JP2644965B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire which can be suitably used particularly as a tire for a passenger car, and can improve wet grip performance and reduce tire noise while maintaining dry grip performance and high-speed durability performance. .

[0002]

2. Description of the Related Art In recent years, with the improvement in quietness of vehicles, the contribution rate of noise generated by tires to the noise of the entire vehicle has been increased, and reduction of the noise is desired. In particular, it is desired to reduce noise in a region near 1 kHz which is easy for a human to hear. One of the main sound sources in such a high frequency region is a so-called air column resonance.

[0003] On the other hand, a plurality of longitudinal grooves which are generally continuous in the tire circumferential direction are arranged on the tire tread in order to maintain a wet grip.

In such a tire, a kind of air column is formed by the road surface and the vertical groove when the tire is in contact with the ground, and air flows into the air column due to deformation of the tire tread during rolling, thereby causing a specific wavelength. That is, a sound having a wavelength twice that of the air column is generated.

[0005] This phenomenon is called air column resonance, and in a tire having a vertical groove, it is a main sound source of 800 to 1.2 kHz noise. The wavelength of the columnar resonance sound becomes a substantially constant frequency irrespective of the speed of the tire, and increases the inside sound and outside sound.

[0006]

In order to prevent this air column resonance, it is known that the number of flutes or the volume of the flute is reduced. Invite.

On the other hand, in order to improve the wet grip performance, it is necessary to increase the number of vertical grooves and the groove volume, but the mere increase is due to the increase in the tire noise and the decrease in the contact area. This leads to a decrease in dry grip performance and a decrease in steering stability performance due to a decrease in rigidity of the tread pattern.

Heretofore, tire performance has been adjusted at the expense of any of these conflicting performances.

An object of the present invention is to provide a pneumatic tire capable of improving wet grip performance without impairing dry grip performance and high-speed durability performance and reducing tire noise by suppressing air column resonance.

[0010]

SUMMARY OF THE INVENTION According to the present invention, there is provided a tread portion having two circumferentially continuous tire equatorial sides.
By providing the vertical grooves, the tread portion and the central portion between a pair of shoulder portions outside the groove bottom edge of the vertical groove in the tire axial direction and the groove bottom edge of the vertical groove in the tire axial direction. In the tire meridional section, the central portion smoothly extends between the inner groove wall surface and the inner groove wall surface extending inward in the tire axial direction with a curve protruding radially outward from the inner groove bottom edge. A central surface using a series of convex curves consisting of a central ground plane to be connected is provided, and the central surface is substantially in contact with a virtual tread line connecting between the ground planes of the shoulder part, and the tread part is Loss tangent tan
Formed using a first rubber composition having δ1 of 0.01 to 0.35 and a second rubber composition having a loss tangent tan δ2 of 1.2 times or more and 10 times or less of the loss tangent tan δ1. And
In addition, a first rubber portion using the first rubber composition is arranged at least on the belt layer side of the central portion,
A plurality of belt plies or belts in which a second rubber portion using a second rubber composition is provided on at least an outer surface side of the tread of at least one shoulder portion, and wherein the belt layer has parallel cords covered with topping rubber; A pneumatic tire, comprising: a ply; and a covering rubber layer extending in the tire axial direction so as to cover a radially outer side of the belt ply located at an outermost side of the belt ply.

[0011]

In the central part surface, the inner groove wall surface is formed as a curved surface protruding radially outward, so that the groove depth of the longitudinal groove gradually increases outward in the tire axial direction. , The raised central portion improves drainage, reduces hydroplaning, and improves wet grip.

[0012] In addition, the dry grip performance can be maintained by providing two vertical grooves and making the center surface contact a virtual tread wire connecting the ground contact surface of the shoulder portion.

Further, by gradually increasing the depth of the vertical groove at the center by a series of convex curves, the width of the groove on the contact surface becomes trumpet-like before and after the contact center of the contact surface (before and after in the traveling direction). An increasing widening is formed, which prevents air column resonance and helps reduce tire noise.

