JP6263081B2 - Pneumatic tire - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a pneumatic tire that can realize a high level of both driving stability and ride comfort while improving rolling resistance performance by defining the structure, loss tangent, and complex elastic modulus of tread rubber. .

  In Patent Document 1 below, in order to achieve both ride comfort and steering stability, a tread rubber is made up of a cap portion that forms the outer surface of the tread portion, and a base portion that is disposed inward in the tire radial direction of the cap portion. A pneumatic tire has been proposed in which the base portion is divided into a pair of outer portions disposed on the outermost side in the tire axial direction and an inner portion extending between the outer portions.

  In the pneumatic tire, the loss tangent tan δ of the outer portion of the base portion is set to be small and the complex elastic modulus E * is set to be large, while the loss tangent tan δ of the inner portion is set to be large and the complex elastic modulus E * is small. Set to As a result, the outer part has low heat generation properties and high elasticity, so while suppressing internal loss due to heat generation, the rigidity of the tread shoulder part is enhanced during turning to exert a large cornering force and improve steering stability. Yes. Further, since the inner portion has flexibility and vibration damping properties, it can absorb the input from the road surface and improve the riding comfort during straight running.

JP 2005-263175 A

  In recent years, in relation to global environmental problems, attention has been focused on pneumatic tires with reduced rolling resistance in order to improve fuel efficiency. However, the pneumatic tire disclosed in Patent Document 1 has a problem that the rolling resistance is large because the loss tangent tan δ of the inner portion that receives a large ground load at all times during straight running is large.

  The present invention has been devised in view of the above circumstances, and improves rolling resistance performance based on limiting the loss tangent tan δ to a small value while suppressing the complex elastic modulus E * of the inner portion of the base portion. However, the main purpose is to provide a pneumatic tire capable of achieving both handling stability and ride comfort.

  The invention according to claim 1 of the present invention includes a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed on the outer side in the tire radial direction of the carcass and inside the tread portion. A tread rubber disposed on the outer side of the belt layer in the tire radial direction, the tread rubber being disposed on the inner side in the tire radial direction of the cap portion, the cap portion forming the outer surface of the tread portion, and A base portion made of a rubber material having a loss tangent tan δ of 0.03 to 0.10, the base portion being arranged on the outermost side in the tire axial direction, and at least the outer end of the belt layer in the tire axial direction A complex elastic modulus E * a of the outer portion is 20 to 50 MPa, and a complex elastic modulus E of the inner portion is included between the pair of outer portions covering the outer portion and an inner portion extending between the outer portions. b is equal to or is from 2 to 15 mPa.

  According to a second aspect of the present invention, the outer portion extends outward in the tire axial direction beyond the outer end of the belt layer, extends inward in the tire radial direction along the carcass, and extends in the tire axial direction of the outer portion. 2. The pneumatic tire according to claim 1, wherein the outer end has a height in a tire radial direction from a bead base line that is 0.6 to 0.9 times a tire cross-sectional height.

  The invention according to claim 3 is the pneumatic tire according to claim 1 or 2, wherein the inner portion has a width in the tire axial direction of 0.4 to 1.1 times the tread ground contact width.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the inner portion is formed with a plurality of divided pieces having different complex elastic moduli E * b arranged in the tire axial direction. It is a pneumatic tire.

  The invention according to claim 5 is the pneumatic tire according to claim 4, wherein the complex elastic modulus E * b is smaller as the divided piece is closer to the tire equator.

  The invention according to claim 6 is the pneumatic tire according to claim 4, wherein the complex elastic modulus E * b is larger as the divided piece is closer to the tire equator.

  Here, the tread contact width is a tread when a normal load is loaded on a normal rim that is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to a flat surface with a camber angle of 0 degrees. It is the distance in the tire axial direction between the ground contact ends. Further, the dimensions and the like of each part of the tire are values in the normal state unless otherwise specified.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA and “Design Rim” for TRA. "If ETRTO," Measuring Rim ".

  Furthermore, “regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. “JAMATA” is the “highest air pressure”, TRA is the table “TIRE LOAD” Maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO.

