JP2024099174A - Pneumatic tire - Google Patents

Abstract

To provide a pneumatic tire that is excellent in steering stability, noise performance and abrasion resistance.SOLUTION: In a tire 1 that is one example of embodiments, in a state where the tire is mounted on a normal rim and is filled with air whose inner pressure is normal, a difference between a height of an equatorial position of a profile surface α along a surface of a tread 10 and a height of a position of a grounding end is 11.5 mm or more and 14.5 mm or less, where the profile surface α includes a first region having a first curvature radius, a second region having a second curvature radius and a third region having a third curvature radius, in this order from the position of the grounding end towards the equatorial position.SELECTED DRAWING: Figure 5

Description

The present invention relates to a pneumatic tire.

It is known that the shape of the profile surface along the tread surface of a pneumatic tire greatly affects tire performance such as steering stability, wear resistance, and noise performance. For example, Patent Document 1 discloses a pneumatic tire in which the profile surface is formed of arcs with multiple different radii of curvature, and the relationship between the radii of curvature of each arc, and the relationship between the radius of curvature of the arc in the tread center and the tread width, etc., satisfy specific conditions. In addition, Patent Document 2 discloses a pneumatic tire in which the profile surface in the tread center is an arc-shaped curved convex radially outward, and the radius of curvature of the profile surface at a specified internal pressure satisfies specific conditions.

JP 2010-126103 A JP 2013-173395 A

As disclosed in Patent Documents 1 and 2, the shape of the tire's profile surface is an important factor in reducing noise generated by the tire and improving wear resistance while ensuring good driving stability. On the other hand, conventional tires, including those disclosed in Patent Documents 1 and 2, still have room for improvement in terms of the balance between driving stability, noise performance, and wear resistance.

The pneumatic tire according to the present invention is a pneumatic tire having a tread, the tread having a main groove extending in the tire circumferential direction and blocks partitioned by the main groove, and when the tire is mounted on a standard rim and filled with air to a standard internal pressure, the difference between the height of the equator position of the profile surface along the surface of the tread and the height of the ground contact edge position is 11.5 mm or more and 14.5 mm or less, and the profile surface includes, from the ground contact edge position toward the equator position, a first region having a first radius of curvature, a second region having a second radius of curvature, and a third region having a third radius of curvature.

The pneumatic tire according to the present invention can reduce noise generated by the tire and improve wear resistance while ensuring good driving stability. The pneumatic tire according to the present invention has a good balance between driving stability, noise performance, and wear resistance, and is suitable for high-performance tires that require high driving performance.

1 is a perspective view of a pneumatic tire as an example of an embodiment. 1 is a plan view of a pneumatic tire as an example of an embodiment, showing an enlarged view of a portion of a tread. FIG. 2 is a plan view of a first mediate block and its vicinity. FIG. 2 is a perspective view of a first mediate block and its vicinity. FIG. 1 is a diagram showing a profile shape of a pneumatic tire as an example of an embodiment. 1 is a diagram showing a portion of an axial cross section of a pneumatic tire as an example of an embodiment.

Below, an example of an embodiment of a pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. In addition, the present invention includes forms that are formed by selectively combining the components of the embodiment described below.

Figure 1 is a perspective view of a pneumatic tire 1 according to an embodiment, and also shows the internal structure of the tire. The pneumatic tire 1 has a tread 10, which is the portion that comes into contact with the road surface. The tread 10 has main grooves that extend in the circumferential direction of the tire, and blocks that are partitioned by the main grooves. In this embodiment, three main grooves 20, 21, and 22 are formed as main grooves that extend in the circumferential direction of the tire. In addition, a first mediate block 30, a second mediate block 40, a first shoulder block 50, and a second shoulder block 60 are formed as blocks.

The pneumatic tire 1 is a tire with a specified mounting direction relative to the vehicle, and is mounted in opposite directions on the right and left sides of the vehicle. The tread 10 has different tread patterns on the left and right of the tire equator CL. The equator CL is an imaginary line that runs through the axial center of the tread 10 along the tire circumferential direction. For convenience of explanation, the terms "left and right" are used in this specification, and these left and right refer to the left and right in the direction of travel of the vehicle when the pneumatic tire 1 is mounted on the vehicle.

The tread 10 has a first main groove 20, a second main groove 21 that is positioned on the vehicle outer side of the equator CL when the tire is mounted on the vehicle, and a mediate block 30 that is partitioned by the main grooves 20, 21. In other words, the pneumatic tire 1 is mounted on the vehicle so that the mediate block 30 is located on the vehicle outer side. The main groove 20 is formed on the equator CL and extends in the tire circumferential direction along the equator CL. The tread 10 may have blocks that are positioned on the equator CL, but in this embodiment, from the viewpoint of drainage in the center region, there are no blocks on the equator CL and the main groove 20 is formed.

The pneumatic tire 1 is a summer tire used on roads that are free of ice and snow, and has a good balance of steering stability, noise performance, and wear resistance, making it suitable, for example, for vehicles with high driving performance. As will be described in detail later, the rounded profile shape of the tread 10 effectively suppresses noise generated by the tire. On the other hand, the rounded profile shape can cause problems such as the center region of the tread becoming more susceptible to wear and reduced steering stability, but the tread pattern of this embodiment ensures good wear resistance and steering stability.

The pneumatic tire 1 has a pair of sidewalls 11 that bulge outward in the tire axial direction, and a pair of beads 12. The sidewalls 11 extend radially inward from both the left and right ends of the tread 10, forming the side surfaces of the pneumatic tire 1. In this embodiment, a side rib 2 that protrudes slightly outward is formed in a ring shape along the tire circumferential direction at the top of the tire side surface, and this side rib 2 is the boundary between the tread 10 and the sidewalls 11.

