Pneumatic tire

A pneumatic tire includes: a tread portion; grooves formed on the tread portion; and land portions defined by the grooves, wherein each of the land portions includes: a pair of side walls which opposedly face each other with the groove sandwiched therebetween; a first projecting ridge formed on one of the pair of side walls; and a second projecting ridge formed on the other side wall, the first projecting ridge and the second projecting ridge extend along the groove, at least one of the first projecting ridge and the second projecting ridge is inclined such that a position of the projecting ridge in a groove depth direction changes along the groove, and the first projecting ridge intersects with the second projecting ridge as viewed in a width direction of the groove.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a pneumatic tire.

Description of the Related Art

With respect to pneumatic tires, there has been known a pneumatic tire provided with land portions defined by grooves formed on a surface of a tread. In such a pneumatic tire provided with such land portions, there may be a case where the land portion falls down due to a stress in a longitudinal direction or a lateral direction generated at the time of traveling or turning of a vehicle thus giving rise to uneven wear where the land portion locally wears.

In view of the above, in JP-A-2006-137231, to prevent a land portion defined by grooves from falling down, there has been proposed an idea of forming a plurality of projections on a side wall of the groove extending in a tire circumferential direction. However, in this literature, the projection is formed of a columnar portion projecting in a groove width direction and hence, rigidity of the projection is low whereby the falling-down land portion cannot be supported by the projections. Accordingly, there may be a case where uneven wear cannot be sufficiently suppressed.

In JP-A-3-86605, to efficiently drain water in the inside of a tire ground contact surface toward the outside of the ground contact surface at the time of high speed traveling, there has been proposed an idea where an inclined circumferential fin is formed on a side wall of a land portion defined by circumferential grooves and lateral grooves which faces the circumferential groove such that the circumferential fin projects from the side wall of the land portion from a position of a step-in side end portion of the land portion close to a tread surface to a position of a kick-out side end portion of the land portion close to a groove bottom of the circumferential groove. In JP-A-3-86605, if the circumferential fins formed on a pair of side walls which opposedly face each other with the circumferential groove sandwiched therebetween were brought into contact with each other, falling down of the land portion could be suppressed. However, the circumferential fins formed on the pair of side walls are inclined in the same direction and are arranged parallel to each other and hence, when the land portion falls down, one circumferential fin is sometimes positionally displaced upward or downward from the other circumferential fin whereby the circumferential fins are not brought into contact with each other thus giving rise to a case where falling down of the land portion cannot be suppressed until the circumferential fin is brought into contact with the side wall which opposedly faces the circumferential fin.

In JP-A-2010-30596, to improve the grounding property of a tire by realizing the uniform distribution of ground contact pressure of a land portion defined by main grooves extending in a tire circumferential direction and lateral grooves intersecting with main grooves, there has been proposed an idea of forming a projecting ridge which projects from a side surface of the land portion and continuously extends over the whole circumference of the side surface and forming the projecting ridge into a zigzag shape or a wave form having amplitude in a height direction of the land portion. However, the arrangement between the projecting ridge and a projecting ridge which is formed on an opposedly facing side wall with the main groove sandwiched therebetween is not taken into consideration. Accordingly, there may be a case where the projecting ridge is not brought into contact with the projecting ridge formed on the opposedly facing side wall so that falling down of the land portion cannot be suppressed until the projecting ridge is brought into contact with the side wall.

SUMMARY OF THE INVENTION

The invention has been made in view of such drawbacks, and it is an object of the invention to provide a pneumatic tire where the occurrence of uneven wear of a land portion can be suppressed by suppressing excessive falling down of the land portion.

According to one aspect of the invention, there is provided a pneumatic tire which includes: a tread portion; grooves formed on the tread portion; and land portions defined by the grooves, wherein each of the land portions includes: a pair of side walls which opposedly face each other with the groove sandwiched therebetween; a first projecting ridge formed on one of the pair of side walls; and a second projecting ridge formed on the other side wall, the first projecting ridge and the second projecting ridge extend along the groove, at least one of the first projecting ridge and the second projecting ridge is inclined such that a position of the projecting ridge in a groove depth direction changes along the groove, and the first projecting ridge intersects with the second projecting ridge as viewed in a width direction of the groove.

