Note: Descriptions are shown in the official language in which they were submitted.
CA 02294418 1999-12-17
WO 98/58810 PCT/US98/12547
PNEUMATIC TIRE INCLUDING BELT AND CIRCUMFERENTIAL RIBS
Background of the Invention
This invention relates to vehicle tires, and more particularly to heavy duty
truck tires
specially designed to be used for long haul trucking operations.
An object of the invention is to provide to the driver a more comfortable
drive.
Another object of the invention is to improve the handling of the tire. More
specifically, an object
of the invention is to address the problem of deterioration of the comfort and
of handling that in
certain circumstances has proved to be caused by the tire after the tire has
been in use for a number
of miles. It may happen that the rolling comfort or the handling becomes
unacceptable to the driver
at a relatively low mileage such that the tire must be removed well before the
end of its normal
service life. The problem of bad evolution of comfort is occurring especially
in front steer axle
tires, in long haul services (i.e. tires which for most of the time do not
pass on the road a torque as
significant as the driven wheels -no driving torque, the braking operations do
not count for a
significant part of the service life-).
Summary of the Invention
According to the present invention, the comfort and handling of the tire is
addressed by
providing a pneumatic tire comprising a tread portion
having a tread design pattern including
-> a lateral, circumferentially continuous rib located at each side of the
tread, and
including a plurality of other circumferentially continuous ribs located
between the two
lateral ribs, said lateral ribs having a radially external surface for
contacting the road and
having lateral flanges defining at least in part circumferential continuous
grooves located
between the ribs, at least the axially outer lateral flange of said lateral
ribs being radially
outwardly terminated by a junction separating said radially external surface
and said
axially outer lateral flange of said lateral ribs,
-~ on each side, a protective cover located axially outwardly of said lateral
ribs,
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~ said tread portion being reinforced by a carcass having at least a ply, and
reinforced by a
belt having at least two working plies extending transversally beneath all
said ribs, said
working plies including parallel cords arranged at an angle in the range of
10°-30°, and said
working plies having an end on both sides of the tread,
~ said end of said working plies being located axially outwards of a limit
line, said limit line
being perpendicular to a tread reference line, said tread reference line being
the virtual line
parallel to the axis of the tire and in contact with the radially outermost
point of the radially
external surface,
~ the thickness T; of the tread between the radially innermost part of said
carcass and said
radially external surface, measured perpendicularly to said tread reference
line, does not
depart from the thickness T~ at the middle point by more than 10%,
the radially external surface of said tire tread portion having a transverse
radius of curvature greater
than 1500 mm, when the tire in mounted on a predefined rim and not inflated.
Description of the Drawings
The invention will be more readily understood from a reading of the following
specification and by reference to the accompanying drawings showing two
examples of the
invention:
Figure 1 is a fragmentary plan view of a first variation of a tire featuring
this invention;
and
Figure 2 is a fragmentary plan view of a second variation of a tire featuring
this
invention.
Detailed Description of the Preferred Embodiment of the Invention
One varia'~-~n of the preferred emb~ _ :vent of the tire T of the present
invention is shown in
Fig. 1 and anotc.N: variation thereof is shu~,n in Fig. 2. Turning to common
features of nre two
variations, the tire T has a tread portion having a tread design pattern. The
invention is related to a
typical tread design pattern having proved being suited for front axle tires
used in long haul. That
tread design pattern comprises essentially parallel ribs separated by parallel
grooves. Those parallel
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WO 98/58810 PCT/US98/12547
ribs here include, located on each respective side of the tread, a lateral rib
1 that is circumferentially
continuous, i.e. not divided into a plurality of blocks. This basic tread
pattern unit is repeated
laterally, with or without changes of actual shape, so that the tread includes
a plurality of other ribs
2, located between the two lateral ribs 1 and also being circumferentially
continuous. Each lateral
rib 1 and other ribs 2 has a radially external surface 10.
