Heavy load tyre

Abstract

Provided is a heavy load tire capable of achieving maintenance of rolling resistance performance and improvement of durability. A heavy load tire (1) has a belt layer (7). The belt layer includes a first belt ply (7A), a second belt ply (7B), a third belt ply (7C), and a fourth belt ply (7D). Each of the first to fourth belt plies has belt cords (11) inclined with respect to a tire equatorial plane (C). A tire radial direction distance between the belt cords of the third belt ply (7C) and the fourth belt ply (7D), that is, a first distance (L1), is set to be equal to or smaller than a tire radial direction distance between the belt cords of the second belt ply (7B) and the third belt ply (7C), that is, a second distance (L2). With respect to a number of the belt cords per unit ply width, that is, a cord count, a cord count (E4) of the fourth belt ply is smaller than a cord count (E3) of the third belt ply.

Description

Technical Field

[0001] This invention relates to tires for heavy loads. Background Technology

[0002] Patent Document 1 describes a heavy-duty pneumatic tire. This heavy-duty pneumatic tire has a sloping belt on the radially outer side of the tire's crown portion. This sloping belt comprises a first belt layer and a second belt layer, and these reinforcing elements extend obliquely in a mutually intersecting manner.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2020-063051

[0004] In recent years, with increasing attention to environmental issues, there has been a growing demand for reduced rolling resistance and improved durability in heavy-duty tires. However, in the aforementioned tires, there is room for improvement in these aspects of durability. Summary of the Invention

[0005] The present invention was made in view of the above-mentioned actual situation, and its main objective is to provide a heavy-duty tire that can maintain rolling resistance performance and improve durability performance.

[0006] This invention relates to a heavy-duty tire, comprising: a carcass extending from the tread portion through the sidewall to the bead portion; and a belt layer disposed outside the tire carcass in the tire radial direction and inside the tread portion, characterized in that the belt layer comprises a first belt ply, a second belt ply, a third belt ply, and a fourth belt ply, sequentially overlapping from the carcass side toward the tire radial direction, each of the first, second, third, and fourth belt ply layers having an inclination relative to the tire equator. The oblique belt cords are defined as follows: the distance in the tire radius direction between the belt cords of the third belt cord layer and the belt cords of the fourth belt cord layer is defined as the first distance L1; the distance in the tire radius direction between the belt cords of the second belt cord layer and the belt cords of the third belt cord layer is defined as the second distance L2; the first distance L1 is set to be less than the second distance L2; the number of belt cords driven per unit width of the cord layer is called the cord count; and the cord count E4 of the fourth belt cord layer is smaller than the cord count E3 of the third belt cord layer.

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

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

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

[0010] In the heavy-duty tire of the present invention, the angle between the belt cord of the fourth belt ply and the tire equatorial plane may be 30° to 60°.

[0011] In the heavy-duty tire of the present invention, the tread may have a main groove extending along the tire circumference, and the shortest distance in the tire radius direction between the main groove and the belt cord of the fourth belt ply is 3mm to 7mm.

[0012] In the heavy-duty tire of the present invention, the angle between the belt cord of the first belt ply and the tire equator may be 30° to 60°, and the angle between the belt cord of the second belt ply and the third belt ply and the tire equator may be 15° to 25°.

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

[0014] By employing the above-described structure, the heavy-duty tire of the present invention can maintain rolling resistance performance and improve durability performance. Attached Figure Description

[0015] Figure 1 This is a radial cross-sectional view of a tire, showing an example of a heavy-duty tire.

[0016] Figure 2 yes Figure 1 A magnified view of a portion of the fetal tummy.

[0017] Figure 3 This is a diagram of the unfolded belt layer.

