JP2002029215A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire improved in rolling resistance and wet braking performance of the tire to be compatible with each other by designing the optimum grounding form and the material quality constitution of the tire. SOLUTION: A tread of the tire is formed by a two-layer structure of a cap layer and a base layer, a groove extending in the circumferential direction is disposed in the tread part of the tread, and the tire is characterized by setting the negative rate to 15 to 30%, setting the rubber thickness of the base layer to 10% or more of the tread thickness, lowering energy loss of the base layer rubber, and setting the rectangle rate 100×(La+Lb)/2/Lc of the grounding form of the tread surface of the tread to 65 to 95%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire having improved braking performance on wet road surfaces without increasing the rolling resistance of the tire.

[0002]

2. Description of the Related Art In order to reduce the rolling resistance of a tire, it is necessary to mix the tread rubber with a material having a low energy loss. On the other hand, in order to improve the braking performance, especially on a wet (wet) road surface. However, it is necessary to use the same material for the tread rubber in a high energy loss composition, which is inconsistent with each other. As means for solving this problem, conventionally, a so-called (cap / cap layer) in which a high-loss compounded rubber layer having good damping properties is formed as a surface layer (cap layer) and a low-loss compounded rubber having low rolling resistance is formed as a base layer (base layer). Base) A tread formed from a two-layer structure has been proposed and put to practical use, but has not yet reached a sufficiently satisfactory state.

[0003] That is, if low-loss rubber is used for the cap layer in order to reduce the rolling resistance, the braking performance on a wet road surface is reduced. There was a problem that the deformation of the belt layer was increased and the rolling resistance was deteriorated.
Providing pneumatic tires that achieve both rolling resistance and wet braking performance, and both have reached a satisfactory level,
Traditionally, it was considered difficult.

[0004]

SUMMARY OF THE INVENTION In consideration of the above facts, the present invention examines the contact behavior of the tread pattern and the compatibility between the tread two-layer structure and optimizes the contact shape and material structure characteristics. It is another object of the present invention to provide a pneumatic tire having improved tire rolling resistance and wet braking performance both practically and economically.

[0005]

According to the first aspect of the present invention, a tread of a tire is formed with a two-layer structure of a cap layer / base layer, and a plurality of treads extending in a circumferential direction are provided on a tread portion of the tread. In a pneumatic tire having a rib pattern provided with circumferential grooves, (1) a negative rate of a tread surface pattern of the tread is 15 to 30%, and (2) a thickness of a base layer rubber of the tread is such that: (3) The rubber composition in which the energy loss of the base layer rubber of the tread is lower than the energy loss of the cap layer rubber, and (4) the tire is incorporated into a standard rim. Lc is the ground contact length at the center of the tire width direction when the tire is grounded by applying a normal internal pressure and applying a 100% load, and the right and left ground lengths at a position of 80% of the maximum ground width are distributed from the center. La, When Lb, rectangular ratio 100 × the contact shape of the tread surface of the tread (La + Lb)
/ 2 / Lc is 65 to 95%.

Here, the negative ratio of the tread tread pattern is a ratio (%) of the sum of all groove areas to the developed area of the tread pattern. In addition, as shown in the footprint of FIG. 2, the rectangular ratio of the tread tread's ground contact shape is determined by incorporating a tire into a standard rim and filling the tire with a regular internal pressure.
Assuming that the contact length at the center of the tire width direction when a 00% load is applied and the contact is made is Lc, and the left and right contact lengths at a position 80% of the maximum contact width from the center are La and Lb, Rectangular ratio (%) of grounded shape = 100 × (La + Lb) /
It is calculated as 2 / Lc.

Next, the operation of the pneumatic tire according to the first aspect will be described. The pneumatic tire according to this aspect has a rib pattern in which a plurality of circumferential grooves extending along a circumferential direction are provided on a tread portion of a tread of the tire, and a negative rate of the tread pattern is 15% or more. Therefore, when the vehicle travels on a wet road surface, the drainage function works well, and the braking performance on the wet road surface is improved. If the negative rate is less than 15%, the proportion of grooves functioning as drainage channels on the tread pattern is too small, and thus the effect of improving the wet braking performance to a sufficient level is lacking. If the negative rate exceeds 30%, the (uneven) abrasion resistance, steering stability, ride comfort, road noise, etc., deteriorate.

