tire

Abstract

To provide a tire that maintains rolling resistance and wear resistance while improving wet performance and heat dissipation from the early to late stages of wear. [Solution] The tire comprises a tread having a tread surface. The tread has a plurality of circumferential grooves. The plurality of circumferential grooves divide the tread into a plurality of land sections and each has a pair of circumferential main grooves and at least one circumferential narrow groove. The circumferential narrow groove has a narrow section and a wide section. The groove width of the narrow section is such that the side wall of the narrow section contacts the road surface when the tire is in contact with it. At least one land section adjacent to the circumferential narrow groove has a plurality of pinholes. The depth of the pinholes is shallower than the depth of the circumferential main grooves. The pinholes are tapered toward the inside in the radial direction of the tire. The relationship between the width L1 of the land section having pinholes and the distance L2 from the circumferential narrow groove to the pinholes satisfies Equation 1. 0.3 ≤ L2 / L1 ≤ 0.7 (Equation 1)

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] Patent Document 1 discloses a tire including a tread having circumferential grooves provided with widened portions on the inner side in the tire radial direction. In the early wear stage of the tire disclosed in Patent Document 1, when the tire comes into contact with the road surface, adjacent land portions support each other through the circumferential grooves, thereby improving the tread rigidity and enhancing the rolling resistance performance and wear resistance performance. Further, in the late wear stage of the tire disclosed in Patent Document 1, the decrease in groove volume is suppressed by the expansion of the groove width of the circumferential grooves, and the wet performance is maintained.

[0003] When the tread surface of the tire in contact with the road surface becomes wide, the tread is likely to generate heat due to friction with the road surface. The heat generation of the tread causes a decrease in the rolling resistance performance and durability. To suppress the heat generation of the tread, it is known to provide pinholes in the tread to improve the heat dissipation property of the tread.

[0004] Patent Document 2 discloses a tire including a tread having a recessed longitudinal groove, a recessed transverse groove, sipes extending between the recessed longitudinal grooves, sipes extending between the recessed transverse grooves, and a sipes intersection groove where the sipes extending between the recessed longitudinal grooves and the sipes extending between the recessed transverse grooves intersect. That is, in the tire disclosed in Patent Document 2, the sipes intersection groove corresponding to the above-mentioned pinholes is provided in the sipes.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The inventors have found that the tire disclosed in Patent Document 1 may experience a decrease in wet performance and tread heat dissipation in the early stages of wear. Furthermore, they have found that the tire disclosed in Patent Document 2 may experience a decrease in tread rigidity due to pinholes in the sipes, potentially preventing the maintenance of rolling resistance and wear resistance.

[0007] This invention has been made in view of these circumstances, and aims to provide a tire that can improve wet performance and heat dissipation from the early to late stages of wear, while maintaining rolling resistance and wear resistance. [Means for solving the problem]

[0008] A tire according to one aspect of the present invention comprises a tread having a tread surface that contacts the road surface, the tread having a plurality of circumferential grooves that extend continuously in the circumferential direction of the tire, the plurality of circumferential grooves dividing the tread into a plurality of land sections aligned in the tire width direction, the plurality of circumferential grooves having a pair of circumferential main grooves and at least one circumferential narrow groove located inward in the tire width direction from the pair of circumferential main grooves, the circumferential narrow groove having a narrow section located outward in the tire radial direction and a wider section located inward in the tire radial direction than the narrow section The tire has a widened section with a groove width, the groove width of the narrowed section is such that the side wall of the narrowed section contacts the road surface when the tire is in contact with it, at least one of the land sections adjacent to the circumferential narrow groove has a plurality of pinholes arranged in the circumferential direction of the tire, the depth of the pinholes is shallower than the depth of the circumferential main groove, the pinholes are tapered toward the inside in the radial direction of the tire, and the relationship between the width L1 of the land section having the pinholes and the distance L2 from the circumferential narrow groove to the pinhole satisfies the following equation (1). 0.3 ≦ L2 / L1 ≦ 0.7 ··· Formula (1) [Effects of the Invention]

[0009] According to the present invention, a tire can be obtained that maintains rolling resistance and wear resistance while improving wet performance and heat dissipation from the early to late stages of wear. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of the tread pattern of a tire according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram of the XX section cross-section in Figure 1. [Figure 3] Figure 3 is a schematic diagram illustrating the structure of a pinhole. [Figure 4] Figure 4 is a schematic diagram illustrating the configuration of the circumferential grooves. [Figure 5] Figure 5 is a schematic diagram of the tire tread pattern according to a modified example. [Modes for carrying out the invention]

[0011] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0012] [Basic Information on the Tire of This Invention] In this invention, the state in which a tire is mounted on a standard rim, its internal pressure is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state. Furthermore, unless otherwise specified, the explanation is based on a tire that has not experienced wear due to driving.

