Heavy-duty tires

Abstract

To provide a heavy-duty tire 2 that can suppress the accumulation of static electricity while maintaining resistance to uneven wear. [Solution] The tire 2 comprises a reinforcing layer 14 and a tread 4. The tread 4 comprises a cap layer 30 and a conductive part 36. The tread 4 comprises at least four land sections 52. The at least four land sections 52 comprise two shoulder land sections 54 and a plurality of main land sections 56. Of the plurality of main land sections 56, at least one main land section 56 comprises a conductive part 36. The reinforcing layer 14 comprises a plurality of belt plies 64 and a full band 70 arranged radially. Each of the plurality of belt plies 64 contains a belt cord 66. The material of each belt cord 66 is steel. The full band 70 contains a helically wound band cord 72. The material of the band cord 72 is steel.

Description

Technical Field

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

Background Art

[0002] Considering the impact on the environment, reducing rolling resistance is strongly demanded for tires. To reduce rolling resistance, applying a low heat-generating crosslinked rubber to the tread is considered. The low heat-generating crosslinked rubber contains a large amount of silica. A tread composed of a low heat-generating crosslinked rubber has a higher electrical resistance than a tread composed of a crosslinked rubber containing a large amount of carbon black. The tire contacts the road surface in the tread. When the tread is composed of a low heat-generating crosslinked rubber, there is a concern that static electricity accumulates in the vehicle. Therefore, for example, as described in Patent Document 1, a conductive bridge (hereinafter, a conductive portion) composed of a conductive crosslinked rubber is provided in the tread.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tire for heavy loads that can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

Means for Solving the Problems

[0005] The heavy-duty tire according to the present invention comprises a pair of beads, a carcass spanning between the pair of beads, a reinforcing layer located radially outside the carcass, and a tread covering the reinforcing layer from the radially outside. The tread comprises a cap layer in contact with the road surface and a conductive portion that penetrates the cap layer radially and connects the road surface and the reinforcing layer. The tread comprises at least three circumferential grooves extending continuously in the circumferential direction. The at least three circumferential grooves constitute at least four land portions of the tread that are aligned axially. The at least four land portions comprise two shoulder land portions located on the outermost axial side and a plurality of main land portions located between the two shoulder land portions. Of the plurality of main land portions, at least one main land portion comprises the conductive portion. The reinforcing layer comprises a belt including a plurality of belt plies and a band including a full band. The plurality of belt plies and the full band are aligned radially. Each of the plurality of belt plies includes a plurality of parallel belt cords. Each of the aforementioned belt cords is made of steel. The full band includes a spirally wound band cord. The band cord is made of steel. [Effects of the Invention]

[0006] According to the present invention, a heavy-duty tire can be obtained that suppresses the accumulation of static electricity while maintaining resistance to uneven wear. The heavy-duty tire of the present invention can achieve a reduction in rolling resistance. [Brief explanation of the drawing]

[0007] [Figure 1] This is a cross-sectional view showing a part of a heavy-duty tire according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the tread portion of the tire in Figure 1. [Figure 3] Figure 2 is a cross-sectional view showing a portion of the tread area. [Figure 4] This is a schematic diagram illustrating the structure of the reinforcement layer. [Figure 5] This is a cross-sectional view showing a part of a heavy-duty tire according to another embodiment of the present invention. [Figure 6] This is a cross-sectional view showing a modified example of a circumferential groove. [Figure 7] This is a cross-sectional view showing a modified example of a circumferential groove. [Figure 8] Figure 8 is a schematic diagram illustrating a device for measuring the electrical resistance of a tire. [Modes for carrying out the invention]

[0008] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0009] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

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

[0011] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire's cross-section, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim. The tire's structure, which cannot be confirmed when the tire is mounted on a standard rim, is confirmed at the aforementioned cross-section.

[0012] A genuine rim refers to a rim defined 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 all considered genuine rims.

[0013] The normal internal pressure means the internal pressure defined in the standard on which the tire depends. The "maximum air pressure" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are the normal 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 the normal loads.

[0015] In the present invention, the crosslinked rubber is a crosslinked product of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is a material obtained by mixing a rubber component and chemicals in a kneader such as a Banbury mixer.

[0016] Examples of the rubber component include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and butyl rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, sulfur, and vulcanization accelerators. The selection of the raw rubber component and chemicals, the content of the selected chemicals, etc. are appropriately determined according to the specifications of elements such as the tread and sidewall to which the rubber composition is applied.

[0017] In the present invention, the conductive crosslinked rubber means a crosslinked rubber having a volume resistivity of less than 1.0×10 8 Ω·cm. The non-conductive crosslinked rubber means a crosslinked rubber having a volume resistivity of 1.0×10 8This refers to cross-linked rubber having a volume resistivity of Ω·cm or greater. The conductivity of cross-linked rubber is controlled, for example, by the carbon black content. The volume resistivity of cross-linked rubber is measured, for example, in accordance with the double-ring electrode method specified in JIS K6271.

[0018] In this invention, the number of cords contained per 50 mm width of a tire element containing parallel cords is expressed as cord ends (unit: ends / 50 mm). Unless otherwise specified, cord ends are obtained at the cross-section of the element, which is obtained by cutting the element with a plane perpendicular to the length direction of the cords. For elements containing helically wound cords, since multiple cords appear to be in parallel, the cord ends can be obtained in the same manner as for tire elements containing parallel cords.

[0019] In this invention, the tread portion of a tire is the part of the tire that contacts the road surface. The bead portion is the part of the tire that is fitted onto the rim. The sidewall portion is the part of the tire that spans the space between the tread portion and the bead portion. The tire comprises the tread portion, a pair of bead portions, and a pair of sidewall portions. The central part of the tread is also called the crown. The edges of the tread are also called the shoulder.

[0020] In this invention, a tire having good conductive performance means that the electrical resistance of the tire is 10 8 This means it is less than or equal to Ω. The electrical resistance of a tire is measured, for example, as follows. A measuring device 110 having the configuration shown in Figure 8 is used for this electrical resistance measurement. The measuring device 110 comprises an insulating plate 112, a metal plate 114, a tire mounting shaft 116, and an electrical resistance meter 118. The electrical resistance value of the insulating plate 112 is 10 12It is greater than Ω. The metal plate 114 is placed on the insulating plate 112. The surface of the metal plate 114 is polished, and the electrical resistance of the metal plate 114 is 10Ω or less. The tire-rim assembly is held on the tire mounting shaft 116. Using this measuring device 110, the electrical resistance of the tire-rim assembly, i.e., the tire, is measured in the following manner. The procedure for measuring the electrical resistance of a tire is as follows: (1) Thoroughly remove any mold release agent or dirt adhering to the surface of the prototype tire SP. After removal, allow the tire SP to dry completely. (2) The prototype tire SP is mounted onto the rim R to prepare the tire-rim assembly. Soap water is used as a lubricant at the contact point between the two. (3) After leaving the tire-rim assembly in the test room for 2 hours, the tire-rim assembly is attached to the tire mounting shaft 116. (4) Apply a load to the tire-rim assembly for 0.5 minutes, then release the load from the tire-rim assembly. Apply a load to the tire-rim assembly for another 0.5 minutes, then release the load from the tire-rim assembly. Apply a load to the tire-rim assembly for another 2 minutes, then release the load from the tire-rim assembly. (5) After the test voltage has been applied and 5 minutes have elapsed, the electrical resistance between the tire mounting shaft 116 and the metal plate 114 is measured using an electrical resistance meter 118. The measurement is performed at 90° intervals (4 locations) in the circumferential direction of the tire SP. The maximum value is used as the measured value of the electrical resistance of the tire SP. Other conditions for measurement are as follows: Rim size, internal pressure, and load are set according to JATMA standards depending on the tire being measured. • Rim material: Aluminum alloy • Test environment temperature (test room temperature): 25℃ ·Humidity: 50% • Measurement range of electrical resistance meter 118: 1.0 × 10 3 ~1.6×10 16 Ω • Test voltage (applied voltage): 1000V

[0021] [Practices that formed the basis of this invention] In addition to passenger car tires, the application of low-heat-generating cross-linked rubber to the tread of heavy-duty tires is being considered to reduce rolling resistance. When low-heat-generating cross-linked rubber is applied to the tread, the aforementioned conductive parts are provided on the tread to suppress the accumulation of static electricity on the vehicle.

[0022] Conductive areas are unique in tread. There are concerns that if conductive areas are included in the tread, these areas may become the starting point for uneven wear or cracks.

[0023] When heavy-duty tires are mounted on a vehicle's steering axle, uneven wear is more likely to occur on the tire's shoulder portion compared to the crown portion. For heavy-duty tires, considering resistance to uneven wear, it is advisable to consider providing conductive material not on the shoulder portion, but on the crown portion, specifically the crown portion or middle portion.

[0024] Incidentally, the contact pressure of a new tire tends to be higher in the crown area. Even if a conductive part is provided in the crown area to reduce the risk of uneven wear in the shoulder area, there is still a risk that the conductive part could become the starting point for uneven wear.

