JPH0740708A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To improve the wet grip performance and reduce the noise without deteriorating the other performances by forming a belt layer by means of a specific belt ply through a process of sectioning a tread part into a pair of shoulder parts and a center part whose front surface has a projecting curved line by means of two flutes on the tire equatorial both sides continuously extended in the circumferential direction. CONSTITUTION:A belt layer 4 is formed by a belt ply coated by topping rubber or a belt layer for covering the outside thereof, and a tread part T is divided into shoulder parts 8 and a center part 9 by flutes 7. The front surface of this center part 9 is so formed as to have a projecting curved line composed of a groove wall surface 9a having a curved line projecting from an inner groove bottom edge 7a to the radial outside, and extended to the tire shaft direction inside and a center contact ground surface 9b for joining them smoothly. First rubber composition having loss tangent tantheta 1 of 0.01 to 0.35 is arranged on the center part belt layer side, while second rubber composition having 1.2tandelta1 to 10tandelta1 is arranged on the tread part T outer surface side. Accordingly, wet grip performance is improved without deteriorating dry grip performance or high-speed durability, and tire noise can be reduced.

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 passenger car tire and which 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 of the quietness of a vehicle, the contribution rate of the noise generated by a tire to the noise of the entire vehicle has become large, and its reduction is desired. Particularly, it is desired to reduce noise in a region around 1 kHz where human beings can easily hear, and one of the main sound sources in such a high frequency region is a so-called air column resonance.

On the other hand, the tire tread is generally provided with a plurality of vertical grooves continuous in the tire circumferential direction 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 in the ground contact state, and the air flows in the air column due to the 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.

This phenomenon is called air column resonance and is a main sound source of noise of 800 to 1.2 kHz in a tire having a vertical groove. The wavelength of the air column resonance sound has a substantially constant frequency regardless of the speed of the tire, increasing the vehicle interior sound and the vehicle exterior sound.

[0006]

In order to prevent the air column resonance, it is known to reduce the number of flutes or the groove volume. However, the reduction of the number of flutes and the groove volume deteriorates the wet grip performance. Invite.

On the other hand, in order to improve the wet grip performance, conversely, the number of vertical grooves and the groove volume may be increased, but the mere increase is due to the above-mentioned increase in tire noise and a decrease in the ground contact area. This leads to a reduction in dry grip performance and a reduction in steering stability due to a reduction in rigidity of the tread pattern.

Conventionally, 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 further reducing tire noise by suppressing air column resonance.

[0010]

SUMMARY OF THE INVENTION The present invention is a tire tread that has two tire equatorial sides extending substantially continuously in the circumferential direction.
By providing the vertical groove of the book, the tread portion is provided with a pair of shoulder portions outside the groove bottom edge on the tire axial direction outer side of the vertical groove and a central portion between the groove bottom edges on the tire axial direction inner side of the vertical groove. In the meridional section of the tire, the central portion smoothly extends between the groove wall surface inside and the 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 grounding surface to be joined, and the central surface is substantially in contact with a virtual tread line joining between the grounding surfaces of the shoulder portion, and the tread portion is, Loss tangent tan
Formed by using a first rubber composition having a 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 the loss tangent tan δ1. Is
Moreover, while arranging a first rubber portion using the first rubber composition on at least the belt layer side of the central portion,
A second rubber portion using the second rubber composition is provided on at least the outer surface side of the tread of at least one shoulder portion, and the belt layer has a plurality of belt plies in which juxtaposed cords are covered with a topping rubber, or a belt. A pneumatic tire comprising: a ply; and a cover rubber layer that extends in the tire axial direction and covers a radially outer side of the belt ply located at the outermost side of the belt ply.

[0011]

In the central surface, the inner wall surface of the groove is formed as a curved surface that protrudes outward in the radial direction, so that the groove depth of the vertical groove gradually increases toward the outer side in the axial direction of the tire, and the surface of the central portion is continuous. By having the convex curve of, the raised central part improves drainage, reduces the hydroplaning phenomenon, and improves wet grip.

