pneumatic tires

Abstract

To provide a pneumatic tire having high design property and capable of reducing noise generated from the tire.SOLUTION: A pneumatic tire 1 as an example of an embodiment includes a tread 10 formed with a main groove 20 extending in a tire circumferential direction. The main groove 20 is a portion including a plurality of thin grooves 21 formed at a predetermined interval in a groove bottom, and includes a first portion 23 arranged with an interval in the tire circumferential direction, and a second portion 24 that is a portion in which the plurality of thin grooves 21 do not exist, and is arranged alternately with the first portion 23 in the circumferential direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to pneumatic tires.

Background Art

[0002] Conventionally, pneumatic tires having a tread with a plurality of grooves extending in the tire circumferential direction or the axial direction and a plurality of blocks partitioned by each groove are widely known. Also, several tires have been proposed for the purpose of reducing the noise generated from the tire during vehicle running. For example, Patent Document 1 discloses a tire provided with protrusions having different heights at the groove bottom in a pattern repeating unevenness along the tire circumferential direction. Patent Document 1 describes an effect that the external noise of the tire can be reduced. Further, Patent Document 2 discloses a tire provided with spiral continuous unevenness on the groove wall and the groove bottom.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, reducing the noise generated from the tire during vehicle running is an important problem. Further, there is a demand for a tire that can reduce noise and has high designability.

[0005] An object of the present invention is to provide a pneumatic tire having high designability and capable of reducing the noise generated from the tire.

Means for Solving the Problems

[0006] The pneumatic tire according to the present invention is a pneumatic tire having a tread formed with a first main groove extending in the circumferential direction of the tire, wherein the first main groove includes a portion containing a plurality of fine grooves formed at predetermined intervals at the bottom of the groove and comprising a first portion arranged at intervals in the circumferential direction of the tire and a second portion where the plurality of fine grooves are absent and arranged alternately with the first portion in the circumferential direction of the tire. [Effects of the Invention]

[0007] The pneumatic tire according to the present invention has a highly aesthetic design and is excellent at reducing noise generated by the tire. The pneumatic tire according to the present invention has a novel tread pattern characterized by an aggressive design. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view of a pneumatic tire, which is an example of an embodiment, and also shows the internal structure of the tire. [Figure 2] This is a plan view of a pneumatic tire, which is an example of an embodiment. [Figure 3] This figure shows a portion of the cross-section along line AA in Figure 2. [Figure 4] This is a magnified view of section F1 in Figure 3. [Figure 5] This is a magnified view of section F2 in Figure 3. [Figure 6] This figure shows a portion of the cross-section of line BB in Figure 2. [Figure 7] This figure shows a portion of the cross-section of the CC line in Figure 2. [Figure 8] This is a cross-sectional view along the DD line in Figure 2. [Figure 9] This figure shows an example of the first region of the main groove. [Figure 10] This figure shows another example of the first region of the main groove. [Figure 11] This diagram shows a modified example of a pneumatic tire. [Figure 12] This diagram shows a modified example of a pneumatic tire. [Figure 13] This diagram shows a modified example of a pneumatic tire. [Figure 14] This figure shows another example of the first region of the main groove. [Modes for carrying out the invention]

[0009] Hereinafter, an example of an embodiment of the pneumatic tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining the various components of the multiple embodiments and modifications described below are also included in the present invention.

[0010] Figure 1 is a perspective view of a pneumatic tire 1, which is an example of an embodiment. Figure 1 also shows the internal structure of the pneumatic tire 1. As shown in Figure 1, the pneumatic tire 1 includes a tread 10 that is in contact with the road surface and is formed in an annular shape along the tire's circumferential direction. The tread 10 has a first main groove 20 that extends in the tire's circumferential direction. The main groove 20 is formed to be substantially straight along the tire's circumferential direction and does not curve in the tire's axial direction. Preferably, the tread 10 has two or more main grooves that extend in the tire's circumferential direction, and in this embodiment, a second main groove 30 is formed that extends in the tire's circumferential direction while repeatedly bending in the tire's axial direction.

[0011] The tread 10 has a trapezoidal center block 40 in plan view. Multiple center blocks 40 are formed at intervals in the circumferential direction of the tire, at the center of the tread 10 in the tire axial direction. The tread 10 further has a first quarter block 50, a second quarter block 70, a first shoulder block 60, and a second shoulder block 80. The tread 10 also has a groove-like recess 55 formed between the center block 40 and the first quarter block 50, and a sub-groove 75 formed between the first shoulder block 60 and the second quarter block 70.

[0012] The pneumatic tire 1 is, for example, a tire with a specified mounting direction for a vehicle. The tread 10 has a tread pattern that is asymmetrical about the tire equator CL (see FIG. 2), and the mounting direction of the pneumatic tire 1 on the vehicle is opposite between the right and left sides of the vehicle. The equator CL means a line along the tire circumferential direction passing exactly through the center in the tire axial direction of the tread 10. The pneumatic tire 1 is preferably mounted on the vehicle such that the first shoulder block 60 is positioned on the inner side of the vehicle. In this specification, the terms "left and right" are used for convenience of explanation, and these left and right mean the left and right in the traveling direction of the vehicle with the tire mounted on the vehicle.

[0013] The pneumatic tire 1 includes a pair of sidewalls 11 bulging outward in the tire axial direction and a pair of beads 12. The bead 12 is a portion fixed to the rim of the wheel and has a bead core 17 and a bead filler 18. The sidewall 11 and the bead 12 are formed annularly along the tire circumferential direction and constitute the side surface of the pneumatic tire 1. The sidewall 11 extends in the tire radial direction from both ends in the tire axial direction of the tread 10.

[0014] A side rib 13 may be formed in the pneumatic tire 1 between the ground contact ends E1, E2 of the tread 10 and the portion that protrudes most outward in the tire axial direction of the sidewall 11. The ground contact end E1 is the ground contact end on the side of the first shoulder block 60, and the ground contact end E2 is the ground contact end on the side of the second shoulder block 80. The side rib 13 protrudes outward in the tire axial direction and is formed annularly along the tire circumferential direction. The portion from the ground contact ends E1, E2 of the pneumatic tire 1 or the vicinity thereof to the left and right side ribs 13 is also called the shoulder or the battless region.