[0013] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. Dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a normal rim, are measured at the cross-section of the tire, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a normal rim. Furthermore, the tire's structure, which cannot be confirmed when the tire is mounted on a normal rim, is confirmed at the aforementioned cross-section.

[0014] A regular rim means a rim defined in the standard that a tire depends on. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

[0015] A regular internal pressure means an internal pressure defined in the standard that a tire depends on. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0016] A regular load means a load defined in the standard that a tire depends on. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0017] In the present invention, a tire includes, as parts, a tread, a pair of beads, and a pair of sidewalls. The tread includes a tread surface that contacts the road surface. The central portion of the tread is also called the crown portion. The end portion of the tread is also called the shoulder portion. The tread is a part of the tire formed of tread rubber including crosslinked rubber. A bead is a part of the tire that is fitted to a rim. A sidewall is a part of the tire that bridges between the tread portion and the bead portion.

[0018] [Findings on which the present invention is based] The inventor obtained the following findings by analyzing the wet performance and heat dissipation of a tire having circumferential grooves with a widened portion on the inner side in the tire radial direction.

[0019] During running, the tread repeats grounding and non-grounding. The circumferential grooves of the tread in the grounded state are in a state where the side walls narrow (hereinafter, may be simply referred to as the "closed state"). The circumferential grooves of the tread in the non-grounded state are in a state where the side walls widen (hereinafter, may be simply referred to as the "open state").

[0020] As described above, a tire having circumferential grooves with widened portions on the inner side in the tire radial direction suppresses a decrease in groove volume by expanding the groove width of the circumferential grooves in the late stage of wear, and maintains wet performance. On the other hand, in the early stage of wear, the side walls of the circumferential grooves are in the closed state, and there is a risk that sufficient wet performance cannot be ensured.

[0021] In a tire having circumferential grooves with widened portions on the inner side in the tire radial direction, the tread surface of the land portion adjacent to the circumferential grooves becomes wider in the early stage of wear. Therefore, in the early stage of wear, the tread of the land portion adjacent to the circumferential grooves is likely to generate heat, and there is a risk that the rolling resistance performance and durability will deteriorate.

[0022] If pinholes are provided in the above-mentioned land portion to improve the heat dissipation of the tread of the land portion adjacent to the circumferential grooves in a tire having circumferential grooves with widened portions on the inner side in the tire radial direction, there is a risk that the wear resistance performance will deteriorate.

[0023] [Basic Structure of Tread] FIG. 1 is a schematic view of a tread pattern of a tire 1 according to an embodiment of the present invention. FIG. 2 is a schematic view of a partial cross-section taken along the line X-X in FIG. 1. The tire 1 is a heavy-duty tire mounted on a vehicle such as a truck or a bus.

[0024] In Figures 1 and 2, PE represents the equator of tire 1. In Figure 2, EL represents the equatorial plane of tire 1. The equatorial PE is the intersection of the tread surface TRS of tread 10 and the equatorial plane EL. The tread surface TRS represents the surface of tread 10 assuming that tread 10 has no grooves. In Figure 1, the tire circumferential direction and tire width direction are indicated by double-headed arrows. In Figure 2, the tire radial direction and tire width direction are indicated by double-headed arrows. The tire width direction is parallel to the rotation axis of tire 1. In the tire width direction, the side of the dashed line EL is the inner side in the tire width direction, and the opposite side is the outer side in the tire width direction. In the tire radial direction, the side of the rotation axis is the inner side in the tire radial direction, and the side of tread 10 is the outer side in the tire radial direction.

[0025] The tread 10 makes contact with the road surface at its tread surface TRS. The tread pattern is formed by carving circumferential grooves 300 that extend continuously in the circumferential direction of the tire into the tread 10. In tire 1, four circumferential grooves 300 are carved into the tread 10. Tire 1 has five land areas 200, each partitioned by the four circumferential grooves 300. The tread 10 has a pair of circumferential narrow grooves 320 and a pair of shoulder circumferential main grooves 330 (hereinafter sometimes simply referred to as "circumferential main grooves 330") as circumferential grooves 300. The tread 10 has one first land area 210, a pair of second land areas 220, and a pair of shoulder land areas 230 as land areas 200.

[0026] A pair of circumferential main grooves 330 are cut into the outermost part of the tread 10 in the tire width direction. A pair of circumferential narrow grooves 320 are cut inward in the tire width direction from the pair of circumferential main grooves 330. The first land portion 210 is located in the area demarcated by the pair of circumferential narrow grooves 320. A pair of second land portions 220 is located in the area demarcated by the pair of circumferential narrow grooves 320 and the pair of circumferential main grooves 330. A pair of shoulder land portions 230 are located in the outermost part of the tire width direction, demarcated by the circumferential main grooves 330.

