Pneumatic tire for heavy load

Abstract

The present invention provides a heavy load pneumatic tire, in which the uneven wear resistance is improved without sacrificing the rolling resistance and wet performance in a heavy load pneumatic tire having a flatness of 65% or less. The heavy load pneumatic tire having a flatness of 65% or less includes a carcass (6) and a belt layer (7). A tread portion (2) includes a plurality of circumferential grooves (10). The circumferential grooves (10) include a shoulder circumferential groove (12) and a crown circumferential groove (11). The crown circumferential groove (11) is a fine groove, and the pair of shoulder circumferential grooves (12) are wide grooves, respectively. The belt layer (7) includes a plurality of metal belt cords inclined with respect to the tire circumferential direction. The outer ends of the belt layer (7) are located at positions axially outward of the pair of shoulder circumferential grooves (12), respectively. A belt half-width (W2) is 55% to 85% of a carcass half-width (W1).

Description

Technical Field

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

[0002] Previously, various pneumatic tires for heavy loads with low aspect ratios have been proposed. For example, Patent Document 1 below proposes a pneumatic tire for heavy loads with an aspect ratio of 65 or less. This pneumatic tire for heavy loads aims to improve resistance to eccentric wear while maintaining formability by determining the positional relationship of the shoulder circumferential grooves, belts, and edge crowns.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2020-152136

[0004] Generally, heavy-duty pneumatic tires tend to experience outer diameter growth due to deterioration caused by use. In particular, heavy-duty pneumatic tires with an aspect ratio of 65% or less exhibit a large difference in outer diameter growth near the tread end and near the tire equator, thus tending to experience uneven wear on the tread. On the other hand, in the aforementioned heavy-duty pneumatic tires, improving resistance to uneven wear tends to sacrifice rolling resistance and wet road performance. Summary of the Invention

[0005] The present invention was made in view of the above-mentioned actual situation, and its main objective is to improve the resistance to eccentric wear in heavy-duty pneumatic tires with an aspect ratio of 65% or less without sacrificing rolling resistance and wet road performance.

[0006] This invention relates to a heavy-duty pneumatic tire with an aspect ratio of 65% or less, comprising: a carcass extending from one bead portion via a tread portion to another bead portion; and a belt layer disposed within the tread portion, the tread portion comprising a plurality of circumferential grooves extending continuously along the tire circumference, the circumferential grooves including a pair of shoulder circumferential grooves and at least one crown circumferential groove disposed between the pair of shoulder circumferential grooves, the crown circumferential groove being a narrow groove that closes when subjected to maximum load, the pair of shoulder circumferential grooves being wide grooves that do not close when subjected to maximum load, the belt layer comprising a plurality of metallic belt cords inclined relative to the tire circumferential direction, one pair of outer ends of the belt layer along the tire axial direction being located further outward than the pair of shoulder circumferential grooves along the tire axial direction, the belt half-width from the tire equator to the one pair of outer ends of the belt layer being 55% to 85% of the carcass half-width, the carcass half-width being the distance along the tire axial direction from the tire equator to the position of the tire's maximum width.

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

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

[0009] In the heavy-duty pneumatic tire of the present invention, preferably the belt layer comprises a plurality of belt ply layers overlapping in the tire radial direction, one of the belt ply layers comprising a plurality of belt cords inclined in the same direction relative to the tire circumference, and at least one group of adjacent belt ply layers in the tire radial direction overlaps in such a manner that the belt cords intersect each other.

[0010] In the heavy-duty pneumatic tire of the present invention, preferably the plurality of belt ply layers include a first belt ply layer, a second belt ply layer, a third belt ply layer, and a fourth belt ply layer that overlap from the inside to the outside in the radial direction of the tire. The angle of the belt cords included in the first belt ply layer relative to the tire circumference is larger than the angle of the belt cords included in the second, third, and fourth belt ply layers relative to the tire circumference.

[0011] In the heavy-duty pneumatic tire of the present invention, it is preferable that the belt cords included in the second belt ply, the third belt ply, and the fourth belt ply are arranged at an angle of 10° to 25° relative to the tire circumference.

[0012] In the heavy-duty pneumatic tire of the present invention, it is preferable that the belt cords included in the first belt ply are arranged at an angle of 40° to 60° relative to the tire circumference.

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

[0014] The heavy-duty pneumatic tire of the present invention, by adopting the above-described structure, can improve its resistance to eccentric wear without sacrificing rolling resistance or wet road performance. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of a heavy-duty pneumatic tire according to one embodiment of the present invention.

