EP0000458A1 - Pneumatic tyre - Google Patents

Abstract

A tire, in particular with a radial carcass and a reinforced crown, in which the beads each comprise at least one bead wire (12) surmounted by a filling profile (14) with a general section tapered towards the sidewall, in a rubbery mixture reinforced with short fibers. The reinforcing fibers of the profile are, at least in part, oriented in the radial direction of the tire so that the mixture of the profile has an anisotropy ratio at least equal to 2/1.

Description

The invention relates to tire casings, in particular to tires with a radial carcass and a reinforced crown and it has more specifically the object of improving the construction of these tires with a view to giving them better endurance and better road behavior.

In current conventional construction, the beads of the tires each comprise at least one inextensible bead surmounted by a hard rubber profile generally having a triangular section, the carcass ply or plies being folded around this bead / profile assembly.

The main function of the filling profile is to achieve a gradual transition in stiffness between the very rigid lower part of the bead and the flexible and thin part of the sidewall. This transition can be measured depending on whether it is desired to accentuate such or such a property of the tire, either for example the property of comfort, or the properties of behavior and handling. This can be achieved by choosing a greater or lesser hardness and height for the filling profile. However, these means are limited by manufacturing requirements and the risks of altering other properties of the tire. Hard rubber filling profiles and great height (rising for example to mid-side) are favorable to road behavior (course stability, quick responses to changes of direction) but they have poor endurance to flexions repeated vertical flanks so that observes tire failures by rupture of the profiles and carcass plies a little above the rim flanges. Low-profile filling profiles give tires with better tire endurance but with worse road handling. This defect can be corrected by introducing additional reinforcing elements such as "flippers" (strips of fabric folded around the rod-profile assembly), reinforcing strips applied to the folded edges of the carcass or transition gums extending the profile towards the side. But these palliatives increase the number of elements to be assembled, the manufacturing cost and the risk of poor workmanship.

As for the nature of the filling profiles, it has already been proposed, as a variant of the conventional mixtures containing high proportions of reinforcing fillers, to use mixtures of rubber and entangled fibers kneaded with the gum. This type of fibrous mixture makes it possible to obtain the high hardnesses generally desired for the filling profiles. However, they do not in any way eliminate the drawbacks mentioned: if the profile has a great height, it breaks; if it is short it does not ensure good road behavior without the use of additional reinforcing elements.

It has now been found that much better compromises can be obtained between the main qualities sought for tires when the beads comprise filling profiles made of a particular mixture of rubber and fibers suitably oriented and when these profiles have suitable heights.

• La figure 1 est une vue en coupe transversale d'un pneu selon l'invention ; la figure 2 est un diagramme illustrant des résultats d'essais d'endurance de pneus de ce genre.

The invention is described below with reference to the accompanying drawings in which:

• Figure 1 is a cross-sectional view of a tire according to the invention; FIG. 2 is a diagram illustrating the results of endurance tests of tires of this kind.

The tire illustrated by way of example in FIG. 1 is a "Tourist" tire. It comprises a radial carcass 10 consisting of a ply or several superimposed plies of rubberized fabric without frame or light frame, made of flexible textile or metallic cords oriented along the meridian planes of the tire. The edges 11 of this carcass are folded each, from the inside to the outside, around the assembly formed by the rod 12 and the filling profile 14 surmounting this rod. These folded edges 11 are covered by the rim gums 13 in a rubbery mixture resistant to abrasion in contact with the rims of the rim. The top of the carcass 10 is hooped by a reinforcement belt 16, circumferentially inextensible, constituted for example by one or more plies of rubberized fabric of textile or metallic cords. This belt is covered by the tread 17 having a tread suitable for the use of the tire. The sides of the carcass are covered by the side strips 18 in flexible rubber mix.

In the construction of the beads of the tire illustrated, the filling profile 14 has a general section of triangular shape tapered upwards with a height such that the top of this profile is located at a distance h from the base of the bead of between 0.2 and 0.5 times the height H of the tire section. This profile 14 is made of a rubbery mixture reinforced with short fibers, this mixture being worked so that at least a significant portion of these fibers are oriented mainly in the radial or meridian direction of the tire. In the finished tire, this mixture has an anisotropy marked by its properties of resistance to elongation, this resistance being in the radial direction at least twice greater than the resistance measured in the other orthogonal directions (anisotropy ratio 2/1 or more).