The dry grip performance can also be maintained by providing two vertical grooves and contacting the surface of the central portion with a virtual tread line joining the ground contact surface of the shoulder portion.

Further, by gradually increasing the groove depth of the vertical groove in the central portion with a series of convex curves, the groove shape width on the contact surface becomes a trumpet shape before and after the contact center of the contact surface (before and after the advancing direction). An increasing widened portion 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 central portion has a loss tangent tan δ1 of 0.
It is set 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, it is possible to suppress the temperature rise of the central portion particularly during high-speed running, and improve the high-speed durability.

[0015]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a tire meridional section of a tire in a standard state attached to a rim R to which the JATMA standard is applied and filled with a normal internal pressure.

The tire 1 includes a carcass 3 in a radial arrangement which is wound around the bead core 2 of the bead portion B from the tread portion T to the sidewall portion S from the inner side to the outer side in the tire axial direction and is locked, and the tread portion. And a belt layer 4 inside T and outside the carcass 3. Bead core 2,
A bead apex 6 extending from the bead core 2 to the outer side in the tire radial direction is arranged between the main body portion of the carcass 3 extending between the two and the winding 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 poor in drainage, especially a flat radial tire for passenger cars. Formed as.

The belt layer 4 is formed by 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 so that the cords cross each other. Further, the belt layer 4 may be formed by only the plurality of belt plies 4A, and may include a covering rubber layer 20 in addition to the belt plies 4A as shown in an enlarged view in FIG.
The covering rubber layer 20 is a thin rubber layer that covers the outer surface of the outermost belt ply 4A located on the outermost side in the radial direction and extends in the tire axial direction. The tread rubber 21 and the belt ply 4A constituting the tread portion T are formed. Improves adhesion to and prevents tread peeling. The covering rubber layer 20 is made of, for example, a rubber composition which is substantially the same as the topping rubber, and the width of the covering rubber layer 20 is the same as the entire width of the tire as shown in FIG. Good. When the carcass 3 is a passenger car tire, organic fiber cords such as nylon, rayon, polyester, etc. can be used.

The tread portion T has a tire equator C on its surface.
It comprises two flutes 7, located on either side of L and extending substantially continuously in the circumferential direction, whereby the flute 7
A pair of shoulder portions 8 outside the groove bottom edge 7b on the tire axial direction outer side, and a central portion 9 located between the groove bottom edges 7a on the tire axial direction inner side of the vertical groove 7 and a tread portion T. Divide.

The vertical groove 7 is preferably located symmetrically with respect to the tire equatorial plane, more preferably the center of the groove bottom 7S is located substantially in the center between the tire equatorial plane and the tread ground contact end TE. And the 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 projecting radially outward from the inner groove bottom edges 7a, 7a in the tire meridional section which is a section including the tire axis. It has a central portion surface using a series of convex curves consisting of inner groove wall surfaces 9a, 9a and a central ground contact surface 9b that smoothly connects between the inner groove wall surfaces 9a, 9a.

The central ground contact surface 9b refers to the area of the tread surface of the central portion 9 that contacts the ground when a normal load is applied in the standard state, and the tread ground contact end TE is the normal load. Is the outer end of the ground contact surface of the shoulder portion 8 when added. Also, the grounding surface of the shoulder portion 8 is
At its inner end a, it intersects with an outer groove wall surface 8a extending radially outward from a groove bottom edge 7b on the outer side of the longitudinal groove 7 in the tire axial direction. Groove wall surface 9
a and 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. Further, 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 between the groove bottom wall and the groove wall surface, and when the groove bottom 7S is a curved surface, as shown in FIG.
Like 2a and 2b, it is formed as a bending point or an inflection point with the groove wall surface.

The convex curve on the surface of the central portion substantially contacts the virtual tread line 10 which extends the ground contact surface of the shoulder portion 8 and joins the ground contact surfaces.

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

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

According to the present invention, the central portion 9 is the surface of the central portion formed of the convex curve as described above, so that a ridge having a relatively small radius of curvature and a width sufficiently narrower than the tire width is provided at the tire center. By providing a part, 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 same phenomenon.

