PNEUMATIC TIRE

Abstract

The pneumatic tire of this disclosure includes on a tread surface four or five circumferential grooves, and includes a pair of shoulder land portions, a pair of intermediate land portions, and one or a pair of central land portions partitioned thereon, wherein: in a tread widthwise cross sectional view at an unloaded condition when the tire is mounted to an applicable rim and applied with a prescribed internal pressure, when drawing a virtual arc R1 protruding to a tire radial outer side, of which a center of curvature is located on a tire equatorial plain, across four tread widthwise edges adjacent to the circumferential grooves of outlines of the pair of intermediate land portions, a correlation among each protrusion amount t1, t2 and t3 of outlines of the central land portions, the intermediate land portions and the shoulder land portions from the virtual arc R1 satisfies:

t1<t2, and t3<t2.

Claims

1. A pneumatic tire, comprising on a tread surface four or five circumferential grooves continuously extending in a tread circumferential direction, five or six land portions partitioned between tread ground contact edges and the circumferential grooves, and between the circumferential grooves, wherein: among the land portions, when a pair of land portions located on tread widthwise outermost sides are shoulder land portions, a pair of land portions adjacent to the shoulder land portions on tread widthwise inner sides are intermediate land portions, and one or a pair of land portions adjacent to the intermediate land portions on tread widthwise inner sides are central land portions, in a tread widthwise cross sectional view at an unloaded condition when the tire is mounted to an applicable rim and applied with a prescribed internal pressure, when drawing a virtual arc R1 protruding to a tire radial outer side, of which a center of curvature is located on a tire equatorial plain, across four tread widthwise edges adjacent to the circumferential grooves of outlines of the pair of intermediate land portions, a correlation among each protrusion amount t1, t2 and t3 of outlines of the central land portions, the intermediate land portions and the shoulder land portions from the virtual arc R1 satisfies:
t1<t2, and t3<t2.

2. The pneumatic tire according to claim 1, wherein: the correlation among the protrusion amounts t1 to t3 satisfies:
t3<t1<t2.

3. The pneumatic tire according to claim 1, wherein: in the tread widthwise cross sectional view, each outline of the land portions protrudes to the tire radial outer side, and simultaneously is formed of a plurality of arcs having radiuses of curvature smaller than a radius of curvature of the virtual arc R1.

4. The pneumatic tire according to claim 1, wherein: in the tread widthwise cross sectional view, the outlines of the shoulder land portions protrude to the tire radial outer side, and simultaneously are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, where: the radiuses of curvature of the plurality of arcs forming the outlines of the shoulder land portions are reduced toward tread ground contact edge sides.

5. The pneumatic tire according to claim 2, wherein: in the tread widthwise cross sectional view, each outline of the land portions protrudes to the tire radial outer side, and simultaneously is formed of a plurality of arcs having radiuses of curvature smaller than a radius of curvature of the virtual arc R1.

6. The pneumatic tire according to claim 2, wherein: in the tread widthwise cross sectional view, the outlines of the shoulder land portions protrude to the tire radial outer side, and simultaneously are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, where: the radiuses of curvature of the plurality of arcs forming the outlines of the shoulder land portions are reduced toward tread ground contact edge sides.

7. The pneumatic tire according to claim 3, wherein: in the tread widthwise cross sectional view, the outlines of the shoulder land portions protrude to the tire radial outer side, and simultaneously are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, where: the radiuses of curvature of the plurality of arcs forming the outlines of the shoulder land portions are reduced toward tread ground contact edge sides.

8. The pneumatic tire according to claim 5, wherein: in the tread widthwise cross sectional view, the outlines of the shoulder land portions protrude to the tire radial outer side, and simultaneously are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, where: the radiuses of curvature of the plurality of arcs forming the outlines of the shoulder land portions are reduced toward tread ground contact edge sides.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a development view illustrating a tread pattern of a pneumatic tire according to an embodiment of this disclosure; and

[0024] FIG. 2 is a partial cross-sectional view illustrating a tread widthwise cross section of the tread portion of the tire of FIG. 1.

DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of this disclosure will be described based on the drawings.

[0026] FIG. 1 is a development view illustrating a tread pattern of a pneumatic tire according to an embodiment of this disclosure (hereinafter referred to as “the tire”). The tire 1, although partially omitted in the drawing, includes a carcass having a radial structure extending in a colloidal shape between bead portions, a belt disposed on a tire radial outer side of the carcass of a tread portion, and a tread rubber disposed on a tire radial outer side of the belt so as to form a tread surface T.

