Heavy-duty tires

Abstract

To provide a heavy duty tire excellent in uneven wear resistance and block chipping resistance while maintaining low rolling resistance.SOLUTION: A heavy duty tire includes the first, second, third and fourth belts 16a, 16b, 16c and 16d. In a tire width direction cross section, the end of the fourth belt 16d is located near a tire equator CL side compared to the other belt ends. A tread has two first major grooves 20 formed so as to pinch the tire equator and extending in a tire circumferential direction, and two second major grooves 21 formed between the first major groove 20 and a ground contact end and extending in the tire circumferential direction. The tire satisfies the relations of 1.0<L1 / L2<1.4 and 1.5<L2 / L3<2.0, when defining the length from the tire equator to the end of the fourth belt 16d along the tire width direction as L1, the length from the tire equator to the width direction center along the tire width direction as L2, and the length from that equator to the width direction center of the first major groove along the tire width direction as L3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a heavy-duty tire, and more particularly to a heavy-duty tire having a tread in which at least four belts and at least four main grooves extending in the circumferential direction of the tire are formed. [Background technology]

[0002] Heavy-duty tires are used on heavy-duty vehicles such as buses and trucks, and therefore tend to have high rolling resistance. In recent years, due to the impact of rising fuel costs and the need to reduce environmental impact, there has been a demand for improved fuel efficiency for heavy-duty vehicles, and development of heavy-duty tires with low rolling resistance has been progressing. For example, Patent Document 1 discloses a technology for reducing rolling resistance by setting the composition of the tread rubber of a heavy-duty tire within a predetermined range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-109935 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the outer diameter shape of the tire and the configuration of the belt also have a great influence on the rolling resistance of the tire, and it is possible to reduce the rolling resistance by optimizing these. In addition to the rolling resistance, heavy-duty tires are required to have performance such as resistance to uneven wear and resistance to block chipping. The cornering power (CP) characteristic has a great influence on the uneven wear resistance of heavy-duty tires, and the grounding property has a great influence on the block chipping of heavy-duty tires. What this means is that when a heavy-duty tire mounted on the first axle of a truck or bus turns the steering wheel during turning, torsion occurs on the tire contact surface, that is, shear deformation occurs in the blocks, and slipping may occur on the outer shoulder block, resulting in uneven wear. In addition, when the blocks on the contact surface are twisted, the grounding property of the blocks on the outer side of the turn may be impaired, and block chipping may be observed.

[0005] An object of the present invention is to provide a heavy-duty tire that maintains a low rolling resistance, has excellent uneven wear resistance without impairing the grounding property.

Means for Solving the Problems

[0006] The heavy-duty tire according to the present invention includes a tread, a carcass, and a belt. The belt includes a first belt, a second belt, a third belt, and a fourth belt in order from the carcass side. In the cross-section in the tire width direction, the end of the fourth belt is located closer to the tire equator side than the ends of the other belts. The tread is formed so as to sandwich the tire equator, and has two first main grooves extending in the tire circumferential direction, and two second main grooves formed between each first main groove and each grounding end and extending in the tire circumferential direction. In the cross-section in the tire width direction, when the length along the tire width direction from the tire equator to the end of the fourth belt is L1, the length along the tire width direction from the tire equator to the width direction center of the second main groove is L2, and the length along the tire width direction from the tire equator to the width direction center of the first main groove is L3, it is characterized by satisfying the relationships of 1.0 < L1 / L2 < 1.4 and 1.5 < L2 / L3 < 2.0.

Effect of the Invention

[0007] The heavy duty tire according to the present invention has low rolling resistance and excellent resistance to uneven wear without impairing ground contact. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a heavy-duty tire that is an example of an embodiment. [Figure 2] FIG. 2 is an enlarged view of the tread and its surroundings in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an example of an embodiment of a heavy-duty tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes selective combinations of the components of the multiple embodiments and modified examples described below.

[0010] Fig. 1 is a cross-sectional view of a heavy-duty tire 1 as an example of an embodiment. As shown in Fig. 1, the heavy-duty tire 1 includes a tread 10 that is the portion that comes into contact with the road surface, a pair of sidewalls 11 that extend radially inward from the tread 10, and a pair of beads 12 that come into contact with the rim of a wheel. The tread 10, the sidewalls 11, and the beads 12 are formed in an annular shape along the circumferential direction of the tire. The sidewalls 11 and the beads 12 form the left and right side surfaces of the heavy-duty tire 1.

