Heavy load reuse pneumatic tire

Abstract

To provide a heavy duty pneumatic tire capable of inhibiting durability deterioration of the tire resulting from heat evolution of a rubber layer while efficiently restraining uneven wear by restraining the variation of a ground plane.SOLUTION: A heavy duty pneumatic tire 100 comprises a carcass ply 40 forming a skeleton of the tire, and a belt layer 15 disposed outside the carcass ply in a tire radial direction in a tread part 10. The carcass ply 40 has a first curvature change part P1 which is a boundary between a first site P0-P1 including a tire equator line CL, and a second site P1-P2 which is disposed outside the first site in a tire width direction and inside in a radial direction and has a cross section curvature larger than that of the first site, and a second curvature change part P2 which is the boundary between the second site and a third site P2-P3 which is disposed inside the second site in the tire radial direction and has the cross section curvature smaller than that of the second site. Further, the tire comprises a cushion rubber 17a whose inside end in a tire width direction is located at the first curvature change part P1 to be disposed between the carcass ply 40 and the belt layer 15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pneumatic tire for heavy loads, comprising a carcass ply having two curvature-changing portions whose curvatures change in the tire width direction, and a cushion rubber disposed between a belt layer and the carcass ply.

Background Art

[0002] As a conventional pneumatic tire, there is known a tire that can suppress slip with respect to the road surface during tire rolling in the shoulder portion and improve uneven wear resistance by optimizing the ground contact shape of the tire (see, for example, Patent Document 1).

[0003] In such a pneumatic tire, in order to suppress fluctuations in the ground contact shape, it is said that premature uneven wear in the tread edge or shoulder portion can be prevented by defining conditions based on the circumferential ground contact length of the tire.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when the circumferential ground contact length of the tire after the ground contact shape fluctuates (which may also be called running growth, the same applies hereinafter) as the running distance of the tire increases is optimized to ensure the ground contact pressure at the shoulder edge, the uneven wear resistance can be improved. However, since the thickness of the rubber layer in the shoulder portion increases, the amount of heat generated in the shoulder portion during tire rolling increases, and thermal deterioration of the shoulder portion progresses, which may reduce the durability of the tire.

[0006] An object of the present invention is to provide a pneumatic heavy-duty tire that can improve the uneven wear resistance after the change in the ground contact shape as the driving distance of the tire increases, and suppress the deterioration of the tire durability due to heat generation of the rubber layer.

Means for Solving the Problems

[0007] A pneumatic heavy-duty tire according to an embodiment of the present invention includes a tread portion that contacts the road surface, a tire side portion that is continuous with the tread portion and is located inside the tread portion in the tire radial direction, a bead portion that is continuous with the tire side portion and is located inside the tire side portion in the tire radial direction, a carcass ply that extends from the tread portion through the tire side portion to the bead portion and forms the skeleton of the tire, and a belt layer that is disposed in the tread portion and is located outside the carcass ply in the tire radial direction. The carcass ply has a first curvature change portion that is a boundary between a first portion including the tire equator line and a second portion that is disposed outside the first portion in the tire width direction and inside the tire radial direction and has a larger curvature in a cross section along the tire width direction and the tire radial direction than the curvature of the first portion, a second portion, and a second curvature change portion that is a boundary between the second portion and a third portion that is disposed inside the second portion in the tire radial direction and has a smaller curvature in the cross section than the curvature of the second portion. The pneumatic heavy-duty tire further includes a cushion rubber whose inner end in the tire width direction is located at the first curvature change portion and is disposed between the carcass ply and the belt layer. In the cross section of the pneumatic tire for heavy load in a no-load state mounted on a regular rim and filled with a regular internal pressure, when the distance in the tire width direction from the tire equator line to the first curvature change portion is W1, the distance in the tire width direction from the tire equator line to the second curvature change portion is W2, and the distance in the tire width direction from the tire equator line to the tread end of the tread portion is TW, the cross-sectional shape of the carcass ply satisfies the relational expressions 0.5 ≦ W1 / TW ≦ 0.8 and W1 / TW < W2 / TW < 1.

