Tire

Abstract

Provided is a tire with which snow performance can be improved without impairing wear resistance. A tread portion 1 is provided with a center land portion 12c, intermediate land portions 12m, and shoulder land portions 12s that are demarcated by four main grooves 11 extending linearly in the circumferential direction of the tire, wherein: the center land portion 12c is demarcated into a plurality of center blocks 14c by center inclined grooves 13c; each intermediate land portion 12m is demarcated into a plurality of intermediate blocks 14m by intermediate inclined grooves 13m; a shoulder circumferential narrow groove 20, first shoulder lateral grooves 21 that are connected to the shoulder circumferential narrow groove 20 and that do not reach the main groove 11, and second shoulder lateral grooves 22 that open in the main groove 11, intersect the shoulder circumferential narrow groove 20, and terminate in a land portion are provided in each shoulder land portion 12s; and two or more sipes 16 that extend in the width direction of the tire are provided in main parts of each of the center block 14c, the intermediate blocks 14m, and the shoulder land portions 12s.

Description

tire

[0001] The present invention relates to a tire having a block-based tread pattern, and more particularly to a tire that enables improved snow performance without sacrificing wear resistance.

[0002] Among tires for vehicles such as SUVs, "highway terrain tires" are known as a category of tires designed specifically for high-speed driving. Tires in this category have a block-based pattern and are required to be able to handle a variety of road conditions (dry, wet, and snowy roads) (see, for example, Patent Document 1). In recent years, emphasis has been placed on snow performance (driving stability on snow-covered roads). For example, increasing the groove area can improve snow performance by making it easier for the tires to grip snow. However, as mentioned above, because tires in this category have a block-based pattern, increasing the groove area can easily reduce the rigidity of the land portion, making it difficult to ensure sufficient wear resistance. Therefore, measures are needed to improve snow performance without compromising wear resistance.

[0003] Japanese Patent Application Publication No. 2019-137218

[0004] An object of the present invention is to provide a tire that enables improved snow performance without impairing wear resistance.

[0005] The tire of the present invention for achieving the above object is a tire having a tread portion extending in a circumferential direction of the tire and forming an annular shape, the tread portion having four main grooves extending linearly along the tire circumferential direction and five rows of land portions defined by these four main grooves, the five rows of land portions including a center land portion disposed on the tire equator, intermediate land portions disposed on both sides of the center land portion in the tire width direction, and shoulder land portions located on the outermost sides in the tire width direction, the center land portion being defined into a plurality of center blocks by center oblique grooves formed at intervals in the tire circumferential direction, the intermediate land portion being defined into a plurality of intermediate blocks by intermediate oblique grooves formed at intervals in the tire circumferential direction, the shoulder land portions being defined by shoulder circumferential narrow grooves extending in the tire circumferential direction parallel to the main grooves located on the outermost sides in the tire width direction, and first shoulder lateral grooves extending in the tire width direction. and a second shoulder lateral groove, the first shoulder lateral groove has an outer end in the tire width direction that opens beyond the ground contact edge and an inner end in the tire width direction that connects to the shoulder circumferential narrow groove and terminates without reaching the main groove, the second shoulder lateral groove has a groove width smaller than that of the first shoulder lateral groove and extends at an angle with respect to the tire width direction, the inner end in the tire width direction connects to the main groove and the outer end in the tire width direction intersects with the shoulder circumferential narrow groove and terminates within the shoulder land portion, two or more sipes extending along the tire width direction are formed in the center block and the intermediate block at intervals in the tire circumferential direction, and two or more sipes extending along the tire width direction are formed at intervals in the tire circumferential direction in each of areas in the shoulder land portion that are surrounded by the shoulder circumferential narrow groove and a pair of the first shoulder lateral grooves adjacent in the tire circumferential direction.

