Tire

Abstract

The present invention provides a tire capable of exhibiting excellent braking performance on ice at the initial stage of wear. This tire is configured so that: at least one of a plurality of land portions 40 formed in a tread portion 1 is a specific land portion provided with at least one sipe S extending along a tire width direction on the tread surface, and a plurality of narrow grooves G extending in a direction intersecting the sipe S; the narrow grooves G are shallower than the sipe S, in which the narrow grooves G have a groove depth of 1.5 mm or less, and a pitch p of 0.3-10.0 mm; the sipe S includes a zigzag-shaped portion, in which there are one to two narrow grooves G arranged per two wavelengths (2λ) of the zigzag shape of the sipe S; and the ratio of the sum of the total area of the narrow grooves G and the total area of the sipe S to the area A of the tread surface of the specific land portion is 7-35%.

Description

tire

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

[0002] In tires designed for icy and snowy roads, such as studless tires, fine irregularities are formed on the tread surface by mixing fillers or air bubbles into the tread rubber. These irregularities provide a water film removal effect, ensuring excellent driving performance on icy and snowy roads. However, before the break-in period, these irregularities are not fully visible on the tread surface, which means that the tire cannot fully demonstrate its intended driving performance in the initial 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 portion divided into sections. In such a tire, even when the above-mentioned irregularities are not fully manifested, the sipes and fine grooves on the land portion surface provide an edge effect and a water film removal effect, thus ensuring driving performance on icy roads 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 needed.

[0004] Japanese Patent Application Publication No. 2005-186827

[0005] The objective of the present invention is to provide a tire that exhibits excellent braking performance on ice, even in the initial stages of wear.

[0006] The present invention, for achieving the above objective, is a tire having a tread portion that extends in the circumferential direction of the tire and forms an annular shape, wherein the tread portion has a plurality of circumferential main grooves extending along the circumferential direction of the tire, 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, and at least one of these land portions is a specific land portion having at least one sipe extending along the tire width direction and a plurality of fine grooves extending in a direction intersecting the sipe on its tread surface, the fine grooves being shallower than the sipe and having a groove depth of 1.5 mm or less, the pitch of the plurality of fine grooves being 0.3 mm to 10.0 mm, the sipe including a zigzag-shaped portion, the number of fine grooves per two wavelengths of the zigzag shape of the sipe being 1 to 2, and the area of ​​the tread surface in the specific land portion A [unit: mm] 2 The ratio of the total area of ​​the fine grooves and the total area of ​​the sipes to the total area of ​​the grooves is 7% to 35%.

[0007] In this invention, since at least one of the multiple land areas is the specified land area described above, excellent ice performance can be achieved. Specifically, since sipes are provided on the specified land area, the water film removal effect and edge effect of the sipes can be ensured, thereby improving ice performance. On the other hand, since multiple fine grooves (fine grooves with a groove depth of 1.5 mm or less) are formed on the tread surface of the specified land area, these fine grooves can also supplement the water film removal effect, thereby improving ice performance (especially ice performance in the initial stages of wear). In particular, since the pitch of the fine grooves and the arrangement (number) of the fine grooves relative to the zigzag shape (wavelength) of the sipes are set as described above, the effects of the sipes and the fine grooves can be balanced well. In addition, when using sipes and fine grooves in combination, the ratio of the total area of ​​sipes and fine grooves to the area A of the tread surface of the specified land area is set within an appropriate range, so that the edge effect and water film removal effect of the sipes and fine grooves can be sufficiently ensured. On the other hand, the reduction in the actual contact area of ​​the specific land portion (the area of ​​the tread surface of the land portion that actually contacts the road surface, excluding the sipes and grooves) due to the sipes and grooves can be suppressed, allowing for excellent braking performance on ice. The area S of the tread surface of the specific land portion is the area inside the outer contour of the specific land portion (the whole area including the sipes and grooves). The area of ​​the sipes and grooves is the area of ​​the openings of the sipes and grooves on the tread surface of the specific land portion.

[0008] In the present invention, it is preferable that the width of each narrow groove is 0.05 mm to 1.0 mm, and the pitch of multiple narrow grooves is 0.5 mm to 5.0 mm. This ensures sufficient actual contact area with the ground on a specific land area to secure braking performance on ice, and further enhances braking performance on ice through the water film removal effect of the narrow grooves, thus being advantageous for improving ice performance.

[0009] In this invention, the area A of the tread surface of a specific land area [unit: mm] 2 It is preferable that the ratio of the total area of ​​the multiple narrow grooves formed on this specific land area to the total area of ​​the specific land area is 5% to 19%. This is advantageous for improving ice performance because it ensures sufficient actual contact area of ​​the specific land area to secure ice braking performance, and further secures ice braking performance through the water film removal effect of the narrow grooves.

[0010] In this invention, it is preferable that the inclination angle of the narrow grooves with respect to the tire circumferential direction is 30° to 70°. This allows for a good balance between the edge effect of the narrow grooves and drainage performance, which is advantageous for improving ice performance. The inclination angle of the narrow grooves is the angle of the acute portion of the angle formed between the narrow grooves and the tire circumferential direction.

