JP2009279948A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire having superior wear resistance and extremely low rolling resistance. <P>SOLUTION: This pneumatic tire has a belt by successively arranging at least two layers of inclined belt layers in which many cords extending in a direction of tilt to a tire equatorial plane at the radially outside of a crown part of a carcass by making the carcass toroidally stretching between a pair of bead parts as a skeleton are coated with rubber. A tread is arranged at the radially outside of the belt. In tire width direction cross section in a state of the tire mounted on an applicable rim, a ratio BD/BW of a diametrical difference BD between a width direction center part and a width direction end part of the outermost side layer to a width BW of the outermost layer of the inclined belt layer is ≥0.01 and ≤0.04. In the tread, an elastic modulus of rubber in a width direction center region is set to be higher than those of both side regions in the center region. <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 2006-327502 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.

  First, the inventors can control the tire shape in detail to improve the expected performance. In particular, the shape design is not only the shape of the outer surface of the tire but also the frame of the tire. Since the shape of the reinforcing structure has a great influence on the tire performance, it has been found that it is effective to individually regulate it. In other words, suppressing the shear deformation in the tire width direction cross section, particularly in the tread on the outer side in the width direction, reduces the rolling resistance as a result of energy loss due to this deformation, and the shear force and slip resulting from this deformation. It has been found that the wear often described can be improved at the same time.

  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,
In a tire width direction cross-section in a state where the tire is mounted on an applicable rim, a ratio of a diameter difference BD between a width direction center portion and a width direction end portion of the outermost layer to a width BW of the outermost layer of the inclined belt layer BD / BW is 0.01 or more and 0.04 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.

  In addition, the outermost layer of the inclined belt layer means a radially outer layer of inclined belt layers having a width corresponding to a substantially contact area at the time of ground contact and having a plurality of different angles. The contact area refers to a range in contact with the road surface when a specified rim, specified internal pressure, and 80% of the specified load are applied.

(2) The line segment drawn parallel to the tire rotation axis at the maximum width position of the carcass and the bead toe parallel to the tire rotation axis with respect to the tire radial distance CSH between the outermost radial direction of the carcass and the bead toe The pneumatic tire according to (1) above, wherein a ratio CSWh / CSH of the shortest distance CSWh to the line segment drawn in is 0.6 to 0.9.

(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 0.5 or more and 0.8 or less, The pneumatic tire as described in said (1) or (2) characterized by the above-mentioned.

(4) A ratio BW / CSW of a width BW of the outermost layer of the inclined belt layer to a maximum width CSW of the carcass is 0.8 or more and 0.94 or less, (1) to (3) The pneumatic tire according to any one of the above.

(5) The ratio TD / (BW / 2) of the diameter difference TD between the center portion in the width direction of the tread and the end portion in the width direction with respect to the half width BW / 2 of the outermost layer of the inclined belt layer is 0.06 or more. The pneumatic tire according to any one of (1) to (4) above, which is 0.145 or less.

(6) In the carcass, corresponding to the widthwise end of the outermost layer of the inclined belt layer with respect to the path length CSP from the position corresponding to the center in the width direction of the outermost layer of the inclined belt layer to just below the bead core. The pneumatic tire according to any one of (1) to (5) above, wherein a ratio CSL / CSP of a path length CSL from a position to the maximum width position is 0.1 or more and 0.25 or less. .

(7) The position on the tread surface, which is separated from the tire equator by a distance 0.4 times the maximum width CSW of the carcass, is 0.91 times or more from the bead toe of the tire cross-section height SH. The pneumatic tire according to any one of the above (1) to (6), which is in a range of 97 times or less.

(8) The pneumatic swing according to any one of (1) to (7) above, wherein a belt swing angle at an end in a width direction of the outermost layer of the inclined belt layer is 0 ° or more and 10 ° or less. tire.

  Here, the belt swing angle is the average (intermediate line segment) of the tangential direction at the end of the inclined belt outermost layer and the tangential direction at the position corresponding to the inclined belt outermost layer end of the inclined belt innermost layer, the tire width It is an angle when the width direction is set to 0 ° when the direction cross section is viewed.

