WO2015132282A1

WO2015132282A1 - Method for testing the resistance of a tyre to a loss of pressure

Info

Publication number: WO2015132282A1
Application number: PCT/EP2015/054467
Authority: WO
Inventors: Christopher CAREME
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2014-03-06
Filing date: 2015-03-04
Publication date: 2015-09-11
Also published as: FR3018353A1; FR3018353B1

Abstract

Method for testing the resistance of a tyre to a loss of pressure following a puncture, comprising a first part performed at an ambient temperature above 10°C in which a plurality of punctures is created in the wall of the tyre by inserting a plurality of piercing objects through the wall, the tyre is run on with the piercing objects in it over a given distance at a regulated inflation pressure, running is halted, an index relating to the resistance to loss of pressure is determined for each puncture on the basis of an estimate of the rate of leakage of said puncture, and a second part performed at an ambient temperature below 10°C in which a plurality of punctures is created in the wall of the tyre or of a similar tyre by inserting a plurality of piercing objects through the wall, a pre-index indicating the cold resistance to loss of pressure is determined for each puncture on the basis of an estimate of the flow rate through the puncture, the plurality of piercing objects is extracted from the wall of the tyre and an index indicating the cold resistance to loss of pressure is determined for each puncture on the basis of an estimate of the leakage flow rate of the puncture.

Description

METHOD FOR TESTING THE RESISTANCE TO A LOSS OF PRESSURE OF A

PNEUMATIC

Field of the Invention [0001] The present invention relates to tires, and more particularly to a method of testing the resistance to pressure loss following perforation of a tire.

State of the art

During a perforation of the wall of a tire by a perforating object such as a screw or a nail, or "puncture", the air inflation of the tire can escape through perforation and pressure loss. consecutive cause a flat tire and a stop of the vehicle.

The delay between the perforation and the flattening of the tire is very variable, depending in particular on the size of the perforating object but also the continuation or not of the rolling with the perforating object in place in the wall of the tire. pneumatic. This rolling causes relative movements between the perforating object and the tire wall which often enlarges the perforation and accelerates the leakage flow.

To solve this problem of punctures which dates from the very beginning of the use of wheels with inflated tires, the usual solution is to stop and replace the wheel concerned by a spare wheel.

Other solutions have been imagined and are available on the market to avoid having to use a spare wheel.

US 5,916,931 discloses an aerosol container comprising an aqueous latex emulsion mixed with various products including fibrous products and a propellant gas. In the case of a flat tire, this container is intended to be fixed to the valve of the tire and to send into the internal cavity of the tire the propellant gas and the sealing / repair emulsion. The tire is then re-inflated at least partially, the emulsion plugs the perforation and can be rolled again, reduced speed first to properly distribute the emulsion over the entire internal surface of the tire and then normally.

There are also repair kits, offered by some car manufacturers in place of a spare wheel. This has the advantage of reducing the weight of the car, so its fuel consumption and free space under the floor of the trunk.

[0008] The puncture kit consists of a compressor, a bottle of sealant, an electrical connection cable and an air hose. Once the product bottle is attached to the compressor, the air hose is screwed onto the cylinder and the tire valve and the electrical cable is connected to the vehicle's cigarette lighter, all you have to do is compressor switch to "on", while letting the engine run so as not to discharge the battery.

The sealant empties into the tire in about 30 seconds during which the pressure in the air hose will rise to about 6 bar. Then, the air will inflate the tire and the theoretical inflation pressure will be reached within 10 minutes. Once the pressure is reached, all you have to do is turn off the compressor and remove the kit.

Once the tire inflated, it is necessary to quickly take the wheel, travel 10 km and check the pressure of the tire using the compressor and the air hose to bring it to the required level.

Once the tire flat repaired, it should not exceed 80 km / h and have control or change his tire quickly. The tire repair kit is only a temporary repair.