The first rubber portion provided at least on the belt layer side of the center portion has a loss tangent tan δ1 of the rubber of 0.1.
It is in the range of 01 to 0.35 and smaller than the loss tangent tan δ1 of the second rubber portion of the shoulder portion. Therefore, a rise in the temperature at the central portion, particularly during high-speed running, can be suppressed, and high-speed durability can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a tire meridional section in a standard state mounted on a JATMA standard applicable rim R and filled with a normal internal pressure.

The tire 1 has a radially arranged carcass 3 which is wound around a bead core 2 of a bead portion B from a tread portion T to a side wall portion S from the inside in the tire axial direction to the outside, and is engaged with the tread portion. And a belt layer 4 inside the T and outside the carcass 3. Also bead core 2,
A bead apex 6 extending radially outward from the bead core 2 in the tire radial direction is disposed between the body portion of the carcass 3 extending between the two and the rewinding portions at both ends thereof, and retains the shape and rigidity of the bead portion B. .

The tire 1 has a flatness ratio of tire cross-section height / tire width of about 0.4 to 0.6, and is a wide flat tire relatively inferior in drainage, particularly a flat radial tire for a passenger car. Is formed as

The belt layer 4 is formed of a plurality of belt plies in which cords having high tensile rigidity such as steel and aromatic polyamide are aligned in parallel with each other and covered with topping rubber. In each belt ply 4A, the cords are arranged at a relatively small angle of 15 to 30 with respect to the tire circumferential direction such that the cords cross each other between the plies. Further, the belt layer 4 may be formed of only the plurality of belt plies 4A, or may include a coating rubber layer 20 in addition to the belt plies 4A, for example, as shown in an enlarged view in FIG.
The covering rubber layer 20 is a thin rubber layer extending in the tire axial direction covering the outer surface of the outer belt ply 4A located on the outermost side in the radial direction, and the tread rubber 21 and the belt ply 4A constituting the tread portion T are formed. To prevent tread peeling. The covering rubber layer 20 is made of, for example, a rubber composition substantially equal to the above-mentioned topping rubber, and its width extends over the entire width of the tire as shown in FIG. Good. When the carcass 3 is a tire for a passenger car, an organic fiber cord such as nylon, rayon, or polyester can be used.

The tread portion T has a tire equator C on its surface.
L and two longitudinal grooves 7, 7 extending substantially continuously in the circumferential direction on both sides of the longitudinal grooves 7,
The tread portion T is formed between the pair of shoulder portions 8 outside the groove bottom edge 7b on the outside in the tire axial direction and the central portion 9 located between the groove bottom edges 7a on the inside of the longitudinal groove 7 in the tire axial direction. Classify.

The longitudinal groove 7 is preferably positioned symmetrically with respect to the tire equatorial plane, and more preferably, the center of the groove bottom 7S is located substantially at the center between the tire equatorial plane and the tread contact edge TE. And its groove depth D
Is 4 to 8% of the tread contact width TW, for example, size 20
In 5 / 55R15, it is 7.5 to 15.0 mm, preferably 8.4 mm.

Further, the surface of the central portion 9 extends inward in the tire axial direction along a curve protruding radially outward from the inner groove bottom edges 7a, 7a in a tire meridional section which is a section including the tire axis. And a central surface using a series of convex curves composed of inner groove wall surfaces 9a, 9a and a central ground contact surface 9b smoothly connecting between the inner groove wall surfaces 9a, 9a.

The center contact surface 9b is an area of the tread surface of the central portion 9 which contacts the ground when a normal load is applied in the standard condition. Means the outer end of the ground surface of the shoulder portion 8 when "." Also, the contact surface of the shoulder 8
At its inner end a, it intersects the outer groove wall surface 8a extending radially outward from the groove bottom edge 7b on the tire axial outside of the vertical groove 7, so that the vertical groove 7 is in contact with the inner and outer groove bottom 7S. Groove wall 9
a, 8a, and the groove width GW of the vertical groove 7
Is defined as the distance in the tire axial direction from the inner end a to the upper edge of the inner groove wall surface 9a. The groove bottom edges 7a and 7b are
When the groove bottom 7S is substantially flat as in this example, it is formed as a bending point with the groove wall surface. When the groove bottom 7S is a curved surface, FIG.
As in 2a and 2b, it is formed as a bending point or an inflection point between the groove wall surface.

