Patent Application
20240190177
The present disclosure relates to a pneumatic tire.
In Patent document 1 below, there has been proposed a pneumatic tire in which a band layer is disposed in a tread portion. And, a hybrid cord obtained by twisting a nylon fiber strand and an aramid fiber strand is used as a band cord of the band layer.
As described above, a pneumatic tire in which a hybrid cord including materials having different elastic moduli is used as a band cord, can be expected to improve riding comfort and steering stability. In recent years, on the other hand, with the improvement of vehicle performance, pneumatic tires are required to further improve steering stability during high-speed running.
The present disclosure has been devised in view of the above circumstances, and
The present disclosure is a pneumatic tire having a tread portion, wherein
By employing the above configurations, the pneumatic tire according to the present disclosure can improve steering stability during high-speed running, while maintaining good ride comfort.
An embodiment of the present disclosures will be described below with reference to the drawings.
As shown in
The “normal state” means, in the case of a tire for which various standards have been established, that the tire is mounted on a regular rim and inflated to a regular internal pressure but loaded with no load. In the case of a tire for which various standards have not been established, the normal state means a standard usage state according to the purpose of use of the tire, which is a state in which the tire is not mounted on the vehicle and no load is applied.
The “regular rim” is a rim defined for each tire in a standard system that includes standards on which the tire is based, for example, “Standard Rim” in JATMA, “Design Rim” in TRA, and “Measuring Rim” in ETRTO.
The “regular internal pressure” is air pressure specified for each tire by each standard in the standard system including the standards on which the tire is based, and is “maximum air pressure” in JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA and “INFLATION PRESSURE” in ETRTO.
In this specification, unless otherwise noted, the dimensions of each part of the tire are the values measured under the normal state.
In the case of a component inside the tire that cannot be measured while maintaining its normal state, its dimensions shall be measured while maintaining its shape under the normal state.
Further, in this specification, unless otherwise noted, the composition of each part of the tire means the composition of the material taken out from a new and unused tire.
As the taking-out method at that time, a method that does not change the composition as much as possible is appropriately adopted.
The tire 1 in the present embodiment has a carcass 6. The carcass 6 is composed of, for example, one carcass ply 6A. The carcass ply 6A comprises a plurality of carcass cords, and topping rubber covering them. The carcass cords are arranged, for example, at an angle of 75 to 90 degrees with respect to the tire circumferential direction. Incidentally, “75 to 90 degrees” means “not less than 75 degrees and not more than 90 degrees”, and the same applies hereinafter in the present specification.
As the carcass cords, preferably used are organic fiber cords such as nylon, polyester or rayon, and the like.
The carcass ply 6A has a main body portion 6a and a folded portion 6b.
The main body portion 6a extends from one bead portion 4 to the other bead portion 4 through one sidewall portion 3, a tread portion 2 and the other sidewall portion 3.
The folded portion 6b continues from the main body portion 6a, and is folded around a bead core 5 from the inside to the outside in the tire axial direction so as to extend outward in the tire radial direction.
The tread portion 2 of the present embodiment is provided with a belt layer 8.
The belt layer 8 comprises, for example, two belt plies 8A and 8B. For example, each of the belt plies 8A and 8B comprises a plurality of belt cords arranged obliquely with respect to the tire circumferential direction, and a topping rubber covering them.
It is preferable that each belt cord is inclined at an angle of 10 to 45 degrees with respect to the tire circumferential direction.
The tread portion 2 comprises a tread rubber 2G forming a ground contacting surface, and a band layer 9 disposed radially inside the tread rubber 2G.
The tread rubber 2G is provided with at least one first circumferential groove 10 extending continuously in the tire circumferential direction in the ground contacting surface. The tread rubber 2G of the present embodiment is provided with three first circumferential grooves 10. The groove width of the first circumferential groove 10 is, for example, 3 to 15 mm.
The depth of the first circumferential groove 10 is, for example, 5 to 10 mm.
However, the groove width and groove depth of the first circumferential groove 10 are not particularly limited as long as a certain degree of drainage can be expected during wet running.
Further, the tread rubber 2G may be provided with a second circumferential groove different from the above-described first circumferential groove 10.
