JP4893355B2 - 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 in a portion corresponding to a sector division position of a circumferential main groove of a tread portion vulcanized by a sectional mold. About.

  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. 8, the bead base width Bs narrows from the state indicated by the two-dot chain line to the state indicated by the solid line so as to coincide with the rim width Rw. Since the radius of curvature R of the 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 tire 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.

  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. Such a phenomenon is particularly prominent in a flat tire having a high internal pressure share of the belt layer.

  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, as shown in FIG. 9A, a rubber thin film G remains in the circumferential main groove 14.

  In the pneumatic tire in which the rubber thin film G is formed in the circumferential main groove 14 as described above, when the rim is assembled and the internal pressure is filled, the stress on the groove bottom of the circumferential main groove 14 is the circumferential main. By concentrating on the contact part a of the groove 14, as shown in FIG. 9B, a crack Gc is generated in the rubber thin film G in the vicinity of the boundary region between the groove bottom and the groove wall (particularly on the shoulder side). However, there is a problem that the crack Gc starts as a starting point and grows toward the groove bottom of the circumferential main groove 14 and further grows in the tire circumferential direction at the groove bottom.

  Further, at the sector division position, a step is likely to occur on the surface of the tread portion of the vulcanized tire, and cracks are generated from the step at the groove bottom on the shoulder side due to stress concentrated on the contact portion a of the circumferential main groove 14. There is a problem that it is easy to do. The occurrence of cracks centered on the sector division positions described above is particularly prominent in heavy-duty pneumatic tires that are loaded with a high load 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, according to this proposal, it is difficult to form the divisional surface of the sector with unevenness, and it is difficult to perform precision processing, and the manufacturing cost of the sectional mold increases. 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. The gist is that a concave groove straddling between adjacent sectors is formed along the division position on the groove bottom corresponding to at least the shoulder side of the circumferential main groove in the corresponding portion.

  According to the present invention, since the groove bottom corresponding to at least the shoulder side of the circumferential main groove in the portion corresponding to the division position of the sector is formed with the concave groove straddling the adjacent sectors along the division position. Since the overflow thin film generated at the division position of the sector is generated based on the groove bottom of the concave groove, compared to the overflow thin film generated at the groove bottom of the conventional tire, at least the shoulder side of the circumferential main groove Since the height of the overflow thin film protruding from the groove bottom is relatively low, the stress generated on the upper edge of the overflow thin film is relaxed when assembling the rim and filling with internal pressure, and cracks are suppressed, and tire durability is reduced. Can be improved.

  In addition, the pneumatic tire of the present invention has an advantage that it can be easily obtained by simply forming a groove for forming a concave groove at a sector division position in a 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 a tread portion in the pneumatic tire according to the first 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, four circumferential main grooves 2 and two left and right circumferential main grooves 2, 2 are formed in a sub-groove 3 that is inclined in the tire width direction and extends 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.

  As shown in FIGS. 3A to 3C and FIGS. 4A to 4D on the tread surface 1, at least at the groove bottom of the circumferential main groove 2 in the portion corresponding to the division position X of the sector. Further, along the division position X, a concave groove 5 is formed to straddle between adjacent sectors.

  As a result, the overflow thin film G generated at the sector division position X in the groove bottom of the circumferential main groove 2 is generated with the groove bottom of the concave groove 5 as a starting point as shown in FIG. For comparison, FIG. 5B shows the form of the overflow thin film G generated at the groove bottom of the circumferential main groove 2 in the conventional tire. As shown in FIGS. 5A and 5B, in the pneumatic tire of the present invention, the height h ′ of the overflow thin film G protruding from the groove bottom of the circumferential main groove 2 is the groove in the conventional pneumatic tire. The height is relatively lower than the height h of the overflow thin film G protruding from the bottom (h ′ <h). Therefore, the tension (stress) generated in the upper edge Ga of the overflow thin film G at the time of assembling the rim and filling with the internal pressure is smaller than the conventional tire in the tire of the present invention, and the occurrence of cracks is suppressed, The durability of the tire can be improved.