[0027] Here, as illustrated in FIG. 1, this tire 1 includes four or five circumferential grooves 2 (four linear circumferential grooves 2 in the illustrated example) disposed on the tread surface T, the circumferential grooves continuously extending in the tread circumferential direction. Further, the circumferential grooves 2 of this embodiment may be of any type as long as continuously extending in the tread circumferential direction, and may be of extending modes such as, e.g., zigzag shape, wavy shape and the like. Moreover, in this embodiment, in the case where four circumferential grooves 2 are disposed, the circumferential grooves 2 may be disposed substantially symmetrically with respect to the tire equatorial plain CL; and in the case where five circumferential grooves 2 are disposed, it is possible to dispose one circumferential groove 2 on the tire equatorial plain CL, and locate the other four circumferential grooves 2 substantially symmetrically with respect to the tire equatorial plain CL.

[0028] The circumferential grooves 2 may respectively have different groove depths and groove widths, and may have, e.g., a groove depth of 6.0 mm to 10.0 mm, and a groove width of 6.0 mm to 20.0 mm. Here, the “groove depth” refers to a length measured along the tire radial direction from a groove bottom to a tread widthwise edge 3 adjacent to the groove (a larger length in the case where the lengths to the two tread widthwise edges adjacent to the groove are different), and the “groove width” refers to a length measured perpendicularly to the extension direction of the groove between both tread widthwise edges 3 adjacent to the groove. Here, in the present embodiment, as illustrated in FIG. 2, as for the circumferential grooves 2, in a tread widthwise cross sectional view, the groove walls on both sides are of a linear shape at least from the tread widthwise edges 3 to a certain position on the tire radial inner side.

[0029] In this tire 1, between the tread ground contact edges E and the circumferential grooves 2 and between the circumferential grooves 2, five or six (five in the illustrated example) land portions 4 are partitioned. Namely, this tire 1 includes a pair of shoulder land portions 4s sandwiched by the circumferential grooves 2 located on tread widthwise outermost sides among the circumferential grooves 2 and the tread ground contact edges E; a pair of intermediate land portions 4m adjacent to the shoulder land portions 4s on the tread widthwise inner sides in a manner sandwiching the circumferential grooves 2; and one or a pair of (one in the illustrated example) of central land portions 4c adjacent to the intermediate land portions 4m on the tread widthwise inner sides in a manner sandwiching the circumferential grooves 2. Here, as mentioned above, in this embodiment, since the circumferential grooves 2 are of a linear shape, each land portion 4c, 4m, 4s extends in a manner such that the land portion width is constant in the tread circumferential direction.

[0030] As illustrated in FIG. 1, disposed on the central land portion 4c are narrow grooves (sipes) 51 with groove widths of 1 mm or less, which extend from a circumferential groove 2 on one tread widthwise side (the right side in the drawing) among the two circumferential grooves 2 partitioning the land portion, in a manner inclined with respected to the tread widthwise direction, and end within the land portion. Moreover, disposed on the intermediate land portions 4m are narrow grooves (sipes) 52 with groove widths of 1 mm or less, which cross the land portions and connect to the two circumferential grooves 2 partitioning the land portions, and are inclined with respect to the tread widthwise direction. Further, disposed on the shoulder land portions 4s are lug grooves 53, 54, 55, which extend from the circumferential grooves 2 partitioning the land portions or from the tread ground contact edges E in a manner inclined with respect to the tread widthwise direction, and end within the land portions.

[0031] In this way, in the present embodiment, none of the land portions 4c, 4m, 4s includes a groove with a groove width of more than 1 mm from one end to the other end, of which both ends connect to a circumferential groove 2 or a tread ground contact edge E. In other words, if including a groove portion with a groove width of 1 mm or less, a groove of which both ends connect to a circumferential groove 2 or a tread ground contact edge E may be disposed on a land portion.

[0032] Here, from the viewpoint of the drainage performance and the silence due to a groove or groove portion with a groove width of 1 mm or less, the groove or groove portion may be subjected to chamfering at the opening position to the tread surface T. Moreover, although omitted in the drawing, it is preferable to dispose, on the shoulder land portions 4s, grooves which have a lug groove portion with a groove width of more than 1 mm, which extends in the tread widthwise direction from a tread ground contact edge E, and ends within the land portion; and have a narrow groove (sipe) portion with a groove width of 1 mm or less, which extend from the tread widthwise inner side edge of the lug groove portion, and opens to a circumferential groove 2 partitioning the shoulder land portions 4s. This is because that the drainage performance can be improved.

