Pneumatic tire for heavy load

Abstract

The heavy-duty pneumatic tire (100) includes a carcass ply (40) constituting the tire skeleton and a belt ply (15) disposed in the tread (10) on the radially outer side of the carcass ply. The carcass ply (40) has a first curvature variation portion (P1) and a second curvature variation portion (P2). The first curvature variation portion (P1) is the boundary between a first portion (P0-P1) and a second portion (P1-P2), which includes the tire equator (CL). The second portion (P1-P2) is disposed on the outer side of the first portion in the tire width direction and is radially inner, and its cross-sectional curvature is greater than that of the first portion. The second curvature variation portion (P2) is the boundary between a second portion and a third portion (P2-P3), which is disposed on the radially inner side of the second portion and its cross-sectional curvature is smaller than that of the second portion. The heavy-duty pneumatic tire (100) also includes a cushioning rubber (17a), the inner end of which is located in the first curvature change portion (P1) in the tire width direction, and the cushioning rubber (17a) is disposed between the carcass ply (40) and the belt ply (15).

Description

Technical Field

[0001] The present invention relates to a heavy-duty pneumatic tire, which includes: a carcass ply having two curvature-changing portions having a curvature that changes in the tire width direction; and a cushioning rubber disposed between the belt layer and the carcass ply. Background Technology

[0002] As existing pneumatic tires, there are known tires that can improve resistance to uneven wear by optimizing the tire's contact patch shape (see, for example, Patent Document 1). In this pneumatic tire, optimizing the tire's contact patch shape can suppress slippage of the tire shoulder portion relative to the road surface during tire rolling.

[0003] In such pneumatic tires, conditions are specified based on the tire's circumferential contact length to suppress changes in the contact patch shape. Furthermore, this structure prevents initial uneven wear at the tread edges or shoulder.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 9-309301 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In existing pneumatic tires, the following structure optimizes the circumferential contact patch length even after the contact patch shape changes (also known as travel evolution) due to increased driving distance. However, while this structure improves resistance to uneven wear by ensuring the contact patch pressure at the tire shoulder, it also increases the thickness of the rubber layer at the tire shoulder, which is associated with the optimization of the circumferential contact patch length. Therefore, existing pneumatic tires pose the risk of increased heat generation at the tire shoulder during tire rolling, leading to thermal aging at the shoulder and decreased tire durability.

[0009] The purpose of this invention is to provide a heavy-duty pneumatic tire that can improve resistance to uneven wear after changes in the contact patch shape associated with extended tire travel distance, and can suppress the decrease in tire durability caused by heat generation in the rubber layer.

[0010] Solution for solving the problem

[0011] One aspect of the present invention provides a heavy-duty pneumatic tire comprising: a tread portion that contacts the road surface; a tire sidewall portion connected to the tread portion and located inside the tire radial direction of the tread portion; a bead portion connected to the tire sidewall portion and located inside the tire radial direction of the tire sidewall portion; a carcass ply extending from the tread portion through the tire sidewall portion to the bead portion and forming the skeleton of the pneumatic tire; and a belt layer disposed on the tread portion and located outside the tire radial direction of the carcass ply. The carcass ply has a first curvature variation portion and a second curvature variation portion. The first curvature variation portion is the boundary between the first and second portions. The first portion includes the tire equator. The second portion is located 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 compared to the curvature of the first portion. The second curvature variation portion is the boundary between the second and third portions. The third portion is located inside the second portion in the tire radial direction and has a smaller curvature in a cross-section compared to the curvature of the second portion. The heavy-duty pneumatic tire also includes a cushioning rubber, the inner end of which in the tire width direction is located at the first curvature variation portion, and the cushioning rubber is disposed between the carcass ply and the belt ply.

[0012] The effects of the invention

[0013] In the above structure, the radius of curvature of the second portion of the carcass ply is reduced. This structure reduces the contact pressure in the tire width direction adjacent to the tread end, making the contact pressure more uniform in the tire width direction. Furthermore, it suppresses changes in the tire's contact patch shape associated with driving. Additionally, this structure eliminates the need to increase the thickness of the rubber layer to optimize the contact patch shape. Therefore, it also suppresses the decrease in tire durability associated with increased heat generation at the tire shoulder during tire rolling. Moreover, a cushioning rubber layer is provided between the belt layer and the carcass ply in the second portion. Therefore, the contact pressure in the tire width direction in this area near the tread end is further uniform, effectively suppressing uneven wear. Attached Figure Description

[0014] Figure 1 This is a cross-sectional view of a heavy-duty pneumatic tire 100 along the tire width direction and the tire radial direction. Detailed Implementation

[0015] Hereinafter, embodiments will be described based on the accompanying drawings. Furthermore, identical or similar reference numerals will be used to label identical functional components and structures, and their descriptions will be omitted where appropriate.

