Tire for heavy load

Abstract

To provide a tire for heavy load that is able to improve uneven wear resistance performance while maintaining wet traction performance.SOLUTION: The present invention provides a tire for heavy load that has a tread portion 2. The tread portion 2 includes a plurality of circumferential grooves 3 and a plurality of land portions 4. The circumferential grooves 3 include two shoulder circumferential grooves 5 and one crown circumferential groove 6. The land portions 4 include two crown land portions 7. Each of the two crown land portions 7 includes a plurality of crown blocks 10. In each of the crown blocks 10, a tread surface 12 has a hexagonal shape; and a ratio L1 / L2 of a maximum length L1 in a tire axial direction of the tread surface 12 to a maximum length L2 in a tire circumferential direction of the tread surface 12 is 95% to 120%. An average of groove widths W1 of the crown lateral grooves 11 is in a range from 70% to 100% of an average of groove widths W2 of the circumferential grooves 3.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 below proposes a pneumatic heavy-duty tire. In this tire, the center land portion is divided into a plurality of center blocks by a plurality of center transverse grooves, and a predetermined center sub-groove is formed in the center block. By setting the groove width of the center sub-groove to be small, this tire is expected to achieve high-dimensional compatibility of traction performance, block chipping resistance performance, and uneven wear resistance performance on a wet road surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, in trucks, buses, etc., the load capacity has been increased and the output has been increased, and in heavy-duty tires as well, further improvement in uneven wear resistance performance has been demanded.

[0005] Also, conventionally, in the above-described vehicles, a mode in which two tires are arranged on both the left and right sides of one drive shaft (hereinafter, this mode is referred to as a "double tire") has been widely adopted. On the other hand, for the purpose of reducing the vehicle weight including the tire and wheel, in recent years, many vehicles have appeared in which the double tire is changed to one wide tire (hereinafter, referred to as a "wide single tire"). In this vehicle, since the load acting on one tire is large, in a wide single tire, further improvement in uneven wear resistance performance is demanded.

[0006] Also, in any aspect, the heavy-duty tire needs to maintain wet traction performance.

[0007] The present invention has been devised in view of the above actual situation, and the main object thereof is to provide a heavy-duty tire capable of improving uneven wear resistance while maintaining wet traction performance.

Means for Solving the Problems

[0008] The present invention is a heavy-duty tire having a tread portion, wherein the tread portion includes a plurality of circumferential grooves extending in a zigzag shape continuously in the tire circumferential direction, and a plurality of land portions divided by the plurality of circumferential grooves. The plurality of circumferential grooves include two shoulder circumferential grooves and one crown circumferential groove provided between the two shoulder circumferential grooves. The plurality of land portions include two crown land portions divided by the two shoulder circumferential grooves and the one crown circumferential groove. Each of the two crown land portions includes a plurality of crown blocks divided by a plurality of crown transverse grooves connected to the shoulder circumferential groove and the crown circumferential groove. Each of the plurality of crown blocks has a hexagonal tread surface, and the ratio L1 / L2 of the maximum length L1 in the tire axial direction of the tread surface to the maximum length L2 in the tire circumferential direction of the tread surface is 95% to 120%. The average groove width W1 of the plurality of crown transverse grooves is 70% to 100% of the average groove width W2 of the plurality of circumferential grooves. It is a heavy-duty tire.

Effects of the Invention

[0009] By adopting the above configuration, the heavy-duty tire of the present invention can improve uneven wear resistance while maintaining wet traction performance.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Although the drawings describe the features of the present invention, in order to assist in understanding the present invention, there may be included exaggerated expressions or expressions different from the actual structural dimensional ratios. Also, throughout each embodiment, the same or common elements are given the same reference numerals, and duplicate explanations are omitted. FIG. 1 is a developed view of the tread portion 2 of a heavy-duty tire 1 (hereinafter, may be simply referred to as "tire 1") showing an embodiment of the present invention.

[0012] As shown in FIG. 1, the tire 1 of the present embodiment is used as a so-called wide single tire. A wide single tire is one in which a double tire, which was conventionally used with two tires arranged side by side in the tire axial direction, is changed to one tire with a large width. For this reason, for the tire 1 of the present embodiment, tire sizes such as 385 / 65R22.5, 425 / 65R22.5, 445 / 65R22.5, etc. are adopted. Therefore, the cross-sectional width of the tire 1 of the present embodiment is, for example, 350 to 480 mm, desirably 370 to 460 mm. Also, the tread width TW of the tread portion 2 of the tire 1 of the present embodiment is, for example, 280 to 370 mm, desirably 300 to 350 mm. However, the present invention is not limited to such an aspect.