The convex curve on the surface of the central portion extends substantially the contact surface of the shoulder portion 8 and substantially touches a virtual tread line 10 extending between the contact surfaces.

Here, "substantially in contact" means that the distance L between the center contact surface 9b and the virtual tread line 10 on the tire equator CL is within 2% of the tread contact width TW. . If it is 2% or more, the difference in the ground pressure between the shoulder portion and the central portion becomes large, grip performance is reduced, and wear resistance is impaired.

Further, a virtual tread wire 10 connecting between the ground planes
Is defined as an arc curve having a single radius of curvature tangent to the tangent at the inner end a of the ground contact surface of the shoulder portion 8 and having both ends at the inner ends a, a. When the tangents are substantially parallel,
It becomes a straight line connecting the inner ends a.

In the present invention, by forming the central portion 9 as a central portion surface having a convex curve as described above, a bulge having a relatively small radius of curvature and a sufficiently small width compared to the tire width is formed at the center of the tire. By providing a portion, the hydroplaning phenomenon is prevented and the wet grip property is improved. This is because a tire having a small width and a small radius of curvature is generally excellent in the effect of preventing the phenomenon.

Furthermore, by reducing the radius of curvature of the central portion 9, particularly the radius of curvature of the central ground contact surface 9a, drainage to both outer sides can be enhanced and drainage effect on a wet road surface can be improved.

The radius of curvature R of the contact surface of the shoulder portion 8
If 2 is also reduced, the grip performance on dry road surfaces due to the decrease in the ground contact area and the steering stability performance during cornering are reduced. Therefore, the radius of curvature R of the ground contact surface of the shoulder portion 8
2 is relatively large, preferably three times or more the contact width TW, and is acceptable until the contact surface of the shoulder portion approaches a straight line parallel to the tire axis.

FIG. 1 shows an example in which the surface of the central portion is formed by a curve composed of a single arc having a radius of curvature R1. This radius of curvature R1 is sufficiently smaller than the radius of curvature R2 of the shoulder portion 8, and in this example, this curve is inscribed in the virtual tread line 10.

The radius of curvature R1 is preferably set in a range of 0.5 to 1.5 times the tread contact width TW.
If it is smaller than 0.5 times, the width SW of the ground contact surface of the central portion 9, that is, the central ground contact surface 9b becomes small, and the decrease in dry grip tends to increase. If it is more than 1.5 times, the drainage effect is insufficient and the wet grip property is impaired. Radius of curvature R
1 and R2 both have their centers on the tire equatorial plane.

In order to maintain the dry grip, abrasion resistance, steering stability, etc., the width SW of the center contact surface 9b is set.
Is about 5 to 40% of the tread contact width TW, preferably 1
5 to 35%. Further, the inner groove bottom edges 7a, 7a
The width CW of the central portion 9, which is the distance between the treads, is the tread contact width T.
It is preferable to set it to about 40 to 55% of W.

Further, in the shoulder portion 8, the groove wall surface 8a outside the longitudinal groove 7 has a relatively steep and non-circular arc having an angle α with the tire radial line X of 0 to 40 °, preferably 5 to 25 °. For example, it is desirable that the shoulder portion 8 has a straight line, whereby an edge effect with the road surface at the inner end a of the shoulder portion 8 having a high contact pressure is exhibited, the lateral force is improved, the cornering power is increased, and the dry grip performance is improved. Help maintain. In addition, the outer groove wall surface 8a may be a convex curve extending outward in the tire axial direction similar to the inner groove wall surface 9a, and particularly, as shown in FIG. 4, the groove is bent in a circumferential direction in a zigzag manner. By using the wall surface 8a, traction can be enhanced.

