Note: Descriptions are shown in the official language in which they were submitted.
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TREAD FOR A PNEUMATIC TIRE
Background of the Invention
The present invention relates generally to
pneumatic tires, and more particularly to the tread
portion of a pneumatic tire wherein said tread portion
is asymmetric with respect to the mid-circumferential
plane of the tire.
It is generally recognized in the tire art that a
tire with a directional tread design has lower noise
generation characteristics, when rotated in the
direction that it is designed to rotate in, than a
tire having a non-directional tread design. As used
herein a "directional tread design" is a tread
structure that is intended to operate more efficiently
when rotated in one direction than in the opposite
direction, and a "non-directional tread design" is a
tread structure that is intended to operate with equal
efficiency regardless of the direction in which it is
rotated.
One of the problems presented by tires with
directional tread designs is that if the tires have
stripes or other ornamentation on a sidewall it is
necessary to either produce different tires for each
side of the vehicle or put the costly ornamentation on
both sidewalls of the tire. The present invention
overcomes this problem by providing a tire having an
asymmetric tread structure with lateral edge portions
that are directional and a central portion that is
non-directional, although the tire has an overall
non-directional tread design.
A pneumatic tire having a tread according to the
preferred and most preferred embodiments of the
present invention may be referred to as an all season
tire. An "all season tire" is a tire with a tread
portion adapted to provide good wet and snow traction
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while still maintaining good dry traction, tread wear,
noise levels and handling. It is understoocl tha-t in
order to provide these desirable characteristics for an
all-season tire, it is necessary to compromise the
levels of some characteristics because, for example, a
tread portion that provides a very good level of wet
traction or snow traction performance generally has
poorer dr~ traction, handling and/or noise levels.
A pneumatic tire having a tread portion according
to either the preferred or most preferred embodiment of
the present invention is suitable for use in all
seasons of the year and provides good wet and snow
traction while still maintaining good dry traction,
tread wear, noise levels, and handling.
There is provided in accordance with one aspect of
the invention a pneumatic tire comprising independent
projections defined by:
(a) first and second sets of circumferentially
spaced apart primary grooves, each primary groove
comprising two straight segments oriented at angular
relationships with respect to each other, said segments
having widths such that the primary grooves remain open
in a footprint of the tire, each groove of said first
set of primary grooves, extending generally axially
inwardly from a first axial edge of the tread but not
intersecting a mid-circumferential plane of the tire,
each groove of said second set of primary grooves
extending generally axially inwardly from a second
axial edge of the tread but not intersec~ing the mid
circumferential plane of the tire, each primary groove
having an axially inner end that is located an axial
distance of not more than 15% of the tread width away
from the mid-circumferential plane of the tire, an
axially outermost segment of each of the grooves of
said first set of primary grooves extending axially
inwardly from the first axial edge of the tread in one
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generally circumferential direction and the other
segments of each of the said grooves extending from an
axially inner end of said axially outermost segment to
an axially inner end of the groove in an opposite
generally circumferential direction, each groove of
said second set of primary grooves extending from the
second axial edge of the tread to the axially inner end
of the groove in only one generally circumferential
direction along its entire length, and
(b) first and second sets of circumferentially
spaced apart secondary grooves, said secondary grooves
having widths such that the secondary grooves remain
open in a footprint of the tire, a secondary groove
extending generally axially outwardly from the axially
inner end of each of the primary grooves and
intersecting a plurality of primary grooves, but no
secondary grooves intersect the axial edges of the
tread.
