Tire

Abstract

Provided is a tire that makes it possible to exhibit an excellent water evacuating effect regardless of the amount of water on a road surface and improve on-ice performance. At least one of a plurality of land parts 40 formed on a tread part 1 is a specific land part having a plurality of short sipes Ss, which extend along the tire width direction and in which the sipe length L is at most 10% of the ground contact width, and a plurality of narrow grooves G, which extend in a direction intersecting the short sipes Ss and have a groove depth smaller than that of the short sipes Ss and not exceeding 1.5 mm, on a tread surface. The ratio of the total area of the plurality of narrow grooves G and the plurality of short sipes Ss formed in the specific land part to the area A [unit: mm2] of the tread surface of the specific land part is 7-35%.

Description

Tire

[0001] The present invention relates to a tire in which a short sipe having a small sipe length is provided in a tread portion.

[0002] In tires for ice and snow roads represented by studless tires, sipes are provided on the tread surface to enhance on-ice performance. That is, on an ice-covered road, the sipes can remove the water film on the surface of the ice-covered road to bring the tire tread into ground contact with the road surface, thereby exhibiting on-ice performance. In addition, to ensure on-ice performance, it is also important to ensure block rigidity, prevent the blocks from collapsing, and sufficiently secure the ground contact area. From these viewpoints, in recent years, it has been proposed to provide short sipes with small sipe lengths (for example, see Patent Document 1). Such short sipes can exert a water film removal effect without reducing block rigidity, and thus can effectively enhance on-ice performance. On the other hand, since the aforementioned short sipes have small individual sipe lengths, there is a concern that a sufficient water removal effect cannot be expected when the air temperature rises and the amount of water on the road surface increases. Therefore, measures are required to exhibit excellent on-ice performance regardless of the amount of water on the road surface.

[0003] Japanese Unexamined Patent Publication No. 2005-186827

[0004] An object of the present invention is to provide a tire that can exhibit an excellent water removal effect regardless of the amount of water on the road surface and improve on-ice performance.

[0005] To achieve the above object, the tire of the present invention is a tire including an annular tread portion extending in the tire circumferential direction, 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 partitioned by the circumferential main grooves and / or the lug grooves. At least one of the plurality of land portions is a specific land portion provided on its tread surface with a plurality of short sipes extending along the tire width direction and having a sipe length L [unit: mm] of 10% or less of the ground contact width, and a plurality of fine grooves having a groove depth smaller than that of the short sipes and 1.5 mm or less, and extending in a direction intersecting the short sipes, and the area S [unit: mm of the tread surface of the specific land portion 2The characteristic feature is that the ratio of the total area of ​​the multiple narrow grooves and the multiple short sipes formed in this specific land area to the total area of ​​the land area is between 7% and 35%.

[0006] In this invention, since at least one of the multiple land sections is the aforementioned specific land section, excellent ice performance can be achieved. Specifically, the specific land section is provided with multiple short sipes that extend along the tire width direction and have a sipe length L [unit: mm] of 10% or less of the contact width. This ensures the block rigidity of the specific land section, prevents the block from collapsing, and thus secures a sufficient contact area to improve ice performance. Furthermore, the water film removal effect by the short sipes also improves ice performance, and these combined effects enable particularly excellent ice performance. In addition, since multiple fine grooves (fine grooves with a groove depth of 1.5 mm or less) are formed on the tread surface of the specific land section, the water film removal effect that may be insufficient with short sipes alone can be compensated for, and ice performance (especially ice performance when the temperature is high and there is a large amount of water on the road surface) can be improved. At this time, the area S [unit: mm] of the tread surface of the specific land section 2 Since the ratio of the total area of ​​the narrow grooves and the short sipes to the total area is set within an appropriate range as described above, the water film removal effect of the short sipes and narrow 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 land portion tread that actually contacts the road surface, excluding the sipes and narrow grooves) due to the short sipes and narrow grooves can be suppressed, and excellent braking performance on ice can be achieved. Note that the area A of the specific land portion tread is the area inside the outer contour of the specific land portion (the whole including the sipes and narrow grooves). Also, the area of ​​the narrow grooves and the area of ​​the short sipes are the areas of the openings of each groove on the tread surface of the tread portion.

[0007] In the present invention, it is preferable that the pitch of the multiple narrow grooves is 0.5 mm to 5.0 mm, and the width of each narrow groove is 0.05 mm to 1.0 mm. This ensures sufficient actual contact area with the ground on a specific land surface 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.

