Heavy-duty tires

Abstract

To provide a heavy-duty tire that ensures heat dissipation and wear resistance while suppressing the occurrence of block breakage. [Solution] The tread surface has one or more zigzag grooves 2 extending in a zigzag pattern in the tire circumferential direction, and a plurality of widthwise grooves 3 extending in the tire width direction. The groove width of the zigzag grooves 2 is 20.0 mm or less, and the groove width of the widthwise grooves is 20.0 mm or less. The zigzag grooves 2 consist of a first portion extending in the tire circumferential direction and a second portion extending at an inclination with respect to the tire circumferential direction. Two adjacent second portions sandwiching the first portion are inclined in opposite directions with respect to the tire circumferential direction, and the second portion is located between two widthwise grooves 3 adjacent in the tire circumferential direction.

Description

Technical Field

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[0001] The present invention relates to a heavy-duty tire.

Background Art

[0002] Conventionally, some heavy-duty tires have grooves provided on the tread surface to improve heat dissipation. In contrast, for example, in Patent Document 1, it has been proposed that by making the grooves into fine grooves, heat dissipation can be ensured while ensuring the rubber volume and improving wear resistance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it has been found that in the method of Patent Document 1, cracking often occurs in the blocks partitioned by the fine grooves.

[0005] Therefore, an object of the present invention is to provide a heavy-duty tire that can suppress the occurrence of cracking in the blocks while ensuring heat dissipation and wear resistance.

Means for Solving the Problems

[0006] The gist configuration of the present invention is as follows. (1) The tread surface has one or more zigzag fine grooves extending in a zigzag shape in the tire circumferential direction and a plurality of widthwise fine grooves extending in the tire width direction, the groove width of the zigzag fine groove is 20.0 mm or less, the groove width of the widthwise fine groove is 20.0 mm or less, The zigzag groove consists of a first portion extending in the circumferential direction of the tire and a second portion extending at an inclination with respect to the circumferential direction of the tire, wherein the two second portions adjacent to the first portion are inclined in opposite directions with respect to the circumferential direction of the tire. A heavy-duty tire characterized in that the second portion is located between two adjacent narrow grooves in the width direction in the tire's circumferential direction.

[0007] Here, "tread surface" refers to the entire circumferential surface of the tread that comes into contact with the road surface when a heavy-duty tire is mounted on an applicable rim, filled to the specified internal pressure, and subjected to the maximum load. "Groove width" refers to the groove width (opening width) when a heavy-duty tire is mounted on the applicable rim, filled to the specified internal pressure, and under no load. Unless otherwise specified, the shapes and dimensions of various grooves refer to these shapes and dimensions under no load.

[0008] In this specification, "applicable rim" refers to the standard rim for the applicable size (Measuring Rim in the ETRTO STANDARDS MANUAL, Design Rim in the TRA YEAR BOOK) which is an industrial standard valid in the region where the tire is produced and used, and which is listed or will be listed in the future in the STANDARDS MANUAL of the ETRTO (The European Tyre and Rim Technical Organisation) in Japan, the STANDARDS MANUAL of the ETRTO (The European Tyre and Rim Technical Organisation) in Europe, and the YEAR BOOK of the TRA (The Tire and Rim Association, Inc.) in the United States, etc. (That is, the "rim" in "wheel" above includes not only current sizes but also sizes that may be included in the above industrial standards in the future. An example of "sizes to be listed in the future" is the size listed as "FUTURE DEVELOPMENTS" in the ETRTO 2013 edition.) However, in the case of a size not listed in the above industrial standards, it refers to a rim with a width corresponding to the tire bead width. Furthermore, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity of a single wheel in the applicable size and ply rating as described in JATMA, etc., and in the case of sizes not listed in the above industrial standards, "specified internal pressure" refers to the air pressure (maximum air pressure) corresponding to the maximum load capacity specified for each vehicle on which the tire is mounted. Furthermore, "maximum load capacity" refers to the load corresponding to the maximum load capacity mentioned above.

[0009] (2) The heavy-duty tire according to (1), wherein part or all of the second portion overlaps the narrow groove in the width direction when projected in the circumferential direction of the tire.

