JP2009262795A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire having superior wear resistance performance and very low resistance to rolling. <P>SOLUTION: This pneumatic tire includes a belt constituted by arranging inclined belt layers composed of at least two layers each and constituted by covering many cords extended in the direction of inclination for an equatorial plane of the tire with rubber on an outer side in the radial direction of a crown part of a carcass extending over a pair of bead parts in a troidal shape by using the carcass as a skeleton in order and arranging a tread on an outer side in the radial direction of the belt. A ratio of difference BD between diameters of a central part in the direction of width of the outermost side layer and an end part in the direction of width to half width HBW of the outermost side layer of the inclined belt layer, namely, BD/HBW, in cross section in the direction of width of the tire being mounted on an application rim is 0.10 or more and 0.13 or less. The tread has higher modulus of elasticity of rubber in a central zone in the direction of width than modulus of elasticity of rubber in both of side zones of the central zone. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire having excellent wear resistance and low rolling resistance.

In recent years, development of products with a smaller environmental load has been actively conducted. This is due to environmental problems such as global warming, and tires are no exception. With respect to this tire, in order to cope with the environmental problem, it is important to secure performance that contributes to reducing fuel consumption of the automobile. One means for achieving this is to reduce the rolling resistance of the tire, and various technical developments have been made in the past.
The following introduces some conventional improvements.

  First, it is known that a large amount of tire rolling resistance occurs in the rubber of the tread portion. As a direct improvement method, it is effective to change the rubber used for the tread portion to one having a small loss tangent (tan δ). However, this method is also known to sacrifice other performance of the tire, such as wear resistance. On the other hand, a method of reducing the thickness of the tread can be easily considered in order to reduce the rubber that is a source of increasing rolling resistance. However, in this case, it is problematic that a sufficient life until the tire wears cannot be secured.

Further, Patent Document 1 proposes reducing the rolling resistance by devising the cross-sectional shape of the tire. With this proposal, it is possible to reduce rolling resistance while ensuring wear resistance.
JP 2006-1360 A

However, when considering environmental considerations in recent years, further reduction of rolling resistance is desired.
SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire that further reduces rolling resistance while ensuring excellent wear resistance.

Now, much of the rolling resistance of the tire is due to strain energy loss generated in the tread rubber. When the phenomenon in the tread portion was analyzed in detail, it was found that the strain energy loss due to shear deformation (circumferential direction and width direction) was dominant, and the strain energy loss was particularly large in the shoulder portion.
Therefore, the inventors have rounded the crown portion of the tread, so that the ground contact width of the tire becomes narrow, and if the ground contact width can be narrowed, the volume of rubber deformed in the tread portion is reduced, and the strain energy loss is reduced. It has been found that the rolling resistance can be reduced.

  In addition, the inventors have intensively studied to further reduce rolling resistance, and as a result, when the tread is divided into a central region in the width direction and both side regions of the central region, the elasticity of the rubber in the central region and both side regions is determined. The inventors have found that regulating the rate is extremely effective, and have completed the present invention.

The gist of the present invention is as follows.
(1) Using a carcass straddling a toroidal shape between a pair of bead portions, a large number of cords extending in a direction inclined with respect to the equatorial plane of the tire are coated with rubber on the radially outer side of the crown portion of the carcass A pneumatic tire having a belt in which at least two inclined belt layers are arranged in order, and a tread is arranged radially outward of the belt,
The ratio of the diameter difference BD between the center portion in the width direction of the outermost layer and the end portion in the width direction with respect to the half width HBW of the outermost layer of the inclined belt layer in the tire width direction cross section in a state where the tire is mounted on the applicable rim. BD / HBW is 0.10 or more and 0.13 or less,
In the tread, the elastic modulus of the rubber in the central region in the width direction is higher than the elastic modulus of the rubber in both side regions of the central region.
A pneumatic tire characterized by that.

  Here, the state in which the tire is mounted on the applicable rim is a state in which the tire is incorporated in a standard rim or other applicable rim stipulated in the Japan Automobile Tire Association Standard (JATMA), without applying internal pressure, or about 30 kPa. This means a state with an extremely low internal pressure of up to.

