JPH0840015A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To reconcile an improvement in wetting performance, particularly hydroplaning performance and reduction of a tire noise, and heighten dry grip performance including turning time. CONSTITUTION:Two longitudinal grooves 5 are arranged on both sides of the tire equator in a tread part 2, and the tread part 2 is divided into a central part 9 and shoulder parts 4 and 4, and this central part 9 is composed of inside groove wall surfaces 9A extending in a projecting curve in the axial direction of a tire from the inside groove bottom edge 6a and a central ground contact surface area 9B to smoothly connect these mutual inside groove wall surfaces 9A to each other, and a profile shape of this central part 9 is asymmetrically formed with a tire equatorial surface CL as the center. A groove width of the longitudinal grooves 5 is set not less than 35mm, and is set not more than 0.35 times of a ground contact width TW of the tread part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire suitable for use as a passenger car tire by improving wet performance, particularly hydroplaning performance and reducing tire noise.

[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 where human beings can easily hear around 1 kHz, and one of the main sound sources in such a high frequency region is 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, 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, 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 which can improve wet grip performance, particularly hydration planing resistance and tire noise, without impairing dry grip performance and steering stability performance.

[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 groove of the book, the tread portion to the center portion between the pair of shoulder portions outside the groove bottom edge on the tire axial direction outer side of the vertical groove and the groove bottom edge on the tire axial direction inner side of the vertical groove. In the pneumatic tire divided, the central portion, in the tire meridional section, an inner groove wall surface extending inward in the tire axial direction with a curve protruding radially outward from the inner groove bottom edge and an inner groove wall surface thereof. It has a central surface shape using a series of curves consisting of a central contact surface area that smoothly joins the spaces, and the central contact surface area is substantially in contact with a virtual tread edge that connects the contact surface areas of the shoulder portion. In addition, in the tire meridional section, the central portion has an asymmetric profile shape that is asymmetric with respect to the tire equatorial plane CL, and the inner edge of the shoulder contact area in the axial direction of the tire and the central contact point on the side adjacent thereto. A pneumatic tire, wherein a groove width GW of the circumferential groove is a distance in the tire axial direction is less than 0.35 times the ground contact width of 35mm or more and a tread portion between the outer edge of the surface area.

In the central portion, the center plane KL passing through the middle of the tire axial direction may coincide with the tire equatorial plane CL,
Further, the position may be displaced with respect to the tire equatorial plane CL.

The two vertical grooves may have different groove widths.

[0013]

In the central surface shape, 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 toward the outer side in the axial direction of the tire. By increasing the groove width GW of at least 35 mm, the drainage performance is improved and the hydroplaning phenomenon is reduced to improve the wet grip performance.

Further, the groove width GW of the vertical groove is set to 35 mm or more, preferably 40 mm or more, and the groove depth of the vertical groove in the central portion is gradually deepened by a series of convex curves.
As shown in, a widened portion in which the width of the groove portion in the ground contact surface F increases like a trumpet is formed in front of and behind the ground contact center Q of the tire ground contact surface F which is a footprint (front and rear in the tire traveling direction). Improves drainage and wet grip. In the figure, Fc represents the ground plane shape or ground area of the central ground plane area, and Fs represents the ground plane shape or ground area of the shoulder plane ground area.

In the present invention, the groove width of the vertical groove GW is set to 35 or more and 0.35 times or less of the ground contact width TW of the tread portion. In controlling the groove width in this way,
The relationship between the groove width and passing noise was determined based on the results of experiments. Tire size is 205/5
In 5R15, as shown in FIG. 8 (A), when the groove width GW is 7 to 35 mm, the contribution to the reduction of the passing noise is small, and the groove width GW is 7 mm or less or 35 mm or more, so that the passing noise is significantly reduced. It was also confirmed to be stable. Furthermore, the tire size is 225 / 50R16
Also in the tire of No. 2, as shown in FIG. 8 (B), substantially the same results as those described above were obtained.

In the test, J
It was carried out in accordance with the ASO standard, and the passing noise when the engine was off was measured at a vehicle speed of 60 km / H.

