pneumatic tires

Abstract

Pneumatic tires, in which a direction of rotation is provided, comprising: a tread section (1) extending in the circumferential direction of the tire and forming a ring shape; a pair of sidewall sections (2) arranged on both sides of the running surface section (1); a pair of bead sections (3) that are from the sidewall sections (2) are arranged inwards in the tire radial direction; wherein lug grooves (20) extending inwards in the tire width direction from a tread edge (E) on one side of a tire equator (CL) and intersecting with the tire equator (CL), and lug grooves (30) extending inwards in the tire width direction from a tread edge (E) on another side of the tire equator (CL) and intersecting with the tire equator (CL), are arranged alternately in the tire circumferential direction on an outer surface of the tread section (1); wherein the respective lug grooves (20, 30) enclose first groove sections (21, 31) and second groove sections (22, 32), wherein the first groove section (21, 31) intersects the tire equator (CL) and extends along the tire width direction, wherein the second groove section (22, 32) is inclined from one end of the first groove section (21, 31) at an angle with respect to the tire circumference direction that is less than the angle of the first groove section (21, 31) with respect to the tire circumference direction and extends to the tread edge (E), wherein the first groove section (21, 31) has another end that is connected to the second groove section (22, 32) of the lug groove (20, 30) adjacent in the tire circumference direction, wherein the first groove section (21, 31) is inclined on an incoming side in relation to an end section on the running surface edge side of the lug groove (20, 30); wherein, where a distance from the tire equator (CL) to the tread edge (E) is designated as W, a region between a position separated from the tire equator (CL) by 0.50 W in the tire width direction and the tire equator (CL) is designated as an inner region (A), and a region between the position separated from the tire equator (CL) by 0.50 W in the tire width direction and the tread edge (E) is designated as an outer region (B), the second groove sections (22, 32) are curved or bent such that an average angle (θa) of the second groove sections (22, 32) with respect to the tire circumference direction in the inner region (A) is smaller than an average angle (θb) of the second groove sections (22, 32) with respect to the tire circumference direction in the outer region (B), wherein the second groove section (22, 32) the cleat groove (20, 30) has a groove depth of 15 mm to 25 mm; and wherein narrow circumferential grooves (40) connecting the mutual second groove sections (22, 32) adjacent in the tire circumferential direction on one side or the other side of the tire equator (CL) are formed, wherein the narrow circumferential grooves (40) are present at an extended position of the first groove sections (21, 31) and a difference between an average angle (θa) of the second groove sections (22, 32) with respect to the tire circumferential direction in the inner region (A) and an inclination angle (α) of the narrow circumferential groove (40) with respect to the tire circumferential direction lies within a range of 90° ± 10°, wherein center blocks (51) at positions intersecting with the tire equator (CL) are defined by the lug grooves (20, 30) and the narrow circumferential grooves (40), wherein a maximum length (L) in the tire width direction of the Middle blocks (51) 25% to 35% of a development width (TW).

Description

Technical field

[0001] The present invention relates to a pneumatic tire suitable as a heavy-duty pneumatic tire, and in particular to a pneumatic tire that improves noise reduction performance while improving driving performance on unpaved roads. State of the art

[0002] Heavy-duty pneumatic tires used on construction vehicles, such as dump trucks, must primarily offer excellent traction on unpaved roads. Therefore, a block-based tread pattern is employed, including a large number of lug grooves extending across the width of the tire (see, for example, JP 4676959 B).

[0003] Meanwhile, the performance demands placed on various tires have increased recently, and tires as described above are now required not only to perform well on unpaved roads but also to improve their performance (e.g., noise reduction) on paved roads. Therefore, there is a need for a countermeasure to improve noise reduction while simultaneously improving traction on unpaved roads.

[0004] JP 2017 128 217 A discloses a pneumatic tire with lug grooves that include first and second groove sections. Circumferential grooves are arranged essentially in the circumferential direction of the tire.

[0005] EP 3 231 639 A1 and JP 2013 136 333 A also reveal pneumatic tires with lug grooves, which include first and second groove sections.

[0006] WO 2018 / 179755 A1 and US 2020 / 0055347 A1 also disclose a pneumatic tire with lug grooves that include first and second groove sections. Circumferential grooves are arranged essentially in the tire's circumferential direction. They are present at an extended position of the first groove sections and extend essentially perpendicular to the lug grooves.

[0007] JP 2010 174 231 A concerns rubber compounds for pneumatic tires, improving traction properties on ice while maintaining excellent mileage and resistance to uneven wear. Brief description of the invention: Technical problem

[0008] One object of the present invention is to provide a pneumatic tire with improved noise reduction performance while improving driving performance on unpaved roads. Solution to the problem

