JP7180307B2 - tire - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire having a tread formed with land extending in the tire circumferential direction.

Patent Literature 1 listed below proposes a tire tread comprising elongated blocks. The elongate block has a plurality of sipes open on the contact surface of the elongate block. The sipes are curved on the contact surface of the elongate block, and at least two sipes have different values of curvature.

Japanese Patent Publication No. 2016-540675

However, the tire tread described above has a problem that uneven wear occurs in the elongated blocks.

As a result of detailed investigation of the uneven wear, the inventors have found that the edge portion of the sipe with a large curvature has less rigidity than the edge portion of the sipe with a small curvature, and is the starting point of uneven wear. Then, the inventors found that uneven wear can be suppressed by defining the depth of the sipe with a large curvature in association with the depth of the sipe with a small curvature.

SUMMARY OF THE INVENTION The present invention has been devised in view of the actual situation as described above, and a main object of the present invention is to provide a tire capable of suppressing uneven wear.

The present invention relates to a tire in which a land portion extending in the tire circumferential direction is formed in a tread portion, and the land portion has a plurality of axial grooves that are curved so as to protrude in one direction in the tire circumferential direction in a plan view. a grooved portion is formed, the axial grooved portion includes a first axially grooved portion and a second axially grooved portion curved less than the first axially grooved portion; A first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than a second depth, which is the maximum depth of the second axial groove-shaped portion.

In the tire according to the present invention, the first depth may be greater than 0.75 times the second depth.

In the tire according to the present invention, the land portion is divided by at least one main groove extending in the tire circumferential direction in the tread portion, and the axial groove-shaped portion has an end portion in the tire axial direction that extends along the main groove. , or may intersect the tread grounding edge.

In the tire according to the present invention, the first depth and the second depth may be 0.5 to 0.8 times the maximum depth of the main groove.

In the tire according to the present invention, the degree of curvature is a radius of curvature, the first depth is D1, the second depth is D2, the maximum depth of the main groove is D, and the first The following equations (1) and (2) may be satisfied, where R1 is the radius of curvature of the axial groove portion and R2 is the radius of curvature of the second axial groove portion.

In the tire according to the present invention, the first axial groove-shaped portion and the second axial groove-shaped portion may be adjacent to each other in the tire circumferential direction.

In the tire according to the present invention, the axial groove-shaped portion has a convex portion that protrudes most in the tire circumferential direction, and the convex portion extends from the center position of the axial width of the land portion in the tire axial direction. within a distance of 30% of said width.

In the tire according to the present invention, the first axial groove portions are arranged on the first deep bottom portion having the first depth and on both outer sides of the first deep bottom portion in the tire axial direction, and and a pair of first shallow portions having a depth less than the first depth.

In the tire according to the present invention, the depth of the first shallow portion may be 0.5 to 0.9 times the first depth.

In the tire according to the present invention, the second axial groove-shaped portions are arranged on the second deep bottom portion having the second depth and on both outer sides of the second deep bottom portion in the tire axial direction, and and a pair of second shallow portions having a depth less than the second depth.

In the tire according to the present invention, the depth of the second shallow portion may be 0.5 to 0.9 times the second depth.

In the tire of the present invention, land portions extending in the tire circumferential direction are formed with a plurality of axial groove-shaped portions that are curved so as to protrude in one direction in the tire circumferential direction in a plan view. The axial groove portion includes a first axial groove portion and a second axial groove portion that is less curved than the first axial groove portion. As a result, in the tire of the present invention, the first axial groove-shaped portion and the second axial groove-shaped portion having different degrees of curvature generate pitch sounds in different frequency bands, respectively. Can be distributed over a wide area. Therefore, the tire of the present invention can improve noise performance.

Further, in the tire of the present invention, the first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than the second depth, which is the maximum depth of the second axial groove-shaped portion. As a result, in the tire of the present invention, the difference in rigidity between the edge portion of the first axial groove-shaped portion and the edge portion of the second axial groove-shaped portion can be reduced in the land portion, thereby suppressing uneven wear. can do.

1 is an exploded view showing an example of a tread portion of a tire of the present invention; FIG. FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1; It is an enlarged view of the 1st land part of FIG. 1, and a 2nd land part. It is an enlarged view of the 1st land part of FIG. 1, and a 3rd land part. It is an enlarged view of the 2nd land part of FIG. 1, and a 4th land part. 2 is a cross-sectional view of the first axial groove portion of FIG. 1 taken along line BB. FIG. FIG. 4 is a partial cross-sectional view of another embodiment of the invention; FIG. 5 is a developed view showing an example of a tread portion of a tire according to another embodiment of the present invention; (a) and (b) are partial development views showing an example of a first land portion according to still another embodiment of the present invention.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a developed view showing an example of the tread portion 2 of the tire 1 of the present invention. FIG. 2 is a cross-sectional view taken along line AA of FIG. The tire 1 of the present embodiment is suitably used for heavy loads such as trucks and buses, but may also be used for passenger cars.

The tread portion 2 is provided with at least one (in this embodiment, a plurality of) main grooves 3 extending in the tire circumferential direction. A land portion 4 extending in the tire circumferential direction is formed in the tread portion 2 by the main groove 3 .

The main groove 3 of this embodiment includes a center main groove 3A and a pair of shoulder main grooves 3B, 3B.

FIG. 3 is an enlarged view of the first land portion 4A and the second land portion 4B of FIG. In FIG. 3, the sipe portion 22, which will be described later, is omitted in the portion where the groove center line 7c (indicated by the dashed-dotted line) is described in the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B, which will be described later. is shown. As shown in FIGS. 1 and 3, the center main groove 3A of this embodiment extends along the tire equator C along the tire circumferential direction. The center main groove 3A may be provided on each side of the tire equator C, for example.

The center main groove 3A of this embodiment extends in a zigzag shape in the tire circumferential direction. As a result, the center main groove 3A is alternately provided with apexes 12 (shown in FIG. 3) that are convex on one side or the other side in the tire axial direction. Such a center main groove 3A can provide an edge in the axial direction of the tire and improve traction performance. Note that the center main groove 3A may, for example, extend linearly or undulatingly in the tire circumferential direction.

