Safety pneumatic tire

Tires are improved against puncture damage by at least partially filling the inside of the tire with hollow spheres which contain a gas and whose thin shell consists of synthetic material, these spheres having a diameter of between 0.01 and 0.04 mm. and a density of 0.005 to 0.25 g/cc., and/or by lining at least a portion of the surface of the inner wall of the tire with a strip of composite material of low density comprising a suspension of said hollow spheres in a mass of liquid or pasty synthetic material of low molecular weight.

The present invention relates to a tire and more particularly to a filling 
material intended to prevent the inflation fluid from escaping when the 
tire has been punctured or to prevent said fluid from escaping to an 
extent which dangerously jeopardizes the road adhering properties and the 
load bearing capacity of the tire; the invention also relates to a tire 
provided with such material. 
The drawbacks and dangers which a tire, which has been damaged in this 
manner, presents for the vehicle and its occupants are well known and 
numerous suggestions have already been made for the remedying thereof. It 
has, for instance, been proposed that the tire be subdivided into a 
plurality of air-filled compartments or that it be provided with a filling 
of synthetic material, cellular rubber, gas-containing balls, etc. 
None of the solutions contemplated up to the present time has been able to 
gain acceptance, because they present too many drawbacks with respect to 
manufacture, with respect to normal travel of the tire, or with respect to 
travel after puncture or else after the tire has remained for a long time 
without traveling. Such drawbacks consist of the formation of excessive 
imbalance, and the disaggregating of the filling of synthetic material or 
cellular rubber under the prolonged action of the heat produced during 
driving. 
In order to avoid the above drawbacks, the invention employs a material 
which is known per se in other applications and which consists of hollow 
spheres containing a gas and the thin shell of which consists of a 
synthetic material, for instance, polyvinylidene chloride, these hollow 
spheres having a diameter of between 0.01 and 0.4 mm., preferably between 
0.02 and 0.1 mm., and a density of 0.005 to 0.25 g./cc., preferably 
between 0.015 and 0.08 g./cc. 
It has been found that these known hollow spheres whose shell consists, for 
instance, of polyvinylidene chloride lend themselves particularly well to 
use in accordance with the invention due to their smooth surface, their 
low coefficient of friction, their ability to withstand high compressive 
forces and the large volume of gas which they contain. A description of 
such hollow spheres is to be found in an article entitled "Expandable 
Filler Catches On" appearing in the magazine "Modern Plastics", August 
1969, pages 55-57. 
The invention contemplates using these hollow spheres either in the form of 
a suspension in a gaseous continuous phase which at least partially fills 
the tire cavity (first embodiment of the invention), or in the form of a 
suspension in a liquid or semi-liquid continuous phase which can be 
adhered on at least the portion of the inner wall of the tire below the 
tread (second embodiment of the invention) or else in the form of a 
combination of these two suspensions (third embodiment of the invention). 
Due to the gaseous, liquid or semi-liquid (pasty) physical state of the 
continuous phases of the suspensions, the suspended hollow spheres therein 
are free to move relative to one another and thus be able to plug and to 
seal a puncture hole in the tire. 
The friction can be decreased even more and the sliding improved, if, in 
accordance with the invention, small amounts by volume of liquid and/or 
solid lubricants are added, such as, for instance, silicone oil and/or 
zinc stearate or powdered graphite. An amount of 0.05 % to 6.5% lubricant, 
referred to the volume of hollow spheres in the total filling, is 
generally sufficient. 
As a result of the favorable ratio between the shell of synthetic material 
and the gaseous center, the hollow spheres which preferably comprise a 
very thin layer of lubricant on their outer surface behave like air 
contained in an airtight tire when they are subjected to compression. 
It has been found that a quasi-suspension composed of the hollow spheres 
and air behaves practically exactly in the same manner as air when it is 
in such an airtight tire from which the air cannot escape. 
When the tire in which these spheres are contained is punctured, the 
spheres are retained in the tire which, even after disappearance of the 
compressed air which it contained, behaves like a tire traveling under 
reduced pressure of inflation. 
In accordance with the invention, the filling material may be composed 
exclusively of individual spheres, i.e., spheres which are separated from 
each other, or the spheres may be loosely connected together by means of a 
lubricant. 
