Tire

Abstract

To provide a tire capable of exhibiting on-ice brake performance that is superior at an early stage of abrasion.SOLUTION: At least one out of a plurality of land parts 40 formed on a tread part 1 is a specific land part comprising at least one sipe s extending along a tire width direction on a tread, and a plurality of thin grooves g whose groove depth is smaller than that of the sipe s and is 1.5 mm or less, A ratio in sum of a groove area of all the grooves formed on the tread part 1 including the sipes s and the thin grooves g relative to an area of a ground contact area of the tread part 1 is 20%-60%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having at least one sipe and a plurality of narrow grooves on its tread surface. [Background technology]

[0002] In snow and ice tires, such as studless tires, minute irregularities are formed on the tread surface by mixing fillers or air bubbles into the tread rubber, and these irregularities have the effect of removing water films, ensuring excellent driving performance on snow and ice. However, before the break-in period, the irregularities are not fully apparent on the tread surface, which is a problem in that the tires are unable to fully demonstrate their inherent driving performance in the early stages of wear.

[0003] To solve these problems, for example, Patent Document 1 proposes forming multiple sipes and numerous fine grooves (minor grooves with a smaller groove depth than sipes) on the tread surface of the land portions defined in the tread. In such tires, even when the above-mentioned unevenness is not fully expressed, the sipes and fine grooves on the land portion surface provide an edge effect and a water film removal effect, so driving performance on icy roads can be ensured even in the early stages of wear. However, in recent years, the performance required of tires has become more sophisticated, and further improvement in braking performance on ice in the early stages of wear is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-034903 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a tire that can exhibit excellent braking performance on ice in the early stages of wear. [Means for solving the problem]

[0006] In order to achieve the above object, the tire of the present invention has a tread portion that extends circumferentially and forms an annular shape, and the tread portion is formed with a plurality of circumferential main grooves that extend along the tire circumferential direction, a plurality of lug grooves that extend in a direction intersecting the circumferential main grooves, and a plurality of land portions that are partitioned by the circumferential main grooves and / or the lug grooves, and at least one of the plurality of land portions is a specific land portion that has at least one sipe that extends along the tire width direction on the tread surface and a plurality of narrow grooves that have a groove depth that is smaller than the sipe and is 1.5 mm or less, and the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and the narrow grooves, to the area of ​​the contact patch of the tread portion is 20% to 60%. [Effects of the Invention]

[0007] In the present invention, to improve ice performance during the early stages of wear using a specific land portion having at least one sipe and multiple fine grooves (fine grooves with a groove depth of 1.5 mm or less) formed on the land portion tread surface, the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and fine grooves, to the area of ​​the contact zone of the tread portion (i.e., the groove area ratio of the tread portion) is set within an appropriate range. This ensures sufficient edge effect and water film removal effects of the sipes and fine grooves while preventing the sipes and fine grooves from reducing the actual contact area of ​​the specific land portion (the area of ​​the land portion tread surface that actually contacts the road surface, excluding the sipes and fine grooves), thereby achieving excellent braking performance on ice. Note that "all grooves formed in the tread portion, including the sipes and fine grooves," refers to main grooves extending along the tire circumferential direction, lug grooves extending along the tire width direction, sipes, fine grooves, and various other grooves formed as appropriate depending on the tire. The areas of these grooves are the areas of the groove openings on the tread surface of the tread portion.

[0008] In the present invention, it is preferable that the pitch of the plurality of fine grooves is 0.5 mm to 5.0 mm and the width of each fine groove is 0.05 mm to 1.0 mm, which is advantageous for improving performance on ice because it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice and also ensures braking performance on ice due to the water film removal effect of the fine grooves.

[0009] In the present invention, it is preferable that the ratio of the total area of ​​the plurality of fine grooves to the area of ​​the ground contact region of the tread portion is 3% to 16%, which is advantageous for improving performance on ice because it ensures a sufficient actual ground contact area of ​​the specific land portion to ensure braking performance on ice and further ensures braking performance on ice due to the water film removal effect of the fine grooves.