Further, in this specification, the loss tangent and the complex elastic modulus are values measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the following conditions in accordance with the provisions of JIS-K6394.
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile measurement temperature: 30 ° C

  The pneumatic tire of the present invention is a rubber material in which a tread rubber is disposed on a cap portion forming the outer surface of the tread portion, and inward in the tire radial direction of the cap portion, and a loss tangent tan δ is 0.03 to 0.10. And a base portion. Such a base portion is set to have a small loss tangent tan δ over the entire width thereof, so that heat generation during running can be suppressed to prevent tire damage and the like, and energy loss can be suppressed and rolling resistance can be reduced. .

  Further, the base portion includes a pair of outer portions that are arranged on the outermost side in the tire axial direction and cover at least the outer end of the belt layer in the tire axial direction, and an inner portion that extends between the outer portions. The complex elastic modulus E * a of the part is set to 20 MPa to 50 MPa, and the complex elastic modulus E * b of the inner part is set to 2 MPa to 15 MPa.

  Thus, since the complex elastic modulus E * a of the outer portion is set to be as large as 20 MPa to 50 MPa, the rigidity of the tread shoulder portion in the radial direction of the tire is increased, and the outer portion is large at the time of turning mainly receiving a ground load. Steering stability can be improved by exerting cornering force. In addition, since the outer portion covers the outer end of the belt layer in the tire axial direction, the distortion at the outer end can be reduced and damage to the belt layer can be suppressed. In addition, since the complex elastic modulus E * b is set to be as small as 2 MPa to 15 MPa, the inner portion can absorb the input from the road surface and improve the riding comfort during the straight traveling mainly receiving the ground load.

It is sectional drawing which shows the pneumatic tire of this embodiment. It is the elements on larger scale of the tread part of FIG. (A) is sectional drawing of the unloaded state of the pneumatic tire which an outer part terminates in a buttress part, (b) is a fragmentary sectional view which shows the state which the load acted on the pneumatic tire of (a). (A) is sectional drawing of the unloaded state of the pneumatic tire of this embodiment, (b) is sectional drawing which shows the state to which the big load was applied to the pneumatic tire of (a). It is sectional drawing which shows the pneumatic tire of other embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire 1 according to the present embodiment includes a carcass 6 that extends from a tread portion 2 through a sidewall portion 3 to a bead core 5 of the bead portion 4, and the carcass 6 on the outer side in the tire radial direction. It comprises a belt layer 7 disposed inside the tread portion 2 and is configured as a radial tire for passenger cars.

  The carcass 6 is composed of at least one carcass ply 6A, in this embodiment, one carcass ply 6A. The carcass ply 6A is folded back from the inner side in the tire axial direction to the outer side around the bead core 5 extending from the main body part 6a and extending from the main body part 6a to the bead core 5 of the bead part 4 through the sidewall part 3 and the bead part 4. And the folded portion 6b. Further, a bead apex 8 made of hard rubber extending from the bead core 5 to the outer side in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b, and the bead portion 4 is appropriately reinforced.

  Further, the carcass ply 6A has carcass cords arranged at an angle of, for example, 80 degrees to 90 degrees with respect to the tire equator C. As the carcass cord, for example, an organic fiber cord such as polyester, nylon, rayon, or aramid is suitably employed.

  The belt layer 7 includes at least two belt plies 7A arranged in such a manner that the belt cord is inclined with respect to the tire equator C at a small angle of, for example, 10 degrees to 40 degrees. , 7B are overlapped in the direction in which the belt cords cross each other. Steel cords are used for the belt cords of the present embodiment, but highly elastic organic fiber cords such as aramid and rayon can also be used as necessary. Further, between the end including the outer end 7t of the belt layer 7 and the carcass 6, a cushion rubber 9 having a substantially triangular cross section for relaxing stress concentration at the outer end 7t in the tire axial direction of the belt layer 7 is arranged. Has been. In this embodiment, the outer end 7t of the belt layer 7 is an outer end in the tire axial direction of the wide belt ply 7A.