Further, in order to reduce air column noise, each of the longitudinal grooves 7 has a groove width GW in a contact state when the regular load is applied of 15% or more of the tread contact width TW.

This is because the groove depth ratio of the tread contact width TW to the groove width GW of the vertical groove 7 is GW /
This is based on the result of measuring the passing noise while changing the TW. The test tire size is 205/55 R15, and two longitudinal grooves each having a U-shaped cross section are provided on the tread surface.

The measurement was carried out by mounting on a 2000 cc domestic passenger car and measuring the passing noise at a speed of 60 km / h according to the JASO standard (microphone position 7.5 m). From FIG. 7, the passing noise increases with an increase in the groove width ratio, and reaches a maximum when the ratio is 13%, and then rapidly decreases. Therefore, the groove width ratio is at least 15%, more preferably at least 20%.

FIG. 8 shows that the groove width ratio GW / TW is 13%.
This is the result of frequency analysis of the sample of FIG. It can be seen that the noise in the vicinity of 1 kHz is reduced in the case of 27%.

As for the vertical groove 7, the total groove width ratio 2GW / TW which is the ratio of the total groove width 2GW of the groove widths GW of the vertical grooves 7 and 7 to the tread contact width TW is determined by the cornering power and the wet grip property. Was found to affect. In the tire of the same size having the central surface shape of a single arc shown in FIG. 1 and the conventional tire having four longitudinal grooves G shown in FIG. 21, the total groove width ratio ΣGW / TW is changed. FIG. 9 shows the result of measuring the cornering power. As the total groove width ratio, the value of 2 GW / TW was used for the example, and the value of (ΔGW) / TW was used for the conventional example.
As for the cornering power, each tire was mounted on a regular rim, filled with a regular internal pressure, and measured with a drum tester on a room bench. It can be seen that the value is larger than that of the conventional tire. This is considered that when the total groove width ratio defined above is fixed, the convex curved groove wall surface 9a contributes to an increase in tire lateral rigidity. However, when the total groove width ratio exceeds 50%, the cornering power is greatly reduced.

Similarly, FIG. 10 shows the result of measuring the speed at which the hydroplaning phenomenon occurred. It can be seen that in the example, the hydroplaning generation speed is higher and the same phenomenon is less likely to occur in the example than in the conventional tire even at the same total groove width ratio. This is because the vertical groove 7 is located before and after the grounding center Q at the time of grounding by providing the grooved wall surface 9a of the convex curved surface at the center portion 9 of the raised small width of the tire of the present invention, as shown in FIG. The widened portion 13 extending in a trumpet shape is formed to improve drainage. Further, the widened portion 13 formed in this way also prevents the occurrence of air column resonance in the vertical groove 7, and as described above, is useful for reducing tire noise.

From the above-mentioned noise, dry grip property by cornering power, and wet grip property by hydroplaning phenomenon, the groove width ratio is preferably 15% or more, more preferably 20% or more, and the total groove width ratio is more preferably 30 to 50%. 40 to 50%.

In the embodiment shown in FIG. 1, the central portion surface is formed by a single circular arc. However, as shown in FIG. 5, it may be formed by an elliptical shape or a curve approximating an ellipse.

FIG. 6 shows the surface of the central portion.
The curvature radius R is different between the groove wall surface 9a and the center contact surface 9b.
3 and R4 are shown. Radius of curvature R3
Is smaller than the radius of curvature R4 of the center tread 9b and the radius of curvature R2 of the shoulder tread, respectively, and preferably has a lower limit of 5% or more of the tread tread width TW. 5%
If it is less, the drainage effect tends to be insufficient. The upper limit is a value that matches the radius of curvature R4. At this time, the central portion surface shape is a single arc. The radius of curvature R4 is the radius of curvature R2.
It is also possible to make them substantially the same by approaching the wet grip property without impairing them.

