JP2866596B2 - Pneumatic tire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention can be suitably used especially as a tire for a passenger car, while maintaining a dry grip performance.
The present invention relates to a pneumatic tire capable of improving wet grip performance and reducing tire noise.

[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, the noise in the region near 1 kHz, which is the peak frequency of the noise generated by the tire,
It is also a region that is easy for humans to listen to, and reduction of this noise is desired. 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 that can improve wet grip performance without impairing dry grip performance and steering stability performance, and can reduce 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 is divided into a pair of shoulder portions outside the groove bottom edge of the vertical groove in the tire axial direction and a central portion between the groove bottom edges of the vertical groove in the tire axial direction. The pneumatic tire is a pneumatic tire, wherein, in the tire meridional section, between the inner groove wall surface extending inward in the tire axial direction with a curve protruding radially outward from the inner groove bottom edge and the inner groove wall surface. And a central tread line using a series of curves consisting of a central tread area that smoothly joins the shoulder portion, and the central portion surface shape substantially touches a virtual tread line connecting the tread regions of the shoulder portions. And the width S of the contact surface area in the tire axial direction of the contact surface area of the one shoulder portion.
W1 is the ground contact area width SW of the contact area of the other shoulder portion
A longitudinal groove which is greater than 2 and which is the distance in the tire axial direction between the inner edge of the shoulder contact area of the one shoulder portion on the inner side in the tire axial direction and the outer edge of the central contact surface area on the side adjacent thereto. A pneumatic tire characterized in that the groove width GW1 is 35 mm or more and the groove width GW2 of the other vertical groove is 35 mm or more.

[0011]

In the surface shape of the central portion, the inner groove wall surface and the central ground contact surface area are formed by convex curved surfaces, so that the groove depth of the vertical groove gradually increases outward in the tire axial direction. By increasing the groove width GW of 35 mm or more, drainage is improved, and the hydroplaning phenomenon is reduced to improve wet grip.

Further, by setting the groove width GW of the vertical groove to 35 mm or more, preferably 40 mm or more, and further gradually increasing the groove depth of the vertical groove at the central portion by a series of convex curves, the contact as a footprint is obtained. Before and after the ground contact center on the ground (before and after in the tire traveling direction), a widened portion is formed in which the width of the groove in the contact surface increases like a trumpet, thereby preventing air column resonance and reducing tire noise.

Further, the convex central portion surface shape helps to increase the rigidity of the central portion. Moreover, since the width of the tread area of one shoulder is larger than the width of the tread area of the other shoulder, by mounting this one shoulder toward the outside of the vehicle body, the tread rigidity on the outer side of the vehicle body is reduced. It is possible to exert a strong lateral force under a limited contact area, for example, to increase the dry grip performance, and to improve the straight running stability and the turning stability.

[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 is composed of 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 sidewall portion S to a bead portion 2 from the inside in the tire axial direction to the outside, and a 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 from the bead core 2 is disposed between the main body portion of the carcass 3 extending between the two and the rewinding portions at both ends thereof, and maintains 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 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.
L, and two wide grooves 7, 7 extending substantially continuously in the circumferential direction and located on both sides of L, so that each groove 7 has a groove bottom edge 7b on the outer side in the tire axial direction. The tread portion T is formed between a pair of outer shoulder portions 8 and a central portion 9 located between groove bottom edges 7a, 7a on the inner side in the tire axial direction of each groove 7.
Is classified. Hereinafter, the vertical grooves 7 are referred to as vertical grooves 71 and 72 when distinguishing each vertical groove 7, and the shoulder portions 8 are referred to as shoulder portions 81 and 82 when distinguishing each shoulder portion 8.

The pair of vertical grooves 7 are formed at positions asymmetric with respect to the tire equatorial plane, and the groove depth D is
4-8% of the total contact width TW of the tread which is the same as each other,
For example, for tire size 205 / 55R15, 7.
It is 5 to 15.0 mm, more 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 the meridional section of the tire including the tire axis. It has a central part surface shape using a series of convex curves composed of inner groove wall surfaces 9A, 9A and a central ground contact surface area 9B smoothly connecting between the inner groove wall surfaces 9A, 9A.