  A tread rubber 2G is disposed on the outer side of the belt layer 7 in the tire radial direction. The pneumatic tire 1 of the present embodiment employs an SOT (Sidewall Over Tread) structure in which the tread rubber 2G is covered with the sidewall rubber 3G at the buttress portion 10 which is the outer portion of the sidewall portion 3 in the tire radial direction. The

  The tread rubber 2G includes a cap portion 11 that forms the outer surface of the tread portion 2 and extends in the tread width direction, and a base portion 12 that is disposed inward in the tire radial direction of the cap portion 11 and extends in the tread width direction. Consists of.

  The cap portion 11 of the present embodiment extends outward in the tire axial direction beyond the outer end 7t of the belt layer 7. As shown in FIG. 2 in an enlarged manner, the outer end 11t of the cap portion 11 in the tire axial direction has a tapered shape and is located on the inner side in the tire radial direction of the outer end 3Gt of the sidewall rubber 3G in the tire radial direction. Then, it is connected to the sidewall rubber 3G. Since such a cap part 11 is in direct contact with the road surface, for example, the loss tangent tan δ is preferably set to 0.10 to 0.30 and the complex elastic modulus E * is set to 4 MPa to 12 MPa. Thereby, abrasion resistance performance and grip performance are exhibited effectively. In addition, although the cap part 11 of this embodiment is formed from one type of compounded rubber, it may be configured by combining different formulations.

  The base portion 12 is disposed between the belt layer 7 and the cap portion 11 and is made of a rubber material having a small heat loss and energy loss with a loss tangent tan δ set to 0.03 to 0.10. The base portion 12 is disposed on the outermost side in the tire axial direction and includes a pair of outer portions 12A that cover at least the outer end 7t of the belt layer 7, and an inner portion 12B that extends between the outer portions 12A and 12A. Composed.

  The outer portion 12A of the present embodiment includes an inner end 12Ai in the tire axial direction located on the tire equator C side with respect to the outer end 7t of the belt layer 7, and an outer end 7t of the belt layer 7 that extends outward in the tire axial direction. And an outer end 12At in the tire axial direction that terminates along the carcass 6 inward in the tire radial direction. The outer portion 12A has a substantially constant thickness outside the belt layer 7, and is tapered from the outer portion 12A toward the outer end 12At. The outer end 12At is connected to the sidewall rubber 3G at a position on the inner side in the tire radial direction than the outer end 11t of the cap portion 11. Further, the outer portion 12A is made of a highly elastic rubber material whose complex elastic modulus E * a is set to 20 MPa to 50 MPa.

  The inner portion 12B extends in the tread width direction with a substantially constant thickness, and the outer end 12Bt in the tire axial direction is connected to the inner end 12Ai of the outer portion 12A. Further, the inner portion 12B is made of one kind of compounded rubber in the present embodiment, and is made of a low elastic rubber material having a complex elastic modulus E * b of 2 MPa to 15 MPa.

  Thus, in the pneumatic tire 1 of the present embodiment, the base portion 12 is set to have a loss tangent tan δ as small as 0.03 to 0.10 over the entire width thereof. In addition to preventing heat generation and preventing damage, it is possible to improve rolling resistance performance by suppressing energy loss. Here, if the loss tangent tan δ of the base portion 12 exceeds 0.10, heat generation may increase and rolling resistance may increase. The loss tangent tan δ of the base portion 12 is preferably as small as possible, but there is a technical limit to making it less than 0.03.

  In the base portion 12, it goes without saying that the loss tangent tan δA of the outer portion 12A and the loss tangent tan δB of the inner portion 12B may be the same or different.

  In addition, the outer portion 12A of the base portion 12 has a complex elastic modulus E * a set to a large value of 20 MPa to 50 MPa, so that a large cornering power is generated during turning that is mainly subjected to a ground load, thereby improving steering stability. it can. Moreover, since the outer portion 12A covers the outer end 7t of the belt layer 7 in the tire axial direction, the distortion at the outer end 7t can be reduced to suppress damage.