Based on this result, the groove width GW can be set to 35 mm or more, and the widened portion formed on the ground contact surface F can prevent the occurrence of air column resonance and can effectively reduce the passing noise. Since the passing noise is caused by the air column resonance as described above, it does not depend on the tire size and changes depending on the size of the groove width GW itself. Also, the groove width GW
Exceeds 0.35 times the ground contact width TW of the tread portion, the ground contact pressure becomes excessive, so that the dry grip property and the steering stability are deteriorated, and the wear resistance is deteriorated and the durability is deteriorated.

Further, the convex central surface shape serves to increase the rigidity of the central portion. Moreover, since the profile shape of the central part is asymmetrical with respect to the equatorial plane of the tire, by mounting the side of this central part toward the outer side of the vehicle body, the tread rigidity on the outer side of the vehicle body becomes large. A strong lateral force can be exerted under a given ground contact area, dry grip performance can be improved, and straight running stability and turning stability can be enhanced.

[0019]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a tire meridian cross section of a tire in a standard state attached to a rim R to which standards such as JATMA TRA and ETRTO are applied and filled with a normal internal pressure determined by these standards.

The pneumatic tire 1 is, in this embodiment,
As a passenger car tire, the tire has a flatness ratio of tire cross-section height / tire width of about 0.4 to 0.6 and is formed as a wide flat tire having relatively poor drainage property.

The tire 1 includes two carcass plies 16A in a radial arrangement which are wound around the bead core 15 of the bead portion 14 from the tread portion 2 to the sidewall portion 13 from the inner side to the outer side in the tire axial direction to be locked. , 16B
And a belt layer 17 disposed inside the tread portion 2 and outside the carcass 16 in the radial direction. Also, a carcass 16 extending between the bead cores 15 and 15.
A bead apex 18 extending from the bead core 15 to the outer side in the tire radial direction is arranged between the main body portion and the winding portions at both ends thereof to maintain the shape and rigidity of the bead portion 14.

The belt layer 17 is composed of a plurality of plies using cords having high tensile rigidity such as steel and aromatic polyamide, and in this embodiment, the cords cross each other so that the cords intersect each other. It is formed by arranging at a relatively small angle of 15 to 30 °. When the carcass 16 is a tire for passenger cars, organic fiber cords such as nylon, rayon, polyester, etc. can be used.

The tread portion 2 has, on its surface, two wide flutes 5 and 5 located on both sides of the tire equator and extending substantially continuously in the circumferential direction. 5 and 5, located between the pair of shoulder portions 4, 4 outside the groove bottom edge 6b on the tire axial direction outer side of the groove bottom 6 and the groove bottom edges 6a, 6a on the tire axial direction inner side of the groove bottom 6. The tread portion 2 is divided into a central portion 9 and a central portion 9.

In this embodiment, the pair of vertical grooves 5, 5 are
It is formed at an asymmetric position with respect to the tire equatorial plane CL. As a result, the center plane KL passing through the center of the central portion 9 in the tire axial direction is displaced from the tire equatorial plane CL.

The groove depth D of the vertical groove 5 is 4 to 6% of the total ground contact width TW of the tread, for example, tire size 205/5.
At 5R15, it is 7.5 to 12.0 mm, and more preferably 8.2 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 6a, 6a in the tire meridional section which is a section including the tire axis. It has a central portion surface shape using a series of convex curves consisting of inner groove wall surfaces 9A, 9A and a central ground contact surface area 9B that smoothly connects between the inner groove wall surfaces 9A, 9A.

The central ground plane area 9B means the central portion 9
Of the surface, it refers to a width region in the tire axial direction that comes into contact with a ground when a normal load determined by the standard is applied in the standard state, and the shoulder ground contact surface area 10 of the shoulder portion 4 is a normal load of the shoulder surface. The width area in the axial direction of the tire that contacts the ground below. Also, the total contact width TW of the tread
Is the distance between the outer end edges e1 and e1 of the shoulder ground contact area 10 on the outer side in the tire axial direction.

Further, the ground contact surface area 10 of the shoulder portion 4 intersects with the outer groove wall surface 8 rising from the outer groove bottom edge 6b of the vertical groove 5, and the intersection is the ground contact surface area 10 of the shoulder portion 4.
The inner edge 12 located on the inner side in the tire axial direction is formed. Therefore, in the ground contact surface area 10 of the shoulder portion 4, the ground contact surface area width SW is defined by the distance between the outer end edge e1 and the inner edge 12 in the tire axial direction.

