JP2017222280A - tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire capable of enhancing wet performance, while maintaining rib rigidity.SOLUTION: A tire comprises: inner main grooves 5, 6 and outer main grooves 3, 4 continuously extending in a tire circumferential direction on both sides in a tread width direction; a central land part 7 partitioned by the inner main grooves; and intermediate land parts 8, 9 partitioned by the outer main grooves and the inner main grooves. The central land part comprises central sipes 14 and central sub grooves 13, alternately formed in the tire circumferential direction, and extending from one of the inner main grooves to the other of the inner main grooves in a direction intersecting the inner main grooves. The intermediate land part comprises intermediate sipes 16 and intermediate sub grooves 15, alternately formed in the tire circumferential direction, and extending in a direction intersecting the outer main grooves and the inner main grooves. The intermediate sub groove comprises: an opening end side extending part 15a, one end of which is opened to the outer main groove or the inner main groove, while the other end of which terminates within the intermediate land; and a closing end side extending part 15b extending from the other end of the opening end side extending part to the tire circumferential direction and terminating within the intermediate land. The closing end side extending part is inclined at 0-10 degrees with respect to the tire circumferential direction.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a tire, and more particularly to a tire capable of improving WET performance while maintaining rib rigidity.

  Conventionally, in a tire, a rib defined by a plurality of main grooves extending continuously in the tire circumferential direction in the tread portion is provided with a sub-groove shallower than the groove depth of the main groove so as to extend in the tire width direction. By increasing the edge component on the contact surface, the WET performance (the removal effect of the water film between the tire contact surface and the road surface) at the beginning of use of the new tire is improved while securing the rib rigidity.

Japanese Patent Laying-Open No. 2015-151023

However, when the secondary groove is disposed so as to terminate in the rib in a state extending in the tire width direction, there is a problem that cracks are likely to occur at the end of the secondary groove terminating in the rib. Since the occurrence of such cracks can cause a tire failure, it is necessary to suppress the occurrence of cracks. For example, as one of the countermeasures, a measure for increasing the shear rigidity when the end portion of the sub-groove rubs against the road surface by setting the groove depth of the sub-groove shallow is conceivable. However, when the groove depth of the sub-groove is reduced, the timing at which the sub-groove disappears due to wear of the tire is advanced, and there is a problem that the edge component disappears at an early stage from the start of use of the tire and the WET performance is deteriorated.
In view of the above problems, an object of the present invention is to provide a tire capable of improving the WET performance while maintaining rib rigidity.

The tire structure for solving the above-described problems includes an outer main groove extending continuously in the tire circumferential direction on both sides in the tread width direction, and provided between each outer main groove and the tire equator, respectively. An inner main groove extending continuously to each other, a central land portion defined by each inner main groove, and an intermediate land portion defined by each outer main groove and each inner main groove, The land portion is formed alternately in the tire circumferential direction, and has a central sipe and a central sub-groove extending in a direction crossing the inner main groove from one inner main groove to the other inner main groove in the width direction. The portion has an intermediate sipe and an intermediate sub-groove that are alternately formed in the tire circumferential direction and extend in a direction crossing the outer main groove and the inner main groove, and one end of the intermediate sub-groove is the outer main groove or the inner main groove. And the other end ends in the middle land It has a mouth end side extension and a closed end side extension extending from the other end in the tire circumferential direction and terminating in the middle land portion, and the angle at which the closed end extension extends is the tire circumferential direction. The configuration is in the range of 0 to 10 degrees.
According to this configuration, the closed end-side extension of the intermediate sub-groove extends toward the tire circumferential direction, maintaining the WET performance (removal of water film between the tire tread and the road surface) at the initial stage of wear. However, it is possible to reduce stress concentration at the closed end of the intermediate sub-groove at the time of tire contact and suppress the occurrence of cracks.
Further, as another configuration of the tire, by reducing the length of the intermediate sub-groove in the tire width direction to 50% to 90% of the ratio to the width of the intermediate land portion, the rigidity of the intermediate land portion is reduced. Edge effect can be obtained.
Further, as another configuration of the tire described above, the length of the intermediate sub-groove in the tire circumferential direction is set to 10 to 50% of the length of the tire in the tire width direction. It is possible to reduce the stress concentration at the portion and suppress the occurrence of cracks.
Further, as another configuration of the tire, since the angle of the opening end side extension portion intersecting the tire circumferential direction is set to 60 to 80 degrees, the water between the tire tread and the road surface removed by the edge effect of the intermediate sub-groove is set. The membrane can be smoothly discharged into the main groove.

