JP2648075B2 - 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, and more particularly to a pneumatic tire which can be used for passenger cars while improving wet grip performance and reducing tire noise while maintaining dry grip 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.

Conventionally, such conflicting performance has been adjusted according to the performance required for the tire.

An object of the present invention is to provide a pneumatic tire that can improve wet grip performance, suppress air column resonance, and reduce tire noise without impairing dry grip performance.

[0010]

SUMMARY OF THE INVENTION The present invention provides:
A pneumatic tire divided into a shoulder portion on the outer side in the axial direction of the vertical groove and a central portion between the vertical grooves by two vertical grooves on both sides of the tire equator extending substantially continuously in the tread portion in the circumferential direction. In the tire meridional section, the central portion has both side wall surfaces extending inward in the axial direction with a curve protruding radially outward from the groove bottom edge on the tire axial direction inside of each of the two longitudinal grooves, It has a central surface shape using a series of curves consisting of a central ground plane that smoothly connects between the wall surfaces, and the central surface shape is in contact with an imaginary line that continuously connects between the ground planes of the shoulder part A pneumatic tire characterized in that:

[0011]

In the surface shape of the central portion, the side wall surfaces on both sides are formed into a curved surface convex outward in the radial direction, so that the groove depth of the longitudinal groove gradually widens outward in the radial direction and the surface shape of the central portion is continuous. , The raised central portion improves drainage, reduces hydroplaning, and improves wet grip.

[0012] Further, dry grip performance can be maintained by providing two vertical grooves and making the central surface shape contact an imaginary line connecting the grounding surface of the shoulder portion.

Further, by gradually increasing the depth of the vertical groove in the central portion by a series of curves, a widened portion is formed so as to increase the width of the groove on the contact surface in a so-called trumpet shape before and after the traveling direction of the contact surface. This prevents air column resonance and helps to reduce tire noise.

[0014]

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 the bead core 2 of the bead portion B from the inner side in the tire axial direction to the outer side in the tire axial direction from the tread portion T to the sidewall portion S, and the tread portion. A bead apex 6 extending inward from the bead core 2 in the tire radial direction is disposed between the carcass main body portion and the rewinding portion, and has a belt layer 4 inside the carcass 3 and outside the carcass 3. And rigidity.

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 radial tire for a passenger car. It is formed.

The belt layer 4 is formed by plying a plurality of plies using cords having high tensile stiffness such as steel or aromatic polyamide by 15 to 30 degrees with respect to the tire circumferential direction so that the cords intersect each other. Are formed at relatively small angles. 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.
By providing two longitudinal grooves 7, 7 extending substantially continuously in the circumferential direction on both sides of L, a shoulder portion 8 axially outside the longitudinal groove 7 and the longitudinal groove 7, 7 are provided. The tread part T is divided into a central part 9 located.

The longitudinal grooves 7 are preferably formed in the tire equatorial plane C.
It is arranged so as to be located substantially at the center between L and the tread ground end TE.

Further, the surface of the central portion 9 is radially outward from the groove bottom edges 7a, 7a inside the two longitudinal grooves 7, 7 in the tire axial direction in a tire meridional section which is a section including the tire center axis. It has a central surface shape using a series of curves consisting of side wall surfaces 9a, 9a rising in a convex curve and extending inward in the axial direction, and a central ground contact surface 9b smoothly connecting between these side wall surfaces 9a, 9a. .

The center contact surface 9b refers to a region of the tread surface which comes into contact when a normal load is applied in the standard condition.

The curve of the surface shape of the central portion substantially touches an imaginary line 10 smoothly connecting between the contact surfaces of the shoulder portion 8.

Here, "substantially in contact" means that the distance L between the center contact surface 9b and the imaginary 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 ground pressure between the shoulder portion and the central portion becomes large, grip performance is reduced, and wear resistance is impaired.

Furthermore, a virtual line 10 smoothly connecting between the ground planes
Is defined as an arc curve or straight line having a single radius of curvature that is in contact with a tangent at the inner edge a of the shoulder portion 8 in the tire axial direction and has both ends at the inner edges a.

