JP3046818B1 - Pneumatic tire - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To improve wet performance, noise performance, and steering stability. SOLUTION: Two vertical grooves 9 provided on a tread surface 2a,
9, the tread surface 2a is divided into a shoulder portion 10 outside the vertical groove 9 and a central portion 11 between the vertical grooves 9, 9. The outer side wall surface 9o of the vertical groove 9 includes a convex large arc portion 14 extending inward in the tire axial direction from the inner edge X on the tread surface 2a of the shoulder portion 10. Curvature radius Ra of large arc portion 14
Makes 10 to 40% of the contact width TW. Shoulder part 1
0 has a horizontal groove 21 communicating from the shoulder portion 10 to the vertical groove 9 through the inner end edge X. The angle θ formed by the lateral groove 21 with respect to the tire axial direction line at the inner edge X is 0 to 15 °.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire which is suitable for a passenger car and has improved wet performance, noise performance and steering stability.

[0002]

2. Description of the Related Art The present applicant has disclosed a pneumatic tire capable of improving wet performance and noise performance, for example, as disclosed in Japanese Unexamined Patent Publication No.
-127215 and JP-A-7-276915. As shown in FIG. 8 (A), this tire is provided with two longitudinal grooves g, g on both sides of the tire equator extending substantially continuously in the circumferential direction on the tread surface t. Is divided into an axially outer shoulder portion b and a central portion e between the vertical grooves g and g, and the groove side wall surface f1 on the central portion side is formed by an arc-shaped curve convex outward in the radial direction. ing.

[0003] Such a tire has reached a high level in wet performance and noise performance, but has a tendency that a contact area with a road surface is relatively small as compared with a conventional general pneumatic tire. For this reason, there is a problem that steering stability, particularly when a high-speed severe steering is performed, a feeling of response of a steering wheel fed back to a driver is insufficient, and initial responsiveness at the time of vehicle turning is low.

Therefore, as shown in FIG. 8 (B), the applicant of the present invention has disclosed in Japanese Patent Application No. 10-353198 that the groove side wall surface f2 on the shoulder portion side is formed by a convex arc-shaped curve. It was proposed to improve the steering stability.

However, in the tire having the groove side wall surface f2 having a convex arc shape, when a lateral groove is provided in the shoulder portion b, the special tread profile causes a different tendency from the conventional one, and the high frequency pattern noise is reduced. It has been found that noise inside the vehicle, such as pitch noise, or noise outside the vehicle caused by air column resonance in the vertical groove, etc., deteriorates.

That is, in a tire having a conventional tread profile, the angle θ of the lateral groove with respect to the tire axial direction is
The larger the noise was, the better the noise was. This is because, when the angle θ is small, when the lateral groove comes into contact with the ground, the lateral groove side edge easily hits the ground contact surface, and the air in the lateral groove is compressed and discharged at a stretch, and as a result, the pitch Noise worsens. However, in the special tread profile shown in FIG. 8B, on the contrary, as the angle θ of the lateral groove increases, the pitch noise increases, and the column sound in the vertical groove is excited by the pitch sound. As a result, high-frequency pattern noise and outside noise also deteriorated.

Accordingly, the present invention provides a tire having a special tread profile in which the groove side wall surface on the shoulder portion side of the vertical groove is formed in a convex arc shape, and has improved wet performance, noise performance and steering stability which are the advantages. While maintaining
It is an object of the present invention to provide a pneumatic tire capable of suppressing a reduction in noise caused when a lateral groove is formed in a shoulder portion.

