LTc at 30°C satisfy the aforementioned formula.

[0027] Preferably, the belt comprises a plurality of parallel belt cords and a belt topping rubber covering the plurality of belt cords, wherein the loss tangent LTb and complex modulus E*b of the belt topping rubber at 70°C satisfy the following formula. 50 ≤ E*b / LTb ≤ 150 This suppresses heat generation in the belt topping rubber and maintains its rigidity appropriately. A belt with this belt topping rubber can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation.

[0028] Preferably, the loss tangent LTb is 0.05 or more and 0.18 or less. This effectively suppresses heat generation in the belt topping rubber. A belt having this belt topping rubber can effectively contribute to reducing thermal fatigue caused by heat generation.

[0029] Preferably, the belt cord is a single wire made of a single steel filament, the cord diameter of the belt cord is 0.36 mm or more and 0.42 mm or less, and the cord strength of the belt cord is 400 N or more and 540 N or less. In this case, the belt cord can contribute to reducing the weight of the belt. A lighter belt can contribute to reducing the centrifugal force generated in the tire during driving. In particular, since the cord diameter and cord strength of the belt cord are set within the above range, the restraining force and centrifugal force are well balanced. This tire belt can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation.

[0030] Preferably, the belt cord is a stranded wire made by twisting together four steel filaments, the cord diameter of the belt cord is 0.36 mm or more and 0.55 mm or less, and the cord strength of the belt cord is 350 N or more and 540 N or less. In this case as well, the belt cord can contribute to reducing the weight of the belt. A lighter belt can contribute to reducing the centrifugal force generated in the tire during driving. In particular, since the cord diameter and cord strength of the belt cord are set within the above range, the restraining force and centrifugal force are well balanced. This tire band can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation.

[0031] Thus, the tire of the present invention can achieve improved durability in environments where loads higher than those previously assumed are applied. This tire can stably perform even when mounted on electric vehicles, which are heavier than conventional gasoline vehicles. This will be explained in detail below using tire 2 shown in Figure 1 as an example.

[0032] [Details of the Embodiments of the Invention]

[0033] Figure 1 shows a part of a tire 2 according to one embodiment of the present invention. This tire 2 is a pneumatic tire for passenger cars. This tire 2 is a HIGH LOAD CAPACITY type tire as defined in the ETRTO 2024 standard manual. The tire 2 shown in Figure 1 is mounted on a rim R (regular rim).

[0034] Figure 1 shows a portion of the cross-section of tire 2 along a plane containing the axis of rotation of tire 2 (not shown). The cross-section shown in Figure 1 is also called a meridian cross-section. The direction indicated by the double arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. The direction indicated by the double arrow RD is the radial direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the circumferential direction of tire 2. The dashed line EL extending radially represents the equatorial plane of tire 2.

[0035] In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2. The direction indicated by arrow RD1 is the radial outward direction of tire 2, and the direction indicated by arrow RD2 is the radial inward direction of tire 2.

[0036] In Figure 1, the position indicated by the symbol Eq is the intersection of the outer surface 2G of tire 2 (specifically, the tread surface, which will be described later) and the equatorial plane. Intersection point Eq is the equator of tire 2. If the groove is located on the equatorial plane, the equatorial Eq is determined based on the virtual outer surface obtained by assuming the absence of the groove. The equatorial Eq is the radial outer end of tire 2.

[0037] In Figure 1, the position indicated by the symbol PW is the axial outer end of tire 2 (hereinafter referred to as outer end PW). If there are decorations such as patterns or letters on the outer surface 2G, outer end PW is identified based on a virtual outer surface (the dashed line LV in Figure 1) obtained by assuming there are no decorations. In Figure 1, the length indicated by the double-headed arrow WA represents the reference width of tire 2. The reference width WA of tire 2 is the axial distance from the equatorial plane to the outer edge PW. Twice the reference width WA corresponds to the maximum width of tire 2. The outer edge PW is also called the maximum width position.

[0038] The tire 2 comprises a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, a pair of chafers 18, and an inner liner 20.

[0039] The tread 4 is located radially outward of the carcass 12. The tread 4 is made of cross-linked rubber. In Figure 1, the length indicated by the double arrow TA represents the thickness of the tread 4 at the equator Eq. The thickness TA is measured along the equatorial plane.

[0040] The tread 4 contacts the road surface at its tread surface 22. The tread 4 includes a tread surface 22 that contacts the road surface. The outer surface 2G of the tire 2 includes the tread surface 22. Tread 4 has grooves 24 cut into it. This forms the tread pattern.

[0041] In Figure 1, the position indicated by the symbol BD is the boundary between the tread 4 and the sidewall 6 (described later) on the outer surface 2G of the tire 2. Boundary BD is also the edge of the outer surface 4G of the tread 4.

[0042] In Figure 1, the position indicated by the symbol PC is the ground contact reference end. In this invention, the ground contact reference end PC is a position on the outer surface 2G of the tire 2 that corresponds to the axial outer end of the contact surface of the tire 2, obtained by applying a longitudinal load to the tire 2 in a reference state using a tire contact surface shape measuring device (not shown) and bringing the tire 2 into contact with a plane. The longitudinal load applied to the tire 2 is the maximum load capacity represented by the load index of a HIGH LOAD CAPACITY type tire, as defined in the ETRTO 2024 standard manual, which has the same dimensional and structural characteristics as the tire nominal size of the tire 2. To obtain contact with the road surface, tire 2 is positioned so that its axial direction is parallel to the road surface. A load is applied to tire 2 in a direction perpendicular to the road surface. In other words, with the camber angle of tire 2 set to 0°, the aforementioned longitudinal load is applied to tire 2.

[0043] The tread 4 has a tread body 26 and a pair of wings 28. The tread body 26 is the main contact point with the road surface. Each wing 28 is positioned between the tread body 26 and the sidewall 6. The tread body 26 and the sidewall 6 are joined via the wings 28. The wings 28 are made of cross-linked rubber with adhesive properties in mind.

[0044] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located on the axially outer side of the carcass 12. The sidewall 6 is made of cross-linked rubber designed for cut resistance.

[0045] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is in contact with the rim R. The clinch 8 is made of cross-linked rubber with wear resistance in mind.