[0010] In the present invention, the inclination angle of the fine grooves relative to the tire circumferential direction is preferably 30° to 70°. This allows the edge effect and drainage performance of the fine grooves to be exhibited in a balanced manner, which is advantageous for improving performance on ice. Note that the inclination angle of the fine grooves is the acute angle between the fine grooves and the tire circumferential direction.

[0011] In the present invention, when the center of the specific land portion in the tire width direction is defined as the central region and both sides of the central region in the tire width direction are defined as edge regions, the inclination direction of the narrow grooves in at least one edge region can be made different from the inclination direction of the narrow grooves in the central region, which improves the water film removal effect of the narrow grooves and is advantageous for improving performance on ice.

[0012] In this case, it is preferable that the area of ​​the edge regions, where the narrow grooves have a different inclination direction from the narrow grooves in the central region, is smaller than the area of ​​the central region, which results in a good balance between the areas of the central region and the edge regions, where the narrow grooves have different inclination directions, and is advantageous for improving the water film removal effect of the narrow grooves and improving performance on ice.

[0013] In this case, it is further preferable that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the central region in the tire width direction of the specific land portion, and 30° to 70° in the end regions in the tire width direction of the specific land portion. This results in a good inclination angle of the narrow groove in each of the central region and the end regions, which is advantageous for improving the water film removal effect of the narrow groove and improving performance on ice. Note that the inclination angle of the narrow groove is an acute angle between the narrow groove and the tire circumferential direction in both the central region and the end regions.

[0014] In the present invention, the area of ​​the contact area of ​​the tread portion (unit: mm 2 The ratio of the total sipe length L (unit: mm) of the sipes projected in the tire width direction to the total sipe length L (unit: mm) is 0.05 mm / mm 2 ~0.21mm / mm 2 By providing a sufficient number of sipes in each specific land portion in this manner, the edge effect and water film removal effect of the sipes can be enhanced, which is advantageous for improving performance on ice.

[0015] In the present invention, the "ground contact area" of the tread is the area that comes into contact with a flat surface when the tire is mounted on a standard rim, inflated to the standard internal pressure (in the case of a pneumatic tire), placed vertically on a flat surface, and subjected to a standard load. The "standard rim" refers to the rim specified for each tire by the standard system, including the standard on which the tire is based. For example, this refers to the standard rim for JATMA, the "Design Rim" for TRA, or the "Measuring Rim" for ETRTO. The "standard internal pressure" refers to the air pressure specified for each tire by the standard system, including the standard on which the tire is based. This refers to the maximum air pressure for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" table for TRA, and the "INFLATION PRESSURE" for ETRTO, but is 180 kPa when the tire is for a passenger car. "Normal load" is the load specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the maximum load capacity, for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "LOAD CAPACITY." However, if the tire is for a passenger car, it is a load equivalent to 88% of the above load. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is a development view showing the tread pattern of the pneumatic tire of FIG. [Figure 3] FIG. 2 is an explanatory diagram schematically illustrating an example of a specific land portion of the present invention. [Figure 4] FIG. 10 is an explanatory diagram schematically illustrating another example of the specific land portion of the present invention. [Figure 5] FIG. 2 is a cross-sectional view showing the shape of the narrow grooves and sipes of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] In the case of a pneumatic tire as shown in FIG. 1, the tire of the present invention includes 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 FIG. 1, the symbol CL indicates the tire equator. Although not depicted in FIG. 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby forming the basic toroidal structure of a pneumatic tire. The following explanation using FIG. 1 will be based basically on the meridian cross-section shape shown, but each tire component also extends in the tire circumferential direction and forms an annular shape.