[0013] The tread width TW corresponds to the distance in the tire axial direction between two tread ends Te in the normal state. The "normal state" means that in the case of a pneumatic tire with various specifications defined, the tire is mounted on a normal rim and filled with the normal internal pressure, and moreover, it is in an unloaded state. In the case of a tire without various defined specifications or a non-pneumatic tire, the "normal state" means a standard usage state according to the usage purpose of the tire, which means the state of not being mounted on a vehicle and being unloaded. In this specification, unless otherwise specified, the dimensions and the like of each part of the tire are the values measured in the normal state.

[0014] The "normal rim" is the rim defined for each tire in the standard system including the standards on which the tire is based. For example, in JATMA, it is the "standard rim", in TRA, it is the "Design Rim", and in ETRTO, it is the "Measuring Rim".

[0015] The "normal internal pressure" is the air pressure defined for each tire in the standard system including the standards on which the tire is based. In JATMA, it is the "maximum air pressure", in TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in ETRTO, it is the "INFLATION PRESSURE".

[0016] Each of the two tread ends Te corresponds to the end of the contact surface when 70% of the normal load is applied to the tire 1 in the normal state and the tread part 2 is grounded on a plane at a camber angle of 0°. Also, the groove edge of each groove means the boundary between the contact surface and the opening of the groove.

[0017] For pneumatic tires with various standards defined, the "normal load" is the load defined for each tire in the standard system including the standards on which the tire is based. For JATMA, it is the "maximum load capacity"; for TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; for ETRTO, it is the "LOAD CAPACITY". Also, for tires without various standards defined, the "normal load" refers to the maximum applicable load when using the tire, in accordance with the above-mentioned standards.

[0018] The tread portion 2 includes a plurality of circumferential grooves 3 and a plurality of land portions 4. The plurality of circumferential grooves 3 each extend in a zigzag shape continuously in the tire circumferential direction. The plurality of land portions 4 are divided by the plurality of circumferential grooves 3. The plurality of land portions 4 in the present embodiment are composed of only four land portions and do not include other land portions.

[0019] The groove width Wa of the circumferential groove 3 is 3.0 mm or more, for example, 3.0% to 6.0% of the tread width TW. In this specification, unless a measurement location is specified, the groove width means the distance between two groove edges (the distance in the direction orthogonal to the groove). Also, the depth of the shoulder circumferential groove 5 is, for example, 15 to 25 mm.

[0020] As described above, when numerical ranges of various parameters are described in this specification, unless otherwise specified, the numerical range means the numerical range for the average value of the parameter. Therefore, for example, the groove width Wa of the circumferential groove 3 described above means the average value measured at a plurality of positions in the tire circumferential direction of the circumferential groove 3. The same applies to other parameters described later.

[0021] The plurality of circumferential grooves 3 includes two shoulder circumferential grooves 5 and one crown circumferential groove 6. The shoulder circumferential grooves 5 are respectively provided between one tread end Te and the tire equator C, and between the other tread end Te and the tire equator C. The distance La in the tire axial direction from the groove center line of the shoulder circumferential groove 5 to the tire equator C is, for example, 20% - 30% of the tread width TW.

[0022] The crown circumferential groove 6 is provided between the two shoulder circumferential grooves 5. At least a part of the crown circumferential groove 6 of the present embodiment is located on the tire equator. In a desirable aspect, the crown circumferential groove 6 is provided such that in a tread plan view, 90% or more of the tire equator C enters the crown circumferential groove 6.

[0023] The plurality of land portions 4 includes two crown land portions 7 divided by two shoulder circumferential grooves 5 and one crown circumferential groove 6. An enlarged view of the two crown land portions 7 is shown in FIG. 2. As shown in FIG. 2, each of the two crown land portions 7 includes a plurality of crown blocks 10 divided by a plurality of crown transverse grooves 11 connected to the shoulder circumferential groove 5 and the crown circumferential groove 6.