[0016] (1) Overall general structure of the tire

[0017] Figure 1 This is a cross-sectional view of the heavy-duty pneumatic tire 100 of this embodiment along the tire width direction and the tire radial direction. Furthermore, Figure 1 Only one side with the tire equator CL as a reference is shown. The structure of the heavy-duty pneumatic tire 100 can be a symmetrical configuration about the tire equator CL. Furthermore, in Figure 1 The diagram of the cross-sectional shadow lines is omitted in the following examples.

[0018] The tread portion 10 has a tread pattern corresponding to the performance requirements of the tire. In this embodiment, the tire is a heavy-duty pneumatic tire, particularly suitable for trucks and buses (TB) that are used for long-distance travel.

[0019] In addition, heavy-duty pneumatic tires are not necessarily used for trucks and buses; they can also be used for other vehicle types such as vans and mini-trucks.

[0020] One embodiment of a heavy-duty pneumatic tire 100 includes a tread portion 10, a sidewall portion 20, a bead portion 30, a carcass ply 40, and a belt layer 15 that are in contact with the road surface. The sidewall portion 20 is connected to the tread portion 10 and is located inside the tire radial direction of the tread portion 10. The bead portion 30 is connected to the sidewall portion 20 and is located inside the tire radial direction of the sidewall portion 20. The carcass ply 40 extends from the tread portion 10, passes through the sidewall portion 20, and reaches the bead portion 30, forming the tire skeleton. The belt layer 15 is disposed on the tread portion 10 and is located outside the tire radial direction of the carcass ply 40.

[0021] like Figure 1 As shown, the tire carcass ply 40 includes: a first portion P0-P1, which includes the tire equator CL; a second portion P1-P2, which is disposed outside the first portion P0-P1 in the tire width direction and inside the tire radial direction; and a third portion P2-P3, which is disposed inside the second portion P1-P2 in the tire radial direction. Compared with the curvature of the first portion P0-P1, the second portion P1-P2 has a larger curvature in the cross section along the tire width direction and the tire radial direction. The first curvature variation portion P1 is defined as the boundary portion between the first portion P0-P1 and the second portion P1-P2 in the cross section along the tire width direction and the tire radial direction, where the curvature changes. Compared with the curvature of the second portion P1-P2, the third portion P2-P3 has a smaller curvature in the cross section. The second curvature variation section P2 is defined as the boundary between the second part P1-P2 and the third part P2-P3 in a cross section along the tire width direction and the tire radial direction, where the curvature changes.

[0022] The heavy-duty pneumatic tire 100 also includes a cushioning rubber 17a, which is disposed between the carcass ply 40 and the belt ply 15. The inner end of the cushioning rubber 17a in the tire width direction is located at the first curvature variation portion P1.

[0023] The tread portion 10 includes tread rubber 11, which has a portion that contacts the road surface (not shown), i.e., the tread surface. A pattern corresponding to the operating environment of the heavy-duty pneumatic tire 100 and the type of vehicle on which it is installed is formed on the tread surface. In this embodiment, as... Figure 1 As shown, as an example, the figure illustrates a pattern formed by a circumferential groove 13 extending along the tire circumference at the tire equator position CL and at a position separating from the tire equator CL in the tire width direction.

[0024] The tire sidewall 20 is connected to the tread portion 10 and is located radially inside the tread portion 10. Specifically, the tire sidewall 20 is the region extending from the outer end of the tread portion 10 in the tire width direction to the outer radial end of the bead portion 30. The tire sidewall 20 includes tire sidewall rubber. Furthermore, the tire sidewall 20 is sometimes also referred to as the tire sidewall, etc.

[0025] A plurality of protrusions 19 are provided in the shoulder area where the tread portion 10 and the sidewall portion 20 are connected. These protrusions 19 protrude outward from the tire surface in the tire width direction and extend along the tire circumference. The protrusions 19 are triangular in cross-section.