[0008]

In order to achieve the above-mentioned object, according to the present invention, the invention as defined in claim 1 is characterized in that two tires on both sides of the tire equator extending substantially continuously in the circumferential direction on the tread surface.
A pneumatic tire divided into a shoulder portion on the outer side in the axial direction of the vertical groove by the vertical groove and a central portion between the vertical grooves, wherein the pneumatic tire is mounted on a normal rim and filled with a normal internal pressure. In the tire meridian section including the tire shaft in the standard state, the outer side wall surface of each of the longitudinal grooves extends inward in the tire axial direction from the inner edge in the tire axial direction on the tread surface of the shoulder portion, and Includes a large arc portion that is convex outward in the radial direction, and the radius of curvature (Ra) of the large arc portion
Is 10 to 40% of the contact width (TW), which is the maximum length of the contact surface in the tire axial direction when a regular load is applied from the standard condition to contact the flat surface, and the shoulder portion is A lateral groove communicating from the shoulder portion to the longitudinal groove through the inner edge, and an angle θ between the lateral groove and the tire axial direction at the inner edge is 0 to 15 °. And

In the invention of a pneumatic tire according to claim 2, the width of the lateral groove on the tread surface is 0.009 to 0.018 times the contact width (TW).

[0010] In the pneumatic tire according to the third aspect of the present invention, the inner side wall surface of each of the vertical grooves extends from the bottom edge of the groove in the tire axial direction to the outer end in the tire axial direction on the central tread surface. The outer edge (Ce) is inclined at a small angle (α) in a direction in which the outer edge (Ce) is located on the tire equator side and extends substantially straight up to the edge (Ce). The maximum groove width (GWmax) in the tire axial direction is 35 mm
It is characterized by the above.

Further, in the pneumatic tire according to the fourth aspect of the present invention, the ground contact surface is formed by a contour of the longitudinal groove extending substantially linearly in the circumferential direction in the tire axial direction, and a contour of the inside. It is characterized in that it has a longitudinal groove which is curved in an arc shape and whose interval gradually increases toward both ends in the circumferential direction and a contour line on the outer side in the tire axial direction.

Here, in this specification, each term is defined as follows. First, the "regular rim" is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, a standard rim for JATMA, a "Design Rim" for TRA, or an ETRTO
Then "Measuring Rim".

[0013] The "normal internal pressure" is the air pressure specified for each tire in the standard system including the standard on which the tire is based. TIRE LOAD LIMITS AT VARIOU
Maximum value described in "S COLD INFLATION PRESSURES", ETR
If it is TO, it is "INFLATION PRESSURE", but if the tire is for a passenger car, it is uniformly 200 (kPa).

Further, the "regular load" is a load defined for each tire in the standard system including the standard on which the tire is based. For JATMA, the maximum load capacity is used. TIRE LOAD LIMITS AT VARIOU
Maximum value described in "S COLD INFLATION PRESSURES", ETR
If it is TO, it will be 70% of "LOAD CAPACITY".

[0015]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a tire meridian section including a tire shaft in a normal state under no load in which the pneumatic tire of the present embodiment is assembled to a regular rim J and filled with a regular internal pressure, and FIG. The contour line 2a is shown enlarged.

In FIG. 1, a pneumatic tire includes a toroidal carcass 6 extending from a tread portion 2 through a sidewall portion 3 to a bead core 5 of a bead portion 4;
And a belt layer 7 disposed radially outside of the tire and inside the tread portion 2 of the tire. Further, in the present embodiment, an example is shown in which the present invention is applied to a flat tire having a flat ratio of about 0.4 to 0.6 and having a relatively poor drainage property and a wide width.

In the present embodiment, the carcass 6 is preferably one or more carcass plies 6a in which an organic fiber cord such as polyester, nylon, rayon or the like is coated with rubber. For example, the carcass 6 is wound around the bead core 5 from the inside in the tire axial direction. It is folded outward and locked. Further, in the present embodiment using a high elastic cord having high tensile rigidity such as steel or aromatic polyamide, the belt layer 7 is formed by connecting two belt plies 7A and 7B inside and outside the tire in the tire radial direction. The carcass 6 is formed by arranging it so as to intersect and incline at a small angle of about 15 to 35 ° with respect to the tire circumferential direction. To improve the high-speed performance, a band or the like in which organic fiber cords such as nylon are spirally arranged substantially in the tire circumferential direction may be provided outside the belt layer 7 in the tire radial direction.

