Tire for heavy load

Abstract

To provide a tire for a heavy load that improves chipping resistance performance, while reducing rolling resistance.SOLUTION: Provided is a tire for a heavy load having a tread part 2. The tread part 2 includes: a pair of shoulder circumferential grooves 3; and a crown area 4. The crown area 4 is provided with circumferential narrow grooves 5; and a plurality of crown land parts 6. The circumferential narrow grooves 5 include: a pair of groove edges 9; and a pair of chamfer parts 10 continuous with the pair of groove edges 9 respectively. The pair of chamfer parts 10 respectively extends continuously in the tire circumferential direction, and includes an inclined plane 11 inclining at an angle of 20-60° relative to a tire normal line passing through the groove edges 9.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 below proposes a heavy-duty pneumatic tire in which the groove width of the crown circumferential groove is 0.01 to 0.2 times the groove width of the shoulder circumferential groove. By setting the groove width of the crown circumferential groove to be small as described above, this tire is expected to improve rolling resistance performance and life performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-116004 Summary of the Invention [Problem to be solved by the invention]

[0004] Heavy-duty tires with circumferential narrow grooves in the crown region, such as the tire described above, are expected to reduce rolling resistance. However, such tires have a new problem in that, because the rigidity of the tire is high near the circumferential narrow grooves, when a torsional force is applied to the land portion in the crown region due to, for example, turning the vehicle while standing on a protrusion on the road surface, the force cannot be released at the groove edges of the circumferential narrow grooves, resulting in chipping or the like in the land portion.

[0005] The present invention has been devised in view of the above-described circumstances, and its main object is to provide a heavy-duty tire that can reduce rolling resistance while improving chipping resistance of the crown land portion. [Means for solving the problem]

[0006] The present invention is a heavy-duty tire having a tread portion, wherein the tread portion includes a pair of shoulder circumferential grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and a crown region between the pair of shoulder circumferential grooves, wherein the crown region is provided with at least one circumferential narrow groove extending continuously in the tire circumferential direction with a groove width smaller than that of the shoulder circumferential groove, and a plurality of crown land portions separated by the circumferential narrow groove, wherein the circumferential narrow groove includes a pair of groove edges and a pair of chamfered portions respectively connected to the pair of groove edges, and wherein the pair of chamfered portions each include an inclined surface extending continuously in the tire circumferential direction and inclined at an angle of 20 to 60° with respect to a tire normal passing through the groove edge. [Effects of the Invention]

[0007] By employing the above-described configuration, the heavy duty tire of the present invention can reduce rolling resistance and improve chipping resistance of the crown land portion. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a development view of a tread portion of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of the crown region of FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. [Figure 4] FIG. 2 is a cross-sectional view taken along line BB in FIG. [Figure 5] FIG. 3 is a cross-sectional view taken along line CC in FIG. 2. [Figure 6] FIG. 3 is a side view of the widened portion of the horizontal narrow groove of FIG. 2. [Figure 7] FIG. 2 is an enlarged view of the shoulder land portion of FIG. [Figure 8] FIG. 2 is a development view of the tread portion of the tire of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described below with reference to the drawings. The drawings are intended to encompass the features of the present invention, but may include exaggerated representations and representations that differ from the dimensional ratios of the actual structure to facilitate understanding of the present invention. Furthermore, identical or common elements are designated by the same reference numerals throughout the embodiments, and redundant explanations will be omitted. Figure 1 is a development view of a tread portion 2 of a heavy-duty tire 1 (hereinafter, sometimes simply referred to as "tire 1") illustrating one embodiment of the present invention.

[0010] As shown in Fig. 1, the tread portion 2 includes two tread edges Te and a pair of shoulder circumferential grooves 3 disposed between them. The two tread edges Te correspond to the edges of the contact patch when a normal load is applied to a tire 1 in a normal state and the tread portion 2 is brought into contact with a flat surface at a camber angle of 0°. The groove edge of each groove refers to the boundary between the contact patch and the opening of the groove.

