JP4528091B2 - Pneumatic tire - Google Patents

Description

  In the tread portion, a plurality of circumferential grooves extending along the tire circumferential direction and a plurality of lateral grooves communicating with at least one of the circumferential grooves are disposed on the tread portion. With respect to a pneumatic tire having a so-called block pattern in which a tread portion is partitioned into a plurality of block land portions by the tread end and the lateral groove, in particular, uneven wear occurring in the block land portion of such a pneumatic tire is detected from the initial stage of tire wear. Effective control over the end of wear.

  Pneumatic tires with a block pattern formed by arranging circumferential grooves and lateral grooves communicating with them in the tread, especially heavy duty pneumatic tires used for trucks, buses, etc., have uneven wear on the block land It is easy to produce. Such uneven wear not only deteriorates the appearance of the tire but also adversely affects grip performance.

  In order to suppress such uneven wear, for example, Patent Document 1 discloses that the outer surface of the block has a circumferential curvature radius on the outer side in the width direction smaller than a circumferential curvature radius on the tire equatorial plane side and an end portion on the outer side in the width direction. A pneumatic tire having a lower portion formed smaller than the tire radius is described. Such a tire is particularly effective in suppressing heel and toe wear.

  Patent Document 2 also provides a block land portion having a lower portion where the land portion height gradually decreases from the inland portion toward the edge or corner, and the circumferential groove has a predetermined static load condition. A pneumatic tire provided with a protrusion that is in sliding contact with a road surface is described. Such a tire can suppress river wear and heel and toe wear, and can prevent stone biting in a circumferential groove.

  In Patent Document 3, a protrusion that slides in contact with the road surface under a predetermined static load condition is provided in the circumferential groove, and the land on the block land portion is directed toward the corner located on the side opposite to the circumferential groove. A pneumatic tire provided with a lower portion where the height of the portion gradually decreases is described. Such a tire can suppress the occurrence of both river wear and heel and toe wear at a high level.

  Patent Document 4 discloses a pneumatic tire provided with chamfered surfaces in which the block height gradually decreases toward the projecting ends of the corners at the two corners at both ends in the tread circumferential direction on the tread end side of the block land portion. Is described. Such tires can improve uneven wear resistance performance without an increase in generated noise.

JP-A-7-304309 JP-A-9-240220 Japanese Patent Laid-Open No. 10-86610 JP 11-48719 A

  However, the tires described in Patent Documents 1 to 4 can effectively suppress the occurrence of uneven wear at the initial stage of wear. However, as wear progresses, the difference in land height between the lower portion and other portions is increased. If the height difference between the protrusion in the circumferential groove and the block land portion disappears and the protrusion does not come into sliding contact or the chamfered surface decreases, there is a risk that uneven wear occurs in the block land portion.

  Therefore, the object of the present invention is to prevent uneven wear generated in the block land portion from the initial stage of tire wear to the end of wear by optimizing the shape of the groove bottom raised portion and the block land portion provided in the circumferential groove. An object of the present invention is to provide a pneumatic tire that can be suppressed.

  In order to achieve the above object, according to the present invention, a plurality of circumferential grooves extending along a tire circumferential direction and a plurality of lateral grooves communicating with at least one of the circumferential grooves are disposed in the tread portion. In the pneumatic tire formed by partitioning the tread portion into a plurality of block land portions by the circumferential groove, both tread ends, and the lateral groove, the groove depth is another portion in at least one circumferential groove. A groove bottom ridge that is shallower and extends along the tire circumferential direction, and the block land portion adjacent to the circumferential groove provided with the groove bottom ridge is at least one end or corner from its inland portion The groove-bottom ridge has an outermost end in the tire radial direction that is a road surface at the initial stage of tire wear under a predetermined static load condition. The tire diameter is in a non-contact state and after the middle of tire wear Direction outermost end is pneumatic tire characterized by having a groove depth which is in contact with the road surface.