[0025] Therefore, in order to obtain a heavy-duty tire that can suppress the accumulation of static electricity while maintaining resistance to uneven wear, the inventors investigated the cause of increased contact pressure at the crown portion of a new tire from the perspective of the contact surface shape. They found that the contact shape of a new tire has a rounded shape, which makes it easy for the contact pressure at the crown portion to increase, and thus completed the present invention described below.

[0026] [Summary of Embodiments of the Invention] The present invention comprises a pair of beads, a carcass spanning between the pair of beads, a reinforcing layer located radially outside the carcass, and a tread covering the reinforcing layer from radially outside the reinforcing layer, wherein the tread comprises a cap layer in contact with the road surface and a conductive portion that penetrates the cap layer radially and connects the road surface and the reinforcing layer, the tread comprises at least three circumferential grooves extending continuously in the circumferential direction, the at least three circumferential grooves forming at least four land portions aligned axially on the tread, and the at least four land portions having two shoulders located on the outermost axial side A heavy-duty tire comprising a land portion and a plurality of main land portions located between two of the shoulder land portions, wherein at least one of the plurality of main land portions is provided with the conductive portion, the reinforcing layer comprises a belt including a plurality of belt plies and a band including a full band, the plurality of belt plies and the full band are arranged radially, each of the plurality of belt plies includes a plurality of parallel belt cords, each belt cord is made of steel, and the full band includes a helically wound band cord, the band cord is made of steel.

[0027] The heavy-duty tire of the present invention can suppress the accumulation of static electricity while maintaining resistance to uneven wear. Although the mechanism by which this effect is achieved is not yet clear, it is presumed to be as follows.

[0028] The conductive section connecting the road surface and the reinforcing layer contributes to the discharge of static electricity to the road surface. In this tire, static electricity that would accumulate in tires without conductive sections is effectively discharged to the road surface. This tire has good conductive performance. This tire can suppress the accumulation of static electricity. The conductive portion is located on the main land area, situated between the two outermost shoulder land areas in the axial direction, rather than on the two outermost shoulder land areas. This prevents an increased risk of uneven wear. A reinforcing layer is located between the tread and the carcass, and this reinforcing layer has a full band. The full band includes a spirally wound band cord. The full band suppresses the tire's tendency to spread outwards. Because the band cord is made of steel cord, this movement is effectively suppressed. The contact patch shape of this tire when new is rectangular, not round. With this tire, the contact pressure on the crown is less likely to increase compared to tires without a full band. Because the change in tire shape due to driving is suppressed, the rectangular contact patch shape is maintained. Even when worn, this tire can maintain a state where the contact pressure on the crown does not increase easily. The conductive part located on the main contact patch is less likely to become the starting point for uneven wear. This tire exhibits improved resistance to uneven wear compared to conventional tires with conductive parts in the crown. This tire maintains good resistance to uneven wear. While maintaining resistance to uneven wear, this tire suppresses the accumulation of static electricity. Even when the tread cap layer is made of low-heat-generating cross-linked rubber, the conductive parts can stably perform their function. This tire achieves reduced rolling resistance.

[0029] Preferably, the ratio of the axial width of the full band to the width of the tread is 0.60 or more. In this case, the full band can effectively contribute to suppressing an increase in contact pressure at the crown portion. This tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0030] Preferably, the code ends of the full band are 20 ends / 50 mm or more. In this case, the full band can effectively contribute to suppressing an increase in contact pressure at the crown portion. This tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0031] Preferably, the width of the conductive portion is 8.0 mm or less. In this case, wear in the conductive portion is suppressed. This tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0032] Preferably, the plurality of belt plies comprises a reference belt ply and a sub-reference belt ply, wherein the reference belt ply is the belt ply having the widest axial width among the plurality of belt plies, the sub-reference belt ply is the belt ply having the second widest axial width among the plurality of belt plies, the direction of inclination of the belt cords included in the sub-reference belt ply is opposite to the direction of inclination of the belt cords included in the reference belt ply, and the full band is located between the reference belt ply and the sub-reference belt ply. In this case, the full band is adequately protected from damage. The full band can perform its function stably. This tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0033] Preferably, of the multiple main land sections, only one main land section is equipped with the conductive part. In this case, the tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0034] Preferably, among the multiple main land sections, the main land section located on the equatorial plane, or the main land section closest to the equatorial plane, is the crown land section, and if the tread has three or more main land sections, the main land section located next to the crown land section is the middle land section, and the main land section on which the conductive part is provided is either the crown land section or the middle land section. In this case, the tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0035] Preferably, a strip layer made of cross-linked rubber is further provided between the carcass and the reinforcing layer, and the strip layer has an axial width approximately the same as the axial width of the full band. In this case, damage between the carcass and the reinforcing layer is suppressed, so that the full band can stably perform its function. This tire can suppress the accumulation of static electricity while maintaining resistance to uneven wear.

[0036] Thus, according to the present invention, a heavy-duty tire can be obtained that suppresses the accumulation of static electricity while maintaining resistance to uneven wear. This will be explained in detail below using the heavy-duty tire 2 shown in Figure 1 as an example.

[0037] [Details of the Embodiments of the Invention] Figure 1 shows a part of a heavy-duty tire 2 according to one embodiment of the present invention. This tire 2 is mounted on vehicles such as trucks and buses. The tire 2 shown in Figure 1 is mounted on a rim R. The rim R is a standard rim.

[0038] Figure 1 shows a portion of the cross-section of tire 2 (hereinafter referred to as the meridian cross-section) along the plane containing the rotation axis of tire 2. Figure 2 shows a portion of the cross-section shown in Figure 1. Figure 2 shows the tread portion T of tire 2. The direction indicated by the double arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. The direction indicated by the double arrow RD is the radial direction of tire 2. The direction perpendicular to the plane of the paper is the circumferential direction of tire 2. The dashed line EL extending radially represents the equatorial plane of tire 2.

[0039] In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2. The direction indicated by arrow RD1 is the radial outward direction of tire 2, and the direction indicated by arrow RD2 is the radial inward direction of tire 2.

[0040] This tire 2 comprises a tread 4, a pair of sidewalls 6, a pair of chafers 8, a pair of beads 10, a carcass 12, a reinforcing layer 14, a pair of cushioning layers 16, a strip layer 18, and an inner liner 20. The internal structure of tire 2 is symmetrical with respect to the equatorial plane, except for the conductive parts which will be described later.

[0041] The tread 4 is located radially outward of the carcass 12. The tread 4 has a tread surface 22. The tire 2 contacts the road surface at the tread surface 22. The tread surface 22 forms part of the outer circumferential surface 4s of the tread 4. The tread 4 is located radially outward of the reinforcing layer 14. The tread 4 covers the reinforcing layer 14 from its radially outward side. The tread 4 is laminated on the reinforcing layer 14. The tread 4 is in contact with the reinforcing layer 14 at its inner circumferential surface 4n.

[0042] The position indicated by the symbol Eq is the equator of tire 2. Equator Eq is the intersection of the tread surface 22 and the equatorial surface. In cases where the grooves, described later, are located on the equatorial surface, as in tire 2, equator Eq is determined based on a virtual tread surface obtained by assuming that there are no grooves on the equatorial surface. The position indicated by the symbol TE is the edge of the tread surface 22. In the case of a tire where the edge of the tread surface is not identifiable by appearance, the position on the outer surface of the tire corresponding to the axial outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and bringing the tire into contact with a plane is used as the edge of the tread surface.

[0043] In Figure 1, the length indicated by the double arrow TW is the width of the tread 4. The width TW of the tread 4 is the axial distance from one end TE to the other end TE of the tread surface 22.

[0044] Each sidewall 6 is connected to the edge of the tread 4. The sidewalls 6 are located axially outward of the carcass 12. The sidewalls 6 are made of conductive cross-linked rubber. The sidewalls 6 may also be made of non-conductive cross-linked rubber.

[0045] Each chafer 8 is located radially inward of the sidewall 6. The chafer 8 is in contact with the rim R. The chafer 8 is made of conductive cross-linked rubber.

[0046] Each bead 10 is located axially inward of the chafer 8. The bead 10 is located radially inward of the sidewall 6. The bead 10 comprises a core 24 and an apex 26. Although not shown, the core 24 includes a circumferentially wound steel wire. The apex 26 is located radially outward of the core 24. The apex 26 is made of conductive cross-linked rubber. The bead 10 is conductive. The apex 26 is tapered. The apex 26 is rigid. This apex 26 may consist of a rigid inner apex and a flexible outer apex. In this case, the inner apex is located radially outward of the core 24, and the outer apex is located radially outward of the inner apex.