The center contact surface area 9B is defined as
Of the surface, a width region in the tire axial direction that comes into contact when a normal load is applied in the standard state, and the shoulder contact surface area 12 of the shoulder portion 8 is contacted with the shoulder portion surface under a normal load. It refers to the width region in the tire axial direction. The total contact width TW of the tread is a distance between the outer edges e1 and e1 of the shoulder contact surface regions 12 on the outer side in the tire axial direction, and is a distance between the outer edge e1 and the inner edge e2 of each shoulder contact surface region 12. Each shoulder contact area 1 depending on the distance
2 is defined. Also, the shoulder contact surface area 12 intersects the outer groove wall surface 8A rising from the outer groove bottom edge 7b of the vertical groove 7 at the inner edge e2,
Therefore, the vertical groove 7 has a groove bottom 7S and inner and outer groove wall surfaces 9A,
8A, and the groove width GW of the vertical groove 7 is
It is defined by the distance between the inner edge e2 and the outer edge e3 of the center contact surface area 9B adjacent to the inner edge e2. Note that the center contact area 9B
Is defined by the distance between the outer edges e3 and e3.

The groove bottom edges 7a, 7b appear to be bent between the groove wall surfaces 8A, 9A when the groove bottom 7S is substantially flat as in this embodiment, and when the groove bottom 7S is a curved surface, as shown in FIG. 3b
And appears as a bending point or an inflection point between the groove wall surfaces 8A and 9A.

The curve of the central surface shape is
The shoulder tread areas 12, 12 are extended to substantially contact the virtual tread line 10 which smoothly joins between the tread areas.

Here, "substantially in contact" means that the distance L between the center contact surface area 9B and the virtual tread wire 10 on the tire equator CL is within 2% of the total contact width TW. Say. If it is 2% or more, the difference in ground pressure between the shoulder 8 and the central portion 9 becomes large, grip performance is reduced, and wear resistance is impaired. Therefore, it is preferably at most 1%, more preferably at most 0.5%.

Further, the virtual tread wire 10 that smoothly connects between the tread regions is defined by the inner edge e2 of the shoulder tread region 12.
Is defined as an arc curve having a single radius of curvature having both ends at the inner edges e2 and e2 in contact with the tangent at the point, and when the tangents are substantially parallel, a straight line connecting the inner edges e2 and e2 is formed.

In the present invention, the central portion 9 has a central portion surface shape formed by the curve as described above, so that a bulge having a relatively small radius of curvature and a sufficiently small width as compared with 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.

It is considered that this is because when the radius of curvature of the central portion 9, particularly the radius of curvature of the central ground contact area 9A, is small, the drainage to both sides is enhanced and the drainage effect on a wet road surface is improved.

The radius of curvature R2 of the shoulder contact surface area 12
When the distance is also reduced, the grip performance on a dry road surface due to the decrease in the ground contact area and the steering stability performance at the time of cornering are reduced. Accordingly, the radius of curvature R2 of the shoulder contact surface area 12 is relatively large, preferably three times or more the total contact width TW, and the upper limit thereof is allowable until the shoulder contact area 12 approaches a straight line parallel to the tire axis. . The radius of curvature R2
Is located on the tire equatorial plane.

FIGS. 1 and 2 show an example in which the central surface shape is formed by a curve formed of a single circular arc having a radius of curvature R1. This radius of curvature R1 is sufficiently smaller than the radius of curvature R2 of the shoulder contact surface area 12, and in this example, this curve is inscribed in the virtual tread line 10 at the contact point K.
Note that the center of the radius of curvature R1 is located on a center plane KL that passes through the contact point K and is parallel to the tire equatorial plane. In this example, the center plane KL is separated from the tire equatorial plane, and the center part surface shape is the center. It is formed in a symmetrical shape about the plane KL.

The radius of curvature R1 is 0.4 times the total contact width TW.
About 1.5 times, more preferably about 0.45 to 0.55 times. If it is smaller than 0.4 times, the width CW of the central contact surface area becomes too small, and the dry grip tends to be greatly reduced. If it is more than 1.5 times, the drainage effect is insufficient and the wet grip property is impaired.