There is provided in accordance with another aspect
of the invention a pneumatic tire comprising a tread
portion having independent projections defined by:
(a) first and second sets of circumferentially
spaced apart primary zig-zag grooves, each primary
zig-zag groove comprising a series of straight segments
communicating with next adjacent segments and oriented
at angular relationships with next adjacent segments,
said segments having widths such tha~ the primary
zig-zag grooves remain open in a footprint of the ~ire,
each groove of said first set of primary zig-zag
grooves extending generally axially inwardly from a
first axial edge of the tread but not intersec~ing a
mid-circumferential plane of the ~ire, each groove of
said second set of primary zig-zag grooves e~tending
generally axially inwardly from a second axial edge of
the tread but not intersecting the mid-circumferential
plane of the tire, each primary zig-zag groove having
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an axially inner end that is located an axial distance
of not more than 15~ of the tread width away from the
mid-circumferential plane of the tire, an axially
outermost segment of each of the grooves of said first
set of primary zig-zag grooves extending axially
inwardly from the first axial edge of the tread in one
generally circumferential direction and the remaining
segments of each of said grooves of said first set of
primary zig-zag grooves extending from an axially inner
end of said axially outermost segment to an a~ially
inner end of the groove in an opposite generally
circumferential direction, each groove of said second
set of primary zig-zag grooves extending from the
second axial edge of the tread to the axially inner end
of the groove in only one generally circumferential
direction along its entire length, every other segment
of each primary zig-zag groove being oriented at
between 0 and 5 with respect to said mid-circum-
ferential plane and the remaining segments of each
primary zig-zag groove being oriented at angles of
greater than 0 but no greater than 90 with respect to
said mid-circumferential plane, the angular orientation
of said remaining segments with respect to said
mid-circumferential plane progressively decreasing as
the axial distance between said remaining segments and
said mid-circumferential plane decreases; and
(b) first and second sets of circumferentially
spaced apart secondary zig-zag grooves, each secondary
zig-zag groove comprising a series of straight segments
communicating with next adjacent segments and oriented
at angular relationships with adjacent segments, said
segments having widths such that the secondary zig-zag
grooves remain open in a footprint of the tire, each
groove of said first set of secondary zig-zag grooves
having an axially innermost segment that intersects the
axially innermost segment of one of the grooves of said
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first set of primary æig-zag grooves, each groo~e of
said second set of zig-zag grooves having an axially
innermost segment that intersects the axially innermost
segment of one of the grooves of said second set of
primary zig-zag grooves, each secondary zig-zag groove
extending generally axially outwardly from its axially
innermost segment and intersecting a plurality of
primary æig-zag grooves but not intersecting an axial
edge of said tread, and portions of at least two
segments of each secondary zig-zag groove being located
between each pair of circumferentially next adjacent
primary zig-zag grooves that the secondar~ zig-zag
groove intersects.
Brief Description of the Drawin~
Fig. 1 is a perspective view of a pneumatic tire
having a tread poriton made in accordance with the msst
preferred embodiment of the present invention.
Fig. 2 is the front eleva~ion view of the tire of
Figure l;
Figure 3 is a fragmentary plan view of the tread
portion of a tire of Figure l;
Fig. 4 is a fragmentary plan view of the tread
portion of a pneumatic tire in accordance with a
preferred embodiment of the present invention, but not
having a continuous center rib; and
Fig. 5 is a fragmentary plan view of ~he tread
portion of a pneumatic tire in accordance with an
alternate embodiment of the present invention.
Detaile_ Description of the ~nvention_
Referring to the drawing, there is illustrated in
Fig. 1 a perspective view of a pneumatic tire 10 having
a tread portion 12 manufactured in accordance with the
most preferred embodiment of the present invention.
Fig. 2 is a front elevation view of the
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pneumatic tire 10 of Fig. 1, and ~ig. 3 is a
fragmentary plan view of the tread portion 12 of the
pneumatic tire 10 of Figs. 1 and 2. The invention may
be most advantageously practiced if the pneumatic tire
is a radial tire intended for use on a passenger car,
but the invention also applies to truck and bus tires.
It is understood that the tread portion e~tends
circumferentially about the tire and comprises a
plurality of independent projections or buttons 14,
and in the most preferred embodiment a continuous rib
16 that extends circumferentially about the tread
portion and contains the mid-circumferential plane of
the tireO In an alternative preferred embodiment of
the invention, as illustrated in Fig. 4, the
continuous rib 16 is replaced by a circumferentially
extending series of independent projections or
buttons. For the purposes of this invention, an
independent projection or button shall be understood
to mean a projection which has a circumferential
length and an axial width that are each substantially
less than one-half the width of the footprint of the
tire. For the purposes of this invention, a rib is
continuous if it is without any axial breaks, that is,
without any notches, slits, blading or other features
which extend continuously axially across the rib.
However, before going into the details of the
preferred and most preferred embodiments of the
invention, the basic structure of the invention may
best be explained with reference to Fig. 5 which is a
fragmentary plan view of the tread portion 60 of a
pneumatic tire in accordance with an alternate
embodiment of the invention.
