Heavy load reuse pneumatic tire

Abstract

To improve performance of uneven wear resistance of a pneumatic tire for heavy load having an aspect ratio of 65% or less without sacrificing rolling resistance and wet performance.SOLUTION: A pneumatic tire for heavy load having an aspect ratio of 65% or less is provided, comprising: a carcass 6; and a belt layer 7. A tread portion 2 includes a plurality of circumferential grooves 10. The circumferential groove 10 includes: a shoulder circumferential groove 12; and a crown circumferential groove 11. The crown circumferential groove 11 is a narrow groove, and a pair of shoulder circumferential grooves 12 are each wide grooves. The belt layer 7 includes a plurality of metal belt cords which are slanted with respect to the tire circumference direction. Outer ends of the belt layer 7 are each positioned at the outside in a tire axial direction in comparison with the pair of shoulder circumferential groove 12. Belt half-width W2 is 55%-85% of carcass half-width W1.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, various pneumatic tires for heavy loads with a small aspect ratio have been proposed. For example, Patent Document 1 below proposes a pneumatic tire for heavy loads with an aspect ratio designation of 65 or less. By specifying the positional relationship of the shoulder circumferential groove, belt, and edge band, this pneumatic tire for heavy loads expects to improve the resistance to uneven wear while maintaining moldability.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, pneumatic tires for heavy loads tend to increase in outer diameter due to deterioration during use. In particular, pneumatic tires for heavy loads with an aspect ratio of 65% or less tend to have uneven wear in the tread portion because the difference in the amount of outer diameter growth is large between near the tread edge and near the tire equator in the tread portion. On the other hand, in the above-mentioned pneumatic tire for heavy loads, when attempting to improve the resistance to uneven wear, the rolling resistance and wet performance tend to be sacrificed.

[0005] The present invention has been devised in view of the above actual situation, and the main problem is to improve the resistance to uneven wear without sacrificing the rolling resistance and wet performance in a pneumatic tire for heavy loads with an aspect ratio of 65% or less.

Means for Solving the Problems

[0006] The present invention relates to a pneumatic heavy-duty tire with a flatness ratio of 65% or less, comprising a carcass extending from one bead portion through a tread portion to the other bead portion, and a belt layer disposed inside the tread portion. The tread portion includes a plurality of circumferential grooves continuously extending in the tire circumferential direction. The circumferential grooves include a pair of shoulder circumferential grooves and at least one crown circumferential groove provided between the pair of shoulder circumferential grooves. The crown circumferential groove is a narrow groove that closes when the maximum load is applied to the ground, and each of the pair of shoulder circumferential grooves is a wide groove that does not close when the maximum load is applied to the ground. The belt layer includes a plurality of metal belt cords inclined with respect to the tire circumferential direction. The pair of outer ends of the belt layer in the tire axial direction are each located outside the tire axial direction of the pair of shoulder circumferential grooves, and the belt half-width from the tire equator to the pair of outer ends of the belt layer is 55% to 85% of the carcass half-width, which is the distance in the tire axial direction from the tire equator to the carcass at the tire maximum width position.

[0007] In the pneumatic heavy-duty tire of the present invention, it is desirable that the distance in the tire axial direction from the tire equator to the groove center of the pair of shoulder circumferential grooves is 40% to 60% of the carcass half-width.

[0008] In the pneumatic heavy-duty tire of the present invention, it is desirable that two crown circumferential grooves are provided between the pair of shoulder circumferential grooves.

[0009] In the pneumatic heavy-duty tire of the present invention, the belt layer includes a plurality of belt plies stacked in the tire radial direction. One of the belt plies includes a plurality of the belt cords inclined in the same direction with respect to the tire circumferential direction, and it is desirable that at least one set of the belt plies adjacent in the tire radial direction is stacked such that the belt cords cross each other.

[0010] In the pneumatic heavy-load tire of the present invention, the plurality of belt plies include first to fourth belt plies stacked from the inner side to the outer side in the tire radial direction, and the angle of the belt cords included in the first belt ply with respect to the tire circumferential direction is preferably larger than the angles of the belt cords included in the second to fourth belt cords with respect to the tire circumferential direction.

[0011] In the pneumatic heavy-load tire of the present invention, the belt cords included in the second to fourth belt plies are preferably arranged at an angle of 10 to 25° with respect to the tire circumferential direction.

[0012] In the pneumatic heavy-load tire of the present invention, the belt cords included in the first belt ply are preferably arranged at an angle of 40 to 60° with respect to the tire circumferential direction.

