JP2009262808A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire can improve braking performance while maintaining satisfactory resistance to rolling. <P>SOLUTION: This pneumatic tire has a belt constituted by arranging inclined belt layers composed of at least two layers each and 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 width directio of the outermost side layer and an end part in the width direction to half width HBW of the outermost side layer of the inclined belt layer, namely, BD/HBW, in cross section in the width direction of the tire 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 width direction than modulus of elasticity of rubber in both of side zones of the central zone in the width direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pneumatic tire having low rolling resistance and high braking performance.

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 steering stability, wear resistance, durability, and the like.
JP 2006-1360 A

Another important performance of the tire is braking performance. However, Patent Document 1 does not disclose improvement of braking performance while reducing rolling resistance. That is, in general, the reduction in rolling resistance and the shortening of the braking distance are in a mutually contradictory relationship, so it is extremely meaningful to achieve both.
Therefore, an object of the present invention is to provide a pneumatic tire with improved braking performance while further reducing rolling resistance performance.

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.

  However, reducing the ground contact width of the tire may be disadvantageous for braking performance. Therefore, the inventors have intensively studied aiming at further reducing rolling resistance and improving braking performance. When the tread is divided into a central region in the width direction and both side regions of the central region, It has been found that it is extremely effective to individually regulate the elastic modulus of the rubber in the region and both sides, and the present invention has been completed.

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,
The tread has a higher elastic modulus of rubber on both sides of the central region in the width direction than the elastic modulus of rubber in the central region in the width direction.
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.

  The elastic modulus uses a modulus of 100% at 30 ° C. This is an extension amount corresponding to a very large deformation acting on the tread block during braking.

(2) The pneumatic tire according to (1), wherein an elastic modulus of the rubber in the both side regions is 10 to 20% higher than an elastic modulus of the rubber in the central region in the width direction.

(3) 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 the bead toe relative to the tire cross-section height SH SWh / SH is 0.55 or less, The pneumatic tire as described in said (1) or (2) characterized by the above-mentioned.

(4) The ratio GB / GA between 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 any one of (1) to (3) above, which is 75 or more.

(5) 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 (1) to (4) above, wherein

  According to the present invention, the ratio BD / HBW of the diameter difference BD between the width direction center portion and the width direction end portion of the outermost layer 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. In addition to further reducing rolling resistance, the braking performance has been improved by increasing the elastic modulus of the rubber in both sides of the tread width direction central region compared to the elastic modulus of the rubber in the tread width direction central region. A pneumatic tire can be provided.

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 divided into a, 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.

Also, in this tire, as a result of intensive studies by the present inventors in order to achieve further demands for improving braking performance, the elastic modulus of the rubber in the tread shoulder portion should be made higher than the elastic modulus of the rubber in the tread center portion. Was found to be effective. 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 based on a position 2/3 from the tire equator CL side of the distance in the contact surface from the tire equator CL to the end of the contact width. The tread center portion 5C is a region on the tire equator CL side from the boundary, and the regions on the outer side in the tread width direction from the boundary are tread shoulder portions 5S ₁ and 5S. ₂ is defined.
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.

Since the behavior at the time of braking was examined about the tire which controlled the crown shape according to the above, it explains below. The load applied to the front wheels increases during vehicle braking as compared to a state where the vehicle is traveling on a flat road surface at a uniform speed. In addition, because the crown has a rounded shape, the ground pressure of the tread shoulder is low when running on a flat road surface, but a large load is applied during braking, causing the tire to bend and the tread shoulder being compared to normal running. Contact with the road surface strongly, and the contact pressure increases. Thus, at the time of braking, the increase rate of the contact pressure of the tread shoulder portion of the tire mounted on the front wheel is larger than that of the tread center portion. Therefore, it was found that the ratio of the braking force carried by the tread shoulder portion is larger than that of the tread center portion. Therefore, the elastic force of the rubber in the tread shoulder portion is increased to increase the rigidity of this portion, thereby increasing the braking force as a whole.
In addition, what is necessary is just to determine suitably the grade which enlarges the elasticity modulus of the rubber | gum of a tread shoulder part according to the contact pressure ratio of a tread center part and a tread shoulder part. In the tire of the present invention having the tire shape described above, the elastic modulus of the rubber in the tread shoulder portion is 1.1 to 1.5 times the elastic modulus of the rubber in the tread center portion from the viewpoint of improving the braking performance. It is preferable. If the elastic modulus of the rubber in the tread shoulder portion is less than 1.1 times the elastic modulus of the rubber in the tread center portion, the difference in the elastic modulus of the rubber between the tread shoulder portion and the tread center portion is too small. The effect of increasing the braking force by increasing the rigidity of is reduced. On the other hand, when it exceeds 1.5 times, the strain energy generated in the tread shoulder portion becomes large, and as a result, the rolling resistance may be deteriorated.
For example, it has been confirmed that the effect is obtained when the elastic modulus of the rubber in the tread center portion is 2.0 MPa and the elastic modulus of the rubber in the tread shoulder portion is 2.4 MPa.
However, from the viewpoint of maintaining good rolling resistance, the upper limit of the elastic modulus difference is preferably 1.2 times, as will be described in the following examples.