In the shoulder portion 8, the vertical groove 7
The groove wall 8A on the outer side in the tire axial direction is preferably a relatively steep and non-circular, for example, a straight line having an angle α formed with the tire radial line X of 0 to 40 °, preferably 5 to 25 °. As a result, an edge effect of the shoulder portion 8 having a high contact pressure with the road surface at the inner edge e2 is exerted, and the lateral force is improved, the cornering power is increased, and the dry grip performance is maintained. Note that the outer groove wall surface 8A may have a convex curve extending outward in the tire axial direction like the inner groove wall surface 9A.

As for the vertical grooves 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 total contact width TW, is defined as the cornering power and wet grip performance. Was found to affect. A tire of the same size having a central surface shape of a single arc shown in FIG. 1,
FIG. 5 shows the results of measuring the cornering power of the conventional tire having four longitudinal grooves G shown in FIG. 14 while changing the total groove width ratio ΣGW / TW. 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 above-defined total groove width ratio is fixed, the convex curved groove wall surface 9A contributes to an increase in tire lateral rigidity.

FIG. 6 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 at the central portion 9 of the raised small width of the tire of the present invention, a convex curved groove wall surface 9A is formed.
As shown in FIG. 7 showing the shape of the ground contact surface when a normal load is applied, the vertical groove 7 has a wide portion 13 which spreads like a trumpet before and after the center Q of the ground. Form and improve drainage. Note that the total groove width ratioΣGW / TW is 5
If it exceeds 0%, as shown in FIG. 6, almost no improvement in the effect of suppressing hydroplaning is expected, and the cornering power becomes insufficient. Therefore, the total groove width ratio Σ
GW / TW is preferably 50% or less, more preferably 4% or less.
5% or less.

The widened portion 13 formed in this way also suppresses the occurrence of air column resonance in the vertical groove 7, and also helps to reduce tire noise as described above.

In order to further enhance the effect of suppressing the columnar resonance, the groove width GW of the vertical groove 7 needs to be 35 mm or more, preferably 40 mm or more. In the range of 50 mm or more, the above-mentioned effect hardly changes.

This is based on the result shown in FIG. 8 in which the passing noise was measured by changing the groove width GW while keeping the depth of the vertical groove 7 constant. As shown in the figure, the passing noise suddenly decreases after reaching a maximum when the groove width GW is 25 mm, and exhibits excellent low noise performance particularly at 35 mm or more.

However, as shown in FIG. 5, although the tire of the present invention has a high cornering power, the increase in the groove width GW causes a decrease in the ground contact area, and decreases the dry grip performance and the steering stability.

Accordingly, in the present invention, in order to further improve the steering stability and dry grip performance while maintaining the excellent low noise and hydroplaning resistance, the shoulder contact surface area width SW1 of one of the shoulder portions 81 is further improved. Is larger than the shoulder contact surface area width SW2 of the other shoulder portion 82 to form an asymmetric tread surface. This is because by mounting the tire with the wider shoulder portion 81 facing the outside of the car body, the tread rigidity on the outside of the car body is increased and a strong lateral force can be exhibited, and steering stability, especially turning stability Can enhance the character.

In this example, the other shoulder contact surface area width SW2 facing inward of the vehicle body is preferably at least 0.09 times the total contact width TW, for example, 15 mm or more at a tire size of 205 / 55R15. When it is smaller than 0.09 times, the contact pressure of the other shoulder contact surface area 12 increases unevenly, and uneven wear occurs.

In this embodiment, the width CW of the central contact surface area is set larger than the width SW2 of the other shoulder contact surface area.
The groove width GW1 of one vertical groove 71 adjacent to the one shoulder portion 81 is smaller than the groove width GW2 of the other vertical groove 72. This is because the stability of the grounding is enhanced by increasing the width CW of the central grounding surface area by setting CW> SW2. Conversely, when CW ≦ SW2, the straightness is reduced, and uneven wear occurs in this surface area. Easy to trigger. Therefore, preferably, the center contact surface area width CW is 1.4 to 2.0 times the other shoulder contact surface area width SW2, more preferably 1.4.
It is about 1.7 times. When the groove width GW1 is set to be equal to or larger than the groove width GW2, the central portion 9 is too close to the tire equator CL on the inward side of the vehicle body, so that the lateral force is reduced and the asymmetry becomes excessively large, thereby impairing the steering stability. Easy to invite.

