JP4940710B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire. More specifically, the present invention relates to a pneumatic tire that suppresses cracks generated at the groove bottom of a circumferential main groove in a portion straddling a sector division position of a tire vulcanized by a sectional mold. Regarding tires.

  In general, pneumatic tires are designed so that the left and right bead base widths of the tire before assembling the rim are larger than the rim width of the wheel to be assembled in order to maintain the air filling characteristics when assembling the rim. This is particularly noticeable in tubeless tires.

  When such a tire is assembled with a rim, as shown in FIG. 4, the bead base width Bs narrows so as to coincide with the rim width Rw, and accordingly, the radius of curvature R of the tire inner surface 11 tends to be reduced. Forces F1 and F2 that are pulled left and right are generated on the tread surface 12 having a large diameter difference with respect to the inner surface. Furthermore, when an internal pressure is applied in the cavity portion 13, the outer diameter of the center portion 12 a of the tread surface 12 grows, so that the forces F <b> 1 and F <b> 2 that are pulled left and right are further increased. In particular, this tendency is greater in a flat tire having a high internal pressure share of the belt layer.

  As a result, the groove wall surface 14a of the circumferential main groove 14 formed on the tread surface 12 expands left and right, and stress is applied to the contact portion a between the groove wall surface 14a located on the shoulder side of the circumferential main groove 14 and the groove bottom surface 14b. Will be concentrated.

  On the other hand, in a pneumatic tire vulcanized with a sectional mold in which a plurality of sectors whose tread portions are divided in the tire circumferential direction are connected, rubber overflow tends to occur at the division position of the sector during vulcanization. After vulcanization, a thin rubber film remains in the circumferential main groove.

  As described above, in the pneumatic tire in which the thin rubber film is formed in the circumferential main groove, when the rim is assembled and the internal pressure is filled, the stress on the groove bottom of the circumferential main groove causes the stress in the circumferential main groove 14. A crack is generated in the rubber thin film by concentrating on the contact portion a, and this crack is the starting point and grows toward the groove bottom of the circumferential main groove, and further grows in the tire circumferential direction at the groove bottom, There is a problem that the tire is eventually destroyed. In particular, in a heavy-duty pneumatic tire loaded with a high load, this tendency is remarkable because the filling internal pressure is high.

  Conventionally, as a countermeasure against this, the overflow thin film is formed into a curved shape by forming the sector dividing surface of the sectional mold on the uneven surface crossed by the dividing line curved at the circumferential main groove, and the transverse length There is a proposal to relieve stress when the circumferential main groove spreads left and right by a thin film having a large thickness (see Patent Document 1).

However, in this proposal, it is difficult to perform precision processing to form the divisional surface of the sector into an uneven surface, and in addition to increasing the manufacturing cost of the sectional mold, the gap between the uneven surfaces is increased by repeated use over a long period of time. There was a problem.
JP 2005-1550 A

  The object of the present invention is to eliminate the above-mentioned problems, and by simply applying a simple process to the sector division position of the sectional mold, cracks generated at the bottom of the circumferential main groove corresponding to that position are suppressed. An object of the present invention is to provide a pneumatic tire.

The pneumatic tire of the present invention that achieves the above object is a pneumatic tire that is vulcanized and molded by a sectional mold including a sector in which a tread portion having a circumferential main groove is divided into a plurality of sectors. Of the left and right land portions partitioned by the circumferential main groove straddling, on the circumferential main groove side in at least one land portion, a local narrow groove extending across the division position is formed , and the The gist is that the length L of the narrow groove is 0.5 W ≦ L ≦ 1.5 W with respect to the groove width W of the circumferential main groove .

According to the present invention, at the location corresponding to the sector division position, the sector division position intersects the circumferential main groove side of at least one of the left and right land portions defined by the circumferential main groove. A narrow groove extending locally is formed, and the length L of the narrow groove is 0.5 to 1.5 times the groove width W of the circumferential main groove. Sometimes, the stress to be generated at the groove bottom of the circumferential main groove based on the lateral force applied to the tread portion can be dispersed by the opening of the narrow groove. As a result, the occurrence of cracks in the overflow thin film that occurs at the sector division position is suppressed, so that cracks at the groove bottom of the circumferential main groove starting from the thin film crack are suppressed, and the durability of the tire is improved. Can do.

  In addition, the pneumatic tire of the present invention has an advantage that it can be easily obtained simply by providing streak projections for forming narrow grooves at the sector division positions in the sectional mold for molding and vulcanizing the pneumatic tire.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a partial plan view showing an example of a tread portion in a pneumatic tire according to an embodiment of the present invention.

  The pneumatic tire of the present invention has a tread portion vulcanized and molded by a sectional mold composed of a plurality of divided sectors, and the tread surface 1 extends in the tire circumferential direction as shown in FIG. A circumferential main groove 2 is formed. The circumferential main groove 2 may be linear or zigzag.