Tire manufacturers have also proposed tires provided on their inner wall or in their structure with a layer of elastic products, viscous or pasty, called "self-sealing products", allowing closure of the perforations. WO 2008/080556 A1 shows an example of such a tire. These tires are not as such indestructible, but the perforations are normally closed or closed by the self-sealing product. The manufacturers of these different solutions all have remarkable results of sealing perforations through their products, especially during a perforation followed by immediate withdrawal of the perforating object. But, no test method corresponding to the usual conditions of rolling exists and so it is very difficult to know the real effectiveness of these different solutions and compare them.

Brief description of the invention

The invention relates to a method for testing the resistance of a tire to a loss of pressure following a perforation, characterized in that:

in a first part carried out at an ambient temperature above 10 ° C:

A plurality of perforations are created in the tire wall by inserting a plurality of perforating objects through the wall;

The tire comprising the perforating objects is rolled over a given distance with a regulated inflation pressure;

• stop driving; and

For each perforation, a heat loss pressure resistance index based on an estimate of the leakage rate of the perforation is determined;

said first part comprising two phases such as:

in the first phase, the plurality of perforating objects is composed of tapered and smooth-walled objects such as nails and the rolling is carried out so that the objects are not ejected during the rolling; and

in the second phase, the plurality of piercing objects is composed of tapered but walled objects having a thread such as screws and the rolling is carried out at speeds below 80 km / h;

in a second part carried out at an ambient temperature below 10 ° C:

A plurality of perforations are created in the wall of the tire or similar tire by inserting through the wall a plurality of piercing objects;

For each perforation, a cold resistance pre-index is determined for the loss of pressure based on an estimate of the flow rate of the perforation;

The plurality of piercing objects is extracted from the wall of the tire; and

For each perforation, a cold resistance index is determined for the loss of pressure based on an estimate of the leakage rate of the perforation. By similar tire means a tire of the same characteristics as the tire initially tested. Both tires are equivalent.

This test method has the advantage of analyzing the resistance to perforation of one or more similar tires under conditions close to the wide use conditions, hot and cold. The first part with a rolling, so hot, is very selective and the second part performed at a low temperature, or cold, complete the analysis. This second part does not include rolling but simply insertion and removal of piercing objects. Indeed, more selective results have been observed following this procedure. The fact of rolling tires in a cold environment provides little additional information, in fact, it tends to find the results of the hot test method, due to warming of the tire during taxiing. The first part is very selective because of the rolling performed in the presence of a plurality of piercing objects. This rolling causes relative displacements of the perforating objects and the wall of the tire which can widen the perforations and make it much more difficult for them to be closed or to maintain their filling. The use of a plurality of perforating objects of various types and diameters coupled with controlled pressure rolling makes it possible, with a single tire or a very small number of similar tires, to obtain numerous results of resistance to perforation and therefore to limit the number of tests required. It is advantageous to regulate the inflation pressure of the tire under test to compensate for any leaks that may appear during taxiing, particularly in the case of perforating object ejection. This makes it possible to study the perforation performance related to the other perforating objects present in the tire.

This test method is particularly useful for tires comprising a self-extinguishing product, for example a layer of self-sealing product disposed on its inner wall or in its wall.

When the tire has no self-sealing product, in the first part, when stopping the rolling and before determining the resistance to loss of pressure index, it is put in place in the internal cavity of the pneumatic shutter product. Similarly, in the second part of the test, cold, after inserting and tearing the perforating objects, is placed in the internal cavity of the tire a product. shutter, the tire is brought back, if necessary, to the test temperature of the second part, and the pressure loss resistance index is determined.

This test method allows to test under realistic conditions all the alternatives of a spare tire in case of puncture, including puncture-resistant bombs and repair kits. Of course, this setting up of a sealing product inside the internal cavity of the tire is to be carried out according to the procedure specific to each sealing solution tested.

The test method according to an object of the invention comprises two parts.

Preferably, in the second part, cold, the plurality of perforating objects consists of tapered objects and smooth walls such as nails.