[0024] An enlarged view of one crown block 10 is shown in FIG. 3. As shown in FIG. 3, the tread surface 12 of each of the plurality of crown blocks 10 is hexagonal. Note that this configuration means that the edge 12e defining the tread surface 12 is composed of six sides and six vertices. Also, each side constituting the edge 12e is not limited to being linear, and may be non-linear (for example, slightly curved) as long as it can be observed that the extending direction is different from that of the adjacent sides. Further, each vertex constituting the edge 12e means a portion where the extending direction of the edge 12e changes abruptly. Therefore, the vertex may be not only formed by the edge 12e being bent, but also formed by the edge 12e being bent in an arc shape with a relatively small radius of curvature. As a desirable aspect, the tread surface 12 of the present embodiment has six sides extending linearly.

[0025] In addition, in the present invention, for each of the plurality of crown blocks 10, the ratio L1 / L2 of the maximum length L1 in the tire axial direction of the tread 12 to the maximum length L2 in the tire circumferential direction of the tread 12 is 95% to 120%.

[0026] Furthermore, as shown in FIG. 2, the average groove width W1 (not shown) of the plurality of crown transverse grooves 11 is 70% to 100% of the average groove width W2 (not shown) of the plurality of circumferential grooves. Note that the above-mentioned groove widths W1 and W2 mean the average of the measurements of the groove widths of the corresponding grooves at a number of positions. Alternatively, as the groove width W1 and the groove width W2, a value obtained by dividing the total opening area of the corresponding grooves by the total length of the grooves may be adopted. By having the above characteristics, the tire 1 of the present invention can improve the uneven wear resistance while maintaining the wet traction performance. The reason is as follows.

[0027] The tire 1 of the present invention includes a plurality of circumferential grooves 3 extending in a zigzag shape, and a plurality of crown transverse grooves 11 connected to the shoulder circumferential grooves 5 and the crown circumferential grooves 6. In the present invention, the wet traction performance can be maintained by these grooves.

[0028] Also, each of the plurality of crown blocks 10 has a hexagonal tread 12, and the ratio L1 / L2 of the tread 12 is 95% to 120%. Such a crown block 10 has uniform rigidity in both the tire circumferential direction and the tire axial direction, and can suppress excessive deformation in a specific direction. Therefore, excellent uneven wear resistance can be exhibited. Note that if the ratio L1 / L2 is less than 95%, the tread 12 of the crown block 10 becomes vertically long in the tire circumferential direction, and the crown block 10 is likely to fall in the tire axial direction, impairing the above effects. Also, if the ratio L1 / L2 is greater than 120%, the tread 12 of the crown block 10 becomes horizontally long in the tire axial direction, and the crown block 10 is likely to fall in the tire circumferential direction, impairing the above effects.

[0029] Furthermore, in the present invention, the average groove width W1 of the plurality of crown transverse grooves 11 is 70% to 100% of the average groove width W2 of the plurality of circumferential grooves 3. Thereby, while maintaining the wet traction performance, excessive deformation of the crown block 10 in the tire circumferential direction can be reliably suppressed, and the uneven wear resistance performance can be further improved. When the groove width W1 is less than 70% of the groove width W2, the drainage performance of the crown transverse groove 11 deteriorates, and the wet traction performance is impaired. When the groove width W1 is greater than 100% of the groove width W2, the amount of deformation of the crown block 10 in the tire circumferential direction becomes relatively large, and the uneven wear resistance performance is impaired.

[0030] From the viewpoint of further enhancing the above effects, the ratio L1 / L2 is desirably 95% to 110%, and more desirably 95% to 105%. Similarly, the groove width W1 is desirably 75% to 90% of the groove width W2, and desirably 75% to 85%.

[0031] Hereinafter, a more detailed configuration of the present embodiment will be described. Each configuration described below shows a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above-described effects even if it does not have the configurations described below. Further, even if any one of the configurations described below is applied alone to the tire 1 of the present invention having the above-described features, an improvement in performance corresponding to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0032] Also, as described above, the tire 1 of the present embodiment is used as a wide single tire. For this reason, each part of the tire 1 of the present embodiment is defined so that the uneven wear resistance performance can be further improved. In addition, since a wide single tire has a large contact area and a large contact load acts thereon, foreign matters such as stones are likely to bite into each groove disposed in the tread portion. Each part of the tire 1 of the present embodiment is defined so as to solve such problems.

[0033] As shown in FIG. 1, the tread portion 2 of the present embodiment has a pattern that is substantially point-symmetrical with respect to a point on the tire equator C. Therefore, the features of one shoulder circumferential groove 5 can also be applied to the other shoulder circumferential groove 5. The same applies to the two crown land portions 7 and the two shoulder land portions 8 (shown in FIG. 1) described later.