[0006] The tire of the present invention has a tread pattern configured as described above, thereby improving snow performance without sacrificing wear resistance. Specifically, the four main grooves extend linearly, ensuring rigidity at the widthwise ends of each block and ensuring wear resistance and uneven wear resistance. The grooves (center oblique groove, intermediate oblique groove) that separate the center land portion and the intermediate land portion are inclined relative to the tire width direction, improving snow performance. Furthermore, the shoulder land portion is formed with a shoulder circumferential narrow groove, a first shoulder lateral groove, and a second shoulder lateral groove. While the first shoulder lateral groove ensures snow performance, the first shoulder lateral groove does not reach the main groove and connects to the shoulder circumferential narrow groove, thereby forming a land portion that extends continuously substantially around the entire tire circumference between the outermost main groove in the tire width direction and the shoulder circumferential narrow groove, thereby ensuring block rigidity. The second shoulder lateral grooves extend from the main grooves across the shoulder circumferential narrow grooves in the tire width direction. However, because the second shoulder lateral grooves are narrower than the first shoulder lateral grooves, block rigidity is not compromised, and the second shoulder lateral grooves are expected to further improve snow performance. In addition, snow performance can be improved by providing an appropriate number of sipes extending in the tire width direction in each block and land portion. These cooperations enable a high level of both wear resistance and snow performance.

[0007] In the present invention, it is preferable that the inner end of the first shoulder lateral groove has a tapered shape in which the groove width narrows toward the shoulder circumferential narrow groove. By having the first shoulder lateral groove have such a tapered shape, it is possible to suppress a decrease in rigidity of the shoulder land portion (particularly in the vicinity of the shoulder circumferential narrow groove) due to the formation of the first shoulder lateral groove, which is advantageous for ensuring wear resistance.

[0008] In the present invention, it is preferable that the groove depth Dc of the shoulder circumferential narrow groove, the groove depth D1 of the first shoulder lateral groove, and the groove depth D2 of the second shoulder lateral groove satisfy the relationship Dc≦D2<D1, which provides a good balance between the snow performance provided by each groove and the reduced block rigidity caused by the formation of each groove, and is advantageous for achieving both snow performance and wear resistance.

[0009] In the present invention, it is preferable that the center block has a center shallow groove at an extension position of the intermediate oblique groove, extending in the same direction as the intermediate oblique groove and terminating within the center block without crossing the tire equator. When the center shallow groove is provided at an extension position of the intermediate oblique groove and extending in the same direction as the intermediate oblique groove, the intermediate oblique groove and the center shallow groove function as a continuous groove, effectively improving snow performance. On the other hand, since the center shallow groove has a groove depth smaller than that of the main groove and terminates within the center block without crossing the tire equator, a decrease in block rigidity due to the center shallow groove is suppressed, and wear resistance can be ensured.

[0010] In the present invention, it is preferable that an intermediate shallow groove be provided between circumferentially adjacent sipes in the intermediate block, the intermediate shallow groove opening into the main groove located at the outermost side in the tire width direction, extending in the same direction as the intermediate oblique groove, and terminating within the intermediate block without passing beyond the tire width center of the intermediate block. This provides an edge effect due to the intermediate shallow groove, further improving snow performance. On the other hand, because the intermediate shallow groove has a groove depth smaller than the main groove and terminates within the intermediate block without passing beyond the center of the intermediate block, a decrease in block rigidity due to the intermediate shallow groove is suppressed, and wear resistance can be ensured.

[0011] In the present invention, it is preferable to provide a raised portion at the bottom of each of the center oblique groove and the intermediate oblique groove, which can maintain block rigidity without reducing the groove area, and is advantageous for achieving both snow performance and wear resistance.

[0012] In the present invention, it is preferable that the intermediate sipes formed in the intermediate blocks extend in the same direction as the intermediate inclined grooves, the center sipes formed in the center blocks extend in the same direction as the center inclined grooves, and the shoulder sipes formed in the shoulder land portions extend in the same direction as the first shoulder lateral grooves. By inclining the inclined grooves and sipes in each block in the same manner, block rigidity can be ensured, which is advantageous for maintaining wear resistance.

[0013] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases.

[0014] Fig. 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention, Fig. 2 is a front view showing a tread surface of a tire according to an embodiment of the present invention, and Fig. 3 is an explanatory view showing a part of Fig. 2.

[0015] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0016] When the tire of the present invention is a pneumatic tire as shown in Figure 1, it comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In Figure 1, the symbol CL denotes the tire equator, and the symbol E denotes the ground contact edge. Although not depicted in Figure 1 because it is a meridian cross section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend circumferentially in the tire direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be basically based on the meridian cross section shown, but each tire component also extends circumferentially in the tire direction and forms an annular shape.

