JP7203594B2 - pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire having a plurality of land portions partitioned by a plurality of circumferential grooves.

Conventionally, a pneumatic tire is known in which a plurality of circumferential grooves extending along the tire circumferential direction and a plurality of land portions partitioned by the circumferential grooves are provided on the tread surface. In order to improve the running performance of pneumatic tires on ice, Patent Documents 1 to 3 disclose pneumatic tires having sipes of various shapes on land portions. If sipes are provided in the land part, not only the running performance on ice but also the running performance on the snowy road surface will be improved due to the edge effect.

By the way, in recent years, there has been a demand for a pneumatic tire that achieves both steering stability performance on a snowy road surface and steering stability performance on a dry road surface. However, generally, when the sipes that contribute to the improvement of the running performance on the snow-covered road surface are opened in the circumferential grooves defining the land portions, the rigidity of the land portions on both outer sides in the tire width direction tends to decrease. If the rigidity of the land portion on both outer sides in the tire width direction is reduced, the land portion cannot counteract lateral forces acting on the tread surface during turning, etc., and the steering stability performance on dry road surfaces tends to deteriorate. Furthermore, if the groove width of the sipes is constant, the sipes tend to close all at once when a large force acts on the tread surface, which may result in insufficient steering stability on snowy road surfaces.

In Patent Document 4 by the present inventor, a first land groove that extends in a land portion so as to have one bent portion that is convex toward one side in the tire circumferential direction, and a land groove that extends toward the other side in the tire circumferential direction. By providing a second land groove extending so as to have one curved portion that becomes convex on a dry road surface while ensuring steering stability performance on snow while having a land groove that opens at the circumferential groove. describes a pneumatic tire with improved turning performance. However, it is desired to achieve a higher level of both steering stability performance on a snowy road surface and steering stability performance on a dry road surface.

JP 2017-087987 A JP 2016-088342 A WO2011/111394 JP 2018-090201 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire that achieves both steering stability performance on a snowy road surface and steering stability performance on a dry road surface.

A pneumatic tire according to the present invention is a pneumatic tire comprising a tread surface having a plurality of circumferential grooves extending along the tire circumferential direction and a plurality of land portions defined by the plurality of circumferential grooves,
At least one of the land portions has one end portion that opens to one side of the circumferential groove that defines the land portion, the other end portion, and a curved bent portion that protrudes toward one side in the tire circumferential direction. Equipped with a narrow groove containing
The vertex of the curved portion of the narrow groove is located in a region including the one end portion of the region obtained by dividing the at least one land portion into three equal parts in the tire width direction,
The groove width of the first groove from the vertex to the one end is smaller than the groove width of the second groove from the vertex to the other end.

The narrow groove has a bent portion that protrudes toward one side in the tire circumferential direction. Therefore, the first groove portion has a portion that extends obliquely with respect to the tire width direction, and the second groove portion has a portion that extends obliquely in a direction opposite to the direction of inclination of the first groove portion. As a result, the directions in which force is applied to loads from various directions are dispersed, and the rigidity of the land portion is increased. Therefore, steering stability performance on a dry road surface is improved.

In addition, the groove width of the first groove portion is reduced. Thereby, it is possible to suppress a decrease in rigidity in a region including one end of the land portion. Moreover, the second groove portion is located closer to the center of the land portion in the tire width direction than the first groove portion. The central side of the land portion in the tire width direction has higher rigidity than both outer sides in the tire width direction. By making the groove width of the second groove portion larger than the groove width of the first groove portion, the high rigidity on the central side can be reduced. As a result, the uniformity of the rigidity of the land portion in the tire width direction is enhanced, and the steering stability performance on dry road surfaces is improved.

In addition, if there is a large difference in groove width in the narrow groove, when a force sufficient to close the narrow groove acts on the tread surface, the narrow groove width portion will close and the large groove width portion will remain unclosed. . In other words, the narrow grooves are prevented from closing all at once, ensuring steering stability on snowy road surfaces. Furthermore, since the second groove portion has a groove width larger than that of the first groove portion, a large edge effect is obtained, and steering stability performance on a snow-covered road surface is improved.

