Heavy load tire

Abstract

To improve tire grounding property on a shoulder land part and further suppress the increase of a rolling resistance coefficient.SOLUTION: A tread 4 of a heavy load tire 2 includes a shoulder land part 331. The shoulder land part 331 includes a base part 34 and a cap part 36. The shoulder land part 331 includes a protrusion 39 that protrudes outside a profile PL in a radial direction. In the protrusion 39, an outermost point PP positioned most outside in the radial direction exists within the range of 5%-30% of an axial size X of the shoulder land part 331 in an axial direction from the intersection point PX of the profile PL with the shoulder land part 331 inside in the axial direction. In the end edge approximate point PN of the shoulder land part 331, the ratio of the thickness TNb of a base part 34 to the thickness TN of the tread 4 is higher than that of the thickness TPb of the base part 34 to the thickness TP of the tread 4 at the outermost point PP.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a tire for heavy loads.

Background Art

[0002] In a tire for heavy loads mounted on a truck or a bus, a plurality of grooves are engraved along the circumferential direction on the tread, thereby having two shoulder lands located on both outer sides in the axial direction and one or a plurality of center lands located between the two shoulder lands. Uneven wear is likely to occur in the shoulder lands, and a tire for suppressing the uneven wear has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the shoulder lands of the tire for heavy loads as described above, efforts to improve various performances such as its ground contact performance have been made from various viewpoints. An object of the present invention is to provide a tire for heavy loads that can improve the ground contact performance of the tire in the shoulder lands and further suppress an increase in the rolling resistance coefficient.

Means for Solving the Problems

[0005] The tire for heavy loads according to the present invention includes a tread having a tread surface that contacts the road surface, wherein the tread has two shoulder lands located on both outer sides in the axial direction and one or a plurality of center lands located between the two shoulder lands by engraving a plurality of grooves along the circumferential direction on the tread surface. The shoulder land portion has a base portion and a cap portion covering the base portion, and the base portion is made of cross-linked rubber having lower heat generation properties than the cap portion. The shoulder land portion has a convex portion that protrudes radially outward from a profile passing through the grounding ends on both axial sides of the tread and the equator. Among the convex portions, the outermost point located most radially outward is present in the range of 5% or more and 30% or less of the axial dimension of the shoulder land portion in the axial direction from the intersection on the inner side in the axial direction between the profile and the shoulder land portion. The ratio of the thickness of the base portion to the thickness of the tread at a point near the edge defined below of the shoulder land portion is higher than the ratio of the thickness of the base portion to the thickness of the tread at the outermost point. Point near the edge: A point on the tread surface located 10 mm inward in the axial direction from the grounding end

Advantages of the Invention

[0006] According to the pneumatic tire of the present invention, the grounding property of the tire at the shoulder land portion is improved, and it is possible to suppress an increase in the rolling resistance coefficient.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0008] 〔Details of Embodiments of the Present Invention〕 Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings.

[0009] The heavy-duty tire of the present invention (hereinafter, also simply referred to as "tire") is assembled to a rim. The inside of the tire is filled with air and the internal pressure of the tire is adjusted. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly has a rim and a tire assembled to this rim.

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

[0011] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the regular state. In the meridian cross-section of the tire, the dimensions and angles of each part that cannot be measured in the state where the tire is assembled to the regular rim are measured in the cross-section of the tire 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 matches the distance between the beads in the tire assembled to the regular rim. The configuration of the tire that cannot be confirmed in the state where the tire is assembled to the regular rim is confirmed in the aforementioned cross-section.

[0012] The regular rim means the rim defined in the standard that the tire depends on. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

[0013] The regular internal pressure means the internal pressure defined in the standard that the tire depends on. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0014] The normal load means the load defined in the standard on which the tire depends. The "maximum load capacity" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0015] A tire has a tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion is the part of the tire that contacts the road surface. The bead portion is the part of the tire that is fitted to the rim. The sidewall portion is the part of the tire that bridges between the tread and the bead.