[0016] Figure 2 yes Figure 1 A magnified view of the tire's tummy.

[0017] Figure 3 yes Figure 1An enlarged view of a portion of the sidewall and half of the tummy rim of one side of the fetus.

[0018] Figure 4 yes Figure 1 A plan view of the tire's tread area.

[0019] Label Explanation

[0020] 2: Tire tread; 4: Bead section; 6: Tire body; 7: Belt layer; 10: Circumferential groove; 11: Crown circumferential groove; 12: Shoulder circumferential groove; W1: Tire body half-width; W2: Belt half-width. Detailed Implementation

[0021] Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 The diagram shows a radial cross-sectional view of the tire, including the tire's axis of rotation, in its normal configuration for a heavy-duty pneumatic tire (hereinafter, sometimes simply referred to as "tire") 1 according to this embodiment. The tire 1 of this embodiment can be used, for example, in small trucks, buses, etc.

[0022] The aforementioned "standard condition" refers to the state where, with all tire specifications defined, the tire is assembled onto a standard rim, inflated to the standard internal pressure, and unloaded. For tires whose specifications are not defined, the aforementioned "standard condition" refers to the standard operating condition corresponding to the tire's intended use, i.e., an unloaded state. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured under the aforementioned standard condition. For internal tire components, their dimensions refer to dimensions that ensure the shape of the tire's cross-section is substantially the same as the shape under the aforementioned standard condition.

[0023] "Standard rim" refers to a rim with a specific specification for each tire within a specification system that includes the specifications the tire is based on. For example, if it is JATMA, it is a "standard rim"; if it is TRA, it is a "Design Rim"; and if it is ETRTO, it is a "Measuring Rim".

[0024] "Standard internal pressure" refers to the air pressure determined for each tire in the specification system, including the specifications on which the tire is based. If it is JATMA, it is "maximum air pressure". If it is TRA, it is the maximum value recorded in the table "TIRE LOAD LIMITSAT VARIOUS COLD INFLATION PRESSURES". If it is ETRTO, it is "INFLATION PRESSURE".

[0025] like Figure 1As shown, the aspect ratio of the tire 1 of the present invention is 65% or less. The aspect ratio refers to the ratio of the tire section height ht to the tire section width Wt in the above-described normal state. Furthermore, when the sidewall portion 3 is provided with small protrusions representing tread patterns, lettering, etc., the tire section width Wt is measured excluding these protrusions. The tire section height ht is the maximum height of the tire section measured from the bead baseline BL. The bead baseline BL is the tire axial line passing through the rim diameter of the rim applicable to the tire 1.

[0026] The tire 1 includes a tread portion 2, a sidewall portion 3 connected to both sides of the tread portion 2 in the tire axial direction, and a bead portion 4 connected to the inner side of the sidewall portion 3 in the tire radial direction.

[0027] exist Figure 2 An enlarged cross-sectional view of the tread portion 2 is shown in the image. Figure 2 As shown, the tread portion 2 includes a plurality of circumferential grooves 10 extending continuously along the tire circumference. Each circumferential groove 10 includes a pair of shoulder circumferential grooves 12 and at least one crown circumferential groove 11 disposed between the pair of shoulder circumferential grooves 12. In this embodiment, two crown circumferential grooves 11 are disposed between the pair of shoulder circumferential grooves 12, separated by the tire equator C.

[0028] The circumferential groove 11 of the tire crown is configured as a narrow groove that closes when the tire touches the ground under maximum load. On the other hand, the pair of circumferential grooves 12 of the tire shoulders are each configured as a wide groove that does not close when the tire touches the ground under maximum load. The aforementioned maximum load refers to the maximum load determined for each tire specification within the specification system, including the specification on which the tire is based, in the case of pneumatic tires with various specifications already defined. For JATMA tires, this is "maximum load capacity"; for TRA tires, it is the maximum value recorded in the table "TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; and for ETRTO tires, it is "LOAD CAPACITY". In the case of tires with undefined specifications, the aforementioned maximum load refers to the maximum load within which the tire can continue to travel.

[0029] like Figure 1 As shown, the tire 1 includes: a tire body 6 that extends 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.

[0030] The tire carcass 6 may, for example, comprise one tire carcass ply 6A. The tire carcass 6 may also be composed of multiple tire carcass ply 6A. The tire carcass ply 6A may be constructed, for example, by arranging steel tire carcass cords at an angle of 70° to 90° relative to the tire circumference.

