Pneumatic safety tire

To improve the load supporting capability of a pneumatic safety tire and to prevent the tire bead portion from coming off from the rim seat both during run-flat (flat punctured tire) travel, the pneumatic safety tire comprises a pair of crescent-shaped cross-section reinforcing rubber layers each having the thicknest portion at the tire side portion and a pair of beak-shaped cross-section rim-fixed protruding hard-rubber members each disposed under the reinforcing rubber layer in such a way that annular circumferential bonding surfaces between the two are inclided axially outwardly or inwardly in annular wedge shape. Further, to prevent creases from being produced during green tire forming process and cracks from being produced during run-flat travel in or near the bonding surfaces, crescent-shaped reinforcing layer and the beak-shaped rim-fixed protruding members are extrusion-formed simultaneously before a green tire is formed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a pneumatic safety tire and more 
specifically to an improvement in a pneumatic safety tire which enables 
run-flat travel (run-flat implies a flat punctured tire) with an aspect 
ratio of a 60% or less (a ratio of height to the maximum width of a tire). 
2. Description of the Prior Art 
In addition to a strong demand for increased high-speed performance tires 
with increasing vehicle speed, ultrahigh performance tires which can 
realize spareless tire or run-flat travel have strongly been required with 
decreasing vehicle weight. 
Requirements for pneumatic safety tires for enabling run-flat travel are as 
follows: 
(a) No cracks will be produced on the boundary between the reinforcing 
rubber layer and the rim-fixed protruding member during run-flat travel. 
(b) A higher load supporting capability is maintained during run-flat 
travel. 
(c) The tire bead portion is not separated from the tire bead seat during 
run-flat travel. 
However, so far there exists no pneumatic safety tire which can satisfy all 
the above-mentioned requirements. 
SUMMARY OF THE INVENTION 
With these problems in mind, therefore, it is the primary object of the 
present invention to provide an excellent pneumatic safety tire for 
enabling run-flat travel while satisfying all the above-mentioned 
requirements. 
To achieve the above-mentioned object, a pneumatic safety tire having a 
carcass layer extending from an outer crown portion, through two side wall 
portions, to two inner bead portions, so as to axially outwardly and then 
upwardly enclose a bead wire at the inner bead portion, respectively 
according to the present invention comprises: (a) a pair of 
crescent-shaped cross-section reinforcing layers each having a thickest 
portion thereof at the side portion and extending from the side portion to 
the crown portion and the bead portion along an inside surface of the 
carcass layer; (b) a pair of beak-shaped cross-section rim-fixed 
protruding members each extending from an innermost end of the tire to an 
innermost end of said reinforcing layer and additionally each extending 
axially outwardly along an innermost end surface of the bead portion; and 
(c) a pair of annular circumferential bonding surfaces between said 
crescent-shaped cross-section rainforcing layer and said beak-shaped 
cross-section rim-fixed protruding member being inclined axially outwardly 
or inwardly so as to form an annular wedge-shape sloped bonding surface, 
respectively. 
The crescent-shaped cross-section reinforcing layer and the beak-shaped 
cross-section rim-fixed protruding member may be extrusion-formed 
simultaneously before a green tire is formed. The height of the annular 
sloped bonding surface between the two is located preferably between an 
outermost end of the bead wire and the middle of the side portion of the 
tire. 
In the pneumatic safety tire according present invention, the load 
supporting capability during run-flat travel can be improved; the tire 
bead portion can be prevented from coming off from the rim seat during 
run-flat travel; creases can be prevented from being produced near the 
boundary between the crescent-shaped cross-section reinforcing rubber 
layer and the beak-shaped cross-section rim-fixed protruding hard-rubber 
layer during green tire forming process; and cracks can be prevented from 
being generated at the boundary between the two during run-flat travel. In 
addition, the productivity in tire forming process can be improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the pneumatic radial tire according to the present 
invention will be described hereinbelow in detail with reference to the 
attached drawing. 
A pneumatic safety tire E comprises a pair of right and left bead portions 
10, a pair of right and left side wall portions 20 connected to the bead 
portions 10, respectively and a crown portion 30 connected between these 
two side wall portions 20. 
The tire is further composed of an inner liner R, two carcass layers 40, 
two belt layers 50 and two auxiliary layers 60. The carcass layer 40 is 
formed by arranging nylon cords substantially perpendicular to an 
equatorial plane 0--0 of the tire. As depicted in FIG. 1, the carcass 
layers 40 extend being inclined inward along the inner surface of a bead 
filler 12 and a bead wire 11 and then is bent outward again along the 
inner surface of the bead wire 11 and upward along the outside surface of 
the bead wire 11 and the bead filler 12 to a position where the outermost 
end thereof is folded over the carcass layers 40, as depicted in FIG. 1, 
in such a way that the bead filler is enclosed by the carcass layers. 