[0011] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, that the tire is mounted on a normal rim, inflated to the normal internal pressure, and is in an unloaded state. In the case of a tire for which various standards are not established or a non-pneumatic tire, the normal condition means a standard use state according to the intended use of the tire, in which the tire is not mounted on a vehicle and is unloaded. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal condition.

[0012] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

[0013] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0014] For pneumatic tires for which various standards are established, "normal load" refers to the load specified for each tire in the standard system including the standard on which the tire is based. For JATMA, this is "maximum load capacity," for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is "LOAD CAPACITY." For tires for which various standards are not established, "normal load" refers to the maximum load that can be applied when using the tire in accordance with the above standards.

[0015] The shoulder circumferential grooves 3 are disposed between one tread edge Te and the tire equator C, and between the other tread edge Te and the tire equator C. The shoulder circumferential grooves 3 of this embodiment extend, for example, in a zigzag pattern with a constant groove width. The groove width W1 of the shoulder circumferential grooves 3 is at least 3.0 mm or greater, for example, 5% to 8% of the tread width TW. In this specification, the groove width means the distance between two groove edges (the distance in a direction perpendicular to the groove) unless a measurement location is specified. The tread width TW corresponds to the axial distance of the tire from one tread edge Te to the other tread edge Te in the normal state. The depth of the shoulder circumferential grooves 3 is, for example, 8 to 12 mm.

[0016] As described above, when the numerical ranges of various parameters are described in this specification, unless otherwise specified, the numerical ranges refer to the average values ​​of the parameters. For example, the groove width W1 of the shoulder circumferential groove 3 described above refers to the average value of measurements taken at multiple positions in the tire circumferential direction of the shoulder circumferential groove 3. The same applies to other parameters described later.

[0017] The distance L1 in the tire axial direction from the tire equator C to the shoulder circumferential groove 3 is, for example, 25% to 35% of the tread width TW, but the present invention is not limited to this embodiment.

[0018] The tread portion 2 includes a crown region 4 partitioned between a pair of shoulder circumferential grooves 3. Fig. 2 shows an enlarged view of the crown region 4. As shown in Fig. 2, the crown region 4 is provided with at least one circumferential narrow groove 5 that extends continuously in the tire circumferential direction and has a groove width smaller than that of the shoulder circumferential groove 3, and a plurality of crown land portions 6 partitioned by the circumferential narrow grooves 5.

[0019] "The groove width of the circumferential narrow groove 5 is smaller than the groove width of the shoulder circumferential groove 3" means that, at least when comparing the groove widths on the contact patch of the tread portion 2, the groove width Wt of the circumferential narrow groove 5 is smaller than the groove width W1 (shown in FIG. 1) of the shoulder circumferential groove 3. However, the groove width of the circumferential narrow groove 5 of this embodiment is set small overall, and specific features will be described later.

[0020] In this embodiment, a pair of circumferential narrow grooves 5 is arranged in the crown region 4, with the tire equator C located between them. The crown region 4 also includes three crown land portions 6 separated by the pair of circumferential narrow grooves 5. The three crown land portions 6 are composed of a first crown land portion 6A, a second crown land portion 6B, and a third crown land portion 6C. The first crown land portion 6A is separated between one shoulder circumferential groove 3 and one circumferential narrow groove 5. The second crown land portion 6B is separated between two circumferential narrow grooves 5 and is located on the tire equator C. The third crown land portion 6C is separated between the other shoulder circumferential groove 3 and the other circumferential narrow groove 5. However, the present invention is not limited to this embodiment.

