This application claims the benefit of foreign priority to Japanese Patent Application No. W2021-103398, filed Jun. 22, 2021. which is incorporated by reference in its entirety.
The present disclosure relates to a tire.
Patent Document 1 below has proposed a pneumatic tire with a tread portion including a base rubber layer having a specified loss tangent. The base rubber layer is made of low heat generation rubber that has a loss tangent smaller than that of a cap rubber layer forming the outer surface of the tread. As a result, the tire is expected to improve wear resistance and fuel efficiency.
In recent years, maintenance-free tires for a long time have been required due to consideration for the environment and the practical application of automatic vehicle driving technology. In particular, tires that can exhibit sufficient wet performance and steering stability until the end of wear of the tread portion are required.
The present disclosure has been made in view of the above circumstances and has a. major object to provide a tire capable of maintaining wet performance and steering stability even as the tread portion wears.
In one aspect of the present disclosure, a tire includes a tread portion including a first cap rubber layer forming a ground contact surface and having a loss tangent tan δ1, and a second cap rubber layer disposed inwardly in a tire radial direction of the first cap rubber layer and having a loss tangent tan δ2, the loss tangent tan δ2 being greater than the loss tangent tan δ1. The tread portion is provided with a plurality of sipes opening to the ground contact surface. The plurality of sipes extends inwardly in a tire radial direction from the ground contact surface to a location beyond a boundary between the first cap rubber layer and the second cap rubber layer. A maximum length L2 of the plurality of sipes in the second cap rubber layer is smaller than a length L1 of the plurality of sipes at the ground contact surface.
Hereinafter, one or more embodiments of the present disclosure will be described with reference to the drawings.
As used herein, when a tire is a pneumatic tire based on a standard, the “normal state” is such that the tire 1 is mounted onto a standard wheel rim with a standard pressure but loaded with no tire load. If a tire is not based on the standards, the normal state is a standard state of use according to the purpose of use of the tire and means a state of no load. As used herein, unless otherwise noted, dimensions of portions of the tire are values measured under the normal state.
As used herein, the “standard wheel rim” is a. wheel rim officially approved for each tire by standards organizations on which the tire is based, wherein the standard wheel rim is the “standard rim” specified in JAIMA, the “Design Rim” in TRA, and the “Measuring Rim” in ETRTO, for example.
As used herein, the “standard pressure” is a standard pressure officially approved for each tire by standards organizations on which the tire is based, wherein the standard pressure is the “maximum air pressure” in JAIMA, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA, and the “Inflation Pressure” in ETRTO, for example.
The tire according to the present embodiment includes tire components therein such as a carcass 6, a belt layer 7 and the like. Known material or members are appropriately adopted for these tire components.
The carcass 6 extends between a pair of bead portions 4 through a pair of sidewall portions 3 and a tread portion 2. In the present embodiment, the carcass 6, for example, includes two carcass plies 6A and 6B. The carcass plies 6A and 6B, for example, include a plurality of organic fiber carcass cords that is oriented at an angle of from 75 to 90 degrees with respect to the tire equator C.
The belt layer 7, for example, includes two belt plies 7A and 7B. The belt plies 7A and 7B, for example, include a plurality of belt cords oriented at an angle of from 10 to 45 degrees with respect to the tire circumferential direction. For the belt cords, organic fiber cords and steel cords may be adopted as appropriate, for example. In another embodiment, a tread reinforcing layer, e.g., a band layer (not illustrated), may be disposed radially outwardly of the belt layer 7.
In the present embodiment, the tread portion 2 is provided with a plurality of circumferential grooves 8 extending continuously in the tire circumferential direction. Thus, the tread portion 2 includes a plurality of land portions 9 which is divided by the plurality of the circumferential grooves 8. Note that the present disclosure is not limited to such an aspect.
In the present disclosure, a loss tangent tan 62 of the second cap rubber layer 12 is greater than a loss tangent tan δ1 of the first cap rubber layer 11. As used herein, loss tangent tan δ is a value measured using a dynamic viscoelasticity measuring device (Iplexer series) manufactured by GABO under the following conditions in accordance with JIS-K6394.
