JP2698739B2 - 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 with reduced tire noise without impairing dry grip performance and wet grip performance.

[0002]

2. Description of the Related Art By arranging a plurality of longitudinal grooves continuous in the circumferential direction of a tire on a tread portion of the tire, water between a tread surface and a road surface during a rainy run is eliminated, and a wet grip property of the tire is maintained. doing. It is known that this vertical groove causes tire noise when traveling on a dry road surface, although it improves drainage.

[0003] One of the noises generated by the flutes is caused by air column resonance. This is because a kind of air column is formed between the vertical groove of the grounded tire and the road surface, and due to the deformation of the tire tread during rolling, air flows into and out of this air column, thereby causing a specific wavelength, That is, a sound having a wavelength about twice that of the air column is generated.

[0004] This phenomenon is called air column resonance and is annoying.
It is a main sound source of noise in the range of 800 to 1.2 kHz centered on KHz. 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.

As means for preventing the air column resonance, it is known to reduce the number of vertical grooves and the groove volume.

[0006]

However, a decrease in the number of vertical grooves and a decrease in the groove volume leads to a decrease in wet drainage performance and a decrease in wet grip performance.

In order to improve the wet grip performance, on the contrary, the number of vertical grooves and the groove volume may be increased. However, this has been considered to increase tire noise as described above. Furthermore, the increase in the number of vertical grooves and groove volume leads to a decrease in dry grip performance due to a decrease in the contact area and a decrease in tread rigidity. Therefore, conventionally, such contradictory performance is adjusted according to the performance required for the tire. Was.

On the other hand, in order to reduce the hydroplaning phenomenon, that is, to improve wet grip performance, Japanese Unexamined Patent Publication No.
JP-A-34204 proposes a tread pattern in which a tread portion has two curved surfaces having a relatively small radius of curvature arranged in the tire axial direction by a groove-like portion having a smoothly curved side wall passing through the tire equator of the tread. . However, such a thing tends to cause a decrease in dry grip performance because the contact area of the entire tread is reduced.

The present invention has been completed by studying the relationship between the width of the vertical groove and the air column resonance, and finding out that the air column resonance is reduced by widening the groove width beyond the range usually considered conventionally. It is an object of the present invention to provide a pneumatic tire capable of reducing tire noise without impairing the wet grip performance and the dry wet performance, which are the performances of the contradictory tires.

[0010]

According to the present invention, the tread surface is formed of a circular arc having a single radius of curvature or a curved surface which is monotonically convex outward in the radial direction in which circular arcs having plural radii of curvature are smoothly connected. Pneumatic tire, on the tread surface,
The tire equator extends continuously in the circumferential direction and the groove width is 25-7.
A single 0 mm vertical groove is provided , and a tie
Outside the tire axial direction starting from a position away from the tire axial direction
Side and open at the tread edge, and the groove width is
In the apparent overall contact area, which is the entire outer peripheral area of the contact with the road surface in the standard state where the lateral groove of 5 to 15% of the groove width of the groove is provided and the rim is assembled to the regular rim and the regular internal pressure and the regular load are applied, The sea / land ratio S / L of the land area L actually touching the ground and the sea area S not touching the ground is 25 to 45.
% Of pneumatic tires.

[0011]

[Function] Since the groove width of the vertical groove passing through the tire equator provided on the tread surface of the outwardly curved surface is 25 to 70 mm,
The compression of air in the groove is reduced to suppress the excitation of columnar resonance.
Noise of 0 Hz to 1.2 kHz can be reduced. Furthermore, since the sea / land ratio L / S is set to 25 to 45%, the ratio of the contact area of the tire is set to an appropriate value, and both wet grip performance and dry grip performance can be prevented from lowering. Also, the lateral groove
By limiting the starting position and groove width of
Tie that prevents disturbance of air flow and has wide flutes
Steering stability while reducing the decrease in rigidity of the
sell.

[0012]

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 meridional section of a tire 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 tread portion T to the side wall portion S from the inside in the tire axial direction to the outside, and is engaged with the tread portion. A bead apex 6 is provided between the carcass main body portion and the rewinding portion, and a bead apex 6 extending radially outward from the bead core 2 is provided between the carcass main body portion and the rewinding portion. And rigidity.

The surface of the tread portion T is composed of a circular arc having a single radius of curvature or a curved surface that is monotonically convex outward in the radial direction in which circular arcs having a plurality of radiuses of curvature are smoothly connected. A central arc surface having a radius of curvature R1 forming a portion and an outer arc surface inscribed in the center arc surface and having a radius of curvature R2 smaller than the radius of curvature R1 and forming both sides of the tread are used.

The tire 1 is formed as a wide flat tire having a relatively poor drainage property with a flat ratio of tire cross section height / tire width of about 0.4 to 0.6, particularly a radial tire for a passenger car. You.