The bead 12 is a part that is fixed to the wheel rim, and has a bead core 13 and a bead filler 14. The bead core 13 is a ring-shaped member made of bundled steel wires (bead wires) covered with rubber. The bead filler 14 is made of a rubber that is harder than the tread rubber and the sidewall rubber, and has the function of increasing the rigidity of the bead 12. The bead fillers 14 are disposed adjacent to the left and right bead cores 13 on the outer side in the tire radial direction. As will be described in detail later, the height of the bead filler 14 is set to, for example, 26 mm or more and 34 mm or less, taking into consideration driving stability, etc.

The ground contact ends E1 and E2 of the pneumatic tire 1, or the portions from the vicinity thereof to the left and right side ribs 2, are also called shoulder or buttress regions. Ground contact end E1 is the ground contact end on the outer side of the vehicle, and ground contact end E2 is the ground contact end on the inner side of the vehicle, located at shoulder blocks 50 and 60, respectively. In this specification, ground contact ends E1 and E2 are defined as both axial ends of the region (ground contact surface) that comes into contact with a flat road surface when an unused pneumatic tire 1 is mounted on a standard rim and filled with air to achieve the standard internal pressure, and a specified load is applied. In the case of passenger car tires, the specified load is a load equivalent to 88% of the standard load.

Here, "regular rim" refers to a rim that is determined by the tire standard, and is "standard rim" for JATMA, and "Measuring Rim" for TRA and ETRTO. "Regular internal pressure" refers to "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 internal pressure is usually 180 kPa for passenger tires, but 220 kPa for tires that are labeled "Extra Load" or "Reinforced." "Regular load" refers to "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.

The pneumatic tire 1 comprises a carcass 15, belts 16, 17, and a cap ply 18. The carcass 15 is a cord layer covered with rubber, and serves as the skeleton of the tire that can withstand loads, impacts, air pressure, etc. The carcass 15 is, for example, composed of two carcass plies, and has a radial structure in which the carcass cords are arranged in a direction perpendicular to the tire circumferential direction. In addition, an inner liner 19, which is a rubber layer for maintaining air pressure, is provided on the inside of the carcass 15.

The belts 16, 17 are reinforcing bands disposed between the rubber constituting the tread 10 and the carcass 15, and tighten the carcass 15 to increase the rigidity of the pneumatic tire 1. The belts 16, 17 are formed, for example, by wrapping a metal cord with rubber. The belts 16, 17 are formed by wrapping a cord around the tire circumferential direction so as to tighten the carcass 15, and it is preferable that the belt cords are arranged in a direction inclined with respect to the tire circumferential direction. The angle of the belt cord with respect to the tire circumferential direction is, for example, 22° or more and 26° or less.

The cap ply 18 is a member that reinforces the belts, and is arranged to cover the entire two belts 16, 17. The cap ply 18 is formed, for example, by covering organic fiber cords such as polyamide fiber with rubber. As will be described in detail later, the first belt 16, the second belt 17, and the cap ply 18 are arranged in order from the radial inside of the tire, with the end of belt 16 located axially outward of the end of belt 17. In addition, the end of the cap ply 18 is located axially outward of the end of belt 17.

Since the pneumatic tire 1 is used as a tire with a specified mounting direction on the vehicle, it is preferable that the tire has a marking to indicate the mounting direction on the vehicle. The marking to indicate the mounting direction may be a letter, symbol, illustration, etc. indicating the inside or outside of the vehicle, and the configuration is not particularly limited. Generally, a symbol called a serial number is provided on the side of the pneumatic tire 1, but a serial number may also be used as a marking to indicate the mounting direction.

The serial number includes information such as a size code, time of manufacture (year and week of manufacture), and place of manufacture (manufacturing factory code). The mounting direction of the pneumatic tire 1 on the vehicle may be specified by providing a serial number only on the side (sidewall 11) of the pneumatic tire 1 facing the outside of the vehicle, or by providing different serial numbers on the side facing the outside and the side facing the inside of the vehicle. A specific example is providing a manufacturing factory code and a size code on both sides of the pneumatic tire 1, and providing the year and week of manufacture only on the side facing the outside of the vehicle.

The tread pattern of the pneumatic tire 1 will be explained in detail below with reference to Figure 2.

Figure 2 is a plan view of the pneumatic tire 1, showing an enlarged portion of the tread 10. The tread 10 has a main groove 20 formed on the equator CL, and has a tread pattern that is asymmetrical with respect to the equator CL. In the following, the region on the ground edge E1 side of the equator CL is referred to as the first region, and the region on the ground edge E2 side of the equator CL is referred to as the second region. When the tire is mounted on a vehicle so that the first region is located on the outer side of the vehicle and the second region is located on the inner side of the vehicle, the tread pattern of the pneumatic tire 1 effectively reduces noise generated by the tire and improves wear resistance while ensuring good steering stability.

In the first region of the tread 10, a first main groove 20, a first mediate block 30, a second main groove 21, and a first shoulder block 50 are formed in order from the equator CL side. The main groove 21 is formed parallel to the main groove 20 and separates the mediate block 30 and the shoulder block 50. In the second region of the tread 10, a first main groove 20, a second mediate block 40, a third main groove 22, and a second shoulder block 60 are formed in order from the equator CL side. The main groove 22 is formed parallel to the main groove 20 and separates the mediate block 40 and the shoulder block 60. The two mediate blocks 30, 40 are also separated by the main groove 20.