[0010] (3) The heavy-duty tire according to (1) or (2), wherein the first portion communicates with the widthwise narrow groove, or with a line projected in the widthwise direction from the end portion of the widthwise narrow groove.

[0011] (4) The heavy-duty tire according to any one of (1) to (3), wherein the circumferential length of the first portion of the tire is 20% or more and 80% or less of the average distance in the circumferential direction between two adjacent narrow grooves in the width direction of the tire.

[0012] (5) The heavy-duty tire according to any one of (1) to (4), wherein the amplitude of the zigzag groove is 5% to 20% of the average distance in the tire width direction between two adjacent zigzag grooves in the tire width direction.

[0013] (6) The heavy-duty tire according to any one of (1) to (5), wherein the inclination angle of the second portion with respect to the tire circumferential direction is 20 to 70°.

[0014] (7) The narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located inside the portion with a constant groove width in the tire diameter direction, where part or all of the groove width is greater than that of the portion with a constant groove width. A heavy-duty tire according to any one of (1) to (6) above, wherein the depth of the portion with a constant groove width is 30% or more and 85% or less of the total depth of the narrow groove in the width direction.

[0015] (8) The heavy-duty tire according to any one of (1) to (7), wherein the narrow groove in the width direction is a flask-shaped groove.

[0016] (9) A heavy-duty tire according to any one of (1) to (8) above, wherein the groove depth of the narrow groove in the width direction is 70 to 200 mm. "Groove depth" refers to the maximum depth of the groove.

[0017] (10) The narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located inside the portion with a constant groove width in the tire diameter direction, where part or all of the groove width is larger than that of the portion with a constant groove width. In a cross-sectional view at a cross-section perpendicular to the groove width, the bottom portion has curvature. The heavy-duty tire according to any one of (1) to (9), wherein the radius of curvature of the bottom surface of the bottom portion is 60% or more and 125% or less of the groove width of the portion with a constant groove width.

[0018] (11) The narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located inside the portion with a constant groove width in the tire diameter direction, where part or all of the groove width is greater than that of the portion with a constant groove width. A heavy-duty tire according to any one of (1) to (10), wherein, in a cross-sectional view at a cross-section perpendicular to the groove width, the maximum width of the bottom portion is 120% or more and 250% or less of the groove width in the portion with a constant groove width.

[0019] (12) A heavy-duty tire as described in any one of (1) to (11) above, having a cross-sectional width of 450 mm or more and an outer diameter of 1750 mm or more. (13) The tread surface has one or more zigzag grooves extending in a zigzag pattern in the circumferential direction of the tire, and multiple widthwise grooves extending in the width direction of the tire, The ratio of the groove width of the zigzag groove to the tread width is 4.5% or less. The ratio of the groove width of the narrow grooves in the width direction to the tread width is 4.5% or less. The zigzag fine groove consists of a first portion extending in the tire circumferential direction and a second portion extending obliquely with respect to the tire circumferential direction. Two adjacent second portions sandwiching the first portion are inclined in opposite directions with respect to the tire circumferential direction. The heavy-duty tire is characterized in that the second portion is located between the two widthwise grooves adjacent in the tire circumferential direction in the tire circumferential direction. Here, the "tread width" refers to the distance in the tire width direction between the grounding ends in the unloaded state, and the "grounding ends" refer to both ends in the tire width direction of the tread surface when the heavy-duty tire is mounted on an application rim, filled with a specified internal pressure, and loaded with a maximum load.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a heavy-duty tire that can suppress the occurrence of block exfoliation while ensuring heat dissipation and wear resistance.

Brief Description of the Drawings

[0021] [Figure 1] It is a developed view showing the tread pattern of a heavy-duty tire according to an embodiment of the present invention. [Figure 2] It is a diagram for explaining the shape and dimensions of the zigzag fine groove. [Figure 3] It is a cross-sectional view for explaining the shape of the widthwise groove. [Figure 4] It is a cross-sectional view for explaining the shape of the widthwise groove. [Figure 5] ]]It is a schematic diagram for explaining the measurement of the strain generated at the bottom of the widthwise groove. [Figure 6] It is a schematic diagram for explaining the time change of the strain generated at the bottom of the widthwise groove in comparison with the case of a small tire size. [Figure 7] It is a schematic diagram for explaining the tensile strain generated during kick-out. [Figure 8] It is a schematic diagram for explaining the tensile strain generated during kick-out when the volume of the groove bottom is large. [Figure 9] This figure shows the tire tread pattern of the comparative example. [Figure 10] This figure shows the tread pattern of a tire according to Invention Example 1. [Figure 11] This figure shows the tread pattern of a tire according to Invention Example 2. [Figure 12] This figure shows the tread pattern of a tire according to Invention Example 3. [Modes for carrying out the invention]

