Patent Application
20220324258
This application claims the benefit of foreign priority to Japanese Patent Application No. JP2021-067845, filed Apr. 13, 2021, which is incorporated by reference in its entirety.
The present disclosure relates to a pneumatic tire.
Conventionally, plies with a plurality of cords are used as a component of pneumatic tires. It is also known that the above cords affect various performances of pneumatic tires. For example, Patent Document 1 below has proposed a pneumatic tire capable of reducing rolling resistance by setting the intermediate elongation of carcass cords. [Patent document]
When tires travel, plies with cords having multiple filaments may undergo repeated compression deformation, causing the multiple filaments to break little by little, and then reducing the rigidity of plies. In particular, when driving at high speeds, tires are often deformed, there has been a problem that the steering stability tends to decrease due to the decrease in rigidity of plies.
The present disclosure has been made in view of the above circumstances and has a major object to provide a pneumatic tire capable of sustaining excellent steering stability at high speeds.
In one aspect of the present disclosure, a pneumatic tire includes a ply having a plurality of cords each having an average cord diameter D, and a sidewall rubber having a loss tangent tan δ, wherein the plurality of cords each includes a plurality of filaments twisted together, the plurality of filaments each having an outer diameter d, the plurality of cords each has a ratio D/d of the average cord diameter D to the outer diameter d being equal to or more than 28, and the ratio D/d and the loss tangent tan δ of the sidewall rubber satisfy the following formula (1);
(tan δ)/(D/d)*1000≤5.5 (1).
Hereinafter, one or more embodiments of the present disclosure will be described with reference to the drawings.
As used herein, when the tire is 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 tire 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 JATMA, 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 JATMA, 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.
As illustrated in
The carcass ply 6A includes a main portion 6a and a pair of turn-up portions 6b. The main portion 6a extends, through a pair of sidewall portions 3 and a tread portion 2, between axially spaced bead portions 4. The turn-up portions 6b are connected to the main portion 6a and turned up around bead cores 5 from axially inside to outside of the tire to extend outwardly in the tire radial direction.
In the present embodiment, the tread portion 2 includes a tread reinforcing layer 7. The tread reinforcing layer 7, for example, includes a belt layer 8. The belt layer 8, for example, includes two belt plies 8A and 8B. The belt plies 8A and 8B, for example, include a plurality of belt cords inclined at an angle with respect to the tire circumferential direction and a topping rubber covering the belt cords. Preferably, the belt cords are oriented at an angle of from 10 to 45 degrees with respect to the tire circumferential direction.
The tread reinforcing layer 7, for example, further includes a band layer 9. The band layer 9, for example, is composed of a single band ply 9A. The band ply 9A includes one or more band cords that are oriented at an angle equal to or less than 5 degrees with respect to the tire circumferential direction. In some preferred embodiments, the band ply 9A is configured as a so-called jointless band ply in which a single band cord is spirally wound in the tire circumferential direction.
Each of the cords 11 has a ratio D/d of an average cord diameter D to the outer diameter d of each filament being equal to or more than 28. In such a cord 11, since the thin filaments 14 are tightly twisted together, even during high-speed running where a large tensile stress repeatedly acts on the cords 11, the deformation generated per filament 14 tends to be small and the stress that the cord 11 can exert can be increased. For this reason, the breakage of the filament 14 inside the cord 11 can be suppressed, and excellent steering stability can be maintained at high-speed running. Note that the cords 11 having the ratio D/d of 28 or more can be produced by appropriately combining known production methods.
The average code diameter D is calculated by the simple average of a major axis D1 and a minor axis D2 in the cross section of each cord 11. The major axis D1 means the maximum diameter of each cord 11. The minor axis D2 means the largest diameter of each cord 11 in the direction orthogonal to the major axis D1. Each cord 11 according to the present embodiment has a constant cross-sectional shape and extends in the length direction of the cord 11. Alternatively, the cross-sectional shape and cross-sectional area of the cord 11 may change in the length direction of the cord 11. In this case, it is preferable that the average cord diameter D be measured at the position where the cross-sectional area of the cord 11 is minimum. This is because the substantial tensile strength of a cord 11 depends on the configuration of the cord 11 at the position where the cross-sectional area of the cord 11 is minimum.
In general, in the ply 10 having the above-mentioned cords 11, one or more of the plurality of filaments 14 constituting the cord 11 are gradually broken due to repeated compression deformation when the tire travels. As a result, the rigidity of the ply 10 may decrease. In particular, when driving at high speeds, the tire is deformed frequently, so the steering stability tends to decrease due to the decrease in rigidity of the ply 10.