[0046] Each bead 10 is located radially inward of the sidewall 6. The bead 10 is located axially inward of the clinch 8. The bead 10 comprises a core 30 and an apex 32. The core 30 extends circumferentially. Although not shown, the core 30 includes a steel wire. The apex 32 is located radially outward from the core 30. The apex 32 is made of cross-linked rubber with high rigidity. The apex 32 tapers radially outward. In Figure 1, the position indicated by the symbol PA is the outer end of the apex 32. The outer end PA of the apex 32 is located radially inward from the axial outer end PW of the tire 2. The outer end PA of the apex 32 is also the outer end of the bead 10.

[0047] The carcass 12 is located inside the tread 4, a pair of sidewalls 6, and a pair of clinches 8. The carcass 12 spans between a pair of beads 10.

[0048] The carcass 12 comprises at least one carcass ply 34. The carcass 12 of this tire 2 is composed of two carcass plies 34. Of the two carcass plies 34, the carcass ply 34 located on the inner side of the radially inner side of the tread 4 is the first carcass ply 36, and the carcass ply 34 located on the outer side is the second carcass ply 38.

[0049] The first carcass ply 36 is folded back axially from the inside to the outside at each bead 10. The first carcass ply 36 comprises a first ply body 36a and a pair of first folded portions 36b. The first ply body 36a spans between the pair of beads 10. Each first folded portion 36b is connected to the first ply body 36a and is folded back at each bead 10. The ends of the first folded portions 36b are located radially outward from the axial outer end PW of the tire 2.

[0050] The second carcass ply 38 is folded back axially from the inside to the outside at each bead 10. The second carcass ply 38 comprises a second ply body 38a and a pair of second folded portions 38b. The second ply body 38a spans between the pair of beads 10. Each second folded portion 38b is connected to the second ply body 38a and is folded back at each bead 10. The ends of the second folded portions 38b are located radially inward of the outer end PA of the apex 32. The ends of the second folded portions 38b are covered by the first folded portion 36b.

[0051] Figure 2 is an explanatory diagram illustrating the configuration of the carcass 12 and belt 14. In Figure 2, the direction indicated by the double arrows CD is the circumferential direction of the tire 2. The front side of the paper is the radially outward direction, and the back side is the radially inward direction.

[0052] The carcass ply 34 that make up the carcass 12 contains a number of parallel carcass cords 40. In Figure 2, for ease of explanation, the carcass cords 40 are represented by solid lines, but the carcass cords 40 are covered with carcass stopping rubber 42. The carcass cords 40 intersect the equatorial plane. The carcass 12 of this tire 2 has a radial structure. The carcass cords 40 are cords made of organic fibers (hereinafter referred to as organic fiber cords). Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0053] The belt 14 is located radially inward of the tread 4. The belt 14 is located radially outward of the carcass 12. In this tire 2, the belt 14 is laminated to the carcass 12 on the radially inward side of the tread 4.

[0054] The belt 14 comprises a plurality of belt plies 44 arranged radially. The plurality of belt plies 44 include an inner belt ply 46 located on the innermost side and an outer belt ply 48 located on the outermost side. The belt 14 of this tire 2 consists of two belt plies 44, specifically an inner belt ply 46 and an outer belt ply 48. The inner belt ply 46 is laminated to the carcass 12 on the radially inner side of the tread 4. The outer belt ply 48 is laminated to the inner belt ply 46. The end of the outer belt ply 48 is located axially inward of the end of the inner belt ply 46. The outer belt ply 48 is narrower than the inner belt ply 46.

[0055] The belt ply 44 constituting the belt 14 includes a large number of parallel belt cords 50. In Figure 2, for ease of explanation, the belt cords 50 are represented by solid lines, but the belt cords 50 are covered with belt topping rubber 52. The belt 14 comprises a large number of parallel belt cords 50 and belt topping rubber 52 covering the large number of belt cords 50. The belt cords 50 are steel cords. The belt topping rubber 52 is cross-linked rubber.

[0056] Each belt cord 50 included in the belt 14 is inclined with respect to the circumferential direction. As shown in Figure 2, the direction of inclination of the belt cord 50 included in the outer belt ply 48 (hereinafter referred to as the outer belt cord 50s) and the direction of inclination of the belt cord 50 included in the inner belt ply 46 (hereinafter referred to as the inner belt cord 50u) are opposite to each other.

[0057] In Figure 1, the length indicated by the double arrow WB is the reference width of belt 14. The reference width WB of belt 14 is the axial distance from the equatorial plane to the end of belt 14. Twice the reference width WB corresponds to the axial width of belt 14. In this tire 2, the standard width WB of the belt 14 is set within the range of 70% to 95% of the standard width WA of tire 2.

[0058] The band 16 is laminated on the belt 14 on the radially inner side of the tread 4. The band 16 is located radially between the tread 4 and the belt 14. The ends of the band 16 are located axially outward from the ends of the belt 14.

[0059] The band 16 of this tire 2 comprises a full band 54 and a pair of edge bands 56. The full band 54 covers the entire belt 14. A pair of edge bands 56 are positioned axially spaced apart on either side of the equatorial plane. Each edge band 56 is located radially outside the full band 54. The edge bands 56 cover the ends of the full band 54. This band 16 may consist only of the full band 54.

[0060] The band 16 of this tire 2 is formed using a band strip 58 shown in Figure 3. The band strip 58 is strip-shaped. The band strip 58 contains one or more band cords 60. The band strip 58 shown in Figure 3 contains eight band cords 60. The band cords 60 are covered with band topping rubber 62. In tire 2, the band topping rubber 62 is crosslinked rubber. The eight band codes 60 are arranged in the width direction of the band strip 58 and extend in the length direction of the band strip 58. The band strip 58 is a code array consisting of one or more band codes 60 arranged in a sequence.

[0061] The band 16 is formed by winding a band strip 58 in a helical shape. The band 16 includes a helically wound band cord 60. In the band 16, the band cord 60 extends substantially in the circumferential direction. In detail, the angle that the band cord 60 makes with respect to the circumferential direction is 5° or less. The band 16 has a jointless structure.