In the alternate embodiment the shape of the
independent projections 61 and the continuous rib 62
are defined by a number of grooves in the tread
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portion. The system of grooves comprise a first set
of primary grooves 63, a second set of primary grooves
6~, and first and second sets of secondary grooves 6S.
Each of the primary grooves 63, 64 comprises two
straight segments having widths such that the primary
grooves remain open in a footprint of the tire. It is
understood that as used herein a footprint, and of
course a tread of a tire, is evaluated when a tire is
mounted upon the specified rim, inflated to its
specified inflation pressure and then subjected to its
rated load. Each groove 63 of the first set of
primary grooves extends generally axially inwardly
from a first axial edge TEl of the tread, but does no~
intersect the mid-circumferential plane M of the tire.
Each groove 64 of the second set of primary grooves
extends generally axially inwardly from a second axial
edge TE2 of the tread, but does not intersect the
mid-circumferential plane M of the tire. As used
herein, "generally axially" refers to a direction that
is not parallel to the axis of rotation of a tire, but
is a direction going away from a tread edge which will
eventually intersect the mid-circumferential plane of
the tire, or vice-versa. Preferably the
circumferential spacing between primary grooves at the
respective axial edge of the tread is in the range of
20 to 40 mm, or put another way about 20 to 40% of the
tread width. As used herein the tread width TW i5 the
axial distance between the axial edges of the tread
TEl and TE2 as measured from the footprint of a tire.
As used herein "axial" and "axially" refer to
directions that are parallel to the axis of rotation
of a tire, and the "mid-circumferential plane" of a
tire is a plane that is perpendicular to a tire's axis
of rotation and is equidistant from the axial edges of
the tread in a tire's footprint.
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Each primary groove 63, 64 has an axially inner
end 66 that is located an axial distance of not more
than 15% of the tread width TW away from the
mid-circumferential plane M of the tire. Preferably,
the axially inner end of each primary groove is
located an axial distance of between 3% to 12% of the
tread width away from ~he mid-circumferential plane of
the tire.
The axially outermost segment 67 of each of the
grooves 63 of the first set of primary grooves extends
axially inwardly from the first axial edge TXl of the
tread in one generally circumferential direction of
the tire at an angle in the range of 50 to 80,
preferably 70 to 80, with respect to the
mid-circumferenti.al plane M. The second segment 68 of
each of the grooves 63 of the first set of primary
grooves extends from the axially inner end of said
axially outermost segment 67 to the axially inner end
66 of the primary groove in an opposite generally
circumferential direction of the tire at an angle in
the range of 10 to 30, prefera~ly 12 to 25 7 with
respect to the mid-circumferential plane M. As used
herein a circumferential direction is a direction in
which the tire rotates about its axis, and a
"generally circumferential direction" means a
direction that would eventually go completely around
the axis of rotation but also extends axially with
respect to the tire.
Each groove 64 of the second set of primary
grooves extends from the second axial edge of the
tread TE2 to the axially inner end 6~ of the groove in
only one generally circumferential direction along its
entire length. That is to say, the axially outermost
segment 69 of each of the grooves 64 of the second set
of primary grooves extends axially inwardly from the
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second axial edge of the tread TE2 at an angle in the
range of 50 to 80, preferably 70 to 80, with
respect to the mid-circumferential plane, and the
second segmen~ 70 extends axially inwardly from the
axially inner of said axially outermost segment 69 to
the axially inner end 66 of primary groove in the same
generally circumferential direction as the axially
outermost segment 69 but at an angle in the range of
10 to 30, preferably 12 to 25, with respect to the
mid-circumferential plane.
The axially outermost segment 67 of each groove
63 of the first set of primary grooves, and the
axially outermost segment 69 of each groove 64 of the
second set of primary grooves extend axially inwardly
from the respective axial edge TEl, TE2 of the tread
an axial distance in the range of 8% to 25~ of the
tread width TW, preferably between 10% and 14% of the
tread width, as measured for example at 71 in Fig. 5.
- If the axially outermost segments 67, 69 of the
primary grooves were to be projected axially inwardly
they would intersect and form a series of V's pointing
in one circumferential direction of the tire. That is
to say, the axially outer lateral edge portions of a
tire tread according to the invention have grooves
therein like a directional tread design.