[0018] Label Explanation

[0019] 1: Heavy-duty tire; 7: Belt layer; 7A: First belt cord layer; 7B: Second belt cord layer; 7C: Third belt cord layer; 7D: Fourth belt cord layer; 11: Belt cord. Detailed Implementation

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] exist Figure 1 The diagram shows a right half of the meridional cross-section of a heavy-duty tire (hereinafter, sometimes simply referred to as "tire") 1, including the tire's axis of rotation (not shown). The tire 1 of this embodiment is preferably used, for example, for trucks, buses, etc. In this specification, unless otherwise specified, the dimensions of the tire are expressed as values ​​measured under normal conditions. Normal conditions refer to the unloaded state in which the tire 1 is assembled onto a normal rim and filled with normal internal pressure.

[0022] "Standard rim" refers to a rim whose specifications are determined for each tire within a specification system that includes the specifications on which tire 1 is based. Therefore, a standard rim is, for example, a "standard rim" if it is JATMA, a "design rim" if it is TRA, and a "measuring rim" if it is ETRTO.

[0023] "Standard internal pressure" refers to the air pressure specified for each tire within a specification system, including the specification on which tire 1 is based. Therefore, standard internal pressure, for example, is "maximum air pressure" if it is JATMA, the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" if it is TRA, and "INFLATION PRESSURE" if it is ETRTO.

[0024] The tire 1 of this embodiment is configured to include: a tire body 6, which extends from the tread portion 2 through the sidewall portion 3 to the bead portion 4 and a bead core 5; and a belt layer 7, which is disposed on the outer side of the tire body 6 in the tire radial direction and inside the tread portion 2.

[0025] [Fetal face]

[0026] A tread compound 2G is provided on the tread portion 2, positioned on the outer side of the belt layer 7 in the radial direction of the tire. A main groove 14 extending in the circumferential direction of the tire is provided on the tread compound 2G. The main groove 14 is recessed from the outer surface of the tread portion 2 in the radial direction of the tire.

[0027] [Fetal body]

[0028] The carcass 6 includes at least one carcass ply 6A (in this embodiment, one ply). The carcass ply 6A includes: a main body portion 6a, which extends from the tread portion 2 through the sidewall portion 3 to the bead portions 4 on both sides, and a pair of folded-back portions 6b connected to the main body portion 6a. A pair of bead triangles 8 extending radially outward from the bead core 5 are provided between the main body portion 6a and the folded-back portions 6b.

[0029] The carcass ply 6A includes, for example, carcass cords (not shown) arranged at an angle of 75° to 90° relative to the tire equatorial plane C. Steel cords are preferably used as the carcass cords.

[0030] [Belt layer]

[0031] Figure 2 yes Figure 1 A partial enlarged view of the tire tread 2. The belt layer 7 is, for example, composed of multiple belt cord layers in which the arrangement of belt cords 11 is covered with adhesive rubber 12. In this embodiment, the belt cords 11 are configured as twisted yarns formed by twisting multiple steel fibers (not shown). In addition, the belt cords 11 are not limited to twisted yarns, and may also be single steel wires, for example.

[0032] like Figure 1 and Figure 2 As shown, the belt layer 7 in 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 overlap sequentially from the tire carcass 6 side toward the outer side in the tire radial direction.

[0033] like Figure 1 As shown, in this embodiment, the tire axial width W2 of the second belt ply 7B among the first belt ply 7A to the fourth belt ply 7D is formed to be the largest, and the tire axial width W4 of the fourth belt ply 7D (hereinafter sometimes referred to as "fourth belt width") is formed to be the smallest. Figure 3 This is a unfolded diagram of the belt layer. Figure 3 In the diagram, simplified belt cords 11 are shown, with some of them omitted.

[0034] like Figure 3 As shown, each of the first belt ply 7A to the fourth belt ply 7D is provided with belt cords 11 that are inclined relative 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 relative 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 relative to the tire equatorial plane C.

[0035] The angle θ1 of the belt cord 11 of the first belt ply 7A relative to the tire equatorial plane C is set to the angle of the carcass ply 6A ( Figure 1The angle θ1 of the carcass cords (shown) relative to the tire equatorial plane C (illustrated but not shown) and the angle θ2 of the belt cords 11 of the second belt ply 7B relative to the tire equatorial plane C are considered. This first belt ply 7A can mitigate shear strain between the carcass ply 6A and the second belt ply 7B, and can improve belt rigidity, further strengthening the tread portion 2. To effectively enhance this effect, the angle θ1 is preferably set to 30° to 60°.