Therefore, the vertical groove 5 is formed by the groove bottom 6 and the inner and outer groove wall surfaces 9A, 8 and the groove width GW of the vertical groove 5 is the ground surface area 1 of the shoulder portion 4.
It is defined by the distance in the tire axial direction between the inner edge 12 of the tire axial direction inner side of 0 and the outer edge 11 of the central ground contact surface area 9B adjacent thereto. In addition, the ground contact surface width C of the central contact area 9B
W is defined by the distance between the outer edges 11 in the tire axial direction.

When the groove bottom edges 6a and 6b are substantially flat as in this example, the groove bottom edges 6a and 6b appear as a bend between the groove wall surfaces 8 and 9A on the outer and inner sides, and the groove bottom 6 has a curved surface. Time, fig. 5
It appears as a bending point or an inflection point between the groove wall surfaces 8 and 9A as in (A) and (B).

In the present application, when the vertical groove 5 and the inner groove wall 9A are distinguished from each other on the left and right sides, the vertical groove 51 and 52 and the groove walls 91A and 9A are separated.
2A, groove width GW, contact area width SW of shoulder
Are distinguished from each other by the groove widths GW1 and GW2 and the ground contact surface area widths SW1 and SW2.

The curve of the central surface shape is
The ground contact areas 10 and 10 of the shoulder portion 4 are extended to substantially contact the virtual tread line 7 that smoothly connects the ground contact areas 10 and 10.

Here, "substantially in contact" means that the distance between the central ground contact area 9B and the virtual tread line 7 is within 2% of the total ground contact width TW. At 2% or more, the difference in ground pressure between the shoulder portion 4 and the central portion 9 becomes large,
Grip performance deteriorates and wear resistance is impaired. Therefore, it is preferably 1% or less, more preferably 0.5% or less.

Further, the virtual tread line 7 that smoothly connects between the ground contact areas is an arc curve having a single radius of curvature which is in contact with the tangent line of the inner edge 12 of the shoulder ground contact area 10 and has both ends at the inner edges 12, 12. When the tangent lines are substantially parallel to each other, a straight line connecting the inner edges 12 is formed.

According to the present invention, the central portion 9 has the curved surface shape of the central portion as described above, so that the radius of curvature is relatively small at the center of the tire and is sufficiently narrow as compared with the tire width. By providing a tread, the hydroplaning phenomenon is prevented and wet grip performance is improved.

It is considered that this is because when the radius of curvature of the central portion 9, particularly the radius of curvature R1 of the central ground contact surface area 9B, is small, the drainability to both outsides is enhanced and the drainage effect on the wet road surface is improved.

The radius of curvature R2 of the virtual tread line 7
If it is too small, the grip performance on a dry road surface due to the reduction of the ground contact area and the steering stability performance during cornering will deteriorate. Therefore, the radius of curvature R2 of the virtual tread line 7 is relatively large, preferably three times or more the total ground contact width TW, and its upper limit can be allowed until the shoulder ground contact area 10 approaches a straight line parallel to the tire axis. . The radius of curvature R2
Is centered on the tire equatorial plane CL. The shoulder portion 4 has an arc portion having a diameter smaller than the radius of curvature R2 near the outer end of the ground contact surface F.

FIGS. 1 and 2 show an example in which the entire surface shape 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 virtual tread line 7, and in the present example, this curve is inscribed at the contact point K on the virtual tread line 7.
The center of the radius of curvature R1 is located on the center plane KL of the central portion 9 which passes through the contact point K and is parallel to the tire equatorial plane CL, and the center plane KL is separated from the tire equatorial plane CL. Further, the profile shape of the central portion 9 is symmetrical with respect to the central plane KL, but the central portion 9 is asymmetrical with respect to the tire equatorial plane CL because the central line plane KL is separated from the tire equatorial plane CL.

The radius of curvature R1 is 0.4 of the total ground contact width TW.
˜1.5 times, more preferably 0.45 to 0.55 times. If it is less than 0.4 times, the central ground contact surface area width CW becomes too small, and the deterioration of dry grip tends to become large. If it is more than 1.5 times, the drainage effect is insufficient and the wet grip performance is impaired.