It is preferable that the groove depth of the first groove portion is smaller than the groove depth of the second groove portion. When the groove depth of the first groove portion is smaller than the groove depth of the second groove portion, it is possible to suppress a decrease in rigidity in a region including one end portion of the land portion. In addition, since the groove depth of the second groove portion is larger than the groove depth of the first groove portion, the rigidity of the land portion on the center side in the tire width direction tends to be reduced. As a result, the uniformity of the rigidity of the land portion in the tire width direction is enhanced, and the steering stability performance on dry road surfaces is improved. Furthermore, the large groove depth of the second groove enhances the edge effect and improves the steering stability performance on the snow-covered road surface.

The other end is closed within the at least one land portion, and at least one of the groove width and the groove depth of the second groove is increased stepwise from the vertex toward the other end. It is preferable to have Since the other end is closed in the land portion, the rigidity in the vicinity of the other end is high. Therefore, in the second groove portion, the groove width and groove depth on the other end side can be made larger than the groove width and groove depth on the first groove portion side while ensuring the uniformity of rigidity. When the groove width and groove depth on the other end side are increased, the edge effect is further enhanced, and steering stability performance on a snow-covered road surface is improved.

The other end is closed within the at least one land portion,
The second groove portion includes a first short groove portion and a second short groove portion in order from the vertex,
In both the first short groove portion and the second short groove portion, the groove width increases toward the other end portion in each short groove portion,
the minimum groove width of the second short groove portion is smaller than the maximum groove width of the first short groove portion;
A maximum groove width of the second short groove portion may be larger than a maximum groove width of the first short groove portion.

Since the other end is closed in the land portion, the rigidity in the vicinity of the other end is high. Therefore, it is possible to secure a large groove width toward the other end portion in each of the first short groove portion and the second short groove portion while ensuring rigidity uniformity. Also, the maximum groove width of the second short groove portion can be made larger than the maximum groove width of the first short groove portion. When the groove width is increased, the edge effect is further enhanced, and steering stability performance on snowy roads is improved.

Further, by making the minimum groove width of the second short groove portion smaller than the maximum groove width of the first short groove portion, it is possible to suppress an excessive decrease in rigidity of the second groove portion. As a result, the uniformity of the rigidity of the land portion in the tire width direction is enhanced, and the steering stability performance on dry road surfaces is improved. Furthermore, if there is a large difference in groove width in the grooves, when a force enough to close the grooves acts on the tread surface, the grooves will not close all at once to maintain the edge effect, and the snow road surface will be improved. It is possible to ensure the steering stability performance at.

It is preferable that both the first short groove portion and the second short groove portion have a groove depth that decreases as the groove width increases within the respective short groove portions. Considering that the rigidity decreases as the groove width and groove depth increase, a small groove depth is applied to a large groove width, and a large groove depth is applied to a small groove width. Thereby, the rigidity uniformity in each of the first short groove portion and the second short groove portion can be improved. Therefore, steering stability performance on a dry road surface is improved.

FIG. 2 is a developed view showing the tread surface in the first embodiment of the pneumatic tire according to the present invention. Enlarged view of part A in FIG. Cross-sectional view along the pp line in FIG. Enlarged view of the tread surface in the second embodiment Cross-sectional view at the qq line segment in FIG. Enlarged view of the tread surface in the third embodiment Cross-sectional view along the rr line segment in FIG.

<First embodiment>
An embodiment of a pneumatic tire according to the present invention will be described below with reference to the drawings. In each drawing, the dimensional ratio of the drawing and the actual dimensional ratio do not necessarily match, and the dimensional ratio between the drawings does not necessarily match.

In FIG. 1, the first direction D1 is the tire width direction D1 that is parallel to the tire rotation axis, and the second direction D2 is the tire circumferential direction D2 that is the direction around the tire rotation axis. as well). One direction (the right direction in FIG. 1) of the tire width direction D1 is called a first width direction D11, and the other direction (the left direction in FIG. 1) is called a second width direction D12. One direction (upward direction in FIG. 1) of the tire circumferential direction D2 is called a first circumferential direction D21, and the other direction (downward direction in FIG. 1) is called a second circumferential direction D22.

A tire radial direction (not shown) is a diameter direction of the pneumatic tire (hereinafter also simply referred to as “tire”) 1 . The tire equatorial plane S1 is a plane orthogonal to the tire rotation axis and located at the center of the tire width direction D1.