[0011] The heavy-duty tire 1 is a pneumatic tire that is inflated with air at a predetermined pressure. The heavy-duty tire 1 generally includes a carcass 15, a belt 16, and an inner liner 17. The carcass 15 is a cord layer coated with rubber, and forms the framework of the heavy-duty tire 1 that can withstand loads, impacts, air pressure, etc. The carcass 15 is folded back at the beads 12 from the inner side in the tire width direction to the outer side in the tire width direction. The belt 16 is a reinforcing band disposed between the tread rubber that constitutes the tread 10 and the carcass 15, and tightly fastens the carcass 15 to increase the rigidity of the heavy-duty tire 1. The belt 16 is formed, for example, from a steel cord coated with rubber. The inner liner 17 is a rubber layer provided on the inner circumferential surface of the carcass 15, and maintains the air pressure of the heavy-duty tire 1.

[0012] The tread 10 has ground contact edges E. In this embodiment, the ground contact edges E are located at both ends of the tread 10 in the tire width direction. In this specification, the ground contact edges E refer to both ends in the tire width direction of an area that comes into contact with a flat road surface when an unused heavy-duty tire 1 is mounted on a standard rim and inflated to a standard internal pressure, and a load of 85% of the standard load (maximum load capacity) at the standard internal pressure is applied.

[0013] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0014] The tread 10 has two first main grooves 20 formed on either side of the tire equator CL and extending in the tire circumferential direction, and two second main grooves 21 formed between the first main grooves 20 and each ground contact edge E and extending in the tire circumferential direction. The tire equator CL refers to a line along the tire circumferential direction that passes through the tire width center. The main grooves 20, 21 function as drainage channels that remove rainwater and the like that exists between the tread 10 and the road surface. The two first main grooves 20 have, for example, approximately the same depth and width. The two second main grooves 21 also have, for example, approximately the same depth and width. Here, the width of a main groove refers to the length along the tire width direction between opposing groove walls.

[0015] In this embodiment, the width of the first main groove 20 gradually narrows from the top surface of the tread 10 toward the groove bottom. Here, the top surface of the tread 10 refers to the outermost surface of the tread 10 facing radially outward in the tire. The width of the second main groove 21 is approximately the same from the top surface of the tread 10 to the groove bottom. The first main groove 20 and the second main groove 21 have approximately the same depth. Note that the cross-sectional shapes of the first main groove 20 and the second main groove 21 are not limited to this example.

[0016] The tread 10 has a plurality of land portions defined by first main grooves 20 and second main grooves 21. The land portions are protrusions that protrude radially outward from the tire. In this embodiment, the tread 10 has center blocks 30, intermediate blocks 40, and shoulder blocks 50 as land portions. Each land portion has a lateral groove formed across it in the tire width direction, and each land portion is defined by the lateral grooves and formed into a block shape.

[0017] The center block 30 is formed in the widthwise center of the tread 10. Shoulder blocks 50 are formed on both sides of the tread 10 in the widthwise direction, and intermediate blocks 40 are formed between the center block 30 and each shoulder block 50. The center block 30 and the intermediate block 40 are separated by the first main groove 20, and the intermediate block 40 and the shoulder block 50 are separated by the second main groove 21. In other words, the lengths of the center block 30, the intermediate block 40, and the shoulder block 50 in the tire width direction are determined by the positions of the first main groove 20 and the second main groove 21.

[0018] The center blocks 30, intermediate blocks 40, and shoulder blocks 50 may have at least one of grooves and sipes extending in a direction intersecting the main grooves 20, 21. Here, sipes are thin linear grooves. Note that instead of the center blocks 30, intermediate blocks 40, and shoulder blocks 50, center ribs, intermediate ribs, and shoulder ribs with continuous land portions in the tire circumferential direction may be provided.

[0019] Next, the configuration of the belt 16 and the positional relationship between the belt 16 and the main grooves 20, 21 formed in the tread 10 will be described in detail with reference to Fig. 2. Fig. 2 is an enlarged view of the tread 10 and its vicinity.

[0020] The belt 16 includes, in order from the carcass 15 side, a first belt 16a, a second belt 16b, a third belt 16c, and a fourth belt 16d. In this embodiment, the second belt 16b is wider than the other belts 16a, 16c, and 16d. Both ends of the second belt 16b in the width direction are located inward of the ground contact edge E in the tire width direction.