In the shoulder portion 4, the vertical groove 6 is formed.
It is desirable that the groove wall surface 8 on the outer side in the tire axial direction is a relatively steep and non-arcuate straight line with an angle α formed with the tire radial line X of 0 to 40 °, preferably 5 to 25 °. As a result, the edge effect with the road surface at the inner edge 11 of the shoulder portion 4 having a high ground contact pressure is exerted, which is useful for improving lateral force and cornering power to maintain dry grip performance. The outer groove wall surface 8 may be a convex curve extending outward in the tire axial direction similar to the inner groove wall surface 9A. The outer groove wall surface 8 may be connected to the ground contact surface area 10 of the shoulder portion 4 via an arc.

In the present embodiment, the central portion 9 has its center plane KL deviated to the right side in FIG. 1 with respect to the tire equatorial plane CL as described above. On the other hand, the two inner edges 1 of the ground contact areas 10, 10 of the shoulders 4, 4 arranged on both sides
2 and 12 are located equidistant from the tire equatorial plane CL, and therefore the ground contact surface area widths SW1 and S of the two shoulder portions 4 are
W2 has equal length.

As a result, the one vertical groove 51 and the other vertical groove 52 have different groove widths GW. Further, in this embodiment, since the inner groove wall surfaces 9A, 9A of both the vertical grooves 51, 52 are formed by the same convex curved surface, the length of the groove bottom 6 of the other vertical groove 51, 52 is one. Are different.

With respect to the vertical groove 5, the total groove width 2GW of the groove width GW of the vertical groove 5 and 5 and the ground contact width TW of the tread portion.
It was found that the ratio of the total groove width of 2 GW / TW, which is the ratio with the above, affects cornering power and wet grip performance. In the tire of the tire size 205 / 55R15 (example) having the surface shape of the central portion of the single arc shown in FIG. 1 and the tire of the conventional example having the four longitudinal grooves G shown in FIG. FIG. 6 shows the result of measuring the cornering power by changing ΣGW / TW. The total groove width ratio is
The value of 2 GW / TW was used for the example, and the value of (ΣGW) / 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 to be because when the total groove width ratio defined above is constant, the inner groove wall surface 9A having a convex curved surface contributes to an increase in tire lateral rigidity.

Similarly, the results of measuring the speed at which the hydroplaning phenomenon occurs are shown in FIG. Compared with the conventional tire, the embodiment has the same total groove width ratio,
It can be seen that the hydroplaning generation rate is high and the same phenomenon is unlikely to occur. This is largely due to the fact that the central portion 9 of the raised narrow width of the tire of the present invention has an inner groove wall surface 9A having a convex curved surface, and shows the tire ground contact surface F when a normal load is applied. As shown in FIG. 4, at the time of grounding, the vertical groove 5 forms a widened portion 5a that spreads like a trumpet before and after the ground contact center Q to improve drainage. The total groove width ratio Σ
When GW / TW exceeds 50%, as shown in FIG. 7, improvement of the effect of suppressing hydroplaning is hardly expected, and the cornering power becomes insufficient. Therefore, the total groove width ratio ΔGW / TW is preferably 50% or less, more preferably 45% or less.

The widened portion 5a formed in this manner also suppresses the occurrence of air column resonance in the vertical groove 5 and, as described above, also helps to reduce tire noise.

In order to further enhance the effect of suppressing the air column resonance, it is necessary to set the groove width GW of the vertical groove 5 to 35 mm or more, preferably 40 mm or more. In the range of 55 mm or more, the above effect hardly changes.

This is (tire size 205 / 55R1
5, 225 / 50R16 tires, respectively) 5 flutes
According to the experimental results shown in FIGS. 8A and 8B, the passing noise was measured by changing the groove width GW while keeping the groove depth constant. The passing noise drops sharply after reaching the maximum in the groove width GW in the range of 7.5 to 25 mm, and particularly exhibits excellent noise reduction at 35 mm or more.

However, even though the tire of the present application has a high cornering power as shown in FIG. 6, the increase in the groove width GW causes a decrease in the ground contact area and deteriorates the dry grip performance and steering stability. Furthermore, the wear resistance is deteriorated due to the increase in the ground contact pressure. Therefore, the groove width GW is set to 0.35 times or less of the ground contact width TW from the viewpoints of such dry grip performance, steering stability, and wear resistance.

