tire

Abstract

To achieve both low air resistance and excellent draining performance.SOLUTION: A tread of a tire comprises: a major groove extending in a tire circumferential direction; a shoulder land part which is formed at the outer side in a tire width direction in comparison with the major groove; and a shoulder groove which extends from the major groove side of the shoulder land part, exceeding a tread ground contact end, to an outer side in the tire width direction. A minimal length (L1) from a tire equator to the outer side end of the shoulder groove in the tire width direction along a top face of the tread is 1.10-1.20 times of a minimal length (L2) from the tire equator to the tread ground contact end along a top face of the tread, and a median value of the shoulder groove width (W3) is 3.5-5.0 mm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire having grooves formed in shoulder land portions of the tread. [Background technology]

[0002] Conventionally, tires in which grooves are formed in shoulder land portions arranged on both sides of the width direction of the tread are widely known. For example, Patent Document 1 discloses a one-way tire having a tread including a center rib and shoulder ribs, in which the width of the lateral grooves formed in the center rib is 0.4 mm to 1.6 mm, and the width of the lateral grooves formed in the shoulder ribs is 2 mm to 8 mm. Patent Document 1 describes the effect that the air column resonance sound and pitch noise can be reduced in a balanced manner while ensuring the drainage performance of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-78984 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the configuration of the grooves formed in the shoulder land portion is important in improving the drainage performance of the tire, but as a result of the study by the present inventor, it was found that it also has a large effect on the air resistance of the tire. In a tire in which grooves are formed in the shoulder land portion of the tread, it is not easy to achieve both low air resistance and good drainage, and conventional tires including the tire of Patent Document 1 still have room for improvement in terms of achieving both of these performances.

[0005] An object of the present invention is to provide a tire that can achieve both low air resistance and good drainage properties. [Means for solving the problem]

[0006] The tire according to the present invention is a tire having a tread, the tread having main grooves extending in the tire circumferential direction, a shoulder land portion formed on the tire widthwise outer side of the main groove, and a shoulder groove extending from the main groove side of the shoulder land portion beyond the tread ground contact edge to the tire widthwise outer side, characterized in that the shortest distance (L1) along the top surface of the tread from the tire equator to the tire widthwise outer end of the shoulder groove is 1.10 to 1.20 times the shortest distance (L2) along the top surface of the tread from the tire equator to the tread ground contact edge, and the median width (W3) of the shoulder groove is 3.5 mm to 5.0 mm. Effect of the Invention

[0007] The tire according to the present invention can achieve both low air resistance and good drainage properties. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing a schematic view of a portion of a tread in a tire that is an example of an embodiment. [Diagram 2] 1 is a diagram showing a schematic view of a portion of a tire widthwise cross section according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An example of an embodiment of a tire according to the present invention will be described in detail below with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes configurations that selectively combine the respective components of the multiple embodiments and modified examples described below. In this specification, the "main tire rotation direction" refers to the rotation direction when a vehicle on which the tire is mounted moves forward.

[0010] Fig. 1 is a plan view showing a schematic view of a part of a tread 2 of a tire 1 according to an embodiment, and Fig. 2 is a schematic view of a part of a widthwise cross section of the tire 1. In Fig. 1, dot hatching is applied to the upper surface of a land portion formed in the tread 2. The upper surface of the land portion means the surface facing outward in the tire radial direction.

[0011] As shown in Figs. 1 and 2, a tire 1 includes a tread 2, which is a portion that comes into contact with the road surface, and a pair of sidewalls 3 that extend radially inward from both ends of the tread 2 in the width direction of the tire. The tread 2 is formed of a tread rubber 2A, and the sidewalls 3 are formed of a sidewall rubber 3A. The tire 1 also includes a pair of beads (not shown) that are fixed to a wheel rim. The tread 2, the sidewalls 3, and the beads are formed in an annular shape along the circumferential direction of the tire. The sidewalls 3 and the beads form the left and right side surfaces of the tire 1.

[0012] The tread 2 has a main groove 10 extending in the tire circumferential direction, and a shoulder rib 11 formed on the outer side of the main groove 10 in the tire width direction. As will be described in detail later, a shoulder groove 14 is formed in the shoulder rib 11, which extends from the main groove 10 side to the outer side in the tire width direction and terminates within the shoulder rib 11. In the example shown in Fig. 1, a plurality of shoulder grooves 14 are formed at regular intervals in the tire circumferential direction. In the tire width direction cross-sectional view of Fig. 2, the positions of the bottom surfaces 14c of the shoulder grooves 14 are indicated by dashed lines.