Further, on the left and right groove wall surfaces 9a, 9a,
For example, when mounting the tire, the curvature radius R3 of one of the groove wall surfaces 9a facing the outside of the vehicle may be made different on the left and right so as to be larger than the other, so that the sound radiation to the outside may be reduced.

Here, in the tire provided with such a protruding central portion 9, the heat generated in the central portion 9 is particularly large as compared with the conventional tire, and the high speed durability is reduced due to this heat generation. It turned out to be.

Therefore, in the present invention, as shown in FIGS. 13 to 18, the tread rubber 21 has a loss tangent δ1 of 0.0
1 to 0.35 of the first rubber composition 22 and a loss tangent tan
δ2 is 1.2 to 10.0 times the loss tangent tan δ1 with the second rubber composition, and the first rubber composition 22 is used at least on the belt layer 4 side of the central portion 9. The first rubber portion 25 that has been
A second rubber portion 26 using the second rubber body 23 is provided on at least the outer surface of the tread of each of the shoulder portions 8.

As described above, the first rubber portion 25 of the central portion 9 is formed.
Is formed of the first rubber composition 22 having a small loss tangent tan δ1, that is, a small energy loss and a low heat build-up. Suppressed and improves high-speed durability.

On the other hand, the second portion of the shoulder portion 8 having a high contact pressure
Is formed of the second rubber composition 23 having a large loss tangent tan δ2, that is, a large energy loss and a high shock absorption, so that the ride comfort can be improved, and the road surface following performance and grip can be improved. As the performance increases, the steering stability can be maintained as a whole when the vehicle is traveling straight and turning.

The rubber structure Y of the tread rubber 21
As shown in FIGS. 13 to 15, a laterally split rubber structure Y1 formed by dividing the first rubber portion 25 and the second rubber portion 26 in the tire axial direction, and FIGS.
As shown in FIG. 5, an upper and lower divided rubber structure Y2 formed by dividing the first rubber portion 25 and the second rubber portion 26 in the tire radial direction can be adopted.

As an example of the rubber structure Y1 of the horizontal division, as shown in FIG. 13, for example, two rubber members extending from the starting point V on the outer surface of the tread to the belt layer at a position separated from the tire equator CL outward in the tire axial direction. The first rubber portion 2 is provided between the boundaries 29, 29.
5 and a second rubber part 2 outside the boundary line 29.
6 and 26 are formed. The starting points V, V are the tire equator C
L and on the outer surface of the tread outside the central ground contact surface 9b, that is, on the outer surface of one of the inner groove wall surface 9a, the groove bottom surface 7S or the outer surface of the shoulder 8, so that the boundary line 29 is provided. , 29 between the central portion 9 and at least the belt layer side (inside in the tire radial direction), and in this example, both the belt layer side and the tread outer surface side (outside in the tire radial direction). Formed. Similarly, the second rubber portion 26 outside the boundary line 29 is formed on at least the tread outer surface side of the shoulder portion 8, in this example, over both the belt layer side and the tread outer surface side.

The starting point V is defined as a distance from the groove wall surfaces 8a, 9b, the groove bottom surface 7S, or the inner end a to a distance equal to the groove bottom width GW1 of the longitudinal groove 7 to the outside of the shoulder portion ground plane in the tire axial direction. It is preferably provided at the end portion a1, and more preferably, the starting point V is provided at the groove bottom surface 7S. The boundary line 29 may be formed in the radial direction, that is, in parallel with the tire equatorial plane. For example, as shown in FIG. 14, the boundary line 29 is inclined in a direction away from the tire equator CL inward in the radial direction or in a direction approaching the tire equator CL. May be formed.

As shown in FIG. 15, a single boundary 29 is formed in the tread portion T, and a first rubber portion 25 is formed inward of the boundary 29 in the tire axial direction. You may. At this time, the second rubber portion 26 is formed only on one shoulder portion 8 which is located outward in the tire axial direction,
In such a case, the tire is mounted with the shoulder portion 8 facing outward of the vehicle.

