TECHNICAL FIELD

The present technology relates to a pneumatic tire.

BACKGROUND ART

For a pneumatic tire, on a tread portion, a tread pattern is formed in which a plurality of main grooves extending in a tire circumferential direction are provided and a plurality of rows of land portions are defined by the plurality of main grooves. In such a pneumatic tire, good drainage performance is achieved by providing a plurality of lug grooves extending in a tire lateral direction in each of the land portions of the tread portion.

However, when the number of the lug grooves in the tread portion is increased, the rigidity of the tread portion (tread rigidity) is degraded, which degrades steering stability performance on dry road surfaces. In contrast, when the number of lug grooves in the tread portion is reduced, drainage performance is degraded, which degrades steering stability on wet road surfaces. Thus, steering stability on dry road surfaces and steering stability on wet road surfaces are inconsistent with each other. Further, pattern noise is increased by providing the lug grooves.

For example, a pneumatic tire capable of achieving steering stability on dry road surfaces and steering stability on wet road surfaces in a compatible manner and further improving uneven wear resistance has been known (see Japan Unexamined Patent Publication No. 2017-30556).

The pneumatic tire includes, in a tread portion, a center main groove extending in tire circumferential direction in a zigzag shape along the tire circumferential direction and a shoulder main groove extending in the tire circumferential direction on an outer side of the center main groove. Further, the pneumatic tire includes, in land portions between the center main groove and the shoulder main groove, a plurality of lug grooves, which extend inward in the tire lateral direction from the shoulder main groove and are terminated without communicating with the center main groove. At a terminating end of each of the lug grooves, a bent portion that is bent toward one side in the tire circumferential direction is formed. In the land portions, a plurality of narrow grooves that extend intermittently along the tire circumferential direction without communicating with the bent portions are formed. The narrow grooves are disposed substantially parallel with the center groove having a zigzag shape.

The pneumatic tire described above is capable of achieving steering stability performance on dry road surfaces and steering stability performance on wet road surfaces in a compatible manner and further improving uneven wear resistance performance. However, pattern noise caused due to the lug grooves provided in the land portions is not reduced and remains loud. When the lug grooves are not provided in the land portions, steering stability performance on wet road surfaces is liable to be degraded.

SUMMARY

The present technology provides a pneumatic tire capable of improving steering stability performance on dry road surfaces and steering stability performance on wet road surfaces compared to the related art and suppressing pattern noise.

An aspect of the present technology is a pneumatic tire. The pneumatic tire, includes:

a tread portion extending in a tire circumferential direction, having an annular shape, and having a tread pattern, wherein

the tread pattern including:

two inner main grooves being positioned on both sides in a tire lateral direction with respect to a tire equator line of the pneumatic tire and being formed in an entire circumference in the tire circumferential direction;

two outer main grooves being provided and sandwiching the two inner main grooves on an inner side in the tire lateral direction;

an inner continuous land portion being sandwiched between the two inner main grooves and being continuously formed in the entire circumference in the tire circumferential direction;

two intermediate continuous land portions being sandwiched between one of the two inner main grooves and one of the two outer main grooves and between the other one of the two inner main grooves and the other one of the two outer main grooves, respectively, the two intermediate continuous land portions being continuously formed in the entire circumference in the tire circumferential direction, the two intermediate continuous land portions being outward in the tire lateral direction of the inner continuous land portion; and

first sipes being provided in regions of the two intermediate continuous land portions and extending inward in the tire lateral direction from the two outer main grooves.

Regions of the inner continuous land portion and the two intermediate continuous land portions being not provided with lug grooves extending from the two inner main grooves or the two outer main grooves.

Edges on both sides of one of the two inner main grooves each including a groove chamfered portion having a chamfered width changing in the tire circumferential direction and forming a zigzag shape as seen from a tread surface of the tread portion. The first sipes each including: a sipe main body portion having a constant distance between sipe wall surfaces on a sipe bottom side in a depth direction of the first sipes; and a sipe chamfered portion inclined so that the sipe wall surfaces are open to the tread surface on a side of the tread surface of the first sipes.

