Pneumatic tire

Abstract: A pneumatic tire in which a block formed in a tread surface has, in a ground contacting surface thereof, a closed sipe which is formed so as to not open onto a groove. The sipe has a first opening formed in the ground-contacting surface of the block, a second opening formed at side surfaces of the block, and a hole which communicates the first opening and the second opening. In accordance with this structure, water taken-in into the sipe from the first opening at the ground-contacting surface of the block is discharged to the second opening contacting at the side surface facing to the groove. As a result, water drainability of the sipe is improved without lowering rigidity of the block. Thus, a ground contacting performance of the block improves. The pneumatic tire therefore has improved performance on wet roads and improved performance on snowy and icy roads without the rigidity of blocks decreasing.

Description: The present invention relates to a pneumatic tire which aims for an improvement in performances on wet roads and in performances on snowy and icy roads. Pneumatic tires are conventionally provided with sipes in the surfaces of blocks formed on the tread surface. Such tires aim to improve driving performances/braking performances and directional stability on wet road surfaces and snowy and icy road surfaces by increasing the edge effect so as to improve the water drainability. However, when a large number of sipes which are opened onto both side surfaces are provided in a block, the problem arises that the rigidity of the block decreases to deteriorate directional stability. Closed sipes, neither of whose ends opens into grooves, are effective in order to ensure the rigidity of the block. However, water cannot drain from the end portions of the sipes into grooves, and thus the problem that drainability is inferior arises. Attention is also drawn to the disclosure of EP-A-0625436. The present invention was developed in order to overcome the above-described drawbacks, and an object of the present invention is to provide a pneumatic tire which aims for an improvement in performances on wet roads and performances on snowy and icy roads by improving drainability while maintaining block rigidity. The present invention provides a pneumatic tire comprising: a tread surface having a plurality of main grooves formed therein along a tire circumferential direction and a plurality of lug grooves formed therein along a tire transverse direction, the main grooves and the lug grooves intersecting one another, thereby defining a plurality of land portions that each have a ground contacting surface and side surfaces; and at least one water drainage passage provided in each land portion, characterized in that the water drainage passage is a sipe formed inside the land portion, and the sipe has two ends, wherein one end is opened at the ground-contacting surface of the land portion and elongated in the tire transverse direction, and the other end is opened at a side surface of the land portion facing the lug groove and elongated in the tire transverse direction. In accordance with the invention; when water is taken-in into the water drainage passage from the portion which is opened at the ground contacting surface, even if the opening portion at the ground-contacting surface closes up by deformation of the block-shaped land portion due to the block-shaped land portion contacting the road surface, the water within the water drainage passage (the sipe) can be discharged to a groove by the end opening at the side surface. Because the sipe, which passes through the interior, is formed as the water drainage passage at the block-shaped land portion, sufficient rigidity of the water drainage passage can be maintained as compared with a block-shaped land portion which is formed with a sipe which is opened at both ends or one end in the contacting surface. Namely, the drainability of the water drainage passage can be improved without lowering the block rigidity, and the ground contacting ability of the block-shaped land portion can be improved by the improvement in the water drainability. Thus, the performance on wet roads and the performance on snowy and icy roads can be markedly improved. The cross-section of the sipe is a thin, elongated configuration having a longitudinal direction and a transverse direction. That is, the opening end of the sipe at the ground-contacting surface is a thin, elongated configuration having a longitudinal direction and a transverse direction. Therefore, the longitudinal direction of the opening end becomes an edge component, and contributes to directional stability and braking performance. The sipe preferably has a curved portion or a bent portion from the ground-contacting surface toward the side surface. That is, by providing a curved portion or a bent portion in the sipe, concentration of stress at specific portions can be prevented, and the generation of cracks and the like can be suppressed. The "curved portion" is a portion which is formed in a continuous curve, and the "bent portion" is a portion bent so as to include an obtuse angle. The invention will be further described with reference to the accompanying drawings, wherein: Fig. 1 is a perspective view of a block of a pneumatic tire relating to a first embodiment of the present invention. Fig. 2 is a plan view of a tread of a pneumatic tire relating to the first embodiment of the present invention. Fig. 3 is a perspective view of a block of a pneumatic tire relating to a modified example of the first embodiment. Fig. 4 is a cross-sectional view taken along line 4-4 of Fig. 3. Fig. 5 is a perspective view of a block of a pneumatic tire used in Comparative Example 1. A pneumatic tire relating to a first embodiment of the present invention will be described in detail hereinafter. The present first embodiment is described in detail with reference to Figs. 1 through 4. As illustrated in Fig. 2, a pneumatic tire 10 comprises a tube-shaped tread 12 which extends across a pair of left and right sidewalls (not illustrated). A plurality of main grooves 14, which are formed along a tire circumferential direction (the direction of arrow P), and a plurality of lug grooves 16, which are formed along the tire transverse direction (the direction of arrow Q), are formed in the tread 12. A plurality of blocks 18 are demarcated by the main grooves 14 and the lug grooves 16. Sipes 22 which extend along the transverse direction of the tire are formed in the blocks 18. As illustrated in Fig. 1, the sipe 22 is formed by an opening 22A (first opening) at a ground contacting surface 20 of the block 18, an opening 22B (second opening) which opens at a side surface 18A of the block 18 which side surface 18A faces a lug groove 16, and a passage 22C which is inclined to the openings 22A and 22B. Effects of the pneumatic tire 10 structured as described above will be described hereinafter. The following effects are obtained by the pneumatic tire 10, which has the blocks 18 in which the sipes 22 are formed, when the pneumatic tire 10 is mounted to a vehicle and the vehicle is run on a wet road surface. Due to the block 18 contacting the road surface, water is taken-in into the passage 22C from the opening 22A of the sipe 22 formed in the ground contacting surface 20. Due to the block 18 deforming or the like, the water is confined in the interior of the sipe 22, but it is possible to discharge the water to the lug groove 16 from the passage 22C via the opening 22B. Thus, the drainability to drain the water from the road surface to the side surface is improved, and the ground contact performance of the tread 12 (block 18) is also improved. Further, the longitudinal direction end portion of the opening 22A of the sipe 22 does not open into a groove on either side. Therefore, the rigidity of the block 18 can be sufficiently ensured, and the rigidity does not become insufficient due to the provision of the passage 22C in the block 18. Moreover, because the cross-sectional configuration of the passage 22C of the sipe 22 is a thin, elongated shape, the edge component is sufficiently maintained. As a result, the directional stability of the pneumatic tire on wet road surfaces improves. The performance of the pneumatic tire 10 of the present invention on wet road surfaces has been described above, and the pneumatic tire 10 also exhibits similar effects on snowy and icy roads. In the present embodiment, the passage 22C of the sipe 22 is inclined. In other examples, the passage may be formed in a curved configuration (a configuration which bends at an obtuse angle). Namely, as illustrated in Figs. 3 and 4, the passage 22C is formed by a vertical portion 22C1 which is formed vertically from the opening 22A to the ground contacting surface 20, a parallel portion 22C2 which is formed from the opening portion 22B and parallel to the ground contacting surface 20, and a curved portion 22C3 which connects the vertical portion 22C1 and the parallel portion 22C2. Examples A directional stability test and a braking performance test were carried out in order to confirm the effects of the pneumatic tire according to the above-described embodiments. Comparative Example 1 Tire and Example 1 Tire had, in the blocks of the tread pattern illustrated in Fig. 2, sipes which extended in the tire transverse direction. These blocks were shaped such that the ground contacting surface 20 thereof was a square having a length L of 20 mm, and the height H of the block was 8 mm. Closed sipes which extended in the tire transverse direction and had a length L3 of 10 mm and a width W of 0.6 mm were formed in the blocks. The Comparative Example 1 Tire was formed such that the sipe 22 had a depth D of 6 mm vertically from the ground contacting surface 20, as illustrated in Fig. 5. As illustrated in Fig. 4, the Example 1 Tire was formed such that a distance L1 from side surfaces 18A to the central position of the opening 22A was 10 mm, a depth D1 of the vertical portion 22C1 of the sipe 22 from the ground contacting surface 20 was 4 mm, a distance L2 from the ground contacting surface 20 to the central position of the opening 20B was 7 mm, and a depth D2 of the parallel portion 22C2 of the sipe 22 from side surfaces 18A was 5 mm. Tests on the directional stability on dry roads, the directional stability on wet roads, and the directional stability on snowy roads were conducted on test courses (having a dry road surface, a wet road surface, and a snowy road surface, respectively), and the directional stability, lane changing stability, and cornering stability were tested. An experienced driver evaluated these respective performances subjectively, and ranked them with 10 being the highest score possible. The comparison value expressed how much the Example 1 Tire improved with respect to the Comparative Example 1 Tire, and these comparison values are listed in Table 1. Directional stability on Dry Roads Directional stability on Wet Roads Directional stability on Snowy Roads Comparison Value ±0 2 2 It was confirmed that, although the directional stability on dry roads of the Example 1 Tire did not differ from that of Comparative Example 1 Tire, the Example 1 Tire did show an improvement with regard to directional stability on wet roads and directional stability on snowy roads. As described above, the present invention provides a pneumatic tire in which, by forming the water drainage passage which communicates from the ground contacting surface to a side surface of a block-shaped land portion, water drainability can be improved without adversely affecting block rigidity, and performance on wet roads and on snowy and icy roads improve.