[0016] In the present invention, among the elements constituting the tire, the loss tangent (tanδ) and the complex elastic modulus of the elements made of crosslinked rubber are measured using a viscoelastic spectrometer in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial strain = 10% Dynamic strain = ±1% Frequency = 10 Hz Mode = elongation mode Temperature = 70 °C

[0017] Regarding the above measurement, a test piece (length 40 mm × width 4 mm × thickness 1 mm) is sampled from the tire. The length direction of the test piece is made to coincide with the circumferential direction of the tire. When a test piece cannot be sampled from the tire, a test piece is sampled from a sheet-shaped crosslinked rubber (rubber sheet) obtained by pressurizing and heating the rubber composition used for forming the element to be measured at a temperature of 170 °C for 12 minutes. In the present invention, the loss tangent and the complex elastic modulus are represented by the loss tangent and the complex elastic modulus at 70 °C.

[0018] 〔Details of Embodiments of the Present Invention〕 FIG. 1 shows a part of a heavy-duty tire 2 (hereinafter, also simply referred to as "tire 2") according to an embodiment of the present invention. This tire 2 is a pneumatic tire for heavy-duty vehicles such as trucks or buses, for example, and is mounted on a heavy vehicle. FIG. 1 shows a cross-section of the first axial side of the tire 2. In the cross-section shown in FIG. 1, the left side of the tire 2 (the side opposite to the first axial side) that is omitted is defined as the second axial side.

[0019] FIG. 1 shows a part of a cross-section of the tire 2 (referred to as a "meridian cross-section") 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, in addition to the direction along the rotation axis of the tire 2, a direction parallel to the rotation axis. In each figure, the axial direction is indicated by the arrow "AD", and the radial direction is indicated by the arrow "RD". FIG. 2 is an enlarged view showing a part of the cross-section shown in FIG. 1. FIG. 2 shows the tread 4 of the tire 2 and the first axial side around it.

[0020] In FIGS. 1 and 2, the one-dot chain line CL extending in the radial direction represents the equatorial plane of the tire 2. The solid line BBL extending in the axial direction in FIG. 1 is the bead base line. The bead base line is a line that defines the rim diameter of the rim (refer to JATMA, etc.). Note that the tire 2 of the present embodiment has a bilaterally symmetric shape with respect to the equatorial plane CL.

[0021] The tire 2 has a tread 4, a pair of sidewalls 6, a pair of chafer 8, a pair of beads 10, a carcass 12, a belt 14, a pair of cushion layers 16, 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 outside the carcass 12. The tread 4 contacts the road surface at the tread surface 30. Two or more grooves 32 are engraved 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 form shown in FIGS. 1 and 2, five grooves 32 are provided in the tread 4, and the tread 4 has six land portions 33 extending in the circumferential direction. The land portions 33 on the most first side and the most second side (the most right side and the most left side in FIGS. 1 and 2) in the axial direction are respectively referred to as shoulder land portions 331. Among the plurality of land portions 33, those other than the shoulder land portions 331 on both axial sides are respectively referred to as center land portions 332.

[0023] The tread 4 has one center groove 321 located across the equatorial plane CL and four shoulder grooves 322 located on both outer sides in the axial direction of the center groove 321. The center groove 321 and the shoulder grooves 322 are circumferential grooves that are continuous in the circumferential direction.

[0024] The number of land portions 33 and the number of grooves 32, which is one less than the number of land portions 33, can be changed. The tread 4 only needs to have two shoulder land portions 331 located on both outer sides in the axial direction and one or more center land portions 332 located between the two shoulder land portions 331 when a plurality of grooves 32 are engraved in the tread surface 30 along the circumferential direction.

[0025] The shoulder land portion 331 has a base portion 34 and a cap portion 36 covering the base portion 34. The center land portion 332 has a base portion 34 and a cap portion 36 covering the base portion 34. That is, 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. In each of the land portions 33, the base portion 34 is made of a crosslinked rubber having lower heat generation property than the cap portion 36. The loss tangent (tanδ) of the base portion 34 is smaller than the loss tangent (tanδ) of the cap portion 36. The base portion 34 has lower heat generation property than the cap portion 36. The cap portion 36 is made of a crosslinked rubber having higher wear resistance and grip performance than the base portion 34. The radially outer surface of the cap portion 36 forms the tread surface 30.

[0026] On the first axial side shown in FIG. 2 (and the second axial side not shown), the base portion 34 of the shoulder land portion 331 and the base portion 34 of the center land portion 332 are continuous in the axial direction, and the cap portion 36 of the shoulder land portion 331 and the cap portion 36 of the center land portion 332 are continuous in the axial direction.

