tire

Abstract

To make both low air resistance and good drainage performance compatible.SOLUTION: In a tire which is one example of embodiments, a tread has a main groove extending in a tire circumferential direction, shoulder land parts formed closer to the outside in a tire width direction than the main groove, and shoulder grooves extending from the main groove side of the shoulder land parts beyond a grounding end of the tread to the outside in the tire width direction. A shortest distance (L1) along an upper surface of the tread from a tire equator to an outside end in the tire width direction of the shoulder groove is 1.15-1.20 times a shortest distance (L2) along the upper surface of the tread from the tire equator to the grounding end. A change point, at which at least either of a side surface and a bottom surface constituting the shoulder groove is bent to the outside of the groove, exists in the vicinity of the grounding end.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, tires with shoulder grooves formed in shoulder land portions located on both sides of the tread in the width direction have been widely known. Patent Document 1 discloses a tire in which the depth of the shoulder groove is greatest at the inner end of the shoulder groove located on the inner side in the tire width direction and gradually decreases from the inner end to the ground-contact edge of the tread. Patent Documents 2 and 3 also disclose tires in which a bottom upper portion is provided at a part of the bottom of the shoulder groove to reduce the depth of the shoulder groove. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-218042 [Patent Document 2] Japanese Patent Application Publication No. 2018-1930 [Patent Document 3] Japanese Patent Application Publication No. 2019-77422 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the configuration of shoulder grooves formed in the shoulder land portion is important for improving the drainage performance of a tire, but as a result of research by the present inventors, it has been found that it also has a significant 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 performance, and conventional tires including the tires of Patent Documents 1 to 3 still have room for improvement in 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, shoulder land portions formed on the tire widthwise outer side of the main grooves, and shoulder grooves extending from the main groove side of the shoulder land portions beyond the ground contact edge of the tread to the tire widthwise outer side, wherein 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 1.15 to 1.20 times the shortest distance (L2) along the top surface of the tread from the tire equator to the ground contact edge, and wherein there is a turning point near the ground contact edge where at least one of the side and bottom surfaces constituting the shoulder groove bends outward of the groove. [Effects of the Invention]

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

[0008] [Figure 1] 1 is a plan view schematically showing a portion of a tread of a tire that is an example of an embodiment. [Figure 2] 1 is a diagram schematically illustrating a portion of a widthwise cross section of a tire that is an example of an embodiment. [Figure 3] 3 is an enlarged view of a shoulder groove formed in the shoulder rib of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[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 components of the multiple embodiments and variations described below. In this specification, the term "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 that schematically shows a portion of a tread 2 of a tire 1 that is an example of an embodiment, and Fig. 2 is a view that schematically shows a portion of a widthwise cross section of the tire 1. In Fig. 1, dot hatching is applied to the upper surfaces of land portions formed in the tread 2. The upper surfaces of the land portions refer to the surfaces that face outward in the tire radial direction.

[0011] As shown in FIGS. 1 and 2, a tire 1 includes a tread 2, which is the 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 tread rubber 2A, and the sidewalls 3 are formed of sidewall rubber 3A. The tire 1 also includes a pair of beads (not shown) that are fixed to the rim of a wheel. The tread 2, sidewalls 3, and beads are formed in an annular shape along the circumferential direction of the tire. The sidewalls 3 and beads form the left and right side surfaces of the tire 1.

[0012] The tread 2 has main grooves 10 extending in the tire circumferential direction and shoulder ribs 11 formed on the outer side of the main grooves 10 in the tire width direction. As will be described in detail later, shoulder grooves 14 are formed in the shoulder ribs 11, extending from the main groove 10 side toward the outer side in the tire width direction and terminating within the shoulder ribs 11. In the example shown in FIG. 1, multiple shoulder grooves 14 are formed at regular intervals in the tire circumferential direction. Note that 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 that is 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 coated with rubber, and forms the skeleton of the tire 1 that can withstand loads, impacts, air pressure, etc. 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 that maintains air pressure, is provided on the inner peripheral surface of the carcass 4.

