Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The foregoing abstract is not to be ta~en as limiting
the invention of this application, and in order to under-
stand the full nature and exten-t of the technical nature
of this application, reference must be made to the
accompanying drawings and the following detailed
description.
Back~round of the Invention
This invention relates to pneumatic tires, and more
particularly, to an improved tread for tires. It is well
known in the tire industry t~at the choice of a particular
tread involves trade-off between specific tire performance
characteristics in order to achieve the overall desired
tire performance. Among such characteristics are those
directed to wear~ comfort, noise~ handling under various
road conditions~ fuel consumption and the like. The
foregoing performance characteristics are quite often at
odds with each other for any given tread design. For
example~ a tread which has good wet traction or good
snow traction is generally obtained at the expense of dry
traction, handling, tread wear and/or noise production;
a tread which has good tread wear is generally obtained at
the expense of wet traction~ ride~ snow traction and/or
comfort; a tread which has good fuel consumption is
generally obtained at the expense of wear and/or traction.
Due to the complex interaction between these performance
characteristics it is difficult to obtain a tread which can
exhibit good wet and snow traction characteristics while
still maintaining good tread wear, dry traction~ handling
and low noise levels.
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Applicants have discovered a particular arrangement by
which good wet traction may ~e obtained while still maintain-
ing good tread wear, dry traction, handling and noise level.
Summary of the Invention
A tire made in accordance with the present invention is
provided with a plurality of spaced independent buttons or
projections placed circumferentially about the tire. The
tread has three relatively narrow zones with respect to the
width of the tread which extend circumferentially about the
tire. The depth of the recesses in between the buttons or
projections in these zones is less than the depth of the
recesses in the remaining portion of the tread.
In accordance with one aspect of this invention there
is provided a pneumatic tire comprising a tread having a
plurality of independent buttons or projections placed cir-
cumferentially about said tire, said tire characterized in
that said tread is provided with a central zone and two
shoulder zones which extend circumferentially about said tire,
the width of said central and shoulder zones being substan-
tially less than the width of said tread, said central zonebeing located such that the longitudinal axial edges of said
zone are spaced substantially equidistant from the mid-
circumferential plane of said tire, said shoulder zones are
spaced from and located axially outward from said central
zone, one on either side of said central zone, and extend
from each tread edge toward the mid-circumferential plane of
said tire, the depth of the recesses in between said projec-
tions in said central zone and shoulder zones is substantial-
ly less than the depth of the recesses in the remaining
portions of the tread in between said central zone and
shoulder zones.
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B ief Description of the Drawings
Fig~ 1 is a fragmentary plan view of a tread of a tire
made in accordance with the present invention; and
Fig. 2 is a cross-sectional view of a tread made in
accordance with the present invention taken along line 2-2 of
Fig. 1.
Description of the Preferred Embodiment
Referring to Fig. 1 there is illustrated a fragmentary
plan view of a tread 12 made in accordance with the present
invention. It is to be understood that the tread continues
in like manner circumferentially about the tire. The
tread 12 comprises a plurality of independent buttons
or projections 14. For the purpose of this invention
independent projections shall be considered projections
which have a length substantially less than the length of
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the foo-tprin-t at design inflation pressures and at rated
load, preferably less than 50~. In the embodiment
illustrated, the projections 14 have an outer configuration
which is basically triangular in configuration as viewed
in a plane perpendicular to the tread; however, any
desired configuration may be used. In order to obtain good
wet traction, there should be sufficient void area in the
tread so that water may be channeled into these void areas
instead of creating a hydrostatic pressure which would
exert a lifting force against the tire. The use of
independently spaced projections and a low net to gross in
the tread allows water to freely escape from the footprint
of the tire. For the purposes of this invention~ the
footprint of the tire is that portion of the tread which
comes in contact with the road surface.