To describe preferred modes of the pneumatic tire according to the invention, the second projecting ridge may be inclined in a reverse direction of an inclination direction of the first projecting ridge. The land portion may be a block defined by the main grooves extending in a tire circumferential direction and the lateral grooves arranged at intervals in the tire circumferential direction. In this case, the first projecting ridge and the second projecting ridge may be formed on the side walls which define the lateral groove. At least one of the first projecting ridge and the second projecting ridge may be formed in plurality on the side wall and arranged at intervals in a groove depth direction.

According to the invention, when the land portion falls down, the projecting ridges are surely brought into contact with each other before the projecting ridge is brought into contact with the opposedly facing side wall of the land portion and hence, the excessive falling down of the land portion can be prevented thus suppressing uneven wear of the land portion.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, one embodiment of the invention is explained with reference to drawings.

Although not shown in the drawing, a pneumatic tire according to this embodiment is constituted of: a pair of left and right bead portions; a pair of left and right side wall portions; and a tread portion10which is disposed between the left and right side wall portions so as to connect radially outer end portions of the left and right side wall portions to each other. The pneumatic tire includes a carcass which extends across between the pair of bead portions.

The carcass is formed of at least one carcass ply which extends from the tread portion10, passes through the side wall portions, and has both end portions thereof engaged with bead cores embedded in the bead portions respectively thus reinforcing the above-mentioned respective portions.

On an outer peripheral side of the carcass at the tread portion10, a belt formed of two or more steel coat layers coated by rubber is mounted thus reinforcing the tread portion10on the outer circumferential side of the carcass. In the pneumatic tire, as shown inFIG. 1, a plurality of grooves12,13, and a plurality of land portions14which are defined by these grooves12,13are formed on a surface of the tread portion10which forms a ground contact surface11.

In this embodiment, four circumferential grooves12which extend in a tire circumferential direction C, a plurality of lateral grooves13which are formed at intervals in the tire circumferential direction and extend in the tire width direction W, and the block-shaped land portions14which are defined by the circumferential grooves12and the lateral grooves13are formed on the tread portion10. In this embodiment, the explanation is made with respect to the case where the circumferential grooves12are formed linearly, and the lateral grooves13are formed perpendicular to the circumferential grooves12. However, by forming the circumferential grooves12in a zigzag manner, or by forming the lateral grooves13in an inclined manner with respect to the circumferential grooves12, the shape of the land portion14in a planar view may be formed into a parallelogram shape, a triangular shape, a trapezoidal shape or the like.

With respect to the land portions14, projecting ridges20a,20bwhich project to the inside of the lateral groove13are formed on a pair of side walls14a,14bwhich faces each other in an opposed manner with the lateral groove13sandwiched therebetween along a direction X in which the lateral groove13extends (in this embodiment, the direction X being equal to a tire width direction W).

The projecting ridges20a,20bformed on the pair of side walls14a,14bwhich faces each other in an opposed manner with the lateral groove13sandwiched therebetween have a rectangular shape having rounded corners in cross section respectively. The projecting ridges20a,20bare inclined such that the position of the projecting ridge in a groove depth direction H changes along the lateral groove13(seeFIG. 2toFIG. 5). InFIG. 3, a long-dashed double-short dashed line indicates a state where the projecting ridge20bformed on the side wall14bof the land portion14which faces the projecting ridge20ain an opposed manner with the lateral groove13sandwiched therebetween is projected on the side wall14ain the width direction Y of the lateral groove13(in this embodiment, the direction Y being equal to the tire circumferential direction C).