  According to the present invention, the ratio BD / BW of the diameter difference BD between the center in the width direction of the outermost layer and the end in the width direction with respect to the width BW of the outermost layer of the inclined belt layer is 0.01 or more and 0.04 or less. In addition, by making the elastic modulus of the rubber in the center region in the width direction of the tread higher than the elastic modulus of the rubber in both sides of the central region, a pneumatic tire having excellent wear resistance and extremely low rolling resistance is provided. be able to.

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 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 cross section in the tire width direction 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 width BW of the outermost layer 3a of the inclined belt layer. Ratio BD / BW of diameter difference BD between the portion (equatorial plane CL) and the width direction end portion is 0.01 ≦ BD / BW ≦ 0.04
It is important to be.

This definition means that the inclined belt layer 3 has a small diameter difference in the width direction. That is, it shows that the belt is almost flat. That is, as described above, the rolling resistance is dominated by the energy loss generated in the rubber of the tire tread portion, and suppressing the shear deformation in the cross section in the width direction, which is one of the deformations, reduces the rolling resistance. It is effective for reduction. The cause of this shear deformation is a deformation in which a curved belt is stretched flat when touched. Further, in a normal radial tire, since the radius of the shoulder relative to the tire center is small and has a diameter difference, the belt near the shoulder is stretched in the tire circumferential direction. Then, the inclined belt layer in which the cords are arranged so as to cross each other is deformed into a pantograph shape and stretched in the circumferential direction, and as a result, contracts in the width direction, thereby promoting the shear deformation. In order to suppress this deformation most simply from the shape of the tire, it is necessary to make the belt as flat as possible. However, in actual tire design, it is necessary to consider the deformation component accompanying the deformation of the side part, the ground contact shape to prevent uneven wear, and the contact pressure distribution. It is important to set the range. As a result of diligent research on this appropriate range, it was found that the above-mentioned 0.01 ≦ BD / BW ≦ 0.04.
In particular, when the improvement that suppresses the above-mentioned shear deformation from the shape of the tread is changed, the shear force and slip distribution in the contact surface also changes in a direction to be reduced, so it is also clarified that the wear resistance can be improved at the same time. I arrived.

The experimental results that led to the above findings will be described in detail below.
That is, using a radial tire of size 195/65 R15, each test of rolling resistance and wear resistance was performed under conditions in which the ratio BD / BW was variously changed. The basic structure of the tire is the same, one carcass ply, and the inclined belt layer is composed of two layers in which the cords arranged at an inclination angle of 24 ° with respect to the tire equator plane intersect each other, A nylon circumferential reinforcement layer is provided on the top.

  Here, in the rolling resistance test, the test tire was mounted on a standard rim and the internal pressure was adjusted to 210 kPa, and then a drum tester (speed: 80 km / h) having a steel plate surface with a diameter of 1.7 m was used. Find the rolling resistance. 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 in a conventional tire (0.04 <BD / BW ≦ 0.07) whose cross-section in the width direction is shown in FIG. 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 addition, the wear resistance test was performed using a rim-assembled test tire similar to the rolling resistance test, using 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 °, The test was carried out at a speed of 80 km / 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.

  As shown in FIG. 3, the above experimental results show that there is a significant difference from the conventional tire in both rolling resistance and wear resistance when the ratio BD / BW is in the range of 0.01 to 0.04. . More desirably, it is 0.02 or more and 0.035 or less.

Furthermore, as shown in FIG. 1, when the tread 5 is partitioned into a tread center portion 5C corresponding to the central region in the width direction and tread shoulder portions 5S ₁ and 5S ₂ corresponding to both side regions of the central region in the width direction. It is important that the elastic modulus of the rubber of the tread center portion 5C is 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 tread center portion 5C has a range within 50% ± 10% of the width BW of the outermost layer 3a of the inclined belt layer with the tire equator CL as the center.

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)

  Here, the tread center portion 5C is crushed by the contact pressure, and strain energy is generated due to a constant-stress circumferential shear in which the tread center portion 5C 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.

