tire

Abstract

To provide a tire configured so that snow performance can be improved while maintaining steering stability on a dry road surface appropriately, and occurrence of squeal sound can be suppressed.SOLUTION: In a tire, a tread part 1 is provided with an inner main groove 11 and an outer main groove 12, a center land part 21 partitioned by the main grooves, an intermediate land part 22 and a shoulder land part 23. A groove area ratio R2in in an inner region 22i of the intermediate land part 22 and a groove area ratio R2out in an outer region 22o of the intermediate land part 22 satisfy a relation of R2inR<2out. A groove area ratio R3in in an inner region 23i of the shoulder land part 23 and a groove area ratio R3out in an outer region 23o of the shoulder land part 23 satisfy a relation of R3in<R3out. A tire grounding width TCW and a tire total width SW satisfy a relation of 0.79≤TCW / SW≤0.85.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire suitable as an all-season tire, and more particularly to a tire that can improve steering stability on dry road surfaces while maintaining good snow performance and suppressing the generation of squealing noise. [Background technology]

[0002] So-called all-season tires, which are designed for use in various weather conditions throughout the year, are required to not only exhibit excellent driving performance on normal dry roads, but also to exhibit excellent snow performance, for example, when it snows. In contrast, conventional all-season tires have been designed to improve snow performance by providing multiple curved lug grooves in the land portion of the tread to allow the edge components of the grooves to act in all directions, and by providing multiple sipes in the land portion of the tread (see, for example, Patent Document 1). However, in recent years, tire performance requirements have become more stringent, and tires are now required to exhibit performance (e.g., handling stability on dry roads) equivalent to or better than that of summer tires (tires not intended for driving on icy and snowy roads) while maintaining snow performance. There is also a need to suppress squealing caused by slippage between the tire and the road surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-205410 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can improve steering stability on dry road surfaces while maintaining good snow performance and can suppress the occurrence of squealing. [Means for solving the problem]

[0005] The tire of the present invention for achieving the above object includes a tread portion that extends in the tire circumferential direction and forms an annular shape, and four main grooves are provided in the tread portion, including a pair of inner main grooves extending in the tire circumferential direction and a pair of outer main grooves arranged outside the pair of inner main grooves in the tire width direction. A center land portion partitioned between the pair of inner main grooves, a pair of intermediate land portions partitioned between the inner main groove and the outer main groove adjacent in the tire width direction outside the center land portion in the tire width direction, and a pair of shoulder land portions partitioned outside the outer main groove outside the intermediate land portion in the tire width direction are formed. In a tire in which grooves and / or sipes are formed in these land portions, when the region inside the tire width direction of the center of the intermediate land portion is defined as the inner region and the region outside the tire width direction of the center of the intermediate land portion is defined as the outer region, the groove area ratio R2in in the inner region of the intermediate land portion and the groove area ratio R2out in the outer region of the intermediate land portion satisfy the relationship R2in < R2out. When the region inside the tire width direction of the center of the shoulder land portion is defined as the inner region and the region outside the tire width direction of the center of the shoulder land portion is defined as the outer region, the groove area ratio R3in in the inner region of the shoulder land portion and the groove area ratio R3out in the outer region of the shoulder land portion satisfy the relationship R3in < R3out, and the tire contact width TCW and the tire total width SW satisfy the relationship 0.79 ≦ TCW / SW ≦ 0.85.

Effect of the Invention

[0006] The inventors of the present invention have conducted extensive research into the arrangement of grooves and sipes in tires with a center land portion, a pair of intermediate land portions, and a pair of shoulder land portions, and have found that by optimizing the balance of groove area ratios between the inner and outer sides of the tire width direction when the intermediate land portion and the shoulder land portion are divided in half in the tire width direction, and by optimizing the ratio TCW / SW of the tire contact width TCW to the total tire width SW, it is possible to achieve both improved snow performance and suppressed squealing. The present invention is based on this finding, and by arranging fewer grooves and sipes on the inner side of the intermediate land portion in the width direction, and making the groove area ratio R2in in the inner region smaller than the groove area ratio R2out in the outer region, it is possible to ensure the rigidity of the intermediate land portion and improve handling stability on dry roads, and by arranging fewer grooves and sipes on the inner side of the shoulder land portion in the width direction and making the groove area ratio R3in in the inner region smaller than the groove area ratio R3out in the outer region, it is possible to increase the rigidity of the shoulder land portion and suppress squealing. Furthermore, because the ratio of the tire contact width TCW to the total tire width SW (TCW / SW) is set within the above-mentioned range, it is possible to ensure tread rigidity and suppress squealing while ensuring contact length and maintaining snow performance. As mentioned above, the balance between the inner and outer regions of the intermediate land portion and the shoulder land portion, as well as the ratio of the tire contact width TCW to the total tire width SW (TCW / SW) are optimized, and the number and arrangement of grooves and sipes are not significantly changed compared to conventional tires, so snow performance can be maintained well. These combined effects improve handling stability on dry roads while maintaining good snow performance and suppressing squealing.