[0008] In this invention, the area A of the tread surface of a specific land area [unit: mm]2 is preferably 5% to 19%, where the ratio is the total area of the plurality of fine grooves formed in this specific land portion. Sufficient actual ground contact area of the specific land portion can be ensured to secure on-ice braking performance, and further the water film removal effect by the fine grooves can secure the on-ice braking performance, which is advantageous for improving on-ice performance.

[0009] In the present invention, the ratio of the total sipe length L [unit: mm] projected in the tire width direction of all sipes formed in this specific land portion to the tread surface area A [unit: mm of the specific land portion 2 is preferably in the range of 0.06 mm / mm 2 to 0.30 mm / mm 2 . By sufficiently providing sipes in each specific land portion in this manner, the edge effect and water film removal effect by the sipes can be enhanced, which is advantageous for improving on-ice performance. The all sipes formed in the specific land portion refer to both the sipes other than short sipes (sipes having a sipe length L [unit: mm] exceeding 10% of the ground contact width) and the short sipes when the sipes other than short sipes are provided in the specific land portion.

[0010] In the present invention, when the tire circumferential center side of the specific land portion is defined as a circumferential central region, both outer sides in the tire circumferential direction of the circumferential central region are respectively defined as circumferential end regions, the area of the circumferential central region is 50% of the area of the specific land portion, and the area of each circumferential end region is 25% of the area of the specific land portion, the ratio Rc of the total sipe length L [unit: mm] projected in the tire width direction of all sipes formed in the circumferential central region to the area [unit: mm of the circumferential central region 2 , and the ratio Re of the total sipe length L [unit: mm] projected in the tire width direction of all sipes formed in the circumferential end region to the area [unit: mm of the circumferential end region 2 satisfy the relationship of Rc>Re, the ratio Rc in the circumferential central region is 0.12 mm / mm 2 to 0.30 mm / mm 2 , and the ratio Re in the circumferential end region is 0.06 mm / mm 2 to 0.24 mm / mm 2This is preferable. By arranging sipes in a balanced manner between the circumferential central region and the circumferential edge region within a single specific land area, it is advantageous to enhance the water film removal effect while maintaining block rigidity, thereby improving ice performance.

[0011] In the present invention, when the central side of a specific land area in the tire's circumferential direction is defined as the circumferential central region, and the outer sides of the circumferential central region in the tire's circumferential direction are defined as the circumferential end regions, with the area of ​​the circumferential central region being 50% of the area of ​​the specific land area, and the area of ​​each circumferential end region being 25% of the area of ​​the specific land area, it is preferable that the multiple sipes provided in the circumferential central region include open sipes that open to one side of a pair of main grooves adjacent to the specific land area. By incorporating open sipes in the circumferential central region in this way, the water removal effect can be effectively enhanced, which is advantageous for improving ice performance.

[0012] 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.

[0013] In the present invention, it is preferable that the ratio of the total groove area of ​​all grooves formed in the tread portion, including short sipes and fine grooves, to the area of ​​the contact area of ​​the tread portion is 20% to 60%. The "all grooves formed in the tread portion, including short sipes and fine grooves," refers to main grooves extending along the circumferential direction of the tire, lug grooves extending along the width direction of the tire, short sipes, sipes other than short sipes, fine grooves, and various other grooves appropriately formed according to the tire. The area of ​​these grooves is the area of ​​the groove openings on the tread surface of the tread portion.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] In this invention, "contact width" refers to the length along the tire width direction between the two ends (contact edges) of the area that contacts the plane (contact area) when a 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. "Standard rim" refers to the rim specified for each tire in the standard system that includes the standard on which the tire is based. For example, it may be 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.

[0018] 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.

[0019] 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.

[0020] The configuration of the present invention will be described in detail below with reference to the attached drawings.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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).

[0026] 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 responsible for 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.

[0027] Of the multiple land sections 40 thus partitioned, at least one has multiple short sipes S extending along the tire width direction on the tread surface, as shown in Figures 3-4. S , groove depth short sipe S S It has multiple fine grooves G that are smaller than the main groove. Short sipes S S This refers to a sipe that extends along the width direction of the tire and has a sipe length L [unit: mm] of 10% or less of the contact width. In the following explanation, these short sipes S S The land section 40, which has 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.

