Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1998-07-28
2001-02-06
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209180, C152S902000, C152SDIG003
Reexamination Certificate
active
06182726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heavy duty pneumatic tire for use in heavy vehicles such as truck, bus and the like having an excellent resistance to uneven wear without increasing noise generated, and more particularly to a heavy duty pneumatic tire having a block pattern.
2. Description of Related Art
In the conventional heavy duty pneumatic tire having a block pattern, the occurrence of uneven wear called as heel and toe wear has been controlled by making a worn amount at a stepping-in side portion of the block large and a worn amount at a kicking-out side region of the block small. That is, when only one block b is schematically shown as a perspective view in
FIG. 5
, it has substantially a semicylindrical shape that an outer profile of the block b at a section perpendicular to a rotating axis of the tire is rendered into an arc shape having a radius of curvature smaller than an outer profile of the tire to lower each of heights at a stepping-in side S and kicking-out side R as compared with the other remaining portion of the block.
In such a conventional technique, it is recognized to improve the heel and toe wear, but when the worn amount at the kicking-out side R is observed in a widthwise direction of the block on and after the middle worn stage, it becomes larger at a side of a tread center rather than at a side of a tread end and hence it is difficult to effectively control the heel and toe wear throughout wear life of the tire. And also, there is a problem that noise is considerably deteriorated as compared with the case of tires not taking the above countermeasure for the uneven wear.
The latter is due to the fact that the stepping-in side portion of the block contacts with ground as a line before the adoption of the countermeasure for the uneven wear but contacts with ground as a plane after the adoption of the above countermeasure.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to solve the afore-mentioned problems of the conventional technique and to provide a heavy duty pneumatic tire advantageously improving the resistance to uneven wear from an initial worn stage up to a last worn stage without increasing noise as in a conventional tire.
According to the invention, there is the provision of a heavy duty pneumatic tire comprising block rows defined in a tread by a plurality of circumferential grooves continuously extending in a circumferential direction of the tread and a plurality of lateral grooves preferentially extending in a widthwise direction of the tread and opening to the circumferential grooves, in which each block in at least one block row other than a block row located astride a center of the tread is provided on two corner portions at a side of a tread end and in the circumferential direction with chamfered regions each gradually decreasing a height of the block toward a tip of the respective corner portion.
The word “block row located astride a center of the tread” used herein means a block row of many blocks that the tread center locates at a widthwise center of each of the blocks or in the vicinity of the widthwise center of the block, but does not include a case that the tread center locates in the vicinity of a widthwise end of each block in the block row.
Further, the word “chamfered region” used herein may include an upwardly somewhat convex curved surface in addition to a slantly flat surface.
In the pneumatic tire according to the invention, the occurrence of heel and toe wear can be advantageously controlled at a portion of the block located at the side of the tread end by easily slipping the stepping-in side through the chamfered region formed in the stepping-in side portion likewise the kicking-out side. Wearing in the portion of the block located at the side of the tread center can effectively be controlled by gradually decreasing the chamfered region in the block located at the side of the tread center to relatively increase the ground contact pressure and hardly cause the slippage, and finally the whole of the block can balancedly be worn from an initial stage up to last stage.
Also, in the pneumatic tire according to the invention, the chamfered regions are formed in only two corner portions of the block facing to the side of the tread end, whereby the ground contact form in the kicking-out side of the block, particularly in the portion of the block located at the side of the tread end can be rendered into an approximately linear form to largely reduce the generated noise as compared with the conventional technique.
In such a pneumatic tire, it is preferable that the chamfering length of the block on a side edge located at the side of the tread end, i.e. the length forming the chamfered region is within a range of 0.3-0.5 times the length between both tips of the corner portions in the circumferential direction of the tread as measured from the tip of the corner portion in the circumferential direction.
Furthermore, it is preferable that the chamfering length of the block on a side edge in the widthwise direction of the tread is within a range of 0.2-0.8 times the length between a tip of a corner portion located at the side of the tread end and a tip of a corner portion located at the side of the tread center in the widthwise direction of the tread as measured from the tip of the corner portion located at the side of the tread end in the widthwise direction.
When the chamfering length on the side edge located at the side of the tread end is within a range of 0.3-0.5 times, the slippage at the stepping-in side can be more sufficiently ensured to effectively improve the resistance to uneven wear. That is, when it is less than 0.3 times, the chamfered region is too small and the effect of improving the resistance to uneven wear is less, while when it exceeds 0.5 times, the chamfered regions from both tips of the corner portions are overlapped with each other to lower the effect by the formation of the chamfered region.
When the chamfering length on the side edge in the widthwise direction of the tread is within a range of 0.2-0.8 times, the increase of the generated noise can be prevented while sufficiently ensuring the slippage at the stepping-in side. That is, when it is less than 0.2 times, the chamfered region is too small and the occurrence of uneven wear can not be decreased to an expected level. When it exceeds 0.8 times, the chamfered region is too large and the increase of the generated noise can not be avoided.
In the pneumatic tire according to the invention, it is preferable that a decreasing quantity of the block height in the chamfered region is within a range of 0.5-3.0 mm, whereby the slippage of the block at the stepping-in side is more sufficient. When the decreasing quantity of the block height is less than 0.5 mm, it is difficult to provide the slipping easiness of the block at the stepping-in side. When it exceeds 3.0 mm, the decreasing quantity of the block volume is too large and it may be inconvenient from a viewpoint of total service life of the tire even if the effect of improving the resistance to uneven wear is expected.
More preferably, a fine groove extending in parallel to the lateral groove and having depth and width fairly smaller than those of the other groove is formed in a highest portion of the block. In this case, the drainage property and function of cutting water film are enhanced by the fine groove itself and the edge thereof to more improve the wet performance of the tire.
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patent: 5-319025 (1993-12-01), None
patent: 7-186633 (1995-07-01), None
patent: 7-304309 (1995-11-01), None
Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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