Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2001-10-19
2004-03-09
Aftergut, Jeff H. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S541000, C152S542000, C152S543000, C152S546000, C152S547000, C152S552000
Reexamination Certificate
active
06701988
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic radial tire, and more particularly to a heavy duty radial tire having an aspect ratio of no more than 60% and largely improving the durability of the bead portion.
2. Description of Related Art
In the pneumatic radial tire running under loading, a pair of sidewall portions located in correspondence to a ground contact face are largely bent, while a bead portion located outward from a rim flange in a radial direction of the tire is deformed toward the outside of the tire or so-called deformation phenomenon of the bead portion is caused, whereby a large compression strain is applied to a turn-up end portion of a carcass ply existing in the bead portion or the sidewall portion.
As a countermeasure for such a compression strain, JP-A-5-16618, JP-A-8-324214 and the like propose an improvement in the structure of a stiffener composed of a soft rubber stock and a hard rubber stock, and an improvement of a cushion rubber arranged at an outside of a turn-up portion of a carcass ply in the widthwise direction of the tire, whereby the improvement of the durability of the bead portion is realized.
On the other hand, the deformation in the circumferential direction is caused at zones ranging from the bead portion to the sidewall portion located in correspondence to a stepping-in part and a kicking-out part of the tread portion in the ground contact face of the tire, respectively, whereby a shearing strain in the circumferential direction is created in the turn-up portion of the carcass ply.
Such a shearing strain can be mitigated by selecting an arranging conformation of the hard rubber stock in the stiffener as disclosed in JP-A-8-225005, whereby the durability of the bead portion can be enhanced.
Recently, the lowering of the aspect ratio of the tire, the increase of the tire size and the like are advanced even in tires for heavy duty vehicles such as trucks, buses and the like and also, the number of tire recappings is increased to increase total input to the bead portion accompanied with the running of the tire under loading. For this end, the durability of the bead portion tends to be lacking even in the aforementioned countermeasures. This is particularly serious in the large-size tires having an aspect ratio of no more than 60%.
That is, the above problem is considered due to the fact that the shearing strain in the circumferential direction is increased in the vicinity of the turn-up end of the carcass ply because the length of a zone ranging from a portion of a maximum tire width to a buttress portion in the cross section, which effectively contributes to absorb the deformation in the circumferential direction of the tire, is decreased accompanied with the lowering of the aspect ratio of the tire, and also the absolute amount of deformation in the circumferential direction in the traction and braking or the shearing strain in the circumferential direction is increased under an advancement in performances of the vehicle and the tire, the increase of the tire size and the like.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a pneumatic radial tire largely improving the durability of the bead portion by decreasing the shearing strain in the circumferential direction in the vicinity of the turn-up portion of the carcass ply.
According to the invention, there is the provision of in a pneumatic radial tire having an aspect ratio of no more than 60% and comprising at least one carcass ply composed of a main body portion extending between a pair of bead cores each embedded in the respective bead portion and a turn-up portion wound outward around each bead core in a radial direction of the tire, a stiffener arranged between the main body portion and the turn-up portion on an outside of the bead core in the radial direction of the tire, extending outward in the radial direction of the tire, and made of a soft rubber stock and a hard rubber stock, and a reinforcing member extending at an outside of the turn-up portion in a widthwise direction of the tire through a cushion rubber, the improvement wherein when the tire is inflated under an air pressure corresponding to 10% of a maximum air pressure, a height of an outer end of the turn-up portion in the radial direction is no more than 0.33 times a section height of the carcass ply, and a ratio of a thickness between the main body portion and the reinforcing member to a thickness between the main body portion and the outer end of the turn-up portion in the radial direction as measured on a normal line drawn from the outer end of the turn-up portion in the radial direction onto an outer surface of the main body portion is within a range of 1.2-1.8, preferably 1.3-1.7.
Moreover, the term “section height of the carcass ply” used herein means a height when measuring along the radial direction of the tire between an innermost position of the carcass in the radial direction and an outermost position thereof.
And also, the term “maximum air pressure” used herein means an air pressure corresponding to a maximum load capacity defined in JATMA YEAR BOOK. When the tire is inflated under the air pressure, the tire is first mounted onto an approved rim defined in JATMA YEAR BOOK.
Although the tire having the aspect ratio of no more than 60% is particularly serious in the lacking of the durability of the bead portion, according to the invention, the height of the outer end of the turn-up portion of the carcass ply in the radial direction is made no more than 0.33 times the section height of the carcass ply, whereby force suppressing the deformation of the tire through the rim flange is sufficiently applied to a portion located in the vicinity of the outer end of the turn-up portion in the radial direction under an action of the bead core at a state of mounting the tire onto the rim to advantageously decrease the deformation in the circumferential direction of the portion located in the vicinity of the outer end of the turn-up portion in the radial direction and hence the shearing strain in the circumferential direction, so that the separation of the outer end of the turn-up portion in the radial direction can effectively be prevented. In other words, when the height of the outer end of the turn-up portion in the radial direction is more than 0.33 times, the outer end of the turn-up portion can not sufficiently be subjected to the force suppressing the deformation of the tire through the rim flange.
And also, according to the invention, the ratio of the thickness between the main body portion and the reinforcing member to the thickness between the main body portion and the outer end of the turn-up portion in the radial direction is made 1.2-1.8, more preferably, 1.3-1.7, whereby the reinforcing member is arranged so as to sufficiently be distant outward from the outer end in the radial direction to the outer portion in the widthwise direction of the tire in which the torsion deformation at a ground contact area is large under loading to thereby largely improve the reinforcing effect by the reinforcing member, whereby the amount of deformation in the circumferential direction can advantageously be decreased. That is, the reinforcing member more reinforces the bead portion to the deformation in the circumferential direction under the decrease of the absorption area thereof resulted from the lowering of the aspect ratio of the tire, so that the shearing strain in the circumferential direction in the vicinity of the outer end of the turn-up portion can effectively be decreased.
Therefore, when the ratio is less than 1.2, it is difficult to sufficiently develop the reinforcing function through the reinforcing member, while when it exceeds 1.8, the quantity of heat generation in the cushion rubber between the turn-up portion and the reinforcing member is increased to prematurely promote the thermal deterioration due to the rise of temperature during the running and hence the durability is not totally improved.
In a preferable embodiment of
Aftergut Jeff H.
Bridgestone Corporation
Fischer Justin
Sughrue & Mion, PLLC
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