Heavy-duty tires

Abstract

To provide a tire for heavy loads that can achieve maintenance of rolling resistance performance and an improvement in durability performance.SOLUTION: A tire 1 for heavy loads comprises a belt layer 7. The belt layer 7 includes a first belt ply 7A, a second belt ply 7B, a third belt ply 7C and a fourth belt ply 7D. The first-the fourth belt plies respectively comprise belt cords 11 inclined with respect to a tire equatorial plane C. A first distance L1 that is the distance in a tire radial direction between the belt cord 11 of the third belt ply 7C and the belt cord 11 of the fourth belt ply 7D is set to be equal to or shorter than a second distance L2 that is the distance in the tire radial direction between the belt cord 11 of the second belt ply 7B and the belt cord 11 of the third belt ply 7C. With regard to ends that are the number of input of the belt cords 11 per unit ply width, ends E4 of the fourth belt ply 7D are smaller than ends E3 of the third belt ply 7C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 below describes a heavy-duty pneumatic tire. This heavy-duty pneumatic tire has an inclined belt provided on the radially outer side of the crown portion of the carcass. This inclined belt includes a first belt layer and a second belt layer, and these reinforcing elements extend obliquely so as to intersect with each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-063051 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with growing concern about global environmental issues, heavy-duty tires are being required to have reduced rolling resistance, while at the same time, there is a strong demand for improved durability. However, there is still room for improvement in the durability of the above-mentioned tires.

[0005] The present invention has been devised in view of the above circumstances, and has as its main object to provide a heavy-duty tire that can maintain rolling resistance performance and improve durability performance. [Means for solving the problem]

[0006] The present invention provides a heavy-duty tire comprising a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed radially outward of the carcass and within the tread portion, wherein the belt layer includes a first belt ply, a second belt ply, a third belt ply, and a fourth belt ply which are sequentially stacked from the carcass side toward the radially outward side of the tire, and each of the first to fourth belt plies has belt cords inclined with respect to the tire equatorial plane, and a first distance L1 which is the distance in the radial direction of the tire between the belt cords of the third belt ply and the belt cords of the fourth belt ply is set to be equal to or less than a second distance L2 which is the distance in the radial direction of the tire between the belt cords of the second belt ply and the belt cords of the third belt ply, and with respect to ends which are the number of belt cords per unit ply width, ends E4 of the fourth belt ply are smaller than ends E3 of the third belt ply.

[0007] In the heavy duty tire according to the present invention, the end E4 of the fourth belt ply may be 65% to 85% of the end E3 of the third belt ply.

[0008] In the heavy duty tire according to the present invention, the first distance L1 may be 80% to 100% of the second distance L2.

[0009] In the heavy duty tire according to the present invention, a cord diameter D4 of the belt cord of the fourth belt ply may be 65% to 100% of a cord diameter D3 of the belt cord of the third belt ply.

[0010] In the heavy duty tire according to the present invention, the angle of the belt cord of the fourth belt ply with respect to the tire equatorial plane may be 30 to 60 degrees.

[0011] In the heavy duty tire according to the present invention, the tread portion may have a main groove extending in the tire circumferential direction, and the shortest distance in the tire radial direction between the main groove and a belt cord of the fourth belt ply may be 3 to 7 mm.

[0012] In the heavy duty tire according to the present invention, the angle of the belt cords of the first belt ply with respect to the tire equatorial plane may be 30 to 60 degrees, and the angles of the belt cords of the second belt ply and the third belt ply with respect to the tire equatorial plane may be 15 to 25 degrees.