It is also possible within the scope of the invention to employ together 
with the spheres, that is to say in addition to them, other known tire 
filling materials, for instance, compressed air contained in an airtight 
rubber enclosure, or else freely movable solid particles of cellular 
material of very low apparent density, which possibly bear a lubricant 
having a low vapor pressure, as described in U.S. application Ser. No. 
535,699, filed Dec. 23, 1974, now Pat. No. 4,003,419. 
The compressed air and spheres may be introduced into the tire in any 
manner, for instance, by means of a valve or a trocar. The spheres are 
preferably introduced into the tire when the latter is mounted on its rim, 
whereupon the air is introduced so that the turbulence caused by the 
introduction of the latter forms the above-mentioned quasi-suspension. 
The ratio of spheres to air results from practical requirements. A 
completed filling preferably comprises from 30 -98% by volume of spheres 
for a pressure of 0.01 to 5.8 bars within the tire. 
It has been found that a known tire mounted on a rim and containing 55% by 
volume of spheres and 45% by volume of air compressed to 1.6 bar assured 
travel under optimum conditions of comfort and safety. 
In case of variations in temperature a tire which contains a filling in 
accordance with the invention behaves in more constant fashion than a 
conventional tire. In particular when a small amount of powdered graphite 
is present as lubricant, the heat produced by the friction on the ground 
is better discharged to the rim than in the case of a conventional tire or 
a tire filled with cellular material. 
The second embodiment of the invention is produced with hollow spheres 
which preferably have different diameters and are loosely connected to 
each other by liquid or pasty synthetic material and then fastened to the 
inner wall of the tire so that they can be detached therefrom, together 
with the synthetic material in which they are contained, under the action 
of an external force. In this second embodiment of the invention, we no 
longer have a suspension of spheres in air as in the first embodiment but 
rather we have a suspension of individual spheres of different diameters 
in a liquid or pasty synthetic material of low molecular weight. 
The composite material thus formed is airtight and of low density, of the 
order of 0.05 to 0.60 g./cc. and preferably from 0.08 to 0.26 g./cc.; a 
relatively large quantity thereof can therefore be introduced into the 
tire without impairing its riding properties. 
Due to the gas (which may be air) occluded within the hollow spheres and 
due to the fact that the liquid or pasty synthetic material of low 
molecular weight cannot migrate into the hollow spheres, the low density 
of the composite material in accordance with the invention continues to 
exist even after a lengthy period of severe service. The risk of this 
composite material accumulating at the bottom of the tire when stopped is 
thus also avoided. 
The use of hollow spheres of different diameters in accordance with the 
second embodiment of the invention has two aspects: 
1. the smaller spheres fill up the spaces between the larger spheres so 
that less liquid or pasty synthetic material of low molecular weight is 
required, which has a favorable effect on the density of the composite 
material; 
2. under the action of the centrifugal force, the smaller spheres gradually 
collect on the inner wall of the tire and immediately and lastingly plug 
there any mechanical damage by infiltrating into the damaged point. The 
small particle size of the spheres (preferably 0.02 to 0.1 mm.) and their 
smooth outer surface favor their penetration into the damaged place. These 
spheres behave at the damaged place like a plug of soft rubber due to 
their elasticity under compression. They are not expelled out of the hole 
under the action of the centrifugal force, since they are of low density. 
The invention is not limited to the polyvinylidene chloride spheres 
mentioned above; any hollow spheres containing a gas occluded within a 
thin envelope can be used. A description of suitable hollow spheres is to 
be found in the magazine "Kunststoffe," Volume 60, 1970, No. 1, pages 19 
to 22. 
In order to combine the spheres with each other and with the inner wall of 
the tire any liquid or pasty synthetic materials of low molecular weight 
of less than 7,500 can be used which have not attacked the thin layer of 
spheres within 172 hours of contact with the spheres at a temperature of 
65.degree. C. Commerical copolyamides known under the trademark VERSAMID 
and a commercial polybutylene known under the trademark OPPANOL B. have 
proved to be particularly suitable. 
In a preferred arrangement, the composite material which is adhered to the 
inner wall of the tire is first of all covered with a thin adherent 
protective layer on the face thereof opposite said wall. 