[0009] To solve the problem described above, a pneumatic tire according to one embodiment of the present invention, in which a direction of rotation is provided, comprises a tread section, a pair of sidewall sections, and a pair of bead sections. The tread section extends in the circumferential direction of the tire and forms a ring shape. The pair of sidewall sections is arranged on both sides of the tread section. The pair of bead sections is arranged inwards from the sidewall sections in the radial direction of the tire.Lug grooves extending inward in the tire width direction from a tread edge on one side of the tire equator and intersecting the tire equator, and lug grooves extending inward in the tire width direction from a tread edge on the opposite side of the tire equator and intersecting the tire equator, are arranged alternately in the tire circumference direction on an outer surface of the tread section. Each lug groove includes first groove sections and second groove sections. The first groove section intersects the tire equator and extends in the tire width direction. The second groove section is inclined from one end of the first groove section at an angle relative to the tire circumference that is smaller than the angle of the first groove section relative to the tire circumference and extends toward the tread edge.The first groove section has a different end that connects to the second groove section of the adjacent lug groove in the tire's circumferential direction. The first groove section is located on the incoming side relative to an end section on the tread edge of the lug groove.If a distance from the tire equator to the tread edge in the tire width direction is designated as W, a region between a position separated from the tire equator by 0.50 W in the tire width direction and the tire equator is designated as an inner region, and a region between the position separated from the tire equator by 0.50 W in the tire width direction and the tread edge is designated as an outer region, then the second groove sections are curved or bent such that the average angle of the second groove sections with respect to the tire circumference in the inner region is smaller than the average angle of the second groove sections with respect to the tire circumference in the outer region. The second groove section of the lug groove has a groove depth of 15 mm to 25 mm.Narrow circumferential grooves are formed, connecting the opposing second groove sections that are adjacent to one side or the other of the tire equator in the tire's circumferential direction. These narrow circumferential grooves are present at an extended position of the first groove sections, and the difference between the average angle of the second groove sections relative to the tire's circumferential direction in the inner area and the inclination angle of the narrow circumferential groove relative to the tire's circumferential direction is within a range of 90° ± 10°. Center blocks are defined by the lug grooves and the narrow circumferential grooves at positions that intersect the tire equator. The maximum length of the center block in the tire's width direction is 25% to 35% of its development width. Advantageous effects of the invention

[0010] In the embodiment of the present invention, as described above, the lug grooves formed by the first and second groove sections are provided in such a way that, in addition to improving traction on unpaved roads, noise reduction performance can also be enhanced. In other words, the first groove sections, which extend along the tire width direction, are arranged at or near the tire equator, where their contribution to traction performance is high, and the first groove sections are connected to the other lug grooves (second groove sections). Accordingly, traction performance can be efficiently improved. Furthermore, the second groove sections, which are curved or bent as described above, allow for an increase in groove length. This enables an improvement in traction performance and suppression of air column resonance.Furthermore, since a maximum width of the center blocks is appropriately ensured, sufficient block stiffness can be guaranteed, resulting in good traction performance. Additionally, the narrow circumferential grooves distribute noise across the grooves, thus improving noise reduction. Moreover, the narrow circumferential grooves allow for the addition of a groove component in the tire's circumference, thereby reducing lateral tire movement under traction and improving stability.

[0011] In the embodiment of the present invention, the angle of the first groove section with respect to the tire's circumferential direction is preferably 80° to 100°. This allows the grooves to be arranged in a direction substantially perpendicular to the tire's circumferential direction at or near the tire's equator, where the contribution to traction performance is high, and enables an effective improvement in traction performance.

[0012] In the embodiment of the present invention, the following is preferred. The average angle of the second groove sections with respect to the tire's circumferential direction in the inner region is 35° to 45°. The average angle of the second groove sections with respect to the tire's circumferential direction in the outer region is 70° to 85°. Accordingly, the angles of the second groove sections in the respective regions are within suitable ranges, and curved or bent shapes of the second groove sections are well achieved. This also increases the length of the tread grooves, which is advantageous in suppressing air column resonance and improving traction performance.

[0013] The narrow circumferential groove is located at an extended position of the first groove sections. The difference between the average angle of the second groove sections relative to the tire's circumference in the inner area and the inclination angle of the narrow circumferential groove relative to the tire's circumference is within a range of 90° ± 10°. Thus, since the narrow circumferential grooves extend essentially perpendicular to the lug grooves, the alignment between the lug grooves and the narrow circumferential grooves is excellent, which is advantageous in reducing lateral tire movement under traction.

[0014] In the embodiment of the present invention, the following is preferred. The groove depth of the first groove section of the lug groove is 65% to 75% of the groove depth of the second groove section. By thus flattening the first groove section sufficiently more than the second groove section, the stiffness of the block adjacent to the first groove section can be increased, which is advantageous for improving traction performance.

[0015] In the embodiment of the present invention, the following is preferred. The groove depth of the narrow circumferential groove is 75% to 85% of the groove depth of the second groove section of the lug groove. By thus flattening the narrow circumferential groove sufficiently more than the second groove section of the lug groove, the stiffness of the block adjacent to the narrow circumferential groove can be increased, which is advantageous for improving traction performance.

[0016] The lug groove has a groove depth of 15 mm to 25 mm. Furthermore, the following is preferred: A tread rubber forming the tread section has a JIS-A hardness of 61 to 70 and a modulus at 100% elongation of 2.0 MPa to 3.0 MPa. The embodiment of the present invention enables a heavy-duty pneumatic tire with such properties to exhibit excellent performance, particularly in terms of traction, resistance to uneven wear, and low noise. It should be noted that in the embodiment of the present invention, "JIS-A hardness" is the hardness measured using a type A durometer at a temperature of 23 °C according to the durometer hardness test regulated in JIS K6253.Furthermore, the “modulus at 100% extension” is a value measured under specific conditions of a drawing speed of 500 mm / minute and a temperature of 23 °C using a No. 3 test bar according to JIS K6251.