[0007] In the present invention, it is preferable that the groove area ratio R2in of the inner region of the intermediate land portion is 15% to 25%, the groove area ratio R2out of the outer region of the intermediate land portion is 25% to 35%, the groove area ratio R3in of the inner region of the shoulder land portion is 10% to 15%, and the groove area ratio R3out of the outer region of the shoulder land portion is 20% to 25%. This results in an adequately small number of grooves and sipes in the inner region of the intermediate land portion and a sufficiently large number of grooves and sipes in the outer region of the intermediate land portion, which is advantageous for achieving both steering stability on dry roads and snow performance. Furthermore, by providing an adequate number of grooves and sipes in the inner region of the shoulder land portion, squealing can be effectively suppressed, and by providing an adequate number of grooves and sipes in the outer region of the shoulder land portion, snow performance can be improved.

[0008] In the present invention, the center land portion may be formed with a plurality of first sipes with a groove width of 1 mm or less extending along the tire width direction, and a plurality of lateral grooves with a groove width of more than 1 mm extending along the tire width direction, the first sipes and the lateral grooves may be arranged at the same angle relative to the tire circumferential direction and connected to each other, each of the first sipes and the lateral grooves may open into one of the pair of inner main grooves, and the first sipes and the lateral grooves may be arranged alternately in the tire circumferential direction. In this specification, the provision of the sipes and lateral grooves as described above can improve snow removal while ensuring the rigidity of the center land portion, which is advantageous for achieving both driving stability on dry roads and snow performance.

[0009] In the present invention, the intermediate land portion may be formed with a plurality of second sipes extending in the tire width direction and a plurality of auxiliary grooves each having one end opening into the outer main groove and the other end closing within the intermediate land portion and having a curved shape, and the auxiliary grooves may have a first groove portion extending from the open end to a bending point and a second groove portion extending from the bending point to a closing end. In this specification, the auxiliary grooves having the aforementioned curved shape can improve snow traction while ensuring the rigidity of the intermediate land portion, which is advantageous for achieving both steering stability on dry roads and snow performance.

[0010] In the present invention, the shoulder land portion may be formed with a plurality of lug grooves extending in the tire width direction and not communicating with the outer main groove, a plurality of sipes disposed between adjacent lug grooves in the tire width direction and not communicating with the outer main groove, and a plurality of longitudinal grooves extending at an angle with respect to the tire circumferential direction and connecting adjacent lug grooves in the tire circumferential direction, and the connecting ends of the longitudinal grooves connecting to one side of a lug groove in the tire circumferential direction and the other side of the tire in the tire circumferential direction may be offset in the tire width direction. In this specification, the provision of the lug grooves, longitudinal grooves, and sipes as described above can improve snow traction while ensuring rigidity of the shoulder land portion, which is advantageous for achieving both driving stability on dry roads and snow performance.

[0011] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases.

[0012] In the present invention, the total tire width SW is measured as the linear distance between the sidewalls (including all parts such as patterns and lettering on the tire sidewalls) when the tire is mounted on a standard rim, pressurized to the standard internal pressure (for pneumatic tires), and unloaded. The tire contact width TCW is the axial contact width (distance between the tire's contact edges) measured when the tire is mounted on a standard rim, inflated to the standard internal pressure (for pneumatic tires), placed vertically on a flat surface, and subjected to a standard load. A "standard rim" is a rim specified for each tire by the standard on which the tire is based, such as a standard rim for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO. "Normal internal pressure" refers to the air pressure specified for each tire in the 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"; for ETRTO, it is "INFLATION PRESSURE," but for tires for passenger cars, it is 180 kPa. "Normal load" refers to the load specified for each tire in the standard system, including the standard on which the tire is based; for JATMA, it is the maximum load capacity; for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; for ETRTO, it is "LOAD CAPACITY," but for tires for passenger cars, it is a load equivalent to 88% of the above load. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a meridian cross-sectional view showing a pneumatic tire according to an embodiment of the present invention. [Figure 2] 1 is a development view showing a tread pattern of a pneumatic tire according to an embodiment of the present invention. [Figure 3] FIG. 4 is a development view showing a tread pattern of a pneumatic tire according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] In the case of a pneumatic tire as shown in Fig. 1, the tire of the present invention comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. Although not depicted in Fig. 1 because it is a meridian cross section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction to form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Fig. 1 will be based basically on the meridian cross section shown, but each tire constituent member also extends in the tire circumferential direction to form an annular shape.

