Pneumatic tire

Abstract

To restrain a tire from being damaged by enhancement of envelop property and heat evolution restraint of a tread.SOLUTION: A pneumatic tire 2 includes three pieces of belt plies 54. A tread 4 includes a base part 34 and a cap part 36. The base part 34 includes low heat evolution property. The tread 4 has three or more land parts 33. In the land part 33, a radially outermost position of a boundary surface between the cap part 36 and the base part 34 is located on the radially outer side more than 50% of height of the land part 33. The belt ply 54 which is located on the radially inner side includes a first division belt ply 541 and a second division belt ply 542 divided into two in an axial direction. Size BI therebetween is 25% or more and 40% or less of size BO between the end of the axial outside of the first division belt ply 541 and the end of the axial outside of the second division belt ply 542. The radially outermost belt ply 54 is located in an overlapping arrangement with a part of the first division belt ply 541 and a part of the second division belt ply 542.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Pneumatic tires are required to have the following performance characteristics: enveloping property and cut resistance. These performance characteristics are particularly required for pneumatic tires for running on rough terrain. For example, in the case of the pneumatic tire disclosed in Patent Document 1, it is proposed that the product of the bending rigidity of the steel cords in each of the radially inner (lower side) and radially outer (upper side) belt plies and the number of such cords is used as a parameter to ensure each performance of the tire. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-287105 Summary of the Invention [Problem to be solved by the invention]

[0004] Efforts to reduce tire damage by improving the performance of pneumatic tires, such as their envelope properties, are being made from various perspectives. An object of the present invention is to provide a pneumatic tire that can reduce damage to the tire by improving the enveloping properties and heat generation suppression of the tread. [Means for solving the problem]

[0005] The pneumatic tire according to the present invention has a tread that comes into contact with a road surface, and a belt that includes three or more belt plies and is located radially inward of the tread, the tread has a base portion and a cap portion that covers the base portion, the base portion is made of a crosslinked rubber that has a lower heat generation property than the cap portion, two or more grooves are engraved in the tread along a circumferential direction, the tread has three or more land portions provided along a circumferential direction, and in at least one of the land portions, the radially outermost position of the interface between the cap portion and the base portion is a front The belt ply located radially outward and radially inward from the 50% position of the height of the land portion has a first divided belt ply and a second divided belt ply divided in two in the axial direction, the dimension between the first divided belt ply and the second divided belt ply is 25% or more and 40% or less of the dimension between the axially outer end of the first divided belt ply and the axially outer end of the second divided belt ply, and the radially outermost belt ply is arranged to overlap with an axially inner part of the first divided belt ply and an axially inner part of the second divided belt ply. Effect of the Invention

[0006] According to the pneumatic tire of the present invention, the enveloping property and heat generation suppression of the tread are improved, making it possible to suppress damage to the tire. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a pneumatic tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of a portion of the cross section shown in FIG. [Diagram 3] FIG. 2 is a cross-sectional view showing a first side in the axial direction of the tread and its surroundings. [Figure 4] FIG. 11 is a cross-sectional view showing a modified example of the base portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Details of the embodiment of the present invention] The present invention will now be described based on preferred embodiments with reference to the drawings.

[0009] The pneumatic tire of the present invention (hereinafter also simply referred to as "tire") is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire mounted on the rim is also called a tire-rim assembly. The tire-rim assembly has a rim and a tire mounted on the rim.

[0010] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state.

[0011] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part of the tire in the meridian section that cannot be measured when the tire is mounted on a regular rim are measured on the tire section obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads is the same as the distance between the beads on the tire mounted on a regular rim. The tire configuration that cannot be confirmed when the tire is mounted on a regular rim is confirmed on the aforementioned section.

[0012] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0013] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0014] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0015] The tire has a tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion is the portion of the tire that comes into contact with the road surface, the bead portion is the portion of the tire that fits onto the rim, and the sidewall portion is the portion of the tire that connects between the tread and the bead.

[0016] In the present invention, the loss tangent (tan δ) and complex modulus of the element made of crosslinked rubber among the elements constituting the tire are measured using a viscoelasticity spectrometer in accordance with the provisions of JIS K 6394. The measurement conditions are as follows. Initial distortion = 10% Dynamic distortion = ±1% Frequency = 10Hz Mode = Decompression mode Temperature=70℃

[0017] For the above measurement, a test piece (length 40 mm x width 4 mm x thickness 1 mm) is sampled from the tire. The length direction of the test piece is aligned with the circumferential direction of the tire. If the test piece cannot be sampled from the tire, the test piece is sampled from a sheet-like crosslinked rubber (rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the loss tangent and the complex modulus are expressed as the loss tangent and the complex modulus at 70°C.

[0018] [Details of the embodiment of the present invention] Fig. 1 shows a part of a pneumatic tire 2 (hereinafter, also simply referred to as "tire 2") according to one embodiment of the present invention. The tire 2 is a pneumatic tire for heavy loads mounted on heavy vehicles such as trucks or buses. Fig. 1 shows a cross section of a first axial side of the tire 2. In the cross section shown in Fig. 1, the omitted left side of the tire 2 (the side opposite to the first axial side) is defined as a second axial side.

