TECHNICAL FIELD

The present technology relates to a pneumatic tire, and more particularly, to a pneumatic tire capable of improving steering stability performance on a dry road surface and improving steering stability performance on a wet road surface and includes a chamfered shape of a sipe.

BACKGROUND ART

Conventionally, in a tread pattern of a pneumatic tire, a plurality of sipes are formed on ribs defined by a plurality of main grooves. Such sipes are provided such that drainage properties are ensured and steering stability performance on a wet road surface is achieved. However, when a large number of sipes are disposed in the tread portion for improving the steering stability performance on the wet road surface, the rigidity of the rib is reduced, so there is a disadvantage that steering stability performance on a dry road surface is deteriorated.

Various proposals have been made on pneumatic tires in which sipes are formed in a tread pattern and chamfered (see, for example, Japan Unexamined Patent Publication No. 2013-537134). When forming a sipe and chamfering it, the edge effect may be lost depending on the shape of chamfer, and improvement in steering stability performance on a dry road surface or steering stability performance on a wet road surface may be insufficient depending on the chamfering size.

SUMMARY

The present technology provides a pneumatic tire capable of achieving both improvement of steering stability performance on a dry road surface and improvement of steering stability performance on a wet road surface and includes a chamfer shape of a sipe.

A pneumatic tire of the present technology includes a plurality of main grooves extending in a tire circumferential direction in a tread portion, and a sipe extending in a tire width direction in a rib defined by the plurality of main grooves. The sipe includes a leading side edge and a trailing side edge, a chamfered portion shorter than a sipe length of the sipe is formed in each of the leading side edge and the trailing side edge, a non-chamfered region including no other chamfered portion is present in a part facing each chamfered portion of the sipe, a maximum depth y (mm) of the chamfered portion is shallower than a maximum depth x (mm) of the sipe, a sipe width of the sipe is constant in a range from an end positioned on a radial direction inside of the chamfered portion to a groove bottom of the sipe, at least one of the chamfered portions when viewed as a cross-section perpendicular to a longitudinal direction of the sipe includes a profile line that is convex inward in a tire radial direction with respect to a chamfer reference line connecting both ends of the chamfered portion, and a cross-sectional area a of a chamfered region surrounded by the profile line, the sipe, and a tread contact surface of the tread portion is equal to or larger than a cross-sectional area b of a reference region surrounded by the chamfer reference line, the sipe, and the tread contact surface.

According to the present technology, in a pneumatic tire including a sipe extending in the tire width direction on a rib defined by a main groove, while a chamfered portion shorter than the sipe length of the sipe is formed in each of the leading side edge and the trailing side edge of the sipe, there is a non-chamfered region including no other chamfered portion in the part facing each chamfered portion in the sipe, thereby improving the drainage effect based on the chamfered portion and at the same time the non-chamfered region is capable of effectively removing the water film by the edge effect. This thereby enables steering stability on wet road surfaces to be significantly improved. Moreover, since the chamfered portion and the non-chamfered region are mixed in each of the leading side edge and the trailing side edge, the beneficial effect of improving the wet performance as described above may be maximized at the time of braking and at the time of accelerating. Further, compared to the sipe chamfered in a conventional manner, since the area to be chamfered can be minimized, improvement in steering stability performance on dry road surfaces is enabled. As a result, achieving both the improvement of steering stability performance on dry road surfaces and the improvement of steering stability performance on wet road surfaces is enabled. Further, since at least one of the chamfered portions when viewed as a cross-section perpendicular to a longitudinal direction of the sipe includes a profile line that is convex inward in a tire radial direction with respect to a chamfer reference line connecting both ends of the chamfered portion, and since a cross-sectional area a of a chamfered region surrounded by the profile line, the sipe, and a tread contact surface of the tread portion is equal to or larger than a cross-sectional area b of a reference region surrounded by the chamfer reference line, the sipe, and the tread contact surface, an increase in the groove volume is enabled without reducing the contact area, thereby enabling the steering stability performance on a wet road surface to be improved while maintaining the steering stability performance on a dry road surface.

In the present technology, the cross-sectional area a of the chamfered region is preferably in the range of from 110% to 210% of the cross-sectional area b of the reference region. More preferably, it is from 130% to 180%. This enables the steering stability performance on the wet road surface to be improved without deteriorating the steering stability performance on the dry road surface.

In the present technology, the volume Va of the chamfered region is preferably in the range of from 110% to 210% of the volume Vb of the reference region. More preferably, it is from 110% to 140%. This enables the steering stability performance on the wet road surface to be improved without deteriorating the steering stability performance on the dry road surface.