[0062] Band cord 60 is an organic fiber cord. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers. There are no particular restrictions on band cord 60; any organic fiber cord commonly used as a tire band cord can be used as band cord 60. The band 16 comprises a band cord 60 which is an organic fiber cord and extends substantially in the circumferential direction.

[0063] In Figure 1, the length indicated by the double-headed arrow WJ represents the reference width of band 16. The reference width WJ of band 16 is the axial distance from the equatorial plane to the end of band 16. Twice the reference width WJ corresponds to the axial width of band 16. In this tire 2, the standard width WJ of band 16 is set within the range of 90% to 110% of the standard width WB of belt 14.

[0064] Each chafer 18 is located radially inward of the bead 10. The chafer 18 is in contact with the rim R. The chafer 18 of this tire 2 consists of cloth and rubber impregnated into this cloth.

[0065] The inner liner 20 is located inside the carcass 12. The inner liner 20 constitutes the inner surface 2N of the tire 2. The inner liner 20 is made of cross-linked rubber with excellent air shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

[0066] Figure 4 shows a portion of the outline of the outer surface 2G of tire 2 in a meridional cross-section of tire 2. The outline of the outer surface 2G is represented by a virtual outer surface obtained by assuming that there are no grooves, patterns, letters, or other decorations. Although not described in detail here, in this invention the outline of the outer surface 2G is obtained, for example, by measuring the outer surface shape of tire 2 using a displacement sensor, with tire 2 assembled on rim R, air filled inside tire 2, and the internal pressure of tire 2 adjusted. The outline of the outer surface 2G shown in Figure 4 represents the outer surface shape of tire 2 in the standard state. The outline of the outer surface 2G represented by the outline has a shape that is symmetrical with respect to the equatorial plane.

[0067] The outer surface 2G of this tire 2 comprises a tread surface 22 and a pair of side surfaces 64 connected to the tread surface 22. The tread surface 22 is divided into seven parts arranged in the axial direction. The seven parts of the tread surface 22 include a crown portion 66, a pair of middle portions 68, a pair of shoulder portions 70, and a pair of corner portions 72.

[0068] The crown portion 66 is located in the axial center. The equatorial plane intersects the crown portion 66. The pair of middle portions 68 are each located axially outward from the crown portion 66. The position indicated by the symbol CM is the boundary between the crown portion 66 and the middle portion 68. The pair of shoulder portions 70 are each located axially outward from the middle portion 68. The position indicated by the symbol MS is the boundary between the middle portion 68 and the shoulder portion 70. The pair of corner portions 72 are each located axially outward from the shoulder portion 70. The position indicated by the symbol SC is the boundary between the shoulder portion 70 and the corner portion 72. The crown portion 66 is the part located in the axial center. The corner portion 72 is the part located on the outermost side in the axial direction. The middle portion 68 and the shoulder portion 70 are the parts located between the crown portion 66 and the corner portion 72.

[0069] As mentioned above, the corner section 72 is the outermost part in the axial direction. The corner section 72 connects to the side surface 64. The position indicated by the symbol CS is the boundary between the corner section 72 and the side surface 64. The boundary CS is also the edge of the tread surface 22. As shown in Figure 4, the boundary BD between the outer surface 4G of the tread 4 and the outer surface 6G of the sidewall 6 is included in the corner portion 72. In this tire 2, the outer surface 4G of the tread 4 is included in the tread surface 22. The outer surface 2G of the tire 2 may be configured such that the boundary BD between the outer surface 4G of the tread 4 and the outer surface 6G of the sidewall 6 coincides with the edge CS of the tread surface 22.

[0070] In Figure 4, the double arrow WCM represents the axial distance from the equatorial plane to the boundary CM between the crown portion 66 and the middle portion 68. The double arrow WMS represents the axial distance from the equatorial plane to the boundary MS between the middle portion 68 and the shoulder portion 70. In this tire 2, the axial distance WCM is set within the range of 30% to 40% of the tire's reference width WA. The axial distance WMS is set within the range of 55% to 65% of the tire's reference width WA.

[0071] In this tire 2, the contours of the crown portion 66, middle portion 68, shoulder portion 70, and corner portion 72 are represented by arcs in its meridian cross-section.

[0072] The contour of the crown portion 66 is represented by a circular arc with its center on the equatorial plane. In Figure 4, arrow TR1 is the radius of the circular arc representing the contour of the crown portion 66. The contour of the middle section 68 is represented by an arc tangent to the arc representing the contour of the crown section 66. In Figure 4, arrow TR2 is the radius of the arc representing the contour of the middle section 68. The arc representing the contour of the middle section 68 is tangent to the arc representing the contour of the crown section 66 at boundary CM. Boundary CM is the point of tangency between the arc representing the contour of the middle section 68 and the arc representing the contour of the crown section 66. The contour of the shoulder portion 70 is represented by an arc tangent to the arc representing the contour of the middle portion 68. In Figure 4, arrow TR3 is the radius of the arc representing the contour of the shoulder portion 70. The arc representing the contour of the shoulder portion 70 is tangent to the arc representing the contour of the middle portion 68 at boundary MS. Boundary MS is the point of tangency between the arc representing the contour of the shoulder portion 70 and the arc representing the contour of the middle portion 68. The contour of the corner portion 72 is represented by an arc tangent to the arc representing the contour of the shoulder portion 70. In Figure 4, arrow TRc is the radius of the arc representing the contour of the corner portion 72. The arc representing the contour of the corner portion 72 is tangent to the arc representing the contour of the shoulder portion 70 at boundary SC. Boundary SC is the point of tangency between the arc representing the contour of the corner portion 72 and the arc representing the contour of the shoulder portion 70. The arc representing the contour of the corner portion 72 is tangent to the contour line of the side surface 64 at boundary CS. Boundary CS is the point of tangency between the arc representing the contour of the corner portion 72 and the contour line of the side surface 64.