Further, when the tire is incorporated into a standard rim and filled with a regular internal pressure, a 100% load is applied and the tire is grounded,
The rectangular ratio of the ground contact shape of the tread tread 100 × (La + L
b) Since / 2 / Lc is 65% or more, that is, since the ground contact shape called a so-called footprint is not an elliptical shape but a rectangular shape, not only the center portion of the tread surface of the tire but also the entire road surface including the shoulder portion. The grip is wide and firm, and the acceleration and braking effects are good and the braking performance is excellent not only on a dry road surface but also on a wet road surface.
The rectangular ratio of the tread tread's ground contact shape is 100 × (La + L
b) If / Lc is less than 65%, the effect of improving the above-mentioned wet braking performance is small, while if the rectangularity of the ground contact shape exceeds 95%, the deformation of the reinforcing belt layer becomes too large, and the rolling resistance deteriorates. Come. Here, the rib pattern of the present invention defines a basic skeleton, and further improves the wet braking performance by appropriately adding lateral grooves, inclined grooves, narrow grooves, side grooves, sipes, and the like. Of course, it is possible to improve or adjust the (uneven) abrasion resistance, riding comfort, road noise, steering stability and the like.

In the tire according to the present invention, the tread has a two-layer structure of a cap layer and a base layer, and the rubber thickness of the base layer is at least 10% of the rubber thickness of the entire tread.
Since the rubber of the base layer is a compound rubber having a low energy loss, the tire has low energy loss (heat generation) in a repeated deformation cycle of the tread base layer when the tire runs, and has low rolling resistance and good fuel economy. If the rubber thickness of the base layer is less than 10% of the rubber thickness of the entire tread, the above-mentioned low energy loss effect contributes too little to the whole. The upper limit of the base layer rubber thickness in the entire tread varies depending on the type and use of the tire,
Generally, it is desirable that the ratio does not exceed 80 to 90% in consideration of the tread wear life.

The rubber material of the cap layer of the tread having a two-layer structure has a relatively high energy loss characteristic in order to secure a coefficient of friction with a dry and wet road surface. The composition and material properties are appropriately adjusted in consideration of reducing damage and suppressing road noise.

According to a second aspect of the present invention, in the pneumatic tire according to the first aspect, the tread is positioned at a central region by a circumferential groove which is initially located more than 50% in the width direction from the center in the width direction of the tread tread surface. And the shoulder region, the average value of the ratio d / D of the base layer rubber thickness d to the total tread thickness D in the shoulder region is the base layer rubber thickness d to the total tread thickness D in the central region. Is 1.5 to 2.0 times the average value of the ratio d / D. Here, as shown in FIGS. 2 and 3, the total thickness D of the tread and the rubber thickness d of the base layer are all set in the normal direction of the crown curved surface of the tread and the radially outermost layer of the belt layer from the ground surface of the tread. It measures the distance of the belt to the coated rubber interface.

Next, the operation of the pneumatic tire according to claim 2 will be described.

Since the rectangular ratio of the ground contact shape of the tread surface of the tire of the present invention is 65 to 95%, the deformation of the reinforcing belt layer is relatively large. However, in the present invention,
In the shoulder area of the tread tread, the overall tread thickness D
The average value of the ratio d / D of the base layer rubber thickness d to
It is larger than the average value of d / D in the central area (1.5 to 2.
By doing so, the rolling resistance can be reduced even though the rectangular ratio of the ground contact shape is high. When the d / D in the shoulder region is less than 1.5 times that of the central region, the effect of improving the rolling resistance has too little effect on the whole. There is a concern that the deformation is too large, which not only increases the rolling resistance but also deteriorates steering stability and road noise.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the pneumatic tire of (1), the dynamic storage elastic modulus (E ′) of the tread base layer rubber is higher than the dynamic storage elastic modulus (E ′) of the cap layer rubber, and the loss tangent (tan δ) of the base layer rubber is Loss tangent (tan) of the cap layer rubber
δ). Here, the dynamic storage modulus (E ′) and the loss tangent (tan δ) are defined by JI
The viscoelasticity value measured by the dynamic viscoelasticity test method specified in K7198 of S. The storage elastic modulus (real part) and energy loss (or heat generation characteristics) of a rubber material under dynamic deformation
Is represented.

Next, the operation of the pneumatic tire according to the third aspect will be described. Generally, the energy loss (heat generation) of a viscoelastic body under a constant load is inversely proportional to the elasticity term of the material constant and proportional to the viscosity term. Therefore, in the pneumatic tire described in this section, the dynamic storage elastic modulus (E ') of the base layer rubber of the tread is higher than the dynamic storage elastic modulus (E') of the cap layer rubber, and the loss tangent of the base layer rubber is reduced. Since (tan δ) is set smaller than the loss tangent (tan δ) of the cap layer rubber, the energy loss under a constant load (heat generation)
Is small, and a tire having low rolling resistance is obtained.