The tread surface 2 includes a plurality of circumferential grooves 3, 4 extending along the tire circumferential direction D2, and a plurality of land portions 5, 6 partitioned by the plurality of circumferential grooves 3, 4. In this embodiment, three circumferential grooves 3 and 4 are provided, and four land portions 5 and 6 are provided. In addition, the numbers of the circumferential grooves 3 and 4 and the land portions 5 and 6 are not limited to such a configuration.

The circumferential groove 3 arranged on the tire equatorial plane S1 is called the center circumferential groove 3, and the circumferential groove 4 arranged outside in the tire width direction D1 is called the shoulder circumferential groove 4. A land portion adjacent to the center circumferential groove 3 is called a center land portion 5 , and a land portion arranged outside the shoulder circumferential groove 4 in the tire width direction D<b>1 is called a shoulder land portion 6 . The center land portion 5 and the shoulder land portion 6 may be composed of ribs, as shown in FIG. 1, or may be composed of blocks repeatedly arranged in the tire circumferential direction D2.

The center land portion 5 will be described in detail. The center land portion 5 (hereinafter also simply referred to as "land portion 5") has a plurality of narrow grooves 7, 8 extending so as to intersect the tire circumferential direction D2. The narrow grooves 7 and 8 are narrower than the circumferential grooves 3 and 4. The narrow grooves 7 and 8 may be shallower than the circumferential grooves 3 and 4. The narrow grooves 7 and 8 include sipes with a groove width of 1.5 mm or less. As shown in FIG. 1, since the center land portion 5 is provided with a large number of fine grooves 7 and 8, a large edge effect is obtained, and the steering stability performance of the tire 1 on a snowy road surface is excellent. Only one of the narrow grooves 7 and 8 may be provided in the land portion 5 .

Here, the fine grooves 7 and 8 provided in the land portion 5 will be described with reference to FIG. 2, which is an enlarged view of the portion A in FIG. The narrow groove 7 extends so as to have one convex bent portion 7a in the first circumferential direction D21. Further, the narrow groove 8 extends so as to have one bent portion 8a that is convex in the second circumferential direction D22. In this way, since the bent portions 7a of the narrow grooves 7 and the bent portions 8a of the narrow grooves 8 are convex in different directions, the decrease in rigidity of the land portion 5 against a force in a specific direction is suppressed. can.

In this embodiment, one thin groove 7 and two thin grooves 8 are repeatedly formed in the tire circumferential direction D2, but this is not restrictive. For example, one thin groove 7 and one thin groove 8 may be repeatedly formed in the tire circumferential direction D2, and one thin groove 7 and three or more thin grooves 8 may be formed in the tire circumferential direction D2. It may be formed repeatedly.

The fine groove 7 will be described in detail. A bent portion 7a of the narrow groove 7 is formed in a curved shape. In addition to the bent portion 7a, the narrow groove 7 has one end portion 7b that opens into the circumferential groove 4 (one of the circumferential grooves 3 and 4 that divide the land portion 5), and the other end portion 7c. The bent portion 7a has a vertex 7t. The vertex 7t is a point on the outer side of the convex shape of the groove walls forming the narrow groove 7 and at the extreme end position in the first circumferential direction D21. A first groove portion 71 is defined from the vertex 7t to the one end portion 7b, and a second groove portion 72 is defined from the vertex 7t to the other end portion 7c. Although it is preferable to include the apex 7t in the first groove portion 71, the apex 7t may be included in the second groove portion 72 as well. Further, the bent portion 7a is preferably formed in a curved shape, but may be bent in a bent shape in which a straight line is bent.

The first groove portion 71 is composed of a portion of the bent portion 7a on the one end portion 7b side of the vertex 7t and an extension portion 7d continuing from the bent portion 7a. The extension portion 7d is inclined with respect to the tire width direction D1. The extended portion 7d preferably forms an angle of 30 degrees or more and preferably 45 degrees or less with respect to the tire width direction D1 at the opening end of the narrow groove 7 . The extension 7d is preferably straight, but it may be a gently curving curve. The bent portion 7a may open into the circumferential groove 4 without the extended portion 7d.

The second groove portion 72 is composed of a portion of the bent portion 7a on the side of the other end portion 7c from the vertex 7t and an extension portion 7e continuing from the bent portion 7a. The extension 7e may be straight or gently curving. The extension portion 7e is inclined with respect to the tire circumferential direction D2. The extension portion 7e is inclined in a direction opposite to the direction of inclination of the extension portion 7d. As a result, the direction in which the force is applied to the load applied to the tire 1 from various directions is dispersed, and the rigidity of the land portion 5 is increased. Therefore, steering stability performance on a dry road surface is improved.

