Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-02-16
2004-03-16
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209120, C152S209280
Reexamination Certificate
active
06705366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic tire and more particularly to a pneumatic radial tire for use in relatively small-size vehicles such as passenger cars, racing cars running on a circuit course and the like designating a rotation direction by a directional tread pattern and having excellent running performances. Especially, the invention relates to a pneumatic radial tire simultaneously and highly establishing a steering stability at wet state inclusive of a resistance to hydroplaning (hereinafter referred to as wet steering performance) and a steering stability at dry state (hereinafter referred to as dry steering performance) while predominantly maintaining other performances such as pattern noise and the like.
2. Description of Related Art
In the conventional high-performance tire having excellent running performances, it is particularly demanded to have an excellent wet steering performance and the following means are applied for satisfying such a demand.
(1) An application of a directional tread pattern as shown in
FIG. 4
, which is defined by a combination of straight circumferential main grooves
21
,
22
and a narrow-width straight circumferential sub-groove
23
, notch grooves
24
each extending from the main groove
21
toward a central rib, slant grooves
25
each extending from the main groove
21
and opening to the main groove
22
and slant grooves
26
extending from the main groove
22
and opening to an end TE of a tread portion, wherein the slant grooves
25
,
26
are inclined in the shape of an unfolded fan from a position near to an equatorial plane E of the tire toward their opening ends and blocks
27
,
28
are defined by these main grooves
21
,
22
and slant grooves
25
,
26
;
(2) An application of means for increasing a negative ratio (ratio of groove area to whole area of a ground contact face) by widening a groove width in at least one of the circumferential grooves
21
to
23
, or by increasing the number of the slant grooves
25
,
26
arranged or by widening a groove width of the slant groove
25
,
26
in order to improve the resistance to hydroplaning in the running on wet road surface;
(3) An application of sharply slant grooves wherein an inclination angle is particularly made small with respect to the equatorial plane E in a central zone of the tread portion different from the gently slant grooves
25
,
26
shown in
FIG. 4
in order to more facilitate the drainage in lateral direction when water entered into the ground contact face of the tread portion is drained in front-back direction (forward running direction) by the circumferential grooves
21
to
23
and in lateral direction by the slant grooves
25
,
26
.
On the other hand, the high-performance tire is demanded to have an excellent dry steering performance, so that the following means are applied while improving the wet steering performance.
(4) Means of forming an upheaved bottom portion (platform) in a part of the slant groove
25
,
26
from a viewpoint of the requirement for enhancing rigidity of the block
27
,
28
;
(5) Means of enhancing a lateral rigidity of a shoulder block
28
for improving the steering stability in quick steering as exemplified by the running on the circuit course; and the like.
However, the aforementioned various means cause the following problems from a viewpoint of the wet steering performance and other performances.
(a) As being represented by the circumferential main grooves
21
,
22
for draining in the front-back direction and the gently slant grooves
25
,
26
or sharply slant groove for draining in the lateral direction, waters flowing from these grooves collide with each other in a joint part between the circumferential main groove and the slant groove having different inclination angles with respect to the equatorial plane E irrespectively of branching or joining of the groove. As a result, the joint part causes disturbance of the water flow to generate bubbles, which considerably degrades the drainage performance and lowers the resistance to hydroplaning.
(b) The upheaved bottom portion applied to the sharply slant groove for enhancing the block rigidity forms a dam against the water flow in the slant groove to degrade the drainage performance. On the other hand, if the upheaved bottom portion is removed, the block rigidity lowers to degrade the steering stability.
(c) When the main groove
22
is located in a ¼ point of the ground contact face or in the vicinity of a position separated from the equatorial plane E by a distance corresponding to ¼ of a developed width of the ground contact face as shown in
FIG. 4
, the tread portion causes a buckling phenomenon about the main groove
22
during the cornering and hence both the dry and wet steering performances are degraded.
(d) In case of the block defined by the sharply slant grooves having no joint part with the other groove along the way, the ground contacting property is lowered and it is apt to degrade the ride comfort and the resistance to irregular wear.
(e) The increase of the negative ratio produces many problems such as rise of pattern noise level, degradation of the steering stability due to the decrease of block rigidity, occurrence of irregular wear, degradation of wear resistance and the like.
The inventor has already proposed the following pneumatic tire in JP-A-9-2025 in order to simultaneously and advantageously improve the aforementioned wet steering performance inclusive of resistance to hydroplaning, dry steering performance and pattern noise while predominantly maintaining the wear resistance including resistance to irregular wear.
Such a pneumatic tire has a tread pattern wherein a pair of circumferential main grooves are arranged in a central region of a tread portion and a plurality of main slant grooves are extended obliquely from each of the circumferential main grooves toward an end of the tread portion in the same direction with respect to the circumferential main groove and opened to a ground contact end of the tread portion, wherein each of the main slant grooves consists of a sharply slant segment located in the neighborhood portion of the central region and a gently slant segment located in the neighborhood portion of the ground contact end of the tread portion, and an inclination angle of the sharply slant segment with respect to the circumferential direction of the tread portion is 0-30° and an inclination angle of the gently slant segment with respect to the circumferential direction of the tread portion is 70-90°, and a surface height of a tapered end portion of a land part defined by the circumferential main grooves and the main slant groove and located at the side of the central region is smoothly decreased toward the side of the tapered end.
SUMMARY OF THE INVENTION
The invention is concerned with an improvement of the above proposed pneumatic tire and mainly aims at more enhancing the drainage performance during the cornering, and is to provide a pneumatic tire more improving the wet steering performance inclusive of the resistance to hydroplaning together with the dry steering performance under all running modes inclusive of straight running and cornering while predominantly maintaining other performances such as low pattern noise and the like.
According to the invention, there is the provision of a pneumatic tire having a directional tread pattern of a designated rotating direction comprising at least one main groove extending in a circumferential direction at a central region of a tread portion, a sub-groove extending in the circumferential direction at each of side regions of the tread portion sandwiching the central region therebetween, a plurality of slant grooves extending from the main groove through the sub-groove toward an end of the tread portion in the shape of an unfolded fan and opening at the end of the tread portion, and blocks defined by these grooves, in which a central block located nearest to an equatorial plane of the tire has such a headland part t
Bridgestone Corporation
Maki Steven D.
Sughrue & Mion, PLLC
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