Heavy duty tire

Abstract

To provide a heavy duty tire 2 which can achieve reduction of rolling resistance while suppressing deterioration of cut chipping resistance performance.SOLUTION: A tire 2 includes a tread 4. The tread 4 includes a base layer 28 and a cap layer 30. The tread 4 includes a plurality of circumferential grooves 34. The plurality of circumferential grooves 34 constitutes a plurality of land parts 36 on the tread 4. The plurality of land parts 36 includes a main land part 36M positioned between two circumferential grooves 34. A boundary face 38 between the cap layer 30 and the base layer 28 is positioned between 50% depth position of groove depth of the circumferential groove 34 and 75% depth position of groove depth of the circumferential groove 34. The main land part 36M includes a traverse siping 40. The traverse siping 40 includes an outside part 42 and an inner part 44. The boundary face 38 crosses the inner part 44. The outside part 42 is connected with each of the two circumferential grooves. The inside part 44 is not connected with each of the two circumferential grooves 34.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] The tread of a tire is made of crosslinked rubber. From the viewpoint of reducing rolling resistance, crosslinked rubber with low heat generation is used for the tread. A tread usually consists of a cap layer and a base layer located inside the cap layer. The cap layer comes into contact with the road surface. Cross-linked rubber is used for the cap layer, taking into consideration grip performance and abrasion resistance. The base layer is covered by the cap layer. Cross-linked rubber is used for the base layer, taking into consideration low heat generation. The cap layer wears away, exposing the base layer. Low heat-generating crosslinked rubber has poor mechanical properties. When the base layer is exposed, the risk of damage such as cuts increases. There is a high level of social demand for reduced rolling resistance. Considering the risk of damage, etc., further reductions in tire rolling resistance are being studied (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-41821 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a heavy-duty tire that can achieve reduced rolling resistance while suppressing a decrease in cut and chipping resistance. [Means for solving the problem]

[0005] The heavy-duty tire according to the present invention comprises a tread that comes into contact with a road surface and a belt located on the radial inside of the tread. The tread comprises a base layer that covers the entire belt, and a cap layer that is located on the radial outside of the base layer. The base layer has a loss tangent that is lower than the loss tangent of the cap layer. The tread has a plurality of circumferential grooves that extend continuously in the circumferential direction. The plurality of circumferential grooves configure the tread with a plurality of land portions that are aligned in the axial direction. The plurality of land portions includes a main land portion that is located between two circumferential grooves. The interface between the cap layer and the base layer in the main land portion is located between a 50% depth position of a circumferential groove located next to the main land portion and a 75% depth position of the circumferential groove. The main land portion comprises a transverse sipe that crosses the main land portion. The transverse sipe comprises an outer portion including a groove mouth of the transverse sipe and an inner portion including a groove bottom of the transverse sipe. The interface between the cap layer and the base layer intersects with the inner portion, the outer portion is connected to each of the two circumferential grooves, and the inner portion is not connected to each of the two circumferential grooves. Effect of the Invention

[0006] The present invention can provide a heavy-duty tire that can achieve reduced rolling resistance while suppressing a decrease in cut-chipping resistance. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a heavy duty tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of a groove formed in a tread. [Diagram 3] FIG. 2 is a development view showing a portion of the tread surface. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 2 is an enlarged cross-sectional view showing a portion of the cross-section shown in FIG. [Figure 6] FIG. 2 is a cross-sectional view showing a portion of the contour line of the tread surface. [Figure 7]FIG. 4 is an enlarged development view showing a part of the tread surface shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The tire of the present invention 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 includes a rim and a tire mounted on the rim.

[0009] 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 called a standard state. 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 5% of the standard internal pressure, and no load is applied to the tire is called a reference state.

[0010] 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 in the meridian section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. 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 of 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 cut surface.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] In the present invention, the tread portion of a tire 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. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions. The center of the tread is also called the crown. The edges of the tread are also called the shoulders.

[0015] In the present invention, the loss tangent (tan δ) of an element made of crosslinked rubber among elements constituting a tire is 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℃ In this 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 it is not possible to sample a test piece from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a 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 of an element made of crosslinked rubber is represented by the loss tangent at 70°C.

[0016] In the present invention, the tensile strength and elongation at break of an element made of crosslinked rubber among the elements constituting a tire are measured in an atmosphere at a temperature of 23° C. using a tensile tester in accordance with the provisions of JIS K6251. In this measurement, a strip (length 150mm x width 25mm x thickness 2mm) is sampled from the tire, and this strip is used to prepare a No. 3 dumbbell test specimen. The length direction of the strip is aligned with the circumferential direction of the tire. If a strip cannot be sampled from the tire, a test specimen is prepared from the rubber sheet mentioned above. In the present invention, the fracture energy is expressed as half the product of the tensile strength and the elongation at break, and the unit of fracture energy is MPa·%.

[0017] [Foundations underlying the present invention] By increasing the volume of the base layer in the tread, a tire can reduce rolling resistance. Increasing the volume of the base layer shortens the distance from the tread surface to the base layer, which brings the base layer closer to the tread surface, increasing the risk of cut chipping at the crown. Since the timing of exposure of the base layer is accelerated, there is a concern that the base layer will become exposed in the later stage of wear when the groove depth of the circumferential groove becomes half or less, a time when exposure of the base layer was not previously anticipated. Since the base layer has inferior mechanical properties compared to the cap layer, the risk of cut chipping increases when the base layer is exposed. To further reduce rolling resistance, it is necessary to take into consideration cut and chipping resistance. Improvement of the crosslinked rubber used in the base layer is one of the means for improving the cut and chipping resistance. When combined with the improvement of the crosslinked rubber, a dramatic improvement in performance can be achieved. Therefore, the present inventors have studied a technology that can suppress the deterioration of the cut and chipping resistance of worn tires from the viewpoint of tire structure, and have completed the invention described below.

[0018] [Overview of the embodiment of the present invention] [Configuration 1] A heavy-duty tire according to one aspect of the present invention is a tire including a tread that comes into contact with a road surface and a belt located radially inside the tread, the tread including a base layer that covers the entire belt and a cap layer that is located radially outside the base layer, the base layer having a loss tangent lower than that of the cap layer, the tread having a plurality of circumferential grooves that extend continuously in the circumferential direction, the plurality of circumferential grooves forming a plurality of land portions in the tread that are aligned in the axial direction, the plurality of land portions including a main land portion located between two circumferential grooves, the main land portion being located between two circumferential grooves, The interface between the cap layer and the base layer in the in-land portion is located between a 50% depth position of the groove depth of the circumferential groove located next to the main land portion and a 75% depth position of the groove depth of the circumferential groove, the main land portion has a transverse sipe that crosses the main land portion, the transverse sipe has an outer portion including a groove mouth of the transverse sipe and an inner portion including a groove bottom of the transverse sipe, the interface between the cap layer and the base layer intersects with the inner portion, the outer portion is connected to each of the two circumferential grooves, and the inner portion is not connected to each of the two circumferential grooves.