[0019] A carcass layer 4 is mounted between a pair of left and right bead portions 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inner side to the outer side in the tire width direction around a bead core 5 disposed in each bead portion 3. A bead filler 6 is disposed on the outer periphery of the bead core 5, and this bead filler 6 is enclosed by the main body portion and folded back portion of the carcass layer 4. The bead filler 6 has a triangular cross section, for example, as shown in the figure, and is made of a rubber composition.

[0020] A plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords (belt cords) inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between 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°. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt reinforcing layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes reinforcing cords (cover cords) oriented in the tire circumferential direction. In the belt cover layer 8, the angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, to 0° to 5°. Organic fiber cords such as nylon and aramid cords are preferably used as the reinforcing cords of the belt cover layer 8.

[0021] In the tread portion 1, a tread rubber layer 11 is disposed on the outer peripheral side of the carcass layer 4, belt layer 7, and belt reinforcing layer 8. The tread rubber layer 11 may have a structure in which two types of rubber layers with different physical properties (a cap tread layer that forms the tread surface of the tread portion 1 and an undertread layer disposed on its inner peripheral side) are laminated in the tire radial direction. A side rubber layer 12 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the sidewall portion 2, and a rim cushion rubber layer 13 is disposed on the outer peripheral side (outer side in the tire width direction) of the carcass layer 4 in the bead portion 3. From the viewpoint of improving performance on ice, it is preferable that the rubber composition that constitutes the tread rubber layer 11 (particularly the cap tread layer) contains fillers and air bubbles so that when the tread surface is worn, fine irregularities that have a water film removal effect appear.

[0022] As described below, the present invention relates to sipes and narrow grooves formed on the surface of the tire tread portion 1, and therefore the basic structure (internal structure) of the tire is not limited to the general structure described above. Also, 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).

[0023] As shown in Figure 2, the surface of the tread portion 1 is formed with a plurality of circumferential main grooves 20 extending in the tire circumferential direction, a plurality of lug grooves 30 extending in the tire width direction, and a plurality of land portions 40 defined by the circumferential main grooves and lug grooves. The circumferential main grooves 20 are grooves that perform the primary drainage function and generally have a groove width of 5.0 mm or more and a groove depth of 6.5 mm or more. The groove width of the lug grooves 30 can be a typical tire width, for example, a groove width of 1.0 mm or more and a groove depth of 3.0 mm or more.

[0024] At least one of the plurality of land portions 40 thus defined and partitioned has at least one sipe s extending along the tire width direction on the tread surface and a plurality of narrow grooves g whose groove depth is smaller than that of the sipe s, as shown in Figures 3 and 4. In the following description, the land portion 40 having these sipes s and narrow grooves g may be referred to as a specific land portion. Since the present invention is primarily related to this specific land portion, the details of the tread pattern are not particularly limited as long as it includes at least one specific land portion.

[0025] As shown in FIG. 5, the sipes s have a groove width Ws of, for example, 0.1 mm to 1.0 mm and a groove depth Ds of, for example, 2.0 mm to 10.0 mm. The sipes s extend primarily along the tire width direction and are spaced apart circumferentially, primarily providing edge effect and drainage. In particular, the sipes s provide edge effect and water film removal even in the early stages of wear (before the tread rubber's inherent performance is fully realized), which is advantageous for improving performance on ice. The shape of each sipe s is not particularly limited, and the zigzag shape shown in the figure can be adopted. Furthermore, the sipes s may be appropriately provided so that both ends communicate with the circumferential main groove 20, one end communicates with the circumferential main groove 20 and the other end terminates within the land portion 40, or both ends terminate within the land portion 40, taking into account the size of the land portion 40, etc.