Effects of the Invention

[0008] According to the above configuration, by reducing the radius of curvature of the second portion of the carcass ply, the contact pressure at the tire width direction position adjacent to the tread edge is reduced, the contact pressure in the tire width direction is made uniform, and fluctuations in the contact surface shape accompanying running growth are suppressed. Further, since it is not necessary to increase the thickness of the rubber layer, it is possible to suppress a decrease in the durability of the tire due to heat generation in the shoulder portion during tire rolling. Furthermore, since a cushion rubber is disposed between the belt layer and the carcass ply of the second portion, the contact pressure in the tire width direction of this region near the tread edge is further made uniform, and uneven wear can be efficiently suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described with reference to the drawings. In addition, the same or similar reference numerals are assigned to the same functions and configurations, and the description thereof will be omitted as appropriate.

[0011] (1) Overall Schematic Configuration of the Tire FIG. 1 is a cross-sectional view along the tire width direction and the tire diameter direction of a pneumatic tire 100 for heavy loads according to the present embodiment. Note that FIG. 1 shows only one side with reference to the tire equator line CL. The configuration of the pneumatic tire 100 for heavy loads may be a structure symmetric with respect to the tire equator line CL. Also, in FIG. 1, the illustration of the cross-sectional hatching is omitted (the same applies hereinafter).

[0012] A tread pattern corresponding to the required performance for the tire is formed on the tread portion 10. In the present embodiment, the tire is a pneumatic tire for heavy loads that can be suitably used particularly for trucks and buses (TB) that travel long distances.

[0013] Note that the heavy load pneumatic tire is not necessarily for trucks and buses, and may be used for other vehicle types such as vans and light trucks, for example.

[0014] The heavy load pneumatic tire 100 according to one embodiment includes a tread portion 10 in contact with the road surface, a tire side portion 20 connected to the tread portion 10 and located inside the tread portion 10 in the tire radial direction, a bead portion 30 connected to the tire side portion 20 and located inside the tire side portion 20 in the tire radial direction, a carcass ply 40 extending from the tread portion 10 through the tire side portion 20 to the bead portion 30 to form the skeleton of the tire, and a belt layer 15 disposed on the tread portion 10 and located outside the carcass ply 40 in the tire radial direction.

[0015] As shown in FIG. 1, the carcass ply 40 has a first curvature change portion P1 which is a boundary between a first portion P0-P1 including the tire equator line CL and a second portion P1-P2 disposed outside the first portion P0-P1 in the tire width direction and inside the first portion P0-P1 in the tire radial direction and having a larger curvature in the cross section along the tire width direction and the tire radial direction than the curvature of the first portion P0-P1, and a second curvature change portion P2 which is a boundary between the second portion P1-P2 and a third portion P2-P3 disposed inside the second portion P1-P2 in the tire radial direction and having a smaller curvature in the cross section than the curvature of the second portion P1-P2.

[0016] The heavy load pneumatic tire 100 further includes a cushion rubber 17a whose inner end in the tire width direction is located at the first curvature change portion P1 and which is disposed between the carcass ply 40 and the belt layer 15.

[0017] The tread portion 10 includes a tread rubber 11 having a tread surface which is a portion in contact with the road surface (not shown). A pattern corresponding to the usage environment of the heavy load pneumatic tire 100 and the type of the vehicle to which it is mounted is formed on the tread surface. In the present embodiment, as shown in FIG. 1, as an example, a circumferential groove 13 extending in the tire circumferential direction is illustrated at the tire equator line position CL and a pattern disposed at a position separated from the tire equator line CL in the tire width direction.

[0018] The tire side portion 20 includes tire side rubber, is continuous with the tread portion 10, and is located on the inner side in the tire radial direction of the tread portion 10. The tire side portion 20 is an area from the side portion of the tread portion 10, specifically from the outer end in the tire width direction, to the outer end in the tire radial direction of the bead portion 30. The tire side portion 20 may also be called a sidewall or the like.

[0019] In the shoulder region where the tread portion 10 and the tire side portion 20 are continuous, a plurality of protrusions 19 that protrude outward in the tire width direction from the tire surface and extend in the tire circumferential direction are provided. The protrusion 19 has a triangular cross-section.

[0020] The bead portion 30 is continuous with the tire side portion 20 and is located on the inner side in the tire radial direction of the tire side portion 20. And the bead portion 30 includes a bead core 31 and a bead filler 33 and is formed in an annular shape. The bead filler 33 tapers outward in the tire radial direction from the bead core 31 and is made of a rubber material.

