tire

Abstract

To provide a tire 2 which can achieve reduction of rolling resistance while minimizing deterioration of durability.SOLUTION: An apex 32 of a bead 10 includes an apex body 48, a strip apex 50, and an intermediate apex 52. An inner end of the strip apex 50 is located between a ply body 38a of a carcass ply 38 and the apex body 48. An inner end of the intermediate apex 52 is located between the strip apex 50 and the apex body 48. An outer end of the apex body 48 is located between the inner end and an outer end of the intermediate apex 52. The intermediate apex 52 is located between the inner end and an outer end of the strip apex 50. The intermediate apex 52 is harder than the apex body 48 and the strip apex 50 is harder than the intermediate apex 52.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire. [Background technology]

[0002] Due to environmental considerations, reduced rolling resistance is required for tires mounted on vehicles. To reduce rolling resistance, for example, thin sidewalls are used. In this case, the rigidity of the side portions decreases. In order to maintain good steering stability, it is known that a tire can maintain good steering stability by configuring the bead apex with an apex main body, which is a conventional bead apex, and a hard strip apex, and by providing the strip apex between the ply main body of the carcass ply and the apex main body (for example, Patent Document 1 listed below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-174515 Summary of the Invention [Problem to be solved by the invention]

[0004] In a tire employing the aforementioned strip apex, the inner end portion of the strip apex is sandwiched between the ply body and the apex body. The apex body tapers outward. Near the outer end of the apex body, there is a large difference in stiffness between the apex body and the strip apex. In the tire, strain is concentrated near the outer end of the apex body. This difference in stiffness may result in a decrease in durability.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tire that can achieve a reduction in rolling resistance while minimizing a decrease in durability. [Means for solving the problem]

[0006] A tire according to one aspect of the present invention includes a pair of beads and a carcass spanning between a first bead and a second bead of the pair. Each bead includes a core and an apex. The carcass includes a carcass ply. The carcass ply includes a ply body spanning between the core of the first bead and the core of the second bead, and a pair of turnup portions connected to the ply body and turned up around the core from the axially inner side to the axially outer side. The apex includes an apex body located radially outward of the core, a strip apex located axially outward of the ply body, and an intermediate apex located axially outward of the strip apex. The apex body tapers outward. An inner end of the strip apex is located between the ply body and the apex body. An inner end of the intermediate apex is located between the strip apex and the apex body. The outer end of the apex body is located between the inner end and outer end of the intermediate apex in the radial direction. The intermediate apex is located between the inner end and outer end of the strip apex in the radial direction. The intermediate apex is harder than the apex body, and the strip apex is harder than the intermediate apex.

[0007] Preferably, in the tire, the intermediate apex has a length of 15 mm or greater and 25 mm or less.

[0008] Preferably, in the tire, the length from the inner end of the intermediate apex to the outer end of the apex body is equal to or greater than 5 mm and equal to or less than 15 mm.

[0009] Preferably, in the tire, the difference (Hm-Ha) between the hardness Hm of the intermediate apex and the hardness Ha of the apex body is 5 or less.

[0010] In the tire, the difference (Hs-Hm) between the hardness Hs of the strip apex and the hardness Hm of the intermediate apex is preferably 5 or less.

[0011] Preferably, in the tire, the apex body has a hardness Ha of 60 or greater and 80 or less.

[0012] Preferably, in the tire, the apex body has a length of 15 mm or greater and 45 mm or less.

[0013] Preferably, in the tire, a ratio of a maximum width of the apex body to a length of the apex body is equal to or greater than 0.2 and is equal to or less than 0.7.

[0014] Preferably, in the tire, a position of the ply body that is 15 mm away from a position of the ply body corresponding to the outer end of the apex body toward the inner end of the strip apex is a first reference position, and a position of the ply body that is 10 mm away from a position of the ply body corresponding to the outer end of the intermediate apex is a second reference position. The stiffness of the apex at each position on the ply body is expressed by a stiffness index R shown in the following formula (1) using a hardness Ha of the apex body, a hardness Hs of the strip apex, and a hardness Hm of the intermediate apex, and a thickness ta of the apex body, a thickness ts of the strip apex, and a thickness tm of the intermediate apex, which are measured along a normal to the ply body. R = Ha×ta+Hs×ts+Hm×tm (1) When the stiffness index R of the apex at the first reference position is defined as a reference stiffness index Rb, the ratio of the stiffness index R of the apex to the reference stiffness index Rb at any position in the zone from the first reference position to the second reference position is 100% or more and 110% or less. [Effects of the Invention]

[0015] According to the present invention, a tire can be obtained that can achieve a reduction in rolling resistance while minimizing a decrease in durability. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a bead portion of a tire. [Figure 3] FIG. 3 is a cross-sectional view illustrating the stiffness control of the apex. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0018] A tire is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. In this disclosure, a tire mounted on a rim is a tire-rim assembly. A tire-rim assembly includes a rim and a tire mounted on the rim.