[0073] In the contour line of the outer surface 4G of the tread 4, the arc representing the contour of the crown portion 66 is represented by the arc that maximizes the overlapping length with the contour line from the equator Eq. The arc representing the contour of the middle portion 68 is tangent to the end of the arc representing the contour of the crown portion 66, and is represented by the arc that maximizes the overlapping length with the contour line from this end. The end of the arc representing the contour of the crown portion 66 is one end of the arc representing the contour of the middle portion 68, and is the boundary CM between the crown portion 66 and the middle portion 68. The arc representing the contour of the shoulder portion 70 is tangent to the other end of the arc representing the contour of the middle portion 68, and is represented by the arc that maximizes the overlapping length with the contour line from this other end. The other end of the arc representing the contour of the middle portion 68 is one end of the arc representing the contour of the shoulder portion 70, and is the boundary MS between the middle portion 68 and the shoulder portion 70. The arc representing the contour of the corner portion 72 is tangent to the other end of the arc representing the contour of the shoulder portion 70, and is represented by the arc that maximizes the overlap length with the contour line from this other end. The other end of the arc representing the contour of the shoulder portion 70 is one end of the arc representing the contour of the corner portion 72, and is the boundary SC between the shoulder portion 70 and the corner portion 72. The other end of this arc representing the contour of the corner portion 72 is the edge CS of the tread surface 22, and is the boundary CS between the tread surface 22 and the side surface 64.

[0074] The straight line LSC is a tangent line that touches the arc representing the contour of corner 72 at boundary SC. The straight line LCS is a tangent line that touches the arc representing the contour of corner 72 at boundary CS. The symbol PE represents the intersection of tangent LSC and tangent LCS. In this invention, this intersection PE is the reference end of the tread 4. The length indicated by the double arrow WT is the axial distance from the equatorial plane to the reference end PE. In this tire 2, the axial distance WT is 85% or more and 100% or less of the reference width WA of the tire 2, preferably 85% or more and less than 100%.

[0075] In two adjacent parts, the arc representing the contour of the part located axially outward has a smaller radius than the arc representing the contour of the part located axially inward. The radius TR1 of the arc representing the contour of the crown portion 66 is greater than the radius TR2 of the arc representing the contour of the middle portion 68. The radius TR2 of the arc representing the contour of the middle portion 68 is greater than the radius TR3 of the arc representing the contour of the shoulder portion 70. And the radius TR3 of the arc representing the contour of the shoulder portion 70 is greater than the radius TRc of the arc representing the contour of the corner portion 72. Of the seven parts that make up the tread surface 22, the arc representing the contour of the crown portion 66 located in the axial center has the largest radius TR1, and the arc representing the contour of the corner portion 72 located on the outermost axial side has the smallest radius TRc. Radius TRc is smaller than radius TR1. Specifically, the ratio of radius TRc to radius TR1, TRc / TR1, is between 0.010 and 0.020.

[0076] In Figure 4, the length indicated by the double arrow CW is the axial distance from the equator Eq of tire 2 to the contact reference end PC. The axial distance CW is also called the contact reference width. The length indicated by the double arrow CD is the radial distance from the equator Eq of tire 2 to the contact reference end. The radial distance CD is the camber amount at the contact reference end PC. In this invention, the contact reference width CW and the camber amount CD at the contact reference end PC are obtained in the tire 2 under standard conditions.

[0077] In the standard state of tire 2, the ratio CD / CW of the camber amount CD at the contact reference edge PC to the contact reference width CW is between 0.040 and 0.092. As a result, the outer surface 4G of the tread 4 is configured in a flat shape when inflated. The amount of deformation of the tread 4 when it contacts the road surface is reduced. The distortion that occurs in the tread 4 due to the action of the load is suppressed. This tire 2 can reduce mechanical fatigue caused by distortion.

[0078] This tire 2 suppresses deformation of the tread 4 caused by load by constructing the outer surface 4G of the tread 4 in an inflated state with a flat shape. Therefore, this tire 2 can use a thinner tread that could not be used in conventional tires. Specifically, the thickness TA of the tread 4 of this tire 2 is 6.0 mm or more and 8.0 mm or less. Since the volume of the tread 4 is reduced, the heat generated by the action of deformation is also suppressed from accumulating in the tread 4. This tire 2 can suppress the temperature rise of the tread 4 during driving. This tire 2 can reduce not only mechanical fatigue due to deformation but also thermal fatigue due to heat generation. This tire 2 can achieve improved durability in environments where loads higher than those previously anticipated are applied.

[0079] As mentioned above, in the standard tire 2, the ratio CD / CW of the camber amount CD at the contact reference end PC to the contact reference width CW is 0.040 or more and 0.092 or less. From the viewpoint of reducing mechanical fatigue due to strain, the ratio CD / CW is preferably 0.040 or more and 0.066 or less, and more preferably 0.040 or more and 0.055 or less.

[0080] As mentioned above, the tread thickness TA of this tire 2 is 6.0 mm or more and 8.0 mm or less. From the viewpoint of reducing thermal fatigue due to heat generation, the tread thickness TA is preferably 6.0 mm or more and 7.5 mm or less, and more preferably 6.0 mm or more and 7.0 mm or less.

[0081] The radius TR1 of the arc representing the contour of the crown portion 66 is preferably 1000 mm or more. This ensures that the outer surface 4G of the tread 4 is flat when inflated. The amount of deformation of the tread 4 when it contacts the road surface is reduced. The strain generated in the tread 4 due to the action of the load is suppressed. This tire 2 can reduce mechanical fatigue due to strain. From this viewpoint, the radius TR1 of the arc representing the contour of the crown portion 66 is preferably 1300 mm or more, and more preferably 1500 mm or more. From the viewpoint of preventing the crown portion 66 from being recessed radially inward and preventing the contact pressure at the shoulder portion 70 from becoming excessively high, the radius TR1 is preferably 3000 mm or less, and more preferably 2500 mm or less.

[0082] As mentioned above, the radius TR1 of the arc representing the contour of the crown portion 66 is larger than the radius TR2 of the arc representing the contour of the middle portion 68. More specifically, the ratio TR2 / TR1 of the radius TR2 of the arc representing the contour of the middle portion 68 to the radius TR1 of the arc representing the contour of the crown portion 66 is preferably between 0.45 and 0.55. This suppresses the distortion that occurs in the tread 4 due to the action of the load. This tire 2 can reduce mechanical fatigue due to distortion. From this viewpoint, it is more preferable that the ratio TR2 / TR1 is between 0.47 and 0.53.