[0027] The position indicated by the symbol PC in FIGS. 1 and 2 is the equator. The equator PC is the intersection of the tread surface 30 and the equatorial plane CL. When the groove 32 is located on the equatorial plane CL as in the tire 2 of the present embodiment, the equator PC is specified based on the virtual tread surface in the center land portion 332 obtained assuming that the groove 32 is not present. The radial distance from the bead base line BBL obtained in the tire 2 in the normal state to the equator PC is the section height of the tire 2 (see JATMA, etc.).

[0028] The sidewall 6 is continuous with both ends of the tread 4 respectively. The sidewall 6 is located radially inside the tread 4. The sidewall 6 is located axially outside the carcass 12. The sidewall 6 is made of a crosslinked rubber considering cut resistance. The complex elastic modulus of the sidewall 6 is 2.0 MPa or more and 6.0 MPa or less.

[0029] The chafer 8 is located radially inside the sidewall 6. The chafer 8 contacts the rim. The chafer 8 is made of a crosslinked rubber considering 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 circumferentially. The core 38 includes a wound steel wire. The core 38 has a substantially 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. The apex 40 has an inner apex 42 and an outer apex 44.

[0031] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of chafe rs 8. The carcass 12 spans 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 FIGS. 1 and 2 consists of one carcass ply 48. The carcass ply 48 is turned back at the bead 10.

[0032] The carcass ply 48 (see FIG. 1) has a ply body 50 and a pair of turned-back portions 52. The ply body 50 spans between the pair of beads 10. Each turned-back portion 52 is continuous with the ply body 50 and is turned back at the bead 10. The turned-back portion 52 is turned back at the bead 10 from the axial inner side to the outer side. The bead 10 is sandwiched between the ply body 50 and the turned-back portion 52.

[0033] Although not shown, the carcass ply 48 (carcass 12) has a plurality of carcass cords arranged in parallel. These carcass cords are covered with topping rubber. Each carcass cord intersects the equatorial plane CL. The material of the carcass cord is steel. A steel cord is used as the carcass cord.

[0034] The belt 14 is located on the radially inner side of the tread 4. The belt 14 has a plurality of belt plies 54. The belt 14 of the present embodiment has four belt plies 54. The belt 14 has, in order from the radially inner side to the outer side, 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 tire 2 of the present embodiment, the second belt ply 54B has the largest axial dimension (the widest width), and the fourth belt ply 54D has the smallest axial dimension (the narrowest width).

[0035] Although not shown, each belt ply 54 includes a number of parallel belt cords. Each belt cord is inclined with respect to the equatorial plane CL. The material of the belt cord is steel. A steel cord is used as the belt cord. In each belt ply 54, the belt cord is covered with topping rubber.

[0036] In the case of the present embodiment (see FIG. 2), an edge member 541 made of a rubber layer is provided between the end of the third belt ply 54C and the end of the second belt ply 54B. The edge member 541 is made of crosslinked rubber. In the present disclosure, it is assumed that the edge member 541 is included in the base portion 34 of the shoulder land portion 331. By the edge member 541, the end of the third belt ply 54C is bent radially outward and is located radially away from the end of the second belt ply 54B.

[0037] The cushion layer 16 is located on both axial sides of the belt 14 and on the radially inner side of the belt 14. The cushion layer 16 is located between the belt 14 and the carcass 12 at the ends of the belt 14. The cushion layer 16 is composed of a soft crosslinked rubber and prevents the occurrence of damage at the axial ends of the belt 14. The complex elastic modulus of the cushion layer 16 is preferably 3.0 MPa or more and 6.0 MPa or less.

[0038] 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 folded back at the bead 10. Although not shown, the steel reinforcing layer 20 includes a plurality of parallel filler cords. The material of the filler cord is steel. That is, the steel reinforcing layer 20 has a plurality of steel cords. In the steel reinforcing layer 20, the steel cords are covered with topping rubber.

[0039] The inner liner 24 is located inside the carcass 12. The inner liner 24 is joined to the inner surface of the carcass 12 via an inflation (not shown) made of cross-linked rubber. The inner liner 24 constitutes the inner surface of the tire 2. The inner liner 24 is made of cross-linked rubber having excellent air barrier properties.