[0019] In this disclosure, 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.

[0020] In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part of the tire's meridian cross section, which cannot be measured when the tire is mounted on a standard rim, are measured by matching the distance between the left and right beads on the cross section of the tire (hereinafter referred to as the reference cross section) obtained by cutting the tire along a plane including the axis of rotation to the distance between the beads on the tire mounted on a standard rim.

[0021] A genuine rim is a rim 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 all genuine rims.

[0022] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0023] 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 the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0024] In the present disclosure, the hardness of an element made of crosslinked rubber among elements constituting a tire is measured using a type A durometer under a temperature condition of 23°C in accordance with the provisions of JIS K6253.

[0025] In this disclosure, 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 side 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 side portions.

[0026] FIG. 1 shows a portion of a tire 2 according to one embodiment of the present invention. This tire 2 is suitable for use on passenger cars, van-type light commercial vehicles, light trucks, and the like. The tire 2 shown in FIG. 1 is a pneumatic tire for passenger cars that can be fitted to pickup trucks. The tire 2 of the present disclosure is not limited to such a usage mode. Tire 2 is mounted on rim R. Rim R is a standard rim. Air is filled inside tire 2, and the internal pressure of tire 2 is adjusted.

[0027] FIG. 1 shows a portion of a cross section (hereinafter referred to as a meridian cross section) of the tire 2 taken along a plane including the rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction 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 represents the equatorial plane of the tire 2.

[0028] In FIG. 1, the position indicated by the symbol PW is the axially outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the axially outer end PW (hereinafter referred to as the outer end PW) is identified based on a virtual outer surface obtained by assuming that the tire 2 is in a normal state and has no decoration. The axial distance from the first outer end PW to the second outer end PW is the cross-sectional width (see JATMA, etc.) of the tire 2. The cross-sectional width is the maximum width of the tire 2, and the outer end PW is the position where the tire 2 shows its maximum width (hereinafter referred to as the maximum width position).

[0029] The tire 2 includes 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 , an inner liner 18 , and a pair of chafers 20 .

[0030] The tread 4 comes into contact with the road surface at a tread surface 22. The tread 4 has a tread surface 22 that comes into contact with the road surface. Grooves 24 are cut into the tread 4. This forms a tread pattern.

[0031] The tread 4 includes a cap portion 26 and a base portion 28 . The cap portion 26 includes the tread surface 22. The cap portion 26 is made of crosslinked rubber in consideration of wear resistance and grip performance. The base portion 28 is located radially inside the cap portion 26. The base portion 28 is covered by the cap portion 26. The base portion 28 covers the belt 14 and the band 16. The base portion 28 is made of low-heat-generating crosslinked rubber.

[0032] Each sidewall 6 is continuous with an edge of the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 is made of crosslinked rubber in consideration of cut resistance. In order to reduce rolling resistance, the sidewall at the maximum width position PW 6 The thickness is preferably 5.0 mm or less. From the viewpoint of ensuring the rigidity of the side portions, the thickness is preferably 3.0 mm or more.

[0033] Each clinch 8 is located radially inside the sidewall 6. The clinch 8 comes into contact with the flange of the rim R. The clinch 8 is made of cross-linked rubber that is designed for wear resistance.

[0034] Each bead 10 is located axially inward of the clinch 8. The beads 10 are located radially inward of the sidewall 6. The bead 10 includes a core 30 and an apex 32. The core 30 extends in the circumferential direction. Although not shown, the core 30 includes a steel wire. The apex 32 is located radially outward of the core 30. The apex 32 is made of cross-linked rubber.

[0035] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between the first bead 10 and the second bead 10 of the pair of beads 10. The carcass 12 includes at least one carcass ply 34.

[0036] The carcass 12 of this tire 2 is composed of two carcass plies 34. Although not shown, each carcass ply 34 includes a large number of carcass cords arranged in parallel. These carcass cords intersect with the equatorial plane. The carcass 12 of this tire 2 has a radial structure. In this tire 2, cords made of organic fibers are used as carcass cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0037] Of the two carcass plies 34, the carcass ply 34 located radially inner on the inner side of the tread 4 is a first carcass ply 36. The carcass ply 34 located radially outer of the first carcass ply 36 on the inner side of the tread 4 is a second carcass ply 38.