Further, by reducing the radius of curvature of the central portion 9, especially the radius of curvature of the central ground contact surface 9a, it is possible to enhance the drainage property to both outer sides and improve the drainage effect on the wet road surface.

The radius of curvature R of the ground contact surface of the shoulder portion 8
If 2 is also reduced, the grip performance on dry road surface due to the reduction of the ground contact area and the steering stability performance at the time of cornering are deteriorated. Therefore, the radius of curvature R of the contact surface of the shoulder portion 8
2 is relatively large, and is preferably 3 times or more of the ground contact width TW and can be allowed until the ground 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 consisting of a single arc having a radius of curvature R1. The radius of curvature R1 is sufficiently smaller than the radius of curvature R2 of the shoulder portion 8, and in the present example, this curve is inscribed in the virtual tread line 10.

The radius of curvature R1 is preferably set in the range of 0.5 to 1.5 times the tread ground contact width TW.
If it is less than 0.5 times, the width SW of the ground contact surface of the central portion 9, that is, the center ground contact surface 9b becomes small, and the deterioration of the dry grip tends to be large. If it is more than 1.5 times, the drainage effect is insufficient and the wet grip performance is impaired. Also the radius of curvature R
The centers of both 1 and R2 are arranged on the tire equatorial plane.

In order to maintain dry grip, abrasion resistance, steering stability, etc., the width SW of the central ground contact surface 9b
Is about 5 to 40% of the tread contact width TW, preferably 1
5 to 35%. Furthermore, the inner groove bottom edges 7a, 7a
The width CW of the central portion 9, which is the distance between the two, 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 vertical groove 7 has a relatively steep and non-arcuate angle α with the tire radial line X of 0 to 40 °, preferably 5 to 25 °. For example, it is desirable to make a straight line, and by this, the edge effect with the road surface at the inner end a of the shoulder portion 8 having a high ground contact pressure is exerted, the lateral force is improved, the cornering power is enhanced, and the dry grip property is improved. Help maintain. The outer groove wall surface 8a may be a convex curve extending outward in the axial direction of the tire similar to the inner groove wall surface 9a, and in particular, as shown in FIG. 4, the groove extends in a zigzag shape in the circumferential direction. By using the wall surface 8a, the traction can be enhanced.

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

This means that the groove depth ratio of the tread ground contact width TW and the groove width GW of the vertical groove 7 is GW /, with the groove depth of the vertical groove 7 being constant.
It depends on the result of measuring the passing noise by changing the TW. The test tire size was 205/55 R15, and each tread surface was provided with two vertical grooves with a U-shaped cross section.

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

Further, in FIG. 8, the groove width ratio GW / TW is 13%.
And 27% are the results of frequency analysis. It can be seen that 27% of the products have reduced noise around 1 kHz.

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

Similarly, the result of measuring the speed at which the hydroplaning phenomenon occurs is shown in FIG. As compared with the conventional tire, it can be seen that, in the example, even if the total groove width ratio is the same, the hydroplaning generation rate is high and the same phenomenon is unlikely to occur. This is because the vertical groove 7 is provided before and after the ground contact center Q at the time of ground contact by providing a groove wall surface 9a having a convex curved surface in the raised narrow central portion 9 of the tire of the present invention, as shown in FIG. A widened portion 13 that spreads like a trumpet is formed to improve drainage. In addition, the widened portion 13 formed in this manner also prevents occurrence of air column resonance in the vertical groove 7, and as described above, also helps to reduce tire noise.

From the above noise, dry grip property due to cornering power, and wet grip property due to 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%. It is 40 to 50%.

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

Further, in FIG. 6, among the surfaces of the central portion,
The groove wall surface 9a and the central ground contact surface 9b have different radii of curvature R
3 shows a case of being formed by an arc of R4. Radius of curvature R3
Are smaller than the radius of curvature R4 of the central ground contact surface 9b and the radius of curvature R2 of the ground contact surface of the shoulder portion, respectively, and the lower limit thereof is preferably 5% or more of the tread ground contact width TW. 5%
When it is less than, the drainage effect tends to be insufficient. The upper limit is a value that matches the radius of curvature R4, and at this time, the surface shape of the central portion is a single arc. The radius of curvature R4 is equal to the radius of curvature R2.
It is also possible to make them so close to each other that the wet grip performance is not impaired and to be substantially the same.