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0023] Figure 1 is an exploded view showing the tread pattern of a heavy-duty tire (hereinafter also simply referred to as a tire) according to one embodiment of the present invention. While the internal structure of the tire can be configured in the same way as conventional tires, and therefore a detailed explanation is omitted, one example is a tire comprising a pair of bead portions, a carcass toroidally spanning the bead portions, a belt positioned radially outward of the carcass, and a tread positioned radially outward of the belt. The tire of this embodiment is a radial tire, and more specifically, a radial tire for mining and construction vehicles.

[0024] As shown in Figure 1, this tire has one or more zigzag grooves 2 extending in a zigzag pattern in the circumferential direction of the tire, and multiple widthwise grooves 3 extending in the tire width direction, on the tread surface 1. This tire also has multiple lug grooves 4 that communicate with the tread edge TE.

[0025] In the illustrated example, three zigzag grooves 2 are arranged on the tread surface 1. In the illustrated example, the tread surface 1 has a zigzag groove 2 extending in a zigzag pattern along the tire equatorial plane CL, a zigzag groove 2 arranged in one half of the tire width direction with the tire equatorial plane CL as the boundary, and a zigzag groove 2 arranged in the other half of the tire width direction with the tire equatorial plane CL as the boundary. On the other hand, the zigzag grooves 2 may also be arranged only in the center (for example, on the tire equatorial plane CL), or the zigzag grooves 2 may be arranged only in the shoulder area.

[0026] The groove width (opening width) of the zigzag groove 2 is 20.0 mm or less. Preferably, the groove width (opening width) of the zigzag groove 2 is 5.0 mm or more. Preferably, the groove depth (maximum depth) of the zigzag groove 2 is 70 mm or more and 200 mm or less. Alternatively, the ratio of the groove width of the zigzag groove 2 to the tread width is 4.5% or less. Preferably, the ratio of the groove width of the zigzag groove 2 to the tread width is 0.3% or more.

[0027] Figure 2 is a diagram illustrating the shape and dimensions of the zigzag groove 2. As shown in Figures 1 and 2, the zigzag groove 2 consists of a first portion 2a extending in the circumferential direction of the tire and second portions 2b1 and 2b2 extending at an angle to the circumferential direction of the tire, with the two adjacent second portions 2b1 and 2b2 flanking the first portion 2a being inclined in opposite directions to each other with respect to the circumferential direction of the tire.

[0028] In the illustrated example, the first portion 2a extends without inclination with respect to the tire circumferential direction, but it may also extend with an inclination angle of 5° or less with respect to the tire circumferential direction. Preferably, the tire circumferential length a of the first portion 2a is 20% to 80% of the average tire circumferential distance between two adjacent widthwise narrow grooves 3 in the tire circumferential direction.

[0029] The second portions 2b1 and 2b2 are preferably inclined at an angle θ of 20 to 70° with respect to the tire circumferential direction. In the illustrated example, the second portion 2b1 extends from the upper right to the lower left, and the second portion 2b2 extends from the upper left to the lower right. The second portions 2b1 and 2b2 are arranged alternately with respect to the first portion 2a in between, forming a zigzag shape, and the second portions 2b1 and 2b2 are inclined in opposite directions with respect to the tire circumferential direction. In the illustrated example, the angle of inclination of the second portion 2b1 with respect to the tire circumferential direction and the angle of inclination of the second portion 2b2 with respect to the tire circumferential direction are the same (although their directions are opposite), but they can also be different. As shown in Figure 2, the amplitude b of the zigzag groove 2 is preferably 5% to 20% of the average distance in the tire width direction between two adjacent zigzag grooves 2 in the tire width direction.

[0030] The zigzag groove 2 can be a flat plate-like shape in which the groove width is approximately constant from the tread surface 1 towards the bottom of the groove.