[0027] Generally, when a tire makes contact with the road surface, the contact pressure on the tread surface is higher on the inner side in the tire width direction than on the outer side in the tire width direction. Therefore, during driving, uneven wear may occur, where the tread on the inner side in the tire width direction wears down more than the tread on the outer side in the tire width direction. Tire 1 has circumferential grooves 320 on the inner side in the tire width direction. As a result, the contact pressure is distributed to each land area 200 of the tread 10 in tire 1, and uneven wear is suppressed.

[0028] The first land section 210 and the second land section 220 are both land sections 200 adjacent to the circumferential grooves 320. In the tread 10, multiple pinholes 100 are provided in a pair of second land sections 220, arranged in the circumferential direction of the tire. The pinholes 100 increase the surface area of ​​the tread 10 that is exposed to air. Also, during driving, air convection occurs into the pinholes 100. As a result, the heat dissipation of the tread 10 of the tire 1 is improved. In addition, the pinholes 100 also function as drainage paths for rainwater. As a result, the wet performance of the tire 1 is improved.

[0029] The pinhole 100 has a tapered hole portion 110 and a first tapered portion 410. The tapered hole portion 110 has a conical tapered hole shape in which the diameter of the hole gradually decreases toward the inside in the radial direction of the tire. The circumferential narrow groove 320 has a narrow groove portion 321, a widened portion 322 and a second tapered portion 420. The circumferential main groove 330 has a tapered groove portion 331 and a third tapered portion 430. Both the pinhole 100 and the circumferential groove 300 have a tapered portion 400 that opens onto the tread surface TRS. As a result, the wet performance of the tire 1 is improved in the early stages of wear. In addition, when foreign objects such as stones enter the pinhole 100 and circumferential narrow groove 320 in the early stages of wear, the foreign objects can easily escape from the pinhole 100 and circumferential narrow groove 320. Therefore, the occurrence of abnormal noises during driving and drilling that damages the inside of the tread 10 due to the aforementioned foreign matter getting stuck in the pinholes 100 or circumferential grooves 320 are suppressed.

[0030] As tire 1 is driven, the tread 10 wears down. As wear progresses, the openings PHO of the pinholes 100 (described later) appear on the tread surface TRS of tire 1. As wear progresses further, the connection points 323 of the circumferential grooves 320 (described later) appear on the tread surface TRS of tire 1. The period when the connection points 323 begin to appear due to wear of the tread 10 caused by driving is called the "late wear stage." The period before the late wear stage is called the "early wear stage." The period before the openings PHO appear in the early wear stage is called the "initial wear stage."

[0031] [Pinhole placement and effects] L1, shown in Figures 1 and 2, indicates the width of the second land section 220 having the pinhole 100. L2, shown in Figures 1 and 2, indicates the distance from the circumferential groove 320 to the pinhole 100. As shown in Figure 2, width L1 indicates the shortest distance in the tire width direction from the opening of the circumferential groove 320 to the opening of the circumferential main groove 330. Distance L2 indicates the shortest distance in the tire width direction from the opening of the circumferential groove 320 to the opening of the pinhole 100. L3, shown in Figure 1, indicates the distance in the tire circumferential direction between two adjacent pinholes 100 on the same second land section 220. Distance L3 indicates the shortest distance in the tire circumferential direction from the opening of one pinhole 100 to the opening of the other pinhole 100.

[0032] Each of the pair of second land sections 220 in the tread 10 has the same width L1. Each of the pair of second land sections 220 has the same distances L2 and L3. The pinholes 100 in each of the pair of second land sections 220 are positioned to be aligned in a straight line in the tire width direction. The pinholes 100 in the same second land section 220 are positioned to be aligned in a straight line in the tire circumferential direction. The first land section 210 of the tread 10 does not have pinholes 100. However, the tire of the present invention can also have pinholes 100 in the first land section 210. In this case, there will be two distances L2 for the pinholes 100 in the first land section 210: the distance from one circumferential groove 320 to the pinhole 100 and the distance from the other circumferential groove 320 to the pinhole 100. Therefore, the pinhole 100 of the first land section 210 is positioned such that both of the above-mentioned distances L2 satisfy equation (1) described later.