[0014] The tread 2 has a ground contact edge E. In this specification, the ground contact edge 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 inflated to the 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 edge E is located on the upper surface of each shoulder rib 11. In this specification, the 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 specified by the tire standard, and is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0016] The tread 2 has a plurality of main grooves 10 formed therein, extending in the tire circumferential direction. 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 protrusions that protrude outward in the tire radial direction.

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

[0019] The center rib 12 and the intermediate rib 13 may have at least one of grooves and sipes extending in a direction intersecting the main grooves 10. Note that instead of the center rib 12 and the intermediate rib 13, a center block and an intermediate block divided into a plurality of blocks may be provided. 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, particularly 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 shoulder grooves 14 extending from the main groove 10 side of the shoulder ribs 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 grooves 14 are not connected to the main grooves 10a, and the shoulder ribs 11 are continuous in the tire circumferential direction at the inner end in the tire width direction.

[0022] The shoulder grooves 14 function as drainage channels together with the main grooves 10, contributing to improved drainage and wet grip performance of the tire 1. The shoulder grooves 14 also affect the rigidity of the shoulder ribs 11, so a reduction in the groove volume increases the rigidity of the shoulder ribs 11, shortening the contact length and potentially reducing drainage performance, particularly under high load conditions. As will be described in more detail later, the tire 1 is designed to ensure good drainage and reduce air resistance by increasing the cross-sectional area of ​​the shoulder grooves 14 near the contact edge E.

[0023] 1, the shoulder grooves 14 are formed symmetrically in each shoulder rib 11 with respect to the tire equator CL, 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 cross-sectional area described below.

[0024] The shoulder ribs 11 are formed further outward in the tire width direction than the main grooves 10a and extend beyond the ground contact edge E of the tread 2 outward in the tire width direction. The upper surfaces of the shoulder ribs 11 are curved significantly inward in the tire radial direction, outside the ground contact edge E. The shoulder grooves 14 are generally shallower than the main grooves 10. Note that the shoulder ribs 11 may be formed with sipes, which are thin grooves. For example, the width of the shoulder grooves 14 is 2.5 mm or more, and the width of the sipes is 1.0 mm or less. Here, the width of the shoulder grooves 14 refers to the length along the tire circumferential direction between opposing groove walls.

[0025] The shoulder grooves 14 are, for example, arranged at equal intervals in the tire circumferential direction. The multiple shoulder grooves 14 aligned in the circumferential direction of the tire 1 extend in a direction intersecting the main groove 10a and are formed parallel to one another. In this specification, the end of the shoulder groove 14 located on the inner side in the tire width direction is referred to as the 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 the ending end 14b. In this embodiment, the shoulder groove 14 does not communicate with the main groove 10a, and the starting end 14a is located within the shoulder rib 11. The shoulder groove 14 may also communicate with the main groove 10a. In this case, the starting end 14a is located at the outer end of the main groove 10a in the tire width direction. The shoulder groove 14 is inclined with respect to the tire width direction, for example, so that the ending end 14b is located rearward of the starting end 14a in the tire main rotation direction. The shoulder groove 14 may be formed in a substantially linear shape in a plan view of the tread 2, or may be gently curved so as to be convex rearward in the tire main rotation direction.

[0026] As described above, the shoulder grooves 14 extend from a position away from the main grooves 10a of the shoulder ribs 11 to beyond the ground contact edge E outward in the tire width direction. The shortest distance (L1) along the top surface of the tread 2 from the tire equator CL to the terminal ends 14b of the shoulder grooves 14 is 1.15 to 1.20 times the shortest distance (L2) along the top surface of the tread 2 from the tire equator CL to the ground contact edge E. The length of the shoulder grooves 14 formed on the outer side in the tire width direction than the ground contact edge E is determined so that the ratio (L1 / L2) is 1.15 to 1.20.

[0027] 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. Note that in Fig. 1, the lengths (L1, L2) are shown as linear distances in a plan view of the tread 2, but these are shown for convenience of explanation, and the lengths (L1, L2) are distances along the upper surface of the tread 2.