The main grooves 20, 21, and 22 extend straight in the tire circumferential direction, and are each formed with a constant width over their entire length. The main grooves 20, 21, and 22 may have the same width, but in this embodiment, the width of the main groove 20 is the largest. The main grooves 21 and 22 are formed with substantially the same width. In this case, good drainage is ensured in the center region of the tread 10. Also, well-balanced drainage is ensured throughout the tread 10, resulting in good wet performance.

In this specification, the groove width means the groove width along the profile surface α of the tread 10 (see FIG. 5 described later), in other words, the groove width at the opening of the groove. Also, a sipe means a narrow groove with a groove width of 1.0 mm or less. The profile surface α is a surface along the surface of the tread 10. The contact width of the pneumatic tire 1 (the length along the tire axial direction between the contact ends E1, E2) is not particularly limited, but is, for example, 110 mm to 120 mm, or 113 mm to 117 mm.

An example of the width of the main groove 20 is 8.5 mm to 9.1 mm, and an example of the width of the main grooves 21, 22 is 7.1 mm to 7.7 mm. The width of the main groove 20 is, for example, 1.1 to 1.3 times the width of the main grooves 21, 22. The walls of each main groove are inclined so that the groove volume gradually decreases toward the groove bottom. The walls of the main groove form the side walls of the blocks, so in other words, the side walls of the blocks are inclined so that the block width increases the further away from the ground contact surface.

The main grooves 20, 21, and 22 may have different depths, but in this embodiment, they are formed to substantially the same depth. In this specification, the depth of the main groove means the length from the profile surface α to the bottom of the deepest part of the groove. The depth of each main groove is, for example, 5.7 mm or more and 6.3 mm or less. Generally, at least one of the three main grooves is provided with a wear indicator (not shown).

The mediate blocks 30, 40 are rib-shaped blocks extending in the tire circumferential direction and are formed at equidistant positions from the equator CL. The mediate block 30 has a secondary groove 31 extending in the tire circumferential direction, a first sipe 32, and a second sipe 33. On the other hand, the mediate block 40 does not have a groove along the tire circumferential direction like the secondary groove 31, but has a slit 41 that is a groove wider than the sipes 32, 33. As will be described in detail later, the configuration of the mediate blocks 30, 40, and in particular the sipe shape of the mediate block 30 located on the outer side of the vehicle, greatly affect the steering stability, wear resistance, and noise performance of the tire.

The mediate block 30 has a slope 34 formed on the edge of the main groove 20 along the tire circumferential direction. The slope 34 is inclined at a predetermined angle from the ground contact surface of the mediate block 30, and is formed so as to chamfer the corners of the block. The inclination angle of the slope 34 is, for example, 30° to 60° with respect to the profile surface α. The slope 34 distributes the ground contact pressure of the mediate block 30 and improves driving stability. The depth of the slope 34 is, for example, 8% to 27% of the depth of the main groove 20. The slope 34 is formed with a constant depth and width along the tire circumferential direction.

The widths of the mediate blocks 30, 40 may be different from each other, but in this embodiment, they are substantially the same. The ratio of the width of the ground contact surface of each block is, for example, 0.95 to 1.05. The width of the ground contact surface of the mediate blocks 30, 40 is, for example, 15% to 20% of the ground contact width of the tread 10, and as an example, 17.7 mm to 18.7 mm. In this case, it is easy to achieve good braking performance, driving stability, etc. Note that the mediate blocks 30, 40 do not have grooves or sipes that cross the blocks.

The secondary groove 31 of the mediate block 30 is formed shallower than the main grooves 20, 21 along the tire circumferential direction. The first sipe 32 extends between the main groove 20 and the secondary groove 31 in a direction intersecting the tire circumferential direction and the axial direction, opens into the main groove 20, and does not open into the secondary groove 31. The second sipe 33 extends between the secondary groove 31 and the main groove 21 in a direction intersecting the tire circumferential direction and the axial direction, and does not open into at least the main groove 21. The sipes 32, 33 are gently curved so as to be convex in the same direction in the tire circumferential direction.

As will be described in more detail later, portions of the sipes 32, 33 overlap in the axial direction of the tire, and the pairs of axially overlapping sipes are spaced apart in the circumferential direction of the tire with no other sipes between them. In other words, the multiple sipes 32 are lined up in the circumferential direction of the tire without any other grooves or sipes between them. Similarly, the multiple sipes 33 are lined up in the circumferential direction of the tire without any other grooves or sipes between them.

The mediate block 40 has multiple slits 41 that extend from the main groove 22 and terminate within the block. The slits 41 are short grooves that open into the main groove 22, but do not open into the main groove 20. No grooves or sipes other than the slits 41 are formed in the mediate block 40. The multiple slits 41 are lined up in the circumferential direction of the tire without any other grooves or sipes in between. The slits 41 are formed, for example, at substantially the same intervals as the sipes 32 of the mediate block 30, and in the same number as the sipes 32. The slits 41 may be formed at a variable pitch that slightly changes the intervals in units of a predetermined number in the circumferential direction of the tire.

The slit 41 is greatly narrowed in a predetermined length range from the tip. The width of the slit 41 is, for example, 3.7 mm or more and 4.7 mm or less in other parts except the narrowed tip. The depth of the slit 41 at its deepest part is preferably 57% or more and 85% or less of the depth of the main groove 22, more preferably 60% or more and 80% or less. The slit 41 is formed to a constant depth in other parts except the narrowed tip, and the tip may be formed shallower than other parts.

The slit 41 extends from the main groove 22 in a direction intersecting the tire circumferential direction and the axial direction, and is formed with a length that does not reach the center of the width direction of the mediate block 40. The inclination angle of the slit 41 with respect to the tire axial direction may be substantially the same as the inclination angle of the sipes 32, 33, and the extension direction of the slit 41 and the extension direction of the sipes 32, 33 may be parallel to each other. The slit 41 is formed at a position overlapping with the sipe 32 in the tire axial direction. A range of 10% to 50% of the length of the slit 41 along the tire circumferential direction from the tip of the slit 41 may overlap with the sipe 32 in the tire axial direction.