Although various studies have been conducted on cords of the plies, much attention has not been paid to the relationship between cords and a rubber member constituting the tire. The inventors of the present disclosure have focused on the relationship between the cords 11 of the ply 10 constituting the pneumatic tire and a rubber member of the tire, which had not received much attention in the past. Then, the inventors have made completed the present disclosure by analyzed these in detail.
As illustrated in
(tan δ)/(D/d)*1000≤5.5 (1).
Here, the loss tangent tan δ of the at least one sidewall rubber 3G is a value measured using a dynamic viscoelasticity measuring device (Iplexer series) manufactured by GABO under the following conditions in accordance with the provisions of JIS-K6394. The test sample at the time of measurement is a rubber piece taken from the sidewall rubber 3G, having a length of 20 mm in the tire circumferential direction, a width of 4 mm in the tire radial direction, and a thickness of 1 mm.
Initial strain: 5%
Amplitude: +/−1%
Frequency: 10 Hz
Deformation mode: tensile deformation
Measurement temperature: 30 degrees C.
In the present disclosure, by satisfying the above formula (1), the heat generation of the sidewall rubber 3G can be reduced, and the decrease in rigidity of the sidewall rubber 3G can be suppressed. On the other hand, since the ratio D/d is sufficiently large for the heat generation of the sidewall rubber 3G, breakage of some filaments 14 (shown in
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 each 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.
In the present disclosure, the ply 10 can be applied to the carcass ply 6A, the belt plies 8A and 8B, and/or the band ply 9A. In this embodiment, the ply 10 described above is applied to the carcass ply 6A and the band ply 9A. By setting the ply 10 which satisfies the above relationship as the carcass ply 6A, it is considered that the reaction force of the ply 10 can be increased while suppressing the decrease in rigidity of the side portions of the tire. In addition, by setting the ply 10 which satisfy the above relationship as the band ply 9A, a large reaction force can be generated by the ply 10 in the tread portion, and the reaction force can be transmitted with good response in the side portions whose rigidity is maintained high. Hence, it is considered that the tire according to the present embodiment can continuously exhibit excellent steering stability at high-speed running.
The present disclosure is not limited to the above-mentioned embodiment, and the above-mentioned ply 10 may be applied to belt plies 8A and 8B. Further, in another embodiment according to the present disclosure, the ply 10 described above may be applied to a reinforcing ply (not illustrated) for reinforcing the tread portion 2, the sidewall portions 3 and/or the bead portions 4. Such a reinforcing ply can help to further improve the steering stability at high-speed running.
In some more preferred embodiments, the ratio D/d and the tan δ of at least one of the sidewall rubbers satisfy the following formula (2);
(tan δ)/(D/d)*1000≤2.0(2).
This can further enhance the above effects.
The loss tangent of the at least one sidewall rubber 3G is preferably equal to or more than 0.05, more preferably equal to or more than 0.07, but preferably equal to or less than 0.18, more preferably equal to or less than 0.16. Such a sidewall rubber 3G can be prepared by appropriately adjusting and combining known materials.
The above-mentioned sidewall rubber 3G can be obtained by appropriately combining known materials. For the rubber components of the sidewall rubber 3G, isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR) and the like can be employed. These may be used alone or in combination of two or more.
Further, fillers such as carbon black and silica, plasticizers such as oil and resin, processing aids such as fatty acids, vulcanization agents such as sulfur, vulcanization accelerators and the like can be appropriately added to the above-mentioned rubber components. The loss tangent tan δ of the sidewall rubber 3G according to the present embodiment can be adjusted by changing the glass transition point of the rubber component and the type and amount of the filler, the plasticizer, the vulcanizing agent, and the vulcanization accelerator as appropriate. In particular, by relatively reducing the amount of filler and plasticizer and relatively increasing the amount of vulcanizing agent and vulcanization accelerator as compared with the conventional rubber material, the loss tangent tan δ of the sidewall rubber 3G can be set in the above range.
As illustrated in
The number of cords 11 contained in a 5 cm width of the ply 10, for example, is in a range of from 40 to 60, preferably 45 to 55. Also, the fineness of each cord 11 is preferably equal to or more than 2000 dtex, more preferably equal to or more than 2500 dtex, still further preferably equal to or more than 3000 dtex, but preferably equal to or less than 7000 dtex, more preferably equal to or less than 6500 dtex, still further preferably equal to or less than 6000 dtex. In the present embodiment, each cord 11 is composed of two preliminary twisted yarns 13. The fineness of each preliminary twisted yarn 13 is preferably equal to or more than 1000 dtex, more preferably equal to or more than 1500 dtex, but preferably equal to or less than 3500 dtex, more preferably equal to or less than 3000 dtex.