A bending angle θ7 of the bending portion 7a is determined by an angle formed between the extension portion 7d and the extension portion 7e. From the viewpoint of improving steering stability performance on a dry road surface, the bending angle θ7 is preferably 90 degrees or more, more preferably 110 degrees or more. The bending angle θ7 is preferably 150 degrees or less, more preferably 130 degrees or less.

By the way, as shown in FIG. 2 , the land portion 5 includes end regions A1 and A2 arranged outside in the tire width direction D1, a central region A3 arranged between the end regions A1 and A2, and 3 equally divided. The end region on the first width direction D11 side is called an end region A1, and the end region on the second width direction D12 side is called an end region A2. The vertex 7t is in the end region A1 including the one end 7b. From the viewpoint of securing an appropriate length of the narrow groove 7, it is preferable that the other end portion 7c is located in the end region A2 and the second groove portion 72 crosses the central region A3 as in the present embodiment.

Since the narrow groove 7 opens into the circumferential groove 4, the end region A1 causes a decrease in rigidity compared to the central region A3. Since the central region A3 is sandwiched between the end regions A1 and A2 on both sides thereof, the rigidity of the central region A3 tends to be higher than that of the end regions A1 and A2. However, in the present embodiment, the groove width w71 of the first groove portion 71 is made smaller than the groove width w72 of the second groove portion 72, thereby suppressing a decrease in rigidity in the end region A1. Moreover, since the groove width w72 of the second groove portion 72 is larger than the groove width w71 of the first groove portion 71, the rigidity of the central region A3 can be reduced. Thereby, the uniformity of the rigidity of the land portion 5 in the tire width direction D1 is enhanced. Moreover, since the second groove portion 72 can ensure a relatively large groove width w72, the edge effect is enhanced. Moreover, if there is a large difference in groove width in the narrow grooves 7, when a force sufficient to close the narrow grooves 7 acts on the tread surface 2, only the portions of the narrow grooves 7 with small groove widths are closed. The large part remains unclosed. In other words, the narrow grooves 7 are prevented from closing all at once, and the edge effect is maintained.

In FIG. 2, the groove walls are smoothly connected at the joint portion between the first groove portion 71 and the second groove portion 72 having different groove widths, but the groove walls do not have to be smoothly connected. For example, the groove wall may be bent at the joint portion between the first groove portion 71 and the second groove portion 72 . The narrow grooves 7 formed so that the groove walls are bent have the advantage that the sipe blade can be easily processed when the tire 1 is vulcanized and formed with the sipe blade.

FIG. 3 is a cross-sectional view along line pp, which is the extending direction of the narrow groove 7 in FIG. As shown in the figure, it is preferable that the groove depth d71 of the first groove portion 71 is smaller than the groove depth d72 of the second groove portion 72 . The groove depth d71 is set to, for example, 60% or less of the groove depth d72. When the groove depth d71 of the first groove portion 71 is smaller than the groove depth d72 of the second groove portion 72, it is possible to suppress a decrease in rigidity in the end region A1. Moreover, since the groove depth d72 of the second groove portion 72 is larger than the groove depth d71 of the first groove portion 71, the rigidity of the central region A3 is likely to be reduced. As a result, the uniformity of the rigidity of the land portion 5 in the tire width direction D1 is enhanced, and the steering stability performance on a dry road surface is improved. Furthermore, the large groove depth of the second groove portion 72 enhances the edge effect. However, the groove depth d71 of the first groove portion 71 and the groove depth d72 of the second groove portion 72 may be the same value.

A wall 77 connects the bottom of the first groove 71 and the bottom of the second groove 72 . The wall 77 may be formed perpendicular to the tread surface 2 or may be inclined. When inclined, it is preferable that the inclination is such that the opening area of the narrow groove 7 increases as the narrow groove 7 becomes shallower. A wall sandwiched between a pair of opposing groove walls at the other end portion 7c is similar to the wall 77 .

It is preferable that the other end portion 7 c is closed within the land portion 5 . Thereby, the rigidity of the end region A2 can be secured, and the groove width and groove depth of the second groove portion 72 on the other end portion 7c side can be made larger than the groove width and groove depth of the first groove portion 71 side. However, the other end portion 7c may be open to the circumferential groove 3.