[0019] By preparing the tire in this manner, the tire can achieve reduced rolling resistance while suppressing a decrease in cut and chipping resistance.

[0020] [Configuration 2] Preferably, in the heavy-duty tire described in the above-mentioned [Configuration 1], the tread has a tread surface that comes into contact with the road surface, and in a meridian section of the tire in a state in which the tire is mounted on a regular rim and the internal pressure of the tire is adjusted to 5% of the regular internal pressure, the contour line of the tread surface is composed of a plurality of arcs, the plurality of arcs include a center arc and a pair of shoulder arcs located axially outboard of the center arc, the center arc has a center on the equatorial plane of the tire and has a radius R1, each of the shoulder arcs is connected to the center arc and has a radius R2, the radius R1 of the center arc is larger than the radius R2 of the shoulder arc, and a position of a boundary between the center arc and the shoulder arc axially coincides with a position on the tread surface that is half the axial distance from the equatorial plane of the tire to an edge of the tread surface, or is located axially inside a position on the tread surface where the boundary is half the axial distance from the equatorial plane of the tire to the edge of the tread surface.

[0021] [Configuration 3] Preferably, in the heavy-duty tire described in the above-mentioned [Configuration 1] or [Configuration 2], the multiple land portions include a center land portion, a pair of middle land portions located axially outside the center land portion, and a pair of shoulder land portions located axially outside the middle land portions, the center land portion includes the equator of the tire, the shoulder land portions include the edge of the tread surface, and the middle land portions include a position on the tread surface that is half the axial distance from the equatorial plane of the tire to the edge of the tread surface, and the boundary between the center arc and the shoulder arc.

[0022] [Configuration 4] Preferably, in the heavy duty tire according to any one of the above-mentioned [Configuration 1] to [Configuration 3], the transverse sipe crossing the main land portion includes a plurality of bent portions bent at an angle θb.

[0023] [Configuration 5] Preferably, in the heavy duty tire according to the above-mentioned [Configuration 4], the angle θb is equal to or greater than 90 degrees.

[0024] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0025] 1 shows a part of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on vehicles such as trucks, buses, etc. This tire 2 is a heavy-duty tire.

[0026] FIG. 1 shows a portion of a cross section of a tire 2 taken along a plane including the rotation axis (not shown) of the tire 2. The cross section shown in FIG. 1 is also called a meridian cross section. The direction indicated by the double arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double arrow RD 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. In FIG. 1, a dashed dotted line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0027] 1, the position indicated by the symbol PC is the intersection point between the outer surface 2G of the tire 2 (specifically, the tread surface described later) and the equatorial plane. The intersection point PC is the equator of the tire 2. When a groove is located on the equatorial plane, the equator PC is determined based on a virtual outer surface obtained by assuming that there is no groove. The equator PC is the radially outer end of the tire 2.

[0028] 1 shows a portion of a tread portion of a tire 2. The tread portion includes a tread 4, a belt 6, a carcass 8, an inner liner 10, a pair of cushion layers 12, a strip layer 14, and a pair of sidewalls 16. In addition to these elements, the tire 2 includes elements such as beads and clinches, which are not shown. The elements other than the tread 4 have a typical configuration as components of a heavy-duty tire, and detailed description of the elements other than the tread 4 will be omitted.

[0029] The belt 6 is located radially inside the tread 4. The belt 6 is laminated on a carcass 8. The belt 6 includes a plurality of belt plies 18 laminated in the radial direction. The belt 6 of the tire 2 includes four belt plies 18. The four belt plies 18 are a first belt ply 18A, a second belt ply 18B, a third belt ply 18C, and a fourth belt ply 18D, which are arranged in this order in the radial direction. The first belt ply 18A is located at the innermost position in the radial direction. The second belt ply 18B has the widest width, and the fourth belt ply 18D has the narrowest width.

[0030] Although not shown, each belt ply 18 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The belt cords of this tire 2 are made of steel cords.

[0031] In this tire 2, the end of the second belt ply 18B and the end of the third belt ply 18C are covered with a rubber layer 20. Two more rubber layers 20 are disposed between the end of the second belt ply 18B covered with the rubber layer 20 and the end of the third belt ply 18C. In this tire 2, an edge member 22 made of a total of four rubber layers 20 is configured between the end of the second belt ply 18B and the end of the third belt ply 18C. The edge member 22 is made of crosslinked rubber. The edge member 22 contributes to maintaining a gap between the end of the second belt ply 18B and the end of the third belt ply 18C. The edge member 22 is a part of the belt 6.

[0032] The carcass 8 is located on the inside of the tread 4 and the pair of sidewalls 16. Although not shown, the carcass 8 bridges between a pair of beads. The carcass 8 includes at least one carcass ply 24. The carcass 8 of the tire 2 is configured with one carcass ply 24.

[0033] Although not shown, the carcass ply 24 is folded back at each bead. The carcass ply 24 includes a number of carcass cords arranged in parallel. These carcass cords intersect with the equatorial plane. The carcass 8 of the tire 2 has a radial structure. The carcass cords of the tire 2 are steel cords. Cords made of organic fibers may be used as the carcass cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0034] The inner liner 10 is positioned inside the carcass 8. The inner liner 10 constitutes the inner surface 2N of the tire 2. The inner liner 10 is made of crosslinked rubber having excellent air barrier properties. The inner liner 10 maintains the internal pressure of the tire 2.

[0035] Each cushion layer 12 is located at an end of the belt 6, between the belt 6 and the carcass 8. The cushion layer 12 is made of a soft crosslinked rubber.

[0036] The strip layer 14 is located between the belt 6 and the carcass 8 on the radially inner side of the tread 4. In the axial direction, the strip layer 14 is located between one cushion layer 12 and the other cushion layer 12. The strip layer 14 is made of crosslinked rubber.

[0037] Each sidewall 16 is continuous with an edge of the tread 4. The sidewall 16 is located on the radially inner side of the tread 4. The sidewall 16 is located on the axially outer side of the carcass 8. The sidewall 16 is made of crosslinked rubber. The sidewall 16 forms a side surface 2Gs of the tire 2. The outer surface 2G of the tire 2 has a pair of side surfaces 2Gs.

[0038] The tread 4 is located on the radially outer side of the tire 2 and extends in the circumferential direction. The tread 4 is laminated on a belt 6. The outer peripheral surface of the tread 4 is a tread surface 26. The tire 2 comes into contact with the road surface at the tread surface 26. The tread 4 has the tread surface 26 that comes into contact with the road surface. The tread surface 26 is included in the outer surface 2G of the tire 2.

[0039] The tread 4 wears. The outer peripheral surface of the worn tread 4 comes into contact with the road surface. The outer peripheral surface of the worn tread 4 is also a tread surface. In contrast, the above-mentioned tread surface 26 is the outer peripheral surface of the unworn tread 4. To distinguish it from the tread surface 26, no reference numeral is attached to the tread surface consisting of the outer peripheral surface of the worn tread 4.