  Here, when the complex elastic modulus E * a of the outer portion 12A is less than 20 MPa, a large cornering power may not be sufficiently generated during turning. Conversely, if the complex elastic modulus E * a exceeds 50 MPa, the rigidity of the outer portion 12A is excessively increased, which may impair the riding comfort. From such a viewpoint, the complex elastic modulus E * a of the outer portion 12A is preferably 25 MPa or more, more preferably 30 MPa or more, and preferably 45 MPa or less, more preferably 40 MPa or less.

  Since a large load acts on the shoulder side of the tread portion 2 during turning, it is preferable that the complex elastic modulus E * a of the outer portion 12A is determined in association with the complex elastic modulus E * of the cap portion 11. Specifically, the ratio E * a / E * between the complex elastic modulus E * a of the outer portion 12A and the complex elastic modulus E * of the cap portion 11 is preferably 1.6 or more, more preferably 4.0. In addition, it is preferably 12.5 or less, more preferably 10.0 or less. When the ratio E * a / E * is less than 1.6, the difference from the complex elastic modulus E * of the cap portion 11 becomes small, and the steering stability may not be sufficiently improved. On the other hand, when the ratio E * a / E * exceeds 12.5, there is a problem in that significant distortion occurs at the interface between the outer portion 12A and the cap portion 11, and boundary peeling is easily induced.

  On the other hand, the inner portion 12B is set to have a complex elastic modulus E * b as small as 2 MPa to 15 MPa. Since the inner portion 12B receives a main ground load during straight traveling, limiting the E * b of the inner portion 12B to the above range absorbs the impact force from the road surface and improves the riding comfort. Here, when the complex elastic modulus E * b of the inner portion 12B is less than 2 MPa, the rigidity of the inner portion 12B is excessively lowered, and the rolling resistance performance may be lowered. On the contrary, if the complex elastic modulus E * b of the inner portion 12B exceeds 15 MPa, the impact force absorbing effect cannot be obtained. From such a viewpoint, the complex elastic modulus E * b of the inner portion 12B is preferably 2 MPa or more, more preferably 4 MPa or more, and preferably 15 MPa or less, more preferably 12 MPa or less.

  Thus, in the pneumatic tire 1 of the present embodiment, the loss tangent tan δ of the base portion 12, the complex elastic modulus E * a of the outer portion 12A, and the complex elastic modulus E * b of the inner portion 12 are within the above ranges. Therefore, it is possible to achieve a high level of handling stability and riding comfort while improving rolling resistance performance.

  Further, the complex elastic modulus E * b of the inner portion 12B can also be regulated in association with the complex elastic modulus E * of the cap portion 11. The ratio E * b / E * of the complex elastic modulus E * b of the inner part 12B and the complex elastic modulus E * of the cap part 11 is preferably 0.17 or more, more preferably 0.33 or more, Preferably it is 3.75 or less, More preferably, it is 1.0 or less. When the ratio E * b / E * is less than 0.17, the cornering force during turning tends to be excessively reduced. On the other hand, when the ratio E * b / E * exceeds 3.75, there is a possibility that a sufficient impact absorbing effect cannot be obtained.

  The outer portion 12A of the present embodiment extends relatively inward along the outer surface of the carcass 6 while reducing the thickness. For this reason, the outer portion 12A can reinforce the buttress portion 10 in a wide range. Note that the outer end 12At of the outer portion 12A in the tire radial direction has excessively increased rigidity of the sidewall portion 3 if the height H2 in the tire radial direction from the bead base line BL is too small with respect to the tire cross-section height H1. However, even if it is too large for the tire cross-section height H1, the buttress portion 10 and the sidewall portion 3 cannot be sufficiently reinforced, and the above-described effects are sufficient. There is a possibility that it cannot be demonstrated. From such a viewpoint, the height H2 of the outer end 12At of the outer portion 12A in the tire radial direction is preferably 0.6 times or more, more preferably 0.7 times or more of the tire cross-section height H1, , Preferably 0.9 times or less, more preferably 0.8 times or less.