[0015] The tread 10 and the sidewall 11 are generally made of different types of rubber. The shoulder may be made of the same rubber as the tread 10 or may be made of different rubber. In this specification, the grounding ends E1, E2 are defined as the two axial ends of the region that contacts the flat road surface when a predetermined load is applied to the unused pneumatic tire 1 mounted on the regular rim and filled with air to reach the regular internal pressure. In the case of a passenger car tire, the predetermined load is a load corresponding to 88% of the regular load.

[0016] Here, the "regular rim" is the rim defined by the tire standard. In the case of JATMA, it is the "standard rim"; in the case of TRA and ETRTO, it is the "Measuring Rim". The "regular internal pressure" is the "maximum air pressure" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO. The regular internal pressure is usually 180 kPa for passenger car tires, but 220 kPa for tires marked Extra Load or Reinforced. The "regular load" is the "maximum load capacity" in the case of JATMA, the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO. In the case of a racing kart tire, the regular load is 392 N.

[0017] The pneumatic tire 1 includes a carcass 14, a belt 15, and an inner liner 16. The carcass 14 is a cord layer coated with rubber and forms the framework of the pneumatic tire 1 that withstands loads, impacts, air pressure, etc. The belt 15 is a reinforcing belt disposed between the rubber constituting the tread 10 and the carcass 14. The belt 15 strongly tightens the carcass 14 to increase the rigidity of the pneumatic tire 1. The inner liner 16 is a rubber layer provided on the inner peripheral surface of the carcass 14 and holds the air pressure of the pneumatic tire 1.

[0018] When a pneumatic tire 1 is used as a directional tire with a specified mounting direction relative to the vehicle, it is preferable that the pneumatic tire 1 has an indication for showing the mounting direction relative to the vehicle. The indication for the mounting direction may be an arrow or the like indicating the main rotation direction of the tire, and its configuration is not particularly limited. Generally, a symbol called a serial is provided on the side of the pneumatic tire 1, but a serial may also be used as an indication for showing the mounting direction.

[0019] The serial number includes information such as the size code, manufacturing date (year and week), and manufacturing location (factory code). The mounting direction of the pneumatic tire 1 to the vehicle may be specified by providing the serial number only on the side (sidewall 11) facing outwards from the vehicle, or by providing different serial numbers on the side facing outwards and the side facing inwards from the vehicle. A specific example is to provide the factory code and size code on both sides of the pneumatic tire 1, and the year and week of manufacture only on the side facing outwards from the vehicle.

[0020] The tread pattern of the pneumatic tire 1 will be explained in detail below with reference to Figure 2. Figure 2 is a plan view of the pneumatic tire 1 (tread 10). In Figure 2, dot hatching is applied to the upper surface of each block. The upper surface of a block is the surface along the profile surface α (see Figure 4, etc.), and in the range from the contact edge E1 to E2, it becomes the contact surface that contacts the road surface. The profile surface α is the surface along the outer circumference of the tread 10.

[0021] As shown in Figure 2, the tread 10 has two main grooves 20, 30 extending in the circumferential direction of the tire, a groove-shaped depression 55 connected to the main groove 20, a secondary groove 75 extending from the axial center side of the tread 10 toward the contact end E1 side, and a plurality of blocks partitioned by each groove. The blocks are portions that protrude outward in the radial direction of the tire and are generally also called the tread blocks. The tread 10 has a center block 40, a first quarter block 50, a first shoulder block 60, a second quarter block 70, and a second shoulder block 80 as blocks.

[0022] The main groove 20 is formed between the center block 40 and the second shoulder block 80 on the contact end E2 side, and extends substantially straight along the circumferential direction of the tire. In this embodiment, on the equator CL, the center block 40 and the first quarter block 50 are alternately arranged in the circumferential direction of the tire via a recess 55. The second shoulder block 80 is a continuous block in the circumferential direction of the tire and is formed parallel to the main groove 20 with a constant width. The main groove 20 is formed in the tread 10 so as to separate the center block 40 and the first quarter block 50 from the second shoulder block 80.

[0023] The main groove 30 is formed between the center block 40 and the first shoulder block 60 on the contact end E1 side, and extends in the circumferential direction of the tire while repeatedly bending in the axial direction of the tire. In this embodiment, the first quarter block 50 and the second quarter block 70 are interposed between the center block 40 and the first shoulder block 60. The first quarter block 50 and the second quarter block 70 are continuous blocks in the circumferential direction of the tire, and extend in the circumferential direction of the tire while bending in the axial direction of the tire so as to avoid the center block 40 and the first shoulder block 60. The main groove 30 is formed in the tread 10 so as to separate the first quarter block 50 and the second quarter block 70.

[0024] The main groove 20 includes a portion containing a plurality of fine grooves 21 formed at predetermined intervals at the bottom of the groove, and comprises a first portion 23 arranged at intervals in the circumferential direction of the tire, and a second portion 24 where the plurality of fine grooves 21 are absent, and which is arranged alternately with the first portion 23 in the circumferential direction of the tire. The plurality of fine grooves 21 formed at predetermined intervals at the bottom of the groove have the function of reducing noise generated from the tire when the vehicle is running. By arranging the first portion 23 of the main groove 20 alternately with the second portion 24 at intervals in the circumferential direction of the tire, the noise reduction effect becomes more pronounced. In addition, the plurality of fine grooves 21 enhance the design by highlighting the shadows and also contribute to reducing the amount of rubber used.