FIG. 4 is an enlarged view of the first land portion 4A and the third land portion 4C of FIG. FIG. 5 is an enlarged view of the second land portion 4B and the fourth land portion 4D of FIG. In FIGS. 4 and 5, in the portion where the groove center line 7c (indicated by a dashed line) is described in the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B described later, the sipe portion 22 described later are omitted.

As shown in FIGS. 1, 4 and 5, the pair of shoulder main grooves 3B, 3B respectively extend along the tire circumferential direction between the center main groove 3A and the tread edge 2e. The pair of shoulder main grooves 3B, 3B of the present embodiment extend in a zigzag shape in the tire circumferential direction. As a result, the pair of shoulder main grooves 3B, 3B are alternately provided with an inner apex 13 that protrudes on the inner side in the tire axial direction and an outer apex 14 that protrudes on the outer side in the tire axial direction. Like the center main groove 3A, the pair of shoulder main grooves 3B, 3B provide edges in the axial direction of the tire and can improve traction performance. The pair of shoulder main grooves 3B, 3B may, for example, extend linearly or undulatingly in the tire circumferential direction.

The "tread edge 2e" is defined as an edge when it can be identified by a clear edge in appearance. When the edge could not be identified, the rim was mounted on a regular rim (not shown), the regular internal pressure was filled, and a regular load was applied to bring the tread portion 2 into contact with a flat surface with a camber angle of 0°. This is the outermost contact point in the axial direction of the tire. In this specification, unless otherwise specified, the dimensions of each part of the tire 1 are values specified in a normal state in which the rim is mounted on a normal rim and filled with a normal internal pressure and no load is applied.

A "regular rim" is a rim defined for each tire in a standard system including the standard on which the tire 1 is based. For example, "standard rim" for JATMA and "design rim" for TRA , ETRTO is "Measuring Rim".

"Normal internal pressure" is the air pressure determined for each tire by each standard in the standard system including the standard on which the tire 1 is based. AT VARIOUS COLD INFLATION PRESSURES" is the maximum value, and ETRTO is "INFLATION PRESSURE".

"Normal load" is the load defined for each tire by each standard in the standard system including the standards on which the tire 1 is based. LIMITS AT VARIOUS COLD INFLATION PRESSURES", or "LOAD CAPACITY" for ETRTO.

As shown in FIG. 1, the axial width W1 and the maximum depth D (shown in FIG. 2) of the center main groove 3A and the shoulder main groove 3B can be appropriately set. It is desirable that the width W1 of the center main groove 3A and the shoulder main groove 3B is set to, for example, about 4.0% to 7.0% of the tread width TW. Here, the tread width TW is the axial distance between the tread edges 2e, 2e. It is desirable that the maximum depth D of the center main groove 3A and the shoulder main groove 3B is set to approximately 10 to 25 mm.

The land portion 4 of the present embodiment includes a first land portion 4A and a second land portion 4B adjacent to each other. Furthermore, the land portion 4 of this embodiment includes a third land portion 4C and a fourth land portion 4D.

The first land portion 4A and the second land portion 4B of the present embodiment are divided by a center main groove 3A and a pair of shoulder main grooves 3B, 3B, respectively. The first land portion 4A is arranged on one side in the tire axial direction with respect to the center main groove 3A. The second land portion 4B is arranged on the other side in the tire axial direction with respect to the center main groove 3A. Therefore, the first land portion 4A and the second land portion 4B are adjacent to each other via the center main groove 3A. The width W2 of the first land portion 4A and the second land portion 4B can be set as appropriate. It is desirable that the width W2 in this embodiment is set to about 20% to 24% of the tread width TW.

As shown in FIG. 3, the edges of the first land portion 4A and the second land portion 4B facing the center main groove 3A are provided with a plurality of convex portions protruding in the tire axial direction by the apex 12 of the center main groove 3A. 15 are provided. Further, the edge portions of the first land portion 4A and the second land portion 4B facing the shoulder main groove 3B protrude in the tire axial direction by the outer top portion 14 (shown in FIGS. 4 and 5) of the shoulder main groove 3B. A plurality of convex portions 15 are provided. Chamfered portions 16 are formed on these convex portions 15 . Such a chamfered portion 16 can prevent wear that tends to occur in the convex portion 15 .

As shown in FIG. 1, the third land portion 4C and the fourth land portion 4D are divided by the shoulder main grooves 3B, 3B and the tread edge 2e, respectively. The third land portion 4C is adjacent to the first land portion 4A via a shoulder main groove 3B arranged on one side in the tire axial direction. The fourth land portion 4D is adjacent to the second land portion 4B via the shoulder main groove 3B arranged on the other side in the tire axial direction. The width W3 of the third land portion 4C and the fourth land portion 4D can be set as appropriate. It is desirable that the width W3 in this embodiment is set to about 18% to 22% of the tread width TW.

As shown in FIGS. 4 and 5, the edge portions of the third land portion 4C and the fourth land portion 4D facing the shoulder main groove 3B protrude in the tire axial direction by the inner apex portion 13 of the shoulder main groove 3B. A plurality of convex portions 15 are provided. A chamfered portion 16 is formed on the convex portion 15 . Such a chamfered portion 16 can prevent wear that tends to occur in the convex portion 15 . Further, in the third land portion 4C and the fourth land portion 4D, the tread edge 2e is provided with a lug groove 11 that communicates with the axial groove portion 7 (third axial groove portion 7C) described later. there is Such a lug groove 11 can discharge the water film on the road surface to the outside in the axial direction of the tire together with the axial groove-shaped portion 7 which will be described later.

As shown in FIG. 1, the land portion 4 (first land portion 4A to fourth land portion 4D in this example) has a plurality of axial directions that bend so as to protrude in one direction in the tire circumferential direction in plan view. A groove 7 is formed. The first land portion 4A to the fourth land portion 4D are divided into a plurality of block-shaped portions 10 by these axial groove-shaped portions 7, respectively.