[0031] The carcass ply 6A has a main body portion 6a and a folded-back portion 6b. The main body portion 6a extends between a pair of bead portions 4. The folded-back portion 6b is connected to the main body portion 6a and folds back from the axial inside to the outer side around the bead core 5.

[0032] The belt layer 7 is disposed, for example, in the tread portion 2, on the outer side of the tire carcass 6 in the tire radial direction. The belt layer 7 comprises a plurality of metal belt cords inclined relative to the tire circumferential direction. Furthermore, one pair of outer ends of the belt layer in the tire axial direction are located on the outer side of the tire axial direction, respectively, compared to the pair of shoulder circumferential grooves 12.

[0033] exist Figure 3 The image shows an enlarged view of a portion of the sidewall 3 and half of the tread portion 2 of the tire. (See image for details.) Figure 3 As shown, the half-width W2 of the belt from the tire equator C to one pair of opposite ends of the belt layer 7 is 55% to 85% of the carcass half-width W1. The carcass half-width W1 is the distance along the tire axis from the tire equator C to the carcass 6 at the position of maximum tire width. In this invention, by adopting the above structure, it is possible to improve resistance to uneven wear without sacrificing rolling resistance and wet road performance. The following mechanism can be inferred as a reason for this.

[0034] In this invention, the circumferential groove 11 of the tread is a narrow groove, which maintains the rigidity of the central part of the tread portion 2 and thus suppresses the increase of rolling resistance. On the other hand, since the circumferential groove 12 of the shoulder is a wide groove, wet road performance can be ensured.

[0035] Typically, in heavy-duty pneumatic tires with an aspect ratio of 65% or less, the difference in restraint of the belt layer 7 is large near the tread end of the tread portion 2 and near the tire equator, tending to result in a large difference in outer diameter growth associated with deterioration during driving. In this invention, by determining the belt half-width W2 to be 55% to 85% of the carcass half-width W1, the outer diameter growth of each part of the tread portion 2 can be made uniform, improving resistance to uneven wear. In this invention, a mechanism is considered that can improve resistance to uneven wear without sacrificing rolling resistance or wet road performance.

[0036] The structure of this embodiment will now be described in more detail. Furthermore, each structure described below represents a specific embodiment. Therefore, the present invention can achieve the aforementioned effects even without the structures described below. Moreover, in the tire of the present invention having the above features, even applying any one of the structures described below individually can result in improved performance corresponding to each structure. Furthermore, when several structures described below are applied in combination, improved composite performance corresponding to each structure can be expected.

[0037] The belt half-width W2 is preferably 60% or more of the carcass half-width W1, more preferably 65% ​​or more, more preferably 80% or less, and more preferably 75% or less. This helps to suppress the increase in rolling resistance and improve resistance to eccentric wear.

[0038] The belt layer 7 comprises multiple belt ply layers overlapping in the tire radial direction. In this embodiment, the belt layer 7 comprises a first belt ply layer 7A, a second belt ply layer 7B, a third belt ply layer 7C, and a fourth belt ply layer 7D overlapping from the inside to the outside in the tire radial direction. That is, the belt layer 7 in this embodiment is composed of four belt ply layers. Each belt ply layer comprises multiple belt cords inclined in the same direction relative to the tire circumference. Furthermore, at least one group of adjacent belt ply layers in the tire radial direction overlaps in a manner where the belt cords intersect each other. Such a belt layer 7 can effectively reinforce the tread portion 2.

[0039] The angle of the belt cords in the first belt ply 7A relative to the tire circumference is preferably larger than the angle of the belt cords in the second belt ply 7B to the fourth belt ply 7D relative to the tire circumference. This configuration of belt cords helps to reduce taper and improve driving stability.

[0040] The angle between the belt cords included in the first belt ply 7A and the tire circumferential direction is preferably 40° or more, more preferably 45° or more, more preferably 60° or less, and more preferably 55° or less.

[0041] The angle of the belt cords included in the second belt ply 7B to the fourth belt ply 7D relative to the tire circumference is preferably 10° or more, more preferably 12° or more, more preferably 25° or less, and more preferably 22° or less. Such second belt ply 7B to fourth belt ply 7D can maintain a small taper and can achieve excellent tread reinforcement.