Initial strain: 5%
Amplitude of dynamic strain: +/−1%
Frequency: 10 Hz
Deformation mode: tensile deformation
Measurement temperature: 30 degrees C.
The tread portion 2 is provided with a plurality of sipes 15 opening to the ground contact surface 2s. In the present embodiment, the plurality of sipes 15 is configured as a plurality of lateral sipes extending in the tire axial direction. Note that in the present disclosure the sipes 15 is not particularly limited to such an embodiment. Thus, the sipes 15 may include one or more circumferential sipes extending in the tire circumferential direction. Further, both lateral sipes and circumferential sipes may be provided on the tread portion 2. Since
As used herein, “sipe” is an incision having a small width. The sipe has includes two opposite inner wall surfaces facing substantially parallel and a width between the two inner wall surfaces is equal to or less than 1.5 mm. Further, “substantially parallel” means that the angle between the two inner wall surfaces is equal to or less than 10 degrees, A width of a. sipe is preferably in a range from 0.5 to 1.5 mm, more preferably 0.4 to 1.0 mm. The configuration of a sipe is not particularly limited. For example, a sipe may have at least one of a pair of sipe edges having a chamfer portion. In addition, the bottom of the sipe may be connected to a flask-bottom having a width greater than 1.5 mm.
The present disclosure, by adopting the above configuration, can maintain wet performance and steering stability even if the tread portion 2 wear progresses. The following mechanism is inferred as the reason,
Further, as illustrated in
In the present disclosure, for the above-mentioned reason, it is considered that wet performance and steering stability can be maintained even if the tread portion 2 has worn down.
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. Thus, the present disclosure can exert the above-mentioned effects even if the tire does not include the configuration described below Further, if any one of the configurations described below is applied independently to the tire of the present disclosure having the above-mentioned characteristics, the performance improvement according. to the additional configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, it is expected that the performance of the additional configurations will be improved.
As illustrated in
A distance L3 in the tire radial direction from the ground contact surface of the tread portion 2 to the boundary 17 between the second cap rubber layer 12 and the base rubber layer 10 is in a range of from 60% to 80% of the maximum depth dl of the circumferential grooves 8. Due to the arrangement of the rubber layers in this way, after the middle stage of wear of the tread portion 2, the second cap rubber layer 12, which can be expected to have a large grip force, is exposed. Thus, wet performance can be reliably maintained. in the present embodiment, the boundary 16 between the first cap rubber layer 11 and the second cap rubber layer 12, and the boundary 17 between the second cap rubber layer 12 and the base rubber layer 10 extend in parallels with the ground contact surface 2s of the tread portion 2 in the land portion.
The loss tangent tan δ1 of the first cap rubber layer 11 is preferably equal to or more than 0.13, more preferably equal to or more than 0.15, but preferably equal to or less than 0.29. more preferably equal to or less than 0.25. The loss tangent tan δ2 of the second cap rubber layer 12 is preferably equal to or more than 0.30, more preferably equal to or more than 0.33, but preferably equal to or less than 0.40, more preferably equal to or less than 0.37. Further, the loss tangent tan δ1 is preferably in a range of from 50% to 65% of the loss tangent tan δ2. Such a first cap rubber layer 11 and a second cap rubber layer 12 can improve the overall performance of the tire in a well-balanced manner, and can suppress the peeling of rubber at the boundary 16 between the first cap rubber layer 11 and the second cap rubber layer 12.
Preferably, the loss tangent tan δ1 of the base rubber layer 10 is smaller than the loss tangent tan δ1 of the first cap rubber layer 11. Specifically, the loss tangent tan δb, for example, is equal to or less than 0.12, preferably in a range of from 0,07 to 0.12. This can suppress excessive heat generation in the tread portion 2 and improve tire durability. However, the loss tangent tan δb of the base rubber layer 10 is not limited to this range.
The values of the loss tangent of the above rubber layers can be obtained by appropriately combining known materials, and the detailed description thereof is omitted herein.