[0013] In the heavy duty tire according to the present invention, the width of the fourth belt ply in the tire axial direction may be 25% to 75% of the tread width. [Effects of the Invention]

[0014] By employing the above-described configuration, the heavy duty tire of the present invention can maintain rolling resistance performance and improve durability. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a tire meridian cross-sectional view showing an example of a heavy-duty tire. [Figure 2] FIG. 2 is a partially enlarged view of the tread portion of FIG. [Figure 3] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a meridian cross section of the right half of a heavy-duty tire (hereinafter, sometimes simply referred to as "tire") 1 including a tire rotation axis (not shown). The tire 1 of this embodiment is suitable for use on trucks, buses, etc. In this specification, unless otherwise specified, the dimensions of each part of the tire are shown as values ​​measured in a normal state. The normal state refers to a state in which the tire 1 is mounted on a normal rim, inflated to a normal internal pressure, and no load is applied.

[0017] A "genuine rim" is a rim that is defined for each tire by a standard system that includes the standard on which tire 1 is based. Therefore, a genuine rim is, for example, a "standard rim" for JATMA, a "design rim" for TRA, or a "measuring rim" for ETRTO.

[0018] The "normal internal pressure" is the air pressure determined for each tire by each standard in a standard system including the standard on which the tire 1 is based. Therefore, the normal internal pressure is, for example, the "maximum air pressure" in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "INFLATION PRESSURE" in the case of ETRTO.

[0019] The tire 1 of this embodiment is composed of a carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a belt layer 7 that is arranged radially outside the carcass 6 and inside the tread portion 2.

[0020] [Tread] The tread portion 2 is provided with a tread rubber 2G arranged radially outward of the belt layer 7. The tread rubber 2G is provided with main grooves 14 extending in the tire circumferential direction. The main grooves 14 are recessed from the outer surface of the tread portion 2 radially inward.

[0021] [Carcass] The carcass 6 includes at least one carcass ply 6A, one carcass ply in this embodiment. The carcass ply 6A includes a main body portion 6a that extends from the tread portion 2 through the sidewall portion 3 to the bead cores 5 of the bead portions 4 on both sides, and a pair of turned-up portions 6b that are continuous with the main body portion 6a. A pair of bead apex rubbers 8 that extend radially outward from the bead cores 5 are provided between the main body portion 6a and the turned-up portions 6b.

[0022] The carcass ply 6A includes carcass cords (not shown) arranged at an angle of, for example, 75 to 90 degrees with respect to the tire equatorial plane C. As the carcass cords, for example, steel cords can be suitably used.

[0023] [Belt layer] Fig. 2 is a partially enlarged view of the tread portion 2 of Fig. 1. The belt layer 7 is composed of, for example, a plurality of belt plies in which an arrangement of belt cords 11 is covered with a topping rubber 12. The belt cords 11 of this embodiment are configured as a twisted wire in which a plurality of steel filaments (not shown) are twisted together. Note that the belt cords 11 are not limited to twisted wires, and may be, for example, solid steel wires.

[0024] 1 and 2, the belt layer 7 of this embodiment is configured to include a first belt ply 7A, a second belt ply 7B, a third belt ply 7C, and a fourth belt ply 7D. The first belt ply 7A to the fourth belt ply 7D are overlapped in order from the carcass 6 side toward the outside in the tire radial direction.

[0025] As shown in Fig. 1, in this embodiment, among the first to fourth belt plies 7A to 7D, the second belt ply 7B has the largest axial width W2, and the fourth belt ply 7D has the smallest axial width W4 (hereinafter sometimes referred to as "fourth belt width"). Fig. 3 is a development view of the belt layers. In Fig. 3, the belt cords 11 are shown in a simplified manner, with some of them omitted.

[0026] 3, each of the first to fourth belt plies 7A to 7D has belt cords 11 that are inclined with respect to the tire equatorial plane C. In this embodiment, the belt cords 11 of the first belt ply 7A and the second belt ply 7B are inclined to one side with respect to the tire equatorial plane C. On the other hand, the belt cords 11 of the third belt ply 7C and the fourth belt ply 7D are inclined to the other side with respect to the tire equatorial plane C.