[0038] The first carcass ply 36 includes a first ply body 36a and a pair of first turned-up portions 36b. The first ply body 36a spans between the core 30 of the first bead 10 and the core 30 of the second bead 10. Each of the first turned-up portions 36b is continuous with the first ply body 36a and is turned up around the core 30 from the inside to the outside in the axial direction.

[0039] The second carcass ply 38 includes a second ply body 38a and a pair of second turned-up portions 38b. The second ply body 38a spans between the first core 30 and the second core 30. Each of the second turned-up portions 38b is continuous with the second ply body 38a and is turned up around the core 30 from the inside to the outside in the axial direction.

[0040] In this tire 2, the end of the first turned-up portion 36b is located radially outward from the axially outer end PW. The end of the second turned-up portion 38b is located radially inward from the axially outer end PW. The end of the second turned-up portion 38b is located radially between the outer end of the apex body (described later) and the core 30. The second turned-up portion 38b is located axially inward from the first turned-up portion 36b.

[0041] The belt 14 is located radially inside the tread 4. The belt 14 is laminated on the carcass 12. The belt 14 includes an inner layer 40 and an outer layer 42. The inner layer 40 is positioned radially outward of the second ply body 38a and is laminated to the second ply body 38a. The outer layer 42 is positioned radially outward of the inner layer 40 and is laminated to the inner layer 40.

[0042] Although not shown, each of the inner layer 40 and the outer layer 42 includes a large number of parallel belt cords. These belt cords are covered with a topping rubber. Each belt cord is inclined with respect to the equatorial plane. The inclination direction of the belt cords included in the inner layer 40 is opposite to the inclination direction of the belt cords included in the outer layer 42. The belt cords are made of steel.

[0043] The band 16 is positioned radially between the tread 4 and the belt 14. The band 16 is laminated on the belt 14. Although not shown, the band 16 includes a spirally wound band cord. The band cord is covered with a topping rubber. The band cord extends substantially in the circumferential direction. Specifically, the angle that the band cord forms with the circumferential direction is 5° or less. The band 16 has a jointless structure. A cord made of organic fiber is used as the band cord. Examples of organic fibers include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0044] The band 16 of the tire 2 includes a full band 44 and a pair of edge bands 46 . The full band 44 has opposite ends across the equator plane. The full band 44 is laminated on the belt 14. The pair of edge bands 46 are arranged axially apart across the equator plane. Each edge band 46 is laminated to a full band 44. The edge bands 46 cover the end portions of the full bands 44. The band 16 may be composed of only the full band 44 or may be composed of only a pair of edge bands 46 .

[0045] The inner liner 18 is located 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 that has excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0046] Each chafer 20 is located radially inside the bead 10. The chafer 20 is made of cloth and rubber impregnated into the cloth. The chafer 20 comes into contact with the seat of the rim R.

[0047] Fig. 2 shows a part of the tire 2 shown in Fig. 1. Fig. 2 shows a bead portion of the tire 2. As described above, the bead 10 of the tire 2 includes the core 30 and the apex 32. The apex 32 of the tire 2 includes the apex body 48, the strip apex 50, and the intermediate apex 52.

[0048] The apex body 48 is located radially outward of the core 30. The apex body 48 is laminated on the core 30. The apex body 48 contacts the core 30 at its bottom surface 48b. In a meridian cross section of the tire 2, the apex body 48 tapers outward. The apex body 48 is made of crosslinked rubber. The hardness Ha of the apex body 48 is preferably 60 or greater and 80 or less.

[0049] 2, the position indicated by the symbol Pm is the center of the bottom surface 48b of the apex body 48. The center Pm is represented by the central position of the bottom surface 48b in the axial direction. The length indicated by the symbol L is the length of the line segment connecting the center Pm and the outer end 48g of the apex body 48. In the present disclosure, this length L is the length of the apex body 48. This length L is 2 When the bottom surface 48b has an outwardly convex shape, the length L of the apex body 48 is represented by the length of a line segment connecting the radially outer end (in other words, the apex) of the bottom surface 48b and the outer end 48g of the apex body 48. In the tire 2, from the viewpoint of improving durability, the length L of the apex body 48 is preferably 15 mm or more. From the viewpoint of suppressing adverse effects on the mass and rolling resistance, the length L is preferably 45 mm or less, more preferably 40 mm or less, and even more preferably 35 mm or less.