[0016] A carcass layer 4 is mounted between a pair of left and right bead portions 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inner side to the outer side in the tire width direction around a bead core 5 disposed in each bead portion 3. A bead filler 6 is disposed on the outer periphery of the bead core 5, and this bead filler 6 is enclosed by the main body portion and folded back portion of the carcass layer 4. The bead filler 6 has a triangular cross section, for example, as shown in the figure, and is made of a rubber composition.

[0017] A plurality of belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of reinforcing cords (belt cords) inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt cover layer 8 is provided on the outer peripheral side of the belt layer 7 for the purpose of improving high-speed durability. The belt cover layer 8 includes reinforcing cords (cover cords) oriented in the tire circumferential direction. In the belt cover layer 8, the angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, to 0° to 5°. Organic fiber cords such as nylon and aramid cords are preferably used as the reinforcing cords of the belt cover layer 8.

[0018] As described below, the present invention mainly relates to a tread pattern (groove area ratio) formed on the surface of the tire tread portion 1, and therefore the basic structure (internal structure) of the tire is not limited to the general structure described above. Also, the following description will be based on the pneumatic tire shown in Fig. 1 etc., but the present invention can be applied to various tires, including non-pneumatic tires, as long as they have a surface that comes into contact with the road surface (a portion corresponding to the surface of the tread portion 1 in a pneumatic tire).

[0019] 2, four main grooves 10 extending in the tire circumferential direction are formed in the tread portion 1. These four main grooves 10 include a pair of inner main grooves 11 extending in the tire circumferential direction on both sides of the tire equator CL, and a pair of outer main grooves 12 arranged outward in the tire width direction from the pair of inner main grooves 11. The main grooves 10 are grooves that perform a primary drainage function, and their groove widths are set in the range of 7 mm to 15 mm, and their groove depths are set in the range of 6 mm to 10 mm.

[0020] The four main grooves 10 define five rows of land portions 20 in the tread portion 1. These five rows of land portions 20 include a center land portion 21 defined between a pair of inner main grooves 11 and located on the tire equator CL, a pair of intermediate land portions 22 defined on the tire width direction outer side of the center land portion 21 and between the inner main groove 11 and the outer main groove 12 adjacent in the tire width direction, and a pair of shoulder land portions 23 defined on the tire width direction outer side of the intermediate land portion 22 and on the tire width direction outer side of the outer main groove 12.

[0021] The center land portion 21 is formed with a plurality of first sipes 31 that have a groove width of 1 mm or less and extend along the tire width direction, and a plurality of lateral grooves 41 that have a groove width of more than 1 mm and extend along the tire width direction. The first sipes 31 and the lateral grooves 41 are arranged at the same angle relative to the tire circumferential direction. Both ends of the first sipes 31 open into a pair of inner main grooves 11. One end of the lateral groove 41 terminates within the center land portion 21, and the other end opens into one of the pair of inner main grooves 11. In particular, in the illustrated example, the lateral grooves 41 that open into one inner main groove 11 and the lateral grooves 41 that open into the other inner main groove 11 are arranged alternately in the tire circumferential direction.

[0022] The intermediate land portion 22 is formed with a plurality of lateral grooves 42 that extend along the tire width direction, with one end opening into the inner main groove 11 and the other end opening into the outer main groove 12, and a plurality of longitudinal grooves 52 that extend at an angle relative to the tire circumferential direction and connect adjacent lateral grooves 42 in the tire circumferential direction. The longitudinal grooves 52 do not extend continuously around the entire tire circumferential direction, but rather the connecting ends of the longitudinal grooves 52 connecting to one side of a lateral groove 42 in the tire circumferential direction and the longitudinal grooves 52 connecting to the other side in the tire circumferential direction are offset in the tire width direction. The lateral grooves 42 and longitudinal grooves 52 in the intermediate land portion 22 have a groove width and groove depth smaller than those of the main grooves 10, with the groove width set to a range of 1.5 mm to 6 mm and the groove depth set to a range of 4 mm to 8 mm.