The tread surface 2a, which is the surface of the tread portion 2, is provided with two longitudinal grooves 9 extending substantially linearly in the circumferential direction on both sides of the tire equator C. The tread surface 2 is provided on a shoulder portion 10 on the outer side in the axial direction of the vertical groove 9 and a central portion 11 located between the vertical grooves 9 and 9.
a. In the present embodiment, the two vertical grooves 9 and 9 are arranged symmetrically with respect to the tire axial direction with respect to the tire equator C. However, the present invention is not limited to this.

In the present embodiment, the central portion 11 is formed by an arc having a radius of curvature Rc having a center on the tire equatorial plane. In this example, the radius of curvature Rc is 500 mm or more, and preferably 1000 mm or more.

According to the present invention, in the tire meridional section in the standard state, the side wall surface 9o of the longitudinal groove 9 on the outer side in the tire axial direction is formed by a curve including a large arc portion 14 which is convex outward in the tire radial direction. In this example, the side wall surface 9i on the inner side in the tire axial direction is formed in a straight line.

More specifically, the inner side wall surface 9i is formed as shown in FIG.
As shown in FIG. 2, the groove has a substantially linear shape extending from the groove bottom edge 13 on the inner side in the tire axial direction to the outer edge Ce in the tire axial direction on the tread surface 2a of the central portion 11, and the outer edge Ce Are inclined at a small angle α in a direction located on the tire equator side.

By forming the inner side wall surface 9i in this way, it is possible to not only increase the groove volume of the vertical groove 9 and increase the contact width of the central portion 11, but also to improve the rigidity of the central portion 11. Also helps. The small angle α is measured with respect to a normal line of the tread raised from the inner groove bottom edge 13, and is preferably 5 to 15 °, more preferably 5 to 12 °, and in this example, The example is set at about 10 °. When the angle α is larger than 15 °, the vertical grooves 9
However, there is a tendency that the increase in the groove volume and the increase in the contact width of the central portion 11 cannot be achieved at the same time.

When the tread surface 2a and the inner side wall surface 9i intersect via a small arc, a small chamfer, or the like, the outer edge Ce of the central portion 11 is in contact with the tread surface 2a and the inner side wall surface 9i. Is defined as the intersection point between the tread normal descended inward in the tire radial direction from the intersection point intersecting the virtual extension and the tire surface. Similarly, when the inner side wall surface 9i and the groove bottom portion 16 intersect via a circular arc, the intersection point at which the side wall surface 9i and the groove bottom portion 16 intersect virtually extends, respectively. Is defined as the intersection of the tread normal extending outward from the tire in the tire radial direction and the tire surface. The inner side wall surface 9i is "substantially" linearly formed when the inner side wall surface 9i is radially inward and outward in the tire radial direction, a small arc having a radius of curvature of about 2 mm, a small chamfered portion, or the like. Means that it may be interposed.

Next, the outer side wall surface 9o extends inward in the tire axial direction from the inner end edge X in the tire axial direction on the tread surface 2a of the shoulder portion 10 and is convex outward in the tire radial direction. It is formed to include the arc portion 14. In addition, one of the features is that the large arc portion 14 is formed with a large radius of curvature that does not exist conventionally, such as setting the radius of curvature Ra of the large arc portion to 10 to 40% of the tire contact width TW.

As described above, since the outer side wall surface 9o includes the large arc portion 14 having a large radius of curvature Ra that protrudes outward in the tire radial direction, the load is applied to the shoulder portion 10 during turning or the like. When moved, this large arc portion 1
4 can be brought into contact with the road surface sufficiently to travel, and the contact area of the shoulder portion 10 can be increased. In particular, since the radius of curvature Ra of the large arc portion 14 is limited as described above, the increase in the contact area of the shoulder portion 10 becomes smooth in proportion to the increase in the load. The characteristics are also very stable, and good steering stability is obtained.

In the present embodiment, in the standard state, the width A of the large arc portion 14 in the tire axial direction is 0. 0 of the tire axial distance GWn between the outer edge Ce and the inner edge X.
This figure illustrates an example provided in a wide range of 4 to 0.7 times. Therefore, it is possible to secure a large area where the large arc portion 14 can touch the ground during turning or the like, which can contribute to improvement in stability during severe maneuvering.