[0028] If the length from the ground contact edge 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 1.15, the shoulder groove 14 will not function sufficiently when the tire 1 wears, and the required drainage performance will not be ensured. Furthermore, the shoulder groove 14 may disappear before signs of tire slip appear, resulting in the apparent deterioration of the tire's wear. On the other hand, if the length from the ground contact edge 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. The ratio (L1 / L2) is more preferably 1.16 to 1.18.

[0029] In this embodiment, each of the shoulder grooves 14 has the same length (L3) in the tire width direction. Here, the length (L3) means the length from the starting end 14a to the ending 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 of the shoulder grooves 14 are formed with a length that extends beyond the tread edge E, but some grooves may not extend beyond the tread edge E as long as the object of the present invention is not impaired. Preferably, 90% or more, and more preferably, substantially all, of the shoulder grooves 14 are formed to extend beyond the tread edge E.

[0030] In this embodiment, the shoulder grooves 14 have the same width (W3). Here, the width (W3) of the shoulder grooves 14 refers to the groove width on the upper surface of the shoulder rib 11. The width (W3) of the shoulder grooves 14 is, for example, 3.5 mm to 5.0 mm, and may be 4.0 mm to 4.5 mm. Each shoulder groove 14 may have two or more groups of shoulder grooves 14 with different widths (W3). The shoulder rib 11 may have multiple regions where the shoulder grooves 14 are arranged so that the width (W3) gradually increases along the tire circumferential direction. In this specification, the width (W3) of the shoulder grooves 14 is the median width of the shoulder grooves 14.

[0031] Next, the cross-sectional shape of the shoulder groove 14 in the vicinity of the ground contact edge E will be described with reference to Fig. 3. Fig. 3 is an enlarged view of the shoulder groove 14 formed in the shoulder rib 11 of Fig. 2.

[0032] The shoulder grooves 14 have a substantially constant depth except for the vicinity of the starting end 14a on the inner side in the tire width direction of the ground contact edge E. On the other hand, on the outer side in the tire width direction of the ground contact edge E, the upper surface of the shoulder rib 11 is inclined toward the inner side in the tire radial direction, and the shoulder grooves 14 become gradually shallower from the ground contact edge E to the terminal end 14b.

[0033] Near the ground contact edge E, there is a change point C where at least one of the side and bottom surfaces constituting the shoulder groove 14 bends outward from the groove. This allows the volume of the shoulder groove 14 to increase from the ground contact edge E to the terminal end 14b, improving the drainage of the tire 1. By placing the change point C near the ground contact edge E, it is possible to increase the rigidity of the shoulder rib 11 while improving drainage.

[0034] The position of the change point C is not particularly limited as long as it is near the ground contact edge E, but it is preferably located more inward in the tire width direction than the ground contact edge E. This further improves the drainage performance of the tire 1. The distance (g) between the change point C and the ground contact edge E is, for example, 3 mm to 5 mm. That is, it is preferable that the change point be located 3 mm to 5 mm more inward in the tire width direction than the ground contact edge E.

[0035] In this embodiment, the inclination of the bottom surface of the shoulder groove 14 changes at the change point C. More specifically, the bottom surface 14d of the shoulder groove 14 located on the outer side in the tire width direction of the change point C is inclined at an angle (θ) toward the inner side in the tire radial direction with respect to an extension line L of the bottom surface 14e of the shoulder groove 14 located on the inner side in the tire width direction of the change point C. The angle (θ) is, for example, 0.9° to 1.2°. Although the angle (θ) is constant in FIG. 3, it may change between the change point C and the terminal end 14b.

[0036] The configuration of the change point C is not limited to the above example, and the slope of the side surface of the shoulder groove 14 may change at the change point C. For example, at the change point C, the width (W3) of the shoulder groove 14 on the upper surface of the shoulder rib 11 may remain unchanged, and the internal width of the shoulder groove 14 may increase. More specifically, the internal width of the shoulder groove 14 on the outer side of the change point C in the tire width direction may be larger than the internal width of the shoulder groove 14 on the inner side of the change point C in the tire width direction. For example, at the change point C, the width of the bottom surface 14c of the shoulder groove 14 may change.