[0021] FIG. 3 shows a cross-sectional view of the circumferential narrow groove 5 taken along line AA in FIG. 2. As shown in FIG. 3, the circumferential narrow groove 5 includes a pair of groove edges 9 and a pair of chamfered portions 10 connected to each of the pair of groove edges 9. Each of the pair of chamfered portions 10 extends continuously in the tire circumferential direction. This configuration means that, as shown in FIG. 2, the pair of chamfered portions 10 facing each other in the tire axial direction have a sufficient length in the tire circumferential direction (at least 30% or more of the entire tire circumference). Furthermore, when the circumferential narrow groove 5 is connected to another lateral groove extending in the tire axial direction, this configuration means that the chamfered portions 10 of the circumferential narrow groove 5 are connected to both sides of the connected portion in the tire circumferential direction. As a more preferable aspect, in this embodiment, the chamfered portions 10 are connected to the entire pair of groove edges 9 of the circumferential narrow groove 5.

[0022] 3, the pair of chamfered portions 10 include inclined surfaces 11 inclined at an angle θ1 of 20 to 60° with respect to the tire normal line passing through the groove edge 9. By employing the above-described configuration, the tire 1 of the present invention can improve the chipping resistance of the crown land portion 6 while reducing the rolling resistance. The reason for this is as follows.

[0023] 1, in the tire 1 of the present invention, the crown region 4 is provided with at least one circumferential narrow groove 5 that extends continuously in the tire circumferential direction and has a groove width smaller than that of the shoulder circumferential groove 3. Therefore, the tire 1 of the present invention has higher rigidity in the crown region 4 and can reduce rolling resistance compared to tires in which circumferential grooves with a conventional groove width are provided in the crown region.

[0024] On the other hand, heavy-duty tires with circumferential narrow grooves arranged in the crown region have high rigidity near the circumferential narrow grooves, so when a torsional force is applied to the land portion of the crown region by turning the tire over a protrusion on the road surface, the force cannot be released at the groove edges of the circumferential narrow grooves, and as a result, chips or the like tend to occur in the land portion.

[0025] In contrast, in the present invention, as shown in Fig. 3, a pair of chamfered portions 10 of the circumferential narrow groove 5 have the above-mentioned inclined surfaces 11. As a result, the tire 1 of the present invention can easily release torsional forces and the like acting near the groove edges 9 of the circumferential narrow groove 5, thereby suppressing the occurrence of chipping around the circumferential narrow groove 5 of the crown land portion 6 (shown in Fig. 2), and thereby improving the chipping resistance of the crown land portion 6.

[0026] If the angle θ1 is outside the above-mentioned range, the above-mentioned effect cannot be fully obtained. Specifically, if the angle θ1 of the inclined surface 11 with respect to the tire normal is less than 20°, chipping is likely to occur around the edge formed by the contact surface of the land portion and the inclined surface 11. If the angle θ1 is more than 60°, the entire inclined surface 11 is likely to come into contact with the ground excessively, and chipping is likely to occur around the edge formed by the inclined surface 11 and the groove wall 12 of the circumferential narrow groove 5 extending along the tire radial direction.

[0027] In the present invention, the above-mentioned effects can be expected as long as the average value of the angle θ1 over the entire circumference of the tire of the circumferential narrow groove 5 is within the above-mentioned numerical range. In a desirable embodiment, the angle θ1 is set within the above-mentioned numerical range in any cross section of the circumferential narrow groove 5 in the tire circumferential direction. In a more desirable embodiment, the angle θ1 is constant in any cross section of the circumferential narrow groove 5 in the tire circumferential direction.

[0028] In this embodiment, the inclined surface 11 is planar, and therefore has a linear contour in the cross section of the circumferential narrow groove 5. However, the invention is not limited to this, and the inclined surface 11 may be configured as a slightly convex or concave curved surface. That is, the inclined surface 11 may have, in the cross section, a curved contour that is convex with respect to an imaginary line connecting both ends of the inclined surface, or a curved contour that is concave with respect to the imaginary line.