[0011] In this invention, the area A of the tread surface of a specific land area [unit: mm] 2 The ratio of the sum of the sipe lengths L [unit: mm] of all sipes formed on this specific land area to 0.06 mm / mm 2 ~0.30mm / mm 2 It is preferable that the range is within this range. By providing sufficient sipes on each specific land area in this way, the edge effect and water film removal effect of the sipes can be enhanced, which is advantageous for improving ice performance.

[0012] In this invention, when the central side of a specific land area in the tire width direction is defined as the widthwise central region, and both sides of the widthwise central region are defined as widthwise end regions, the inclination direction of the narrow grooves in at least one of the widthwise end regions can be specified to be different from the inclination direction of the narrow grooves in the widthwise central region. This improves the water film removal effect by the narrow grooves, which is advantageous for improving ice performance.

[0013] In this case, it is preferable that the area of ​​the end region in the width direction, which is provided with fine grooves having a different inclination direction than the fine grooves in the central region in the width direction, is smaller than the area of ​​the central region in the width direction. This results in a good balance between the area of ​​the central region and the end region, where the inclination directions of the fine grooves are different, which is advantageous for improving the water film removal effect by the fine grooves and enhancing ice performance.

[0014] Furthermore, it is preferable that the inclination angle of the narrow grooves with respect to the tire circumferential direction is 30° to 60° in the central region in the width direction of a specific land area, and 30° to 70° in the end region in the width direction of a specific land area. This results in a good inclination angle of the narrow grooves in both the central and end regions, which is advantageous for improving the water film removal effect by the narrow grooves and enhancing ice performance. Note that the inclination angle of the narrow grooves in both the central and end regions is the angle of the acute portion of the angle formed between the narrow grooves and the tire circumferential direction.

[0015] In the present invention, it is preferable that the inclination angle of the sipes in the tire circumferential direction with respect to the normal direction of the tread surface of the tread portion is 3° to 40°. By setting the sipe shape inside the land portion in this way, it is possible to prevent the land portion from collapsing, increase the rigidity of the land portion during braking and driving, and improve ice performance.

[0016] In this case, the sipes have bends that extend in the tire width direction, with one or more points in the tire diameter direction within the land portion of the tire, and the inclination angle of the sipes in the tire circumferential direction relative to the normal direction of the tread surface of the tread is set to be greater on the tread surface side than on the bottom side of the sipes, with the inclination angle of the part closest to the tread surface being 10° to 40° and the inclination angle of the part closest to the bottom of the sipes being 3° to 20°. By bending the sipes within the land portion in this way and setting the inclination angle as described above, it is advantageous to prevent the land portion from collapsing, increase the rigidity of the land portion during braking and driving, and improve ice performance.

[0017] In the present invention, it is preferable that the sipes bend in the tire circumferential direction at one or more points in the tire radial direction within the land portion, forming a bent portion that continues in the tire width direction, and that the bent portion forms a zigzag shape with an amplitude of 0.5 mm to 5.0 mm in the tire radial direction. By bending the sipes within the land portion in this way, it is possible to prevent the land portion from collapsing, increase the rigidity of the land portion during braking and driving, and improve ice performance.

[0018] In this invention, the "contact area" of the tread portion is the area that contacts the plane when the tire is mounted on a standard rim, filled to the standard internal pressure (in the case of a pneumatic tire), placed vertically on a plane, and subjected to a standard load. The "standard rim" is the rim specified for each tire in the standard system that includes the standard on which the tire is based. For example, it is a standard rim for JATMA, a "Design Rim" for TRA, or a "Measuring Rim" for ETRTO. "Regular internal pressure" refers to the air pressure specified for each tire in the tire standard system, including the standard on which the tire is based. For JATMA, it is the maximum air pressure; for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and for ETRTO, it is "INFLATION PRESSURE," however, if the tire is for a passenger car, it should be 180 kPa. "Regular load" refers to the load specified for each tire in the standards system, including the standards 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 "LOAD CAPACATY." However, if the tire is for a passenger car, it shall be a load equivalent to 88% of the above load.

[0019] 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, it can be filled with air, an inert gas such as nitrogen, or other gases.

[0020] Figure 1 is a meridian cross-sectional view showing an example of a pneumatic tire according to an embodiment of the present invention. Figure 2 is an unfolded view showing the tread pattern of the pneumatic tire of Figure 1. Figure 3 is a schematic explanatory diagram showing an example of a specific land portion of the present invention. Figure 4 is a schematic explanatory diagram showing another example of a specific land portion of the present invention. Figure 5 is a cross-sectional view showing the shape of the fine grooves and sipes of the present invention. Figure 6 is a perspective view showing a cutaway portion of the land portion of the present invention. Figure 7 is a side view of the land portion of Figure 6. Figure 8 is a side view of a land portion according to another embodiment of the present invention. Figure 9 is a side view showing the inner wall surface of the sipes in the block of Figure 6.