[0017] In addition, if the tire is a pneumatic tire, the contact edge E is the end in the tire width direction of the contact area formed when the tire is mounted on a regular rim, inflated to the regular internal pressure, placed vertically on a flat surface, and subjected to a regular load. A "regular rim" is a rim determined for each tire by the standard system that includes the standard on which the tire is based, and is, for example, a standard rim for JATMA, a "Design Rim" for TRA, or a "Measuring Rim" for ETRTO. "Normal internal pressure" refers to the air pressure determined for each tire by the respective standards, including the standards on which the tire is based, and is the maximum air pressure in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO, but is set to 180 kPa when the tire is for a passenger car. The "normal load" is the load determined for each tire by the respective standards, including the standards on which the tire is based, and is the maximum load capacity in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO. However, if the tire is for a passenger car, it is a load equivalent to 88% of the above load.

[0018] A carcass layer 4 is installed between a pair of left and right bead portions 3. The carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around bead cores 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of each bead core 5, and this bead filler 6 is wrapped by the main portion and folded back portion of the carcass layer 4. Meanwhile, multiple belt layers 7 (two layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, at least one belt reinforcing layer 8 (two layers in FIG. 1 ) is provided on the outer periphery of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction.

[0019] As described below, the present invention relates to a tread pattern formed on the surface of the tire tread portion 1, and therefore the basic structure (cross-sectional structure) of the tire is not limited to the general structure described above. Furthermore, the following description will be based on the pneumatic tire shown in Fig. 1 etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as they have a surface that comes into contact with the road surface (a region corresponding to the surface of the tread portion 1 in a pneumatic tire).

[0020] As shown in FIG. 2 , the surface of the tread portion 1 of the tire of the present invention is provided with four main grooves 11 extending linearly along the tire circumferential direction. In the following description, pairs of the four main grooves 11, one on each side of the tire equator CL, may be referred to as inner main grooves 11i, and pairs of the four main grooves 11 arranged on the outer side of each inner main groove 11i in the tire width direction, may be referred to as outer main grooves 11o. The depth of each main groove 11 is not particularly limited, but may be set to, for example, 7.0 mm to 16.0 mm. Because the four main grooves 11 extend linearly in this manner, rigidity can be ensured at the widthwise ends of the land portions 12 (blocks) described below, and wear resistance and uneven wear resistance can be ensured.

[0021] These four main grooves 11 define five rows of land portions 12 extending along the tire circumferential direction. Specifically, the rows define a center land portion 12c defined between a pair of inner main grooves 11i, an intermediate land portion 12m defined between the inner main groove 11i and the outer main groove 11o, and shoulder land portions 12s defined on the outer side of the outer main groove 11o in the tire width direction. In other words, the center land portion 12c is a land portion located on the tire equator CL, the intermediate land portions 12m are land portions located adjacent to the center land portion 12c on both sides of the tire width direction with the inner main groove 11i in between, and the shoulder land portions 12s are land portions located on the outermost sides in the tire width direction, including the ground contact edge E.

[0022] The center land portion 12c is divided into a plurality of center blocks 14c by center inclined grooves 13c formed at intervals in the tire circumferential direction. The intermediate land portion 12m is divided into a plurality of intermediate blocks 14m by intermediate inclined grooves 13m formed at intervals in the tire circumferential direction. The center inclined groove 13c extends at an angle with respect to the tire width direction, and both ends thereof open into a pair of inner main grooves 11i arranged on both sides of the center land portion 12c. The intermediate inclined groove 13m extends at an angle with respect to the tire width direction, and both ends thereof open into the inner main groove 11i and the outer main groove 11o arranged on both sides of the intermediate land portion 12m. The center inclined groove 13c and the intermediate inclined groove 13m are preferably inclined in opposite directions with respect to the tire width direction. As shown in the illustrated example, the center oblique groove 13c extends linearly, while the intermediate oblique groove 13m is preferably curved. (In the illustrated example, the intermediate oblique groove 13m has a zigzag shape consisting of a first portion that opens into the inner main groove 11i and extends linearly at an angle relative to the tire width direction, a second portion that extends linearly in the same direction as the first portion and opens into the outer main groove 11o, and a third portion that connects the first and second portions and is inclined in the opposite direction to the first and second portions.) In the following description, the center oblique groove 13c and the intermediate oblique groove 13m may be collectively referred to as "inclined grooves." These inclined grooves can improve snow performance. In particular, if the center oblique groove 13c and the intermediate oblique groove 13m are inclined in opposite directions or if the intermediate oblique groove 13m has the above-mentioned curved shape, an edge effect can be exerted in various directions, effectively improving snow performance.