[0019] FIG. 1 shows a portion of a cross section (referred to as a "meridian cross section") of a tire 2 taken along a plane including the rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. The axial direction includes not only the direction along the rotation axis of the tire 2, but also the direction parallel to the rotation axis. In each drawing, the axial direction is indicated by an arrow "AD" and the radial direction is indicated by an arrow "RD". Figure 2 shows an enlarged view of a portion of the cross-section shown in Figure 1. Figure 2 shows the tread 4 of a tire 2 and its surroundings.

[0020] 1 and 2, a dashed line CL extending in the radial direction represents the equatorial plane of the tire 2. A solid line BBL extending in the axial direction in Fig. 1 is a bead base line. The bead base line is a line that defines the rim diameter of the rim (see JATMA, etc.).

[0021] The tire 2 has a tread 4, a pair of sidewalls 6, a pair of chafers 8, a pair of beads 10, a carcass 12, a belt 14, a pair of cushion layers 16, a strip layer 18, a pair of steel reinforcing layers 20, a pair of interlayer strips 22, an inner liner 24, and a pair of fiber reinforcing layers 26.

[0022] The tread 4 is located radially outward of the carcass 12. The tread 4 comes into contact with the road surface at a tread surface 30. Two or more grooves 32 are cut in the tread 4 along the circumferential direction, and the tread 4 has three or more land portions 33 provided along the circumferential direction. In the case of the embodiment shown in Figures 1 and 2, three grooves 32 are provided in the tread 4, and the tread 4 has four land portions 33 extending in the circumferential direction.

[0023] The tread 4 has one center groove 321 located across the equatorial plane, and two shoulder grooves 322 located on both sides in the axial direction. The center groove 321 and the shoulder grooves 322 are circumferential grooves that are continuous in the circumferential direction, and in this embodiment, are zigzag grooves. The zigzag groove is a groove between one land portion 33 and another land portion 33 located adjacent to the one land portion 33, and extends along the circumferential direction. The zigzag groove is a groove whose opening edge shape that opens on the tread surface 30 is a zigzag shape in which peaks and valleys are repeated along the circumferential direction.

[0024] The tread 4 has a base portion 34 and a cap portion 36 located radially outside the base portion 34 and covering the base portion 34. The base portion 34 is made of a crosslinked rubber having lower heat generation than the cap portion 36. The loss tangent (tan δ) of the base portion 34 is made smaller than the loss tangent (tan δ) of the cap portion 36, so that the base portion 34 has lower heat generation than the cap portion 36. The cap portion 36 is made of a crosslinked rubber having higher abrasion resistance and grip performance than the base portion 34. The radially outer surface of the cap portion 36 becomes the tread surface 30.

[0025] 1 and 2, the position indicated by the symbol PC is the equator. The equator PC is the intersection of the tread surface 30 and the equatorial plane. When the grooves 32 are located on the equatorial plane, as in the tire 2 of the present embodiment, the equator PC is determined based on a virtual tread surface obtained by assuming that the grooves 32 do not exist. The radial distance from the bead base line BBL to the equator PC obtained in the tire 2 in a normal state is the section height of the tire 2 (see JATMA, etc.).

[0026] The sidewalls 6 are connected to both ends of the tread 4. The sidewalls 6 are located on the radially inner side of the tread 4. The sidewalls 6 are located on the axially outer side of the carcass 12. The sidewalls 6 are made of crosslinked rubber with cut resistance taken into consideration. The complex elastic modulus of the sidewalls 6 is 2.0 MPa or more and 6.0 MPa or less.

[0027] The position indicated by the symbol PW is the axial outer end of the tire 2 (hereinafter also referred to as the "outer end PW"). When there is a decoration such as a pattern or letters on the outer surface, the outer end PW is identified based on a virtual outer surface obtained assuming that there is no decoration. The maximum width of the tire 2 is defined at the outer end PW. In the present invention, the outer end PW obtained for the tire 2 in a normal state is also called the maximum width position. The axial distance from the outer end PW on the first axial side (see FIG. 1) to the outer end PW on the second axial side (not shown) obtained for the tire 2 in a normal state is the cross-sectional width of the tire 2 (see JATMA, etc.).

[0028] 1, the length indicated by the symbol H is the radial distance from the bead base line BBL to the maximum width position PW. The radial distance H is also called the radial height of the maximum width position PW. In the tire 2 in a normal state, the ratio of the radial height H of the maximum width position PW to the cross-sectional height is equal to or greater than 0.40 and is equal to or less than 0.60.

[0029] The chafer 8 is located on the radially inner side of the sidewall 6. The chafer 8 contacts the rim. The chafer 8 is made of crosslinked rubber with consideration given to wear resistance. The complex elastic modulus of the chafer 8 is 10 MPa or more and 15 MPa or less. The chafer 8 is harder than the sidewall 6.

[0030] The bead 10 is located axially inward of the chafer 8. The bead 10 is located radially inward of the sidewall 6. The bead 10 has a core 38 and an apex 40. The core 38 extends in the circumferential direction. The core 38 includes wound steel wire. The core 38 has a generally hexagonal cross-sectional shape. The apex 40 is located radially outside the core 38 and extends radially outward from the core 38. The apex 40 tapers outward.

[0031] The apex 40 has an inner apex 42 and an outer apex 44. The inner apex 42 is located radially outward of the core 38. The outer apex 44 is located radially outward of the inner apex 42.