According to the present invention, the central portion 9 is formed into a curved surface at the central portion as described above, so that a bulge having a relatively small radius of curvature and a width sufficiently smaller than 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.

Further, 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 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 that the surface shape at the center is defined by a radius of curvature R1.
The example formed by the curve which consists of a single circular arc is shown.
The radius of curvature R1 is the radius of curvature R of the shoulder portion 8.
2, which in this example is inscribed in the imaginary 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 of the contact surface of the central portion 9, that is, the central 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. In addition, the curvature radii R1, R
2 has their centers arranged on the tire equatorial plane including the equator CL.

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 width CW of the central portion 9 between the groove bottom edges 7a, 7a is 40 to 55% of the tread contact width TW.
It is good to be about.

Further, the shoulder portion 8 has a side wall surface 8a in the tire axial direction, that is, a groove wall on the axially outer side of the longitudinal groove 7, having an angle α with the tire radial line X of 0 to 40 °, preferably 5 to 2 °.
The inner edge a of the shoulder portion 8 having a high contact pressure is formed by forming a relatively steep and non-circular, for example, straight line of about 5 °.
It exerts an edge effect with the road surface, improves lateral force, increases cornering power and helps maintain dry grip. In addition, a convex curve extending outward in the tire axial direction similar to the side wall surface 9a of the central portion 9 may be used.
By forming the side wall surface 8a which is bent in a zigzag manner in the circumferential direction and extends, traction can be enhanced.

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

This is because the groove width GW / T of the tread contact width TW and the groove width GW of the vertical groove 7 is determined while keeping the groove depth of the vertical groove 7 constant.
According to the result of measuring the passing noise while changing W. The 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 it on a 2000 cc domestic 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. 4, it increases with an increase in the groove width ratio, reaches a maximum when the ratio is 13%, and then rapidly decreases. Therefore, it is understood that 15% or more is preferable.

FIG. 5 shows that the groove width 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%.

Further, with respect to the vertical groove 7, the width G of the vertical groove
It has been found that the total groove width ratio 2 GW / TW, which is the ratio of the total groove width 2 GW of W to the tread contact width TW, affects the cornering power and wet grip. By changing the total groove width ratio ΣGW / TW between the tire of the same size having the central surface shape of the single circular arc shown in FIG. 1 and the tire of the comparative example having four longitudinal grooves G shown in FIG. FIG. 6 shows the result of measuring the cornering power. As the total groove width ratio, the value of 2 GW / TW described above was used for the examples, and the value of (ΔGW) / TW was used for the comparative examples. 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 because, when the total groove width ratio defined above is constant, the tire of the present invention having a convex curved side wall has a large tread area in a meridional section of the tire and also contributes to an increase in lateral rigidity. It is thought that it is. However, when the total groove width ratio exceeds 50%, the cornering power is greatly reduced.

FIG. 7 shows the result of measuring the speed at which the hydroplaning phenomenon occurred in the same manner. Compared with the conventional tire, the embodiment has the same total groove width ratio,
It can be seen that the hydroplaning generation speed is high and the phenomenon is unlikely to occur. This is because the tire of the present invention has a raised central portion 9 having a small width and a central surface shape including a side wall having a convex curved surface. It is considered to have a widened portion 13 extending in a trumpet shape to improve drainage.

From the above noise, dry grip property by cornering power, and wet grip property by hydroplaning phenomenon, the groove width ratio is 15% or more, and the total groove width ratio is 3
It can be seen that it is better to set it to about 0 to 50%.

In the example of FIG. 1, the central portion surface shape is formed by a single circular arc, but may be formed by an elliptical shape or a curve approximating an ellipse.

FIG. 3 shows a case where the side wall surface 9a and the central ground contact surface 9b are formed by arcs having different radii of curvature R3 and R4 in the surface shape of the central portion. The radius of curvature R3 is smaller than the radius of curvature R4 of the center contact surface 9b and the radius of curvature R2 of the contact surface of the shoulder portion, and is preferably set within a range of 5% or more of the tread contact width TW. If it is less than 5%, the drainage effect tends to be insufficient, and the maximum value is a value that results in the central surface shape of a single arc as described above. The radius of curvature R4 can be made substantially the same as the radius of curvature R2 so as not to impair the wet gripping property.