[0023] The inclination angle of each inclined groove can be set to, for example, 10° to 50° with respect to the tire width direction. Specifically, the inclination angle θc of the center inclined groove 13c with respect to the tire width direction can be set to preferably 10° to 50°, more preferably 10° to 30°. The inclination angle θm of the intermediate inclined groove 13m with respect to the tire width direction, where the inclination direction of the aforementioned center inclined groove 13c is expressed as a positive (+) value, can be set to preferably -10° to -50°, more preferably -10° to -30°. The inclination angles θc and θm may be the same angle with the inclination direction (positive and negative) reversed, but it is preferable to set the absolute value of the inclination angle θm greater than the absolute value of the inclination angle θc. By inclining the intermediate inclined groove 13m with respect to the tire width direction more than the center inclined groove 13c in this way, snow performance can be effectively improved. As shown in FIG. 3, the inclination angles θc and θm are the angles formed by a straight line connecting the groove width centers at the opening ends of each inclined groove with respect to the tire width direction.

[0024] The groove depth of each of the inclined grooves is preferably set to 20% to 100%, more preferably 50% to 100%, of the groove depth of the main groove 11 .

[0025] The shoulder land portion 12s is formed with a shoulder circumferential narrow groove 20 extending in the tire circumferential direction, and a first shoulder lateral groove 21 and a second shoulder lateral groove 21 extending in the tire width direction. More specifically, the shoulder circumferential narrow groove 20 extends in the tire circumferential direction parallel to the main groove 11 located on the outermost side in the tire width direction (i.e., the outer main groove 11o), and a continuous rib 23 extending continuously around substantially the entire tire circumference is formed between the outer main groove 11o and the shoulder circumferential narrow groove 20. The outer end of the first shoulder lateral groove 21 in the tire width direction opens beyond the ground contact edge E, and the inner end in the tire width direction connects to the shoulder circumferential narrow groove 20. The first shoulder lateral groove 21 is discontinued by connecting to the shoulder circumferential narrow groove 20, and does not reach the continuous rib 23 or the outer main groove 11o. The second shoulder lateral grooves 22 extend at an angle relative to the tire width direction so as to intersect with the shoulder circumferential narrow groove 20. Their inner ends connect to the outer main groove 11o, and their outer ends terminate within the shoulder land portion 12s. Because the shoulder circumferential narrow groove 20 and the second shoulder lateral groove 22 have narrower groove widths than the first shoulder lateral groove 21, the areas defined by the shoulder circumferential narrow groove 20 and the second shoulder lateral groove 22 are not completely separated compared to the areas defined by the first shoulder lateral groove 21, maintaining block rigidity. Snow performance is ensured by the edge effect of each groove formed in the shoulder land portion 12s. As described above, the first shoulder lateral groove 21 does not reach the outer main groove 11o, forming a continuous rib 23, thereby ensuring block rigidity. Because the shoulder circumferential narrow groove 20 and the second shoulder lateral groove 22 have narrow groove widths, block rigidity is not significantly reduced even when these grooves apparently define land portions, ensuring wear resistance.

[0026] As described above, the shoulder circumferential narrow groove 20 and the second shoulder lateral groove 22 have smaller groove widths than the first shoulder lateral groove 21. However, when the groove width of the shoulder circumferential narrow groove 20 is Gc, the groove width of the first shoulder lateral groove 21 is G1, and the groove width of the second shoulder lateral groove 22 is G2, the groove width G1 of the first shoulder lateral groove 21 is preferably 1.5 to 3.0 times, and more preferably 1.8 to 2.7 times, the groove width Gc of the shoulder circumferential narrow groove 20 or the groove width G2 of the second shoulder lateral groove 22. In the case of a tapered shape described below, the groove width G1 of the first shoulder lateral groove is the groove width at the main portion excluding the narrow portion.

[0027] Furthermore, when the groove depth of the shoulder circumferential narrow groove 20 is Dc, the groove depth of the first shoulder lateral groove 21 is D1, and the groove depth of the second shoulder lateral groove 22 is D2, it is preferable that these groove depths satisfy the relationship Dc≦D2<D1. This achieves a good balance between the snow performance added by each groove and the block rigidity reduced by the formation of each groove, which is advantageous for achieving both snow performance and wear resistance. While the specific groove depth is not particularly limited, the groove depth D1 of the first shoulder lateral groove 21 is preferably 60% to 100%, more preferably 70% to 90%, of the groove depth of the main groove 11. The groove depth Dc of the shoulder circumferential narrow groove 20 and the groove depth D2 of the second shoulder lateral groove 22 are preferably 20% to 70%, more preferably 30% to 60% of the groove depth of the main groove 11.

