pneumatic tires

Abstract

To provide a pneumatic tire which can secure a drainage property and an abrasion property while suppressing an increase of air resistance.SOLUTION: A pneumatic tire includes a pair of beads 10, a pair of side walls 20, and a tread 30 having a plurality of lands 60 and main grooves 70. The plurality of main grooves 70 includes an outside main groove 73 disposed closer to the outside in a vehicle width direction, and an inside main groove 74 disposed closer to the inside in the vehicle width direction. The lands 60 include an outside shoulder land 63 disposed in the outside in the vehicle width direction, and an inside shoulder land 64 disposed in the inside in the vehicle width direction. A plurality of slits 98 extending in a direction crossing a tire circumferential direction and disposed with intervals in the tire circumferential direction are provided only in the outside shoulder land 63. Each of the plurality of slits 98 communicates with the inside main groove 74. An angle θ between root parts 98a of the plurality of slits 98 extending from the inside main groove 74 toward the inside in the vehicle width direction and the tire width direction is 30° or more and 36° or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pneumatic tire.

Background Art

[0002] Conventionally, pneumatic tires having a tread in which a tread pattern is formed by a plurality of grooves are known. Examples of the plurality of grooves include main grooves along the tire circumferential direction, and slits, sipes and the like that extend in a direction intersecting the tire circumferential direction and are narrower than the main grooves. Patent Document 1 discloses a tire in which a plurality of slits are arranged at intervals in the tire circumferential direction on each of a pair of shoulder land portions forming both ends of the tread in the tire width direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] The slits provided in the tread improve drainage performance, but increasing the number or volume of the slits brings about the disadvantage of increased air resistance. In addition, uneven wear caused by the formation of slits is also a concern.

[0005] An object of the present invention is to provide a pneumatic tire capable of suppressing an increase in air resistance while ensuring drainage performance and wear resistance.

Means for Solving the Problems

[0006] The pneumatic tire of the present invention is a pneumatic tire mounted on a vehicle, comprising: a pair of beads; a pair of sidewalls extending radially outward from each of the pair of beads; and a tread positioned between the pair of sidewalls and having a plurality of ridges and a plurality of main grooves positioned between the plurality of ridges and extending circumferentially in the tire direction, wherein, when mounted on a vehicle, the plurality of main grooves include an outer main groove positioned furthest outward in the vehicle width direction and an inner main groove positioned furthest in the vehicle width direction, and the ridges are positioned further outward in the vehicle width direction than the outer main grooves The tire includes an outer shoulder plate and an inner shoulder plate positioned inward in the vehicle width direction from the inner main groove, and a plurality of slits extending in a direction intersecting the tire circumferential direction and spaced apart in the tire circumferential direction are provided only on the inner shoulder plate in both the outer and inner shoulder plates, each of the plurality of slits is in communication with the inner main groove, and the angle between the root portion of each of the plurality of slits extending inward from the inner main groove in the vehicle width direction and the tire width direction is 30° or more and 36° or less. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a pneumatic tire that can suppress an increase in air resistance while ensuring drainage and wear resistance. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows a half-cross section in the tire width direction of the tire according to the embodiment. [Figure 2] This is a partially enlarged plan view showing the tread surface of a tire according to an embodiment. [Figure 3] This is an enlarged view of the area shown in III in Figure 2. [Modes for carrying out the invention]

[0009] The embodiments will be described below with reference to the drawings. Figure 1 is a diagram showing the internal structure of a tire 1, which is a pneumatic tire according to the embodiment, and shows a half cross-section in the tire width direction. Figure 2 is a partially enlarged view of a top view of the tire 1, and shows the tread surface 37 of the tire 1 on which the tread pattern 80 is formed. The tire 1 according to the embodiment is, for example, a pneumatic tire for a passenger car.

[0010] First, the internal structure of tire 1 will be explained with reference to Figure 1. In Figure 1, the symbol S1 indicates the tire equatorial plane perpendicular to the rotation axis of tire 1. The basic internal structure of tire 1 is symmetrical with respect to the tire equatorial plane S1. Figure 1 shows a half-cross section of the right half of tire 1, and the left half, which is not shown, has the same structure. Figure 2 shows the tire equator S2, which corresponds to the tire equatorial plane S1 and extends in the circumferential direction on the tread surface 37.