[0021] The carcass ply 40 forms the framework of the heavy-duty pneumatic tire 100. The carcass ply 40 has a radial structure having carcass cords (not shown) arranged radially along the tire radial direction. However, the carcass ply 40 is not limited to a radial structure and may be a bias structure in which the carcass cords are arranged so as to cross in the tire radial direction. As shown in FIG. 1, the carcass ply 40 of the present embodiment extends from the tread portion 10 through the tire side portion 20 to the bead portion 30, and the carcass ply 40 is folded back from the inner side in the tire width direction to the outer side in the tire width direction around the bead core 31 of the bead portion 30.

[0022] The carcass cords of the carcass ply 40 may be steel cords, or may be composed of a plurality of plies made of organic fiber cords such as aramid, nylon, rayon, and polyester.

[0023] The belt layer 15 is provided on the inner side in the tire diameter direction of the tread portion 10. Note that the belt layer 15 is located on the outer side in the tire diameter direction of the carcass ply 40 within the tread portion 10. The belt layer 15 includes a pair of crossed belts in which cords are crossed and a reinforcing belt provided on the outer side in the tire diameter direction of the crossed belts. Note that the belt layer 15 is formed by stacking a plurality of layers along the tire circumferential direction as shown in FIG. 1.

[0024] As the belt cord of the belt layer 15, in addition to a steel cord, an organic fiber cord such as aramid, nylon, rayon, or polyester can be used.

[0025] The cushion rubber 17a is disposed between the carcass ply 40 and the belt layer 15 with the inner end in the tire width direction located at the first curvature change portion P1.

[0026] In the present embodiment, the inner end in the tire width direction of the cushion rubber 17a is disposed at the first curvature change portion P1, which is the position in the tire width direction where the distance in the tire diameter direction between the carcass ply 40 and the belt layer 15 begins to increase, that is, the boundary where a difference in curvature occurs between the carcass ply 40 and the belt layer 15.

[0027] Then, the outer end in the tire width direction of the cushion rubber 17a is disposed at the end position located most on the outer side in the tire width direction of the belt layer 15 or on the outer side in the tire width direction from the end position.

[0028] The cross-sectional shape of the cushion rubber 17a in the cross-section along the tire width direction and the tire diameter direction is a substantially triangular shape in which the tire diameter direction width increases from the center side in the tire width direction toward the outer side in the tire width direction as shown in FIG. 1. In the present embodiment, the lower end and the upper end in the radial direction of the cushion rubber 17a are in contact with the carcass ply 40 and the belt layer 15, respectively.

[0029] The cushion rubber 17a may be made of, for example, a soft cross-linked rubber. The cushion rubber 17a absorbs the stress generated near the end of the belt layer 15, suppresses the damage of the tread portion 10 starting from the end of the belt layer 15, and suppresses the uneven wear near the tread end TE. The elastic modulus of the soft cross-linked rubber constituting the cushion rubber 17a may be 1.0 to 4.5 MPa.

[0030] The tread end TE refers to the outermost position in the tire width direction of the surface where the tread portion 10 contacts the road surface. The tread end TE may be, for example, based on the grounding end of the tread portion 10 in a state where a normal load is applied to the heavy-duty pneumatic tire 100 set to the normal internal pressure and grounded on a plane at a camber angle of 0 degrees.

[0031] Here, the normal internal pressure is the air pressure corresponding to the maximum load capacity in the YearBook of JATMA (Japan Automobile Tire Association) in Japan, and the normal load is the maximum load capacity (maximum load) corresponding to the maximum load capacity (load index) in the JATMA YearBook. In Europe, it corresponds to ETRTO, in the United States to TRA, and to the tire standards of other countries.

[0032] Also, in the present embodiment, a second cushion rubber 17b is disposed on the outer side in the tire radial direction and covers the outer end in the tire width direction of the belt layer 15. The second cushion rubber 17b covers the outer end in the tire width direction of the belt layer 15 and contacts the cushion rubber 17a disposed on the inner side in the tire radial direction on the outer side in the tire width direction, thereby preventing the peeling of the ply end.

[0033] The heavy-duty pneumatic tire 100 is assembled so that the bead portion 30 is locked to the rim flange (not shown) of the rim wheel. Note that the internal space formed by being assembled to the rim wheel is filled with air. However, the gas filled in the internal space is not limited to air and may be an inert gas such as nitrogen gas.