[0040] In Fig. 1, the symbol TE denotes an end of the tread surface 26. Of the two ends TE of the tread surface 26, one end TE is called a first end TE1, and the other end TE is called a second end TE2. In this specification, the end TE of the tread surface 26 located on the side indicated by the arrow AD1 in Fig. 1 is called the first end TE1, and the end TE of the tread surface 26 located on the side indicated by the arrow AD2 is called the second end TE2.

[0041] The length indicated by the double-headed arrow WT is the width of the tread surface 26. The width WT of the tread surface 26 is represented by the axial distance from a first end TE1 to a second end TE2 of the tread surface 26. In the case where the end TE of the tread surface 26 cannot be identified externally in the tire 2, the end TE of the tread surface 26 is defined as a position on the outer surface 2G corresponding to the axial outer end of the contact patch obtained by applying a normal load to the tire 2 in a normal state, setting the camber angle to 0°, and bringing the tire 2 into contact with a flat surface.

[0042] The tread 4 is made of crosslinked rubber. The tread 4 includes a base layer 28 and a cap layer 30. The tread 4 is composed of the base layer 28 and the cap layer 30 which are arranged in the radial direction. The base layer 28 is located between the belt 6 and the cap layer 30. The base layer 28 covers the entire belt 6. The cap layer 30 is located radially outside the base layer 28. The cap layer 30 covers the entire base layer 28. The cap layer 30 includes the tread surface 26. The cap layer 30 is made of a crosslinked rubber that takes into consideration grip performance and abrasion resistance. The base layer 28 is made of a crosslinked rubber that takes into consideration low heat generation. The loss tangent LTb of the base layer 28 is lower than the loss tangent LTc of the cap layer 30. The base layer 28 has a loss tangent LTb lower than the loss tangent LTc of the cap layer 30.

[0043] Grooves 32 are cut into the tread 4. This forms a tread pattern. Fig. 2 shows an example of a groove 32 cut into the tread 4. Fig. 2 shows a cross section of this groove 32. The main configuration of the groove 32 will be described based on Fig. 2.

[0044] The groove 32 has a pair of wall surfaces 32W including a groove mouth 32M, and a bottom surface 32B including a groove bottom 32T. The groove width of the groove 32 is represented by the distance between the pair of wall surfaces 32W, that is, the first wall surface 32W and the second wall surface 32W, i.e., the wall-to-wall distance. 2, the length indicated by the double-headed arrow WG is the groove width at the groove mouth 32M. The groove width WG is represented by the shortest distance between the pair of edges 32E that form the groove mouth 32M. When the groove mouth 32M of the groove 32 is machined to have a tapered shape, the groove width at the groove mouth 32M is represented based on a virtual edge that is obtained by assuming that the groove mouth 32M is not machined to have a tapered shape. The length indicated by the double-headed arrow DG is the groove depth of the groove 32. The groove depth DG of the groove 32 is represented by the shortest distance from the line segment connecting the left and right edges 32E to the groove bottom 32T of the groove 32. When a convex portion such as a weighing indicator is provided at the groove bottom 32T, the groove depth DG is expressed as the groove depth at a position where the convex portion is not provided, or the groove depth obtained assuming that the convex portion is not provided. The position, groove width WG and groove depth DG of the groove 32 are determined appropriately according to the specifications of the tire 2.

[0045] A groove 32 having a groove width WG of less than 1.0 mm at a groove mouth 32M and capable of contacting a pair of wall surfaces 32W with each other by contacting with the road surface is also called a sipe.

[0046] A plurality of circumferential grooves 34 are formed in the tread 4 of the tire 2. Four circumferential grooves 34 are formed in the tread 4 shown in Fig. 1. These circumferential grooves 34 are arranged in parallel in the axial direction. Each of the circumferential grooves 34 extends continuously in the circumferential direction.

[0047] Of the four circumferential grooves 34 aligned in the axial direction, the two circumferential grooves 34 located on the outermost sides are shoulder circumferential grooves 34s. The circumferential grooves 34 located axially inside the respective shoulder circumferential grooves 34s are middle circumferential grooves 34m. The tread 4 of this tire 2 has two middle circumferential grooves 34m and two shoulder circumferential grooves 34s. 1, the length indicated by the double arrow DGm is the groove depth of the middle circumferential groove 34m, and the length indicated by the double arrow DGs is the groove depth of the shoulder circumferential groove 34s.

[0048] The circumferential groove 34 has a groove width of 1.0 mm or more. In the tire 2, from the viewpoint of contributing to drainage and traction performance, the groove width of the middle circumferential groove 34m is preferably about 2 to 10% of the width WT of the tread surface 26. The groove depth DGm of the middle circumferential groove 34m is preferably 13 to 25 mm. The groove width of the shoulder circumferential groove 34s is preferably about 1 to 7% of the width WT of the tread surface 26. The groove depth DGs of the shoulder circumferential groove 34s is preferably 13 to 25 mm.

[0049] The multiple circumferential grooves 34 define multiple land portions 36 aligned in the axial direction in the tread 4. As described above, the tread 4 has four circumferential grooves 34. Five land portions 36 are defined in the tread 4. The outer surfaces of the land portions 36 (hereinafter also referred to as the land surface) are included in the tread surface 26. An edge 34E that constitutes a groove mouth 34M of the circumferential groove 34 is also an edge of the land surface. The edge 34E is a boundary between the land surface and the circumferential groove 34.

[0050] Of the multiple land portions 36 aligned in the axial direction, the two land portions 36 located on the outermost sides are shoulder land portions 36s. The shoulder land portions 36s include the edge TE of the tread surface 26. The land portions 36 located axially inward of the respective shoulder land portions 36s are middle land portions 36m. The land portion 36 located between the two middle land portions 36m is a center land portion 36c. In this tire 2, the center land portion 36c is the land portion 36 located in the center. The center land portion 36c includes the equator PC. This tread 4 is configured with one center land portion 36c, two middle land portions 36m, and two shoulder land portions 36s. Although not described in detail, the width of each land portion 36 is determined appropriately according to the specifications of the tire 2. The width of the land portion 36 is represented by the axial distance from one edge to the other edge of the land surface. When the width of the land portion 36 varies in the circumferential direction, the width of the land portion 36 is represented by the average value of the maximum width and the minimum width.

[0051] In the tire 2, the land portion 36 located between the two circumferential grooves 34 is also called a main land portion 36M. In the tread 4 shown in Fig. 1, the center land portion 36c and the middle land portion 36m are the main land portion 36M.

[0052] As described above, the tread 4 is composed of a base layer 28 and a cap layer 30 aligned in the radial direction. The tread 4 includes an interface 38 between the base layer 28 and the cap layer 30. The interface 38 extends along the tread surface 26 except for the edge portions of the tread 4. The interface 38 is configured as a flat surface. In the portion where the circumferential groove 34 is formed, as shown in Fig. 1, a detour portion 38u that detours around the circumferential groove 34 may be formed at the interface 38. In this case, the detour portion 38u is formed within a range of 2 mm from the circumferential groove 34. The distance from the circumferential groove 34 to the detour portion 38u is 2 mm or less. The thickness of the cap layer 30 at the circumferential groove 34 is 2 mm or less. The interface 38 may be configured to traverse the circumferential groove 34 without bypassing the circumferential groove 34 .