[0047] The carcass 12 is located inside the tread 4, a pair of sidewalls 6, and a pair of chafers 8. The carcass 12 spans between a pair of beads 10. The carcass 12 comprises at least one carcass ply 28. The carcass 12 of this tire 2 consists of one carcass ply 28. The carcass ply 28 is folded back axially from the inside to the outside at each bead 10. Although not shown in the diagram, the carcass ply 28 contains numerous parallel carcass cords. These carcass cords are covered with topping rubber and intersect with the equatorial plane. This carcass 12 has a radial structure. The material of the carcass cords is steel. In other words, the carcass cords are steel cords. The topping rubber is made of conductive cross-linked rubber. The carcass ply 28, i.e., the carcass 12, is conductive.

[0048] The reinforcing layer 14 is located radially outward of the carcass 12. The reinforcing layer 14 is located radially between the tread 4 and the carcass 12. As mentioned above, the reinforcing layer 14 is covered by the tread 4.

[0049] Each cushion layer 16 is located between the reinforcing layer 14 and the carcass 12 at the end of the reinforcing layer 14 (specifically, the belt described later). The cushion layer 16 is made of soft cross-linked rubber. The cushion layer 16 is conductive.

[0050] The strip layer 18 is located radially inward of the tread 4, between the carcass 12 and the reinforcing layer 14. The strip layer 18 is laminated onto the carcass 12, and the reinforcing layer 14 is laminated onto the strip layer 18. In the axial direction, the strip layer 18 is located between one cushion layer 16 and the other cushion layer 16. The strip layer 18 is made of conductive cross-linked rubber. If the strip layer 18 is not provided, the reinforcing layer 14 is laminated onto the carcass 12.

[0051] The inner liner 20 is located inside the carcass 12. The inner liner 20 forms the inner surface of the tire 2. The inner liner 20 is made of cross-linked rubber with excellent air-shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

[0052] The tread 4 of this tire 2 comprises a cap layer 30 and a base layer 32. The cap layer 30 has the aforementioned tread surface 22. The cap layer 30 is in contact with the road surface. The cap layer 30 is made of cross-linked rubber that takes into account wear resistance and grip performance. This cap layer 30 may be made of cross-linked rubber that takes into account not only wear resistance and grip performance but also low heat generation. Cross-linked rubber that takes low heat generation into account contains silica. If the silica content is high, the cap layer 30 is made of non-conductive cross-linked rubber. The base layer 32 is located radially inward of the cap layer 30. The cap layer 30 and the base layer 32 are aligned radially. The entire base layer 32 is covered by the cap layer 30. The base layer 32 is made of cross-linked rubber that is designed to generate little heat. If the silica content of the base layer 32 is high, it is also made of non-conductive cross-linked rubber.

[0053] In the tread portion T of tire 2, the part composed of the cap layer 30 and the base layer 32 is the main body 34 of the tread 4. The tread 4 of this tire 2 further comprises a conductive portion 36 in addition to the main body 34. The conductive portion 36 penetrates the main body 34, and more specifically the cap layer 30 and the base layer 32 in the radial direction. The conductive portion 36 extends straight from the radially outer end face (hereinafter referred to as the first end face 38) to the radially inner end face (hereinafter referred to as the second end face 40). The conductive portion 36 has a uniform width in the meridional cross-section of the tire 2.

[0054] The first end face 38 of the conductive portion 36 forms part of the outer circumferential surface 4s (specifically the tread surface 22). The second end face 40 of the conductive portion 36 forms part of the inner circumferential surface 4n of the tread 4. The conductive portion 36 bridges the gap between the tread surface 22 and the inner circumferential surface 4n. As described above, the tread 4 contacts the road surface at the tread surface 22 and contacts the reinforcing layer 14 at the inner circumferential surface 4n. The conductive portion 36 connects the road surface and the reinforcing layer 14. The tread 4 of this tire 2 comprises a cap layer 30 that contacts the road surface and a conductive portion 36 that penetrates the cap layer 30 radially and connects the road surface and the reinforcing layer 14.

[0055] The conductive portion 36 extends continuously in the circumferential direction. Although not shown, the conductive portion 36 may also be formed by arranging multiple conductive elements at predetermined intervals in the circumferential direction. In this case, the conductive portion 36 extends intermittently in the circumferential direction.

[0056] The conductive part 36 is made of conductive cross-linked rubber. When the conductive part 36 comes into contact with the road surface, an electrical connection is made between the road surface and the reinforcing layer 14.

[0057] Grooves 42 are cut into the tread 4. This forms the tread pattern. The tread 4 has a tread pattern. The tread 4 of this tire 2 is provided with at least three circumferential grooves 44. Each circumferential groove 44 extends continuously in the circumferential direction. The circumferential grooves 44 are not sipes with a groove width of less than 1.0 mm.

[0058] Figure 3 shows a cross-section of the circumferential groove 44. The circumferential groove 44 has a pair of wall surfaces 44S including the groove opening 44M and a bottom surface 44B including the groove bottom 44T.

[0059] In this invention, a circumferential groove having a wide groove width, in which the pair of wall surfaces do not come into contact with each other even when the tread deforms upon contact with the road surface, is called a circumferential main groove. A circumferential groove having a narrow groove width, in which the pair of wall surfaces can come into contact with each other when the tread deforms upon contact with the road surface, is called a circumferential narrow groove.

[0060] All of the circumferential grooves 44 provided in this tread 4 have a wide groove width. Even when the tread 4 deforms in contact with the road surface, the pair of wall surfaces 44S of the circumferential grooves 44 do not come into contact with each other. All of the circumferential grooves 44 provided in this tread 4 are circumferential main grooves 46. From the viewpoint of enabling tire 2 to exhibit good wet performance, the groove depth of the circumferential main groove 46 is preferably 8 mm or more and 21 mm or less, and more preferably 13 mm or more and 18 mm or less. The groove width of the circumferential main groove 46 is preferably 4.0% or more and 10% or less of the width TW of the tread 4.

[0061] In this invention, when the tread has multiple circumferential grooves arranged in the axial direction, the two circumferential grooves located on the outermost axial side of these grooves are the shoulder circumferential grooves. The circumferential groove located on the equatorial plane is the center circumferential groove. If no circumferential grooves are provided on the equatorial plane, the circumferential groove closest to the equatorial plane among the circumferential grooves located in the zone between the equatorial plane and the edge of the tread surface is the center circumferential groove. If a circumferential groove is located between the center circumferential groove and the shoulder circumferential groove, the circumferential groove located between the center circumferential groove and the shoulder circumferential groove is the middle circumferential groove.

[0062] The tread 4 of this tire 2 is equipped with three circumferential grooves 44. Of the three circumferential grooves 44, the circumferential groove 44 located on the outermost axial side is the shoulder circumferential groove 48. The circumferential groove 44 located on the equatorial plane is the center circumferential groove 50. This tread 4 has the center circumferential groove 50 and a pair of shoulder circumferential grooves 48.

[0063] As mentioned above, the tread 4 is provided with at least three circumferential grooves 44. The at least three circumferential grooves 44 constitute at least four land portions 52 on the tread 4. The at least four land portions 52 are aligned in the axial direction.

[0064] In this invention, of the at least four land sections that make up the tread, the two land sections located on the outermost axial sides are the shoulder land sections. The multiple land sections located between the two shoulder land sections are the main land sections. The at least four land sections comprise two shoulder land sections and multiple main land sections located between the two shoulder land sections. If any of the multiple main landmasses are located on the equatorial plane, that main landmass is the Crown Landmass. If there are no main landmasses on the equatorial plane, the main landmass located between the equatorial plane and the Shoulder Landmass that is closest to the equatorial plane is the Crown Landmass. If there are three or more main landmasses, the main landmass adjacent to the Crown Landmass is the Middle Landmass.

[0065] The tread 4 of this tire 2 has four land sections 52. Of the four land sections 52, the two land sections 52 located on the outermost axial sides are the shoulder land sections 54. The shoulder land sections 54 include the edge TE of the tread surface 22. The two land sections 52 located between the two shoulder land sections 54 are the main land sections 56. In the case of this tire 2, the two main land sections 56 are each the main land section closest to the equatorial plane and are therefore also called crown land sections 58.

[0066] The aforementioned conductive portion 36 is provided on one of the two main land portions 56 provided on the tread 4. In this tire 2, at least one of the multiple main land portions 56 is equipped with the conductive portion 36. As mentioned above, the two main land portions 56 of this tire 2 are crown land portions 58. The conductive portion 36 is provided on the crown land portion 58. Of the two crown land portions 58, the conductive portion 36 is provided on one of the crown land portions 58.

[0067] The reinforcing layer 14 of this tire 2 comprises a belt 60. The belt 60 includes a plurality of belt plies 64 arranged radially. Specifically, the belt 60 of this tire 2 includes three belt plies 64. This belt 60 may be composed of four or more belt plies 64. From the viewpoint of reducing rolling resistance, it is preferable that this belt 60 is composed of three or fewer belt plies 64.

[0068] The three belt plies 64 are, from radially inward, the first belt ply 64A, the second belt ply 64B, and the third belt ply 64C. The first belt ply 64A is the innermost belt ply 64 in the radial direction. The third belt ply 64C is the outermost belt ply 64 in the radial direction.