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

Here, in the tire provided with such a raised central portion 9, the heat generated in the central portion 9 is particularly large as compared with the conventional tire, and the high temperature causes deterioration in high-speed durability. 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.
5 to 0.25 of the first rubber composition 22 and the loss tangent tan
The second rubber composition having a δ2 of 1.2 to 10.0 times the loss tangent tan δ1 is used, 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, which has been
A second rubber portion 26 using the second rubber body 23 is provided on at least the outer surface side of the tread of one of the shoulder portions 8.

Thus, the first rubber portion 25 of the central portion 9
Is formed of the first rubber composition 22 having a small loss tangent tan δ1, that is, low energy loss and low exothermicity, the above-mentioned increase in internal temperature that is excessive in the central portion 9 is effective. Suppressed and improve high speed durability.

On the other hand, the second portion of the shoulder portion 8 having a high ground contact pressure
The rubber portion 26 of No. 2 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 absorbing property, so that the riding comfort can be improved and the road surface following performance and the grip can be improved. With the increase in performance, steering stability can be maintained for the entire tire when going straight and turning.

The rubber structure Y of the tread rubber 21
As shown in FIGS. 13 to 15, a horizontally divided 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, a vertically divided rubber structure Y2 formed by dividing the first rubber portion 25 and the second rubber portion 26 in the tire radial direction may be employed.

One example of the laterally divided rubber structure Y1 is, as shown in FIG. 13, a belt layer extending from a starting point V on the outer surface of the tread to a belt layer at a position separated from the tire equator CL on the outer side in the tire axial direction. A book boundary 29 is provided, and the first rubber part 2 is provided between the book boundaries 29, 29.
5 and also on the outside of the boundary line 29 the second rubber part 2
6 and 26 are formed. The starting points V and V are the tire equator C.
It is provided on both sides of 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 wall surface 9a of the groove, the bottom surface 7S of the groove or the outer surface of the shoulder 8, and therefore the boundary line 29 , 29 between at least the belt layer side of the central portion 9 (inner side in the tire radial direction), in this example, both the belt layer side and the tread outer surface side (tire radial direction outer side). Formed. Similarly, the second rubber portion 26 outside the boundary line 29 is also formed on at least the tread outer surface side of the shoulder portion 8, in this example, both the belt layer side and the tread outer surface side.

The starting point V is defined by the groove wall surfaces 8a, 9b, the groove bottom surface 7S, or the inside of the shoulder contact surface that separates a distance equal to the groove bottom width GW1 of the vertical groove 7 from the inner end a to the outer side in the tire axial direction. It is preferable to provide it on the end portion a1, and more preferably, the starting point V is provided on the groove bottom surface 7S. The boundary line 29 may be formed in the radial direction, that is, in parallel with the tire equator plane, but as shown in FIG. 14, for example, the boundary line 29 is inclined inward in the radial direction toward or away from the tire equator CL or toward the approaching direction. You may form it.

In the rubber structure Y1, as shown in FIG. 15, one boundary line 29 is formed in the tread portion T, and the first rubber portion 25 is formed inwardly of the boundary line 29 in the tire axial direction. May be. At this time, the second rubber portion 26 is formed only on the one shoulder portion 8 which is outward in the tire axial direction,
In such a case, the tire is mounted with the shoulder portion 8 facing the outer side of the vehicle.