When the outer side wall surface 9o is provided with, for example, a linear inclined portion 19 as shown in FIG.
There is a problem that a rigidity step occurs, and the contact area during turning tends to increase rapidly irrespective of an increase in load, so that steering stability is relatively reduced.

By the way, looking only at the large arc portion 14 which is convex outward in the tire radial direction, it is not necessarily preferable from the viewpoint of securing a large groove volume of the vertical groove 9, but as described above, By forming the longitudinal groove 9 in combination with the substantially linear inner side wall surface 9i inclined at a small angle α toward the equator C side, a relatively large groove is formed in the longitudinal groove 9 toward the tire equator C side. It is possible to secure a volume portion.

As a result of various experiments, the inventors have found that when the groove volume of the vertical groove 9 is the same, when the groove depth is uniform in the groove width direction and when the groove depth is deeper in the tire equator C side, the tread is deeper. With respect to the case where the end side changes shallowly, it has been found that a vertical groove having a large groove volume on the tire equator C side can obtain better hydroplaning resistance. The reason is that during running of the tire, the water film on the road surface enters from the tire equator C side (center side) and is drained to the rear end side of the ground contact.
It is considered that the provision of a large groove volume on the tire equator side can effectively guide a large amount of water to the outside of the ground contact surface at the initial stage of drainage, thereby increasing drainage efficiency.

The radius of curvature Ra of the large arc portion 14 is
When the contact width TW of the tire is less than 10%, the effect of increasing the contact area of the shoulder portion 10 at the time of turning is not sufficient, and when it exceeds 40%, the groove volume of the vertical groove 9 is significantly increased. Since it tends to be damaged, improvement in wet performance cannot be expected. Preferably, the curvature radius R of the large arc portion 14
a is desirably 20 to 30% of the contact width TW.
As shown in FIG. 3, the contact width TW can be defined as the maximum length of the contact surface P in the tire axial direction when a normal load is applied to the tire from the standard state to contact the flat surface.

In the present embodiment, the large arc portion 14 is smoothly connected to the curvature radius Rs forming the main portion of the tread surface 2a of the shoulder portion 10 by the inner edge X. If the radius of curvature Rs of the shoulder portion 10 is excessively small, a sufficient contact area cannot be obtained, and the shoulder portion 10
The contact pressure tends to be non-uniform.
It is desirable to have a relatively large radius of curvature of 100% or more, preferably 150% or more of W. In the present example, the shoulder portion 10 includes an arc portion having a small radius of curvature Re passing through the tread end TE on the outer end side in the tire axial direction.

As shown in FIG. 3, each of the longitudinal grooves 9 has a maximum groove width GWma in the tire axial direction measured at the ground plane P.
x is preferably 35 mm or more, and the center position of the radius of curvature Ra of the large arc portion 14 and the like are determined so as to satisfy this requirement. Accordingly, sufficient drainage can be ensured and wet performance can be improved, and air column resonance of the vertical groove 9 can be reduced.

In general, in the longitudinal groove 9 extending continuously in the tire circumferential direction, air column resonance occurs due to running of the tire,
It was thought that the noise level increased in proportion to the groove width. However, as a result of various experiments by the inventors, such a proportional relation shows that the groove width of the vertical groove 9 is remarkably increased as in this example. It has been found that this does not hold when the value is increased, but rather the noise level decreases. Preferably, the maximum groove width GWma
x is preferably 35 to 55 mm.

Further, the maximum groove width GWma of 35 mm or more.
x has the above-mentioned effect if it is formed in a part of the vertical groove 9 on the ground plane P. In the present embodiment,
This figure shows an example in which portions forming the maximum groove width (GWmax) are formed at both ends in the tire circumferential direction. Also, the ground plane P
When the minimum groove width of the vertical groove 9 is GWmin, this minimum groove width portion is formed substantially at the middle of the circumferential length of the vertical groove 9.

That is, in the present embodiment, the shape of the vertical groove 9 on the ground contact surface P is such that it is substantially linear in the circumferential direction and the contour line Ei on the inner side in the tire axial direction is curved in an arc shape. Distance (groove width) from the inner contour line Ei
Has a so-called trumpet shape sandwiched between outer contour lines Eo in the tire axial direction that gradually increase toward both ends in the circumferential direction.