The shoulder block 50 has lateral grooves 51 and shoulder sipes 52 (hereinafter simply referred to as "sipes 52") formed alternately in the tire circumferential direction. Similarly, the shoulder block 60 has lateral grooves 61 and shoulder sipes 62 (hereinafter simply referred to as "sipes 62") formed alternately in the tire circumferential direction. In a plan view of the tread 10, the lateral grooves 51 and sipes 52 are gently curved to be convex on one side in the tire circumferential direction, and the lateral grooves 61 and sipes 62 are gently curved to be convex on the other side in the tire circumferential direction, i.e., in the direction opposite to the direction in which the lateral grooves 51 and sipes 52 are convex.

The lateral grooves 51 of the shoulder block 50 are not connected to the main groove 21, but are separated from the main groove 21. In this case, the block rigidity can be increased and the cornering power characteristics (hereinafter referred to as "CP characteristics") are improved compared to when the lateral grooves 51 are connected to the main groove 21. The lateral grooves 51 are formed from a position between the main groove 21 and the ground contact edge E1 to the side rib 2. The width of the lateral grooves 51 is, for example, 3.7 mm or more and 4.7 mm or less, and is constant over the entire length. The width of the lateral grooves 51 may be substantially the same as the width of the slits 41. The depth of the lateral grooves 51 is, for example, 60% to 80% of the depth of the main groove 21 at the deepest part.

The lateral grooves 61 of the shoulder blocks 60 are connected to the main grooves 22 via sipes 63. In this case, drainage is improved in the second region R2 of the tread 10 located on the vehicle inner side, and good wet braking performance is obtained. The lateral grooves 61 are formed from a position between the main grooves 22 and the ground contact edge E2 to the side rib 2. The width and depth of the lateral grooves 61 are, for example, substantially the same as the width and depth of the lateral grooves 51. The sipes 63 extend parallel to the sipes 62, and connect the main grooves 22 and the lateral grooves 61. The sipes 63 are formed deeper than the sipes 62.

The multiple lateral grooves 51 are arranged at a predetermined interval in the tire circumferential direction with one sipe 52 between each of them. The lateral grooves 51 and sipes 52 may be arranged parallel to each other and formed at a variable pitch in which the intervals vary slightly in units of a predetermined number in the tire circumferential direction, or may be formed at the same interval. Similarly, the lateral grooves 61 and sipes 62 may be formed at a variable pitch in which the intervals vary slightly in units of a predetermined number in the tire circumferential direction.

The sipes 52 of the shoulder blocks 50 are formed from the main groove 21 to a position beyond the ground contact end E1. That is, the sipes 52 open into the main groove 21. The depth of the sipes 52 is, for example, shallower than the lateral grooves 51, and is 20% to 50% of the depth of the main groove 21 at its deepest point. Similarly, the sipes 62 of the shoulder blocks 60 are formed from the main groove 22 to a position beyond the ground contact end E2, and open into the main groove 22. The depth of the sipes 62 is, for example, substantially the same as the depth of the sipes 52.

The groove area ratio in the ground contact range of the tread 10 (range from ground contact end E1 to ground contact end E2) is preferably 25% to 30%, more preferably 26% to 28%. In this case, good drainage and driving stability can be achieved at the same time. Here, a void means a recess that does not contact the road surface, and the recesses counted in the groove area ratio are the main grooves 20, 21, 22, the lateral grooves 51, 61 of the shoulder blocks 50, 60, the sipes of each block, and the slopes 34, 35 of the mediate block 30. The groove area ratio is calculated by dividing the opening area of the recess in the ground contact range by the area of the profile surface α.

The mediate blocks 40 and shoulder blocks 50 formed in the first region of the tread 10 improve the driving stability such as CP characteristics by their interaction. The mediate blocks 40 have sipes 32, 33 formed therein, and the shoulder blocks 50 have sipes 52 formed therein. The pairs of one sipe 32 and one sipe 33 aligned in the tire axial direction are formed at a ratio of one pair for every two sipes 52. In other words, the number of pairs of sipes 32, 33 is half the number of sipes 52 (lateral grooves 51). In this case, the order of the pattern noise (the matching period during tire rotation) can be dispersed, improving noise performance.

Sipe 32 is formed so as to overlap two sipes 52 in the tire axial direction. Sipe 33 is shorter than sipe 32 and is formed so as to overlap one sipe 52 in the tire axial direction. Sipe 52 is gently curved so as to be convex on one side in the tire circumferential direction, and sipes 32 and 33 are gently curved so as to be convex on the other side in the tire circumferential direction, i.e., in the direction opposite to the direction in which sipe 52 is convex. In addition, the extension direction of sipes 32 and 33 and the extension direction of sipe 52 form an angle close to perpendicular.

The angle between the virtual line X along the direction in which the sipe 32 extends and the virtual line Y along the direction in which the sipe 52 extends is, for example, 90°±10° or 90°±5°, and may be 90° (the virtual lines X and Y are perpendicular). In this case, the effect of improving the steering stability is further improved. The virtual lines X and Y are straight lines connecting both ends of the length of the sipe. The angle between the virtual line Z (a straight line connecting both ends of the length of the slit 41) along the direction in which the slit 41 of the mediate block 40 extends and the virtual line X is, for example, 20° or less or 15° or less, and may be 0° (the virtual lines X and Z are parallel). The angle between the virtual line (not shown) along the direction in which the sipe 33 extends and the virtual line X is, for example, 15° or less or 10° or less, and may be 0°.