[0013] In the pneumatic heavy-load tire of the present invention, for each of the second to fourth belt plies, the ply half-width from the tire equator to the ply outer end in the tire axial direction is preferably 110% to 170% of the distance in the tire axial direction from the tire equator to the groove center of the shoulder circumferential groove.

Advantages of the Invention

[0014] By adopting the above configuration, the pneumatic heavy-load tire of the present invention can improve the resistance to uneven wear without sacrificing the rolling resistance and wet performance.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a tire meridian cross-sectional view including a tire rotation axis in a normal state of a pneumatic tire for heavy loads (hereinafter sometimes simply referred to as "tire") 1 according to the present embodiment. The tire 1 of the present embodiment is used, for example, for small trucks, buses, etc.

[0017] The "normal state" means that in the case of a tire with various standards defined, the tire is rim-mounted on a normal rim and filled with a normal internal pressure, and moreover, it is in a no-load state. In the case of a tire for which various standards are not defined, the "normal state" means a standard use state according to the purpose of use of the tire and is a no-load state. In this specification, unless otherwise specified, the dimensions of each part of the tire are values measured in the normal state. In the case of a member inside the tire, the dimensions thereof refer to the dimensions in a state where the shape of the tire cross-section is substantially the same as the shape in the normal state.

[0018] The "normal rim" is a rim defined for each tire in a standard system including the standards on which the tire is based. For example, in the case of JATMA, it is the "standard rim", in the case of TRA, it is the "Design Rim", and in the case of ETRTO, it is the "Measuring Rim".

[0019] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standards on which the tire is based. In the case of JATMA, it is the "maximum air pressure", in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "INFLATION PRESSURE".

[0020] As shown in FIG. 1, the tire 1 of the present invention has an aspect ratio of 65% or less. The aspect ratio is the ratio of the tire cross-sectional height ht to the tire cross-sectional width Wt in the normal state. When minute convex portions indicating patterns, characters, etc. are arranged on the sidewall portion 3, the tire cross-sectional width Wt is measured excluding the convex portions. Further, the tire cross-sectional height ht is the maximum height of the tire cross-section measured from the bead base line BL. The bead base line BL is a tire axial direction line passing through the rim diameter position of the rim applied to the tire 1.

[0021] The tire 1 includes a tread portion 2, sidewall portions 3 continuous with both sides of the tread portion 2 in the tire axial direction, and bead portions 4 continuous with the inner side of the sidewall portions 3 in the tire radial direction.

[0022] FIG. 2 shows an enlarged cross-sectional view of the tread portion 2. As shown in FIG. 2, the tread portion 2 includes a plurality of circumferential grooves 10 continuously extending in the tire circumferential direction. The circumferential grooves 10 include a pair of shoulder circumferential grooves 12 and at least one crown circumferential groove 11 provided between the pair of shoulder circumferential grooves 12. In the present embodiment, two crown circumferential grooves 11 are provided so as to sandwich the tire equator C between the pair of shoulder circumferential grooves 12.

[0023] The crown circumferential groove 11 is configured as a narrow groove that closes when the maximum load is applied during grounding. On the other hand, each of the pair of shoulder circumferential grooves 12 is configured as a wide groove that does not close when the maximum load is applied during grounding. The maximum load is, in the case of a pneumatic tire with various standards defined, the maximum load defined for each tire in the standard system including the standards on which the tire is based. For JATMA, it means "maximum load capacity", for TRA, it means the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and for ETRTO, it means "LOAD CAPACITY". In the case of a tire for which various standards are not defined, the maximum load means the maximum of the loads under which the tire can continuously run.

[0024] As shown in FIG. 1, the tire 1 includes a carcass 6 extending from one bead portion 4 through one sidewall portion 3, a tread portion 2, and the other sidewall portion 3 to the other bead portion 4, and a belt layer 7 disposed inside the tread portion 2.

[0025] The carcass 6 includes, for example, a single carcass ply 6A. The carcass 6 may be composed of a plurality of carcass plies 6A, for example. The carcass ply 6A is configured such that, for example, steel carcass cords are arranged at an angle of 70 to 90° with respect to the tire circumferential direction.

[0026] The carcass ply 6A includes a main body portion 6a and a turned-back portion 6b. The main body portion 6a extends between a pair of bead portions 4. The turned-back portion 6b is continuous with the main body portion 6a and is turned back around the bead core 5 from the inner side to the outer side in the tire axial direction.

[0027] The belt layer 7 is disposed, for example, outside the carcass 6 in the tire radial direction in the tread portion 2. The belt layer 7 includes a plurality of metal belt cords inclined with respect to the tire circumferential direction. Also, a pair of outer ends of the belt layer in the tire axial direction are each located outside the tire axial direction of a pair of shoulder circumferential grooves 12.