[0026] The bead portion 30 is connected to the tire sidewall 20 and is located radially inside the tire sidewall 20. The bead portion 30 has a bead core 31 and a bead filler 33, and is formed in a circular shape. The bead filler 33 is made of rubber material and tapers at the tip from the bead core 31 toward the radially outer side of the tire.

[0027] The carcass ply 40 forms the skeleton 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's radial direction. However, the carcass ply 40 is not limited to a radial structure. For example, the carcass ply 40 can also be a bias-ply structure where the carcass cords are staggered in the tire's radial direction. Figure 1 As shown, in this embodiment, the carcass ply 40 extends from the tread portion 10, passes through the tire side portion 20, and reaches the bead portion 30. Within the bead portion 30, the carcass ply 40 folds back from the inside in the tire width direction to the outside in the tire width direction around the bead core 31.

[0028] The carcass cords of the carcass ply 40 can be steel cords or multiple ply layers composed of organic fiber cords such as aramid, nylon, rayon, and polyester.

[0029] The belt layer 15 is located radially inside the tread portion 10. Furthermore, the belt layer 15 is located radially outside the carcass ply 40 within the tread portion 10. The belt layer 15 includes a pair of interlaced belts with interlaced cords, and a reinforcing belt located radially outside the interlaced belts. Additionally, as... Figure 1 As shown, multiple belt layers 15 are formed overlappingly along the tire circumference.

[0030] In addition to steel wire cords, the belt cords of the belt layer 15 can also be made of organic fibers such as aramid, nylon, rayon, and polyester.

[0031] The cushioning rubber 17a is disposed between the tire carcass ply 40 and the belt ply 15. The inner end of the cushioning rubber 17a in the tire width direction is located at the first curvature change section P1.

[0032] In this embodiment, the inner end of the buffer rubber 17a in the tire width direction is disposed at the first curvature change portion P1, which is the tire width direction position where the radial distance between the tire carcass ply 40 and the belt ply 15 begins to increase. That is, the first curvature change portion P1 is the boundary where the curvature of the tire carcass ply 40 and the belt ply 15 differs.

[0033] Furthermore, the outer end of the buffer rubber 17a in the tire width direction is disposed at the end position of the belt layer 15 located at the outermost end position in the tire width direction, or at a position further outward in the tire width direction than that end position.

[0034] like Figure 1 As shown, the cross-sectional shape of the cushioning rubber 17a along the tire width direction and the tire radial direction is an approximately triangular shape that increases in radial width from the center side of the tire width direction toward the outer side of the tire width direction. In this embodiment, the lower radial end and the upper radial end of the cushioning rubber 17a are in contact with the carcass ply 40 and the belt layer 15, respectively.

[0035] The cushioning rubber 17a can be made of, for example, a soft cross-linked rubber. The cushioning rubber 17a absorbs stress generated near the end of the belt layer 15, thereby suppressing damage to the tread 10 originating from the end of the belt layer 15 and suppressing uneven wear near the tread end TE. The elastic modulus of the soft cross-linked rubber constituting the cushioning rubber 17a can be from 1.0 MPa to 4.5 MPa.

[0036] The tread end TE refers to the outermost position of the surface of the tread portion 10 that contacts the road surface in the tire width direction. The tread end TE can be referenced, for example, the contact end of the tread portion 10 when a heavy-duty pneumatic tire 100 with a standard internal pressure is loaded with a standard load and has a camber angle of 0 degrees touching the ground.

[0037] In Japan, standard internal pressure refers to the air pressure corresponding to the maximum load capacity in the JATMA (Japan Automobile Tire Association) Yearbook. Standard load refers to the maximum load capacity (maximum load) corresponding to the maximum load capacity (Load Index) in the JATMA Yearbook. Furthermore, it corresponds to ETRTO in Europe, TRA in the United States, and other tire specifications in various countries.

[0038] In addition, in this embodiment, a second buffer rubber 17b is disposed on the radially outer side of the tire. The second buffer rubber 17b covers the outer end of the belt layer 15 in the tire width direction. The second buffer rubber 17b covers the outer end of the belt layer 15 in the tire width direction, thereby contacting the buffer rubber 17a disposed on the radially inner side of the tire on the outer side in the tire width direction. With this structure, peeling of the ply ends in the heavy-duty pneumatic tire 100 can be prevented.

[0039] The heavy-duty pneumatic tire 100 is assembled by securing the bead portion 30 to the rim flange (not shown). Furthermore, air is filled into the internal space formed by the assembly with the rim. However, the gas filling this internal space is not limited to air; it can also be a non-reactive gas such as nitrogen.