Each of the lateral rib 1 and the other ribs 2 are limited laterally by
flanges 11, 12 defining
at least in part and two by two circumferential continuous grooves 13. In the
embodiments
illustrating the invention, at least the axially outer lateral flange 11 of
the lateral rib 1 is radially
outwardly terminated by a junction interconnecting the radially external
surface 10 and the axially
outer lateral flange 11. In the described embodiment, the junction is an edge
14. In the two
variations of the embodiment, all of the lateral ribs l and other ribs 2 are
bordered laterally by
edges forming a sharp angle. The axially outer lateral flange 11 of lateral
rib 1 and the radially
external surface 10 of the lateral rib 1, as viewed in a radial section like
the one of figures 1 and 2,
define an angle a ranging between 90° and 110°. In other words,
the axially outer lateral flange 11
of lateral rib I and the radially external surface 10 of the lateral rib 1, as
viewed in a radial section
like the one of figures 1 and 2, define a sharp angle.
The tire T is reinforced by a carcass comprising at least one carcass ply 5
and by a belt. The
belt, as shown in the figures, includes two working plies 61, 62, and a
protective ply 63. The means
to realize the so-called working plies and protective ply are well known in
the art. Thus, further
details are not given in the present disclosure. It is enough to recall that
the working plies generally
are made essentially of inextensible parallel cords arranged at an angle in
the range of 15°-30°, and
that a protective ply is generally a ply which can be more extendible. Also it
is enough to recall that
the belt could also include other reinforcing means like cords arranged at a
zero angle with respect
to the mid circumferential plane of the tire T, also called "jointless
reinforcing ply or plies", having
cord or cords substantially parallel to the mid circumferential plane of the
tire T (a plane
perpendicular 'to the axis of the tire T), that latter reinforcement being
useful namely to keep
unchanged after breaking in the shape and properties of the tire T.
All the lateral and other ribs 1, 2 have a radially external surface 10 for
contacting the road.
Assuming that the surface of the road is flat (bearing in mind that the tire T
of the invention is
designed for long haul applications, this assumption is close to reality) the
radially external surface
10 will be urged to become flat during rolling. According to an aspect of the
invention, the belt and
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more generally the tread portion as a whole is so designed as to achieve a
normal stress
perpendicular to radially external surface 10 in the tread as even or uniform
as possible in a loaded
static condition of the tire T. One could suppose that uniform normal stresses
will also be
experienced during dynamic rolling of the tire T and that such conditions will
enhance the comfort
and handling of the tire T. According to a feature of the invention, the belt,
more precisely at least
the working plies 61, 62 of the belt, extend beneath all the lateral ribs 1
and other ribs 2 for
providing an equal support thereof. In other words, with reference to the
drawings, the ends 610,
620 of the working plies 61, 62 is extended beyond a limit line 7 (shown in
dotted line). The limit
line 7 is defined by a perpendicular to a tread reference Line 8. The tread
reference line 8, as viewed
in a radial section of the tire T like the one shown in figures 1 and 2, is
the imaginary line parallel
to the axis of the tire T and in contact with the radially outermost point of
the radially external
surface 10. A second condition that the limit line 7 has to fulfill is to pass
through the edge 14 of
the lateral rib 1.
It is to be noticed that the tire T tread portion is molded so that the
radially external surface
10 of the lateral and other ribs defines a transverse profile which is close
to a cylinder when the tire
T in mounted on a predefined rim and non inflated. The transverse radius of
curvature R is the
range of 1,500 mm to an infinite value. Advantageously, the transverse radius
of curvature is
greater than 5,000 mm. For instance, the two variations show a transverse
radius of curvature R
reaching 20,000 mm.
With reference to the drawings, one see that the thickness T; of the tread is
pointed out at
different location: thickness T1 at the axially outer border of lateral rib 1,
thickness T2 for
respective adjacent other rib 2, and thickness T~ in the middle of the tire T
(thickness measured at
the mid circumferential plane, i.e. the plane perpendicular to the tire's axis
of rotation and passing
through the center of its tread). The thickness T; is measured between the
radially innermost part of
the carcass ply 5 and the radially external surface 10. The thickness T; is
measured perpendicularly
to the tread reference line 8. The portion of the tread measured by the
thickness T; includes
reinforcing members of the belt 've rubber compounds and the carcass ply. If -
he carcass inci;:.ies
more than a single carcass ply ~ thickness is measured from the radially
innermost part of the
radially innermost ply. It is thereby established a reference referred to in
general by "the radially
innermost part of the carcass".