However; if the other segments 68, 70 of the
primary grooves are projected axially inwardly they
will not intersect in a V. That is to say, the
central portion of a tire tread according to the
invention has grooves therein like a non-directional
tread design.
It is apparent that a tire in accordance with any
of the embodiments of the present invention will
exhibit at least some of the advantages of both
directional and non-directional tread structures.
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Each secondary groove 65 has a width such that
the secondary grooves remain open in a footprint of
the tire. A secondary groove extends generally
axially outwardly from the axially inner end 66 of
each of the primary grooves 63, 6~ and intPrsects a
plurality, preferably four, primary grooves, but does
not intersect an axial edge TEl, TE2 of the tread .
The secondary grooves are oriented at an angle of 40
to 80, preferably 45 to 75, with respect to the
mid-circumferential plane M of the tire.
Referring once again to the preferred and most
preferred embodiments shown in Figs. 1 through 4, the
shape of the independent projections 14 and the
continuous rib 16 are defined by a number of zi.g-zag
grooves in the tread portion. The system of grooves
comprise a first set of primary zig-zag grooves 18, a
second set of primary zig-zag grooves 19, and first
and second sets of secondary zig-zag grooves 20. The
irregular shapes of the independent projections gives
the preferred and most preferred embodiments goo~
all-sea~on characteristics.
Each of the p~-imary zig-zag grooves 18,19
comprises a series of straight segments communicating
with next adjacent segments and oriented at angular
relationships with the next adjacent segments. The
segments have widths such that the primary zig-zag
grooves remain open in a footprint of the tire. Each
groove 18 of the first set of primary zig-zag grooves
extends generally axially inwardly from a first axial
edge TEl of the tread, but does not intersect the
mid-circumferential plane M of the tire. ~ach groove
19 of ~he second set of primary zig-zag grooves
extends generally axially inwardly from a second axial
edge TE2 of the tread, but does not intersect the
mid-circu~ferential plane M of the tire. Preferably
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the circumferential spacing between primary zig-zag
grooves at the respective axial edge TEl, TE2 of the
tread is in the range of 20 to 40 mm, or put anothPr
way about 20 to 40% of the tread width TW.
Each primary zig-zag groove 18,19 has an axially
inner end 22 that is located an axial distance of not
more than 15% of the tread width TW away from the
mid-circumferential plane M of the tire. Preferably,
the axially inner end of each primary zig-zag groove
is located an axial distance of between 3% to 12% of
the tread width away from the mid-circumferential
plane of the tire. Every other segment 24 of each
primary zig-zag groove 18,19 is oriented at between 0
and 5 with respect to the mid-circumferential plane
M, preferably at 0. The remaining segments 26 of
each primary zig-zag groove 18,19 are oriented at
angles of greater than 0 but not greater than 90
with respect to the mid-circumferential plane, with
the angular orientation of said remaining segments
with respect to the mid-circumferential plane
progressively decreasing as the axial distance between
said remaining segments and said mid-circumferential
plane decreases.
The axially outermost segment 21 of each of the
grooves 18 of the first set of primary zig-zag grooves
extends axially inwardly from the first axial edge TE
of the tread in one generally circumferential
direction of the tire at an angle in the range of 50
to 80, preferably 70 to 80, with respect to the
mid-circumferential plane M. The remainder of the
segments 24 and 26 of each of the grooves 18 of the
first set of primary zig-zag grooves extend from the
axially inner end of said axially outermost segment 21
to the axially inner end 22 of the primary zig-zag
groove in an opposite generally circumferential
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direction of the tire at a nominal angle in the range
of 10 to 30, preferably 12 to 25, with respect to
the mid-circumferential plane M.
Each groove 19 of said second set of primary
zig-zag grooves extends from the second axial edge TE2
of the tread to the axially inner end 22 of the
groove in only one generally circumferential direction
along its entire length. The grooves 19 of the second
set of primary zig-zag grooves extend from the second
axial edge TE2 of the tread towards the
mid-circumferential plane M at a nominal angle in the
range of 10 to 30, preferably 12 to 25 with
respect to the mid-circumferential plane.