In this embodiment, the projecting ridge20ais inclined so that the more the projecting ridge20aformed on one side wall14aextends toward one side X1along the direction in which the lateral groove13extends, the more it approaches a groove bottom13a. On the other hand, the projecting ridge20bis inclined so that the more the projecting ridge20bformed on the other side wall14bwhich faces one side wall14ain an opposed manner extends toward the other side X2along the direction in which the lateral groove13extends, the more it approaches a groove bottom13a. In this case, the projecting ridge20bformed on the other side wall14bis inclined in a reverse direction of the inclination direction of the projecting ridge20aformed on one side wall14a. Due to such a constitution, the projecting ridges20a,20bformed on the pair of side walls14a,14bare arranged such that the projecting ridges20a,20bintersect with each other at a center portion of the land portions14in the direction X in which the lateral groove13extends as viewed in the width direction Y of the lateral groove13(seeFIG. 4).

Although the positions where the projecting ridges20a,20bare formed in the depth direction H of the lateral groove13can be arbitrarily set, it is preferable to set the positions of the projecting ridges20a,20bas follows. An end portion of the projecting ridge20a,20bwhich approaches the groove bottom13ais arranged on the ground contact surface11side of a position which corresponds to 40% of depth h of the lateral groove13measured from the groove bottom13a. An end portion of the projecting ridge20a,20bwhich approaches the ground contact surface11is arranged on the groove bottom13aside of a position which corresponds to 90% of depth h of the lateral groove13measured from the groove bottom13a. An intersection where the projecting ridges20a,20bintersect with each other is arranged on the ground contact surface11side of a position which corresponds to 50% of the depth h of the lateral groove13measured from the groove bottom13a.

In the pneumatic tire having the above-mentioned configuration according to this embodiment, the pair of projecting ridges20a,20bwhich are formed on the pair of side walls14a,14bopposedly facing each other with the lateral groove13sandwiched therebetween are inclined such that the position of each projecting ridge in the groove depth direction H changes along the lateral groove13, and the pair of projecting ridges20a,20bis arranged such that the projecting ridges20a,20bintersect with each other as viewed in the width direction Y of the lateral groove13. Due to such a configuration, when the land portion14falls down toward the inside of the lateral groove13, before the projecting ridges20a,20bare brought into contact with the side walls14b,14aof the land portions14which face each other in an opposed manner, the projecting ridges20a,20bare surely brought into contact with each other. Accordingly, it is possible to prevent the excessive falling down of the land portions14thus suppressing the occurrence of uneven wear of the land portions14.

In this embodiment, the projecting ridges20a,20bare formed on both of the pair of side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween and hence, compared to a case where a projecting ridge is formed only on one side wall, it is possible to reduce projecting amounts of the projecting ridges20a,20b. Accordingly, when the projecting ridges20a,20bare brought into contact with each other, the projecting ridges20a,20bare minimally deformed so that the projecting ridges20a,20bcan surely support the falling land portions14.

The projecting ridges20a,20bformed on the side walls14a,14bare inclined such that the position of the projecting ridge in the groove depth direction H changes along the direction X in which the lateral groove13extends. Accordingly, even when a portion of the projecting ridge20a,20bis exposed to the ground contact surface11due to wear of the land portion14, there is no possibility that the whole projecting ridge20a,20bis exposed to the ground contact surface11in the longitudinal direction of the projecting ridge20a,20b(in the direction X in which the lateral groove13extends). Accordingly, an area where the lateral groove13is clogged by the projecting ridges20a,20bcan be reduced and hence, the lowering of drainage performance of the lateral groove13caused by the projecting ridges20a,20bcan be suppressed.

In this embodiment, the intersection where the projecting ridges20a,20bintersect with each other is arranged on the ground contact surface11side of the position which corresponds to 50% of the depth h of the lateral groove13measured from the groove bottom13a. Accordingly, when the land portion14falls down toward the inside of the lateral groove13, the projecting ridges20a,20bare brought into contact with each other at an early stage of the falling and hence, the falling of the land portion14can be suppressed more effectively.