[0025] The main groove 30, like the main groove 20, is provided with a first portion 33 which includes a plurality of fine grooves 31 formed at predetermined intervals at the bottom of the groove, and a second portion 34 which does not have the plurality of fine grooves 31. The main groove 30 is constructed by arranging the first portion 33 and the second portion 34 alternately in the circumferential direction of the tire. The first portion 33 contributes to reducing tire noise, improving design aesthetics, and reducing rubber usage. In this embodiment, the first portion 23 of the main groove 20 and the first portion 33 of the main groove 30 are arranged side by side in the axial direction of the tire. In this case, for example, the noise reduction effect becomes more pronounced, and the design becomes more cohesive, giving a sophisticated impression.

[0026] The tread 10 has a first shoulder block 60, a second quarter block 70, a first quarter block 50, a center block 40, and a second shoulder block 80 formed in order from the contact end E1 side. The center block 40 and the first shoulder block 60 are not continuous in the circumferential direction of the tire, but are formed in multiples with intervals in the circumferential direction of the tire. The first quarter block 50, the second quarter block 70, and the second shoulder block 80 are continuous blocks in the circumferential direction of the tire and are formed in an annular shape along the circumferential direction of the tire.

[0027] The center block 40 and the first shoulder block 60 are trapezoidal blocks in plan view, and are arranged in a single row at equal intervals in the circumferential direction of the tire. The first shoulder block 60 is formed at one axial end on the contact end E1 side of the tread 10 so as to alternate with the center block 40 in the circumferential direction of the tire. Parts of the center block 40 and parts of the first shoulder block 60 overlap in the circumferential direction of the tire, and the first quarter block 50, the second quarter block 70, and the main groove 30 are formed in a zigzag pattern between the center block 40 and the first shoulder block 60.

[0028] The center block 40 and the first shoulder block 60 are positioned so that the short and long sides, which form the base of the trapezoid, are aligned along the circumferential direction of the tire. That is, the hypotenuse of each block's trapezoid is inclined in the circumferential and axial directions of the tire. By arranging the trapezoidal blocks in this way, stable traction performance is achieved. The short and long sides of the trapezoid are also called the upper and lower bases, respectively. In addition, the short sides of the trapezoids of the center block 40 and the first shoulder block 60 are positioned towards the main groove 30. In this case, it becomes easy to arrange the center block 40 and the first shoulder block 60 regularly along the circumferential direction of the tire.

[0029] The center block 40 may be the same size as the first shoulder block 60, or it may be larger than the first shoulder block 60, but in this embodiment it is formed to be slightly smaller than the first shoulder block 60. As will be described in detail later, the first slope 41, the second slope 42, and the third slopes 43, 44 are formed along the short side, long side, and hypotenuse of the trapezoid of the center block 40, respectively. Similarly, a slope 61 is formed along the short side of the trapezoid of the first shoulder block 60.

[0030] The center block 40 is surrounded by a groove-shaped recess 55 and a main groove 20. The recess 55 is formed in a roughly U-shape in plan view along the slopes 41, 43, and 44, and together with the main groove 20 extending along the slope 42, it surrounds the center block 40. Each slope of the center block 40 constitutes part of the groove wall and groove bottom of the recess 55 and the main groove 20. Outside the recess 55, the first quarter block 50 is formed together with the center block 40, sandwiching the recess 55.

[0031] The first quarter block 50 includes a first zone 51 formed along a recess 55 so as to be convex in the direction of the contact edge E1, and a second zone 52 extending straight in the circumferential direction of the tire, with the first zone 51 and the second zone 52 alternating in shape. The main groove 30 is formed along the first quarter block 50, and the second quarter block 70 is formed opposite the first quarter block 50 across the main groove 30. The second quarter block 70, like the first quarter block 50, includes a first zone 71 formed so as to be convex in the direction of the contact edge E1, and a second zone 72 extending straight in the circumferential direction of the tire. The first zone 71 is formed between adjacent first shoulder blocks 60 in the circumferential direction of the tire and extends beyond the contact edge E1.

[0032] Sub-grooves 75 are formed in the tread 10 along the short and slanted sides of the trapezoid of the first shoulder block 60, enclosing three sides of the trapezoid. The sub-grooves 75 are formed in a roughly U-shape in plan view and divide the first shoulder block 60 and the second quarter block 70. The sub-grooves 75 extend axially outward from the equator CL side of the tread 10 and are formed beyond the contact end E1. In other words, the trapezoid of the first shoulder block 60 is formed by the contact end E1 and the sub-grooves 75 connected to the contact end E1.

[0033] Below, in addition to Figure 2, we will further explain each component of the tread pattern, referring to Figures 3 to 7 as appropriate. Figures 3, 6, and 7 show parts of the cross-sections along lines AA, BB, and CC in Figure 2, respectively. Figure 4 is an enlarged view of section F1 in Figure 3, and Figure 5 is an enlarged view of section F2 in Figure 3.

[0034] [Main groove 20,30] As shown in Figure 2, the main grooves 20 and 30 are formed on both sides of the equator CL and extend in the circumferential direction of the tire without intersecting the equator CL. The main grooves 20 and 30 are also formed to sandwich the center block 40 and the first quarter block 50, which are located in the center of the tread 10 in the axial direction of the tire, from both sides. As described above, the main groove 20 is formed in a nearly straight line along the circumferential direction of the tire, while the main groove 30 extends in a zigzag pattern along the circumferential direction of the tire. The depth of the main grooves 20 and 30 is not constant along the circumferential direction of the tire; for example, shallow and deep sections are regularly repeated. The deepest points of the main grooves 20 and 30 are deeper than the deepest points of the depressions 55 and the secondary grooves 75.

[0035] The main groove 20 has multiple fine grooves 21 formed at the bottom of the groove and is formed slightly wider than the second portion 24 in the first portion 23 which has a tire noise reduction function. The first portion 23 includes a first region 25a in which multiple fine grooves 21 are formed and a second region 25b which is inclined to gradually deepen toward the first region 25a. The first region 25a is formed adjacent to the second shoulder block 80 and the second region 25b is formed adjacent to the equatorial CL side of the first region 25a. The first region 25a is formed in a trapezoidal shape in plan view that is elongated along the main groove 20, with the base of the trapezoid parallel to the tire circumferential direction and the shorter side facing toward the equatorial CL side. The inclination angle of the second region 25b with respect to the profile surface α of the tread 10 is, for example, 30° to 70°.