[0053] 1, a flat portion 38h is formed between two adjacent detour portions 38u. The main land portion 36M includes the flat portion 38h of the interface 38. In the flat portion 38h, the cap layer 30 has a uniform thickness. In the following description, the interface 38 in the main land portion 36M means the portion included in the main land portion 36M other than the detour portion 38u, that is, the flat portion 38h.

[0054] 3 is a development view showing a part of the tread surface 26. The direction indicated by the double arrow CD in FIG. 3 shows the middle land portion 36m, the middle circumferential groove 34m, and the shoulder circumferential groove 34s. In other words, FIG. 3 shows the main land portion 36M located between the two circumferential grooves 34.

[0055] 3, the middle circumferential groove 34m and the shoulder circumferential groove 34s extend in a zigzag shape. In the tire 2, the middle circumferential groove 34m and the shoulder circumferential groove 34s may be configured as circumferential grooves extending in a wavy shape or as circumferential grooves extending in a straight shape.

[0056] The main land portion 36M includes a transverse sipe 40 that crosses the main land portion 36M. A plurality of transverse sipes 40 are provided in the main land portion 36M of the tire 2. The plurality of transverse sipes 40 are arranged at intervals in the circumferential direction.

[0057] Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 4 shows a cross section of the transverse sipe 40 at the center of the width of the main land portion 36M. The transverse sipe 40 extends straight in the depth direction. The transverse sipe 40 has a pair of wall surfaces 40W including a groove mouth 40M, and a bottom surface 40B including a groove bottom 40T. 4, the length indicated by the double arrow WGp is ​​the groove width at the groove mouth 40M of the transverse sipe 40. The length indicated by the double arrow DGp is ​​the groove depth of the transverse sipe 40.

[0058] The transverse sipes 40 cross the main land portion 36M. The transverse sipes 40 bridge between one circumferential groove 34 and the other circumferential groove 34 located next to the main land portion 36M. The edges 40E constituting the groove mouths 40M of the transverse sipes 40 can function as edge components that dig into the road surface. The transverse sipes 40 can contribute to improving wet performance.

[0059] The transverse sipes 40 are the sipes described above. The groove width WGp of the transverse sipes 40 is less than 1.0 mm. When the main land portion 36M comes into contact with the road surface, a load acts on the main land portion 36M, causing the main land portion 36M to deform. This causes a pair of wall surfaces 40W of the transverse sipes 40 to come into contact with each other. The pair of wall surfaces 40W support each other, thereby increasing the apparent rigidity of the main land portion 36M. Deformation of the main land portion 36M is suppressed. This tire 2 can reduce rolling resistance while improving wet performance. The transverse sipes 40 can contribute to improving wet performance and reducing rolling resistance.

[0060] In the tire 2, the transverse sipes 40 are shallower than the circumferential grooves 34. From the viewpoint that the transverse sipes can effectively contribute to improving wet performance and reducing rolling resistance, the ratio of the groove depth DGp of the transverse sipes 40 to the groove depth of the circumferential grooves 34 is preferably 60% or more and 80% or less.

[0061] In this tire 2, when the two circumferential grooves 34 located adjacent to the main land portion 36M have different groove depths, the ratio of the groove depth DGp of the transverse sipe 40 to the groove depth of the circumferential groove 34 described above is determined based on the groove depth of the deep circumferential groove 34. The two circumferential grooves 34 located next to the middle land portion 36m, which is the main land portion 36M, are the middle circumferential groove 34m and the shoulder circumferential groove 34s. Of the two circumferential grooves 34 located next to the middle land portion 36m, the groove depth DGs of the shoulder circumferential groove 34s is deeper than the groove depth DGm of the middle circumferential groove 34m. The ratio of the groove depth DGp of the transverse sipe 40 shown in FIG. 3 to the groove depth of the circumferential groove 34 is expressed as the ratio (DGp / DGs) of the groove depth DGp of the transverse sipe 40 to the groove depth DGs of the shoulder circumferential groove 34s.

[0062] As described above, in the tire 2, the center land portion 36c and the middle land portion 36m are the main land portion 36M. In the tire 2, the center land portion 36c and the middle land portion 36m are each provided with a transverse sipe 40. The transverse sipe 40 may be provided only in the center land portion 36c, or the transverse sipe 40 may be provided only in the middle land portion 36m. From the viewpoint of effectively improving wet performance and reducing rolling resistance, it is preferable that the transverse sipe 40 is provided in each of the center land portion 36c and the middle land portion 36m. In other words, it is preferable that the transverse sipe 40 is provided in all the main land portions 36M formed in the tread 4.

[0063] FIG. 5 shows a part of the cross section shown in FIG. 1. The position indicated by the symbol P50 in FIG. 5 is the 50% depth position of the groove depth of the circumferential groove 34. The solid line L50 is parallel to a straight line passing between one edge 34E and the other edge 34E of the land surface of the main land portion 36M, and is a straight line passing through the 50% depth position P50. The solid line L50 is also called the 50% depth position line. The position indicated by the symbol P75 is the 75% depth position of the groove depth of the circumferential groove 34. The solid line L75 is parallel to the 50% depth position line L50, and is a straight line passing through the 75% depth position P75. The solid line L75 is also called the 75% depth position line.

[0064] When the two circumferential grooves 34 adjacent to the main land portion 36M have different groove depths, the 50% depth position line L50 and the 75% depth position line L75 are defined based on the groove depth of the deeper circumferential groove 34. Fig. 5 shows a cross section of the middle land portion 36m as the main land portion 36M. As described above, of the two circumferential grooves 34 located next to the middle land portion 36m, the groove depth DGs of the shoulder circumferential groove 34s is deeper than the groove depth DGm of the middle circumferential groove 34m. The 50% depth position line L50 and the 75% depth position line L75 shown in Fig. 5 are set based on the groove depth DGs of the shoulder circumferential groove 34s.

[0065] The base layer has inferior mechanical properties compared to the cap layer, and is therefore more susceptible to damage when it comes into contact with the road surface. For this reason, conventional treads are designed so that the base layer is not exposed at the end of the wear stage, when the groove depth of the circumferential groove is less than 1 / 4. In conventional treads, the interface between the cap layer and the base layer in the main land portion is located radially inward of the 75% depth position of the circumferential groove depth.

[0066] In contrast, in the tire 2, as shown in Fig. 5, the interface 38 in the main land portion 36M is located radially inward of the 50% depth position line L50. Although not shown, the position of the interface 38 may coincide with the position of the 50% depth position line L50 in the radial direction. As shown in Fig. 5, the interface 38 in the main land portion 36M is located radially outward of the 75% depth position line L75. Although not shown, the position of the interface 38 may coincide with the position of the 75% depth position line L75 in the radial direction.

