pneumatic tires

Abstract

In pneumatic tires, regardless of the configuration having blocks with sipes running through the middle of the tire's circumferential direction, the aim is to improve braking performance in the initial stages of tire use while suppressing a decrease in tire rigidity. [Solution] The pneumatic tire includes a tread 10, and the main rotation direction of the tire is specified as α. The tread includes a plurality of blocks partitioned by a plurality of grooves. At least some of the blocks have sipes 40 that pass through the middle of the tire circumferential direction, and at least one shallow groove 50, 51, 52, 53 is formed in each region separated by the sipes of at least some of the blocks. The sipes have a maximum depth of 3 mm or more, and the shallow grooves have a depth of 1 mm or less. In each region, the sum of the lengths of all shallow grooves located on the rear side of the main rotation direction α is greater than the sum of the lengths of all shallow grooves located on the front side of the main rotation direction α.

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] In the tread of a pneumatic tire, there may be provided a plurality of blocks partitioned by a plurality of grooves. Also, the main rotation direction of the tire may be specified, for example, by forming a shape having a so-called V-pattern in which the inclination of the main groove of the tread with respect to the tire axis direction is larger on the equator side than on the ground contact end side.

[0003] Patent Document 1 describes that in a pneumatic tire with a specified main rotation direction, shallow grooves having a groove depth smaller than that of lug grooves and circumferential fine grooves are formed on the tread surface of the block.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a pneumatic tire, it is conceivable to form a sipe that passes through the middle in the tire circumferential direction and has a depth of 3 mm or more at the deepest part in the block provided in the tread. However, in this case, the block is likely to fall during braking. When the block falls, the braking ability of the tire decreases. On the other hand, in order to improve the braking ability at the initial stage of tire use, shallow grooves with a depth of 1 mm or less may be formed on the surface of the block. However, if many shallow grooves are formed in the block, the rigidity of the tire decreases.

[0006] The object of the present invention is to improve the braking performance of a pneumatic tire in the initial stages of use, while suppressing a decrease in tire rigidity, regardless of the configuration of the pneumatic tire having blocks with sipes passing through the middle of the tire's circumferential direction. [Means for solving the problem]

[0007] The pneumatic tire according to the present invention is a pneumatic tire having a tread, wherein the main direction of rotation of the tire is specified, and the tread includes a plurality of blocks partitioned by a plurality of grooves, at least some of the blocks have sipes that pass through the middle of the tire circumferential direction, at least one shallow groove is formed in each region separated by the sipes of at least some of the blocks, the sipes have a maximum depth of 3 mm or more, the shallow grooves have a depth of 1 mm or less, and in each of the regions, the sum of the lengths of all the shallow grooves located on the rear side in the main direction of rotation of the tire is greater than the sum of the lengths of all the shallow grooves located on the front side in the main direction of rotation of the tire. [Effects of the Invention]

[0008] The pneumatic tire according to the present invention can improve braking performance in the initial stages of tire use while suppressing a decrease in tire rigidity, regardless of the configuration having blocks with sipes passing through the middle of the tire's circumferential direction. [Brief explanation of the drawing]

[0009] [Figure 1] This is a plan view of a pneumatic tire, one example of an embodiment. [Figure 2A] This is an enlarged view of section A in Figure 1. [Figure 2B] This is a partially enlarged view of Figure 2A, showing shallow grooves with thin lines. [Figure 3] This is a cross-sectional view of BB in Figure 2A. [Figure 4] This is a cross-sectional view of CC in Figure 2A. [Figure 5]In the pneumatic tire of the embodiment, (a) is a schematic diagram showing the state in which the mediate block is in contact with the ground when the tire is stopped, and (b) is a schematic diagram showing the state in which the mediate block is tilted when the vehicle is braking. [Figure 6] This figure shows the results of a test conducted to confirm the preferred range for forming shallow grooves in the pneumatic tire of the embodiment, and also shows the results of measuring the portion of the pneumatic tire of the comparative example where the ground pressure on the contact area exceeds a predetermined value, at the initial braking stage (a) and the final braking stage (b). [Figure 7] This figure shows the results of a test conducted to confirm the preferred range for forming shallow grooves in the pneumatic tire of the embodiment, and also shows the measurement results of the time change in the ratio of the contact area relative to the initial braking state for the contact area of ​​the pneumatic tire of the comparative example where the contact pressure of the contact area is above a predetermined value. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiments described below are merely examples, and the present invention is not limited to these embodiments. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in the present invention.