[0011] The cross-sectional view in Figure 1 is a half-cross-sectional view in the tire width direction of tire 1 in an unloaded state, mounted on a specified rim (not shown) and filled with the specified internal pressure. The specified rim refers to the standard rim defined by JATMA corresponding to the tire size. The specified internal pressure is, for example, 180 kPa if the tire is for a passenger car.

[0012] In Figure 1, the tire width direction is indicated by arrow X, and the tire diameter direction is indicated by arrow Y. The tire width direction is the direction parallel to the tire rotation axis, and corresponds to the left-right direction on the page in Figure 1. The inside of the tire width direction is the direction approaching the tire equatorial plane S1 in the tire width direction, and corresponds to the left side of the page in Figure 1. The outside of the tire width direction is the direction away from the tire equatorial plane S1 in the tire width direction, and corresponds to the right side of the page in Figure 1.

[0013] Furthermore, the tire radial direction is the direction perpendicular to the tire rotation axis, and corresponds to the vertical direction in Figure 1. In Figure 1, it is shown as the tire radial direction Y. The outer side of the tire radial direction is the direction away from the tire rotation axis, and corresponds to the upper side of the paper in Figure 1. The inner side of the tire radial direction is the direction closer to the tire rotation axis, and corresponds to the lower side of the paper in Figure 1.

[0014] The tire 1 of the embodiment has a designated orientation for mounting on a vehicle (not shown), that is, one side facing outwards and the other facing inwards when mounted on a vehicle, in the tire width direction. This orientation for mounting on a vehicle is determined based on the tread pattern 80 formed on the tread surface 37. In Figures 1 and 2, the side facing outwards on the vehicle is shown as the outer side in the vehicle width direction, and the side facing inwards on the vehicle is shown as the inner side in the vehicle width direction. That is, in Figures 1 and 2, the right side of the paper is the outer side in the vehicle width direction, and the left side of the paper is the inner side in the vehicle width direction.

[0015] As shown in Figure 1, the tire 1 comprises a pair of beads 10 provided on both sides in the tire width direction, a pair of sidewalls 20 extending radially outward from each of the pair of beads 10, a tread 30 positioned between the pair of sidewalls 20, a shoulder 25 positioned between the tread 30 and the sidewalls 20, a carcass ply 40 positioned across the pair of beads 10, and an inner liner 50 positioned on the inner side of the carcass ply 40.

[0016] The bead 10 includes a bead core 11 and a bead filler 12 extending radially outward from the bead core 11.

[0017] The bead core 11 is an annular member formed by winding a rubber-coated metal bead wire a plurality of times in the tire circumferential direction. The bead core 11 is a member that serves to fix the tire 1 inflated with air to a rim. The bead filler 12 has a tapered shape whose thickness decreases as it extends from the tire radial direction inner side to the tire radial direction outer side. The bead filler 12 is provided to increase the rigidity of the peripheral portion of the bead 10 and ensure high maneuverability and stability. The bead filler 12 is made of, for example, rubber having a higher hardness than the surrounding rubber members.

[0018] The bead 10 is surrounded by rim strip rubber 13 with the carcass ply 40 interposed therebetween. The rim strip rubber 13 is disposed on the tire radial direction inner side of the tire 1 in a manner that wraps around from the tire width direction inner side of the bead 10 through the tire radial direction inner end to the tire width direction outer side. The rim strip rubber 13 comes into contact with the inner surface of a rim on which the tire 1 is mounted. A rim line 13a extending along the tire circumferential direction is formed on the outer surface of the rim strip rubber 13 on the tire width direction outer side.

[0019] The sidewall 20 includes sidewall rubber 21 disposed on the tire width direction outer side of the carcass ply 40. The sidewall rubber 21 constitutes the outer and inner side wall surfaces of the tire 1. The sidewall rubber 21 is the portion that flexes the most when the tire 1 exerts a cushioning effect, and usually a flexible rubber having fatigue resistance is employed therefor.