[0021] The configuration of the present invention will be described in detail below with reference to the attached drawings.

[0022] The tire of the present invention, in the case of a pneumatic tire as shown in Figure 1, 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-sectional view, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the circumferential direction of the tire and form an annular shape, thereby forming the basic toroidal structure of the pneumatic tire. The following explanation using Figure 1 is basically based on the illustrated meridian cross-sectional shape, but each tire component extends in the circumferential direction of the tire and forms an annular shape.

[0023] A carcass layer 4 is mounted between a pair of left and right bead sections 3. This carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction and is folded back from the inside to the outside in the tire width direction around a bead core 5 located in each bead section 3. A bead filler 6 is placed on the outer circumference of the bead core 5, and this bead filler 6 is enclosed by the main body and folded 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.

[0024] Multiple belt layers 7 are embedded on the outer circumference 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 to intersect 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 to a range of, for example, 10° to 40°. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt reinforcement layer 8 is provided on the outer circumference of the belt layers 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 to, for example, 0° to 5°. Organic fiber cords such as nylon or aramid are preferably used as the reinforcing cords of the belt cover layer 8.

[0025] In the tread portion 1, a tread rubber layer 11 is arranged on the outer periphery of the carcass layer 4, belt layer 7, and belt reinforcement layer 8 described above. 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 constitutes the tread surface of the tread portion 1 and an under tread layer arranged on its inner periphery) are laminated in the tire diameter direction. In the sidewall portion 2, a side rubber layer 12 is arranged on the outer periphery (outer side in the tire width direction) of the carcass layer 4. In the bead portion 3, a rim cushion rubber layer 13 is arranged on the outer periphery (outer side in the tire width direction) of the carcass layer 4. From the viewpoint of improving ice performance, the rubber composition constituting the tread rubber layer 11 (especially the cap tread layer) is preferably mixed with fillers and air bubbles so that when the tread surface wears down, fine irregularities appear that have a water film removal effect.

[0026] Since the present invention relates to sipes and fine grooves formed on the surface of the tread portion 1 of a tire, as described later, the basic structure (internal structure) of the tire is not limited to the general structure described above. Furthermore, although the following explanation will be based on the pneumatic tire shown in Figure 1, the present invention can be applied to various types of tires, including non-pneumatic tires, as long as they have a surface that contacts the road surface (a portion corresponding to the surface of the tread portion 1 in a pneumatic tire).

[0027] As shown in Figure 2, the surface of the tread portion 1 is formed with a plurality of circumferential main grooves 20 extending along the tire's circumferential direction, a plurality of lug grooves 30 extending along the tire's width direction, and a plurality of land portions 40 partitioned by these circumferential main grooves 20 and lug grooves 30. The circumferential main grooves 20 are grooves that carry the main 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 common dimension for tires, for example, a groove width of 1.0 mm or more and a groove depth of 3.0 mm or more.

[0028] Of the multiple land sections 40 thus partitioned, at least one is provided with at least one sipe S extending along the tire width direction and multiple narrow grooves G having a groove depth smaller than that of the sipe S on its tread surface, as shown in Figures 3-4. In the following description, the land section 40 equipped with these sipes S and narrow grooves G may be referred to as a specific land section. Since the present invention mainly relates to this specific land section, the details of the tread pattern are not particularly limited as long as it includes at least one specific land section.

[0029] As shown in Figure 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 mainly extend along the tire width direction and are arranged at intervals in the tire circumferential direction, primarily providing an edge effect and drainage. In particular, even in the early stages of wear (before the original performance of the tread rubber is fully realized), the edge effect and water film removal effect provided by the sipes S are obtained, which is advantageous for improving ice performance. Each sipe S has a shape that includes a zigzag shape in at least a part of the tread surface of a specific land area, as shown in the figure. More specifically, on the tread surface of a specific land area, each sipe S always includes a zigzag shape where a straight section inclined in one direction with respect to the extension direction of the sipe S and a straight section inclined in the other direction are alternately connected along the extension direction of the sipe S and bent in a triangular wave shape. Furthermore, as long as the sipe S has the aforementioned zigzag shape, it can be appropriately provided with both ends communicating with the circumferential main groove 20, one end communicating with the circumferential main groove 20 while the other end terminates within the land portion 40, or both ends terminating within the land portion 40, taking into consideration the size of the land portion 40.