  At the same time, by forming the concave groove 5 described above, the contact portion between the groove wall surface located on the shoulder Sh side of the circumferential main groove 2 formed in the tread portion and the groove bottom surface when assembling the rim or filling the internal pressure ( Since the stress concentrated on a) in FIG. 8 is relieved, the occurrence of cracks from the step on the tread surface at the groove bottom on the shoulder Sh that occurs at the division position X of the sector is 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 by simply forming the groove for forming the concave groove 5 at each sector division position X in the sectional mold for molding and vulcanizing the pneumatic tire. is there.

  In the present invention, the concave groove 5 described above may be formed in the groove bottom on the shoulder Sh side of the circumferential main groove 2. Furthermore, the concave groove 5 can be formed only in the groove bottom on the shoulder Sh side of the circumferential main groove 2 located closest to the shoulder Sh side in the circumferential main groove 2. Thereby, generation | occurrence | production of the crack from the groove bottom of the circumferential direction main groove 2 can be suppressed efficiently.

  FIG. 1 shows a case where the concave grooves 5 are formed in the portions corresponding to the sector division positions X of all the circumferential main grooves 2 in the four circumferential main grooves 2. As described above, 5 can be formed only in a portion corresponding to the division position X of the sector of the circumferential main groove 2 on the tire shoulder Sh side where stress tends to concentrate particularly on the groove bottom of the circumferential main groove 2. . That is, if necessary, the concave groove 5 may not be formed in a portion corresponding to the sector division position X of the two circumferential main grooves 2 and 2 on the center side.

  The cross-sectional shape of the groove 5 in the present invention is not particularly limited, and it is formed in a semicircular shape as shown in FIG. 3 (a) or in a V shape as shown in FIG. 3 (b). Alternatively, it may be formed in a quadrangular shape as shown in FIG. The opening width W measured in the longitudinal direction of the circumferential main groove 2 of the concave groove 5 is set to 0.5 mm or more and 6 times or less of the depth GD of the circumferential main groove 2, preferably 0.5 to 5.0 mm. Good. If the opening width W is less than 0.5 mm, the crack suppression effect due to the formation of the concave groove 5 is not sufficiently obtained, and if it exceeds 6 times the depth GD of the circumferential main groove 2, the rigidity of the land portion on the side of the adjacent shoulder Sh In addition, the circumferential main groove 2 tends to open toward the shoulder Sh when assembling the rim or filling the internal pressure, and it becomes difficult to ensure the tire running performance.

  The opening width W of the groove 5 described above refers to the distance between the opening ends in the width direction of the groove 5, and when the opening end of the groove 5 is chamfered, The distance between the intersections of the extension line of the wall and the extension line of the groove wall of the circumferential main groove 2 is said.

  Moreover, in this invention, it is good to set the depth D of the ditch | groove 5 to 0.5 mm or more. If the depth D is less than 0.5 mm, the stress applied to the overflow thin film G at the time of assembling the rim or filling the internal pressure cannot be sufficiently suppressed, and the thin film G is likely to crack. The upper limit of the depth D of the concave groove 5 is not particularly limited, but it suppresses the biting of the rubber between the sectors at the time of tire vulcanization molding and changes in the circumferential rigidity of the tread portion. From the viewpoint of preventing a decrease in tire performance due to the above, it may be set to 5.0 mm or less.

  The concave groove 5 in the present invention is formed at least on the groove bottom of the circumferential main groove 2 at the division position X of the sector. That is, the concave groove 5 may be formed over the entire groove wall of the circumferential main groove 2 at the division position X of the sector as shown in FIG. 4A, or in the circumferential direction as shown in FIG. It may be formed over the groove wall in the portion close to the groove bottom with the groove bottom of the main groove 2 as the center, as shown in FIG. 4C, from the groove bottom corresponding to the shoulder Sh side of the circumferential main groove 2 to the groove bottom. It may be formed over the groove wall at a portion close to, or may be formed at the groove bottom corresponding to the shoulder Sh side of the circumferential main groove 2 as shown in FIG. Furthermore, as shown in FIG. 4E, the depth D of the groove 5 may be formed so as to gradually decrease from the groove bottom of the circumferential main groove 2 toward the opening.

  FIG. 6 is a partial plan view showing a tread portion in the pneumatic tire according to the second embodiment of the present invention. In the present embodiment, two straight circumferential main grooves 22A extending in the tire circumferential direction on the center side and 2 extending in the tire circumferential direction on the shoulder Sh side across the center line of the tread surface 1. A zigzag-shaped circumferential main groove 22B is formed. Further, the straight circumferential main groove 22A and the zigzag circumferential main groove 22B are connected to each other by sub-grooves 23 inclined in the tire width direction to form a block.

