JP2007161009A - Pneumatic tire, sectional type mold for tire, and pneumatic tire manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire to be manufactured by using a sectional type mold and capable of suppressing the generation of cracks at a groove bottom located at a section connection part of a circumferential groove, a sectional type mold for the tire, and a pneumatic tire manufacturing method. <P>SOLUTION: The pneumatic tire has a circumferential groove 2 extending in the tire circumferential direction TC on a tread surface 1, and the tread surface 1 is molded by annularly articulating a plurality of divided sectors 11 of the sectional type mold with each other. In a groove wall 2Y located on at least on the shoulder side out of both groove walls 2X, 2Y of the circumferential groove 2, the angle θ2 of the groove wall surface 2Ya located on a connection part 11a of the sector 11 is larger than the angle θ1 of the groove wall surface 2Yb located in a vicinity of the connection part 11a of the sector 11 on the groove bottom side of at least the circumferential groove 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire, a sectional mold for tires used for manufacturing the pneumatic tire, and a method for manufacturing a pneumatic tire manufactured using the mold, and more specifically, a tire circumferential groove. The present invention relates to a pneumatic tire, a sectional mold for tires, and a method for manufacturing a pneumatic tire in which cracks generated at the bottom of the groove are suppressed.

  In general, pneumatic tires maintain the air filling ability when assembling rims, so that the distance between the left and right bead portions of the tire before rim assembly (hereinafter referred to as the bead base width) exceeds the rim width of the wheel to be assembled. This tendency is particularly noticeable in tubeless tires.

  When such a tire is assembled to the rim, as shown in FIG. 10, the bead base interval Bs is narrowed to coincide with the rim width Rw, and accordingly, the radius of curvature R of the tire inner surface 21 tends to be reduced. On the tread surface 22 having a large diameter difference between the side and the shoulder, forces F1 and F2 that are pulled to the left and right are generated. Furthermore, when an internal pressure is applied in the cavity 23, the forces F1 and F2 pulled to the left and right are increased by the growth of the outer diameter of the center portion 22a of the tread surface 22. In particular, this tendency is greater in a flat tire having a high internal pressure share of the belt layer.

  As a result, the circumferential groove 24 formed in the tread surface 22 expands left and right, and stress is concentrated particularly on the contact portion a between the groove wall surface 24a and the groove bottom surface 24b located on the shoulder side of the circumferential groove 24. .

  On the other hand, pneumatic tires manufactured using a sectional mold that forms a tread surface by connecting a plurality of divided sectors in a ring shape are caused by subtle deviations between connected sectors and gaps between sectors caused by repeated use. Steps and overflows are likely to occur at the connecting positions of sectors. When such a step or overflow occurs at the groove bottom of the circumferential groove 24, stress concentration tends to occur at that portion.

  When a pneumatic tire as described above, particularly a heavy-duty pneumatic tire loaded with a high load, is used at a relatively low air pressure, the stress on the groove bottom of the circumferential groove increases, while the heat generation increases rubber. Decrease in physical properties is promoted. As a result, a crack is generated in the contact portion a located at the sector connection portion of the circumferential groove 24, which becomes a starting point, and the crack grows in the circumferential direction and further in the radial direction, thereby reducing the durability of the tire. It was.

Conventionally, the problem of stress concentration on the former contact portion a has been dealt with by using rubber having enhanced resistance to rubber physical properties against stress. In addition, for the problem of cracks caused by steps or overflow at the bottom of the latter circumferential groove, a technique has been proposed that suppresses the generation of cracks by devising the sector dividing surface. (For example, refer to Patent Document 1).
JP 2005-001550 A

  An object of the present invention is a pneumatic tire manufactured using a sectional mold, and for a pneumatic tire and a tire capable of suppressing the occurrence of cracks at a groove bottom located at a sector connecting portion of a circumferential groove. It is providing the manufacturing method of a sectional type mold and a pneumatic tire.

  The pneumatic tire of the present invention that achieves the above object has a circumferential groove extending in the tire circumferential direction on the tread surface, and the tread surface is formed by annularly connecting a plurality of divided sectors. The groove wall located at least on the shoulder side of both groove walls of the circumferential groove is at least the angle θ2 of the groove wall surface located at the connecting portion of the sector. It is characterized in that it is made larger than the angle θ1 of the groove wall surface located around the connecting portion of the sector on the groove bottom side.