  Here, “extending along the tire circumferential direction” means that the extending direction of the entire groove or groove bottom raised portion is the tire circumferential direction, and has a zigzag or wavy extending shape. There may be. The “predetermined static load condition” is a static load radius measurement condition defined by JATMA, that is, a pneumatic pressure corresponding to the maximum load capacity when a tire is mounted on an applicable rim (180 kPa in the case of a passenger car tire). ) And a condition under which a mass corresponding to the maximum load capacity (88% of the maximum load capacity in the case of a passenger car tire) is loaded. Furthermore, the amount of wear of the block land portion before the tire reaches the service life is defined as the block maximum wear amount, and “the tire wear initial stage” means that the wear amount of the block land portion is in the range of 0 to 40% of the block maximum wear amount. The term “after mid-tire wear” refers to a state where the wear amount of the block land portion is in the range of 40 to 100% of the block maximum wear amount.

  Moreover, it is preferable that the groove depth at the groove bottom raised portion is deeper than the groove depth of the lateral groove opened to the circumferential groove provided with the groove, particularly 2 mm or more. Here, the “groove depth” refers to a distance measured between the tread surface and the groove bottom along the tire radial direction.

  Furthermore, it is preferable that the groove depth in the groove bottom raised portion is in the range of 5 to 7 mm.

  Furthermore, it is preferable that the groove depth in the groove bottom raised portion is in the range of 30 to 45% of the land portion height at the end of the block land portion adjacent to the circumferential groove provided with the groove.

  In addition, the groove depth of the lateral groove adjacent to the circumferential groove provided with the groove bottom raised portion is preferably in the range of 3 to 5 mm.

  In addition, it is preferable that a groove bottom raised portion is provided in a circumferential groove located on the outermost side in the tire width direction.

  According to the present invention, by optimizing the shape of the groove bottom raised portion and the block land portion provided in the circumferential groove of the pneumatic tire, uneven wear occurring in the block land portion is prevented from the tire wear initial stage to the wear end stage. It is possible to effectively suppress over the range.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a developed part of a tread portion of a typical pneumatic tire (hereinafter referred to as “tire”) according to the present invention. FIG. The cross section is shown, FIG.2 (b) has shown the cross section on the II-II line | wire of FIG. FIG. 3 is a perspective view when one of the block land portions 5b shown in FIG. 1 is extracted and viewed from the circumferential groove side.

  The tire shown in FIG. 1 has a plurality of circumferential grooves extending in the tire circumferential direction in the tread portion 1, in FIG. 1, four circumferential grooves 2a, 2b, 2c, and 2d, and circumferential grooves 2a to 2d. A plurality of lateral grooves 3a, 3b, 3c, 3d, and 3e communicating with at least one of these are disposed. The lateral grooves 3a to 3e may extend substantially in the tire width direction as in 3a and 3e, or may extend incline with respect to the tire width direction as in 3b and 3d. It may be crank-shaped as in 3c. The tread portion 1 is partitioned into a large number of block land portions 5a, 5b, 5c, 5d, and 5e by circumferential grooves 2a to 2d, both tread ends 4a and 4b, and lateral grooves 3a to 3e.

