JP2015123782A - Pneumatic tire and method for manufacturing the same - Google Patents

Abstract

A pneumatic tire having a structure in which cracks are unlikely to occur at the bottom of a main groove is provided.
A main groove 2 extending in a tire circumferential direction is provided. A connecting portion between the inner side surface and the bottom surface on both sides constituting the main groove 2 includes a first curved surface 11 and a second curved surface 12. The first curved surface 11 has a longitudinal cross-sectional shape with a radius of curvature R <b> 1, and a boundary position with the bottom surface extends beyond the center position of the groove 2 to the opposite side. The second curved surface 12 has a curvature radius R2 whose longitudinal cross-sectional shape is smaller than the curvature radius R1. The first curved surface 11 and the second curved surface 12 are alternately arranged along the tire circumferential direction.
[Selection] Figure 1

Description

  The present invention relates to a pneumatic tire and a method for manufacturing the same.

Conventionally, a pneumatic tire having the following configuration is known.
In Patent Document 1, the surface width of the rib partitioned by the main groove is larger than the base width, and the depth and width of at least one of the side walls expands closer to the base of the rib connected to the bottom of the main groove. A configuration in which a cut portion is formed is disclosed.
Patent Document 2 discloses a configuration including a linear region in which the groove wall of the main groove is a straight line in the circumferential direction and a zigzag lower region that is zigzag.
Patent Document 3 discloses a configuration in which the main groove has a zigzag shape that swings in the tire width direction, and a rigidity adjusting portion that is further recessed in the tire width direction is formed in the bent portion.
Patent Document 4 discloses a configuration in which the center of the main groove is displaced to the second rib side, and the inclination angle of the second rib side groove wall from the tread surface is made smaller than that of the shoulder rib side groove wall.

However, in patent document 1, although the notch part is formed, there is no mention about the curvature radius of the circular arc which comprises the longitudinal cross-sectional shape of the base part side of the rib connected to the bottom part of a main groove. Without the idea to increase the radius of curvature, the problem that cracks are likely to occur due to stress concentration cannot be solved.
In Patent Document 2, there is no mention of the radius of curvature of the arc constituting the longitudinal cross-sectional shape of the lower zigzag region, and the problem that cracks are likely to occur is not solved as in Patent Document 1.
In Patent Document 3, since it is formed discontinuously in the tire circumferential direction, there is a problem that stress tends to concentrate on this portion and cracks are likely to occur.
In Patent Document 4, although the radius of curvature of the arc constituting the longitudinal cross-sectional shape can be increased on the base side of the shoulder rib side groove wall of the main groove, the opposite side second rib side groove wall is conversely smaller than the normal value. There is a problem that cracks are more likely to occur.

JP-A-7-164827 Japanese Patent Laid-Open No. 10-24705 JP 2002-2225 A JP 2006-27465 A

  This invention makes it a subject to provide the pneumatic tire which has a structure where a crack is hard to generate | occur | produce at the bottom part of a main groove, and its manufacturing method.

As a means for solving the above problems, the present invention provides:
A pneumatic tire having a groove formed on a tread surface,
The inner side portions of the inner side surfaces on both sides constituting the main groove are composed of a first curved surface and a second curved surface,
The first curved surface has a longitudinal cross-sectional shape with a radius of curvature R1 and an end position on the inner side extends beyond the center position of the groove portion to the opposite side,
The second curved surface has a curvature radius R2 whose longitudinal cross-sectional shape is smaller than the curvature radius R1,
The first curved surface and the second curved surface are alternately arranged along the tire circumferential direction.

  With this configuration, since the radius of curvature can be sufficiently increased at least on the first curved surface, the stress concentration can be relaxed and the occurrence of cracks can be prevented.

  The second curved surface is preferably formed in a concave shape recessed from the inner side surface.

  With this configuration, the radius of curvature can be sufficiently increased not only in the first curved surface but also in the second curved surface, so that generation of cracks can be prevented over the entire bottom portion of the main groove.

  It is preferable that the dimension from the center position of the groove part to the boundary position is the same as the depth dimension of the second curved surface from the inner side surface.

  With this configuration, it is possible to form the first curved surface having substantially the same radius of curvature on both sides of the bottom of the main groove, and it is possible to alleviate stress concentration in a well-balanced manner and more appropriately prevent the occurrence of cracks. Become.

  It is preferable that the inner end position of the first curved surface is matched with the inner end position of the second curved surface.

  With this configuration, the occurrence of cracks can be effectively prevented while suppressing the width dimension of the main groove.