Wnfortunately, the use of independent projections
and a low nst to gross in the tread of a tire generally
detracts from handling, dry traction, and increases noise
production. In order to overcome these disadvantages~ the
tread 12 is provided with three circumferentially extending
zones in which the recesses in between the projections 14
are substantially less than the recesses in between the
projections 14 in the remaining portion of the tread 12.
The tread 12 is provided with a central zone C and two
shoulder zones A~ B , respectively, in which the depth of -
the recesses in between the projections 14 is less than
the depth of the recesses in the remaining portions D and
E of the tread 12. The full depth recesses provide the
necessary void area between the independent projections
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for good wet traction whil~ th~ reduced recess depth
portions A and B provide the stiffening necessary between
the projections for good tread wear, handling~ and
noise levels. Additionally, tread 12 is provided with a
low nèt to gross tread. ~or purposes of this invention
net to gross shall be defined as the net contact area
of tread with the road as a percentage of the total
contact area. The tread 12 should have a net to gross
of less -than 65%, prefereably between 65~ and 5~ .
The full depth recesses are located in that portion
of the tread wherein the unit pressure is lower than the
adjacent area~ thus allowing the water to be channeled
into these voids rather than creating the hydrostatic
pressure which would exert a lifting force against the
tread 12. Accordingly~ the reduced recess depths are
located in the portion of the tread 12 between the
projections wherein the unit pressure is high. The unit
pressure exerted on a tire in the footprint thereof
varies axially across the tread 12; this variation
being more pronounced in passenger tires. The unit
pressure is greatest at the lateral edges of the tread
and decreases to a low ~omewhere in between the tread
edge and the mid-circumferential centerplane CP of the
tire and then gradually increases to a higher unit
pressure in the central area of the tread~ the highest
unit pressures occurring at the lateral edges. A
graphical representation of the unit pressure as viewed
in a radial cross-sectional plane would be in the sahpe
of a "W"~ the peaks being at the shoulder areas and at
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the central area of the tread. The reduced recess depth
in zonès A,B,C serve to buttress projections 14 and to
reduce deformation and squirm which lead to u~desirable
tread wear and tread noise produced in these areas.
Additionally~ the increased s-tiffness in these zones allow
the tread 12 to respond more positively to slight straight
ahead steering corrections (more commonly referred to in
the industry as "on center eel") and to more exaggerated
handling maneuvers. The reduced depth recesses further
serve to reduce the noise generated in the central portion
of the tread.
The central zone ~ is located approximately in the
central portion of the tread 12 and extends circumferen-
tially about the tire. Preferably, the central zone C
is located so that the axial edges are spaced equidistant
from the mid-circumferential plane CP of the tire. The
width of the central zone A may range from 5% to 20%;
preferably~ 15% of the width W of the tread 12. For the
purposes of this invention the width W of the tread shall
be defined as the axial distance between the edges of the
tread as determined from the footprint of the tire mounted
on a wheel and loaded to design specification. The depth
F of the recesses 20 in the central zone C is between 25%
and 60% of the depth G of the recesses 22 in zones D and
E, preferably about 35%.
The shoulder zones extend axially inward from the
tread edges toward the mid-circumferential plane CP of the
tire and extend circumferentially about the tire. The
width of each shoulder zone is equal to approximately
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10% to 2C% of the tread width W, preferably 15%. The
depth I of the recesses 24 in zones A, B is equal to
approximately 25% to 60% of the depth of the recesses 22
in zones D and E, preferably 40%.
The total width of the three zones A, B~ C preferably
does not exceed 60% of the width W of the tread 12.
The bottom of the reduced recesses 20 and 24 in zones
A~ B, C may be further provided with blading 26 for
continued acceptable traction as the surface of the
projections 14 wear to the bottom of the recesses in these
zones.
While certain representative embodiments and details
have been shown for purposes of illustrating the invention,
it will be apparent to those skilled in this art that
various changes and modifications may be made therein
without departing from the spirit or scope of the
invention.