(2) The ratio of the shortest distance SWh between the line segment drawn parallel to the tire rotation axis at the maximum width position of the tire and the line segment drawn parallel to the tire rotation axis at bead toe with respect to the tire cross-section height SH SWh / SH is 0.55 or less, The pneumatic tire as described in said (1) characterized by the above-mentioned.

(3) The ratio GB / GA of the tread rubber thickness GA at the center in the width direction of the outermost layer of the inclined belt layer and the tread rubber thickness GB at the end in the width direction of the outermost layer of the inclined belt layer is 0. The pneumatic tire according to (1) or (2) above, wherein the pneumatic tire is 75 or more.

(4) The portion showing the minimum curvature in the carcass line extending from the widthwise end of the outermost layer of the inclined belt layer to the inside of the bead core is located radially inward from the 1/2 point of the tire cross-section height SH. The pneumatic tire according to any one of the above (1) to (3), wherein

  According to the present invention, it is possible to provide a pneumatic tire having excellent wear resistance and extremely low rolling resistance.

Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 1 is a cross section in the width direction of a tire half according to the present invention. A cord that extends in a toroidal manner between a pair of bead cores 1 and has a carcass 2 made of a radial arrangement ply of cords and that extends radially outward of the crown portion of the carcass 2 in a direction inclined with respect to the equatorial plane CL of the tire Cords of which at least two layers, in the illustrated example, two inclined belt layers 3a and 3b, which are coated with rubber, are arranged, and further extend along the equatorial plane CL of the tire on the radially outer side of the inclined belt layer 3a. A circumferential belt layer 4 of at least one layer, in the example shown in the figure, is disposed by covering a large number of these with rubber, and a tread 5 is disposed on the outer side in the radial direction of these belts.

Such a tire 6 is mounted on the application rim 7 and used. Here, in the tire width direction cross section in a state where the tire 6 is mounted on the applied rim 7, as shown in FIG. 1, the center in the width direction of the outermost layer 3a with respect to the half width HBW of the outermost layer 3a of the inclined belt layer. Ratio BD / HBW of diameter difference BD between the portion (equatorial plane CL) and the width direction end portion is 0.10 ≦ BD / HBW ≦ 0.13
It is important to be.

This definition means that the inclined belt layer 3 has a large diameter difference in the width direction. This is to round the crown portion of the tread, and as a result, the ground contact width of the tire is narrowed. If the ground contact width can be reduced, the volume of rubber deformed at the tread portion is reduced, and strain energy loss can be reduced. However, if the ground contact width is too narrow, the wear resistance deteriorates.
That is, when the ratio BD / HBW is less than 0.10, the ground contact width becomes wide and it becomes difficult to reduce the strain energy loss. On the other hand, if the ratio BD / HBW exceeds 0.13, the ground contact width becomes too narrow and the wear resistance performance is deteriorated.

As shown in FIG. 1, in the tire according to the above-described shape, the tread 5 includes a tread center portion 5C corresponding to the central region in the width direction, and tread shoulder portions 5S ₁ , 5S ₂ corresponding to both side regions of the central region in the width direction. (tread shoulder portion 5S ₁ is not shown) when partitioned, by reducing the circumferential shear strain of the tread to increase the eccentric deformation of the tread center portion 5C, thereby reducing the rolling resistance. In addition, since the crown portion is rounded, the widths of the tread shoulder portions 5S ₁ and 5S ₂ are narrowed, and as a result, the area having a large shear strain in the tread cross section is reduced. As a result, rolling resistance is reduced.

Here, when the strain energy generated in the tread portion of the tire having the shape shown in FIG. 1 was analyzed in detail using the finite element method, the ratio of the strain energy in the tread portion was as shown in FIG.
According to FIG. 2, the strain energy generated in the tread portion is 40% in the tread center portion and 60% in the tread shoulder portion, and further reducing the strain energy in the tread shoulder portion is effective in reducing rolling resistance. I understood that.

