Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2000-10-26
2003-03-04
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209220, C152S902000, C152SDIG003
Reexamination Certificate
active
06527023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an all-season pneumatic radial tire which can maintain steering stability and resistance to uneven wear on a dry road, a high performance of traction on a snow-covered road, and an improved resistance to wandering on a rainy road, throughout the whole period from the beginning to the end of its use.
2. Description of the Related Art
The provision of a light truck, particularly a sport utility vehicle (SUV) having a large body weight, has recently brought about a demand for the provision of all-season pneumatic tires having a high block rigidity as required for withstanding the weight of the vehicle body, and yet showing an excellent performance on a snow-covered road.
There is known a pneumatic radial tire having blocks defined by a plurality of circumferentially extending main grooves and a multiplicity of transverse grooves spaced apart from one another along the circumference of the tire. This type of tire usually has sipes formed in the blocks and extending along its width for achieving an improved traction on a snow-covered road, an improved resistance to wandering on a rainy road, a reduction of pattern noise made by the tread contacting the ground and an improved riding comfort.
There have been proposed various forms of sipes, and they can be classified mainly into OA and OB types by their cross sectional shape along their depth.
Examples of OA type sipes are shown at
801
and
802
in
FIGS. 4 and 5
. The sipes
801
and
802
made in two adjoining blocks
401
and
402
, respectively, which are separated from each other by a circumferentially extending main groove
201
, have portions
801
a
and
802
a
opening in the main groove
201
for connecting the sipes therewith, and having a horizontally straight cross section with a small depth above shelves
901
a
and
902
a
formed on the blocks
401
and
402
. The sipes
801
and
802
have inwardly of the connecting portions
801
a
and
802
a
inner portions
801
b
and
802
b
cut with a greater depth and having a substantially semi-circular, or rectangular cross section. Tires having OA type sipes formed in the blocks are used mainly in summer, or throughout the year.
FIG. 4
also shows a tread
101
, circumferentially extending grooves
701
having a smaller open width than the main grooves
201
, and transverse grooves
301
. It also shows shoulder ends
501
and
502
, and a tire centerline TC. It also shows by an arrow R the direction in which the circumference of the tire extends.
Examples of OB type sipes are shown in FIGS.
7
(
a
0
) and
7
(
b
0
), which correspond to
FIGS. 4 and 5
, respectively, and show a tire having the same tread pattern as shown in
FIG. 4
, but a different form of sipes. The sipes
811
and
812
are formed in two adjoining blocks
411
and
412
, respectively, which are separated from each other by a circumferentially extending main groove
211
. Neither of the blocks
411
and
412
, however, has any shelf as shown at
901
a
or
902
a
in
FIG. 5
, and each sipe
811
or
812
, therefore, does not have any connecting portion of reduced width as shown at
801
a
or
802
a
in
FIG. 5
, but is cut with a substantially equal depth from its end
811
a
or
812
a
opening in the main groove
211
through its inner portion
811
b
or
812
b
and has a rectangular cross section substantially like a parallelogram. Tires having OB type sipes formed in the blocks are used mainly in winter. FIG.
7
(
a
0
) also shows transverse grooves
311
. It also shows by an arrow R the direction in which the circumference of the tire extends.
When a tire having OA type sipes is new, or in the beginning stage of its wear as shown in FIGS.
6
(
a
0
) and
6
(
b
0
), the sipes
801
and
802
having the cross sectional shapes as described make it possible to achieve steering stability and resistance to uneven wear on a dry road, a good performance of traction on a snow-covered road and resistance to wandering on a rainy road. As the wear of its tread surface proceeds, however, the connecting portions
801
a
and
802
a
of the sipes
801
and
802
have a reduced depth, and the shelves
901
a
and
902
a
are finally exposed on the tread surface with the loss of the sipes
801
and
802
as shown in FIG.
6
(
b
1
), resulting in an increase in rigidity of the blocks along the main groove
201
and a lowering of the traction on a snow-covered road and the resistance to wandering on a rainy road. Therefore, this type of tire is not necessarily satisfactory for use throughout the year, though it may be suitable in summer. FIGS.
6
(
a
0
) and
6
(
a
1
) show by an arrow R the direction in which the circumference of the tire extends.
On the other hand, a tire having OB type sipes
811
and
812
exhibits an improved traction on a snow-covered road, since the sipes
811
and
812
having the cross sectional shapes as described lower the rigidity of the blocks
411
and
412
, but the lower rigidity of the blocks also brings about a lowering of steering stability on a dry road and the uneven wear, such as toe-and-heel wear, of the blocks
411
and
412
along their edges. Therefore, a tire having OB type sipes is not necessarily preferable for use throughout the year, though it may be suitable in winter. Moreover, it is too low in block rigidity for a tire used on a light truck, and particularly on a sport utility vehicle (SUV) having a large body weight. Therefore, the improvement in the block rigidity is required.
SUMMARY OF THE INVENTION
This invention has adopted a pneumatic radial tire having blocks formed on its tread by transverse grooves extending along its width and main grooves extending circumferentially across the transverse grooves, wherein every two of the blocks that are transversely spaced apart from each other by one of the main grooves have a sipe which extends transversely from one block to the other across the main groove and is open in the surface of the tread and the main groove throughout its length, the sipe having along its length and depth a cross section defined by an inner portion made in each block, a substantially U-shaped portion made in the bottom and side walls of the main groove, and a portion made in each block for connecting the inner and substantially U-shaped portions, the connecting portion having a depth reduced by a shelf formed on each block, the main grooves having a depth which is smaller than that of the transverse grooves, but which is equal to that of the transverse grooves where they cross the transverse grooves.
The tire of this invention, as described, differs from any known OA type tire mentioned in that its sipes have substantially U-shaped portions extending across the main grooves and remaining open therein for preventing any undesirable increase in rigidity of the blocks along the main grooves, even after the tire has got considerably worn, while the sipes always remain effective in forming edges on a snow-covered road. Thus, the tire of this invention exhibits an improved traction on a snow-covered road and an improved resistance to wandering on a rainy road over any known OA type tire mentioned.
The tire of this invention has a block rigidity which is not so low as that of any known OB type tire mentioned, but is comparable to that of any known OA type tire, since each of the blocks between which a sipe extends across a main groove has a shelf formed below the sipe portion of reduced depth connecting its inner and substantially U-shaped portions. Although the sipes extending between the adjoining blocks across the main grooves may lower the rigidity of the blocks along the main grooves, the circumferentially extending main grooves, which are smaller in depth than the transvserse grooves, except where the former cross the latter, make it possible to prevent any undesirably great lowering of block rigidity, while also restraining any unnecessary movement of the tire around its circumference. Thus, the tire of this invention maintains a satisfactorily high steering stability o
Maki Steven D.
Merchant & Gould P.C.
Toyo Tire & Rubber Co., Ltd.
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