[0028] The angle θ1 of the first shoulder lateral groove relative to the tire width direction can be preferably set to 0°±15°, more preferably 0°±10°. The inclination angle θ2 of the second shoulder lateral groove relative to the tire width direction can be preferably set to 10° to 50°, more preferably 10° to 30° (when the inclination direction of the center inclined groove 13c is expressed as a positive (+) value, it is preferably set to −10° to −50°, more preferably −10° to −30°). These angles θ1 and θ2, like the inclination angles θc and θm, are measured as the angle formed with a straight line connecting the groove width center at the opening end of the main groove 11 or shoulder circumferential narrow groove 20 to the groove width center at the ground contact edge E or at the terminal end, relative to the tire width direction.

[0029] Two or more sipes 16, preferably two to four sipes, extending along the tire width direction are formed at intervals in the tire circumferential direction in each of the center blocks 14c and intermediate blocks 14m. In the shoulder land portions 12s, two or more sipes, preferably two to four sipes 16, extending along the tire width direction are formed at intervals in the tire circumferential direction in each region surrounded by a pair of circumferentially adjacent first shoulder lateral grooves 21 and shoulder circumferential narrow grooves 20. The shape of each sipe 16 is not particularly limited, but it is preferable for each block or land portion to have a zigzag shape on the tread surface as shown in the figure. The groove width of these sipes 16 can be set to, for example, 1.5 mm or less, and the groove depth of these sipes 16 can be set to, for example, 50% to 100% of the groove depth of the main groove 11. By appropriately providing sipes 16 in each block or land portion in this manner, snow performance can be effectively improved.

[0030] Since the tire of the present invention has a tread pattern configured as described above, the above-mentioned effects of each element (ensuring wear resistance with the four straight main grooves 11, improving snow performance with the center inclined groove 13c and intermediate inclined grooves 13m, maintaining wear resistance and improving snow performance with the shoulder circumferential narrow grooves 20, first shoulder lateral grooves 21, and second shoulder lateral grooves 22 provided in the shoulder land portion 12s, and improving snow performance with the sipes 16) work together to achieve a high level of both wear resistance and snow performance.

[0031] The groove width of the first shoulder lateral grooves 21 does not need to be constant. Preferably, at least some, and preferably all, of the multiple first shoulder lateral grooves 21 have a tapered shape in which the groove width narrows toward the shoulder circumferential narrow groove 20 at the inner end in the tire width direction. The tapered shape may be a structure in which the groove width converges toward the groove tip (a V-shaped end), or, as in the illustrated example, a shape that includes a narrow portion where the first shoulder lateral groove 21 connects to the shoulder circumferential narrow groove 20 and a connecting portion where the groove width gradually decreases from the main portion of the first shoulder lateral groove 21 toward the narrow portion. When a narrow portion is present as in the illustrated example, the groove width at this narrow portion is preferably 0.5 to 2.0 times the groove width of the shoulder circumferential groove 20. The length of the narrow portion is preferably 0% to 30% of the tire width length from the shoulder circumferential groove 20 to the ground contact edge E. By tapering the first shoulder lateral grooves 21 in this way, it is possible to suppress a decrease in rigidity of the shoulder land portion 12s (particularly in the vicinity of the shoulder circumferential narrow grooves 20) due to the formation of the first shoulder lateral grooves 21, which is advantageous for ensuring wear resistance.

[0032] At the extension position of the intermediate oblique groove 13m in the center block 14c, a center shallow groove 15c can be formed, extending in the same direction as the intermediate oblique groove 13m and terminating within the center block 14c without crossing the tire equator CL. The center shallow groove 15c has a smaller groove depth than the main groove 11 and the oblique grooves (particularly the intermediate oblique groove 13m), and its groove depth is preferably set to 10% to 80%, more preferably 30% to 60%, of the groove depth of the main groove 11. The extension position of the intermediate oblique groove 13m is a position where at least a portion of the opening end of the intermediate oblique groove 13m overlaps with the region (hatched area in FIG. 3 ) between the extension lines of the groove walls (dashed lines in FIG. 3 ). By providing the center shallow groove 15c in this manner, the intermediate oblique groove 13m and the center shallow groove 15c function as a continuous groove, effectively improving snow performance. On the other hand, since the center shallow groove 15c has a groove depth smaller than that of the main groove 11 and terminates within the center block 14c without exceeding the tire equator CL, the provision of the center shallow groove 15c suppresses a decrease in block rigidity and ensures wear resistance.