The ratio of the width of the ground contact surface of the mediate block 30 to the width of the ground contact surface of the shoulder block 50 is preferably 41:59 to 49:51, and more preferably 43:57 to 47:53. In this case, the effect of improving steering stability is further enhanced. One suitable example of the width of the ground contact surface of each block is the width of the ground contact surface of the mediate block 30: the width of the ground contact surface of the shoulder block 50 = 45:55.

The groove area ratio in the mediate block 30 and the shoulder block 50 is preferably 37:63 to 47:53, and more preferably 40:60 to 44:56. In this case, the effect of improving steering stability is further enhanced. One suitable example of the groove area ratio of each block is void area of the mediate block 30: void area of the shoulder block 50 = 42:58.

The mediate blocks 30 that make up the tread pattern will be described in more detail below with reference to Figures 3 and 4.

Figure 3 is a plan view of the mediate block 30 and its vicinity, and Figure 4 is a perspective view of the mediate block 30 and its vicinity. As described above, the mediate block 30 is a rib-shaped block partitioned by the main grooves 20, 21, and has a secondary groove 31, a first sipe 32, and a second sipe 33. The mediate block 30 also has a slope 34 formed on the edge of the main groove 20 along the tire circumferential direction. The width of the ground contact surface of the mediate block 30 is smaller than the width of the ground contact surface of the mediate block 40, for example, by the width of the slope 34.

The mediate block 30 further has a slope 35 formed on part of the edge of the sipe 32 and a slope 36 formed on part of the edge of the sipe 33. The slope 35 gradually becomes deeper toward the sipe 32, and is formed as if a part of the block was cut out at the edge of the sipe 32. Similarly, the slope 36 gradually becomes deeper toward the sipe 33, and is formed as if a part of the block was cut out at the edge of the sipe 33. By forming the slopes 35 and 36, the ground pressure that tends to concentrate on the edges of the sipes 32 and 33 can be dispersed, improving the effect of improving steering stability. Furthermore, the uniformity of the ground pressure of the block also improves wear resistance and noise performance.

The secondary groove 31 extends parallel to the main grooves 20, 21 and is formed in a ring shape along the tire circumferential direction. The ground contact surface of the mediate block 30 is divided into two regions by the secondary groove 31. The secondary groove 31 is formed closer to the main groove 21 side than the widthwise center of the mediate block 30. Therefore, the region A1 sandwiched between the main groove 20 and the secondary groove 31 is larger than the region A2 sandwiched between the main groove 21 and the secondary groove 31. The width of the ground contact surface of the region A1 is, for example, 1.1 to 1.3 times the width of the ground contact surface of the region A2. The sipes 32, 33 are arranged so that at least a portion of them face each other in the tire axial direction, sandwiching the secondary groove 31 between them.

The width of the sub-groove 31 is greater than the width of the sipes 32, 33, and is preferably 1.1 to 2.5 times the width of the sipes 32, 33. A suitable example of the width of the sub-groove 31 is 0.5 mm to 1.5 mm, and more preferably 0.9 mm to 1.1 mm. The depth of the sub-groove 31 is shallower than the sipes 32, 33, and is preferably 5% to 30% of the depth of the main groove 21, and more preferably 8% to 27%. In this case, the effect of improving the steering stability is further improved. The sub-groove 31 is formed, for example, with a constant width and depth over the entire length. The sub-groove 31 may also be formed with substantially the same depth as the slope 34 formed along the main groove 20.

The sipe 32 is formed in the region A1 between the main groove 20 and the sub groove 31, and is connected to the main groove 20 but not to the sub groove 31. The depth of the sipe 32 is deeper than the sub groove 31 and shallower than the main grooves 20 and 21. The depth of the sipe 32 is preferably 130% to 160% of the depth of the sub groove 31, and more preferably 136% to 148%. The depth of the sipe 32 at the deepest part is preferably 57% to 85% of the depth of the main groove 22, and more preferably 60% to 80%. A suitable example of the width of the sipe 32 is 0.3 mm to 1.0 mm, and more preferably 0.5 mm to 0.8 mm. The sipe 32 is formed, for example, with a constant width and depth over the entire length.

The sipes 32 may be curved over their entire length, but in this embodiment, the portion of the sipes 32 located in the widthwise center of the region A1 is curved, and the portions from the curved portion to both ends in the lengthwise direction are each formed straight. The sipes 32 include a curved portion 32a, a first straight portion 32b formed straight from the main groove 20 to the curved portion 32a, and a second straight portion 32c formed straight from the curved portion 32a to near the secondary groove 31.

The first straight portion 32b of the sipe 32 is longer than the second straight portion 32c and has a larger inclination angle with respect to the tire axial direction. The inclination angle of the first straight portion 32b with respect to the tire axial direction is, for example, 60° to 80°, or 65° to 75°. The inclination angle of the second straight portion 32c with respect to the tire axial direction is, for example, 40° to 60°, or 45° to 55°. In this case, the water removal effect of the sipe 32 is improved, making it easier to achieve both good drainage and steering stability.

The slope 35 is an edge on the side where the sipe 32 is convex, and is formed on the edge of the first straight portion 32b. The slope 35 is also formed on a part of the edge of the curved portion 32a, but is not formed on the edge of the second straight portion 32c. In addition, no slope is formed on the edge opposite to the side where the sipe 32 is convex (the side where the sipe 32 is concave). The slope 35 is formed between the curved portion 32a and the slope 34 on the edge of the main groove 20, and at the intersection with the main groove 20 of the first straight portion 32b and in the vicinity thereof, it crosses the slope 34 and connects to the main groove 20. In addition, the slope 35 gradually becomes deeper from the curved portion 32a side toward the intersection with the main groove 20 of the first straight portion 32b. By forming such a slope 35, the volume of the recess that can take in water from the road surface increases, and good drainage is obtained.