Further, in order to enhance the steering stability and the dry grip property due to the increase of the groove width GW, as described above, the center plane KL of the central portion 9 is displaced with respect to the tire equatorial plane CL, and the central ground contact area is obtained. The profile shape of 9B is formed asymmetrically around the tire equatorial plane CL. This is because by mounting the tire with the side where the center portion 9 is displaced toward the outside of the vehicle body, the tread rigidity on the outside of the vehicle body becomes large and a strong lateral force can be exerted, and steering stability, particularly turning stability Can be increased.

On the contrary, when the side of the central portion 9 deviated from the tire equatorial plane CL is attached to the outside of the vehicle body,
It is easy to cause a hindrance such as reduced steering stability due to less cornering force and excessive asymmetry.

In order to maintain dry grip, wear resistance, steering stability, etc., the central ground contact area width CW is
It is preferably about 5 to 40% of the ground contact width TW of the tread portion 2, and more preferably 15 to 35%. Further, the width 9W of the central portion 9, which is the distance between the groove bottom edges 6a and 6a, is
It is preferable to set the contact width TW to about 40 to 55%.

The surface shape of the central portion may be formed in an elliptical shape as shown in FIG. 12 or a curve approximate to an ellipse. Further, in this example, one of the other shoulder ground contact surface widths SW1 and SW2 is 0.09 times or more the ground contact width TW, for example, 1 in the tire size 205 / 55R15.
It is preferably 5 mm or more, and when it is less than 0.09 times, the ground contact pressure in the shoulder ground contact areas 10, 10 increases and uneven wear occurs.

The central portion 9 has a central ground plane 9B.
In addition, a narrow groove 20 formed of a linear groove that is continuous in the tire circumferential direction is provided. The narrow groove 20 has a groove width W1 of 7 mm or less and 1.5 mm or more and a groove depth D1 of 0.4 to 0.9 times the groove depth D of the vertical groove 5. In this embodiment, the narrow groove 20 is provided on the center plane KL.

By providing such a narrow groove 20,
The drainage property in the central portion 9 is further improved, the wet grip property is further improved, and the necessary heat dissipation effect is exhibited while maintaining the pattern rigidity and the low noise property. When the groove width W1 is larger than 7.5 mm, and the groove depth D
When 1 is greater than 0.9 times the groove depth D, air column resonance occurs and tire noise is deteriorated. Further, when the groove depth D1 is less than 0.4 times the groove depth D and when it is less than 1.5 mm, the heat radiation effect becomes insufficient.

In this example, as shown in FIG. 3, a lateral groove 21 is formed in the shoulder portion 4 and a lateral groove 22 is formed in the central portion 9.
Are provided respectively. The lateral groove 21 extends axially outward from a position axially outward from the vertical groove 5, and communicates with the vertical groove 5 and a lateral groove 25 that closes before the tread end E and opens beyond the tread end E. The horizontal groove 26 is included.
By alternately arranging each of the lateral grooves 25 and 26,
The wet grip performance is improved while preventing the rigidity of the shoulder portion 4 from being lowered.

Only one end of the lateral groove 22 of the central portion 9 is opened to the longitudinal groove 5, and the inner side in the axial direction is interrupted near the central plane KL. By not providing the lateral groove near the center plane KL in this way, the rigidity of the central portion 9 is maintained and the steering stability performance is secured. The lateral grooves 21, 22 have their groove bottoms substantially parallel to the belt layer 17, and the axial inner end surfaces 21b, 22b of the lateral grooves 21, 22 are surfaces parallel to the tire equatorial plane CL. Also, the inclination angle of the groove wall surface with respect to the tire radius line is 1
A small angle of less than 5 ° is preferable.

As a result, 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. The circumferential pitch,
Other tire specifications such as depth can be selected according to the purpose.

Next, FIGS. 9 and 10 show another embodiment in which the profile shape of the central portion 9 is asymmetric with respect to the tire equatorial plane CL because the center plane KL is displaced from the tire equatorial plane CL.