[0036] Each first portion 23 of the main groove 20 is adjacent to the second zone 52 of the first quarter block 50, and each second portion 24 is adjacent to the center block 40. That is, the first portions 23 and 24 of the main groove 20 are formed along the tire circumferential direction with the same repeating unit length (pitch) as the block in the center of the tire axial direction of the tread 10. Similarly, the first portions 33 and 24 of the main groove 30 are formed with the same pitch as the block in the center of the tire axial direction of the tread 10.

[0037] The main groove 30 is wider than the second portion 34 in the first portion 33, where a plurality of narrow grooves 31 are formed at the bottom of the groove. The plurality of narrow grooves 31 are formed over the entire width of the main groove 30, and the first portion 33 as a whole is formed in a trapezoidal shape in plan view. The trapezoid of the first portion 33 has its base parallel to the tire circumferential direction and its short side facing the equator CL. The second portion 34 is a narrow groove portion that extends along the first zone 51 of the first quarter block 50 and is formed in a roughly U-shape in plan view so as to be convex toward the contact end E1.

[0038] The multiple narrow grooves 21, 31 may be formed in a random pattern with different groove widths and in different directions, for example, but it is preferable that they be formed somewhat regularly in order to exhibit a stable noise reduction effect and enhance the design. The narrow grooves 21, 31 may extend in directions intersecting the tire axial direction and circumferential direction, but in this embodiment they are formed along the tire axial direction or circumferential direction. Noise generated from the pneumatic tire 1 can be broadly classified into road noise and pattern noise. The narrow grooves 21, 31 reduce noise generated from the tire by shifting the frequency band of the pattern noise.

[0039] Multiple narrow grooves 21 are formed, for example, parallel to each other, and in the first portion 23, the narrow grooves 21 and the ribs 22, which are the portions sandwiched between the multiple narrow grooves 21, are alternately repeated to form an uneven structure at the bottom of the grooves (the same applies to the narrow grooves 31). As will be described in more detail later, the narrow grooves 21 and 31 extend in the axial direction of the tire at the center of the first portions 23 and 33 in the circumferential direction of the tire, and extend in the circumferential direction of the tire at both ends of the first portions 23 and 33 in the circumferential direction of the tire.

[0040] The first portion 23 of the main groove 20 and the first portion 33 of the main groove 30 are arranged side by side in the tire axial direction, separated by the second zone 52 of the first quarter block 50. The shorter side of the trapezoid of the first region 25a and the shorter side of the trapezoid of the first portion 33 face each other across the second zone 52. In plan view, the area of ​​the first region 25a is, for example, greater than or equal to the area of ​​the first portion 33, and less than or equal to 1.3 times the area of ​​the first portion 33. The second portion 24 of the main groove 20 and the second portion 34 of the main groove 30 are also arranged side by side in the tire axial direction, separated by the center block 40, the recess 55, and the first quarter block 50.

[0041] As shown in Figures 3 to 5, the second portion 24 of the main groove 20 has a slope 26 that gradually deepens toward the ground contact end E1, and a side groove 27 that extends along the second shoulder block 80. The side groove 27 extends straight in the circumferential direction of the tire and, like the second portion 34 of the main groove 30, is formed to be narrow and deep. In this embodiment, the bottom of the side groove 27 and the bottom of the narrow groove 21 are formed to the same depth, forming the deepest part of the main groove 20. Similarly, the bottom of the narrow groove 31 of the main groove 30 and the bottom of the second portion 34 are formed to the same depth, forming the deepest part of the main groove 30.

[0042] The depth of the second section 24 gradually increases from the center block 40 side toward the second shoulder block 80 side. The inclined surface 42 of the center block 40 that forms the groove wall of the second section 24 is inclined at an angle θ2 with respect to the profile surface α. The inclined surface 26 is inclined at an angle θ5 with respect to a surface β parallel to the profile surface α and is formed with a width exceeding 50% of the width of the second section 24, extending from the lower end of the inclined surface 42 to the side groove 27. An example of the width of the inclined surface 26 is 50% to 95%, or 60% to 90%, of the width of the second section 24.

[0043] The slope 26 of the second part 24 is formed in continuity with the second region 25b of the first part 23. As described above, the second region 25b is a slope that gradually deepens toward the first region 25a, where multiple narrow grooves 21 are formed. The inclination angle θ5 of the slope 26 is smaller than the inclination angle θ2 of the slope 42, and also smaller than the inclination angle of the second region 25b. The slope of the second region 25b gradually becomes gentler toward the slope 26, for example.

[0044] As shown in Figure 7, in the first sections 23 and 33, the narrow grooves 21 and 31 are formed to the same depth, and the ribs 22 and 32 are formed to the same height. The tread 10 is provided with a wear indicator (not shown). The wear indicator is a projection located at the bottom of at least one of the main grooves 20 and 30, and is an indicator for checking the wear level of the tread rubber. The height of the ribs 22 and 32 is preferably less than or equal to the height of the wear indicator, and is particularly preferably equal to the height of the wear indicator. In this case, even if the tread rubber wears down to the height level of the wear indicator, the noise reduction function, i.e., the uneven structure at the bottom of the grooves, can be ensured.

[0045] [Center Block 40] As shown in Figure 2, the center block 40 is a trapezoidal block in plan view, formed in the center of the tread 10 in the axial direction of the tire, and has slopes along each side of the trapezoid. The center block 40 only needs to have a trapezoidal top surface (contact surface). The trapezoid includes those that are substantially recognizable as trapezoids, and may, for example, be a roughly trapezoid with rounded corners. The center block 40 is positioned so that the short side of the trapezoid faces the contact end E1 and the long side faces the contact end E2, and the short and long sides are parallel to the circumferential direction of the tire. The long side of the trapezoid of the center block 40 is located closer to the equator CL than the short side.