[0011] Figure 1 is a plan view of a pneumatic tire 1, which is an example of an embodiment. Figure 2A is an enlarged view of part A in Figure 1. Figure 2B is a partially enlarged view of Figure 2A, in which shallow grooves 50, 51, 52, and 53 are shown as thin lines. As shown in Figure 1, the pneumatic tire 1 includes a tread 10, which is the part that contacts the road surface. In the drawings described below, the tire circumferential direction is indicated by Y and the tire axial direction by X. The tread 10 has a so-called V-shaped pattern, with a plurality of main grooves 20, 21 that extend from the equator CL side toward the contact edges E1 and E2 sides, and the angle of inclination with respect to the tire axial direction Y is larger on the equator CL side than on the contact edges E1 and E2 sides. Furthermore, the tread 10 has a plurality of sub-grooves 22, 23 that connect adjacent main grooves 20, 21 in the tire circumferential direction X in a direction inclined with respect to the tire circumferential direction X, and a plurality of blocks 28 that are separated in both the tire circumferential direction X and the tire axial direction Y, and are partitioned by the plurality of main grooves 20, 21 and the plurality of sub-grooves 22, 23. Hereinafter, the pneumatic tire 1 will be referred to as tire 1.

[0012] Multiple blocks 28 are formed along main grooves 20, 21, and include outer block 30 with respect to the tire equator CL and inner block 31 with respect to the tire equator CL. The main grooves 20 and block 30 extend from the equator CL side to the contact end E1 side, while the main grooves 21 and block 31 extend from the equator CL side to the contact end E2 side.

[0013] The equator CL refers to a line along the tire's circumferential direction that passes through the center of the tire's axial direction Y of the tread 10 (equally distanced from the contact points E1 and E2). In this specification, the contact points E1 and E2 are defined as the axial ends of the tire's contact area with a flat road surface when a predetermined load is applied to an unused pneumatic tire 1 mounted on a normal rim and filled with air to the normal internal pressure. For passenger car tires, the predetermined load is equivalent to 88% of the normal load.

[0014] Here, "standard rim" refers to the rim defined by the tire standard; for JATMA, it is the "standard rim," and for TRA and ETRTO, it is the "Measuring Rim." "Standard internal pressure" refers to the "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. The standard internal pressure is usually 180kPa for passenger car tires, but 220kPa for tires marked Extra Load or Reinforced. "Standard load" refers to the "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. For racing kart tires, the standard load is 392N.

[0015] Tire 1 is a directional tire with a specified main rotation direction. Figures 1 to 2B illustrate arrow α indicating the main rotation direction of tire 1. In this specification, the "main rotation direction" of a tire means the direction of rotation when the vehicle on which tire 1 is mounted is moving forward. Figure 1 is a plan view of tire 1, but when tire 1 is viewed from below, the direction of vehicle travel is opposite to the main rotation direction α of the tire. It is preferable that the pneumatic tire 1 has an indication for the mounting direction to the vehicle. For example, at least one of letters and an arrow indicating the main rotation direction is provided on the side of the pneumatic tire 1.

[0016] The tread 10 has a tread pattern in which blocks 30 and 31 are arranged in a staggered pattern along the tire circumferential direction X. Most of the blocks 30 and 31 are arranged on the left and right sides of the tread 10, with the equator CL in between.

[0017] The block 30 is formed along the main groove 20 and is alternately arranged with the main groove 20 in the tire circumferential direction X. The block 30 includes a center block 32 located on the equator CL side, a shoulder block 34 located on the ground contact end E1 side, and a mediate block 33 sandwiched between the center block 32 and the shoulder block 34. Thus, the block 30 has the center block 32, the mediate block 33, and the shoulder block 34 arranged in order from the equator CL side toward the outer side in the tire axial direction Y of the ground contact end E1 side. Between the center block 32 and the mediate block 33, and between the mediate block 33 and the shoulder block 34, auxiliary grooves 22 are formed to connect two main grooves 20 in the tire circumferential direction X or in a direction inclined with respect to the tire circumferential direction X. The auxiliary grooves 22 divide the block 30 into three blocks.

[0018] The block 31 is formed along the main groove 21 and is alternately arranged with the main groove 21 in the tire circumferential direction X. The block 31 includes a center block 35 located on the equator CL side, a shoulder block 37 located on the ground contact end E2 side, and a mediate block 36 sandwiched between the center block 35 and the shoulder block 37. Thus, the block 31 has the center block 35, the mediate block 36, and the shoulder block 37 arranged in order from the equator CL side toward the outer side in the tire axial direction Y of the ground contact end E2 side. Between the center block 35 and the mediate block 36, and between the mediate block 36 and the shoulder block 37, auxiliary grooves 23 are formed to connect two main grooves 21 in the tire circumferential direction X or in a direction inclined with respect to the tire circumferential direction X. The auxiliary grooves 23 divide the block 31 into three blocks.

[0019] As described above, the plurality of blocks 30 and 31 are separated in both the tire circumferential direction X and the tire axial direction Y by being partitioned by the plurality of main grooves 20 and 21 and the plurality of sub - grooves 22 and 23. The plurality of blocks 30 and 31 are elongated along the extending direction of the adjacent main grooves 20 and 21. Therefore, for each block 30 and 31, the direction along the adjacent main grooves 20 and 21 is the block longitudinal direction, and the direction orthogonal to the block longitudinal direction is the block width direction.