It is a top view of a tread pattern. It is sectional drawing of a tire. It is an enlarged view of a tread. It is the elements on larger scale of a central land part. It is the elements on larger scale of a middle land part. It is the elements on larger scale of a belt layer. It is a top view of the tread pattern of a prior art example. It is the table | surface which put together evaluation conditions. It is the table | surface which put together the evaluation result. It is the table | surface which put together the Example and evaluation result.

  Hereinafter, the present invention will be described in detail through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are included in the invention. It is not necessarily essential to the solution, but includes a configuration that is selectively adopted.

FIG. 1 is a plan view of a tread pattern formed on a tread portion of a tire T according to the present embodiment, and FIG. 2 is a cross-sectional view of the tire T according to the present embodiment. The tire T shown in FIG. 2 has a structure applied to heavy-duty vehicles such as trucks and buses, for example.
As shown in FIG. 2, the tire T has a pair of bead cores 51 mainly composed of a cord member, a carcass 53, a belt layer 54 composed of a plurality of belt plies, and a bead filler 52 composed mainly of a rubber member. Belt under rubber 55, base rubber 56, tread rubber 57, rim cushion rubber 58, side rubber 59, mini side rubber 60, inner liner 62, and the like.

  The tire T includes one or more belts on the outer peripheral side of the crown region of the carcass 53 including one or more carcass plies extending in a toroidal shape between a pair of bead stiffeners formed by the bead core 51 and the bead filler 52. A belt layer 54 made of a ply (hereinafter simply referred to as a belt) is provided. A belt under rubber 55 is provided between the carcass 53 and the end side of the belt layer 54. A base rubber 56 and a tread rubber 57 are provided in this order on the outer side of the belt layer 54 in the tire radial direction. A rim cushion rubber 58 and a side rubber 59 that come into contact with the rim from the bead portion side are provided outside the side region of the carcass 53. Further, on the tire side surface, a mini side rubber 60 is provided that covers the radially outer end of the side rubber 59 and the outer ends of the base rubber 56 and the tread rubber 57 in the tire width direction. An inner liner 62 is provided on the entire inner side of the carcass 53 to enhance the airtightness of the air chamber.

  As shown in FIG. 1, the tread pattern formed in the tread portion 2 according to the present embodiment has a rib pattern that is partitioned by a plurality of main grooves extending continuously in the tire circumferential direction. Yes. Specifically, the outer main grooves 3 and 4 respectively provided on the left and right end sides, and the inner main grooves provided between the left and right outer main grooves 3 and 4 and the tire center CL that is the equator of the tire. 5 and 6 are included. The main groove is a groove having a wear indicator (not shown) indicating the use limit of the tire T, and is a groove serving as a criterion for determining the wear use limit of the tire T. In the following description, for convenience of description, the tire center CL is referred to as the left and right, and the direction is defined with the tire center CL side as the inside and the left and right tread ends 2t as the outside.

The outer main grooves 3 and 4 extend linearly along the tire circumferential direction, and the inner main grooves 5 and 6 extend zigzag along the tire circumferential direction. The inner main grooves 5 and 6 are not limited to a zigzag shape, and may extend linearly like the outer main grooves 3 and 4.
The groove widths m3 and m4 of the outer main grooves 3 and 4 and the groove widths m5 and m6 of the inner main grooves 5 and 6 are set in the range of 5 mm to 30 mm, respectively. For example, the groove widths m3 and m4 of the outer main grooves 3 and 4 and the groove widths m5 and m6 of the inner main grooves 5 and 6 may all be the same, and all the groove widths m3 while satisfying the above range. , M4, m5, m6 may be different. The outer main grooves 3 and 4 have the same groove widths m3 and m4, the inner main grooves 5 and 6 have the same groove widths m5 and m6, and the outer main grooves 3 and 4 have the same groove widths m3 and m4. , 6 may be different from the groove widths m5, m6. The groove widths m3, m4, m5, and m6 are measured by the shortest distance between the groove walls facing each other on the treads of the main grooves 3, 4, 5, and 6.