In the above-mentioned embodiment, the projecting ridges20a,20bare formed into a rectangular shape having rounded corners in cross section as shown inFIG. 4andFIG. 5. However, a cross-sectional shape of the projecting ridges20a,20bis not particularly limited, and may be a semicircular shape shown inFIG. 6, a triangular shape having rounded corners shown inFIG. 7or the like. For example, as shown inFIG. 7, when a cross-sectional shape of the projecting ridges20a,20bis a triangular shape having: a surface which is perpendicular to the side wall14a,14band is arranged on a ground contact surface11side; and an inclined surface which is inclined such that a projecting amount of the inclined surface from the side wall14a,14bis gradually decreased as the inclined surface approaches the groove bottom13aand is arranged on a groove bottom13side. With such a configuration, at the time of removing a building mold for molding a pneumatic tire, the building mold is minimally caught by the projecting ridges20a,20band hence, the projecting ridges20a,20bare minimally broken. Accordingly, it is preferable to form the projecting ridges20a,20binto such a triangular shape in cross section.

In the above-mentioned embodiment, the explanation has been made with respect to the case where both of the projecting ridges20a,20bare formed in an inclined manner such that the position of the projecting ridge in the groove depth direction H changes along the direction X in which the lateral groove13extends. However, it is sufficient that at least one projecting ridge (for example, the projecting ridge20a) is formed in an inclined manner and one projecting ridge (the projecting ridge20a) and the other projecting ridge (for example, the projecting ridge20b) intersect with each other as viewed in the width direction Y of the lateral groove13. For example, as shown inFIG. 8andFIG. 9, one projecting ridge (projecting ridge20a) may be formed in an inclined manner, and the other projecting ridge (projecting ridge20b) may be formed parallel to the groove bottom13a. Also with such a configuration, before the projecting ridges20a,20bare brought into contact with the side walls14a,14bof the land portions14which face each other in an opposed manner, the projecting ridges20a,20bare surely brought into contact with each other and hence, the excessive falling of the land portions14can be suppressed thus suppressing the occurrence of uneven wear of the land portions14.

In the above-mentioned embodiment, as shownFIG. 2andFIG. 3, the end portions of the projecting ridge20a,20bin the direction X in which the lateral groove13extends are positioned inside the edge portions of the land portion14respectively. However, as shown inFIG. 10andFIG. 11, the end portions of the projecting ridge20a,20bin the direction X in which the lateral groove13extends may be positioned at the edge portions of the land portion14respectively.

In the above-mentioned embodiment, as shown inFIG. 3, the projecting ridges20a,20bis formed into a straight line shape as viewed in the width direction Y of the lateral groove13where the inclination direction of the projecting ridge20a,20bwith respect to the direction X in which the lateral groove extends is fixed and does not change. However, the projecting ridges20a,20bmay be formed into a bent shape where the inclination direction of the projecting ridge20a,20bchanges with respect to the direction X in which the lateral groove13extends as shown inFIG. 12or into a zigzag shape where an inclination direction changes as shown inFIG. 13.

In the above-mentioned embodiment, as shown inFIG. 2toFIG. 5, the projecting ridges20a,20bare formed on the pair of side walls14a,14bwhich faces each other in an opposed manner with the lateral groove13sandwiched therebetween on a one-to-one basis. However, as shown inFIG. 14toFIG. 16, a plurality of projecting ridges20a1,20a2,20b1,20b2may be formed on each one of side walls14aat intervals in the groove depth direction H of the lateral groove13.

In the above-mentioned embodiment, as shown inFIG. 1andFIG. 2, the projecting ridges20a,20bare formed such that a projecting amount from the side wall14a,14bis fixed in the direction X in which the lateral groove13extends. However, as shown inFIG. 17, the projecting ridges20a,20bmay be formed such that a projecting amount from the side wall14a,14bis greater at a center portion of the land portion14in the direction X in which the lateral groove13extends, and a projecting amount is gradually decreased toward both end portions of the projecting ridge in the direction X in which the lateral groove13extends. Further, as shown inFIG. 18, cutout portions22which are recessed toward the side wall14a,14bmay be formed on the projecting ridge20a,20b.