[0026] As described above, the narrow grooves g are shallower than the sipes s, and as shown in FIG. 5, their groove depth Dg is set to 1.5 mm or less, preferably 0.1 mm to 1.0 mm. The groove width Wg of the narrow grooves g is preferably 0.05 mm to 1.0 mm, more preferably 0.1 mm to 0.8 mm. Thus, the narrow grooves g are minute grooves that extend in a direction intersecting the sipes as shown in the figure, and are arranged in a plurality of rows in the tire circumferential direction. In particular, as shown in FIGS. 3 and 4, it is preferable that a plurality of narrow grooves g are periodically and repeatedly arranged evenly over the entire surface of the land portion 40 (specific land portion). By providing a plurality of narrow grooves g, the narrow grooves g can remove water film even in the early stages of wear (before the tread rubber's inherent performance is fully exerted), thereby achieving excellent braking performance on ice. If the groove depth Dg of the narrow grooves g exceeds 1.5 mm, it becomes difficult to ensure the rigidity of the land portion 40. If the groove width Wg of the narrow groove g is less than 0.05 mm, the narrow groove g will be too small to achieve sufficient water removal, making it difficult to improve braking performance on ice.If the groove width Wg of the narrow groove g is more than 1.0 mm, the actual contact area will be reduced, making it difficult to improve braking performance on ice.

[0027] The cross-sectional shape of the narrow grooves g is not particularly limited. For example, a shape with a flat groove bottom (rectangular) as shown in FIG. 5 can be used, as well as a U-shaped or V-shaped cross section. When multiple narrow grooves g are periodically arranged as shown in FIGS. 3 and 4, the pitch p of the multiple narrow grooves g (the distance between the periodically arranged narrow grooves g) shown in FIG. 5 is preferably 0.5 mm to 5.0 mm, more preferably 0.7 mm to 4.0 mm. This is advantageous for improving ice performance, as it ensures a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice and further ensures braking performance on ice through the water film removal effect of the narrow grooves g. If the pitch p of the narrow grooves g is less than 0.5 mm, it becomes difficult to improve braking performance on ice due to the reduced actual contact area. If the pitch p of the narrow grooves g is greater than 5.0 mm, it becomes difficult to arrange a sufficient number of narrow grooves g within the specific land portion, which results in insufficient water removal effect, making it difficult to improve braking performance on ice.

[0028] As described above, the present invention is not particularly limited in detail to the tread pattern as long as it includes at least one specific land portion. However, the tread pattern of the example in Fig. 2 includes, as circumferential main grooves 20, a pair of inner main grooves 21 arranged on both sides of the tire equator CL and a pair of outer main grooves 22 arranged outward in the tire width direction from the inner main grooves 21. One of the pair of inner main grooves 21 (the inner main groove 21a on the right in the figure) extends in a zigzag pattern along the tire circumferential direction, while the other of the pair of inner main grooves 21 (the inner main groove 21b on the left in the figure) extends so that the groove width varies along the tire circumferential direction due to the groove wall on the outer side in the tire width direction being zigzag. Both outer main grooves 22 extend linearly along the tire circumferential direction.

[0029] In the illustrated example, a plurality of block-shaped land portions (center land portions 41) are arranged in the tire circumferential direction between a pair of inner main grooves 21, each defined by the pair of inner main grooves 21 and a lug groove 30 (center lug groove 31). On one side of the tire equator (the right side in the drawing), a plurality of block-shaped land portions (intermediate land portions 42a) are arranged in the tire circumferential direction between the zigzag inner main groove 21a and outer main groove 22, each defined by the grooves and the lug groove 30 (intermediate lug groove 32a). Each intermediate land portion 42 is provided with a circumferential auxiliary groove 51 that extends in a zigzag pattern along the tire circumferential direction and connects adjacent lug grooves in the tire circumferential direction. On the other side of the tire equator (the left side in the drawing), a rib-shaped land portion (intermediate land portion 42b) is formed between the inner main groove 21b and outer main groove 22, whose groove widths vary, defined by these grooves and continuing around the entire tire circumference. The intermediate land portion 42b is provided with lug grooves 30 (intermediate lug grooves 32b) that are connected to the inner main groove 21b and the outer main groove 22 and terminate within the land portion. On the outer side of the pair of outer main grooves 22 in the tire width direction, a plurality of block-shaped land portions (shoulder land portions 43) that are partitioned by the outer main grooves 22 and the lug grooves 30 (shoulder lug grooves 33) are arranged in the tire circumferential direction. Each shoulder land portion 43 is provided with a circumferential narrow groove 52 that is connected to the shoulder lug groove 33, extends along the tire circumferential direction, and terminates within the land portion.

