Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to pneuma-tic tires ~or
vehicle wheels and in particular to tires provided with a radial
carcass (i.e., a carcass whose cords lie on meridian planes or
, form small angles with the planes) particularly suitable for heavy'
vehicles for normal and heavy duty and intended to be u,sed for
long dis-tances at normal and high speed.
It is known that radial tires are usually provided with a
structure which includes one or more reinforcing layers arranged
at the crown zone of the carcass below the tread. The reinforcing .
layer is provided to wi-thstand the tension stresses to which the
. tire is subjected, either because of the inflation pressure or in
heavy service conditions due to the high speed.
Clearl.y, in case of laxge tires intended to be used on
motor vehicles for normal ~nd heavy duty, such as buses or coaches ,
or motor vehicles for industrial use, the tension stresses which
are e,xerted on the reinforcing structure are very high. Hence,
it is necessary to provide such tires with a reinforcing struc-turl~
which is extremely resistant to tension stxesses wi-thout using
too many layers o reinforcing material because this would produc~
an increase of the weight and/or size of the -tire and would re-
quire an incxease of the inflation pressure with the consequent
increase o the tension stresses on the reinforcing structure.
For these reasons, the trend cor.~ercially is to form the
reinforcing structure with the lowest number of layers possible .,
of reinorcing material havin~ a high modulus oE elas-ticity. .
Theoretically, the reinforcing structure which would assure the
: maximum resistance to tension stresses should be that constituted
by one or more layers of metallic cords, having an ul-timclte
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elongation of about 3% and oriented according to a direction which
is substantially parallel to ~he longitudinal direction of the
tire. However, such a rein~orcing structure is not satisfactory -
because the tire has an undesirable driving behavior, particularly
as regards transverse stability when the tire runs both along a
curved trajectory and along a straight onle.
Consequently, the reinforcing structure usually used to
achieve the above described aims has two layers of metallic cords
arranged so that the cords are parallel to one an~ther in each
layer-and are symmetrically inclined with respect to the longitu-
dinal airection of the tire at a relatively small angle of betweer
about 5 and about 30.
In such a way, the intrinsic rigidity of the material of
the two Iayers is attenuated by a certain flexibility of the re-
sulting reinforcing structure. In fact, the tension strezses due
to the tire inflation result in a reduction of the angle of incli - -
nation of the cords of the two layers and a consequent increase
of the tire diameter. Consequently, the reinforcing structure is
qulte satisfactory also as regards the torsional or transverse
stiffness. This provides a tire which offers a good driving
behav~or, particularly as regards both the driving stability when
the tire runs along a straight trajectory and the lack of drift
when the tire runs along a curved trajectory. ,
However, especially in the large size tires which utilize
a radial carcass having a mono-ply of metallic cords, it is found
that, although the aforesaid reinforcing s-tructure e~fectively
withstands the tension stresses to which the tire is subjected,
the reinforcing structure is not sufficient to co~mterbalance ~he -
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high carcass flexibility. Consequently, the tire does
not respond satisfactorily -to s-teering. Therefore, it
is necessary to add other layers to the reinforcing
structure which act as a stabilizer. In general, a
further strip of metallic cords is used which is arrang-
ed so -that ~he cords are inclined with respect to -the
longitudinal direction at a high angle, for example,
an angle of 60.
It is an object of this invention -to provide a
pneumatic tire having a radial carcass which combines
high resistance to tension stresses and good driving -
stability. Another object of the invention is to pro-
vide a pneumatic tire having a radial carcass and a
tread with a reinforcing structure between the carcass
and tread which has su~ic:ien-t resistance to tension
stresses to adap-t the tire for use on heavy vehicles
such as buses, trucks and the like and which does not
significantly adversely effect the s-teering charac-ter-
istics of the tire.
Other cobjects will become apparent from the follow-
ing description of the inven-tion wi-th reference to -the
accompanying drawing wherein.
Figure 1 illustrates in a partial cross-sec-tion one
embodiment of the tire provided by the invention;
Figure 2 illustrates in a fragmentary perspective
view the tir-e shown in Figure 1 with parts removed in
order to better illustrate the arrangement of the various
cords; and
Figure 3 illustrates in cross-section a second em-
bodiment of the tire of the presen-t invention.