[0031] In the illustrated example, the first portion 2a of the zigzag groove 2 located in one half and the other half of the tire, with the tire equatorial plane CL as the boundary, are aligned in the circumferential direction of the tire. On the other hand, the circumferential position of the first portion 2a of the zigzag groove 2 extending along the tire equatorial plane CL is different in the circumferential direction from the circumferential position of the first portion 2a of the zigzag groove 2 located in one half and the other half of the tire, with the tire equatorial plane CL as the boundary. Furthermore, when projected in the tire width direction, the first portion 2a of the zigzag groove 2 extending along the tire equatorial plane CL partially overlaps with the first portion 2a of the zigzag groove 2 located in one half and the other half of the tire, with the tire equatorial plane CL as the boundary. On the other hand, this disclosure also includes cases where, when projected in the tire width direction, the first portion 2a of one or more of the multiple zigzag grooves 2 does not overlap at all with the first portion 2a of the other zigzag grooves 2 (their positions in the tire circumferential direction are completely different). Furthermore, it also includes cases where all the first portions 2a of the zigzag grooves 2 are arranged in a completely alternating manner so that when projected in the tire width direction, they do not overlap at all with the first portion 2a of the other zigzag grooves 2.

[0032] The widthwise narrow groove 3 is positioned between two adjacent zigzag narrow grooves 2 in the tire width direction. In the illustrated example, both ends of the widthwise narrow groove 3 are in communication with the zigzag narrow grooves 2 (in the illustrated example, the first portion 2a (at the center position in the tire circumferential direction)).

[0033] In the illustrated example, the widthwise narrow groove 3 has a curved shape in which a portion that curves on one side in the tire circumferential direction and a portion that curves on the other side in the tire circumferential direction are connected, but it may also extend in a straight line.

[0034] In the illustrated example, the widthwise narrow groove 3, mainly located in one half of the tire width direction, extends beyond the tire equatorial plane CL to the other half of the tire width direction. Conversely, the widthwise narrow groove 3, mainly located in the other half of the tire width direction, extends beyond the tire equatorial plane CL to the one half of the tire width direction. Therefore, the widthwise narrow groove 3 mainly located in one half of the tire width direction and the widthwise narrow groove 3 mainly located in the other half of the tire width direction are arranged so that they partially overlap when projected in the circumferential direction of the tire. The widthwise narrow groove 3 mainly located in one half of the tire width direction and the widthwise narrow groove 3 mainly located in the other half of the tire width direction are arranged with a staggered position in the circumferential direction of the tire. In the illustrated example, the widthwise narrow groove 3 mainly located in one half of the tire width direction and the widthwise narrow groove 3 mainly located in the other half of the tire width direction extend inclined in the same direction in the circumferential direction with respect to the tire width direction, but they may also extend inclined in opposite directions. On the other hand, in this disclosure, the narrow grooves 3 located in the width direction of one half and the other half of the tire may be in communication with each other (for example, in the tire equatorial plane CL).

[0035] The groove width (opening width) of the narrow groove 3 in the width direction is 20.0 mm or less. Preferably, the groove width (opening width) of the narrow groove 3 in the width direction is 5.0 mm or more. Preferably, the groove depth (maximum depth) of the narrow groove 3 in the width direction is 70 mm or more and 200 mm or less. Alternatively, the ratio of the groove width of the narrow grooves 3 in the width direction to the tread width is 4.5% or less. Preferably, the ratio of the groove width of the narrow grooves 3 in the width direction to the tread width is 0.3% or more.

[0036] The lateral groove 3 may extend without inclination in the tire width direction. If the lateral groove 3 extends with respect to the tire width direction, the inclination angle with respect to the tire width direction is preferably greater than 0° and 45° or less. However, if the lateral groove 3 is curved as shown in the illustrated example, the above inclination angle shall mean the angle of inclination with respect to the tire width direction of the line segment connecting both ends of the lateral groove 3.

[0037] Figures 3 and 4 are cross-sectional views illustrating the shape of the widthwise narrow groove 3. As shown in Figures 3 and 4, in this example, the widthwise narrow groove 3 consists of a constant groove width portion 3a and a bottom portion 3b located radially inward of the constant groove width portion 3a, where part or all of the bottom portion is wider than the constant groove width portion 3a. In this example, the depth of the constant groove width portion 3a is 30% to 85% of the total depth of the widthwise narrow groove 3.