FIG. 4 shows the result of detailed analysis using the finite element method for the strain energy (SE) generated in the tread shoulder portions 5S ₁ and 5S ₂ of the pneumatic tire of the present invention shown in FIG.
In FIG. 4, the strain of the tread shoulder is represented by the vertical strain R in the radial direction, the vertical strain C in the circumferential direction, the vertical strain Z in the width direction, the shear strain RC in the circumferential cross section, the shear strain RZ in the cross section in the width direction, and It is represented by the ratio of the shear strain CZ in the radial cross section.
As shown in FIG. 5A, the shear strain RC in the circumferential section is a shear strain in a section parallel to the tire equatorial plane, and the shear strain RZ in the width section is As shown in FIG. 5 (b), it is the shear strain in the cross section including the tire rotation axis, and the shear strain CZ in the radial cross section is as shown in FIG. 5 (c). The shear strain orthogonal to the shear strain RC and the shear strain RZ in the cross section in the width direction.

4 that the shear strain RZ in the cross section in the width direction is 43%, which is dominant in the strain energy generated in the tread shoulder portion. This shear strain RZ 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.

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, at the boundary between the tread center portion 5C and the tread shoulder portion _5S 1, 5S ₂ respectively, the tread shoulder portion _5S 1, 5S ₂ are arranged radially outside the tread center portion 5C However, on the contrary, the tread center portion 5C may be arranged on the outer side in the radial direction of the tread shoulder portions 5S ₁ and 5S ₂ . Alternatively, the boundary line between the tread center portion 5C and the tread shoulder portions 5S ₁ , 5S ₂ passes through a position half the width BW of the outermost layer 3a of the inclined belt layer around the tire equator CL, and the equator plane CL. It may be a line segment parallel to.
However, the case of FIG. 1 is most preferable. 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. .

  Next, as shown in FIG. 1, with respect to the distance CSH in the tire radial direction between the outermost radial direction of the carcass and the bead toe, a line segment drawn in parallel to the tire rotation axis at the maximum width position of the carcass and the bead toe It is preferable that the ratio CSWh / CSH of the shortest distance CSWh to the line drawn parallel to the tire rotation axis is 0.6 or more and 0.9 or less. More desirably, it is 0.7 or more and 0.8 or less.

  According to this rule, the carcass line of the tire side portion has a region that is locally bent particularly at a position close to the road surface, and the bending rigidity is reduced at this portion. Then, since the periphery of the bent portion, which is on the outer side in the width direction than the belt width, is greatly deformed when loaded, deformation at the tread portion is reduced. That is, the shear deformation in the cross section can be reduced in the tread. As a result of various trials of dimensions for effectively reducing deformation during loading, it was found that the ratio CSWh / CSH was 0.6 or more and 0.9 or less.

  Further, as shown in FIG. 1, with respect to the tire cross-section height SH, a line segment drawn parallel to the tire rotation axis at the maximum width position of the tire and a line segment drawn parallel to the tire rotation axis on the bead toe 10 The ratio SWh / SH of the shortest distance SWh is preferably 0.5 or more and 0.8 or less. More preferably, it is 0.6 or more and 0.75 or less.

  Now, it is important to originally define the shape of the side portion with a carcass line that is a skeleton. However, in the phenomenon that energy loss occurs inside the rubber and contributes to rolling resistance, the side portion is no exception. In other words, it can be said that taking the shape of the side portion following the carcass line and different from that of the conventional tire leads to efficient improvement. This means, for example, that the side rubber is thinned. If it is obvious that the side rubber can be eliminated, this dimension indicates the same position as the maximum width of the carcass line. Actually, since it is necessary to give the side rubber a predetermined thickness from the role of protecting the carcass when contacting the curbstone, the maximum width position of the side part at this time is compared with the tire cross section height, It was found to be in the ratio range. Moreover, in the tire design, the design of the vulcanization mold is also an important point, so it is necessary as a tire design method to define it as the outer surface dimension.

