Tire

Abstract

The present invention provides a tire capable of exhibiting excellent braking performance on ice at an early stage of wear. In the present invention, at least one of a plurality of land parts 40 formed in a tread part 1 is a specific land part including at least one sipe s extending along the tire width direction on a tread surface and a plurality of fine grooves g having a groove depth smaller than that of the sipe s and equal to or less than 1.5 mm. The ratio of the sum of the total area of the sipe s and the total area of the fine grooves g to an area S of the tread surface in the specific land part is 7-35%.

Description

tire

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

[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 (fine 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.

[0004] Japanese Patent Application Publication No. 2004-034903

[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.

[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 that intersects with 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 extend in a direction that intersects with the sipes, and the narrow grooves are shallower than the sipes and have a groove depth of 1.5 mm or less, and the ratio of the sum of the total area of ​​the narrow grooves and the total area of ​​the sipes to the tread area S in the specific land portion is 7% to 35%.

[0007] In the present invention, when improving ice performance during the early stages of wear by 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, the ratio of the total area of ​​the sipes and fine grooves to the tread area S of the specific land portion is set within an appropriate range, thereby ensuring sufficient edge effect and water film removal effect 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 that actually contacts the road surface, excluding the sipes and fine grooves), thereby achieving excellent braking performance on ice. The tread area S of the specific land portion is the area inside the outer contour of the specific land portion (the entire area including the sipes and fine grooves). The area of ​​the sipes and fine grooves is the area of ​​the openings of the sipes and fine grooves on the tread surface of the specific land 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 tread area S of the specific land portion is 5% to 19%. This is advantageous for improving performance on ice, since 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 due to the water film removal effect of the fine grooves.

[0010] In the present invention, the inclination angle of the narrow grooves relative to the tire circumferential direction is preferably 30° to 70°. This allows the edge effect and drainage performance of the narrow grooves to be exhibited in a balanced manner, which is advantageous for improving performance on ice. Note that the inclination angle of the narrow grooves is the acute angle between the narrow 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 the acute angle of the angle formed 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 S of the tread surface of the specific land portion [unit: mm2 The ratio of the total sipe length L (unit: mm) of all sipes included in the specific land portion projected in the tire width direction to ... is 0.06 mm / mm 2 ~0.30mm / mm 2 By providing a sufficient number of sipes on 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 ratio of the total groove area of ​​all grooves formed in the tread portion, including sipes and narrow grooves, to the area of ​​the contact zone of the tread portion is preferably 20% to 60%. This allows the groove area ratio of the tread portion to be set within an appropriate range, ensuring sufficient edge effect and water film removal effect of the sipes and narrow grooves while suppressing a reduction in the actual contact area of ​​a specific land portion (the area of ​​the land portion tread surface that actually contacts the road surface, excluding the sipes and narrow grooves) due to the sipes and narrow grooves, which is advantageous for improving braking performance on ice. Note that "all grooves formed in the tread portion, including sipes and narrow grooves," refers to main grooves extending along the tire circumferential direction, lug grooves extending along the tire width direction, sipes, narrow grooves, and various other grooves formed as appropriate depending on the tire. The area of ​​these grooves is the area of ​​the groove openings on the contact surface of the tread portion.

[0016] 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. A "standard rim" is a rim that is 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 in the case of JATMA, a "Design Rim" in the case of TRA, or a "Measuring Rim" in the case of 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.

[0017] Fig. 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. Fig. 2 is a development view showing the tread pattern of the pneumatic tire of Fig. 1. Fig. 3 is an explanatory diagram showing a schematic view of an example of a specific land portion of the present invention. Fig. 4 is an explanatory diagram showing a schematic view of another example of a specific land portion of the present invention. Fig. 5 is a cross-sectional view showing the shape of a fine groove and a sipe of the present invention.