An example tire having the tread rubber structure shown in FIG. 13 and a comparative example tire having the tread profile of the conventional tire shown in FIG. (Figure 2
2) are formed using the first and second rubber compositions 22 and 23, respectively, and the loss tangent ratio tan δ2 / tan δ1 at that time.
And the relationship between high-speed durability was measured. As shown in the measurement results in FIG. 19, in the tire having the tread profile of the present application, the high-speed durability is significantly improved when the ratio tan δ2 / tan δ1 is in the range of 1.2 to 2.0, and the high-speed durability is improved. It can be improved to the same level as a conventional tread profile.

That is, the ratio tan δ2 / tan δ1 is 1.2 to
In the range of 2.0, the rubber structure Y works most effectively,
The ratio tan δ2 / tan δ1 is more preferably 2.0 or more
And 6.0 times or less. When the ratio is less than 1.2
The effect of improving the fast durability is insufficient, and the ratio is greater than 10.
In this case, the physical properties between the first and second rubber compositions 22 and 23 are excessive.
Each time, a separation is induced between the compositions 22 and 23.
Fire. When the loss tangent tan δ1 is smaller than 0.01,
Lack of rubber properties, High speed resistance when it is larger than 0.35
The durability is insufficient. Therefore, preferably, the loss tangent tan δ
1 is in the range of 0.05 to 0.25. Loss tangent tan
δ2 is required to obtain the required steering stability.Preferably
0.25 or more,furtherPreferably it is 0.30 or more.

Here, the loss tangent is determined under the conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz.
It is a value measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho.

As an example of the rubber structure Y2 of the upper and lower divisions, as shown in FIG.
And the first rubber portion 2 arranged on the belt layer side (inside of the tire radius) over the entire width of the tread reaching the shoulder portion 8
5 and a cap rubber 31 on the outer surface of the tread, which is a second rubber portion 26 disposed outside the base rubber 30 to cover the base rubber 30.

In this embodiment, the base rubber 30 has a substantially constant small thickness and extends substantially below the shoulder portion 8 and the bottom surface 7S of the groove and substantially parallel to the surface of the central portion below the central portion 9 below the central portion 9. And an inner part 30B extending with a convex outer surface. Therefore, the base rubber 30 forms a maximum thickness on the tire equator CL, which is the maximum thickness.
The thickness ta of the base rubber from the belt layer 4 at the tire equator CL is larger than the total thickness tb from the belt layer 4 at the groove bottom surface 7S of the entire tread rubber.

As shown in Table 2 of the specific examples, Example Tires 5 to 12 having the tread structure shown in FIG. 16 were formed, and the relationship between the thickness ratio ta / tb and the high-speed durability was measured. As the measurement conditions, the ratio tan δ2 / tan δ1 was set to 0.
30 / 0.15 (= 2.0) is constant and the total thickness tb is constant at 3.0 mm. As shown in Table 2, the ratio ta /
It can be seen that high-speed durability increases as tb increases.
Particularly when the thickness ratio ta / tb is in the range of 1.0 to 1.3, the high-speed durability is significantly improved. That is, the thickness ratio ta / tb is 1.0
The rubber structure Y2 works most effectively in the range of 1.3 to 1.3, and the thickness ratio ta / tb is more preferably 1.3 or more.

The total thickness tb is usually 3 for a tire.
mm, so that the thickness ratio ta / tb is allowed up to a range of the thickness ta where the base rubber 30 is not exposed from the tire outer surface.

As shown in FIG. 17, the rubber structure Y2 has a maximum rubber thickness t of the outer portion 30A of the base rubber 30.
c may be increased to a value substantially equal to the rubber thickness ta. Alternatively, as shown in FIG. 18, the outer portion 30A may be eliminated and the base rubber 30 may be formed only by the inner portion 30B.

In this embodiment, the shoulder portion 8 and the central portion 9
In addition, a lateral groove extending substantially in the tire axial direction is provided, so that wet grip performance can be improved.