Furthermore, as shown in FIG. 1, it is preferable that the ratio BW / CSW of the width BW of the outermost layer 3a of the inclined belt layer to the maximum width CSW of the carcass is 0.8 or more and 0.94 or less. More desirably, it is 0.84 or more and 0.93 or less.
That is, in the tire of the present invention, the crown portion has a flat shape. At this time, as a matter of course, the ground contact shape also tends to spread in the width direction, and the configuration of the reinforcing layer corresponding to that tends to be required. In particular, from the viewpoint of preventing wear, the ground contact width is desirably equal to or less than the width where a plurality of reinforcing layers exist. For this reason, it has been found that the belt width in the case where the tire shape according to the present invention is adopted needs to be set wider than usual, and the width should be in accordance with the above-mentioned regulations. On the other hand, as described regarding the shear deformation in the cross section, if there is an extra belt outside the ground plane, it acts in a worsening direction on the rolling resistance. For this reason, both the lower limit value regulated for wear and the upper limit value regulated for rolling resistance are important.

As shown in FIG. 1, the ratio TD / of the diameter difference TD between the center portion in the width direction of the tread 5 (tire equatorial plane CL) and the end portion in the width direction with respect to the half width BW / 2 of the outermost layer 3a of the inclined belt layer. (BW / 2) is preferably 0.06 or more and 0.11 or less. More desirably, it is 0.075 or more and 0.095 or less.
This is a regulation for the tread surface position directly above the inclined belt layer. As described above, the belt is flattened for the aforementioned shear deformation. At this time, it is preferable to set the outer surface of the tread at an appropriate position. If the rubber thickness is distributed so that the crown shape (see Fig. 2) remains on the tread surface, not only will the wear due to the diameter difference at the time of contact occur, but the thin rubber will also wear out completely. Life is shortened. for that reason. The ratio TD / (BW / 2), which is the tread drop height as well as the belt, is preferably clearly defined, and may be within a predetermined range.

  Incidentally, the carcass line in the region between the maximum width position of the carcass and the end in the width direction of the outermost layer 3a of the inclined belt layer preferably has a minimum radius of curvature of 5 mm or more and 25 mm or less. That is, it is better to define the radius of curvature when the carcass maximum width position and the belt lower position are approximated by an arc. As described above, the design of the mold is also an important point in the tire design, and it is meaningful to specify the radius of curvature of this portion as a design method.

  As shown in FIG. 1, the inclined belt with respect to the path length CSP from the position (tire equatorial plane CL) corresponding to the center in the width direction of the outermost layer 3 a of the inclined belt layer in the carcass 2 directly below the bead core 1. The ratio CSL / CSP of the path length CSL from the position corresponding to the width direction end of the outermost layer of the layer to the maximum width position is preferably 0.1 or more and 0.25 or less. More desirably, it is 0.12 or more and 0.18 or less. The path length CSP just below the bead core 1 is a substantial path length of the carcass, and the sandwiched bead core has a length of the sandwiched path as shown in FIG.

  This defines the length of the carcass where the carcass described above bends locally. That is, a desired local deformation can be caused by optimizing the length of the carcass in the region in the smooth curve connecting the maximum position of the carcass line and the point under the belt. The short carcass length in this region means that the direction is changed from the radial direction to the approximate width direction by the short length, so that the shape characteristic of being locally bent can be reinforced.

As shown in FIG. 1, a position P at a distance of 0.4 times the maximum width CSW of the carcass from the tire equator CL on the tread surface is 0.91 starting from a bead toe 10 having a tire cross-section height SH. It is preferably in the range of not less than twice and not more than 0.97 times. More desirably, it is 0.92 times or more and 0.96 times or less.
Here, the tread drop height at the position of 80% of the maximum tire width is simply defined. By setting the tread drop height within this range, bending deformation in the cross section in the width direction of the tread and the belt portion can be suppressed. In addition, if it is made completely flat, the contact pressure at the shoulder end is extremely increased and the wear is deteriorated, so there is an appropriate upper limit value.