[0030] Among the land portions 40 of various shapes included in the tread pattern as described above, if they are provided with sipes s and narrow grooves g, they are considered to be specific land portions in the present invention. In particular, in the example of Figure 2, all land portions 40 are specific land portions, and the area relationships described below are applied to all land portions 40.

[0031] As described above, by providing at least one sipe s and multiple narrow grooves g, it is possible to ensure ice performance in the early stages of wear in a specific land portion, and in this case, the ratio of the total groove area of ​​all grooves formed in the tread portion 1, including the sipes s and narrow grooves g, to the area of ​​the contact patch of the tread portion 1 (i.e., the groove area ratio of the tread portion 1) is set to 20% to 60%, preferably 30 to 55%, and more preferably 35 to 50%. In the case of Figure 2, all grooves formed in the tread portion 1, including the sipes s and narrow grooves g, are the circumferential main grooves 20 (inner main groove 21 and outer main groove 22), lug grooves 30 (center lug groove 31, intermediate lug grooves 32a and 32b, and shoulder lug grooves 33), circumferential auxiliary groove 51, circumferential narrow groove 53, sipes s, and narrow grooves g. By optimizing the overall groove area ratio of the tread portion 1 in this way, the water film removal effect of the sipes (s) and narrow grooves (g) is sufficiently ensured, while the reduction in the actual contact area of ​​specific land areas due to the sipes (s) and narrow grooves (g) is suppressed, resulting in excellent braking performance on ice. In this case, if the groove area ratio of the tread portion 1 is less than 20%, the water removal effect of the entire tread portion is reduced, making it difficult to improve braking performance on ice. If the groove area ratio of the tread portion 1 is more than 60%, the actual contact area is reduced, making it difficult to improve braking performance on ice.

[0032] It is effective to provide a sufficient number of fine grooves g, which contribute greatly to ice performance in the early stages of wear. The ratio of the total area of ​​the multiple fine grooves g to the area of ​​the contact patch of the tread portion 1 is preferably 3% to 16%, more preferably 5% to 14%. This ensures sufficient actual contact patch area of ​​the specific land portion where the fine grooves g are provided, ensuring braking performance on ice, and further ensures braking performance on ice through the water film removal effect of the fine grooves g, which is advantageous for improving performance on ice. If the ratio of the total area of ​​the multiple fine grooves g to the area of ​​the contact patch of the tread portion 1 is less than 3%, the water removal performance of the fine grooves g will not be sufficient, making it difficult to improve braking performance on ice. If the ratio of the total area of ​​the multiple fine grooves g to the area of ​​the contact patch of the tread portion 1 exceeds 16%, the actual contact patch area will be reduced, making it difficult to improve braking performance on ice.

[0033] The inclination angle θ of the narrow grooves g relative to the tire circumferential direction is preferably 30° to 70°, more preferably 35° to 55°. This allows the narrow grooves g to achieve a good balance between the edge effect and drainage performance, which is advantageous for improving performance on ice. If the inclination angle θ of the narrow grooves g is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect cannot be sufficiently secured. If the inclination angle θ of the narrow grooves g exceeds 70°, it becomes difficult to improve braking performance on ice because the narrow grooves g cannot sufficiently remove water.