Advantageously, the whole of the second part is performed when the tested tire is at a temperature between -20 ° C and + 10 ° C.

The test temperature is to be adapted according to the conditions of use provided for the tires. The first part of the test method according to an object of the invention comprises several phases, each phase using different types of perforating objects and suitable test conditions.

The applicants have indeed found that the performance of a self-sealing product or a layer of self-sealing product may be different depending on the shape of the obturating objects.

It is found that when the perforating objects are tapered smooth wall objects such as nails, the performance is constant at low speed and then gradually decreases from a certain threshold speed. The first phase of the first part of the test method with such nails as perforating objects has the advantage of testing the perforation resistance performance at a speed sufficient for the test to be selective but insufficient to cause a significant ejection of piercing objects. Preferably, the driving speed Vi for this first phase is fixed and greater than 80 km / h, very preferably between 90 and 120 km / h. Below 80 km / h, the test method does not classify close self-sealing product solutions and beyond 120 km h, the proportion of ejected nails becomes too important.

Indeed, it has been found that the performance of a self-sealing product or a self-sealing layer after ejection of the perforating object, and particularly nails, is very random. It is not therefore possible to have a selective and reproducible test in the presence of numerous ejections piercing objects.

The test method comprises in its first part a second phase in which the plurality of perforating objects consists of tapered objects and walls with a thread, such as screws.

It is found that the self-sealing performance in the presence of such perforating objects is less good at rest and at low speed but evolves positively depending on the speed at which the rolling is performed.

In the presence of such screw-type perforating objects, it is found that a preheating of the tire between 50 and 60 degrees Celsius at the time of insertion of these objects improves the performance before the rolling and also after rolling. Advantageously, such preheating can be part of this second phase to the extent that one gets closer to the conditions of use: the majority of cases punctures occur when the tire is running, so hot. The rolling of the second phase is preferably carried out at a speed below 80 km / h. This makes it possible to clearly differentiate the behavior of different anti-blocking solutions in the presence of perforations in the crown of the tire due to screws. Advantageously, the driving speed V ₂ is between 50 and 75 km / h.

Advantageously, this second phase of the test method is completed by carrying out a test with screw-type perforating objects with a higher fixed speed V ₂ _ ₂ , greater than 80 km / h.

This allows to appreciate for each solution the slope of the improvement of the anti-sealing performance as a function of speed.

The test method thus described makes it possible to assess the resistance to pressure loss of a hot self-sealing solution in two complementary cases of objects. piercing. It can be seen that the rankings of the solutions are independent of each other in these two cases.

Advantageously, the first part of the test method further comprises a third phase with the following steps: - creating in the wall of said tire a plurality of perforations by inserting through said wall a plurality of piercing objects;

extracting from the wall of said tire the plurality of piercing objects;

- Roll the tire after extraction of perforating objects at a speed V ₃ greater than 120 km / h for a given distance with a regulated inflation pressure; - stop taxiing; and

determining for each perforation a pressure loss resistance index based on an estimate of the leakage rate of said perforation.

Preferably, the speed V ₃ is fixed and less than 180 km / h.

This third phase of the first part has the advantage of characterizing the performance of a self-sealing solution in a third case independent of the first two already described. It is a question of testing the high-speed mechanical resistance of the plugs of self-sealing product which fill the perforations after the perforating object has been extracted. The results of this third phase are complementary to those of the first two. The driving distance for each phase of the test method is preferably greater than 200 km and very advantageously greater than 500 km.

Of course, depending on the circumstances and the number of piercing objects used for each phase, one can use the same tire for the three phases of the first part of the test method or several similar tires, each equipped with the same self-sealing solution, to test this self-sealing solution.

Advantageously, the first part of the test method comprises a complementary calculation step for each phase of a mean pressure loss resistance index (I _M i, I _M2 , I _M3 ) for all perforations.

These indices complete the similar index of resistance to the average cold pressure loss that can be calculated for the second part. It is also advantageous to determine each index by combining the notations of perforating objects and weighting them with a frequency curve of appearance of objects in the customer.