  It is preferable that the inward end positions of the first curved surface and the second curved surface constitute a sin waveform extending in the circumferential direction of the tire.

  With this configuration, the first curved surface and the second curved surface can be arranged with good balance on both sides of the bottom of the main groove, and the generation of cracks can be further suppressed.

Further, the present invention provides a means for solving the above-described problems,
A method of manufacturing a pneumatic tire having a main groove extending in the tire circumferential direction,
A first curved surface and a second curved surface are formed at a connection portion between the inner side surface and the bottom surface on both sides constituting the main groove, and the first curved surface has a longitudinal radius of curvature R1 and a boundary position with the bottom surface. However, the second curved surface has a curvature radius R2 whose longitudinal cross-sectional shape is smaller than the curvature radius R1, and the first curved surface and the second curved surface are tire circumferences. They are arranged alternately along the direction.

  According to the present invention, at least the first curved surface has a longitudinal cross-sectional shape with a curvature radius R1 that extends to the opposite side beyond the center position of the groove portion at the boundary position with the bottom surface, so stress concentration is relieved, The occurrence of cracks can be sufficiently suppressed.

It is a development schematic diagram of the tread part of the pneumatic tire concerning this embodiment. (A) is the sectional view on the AA line of FIG. 1, (b) is the sectional view on the BB line of FIG. 1, (c) is the sectional view on the CC line of FIG. FIG. 3 is a partially enlarged view of FIG. It is a fragmentary sectional view in the tread part of the pneumatic tire concerning other embodiments. (A) is the partial expansion schematic of the tread part of the tire which concerns on the comparative example 1, and its sectional drawing, (b) is the partial expansion schematic and sectional drawing of the comparative example 2, (c) is a part of Example 1 FIG. 4D is a developed schematic view and a sectional view taken along the line C-C, FIG. 4D is a partially developed schematic view of the embodiment 2 and a sectional view taken along the line D-D, and FIG. It is line sectional drawing.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the following description, terms indicating specific directions and positions (for example, terms including “up”, “down”, “side”, “end”) are used as necessary. Is for facilitating understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms. Further, the following description is merely illustrative in nature and is not intended to limit the present invention, its application, or its use. Further, the drawings are schematic, and the ratio of each dimension is different from the actual one.

  FIG. 1 is a development view showing a part of a tread surface 1 of a tire according to the present embodiment. A plurality of land portions (ribs) 3 are formed on the tread surface 1 by a plurality of main grooves 2 extending in the tire circumferential direction. FIG. 1 shows one main groove 2 and a first land portion 4 and a second land portion 5 located on both sides thereof.

  As shown in FIG. 2 and specifically FIG. 3, the outer side region of the main groove 2 gradually inclines toward the center line C side of the main groove 2 from the tread surface 1 toward the inner side. It is comprised by the inner surface (1st inclined surface 6) of the part 4, and the inner surface (2nd inclined surface 7) of the 2nd land part 5. FIG. As shown in FIG. 1, the inner region of the main groove 2 is composed of first regions 8 and second regions 9 that are alternately arranged in the tire circumferential direction.

  In the first region 8, the inner surface of the first land portion 4 shown in FIG. 2A, specifically, FIG. 3, includes the first inclined surface 6 and the deepest virtual bottom surface 10 of the main groove 2 (in FIG. 3, The first curved surface 11 is in contact with a circumferential surface passing through a two-dot chain line). As for the 1st curved surface 11, the longitudinal cross-sectional shape in the meridian surface of a tire is the curvature radius RA, and this curvature radius RA is increased / decreased by shifting in the tire circumferential direction. That is, the inner end position E1 of the arc having the radius of curvature RA is located on the virtual bottom surface 10, and this position forms a half wave of a sin waveform with respect to the center line C of the main groove 2 as shown in FIG. Increase or decrease as you do. The amplitude is set in the range of 1/10 to 1/4 of the width dimension of the virtual bottom surface 10. As shown in the cross section along line A-A in FIG. 1, that is, in FIGS. 2A and 3, the first curved surface 11 swells most on the opposite side beyond the center line C of the main groove 2. The radius of curvature is RA1. As shown in the cross section along line BB in FIG. 1, that is, FIG. 2B, the first curved surface 11 has the smallest radius of curvature RA <b> 2 where the inner end position E <b> 1 is located on the center line C of the main groove 2. ing. The curved surface is curved so that the radius of curvature of the arc in the longitudinal section gradually decreases from RA1 to RA2.