[0034] As shown in Figure 4, when the center side of the specific land portion in the tire width direction is designated as a central region C and both sides of the central region in the tire width direction are designated as edge regions E, the inclination direction of the narrow grooves g in at least one edge region E can be made different from the inclination direction of the narrow grooves g in the central region C. This design is advantageous for improving performance on ice because it can enhance the water film removal effect of the narrow grooves g compared to when the narrow grooves g extend in a single direction. In this case, it is preferable that the area of ​​the edge region E, in which narrow grooves g having an inclination direction different from the inclination direction of the narrow grooves g in the central region C are provided, is smaller than the area of ​​the central region C. In particular ... specific land portion is smaller than the area of ​​the central region C. L Width W of the end region E (the part where the inclination direction of the narrow groove is different) E It is preferable that the ratio is 5% to 49%. This provides a good balance between the areas of the central region C and the end regions E, where the inclination directions of the narrow grooves g are different from each other, which is advantageous for improving the water film removal effect of the narrow grooves g and improving performance on ice.

[0035] As mentioned above, when the inclination direction of the narrow grooves g differs between the central region C and the edge regions E, the inclination angle θc in the central region C is preferably 30° to 60°, more preferably 35° to 55°, and the inclination angle θe in the edge regions E is preferably 30° to 70°, more preferably 35° to 60°. This ensures a good inclination angle of the narrow grooves g in both the central region C and the edge regions E, which is advantageous for improving the water film removal effect of the narrow grooves g and improving performance on ice. If the inclination angle θc in the central region C is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect is insufficient. If the inclination angle θc in the central region C is more than 60°, it becomes difficult to improve braking performance on ice because the water removal performance of the narrow grooves g is insufficient. If the inclination angle θe in the edge regions E is less than 30°, it becomes difficult to improve braking performance on ice because the edge effect is insufficient. If the inclination angle θe in the end region E exceeds 70°, the fine grooves g will not be able to provide sufficient water removal performance, making it difficult to improve braking performance on ice.

[0036] It is preferable that the sipes s are provided in sufficient length over the entire tread portion 1, and it is particularly desirable that the component in the tire width direction has a sufficient length. Specifically, the ratio of the total sipe length L of the sipes s projected in the tire width direction to the area of ​​the contact patch of the tread portion 1 (hereinafter referred to as sipe density) is preferably 0.05 mm / mm 2 ~0.21mm / mm 2 , more preferably 0.07 mm / mm 2 ~0.17mm / mm 2 By providing sufficient sipes in this way, the edge effect and water film removal effect of the sipes can be enhanced, which is advantageous for improving performance on ice. 2 If the sipe density is less than 0.21 mm / mm, the sipe length cannot be secured sufficiently, and the edge effect and water removal effect of the sipes will be limited. 2 If the value exceeds this, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0037] As described above, the present invention optimizes the arrangement of sipes s and narrow grooves g throughout the entire tread portion 1 (the area of ​​the contact patch of the tread portion 1). However, it is also preferable to improve the arrangement of sipes s and narrow grooves g in each specific land portion where the sipes s and narrow grooves g are formed. For example, the ratio of the total area of ​​the narrow grooves g and the total area of ​​the sipes s to the tread area S of the specific land portion is preferably set to 7% to 35%, more preferably 10% to 27%. Furthermore, the ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion is preferably set to 5% to 19%, more preferably 7% to 17%. This ensures sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice, and further ensures braking performance on ice due to the water film removal effect of the narrow grooves, which is advantageous for improving performance on ice. If the ratio of the total area of ​​the fine grooves g and the total area of ​​the sipes s to the tread area S of the specific land area is less than 7%, the number of sipes s and fine grooves g formed in the specific land area will be small, making it difficult to obtain sufficient water removal performance and improving braking performance on ice. If the ratio of the total area of ​​the fine grooves g and the total area of ​​the sipes s to the tread area S of the specific land area is more than 35%, the actual contact area will be reduced, making it difficult to improve braking performance on ice. If the ratio of the total area of ​​the multiple fine grooves g to the tread area S of the specific land area is less than 5%, the fine grooves g will not provide sufficient water removal performance and making it difficult to improve braking performance on ice. If the ratio of the total area of ​​the multiple fine grooves g to the tread area S of the specific land area is more than 19%, the actual contact area will be reduced, making it difficult to improve braking performance on ice. Note that the tread area S of the specific land area is the area inside the outer contour of the specific land area (the entire area including sipes and fine grooves).