[0029] The following describes the configuration of this embodiment in more detail. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-described effects even if it does not include the configuration described below. Furthermore, even if any one of the configurations described below is applied alone to the tire 1 of the present invention having the above-described characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, an improvement in combined performance corresponding to each configuration can be expected.

[0030] As shown in Fig. 1, the shoulder circumferential groove 3 extends, for example, in a zigzag pattern. Specifically, the shoulder circumferential groove 3 includes first groove portions 3a and second groove portions 3b that are inclined in opposite directions relative to the tire circumferential direction, alternately arranged in the tire circumferential direction. The first groove portions 3a and second groove portions 3b are preferably linear. The angle θ2 of the first groove portions 3a and second groove portions 3b relative to the tire circumferential direction is, for example, 10 to 20°.

[0031] FIG. 4 shows a cross-sectional view taken along line BB in FIG. 1. As shown in FIG. 4, the shoulder circumferential groove 3 includes a pair of groove walls 15 extending at an angle θ3 of 20 to 35 degrees with respect to a normal line passing through the groove edge 3e of the shoulder circumferential groove 3, and a groove bottom surface 16 disposed therebetween. The groove wall 15 is substantially flat between the groove edge 3e and the groove bottom surface 16. The groove bottom surface 16 is configured as a curved surface concave toward the tire radially inward. As a result, the depth d1 of the shoulder circumferential groove 3 is smaller than its groove width W1, specifically, 70% to 85% of the groove width W1. Furthermore, in the shoulder circumferential groove 3, for example, even when a normal load is applied to the tread portion 2, the pair of groove walls 15 do not come into contact with each other. Such a shoulder circumferential groove 3 can exhibit sufficient drainage while suppressing an excessive increase in rolling resistance.

[0032] As shown in Fig. 2, the circumferential narrow grooves 5 extend, for example, in a zigzag pattern. In this embodiment, the circumferential narrow grooves 5 extend with an amplitude such that the distance L2 from the tire equator C to the circumferential narrow groove 5 is 5% to 12% of the tread width TW (shown in Fig. 1). In this embodiment, one circumferential narrow groove 5 extends in a zigzag pattern in an opposite phase to the shoulder circumferential groove 3 adjacent to it on the axially outer side of the tire.

[0033] The circumferential narrow groove 5 includes first narrow groove portions 5a and second narrow groove portions 5b that are inclined in opposite directions relative to the tire circumferential direction and are arranged alternately in the tire circumferential direction. The first narrow groove portions 5a and second narrow groove portions 5b are preferably linear. The angle θ4 of the first narrow groove portions 5a and second narrow groove portions 5b relative to the tire circumferential direction is, for example, 10 to 20 degrees.

[0034] 3, the groove width of the circumferential narrow groove 5 is set to a width that allows at least a portion of adjacent crown land portions 6 (shown in FIG. 2) to come into contact with each other via the circumferential narrow groove 5 when the circumferential narrow groove 5 comes into contact with the ground. This increases the rigidity of the crown region 4, and ensures a reduction in rolling resistance.

[0035] To achieve the above-described effect, the circumferential narrow groove 5 is connected to a narrow groove main body 18 extending inside the chamfered portion 10 with a groove width W2 smaller than that of conventional grooves. The groove width W2 is constant in the depth direction of the circumferential narrow groove 5. The groove width W2 of the narrow groove main body 18 is, for example, 3.0 mm or less, preferably 2.0 mm or less, and more preferably 1.5 mm or less. Furthermore, to reliably release forces acting on the crown region 4 (shown in FIG. 2) and ensure wet performance, the groove width W2 of the narrow groove main body 18 is, for example, 0.5 mm or more, preferably 1.0 mm or more.

[0036] The overall depth d2 of the circumferential narrow groove 5 is, for example, 8 to 12 mm. In a preferred embodiment, the depth d2 of the circumferential narrow groove 5 of this embodiment is 80% to 120% of the depth d1 (shown in FIG. 4) of the shoulder circumferential groove 3, and more preferably, these depths are the same. This allows wet performance to be maintained.