[0069] In Figure 1, the length indicated by the double arrow W1 is the axial width of the first belt ply 64A. The length indicated by the double arrow W2 is the axial width of the second belt ply 64B. The length indicated by the double arrow W3 is the axial width of the third belt ply 64C. The axial width of each belt ply 64 is expressed as the axial distance from one end of the belt ply 64 to the other end.

[0070] In this tire 2, the first belt ply 64A has the widest axial width W1. The axial width W1 of the first belt ply 64A is the axial width of belt 60, and the end 64Ae of the first belt ply 64A is the end 60e of belt 60. The third belt ply 64C has the narrowest axial width W3. The axial width W2 of the second belt ply 64B is narrower than the axial width W1 of the first belt ply 64A and wider than the axial width W3 of the third belt ply 64C. The end 64Be of the second belt ply 64B is located axially inward from the end 64Ae of the first belt ply 64A and axially outward from the end 64Ce of the third belt ply 64C. As shown in Figure 2, the end 64Be of the second belt ply 64B is located axially outward of the shoulder circumferential groove 48, and the end 64Ce of the third belt ply 64C is located axially inward of the shoulder circumferential groove 48. The end 64Ce of the third belt ply 64C may also be located axially outward of the shoulder circumferential groove 48.

[0071] From the viewpoint of ensuring the rigidity of the tread section T, the ratio of the axial width W1 of the first belt ply 64A to the width TW of the tread 4 (W1 / TW) is preferably 0.85 or more and 0.95 or less. The ratio of the axial width W2 of the second belt ply 64B to the width TW of the tread 4 (W2 / TW) is preferably 0.80 or more and 0.90 or less. The axial width W3 of the third belt ply 64C is set appropriately according to the specifications of the tire 2.

[0072] As shown in Figure 4, each belt ply 64 constituting the belt 60 contains a number of parallel belt cords 66. The cord ends of each belt ply 64 are between 15 ends / 50 mm and 30 ends / 50 mm. Each belt cord 66 is made of steel. In Figure 4, for ease of explanation, the belt cords 66 are represented by solid lines, but the belt cords 66 are covered with belt topping rubber 68. The belt topping rubber 68 is made of conductive cross-linked rubber. The belt ply 64 is conductive.

[0073] The belt cords 66 of each belt ply 64 are inclined with respect to the circumferential direction. The direction of inclination of the belt cords 66 included in the second belt ply 64B (hereinafter, second belt cord 66B) is opposite to the direction of inclination of the belt cords 66 included in the first belt ply 64A (hereinafter, first belt cord 66A). The direction of inclination of the belt cords 66 included in the third belt ply 64C (hereinafter, third belt cord 66C) is the same as the direction of inclination of the second belt cord 66B. The direction of inclination of the third belt cord 66C may be opposite to the direction of inclination of the second belt cord 66B.

[0074] In Figure 4, angle θ1 is the angle that the first belt cord 66A makes with respect to the circumferential direction (hereinafter referred to as inclination angle θ1). Angle θ2 is the angle that the second belt cord 66B makes with respect to the circumferential direction (hereinafter referred to as inclination angle θ2). Angle θ3 is the angle that the third belt cord 66C makes with respect to the circumferential direction (hereinafter referred to as inclination angle θ3). In the present invention, unless otherwise specified, the inclination angle of each belt cord 66 is expressed as the angle that the belt cord 66 makes with respect to the equatorial plane.

[0075] The inclination angles θ1 of the first belt cord 66A, θ2 of the second belt cord 66B, and θ3 of the third belt cord 66C are preferably between 10 degrees and 60 degrees. From the viewpoint of effectively restraining the tread portion T and obtaining a stable contact surface with minimal shape change, the inclination angle θ1 of the first belt cord 66A is more preferably between 15 degrees and 30 degrees, and even more preferably between 15 degrees and 20 degrees. The inclination angle θ2 of the second belt cord 66B is more preferably between 15 degrees and 30 degrees, and even more preferably between 15 degrees and 20 degrees. The inclination angle θ3 of the third belt cord 66C is more preferably between 15 degrees and 50 degrees.

[0076] In this invention, among the multiple belt plies that make up the belt, the belt ply having the widest axial width is called the reference belt ply, and the belt ply having the next widest axial width after the reference belt ply is called the sub-reference belt ply.

[0077] In this tire 2, among the multiple belt plies 64 that make up the belt 60, the first belt ply 64A has the widest axial width W1, and the second belt ply 64B has the next widest axial width W2 after the first belt ply 64A. The first belt ply 64A is the reference belt ply BP, and the second belt ply 64B is the sub-reference belt ply BPS. If the belt ply 64 with the widest axial width among the multiple belt plies 64 is the second belt ply 64B, and the belt ply 64 with the next widest axial width after the second belt ply 64B is the first belt ply 64A, then the second belt ply 64B is the reference belt ply BP and the first belt ply 64A is the sub-reference belt ply BPS.

[0078] The reinforcing layer 14 of this tire 2 comprises a belt 60 including a plurality of belt plies 64, the plurality of belt plies 64 comprising a reference belt ply BP having the widest axial width among the plurality of belt plies 64, and a sub-reference belt ply BPS having the second widest axial width among the plurality of belt plies 64. As mentioned above, the direction of inclination of the second belt cord 66B is opposite to the direction of inclination of the first belt cord 66A. Therefore, the direction of inclination of the belt cord 66 included in the sub-reference belt ply BPS is opposite to the direction of inclination of the belt cord 66 included in the reference belt ply BP.

[0079] The reinforcing layer 14 of this tire 2 further comprises a band 62. This reinforcing layer 14 comprises a belt 60 and a band 62. Band 62 includes a full band 70. More specifically, this band 62 consists of one full band 70. This band 62 may consist of two or more full bands 70. This band 62 may further include a pair of edge bands that are spaced apart axially across the equatorial plane. From the viewpoint of reducing rolling resistance, it is preferable that this band 62 consists of one full band 70.

[0080] In Figure 1, the length indicated by the double arrow WF is the axial width of the full band 70. The axial width WF of the full band 70 is represented by the axial distance from one end 70e to the other end 70e of the full band 70. As mentioned above, the band 62 of this tire 2 is composed of one full band 70. The end 70e of the full band 70 is the end 62e of the band 62, and the axial width WF of the full band 70 is also the axial width of the band 62.

[0081] The end 70e of the full band 70, which is the end 62e of band 62, is located axially inward of the end 64Ae of the first belt ply 64A, which is the end 60e of belt 60. Band 62 of this tire 2 is narrower than belt 60. Thus, the end 60e of belt 60 is the end 14e of reinforcing layer 14.

[0082] The end 70e of the full band 70 is located axially inward of the end 64Be of the second belt ply 64B. The full band 70 is narrower than the first belt ply 64A and the second belt ply 64B. The end 70e of the full band 70 is located axially outward of the end 64Ce of the third belt ply 64C. The full band 70 is wider than the third belt ply 64C.

[0083] As shown in Figure 4, the full band 70 includes a band cord 72. In Figure 4, for ease of explanation, the band cord 72 is represented by a solid line, but the band cord 72 is covered with band topping rubber 74. The material of the band cord 72 is steel. The band topping rubber 74 is made of conductive cross-linked rubber. The full band 70 is conductive.

[0084] Although not described in detail, the full band 70 is formed by spirally winding a band strip (not shown) containing a band code 72. The full band 70 constituting band 62 includes the spirally wound band code 72. The full band 70 has a jointless structure.

[0085] Since the full band 70 is formed by spirally winding a band strip, the band code 72 is slightly inclined with respect to the circumferential direction. In Figure 4, angle θd is the angle that the band code 72 makes with respect to the circumferential direction (hereinafter referred to as the inclination angle θd). In this invention, unless otherwise specified, the inclination angle θd of the band code 72 is expressed as the angle that the band code 72 makes with respect to the equatorial plane. The inclination angle θd of the band cord 72 of this tire 2 is 5 degrees or less, preferably 2 degrees or less. The band cord 72 extends substantially in the circumferential direction.

[0086] For example, as shown in Figure 2, the full band 70 is located radially between the first belt ply 64A and the second belt ply 64B. The full band 70 may also be located radially outward of the third belt ply 64C. The full band 70 may also be located radially between the second belt ply 64B and the third belt ply 64C. The full band 70 may also be located radially inward of the first belt ply 64A. In the reinforcing layer 14 of this tire 2, the multiple belt plies 64 of the belt 60 and the full band 70 of the band 62 are aligned radially.

[0087] As mentioned above, the belt plies 64 and the full bands 70 are conductive. The reinforcing layer 14, which is composed of multiple belt plies 64 and full bands 70 arranged radially, is also conductive.

[0088] As shown in Figure 1, the rim R is in contact with the chafer 8. The chafer 8 is in contact with the carcass 12. The carcass 12 is in contact with the reinforcing layer 14. And, as previously mentioned, the conductive part 36 connects the road surface and the reinforcing layer 14. The chafer 8, carcass 12, reinforcing layer 14, and conductive part 36 are conductive. The chafer 8, carcass 12, reinforcing layer 14, and conductive part 36 constitute a conductive path connecting the rim R and the road surface. Static electricity generated in the vehicle and tire 2 flows from the rim R to the road surface through this conductive path.