The tread pattern according to the present embodiment is set to be a point object in plan view so as not to specify the orientation when the tire is mounted on the vehicle. That is, the left and right outer main grooves 3 and 4 are provided at the same distance in the tire width direction from the tire center CL, and the left and right inner main grooves 5 and 6 are provided at the same distance in the tire width direction from the tire center CL.
On the groove bottoms of the inner main grooves 5 and 6, stone biting prevention protrusions for preventing stone biting are formed intermittently along the extending direction of the groove.

  Therefore, the tread rubber 57 has an outer land portion 11 between the left tread end 2t and the outer main groove 4 and an intermediate portion between the outer main groove 4 and the inner main groove 6 on the left side of the tire center CL. The land portion 9 is partitioned, and on the right side, the outer land portion 10 is partitioned between the right tread end 2t and the outer main groove 3, and the intermediate land portion 8 is partitioned between the outer main groove 3 and the inner main groove 5, A central land portion 7 is defined between the left and right inner main grooves 5 and 6 across the tire center CL.

  FIG. 3 is an enlarged view of the tread. As shown in FIG. 3, the central land portion 7 is provided with sub-grooves 13 and sipes 14 that extend in a direction intersecting the inner main grooves 5 and 6 alternately in the tire circumferential direction. The sub-groove 13 and the sipe 14 are formed so that one end side opens into the inner main groove 5 and the other end side opens into the inner main groove 6. The sub-groove 13 and the sipe 14 are set to be point-symmetric so that the shapes in plan view of the tread shown in FIG. 3 coincide with each other before and after rotation when rotated 180 degrees around the tire center CL. Thereby, the symmetry of the subgroove 13 and the sipe 14 in the central land portion 7 is secured.

One end 13A that opens in the inner main groove 6 of the sub-groove 13 and the other end 13B that opens in the inner main groove 5 are formed so as to be displaced in the tire circumferential direction.
Specifically, the sub-groove 13 is inclined from one inner main groove 6 and extends from the first section 13a, and continues from the first section 13a, and the tire circumferential direction with respect to the extending direction of the first section 13a. A second section 13b that extends in the opposite direction and a third section 13c that continues from the second section 13b and inclines in a direction parallel to the first section 13a and extends to the other inner main groove 5 are provided.
The first section 13 a starts from the opening with the inner main groove 6, extends in a state inclined by a predetermined inclination angle a <b> 1 with respect to the tire width direction, and terminates in the central land portion 7. The extending length of the first section 13a is set so as to end before reaching the tire center CL, for example. The second section 13b starts from the end of the first section 13a and extends at an inclination angle a2 with respect to the tire width direction opposite to the tire circumferential direction from the inclination direction of the first section 13a. Terminate in the central land 7 beyond CL. The third section 13c starts from the end of the second section 13b and extends at an inclination angle a3 with respect to the tire width direction in the direction opposite to the tire circumferential direction opposite to the inclination direction of the second section 13b. Open in the groove 5 and terminate.
The first section 13a and the third section 13c are set to have the same inclination angle a1 and inclination angle a3 with respect to the tire width direction and the same length in the tire width direction.
The sub-groove 13 has a uniform groove depth d13 and groove width m13 in the extending direction.
For example, the groove depth d13 of the sub-groove 13 is preferably set in the range of 1 mm to 2 mm, and the groove width m13 is preferably set in the range of 1 mm to 2 mm.