[0037] As shown in FIG. 2, in this embodiment, one chamfered portion 10 extends in the tire circumferential direction while maintaining a constant width. However, the present invention is not limited to this configuration. The width of the chamfered portion 10 is measured in a direction perpendicular to the longitudinal direction of the circumferential narrow groove 5 in a plan view of the tread. The width W4 of one chamfered portion 10 in a plan view of the tread portion 2 is 3% to 9% of the maximum axial width W3 (the width of the contact patch) of the crown land portion 6 in which the chamfered portion 10 is arranged. This makes it possible to obtain the above-mentioned effects while ensuring the contact area of ​​the land portion.

[0038] 3, the pair of chamfered portions 10 includes an inner chamfered portion 21 on the tire equator C side and an outer chamfered portion 22 on the opposite side of the inner chamfered portion 21. In a plan view of the tread portion 2, the width Wo of the outer chamfered portion 22 is larger than the width Wi of the inner chamfered portion 21. Specifically, the width Wo is 130% to 170% of the width Wi.

[0039] Generally, the tread portion 2 experiences greater radial growth during inflation and greater radial deformation during rolling in the region closer to the tread edge Te than the region closer to the tire equator C. Therefore, it is desirable to increase the width of the chamfered portion 10 closer to the tread edge Te in order to improve chipping resistance. From this perspective, in this embodiment, the width Wo of the outer chamfered portion 22 is set relatively large, as described above. This is expected to further improve chipping resistance.

[0040] By defining the width of chamfered portion 10 as described above, the angle θ1 of outer chamfered portion 22 is, for example, 40 to 50°. The angle θ1 of inner chamfered portion 21 is, for example, 30 to 40°. However, the present invention is not limited to this embodiment, and outer chamfered portion 22 and inner chamfered portion 21 may have symmetrical shapes.

[0041] The outer chamfered portion 22 and the inner chamfered portion 21 have the same depth. The depth d3 of this pair of chamfered portions 10 is 15% to 35% of the overall depth d2 of the circumferential narrow groove 5. This achieves a good balance between reduced rolling resistance and improved chipping resistance.

[0042] As shown in FIG. 2 , each of the multiple crown land portions 6 is divided into multiple blocks 24 by multiple lateral narrow grooves 25 extending in the tire axial direction. In the first crown land portion 6A, each of the multiple lateral narrow grooves 25 communicates with the shoulder circumferential grooves 3 in a portion that convex toward the tire equator C and with the circumferential narrow grooves 5 in a portion that convex toward the tire axial outward (the side opposite the tire equator C). The same is true for the third crown land portion 6C. In the second crown land portion 6B, each of the multiple lateral narrow grooves 25 communicates with the pair of circumferential narrow grooves 5 in a portion that convex toward the tire equator C. As a result, each of the multiple blocks 24 has a hexagonal tread surface. The ground-contact surfaces of the blocks 24 are free of any grooves or recesses.

[0043] The lateral narrow groove 25 includes a constant width portion 26 and a wide width portion 27. The constant width portion 26 has a constant groove width and extends in the longitudinal direction of the lateral narrow groove 25. The wide width portion 27 is continuous with the constant width portion 26, and the groove width increases toward the axial end of the tire. In this embodiment, the lateral narrow groove 25 including the constant width portion 26 and the wide width portion 27 is arranged in the first crown land portion 6A and the third crown land portion 6C. In this lateral narrow groove 25, the length of the constant width portion 26 (so-called periphery length) is 65% to 75% of the total length of the lateral narrow groove 25. The remaining portion is configured as the wide width portion 27. The groove width of the lateral narrow groove 25, including the wide width portion 27, is preferably 3.0 mm or less. In this embodiment, the second crown land portion 6B is provided with a lateral narrow groove 25 entirely configured of the constant width portion 26.