[0013] The tire 1 is a pneumatic tire filled with air at a predetermined pressure. The tire 1 generally includes a carcass 4 and a belt 5. The carcass 4 is a cord layer covered with rubber, and forms the framework of the tire 1 that can withstand load, impact, air pressure, and the like. The belt 5 is a reinforcing band disposed between the tread rubber 2A and the carcass 4, and tightens the carcass 4 to increase the rigidity of the tire 1. An inner liner 6, which is a rubber layer for retaining air pressure, is provided on the inner peripheral surface of the carcass 4.

[0014] The tread 2 has a ground contact end E. In this specification, the ground contact end E refers to both ends in the tire width direction of the area that comes into contact with a flat road surface when an unused tire 1 is mounted on a standard rim and filled with air to achieve a standard internal pressure, and a load of 70% of the standard load (maximum load capacity) at the standard internal pressure is applied. Shoulder ribs 11 are formed on both sides in the width direction of the tread 2, and the ground contact end E exists on the upper surface of each shoulder rib 11. In this specification, a position along the end 14b of each shoulder groove 14 is defined as the outer end of the shoulder rib 11 in the tire width direction. The portion located between the outer end of the shoulder rib 11 in the tire width direction and the sidewall 3 is generally called the shoulder of the tire 1.

[0015] Here, a "regular rim" is a rim determined by the tire standard, which is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0016] A plurality of main grooves 10 extending in the tire circumferential direction are formed in the tread 2. The main grooves 10 function as drainage channels that remove rainwater and the like that exists between the tread 2 and the road surface. In this embodiment, four main grooves 10 are formed in the tread 2. The four main grooves 10 have, for example, approximately the same depth and approximately the same width. The tread 2 has a plurality of land portions defined by the four main grooves 10. The land portions are protruding portions that protrude from a reference surface of the tread 2 toward the outside in the tire radial direction. The reference surface is a virtual surface that follows the bottom surface of the main grooves 10, and means the surface of the tread 2 when no land portions exist.

[0017] The tread 2 has a shoulder rib 11, a center rib 12, and an intermediate rib 13 as the land portion. The shoulder rib 11 is formed on both sides in the width direction of the tread 2. The center rib 12 is formed in the center of the tread 2 in the width direction, and the intermediate ribs 13 are formed between the shoulder rib 11 and each center rib 12. Each rib is a belt-shaped land portion in a plan view that is continuous in the tire circumferential direction, and the shoulder rib 11 and the center rib 12 are partitioned by the first main groove 10a, and the center rib 12 and the intermediate rib 13 are partitioned by the second main groove 10b.

[0018] The center rib 12 is formed on the tire equator CL along the tire circumferential direction. The tire equator CL means a line along the tire circumferential direction passing through the center in the tire width direction. The intermediate ribs 13 are formed on both sides of the center rib 12 in the tire width direction, separated by the main groove 10b. That is, the two intermediate ribs 13 are arranged to sandwich the center rib 12 via the main groove 10b. In addition, the shoulder ribs 11 are formed on the outer side of the intermediate ribs 13 in the tire width direction, with the main groove 10a between them.

[0019] At least one of grooves and sipes extending in a direction intersecting the main grooves 10 may be formed in the center rib 12 and the intermediate rib 13. Note that a center block and an intermediate block partitioned into a plurality of blocks may be provided instead of the center rib 12 and the intermediate rib 13. In the present invention, the tread pattern other than that of the shoulder ribs 11 is not particularly limited.

[0020] The configuration of the shoulder rib 11, and in particular the configuration of the shoulder groove 14 formed in the shoulder rib 11, will be described in detail below.

[0021] The tread 2 has two shoulder ribs 11 and a shoulder groove 14 extending from the main groove 10 side of the shoulder rib 11 beyond the ground contact edge E to the outside in the tire width direction. A plurality of shoulder grooves 14 are formed in each shoulder rib 11 arranged on both sides in the width direction of the tread 2. In this embodiment, the shoulder groove 14 is not connected to the main groove 10b, and the shoulder rib 11 is continuous in the tire circumferential direction at the inner end in the tire width direction.