[0034] The shoulder circumferential groove 5 and the crown circumferential groove 6 extend in a zigzag shape so that their phases are opposite. The shoulder circumferential groove 5 alternately includes a first groove portion 5a and a second groove portion 5b that are inclined in opposite directions in the tire circumferential direction. The first groove portion 5a and the second groove portion 5b each extend linearly with a constant groove width. The first groove portion 5a and the second groove portion 5b are each inclined at an angle of 10 to 20° with respect to the tire circumferential direction. The same applies to the crown circumferential groove 6. Such circumferential grooves 3 have excellent drainage performance and are useful for enhancing wet performance.

[0035] FIG. 4 shows a cross-sectional view taken along line A-A of FIG. 2. As shown in FIG. 4, the total depth d1 of the shoulder circumferential groove 5 is, for example, 120% to 150% of the groove width W3 of the shoulder circumferential groove 5. Thereby, the wet traction performance and the resistance to uneven wear performance are improved in a well-balanced manner.

[0036] The shoulder circumferential groove 5 includes a pair of groove edges 15 and a pair of groove walls 16 that extend inclined with respect to the tire normal passing through the groove edges 15. These groove walls 16 extend from the groove edges 15 to the bottom surface 17 at a constant angle θ2 with respect to the tire normal. The angle θ2 is, for example, 5 to 15°.

[0037] As shown in FIGS. 2 and 4, a plurality of shoulder protrusions 18 protruding radially outward of the tire are intermittently arranged in the tire circumferential direction on the bottom surface 17 of the shoulder circumferential groove 5. As shown in FIG. 4, the width W4 of the shoulder protrusion 18 (the width parallel to the groove width direction of the shoulder circumferential groove 5) is, for example, 10% to 20% of the groove width W3 of the shoulder circumferential groove 5. The height h1 of the shoulder protrusion 18 is 10% to 20% of the total depth d1 of the shoulder circumferential groove 5. Such shoulder protrusions 18 are useful for preventing foreign objects such as stones from biting into the groove while maintaining the drainage performance of the shoulder circumferential groove 5 (hereinafter, this performance is referred to as "stone biting resistance performance").

[0038] From the same perspective, as shown in FIG. 2, in the tread plan view, the distance L4 between two adjacent shoulder protrusions 18 is 40% to 60% of the length L3 of the shoulder protrusion 18. However, the shoulder protrusion 18 is not limited to such a mode.

[0039] FIG. 5 shows a cross-sectional view taken along line B-B of FIG. 2. As shown in FIG. 5, the total depth d2 of the crown circumferential groove 6 is, for example, 120% to 150% of the groove width W5 of the crown circumferential groove 6.

[0040] The crown circumferential groove 6 includes a pair of groove edges 20, a pair of first groove walls 21, and a pair of second groove walls 22. The first groove wall 21 is inclined at an angle θ3 of 5 to 15° with respect to the tire normal passing through the groove edge 20. The second groove wall 22 is continuous with the first groove wall 21 on the radially inner side of the tire. Further, the second groove wall 22 extends parallel to the tire normal. Note that this configuration includes not only the mode in which the second groove wall 22 and the tire normal are completely parallel, but also the mode in which the angle difference between them is 2° or less. Such a crown circumferential groove 6 can secure the volume at the groove bottom portion by the second groove wall 22 and can maintain the wet performance.

[0041] In a more desirable aspect, the intersection 23 of the first groove wall 21 and the second groove wall 22 is located radially outside the tire than the bottom surface of the end on the crown circumferential groove 6 side of the crown transverse groove 11 (shown in FIG. 2). Thereby, even when foreign matter such as a stone enters between the pair of second groove walls 22, the crown transverse groove 11 opens appropriately, so that the foreign matter can be discharged promptly.

[0042] As shown in FIGS. 2 and 5, on the bottom surface of the crown circumferential groove 6, there is arranged a crown protrusion 25 that protrudes radially outside the tire and extends continuously in the tire circumferential direction. Thereby, the stone biting resistance performance of the crown circumferential groove 6 is improved.

[0043] The crown protrusion 25 alternately includes a first portion 26 and a second portion 27 having a smaller cross-sectional area than the first portion 26 in the tire circumferential direction. As shown in FIG. 5, the width W6 of the first portion 26 is larger than the width W4 of the shoulder protrusion 18 (shown in FIG. 4), specifically, 150% to 250% of the width W4. The width W7 of the second portion 27 is smaller than the width W4 of the shoulder protrusion 18, specifically, 60% to 70% of the width W4. Thereby, while the shoulder circumferential groove 5 (shown in FIG. 2) and the crown circumferential groove 6 cooperate to exhibit high drainage performance, the stone biting resistance performance of these grooves can be improved.