Each block-shaped portion 10 is formed in a horizontally long rectangular shape in plan view. Such a block-shaped portion 10 can increase rigidity in the axial direction of the tire, thereby improving steering stability performance. When comparing the areas of the tread surfaces 10s of the block-shaped parts 10, it is desirable that the largest area be 1.2 times or less the smallest area. As a result, the rigidity of the block-shaped portions 10, 10 can be made nearly uniform, so uneven wear can be suppressed. From this point of view, the largest area of the tread surface 10s of each block-shaped portion 10 is preferably 1.1 times or less, more preferably 1.05 times or less, most preferably 1.05 times or less than the smallest area. , 1.0 times.

The axial groove portion 7 of the present embodiment extends in an arc shape in plan view. Such an axial groove-shaped portion 7 can provide edges in the tire axial direction and tire circumferential direction, so that traction performance can be improved.

The projecting direction of the axial groove-shaped portion 7 of the first land portion 4A and the projecting direction of the axial groove-shaped portion 7 of the second land portion 4B are desirably set in opposite directions in the tire circumferential direction. Moreover, the projecting direction of the axial groove-shaped portion 7 of the first land portion 4A and the projecting direction of the axial groove-shaped portion 7 of the third land portion 4C are set in opposite directions in the tire circumferential direction. desirable. Furthermore, the projecting direction of the axial groove-shaped portion 7 of the second land portion 4B and the projecting direction of the axial groove-shaped portion 7 of the fourth land portion 4D are set in opposite directions in the tire circumferential direction. desirable. As a result, each axial groove-shaped portion 7 of the first land portion 4A to the fourth land portion 4D can provide an edge regardless of the rotation direction of the tire, thereby improving traction performance and wet performance. can be done.

As shown in FIGS. 3 to 5, the axial end portions 7t, 7t of the axial groove portion 7 of the present embodiment extend along the main groove 3 (in this example, the center main groove 3A or the shoulder main groove 3B). ), or crosses the tread ground edge 2e. In this embodiment, when the end portion 7t of the axial groove portion 7 intersects the chamfered portions 16, 16 provided in the land portion 4 or the lug groove 11, the end portion 7t It is assumed that it intersects with the groove 3 or the tread edge 2e.

Since such an axial groove-shaped portion 7 is provided across the land portion 4 in the tire axial direction, for example, an axial groove-shaped portion (not shown) whose end portion 7t terminates within the land portion 4 is formed. As compared with , it is possible to prevent unevenness in rigidity of the land portion 4 in the axial direction of the tire. Therefore, the axial grooved portion 7 can prevent the land portion 4 from being unevenly worn.

As shown in FIG. 3, the axial groove portion 7 has a convex portion 17 that protrudes most in the tire circumferential direction. This convex portion 17 is specified based on the groove center line 7 c of the axial groove portion 7 . The convex portions 17 of the present embodiment are arranged on both sides in the tire axial direction from the center position 18 of the width of the land portion 4 in the tire axial direction (the width W2 or the width W3 shown in FIG. 1) by 30% of the width of the land portion 4. are arranged within a range T1 separated by a distance of . As a result, the rigidity of the edge portions 20 , 20 of the axial groove portion 7 can be substantially uniform on both sides of the protrusion 17 in the tire axial direction. Uneven wear can be prevented. In order to prevent uneven wear more effectively, it is desirable that the convex portion 17 be arranged within a range (not shown) separated from the center position 18 by a distance of 15% of the width of the land portion 4 .

The axial groove portion 7 of the present embodiment is formed in an arc shape over its entire length in plan view. Here, the total length of the axial groove-shaped portion 7 is the length of the axial groove-shaped portion 7 where the groove center line 7c of the axial groove-shaped portion 7 intersects with the main groove 3 (the center main groove 3A or the shoulder main groove 3B). It is defined as the distance along the groove centerline 7c between the ends 7t, 7t. Such an axial groove 7 can provide edges in the tire axial direction and the tire circumferential direction over its entire length. It should be noted that the axial groove portion 7 is not limited to being formed in an arc shape over its entire length, and for example, a part of its entire length may be formed in a linear shape or a wavy shape.

The axial groove portion 7 of the present embodiment includes a first axial groove portion 7A and a second axial groove portion 7B that is less curved than the first axial groove portion 7A. In this embodiment, the first axial groove portion 7A and the second axial groove portion 7B are provided on the first land portion 4A and the second land portion 4B, respectively.

In this specification, the "degree of curvature" refers to the intermediate portion 8a of the entire length of the axial groove portion 7, and the length L6 of 25% of the entire length from both ends 7t, 7t of the axial groove portion 7 to the intermediate portion. It is defined as the radius of curvature of a three-point arc with a first end 8b and a second end 8c spaced apart on the side 8a. The intermediate portion 8a, the first end portion 8b and the second end portion 8c are specified on the groove center line 7c of the axial groove portion 7. As shown in FIG.

The first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B of the present embodiment extend between the top portion 12 of the center main groove 3A and the outer top portion 14 (shown in FIG. 4) of the shoulder main groove 3B. are in communication. Further, the first axial groove-shaped portions 7A and the second axial groove-shaped portions 7B are provided alternately in the tire circumferential direction on the first land portion 4A and the second land portion 4B, respectively.

In this embodiment, the radius of curvature R1 of the first axial groove-shaped portion 7A is smaller than the radius of curvature R2 of the second axial groove-shaped portion 7B (that is, the first axial groove-shaped portion 7A is less than the second axial groove-shaped portion 7A). The degree of curvature is greater than that of the directional groove portion 7B).

Since the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B configured as described above can provide different edges, traction performance and wet performance can be effectively improved. can.

Since the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B have different degrees of curvature, they can generate pitch sounds in different frequency bands. Therefore, since the tire 1 can disperse the frequency band of the pitch sound over a wide range, the noise performance can be improved.

In order to effectively exhibit the above effects, it is desirable that the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B are adjacent to each other in the tire circumferential direction. As a result, pitch sounds in different frequency bands are alternately generated, so that pitch sounds can be effectively prevented from being superimposed. Furthermore, it is desirable that the interval L5 between the first axial groove portion 7A and the second axial groove portion 7B in the tire circumferential direction is set to 20 to 40 mm. Note that the interval L5 is specified based on the groove center line 7c of the axial groove portion 7. As shown in FIG.