[0033] Although the shape of the center shallow grooves 15c is not particularly limited, it is preferable that at least some, and preferably all, of the plurality of center shallow grooves 15c have a tapered shape in which the groove width narrows toward the end. The tapered shape may be a structure in which the groove width converges toward the tip of the groove (a V-shaped end), or, as shown in the example, a shape that includes a narrow portion at the end where the groove width is narrow and a connecting portion where the groove width gradually decreases from the main portion of the center shallow groove 15c toward the narrow portion. Providing such a tapered center shallow groove 15c can prevent a decrease in the rigidity of the center block 14c due to the formation of the center shallow groove 15c, which is advantageous for ensuring wear resistance.

[0034] Between adjacent sipes 16 in the tire circumferential direction, intermediate shallow grooves 15m can be formed in the intermediate blocks 14m. The intermediate shallow grooves 15m open into the main grooves 11 (outer main grooves 11o) located on the outermost side in the tire width direction, extend in the same direction as the intermediate oblique grooves 13m, and terminate within the intermediate blocks 14m without passing the tire width center of the intermediate blocks 14m. The intermediate shallow grooves 15m have a groove depth smaller than that of the main grooves 11 and the oblique grooves (particularly the intermediate oblique grooves 13m), and their groove depth is preferably set to 10% to 80%, more preferably 30% to 60%, of the groove depth of the main grooves 11. By providing the intermediate shallow grooves 15m in this manner, the edge effect of the intermediate shallow grooves 15m can be added, further improving snow performance. Meanwhile, because the intermediate shallow grooves 15m have a groove depth smaller than that of the main grooves 11 and terminate within the intermediate blocks 14m without passing the center of the intermediate blocks 14m, a decrease in block rigidity due to the provision of the intermediate shallow grooves 15m can be suppressed, and wear resistance can be ensured.

[0035] The sipes 16 formed in each block (center block 14c, intermediate block 14m) and land portion (shoulder land portion 12s) preferably extend in the same direction as the grooves (center inclined groove 13c, intermediate inclined groove 13m, first shoulder lateral groove 21) that define each block or land portion. Specifically, the intermediate sipes 16m formed in the intermediate block 14m preferably extend in the same direction as the intermediate inclined groove 13m, the center sipes 16c formed in the center block 14c preferably extend in the same direction as the center inclined groove 13c, and the shoulder sipes 16s formed in the shoulder land portion 12s preferably extend in the same direction as the first shoulder lateral groove 21. Having the grooves extending in the width direction of each block or land portion and the sipes 16 extend approximately parallel to each other ensures block rigidity, which is advantageous for maintaining wear resistance. If the inclination directions of these grooves and sipes 16 are opposite, it becomes difficult to maintain good block rigidity. In addition, the angle difference between the grooves (center inclined groove 13c, intermediate inclined groove 13m, first shoulder lateral groove 21) extending in the width direction in each block and the sipes (center sipe 16c, intermediate sipe 16m, shoulder sipe 16s) is preferably 0° to 10°, more preferably 0° to 5°.

[0036] In the present invention, the center oblique groove 13c, the intermediate oblique groove 13m, and the first shoulder lateral groove 21 may each have a raised bottom portion A at their bottom. The raised bottom portion A is a portion of each groove where the groove bottom is raised higher than other portions. The raised bottom portion A may be provided at a position where each groove communicates with a groove (main groove 11 or shoulder circumferential narrow groove 20) extending along the tire circumferential direction. When the raised bottom portion A is provided at a position where it communicates with the main groove 11, the raised bottom portion A should preferably be 20% to 80%, more preferably 40% to 60%, of the depth of the main groove 11. When the raised bottom portion A is provided at a position where it communicates with the shoulder circumferential narrow groove 20, the groove depth at the raised bottom portion A should be equal to or less than that of the shoulder circumferential narrow groove 20. Specifically, the raised bottom portion A should preferably be 10% to 50%, more preferably 20% to 30%, of the depth of the main groove 11. The raised-bottom amount is the height of the groove from the bottom of the groove in which the raised-bottom portion A is formed to the top surface of the raised-bottom portion A. By providing the raised-bottom portion A in this manner, block rigidity can be maintained without reducing the groove area, which is advantageous for achieving both snow performance and wear resistance. If the raised-bottom amount is below the above-mentioned range, there is no substantial difference from when the raised-bottom portion A is not present, and the effect of the raised-bottom portion A cannot be fully expected. If the raised-bottom amount exceeds the above-mentioned range, the groove depth cannot be sufficiently ensured in the area in which the raised-bottom portion A is provided, making it difficult to ensure sufficient snow performance.