[0050] The length indicated by the symbol C in Figure 2 is the maximum width of the apex body 48. As described above, the apex body 48 of the tire 2 tapers outward. The axial width of the apex body 48 indicates the maximum width C at the center Pm. The maximum width C is expressed as the length of the intersection line between the apex body 48 and a straight line that passes through the center Pm and extends in the axial direction. In this tire 2, from the viewpoint of improving durability, it is preferable that the ratio (C / L) of the maximum width C of the apex body 48 to the length L of the apex body 48 is 0.2 or more. From the viewpoint of stably manufacturing the tire 2, it is preferable that the ratio (C / L) is 0.7 or less.

[0051] The strip apex 50 is located axially outward of the second ply body 38a. The strip apex 50 is made of a sheet-like member. The entire strip apex 50 is laminated on the second ply body 38a. The inner end 50n of the strip apex 50 is sandwiched between the second ply body 38a and the apex body 48. The inner end 50n of the strip apex 50 is located radially inward of the outer end 48g of the apex body 48. The outer end 48g of the apex body 48 is located radially between the inner end 50n and the outer end 50g of the strip apex 50. The outer end 50g of the strip apex 50 is located radially inward of the end of the first turned-up portion 36b. The outer end 50g of the strip apex 50 is located between the second ply body 38a and the first turned-up portion 36b. The outer end 50g of the strip apex 50 is sandwiched between the second ply body 38a and the first turned-up portion 36b. The strip apex 50 is made of crosslinked rubber. The hardness Hs of the strip apex 50 is preferably 80 or more and 100 or less.

[0052] The intermediate apex 52 is located axially outward of the strip apex 50. The intermediate apex 52 is made of a sheet-like member. The entire intermediate apex 52 is laminated on the strip apex 50. The inner end 52n of the intermediate apex 52 is located radially outward from the inner end 50n of the strip apex 50. The inner end 52n of the intermediate apex 52 is located radially inward from the outer end 48g of the apex body 48. The inner end 52n of the intermediate apex 52 is sandwiched between the strip apex 50 and the apex body 48. The outer end 52g of the intermediate apex 52 is located radially inward of the outer end 50g of the strip apex 50. The outer end 52g of the intermediate apex 52 is located radially outward of the outer end 48g of the apex body 48. The outer end 52g of the intermediate apex 52 is located between the strip apex 50 and the first folded portion 36b. The outer end 52g of the intermediate apex 52 is sandwiched between the strip apex 50 and the first folded portion 36b. The intermediate apex 52 is made of crosslinked rubber and preferably has a hardness Hm of 70 or more and 90 or less.

[0053] In the tire 2, the inner end 50n of the strip apex 50 is located between the second ply body 38a and the apex body 48. The inner end 52n of the intermediate apex 52 is located between the strip apex 50 and the apex body 48. The outer end 48g of the apex body 48 is located radially between the inner end 52n and the outer end 52g of the intermediate apex 52. The intermediate apex 52 is located radially between the inner end 50n and the outer end 50g of the strip apex 50. In the tire 2, the intermediate apex 52, which is entirely laminated on the strip apex 50, is located between the outer end 48g of the apex body 48 and the strip apex 50. Moreover, the intermediate apex 52 is harder than the apex body 48, and the strip apex 50 is harder than the intermediate apex 52. In other words, the intermediate apex 52 is harder than the apex body 48 and softer than the strip apex 50. As described above, the apex body 48 is tapered outward. The outer end 48g of the apex body 48 has lower rigidity than the other portions. The difference in rigidity between the outer end 48g of the apex body 48 and the strip apex 50 is quite large. In this tire 2, an intermediate apex 52, which is softer than the strip apex 50 and harder than the apex main body 48, is located between the outer end 48g of the apex main body 48 and the strip apex 50. This intermediate apex 52 reduces the difference in rigidity between the strip apex 50 and the apex main body 48. In this tire 2, concentration of strain near the outer end 48g of the apex main body 48 is suppressed. This tire 2 has higher durability than conventional tires that do not have the intermediate apex 52 between the strip apex 50 and the apex main body 48. Despite adopting the strip apex 50 to reduce rolling resistance and improve handling stability, this tire 2 also has improved durability. Even if the tire 2 employs a thin sidewall for reducing rolling resistance, it is possible to obtain the required durability while maintaining good steering stability. The tire 2 can achieve a reduction in rolling resistance while minimizing the deterioration in durability.