[0020] The tire 1 includes a pair of sidewalls bulging outward in the tire axial direction Y and a pair of beads. The bead is a portion fixed to the rim of the wheel and has a bead core and a bead filler. The sidewall and the bead are formed annularly along the tire circumferential direction and form the side surface of the pneumatic tire 1. The sidewall extends in the tire radial direction from both ends in the tire axial direction of the tread 10.

[0021] Hereinafter, the tread pattern of the tire 1 will be described in detail. The main grooves 20 are formed at arbitrary intervals in the tire circumferential direction X. Similarly, the main grooves 21 are formed at arbitrary intervals in the tire circumferential direction X. The tread 10 has a tread pattern in which most of the main grooves 20 and the blocks 30 are arranged on the ground - contact end E1 side (the left - hand region of the tread 10) with respect to the equator CL, and most of the main grooves 21 and the blocks 31 are arranged on the ground - contact end E2 side (the right - hand region of the tread 10) with respect to the equator CL. A block is a portion protruding toward the outer side in the tire radial direction.

[0022] At the center in the tire axial direction Y of the tread 10, the center blocks 32 and 35 are alternately arranged along the tire circumferential direction X. Also, the center blocks 32 and 35 are arranged in a staggered pattern along the equator CL.

[0023] The tread pattern of this embodiment, in a plan view, is a pattern in which blocks 30 and 31 are arranged symmetrically on the left and right sides, shifted by a predetermined pitch in the tire circumferential direction X with respect to the equator CL. The shape of block 30 is the same as the shape of block 31 when it is inverted with respect to the equator CL (the same applies to the main grooves 20 and 21). If block 31, which has been inverted at the equator CL, is slid in the tire circumferential direction X, it will coincide with block 30. The tread pattern of this embodiment has good left-right balance and is effective in improving handling stability.

[0024] The main groove 20 and block 30 have a plan view shape that is curved so as to be convex toward the rear in the main rotation direction α of the tire. Similarly, the main groove 21 and block 31 also have a plan view shape that is curved so as to be convex toward the rear in the main rotation direction α of the tire. The main grooves 20, 21 and blocks 30, 31 are inclined with respect to the tire axial direction Y, so that they are positioned gradually toward the rear in the main rotation direction α of the tire, starting from the center side of the tire axial direction Y toward both sides of the axial direction Y of the pneumatic tire 1.

[0025] As described above, the main grooves 20 and 21 have a greater angle of inclination with respect to the tire axis Y on the equator CL side than on the contact end E1 and E2 side. In other words, the main grooves 20 and 21 gradually become more aligned with the tire axis Y from the equator CL side toward the contact end E1 and E2, and the angle of inclination with respect to the tire axis Y becomes gentler. The angle of inclination of the main grooves 20 and 21 with respect to the tire axis Y is, for example, 20° to 50° or 25° to 40° on the equator CL side.

[0026] The main groove 20 connects to the main groove 21 near the equator CL. The main groove 20 extends from the intersection with the main groove 21 toward the contact end E1 and extends beyond the contact end E1 to the left annular side rib (not shown). The main groove 21 extends from the intersection with the main groove 20 near the equator CL toward the contact end E2 and extends beyond the contact end E2 to the right annular side rib (not shown). Each side rib is formed at each end in the tire axial direction Y between the contact ends E1, E2 of the tread 10 and the part of the sidewall 11 that protrudes most outward in the tire axial direction Y. The side ribs project outward in the tire axial direction Y and are formed in an annular shape along the tire circumferential direction X. The side ribs may be omitted.

[0027] The width of the main grooves 20 and 21 may be constant along their entire length, but in this embodiment, it gradually increases from the equator CL side toward the ground contact ends E1 and E2. The width of the main grooves 20 and 21 may be maximum, for example, at or near the ground contact ends E1 and E2, or at or near the intersection with the secondary grooves 22 and 23. In this case, drainage performance is improved, and the snow column shear force that grips and compacts the snow is also improved, resulting in good snow performance. The main grooves 20 and 21 are formed to the same depth, for example.

[0028] The sub-grooves 22 and 23 are narrower in width (maximum width) than the main grooves 20 and 21. The sub-groove 22 extends in the tire circumferential direction X or in a direction inclined with respect to the tire circumferential direction X, dividing the block 30 and connecting adjacent main grooves 20. In the example shown in Figure 1, the sub-groove 22 is inclined with respect to the tire circumferential direction so as it moves gradually away from the contact edge E1 from the front to the rear in the main rotation direction α of the tire. Similarly, the sub-groove 23 divides the block 31 and connects adjacent main grooves 21, and is inclined with respect to the tire circumferential direction X so as it moves gradually away from the contact edge E2 from the front to the rear in the main rotation direction α of the tire. The sub-grooves 22 and 23 may be shallower or deeper than the main grooves 20 and 21, but it is preferable that they be formed to the same depth as the main grooves 20 and 21. In this case, compared to when the groove depth changes, the water flow for drainage is not disturbed, thus improving drainage performance.