[0023] The shoulder land portion 23 is formed with a plurality of lug grooves 43 extending in the tire width direction and not communicating with the outer main groove 12, a plurality of sipes 33 disposed between adjacent lug grooves 43 in the tire width direction and not communicating with the outer main groove 12, and a plurality of longitudinal grooves 53 extending along the tire circumferential direction and connecting adjacent lug grooves in the tire circumferential direction. In the illustrated example, the longitudinal grooves 53 in the shoulder land portion 23 extend along the tire circumferential direction, unlike the longitudinal grooves in the intermediate land portion 22. Therefore, the plurality of longitudinal grooves 53 extend substantially around the entire tire circumference as a single continuous groove. Like the lateral grooves 42 in the intermediate land portion 22, the lug grooves 43 in the shoulder land portion 23 have a groove width and groove depth smaller than the main grooves 10, with the groove width set to a range of 1.5 mm to 8 mm and the groove depth set to a range of 4 mm to 8 mm. The longitudinal grooves 53 of the shoulder land portion 23, like the longitudinal grooves 52 of the intermediate land portion 22, are grooves whose groove width and groove depth are smaller than those of the main grooves 10, and whose groove width is set in the range of 1 mm to 6 mm and whose groove depth is set in the range of 2 mm to 6 mm.

[0024] The present invention optimizes the arrangement of grooves and sipes in a tire having a center land portion 21, a pair of intermediate land portions 22, and a pair of shoulder land portions 23, particularly in the intermediate land portions 22 and shoulder land portions 23, and the groove area ratios of the intermediate land portions 22 and shoulder land portions 23 are set as described below. Note that the tread pattern in Fig. 2 above is just one example, and the specific tread pattern is not limited to the example in Fig. 2 as long as it satisfies the groove area ratio relationships described below.

[0025] First, regarding the intermediate land portion 22, when the region inside the tire width direction from the center in the tire width direction of the intermediate land portion 22 is defined as the inner region 22i, and the region outside the tire width direction from the center in the tire width direction of the intermediate land portion 22 is defined as the outer region 22o, the groove area ratio R2in in the inner region 22i of the intermediate land portion 22 and the groove area ratio R2out in the outer region 22o of the intermediate land portion 22 always satisfy the relationship R2in < R2out. Under this magnitude relationship, the groove area ratio R2in is preferably 15% to 25%, more preferably 18% to 22%, and the groove area ratio R2out is preferably 25% to 35%, more preferably 28% to 32%. Incidentally, the center in the tire width direction of the intermediate land portion 22 is the center in the tire width direction between the edge on the inner main groove 11 side of the intermediate land portion 22 and the edge on the outer main groove 12 side of the intermediate land portion 22.

[0026] Next, regarding the shoulder land portion 23, when the region inside the tire width direction from the center in the tire width direction of the shoulder land portion 23 is defined as the inner region 23i, and the region outside the tire width direction from the center in the tire width direction of the shoulder land portion 23 is defined as the outer region 23o, the groove area ratio R3in in the inner region 23i of the shoulder land portion 23 and the groove area ratio R3out in the outer region 23o of the shoulder land portion 23 always satisfy the relationship R3in < R3out. Under this magnitude relationship, the groove area ratio R3in is preferably 10% to 15%, more preferably 12% to 14%, and the groove area ratio R3out is preferably 20% to 25%, more preferably 22% to 24%. Incidentally, the center in the tire width direction of the shoulder land portion 23 is the center in the tire width direction between the grounding end E and the edge on the outer main groove 12 side of the shoulder land portion 23.

[0027] In addition to the above groove area ratio, in the present invention, the tire contact width TCW and the total tire width SW satisfy the relationship 0.79 ≦ TCW / SW ≦ 0.85, preferably 0.81 ≦ TCW / SW ≦ 0.83.

[0028] As described above, by arranging fewer grooves and sipes on the widthwise inner side of the intermediate land portion 22 and making the groove area ratio R2in of the inner region 22i smaller than the groove area ratio R2out of the outer region 22o, the rigidity of the intermediate land portion 22 is increased, improving steering stability on dry roads. Furthermore, by arranging fewer grooves and sipes on the widthwise inner side of the shoulder land portion 23 and making the groove area ratio R3in of the inner region 23i smaller than the groove area ratio R3out of the outer region 23o, the rigidity of the shoulder land portion 23 is increased, reducing squealing. Furthermore, because the ratio TCW / SW of the tire contact width TCW to the total tire width SW is set within the above range, tread rigidity is ensured, reducing squealing, while ensuring contact length and improving snow performance. Furthermore, because the balance between the inner and outer regions of the intermediate land portion 22 and the shoulder land portion 23 is optimized as described above, good snow performance can be maintained without significantly changing the number and arrangement of grooves and sipes compared to conventional tires. These cooperations improve steering stability on dry roads while maintaining good snow performance, and suppress the occurrence of squealing.