[0032] The inner apex 42 is tapered radially outward. The inner apex 42 is made of a hard crosslinked rubber. The complex elastic modulus of the inner apex 42 is 60 MPa or more and 90 MPa or less. The outer apex 44 is thick near the outer end PU of the inner apex 42. The outer apex 44 tapers radially inward from this thick portion and then tapers radially outward.

[0033] The outer apex 44 is made of a crosslinked rubber. The outer apex 44 is softer than the inner apex 42. The complex elastic modulus of the outer apex 44 is equal to or greater than 3.0 MPa and equal to or less than 6.0 MPa.

[0034] The apex 40 further has an edge strip 46. The edge strip 46 is located axially outward of the outer apex 44 and constitutes a part of the outer surface of the apex 40. The edge strip 46 is made of crosslinked rubber. The edge strip 46 is softer than the chafer 8 and harder than the outer apex 44. The complex elastic modulus of the edge strip 46 is 7.0 MPa or more and 12 MPa or less.

[0035] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of chafers 8. The carcass 12 bridges between the pair of beads 10. The carcass 12 has a radial structure. The carcass 12 has at least one carcass ply 48. The carcass 12 shown in Figures 1 and 2 is made of one carcass ply 48. The carcass ply 48 is turned up at the bead 10.

[0036] The carcass ply 48 (see FIG. 1 ) has a ply body 50 and a pair of turnup portions 52. The ply body 50 spans between a pair of beads 10, i.e., between a first bead 10 and a second bead 10 (not shown). Each turnup portion 52 is continuous with the ply body 50 and is turned up at the bead 10. The turnup portions 52 are turned up at the bead 10 from the inside toward the outside in the axial direction. The bead 10 is sandwiched between the ply body 50 and the turnup portions 52.

[0037] Although not shown, the carcass ply 48 (carcass 12) has a plurality of carcass cords arranged in parallel. These carcass cords are covered with a topping rubber. Each carcass cord intersects with the equator plane. The material of the carcass cords is steel. Steel cords are used as the carcass cords.

[0038] The belt 14 is located radially inside the tread 4. The belt 14 has three or more belt plies 54. The tire 2 may have a configuration in which the belt 14 has three or more belt plies 54, or a configuration in which the belt 14 has four or more belt plies 54. The belt 14 of the present embodiment has four belt plies 54. The belt 14 has, in order from the inside to the outside in the radial direction, a first belt ply 54A, a second belt ply 54B, a third belt ply 54C, and a fourth belt ply 54D. The four belt plies 54 are arranged in a radially overlapping state. In the case of the tire 2 shown in FIG. 1, the second belt ply 54B has the widest width, and the fourth belt ply 54D has the narrowest width. Although not shown, the belt ply 54 may be three plies.

[0039] Although not shown, each belt ply 54 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cord is made of steel. Steel cords are used as the belt cords. In the belt ply 54, the belt cords are covered with a topping rubber.

[0040] The cushioning layer 16 is located between the belt 14 and the carcass 12 at the end of the belt 14. The cushioning layer 16 is made of a soft crosslinked rubber. The strip layer 18 is located between the carcass 12 and the belt 14 on the radially inner side of the tread 4. The strip layer 18 is located between the cushion layer 16 on the first side in the axial direction and the cushion layer 16 on the second side in the axial direction. The strip layer 18 is made of crosslinked rubber.

[0041] The steel reinforcing layer 20 is located between the bead 10 and the chafer 8. The steel reinforcing layer 20 is located between the carcass 12 and the fiber reinforcing layer 26. The steel reinforcing layer 20 has a shape that is turned up at the bead 10. Although not shown, the steel reinforcing layer 20 includes a plurality of first filler cords arranged in parallel. The material of the first filler cords is steel. That is, the steel reinforcing layer 20 has a plurality of steel cords. In the steel reinforcing layer 20, the steel cords 21 are covered with a topping rubber.

[0042] The inner liner 24 is positioned inside the carcass 12. The inner liner 24 is joined to the inner surface of the carcass 12 via an insulation (not shown) made of crosslinked rubber. The inner liner 24 constitutes the inner surface of the tire 2. The inner liner 24 is made of crosslinked rubber with excellent air barrier properties.

[0043] The fiber reinforcement layer 26 is located between the steel reinforcement layer 20 and the chafer 8. The fiber reinforcement layer 26 has a shape folded back at the bead 10 in a small dimension from the outer side toward the inner side in the axial direction. Although not shown, the fiber reinforcement layer 26 includes a plurality of second filler cords arranged in parallel. The material of the second filler cords is fiber, particularly organic fiber. That is, the fiber reinforcement layer 26 has a plurality of fiber cords 27. Nylon fiber is preferable as the organic fiber. In the fiber reinforcement layer 26, the fiber cords 27 are covered with a topping rubber.

[0044] [About Tread 4] As described above, the tread 4 has a base portion 34 and a cap portion 36 that covers the base portion 34. In the case of the embodiment shown in Figures 1 and 2, three grooves 32 are provided in the tread 4, and the tread 4 has four land portions 33 extending in the circumferential direction. Each land portion 33 has a base portion 34 and a cap portion 36. The two land portions 33 located toward the center in the axial direction are called "center land portions 33," and the remaining (two) land portions 33 located on both sides of the two center land portions 33 in the axial direction are called "shoulder land portions 33."