  In the embodiment shown in FIG. 1, the four circumferential main grooves 2 and the left and right circumferential main grooves 2, 2 are formed with a sub-groove 3 inclined in the tire width direction and extending in a zigzag shape. The circumferential main groove 2 and the sub-groove 3 form a block-shaped or rib-shaped land portion 4. In addition, X shown with the dotted line in a figure has shown the position of the division surface of the sector in a sectional type mold at the time of vulcanization-molding a tread part.

  On the tread surface 1, at least one land portion 4 (left and right land portions 4, 4 in the figure) among the left and right land portions 4, 4 partitioned by the circumferential main groove 2 straddling the sector division position X A local narrow groove 5 is formed on the circumferential main groove 2 side so as to extend along the circumferential main groove 2 so as to cross the sector division position X.

By forming the local narrow groove 5 in this way, the groove on the bottom of the circumferential main groove 2 straddling the sector division position X is based on the lateral force applied to the tread portion when assembling the rim or filling the internal pressure. The stress to be generated can be dispersed by opening the narrow grooves 5. As a result, the occurrence of cracks in the overflow thin film occurring at the sector division position X is suppressed, so that cracks at the groove bottom of the circumferential main groove 2 starting from the thin film cracks are suppressed and tire durability is improved. Can be made. Moreover, the pneumatic tire of the present invention has an advantage that it can be obtained simply by providing a streak for forming the narrow groove 5 at the sector division position X in the sectional mold for molding and vulcanizing the pneumatic tire. is there.
In the present invention, the length L of the narrow groove 5 is 0.5 W ≦ L ≦ 1.5 W, preferably 0.7 W ≦ L ≦ 1.3 W with respect to the groove width W of the circumferential main groove 2. Is set. Here, if the length L of the narrow groove 5 is less than 0.5 times the groove width W, the effect of dispersing stress concentrated on the groove bottom of the circumferential main groove 2 is reduced. Cracks are likely to occur in the circumferential direction from the front and rear end portions.

  FIG. 1 shows the case where the narrow grooves 5 are formed along all the circumferential main grooves 2 out of the four circumferential main grooves 2, but the narrow grooves 5 are particularly grooves of the circumferential main grooves 2. It is preferable to form along the two circumferential main grooves 2 and 2 on the tire shoulder Sh side where stress tends to concentrate on the bottom. Therefore, if necessary, the narrow groove 5 may not be formed at a position along the two circumferential main grooves 2 and 2 on the center side.

  1 shows the case where the narrow grooves 5 and 5 are formed in the left and right land portions 4 and 4 defined by the circumferential main groove 2, the narrow groove 5 is either the left or right land portion 4. In this case, it may be formed on the land portion 4 on the tire shoulder Sh side with the circumferential main groove 2 interposed therebetween.

2 is an enlarged plan view showing a Y portion in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line AA in FIG.
In the present invention, the position of the narrow groove 5 formed along the circumferential main groove 2 is such that the interval T between the narrow groove 5 and the circumferential main groove 2 on the tread surface 1 is 1.5 to 3.0 mm, preferably 1 It is good to set so that it may become 8-2.5mm. When the interval T is 1.5 mm, the effect of dispersing the stress concentrated on the groove bottom of the circumferential main groove 2 is not sufficiently obtained, and the crack suppressing effect at the groove bottom of the circumferential main groove 2 is reduced, and the narrow groove The land portion between 5 and the circumferential main groove 2 is easily damaged. On the other hand, when the interval T exceeds 3.0 mm, the effect of dispersing the stress concentrated on the groove bottom of the circumferential main groove 2 cannot be sufficiently obtained as described above, and cracks at the groove bottom of the circumferential main groove 2 are not obtained. The suppression effect will be reduced.

  The interval T between the narrow groove 5 and the circumferential main groove 2 described above is the groove of the narrow groove 5 when the narrow groove 5 and / or the opening of the circumferential main groove 2 is chamfered. The distance between the intersection of the extended line of the wall and / or the extended line of the groove wall of the circumferential main groove 2 and the extended virtual line of the tread surface 1 is said.

  In addition, the groove width W of the circumferential main groove 2 is the extension of the groove wall of the circumferential main groove 2 in the same manner as described above when the opening of the circumferential main groove 2 is chamfered. The distance between the intersections of the line and the extended virtual line of the tread surface 1 is said.

  The groove width S of the narrow groove 5 in the present invention is set to 1.5 to 3.0 mm, preferably 1.8 to 2.5 mm, and the depth h of the narrow groove 5 is set to the depth D of the circumferential main groove 2. In contrast, 0.5D ≦ h ≦ 1.0D, preferably 0.6D ≦ h ≦ 0.9D. If the groove width S of the narrow groove 5 is less than 1.5 mm, cracks are likely to occur at the groove bottom of the narrow groove 5, and if it exceeds 3.0 mm, the effect of dispersing stress concentrated on the groove bottom of the circumferential main groove 2 is reduced. Will do. If the depth h of the narrow groove 5 is less than 0.5 times the depth D of the circumferential main groove 2, the effect of dispersing stress concentrated on the groove bottom of the circumferential main groove 2 is reduced. If it exceeds 0.0 times, the rubber thickness between the groove bottom of the narrow groove 5 and the belt layer is insufficient, which causes a decrease in durability of the tread portion.