[0037] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

[0038] Eight types of pneumatic tires (Conventional Example 1, Comparative Example 1, and Examples 1 to 6) were manufactured, each having a tire size of 265 / 70R17 115H and the basic structure (cross-sectional structure) illustrated in FIG. 1 . The following settings were made as shown in Table 1: the inclination angle θc of the center oblique groove, the inclination angle θm of the intermediate oblique groove, the presence or absence of shoulder circumferential narrow grooves, the presence or absence of first shoulder lateral grooves, the presence or absence of second shoulder lateral grooves, the number of sipes in each land portion (center block, intermediate block, and shoulder land portion), the groove depth of each groove (shoulder circumferential narrow groove, first shoulder lateral groove, and second shoulder lateral groove) formed in the shoulder land portion, the shape of the first shoulder lateral groove, the presence or absence of a center shallow groove, the presence or absence of an intermediate shallow groove, the presence or absence of a bottom-up portion in each oblique groove (center oblique groove, intermediate oblique groove), and the angle difference between the groove (center oblique groove, intermediate oblique groove, and first shoulder lateral groove) and the sipe in each block or land portion.

[0039] All examples had four straight main grooves. The angle of the first shoulder lateral groove was 0° relative to the tire width direction, and the angle of the second shoulder lateral groove, if provided, was the same as the angle θm of the intermediate oblique groove. The groove width of the shoulder circumferential narrow groove was 2 mm, the groove width of the first shoulder lateral groove was 5 mm, and the groove width of the second shoulder lateral groove was 2 mm. When the first shoulder lateral groove had a tapered shape, the groove width at its narrow portion was 2 mm. Note that Conventional Example 1 does not have a shoulder circumferential narrow groove or a second shoulder lateral groove, so the shoulder land portion is divided into multiple blocks by the first shoulder lateral groove and has a structure that does not include a "continuous rib" as shown in Figure 2.

[0040] In Table 1, the "Center Slant Groove Angle θc" and "Intermediate Slant Groove Angle θm" columns indicate the center slant groove angle θc as a positive (+) value (a negative (-) value indicates an angle opposite to that of the center slant groove). In the "Number of Sipes in Shoulder Land Portion" column, when the shoulder land portion is divided into multiple blocks (Conventional Example 1), the number of sipes in each block is listed. For Examples 1 to 6, the number of sipes included in the region surrounded by a pair of circumferentially adjacent first shoulder lateral grooves and shoulder circumferential narrow grooves is listed. Comparative Example 1 does not have a first shoulder lateral groove and therefore does not include a divided region like Examples 1 to 6. However, since the sipe arrangement is the same as Examples 1 to 6 except for the absence of a first shoulder lateral groove, the same values ​​as Examples 1 to 6 are listed in parentheses for reference. The "Groove Depth" column indicates the percentage (%) of the main groove depth. In the column "Shape of first shoulder lateral groove," a groove with a constant width is labeled "Constant width," and a tapered shape is labeled "Tapered." In the column "Presence or absence of raised bottom portion," examples labeled "Present" indicate that each groove has a raised bottom portion or a narrowed width portion, as shown in Figure 2.

[0041] The snow performance and wear resistance of these pneumatic tires were evaluated by the following evaluation methods, and the results are shown in Table 1.

[0042] Snow Performance Each test tire was mounted on a wheel with a rim size of 17x8J, and the front tire and rear tire were inflated to an air pressure of 230 kPa and mounted on a test vehicle (four-wheel drive SUV). A test driver then conducted a sensory evaluation of the handling stability on a test course consisting of a snowy road surface. The evaluation results were expressed as an index, with Conventional Example 1 being given a value of 100. A higher index value indicates better snow performance.