In this example, the central contact surface area 9 having a radius of curvature R1
B is symmetric with respect to the tire equatorial plane CL, but the profiles of the groove wall surfaces 91A and 92A are different from each other, and one inner groove wall surface 91A is an arc having a radius of curvature R3a and the other inner groove wall 91A. The wall surface 92A has the radius of curvature R
1 and a radius of curvature R3b larger than R3a. Furthermore, the ground contact surface area width S in both shoulder portions 4 and 4
W1 and SW2 are the same, and grooves 5 and 5 when new
In order to equalize the groove widths GW1 and GW2 of the above, the groove bottom lengths 61W and 62W, which are the distances between the groove bottom edges 6a and 6b on the outside of the groove bottom 6, are different.

Therefore, in this example, as shown in FIG. 16 (A), the ground contact surface shape F at the time of new article is bilaterally symmetrical with respect to the tire equatorial plane CL. In this case, the tire is mounted so that the groove wall 92A faces the outside of the vehicle.

In a normal tire, when a lateral force is applied to the tire during cornering or the like, the ground contact surface shape F changes greatly from FIG. 18 (A) to FIG. 18 (B), and the ground contact area as a whole also changes from that when straight ahead. It tends to be about the same, or rather slightly decreased.

On the other hand, the tire having the tread profile shape shown in FIGS.
As shown in (B), there is little change in the total contact shape and contact area from straight ahead to cornering when a large lateral force is applied, and the cornering power generated on the bench is superior to the conventional tire of FIG. ing. Further, the tire of this example can exhibit the same or more steering characteristics in an actual vehicle as compared with a conventional tire having a small ΣGW.

Further, in the tires shown in FIGS. 9 and 10, the groove wall surface 92A located on the vehicle outer side when the vehicle is mounted has a single central portion 9 as shown in FIGS. The radius of curvature R1 is larger than that of the radius of curvature R1. As a result, as shown in FIGS. 16 (A) and 16 (B), the contact area Fc of the central contact area 9B during cornering is equal to the lateral force during cornering. Due to the increase
Rather, it will gradually increase. As a result, in addition to good steering characteristics, the maximum cornering force can be increased to obtain a high limit grip.

On the other hand, when the radius of curvature R3b of the inner groove wall surface 92A is simply increased and the width 62W of the groove bottom portion 6 is decreased, the groove width (GW) decreases as the wear progresses, and the groove depth In addition to the decrease in the thickness, the hydroplaning resistance is deteriorated when the wear progresses. Therefore, the radius of curvature R3 of the groove wall surface 91A on the inner side when the vehicle is mounted is
By reducing a, groove widths GW1 'and GW in the middle stage of wear
By substantially maintaining the sum of 2 ', it is possible to secure the same level of anti-hydroplaning performance as when the central portion 3 is formed with a single radius of curvature R1.

Still another embodiment is shown in FIG. In the present example, the center plane KL passing through the center of the central portion 9 in the tire axial direction coincides with the tire equatorial plane CL. In this example, at least the profile shapes of the groove walls 91A and 92A are made different from each other so that the profile shape of the central portion 9 is changed to the tire equatorial plane CL.
It is asymmetrical with respect to. The central portion 9 is provided with groove walls 91A and 92A having different radii of curvature R3a and R3b, and the central ground plane 9B has a central plane JL.
Be symmetrical with respect to. The center plane JL is a plane that divides the central ground contact area 9B into two equal parts in the width direction, and is separated from the tire equatorial plane CL in this example, but may be aligned as shown in FIG.

The tire having the profile shape of FIG. 13 is similar to that of FIG. 9, FIG. 10, and FIG. 11 in that the central contact surface groove Fc increases as the lateral force increases during cornering.
Has the effect of smoothly increasing the grip, and improves the limit grip and turning stability.

In the present invention, the central ground plane 9B may be asymmetric with respect to its central plane JL (FIG. 14),
Due to this asymmetry, the profile shape of the central portion 9B may be asymmetric with respect to the tire equatorial plane CL.

(Specific example) Tire size 205 / 55R1
The tires of No. 5 were manufactured according to the specifications of Table 1, the passing noise, the cornering power, and the hydroplaning generation speed were measured, and these were compared, and the results are shown in the same table.

[0069]

[Table 1]

[0070]

As described above, the pneumatic tire of the present invention having the above-mentioned structure can improve wet performance, particularly hydroplaning performance and reduce tire noise, and can be used for dry running. It has improved grip performance and can be suitably used as a passenger car tire.