[0046] The trapezoidal sides of the center block 40 are inclined with respect to the tire circumferential direction and the axial direction. The two inclined sides of the trapezoid are inclined away from each other with respect to the tire axial direction, from the contact end E1 side to the contact end E2 side, but for example, the angle of inclination of each inclined side with respect to the tire axial direction is the same, and the length of each inclined side is also the same. Third inclined surfaces 43 and 44 are formed at both ends of the center block 40 in the tire circumferential direction, along the trapezoidal sides. The inclined surfaces 43 and 44 are formed to be the same size as each other.

[0047] As described above, the center blocks 40 are arranged in a single line at equal intervals in the circumferential direction of the tire. Here, equal intervals include not only perfectly equal intervals but also cases where they are considered to be substantially equal intervals. By arranging the center blocks 40 at equal intervals, stable traction performance can be ensured. The distance between adjacent center blocks 40 in the circumferential direction of the tire (the shortest distance between the slope 43 of the first center block 40 and the slope 44 of the second center block 40) is, for example, longer than the length of the shorter side of the trapezoid of the center block 40 and shorter than the length of the longer side of the trapezoid. An example of the number of center blocks 40 along the circumferential direction of the tire is 20 to 30.

[0048] As shown in Figures 4 to 6, the inclination angles of each slope with respect to the profile surface α along the outer circumference of the tread 10 gradually increase in the order of the third slope 43, 44, the first slope 41, and the second slope 42 (θ3, θ4 < θ1 < θ2). The inclination angles θ3 and θ4 of the slopes 43 and 44 with respect to the profile surface α may be different from each other, but in this embodiment they are the same. That is, the slopes 43 and 44 facing in the circumferential direction of the tire have a gentle slope, while the slopes 41 and 42 facing in the axial direction of the tire have a steep slope. In this case, traction performance can be improved while ensuring good ride comfort. In particular, by increasing the inclination angle θ2 of the slope 42 facing outward from the vehicle, for example, cornering power (CP) can be improved.

[0049] The inclination angle θ1 of the slope 41 with respect to the profile surface α is preferably 30° to 70°, and more preferably 40° to 60°. The inclination angle θ2 of the slope 42 with respect to the profile surface α is preferably 60° to 80°, and more preferably 65° to 75°. The inclination angle θ3 of the slope 43 with respect to the profile surface α is preferably 20° to 50°, and more preferably 25° to 45°. If the inclination angles of each slope of the center block 40 are within these ranges, good ride comfort and traction performance can be more effectively achieved.

[0050] [First Quarter Blocks: 50] As shown in Figure 2, the first quarter block 50 is formed to surround three sides of the center block 40, separated by a recess 55, and is continuous in the circumferential direction of the tire along the main groove 30. The first zone 51 of the first quarter block 50 is formed in a narrow strip shape with a certain width and extends along the trapezoidal short side and two hypotenuses of the center block 40, separated by the recess 55. The first zone 51 is formed in a roughly U-shape in plan view, convex toward the contact end E1. The second zone 52 of the first quarter block 50 extends along the circumferential direction of the tire between each center block 40 and connects the two first zones 51.

[0051] The height of the first quarter block 50 is preferably less than or equal to the height of the center block 40 and higher than the height of the wear indicator. In this specification, the height of the block means the shortest distance from the reference plane of the tread 10 along the deepest part of the main grooves 20, 30 to the top surface of the block (the same applies to the wear indicator). In this embodiment, the first quarter block 50 is formed to the same height as the center block 40, and the top surface of the first quarter block 50 is the contact surface that contacts the road surface.

[0052] As shown in Figures 3 and 4, the first zone 51 of the first quarter block 50 is sandwiched between the main groove 30 and the recess 55. By providing the first quarter block 50 between the main groove 30 and the recess 55, the overall block rigidity of the tread 10 can be increased while ensuring good drainage. In addition, the contact area is increased, improving, for example, traction performance and braking performance. The width of the first zone 51 is not particularly limited, but in this embodiment, it is narrower than the width of the recess 55 and wider than the width of the second portion 34 of the main groove 30.

[0053] As shown in Figure 6, along the equator CL of the tread 10, the second zone 52 of the center block 40 and the first quarter block 50 are alternately arranged with a depression 55 in between, along the circumferential direction of the tire. The length of the center block 40 along the circumferential direction of the tire is longer on the main groove 20 side and shorter on the main groove 30 side, while the length of the second zone 52 along the circumferential direction of the tire is shorter on the main groove 20 side and longer on the main groove 30 side. Furthermore, along the equator CL, the length of the center block 40 along the circumferential direction of the tire is longer than the length of the second zone 52 along the circumferential direction of the tire.

[0054] As shown in Figure 7, the second zone 52 of the first quarter block 50 is sandwiched from both sides in the tire axial direction by the first portions 23 and 33, which have wider main grooves 20 and 30. In the first portions 23 and 33, the distance between the main grooves 20 and 30 is minimized. The second zone 52 is formed to be wider than the first portions 23 and 33. In this case, the block rigidity of the tread 10 can be increased in the portion where the width of the two main grooves is widened and close together, and the durability of the block can be effectively improved. Furthermore, the second zone 52 is reinforced by the ribs 22 and 32 formed in the first portions 23 and 33.

[0055] [Indentation 55] As shown in Figure 2, the depression 55 is formed between the center block 40 and the first quarter block 50, surrounding the center block 40 on three sides like a trench. The depression 55 extends in a groove-like manner along the short and slanted sides of the trapezoidal shape of the center block 40, and is formed in a roughly U-shape in plan view. Both ends of the depression 55 on the contact end E2 side are in communication with the main groove 20, allowing rainwater and other fluids around the center block 40 to flow into the main groove 20. The depression 55 is wider along the slanted side than along the short side of the trapezoidal shape of the center block 40, and its width gradually widens as it approaches the main groove 20. In this case, the drainage performance at the center of the tread 10 in the tire axial direction is improved.