The sipes 33 are formed in the region A2 between the main groove 21 and the sub groove 31, and are not connected to at least the main groove 21. The sipes 33 may open into the sub groove 31, but in this embodiment, they are not connected to the sub groove 31. The shortest distance between the sub groove 31 and the sipes 33 is shorter than the shortest distance between the main groove 21 and the sipes 33. Note that some of the multiple sipes 33 may be connected to the sub groove 31, and other parts may not be connected to the sub groove 31. The depth of the sipes 33 is deeper than the sub groove 31 and shallower than the main grooves 20 and 21. The sipes 33 have, for example, substantially the same depth and width as the sipes 32, and are formed with a constant width and depth over the entire length.

The sipes 33 may be curved over their entire length, but in this embodiment, the portion of the sipes 33 located in the widthwise center of the region A1 is curved, and the portions from the curved portion to both ends in the lengthwise direction are each formed straight. The sipes 33 include a curved portion 33a, a first straight portion 33b formed straight from near the secondary groove 31 to the curved portion 33a, and a second straight portion 33c formed straight from the curved portion 33a to near the primary groove 21.

The first straight portion 33b of the sipe 33 may be longer or shorter than the second straight portion 33c, but in this embodiment, it has substantially the same length as the second straight portion 33c and has a larger inclination angle with respect to the tire axial direction. The inclination angle of the first straight portion 33b with respect to the tire axial direction may be substantially the same as the inclination angle of the first straight portion 32b of the sipe 32 with respect to the tire axial direction. In addition, the inclination angle of the second straight portion 33c with respect to the tire axial direction may be substantially the same as the inclination angle of the second straight portion 32c of the sipe 32 with respect to the tire axial direction, and the second straight portion 33c may be arranged on the same straight line as the second straight portion 32c.

The slope 36 is the edge of the side where the sipe 33 is convex, and is formed on the edges of the curved portion 33a and the first straight portion 33b. On the other hand, no slope is formed on the edge of the second straight portion 33c or on the edge opposite the side where the sipe 33 is convex (the side where the sipe 33 is concave). The slope 36 is formed in the range between the curved portion 33a, the first straight portion 33b, and the secondary groove 31, and gradually deepens from the curved portion 33a side toward one end of the first straight portion 33b on the secondary groove 31 side in the longitudinal direction, and connects to the secondary groove 31. Like the slope 35, such a slope 36 increases the volume of the recess that can take in water from the road surface, improving drainage.

By not connecting the secondary grooves 31 and sipes 32, and the primary grooves 21 and sipes 33, it is possible to, for example, prevent air vibrations traveling through a circumferentially extending groove from being transmitted to adjacent circumferential grooves, thereby reducing noise. In addition, the mediate blocks 30 are circumferentially continuous rib-like blocks, which increases rigidity, so that excessive collapse of the blocks and lifting due to block deformation are suppressed even when cornering, resulting in good CP characteristics (driving stability). Furthermore, the contact area of the mediate blocks 30 is increased, reducing ground pressure, thereby suppressing block wear.

The shortest distance between the secondary groove 31 and the sipe 32, and the shortest distance between the main groove 21 and the sipe 33 are preferably 0.3 mm or more and 2.0 mm or less, and more preferably 0.7 mm or more and 1.5 mm or less. The shortest distances may be different from each other or may be substantially the same. By ensuring that the distance between the secondary groove 31 and the sipe 32 and the distance between the main groove 21 and the sipe 33 is 0.3 mm or more, the rigidity of the block can be ensured and good CP characteristics can be obtained. From the viewpoint of ensuring the length of the sipes 32 and 33, the distance is preferably 2.0 mm or less. If the distance is less than 0.3 mm, there is a concern that the connection part will be cut during driving and the handling stability will decrease. In addition, if the distance exceeds 2.0 mm, there is a concern that noise will increase due to increased input from the road surface and fuel efficiency will deteriorate due to increased weight.

The total length of the sipes 32, 33 along the tire axial direction is preferably 70% to 90% of the width of the mediate block 30 (length along the tire axial direction), and more preferably 76% to 86%. In this case, it becomes easier to achieve both good drainage and steering stability. The ratio of the lengths of the sipes 32, 33 along the tire axial direction is, for example, 40:60 to 45:55.

The profile shape of the tread 10 and the internal structure of the pneumatic tire 1 will be explained in more detail below with reference to Figures 5 and 6.

Figure 5 is a diagram showing the shape of the profile surface α along the surface of the tread 10. When the pneumatic tire 1 is mounted on a standard rim and filled with air to the standard internal pressure, the height difference Hp between the equator position of the profile surface α and position P1 corresponding to the axially outer end of the sipe 52 of the shoulder block 50 is 11.5 mm or more and 14.5 mm or less. The length along the tire axial direction from the equator CL to position P2 corresponding to the axially outer end of the sipe 62 of the shoulder block 60 is equal to the length along the tire axial direction from the equator CL to position P1, and the height difference between the equator position and position P2 is equal to Hp.

In this specification, the height difference Hp means the length along the tire radial direction from the position of the equator CL on the profile surface α to P1. The height difference Hp is more preferably 12.0 mm or more and 14.0 mm or less, and particularly preferably 12.0 mm or more and 13.0 mm or less. The length TW along the tire axial direction between positions P1 and P2 is, for example, 130 mm or more and 136 mm or less. One suitable example of the length TW is 133 mm.