[0020] The tread 30 includes an endless belt 31, a cap ply 34, an edge ply 35, and tread rubber 36. The belt 31 is disposed on the tire radial direction outer side of the carcass ply 40. The cap ply 34 is disposed on the tire radial direction outer side of the belt 31. The tread rubber 36 is disposed on the tire radial direction outer side of the cap ply 34.

[0021] The belt 31 is a member that reinforces the tread 30. The belt 31 of the embodiment has a two-layer structure including an inner belt 32 arranged on the outer side in the tire radial direction of the inner liner 50, and an outer belt 33 arranged on the outer side in the tire radial direction of the inner belt 32. Each of the inner belt 32 and the outer belt 33 has a structure in which a plurality of belt cords such as steel cords are covered with rubber.

[0022] The inner belt 32 is wider than the outer belt 33. By providing the belt 31, the rigidity of the tire 1 is secured, and the ground contact property of the tread 30 with respect to the road surface is improved. Note that the belt 31 is not limited to a two-layer structure, and may have a single-layer structure or a structure of three or more layers.

[0023] The cap ply 34 is a member that reinforces the tread 30 together with the belt 31. The cap ply 34 has, for example, a structure in which a plurality of insulating organic fiber cords such as polyamide fibers are covered with rubber. The cap ply 34 covers the entire belt 31 from the tire outer surface side. The edge ply 35 is sandwiched between the end 34a of the cap ply 34 on the outer side in the tire width direction and the end 31a of the belt 31 on the outer side in the tire width direction, and is configured to press the end 31a of the belt 31 on the outer side in the tire width direction toward the tire inner cavity side. Note that the edge ply 35 may be sandwiched between the end 34a of the cap ply 34 on the outer side in the tire width direction and the tread rubber 36. By providing the cap ply 34, it is possible to improve durability and reduce road noise during traveling. Although the cap ply 34 in the embodiment has a single layer, it may have a structure of two or more layers.

[0024] The tread rubber 36 is arranged on the outer side in the tire radial direction of the cap ply 34. The tread rubber 36 is a member that constitutes the tread surface 37 which is the outer surface of the tread 30 and comes into contact with the road surface. The end 36a of the tread rubber 36 on the outer side in the tire width direction curves inward in the tire radial direction beyond the end 34a of the cap ply 34 on the outer side in the tire width direction. The end 34a of the cap ply 34 on the outer side in the tire width direction is covered by the end 21a of the sidewall rubber 21 on the outer side in the tire radial direction.

[0025] A tread pattern 80 is provided on the tread surface 37. The tread pattern 80 has a distinctive configuration in this disclosure, which will be described in detail later.

[0026] The shoulder 25 of this embodiment is a curved portion extending from the outer edge in the tire width direction of the tread surface 37 that contacts the road surface to the outer edge in the tire radial direction of the sidewall 20. The shoulder 25 includes the outer edge 36a in the tire width direction of the tread rubber 36 and the outer edge 21a in the tire radial direction of the sidewall rubber 21.

[0027] The carcass ply 40 is stretched between a pair of beads 10. The carcass ply 40 constitutes the skeletal ply of the tire 1. The carcass ply 40 is embedded in the tire 1 in such a manner that it passes between the pair of beads 10 and through the inner side of the tire cavity of the pair of sidewalls 20 and the tread 30. In the tread 30, a belt 31 is positioned on the radially outer side of the carcass ply 40.

[0028] The carcass ply 40 has a ply body portion 40A, a pair of left and right folded portions 40B, and a pair of left and right bent portions 40C. The ply body portion 40A is the portion that extends from the inner side in the tire width direction of the bead core 11 of one bead 10, through one sidewall 20, the tread 30, and the other sidewall 20, to the vicinity of the inner side in the tire width direction of the bead core 11 of the other bead 10.

[0029] The folded portion 40B is the part that extends radially outward on the outer side of the bead 10 in the tire width direction, by being folded back from the inner side of the ply body 40A in the tire radial direction around the bead core 11. The folded portion 40B extends radially outward beyond the bead filler 12 to the inner side of the tire radial direction beyond the vicinity of the maximum width position of the tire 1. The portion of the folded portion 40B that is radially outward beyond the bead filler 12 overlaps with the outer side of the ply body 40A in the tire width direction.