[0018] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] In the case of a pneumatic tire as shown in Figure 1, the tire of the present invention 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 indicates the tire equator. 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 in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be based basically on the meridian cross-section shape shown, but each tire constituent member also extends in the tire circumferential direction and forms an annular shape.

[0020] 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 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.

[0021] Multiple 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 multiple 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 reinforcing cords are set, for example, at an angle of 0° to 5° with respect to the tire circumferential direction. Organic fiber cords such as nylon and aramid cords are preferably used as the reinforcing cords of the belt cover layer 8.

[0022] 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 (outside 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 (outside 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.

[0023] 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 portion corresponding to the surface of the tread portion 1 in a pneumatic tire).

[0024] 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 dimensions of the lug grooves 30 can be those typically used in tires, such as a groove width of 1.0 mm or more and a groove depth of 3.0 mm or more.

[0025] 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.

[0026] 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 arranged, taking into account factors such as the size of the land portion 40, such as those that communicate with the circumferential main groove 20 at both ends, those that communicate with the circumferential main groove 20 at one end and terminate within the land portion 40 at the other end, or those that terminate within the land portion 40 at both ends.

[0027] As mentioned above, the narrow grooves g are shallower than the sipes s. As shown in FIG. 5, the 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 s as shown in the figure, and are arranged in multiple rows around the tire circumferential direction. In particular, as shown in FIGS. 3 and 4, multiple narrow grooves g are preferably arranged periodically and repeatedly evenly across the entire surface of the land portion 40 (specific land portion). By providing multiple narrow grooves g, the narrow grooves g can effectively remove water film even in the early stages of wear (before the tread rubber's inherent performance is fully realized), 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 is too small to achieve sufficient water removal performance, 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 decreases, making it difficult to improve braking performance on ice.

[0028] The cross-sectional shape of the narrow grooves g is not particularly limited. For example, in addition to a shape (rectangular) with a flat groove bottom in cross section as shown in FIG. 5, a U-shaped or V-shaped cross section can be adopted. 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 by ensuring a sufficient actual contact area of ​​the specific land portion to ensure braking performance on ice, and further by ensuring 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 exceeds 5.0 mm, it becomes difficult to arrange a sufficient number of narrow grooves g within the specific land portion, and the water removal effect cannot be ensured, making it difficult to improve braking performance on ice.

[0029] As described above, the present invention is not particularly limited in terms of the details of the tread pattern as long as it includes at least one specific land portion. However, the tread pattern of the example in Figure 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.

[0030] In the illustrated example, a plurality of block-shaped land portions (center land portions 41) defined by the pair of inner main grooves 21 and lug grooves 30 (center lug grooves 31) are arranged in the tire circumferential direction between the pair of inner main grooves 21. On one side of the tire equator (the right side in the figure), a plurality of block-shaped land portions (intermediate land portions 42a) defined by the zigzag inner main grooves 21a and outer main grooves 22 and the lug grooves 30 (intermediate lug grooves 32a) are arranged in the tire circumferential direction between the inner main grooves 21a and outer main grooves 22. Each intermediate land portion 42 is provided with a circumferential auxiliary groove 51 extending in a zigzag pattern along the tire circumferential direction and connecting adjacent lug grooves in the tire circumferential direction. On the other side of the tire equator (the left side in the figure), a rib-shaped land portion (intermediate land portion 42b) defined by these grooves and continuing around the entire tire circumference is formed between the inner main groove 21b and outer main groove 22, whose groove widths vary. The intermediate land portion 42b is provided with lug grooves 30 (intermediate lug grooves 32b) that communicate with the inner main groove 21b and the outer main groove 22 and terminate within the land portion. A plurality of block-shaped land portions (shoulder land portions 43) defined by the outer main grooves 22 and the lug grooves 30 (shoulder lug grooves 33) are arranged in the tire circumferential direction on the outer side of the pair of outer main grooves 22 in the tire width direction. Each shoulder land portion 43 is provided with a circumferential narrow groove 52 that communicates with the shoulder lug groove 33, extends along the tire circumferential direction, and terminates within the land portion.