The belt 50 includes two plies each formed by arranging non-stretchable 
cords on the carcass layer so as to cross the tire equatorial plane 0--0 
at an angle (10 to 30 degrees) and laid one upon another so that the 
arranged cords of the two plies intersect each other. The two auxiliary 
layers 60 are formed by arranging heat-shrinkable cords all over the belt 
layers 50 substantially in parallel to the tire equatorial plane. 
In FIG. 1, the auxiliary layer 60 is formed with two plies. However, the 
layer 60 may be formed with only a single layer, and the number of the 
layers 60 is increased or decreased according to the tire usage. Further, 
the width of the layer 60 is preferably equal to or a little wider than 
that of the belt layers 50 from the standpoint of hoop effect upon the 
belt layers 50. 
In the safety tire thus constructed, the present invention provides a pair 
of crescent-shaped cross-section reinforcing rubber layers 70 and a pair 
of beak-shaped rim-fixed protruding hard rubber members 80 in such a way 
that the innermost end 71 of the reinforcing rubber layer 70 and the 
outermost end 81 of the hard rubber member 80 are bonded with each other 
being inclined axially outwardly or inwardly so as to form an annular 
wedge-shape sloped bonding surface. 
Each of the crescent-shaped cross-section reinforcing rubber layers 70 has 
the thickest portion roughly at the middle of the side wall portion 20 and 
extends therefrom to the crown portion 30 and the bead portion 10 along 
the inner circumferential surface of the carcass layers 40. Each of the 
beak-shaped cross-section rim-fixed protruding hard rubber members 80 
extends from the innermost end or toe portion 82 of the tire to the 
innermost end of the crescent-shaped reinforcing layer and additionally 
extends axially and radially outwardly along the innermost end surface 11a 
of the bead portion 11 located radially inside the bead wire 11. 
The crescent-shaped reinforcing rubber layer 70 serves to support a load 
applied to the tire in dependence upon the rigidity produced at the tire 
side wall portion 20, particularly during run-flat travel. 
In the drawing, the crescent-shaped cross-section reinforcing rubber layer 
70 is shown as a single body. Without being limited to this, however, it 
is also possible to form this reinforcing rubber layer 70 by joining a 
plurality of different rubber layers one upon another in the radial or 
axial direction of the tire according to the usage and object as long as a 
crescent-shaped layer can be formed in cross section. The hardness of the 
crescent-shaped layer 70 is in the range of 65.degree.-85.degree. Shore A. 
It is preferable to determine the maximum wall thickness of this 
reinforcing rubber layer 70 to lie between 1 and 12 mm although the 
thickness is dependent upon the properties of the rubber. When the 
thickness is too small, it is impossible to provide a sufficient 
reinforcement effect such that load can be supported by the rigidity 
produced at the tire side wall portion 20. On the other hand, when the 
thickness is too large, heat will be excessively generated during run-flat 
travel and additionally riding comfort will be degraded during the 
ordinary travel. 
The rim-fixed protruding hard rubber member 80 serves to reinforce the bead 
portion 10 to prevent the bead 10 from coming off during run-flat travel. 
Further, the protruding rubber member 80 is supported by a rubber member 
91 bonded to the axially outward side surface (bead heel 11b) of the bead 
portion 10 and by a fabric member 90 made of textile cord bonded to the 
inner liner R extending to a somewhat upper portion of the inner end 71 of 
the crescent-shaped cross-section reinforcing layer 70. 
The hardness (in shore A) of this beak-shaped protruding member 80 (after 
vulcanization) is from 65 to 85 and more preferably from 70 to 80; while 
the elastic modulus is from 50 to 120 kg/cm.sup.2 and more preferably from 
75 to 95 kg/cm.sup.2, (in tensile stress when the elongation strain is 
100%). 
In FIG. 1, the bonding position between the reinforcing rubber layer 70 and 
the rim-fixed protruding hard rubber member 80 is located near a height of 
H/6 where H denotes the section height of the tire. However, the bonding 
position can be located within a height range between the bead wire 11 and 
the middle (H/2) of the side wall portion 20 and more proferably within a 
range S between the outermost end surface of the bead wire 11 and the 
middle (H/2) of the side wall portion 20, as depicted in FIG. 1. 