[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 sectional view showing the surface shape of the tread portion.

FIG. 3 is a partial plan view showing the tread pattern.

FIG. 4 is a plan view showing the shape of the tread contact surface.

5A and 5B are cross-sectional views showing another aspect of the groove bottom of the vertical groove.

FIG. 6 is a graph showing the relationship between the total groove width ratio of vertical grooves and cornering power.

FIG. 7 is a graph showing the relationship between the total groove width ratio of vertical grooves and the hydroplaning generation rate.

FIG. 8A and FIG. 8B are graphs showing the relationship between the groove width of the vertical groove and the noise level.

FIG. 9 is a tire cross-sectional shape of another example.

FIG. 10 is a sectional view showing the surface shape of the tread portion.

FIG. 11 is a cross-sectional view showing the surface shape of the tread portion of another embodiment.

FIG. 12 is a cross-sectional view showing the surface shape of the tread portion of another embodiment.

FIG. 13 is a cross-sectional view showing the surface shape of the tread portion of another embodiment.

FIG. 14 is a cross-sectional view showing the surface shape of the tread portion of another embodiment.

FIG. 15 is a sectional view of a tread portion of a conventional tire.

16 (A) and (B) are cross-sectional views showing the ground contact surface shape of the tire of the present invention shown in FIGS. 9 to 10.

17 (A) and (B) are cross-sectional views showing the ground contact surface shape of the tire of the present invention shown in FIGS.

18 (A) and 18 (B) are cross-sectional views showing the contact surface shape of a conventional tire.

FIG. 19 is a sectional view of a tread portion of a comparative tire used in Table 1.

[Explanation of symbols]

 2 tread portion 4 shoulder portion 5 vertical groove 6 groove bottom 6a inner groove bottom edge 6b outer groove bottom edge 8 outer groove wall surface 9 central portion 9A, 91A, 92A inner groove wall surface 9B center ground contact area 10 shoulder portion Ground contact area 11 Inner edge 12 Outer edge CL Tire equatorial surface GW, GW1, GW2 Vertical groove width KL Center surface SW1 Ground contact surface area of one shoulder SW2 Ground contact area width of the other shoulder TW Ground width

Claims (7)

[Claims] 1. A tread portion is provided with two vertical grooves extending on both sides of a tire equator substantially continuously in a circumferential direction, so that the tread portion is located more than the groove bottom edge of the vertical groove on the outer side in the tire axial direction. A pneumatic tire that is divided into a pair of outer shoulder portions and a central portion between groove bottom edges on the tire axial direction inner side of the longitudinal groove, wherein the central portion is a tire meridional section from the inner groove bottom edge. It has a central surface shape that uses a series of curves consisting of an inner groove wall surface that extends inward in the tire axial direction with a curve that is convex outward in the radial direction, and a central ground contact surface area that smoothly connects between the inner groove wall surfaces, and , The central ground contact area is substantially in contact with a virtual tread edge connecting between the ground contact areas of the shoulder portion, and in the meridional section of the tire, the central area has an asymmetric profile shape that is asymmetric with respect to the tire equatorial plane CL. , The groove width GW of the vertical groove, which is the distance in the tire axial direction, between the inner edge on the inner side of the tire contact surface area in the axial direction of the tire and the outer edge of the central contact surface area on the side adjacent to this is 35 mm or more and the tread portion. A pneumatic tire having a ground contact width of 0.35 times or less. 2. The pneumatic tire according to claim 1, wherein a center plane KL passing through the center of the central portion in the axial direction of the tire coincides with a tire equatorial plane CL. 3. The pneumatic tire according to claim 1, wherein a center plane KL passing through the center of the tire in the axial direction of the center portion is displaced from a tire equatorial plane CL. 4. The profile shape of the central ground plane is
The tire according to claim 3, which is symmetrical with respect to the tire equatorial plane CL. 5. The profile shape of the central portion is symmetrical with respect to the central plane KL.
Tires listed. 6. The pneumatic tire according to claim 1, wherein the two vertical grooves have different groove widths GW. 7. A contact surface area width SW1 in the tire axial direction of a contact surface area of the one shoulder portion is equal to a contact surface area width SW2 of a contact surface area of the other shoulder portion. Or the pneumatic tire described in 3.