[0040] (2) Outline of the carcass ply

[0041] Next, the outline of the carcass ply 40 will be described. For example... Figure 1 As shown, in a cross-section along the tire width direction and the tire radial direction, the carcass ply 40 has a first curvature variation portion P1 at a distance W1 from the equator CL in the tire width direction. At this first curvature variation portion P1, the curvature of the carcass ply 40 is different on the inner and outer sides in the tire width direction. Furthermore, the carcass ply 40 has a second curvature variation portion P2 located between the first curvature variation portion P1 and the tread end TE of the tread portion 10, at a distance W2 from the equator CL in the tire width direction. At this second curvature variation portion P2, the curvature of the carcass ply 40 is different on the inner and outer sides in the tire width direction.

[0042] That is, such as Figure 1As shown, the carcass ply 40 has a first portion P0-P1 encompassing the tire equator CL. This first portion P0-P1 is the portion of the carcass ply 40 located between point P0 in the tire width direction on the tire equator CL and a first curvature change portion P1. Within the range of the first portion P0-P1, the carcass ply 40 is curved with a radius of curvature R1. In the carcass ply 40, a second portion P1-P2 is located between the first curvature change portion P1 and the second curvature change portion P2. The second portion P1-P2 is positioned outside the first portion P0-P1 in the tire width direction and inside the tire radial direction. Within the range of the second portion P1-P2, the carcass ply 40 is curved with a radius of curvature R2 smaller than the radius of curvature R1 of the first portion P0-P1. That is, the first curvature change section P1 is the boundary between the first part P0-P1 and the second part P1-P2, which has a greater curvature than the first part P0-P1, in the cross section along the tire width direction and the tire radial direction. The tire carcass ply 40 has a greater curvature on the outer side in the tire width direction, with the first curvature change section P1 as the boundary.

[0043] The carcass ply 40 has a third portion P2-P3 disposed on the inner radial side of the second curvature change portion P2. Within the range of the third portion P2-P3, the carcass ply 40 bends with a curvature radius R3 that is larger than the curvature radius R2 of the second portion P1-P2. That is, the second curvature change portion P2 is the boundary portion in the cross section along the tire width direction and the tire radial direction between the second portion P1-P2 and the third portion P2-P3, whose curvature is smaller than that of the second portion P1-P2. The carcass ply 40 has a smaller curvature on the inner radial side of the tire with the second curvature change portion P2 as the boundary.

[0044] The cross-sectional shape of the carcass ply 40 can satisfy Equation 1: 0.5 ≤ W1 / TW ≤ 0.8 and Equation 2: W1 / TW < W2 / TW < 1. Here, the cross-section of the carcass ply 40 is defined as the cross-section along the tire width and radial direction of a heavy-duty pneumatic tire 100 mounted on a standard rim (not shown), filled with standard internal pressure, and in an unloaded state. Furthermore, reference numeral W1 represents the tire width direction distance from the tire equator CL to the first curvature change portion P1. Reference numeral W2 represents the tire width direction distance from the tire equator CL to the second curvature change portion P2. Reference numeral TW represents the tire width direction distance from the tire equator CL to the tread end TE.

[0045] In Japan, "standard rim" refers to the rim that corresponds to the standard rim in the JATMA (Japan Automobile Tire Association) Yearbook. Furthermore, in Europe, it corresponds to ETRTO; in the United States, it corresponds to TRA; and it corresponds to tire standards in other countries.

[0046] The cross-sectional shape of the carcass ply 40 can also satisfy Equation 3: a1 / W1≤0.06<a2 / W2≤0.15. Here, reference numeral a1 is the radial distance from the height position of the carcass ply 40 on the tire equator CL to the height position of the first curvature change section P1. Reference numeral a2 is the radial distance from the height position of the carcass ply 40 on the tire equator CL to the height position of the second curvature change section P2.

[0047] Furthermore, the cross section of the carcass ply 40 along the tire width direction and the tire radial direction has a smooth and continuous cross section shape passing through the position P0 where the carcass ply 40 intersects with the tire equator CL, the first curvature change portion P1 and the second curvature change portion P2.