[0033] The relationship between width L1 and distance L2 satisfies equation (1) below. 0.3 ≦ L2 / L1 ≦ 0.7 ··· Formula (1) By providing the pinhole 100 near the circumferential groove 320 where L2 / L1 is less than 0.3 or on the circumferential groove 320 referring to Patent Document 2, the wet performance and heat dissipation of the tire 1 can be improved. However, if the pinhole 100 is arranged at a position where L2 / L1 is less than 0.3, the rigidity of the tread around the pinhole 100 and the circumferential groove 320 existing in its vicinity decreases. Therefore, during driving, the pinhole 100 and the circumferential groove 320 existing in its vicinity are likely to deform. Similarly, if the pinhole 100 is arranged at a position where L2 / L1 exceeds 0.7, the wet performance and heat dissipation can be improved, but the rigidity of the tread around the pinhole 100 and the circumferential main groove 330 existing in its vicinity decreases. Therefore, during driving, the pinhole 100 and the circumferential main groove 330 existing in its vicinity are likely to deform. Thus, when L2 / L1 is less than 0.3 or exceeds 0.7, chipping and uneven wear are likely to occur starting from the periphery of the pinhole 100. As a result, the rolling resistance performance and wear resistance performance of the tire 1 may decrease. If L2 / L1 is 0.3 or more and 0.7 or less, the rigidity of the second land portion 220 is ensured. Thereby, the rolling resistance performance and wear resistance performance of the tire 1 are maintained, and chipping and uneven wear of the edge portion existing at the boundary between the second land portion 220 and the circumferential groove 300 are suppressed. Note that L2 / L1 is preferably 0.4 or more and 0.6 or less, and particularly preferably 0.45 or more and 0.55 or less. Thereby, the rigidity of the second land portion 220 is more ensured.

[0034] The relationship between the width L1 and the distance L3 satisfies the following formula (2). L1 < L3 ··· Formula (2) If L1 < L3, the rigidity of the second land portion 220 is improved. Thereby, the rolling resistance performance and wear resistance performance of the tire 1 are improved.

[0035] The relationship between the distance L3 and the tire circumference L4 satisfies the following formula (3). 0.003 ≦ L3 / L4 ≦ 0.03 ··· Formula (3) The tire circumference L4 is the total length of the equator of tire 1. If L3 / L4 is 0.003 or more, preferably 0.005 or more, a sufficient number of pinholes 100 for heat dissipation are provided in the second land portion 220. If L3 / L4 is 0.03 or less, preferably 0.015 or less, the rigidity of the second land portion 220 is ensured, and the rolling resistance performance and wear resistance performance of tire 1 can be maintained.

[0036] [Pinhole structure and effects] Figure 2 shows that PHD indicates the depth of the pinhole 100 in the tire radial direction, from the tread surface TRS to the bottom 112 of the pinhole described later. FGD indicates the depth of the circumferential narrow groove 320 in the tire radial direction, from the tread surface TRS to the bottom 325 of the widened section described later. CMD indicates the depth of the circumferential main groove 330 in the tire radial direction, from the tread surface TRS to the bottom of the tapered groove section 331.

[0037] As shown in Figure 2, the depth PHD of the pinhole 100 is shallower than the depth CMD of the circumferential main groove 330. This suppresses defects in the tire 1, such as chipping of the land area and bending of the pinhole, during the manufacturing process, especially during mold release. Furthermore, the depth FGD of the circumferential fine groove 320 is configured to be less than or equal to the depth CMD. Moreover, the depth PHD is configured to be shallower than the depth FGD. As shown in Figure 2, in tire 1, the depth FGD and the depth CMD are configured to be the same depth. That is, the relationship between the depth PHD, the depth FGD, and the depth CMD satisfies the following equation (4). Depth PHD < Depth FGD ≤ Depth CMD ... Equation (4) As a result, tire 1 maintains well-balanced wet performance from the early to late stages of wear. The depth CMD is, for example, 10 mm to 21 mm. The depth FGD is, for example, 10 mm to 21 mm. The depth PHD is, for example, 4 mm to 19 mm.

[0038] Figure 3 is a schematic diagram illustrating the configuration of the pinhole 100. As described above, the pinhole 100 has a tapered hole portion 110 and a first tapered portion 410. The tapered hole portion 110 has an inclined portion 111 that forms a conical slope and a bottom portion 112 having an R surface with a first radius of curvature RC1. The first radius of curvature RC1 is preferably 0.5 mm or more and 1.0 mm or less. If the first radius of curvature RC1 is 0.5 mm or more, the distortion of the bottom portion 112 during tire 1 operation is reduced, and crack resistance is improved. If the first radius of curvature RC1 is 1.0 mm or less, the rigidity of the tread 10 is ensured, and rolling resistance and wear resistance are improved.

[0039] AW1 shown in Figure 3 is the opening width of the first tapered portion 410 (hereinafter sometimes referred to as "first opening width AW1"). POW is the opening width of the tapered hole portion 110 on the hypothetical tread surface TRS when the pinhole 100 does not have the first tapered portion 410. PBW is the opening width of the bottom portion 112 of the tapered hole portion 110. FTD indicates the depth of the first tapered portion 410 in the tire radial direction.