In the above-mentioned embodiment, in all land portions14, the projecting ridges20a,20bare formed on the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween. However, the projecting ridges20a,20bmay be formed on only some land portions14out of the plurality of land portions14. For example, the projecting ridge20may be formed on the land portions14positioned at the center portion in the tire width direction W.

In the above-mentioned embodiment, the projecting ridges20a,20bare formed on the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween respectively. However, as shown inFIG. 19, in addition to the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween, projecting ridges20c,20dmay be also formed on side walls14c,14dwhich face each other in an opposed manner with the circumferential groove12sandwiched therebetween such that the projecting ridges20c,20dare arranged in an inclined manner such that a position of the projecting ridge20c,20din the groove depth direction H changes along the circumferential groove12and intersect with each other as viewed in the width direction of the circumferential groove12(in this modification, in the direction equal to the tire width direction W and the direction X in which a lateral groove13extends). Alternatively, the projecting ridges20c,20dmay be formed only on side walls14c,14dwhich face each other in an opposed manner with the circumferential groove12sandwiched therebetween such that the projecting ridges20c,20dare arranged in an inclined manner such that a position of the projecting ridge20c,20din the groove depth direction H changes along the circumferential groove12and intersect with each other as viewed in the width direction Z of the circumferential groove12. In this case, land portions14on which the projecting ridges20c,20dare formed may be block-shaped land portions14which are divided by lateral grooves13in the tire circumferential direction C as in the case of the above-mentioned embodiment or may be rib-shaped land portions14which are continuous in the tire circumferential direction C.

Other Embodiments

The above-mentioned embodiments and modifications have been proposed as examples, and are not intended to restrict the scope of the invention. These novel embodiments and modifications can be carried out in other various modes, and various omissions, replacements and changes can be made without departing from the gist of the invention.

EXAMPLES

Hereinafter, the invention is explained more specifically with reference to examples. It must be noted here, however, that the invention is not limited to such examples.

Pneumatic tires according to the example and comparison examples 1 to 3 (tire size: 11R22.5 16P. R.) were manufactured as specimen tires. These specimen tires were manufactured under a condition that these specimen tires have the same tire internal structure and the same basic tread pattern, while these specimen tires differ from each other in the projecting ridges20a,20bformed on the side walls14a,14bof the land portions14respectively.

To be more specific, the example correspond to the above-mentioned embodiments. That is, the projecting ridges20a,20bare formed on the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween respectively such that the projecting ridges20a,20bare arranged in an inclined manner such that a position of the projecting ridge in the groove depth direction H changes along the lateral groove13, and the projecting ridges20a,20bintersect with each other as viewed in the width direction Y of the lateral groove13. The comparison example 1 is an example where no projecting ridge is formed on the side wall of the land portion14. The comparison example 2 is an example where a projecting ridge is formed only on one side wall14aout of the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween. The comparison example 3 is an example where projecting ridges are formed on the side walls14a,14bwhich face each other in an opposed manner with the lateral groove13sandwiched therebetween in a state where the projection ridges are arranged parallel to the groove bottom13a. A groove width of the lateral groove13was set to 10 mm, and a projecting amount of the projecting ridge from the side walls14a,14bin the example and the comparison examples 2, 3 was set to 4 mm.

The wear resistant performance was evaluated with respect to the respective pneumatic tires according to the example and the comparison examples 1 to 3. The evaluation method was as follows.

The respective pneumatic tires according to the example and the comparison examples 1 to 3 were assembled to rims having a size of 22.5×7.50 respectively, air was filled in the tires until an inner pressure became 700 Kpa, and the tires were mounted on an axle of a large truck having a total vehicle weight of 20 t and, thereafter, an amount of step wear between a step-in side of the land portion and a kick-out side of the land portion was measured under a load condition of 80% of maximum loading capacity after the truck traveled 10000 Km and 40000 Km on a pavement road.

The result of the evaluation is shown in Table 1. The tire of the example could suppress uneven wear of the land portion compared to the tires of the comparison examples 1 to 3.