[0040] The fiber reinforcing layer 26 is located between the steel reinforcing layer 20 and the chafer 8. Although not shown, the fiber reinforcing layer 26 includes a plurality of parallel filler cords. The material of the filler cord is fiber, particularly organic fiber. That is, the fiber reinforcing layer 26 has a plurality of fiber cords. Nylon fiber is preferable as the organic fiber. In the fiber reinforcing layer 26, the fiber cords are covered with topping rubber.

[0041] The tread 4 will be further described. As shown in FIG. 2, the shoulder land portion 331 has a convex portion 39 protruding radially outward. The convex portion 39 protrudes radially outward from the profile PL passing through the grounding ends PE on both axial sides of the tread 4 and the equator PC. In FIG. 2, the profile PL is indicated by a two-dot chain line. In the case of the present embodiment, since the groove 32 is located on the equatorial plane CL, the equator PC is specified based on the virtual tread surface at the two center land portions 332 sandwiching the groove 32, and the profile PL coincides with the virtual tread surface.

[0042] The grounding end PE is located on the outer surface of the tread 4 and is the axial outer end of the contact surface with the road surface in the tire 2. The grounding end PE is the axial outer end of the contact surface obtained by applying a load of 80% of the load index to the tire 2 assembled on a regular rim with an internal pressure of 230 kPa, setting the camber angle to 0°, and bringing the tire 2 into contact with a flat road surface. The load index is, for example, an index defined in the JATMA standard and representing, by an exponent, the maximum mass, i.e., the maximum load capacity, that is allowed to be applied to a tire under specified conditions.

[0043] The profile PL is defined, in the meridian cross-section, by a curve passing through at least the grounding ends PE on both axial sides of the tread 4 and the equator PC. In the case of the tire 2 of the present embodiment, the shape of the tread surface 30 at the center land portion 332 is the shape along the profile PL. For this reason, the profile PL is defined, in addition to the grounding ends PE on both axial sides of the tread 4 and the equator PC, by a curve passing through both axial ends of each of all the center land portions 332. Note that the curve is composed of one or a plurality of circular arcs.

[0044] The outer peripheral surface of the convex portion 39 becomes the tread surface 30 at the shoulder land portion 331. The outer peripheral surface of the convex portion 39 is located radially outside the profile PL and has a curved surface shape that is convex radially outward. The outer peripheral surface of the convex portion 39 is in the shape along the curve LL in the meridian cross-section, and the curve LL is composed of a plurality of circular arcs. That is, the shoulder land portion 331 has a spherical rib on its outer peripheral surface.

[0045] In contrast, the center land portion 332 does not have a spherical rib. That is, in the case of the present embodiment, as described above, in the meridian cross-section, the shape of the tread surface 30 at the center land portion 332 is the shape along the profile PL. That is, the tread surface 30 of the center land portion 332 coincides with the profile PL.

[0046] The shoulder land portion 331 has a convex portion 39 that protrudes radially outward from the profile PL, so that the shoulder land portion 331 becomes thicker. Due to the convex portion 39, the grounding performance of the tire at the shoulder land portion 331 is improved. Furthermore, the braking performance and handling performance of the tire 2 are excellent. The land portion 33 where the tread surface 30 is located radially outside the profile PL is only the shoulder land portion 331. In the case of this embodiment, the grounding area of one shoulder land portion 331 is larger than the grounding area of one center land portion 332.

[0047] In the case of this embodiment, since the tread surface 30 of the center land portion 332 coincides with the profile PL, the convex portion 39 of the shoulder land portion 331 can be defined as follows. That is, in the meridian cross section, a line obtained by extending the tread surface 30 of the adjacent center land portion 332 toward the shoulder land portion 331 side on the axially inner side of the shoulder land portion 331 is defined as a "virtual extension line". Here (in FIG. 2), the virtual extension line coincides with the profile PL. The shoulder land portion 331 has a convex portion 39 that protrudes radially outside the virtual extension line.