It has now been found, surprisingly, that the appli-
cation to a reinforcing structure having two layers of
metallic cords of
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the type described of a third layer of metallic cords having a
relatively high elongation and arranged in a direction which is
substantially parallel to the longitudinal direction of the tire,
not only provides the tires with the driv:ing stability effects :
which until now were considered due exclusively to the strips of
metallic cords having a high inclination with respect to the
longitudinal direction, but also a very high resistance to the
tension stresses. More specifically, such a reinforcing structur~
has a high enough resistance so that it withstands not only the .
tension stresses due to the inflation pressure of the tire, but .
also those which occur when the tire r~ms at high speed. .
Accordingly, the present invention provides a pneumatic .
~ixe for motor ~ehicles adapted to be used for normal or.heavy
duty vehicles having a reinorcing structure comprising at least
two layers which have widths which are about equal to the width .
of the tread and are formed by me:tallic cords having an ultimate
elongation of about 3%, the cords being parallel to one.another
: in each layer and crossed with respect to those o the other
. layer, the two layers arrangecl so that the cords are inclined with
' respect to the longitudinal direction of the tire at an angle of ¦
5 to 30. The tire has radially outwardly from the first two
layers at least one layer of metallic cords ha~ing a width which .
is substantially equal to that of the tread, the outer layer bein
composed of metallic cords which are parallel to one another and
are arranged in a longitudinal direction, the metallic cords
having an ultimate elongation of about 4% ~o about 8~. :
The tires having the assembly of reinforcing layers as ~
described above can be of the type intended to be mounted on the : :
1()9~5532 ' ~
motor vehicle with or without the inner tube; moreover, al-though
the assembly of rein~orcing layers is extremely advantageous for
tires having large sizes provided with a carcass constituted by a
radial metallic mono-ply, it is understood that it will produce
just as good results if applied to tires provided with a radial
carcass having a plurality of plies and constituted by cords of
-textile material.
Preferably, the layer of metallic cords belong:ing to the
reinforcing structure, which is immediately below the layer of
metallic cords arranged in a longitudinal direction, has a width
which is at least equal to that of the layer. The other layer of
the r~inforcing structure has a slightly smaller width, so that
it is disposed inwardly with respect to the overhanging layer.
As set forth above, it has been found that the large size
~15 tires, particularly those intended to be used for normal and
heavy duty, which are provided with the assembly of reinforcing
layers of this invention are able to offer high perfoxmances not ~ :
A . only in service conditions at normal speed but also at higher
speeds, and they have a very good driving behavior.
The effect of the assembly of reinforcing layers appears
to be still more surprising, if it is taken into account that
tests carried out on similar tires, having the same reinforcing --
structure of the first and second layers of metallic cords having -~
an ultimate elvngation of about 3% plus a third superimposed laye
of metallic cords like those of the first ana second layer except
that the cords are arranged in the longitudinal direction have
shown a clear adverse effect on the driving and comfort charac-
teristics of the tire. In other words, an assembly of reinforcin
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layers which combines a layer of metallic cords of
about 3% elongation arranged in the longitudinal direc-
tion with the first and second layers used in this
inven-tion improves the resistance to -tension stresses
bu-t the combination has the disadvantage of making
steering of the vehicle more difficult. It has been
found that in the assembly of the three layers of this
invention, the layer of longitudinally disposed met-
allic cords supports almos-t all of the stresses. There-
fore, the first and second layers are no-t under tension
and do not interfere with the driving stabili-ty charac-
teristics of the -tire.
The improvement provided by the reinforcing assembly
of the invention is probably due to the unique combina-
tion of relative inextensible metallic cords in -the
first two layers disposed at an angle inclined with res-
pect to the longitudinal axis of the tire with the more
extensible metallic cords of the radial outer layer.
Apparently, the radial outer layer has a bearing ac-tion
and cooperates wi-th the other two layers.
The metallic cords having an ultimate elonga-tion be-
tween ~% and 8%, which hereinaf-ter we will can "ex-tens-
ible", are per se widely known to one skilled in -the
arts. They are consti-tuted by s-trands formed by a
plurality of wires twisted together, and ei-ther the
individual strands or the cord are all wound up heli-
cally in the same sense.
Vice versa, the metallic cords having an ultimate
elongation of about 3%, which are also known per se, ~re
cons-tituted by strands formed by a plurali-ty of wires
helically wound up in an opposite sense with respect to
that of the cord.
According to a preferred embod:imen-t of the present
invention, the layer or the layers of the extensible
me-tallic cords
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are formed by a single extensible cord helically wound
with the convolutions of the helix arranged in -the long-
itudinal direc-tion.