Therefore, in the present invention, the elastic modulus of the rubber of the tread center portion 5C is set to be higher than the elastic modulus of the rubber of the tread shoulder portions 5S ₁ and 5S ₂ . Hereinafter, the reason will be described.
The boundary between the tread center portion 5C and the tread shoulder portions 5S ₁ and 5S ₂ is a position 2/3 from the tire equator CL side of the distance HCW in the contact surface from the tire equator CL to the end of the contact width. As a base point, it exists in a region of ± 10% in the tread width direction, a region on the tire equator CL side from this boundary is a tread center portion 5C, and a region outside the tread width direction from this boundary is a tread shoulder portion 5S ₁ , respectively. It is defined as 5S _2.
As specified in JATMA, the ground contact width means that the tire is mounted on the applicable rim, set to the specified air pressure, placed in a stationary state perpendicular to the flat plate, and a load of 80% of the maximum load capacity is applied. This is the maximum linear distance in the tire axial direction on the contact surface with the flat plate.

The rolling resistance (RR) of the tire is considered to be obtained by multiplying the strain energy (SE) by the loss tangent (tan δ) of the tread rubber and the volume (Vol) of the tread rubber. That is,
RR = SE × tan δ × Vol
Given in. When the tread portion is regarded as an elastic body, the strain energy (SE) of the elastic body is given by the following equation using stress (σ) and strain (ε).
SE = (1/2) × σ × ε
Therefore, it can be seen that stress (σ) and strain (ε) may be reduced in order to reduce rolling resistance without changing the loss tangent (tan δ) and volume (Vol) of the tread rubber.
If the elastic body is a linear elastic body, the elastic modulus (E) is given by the following equation.
E = σ / ε
Therefore, the strain energy (SE) of the elastic body can be deformed as in the following formula (1) or (2).
SE = (1/2) × σ ² × (1 / E) (1)
SE = (1/2) × E × ε ² (2)

When the tread shoulder portions 5S ₁ and 5S ₂ are grounded during load rolling of the tire, shear strain mainly occurs in the cross section in the width direction. This shear strain is caused by deformation when the tread shoulder portion comes into contact with the ground, and the displacement is determined by the crown shape, and the crown shape is considered to be constant in the same type of tire. When the crown shape is constant, that is, the strain (ε) is constant, it can be seen from the above formula (2) that the strain energy (SE) can be reduced by reducing the elastic modulus (E). Therefore, in the present invention, by setting the elastic modulus of the rubber of the tread shoulder portions 5S ₁ and 5S ₂ to be low, strain energy is reduced, which further contributes to reduction of rolling resistance.

  On the other hand, the tread center portion 5C is crushed by the contact pressure, and strain energy is generated due to a constant-stress circumferential shear that is supported by belt tension, which leads to generation of rolling resistance. That is, since the stress (σ) is constant, it can be seen that when the elastic modulus (E) is increased, the strain energy (SE) can be reduced from the above equation (1). Therefore, in the present invention, by setting the elastic modulus of the rubber of the tread center portion 5C to be high, the strain energy is reduced, which further contributes to the reduction of rolling resistance.

As described above, by setting the elastic modulus of the rubber of the tread center portion 5C to be high and setting the elastic modulus of the rubber of the tread shoulder portions 5S ₁ and 5S ₂ to be low, the strain energy is reduced and the rolling resistance is further reduced. I explained that it contributed. Here, it is important to make the elastic modulus of the rubber of the tread center portion 5C higher than the elastic modulus of the rubber of the tread shoulder portions 5S ₁ and 5S ₂ , and it is effective if there is even a slight difference in elastic modulus.
However, it was found that when the difference in the elastic modulus of the rubber between the tread center portion 5C and the tread shoulder portions 5S ₁ and 5S ₂ is 10% or more, the rolling resistance can be significantly reduced.
On the other hand, if the difference in elastic modulus is larger than 30%, there is a possibility that peeling is likely to occur between tread rubbers having different elastic moduli with a large input as in cornering.
For example, it has been confirmed that an effect is obtained when the elastic modulus of the rubber in the tread center portion is 2.7 MPa and the elastic modulus of the rubber in the tread shoulder portion is 2.4 MPa.