[0048] FIG. 3 is an enlarged cross-sectional view of the shoulder land portion 331. FIG. 3 also shows a meridian cross section, the same as FIG. 2. In the meridian cross section, among the convex portions 39, a point located most radially outside is defined as the "outermost point PP". In FIG. 3, an axially inner intersection point of the profile PL and the shoulder land portion 331 is designated as "PX", and the axial dimension of the shoulder land portion 331 is designated as "X". The axial dimension X is the axial dimension from the intersection point PX to the grounding end PE.

[0049] The outermost point PP exists in the range of 5% or more and 30% or less of the axial dimension X of the shoulder land portion 331 in the axial direction from the intersection point PX. That is, in the shoulder land portion 331, the outermost point PP of the convex portion 39 exists in the range on the axially inner side rather than the central position in the axial direction.

[0050] In this way, since the outermost point PP exists in the range of 5% or more and 30% or less of the axial dimension X, that is, the outermost point PP exists in a relatively axially inner range in the convex portion 39, the contact pressure is prevented from concentrating on the outermost point PP, and uneven wear is suppressed.

[0051] At the outermost point PP of the convex portion 39, the ratio (ratio value: TPb / TP) of the thickness TPb of the base portion 34 to the thickness TP of the tread 4 is about 35%. Note that the thickness TPb of the base portion 34 at the outermost point PP is the dimension of the base portion 34 in the normal direction at the outermost point PP. The thickness TP of the tread 4 at the outermost point PP is the dimension of the tread 4 in the normal direction at the outermost point PP, and is the total thickness dimension of the base portion 34 and the cap portion 36 along the normal direction.

[0052] As shown in FIG. 3, a point on the tread surface 30 at a position 10 mm axially inward from the grounding end PE in the shoulder land portion 331 is defined as the "near-edge point PN". In the case of this embodiment, the near-edge point PN is included in the convex portion 39.

[0053] At the near-edge point PN, the ratio (ratio value: TNb / TN) of the thickness TNb of the base portion 34 to the thickness TN of the tread 4 is about 38%. Note that the thickness TNb of the base portion 34 at the near-edge point PN is the thickness dimension of the base portion 34 in the normal direction at the near-edge point PN. The thickness TN of the tread 4 at the near-edge point PN is the dimension of the tread 4 in the normal direction at the near-edge point PN, and is the total thickness dimension of the base portion 34 and the cap portion 36 along the normal direction.

[0054] Since the thickness of each part is likely to vary due to the rubber flow during tire molding at the grounding end PE, instead of the grounding end PE, the near-edge point PN located radially inward by a predetermined dimension (10 mm) from the grounding end PE is used as the measurement target for the thickness of each part.

[0055] Thus, the ratio (TNb / TN = approximately 38%) of the thickness TNb of the base portion 34 at the near-edge point PN is higher than the ratio (TPb / TP = approximately 35%) of the thickness TPb of the base portion 34 at the outermost point PP.

[0056] If this relationship is satisfied, the ratio (ratio value: TNb / TN) at the near-edge point PN may be, for example, 28% or more and 48% or less, and the ratio (ratio value: TPb / TP) at the outermost point PP may be, for example, 25% or more and 45% or less. At the near-edge point PN rather than the outermost point PP, the ratio of the thickness of the base portion 34 with excellent heat resistance is higher. It becomes possible to suppress an increase in the rolling resistance coefficient of the tire 2.

[0057] In the case of the form shown in FIG. 3, the normal line at the near-edge point PN intersects the third belt 54C. The thickness TN of the tread 4 and the thickness TNb of the base portion 34 are thickness dimensions from the position where the normal line intersects the third belt ply 54C. That is, the thickness dimensions of each part and the ratio (TNb / TN) are based on the third belt ply 54C (the radially outer surface of the third belt ply 54C). In addition, for the thickness dimensions of each part and the ratio (TPb / TP) at the outermost point PP, the third belt ply 54C is also used as a reference.

[0058] As shown in FIG. 3, instead of using the third belt ply 54C as a reference, among the plurality of belt plies, the belt ply located radially inside the shoulder land portion 331 and having the longest axial direction may be used as a reference (reference belt ply). In the case of the present embodiment, the belt ply located radially inside the shoulder land portion 331 and having the longest axial direction is the second belt ply 54B. Therefore, as shown in FIG. 4, with respect to the thickness dimensions of each part and the ratio of the thickness at each point, the second belt ply 54B (the radially outer surface of the second belt ply 54B) may be used as a reference. That is, the second belt ply 54B may be used as the reference belt ply. In this case, the edge member 541 may be included in the thickness of the base portion 34.