In the present technology, when a position at which the chamfer reference line and the profile line of the chamfered portion are farthest apart is set as an offset position, it is preferable that an offset distance A, which is a distance from a width direction end of the sipe on a tire surface to the offset position, be in a range of from 105% to 200% of a reference distance B, which is on a same straight line as the offset distance A and which is also a distance from a width direction end of the sipe on a tire surface to the chamfer reference line. More preferably, it is from 110% to 140%. This enables the steering stability performance on the wet road surface to be improved without deteriorating the steering stability performance on the dry road surface.

In the present technology, it is preferable that the maximum depth x (mm) of the sipe and the maximum depth y (mm) of the chamfered portion satisfy the relationship of the following formula (1). This enables the steering stability performance on the dry road surface and the steering stability performance on the wet road surface to be improved effectively.
x×0.1≤y≤x×0.3+1.0  (1)

In the present technology, when a distance from a width direction end of the sipe on a tire surface to an offset position, which is a position at which the chamfer reference line and the profile line of the chamfered portion are most distant from each other, is set as an offset distance A, it is preferable that at least one side of the chamfered portions be open to the main groove, and in the chamfered portion open to the main groove, the offset distance A at a main groove side end be larger than the offset distance A at a rib center side end. This enables the groove volume to be increased as it is positioned toward the main groove side in the chamfered portion open to the main groove, such that the drainage property is effectively improved and the steering stability performance on the wet road surface is improved.

In the present technology, it is preferable that in the chamfered portion open to the main groove, the offset distance A at the rib center side end be 0.5 to 0.9 times the offset distance A at the main groove side end. More preferably, it is 0.6 to 0.8 times. This enables the groove volume to be increased as it is positioned toward the main groove side in the chamfered portion open to the main groove, such that the drainage property is effectively improved and the steering stability performance on the wet road surface is improved.

In the present technology, it is preferable that at least one side of the chamfered portions be open to the main groove, and in the chamfered portion open to the main groove, a cross-sectional area a of the chamfered region at the main groove side end be larger than a cross-sectional area a of the chamfered region at the rib center side end. This enables the groove volume to be increased as it is positioned toward the main groove side in the chamfered portion open to the main groove, such that the drainage property is effectively improved and the steering stability performance on the wet road surface is improved.

In the present technology, it is preferable that in the chamfered portion open to the main groove, the cross-sectional area a of the chamfered region at the rib center side end be 0.5 to 0.9 times the cross-sectional area a of the chamfered region at the main groove side end. More preferably, it is 0.6 to 0.8 times. This enables the groove volume to be increased as it is positioned toward the main groove side in the chamfered portion open to the main groove, such that the drainage property is effectively improved and the steering stability performance on the wet road surface is improved.

In the present technology, a mounting direction of the pneumatic tire with respect to a vehicle is designated, the pneumatic tire having a tread pattern asymmetric with respect to two sides of a tire center line, and when a distance from a width direction end of the sipe on a tire surface to an offset position, which is a position at which the chamfer reference line and the profile line of the chamfered portion are most distant from each other, is set as an offset distance A, it is preferable that in the rib, the offset distance A of the chamfered portion located toward the vehicle inner side be larger than the offset distance A of the chamfered portion located toward the vehicle outer side. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

In the present technology, it is preferable that the offset distance A of the chamfered portion located toward the vehicle outer side be 0.5 to 0.9 times the offset distance A of the chamfered portion located toward the vehicle inner side. More preferably, it is 0.6 to 0.8 times. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

In the present technology, a mounting direction of the pneumatic tire with respect to a vehicle is designated, the pneumatic tire having a tread pattern asymmetric with respect to two sides of a tire center line, and it is preferable that, in the rib, a cross-sectional area a of the chamfered region at the chamfered portion located toward the vehicle inner side be larger than a cross-sectional area a of the chamfered region at the chamfered portion located toward the vehicle outer side. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

In the present technology, it is preferable that the cross-sectional area a of the chamfered region at the chamfered portion located toward the vehicle outer side be 0.5 to 0.9 times the cross-sectional area a of the chamfered region at the chamfered portion located toward the vehicle inner side. More preferably, it is 0.6 to 0.8 times. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

In the present technology, a mounting direction of the pneumatic tire with respect to a vehicle is designated, the pneumatic tire having a tread pattern asymmetric with respect to two sides of a tire center line, and it is preferable that, in the rib, a volume Va of the chamfered region at the chamfered portion located toward the vehicle inner side be larger than a volume Va of the chamfered region at the chamfered portion located toward the vehicle outer side. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

In the present technology, it is preferable that a volume Va of the chamfered region at the chamfered portion located toward the vehicle outer side be 0.5 to 0.9 times a volume Va of the chamfered region at the chamfered portion located toward the vehicle inner side. More preferably, it is 0.6 to 0.8 times. This enables the steering stability performance on the wet road surface to be improved effectively without deteriorating the steering stability performance on the dry road surface.