[0045] In FIG. 2, the right side is defined as a first axial side, and the left side is defined as a second axial side. FIG. 3 is a cross-sectional view showing the first axial side of the tread 4 and its periphery. In FIG. 2 and FIG. 3, the center land portion 33 on the right side of the equatorial plane is defined as the "first center land portion 33", and the shoulder land portion 33 on the right side of the equatorial plane is defined as the "first shoulder land portion 33". In FIG. 2, the center land portion 33 on the left side of the equatorial plane is defined as the "second center land portion 33", and the shoulder land portion 33 on the left side of the equatorial plane is defined as the "second shoulder land portion 33". The tire 2 of this embodiment has a bilaterally symmetrical shape with respect to the equatorial plane.

[0046] 2, the base portion 34 is continuous and uninterrupted over the entire axial area of ​​the tread 4. In other words, the base portion 34 is continuous from the shoulder land portion 33 on the first side in the axial direction, through the two center land portions 33, to the shoulder land portion 33 on the second side in the axial direction.

[0047] The cap portion 36 is continuous and uninterrupted over the entire axial area of ​​the tread 4. That is, the cap portion 36 is continuous from the shoulder land portion 33 on the first axial side, through the two center land portions 33, to the shoulder land portion 33 on the second axial side. The continuous cap portion 36 is connected to the sidewall 6 on the first and second axial sides.

[0048] In each of the two center land portions 33, the radially outermost position F1 of the interface F between the cap portion 36 and the base portion 34 (see Figure 3) is located radially outer than the 50% position (1 / 2 position) of the height of that center land portion 33. In each of the two shoulder land portions 33, the radially outermost position F2 of the interface F between the cap portion 36 and the base portion 34 (see Figure 3) is located radially outer than the 50% position (1 / 2 position) of the height of that shoulder land portion 33. Each of the positions F1 and F2 is located radially outward of a 50% position of the height of the land portion 33, so that the proportion of the base portion 34 in the land portion 33 increases.

[0049] Here, the "height of the land portion 33" will be explained. When grooves 32 are present on both axial sides of the land portion 33 (that is, in the case of a center land portion 33), the following applies. In the cross section (meridian cross section) shown in Figure 3, an imaginary line Li1 is defined that connects an end Q1 on the axially outer side (first axial side) of the tread surface 30 of the land portion 33 (center land portion 33) and an end Q2 on the axially inner side (second axial side) of the tread surface 30 of the land portion 33. Of the grooves 32 located on both sides of the land portion 33, a line that passes through the groove bottom 32b of the deeper groove 32 and is parallel to the imaginary line Li1 is the reference line LB for the height of that land portion 33 (center land portion 33).

[0050] When the groove 32 is present only on one axial side of the land portion 33 (the case of a shoulder land portion 33), the following applies. In the cross section (meridian cross section) shown in Figure 3, an imaginary line Li2 is defined that connects an end Q3 on the axially outer side (first axial side) of the tread surface 30 of the land portion 33 (shoulder land portion 33) and an end Q4 on the axially inner side (second axial side) of the tread surface 30 of the land portion 33. A line that passes through the groove bottom 32b of one groove 32 and is parallel to the imaginary line Li2 is the reference line LB for the height of that land portion 33 (shoulder land portion 33).

[0051] The position on the reference line LB is the 0% position of the height of the land portion 33, and the position on the imaginary line Li1 (Li2) is the 100% position of the height of the land portion 33. Note that, of the outer circumferential surface (tread surface 30) of the land portion 33, a portion located radially outward of the imaginary line Li1 (Li2) has a height exceeding 100%, for example, 102%.

[0052] In each of the two central land portions 33, the radially outermost position F1 of the interface F is located radially inward from the 80% position of the height of the central land portion 33. In each of the two shoulder land portions 33, the radially outermost position F2 of the interface F is located radially inward from the 80% position of the height of the center land portion 33. Each of the positions F1 and F2 is located radially inward from a position that represents 80% of the height of the land portion 33, thereby ensuring the thickness of the cap portion .

[0053] In the case of the configuration shown in Figure 2, in all four land portions 33, the radially outermost positions (F1, F2) of the interface F are located radially outward from the 50% position of the height of the land portion 33 and radially inward from the 80% position of the height of the land portion 33.

[0054] It is not necessary that the positions (F1, F2) are located between the 50% position and the 80% position in all land portions 33. It is also possible that the positions (F1, F2) are located between the 50% position and the 80% position in only the center land portion 33, and the shoulder land portion 33 is not configured in this manner. Or, conversely, it is also possible that the positions (F1, F2) are located between the 50% position and the 80% position in only the shoulder land portion 33, and the center land portion 33 is not configured in this manner.

[0055] It is sufficient that, in at least one of the four land portions 33, the radially outermost position of the interface F between the cap portion 36 and the base portion 34 is located radially outward from a position corresponding to 50% of the height of the land portion 33. Also, it is sufficient that, in at least one of the land portions 33, the radially outermost position of the interface F between the cap portion 36 and the base portion 34 is located radially inward from a position corresponding to 80% of the height of the land portion 33.

[0056] In the cross section (meridian cross section) shown in Fig. 3, the base portion 34 has a convex shape that protrudes radially outward. The convex base portion 34 will be specifically described. The base portion 34 has an outer side surface 341 located on the radially outer side, a slope 342 that extends radially inward from the axial end of the outer side surface 341, and an inner side surface 343 that is connected to the slope 342 and located radially inward.