The first sipes are preferably provided to be inclined in the tire lateral direction from the two outer main grooves to the inner continuous land portion and to be closed in the regions of the two intermediate continuous land portions. As seen from the tread surface, a surface contour shape of each of first sipes a of the first sipes, which extends from an outer main groove A being one of the two outer main grooves, preferably has: an extending portion extending constantly in an extension direction or with smooth change from the outer main groove A; and a bent portion provided on a side of a closed end portion of each of the first sipes a, the bent portion bending each of the first sipes a from the extending portion and extending to a direction opposite a direction to which the extending portion extends in the tire circumferential direction. In the bent portion, the sipe main body portion preferably extends from the extending portion constantly in the extension direction or with smooth change without being bent and is closed, and the sipe chamfered portion preferably forms a bent shape of the bent portion.

Further, a sipe wall surface being one of two facing sipe wall surfaces of the sipe chamfered portion preferably includes a first chamfered surface and a second chamfered surface at different positions in a sipe depth direction, an inclination angle of each of the first chamfered surface and the second chamfered surface with respect to the depth direction of the first sipes being different each other, and the sipe chamfered portion preferably forms a bent shape of the bent portion.

The inclination angle of the first chamfered surface is preferably identical to that of a counter chamfered surface opposing the first chamfered surface.

Further, the inclination angle of the second chamfered surface is preferably larger than the inclination angle of the first chamfered surface. In this case, the second chamfered surface is preferably positioned on the side of the tread surface with respect to the first chamfered surface.

A chamfered width of the two facing chamfered surfaces is preferably reduced as approaching to a closed end of the sipe main body portion.

Narrow grooves each being prevented from communicating with the bent portion are preferably formed intermittently in the tire circumferential direction in a region of an intermediate continuous land portion α of the two intermediate continuous land portions in which the first sipes a are provided, and an extension direction of the narrow grooves is preferably parallel with an extension direction of an edge of the surface contour shape on a side of the two inner main grooves.

The pneumatic tire preferably has a mounting direction that is specified with respect to a vehicle, and the outer main groove A preferably is instructed, +−by the mounting direction to be positioned on an outer vehicle side with respect to an outer main groove B of the two outer main grooves, the outer main groove B being different from the outer main groove A.

Second sipes are preferably provided in a region of an intermediate continuous land portion β of the two intermediate continuous land portions, which is sandwiched between an outer main groove of the two outer main grooves different from the outer main groove A and one of the two inner main grooves, the second sipes extending from one of the two inner main grooves and being closed without communicating with the outer main groove. Third sipes are preferably provided in the region of the inner continuous land portion, the third sipes extending from an inner main groove of the two inner main grooves, which is in contact with the intermediate continuous land portion β, to the other inner main groove and being closed without communicating with the other inner main groove. Inclination directions of the second sipes and the third sipes with respect to the tire lateral direction and positions thereof in the tire circumference are preferably set, and the second sipes are positioned on extension lines of the third sipes.

As seen from the tread surface, first sipes b of the first sipes, which are provided in a region of the intermediate continuous land portion β, and the second sipes are preferably inclined to different directions in the tire circumferential direction as extending inward in the tire lateral direction.

As seen from the tread surface, the first sipes provided in the regions of the two intermediate continuous land portions are preferably inclined to different sides in the tire circumferential direction as extending inward in the tire lateral direction.

An outer land portion is preferably provided on an outer side of the outer main groove B of the two outer main grooves in the tire lateral direction. A circumferential auxiliary groove and outer lug grooves are preferably provided in a region of the outer land portion, the circumferential auxiliary groove formed in the entire circumference in the tire circumferential direction, the outer lug grooves extending in the tire lateral direction from the outer side in the tire lateral direction and being closed without communicating with the outer main groove B. The outer lug grooves preferably intersect the circumferential auxiliary groove.

According to the pneumatic tire described above, steering stability performance on dry road surfaces and steering stability performance on wet road surfaces can be improved compared to the related art, and pattern noise can be suppressed.