  The groove width S of the narrow groove 5 described above is the same as the above in the case where the opening of the narrow groove 5 is chamfered, and the extension line of the groove wall of the narrow groove 5 and the tread surface 1. The distance between the intersections with the extended virtual line.

  In the present invention, the local narrow groove 5 formed so as to cross the sector division position X is preferably formed so as to be substantially parallel to the circumferential main groove 2, but the tread pattern formed on the tread surface 1. Depending on the tire circumferential direction, it is allowed to form within an angular range of ± 20 °. If this angle deviates from the above range, the effect of dispersing stress concentrated on the groove bottom of the circumferential main groove 2 will be reduced.

  The pneumatic tire of the present invention is particularly preferably applied as a heavy-duty pneumatic tire used for heavy-duty vehicles such as trucks and buses, and is particularly preferably applied to a heavy-duty pneumatic tire having a flatness ratio of 70% or less. However, it can be widely applied to pneumatic tires for other uses such as passenger cars.

  As described above, the pneumatic tire of the present invention is obtained by forming a local narrow groove along the circumferential main groove 2 in the land portion 4 at a location corresponding to the sector division position X of the sectional mold. As a sectional mold for vulcanizing and molding this, simply providing a streak for forming the narrow groove 5 across the division positions X of adjacent sectors in the conventional sectional mold. There are advantages that can be manufactured.

  The tire size is 275 / 70R22.5 and the tread pattern is the same as in Fig. 1. Using a sectional mold consisting of 9 divided sectors, the tire size is reduced along the 4 main grooves in the circumferential direction across the division position of each sector. A conventional tire (former example) that does not form a groove, a tire of the present invention (Examples 1 to 3) that is formed by varying the length L of the narrow groove as shown in Table 1, and a narrow groove that is formed over the entire circumference of the tire. Comparative tires (comparative examples) were produced.

The groove width W and the depth D of the circumferential main groove in each tire are W = 13.0 mm and D = 15.7 mm, respectively, and the distance between the narrow groove and the circumferential main groove in the tire of the present invention and the comparative tire. T was set to T = 2.0 mm, the depth h of the narrow groove and the groove width S were set to h = 15.0 mm and S = 2.0 mm, respectively.

  These five types of tires are filled with air pressure of 900 kPa and mounted on the drive shaft of a heavy-duty vehicle (2-D) with a total vehicle weight of 20 tons. After running the paved test course for 50,000 km, each sector The occurrence of cracks in the groove bottom of the circumferential main groove corresponding to the divided position was examined, and the results were classified according to the following criteria and are also shown in Table 1.

Furthermore, the occurrence of cracks at the groove bottoms of the narrow grooves formed in the tires of the present invention and the comparative tire and the damage situation of the land between the circumferential main grooves and the narrow grooves were examined, and the results were classified according to the following criteria. These are also shown in Table 1.
<Occurrence of cracks at the groove bottom of the circumferential main groove and the groove bottom of the narrow groove>
○: No occurrence of cracks
Δ: Some cracking and growth are observed
×: Many occurrences of cracks and growth are observed <Damage in the land between the circumferential main grooves and narrow grooves>
○: No damage at all
Δ: Some damage is seen
×: Many damages are seen

  From Table 1, it can be seen that, in the tire of the present invention, the occurrence of cracks at the groove bottom of the circumferential main groove corresponding to the division position of the sector is greatly suppressed as compared with the conventional tire.

  In the comparative tire, although crack generation at the groove bottom of the circumferential main groove corresponding to the division position of the sector is suppressed, cracks are generated at the groove bottom of the narrow groove, and further, Land damage between narrow grooves was observed.

It is a partial top view which shows an example of the tread part in the pneumatic tire by embodiment of this invention. It is a top view which expands and shows the Y section of FIG. It is AA arrow sectional drawing of FIG. It is sectional drawing which shows the state which mounted | wore the pneumatic tire with the pneumatic tire.

Explanation of symbols

1 Tread surface 2 Circumferential main groove 3 Sub groove 4 Land portion 5 Narrow groove Sh Tire shoulder X Sector division position

Claims (4)

In a pneumatic tire vulcanized by a sectional mold composed of a sector in which a tread portion having a circumferential main groove is divided into a plurality of sectors,
Of the left and right land portions partitioned by the circumferential main groove straddling the division position of the sector, a local narrow groove extending across the division position on the circumferential main groove side in at least one land portion And the length L of the narrow groove is 0.5 W ≦ L ≦ 1.5 W with respect to the groove width W of the circumferential main groove .   The pneumatic tire according to claim 1, wherein an interval T between the narrow groove and the circumferential main groove is 1.5 to 3.0 mm. The groove width S of the narrow groove is 1.5 to 3.0 mm, and the depth h of the narrow groove is 0.5D ≦ h ≦ 1.0D with respect to the depth D of the circumferential main groove. The pneumatic tire according to claim 1 or 2, comprising: The pneumatic tire according to claim 1, 2 or 3, wherein the narrow groove is formed in an angle range of ± 20 ° with respect to the tire circumferential direction.

Images