[0027] An angle θ1 of the belt cords 11 of the first belt ply 7A relative to the tire equatorial plane C is set to a value between the angle (not shown) of the carcass cords of the carcass ply 6A (shown in FIG. 1) and the angle θ2 of the belt cords 11 of the second belt ply 7B. Such a first belt ply 7A can increase the belt rigidity while mitigating shear strain between the carcass ply 6A and the second belt ply 7B, and can further reinforce the tread portion 2. To effectively enhance such effects, the angle θ1 is desirably set to 30 to 60 degrees.

[0028] The belt cords 11 of the second belt ply 7B intersect with the belt cords 11 of the third belt ply 7C. Such second belt ply 7B and third belt ply 7C can increase the binding force in the tire circumferential direction. Therefore, the second belt ply 7B and the third belt ply 7C have a hoop effect and can firmly reinforce the tread portion 2, thereby improving durability.

[0029] The angle θ2 of the second belt ply 7B relative to the tire equatorial plane C and the angle θ3 of the belt cord 11 of the third belt ply 7C relative to the tire equatorial plane C are desirably set to 15 to 25°. By setting the angles θ2 and θ3 to 25° or less, the tread portion 2 can be strongly reinforced, and durability can be improved. On the other hand, by setting the angles θ2 and θ3 to 15° or more, it is possible to prevent the binding force in the tire circumferential direction from becoming higher than necessary, and therefore ride comfort can be maintained. From this perspective, the angles θ2 and θ3 are preferably 22° or less, and preferably 18° or more.

[0030] 1, the fourth belt ply 7D is disposed on the outermost side in the tire radial direction in the belt layer 7. Such a fourth belt ply 7D is useful for improving the cut resistance of the tread portion 2.

[0031] 2, the first distance L1 is set to be equal to or shorter than the second distance L2. The first distance L1 is the distance in the tire radial direction between the belt cord 11 of the third belt ply 7C and the belt cord 11 of the fourth belt ply 7D. On the other hand, the second distance L2 is the distance in the tire radial direction between the belt cord 11 of the second belt ply 7B and the belt cord 11 of the third belt ply 7C.

[0032] The first distance L1 and the second distance L2 (including a third distance L3 described later) are specified as the average values ​​of the distances between the belt cords 11, 11 adjacent in the tire radial direction in a region 20 where all of the first to fourth belt plies 7A to 7D overlap in the tire radial direction. Note that the overlapping region 20 in this embodiment is a region corresponding to a fourth belt width W4 (shown in FIG. 1) of the fourth belt ply 7D.

[0033] In the tire 1 of this embodiment, by setting the first distance L1 to be equal to or less than the second distance L2, a relative increase in the amount of rubber (topping rubber 12) constituting the fourth belt ply 7D can be prevented. The fourth belt ply 7D has a greater effect on rolling resistance performance than the first belt ply 7A to the third belt ply 7C arranged radially inward of it. Therefore, in the tire 1 of this embodiment, by setting the first distance L1 to be equal to or less than the second distance L2, an increase in energy loss in the belt layer 7 (fourth belt ply 7D) can be prevented, thereby maintaining rolling resistance performance. Furthermore, by preventing an increase in the amount of rubber (topping rubber 12) in the fourth belt ply 7D, an increase in the mass of the tire 1 (shown in FIG. 1) can be suppressed.

[0034] The first distance L1 is desirably set to 80% to 100% of the second distance L2. By setting the first distance L1 to 100% or less of the second distance L2, rolling resistance performance can be maintained. On the other hand, by setting the first distance L1 to 80% or more of the second distance L2, cord loosening, in which the belt cord 11 separates from the rubber, can be suppressed, and durability performance can be maintained. From this perspective, the first distance L1 is preferably 95% or less of the second distance L2, and preferably 85% or more of the second distance L2.

[0035] The fourth belt ply 7D has a smaller effect on the airtightness (air retention) of the tire cavity than the first to third belt plies 7A to 7C. Therefore, the tire 1 (shown in FIG. 1) can maintain the airtightness of the tire cavity even if the first distance L1 is set to be smaller than the second distance L2.