[0067] In this tire 2, the interface 38 between the cap layer 30 and the base layer 28 in the main land portion 36M is located between a 50% depth position P50 of the groove depth of the circumferential groove 34 located next to the main land portion 36M and a 75% depth position P75 of the groove depth of the circumferential groove 34. The volume of the base layer 28 included in the tread 4 of this tire 2 is larger than that of a conventional tread. As described above, the base layer 28 is made of a crosslinked rubber with low heat buildup. The tread 4 of this tire 2 can contribute to reducing rolling resistance.

[0068] As described above, in the tire 2, the interface 38 between the cap layer 30 and the base layer 28 in the main land portion 36M is located between the 50% depth position P50 of the circumferential groove 34 and the 75% depth position P75 of the circumferential groove 34. The distance from the tread surface 26 to the base layer 28 of the tire 2 is shorter than that of the conventional tire. Since the base layer 28 is closer to the tread surface 26 than in the conventional tire, the risk of cut chipping in the crown portion increases. Furthermore, the timing of exposure of the base layer 28 is accelerated, so there is a concern that the base layer 28 will be exposed in the later stage of wear when the groove depth of the circumferential groove 34 becomes half or less, which was not expected until now. Since the base layer 28 has inferior mechanical properties to the cap layer 30, the risk of cut chipping increases when the base layer 28 is exposed.

[0069] As described above, the transverse sipes 40 are provided in the main land portion 36M of the tread 4 of the tire 2. The transverse sipes 40 of the tire 2 include an outer portion 42 and an inner portion 44. The outer portion 42 includes a groove mouth 40M of the transverse sipe 40. The inner portion 44 includes a groove bottom 40T of the transverse sipe 40. The inner portion 44 is located radially inward of the outer portion 42. 5, the interface 38 between the cap layer 30 and the base layer 28 is located between the outer portion 42 and the groove bottom 40T. The outer portion 42 is entirely contained within the cap layer 30.

[0070] In this tire 2, the outer portion 42 is connected to each of the two circumferential grooves 34 located next to the main land portion 36M. The outer portion 42 imparts flexibility to the surface layer portion of the main land portion 36M. Since the surface layer portion can deform according to the condition of the road surface, the surface layer portion can expand and come into contact with the road surface. Since an excessive increase in ground pressure is suppressed, the occurrence of cut chipping is suppressed.

[0071] Wear causes the circumferential grooves 34 to become shallower. This increases the rigidity of the land portion 36. As wear progresses in the tread 4, there is a concern that the sipes crossing the land portion 36 may become the starting point of cracks, promoting the occurrence of cut chipping.

[0072] In this tire 2, when the outer portion 42 disappears due to wear, the inner portion 44 is exposed. Since the inner portion 44 can function as an edge component that grips the road surface, good wet performance is maintained. As shown in Fig. 5, the inner portion 44 of the tire 2 is not connected to each of the two circumferential grooves 34 located next to the main land portion 36M. In other words, the inner portion 44 is disposed at a distance from the circumferential groove 34. In the main land portion 36M where the inner portion 44 is exposed, the rigidity of the main land portion 36M is appropriately maintained without being excessively reduced. The inner portion 44 is unlikely to become a starting point of cracks. In the tire 2, the occurrence of cut chipping is suppressed.

[0073] As described above, the base layer 28 is located radially inward of the cap layer 30. As the tread 4 wears, the base layer 28 becomes exposed. In this tire 2, in the main land portion 36M, the interface 38 between the cap layer 30 and the base layer 28 intersects with an inner portion 44 of the transverse sipe 40. When the tread 4 further wears, the base layer 28 including the inner portion 44 becomes exposed. Since the base layer 28 has inferior mechanical properties to the cap layer 30, there is a concern that the inner portion 44 may become a starting point of cracks and promote the occurrence of cut chipping.

[0074] However, as described above, the inner portion 44 is disposed at a distance from the circumferential groove 34. Even in a state where the base layer 28 is exposed, the rigidity of the main land portion 36M is appropriately maintained without being excessively reduced. The inner portion 44 is unlikely to become a starting point of cracks. In the tire 2, the occurrence of cut chipping is suppressed.

[0075] In this tire 2, the occurrence of cut chipping is effectively suppressed even though the volume of the base layer 28 included in the tread 4 is larger than that of a conventional tread. Moreover, since the tread 4 of this tire 2 includes a larger amount of the base layer 28 than that of a conventional tread, this tire can further reduce the rolling resistance. The tire 2 can achieve a reduction in rolling resistance while suppressing a decrease in cut and chipping resistance.

[0076] As described above, in the main land portion 36M, the interface 38 between the cap layer 30 and the base layer 28 intersects with the inner portion 44 of the transverse sipe 40. A part of the inner portion is located radially inward of the interface 38 between the cap layer 30 and the base layer 28. 5, the length indicated by the double-headed arrow PD is the length of the inner portion 44 that extends radially inward from the interface 38 between the cap layer 30 and the base layer 28 in the main land portion 36M. This length PD is also called the extension length of the inner portion 44.

[0077] In the tire 2, the ratio of the intrusion length PD of the inner portion 44 to the groove depth of the circumferential groove 34 is preferably equal to or greater than 5% and equal to or less than 20%. By setting the ratio of the intrusion length PD of the inner portion 44 to the groove depth of the circumferential groove 34 to 5% or more, the inner portion 44 can effectively contribute to suppressing the occurrence of cut chipping. The tire 2 can achieve a reduction in rolling resistance while suppressing a decrease in cut chipping resistance. From this viewpoint, it is more preferable that the ratio is 10% or more. The transverse sipes 40 having an appropriate groove depth DGp are formed by setting the ratio of the intrusion length PD of the inner portion 44 to the groove depth of the circumferential groove 34 to 20% or less. The transverse sipes 40 can effectively contribute to improving wet performance and reducing rolling resistance. From this viewpoint, it is more preferable that the ratio is 15% or less.

[0078] In this tire 2, when the two circumferential grooves 34 located adjacent to the main land portion 36M have different groove depths, the ratio of the intrusion length PD of the inner portion 44 to the groove depth of the circumferential groove 34 is expressed based on the groove depth of the deeper circumferential groove 34. As described above, the main land portion 36M shown in Fig. 5 is the middle land portion 36m, and of the two circumferential grooves 34 located next to the middle land portion 36m, the groove depth DGs of the shoulder circumferential groove 34s is deeper than the groove depth DGm of the middle circumferential groove 34m. In the main land portion 36M shown in Fig. 5, the ratio of the intrusion length PD of the inner portion 44 to the groove depth of the circumferential groove 34 is expressed as the ratio (PD / DGs) of the intrusion length PD of the inner portion 44 to the groove depth DGs of the shoulder circumferential groove 34s.