[0036] The belt cords 11 of the second belt ply 7B intersect with those of the third belt ply 7C. This arrangement of the second belt ply 7B and the third belt ply 7C enhances the tire's circumferential restraint. Therefore, the second belt ply 7B and the third belt ply 7C possess a hoop effect, firmly reinforcing the tread portion 2 and improving durability.

[0037] The angles θ2 of the belt cord 11 of the second belt ply 7B relative to the tire equatorial plane C and θ3 of the belt cord 11 of the third belt ply 7C relative to the tire equatorial plane C are preferably set to 15° to 25°. By setting angles θ2 and θ3 to 25° or less, the tread portion 2 can be firmly reinforced, and durability can be improved. On the other hand, by setting angles θ2 and θ3 to 15° or more, excessive circumferential restraint forces on the tire can be prevented, thus maintaining ride comfort. From this viewpoint, angles θ2 and θ3 are preferably 22° or less, and more preferably 18° or more.

[0038] like Figure 1 As shown, the fourth belt ply 7D is positioned on the outermost side in the radial direction of the tire within the belt ply 7. This fourth belt ply 7D helps to improve the cut resistance of the tread portion 2.

[0039] like Figure 2 As shown, the first distance L1 is set to be less than or equal to the second distance L2. The first distance L1 is the tire radius distance 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 tire radius distance between the belt cord 11 of the second belt ply 7B and the belt cord 11 of the third belt ply 7C.

[0040] The first distance L1 and the second distance L2 (including the third distance L3 described later) are determined as the average distance between adjacent belt cords 11, 11 in the tire radial direction within the region 20 where all of the first belt ply 7A to the fourth belt ply 7D repeat in the tire radial direction. Furthermore, the repeating region 20 in this embodiment corresponds to the fourth belt width W4 of the fourth belt ply 7D. Figure 1 The area shown.

[0041] In this embodiment, by setting the first distance L1 to a second distance L2 or less, the amount of rubber (adhesive rubber 12) constituting the fourth belt ply 7D can be prevented from relatively increasing. This fourth belt ply 7D, compared to the first belt ply 7A to the third belt ply 7C disposed on the inner side in the tire radial direction, affects rolling resistance performance. Therefore, by setting the first distance L1 to a second distance L2 or less, the tire 1 of this embodiment can prevent an increase in energy loss of the belt layer 7 (fourth belt ply 7D), thus maintaining rolling resistance performance. Furthermore, since an increase in the amount of rubber (adhesive rubber 12) in the fourth belt ply 7D can be prevented, the tire 1 ( Figure 1 The mass of (as shown) increases.

[0042] The first distance L1 is preferably set to 80% to 100% of the second distance L2. By setting the first distance L1 to less than 100% of the second distance L2, rolling resistance performance can be maintained. On the other hand, by setting the first distance L1 to more than 80% of the second distance L2, loosening of the cord 11 that peels off from the rubber can be suppressed, and durability performance can be maintained. From this point of view, the first distance L1 is preferably less than 95% of the second distance L2, and more preferably more than 85% of the second distance L2.

[0043] Furthermore, compared to the first belt ply 7A to the third belt ply 7C, the fourth belt ply 7D has a smaller impact on the air tightness (air retention) of the tire cavity. Therefore, even if the first distance L1 is set to be smaller than the second distance L2, the tire 1 ( Figure 1 (As shown) It can also maintain the airtightness of the tire cavity.

[0044] By maintaining the aforementioned relationship with the second distance L2, the first distance L1 can be appropriately set. In this embodiment, the first distance L1 is preferably set to 0.4 mm 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, the reduction in the cut resistance of the fourth belt cord fabric layer 7D can be suppressed, and durability performance can be maintained. From this viewpoint, the first distance L1 is preferably 0.8 mm or less, and more preferably 0.6 mm or more.