As described above, since the width of the vertical groove 9 on the ground contact surface P is formed in a trumpet shape in which the groove width changes in the circumferential direction of the tire, drainage is increased, and resonance disturbance of air passing through the inside of the vertical groove 9 is reduced. It is useful and is preferable in that the passing noise can be further suppressed. In order to further enhance such an effect, the maximum groove width (GWmax) and the minimum groove width (GWmi) are required.
It is particularly desirable that the difference from n) is, for example, 4 to 15 mm.

In such a ground contact surface P, the central portion 11 has, for example, a maximum width CW in the tire axial direction of 15 to 3 times the ground contact width TW in order to improve steering stability.
0%, preferably 15-20%,
The maximum width SW of the shoulder portion 10 in the tire axial direction.
Is preferably 80% or more, and more preferably 100% or more of the width CW of the central portion 11.

As shown in FIG. 2, each of the vertical grooves 9 has a groove bottom portion 16 between the outer side wall surface 9o and the inner side wall surface 9i. In this example, the groove bottom portion 16 is a first groove extending outward in the tire axial direction from the inner groove bottom edge 13.
And a second groove bottom 16b which protrudes from the first groove bottom 16a in a step-like manner and smoothly continues to the large arc portion 14.

As described above, when the shoulder portion 10 is raised at the groove bottom 16, the shoulder portion 10 is raised.
Pattern rigidity is increased, and as a result, the shoulder 10
Can generate a large cornering force due to deformation resistance against a lateral load during turning or the like, so that higher steering stability can be obtained. In addition, molding defects such as a tread bear can be prevented. In addition, if the portion where the rubber thickness at the bottom of the groove is small has a wide range, the portion tends to be damaged due to stone biting or the like, but in this example, the shoulder portion 10 is raised at the bottom of the groove 16 so that the scratch resistance of the groove bottom 16 is improved. Can be improved.

The tread surface 2 of each shoulder portion 10
The first groove bottom 16 from the imaginary line VL that smoothly connects
The maximum groove depth D1 is, for example, three to three times the ground width TW.
It is preferably 7%, and in this example, it is set to about 9 mm. The maximum groove depth D2 from the virtual line VL to the second groove bottom 16b is, for example, the first groove depth D1.
1.5 mm or more, preferably 2.0 to 4.5 mm
It is desirable to make it small.

Accordingly, the rigidity of the shoulder portion 10 can be more suitably improved. In this example, the second groove bottom portion 16b includes a small arc portion 17 which is convex inward in the tire radial direction and has a radius of curvature Rb smaller than the radius of curvature Ra of the large arc portion 14 as a part thereof. Are illustrated. As a result, the large arc portion 14 moves to the second groove bottom 16b.
And the groove is also useful for increasing the groove volume of the vertical groove 9.

Next, in the present invention, as shown in FIG. 5, the tread portion 2 has a tread groove including at least a horizontal groove 21 communicating from the shoulder portion 10 to the vertical groove 9 through the inner edge X. It is formed.

In the present embodiment, the tread groove has a narrow groove 20 extending in the tire circumferential direction. The narrow groove 20 has a groove width W1 of, for example, 5 mm or less, preferably 4 mm or less.
More preferably, the depth is 3 mm or less, and the groove depth is 0.3 times or less the groove depth D1 of the vertical groove 9, for example, 2 times.
mm. In this example, two narrow grooves 20 are formed in the large arc portion 14. One is disposed near the groove bottom 16 and the other is disposed near the inner edge X.
The narrow groove 20 is useful for improving the wear resistance of the large arc portion 14 and optimizing the wear balance with the shoulder portion 10. The narrow groove 20 can be provided at an appropriate position without being limited to this, and the narrow groove 20 may not be formed as required.

The horizontal groove 21 communicating with the vertical groove 9 is
In this example, a first lateral groove 21A whose inner end terminates in the central portion 11 through the vertical groove 9 and a second lateral groove 21B terminating at the groove bottom 16 of the vertical groove 9 are provided. The directions are alternately spaced. In this embodiment, the first and second lateral grooves 2 are used.
Between 1A and 21B, a horizontal groove 22 not communicating with the vertical groove 9 is interposed by terminating the inner end outside the inner end edge X in the tire axial direction.