[0054] 2 , the length indicated by the symbol a is the length of the intermediate apex 52. The length a is obtained by measuring the length from the inner end 52n to the outer end 52g of the intermediate apex 52 along the interface between the intermediate apex 52 and the strip apex 50 in the meridian cross section of the tire 2. The length indicated by the symbol b is the length from the inner end 52n of the intermediate apex 52 to the outer end 48g of the apex body 48. This length b is also the overlap length between the intermediate apex 52 and the apex body 48. This overlap length b is obtained by measuring the length from the inner end 52n of the intermediate apex 52 to the outer end 48g of the apex body 48 along the interface between the intermediate apex 52 and the apex body 48 in the meridian cross section of the tire 2.

[0055] In the tire 2, the length a of the intermediate apex 52 is preferably 15 mm or greater and 25 mm or less. By setting the length a to 15 mm or more, the intermediate apex 52 can effectively contribute to reducing the difference in rigidity between the strip apex 50 and the apex body 48. This improves the durability of the tire 2. From this viewpoint, it is more preferable that the length a be 17 mm or more. By setting the length a to 25 mm or less, the effect of the intermediate apex 52 on the rolling resistance is suppressed, and low rolling resistance is maintained. From this viewpoint, it is more preferable that the length a be 23 mm or less.

[0056] In the tire 2, it is preferable that the length b from the inner end 52n of the intermediate apex 52 to the outer end 48g of the apex body 48 is 5 mm or more and 15 mm or less. By setting the length b to 5 mm or more, the intermediate apex 52 can effectively contribute to reducing the difference in rigidity between the strip apex 50 and the apex body 48. This improves the durability of the tire 2. From this viewpoint, it is more preferable that the length b be 7 mm or more. By setting the length b to 15 mm or less, the influence of the intermediate apex 52 on the rolling resistance is suppressed, and low rolling resistance is maintained. From this viewpoint, it is more preferable that the length b be 13 mm or less.

[0057] As described above, in the tire 2, the intermediate apex 52 is harder than the apex body 48. If the intermediate apex 52 is too hard compared to the apex body 48, a large difference in rigidity will occur between the intermediate apex 52 and the apex body 48, which may result in reduced durability. From the viewpoint of maintaining good durability, it is preferable that the difference (Hm-Ha) between the hardness Hm of the intermediate apex 52 and the hardness Ha of the apex body 48 be 5 or less. From the viewpoint that the intermediate apex 52 can effectively contribute to reducing the difference in rigidity between the strip apex 50 and the apex body 48, it is preferable that the difference (Hm-Ha) be 2 or more, and more preferably 3 or more.

[0058] As described above, in the tire 2, the strip apex 50 is harder than the intermediate apex 52. In other words, the intermediate apex 52 is softer than the strip apex 50. If the intermediate apex 52 is too softer than the strip apex 50, a large difference in rigidity will occur between the strip apex 50 and the intermediate apex 52, which may result in a decrease in durability. From the viewpoint of maintaining good durability, it is preferable that the difference (Hs-Hm) between the hardness Hs of the strip apex 50 and the hardness Hm of the intermediate apex 52 be 5 or less. From the viewpoint that the intermediate apex 52 can effectively contribute to reducing the difference in rigidity that occurs between the strip apex 50 and the apex body 48, it is preferable that the difference (Hs-Hm) be 2 or more, and more preferably 3 or more.

[0059] In this tire 2, from the viewpoint of obtaining good durability, it is more preferable that the difference (Hm-Ha) between the hardness Hm of the intermediate apex 52 and the hardness Ha of the apex body 48 is 5 or less, and that the difference (Hs-Hm) between the hardness Hs of the strip apex 50 and the hardness Hm of the intermediate apex 52 is 5 or less.

[0060] In this tire 2, the rigidity of the apex 32 near the outer end 48g of the apex body 48 is preferably controlled using a rigidity index expressed as the product of the hardness and thickness of the elements that make up this apex 32 (i.e., the apex body 48, the strip apex 50, and the intermediate apex 52). 3 is a cross-sectional view illustrating the stiffness control of the apex 32. In order to explain the stiffness index used in the stiffness control of the apex 32, this FIG. 3 shows a cross-section of the apex 32 as a conceptual diagram.