[0028] FIG. 3 shows an enlarged view of a part of one sidewall portion 3 and half of the tread portion 2. As shown in FIG. 3, the belt half-width W2 from the tire equator C to a pair of outer ends of the belt layer 7 is 55% to 85% of the carcass half-width W1. The carcass half-width W1 is the distance in the tire axial direction from the tire equator C to the carcass 6 at the tire maximum width position. In the present invention, by adopting the above configuration, the uneven wear resistance can be improved without sacrificing the rolling resistance and wet performance. The reason is speculated to be the following mechanism.

[0029] In the present invention, since the crown circumferential groove 11 is the above-mentioned narrow groove, the rigidity of the central portion of the tread portion 2 is maintained, and thus an increase in rolling resistance can be suppressed. On the other hand, since the shoulder circumferential groove 12 is the above-mentioned wide groove, wet performance is ensured.

[0030] Generally, in a pneumatic tire for heavy loads with an aspect ratio of 65% or less, there is a large difference in the restraint force of the belt layer 7 between the vicinity of the tread edge of the tread portion 2 and the vicinity of the tire equator, and there is a tendency for a large difference in the amount of outer diameter growth due to deterioration during running. In the present invention, by specifying that the belt half-width W2 is 55% to 85% of the carcass half-width W1, the amount of outer diameter growth of each part of the tread portion 2 can be made uniform, and the resistance to uneven wear performance can be improved. In the present invention, it is considered that such a mechanism can improve the resistance to uneven wear performance without sacrificing rolling resistance and wet performance.

[0031] Hereinafter, a more detailed configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above-described effects even if it does not have the configurations described below. Further, even if any one of the configurations described below is applied alone to the tire of the present invention having the above-described features, an improvement in performance corresponding to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a combined improvement in performance corresponding to each configuration can be expected.

[0032] The belt half-width W2 is desirably 60% or more, more desirably 65% or more, desirably 80% or less, and more desirably 75% or less of the carcass half-width W1. Thereby, while suppressing an increase in rolling resistance, the resistance to uneven wear performance can be improved.

[0033] The belt layer 7 includes a plurality of belt plies stacked in the tire radial direction. The belt layer 7 of the present embodiment includes a first belt ply 7A, a second belt ply 7B, a third belt ply 7C, and a fourth belt ply 7D stacked from the inner side to the outer side in the tire radial direction. That is, the belt layer 7 of the present embodiment is composed of four belt plies. One of the belt plies includes a plurality of belt cords inclined in the same direction with respect to the tire circumferential direction. Further, at least one pair of the belt plies adjacent in the tire radial direction are stacked such that the belt cords cross each other. Such a belt layer 7 can effectively reinforce the tread portion 2.

[0034] It is desirable that the angle of the belt cords included in the first belt ply 7A with respect to the tire circumferential direction is larger than the angle of the belt cords included in the second to fourth belt plies 7B to 7D with respect to the tire circumferential direction. Such an arrangement of the belt cords helps to reduce the conicity and enhance the straight-ahead stability.

[0035] The angle of the belt cords included in the first belt ply 7A with respect to the tire circumferential direction is desirably 40° or more, more desirably 45° or more, desirably 60° or less, and more desirably 55° or less.

[0036] The angle of the belt cords included in the second to fourth belt plies 7B to 7D with respect to the tire circumferential direction is desirably 10° or more, more desirably 12° or more, desirably 25° or less, and more desirably 22° or less. Such second to fourth belt plies 7B to 7D can exhibit an excellent tread reinforcing effect while maintaining a small conicity.

[0037] In this embodiment, for each of the first to fourth belt plies 7A to 7D, the outer end is located axially outside the tire of the shoulder circumferential groove 12. Further, at least the ply half-width from the tire equator to the ply outer end in the tire axial direction of the second to fourth belt plies 7B to 7D is 110% to 170% of the tire axial distance L1 (shown in FIG. 2) from the tire equator to the groove center of the shoulder circumferential groove 12. In a desirable aspect, the ply half-width of the first belt ply 7A is also within the above range. The belt layer 7 including such a belt ply can surely suppress the growth of the outer diameter near the tread edge while suppressing an increase in rolling resistance.

[0038] The first belt half-width Wa, which is the belt half-width of the first belt ply 7A, is, for example, 65% to 80% of the carcass half-width W1. The second belt half-width Wb, which is the belt half-width of the second belt ply 7B, is, for example, 75% to 85% of the carcass half-width W1. The third belt half-width Wc, which is the belt half-width of the third belt ply 7C, is, for example, 65% to 80% of the carcass half-width W1. The fourth belt half-width Wd, which is the belt half-width of the fourth belt ply 7D, is, for example, 50% to 70% of the carcass half-width W1. However, the present invention is not limited to such an aspect.