[0017] In the embodiment of the present invention, the “tread edges” refer to both ends of a tread pattern portion of the tire when the tire is mounted on a regular rim, inflated to a regular internal pressure, and unloaded (unloaded condition). The “distance W from the tire equator to the tread edge in the tire width direction” corresponds, in the embodiment of the present invention, to 1 / 2 of a stretched tread width (“tread width” specified by JATMA), which is a linear distance between the tread edges measured along the tire width direction in the condition described above.“Regular rim” is a rim defined by a standard for each tire according to a system of standards that includes standards on which tires are based, and refers to a “standard rim” in the case of JATMA, a “design rim” in the case of TRA, and a “measuring rim” in the case of ETRTO. In the system of standards, including standards that tires meet, “regular internal pressure” is an air pressure defined by each of the standards for each tire and is referred to as “maximum air pressure” in the case of JATMA, as the maximum value in the “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” table in the case of TRA, and as “INFLATION PRESSURE” in the case of ETRTO. However, the "regular internal pressure" is 180 kPa in a case where a tire is a tire for a passenger car. Brief description of the drawings Fig. Figure 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. Fig. Figure 2 is a front view showing a tread surface of the pneumatic tire according to the embodiment of the present invention. Fig. Figure 3 is a front view illustrating an example of the tread surface of a pneumatic tire, representing a prior art example. Description of embodiments

[0018] Configurations of embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0019] As in Fig.As illustrated in Figure 1, a pneumatic tire of an embodiment of the present invention includes a tread section 1, a pair of sidewall sections 2 arranged on both sides of the tread section 1, and a pair of bead sections 3 arranged inwards from the sidewall sections 2 in the tire radial direction. Fig. 1. The reference symbol “CL” denotes a tire equator and the reference symbol “E” denotes a tread edge. In the illustrated example, the tread edges E correspond to the outer edges in the tire width direction of blocks at the very outer edge in the tire width direction (edge ​​sections formed by the road contact surfaces of the blocks facing outwards in the tire width direction and the side surfaces facing outwards in the tire width direction). Although in Fig. 1 not illustrated, since Fig.Figure 1 shows a meridian cross-sectional view. The tread section 1, the sidewall sections 2, and the bead sections 3 each extend in the tire's circumferential direction to form a ring shape. This configures a torus-shaped basic structure of the pneumatic tire. Although the description uses Fig. 1. Essentially based on the illustrated meridian cross-section, all tire components extend in the direction of the tire's circumference and form the ring shape.

[0020] A carcass layer 4 is positioned between the pair of left and right bead sections 3. The carcass layer 4 incorporates a plurality of reinforcing cord threads extending in the tire's radial direction and is folded back from the inside of the vehicle to the outside of a tire bead core 5 located in each of the tire bead sections 3. Bead fillers 6 are also arranged on the outer circumferential side of the bead cores 5, and each bead filler 6 is enclosed by a main body section and a folded-back section of the carcass layer 4. Furthermore, in the tread section 1, a plurality of belt layers 7 (four layers in Fig.1) embedded on an outer circumferential side of the carcass layer 4. The belt layers 7 each contain a plurality of reinforcing cords inclined with respect to the tire's circumferential direction, the reinforcing cords of the different layers being arranged crosswise. In these belt layers 7, an angle of inclination of the reinforcing cord threads with respect to the tire's circumferential direction is specified in a range of, for example, 10° to 60°. Although not in the pneumatic tire of Fig.In the embodiment of the present invention, a belt reinforcement layer (not illustrated) can additionally be provided on the outer circumferential side of the belt layers 7. When the belt reinforcement layer is provided, it includes, for example, an organic fiber cord thread oriented in the tire's circumferential direction. The angle of the organic fiber cord thread with respect to the tire's circumferential direction can, for example, be set to 0° to 5°.

[0021] A tread rubber layer 11 is arranged on an outer circumferential side of the carcass layer 4 and the belt layers 7 in the tread section 1. A sidewall rubber layer 12 is arranged on an outer circumferential side of the carcass layer 4 (outward in the tire width direction) in the sidewall sections 2. A rim cushion rubber layer 13 is arranged on the outer circumferential side of the carcass layer 4 (outward in the tire width direction) in the bead sections 3. The tread rubber layer 11 can have a structure in which two types of rubber layers (a crown tread rubber layer and an undertread rubber layer) with different physical properties are layered in the tire radial direction.

[0022] The embodiment of the present invention can be applied to such a general pneumatic tire; however, its cross-sectional structure is not limited to the basic structure described above. It should be noted that the embodiment according to the invention is primarily intended for use as a heavy-duty pneumatic tire. In this case, the tread rubber layer 11 is a rubber compound with a JIS-A hardness of preferably 61 to 70 and more, preferably 61 to 65, and a modulus at 100% elongation of preferably 2.0 MPa to 3.0 MPa and preferably 2.0 MPa to 2.8 MPa.

[0023] As in Fig.As illustrated in Figure 2, the lug grooves 20 (which may be referred to in the following description as "lug grooves 20 on one side") and the lug groove 30 (which may be referred to in the following description as "lug grooves 30 on the other side") are provided on a surface of the tread section 1 of the pneumatic tire according to the embodiment of the present invention. The lug groove 20 extends inward from the tread edge E on one side (the right side in the drawing) of the tire equator CL in the direction of the tire width and overlaps with the tire equator CL. The lug groove 30 extends inward from the tread edge E on the other side (the left side in the drawing) of the tire equator CL in the direction of the tire width and overlaps with the tire equator CL. The majority of lug grooves 20 on one side and the majority of lug grooves 30 on the other side are provided.

[0024] The lug grooves 20, 30 enclose first groove sections 21, 31, which intersect the tire equator CL and extend along the tire width direction, and second groove sections 22, 32, which are inclined from one end of the first groove sections 21, 31 at a smaller angle than that of the first groove sections 21, 31 with respect to the tire circumference direction and each extend to the tread edges E. In particular, the lug groove 20 encloses the first groove section 21 and the second groove section 22 on one side. The first groove section 21 intersects the tire equator CL and extends along the tire width direction.The second groove section 22 is inclined from one end of the first groove section 21 (the end section on one side (the right side in the drawing) of the tire equator) at a smaller angle than that of the first groove section 21 with respect to the tire's circumferential direction and extends to the tread edge E. Similarly, the lug groove 30 on the other side encloses the first groove section 31 and the second groove section 32. The first groove section 31 intersects the tire equator CL and extends along the tire's width direction. The second groove section 32 is inclined from one end of the first groove section 31 (the end section on the other side (the left side in the drawing) of the tire equator) at a smaller angle than that of the first groove section 31 with respect to the tire's circumferential direction and extends to the tread edge E.