[0038] Figure 3 shows an example where the narrow groove 3 in the width direction is flask-shaped. In a cross-sectional view perpendicular to the groove width, the bottom 3b has curvature, and the radius of curvature R of the bottom surface of the bottom 3b is between 60% and 125% of the groove width of the constant groove width portion 3a.

[0039] Figure 4 shows an example where the narrow groove 3 in the width direction is a paddle groove. In a cross-sectional view perpendicular to the groove width, the maximum width of the bottom 3b is between 120% and 250% of the groove width of the constant groove width portion 3a. Examples are shown in Figures 3 and 4, but the bottom 3b can have various shapes.

[0040] In the illustrated example, the lug groove 4 communicates with the tread edge TE and the zigzag groove 2. In the illustrated example, the lug groove 4 communicates with the center of the first portion 2a of the zigzag groove 2 in the tire circumferential direction, but this is not limited to this case. In the illustrated example, the lug groove 4 located in one half of the tire width direction and the lug groove 4 located in the other half of the tire width direction are positioned with a phase difference in the tire circumferential direction so that they do not overlap when projected in the tire width direction. In the illustrated example, the lug groove 4 located in one half of the tire width direction and the lug groove 4 located in the other half of the tire width direction are inclined in opposite directions in the tire circumferential direction with respect to the tire width direction, but they may be inclined in the same direction. On the other hand, in this disclosure, the lug grooves 4 located in one half and the other half in the tire width direction may be arranged such that they overlap each other when projected in the tire width direction.

[0041] The groove width (opening width) of the lug groove 4 is not particularly limited, but can be, for example, 30 to 100 mm. The groove depth (maximum depth) of the lug groove 4 is not particularly limited, but can be, for example, 40 to 200 mm. The lug groove 4 may extend without inclination in the tire width direction. If the lug groove 4 extends inclined with respect to the tire width direction, it is preferable that the inclination angle with respect to the tire width direction be greater than 0° and 45° or less.

[0042] Multiple blocks 5 are partitioned by zigzag grooves 2 and widthwise grooves 3. In the illustrated example, the blocks 5 have a roughly parallelogram shape, but they can also be roughly rectangular, for example.

[0043] In the illustrated example, the first portion 2a is in communication with the widthwise narrow groove 3. On the other hand, the first portion 2a may intersect with the extension of the widthwise narrow groove 3. In other words, the block 5 does not have to be completely separated by the widthwise narrow groove 3. The following describes the effects and benefits of the heavy-duty tires of this embodiment (in this example, for construction and mining vehicles).

[0044] First, we will explain the mechanism by which breakage occurs in blocks partitioned by narrow grooves, as discovered by the inventors. Figure 5 is a schematic diagram illustrating the measurement of strain occurring at the bottom of a narrow groove in the width direction. Figure 6 is a schematic diagram illustrating the time change of strain occurring at the bottom of a narrow groove in the width direction in comparison with the case of a small tire size.

[0045] As schematically shown in Figure 5, the inventors analyzed the distortion at the bottom of the narrow grooves in the width direction where cracks that cause block breakage occur. As schematically shown in Figure 6, it was found that the distortion occurred more significantly when the block was pressed down compared to the case of a tire size with small compressive strain (a small tire size was used for comparison, although it is for heavy loads). Furthermore, it was found that the distortion occurred significantly more significantly when the block was kicked out compared to the case of a tire size with small tensile strain. From these findings, the inventors determined that the significant change in the amount of distortion from compressive strain to tensile strain at the bottom of the narrow grooves in the width direction from the time of pressing down to the time of kicking out was the cause of cracking at the bottom of the grooves and, consequently, block breakage. In particular, the amount of change compared to the case of a tire size with small tensile strain when the block was kicked out was large.

[0046] It was found that the reason why large compressive strain occurs when the tire is pressed down in narrow grooves in the width direction (compared to the case of small tire sizes) is that, under the very large load of heavy-duty tires, the narrow groove width in the width direction causes the groove walls to come into contact and collapse near the bottom of the groove.