[0048] Here, the radius of curvature R1 of the first portion P0-P1 is the radius of curvature of the cross-sectional shape of the carcass ply 40 from position P0 on the tire equator CL to the first curvature change portion P1. The radius of curvature R2 of the second portion P1-P2 is the radius of curvature of the cross-sectional shape of the carcass ply 40 from the first curvature change portion P1 to the second curvature change portion P2. The cross-sectional shape of the carcass ply 40 smoothly passes through the three points: position P0, the first curvature change portion P1, and the second curvature change portion P2. Furthermore, the cross-sectional shape of the carcass ply 40 is set to satisfy relations 1 and 2. Based on this structure, the acceptable ranges of the radius of curvature R1 of the first portion P0-P1 and the radius of curvature R2 of the second portion P1-P2 of the carcass ply 40 are determined. Furthermore, the range of acceptable radii of curvature R1 and R2 can also be determined to satisfy not only relations 1 and 2 but also relations 3.

[0049] The cross-sectional shape of the carcass ply 40 can satisfy Equation 4: R2 / R3 ≤ 0.5. Here, reference numeral 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 portion P3, which is located inside the tire width direction of the area where a plurality of protrusions 19 are disposed, and these protrusions 19 are provided on the tire surface. Furthermore, in the carcass ply 40, the tire radial position of portion P3, which becomes the inner radial end of the third portion P2-P3, can be set at the midpoint between the tire radial position of the first protrusion 19a and the tire radial position of the second protrusion 19b. The first protrusion 19a is included in the plurality of protrusions 19 and is located at the outer radial end of the tire, and the second protrusion 19b is adjacent to the first protrusion 19a. In this embodiment, as Figure 1 As shown, part P3 is positioned at the midpoint (center position in the radial direction of the tire) between the radial position of the first protrusion 19a and the radial position of the second protrusion 19b.

[0050] (3) Function and Effect

[0051] In heavy-duty tires for trucks and buses, generally, the circumferential contact length near the tread end is shorter than the circumferential contact length from the tire equator line to the inner position in the tire width direction near the tread end. Therefore, in heavy-duty tires for trucks and buses, the contact pressure ratio near the tread end is relatively lower than the contact pressure ratio on the tire equator line side. In this case, when the tire rolls, the area near the tread end is dragged, and abnormal wear such as stepped wear (Japanese: danzukimo) where the area near the tread end wears into a step shape may occur. Additionally, even when the tire is used under conditions that suppress such stepped wear, the circumferential contact length changes as the driving distance of the tire increases. Specifically, the intermediate position between the tire equator line and the area near the tread end develops relatively more during driving, and the circumferential contact length at this intermediate position becomes longer. Therefore, the contact pressure ratio near the tread end is relatively lower than that at the intermediate position, and uneven wear may occur.

[0052] In the heavy-duty pneumatic tire 100 of the present embodiment, the carcass ply 40 includes: a first portion P0 - P1 that includes the tire equator line CL; a second portion P1 - P2 that is disposed on the outer side in the tire width direction and the inner side in the tire radial direction of the first portion P0 - P1; and a third portion P2 - P3 that is disposed on the inner side in the tire radial direction of the second portion P1 - P2. The curvature of the second portion P1 - P2 is larger than the curvature of the first portion P0 - P1 in a cross-section along the tire width direction and the tire radial direction. The first curvature change portion P1 is defined as the boundary portion between the first portion P0 - P1 and the second portion P1 - P2 where the curvature changes in the cross-section along the tire width direction and the tire radial direction. The curvature of the third portion P2 - P3 is smaller than the curvature of the second portion P1 - P2 in the cross-section. The second curvature change portion P2 is defined as the boundary portion between the second portion P1 - P2 and the third portion P2 - P3 where the curvature changes in the cross-section along the tire width direction and the tire radial direction. 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.

[0053] The wear caused by tire internal pressure is promoted by the portion with a relatively large radius of curvature (parts 1 P0-P1 and 3 P2-P3) and suppressed by the portion with a relatively small radius of curvature (parts 2 P1-P2). Therefore, excessive wear can be suppressed at the intermediate position near the tire equator CL and the tread end TE, including parts 2 P1-P2. Thus, in the heavy-duty pneumatic tire 100 of this embodiment, the circumferential contact length in the tire width direction can be optimized without increasing the thickness of the rubber layer near the tread end TE (shoulder). In other words, the heavy-duty pneumatic tire 100 according to this embodiment can improve resistance to uneven wear after wear and suppress the decrease in tire durability caused by heat generation in the rubber layer.

