FORMED THEREOF

The present invention relates to a pneumatic tyre intended for use on a rim with an emergency-driving device, and/or in a vehicle drive where the pneumatic tyre supports and drives a track.

For instance US-Patent Specifications 3,038,900, 4,183,388 and 4,258,767 disclose emergency-driving wheels . which are based on the provision of an inner supporting device or inner wheel serving to prevent a deflated tyre from collapsing entirely. Such a supporting device reduces deformation of the tyre sides, and thus considerably pro- longes the distance that the tyre can run flat. However, emergency driving with an empty tyre mounted on a rim with an emergency-driving device suffers from the disadvantage that the supporting device or inner wheel is of smaller circumference than the tyre, resulting in a relative move¬ ment between the inside of the tyre and the emergency- driving device. Such relative movement or slipping wears the inside of the tyre which thus is rapidly worn down from within, with the risk that the tyre may split up in the radial plane or the tread of the tyre come loose so that continued driving usually becomes impossible. In the above US patent specifications, it is suggest¬ ed that a rubber layer be arranged on the outer tread of the emergency-driving device or an inner emergency-driving device made of nothing but rubber or plastic be provided. An alternative is to coat the inside of the tyre with a low-friction layer of ethylene polyterephthalate (US-A-

4,007,769 and SE-B-379,313) or a suitable lubricant (US-A- 4,007,769 and SE-B-379,313) which is either applied to the inside of the tyre when the wheel is mounted or distribut¬ ed thereon when the tyre becomes flat. In some cases, this distribution may be carried out by the lubricant being discharged from a container arranged in the wheel and designed to break at the occasion of emergency drivning.

The use of emergency-driving devices of the type de¬ scribed in US Patent Specification 3,028,900 has shown that a large amount of heat is generated by the wear or slipping between the rubber layer arranged on the emerg- ency-driving device and the inside of the pneumatic tyre. With the rapid build-up of heat, there is a risk that the tyre rapidly catches fire and is destroyed. This risk is probably less pronounced when the coating on the emerg¬ ency-driving device or the inside of the tyre consists of a layer of polytetrafluoroethylene, but the risk still remains.

In tests, the use of lubricants in the tyre has given excellent results in emergency driving on consolidated roads. Tyres equipped with emergency-driving devices are, however, mostly intended for cross-country vehicles, such as military vehicles. Thus, in emergency driving with punctured tyres in e.g. deserts or other extremely dry and dusty areas, the lubricant dries very quickly, probably since it takes up the fine-grained dust in the surround- ings. As a result, the lubricating effect is rapidly lost, and the tyre is destroyed as if there had been no lubri¬ cant at all. The provision of ethylene polyterephthalate layers on the emergency-driving device or on the inside of the tyre is impaired by the same drawback, since ethylene polyterephthalate has a poor wear resistance and thus can¬ not withstand the wear caused by dust and other solid particles penetrating into the punctured tyre.

A further difficulty encountered in vehicle drives of the type comprising pneumatic tyres and a track running over the tyres and driven thereby in order to propel the vehicle, is the wear of the tyre portions which come into contact with tyre-supporting elements serving to position the tyres in relation to the track. This is especially pronounced under hot and/or dry conditions. The present invention aims at providing a pneumatic tyre which has a higher resistance to inner or outer wear and, consequently, has a longer service life. The inven-

tion further aims at providing a wheel structure compris¬ ing a rim on which a pneumatic tyre is mounted, and an inner wheel for emergency driving which is mounted on the rim in the pneumatic tyre, said wheel structure being de- signed so as to acquire better emergency-driving proper¬ ties, especially in deserts and other dry and dusty areas, than prior art wheel structures of this type.

In addition, the invention aims at providing a vehicle drive comprising a track and pneumatic tyres which cooperate therewith, said vehicle drive having a longer service life than prior art vehicle drives of this type.

These and other aims of the invention are achieved by a pneumatic tyre having an inner and/or an outer layer with low-friction properties, said tyre being characteris- ed in that said layer is a rubber layer which has a high wear resistance and in which 50-100% of the polymer mate¬ rial is butadiene rubber. When the invention is applied to pneumatic tyres intended to be mounted on rims with an emergency-driving device of the type mentioned above, the low-friction rubber layer is arranged on the inside of the tyre body, at least opposite to the inner wheel of the emergency-driving device. When the pneumatic tyre is tube- less and has an air-sealing layer of butyl rubber, the low-friction rubber layer may be arranged either on the inside of the butyl rubber layer or between this layer and the tyre body.

When the pneumatic tyre is to be used as a driving or supporting wheel for tracks with tyre-supporting elements, the low-friction rubber layer should, according to the invention, be arranged on the outside of the tyre sides, at least in the areas which come into contact with the tyre-supporting elements.

According to the invention, the low-friction rubber layer consists of butadiene rubber, optionally with a minor addition of natural rubber and/or styrene-butadiene rubber in an amount less than 50% of the polymer material, i.e. the amount of natural rubber and/or styrene-butadiene

rubber should be less than one part by weight per part by weight of butadiene rubber.

DE-A-2,658,049 discloses an emergency-driving tyre which, on its inside, is provided with an extra rubber layer having a hardness of 65-85 Shore A and formed from a mixture of styrene-butadiene rubber and butadiene rubber, in which case more than 50% should be synthetic rubber and the synthetic-rubber mixture should contain more than 10% styrene. In addition, the rubber mixture may contain natural rubber. According to this specification, it is preferred that the hardness is in the upper range of the hardness scale indicated. This specification points away from the invention, stating as it does a different rubber mixture which does not chiefly consist of butadiene rubber.