[0030] The bent portion 40C is the part that bends in a U-shape from the ply body portion 40A around the bead core 11 and connects to the folded portion 40B. The bent portion 40C is in contact with the inner side of the bead core 11 in the tire width direction. The ply body portion 40A and the folded portion 40B are continuous via the bent portion 40C.

[0031] The carcass ply 40 has a structure in which multiple parallel ply cords are covered with rubber. The ply cords are made of steel cords, or insulating organic fiber cords such as polyester or polyamide, and function as the skeleton of the tire 1. In this embodiment, the carcass ply 40 has a single-layer structure, but the carcass ply 40 may have a structure of two or more layers.

[0032] The rim strip rubber 13 described above surrounds the radially inner end of the carcass ply 40, including the bent portion 40C.

[0033] The inner liner 50 covers the inner surface of the ply body portion 40A of the carcass ply 40 between the pair of beads 10. The inner edge of the inner liner 50 in the tire radial direction covers the inner portion of the rim strip rubber 13 in the tire width direction. The inner liner 50 of this embodiment has a two-layer structure in which a first inner liner 51 and a second inner liner 52 are stacked on top of each other. The first inner liner 51 is positioned on the inner side of the tire cavity of the second inner liner 52. The first inner liner 51 and the second inner liner 52 are made of air-permeable rubber to prevent air inside the tire cavity from leaking to the outside.

[0034] Here, the rubber used for the bead filler 12 is one that is at least harder than the sidewall rubber 21 and the inner liner 50. The hardness of the rubber is Type A durometer hardness according to JIS K6253-3:2012.

[0035] For example, using the hardness of the sidewall rubber 21 as a reference, the hardness of the bead filler 12 is preferably about 1.2 to 2.3 times the hardness of the sidewall rubber 21. The hardness of the rim strip rubber 13 is more preferably about 1 to 1.6 times the hardness of the sidewall rubber 21. By setting the hardness in this way, a balance between the flexibility of the tire and the rigidity around the bead 10 can be ensured. Furthermore, the hardness of the tread rubber 36 is preferably relatively low from the viewpoint of good contact and low fuel consumption, for example, a durometer hardness of type A of about 50 to 60 is preferred.

[0036] The above describes the internal structure of the tire 1 according to the embodiment. Next, the tread pattern 80 formed on the tread surface 37 will be described with reference to Figure 2. Figure 2 shows the tire width direction X and the tire circumferential direction C. As mentioned above, Figure 2 is a part of the plan view of the tread surface 37, but in Figure 2, the front side of the vehicle is considered the upper side and the rear side of the vehicle is considered the lower side when the tire 1 is mounted on the vehicle. In the following description, the front and rear sides correspond to this, with the upper side being the front side and the lower side being the rear side. Also, in the following description, the outer side in the vehicle width direction when the tire 1 is mounted on the vehicle is referred to as the outer side in the vehicle width direction or the right side, and the inner side in the vehicle width direction is referred to as the inner side in the vehicle width direction or the left side.

[0037] The tread pattern 80 of the embodiment has a plurality of ribs 60 and a plurality of main grooves 70 positioned between the plurality of ribs 60 and extending in the circumferential direction of the tire. Each of the plurality of ribs 60 is a rib that extends in an annular shape along the circumferential direction of the tire. Each of the plurality of main grooves 70 is a relatively wide groove that extends in an annular shape along the circumferential direction of the tire. The ribs 60 are responsible for contacting and rubbing against the road surface and for transmitting vehicle power to the road surface and for braking. The main grooves 70 are mainly responsible for the drainage function of the tire 1. In the following description, the width direction in the ribs 60 and main grooves 70 is synonymous with the tire width direction, and the width in the ribs 60 and main grooves 70 refers to the dimension in the tire width direction.

[0038] The multiple main grooves 70 include a first central main groove 71 and a second central main groove 72 located in the center of the tire width direction, and an outer main groove 73 and an inner main groove 74. The first central main groove 71 is located on the outer side of the tire equator S2 in the vehicle width direction. The second central main groove 72 is located on the inner side of the tire equator S2 in the vehicle width direction. The outer main groove 73 is located on the outer side of the first central main groove 71 in the vehicle width direction. The inner main groove 74 is located on the inner side of the second central main groove 72 in the vehicle width direction. In this embodiment, the widths of the four main grooves 70 are the same, but they may be different.