[0028] Short Sipe S S As mentioned above, it has a sipe length L [unit: mm] of 10% or less of the contact width, but the sipe length L referred to here is short sipe S as shown in the figure. S This is the length projected onto the projection plane in the tire width direction (i.e., the length projected in the circumferential direction). Short sipe S S The sipe length L is preferably 8% or less of the contact width, more preferably 5% or less of the contact width. However, in order for the sipe to fully perform its function, short sipes S S The sipe length L should be 1.5 mm or more. S By making the sipe length L sufficiently small, short sipes S can be used without reducing the rigidity of the land section. S This allows for the dewatering effect.

[0029] Short Sipe S S As shown in Figure 5, the groove width Ws is set to a range of, for example, 0.1 mm to 1.0 mm, and the groove depth Ds is set to a range of, for example, 2.0 mm to 10.0 mm. Short sipe S S These primarily extend along the tire width direction, are spaced apart in the tire circumferential and / or tire width directions, and primarily provide edge effect and drainage. S The shape is not particularly limited; for example, the zigzag shape shown in the illustration can be used.

[0030] As mentioned above, the narrow groove G has short sipes S S The grooves are shallower than the grooves shown in Figure 5, and 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 fine groove G is preferably 0.05 mm to 1.0 mm, more preferably 0.1 mm to 0.8 mm. Thus, the fine groove G is a very fine groove, and as shown in the figure, it has short sipes S S They extend in a direction intersecting the sipes and are arranged in multiples in the circumferential direction of the tire. In particular, as shown in Figures 3-4, 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, even on an icy road, when the temperature is high and a large water film is formed on the road surface, the short sipes S S In addition, the water film removal effect of the narrow grooves G can be added, resulting in 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 grooves G is less than 0.05 mm, the groove width of the narrow grooves G is small and sufficient water removal performance cannot be obtained, making it difficult to improve braking performance on ice. If the groove width Wg of the narrow grooves 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 multiple narrow grooves G are arranged 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 preferably 0.5 mm to 5.0 mm, more preferably 0.7 mm to 4.0 mm. This is advantageous for improving ice performance because it ensures sufficient actual contact area on specific land areas to secure ice braking performance, and further enhances ice braking performance 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 ice braking performance because the actual contact area decreases. If the pitch p of the narrow grooves G exceeds 5.0 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] The specific land portion of the present invention comprises a plurality of short sipes S S It is always equipped with multiple fine grooves G and these short sipes S S The combination of the narrow grooves G provides the excellent ice performance described above. On the other hand, as long as the rigidity of the land section is not significantly impaired, short sipes S S In addition, sipes with a sipe length L exceeding 10% of the contact width can also be provided. In the following explanation, these sipes will be referred to as "long sipes S L " and short sipe S S and long sipe S L These are sometimes collectively referred to as "Sipe S". L Except for the sipe length L which exceeds 10% of the contact width, the groove width Ws and groove depth Ds are short sipes S S It can be set to the same range. Preferably, all sipes installed in a specific land area are short sipes S S It would be good if that were the case.

[0033] As mentioned 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 area, but the tread pattern in the example of Figure 2 includes a pair of inner main grooves 21 arranged on both sides of the tire equator CL as circumferential main grooves 20, and a pair of outer main grooves 22 arranged on the outside of the inner main grooves 21 in the tire width direction. One of the pair of inner main grooves 21 (the inner main groove 21a on the right in the figure) extends while bending in a zigzag manner along the tire circumferential direction, and the other of the pair of inner main grooves 21 (the inner main groove 21b on the left in the figure) extends such that the groove width varies along the tire circumferential direction by bending the groove wall on the outside in the tire width direction in a zigzag manner. Both outer main grooves 22 extend linearly along the tire circumferential direction.

[0034] In the illustrated example, between a pair of inner main grooves 21, a plurality of block-shaped land sections (center land section 41), demarcated by the pair of inner main grooves 21 and the lug groove 30 (center lug groove 31), are arranged in the circumferential direction of the tire. On one side of the tire equator (right side in the figure), between the zigzag-shaped inner main groove 21a and the outer main groove 22, a plurality of block-shaped land sections (intermediate land section 42a), demarcated by these grooves and the lug groove 30 (intermediate lug groove 32a), are arranged in the circumferential direction of the tire. Each intermediate land section 42a is provided with a circumferential auxiliary groove 51 that extends in a zigzag pattern along the circumferential direction of the tire and connects adjacent lug grooves in the circumferential direction of the tire. On the other side of the tire equator (left side in the figure), between the inner main groove 21b and the outer main groove 22, where the groove width varies, a rib-shaped land section (intermediate land section 42b) is formed, demarcated by these grooves and continuous around the entire circumference of the tire. Furthermore, 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, respectively, 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), each demarcated by the outer main groove 22 and the lug groove 30 (shoulder lug groove 33), are arranged in the tire circumferential 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.