[0034] (2) Profile of carcass ply Next, the profile of the carcass ply 40 will be described. As shown in FIG. 1, in a cross section along the tire width direction and the tire diameter direction, the carcass ply 40 has a first curvature change portion P1 at a position where the tire width direction distance from the equator line CL is W1, and the curvature of the carcass ply 40 is different between the inner side and the outer side in the tire width direction. Further, at a position where the tire width direction distance from the equator line CL located between the first curvature change portion P1 and the tread end TE of the tread portion 10 is W2, the carcass ply 40 has a second curvature change portion P2 where the curvature is different between the inner side and the outer side in the tire width direction.

[0035] That is, as shown in FIG. 1, if the point at the tire width direction position on the tire equator line CL of the carcass ply 40 is P0, the carcass ply 40 has a first portion P0-P1 including the tire equator line CL, and a second portion P1-P2 which is arranged outside the first portion P0-P1 in the tire width direction and inside in the tire diameter direction and has a larger curvature in the cross section along the tire width direction and the tire diameter direction than the curvature of the first portion P0-P1. That is, the radius of curvature R1 in the first portion P0-P1 is larger than the radius of curvature R2 in the second portion P1-P2, and the carcass ply 40 is curved more greatly on the outer side in the tire width direction with the first curvature change portion P1 as the boundary.

[0036] Furthermore, the carcass ply 40 has a second curvature change portion P2 which is the boundary between the second portion P1-P2 and a third portion P2-P3 which is arranged inside the second portion P1-P2 in the tire diameter direction and has a smaller curvature in the cross section than the curvature of the second portion P1-P2. That is, the radius of curvature R2 in the second portion P1-P2 is smaller than the radius of curvature R3 in the third portion P2-P3, and the carcass ply 40 has a smaller curvature on the inner side in the tire diameter direction with the second curvature change portion P2 as the boundary.

[0037] In the cross-section along the tire width direction and the tire diameter direction of a pneumatic tire 100 for heavy loads, which is mounted on a standard rim (not shown) and filled with a standard internal pressure and is in an unloaded state, the cross-sectional shape of the carcass ply 40 may satisfy the relational expressions 1: 0.5 ≦ W1 / TW ≦ 0.8 and relational expression 2: W1 / TW < W2 / TW < 1. Here, W1 is the tire width direction distance from the tire equator line CL to the first curvature change portion P1, W2 is the tire width direction distance from the tire equator line CL to the second curvature change portion P2, and TW is the tire width direction distance from the tire equator line CL to the tread end TE.

[0038] Here, the standard rim is a rim wheel corresponding to the standard rim in the YearBook of JATMA (Japan Automobile Tire Association) in Japan. In Europe, it corresponds to ETRTO, in the United States, it corresponds to TRA, and other tire standards in each country.

[0039] The cross-sectional shape of the carcass ply 40 may satisfy the relational expression 3: a1 / W1 ≦ 0.06 < a2 / W2 ≦ 0.15. Here, a1 is the tire diameter direction distance from the height position of the carcass ply 40 at the tire equator line CL to the height position of the first curvature change portion P1, and a2 is the tire diameter direction distance from the height position of the carcass ply 40 at the tire equator line CL to the height position of the second curvature change portion P2.

[0040] Note that the cross-sectional shape of the carcass ply 40 in the cross-section along the tire width direction and the tire diameter direction is smoothly continuous through the position P0 of the carcass ply 40 intersecting the tire equator line CL, the first curvature change portion P1, and the second curvature change portion P2.

[0041] The radius of curvature R1 of the cross-sectional shape of the carcass ply 40 (first portion P0-P1) from the position P0 on the tire equator line CL to the first curvature change portion P1 and the radius of curvature R2 of the cross-sectional shape of the carcass ply 40 (second portion P1-P2) from the first curvature change portion P1 to the second curvature change portion P2 form a smooth cross-sectional shape passing through the three points of the position P0, the first curvature change portion P1, and the second curvature change portion P2 of the carcass ply 40, and by setting the range to satisfy the relational expressions 1, 2, and 3, the range of the possible radii of curvature R1 and R2 can be determined.