[0057] The outer side surface 341 has a shape that follows the tread surface 30. The inclined surface 342 and the inner side surface 343 have shapes that follow the grooves 32. The inner side surface 343 is connected to the inner side surface 343 of the adjacent base portion 34 in the axial direction. In the present embodiment, in each land portion 33, the entire outer side surface 341 is located radially outward from a 50% position of the height of the land portion 33. The entire outer side surface 341 is located radially inward from a 80% position of the height of the land portion 33. In each land portion 33, the proportion of the base portion 34 becomes high.

[0058] [Modifications of the base portion 34] Fig. 4 is a cross-sectional view showing a modified example of the base portion 34. Fig. 4 shows the tread 4 and its periphery on a first side in the axial direction. The tread 4 shown in Fig. 4 has the base portion 34 and a cap portion 36 located radially outward of the base portion 34 and covering the base portion 34. In this respect, the tread 4 shown in Fig. 4 is the same as the tread 4 shown in Fig. 3. In the case of the tread 4 shown in Fig. 4, the base portion 34 has a two-layer structure. That is, the base portion 34 has a first base portion 34A as an intermediate portion and a second base portion 34B as a radially inner portion. The cap portion 36 covers the first base portion 34A.

[0059] The loss tangent (tan δ) of the first base portion 34A is smaller than the loss tangent (tan δ) of the cap portion 36 and is larger than the loss tangent (tan δ) of the second base portion 34B. The ratio of the loss tangent (tan δ) of the first base portion 34A to the loss tangent (tan δ) of the cap portion 36 is, for example, 0.6 or more and 0.7 or less. The ratio of the loss tangent (tan δ) of the second base portion 34B to the loss tangent (tan δ) of the cap portion 36 is, for example, 0.4 or less. The base portion 34 including the first base portion 34A and the second base portion 34B is made of a crosslinked rubber having a lower heat generation property than the cap portion 36.

[0060] The radially outermost position F1 (F2) of the interface F between the cap portion 36 and the base portion 34 (first base portion 34A) is located radially outward of a 50% position (1 / 2 position) of the height of the land portion 33. The position F1 (F2) is located radially inward of an 80% position of the height of the land portion 33.

[0061] [About Belt 14] As described above, the belt 14 has four belt plies 54. The first belt ply 54A located at the innermost radial direction is divided into two in the axial direction, and has a first divided belt ply 541 and a second divided belt ply 542 (see FIG. 2). A rubber sheet 543 is provided between the first divided belt ply 541 and the second divided belt ply 542 (split portion).

[0062] Each of the first and second divided belt plies 541 and 542 has a large number of belt cords (steel cords) arranged in parallel. The belt cords are covered with a topping rubber. The rubber sheet 543 does not have belt cords (steel cords) and is entirely made of rubber. The first and second divided belt plies 541 and 542 have the same thickness.

[0063] In this manner, the rubber sheet 543 is provided between the first divided belt ply 541 and the second divided belt ply 542. The rubber sheet 543 may be made of a different material from the topping rubber covering the belt cords, or may be made of the same material. In particular, the rubber sheet 543 and the topping rubber covering the belt cord of the first belt ply 54A may have the same loss tangent (tan δ) (however, the tolerance is within ±0.01).

[0064] The split portion reduces the bending rigidity of the belt 14, and the movement of the belt 14 becomes relatively large. If there is a large difference in physical properties between the rubber sheet 543 located at the split portion and the topping rubber of the first belt ply 54A, peeling may occur due to heat generation. If the rubber sheet 543 is made of the same material as the topping rubber covering the belt cord, heat generation can be suppressed.

[0065] 2, the dimension between the axially inner end 541b of the first separate belt ply 541 and the axially inner end 542b of the second separate belt ply 542 is defined as "BI". The dimension between the axially outer end 541a of the first separate belt ply 541 and the axially outer end 542a of the second separate belt ply 542 is defined as "BO". The dimension BI is 25% or more and 40% or less of the dimension BO.

[0066] The fourth belt ply 54D located at the outermost side in the radial direction is disposed so as to overlap an axially inner portion 541c of the first separate belt ply 541 and an axially inner portion 542c of the second separate belt ply 542. The fourth belt ply 54D overlaps the portion 541c of the first separate belt ply 541 and the portion 542c of the second separate belt ply 542, with the second belt ply 54B and the third belt ply 54C sandwiched therebetween in the radial direction.

[0067] The overlapping range of the fourth belt ply 54D and the axially inner part 541c of the first separate belt ply 541 is located within the range of the first center land portion 33 in the axial direction. The "axial range of the first center land portion 33" (see Figure 3) refers to the range on the radial outer surface (tread surface 30) of the first center land portion 33, that is, the range on the radial outer surface (tread surface 30) between an imaginary plane K1 that passes through the axial first side end Q1 and is parallel to the equatorial plane, and an imaginary plane K2 that passes through the axial second side end Q2 and is parallel to the equatorial plane.

[0068] The overlapping range of the fourth belt ply 54D and the axially inner part 542c of the second separate belt ply 541 is located within the axial range of the second center land portion 33. Note that the "axial range of the second center land portion 33" is the same as the first center land portion 33, and refers to the range on the radially outer side surface (tread surface 30) of the second center land portion 33.