The radius of curvature R2 of the second axial groove portion 7B is preferably 1.1 to 10 times the radius of curvature R1 of the first axial groove portion 7A. By limiting the curvature radius R2 to 1.1 times or more the curvature radius R1, the frequency band of the pitch sound can be dispersed over a wide range, and noise performance can be improved. On the other hand, by limiting the curvature radius R2 to ten times or less of the curvature radius R1, the block-shaped portions 10 adjacent in the tire circumferential direction via the first axial groove-shaped portion 7A or the second axial groove-shaped portion 7B , 10 can be prevented from becoming uneven, and uneven wear can be suppressed. From this point of view, the curvature radius R2 is preferably twice or more the curvature radius R1, and preferably eight times or less.

The curvature radius R1 of the first axial groove-shaped portion 7A and the curvature radius R2 of the second axial groove-shaped portion 7B can be appropriately set as long as the curvature radius R1 is smaller than the curvature radius R2. When the radius of curvature R1 and the radius of curvature R2 are small, the rigidity of the edge portions 20A, 20A of the first axial groove portion 7A and the edge portions 20B, 20B of the second axial groove portion 7B is reduced, resulting in uneven wear. It becomes easier to become the starting point of Conversely, when the radius of curvature R1 and the radius of curvature R2 are large, wet performance may deteriorate. From this point of view, the radius of curvature R1 is preferably set to 20-100 mm, and the radius of curvature R2 is preferably set to 60-200 mm.

The axial groove portion 7 formed in the first land portion 4A is desirably formed at a different position in the tire circumferential direction with respect to the axial groove portion 7 formed in the second land portion 4B. . As a result, it is possible to shift the timing of generating the pitch sound between the first land portion 4A and the second land portion 4B, so that it is possible to effectively prevent the pitch sound from being superimposed.

The axial groove-shaped portion 7 formed in the first land portion 4A of the present embodiment is located at a different position in the tire circumferential direction by a distance L1 from the axial groove-shaped portion 7 formed in the second land portion 4B. formed. In this embodiment, the distance L1 is based on the end portion 7t of the first axial groove portion 7A of the first land portion 4A and the end portion 7t of the first axial groove portion 7A of the second land portion 4B. defined as Further, the distance L1 is defined as the distance in which the projecting direction of the first axial groove-shaped portion 7A of the first land portion 4A is separated from the projecting direction of the first axial groove-shaped portion 7A of the second land portion 4B. be done.

If the distance L1 is smaller than the pitch P in the tire circumferential direction of the first axial groove portion 7A, the timing of generating the pitch sound cannot be shifted sufficiently. Conversely, if the distance L1 is large with respect to the pitch P, the distance L1 with respect to other axial groove portions 7 adjacent in the tire circumferential direction may become small. From this point of view, the distance L1 is preferably 0.1 times the pitch P or more, and preferably 0.9 times the pitch P or less. The pitch P of the first axial groove portion 7A is defined based on the end portion 7t of the axial groove portion 7. As shown in FIG. Further, the distance (not shown) between the second axial groove-shaped portion 7B of the first land portion 4A and the second axial groove-shaped portion 7B of the second land portion 4B is also set within the same range. is desirable.

FIG. 6 is a BB cross-sectional view of the first axial groove portion 7A of FIG. As shown in FIGS. 2 and 6, each of the first axial groove portion 7A and the second axial groove portion 7B of the present embodiment includes a body portion 21 and a sipe portion 22. . The first axial grooved portion 7A and the second axially grooved portion 7B may be composed only of the main body portion 21, or may be composed of only the sipe portion 22. As shown in FIG.

As shown in FIG. 6 , the main body portion 21 has a width greater than that of the sipe portion 22 . Such a main body portion 21 can increase the groove volume of the first axial groove portion 7A and the second axial groove portion 7B, which helps improve drainage performance. The width W4 and the maximum depth D3 of the body portion 21 can be set as appropriate. The width W4 in this embodiment is set to, for example, approximately 2.5 to 3.5 mm, and the maximum depth D3 is set to, for example, approximately 1.5 to 2.5 mm.

The sipe portion 22 is a cut having a width smaller than that of the main body portion 21 (for example, the width W5 is 1.5 mm or less). The sipe portion 22 extends inward in the tire radial direction from the bottom portion 21b of the body portion 21 . As shown in FIG. 2, the bottom portion 22b of the sipe portion 22 of this embodiment extends between the ends 7t, 7t (shown in FIG. 3) of the first axial groove portion 7A and the second axial groove portion 7B. extends in the axial direction of the tire at a constant depth (maximum depth D4 (shown in FIG. 6)). Such a sipe portion 22 can effectively suppress deformation of the block-shaped portion 10 on both sides of the axial groove portion 7 by supporting the wall surfaces 22w on both sides thereof. Therefore, the axially grooved portion 7 helps improve wear resistance and drainage performance. The maximum depth D4 of the sipe portion 22 can be set as appropriate. The maximum depth D4 in this embodiment is set to approximately 11 to 17 mm.

As shown in FIG. 2, a first depth D1, which is the maximum depth of the first axial groove-shaped portion 7A, and a second depth D2, which is the maximum depth of the second axial groove-shaped portion 7B, are , as shown in FIG. 6, it is specified as the maximum depth among the depths from the tread surface 2s to the bottom portion 22b of the sipe portion 22. As shown in FIG.

As shown in FIG. 2, the first depth D1 and the second depth D2 are preferably 0.5 times or more, more preferably 0.55 times or more, the maximum depth D of the main groove 3, Also, it is preferably 0.8 times or less, more preferably 0.75 times or less. By setting the first depth D1 and the second depth D2 to 0.5 times or more the maximum depth D of the main groove 3, the land portion 4 (the first land portion 4A and the second land portion 4B) and the road surface can be effectively discharged toward the center main groove 3A and the shoulder main groove 3B. On the other hand, by setting the first depth D1 and the second depth D2 to 0.8 times or less of the maximum depth D of the main groove 3, the rigidity of the first land portion 4A and the second land portion 4B is reduced. can be prevented, the wear resistance performance can be improved.