[0029] If the magnitude relationship between the groove area ratios R2in and R2out in the intermediate land portion 22 is reversed, the balance between the inner region 22i and the outer region 22o will be worsened, making it difficult to achieve both steering stability on dry roads and snow performance. If the groove area ratio R2out is less than 25%, the outer region 22o of the intermediate land portion 22 will not have enough groove area, making it difficult to maintain good snow performance. If the groove area ratio R2out exceeds 35%, the rigidity of the intermediate land portion 22 will decrease, limiting its effectiveness in improving steering stability on dry roads. If the groove area ratio R2in is less than 15%, the groove area in the inner region 22i of the intermediate land portion 22 will be too small, making it difficult to achieve good snow performance. If the groove area ratio R2in exceeds 25%, the difference in the groove area ratio between the inner region 22i and the outer region 22o will be small, making it difficult to achieve a good balance between steering stability on dry roads and snow performance.

[0030] If the magnitude relationship between the groove area ratios R3in and R3out in the shoulder land portion 23 is reversed, the balance between the inner region 23i and the outer region 23o will be impaired, making it difficult to maintain snow performance and suppress squealing at the same time. If the groove area ratio R3in is less than 10%, the groove area in the inner region 23i of the shoulder land portion 23 will be too small, making it difficult to ensure snow performance. If the groove area ratio R3in exceeds 15%, the difference in groove area ratio between the inner region 23i and the outer region 23o will be small, making it difficult to maintain a good balance between maintaining snow performance and suppressing squealing. If the groove area ratio R3out is less than 20%, the groove area in the outer region 23o of the shoulder land portion 23 will be insufficient, making it difficult to maintain good snow performance. If the groove area ratio R3out exceeds 25%, the rigidity of the shoulder land portion 23 will be reduced, limiting the effect of improving steering stability on dry roads.

[0031] If the ratio of the tire contact width TCW to the total tire width SW (TCW / SW) is less than 0.79, the tread rigidity cannot be ensured sufficiently, and the effect of suppressing squealing is limited. If the ratio of the tire contact width TCW to the total tire width SW (TCW / SW) is more than 0.85, the contact length becomes short, resulting in poor snow performance.

[0032] As described above, the present invention sets the groove area ratio and the like, and the specific tread pattern is not particularly limited, but it is preferable to provide grooves and sipes in each land portion as exemplified in FIG.

[0033] In the example of FIG. 3 , similar to the example of FIG. 2 , the center land portion 21 is formed with multiple first sipes 31 with a groove width of 1 mm or less extending along the tire width direction, and multiple lateral grooves 41 with a groove width of more than 1 mm extending along the tire width direction. However, in the example of FIG. 3 , the first sipes 31 and the lateral grooves 41 are arranged at the same angle relative to the tire circumferential direction, and further, the first sipes 31 and the lateral grooves 41 are connected to each other. In this case, each of the first sipes 31 and the lateral grooves 41 opens into one of the pair of inner main grooves 11, and the first sipes 31 and the lateral grooves 41 are arranged alternately in the tire circumferential direction. This arrangement of the sipes 31 and the lateral grooves 41 improves snow removal while maintaining the rigidity of the center land portion 21, which is advantageous for ensuring snow performance while improving driving stability on dry roads.

[0034] Instead of the lateral grooves 42 and longitudinal grooves 52 shown in FIG. 2 , the intermediate land portion 22 is provided with multiple second sipes 32 with a groove width of 1 mm or less extending along the tire width direction, and multiple auxiliary grooves 62 with one end opening to the outer main groove 12 and the other end closing within the intermediate land portion 22 and having a curved shape. Each auxiliary groove 62 has a first groove portion 62a extending from the open end to a bending point and a second groove portion 62b extending from the bending point to a closing end. In the illustrated example, the second sipes 32 and the first groove portion 62a of the auxiliary grooves 62 are inclined in opposite directions, and the second sipes 32 and the auxiliary grooves 62 intersect. Providing such curved auxiliary grooves 62 and sipes 32 enhances snow traction while maintaining the rigidity of the intermediate land portion 22, which is advantageous for ensuring snow performance while improving handling stability on dry roads. The auxiliary grooves 62 of the intermediate land portion 22 are grooves whose groove width and groove depth are smaller than those of the main grooves 10, with the groove width set in the range of 1.5 mm to 6 mm and the groove depth set in the range of 4 mm to 8 mm.