As shown in FIG. 4, the sipe 14 is formed in a gentle S-shape so as to follow the shape of the sub-groove 13, and has one end portion 14 </ b> A that opens to the inner main groove 6 and the inner main groove 5. The other end portion 14B is formed so as to be displaced in the tire circumferential direction. Specifically, the sipe 14 includes a first section 14 a that extends along the first section 13 a of the sub-groove 13, a second section 14 b that extends along the second section 13 b of the sub-groove 13, and the sub-groove 13. And a third section 14c extending along the third section 13c. In the sipe 14, the first section 14a and the second section 14b are connected by an arc-shaped smooth curve, and the second section 14b and the third section 14c are connected by an arc-shaped smooth curve.
The inclination angle b1 at which the first section 14a opens into the inner main groove 6 is set to be the same angle as the inclination angle a1 of the first section 13a of the sub groove 13.
The inclination angle b2 that the second section 14b extends is set to be the same angle as the inclination angle a2 of the second section 13b of the sub groove 13.
The inclination angle b3 at which the third section 14c opens into the inner main groove 5 is set to be parallel to the third section 13c of the sub-groove 13.
The groove width m14 of the sipe 14 is preferably in the range of 0.3 mm to 1.5 mm.

  The interval p7 between the auxiliary groove 13 and the sipe 14 is set, for example, in the range of 0.1% to 1.1% of the tire circumferential length. The interval p7 may be the same interval as long as it is within the above range, or may be formed so as to gradually widen. Preferably, the interval p7 has three values, p71 is 0.10 to 0.90%, p72 is 0.11 to 0.98%, and p73 is 0.12 to 1.05%.

Sub-grooves 15 and sipes 16 are alternately provided in the tire circumferential direction in the left and right intermediate land portions 8 and 9. As described above, since the tread pattern according to the present embodiment is set to be a point object in plan view, the sub-groove 15 and the sipe 16 have a point object relationship in each of the intermediate land portions 8 and 9. is there. Therefore, in the following description, as shown in the partially enlarged view of FIG. 5, the configuration of the auxiliary groove 15 and the sipe 16 will be described using the right intermediate land portion 8.
The auxiliary groove 15 is formed so as to extend mainly in the tire width direction and then to change its direction so as to bend in the tire circumferential direction. Specifically, the sub-groove 15 extends toward the outer main groove 3 so that one end opens into the inner main groove 5 defining the intermediate land portion 8 and the other end terminates in the intermediate land portion 8. The opening end side extension 15a and the opening end side extension 15a extend in the tire circumferential direction from the bent portion 15B that terminates in the intermediate land portion 8, and are closed end side extensions that terminate in the intermediate land portion 8. Part 15b.

  The opening end extension 15 a is set so as to be located on the extension line of 14 c of the sipe 14 provided in the central land portion 7. The opening end extension 15a is formed, for example, so as to extend linearly from the inner main groove 5 with respect to the tire width direction at a predetermined inclination angle c1 and terminate in the intermediate land portion 8. The inclination angle c1 of the opening end side extension 15a is set to be the same as the inclination angle b3 of the sipe 14, for example. The inclination angle c1 is set in a range of 10 degrees to 30 degrees with respect to the tire width direction (60 degrees to 80 degrees with respect to the tire circumferential direction).

The closed end extension 15b starts from the end of the opening end extension 15a that terminates in the intermediate land portion 8, and the opening end extension 15a is inclined in the tire circumferential direction with respect to the tire width direction. It extends in a straight line toward the end and ends in the intermediate land portion 8.
The direction in which the closed end extending portion 15b extends is set, for example, within a range of 0 degrees to 10 degrees from the straight line in the tire circumferential direction extending from the bent portion 15B to the left and right with respect to the tire circumferential direction. Is done. The range of 0 to 5 degrees is preferable, and the inclination angle c2 is more preferably set to 0 degree that matches the tire circumferential direction.
In addition, that the opening end side extension part 15a and the closing end side extension part 15b of the subgroove 15 extend linearly is a concept including a curve that gently curves in an arc shape.

The minor groove 15 is set such that the length dimension w15 in the tire width direction is in the range of 50 to 90% of the width dimension w8 of the intermediate land portion 8. Note that the length dimension w15 in the tire width direction of the auxiliary groove 15 is from the opening end 15A to the closing end 15C when the closing end 15C is inclined so as to be positioned on the outer main groove 3 side. The length in the tire width direction. When the closed end 15C is inclined so as to be located on the inner main groove 5 side, the length in the tire width direction from the open end 15A to the bent portion 15B is used.
The width dimension w8 of the intermediate land portion 8 is the length in the tire width direction from the outer edge 5o where the inner main groove 5 opens to the tread to the inner edge 3i where the outer main groove 3 opens to the tread.