[0025] The lug grooves 20 on one side and the lug grooves 30 on the other side are arranged alternately in the circumferential direction of the tire. It should be noted that, as described above, since the lug grooves 20 and 30 extend essentially in opposite directions from the tire equator CL, the first groove sections 21 of the lug grooves 20 on one side and the first groove sections 31 of the lug grooves 30 on the other side are arranged alternately in the circumferential direction of the tire on the tire equator CL. Meanwhile, the second groove sections 22 of the lug grooves 20 on one side are arranged at intervals in the circumferential direction on one side of the tire equator CL, and the second groove sections 32 of the lug grooves 30 on the other side are arranged at intervals in the circumferential direction on the opposite side of the tire equator CL.In the embodiment of the present invention, as long as the first groove sections 21, 31 are arranged alternately such that they are adjacent to the tire equator CL, the lug grooves 20, 30 are considered to be arranged alternately, unless otherwise specified.

[0026] The other ends of the first groove sections 21, 31 of the respective lug grooves 20, 30 are connected to the second groove sections 32, 22 of the other lug grooves 30, 20 adjacent in the circumferential direction of the tire. In other words, the first groove section 21 of lug groove 20 on one side is connected to the second groove section 32 of lug groove 30 on the other side, adjacent in the circumferential direction of the tire, and the first groove section 31 of lug groove 30 on the other side is connected to the second groove section 22 of lug groove 20 on one side, adjacent in the circumferential direction of the tire.

[0027] The first groove sections 21, 31 of the respective lug grooves 20, 30 are located on an incoming side with respect to the end sections on the side of the tread edge E of the respective lug grooves 20, 30. That is, the pneumatic tire of the embodiment of the present invention is a tire in which a direction of rotation R is provided. Meanwhile, the respective lug grooves 20, 30 as a whole have a shape that is inclined in a direction opposite to the direction of rotation R from the side of the tire equator CL outwards in the tire width direction.

[0028] If a distance from the tire equator CL to the tread edge E in the tire width direction is designated as W, a region between a position separated by 0.50 W in the tire width direction from the tire equator CL and the tire equator CL is designated as an inner region A, and a region between a position separated by 0.50 W in the tire width direction from the tire equator CL and the tread edge E is designated as an outer region B, then in the respective lug grooves 20, 30 the second groove sections 22, 32 are curved or bent such that an average angle θa of the second groove sections 22, 32 with respect to the tire circumference direction in the inner region A is smaller than an average angle θb of the second groove sections 22, 32 with respect to the tire circumference direction in the outer region B.In other words, the second groove sections 22, 32 of the lug grooves 20, 30 curve gently, so that the angles of inclination with respect to the tire circumferential direction gradually decrease from the side of the tread edge E to the side of the tire equator CL, or are curved with at least one bending point.

[0029] It should be noted that the average angle of the second groove sections 22, 32 of the lug grooves 20, 30 can be obtained as an angle formed by a straight line connecting the centers in the groove width directions of the lug grooves 20, 30 at boundary positions of the respective areas and the tire circumference direction. It should be noted that, as illustrated, on the tire equator CL and the tread edge E, the midpoint of an extension line of the second groove section 22, 32, drawn to the tire equator CL or the tread edge E, is used.

[0030] In the embodiment of the present invention, narrow circumferential grooves 40 are provided in addition to the lug grooves 20, 30. The narrow circumferential groove 40 extends along the tire's circumferential direction such that it connects the second groove sections that are adjacent on one side of the tire equator CL in the tire's circumferential direction, i.e., the second groove sections 22 of the lug grooves 20 on one side, which are adjacent on one side of the tire equator CL in the tire's circumferential direction, or the second groove sections 32 of the lug grooves 30 on the other side, which are adjacent on the other side of the tire equator CL in the tire's circumferential direction.

[0031] The narrow circumferential groove 40 is a groove with a width smaller than that of the lug grooves 20 and 30. Specifically, the lug grooves 20 and 30 have widths of, for example, 5 mm to 30 mm and a groove depth of, for example, 8 mm to 25 mm. In particular, if the tire is a heavy-duty pneumatic tire, the groove depth is preferably, for example, 15 mm to 25 mm. In contrast, the narrow circumferential groove 40 has a width of, for example, 7 mm to 11 mm and a groove depth of, for example, 15 mm to 20 mm.

[0032] The lug grooves 20, 30 and the narrow circumferential grooves 40 separate a plurality of blocks 50. Among the plurality of blocks 50, a block positioned on the side of the tire equator CL with respect to the narrow circumferential groove 40 is designated as a center block 51, and a block positioned on the side of the tread edge E with respect to the narrow circumferential groove 40 is designated as a shoulder block 52. At least some of the center blocks 51 are present on the tire equator CL due to the groove shape described above. The center block 51 has a maximum length L in the tire width direction, which is set at 25% to 35% of a development width TW.