Due to the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B as described above, the first land portion 4A and the second land portion 4B are substantially aligned in the tire circumferential direction as shown in FIG. It is formed as a rib continuous to the Here, "continuous" with respect to the rib means that the rib is not divided in the tire circumferential direction by lateral grooves (not shown) that are cuts having a width greater than 3.5 mm. The first land portion 4A and the second land portion 4B can increase the rigidity in the tire circumferential direction and the tire axial direction, for example, compared to a row of blocks divided by lateral grooves or the like. Therefore, the tire 1 can improve running performance on dry road surfaces.

The first axial groove portion 7A and the second axial groove portion 7B may be configured as lateral grooves (not shown) having a width W4 of the body portion 21 larger than 3.5 mm. Such first axial groove 7A and second axial groove 7B can effectively drain the water film on the road surface while providing edges.

By the way, as shown in FIG. 3, the land portion 4 (in this example, the first land portion 4A and the second land portion 4B) has a first axial groove portion 7A and a second axial groove portion 7A having different degrees of curvature. When the grooved portion 7B is provided, the land portion 4 is likely to be unevenly worn. As a result of a detailed investigation of uneven wear, the inventors found that the edge portions 20A, 20A of the first axial groove 7A, which have a large degree of curvature (i.e., a small curvature radius R1), have a small degree of curvature (i.e., It was found that the edge portions 20B, 20B of the second axial groove portion 7B shown in FIG. 3, which have a large radius of curvature R2, have a lower rigidity than the edge portions 20B, 20B, and become the starting point of uneven wear.

Based on the above knowledge, as shown in FIG. 2, in the present embodiment, the first depth D1 of the first axial groove portion 7A is set larger than the second depth D2 of the second axial groove portion 7B. is also smaller. As a result, in the present embodiment, the rigidity of the edge portions 20A, 20A (shown in FIG. 3) of the first axial groove 7A, which tend to be the starting points of uneven wear, can be relatively increased. As a result, the difference in rigidity between the edge portions 20A, 20A of the first axial groove portion 7A and the edge portions 20B, 20B (shown in FIG. 3) of the second axial groove portion 7B can be reduced. , uneven wear of the land portion 4 (in this example, the first land portion 4A and the second land portion 4B) can be suppressed.

In order to effectively prevent uneven wear, the first depth D1 of the first axial groove 7A is preferably 0.95 times or less the second depth D2 of the second axial groove 7B. and more preferably 0.93 times or less of the second depth D2. Note that if the first depth D1 is excessively smaller than the second depth D2, the drainage performance will deteriorate and the rigidity of the edge portions 20A, 20A (shown in FIG. 3) of the first axial groove 7A will increase. becomes larger than necessary, and uneven wear may occur. From this point of view, the first depth D1 is preferably greater than 0.75 times the second depth D2, more preferably 0.8 times or more the second depth D2. Thereby, uneven wear of land part 4 (this example, the 1st land part 4A and the 2nd land part 4B) can be controlled.

As shown in FIG. 3, the greater the difference between the degree of curvature (curvature radius R1) of the first axial groove portion 7A and the degree of curvature (curvature radius R2) of the second axial groove portion 7B, the more The difference in rigidity between the edge portions 20A and 20B of the ring becomes large, and uneven wear tends to occur. Therefore, the greater the difference in the degree of curvature, the greater the depth of the axial groove portion 7 (the first depth D1 of the first axial groove portion 7A and the second depth of the second axial groove portion 7B). It is desirable to reduce the height D2). As a result, the difference in rigidity between the edge portions 20A and 20B can be reduced, so uneven wear can be prevented.

In order to effectively exhibit the above action, the first depth D1 of the first axial groove-shaped portion 7A and the second depth D2 of the second axial groove-shaped portion 7B shown in FIG. It is desirable to satisfy 1) and (2).
D1/D<(R1+R2)/(R2×2) (1)
D2/D<(R1+R2)/(R2×2) (2)
here,
D1: First depth of the first axial groove D2: Second depth of the second axial groove D: Maximum depth of the main groove R1: Radius of curvature of the first axial groove R2: Curvature radius of the second axial groove

By satisfying the above formulas (1) and (2), the degree of curvature of the first axial grooved portion 7A (curvature radius R1 shown in FIG. 3) and the degree of curvature of the second axially grooved portion 7B ( The larger the difference from the radius of curvature R2) shown in FIG. The second depth D2 of 7B can be reduced. As a result, the difference in rigidity between the edge portions 20A, 20A of the first axial groove portion 7A and the edge portions 20B, 20B of the second axial groove portion 7B can be reduced, and uneven wear can be suppressed.

As shown in FIG. 1, the axial groove-shaped portion 7 of the present embodiment is a third axial groove-shaped portion having a different degree of curvature from the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B. Contains 7C. The third axial groove portions 7C of the present embodiment are provided in the third land portion 4C and the fourth land portion 4D, respectively, and spaced apart in the tire circumferential direction. Such a third axial groove-shaped portion 7C can provide an edge different from that of the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B, thereby effectively improving traction performance and wet performance. be able to.

The width W6 and the maximum depth D6 (shown in FIG. 2) of the third axial groove portion 7C can be appropriately set. The width W6 of the third axial groove portion 7C is set smaller than the width W4 (shown in FIG. 6) of the body portion 21 of the first axial groove portion 7A and the second axial groove portion 7B, For example, it is set to about 1.3 to 2.0 mm. Due to such a third axial groove portion 7C, the rigidity of the third land portion 4C and the fourth land portion 4D, which have a relatively large contact pressure during turning, is relatively increased, thereby suppressing uneven wear. be able to. The maximum depth D6 of the third axial groove-shaped portion 7C is the same as the maximum depth D3 (shown in FIG. 6) of the main body portion 21 of the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B. It is desirable to set them in the same range.