[0035] When providing the auxiliary groove 62 as described above, in order to moderately reduce the groove area ratio R2in of the inner region 22i compared to the groove area ratio R2out of the outer region 22o, the bending point of the auxiliary groove 62 may be sufficiently separated from the inner main groove 11. Specifically, the distance d along the tire width direction from the edge on the inner side in the tire width direction at the bending point of the auxiliary groove 62 to the inner main groove 11 may be set to preferably 20% to 45%, more preferably 25% to 40% of the width w2 of the intermediate land portion. In the structure of FIG. 3, in addition to the auxiliary groove 62 being separated from the inner main groove 11 as described above, the relationship of R2in < R2out is also easily achieved in that the number of the second sipes 32 arranged on the inner side in the tire width direction of the auxiliary groove 62 is less than the number of the second sipes 32 arranged on the outer side in the tire width direction of the auxiliary groove 62.

[0036] In the shoulder land portion 32, as in the example of FIG. 2, a plurality of lug grooves 43 extending in the tire width direction and non - communicating with the outer main groove 12, and a plurality of sipes 33 arranged between adjacent lug grooves in the tire circumferential direction and extending in the tire width direction and non - communicating with the outer main groove 12 are formed. Also, similar to the example of FIG. 2, a plurality of vertical grooves 53 connecting adjacent lug grooves 43 to each other in the tire circumferential direction are formed. However, the vertical grooves 53 in the example of FIG. 3 extend obliquely with respect to the tire circumferential direction, and the connection ends of the vertical grooves 53 connecting to one side in the tire circumferential direction and the other side in the tire circumferential direction of one lug groove 43 are displaced in the tire width direction. By providing such lug grooves 43, vertical grooves 53, and sipes 33, it is possible to enhance snow traction while ensuring the rigidity of the shoulder land portion, which is advantageous for ensuring snow performance while improving the handling stability on a dry road surface.

[0037] 3, the groove area ratios and the ratio TCW / SW of the intermediate land portion 22 and the shoulder land portion 23 satisfy the above-mentioned relationship, and the effect based on this (the effect of improving steering stability on dry roads while maintaining good snow performance and suppressing the occurrence of squealing) can be obtained. In addition, the effect of the arrangement of grooves and sipes in each land portion described above is added, so it is possible to expect further improvements in the effect of exhibiting excellent snow performance while improving steering stability on dry roads and suppressing the occurrence of squealing.

[0038] The tire of the present invention is primarily intended as an all-season tire. To ensure snow performance, the hardness of the rubber (tread rubber) constituting the tread portion 1 is preferably set to 60 to 70, more preferably 63 to 67. Tread rubber with such hardness generally tends to generate squealing, but when the present invention is applied, squealing can be effectively suppressed by setting the groove area ratio and TCW / SW ratio of the present invention, and the shape and arrangement of the grooves and / or sipes. If the hardness of the tread rubber is less than 60, the tread rigidity decreases, and the effect of suppressing squealing is limited. If the hardness of the tread rubber exceeds 70, it becomes difficult to ensure snow performance. The hardness of the tread rubber is a value measured at a temperature of 20°C using a durometer type A in accordance with JIS K6253.

[0039] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples. [Example]

[0040] Tires (test tires) of Conventional Example 1 and Examples 1 to 15 were manufactured with a tire size of 215 / 55R16 and the basic structure (internal structure) illustrated in FIG. 1, with the basic tread pattern, groove area ratio R2in in the inner region of the intermediate land portion, groove area ratio R2out in the outer region of the intermediate land portion, groove area ratio R3in in the inner region of the shoulder land portion, groove area ratio R3out in the outer region of the shoulder land portion, and ratio TCW / SW set as shown in Tables 1 and 2, respectively.

[0041] The "Base tread pattern" column in Tables 1 and 2 indicates whether the center land portion, intermediate land portion, and shoulder land portion are based on Figure 2 or Figure 3. For example, Example 3 refers to a pattern in which the intermediate land portion and shoulder land portion are based on Figure 2, and only the center land portion is based on Figure 3 (i.e., in Figure 2, only the center land portion is changed to the structure of Figure 3 (a structure in which the first sipes and lateral grooves are arranged at the same angle relative to the tire circumferential direction, and further the first sipes and lateral grooves are connected to each other)).

[0042] These test tires were evaluated for snow performance, squealing noise, and steering stability by the following test methods, and the results are shown in Tables 1 and 2.