[0083] As mentioned above, the radius TR2 of the arc representing the contour of the middle section 68 is larger than the radius TR3 of the arc representing the contour of the shoulder section 70. Since the radius TR1 of the arc representing the contour of the crown section 66 is larger than the radius TR2 of the arc representing the contour of the middle section 68, the radius TR3 of the arc representing the contour of the shoulder section 70 is smaller than the radius TR1 of the arc representing the contour of the crown section 66. More specifically, the ratio TR3 / TR1 of the radius TR3 of the arc representing the contour of the shoulder section 70 to the radius TR1 of the arc representing the contour of the crown section 66 is preferably between 0.05 and 0.15. This suppresses the distortion that occurs in the tread 4 due to the action of the load. This tire 2 can reduce mechanical fatigue due to distortion. From this viewpoint, it is more preferable that the ratio TR3 / TR1 is between 0.07 and 0.13.

[0084] In Figure 1, the length indicated by the double arrow TC represents the thickness of the tread 4 at the end of the belt 14. The thickness TC is measured in the meridional cross-section of the tire 2 along the normal to the outer surface 2G of the tire 2, passing through the end of the belt 14.

[0085] The ratio TC / TA of the thickness TC of the tread 4 at the end of the belt 14 to the thickness TA of the tread 4 at the equator Eq is preferably 0.40 or more and 0.85 or less. This effectively reduces the volume of the tread 4, thereby suppressing the accumulation of heat in the tread 4 due to the action of strain. This tire 2 can suppress the temperature rise of the tread 4 due to driving. This tire 2 can reduce thermal fatigue due to heat generation. From this viewpoint, the ratio TC / TA is more preferably 0.43 or more and 0.65 or less, and even more preferably 0.45 or more and 0.55 or less.

[0086] Figure 5 shows a portion of the cross-section shown in Figure 1. Figure 5 shows a portion of the tread section T. In Figure 5, the length indicated by the double arrow ACW is the axial width of the grounding surface, i.e., the grounding width. The grounding width ACW is the axial distance from one grounding reference end PC to the other grounding reference end PC. The grounding width ACW is equal to twice the grounding reference width CW mentioned above.

[0087] The symbol PS represents a position on the outer surface 2G of tire 2, located axially outward from the ground contact reference end PC. The solid line LS is a straight line extending radially through position PS. In this tire 2, the region from one straight line LS to the other straight line LS is called the reference region RB. The length indicated by the double arrow SCW is the axial width of the reference region RB. The equator Eq is located at the axial center of the reference region RB. In this tire 2, the axial width SCW of the reference area RB is set to 110% of the contact width ACW. The reference area RB is the area centered on the equator Eq and has an axial width of 110% of the axial width ACW of the contact surface.

[0088] The symbol PU represents a position on the outer surface 2G of tire 2, located axially inward from the ground contact reference end PC. The solid line LU is a straight line extending radially through position PU. In this tire 2, the region from one straight line LU to the other is called the center region RC. The length indicated by the double arrow UCW is the axial width of the central region RC. The equator Eq is located at the axial center of the central region RC. In this tire 2, the axial width UCW of the center region RC is set to 55% of the contact width ACW. The center region RC is the region within the reference region RB that is centered on the equator Eq and has an axial width of 55% of the axial width ACW of the contact surface. In Figure 5, the region from line LU to line LS is called the shoulder region RS. The shoulder region RS is the axially outer portion of the center region RC within the reference region RB. The shoulder region RS is located axially outside the center region RC. The reference region RB consists of the center region RC and a pair of shoulder regions RS.

[0089] Figure 6 shows a portion of Figure 5. Figure 6 shows a portion of the central region RC. Figure 7 also shows a portion of Figure 5. Figure 7 shows a portion of the shoulder region RS. As mentioned above, the band 16 of this tire 2 is made by spirally winding band strips 58. As shown in Figures 6 and 7, the cross-section of the band 16 includes the cross-sections of multiple band strips 58. The code endings of the full band 54 and edge band 56 in band 16 are controlled by adjusting the number of band cords 60 contained in the band strip 58 and the way the band strip 58 is wound.

[0090] In the full band 54 in the center region RC, the band strips 58 are wound spirally with gaps between them. As shown in Figure 6, in the full band 54 in the center region RC, the cross-sections of the band strips 58 are aligned with gaps between them. In Figure 6, for the sake of explanation, the gaps are shown as spaces, but in the actual tire 2, there are no such gaps, and the areas corresponding to the gaps are filled with rubber. In contrast, in the full band 54 in the shoulder region RS, the band strips 58 are wound spirally without gaps. In the edge band 56 as well, the band strips 58 are wound spirally without gaps. As shown in Figure 7, in the full band 54 in the shoulder region RS, the cross-sections of the band strips 58 are aligned without gaps. In the edge band 56 in the shoulder region RS as well, the cross-sections of the band strips 58 are aligned without gaps.

[0091] In the center region RC, the full band 54 is formed by loosely winding the band strip 58, while in the shoulder region RS, the full band 54 is formed by tightly winding the band strip 58. The code end Es of the full band 54 in the shoulder region RS is greater than the code end Ec of the full band 54 in the center region RC. More specifically, the ratio Es / Ec of the code end Es of the full band 54 in the shoulder region RS to the code end Ec of the full band 54 in the center region RC is preferably between 1.2 and 1.6. In this case, the full band 54 in the shoulder region RS has a high code end Es. The full band 54 in the shoulder region RS can contribute to reducing the strain generated at the end of the belt 14. The full band 54 in the center region RC has a low code end Ec. The full band 54 in the center region RC can contribute to reducing the weight of the band 16. A lighter band 16 can contribute to reducing the centrifugal force generated on the tire 2 during driving. In particular, since the ratio Es / Ec is set within the aforementioned range, the restraining force and centrifugal force are well balanced. The band 16 of this tire 2 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation. From this viewpoint, it is more preferable that the ratio Es / Ec is between 1.3 and 1.5.