[0037] The depth of the shoulder groove 14 at the ground contact edge E is, for example, 4.8 mm to 5.3 mm. If the depth of the shoulder groove 14 is within this range, the drainage performance of the tire 1 can be effectively improved.

[0038] 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.

[0039] As described above, the tire 1 is designed to reduce air resistance by reducing the ratio (L1 / L2) in the shoulder grooves 14, while ensuring the drainage performance that would otherwise deteriorate as a result by providing the change point C, thereby achieving both low air resistance and good drainage performance.

[0040] 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. [Example]

[0041] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[0042] <Example> A test tire (tire size: 225 / 60R18 100H) having the tread pattern shown in Figures 1 to 3 was manufactured. 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 shape in plan view that was convex rearward in the main tire rotation direction.

[0043] The dimensions of the shoulder grooves are as follows: The ratio (L1 / L2), the depth (D) of the shoulder grooves 14 at the ground contact edge E, and the spacing (g) are shown in Table 1. Distance (L1): 102mm Distance (L2): 87mm Ratio (L1 / L2): 1.17 Depth (D): 5.0 mm Spacing (g): 4mm Angle (θ): 0.98° Length (L3): 37mm Width (W3): 4.2 mm

[0044] <Comparative Examples 1 to 6> Test tires of Comparative Examples 1 to 6 were produced with different ratios (L1 / L2), D, and g, as shown in Table 1. In Comparative Examples 1 to 6, L2 was 87 mm, the same as in the examples, and the distance (L1) was changed to vary the ratio (L1 / L2). The ratio (L1 / L2) and depth (D) in Comparative Example 1 were equivalent to those in a general tire.

[0045] For each tire of the examples and comparative examples, the air resistance and drainage performance were evaluated by the following methods.

[0046] [Air resistance evaluation] Each tire was mounted in 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 efficiency when the vehicle was run a predetermined 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 set at 100, and a larger value indicates a lower 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)

[0047] [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 Comparative Example 1 tire being set at 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) Furthermore, if a tire's drainage is poor, it will not be able to remove water from the contact area with the road surface in time while driving. The remaining water will form 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 indicator of drainage.

[0048] [Table 1]

[0049] As shown in Table 1, the tires of the Examples have reduced air resistance while maintaining equivalent drainage compared to the tire of Comparative Example 1. On the other hand, the tires of Comparative Examples 2 to 6 have reduced air resistance but poorer drainage compared to the tire of Comparative Example 1. In other words, the tires of the Examples can achieve both low air resistance and good drainage. Note that the results of the tires of the Examples and Comparative Examples show that air resistance is significantly reduced when the ratio (L1 / L2) is in the range of 1.15 to 1.20. Also, the results of the tires of the Example and Comparative Example 5 show that the presence of a change point improves drainage. [Explanation of symbols]

[0050] 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, 14d, 14e bottom surface, E ground contact edge

Claims

1. A tire having a tread, the tread comprising: a main groove extending in the 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 the ground contact edge of the tread toward the outside in the tire width direction; and The shoulder groove has a shape in a plan view that is gently curved so as to be convex rearward in the main rotation direction of the tire, The depth of the shoulder groove at the ground contact edge is 4.8 mm to 5.3 mm, The width of the shoulder groove is 4.0 mm to 4.5 mm, the shortest distance (L1) along the top surface of the tread from the tire equator to the outer end of the shoulder groove in the tire width direction is 1.16 to 1.18 times the shortest distance (L2) along the top surface of the tread from the tire equator to the ground contact edge, A tire in which a transition point where a bottom surface constituting the shoulder groove bends outward in the vicinity of the ground contact edge exists, and the transition point is located 3 mm to 5 mm inward in the tire width direction from the ground contact edge.

2. The tire according to claim 1 , wherein an inclination of the bottom surface of the shoulder groove changes at the change point.

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

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