[0042] The cross-sectional shape of the carcass ply 40 may satisfy the relational expression R2 / R3 ≤ 0.5. Here, R3 is the radius of curvature of the cross-sectional shape of the carcass ply 40 (third portion P2-P3) from the second curvature change portion P2 to the portion P3 located at the inner position in the tire width direction of the region where a plurality of protrusions 19 are provided. In the carcass ply, the tire radial position of the portion P3, which is the inner end in the tire radial direction of the third portion P2-P3, may be set at an intermediate position in the tire radial position between the tire radial position of the first protrusion 19a, which is the outer end in the tire radial direction included in the plurality of protrusions 19, and the second protrusion 19b adjacent to the first protrusion 19a. In the present embodiment, as shown in FIG. 1, the portion P3 is arranged at the tire radial position that is the midpoint (central position in the tire radial direction) between the tire radial position of the first protrusion 19a and the tire radial position of the second protrusion 19b.

[0043] (3) Function and Effect In the case of heavy-duty tires for trucks and buses, generally, with respect to the circumferential contact length from the tire equator line to a position near the tread edge on the inner side in the tire width direction, the circumferential contact length near the tread edge becomes shorter, and the contact pressure near the tread edge becomes relatively lower than that on the tire equator line side. In this case, when the tire rolls, the area near the tread edge will be dragged, and abnormal wear such as stepped wear that wears in a stepped manner may occur near the tread edge. Also, even when the tire is used under conditions where such stepped wear is suppressed, due to the variation in the circumferential contact length accompanying the increase in the driving distance of the tire, the intermediate position between the tire equator line and the vicinity of the tread edge grows relatively large in the driving direction, resulting in an increase in the circumferential contact length. Since the contact pressure near the tread edge becomes relatively lower than that at the intermediate position, uneven wear may occur.

[0044] The heavy-duty pneumatic tire 100 of the present embodiment has a carcass ply 40 with a first portion P0 - P1 including the tire equator line CL, and a second portion P1 - P2 that is disposed outside the first portion P0 - P1 in the tire width direction and inside in the tire radial direction and has a larger curvature in the cross section along the tire width direction and the tire radial direction than the curvature of the first portion P0 - P1. The first curvature change portion P1 is the boundary between them. The second portion P1 - P2 and the third portion P2 - P3 that is disposed inside the second portion P1 - P2 in the tire radial direction and has a smaller curvature in the cross section than the curvature of the second portion P1 - P2. The second curvature change portion P2 is the boundary between them. That is, the radius of curvature R1 of the first portion P0 - P1 is larger than the radius of curvature R2 of the second portion P1 - P2, and the radius of curvature R2 of the second portion P1 - P2 is smaller than the radius of curvature R3 of the third portion P2 - P3.

[0045] The running growth due to the internal pressure of the tire is promoted in the portions where the radius of curvature is relatively large (the first portion P0 - P1 and the third portion P2 - P3), and suppressed in the portion where the radius of curvature is relatively small (the second portion P1 - P2). Therefore, excessive running growth at an intermediate position between the tire equator line CL and the vicinity of the tread end TE is suppressed. As a result, in the heavy-duty pneumatic tire 100 of the present embodiment, the circumferential contact length in the tire width direction can be optimized without increasing the thickness of the rubber layer. In other words, according to the heavy-duty pneumatic tire 100 of the present embodiment, it is possible to improve the resistance to uneven wear performance after running growth while suppressing a decrease in the durability of the tire due to heat generation of the rubber layer.

[0046] Furthermore, the heavy-duty pneumatic tire 100 of the present embodiment includes a cushion rubber 17a whose inner end in the tire width direction is located at the first curvature change portion P1 and is disposed between the carcass ply 40 and the belt layer 15.

[0047] Since the cushion rubber 17a is disposed on the outer side in the tire width direction of the first curvature change portion P1, specifically, at least a part of the second portion P1 - P2, the contact pressure is further reduced at the position where the cushion rubber 17a is installed, and uneven wear caused by the vicinity of the tread end TE being dragged during tire rolling is suppressed.

[0048] Also, as shown in FIG. 1, when the outer end in the tire width direction at the outer position in the tire diameter direction of the cushion rubber 17a is disposed up to the outer end in the tire width direction of the belt layer 15, the movement of the outer end in the tire width direction of the belt layer 15 can be suppressed to prevent damage to the adjacent rubber layer.