[0054] The heavy-duty pneumatic tire 100 of this embodiment also includes a cushioning rubber 17a, which is disposed between the carcass ply 40 and the belt ply 15. The inner end of the cushioning rubber 17a in the tire width direction is located at the first curvature change portion P1.

[0055] At least partially, a cushioning rubber 17a is provided on the outer side of the first curvature variation section P1 in the tire width direction, specifically on the second section P1-P2. Therefore, the ground contact pressure at the location where the cushioning rubber 17a is provided in the middle position is further reduced. This further suppresses uneven wear caused by dragging near the tread end TE during tire rolling.

[0056] In addition, such as Figure 1 As shown, when the outer end of the buffer rubber 17a in the tire width direction is positioned at the outer end of the belt layer 15 in the tire width direction, movement of the outer end of the belt layer 15 in the tire width direction can be suppressed to prevent damage to the nearby rubber layer.

[0057] Furthermore, when the cross-sectional shape of the carcass ply 40 of the heavy-duty tire 100 for trucks and buses satisfies the relationships 0.5 ≤ W1 / TW ≤ 0.8 and W1 / TW < W2 / TW < 1, it is possible to effectively suppress the development of travel near the inner side of the tire width direction of the shoulder contact patch adjacent to the tread end TE. Here, the cross-sectional shape of the carcass ply 40 is the cross-sectional shape of the heavy-duty pneumatic tire in its unloaded state when mounted on a standard rim and filled with standard internal pressure.

[0058] Furthermore, the radial distance from the tire equator CL position (P0) of the carcass ply 40 to the radial distance from the first curvature change section P1 is defined as a1. Also, the radial distance from the tire equator CL position (P0) of the carcass ply 40 to the radial distance from the second curvature change section P2 is defined as a2. In this case, if the cross-sectional shape also satisfies the relationship a1 / W1≤0.06<a2 / W2≤0.15, the contact pressure ratio from the tire equator 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.

[0059] Furthermore, in the heavy-duty pneumatic tire 100 of this embodiment, a plurality of protrusions 19 are formed on the tire surface in the shoulder region where the tread portion 10 and the tire side portion 20 are connected. These protrusions 19 protrude outward from the tire surface in the tire width direction and extend circumferentially along the tire. When the radius of curvature R2 of the second portion (P1-P2) of the carcass ply 40 in the stated cross-section and the radius of curvature R3 of the portion of the carcass ply 40 located between the second curvature change portion P2 and portion P3 satisfy the relationship R2 / R3≤0.5, the ground contact pressure at the tread end TE, where portion P3 is located inside the tire width direction of the area of ​​the carcass ply 40 where the plurality of protrusions 19 are provided, can be more reliably ensured. Therefore, the resistance to uneven wear in the tire width direction of the heavy-duty pneumatic tire 100 can be improved.

[0060] (4) Examples

[0061] To confirm the effectiveness of the present invention, the specifications in Table 1 were compared with those in Table 1. Figure 1 The uneven wear resistance and heat-generating durability of 11R22.5 pneumatic tires for buses and trucks were predicted. The tread patterns are identical. They are substantially common except for the parameters shown in Table 1. Only tire 1 was prototyped and its performance was tested. The performance of tires 2–4 was predicted based on measured values ​​of the contact patch shape.

[0062] [Table 1]

[0063]

[0064] In the heavy-duty tires of this embodiment, tire 1 is a tire that uses existing case lines and has its circumferential ground contact length optimized. Tire 2 is a tire that uses existing case lines and has its circumferential ground contact length at the ground contact end extended by utilizing the thickness of the rubber layer when it is a new tire. Tire 3 is a tire that incorporates the case lines of this embodiment and has its circumferential ground contact length optimized. Tire 4 is a tire that incorporates the case lines of this embodiment and has its circumferential ground contact length at the ground contact end extended when it is a new tire.

[0065] Furthermore, the dimensions of the tire carcass profiles for each experimental example shown in Table 1 are measured values ​​obtained by CT scanning under standard conditions after rim assembly with the following rims.

[0066] Wheel rim: 8.25×22.5

[0067] The evaluation method for heavy-duty tires is as follows.