[0031] 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.

[0032] As described above, by providing at least one sipe (s) and multiple narrow grooves (g), it is possible to ensure ice performance in the initial stage of wear in the specific land portion. In this case, the ratio of the sum 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 set to 7% to 35%, preferably 10% to 27%. By satisfying this relationship, the water film removal effect of the sipes (s) and the narrow grooves (g) is sufficiently ensured, while the reduction in the actual contact area of ​​the specific land portion due to the sipes (s) and the narrow grooves (g) can be suppressed, resulting in excellent braking performance on ice. If the ratio of the sum 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 less than 7%, the number of sipes (s) and the narrow grooves (g) formed in the specific land portion will be small, resulting in insufficient water removal performance and making it difficult to improve braking performance on ice. If the ratio of the sum 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 exceeds 35%, the actual contact area will be reduced, making it difficult to improve braking performance on ice.

[0033] The ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion is preferably 5% to 19%, and more preferably 7% to 17%. This 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, which is advantageous for improving performance on ice. If the ratio of the total area of ​​the multiple narrow grooves g to the tread area S of the specific land portion is less than 5%, the water removal performance of the narrow 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 narrow grooves g to the tread area S of the specific land portion exceeds 19%, the actual contact area will be reduced, making it difficult to improve braking performance on ice.

[0034] 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.

[0035] As shown in Figure 4, when the center side of the specific land portion in the tire width direction is defined as a central region C and both sides of the central region in the tire width direction are defined 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, the maximum width W of the specific land portion L The width W of the end region E (the portion where the inclination direction of the narrow groove is different) E As shown in the figure, when the inclination direction of the narrow groove g is different in the end regions E on both sides in the tire width direction, the width W E is the sum of the widths of the two end regions E. 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.

[0036] As described 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 improves the inclination angles 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 cannot be sufficiently secured. If the inclination angle θc in the central region C exceeds 60°, it becomes difficult to improve braking performance on ice because the water removal performance of the narrow grooves g cannot be sufficiently secured. 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 cannot be sufficiently secured. If the inclination angle θe in the end region E exceeds 70°, the fine grooves g will not be able to sufficiently remove water, making it difficult to improve braking performance on ice.

[0037] At least one sipe s is provided in each specific land portion, and it is desirable that each specific land portion has a sufficient length. Specifically, the ratio of the total sipe length L of all sipes s included in the specific land portion projected in the tire width direction to the tread area S of the specific land portion (hereinafter referred to as sipe density) is preferably 0.06 mm / mm 2 ~0.30mm / mm 2 , more preferably 0.12 mm / mm 2 ~0.24mm / mm 2 By providing a sufficient number of 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 0.30 mm / mm, the sipe length cannot be ensured sufficiently, and the edge effect and water removal effect of the sipes are limited. 2 If the value exceeds this, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0038] As described above, the present invention relates to specific land portions (particularly sipes (s) and narrow grooves (g)), and therefore the overall structure (tread pattern) of the tread portion 1 is not particularly limited. However, from the viewpoint of improving performance on ice, 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 ground contact patch of the tread portion 1 (i.e., the groove area ratio of the tread portion 1) is preferably 20% to 60%, more preferably 25% to 55%, even more preferably 30% to 55%, and particularly preferably 35% to 50%. Note that, in the case of FIG. 2 , all grooves formed in the tread portion 1, including the sipes (s) and narrow grooves (g), refer to, for example, the circumferential main grooves 20 (inner main groove 21 and outer main groove 22), the lug grooves 30 (center lug groove 31, intermediate lug grooves 32a and 32b, and shoulder lug grooves 33), the circumferential auxiliary groove 51, the circumferential narrow groove 53, the sipes (s), and the narrow grooves (g). By optimizing the overall groove area ratio of the tread 1 in this way, a sufficient actual contact area is secured to ensure braking performance on ice, and the water film removal effect of the fine grooves g further ensures braking performance on ice, which is advantageous for improving performance on ice. If the groove area ratio of the tread 1 is less than 20%, the drainage performance of the tread 1 as a whole cannot be ensured sufficiently, so even if the specific land portion of the present invention is adopted, the effect of improving performance on ice will be limited. If the groove area ratio of the tread 1 exceeds 60%, the actual contact area of ​​the tread 1 as a whole cannot be ensured sufficiently, so even if the specific land portion of the present invention is adopted, the effect of improving performance on ice will be limited.