[0035] Even in land portions 40 of various shapes included in the tread pattern as described above, those provided with short sipes S S and narrow grooves G are regarded as the specific land portions in the present invention.

[0036] As described above, the present invention is provided with a plurality of short sipes S S and a plurality of narrow grooves G, whereby excellent on-ice performance can be ensured in the specific land portion. In this case, the ratio of the sum of the area of the plurality of narrow grooves G and the area of the plurality of short sipes S 2 formed in the specific land portion to the tread surface area A [unit: mm S of the specific land portion is set to 7% to 35%, preferably 10% to 27%. Thereby, the actual ground contact area of the specific land portion can be sufficiently ensured to secure on-ice braking performance, and further the on-ice braking performance can be secured by the water film removing effect of the narrow grooves G, which is advantageous for improving the on-ice performance. When the ratio of the sum of the total area of the narrow grooves G and the total area of the short sipes S S to the tread surface area A in the specific land portion is less than 7%, the number of the short sipes S S and the 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. When the ratio of the sum of the total area of the narrow grooves G and the total area of the short sipes S S to the tread surface area A in the specific land portion exceeds 35%, it becomes difficult to improve the on-ice braking performance in that the actual ground contact area decreases. In addition, when the specific land portion includes long sipes S S in addition to the short sipes S L , it is preferable that the ratio of the sum of the area of the plurality of narrow grooves G and the area of the plurality of sipes S (the short sipes S S and the long sipes S L ) formed in the specific land portion satisfies the above range.

[0037] From the viewpoint of improving on-ice performance when there is a large amount of water film, it is effective to sufficiently provide the narrow grooves G, and the tread surface area A of the specific land portion [unit: mm 2The ratio of the total area of ​​the multiple narrow grooves G formed on this specific land area to the area A of the tread surface is preferably 5% to 19%, more preferably 7% to 17%. This ensures sufficient actual contact area of ​​the specific land area where the narrow grooves g are provided, thereby ensuring braking performance on ice, and further ensures braking performance on ice through the water film removal effect of the narrow grooves g, thus being advantageous for improving ice performance. If the ratio of the total area of ​​the multiple narrow grooves G to the area A of the tread surface of the specific land area is less than 5%, sufficient water removal performance by the narrow grooves G cannot be obtained, making it difficult to improve braking performance on ice. If the ratio of the total area of ​​the multiple narrow grooves G to the area A of the tread surface of the specific land area exceeds 19%, it becomes difficult to improve braking performance on ice because the actual contact area decreases. Note that the area A of the tread surface of the specific land area is the area inside the outer contour of the specific land area (including sipes and narrow grooves).

[0038] Sipe S (Short Sipe S) S and long sipe S L It is preferable that the tread portion 1 is sufficiently provided over the entire surface, and in particular, it is desirable that the component in the tire width direction has a sufficient length. Specifically, the area A of the tread surface of the specific land portion [unit: mm] 2 ) vs. Sipe S (Short Sipe S S and long sipe S L The ratio of the total sipe length L (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 It is preferable that the sipes are within this range. By providing a sufficient number of sipes in this way, the edge effect and water film removal effect of the sipes S can be enhanced, which is advantageous for improving ice performance. Sipe density is 0.06 mm / mm 2 If the sipe density is less than 0.30 mm / mm², the sipe length L cannot be sufficiently secured, resulting in limited edge effect and water removal effect from the sipe S. 2 Beyond this point, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0039] As shown in Figure 3, when a specific land area is a block (an independent land area surrounded by a groove), the circumferential center of the specific land area is defined as the circumferential central region C, and the circumferential outer sides of the circumferential central region C are defined as circumferential end regions E. When the area of ​​the circumferential central region C is 50% of the area of ​​the specific land area, and the areas of the circumferential end regions E are 25% of the area of ​​the specific land area, the area of ​​the circumferential central region C [unit: mm] 2 All sipes S (short sipes S) formed in the circumferential central region C of ] S and long sipe S L The ratio Rc of the total sipe length L [unit: mm] of the sipes, and the area [unit: mm] of the circumferential end region E. 2 All sipes S (short sipes S) formed in the circumferential end region E of ] S and long sipe S L The ratio Re of the total sipe lengths L (unit: mm) of the blocks preferably satisfies the relationship Rc > Re. Having such a relative size relationship allows for a balanced arrangement of sipes S in the circumferential central region C and the circumferential end region E, which is advantageous for improving ice performance by enhancing the water film removal effect while maintaining block rigidity.