Further, in the example shown in FIG. 1, the tread center portion 5C and the boundary line between the tread shoulder portion 5S ₂ is tires equator CL are substantially parallel, tread shoulder portion 5S ₁ radially outward of the tread center portion 5C, 5S ₂ may be disposed, or conversely, the tread center portion 5C may be disposed on the radially outer side of the tread shoulder portions 5S ₁ and 5S ₂ .
However, it is most preferable that the tread shoulder portions 5S ₁ and 5S ₂ are arranged on the outer side in the radial direction of the tread center portion 5C (when the boundary line forms a letter C). This is because when a lateral force is applied from the tread surface during cornering, this force is particularly large outside the cornering, and the occurrence of cracks can be reduced at the contact portion of the boundary where the elastic modulus of the rubber changes. .

  Further, as shown in FIG. 1, a line segment drawn parallel to the tire rotation axis at the tire maximum width position D and a line segment drawn to the bead toe 10 parallel to the tire rotation axis with respect to the tire cross-section height SH. The ratio SWh / SH of the shortest distance SWh is preferably 0.55 or less. That is, when SWh / SH is 0.55 or less, the carcass ply has a line that hangs with a small curvature from the belt width direction end portion to the bead portion side. The belt tension at the center in the width direction increases. Then, as a result of suppressing the circumferential shear deformation that occurs between the stepped-in portion and the kicked-out portion in the ground plane, strain energy loss can be reduced.

  Furthermore, when both 0.10 ≦ BD / BW ≦ 0.13 and SWh / SH ≦ 0.55 are satisfied, the ground contact width is narrowed and the belt tension in the region is increased, so that the circumferential shear deformation is greatly reduced, Strain energy loss can be suppressed. SWh / SH is preferably 0.4 or more. This is because if SWh / SH is less than 0.4, the belt tension of the shoulder portion is lowered and it is difficult to suppress the wear of the shoulder portion.

Next, the ratio GB / GA between the tread rubber thickness GA at the center in the width direction of the outermost layer 3a of the inclined belt layer and the tread rubber thickness GB at the end in the width direction is preferably 0.75 or more. That is, the rolling resistance decreases as the tread rubber becomes thinner. However, if it is too thin, the wear resistance will deteriorate. Further, as described above, since the strain energy loss generated in the tread shoulder portion is large, reducing the tread rubber thickness of the tread shoulder portion is efficient in reducing rolling resistance. For that purpose, it is effective to have a distribution in the tread rubber thickness within a range of GB / GA of 0.75 or less. As a result, it is possible to achieve both reduction in rolling resistance and improvement in wear resistance. Become.
The ratio GB / GA is preferably 0.95 or less. Because if it exceeds 0.95, there is a possibility that improvement in heat generation durability and reduction in rolling resistance are not sufficiently achieved.

Furthermore, as shown in FIG. 3, a portion showing the minimum curvature in the carcass line extending from the widthwise end (see dotted line) of the outermost layer 3a of the inclined belt layer to the inside (see dotted line) of the bead core 1, an example shown in the figure It is preferable that R is located radially inward from the half point of the tire cross-section height SH.
That is, by setting the minimum curvature portion of the carcass line on the bead portion side, the carcass can be easily deformed on the bead portion side. As a result, deformation of the tread portion can be suppressed, and strain energy loss can be reduced.

  Inventive tires of size 225 / 45R17, conventional tires, and comparative tires were prototyped under the specifications shown in Table 1, and the wear resistance and rolling resistance of each test tire were measured. explain. The basic structure of each test tire is as shown in FIG. 1, and the inclined belt layers 3a and 3b are made of two layers in which steel cords arranged at an inclination angle of 24 ° with respect to the equator plane CL are crossed with each other. And further comprises a circumferential belt layer 4 of nylon cord.

  In the rolling resistance test, the test tire is mounted on a standard rim, the internal pressure is adjusted to 230 kPa, and then the rolling resistance of the axle is measured using a drum testing machine (speed: 80 km / h) with a steel plate surface with a diameter of 1.7 m. Ask for. This rolling resistance measurement was performed in accordance with ISO18164 using a smooth drum and a force type. The measurement results were indexed with the rolling resistance of a conventional tire as 100. It shows that rolling resistance is so small that this index | exponent is small. As an evaluation, a difference of 5% or more is regarded as a significant difference from the viewpoint of market superiority excluding errors. In particular, it can be said that it is a great effect when the rolling resistance is reduced by 10% or more.