In
The band layer 9 is composed of, for example, one band ply 11. The band ply 11 comprises band cords 12 arranged substantially parallel to the tire circumferential direction, and a topping rubber 13 covering the band cords 12. For example, the band layer 9 may be a plurality of superimposed band plies 11, or a plurality of band plies 11 arranged in the tire axial direction apart from each other. In the present embodiment, the band ply 11 is configured as a so-called jointless band in which, for example, a single band cord is wound in the tire circumferential direction. In another embodiment, the band ply 11 may include a plurality of band cords 12 arranged substantially parallel to the tire circumferential direction.
The expression “the band cord 12 extends substantially parallel to the tire circumferential direction” includes at least such a mode that the band cord 12 extends at an angle of 5 degrees or less with respect to the tire circumferential direction.
As shown in
In
According to the present disclosure, as shown in
The outer surface 9s of the band layer 9 means the outer surface of the topping rubber 13 covering the band cord 12.
The tire normal direction means a direction normal to the ground contacting surface of the tread portion 2. In this specification, the ground contacting surface of the tread portion 2 means a surface contacting with a plane when the tire 1 under the normal state is contacted with the plane at a camber angle of 0 degrees under the normal load. Further, the groove edge means the boundary between the opening area of the groove and the ground contacting surface. The ground contacting surface and the groove edge can be imaged by a known method such as CT imaging.
In the case of a pneumatic tire for which various standards have been established, the “normal load” is the load defined for each tire by each standard in the standard system including the standards on which that the tire is based, and is “maximum load capacity” in JATMA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA, and “LOAD CAPACITY” in ETRTO.
In the case of a tire for which various standards have not been established, the “normal load” refers to the load acting on one tire when the tire is in the standard mounting state.
The “standard mounting state” refers to a state in which the tire is mounted on a standard vehicle according to the purpose of use of the tire, and the vehicle is standing still on a flat road surface in a drivable state.
By employing the above configurations, the tire 1 of the present disclosure can improve steering stability during high-speed running while maintaining good ride comfort. As the reason therefor, it is presumed to be the following mechanism.
In general, the band layer 9 greatly influences the degree of vibration absorption of the tread portion 2 and the degree of outer diameter increase of the tread portion 2.
In other words, the band layer 9 has a great influence on ride comfort during normal running and steering stability during high-speed running.
In the present disclosure, a hybrid cord is used for the band cord 12 of the band layer 9.
Thereby, during normal running in which the outer diameter increase of the tread portion 2 is small, the second filament 17 (shown in
During high-speed running, the first filament 16 (shown in
The developers have found, as a result of intensive research, that it is possible to further improve the steering stability by specifying the thickness of the rubber around the band layer 9, and have completed the present disclosures.
In the present disclosure, as described above, the thickness t1 is defined as 1.0 mm or less, the distance d1 is defined as 2.0 mm or less, and the distance d2 is defined as 15.0 mm or less. Thereby, the thickness of the rubber on the radially outside of the band cords 12 included in the band layer 9, can be set smaller, and the influence of the centrifugal force acting on the tread portion 2 during high-speed running can be reduced.
Therefore, the increase of the outer diameter of the tread portion 2 is suppressed, the tread profile can be maintained even during high-speed running, and the ground contact of the tread portion 2 is improved.
It is believed that, by the mechanism described above, the present disclosure can improve steering stability during high-speed running while maintaining good ride comfort.
More detailed configurations of the present embodiment will be described below.
Each configuration described below represents a specific aspect of the present embodiment.
Therefore, it goes without saying that the present disclosure can exhibit the above 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 disclosure having the features described above, an improvement in performance according to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, it is possible to expect a combined improvement in performance according to the respective configurations.
As shown in
The difference in elastic modulus between the first filament 16 and the second filament 17 is determined, for example, by tensile strength specified in JIS L1017. The conditions for measuring the tensile strength are not particularly limited as long as the tensile strength of the first filament 16 and the tensile strength of the second filament 17 are measured under the same conditions.
The total fineness of one band cord 12 is, for example, not more than 4400 dtex, preferably 2000 to 4000 dtex, more preferably 2500 to 3500 dtex.
Such band cord 12 is helpful for improving riding comfort and steering stability in a well-balanced manner.