As shown in FIGS. 4 and 5, the third axial groove portion 7C of this embodiment is a circular arc having a center (not shown) within the outer region To of the third land portion 4C and the fourth land portion 4D. is formed in Here, the "outer region To" is a region of the third land portion 4C and the fourth land portion 4D that is axially outside of the center position 4c in the width direction.

Such a third axial groove portion 7C can effectively provide an edge during turning when the ground contact pressure is relatively large in the outer regions To of the third land portion 4C and the fourth land portion 4D. Turning performance can be improved. Furthermore, since the end portion 7t of the third axial groove portion 7C communicates with the lug groove 11, the water film on the road surface can be effectively drained from the lug groove 11, thereby improving wet performance. can be made

The curvature radius R3 of the third axial groove portion 7C can be set appropriately. From the same viewpoint as the curvature radius R1 of the first axial groove-shaped portion 7A and the curvature radius R2 of the second axial groove-shaped portion 7B shown in FIG. It is desirable to set it to 40 to 200 mm.

As shown in FIG. 4, the third axial groove portion 7C of the third land portion 4C corresponds to the axial groove portion 7 of the first land portion 4A (in this embodiment, the first axial groove portion 7A). ) in the tire circumferential direction at a distance of L3. The distance L3 is defined based on the end portion 7t of the third axial groove portion 7C of the third land portion 4C and the end portion 7t of the first axial groove portion 7A of the first land portion 4A. . Further, the distance L3 is defined as the distance in which the projecting direction of the third axial groove-shaped portion 7C of the third land portion 4C and the projecting direction of the first axial groove-shaped portion 7A of the first land portion 4A are separated from each other. be done.

Two third axial groove portions 7C of the third land portion 4C are formed in a pair of first axial groove portions 7A, 7A adjacent in the tire circumferential direction. For this reason, two distances L3 are defined, one large and one small. As a result, the tire 1 shifts the timing of generating the pitch sound between the third land portion 4C and the first land portion 4A, so that it is possible to effectively prevent the pitch sound from being superimposed. In order to effectively exhibit such an action, the smaller distance L3 of the two distances L3 is set to 0 of the pitch P (shown in FIG. 3) of the first axial groove 7A in the tire circumferential direction. .1 to 0.4 times, and the larger distance L3 is preferably set to 0.6 to 0.9 times the pitch P.

As shown in FIG. 5, the third axial groove portion 7C of the fourth land portion 4D is similar to the third axial groove portion 7C (shown in FIG. 4) of the third land portion 4C shown in FIG. Similarly, it is formed at a different position in the tire circumferential direction by a distance L4 from the axial groove-shaped portion 7 (first axial groove-shaped portion 7A in this embodiment) of the second land portion 4B. desirable. The distance L4 is defined based on the end portion 7t of the third axial groove portion 7C of the fourth land portion 4D and the end portion 7t of the first axial groove portion 7A of the second land portion 4B. . As with the distance L3 (shown in FIG. 4), two large and small distances are defined for the distance L4. ), and the larger distance L4 is preferably set to 0.6 to 0.9 times the pitch P.

As shown in FIG. 2, in the embodiments described so far, in the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B, the bottom portion 22b of the sipe portion 22 has a constant depth (maximum Depth) D4 has been exemplified, but it is not limited to such an aspect. FIG. 7 is a partial cross-sectional view of another embodiment of the invention. In this embodiment, the same reference numerals are assigned to the same configurations as in the previous embodiments, and the description may be omitted.

The first axial groove portion 7A of this embodiment includes a first deep bottom portion 25 and a pair of first shallow bottom portions 26, 26 disposed on both outer sides of the first deep bottom portion 25 in the tire axial direction. It is configured. In this embodiment, the first deep portion 25 and the first shallow portion 26 are formed in the sipe portion 22 of the first axial groove portion 7A. The first deep bottom portion 25 extends in the tire axial direction and has a first depth (that is, the maximum depth of the first axial groove portion 7A) D1. On the other hand, the pair of first shallow bottom portions 26 , 26 extend axially outward from the first deep bottom portion 25 via the stepped portion 27 . As a result, the first axial groove portion 7A (sipe portion 22) is formed in a tongue-like shape with a relatively large depth at the central portion in the axial direction of the tire.

The first axial groove portion 7A configured as described above increases the rigidity of both sides in the axial direction of the first land portion 4A, which are relatively likely to be worn, by the pair of first shallow bottom portions 26, 26. Therefore, uneven wear of the first land portion 4A can be prevented. Further, the first deep bottom portion 25 of the first axial groove portion 7A can maintain the drainage performance.

In order to effectively exhibit such action, the depth (maximum depth) D7 of the first shallow portion 26 is preferably set to 0.5 to 0.9 times the first depth D1. . By setting the depth D7 of the first shallow portion 26 to be 0.9 times or less the first depth D1, the rigidity of both sides of the first land portion 4A in the tire axial direction can be increased. On the other hand, by setting the depth D7 of the first shallow portion 26 to be 0.5 times or more the first depth D1, the drainage performance can be maintained. From this point of view, the depth D7 of the first shallow portion 26 is more preferably 0.8 times or less the first depth D1, and more preferably 0.6 times or more.

As with the first axial groove portion 7A, the second axial groove portion 7B of this embodiment includes a second deep bottom portion 28 and a pair of grooves disposed on both outer sides of the second deep bottom portion 28 in the tire axial direction. second shallow bottom portions 29, 29. In this embodiment, the second deep portion 28 and the second shallow portion 29 are formed in the sipe portion 22 of the second axial groove portion 7B. The second deep bottom portion 28 extends in the tire axial direction and has a second depth (that is, the maximum depth of the second axial groove portion 7B) D2. On the other hand, the pair of second shallow bottom portions 29 , 29 extend outward in the tire axial direction from the second deep bottom portion 28 via the stepped portion 30 . As a result, the second axial groove portion 7B (sipe portion 22) is formed in a tongue-like shape with a relatively large depth at the central portion in the axial direction of the tire.

The second axial groove portion 7B configured as described above increases the rigidity of both sides in the axial direction of the second land portion 4B, which are relatively prone to wear, by the pair of second shallow bottom portions 29, 29. Therefore, uneven wear of the second land portion 4B can be prevented. Further, the drainage performance can be maintained by the second deep bottom portion of the second axial groove portion 7B.