Claims: A pneumatic tire (10) comprising: a tread surface having a plurality of main grooves (14) formed therein along a tire circumferential direction and a plurality of lug grooves (16) formed therein along a tire transverse direction, the main grooves and the lug grooves intersecting one another, thereby defining a plurality of land portions (18) that each have a ground contacting surface (20) and side surfaces (18A); and at least one water drainage passage provided in each land portion, characterized in that the water drainage passage is a sipe (22) formed inside the land portion (18), and the sipe has two ends, wherein one end (22A) is opened at the ground-contacting surface of the land portion and elongated in the tire transverse direction, and the other end (22B) is opened at a side surface (18A) of the land portion facing the lug groove (16) and elongated in the tire transverse direction. A pneumatic tire as claimed in claim 1, characterized in that the one end (22A) of the sipe (22) at the ground-contacting surface (20) of the land portion (18) is formed within the ground contacting surface without opening into a main groove (14). A pneumatic tire as claimed in claim 2, characterized in that the other end (22B) of the sipe (22) at the side surface (18A) of the land portion (18) is formed within the side surface without opening into a main groove (14). A pneumatic tire as claimed in any of claims 1 to 3, characterized in that the sipe (22) is inclined linearly from the one end (22A) towards the other end (22B). A pneumatic tire as claimed in any of claims 1 to 3, characterized in that the sipe (22) has a portion that bends from the one end (22A) towards the other end (22B). A pneumatic tire as claimed in claim 5, characterized in that the sipe (22) bends at an obtuse angle at said portion. A pneumatic tire as claimed in any of claims 1 to 6, characterized in that a cross-section of the sipe is formed in a thin, elongated configuration. A pneumatic tire as claimed in any of claims 1 to 7, characterized in that the land portions (18) are block-shaped.

Inventors: ISHIYAMA MAKOTO, ISHIYAMA, MAKOTO
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 2000
Main classification: B60C11
IPC codes: B60C11