[0079] FIG. 6 is a cross-sectional view showing a portion of the contour line of the tread surface 26 in a meridian section of the tire 2. As shown in FIG. Although not described in detail, in the present invention, the contour line of the tread surface 26 is obtained by using, for example, a displacement sensor to measure the outer surface shape of the tire 2 in a reference state, that is, a state in which the tire 2 is mounted on a regular rim and the internal pressure of the tire 2 is adjusted to 5% of the regular internal pressure. The contour line of the tread surface 26 may be specified based on the shape of a cavity surface of a mold (not shown) that shapes the outer surface 2G of the tire 2.

[0080] In a meridian cross section, the contour line of the tread surface 26 is composed of a plurality of circular arcs arranged in the axial direction. The plurality of circular arcs constituting the contour line of the tread surface 26 shown in Fig. 6 include a center circular arc and a pair of shoulder circular arcs. The center arc is located between a pair of shoulder arcs. The center arc includes an equator PC. In Fig. 6, an arrow R1 indicates the radius of the center arc. Although not shown, the center arc has a center on the equatorial plane. Each shoulder arc is located axially outward of the center arc. The shoulder arcs include an edge TE of the tread surface 26. The shoulder arcs are continuous with the center arc. The position on the contour line of the tread surface 26 indicated by the symbol CS is the boundary between the shoulder arcs and the center arc. In FIG. 6, the arrow R2 indicates the radius of the shoulder arc. Although not shown, the shoulder arc has a center on a straight line connecting the boundary CS and the center of the center arc. The shoulder arc is tangent to the center arc at the boundary CS.

[0081] 6, the length indicated by the double-headed arrow HWT is the axial distance from the equatorial plane to the end TE of the tread surface 26. The position on the contour line of the tread surface 26 indicated by the symbol PH is the position where the axial distance HWT is half. The length indicated by the double-headed arrow HCS is the axial distance from the equatorial plane to the boundary CS between the center arc and the shoulder arc.

[0082] As described above, in the tire 2, the center land portion 36c includes the equator PC, and the shoulder land portion 36s includes the edge TE of the tread surface 26. The middle land portion 36m includes the boundary CS. As shown in Fig. 6, the middle land portion 36m includes a position PH where the axial distance HWT from the equatorial plane to the edge TE of the tread surface 26 is half.

[0083] The radius R1 of the center arc is greater than the radius R2 of the shoulder arc. In this tire 2, the crown portion of the tread surface 26 can be made flatter than the shoulder portions. In this tire 2, the ground contact pressure in the crown portion can be reduced, thereby reducing the risk of cut and chipping. In this tire 2, the reduction in cut and chipping resistance, which was a concern when the tread 4 contains a large amount of the base layer 28, can be effectively suppressed. From this viewpoint, it is preferable that the radius R1 of the center arc be larger than the radius R2 of the shoulder arc. Specifically, the ratio (R2 / R1) of the radius R2 of the shoulder arc to the radius R1 of the center arc is more preferably 0.12 or greater and 0.20 or less, and further preferably 0.16 or greater and 0.18 or less.

[0084] 6, the boundary CS between the center arc and the shoulder arc is located axially inward of a position PH on the tread surface 26, which is half the axial distance HWT from the equatorial plane of the tire 2 to the end TE of the tread surface 26. Although not shown, the position of this boundary CS may coincide with the position PH on the tread surface 26, which is half the axial distance HWT, in the axial direction. This tire 2 can maintain the crown portion in a flat state at the contour line of the tread surface 26 even if the load acting on the tread 4 fluctuates. Even if the load fluctuates, the circumferential edge of the shape of the contact surface with the road surface can be maintained in a flat state. This tire 2 can reduce the ground contact pressure at the crown portion, so that the decrease in cut and chipping resistance can be effectively suppressed. This tire 2 can effectively reduce the risk of cut and chipping. From this viewpoint, it is preferable that the position of the boundary CS between the center arc and the shoulder arc coincides in the axial direction with a position PH on the tread surface 26 which is half the axial distance HWT from the equatorial plane of the tire 2 to the end TE of the tread surface 26, or that the boundary CS is located axially inside of a position PH on the tread surface 26 which is half the axial distance HWT from the equatorial plane of the tire 2 to the end TE of the tread surface 26. Specifically, the ratio of the axial distance HCS from the equatorial plane to the boundary CS between the center arc and the shoulder arc to the axial distance HWT from the equatorial plane to the end TE of the tread surface 26 is more preferably 0.35 to 0.50, and even more preferably 0.40 to 0.45.

[0085] From the viewpoint of effectively suppressing a decrease in chipping resistance, it is more preferable that the radius R1 of the center arc is larger than the radius R2 of the shoulder arc, and that the position of the boundary CS between the center arc and the shoulder arc coincides in the axial direction with a position PH on the tread surface 26 which is half the axial distance HWT from the equatorial plane of the tire 2 to the end TE of the tread surface 26, or that the boundary CS is located axially inside the position PH on the tread surface 26 which is half the axial distance HWT from the equatorial plane of the tire 2 to the end TE of the tread surface 26.

[0086] As described above, the main land portion 36M of the tire 2 includes the transverse sipe 40 that crosses the main land portion 36M. As shown in FIG. 3, the transverse sipe 40 can include a plurality of bent portions 46. The transverse sipe 40 bends at the bent portions 46. This allows the pair of wall surfaces 40W of the transverse sipe 40 to effectively restrain each other from moving when the main land portion 36M is deformed by contacting with the road surface. The rigidity of the main land portion 36M is apparently increased, and deformation of the main land portion 36M is suppressed. The tire 2 can reduce rolling resistance. The transverse sipe 40 that includes a plurality of bent portions 46 can effectively contribute to reducing rolling resistance. From this viewpoint, it is preferable that the transverse sipe 40 includes a plurality of bent portions 46.

[0087] The transverse sipe 40 being bent at the bend 46 means that the orientation of the transverse sipe 40 changes at the bend 46 in the development view shown in FIG.

[0088] In the development shown in Fig. 3, the angle θb indicates the degree of bending of the transverse sipe 40 at the bend portion 46. The angle θb is expressed as the angle formed by two extension lines that can be understood by drawing extension lines from both ends of the bend portion 46. The angle θb is specified at the inner edge of the bend portion 46. From the viewpoint that the transverse sipes 40 can effectively contribute to reducing rolling resistance, the angle θb is preferably equal to or greater than 90 degrees.

[0089] As shown in Fig. 3, the bent portion 46 of the transverse sipe 40 has a rounded shape. The bent portion 46 may be configured to have an angular shape. From the viewpoint of effectively suppressing the concentration of strain at the bent portion 46, it is preferable that the bent portion 46 has a rounded shape. In this case, it is more preferable that the shape of the bent portion 46 is represented by a circular arc.