[0043] Wear Resistance Each test tire was mounted on a wheel with a rim size of 17x8J, and the front tire and rear tire were air-pressurized to 230 kPa and 230 kPa, respectively, and mounted on a test vehicle (four-wheel drive SUV). A test driver drove the tire on a test course, measuring the distance traveled (unit: km) until complete wear. The evaluation results were expressed as an index, with the value of Conventional Example 1 being 100. The larger the index value, the longer the distance traveled until complete wear, indicating superior wear resistance.

[0044]

[0045] As is clear from Table 1, the pneumatic tires of Examples 1 to 6 had improved snow performance and wear resistance, achieving a good balance between these performances, compared to Conventional Example 1. On the other hand, Comparative Example 1 had worse snow performance because it had shoulder circumferential narrow grooves and second shoulder lateral grooves in the shoulder land portion but no first shoulder lateral grooves.

[0046] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 11 main groove 11i inner main groove 11o outer main groove 12 land portion 12c center land portion 12m intermediate land portion 12s shoulder land portion 13c center inclined groove 13m intermediate inclined groove 14c center block 14m intermediate block 15 shallow groove 16 sipe 16c center sipe 16m intermediate sipe 16s shoulder sipe 20 shoulder circumferential narrow groove 21 first shoulder lateral groove 22 second shoulder lateral groove 23 continuous rib A bottom raised portion B narrow width portion CL tire equator E ground contact edge

Claims

1. A tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, the tread portion having four main grooves extending linearly along the tire circumferential direction and five rows of land portions defined by these four main grooves, the five rows of land portions including a center land portion disposed on the tire equator, intermediate land portions disposed on both sides of the center land portion in the tire width direction, and shoulder land portions located on the outermost sides in the tire width direction, the center land portion being defined into a plurality of center blocks by center inclined grooves formed at intervals in the tire circumferential direction, the intermediate land portion being defined into a plurality of intermediate blocks by intermediate inclined grooves formed at intervals in the tire circumferential direction, the shoulder land portions being formed with shoulder circumferential narrow grooves extending along the tire circumferential direction in parallel with the main grooves located on the outermost sides in the tire width direction, and first shoulder lateral grooves and second shoulder lateral grooves extending along the tire width direction, the first shoulder lateral grooves having an outer end in the tire width direction that is open beyond the ground contact edge, and an inner end in the tire width direction that is connected to and discontinued by the shoulder circumferential narrow grooves without reaching the main grooves, the second shoulder lateral groove has a groove width smaller than that of the first shoulder lateral groove, extends at an angle with respect to the tire width direction, has an inner end in the tire width direction connected to the main groove and an outer end in the tire width direction intersects with the shoulder circumferential narrow groove and terminates within the shoulder land portion, two or more sipes extending along the tire width direction are formed in the center block and the intermediate block at intervals in the tire circumferential direction, and two or more sipes extending along the tire width direction are formed at intervals in the tire circumferential direction in each of areas surrounded by the shoulder circumferential narrow groove and a pair of the first shoulder lateral grooves adjacent in the tire circumferential direction in the shoulder land portion.

2. The tire according to claim 1, wherein the first shoulder lateral groove has an inner end in the tire width direction that tapers toward the shoulder circumferential narrow groove.

3. The tire as described in claim 1 or 2, characterized in that the groove depth Dc of the shoulder circumferential narrow groove, the groove depth D1 of the first shoulder lateral groove, and the groove depth D2 of the second shoulder lateral groove satisfy the relationship Dc≦D2<D1.

4. A tire as described in any one of claims 1 to 3, characterized in that the center block has a shallow center groove at an extension position of the intermediate inclined groove, extending in the same direction as the intermediate inclined groove and terminating within the center block without passing the tire equator.

5. A tire as described in any one of claims 1 to 4, characterized in that in each of the intermediate blocks, between adjacent sipes in the tire circumferential direction, there is provided an intermediate shallow groove that opens into the main groove located at the outermost side in the tire width direction, extends in the same direction as the intermediate oblique groove, and terminates within the intermediate block without passing beyond the center of the intermediate block in the tire width direction.

6. A tire according to any one of claims 1 to 5, characterized in that a bottom raised portion is provided at the bottom of each of the center oblique groove and the intermediate oblique groove.

7. A tire as described in any one of claims 1 to 6, characterized in that, of the sipes, intermediate sipes formed in the intermediate block extend in the same direction as the intermediate inclined groove, center sipes formed in the center block extend in the same direction as the center inclined groove, and shoulder sipes formed in the shoulder land portion extend in the same direction as the first shoulder lateral groove.

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