[0044] FIG. 5 shows a cross-sectional view of the constant-width portion 26 of the lateral narrow groove 25, taken along line CC in FIG. 2. As shown in FIG. 5, the constant-width portion 26 of the lateral narrow groove 25 also has a constant groove width W5 in the depth direction. The groove width W5 of the constant-width portion 26 of the lateral narrow groove 25 is, for example, 3.0 mm or less, and preferably 2.0 mm or less. The groove width W5 of the lateral narrow groove 25 is preferably smaller than the groove width W2 (shown in FIG. 3) of the narrow groove main body 18 of the circumferential narrow groove 5. Specifically, the groove width W5 is 1.5 mm or less, and more preferably 0.5 to 1.2 mm. Such a lateral narrow groove 25 can improve wet performance while maintaining the rigidity of the crown land portion 6.

[0045] Fig. 6 shows a side view of the widened portion 27 as viewed from the arrow D in Fig. 2. As shown in Fig. 6, the widened portion 27 includes a first groove edge 27a and a second groove edge 27b. As shown in Fig. 2, the first groove edge 27a extends linearly integrally with the groove edge 26e of the constant width portion 26. The second groove edge 27b is connected to the groove edge 26e of the constant width portion 26 so as to bend at an obtuse angle, and extends toward the end of the tire axial direction so as to widen the groove width in a tread plan view.

[0046] As shown in FIG. 6 , the widened portion 27 includes a first groove wall 28 and a second groove wall 29. To facilitate understanding of the characteristics of the widened portion 27, the second groove wall 29 is dotted in FIG. 6 . The first groove wall 28 is a flat surface extending radially inward from the first groove edge 27a. The second groove wall 29 is a flat surface extending obliquely from the second groove edge 27b. The second groove wall 29 is connected to the groove wall 26w (shown in FIG. 5 ) of the constant width portion 26 via a ridge line 29e. The second groove wall 29 extends to the bottom of the lateral narrow groove 25 while remaining non-parallel to the first groove wall 28. The widened portion 27 having such a second groove wall 29 reliably improves wet performance.

[0047] As shown in Fig. 1, the tread portion 2 of this embodiment includes a shoulder land portion 7 that is located axially outward of the shoulder circumferential groove 3. The shoulder land portion 7 includes the tread edge Te. Fig. 7 shows an enlarged view of the shoulder land portion 7 located on the left side in Fig. 1. As shown in Fig. 7, the shoulder land portion 7 is provided with, for example, a plurality of shoulder lateral grooves 31 and a plurality of short thin grooves 32.

[0048] The shoulder lateral grooves 31 extend, for example, from the shoulder circumferential groove 3 to the tread edge Te. The shoulder lateral grooves 31 include a first portion 31a extending with a constant groove width from the shoulder circumferential groove 3 and a second portion 31b whose groove width increases from the first portion 31a to the tread edge Te. Such shoulder lateral grooves 31 can improve wet performance while maintaining the rigidity of the shoulder land portion 7.

[0049] The short narrow grooves 32 extend from the tread edge Te and terminate within the shoulder land portion 7. For example, the short narrow grooves 32 terminate closer to the tread edge Te than the axial center position of the tire in the shoulder land portion 7. The groove width of the short narrow grooves 32 can be the same as the groove width of the constant width portion 26 (shown in FIG. 2) of the lateral narrow groove 25 described above. Such short narrow grooves 32 help to reduce the rigidity around the tread edge Te and improve the tire wandering performance.