[0090] The shape of the bent portion 46 of the transverse sipe 40 is represented by a circular arc. The contour of the outer edge and the contour of the inner edge of the bent portion 46 are represented by circular arcs. In FIG. 3, the arrow Rb indicates the radius of the circular arc representing the contour of the inner edge of the bent portion 46. In the present invention, when the shape of the bent portion 46 of the transverse sipe 40 is represented by a circular arc, the radius of the circular arc is represented by the radius Rb of the circular arc representing the contour of the inner edge of the bent portion 46 .

[0091] When the shape of bent portion 46 is represented by a circular arc as shown in FIG. 3, from the viewpoint of suppressing the concentration of strain at bent portion 46, the radius Rb of this arc is preferably 3.0 mm or more and 15 mm or less, and more preferably 5.0 mm or more and 15 mm or less.

[0092] 3 includes two bent portions 46. The two bent portions 46 are connected via a central connecting portion 48 that extends straight. The bent portion 46 (hereinafter, the first bent portion 50) on the first end TE1 side of the tread surface 26 is connected to the circumferential groove 34 (in this Figure 3, the middle circumferential groove 34m) located on the first end TE1 side of the tread surface 26 via a first connecting portion 52. The bent portion 46 (hereinafter, the second bent portion 54) on the second end TE2 side of the tread surface 26 is connected to the circumferential groove 34 (in this Figure 3, the shoulder circumferential groove 34s) located on the second end TE2 side of the tread surface 26 via a second connecting portion 56. The transverse sipe 40 includes a first connecting portion 52 , a first bend portion 50 , a central connecting portion 48 , a second bend portion 54 and a second connecting portion 56 . As shown in FIG. 3, the first connecting portion 52, the central connecting portion 48 and the second connecting portion 56 are inclined with respect to the axial direction.

[0093] Fig. 7 is an enlarged development view showing a part of the development view shown in Fig. 3. This Fig. 7 shows the middle land portion 36m as the main land portion 36M. 7, angle θf is the angle that first connecting portion 52 makes with respect to the axial direction. Angle θc is the angle that central connecting portion 48 makes with respect to the axial direction. Angle θs is the angle that second connecting portion 56 makes with respect to the axial direction. Angle θf is called the inclination angle of first connecting portion 52, angle θc is called the inclination angle of central connecting portion 48, and angle θs is called the inclination angle of second connecting portion 56.

[0094] In this tire 2, the first connecting portion 52, the central connecting portion 48, and the second connecting portion 56 have the same inclination direction. However, the inclinations of the first connecting portion 52 and the second connecting portion 56 are gentle, while the inclination of the central connecting portion 48 is steep. In other words, the inclination angle θc of the central connecting portion 48 is greater than the inclination angle θf of the first connecting portion 52, and is greater than the inclination angle θs of the second connecting portion 56. In the main land portion 36M having the transverse sipes 40, when the main land portion 36M is deformed by contacting with the road surface, the pair of wall surfaces 40W of the transverse sipes 40 can more effectively restrain each other's movement. The rigidity of the main land portion 36M is apparently increased, and deformation of the main land portion 36M is suppressed. The tire 2 can reduce rolling resistance. From this viewpoint, the transverse sipes 40 preferably include a first connecting portion 52, a central connecting portion 48, and a second connecting portion 56 that are inclined with respect to the axial direction, and the central connecting portion 48 located in the center has a steep inclination, and the first connecting portion 52 and the second connecting portion 56 have a gentle inclination.

[0095] From the viewpoint of enabling the transverse sipes 40 to more effectively contribute to reducing rolling resistance, the difference (θc-θf) between the inclination angle θc of the central connecting portion 48 and the inclination angle θf of the first connecting portion 52 is preferably greater than or equal to 30 degrees and less than or equal to 70 degrees, and more preferably greater than or equal to 40 degrees and less than or equal to 60 degrees. From the same viewpoint, the difference (θc-θs) between the inclination angle θc of the central connecting portion 48 and the inclination angle θs of the second connecting portion 56 is preferably 30 degrees or more and 70 degrees or less, and more preferably 40 degrees or more and 60 degrees or less.

[0096] In the tire 2, the first connecting portion 52 includes a first end portion 52a and a first main body portion 52b. The first end portion 52a and the first main body portion 52b extend straight. The first end portion 52a is connected to the middle circumferential groove 34m. The first end portion 52a is located between the middle circumferential groove 34m and the first main body portion 52b. The first end portion 52a and the first main body portion 52b may be connected directly or via an arc portion. In the first connecting portion 52 shown in FIG 3, the first end portion 52a and the first main body portion 52b are connected via a first arc portion 52c. 3, the inclination angle of the first main body portion 52b is larger than that of the first end portion 52a. The inclination angle θf of the first connecting portion 52 described above is represented by the inclination angle of the first main body portion 52b.

[0097] In the tire 2, the second connecting portion 56 includes a second end portion 56a and a second main body portion 56b. The second end portion 56a and the second main body portion 56b extend straight. The second end portion 56a is connected to the shoulder circumferential groove 34s. The second end portion 56a is located between the shoulder circumferential groove 34s and the second main body portion 56b. The second end portion 56a and the second main body portion 56b may be directly connected to each other, or may be connected to each other via an arc portion. In the second connecting portion 56 shown in FIG 3, the second end portion 56a and the second main body portion 56b are connected to each other via a second arc portion 56c. 3, the inclination angle of the second main body portion 56b is larger than that of the second end portion 56a. The inclination angle θs of the second connecting portion 56 described above is represented by the inclination angle of the second main body portion 56b.

[0098] 7, the length indicated by the double arrow L1a is the length of the first end portion 52a. The length indicated by the double arrow L1b is the length of the first body portion 52b. The length indicated by the double arrow L2a is the length of the second end portion 56a. The length indicated by the double arrow L2b is the length of the second body portion 56b. The lengths L1a and L1b, and the lengths L2a and L2b, are measured along the width centerline of the transverse sipe 40.

[0099] In the tire 2, from the viewpoint of enabling the transverse sipes 40 to more effectively contribute to reducing rolling resistance, the ratio (L1a / L1b) of the length L1a of the first end portion 52a to the length L1b of the first main body portion 52b is preferably 5% or more and 25% or less, and more preferably 10% or more and 20% or less. From the same viewpoint, the ratio (L2a / L2b) of the length L2a of the second end portion 56a to the length L2b of the second main body portion 56b is preferably 5% or more and 25% or less, and more preferably 10% or more and 20% or less.

[0100] As shown in FIG. 3, the tire 2 can be provided with a protrusion 58 at the groove bottom of the middle circumferential groove 34m. The protrusion 58 restrains the movement of the groove bottom of the middle circumferential groove 34m. This increases the rigidity of the crown portion and suppresses deformation. The tire 2 can maintain the crown portion in a flat state at the contour line of the tread surface 26 even if the load acting on the tread 4 fluctuates. Even if the load fluctuates, the edge on the circumferential side can be maintained in a flat state in the shape of the contact surface with the road surface. Since the tire 2 can reduce the ground contact pressure at the crown portion, the tire 2 can effectively suppress the decrease in cut chipping resistance. The tire 2 can effectively reduce the risk of cut chipping. From this viewpoint, it is preferable that the groove bottom of the middle circumferential groove 34m is provided with a protrusion 58.