For a tire which is subjected to normal stresses, it is generally 
sufficient to arrange the composite material in the tread region of the 
tire, since practically all damage occurs in this region. 
For a tire for military vehicles a larger quantity is necessary, preferably 
in combination with a filling in accordance with the first embodiment of 
the invention, that is to say with a gaseous suspension of hollow spheres 
so that the side walls of the tire are also protected. This arrangement 
constitutes the third embodiment of the invention. 
While in the second embodiment of the invention the hollow spheres act only 
to plug a hole thus preventing any substantial loss of inflation fluid 
from the tire, they play a twofold role in the first embodiment, namely, 
in the same manner as in the second embodiment, they rapidly plug the 
hole; furthermore, even if the inflation pressure of the tire has dropped 
substantially, the mass of these spheres with which the tire is at least 
partially filled contributes to supporting the load. 
One method of manufacturing a tire provided with the composite material in 
accordance with the invention consists in distributing in any manner 
within the liquid or pasty synthetic material of low molecular weight, 
possibly together with other bodies, compact particles of synthetic 
material which contain an inflating agent and which will form the hollow 
spheres. This mixture is then heated to about 70.degree. C. which causes 
the formation of hollow spheres; the filling material is then practically 
ready for use. Thereupon, a strip of filling material corresponding to the 
inner wall of the tire to be filled is formed out of said material by 
means of molding or extrusion, the strip being preferably engaged between 
two thin protective sheets. One of these sheets is withdrawn before 
applying the strip of material against the inner wall of the tire and 
pressure is applied to said strip in order to cause it to adhere to the 
said inner wall on the face thereof which does not bear a protective 
sheet. The tire can then be mounted on its rim and inflated as in the case 
of an ordinary tire. 
It is also possible to produce the hollow spheres by heating the above 
mixture directly in the tire. A description of the formation of hollow 
spheres is to be found in the magazine "Modern Plastics", August, 1969, 
pages 55-57. 
The invention will now be described in further detail on the basis of an 
example. 
In a tubeless tire of size 175/70 SR 13, a strip of filling material in 
accordance with the invention was applied to the portion of the inner wall 
located below the tread. The protective sheet, which covered the face of 
said strip which was intended to adhere to said wall, had been first 
removed. The tire was then mounted on its standard rim, inflated with air 
to 1.9 bar and the assembly balanced. The wheel being fastened to the hub. 
The tire was punctured in a groove of its tread by means of a pointed tool 
having a diameter of 5 mm. which also punctured the strip of material 
having a thickness of about 5 mm., after which this tool was withdrawn. 
After traveling for 1,100 km., this tire was still capable of traveling at 
normal speed, whereas a tire containing only air and punctured with the 
same tool had become unusable at the end of 5 km. The tire which had been 
punctured the first time was then punctured at two other places of the 
tread, also in a groove. After traveling an additional 210 km. and being 
placed for 8 hours at 50.degree. C. in a drying furnace, this tire was 
allowed to cool and its pressure measured; it was found to be 1.75 bar, 
namely, a minimum loss of 0.15 bar. The good traveling properties were not 
impaired by this heating.

FIG. 1 shows a tire 10 mounted on a rim 11 which is provided with an 
inflation valve 12. This tire contains hollow spheres 13 in accordance 
with the invention which, before inflation of the tire by compressed air 
introduced through the valve 12, fill up about 95% of the inside volume of 
the tire. 
The tire 20 shown in FIG. 2, is mounted on a rim 21 provided with an 
inflation valve 22. The tire 20 has an inner wall 23. On the portion of 
this wall which is located below the tread 24 there is fastened by 
adherence a strip 25 of composite material in accordance with the 
invention. In a variant (not shown) this strip extends over the entire 
inner wall of the tire. 
In the third embodiment of the invention, shown in FIG. 3, a strip 35 of 
composite material in accordance with the invention covers the entire 
inner wall 33 of the tire 30. Furthermore, this tire is filled with hollow 
spheres 36 in accordance with the invention in a quantity equal to 98% of 
its inner volume, this percentage of filling being measured before the 
inflation of the tire.