In order to maintain dry grip, abrasion resistance, steering stability, etc., the central contact surface area width CW is:
Preferably, it is about 5 to 40% of the total contact width TW, more preferably 15 to 35%. Further, the inner bottom edge 7
The width 9W of the central portion 9, which is the distance between the a and 7a,
It is preferable to set it to about 40 to 55% of W.

In this embodiment, the center plane KL of the central portion 9 is used.
Are arranged at a distance from the tire equatorial plane, but as shown in FIG. 9, the center plane KL matches the tire equatorial plane, and the left and right groove widths GW1 and GW2 are changed, so that one ground plane area is obtained. The width SW1 may be larger than the other ground surface area width SW2.

As shown in FIG. 10, the surface of the central portion may be formed as an elliptical shape or a curve approximated to an ellipse.

FIG. 11 shows a case in which the groove wall surface 9A and the center ground contact surface 9B are formed by arcs having different radii of curvature R3 and R4 in the center surface shape. 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 region 12 of the shoulder portion 8, respectively.
Preferably, the lower limit is 5% or more of the total contact width TW. If it is less than 5%, 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 can be made substantially the same as the radius of curvature R2 so as not to impair the wet grip performance.

Further, on the left and right groove wall surfaces 9A, 9A,
The radius of curvature R3 of one of the groove wall surfaces 9A on the side facing the outside of the vehicle body may be made larger than the other, so that sound radiation to the outside may be reduced.

In this embodiment, as shown in FIG. 4, a radiation groove 21 including at least a vertical radiation groove 20 for heat radiation is formed in the central portion 9.

In this embodiment, the radiation grooves 21 are formed by the vertical radiation grooves 20 and the horizontal radiation grooves 22.
The vertical radiation groove 20 extends substantially continuously in the circumferential direction over the center plane KL.
In this example of the book, it is formed as a linear narrow groove. The vertical radiation groove 20 has a groove depth D1 of 0.4 to 0.9 times the groove depth D of the vertical groove 7, and a groove width W1 of 5 times.
By setting the diameter to be equal to or less than mm, the required heat radiation effect is exhibited while maintaining the block rigidity. When the groove width W1 is larger than 5 mm and when the groove depth D1 is larger than 0.9 times the groove depth D, air column resonance occurs and tire noise is deteriorated. When the groove depth D1 is smaller than 0.4 times the groove depth D, the heat radiation effect becomes insufficient.

The horizontal radiation groove 22 has an inclination angle θ of 10 degrees or more with respect to the tire axial direction from the inner end position separated from the vertical radiation groove 20 and extends outward in the tire axial direction. As it grows, its outer edge
It opens in the vertical groove 7.

As described above, the lateral radiation grooves 22
Since it is separated from the vertical radiation groove 20, the required rigidity of the central portion 9 can be maintained, and steering stability is secured.

Similarly, the lateral radiation groove 22 has a groove depth D2 of 0.4 to 0.9 times the groove depth D, and the groove depth D2 is 0.9 times the groove depth D. When the angle is larger than twice and when the inclination angle θ is smaller than 10 degrees, the pitch sound of the lateral radiation groove 22 becomes excessive. When the groove depth D2 is smaller than 0.4 times the groove depth D, a satisfactory heat radiation effect cannot be expected.

The vertical radiation groove 20 and the horizontal radiation groove 22 each have an angle between the groove wall surface in each groove 20 and 22 and the normal to the tread surface, that is, the inclination gradient of the groove wall surface is preferably 15 degrees or less, more preferably. Is less than or equal to 5 degrees, thereby suppressing a dimensional change of the radiation groove 21 due to tire wear.

In this embodiment, a shoulder groove 23 is formed in the shoulder portion 8. Shoulder groove 23
A lug groove whose inner end is open in the vertical groove 7 and whose outer end is open at the tread end. Opening in the vertical groove 7 further enhances the heat radiation effect and increases the temperature rise of the shoulder groove 8. It controls the width and improves drainage.