[0022] The shoulder groove 14 functions as a drainage channel together with the main groove 10, and contributes to improving the drainage and wet grip performance of the tire 1. The shoulder groove 14 also affects the rigidity of the shoulder rib 11, so that a reduction in the groove volume increases the rigidity of the shoulder rib 11 and shortens the contact length, which may reduce the drainage performance, especially under high load conditions. As will be described in detail later, the tire 1 is designed to reduce air resistance while ensuring good drainage by limiting the length and width of the shoulder groove 14 to a specific range.

[0023] 1, the shoulder grooves 14 are formed symmetrically with respect to the tire equator CL in each shoulder rib 11, but the shoulder grooves 14 do not have to be formed symmetrically. For example, the shoulder grooves 14 may be arranged in a staggered pattern along the tire circumferential direction in each shoulder rib 11 rather than aligned in the tire width direction. However, from the viewpoint of achieving both low air resistance and good drainage performance of the tire 1, it is preferable that the shoulder grooves 14 are formed in each shoulder rib 11 so as to satisfy the relationship between length and width described below.

[0024] The shoulder rib 11 is formed on the outer side of the main groove 10a in the tire width direction, and extends beyond the ground contact edge E of the tread 2 toward the outer side in the tire width direction. The upper surface of the shoulder rib 11 is curved largely toward the inner side in the tire radial direction outside the ground contact edge E. The shoulder groove 14 is generally formed shallower than the main groove 10. Note that the shoulder rib 11 may be formed with sipes, which are thin grooves. For example, the width (W3) of the shoulder groove 14 is 2.5 mm or more, and the width of the sipes is 1.0 mm or less. Here, the width (W3) of the shoulder groove 14 means the length along the tire circumferential direction between opposing groove walls.

[0025] The shoulder grooves 14 are arranged, for example, at equal intervals in the tire circumferential direction. The shoulder grooves 14 aligned in the circumferential direction of the tire 1 extend in a direction intersecting with the main grooves 10a and are formed parallel to each other. In this specification, the end of the shoulder groove 14 located on the inner side in the tire width direction is referred to as a starting end 14a, and the end of the shoulder groove 14 located on the outer side in the tire width direction is referred to as a terminal end 14b. The shoulder groove 14 is inclined with respect to the tire width direction, for example, so that the terminal end 14b is located rearward in the tire main rotation direction from the starting end 14a. In addition, the shoulder groove 14 may be formed in a substantially straight shape in a plan view of the tread 2, or may be gently curved so as to be convex toward the rear in the tire main rotation direction.

[0026] Each of the shoulder grooves 14 has the same tire width direction length (L3). Here, the length (L3) means the length from the start end 14a to the end end 14b of the shoulder groove 14 along the tire width direction. An example of the length (L3) of the shoulder groove 14 is 30 mm to 45 mm. The lengths (L3) of the shoulder grooves 14 adjacent to each other in the tire circumferential direction may be different. In this embodiment, all the shoulder grooves 14 are formed with a length that exceeds the ground contact edge E, but there may be grooves that do not exceed the ground contact edge E within a range that does not impair the object of the present invention. Preferably, 90% or more, more preferably, substantially all of the shoulder grooves 14 are formed beyond the ground contact edge E.

[0027] Although each of the shoulder grooves 14 may have the same width (W3), in this embodiment, there are two or more groups of shoulder grooves 14 having different widths (W3). The number of groups of shoulder grooves 14 having different widths (W3) is, for example, 3 to 7. The shoulder rib 11 may have multiple regions in which the shoulder grooves 14 are arranged so that the width (W3) gradually increases along the tire circumferential direction. As will be described in detail later, the median width (W3) of the shoulder grooves 14 needs to be adjusted to a range of 3.5 mm to 5.0 mm.

[0028] The depth of the shoulder groove 14 may be substantially constant over the entire length of the shoulder groove 14, or may vary along the length of the shoulder groove 14. For example, the bottom surface 14c of the shoulder groove 14 is inclined so that the area near the starting end 14a becomes gradually deeper toward the end 14b, and the remaining 50 to 90% of the area is substantially flat. In this embodiment, the starting end 14a of the shoulder groove 14 is located near the ground contact edge E and away from the main groove 10a. That is, the shoulder groove 14 does not communicate with the main groove 10a, and the starting end 14a is present within the shoulder rib 11.