[0016] The invention according to claim 4 is the invention according to claims 1 to 3.
Is characterized in that the negative rate of the tread tread pattern is 20 to 24%. According to the invention of this item in which the negative rate of the tread tread pattern is set in a more preferable range of 20 to 24%, tires such as drainage (wet braking) and abrasion resistance, handling stability, ride comfort, road noise, etc. It is possible to provide a high-performance tire having a good balance of various performances.

[0017] The invention according to claim 5 is the invention according to claims 1 to 3.
Is characterized in that the thickness of the base layer rubber of the tread is 13% or more of the total thickness of the tread rubber. According to the invention of the present item in which the thickness of the base layer rubber having small heat generation and small energy loss is more preferably set to 13% or more, a high-performance tire having further reduced rolling resistance can be provided.

The invention according to claim 6 is the invention according to claims 1 to 3
Is characterized in that the thickness of the base layer rubber of the tread is 1.4 to 2.0 mm. Especially for radial tires for passenger cars, the gauge of the base layer rubber with low heat generation and energy loss is 1.4 to
According to the invention of the present item set in a preferable range of 2.0 mm, a high-performance radial tire having particularly small rolling resistance can be provided.

The invention according to claim 7 is the invention according to claims 1 to 3
In the pneumatic tire, the rectangular ratio of the ground contact shape of the tread surface of the tread is 100 × (La + Lb) / 2 / Lc of 70 to 8.
2%. According to the invention of this section in which the rectangular ratio of the tread contact shape is more preferably 70 to 82%, it is possible to provide a tire excellent in wet braking performance with low rolling resistance and better road surface grasping force.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a pneumatic tire according to the present invention will be described with reference to FIGS.

As shown in FIG. 1, the tread 5 of the pneumatic tire of the present invention is formed in a two-layer structure of a cap layer 7 and a base layer 8, and is provided on a tread surface portion of the tread along a circumferential direction. A pneumatic tire having a rib pattern in which circumferential grooves (three are illustrated in the figure) are provided,
(1) The negative rate of the tread tread pattern is 15
(2) the rubber thickness d of the base layer of the tread is 10% or more of the rubber thickness D of the entire tread; and (3) the energy loss of the base layer rubber 8 of the tread is a cap. The rubber composition is lower than the energy loss of the rubber layer 7, and (4) As shown in the footprint of FIG.
Lc is the contact length at the center of the tire width direction when a 00% load is applied, and La is the right and left contact length at a position 0.8 Wmax at 80% of the maximum contact width Wmax distributed from the center. The pneumatic tire is characterized in that a rectangular ratio 100 × (La + Lb) / 2 / Lc of the ground contact shape of the tread surface of the tread is 65 to 95%.

Here, the 100% load is the maximum load (maximum load capacity) of a single wheel in the applicable size (ply rating) described in the following standard, and the normal internal pressure is described in the following standard. Is the air pressure corresponding to the maximum load (maximum load capacity) of a single wheel in the applicable size, and the standard rim is the standard rim in the applicable size described in the following standard.

The standard is determined by an industrial standard effective in a region where the tire is manufactured or used. For example,
In the United States, the “The Tire and Rim Association
Inc.'s Year Book, and in Europe, "European T
Standards Manu of ire and Rim Technical Organization
al ”in Japan and the Japan Automobile Tire Association's“ JATMA
Year Book ”.

Another preferred pneumatic tire of the present invention
One embodiment will be described with reference to FIG. As can be seen from the right half cross-sectional view of FIG. 3, the tread is defined as the central region by the circumferential groove 9 which is initially located more than 50% in the width direction from the center in the width direction of the tread tread of the pneumatic tire of the present invention. When divided into the shoulder region, the average value of the ratio d / D of the base layer rubber thickness d to the total tread thickness D in the shoulder region is the ratio of the base layer rubber thickness d to the total tread thickness D in the central region. A pneumatic tire characterized by being 1.5 to 2.0 times the average value of the ratio d / D.

The internal (case) structure of the pneumatic tire of the present invention is not particularly limited, and may be the same as that of a normal general radial tire according to the size and use. Is omitted. (Operation) In the pneumatic tire according to the embodiment of the present invention, the rectangular ratio of the ground contact shape of the tread tread is 100 × (La + Lb) /
By setting 2 / Lc in the range of 65 to 95%, that is, by increasing the rectangular ratio (footprint close to a rectangle), the force for grasping the road surface as a whole is strong, and the braking performance on a wet road surface is excellent.
At the same time, the reinforcing belt layer undergoes relatively large deformation, but the rolling resistance is reduced by arranging thick rubber with low energy loss on the base layer rubber in the shoulder region with a tread having a two-layer structure. ing.