[0038] 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. [Example]

[0039] Sixteen types of pneumatic tires (test tires) were manufactured: Conventional Example 1, Comparative Examples 1 and 2, and Examples 1 to 13, each having a tire size of 195 / 65R15 91Q, the basic structure (internal structure) shown in FIG. 1, and the tread pattern shown in FIG. 2 as the base. The groove area ratio, narrow groove width, narrow groove pitch, narrow groove inclination direction, narrow groove inclination angle, and sipe density were set as shown in Tables 1 and 2, respectively.

[0040] In Tables 1 and 2, "groove area ratio" indicates the ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and fine grooves, to the area of ​​the contact area of ​​the tread portion (the "Total Grooves" column in the table), and the ratio of the total area of ​​fine grooves to the area of ​​the contact area of ​​the tread portion (the "Fine Grooves" column in the table). In the "Fine Groove Inclination Direction" column, cases where the inclination direction of the fine grooves is the same in the central region and edge region of a specific land portion are indicated as "Same Direction", and cases where the inclination direction of the fine grooves is different in the central region and edge region of a specific land portion are indicated as "Different Directions". For "Fine Groove Inclination Angle", two columns, one for "Central Region" and one for "Edge Region", are provided, and when the "Fine Groove Inclination Direction" is "Different Direction", both the inclination angle of the fine groove in the central region of a specific land portion and the inclination angle of the fine groove in the edge region are indicated. When the "Fine Groove Inclination Direction" is "Same Direction", the inclination angle value is indicated only in the "Central Region" column. "Sipe Density" refers to the ratio of the area of ​​the contact area of ​​the tread portion [unit: mm 2 ], the ratio of the total sipe length L (unit: mm) of all sipes included in the specific land area projected in the tire width direction to the total sipe length L (unit: mm / mm 2 〕

[0041] The test tires were evaluated for braking performance on ice using the following test method, and the results are shown in Tables 1 and 2.

[0042] Braking performance on ice Each test tire was mounted on a 15x6.5J rim wheel and fitted to all wheels of a front-wheel drive vehicle with an 1800cc engine displacement, and the tires were inflated to an air pressure of 250 / 240kPa. A braking test (20km / h) was conducted by a test driver on an ice rink. The evaluation results were expressed as an index using the reciprocal of the measured value, with Conventional Example 1 being 100. The higher the index value, the shorter the braking distance and the better the braking performance on ice.

[0043] [Table 1]

[0044] [Table 2]

[0045] As can be seen from Tables 1 and 2, the tires of Examples 1 to 13 had improved braking performance on ice compared to Conventional Example 1. On the other hand, the tire of Comparative Example 1 had a large ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and fine grooves, to the area of ​​the contact patch of the tread, so the effect of improving braking performance on ice was limited. The tire of Comparative Example 2 had a small ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and fine grooves, to the area of ​​the contact patch of the tread, so the effect of improving braking performance on ice was limited.