  In addition, the minor groove 15 has a length dimension L15 in the tire circumferential direction set in a range of 10% to 50% of a length dimension w15 of the minor groove 15 in the tire width direction. The length L15 of the auxiliary groove 15 in the tire circumferential direction is linear toward the side where the closed end extension 15b is inclined in the tire circumferential direction with respect to the tire width direction of the opening end extension 15a. Is defined by the length in the tire circumferential direction from the open end 15A to the closed end 15C. Further, when the closed end side extension portion 15b extends toward the side opposite to the side inclined in the tire circumferential direction with respect to the tire width direction of the opening end side extension portion 15a, the closed end side extension portion 15b is closed from the bent portion 15B. It is defined by the length in the tire circumferential direction to the end portion 15C or the length in the tire circumferential direction from the opening end portion 15A to the bent portion 15B.

As the groove width of the sub-groove 15, the groove depth d15 and the groove width m15 in the extending direction in plan view are set uniformly. For example, the groove depth d15 of the auxiliary groove 15 is preferably set in the range of 1 mm to 2 mm, and the groove width m15 is preferably set in the range of 1 mm to 2 mm.
Further, the auxiliary groove 15 has a distance L30 to the sipe 16 of the closed end 15C in a range of 25% to 40% with respect to the distance L20 in the tire circumferential direction between the sipe 16 adjacent to the auxiliary groove 15; Preferably it is formed. For example, when it is less than 25%, the sub-groove 15 is too close to the sipe 16, so that deformation at the time of stepping on the road surface or kicking out becomes large, and there is a concern that the performance of suppressing crack generation may be reduced. Further, if it exceeds 40%, the sub-groove 15 approaches the center side in the circumferential direction of the block of the block defined by the adjacent sipes 16; 16, and therefore, it is difficult to dissipate heat and easily generates heat. There is a possibility that the suppression performance is lowered.

The sipe 16 is formed so as to be located on the extension of the third section 13 c of the sub-groove 13 provided in the central land portion 7. The sipe 16 is inclined and extended at a predetermined inclination angle d with respect to the tire width direction. One end of the sipe 16 opens into the inner main grooves (center main grooves) 5 and 6 on the tire center CL side, and the other end opens into the outer main grooves 3 and 4.
The groove width m16 of the sipe 16 is preferably in the range of 0.3 mm to 1.5 mm.

The auxiliary groove 17 is provided corresponding to the sipe 16 so as to be positioned on the extension of the sipe 16 provided in the intermediate land portion 8. One end of the auxiliary groove 17 opens into the outer main groove 3, extends linearly outward in the tire width direction at the same inclination angle e as the inclination angle d of the sipe 16, and terminates in the outer land portion 10.
In addition, the position on the extension in the above description is not only that the center line of each sipe or each sub-groove is located on the same straight line, but also, for example, within the range of the groove width of each sipe or sub-groove, Means that the centerline is included.

As described above, the sub-grooves 13, 15, and 17 formed in the land portions 7, 8, 9, 10, and 11 preferably have the following relationship in the length dimension in the tire width direction.
(Width direction length dimension w13 of sub-groove 13 / width dimension w7 of central land portion 7)>
(Width direction length dimension w15 of sub-groove 15 / width dimensions w8 and w9 of intermediate land portions 8 and 9)>
(Width direction length dimension w17 of sub-groove 17 / width dimensions w10, w11 of outer land portions 10, 11).
Thus, the rigidity of each land part 7-11 is set by setting the width direction length dimension w13, w15, 17 of the subgroove 13,15,17 with respect to the width dimension w7-w11 of each land part 7-11. The edge component by each subgroove 13,15,17 can be obtained suitably, maintaining. The width dimension w10 of the outer land portion 10 is the length in the tire width direction from the outer edge 3o where the outer main groove 3 opens to the tread to the tread end 2t.

