Note: Descriptions are shown in the official language in which they were submitted.
The foregoing abstract is not to be taken as limiting
the invention of this application, and in oxder to understand
the full nature and extent of the technical nature of this
application, reference must be made to the accompanying drawings
and the following detailed description.
Background of the Invention
This invention relates to pneumatic tires, more
particularly to the tread portion of a pneumatic tire.
It is well-known in the tire industry that the choice
of a particular tread design involves trade-off between specific
tire performance characteristics in order to achieve the over-
all desired tire performance. For example, a tread design
which has good wet traction or snow traction generally has
poor dry traction, handling, and/or noise levels; a tire
which generally has good dry traction, handling and tread wear
characteristics generally has poor wet and snow traction.
Conflicting tire characteristics such as these make it
difficult to produce a tread pattern suitable for the various
road conditions experienced during the entire year.
Applicants have discovered a particular tread
arrangement suitable for use in all seasons which provides for
good wet and snow traction while still maintaining good dry
traction, tread wear, noise levels and handling.
Summary of the Invention
In accordance with one aspect of this invention there
is provided a tread for a pneumatic tire comprising a con-
tinuous circumferentially extending rib located substantially
in the central portion of the tread; a plurality of independent
projections placed circumferentially about the tire so as to
provide two circumferentially extending grooves, one on either
side of said central rib, and a plurality of lateral grooves
- 1
which extend from each of said central grooves axially out-
ward to its closest respective tread edge.
Brief Description of the Drawing
Fig. 1 is a fragmentary plan view of a tread of a
pneumatic tire made in accordance with the present invention;
and
Fig. 2 is a fragmentary plan view of a modified
tread of a pneumatic -tire made in accordance wi-th the
presen~ invention.
p$tai1~-ls~ Lt n-5 ~ L.~L -~
Re~`erring to the drawing, there ls lllustrated a
fragmentary view of a tlre :L0 made in accordance with
the present invention having a -tread portion 12. I-t
should be understood that the tread portion 12 extends
circumferentially about the tire 10 in like manner. The
tread por-tion 12 comprises of a circumferentially
extending central rib 14 and a plurality of independent
projections or buttons 16 placed in the remaining portion.
For the purposes of this invention~ an independent
projection or button shall be considered a projection
which has its length substantially less than one-half
the width of the footprint of the tire.
The central rib lL~ is continuous without any a~ial
breaks, that is~ without any notches~ bladings or other
features which extend continuously axially across the
rib 14 and is loca-ted substantially in the central portion
of tread portion 12. The axial edges 18 of rib 14 form
an angle with the mid-circumferential plane not greater
than 10~ preferably~ the edges 18 form an angle not
greater than 5. The width of rib 14 may range from about
5~ to 20% of the tread width W, preferably approximately
12%. For the purposes of this invention~ -the tread width
W is the axial distance between the tread edges as
measured from the footprint of the tire inflated to
design inflation pressures and at rated load. The rib 14
~4479
contributes to noise reduction by minimizing vibrations in
the central portion of the tread 12. The central rib 14
may be further provided with substantially axially
extending sipes or notches for improved traction,
preferably, the radial depth of these sipes or notches is
at least 25~ the depth of grooves 30 in between
projections 16. It is desirable that the notches or
sipes 32 do not extend axially across rib 14 more than
50% of the axial width of the rib 14.
Adjacent longitudinal edges 18 of rib 14 are
continuous circumferentially extending grooves 20.
Preferably there are no other continuous grooves in tread
12 which extend substantially about the circumference
of tire 10.
Extending from each central groove 20 axially outward
to the nearest respective tread edge 24 are a plurality
of lateral grooves 22. The lateral grooves 22 extend
from said central grooves to tread edges 24 in a
substantially uninterrupted manner. For the purpose of
this invention~ a substantially uninterrupted groove
shall be defined as a groove in which its width remains
substantially the same over its entire length. In order
to improve water removal from the contact area of the
tire, grooves 22 preferably extend in a substantially
radial direction in the areas of high unit pressure.
The unit pressure exerted on a tire in the footprint
thereof generally varies axially across the tread 12;
this variation being more pronounced in passenger tires.
The unit pressure is greatest at the lateral edges of
~ 4 ~ 7 ~
the tread and decreases to a low somewhere 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 represen~ation of the unit pressure as viewed
in a radial cross-sectional plane would be in the shape
of a "W"~ the peaks being at the shoulder areas and at
the center line. Therefore, lateral grooves 22 in the
central portion of the tread extend substantially in a
radial direction from central grooves 20 to a point
spaced approximately a distance of 10% to 20~, preferably
15%, of the tread width W from the centerplane CP.
Grooves 22~ from this point~ travel in a direction such
that it forms an angle which is equal to or greater than
50 with respect to the mid-circumferential plane CP of
the tire 10 to a point spaced a distance from the tread
edge approximately 15~ to 25%~ preferably 2 ~ ~ of the
tread width W and then travels in a substantially radial
direction.
The tread 12 is such that the net to gross ratio
is less than 65%. For the purposes of this invention,
net to gross is defined as the ratio between the area of
the tread that is in actual contact with the road as a
percentage of the total gross area of the footprint.
In the embodiment illustrated~ the projections 16
are illustrated as block-type in configuration. However,
it should be understood that projections 16 may take
many other forms. For example, Fig. 2 illustrates an
1 1~ 4 ~
alternative configuration of projections 16. The tread
illustrated in Fig. 2 is a plurality of projections 116
provided with internal blading. It can further be seen
that grooves 122a which correspond to grooves 22 in
Fig. 1, need not be straight but may have small jogs
therein, preferably, these jogs are no greater than the
width of the lateral grooves in the tread 12.
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 other modifications may be
made therein without departing from the invention.