[0044] From the same viewpoint, the height h2 of the first portion 26 of the crown protrusion 25 is 15% to 30% of the total depth d2 of the crown circumferential groove 6. Also, the height h3 of the second portion 27 of the crown protrusion 25 is 5% to 15% of the total depth d2 of the crown circumferential groove 6.

[0045] As a more desirable aspect, it is desirable that the outer surface 26o in the tire radial direction of the first portion 26 is arranged at a position where the radial distance from the intersection 23 of the first groove wall 21 and the second groove wall 22 is 3 mm or less. Also, the outer surface 27o in the tire radial direction of the second portion 27 is located radially inside the intersection 23. Thereby, while maintaining the wet performance, the stone biting resistance performance of the crown circumferential groove 6 is further improved.

[0046] As shown in Fig. 2, the plurality of crown transverse grooves 11 each extend linearly with a constant groove width. The crown transverse grooves 11 are connected to the communication portions between the first groove portion 5a and the second groove portion 5b of the shoulder circumferential groove 5 and the communication portions between the first groove portion 6a and the second groove portion 6b of the crown circumferential groove 6. Also, the plurality of crown transverse grooves 11 are each inclined in a first direction (downward to the right in each figure of this specification) with respect to the tire axial direction. The angle θ4 of the crown transverse groove 11 with respect to the tire axial direction is, for example, 5 to 15°. As a desirable aspect, the plurality of crown transverse grooves 11 are arranged parallel to each other. Such crown transverse grooves 11 surely improve wet traction performance.

[0047] Fig. 6 shows a cross-sectional view taken along line C-C of Fig. 2. As shown in Fig. 6, the plurality of crown transverse grooves 11 each include a central bottom surface 30 and an outer bottom surface 31 in a cross-section along the groove longitudinal direction. The central bottom surface 30 is arranged so as to include the center position in the groove longitudinal direction of the crown transverse groove 11. Also, the central bottom surface 30 extends along the tread surface. The outer bottom surface 31 continuously increases in depth from the central bottom surface 30 toward both ends in the tire axial direction of the crown transverse groove 11. Such crown transverse grooves 11 increase the rigidity of the crown land portion 7 and improve the resistance to uneven wear, while the both ends are easily opened, which helps to easily discharge foreign matters such as stones that have entered the communication portion with the circumferential groove. Such an effect can significantly improve the stone trapping resistance performance, especially in a wide single tire with a large tread width TW (shown in Fig. 1) as in this embodiment.

[0048] The depth d3 from the tread surface 12 to the central bottom surface 30 is 40% to 60% of the total depth d1 of the shoulder circumferential groove 5 (shown in FIG. 4). Also, the length L5 of the central bottom surface 30 in the tire axial direction is 30% to 40% of the maximum length L1 of the tread surface 12 in the tire axial direction (shown in FIG. 3). Further, in the case of a wide single tire as in this embodiment, it is desirable to define the length L5 of the central bottom surface 30 in association with the tread width TW (shown in FIG. 1). From this viewpoint, the length L5 of the central bottom surface 30 is desirably 10% to 25% of the tread width TW. Thereby, in a wide single tire, while ensuring wet performance, chipping resistance performance can be improved.

[0049] Further, the above-described crown lateral groove 11, when employed in combination with the crown circumferential groove 6 (shown in FIG. 2) having the above-described crown protrusion 25 and the second groove wall 22 (shown in FIG. 5), can significantly improve chipping resistance performance due to these synergistic effects.

[0050] The maximum depth d4 from the tread surface 12 to the outer bottom surface 31 is 80% to 95% of the total depth d1 of the shoulder circumferential groove 5. As a desirable aspect, the bottom surface of the end of the crown lateral groove 11 on the shoulder circumferential groove 5 side is inside the tire radial direction from the outer surface in the tire radial direction of the shoulder protrusion 18 (shown in FIG. 4). Also, the bottom surface of the end of the crown lateral groove 11 on the crown circumferential groove 6 side is inside the tire radial direction from the outer surface in the tire radial direction of the first portion 26 (shown in FIG. 5) of the crown protrusion 25. Such a crown lateral groove 11 helps to enhance the chipping resistance performance of each circumferential groove 3 (shown in FIG. 2).