According to ano-ther preferred embodimen-t, the layer
or each of the ex-tensible metallic cords layers is
formed by strips placed side by side, each of which has
a width equal -to a portion of the tread width and
extends longitudinally on the whole development of the
tire-
Referring now to Figure l, one embodimen-t of a
tubeless tire of the size llR22.5 has a tread 1 and a
carcass 2 constituted by a mono-ply of metallic cords
lying in a radial plane or forming small angles with
the radial planes.
Between the tread l and the carcass 2 an assembly
of reinforcing layers is inserted. This assembly has
first and second layers 3 and 4 of me~allic cords
having an ultimate elongation of about 3% and a third
layer 5 radially outwardly with respect to -the o-ther
two layers 3 and 4 of metallic cords having an ulti-
mate elongation of 7%. The layers 3 and 4, as shown
more clearly in Figure 2, are arranged so that -their
metallic cords are parallel -to one ano-ther in each layer
and are inclined respectively at an angleC~?nd L~ 18
with respect to the longi-tudinal direction of the tire.
The layer 5 has its own metallic cords arranged in a
longitudinal direction.
The aforesaid assembly of layers 3,4 and 5 has a
width substantially equal to -that of the tread l.
Since, as is customary, the reinforcing layers are
arranged according to a certain gradua-tion, it is pre-
ferred according to the present invention -that -the
layer 4 has, in the reinforcing struc-ture, the wider
wid-th so as to project slightly from bo-th sides with
respec-t to -the layer 5, while -the layer 3 has a
slightly smaller w1~th with
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respect to tha-t of the layer 4. In such a way, the
layer 5 has the me-tallic cords completely suppor-ted by
the layer 4 along its whole width. This insures a
lower elongation of the reinforcing assembly at its
lateral ends, with consequen-t high perfc>rmance of the
tire in service at high speeds. Layer 5 is disposed on
the layer 4 by helically winding an extensible metallic
cord over layer 4 or one or more strips of cord fabric
of extensible metallic cords are superimposed on layer
4.
Specifically as regards the metallic cords, those
of layers 3 and 4 which, as aforesaid, have an ultima-te
elongation equal -to about 3%, are each Eormed by seven
strands twisted together, each strand being formed by
the helical winding of four steel wires having a d:ia-
me;terequal to 0.22 mm. The strands are twisted toge-
ther according to a winding sense opposite to that of
the bwisting of the individual strands. The metallic
cords forming the layer 5 and having an ultimate elong-
ation of 7% are each composed of three strands, twisted
together, each strand being formed by the winding of
seven steel wires having a diame-ter equal to 0.20 mm.
The s-trands are twisted -together accord:ing to a wind-
ong sense equal to that of the twis-ting of the indiv-
idual strands, with the twisting pi-tch of each strand -
being equal to about 4 mm and wi-th the twisting pitch
of the cord being equal to abo~t 6.5 mm. -
Figure 3 illus-trates an alternate embodiment of the
presen-t invention according to which the -tire 6 has
the ass~mbly of reinforcing layers constitu-ted by two
layers of metallic cords 7 and 8, abou-t equal to -the
two layers 3 and 4 of Figures 1 and 2 and by -the layer
9 of metallic cords having an ultima-te elongation equal
to 7%. Layer 9 consists of -three s-trips, respec-tively ~,
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ll and 12, placed side by side with respec-t -to one
another so as to cover the whole width of the under-
lying strip 8.
The central s-trip ll is a-t leas-t twice the wid-th
of the two other strips lO and 12. In order to dis-
tinguish layers lO, ll and 12 from each other, the
cords of strips lO and 12 are indica-ted in Figure 3
with filled circular section while the cords of strip ~:
11 are shown as mere circular sections. Actually the .
cords of all three strips may be the same. : -
Because of the curvature of the assembly of the
reinforcing layers, these s-trips 10 and 12 have a
longitudinal development lower than the corresponding
development of the strip 11. Preferably the ends of
each strip are joined together a-t poin-ts so -that each . ~:
joint is staggered with respect to the other, for .:.
example by 120. .
In order to demonstrate -the improvement of -the :
tires of the.invention, the embodiment illustra-ted
in Figures~ to 3 of the drawing were compared both
with conventional tires and with tires having rein- .~ ;
forcing structure comprising, in a way per se known,
longitudinally arranged, reinforcing elements differen-t
from those of the present invention.