[0039] 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.

[0040] Sixteen types of pneumatic tires (test tires) were produced: 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 a base, with the groove area ratio, narrow groove width, narrow groove pitch, narrow groove inclination direction, narrow groove inclination angle, and sipe density set as shown in Tables 1 and 2.

[0041] In Tables 1 and 2, "groove area ratio" indicates the ratio of the sum of the total area of ​​fine grooves and the total area of ​​sipes to the tread area S of a specific land portion (the "fine groove + sipe" column in the table), and the ratio of the total area of ​​fine grooves to the tread area S of a specific land portion (the "fine groove" 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 the end region of the 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 the end region of the specific land portion are indicated as "different directions." For "fine groove inclination angle," two columns, one for "central region" and one for "end region," are provided, and when the "fine groove inclination direction" is "different directions," both the inclination angle of the fine groove in the central region of the specific land portion and the inclination angle of the fine groove in the end region are indicated. Note that 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 tread area S of a specific land portion [unit: mm 2 ] to the total ratio of the sipe lengths L [unit: mm] of all sipes included in the specific land portion projected in the tire width direction [unit: mm / mm 2 〕

[0042] The test tires were evaluated for braking performance on ice by the following test method, and the results are shown in Tables 1 and 2.

[0043] 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 / 240 kPa. A braking test (20 km / 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 set at 100. The higher the index value, the shorter the braking distance and the better the braking performance on ice.

[0044]

[0045]

[0046] 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 sum of the total area of ​​the fine grooves and the total area of ​​the sipes to the tread area S in the specific land portion, so the effect of improving braking performance on ice was limited. The tire of Comparative Example 2 had a small ratio of the sum of the total area of ​​the fine grooves and the total area of ​​the sipes to the tread area S in the specific land portion, so the effect of improving braking performance on ice was limited.

[0047] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 20 circumferential main groove 30 lug groove 40 land portion s sipe g fine groove CL tire equator

Claims

1. A tire having a tread portion extending circumferentially and forming an annular shape, wherein 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 extending in a direction intersecting the sipe, the narrow grooves being shallower than the sipes and having a groove depth of 1.5 mm or less, and the ratio of the sum of the total area of ​​the narrow grooves and the total area of ​​the sipes to the tread area S in the specific land portion is 7% to 35%.

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. A tire according to claim 1 or 2, characterized in that the ratio of the total area of ​​said narrow grooves to the tread area S in said specific land portion is 5% to 19%.

4. A tire according to any one of claims 1 to 3, characterized in that the narrow grooves have an inclination angle of 30° to 70° with respect to the tire circumferential direction.

5. A tire as described in any one of claims 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 differs from the inclination direction of the narrow grooves in the central region.

6. A tire according to claim 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.

7. A tire as described in claim 5 or 6, characterized in that the inclination angle of the narrow groove relative 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.

8. Area S of the tread surface of the specific land portion [unit: mm 2 the ratio of the total sipe length L (unit: mm) of all sipes included in the specific land portion projected in the tire width direction to ... is 0.06 mm / mm 2 ~0.30mm / mm 2 The tire according to any one of claims 1 to 7, characterized in that the range of 9. A tire according to any one of claims 1 to 8, characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the sipes and narrow grooves, to the area of ​​the contact patch of the tread portion is 20% to 60%.

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