Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC TIRES
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Background of the Invention
This invention relates to pneumatic tires and in
particular to radial tires for passenger cars.
Passenger radial car tires of present day
construction typically have tire beads in which a bead
core is surmounted by a filler strip of hard rubber
having a triangular cross-section. The function of the
filler strip is to bring about a gradual transition
between the stiff bead portion of the tire and the very
flexible sidewall areas. Such tires are illustrated in
US Patents Nos 4,258,775, 4,236,563 and 3,232,331.
The present invention is a new and improved tire
construction which achieves to good compromise between
the requirements of the filler strip (sometimes called
an apex strip), the requirements for sealing against a
wheel rim, and a carcass construction in the bead area
which reduces tension between the carcass plies and the
filler strip.
Summary of Invention
According to the present invention there is
provided a pneumatic tire having a carcass with a pair
of bead portions each of which contains a
circumferentially extending bead core, at least one
reinforcing ply extending between the bead cores and
which passes on the axially inner side of each bead
core and has turn-up portions wrapped around the outer
side of each core into overlapping contact with the
ply, an apex strip located in each bead portion and
placed in direct contact with the outside of both the
ply and the turn-up and being formed of an elastomeric
material having a hardness in excess of 80 Shore A,
and a chafer strip located in each bead portion
adjacent and in contact with the axial outer side of
the apex strip, said chafer strip extending at least to
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the axially outer side of the bead core and being
formed of an elastomeric material having a hardness
of between 60-85 Shore A, there being at least a 10
Shore A hardness difference between the hardnesses of
the elastomeric materials of the apex strip and chafer
strip.
Preferably each of said turn-up portions ls in
overlapping contact with the carcass ply for a distance
of at least 10 mm, as measured along the ply, and each
apex strip is triangular in radial cross-section and
extends radially outwardly in contact with the ply for
a distance G which is between 60 % to 80 % af the
distance X, where X is the height between a first axial
plane passing through the middle of the bead core and a
second axial plane passing through the mid-point of the
sidewall, and G is a radius measured from the point of
intPrsection of said first axial plane and the external
surface of the tire, and each of said chafer strips
extends radially outwardly in contact with i~s
respective apex strip for a distance H measured as a
radius from said point, and the distance H is between
50 % to 80 % of the distance G.
Brief Description of Drawings
The invention will be described by way of example
and with reference to the accompanying drawing in which
a radial cross-sectional view of one half of a tire
according to this invention is illustrated.
Detailed Description of the Invention
With reference to the accompanying drawing there
is illustrated a radial cross-section through one half
of a pneumatic tire for a passenger car. The tire
construction is symmetrical about the mid-circumferential
plane M-M of the tire 10 and the tire will be described
with reference to the drawing as if the drawing were a
complete radial cross-section. The tire comprises a
pair of annular bead portions 11 for engaging the bead
seats of a wheel rim. Each annular bead portion 11
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contains a substantially inextensible annular bead cord
13. A sidewall 12 extends radially outwardly from each
bead portion 11 into a crown portion 14 of the tire.
The crown portion 14 has a ground contacting tread 16
extending circumferentially thereabout.
The tire 10 has a radial carcass 17 extending from
bead core 13 to bead core 13 and which comprises a
singl~ elastomeric ply reinforced by cords of a
suitable material such as steel, rayon, or polyamide.
The cords in the carcass ply are parallel to each
other, and for the purposes of this invention a radial
tire is a tire in which the cords are orientated at an
angle of between 75 and 90 with respect to the
mid-circumferential plane M-M of the tire. The tire 10
is further reinforced in the crown portion 14 by a
circumferentially extending belt structure 18 disposed
radially outside the carcass ply 17. The belt
structure 18 comprises two reinforced plies 20A and 20B
which are superimposed one on the other, but could also
comprise other belt structures which are practiced in
art, for example it could comprise folded belts.