The belt layer 4 is formed by plying a plurality of plies using cords having high tensile rigidity such as steel or aromatic polyamide by 15 to 30 ° 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 a longitudinal groove 7 extending substantially continuously in the circumferential direction of L, land portions 9, 9 that can be in contact with the road surface are formed outside the longitudinal groove 7 in the axial direction.

The longitudinal groove 7 is preferably formed as a straight groove extending in the circumferential direction around the tire equatorial plane CL.

Further, a groove wall 7a on the axially outer side of the vertical groove 7 is
By making the angle α between the tire radial line X and the straight line relatively sharp and non-circular, for example, about 0 to 30 °, preferably about 5 to 20 °, an edge effect with the road surface is exhibited and the lateral force is improved. It helps to increase cornering power and maintain dry grip. The groove bottom 7b is the belt layer 4
And the groove bottom 7b and the groove wall 7
a is a radius of curvature r of about 0.1 to 0.5 times the groove depth D;
, Whereby the vertical groove 7 has a rectangular or outwardly extending trapezoidal cross section.

Further, the vertical groove 7 is provided to reduce air column noise.
The groove width W measured in the tire axial direction is in the range of 25 to 70 mm. The nominal size specified in JISD4202 as a radial tire for passenger cars is 155 / ~.
225 / tires and the corresponding tires.

This is based on the assumption that the groove depth D of the vertical groove 7 is constant.
Eight types of tires having different groove widths GW were manufactured by hand carving, and the results were measured by an indoor bench tester. The tire size is 205/55 R15, and the result is shown in FIG. 3 as the sound pressure level dB (L) at 800 Hz on the vertical axis.

The measurement is performed at a rotational speed corresponding to 50, 60, and 70 km / h, and the average value is shown for each groove width W. The air column resonance increases with an increase in the groove width of the vertical groove 7, decreases when the groove width exceeds 25 mm, and largely decreases when the groove width exceeds 50 mm. It is considered that when the distance exceeds 25 mm, the air in the groove becomes hard to be compressed, and air column resonance hardly occurs.

If it is less than 25 mm, the effect of preventing air column resonance is inferior as described above, and the wet grip tends to be insufficient. Even if the distance exceeds 70 mm, no further noise reduction effect can be expected, and the dry grip performance and steering stability performance deteriorate. For this purpose, the groove width GW is set to 25 to 70 mm.
And More preferably, it is set in the range of 35 to 50 mm.

The depth D of the vertical groove 7 is the same as the depth of a normal tire, and the ratio D / W to the groove width W of the vertical groove is set to 0.1.
It is preferable to set in the range of 1 to 0.3. If it is less than 0.1, the groove volume is reduced and the wet grip performance is insufficient, and if it is more than 0.3, the effect of preventing air column resonance tends to be inferior.

The surface of the tread portion T may be provided with a groove having a groove width which does not affect noise, for example, a sipe or a circumferential narrow groove close to the sipe.

Further, in the present invention, the sea / land ratio S / L is in the range of 25 to 45%. Here, the sea / land ratio S / L is defined as the land area L and the groove in the apparent total ground contact area where the tire is grounded on a flat road surface in a standard state where the tire is assembled on a regular rim and a regular internal pressure and a regular load are applied. It is defined as the ratio to the area S.

The apparent total ground area is the entire outer peripheral area inside the outer edge line a surrounding the outer edge of the ground area in the ground pattern illustrated in FIG. 4, and the land area L is the apparent total ground area. , The total area of the hatched portion L1 that is actually in contact with the road surface, and the sea area S is the total area of the portion S1 that is not grounded by the groove.

As a result of the experiment, the sea / land ratio L / S was 25.
%, Wet grip performance is insufficient and
When it exceeds 5%, it has been found that the dry grip performance and the wear resistance performance decrease, and therefore, the sea / land ratio L / S is set in the above range.

The sea area S of the sea / land ratio L / S is a value including the horizontal grooves 10. In the above ratio, the land portions 9 are provided with the horizontal grooves 10 which do not defeat the object of the present invention. be able to. In the present invention , as shown in FIG. 2, the width of the horizontal groove 10 is relatively small, that is, about 5 to 15% of the groove width GW of the vertical groove 7.
Are circumferentially spaced.

The lateral groove 10 extends outward in the tire axial direction from a position away from the longitudinal groove 7 outward in the tire axial direction as a starting point 12, thereby ensuring a stable steering performance while reducing a decrease in rigidity of the ground contact portion. . The lateral groove 10 opens at the tread end 13. As shown in FIG. 1, the tread end 13 refers to the axially outermost point of the tire contact width TW when a normal load is applied. By opening at the tread end 13 in this manner, water between the tread surface and the road surface in the vertical groove 7 and the ground contact area other than the surrounding area is effectively excluded from the outside of the contact area, and wet grip performance is secured. The groove bottom of the lateral groove 10 is also formed substantially parallel to the outermost ply of the belt layer 4.