[0061] In the tire 2, the rigidity of the apex 32 at each position on the second ply body 38a where the entire strip apex 50 is laminated is expressed by a rigidity index. When this rigidity index is R, the rigidity index R is expressed by the following formula (1) using the hardness Ha of the apex body 48, the hardness Hs of the strip apex 50, the hardness Hm of the intermediate apex 52, and the thickness ta of the apex body 48, the thickness ts of the strip apex 50, and the thickness tm of the intermediate apex 52, which are measured along the normal to the second ply body 38a. R = Ha×ta+Hs×ts+Hm×tm (1)

[0062] Next, a method for calculating the stiffness index R using this formula (1) will be explained. 3 is the intersection of a normal to the outer surface of the second ply body 38a and the outer surface, the normal passing through the outer end 48g of the apex body 48. This position Pag is the position on the second ply body 38a corresponding to the outer end 48g of the apex body 48. This position Pag is also referred to as a position corresponding to the outer end of the apex body 48. The position indicated by the symbol PB1 is a position on the outer surface of the second ply body 38a. This position PB1 is a position 15 mm away from the position Pag corresponding to the outer end of the apex body 48 toward the inner end 50n of the strip apex 50. In the present disclosure, this position PB1 is a first reference position. The length from the position Pag corresponding to the outer end to the first reference position PB1 is measured along the interface between the second ply body 38a and the strip apex 50. Figure 3 shows, as an example, a case where the first reference position PB1 is located radially inside the inner end 52n of the intermediate apex 52, but the position of this first reference position PB1 may coincide with the position of the inner end 52n of the intermediate apex 52, or the first reference position PB1 may be located radially outside the inner end 52n of the intermediate apex 52.

[0063] 3 is the intersection point between the outer surface of the second ply body 38a and a line normal to the outer surface of the second ply body 38a, the line passing through the outer end 52g of the intermediate apex 52. This position Pmg is a position on the second ply body 38a corresponding to the outer end 52g of the intermediate apex 52. This position Pmg is also referred to as a position corresponding to the outer end of the intermediate apex 52. The position indicated by the symbol PB2 is a position on the outer surface of the second ply body 38a. This position PB2 is a position 10 mm away from the outer end corresponding position Pmg of the intermediate apex 52 toward the outer end 50g of the strip apex 50. In the present disclosure, this position PB2 is a second reference position. The length from the outer end corresponding position Pmg to the second reference position PB2 is determined by the distance between the second ply body 38a and the strip apex 50. 50 The measurement is taken along the interface with

[0064] 3, the solid line L1 is a normal to the outer surface of the second ply body 38a. This normal line L1 is located in a zone (hereinafter referred to as the first zone) between the first reference position PB1 and the inner end 52n of the intermediate apex 52. As shown in FIG. 3, the elements of the apex 32 located in the first zone are the apex body 48 and the strip apex 50. 3, the length indicated by the symbol ts1 is the thickness of the strip apex 50 at the position of the normal line L1. The length indicated by the symbol ta1 is the thickness of the apex body 48 at the position of the normal line L1. The thicknesses ts1 and ta1 are measured along the normal line L1. This first zone does not include the intermediate apex 52. Therefore, the thickness tm1 of the intermediate apex 52 in this first zone is 0 (zero) mm. Therefore, in this first zone, the stiffness index R1 of the apex 32 at each position of the second ply body 38a is expressed by the following equation (1a). R1 = Ha×ta1+Hs×ts1 (1a)

[0065] 3, the solid line L2 is also a normal to the outer surface of the second ply body 38a. This normal line L2 is located in a zone (hereinafter referred to as the second zone) between the second reference position PB2 and the outer end 52g of the intermediate apex 52. As shown in FIG. 3, the element of the apex 32 located in the second zone is the strip apex 50. 3, the length indicated by the symbol ts2 is the thickness of the strip apex 50 at the position of the normal line L2. The thickness ts2 is measured along the normal line L2. This second zone does not include the apex body 48 or the intermediate apex 52. Therefore, the thickness ta2 of the apex body 48 in this second zone is 0 (zero) mm, and the thickness tm2 of the intermediate apex 52 is also 0 (zero) mm. Therefore, in this second zone, the stiffness index R2 of the apex 32 at each position of the second ply body 38a is expressed by the following equation (1b). R2 = Hs × ts2 (1b)