[0029] As described above, the shoulder groove 14 extends from a position away from the main groove 10a of the shoulder rib 11 to the outside in the tire width direction beyond the ground contact edge E. The shortest distance (L1) along the upper surface of the tread 2 from the tire equator CL to the terminal end 14b of the shoulder groove 14 is 1.10 to 1.20 times the shortest distance (L2) along the upper surface of the tread 2 from the tire equator CL to the ground contact edge E. The length of the shoulder groove 14, which is formed on the outside in the tire width direction from the ground contact edge E, is determined so that the ratio (L1 / L2) is 1.10 to 1.20.

[0030] Here, the upper surface of the tread 2 means a surface along the upper surface of the land portion hatched with dots in Fig. 1. In Fig. 1, the lengths (L1, L2) are illustrated as linear distances in a plan view of the tread 2, but these are illustrated for the sake of convenience of explanation, and the lengths (L1, L2) are distances along the upper surface of the tread 2.

[0031] If the length from the ground contact end E of the tread 2 to the terminal end 14b of the shoulder groove 14 is shortened and the ratio (L1 / L2) is less than 1.10, the shoulder groove 14 will not function sufficiently when the tire 1 wears, and the required drainage performance will not be ensured. In addition, the shoulder groove 14 may disappear before the tire 1 shows signs of slipping. On the other hand, if the length from the ground contact end E to the terminal end 14b is lengthened and the ratio (L1 / L2) exceeds 1.20, the air resistance of the tire 1 will increase significantly. It is more preferable that the ratio (L1 / L2) is 1.12 to 1.17.

[0032] As long as the median width (W3) of the shoulder grooves 14 is 3.5 mm to 5.0 mm, the width (W3) of each shoulder groove 14 may be constant or may be different. If the median width (W3) is less than 3.5 mm, the volume of the shoulder grooves 14 becomes too small to ensure the required drainage performance. Also, although this depends on the number of shoulder grooves 14, if the volume of the shoulder grooves 14 becomes too small, the rigidity of the shoulder rib 11 increases and the contact area decreases, resulting in poor drainage performance, especially under high load conditions. On the other hand, if the median width (W3) exceeds 5.0 mm, the air resistance of the tire 1 increases significantly.

[0033] The width (W3) of each shoulder groove 14 varies within a range of, for example, 3.0 mm to 5.5 mm. Three to seven types of shoulder grooves 14 with different widths (W3) are formed in the shoulder rib 11, and the widths (W3) of the shoulder grooves 14 adjacent in the tire circumferential direction are different from each other. The multiple types of shoulder grooves 14 with different widths (W3) are arranged, for example, such that the width (W3) gradually increases along the tire circumferential direction, and 10 to 20 groups, each of which is made up of 3 to 7 shoulder grooves 14 with different widths (W3), are arranged in the tire circumferential direction.

[0034] The tire 1 is designed to reduce air resistance by shortening the shoulder groove 14, and to ensure drainage performance that deteriorates as a result by increasing the width (W3) of the shoulder groove 14, thereby achieving both low air resistance and good drainage. As shown in the examples described later, low air resistance and good drainage can be effectively achieved only when the ratio (L1 / L2) and the width (W3) are within the above ranges. The median width (W3) of the shoulder groove 14 may be within the range of 3.5 mm to 5.0 mm, and more preferably 4.0 mm to 4.5 mm.

[0035] The number of shoulder grooves 14 aligned in the circumferential direction of the tire 1 is preferably 56 to 64, and more preferably 57 to 63. The relationship between the number of shoulder grooves 14 in each shoulder rib 11 is not particularly limited, but in this embodiment, the number of shoulder grooves 14 is the same in each shoulder rib 11. If the number of shoulder grooves 14 is within this range, it is possible to more effectively achieve both low air resistance and good drainage.

[0036] In this embodiment, the shoulder land portion is exemplified by the shoulder rib 11 that is connected in the tire circumferential direction within the contact patch, but the shoulder land portion may be formed with a shoulder groove that crosses the land portion and connects to the main groove 10. In other words, the shoulder land portion may be formed in a block shape partitioned by the shoulder groove. EXAMPLES

[0037] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0038] <Example 1> A test tire (tire size: 225 / 60R18 100H) having the tread pattern shown in Figures 1 and 2 was produced. Shoulder grooves were formed at equal intervals in the shoulder rib along the tire circumferential direction. The number of grooves aligned in the tire circumferential direction was 60. The grooves were formed approximately parallel to each other and had a gently curved planar shape that was convex toward the rear in the main tire rotation direction.