Further, on the left and right side wall surfaces 9a, 9a,
For example, it is also possible to make the curvature radius R3 of the side wall surface 9a facing the outside of the vehicle different on the left and right so as to increase the radius of curvature R3, thereby reducing the sound radiated to the outside.

Further, in the tire of the present invention, the depth of the vertical groove 7 is set to about 4 to 8% of the tread contact width TW, and extends substantially in the axial direction at the shoulder portion 8 and the central portion 9. A lateral groove is provided to improve wet grip performance.

As shown in FIG. 2, the shoulder portion 8 is provided with a lateral groove 11 in this embodiment. The lateral groove 11
Extends axially outward from a position away from the longitudinal groove 7 in the axial direction and opens at the tread end TE. By not connecting to the vertical groove 7, the reduction in rigidity of the shoulder portion is prevented, and the wet grip performance is improved by opening the tread end TE.

Only one end of the lateral groove 12 in the central portion 9 is open to the longitudinal groove 7, and the inner side in the 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 a small angle of less than 15 °.

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.

[0046]

[Specific example] A tire having a tire size of 205/55 R15 is manufactured according to the specifications shown in Table 1, and noise, cornering power,
The results of measuring the hydroplaning generation speed are shown in the same table in the same table as the cornering power and the hydroplaning generation speed by an index with Comparative Example 1 being 100. In each case, the measurement conditions are as described above, and the larger the index, the better. It can be seen that the tires of the examples have excellent hydroplaning characteristics and, compared to comparative tires in which the total longitudinal groove width ratio is close, the noise is reduced without impairing the hydroplaning characteristics and cornering power. . Since all of the comparative examples have four vertical grooves, it is considered that the noise performance is increased even if the vertical groove width ratio is constant.

[0047]

[Table 1]

[0048]

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.

[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 partial plan view showing the appearance of the tread surface.

FIG. 3 is a sectional view of a tire according to another embodiment.

FIG. 4 is a diagram showing the results of a noise test.

FIG. 5 is a diagram showing a result of a noise test.

FIG. 6 is a diagram showing a relationship between a total groove width ratio and cornering power.

FIG. 7 is a graph showing the relationship between the total groove width ratio and the speed of hydroplaning.

FIG. 8 is a plan view schematically showing a tread contact surface of the tire according to one embodiment of the present invention.

FIG. 9 is a sectional view of a tread portion of a conventional tire.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tire 2 Bead core 3 Carcass 4 Belt layer 6 Bead apex 7 Vertical groove 8 Shoulder part 9 Central part 9a Side wall surface 9b Central ground plane 10 Virtual line between shoulder ground planes 11, 12 Horizontal groove

Claims (5)

(57) [Claims] 1. Two longitudinal grooves on both sides of the tire equator extending substantially continuously in the circumferential direction of the tread portion and divided into a shoulder portion axially outside the longitudinal groove and a central portion between the longitudinal grooves. The pneumatic tire described above, wherein the central portion, on the meridional section of the tire, both sides extending inward in the axial direction with a curve that protrudes radially outward from the groove bottom edge on the tire axial direction inside of each of the two longitudinal grooves. A wall surface and a central portion surface shape using a series of curves consisting of a central contact surface that smoothly joins between the side wall surfaces are provided, and the central portion surface shape connects the contact portions of the shoulder portion to each other. A pneumatic tire characterized by being substantially in contact with a connecting virtual line. 2. The pneumatic tire according to claim 1, wherein the surface shape of the central portion is formed by a curve formed by an arc having a single radius of curvature. 3. The pneumatic tire according to claim 1, wherein the surface shape of the central portion is formed by arcs having different radii of curvature between the groove wall and the central ground contact surface. 4. The surface shape of the central portion is such that the central contact surface is formed by a first arc having a radius of curvature substantially equal to the contact surface of the shoulder portion, and the side wall surface is smaller than the first arc. The pneumatic tire according to claim 3, wherein the pneumatic tire is formed by a curve formed by a second arc having a radius of curvature. 5. The pneumatic tire according to claim 1, wherein the central portion surface shape is formed by a substantially elliptical curve formed by the groove wall and the central ground contact surface.