  In the first region 8, a second curved surface 12 that is recessed in a concave shape is formed on the inner surface of the second land portion 5. The second curved surface 12 is constituted by a part of a spherical surface having a curvature radius RB. Therefore, the longitudinal cross-sectional shape at each position shifted in the tire circumferential direction is the cross section along the line BB in FIG. 1 from the cross section along the line AA in FIG. 1, that is, the maximum radius of curvature RB1 in FIG. That is, it gradually changes to the minimum curvature radius RB2 in FIG. The arcs formed in the respective longitudinal sections are in contact with the virtual bottom surface 10 of the main groove 2 and are formed so as to terminate at the inner end position E1 of the first curved surface 11. Further, the depth D from the virtual inner side surface 13 (indicated by a two-dot chain line in FIG. 2) of the second curved surface 12 in the cross section along line AA in FIG. It is the same as the dimension L up to the inner end position E2 of the first curved surface 11.

  In the second region 9, as shown in FIG. 2 (c), the second curved surface 12 is formed in the lower region of the inner surface of the first land portion 4, contrary to the first region 8, and the second land A first curved surface 11 is formed in a lower region of the inner side surface of the part 5. That is, the second region 9 is configured to be plane-symmetric with respect to the first region 8 with the center line C of the main groove 2 interposed therebetween. Then, in the first region 8 and the second region 9, the inner end position E1 of the first curved surface 11 and the inner end position E2 of the second curved surface 12 at the bottom of the main groove 2 are equivalent to one cycle of the sin waveform. Is formed. This sin waveform extends over the entire circumference in the tire circumferential direction and is connected in an annular shape. Here, the period is connected at 12 to 24 times the amplitude.

  As described above, in the main groove 2 having the above-described configuration, the first curved surface having a sufficiently large radius of curvature RA compared to the main groove 2 having the same width as the tread surface 1 and having the same width dimension in one of the opposed land portions 3. 11. Further, the land portion 3 on the opposite side to the first curved surface 11 is formed with a second curved surface 12 that constitutes a part of the spherical surface, thereby forming an arc having a large curvature radius. Therefore, unlike the conventional first curved surface 11 having a small curvature radius, there is no fear that stress is concentrated on a part and cracks are generated. Further, the thinned portions of the land portion 3 due to the formation of the second curved surface 12 are arranged in a staggered manner in the tire circumferential direction. For this reason, although the 2nd curved surface 12 is formed in the tire circumferential direction in the land part 3, the fall of the rigidity can be suppressed. Moreover, even if the width dimension of the main groove 2 is any position in the tire circumferential direction, the desired drainage can be maintained without being narrowed.

  A comparative experiment was conducted as to whether or not a crack occurred at the bottom of the main groove 2 between the tire according to Comparative Examples 1 and 2 and the tire according to Examples 1, 2, and 3. Here, a tire having a size of 275 / 80R22.5 and an air pressure of 900 kPa is visually checked for cracks at the bottom of the main groove 2 after running at 150,000 km at a tire load of 4485 kg and a speed of 80 km / h. Confirmed by

As shown in FIG. 5A, Comparative Example 1 is a tire in which the longitudinal cross-sectional shape on both sides of the bottom of the main groove 2 is an arc having a curvature radius of 3.5 mm.
In Comparative Example 2, as shown in FIG. 5 (b), by forming a curved surface 15 recessed from the inner surface only on one side of the bottom of the main groove 2, an arc having a curvature radius of 3.5 mm is formed on both sides of the bottom. Each tire has a 5.5 mm arc.
In the first embodiment, as shown in FIG. 5 (c), a curved surface 16 having a larger radius of curvature than the opposite portion is formed in a staggered manner on both sides of the bottom of the main groove 2, thereby providing a radius of curvature on both sides of the bottom. The tire is formed with a 2.5 mm arc and a 4.5 mm arc, respectively.
In the second embodiment, as shown in FIG. 5 (d), by forming the second curved surface 12 recessed from the inner side surface in a staggered manner on both sides of the bottom of the main groove 2, the curvature radius is 3.5 mm on both sides of the bottom. And a 5.5 mm arc. However, regions where the first curved surfaces 11 face each other and regions where the first curved surface 11 and the second curved surface 12 face each other are alternately arranged along the tire circumferential direction.
In Example 3, as shown in FIG. 5 (e), by forming the second curved surface 12 recessed from the inner surface in a staggered manner on both sides of the bottom portion of the main groove 2, the curvature radius of 3.5 mm is formed on both sides of the bottom portion. And a 5.5 mm arc. In the third embodiment, unlike the second embodiment, there is no region where the first curved surfaces 11 face each other, and the region where the first curved surface 11 and the second curved surface 12 face each other in the tire circumferential direction. The two curved surfaces 12 are arranged while being exchanged.