[0068] <Resistance to uneven wear>

[0069] The tires of each test example were mounted on all wheels of the vehicle under the conditions of rim size (8.25×22.5), internal pressure (775kPa), and load (25.80kN), and load tests were conducted at actual usage speeds. The condition of single-shoulder wear on the tire shoulder when the tire reached 50% wear was evaluated. Uneven wear of tire 1 was the subject of the study. Here, as the evaluation criterion, with the single-shoulder wear of tire 1 set as 1, an "A" (excellent) rating of 0.6 or less, a "B" (good) rating of 0.8 or less, a "C" (acceptable) rating of 1 or less, and a "D" (unacceptable) rating of 1 or more was used.

[0070] <Heat-generating durability>

[0071] The time taken to travel at 90 km / hr until the vehicle malfunctioned was evaluated. The heat resistance of tire 1 fully meets market requirements. Here, as the evaluation criterion, with the travel time of tire 1 until the malfunction set as 1, the evaluation criteria are: "A" (excellent) 1 or above, "B" (good) 0.8 or above, "C" (acceptable) 0.6 or above, and "D" (unacceptable) less than 0.6.

[0072] [Table 2]

[0073] Resistance to uneven wear Heat preservation Tire 1 C A Tire 2 A C Tire 3 B A Tire 4 A B

[0074] As shown in Table 2, tires 1 and 2, which are equipped with existing outer surface lines, struggle to achieve high ratings in both resistance to uneven wear and heat-generating durability. In contrast, tires 3 and 4, equipped with outer surface lines that meet the conditions of this embodiment, can achieve a balance between resistance to uneven wear and heat-generating durability.

[0075] The full contents of Japanese Special Appeal No. 2021-210405 (application date: December 24, 2021) are quoted here.

[0076] Embodiments of the present invention have been described above, but should not be construed as limiting the invention by the descriptions and drawings that constitute a part of this disclosure. Various alternative embodiments, examples, and application techniques will be apparent to those skilled in the art based on this disclosure.

Claims

1. A heavy-duty pneumatic tire, wherein, This heavy-duty pneumatic tire features: The tread section, which contacts the road surface; The tire sidewall is connected to the tread portion and is located radially inside the tread portion of the tire. The bead portion is connected to the tire sidewall and is located inside the tire radial direction of the tire sidewall; The tire carcass ply extends from the tread portion, through the tire sidewall, to the bead portion, and forms the skeleton of the pneumatic tire; and A belt layer, disposed on the tread portion and located radially outside the carcass ply of the tire. The tire carcass ply has a first curvature variation portion and a second curvature variation portion. The first curvature variation portion is the boundary between the first and second portions. The first portion includes the tire equator. The second portion is located 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 compared to the curvature of the first portion. The second curvature variation portion is the boundary between the second and third portions. The third portion is located inside the second portion in the tire radial direction and has a smaller curvature in a cross-section compared to the curvature of the second portion. The heavy-duty pneumatic tire also includes a cushioning rubber, the inner end of which in the tire width direction is located at the first curvature change portion, and the cushioning rubber is disposed between the carcass ply and the belt ply. Under no-load conditions, when mounted on a standard rim and filled with standard internal pressure, for the cross-sectional shape of the heavy-duty pneumatic tire, the distance in the tire width direction from the tire equator to the first curvature change portion is defined as W1, the distance in the tire width direction from the tire equator to the second curvature change portion is defined as W2, and the distance in the tire width direction from the tire equator to the tread end of the tread portion is defined as TW. In the above case, the cross-sectional shape of the carcass ply satisfies the relationships 0.5 ≤ W1 / TW ≤ 0.8 and W1 / TW < W2 / TW < 1. The tire surface in the shoulder region where the tread and the tire sidewall connect is provided with a plurality of protrusions. These protrusions protrude outward from the tire surface in the tire width direction and extend along the tire circumferential direction. The plurality of protrusions includes a first protrusion located at the radially outer end of the tire and a second protrusion adjacent to the first protrusion. In the cross section, the radius of curvature R2 of the second part and the radius of curvature R3 of the third part satisfy the relationship R2 / R3≤0.

5. The second part is located between the first curvature change part and the second curvature change part, and the third part is located between the midpoint of the radial position of the tire carcass ply, the first protrusion and the second protrusion.

2. The heavy-duty pneumatic tire according to claim 1, wherein, Let a1 be the distance in the radial direction from the position of the carcass ply at the tire equator to the radial direction of the first curvature change portion, and let a2 be the distance in the radial direction from the position of the carcass ply at the tire equator to the radial direction of the second curvature change portion. In the above case, the relationship a1 / W1≤0.06<a2 / W2≤0.15 is satisfied.

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