[0030] As mentioned above, the fine grooves G are shallower than the sipes S, and as shown in Figure 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 fine grooves G is preferably 0.05 mm to 1.0 mm, more preferably 0.1 mm to 0.8 mm. Thus, the fine grooves G are minute grooves, and as shown in the figure, they extend in a direction intersecting the sipes S, and multiple fine grooves are arranged in a row in the circumferential direction of the tire. In particular, as shown in Figures 3 to 4, it is preferable that multiple fine grooves G are arranged periodically and repeatedly evenly across the entire surface of the land portion 40 (specific land portion). By providing multiple fine grooves G, the water film removal effect by the fine grooves G can be obtained even in the early stages of wear (before the original performance of the tread rubber is fully exhibited), so that excellent braking performance on ice can be achieved. If the groove depth Dg of the fine 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 groove width of the narrow groove G is small, making it difficult to obtain sufficient water removal performance and thus difficult to improve braking performance on ice. If the groove width Wg of the narrow groove G exceeds 1.0 mm, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0031] Furthermore, the cross-sectional shape of the narrow groove G is not particularly limited. For example, in addition to a shape with a flat groove bottom in cross-sectional view (rectangular) as shown in Figure 5, a U-shaped or V-shaped cross-section can be adopted. When arranging multiple narrow grooves G periodically as shown in Figures 3-4, the pitch p of the multiple narrow grooves G shown in Figure 5 (the interval between periodically arranged narrow grooves G, more precisely the distance from one wall surface of any narrow groove G to one wall surface of the adjacent narrow groove G as shown in the figure) is set to 0.3 mm to 10.0 mm, preferably 0.5 mm to 5.0 mm, and more preferably 0.7 mm to 4.0 mm. This ensures sufficient actual contact area on a specific land area to secure braking performance on ice, and further enhances braking performance on ice through the water film removal effect of the narrow grooves G, thus being advantageous for improving ice performance. If the pitch p of the narrow grooves G is less than 0.3 mm, it becomes difficult to improve braking performance on ice because the actual contact area decreases. If the pitch p of the narrow grooves G exceeds 10.0 mm, it becomes impossible to arrange a sufficient number of narrow grooves G within a specific land area, making it difficult to ensure sufficient water removal and thus hindering the improvement of braking performance on ice.

[0032] As mentioned above, since the sipe S has a zigzag shape, the length from any phase of the sipe (waveform) back to the same phase can be defined as the wavelength λ. In other words, as shown in the figure, the distance along the extension direction of the sipe S between adjacent vertices on one side in the amplitude direction of the sipe S can be defined as the wavelength λ. When considering the wavelength λ of the sipe S in this way, not only are the fine grooves G arranged to satisfy the above pitch p range, but the number of fine grooves G arranged per two wavelengths of the zigzag shape of the sipe S is set to one to two. That is, when focusing on any sipe S, it is desirable that multiple fine grooves G be arranged at intervals where one to two fine grooves G intersect in the portion of two wavelengths (length 2λ) along the extension direction of the sipe S. As a result, the fine grooves G are arranged in an appropriate balance with respect to the zigzag shape (bent shape) of the sipe S, so that the actual contact area of ​​the specific land area is sufficiently secured to ensure ice braking performance, and further ice braking performance can be ensured by the water film removal effect of the fine grooves G. If the number of fine grooves G per two wavelengths of sipe S is less than one, the fine grooves G are sparsely arranged relative to the zigzag shape (bent shape) of sipe S, and it becomes impossible to arrange a sufficient number of fine grooves G within a specific land area, thus limiting the effect of improving ice braking performance. If the number of fine grooves G per two wavelengths of sipe S exceeds two, the fine grooves G are densely arranged relative to the zigzag shape (bent shape) of sipe S, and it becomes difficult to improve ice braking performance as the actual contact area decreases. The wavelength λ varies depending on the shape and size of sipe S (sipe length and amplitude of zigzag shape), but the wavelength λ is preferably 1 mm to 10 mm, more preferably 1.5 mm to 6 mm, and even more preferably 2 mm to 4 mm. If the wavelength λ is less than 1 mm, even if the pitch p is set small and the fine grooves G are densely arranged, it becomes difficult to set the number of fine grooves G per two wavelengths of sipe S to the above 1 to 2. When the wavelength λ exceeds 10 mm, if the number of narrow grooves G per two wavelengths of sipe S is set to the above-mentioned 1 to 2, the number of narrow grooves G provided in each land area decreases, thus limiting the water removal effect of the narrow grooves G.

[0033] As described above, in the present invention, the details of the tread pattern are not particularly limited as long as it includes at least one specific land portion. The tread pattern in the example of FIG. 2 includes, as circumferential main grooves 20, a pair of inner main grooves 21 disposed on both sides of the tire equator CL, and a pair of outer main grooves 22 disposed on the outer side in the tire width direction of the inner main grooves 21. One of the pair of inner main grooves 21 (the inner main groove 21a on the right side in the drawing) extends while bending in a zigzag shape along the tire circumferential direction, and the other of the pair of inner main grooves 21 (the inner main groove 21b on the left side in the drawing) extends such that the groove width varies along the tire circumferential direction as the groove wall on the outer side in the tire width direction bends in a zigzag shape. Each of the outer main grooves 22 extends linearly along the tire circumferential direction.