[0056] The depression 55 extends from the main groove 20 toward the contact end E1 and is formed in a position that overlaps with the secondary groove 75 in the circumferential direction of the tire. The secondary groove 75 is formed at one end of the tread 10 in the axial direction of the tire, spaced apart in the circumferential direction of the tire, and the depression 55 is formed to fit between adjacent secondary grooves 75 in the circumferential direction of the tire. By arranging the depression 55 and the secondary groove 75 to overlap in the circumferential direction of the tire, drainage performance can be more effectively enhanced.

[0057] As shown in Figures 3, 4, and 6, the depth of the recess 55 is shallower than the main grooves 20 and 30, and gradually deepens as it approaches the main groove 20. In this case, drainage can be improved while ensuring the durability of the center block 40 and the first quarter block 50. Furthermore, the depth of the recess 55 in the width direction gradually deepens along the trapezoidal slope of the center block 40, and is deepest at the lower end of the slope. Preferably, the recess 55 is formed deeper than the upper surface of the wear indicator at its shallowest point.

[0058] [First shoulder block 60] As shown in Figure 2, the first shoulder block 60 is a trapezoidal block in plan view formed at the axial end of the tread 10, and has a slope 61 along at least its short side. The pneumatic tire 1 is preferably mounted on the vehicle such that the first shoulder block 60 is located on the inside of the vehicle. The first shoulder block 60 only needs to have a shape in which the contact surface is substantially recognized as trapezoidal. The short side and slope of the trapezoid of the first shoulder block 60 are formed by sub-grooves 75, and the contact end E1 is the long side of the trapezoid.

[0059] The first shoulder block 60 is positioned with its trapezoidal shape, with the shorter side facing the equator CL, and its shorter and longer sides parallel to the tire's circumferential direction. The hypotenuse of the trapezoid of the first shoulder block 60 is inclined with respect to the tire's circumferential and axial directions, similar to the case of the center block 40. The two hypotenuses of the trapezoid are inclined to move away from each other with respect to the tire's axial direction, from the equator CL towards the contact end E1, but for example, the angle of inclination of each hypotenuse with respect to the tire's axial direction is the same, and the length of each hypotenuse is also the same. A slope may be formed along the hypotenuse of the trapezoid of the first shoulder block 60.

[0060] The first shoulder blocks 60 are positioned between adjacent center blocks 40 in the circumferential direction of the tire, overlapping with the center blocks 40 in the circumferential direction of the tire. In this case, the overall block rigidity of the tread 10 can be increased, resulting in stable block durability and traction performance. The contact area of ​​the first shoulder blocks 60 may be larger than that of the center blocks 40, for example, 1.1 to 1.5 times. The same number of first shoulder blocks 60 are formed in the circumferential direction of the tire at the same pitch as the center blocks 40.

[0061] As shown in Figure 7, the inclined surface 61 along the trapezoidal short side of the first shoulder block 60 may be formed to a depth equal to or greater than that of the ribs 22 and 32 of the main grooves 20 and 30. The inclined surface 61 forms the groove wall and groove bottom of the secondary groove 75, and the depth of the secondary groove 75 is greatest at the lower end of the inclined surface 61. The inclination angle of the inclined surface 61 with respect to the profile surface α may be greater than the inclination angle of the second region 25b of the main groove 20 and less than the inclination angle θ2 of the inclined surface 42 of the center block 40. By increasing the inclination angle of the inclined surface 61 facing outward from the vehicle, for example, the CP characteristics can be improved.

[0062] [70 blocks in the second quarter] As shown in Figure 2, the second quarter block 70 is formed to surround the first shoulder block 60 on three sides, separated by a sub-groove 75. Similar to the first quarter block 50, it is formed along the main groove 30 and is continuous in the circumferential direction of the tire. The first zone 71 of the second quarter block 70 extends from the equator CL side towards the contact edge E1 side, entering between adjacent first shoulder blocks 60 in the circumferential direction of the tire, and extending beyond the contact edge E1. The second zone 72 of the second quarter block 70 extends along the circumferential direction of the tire between each center block 40, connecting the two first zones 71.

[0063] The height of the second quarter block 70 is the same as that of the center block 40, the first shoulder block 60, etc., and the upper surface of the second quarter block 70 is the contact surface that contacts the road surface. The first zone 71 of the second quarter block 70 includes a first portion that expands so that the tire circumferential length gradually increases from the contact end E1 side toward the equator CL side, and a second portion that branches into two along the main groove 30 from the first portion.

[0064] As shown in Figure 7, the second zone 72 of the second quarter block 70 is the portion sandwiched between the first portion 33 and the sub-groove 75 of the main groove 30, and is formed parallel to the second zone 52 of the first quarter block 50. The width of the second zone 72 is, for example, equivalent to the width of the sub-groove 75, and narrower than the width of the first portion 33. In this embodiment, the second zones 52 and 72 are connected by the ribs 32 of the first portion 33. Furthermore, the side walls of the second zone 72 that form the groove walls and groove bottom of the sub-groove 75 are gently inclined toward the first shoulder block 60. Therefore, high durability of the block can be ensured even in the portion where the groove width is widened.

[0065] [Sub-groove 75] As shown in Figure 2, the sub-grooves 75 extend along the short and slanted sides of the trapezoid of the first shoulder block 60 and are formed in a roughly U-shape in plan view. The sub-grooves 75 are wider than other parts between the short side of the trapezoid and the second quarter block 70. The sub-grooves 75 are formed at equal intervals in the circumferential direction of the tire, are not connected in the circumferential direction of the tire, and are not connected to the main grooves 30. Furthermore, the sub-grooves 75 extend from the axial center of the tread 10 to a position beyond the contact edge E1, allowing rainwater and other liquids to be easily drained from this center. In this case, good drainage can be achieved while ensuring high block rigidity.