In FIG. 1, the bonding surface between the reinforcing rubber layer 70 and 
the rim-fixed protruding hard rubber member 80 is inclined axially outward 
so that the innermost end 71 of the layer 70 and the outermost end 81 of 
the member 80 are bonded to each other in wedge form. However, it is of 
course possible to incline the bonding surface axially inward. The 
above-mentioned inclined bonding surface serves to widen the bonding 
surface area between the reinforcing rubber layer 70 and the rim-fixed 
protruding member 80, thus increasing bonding strength during the green 
tire forming process, while improving the productivity thereof. 
It is particularly preferable to form the reinforcing layer 70 and the 
protruding member 80 integral with each other in accordance with extrusion 
forming method, before forming the green tire, because it is possible to 
prevent creases or cracks from being produced when internal stresses are 
concentrated to the boundary between the two during the green tire forming 
process or run-flat travel. 
In particular, when the reinforcing rubber layer 70 is formed of rubber 
having a relatively high shore hardness after vulcanization equivalent to 
that of the protruding member 80, the previous integral extrusion forming 
of both is desirable. 
The mechanism of generation of creases or cracks at the boundary between 
the two 70 and 80 will be described hereinbelow in further detail. 
In vulcanization process of a green tire, a green tire is put into a hollow 
cavity formed in a roughly rectangular vulcanization mold and then a 
bladder (for simultaneously forming and vulcanizing a green tire) is 
brought into contact with the inner side of the green tire while heating a 
vulcanizing mold, in order to vulcanize it by applying steam pressure. In 
this process, the bladder first applies pressure to relatively flat 
portions of the tire (i.e. the middles of the crown portion 30 and the 
side wall portion 20) and then to curved portions (i.e. the shoulder 
portion 31 and the bead portion 10) with a time delay. Therefore, the 
rubber first heated and pressurized is softened and therefore tends to 
flow toward the rubber portions heated and pressurized with a time delay, 
so that creases are easily produced at the rubber portions heated 
afterward. 
The reinforcing cord of the carcass layer is organic fiber cord represented 
by nylon, polyester, rayon, aromatic polyamide fiber cord or metal cord 
such as steel cord. The reinforcing cord of the belted layer 50 is 
non-stretchable cord such as aromatic polyamide fiber code or steel cord. 
The cord of the auxiliary layer is organic fiber cord having an 
appropriate heat shrinkability such as nylon cord, polyester cord, etc. 
Test Results 
The following tests have been effected to verify the effects of the safety 
tire according to the present invention. 
[1] Specifications of Test Tires of Present Invention 
(a) Tire size: 255/40VR 17 
(b) Tire structure: As shown in FIG. 1. 
(c) Carcass layers 40: Two plies are formed by use of nylon cord 1260d/2 
(the number of cord ends: 26.4 cords/25 mm) inclined at 90 degrees with 
respect to the tire equatorial plane. 
(d) Belt layer 50: Two plies are formed so as to intersect each other by 
use of steel cord 1.times.5.times.0.23 inclined at 24 degrees with respect 
to the tire equatorial plane. 
(e) Aux. layer 60: Two plies are formed by use of nylon cord 1260d/2 (the 
number of cord ends: 28.6 cords/25 mm) parallel to the tire equatorial 
plane. 
(f) Reinforcing layer 70: As shown in FIG. 1. Shore hardness (A) is 80. The 
maximum thickness is 9 mm. 
(g) Rim-fixed Protruding member 80: As shown in FIG. 1. Shore hardness (A) 
is 75. 
(h) Bonding method: The reinforcing layer 70 and the rim-fixed protruding 
member 80 were formed integral with each other through an extrusion 
forming process, before green tire forming process. 
[2] Specifications of Test Tires for Comparison 
(a) to (g): The same as the Tires for the invention. 
(h) Bonding method: The reinforcing layer 70 and the rim-fixed protruding 
member 80 were formed separately through two different extrusion forming 
processes before green tire forming process. 
[3] Test Results 
Table 1 below shows test results, in which productivity is indicated as 
indices in comparison with the tire for comparison (100). The smaller the 
indices are, the better will be the productivity. 
TABLE 1 
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Tires for Comparison 
invention 
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Crease generation 
Creases appear along the 
None 
during molding 
circumference near the 
process boundary between the 
layer 70 and the member 
80 
Crack generation 
Cracks appear along the 
None 
after 30 km boundary between the two 
run-flat travel 
Productivity 
100 98 
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