[0029] Within the tread surface of each block 32, 33, 34, 35, 36, 37, a sipe 40 is formed that passes through the middle of the tire, approximately in the circumferential direction, and has a maximum depth shallower than the maximum depth of the multiple main grooves 20, 21 and secondary grooves 22, 23. The maximum depth of the deepest part of each sipe 40 is 3 mm or more. The maximum depth of each sipe 40 is, for example, 40% to 95% of the maximum depth of the main grooves 20, 21. In Figure 2B, the width of the sipe 40 is made larger than the width of the shallow grooves 50, 51, 52, 53 to make the difference between the sipe 40 and the shallow grooves 50, 51, 52, 53 described later easier to understand, but their widths may be the same.

[0030] The sipes 40 formed on the center blocks 32, 35 and mediate blocks 33, 36 are aligned along the longitudinal direction of each block so as to reach two adjacent sub-grooves 22, 23 at both ends of the tread axial direction of each block. The sipes 40 formed on the shoulder blocks 34, 37 are aligned along the longitudinal direction of the shoulder blocks 34, 37 so that one end reaches the adjacent sub-grooves 22, 23 on the inner side of the tread axial direction of the shoulder blocks 34, 37, while the other end terminates within the shoulder blocks 34, 37. The depth of the sipes 40 near the end that opens into the sub-grooves 22, 23 may be smaller than the depth in the middle of the longitudinal direction. In this case, the rigidity of the block can be increased despite the formation of sipes 40 on the block. The sipes 40 may be formed on only some of the blocks of the tread 10.

[0031] In each block, at least one shallow groove 50, 51, 52, 53 is formed on the tread surface, which is the radially outer surface of the tire, in the front regions 444, 45, 46 on the front side of the tire's main rotation direction α and the rear regions 47, 48, 49 on the rear side of the tire's main rotation direction α, within the regions separated by the sipes 40 of each block. The depth of each shallow groove 50, 51, 52, 53 is 1 mm or less. Furthermore, in each of the front regions 44, 45, 46 and rear regions 47, 48, 49 of each block, the sum of the lengths of all the shallow grooves 50, 51, 52, 53 located on the rear side of the tire's main rotation direction α is greater than the sum of the lengths of all the shallow grooves 52, 53 located on the front side of the tire's main rotation direction α. ​​As a result, as described later, regardless of the configuration of the block having sipes 40 passing through the middle of the tire's circumferential direction, it is possible to improve the braking performance of the tire 1 in the initial stages of use while suppressing a decrease in the rigidity of the tire 1.

[0032] The shallow grooves on the tread surface of the block will be explained in detail below using Figures 1 to 2B, and Figures 3 and 4. Figure 3 is a cross-sectional view of BB in Figure 2A. Figure 4 is a cross-sectional view of CC in Figure 2A.

[0033] In the following, we will mainly describe the shallow grooves of the center block 32, mediate block 33, and shoulder block 34 of the multiple blocks 30, but the shallow grooves of the center block 35, mediate block 36, and shoulder block 37 of the multiple blocks 31 are similar, except that they have a shape that is symmetrical with respect to the equator CL with respect to blocks 32, 33, and 34. Of the center block 32, mediate block 33, and shoulder block 34 of block 30, we will first describe the shallow groove 51 of the mediate block 33.

[0034] As shown in Figures 2A, 2B, and 3, each mediate block 33 is separated from the other blocks 32, 33, and 34 by two main grooves 20 spaced apart in the tire circumferential direction X, and two spaced secondary grooves 22 intersecting each main groove 20. The distance between the two secondary grooves 22 is longer than the distance between the two main grooves 20. In plan view, the shape of the mediate block 33 is a long, roughly rectangular shape along the main grooves 20.

[0035] Shallow grooves 51 are formed on the tread surfaces of the front region 45 and rear region 48 of the mediate block 33. The shallow grooves 51 are located only above the region center line 55 in Figure 2B, which is on the rear side of the main rotation direction α of the tire, in both the front region 45 and rear region 48. The region center line 55 is an imaginary line that passes through the center of the block width direction of each region 45 and 48 along the entire longitudinal direction of the tread surface of each region 45 and 48.

[0036] As a result, in both the front region 45 and the rear region 48, there are no shallow grooves in front of the region centerline 55 in the main rotation direction α of the tire. Therefore, in each region 45 and 48, the sum of the lengths of all shallow grooves 51 located behind the main rotation direction α of the tire is greater than the sum of the lengths of all shallow grooves located in front of the main rotation direction α of the tire. "Length of the shallow groove" refers to the longitudinal length of the shallow groove in a plan view. Therefore, as will be explained in detail later, in the initial stages of tire use, the shallow grooves 51 are formed in a concentrated area where the contact pressure during braking is high, thereby improving the braking performance in the initial stages of tire use while suppressing a decrease in the rigidity of the mediate block 33.

[0037] The shallow groove 51 has a width of, for example, 0.2 mm or more and 1.0 mm or less. The depth of the shallow groove 51 is 1.0 mm or less, but preferably it can be less than 1.0 mm, for example, 0.9 mm or less. In this specification, including shallow grooves and sipes described later, the groove depth refers to the depth of the groove along the tire radial direction. The groove may be formed to be inclined with respect to the tire radial direction.