  In the present embodiment, each of the circumferential main grooves 22A and 22B has a groove bottom on the shoulder Sh side along the division position X of the sector of the two circumferential main grooves 22B and 22B located closest to the shoulder Sh. A concave groove 5 having a square cross section is formed as illustrated in FIG. Then, as shown in FIG. 7, the surface shape of the groove 5 is an extension line 22 </ b> Y of the groove wall on the shoulder Sh side of the circumferential main groove 22 </ b> B and a groove bottom of the circumferential main groove 22 </ b> B. It is formed in an arc 5R that includes a region 5Q (hatched portion in the figure) surrounded by a straight line 22X that is in parallel with the tread surface 1.

  Thereby, when assembling the rim or filling the internal pressure, stress concentrated on the contact portion (a in FIG. 6) between the groove wall surface and the groove bottom surface located on the shoulder Sh side of the circumferential main groove 22B formed in the tread portion. Since it can be efficiently mitigated, it is possible to reliably suppress the occurrence of cracks caused by the overflow thin film and the tread surface step occurring at the division position X of the sector, and to further improve the durability of the tire. it can.

  In the tire shown in FIG. 6, the sector division position X is set to the bending position of the zigzag circumferential main groove 22B. However, the sector division position X is not limited to this, and the circumferential direction It may be set to a straight position of the main groove 22B.

  FIG. 7 shows the case where the arc 5R is formed as an arc inscribed at the intersection P between the extension line 22Y and the horizontal line 22X in the region 5Q, but the intersection P is located inside the arc 5R (tread surface 1 side). Can be formed. Thereby, generation | occurrence | production of the crack from the division position X of a sector can be suppressed more reliably.

  When the concave groove 5 is formed only in the groove bottom on the shoulder Sh side of the two circumferential main grooves 22B and 22B located closest to the shoulder Sh as in the present embodiment, the opening width W of the concave groove 5 is set to The depth GD of the circumferential main groove 22B may be set to 6 times or less, preferably 0.2 times or more. If the opening width W is less than 0.2 times the depth GD, the crack suppressing effect due to the formation of the concave groove 5 is not sufficiently obtained. If the opening width W is more than 6 times the depth GD, the adjacent shoulder Sh side land portion In addition to a decrease in rigidity, the circumferential main groove 2 is likely to open to the shoulder Sh side when assembling the rim or filling the internal pressure, making it difficult to ensure tire running performance.

  In this embodiment, a chamfer is formed at the boundary (position S in FIG. 3C) with the groove wall of the circumferential main groove 22B at the front and rear in the tire circumferential direction of the bottom surface of the groove 5 formed in the arc 5R. It is recommended to apply. Thereby, generation | occurrence | production of the crack from the front-and-rear end of the ditch | groove 5 can be prevented.

  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 concave groove on the groove bottom corresponding to at least the shoulder side of the circumferential main groove in the portion corresponding to the sector division position X of the sectional mold. As a sectional mold for vulcanization molding, the advantage is that it can be easily manufactured simply by providing a build-up for forming the concave groove 5 at the sector division position X in the conventional sectional mold. There is.

<Conventional Example 1, Examples 1 to 4, Comparative Examples 1 and 2>
The tire size is 275 / 70R22.5 and the tread pattern is the same as in FIG. 1, and a sectional mold composed of nine divided sectors is used to form the groove walls of the four circumferential main grooves 2 at the division positions of each sector. A conventional tire (conventional example 1) that does not form a groove, and a groove of the circumferential main grooves 2 and 2 on both shoulder sides by changing the groove formation position, opening width W and depth D as shown in Table 1. The tires of the present invention (Examples 1 to 4) and comparative tires (Comparative Examples 1 and 2) in which a groove having a semicircular cross section was formed on the wall as shown in FIG. In each tire, the groove width of the circumferential main groove was 13.0 mm and the depth was 15.7 mm.