It should be noted that a comparative example tire having the tread rubber structure shown in FIG. 13 and the conventional tire shown in FIG. 20 and having a rubber structure in which the tread rubber is divided with the same width dimension as in FIG. (Fig. 2
2) and 2) are formed by using the first and second rubber compositions 22 and 23, respectively, and the loss tangent ratio tan δ2 / tan δ1 at that time is formed.
The relationship between the high speed durability and the 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 remarkably improved when the ratio tan δ2 / tan δ1 is in the range of 1.2 to 2.0, and the high speed durability is It can be improved to the level of 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 high-speed durability is insufficient, and when the ratio is more than 10, the physical properties of the first and second rubber compositions 22 and 23 are excessively different. , Induces a separation between the compositions 22 and 23. When the loss tangent tan δ1 is less than 0.01,
The steering stability is impaired, and high speed durability becomes insufficient when the value is larger than 0.35. Therefore, the loss tangent tan δ1 is preferably in the range of 0.05 to 0.25. Loss tangent tan δ2
Is at least 0.2 in order to obtain the required steering stability.
It is 5 or more, preferably 0.30 or more.

Here, the loss tangent is as follows: temperature 70 ° C., initial strain 10%, dynamic strain 2%, frequency 10 Hz,
It is a value measured using a viscoelasticity spectrometer manufactured by Iwamoto Seisakusho.

As an example of the vertically divided rubber structure Y2, as shown in FIG. 16, the central portion 9 and the groove bottom surface 7S are provided.
And the first rubber portion 2 disposed on the belt layer side (inside 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 side of the tread, which is a second rubber portion 26 arranged 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 below the shoulder portion 8 and the groove bottom surface 7S, and is substantially parallel to the central portion surface below the central portion 9 and the outer portion 30A. An inner portion 30B extending with a convex outer surface. Therefore, the base rubber 30 forms the 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 a measurement condition, the ratio tan δ2 / tan δ1 was set to 0.
30 / 0.15 (= 2.0) is constant, and the total thickness tb is 3.0 mm. As shown in Table 2, the ratio ta /
It can be seen that the 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 remarkably 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 in a tire.
Therefore, the thickness ratio ta / tb is allowed up to the range of the thickness ta where the base rubber 30 is not exposed from the tire outer surface.

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

Further, in this example, the shoulder portion 8 and the central portion 9
Further, a lateral groove extending substantially in the tire axial direction can be provided to improve the wet grip performance.

As shown in the example 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 apart from the longitudinal groove 7 in the tire axial direction and opens at the tread end. By not connecting to the vertical groove 7, the rigidity of the shoulder portion is prevented from being lowered, and the wet grip performance is improved by opening at the tread end.

Only one end of the lateral groove 12 of the central portion 9 is opened to the longitudinal groove 7, and the inner side in the tire axial direction is interrupted near the equator CL. By thus not providing the lateral groove near the tire equator CL, the rigidity of the central portion is maintained and the steering stability performance 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 surfaces 11b and 12b of the lateral grooves 11 and 12 are surfaces parallel to the tire equator CL. Or the angle β formed with the radius line Y is 15
The angle is less than °.

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

[0063]

[Specific Example] Tires of tire size 205/55 R15 were manufactured according to the specifications in Tables 1 and 2, and the steering stability performance when traveling straight, the steering stability performance when cornering, and the high-speed endurance performance were measured. Shown in the table. Each performance is shown by an index with the value of Conventional Example 1 being 100, and the larger the index, the better. The tire of Comparative Example 5 having the tread profile of the present invention is remarkably effective in terms of tire noise and wet grip performance as described above, but heat generation in the tread central portion is large as compared with the conventional tire having the same tread rubber composition, Inferior in high speed durability. By using such a tread profile and the tread rubber structure of the present application together, 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 is formed of one rubber composition, it is difficult to achieve both high speed durability and driving stability.

Further, 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 drawings]

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

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

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

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

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

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

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 the relationship between the total groove width ratio and the cornering power.

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

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

FIG. 12 is a cross-sectional view illustrating a groove bottom edge in both a and b.