[0036] The first distance L1 can be set appropriately as long as the above-mentioned relationship with the second distance L2 is maintained. In this embodiment, the first distance L1 is preferably set to 0.4 to 1.0 mm. By setting the first distance L1 to 1.0 mm or less, rolling resistance performance can be maintained. On the other hand, by setting the first distance L1 to 0.4 mm or more, a decrease in cut resistance performance of the fourth belt ply 7D can be suppressed, and durability performance can be maintained. From this perspective, the first distance L1 is preferably 0.8 mm or less, and preferably 0.6 mm or more.

[0037] In this embodiment, the third distance L3, which is the distance in the tire radial direction between the belt cords 11 of the second belt ply 7B and the belt cords 11 of the first belt ply 7A, is set to be the same as the second distance L2. This makes it possible to maintain a reduction in the amount of rubber (topping rubber 12) constituting the first belt ply 7A and the second belt ply 7B, thereby maintaining the airtightness (air retention) of the tire cavity. In this specification, the term "same" is intended to allow for slight variations (errors) in manufacturing.

[0038] In this embodiment, the end E4 of the fourth belt ply 7D (hereinafter sometimes referred to as the "fourth end") is set smaller than the end E3 of the third belt ply 7C (hereinafter sometimes referred to as the "third end"). Here, the "end" refers to the number of belt cords 11 per unit ply width. The unit ply width is the length measured along the belt ply where the end is identified in a meridian cross section of the tire in a normal state. The unit ply width in this embodiment is 50 mm.

[0039] In this embodiment, the fourth ends E4 are set smaller than the third ends E3, so the proportion of the belt cords 11 in the fourth belt ply 7D can be reduced while the proportion of the rubber covering the belt cords 11 (topping rubber 12) can be increased. This allows the tire 1 to improve adhesion between the belt cords 11 and the rubber in the fourth belt ply 7D, thereby preventing cord loosening, in which the belt cords 11 are separated from the rubber. Therefore, the tire 1 can improve durability (cord loosening resistance).

[0040] In this embodiment, since the fourth ends E4 are set to be smaller than the third ends E3, adhesion between the belt cords 11 of the fourth belt ply 7D and the rubber can be increased even if the first distance L1 is set to be equal to or shorter than the second distance L2. Therefore, the tire 1 of this embodiment can maintain rolling resistance performance and improve durability.

[0041] The fourth ends E4 are preferably set to 65% to 85% of the third ends E3. By setting the fourth ends E4 to 85% or less of the third ends E3, cord loosening of the fourth belt ply 7D can be effectively prevented, improving durability. On the other hand, by setting the fourth ends E4 to 65% or more of the third ends E3, the proportion of the belt cords 11 can be prevented from becoming smaller than necessary, thereby maintaining rolling resistance and cut resistance. From this perspective, the fourth ends E4 are preferably set to 80% or less of the third ends E3, and more preferably 70% or more.

[0042] In this embodiment, the ends E1 of the first belt ply 7A (hereinafter sometimes referred to as "first ends") and the ends E2 of the second belt ply 7B (hereinafter sometimes referred to as "second ends") are set to be the same as the third ends E3 of the third belt ply 7C. This enables the first belt ply 7A to the third belt ply 7C to strongly reinforce the tread portion 2 and improve durability.

[0043] The number of ends per 50 mm ply width can be set appropriately as long as the above relationship is maintained. The number of the fourth ends E4 can be set to, for example, 12 to 22. The number of the first ends E1 to the third ends E3 can be set to, for example, 19 to 27.

