Resilient tires and wheels – Tires – resilient – With wear indicating feature
Reexamination Certificate
2001-09-12
2004-05-18
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
With wear indicating feature
C152S209400, C152S209500, C152S458000
Reexamination Certificate
active
06736174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire in which heat-generation can be controlled and tire wear resistance can be improved simultaneously. More particularly, the present invention relates to a pneumatic tire suitable for off-the-road, for example vehicle for construction in which deterioration in tire wear resistance is minimized and tire life can be prolonged by suppressing generation of heat.
2. Description of the Related Art
Conventionally, in order to suppress generation of heat in a tread of a pneumatic tire, physical properties of a rubber material of a tread rubber layer have been controlled.
However, because deterioration in tire wear resistance generally arises in tread rubbers which have physical properties controlled so as to suppress generation of heat, it was difficult to suppress generation of heat without causing any deterioration of tire wear resistance.
SUMMARY OF THE INVENTION
In view of the aforementioned facts, an object of the present invention is to provide a pneumatic tire in which generation of heat can be suppressed without causing any deterioration of tire wear resistance.
In order to attain the above object, a first aspect of the present invention is a pneumatic tire which comprises: a tread portion constituted with a tread rubber layer and including grooves formed at a radially outer surface thereof i.e., a tread surface of a tire; and a thin tread reinforcing layer provided at a middle portion, in the thickness direction (“the thickness direction” indicates the direction normal to the tread surface as the ground-contacting portion hereinafter), of the tread rubber layer so as to extend over at least one portion of the tread rubber layer in the tire widthwise direction thereof, the tread reinforcing layer being composed of a material (such as rubber) having larger tensile modulus of elasticity than that of a rubber composing the tread rubber layer. Note that the aforementioned expression of “the middle portion” indicates the middle portion of a gauge of the tread rubber layer in the thickness direction.
A pneumatic tire according to the first aspect achieves the following effects.
FIG. 14A
is a schematic view of a conventional tread rubber layer. The tread rubber layer
100
, when contacting the ground, undergoes compressive deformation in the vertical direction thereof due to force F, and a middle portion of the tread rubber layer
100
in the vertical direction thereof expands in the lateral direction.
When a tire rotates during running, the tread rubber layer
100
repeatedly undergoes the above-described deformation and generates heat.
As shown in
FIG. 14B
, the pneumatic tire according to the present aspect includes a tread reinforcing layer
102
(for example, the tread reinforcing rubber layer) which is composed of a material (e.g., rubber) having larger tensile modulus of elasticity, i.e., being less stretchable than a rubber composing the tread rubber layer
100
, at the middle portion of the tread rubber
100
in the vertical (thickness) direction thereof. The tread reinforcing layer
102
suppresses the lateral expansion of the tread rubber layer
100
. As a result, the compressive deformation of the tread rubber layer
100
is also suppressed.
As the amount of lateral expansion and the amount of vertical compressive deformation is decreased, generation of heat in the tread rubber layer can be suppressed.
According to the present aspect, providing the tread reinforcing layer (the aforementioned tread reinforcing rubber layer, for example) can effectively suppress generation of heat in the tread rubber layer. In the case of a tread structure which includes the tread reinforcing rubber layer as described above, in addition to suppression of heat-generation, tire wear resistance can be ensured by choosing the rubber having physical property for tire wear resistance of the tread rubber layer. Thus, suppression of heat-generation is readily achieved without causing any deterioration of tire wear resistance.
In a second aspect of the present invention, in the pneumatic tire having the first aspect, a thickness of the tread reinforcing layer is in a range of from 2 to 5% of a thickness of the tread rubber layer.
A pneumatic tire according to the second aspect achieves the following effects.
When the thickness of the tread reinforcing layer is less than 2% of the thickness of the tread rubber layer, the capacity of the tread reinforcing layer to suppress the lateral expansion of the tread rubber layer is lowered.
On the other hand, when the thickness of the tread reinforcing layer exceeds 5% of the thickness of the tread rubber layer, the influence of the wear resistance of the tread reinforcing layer on the wear property of the entire tread rubber layer will increase to such an extent that it cannot be ignored. In addition, the influence of the heat generated by the tread reinforcing layer on the heat-generation property of the entire tread rubber layer will increase to such an extent that it cannot be ignored.
Accordingly, it is preferable to set the thickness of the tread reinforcing layer to the range of from 2 to 5% of the thickness of the tread rubber layer.
In a third aspect of the present invention, in the pneumatic tire having the first and second aspects and including the tread reinforcing rubber layer, tensile stress at 50% elongation of the rubber composing the tread reinforcing rubber layer is in a range of from 2 to 4 times as large as the tensile stress at 50% elongation of the rubber composing the tread rubber layer.
A pneumatic tire according to the third aspect achieves the following effects.
When the tensile stress at 50% elongation of the rubber composing the tread reinforcing rubber layer is less than 2 times as large as the tensile stress at 50% elongation of the rubber composing the tread rubber layer, the capacity of the tread reinforcing rubber layer to suppress the lateral expansion of the tread rubber layer is lowered.
On the other hand, when the tensile stress at 50% elongation of the rubber composing the tread reinforcing rubber layer exceeds 5 times as large as the tensile stress at 50% elongation of the rubber composing the tread rubber layer, there is a possibility that the rubber layers of different types (physical properties) separate from each other.
Accordingly, it is preferable to set the tensile stress at 50% elongation of the rubber composing each tread reinforcing rubber layer to the range of from 2 to 4 times as large as the tensile stress at 50% elongation of the rubber composing the tread rubber layer.
In a case in which a plurality of tread rubber layers are used, the tensile stress at 50% elongation of each tread reinforcing rubber layer must be set to the range of from 2 to 4 times as large as a tensile stress at 50% elongation of an adjacent rubber composing the tread rubber layer.
In a fourth aspect of the present invention, in the pneumatic tire having any one of above aspects, the tread rubber layer is made up of a plurality of rubber layers stacked in the tire radial direction, and each of the plurality of rubber layers has different physical properties.
A pneumatic tire according to the fourth aspect achieves the following effects.
If only one type of rubber is used, there may be cases where properties which are incompatible to each other cannot be improved simultaneously. In the pneumatic tire according to the present aspect, however, tire wear resistance and suppression of heat-generation can be further improved, simultaneously, with a structure in which, for example, an outer layer in the tread rubber layer at a ground-contact surface side thereof is composed of an NR-based or a SBR-based cap rubber which improves tire wear resistance, and an inner layer in the tread rubber layer near a carcass side thereof is composed of an NR-based base rubber which suppresses generation of heat.
In a fifth aspect of the present invention, in the pneumatic tire having any one of above aspects, a position depth that is a distance from the tr
Inoue Takumi
Kusano Tomohiro
Bridgestone Corporation
Maki Steven D.
LandOfFree
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