When the other end 7c opens into the circumferential groove 3, in order to prevent a decrease in rigidity in the end region A2, a bent portion having the same shape as that of the end region A1 is also formed on the side of the end region A2 so as to protrude in the D22 direction. , the groove depth of the thin grooves 7 in the end region A2 is shallow, the number of the thin grooves 7 is reduced with respect to the thin grooves 8, and the grooves are repeatedly formed in the tire circumferential direction D2, or these are combined. It is good to apply.

The embodiment described above can be applied not only to the fine grooves 7 provided in the land portion 5 but also to the fine grooves 8 . The same shape, same groove width and groove depth may be applied to the narrow grooves 7 and 8, or different shapes or different groove widths and groove depths may be applied.

As shown in FIG. 2, the shape of the fine groove 8 corresponds to the shape of the fine groove 7 inverted vertically and horizontally. In addition to the bent portion 8a, the narrow groove 8 has one end portion 8b that opens into the circumferential groove 3 (one of the circumferential grooves 3 and 4 that divide the land portion 5), and the other end portion 8c. Since the thin grooves 7 and 8 open to the circumferential grooves 3 and 4 on both left and right sides of the land portion 5 , the rigidity of the land portion 5 is made uniform.

Moreover, the vertex 8t of the bent portion 8a of the narrow groove 8 is positioned in the end region A2. The narrow grooves 7 and 8 provide bent portions 7a and 8a in the end regions A1 and A2, respectively. The other end 7c of the narrow groove 7 is located in the end region A2, while the other end 8c of the fine groove 8 is located in the end region A1. contribute. Further, the first groove portion 71 of the narrow groove 7 and the second groove portion 82 of the narrow groove 8 are adjacent to each other in the tire circumferential direction D2, and the second groove portion 72 of the narrow groove 7 and the first groove portion 82 of the narrow groove 8 are adjacent to each other. The fact that the groove portions 81 are adjacent to each other in the tire circumferential direction D2 also contributes to the uniformity of the rigidity of the land portion 5 .

The embodiment described above can be applied not only to the center land portion 5 but also to the fine grooves provided in the shoulder land portion 6 and the like.

<Second embodiment>
The second embodiment has the same configuration as the first embodiment except for the configuration described below, so common points will be omitted and differences will be mainly described. Parts that are the same as those described in the first embodiment are denoted by the same reference numerals, and redundant explanations are omitted. Also, the multiple modified examples described above can be combined and employed without any particular restrictions. This also applies to the third embodiment.

A second embodiment will be described with reference to FIG. The second groove portion 72' includes a first short groove portion 73 and a second short groove portion 74 in order from the vertex 7t. A groove width w74 of the second short groove portion 74 is larger than a groove width w73 of the first short groove portion 73 . A groove width w73 of the first short groove portion 73 is larger than a groove width w71 of the first groove portion 71 . The groove width of the second groove portion 72' increases stepwise from the vertex 7t toward the other end portion 7c. Since the other end 7c is closed within the land portion 5, the rigidity in the vicinity of the other end 7c is high. Therefore, the groove width w74 of the second short groove portion 74 can be made larger than the groove width w73 of the first short groove portion 73 while ensuring the uniformity of the rigidity of the land portion 5 . Since the groove width w74 of the second short groove portion 74 can be increased, the edge effect is further enhanced. Furthermore, if there is a large difference in groove width in the narrow groove 7, when a force sufficient to close the narrow groove 7 acts on the tread surface 2, only the portion of the narrow groove 7 with a small groove width closes, The large part remains unclosed. In other words, the narrow grooves 7 are prevented from closing all at once, and the edge effect is maintained.

FIG. 5 is a cross-sectional view along line qq, which is the extending direction of the narrow groove 7' in FIG. As shown in the figure, the groove depth is increased stepwise from the vertex 7t toward the other end 7c. Since the rigidity near the other end portion 7c is high, the groove depth d74 of the second short groove portion 74 can be made larger than the groove depth d73 of the first short groove portion 73 while ensuring the uniformity of the rigidity of the land portion 5. . Since the groove depth d74 of the second short groove portion 74 can be increased, the edge effect is further enhanced. Also, both the groove width w74 and groove depth d74 of the second short groove portion 74 may be larger than the groove width w73 and groove depth d73 of the first short groove portion 73 .