The average pitch length in the circumferential direction of the lateral groove of a normal tire is about 30 mm, for example, at a speed of 60 km / h.
Is 500 to 600 Hz in FIG.
As shown in FIG. 2, the frequency coincides with the frequency of a noise peak in a tire having a tread profile having the raised central portion 9. Therefore, in this example, the horizontal radiation grooves 2
2 and the average pitch length P2 of the shoulder groove 23 are set to 40 mm or more, respectively.
Preferably, the pitch primary frequency of 3 is different from the noise peak.

As shown in FIG. 13, the vertical radiation groove 20 can be formed in a zigzag shape, and the groove wall surface 8A outside the vertical groove 7 can also be formed in a zigzag surface.

[0055]

[Specific example] A tire having a tire size of 255 / 40ZR17 was manufactured according to the specifications shown in Table 1. Passing noise, hydroplaning generation speed, straight running stability, turning stability, and abrasion resistance were measured and compared. Are shown in the same table.

[0056]

[Table 1]

[0057]

Since the pneumatic tire of the present invention is constructed as described above, it is possible to improve wet grip performance without impairing dry grip performance and reduce tire noise due to air column resonance.

[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 an enlarged sectional view showing the surface shape of the central part.

FIGS. 3A and 3B are schematic cross-sectional views showing another example of a vertical groove and a groove bottom.

FIG. 4 is a partial plan view illustrating an example of a tread pattern.

FIG. 5 is a diagram showing a relationship between a total groove width ratio and a cornering power.

FIG. 6 is a graph showing a relationship between a total groove width ratio and a hydroplaning generation speed.

FIG. 7 is a plan view schematically showing the shape of the ground contact surface of the tire according to one embodiment of the present invention.

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

FIG. 9 is a sectional view of a tire showing another example of the surface shape of the central portion.

FIG. 10 is a sectional view of a tire showing still another example of the surface shape of the central portion.

FIG. 11 is a sectional view of a tire showing still another example of the surface shape of the central portion.

FIG. 12 is a diagram showing the result of frequency analysis of tire noise in the tread profile of the present invention.

FIG. 13 is a partial plan view of a tread pattern showing another example of a vertical radiation groove and a vertical groove.

FIG. 14 is a sectional view of a tread portion of a conventional tire.

[Explanation of symbols]

 7, 71, 72 Vertical groove 7a Inner groove bottom edge 7b Outer groove bottom edge 8, 81, 82 Shoulder portion 9 Central portion 9A Inner groove wall surface 9B Central ground plane 10 Virtual tread line between shoulder ground plane areas CL Tire equator T tread section

Claims (3)

(57) [Claims] 1. The tread portion is provided with two longitudinal grooves extending substantially continuously in the circumferential direction on both sides of the tire equator, so that the tread portion is located outside the bottom edge of the longitudinal groove in the tire axial direction. A pneumatic tire divided into a pair of shoulder portions and a central portion between groove bottom edges inside the longitudinal groove in the tire axial direction, wherein the central portion has a radius from the inside groove bottom edge in a tire meridional section. A central surface shape using a series of curves consisting of an inner groove wall surface extending inward in the tire axial direction with a curve convex outward in the direction and a central ground contact surface area smoothly connecting between the inner groove wall surfaces. The central portion surface shape substantially contacts a virtual tread line connecting between the contact surface regions of the shoulder portion, and the contact surface region width SW1 in the tire axial direction of the contact surface region of one shoulder portion is equal to that of the other shoulder portion. Ground plane in the ground plane area One longitudinal groove which is larger than the width SW2 and which is a distance in the tire axial direction between an inner edge of the one shoulder portion inside the contact surface area in the tire axial direction and an outer edge of the central contact surface area on the side adjacent thereto; A pneumatic tire characterized in that the groove width GW1 of the other vertical groove is 35 mm or more and the groove width GW2 of the other vertical groove is 35 mm or more. 2. The groove width GW1 of the one vertical groove is smaller than the groove width GW2 of the other vertical groove.
The pneumatic tire as described. 3. The width SW of the contact surface area of the other shoulder portion.
2. The pneumatic tire according to claim 1, wherein 2 is smaller than a center contact surface area width CW of the center contact surface area.