[0092] Figure 8 shows a portion of Figure 6. Figure 8 shows the configuration of belt 14 and band 16 in the center region. As mentioned above, in the full band 54 of the center region RC, the cross-sections of the band strips 58 are arranged with gaps between them. In Figure 8, the length indicated by the double arrow G represents the size of the gap formed between two adjacent band strip cross-sections 58 (hereinafter referred to as band strip cross-sections) in the cross-section of the full band 54. The gap G is represented by the shortest distance between a band code cross-section located on the side of the adjacent band strip cross-section (hereinafter referred to as band code cross-section) among the multiple band code cross-sections included in one band strip cross-section (hereinafter referred to as band code cross-section), and a band code cross-section located on the side of the first band strip cross-section (among the multiple band code cross-sections included in the other band strip cross-section).

[0093] As mentioned above, twice the standard width WA of tire 2 corresponds to the maximum width of tire 2. From the viewpoint that the band 16 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation, the ratio of the gap G to the maximum width of tire 2 is preferably 0.8% or more and 1.5%, and more preferably 1.2% or more and 1.4%.

[0094] The tread 4 of this tire 2, more specifically the tread body 26, typically comprises multiple rubber layers 74 arranged radially. Of the multiple rubber layers 74, the outermost rubber layer 74 in the radial direction is the cap layer 76. Of the multiple rubber layers 74, the innermost rubber layer 74 in the radial direction is the base layer 78. The tread body 26 of this tire 2 is composed of two layers: the cap layer 76 and the base layer 78. The cap layer 76 uses cross-linked rubber, taking into consideration contact with the road surface, wear resistance, and grip performance. The base layer 78 is located radially inside the cap layer 76. The base layer 78 is covered by the cap layer 76. The base layer 78 uses cross-linked rubber, taking into consideration its effect on rolling resistance and adhesion. The tread body 26 may be composed of three radially aligned rubber layers 74. In this case, an intermediate layer is provided between the radially outermost cap layer 76 and the radially innermost base layer 78. The characteristics of the intermediate layer are adjusted according to the specifications of the vehicle on which the tire 2 is mounted. The tread body 26 may also be composed of one rubber layer 74. In this case, the tread body 26 consists only of the cap layer 76.

[0095] In Figure 6, the length indicated by the double-headed arrow TAc represents the thickness of the cap layer 76 at the equatorial Eq. The thickness TAc is measured along the equatorial plane. In this tire 2, the ratio Tac / TA of the thickness TAc of the cap layer 76 to the thickness TA of the tread 4 is set in the range of 70% to 100%. If the tread body 26 is composed of three layers, this ratio Tac / TA is set in the range of 30% to 40%. In this case, the thickness of the intermediate layer and base layer 78 is set according to the specifications of the vehicle on which the tire 2 is mounted. A ratio Tac / TA of 100% means that the entire tread body 26 is composed of the cap layer 76.

[0096] In this tire 2, it is preferable that the tensile strength TB of the cap layer 76, the elongation at break EB, and the loss tangent LTc at 30°C satisfy the following equation. 20000 ≤ TB × EB / LTc ≤ 100000 In this tire 2, the mechanical strength of the cap layer 76 of the tread 4 is increased, and heat generation in the cap layer 76 is suppressed. This cap layer 76 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation. From this viewpoint, it is more preferable that the tensile strength TB, elongation at break EB, and loss tangent LTc at 30°C satisfy the following equation. 30000 ≤ TB × EB / LTc ≤ 50000

[0097] The tensile strength TB of the cap layer 76 is preferably 15 MPa or more and 30 MPa or less. This effectively reduces mechanical fatigue due to strain in the tread portion T. From this viewpoint, the tensile strength TB is more preferably 18 MPa or more and 25 MPa or less, and even more preferably 20 MPa or more and 24 MPa or less.

[0098] The elongation EB of the cap layer 76 at break is preferably 350% to 650%. This effectively reduces mechanical fatigue due to strain in the tread portion T. From this viewpoint, the elongation EB at break is more preferably 400% to 600%, and even more preferably 450% to 550%.

[0099] The loss tangent LTc of the cap layer 76 at 30°C is preferably 0.15 or more and 0.45 or less. This effectively reduces thermal fatigue due to heat generation in the tread portion T. From this viewpoint, the loss tangent LTc at 30°C is more preferably 0.20 or more and 0.40 or less, and even more preferably 0.25 or more and 0.35 or less.

[0100] In this tire 2, it is preferable that the loss tangent LTb and complex modulus E*b of the belt topping rubber 52 at 70°C satisfy the following equation. 50 ≤ E*b / LTb ≤ 150 In this tire 2, heat generation in the belt topping rubber 52 is suppressed, and the rigidity of the belt topping rubber 52 is appropriately maintained. The belt 14 having this belt topping rubber 52 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation. From this viewpoint, it is more preferable that the loss tangent LTb and the complex modulus of elasticity E*b satisfy the following equations. 75 ≤ E*b / LTb ≤ 115

[0101] In this tire 2, it is preferable that the loss tangent LTb of the belt topping rubber 52 at 70°C is 0.05 or more and 0.18 or less. In this tire 2, heat generation in the belt topping rubber 52 is effectively suppressed. The belt 14 having this belt topping rubber 52 can effectively contribute to reducing thermal fatigue due to heat generation. From this viewpoint, the loss tangent LTb is more preferably 0.09 or more and 0.13 or less, and even more preferably 0.10 or more and 0.12 or less.

[0102] In this tire 2, from the viewpoint that the belt 14 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation, the loss tangent LTb and complex modulus E*b of the belt topping rubber 52 at 70°C satisfy the following equations, and it is more preferable that the loss tangent LTb is 0.05 or more and 0.18 or less. 50 ≤ E*b / LTb ≤ 150

[0103] In the tread portion T, from the viewpoint of effectively reducing mechanical fatigue due to strain and thermal fatigue due to heat generation, it is preferable that the tensile strength TB, elongation at break EB, and loss tangent LTc at 30°C of the cap layer 76 satisfy the following equation (1), and that the loss tangent LTb and complex modulus E*b of the belt topping rubber 52 at 70°C satisfy the following equation (2), with the loss tangent LTb being 0.05 or more and 0.18 or less. 20000≦TB×EB / LTc≦100000...Formula (1) 50≦E*b / LTb≦150...Equation (2)

[0104] As mentioned above, the belt 14 includes a belt cord 50, and the belt cord 50 is a steel cord. The belt cord 50 includes one or more steel filaments 80. Considering the strength of the belt 14 and its effect on the mass of the tire 2, if the belt cord 50 includes multiple steel filaments 80, it is preferable that the number of steel filaments 80 included in the belt cord 50 is between two and four. The belt cord 50 of this tire 2 is preferably a single wire consisting of one steel filament 80, or a stranded wire made by twisting together two to four steel filaments 80.