[0089] Furthermore, the conductive paths covered by the present invention are not limited to the conductive paths shown in Figure 1, as long as they pass through the conductive parts 36 configured in the tread 4. The conductive paths shown in Figure 1 are just one example of the conductive paths covered by the present invention.

[0090] The conductive portion 36 can contribute to the discharge of static electricity generated in the vehicle to the road surface. In this tire 2, static electricity that would accumulate in a tire without the conductive portion 36 is effectively discharged to the road surface. This tire 2 has good conductive performance. This tire 2 can suppress the accumulation of static electricity. The conductive portion 36 is located on the main land portion 56, which is situated between the two shoulder land portions 54, rather than on the two shoulder land portions located on the outermost axial sides. This prevents an increased risk of uneven wear.

[0091] A reinforcing layer 14 is located between the tread 4 and the carcass 12, and this reinforcing layer 14 comprises a full band 70. As mentioned above, the full band 70 includes a helically wound band cord 72. The full band 70 suppresses the movement of the tire 2 to spread outward. Since the band cord 72 is a steel cord, this movement is effectively suppressed. The contact shape of this new tire 2 is rectangular, not round. Since the change in shape of the tire 2 due to driving is suppressed, the rectangular contact shape is maintained. With this tire 2, the contact pressure of the crown portion does not easily increase, and the state in which the contact pressure of the crown portion does not easily increase can be maintained. The conductive portion 36 provided on the main land portion 56 located between the two shoulder land portions 54, in other words, the conductive portion 36 provided on the crown portion, is less likely to become the starting point of uneven wear. The uneven wear resistance of this tire 2 is improved compared to conventional tires with a conductive part on the crown. This tire 2 can maintain good uneven wear resistance. This tire 2 can suppress the accumulation of static electricity while maintaining uneven wear resistance. Even if the cap layer 30 of the tread 4 is made of low-heat-generating cross-linked rubber, the conductive part 36 can stably perform its function. This tire 2 can achieve a reduction in rolling resistance.

[0092] The ratio (WF / TW) of the axial width WF of the full band 70 to the width TW of the tread 4 is preferably 0.60 or higher. This allows the full band 70 to effectively contribute to suppressing an increase in contact pressure at the crown portion. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, the ratio (WF / TW) is more preferably 0.65 or higher, and even more preferably 0.70 or higher. From the viewpoint that the full band 70 can contribute to reducing rolling resistance, the ratio (WF / TW) is preferably 0.90 or lower, more preferably 0.85 or lower, and even more preferably 0.80 or lower.

[0093] For example, as shown in Figure 2, the end 70e of the full band 70 is located axially outward of the shoulder circumferential groove 48. This allows the full band 70 to effectively contribute to suppressing an increase in ground pressure in the crown portion. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, it is preferable that the end 70e of the full band 70 is located axially outward of the shoulder circumferential groove 48.

[0094] The code ends of the full band 70 are preferably 20 ends / 50 mm or more. This allows the full band 70 to effectively contribute to suppressing changes in the shape of the tire 2 due to driving. Increased contact pressure in the crown portion is suppressed. Uneven wear originating from the conductive part 36 is suppressed, allowing the conductive part 36 to stably perform its function. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, the code ends of the full band 70 are preferably 22 ends / 50 mm or more. From the viewpoint that the full band 70 can contribute to reducing rolling resistance, the code ends of the full band 70 are preferably 30 ends / 50 mm or less, and more preferably 28 ends / 50 mm or less.

[0095] In Figure 2, the length indicated by the double arrow CW is the width of the conductive part 36. In this tire 2, the width CW of the conductive part 36 is preferably 8.0 mm or less. This suppresses wear in the conductive part 36. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, the width CW of the conductive part 36 is more preferably 6.0 mm or less, and even more preferably 4.0 mm or less. From the viewpoint that the conductive part 36 can perform its function, the width CW of the conductive part 36 is preferably 1.0 mm or more.

[0096] As mentioned above, in the reinforcing layer 14 of this tire 2, the first belt ply 64A is the reference belt ply BP, and the second belt ply 64B is the sub-reference belt ply BPS. The full band 70 of the reinforcing layer 14 is located radially between the first belt ply 64A and the second belt ply 64B. The direction of inclination of the second belt cord 66B is opposite to the direction of inclination of the first belt cord 66A. In other words, the full band 70 of this tire 2 is located between the reference belt ply BP and the sub-reference belt plies BPs, whose belt cords 66 have opposite directions of inclination. The reinforcing layer 14, including the reference belt ply BP, the sub-reference belt plies BPs, and the full band 70, can effectively contribute to suppressing outer diameter growth due to driving. Since the band cords 72 included in the full band 70 extend substantially in the circumferential direction, and the belt cords 66 included in the sub-reference belt plies BPs are arranged to intersect with the belt cords 66 included in the reference belt plies BP, the shear strain generated in the rubber located between the band cords 72 and the belt cords 66 is reduced. The full band 70 can stably continue to exhibit its function of suppressing outer diameter growth. This tire 2 is less prone to increased ground pressure at the crown portion, and can maintain a state where the ground pressure at the crown portion is less prone to increased ground pressure. The conductive portion 36 of this tire 2 is provided in the crown portion, but the conductive portion 36 is less likely to become the starting point of uneven wear. The uneven wear resistance of this tire 2 is improved, and moreover, this tire 2 can maintain good uneven wear resistance. From this viewpoint, it is preferable that the multiple belt plies 64 include a reference belt ply BP and a sub-reference belt ply BPS in which the inclination direction of the belt cords 66 is opposite to that of each other, and that the full band 70 is located radially between the reference belt ply BP and the sub-reference belt ply BPS. In this case, it is more preferable that the reference belt ply BP is located radially inside the full band 70, and the sub-reference belt ply BPS is located radially outside the full band 70.

[0097] As mentioned above, in this tire 2, at least one of the multiple main land areas 56 is equipped with a conductive part 36. A preferred position for the conductive part 36 on the main land area 56 will be explained with reference to Figure 2.

[0098] In Figure 2, the length indicated by the double arrow WM is the axial width of the crown land portion 58. As mentioned above, the crown land portion 58 of this tire 2 is the main land portion 56. The axial width WM of the crown land portion 58 is the axial width of the main land portion 56. The axial width WM of the main land portion 56 is expressed as the axial distance from one edge 56e of the main land portion 56 to the other edge 56e. The dashed line CL is the width centerline of the conductive portion 36. The length indicated by the double arrow WC is the axial distance from the edge 56e on the TE side of the tread surface 22 to the width centerline CL of the conductive portion 36, which is one of the two edges 56e of the main land portion 56.

[0099] The ratio (WC / WM) of the axial distance WC from the edge 56e on the TE side of the tread surface 22 to the width centerline CL of the conductive part 36 to the axial width WM of the main land area 56 is preferably 0.30 or more and 0.70 or less. This ensures that the conductive part 36 is positioned at an appropriate distance from the edge 56e of the main land area 56. This suppresses the occurrence of peculiar strain in the conductive part 36. This suppresses the occurrence of wear originating from the conductive part 36. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, the ratio (WC / WM) is more preferably 0.40 or more and 0.60 or less, and even more preferably 0.45 or more and 0.55 or less.

[0100] In Figure 2, the length indicated by the double arrow WS represents the axial width of the shoulder land portion 54. The axial width WS is represented by the axial distance from one edge 54e of the shoulder land portion 54 to the other edge, i.e., the edge TE of the tread surface 22. The length indicated by the double arrow WB represents the axial distance from the equatorial-side edge 54e of the shoulder land portion 54 to the edge 70e of the full band 70.

[0101] As mentioned above, the end 70e of the full band 70 is located axially outward of the shoulder circumferential groove 48. Therefore, the end 70e of the full band 70 is positioned within the shoulder land portion 54. In the tire 2 shown in Figure 1, the end 70e of the full band 70 is located axially inward from the position that is half the axial width WS of the shoulder land portion 54. The full band 70 restrains the movement of the shoulder land portion 54. The full band 70 effectively suppresses changes in the shape of the entire tread portion T. This tire 2 can maintain good resistance to uneven wear. From this viewpoint, the ratio (WB / WS) of the axial distance WB from the equatorial edge 54e of the shoulder land portion 54 to the axial width WS of the shoulder land portion 54 is preferably 0.10 or more, more preferably 0.20 or more, and even more preferably 0.25 or more. From the viewpoint that the full band 70 can contribute to reducing rolling resistance, the ratio (WB / WS) is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.50 or less.

[0102] In Figure 2, the length indicated by the double arrow WP represents the axial width of the strip layer 18. The axial width WP is represented by the axial distance from one end 18e to the other end 18e of the strip layer 18.