  3 (a) and 3 (b) show no load on a pneumatic tire in which the height H2 (shown in FIG. 2) of the outer end 12At of the outer portion 12A is 0.9 times the tire cross-sectional height H1. Sectional drawing which shows the state and the state which the load acted is shown. When a load acts on such a pneumatic tire, the vicinity of buttress portion 10 having relatively small rigidity is locally deformed, and accordingly, a pinch cut is likely to occur in the carcass cord. On the other hand, in a pneumatic tire in which the height H2 (shown in FIG. 2) of the outer end 12At is 0.6 times the tire cross-section height H1, for example, it is shown in FIGS. 4 (a) and 4 (b). Thus, the local deformation | transformation in the vicinity of the buttress part 10 is suppressed, and this buttress part 10, the side wall part 3, and the bead part 4 can support a load with sufficient balance as a whole. Therefore, the pneumatic tire 1 of the present embodiment can suppress damage such as pinch cuts and flat spots where the tread surface is deformed flat, and can further improve riding comfort and rolling resistance performance.

  Further, since the outer portion 12A is reinforced in a wide range from the buttress portion 10 to the sidewall portion 3, the rubber thickness of the buttress portion 10 and the sidewall portion 3 can be reduced to reduce the weight of the tire. it can. Moreover, when the pneumatic tires 1 are stacked and stored in a horizontal state (horizontally stacked), the buttress part 10 and the sidewall part 3 are easily deformed by bending inward in the tire axial direction. Such a shape deformation can be suppressed by extending inward of the sidewall portion 3.

  As shown in FIG. 2, the width W2 in the tire axial direction between the outer ends 12Bt and 12Bt of the inner portion 12B can be set as appropriate. If the width W2 is too small, it may not be possible to sufficiently absorb the impact input from the road surface during straight traveling. On the other hand, if the width W2 is too large, the portion occupied by the outer portion 12A becomes small, and there is a possibility that a large cornering power cannot be generated. From such a point of view, the width W2 is preferably 0.4 times or more, more preferably 0.6 times or more, more preferably 1.1 times or less, more preferably 0. 9 times or less. In the present embodiment, the position of the outer end 12Bt of the inner portion 12B is provided symmetrically with respect to the tire equator C, but can also be provided at an asymmetric position depending on the mounting position of the tire.

  Furthermore, the thickness T2 of the base portion 12 can be set as appropriate. In addition, when thickness T2 is too small, there exists a possibility that the said effect | action cannot fully be exhibited. On the other hand, even if the thickness T2 is too large, it may be exposed to the outer surface of the tread portion during the middle period of wear and the grounding property may be impaired. From such a viewpoint, the thickness T2 of the base portion 12 is preferably 0.1 times or more, more preferably 0.2 times or more, more preferably 0.2 times or more the total thickness T1 of the tread rubber 2G. 5 times or less, more preferably 0.3 times or less. Needless to say, a small thickness of an under tread rubber or a band layer may be disposed between the tread rubber 2G and the belt layer 7.

FIG. 5 shows a pneumatic tire 1 according to another embodiment of the present invention.
In the inner portion 12B of this embodiment, a plurality of divided pieces 13 having different complex elastic moduli E * are formed side by side in the tire axial direction. The inner portion 12B of the present embodiment includes a pair of outer divided pieces 13A arranged on both sides in the tire axial direction and one inner divided piece 13B, 13B arranged between the outer divided pieces 13A, 13A. Are comprised of a total of two types of divided pieces 13.

  Further, the closer to the tire equator C, the smaller the complex elastic modulus E * of the divided piece 13 of the present embodiment is set. Specifically, the complex elastic modulus E * b2 of the inner divided piece 13B is set smaller than the complex elastic modulus E * b1 of the outer divided piece 13A. That is, the complex elastic modulus E * of the base portion 12 satisfies the relationship of inner divided piece 13B <outer divided piece 13A <outer portion 12A.

  In such an inner portion 12B, the inner divided piece 13B, which is less rigid than the outer divided piece 13A, can mainly receive the ground load during straight traveling and effectively absorb the input from the road surface. Further, since the rigidity of the base portion 12 increases smoothly from the tire equator C toward the outer side in the tire axial direction, the occurrence of cornering force according to the slip angle, for example, during a transition from straight running to turning It will change linearly and handling stability will be greatly improved.