[0038] Preferably, at least a portion of the shallow grooves 51 in each region 45, 48 is located in a range of 40% or less of the length in the block width direction between the rear edge T1a, T2a in the main rotation direction α of the tire and the side edge T1a, T1b, T2a, T2b in the circumferential direction of the tire. This allows the shallow grooves 51 to be formed more concentrated in the areas where the ground pressure is high during braking.

[0039] Furthermore, more preferably, at least a portion of the shallow grooves 51 in each region 45, 48 is located in a range of 5% or more of the length in the block width direction between the rear edge T1a, T2a in the main rotation direction α of the tire and the side edge T1a, T1b, T2a, T2b in the circumferential direction of the tire. In this case, the edge T1a, T2b are the open edge of the sipe 40. For example, at least a portion of the shallow grooves 51 in each region 45, 48 of each mediate block 33 is located in a range of 4 mm or less in the block width direction from the rear edge T1a, T2a in the main rotation direction α of the tire.

[0040] More preferably, in plan view, the shallow groove 51 is shaped to follow 30% or more of the rear edge T1a, T2a (Figure 2B) in the main rotation direction α of the tire in the corresponding regions 45, 48, and is positioned in a range of 40% or less, more preferably 5% or more, of the length in the block width direction between the rear edge T1a, T2a in the main rotation direction α of the tire and the side edge T1a, T1b, T2a, T2b in the circumferential direction of the tire. For example, in the front region 45, the shallow groove 51 follows the entire longitudinal direction of the rear edge T1a. On the other hand, in the rear region 48, the shallow groove 51 follows the entire longitudinal direction of the mediate block 33, but the longitudinal ends of the rear edge T2a of the mediate block 33 have roughly triangular corner chamfers 62 in plan view. Even in this case, the shallow groove 51 of the rear region 48 is formed to follow an intermediate region of 30% or more of the longitudinal direction of the rear edge T2a in a plan view.

[0041] Thus, in a plan view, it is preferable that the shallow grooves 51 are shaped to follow 30% or more of the rear edge T1a, T2a of the corresponding regions 45, 48 in the main rotation direction α of the tire, and are arranged in a range of 40% or less of the length in the block width direction between the rear edge T1, T2 in the main rotation direction α of the tire and the two side edge in the circumferential direction of the tire. With this preferred configuration, in the initial stages of tire use, the deformation during braking is greater in the portion of the block adjacent to the contact surface, and the contact pressure is higher, making it easier to form shallow grooves 51 more concentrated on the contact surface. This makes it possible to improve the braking performance in the initial stages of tire use while suppressing a decrease in the rigidity of the mediate block 33.

[0042] The above describes the shallow grooves 51 formed in the mediate block 33, but shallow grooves 50 are also arranged only on the rear side of the front region 44 and rear region 47 of the center block 32 shown in Figure 2A, in the tire's main rotation direction α. ​​The formation state and range of the shallow grooves 50 are the same except that the block is changed from the mediate block 33 to the center block 32.

[0043] The shallow grooves 52 and 53 of the shoulder block 34 will be explained using Figures 1 to 2B and Figure 4. Each shoulder block 34 is separated from the other blocks 33 and 34 by two main grooves 20 that are separated in the tire circumferential direction X, and one secondary groove 22 that intersects each of the main grooves 20. In plan view, the shape of the shoulder block 34 is a long, roughly fan-shaped structure along the main grooves 20.

[0044] Shallow grooves 52 and 53 are formed on the tread surfaces of the front region 46 and rear region 49 of the shoulder block 34, respectively. As shown in Figure 2B, the shallow groove 52 is formed on the tread surface of the front region 46 and, in a plan view, is substantially T-shaped, having a first portion 52a extending along the block length direction and a second portion 52b connected to one end of the first portion 52a and extending along the block width direction. The first portion 52a is located only above the region center line 56 (Figure 2B), which is the rear side of the front region 46 in the main tire rotation direction α. ​​The region center line 56 is an imaginary line that passes through the center of each region 46 and 49 in the block width direction along the entire longitudinal direction of the tread surface of each region 46 and 49.

[0045] As a result, in the front region 46, the sum of the lengths of all the shallow grooves 52 located on the rear side of the tire's main rotation direction α is greater than the sum of the lengths of all the shallow grooves 52 located on the front side of the tire's main rotation direction α.

[0046] The shallow groove 53 is formed on the tread surface of the rear region 49 and, in a plan view, is substantially L-shaped, having a first portion 53a extending along the block length direction and a second portion 53b connected to one end of the first portion 53a and extending along the block width direction. The first portion 53a is positioned only above the region centerline 56 (Figure 2B), which is the rear side of the rear region 49 in the main tire rotation direction α, as shown in Figure 2B.