[0103] The reinforcing layer 14 of this tire 2 includes a full band 70 in addition to multiple belt plies 64. The full band 70 suppresses the outward spreading motion of the tire 2. The space between the carcass 12 and the reinforcing layer 14 is prone to strain. However, between the carcass 12 and the reinforcing layer 14 of this tire 2 is a strip layer 18 that is softer than the carcass 12 and the reinforcing layer 14. Moreover, this strip layer 18 has an axial width WP that is about the same as the axial width WF of the full band 70. This strip layer 18 can contribute to mitigating the strain that occurs between the reinforcing layer 14 and the carcass 12. Since damage between the carcass 12 and the reinforcing layer 14 is suppressed, the full band 70 can stably perform its function. This tire 2 can maintain good resistance to uneven wear. Since the occurrence of uneven wear starting from the conductive part 36 is suppressed, the conductive part 36 can stably perform its function. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, it is preferable that the tire 2 includes a strip layer 18 made of cross-linked rubber between the carcass 12 and the reinforcing layer 14, and that this strip layer 18 has an axial width WP that is about the same as the axial width WF of the full band 70. From a similar viewpoint, specifically, the ratio of the axial width WP of the strip layer 18 to the axial width WF of the full band 70 (WP / WF) is preferably 0.80 or more and 1.2 or less, and more preferably 0.90 or more and 1.1 or less.

[0104] Figure 5 is an enlarged cross-sectional view showing a modified example of the tread portion T. Figure 5 shows a portion of the meridian cross-section of a tire 82 according to another embodiment of the present invention. Components that are the same as those of the tire 2 shown in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted.

[0105] The tread 4 of this tire 82 also has multiple circumferential grooves 44. Four circumferential grooves 44 are engraved on the tread 4 of this tire 82. These four circumferential grooves are also the aforementioned circumferential main grooves 46. Of the four circumferential grooves 44, the circumferential groove 44 located on the outermost axial side is the shoulder circumferential groove 48. Among the circumferential grooves 44 located in the zone between the equatorial plane and the edge TE of the tread surface 22, the circumferential groove 44 closest to the equatorial plane is the center circumferential groove 50. This tread 4 has a pair of center circumferential grooves 50 and a pair of shoulder circumferential grooves 48.

[0106] The tread 4 consists of five land sections 52. Of the five land sections 52, the two land sections 52 located on the outermost axial sides are the shoulder land sections 54. The three land sections 52 located between the two shoulder land sections 54 are the main land sections 56. Of the three main land sections 56, the main land section 56 located on the equatorial plane is the crown land section 58. The main land section 56 located next to the crown land section 58 is the middle land section 84. This tread 4 has a crown land section 58, a pair of middle land sections 84, and a pair of shoulder land sections 54.

[0107] In this tire 82 as well, the conductive part 36 is provided on the main land portion 56. More specifically, the conductive part 36 is provided on the middle land portion 84, which is the main land portion 56. This conductive part 36 may also be provided on the crown land portion 58, which is located on the equatorial plane and is also the main land portion 56. As mentioned above, the conductive portion 36 may become the starting point for uneven wear. From the viewpoint of reducing the risk of uneven wear, it is preferable that only one of the multiple main land portions 56 provided on the tread 4 is equipped with the conductive portion 36. In this case, if the tread 4 has three or more main land portions 56, it is more preferable that the main land portion 56 on which the conductive portion 36 is provided is either the crown land portion 58 or the middle land portion 84 located next to the crown land portion 58. Note that if the tread 4 is provided with two main land portions 56, as in the tread 4 shown in Figure 2, or if the tread 4 is provided with one main land portion 56 (not shown), the main land portion 56 provided on the tread 4 is the crown land portion 58. If the tread 4 has two or fewer main land portions 56, the main land portion 56 on which the conductive portion 36 is provided is naturally the crown land portion 58. In other words, if only one of the multiple main land sections 56 provided on the tread 4 is equipped with a conductive part 36, it is preferable that the main land section 56 equipped with the conductive part 36 is either the crown land section 58 or the middle land section 84.

[0108] In the tread section T shown in Figure 5, the center circumferential groove 50 is located between the crown land portion 84 and the middle land portion 86. In the tread section T shown in Figure 2, the center circumferential groove 50 is located between the two crown land portions 84. Both the center circumferential groove 50 shown in Figure 5 and the center circumferential groove 50 shown in Figure 2 are located between two adjacent main land portions 56 in the axial direction. The center circumferential groove 50 in Figure 5 and the center circumferential groove 50 in Figure 2 are circumferential main grooves 46, but the circumferential groove 44 located between two adjacent main land portions 56 in the axial direction may be configured as the circumferential groove 44 in Figure 6.

[0109] Figure 6 shows a modified example of the circumferential groove 44. The cross-section of the circumferential groove 44 shown in Figure 6 is a cross-section of the circumferential groove 44 along a plane perpendicular to the longitudinal direction of the circumferential groove 44.

[0110] As described above, the circumferential groove 44 has a pair of wall surfaces 44S including the groove opening 44M and a bottom surface 44B including the groove bottom 44T. The dashed line LC is the centerline of the circumferential groove 44. The circumferential groove 44 has a cross-sectional shape symmetrical with respect to the centerline LC. The centerline LC extends in the depth direction of the circumferential groove 44 and passes through the groove bottom 44T.

[0111] The circumferential groove 44 in Figure 6 is a groove (hereinafter referred to as a circumferential narrow groove 88) that has a narrow groove width and allows a pair of wall surfaces 44S to come into contact with each other when the tread 4 deforms in contact with the road surface.

[0112] The circumferential groove 88 comprises a body portion 90 and a widened portion 92. The body portion 90 includes the groove opening 44M of the circumferential groove 88. The widened portion 92 includes the groove bottom 44T of the circumferential groove 88. When the tread 4 wears down and the circumferential groove portion 94 disappears, the widened portion 92 is exposed. In Figure 6, the length indicated by the double arrow WC1 is the minimum groove width of the circumferential groove 88, and the length indicated by the double arrow WC2 is the maximum groove width of the circumferential groove 88. The circumferential groove 88 shows the minimum groove width WC1 in the body portion 90 and the maximum groove width WC2 in the widened portion 92.

[0113] The body 90 is provided with a narrow groove section 94. The narrow groove section 94 of this tire 2 extends from the groove opening 44M of the circumferential narrow groove 88 in the depth direction of the circumferential narrow groove 88. This narrow groove section 94 includes the groove opening 44M of the circumferential narrow groove 88. The body 90 has a minimum groove width WC1 in the narrow groove section 94. The minimum groove width WC1 is set so that when the tread 4 deforms in contact with the road surface, a pair of wall surfaces 44S of the circumferential narrow groove 88 come into contact with each other in the narrow groove section 94.

[0114] The narrow groove section 94 has a portion that extends straight in the depth direction (hereinafter also referred to as the straight section 96). The straight section 96 is the portion of the narrow groove section 94 that has a uniform groove width WC1 in the depth direction. The narrow groove section 94 includes the straight section 96 that has a uniform groove width WC1 in the depth direction. Although not shown, the narrow groove section 94 may be configured such that, for example, the groove width gradually widens from the position showing the minimum groove width WC1 toward the groove opening 44M and the widening section 92, respectively.

[0115] The widened portion 92 is located radially inward of the body portion 90. The groove width of the widened portion 92 is wider than the groove width of the body portion 90. The position indicated by the symbol PX is the position where the widened portion 92 shows the maximum groove width WC2 (hereinafter referred to as the maximum groove width position). The widened portion 92 tapers outward from the maximum groove width position PX and then tapers inward from the maximum groove width position PX.

[0116] In Figure 6, the position indicated by the solid line LPE is the boundary between the body portion 90 (specifically the narrow groove portion 94) and the widened portion 92. This boundary LPE is represented by the position where the circumferential narrow groove 88 has a width Wb that is 1.1 times the minimum groove width WC1 of the narrow groove portion 94. If the portion that has a width Wb that is 1.1 times the minimum groove width WC1 has a certain length, the radial outer end of that portion is the boundary LPE.

[0117] The widened portion 92 of this circumferential groove 88 includes a curved portion 98 and a bottom portion 100. The widened portion 92 exhibits a maximum groove width WC2 at the bottom portion 100. In Figure 6, the position indicated by reference numeral H4 is the boundary between the curved portion 98 and the bottom portion 100. The inflection section 98 connects the narrow groove section 94 and the bottom section 100. The groove width of the inflection section 98 gradually increases from the boundary LPE with the narrow groove section 94 towards the boundary H4 with the bottom section 100. The inflection section 98 curves inward from its outside. Specifically, in the cross-section of the circumferential narrow groove 88, the contour of the inflection section 98 is represented by a circular arc. In Figure 6, arrow RC1 is the radius of the circular arc representing the contour of the inflection section 98. The circular arc representing the contour of the inflection section 98 is tangent to the straight line representing the contour of the straight section 96 at the boundary H3 between the inflection section 98 and the straight section 96.