In the wear resistance test, a rim-assembled test tire similar to the rolling resistance test was tested with an indoor drum tester (with a safety walk on the surface) with a diameter of 1.7 m, with a strip angle and a chamber angle of 0 °, and a speed of 80 km. The test was carried out at / h. The input is alternately repeated for 10 minutes without braking / driving and 0.1G for 10 minutes in the braking direction. Under these conditions, the wear weight (amount of worn rubber) after traveling 1200 km was indexed and evaluated in comparison with the conventional example. The smaller the wear weight, the better. If the difference is less than 5%, it is considered equivalent, and if there is a difference of 10% or more, it can be said that there is a remarkable difference. In this test method, since the worn weight is compared, the meaning of the wear resistance test is strong. However, tires with poor partial wear performance wear early, and can be detected in this test. That is, this view can be viewed from both sides of uneven wear resistance and wear resistance, but here is collectively referred to as wear resistance performance.

  From the results of Table 1, the conventional example has the tire shape and structure according to the present invention, and further, the elastic modulus of the rubber in the central region in the width direction of the tread is higher than the elastic modulus of the rubber in both side regions of the central region. It can be seen that the rolling resistance can be reduced while maintaining excellent wear resistance performance as compared with the tire and the comparative example tire.

  As described above, the ratio BD / HBW of the diameter difference BD between the center portion in the width direction of the outermost layer and the end portion in the width direction with respect to the half width HBW of the outermost layer of the inclined belt layer is set to 0.10 or more and 0.13 or less. By making the elastic modulus of the rubber in the central region in the width direction of the tread higher than the elastic modulus of the rubber in both side regions of the central region, it is possible to provide a pneumatic tire having excellent wear resistance and low rolling resistance.

It is sectional drawing of the width direction of the tire half part according to this invention. It is a figure which shows the result analyzed using the finite element method about the distortion energy which generate | occur | produces in the tread part of the tire according to this invention. It is sectional drawing of the width direction of the tire half part according to this invention.

Explanation of symbols

1 Bead core 2 Carcass 3a Inclined belt layer (outermost layer)
3b slant belt layer 4 circumferential belt layer 5 a tread 5C tread center portion 5S _1, 5S ₂ tread shoulder portion 6 tire 7 approved rim 10 bead toe CL tire equator

Claims (4)

A carcass straddling a toroidal shape between a pair of bead portions, and a large number of cords extending in a direction inclined with respect to the equatorial plane of the tire are coated with rubber on the radially outer side of the crown portion of the carcass. A pneumatic tire having a belt formed by sequentially arranging an inclined belt layer of a layer, and a tread disposed on a radially outer side of the belt,
The ratio of the diameter difference BD between the center portion in the width direction of the outermost layer and the end portion in the width direction with respect to the half width HBW of the outermost layer of the inclined belt layer in the tire width direction cross section in a state where the tire is mounted on the applicable rim. BD / HBW is 0.10 or more and 0.13 or less,
In the tread, the elastic modulus of the rubber in the central region in the width direction is higher than the elastic modulus of the rubber in both side regions of the central region.
A pneumatic tire characterized by that.   Ratio SWh / SH of the shortest distance SWh between the line segment drawn parallel to the tire rotation axis at the maximum width position of the tire and the line segment drawn parallel to the tire rotation axis at the bead toe with respect to the tire cross-section height SH The pneumatic tire according to claim 1, wherein is 0.55 or less.   The ratio GB / GA of the tread rubber thickness GA at the center in the width direction of the outermost layer of the inclined belt layer and the tread rubber thickness GB at the end in the width direction of the outermost layer of the inclined belt layer is 0.75 or more. The pneumatic tire according to claim 1, wherein the pneumatic tire is provided. The portion showing the minimum curvature in the carcass line extending from the widthwise end of the outermost layer of the inclined belt layer to the inside of the bead core is located radially inward from the half point of the cross-sectional height SH of the tire. The pneumatic tire according to any one of claims 1 to 3.

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