[0069] Of the fourth belt ply 54D, at least a part of a first overlapping portion 54D1 overlapping with the first separate belt ply 541 is located radially inward of the first center land portion 33. In the case of the embodiment shown in Figs. 2 and 3, the entirety of the first overlapping portion 54D1 is located radially inward of the first center land portion 33.

[0070] Of the fourth belt ply 54D, at least a part of a double overlapping portion 54D2 overlapping with the second separate belt ply 542 is located radially inward of the second center land portion 33. In the case of the embodiment shown in FIG. 2, the entirety of the double overlapping portion 54D2 is located radially inward of the second center land portion 33.

[0071] That is, the range where the fourth belt ply 54D overlaps with each of the first and second separate belt plies 541 does not exist within the axial range of the groove 32. Note that the "axial range of the groove 32" refers to the range at the opening edge of the groove 32 (the outermost in the radial direction).

[0072] The first overlapping portion 54D1 is located radially inward of the first central land portion 33, and thus the first overlapping portion 54D1 is protected by the first central land portion 33. The double overlapping portion 54D2 is located radially inward of the second center land portion 33, and thus the double overlapping portion 54D2 is protected by the second center land portion 33.

[0073] 2, the axial dimension of the first overlapping portion 54D1 is "W1", and the axial dimension of the first central land portion 33 is "W2". The ratio of the axial dimension W1 to the axial dimension W2 is 0.1 or more and 0.4 or less (0.1≦W1 / W2≦0.4). The axial dimension W2 is the axial dimension of the radially outer surface (tread surface 30) of the first central land portion 33.

[0074] 2, the axial dimension of the first double overlap portion 54D1 is "W3", and the axial dimension of the second center land portion 33 is "W4". The ratio of the axial dimension W3 to the axial dimension W4 is 0.1 or more and 0.4 or less (0.1≦W3 / W4≦0.4). The axial dimension W3 is the axial dimension of the radially outer surface (tread surface 30) of the second center land portion 33.

[0075] 2, a dashed dotted line L1 extending radially through the first center land portion 33 is a line that bisects the first center land portion 33 in the axial direction on its radially outer surface (tread surface 30). A dashed dotted line L2 extending radially through the second center land portion 33 is a line that bisects the second center land portion 33 in the axial direction on its radially outer surface (tread surface 30).

[0076] The range where the portion 541c of the first separate belt ply 541 overlaps with the fourth belt ply 54D (first overlapping portion 54D1) intersects with the bisecting line L1. The range where the portion 542c of the second separate belt ply 542 overlaps with the fourth belt ply 54D (a second overlapping portion 54D2) intersects with the bisecting line L2.

[0077] According to the arrangement of the first overlap portion 54D1 and the double overlap portion 54D2 relative to the land portion 33 in this embodiment as described above, the rigidity of the entire tire is increased compared to when the overlap portions (54D1, 54D2) are located within the axial range of the groove 32.

[0078] As described above, the rubber sheet 543 is provided between the first separate belt ply 541 and the second separate belt ply 542 (split portion). The rubber sheet 543 is located radially inside the center groove 321. The ratio of the axial dimension W5 at the opening edge of the center groove 321 to the axial dimension (BI) of the split portion is 0.1 or more and 0.3 or less (0.1≦W5 / BI≦0.3).

[0079] [Regarding tire 2 of this embodiment] According to the tire 2 according to this embodiment having the above configuration, as described below, damage to the tire 2 is suppressed and the life span can be improved by suppressing heat generation in the tread 4 and improving the enveloping property. That is, the tire 2 according to this embodiment has the belt 14 located on the radially inner side of the tread 4, and the belt 14 has four belt plies 54. The tread 4 has a base portion 34 and a cap portion 36 that covers the base portion 34. The base portion 34 is made of a crosslinked rubber having lower heat generation than the cap portion 36.

[0080] Three grooves 32 are formed in the tread 4 along the circumferential direction, and the tread 4 has four land portions 33 provided along the circumferential direction. In the land portions 33, the radially outermost positions (F1, F2) of the interface F between the cap portion 36 and the base portion 34 are located radially outward from the 50% position of the height of the land portions 33. In particular, as shown in FIG. 3, the entire outer surface 341 of the base portion 34 is located radially outward from the 50% position of the height of the land portion.

[0081] Furthermore, the first belt ply 54A located at the innermost side in the radial direction is divided into two in the axial direction, and has a first divided belt ply 541 and a second divided belt ply 542. A dimension BI between the first divided belt ply 541 and the second divided belt ply 542 is 25% or more and 40% or less of a dimension BO between an axially outer end 541a of the first divided belt ply 541 and an axially outer end 542a of the second divided belt ply 542. The dimension BI is smaller than half of the dimension BO, and the split portion between the first and second separate belt plies 541, 542 is partial in the first belt ply 54A.

[0082] The radially outermost fourth belt ply is disposed so as to overlap an axially inner portion 541 c of the first separate belt ply 541 and an axially inner portion 542 c of the second separate belt ply 542 .