[0034] In the illustrated example, between the pair of inner main grooves 21, 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. On one side of the tire equator (the right side in the drawing), between the zigzag-shaped inner main groove 21a and the outer main groove 22, a plurality of block-shaped land portions (intermediate land portions 42a) defined by these grooves and lug grooves 30 (intermediate lug grooves 32a) are arranged in the tire circumferential direction. Each of the intermediate land portions 42a is provided with a circumferential auxiliary groove 51 that extends in a zigzag shape along the tire circumferential direction and connects the lug grooves adjacent to each other in the tire circumferential direction. On the other side of the tire equator (the left side in the drawing), between the inner main groove 21b with a varying groove width and the outer main groove 22, a rib-shaped land portion (intermediate land portion 42b) defined by these grooves and continuous over the entire tire circumference is formed. The intermediate land portion 42b is provided with lug grooves 30 (intermediate lug grooves 32b) that communicate with each of the inner main groove 21b and the outer main groove 22 and terminate within the land portion. On the outer side in the tire width direction of the pair of outer main grooves 22, a plurality of block-shaped land portions (shoulder land portions 43) defined by the outer main grooves 22 and lug grooves 30 (shoulder lug grooves 33) are arranged in the tire circumferential direction. Each of the shoulder land portions 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.

[0035] Even for land portions 40 of various shapes included in the tread pattern as described above, when the sipes S and the narrow grooves G are provided in the balance described above, they are regarded as the specific land portions in the present invention. In particular, in the example of FIG. 2, all the land portions 40 are the specific land portions, and the area relationships and the like described later are applied to all the land portions 40.

[0036] As described above, by arranging at least one sipe S and the plurality of narrow grooves G in the balance described above, it is possible to ensure the on-ice performance at the initial stage of wear in the specific land portion. At that time, 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 surface area A of the specific land portion is set to 7% to 35%, preferably 10% to 27%. By satisfying such a relationship, the water film removing effect by the sipes S and the narrow grooves G can be sufficiently ensured, while the reduction of the actual ground contact area of the specific land portion caused by the sipes S and the narrow grooves G can be suppressed, and excellent on-ice braking performance can be exhibited. At this time, 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 surface area A of the specific land portion is less than 7%, the number of sipes S and narrow grooves G formed in the specific land portion decreases, so that sufficient water removal performance cannot be obtained, and it becomes difficult to improve the on-ice braking performance. 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 surface area A of the specific land portion exceeds 35%, it becomes difficult to improve the on-ice braking performance in that the actual ground contact area decreases.

[0037] The ratio of the total area of the plurality of narrow grooves G to the tread surface area A of the specific land portion is preferably 5% to 19%, and more preferably 7% to 17%. Thereby, the actual ground contact area of the specific land portion can be sufficiently ensured to secure the on-ice braking performance, and further the on-ice braking performance can be secured by the water film removing effect of the narrow grooves, which is advantageous for improving the on-ice performance. If the ratio of the total area of the plurality of narrow grooves G to the tread surface area A of the specific land portion is less than 5%, sufficient water removal performance by the narrow grooves G cannot be obtained, so that it becomes difficult to improve the on-ice braking performance. If the ratio of the total area of the plurality of narrow grooves G to the tread surface area A of the specific land portion exceeds 19%, it becomes difficult to improve the on-ice braking performance in that the actual ground contact area decreases.

[0038] The inclination angle θ of the narrow groove G with respect to the tire circumferential direction is preferably 30° to 70°, more preferably 35° to 55°. This allows for a good balance between the edge effect and drainage performance of the narrow groove G, which is advantageous for improving ice performance. If the inclination angle θ of the narrow groove G is less than 30°, it becomes difficult to improve ice braking performance because the edge effect cannot be sufficiently secured. If the inclination angle θ of the narrow groove G exceeds 70°, it becomes difficult to improve ice braking performance because sufficient water removal performance from the narrow groove G cannot be obtained.

[0039] As shown in Figure 4, when the central area in the tire width direction of a specific land area is defined as the central region C, and the areas on both sides of the central region in the tire width direction are defined as end regions E, the inclination direction of the narrow grooves G in at least one end region E can be different from the inclination direction of the narrow grooves G in the central region C. In this specification, the water film removal effect by the narrow grooves G can be enhanced compared to when the narrow grooves G extend in a single direction, which is advantageous for improving ice performance. In this case, it is preferable that the area of ​​the end region E provided with narrow grooves G having an inclination direction different from that of the narrow grooves G in the central region C is smaller than the area of ​​the central region C. In particular, the maximum width W of the specific land area 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%. If the inclination direction of the narrow groove G is different in the end regions E on both sides in the tire width direction as shown in the figure, then the width W E This is the sum of the widths of the two end regions E. This results in a good balance between the area of ​​the central region C and the end regions E, where the inclination directions of the narrow grooves G are different, which is advantageous for improving the water film removal effect of the narrow grooves G and enhancing ice performance.