[0039] The multiple ridges 60 include a central ridge 65 between the first central main groove 71 and the second central main groove 72, a first intermediate ridge 61 and a second intermediate ridge 62 located outside the central ridge 65 in the tire width direction, and an outer shoulder ridge 63 and an inner shoulder ridge 64 located at the outer edge of the tread 30 in the tire width direction. The central ridge 65 is positioned so that the tire equator S2 passes through its center in the width direction. The first intermediate ridge 61 is located between the first central main groove 71 and the outer main groove 73. The second intermediate ridge 62 is located between the second central main groove 72 and the inner main groove 74. The outer shoulder ridge 63 is located outside the outer main groove 73 in the tire width direction. The inner shoulder ridge 64 is located outside the inner main groove 74 in the tire width direction. Of the multiple ridges 60, the outer shoulder ridge 63 is located furthest out in the vehicle width direction, and the inner shoulder ridge 64 is located furthest in the vehicle width direction. The outer shoulder 63 and the inner shoulder 64 each connect to the shoulder 25.

[0040] In this embodiment, the first intermediate ridge 61 and the second intermediate ridge 62 have the same width, and the width of the central ridge 65 is smaller than the widths of the first intermediate ridge 61 and the second intermediate ridge 62, but is not limited to this. In this embodiment, the outer shoulder ridge 63 and the inner shoulder ridge 64 have the same width and are larger than the central ridge 65 and each of the intermediate ridges 61 and 62, but is not limited to this.

[0041] An annular sub-groove 75 is formed in the center of the width direction of the first intermediate groove 61, extending along the circumferential direction of the tire. The width of this sub-groove 75 is narrower than that of each main groove 70.

[0042] On the surface of each of the multiple land surfaces 60, multiple grooves are formed that extend in a direction intersecting the circumferential direction of the tire, forming the tread pattern 80. These grooves are sipes and slits, and are both spaced apart in the circumferential direction of the tire. Here, a sipe is a groove with a width of 1 mm or less, and a slit is a groove with a width of more than 1 mm.

[0043] Multiple first sipes 91 are formed in the central groove 65. The first sipes 91 open into the first central main groove 71, and from their opening ends, they extend diagonally towards the rear, curving slightly towards the rear as they extend inward in the vehicle width direction, crossing the tire equator S2, and terminating without reaching the second central main groove 72.

[0044] Multiple second sipes 92 and multiple third sipes 93 are formed in the first intermediate groove 61. The second sipes 92 open into the first central main groove 71 and extend diagonally forward almost straight from their opening end as they extend outward in the vehicle width direction, terminating without reaching the secondary groove 75. The third sipes 93 open into the secondary groove 75 and extend diagonally forward as they extend outward in the vehicle width direction, curving slightly rearward as they extend, terminating without reaching the outer main groove 73. These sipes are arranged such that the second sipes 92 extend on the rightward extension of the first sipes 91, and the third sipes 93 extend on the rightward extension of the second sipes 92.

[0045] Multiple fourth sipes 94 and multiple fifth sipes 95 are formed in the second intermediate groove 62. The fourth sipes 94 open into the inner main groove 74 and extend diagonally forward from their opening end, curving slightly forward as they extend outward in the vehicle width direction, and terminate without reaching the second central main groove 72. The fifth sipes 95 open into the inner main groove 74 and extend diagonally almost straight forward from their opening end as they extend outward in the vehicle width direction, and terminate slightly closer to the second central main groove 72 from the center of the second intermediate groove 62 in the width direction. The length of the fourth sipes 94 in the tire width direction is longer than the length of the fifth sipes 95 in the tire width direction. The fifth sipes 95 are positioned one at a time between the fourth sipes 94 which are arranged in the circumferential direction of the tire. The diagonal forward extension directions of the fourth sipes 94 and fifth sipes 95 are at approximately the same angle and are generally almost parallel to each other. Regarding groove width, the 4th sipe (94) is larger than the 5th sipe (95).