SE-B-397,305 discloses a tyre which, on its inside, is provided with a ^" protective rubber layer having a spe¬ cified tear strength of at least 90 kp/cm. By way of example, mention is made of a rubber mixture consisting mainly of natural rubber and a minor amount of styrene- butadiene rubber. This specification teaches away from the invention by requiring a rubber mixture of high tear strength, whereas an addition according to the invention of a large amount of butadiene rubber reduces the tear strength.

The invention will now be described in more detail below, reference being had to the accompanying drawings, in which

Fig. 1 illustrates the deformation of a pneumatic tyre when used for emergency driving in flat condition.

Fig. 2 is an analogous view showing the tyre mounted on a rim with an emergency-driving device,

Fig. 3 is a sectional view of a pneumatic tyre according to the invention, which is mounted on a rim with an emergency-driving device,

Figs 4 and 5 illustrate two embodiments of a vehicle tyre intended for use with an emergency-driving device as shown in Fig. 3,

Fig. 6 is a sectional view of a vehicle drive with tracks and tyres, and

Fig. 7 is a side view of a small portion of the vehicle drive.

Fig. 1 shows a rim 10 on which a pneumatic tyre 11 is

^' -; mounted. The pneumatic tyre is flat, and when the vehicle is propelled, the tyre sides 12 will bend outwards and be pressed against the tread 14 of the tyre by the rim edges

13. This not only entails a substantial deformation, but also relative movements owing to the diameter of the rim being smaller than the normal diameter of the tyre. Driv¬ es- ing with flat tyres thus rapidly results in the tyre sides being cut to pieces by the rim edges.

Fig. 2 also illustrates the prior art. In this case, the rim 10 is equipped with an inner emergency-driving device 15 in the form of an extra wheel-rim which may be made of steel or be designed in accordance with any one of the above-mentioned US patent specifications. In this case, the inner ring 15 will act upon the inside of the tyre body 14, thereby relieving the pressure on the tyre sides 12. As mentioned earlier, also such emergency driving rapidly wears down the tyre.

Fig. 3 illustrates a wheel structure comprising a pneumatic tyre according to the invention. This embodiment thus consists of a wheel structure including the rim 10 and, mounted thereon, the pneumatic tyre 11, as well as an inner wheel 15 for emergency driving mounted on the rim in the pneumatic tyre. The inner wheel or extra wheel-rim is made of steel or any other suitable metal. According to the invention, the pneumatic tyre has an inner layer 20 made of low-friction rubber of high wear resistance. Thus, the layer 20 is located between the tyre body and the inner wheel 15.

Fig. 4, which illustrates a possible placement of the layer 20, is a sectional view of a portion of the tyre and its tread. In this case, the layer 20 is arranged on the inside of the tyre, inwardly of a butyl rubber layer 21 serving as air-sealing layer. The layer 21 is applied to the inside of the tyre body 22. On the outside of the tyre body 22, there are arranged a tiegum layer 23, a breaker strip 24, and the .tread 25 proper.

Fig. 5 illustrates that, according to the invention, the low-friction rubber layer 20 may also be arranged between the butyl-rubber layer 21 and the tyre body 22. The various layers bear the same reference numerals in Figs 4 and 5.

Fig. 6 illustrates a vehicle drive comprising tyres 11 which are mounted on rims 10 and serve to drive a track 30. Further, tyre-supporting elements 31 are fixed to the inside of the track 30 and serve to position the latter in relation to the vehicle tyres 11. The invention employs a pneumatic tyre which, on its outside, has a low- friction rubber layer with a high wear resistance in the areas which come into contact with the tyre-supporting elements 31. This layer is designated 32 in Figs 6 and 7. As indicated by dash lines in Fig. 6, an emergency- driving device of the type illustrated in Fig. 3 can be used also in this vehicle drive. If so, the pneumatic tyre is provided with a low-friction rubber layer 20 on its inside, corresponding to Figs 3-5.

According to the invention, the low-friction rubber layer is made of butadiene rubber, optionally with an addition of natural rubber and/or styrene-butadiene rubber in an amount less than one part by weight per part by weight of butadiene rubber. The table below illustrates the composition of a suitable low-friction rubber mate¬ rial, as well as a preferred embodiment of such a ma- terial.

Low- friction rubber

Material

Butadiene rubber ( BR)

Natural rubber (NR) and/or styrene-butadiene rubber (SBR)

Peptiser

Intensifying carbon black (ISAF)

Processing oil

Processing aid

Antiozonant

Antioxidant

Ozone-proof wax

Zinc oxide

Stearic acid

Accelerating agent

Retarding agent

Soluble or insoluble sulphur

As peptiser, one may advantageously use pentachloro- thiophenol, e.g. RENASIT-VII (Rhein-Chemie, Mannheim, Germany). The processing oil employed is suitably a high- aromatic mineral oil, and the processing aid is a homo¬ genising agent, advantageously STRUKTOL 40 MS which is a synthetic resin based on alkyl naphthalene and an aromatic compound with an alkyl group (Schill & Seilacher, Hamburg, Germany). A suitable antiozonant is 6-paraphenylene dia- mine, and e.g. a polar trimethyl dihydrochinoline may be used as. antioxidant. As accelerating agent, one may use e.g. cyclohexyl benzothiazyl sulphonamide. A suitable retarding agent is n-(cyclohexyl phthalimide).

Although other low-friction rubber mixtures of high wear resistance may be employed, the most preferred mixtures are based on high concentrations of butadiene rubber.