[0066] 3, the solid line L3 is also a normal to the outer surface of the second ply body 38a. This normal line L3 is located in a zone (hereinafter referred to as the third zone) between the inner end 52n of the intermediate apex 52 and the outer end 48g of the apex body 48. As shown in FIG. 3, the elements of the apex 32 located in the third zone are the apex body 48, the strip apex 50, and the intermediate apex 52. In FIG. 3, the length indicated by the symbol ts3 is the thickness of the strip apex 50 at the position of the normal line L3. The length indicated by the symbol tm3 is the thickness of the intermediate apex 52 at the position of the normal line L3. The length indicated by the symbol ta3 is the thickness of the apex body 48 at the position of the normal line L3. 3 , thickness tm3 and thickness ta3 are measured along normal L3. This third zone includes all elements that make up the apex 32. Therefore, in this third zone, the stiffness index R3 of the apex 32 at each position of the second ply body 38a is expressed by the following formula (1c). R3 = Ha×ta3+Hs×ts3+Hm×tm3 (1c)

[0067] 3, the solid line L4 is also a normal to the outer surface of the second ply body 38a. This normal line L4 is located in a zone (hereinafter referred to as the fourth zone) between the outer end 48g of the apex body 48 and the outer end 52g of the intermediate apex 52. As shown in FIG. 3, the elements of the apex 32 located in the fourth zone are the strip apex 50 and the intermediate apex 52. 3, the length indicated by the reference symbol ts4 is the thickness of the strip apex 50 at the position of the normal line L4. The length indicated by the reference symbol tm4 is the thickness of the intermediate apex 52 at the position of the normal line L4. The thicknesses ts4 and tm4 are measured along the normal line L4. The fourth zone does not include the apex body 48. Therefore, the thickness ta4 of the apex body 48 in the fourth zone is 0 (zero) mm. Therefore, in the fourth zone, the stiffness index R4 of the apex 32 at each position of the second ply body 38a is expressed by the following formula (1d). R4 = Hs×ts4+Hm×tm4 (1d)

[0068] In the tire 2, the apex at any position in the zone from the first reference position PB1 to the second reference position PB2 32The stiffness index R of the apex 32 at the first reference position PB1 is obtained by using any one of the above-described formulas (1a) to (1d). index When the stiffness index R of the apex 32 is Rb, the ratio (R / Rb) of the stiffness index R of the apex 32 to the reference stiffness index Rb at any position in the zone from the first reference position PB1 to the second reference position PB2 is preferably 100% or more and 110% or less. This prevents the apex 32 from having an excessively high stiffness or an excessively low stiffness in the vicinity of the outer end 48g of the apex body 48. In the tire 2, strain concentration in the vicinity of the outer end 48g of the apex body 48 is effectively prevented. In this tire 2, durability is improved even though the strip apex 50 is adopted to reduce rolling resistance and improve steering stability. Even if the tire 2 employs a thin sidewall for reducing rolling resistance, it is possible to obtain the required durability while maintaining good steering stability.

[0069] As described above, according to the present invention, a tire 2 can be obtained that can achieve a reduction in rolling resistance while minimizing a decrease in durability. [Example]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0071] [Example 1] A pneumatic tire for a passenger car (tire nominal size = 215 / 70R16) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below was obtained.

[0072] In this Example 1, the hardness Ha of the apex body, the hardness Hs of the strip apex, the hardness Hm of the intermediate apex, and the length L of the apex body were set as shown in Table 1. The length a of the intermediate apex was set to 20 mm, and the length b from the inner end of the intermediate apex to the outer end of the apex body was set to 10 mm. The thickness of the sidewall at the maximum width position PW was set to 3.0 mm.

[0073] [Comparative Example 1] Comparative Example 1 is a conventional tire. The sidewall thickness was 5.0 mm. The apex was composed of only the apex body. In this Comparative Example 1, a strip apex and an intermediate apex were not used. The hardness Ha of the apex body was 80.

[0074] Comparative Example 2 A tire of Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that a thin sidewall was used.

[0075] Comparative Example 3 A tire of Comparative Example 3 was obtained in the same manner as Comparative Example 2, except that the length L of the apex body was set to 40 mm.

[0076] Comparative Example 4 A tire of Comparative Example 4 was obtained in the same manner as Comparative Example 2, except that a strip apex (hardness Hs=80) was added. The specifications of the strip apex were set to have the same configuration as Example 1, except for the hardness.

[0077] [Examples 2-7 and Comparative Examples 5-8] Tires of Examples 2-7 and Comparative Examples 5-8 were obtained in the same manner as in Example 1, except that the hardness Hs, hardness Hm, and hardness Ha were set as shown in Tables 2-3 below.