For example, one can refer to the distribution curve of the diameters of nails and / or screws observed in a given country. This makes it possible to get closer to the real conditions of use in a given country.

The three indices thus obtained I _MI , I _M2 , I _M3 make it possible to characterize very selectively the hot resistance to the loss of pressure following a perforation of a tire, that this tire is equipped from the outset a self-sealing product or not.

The rolling of the tire can be performed on a steering wheel.

Preferably, the tire is inflated before inserting the perforating objects through its wall. This facilitates the insertion of piercing objects.

During both parts of the test and in particular during rolling, the inflation pressure of the tire is preferably regulated and very preferably regulated at a pressure of between 1.8 and 5 bar depending on the type of tire being tested.

Advantageously, the plurality of perforating objects comprises screws and nails of diameters and / or of various lengths.

The diameter of the perforating objects is preferably 3 to 5 mm. Advantageously, the plurality of perforating objects comprises from 10 to 50 perforating objects, preferably between 20 and 40.

The perforating objects can be inserted into the crown of the tire from the outer surface of the tread grooves of the tire.

They can also be inserted into the sculpture patterns of the tire. Advantageously, a surfactant is used to visualize and qualitatively assess the leakage rate of each perforation.

The following scale can be used to assess the leakage rate of a perforation:

- 100: no bubble is visible, no leak; - 80: nano-leakage, very small bubbles less than 0.1 mm in diameter, visible only by magnifying glass;

- 60: micro-leakage, small bubbles visible to the naked eye, with a diameter of between 0.1 and 1 mm;

- 0: leakage, evolutionary bubbles of diameter greater than 1 mm, or no bubble due to too much air flow.

Description of the Figures

The appended figures illustrate different aspects of the method for testing the resistance to a loss of pressure of a tire in the case of a tire comprising a self-sealing layer on its inner wall:

- Figure 1 shows some perforating objects;

FIG. 2 is a curve, in cumulative frequency, of the distribution of nail diameters observed in China and in the United States;

- Figure 3 is a partial top view of a tire crown with three perforations;

FIG. 4 illustrates the case of a perforation with zero leakage flow;

FIGS. 5 (a) and (b) illustrate the case of a perforation with a very low leakage rate;

FIG. 6 illustrates the cases of a perforation with a low leakage rate;

FIGS. 7 (a) and (b) illustrate the cases of rapid leakage perforation; and

- Figure 8 shows schematically the influence of the rolling speed on the performance of a self-sealing solution.

Detailed description of the invention

We test a tire 1 of size 205/55 R 16 Michelin Energy Saver provided with a layer of self-sealing product as presented in the application WO 2008/080556 A1 cited above.

We will now describe the first part of the test for resistance to a loss of pressure of this tire.

Figure 8 shows very schematically the influence of the rolling speed on the performance of a given self-sealing solution. The driving conditions are those of the different phases of the test method according to an object of the invention. The graph (a) shows the case of nail-like perforating objects, tapered objects whose side wall is smooth (phase 1). The performance is excellent at low driving speed but then gradually decreases with speed beyond a speed of the order of 70 km / h. The graph (b-1) illustrates the case of perforating objects of screw type, tapered objects whose side wall has a net (phase 2). The screws are inserted into the top of the cold tire, that is to say at ambient temperature, of the order of 20 degrees Celsius. The performance is not good at standstill and at low speed but then gradually improves with it. The graph (b-2) illustrates the case of perforating objects of the screw type, when the insertion of the screw-type perforating objects is carried out hot, that is to say when the tire has been brought to a top temperature of the order of 50 to 60 degrees Celsius. There is an improvement in the performance of resistance to pressure loss, which is noticeable over the entire speed range of the test. Finally, the graph (c) illustrates the performance obtained during a run performed after extraction of the perforating objects immediately after their introduction in the crown of the tire (phase 3). There is excellent performance at low speeds and it is only after a high speed of around 130 km / h that the average performance can begin to decrease. This characterizes the high-temperature mechanical resistance of self-sealing product plugs.