The main features of the configuration of the present invention are as follows. That is, at least one circumferential groove, into two circumferential grooves 2a and 2d in Figure 1, groove depth d ₁ is shallower than the groove depth d ₂ of the other part, and along the tire circumferential direction An extending groove bottom ridge 6 is provided. The block land portions 5a and 5b, 5d and 5e adjacent to the circumferential grooves 2a and 2d provided with the groove bottom raised portion 6 have at least a part of the top surface in a dome shape. Here, when the block land portion 5b is taken as an example of the dome-shaped land portion, the end portions 8a and 8b formed by the lateral grooves 3b and 3b from the inland portion 7 or the lateral grooves 3b and 3b and the circumferential groove 2a 2b and a land portion having a curved top surface in which the land height h gradually decreases toward at least one of the corner portions 9a, 9b, 9c, 9d. . That is, as shown in FIG. 3 (a), the land portion where the land height h gradually decreases from the inland portion 7 toward at least one end (both ends 8a and 8b in FIG. 3 (a)), As shown in FIGS. 3 (b) and 3 (c), land from the inland portion 7 toward at least one corner (corner 9a in FIG. 3 (b) and corners 9a and 9c in FIG. 3 (c)). The land portion where the height h gradually decreases, or, as shown in FIG. 3 (d), from the inland portion 7 to one end (the end 8b in FIG. 3 (d)) and at least one corner (FIG. 3 ( d) includes a land portion where the land height h gradually decreases toward the corner portion 9a). Then, the groove depth d ₁ of the groove bottom raised portion 6 is set to the outermost end in the tire radial direction at the initial stage of tire wear under a predetermined static load condition, and the top surface 10 in FIG. 2 is not in contact with the road surface. In the state, the outermost end in the tire radial direction is set in contact with the road surface after the middle stage of tire wear.

  As described above, as means for suppressing uneven wear occurring in the block land portion, the top surface of the block land portion is formed in a dome shape, or a groove bottom raised portion is provided in a circumferential groove adjacent to the block land portion. It was general. In a tire having a block land portion having a dome shape, uneven wear is prevented by forming in advance a portion where uneven wear is likely to occur as a lower portion having a low land portion height. Also, in tires with groove bottom ridges, the groove bottom ridges have a force that promotes wear of the block land by making the groove depth at the groove bottom ridges small and sliding the groove bottom ridges against the road surface. Uneven wear is prevented by concentrating on the part. However, in any of these tires, although the expected uneven wear prevention effect can be obtained in the early stage of wear, the uneven wear preventive effect may not be sufficient after the middle wear stage. This is because, as the tire wears and the land height of the block land portion decreases, in the tire having the dome-shaped block land portion, there is no difference in the land height between the lower portion and the other portions, This is because uneven wear is likely to occur in the lower part, and in tires with groove bottom ridges, the top surface of the groove bottom ridge and the top surface of the block land part substantially coincide, and the road surface and the groove bottom ridge are in sliding contact. This is because, as a result of normal contact, the force that promotes wear cannot be concentrated.

  On the other hand, the tire according to the present invention effectively prevents uneven wear until the tire reaches its wear life by using different uneven wear prevention means depending on the wear stage. Specifically, the top surface of the block land portion is formed in a dome-like contour shape, and the groove bottom raised portion is formed so as to come into contact with the road surface only after the middle stage of wear. Only the block-shaped block land portion acts as a means for preventing uneven wear, while the block land portion is worn and the bottom of the groove provided in the circumferential groove is in the middle of the wear where the contour shape of the top surface approaches flat. When the raised portion is in sliding contact with the road surface, it acts as a means for preventing uneven wear. As a result, a high uneven wear prevention effect can be maintained even after the middle stage of wear of the tire, where the effect of suppressing uneven wear has been reduced in the conventional tire.

  Furthermore, in a tire having a conventional groove bottom raised portion, the groove bottom raised portion and the road surface are always in contact with each other, so that there is a flow of water moving to the tread end through the lateral groove, which was present on the inner side in the tire width direction. There is a concern about the deterioration of drainage because it is hindered by the groove bottom bulge, but in the tire according to the present invention, there is a gap between the groove bottom bulge and the road surface at the initial stage of wear. The flow of water is not hindered, and the drainage performance is not deteriorated.