[0033] Since a tread pattern is configured as described above, both traction performance on unpaved roads and noise reduction performance can be improved. In other words, the first groove sections 21, 31, which extend along the tire width direction, are located at or near the tire equator CL, where their contribution to traction performance is high, and the first groove sections 21, 31 are connected to the second groove sections 32, 22 of the other lug grooves. Accordingly, traction performance can be efficiently improved. Furthermore, the second groove sections 22, 32, which are curved or bent as described above, allow for an increase in groove lengths. This enables improved traction performance and suppression of air column resonance.Furthermore, since the maximum width of the center blocks 51 is appropriately ensured, sufficient block stiffness can be guaranteed, and good traction performance can be achieved. Additionally, the provision of narrow circumferential grooves 40 distributes noise across these grooves, thereby improving noise reduction. Moreover, the narrow circumferential grooves 40 allow for the addition of a groove component in the tire's circumferential direction, thus reducing lateral tire displacement under traction and improving stability.

[0034] At this point, because the lug grooves 20, 30 do not have the shape described above, the groove shape becomes unsuitable, and the effects described above are not guaranteed. In particular, if the first groove sections 21, 31, which intersect the tire equator CL and extend along the tire width direction, are not provided, the traction performance cannot be sufficiently improved. If the size ratio between the average angles θa, θb of the second groove sections 22, 32 is reversed, the curved or bent shape of the second groove sections 22, 32 becomes unsuitable, and the effect of improving traction performance cannot be sufficiently achieved. The absence of the narrow circumferential grooves 40 means that the groove component is not added in the circumferential direction.If the maximum length L in the tire width direction of the center block 51 is less than 25% of the development width TW, the stiffness of the center block 51 is reduced and traction performance cannot be sufficiently improved. A maximum length L in the tire width direction of the center block 51 of more than 35% of the development width TW results in an excessively large center block 51. This may generate pattern noise originating from the center block 51 and may impair noise reduction performance.

[0035] As described above, the first groove sections 21, 31 are positioned such that they primarily ensure the groove portion in the tire width direction at or near the tire equator CL, where the contribution to traction performance is high. Accordingly, the first groove sections 21, 31 preferably extend in a direction that is substantially perpendicular to the tire's circumferential direction. In particular, the angle θc of the first groove sections 21, 31 with respect to the tire's circumferential direction is preferably between 80° and 100°. This enables an efficient improvement in traction performance by the first groove sections 21, 31.If the angle θc of the first groove sections 21, 31 is less than 80° or more than 100°, the inclination of the first groove sections 21, 31 with respect to the tire width direction increases and the groove component in the tire width direction cannot be sufficiently ensured and thus the effect of improving traction performance is limited.

[0036] Although the angles of the second groove sections 22, 32 in the respective areas can be suitably determined according to the performance considered important for the tire, the average angle θa of the second groove sections 22, 32 with respect to the tire's circumferential direction in the inner area A is preferably set to be 35° to 45°, and the average angle θb of the second groove sections 22, 32 with respect to the tire's circumferential direction in the outer area B is preferably set to be 70° to 85°. Accordingly, the angles of the second groove sections 22, 32 in the respective areas are optimized, as are the curved or bent shapes of the second groove sections 22, 32. Consequently, the lug groove lengths are increased, which is advantageous in suppressing air column resonance and improving traction performance.An average angle θa of less than 35° for the second groove sections 22, 32 reduces the groove component in the tire width direction, making it difficult to sufficiently improve traction performance. If the average angle θa of the second groove sections 22, 32 exceeds 45°, the difference to the average angle θb becomes small, and the second groove sections 22, 32 cannot be sufficiently bent or curved, and the lug groove lengths do not increase sufficiently, making it difficult to adequately improve traction performance. If the average angle θb of the second groove sections 22, 32 is less than 70°, the difference to the average angle θa becomes small, the second groove sections 22, 32 cannot be sufficiently bent or curved, and the lug groove lengths do not increase sufficiently, making it difficult to adequately improve traction performance.If the average angle θb of the second groove sections 22, 32 exceeds 85°, the difference to the average angle θa becomes large, and the second groove sections 22, 32 are strongly curved or bent, making it difficult to ensure good groove shapes.

[0037] As described above, although the narrow circumferential groove 40 is a groove connecting the second groove sections 22, 32, which are adjacent in the tire circumferential direction on one side of the tire equator CL, the narrow circumferential groove 40 is preferably arranged at an extended position of the other ends of the first groove sections 21, 31. With such a configuration, for example, if the groove is traced from the tread edge E on one side, the groove runs through the first groove section 21 of the second groove section 22 of the lug groove 20 on one side, crosses the lug groove 30 (the second groove section 32) on the other side, and then reaches the narrow circumferential groove 40 on the other side of the tire equator CL. These grooves are arranged in a well-coordinated manner as a series of grooves, which is advantageous in improving traction performance.It should be noted that if the groove is traced from the tread edge E on the other side, the groove passes through the first groove section 31 of the second groove section 32 of the lug groove 30 on the other side, crosses the lug groove 20 (the second groove section 22) on one side and then reaches the narrow circumferential groove 40 on one side of the tire equator CL.

[0038] As described above, although the narrow circumferential groove 40 is intended to add the groove component in the tire's circumferential direction, the narrow circumferential groove 40 is preferably inclined in a suitable manner with respect to the tire's circumferential direction to provide the groove component in the tire's width direction, in addition to the groove component in the tire's circumferential direction. Therefore, the narrow circumferential grooves 40 extend substantially perpendicular to the lug grooves 20, 30. In particular, the difference between the average angle θa of the second groove sections 22, 32 with respect to the tire's circumferential direction in the inner region A and an inclination angle α of the narrow circumferential groove 40 with respect to the tire's circumferential direction lies within a range of 90° ± 10°.This provides the optimal shape for the narrow circumferential groove 40 and a good match between the groove component in the tire's circumferential direction and the groove component in the tire's width direction, which are advantageous for improving traction performance. If the difference between the average angle θa and the angle α lies outside the range of 90° ± 10°, the groove component in the tire's circumferential or width direction increases, and the match between the respective groove components becomes poor, thus limiting the effect of improving traction performance.