In order to effectively exhibit such an action, the depth (maximum depth) D8 of the second shallow portion 29 is preferably 0.9 times or less the second depth D2, more preferably the second depth D2. It is 0.8 times or less the depth D2, preferably 0.5 times or more the second depth D2, and more preferably 0.6 times or more the second depth D2.

The depth D7 of the first shallow portion 26 is preferably set smaller than the depth D8 of the second shallow portion 29 . As a result, the edge portions 20A, 20A (shown in FIGS. 3 and 6) of the first axial groove portion 7A and the edge portions 20B, 20B (shown in FIG. 3) of the second axial groove portion 7B are separated from each other. Since the rigidity difference can be reduced, uneven wear of the land portion 4 (in this example, the first land portion 4A and the second land portion 4B) can be suppressed. Similar to the relationship between the first depth D1 and the second depth D2 described above, the depth D7 is preferably less than 1.0 times the depth D8 and more than 0.75 times the depth D8. Larger is desirable.

As shown in FIG. 1, in the above-described embodiments, the first axial groove portion 7A and the second axial groove portion 7B extending in an arc shape were exemplified, but the present invention is not limited to such an aspect. FIG. 8 is a developed view showing an example of a tread portion 2 of a tire 1 according to another embodiment of the invention. In this embodiment, the same reference numerals are assigned to the same configurations as in the previous embodiments, and the description may be omitted.

As shown in FIG. 8, the first axial groove portion 7A and the second axial groove portion 7B of this embodiment extend in a V shape in plan view. The degree of curvature of the V-shaped axial groove portion 7 is the same as the degree of curvature of the arc-shaped axial groove portion 7, and is similar to that of the first end portion 8b and the second end portion 8c shown in FIG. is defined as the radius of curvature of a three-point arc using

Such a V-shaped axial groove portion 7 is easier to machine with a knife blade than the arc-shaped axial groove portion 7 shown in FIG. can be expanded. Further, the third axial groove-shaped portion 7C may also extend in a V-shape like the first axial groove-shaped portion 7A and the second axial groove-shaped portion 7B.

FIGS. 9A and 9B are partial development views showing an example of a first land portion 4A according to still another embodiment of the present invention. In this embodiment, the same reference numerals are assigned to the same configurations as in the previous embodiments, and the description may be omitted.

In the embodiment of FIG. 9A, in plan view, the first axial groove portion 7A extends in a V shape, and the second axial groove portion 7B extends in an arc shape. On the other hand, in the embodiment of FIG. 9(b), the first axial groove portion 7A extends in an arc shape and the second axial groove portion 7B extends in a V shape in plan view. Thus, in these embodiments, the first axial groove portion 7A or the second axial groove portion 7B extending in an arc shape and the first axial groove portion 7A or the second axial groove portion 7A extending in a V shape are provided. Since the directional groove portion 7B can be mixed, the traction performance and the wet performance can be improved while effectively preventing the pitch sound from being superimposed.

Although the particularly preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the illustrated embodiments and can be modified in various ways.

Tires having the basic structure shown in FIG. 1 and having the axial grooves shown in Table 1 were prototyped (Examples 1 to 7, Comparative Example). The axial groove portions of Examples 1 to 7 and Comparative Example include a first axial groove portion and a second shaft having a smaller degree of curvature (a larger radius of curvature) than the first axial groove portion. Directional grooves are included.

In Examples 1 to 7, the first depth D1 of the first axial groove-shaped portion was set smaller than the second depth D2 of the second axial groove-shaped portion. Further, the first shallow portion shown in FIG. 7 was provided in the first axial groove portion of Example 7, and the second shallow portion was provided in the second axial groove portion. On the other hand, in the axial groove-shaped portion of the comparative example, the first depth D1 of the first axial groove-shaped portion was set to be the same as the second depth D2 of the second axial groove-shaped portion. Then, the performances of the tires of Examples 1 to 7 and the tire of Comparative Example were evaluated. Specifications common to each example and comparative example are as follows.
Size: 275/70R22.5
Rim: 22.5 x 8.25
Tire internal pressure: 900kPa
Test vehicle: CITYBUS (patrol bus)
Mounting position of test tires: All wheels Tread width TW: 246mm
Main groove:
Width W1/TW: 5.5% to 6.8%
Maximum depth D: 20.0mm
Width W2/TW of first land portion and second land portion: 21.9%
Width W3/TW of third land portion and fourth land portion: 19.2%
First axial groove:
Pitch P: 60.7mm
Curvature (curvature radius) R1: 40mm
Body:
Width W4: 2.8mm
Maximum depth D3: 2.1mm
Second axial groove:
Degree of bending (curvature radius) R2: 100mm
Body:
Width W4: 2.8mm
Maximum depth D3: 2.1mm
Third axial groove:
Degree of bending (radius of curvature) R3: 80mm
Width W6: 1.7mm
Maximum depth D6: 2.1mm
Distance L1/pitch P between the axial groove-shaped portion of the first land portion and the axial groove-shaped portion of the second land portion: 0.32
Distance L3 between the third axial groove-shaped portion of the third land portion and the first axial groove-shaped portion of the first land portion/pitch P: 0.32, 0.82
Distance L4 between the third axial groove-shaped portion of the fourth land portion and the first axial groove-shaped portion of the second land portion/pitch P: 0.32, 0.82
The test method is as follows

<Uneven wear resistance performance>
After running the test vehicle on a dry paved road surface for 10,000 km, the amount of wear was measured at a plurality of locations on the first land portion and the second land portion, and the variation in the amount of wear was determined. The results are expressed as an index, with the variation in wear amount in Example 1 being 100. The smaller the numerical value, the smaller the uneven wear and the better.

<Noise resistance performance>
The test vehicle was run on a dry paved road at a speed of 60 km/h, and the noise heard in the vehicle was evaluated by the driver's sensory perception. The results are shown as indices with Example 1 being 100. The smaller the numerical value, the smaller the noise and the better.