[0050] Although a tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and practiced in various aspects. [Example]

[0051] As an example, a heavy-duty tire having a size of 275 / 80R22.5 and the basic pattern shown in FIG. 1 was prototyped. As comparative example 1, a tire having the pattern shown in FIG. 8 was prototyped. As shown in FIG. 8, the tire of comparative example 1 has a crown circumferential groove b on the inside of the shoulder circumferential groove a, the crown circumferential groove b having the same groove width as the shoulder circumferential groove a. Note that the shoulder circumferential groove a and the crown circumferential groove b do not include chamfered portions. Furthermore, as comparative examples 2 and 3, tires having the basic pattern shown in FIG. 1 were prototyped, but in which the angle θ1 of the inclined surface of the chamfered portion was outside the numerical range specified in the present invention. Except for the above-mentioned features, the tires of comparative examples 1 to 3 had substantially the same configuration as the tire of the example. These test tires were tested for rolling resistance and chipping resistance. The common specifications and test methods for each test tire are as follows. Mounted rim: 22.5 x 8.25 Tire pressure: 900kPa

[0052] <Rolling resistance> Using a rolling resistance tester, the rolling resistance of each test tire was measured under conditions of a vertical load of 28.76 kN and a speed of 60 km / h. The results were expressed as an index, with the reciprocal of the measurement result being expressed as an index; the larger the index, the lower the rolling resistance and the better the tire.

[0053] <Chipping resistance> Using a drum testing machine with protrusions on the running surface, each test tire was run for a certain distance under conditions of a vertical load of 14.7 kN and a speed of 10 km / h. After that, the chipping resistance of the crown land portion was evaluated visually. The results were expressed as a numerical score based on the evaluation, with a higher score indicating better chipping resistance. The test results are shown in Table 1.

[0054] [Table 1]

[0055] As shown in Table 1, the tire of Comparative Example 1 having the pattern shown in Fig. 8 has a rolling resistance of 100 points and a chipping resistance of 100 points. On the other hand, the tire of Comparative Example 2 having circumferential narrow grooves and having inclined surfaces at an angle of 15° on the inner and outer chamfers has an improved rolling resistance of 115 points, but a low chipping resistance of 102 points.

[0056] Furthermore, the tire of Comparative Example 3, in which the angle of the inclined surfaces of the inner and outer chamfered portions of the circumferential narrow grooves is 65°, has rolling resistance and chipping resistance each of 105 points, which shows a tendency for improvement but is not sufficient. In contrast, the tire of Example 1 has a rolling resistance of 110 points and a chipping resistance of 110 points, and it can be seen that these performances are significantly improved compared to Comparative Examples 1 to 3. That is, it has been confirmed that the present invention reduces rolling resistance while improving the chipping resistance of the crown land portion by optimizing the angle of the inclined surfaces of the chamfered portions of the circumferential narrow grooves.

[0057] [Note] The present invention includes the following aspects.

[0058] [Invention 1] A heavy-duty tire having a tread portion, the tread portion includes a pair of shoulder circumferential grooves extending continuously in the tire circumferential direction on both sides of a tire equator, and a crown region between the pair of shoulder circumferential grooves, the crown region is provided with at least one circumferential narrow groove that extends continuously in the tire circumferential direction and has a groove width smaller than that of the shoulder circumferential groove, and a plurality of crown land portions that are separated by the circumferential narrow groove, the circumferential narrow groove includes a pair of groove edges and a pair of chamfered portions respectively connected to the pair of groove edges, Each of the pair of chamfered portions includes an inclined surface that extends continuously in the tire circumferential direction and is inclined at an angle of 20 to 60 degrees with respect to a tire normal line passing through the groove edge. Heavy duty tires. [Invention 2] The heavy-duty tire according to present invention 1, wherein the groove width of the circumferential narrow groove is set to a width that allows at least a portion of the adjacent crown land portions to come into contact with each other via the circumferential narrow groove when the circumferential narrow groove comes into contact with the ground. [Invention 3] The circumferential narrow grooves include a pair arranged such that the tire equator is located therebetween, the pair of chamfered portions includes an inner chamfered portion on the tire equator side and an outer chamfered portion opposite the inner chamfered portion, 3. The heavy-duty tire according to claim 1, wherein, in a plan view of the tread portion, a width Wo of the outer chamfer portion is larger than a width Wi of the inner chamfer portion. [Invention 4] A heavy duty tire according to invention 3, wherein the width Wo is 130% to 170% of the width Wi. [Invention 5] Each of the plurality of crown land portions is divided into a plurality of blocks by a plurality of lateral narrow grooves extending in the tire axial direction, 5. The heavy-duty tire according to any one of claims 1 to 4, wherein the lateral narrow groove has a groove width of 3.0 mm or less. [Invention 6] 6. A heavy-duty tire according to claim 5, wherein the lateral narrow grooves include widened portions whose groove width increases toward the ends in the tire axial direction. [Invention 7] 7. The heavy-duty tire according to any one of claims 1 to 6, wherein the depth of the pair of chamfered portions is 15% to 35% of the depth of the circumferential narrow groove. [Invention 8] The heavy-duty tire according to any one of claims 1 to 7, wherein the width of one of the chamfered portions in a plan view of the tread portion is 3% to 9% of the maximum axial width of the crown land portion. [Invention 9] 9. The heavy-duty tire according to any one of claims 1 to 8, wherein the circumferential narrow groove extends in a zigzag pattern. [Explanation of symbols]