[0118] The bottom portion 100 is located radially inward of the inflection portion 98. The bottom portion 100 includes the groove bottom 44T of the circumferential groove 88. The contour of the bottom portion 100 of this circumferential groove 88 is represented by a single circular arc with radius Rw in the cross-section of the circumferential groove 88 shown in Figure 6. The center of the circular arc representing the contour of the bottom portion 100 lies on the centerline LC of the circumferential groove 88. The radius Rw of the circular arc representing the contour of the bottom portion 100 is equal to half the length of the maximum groove width WC2 of the widening portion 92. The circular arc representing the contour of the bottom portion 100 is tangent to the circular arc representing the contour of the inflection portion 98 at boundary H4. The radius Rw of this circular arc is, for example, between 1.5 mm and 3.5 mm.

[0119] In Figure 6, the length indicated by the double arrow D1 is the groove depth of the circumferential groove 88. The length indicated by the double arrow D2 is the groove depth of the body portion 90 of the circumferential groove 88. The groove depth D2 represents the distance in the depth direction from the groove opening 44M of the circumferential groove 88 to the boundary LPE. The length indicated by the double arrow D3 is the groove depth from the groove opening 44M of the circumferential groove 88 to the position PX where the widened portion 92 shows the maximum groove width WC2.

[0120] For example, by configuring the center circumferential groove 50 in Figure 5 with a circumferential narrow groove 88, when the tread 4 deforms upon contact with the road surface, the pair of wall surfaces 44S of the circumferential narrow groove 88 come into contact with each other in the narrow groove portion 94. Since the land portions 52 located on both sides of the circumferential narrow groove 88 support each other, deformation of the tread 4 is suppressed. As the shape change of the tire 2 due to driving is suppressed, a rectangular contact shape is maintained. This tire 2 is less prone to increased contact pressure on the crown portion, and can maintain a state where the contact pressure on the crown portion is less prone to increased contact pressure. The conductive portion 36 provided on the main land portion 56 located between the two shoulder land portions 54 is less likely to become the starting point for uneven wear. This tire 2 can maintain good resistance to uneven wear. This tire 2 can suppress the accumulation of static electricity while maintaining resistance to uneven wear. From this viewpoint, it is preferable that the circumferential groove 44 located between two adjacent main land portions is a circumferential narrow groove 88. In this case, from the viewpoint of suppressing a decrease in driving performance on wet road surfaces (hereinafter referred to as wet performance), it is preferable that the circumferential groove 44 located between the shoulder land portion 54 and the main land portion 56 located next to the shoulder land portion 54 is a circumferential main groove 46.

[0121] When a circumferential groove 44 located between two adjacent main land sections is composed of a circumferential narrow groove 88, and a circumferential groove 44 located between a shoulder land section 54 and a main land section 56 adjacent to this shoulder land section 54 is composed of a circumferential main groove 46, from the viewpoint of enabling the circumferential narrow groove 88 to fully perform its function, it is preferable that the groove depth D1 of the circumferential narrow groove 88 is the same as the groove depth of the circumferential main groove 46, or that the circumferential narrow groove 88 is shallower than the circumferential main groove 46. Specifically, the groove depth D1 of the circumferential narrow groove 88 is preferably 0.75 times or more and preferably 1.00 times or less the groove depth of the circumferential main groove 46.

[0122] As mentioned above, the conductive part 36 is made of conductive cross-linked rubber. It is conceivable that the conductive part 36 will generate heat when the tire 2 is driven. This tire 2 is a heavy-duty tire, and its tread 4 is thicker than that of a passenger car tire. There is a concern that the heat generated by the conductive part 36 will raise the ambient temperature around the conductive part 36, and depending on the degree of this, the resistance to uneven wear may decrease.

[0123] However, as mentioned above, the circumferential groove 88 has a widened section 92 radially inward of the narrow groove section 94, and the maximum groove width WC2 of the widened section 92 is wider than the minimum groove width WC1 of the narrow groove section 94. The widened section 92 contributes to increasing the surface area of ​​the circumferential groove 88. The surface area of ​​this circumferential groove 88 is larger than that of a circumferential groove composed only of the narrow groove section 94. This circumferential groove 88 can contribute to the dissipation of heat generated in the conductive section 36. Even if the conductive section 36 generates heat, the rise in the ambient temperature of the conductive section 36 is suppressed. This tire 2 can minimize the effect of temperature rise on its resistance to uneven wear. Furthermore, as the tread 4 wears down, the circumferential grooves 88 gradually disappear. After the grooves 94 disappear, the widened sections 92 are exposed. In the circumferential grooves 88, the maximum groove width WC2 of the widened sections 92 is wider than the minimum groove width WC1 of the grooves 94. From the mid-stage of wear, when the grooves 94 disappear due to tread wear, the exposed widened sections 92 can help suppress the deterioration of wet performance. From the viewpoint of suppressing the deterioration of uneven wear resistance and wet performance, it is preferable that the circumferential narrow groove 88 comprises a narrow groove section 94 and a widened section 92, and that the widened section 92 has a maximum groove width WC2 that is wider than the minimum groove width WC1 of the narrow groove section 94. In this case, it is preferable that the maximum groove width WC2 of the widened section 92 is at least twice the minimum groove width WC1 of the narrow groove section 94, and more preferably three times or more. From the viewpoint of suppressing the influence on the rigidity of the crown portion of the tread 4 and enabling the tire 2 to maintain good resistance to uneven wear, it is preferable that the maximum groove width WC2 of the widened section 92 is eight times or less the minimum groove width WC1 of the narrow groove section 94, and more preferably seven times or less.

[0124] The minimum groove width WC1 of the narrow groove section 94 is preferably 2.5 mm or less. This allows the pair of wall surfaces 44S of the circumferential narrow grooves 88 to effectively contact the narrow groove section 94 when the tread 4 deforms in contact with the road surface. This suppresses deformation of the tread 4, and the tire 2 can maintain good wear resistance. From this viewpoint, the minimum groove width WC1 is more preferably 2.0 mm or less. From the viewpoint of effectively draining water present between the tread 4 and the wet road surface through the circumferential narrow grooves 88, the minimum groove width WC1 is preferably 1.0 mm or more.

[0125] In this tire 2, the radius RC1 of the arc representing the contour of the curved portion 98 is greater than the radius Rw of the arc representing the contour of the bottom portion 100. This allows the circumferential grooves 88 to fully perform their function. From this viewpoint, it is preferable that the ratio of radius RC1 to radius Rw, RC1 / Rw, is between 1.5 and 20. By setting the ratio RC1 / Rw to 1.5 or higher, tire 2 can suppress uneven wear caused by sudden changes in stiffness. From this viewpoint, a ratio RC1 / Rw of 2.0 or higher is more preferable. By setting the ratio RC1 / Rw to 20 or less, the deterioration of the wet performance of tire 2 can be suppressed. From this perspective, a ratio RC1 / Rw of 15 or less is more preferable.

[0126] The ratio D2 / D1 of the groove depth D2 of the body portion 90 to the groove depth D1 of the circumferential narrow groove 88 is preferably 0.25 or more and 0.70 or less. By setting the ratio D2 / D1 to 0.25 or higher, the groove depth D2 of the body 90 is appropriately maintained. As the tread 4 deforms in contact with the road surface, the pair of wall surfaces 44S of the circumferential narrow grooves 88 can make sufficient contact in the narrow groove section 94. This tire 2 can maintain good resistance to uneven wear. From this viewpoint, a ratio D2 / D1 of 0.30 or higher is more preferable. By setting the ratio D2 / D1 to 0.70 or less, the tire 2 can form a widened section 92 with the necessary groove volume. The exposed widened section 92 can effectively contribute to suppressing a decrease in wet performance. From this viewpoint, a ratio D2 / D1 of 0.65 or less is more preferable.

[0127] From the viewpoint that the widened portion 92 can effectively contribute to the dissipation of heat generated in the conductive portion 36, it is preferable that the ratio D3 / D1 of the groove depth D3 from the groove opening 44M of the circumferential narrow groove 88 to the groove depth D1 of the circumferential narrow groove 88, with respect to the groove depth D1, be 0.75 or more and 0.95 or less.

[0128] Figure 7 shows a modified example of the circumferential groove 88. In this circumferential groove 88, the groove opening 44M is machined to be tapered. The body 90 of this circumferential groove 88 is provided with a funnel portion 102 on the radially outer side of the groove portion 94.

[0129] In Figure 7, the position indicated by the solid line LTP is the boundary between the funnel portion 102 and the narrow groove portion 94. This boundary LTP is represented by the position at the boundary between the funnel portion 102 and the narrow groove portion 94 where the circumferential narrow groove 88 has a width Wa that is 1.1 times the minimum groove width WC1 of the narrow groove portion 94. If the portion with a width Wa that is 1.1 times the minimum width WC1 has a certain length, the radial inner end of that portion is used as the boundary LTP.