The profile surface α includes, from position P1 toward the equator position, a first region having a first radius of curvature R1, a second region having a second radius of curvature R2, and a third region having a third radius of curvature R3. The magnitudes of the radii of curvature are R1<R2<R3, and the degree of curvature of the profile surface α becomes gentler in stages from position P1 toward the equator position. In the range from position P1 to the equator position, the profile surface α may include a fourth region having a fourth radius of curvature, but it is preferable that the change in the radius of curvature is in three stages, and the profile surface α includes only the first to third regions. Note that the profile surface α includes the first to third regions from position P2 toward the equator position.

The first to third radii of curvature each have a suitable range. The first radius of curvature R1 is preferably 100 mm or more and less than 120 mm, and more preferably 105 mm or more and 115 mm or less. The second radius of curvature R2 is preferably 120 mm or more and 180 mm or less, and more preferably 150 mm or more and 170 mm or less. The third radius of curvature R3 is preferably 450 mm or more and 750 mm or less, and more preferably 480 mm or more and 550 mm or less.

If the height difference Hp is 11.5 mm or more and 14.5 mm or less, and the profile surface α includes the first to third regions and has a radius of curvature within the above range, the profile surface α can be appropriately rounded, improving noise performance. When the profile surface α is rounded, the area in contact with the road surface decreases and the input from the road surface decreases, which is thought to effectively reduce noise.

On the other hand, if the profile surface α is rounded, the center region of the tread becomes more susceptible to wear, and a decrease in the contact area of the shoulder blocks can lead to problems with reduced steering stability. For this reason, in the pneumatic tire 1, the contact width of each block, groove area ratio, sipe shape, and main groove depth are adjusted to appropriate conditions and ranges, as described above, to ensure good wear resistance and steering stability. In other words, the pneumatic tire 1 has an excellent balance of steering stability, noise performance, and wear resistance.

In this embodiment, shoulder blocks 50, 60 are arranged in the first region of profile surface α. Mediate blocks 30, 40 are arranged in the second and third regions of profile surface α. That is, the contact surface of mediate block 30 that contacts the road surface includes two curved surfaces with different radii of curvature (the same applies to mediate block 40). Mediate block 30 may have different radii of curvature in regions A1, A2 separated by secondary groove 31, for example, with the radius of curvature of the contact surface in region A1 being R3 and the radius of curvature of the contact surface in region A2 being R2.

Figure 6 is a diagram showing a portion of the axial cross section of the pneumatic tire 1. β in Figure 6 is a virtual line indicating the equator position, which extends in the tire radial direction and is perpendicular to the equator CL. As described above, the pneumatic tire 1 includes the first belt 16, the second belt 17 arranged on the tire radial outside of the belt 16, and the cap ply 18 covering the belts 16, 17 and arranged on the tire radial outside of the belt 17. The belt 16 is formed wider than the belt 17, and the cap ply 18 is further formed wider than the belt 16. The cap ply 18, together with the carcass 15, sandwiches the two belts and covers the entire two belts.

When the TW of the tread 10 is 130 mm or more and 136 mm or less, the belt end 16E of the belt 16 is preferably located in a range in which the length _W16 from the equator position (virtual line β) along the tire axial direction is 62 mm or more and 66 mm or less. The left and right belt ends 16E are equidistant from the equator position. Therefore, the suitable width of the belt 16 is 124 mm or more and 132 mm or less ( _W16 x 2). In addition, the belt end 17E of the belt 17 is preferably located in a range in which the length from the equator position along the tire axial direction is 56 mm or more and 60 mm or less. Similarly, the left and right belt ends 17E of the belt 17 are equidistant from the equator position. The suitable width of the belt 17 is 112 mm or more and 120 mm or less ( _W17 x 2).

The ply end 18E of the cap ply 18 is preferably located within a range of 65 mm to 69 mm in length from the equator along the tire axial direction. The left and right ply ends 18E are equidistant from the equator, and the preferred width of the cap ply 18 is 130 mm to 138 mm ( _W18 x 2). When the positional relationship between the belt end 16E, the belt end 17E, and the ply end 18E satisfies the above conditions, it becomes easy to appropriately round the profile surface α. The pneumatic tire 1 may have an additional reinforcing member covering the cap ply 18 as long as it does not impair the object of the present invention.

In this embodiment, the ply end 18E is located closer to the equator CL than the positions P1 and P2. The belt end 17E overlaps with the ground contact ends E1 and E2 in the tire radial direction, or is located closer to the equator CL than the ground contact ends E1 and E2. In this case, it becomes easier to appropriately round the profile surface α.

As described above, the belt cords constituting the belts 16 and 17 are preferably arranged in a direction inclined with respect to the tire circumferential direction. A suitable example of the inclination angle of the belt cord with respect to the tire circumferential direction is 23° or more and 25° or less from the viewpoint of rounding the profile surface α. In this case, an appropriate binding force by the belts 16 and 17 is obtained. In addition, the height H ₁₄ of the bead filler 14 is preferably 26 mm or more and 34 mm or less. In this case, the rigidity of the tire is improved, and the driving stability and the damping property against the input from the road surface are improved. The height H ₁₄ is the length along the tire radial direction from the inner end to the outer end of the bead filler 14 in the tire radial direction.

The contact surface of the tread 10 has a rectangular ratio (L2/L1) of 0.74 to 0.85, more preferably 0.80 to 0.83, which is the ratio of the contact length (L2) near the contact end to the contact length (L1) which is the length along the tire circumferential direction on the equator CL. Here, the contact length (L1) is the length along the tire circumferential direction on the equator CL of the contact surface when an unused pneumatic tire is mounted on a standard rim, filled with air to a specified internal pressure, and a load equivalent to 70.4% of the standard load is applied. The contact length (L2) is the length along the tire circumferential direction of the contact surface at a position 10 mm axially inward from both axial ends of the contact surface determined under the above measurement conditions.