<Wet Performance>
The above test vehicle entered an asphalt road surface with a water film of 2 mm in thickness at a speed of 65 km/h, and abrupt braking was performed. At this time, the time required for the test vehicle to decelerate from 60 km/h to 20 km/h was measured. The results are shown as indices with Example 1 being 100, and the smaller the number, the better.
Table 1 shows the results of the tests.

As a result of the test, the tires of Examples 1 to 7 were able to reduce uneven wear compared to the tires of Comparative Examples. Therefore, the tires of Examples 1 to 7 were able to suppress uneven wear while maintaining noise resistance performance and drainage performance.

Furthermore, in Examples 1 and 5, the ratio D1/D between the first depth and the maximum depth of the main groove and the ratio D2/D between the second depth and the maximum depth of the main groove are (R1+R2)/ It was set smaller than (R2×2). As a result, the degree of curvature (curvature radius R1) of the first axial groove-shaped portion and the degree of curvature of the second axial groove-shaped portion (curvature radius R2), the first depth D1 of the first axial groove-shaped portion and the second depth D2 of the second axial groove-shaped portion are decreased with respect to the maximum depth D of the main groove. Therefore, it was possible to effectively prevent uneven wear.

In Example 7, since the first shallow portion and the second shallow portion shown in FIG. 7 were provided, uneven wear could be suppressed as compared with Example 1.

REFERENCE SIGNS LIST 1 tire 2 tread portion 4 land portion 7 axial groove portion 7A first axial groove portion 7B second axial groove portion

Claims (13)

A tire in which a land portion extending in the tire circumferential direction is formed in the tread portion,
The land portion is formed with a plurality of axial groove-shaped portions that are curved so as to protrude in one direction in the tire circumferential direction in a plan view,
the axial groove-shaped portion includes a first axial groove-shaped portion and a second axial groove-shaped portion having a smaller degree of curvature than the first axial groove-shaped portion;
a first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than a second depth, which is the maximum depth of the second axial groove-shaped portion;
The land portion is divided by at least one main groove extending in the tire circumferential direction in the tread portion,
an axial end of the axial groove-shaped portion intersects the main groove or the tread ground contact edge;
tire. 2. The tire of claim 1, wherein said first depth is greater than 0.75 times said second depth. The tire according to claim 1 or 2, wherein said first depth and said second depth are 0.5 to 0.8 times the maximum depth of said main groove. The degree of curvature is a radius of curvature,
D1 is the first depth, D2 is the second depth, D is the maximum depth of the main groove, R1 is the radius of curvature of the first axial groove portion, and R1 is the radius of curvature of the first axial groove portion. 4. The tire according to any one of claims 1 to 3, which satisfies the following formulas (1) and (2), where R2 is the radius of curvature of the contoured portion.
D1/D<(R1+R2)/(R2×2) (1)
D2/D<(R1+R2)/(R2×2) (2) The tire according to any one of claims 1 to 4, wherein the first axial groove portion and the second axial groove portion are adjacent in the tire circumferential direction. The axial grooved portion has a convex portion that protrudes most in the tire circumferential direction,
6. The projection according to any one of claims 1 to 5, wherein the protrusions are arranged on both sides in the tire axial direction from a center position of the width of the land portion in the tire axial direction within a range spaced apart by a distance of 30% of the width of the land portion. The tires described in . The first axial groove-shaped portion is arranged on the first deep bottom portion having the first depth and on both outer sides of the first deep bottom portion in the tire axial direction, and has a depth smaller than the first depth. 7. A tire according to any one of claims 1 to 6, comprising a pair of first shallow portions having The second axial groove-shaped portion is arranged on the second deep bottom portion having the second depth and on both outer sides of the second deep bottom portion in the axial direction of the tire, and has a depth smaller than the second depth. 8. A tire according to any one of claims 1 to 7, comprising a pair of second shallow portions having A tire in which a land portion extending in the tire circumferential direction is formed in the tread portion,
The land portion is formed with a plurality of axial groove-shaped portions that are curved so as to protrude in one direction in the tire circumferential direction in a plan view,
the axial groove-shaped portion includes a first axial groove-shaped portion and a second axial groove-shaped portion having a smaller degree of curvature than the first axial groove-shaped portion;
a first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than a second depth, which is the maximum depth of the second axial groove-shaped portion;
The axial grooved portion has a convex portion that protrudes most in the tire circumferential direction,
The convex portion is arranged on both sides in the tire axial direction from the center position of the width of the land portion in the tire axial direction, within a range separated by a distance of 30% of the width.
tire. A tire in which a land portion extending in the tire circumferential direction is formed in the tread portion,
The land portion is formed with a plurality of axial groove-shaped portions that are curved so as to protrude in one direction in the tire circumferential direction in a plan view,
the axial groove-shaped portion includes a first axial groove-shaped portion and a second axial groove-shaped portion having a smaller degree of curvature than the first axial groove-shaped portion;
a first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than a second depth, which is the maximum depth of the second axial groove-shaped portion;
The first axial groove-shaped portion is arranged on the first deep bottom portion having the first depth and on both outer sides of the first deep bottom portion in the tire axial direction, and has a depth smaller than the first depth. and a pair of first shallow bottoms having
tire. The tire according to claim 10, wherein the depth of the first shallow portion is 0.5 to 0.9 times the first depth. A tire in which a land portion extending in the tire circumferential direction is formed in the tread portion,
The land portion is formed with a plurality of axial groove-shaped portions that are curved so as to protrude in one direction in the tire circumferential direction in a plan view,
the axial groove-shaped portion includes a first axial groove-shaped portion and a second axial groove-shaped portion having a smaller degree of curvature than the first axial groove-shaped portion;
a first depth, which is the maximum depth of the first axial groove-shaped portion, is smaller than a second depth, which is the maximum depth of the second axial groove-shaped portion;
The second axial groove-shaped portion is arranged on the second deep bottom portion having the second depth and on both outer sides of the second deep bottom portion in the axial direction of the tire, and has a depth smaller than the second depth. and a pair of second shallow bottoms having
tire. The tire according to claim 12, wherein the depth of the second shallow portion is 0.5 to 0.9 times the second depth.

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