FIG. 6 is a partially enlarged view of the belt layer 54. As shown in the figure, the widths of the belts 71 to 74 constituting the belt layer 54 are set. The belt layer 54 according to the present embodiment has a four-layer structure in which the belts 71, 72, 73, and 74 are laminated on the outer side in the tire radial direction in the order from the inner side in the tire radial direction. Each of the belts 71 to 74 is set such that the belt width is belt 72> belt 71> belt 73> belt 74.
Belt widths of the belts 71 to 73 are set so that ends in the tire width direction are located on the inner side in the tire radial direction of the outer land portions 10 and 11.

More specifically, the belt width w72 of the belt 72 is such that the end portion 72t in the tire width direction is the width dimension of the outer land portions 10 and 11 from the outer edge in the tire width direction of the outer main grooves 3 and 4 toward the tread end 2t. It is set so as to be in a range larger than 70% and smaller than 95% of w10 and w11. Preferably, it is greater than 70% and 90% or less.
For example, when the position of the end 72t of the belt 72 is 70% or less from the outer main groove 3, the cut resistance may be lowered. Moreover, when it is 95% or more, there is a possibility that the strain at the belt end is deteriorated.

Further, the belt width w73 of the belt 73 is such that the end portion 73t in the tire width direction is the width dimension w10, w11 of the outer land portion 10, 11 from the outer edge of the outer main groove 3, 4 toward the tread end 2t. Of 40% to 70%.
For example, when the position of the end 73t of the belt 73 is 40% or less from the outer main groove 3, the cut resistance may be reduced. Moreover, when it is set to 70% or more, there is a possibility that the strain at the belt end is deteriorated.

Further, the belt width w74 of the belt 74 is such that the end 74t in the tire width direction is 75% to 95% of the width dimension w8, 9 of the intermediate land portions 8, 9 from the outer edge in the tire width direction of the inner main grooves 5, 6. It is set to be located in the range of.
For example, when the position of the end 74t of the belt 74 is 75% or less from the inner main groove 5, the cut resistance may be reduced. Moreover, when it is 95% or more, there is a possibility that the strain at the belt end is deteriorated.

Further, as the belt cords constituting the belts 71 to 74, cords having excellent cut resistance are preferably used in the order of belt 71 → belt 72 → belt 73 → belt 74 in the tire radial direction.
In particular, the belt 74 located on the outermost layer on the outer side in the tire radial direction has eight sheath filaments made of brass-plated steel cord on the outer periphery obtained by twisting two core filaments made of brass-plated steel cord. It is preferable to use a belt cord having a two-layer twisted structure obtained by twisting together.

  In addition, dimensions, such as the width of each belt 71-74, are the dimensions measured in a no-load state by filling the tire T assembled to the applicable rim with the specified internal pressure. The “applicable rim” refers to a rim defined in the following standards according to the tire size. Specifically, it is an industrial standard that is effective in the region where tires are produced or used. In Japan, “JATMA YEAR BOOK” of the Japan Automobile Tire Association, and in the United States, THE TIRE AND RIM ASSOCIATION INC. "YEAR BOOK" in Europe, and in Europe, the standard rim (Approved Rim, Recommended Rim) applicable to tires described in "STANDARDS MANUAL" of the European Tire and Rim Technical Organization. Further, the “specified internal pressure” is an air pressure that is specified in accordance with the maximum load capacity in each of the above standards. The “maximum load capacity” is the maximum mass that is allowed to be applied to the tire according to each of the above standards. Further, the “tread end 2t” in the above description is the outermost contact position in the tire width direction on the contact surface when a load corresponding to the maximum load capacity is applied to the tire T in the above state.

[Example]
In order to verify the effect of the tire T according to the present embodiment, conventional tires (hereinafter referred to as conventional examples) 1 and 2 (see FIG. 7) set as shown in the table of FIG. 8, and the tire according to the present embodiment Five types of tires (hereinafter referred to as “Examples”), 1, 2 and 3 were prototyped, assembled to the rim specified by JATMA and applied with the specified internal pressure, and the start / acceleration performance evaluation at the time of WET, braking Performance evaluation, feeling evaluation at 5%, 10%, 15% wear and crack generation state evaluation were performed. The tire sizes of the tires of the conventional examples 1 and 2 and the examples 1, 2 and 3 are 12R22.5 inches.