[0040] The pinhole 100 has a tapered hole portion 110 and a first tapered portion 410 that taper inward in the tire radial direction. As described above, when foreign objects such as stones get trapped inside, these objects can easily be removed. Therefore, the occurrence of abnormal noises during driving and drilling that damages the inside of the tread 10 are suppressed. Also, as shown in Figure 3, the angle of the first tapered portion 410 is more obtuse than the angle of the inclined portion 111 of the tapered hole portion 110 with respect to the tread surface TRS. Therefore, the pinhole 100 suppresses chipping and uneven wear of the edge portion in the early stages of wear. Furthermore, the first tapered portion 410 improves wet performance in the early stages of wear.

[0041] The opening width PBW of the bottom portion 112 is 1.0 mm or more and 2.0 mm or less. If the opening width PBW is 1.0 mm or more, sufficient heat dissipation is ensured. If the opening width PBW is 2.0 mm or less, the intrusion of foreign objects such as stones that have entered the tapered hole portion 110 into the interior of the tread 10 is reduced. This suppresses the occurrence of drilling. The opening width POW of the tapered hole portion 110 is 2.0 mm or more and 4.0 mm or less. If the opening width POW is 2.0 mm or more, sufficient heat dissipation is ensured. If the opening width POW is 4.0 mm or less, the rigidity of the second land portion 220 is ensured, and the rolling resistance performance and wear resistance performance of the tire 1 can be maintained. The first opening width AW1 can be wider than the opening width POW, for example, 2.5 mm or more and 6.0 mm or less.

[0042] In the initial stages of wear, the tread 10 wears down to the FTD depth through driving. The FTD depth is configured to be 10-20% of the PHD depth. This ensures drainage in the early stages of wear and improves wet performance.

[0043] [Structure and effects of circumferential grooves] Figure 4 is a schematic diagram illustrating the configuration of the circumferential groove 320. The circumferential groove 320 includes a widened section 322 on the inner side in the tire radial direction, a narrow groove section 321 on the outer side of the widened section 322 in the tire radial direction, and a second tapered section 420 on the outer side of the narrow groove section 321 in the tire radial direction. The narrow groove section 321 and the widened section 322 are connected at a connection position 323. The bottom 325 of the circumferential groove 320 is also the bottom of the widened section 322. The maximum width position 326 of the widened section 322 is also the maximum width position of the circumferential groove 320.

[0044] In Figure 4, CB indicates the length from the connection point 323 to the bottom 325 in the tire radial direction. CW indicates the length from the connection point 323 to the maximum width position 326 in the tire radial direction. CM indicates the length from the connection point 323 to the midpoint of length CB in the tire radial direction. The wall surface of the widened section 322 within the region of length CM is formed in a curved shape drawn by a single arc. This suppresses chipping and uneven wear of the edge portion of the widened section 322 in the later stages of wear. NIW indicates the groove width of the narrow groove section 321. NAW indicates the maximum width of the widened section 322 at the maximum width position 326. AIW indicates the width of the opening NGO of the narrow groove section 321. AW2 indicates the width of the opening TO2 of the second tapered section 420 (hereinafter sometimes referred to as "second opening width AW2"). ​​STD indicates the depth of the second tapered section 420. In addition, in tire 1, the standard depth (STD) is configured to be approximately the same as the first tapered section (FTD).

[0045] As shown in Figure 4, the second tapered section 420 is configured to gradually widen from the opening width AIW of the opening NGO to the second opening width AW2 of the opening TO2. Therefore, the angle of the second tapered section 420 is more obtuse than the angle of the narrow groove section 321 with respect to the tread surface TRS. As a result, chipping and uneven wear of the edges of the circumferential narrow groove 320 are suppressed in the early stages of wear. Furthermore, the second tapered section 420 improves wet performance in the early stages of wear. In tire 1, the second opening width AW2 of the second tapered section 420 is configured to be less than or equal to the maximum width NAW of the widened section 322.

[0046] The narrow groove section 321 has a substantially uniform groove width NIW from the opening NGO to the connection position 323. That is, in the circumferential narrow groove 320, the opening width AIW of the opening NGO and the groove width NIW of the narrow groove section 321 are configured to be substantially the same. The groove width NIW is configured to be the width at which the side walls 321a and 321b of the narrow groove section 321 touch each other when the tire 1 makes contact with the road surface. Side wall 321a is also the side wall of the first land section 210. Side wall 321b is also the side wall of the second land section 220. That is, when the tire 1 makes contact with the road surface, the first land section 210 and the second land section 220 are configured to support each other. As a result, the rigidity of the tread 10 is improved in the early stages of wear in the tire 1. Therefore, the rolling resistance performance and wear resistance performance of the tire 1 are improved. The circumferential main grooves 330 are configured such that when the tire 1 is in contact with the road surface, the side walls of the circumferential main grooves 330 do not touch each other. The groove width NIW is 1.0 mm or more and 3.0 mm or less, preferably 1.5 mm or more and 2.5 mm or less. This maintains the rolling resistance performance and wear resistance performance of the tire 1 in the early stages of wear. Note that grooves with a width of less than 1.0 mm are called sipes and are distinguished from narrow grooves.