[0021] As shown in Fig. 2, in the cross-section in the tire width direction, the ends of the fourth belt 16d are located closer to the tire equator CL side than the ends of the other belts 16a, 16b, and 16c. In the heavy load tire 1, it is generally known that the CP characteristics are improved by increasing the width of the shoulder block 50. However, there is a concern that the rolling resistance increases when the width of the shoulder block 50 is increased. The inventor of the present invention has found that, as described later, by setting the positions of both ends of the fourth belt 16d and the positions of the main grooves 20 and 21 within a specific range, it is possible to achieve both wear resistance against uneven wear due to improved CP characteristics and low rolling resistance.

[0022] In the cross-section in the tire width direction, when the length along the tire width direction from the tire equator CL to the end of the fourth belt 16d is L1, and the length along the tire width direction from the tire equator CL to the center in the width direction of the second main groove 21 is L2, the relationship of 1.0 < L1 / L2 < 1.4 is satisfied. By setting L1 / L2 > 1.0, the end of the fourth belt 16d overlaps with the shoulder block 50 in the tire radial direction, so the rigidity of the shoulder block 50 is improved, and while the wear resistance against uneven wear is improved due to the improved CP characteristics, the rolling resistance can be reduced. Also, when L1 / L2 ≥ 1.4, the width of the fourth belt 16d becomes too wide, and the rolling resistance increases.

[0023] In the cross-section in the tire width direction, when the length along the tire width direction from the tire equator CL to the center in the width direction of the first main groove 20 is L3, the relationship of 1.5 < L2 / L3 < 2.0 is satisfied. By setting L2 / L3 < 2.0, the rigidity of the center block 30 is improved, and while the CP characteristics are improved, the rolling resistance can be reduced. Also, when L2 / L3 ≤ 1.5, the width of the intermediate block 40 becomes too narrow, deteriorating the ground contact performance and the resistance to block chipping.

[0024] In the cross-section in the tire width direction, when the depth of the second main groove 21 is D1 and the distance from the bottom of the second main groove 21 to the fourth belt 16d is D2, it is preferable to satisfy the relationship of 0.65 < D1 / (D1 + D2) < 0.77. By setting D1 / (D1 + D2) within the above range, while maintaining drainage performance, the rigidity of the tread 10 can be maintained. As a result, it becomes easier to design the tread 10 such that both the uneven wear resistance due to CP characteristics and the low rolling resistance can be achieved. Here, D1 is the length along the tire radial direction from the upper surface of the tread 10 to the bottom of the second main groove 21. D2 is the length along the tire radial direction from the bottom of the second main groove 21 to the outermost peripheral surface of the fourth belt 16d facing outward in the tire radial direction.

[0025] When the thickness of the tread 10 at the tire equator CL is D3, it is preferable to satisfy the relationship of (D1 + D2) / D3 < 0.95. Thereby, the rigidity of the tread 10 can be maintained, so that it becomes easier to design the tread 10 such that both the uneven wear resistance due to CP characteristics and the low rolling resistance can be achieved. Here, D3 is the length along the tire radial direction from the upper surface of the tread 10 to the outermost peripheral surface of the fourth belt 16d facing outward in the tire radial direction. The lower limit value of (D1 + D2) / D3 is, for example, 0.8, and thereby, good belt durability can be obtained.

[0026] In the cross-section in the tire width direction, when the length along the tire width direction from the tire equator CL to the ground contact end E is L4, it is preferable to satisfy the relationship of 0.6 < L1 / L4 < 0.8. Thereby, it becomes easier to design the tread 10 such that both the uneven wear resistance due to CP characteristics and the low rolling resistance can be achieved.

[0027] Next, Table 1 shows the results of performing performance evaluation of the tire using computer simulation. In Table 1, Examples 1 to 3 are the results for tires in which the values of L1 to L4 and D1 to D3 are within the above ranges, and Comparative Examples 1 to 4 are the results for tires in which any of the values of L1 to L4 and D1 to D3 are outside the above ranges. In Comparative Example 1, since L1 is short and the end of the fourth belt 16d is located inside the second main groove 21 in the tire width direction, D2 does not exist.

[0028] The computer simulation is based on the finite element method (FEM). In FEM, the structure to be analyzed is divided into finite elements, and the analysis is performed by calculating the equation of motion for each element. A three-dimensional tire model with a two-dimensional cross section, as shown in Figure 1, is created and the computer simulation is performed by dividing it into multiple mesh elements.

[0029] The rolling resistance was measured using the energy loss rate calculated through ground contact analysis. The evaluation results (RR) shown in Table 1 are relative values, with the evaluation result of the tire of Comparative Example 1 taken as 100, and the smaller the value, the better the rolling resistance.