As shown in FIG. 1, it is preferable that the belt swing angle θ at the end in the width direction of the outermost layer 3a of the inclined belt layer is 0 ° or more and 10 ° or less. More desirably, the angle is 3 ° or more and 7 ° or less.
Here, the swing angle of the belt end is defined. As described above, it is preferable that the belt shape is flat, but it is preferable to finely regulate the end shape of the belt. In the present invention, the shape may be flat near the center of the belt and suddenly curved at the belt end. However, since it is known that most of the shear deformation in the cross section occurs on the outer side in the tire width direction, it is meaningful to define the shape particularly finely at the belt end. In particular, when the belt end is curved and the swing angle is large, the end of the belt is locally curved, so the shear deformation is likely to occur. For this reason, it is desirable that the angle is ideally close to flat. If this is defined from the balance with the ground contact shape, the belt swing angle θ is preferably 0 ° or more and 10 ° or less.

Example tires of size 225 / 45R17, conventional tires, and comparative tires were prototyped according to the specifications shown in Table 1, and the wear resistance and rolling resistance of each prototype tire were measured and described below. To do. 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.
These test tires were assembled in 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.

  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 in a conventional tire (0.04 <BD / BW ≦ 0.07) whose cross-section in the width direction is shown in FIG. 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) having 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 0.1G10 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 regarded as equivalent, and if there is a difference of 10% or more, it can be said that there is a significant 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 shown in 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 and the wear resistance can be improved as compared with the tire and the comparative example tire.

  As described above, the ratio BD / BW 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 width BW of the outermost layer of the inclined belt layer is set to 0.01 to 0.04. 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 a figure which shows the cross section of the width direction of the tire according to this invention. It is a figure which shows the width direction cross section of the conventional tire. It is a figure which shows the influence which ratio BD / BW has on rolling resistance and abrasion resistance performance. It is a figure which shows the result analyzed in detail using the finite element method about the distortion energy which generate | occur | produces in the tread shoulder part of the tire according to this invention. It is a figure for demonstrating the shear strain in each cross section.

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 CL tire equatorial

Claims (8)

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,
In a tire width direction cross-section in a state where the tire is mounted on an applicable rim, a ratio of a diameter difference BD between a width direction center portion and a width direction end portion of the outermost layer to a width BW of the outermost layer of the inclined belt layer BD / BW is 0.01 or more and 0.04 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.   With respect to the distance CSH in the tire radial direction between the outermost radial direction of the carcass and the bead toe, the line segment drawn parallel to the tire rotation axis at the maximum width position of the carcass and the bead toe are drawn parallel to the tire rotation axis. 2. The pneumatic tire according to claim 1, wherein a ratio CSWh / CSH of the shortest distance CSWh to the line segment is 0.6 or more and 0.9 or less.   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 or 2, wherein is 0.5 or more and 0.8 or less.   The ratio BW / CSW of the width BW of the outermost layer of the inclined belt layer to the maximum width CSW of the carcass is 0.8 or more and 0.94 or less. Pneumatic tires.   The ratio TD / (BW / 2) of the diameter difference TD between the center portion in the width direction of the tread and the end portion in the width direction with respect to the half width BW / 2 of the outermost layer of the inclined belt layer is 0.06 or more and 0.145. The pneumatic tire according to any one of claims 1 to 4, wherein:   From the position corresponding to the end in the width direction of the outermost layer of the inclined belt layer to the path length CSP from the position corresponding to the center in the width direction of the outermost layer of the inclined belt layer to the position just below the bead core in the carcass. The pneumatic tire according to any one of claims 1 to 5, wherein a ratio CSL / CSP of the path length CSL to the maximum width position is 0.1 or more and 0.25 or less.   The position on the tread surface that is separated from the tire equator by 0.4 times the maximum width CSW of the carcass is 0.91 times or more and 0.97 times or less starting from a bead toe having a cross-sectional height SH of the tire. The pneumatic tire according to any one of claims 1 to 6, wherein the pneumatic tire is in the range.   The pneumatic tire according to any one of claims 1 to 7, wherein a belt swing angle at an end portion in the width direction of the outermost layer of the inclined belt layer is not less than 0 ° and not more than 10 °.

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