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WO 98/58810 PCT/US98/12547
According to another feature of the invention, the thickness T;, in any point
between the
middle of the tire tread and the axially outermost part of the lateral rib 1,
does not depart from the
thickness T~ at the middle point by more than 10%, and preferably not more
than 8%. In any case,
the thickness is greater than 20 mm, as it is a tire T for heavy truck. The
following table is an
example of thickness T; taken on a tire T according to the invention.
Thickness in mm
T~ 27
T2 27
TI 28.6
(28.6-27)
In this tire T, the difference of thickness is 27 = 5.9% , thus less than 8%.
The onset of unacceptable comfort or unacceptable handling, or the rate of
deterioration
thereof if any, is thus kept within limits that are by far more compatible
with the normal service life
of the tire T, thereby avoiding the removal of the tire T well before that the
height of the ribs has
decreased up to the preset wearing limit.
On each side of the tread, a protective cover is located axially outwardly of
the lateral ribs.
The two examples illustrating the invention differ by the embodiment of the
cover. The cover on
figure 1 is a narrow shoulder rib 3. Standard tread rubber materials can be
used for the shoulder rib
3 as for lateral ribs l and other ribs 2. The shoulder rib 3 is laterally
recessed from the lateral rib 1
by a narrow groove 31. In other words, the surface 30 of the shoulder rib 3 is
recessed with respect
to the radially external surface 10 of the lateral rib 1. According to the
need tQ protect the extended
belt of the invention, a preferred width of the shoulder rib 3 is in a range
of about 10 millimeters to
about 20 millimeters. The dimensions and geometry of the shoulder rib 3 are
selected such that,
during normal running of the tire T, experiences different stresses than
lateral ribs 1 and other ribs
2. This feature helps to maintain a sharp edge 14 on the lateral ribs 1. In
the particular geometry of
the shoulder rib 3, the radial height of the shoulder rib 3 is below the
radially external surface 10 by
a distance in the range of 1 mm to 2 mm.
Figure 2 shows another cover which is not a wearing part of the tread and has
no
contribution whatsoever to sustain the load. Its function merely is to protect
the ends 610, 620 of
the working plies 61, 62 and the end 630 of the protective ply 63. The
protective cover is a rubber
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WO 98/58810 PCT/US98/12547
product 4 having an axially inner end joined with the bottom of the axially
outer lateral flange 11.
In other words, the radially outer surface 40 of the rubber product 4 is
approximately even with the
bottom of the grooves 13. This variation may be used to improve cooling of the
shoulder part if the
help of the shoulder rib appears not being needed.
To be more general, the protective cover could have any radial height between
the limits set
forth by the above variations illustrating the invention. The protective cover
could be made even
with the radially external surface 10, and in that case one would use another
rubber material than
the one of main part of the tread: the rubber material of the protective cover
would ideally be less
hysteretic than the rubber material of the lateral ribs 1 and the other ribs
2.
In the two variations of the preferred embodiment, the carcass is a radial
carcass. The tire T
is designed to be mounted on a rim the shape and dimensions of which is
defined by well
established standards (See e.g. "The Tire and Rim Association, Inc." or "The
European Tire & Rim
Technical Organization"). According to the well known way of designing tires,
a tire T of a
preselected size is designed to work on one or a couple of desired rim sizes
selected among the
above mentioned standards. The tire T also is designed to work at a so-called
"nominal inflation
pressure". In the described embodiment, the carcass is designed to assume, if
the tire T is mounted
on the specific rim and inflated at the nominal inflation pressure, a natural
shape of equilibrium in
the sidewalls. In the tread area, the carcass is adhered on the belt and works
as a unit with the
working plies; the carcass tends to assume a cylindrical shape. In the
shoulder portion, beyond the
protective cover, the carcass is connected to that part having a cylindrical
shape (into the tread
portion) and to that part having a natural shape of equilibrium (in the
sidewalls) in a manner as
progressive and smooth as possible.
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