Further, in the present embodiment, the lateral groove 10 has an angle β between the tire circumferential direction and the starting point 12 of the axially innermost end of the lateral groove 10.
And has a convex portion which becomes larger as going outward in the axial direction, becomes larger at the tread end 13, and is in the tire axial direction between the length in the tire axial direction from the starting point 12 to the tread end 13. The lateral grooves 10, 10 on both sides of the tire equator CL are curved in the opposite directions. Note that the angle β formed with the tire circumferential direction is an angle formed with a tangent at the edge of the groove wall of the lateral groove 10 on the side of the acute angle at the starting point 12.

Thus, the drainage effect in the ground contact area can be enhanced together with the dry grip property, and the wet grip performance can be further improved. In the example shown in FIG. 2, the angle β1 with respect to the tire circumferential direction at the starting point 12 of the lateral groove 10 is approximately 45 °, and the point 10 which is 1/3 of the axial length of the lateral groove 10 is outside.
The angle β2 at the point b is about 75 °, the angle β3 at the point 2c outside the point ／ is 90 °, and the angle β4 at the tread end 13 is about 1 °.
The angle is 30 °.

As described above, by changing the inclination and having an inflection point near the shoulder portion, the effective length of the lateral groove 10 can be increased without lowering the tread lateral rigidity. Without using for the shoulder part,
The wet grip performance can be maintained and improved.

(Specific Example) A tire having a size of 205 / 55R15 and a pattern shown in FIGS.

[0035]

[Table 1]

The tires were tested for noise, dry grip performance, and wet grip performance.

FIG. 5 shows the result of measuring the noise based on the JASO standard by mounting the tire on a 2000 cc domestic passenger car. The vertical axis indicates the noise level dB (A), and the horizontal axis indicates the speed. As a result, compared with the comparative example, about 3
dB (A) was reduced.

FIG. 6 is a result of frequency analysis of the result at 60 km / h. It can be seen that the example has lower noise around 1 kHz than the comparative example. This is a result of suppression of air column resonance. Further, as a result of performing a wet grip test and a dry grip test on an actual vehicle, the example product was at the same level as the comparative example product. In addition, as dry grip property,
Each tire was mounted on a regular rim, filled with a regular internal pressure, and measured with an indoor bench drum tester. As the wet grip property, the speed at which the hydroplaning phenomenon occurred was measured.

[0039]

As described above, the pneumatic tire of the present invention can reduce tire noise due to air column resonance without impairing dry grip performance and wet 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 diagram showing a result of a noise test.

FIG. 4 is a diagram illustrating the shape of a ground plane;

FIG. 5 is a diagram showing the results of a noise test.

FIG. 6 is a diagram showing a result of a noise test.

FIG. 7 is a plan view illustrating 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

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-139402 (JP, A) JP-A-60-116507 (JP, A) JP-A-2-234810 (JP, A) JP-A-4- 218409 (JP, A) JP-A-3-279005 (JP, A) JP-A-3-295707 (JP, A) JP-A-4-193610 (JP, A) JP-A-4-215504 (JP, A) JP-A-3-136908 (JP, A) JP-A-63-121506 (JP, A) JP-A-62-214004 (JP, A) JP-A-6-127216 (JP, A) JP-A-61-60304 (JP, A) JP-A-4-317804 (JP, A) JP-A-1-115705 (JP, A) JP-A-2-6204 (JP, A) JP-A-61-47702 (JP, U) Kohei 7-41774 (JP, B2)

Claims (3)

(57) [Claims] An arc of a single radius of curvature;
Or more A pneumatic tire comprising a curved surface becomes a monotonically convex radially outwardly with smooth lined with arc radius of curvature, the tread surface, or extend continuously tire equator in the circumferential direction
One groove with a width of 25 to 70 mm is provided .
Starting from the position away from the longitudinal groove in the tire axial direction
Extend outward in the tire axial direction and open at the tread edge.
The apparent groove width is 5% to 15% of the width of the vertical groove and is the entire outer peripheral range of the ground contact with the road surface in a standard state where a normal internal pressure and a normal load are applied when a rim is assembled to a normal rim. Of the land area L that is actually touching the ground and the sea area S that is not touching the ground, the sea / land ratio S
/ L is 25 to 45%. 2. The pneumatic tire according to claim 1, wherein the tread surface has no circumferentially continuous groove other than the longitudinal groove. 3. The inclination angle of the lateral groove with respect to the tire circumferential direction.
Degree gradually increases from the starting point to the tread edge.
The pneumatic tire according to claim 1 or 2, wherein