[0059] Even in the case shown in FIG. 4, the ratio (TNb / TN = about 51%) of the thickness TNb of the base portion 34 to the thickness TN of the tread 4 at the point PN near the edge is higher than the ratio (TPb / TP = about 40%) of the thickness TPb of the base portion 34 to the thickness TP of the tread 4 at the outermost point PP ((TNb / TN) > (TPb / TP)). At the point PN near the edge rather than the outermost point PP, the ratio of the thickness of the base portion 34, which is excellent in heat resistance, is high. It becomes possible to suppress an increase in the rolling resistance coefficient of the tire 2.

[0060] The case where the second belt ply 54B that is the longest in the axial direction is used as the reference belt ply (see FIG. 4) will be further described. At the outermost point PP, the portion (thickness TPb) including the base portion 34 from the reference belt ply (54B) to the interface F between the base portion 34 and the cap portion 36 is thinner than the cap portion 36 (thickness TPc) (TPb < TPc).

[0061] On the other hand, at the point PN near the edge, the portion (thickness TNb) including the base portion 34 from the reference belt ply (54B) to the interface F between the base portion 34 and the cap portion 36 is thicker than the cap portion 36 (thickness TNc) (TNb > TNc). Thus, in the case of the present embodiment, in one shoulder land portion 331, the magnitude relationship between the thickness of the base portion 34 and the thickness of the cap portion 36 is opposite between the outermost point PP and the point PN near the edge.

[0062] When the second belt ply 54B is used as the reference belt ply, at the point PN near the edge, the base portion 34, which is excellent in heat resistance, is thicker than the cap portion 36. For this reason, heat generation is suppressed in the shoulder land portion 331, and it becomes possible to suppress an increase in the rolling resistance coefficient of the tire 10.

[0063] In the form shown in FIG. 4, at the point PN near the edge, the ratio (TNb / TNc) of the thickness TNb of the base portion 34 to the thickness TNc of the cap portion 36 may be 0.5 or more and 1.5 or less.

[0064] The cushion layer 16 will be further described. As shown in FIG. 2, the cushion layer 16 is located at the axial end of the belt 14. The cushion layer 16 is located between the second belt ply 54B and the carcass 12. In the meridian cross section, the cushion layer 16 is thickest at a position corresponding to the end 54e of the second belt ply 54B. The cushion layer 16 has a shape that gradually thins from the thickest portion toward the inner side in the axial direction, and has a shape that gradually thins along the sidewall 6 from the thickest portion.

[0065] The outer axial ends of the first belt ply 54A and the second belt ply 54B are each located radially inward of the shoulder land portion 331 and overlap the cushion layer 16 in the radial direction. The outer axial end of the third belt ply 54C is located radially inward of the shoulder land portion 331 and overlaps radially outside the second belt ply 54B with the edge member 541 interposed therebetween. The inner axial portion 162 of the cushion layer 16 is located radially inward of the first belt ply 54A, the second belt ply 54B, and the third belt ply 54C. As described above, the shoulder land portion 331 has a convex portion 39.

[0066] The inner axial end (innermost point) 161 of the cushion layer 16 is located axially inward of the axial inner intersection point PX between the shoulder land portion 331 and the profile PL. The inner axial end 161 of the cushion layer 16 is located axially inward of the convex portion 39. As described above, the shoulder land portion 331 has the convex portion 39, which may increase the ground contact pressure and reduce the durability. In the case of this embodiment, the inner end 161 in the axial direction of the cushion layer 16 is located more axially inward than the convex portion 39. That is, the cushion layer 16 is disposed over the entire radially inner side of the shoulder land portion 331 having the convex portion 39. The cushion layer 16 can suppress the reduction in the durability of the shoulder land portion 331.

[0067] The inner end 161 in the axial direction of the cushion layer 16 is inner in the axial direction from the intersection point PX and exists in the range of 5% or more and 30% or less of the axial dimension X of the shoulder land portion 331. That is, the inner end 161 in the axial direction of the cushion layer 16 is axially inward from the intersection point PX with respect to the axial position, but does not largely enter the radially inner region of the center land portion 332 adjacent to the shoulder land portion 331. In the case of the form shown in FIGS. 2 and 3, the inner end 161 in the axial direction of the cushion layer 16 is located in the radially inner region of the shoulder groove 322 and does not enter the radially inner region of the center land portion 332.