[0046] The present disclosure includes the following inventions. Invention [1] A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion is formed with a plurality of circumferential main grooves extending along the tire circumferential direction, a plurality of lug grooves extending in a direction intersecting the circumferential main grooves, and a plurality of land portions defined by the circumferential main grooves and / or the lug grooves, At least one of the plurality of land portions is a specific land portion having at least one sipe extending along the tire width direction on the tread surface and a plurality of narrow grooves having a groove depth smaller than that of the sipe and 1.5 mm or less, A tire characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and the narrow grooves, to the area of ​​the ground contact region of the tread portion is 20% to 60%. Invention [2] The tire according to invention [1], wherein the pitch of the plurality of narrow grooves is 0.5 mm to 5.0 mm, and the groove width of each of the narrow grooves is 0.05 mm to 1.0 mm. Invention [3] The tire according to invention [1] or [2], characterized in that the ratio of the total area of ​​the plurality of narrow grooves to the area of ​​the contact area of ​​the tread portion is 5% to 19%. Invention [4] The tire according to any one of inventions [1] to [3], characterized in that the narrow grooves have an inclination angle of 30° to 70° with respect to the tire circumferential direction. Invention [5] A tire according to any one of inventions [1] to [4], characterized in that when the center side of the specific land portion in the tire width direction is defined as a central region and both sides of the central region in the tire width direction are defined as end regions, the inclination direction of the narrow grooves in at least one of the end regions is different from the inclination direction of the narrow grooves in the central region. Invention [6] A tire according to invention [5], characterized in that the area of ​​the end regions, in which the narrow grooves having an inclination direction different from the inclination direction of the narrow grooves in the central region are provided, is smaller than the area of ​​the central region. Invention [7] A tire according to invention [5] or [6], characterized in that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the central region in the tire width direction of the specific land portion, and 30° to 70° in the end region in the tire width direction of the specific land portion. Invention [8] The area of ​​the contact area of ​​the tread portion [unit: mm 2 ) to the sum of the sipe lengths L (unit: mm) of the sipes projected in the tire width direction is 0.06 mm / mm 2 ~0.30mm / mm 2 The tire according to any one of inventions [1] to [7], characterized in that: [Explanation of symbols]

[0047] 1 Tread section 2 Sidewall 3 Bead section 20 Circumferential main groove 30 lug grooves 40 Land s sipe g narrow groove CL Tire Equator

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, The tread portion is formed with a plurality of circumferential main grooves extending along the tire circumferential direction, a plurality of lug grooves extending in a direction intersecting the circumferential main grooves, and a plurality of land portions partitioned by the circumferential main grooves and / or the lug grooves, At least one of the plurality of land portions is a specific land portion having at least one sipe extending along the tire width direction on the tread surface and a plurality of narrow grooves having a groove depth smaller than that of the sipe and 1.5 mm or less, A tire characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and the narrow grooves, to the area of ​​the ground contact region of the tread portion is 20% to 60%.

2. 2. The tire according to claim 1, wherein the pitch of the plurality of narrow grooves is 0.5 mm to 5.0 mm, and the groove width of each of the narrow grooves is 0.05 mm to 1.0 mm.

3. 3. The tire according to claim 1, wherein the ratio of the total area of ​​the plurality of narrow grooves to the area of ​​the ground contact region of the tread portion is 3% to 16%.

4. The tire according to claim 1 or 2, characterized in that the narrow groove has an inclination angle of 30° to 70° with respect to the tire circumferential direction.

5. 3. The tire according to claim 1, wherein the central side of the specific land portion in the tire width direction is defined as a central region, and both sides of the central region in the tire width direction are defined as end regions, and the inclination direction of the narrow grooves in at least one of the end regions is different from the inclination direction of the narrow grooves in the central region.

6. 6. The tire according to claim 5, wherein the area of ​​the end regions, in which the narrow grooves having an inclination direction different from the inclination direction of the narrow grooves in the central region are provided, is smaller than the area of ​​the central region.

7. The tire according to claim 5, characterized in that the inclination angle of the narrow groove with respect to the tire circumferential direction is 30° to 60° in a central region in the tire width direction of the specific land portion, and is 30° to 70° in an end region in the tire width direction of the specific land portion.

8. The area of ​​the contact area of ​​the tread portion [unit: mm 2 ) to the tire width direction of the sipes L [unit: mm] ratio of 0.05 mm / mm 2 ~0.21mm / mm 2 3. The tire according to claim 1, wherein the range is:

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