[0030] The CP property, which affects uneven wear resistance, was calculated by performing a rolling analysis. The evaluation results (CP) shown in Table 1 are relative values, with the evaluation result of the tire of Comparative Example 1 being set at 100, and a larger value indicates a higher CP and better uneven wear resistance.

[0031] Block chipping resistance was evaluated using the results of the rolling analysis described above. This rolling analysis was performed when a slip angle of 1° was applied. Applying a slip angle causes shear deformation in the blocks on the contact surface, impairing ground contact and causing block chipping, so the variance value of the tire contact pressure distribution was used as an index. The evaluation results (PD) shown in Table 1 are relative values, with the evaluation result of the tire of Comparative Example 1 being 100, and the smaller the value, the better the contact pressure distribution and the less likely block chipping will occur.

[0032] The conditions other than the size shown in Table 1 are as follows. Tire size: 245 / 70R19.5 Wheel size: 19.5 x 6.75 (rim diameter x rim width) Second belt width: 210 mm Third belt width: 186 mm Internal pressure: 850kPa Load: 2240kgf (100% of JATMA standard)

[0033] [Table 1]

[0034] As shown in Table 1, the tires of Examples 1 to 3 maintain low rolling resistance while exhibiting excellent uneven wear resistance and block chipping resistance. On the other hand, the tires of Comparative Examples 1 to 4 are inferior to the tires of the Examples in any of rolling resistance, uneven wear resistance, and block chipping resistance. Based on the results of the FEM analysis, heavy-duty tires were actually manufactured, and it was confirmed that these tires had low rolling resistance and excellent uneven wear resistance and block chipping resistance. While rolling resistance, uneven wear resistance, and block chipping resistance are also affected by the tread pattern, any tread pattern can achieve low rolling resistance while improving uneven wear resistance and block chipping resistance as long as the relationships L1 to L4 and D1 to D3 above are satisfied.

[0035] As described above, the heavy-duty tire according to the present invention has low rolling resistance and excellent resistance to uneven wear and block chipping. More specifically, by satisfying a predetermined relationship between the width of the fourth belt 16d included in the belt 16 and the length along the tire width direction from the tire equator CL to the center of the main grooves 20, 21 in the width direction, it is possible to obtain a heavy-duty tire 1 that has excellent resistance to uneven wear and block chipping while maintaining low rolling resistance. Furthermore, by setting the length along the tire width direction from the tire equator to the tread edge and the depth of the second main groove 21 within a predetermined range, it becomes easier to design the tread 10 while maintaining the above characteristics. [Explanation of symbols]

[0036] 1 heavy duty tire, 10 tread, 11 sidewall, 12 bead, 15 carcass, 16 belt, 16a first belt, 16b second belt, 16c third belt, 16d fourth belt, 17 inner liner, 18 bead core, 19 bead filler, 20 first main groove, 21 second main groove, 30 center block, 40 mediate block, 50 shoulder block, CL tire equator, E ground contact edge

Claims

1. A heavy-duty tire having a tread, a carcass, and a belt, the belt includes, in order from the carcass side, a first belt, a second belt, a third belt, and a fourth belt, and an end of the fourth belt is located closer to the tire equator than ends of the other belts in a cross section in the tire width direction, the tread has two first main grooves formed on either side of the tire equator and extending in the tire circumferential direction, and two second main grooves formed between each of the first main grooves and each of the ground contact edges and extending in the tire circumferential direction, A heavy-duty tire in which, in a cross section in the tire width direction, the length from the tire equator to the end of the fourth belt along the tire width direction is defined as L1, the length from the tire equator to the center in the tire width direction of the second main groove is defined as L2, and the length from the tire equator to the center in the tire width direction of the first main groove is defined as L3, satisfying the relationships 1.0 < L1 / L2 < 1.4 and 1.5 < L2 / L3 < 2.

0.

2. 2. The heavy-duty tire according to claim 1, wherein, in a cross section in the tire width direction, when a depth of the second main groove is D1 and a distance from a bottom of the second main groove to the fourth belt is D2, a relationship of 0.65<D1 / (D1+D2)<0.77 is satisfied.

3. 3. The heavy-duty tire according to claim 2, wherein, when the thickness of the tread at the tire equator is D3, the relationship (D1+D2) / D3<0.95 is satisfied.

4. 4. The heavy-duty tire according to claim 1, wherein, in a cross section in the tire width direction, when a length from the tire equator to the ground contact edge along the tire width direction is defined as L4, the heavy-duty tire satisfies the relationship of 0.6<L1 / L4<0.8.

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