More particularly, the tires subjected to the tests
were:
Tires:A
Tubeless tires, size llR22.5 (in accordance with -the
present invention) provided with a mono-ply radial met-
allic carcass 7 with a reinforcing struc-ture, arranged
between the tread and the carcass, consisting of first
and second layers of metallic cords having an ultimate
elongation of about 3~, crossed with one another and
inclined with respect to the longi-tudinal d:irecti.on of
the tire at an angle of 18 and wi-th a third layer of
me-tallic :~ .
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504553Z
cords having an ultimate elongation of 7%, the third layer
being arranged radially out~ide the first and second layers
and having its cords arranged in the longitudinal direction
of th~ tire.
Tires B
' :'
Tubeless tires, size llR22.5, provided with a mono-ply
radial metallic carcass, with a reinforcing structure consisting
of first and second layers of metallic cordc having an ultimate -
elongation of about 3%, crossed with one another and inclined
with respect to the longitudinal direction of the tire at an
angle of 18, and with a stabilizer strip, arranged in a radially
inner position with respect to the first and second layers,
constituted by me*allic cords having an ultimate elongation of
; about 3% and inclined at an angle of 60 with respect to the -
longitudinal direction (conventIonal tires).
Tires C
Tubeless tires, size llR22.5, provided with a mono-ply
radial metallic carcass and with a reinforcing structure consist-
ing of three layers of metallic cords, all the cords having an
ultimate elongation o~ about 3%, two of the layers having the
cords inclined at an angle of 18 and crossed with one another, -
while the third layer, radially outward to the ~irst ones, had
the cords arranged in a longitudinal direction.
Tires ~
Tubeless tires~ size llR22.5, provided with a mono-ply
radial metallic carcass, with a reinforcing structure consisting
of two layers of metallic cords having an ultimate elongation of
about 3% cros~ed with one another and inclined at an angle of 18
with respect t~ the 1ongltudinal directio j and wi~h a lay~r of
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polyamide cords arranged in a longitudinal direction, in a rad:i-
ally outer position wi~h respect to ~he first ones.
Tests
The above indicated tires were first o~ all subjected to
laboratory tests in order to evaluate the detachment re~istance o~
the reinforcing structure, par-ticularly at high speeds. In prac-
tice, the test consisted of subjecting the tires to increasing
speeds, each tire being mounted on a rim, in~lated to a pressure
o~ 8 kg/cm~ and put under a load of 2,550 kg (pressure and load
comparable with those maximum advissible in use). The imposed
speeds were at first 70 km/h for 5 hours, with an increasing of
the speed of 10 km/h every -two hours. The obtained results wexe:
Tire~ A reached 160 km/h before detachment of the re:in-
Eorcing structure.
Tires B reached 14~ km/h before detachment of the rein-
forcing structure.
Tires C reached 160 km/h before detachment of the rein-
forcing struc~ure.
Tixes D reached 140 km/h before detachment of the rein-
forcincJ structure.
From the above, :it is noted that tires whose rein~orcing
structure comprises metallic cords arranged in the longitudinal
direction (both having a low and high elongation) givé the better
results.
Then the power consumption resulting from using the differ-
ent types of test tires was de-termined. It was found -that tires
A, C and D gave a power consu~ption analogous and lower than that
resulting ~rom using tires B.
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Then the steering response (an extremely important
characteristic, as the test tires were intended -to be
used for duty at high speeds) was checked. It was
-found that tires A and B had good steering characteris-
tics while tires C and D had very poor steering charac-
teristics.
Because of the poor steering characteristics oftires C and D -they were not road tested .
Road tests with tires A and B werecarried out on a
running track. Each typelof tire was mounted on a truck
each tire having an overload of 20% with respect -to
its maximum capaci-ty. The tires were first run 30,000
; Icm, at a speed of 122 km/h, along a straight stretch.
At the end of this firs-t par-t of the -test it was noted
that the tread of -tires A and B showed an equivalen-t
wear, and neither type had significant craclcings or
damages. In the second part of -the -test, the truck
was run over a curved -track and reverse curved -track.
After a run o-f 1100-1900 km, tires B showed detachments
among the layers of the reinforcing struc-ture so that ~-
the test had to be stopped. Tires A ins-tead ran with-
out de-tachmen-t until the whole tread was worn.
The results obtained from all these tests demonstrate
that the -tires according to -the present invention have
improved performances in every sense over the o-ther
test tires although the structure of the reinforcing
layers at first sight may appear to be only slightly
different from that of the known tires.
Although the invention has been described in detail
for the purpose of illustration, it is to be understood
-that such detail is solely for -that purpose and that
variations can be made therein by those skilled in the
art without departing from -the spirit and scope of -the
invention except as it may be limi-ted by -the claims.
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