The specified internal pressure under the above measurement conditions is 200 kPa when the aspect ratio of the tire is 60% or more, and 220 kPa when the aspect ratio is less than 60%. In addition, for tires described as Extra Load, the specified internal pressure under the above measurement conditions is 240 kPa when the aspect ratio is 60% or more, and 260 kPa when the aspect ratio is less than 60%.

For a pneumatic tire having the tread pattern of the above embodiment (see Figures 1 to 4), the radii of curvature of the first to third regions of the profile surface α and the height difference Hp were changed as shown in Table 1, and the CP characteristics and noise performance were evaluated. The rectangular ratio of each tire was also calculated. Note that all of the tires in the examples and comparative examples have a TW of 133 mm, a tread contact width of 115 mm, and an internal structure as shown in Figure 6.

The evaluation method for CP characteristics and noise performance is as follows:

[Cornering power (CP) evaluation]
A drum tester with a diameter of 2500 mm was used to measure the cornering force generated in each of the 175/65R18 82H tires of the examples and comparative examples by applying a load of 240 kPa internal pressure and 70% of the maximum load of the load index, and a cornering power evaluation test was performed by determining the cornering power at a slip angle of 1 degree. The result of Example 1 was set to 100 and the evaluation was performed using an index.

[Noise performance evaluation]
The tires of each Example and Comparative Example were mounted on a test vehicle, and the vehicle was driven at 80 km/h on a flat, dry asphalt road surface, and the noise level was evaluated sensorily. In Table 1, ◯ means that the noise was small, and × means that the noise was larger than that of ◯.

Tires with a CP value of 100 or more shown in Table 1 can be said to have good steering stability. That is, all of the tires in the examples can achieve good steering stability. For the tires in Comparative Examples 1 and 2, the CP characteristics are good, but the noise generated by the tires is greater than that of the tires in Examples 1 to 6. In contrast, the tires in Examples 1 to 6 achieve both good steering stability and noise performance.

As described above, the pneumatic tire 1 having the above configuration can reduce noise generated by the tire and improve wear resistance while ensuring good steering stability. The pneumatic tire 1 has a good balance of steering stability, noise performance, and wear resistance, and is suitable as a high-performance summer tire that requires high driving performance.

The above embodiment may be modified as appropriate without impairing the object of the present invention. For example, the above embodiment illustrates the first mediate block 30 that is disposed on the outer side of the vehicle and has the secondary groove 31 and sipes 32, 33 formed therein, but the first mediate block may be a block that does not have at least one of these. In addition, the internal structure of the tire is not limited to the structure illustrated in FIG. 6.

1 Pneumatic tire, 10 Tread, 11 Sidewall, 12 Bead, 13 Bead core, 14 Bead filler, 15 Carcass, 16, 17 Belt, 16E, 17E Belt end, 18 Cap ply, 18E Ply end, 19 Inner liner, 20, 21, 22 Main groove, 30, 40 Mediate block, 31 Secondary groove, 32, 33, 52, 62, 63 Sipes, 32a, 33a Curved portion, 32b, 33b First straight portion, 32c, 33c Second straight portion, 34, 35, 36 Slope, 41 Slit, 50, 60 Shoulder block, 51, 61 Lateral groove, CL Equator, E1, E2 Ground contact edge

Claims (8)

A pneumatic tire having a tread,
The tread is
A main groove extending in a tire circumferential direction;
A block defined by the main groove;
having
The blocks include shoulder blocks having shoulder sipes formed therein,
When the tire is mounted on a standard rim and filled with air to the standard internal pressure,
A difference in height between an equator position of a profile surface along the surface of the tread and a position corresponding to an axially outer end of the shoulder sipe is 11.5 mm or more and 14.5 mm or less,
The profile surface includes, from a ground contact end position toward the equator position, a first region having a first radius of curvature, a second region having a second radius of curvature, and a third region having a third radius of curvature. The pneumatic tire according to claim 1, wherein the first radius of curvature is 100 mm or more and less than 120 mm, the second radius of curvature is 120 mm or more and 180 mm or less, and the third radius of curvature is 450 mm or more and 750 mm or less. a carcass; a first belt disposed on the outer side of the carcass in the tire radial direction; a second belt disposed on the outer side of the first belt in the tire radial direction; and a cap ply covering the first and second belts and disposed on the outer side of the second belt in the tire radial direction,
an end of the first belt is located within a range of a length from the equator position along the tire axial direction of 62 mm to 66 mm,
an end of the second belt is located within a range of 56 mm or more and 60 mm or less in length along the tire axial direction from the equator position,
The pneumatic tire according to claim 1 , wherein the end of the cap ply is located within a range of a length from the equator position along the tire axial direction that is 65 mm or more and 69 mm or less. The pneumatic tire according to claim 3, wherein the angle of the cords constituting the first and second belts with respect to the tire circumferential direction is 22° or more and 26° or less. The blocks include a mediate block and a shoulder block.
2. The pneumatic tire according to claim 1, wherein a ratio of a width of the ground contact surface of the mediate block to a width of the ground contact surface of the shoulder block is 43:57 to 47:53. A groove area ratio in the ground contact area of the tread is 26% or more and 28% or less,
6. The pneumatic tire according to claim 5, wherein a groove area ratio of the mediate block to the shoulder block is 40:60 to 44:56. It also has a bead filler.
The pneumatic tire according to claim 1 , wherein the height of the bead filler is equal to or greater than 26 mm and equal to or less than 34 mm. 2. The pneumatic tire according to claim 1, wherein a rectangular ratio of the contact surface of the tread is 0.80 to 0.83.

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