[0043] Snow performance Each test tire was mounted on a wheel with a rim size of 18x7J, aired to 250kPa, and mounted on a four-wheel drive test vehicle. The vehicle was then braked from a speed of 40km / h on an icy and snowy road, and the braking distance until the vehicle came to a complete stop was measured. The evaluation results were expressed as an index using the reciprocal of the measured value, with standard example 1 being 100. The higher the index value, the shorter the braking distance and the better the braking performance (snow performance) on icy and snowy roads.

[0044] Squealing Each test tire was mounted on a rim size 18x7J wheel, inflated to 250kPa, and mounted on a four-wheel drive test vehicle. The vehicle was then turned on a smooth, dry road at a speed of 80km / h with the steering angle fixed at the grip limit. A test driver then conducted a sensory evaluation of the volume of squealing that occurred (the more suppressed the squealing, the higher the score). The evaluation results were expressed as an index, with the conventional example being 100. The higher the index value, the quieter the squealing.

[0045] Steering stability Each test tire was assembled onto a wheel with a rim size of 18×7J, mounted on a four-wheel drive test vehicle at an air pressure of 250 kPa, and a sensory evaluation by a test driver was conducted on the handling stability when driving on a dry road surface. The evaluation results were shown by an index with the conventional example set as 100. A larger value of this index means better handling stability.

[0046]

Table 1

[0047]

Table 2

[0048] As can be seen from Tables 1 and 2, the tires of Examples 1 to 15 improved the handling stability on a dry road surface while maintaining good snow performance in comparison with the conventional example, and suppressed the generation of skid noise.

[0049] This disclosure includes the following inventions. Invention [1] A tire having a tread portion that extends in the tire circumferential direction and forms an annular shape, the tread portion being provided with four main grooves including a pair of inner main grooves extending in the tire circumferential direction and a pair of outer main grooves disposed outside the pair of inner main grooves in the tire width direction, a center land portion partitioned between the pair of inner main grooves, a pair of intermediate land portions partitioned between the inner main grooves and the outer main grooves that are adjacent in the tire width direction and are outside the center land portion in the tire width direction, and a pair of shoulder land portions partitioned outside the intermediate land portions in the tire width direction and outside the outer main grooves in the tire width direction, and grooves and / or sipes being formed in these land portions. When an inner region is defined as a region of the intermediate land portion that is inside the tire width direction center of the intermediate land portion and an outer region is defined as a region of the intermediate land portion that is outside the tire width direction center of the intermediate land portion, the groove area ratio R2in in the inner region of the intermediate land portion and the groove area ratio R2out in the outer region of the intermediate land portion satisfy the relationship R2in < R2out. When the region of the shoulder land part on the inner side in the tire width direction from the center in the tire width direction of the shoulder land part is defined as the inner region, and the region of the shoulder land part on the outer side in the tire width direction from the center in the tire width direction of the shoulder land part is defined as the outer region, the groove area ratio R3in in the inner region of the shoulder land part and the groove area ratio R3out in the outer region of the shoulder land part satisfy the relationship R3in < R3out, A tire characterized in that the tire contact width TCW and the tire total width SW satisfy the relationship 0.79 ≦ TCW / SW ≦ 0.85. Invention [2] The groove area ratio R2in of the inner region of the intermediate land part is 15% - 25%, the groove area ratio R2out of the outer region of the intermediate land part is 25% - 35%, the groove area ratio R3in of the inner region of the shoulder land part is 10% - 15%, and the groove area ratio R3out of the outer region of the shoulder land part is 20% - 25%. The tire according to Invention [1], characterized in that. Invention [3] In the center land part, a plurality of first sipes having a groove width of 1 mm or less and extending along the tire width direction, and a plurality of transverse grooves having a groove width of more than 1 mm and extending along the tire width direction are formed. The first sipes and the transverse grooves are arranged at the same angle with respect to the tire circumferential direction and are connected to each other. Each of the first sipes and the transverse grooves opens to one of the pair of inner main grooves, and the first sipes and the transverse grooves are alternately arranged in the tire circumferential direction. The tire according to Invention [1] or [2], characterized in that. Invention [4] In the intermediate land part, a plurality of second sipes extending in the tire width direction, and a plurality of auxiliary grooves having one end opening to the outer main groove and the other end being blocked inside the intermediate land part and having a bent shape are formed. The auxiliary groove has a first groove portion extending from the opening end to the bending point and a second groove portion extending from the bending point to the blocking end. The tire according to any one of Inventions [1] to [3], characterized in that. Invention [5] A tire according to any one of inventions [1] to [4], characterized in that the shoulder land portion is formed with a plurality of lug grooves extending in the tire width direction and not communicating with the outer main groove, a plurality of sipes arranged between adjacent lug grooves in the tire circumferential direction, extending in the tire width direction and not communicating with the outer main groove, and a plurality of longitudinal grooves extending at an angle with respect to the tire circumferential direction and connecting adjacent lug grooves in the tire circumferential direction, and the respective connecting ends of the longitudinal groove connected to one side of one lug groove in the tire circumferential direction and the longitudinal groove connected to the other side in the tire circumferential direction are arranged offset in the tire width direction. [Explanation of symbols]