For the production of fibrous mixtures, it is possible to use various fiber contents as well as various kinds of fibers as to their nature, their length and their fineness, according to the techniques adopted for their mixing with the rubber matrix and for giving them a more or less advanced degree of orientation, the main thing being to obtain for these mixtures the desired anisotropy characteristics. Good results have been obtained with fibrous mixtures containing from 10 to 75 parts of fibers by weight per 100 parts of rubber, the fibers incorporated being cellulose fibers "Santoweb" from the company Monsanto Cy having lengths between 0.5 at 3 mm and a diameter of the order of 0.01 mm. Mixtures comprising these fiber contents and worked to orient at least a portion of the fibers in the radial direction of the tire make it possible to obtain, after vulcanization, anisotropy ratios clearly greater than 2/1 and up to 10/1. Some mixtures tested had an elongation resistance of 100 kg / cm2 at 10% elongation in the radial direction and an elongation resistance of 14 kg / cm2 at 10% elongation in the circumferential or longitudinal direction of the tire.

The superiority of the results obtained by using filling profiles 14 in an anisotropic fibrous mixture has been demonstrated by comparative tests of behavior and endurance of passenger tires comprising filling profiles in various mixtures, the compositions of which are indicated below. below (conventional orthotropic mixtures A reinforced with pulverulent fillers, fibrous mixtures B with fibers more or less oriented in the circumferential direction of the tire, fibrous mixtures C with fibers oriented in the radial direction of the tire) and, for each type of mixture, profiles of various heights corresponding to h / h ratios of 0.25, 0.40, 0.50 and 0.60.

The test used to assess the endurance of the beads consists in turning the tires in contact with a rotary flywheel at a speed of 80 km / hour under a load and a pressure equal to 165% of the load and the normal pressure and to measure the time necessary for the appearance of a failure in the area of the beads.

The results of the tests are illustrated graphically in FIG. 2 which is an endurance diagram giving the times T from which the tires tested show a failure putting them out of use, these times being worn as a function of the h / h ratios. It can be seen that the tires comprising filling profiles 14 in mixtures A or B not in accordance with the invention have good endurance of the beads only when the heights of the filling profiles are less than 0.3H, an average endurance when '' they have a height greater than 0.5 H and a significantly worse endurance in the range of heights between 0.3 and 0.5 H. But, as was indicated above when the ratio h / H is lower at 0.3, it is noted during the road tests of lateral floats giving the impression that the vehicle has a soft direction, imprecise when cornering and swaying when brought back into line at the exit of the corners; tires with filling profiles higher than 0.5 H have very short response times, giving the impression that the vehicle has a rough and poorly steered direction when entering and exiting corners. In both cases, the tires tested have unpleasant behaviors for average drivers and can be dangerous for inexperienced drivers.

On the other hand, those of the tourist tires tested having filling profiles 14 in an anisotropic fibrous mixture C according to the invention show excellent fatigue endurance. in the range of heights between 0.3 and 0.5 H for which the tires have the best and most pleasant driving behavior for the majority of drivers. It turns out that these filling profiles in anisotropic fibrous mixture have their greatest resistance to elongation in the radial direction of the tire, making it possible to obtain the best endurance / road behavior compromises.

The tires tested included the bead construction illustrated in FIG. 1. It should be noted in this regard that this bead construction makes it possible to exclude the use of other additional reinforcements often used and such as pinballs in fabric wrapping the rod / profile assembly, and opposing fabric stiffening strips against the folded edges 11 of the carcass. Construction is therefore simple and economical.

The folded edges 11 of the carcass can be provided to rise more or less high towards the side so as to completely or partially envelop the external face of the filling profile 14, this in order to adjust the behavior properties at will. However, this adjustment can also be made by acting on the properties of the profiles 14 by varying the content or characteristics of the fibers or the hardness of the mixture by the usual routes. It is thus possible to minimize the length of the folded edges 11 of the carcass so that they do not substantially exceed the upper level of the rods, which saves relatively expensive material.

The invention is not limited to the application to the radial tourist tires described above. It can also be applied to other categories than tourist tires, namely tires for trucks and vans, agrarian, civil engineering or aircraft.

Claims (5)

1. A tire, in particular with a radial carcass and a reinforced crown, in which the beads each comprise at least one bead wire surmounted by a filling profile with a general section tapered towards the sidewall, in a rubber mixture reinforced with short fibers, characterized in that the reinforcing fibers of the profile are, at least in part, oriented in the radial direction of the tire so that the mixture of the profile has an anisotropy ratio at least equal to 2/1. 2. Tire according to 1 ° and in which the filling profile in fibrous mixture oriented in the radial direction rises in the direction of the sidewall up to a height h of between 0.2 and 0.5 times the height H of the section of the tire. 3. Tire according to 1 ° in which the rubber mixture of the filling profile contains from 10 to 75 parts by weight of short fibers per 100 parts of rubber. 4. Tire according to 1 ° in which the short reinforcing fibers of the profile have a length of 0.5 to 3 mm and a diameter of the order of 0.01 mm. 5. Tire according to one of claims 1 to 4 wherein the edges of the carcass are in a manner known per se, folded around the bead from the inside to the outside, said folded edges not substantially exceeding the level upper rods.

Images