  The tire sectional mold of the present invention has a plurality of divided sectors, a tread surface having a circumferential groove extending in the circumferential direction of the tire, and a circumferential groove forming protrusion protruding from the tread molding surface. A sectional type mold for a tire, which is formed by connecting the plurality of sectors in an annular shape, and at least a side wall located on a tire shoulder side among both side walls of the circumferential groove forming ridge, to a connecting portion of the sectors The angle α2 of the positioned side wall surface is set to be larger than the angle α1 of the side wall surface positioned around the connecting portion of the sector at least on the projecting end side of the circumferential groove forming ridge.

  The method for producing a pneumatic tire according to the present invention is characterized in that the above-mentioned tire sectional mold is used when a pneumatic tire is produced by vulcanizing a green tire in a tire sectional mold.

  According to the present invention described above, the angle θ2 of the groove wall surface at least on the shoulder side located at the connecting portion of the sector where cracks are likely to occur, and the angle θ1 of the groove wall surface positioned at the periphery of the connecting portion of the sector at least on the groove bottom side. Since it is made larger, the rigidity of the groove wall on the shoulder side can be increased from the periphery of the groove wall surface portion located at the connecting portion of the sector. Therefore, it is possible to disperse stress concentrated on the contact portion between the groove wall surface on the shoulder side and the groove bottom surface located at the connecting portion of the sector to reduce the tensile stress acting on the contact portion.

  Therefore, it is possible to suppress the occurrence of cracks in the contact portion located at the sector connection location of the circumferential groove, thereby improving the deterioration of the tire durability caused by the crack occurring at the groove bottom of the circumferential groove. It becomes possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an embodiment of a pneumatic tire according to the present invention, and a tread surface 1 is provided with a plurality of circumferential grooves 2 extending in the tire circumferential direction TC. Between the two circumferential grooves 2A located on the tire center side, lateral grooves 3 extending in the tire width direction are arranged at predetermined intervals in the tire circumferential direction TC, and are blocked by the circumferential grooves 2A and the lateral grooves 3 (land Part) 4 is defined. Ribs (land portions) 5 are separately formed on the tire outer sides of the two circumferential grooves 2A.

  This pneumatic tire is a tire formed by treading the tread surface 1 by connecting a plurality of divided sectors 11 of the sectional mold shown in FIG. 2 in a ring shape, where P is the connecting position of the divided surfaces 11p of the sectors 11 Is a position corresponding to.

  Of the both groove walls 2X and 2Y of the circumferential groove 2, as shown in FIGS. 3 and 4, the groove wall surface 2Ya positioned at the connecting portion 11a of the sector 11 is at least the groove wall 2Y positioned on the shoulder side. On the groove bottom side connected to the groove bottom surface 2g of the circumferential groove 2, it is formed on the recessed surface 6 that is recessed outward in the groove width direction from the groove wall surface 2Yb located in the connection peripheral portion 11b around the connection portion 11a of the sector 11, The angle θ2 of the groove wall surface 2Ya (the recessed surface 6) is larger than the angle θ1 of the groove wall surface 2Yb. As shown in FIG. 4, the angles θ1 and θ2 referred to here are on the land side between the line q orthogonal to the center line O of the circumferential groove 2 and the groove wall surfaces 2Ya and 2Yb in the tire meridian cross section. Is the angle. Preferably, the groove wall 2X, 2Y has the above configuration.

  The hollow surface 6 is formed as a flat surface that is entirely recessed in FIG. 3, but is not limited thereto, and may be a recessed surface 6 that is recessed in a triangular shape as shown in FIG. 5, for example.

  A tire sectional mold for molding a pneumatic tire having such a tread surface 1 is arranged between an upper mold and a lower mold (not shown) for molding both sidewall surfaces, and between the upper mold and the lower mold. The sector 11 shown in FIG. 2 divided into a plurality of parts for molding the tread surface 1 is provided.

  Each sector 11 has a configuration in which a circumferential groove forming protrusion 12 for forming the circumferential groove 2 and a horizontal groove forming protrusion 13 for forming the lateral groove 3 are provided on the tread forming surface 11X.