As illustrated in
As illustrated in
The bottom 15d of each sipe 15, for example, is located in the base rubber layer 10. Note that the bottom 15d of each sipe 15 may be located in the second cap rubber layer 12. The maximum depth d2 of each sipe 15, for example, is preferably in a range of from 75% to 100% of the maximum depth d1 of the circumferential grooves 8. Such a sipe 15 can help to improve wet performance.
The shape of the cross section of each Sipe 15 along the sipe length direction is not limited to the above-mentioned embodiment.
In
While the particularly preferable embodiments of the tire in accordance with the present disclosure have been described in detail, the present disclosure is not limited to the illustrated embodiments, but can be modified and carried out in various aspects within the scope of the disclosure.
As tires according to the present disclosure, pneumatic tires of size 235/65R16C were prepared (Examples). These tires have the basic structure shown in
Wet performance test (new and 50% worn conditions):
The wet performance when driving on a wet road surface with the test vehicle equipped with test tires was evaluated by the driver's sensuality. The test results are indicated in Tables 1 and 2 using a score with the wet performance of the comparative example as a new product as 100, and the larger the value, the better the wet performance.
The steering stability when driving on a dry road surface with the test vehicle equipped with test tires was evaluated by the driver's sensuality. The test results are indicated in Tables 1 and 2 using a score with the steering stability of the comparative example as a new product as 100, and the larger the value, the better the steering stability.
Tables 1 and 2 show the test results.
As shown in Tables 1 and 2, in the comparative example, the wet performance was 60 points and the steering stability was 80 points in the 50% worn condition. On the other hand, the tires of the examples maintained a high wet performance of 77 to 85 points in the 50% worn condition. In addition, the tires of the examples maintained a high steering stability of 87 to 92 points in the 50% worn condition. As described above, it was confirmed that the tires of the examples can maintain wet performance and steering stability even when the tread portion was worn.
The present disclosure includes the following aspects.
A tire comprising:
a tread portion comprising
the tread portion is provided with a plurality of sipes opening to the ground contact surface,
the plurality of sipes, at least partially, extends inwardly in a tire radial direction from the ground contact surface to a location beyond a boundary between the first cap rubber layer and the second cap rubber layer, and
a maximum length L2 of the plurality of sipes in the second cap rubber layer is smaller than a length L1 of the plurality of sipes at the ground contact surface.
The tire according to note 1, wherein
the loss tangent tan δ1 is in a range from 0.13 to 0.29.
The tire according to note 1 or 2, wherein
the loss tangent tan δ2 is in a range from 0.30 to 0.40.
The tire according to any one of notes 1 to 3, the tread portion further comprising a base rubber layer disposed inwardly in the tire radial direction of the second cap rubber layer, wherein
the base rubber layer has a loss tangent tan δb smaller than the loss tangent tan δ1
The tire according to note 4, wherein
the loss tangent tan δb is equal to or less than 0.12.
The tire according to any one of notes 1 to 5, wherein
the tread portion is provided with a plurality of circumferential grooves extending continuously in a tire circumferential direction, and
a maximum depth of the plurality of sipes is in a range from 75% to 100% of a maximum depth of the plurality of circumferential grooves.
The tire according to any one of notes 1 to 6, wherein
the maximum length L2 of the plurality of sipes in the second cap rubber layer is in a range from 60% to 80% of the length L1 of the plurality of sipes at the ground contact surface.
The tire according to any one of notes 1 to 7, wherein
in a cross-sectional view of each of the plurality of sipes the plurality of sipes extends in a wavy manner in the tire radial direction.
The tire according to note 8, wherein
each of the plurality of sipes has a wavelength in a range from 20% to 60% of a thickness in the tire radial direction of the second cap rubber layer.
The tire according to any one of notes 1 to 9, wherein the plurality of sipes comprises one or more lateral sipes extending in a tire axial direction.
The tire according to any one of notes 1 to 10, wherein the plurality of sipes comprises one or more circumferential sipes extending in a tire circumferential direction.
Number | Date | Country | Kind |
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2021-103398 | Jun 2021 | JP | national |