[0068] As described above, with the configuration in which the inner end 161 in the axial direction of the cushion layer 16 is located more axially inward than the intersection point PX, it is possible to suppress the reduction in the durability of the shoulder land portion 331.

[0069] According to the tire 2 according to this embodiment having each of the above configurations, as described below, it is possible to improve the ground contact performance of the tire 2 in the shoulder land portion 331 and further suppress an increase in the rolling resistance coefficient. That is, the tread 4 of the tire 2 according to this embodiment has two shoulder land portions 331 located on both outer sides in the axial direction. The shoulder land portion 331 has a base portion 34 and a cap portion 36 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 shoulder land portion 331 has a convex portion 39 protruding radially outward from the profile PL.

[0070] Of the convex portions 39, the outermost point PP located most radially outward is present in a range of 5% or more and 30% or less in the axial direction from the intersection point PX on the inner side in the axial direction between the profile PL and the shoulder land portion 331. As described above (see FIG. 3 or FIG. 4), the ratio (TNb / TN) of the thickness TNb of the base portion 34 to the thickness TN of the tread 4 at the point PN near the edge of the shoulder land portion 331 is higher than the ratio (TPb / TP) of the thickness TPb of the base portion 34 to the thickness TP of the tread 4 at the outermost point PP.

[0071] The shoulder land portion 331 has the convex portion 39 protruding radially outward from the profile PL, so that the shoulder land portion 331 becomes thicker. For this reason, the grounding performance of the tire at the shoulder land portion 331 is improved. Furthermore, the braking performance and the handling performance are excellent. On the other hand, in the shoulder land portion 331, there is a possibility that heat generation increases and the rolling resistance coefficient increases. Therefore, in the case of this embodiment, in the shoulder land portion 331, the outermost point PP of the convex portion 39 exists in a relatively inner range of 5% or more and 30% or less in the axial direction from the intersection point PX. Furthermore, at the edge vicinity point PN located axially outside the outermost point PP, the ratio of the thickness TNb of the base portion 34 excellent in heat resistance is high. For this reason, it is possible to suppress an increase in the rolling resistance coefficient of the tire 2 in the shoulder land portion 331.

[0072] Particularly as described with reference to FIG. 4, at the outermost point PP, the portion including the base portion 34 from the reference belt ply (54B) to the interface F between the base portion 34 and the cap portion 36 is thinner than the cap portion 36, but at the edge vicinity point PN, the portion including the base portion 34 from the reference belt ply (54B) to the interface F between the base portion 34 and the cap portion 36 is thicker than the cap portion 36. In this way, at the edge vicinity point PN, since the thickness ratio of the base portion 34 having better heat resistance than the cap portion 36 is high, heat generation in the shoulder land portion 331 can be suppressed, and it is possible to suppress an increase in the rolling resistance coefficient.

[0073] As described above, the shoulder land portion 331 has a convex portion 39, which may increase the ground pressure and reduce the durability. However, in the case of the present embodiment, the inner end 161 in the axial direction of the cushion layer 16 is located more axially inward than the intersection point PX. The inner end 161 in the axial direction of the cushion layer 16 is located more axially inward than the convex portion 39. This cushion layer 16 can suppress the decrease in the durability of the shoulder land portion 331.

Industrial Applicability

[0074] The technology for improving the ground contact performance and the like of the tire 2 described above can be applied to various tires.

[0075] 〔Supplementary Note〕 The present invention includes the following aspects. (1) The heavy-duty tire includes a tread having a tread surface that contacts the road surface. The tread has a plurality of grooves engraved along the circumferential direction on the tread surface, thereby having two shoulder land portions located on both outer sides in the axial direction and one or more center land portions located between the two shoulder land portions. The shoulder land portion has a base portion and a cap portion covering the base portion. The base portion is composed of a cross-linked rubber having lower heat generation than the cap portion. The shoulder land portion has a convex portion that protrudes radially outward from a profile passing through the ground contact ends on both axial sides of the tread and the equator. Among the convex portions, the outermost point located most radially outward is in the range of 5% or more and 30% or less of the axial dimension of the shoulder land portion in the axial direction from the intersection point on the inner side in the axial direction between the profile and the shoulder land portion. The ratio of the thickness of the base portion to the thickness of the tread at the point near the edge defined below of the shoulder land portion is higher than the ratio of the thickness of the base portion to the thickness of the tread at the outermost point. Point near the edge: A point on the tread surface located 10 mm inward in the axial direction from the ground contact end