[0040] In this case, the ratio Rc in the circumferential central region is preferably 0.12 mm / mm 2 ~0.30mm / mm 2 , more preferably 0.18 mm / mm 2 ~0.24mm / mm 2 It is preferable that the ratio Re in the circumferential end region is 0.06 mm / mm. 2 ~0.24mm / mm 2 , more preferably 0.12 mm / mm 2 ~0.18mm / mm 2 This is desirable. This allows for a balanced arrangement of sipes S in the circumferential central region C and circumferential end regions E within a specific land area, which is advantageous for improving ice performance by enhancing the water film removal effect while maintaining block rigidity. The ratio Rc is 0.12 mm / mm 2 If the ratio Rc is less than 0.30 mm / mm, the sipe length L cannot be sufficiently secured, resulting in limited edge effect and water removal effect from the sipe S.2 Beyond this point, it becomes difficult to improve braking performance on ice because the actual contact area decreases. (Ratio Re is 0.06 mm / mm) 2 If the ratio Re is less than 0.24 mm / mm, the sipe length L cannot be sufficiently secured, resulting in limited edge effect and water removal effect from the sipe S. 2 Beyond this point, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0041] As for the sipes S, those with both ends communicating with the circumferential main groove 20, those with one end communicating with the circumferential main groove 20 while the other end terminates within the land area 40, and those with both ends terminated within the land area 40 can be appropriately provided considering the size of the land area 40, etc. However, when the circumferential central region C and the circumferential end region E are divided as described above, it is preferable that the multiple sipes S provided in the circumferential central region C include open sipes (sipes with one end communicating with the circumferential main groove 20 while the other end terminates within the land area 40) that open to one side of a pair of main grooves adjacent to a specific land area. In other words, it is preferable that all sipes S provided in the circumferential end region E are closed sipes with both ends terminated within the land area. By mixing open sipes in the circumferential central region C in this way, the water removal effect can be effectively enhanced, which is advantageous for improving ice performance.

[0042] As mentioned above, the present invention only needs to include at least one specific land area, but from the viewpoint of drainage, it is preferable that grooves are sufficiently provided throughout the entire tread portion 1. Specifically, the short sipes S relative to the area of ​​the contact area of ​​the tread portion 1. S The ratio of the total groove area of ​​all grooves formed in the tread portion 1, including the fine grooves G (i.e., the groove area ratio of the tread portion 1), is preferably set to 20% to 60%, more preferably 30% to 55%, and even more preferably 35% to 50%. In the case of Figure 2, the short sipe S S All grooves formed in the tread portion 1, including the fine grooves G, are: circumferential main grooves 20 (inner main groove 21 and outer main groove 22), lug grooves 30 (center lug groove 31, intermediate lug grooves 32a, 32b, and shoulder lug groove 33), circumferential auxiliary grooves 51, circumferential fine grooves 53, and sipes S (short sipes S S and long sipe SL ), and narrow grooves G. By optimizing the overall groove area ratio of the tread section 1 in this way, it is possible to achieve excellent drainage performance while ensuring the actual contact area of ​​the tread section 1 as a whole. At this time, if the groove area ratio of the tread section 1 is less than 20%, the water removal effect of the entire tread section decreases, making it difficult to improve braking performance on ice. If the groove area ratio of the tread section 1 exceeds 60%, it becomes difficult to improve braking performance on ice because the actual contact area decreases.

[0043] 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.

[0044] As shown in Figure 4, when the central side of a specific land area in the tire width direction is defined as the widthwise central region C', and the sides of the widthwise central region C' in the tire width direction are defined as the widthwise 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 widthwise 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 widthwise end region E' is smaller than the area of ​​the widthwise central region C'. In particular, the maximum width W of the specific land area L Width W of the widthwise end region E' (the part where the inclination direction of the narrow groove is different) E It is preferable that the ratio is between 5% and 49%. This results in a good balance between the area of ​​the central region C' and the end region E' in the width direction, where the inclination directions of the narrow grooves G are different, which is advantageous for improving the water film removal effect by the narrow grooves G and enhancing ice performance.