[0059] 2 Tread section 3 Shoulder circumferential groove 4 Crown area 5 Circumferential thin groove 6 Crown Land Division 9 Groove Edge 10 Chamfered part 11 Slope

Claims

1. A heavy-duty tire having a tread portion, the tread portion includes a pair of shoulder circumferential grooves extending continuously in the tire circumferential direction on both sides of a tire equator, and a crown region between the pair of shoulder circumferential grooves, the crown region is provided with at least one circumferential narrow groove that extends continuously in the tire circumferential direction and has a groove width smaller than that of the shoulder circumferential groove, and a plurality of crown land portions that are separated by the circumferential narrow groove, the circumferential narrow groove includes a pair of groove edges and a pair of chamfered portions respectively connected to the pair of groove edges, Each of the pair of chamfered portions includes an inclined surface that extends continuously in the tire circumferential direction and is inclined at an angle of 20 to 60 degrees with respect to a tire normal line passing through the groove edge. Heavy duty tires.

2. 2. The heavy-duty tire according to claim 1, wherein the groove width of the circumferential narrow groove is set to a width that allows at least a portion of the crown land portions adjacent to each other via the circumferential narrow groove to come into contact with each other when the circumferential narrow groove comes into contact with the ground.

3. The circumferential narrow grooves include a pair arranged such that the tire equator is located therebetween, the pair of chamfered portions includes an inner chamfered portion on the tire equator side and an outer chamfered portion opposite the inner chamfered portion, The heavy-duty tire according to claim 1 or 2, wherein, in a plan view of the tread portion, a width Wo of the outer chamfer portion is larger than a width Wi of the inner chamfer portion.

4. 4. The heavy duty tire according to claim 3, wherein the width Wo is 130% to 170% of the width Wi.

5. Each of the plurality of crown land portions is divided into a plurality of blocks by a plurality of lateral narrow grooves extending in the tire axial direction, 3. The heavy duty tire according to claim 1, wherein the lateral narrow groove has a groove width of 3.0 mm or less.

6. The heavy-duty tire according to claim 5 , wherein the lateral narrow groove includes a widened portion whose groove width increases toward an end in the tire axial direction.

7. 3. The heavy-duty tire according to claim 1, wherein a depth of the pair of chamfered portions is 15% to 35% of a depth of the circumferential narrow groove.

8. 3. The heavy-duty tire according to claim 1, wherein the width of one of the chamfered portions in a plan view of the tread portion is 3% to 9% of the maximum axial width of the crown land portion.

9. 3. The heavy duty tire according to claim 1, wherein the circumferential narrow grooves extend in a zigzag pattern.

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