[0040] As described above, when the inclination directions of the thin grooves G are different between the central region C and the end region 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 end region E is preferably 30° to 70°, more preferably 35° to 60°. This optimizes the inclination angles of the thin grooves G in each of the central region C and the end region E, which is advantageous for improving the water film removal effect of the thin grooves G and enhancing on-ice performance. If the inclination angle θc in the central region C is less than 30°, it becomes difficult to improve the on-ice braking performance because the edge effect cannot be sufficiently ensured. If the inclination angle θc in the central region C exceeds 60°, the water removal performance by the thin grooves G cannot be sufficiently obtained, making it difficult to improve the on-ice braking performance. If the inclination angle θe in the end region E is less than 30°, it becomes difficult to improve the on-ice braking performance because the edge effect cannot be sufficiently ensured. If the inclination angle θe in the end region E exceeds 70°, the water removal performance by the thin grooves G cannot be sufficiently obtained, making it difficult to improve the on-ice braking performance.

[0041] At least one siping 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 sum of the siping lengths L of all the sipings S included in the specific land portion projected in the tire width direction to the tread surface area A of the specific land portion (hereinafter referred to as siping density) is preferably 0.06 mm / mm 2 to 0.30 mm / mm 2 , more preferably 0.12 mm / mm 2 to 0.24 mm / mm 2 It is preferred to be in the range of. By sufficiently providing the sipings S in this way, the edge effect and water film removal effect by the sipings S can be enhanced, which is advantageous for improving on-ice performance. When the siping density is 0.06 mm / mm 2 If it is less than that, the siping length cannot be sufficiently ensured, so the edge effect and water removal effect by the sipings S are limited. When the siping density is 0.30 mm / mm 2 If it exceeds this value, it becomes difficult to improve the on-ice braking performance as the actual ground contact area decreases.

[0042] As described above, the present invention relates to a specific land area (particularly sipes S and fine grooves G), so the overall structure (tread pattern) of the tread portion 1 is not particularly limited. However, from the viewpoint of improving ice performance, the ratio of the total groove area of ​​all grooves formed in the tread portion 1, including sipes S and fine grooves G, to the area of ​​the contact area 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%. All grooves formed in the tread portion 1, including sipes S and fine grooves G, are, for example, in the case of Figure 2, circumferential main grooves 20 (inner main grooves 21 and outer main grooves 22), lug grooves 30 (center lug groove 31, intermediate lug grooves 32a, 32b, and shoulder lug grooves 33), circumferential auxiliary grooves 51, circumferential fine grooves 53, sipes S, and fine grooves G. Optimizing the overall groove area ratio of the tread section 1 in this way ensures sufficient contact area and thus secures braking performance on ice. Furthermore, the water film removal effect of the fine grooves ensures braking performance on ice, which is advantageous for improving ice performance. If the groove area ratio of the tread section 1 is less than 20%, sufficient drainage performance of the tread section 1 as a whole cannot be ensured, and even if the specific land section of the present invention is adopted, the effect of improving ice performance will be limited. If the groove area ratio of the tread section 1 exceeds 60%, sufficient contact area of ​​the tread section 1 as a whole cannot be ensured, and even if the specific land section of the present invention is adopted, the effect of improving ice performance will be limited.

[0043] As described above, the sipe S in the present invention has the aforementioned zigzag shape on the tread surface of the land portion, but in addition to this, various structures described below can be adopted inside the land portion. For example, as shown in Figure 6, while the sipe S has the aforementioned zigzag shape on the tread surface of the tread portion 1, inside the block it bends in the tire circumferential direction (Tc) at one or more locations in the tire radial direction (Tr) and forms a plurality of bent portions s that connect in the tire width direction (Tw). These bent portions s are convex bent portions s ａ and a concave bent portion s ｂ It has a convex bent portion s on one wall surface of the sipe S. ａ and a concave bent portion s ｂ These are arranged alternately, and on the other wall surface (not shown) opposite them, there is a convex bend s ａand a concave bent portion s ｂ The positional relationship is reversed. When a bent portion s that bends in the circumferential direction of the tire is provided in the sipe S in this way, the small blocks on both sides of the sipe S interlock with each other during braking and driving, suppressing deformation of the land portion 40 and preventing the land portion 40 from collapsing in the circumferential direction of the tire. Note that the fine grooves G are omitted in the drawings from Figure 6 onward as they are intended to illustrate the shape of the sipe S.

[0044] When a bent portion s is present in this manner, as shown in Figure 7, the inclination angle α of the sipe S in the tire circumferential direction (Tc) with respect to the normal direction of the tread surface of the tread portion 1 is preferably set to 3° to 40°, more preferably to 5° to 35°. If this inclination angle α is less than 3°, the effect of supporting the collapse of the land portion 40 during braking and driving will be limited. If this inclination angle α exceeds 40°, there is a concern that the release properties from the mold during tire manufacturing will decrease. As shown in Figure 8, the sipe S may extend linearly along the tire radial direction (Tr) without having a bent portion s inside the land portion, and in this case, the sipe S can also extend at an inclination with respect to the normal direction of the tread surface of the tread portion 1. In this case, the inclination angle α is also preferably 3° to 40°, more preferably to 5° to 35°, similar to the above.