As shown in FIG. 3, the shoulder portion 8 is provided with a lateral groove 11 in this example. The lateral groove 11
Extends outward from a position away from the longitudinal groove 7 in the tire axial direction and opens at the tread end. By not connecting to the longitudinal groove 7, the rigidity of the shoulder portion is prevented from being reduced, and the wet grip performance is improved by opening at the tread end.

Only one end of the lateral groove 12 in the central portion 9 opens into the longitudinal groove 7, and the inner side in the tire axial direction is interrupted near the equator CL. By not providing a lateral groove in the vicinity of the tire equator CL, the rigidity of the central portion is maintained, and the steering stability is secured. The lateral grooves 11 and 12 have the groove bottoms 11a and 12a substantially parallel to the belt layer 4 and the axial inner end faces 11b and 12b of the lateral grooves 11 and 12 are parallel to the tire equator CL. Alternatively, the angle β formed with the radius line Y is 15
It shall be a small angle of less than °.

Thus, it is possible to suppress a decrease in wet grip due to a decrease in the length of the lateral groove as the tire wears. Note that the circumferential pitch,
Other tire specifications such as depth can be selected according to the purpose.

[0063]

[Specific example] A tire having a tire size of 205/55 R15 was manufactured according to the specifications shown in Tables 1 and 2, and the steering stability performance when traveling straight ahead, the steering stability performance when cornering, and the high-speed durability performance were measured. It is shown in the table. Each performance is indicated by an index with Conventional Example 1 being 100, and the larger the index is, the better. The tire of Comparative Example 5 having the tread profile of the present invention has a remarkable effect on the tire noise and wet grip performance as described above, but generates a large amount of heat in the central portion of the tread as compared with the conventional tire having the same tread rubber composition, Poor high-speed durability. By using such a tread profile in combination with the tread rubber structure of the present invention, high-speed durability is improved while maintaining steering stability, as shown in Examples 1, 2, 3, and 4. As shown in Comparative Examples 5 to 7, when the tread rubber was formed with one rubber composition, it was difficult to achieve both high-speed durability and steering stability.

As shown in Examples 5 to 12, the thickness ratio t
It can be seen that the larger a / tb, the better the durability.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

As described above, the pneumatic tire of the present invention can improve wet grip performance and reduce tire noise due to air column resonance without impairing dry grip performance and high-speed durability.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing another example of the belt layer.

FIG. 3 is a partial plan view illustrating an example of a tread pattern.

FIG. 4 is a partial plan view of a tread pattern showing another example of a vertical groove.

FIG. 5 is a sectional view of a tire showing another example of the surface shape of the central portion.

FIG. 6 is a cross-sectional view of a tire showing still another example of the surface shape of the central portion.

FIG. 7 is a diagram showing the results of a noise test.

FIG. 8 is a diagram showing the results of a noise test.

FIG. 9 is a diagram showing a relationship between a total groove width ratio and a cornering power.

FIG. 10 is a graph showing a relationship between a total groove width ratio and a hydroplaning generation speed.

FIG. 11 is a plan view schematically showing a tread contact surface of the tire according to one embodiment of the present invention.

12A and 12B are cross-sectional views illustrating a bottom edge of a groove.

FIG. 13 is a sectional view showing an example of a tread rubber structure.

FIG. 14 is a sectional view showing another example of the tread rubber structure.

FIG. 15 is a sectional view showing another example of the tread rubber structure.

FIG. 16 is a sectional view showing another example of the tread rubber structure.

FIG. 17 is a sectional view showing another example of the tread rubber structure.

FIG. 18 is a sectional view showing another example of the tread rubber structure.

FIG. 19 is a diagram showing a relationship between a loss tangent ratio tan δ2 / tan δ1 and high-speed durability.

FIG. 20 is a diagram showing a tread profile of a conventional tire.

FIG. 21 is a cross-sectional view showing a tread rubber structure of a conventional tire used in a specific example.