[0101] As shown in Fig. 3, the protrusion 58 can include wide portions 60 having a large width and narrow portions 62 having a small width. The protrusion 58 shown in Fig. 3 includes a plurality of wide portions 60 and a plurality of narrow portions 62. The wide portions 60 and the narrow portions 62 are alternately arranged in the circumferential direction. The ridges 58 are softer than the ridges entirely composed of the wide portions 60, and harder than the ridges entirely composed of the narrow portions 62. The ridges 58 effectively restrain the movement of the bottom of the middle circumferential grooves 34m. The tire 2 can maintain the crown portion in a flat state at the contour line of the tread surface 26 even if the load acting on the tread 4 fluctuates. The tire 2 can maintain the circumferential edge in a flat state in the shape of the contact surface with the road surface even if the load fluctuates. The tire 2 can reduce the ground contact pressure at the crown portion, and therefore can effectively suppress the decrease in cut and chipping resistance. From this viewpoint, it is preferable that the ridges 58 include a plurality of wide portions 60 and a plurality of narrow portions 62, and the wide portions 60 and the narrow portions 62 are alternately arranged in the circumferential direction.

[0102] 3, the length indicated by the double-headed arrow WW is the width of the wide portion 60. The length indicated by the double-headed arrow WN is the width of the narrow portion 62. From the viewpoint of enabling the protrusion 58 to effectively contribute to the stiffness control of the groove bottom of the middle circumferential groove 34m, the width WW of the wide portion 60 is preferably 25% to 45% of the groove width at the groove mouth of the middle circumferential groove 34m, and more preferably 30% to 40%. The ratio (WN / WW) of the width WN of the narrow portion 62 to the width WW of the wide portion 60 is preferably 0.3 to 0.7, and more preferably 0.4 to 0.6.

[0103] As described above, the circumferential groove 34 cut in the tread 4 extends in a zigzag shape. The circumferential groove 34 has an apex T that protrudes toward the end TE of the tread surface 26. As shown in FIG. 3, the wide portion 60 of the protrusion 58 is disposed at the apex T of the circumferential groove 34 that extends in a zigzag shape. The protrusion 58 effectively restrains the movement of the groove bottom of the middle circumferential groove 34m. From the viewpoint of effectively suppressing the deterioration of cut-and-chip resistance, when the circumferential groove 34 cut in the tread 4 extends in a zigzag shape, it is preferable that the wide portion 60 of the protrusion 58 is disposed at the apex T that protrudes toward the end TE of the tread surface 26 of the circumferential groove 34 that extends in a zigzag shape.

[0104] As described above, the base layer 28 has a loss tangent LTb lower than the loss tangent LTc of the cap layer 30. Specifically, in the tire 2, the ratio (LTb / LTc) of the loss tangent LTb of the base layer 28 to the loss tangent LTc of the cap layer 30 is preferably 0.38 or less. This allows the base layer 28 to effectively contribute to reducing the rolling resistance. From this viewpoint, the ratio (LTb / LTc) is more preferably 0.30 or less.

[0105] In the tire 2, the fracture energy of the base layer 28 is preferably 7500 MPa·% or more. The base layer 28 can contribute to improving cut and chipping resistance. From this viewpoint, the fracture energy of the base layer 28 is more preferably 8000 MPa·% or more, and further preferably 8500 MPa·% or more.

[0106] As is clear from the above description, according to the present invention, a heavy duty tire can be obtained that can achieve a reduction in rolling resistance while suppressing a decrease in cut and chipping resistance. [Industrial Applicability]

[0107] The above-described technology capable of reducing rolling resistance while suppressing deterioration in cut and chipping resistance can be applied to various tires. [Explanation of symbols]

[0108] 2. Tires 4. Tread 6. Belt 8. Carcass 16. Sidewall 18...Belt ply 24···Carcass ply 26 Tread surface 28...Base layer 30 Cap layer 32...Groove 34, 34s, 34m...Circumferential groove 36, 36s, 36m, 36c, 36M...Land 38...interface 38u...Detour section 38h...Flat area 40. Transverse sipes 42...outer part 44...Inner part 46...Bend 58...projection 60 Wide section 62...Narrow part

Claims

1. A tire having a tread that comes into contact with a road surface and a belt located radially inside the tread, The tread includes a base layer that covers the entire belt, and a cap layer that is located radially outward of the base layer, the base layer has a loss tangent that is lower than the loss tangent of the cap layer; The tread has a plurality of circumferential grooves extending continuously in a circumferential direction, The circumferential grooves define a plurality of land portions arranged in an axial direction in the tread, The plurality of land portions include a main land portion located between two circumferential grooves, an interface between the cap layer and the base layer in the main land portion is located between a 50% depth position of a circumferential groove located adjacent to the main land portion and a 75% depth position of a groove depth of the circumferential groove, The main land portion includes a transverse sipe that crosses the main land portion, The transverse sipe has an outer portion including a groove mouth of the transverse sipe and an inner portion including a groove bottom of the transverse sipe, an interface between the cap layer and the base layer intersects with the inner portion; the outer portion is connected to each of the two circumferential grooves, The inner portion is not connected to either of the two circumferential grooves. Heavy duty tires.

2. The tread has a tread surface that comes into contact with a road surface, In a meridian cross section of the tire in a state in which the tire is mounted on a regular rim and the internal pressure of the tire is adjusted to 5% of the regular internal pressure, a contour line of the tread surface is composed of a plurality of circular arcs, and the plurality of circular arcs include a center circular arc and a pair of shoulder circular arcs located axially outward of the center circular arc, The center arc has a center on the equatorial plane of the tire and has a radius R1, Each shoulder arc is continuous with the center arc and has a radius R2; The radius R1 of the center arc is larger than the radius R2 of the shoulder arc, The position of the boundary between the center arc and the shoulder arc coincides in the axial direction with a position on the tread surface that is half the axial distance from the equatorial plane of the tire to the end of the tread surface, or the boundary is located axially inside of a position on the tread surface that is half the axial distance from the equatorial plane of the tire to the end of the tread surface.

2. A heavy duty tire according to claim 1.

3. The plurality of land portions include a center land portion, a pair of middle land portions located axially outward of the center land portion, and a pair of shoulder land portions located axially outward of the middle land portions, The center land portion includes the equator of the tire, The shoulder land portion includes an edge of the tread surface, the middle land portion includes a position on the tread surface that is half the axial distance from the equatorial plane of the tire to an end of the tread surface, and a boundary between the center arc and the shoulder arc, 3. A heavy duty tire according to claim 2.

4. The transverse sipe crossing the main land portion includes a plurality of bent portions bent at an angle θb.

2. A heavy duty tire according to claim 1.

5. The angle θb is 90 degrees or more.

5. A heavy duty tire according to claim 4.

Images