[0039] The shoulder groove dimensions are as follows. The ratio (L1 / L2) and width (W3) are shown in Table 1. Distance (L1): 99mm Distance (L2): 87mm Ratio (L1 / L2): 1.14 Length(L3):37mm Width (W3): The same number of grooves having five different widths (3.3 mm, 3.7 mm, 4.2 mm, 4.7 mm, 5.3 mm) were formed in the range of 3.3 mm to 5.3 mm. The five types of grooves were arranged so that the width gradually increased along the tire circumferential direction. Fifteen sets of the five types of grooves were arranged along the tire circumferential direction. Median width (W3): 4.2 mm

[0040] <Examples 2 to 5 and Comparative Examples 1 to 3> Test tires were produced in the same manner as in Example 1, except that the distance (L1) and width (W3) were changed so that the median values ​​of the ratio (L1 / L2) and width (W3) were the values ​​shown in Table 1.

[0041] For each of the test tires of the Examples and Comparative Examples, the air resistance and drainage properties were evaluated by the following methods.

[0042] [Air resistance evaluation] Each tire was mounted at the front tire position of a vehicle, and the air resistance of the tire was measured while the vehicle was running. The air resistance was calculated based on the fuel consumption when the vehicle was run a specified distance. The evaluation results are shown in Table 1. The evaluation results shown in Table 1 are relative values ​​with the evaluation result of the tire of Comparative Example 1 being 100, and the larger the value, the lower the air resistance. Vehicle: 3500cc gasoline vehicle (drive system: FF) Vehicle speed: 60km / h Tire installation conditions: Air pressure: 240kPa, Load: 656kgf (single wheel) Tire size: 225 / 60R18 100H (rim size 18X7.0J)

[0043] [Evaluation of drainage] Each tire was rotated on a wet road surface with water 8 mm deep, and the speed at which hydroplaning occurred was measured. The evaluation results shown in Table 1 are relative values ​​with the evaluation result of the tire of Comparative Example 1 taken as 100, and indicate that the speed at which hydroplaning occurred was high and that the tire had excellent hydroplaning resistance. Tire installation conditions: Air pressure: 240kPa, Load: 656kgf (single wheel) Tire size: 225 / 60R18 100H (rim size 18X7.0J) If a tire's drainage is poor, the tire cannot remove water from the contact area with the road surface in time while driving. The remaining water forms a water film between the road surface and the tire tread, causing the tire to lose contact with the road surface and resulting in hydroplaning. Therefore, the speed at which hydroplaning occurs was measured as an index of drainage.

[0044] [Table 1]

[0045] As shown in Table 1, all of the tires of the examples have reduced air resistance while having the same or better drainage performance as the tire of Comparative Example 1. Also, all of the tires of the examples have excellent drainage performance while having the same air resistance as the tire of Comparative Example 2. In other words, the tires of the examples can achieve both low air resistance and good drainage performance. [Explanation of symbols]

[0046] 1 tire, 2 tread, 2A tread rubber, 3 sidewall, 3A sidewall rubber, 10, 10a, 10b main groove, 11 shoulder rib, 12 center rib, 13 intermediate rib, 14 shoulder groove, 14a starting end, 14b ending end, 14c bottom surface, E ground contact edge

Claims

1. A tire having a tread, the tread comprising: A main groove extending in a tire circumferential direction; A shoulder land portion formed on the outer side of the main groove in the tire width direction; A shoulder groove extending from the main groove side of the shoulder land portion beyond a tread ground contact edge toward an outer side in the tire width direction; having A tire in which the shortest distance (L1) along the top surface of the tread from the tire equator to an outer end of the shoulder groove in the tire width direction is 1.10 to 1.20 times the shortest distance (L2) along the top surface of the tread from the tire equator to the tread ground contact end, and the median width (W3) of the shoulder groove is 3.5 mm to 5.0 mm.

2. The tire according to claim 1, wherein the number of the shoulder grooves aligned in the tire circumferential direction is 56 to 64.

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