[0039] Although the lug grooves 20, 30 can have a uniform groove depth throughout, the first groove sections 21, 31 are preferably configured to be sufficiently shallower than the second groove sections 22, 32. In particular, the groove depth of the first groove sections 21, 31 of the lug grooves 20, 30 is preferably 65% ​​to 75% of the groove depth of the second groove sections 22, 32. This allows for an increase in the stiffness of the block (central block 51) adjacent to the first groove sections 21, 31, which is advantageous for improving traction performance. If the groove depth of the first groove sections 21, 31 is less than 65% of the groove depth of the second groove sections 22, 32, the first groove sections 21, 31 become too shallow, making it difficult to adequately define the edge of the groove.The groove depth of the first groove sections 21, 31 of more than 75% of the groove depth of the second groove sections 22, 32 essentially eliminates the difference in groove depth between the first groove sections 21, 31 and the second groove sections 22, 32, and the effect produced by changing the groove depth is not sufficiently expected.

[0040] Although the respective groove depths of the lug grooves 20, 30 and the narrow circumferential groove 40 can be set to the areas described above, the narrow circumferential groove 40 is preferably configured to be sufficiently shallower than the lug grooves 20, 30. In particular, the groove depth of the narrow circumferential groove 40 is preferably set to be 75% to 85% of the groove depth of the second groove sections 22, 32 of the lug grooves 20, 30. By thus flattening the narrow circumferential groove 40 to a sufficiently greater extent than the second groove sections 22, 32, the stiffness of the blocks adjacent to the narrow circumferential grooves 40 (the center block 51 and the shoulder block 52) can be increased, which is advantageous for improving traction performance.If the groove depth of the narrow circumferential groove 40 is less than 75% of the groove depth of the second groove sections 22, 32, the narrow circumferential groove 40 becomes too shallow, making it difficult to adequately demonstrate the edge effect as a groove. A groove depth of the narrow circumferential groove 40 greater than 85% of the groove depth of the second groove sections 22, 32 essentially eliminates the difference in groove depth between the narrow circumferential groove 40 and the second groove sections 22, 32, and the effect produced by changing the groove depth is not sufficiently achieved. Example

[0041] 25 types of pneumatic tires of the prior art example 1, comparative examples 1 and 2 and examples 1 to 22, which have a tire size of 315 / 80R22.5 and which are in Fig.1. The basic structure is illustrated as an example and includes the following: the based tread pattern, the average angle θa of the second groove section of the lug groove with respect to the tire circumference direction in the inner area A, the average angle θb of the second groove section of the lug groove with respect to the tire circumference direction in the outer area B, the angle θc of the first groove section of the lug groove with respect to the tire circumference direction, the size ratio between the average angles θa and θb, a ratio of the maximum length L of the center groove to the stretched tread width TW (L / TW × 100%), the position of the narrow circumferential groove, a difference between the average angle θa of the second groove sections with respect to the tire circumference direction in the inner area and the inclination angle α of the narrow circumferential groove with respect to the tire circumference direction (α - θa).The following parameters were determined as shown in Tables 1 to 3: the depth of the second groove section of the lug groove, the ratio of the depth of the first groove section of the lug groove to the depth of the second groove section of the lug groove (%), the ratio of the depth of the narrow circumferential groove to the depth of the second groove section of the lug groove (%), the hardness of the rubber compound (tread rubber) forming the tread section, and the modulus at 100% extension of the rubber compound (tread rubber) forming the tread section.

[0042] The corresponding drawing numbers are described in the "Running Surface Pattern" columns in Tables 1 to 3. It should be noted that, although the pattern of the prior art example 1 ( Fig. 3) strongly deviates from the pattern of Fig.2 deviates, for example, the angles of the respective sections in accordance with Fig. 2 were brought as described in the drawing to obtain values ​​for the respective elements. Although comparison examples 1 and 2 are patterns where the curvature or bending of the lug grooves is small, for convenience, values ​​for the respective elements have been shown as examples that correspond to the pattern of Fig. 2 correspond. In the columns “Position of the narrow circumferential groove” in Tables 1 to 3, the case in which the narrow circumferential groove was present at the extended position of the first groove sections of the cleat grooves was described as “Continuous”, and the case in which the narrow circumferential groove was not present at the extended position was described as “Non-continuous”.

[0043] These pneumatic tires were evaluated for traction performance and noise reduction performance according to the following evaluation procedures. The results are shown in Tables 1 to 3. Traction performance

[0044] The respective test tires were mounted on wheels with a rim size of 22.5 × 9.00, inflated to a pressure of 850 kPa, and mounted on a drive shaft of a test vehicle (a 6 × 4 axle configuration truck). Each test tire underwent a sensory evaluation by a test driver on a test track with a paved surface and a test track with an unpaved road. The evaluation results were expressed as index values, with the state-of-the-art example 1 being assigned an index value of 100. Higher index values ​​indicate excellent traction performance. Low noise performance

