Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-01-15
2001-03-20
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209280, C152SDIG003, C425S028100, C425S035000, C425S046000
Reexamination Certificate
active
06202725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic tire comprising a tread provided on its land portion or block with a plurality of sipes each cut into a radial direction of the tire and extending substantially in a widthwise direction of the tread and developing excellent wet performances, performances on the ice and the like. This invention also relates to a vulcanization mold used for manufacturing the tire.
2. Description of Related Art
For example, if the sipe is formed in the block, the rigidity of the block having the sipe is necessarily lowered as compared with that of the block having no sipe, whereby it is apt to cause uneven wear such as heel and toe wear or the like. In order to control of the occurrence of such an uneven wear, for example, JP-A-5-58118 has proposed a technique wherein a convex portion is formed in a wall face of the sipe formed in the block to extend in the widthwise direction of the tire and a dimple engaging with such a convex portion is formed in the other wall face of the sipe. This publication discloses that according to this technique, sub-block portions of the block divided by the sipe control the falling with each other based on the engagement between the convex portion and the dimple in the application of braking force to the tire and hence the fallen quantity can be decreased to shorten the braking distance in case of braking on a frozen road surface and control the occurrence of heel and toe wear on a dry road surface.
In such a conventional technique, however, the sizes of the convex portion and the dimple to be formed on the sipe wall faces are small. Hence it is difficult to always produce a reliable engagement of both and hence there is highly caused a fear of providing no given effect. Additionally, when the braking force is applied to the tire, as shown in
FIG. 5
, the convex portion p of the sipe wall face is engaged with the dimple d of the opposite sipe wall face to restrain the fallings of the sub-blocks sb to each other as shown in
FIG. 5
a
. On the other hand, when the traction force is applied to the tire, the engagement between the convex portion and the dimple is loosened to decrease the restraining force against the falling of the sub-block sb as shown in
FIG. 5
b
. In the conventional tire, therefore, there is a problem that uneven wear is unavoidably caused in the application of the traction force.
SUMMARY
0
F THE INVENTION
It is, therefore, an object of the invention to solve the above problem of the conventional technique and to provide a pnenmatic tire capable of always and effectively stopping the falling deformation of land portions defined by sipes irrespectively of braking and traction states to effectively prevent the occurrence of uneven wear as well as a vulcanization mold used for the manufacture of such a tire.
According to a first aspect of the invention, there is the provision of a pneumatic tire comprising a tread provided on its land portion with a plurality of sipes each cut into a radial direction of the tire and extending substantially in a widthwise direction of the tread, in which one of opposed wall faces of the sipe is a concave face arc-shapedly curved over a whole of the sipe in a depth direction thereof at a section in a normal direction with respect to the tread surface and the other wall face of the sip* is a convex face just fitted to the above concave face, and a curvature of each of the concave and convex faces is substantially constant over a full length in a longitudinal direction of the sipe.
In such a pneumatic tire, the concave face and the convex face are formed over the whole of the wall face of the sipe in the depth direction and the longitudinal direction thereof, respectively. Also, the sizes thereof are fairly large as compared with those of the conventional technique, so that the fitting of the convex face into the concave face is carried out smoothly and surely. Even if a top of the convex face does not surely correspond to a valley of the concave face, such a top is always contacted with any portion of the concave face, so that the falling deformation of the land portions defined by the sipe are sufficiently restrained by engaging the land portions with each other. This is caused in both the application of braking force to the tire and the application of traction force to the tire, so that the occurrence of uneven wear in the land portion can effectively be prevented.
In the invention, it is enough to arrange the sipe having the concave face and the convex face at its opposed wall faces in at least a shoulder region for controlling the occurrence of uneven wear, particularly step-wise wear at this region. If necessary, when sipes existing in the side region and central region of the tread are also rendered into the structure having a concave face and a convex face at opposed wall faces, the effect of preventing the occurrence of uneven wear can be more improved. In the pneumatic tire, the sipes open at one widthwise end to a circumferentially extending groove. The sipes open at another widthwise end to a second circumferentially extending groove. At the tread surface, each of the sipes are arcuate. The sipes are aligned at a widthwise end with laterally extending grooves. The land portion is separated from another land portion by a circumferentially extending groove and the sipes are aligned with sipes in the another land portion.
According to a second aspect of the invention, there is the provision of a vulcanization mold comprising a plurality of blades for the formation of sipes, each of the blades projecting inward in a radial direction on a mold surface for the formation of a land portion of a tire tread and extending substantially in a widthwise direction of the tread, said blade being rendered into a curved shape arc-shapedly curving over a whole of the blade at a section in a direction perpendicular to an extending direction of a top face of the blade and the curved shape being substantially constant over a length of the blade in a longitudinal direction thereof.
In such a vulcanization mold, a sipe having a concave face and a convex face at its opposed wall faces can be formed simply and easily and exactly by the action of the blade arc-shapedly curved over a whole of the blade in the projecting direction.
Since the blade has a curved shape over the whole thereof in the projecting direction, the depth of the concave face and the height of the convex face in the wall faces of the sipe can sufficiently be made large. On the other hand, the gradient of the curved shape of the blade is made sufficiently small, whereby the resulting vulcanized tire can easily and smoothly be taken out from the mold.
Moreover, the curved shape of the blade is substantially constant over the full length thereof and the blade itself has substantially a simple gutter shape, so that the blade having given shape and size can be produced fairly simply, easily and exactly as compared with a case of gradually changing a form of the blade at any positions in the projecting direction and at any positions in the longitudinal direction.
It is favorable that the curved shape of the blade has a relation of d≧2t wherein d is a most depth of an inner concave face in the projecting direction and t is a thickness of the blade.
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Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
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