As illustrated in
As illustrated in
Preferably, the cords 11 has a small heat shrinkage rate. The heat shrinkage rate of the cords 11 is preferably equal to or less than 5.0%, more preferably equal to or less than 4.0%, still further preferably equal to or less than 3.0%. Such a cord 11 does not shrink excessively even at high-speed running, and can further improve steering stability of the tire.
As used herein, the “heat shrinkage rate” means the “dry heat shrinkage rate after heating” of the cord after heating at a temperature of 180 degrees C. for five minutes under no load, which is measured in accordance with JIS-L1017, Section 8.10 (b) “Dry heat shrinkage rate after heating (method B)”.
Preferably, the cords 11 has an intermediate elongation equal to or less than 6.5%, more preferably equal to or less than 5.0%, still further preferably equal to or less than 4.5%. Such a cord 11 can help to sustain excellent steering stability of the tire. As used herein, the “intermediate elongation” means the elongation (%) when a constant load specified by the standard is applied in accordance with the chemical fiber tire cord test method of JIS L1017.
The composition of the cords 11 above applies to the composition of the cords taken from new and unused tire 1.
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.
Pneumatic tires of size 215/60R16 that satisfy the present disclosure were prepared based on the specifications in Tables 1-3. For comparison, pneumatic tires of reference examples 1 to 4 were also prepared. The tires of reference examples 1 to 4 had substantially the same configuration as the tires of Examples except for the specifications shown in Tables 1 to 3. For each test tire, steering stability at high speeds (when the tire is new and when the tire is used late) was tested. The common specifications and test methods for test tires are as follows.
Rim size: 16×6.5J
Tire inner pressure: 210 kPa
Displacement of test vehicle: 2000 cc
Drive system: FF
Test tire mounting position: All wheels
Steering stability at high speeds test (new and used tires):
Steering stability when driving at high speeds in the above test vehicle was evaluated by the driver's sensuality. In Tables, “steering stability of new tire” is an evaluation of the steering stability of a new test tire that has been run-in. In Tables, “Steering stability of used tire” is an evaluation of the steering stability of the test tire after traveling 3000 km on a general road. The test results are indicated in Tables using a score with the steering stability of Ref 1 as 100. The larger the value, the better the steering stability at high speeds.
Tables 1 to 3 show the test results.
The sidewall rubber compounds A to C shown in Tables 1 to 3 are as shown in Table 4 below.
Note that the total score of steering stability when the tire is new and when the tire is used late may be used as an index for comprehensive evaluation of steering stability during high-speed running.
As shown in Tables 1 to 3, it was confirmed that the tires of the examples continuously exhibited excellent steering stability at high speeds.
The following notes are disclosed regarding the above-described embodiments.
A pneumatic tire comprising:
a ply having a plurality of cords each having an average cord diameter D; and
a sidewall rubber having a loss tangent tan δ,
wherein
the plurality of cords each comprises a plurality of filaments twisted together, the plurality of filaments each having an outer diameter d,
the plurality of cords each has a ratio D/d of the average cord diameter D to the outer diameter d being equal to or more than 28, and
the ratio D/d and the loss tangent tan δ of the sidewall rubber satisfy the following formula (1);
(tan δ)/(D/d)*1000≤5.5 (1).
The pneumatic tire according to note 1, wherein
the ratio D/d is equal to or more than 32.
The pneumatic tire according to note 1 or 2, wherein
the ratio D/d is equal to or more than 35.
The pneumatic tire according to any one of notes 1 to 3, wherein
the ratio D/d and the tan δ of the sidewall rubber satisfy the following formula (2);
(tan δ)/(D/d)*1000≤2.0 (2).
The pneumatic tire according to any one of notes 1 to 4, wherein
the plurality of filaments of the plurality of cords comprises polyester fibers.
The pneumatic tire according to any one of notes 1 to 5, wherein
the plurality of cords has a heat shrinkage rate equal to or less than 3.0%.
The pneumatic tire according to any one of notes 1 to 6, wherein
the plurality of cords has an intermediate elongation equal to or less than 6.5%.
The pneumatic tire according to any one of notes 1 to 8, wherein
the ply comprises a carcass ply.
The pneumatic tire according to any one of notes 1 to 8, wherein
the ply comprises a reinforcing ply that reinforces a tread portion, a sidewall portion, and/or a bead portion.
The pneumatic tire according to any one of notes 1 to 9, wherein
the plurality of cords each comprises a plurality of preliminary twisted yarns twisted together, and the plurality of preliminary twisted yarns comprises some of the plurality of filaments.
The pneumatic tire according to note 10, wherein
each of the plurality of cords consists of two preliminary twisted yarns.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-067845 | Apr 2021 | JP | national |