[0047] As described above, the narrow groove section 321 of tire 1 has a nearly uniform groove width NIW. Therefore, in tire 1, the connection position 323 is the position where the width radially outward from the maximum width NAW of the widened section 322 is equal to the groove width NIW. If the groove width NIW of the narrow groove section 321 is not uniform, the connection position 323 is the position where the width radially outward from the maximum width NAW of the widened section 322 is 3.0 mm or less.

[0048] The maximum width NAW is three times or more the groove width NIW, preferably four times or more. If the maximum width NAW is three times or more the groove width NIW, the increase in rigidity of the tread 10 in the later stages of wear is suppressed. Therefore, grip performance is improved in the later stages of wear. In addition, drainage is ensured in the later stages of wear, and wet performance is improved. If the maximum width NAW is four times or more the groove width NIW, excellent grip performance and wet performance are exhibited in the later stages of wear. The maximum width NAW is seven times or less the groove width NIW, preferably six times or less. If the maximum width NAW is seven times or less the groove width NIW, rigidity of the tread 10 is ensured in the early stages of wear, and rolling resistance performance and wear resistance performance are maintained. If the maximum width NAW is six times or less the groove width NIW, excellent rolling resistance performance and wear resistance performance are exhibited in the early stages of wear. The maximum width NAW is preferably 7.0 mm or less.

[0049] RC2 shown in Figure 4 represents the radius of curvature of the bottom surface of the widened portion 322 (hereinafter sometimes referred to as the "second radius of curvature RC2"). The second radius of curvature RC2 is preferably 1.5 mm or more and 3.5 mm or less. If the second radius of curvature RC2 is 1.5 mm or more, the distortion of the bottom portion 325 during tire 1 operation is reduced, improving crack resistance. If the second radius of curvature RC2 is 3.5 mm or less, the rigidity of the tread 10 is ensured, improving wear resistance.

[0050] [Relationship and effect between pinhole depth, connection position and maximum width position of circumferential grooves] The depth PHD of the pinhole 100 is configured to be deeper than the connection point 323 between the narrow section 321 and the widened section 322 of the circumferential groove 320 in the radial direction of the tire. Furthermore, the depth PHD of the pinhole 100 is configured to be shallower than the maximum width position 326 where the widened section 322 of the circumferential groove 320 reaches its maximum width in the radial direction of the tire. In other words, the depth PHD of the pinhole 100 is configured to be the depth within the region of length CW from the connection point 323 to the maximum width position 326 in the radial direction of the tire. In tire 1, the depth PHD is configured to be the depth at the position of length CM, which is the midpoint of length CB, on the inside of the tire in the radial direction.

[0051] In the early stages of wear, the side walls 321a and 321b of the groove portion 321 of the circumferential groove 320 are closed. Therefore, in the early stages of wear, the drainage function of the circumferential groove 320 is reduced. On the other hand, in the early stages of wear, the drainage function of the pinholes 100 is high. In the later stages of wear, the widened portion 322 of the circumferential groove 320 appears on the tread surface TRS. Therefore, in the later stages of wear, the drainage function of the circumferential groove 320 is enhanced. On the other hand, in the later stages of wear, the volume of the pinholes 100 decreases, and the drainage function is reduced. As a result, the tire 1 maintains a balanced wet performance from the early stages of wear to the later stages of wear.

[0052] [Differentiation] Figure 5 is a schematic diagram of the tread pattern of a modified tire 2. Three circumferential grooves 300 are engraved in the tread 11 of tire 2. Tire 2 has four land areas 200, each partitioned by the three circumferential grooves 300. The tread 11 has one circumferential narrow groove 320 at the equator PE and a pair of shoulder circumferential main grooves 330 as circumferential grooves 300. The tread 11 has a pair of fourth land areas 240 and a pair of shoulder land areas 230 as land areas 200. The tire of the present invention only needs to have at least one circumferential narrow groove 320 located inward in the tire width direction from the pair of circumferential main grooves 330. More specifically, the tire of the present invention can be a 5-rib pattern having the pair of circumferential narrow grooves 320 shown in tire 1, or a 4-rib pattern having one circumferential narrow groove 320 shown in tire 2.

[0053] In tire 1, a pinhole 100 having a tapered hole portion 110 and a first tapered portion 410 is shown, but the present invention is not limited thereto. For example, a tapered hole portion 110 without the first tapered portion 410 can also be applied as the pinhole 100. Alternatively, a square pyramidal hole portion 120 (hereinafter sometimes referred to as "square hole portion 120") that tapers inward in the radial direction of the tire can also be applied. From the viewpoint of suppressing the occurrence of drilling, chipping, and uneven wear, it is preferable that the pinhole 100 has a tapered hole portion 110.