The stress σ1 of the band cord 12 when elongated by 3% is, for example, not more than 0.030 (N/tex). The stress σ1 is preferably not less than 0.005 (N/tex), more preferably not less than 0.010 (N/tex), and preferably not more than 0.025 (N/tex), more preferably not more than 0.020 (N/tex).
Such band cord 12 can exhibit excellent ride comfort, while maintaining the durability of the tread portion 2.
The stress σ2 of the band cord 12 when elongated by 5% is, for example, not less than 0.04 (N/tex). The stress σ2 is preferably not less than 0.043 (N/tex), more preferably not less than 0.045 (N/tex), and preferably not more than 0.06 (N/tex), more preferably not more than 0.055 (N/tex).
Such band cord 12 is helpful for improving ride comfort and steering stability at high speeds in a well-balanced manner.
The ratio σ1/σ2 (%) between the stress σ1 and the stress σ2 is preferably not less than 25%, more preferably not less than 29%, and preferably not more than 50%, more preferably not more than 43%.
The stress σ1 and the stress σ2 described above are measured, for example, by the method of measuring load under constant extension specified in JIS L1017.
As shown in
From the viewpoint of achieving both ride comfort and steering stability, the sea ratio of the ground contacting surface of the tread portion 2 is preferably not less than 15%, more preferably not less than 20%, and preferably not more than 50%, more preferably not more than 40%, still more preferably not more than 30%.
Incidentally, the sea ratio is the ratio of the sum of the opening areas of all the grooves to the total area of the virtual ground contacting surface in such a state that all the grooves in the ground contacting surface of the tread rubber 2G are filled up.
It is preferable that the ratio σ1/σ2 (%) of the stress σ1 (N/tex) when the band cord 12 is stretched by 3% to the stress σ2 (N/tex) when the band cord 12 is stretched by 5% is larger than the sea ratio (%) of the ground contacting surface of the tread portion.
Specifically, the ratio σ1/σ2 (%) is preferably not less than 1.50 times, more preferably not less than 1.90 times, and preferably not more than 3.00 times, more preferably not more than 2.86 times the sea ratio (%).
Thereby, the ratio σ1/σ2 is optimized, and excellent steering stability is exhibited both during low-to-medium speed running and high speed running.
The tread rubber 2G includes, for example, a rubber compound having a complex elastic modulus E*1 of 10 to 20 (MPa) at 30 degrees C.
The complex elastic modulus E*1 is more preferably 12 to 18 (MPa).
On the other hand, in the case of a tire in which riding comfort is important, the complex elastic modulus E*1 at 30 degrees C. of the tread rubber 2G may be not more than 10 (MPa).
The complex elastic modulus E*1 is a value measured using a “viscoelastic spectrometer” manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions in accordance with JIS-K6394.
As a test sample for measurement, there is used, for example, a rubber piece obtained from the tread rubber 2G so that the long side is in the tire circumferential direction, the short side is in the tire axial direction, and the thickness is in the tire radial direction.
for example, the size of the rubber piece is 20 mm long side×4 mm short side×1 mm thick.
The developers have found, as a result of various experiments, that specifying the complex elastic modulus E*1 of the tread rubber 2G according to the sea ratio, contributes to both ride comfort and steering stability. Specifically, the product of the complex elastic modulus E*1 (MPa) and the sea ratio (%) is preferably not less than 3.0 (MPa), more preferably not less than 4.3 (MPa), and preferably not more than 9.0 (MPa), more preferably not more than 7.5 (MPa).
Thereby, the amount of deformation of the tread portion 2 during running is optimized, and ride comfort and steering stability can be improved in a well-balanced manner.
Further, the product σ2·E*1 of the stress σ2 (N/tex) at 5% elongation of the band cord and the complex elastic modulus E*1 (MPa) is preferably not less than 0.45 (N. MPa/tex), more preferably not less than 0.60 (N·MPa/tex), and preferably not more than 1.05 (N·MPa/tex), more preferably not more than 0.90 (N·MPa/tex).
Thereby, the amount of deformation of the tread portion 2 and the band layer 9 during high-speed running is optimized, and ride comfort and steering stability are improved in a well-balanced manner.