[0033] As illustrated, on this tire 1, a virtual arc R1 protruding to the tire radial outer side, of which the center of curvature is located on the tire equatorial plain CL, may be drawn across four tread widthwise edges 3 adjacent to the circumferential grooves 2 of the outlines of the pair of intermediate land portions 4m. Here, the virtual arc R1 may have a radius of curvature of 400 mm to 2400 mm.

[0034] In this embodiment, as illustrated, in a tread widthwise cross sectional view, the outlines of each land portion 4c, 4m, 4s protrude to the tire radial outer sides. Moreover, in a tread widthwise cross sectional view, the entire outlines of the intermediate land portions 4m are located on a tire radial side outer than the virtual arc R1 crossing the tread widthwise edges 3 on both tread widthwise sides of the intermediate land portions 4m. Moreover, the outlines of the central land portion 4c and the shoulder land portions 4s and the virtual arc R1 cross each other.

[0035] Here, in this tire 1, the correlation among each protrusion amount t1, t2 and t3 from the virtual arc R1 of the outlines of the central land portion 4c, the intermediate land portions 4m and the shoulder land portions 4s satisfies:

t1<t2, and t3<t2.

[0036] The effect of the tire 1 of the present embodiment is described below.

[0037] Conventionally, for example, in a tire concentrating on a central land portion among the tread surface, since the central land portion is of a shape protruding to the tire radial outer side, it is possible to achieve both the steering stability and the hydroplaning preventing performance. However, there is a risk that uneven wear of this land portion becomes severe. Moreover, in a pneumatic tire having a land portion partitioned by a plurality of circumferential grooves, further improvement in the wet braking performance is desired.

[0038] Then, having intensively studied methods for improving the uneven wear resistance and the wet braking performance, we discovered that by specifying the correlation among the shapes of a plurality of land portions in a tread widthwise cross section, it is possible to improve both the uneven wear resistance and the wet braking performance.

[0039] Namely, in this tire 1, since each protrusion amount t1 to t3 from the virtual arc R1 of the outlines of the central land portion 4c, the intermediate land portions 4m and the shoulder land portions 4s satisfies the aforementioned correlation, it is possible to improve both the uneven wear resistance and the wet braking performance. Specifically, the central portion of the tread surface T is an area with a large ground contact length to the road surface among ground contact areas (footprint), and thus is likely to be worn comparatively (likely to generate uneven wear). Therefore, by setting the protrusion amount t1 of the outline of the central land portion 4c with respect to the virtual arc R1 smaller than the protrusion amount t2 of the outlines of the intermediate land portions 4m, it is possible to suppress the wearing of the central land portion 4c located on the central portion, and to thereby improve the uneven wear resistance.

[0040] Moreover, by setting the protrusion amount t3 of the outlines of the shoulder land portions 4s with respect to the virtual arc R1 smaller than the protrusion amount t2 of the outlines of the intermediate land portions 4m, even if the protrusion amount t1 of the outline of the central land portion 4c with respect to the virtual arc R1 is set smaller than the protrusion amount t2 of the outlines of the intermediate land portions 4m, it is possible to set the ground contact length of a central area (an area inclusive of the central land portion 4c and the intermediate land portions 4m; the same below.) larger than the ground contact length of a shoulder area (an area inclusive of the shoulder land portions 4s; the same below.), and to set the entire ground contact area to a sharp-pointed shape. Therefore, the drainage to the tread widthwise outer side becomes easy, and thus it is possible to improve the wet braking performance.

[0041] In the tire 1 of the present embodiment, the correlation among the protrusion amounts t1 to t3 of the outlines of each land portion 4c, 4m, 4s preferably satisfies:

t3<t1<t2.

[0042] According to this configuration, it is possible to further improve the wet braking performance. Specifically, if the ground contact pressure of the shoulder land portions 4s becomes high when braking, the shoulder land portions 4s themselves are likely to hinder the drainage to the tread widthwise outer side. However, by comparatively reducing the protrusion amount t3 of the shoulder land portions 4s, it is possible to avoid increase of the ground contact pressure, and to further improve the wet braking performance. Moreover, by setting the protrusion amounts to the aforementioned correlation, the ground contact length of the central area becomes larger than the ground contact length of the shoulder area, and it is possible to set the entire ground contact area to a sharp-pointed shape. Therefore, it is possible to further improve the wet braking performance.