The groove depth _{d 1} at the groove bottom ridges 6, the circumferential grooves 2a provided this lateral groove 3a and 3b open to 2d, it is preferable deeper than 3d and 3e groove depth _{d 3} of the. According to this, the shallower the groove depth d _3, the block land portion 3b adjacent thereto in the tire circumferential direction, a result of the land portion rigidity of the 3d increases, is because the effect of inhibiting uneven wear is further improved, Further, This is because when the groove bottom ridge 6 comes into contact with the road surface, the groove bottom ridge 6 can prevent the flow of water toward the tread end from being obstructed. More preferably, deeper than 2mm than the groove depth _{d 3} of the groove depth _{d 1.}

Furthermore, it is preferable that the groove depth d1 at the groove bottom raised portion 6 is in the range of ₅ to 7 mm. This is because if the groove depth d ₁ is less than 5 mm, the groove bottom raised portion 6 may come into contact with the road surface from the beginning of wear of the tire. If the groove depth d ₁ exceeds 7 mm, the uneven wear suppression effect by the dome-shaped block land portion is likely. This is because the groove-bottom ridge 6 is not in contact with the road surface over a considerable travel distance even after the reduction of the travel distance, and uneven wear may occur.

Furthermore, the groove depth _{d 1} at the groove bottom ridges 6, the circumferential grooves 2a provided this, the block land portions 5a and 5b adjacent to 2d, 5d and 5e of the end portion 8a, the land portion at the 8b It is preferable to be in the range of 30 to 45% of the height h. This is because the effect of suppressing uneven wear by the dome-shaped block land portions 5a, 5b, 5d, and 5e is reduced, and at the same time, the groove bottom raised portion 6 is brought into contact with the road surface.

In addition, the groove depth d3 of the lateral grooves 3a and 3b, 3d and 3e adjacent to the circumferential grooves 2a and 2d provided with the groove bottom raised portion 6 is preferably in the range of ₃ to 5 mm. If the groove depth d3 of the lateral grooves 3a, 3b, 3d, and 3e is less than ₃ mm, the amount of water that can be discharged outwardly in the tire width direction is reduced through this, and the drainage performance may be impaired. This is because if it exceeds 5 mm, the block land portions 5a and 5b, 5d and 5e adjacent to the block land portion may have a reduced block rigidity and may cause uneven wear.

  As shown in FIG. 1, the groove bottom raised portion 6 is preferably provided in the circumferential grooves 2 a and 2 d located on the outermost side in the tire width direction. This is because uneven wear tends to occur in the block land portion located on the outer side in the tire width direction.

  In addition, the place mentioned above only showed a part of embodiment of this invention, and can add a various change in a claim. For example, as shown in FIG. 1, by providing the short sipe 11 in the block land portions 5a to 5e, the effect of suppressing uneven wear can be further enhanced, and the narrow groove 12 is provided in the block land portion 5c located in the central region. Although it can improve drainage by providing, these are not essential. In addition, although FIG. 1 shows an aspect with four circumferential grooves, there may be three circumferential grooves as shown in FIG. 4, although illustration is omitted, there are five or more circumferential grooves. There may be. Further, as shown in FIG. 3A, the dome-shaped land portion may have a curved surface as a whole, but as shown in FIGS. 3B to 3D, Only the part may be curved.

  Next, a pneumatic tire according to the present invention was prototyped and performance evaluation was performed, which will be described below.

  The tires of Examples 1 and 2 are radial tires for trucks having a tire size of 11R22.5, have the tread pattern shown in FIG. 4, and each of the block land portions has a dome-shaped top surface contour shape, It has the specifications shown in Table 1.

  For comparison, the tire size is the same as in Examples 1 and 2 and has a tread pattern similar to that shown in FIG. 4, but the groove bottom raised portion is in contact with the road surface from the beginning of wear, and is shown in Table 1. A tire (conventional example) was also prototyped.

  Each of the test tires is attached to a rim of size 7.50 × 22.5 to form a tire wheel. The tire wheel and a test vehicle are attached to the tire, and an air pressure of 900 kPa (relative pressure) is applied. went.

(Treatment on wet road surface)
Applying a tire load equivalent to an empty vehicle, using a wet road surface test course with a water depth of 2 mm, measure the time required to travel a distance of 15 m by accelerating from a stationary state. Traction was evaluated. The evaluation results are shown in Table 1.