[0051] As shown in FIG. 3, at least one tread surface 12 of the plurality of crown blocks 10 is provided with a single shallow groove 33. This shallow groove 33 has, for example, a groove width W8 of 2.0 to 4.0 mm. Also, the shallow groove 33 has a groove depth of 2.0 to 4.0 mm. Such a shallow groove 33 helps to enhance wet traction performance and uneven wear resistance performance in a well-balanced manner, especially in a wide single tire as in this embodiment.

[0052] From the viewpoint of obtaining sufficient frictional force by the shallow groove 33, the total length of the shallow groove 33 (the so-called peripheral length) is desirably 50% or more of the maximum length L1 in the tire axial direction of the tread 12, more desirably 60% or more. Further, from the viewpoint of suppressing uneven wear of the tread 12, the shortest distance from the edge 12e defining the tread 12 to the shallow groove 33 is desirably 20% or more of the maximum length L1. In the present embodiment, only one such shallow groove 33 is arranged on one tread 12.

[0053] The shallow groove 33 includes an inclined central portion 41 and two steeply inclined portions 42 continuous on both sides thereof. The inclined central portion 41 is inclined in a second direction (in each figure of the present specification, it is upward to the right) opposite to the first direction with respect to the tire axial direction. The angle θ5 of the inclined central portion 41 with respect to the tire axial direction is larger than the angle θ4 (shown in FIG. 2) of the crown transverse groove 11 with respect to the tire axial direction, and specifically, it is 15 to 25°. The shallow groove 33 having such an inclined central portion 41 can provide frictional force in a direction different from that of the crown transverse groove 11, and can stably exhibit excellent traction performance on various road surfaces.

[0054] One steeply inclined portion 42 is continuous with one end of the inclined central portion 41 and extends at an angle close to perpendicular to the inclined central portion 41. The other steeply inclined portion 42 is continuous with the other end of the inclined central portion 41 and extends at an angle close to perpendicular to the inclined central portion 41 in a direction opposite to that of the one steeply inclined portion 42. Thereby, the steeply inclined portion 42 has a larger angle with respect to the tire axial direction compared to the inclined central portion 41. The angle θ6 of the steeply inclined portion 42 with respect to the tire axial direction is, for example, 70 to 80°. Such a steeply inclined portion 42 can provide frictional force in the tire axial direction and can improve the turning performance on a wet road surface.

[0055] By including the above-described inclined central portion 41 and steeply inclined portion 42, the shallow groove 33 includes a bent portion 43 that bends at an angle θ7 of 70 to 110°. Further, the shallow groove 33 includes a bent portion 43 that bends in a direction convex in one direction and a bent portion 43 that bends in a direction convex in the opposite direction. Such a shallow groove 33 can provide frictional force in multiple directions.

[0056] As shown in FIG. 1, the tread portion 2 includes two shoulder land portions 8 arranged so as to sandwich two crown land portions 7. The two shoulder land portions 8 are respectively divided on the outer side in the tire axial direction of the shoulder circumferential groove 5 and include the tread end Te.

[0057] FIG. 7 shows an enlarged view of the shoulder land portion 8. As shown in FIG. 7, the shoulder land portion 8 includes a plurality of shoulder blocks 34 divided by a plurality of shoulder transverse grooves 35.

[0058] The shoulder transverse groove 35 extends from the shoulder circumferential groove 5 to at least the tread end Te. The shoulder transverse groove 35 includes, for example, an inner groove portion 36 and an outer groove portion 37 having different extending directions. The inner groove portion 36 communicates with the shoulder circumferential groove 5 and extends in the tire axial direction. The outer groove portion 37 is continuous with the inner groove portion 36 and extends to at least the tread end Te.

[0059] The inner groove portion 36 is inclined in the second direction with respect to the tire axial direction. The angle θ8 of the inner groove portion 36 with respect to the tire axial direction is, for example, 10° or less. The length of the inner groove portion 36 (the so-called peripheral length, and the same applies to the length of the grooves described below) is, for example, 30% to 50% of the length of the shoulder transverse groove 35 from the shoulder circumferential groove 5 to the tread end Te. Also, it is desirable that the groove width of the inner groove portion 36 continuously decreases toward the tread end Te side. Such an inner groove portion 36 helps to maintain the rigidity of the central portion in the tire axial direction of the shoulder land portion 8 and improve the resistance to uneven wear performance.