[0045] As mentioned above, when the inclination direction of the narrow grooves G differs between the central region C' and the end region E' in the width direction, the inclination angle θc in the central region C' is preferably 30° to 60°, more preferably 35° to 55°. Similarly, the inclination angle θe in the end region E' is preferably 30° to 70°, more preferably 35° to 60°. This results in favorable inclination angles of the narrow grooves G in both the central region C' and the end region E', which is advantageous for improving ice performance by enhancing the water film removal effect of the narrow grooves G. If the inclination angle θc in the central region C' is less than 30°, it becomes difficult to improve ice braking performance 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 ice braking performance because sufficient water removal performance by the narrow grooves G cannot be obtained. If the inclination angle θe in the widthwise end region E' is less than 30°, it becomes difficult to improve ice braking performance because the edge effect cannot be sufficiently secured. If the inclination angle θe in the widthwise end region E' exceeds 70°, it becomes difficult to improve ice braking performance because sufficient water removal performance cannot be obtained by the narrow grooves G.

[0046] 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.

[0047] Twenty types of pneumatic tires (test tires) were manufactured, consisting of Standard Example 1, Comparative Examples 1-3, and Examples 1-16. Each tire had a size of 195 / 65R15 91Q, a basic structure (internal structure) as shown in Figure 1, and a tread pattern as shown in Figure 2. The ratio of groove area to the area A of a specific land area, the width of the fine grooves, the pitch of the fine grooves, the sipe density, the ratio Rc, Re, the presence or absence of open sipes, the inclination direction of the fine grooves, and the inclination angle of the fine grooves were set as shown in Tables 1-2.

[0048] In Tables 1 and 2, the "ratio of groove area to area A" is the area A of the tread surface of the specific land area [unit: mm]. 2The table shows the ratio of the total area of ​​multiple narrow grooves and multiple short sipes formed on this specific land area (the "Narrow Grooves + Short Sipes" column in the table) and the ratio of the total area of ​​multiple narrow grooves formed on this specific land area (the "Narrow Grooves" column in the table), respectively. "Sipe density" refers to the area of ​​the contact area of ​​the tread [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 ]

[0049] In Tables 1 and 2, "Ratio Rc" refers to the area of ​​the circumferential central region [unit: mm²] when the area extending 50% of the tire's circumferential length from the tire's circumferential center of the specific land area to both sides of the circumferential center is defined as the circumferential end region, and the areas on both outer sides of the circumferential central region are defined as the circumferential end regions. 2 This is the ratio of the sum of the front sipe lengths L [unit: mm] of all sipes formed in the circumferential central region to the area of ​​the circumferential end region [unit: mm]. 2 This is the ratio of the total sipe length L [unit: mm] of all sipes formed in the circumferential end region to ]. The "Presence or Absence of Open Sipes" column indicates that when the specific land area is divided into a circumferential central region and a circumferential end region as described above, if the multiple sipes provided in the circumferential central region include open sipes that open to one side of a pair of main grooves adjacent to the specific land area, it is indicated as "Present," and if such open sipes are not included (when both ends of all sipes are closed within the land area).

[0050] In Tables 1 and 2, the "Direction of Groove Inclination" column is defined as follows: when the central side of a specific land area in the tire width direction is considered the widthwise central region, and the sides of this widthwise central region in the tire width direction are considered the widthwise end regions, "Same Direction" is indicated when the groove inclination direction is the same in the widthwise central region and the widthwise end regions of the specific land area, and "Different Directions" is indicated when the groove inclination direction is different in the widthwise central region and the widthwise end regions of the specific land area. The "Groove Inclination Angle" column has two columns, "Central Region" and "End Region," and when the "Direction of Groove Inclination" is "Different Directions," both the groove inclination angle in the central region and the groove inclination angle in the end region of the specific land area are indicated. However, when the "Direction of Groove Inclination" is "Same Direction," the inclination angle value is displayed only in the "Central Region" column.

[0051] 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.