In the above-described embodiment, both the groove width and the groove depth are increased stepwise in the second groove portion 72'. Alternatively, the groove depth may be increased stepwise while keeping the groove width constant. Also, in the above-described embodiment, the second groove portion 72' is composed of two short groove portions, but may be composed of three or more short groove portions. As the number of stages increases, the uniformity of the rigidity of the land portion 5 and the expansion of the groove width of some of the short groove portions become easier.

<Third Embodiment>
A third embodiment will be described with reference to FIG. The second groove portion 72'' is configured in a sawtooth shape. That is, the second groove portion 72'' includes a first short groove portion 75 and a second short groove portion 76 in order from the first groove portion 71, and the first short groove portion 75 and the second short groove portion 76 are respectively , the width of the groove increases toward the other end 7c. The other end portion 7c is closed within the land portion 5, and the rigidity in the vicinity of the other end portion 7c is high. Therefore, the uniformity of the rigidity of the land portion 5 can be ensured even if the groove width is increased toward the other end portion 7c. Further, even if the maximum groove width of the second short groove portion 76 is made larger than the maximum groove width of the first short groove portion 75, the rigidity uniformity of the land portion 5 can be ensured.

The minimum groove width of the second short groove portion 76 is smaller than the maximum groove width of the first short groove portion 75 . As a result, the rigidity of the land portion 5, which tends to be excessively lowered by increasing the groove width, can be maintained. Further, by partially forming a portion with a large groove width, the edge effect is enhanced. Furthermore, if there is a large difference in groove width in the narrow groove 7, when a force sufficient to close the narrow groove 7 acts on the tread surface, only the small groove width portion in the narrow groove 7 will be closed and the width will be large. The part remains open. In other words, the narrow grooves 7 are prevented from closing all at once, and the edge effect is maintained.

FIG. 7 is a cross-sectional view taken along line rr, which is the extending direction of the narrow groove 7'' in FIG. As shown in the drawing, the second groove portion 72 ″ includes a first short groove portion 75 and a second short groove portion 76 in order from the first groove portion 71 . In both the first short groove portion 75 and the second short groove portion 76, the groove depth becomes smaller as the groove width becomes larger in each short groove portion. As the groove width and groove depth both increase, the rigidity decreases. Therefore, by applying a small groove depth to a large groove width and applying a large groove depth to a small groove width in each of the short groove portions with different groove widths, the first short groove portion 75 , and the second short groove portion 76 can be finely adjusted. This can improve uniformity of rigidity. However, in this embodiment, the cross-sectional shape shown in FIG. 7 is not an essential configuration. There may be a constant groove depth within each short groove as in the cross-sectional shape shown in FIG. 5, and a constant groove depth in the second groove portion 72'' as in the cross-sectional shape shown in FIG. may have a

The tire according to the present invention can be constructed in the same manner as a normal tire except that the tread surface 2 is constructed as described above, and any of conventionally known materials, shapes, structures, manufacturing methods, etc. can be employed. Although not shown, the tire of this embodiment includes a pair of bead portions, sidewall portions extending radially outward from each of the bead portions, and outer ends of the sidewall portions in the tire radial direction. a tread portion continuing to the tread portion, the surface of the tread portion including a tread surface 2;

The present invention is by no means limited to the above-described embodiments, and various improvements and modifications are possible without departing from the scope of the present invention.

As Example 1, a tire in which all fine grooves provided in a pair of center land portions on the tread surface shown in FIG. 1 have the form shown in the first embodiment was evaluated. The narrow groove is composed of a first groove portion and a second groove portion, the groove width of the first groove portion being 0.6 mm, and the groove width of the second groove portion being 1.5 mm. The groove depth of the first groove portion and the groove depth of the second groove portion are both 7 mm.
As Example 2, a tire in which all fine grooves provided in a pair of center land portions on the tread surface shown in FIG. 1 have the form shown in the first embodiment was evaluated. The narrow groove is composed of a first groove portion and a second groove portion, the groove width of the first groove portion being 0.6 mm, and the groove width of the second groove portion being 1.5 mm. The groove depth of the first groove portion is 3 mm, and the groove depth of the second groove portion is 7 mm.
As Example 3, a tire in which all fine grooves provided in a pair of center land portions on the tread surface shown in FIG. 1 had the form shown in the second embodiment was evaluated. The narrow groove is composed of a first groove portion and a second groove portion, and the second groove portion is composed of a first short groove portion and a second short groove portion in order from the first groove portion. The groove width of the first short groove portion is 1.2 mm, the groove width of the second short groove portion is 2.0 mm, and the groove width of the first groove portion is 0.6 mm. The groove depth of the first short groove portion is 5 mm, the groove depth of the second short groove portion is 7 mm, and the groove depth of the first groove portion is 3 mm.
As a comparative example, a tire having the tread surface shown in FIG. 1 was evaluated. The thin grooves provided in the pair of center land portions have curved bent portions that protrude toward one side in the tire circumferential direction, as in each embodiment. However, the groove width of the narrow groove is constant at 0.8 mm, and the groove depth is constant at 7 mm.