[0054] In Figure 5, L2a indicates a distance of 0.7 × L1 from the circumferential groove 320. L2b indicates a distance of 0.3 × L1 from the circumferential groove 320. In tire 1, the pinholes 100 are provided in a straight line in the circumferential direction of the tire, but the present invention is not limited to this. The pinholes 100 should be provided in a position where L2 / L1 is 0.3 or more and 0.7 or less, preferably 0.4 or more and 0.6 or less, and particularly preferably 0.45 or more and 0.55 or less. In tire 2, staggered square holes 120 are shown in the region between L2a and L2b. This maintains the rolling resistance performance and wear resistance performance of tire 2, and suppresses chipping and uneven wear of the edge portion at the boundary between the fourth land portion 240 and the circumferential groove 300.

[0055] L3a shown in Figure 5 indicates the distance in the tire circumferential direction between two pinholes 100 consisting of two square holes 120 that are adjacent in the tire circumferential direction on the same fourth land portion 240. L3b indicates the distance in the tire circumferential direction between two pinholes 100 consisting of two tapered holes 110 that are adjacent in the tire circumferential direction on the same fourth land portion 240. In tire 1, the pinholes 100 provided on each of the pair of second land portions 220 are all located at positions where they have the same distance L3 and are aligned in a straight line in the tire width direction, but the present invention is not limited to this. The relationship between the tire circumferential distance L3 between the pinholes 100 and the tire circumference L4 only needs to satisfy the above equation (3). In tire 2, distances L3a and L3b are different distances, and the square holes 120 and tapered holes 110 are located at positions where they are not aligned in a straight line in the tire width direction. On the other hand, in tire 2, both L3a / L4 and L3b / L4 are between 0.003 and 0.03. This maintains the resistance and wear resistance of tire 2, while also improving heat dissipation.

[0056] If equation (3) above is satisfied, the distance L3 in the same land area 200 can be configured to be different. That is, in the same land area 200, if a predetermined pinhole 100 is used as a reference (hereinafter sometimes referred to as the "reference pinhole"), then among the pinholes 100 adjacent to the reference pinhole in the tire circumferential direction, there are pinholes 100 adjacent to the reference pinhole on one side in the tire circumferential direction (hereinafter sometimes referred to as the "first adjacent pinhole") and pinholes 100 adjacent on the other side (hereinafter sometimes referred to as the "second adjacent pinhole"). Here, if equation (3) above is satisfied, the distance L3 between the reference pinhole and the first adjacent pinhole and the distance L3 between the reference pinhole and the second adjacent pinhole can be configured to be different. However, from the viewpoint of tire grip performance, it is preferable that the distance L3 in the same land area 200 be the same.

[0057] [Other variations] Tire 1 is a heavy-duty tire, but the present invention is not limited to this. For example, the present invention can be applied to passenger car tires.

[0058] The groove width of the narrow groove section 321 can be configured to vary from 1.5 to 3.0 mm. For example, the narrow groove section of the tire of the present invention can be configured so that the groove width at the opening is 1.5 mm, the groove width at the connecting section is 3.0 mm, and the groove width gradually widens. [Industrial applicability]

[0059] The technology described above, which improves wet performance and heat dissipation from the early to late stages of wear while maintaining rolling resistance and wear resistance, can be applied to various types of tires.

[0060] [Note] (1) One embodiment of the present invention is Equipped with a tread having a tread surface that contacts the road surface, The above tread has multiple circumferential grooves that extend continuously in the circumferential direction of the tire. Multiple circumferential grooves divide the tread into multiple land sections aligned in the tire width direction, Multiple circumferential grooves are, A pair of circumferential main grooves, and At least one circumferential groove located inward in the tire width direction from the pair of circumferential main grooves, It has, The above circumferential grooves are, The narrow section located on the outer side in the radial direction of the tire, and A widened section located on the inner side in the radial direction of the tire, having a groove width wider than the narrow section mentioned above. It has, The groove width of the narrow section described above has the width at which the side wall of the narrow section makes contact when the tire is in contact with the road surface. At least one of the above-mentioned land portions adjacent to the above-mentioned circumferential grooves has a plurality of pinholes arranged in the circumferential direction of the tire, The depth of the above pinhole is shallower than the depth of the above circumferential main groove. The above pinholes have a shape that tapers inward in the radial direction of the tire. The relationship between the width L1 of the land portion having the pinhole and the distance L2 from the circumferential groove to the pinhole satisfies the following equation (1): 0.3 ≦ L2 / L1 ≦ 0.7 ··· Formula (1) It's a tire.

[0061] (2) The depth of the pinhole is, in the radial direction of the tire, The above circumferential groove is deeper than the connection point between the narrow portion and the wide portion. The circumferential groove described above is shallower than the position where the widened portion reaches its maximum width. (1) These are the tires described.