[0066] In this embodiment, as described above, a portion of the recess 55 and a portion of the sub-groove 75 overlap in the circumferential direction of the tire, and the recess 55 and sub-groove 75 are formed to be arranged alternately in the circumferential direction of the tire. That is, the recess 55 and sub-groove 75 are arranged in a staggered pattern along the circumferential direction of the tire, similar to the arrangement of the center block 40 and the first shoulder block 60. In addition, a main groove 30 is formed between the recess 55 and the sub-groove 75 via the first quarter block 50 and the first shoulder block 60. This makes it easy to achieve both high block rigidity and good drainage.

[0067] As shown in Figure 7, in the portion of the sub-groove 75 where the width is increased, that is, the portion located between the trapezoidal short side of the first shoulder block 60 and the second quarter block 70, slopes are formed from both sides in the width direction of the sub-groove 75 toward the groove bottom. These slopes are the slope 61 formed along the short side of the first shoulder block 60 and the side wall of the second zone 72 of the second quarter block 70. The slope 61 has a larger angle of inclination with respect to the profile surface α than the side wall of the second zone 72.

[0068] [Second shoulder block 80] As shown in Figure 2, the second shoulder block 80 is formed at the other end of the tread 10 in the tire axial direction, extending from a position adjacent to the main groove 20 to a position beyond the contact edge E2. In Figure 2, the groove in the second shoulder block 80 is not shown, but for example, a groove extending in the tire axial direction may be formed. The groove shape formed in the second shoulder block 80 is not particularly limited. As described above, the second shoulder block 80 is formed parallel to the main groove 20 with a constant width.

[0069] Figure 8 shows a portion of the tire circumferential cross-section (cross-section along line DD in Figure 2) of the first portion 23 of the main groove 20. The cross-sectional structure of the first portion 33 of the main groove 30 is the same as the cross-sectional structure shown in Figure 8.

[0070] As shown in Figure 8, in the first portion 23 (first region 25a) of the main groove 20, multiple fine grooves 21 are formed at predetermined intervals at the bottom of the groove, creating a groove bottom uneven shape in which the fine grooves 21 and ribs 22 are arranged alternately. The multiple fine grooves 21 formed at predetermined intervals shift the frequency band of pattern noise, reducing noise generated from the tire, and also enhance the shadows in terms of design, giving a more sophisticated impression. Furthermore, it contributes to reducing the amount of rubber used.

[0071] An example of the depth Dp of the narrow groove 21 is 0.5 mm to 2 mm. In other words, the depth Dp of the narrow groove 21 is the height of the rib 22 from the bottom of the narrow groove 21. The upper surface of the rib 22 is formed to a depth similar to that of the inclined surface 26 of the second portion 24 of the main groove 20, and can be called the first groove bottom of the main groove 20. The upper surface of the rib 22 may be inclined similarly to the second region 25b, but in this embodiment, it is formed parallel to the profile surface α. The bottom of the narrow groove 21 is to a depth similar to that of the bottom of the side groove 27 of the second portion 24, and can be called the second groove bottom. That is, the main groove 20 is formed to a depth of at least two stages.

[0072] The widths of the multiple narrow grooves 21 may differ from one another, but in this embodiment, each narrow groove 21 is formed with the same width W. An example of the width of the narrow groove 21 is 0.1 mm to 0.5 mm. The width of the rib 22 may be less than or equal to the width W of the narrow groove 21, but in this embodiment, it is greater than the width W of the narrow groove 21. The rib 22 may include a first rib 22a with a width W1 and a second rib 22b with a width W2, and may include three or more types of ribs with different widths. Alternatively, the width of each rib 22 may be the same. From the viewpoint of design, block durability, etc., a suitable example of a groove bottom uneven structure is a structure in which the spacing of the narrow grooves 21 is uniform (the width of the rib 22 is constant) and the width of the rib 22 is greater than the width of the narrow groove 21.

[0073] The side walls of the rib 22 (groove walls of the narrow grooves 21) are inclined so that they widen towards the lower end of the rib 22. The inclination angles θa and θb of the side walls with respect to a virtual line perpendicular to the bottom of the narrow groove 21 are, for example, 1° or more, preferably 1° to 5°. The lower end portion of the side wall of the rib 22 may also be curved toward the inside of the rib 22. When the rib 22 has such a side wall shape, it can be easily released from the mold during tire manufacturing. In addition, the multiple narrow grooves 21 may be formed at a distance from the side walls of the main groove 20 that corresponds to at least 10% of the groove width, as shown in Figure 14 described later.

[0074] Figures 9 and 10 are enlarged views of the first portion 33 of the main groove 30. In Figures 9 and 10, dot hatching is applied to the upper surface of the rib 32 for clarity. The following description can also be applied to the first portion 23 of the main groove 20. As described above, the multiple fine grooves 31 formed at the bottom of the groove extend in the axial direction of the tire at the center of the first portion 33 in the circumferential direction of the tire, and extend in the circumferential direction of the tire at both ends of the first portions 23 and 33 in the circumferential direction of the tire. In this case, the frequency band of pattern noise can be shifted more effectively, and the noise reduction effect becomes more pronounced. It also gives a novel and sophisticated impression in terms of design.

[0075] In the example shown in Figure 9, the groove bottom is formed with a narrow groove 31a extending in the tire axial direction, a narrow groove 31b extending in the tire circumferential direction, and a narrow groove 31c that is bent midway. The narrow groove 31c has a bent portion that is turned at a right angle midway, and includes a portion that extends in the tire circumferential direction and a portion that extends in the tire axial direction. Two narrow grooves 31b and one narrow groove 31c are formed at both ends of the first portion 33 in the tire circumferential direction. As shown in Figure 10, the first portion 33 may have only narrow grooves 31a extending in the tire axial direction and narrow grooves 31b extending in the tire circumferential direction, and may not have a narrow groove 31c with a bent portion.