[0044] It is desirable that the cord diameter D4 of the belt cords 11 of the fourth belt ply 7D (hereinafter sometimes referred to as the "fourth cord diameter") be set equal to or smaller than the cord diameter D3 of the belt cords 11 of the third belt ply 7C (hereinafter sometimes referred to as the "third cord diameter"). This allows the fourth belt ply 7D to have a small proportion of the belt cords 11 while having a large proportion of the rubber (topping rubber 12) covering the belt cords 11. This makes it possible to prevent the cords of the fourth belt ply 7D from becoming loose, thereby improving the durability of the tire 1. Note that, when the belt cords 11 are configured as a twisted wire in which multiple steel filaments are twisted together, the cord diameter can be specified as the diameter of a circumscribing circle of an assembly of steel filaments.

[0045] The fourth cord diameter D4 of the fourth belt ply 7D is desirably set to 65% to 100% of the third cord diameter D3 of the third belt ply 7C. By setting the fourth cord diameter D4 to 100% or less of the third cord diameter D3, cord loosening of the fourth belt ply 7D can be prevented, and durability can be improved. On the other hand, by setting the fourth cord diameter D4 to 65% or more of the third cord diameter D3, the proportion of the belt cords 11 can be prevented from becoming smaller than necessary, and rolling resistance and cut resistance can be maintained. From this perspective, the fourth cord diameter D4 is preferably 90% or less, and more preferably 75% or more, of the third cord diameter D3.

[0046] In this embodiment, the cord diameter D1 of the first belt ply 7A (hereinafter sometimes referred to as the "first cord diameter") and the cord diameter D2 of the second belt ply 7B (hereinafter sometimes referred to as the "second cord diameter") are set to be the same as the third cord diameter D3 of the third belt ply 7C. This enables the first to third belt plies 7A to 7C to strongly reinforce the tread portion 2 and improve durability.

[0047] As shown in FIG. 3, the angle θ4 of the belt cord 11 of the fourth belt ply 7D with respect to the tire equatorial plane C is desirably set to 30 to 60 degrees. By setting the angle θ4 to 30 degrees or more, the tire 1 (shown in FIG. 1) can be eccentrically deformed (the tread ring can be displaced in the tire radial direction while maintaining its circular shape) when the tire 1 rolls. This reduces the strain generated in the fourth belt ply 7D when the tire rolls. Therefore, the fourth belt ply 7D can prevent cord loosening and improve durability. On the other hand, by setting the angle θ4 to 60 degrees or less, cut resistance can be maintained. From this perspective, the angle θ4 is preferably 40 degrees or more and preferably 50 degrees or less.

[0048] As shown in FIG. 2, the shortest distance L4 in the tire radial direction between the main groove 14 and the belt cord 11 of the fourth belt ply 7D is desirably set to 3 to 7 mm. Setting the shortest distance L4 to 3 mm or more can improve the adhesion between the tread rubber 2G and the belt cord 11. This can prevent cord loosening in the fourth belt ply 7D in the tire 1, improving durability. On the other hand, setting the shortest distance L4 to 7 mm or less can prevent an increase in energy loss in the tread rubber 2G and the fourth belt ply 7D, maintaining rolling resistance performance. From this perspective, the shortest distance L4 is preferably 4 mm or more and preferably 6 mm or less.

[0049] As shown in FIG. 1, the fourth belt width W4 of the fourth belt ply 7D in the tire axial direction is desirably set to 25% to 75% of the tread width TW. By setting the fourth belt width W4 to 75% or less of the tread width TW, the amount of rubber (topping rubber 12 (shown in FIG. 2)) constituting the fourth belt ply 7D can be reduced. This makes it possible to prevent an increase in energy loss in the fourth belt ply 7D and improve rolling resistance performance of the tire 1. On the other hand, by setting the fourth belt width W4 to 25% or more of the tread width TW, cut resistance performance can be maintained. From this perspective, the fourth belt width W4 is preferably 60% or less of the tread width TW, and preferably 40% or more.

[0050] The tread width TW is defined as the axial distance between the tread ends 2t, 2t, which are the axially outermost contact points of the tire when the tire 1 is in a normal state and placed on a flat surface with a normal load and a camber angle of 0 degrees.