[0045] In this embodiment, the tire radial distance L3, i.e., the distance 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 maintains the condition that the amount of rubber (adhesive rubber 12) constituting the first belt ply 7A and the second belt ply 7B is reduced, thus maintaining the airtightness (air retention) of the tire cavity. In this specification, "same" means that slight manufacturing deviations (errors) are permissible.

[0046] In this embodiment, the number of cords (hereinafter, sometimes referred to as "the fourth cord count") E4 of the fourth belt ply 7D is set to be smaller than the number of cords (hereinafter, sometimes referred to as "the third cord count") E3 of the third belt ply 7C. Here, the cord count refers to the number of belt cords 11 driven in per unit ply width. Furthermore, the unit ply width is the length measured along the belt ply with a defined cord count in the radial section of the tire in its normal state. In this embodiment, the unit ply width is 50 mm.

[0047] In this embodiment, since the fourth cord number E4 is set to be smaller than the third cord number E3, the proportion of belt cords 11 in the fourth belt ply 7D can be reduced, and the proportion of rubber (adhesive rubber 12) covering the belt cords 11 can be increased. Therefore, the tire 1 can improve the adhesion between the belt cords 11 and the rubber in the fourth belt ply 7D, thus preventing the belt cords 11 from detaching from the rubber. Therefore, the tire 1 can improve its durability (resistance to cord detachment).

[0048] In this embodiment, since the fourth cord number E4 is set to be smaller than the third cord number E3, the adhesion between the belt cord 11 of the fourth belt ply 7D and the rubber can be improved even if the first distance L1 is set to be less than or equal to the second distance L2. Therefore, the tire 1 of this embodiment can maintain rolling resistance performance and improve durability performance.

[0049] The fourth cord count E4 is preferably set to 65% to 85% of the third cord count E3. By setting the fourth cord count E4 to 85% or less of the third cord count E3, loosening of the cords in the fourth belt cord layer 7D can be effectively prevented, thus improving durability. On the other hand, by setting the fourth cord count E4 to 65% or more of the third cord count E3, the proportion of belt cords 11 can be prevented from being too small, thereby maintaining rolling resistance and cut resistance. From this viewpoint, the fourth cord count E4 is preferably 80% or less of the third cord count E3, and more preferably 70% or more.

[0050] In this embodiment, the number of cords (hereinafter sometimes referred to as "first cord count") E1 of the first belt ply 7A and the number of cords (hereinafter sometimes referred to as "second cord count") E2 of the second belt ply 7B are set to be the same as the third cord count E3 of the third belt ply 7C. Therefore, the first belt ply 7A to the third belt ply 7C can firmly reinforce the tread portion 2, thereby improving durability.

[0051] Regarding the number of cords per 50mm fabric layer width, as long as the above relationship is maintained, the number of cords from the first cord E1 to the fourth cord E4 can be appropriately set. The fourth cord E4 can be set to, for example, 12 to 22 cords. Furthermore, the number of cords from the first cord E1 to the third cord E3 can be set to, for example, 19 to 27 cords.

[0052] The cord diameter (hereinafter, sometimes referred to as "fourth cord diameter") D4 of the belt cord 11 of the fourth belt ply 7D is preferably set to be less than or equal to the cord diameter (hereinafter, sometimes referred to as "third cord diameter") D3 of the belt cord 11 of the third belt ply 7C. This allows the fourth belt ply 7D to reduce the proportion of the belt cord 11 and increase the proportion of the rubber (adhesive rubber 12) covering its belt cord 11. Consequently, the tire 1 can prevent the cords of the fourth belt ply 7D from loosening and improve durability. Furthermore, when the belt cord 11 is configured as a twisted yarn made by twisting multiple steel fibers together, the cord diameter can be determined as the diameter of the circumcircle of the steel fiber assembly.