[0039] As shown in FIG. 1, in this embodiment, since the belt layer 7 has the above-described configuration, a sufficient reinforcing effect can be exhibited, and the growth of the outer diameter of the tread portion 2 can be surely suppressed. Therefore, only the belt layer 7 is provided as a reinforcing member in the tread portion 2 of this embodiment, and no other reinforcing member (for example, a band layer in which cords are wound spirally) is provided. Thereby, an increase in the weight of the tread portion 2 is suppressed, and the rolling resistance can be kept small.

[0040] As shown in FIG. 2, the tire axial distance L1 from the tire equator C to the groove center of the pair of shoulder circumferential grooves 12 is desirably 40% or more, more desirably 45% or more, of the carcass half-width W1 (shown in FIG. 3, and the same applies hereinafter), and desirably 60% or less, more desirably 55% or less. Thereby, the shoulder circumferential groove 12 can exhibit excellent drainage performance.

[0041] The maximum groove width of the shoulder circumferential groove 12 is, for example, 6.0 to 16.0 mm, and desirably 8.0 to 14.0 mm. Such a shoulder circumferential groove 12 can exhibit excellent drainage performance as a wide groove while suppressing an increase in rolling resistance.

[0042] The tire axial distance L2 from the tire equator C to the groove center of the pair of crown circumferential grooves 11 is desirably 10% to 20% of the carcass half-width W1. Thereby, it is possible to suppress uneven wear at the center of the tread portion 2 while enhancing wet performance.

[0043] The maximum groove width of the crown circumferential groove 11 is, for example, 1.0 to 3.0 mm, and desirably 1.5 to 2.5 mm. Such a crown circumferential groove 11 can exhibit excellent drainage performance as a narrow groove while suppressing an increase in rolling resistance.

[0044] FIG. 4 shows a plan view of the tread portion 2. As shown in FIG. 4, the shoulder circumferential groove 12 and the crown circumferential groove 11 desirably extend in a zigzag shape, respectively. Such shoulder circumferential grooves 12 and crown circumferential grooves 11 are useful for enhancing traction performance during wet running.

[0045] In a more desirable aspect, it is desirable that the minimum tire axial distance L3 between the shoulder circumferential groove 12 and the crown circumferential groove 11 extending in a zigzag shape is larger than the maximum distance L4 (shown in FIG. 2) between the outer ends of the belt plies included in the belt layer 7. Thereby, a sufficient distance between the crown circumferential groove 11 and the shoulder circumferential groove 12 is ensured, and the uneven wear resistance performance is further improved.

[0046] Further, it is desirable that the amount of amplitude in the tire axial direction of the groove center line of the crown circumferential groove 11 in the tread plan view is smaller than the distance d1 (shown in FIG. 2) from the bottom of the crown circumferential groove 11 to the belt layer 7. Similarly, it is desirable that the amount of amplitude in the tire axial direction of the groove center line of the shoulder circumferential groove 12 in the tread plan view is larger than the distance d2 (shown in FIG. 2) from the bottom of the shoulder circumferential groove 12 to the belt layer 7. Thereby, while suppressing uneven wear around the crown circumferential groove 11, the shoulder circumferential groove 12 can exhibit excellent drainage performance.

[0047] In the tread portion 2 of the present embodiment, only two shoulder circumferential grooves 12 and two crown circumferential grooves 11 are provided, and no other circumferential grooves are provided. Thereby, the above-described effects are surely exhibited.

[0048] As described above in detail, the heavy-duty pneumatic tire according to an embodiment of the present invention has been described. However, the present invention is not limited to the above specific embodiments and can be implemented in various modes.

Example

[0049] A size 295 / 60R22.5 heavy-duty pneumatic tire having the basic structure of FIG. 1 was prototyped based on the specifications in Tables 1 to 2. As Comparative Example 1, a tire in which the crown circumferential groove 11 was configured as a wide groove with a groove width of 10 mm was prototyped. As Comparative Examples 2 to 3, tires in which the belt half-width deviated from the range defined in the present invention were prototyped. Each test tire has substantially the same configuration except for the specifications shown in Tables 1 to 2. The rolling resistance, wet performance, and uneven wear resistance performance of each test tire were tested. The common specifications and test methods of each test tire are as follows. Mounting rim: 9.00×22.5 Tire internal pressure: 1000 kPa

[0050] <Rolling resistance> A constant vertical load was applied on a drum tester and the test tire was run at a constant speed, and its rolling resistance was measured. The results are shown by an index with the rolling resistance of Comparative Example 1 being 100. The smaller the numerical value, the smaller the rolling resistance.