[0060] The outer groove portion 37 is inclined, for example, in the first direction with respect to the tire axis direction. The angle θ9 of the outer groove portion 37 with respect to the tire axis direction is, for example, 15 to 25°. The length of the outer groove portion 37 is, for example, 50% to 70% of the length of the shoulder lateral groove 35. Further, the outer groove portion 37 includes a constant-width portion 37a that extends from the inner groove portion 36 with a constant groove width, and a widened portion 37b that is continuous with the outer side in the tire axis direction of the constant-width portion 37a and has an increasing groove width toward the tread edge Te. Such an outer groove portion 37 can easily guide the water in the shoulder lateral groove 35 toward the tread edge Te side during wet road surface driving, thereby enhancing the wet performance.

[0061] FIG. 8 shows a cross-sectional view taken along line D-D of FIG. 7. As shown in FIG. 8, the bottom surface 36d of the inner groove portion 36 is inclined in a direction in which the depth increases toward the shoulder circumferential groove 5 side. The bottom surface 37d of the outer groove portion 37 extends parallel to the tread surface 8s of the shoulder land portion 8 at least in a region where the constant-width portion 37a (shown in FIG. 7) is formed. The shoulder lateral groove 35 having such a bottom surface can improve the chipping resistance performance of the shoulder circumferential groove 5, enhance the rigidity of the shoulder land portion 8, and suppress its uneven wear.

[0062] As shown in FIG. 1, the number of blocks included in each land portion 4 over the entire circumference of the tire is, for example, 36 to 44. Thus, in combination with the above-described tread width TW, each block has a sufficient size, and the uneven wear resistance performance is further improved. Also, when each block is large, there is a concern about chipping. However, in the present embodiment, since each groove has the above-described characteristics, excellent chipping resistance performance can be exhibited. Therefore, the tire 1 of the present embodiment is excellent in both uneven wear resistance performance and chipping resistance performance, and can be suitably used as a wide single tire.

[0063] As described above, the tire according to an embodiment of the present invention has been described in detail. However, the present invention is not limited to the above-described specific embodiments, and can be implemented in various modes.

[0064] [Appendix] The present invention includes the following aspects.

[0065] [Invention 1] A heavy-duty tire having a tread portion, The tread portion includes a plurality of circumferential grooves that extend continuously in a zigzag shape in the tire circumferential direction, and a plurality of land portions divided by the plurality of circumferential grooves. The plurality of circumferential grooves include two shoulder circumferential grooves and one crown circumferential groove provided between the two shoulder circumferential grooves. The plurality of land portions include two crown land portions divided by the two shoulder circumferential grooves and the one crown circumferential groove. Each of the two crown land portions includes a plurality of crown blocks divided by a plurality of crown transverse grooves that are continuous with the shoulder circumferential groove and the crown circumferential groove. Each of the plurality of crown blocks, has a hexagonal tread surface, and the ratio L1 / L2 of the maximum length L1 in the tire axial direction of the tread surface to the maximum length L2 in the tire circumferential direction of the tread surface is 95% to 120%. The average groove width W1 of the plurality of crown transverse grooves is 70% to 100% of the average groove width W2 of the plurality of circumferential grooves. Heavy-duty tire. [Invention 2] The plurality of land portions are composed of only four land portions, the heavy-duty tire according to Invention 1. [Invention 3] The cross-sectional width of the tire is 350 to 450 mm, the heavy-duty tire according to Invention 1 or 2. [Invention 4] At least one of the tread surfaces of the plurality of crown blocks is provided with one shallow groove having a groove width and a groove depth of 2.0 to 4.0 mm. The shallow groove includes a portion that bends at an angle of 70 to 110°, the heavy-duty tire according to any one of Inventions 1 to 3. [Invention 5] Each of the plurality of crown transverse grooves is inclined in a first direction with respect to the tire axial direction. The heavy-duty tire according to Invention 4, wherein the shallow groove includes an inclined central portion inclined in a second direction opposite to the first direction with respect to the tire axial direction. [Invention 6] The heavy-duty tire according to any one of Inventions 1 to 5, wherein each of the plurality of crown lateral grooves includes a central bottom surface extending along the tread surface and an outer bottom surface whose depth continuously increases from the central bottom surface toward both ends in the tire axial direction in a cross section along the groove longitudinal direction. [Invention 7] On the bottom surface of the shoulder circumferential groove, a plurality of shoulder protrusions protruding outward in the tire radial direction are arranged in the tire circumferential direction. The heavy-duty tire according to any one of Inventions 1 to 6, wherein on the bottom surface of the crown circumferential groove, a crown protrusion protruding outward in the tire radial direction and continuously extending in the tire circumferential direction is arranged. [Invention 8] The heavy-duty tire according to Invention 7, wherein the crown protrusion alternately includes in the tire circumferential direction a first portion having a width larger than that of the shoulder protrusion and a second portion having a width smaller than that of the shoulder protrusion. [Invention 9] The crown circumferential groove includes a pair of groove edges, a pair of first groove walls inclined with respect to the tire normal passing through the groove edges, and a pair of second groove walls connected to the inner side in the tire radial direction of the first groove walls and extending parallel to the tire normal. The heavy-duty tire according to any one of Inventions 1 to 8, wherein the intersection edge of the first groove wall and the second groove wall is located outside the bottom surface of the end on the crown circumferential groove side of the crown lateral groove in the tire radial direction.