The evaluation criteria are as follows.
◎: No crack occurred after running 150,000 km ○: Permissible crack occurred after running 150,000 km △: Crack occurred after running 130,000 km ×: Crack occurred after running 120,000 km

なお、表１中、λは、ｓｉｎ波の波長を意味する。

In Table 1, λ means the wavelength of the sin wave.

  As can be seen from Table 1, with the tire of Example 1, the occurrence of cracks at the bottom of the main groove 2 could be extended to a travel distance of 130,000 km. This is considered to be because the rigidity balance was improved by arranging curved surfaces having a larger curvature radius than the comparative example 1 in a staggered manner along the tire circumferential direction. Further, in the case of the tire of Example 2, the crack generated at the bottom of the main groove 2 could be suppressed to an acceptable level even after traveling 150,000 km. This is considered to be because the second curved surface 12 having a larger radius of curvature was formed by depression on one side in the tire width direction. Furthermore, in the case of the tire of Example 3, no cracks occurred at the bottom of the main groove 2 even after traveling 150,000 km. This is considered to be because the stress concentration can be alleviated more effectively and the rigidity balance can be improved by arranging the second curved surfaces 12 in a zigzag manner in the tire circumferential direction and continuing them.

In addition, this invention is not limited to the structure described in the said embodiment, A various change is possible.
For example, in the above-described embodiment, a tire in which only the main groove 2 is formed on the tread surface 1 has been described. However, a plurality of blocks are formed by having a lateral groove that intersects the main groove 2 and extends in the tire width direction. Even in the case of a tire, a configuration including the first curved surface 11 and the second curved surface 12 can be employed. In this case, you may make it form the 1st curved surface 11 and the 2nd curved surface 12 in the inner surface of both the blocks which comprise a horizontal groove, respectively.

  Moreover, in the said embodiment, although the main groove 2 was made into the structure without a flat part (circumferential surface extended in a tire circumferential direction) in a bottom part, as shown in FIG. Is also possible. That is, the inward end position E1 of the first curved surface 11 and the inward end position E2 of the second curved surface 12 do not coincide with each other, and are separated by a constant interval in the width direction. You may form the flat part 14 which forms.

  The pneumatic tire according to the present invention is particularly suitable for use as a high-load tire such as a truck or a bus.

1 ... Tread surface 2 ... Main groove (groove)
3 ... Land (rib)
4 ... 1st land (rib)
5 ... Second land (rib)
DESCRIPTION OF SYMBOLS 6 ... 1st inclined surface 7 ... 2nd inclined surface 8 ... 1st area | region 9 ... 2nd area | region 10 ... Virtual bottom surface 11 ... 1st curved surface 12 ... 2nd curved surface 13 ... Virtual inside surface 14 ... Flat part

Claims (6)

A pneumatic tire having a groove formed on a tread surface,
The inner side portions of the inner side surfaces on both sides constituting the groove part are composed of a first curved surface and a second curved surface,
The first curved surface has a longitudinal cross-sectional shape with a radius of curvature R1 and an end position on the inner side extends beyond the center position of the groove portion to the opposite side,
The second curved surface has a curvature radius R2 whose longitudinal cross-sectional shape is smaller than the curvature radius R1,
The pneumatic tire according to claim 1, wherein the first curved surface and the second curved surface are alternately arranged along a tire circumferential direction.   The pneumatic tire according to claim 1, wherein the second curved surface is formed in a concave shape that is recessed from the inner surface.   The pneumatic tire according to claim 2, wherein a dimension from a center position of the groove portion to the boundary position is the same as a depth dimension of the second curved surface from the inner side surface.   The pneumatic tire according to any one of claims 1 to 3, wherein an inner end position of the first curved surface is matched with an inner end position of the second curved surface.   5. The pneumatic tire according to claim 4, wherein inner end positions of the first curved surface and the second curved surface constitute a sin waveform extending in a circumferential direction of the tire. A method for manufacturing a pneumatic tire having a groove formed on a tread surface,
The inner side portions of the inner side surfaces on both sides constituting the groove portion are composed of a first curved surface and a second curved surface, and the first curved surface has a longitudinal sectional shape with a radius of curvature R1 and a boundary position with the bottom surface is a groove portion. The second curved surface has a curvature radius R2 whose longitudinal cross-sectional shape is smaller than the curvature radius R1, and the first curved surface and the second curved surface are along the tire circumferential direction. And a method for manufacturing a pneumatic tire, wherein the tires are alternately arranged.

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