  Of the side walls 12X and 12Y of each circumferential groove forming protrusion 12, at least on the side wall 12Y located on the shoulder side of the tire to be molded, it is located at the connecting portion 11a of the sector 11 as shown in FIGS. The side wall surface 12Ya is formed on the protruding surface 14 that protrudes outward in the ridge width direction from the side wall surface 12Yb located at the connecting peripheral portion 11b around the connecting portion 11a of the sector 11 at least on the protruding end 12a side of the circumferential groove forming ridge 12. The angle α2 of the side wall surface 12Ya (projecting surface 14) is larger than the angle α1 of the side wall surface 11Yb on the protruding end 12a side. As shown in FIG. 6, the angles α1 and α2 referred to here are the centers of the circumferential groove forming ridges 12 in the radial section corresponding to the tire meridian section (the radial section of the sector arranged in an annular shape). This is the angle on the ridge side between the line q ′ orthogonal to the line O ′ and the side wall surfaces 11Ya, 11Yb.

  After carrying the green tire into the tire sectional mold thus configured, the sector 11 is connected in an annular shape with the dividing surface 11p in contact, and the green tire is set in the tire sectional mold. Subsequently, the pneumatic tire mentioned above is manufactured by vulcanizing.

  Cracks occurring in the tire occur when the relationship between the tensile stress and the breaking resistance is such that the tensile stress> the breaking resistance, but in the present invention described above, the crack is likely to occur and is located at the connecting portion 11a of the sector 11. By making the angle θ2 of the groove wall surface 2Ya on the shoulder side to be larger than the angle θ1 of the groove wall surface 2Yb located around the connecting portion 11a of the sector 11 at least on the groove bottom side, the rigidity of the groove wall 2Y is increased. Since the stress can be increased from the periphery on the side, the stress concentrated on the contact portion b between the groove wall surface 2Ya on the shoulder side and the groove bottom surface 2g located at the connecting portion of the sector 11 is dispersed to the periphery and acts on the contact portion b. Tensile stress can be reduced.

  Therefore, it is possible to suppress the occurrence of cracks in the contact portion b of the circumferential groove 2, and therefore it is possible to improve the decrease in tire durability caused by the cracks generated at the groove bottom of the circumferential groove 2. .

  In the pneumatic tire of the present invention, the angle θ2 of the groove wall surface 2Ya is preferably 4 ° to 20 ° larger than the angle θ1 of the groove wall surface 2Yb in order to more effectively suppress the occurrence of cracks. The angle θ1 of the groove wall surface 2Yb is a range employed in a circumferential groove of a normal pneumatic tire, and can be in a range of 60 ° to 90 °.

  The ratio L / W between the recess width L (mm) of the recess surface 6 and the recess amount W (mm) is in the range of 2.0 to 5.0, and the generation of cracks is more effectively suppressed. Preferred above. When the ratio L / W is smaller than 2.0, the stress reduction effect decreases, and conversely, when the ratio L / W is larger than 5.0, it acts on the connecting portion between the recessed surface 6 and the groove wall surface 2Yb. Since the stress increases, the effect of suppressing cracks is reduced. As the actual dimensions of the dent width L and the dent amount W, the dent width L can be set to 2 to 25 mm and the dent amount W can be set to a range of 1 to 5 mm, and appropriately selected according to the type and size of the tire within the ranges. can do.

  In addition, the hollow width L said here is the length measured in the tire circumferential direction along the circumferential groove | channel 2 as shown in FIG. The depression amount W is the depression amount at the groove bottom position at the position P corresponding to the connection position of the dividing surface 11p of the sector 11.

  The ratio h / D between the height h of the recessed surface 6 formed from the groove bottom of the circumferential groove 2 to the height h (mm) and the groove depth D (mm) of the circumferential groove 2 is 0. It is preferable that the number is 3 or more in order to more effectively suppress the generation of cracks. When the ratio h / D is smaller than 0.3, the recessed surface 6 is small and notched, so that the stress reduction effect is reduced. The recessed surface 6 may extend to the upper end 2Yx of the groove wall surface 2Y (h / D = 1) from the viewpoint of the crack suppression effect, but is 0.6 or less from the point of uneven wear of the tread surface 1. It is good to do.