[0051] "Normal load" refers to the load specified for each tire in the standard system that includes the standard on which the tire is based. Therefore, normal load is, for example, "Maximum Load Capacity" in JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and "LOAD CAPACITY" in ETRTO.

[0052] Although a particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the illustrated embodiment and can be modified and implemented in various ways. [Example]

[0053] [Example A] Heavy-duty tires having the basic structure shown in Fig. 1 were prototyped based on the specifications in Table 1 (Examples 1 to 9 and Comparative Example). Each prototype tire was evaluated for durability (drum test, presence or absence of belt cord peeling), durability (plunger test), and rolling resistance. The common specifications are as follows: Tire size: 275 / 80R22.5 Rim size: 8.25 x 22.5 Internal pressure: 900kPa Load: 28.8kN Tread width TW: 240mm Slip angle: 0 degrees First Belt Ply: Belt cord angle θ1: 50° No. 1 Ends E1 (per 50mm ply width): 19 First distance between belt cords L1: 0.5 mm 2nd Belt Ply & 3rd Belt Ply: Belt cord angles θ2, θ3: 15° Second Ends E2 and Third Ends E3 (per 50mm ply width): 27 4th Belt Ply: Belt cord angle θ1: 50° Shortest distance between main grooves L4: 4.0mm 4th belt width W4 / tread width TW: 40%

[0054] <Durability performance (drum test, belt cord peeling)> Each prototype tire was mounted on the rim and inflated to the internal pressure. Based on the load, slip angle, and running speed of 80 km / h, each prototype tire was run on a drum testing machine, and the running speed was increased by 10 km / h every two hours from the start of running, and the running time until the tire broke was measured. The results are expressed as an index, with Example 3 being set at 100. The higher the index, the better; an index of 95 or higher indicates that the durability (cord looseness resistance) required for heavy-duty tires is maintained. In addition, the destroyed prototype tire was disassembled to check for the presence or absence of separation (loose cord) at the interface between the belt cord and the tread rubber.

[0055] <Durability performance (plunger test)> Each prototype tire was mounted on the rim and inflated to the internal pressure. A plunger breaking test was then conducted in accordance with JIS D4230, and the breaking energy was measured. The results are expressed as an index, with Example 3 being 100. The higher the index, the better; an index of 95 or higher indicates that the cut resistance required for a heavy-duty tire is maintained.

[0056] <Rolling resistance performance> Each prototype tire was mounted on the rim and inflated to the internal pressure. Using a rolling resistance tester, rolling resistance was measured at a running speed of 60 km / h and under the above load. The evaluation is expressed as an index, with Example 3 being set at 100. The smaller the index, the better; if it is 105 or less, the rolling resistance performance required for a heavy-duty tire is maintained. The test results are shown in Table 1.

[0057] [Table 1]

[0058] As a result of the test, the heavy duty tires of the example exhibited improved durability performance while maintaining rolling resistance performance compared to the heavy duty tires of the comparative example.

[0059] [Example B] Heavy-duty tires having the basic structure shown in Fig. 1 were prototyped based on the specifications in Table 2 (Example 3 and Examples 10 to 18). Each prototype tire was evaluated for durability (drum test, presence or absence of belt cord peeling), durability (plunger test), and rolling resistance. The common specifications were the same as those of Example A, except for the following specifications and those in Table 2. 1st distance L1 / 2nd distance L2: 100% 4th End E4 / 3rd End E3: 74% 4th cord diameter D4: 1.0 mm The test method was as described in Example A, and the test results are shown in Table 2.

[0060] [Table 2]

[0061] As a result of the test, Example 3 and Examples 10 to 12, in which the fourth cord diameter D4 / third cord diameter D3 was within the preferred range, were able to maintain rolling resistance performance and durability performance (cut resistance) and showed improved durability performance (cord loosening resistance) compared to Example 13, in which the fourth cord diameter D4 / third cord diameter D3 was outside the preferred range. Furthermore, Example 3 and Examples 15 to 17, in which the angle θ4 of the fourth belt ply was within the preferred range, suppressed deterioration in rolling resistance performance and durability performance (cut resistance) and showed improved durability performance (cord loosening resistance) compared to Examples 14 and 18, in which the angle θ4 was outside the preferred range.