[0105] Figure 9 shows an example of a belt cord 50 included in belt 14. The belt cord 50a shown in Figure 9 is a stranded wire made by twisting together two steel filaments 80. The belt cord 50a shown in Figure 9 is a conventional belt cord. In Figure 9, the length indicated by the double arrow CDa is the cord diameter of the belt cord 50a. The cord diameter CDa of the belt cord 50a is 0.55 mm or more and 0.65 mm or less. The cord strength of the belt cord 50a is 400 N or more and 500 N or less.

[0106] As mentioned above, this tire 2 has a flat outer surface 4G of the tread 4 when inflated, which suppresses the deformation that occurs in the tread 4 due to the action of load. Because this tire 2 has a thin tread 4, it can also suppress the accumulation of heat in the tread 4 due to the action of deformation. Therefore, even when a conventional belt cord is used as the belt cord 50, this tire 2 can reduce not only mechanical fatigue due to deformation but also thermal fatigue due to heat generation.

[0107] Figure 10 shows a modified example (first modified example) of the belt cord 50. The belt cord 50b shown in Figure 10 is a single wire consisting of one steel filament 80. The length indicated by the double arrow CDb in Figure 10 is the cord diameter of the belt cord 50c.

[0108] The belt cord 50b shown in Figure 10 allows for a better balance between the strength and weight reduction of the belt 14 compared to the belt cord 50a. From this viewpoint, the belt cord 50b shown in Figure 10 is preferred as the belt cord 50 of the tire 2. In this case, the cord diameter CDb of the belt cord 50b is preferably 0.36 mm or more and 0.42 mm or less, and the cord strength of the belt cord 50b is preferably 400 N or more and 540 N or less. This allows the belt cord 50b to contribute to the weight reduction of the belt 14. A lighter belt 14 can contribute to reducing the centrifugal force generated in the tire 2 during driving. In particular, since the cord diameter CDb and cord strength of the belt cord 50b are set within the aforementioned range, the restraining force and centrifugal force are well balanced. This belt 14 of the tire 2 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation. From this perspective, it is more preferable that the cord diameter CDb of the belt cord 50b is 0.38 mm or more and 0.40 mm or less, and the cord strength of the belt cord 50b is 420 N or more and 480 N or less.

[0109] Figure 11 shows a modified version (second modified version) of the belt cord 50. The belt cord 50c shown in Figure 11 is a stranded wire made by twisting together four steel filaments 80. The length indicated by the double arrow CDc in Figure 11 is the cord diameter of the belt cord 50c.

[0110] The belt cord 50c shown in Figure 11, like the belt cord 50b mentioned above, allows for a better balance between the strength and weight reduction of the belt 14 compared to the belt cord 50a. From this perspective, the belt cord 50c shown in Figure 11 may be used as the belt cord 50 of the tire 2. In this case, it is preferable that the cord diameter CDc of the belt cord 50c is 0.36 mm or more and 0.55 mm or less, and the cord strength of the belt cord 50c is 350 N or more and 540 N or less. This allows the belt cord 50c to contribute to the weight reduction of the belt 14. A lighter belt 14 can contribute to reducing the centrifugal force generated in the tire 2 during driving. In particular, since the cord diameter CDc and cord strength of the belt cord 50c are set within the ranges mentioned above, the restraining force and centrifugal force are well balanced. The belt 14 of this tire 2 can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation. From this perspective, it is more preferable that the cord diameter CDc of the belt cord 50c is 0.39 mm or more and 0.52 mm or less, and the cord strength of the belt cord 50b is 430 N or more and 530 N or less.

[0111] From the viewpoint of constructing a belt 14 that can effectively contribute to reducing mechanical fatigue due to strain and thermal fatigue due to heat generation, it is more preferable that the belt cord 50 is the belt cord 50c shown in Figure 11, that is, a stranded wire made by twisting together four steel filaments 80.

[0112] In Figure 8, the length indicated by the double arrow TP represents the thickness of the belt ply 44. From the viewpoint of reducing the weight of the belt, when the belt cord 50c shown in Figure 11 is used as belt cord 50, the thickness TP of the belt ply 44 is preferably 0.66 mm or more and 0.98 mm or less. When the belt cord 50a shown in Figure 9 is used as belt cord 50, the thickness TP of the belt ply 44 is preferably 0.84 mm or more and 1.06 mm or less. When the belt cord 50b shown in Figure 10 is used as belt cord 50, the thickness TP of the belt ply 44 is preferably 0.63 mm or more and 0.83 mm or less.

[0113] The distance between the belt cord 50 of one belt ply 44 and the belt cord 50 of the other belt ply 44 of two adjacent belt plies 44 (in this tire 2, the distance between the belt cord 50 of the inner belt ply 46 and the belt cord 50 of the outer belt ply 48) is also called the cord-to-cord distance. In Figure 8, the length indicated by the double arrow DP represents the cord-to-cord distance. From the viewpoint of achieving a reinforcing effect on the tread portion T by the belt 14 and reducing the weight of the belt 14, the cord-to-cord distance DP is preferably 0.30 mm or more and 0.42 mm or less, and more preferably 0.33 mm or more and 0.38 mm or less.

[0114] From the perspective of providing a reinforcing effect on the tread section T by the belt 14 and reducing the weight of the belt 14, the mass per unit area of ​​one belt ply 44 is 1350 g / m². 2 More than 1980g / m 2 Preferably, the weight of the belt topping rubber 52 contained per unit area of ​​one belt ply 44 is 600 g / m². 2 More than 1300g / m 2 The following is preferable:

[0115] As is clear from the above explanation, the present invention provides a tire 2 that can achieve improved durability in environments where loads higher than those previously assumed are applied. The tire 2 of the present invention can stably perform even when mounted on an electric vehicle, which is heavier than a conventional gasoline vehicle. [Industrial applicability]

[0116] The technologies described above, which can improve durability under loads higher than those previously anticipated, can be applied to various types of tires.