[0046] Multiple sixth sipes 96 are formed on the outer shoulder 63. The sixth sipes 96 are lateral grooves that generally follow the tire width direction and extend diagonally forward as they move to the right. The sixth sipes 96 open into the outer main groove 73, and from their opening ends, they extend diagonally forward as they extend outward in the vehicle width direction, then curve and bend, the angle of inclination becomes gentler, and then extend straight diagonally forward as they continue to extend outward in the vehicle width direction. The outer end of the sixth sipes 96 in the vehicle width direction extends to the vicinity of the outer shoulder 25, where it terminates.

[0047] Multiple seventh sipes 97 and multiple slits 98 are formed on the inner shoulder 64. Both the seventh sipes 97 and the slits 98 are transverse grooves that generally follow the tire width direction and extend diagonally towards the rear as they move inward in the vehicle width direction. The seventh sipes 97 open into the inner main groove 74, and from their opening ends, they extend diagonally and briefly towards the rear as they extend inward in the vehicle width direction, then gently curve to become convex towards the rear, and then the angle of inclination becomes gentler as they extend straight inward in the vehicle width direction.

[0048] The slit 98 has a shape that follows the seventh sipe 97. That is, the slit 98 opens into the inner main groove 74, and from its opening end, as it extends inward in the vehicle width direction, it shortens diagonally toward the rear, then gently curves so as to become convex toward the rear, and then the angle of inclination becomes gentler as it extends straight inward in the vehicle width direction. The right end of each of the multiple slits 98 opens into the inner main groove 74. Therefore, the multiple slits 98 are in communication with the inner main groove 74.

[0049] The inner ends of the 7th sipe 97 and slit 98 in the vehicle width direction both extend to the vicinity of the shoulder 25 on the inner side in the vehicle width direction, where they terminate. The length of slit 98 in the tire width direction is longer than the length of the 7th sipe 97 in the tire width direction.

[0050] As described above, the first sipe 91 to the seventh sipe 97 are all narrow grooves with a groove width of 1 mm or less. On the other hand, the groove width of the slit 98 is greater than 1 mm and is larger than the groove widths of the first sipe 91 to the seventh sipe 97. The spacing between the first sipe 91 to the seventh sipe 97 and the slit 98, which are arranged in the circumferential direction of the tire, may be equal or unequal.

[0051] In this embodiment, the tire 1 has multiple slits 98 on both the outer shoulder ridge 63 and the inner shoulder ridge 64, but only on the inner shoulder ridge 64. The outer shoulder ridge 63 has multiple sipes, i.e., the sixth sipe 96.

[0052] Figure 3 is an enlarged view of the portion shown in III of Figure 2. As shown in Figure 3, the slit 98 provided in the inner shoulder ridge 64 has a root portion 98a that extends inward in the vehicle width direction from the opening end to the inner main groove 74. The angle θ between this root portion 98a and the line W1 parallel to the tire width direction is preferably 30° or more and 36° or less.

[0053] Generally, in pneumatic tires having shoulder ridges on both sides of the tire width direction of the tread, the presence or absence of slits, such as the slit 98 in the embodiment, on these shoulder ridges affects the vortex structure around the rotating tire and thus the Cd value (coefficient of air resistance). Furthermore, when the shoulder ridges do not have slits, the Cd value is lower and air resistance is lower than when they do. Moreover, slits provided on the shoulder ridges on the outer side in the vehicle width direction have a relatively greater impact on the Cd value than slits provided on the inner side in the vehicle width direction. This is because the shoulder ridges on the outer side in the vehicle width direction are less affected by the vehicle body, and the airflow to the shoulder ridges on the outer side in the vehicle width direction has a greater impact on the Cd value.

[0054] In this embodiment, the tire 1 has multiple slits 98 on the inner shoulder 64 only, while the outer shoulder 63, which has a relatively large impact on air resistance, does not have slits 98. This suppresses the increase in air resistance. On the other hand, the slits 98 on the inner shoulder 64 ensure drainage.