The tires of Examples 1 to 3 and Comparative Example were mounted on a test vehicle to evaluate steering stability performance and cornering power on a snow-covered road surface. In addition, the braking performance on dry road surfaces was evaluated. Conditions for each evaluation item are shown below.

<Evaluation of steering stability performance on snowy road surface>
A vehicle was equipped with 195/65R15 tires, and the vehicle was run straight ahead or changed lanes on a snowy road surface, and evaluated by the driver's sensory test. The result of the comparative example is rated as "4" and evaluated on a 7-point scale.

<Evaluation of cornering power>
Using a drum tester with a diameter of 2500 mm, the cornering force generated in a 195/65R15 tire at an internal pressure of 200 kPa and a load of 4.2 kN was measured to obtain the cornering power at a slip angle of 1 degree. The result of the comparative example is indexed as 100, and the larger the value, the greater the cornering power and the better the steering stability performance on dry road surfaces.

<Evaluation of braking performance on dry road surface>
A tire of 195/65R15 was mounted on a vehicle, and braking force was applied from a speed of 100 km/h on a dry road surface to evaluate the reciprocal of the braking distance when the ABS was operated. The result of the comparative example is indexed as 100, and the larger the number, the better the braking performance on the dry road surface.

Table 1 shows the evaluation results. Thus, in comparison with the comparative example, Examples 1 and 2 ensured the same steering stability performance on snow-covered road surfaces, and also obtained excellent results in terms of cornering power and braking performance on dry road surfaces. . Example 3 obtained excellent results not only in cornering power and braking performance on dry road surfaces but also in steering stability performance on snow-covered road surfaces, compared to the comparative examples. In other words, Examples 1 to 3 achieve a higher level of both steering stability performance on a snowy road surface and steering stability performance on a dry road surface than in the comparative example.

Reference Signs List 1 Tire 2 Tread surface 3 Center circumferential groove 4 Shoulder circumferential groove 5 Center land portion 6 Shoulder land portions 7, 8 Thin groove 7a Bent portion 7b One end 7c Other end 7d, 7e Extension portion 7t Vertex 71 First grooves 72, 72', 72'' Second grooves 73, 75 First short grooves 74, 76 Second short grooves

Claims (4)

A pneumatic tire comprising a tread surface having a plurality of circumferential grooves extending along the tire circumferential direction and a plurality of land portions defined by the plurality of circumferential grooves,
At least one of the land portions has one end portion that opens into one of the two circumferential grooves that divide the land portion, and does not open into the other circumferential groove of the two circumferential grooves. At least one narrow groove including the other end that closes in the land portion and a curved bent portion that is convex toward one side in the tire circumferential direction,
The apex of the bent portion is located in a region including the one end portion among the regions obtained by dividing the at least one land portion into three equal parts in the tire width direction,
The groove width of the first groove portion from the vertex to the one end portion is smaller than the groove width of the second groove portion from the vertex to the other end portion, and the groove depth of the first groove portion is smaller than the groove depth of the first groove portion. A pneumatic tire characterized by having a groove depth smaller than that of two groove portions . The pneumatic tire according to claim 1 , wherein at least one of groove width and groove depth of said second groove portion is increased stepwise from said vertex toward said other end portion. The second groove portion includes a first short groove portion and a second short groove portion in order from the vertex,
Both the first short groove portion and the second short groove portion increase in width as they approach the other end,
the minimum groove width of the second short groove portion is smaller than the maximum groove width of the first short groove portion;
The pneumatic tire according to claim 1 , wherein the maximum groove width of the second short groove portion is larger than the maximum groove width of the first short groove portion. The pneumatic tire according to claim 3 , wherein both the first short groove portion and the second short groove portion have a groove depth that decreases as the groove width increases.

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