  These seven types of tires are assembled into a rim (rim size: 22.5 × 7.50), filled with air pressure of 900 kPa, mounted on the drive shaft of a heavy-duty vehicle (2-D) with a total vehicle weight of 20 t, and paved. After running the test course for 50,000 km, the incidence (%) of cracks generated at the groove bottom of the circumferential main groove corresponding to the division position of each sector was examined, and the results are also shown in Table 1.

  From Table 1, the conventional tire and the comparative tire had cracks at the groove bottoms of the circumferential main grooves corresponding to the division positions of the sectors, whereas the tires of the present invention had cracks at the groove bottoms of the circumferential main grooves. Did not occur at all.

<Conventional Example 2, Examples 5 and 6>
The tire size is 265 / 60R22.5 and the tread pattern is the same as in FIG. 6, and a sectional mold composed of 9 divided sectors is used to dent the groove walls of the four circumferential main grooves at each sector division position. A conventional tire (conventional example 2) in which grooves are not formed is different from the groove width on the shoulder side of the circumferential main grooves 22B and 22B on both shoulder sides with the opening width W of the recessed grooves being different as shown in Table 2 The tires of the present invention (Examples 5 and 6) in which concave grooves having a square cross section were formed as shown in FIG. In each tire, the groove width of the circumferential main groove 22B was 12 mm, the depth was 14 mm, the angle of the groove wall with respect to the tire radial direction was 10 °, and the average curvature radius of the groove bottom surface was 2 mm.

  These three types of tires are assembled into rims (rim size: 22.5 × 7.50), filled with air pressure of 900 kPa, mounted on the drive shaft of a heavy-duty vehicle (2-D) with a total vehicle weight of 20 t, and paved. After traveling the test course for 50,000 km, the incidence (%) of cracks generated at the groove bottom of the circumferential main groove corresponding to the division position of each sector was examined, and the results are also shown in Table 2.

  From Table 2, cracks occurred in the groove bottom of the circumferential main groove 22B corresponding to the division position of the sector in the conventional tire, whereas cracks occurred in the groove bottom of the circumferential main groove 22B in the tire of the present invention. It did not occur at all.

It is a partial top view which shows the tread part in the pneumatic tire by 1st embodiment of this invention. It is a top view which expands and shows the Y section of FIG. (A) is AA arrow sectional drawing of FIG. 2, (b) And (c) is sectional drawing corresponded to (a) by other embodiment, respectively. (A) is a BB arrow sectional drawing of Drawing 2, (b)-(e) is a sectional view equivalent to (a) by other embodiments, respectively. (A) And (b) is sectional drawing explaining the form of the overflow thin film generated along the division | segmentation position of a sector. It is a partial top view which shows the tread part in the pneumatic tire by 2nd embodiment of this invention. It is CC sectional view taken on the line of FIG. It is sectional drawing which shows the state which mounted | wore the pneumatic tire with the pneumatic tire. (A) And (b) is sectional drawing explaining the generation | occurrence | production state of the overflow rubber | gum which generate | occur | produces in a circumferential main groove along the division | segmentation position of the sector in a conventional pneumatic tire, and the generation | occurrence | production state of a crack, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread surface 2, 22A, 22B Circumferential main groove 3, 23 Sub groove 4 Land part 5 Concave groove G Overflow thin film Sh Tire shoulder X Sector division position

Claims (6)

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,
The pneumatic tire which formed the ditch | groove in the groove | channel bottom of the said circumferential direction main groove in the part corresponding to the division position of the said sector.   The pneumatic tire according to claim 1, wherein the concave groove is formed in a groove bottom on a shoulder side of the circumferential main groove.   The concave groove is formed on the shoulder bottom of the circumferential main groove located closest to the shoulder in the circumferential main groove, and the cross section of the concave groove is an extension of the groove wall of the circumferential main groove. The pneumatic tire according to claim 2, wherein the pneumatic tire is formed so as to include a region surrounded by the groove bottom and a straight line in parallel with the tread surface.   The pneumatic according to claim 1, 2 or 3, wherein the opening width W measured in the longitudinal direction of the circumferential main groove of the concave groove is 0.5 mm or more and 6 times or less of the depth of the circumferential main groove. tire.   The pneumatic tire according to claim 1, 2, 3 or 4, wherein the depth D of the concave groove is 0.5 mm or more.   The pneumatic tire according to claim 5, wherein the depth D of the concave groove is gradually reduced from the groove bottom of the circumferential main groove toward the opening.

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