[0055] The angle θ shown in Figure 3 affects the drainage and wear performance of the tire 1. Specifically, a larger angle θ brings the root portion 98a of the slit 98 closer to the direction aligned with the tire circumferential direction, i.e., the drainage direction, thus improving drainage. However, a larger angle θ leads to lower pattern rigidity and deterioration of wear performance. In this embodiment, setting the angle θ between 30° and 36° makes it possible to achieve a good balance between drainage and wear performance, with an angle of around 33° being particularly preferable.

[0056] Furthermore, since all of the multiple slits 98 are connected to the inner main groove 74, drainage is improved.

[0057] Furthermore, as shown in Figure 2, the opening end 98b of each slit 98 into the inner main groove 74, the opening end 94b of each fourth sipe 94 into the inner main groove 74, and the opening end 95b of each fifth sipe 95 do not coincide in the circumferential direction of the tire, but are offset from each other in the circumferential direction of the tire. This helps to suppress the increase in pattern noise during driving.

[0058] The tire 1 of the above embodiment provides the following effects.

[0059] (1) The tire 1 according to the embodiment is a pneumatic tire mounted on a vehicle, comprising: a pair of beads 10; a pair of sidewalls 20 extending radially outward from each of the pair of beads 10; and a tread 30 positioned between the pair of sidewalls 20 and having a plurality of ridges 60, and a plurality of main grooves 70 positioned between the plurality of ridges 60 and extending in the circumferential direction of the tire, wherein when mounted on a vehicle, the plurality of main grooves 70 include an outer main groove 73 positioned furthest outward in the vehicle width direction and an inner main groove 74 positioned furthest inward in the vehicle width direction, and the ridges 60 extend further in the vehicle width direction than the outer main groove 73. The tire includes an outer shoulder plate 63 positioned on the outside and an inner shoulder plate 64 positioned inward in the vehicle width direction from the inner main groove 74. Multiple slits 98 are provided in a direction intersecting the tire circumferential direction and spaced apart in the tire circumferential direction, provided only on the inner shoulder plate 64 in both the outer shoulder plate 63 and the inner shoulder plate 64. Each of the multiple slits 98 communicates with the inner main groove 74, and the angle between the root portion 98a of each of the multiple slits 98, which extends inward from the inner main groove 74 in the vehicle width direction, and the tire width direction is 30° or more and 36° or less.

[0060] In the embodiment, the tire 1 has multiple slits 98 on both the outer shoulder ridge 63 and the inner shoulder ridge 64, but only on the inner shoulder ridge 64, and the angle θ between the root portion 98a of each slit 98, which communicates with the inner main groove 74, and the tire width direction is 30° to 36°. This makes it possible to suppress an increase in air resistance while ensuring drainage and wear resistance. Drainage is also improved because the slits 98 communicate with the inner main groove 74.

[0061] Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., made to the extent that the objectives of the present invention can be achieved are also included within the scope of the present invention.

[0062] The configuration of the embodiment described above can be used as a tire for various vehicles other than passenger cars, such as light trucks, trucks, and buses. [Examples]

[0063] The following describes the examples. As in the above embodiment, tires for Examples 1 to 3 shown in Table 1 were prepared, in which multiple slits were provided only on the inner shoulder ridge, and the angle θ at the base of the slits was in the range of 30° to 36°. On the other hand, comparative examples 1 and 2 shown in Table 1 were prepared, in which the angle θ was 27° and 39°, and the other configurations were the same as in the examples, and comparative example 3 was prepared, in which slits were formed on both the inner and outer shoulder ridges, and the angle θ was 27° in both cases. The "slit angle" shown in Table 1 refers to the angle θ. For each tire, both an actual machine model and a simulation model were prepared, and the Cd value and wear resistance evaluation below were performed using the simulation model, while the drainage performance evaluation was performed using the actual machine model.

[0064] The Cd value, drainage performance, and abrasion performance of the tires in Examples 1-3 and Comparative Examples 1-3 were evaluated according to the following procedure. The evaluation results are shown in Table 1. In Table 1, the tire of Comparative Example 1 is set to an index of 100, and the other tires are evaluated using this index. A smaller Cd value indicates lower air resistance and is considered better. A larger Cd value indicates better drainage and is considered better. A larger Cd value indicates less wear and is considered better.