[0045] As shown in the example in Figure 7, when a sipe S bends in the circumferential direction (Tc) of the tire at one or more points in the radial direction (Tr) of the tire within the block, each bending point s will have an inclination angle α. However, these multiple inclination angles α do not need to be constant, and it is possible to have a specification where the inclination angle α is larger on the tread surface side of the tread portion 1 than on the sipe bottom side. In this case, the inclination angle α1 on the tread surface side is preferably set to 10° or more and 40° or less, more preferably 12° or more and 35° or less, and the inclination angle α2 on the sipe bottom side is preferably set to 3° or more and 20° or less, more preferably 5° or more and 15° or less. As mentioned above, the inclination angle α is larger on the tread surface side than on the sipe bottom side, so the inclination angles α1 and α2 preferably satisfy the relationship α1 > α2, and the difference between them (α1 - α2) is preferably 5° to 20°. Setting the bending angles in this way is advantageous for preventing the land portion from collapsing, increasing the rigidity of the land portion during braking and driving, and improving ice performance. If the inclination angles α1 and α2 are smaller than the above range, proper bending will not occur, and the additional effects of setting the inclination angles α1 and α2 as described above will not be fully obtained. If the inclination angles α1 and α2 are larger than the above range, there is a concern that the release properties from the mold during tire manufacturing will decrease.

[0046] Furthermore, as described above, when the sipe S has a bend s that bends in the tire circumferential direction at one or more locations in the tire radial direction (Tr) within the land portion and continues in the tire width direction, it is also possible to have a zigzag shape with amplitude T in the tire radial direction (Tr) at this bend s, as shown in Figure 9. When the sipe S has amplitude T in the tire radial direction (Tr) at the bend s in this way, the small blocks on both sides of the sipe S interlock with each other during cornering, suppressing deformation of the land portion 40 and suppressing the collapse of the land portion 40 in the tire width direction. The amplitude T at the bend s is preferably 0.5 mm to 5.0 mm, more preferably 1.0 mm to 4.0 mm. If the amplitude T is less than 0.5 mm, there is virtually no amplitude, and the above additional effects cannot be sufficiently obtained. If the amplitude T exceeds 5.0 mm, there is a concern that the release properties from the mold will decrease during tire manufacturing.

[0047] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0048] Nineteen types of pneumatic tires (test tires), including Conventional Example 1, Comparative Examples 1-2, and Examples 1-16, were manufactured. These tires had a tire size of 195 / 65R15 91Q, a basic structure (internal structure) as shown in Figure 1, and a tread pattern based on Figure 2. The groove area ratio, groove width, groove pitch, number of grooves per two sipe wavelengths, groove inclination direction, groove inclination angle, sipe density, presence or absence of sipe bends, sipe inclination angle, and sipe radial amplitude T were set as shown in Tables 1-2.

[0049] In Tables 1 and 2, "Grove Area Ratio" refers to the ratio of the total area of ​​grooves and sipes to the total area of ​​the tread surface S in the specified land area (the "Grove + Sipe" column in the table) and the ratio of the total area of ​​grooves to the total area of ​​the tread surface S in the specified land area (the "Grove" column in the table). In the "Grove Slope Direction" column, "Same Direction" is indicated when the groove slope direction is the same in the central and end regions of the specified land area, and "Different Directions" is indicated when the groove slope direction is different in the central and end regions of the specified land area. "Grove Slope Angle" has two columns, "Central Region" and "End Region," and when the "Grove Slope Direction" is "Different Directions," both the groove slope angle in the central region and the groove slope angle in the end region of the specified land area are indicated. However, when the "Grove Slope Direction" is "Same Direction," the slope angle value is displayed only in the "Central Region" column. "Sipe Density" refers to the area of ​​the tread surface S of the specified land area [unit: mm] 2 The ratio of the total sipe length L [unit: mm] projected in the tire width direction for all sipes included in the specific land area to [unit: mm / mm] 2 ]

[0050] In Tables 1 and 2, the "Presence or Absence of Sipe Bending" column indicates whether the sipe has bending sections that extend in the tire width direction at one or more points (four points in Examples 15 and 16) in the tire diameter direction within the land portion of the sipe, and whether it does not have such bending sections and whether the sipe extends linearly toward the bottom of the sipe within the land portion of the sipe. The "Sipe Inclination Angle" column shows the inclination angle of the sipe in the tire circumferential direction with respect to the direction normal to the tread surface of the tread. In particular, if the "Presence or Absence of Sipe Bending" column is "Presence," the inclination angle at the point closest to the tread surface and the inclination angle at the point closest to the bottom of the sipe are listed, respectively. If the "Presence or Absence of Sipe Bending" column is "Absence," a value is conveniently entered in the "Tread Side" column. "Radial amplitude T of the sipe" represents the value of the radial amplitude T at the aforementioned bend in the tire, when the sipe forms a zigzag shape with amplitude in the radial direction of the tire at this bend.

[0051] In Comparative Example 2, since one fine groove is provided so as to intersect a portion of the sipe that spans four wavelengths along its extension direction, the value "0.5" is displayed in the "Number of fine grooves per two sipe wavelengths" column for convenience. Furthermore, even if the "Number of fine grooves per two sipe wavelengths" is common to two, as in Examples 3 to 5, if the groove pitch is different, the sipe wavelength can be adjusted appropriately to satisfy the requirement of two "Number of fine grooves per two sipe wavelengths".