The axially outermost segment 21 of each groove
18 of the first set of primary zig~zag grooves, and
the axially outermost segment 23 of each groove 19 of
the second set of primary zig-zag grooves extend
axially inwardly from the respective axial edge TEl,
TE2 of the tread an axial distance in the range of 8%
to 25% of the tread width TW, preferably between 10%
and 14% of the tread width, as measured for example at
25 in Fig. 3.
Each secondary zig-zag groove 20 comprises a
series of straight segments communicating with next
adjacent segments and oriented at angular
relationships with adjacent segments. The segments
have widths such that the secondary zig-zag grooves
remain open in a footprint of the tire. Each groove
of a first set of secondary zig-zag grooves has an
axially innermost segment 28 that intersects the
axially innermost segment 30 of one of the grooves of
said first set of primary zig-zag grooves. Each
groove of said second set of secondary zig-zag grooves
has an axially innermost segment 32 that intersects
the axially innermost segment 34 of one of the grooves
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of said second set of primary æig-zag grooves. ~ach
secondary zig-zag groove extends generally axially
outwardly from its axially innermost segment and
intersects a plurality~ preferably four, primary
zig-zag grooves, but does not intersect an axial edge
of the tread. Portions of at least two segments of
each secondary zig-zag groove are located between each
pair of circumferentially next adjacent primary
zig-zag grooves that a secondary zig-zag groove
intersects. The secondary zig-zag grooves are
oriented at a nominal angle of 40 to 80, preferably
45 to 75, with respect to the mid-circumferen~ial
plane of the tire.
The zig-zag configuration of the grooves provides
a tire that has good traction on wet or snow covered
surfaces, along with good wet skid characteristics.
The varying angular orientation of said remaining
segments of the primary zig-zag grooves, as a function
of the distance of said remaining segments from the
mid-circumferential plane provides noise levels that
are very acceptable by increasing the stiffness of the
leading edges of the independent projections as they
enter the footprint of the tire and minimizing impact
noise.
As shown in Figs. 1, 2 and 3, it is preferred
that the first and second sets of primary zig-zag
grooves be separated from one another by a continuous
rib 16 extending circumferentially about the tread
portion and containing the mid-circumferential plane
16. This center rib embodiment of the invention is
the most preferred embodiment because it aids in noise
abatement and improves the performance of the tire
under a variety of operating conditions. ~owever, as
illustrated in Fig. 4, in a tire tread portion 40,
according to an alternative preferred embodiment, the
axially inner segment 50 of each groove of the first
set of primary zig-zag groO~JeS communicates with the
axially innermost segment 52 of a groove of the second
set of primary zig-zag grooves by means of a
connecting groove 54. In all other respects the tire
tread portion 40 of the alternative preferred
embodiment shown in Fig. 4 is substantially the same
as that of the most preferred embodiment shown in
Figs. 1, 2 and 3.
In order to obtain the most efficient evacuation
of water, mud or snow from the footprint of a tire
according to the invention, the tread portion should
have a net to gross ratio in the range of ~0% to 80%,
preferably 65% to 75%. Net to gross ratio is
understood to mean the ratio between the area of a
tread portion in a tire footprint that is in actual
contact with the ground and the total gross area of
the tire footprint.
Referring once again to Figs. 1, 2 and 3, it may
be observed that the tread portion of a tire according
to any of the embodiments of the invention may have a
plurality of narrow slits 36 therein. These narrow
slits are sometimes referred to as blades or sipes,
and have a width such that the narrow slits are closed
in a footprint of the tire. Each narrow slit 36
intersects the vertex of a projecting angle of one of
the primary zig-zag grooves. The narrow slits extend
in either axially or generally axially directions, but
do not extend across the entire width of an
independent projection or rib. The narrow slits may
be incorporated in a tread portion to provide some
flexibility to the independent projections and/or the
center rib, while the zig-zag grooves make the leading
edges of the independent projections stiff for noise
abatement and traction purposes.
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The most preferred embodiment illustrated in
Figs. 1, 2 and 3, the alternate preferred embodiment
illustrated in Fig. 4 and the alternate embodiment
illustrated in Fig. S are non-directional tires, that
is to say tires that will operate the same regardless
of the direction in which they are rotated.
While certain representative embodiments and
details have been shown for the purpose of
illustrating the invention, it will be apparent to
those skilled in the art that various changes and
modifications may be made therein without departing
from the invention.