The lateral grooves 21 and 22 are effective in preventing a decrease in the rigidity of the shoulder portion 10, increasing drainage to the tread end TE side, and improving abrasion resistance and the like. On the other hand, there is a problem that, in a tendency different from the conventional one, deterioration of in-vehicle noise such as pattern noise and pitch noise and in-vehicle noise (passing noise) such as air column resonance are induced.

That is, in the conventional tread profile tire in which the outer side wall surface is linear, the noise is smaller and better as the angle θ of the lateral groove with respect to the tire axial direction is larger. However, in the tire 1 having the profile of the present application, conversely, as the angle θ of the lateral groove 21 increases, the vehicle interior noise such as pitch noise increases, and the column sound in the vertical groove 9 is excited by the pitch sound. High frequency pattern noise and vehicle exterior noise (passing noise)
Also worsens.

Accordingly, in the present application, the angle θ of the lateral groove 21 at the inner edge X with respect to the tire axial line is restricted in the range of 0 to 15 °. Thus, contrary to the conventional art, the noise caused by the lateral groove can be improved. If the angle exceeds 15 °, the noise performance is significantly reduced. In the present embodiment, the lateral grooves 21 and 22 are formed in a substantially arc shape in which the inclination angle is reduced from the tire equator side toward the tread end side from the viewpoint of drainage and steering stability.

From the viewpoint of noise performance, the lateral grooves 21,
The groove width W3 on the tread surface 2a of the tread 22 is equal to the contact width T.
It is preferably 0.009 to 0.018 times W.
If it exceeds 0.018 times, the noise performance will be reduced, and if it is less than 0.009 times, drainage will be impaired and pitch noise will easily occur. Therefore, preferably, the groove width W3 is in the range of 0.013 to 0.018 times.

The tread surface 2a of the lateral grooves 21, 22
From the groove depth D1 of the vertical groove 9 is 1.0.
It is preferable that the ratio is twice or less for the rigidity of the shoulder portion 10, and in this example, it is set in the range of D2 ≦ D3 ≦ D1. The circumferential pitch of these lateral grooves 21 is
Various selections can be made according to the purpose, and although not shown, siping or the like can be provided.

Although the preferred embodiment of the present invention has been described in detail, the present invention is not limited to the illustrated embodiment. For example, the stepped second groove bottom 1 is formed in the groove bottom 16.
The embodiment may be modified in various modes, such as not having the 6b.

[0051]

EXAMPLE A tire having a tire size of 245 / 45ZR16 was manufactured according to the specifications shown in Table 1, and its noise performance such as passing noise (external noise), high-frequency pattern noise (in-vehicle noise), and pitch noise (in-vehicle noise) was tested. The basic tread pattern is based on FIG. 5, and the specifications other than the lateral groove angle θ and the groove width W3 are the same as shown in Table 2. The test method is as follows.

<Passing noise (noise outside the vehicle)> JASO / C /
According to the actual vehicle coasting test specified in 606, the vehicle travels on a linear test course (asphalt road surface) at a speed of 60 km / h.
Coasting at a distance of 50 m at the course, and the maximum level dB (A) of the passing noise by a fixed microphone installed at a position 7.5 m laterally from the traveling center line and 1.2 m from the road surface at the middle point of the course. It was measured. The results are indicated by an index with the value of Example 3 being 100. The larger the index is, the smaller the passing noise is and the better.

<High-frequency pattern noise and pitch noise (in-vehicle noise)> Using the vehicle under the same conditions as above, the test course (asphalt road surface) was run at a speed of 60 km / h. And pitch noise, x (bad), △
(Normal), （(good), and ◎ (very good) were evaluated.

[0054]

[Table 1]

[0055]

[Table 2]

The angle θ of the lateral groove obtained from the test results
FIG. 6 shows the relationship between the noise, the passing noise, the high-frequency pattern noise, and the pitch noise. FIG. 7 shows the relationship between the width W3 of the lateral groove and the passing noise, the high-frequency pattern noise, and the pitch noise.