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

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

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

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

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

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

FIG. 19 is a diagram showing the relationship between the 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]

 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 grounding surface 10 Virtual tread line between the grounding surface of the shoulder 20 Coated rubber layer 22 First rubber Composition 23 Second rubber composition 25 First rubber part 26 Second rubber part 29 Boundary line 30 Base rubber 31 Cap rubber CL Tire equator T Tread part

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 31, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

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 the loss tangent tan
The second rubber composition having a δ2 of 1.2 to 10.0 times the loss tangent tan δ1 is used, 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, which has been
A second rubber portion 26 using the second rubber body 23 is provided on at least the outer surface side of the tread of one of the shoulder portions 8.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction content]

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. Higher when the ratio is less than 1.2
The effect of improving quick durability is insufficient, and the ratio is greater than 10.
When, the physical properties between the first and second rubber compositions 22 and 23 are excessive.
In some cases, a separation is introduced between the compositions 22 and 23.
To emit. When the loss tangent tan δ1 is less than 0.01,
Lack of properties as rubberAlso, high speed resistance when larger than 0.35
Not long lasting. Therefore, the loss tangent tan δ is preferable.
1 is in the range of 0.05 to 0.25. Also loss tangent tan
δ2 is to obtain the necessary steering stability,Preferably
0.25 or more,furtherIt is preferably 0.30 or more.

Claims (9)

[Claims] 1. A tread portion is provided with two longitudinal grooves on both sides of a tire equator that extend substantially continuously in a circumferential direction, so that the tread portion is formed from a groove bottom edge of the longitudinal groove on the outer side in the tire axial direction. Also divided into a pair of outer shoulder portions and a central portion between the groove bottom edges on the tire axial direction inner side of the longitudinal groove, the central portion, in the tire meridional section, from the inner groove bottom edge to the radial outside. It has a central part surface using a series of convex curves consisting of an inner groove wall surface that extends inward in the tire axial direction with a convex curve and a central ground contact surface that smoothly connects between the inner groove surface parts, and the central part surface is The tread portion is substantially in contact with a virtual tread line connecting the ground contact surfaces of the shoulder portion, and the tread portion has a loss tangent tan δ1 of 0.01 to 0.
No. 35 of the first rubber composition 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. A first rubber portion using the first rubber composition is arranged on the belt layer side, and
A second rubber portion using the second rubber composition is provided on at least the outer surface of the tread of at least one shoulder portion, and the belt layer has a plurality of belt plies in which juxtaposed cords are covered with a topping rubber, or a belt. A pneumatic tire comprising: a ply; and a cover rubber layer that covers the outer side of the belt ply located on the outermost side in the radial direction and extends in the tire axial direction. 2. The tread portion has a boundary line from the outer surface of the tread to the belt layer at a position separated from the tire equator to the outer side in the tire axial direction in a tire meridian section, and the first rubber portion is a boundary line. By arranging the second rubber portion on the inner side in the axial direction of the tire and on the outer side of the boundary line, the first rubber portion is provided on at least the belt layer side in the central portion, and the tread outer surface side on the shoulder portion. To the second
2. The pneumatic tire according to claim 1, wherein the rubber portion is provided. 3. The boundary line starts from the groove bottom surface of the vertical groove, the outer surface of the shoulder portion, or the outer surface of one of the groove wall surfaces in the center portion. Pneumatic tire. 4. The pneumatic tire according to claim 3, wherein the boundary line extends in the radial direction. 5. The pneumatic tire according to claim 3, wherein the boundary line inclines radially inward from the outer surface of the tread in a direction away from or closer to the tire equator. 6. The tread portion is characterized in that a central portion thereof is composed of a belt rubber side base rubber which is a first rubber portion and a cap rubber which is a second rubber portion covering the base rubber. The pneumatic tire according to claim 1. 7. The thickness ta of the base rubber from the belt layer at the tire equator is greater than the total thickness tb from the belt layer at the groove bottom surface of the longitudinal groove. Pneumatic tire. 8. The tread portion has a central portion, a bottom surface of a vertical groove, and a shoulder portion, which are a base rubber on the belt layer side which is a first rubber portion, and a second rubber portion which covers the base rubber. The pneumatic tire according to claim 1, comprising a cap rubber. 9. The thickness ta of the base rubber from the belt layer at the tire equator is larger than the total thickness tb from the belt layer at the groove bottom of the vertical groove. Pneumatic tire.