[0049] Also, in the cross-section of the heavy-duty pneumatic tire in a no-load state where it is mounted on a standard rim and filled with a standard internal pressure, when the cross-sectional shape of the carcass ply 40 satisfies the relational expressions 0.5 ≦ W1 / TW ≦ 0.8 and W1 / TW < W2 / TW < 1, the running growth in the vicinity of the inner side in the tire width direction of the shoulder land portion adjacent to the vicinity of the tread end TE of the heavy-duty tire 100 for trucks and buses can be effectively suppressed.

[0050] Further, when the distance in the tire radial direction from the height position in the tire radial direction of the carcass ply 40 at the position (P0) of the tire equator line CL to the height position in the tire radial direction of the first curvature change portion P1 is a1, and the distance in the tire radial direction from the height position in the tire radial direction of the carcass ply 40 at the position (P0) of the tire equator line CL to the height position in the tire radial direction of the second curvature change portion P2 is a2, when the relational expression a1 / W1 ≦ 0.06 < a2 / W2 ≦ 0.15 is satisfied, the contact pressure from the tire equator line CL to the tread end TE of the heavy-duty tire 100 for trucks and buses can be made more uniform in the tire width direction.

[0051] Further, in the heavy-duty pneumatic tire 100 of the present embodiment, on the tire surface in the shoulder region where the tread portion 10 and the tire side portion 20 are continuous, a plurality of protrusions 19 protruding outward in the tire width direction from the tire surface and extending in the tire circumferential direction are formed. In the cross section, when the radius of curvature R2 of the second portion (P1 - P2) of the carcass ply 40 located between the first curvature change portion P1 and the second curvature change portion P2 and the radius of curvature R3 of the carcass ply 40 located between the second curvature change portion P2 and the inner position in the tire width direction of the region where the plurality of protrusions 19 of the carcass ply 40 are provided satisfy the relational expression R2 / R3 ≦ 0.5, it becomes possible to more reliably secure the contact pressure up to the tread end TE, and the uneven wear resistance performance in the tire width direction can be improved.

[0052] (4) Examples To confirm the effects of the present invention, the uneven wear resistance performance and heat generation durability performance of a size 11R22.5 heavy-duty pneumatic tire for buses and trucks having the basic structure of FIG. 1 were predicted based on the specifications in Table 1. The tread patterns are the same. Substantially common except for the parameters shown in Table 1. Among these, only tire 1 was prototyped and a performance test was conducted. For tires 2 to 4, the performance was predicted based on the measured values of the contact surface shape.

[0053]

Table 1

[0054] The heavy-load tires of the embodiments are, respectively, Tire 1 with a circumferential contact length before optimization using a conventional case line, Tire 2 with a circumferential contact length of the grounding end at the time of new product increased by the thickness of the rubber layer using a conventional case line, Tire 3 equipped with the case line of the present embodiment and having a circumferential contact length before optimization, and Tire 4 equipped with the case line of the present embodiment and having a circumferential contact length of the grounding end at the time of new product increased.

[0055] Note that each dimension of the carcass profile of the tires in each experimental example shown in Table 1 is a measured value measured by CT scan in a normal state after being rim-mounted on the following rim. Rim: 8.25×22.5 The method for evaluating the heavy-load tires is as follows.

[0056] <Resistance to uneven wear performance> The tires of each experimental example were mounted on all wheels of a vehicle under the conditions of a rim (8.25×22.5), an internal pressure (775 kPa), and a load (25.80 kN), and load-tested at the actual use speed until reaching 50% wear. The occurrence situation of shoulder drop wear in the shoulder part was evaluated. Conventional Tire 1 has a problem of uneven wear. Therefore, taking the shoulder drop wear amount of Tire 1 as 1 as the index of the judgment criterion, it was evaluated that excellent ◎ is 0.6 or less, good 〇 is 0.8 or less, acceptable △ is 1 or less, and unacceptable × is 1 or more.

[0057] <Heat generation durability performance> Using the above vehicle, the time when traveling until failure at 90 km / hr was evaluated. The heat generation durability of Conventional Tire 1 fully meets the market requirements. Therefore, taking the traveling time until failure of Tire 1 as 1 as the index of the judgment criterion, it was evaluated that excellent ◎ is 1 or more, good 〇 is 0.8 or more, acceptable △ is 0.6 or more, and unacceptable × is less than 0.6.