As shown in
The distance d1 is preferably not less than 0.5 mm, more preferably not less than 1.0 mm, and preferably not more than 1.8 mm, more preferably not more than 1.5 mm. Thereby, at the groove bottom of the first circumferential groove 10, the thickness of the rubber is optimized, and the above-described effects are exhibited more reliably.
The distance d2 is preferably not less than 5.0 mm, more preferably not less than 7.0 mm, and preferably not more than 12.0 mm, more preferably not more than 10.0 mm. Thereby, the thickness of the tread rubber 2G is optimized.
The developers have found that the above-described effect can be further improved by specifying the stress σ1 of the band cord 12 when elongated by 3% and the distance d2 in association with each other.
Specifically, the product σ1·d2 of the stress σ1 (N/tex) and the distance d2 (mm) is preferably 0.05 to 0.40 (N·mm/tex), more preferably 0.08 to 0.18.
Thereby, the amount of deformation of the tread portion 2 during medium to low speed running is optimized, and ride comfort can be further improved.
Similarly, it was found that the steering stability is further improved by specifying the stress σ2 of the band cord 12 when elongated by 5% and the distance d2 in association with each other.
Specifically, the product σ2·d2 of the stress σ2 (N/tex) and the distance d2 (mm) is preferably 0.30 to 0.60 (N·mm/tex), more preferably, 0.35 to 0.50.
Thereby, the amount of deformation of the tread portion 2 during high-speed running is optimized, and steering stability during high-speed running is further improved.
A ratio t1/d1 (%) between the thickness t1 and the distance d1 is preferably not less than 5%, more preferably not less than 6.7%, and preferably not more than 46.2%, more preferably not more than 30.8%.
Further, it is preferable that the ratio t1/d1 (%) between the thickness t1 and the distance d1 is smaller than the sea ratio (%). Specifically, the ratio t1/d1 (%) is preferably not less than 0.15 times, more preferably not less than 0.26 times, and preferably not more than 0.77 times, more preferably not more than 0.67 times the sea ratio (%). Thereby, the thickness t1 is optimized, and ride comfort is improved while maintaining the durability of the band layer 9.
In addition, it was found that the distance d1 and the complex elastic modulus E*1 have a large effect on ride comfort and steering stability, and it is preferable for improving these performances in a well-balanced manner, to define the distance d1 and the complex elastic modulus E*1 in association with each other.
Specifically, the product of the distance d1 (mm) and the complex elastic modulus E*1 (MPa) is preferably not less than 12.0 (MPa·mm), more preferably not less than 15.0 (MPa·mm), and preferably not more than 30.0 (MPa·mm), more preferably not more than 22.5 (MPa·mm).
Thereby, deformation of the rubber near the groove bottom of the first circumferential groove 10 is optimized, and steering stability during high-speed running can be improved while maintaining good ride comfort.
As shown in
In a more desirable mode, all of the plurality of first circumferential grooves 10 disposed in the tread rubber 2G satisfy the above-described configuration. Thereby, the above-described effects can be reliably exhibited.
while detailed description has been made of an especially preferable embodiment of the present disclosure, the present disclosure can be embodied in various modes without being limited to the illustrated embodiment.
Pneumatic tires of size 215/60R16 satisfying the requirements of the present disclosure were experimentally manufactured based on the specifications shown in Tables 1-4. As Comparative Example 1, a pneumatic tire was experimentally manufactured, wherein a band cord was a hybrid cord, and a thickness t1, a distance d1 and a distance d2 did not satisfy the requirements of the present disclosure.
As Comparative Example 2, a pneumatic tire was experimentally manufactured, wherein a band cord is made of nylon material only, and a thickness t1, a distance d1 and a distance d2 did not satisfy the requirements of the present disclosure.
Except for the specifications shown in Tables 1-4, the tires of Comparative Examples 1 and 2 had configurations substantially the same as those of the tires of Embodiments.
Each test tire was tested for ride comfort and steering stability at high speeds.
The common specifications of the test tires and test methods are as follows.
Ride comfort when the test vehicle was run on a general road was evaluated by the following method.
Each of 20 test drivers conducted a test drive, and scored the ride comfort on a scale of 1 to 10 points (higher number is better), and the total score of the 20 test drivers was calculated.