[0047] As a result, in the rear region 49, the sum of the lengths of all shallow grooves 53 located on the rear side of the tire's main rotation direction α is greater than the sum of the lengths of all shallow grooves 53 located on the front side of the tire's main rotation direction α. ​​The width and depth of the shallow grooves 52 and 53 are the same as those of the shallow grooves 50 and 51. As a result, as with the mediate block 33, the braking performance in the initial stages of tire use can be improved while suppressing a decrease in the rigidity of the shoulder block 34.

[0048] Preferably, at least a portion of the shallow grooves 52, 53 in each region 46, 49 is located within a range of 40% or less of the length in the block width direction between the rear edge in the main rotation direction α of the tire and the edges on both sides in the circumferential direction of the tire. This allows the shallow grooves 52, 53 to be more concentrated in the areas where the ground pressure is high during braking. For example, at least a portion of the shallow grooves 52, 53 in each region 46, 49 of each shoulder block 34 is located within a range of 4 mm or less in the block width direction from the rear edge in the main rotation direction α of each region 46, 49.

[0049] More preferably, in a plan view, the shallow grooves 52 and 53 are shaped to follow 30% or more of the rear edge in the main rotation direction α of the tire in the corresponding regions 46 and 49, and are positioned within a range of 40% or less, more preferably 5% or more, of the length in the block width direction between the rear edge in the main rotation direction α of the tire in each region 46 and 49 in the circumferential direction of the tire. In this case as well, similar to the case of the mediate block 33, it is possible to further improve the braking performance in the initial stages of tire use while suppressing a decrease in the rigidity of the shoulder block 34.

[0050] Furthermore, shallow grooves 50, 51, 53, and 53 are placed in all blocks 32, 33, 34, 35, 36, and 37 of the tread 10. This allows for improved braking performance in the initial stages of tire use.

[0051] Furthermore, at least a portion of each shallow groove 52, 53 of the shoulder block 34 is positioned axially outward from the contact end E1. As a result, the shallow grooves 52, 53 are formed in the region axially outward from the contact end E1 where the pressure at ground contact is concentrated during cornering. This makes it easier for the edges of the shallow grooves 52, 53 to catch on the road surface during cornering, thereby improving braking performance during cornering.

[0052] Furthermore, in the shoulder block 34, the second portions 52b and 53b (Figure 2B), which are part of the shallow grooves 52 and 53, are positioned along the sub-groove 22, within a range of 4 mm or less from the sub-groove 22. This suppresses tire lateral slippage in response to centrifugal force during cornering, thereby improving cornering performance.

[0053] Furthermore, as shown in Figures 2B and 4, in the shoulder block 34 where shallow grooves 52 and 53 are formed, a chamfer 60 is formed on at least the rear edge in the main tire rotation direction α of the tread surface. In addition, a roughly triangular corner chamfer 61 is formed on the rear corner of the shoulder block 34 on the sub-groove 22 side in the main tire rotation direction α, so as to be continuous with the chamfer 60 in plan view.

[0054] This prevents the shoulder block 34 from tilting excessively when it tilts downwards toward the rear in the direction of vehicle travel during braking, and also makes it easier to increase the contact area even if the shoulder block 34 does tilt. As a result, braking performance can be increased. In addition, during braking, the contact pressure on the shoulder block 34 tends to increase, and a load is easily applied in the direction that causes the block to tilt. Therefore, by forming a chamfer 60 on the shoulder block 34, braking performance can be increased even more significantly. The same applies to the shoulder block 37 as to the shoulder block 34.

[0055] Figure 4 shows the case where the chamfer 60 has a straight cross-sectional shape, but it is not limited to this, and may also be a chamfer with a circular arc cross-section. The chamfer on the rear edge of the tread surface in the main rotation direction α of the tire may be provided together with the shoulder blocks 34 and 37, or instead of the shoulder blocks 34 and 37, it may be provided on one or both of the center blocks 32 and 35 and the mediate blocks 33 and 36.

[0056] According to the tire 1 described above, in the front and rear regions of each block, the sum of the lengths of all shallow grooves located on the rear side in the main rotation direction α of the tire is greater than the sum of the lengths of all shallow grooves located on the front side in the main rotation direction α of the tire. As a result, regardless of the configuration of the block having a sipe 40 passing through the middle of the tire circumferential direction, it is possible to improve the braking performance of the tire 1 in the initial stages of use while suppressing a decrease in the rigidity of the tire 1.

[0057] This reason will be explained in more detail using Figure 5, which will represent the mediate block 33. In Figure 5, (a) is a schematic diagram showing the contact state of the mediate block 33 when the tire 1 is stopped, and (b) is a schematic diagram showing the state in which the mediate block 33 falls when the vehicle is braking.

[0058] As shown in Figure 5(a), when the tire 1 is stopped, the tilting of the mediate block 33 can be ignored. Therefore, the tread surfaces 45a and 48a of the front region 45 and rear region 48 of the contact area can be easily brought into overall contact with the road surface 80.