[0047] Figure 7 is a schematic diagram illustrating the tensile strain that occurs during push-off. As schematically shown in Figure 7, under load, the blocks undergo crushing deformation due to the incompressibility of the rubber. In the narrow grooves in the width direction, because the groove width is small, the two adjacent blocks separated by the narrow grooves exert a strong pushing force on each other. During push-off, the frictional force between the adjacent blocks and the road surface that was supporting the pushing force is lost, so the block that is pushed off first receives a larger pushing force. Consequently, the grooves open up, and a large tensile strain occurs at this time.

[0048] The heavy-duty tire of this embodiment first has one or more zigzag grooves 2 extending in a zigzag pattern in the circumferential direction of the tire and multiple widthwise grooves 3 extending in the tire width direction on the tread surface 1, the groove width of the zigzag grooves 2 is 20.0 mm or less (or the ratio of the groove width of the zigzag grooves 2 to the tread width is 4.5% or less), and the groove width of the widthwise grooves 3 is 20.0 mm or less (or the ratio of the groove width of the widthwise grooves 3 to the tread width is 4.5% or less), so that heat dissipation can be improved (compared to, for example, a case where no grooves are provided), and the rigidity of the block 5 can be ensured and wear resistance can be improved (compared to, for example, a case where heat dissipation is improved with wide grooves). In the heavy-duty tire of this embodiment, the zigzag groove 2 consists of a first portion 2a extending in the tire circumferential direction and a second portion 2b extending at an inclination with respect to the tire circumferential direction. The two adjacent second portions 2b1 and 2b2, flanking the first portion 2a, are inclined in opposite directions with respect to the tire circumferential direction, and the second portion 2b is located between two adjacent widthwise grooves 3 in the tire circumferential direction. As a result, the wall surface partitioned by the second portion 2b acts as a resistance component against the force with which block 5 is pushed out during the aforementioned kick-off, thereby suppressing the aforementioned groove opening and preventing large tensile strain from occurring at the bottom of the narrow groove 3 in the width direction. Thus, in the heavy-duty tire of this embodiment, the tensile strain that can occur at the bottom of the narrow grooves 3 in the width direction during kick-off, which was a particularly major cause of block breakage, can be reduced. As described above, the heavy-duty tire of this embodiment can suppress the occurrence of block breakage while ensuring heat dissipation and wear resistance.

[0049] Here, it is preferable that part or all of the second portion 2b overlaps the narrow groove 3 in the width direction when projected in the circumferential direction of the tire. This is because the effect of suppressing groove opening by the second portion 2b, as described above, can be made more reliable, and the occurrence of block breakage can be further suppressed.

[0050] Furthermore, it is preferable that the first portion 2a communicates with the widthwise narrow groove 3 or intersects with the extension of the widthwise narrow groove 3. This ensures that the corners of the block 5 are approximately right angles, thereby ensuring the rigidity of the corners of the block 5 and thus the wear resistance of the block 5.

[0051] The circumferential length of the first portion 2a is preferably 20% to 80% of the average circumferential distance between two adjacent narrow grooves 3 in the width direction.

[0052] The amplitude of the zigzag groove 2 is preferably 5% to 20% of the average distance in the tire width direction between two adjacent zigzag grooves 3. Setting it to 5% or more makes the effect of suppressing groove opening by the second portion 2b mentioned above more reliable and further suppresses the occurrence of block breakage. On the other hand, setting it to 20% or less prevents large sharp angles from being formed on the block 5.

[0053] The inclination angle of the second portion 2b with respect to the tire circumferential direction is preferably 20 to 70°. Setting it to 20° or more makes the effect of suppressing groove opening by the second portion 2b, as described above, more reliable and further suppresses the occurrence of block breakage. On the other hand, setting it to 70° or less prevents the formation of excessively sharp angles on the block 5.