  The complex elastic modulus E * of each of the divided pieces 13A and 13B can be appropriately set as long as it is within the above range of the complex elastic modulus E * b of the inner portion 12B, but the complex elastic modulus E * b1 of the outer divided piece 13A is If it is too small, the change in rigidity with the outer portion 12A becomes excessive, and the steering feeling at the time of transition from straight running to turning may be deteriorated. From such a viewpoint, the complex elastic modulus E * b1 of the outer divided piece 13A is preferably 5 MPa or more, more preferably 10 MPa or more. Similarly, the complex elastic modulus E * b2 of the inner divided piece 13B is preferably 2 MPa or more, more preferably 5 MPa or more.

  Further, the width W3 in the tire axial direction of the inner divided piece 13B can be set as appropriate, but if it is too small, the input from the road surface may not be absorbed effectively. On the other hand, if it is too large, the ratio of the outer divided pieces 13A becomes small and the steering feeling may be deteriorated. From such a viewpoint, the width W3 of the inner divided piece 13B is preferably 0.2 times or more, more preferably 0.3 times or more, and preferably 0.3 times or more the width W2 of the inner portion 12B in the tire axial direction. 0.7 times or less, more preferably 0.6 times or less are desirable.

  Moreover, the inner side part 12B can also enlarge the complex elastic modulus E * as the division | segmentation piece 13 near the tire equator C contrary to the said embodiment. In this case, the complex elastic modulus E * b of the base portion 12 satisfies the relationship of the outer divided piece 13A <the inner divided piece 13B <the outer portion 12A.

  In such an embodiment, the inner divided piece 13B has a larger complex elastic modulus E * than the outer divided piece 13A, so that the transient characteristics of cornering force during turning and the stability during lane change are improved. This is desirable in terms of

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

Pneumatic tires having the basic structure shown in FIG. 1 and a base portion having the specifications shown in Table 1 were manufactured, and their performance was tested. The common specifications are as follows.
Tire size: 225 / 55R17
Rim size: 17 × 7.5J
Tread contact width W1: 174mm
Tire cross-section height H1: 122mm
Loss tangent tan δ of cap part: 0.20
Complex elastic modulus E * of the cap part: 6.6 MPa
Total thickness of tread rubber at tire equator T1: 10.0mm
Base part thickness T2 at the tire equator: 2.0mm

Further, Table 2 shows the blending A of the outer part and the blending B of the inner part in Example 5. Details are as follows.
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): VCR412 manufactured by Ube Industries, Ltd.
Carbon (N351): Seest NH manufactured by Tokai Carbon Co., Ltd.
Carbon (FEF): Diamond Black E (FEF, N2SA: 41 m2 / g, DBP oil absorption: 115 ml / 100 g) manufactured by Mitsubishi Chemical Corporation
Stearic acid: Zinc oxide manufactured by Nippon Oil & Fats Co., Ltd .: Two types of zinc oxide manufactured by Mitsui Metal Mining Co., Ltd. Anti-aging material: Antigen 6C (N- (1,3-dimethylbutyl) manufactured by Sumitomo Chemical Co., Ltd. ) -N'-phenyl-p-phenylenediamine)
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Vulcanization accelerator NS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Insoluble sulfur: Mukuron OT manufactured by Shikoku Chemical Industry Co., Ltd.
In addition, about another Example, the outer part and inner part from which loss tangent tan-delta and complex elastic modulus E differ can be obtained by increasing / decreasing the ratio of the said chemical | medical agent suitably.
The test method is as follows.

<Rolling resistance performance>
Using a rolling resistance tester, rolling resistance was measured under the following conditions. Evaluation was made with an index with Comparative Example 1 as 100. The larger the value, the smaller the rolling resistance and the better.
Internal pressure: 230 kPa
Load: 4.5kN
Speed: 80km / h

<Tire mass>
The mass per tire was measured and displayed as an index with Comparative Example 1 taken as 100. The larger the value, the lighter.