[0052] For the ice braking performance test, each test tire was mounted on a rim size 15 x 6.5J wheel and fitted to all wheels of a 1800cc front-wheel-drive vehicle. The tires were filled to an air pressure of 250 / 240 kPa, and a test driver conducted a braking test (20 km / h) on an icy surface under conditions of ice temperature -1°C. Note that a braking test at -1°C (a temperature close to the melting point of water, 0°C) is an indicator of ice braking performance when the amount of water on the road surface increases, as a large amount of ice melts due to friction during braking. The evaluation results are shown as an index using the reciprocal of the measured value, with standard example 1 set to 100. A higher index value indicates a shorter braking distance and superior ice braking performance.

[0053]

[0054]

[0055] As can be seen from Tables 1 to 2, the tires of Examples 1 to 16 have improved on-ice braking performance in comparison with Standard Example 1. On the other hand, the tire of Comparative Example 1 has no narrow grooves and is only provided with short sipes, resulting in degraded on-ice braking performance. In the tire of Comparative Example 2, the ratio of the total area of the plurality of narrow grooves and the plurality of short sipes formed in the specific land portion to the tread surface area A of the specific land portion is large, so the effect of improving on-ice braking performance is limited. In the tire of Comparative Example 3, the ratio of the total area of the plurality of narrow grooves and the plurality of short sipes formed in the specific land portion to the tread surface area A of the specific land portion is small, so the effect of improving on-ice braking performance is limited.

[0056] 1 Tread portion 2 Sidewall portion 3 Bead portion 20 Circumferential main groove 30 Lug groove 40 Land portion S Sipe S S Short sipe G Narrow 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 a tread surface with a plurality of short sipes extending along the tire width direction and having a sipe length L [unit: mm] of 10% or less of the contact width, and a plurality of narrow grooves having a groove depth smaller than the short sipes and 1.5 mm or less and extending in a direction intersecting the short sipes, and the area A [unit: mm] of the tread surface of the specific land portion 2 A tire characterized in that the ratio of the total area of ​​the multiple narrow grooves and the multiple short sipes formed in the specific land portion to the total area of ​​the land portion is between 7% and 35%.

2. The tire according to claim 1, characterized in that the pitch of the plurality of fine grooves is 0.5 mm to 5.0 mm, and the groove width of each of the fine grooves is 0.05 mm to 1.0 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. 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 3, characterized in that it is within the range.

5. A center side in the tire circumferential direction of the specific land portion is defined as a circumferential center region, both outer sides in the tire circumferential direction of the circumferential center region are respectively defined as circumferential end regions, the area of the circumferential center region is 50% of the area of the specific land portion, and the area of each of the circumferential end regions is 25% of the area of the specific land portion, a ratio Rc of the total of the sipe lengths L [unit: mm] of all sipes formed in the circumferential center region to the area [unit: mm 2 of the circumferential center region, and a ratio Re of the total of the sipe lengths L [unit: mm] of all sipes formed in the circumferential end regions to the area [unit: mm 2 of each of the circumferential end regions satisfy a relationship of Rc>Re, the ratio Rc in the circumferential center region is 0.12 mm / mm 2 to 0.30 mm / mm 2 , and the ratio Re in each of the circumferential end regions is 0.06 mm / mm 2 to 0.24 mm / mm 2 . The tire according to any one of claims 1 to 4.

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's circumferential direction is defined as the circumferential central region, the outer sides of the circumferential central region in the tire's circumferential direction are each defined as the circumferential end regions, the area of ​​the circumferential central region is 50% of the area of ​​the specific land portion, and the area of ​​the circumferential end regions is each 25% of the area of ​​the specific land portion, a plurality of sipes provided in the circumferential central region include open sipes that open to one side of a pair of main grooves adjacent to the specific land portion.

7. The tire according to any one of claims 1 to 6, characterized in that the angle of inclination of the narrow groove with respect to the circumferential direction of the tire is 30° to 70°.

8. The tire according to any one of claims 1 to 7, characterized in that the ratio of the total groove area of ​​all grooves formed in the tread portion, including the short sipes and the fine grooves, to the area of ​​the contact area of ​​the tread portion is 20% to 60%.

9. The tire according to any one of claims 1 to 8, 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.

10. The tire according to claim 9, characterized in that the area of ​​the end region in the width direction provided with the fine groove having an inclination direction different 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.

11. The tire according to claim 9 or 10, characterized in that the angle of inclination of the narrow groove with respect to the tire circumferential direction is 30° to 60° in the widthwise central region of the specific land portion, and 30° to 70° in the widthwise end region of the specific land portion.

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