[0076] The narrow grooves 31a are formed parallel to each other and of the same width. In the center of the first section 33 in the tire circumferential direction, there is a rib 32a at the center, and two ribs 32b, which are slightly narrower than the rib 32a, are formed on each side in the tire circumferential direction. Note that the width of each rib may be the same, and the narrow grooves 31a may be arranged at equal intervals. At both ends of the first section 33 in the tire circumferential direction, there is a rib 32c which is formed by connecting a rib portion that extends in the tire axial direction with multiple rib portions that extend in the tire circumferential direction, and forming a comb-like structure overall.

[0077] As described above, the pneumatic tire 1 has a highly aesthetic design and generates little noise during vehicle operation. Multiple fine grooves 21, 31 formed at predetermined intervals at the bottom of the main grooves 20, 30 accentuate the shadows, giving a novel and sophisticated impression, while also effectively shifting the frequency band of pattern noise and reducing noise generated from the tire. Furthermore, by arranging the first sections 23, 33 and the second sections 24, 34, which have multiple fine grooves 21, 31 formed thereon, alternately in the circumferential direction of the tire, the noise reduction effect becomes even more pronounced.

[0078] The tread pattern of the pneumatic tire 1 features an aggressive and innovative design, while also achieving high block durability and excellent traction performance. For example, the pneumatic tire 1 also has good water drainage and excellent wet grip performance.

[0079] The above-described embodiments can be modified as appropriate without impairing the objectives of the present invention. For example, as shown in Figure 11, the groove bottom structure for noise reduction may be formed only by a plurality of narrow grooves 21x, 31x extending in the tire axial direction. In the first portion 23x (first region 25x) of the main groove 20x, narrow grooves 21x and ribs 22x extending in the tire axial direction are arranged alternately, and the narrow grooves 21x are arranged at equal intervals along the tire circumferential direction. Similarly, in the first portion 33x of the main groove 30x, narrow grooves 31x extending in the tire axial direction and ribs 32x are formed alternately in the tire circumferential direction along its entire length.

[0080] As shown in Figure 12, the groove bottom structure for noise reduction may be formed only by a plurality of narrow grooves 21x, 31x extending in the circumferential direction of the tire. In the first portion 23y (first region 25y) of the main groove 20y, narrow grooves 21y and ribs 22y extending in the circumferential direction of the tire are alternately arranged in the axial direction of the tire. Similarly, in the first portion 33y of the main groove 30y, narrow grooves 31y and ribs 32y extending in the circumferential direction of the tire are alternately formed in the axial direction of the tire along its entire length.

[0081] Furthermore, the tread according to the present invention may have main grooves formed that include two or more of the fine groove formation patterns described above. In the main groove 20z shown in Figure 13, the first portion 23x (first region 25x) shown in Figure 11 and the first portion 23y (first region 25y) shown in Figure 12 are alternately formed in the tire circumferential direction via the second portion 24. Similarly, in the main groove 30z, the first portion 33x and the first portion 33y are alternately formed in the tire circumferential direction via the second portion 34. In the example shown in Figure 13, the first region 25x and the first portion 33y are aligned in the tire axial direction, and the first region 25y and the first portion 33x are aligned in the tire axial direction, but the combination of arrangements of the fine groove formation patterns is not limited to this.

[0082] In the first portion 33z of the main groove illustrated in Figure 14, multiple narrow grooves 31z are formed at intervals corresponding to at least 10% of the groove width from the side wall of the main groove. In the example shown in Figure 14, on both sides of the narrow groove 31z in the tire axial direction, a gap of a length corresponding to 10% of the width A of the main groove is provided between the narrow groove 31z and the side wall of the main groove. In this case, the durability of the block is further improved. The rib 32z is connected in the circumferential direction of the tire. [Explanation of Symbols]

[0083] 1 pneumatic tire, 10 tread, 11 sidewall, 12 bead, 13 side rib, 14 carcass, 15 belt, 16 inner liner, 17 bead core, 18 bead filler, 20,30 main groove, 21,31 minor groove, 22,32 rib, 22a first rib, 22b second rib, 23,33 first section, 24,34 second section, 25a first area, 25b second area, 26,41,42,43,44,61 slope, 27 side groove, 40 center block, 50 first quarter block, 51,71 first zone, 52,72 second zone, 55 depression, 60 first shoulder block, 70 second quarter block, 75 secondary groove, 80 second shoulder block, CL equator, E1,E2 contact point

Claims

1. A pneumatic tire having a tread formed with a first main groove extending in the circumferential direction of the tire, The first main groove is, A portion including a plurality of fine grooves formed at predetermined intervals at the bottom of the groove, comprising a first portion arranged at intervals in the circumferential direction of the tire, In the portion where the aforementioned plurality of fine grooves are absent, a second portion is arranged alternately with the first portion in the circumferential direction of the tire, Includes, A pneumatic tire wherein the first portion of the first main groove includes a first region in which the plurality of fine grooves are formed and a second region that is inclined to gradually deepen toward the first region.

2. The pneumatic tire according to claim 1, wherein the second portion of the first main groove is sloped to gradually deepen toward the contact edge of the tread, and has a continuous slope with the second region of the first portion.

3. The aforementioned tread is A center block formed in the axial center of the tread, A second main groove is formed to sandwich the center block together with the first main groove and extends in the circumferential direction of the tire, It has, The pneumatic tire according to claim 1 or 2, wherein the second main groove includes the first portion and the second portion arranged alternately in the circumferential direction of the tire.

4. The pneumatic tire according to claim 3, wherein the first portion of the first main groove and the first portion of the second main groove are arranged side by side in the tire axial direction.

5. The tread has a wear indicator, The pneumatic tire according to any one of claims 1 to 4, wherein the height of the portion sandwiched between the plurality of narrow grooves is less than or equal to the height of the wear indicator.

6. The pneumatic tire according to any one of claims 1 to 5, wherein the plurality of fine grooves are formed at intervals corresponding to at least 10% of the groove width from the side walls of each main groove.

7. The pneumatic tire according to any one of claims 1 to 6, wherein the plurality of fine grooves extend in the tire axial direction at the longitudinal center of the first portion and extend in the tire circumferential direction at both longitudinal ends of the first portion.

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