<Ride comfort>
The test tire is assembled on the rim, filled with 230 kPa of internal pressure, and mounted on four wheels of a domestic FR automobile with a displacement of 2500 cc. The road was covered with pebbles). Then, the driver's sensuality was comprehensively evaluated for ruggedness, push-up and damping. The evaluation was expressed as an index with Comparative Example 1 as 100. The larger the value, the better.

<Pinch-cut performance>
With respect to an iron projection having a height of 110 mm, a width of 100 mm, and a length of 1500 mm provided on the side of the test road, the vehicle on which the test tires are mounted under the above conditions is set to 15 ° with respect to the length direction of the projection. A protrusion overpass test was conducted in which the protrusion was entered at an angle of At this time, the approach speed was sequentially increased in steps of 15 km / h to 1 km / h, and the speed when puncture occurred was displayed as an index with Comparative Example 1 being 100. The larger the value, the better.

<Flat spot resistance>
Each sample tire was assembled on the rim, filled with an internal pressure of 200 kPa, and run on a drum tester having a diameter of 1.7 m at a longitudinal load of 4.5 kN and a speed of 120 km / h for 2 hours, and then a load of 6.4 kN. The ground was placed on a flat surface and allowed to cool naturally. Thereafter, the vehicle was run again under the above conditions, and the time until force variation (vibration) was settled was measured. The evaluation was expressed as an index with Comparative Example 1 as 100. The larger the value, the better.

<Horizontal storage performance>
Each test tire was stored for 14 days in a state where 10 tires were horizontally stacked on the ground (with the tire rotation axis vertical) without being mounted on the rim. Thereafter, the remaining deformation of the buttress portion of the lowermost test tire was observed and displayed as an index with the reciprocal of the deformation amount of Comparative Example 1 being 100. The larger the value, the better.

<Steering stability>
Each test tire is assembled to the above rim under the above conditions and mounted on the above vehicle, and the vehicle runs on a dry asphalt road test course to check straightness, stability during turning, vehicle behavior during braking, etc. Overall evaluation was conducted by sensory evaluation by a professional driver. The results are displayed as an index with the score of Example 1 being 100. The larger the value, the better.
Tables 1 and 2 show test results and the like.

  As a result of the test, it was confirmed that the pneumatic tire of the example can improve the rolling resistance performance while maintaining the riding comfort.

2 Tread part 2G Tread rubber 3 Side wall part 6 Carcass 7 Belt layer 11 Cap part 12 Base part 12A Outer part 12B Inner part

Claims (6)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a belt layer disposed outside the carcass in the tire radial direction and inside the tread portion, and disposed outside the tire layer in the tire radial direction. With tread rubber made,
The tread rubber includes a cap portion forming an outer surface of the tread portion, and a base portion made of a rubber material disposed inward in the tire radial direction of the cap portion and having a loss tangent tan δ of 0.03 to 0.10. Including
The base portion is disposed on the outermost side in the tire axial direction, and includes at least a pair of outer side portions covering the outer end of the belt layer in the tire axial direction, and an inner side portion extending between the outer side portions,
A pneumatic tire, wherein the outer part has a complex elastic modulus E * a of 20 MPa to 50 MPa, and the inner part has a complex elastic modulus E * b of 2 MPa to 15 MPa. The outer portion extends outward in the tire axial direction beyond the outer end of the belt layer, extends inward in the tire radial direction along the carcass,
2. The pneumatic tire according to claim 1, wherein the outer end of the outer portion in the tire axial direction has a height in a tire radial direction from a bead base line that is 0.6 to 0.9 times a tire cross-sectional height. .   The pneumatic tire according to claim 1, wherein the inner portion has a width in the tire axial direction that is 0.4 to 1.1 times a tread contact width.   The pneumatic tire according to any one of claims 1 to 3, wherein the inner portion is formed with a plurality of divided pieces having different complex elastic moduli E * b arranged in the tire axial direction.   The pneumatic tire according to claim 4, wherein the divided piece has a smaller complex elastic modulus E * b as it is closer to the tire equator.   The pneumatic tire according to claim 4, wherein the divided piece has a higher complex elastic modulus E * b as it is closer to the tire equator.

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