[0053] The diameter D4 of the fourth cord in the fourth belt-stayed fabric layer 7D is preferably set to 65% to 100% of the diameter D3 of the third cord in the third belt-stayed fabric layer 7C. By setting the fourth cord diameter D4 to less than 100% of the third cord diameter D3, loosening of the cords in the fourth belt-stayed fabric layer 7D can be prevented, thus improving durability. On the other hand, by setting the fourth cord diameter D4 to more than 65% of the third cord diameter D3, the proportion of the belt-stayed cord 11 can be prevented from being too small, thereby maintaining rolling resistance and cut resistance. From this viewpoint, the fourth cord diameter D4 is preferably less than 90% of the third cord diameter D3, and more preferably more than 75%.

[0054] In this embodiment, the cord diameter (hereinafter, sometimes referred to as "first cord diameter") D1 of the first belt ply 7A and the cord diameter (hereinafter, sometimes referred to as "second cord diameter") D2 of the second belt ply 7B are set to be the same as the third cord diameter D3 of the third belt ply 7C. Therefore, the first belt ply 7A to the third belt ply 7C can firmly reinforce the tread portion 2, thereby improving durability.

[0055] like Figure 3As shown, the angle θ4 of the belt cord 11 of the fourth belt ply 7D relative to the tire equatorial plane C is preferably set to 30° to 60°. By setting the angle θ4 to 30° or more, when the tire 1 rolls, it is possible to make the tire 1 ( Figure 1 (As shown) Eccentric deformation (displacement along the tire radius while the tread ring remains circular). This reduces deformation in the fourth belt ply 7D during tire rolling. Therefore, the fourth belt ply 7D prevents cord loosening and improves durability. On the other hand, by setting the angle θ4 to 60° or less, cut resistance can be maintained. From this perspective, the angle θ4 is preferably 40° or more, and more preferably 50° or less.

[0056] like Figure 2 As shown, 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 preferably set to 3mm to 7mm. By setting the shortest distance L4 to 3mm or more, the adhesion between the tread compound 2G and the belt cord 11 can be improved. As a result, the tire 1 can prevent the cords at the fourth belt ply 7D from loosening and can improve durability. On the other hand, by setting the shortest distance L4 to 7mm or less, the energy loss at the tread compound 2G and the fourth belt ply 7D can be prevented from increasing, and rolling resistance performance can be maintained. From this point of view, the shortest distance L4 is preferably 4mm or more, and preferably 6mm or less.

[0057] like Figure 1 As shown, the fourth belt width W4 in the tire axial direction of the fourth belt ply 7D is preferably set to 25% to 75% of the tread width TW. By setting the fourth belt width W4 to less than 75% of the tread width TW, the amount of rubber (adhesive rubber 12) constituting the fourth belt ply 7D can be reduced. Figure 2 The amount shown is such that the tire 1 can prevent the energy loss of the fourth belt ply 7D from increasing, thereby improving rolling resistance performance. On the other hand, by setting the width W4 of the fourth belt to 25% or more of the tread width TW, cut resistance performance can be maintained. From this point of view, the width W4 of the fourth belt is preferably 60% or less of the tread width TW, and more preferably 40% or more.

[0058] The tread width TW is defined as the distance between the two outermost contact points on the tire axis when a normal load is applied to the tire 1 in normal condition and it contacts the plane at a camber angle of 0 degrees, i.e., the distance between the two outermost contact points on the tread ends 2t and 2t.

[0059] "Regular load" refers to the load specified for each tire within a specification system that includes the specifications on which the tire is based. Therefore, regular load, for example, is "maximum load capacity" if it is JATMA, the maximum value recorded in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" if it is TRA, and "LOAD CAPACITY" if it is ETRTO.

[0060] The above describes in detail the particularly preferred embodiments of the present invention, but the present invention is not limited to the embodiments shown in the figures and can be implemented in various ways.

[0061]

Example

[0062] [Example A]

[0063] Based on the specifications in Table 1, a prototype with... Figure 1 The basic structure of the heavy-duty tires shown is illustrated in Examples 1-9 and Comparative Examples. Furthermore, for each prototype tire, durability (drum test, presence or absence of belt cord peeling), rolling resistance performance was evaluated. Common specifications are as follows.