[0043] In the tire 1 of the present embodiment, the correlation between the protrusion amounts t1, t2 of the outlines of the central land portion 4c and the intermediate land portions 4m preferably satisfies:

0.4×t2≦t1≦0.9×t2.

[0044] By satisfying 0.4×t2≦t1, the ground contact length of the ground contact area of the central area in the tread surface T does not become excessively small, and thus it is possible to sufficiently maintain a sharp-pointed ground contact area, and to further improve the wet braking performance. Moreover, by satisfying t1≦0.9×t2, it is possible to sufficiently shorten the ground contact length of the central land portion 4c, and to thereby further improve the uneven wear resistance.

[0045] Further, from the same viewpoint, the correlation between the protrusion amounts t1, t2 preferably satisfies:

0.5×t2≦t1≦0.7×t2.

[0046] The correlation among the protrusion amounts t1 to t3 of the outlines of each land portion 4c, 4m, 4s preferably satisfies:

t2−t1<t1−t3.

[0047] By satisfying the aforementioned correlation among the protrusion amounts, the ground contact length of the central area becomes sufficiently larger than the ground contact length of the shoulder area, and it is possible to further improve the wet braking performance.

[0048] Here, in a tread widthwise cross sectional view, the outlines of each land portion 4c, 4m, 4s are not limited, but as mentioned above, preferably protrude to the tire radial outer side, and preferably are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1. According to this configuration, it is possible to further improve the wet braking performance. Specifically, by setting the outlines of each land portion 4c, 4m, 4s to the aforementioned shapes, it is possible to adjust the outlines of each land portion 4c, 4m, 4s in order to concentrate the ground contact pressure of each land portion when the vicinity of their widthwise central sides contact the road surface. In this case, the tread surface T becomes likely to bite into the road surface, and simultaneously, water between the tread surface T and the road surface becomes likely to be smoothly drained into the circumferential grooves 2, and thus it is possible to further improve the wet braking performance. Moreover, in this case, by suppressing the increase of the ground contact pressure of the tread widthwise edges 3 of each land portion, the uneven wear on the tread widthwise edge 3 sides of the land portions can be suppressed as well.

[0049] Further, when the outlines of each land portion 4c, 4m, 4s are respectively formed of one arc, if the arc is excessively large, there is a risk that it is impossible to sufficiently concentrate the ground contact pressure to the vicinity of the widthwise central sides of each land portion 4c, 4m, 4s during ground contact to the road surface, which renders the drainage difficult. Alternatively, if the arc is excessively small, there is a risk that the ground contact pressure excessively concentrate to the vicinity of the widthwise central sides of each land portion 4c, 4m, 4s, which deteriorates the uneven wear resistance; or the tread widthwise edge 3 sides of each land portion 4c, 4m, 4s do contact the ground, which deteriorates the steering stability.

[0050] As mentioned above, the outlines of each land portion 4c, 4m, 4s preferably protrude to the tire radial outer side, and preferably are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, while from the viewpoint of improving the wet braking performance and suppressing the uneven wear, the radiuses of curvature of the plurality of arcs are preferably reduced from the widthwise central portions toward the outer sides of the land portions.

[0051] In a tread widthwise cross sectional view, it is preferable that the outlines of the shoulder land portions 4s are formed of a plurality of arcs having radiuses of curvature smaller than the radius of curvature of the virtual arc R1, and that the radiuses of curvature of the plurality of arcs for forming the outlines of the shoulder land portions are reduced toward the tread ground contact edge sides. According to this configuration, it is possible to further improve the wet braking performance. Specifically, by setting the outlines of the shoulder land portions 4s as mentioned above, when braking, it is possible to further reduce the ground contact pressure of shoulder land portions 4s, particularly on the tread ground contact edge E sides, and thus it is possible to sufficiently improve the drainage performance and the wet braking performance.

[0052] From the viewpoint of improving the wet braking performance, it is preferable that the radiuses of curvature of all the arcs for forming the outlines of the shoulder land portions 4s are 1/20 to ½ of the radius of curvature of the virtual arc R1. By setting the radiuses of curvature to 1/20 or more of the radius of curvature of the virtual arc R1, it is possible to prevent the ground contact pressure of the shoulder land portions 4s from being excessively low, and by setting the same to ½ or less of the radius of curvature of the virtual arc R1, it is possible to prevent the ground contact pressure of the shoulder land portions 4s from being excessively high.