[0058]

Table 2

[0059] As shown in Table 2, it is difficult for Tires 1 and 2 equipped with the conventional case line to obtain high evaluations in both the uneven wear resistance performance and the heat generation durability performance. On the other hand, Tires 3 and 4 equipped with the case line satisfying the conditions of the present embodiment can achieve both uneven wear resistance performance and heat generation durability performance.

[0060] As described above, the embodiments of the present invention have been described, but it should not be understood that the descriptions and drawings forming a part of this disclosure limit this invention. Various alternative embodiments, examples, and operation techniques will be apparent to those skilled in the art from this disclosure.

Explanation of Signs

[0061] 100 Heavy-duty tire 10 Tread portion 15 Belt layer 17a Cushion rubber 19 Protrusion 20 Tire side portion 30 Bead portion 40 Carcass ply CL Tire equator line P0 Position of the carcass ply on the tire equator line P1 First curvature change portion P2 Second curvature change portion W1 Distance between P0 and P1 W2 Distance between P0 and P2 TW Distance between P0 and TE a1 Tire radial distance between P0 and P1 a2 Tire radial distance between P0 and P2 R2 Curvature radius between P1 and P2 R3 Curvature radius between P2 and P3

Claims

Claim 1. A pneumatic tire for heavy loads, comprising: a tread portion that contacts the road surface; a tire side portion that is continuous with the tread portion and is located inside the tread portion in the tire radial direction; a bead portion that is continuous with the tire side portion and is located inside the tire side portion in the tire radial direction; a carcass ply that extends from the tread portion through the tire side portion to the bead portion and forms the skeleton of the tire; a belt layer that is disposed in the tread portion and is located outside the carcass ply in the tire radial direction; wherein the carcass ply:[[]]END]] has a first curvature change portion that is a boundary between a first portion including the tire equator line and a second portion that is disposed outside the first portion in the tire width direction and inside the tire radial direction and has a greater curvature in a cross section along the tire width direction and the tire radial direction than the curvature of the first portion; has a second curvature change portion that is a boundary between the second portion and a third portion that is disposed inside the second portion in the tire radial direction and has a smaller curvature in the cross section than the curvature of the second portion; and further comprises cushion rubber, the inner end in the tire width direction of which is located at the first curvature change portion and is disposed between the carcass ply and the belt layer; in the cross section of the pneumatic tire for heavy loads in a non-loaded state mounted on a standard rim and filled with a standard internal pressure, when the distance in the tire width direction from the tire equator line to the first curvature change portion is W1, the distance in the tire width direction from the tire equator line to the second curvature change portion is W2, and the distance in the tire width direction from the tire equator line to the tread end of the tread portion is TW, the cross-sectional shape of the carcass ply satisfies the relational expressions 0.5 ≦ W1 / TW ≦ 0.8 and W1 / TW < W2 / TW < 1. A pneumatic tire for heavy loads.[[]]END]] Claim 2.[[]]END]] The pneumatic tire for heavy loads according to claim 1, wherein when the distance in the tire radial direction from the height position in the tire radial direction of the carcass ply at the position of the tire equator line to the height position in the tire radial direction of the first curvature change portion is a1, and the distance in the tire radial direction from the height position in the tire radial direction of the carcass ply at the position of the tire equator line to the height position in the tire radial direction of the second curvature change portion is a2, the relational expression a1 / W1 ≦ 0.06 < a2 / W2 ≦ 0.15 is satisfied.[[]]END]] Claim 3.[[]]END]] On the tire surface in the shoulder region where the tread portion and the tire side portion are continuous, a plurality of protrusions are provided that protrude outward in the tire width direction from the tire surface and extend in the tire circumferential direction. The plurality of protrusions include a first protrusion located at the outer end in the tire radial direction and a second protrusion adjacent to the first protrusion. In the cross section, the curvature radius R2 of the carcass ply located between the first curvature change portion and the second curvature change portion, and the second curvature change portion, and the position in the tire radial direction that is the midpoint between the tire radial position of the first protrusion and the tire radial position of the second protrusion. The curvature radius R3 of the carcass ply located between the carcass ply portions arranged satisfies the relational expression R2 / R3 ≤ 0.

5. The pneumatic heavy-duty tire according to claim 1 or claim 2.

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