[0054] Furthermore, the widthwise narrow groove 3 consists of a constant groove width portion 3a and a bottom portion 3b located radially inward of the constant groove width portion 3a, where part or all of the groove width is greater than that of the constant groove width portion. Preferably, the depth of the constant groove width portion 3a is 30% to 85% of the total depth of the widthwise narrow groove 3. By having a bottom portion 3b, and by having a depth of the constant-width portion 3a that is 85% or less of the total depth of the narrow groove 3 in the width direction, it is possible to ensure a gap between the groove walls at the bottom of the groove and reduce the compressive strain that occurs at the bottom of the groove when stepped on. Figure 8 is a schematic diagram illustrating the tensile strain that occurs during push-off when the volume of the groove bottom is large. Furthermore, by having a bottom portion 3b, and by ensuring that the depth of the constant groove width portion 3a is 85% or less of the total depth of the narrow groove 3 in the width direction, even when kicking off, the force with which adjacent blocks 5 push against each other near the bottom of the groove is weakened (or they are prevented from pushing against each other near the bottom of the groove), weakening the pushing force generated when the blocks 5 leave the road surface, thereby suppressing groove opening and reducing tensile strain. As described above, by having a bottom portion 3b, and by ensuring that the depth of the constant-width portion 3a is 85% or less of the total depth of the narrow groove 3 in the width direction, both the compressive strain at the bottom of the groove during footing and the tensile strain at the bottom of the groove during kicking can be reduced, thereby further suppressing the occurrence of block breakage. Furthermore, if the depth of the constant-width groove portion 3a is 15% or more of the total depth of the narrow groove 3 in the width direction, the rigidity of the block 5 can be ensured even when the volume of the groove bottom is increased.

[0055] The widthwise narrow groove 3 consists of a constant groove width portion 3a and a bottom portion 3b located inside the constant groove width portion 3a in the tire radial direction, where part or all of the bottom portion 3b has a wider groove width than the constant groove width portion 3a. In a cross-sectional view perpendicular to the groove width, the bottom portion 3b has curvature, and the radius of curvature R of the bottom surface of the bottom portion 3b is preferably 60% to 125% of the groove width of the constant groove width portion 3a. As an example of such a shape, the widthwise narrow groove 3 is preferably flask-shaped.

[0056] The widthwise narrow groove 3 consists of a constant groove width portion 3a and a bottom portion 3b located radially inward of the constant groove width portion 3a, where part or all of the groove width is greater than that of the constant groove width portion 3a. Preferably, in a cross-sectional view perpendicular to the groove width, the maximum width of the bottom portion 3b is 120% to 250% of the groove width of the constant groove width portion 3a. The widthwise narrow groove 3 may also be a paddle groove.

[0057] The groove depth of the lateral narrow groove 3 is preferably 70 to 200 mm. This is because, in large tires where the groove depth of the lateral narrow groove 3 is 70 mm or more, the blocks 5 are particularly prone to breaking off. Also, by setting the groove depth of the lateral narrow groove 3 to 200 mm or less, the rigidity of the blocks 5 can be ensured.

[0058] The tire of this disclosure is used as a heavy-duty tire and is preferably used as a tire for construction and mining vehicles. Such a tire has, for example, a section width of 450 to 1550 mm and an outer diameter of 1750 to 4100 mm.

[0059] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the embodiments described above. Furthermore, although embodiments of the present invention will be described below, the present invention is not limited in any way to the following embodiments either. [Examples]

[0060] A tire model simulating a pneumatic radial tire for construction and mining vehicles, with a tire size of 59 / 80R63 and featuring zigzag and lateral narrow grooves, is mounted on a standard rim as defined by TRA (standard). With an internal pressure of 600kPa and a load of 996.4kN, the amount of groove opening during push-off is simulated using FEM under free-rolling conditions.

[0061] Figure 9 shows the tread pattern of a tire according to a comparative example, Figure 10 shows the tread pattern of a tire according to Invention Example 1, Figure 11 shows the tread pattern of a tire according to Invention Example 2, and Figure 12 shows the tread pattern of a tire according to Invention Example 3. The specifications and evaluation results for each tire are shown in Table 1 below. In Table 1, "Zigzag groove inclination angle θ" refers to the inclination angle θ of the second section relative to the tire circumferential direction; "Zigzag groove amplitude b" is the amplitude b shown in Figure 2, expressed as a ratio to the maximum width of the block in the tire width direction; "Extension length of the second section" is expressed as a ratio to the maximum width of the block in the tire circumferential direction; and "FEM calculation result of groove opening" is expressed as an index with the result of the comparative example set to 100, where a smaller value means a smaller groove opening.