[0059] On the other hand, as shown in Figure 5(b), when the vehicle is braking, the contact portion of the mediate block 33 tends to tilt downwards towards the rear in the direction of travel β. In this case, the tread surfaces 45a and 48a of each region 45 and 48 of the mediate block 33 tend to have lower contact pressure because they are further away from the road surface 80 in the rear portion of the tread surface β in the direction of travel. Conversely, the contact pressure tends to be higher in the front portion of the tread surfaces 45a and 48a in the direction of travel β. According to this embodiment, in the initial stages of tire use, shallow grooves are formed concentrated in the front portion of the tread surface β in the direction of travel, which is the rear of the main rotation direction α of the tire in each region 45 and 48 where the contact pressure tends to be high during braking. Therefore, since an excessive number of shallow grooves are not formed on the tread surfaces 45a and 48a, the braking ability of the tire 1 in the initial stages of use can be improved while suppressing a decrease in block rigidity. In addition, since the shallow grooves are less than 1 mm deep, a decrease in block rigidity is unlikely to occur. Furthermore, during braking, pressure concentrates on the edges of the blocks, and if the pressure is too high, the coefficient of friction may decrease. According to this embodiment, shallow grooves increase the number of edges other than the edges of the blocks, thus easing the pressure on the edges of the block edges during braking. This suppresses the decrease in the coefficient of friction of the blocks. This also improves the braking performance of the tire 1 in the initial stages of use.

[0060] Next, in the embodiment, we will describe a test conducted to confirm that a higher effect can be obtained when the shallow grooves 50, 51, 52, 53 are shaped to follow 30% or more of the rear edge in the tire's main rotation direction α of the corresponding area of ​​the corresponding block, and are positioned within a range of 40% or less of the length in the block width direction between the two side edges in the tire's circumferential direction α from the rear edge in the tire's main rotation direction α.

[0061] The test was conducted using a comparative example tire. The comparative example tire has a tread with the same basic shape as the embodiment, but the tread surface, which is the radially outer surface of each block, is smooth and does not have shallow grooves. In addition, a sipe 40 extending along the longitudinal direction of the main groove is formed in the middle of the circumferential direction of the tread surface of each block, similar to the configuration in Figures 1 to 5.

[0062] Figure 6 shows the results of measuring the contact pressure of the tire of the comparative example at the initial braking stage (a) and the final braking stage (b), where the contact pressure exceeds a predetermined value. In Figure 6, the right side is the front side in the direction of vehicle travel β. In Figure 6, the black areas indicate the portions of the tread where the contact pressure of the center block 35, mediate block 36, and shoulder block 37 on one side of the tire axial direction exceeds a predetermined value. These black areas are essentially the contact surface during braking.

[0063] As shown in the measurement results in Figure 6, in the comparative example tire, the effective contact area decreases to approximately 70% in both the front and rear regions of the vehicle direction β, separated by the sipes 40 of each block, at the end of braking compared to the initial braking stage. From this, it can be concluded that in the tread surface of each region of each block, approximately 30% of the longitudinal portion does not have sufficient contact area compared to when the tire is stationary. For this reason, a preferred configuration in which shallow grooves are formed along 30% or more of the rear edge in the main rotation direction of the tire in each region is preferable. In the initial stages of tire use, the deformation of adjacent portions of the block during braking is large, and the adjacent portions do not make sufficient contact, resulting in higher contact pressure. This makes it easier to form shallow grooves more concentrated on the contact surface. This allows for higher braking performance in the initial stages of tire use while suppressing a decrease in the rigidity of each block. For this reason, it was confirmed that forming shallow grooves along 30% or more of the rear edge in the main rotation direction of the tire in each region of each block is effective.

[0064] Figure 7 shows the measurement results of the change in the ratio of the contact area relative to the initial braking state, for the contact pressure of the tire's contact area that is above a predetermined value. From the measurement results shown in Figure 7, it can be seen that at the initial stage of braking, the tire's contact load becomes excessively high due to the sinking of the front of the vehicle, causing the contact area to increase from the standard value of 100%. Furthermore, as the sinking subsides and the blocks of the contact area collapse, the contact area decreases, and it was confirmed that the ratio of this contact area becomes approximately 70% of the standard value. From this, it can be seen that in the tread surface of each region of each block, approximately 30% of the longitudinal portion does not provide sufficient contact area compared to the tire when it is stopped. From this, it can be seen that forming shallow grooves along 30% or more of the rear edge in the main rotation direction of the tire in each region of each block is effective.

[0065] Furthermore, even if shallow grooves are formed in only a portion of each block, along 30% or more of the rear edge in the main rotation direction of the tire in each region, this is also effective in suppressing a decrease in block rigidity while further improving the braking performance in the initial stages of tire use.

[0066] Furthermore, although the embodiment described a case in which shallow grooves are provided in all blocks of the tread, even when shallow grooves are provided in only some of the blocks of the tread, it is possible to obtain the effect of improving braking performance in the initial stages of tire use while suppressing a decrease in block rigidity.