In each bead portion 11, the carcass ply 17 passes
on the axially inner side of each bead core 13 and has
a turn-up portion 19 which is wrapped back around the
axially outer side of each core 13 into overlapping
contact with the ply 17, so as to completely envelop
the core 13. The terms 'axial' and 'axially' refer to
displacements along the rotational axis of the tlre and
the terms inner and outer refer to axial positions
relative to the mid-circumferential plane M-M. The
turn-up portion 19 should follow the external surface
of the core 13 as closely as possible. However, during
manufacture of the tire the bead coat, that is the
elastomer surrounding the bead wire, is sometimes
squeezed into the space 29 located between the core 13,
the ply 17, and the turn-up portion 19. It is
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preferable for this space 29 to be as small as possible
and its radially outmost point should not be more than
10 mm above the bead core. The overlapping contact
between the turn-up portion 19 and the ply 17 should be
for a distance of at least 10 mm measured radially
outwardly along the ply line but is preferably in the
order of 1/3 X where X is the height between a first
plane passing through the middle of the bead core 13
parallel to the rotational axis, and a second plane
passing through the mid-point on the sidewall 12 of the
tire also parallel to said axis, the mid point
corresponding with the section diameter SD oE the tire,
that is where the tire has a maximum width between the
sidewalls.
A filler strip 21, usually known as an apex
strip, is located in each bead portion 11 and extend
circumferentially around the tire. Each apex strip 21
is subs-tantially triangular in radial cross-section and
is placed axially outside the ply 17 and the turn-up
portion 19 and is in direct contact with said ply 17
and turn-up portion 19. The base of the triangular
apex strip is adjacent the bead core 13. The apex
strips are formed from an elastomeric material of a
hardness greater than 80 Shore A and preferably about
90 to 95 Shore A.
The advantage of bringing the turn-up portion 19
back into contact with the ply 17 is that, because the
ply end 2~ is closer to the neutral axis in the
sidewall, there is less load acting on the ply end to
initiate separation between the turn-up 19 and the apex
strip 21. The neutral axis is usually followed by the
carcass ply and is the boundary line in the sidewall
between compression stresses and tension stresses.
A chafer strip 22 is located in each bead portion
11, and is adjacent the axially outer side of the
respective apex strip 21. Each chafer strip extends
radially inwardly at least to the outer side of the
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bead core 13 and is formed from an elastomeric material
having a hardness of between 60-85 Shore A. In the
present invention there is a difference in hardnesses
of the elastomeric materials of the apex strip 21 and
the chafer strip 22 of 10 Shore A and of preferably
about 15 Shore A. Preferably the chafer strips 22 in
each bead portion 11, forms a portion of the outer
surface of the tire extending from adjacent the bead
core 13 radially outwardly for a distance V of
approximately 1/4 to 1/3 X where it becomes overlapped
by the elastomer of the sidewall 12. At the point of
overlap an annular raised rib 23 runs circumferentially
around the tire. The rib 23 is arranged to be radially
outside a wheel rim flange and is a visual aid for
helping judge if the tire is correctly fitted onto the
wheel rim. The chafer strips 22 therefore help prevent
abrasion of the bead portion 11 on the wheel rim on
which the tire is mounted since the sidewalls 12 are
generally formed of softer elastomeric material having
a hardness of less than 60 Shore A.
The turn-up portion 19 has its ply end 2~ at a
distance K radially outwardly from a point P, which is
the intersection of the axial plane passing through the
middle of the bead core 13 and the external surface 27
of the tire. The apex strip 21 extends radially
outwards in contact with the ply 17 and its radîally
outermost point 28 is a distance G, measured as a
radius distance from the point P, of approximately
60 % to 80 % of the height X. The distance K for the
ply end 2~, also measured as a radius from the point P
should lie between 25 % to 65 % of the distance G for
the apex strip. The chafer strip 22 extends radially
outwards for a distance Ht also measured as a radius
from P, in contact with the apex strip 21. The
distance H should lie between 50 % to 75 % of the
dis-tance G.
At the turn-up ply end 24 the thickness Tl of the
apex strips 21 and the thickness T2 of the chafer
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strips 22 when measured perpendicular to the ply line
are in the ratio of between 1.5:1 and 3.5:1.
Although there has been shown and described a
specific embodiment of the invention it is to be
clearly understood that certain changes and
modifications can be made by those skilled in the art
without departing from the spirit and scope o the
invention. For instance the carcass could be formed of
more than one ply.