[0062] (3) The pinhole is the tire described in (1) or (2), having a first tapered portion that opens to the tread surface.

[0063] (4) The pinhole has a tapered hole portion, The tapered hole portion described above is The diameter of the bottom is 1.0 mm or more and 2.0 mm or less, and the diameter of the opening on the tread surface is 2.0 mm or more and 4.0 mm or less. The tire according to any one of (1) to (3).

[0064] (5) The relationship between the width L1 and the circumferential distance L3 between two adjacent pinholes in the circumferential direction of the same land portion of the tire satisfies the following formula (2). L1 < L3 ··· Formula (2) (1) The tire according to any one of (1) to (4).

[0065] (6) The relationship between the circumferential distance L3 between two adjacent pinholes in the circumferential direction of the same land portion of the tire and the tire circumferential length L4 satisfies the following formula (3). 0.003 ≦ L3 / L4 ≦ 0.03 ··· Formula (3) (1) The tire according to any one of (1) to (5).

[0066] (7) The circumferential groove has a second tapered portion that opens to the tread surface, and the tire according to any one of (1) to (6).

Explanation of Signs

[0067] 1, 2 Tire 10, 11 Tread 100 Pinhole 110 Tapered hole portion 111 Inclined portion 112 Bottom of the pinhole 120 Square hole 200 Land portion 210 First land portion 220 Second land portion 240 Third land portion 230 Shoulder land portion 300 Circumferential groove 320 Circumferential fine groove 321 Fine groove portion 321a Side wall of the fine groove portion 321b Side wall of the fine groove portion 322 Widening section 323 Connection location 325 Bottom of the widened section 326 Maximum width position 330 Shoulder circumferential main groove 331 Tapered groove section 400 Tapered section 410 First tapered section 420 Second tapered section 430 Third tapered section PE equator EL equatorial plane TRS tread surface L1 Width of the land area with a pinhole L2 Distance from narrow groove to pinhole L2b maximum distance L2a minimum distance L3 Distance between pinholes NGO narrow groove opening PHO pinhole opening TO1 First tapered section opening TO2 Opening of the second tapered section Depth of the second tapered section of the FTD STD Depth of the second tapered section PHD pinhole depth FGD fine groove depth CMD main groove depth AW1 1st opening width AW2 Second opening width POW pinhole opening diameter PBW pinhole bottom diameter NIW Groove width of the narrow groove section AIW narrow groove opening width NAW widening section maximum width RC1 1st radius of curvature RC2 2nd radius of curvature

Claims

1. Equipped with a tread having a tread surface that contacts the road surface, The tread has a plurality of circumferential grooves that extend continuously in the circumferential direction of the tire, The multiple circumferential grooves divide the tread into multiple land sections arranged in the tire width direction, The multiple circumferential grooves are, A pair of circumferential main grooves, and At least one circumferential groove located inward in the tire width direction from the pair of circumferential main grooves, It has, The aforementioned circumferential grooves are The narrow section located on the outer side in the radial direction of the tire, and A widened section located on the inner side in the radial direction of the tire, having a groove width wider than the narrow section, It has, The groove width of the narrow portion has a width that the side wall of the narrow portion contacts when the tire is in contact with the road surface. At least one of the land portions adjacent to the circumferential grooves has a plurality of pinholes arranged in the circumferential direction of the tire, The depth of the pinhole is shallower than the depth of the circumferential main groove. The aforementioned pinhole has a shape that tapers inward in the radial direction of the tire. The relationship between the width L1 of the land portion having the pinhole and the distance L2 from the circumferential groove to the pinhole satisfies the following equation (1): 0.3 ≦ L2 / L1 ≦ 0.7 ... Formula (1) tire.

2. The depth of the aforementioned pinhole is, in the radial direction of the tire, The circumferential groove is located deeper than the connection point between the narrow portion and the wide portion. The circumferential narrow groove is shallower than the position where the widened portion reaches its maximum width. The tire according to claim 1.

3. The tire according to claim 1, wherein the pinhole has a first tapered portion that opens to the tread surface.

4. The aforementioned pinhole has a tapered hole portion, The tapered hole portion is, The diameter of the base is 1.0 mm or more and 2.0 mm or less. The diameter of the opening on the tread surface is 2.0 mm or more and 4.0 mm or less. The tire according to claim 1.

5. The relationship between the width L1 and the tire circumferential distance L3 between two adjacent pinholes in the same land area in the tire circumferential direction satisfies the following equation (2): L1<L3... Formula (2) The tire according to claim 1.

6. The relationship between the tire circumference distance L3 between two adjacent pinholes in the same land area in the tire circumference direction and the tire circumference L4 satisfies the following equation (3): 0.003≦L3 / L4≦0.03... Formula (3) The tire according to claim 1.

7. The tire according to claim 1, wherein the circumferential groove has a second tapered portion that opens to the tread surface.

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