  The tread patterns of Conventional Examples 1 and 2 are shown in FIG. Similar to the present embodiment (Examples 1, 2 and 3), the tires of the conventional example are provided on the left and right end sides, respectively, and have outer main grooves 83 and 84 extending continuously in the tire circumferential direction, A rib pattern is formed between the outer main grooves 83 and 84 and the tire center CL, and is partitioned by four main grooves of the inner main grooves 85 and 86 extending continuously in the tire circumferential direction. ing. The tire of Conventional Example 1 is provided with a sipe 92 in the central land portion 87 defined by the inner main grooves 85 and 86, and the tire of Conventional Example 2 is provided in the central land portion 87 defined by the inner main grooves 85 and 86. A sipe 92 is provided. The sipes 92 provided in the conventional examples 1 and 2 are provided at predetermined intervals in the tire circumferential direction, and are formed so as to communicate with the left and right inner main grooves 85 and 86. The sub-groove 93 provided in the conventional example 2 is formed so as to extend in the center circumferential portion 87 in a wavy shape in the tire circumferential direction. Further, in the intermediate land portions 88 and 89 defined by the outer main groove 83 and the inner main groove 85 and the outer main groove 84 and the inner main groove 86, sipes 94 and sub grooves 95 are alternately provided in the tire circumferential direction. It is done. The sipe 94 is formed in an arc shape so as to communicate the outer main groove 83 and the inner main groove 85, the outer main groove 84 and the inner main groove 86 in each of the intermediate land portions 88 and 89. Further, the sub-groove 95 has one end opened to the inner main grooves 85 and 86 in each of the intermediate land portions 88 and 89, and extends outward in the tire width direction in parallel with the sipe 94. It is formed to terminate.

The start / acceleration performance was evaluated based on the time index by the start / acceleration test on the iron plate road in the WET state.
Moreover, the brake evaluation was evaluated by the WETμ test.
In addition, the feeling evaluation at the time of 5%, 10%, and 15% wear was evaluated by the drivability at the time of wear by an actual test.
In the crack generation state evaluation, the crack generation state at the time of 15% wear from the new state was evaluated by visual confirmation.
Each evaluation result is shown in the table of FIG. In addition, each evaluation was indexed by setting the result of Example 1 as 100, and relative evaluation was performed. In each evaluation, the larger the value, the better the performance.

  As shown in the table of FIG. 9, in all of Examples 1 to 3, the sub-groove in the intermediate land portion is provided with the closed end side extension portion 15 b, so that in the crack occurrence state evaluation compared to the conventional examples 1 and 2. It turns out that it is excellent. Further, in Examples 1 to 3, there is no deterioration in performance in starting / acceleration evaluation, brake evaluation, and feeling evaluation. In particular, in the feeling evaluation, even if the depth of the sub-grooves of the intermediate land portions 8 and 9 is increased as in Examples 2 and 3, the performance at the initial use of the tire is improved without decreasing the performance. I understood.

  In FIG. 10, other conditions excluding the width direction length dimension w8 of the sub-groove 15 are constant, the width dimension w8 of the intermediate land portion 8 is changed, and the width direction length dimension w8 of the sub-groove 15 in the intermediate land portion 8 is changed. As a result of the wet evaluation and the crack generation state evaluation when the ratio of the width of the sub-groove is changed and the other conditions except for the length L15 of the sub-groove 15 in the tire circumferential direction are made constant, the length dimension of the sub-groove 15 in the width direction is constant. The other conditions except for the results of wet evaluation and crack generation state evaluation when the length dimension L15 of the auxiliary groove 15 in the tire circumferential direction with respect to w15 is changed and the distance L30 of the auxiliary groove 15 with respect to the sipe 16 are made constant. It is the table | surface which put together the result of the wet evaluation and crack generation state evaluation when changing distance L30 of the subgroove 15 with respect to the distance L20 between the sipes of adjacent sipes 16; 16.