[0076] (2) The heavy-duty tire of (1) includes a plurality of belt plies and has a belt located radially inside the tread. Among the plurality of belt plies, when the belt ply located radially inside the shoulder land portion and having the longest axial length is used as the reference belt ply, at the outermost point, the portion including the base portion from the reference belt ply to the interface between the base portion and the cap portion is thinner than the cap portion, and at the point near the edge, the portion including the base portion from the reference belt ply to the interface between the base portion and the cap portion is thicker than the cap portion.

[0077] (3) The tread surface of the center land portion of the heavy-duty tire of (1) or (2) that matches the profile.

[0078] (4) Any one of the heavy-duty tires of (1) to (3) has a belt located radially inside the tread and a cushion layer located radially inside the belt on both axial sides of the belt. The inner end of the cushion layer in the axial direction is located axially inside the intersection of the shoulder land portion and the profile in the axial direction.

[0079] (5) In the heavy-duty tire of (4), the inner end of the cushion layer in the axial direction is axially inside the intersection of the profile and the shoulder land portion in the axial direction and exists in the range of 5% or more and 30% or less of the axial dimension of the shoulder land portion.

Explanation of reference numerals

[0080] 2 Heavy-duty tire 4 Tread 14 Belt 16 Cushion layer 161 End 30 Tread surface 32 Groove 33 Land portion 34 Base portion 36 Cap portion 39 Protrusion 54 Belt ply 331 Shoulder land part 332 Center land part F interface PE grounding terminal PC equator PL profile PN near-edge point PP outermost point PX intersection point TP tread thickness TPb base part thickness TN tread thickness TNb base part thickness X axial dimension of shoulder land part

Claims

1. A tread having a tread surface that contacts the road surface, wherein the tread has two shoulder lands located on both outer sides in the axial direction and one or more center lands located between the two shoulder lands by engraving a plurality of grooves along the circumferential direction on the tread surface, the shoulder land has a base portion and a cap portion covering the base portion, and the base portion is made of a crosslinked rubber having lower heat generation than the cap portion, the shoulder land has a convex portion protruding radially outward from a profile passing through the grounding ends on both axial sides and the equator of the tread, among the convex portions, the outermost point located most radially outward is present in a range of 5% or more and 30% or less of the axial dimension of the shoulder land in the axial direction from the intersection on the inner side in the axial direction between the profile and the shoulder land, the ratio of the thickness of the base portion to the thickness of the tread at a point near the edge defined below of the shoulder land is higher than the ratio of the thickness of the base portion to the thickness of the tread at the outermost point, A tire for heavy loads. Point near the edge: A point on the tread surface located 10 mm inward in the axial direction from the grounding end

2. having a belt located radially inside the tread and including a plurality of belt plies, when, among the plurality of belt plies, the belt ply located radially inside the shoulder land and having the longest axial length is used as a reference belt ply, at the outermost point, the portion including the base portion from the reference belt ply to the interface between the base portion and the cap portion is thinner than the cap portion, at the point near the edge, the portion including the base portion from the reference belt ply to the interface between the base portion and the cap portion is thicker than the cap portion, The heavy load tire according to claim 1.

3. The tread surface of the center land coincides with the profile, The heavy load tire according to claim 1 or claim 2.

4. a belt located radially inside the tread, and a cushion layer located on both axial sides of the belt and radially inside the belt, having, the inner end in the axial direction of the cushion layer is located axially inward from the intersection on the inner side in the axial direction between the shoulder land and the profile, The heavy load tire according to claim 1 or claim 2.

5. The inner end of the cushion layer in the axial direction is inside in the axial direction from the inner intersection of the profile and the shoulder land portion, and exists within a range of 5% or more and 30% or less of the axial dimension of the shoulder land portion. The heavy load tire according to claim 4.

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