  As shown in FIG. 8, the groove wall surface 2Yb located in the periphery of the connecting portion 11a of the sector 11 and the groove bottom surface 2g of the circumferential groove 2 are connected by a curved surface 7 having an arcuate section having a radius of curvature R1. The groove wall surface 2Ya located at the connecting portion 11a and the groove bottom surface 2g of the circumferential groove 2 are connected by a curved surface 8 having an arcuate cross section having a radius of curvature R2, and the relationship is R1 <R2. It is preferable for more effectively suppressing the occurrence.

  In the sectional mold for tires of the present invention used for manufacturing the pneumatic tire, the angle α2 of the side wall surface 12Ya is 4 ° to 20 ° larger than the angle α1 of the side wall surface 12Yb. This is good for the same reason as θ2. The angle α1 of the side wall surface 12Yb can be in the range of 60 ° to 90 °.

  The ratio M / N between the protrusion width M (mm) of the protrusion surface 14 and the protrusion amount N (mm) is in the range of 2.0 to 5.0 for the same reason as the ratio L / W described above. Good. The range of the protrusion width M is the same as the recess width L, and the range of the protrusion amount N is the same as the recess amount W.

  The length k of the protruding surface 14 formed from the protruding end 12a of the circumferential groove forming ridge 12 to the position of the length k (mm) on the tread molding surface 11X side and the height H (mm) of the circumferential groove forming ridge 12 The ratio k / H is preferably in the range of 0.3 to 0.6 for the same reason as the ratio h / D described above. The protruding surface 14 may extend to the tread molding surface 11X (k / H = 1) from the viewpoint of crack suppression effect, but it is preferable that the protruding surface 14 be 0.6 or less from the viewpoint of uneven wear.

  As shown in FIG. 9, the connecting portion between the side wall surface 12Yb located in the periphery of the connecting portion 11a of the sector 11 and the protruding end surface 12b of the circumferential groove forming ridge 12 is a curved surface 15 having an arcuate cross section having a curvature radius R1 ′. On the other hand, the connecting portion between the side wall surface 12Ya located at the connecting portion 11a of the sector 11 and the projecting end surface 12b of the circumferential groove forming ridge 12 is chamfered by a curved surface 16 having an arcuate cross section having a curvature radius R2 ′. In order to more effectively suppress the occurrence of cracks, it is preferable that the relationship is R1 ′ <R2 ′.

  The present invention is particularly suitable for heavy-duty pneumatic tires used in heavy-duty vehicles such as trucks and buses, and has a flatness ratio of 70% or less. It can also be suitably used for pneumatic tires for other purposes such as for use.

  The tire size is 275 / 70R22.5, the tread pattern is the same as in FIG. 1, and a section type mold having 9 divided sectors is used. 15 specifications shown in Table 1 (conventional example and examples 1 to 15) Test tires formed to (3 specifications per tire) were produced.

  Each of these test tires was mounted on a rim, applied with an internal pressure of 80% of the air pressure corresponding to the maximum load capacity specified by JATMA, mounted on the drive shaft of the truck, and laid on a paved test course for 50,000 km. Later, when the incidence of cracks at the groove bottom located at the sector connection portion of the circumferential groove was examined, the results shown in Table 1 were obtained.

  From Table 1, it can be seen that the tire of the present invention can suppress the occurrence of cracks at the groove bottom located at the sector connection portion of the circumferential groove.

  Further, by making the angle θ2 larger by 4 ° to 20 ° than the angle θ1, and by setting the ratio L / W in the range of 2.0 to 5.0, the ratio h / D is set to 0.3 to 0.00. It can be seen that the occurrence of cracks can be more effectively suppressed by setting the ratio to 6.

It is a principal part expanded view of the tread surface which shows one Embodiment of the pneumatic tire of this invention. It is the figure which looked at the sector part which connected the sectional type mold for tires used in manufacturing the pneumatic tire of Drawing 1 from the inside. It is an expansion partial perspective view which shows an example of the groove wall located in the shoulder side of the circumferential groove | channel. FIG. 4 is a cross-sectional view taken along position P in FIG. It is an expansion partial perspective view which shows the other example of the groove wall located in the shoulder side of the circumferential groove | channel. It is a principal part enlarged view which shows an example of the sector seen from the division surface side. It is the figure which looked at FIG. 6 from the top. It is principal part sectional drawing which shows the other example of the shoulder side groove wall of the circumferential groove when it cut | disconnects along the position P. FIG. It is a principal part enlarged view which shows the other example of the sector seen from the division surface side. It is sectional drawing of the pneumatic tire with which the rim | limb was mounted | worn.