  When the width dimension w8 of the intermediate land portion 8 is changed and the ratio of the width direction length dimension w8 of the sub-groove 15 in the intermediate land portion 8 is changed, as shown in Examples 4 to 6, the conventional example 3 It can be seen that the brake evaluation and the crack occurrence state evaluation are superior to those in FIG. That is, when forming the secondary groove 15 in the intermediate land portion 8, the width direction length dimension w15 of the secondary groove 15 is set to be in the range of 50% to 90% with respect to the width dimension w8 of the intermediate land portion 8. Then you can see that it is good. In addition, as shown in Comparative Example 1, when the ratio of the width direction length dimension w15 of the sub-groove 15 to the width dimension w8 of the intermediate land portion 8 exceeds 50% to 90%, the brake evaluation and the crack generation state evaluation are degraded. I understand that

  Further, when the length dimension L15 in the tire circumferential direction of the sub-groove 15 with respect to the width direction length dimension w15 of the sub-groove 15 is changed, as shown in Examples 7 to 11, compared with the conventional example 3. It turns out that it is excellent in brake evaluation and crack generation state evaluation. In other words, it can be seen that the ratio of the length dimension L15 in the tire circumferential direction of the sub-groove 15 to the width dimension w15 in the width direction of the sub-groove 15 may be set in the range of 10% to 70%. More preferably, it is good to set it as the range of 20%-50%. Moreover, if the ratio of the width direction length dimension w15 of the subgroove 15 to the width dimension w8 of the intermediate land portion 8 is less than 10%, as shown in Comparative Example 2, the brake evaluation and the crack generation state evaluation may be reduced. I understand.

Moreover, when changing distance L30 of the subgroove 15 with respect to the distance L20 between sipes, as shown in Example 12 to Example 14, it turns out that it is excellent in crack generation state evaluation compared with the prior art example 3. FIG. That is, it can be seen that the ratio of the distance L30 of the sub-groove 15 to the inter-sipe distance L20 is preferably set to be in the range of 20% to 40%. More preferably, it is good to set it as the range of 25%-35%.
Moreover, when the ratio of the distance L30 of the subgroove 15 with respect to the distance L20 between sipes exceeds 40%, as shown in the comparative example 3, it turns out that brake evaluation and crack generation state evaluation fall.

2 tread part, 2t tread end, 3, 4 outer main groove, 5, 6 inner main groove,
7 Central land, 13, 15 minor groove, 14, 16 sipes,
15a Open end extension, 15b Close end extension,
CL tire center, T tire.

Claims (4)

An outer main groove extending continuously in the tire circumferential direction on both sides in the tread width direction;
An inner main groove provided between each outer main groove and the tire equator, and extending continuously in the tire circumferential direction;
A central land section defined by each inner main groove, and
An intermediate land portion defined by each outer main groove and each inner main groove,
A tire comprising:
The central land portion is formed alternately in the tire circumferential direction, and has a central sipe and a central sub-groove extending from one inner main groove in the width direction to the other inner main groove in a direction crossing the inner main groove. ,
The intermediate land portion is formed alternately in the tire circumferential direction, and has intermediate sipe and intermediate sub-groove extending in a direction intersecting with the outer main groove and the inner main groove,
The intermediate sub-groove has one end opened in the outer main groove or the inner main groove, and the other end terminated in the intermediate land portion.
Extending from the other end in the circumferential direction of the tire, and having a closed end side extension portion terminating in the intermediate land portion,
The tire is characterized in that the extending angle of the closed end side extension is in the range of 0 to 10 degrees with respect to the tire circumferential direction.   The tire according to claim 1, wherein a length dimension of the intermediate minor groove in a tire width direction is 50% to 90% of a width dimension of the intermediate land portion.   The tire according to claim 1 or 2, wherein a length dimension of the intermediate sub groove in the tire circumferential direction is 10 to 50% of a length dimension of the intermediate sub groove in the tire width direction.   The tire according to any one of claims 1 to 3, wherein the opening end side extension portion is inclined and extended in a range of 60 to 80 degrees with respect to a tire circumferential direction.

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