[0042] In this embodiment, the outer ends of each of the first belt ply 7A to the fourth belt ply 7D are located axially outer of the shoulder circumferential groove 12. Furthermore, at least the half-width of the outer end of the ply from the tire equator to the tire axial direction of the second belt ply 7B to the fourth belt ply 7D is the tire axial distance L1 from the tire equator to the center of the groove in the shoulder circumferential groove 12. Figure 2 The width of the first belt ply 7A is set to 110% to 170% of the width of the first belt ply 7A. In a preferred embodiment, the half-width of the ply is also set to the range described above. The belt ply 7 containing such a belt ply can suppress the increase in rolling resistance and can reliably suppress the growth of the outer diameter near the tread end.

[0043] 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 a configuration.

[0044] like Figure 1 As shown, in this embodiment, by arranging the belt layer 7 with the above-described structure, the reinforcing effect can be fully realized, and the outer diameter growth of the tread portion 2 can be reliably suppressed. Therefore, in this embodiment, the tread portion 2, as its reinforcing component, is provided only with the belt layer 7, and no other reinforcing components (e.g., a crown belt layer with cords wound into a spiral shape) are provided. As a result, the weight increase of the tread portion 2 is suppressed, and the rolling resistance can be maintained at a low level.

[0045] like Figure 2 As shown, the axial distance L1 from the tire equator C to the center of the grooves of a pair of tire shoulder circumferential grooves 12 is preferably the tire carcass half-width W1. Figure 3 As shown, and so on below, the percentage is 40% or more, more preferably 45% or more, more preferably 60% or less, and more preferably 55% or less. This allows the excellent drainage performance of the shoulder circumferential groove 12 to be fully utilized.

[0046] The maximum width of the shoulder circumferential groove 12 is, for example, 6.0 mm to 16.0 mm, preferably 8.0 mm to 14.0 mm. Such a shoulder circumferential groove 12 can suppress the increase of rolling resistance and can exert excellent drainage performance as a wide groove.

[0047] The tire axial distance L2 from the tire equator C to the center of the grooves of the pair of circumferential grooves 11 is preferably 10% to 20% of the tire carcass half-width W1. This can suppress uneven wear in the center of the tread portion 2 and improve wet road performance.

[0048] The maximum width of the circumferential groove 11 of the tire crown is, for example, 1.0 mm to 3.0 mm, preferably 1.5 mm to 2.5 mm. Such a circumferential groove 11 of the tire crown can suppress the increase of rolling resistance and can exert excellent drainage performance as a fine groove.

[0049] exist Figure 4 The diagram shows a plan view of the tread area 2. (See figure.) Figure 4 As shown, the shoulder circumferential groove 12 and the crown circumferential groove 11 are preferably serrated. Such shoulder circumferential grooves 12 and crown circumferential grooves 11 help improve traction performance when driving on wet roads.

[0050] In a more preferred embodiment, the minimum distance L3 between the serrated shoulder circumferential groove 12 and the crown circumferential groove 11 along the tire axial direction is preferably greater than the maximum distance L4 between the outer ends of the belt ply included in the belt layer 7. Figure 2 (As shown) This ensures a sufficient distance between the circumferential groove 11 of the tire crown and the circumferential groove 12 of the tire shoulder, further improving the resistance to uneven wear.

[0051] Furthermore, the amplitude of the tire axial vibration of the center line of the circumferential groove 11 of the tread when viewed from above is preferably greater than the distance d1 from the bottom of the circumferential groove 11 to the belt layer 7. Figure 2 (As shown) is smaller. Similarly, the amplitude of the tire axial oscillation of the center line of the shoulder circumferential groove 12 when viewed from above is preferably smaller than the distance d2 from the bottom of the shoulder circumferential groove 12 to the belt layer 7. Figure 2 (As shown) This can suppress uneven wear around the circumferential groove 11 of the tire crown and enable the excellent drainage performance of the circumferential groove 12 of the tire shoulder.

[0052] In this embodiment, the tread portion 2 is provided with only two shoulder circumferential grooves 12 and two crown circumferential grooves 11, and no other circumferential grooves are provided. As a result, the above-mentioned effects can be reliably achieved.

[0053] The above provides a detailed description of a heavy-duty pneumatic tire according to one embodiment of the present invention. However, the present invention is not limited to the specific embodiment described above and can be implemented in various ways.

[0054]

Example

[0055] Based on the specifications in Tables 1-2, a prototype with... Figure 1 The basic structure is a heavy-duty pneumatic tire with dimensions of 295 / 60R22.5. As Comparative Example 1, a tire with a 10mm wide circumferential groove 11 in the tread was prototyped. As Comparative Examples 2 and 3, tires with belt half-widths deviating from the range specified in this invention were prototyped. All test tires have substantially the same structure except for the specifications shown in Tables 1 and 2. Rolling resistance, wet road performance, and resistance to uneven wear were tested on each test tire. The common specifications and test methods for each test tire are as follows.