[0062] [Table 1]

[0063] As shown in Tables 1-3, it can be seen that the groove opening is smaller in Invention Examples 1-3 compared to the comparative example. [Explanation of Symbols]

[0064] 1: Tread surface, 2: Zigzag fine grooves, 3: Thin groove in the width direction, 4: Lug grooves, 5: Block CL: Tire equatorial plane, TE: Tread edge

Claims

1. The tread surface has one or more zigzag grooves extending in a zigzag pattern in the circumferential direction of the tire, and multiple widthwise grooves extending in the width direction of the tire. The groove width of the aforementioned zigzag narrow groove is 20.0 mm or less. The groove width of the aforementioned narrow groove in the width direction is 20.0 mm or less. The zigzag groove consists of a first portion extending in the circumferential direction of the tire and a second portion extending at an inclination with respect to the circumferential direction of the tire, wherein two adjacent second portions sandwiching the first portion are inclined in opposite directions with respect to the circumferential direction of the tire. A heavy-duty tire characterized in that the second portion is located between two adjacent narrow grooves in the width direction in the tire circumferential direction.

2. The heavy-duty tire according to claim 1, wherein part or all of the second portion overlaps the narrow groove in the width direction when projected in the circumferential direction of the tire.

3. The heavy-duty tire according to claim 1 or 2, wherein the first portion communicates with the widthwise narrow groove, or communicates with a line projected in the widthwise direction from the end portion of the widthwise narrow groove.

4. The heavy-duty tire according to claim 1 or 2, wherein the circumferential length of the first portion of the tire is 20% or more and 80% or less of the average distance in the circumferential direction between two adjacent narrow grooves in the width direction of the tire.

5. The heavy-duty tire according to claim 1 or 2, wherein the amplitude of the zigzag grooves is 5% to 20% of the average distance in the tire width direction between two adjacent zigzag grooves in the tire width direction.

6. The heavy-duty tire according to claim 1 or 2, wherein the inclination angle of the second portion with respect to the tire circumferential direction is 20 to 70°.

7. The aforementioned narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located radially inward of the portion with a constant groove width, where part or all of the groove width is greater than that of the portion with a constant groove width. The heavy-duty tire according to claim 1 or 2, wherein the depth of the portion with a constant groove width is 30% or more and 85% or less of the total depth of the narrow groove in the width direction.

8. The heavy-duty tire according to claim 1 or 2, wherein the aforementioned narrow grooves in the width direction are flask-shaped grooves.

9. The heavy-duty tire according to claim 1 or 2, wherein the groove depth of the narrow groove in the width direction is 70 to 200 mm.

10. The aforementioned narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located radially inward of the portion with a constant groove width, where part or all of the groove width is greater than that of the portion with a constant groove width. In a cross-sectional view at a cross-section perpendicular to the groove width, the bottom portion has curvature. The heavy-duty tire according to claim 1 or 2, wherein the radius of curvature of the bottom surface of the bottom portion is 60% or more and 125% or less of the groove width of the portion with a constant groove width.

11. The aforementioned narrow groove in the width direction consists of a portion with a constant groove width and a bottom portion located radially inward of the portion with a constant groove width, where part or all of the groove width is greater than that of the portion with a constant groove width. The heavy-duty tire according to claim 1 or 2, wherein, in a cross-sectional view at a cross-section perpendicular to the groove width, the maximum width of the bottom portion is 120% or more and 250% or less of the groove width in the portion with a constant groove width.

12. A heavy-duty tire according to claim 1 or 2, wherein the cross-sectional width is 450 mm or more and the outer diameter is 1750 mm or more.

13. The tread surface has one or more zigzag grooves extending in a zigzag pattern in the circumferential direction of the tire, and multiple widthwise grooves extending in the width direction of the tire. The ratio of the groove width of the zigzag groove to the tread width is 4.5% or less. The ratio of the groove width of the narrow grooves in the width direction to the tread width is 4.5% or less. The zigzag groove consists of a first portion extending in the circumferential direction of the tire and a second portion extending at an inclination with respect to the circumferential direction of the tire, wherein two adjacent second portions sandwiching the first portion are inclined in opposite directions with respect to the circumferential direction of the tire. A heavy-duty tire characterized in that the second portion is located between two adjacent narrow grooves in the width direction in the tire circumferential direction.

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