As can be seen from Table 1 and FIGS. 6 and 7, it can be confirmed that the tire of the example has improved noise performance.

[0058]

As described above, the present invention relates to a tire having a special tread profile in which the side wall surface on the shoulder portion side of the vertical groove is formed in a convex arc shape, which has advantages of wet performance, noise performance and steering. While maintaining high stability, it is possible to suppress a decrease in noise caused when a lateral groove is formed in the shoulder portion.

[Brief description of the drawings]

FIG. 1 is a meridional section of a tire showing one embodiment of the present invention.

FIG. 2 is an enlarged contour view showing a part of the contour of the tread surface.

FIG. 3 is a plan view showing the ground plane.

FIG. 4 is a contour diagram of a tread surface for explaining a comparative example of a vertical groove.

FIG. 5 is a development view showing a tread pattern.

FIG. 6 is a diagram showing a relationship between an angle θ of a lateral groove and passing noise, high-frequency pattern noise, and pitch noise.

FIG. 7 is a diagram showing a relationship between a groove width W3 of a lateral groove and passing noise, high-frequency pattern noise, and pitch noise.

FIGS. 8A and 8B are diagrams showing a contour shape of a tread portion for explaining a conventional technique.

[Explanation of symbols]

 2 Tread portion 2a Tread surface 9 Vertical groove 9i Inner side wall surface 9o Outer side wall surface 10 Shoulder portion 11 Central portion 13 Groove bottom edge 14 Large arc portion 21 Lateral groove C Tire equator Ce Central outer edge Ei Inner contour Eo Outer contour P Grounding surface TW Grounding width X Inner edge of shoulder

Continuation of the front page (56) References JP-A-9-193615 (JP, A) JP-A-5-147407 (JP, A) JP-A-6-127215 (JP, A) JP-A-7-40708 (JP) JP-A-7-47808 (JP, A) JP-A-7-186628 (JP, A) JP-A-7-195911 (JP, A) JP-A-7-232515 (JP, A) 7-276915 (JP, A) JP-A-8-4015 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 11/00 B60C 11/04 B60C 11/13

Claims (4)

(57) [Claims] 1. A tire has two longitudinal grooves extending substantially continuously in the circumferential direction on a tread surface, and is divided into a shoulder portion axially outside the longitudinal groove and a central portion between the longitudinal grooves. In a tire meridian cross-section including a tire shaft in a standard state with no load filled with a regular rim and filled with a regular internal pressure, an outer side wall surface of each of the longitudinal grooves is the shoulder. A large arc portion extending inward in the tire axial direction from the inner edge in the tire axial direction on the tread surface of the portion and projecting outward in the tire radial direction, and the radius of curvature (Ra) of the large arc portion is When a normal load is applied from the standard state and the flat surface is grounded, the ground contact width (T) which is the maximum length of the ground contact surface in the tire axial direction.
W), the shoulder portion has a lateral groove communicating from the shoulder portion to the longitudinal groove through the inner edge, and the lateral groove extends in the tire axial direction at the inner edge. Angle θ
A pneumatic tire characterized in that the angle is 15 °. 2. The pneumatic tire according to claim 1, wherein the width of the lateral groove on the tread surface is 0.009 to 0.018 times the contact width (TW). 3. The inner side wall surface of each of the longitudinal grooves extends from the bottom edge of the groove in the tire axial direction to the outer edge (Ce) of the central portion on the tread surface in the tire axial direction. Ce) is inclined at a small angle (α) in a direction located on the tire equator side and extends substantially linearly, and each of the vertical grooves has a maximum groove width (GWmax) in the tire axial direction measured at the ground contact surface. 3) is 35 mm or more.
The pneumatic tire as described. 4. A contact surface of the vertical groove extending substantially linearly in the circumferential direction, and a distance between the inner contour of the longitudinal groove and the inner contour is gradually increased toward both ends in the circumferential direction. The pneumatic tire according to claim 1, 2 or 3, further comprising a contour of a longitudinal groove curved in an arc shape outside the tire axial direction.