Explanation of Reference Numerals

[0066] 2 Tread portion 3 Circumferential groove 4 Land portion 5 Shoulder circumferential groove 6 Crown circumferential groove 7 Crown land portion 10 Crown block 11 Crown transverse groove 12 Tread L1 Maximum length of the tread in the tire axis direction L2 Maximum length of the tread in the tire circumferential direction W1 Average groove width of a plurality of crown transverse grooves W2 Average groove width of a plurality of circumferential grooves

Claims

1. A heavy-duty tire having a tread portion, wherein the tread portion includes a plurality of circumferential grooves extending in a zigzag shape continuously in the tire circumferential direction, and a plurality of land portions divided by the plurality of circumferential grooves, the plurality of circumferential grooves include two shoulder circumferential grooves and one crown circumferential groove provided between the two shoulder circumferential grooves, the plurality of land portions include two crown land portions divided by the two shoulder circumferential grooves and the one crown circumferential groove, each of the two crown land portions includes a plurality of crown blocks divided by a plurality of crown transverse grooves connecting the shoulder circumferential groove and the crown circumferential groove, each of the plurality of crown blocks has a hexagonal tread surface, the ratio L1 / L2 of the maximum length L1 in the tire axial direction of the tread surface to the maximum length L2 in the tire circumferential direction of the tread surface is 95% to 120%, the average groove width W1 of the plurality of crown transverse grooves is 70% to 100% of the average groove width W2 of the plurality of circumferential grooves, A heavy-duty tire.

2. The heavy-duty tire according to claim 1, wherein the plurality of land portions are composed of only four land portions.

3. The heavy-duty tire according to claim 1 or 2, wherein the cross-sectional width of the tire is 350 to 450 mm.

4. At least one of the tread surfaces of the plurality of crown blocks is provided with a shallow groove having a groove width and a groove depth of 2.0 to 4.0 mm, The heavy-duty tire according to claim 1 or 2, wherein the shallow groove includes a bent portion that bends at an angle of 70 to 110°.

5. Each of the plurality of crown transverse grooves is inclined in a first direction with respect to the tire axial direction, The heavy-duty tire according to claim 4, wherein the shallow groove includes an inclined central portion inclined in a second direction opposite to the first direction with respect to the tire axial direction.

6. The heavy-duty tire according to claim 1 or 2, wherein each of the plurality of crown transverse grooves includes a central bottom surface extending along the tread surface and an outer bottom surface whose depth continuously increases toward both ends in the tire axial direction of the crown transverse groove in a cross-section along the groove longitudinal direction.

7. A plurality of shoulder protrusions protruding radially outward of the tire are arranged in the tire circumferential direction on the bottom surface of the shoulder circumferential groove, The heavy-duty tire according to claim 1 or 2, wherein a crown protrusion that protrudes outward in the tire radial direction and extends continuously in the tire circumferential direction is disposed on the bottom surface of the crown circumferential groove.

8. The heavy-duty tire according to claim 7, wherein the crown protrusion alternately includes in the tire circumferential direction a first portion having a width larger than that of the shoulder protrusion and a second portion having a width smaller than that of the shoulder protrusion.

9. The crown circumferential groove includes a pair of groove edges, a pair of first groove walls inclined with respect to the tire normal passing through the groove edges, and a pair of second groove walls that are continuous with the inside in the tire radial direction of the first groove walls and extend parallel to the tire normal. The heavy-duty tire according to claim 1 or 2, wherein the intersection of the first groove wall and the second groove wall is located outside the tire radial direction from the bottom surface of the end on the crown circumferential groove side of the crown transverse groove.

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