Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-07-20
2004-09-07
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209230, C152S902000, C152SDIG003
Reexamination Certificate
active
06786257
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a pneumatic tire which exhibits an excellent performance on ice and snow.
BACKGROUND TECHNOLOGY
Conventionally, a pneumatic tire which is provided with a plurality of blocks on a tread surface, wherein the blocks are defined by main grooves formed in the tire circumferential direction, lug grooves formed in the tire transverse direction and the like has existed. By providing blocks on a tread surface in such a manner, a pneumatic tire ensures favorable braking and traction force, steering stability and the like.
Also, improvement in performance on ice and snow and a wet property has been attempted by providing sipes in the blocks to increase an edge length and to increase gripping force.
Further, under the tread surface of the pneumatic tire formed in this way, reinforcing layers in which a number of steel cords are provided parallel to each other are laminated in order to strengthen stiffness of the tread.
In the pneumatic tire structured as described above, the contact patch area side of each block is divided by sipes into a plurality of small blocks. When the tire rotates, each of the small blocks tends to lean backward due to the frictional force exerted between itself and the road surface. When the degree of leaning becomes large, a contact patch area area of the contact patch area decreases, so that there is a possibility that the performance on ice and snow may deteriorate.
However, the small blocks are compressed in a height direction (the direction oriented toward the tire axis from the contact patch area) by ground contact pressure from the contact patch area and expand in a cross direction (the direction perpendicular to the height direction). As a result, the small blocks abut the adjacent small blocks across the sipes, so that leaning thereof is suppressed to a certain extent.
However, if the sipes are formed straight in the sipe depth direction, deformation of the small blocks due to ground contact is not capable enough of causing the small blocks to contact the adjacent small blocks with sufficient force. Accordingly, leaning suppression is weak and thus it can hardly be said that contact patch area area of the contact patch area is sufficiently ensured.
Further, a plurality of steel cords disposed in each of the reinforcing layers are provided parallel to each other and inclined at a predetermined angle with respect to the tire circumferential direction. Thus, there has been a problem in that when a vehicle on which the pneumatic tires are actually fitted is driven, the steel cords provided in the reinforcing layer closest to the tread surface side lean toward the tire circumferential direction, thereby generating a force to restore the tire distorted by ground contact pressure to the original shape (Self Alignment Torque, referred to as SAT hereinafter).
In view of the above-described circumstances, an object of the present invention is to provide a pneumatic tire which exhibits an excellent performance on ice and snow by suppressing leaning of blocks having sipes, and which suppresses SAT.
DISCLOSURE OF THE INVENTION
A first aspect of the present invention is a pneumatic tire comprising: a plurality of reinforcing layers in which cords, which are inclined at a predetermined angle with respect to a tire circumferential direction, are provided parallel to each other; a tread provided on a top of the reinforcing layers which are laminated; and a block-shaped land portion having a sipe, the block-shaped land portion being defined on a tread surface by main grooves formed in the tire circumferential direction and by lug grooves formed in a direction intersecting the main grooves; wherein the sipe is shaped so as to be twisted around a first central axis of twisting extending in a tire radial direction in the block-shaped land portion and a second central axis of twisting extending substantially in a tire transverse direction, a position P
1
of the first central axis of twisting in a region between one end surface of the block-shaped land portion and another end surface in the tire transverse direction and a position P
2
of the second central axis of twisting in a region between a contact patch area and a bottom of the sipe in the tire radial direction being within ranges satisfying the following relational expressions:
0.2 W≦P
1
≦0.8 W
0.2 F≦P
2
≦0.6 F
wherein P
1
, P
2
represent the position of the first and second central axes of twisting respectively; W represents a distance from the one end surface to the other end surface of the block-shaped land portion in the tire transverse direction; and F represents a distance from the contact patch area to the bottom of the sipe in the tire radial direction.
In the first aspect of the invention, since the sipe is shaped so as to be twisted around the first central axis of twisting extending in the tire radial direction and the second central axis of twisting extending substantially in the tire transverse direction, the block-shaped land portion is compressed in a height direction due to ground contact pressure and expands in a cross direction, and as a result, small blocks divided by the sipe abut each other. Moreover, since the sipe is twisted, the small blocks abut each other not only due to a force exerted in the tire circumferential direction (the tire rotation direction), but also due to forces exerted from other directions. Further, since the small blocks perform a rotational motion due to ground contact pressure, the adjacent small blocks abut each other with a strong force.
Moreover, the position P
1
of the first central axis of twisting is within the range of 0.2 W≦P
1
≦0.8 W with respect to a distance W (referred to as width W hereinafter) from one end surface to the other end surface of the block-shaped land portion in the tire transverse direction, and the position P
2
of the second central axis of twisting is within the range of 0.2 F≦P
2
≦0.6 F with respect to a distance F (referred to as sipe depth F hereinafter) from the contact patch area to the bottom of the sipe in the tire radial direction, and because of this positioning, stiffness of the small blocks increases further and leaning thereof is suppressed compared to structures with positioning in which the first central axis of twisting and the second central axis of twisting are located at positions not within the above-mentioned ranges (see FIG.
24
and FIG.
25
).
In this way, the small blocks abut each other with a strong force due to the sipes being formed with a twist, and stiffness of the small blocks can be increased by positioning the first central axis of twisting and the second central axis of twisting of the sipe within the predetermined ranges. Accordingly, leaning can be suppressed with certainty. As a result, a contact patch area area on the contact patch area of the small blocks increases, and performance on ice and snow improves.
Further, when ground contact pressure acts on the contact patch area of the block-shaped land portion, the block-shaped land portion is compressed in the height direction, so that each of the small blocks, while guided by the sipe, rotationally deforms in a direction in which the sipe is further twisted. Due to this deformation, an SAT (a torque for restoring the small blocks to the original shapes) exerted in a direction opposite to the twisting direction of the sipe is generated on each of the small blocks.
Thus, by forming the block-shaped land portion, in which the sipes are twisted in an appropriate direction, on the tread surface, the SAT generated by an inclination, relative to the tire circumferential direction, of the cords which form an outermost layer of the reinforcing layers is reduced. That is, the SAT due to the cords can be suppressed by the SAT generated at the block-shaped land portion.
Accordingly, a favorable steering stability on icy and snowy roads and the like can be obtained with a vehicle to which such pneumatic tires are mounted.
A second aspect is a pneumatic tire comprising: a plurality of reinforcing l
Bridgestone Corporation
Maki Steven D.
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