[0064] Tire size: 275 / 80R22.5

[0065] Wheel rim size: 8.25×22.5

[0066] Internal pressure: 900 kPa

[0067] Load: 28.8kN

[0068] Tread width TW: 240mm

[0069] Slip angle: 0 degrees

[0070] First layer of curtain fabric:

[0071] Angle θ1 of the cord with tension: 50°

[0072] Number of first curtain threads E1 (per 50mm curtain layer width): 19 threads

[0073] The first distance L1 between the corded curtain wires is 0.5mm.

[0074] Second and third belts of curtain fabric:

[0075] Angles θ2 and θ3 of the cord with tension: 15°

[0076] Number of second and third curtain threads (E2 and E3, per 50mm fabric layer width): 27 threads

[0077] Fourth layer of curtain fabric:

[0078] Angle θ1 of the cord with tension: 50°

[0079] Minimum distance L4 between the main channel and the main channel: 4.0mm

[0080] Belt width W4 / tread width TW: 40%

[0081] <Durability performance (drum test, presence of delamination in the belt cord)>

[0082] Each prototype tire rim was assembled onto the aforementioned rim and filled with the aforementioned internal pressure. Then, based on the aforementioned load, slip angle, and a driving speed of 80 km / h, each prototype tire was driven on a drum tester, with the driving speed increased by 10 km / h every 2 hours from the start of driving, and the driving time until tire failure was measured. The results were expressed using an index of 100 (Example 3). A higher value is better; if it is 95 or higher, the required durability performance (resistance to cord loosening) for heavy-duty tires is maintained.

[0083] Furthermore, the damaged prototype tire was disassembled to check for any separation (loosening of the cords) at the interface between the belt cords and the tread rubber.

[0084] <Durability Performance (Plunger Test)>

[0085] Each prototype tire rim was assembled onto the aforementioned rim and filled with the aforementioned internal pressure. Then, a plunger failure test based on JIS D4230 was performed, and the failure energy was measured. The results were expressed using an index of 100 (Example 3). A higher value is better; a value of 95 or higher indicates that the cut resistance required for heavy-duty tires is maintained.

[0086] <Rolling resistance performance>

[0087] Each prototype tire rim was assembled onto the aforementioned rim and filled with the aforementioned internal pressure. Then, rolling resistance was measured using a rolling resistance testing machine based on a driving speed of 60 km / h and the aforementioned load. Evaluation was expressed using an index of 100, with Example 3 as the benchmark. A lower value is better; if it is below 105, the rolling resistance performance required for heavy-duty tires is maintained.

[0088] The test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] The test results show that, compared with the heavy-duty tire of the comparative example, the heavy-duty tire of the embodiment maintained rolling resistance performance and improved durability performance.

[0092] [Example B]

[0093] Based on the specifications in Table 2, a prototype with... Figure 1 The basic construction of the heavy-duty tires shown is illustrated in Examples 3 and 10-18. Then, for each prototype tire, durability (drum test, presence or absence of belt cord peeling), rolling resistance performance was evaluated. Except for the specifications described below and those in Table 2, the common specifications are the same as in Example A.

[0094] Distance L1 (first distance) / Distance L2 (second distance): 100%

[0095] 4th cord number E4 / 3rd cord number E3: 74%

[0096] 4th cord diameter D4: 1.0mm

[0097] The test method is as described in Example A, and the test results are shown in Table 2.

[0098] Table 2

[0099]

[0100] The test results show that, compared to Example 13 which is outside the preferred range, Examples 3 and Examples 10-12, where the diameter of the fourth cord D4 / diameter of the third cord D3 is within the preferred range, maintain rolling resistance performance and durability performance (cut resistance) and improve durability performance (cord loosening resistance). Furthermore, compared to Examples 14 and 18 which are outside the preferred range, Examples 3 and Examples 15-17, where the angle θ4 of the fourth belt cord layer is within the preferred range, suppress the decrease in rolling resistance performance and durability performance (cut resistance) and improve durability performance (cord loosening resistance).