[0051] <Wet performance> The braking distance was measured when a test vehicle equipped with the test tire entered a wet road surface at 60 km / h and suddenly braked. The results are shown by an index with the braking distance of Comparative Example 1 being 100. The smaller the numerical value, the better the wet performance.

[0052] <Resistance to uneven wear performance> After a test vehicle equipped with the test tire traveled a certain distance in an urban area, the wear amount of the tread part was measured. The results are shown by an index with Comparative Example 1 being 100 for the difference between the wear amount of the most worn part of the tread part and the wear amount of the least worn part of the tread part. The smaller the numerical value, the better the resistance to uneven wear performance. The test results are shown in Tables 1 to 2.

[0053]

Table 1

[0054]

Table 2

[0055] As a result of the test, it was confirmed that the tires of the examples improved the resistance to uneven wear performance without sacrificing the rolling resistance and wet performance.

Explanation of symbols

[0056] 2 Tread part 4 Bead part 6 Carcass 7 Belt layer 10 Circumferential groove 11 Crown circumferential groove 12 Shoulder circumferential groove W1 Carcass half-width W2 Belt half-width

Claims

1. A pneumatic tire for heavy loads with a flat rate of 65% or less, comprising a carcass extending from one bead portion through a tread portion to the other bead portion, and a belt layer disposed inside the tread portion, wherein the tread portion includes a plurality of circumferential grooves continuously extending in the tire circumferential direction, the circumferential grooves include a pair of shoulder circumferential grooves and at least one crown circumferential groove provided between the pair of shoulder circumferential grooves, the crown circumferential groove is a narrow groove that closes when the maximum load is applied to the ground, each of the pair of shoulder circumferential grooves is a wide groove that does not close when the maximum load is applied to the ground, the belt layer includes a plurality of metal belt cords inclined with respect to the tire circumferential direction, the pair of outer ends of the belt layer in the tire axial direction are each located outside the tire axial direction of the pair of shoulder circumferential grooves, the belt half-width from the tire equator to the pair of outer ends of the belt layer is 70% to 79% of the carcass half-width which is the distance in the tire axial direction from the tire equator to the carcass at the tire maximum width position, the crown circumferential groove extends in a zigzag shape, and in a tread plan view, the amplitude amount in the tire axial direction of the groove center line of the crown circumferential groove is smaller than the distance d1 from the bottom of the crown circumferential groove to the belt layer, the shoulder circumferential groove extends in a zigzag shape, and in a tread plan view, the amplitude amount in the tire axial direction of the groove center line of the shoulder circumferential groove is larger than the distance d2 from the bottom of the shoulder circumferential groove to the belt layer, A pneumatic tire for heavy loads.

2. The pneumatic tire for heavy loads according to claim 1, wherein the distance in the tire axial direction from the tire equator to the groove center of the pair of shoulder circumferential grooves is 40% to 60% of the carcass half-width.

3. The pneumatic tire for heavy loads according to claim 1 or 2, wherein two crown circumferential grooves are provided between the pair of shoulder circumferential grooves.

4. the belt layer includes a plurality of belt plies stacked in the tire radial direction, one of the belt plies includes a plurality of the belt cords inclined in the same direction with respect to the tire circumferential direction, The heavy-load pneumatic tire according to any one of claims 1 to 3, wherein at least one pair of the belt plies adjacent to each other in the tire radial direction are overlapped such that the belt cords cross each other.

5. The plurality of belt plies include first to fourth belt plies overlapped from the inner side to the outer side in the tire radial direction. The heavy-load pneumatic tire according to claim 4, wherein the angle of the belt cord included in the first belt ply with respect to the tire circumferential direction is larger than the angles of the belt cords included in the second to fourth belt plies with respect to the tire circumferential direction.

6. The heavy-load pneumatic tire according to claim 5, wherein the belt cords included in the second to fourth belt plies are arranged at an angle of 10 to 25° with respect to the tire circumferential direction.

7. The heavy-load pneumatic tire according to claim 5 or 6, wherein the belt cord included in the first belt ply is arranged at an angle of 40 to 60° with respect to the tire circumferential direction.

8. For each of the second to fourth belt plies, The heavy-load pneumatic tire according to any one of claims 5 to 7, wherein the ply half-width from the tire equator to the ply outer end in the tire axial direction is 110% to 170% of the distance in the tire axial direction from the tire equator to the groove center of the shoulder circumferential groove.

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