[0052] The ice braking performance of these test tires was evaluated using the following test method, and the results are shown in Tables 1 and 2.

[0053] For the ice braking performance test, each test tire was mounted on a rim size of 15 x 6.5J and fitted to all wheels of a 1800cc front-wheel-drive vehicle. The tires were inflated to an air pressure of 250 / 240 kPa, and a test driver conducted a braking test (20 km / h) on an icy surface. The evaluation results were shown as an index, with the reciprocal of the measured value set to 100 (Conventional Example 1). A higher index value indicates a shorter braking distance and superior ice braking performance.

[0054]

[0055]

[0056] As can be seen from Tables 1-2, the tires of Examples 1-16 showed improved braking performance on ice compared to Conventional Example 1. On the other hand, Comparative Example 1 had a large number of fine grooves intersecting the two wavelengths of the sipes, and a large groove area ratio (the ratio of the total area of ​​multiple fine grooves and multiple sipes formed on a specific land area to the area of ​​the tread on that specific land area), so it did not sufficiently improve ice performance. Comparative Example 2 had a small number of fine grooves intersecting the two wavelengths of the sipes, and a small groove area ratio (the ratio of the total area of ​​multiple fine grooves and multiple sipes formed on a specific land area to the area of ​​the tread on that specific land area), so it did not sufficiently improve ice performance.

[0057] 1. Tread section 2. Sidewall section 3. Bead section 20. Circumferential main groove 30. Lug groove 40. Land section S. Sipes G. Fine groove CL. Tire equator

Claims

1. A tire having a tread portion that extends in the circumferential direction and forms an annular shape, wherein the tread portion has a plurality of circumferential main grooves extending along the circumferential direction of the tire, 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, and at least one of these land portions is a specific land portion having at least one sipe extending along the tire width direction and a plurality of fine grooves extending in a direction intersecting the sipe on its tread surface, the fine grooves being shallower than the sipe and having a groove depth of 1.5 mm or less, the pitch of the plurality of fine grooves being 0.3 mm to 10.0 mm, the sipe including a zigzag-shaped portion, the number of fine grooves per two wavelengths of the zigzag shape of the sipe being 1 to 2, and the area of ​​the tread surface in the specific land portion A [unit: mm] 2 A tire characterized in that the ratio of the total area of ​​the fine grooves and the total area of ​​the sipes to the total area of ​​the grooves is between 7% and 35%.

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

3. Area A of the tread surface of the specified land area [unit: mm] 2 The tire according to claim 1 or 2, characterized in that the ratio of the total area of ​​the multiple narrow grooves formed in this specific land area to the total area of ​​the land area is 5% to 19%.

4. The tire according to any one of claims 1 to 3, characterized in that the angle of inclination of the narrow groove with respect to the circumferential direction of the tire is 30° to 70°.

5. Area A of the tread surface of the specified land area [unit: mm] 2 The ratio of the total sipe length L [unit: mm] of all sipes formed on this specific land area to 0.06 mm / mm 2 ~0.30mm / mm 2 A tire according to any one of claims 1 to 4, characterized in that it is within the range.

6. The tire according to any one of claims 1 to 5, characterized in that when the central side of the specific land portion in the tire width direction is defined as the widthwise central region, and both sides of the widthwise central region are defined as widthwise end regions, the inclination direction of the narrow groove in at least one of the widthwise end regions is different from the inclination direction of the narrow groove in the widthwise central region.

7. The tire according to claim 6, characterized in that the area of ​​the end region in the width direction where the fine groove is provided, having a different inclination direction from the inclination direction of the fine groove in the central region in the width direction, is smaller than the area of ​​the central region in the width direction.

8. The tire according to claim 6 or 7, characterized in that the angle of inclination of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the central region in the width direction of the specific land portion, and 30° to 70° in the end region in the width direction of the specific land portion.

9. The tire according to any one of claims 1 to 8, characterized in that the angle of inclination of the sipes in the tire circumferential direction with respect to the normal direction of the tread surface of the tread portion is 3° to 40°.

10. The tire according to claim 9, characterized in that the sipe has a bent portion that bends in the tire circumferential direction at one or more locations in the tire radial direction within the land portion and continues in the tire width direction, while the inclination angle of the sipe in the tire circumferential direction with respect to the normal direction of the tread surface of the tread portion is set to be greater on the tread surface side than on the sipe bottom side, the inclination angle of the portion closest to the tread surface is 10° or more and 40° or less, and the inclination angle of the portion closest to the sipe bottom is 3° or more and 20° or less.

11. The tire according to any one of claims 1 to 10, characterized in that the sipe has a bent portion that is bent in the tire circumferential direction at one or more locations in the tire radial direction within the land portion and is connected in the tire width direction, and the bent portion forms a zigzag shape with an amplitude of 0.5 mm to 5.0 mm in the tire radial direction.

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