[0083] According to the tire 2 having the above-mentioned configuration, the proportion of the base portion 34 having low heat generation properties in the tread 4 is increased, and heat generation in the tread 4 is suppressed. In the case of this embodiment, in all of the four land portions 33, the radially outermost positions (F1, F2) of the interfaces F are located radially outward from a 50% position of the height of the land portion 33. This increases the proportion of the base portion 34 in all of the land portions 33 of the tread 4, and thus the effect of suppressing heat generation in the tread 4 is expected to be further improved.

[0084] On the other hand, the base portion 34 tends to have low cut resistance, and when the cap portion 36 becomes thinner after the middle stage of wear of the tread 4, cuts and other damage are likely to occur in the tread 4. Therefore, in the tire 2 according to the present embodiment, as described above, the first belt ply 54A is divided into two in the axial direction, which increases the flexibility of the tread 4 and improves the cut resistance and the envelope property.

[0085] In addition, since the first belt ply 54A is divided into two in the axial direction, the rigidity of the belt 14 including the first belt ply 54A may become non-uniform. Therefore, in the tire 2 according to the present embodiment, the fourth belt ply 54D is disposed to overlap with an axially inner portion 541c of the first separate belt ply 541 and an axially inner portion 542c of the second separate belt ply 542. For this reason, non-uniformity in the rigidity of the belt 14 is suppressed.

[0086] As described above, the tire 2 according to this embodiment can suppress heat generation in the tread 4, improve the enveloping property, and further improve the cut resistance. Moreover, it is possible to suppress non-uniformity in the rigidity of the belt 14. As a result, damage to the tire 2 is suppressed, and the life span can be improved.

[0087] In this embodiment, the tread 4 has four land portions 33 extending in the circumferential direction. A zigzag groove extends along the circumferential direction between one land portion 33 and another land portion 33 adjacent to the one land portion 33. In other words, each of the shoulder grooves 322 and the center groove 321 is a zigzag groove. The center groove 321 is a zigzag groove and is located at the center in the axial direction of the tread 4. The zigzag groove (center groove 321) and the split portion (rubber sheet 543 where no cord exists) between the first separate belt ply 541 and the second separate belt ply 542 are located at the center in the axial direction. This further improves the enveloping property.

[0088] The ratio of the loss tangent (tan δ) of the base portion 34 of the tread 4 to the loss tangent (tan δ) of the rubber sheet 543 is, for example, 0.25 or more and 0.40 or less. Since the loss tangent of the base portion 34 is small, the amount of heat generated by the entire tread 4 is suppressed, and the effect of suppressing damage is enhanced.

[0089] In the present embodiment, as described above, in all of the four land portions 33, the radially outermost positions F1, F2 of the interfaces F are located radially outward of the 50% position of the land portion 33 in height. While maintaining a configuration in which the positions F1 and F2 are located radially outward from the 50% position, the base portion 34 (outer surface 341) of the center land portion 33 may be located at a higher position (higher in terms of percentage) from the reference line LB than the base portion 34 (outer surface 341) of the shoulder land portion 33.

[0090] Alternatively, while maintaining a configuration in which the positions F1 and F2 are located radially outward from the 50% position, the base portion 34 (outer surface 341) of the center land portion 33 may be located lower from the reference line LB (lower in terms of percentage) than the base portion 34 (outer surface 341) of the shoulder land portion 33.

[0091] As is clear from the above description, according to the present invention, a pneumatic tire 2 can be obtained that can suppress damage to the tire 2 and extend its lifespan. [Industrial Applicability]

[0092] The above-described technology that enables the durability of the tire 2 to be increased can be applied to various tires.

[0093] [Additional Notes] The present invention includes the following aspects. (1) A pneumatic tire has a tread that comes into contact with a road surface, and a belt that includes four or more belt plies and is located radially inward of the tread, the tread has a base portion and a cap portion that covers the base portion, the base portion is made of a crosslinked rubber that has a lower heat buildup than the cap portion, two or more grooves are engraved in the tread along a circumferential direction, the tread has three or more land portions provided along a circumferential direction, and in at least one of the land portions, the radially outermost position of the interface between the cap portion and the base portion is a groove formed on the land portion. The belt plies positioned radially outward from a 50% position of the height of the portion and positioned radially inward have a first divided belt ply and a second divided belt ply divided in two in the axial direction, the dimension between the first divided belt ply and the second divided belt ply is 25% to 40% of the dimension between the axially outer end of the first divided belt ply and the axially outer end of the second divided belt ply, and the radially outermost belt ply is arranged to overlap an axially inner part of the first divided belt ply and an axially inner part of the second divided belt ply.

[0094] (2) The pneumatic tire of (1) above, wherein in the at least one land portion, the radially outermost position of the interface between the cap portion and the base portion is located radially inward from a position that represents 80% of the height of the land portion.

[0095] (3) The pneumatic tire of (1) or (2) above, wherein the tread has four land portions extending in a circumferential direction, and a zigzag groove extending along the circumferential direction is formed between one land portion and another land portion adjacent to the one land portion.

[0096] (4) The pneumatic tire according to any one of (1) to (3), wherein at least a portion of an overlapping portion of the radially outermost belt ply that overlaps with the first separate belt ply is located radially inside the land portion, and a ratio of an axial dimension of the overlapping portion to an axial dimension of the land portion is 0.3 or more and 0.5 or less.