[0130] The funnel portion 102 tapers inward from the groove opening 44M. In Figure 6, the length indicated by the double arrow WA is the groove width at the groove opening 44M of the funnel portion 102. Preferably, the groove width WA of the funnel portion 102 is 0.15 times or more and 0.45 times or less the groove width of the circumferential main groove 46.

[0131] The funnel portion 102 comprises an inclined portion 104 and a connecting portion 106. The position indicated by reference numeral H1 is the boundary between the inclined portion 104 and the connecting portion 106. The inclined portion 104 includes the groove opening 44M of the circumferential narrow groove 88. The groove width of the inclined portion 104 gradually decreases from the groove opening 44M toward the connecting portion 106. In the cross-section of the circumferential narrow groove 88 shown in Figure 6, the contour of the inclined portion 104 is represented by a straight line. The connecting portion 106 connects the inclined portion 104 and the narrow groove portion 94. The groove width of the connecting portion 106 gradually decreases from the boundary H1 toward the narrow groove portion 94. In the cross-section of the circumferential narrow groove 88 shown in Figure 6, the contour of the connecting portion 106 is represented by an arc. The arrow Rb is the radius of the arc representing the contour of the connecting portion 106. This arc representing the contour of the connecting portion 106 is tangent to the straight line representing the contour of the inclined portion 104 at boundary H1. This arc representing the contour of the connecting portion 106 is tangent to the straight line representing the contour of the straight portion 96 of the narrow groove portion 94 at the boundary H2 between the connecting portion 106 and the straight portion 96. The radius Rb of the arc representing the contour of the connecting portion 106 is determined appropriately, taking into consideration the shape of the inclined portion 104.

[0132] The funnel portion 102 can contribute to increasing the groove volume of the circumferential groove 88 and can effectively suppress the concentration of strain on the edges of the land portions 52 located on both sides of the circumferential groove 88. From this viewpoint, it is preferable that the body portion 90 of the circumferential groove 88 is provided with a funnel portion 102 including the groove opening 44M of the circumferential groove 88 on the radially outer side of the groove portion 94.

[0133] The length indicated by the double arrow D4 is the groove depth of the funnel portion 102. The groove depth D4 is represented by the distance in the depth direction from the groove opening 44M of the circumferential narrow groove 88 to the boundary LTP between the funnel portion 102 and the narrow groove portion 94.

[0134] The ratio D4 / D1 of the groove depth D4 of the funnel portion 102 to the groove depth D1 of the circumferential narrow groove 88 is preferably 0.12 or more and 0.14 or less. By setting the ratio D4 / D1 to 0.12 or higher, the funnel section 102 can effectively suppress the concentration of strain at the groove opening 44M of the circumferential narrow groove 88. This effectively suppresses damage such as chipping on the edges of the land section 52. This tire 2 has good durability. By setting the ratio D4 / D1 to 0.14 or less, the length of the narrow groove section 94 is appropriately maintained. As the tread 4 deforms in contact with the road surface, the pair of wall surfaces 44S of the circumferential narrow groove 88 can make sufficient contact with the narrow groove section 94. This tire 2 can maintain good resistance to uneven wear.

[0135] As is clear from the above description, the present invention provides a heavy-duty tire that can suppress the accumulation of static electricity while maintaining resistance to uneven wear. [Industrial applicability]

[0136] The technology described above, which suppresses static electricity buildup while maintaining resistance to uneven wear, can be applied to various types of tires.

[0137] [Note] The present invention includes the following embodiments.

[0138] [1] A tire comprising a pair of beads, a carcass spanning between the pair of beads, a reinforcing layer located radially outward of the carcass, and a tread covering the reinforcing layer from radially outward, wherein the tread comprises a cap layer in contact with the road surface and a conductive portion extending radially through the cap layer and connecting the road surface and the reinforcing layer, the tread comprises at least three circumferential grooves extending continuously in the circumferential direction, the at least three circumferential grooves forming at least four land portions aligned axially on the tread, and the at least four land portions having two shoulders located on the outermost axial side A heavy-duty tire comprising a land portion and a plurality of main land portions located between two of the shoulder land portions, wherein at least one of the plurality of main land portions comprises the conductive portion, the reinforcing layer comprises a belt comprising a plurality of belt plies and a band comprising a full band, the plurality of belt plies and the full band are arranged radially, each of the plurality of belt plies comprises a plurality of parallel belt cords, each belt cord is made of steel, and the full band comprises a helically wound band cord, the band cord is made of steel. [2] The heavy-duty tire described in [1] above, wherein the ratio of the axial width of the full band to the width of the tread is 0.60 or more. [3] The heavy-duty tire described in [1] or [2] above, wherein the full band code ends are 20 ends / 50 mm or more. [4] A heavy-duty tire according to any of the above [1] to [3], wherein the width of the conductive part is 8.0 mm or less. [5] A heavy-duty tire according to any of [1] to [4] above, wherein the plurality of belt plies comprises a reference belt ply and a sub-reference belt ply, the reference belt ply being the belt ply having the widest axial width among the plurality of belt plies, the sub-reference belt ply being the belt ply having the second widest axial width among the plurality of belt plies, the direction of inclination of the belt cords included in the sub-reference belt ply being opposite to the direction of inclination of the belt cords included in the reference belt ply, and the full band being located between the reference belt ply and the sub-reference belt ply. [6] A heavy-duty tire according to any one of the above [1] to [5], wherein of the multiple main land sections, only one main land section is equipped with the conductive part. [7] The heavy-duty tire according to [6] above, wherein, among the multiple main land sections, the main land section located on the equatorial plane, or the main land section closest to the equatorial plane, is the crown land section, and if the tread has three or more main land sections, the main land section located next to the crown land section is the middle land section, and the main land section on which the conductive part is provided is either the crown land section or the middle land section. [8] A heavy-duty tire according to any one of [1] to [7] above, further comprising a strip layer made of cross-linked rubber between the carcass and the reinforcing layer, wherein the strip layer has an axial width in the same manner as the axial width of the full band. [Explanation of symbols]

[0139] 2.82... Tires 4. Tread 10...bead 12...Carcass 14. Reinforcement layer 22...Tread surface 28...Carcass ply 30...Cap layer 32...Base layer 34...Main unit 36. Conductive part 44, 48, 50...Circumferential groove 46...Circumferential main groove 52, 54, 56, 58, 84, 86... Rikubu 60... belt 62 bands 64, 64A, 64B, 64C... Belt ply 66, 66A, 66B, 66C... Belt cord 70... Full Band 72... Band Code 88... Circumferential narrow groove 110... Measuring device

Claims

1. A pair of beads, A carcass spanning between the pair of aforementioned beads, A reinforcing layer located radially outward of the carcass, The tread covering the reinforcing layer extends radially outward from the reinforcing layer Equipped with, The tread comprises a cap layer that contacts the road surface and a conductive portion that extends radially through the cap layer and connects the road surface and the reinforcing layer. The tread comprises at least three circumferential grooves that extend continuously in the circumferential direction, At least three of the circumferential grooves constitute the tread, forming at least four land sections aligned in the axial direction. At least four of the aforementioned land sections comprise two shoulder land sections located on the outermost axial sides, and a plurality of main land sections located between the two shoulder land sections. Of the multiple main land sections, at least one main land section is equipped with the conductive part. The reinforcing layer comprises a belt including a plurality of belt plies and a band including a full band, Multiple of the belt plies and the full band are arranged radially, Each of the aforementioned belt plies includes a number of belt cords arranged in parallel, Each of the aforementioned belt cords is made of steel. The aforementioned full band includes a spirally wound band cord, The material of the aforementioned band cord is steel. Heavy-duty tires.

2. The ratio of the axial width of the full band to the width of the tread is 0.60 or more. A heavy-duty tire according to claim 1.

3. The aforementioned full-band code ends are 20 ends / 50 mm or more. A heavy-duty tire according to claim 1.

4. The width of the conductive part is 8.0 mm or less. A heavy-duty tire according to claim 1.

5. Multiple belt plies comprise a reference belt ply and a sub-reference belt ply, The reference belt ply is a belt ply having the widest axial width among the plurality of belt plies. The sub-reference belt ply is a belt ply having the second widest axial width among the plurality of belt plies, after the reference belt ply. The direction of inclination of the belt cord included in the sub-reference belt ply is opposite to the direction of inclination of the belt cord included in the reference belt ply, The full band is located between the reference belt ply and the sub-reference belt ply. A heavy-duty tire according to claim 1.

6. Of the multiple main land sections, only one main land section is equipped with the conductive part. A heavy-duty tire according to claim 1.

7. Of the multiple main land areas, the main land area located on the equatorial plane, or the main land area closest to the equatorial plane, is the Crown Land Area. If the tread has three or more main land sections, the main land section located next to the crown land section is the middle land section. The main land area on which the conductive part is provided is either the crown land area or the middle land area. A heavy-duty tire according to claim 6.

8. A strip layer made of cross-linked rubber is further provided between the carcass and the reinforcing layer. The strip layer has an axial width approximately the same as the axial width of the full band. A heavy-duty tire according to any one of claims 1 to 7.

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