[0050] 1 Tread section 2 Sidewall 3 Bead section 10 Main groove 11 Inner main groove 12 Outer main groove 20 Land 21 Center Land Section 22 Intermediate land area 23 Shoulder land area 31, 32, 33 Sipe 41 Yokomizo 43 Lug groove 53 Vertical grooves 62 Auxiliary groove CL Tire Equator E Ground end

Claims

1. A tire having a tread portion extending in the tire circumferential direction and forming an annular shape, in which four main grooves are provided in the tread portion, including a pair of inner main grooves extending in the tire circumferential direction and a pair of outer main grooves arranged on the tire width direction outer sides of the pair of inner main grooves, and in which a center land portion is defined between the pair of inner main grooves, a pair of intermediate land portions defined on the tire width direction outer sides of the center land portion and between the inner main groove and the outer main groove that are adjacent in the tire width direction, and a pair of shoulder land portions defined on the tire width direction outer sides of the intermediate land portions and on the tire width direction outer sides of the outer main grooves, and in which grooves and / or sipes are formed in these land portions, When a region on the inner side in the tire width direction of the center of the intermediate land portion in the tire width direction is defined as an inner region, and a region on the outer side in the tire width direction of the center of the intermediate land portion in the tire width direction is defined as an outer region, a groove area ratio R2in in the inner region of the intermediate land portion and a groove area ratio R2out in the outer region of the intermediate land portion satisfy the relationship R2in < R2out, When an area on the inner side of the center of the shoulder land portion in the tire width direction in the tire width direction is defined as an inner area, and an area on the outer side of the center of the shoulder land portion in the tire width direction in the tire width direction is defined as an outer area, a groove area ratio R3in in the inner area of ​​the shoulder land portion and a groove area ratio R3out in the outer area of ​​the shoulder land portion satisfy the relationship R3in < R3out, A tire characterized in that the tire contact width TCW and the tire total width SW satisfy the relationship 0.79≦TCW / SW≦0.

85.

2. The tire according to claim 1, characterized in that the groove area ratio R2in of the inner region of the intermediate land portion is 15% to 25%, the groove area ratio R2out of the outer region of the intermediate land portion is 25% to 35%, the groove area ratio R3in of the inner region of the shoulder land portion is 10% to 15%, and the groove area ratio R3out of the outer region of the shoulder land portion is 20% to 25%.

3. 3. The tire according to claim 1, wherein the center land portion is formed with a plurality of first sipes each having a groove width of 1 mm or less and extending along the tire width direction, and a plurality of lateral grooves each having a groove width of more than 1 mm and extending along the tire width direction, the first sipes and the lateral grooves are arranged at the same angle relative to the tire circumferential direction and are connected to each other, each of the first sipes and the lateral grooves opens into one of the pair of inner main grooves, and the first sipes and the lateral grooves are arranged alternately in the tire circumferential direction.

4. 3. The tire according to claim 1, wherein the intermediate land portion is formed with a plurality of second sipes extending in the tire width direction and a plurality of auxiliary grooves each having one end opening into the outer main groove and the other end closing within the intermediate land portion and having a curved shape, and the auxiliary grooves each having a first groove portion extending from the open end to a bending point and a second groove portion extending from the bending point to a closed end.

5. 3. The tire according to claim 1, wherein the shoulder land portion is formed with a plurality of lug grooves extending in the tire width direction and not communicating with the outer main groove, a plurality of sipes disposed between adjacent lug grooves in the tire circumferential direction, extending in the tire width direction and not communicating with the outer main groove, and a plurality of longitudinal grooves extending at an angle with respect to the tire circumferential direction and connecting adjacent lug grooves in the tire circumferential direction, and wherein connection ends of the longitudinal groove connected to one side of one lug groove in the tire circumferential direction and the longitudinal groove connected to the other side of the tire circumferential direction are arranged offset in the tire width direction.

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