FIG. 22 is a cross-sectional view showing a tread rubber structure of a comparative tire used in a specific example.

FIG. 23 is a cross-sectional view showing a tread rubber structure of a comparative tire used in a specific example.

[Explanation of symbols]

 Reference Signs List 7 vertical groove 7a inner groove bottom edge 7b outer groove bottom edge 8 shoulder part 9 central part 9a groove wall surface 9b central ground plane 10 virtual tread line between ground planes of shoulder part 20 covering rubber layer 22 first rubber Composition 23 Second rubber composition 25 First rubber portion 26 Second rubber portion 29 Boundary line 30 Base rubber 31 Cap rubber CL Tire equator T Tread portion

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B60C 9/22 B60C 9/22 C 11/04 11/06 B

Claims (9)

(57) [Claims] 1. A tread portion provided with two longitudinal grooves extending substantially continuously in a circumferential direction on both sides of a tire equator, so that the tread portion is located closer to a groove bottom edge of the longitudinal groove than the groove axially outside. Also divided into a pair of outer shoulder portions and a central portion between the groove bottom edges of the longitudinal grooves in the tire axial direction inside, and the central portion is radially outward from the inside groove bottom edge in the tire meridional section. It has a central surface using a series of convex curves consisting of a groove surface extending inward in the tire axial direction with a convex curve and a central ground contact surface that smoothly connects between the groove wall surfaces. The tread portion substantially contacts a virtual tread line connecting between the contact surfaces of the shoulder portion, and the tread portion has a loss tangent tan δ1 of 0.01 to 0.1.
35, and a second rubber composition having a loss tangent tan δ2 of 1.2 times or more and 10 times or less of the loss tangent tan δ1 and at least the central portion. A first rubber portion using the first rubber composition is arranged on the belt layer side,
A plurality of belt plies or belts in which a second rubber portion using a second rubber composition is provided on at least one tread outer surface side of at least one shoulder portion, and the belt layer has a parallel cord covered with topping rubber. A pneumatic tire comprising: a ply; and a covering rubber layer that extends in the tire axial direction so as to cover a radially outer side of the belt ply located at an outermost side of the belt ply. 2. The tread portion has a boundary line extending from the outer surface of the tread to the belt layer at a position separated from the tire equator in the tire axial direction in a cross section of the tire meridian, and the first rubber portion has a boundary line. The second rubber portion is disposed inward in the tire axial direction, and the second rubber portion is disposed outside the boundary line, so that the first rubber portion is provided at least on the belt layer side of the central portion, and at least the tread outer surface side of the shoulder portion is provided. Second
The pneumatic tire according to claim 1, wherein a rubber portion is disposed. 3. The tread according to claim 2, wherein the boundary line starts from a groove bottom surface of the vertical groove, an outer surface of a shoulder portion, or one tread outer surface of a groove wall surface in a central portion. Pneumatic tires. 4. The pneumatic tire according to claim 3, wherein said boundary line extends in a radial direction. 5. The pneumatic tire according to claim 3, wherein the boundary line is inclined in a direction away from or close to the tire equator from the outer surface of the tread radially inward. 6. The tread portion has a central portion formed of a base rubber on a belt layer side as a first rubber portion and a cap rubber as a second rubber portion covering the base rubber. The pneumatic tire according to claim 1, wherein 7. The tire according to claim 6, wherein the thickness ta of the base rubber from the belt layer at the equator of the tire is greater than the total thickness tb from the belt layer at the bottom of the longitudinal groove. Pneumatic tires. 8. The tread portion has a central portion, a bottom surface of a vertical groove and a shoulder portion, a base rubber on a belt layer side as a first rubber portion, and a second rubber portion covering the base rubber. The pneumatic tire according to claim 1, comprising a cap rubber. 9. The tire according to claim 8, wherein a thickness ta of the base rubber from the belt layer at the tire equator is larger than a total thickness tb of the longitudinal groove from the belt layer at the groove bottom. Pneumatic tires.