The results are indicated by a score based on the sum of the above-mentioned scoring result of Comparative Example 1 being 100, wherein the larger the value, the better the riding comfort.
Steering stability when the test vehicle was run at high speed, was evaluated by the following method.
Each of the 20 test drivers conducted a test drive, and scored the steering stability on a scale of 1 to 10 points (higher number is better), and the total score of the 20 test drivers was calculated.
The results are indicated by a score based on the sum of the above-mentioned scoring result of Comparative Example 1 being 100, wherein the larger the value, the better the steering stability during high-speed running.
Comprehensive performance including the above-mentioned ride comfort and steering stability at high speeds, was evaluated. The results are the sum of the scores for ride comfort and steering stability during high-speed running, wherein the larger the number, the better the overall performance. The test results are shown in Tables 1-4.
In Tables 1 to 4, with respect to the ride comfort, when the score is higher than 96 of Comparative Example 2, it can be evaluated as “good ride comfort is maintained.” Further, with respect to the steering stability during high-speed running, when the score is higher than 100 of Comparative Example 1, it can be evaluated as the steering stability is improved.
As a result of the test, it was confirmed that the embodiment tires were improved in the steering stability at high speed while maintaining good ride comfort, and improved in the overall performance including the ride comfort and steering stability.
The present disclosure includes the following aspects.
A pneumatic tire having a tread portion, wherein
The pneumatic tire according to Present disclosure 1, wherein the first filament and the second filament are made of organic fibers.
The pneumatic tire according to Present disclosure 1 or 2, wherein the band cord has a total fineness of not more than 4400 dtex.
The pneumatic tire according to any one of Present disclosures 1 to 3, wherein a stress σ1 of the band cord when elongated by 3% is not more than 0.03 (N/tex).
The pneumatic tire according to Present disclosure 4, wherein a product σ1·d2 of the stress σ1 (N/tex) and the distance d2 (mm) is 0.05 to 0.40 (N·mm/tex).
The pneumatic tire according to any one of Present disclosures 1 to 5, wherein a stress σ2 of the band cord when elongated by 5% is 0.04 to 0.06 (N/tex).
The pneumatic tire according to Present disclosure 6, wherein the product σ2·d2 of the stress σ2 (N/tex) and the distance d2 (mm) is 0.30 to 0.60 (N·mm/tex).
The pneumatic tire according to any one of Present disclosures 1 to 7, wherein a sea ratio of the ground contacting surface of the tread portion is 15% to 50%.
The pneumatic tire according to Present disclosure 8, wherein a ratio t1/d1 (%) between the thickness t1 and the distance d1 is smaller than the shear ratio (%).
The pneumatic tire according to any one of Present disclosures 1 to 9, wherein the tread rubber includes a rubber compound having a complex elastic modulus E*1 of not more than 10 (MPa) at 30 degrees C.
The pneumatic according to Present disclosure 10, wherein the product d1·E*1 of the distance d1 (mm) and the complex elastic modulus E*1 (MPa) is 5.0 to 30.0 (MPa·mm).
The pneumatic tire according to Present disclosure 10 or 11, wherein the product σ2·E*1 of the stress σ2 (N/tex) at 5% elongation of the band cord and the complex elastic modulus E*1 (MPa) is 0.40 to 1.60 (N·MPa/tex).
The pneumatic tire according to any one of Present disclosures 10 to 12, wherein the product of the complex elastic modulus E*1 (MPa) and the sea ratio (%) of the ground contacting surface of the tread portion is not more than 5.0 (MPa).
The pneumatic tire according to any one of Present disclosures 1 to 13, wherein a ratio σ1/σ2 (%) of the stress σ1 (N/tex) at 3% elongation of the band cord to the stress σ2 (N/tex) at 5% elongation of the band cord is greater than the sea ratio (%) of the ground contacting surface of the tread portion.
The pneumatic tire according to any one of Present disclosures 1 to 14, wherein the thickness t1 is 0.05 to 0.30 mm, the distance d1 is 0.5 to 1.5 mm, and the distance d2 is 5.0 to 12.0 mm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-072796 | Apr 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/010235 | 3/9/2022 | WO |