[0056] Wheel rim: 9.00×22.5

[0057] Tire internal pressure: 1000 kPa

[0058] <Rolling resistance>

[0059] A certain longitudinal load was applied on a drum tester, and the test tire was driven at a certain speed to measure its rolling resistance. The results were expressed as an index of 100 for the rolling resistance of Comparative Example 1; the smaller the value, the smaller the rolling resistance.

[0060] <Wet road performance>

[0061] A test vehicle equipped with test tires was driven at 60 km / h onto a wet road surface, and the braking distance during emergency braking was measured. The results were expressed using an index of 100, with the braking distance of Comparative Example 1 being the highest value. The smaller the value, the better the wet road performance.

[0062] <Resistance to eccentric wear>

[0063] After driving a test vehicle equipped with test tires for a certain distance in urban areas, the wear on the tire tread was measured. The results were used to represent the difference between the wear of the most worn part of the tire tread and the wear of the least worn part of the tire tread, using an index of 100 as a comparison example. The smaller the value, the better the resistance to uneven wear.

[0064] The test results are shown in Tables 1 and 2.

[0065] Table 1

[0066]

[0067] Table 2

[0068]

[0069] The test results confirm that the tires in this embodiment improve resistance to uneven wear without sacrificing rolling resistance or wet road performance.

Claims

1. A pneumatic tire for heavy load, which has a flatness of 65% or less, wherein, the pneumatic tire for heavy load comprises: a carcass which extends from a bead portion on one side via a tread portion to a bead portion on the other side; and a belt which is disposed inside the tread portion, the tread portion comprises a plurality of circumferential grooves which extend continuously along the tire circumferential direction, the circumferential grooves comprise a pair of shoulder circumferential grooves and at least one crown circumferential groove which is disposed between the pair of shoulder circumferential grooves, the crown circumferential groove is a fine groove which is closed at the time of grounding under the maximum load, the pair of shoulder circumferential grooves are wide grooves which are not closed at the time of grounding under the maximum load, respectively, the belt comprises a plurality of metal belt cords which are inclined with respect to the tire circumferential direction, a pair of outer ends of the belt in the tire axial direction are located at positions which are located outside the pair of shoulder circumferential grooves in the tire axial direction, respectively, a belt half-width from the tire equator to the pair of outer ends of the belt is 70% to 79% of a carcass half-width which is a distance from the tire equator to the tire axial direction of the carcass at a position of the maximum width of the tire, the crown circumferential groove extends in a zigzag shape, and an amplitude amount of the tire axial direction of a groove center line of the crown circumferential groove is smaller than a distance from a bottom of the crown circumferential groove to the belt when the tread is viewed from above, the shoulder circumferential groove extends in a zigzag shape, and an amplitude amount of the tire axial direction of a groove center line of the shoulder circumferential groove is larger than a distance from a bottom of the shoulder circumferential groove to the belt when the tread is viewed from above.

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

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

4. The pneumatic tire for heavy load according to claim 1 or 2, wherein, the belt comprises a plurality of belt plies which overlap in the tire radial direction, one belt ply comprises a plurality of the belt cords which are inclined in the same direction with respect to the tire circumferential direction, at least one group of the belt plies which are adjacent in the tire radial direction overlap in a manner in which the belt cords cross each other.

5. The pneumatic tire for heavy load according to claim 4, wherein, the plurality of belt plies comprise a first belt ply, a second belt ply, a third belt ply, and a fourth belt ply which overlap from the inside toward the outside in the tire radial direction, an angle of the belt cords included in the first belt ply with respect to the tire circumferential direction is larger than an angle of the belt cords included in the second belt ply, the third belt ply, and the fourth belt ply with respect to the tire circumferential direction.

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

7. The pneumatic tire for heavy load according to claim 5, wherein, The belt cords included in the first belt ply are arranged at an angle of 40° to 60° with respect to the tire circumferential direction.

8. The heavy load pneumatic tire of claim 5 wherein, With respect to each of the second belt ply, the third belt ply, and the fourth belt ply, The half width of the belt ply from the tire equator to the outer end of the belt ply in the tire axial direction is 110% to 170% of the distance from the tire equator to the center of the groove of the shoulder circumferential groove in the tire axial direction.

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