  However, from the viewpoint of reducing the rolling resistance of the tire, it is preferable that the elastic modulus of the rubber in the tread shoulder portion is low as described below. Therefore, it is important to define the elastic modulus of the tread rubber that improves the braking performance while minimizing the increase in rolling resistance.

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).
SE = (1/2) × E × ε ² (1)

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, the strain energy (SE) increases when the elastic modulus (E) is increased from the above equation (1). When the strain energy increases, the rolling resistance increases, which is considered undesirable.

However, when the strain energy generated in the tread portion of the tire shown in FIG. 1 was analyzed in detail using the finite element method, the strain energy ratio in the tread portion was as shown in FIG. .
In addition, A, B, and C shown in FIG. 2 (a) indicate regions from the tire equator side when the half width of the contact width is divided into three equal parts as shown in FIG. 2 (b). Regions A and B correspond to the tread center portion, and region C corresponds to the tread shoulder portion.
The strain energy generated in the tread portion is 65% in the tread center portion (region A: 25%, region B: 40%) and 35% in the tread shoulder portion. The contribution of strain energy in the tread shoulder portion is the tread center portion. It was found that the tread shoulder portion was smaller than the tread center portion, in other words, the influence on the rolling resistance was smaller than that of the tread center portion. Therefore, it is apparent from the examples shown below that the braking performance can be improved while increasing the rolling resistance to a minimum by increasing the elastic modulus of the rubber of the tread shoulder portion.

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 according to the specifications shown in Table 1, and rolling resistance and braking distance were measured for each prototype tire, which will be described below. . The basic structure of each prototype tire is as shown in FIG. 1, and the inclined belt layers 3a and 3b are composed of two layers in which steel cords arranged at an inclination angle of 24 ° with respect to the equatorial plane CL are crossed between each other. Further, a circumferential belt layer 4 made of nylon cord is provided.
These prototype tires were incorporated into a rim having a size of 7.5 J × 17, the internal pressure was adjusted to 230 kPa, and rolling resistance was measured under the conditions of a load of 4.5 kN and a speed of 80.0 km / h. Note that this rolling resistance measurement was performed with a smooth drum and a force type in accordance with ISO18164. The rolling resistance index is expressed as an index with the measured value of the rolling resistance of the comparative tire 1 as 100, and the smaller the value, the lower the resistance and the better the rolling resistance performance.
Further, using the prototype tire described above, a braking distance was measured after running on a road surface having a depth of 1 mm at a speed of 80.0 km / h and applying a brake. The braking distance index is represented by the reciprocal of the index with the braking distance of the comparative example tire 1 being 100, and the larger the value, the shorter the braking distance, that is, the better the braking performance.
Note that, as described above, the ratio BD / HBW is the center portion in the width direction of the outermost layer 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 each prototype tire is mounted on the applied rim. And the diameter difference BD between the width direction end portions.

  From the results in Table 1, it can be seen that the inventive tires 1 to 4 and the comparative tires 1 to 3 having the tire shape according to the present invention have reduced rolling resistance as compared to the conventional tires. Furthermore, when the elastic modulus of the rubber in the tread shoulder portion is 1.1 to 1.2 times the elastic modulus of the rubber in the tread center portion, the rolling resistance index is not increased, that is, good rolling resistance performance is obtained. It can be seen that the braking performance can be improved while maintaining.

  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. Air that has improved braking performance while maintaining good rolling resistance by increasing the elastic modulus of rubber on both sides of the tread width direction central area compared to the elastic modulus of the rubber in the tread width direction central area An inset tire can be provided.

It is sectional drawing of the width direction of the tire half part according to this invention. (A) is a figure which shows the result of having 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, (b) is for demonstrating area | region ABC of Fig.2 (a). FIG. 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 (5)

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,
The tread has a higher elastic modulus of rubber on both sides of the central region in the width direction than the elastic modulus of rubber in the central region in the width direction.
A pneumatic tire characterized by that.   2. The pneumatic tire according to claim 1, wherein an elastic modulus of the rubber in the both side regions is 10 to 20% higher than an elastic modulus of the rubber in the central region in the width direction.   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 the tire 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 any one of claims 1 to 3, 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 4.

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