[0053] The protrusion amount t1 of the outline of the central land portion 4c is preferably 0.2 mm to 0.9 mm, and in a tread widthwise cross sectional view, a length measured along the radial direction of the virtual arc R1 from the tread widthwise edges 3 of the central land portion 4c to a position farthest from the center of curvature of the virtual arc R1 is preferably 0.3 mm to 1.0 mm. Moreover, the protrusion amount t2 of the outlines of the intermediate land portions 4m is preferably 0.3 mm to 1.0 mm. The protrusion amount t3 of the outlines of the shoulder land portions 4s are preferably 0 to 0.7 mm, and in a tread widthwise cross sectional view, a length measure along the radial direction of the virtual arc R1 from the tread widthwise edges 3 adjacent to circumferential grooves 2 of the shoulder land portions 4s to a position farthest from the center of curvature of the virtual arc R1 is preferably 00.3 mm to 0.8 mm.

[0054] The embodiment of this disclosure is described in the above by referring to the drawings, while the pneumatic tire of this disclosure may be appropriately varied without being limited to the aforementioned example.

EXAMPLES

[0055] This disclosure will be described further in detail by Examples hereinafter without being restricted thereto by any means.

[0056] In order to certify the effect of this disclosure, the tires of the following Examples 1, 2 and Comparative Examples 1 to 4 were respectively produced experimentally.

Example 1

[0057] The tire of Example 1 has a tire size of 225/45R17 and is configured according to the dimensions as shown in Table 1, and as illustrated in FIGS. 1 and 2, has four circumferential grooves, one central land portion, a pair of intermediate land portions and a pair of shoulder land portions disposed on the tread surface T. Moreover, in the tire of Example 1, the radius of curvature of the virtual arc R1 is 765 mm, and the protrusion amounts t1 to t3 of each land portion are respectively 0.4 mm, 0.8 mm, and 0.2 mm.

Example 2, Comparative Examples 1 to 4

[0058] The tires of Example 2 and Comparative Examples 1 to 4 are the same as the tire of Example 1, except that the protrusion amounts of each land portion are varied according to Table 1.

[0059] Each aforementioned sample tire was evaluated according to the following methods.

[Wet Braking Performance]

[0060] Each aforementioned sample tire was mounted to a rim with a rim size of 7.5 J and applied with an internal pressure of 240 kPa, installed to a vehicle, and then, the vehicle was travelled on a wet road surface at a speed for hour of 80 km/h. After travelling at the aforementioned state, the stopping distance (m) when performing full brake was measured. The evaluation results were shown via index by using reciprocals of the values of each sample tire, with the tire of Comparative Example 1 as 100. A larger value of this index shows a better wet braking performance.

[Uneven Wear Resistance]

[0061] Each aforementioned sample tire was mounted to a rim with a rim size of 7.5 J, applied with an internal pressure of 240 kPa, installed to a vehicle, and then, the vehicle was travelled for 10000 km. Further, the wear amounts from new tires after travelling were measured and compared. The evaluation results were shown via index by using reciprocals of the values of each sample tire, with the tire of Comparative Example 1 as 100, and a larger value shows a better wear resistance.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Protrusion Central land portion t1 0.8 0.2 0.8 0.8 0.4 0.4 amount (mm) Intermediate land portion t2 0.4 0.4 0.2 0.8 0.8 0.8 Shoulder land portion t3 0.2 0.8 0.4 0.8 0.2 0.2 Number of land portion arcs Plural Plural Plural Plural Plural Single Performances Wet braking performance 100 97 97 97 104 102 Uneven wear resistance 100 95 95 90 100 100

[0062] According to Table 1, it is understood that as compared to the tires of Comparative Examples 1 to 4, Examples 1 and 2 have improved uneven wear resistance and wet braking performance.

INDUSTRIAL APPLICABILITY

[0063] According to this disclosure, it is possible to provide a pneumatic tire capable of improving both the uneven wear resistance and the wet braking performance.

REFERENCE SIGNS LIST

[0064] 1 pneumatic tire [0065] 2 circumferential groove [0066] 3 tread widthwise edge [0067] 4 land portion [0068] 4c central land portion [0069] 4m intermediate land portion [0070] 4s shoulder land portion [0071] 51, 52 narrow groove [0072] 53, 54, 55 lug groove [0073] CL tire equatorial plain [0074] E tread ground contact edge [0075] R1 virtual arc [0076] T tread surface [0077] t1, t2, t3 protrusion amount