(Uneven wear resistance)
Apply tire load equivalent to the maximum load capacity specified in JATMA, drive 50,000km on the highway mainly on the highway, visually inspect the tread part, measure the volume of uneven wear generated in the block land part, The uneven wear resistance was evaluated based on this measured value. The evaluation results are shown in Table 1.

  The evaluation results in Table 1 are shown as an index ratio when the evaluation result of the tire of the conventional example is set to 100. The larger the numerical value, the better the traction on the wet road surface. The smaller the numerical value, the better the performance.

  From the results shown in Table 1, it can be seen that the tires of Examples 1 and 2 are superior in drainage performance at the initial stage of wear and superior in uneven wear resistance as compared with the conventional tire.

  According to the present invention, the shape of the groove bottom raised portion and the block land portion provided in the circumferential groove is optimized, and uneven wear occurring in the block land portion is effectively suppressed from the initial stage of tire wear to the end of wear. It became possible to provide a pneumatic tire that can be used.

1 is a development view of a part of a tread portion of a typical pneumatic tire according to the present invention. (A) is sectional drawing on the II line of FIG. 1, (b) is sectional drawing on the II-II line of FIG. (A)-(d) is a perspective view when extracting one of the block land parts 5b shown in FIG. 1, and seeing from the circumferential direction groove | channel side. FIG. 6 is a development view of a part of a tread portion of another pneumatic tire according to the present invention.

Explanation of symbols

1 tread portion 2, 2a, 2b, 2c, 2d circumferential groove 3, 3a, 3b, 3c, 3d, 3e lateral groove 4a, 4b tread end 5, 5a, 5b, 5c, 5d, 5e block land portion 6 groove bottom bulge Part 7 Inland part of block land part 8a, 8b End part of block land part 9a, 9b, 9c, 9d Corner part of block land part 10 Top surface of groove bottom raised part 11 Short sipe 12 Narrow groove

Claims (7)

The tread portion is provided with a plurality of circumferential grooves extending along the tire circumferential direction and a plurality of lateral grooves communicating with at least one of the circumferential grooves, the circumferential grooves, both tread ends, In the pneumatic tire formed by dividing the tread part into a large number of block land parts by lateral grooves,
At least one circumferential groove is provided with a groove bottom ridge that has a groove depth shallower than the other part and extends along the tire circumferential direction,
The block land portion adjacent to the circumferential groove provided with the groove bottom raised portion has a curved top surface in which the land height gradually decreases from the inland portion toward at least one end portion or corner portion,
The groove bottom bulge portion has a tire radial direction outermost end in a non-contact state with the road surface at the initial stage of tire wear under a predetermined static load condition, and the tire radial direction outermost end after the middle stage of tire wear. A pneumatic tire characterized by having a groove depth in contact with the road surface.   The pneumatic tire according to claim 1, wherein a groove depth at the groove bottom raised portion is deeper than a groove depth of a lateral groove that opens to a circumferential groove provided with the groove bottom raised portion.   The pneumatic tire according to claim 2, wherein a groove depth at the groove bottom raised portion is 2 mm or more deeper than a groove depth of a lateral groove opened to a circumferential groove provided with the groove bottom raised portion.   The pneumatic tire according to any one of claims 1 to 3, wherein a groove depth at the groove bottom raised portion is in a range of 5 to 7 mm.   The groove depth at the groove bottom raised portion is in a range of 30 to 45% of a land portion height at an end portion of a block land portion adjacent to a circumferential groove provided with the groove bottom raised portion. The pneumatic tire according to any one of the above.   The pneumatic tire according to any one of claims 1 to 5, wherein a groove depth of a lateral groove adjacent to a circumferential groove provided with the groove bottom raised portion is in a range of 3 to 5 mm. The pneumatic tire according to any one of claims 1 to 6, wherein a groove bottom raised portion is provided in a circumferential groove located on the outermost side in the tire width direction.

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