[0078] [Tire mass] The mass of the tire was measured. The results are shown in Table 1-3 below as an index, with Comparative Example 1 being set at 100. The smaller the value, the lighter the tire.

[0079] [Rolling resistance] Using a rolling resistance tester, the rolling resistance coefficient (RRC) was measured when the prototype tire ran on a drum at a speed of 80 km / h under the following conditions. The results are shown in Tables 1-3 below as an index, with Comparative Example 3 set to 100. The higher the value, the lower the rolling resistance of the tire. Rim: 16 x 6.5J Internal pressure: 240kPa Vertical load: 4.82kN

[0080] [Durability] The prototype tire was mounted on a rim (size = 16 x 6.5J) and inflated to an internal pressure of 375 kPa. This tire was then mounted on a drum-type running test machine. A vertical load of 14 kN was applied to the tire, and the tire was run on a drum (radius = 1.7 m) at a speed of 80 km / h. The running distance until damage to the tire was confirmed was measured. The results are shown as an index in Table 1-3 below. The higher the value, the less likely damage will occur and the better the durability.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] As shown in Tables 1-3, it has been confirmed that the Examples achieve a reduction in rolling resistance while minimizing the decrease in durability. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0085] The above-described technology that can achieve a reduction in rolling resistance while minimizing a decrease in durability can be applied to various types of tires. [Explanation of symbols]

[0086] 2. Tires 4. Tread 6. Sidewall 10 Bead 12. Carcass 32 Apex 34, 36, 38... Carcass ply 36a, 38a... Ply body 48···Apex main body 50 Strip Apex 52···Middle apex

Claims

1. A tire comprising a pair of beads and a carcass spanning between a first bead and a second bead of the pair of beads, Each bead has a core and an apex, the carcass comprises a carcass ply; The carcass ply includes a ply body that spans between the core of the first bead and the core of the second bead, and a pair of turn-up portions that are connected to the ply body and are turned up around the core from the inside to the outside in the axial direction, the apex includes an apex body located radially outward of the core, a strip apex located axially outward of the ply body, and an intermediate apex located axially outward of the strip apex, The apex body is tapered outward, an inner end of the strip apex is located between the ply body and the apex body; an inner end of the intermediate apex is located between the strip apex and the apex body; an outer end of the apex body is located between an inner end and an outer end of the intermediate apex in the radial direction; the intermediate apex is located between the inner end and the outer end of the strip apex in the radial direction, The intermediate apex is harder than the apex body, The strip apex is harder than the intermediate apex. tire.

2. The length of the intermediate apex is 15 mm or more and 25 mm or less.

2. The tire of claim 1.

3. The length from the inner end of the intermediate apex to the outer end of the apex body is 5 mm or more and 15 mm or less.

3. The tire according to claim 1 or 2.

4. the difference (Hm-Ha) between the hardness Hm of the intermediate apex and the hardness Ha of the apex body is 5 or less; A tire according to any one of claims 1 to 3.

5. The difference (Hs-Hm) between the hardness Hs of the strip apex and the hardness Hm of the intermediate apex is 5 or less.

5. A tire according to any one of claims 1 to 4.

6. The hardness Ha of the apex body is 60 or more and 80 or less.

6. A tire according to any one of claims 1 to 5.

7. The length of the apex body is 15 mm or more and 45 mm or less.

7. A tire according to any one of claims 1 to 6.

8. a ratio of a maximum width of the apex body to a length of the apex body is 0.2 or more and 0.7 or less; 8. The tire of claim 7.

9. a first reference position is a position of the ply body that is 15 mm away from a position of the ply body toward the inner end of the strip apex, the position corresponding to the outer end of the apex body; a second reference position of the ply body, the second reference position being 10 mm away from the ply body corresponding to the outer end of the intermediate apex toward the outer end of the strip apex; The rigidity of the apex at each position on the ply body is expressed by a rigidity index R expressed by the following formula (1) using the hardness Ha of the apex body, the hardness Hs of the strip apex, and the hardness Hm of the intermediate apex, as well as the thickness ta of the apex body, the thickness ts of the strip apex, and the thickness tm of the intermediate apex, which are measured along the normal to the ply body: R = Ha×ta+Hs×ts+Hm×tm (1) when a stiffness index R of the apex at the first reference position is defined as a reference stiffness index Rb, a ratio of the stiffness index R of the apex at any position in a zone from the first reference position to the second reference position to the reference stiffness index Rb is 100% or more and 110% or less.

9. A tire according to any one of claims 1 to 8.

Images