[0062] [Example C] Heavy-duty tires having the basic structure shown in Fig. 1 were prototyped based on the specifications in Table 3 (Example 3 and Examples 19 to 28). Each prototype tire was evaluated for durability (drum test, presence or absence of belt cord peeling), durability (plunger test), and rolling resistance. The common specifications were the same as those of Example A, except for the following specifications and those in Table 3. 1st distance L1 / 2nd distance L2: 100% 4th End E4 / 3rd End E3: 74% The test method was as described in Example A, and the test results are shown in Table 2.

[0063] [Table 3]

[0064] As a result of the test, Examples 3, 20, and 22, in which the shortest distance L4 was within the preferred range, had improved durability (cord loosening resistance) while maintaining rolling resistance performance, compared to Examples 19 and 23, which were outside the preferred range. Also, Examples 3, 25 to 27, in which the fourth belt width W4 / tread width TW was within the preferred range, had improved durability (cut resistance) while maintaining rolling resistance performance, compared to Examples 24 and 28, which were outside the preferred range. [Explanation of symbols]

[0065] 1 Heavy duty tires 7 Belt Layer 7A First Belt Ply 7B 2nd belt ply 7C 3rd belt ply 7D 4th belt ply 11 Belt cord

Claims

1. A heavy-duty tire comprising a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a belt layer disposed radially outward of the carcass and inside the tread portion, the belt layer includes a first belt ply, a second belt ply, a third belt ply, and a fourth belt ply that are stacked in this order from the carcass side toward an outer side in the tire radial direction, Each of the first to fourth belt plies includes a belt cord inclined with respect to the tire equatorial plane, a first distance L1 which is a distance in the tire radial direction between the belt cords of the third belt ply and the belt cords of the fourth belt ply is set to be equal to or less than a second distance L2 which is a distance in the tire radial direction between the belt cords of the second belt ply and the belt cords of the third belt ply, With respect to ends, which are the number of belt cords per 50 mm of ply width, ends E4 of the fourth belt ply are smaller than ends E3 of the third belt ply, The ends E1 of the first belt ply and the ends E2 of the second belt ply are set to be the same as the ends E3 of the third belt ply, the number of ends E1 of the first belt ply, the number of ends E2 of the second belt ply, and the number of ends E3 of the third belt ply are 19 to 27, The number of ends E4 of the fourth belt ply is 12 to 22, an angle of the belt cord of the fourth belt ply with respect to the tire equatorial plane of 30 to 60 degrees; Heavy duty tires.

2. A heavy-duty tire as described in claim 1, wherein the cord diameter D4 of the belt cord of the fourth belt ply is 65% to 90% of the cord diameter D3 of the belt cord of the third belt ply.

3. The heavy duty tire according to claim 1 or 2, wherein the end E4 of the fourth belt ply is 65% to 85% of the end E3 of the third belt ply.

4. 4. The heavy duty tire according to claim 1, wherein the first distance L1 is 80% to 100% of the second distance L2.

5. The tread portion has a main groove extending in the tire circumferential direction, 5. The heavy duty tire according to claim 1, wherein the shortest distance in the tire radial direction between the main groove and the belt cord of the fourth belt ply is 3 to 7 mm.

6. An angle of the belt cord of the first belt ply with respect to the tire equatorial plane is 30 to 60 degrees, 6. The heavy duty tire according to claim 1, wherein the angles of the belt cords of the second belt ply and the third belt ply with respect to the tire equatorial plane are 15 to 25 degrees.

7. A heavy-duty tire as described in any one of claims 1 to 6, wherein the axial width of the fourth belt ply is 25% to 75% of the tread width.

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