[0097] (5) The pneumatic tire according to any one of (1) to (4), wherein an overlapping range between the radially outermost belt ply and an axially inner part of the first separate belt ply that is a first side in the axial direction is located within an axial range of the land portion on the first side in the axial direction, and an overlapping range between the radially outermost belt ply and an axially inner part of the second separate belt ply that is a second side in the axial direction is located within an axial range of the land portion on the second side in the axial direction.

[0098] (6) The pneumatic tire of (5) above, wherein an area where the portion of the first separate belt ply overlaps with the belt ply intersects with a line that axially bisects the land portion on a first side in the axial direction, and an area where the portion of the second separate belt ply overlaps with the belt ply intersects with a line that axially bisects the land portion on a second side in the axial direction.

[0099] (7) A pneumatic tire according to any one of (1) to (6), wherein in all of the three or more land portions, the radially outermost position of the interface between the cap portion and the base portion is located radially outer than a 50% position of the height of the land portion.

[0100] (8) A pneumatic tire described in any one of (1) to (7), wherein the base portion has an outer surface located radially outward, a slope extending radially inward from the axial end of the outer surface, and an inner surface connected to the slope and located radially inward, and the entire outer surface is located radially outward from a 50% position of the height of the land portion.

[0101] (9) A pneumatic tire according to any one of (1) to (8), wherein the base portion has a first base portion on the radial outer side and a second base portion located radially inward of the first base portion, and a loss tangent of the first base portion is smaller than a loss tangent of the cap portion and larger than a loss tangent of the second base portion. [Explanation of symbols]

[0102] 2. Tires 4. Tread 14. Belt 32...Groove 33... Rikubu 34 Base section 341...outer surface 342...Slope 343...Inner surface 34A...First base part 34B Second base part 36 Cap section 54 Belt ply 54A···First belt ply 54B Second belt ply 54C···Third belt ply 54D...Fourth belt ply 54D1 First overlapping portion (overlapping portion) 54D2: Second overlapping section (overlapping section) 541 First split belt ply 541a... Axial outer end 541c: A part of the inner axial direction 542 Second split belt ply 542a... Axial outer end 542c: A part of the inner axial direction BI···Dimensions BO... Dimensions F...Interface F1: The outermost position in the radial direction F2: The outermost position in the radial direction L1: Bisecting line L2: Bisecting line W1, W3: Axial dimensions of overlapping area W2, W4: Axial dimension of land portion

Claims

1. A tread that comes into contact with the road surface; A belt including three or more belt plies and positioned radially inside the tread; having The tread has a base portion and a cap portion covering the base portion, the base portion being made of a crosslinked rubber having a lower heat buildup than the cap portion, Two or more grooves are formed in the tread along a circumferential direction, and the tread has three or more land portions provided along a circumferential direction, In at least one of the land portions, a radially outermost position of an interface between the cap portion and the base portion is located radially outward from a 50% position of a height of the land portion, The belt ply located on the radially inner side has a first divided belt ply and a second divided belt ply divided in two in the axial direction, a dimension between the first and second separate belt plies is 25% or more and 40% or less of a dimension between an axially outer end of the first separate belt ply and an axially outer end of the second separate belt ply, The radially outermost belt ply is disposed so as to overlap an axially inner part of the first divided belt ply and an axially inner part of the second divided belt ply. Pneumatic tires.

2. In the at least one land portion, a radially outermost position of an interface between the cap portion and the base portion is located radially inward from a position that is 80% of a height of the land portion. The pneumatic tire according to claim 1.

3. The tread has four land portions extending in a circumferential direction, A zigzag groove extends along the circumferential direction between one land portion and another land portion adjacent to the one land portion. The pneumatic tire according to claim 1 or 2.

4. At least a portion of an overlapping portion of the radially outermost belt ply that overlaps with the first separate belt ply is located radially inside the land portion, a ratio of an axial dimension of the overlapping portion to an axial dimension of the land portion is 0.3 or more and 0.5 or less; The pneumatic tire according to claim 1 or 2.

5. an overlapping range of the radially outermost belt ply and an axially inner part of the first divided belt ply that is a first side in the axial direction is located within an axial range of the land portion on the first side in the axial direction, The range in which the radially outermost belt ply and a part of the axially inner side of the second divided belt ply that is the second side in the axial direction overlap is located within the axial range of the land portion on the second side in the axial direction. The pneumatic tire according to claim 1 or 2.

6. A range in which the portion of the first split belt ply overlaps with the belt ply intersects with a line that bisects the land portion on the first side in the axial direction, The range in which the portion of the second divided belt ply overlaps with the belt ply intersects with a line that bisects the land portion on the second side in the axial direction in an axial direction. The pneumatic tire according to claim 5.

7. In each of the three or more land portions, a radially outermost position of an interface between the cap portion and the base portion is located radially outward from a 50% position of a height of the land portion. The pneumatic tire according to claim 1 or 2.

8. The base portion has an outer surface located radially outward, a sloped surface extending radially inward from an axial end of the outer surface, and an inner surface connected to the sloped surface and located radially inward, The entire outer surface is located radially outward from a 50% position of the height of the land portion. The pneumatic tire according to claim 1 or 2.

9. The base portion has a first base portion on a radially outer side and a second base portion located on a radially inner side of the first base portion, a loss tangent of the first base portion is smaller than a loss tangent of the cap portion and is larger than a loss tangent of the second base portion; The pneumatic tire according to claim 1 or 2.

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