[0117] [Note] The present invention includes the following embodiments.

[0118] [1] A tire comprising a pair of beads, a carcass spanning between the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt, wherein the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire, and the reference state of the tire is the position on the outer surface of the tire corresponding to the axial outer end of the contact surface of the tire obtained by applying a longitudinal load to the tire in the reference state and bringing the tire into contact with a plane, and the longitudinal load has the same dimensional and structural characteristics as the tire nominal size, as defined in the ETRTO 2024 standard manual, and the tire has a high load capacity. A tire whose load index represents the maximum load capacity, wherein, in the tire in the reference state, the ratio CD / CW of the radial distance CD from the tire's equator to the ground contact reference end to the tire's axial distance CW from the tire's equator to the ground contact reference end is 0.040 or more and 0.092 or less, and the tread thickness TA at the equator is 6.0 mm or more and 8.0 mm or less. [2] The tire according to [1] above, wherein the reference region is centered on the equator and has an axial width of 110% of the axial width of the contact surface, the center region is centered on the equator and has an axial width of 55% of the axial width of the contact surface, the shoulder region is the axial outer portion of the center region, the band is made by spirally winding a band strip, the band strip is a cord array in which one or more band cords are arranged, the band comprises a full band that covers the entire belt, and the ratio Es / Ec of the cord ends Es of the full band in the shoulder region to the cord ends Ec of the full band in the center region is 1.2 or more and 1.6 or less. [3] The tire according to [1] or [2] above, wherein the tread comprises a plurality of rubber layers arranged radially, the outermost rubber layer in the radial direction being a cap layer, and the tensile strength TB, elongation at break EB, and loss tangent LTc at 30°C of the cap layer satisfy the following formula. 20000 ≤ TB × EB / LTc ≤ 100000 [4] The tire according to any one of [1] to [3] above, wherein the belt comprises a plurality of parallel belt cords and a belt topping rubber covering the plurality of belt cords, and the loss tangent LTb and complex modulus E*b of the belt topping rubber at 70°C satisfy the following formula. 50 ≤ E*b / LTb ≤ 150 [5] The tire described in [4] above, wherein the loss tangent LTb is 0.05 or more and 0.18 or less. [6] The tire according to [4] or [5] above, wherein the belt cord is a single wire made of a single steel filament, the cord diameter of the belt cord is 0.36 mm or more and 0.42 mm or less, and the cord strength of the belt cord is 400 N or more and 540 N or less. [7] The tire according to [4] or [5] above, wherein the belt cord is a stranded wire made by twisting together four steel filaments, the cord diameter of the belt cord is 0.36 mm or more and 0.55 mm or less, and the cord strength of the belt cord is 350 N or more and 540 N or less. [Explanation of Symbols]

[0119] 2... Tires 4. Tread 10...bead 12...Carcass 14. Belt 16 bands 22...Tread surface 44, 46, 48... Belt ply 50... Belt cord 52... Belt topping rubber 54...Full Band 58... Band strip 60-band code 74.. Rubber layer 76... Cap layer 78...Base layer

Claims

1. A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass and in contact with the road surface, a belt located radially inward of the tread and radially outward of the carcass, and a band located radially between the tread and the belt, The tire is mounted on a standard rim, its internal pressure is adjusted to 290 kPa, and no load is applied to the tire; this is the standard state of the tire. The reference end of the tire is the position on the outer surface of the tire that corresponds to the axial outer end of the tire's contact surface, obtained by applying a longitudinal load to the tire in the aforementioned reference state and bringing the tire into contact with a plane. The aforementioned longitudinal load is the maximum load capacity represented by the load index of a HIGH LOAD CAPACY type tire, as defined in the ETRTO 2024 standard manual, which has the same dimensional and structural characteristics as the tire nominal designation of the tire. In the tire in the aforementioned reference state, the ratio CD / CW of the radial distance CD from the tire's equator to the ground contact reference end to the axial distance CW from the tire's equator to the ground contact reference end is 0.040 or more and 0.092 or less. The tread thickness TA at the equator is 6.0 mm or more and 8.0 mm or less. tire.

2. The reference region is a region centered on the equator and having an axial width of 110% of the axial width of the ground surface. Of the aforementioned reference region, the region centered on the equator and having an axial width of 55% of the axial width of the ground surface is the center region. Of the aforementioned reference region, the region in the axial direction outward of the center region is the shoulder region. The aforementioned band is formed by winding a band strip in a spiral shape. The band strip is a code array in which one or more of the band codes are arranged, The band comprises a full band that covers the entire belt, The ratio Es / Ec of the full-band code end Es in the shoulder region to the full-band code end Ec in the center region is 1.2 or more and 1.6 or less. The tire according to claim 1.

3. The tread comprises a plurality of rubber layers arranged radially, Of the multiple rubber layers, the outermost rubber layer in the radial direction is the cap layer. The tensile strength TB, elongation at break EB, and loss tangent LTc of the cap layer satisfy the following equation: The tire according to claim 1. 20000 ≤ TB × EB / LTc ≤ 100000

4. The belt comprises a number of parallel belt cords and a belt topping rubber covering the number of belt cords. The loss tangent LTb and complex modulus E*b of the belt topping rubber at 70°C satisfy the following equation: A tire according to any one of claims 1 to 3. 50≦E*b / LTb≦150

5. The loss tangent LTb is 0.05 or more and 0.18 or less. The tire according to claim 4.

6. The aforementioned belt cord is a single wire consisting of one steel filament, The cord diameter of the aforementioned belt cord is 0.36 mm or more and 0.42 mm or less. The cord strength of the aforementioned belt cord is 400N or more and 540N or less. The tire according to claim 4.

7. The aforementioned belt cord is a stranded wire made by twisting together four steel filaments. The cord diameter of the aforementioned belt cord is 0.36 mm or more and 0.55 mm or less. The cord strength of the aforementioned belt cord is 350N or more and 540N or less. The tire according to claim 4.

Images