Explanation of symbols

1 tread surface 2 circumferential groove 2X, 2Y groove wall 2Ya, 2Yb groove wall surface 2g groove bottom surface 6 hollow surface 7, 8 curved surface 11 sector 11X tread molding surface 11a connecting portion 11b connecting peripheral portion 11p dividing surface 12 circumferential groove forming ridge 12X, 12Y side wall 12Ya, 12Yb side wall surface 12a protruding end 12b protruding end surface 14 protruding surface 15, 16 curved surface TC tire circumferential direction α1, α2 angle θ1, θ2 angle

Claims (11)

A pneumatic tire having a circumferential groove extending in the tire circumferential direction on the tread surface, and forming the tread surface by annularly connecting a plurality of sectors divided by the sectional mold,
The groove wall located at least on the shoulder side of both groove walls of the circumferential groove has an angle θ2 of the groove wall surface located on the connecting part of the sector at least on the groove bottom side of the circumferential groove. A pneumatic tire that is larger than the angle θ1 of the groove wall surface located in the periphery.   The pneumatic tire according to claim 1, wherein the angle θ <b> 2 is 4 ° to 20 ° larger than the angle θ <b> 1.   The groove wall surface located at the connecting portion of the sector is formed in a recessed surface that is recessed at least on the groove bottom side of the circumferential groove from the groove wall surface positioned around the connecting portion of the sector, and the recess width L (mm ) And the indentation amount W (mm), the pneumatic tire according to claim 1 or 2, wherein the ratio L / W is in the range of 2.0 to 5.0.   The indented surface is formed from the groove bottom of the circumferential groove to a height h (mm), and a ratio h / D between the height h and the groove depth D (mm) of the circumferential groove is set to 0. The pneumatic tire according to claim 3, wherein the pneumatic tire is 3 to 0.6.   The groove wall surface located at the periphery of the connecting portion of the sector and the groove bottom surface of the circumferential groove are connected by a curved surface having an arcuate cross section having a radius of curvature R1, while the groove wall surface positioned at the connecting portion of the sector and the circumferential direction The pneumatic tire according to any one of claims 1 to 4, wherein the groove bottom surface is connected by a curved surface having an arcuate cross section having a radius of curvature R2 and R1 <R2. A tread surface having a plurality of divided sectors and having a circumferential groove extending in the tire circumferential direction is connected to the plurality of sectors in which the circumferential groove forming protrusions project on the tread molding surface in an annular shape. It is a sectional mold for tires to be molded,
Of the side walls located at least on the tire shoulder side, the angle α2 of the side wall surface located at the connecting portion of the sector is at least at the projecting end side of the circumferential groove forming ridge. Sectional mold for tires, which is larger than the angle α1 of the side wall surface located around the connecting part of the sector.   The tire sectional mold according to claim 6, wherein the angle α2 is larger than the angle α1 by 4 ° to 20 °.   The side wall surface located at the connecting portion of the sector is formed as a protruding surface that protrudes from the side wall surface located around the connecting portion of the sector at least on the protruding end side of the circumferential groove forming protrusion, and the protruding width M of the protruding surface The sectional mold for tire according to claim 6 or 7, wherein a ratio M / N between (mm) and a protrusion amount N (mm) is in a range of 2.0 to 5.0.   The protruding surface is formed from the protruding end of the circumferential groove forming ridge to a position of a length k (mm) on the tread molding surface side, and the length k and the height H (mm of the circumferential groove forming ridge) The sectional mold for tires according to claim 8, wherein the ratio k / H to 0.3 to 0.6.   The connecting portion between the side wall surface located around the connecting portion of the sector and the projecting end surface of the circumferential groove forming ridge is chamfered with a curved surface having an arcuate cross section having a radius of curvature R1 ′, while being positioned at the connecting portion of the sector. The connecting portion between the side wall surface to be formed and the projecting end surface of the circumferential groove forming ridge is chamfered by a curved surface having an arcuate cross section having a radius of curvature R2 ′, and R1 ′ <R2 ′. The sectional mold for tires according to 1.   The manufacturing method of the pneumatic tire which uses the sectional type mold for tires of any one of Claim 6 thru | or 10 when manufacturing a pneumatic tire by vulcanizing a green tire in the sectional type mold for tires.

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