[0045] The respective test tires were mounted on wheels with a rim size of 22.5 × 9.00 and attached to a driveshaft of a test vehicle (a 6 × 4 axle configuration truck). The pass-by noise outside the vehicle was measured according to the tire noise test procedure specified in Revision 2 of ECE Regulation No. 117 (ECE R117-02). In particular, the test vehicle was driven a sufficient distance before a noise measurement section, and one engine was switched off immediately before the section.The maximum noise level (dB) (a noise level in a frequency range of 800 to 1200 Hz) in the noise measurement section while idling was measured at a plurality of speeds, provided by dividing a speed range of ±10 km / h relative to a reference speed into approximately equal intervals of eight or more, and the average was determined as the pass-by noise outside the vehicle. The maximum noise level dB is a sound pressure [dB(A)] measured by an A-characteristic frequency correction circuit using a stationary microphone installed 7.5 m laterally from a vehicle centerline at a midpoint in the noise measurement section and at a height of 1.2 m from the road surface.The evaluation results are expressed as indices using the reciprocal of the measured values, with the state-of-the-art example 1 being assigned the index 100. Higher index values ​​indicate lower pass-by noise outside the vehicle and better noise reduction performance. [Table 1-I] State of the art example 1 Comparative example 1 Comparative example 2 Example 1 Tread pattern Fig. 3 Fig. 2 Fig. 2 Fig. 2 ya ◯ 51 80 85 80 θb ◯ 68 80 80 85 θc ◯ 138 90 90 90 Size ratio between θa and θb θa < θb θa = θb θa > θb θa < θb L / TW × 100 % 35 30 30 30 Position of the narrow circumferential groove Not continuous Not continuous Not continuous Not continuous Difference (α - θa) ◯ 90 90 90 90 Groove depth of the second groove section mm 22 22 22 22 Groove depth of the first groove section % 40 40 40 40 Groove depth of the narrow circumferential groove % 70 70 70 70 tread rubber hardness 63 60 60 60 Module of the tread rubber MPa 2,4 1,9 1,9 1,9 Traction performance Index value 100 103 98 104 Low noise performance Index value 100 97 100 102 [Table 1-II] Example 2 Example 3 Example 4 Example 5 Tread pattern Fig. 2 Fig. 2 Fig. 2 Fig. 2 ya ◯ 80 80 80 80 θb ◯ 85 85 85 85 θc ◯ 90 90 80 100 Size ratio between θa and θb θa < θb θa < θb θa < θb θa < θb L / TW × 100 % 25 35 30 30 Position of the narrow circumferential groove Not continuous Not continuous Not continuous Not continuous Difference (α - θa) ◯ 90 90 90 90 Groove depth of the second groove section mm 22 22 22 22 Groove depth of the first groove section % 40 40 40 40 Groove depth of the narrow circumferential groove % 70 70 70 70 tread rubber hardness 60 60 60 60 Module of the tread rubber MPa 1,9 1,9 1,9 1,9 Traction performance Index value 102 107 106 106 Low noise performance Index value 103 100 104 104 [Table 2-I] Example 6 Example 7 Example 8 Example 9 Tread pattern Fig. 2 Fig. 2 Fig. 2 Fig. 2 ya ◯ 45 50 35 40 θb ◯ 80 80 80 65 θc ◯ 90 90 90 90 Size ratio between θa and θb θa < θb θa < θb θa < θb θa < θb L / TW × 100 % 30 30 30 30 Position of the narrow circumferential groove Not continuous Not continuous Not continuous Not continuous Difference (α - θa) ◯ 90 90 90 90 Groove depth of the second groove section mm 22 22 22 22 Groove depth of the first groove section % 40 40 40 40 Groove depth of the narrow circumferential groove % 70 70 70 70 tread rubber hardness 60 60 60 60 Module of the tread rubber MPa 1,9 1,9 1,9 1,9 Traction performance Index value 108 110 107 105 Low noise performance Index value 108 108 109 112 [Table 2-II] Example 10 Example 11 Example 12 Example 13 Example 14 Tread pattern Fig. 2 Fig. 2 Fig. 2 Fig. 2 Fig. 2 ya ◯ 40 40 40 40 40 θb ◯ 70 85 80 80 80 θc ◯ 90 90 90 90 90 Size ratio between θa and θb θa < θb θa < θb θa < θb θa < θb θa < θb L / TW × 100 % 30 30 30 30 30 Position of the narrow circumferential groove Not continuous Not continuous Ongoing Ongoing Ongoing Difference (α - θa) ◯ 90 90 90 80 100 Groove depth of the second groove section mm 22 22 22 22 22 Groove depth of the first groove section % 40 40 40 40 40 Groove depth of the narrow circumferential groove % 70 70 70 70 70 tread rubber hardness 60 60 60 60 60 Module of the tread rubber MPa 1,9 1,9 1,9 1,9 1,9 Traction performance Index value 106 109 111 114 114 Low noise performance Index value 111 109 110 113 113 [Table 3-I] Example 15 Example 16 Example 17 Example 18 Tread pattern Fig. 2 Fig. 2 Fig. 2 Fig. 2 ya ◯ 40 40 40 40 θb ◯ 80 80 80 80 θc ◯ 90 90 90 90 Size ratio between θa and θb θa < θb θa < θb θa < θb θa < θb L / TW × 100 % 30 30 30 30 Position of the narrow circumferential groove Ongoing Ongoing Ongoing Ongoing Difference (α - θa) ◯ 90 90 90 90 Groove depth of the second groove section mm 15 25 22 22 Groove depth of the first groove section % 40 40 65 75 Groove depth of the narrow circumferential groove % 70 70 70 75 tread rubber hardness 60 60 60 60 tread rubber module MPa 1,9 1,9 1,9 1,9 Traction performance Index value 114 114 117 114 Low noise performance Index value 114 112 113 109 [Table 3-II] Example 19 Example 20 Example 21 Example 22 Tread pattern Fig. 2 Fig. 2 Fig. 2 Fig. 2 ya ◯ 40 40 40 40 θb ◯ 80 80 80 80 θc ◯ 90 90 90 90 Size ratio between θa and θb θa < θb θa < θb θa < θb θa < θb L / TW × 100 % 30 30 30 30 Position of the narrow circumferential groove Ongoing Ongoing Ongoing Ongoing Difference (α - θa) ◯ 90 90 90 90 Groove depth of the second groove section mm 22 22 22 22 Groove depth of the first groove section % 70 70 70 70 Groove depth of the narrow circumferential groove % 85 85 85 80 tread rubber hardness 60 61 65 63 tread rubber module MPa 1,9 2 2,8 2,4 Traction performance Index value 116 117 120 118 Low noise performance Index value 111 113 109 111

[0046] As can be seen from Tables 1 to 3, all of the examples 1 to 22 improved the traction performance and the noise reduction performance compared to those of the prior art example 1.