[0067] This disclosure is further illustrated by the following embodiments. Configuration 1: A pneumatic tire having a tread, The main rotation direction of the tire is specified, and The tread includes a plurality of blocks partitioned by a plurality of grooves, At least some of the aforementioned blocks have sipes that pass through the middle of the tire circumferential direction. At least one shallow groove is formed in each region separated by the sipes of at least a portion of the block. The sipe has a maximum depth of 3 mm or more. The depth of the aforementioned shallow groove is 1 mm or less. In each of the aforementioned regions, the sum of the lengths of all the shallow grooves located on the rear side in the main rotation direction of the tire is greater than the sum of the lengths of all the shallow grooves located on the front side in the main rotation direction of the tire. Pneumatic tires. Configuration 2: In each of the aforementioned regions, at least a portion of the shallow groove is located within a range of 40% or less of the length in the block width direction between the rear edge in the main rotation direction of the tire and the two side edges in the circumferential direction of the tire. The pneumatic tire described in Component 1. Configuration 3: In each of the aforementioned regions, the shallow groove is arranged only on the rear side in the main rotation direction of the tire. A pneumatic tire as described in Configuration 1 or Configuration 2. Configuration 4: The shallow groove is shaped to follow 30% or more of the rear edge in the main rotation direction of the tire in the corresponding area when viewed from above, and is positioned within a range of 40% or less of the length in the block width direction between the rear edge in the main rotation direction of the tire and the edges on both sides in the circumferential direction of the tire. A pneumatic tire as described in any one of configurations 1 through 3. Configuration 5: The aforementioned shallow groove is positioned such that at least a portion of it is located axially outward from the contact edge of the tire. A pneumatic tire as described in any one of the components 1 through 4. Configuration 6: The shallow grooves are arranged in all of the blocks provided in the tread. A pneumatic tire as described in any one of the components 1 through 5. Composition 7: The plurality of grooves extend from the equator towards the contact end, and have a plurality of main grooves whose inclination with respect to the tire axis is greater on the equator side than on the contact end side, and sub-grooves that connect adjacent main grooves in the tire circumferential direction or in an inclined direction with respect to the tire circumferential direction. At least a portion of the shallow groove is arranged along the sub-groove, within a range of 4 mm or less from the sub-groove. A pneumatic tire as described in any one of the components 1 through 6. Composition 8: A chamfer is formed on at least the rear edge of the block in which the shallow groove is formed, in the main rotation direction of the tire. A pneumatic tire as described in any one of the components 1 through 7. [Explanation of Symbols]

[0068] 1 Pneumatic tire (tire), 10 Tread, 20,21 Main grooves, 22,23 Secondary grooves, 28,30,31 Blocks, 32,35 Center block, 33,36 Mediate block, 34,37 Shoulder block, 40 Sipes, 44,45,46 Front area, 47,48,49 Rear area, 50,51,52,53 Shallow grooves, 55,56 Area center line, 60 Chamfer, 61,62 Corner chamfer, CL Equator, E1,E2 Contact edge.

Claims

1. A pneumatic tire having a tread, The main rotation direction of the tire is specified, and The tread includes a plurality of blocks partitioned by a plurality of grooves, At least some of the aforementioned blocks have sipes that pass through the middle of the tire circumferential direction. At least one shallow groove is formed in each region separated by the sipes of at least a portion of the block. The sipe has a maximum depth of 3 mm or more. The depth of the aforementioned shallow groove is 1 mm or less. In each of the aforementioned regions, the sum of the lengths of all the shallow grooves located on the rear side in the main rotation direction of the tire is greater than the sum of the lengths of all the shallow grooves located on the front side in the main rotation direction of the tire. Pneumatic tires.

2. In each of the aforementioned regions, at least a portion of the shallow groove is located within a range of 40% or less of the length in the block width direction between the rear edge in the main rotation direction of the tire and the two side edges in the circumferential direction of the tire. The pneumatic tire according to claim 1.

3. In each of the aforementioned regions, the shallow groove is arranged only on the rear side in the main rotation direction of the tire. The pneumatic tire according to claim 1.

4. The shallow grooves, in a plan view, are shaped to follow 30% or more of the rear edge in the main rotation direction of the tire in the corresponding area, and are arranged in a range of 40% or less of the length in the block width direction between the rear edge in the main rotation direction of the tire and the two side edges in the circumferential direction of the tire. The pneumatic tire according to claim 1.

5. The aforementioned shallow groove is positioned such that at least a portion of it is located axially outward from the contact edge of the tire. The pneumatic tire according to claim 1.

6. The shallow grooves are arranged in all of the blocks provided in the tread. The pneumatic tire according to claim 1.

7. The plurality of grooves extend from the equator towards the contact end, and have a plurality of main grooves whose inclination with respect to the tire axis is greater on the equator side than on the contact end side, and sub-grooves that connect adjacent main grooves in the tire circumferential direction or in an inclined direction with respect to the tire circumferential direction. At least a portion of the shallow groove is arranged along the sub-groove, within a range of 4 mm or less from the sub-groove. The pneumatic tire according to claim 1.

8. A chamfer is formed on at least the rear edge of the block in which the shallow groove is formed, in the main rotation direction of the tire. The pneumatic tire according to claim 1.

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