[0101] [Example C]

[0102] Based on the specifications in Table 3, a prototype with... Figure 1 The basic construction of the heavy-duty tires shown is illustrated in Examples 3 and 19-28. Then, for each prototype tire, durability (drum test, presence or absence of belt cord peeling), rolling resistance performance was evaluated. Except for the specifications described below and those in Table 3, the common specifications are the same as in Example A.

[0103] Distance L1 (first distance) / Distance L2 (second distance): 100%

[0104] 4th cord number E4 / 3rd cord number E3: 74%

[0105] The test method is as described in Example A, and the test results are shown in Table 2.

[0106] Table 3

[0107]

[0108] The test results show that, compared to Examples 19 and 23 which are outside the preferred range, Examples 3, 20, and 22, where the shortest distance L4 is within the preferred range, maintained rolling resistance performance and improved durability performance (resistance to cord loosening). Furthermore, compared to Examples 24 and 28 which are outside the preferred range, Examples 3, 25 to 27, where the fourth belt width W4 / tread width TW is within the preferred range, maintained rolling resistance performance and improved durability performance (resistance to cuts).

Claims

1. A heavy-duty tire comprising: a carcass extending from the tread portion through a sidewall portion to a bead portion; and a belt layer disposed outside the tire carcass in the tire radial direction and inside the tread portion, wherein... The belt layer comprises a first belt ply, a second belt ply, a third belt ply, and a fourth belt ply, which overlap sequentially from the carcass side toward the outer side of the tire radius. The first belt cord layer, the second belt cord layer, the third belt cord layer, and the fourth belt cord layer each have belt cords that are inclined relative to the tire equatorial plane. The distance in the tire radius direction between the belt cords of the third belt ply and the belt cords of the fourth belt ply is defined as the first distance L1, and the distance in the tire radius direction between the belt cords of the second belt ply and the belt cords of the third belt ply is defined as the second distance L2. The first distance L1 is set to be less than or equal to the second distance L2. The number of cords driven into the belted fabric layer per 50mm width is called the cord count. The cord count E4 of the fourth belted fabric layer is smaller than the cord count E3 of the third belted fabric layer. The number of cords E1 in the first belted fabric layer and the number of cords E2 in the second belted fabric layer are set to be the same as the number of cords E3 in the third belted fabric layer. The number of cords E1 in the first belted fabric layer, the number of cords E2 in the second belted fabric layer, and the number of cords E3 in the third belted fabric layer are 19 to 27. The number of cords E4 in the fourth belted fabric layer is 12 to 22. The first distance L1 is set to 0.4mm to 1.0mm. Of the first to the fourth belt ply, the fourth belt ply has the smallest axial width, and its axial width is 25% to 75% of the tread width. The angle between the belt cord of the fourth belt ply and the tire equatorial plane is 30° to 60°.

2. The heavy-duty tire according to claim 1, wherein, The number of cords E4 in the fourth belted fabric layer is 65% to 85% of the number of cords E3 in the third belted fabric layer.

3. The heavy-duty tire according to claim 1 or 2, wherein, The first distance L1 is 80% to 100% of the second distance L2.

4. The heavy-duty tire according to claim 1 or 2, wherein, The cord diameter D4 of the fourth belted curtain layer is 65% to 100% of the cord diameter D3 of the third belted curtain layer.

5. The heavy-duty tire according to claim 1 or 2, wherein, The tread portion has a main groove extending circumferentially along the tire. The shortest distance in the tire radius direction between the main groove and the belt cord of the fourth belt ply is 3mm to 7mm.

6. The heavy-duty tire according to claim 1 or 2, wherein, The angle between the belt cord of the first belted ply and the tire equatorial plane is 30° to 60°. The angle between the belt cords of the second and third belt cord layers and the tire equator is 15° to 25°.

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