[0047] On the other hand, in comparison example 1, the average angle of the second groove segments of the lug grooves was constant throughout, and the lug grooves were not curved or bent, thus impairing noise reduction performance. In comparison example 2, the shape of the lug grooves was unsuitable, and the angle of the lug grooves gradually increased towards the center of the tire. Consequently, the effects of improved traction and noise reduction performance were not achieved. List of reference symbols 1 tread section 2 Side wall section 3 bead section 4 Carcass layer 5 bead core 6 bead fillers 7th belt layer 20, 30 cleat groove 21, 31 First groove section 22, 32 Second groove section 40 Narrow circumferential groove 51 Middle Block 52 Shoulder block An inner area B Outer area CL tire equator E tread edge

Claims

[1] A pneumatic tire in which a direction of rotation is provided, comprising: a tread portion (1) extending in the tire circumferential direction and forming a ring shape; a pair of sidewall portions (2) arranged on both sides of the tread portion (1); a pair of bead portions (3) which are formed by the sidewall sections (2) are arranged inwards in the tire radial direction; wherein lug grooves (20) extending inward in the tire width direction from a tread edge (E) on one side of a tire equator (CL) and intersecting with the tire equator (CL), and lug grooves (30) extending inward in the tire width direction from a tread edge (E) on another side of the tire equator (CL) and intersecting with the tire equator (CL) are arranged alternately in the tire circumferential direction on an outer surface of the tread portion (1); wherein the respective lug grooves (20, 30) include first groove portions (21, 31) and second groove portions (22, 32), wherein the first groove portion (21, 31) intersects with the tire equator (CL) and extends along the tire width direction, wherein the second groove portion (22, 32) is inclined from one end of the first groove portion (21, 31) at an angle with respect to the tire circumferential direction that is smaller than an angle of the first groove portion (21, 31) with respect to the tire circumferential direction and extends to the tread edge (E), wherein the first groove portion (21, 31) has another end connected to the second groove portion (22, 32) of the lug groove (20, 30) adjacent in the tire circumferential direction, wherein the first groove portion (21, 31) is located on a entering side with respect to an end portion on the tread edge side of the lug groove (20, 30); wherein, when a distance from the tire equator (CL) to the tread edge (E) is referred to as W, a region between a position separated by 0.50 W in the tire width direction from the tire equator (CL) and the tire equator (CL) is referred to as an inner region (A), and a region between the position separated by 0.50 W in the tire width direction from the tire equator (CL) and the tread edge (E) is referred to as an outer region (B), the second groove portions (22, 32) are curved or bent such that an average angle (θa) of the second groove portions (22, 32) with respect to the tire circumferential direction in the inner region (A) becomes smaller than an average angle (θb) of the second groove portions (22, 32) with respect to the tire circumferential direction in the outer region (B), wherein the second groove portion (22, 32) the lug groove (20, 30) has a groove depth of 15 mm to 25 mm; and wherein narrow circumferential grooves (40) connecting the mutual second groove portions (22, 32) adjacent in the tire circumferential direction on one side or the other side of the tire equator (CL) are formed, wherein the narrow circumferential grooves (40) are present at an extended position of the first groove portions (21, 31), and a difference between an average angle (θa) of the second groove portions (22, 32) with respect to the tire circumferential direction in the inner region (A) and an inclination angle (α) of the narrow circumferential groove (40) with respect to the tire circumferential direction is within a range of 90° ± 10°, wherein center blocks (51) at positions intersecting with the tire equator (CL) are determined by the lug grooves (20, 30) and the narrow circumferential grooves (40), wherein a maximum length (L) in Tire width direction of the center block (51) is 25% to 35% of a development width (TW). [2] A pneumatic tire according to claim 1, wherein an angle (θc) of the first groove portion (21, 31) with respect to the tire circumferential direction is 80° to 100°. [3] A pneumatic tire according to claim 1 or 2, wherein the average angle (θa) of the second groove portions (22, 32) with respect to the tire circumferential direction in the inner region (A) is 35° to 45°, and the average angle (θb) of the second groove portions (22, 32) with respect to the tire circumferential direction in the outer region (B) is 70° to 85°. [4] A pneumatic tire according to any one of claims 1 to 3, wherein a groove depth of the first groove portion (21, 31) of the lug groove (20, 30) is 65% to 75% of a groove depth of the second groove portion (22, 23). [5] A pneumatic tire according to any one of claims 1 to 4, wherein a groove depth of the narrow circumferential groove (40) is 75% to 85% of a groove depth of the second groove portion (22, 32) of the lug groove (20, 30). [6] A pneumatic tire according to any one of claims 1 to 5, wherein a tread rubber (11) constituting the tread portion (1) has a JIS-A hardness of 61 to 70 and a 100% elongation modulus of 2.0 MPa to 3.0 MPa.

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