[0065] (Method for evaluating Cd value) For each tire, the drag force (the force acting on the tire placed in the airflow, parallel to the flow and in the same direction) was measured, and the drag coefficient Cd value was calculated using equation (1) below. The drag force was determined from the pressure difference across the front and rear of the tire through simulation. Cd value = D / (1 / 2ρU2S) ... (1) Note that D is the drag force generated. ρ is the air density, which is 1.225 [kg / m³]. 3 U is the representative velocity, which is the relative velocity between the tire and the air, and is set to 27.8 [m / s]. S is the representative area (frontal projected area) of the tire.

[0066] (Method for evaluating drainage performance) With each tire mounted on the vehicle as the front and rear wheels, the tires were rotated on a wet road surface with a water depth of 8 mm, and the speed at which hydroplaning occurred was measured. The tire mounting conditions were as follows: air pressure: front wheels: 230 kPa, rear wheels: 220 kPa; load: front wheels: 913 kgf, rear wheels: 772 kgf. Regarding the drainage performance of the tires, if the drainage performance is poor, the water from within the contact surface with the road surface cannot be removed in time during driving, and the remaining water forms a water film between the road surface and the tread surface, causing a loss of contact with the road surface and leading to hydroplaning. Therefore, the speed at which hydroplaning occurs was measured as an indicator of drainage performance, and the slower the speed, the more likely hydroplaning is to occur, i.e., the lower the drainage performance.

[0067] (Method for evaluating abrasion resistance) With each tire mounted on the vehicle as the front and rear wheels, the wear resistance was simulated and evaluated by calculating the distance Dmm required for the tread contact surface to wear down to a thickness of 1mm using the following formula (2). Wear resistance is evaluated as good when Dmm is large. Dmm = D / Ce ave The tire mounting conditions were as follows: air pressure was set to 230kPa for the front wheels and 220kPa for the rear wheels, and the load was set to 913kgf for the front wheels and 772kgf for the rear wheels.

[0068] [Table 1]

[0069] According to Table 1, Examples 1 to 3, which have slits only on the outer shoulder and whose angle θ (slit angle) between the base of the slit and the tire width direction is in the range of 30° to 36°, are practically sufficient in terms of air resistance based on the Cd value without a significant increase. While drainage performance improves with a larger slit angle, wear resistance tends to decrease. Examples 1 to 3 have better drainage performance than Comparative Example 1, and wear resistance is also ensured at a practical level. Comparative Example 2, which has a relatively large slit angle, improves drainage performance as the direction of slit extension approaches the tire circumferential direction, but wear resistance worsens. Comparative Example 3, which also has slits on the outer shoulder, improves drainage performance due to the increased number of slits, but air resistance increases. Therefore, when slits are provided only on the outer shoulder and the slit angle is between 30° and 36°, it is possible to ensure drainage performance and wear resistance while suppressing an increase in air resistance. [Explanation of Symbols]

[0070] 1. Tire (pneumatic tire) 10 beads 20 Sidewall 30 tread 60 land 63 Outer shoulder land 64 Inner shoulder land 70 Main groove 73 Outer main groove 74 Inner main groove 98 Slits

Claims

[Claim 1] A pneumatic tire fitted to a vehicle, A pair of beads, A pair of sidewalls extending radially outward from each of the aforementioned pair of beads, A tread having a plurality of ridges and a plurality of main grooves positioned between the plurality of ridges and extending in the circumferential direction of the tire, When mounted on a vehicle, the plurality of main grooves include an outer main groove located furthest out in the vehicle width direction and an inner main groove located furthest in the vehicle width direction, and the land includes an outer shoulder land located further out in the vehicle width direction than the outer main groove and an inner shoulder land located further in the vehicle width direction than the inner main groove. Multiple slits extending in a direction intersecting the tire circumferential direction and spaced apart in the tire circumferential direction are provided only on the inner shoulder land in both the outer shoulder land and the inner shoulder land. Each of the aforementioned multiple slits is in communication with the inner main groove, A pneumatic tire in which the angle between the root portion of each of the plurality of slits, which extends inward in the vehicle width direction from the inner main groove, and the tire width direction is 30° or more and 36° or less.

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