[0026]

EXAMPLE In order to confirm the effect of the present invention, a size 17
For 5 / 80R14 radial tires, three types of tires of the example to which the present invention was applied and a tire of a comparative example were produced.
A comparative test of rolling resistance and wet road braking was performed. The negative rate of the tread pattern, the thickness of the base layer rubber, and the energy loss (relative value of tan δ) of the base layer rubber were 22% and 1.6 m for both the example tire and the comparative example tire.
m and 0.6. The tire of the example is the pneumatic tire of the embodiment illustrated in FIG.
The average value of the ratio d / D of the base layer rubber thickness d to the total tread thickness D in the shoulder region is 0.1%.
The average value of the same ratio d / D in the central region is 0.11 and the ratio between the two is 1.6 to 2.0 times. In the tire of the comparative example, both the shoulder region and the central region,
The ratio d / D of the thickness d of the base layer rubber to the total thickness D of the tread is 0.11, and the ratio between the two is 1.0. A comparative test was conducted on these four tires,
Table 1 shows the results.

[0027]

[Table 1]

As a result of the test, the tires 1 to 3 of the embodiment to which the present invention is applied have lower rolling resistance and a shorter braking distance on a wet road surface than the tire of Comparative Example 1, that is, excellent braking performance. It turned out to be a high performance pneumatic tire with improved rolling resistance.

The test method performed in the present embodiment is as follows.

<Rolling Resistance Coefficient> A test was performed in accordance with SAE J1269 to calculate a rolling resistance coefficient.

<Actual braking distance on wet road surface> The test tire was mounted on a test passenger car and tested on a wet road surface test course.
The braking distance was measured at an initial speed of 100 km / h.

[0032]

According to the present invention, it is possible to solve the conventional problems, and to provide a tread structure and material which have greatly improved tire rolling resistance and braking performance on a wet road surface, and are greatly improved. As a result, it has become possible to provide an economical and safe pneumatic tire with low rolling resistance and good braking performance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pneumatic tire according to one embodiment of the present invention.

FIG. 2 is a ground contact shape (footprint) diagram of a tread tread surface of a pneumatic tire according to an embodiment of the present invention.

FIG. 3 is a sectional view of a pneumatic tire according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 bead core 2 carcass 3 outermost belt 4 belt 5 tread 6 side 7 cap layer 8 base layer 9 circumferential groove D rubber thickness of entire tread d rubber thickness of base layer

Claims (7)

[Claims] 1. An air having a rib pattern in which a tread of a tire is formed in a two-layer structure of a cap layer / base layer, and a plurality of circumferential grooves extending in a circumferential direction are provided on a tread portion of the tread. (1) The negative rate of the tread tread pattern is 15
(2) the thickness of the base layer rubber of the tread is 10% or more of the total thickness of the tread rubber; and (3) the energy loss of the base layer rubber of the tread is:
The rubber compounding is lower than the energy loss of the cap layer rubber. (4) Grounding at the center in the tire width direction when the tire is built into a standard rim, filled with a normal internal pressure, and grounded by applying a 100% load. The length Lc is distributed from the center, and the right and left contact lengths at the position of 80% of the maximum contact width are La and Lb.
Then, the rectangular ratio of the ground contact shape of the tread tread is 10
0 × (La + Lb) / 2 / Lc is 65 to 95%,
A pneumatic tire, characterized in that: 2. When the tread is divided into a central region and a shoulder region by a circumferential groove that is initially located in the width direction exceeding 50% from the center of the tire tread surface in the width direction of the tire, the total thickness of the tread in the shoulder region is obtained. The average value of the ratio d / D of the base layer rubber thickness d to the thickness D is 1.5 to 2. the average value of the ratio d / D of the base layer rubber thickness d to the total tread thickness D in the central region. The pneumatic tire according to claim 1, wherein the pneumatic tire is 0 times. 3. The dynamic storage elastic modulus (E ′) of the base layer rubber of the tread is higher than the dynamic storage elastic modulus (E ′) of the cap layer rubber, and the loss tangent (tan) of the base layer rubber is
The pneumatic tire according to claim 1 or 2, wherein δ) is smaller than a loss tangent (tan δ) of the cap layer rubber. 4. The negative ratio of the tread pattern of the tread is 20 to 24%.
4. The pneumatic tire according to any one of items 1 to 3. 5. The thickness of the base layer rubber of the tread,
The pneumatic tire according to any one of claims 1 to 3, wherein the thickness is 13% or more of the thickness of the tread rubber. 6. The thickness of the base layer rubber of the tread,
The pneumatic tire according to any one of claims 1 to 3, wherein the diameter is 1.4 to 2.0 mm. 7. The air according to claim 1, wherein a rectangular ratio of a ground contact shape of the tread surface of the tread, 100 × (La + Lb) / 2 / Lc, is 70 to 82%. Containing tires.