Figure 1 shows some examples of perforating objects commonly used for the test method. They are nails 21 with a diameter of 3 mm, nails 22 with a diameter of 4 mm and nails 23 with a diameter of 5 mm, and screws with a diameter of 3.5 mm and a length of 30 or 40 mm. The diameters of these perforating objects are quite realistic piercing objects encountered in real rolling conditions. Figure 2 presents the cumulative frequency of the distribution of nails observed on roads in China and the United States. It can be seen that all nails with diameters less than or equal to 5 mm correspond to more than 90% of the objects encountered. After having mounted the tire 1 on a suitable wheel and having inflated it to 2.5 bars, the tire and the wheel are rigidly attached to a non-rotating hub. shown and is inserted through the top 3 of the tire 1 a plurality of perforating objects.

[0068] FIG. 3 shows a fragmentary top view of the top 3 of a tire 1. The sculpture of this tire comprises three longitudinal grooves, inner, central 7 and outer 9 and an outer shoulder 5 with a set of grooves. or transverse hollow 11. By inside or outside, one refers to the side of the tire intended to be mounted towards the inside of the vehicle or towards the outside of the vehicle, the sculpture of this tire being asymmetrical. In FIG. 3, three perforations are seen by nails 21 arranged in the central longitudinal groove 7 (SC), the outer longitudinal groove 9 (SE) and in the transverse hollow (CT) 11 of the outer shoulder 5.

For the first phase of the test method or "protocol nails" was inserted on the entire top twelve nails 3 mm diameter and length between 45 and 60 mm, six nails 4 mm diameter and of similar length and six nails 5 mm in diameter and similar length. For the second phase of the test method or "protocol screw", after bringing the top of the tire to a temperature of the order of 50 to 60 degrees Celsius, it was inserted on the entire top twelve screws diameter 3.5 mm and length 30 mm and twelve screws with a diameter of 3.5 mm and a length of 40 mm. Piercing objects are regularly distributed over the circumference of the summit. The tire assembly and inflated wheel is then fixed on the hub of a rolling machine having a development of five to six meters.

The rolling conditions are as follows: the inflation pressure is regulated, for example at 2.5 bar, the applied load is of the order of 70% of the load capacity of the tire, the temperature in the The caster's enclosure is regulated at approximately 20 ° C and the rolling is a straight run, without torque, drift or camber applied.

The speed conditions depend on the protocol:

- for the nails protocol, the driving time is six hours at Vi = 100 km / h; at this speed, there is practically no ejection of nails; for the screw protocol, a ¹ driving is performed for six hours at a speed V ₂ = 70 km / h; then, after analyzing the results of the first taxi, a second taxiing is carried out for six hours at a speed V ₂ _ ₂ = 130 km / h;

- for the third phase or "traffic jam protocol", the taxi is six hours at 150 km / h.

It is possible that the largest nails are ejected during taxiing. The analytical conditions of the test (new nail, not rusty, planted straight) favor the appearance of ejection. In this case, the ejected nail is not taken into account in the calculation of the final grades. The screws are not expelled while driving, the thread increases the effort required to extract them.

After rolling, a cooling phase of at least two hours is respected.

The analysis of the results is carried out half-vertex by half-vertex.

The course of the second part of the test is now described taking as an example a first cold test temperature of 0 ° C and a second cold test temperature of -10 ° C.

We choose four tires similar to the (x) tire (s) tested (s) in the first part, they are mounted on four wheels and inflated to their recommended inflation pressure, here 2.5 bars. The four tire / wheel assemblies are installed in a cold room or a refrigerated container.

The temperature of the container is lowered to a temperature θι of 0 ° C. and this temperature is maintained for at least 4 hours.

24 nails are implanted in each tire: 8 of diameters 3 mm, 8 of diameters 4 mm and 8 of diameters 5 mm. The nails are hammered regularly: 12 in the central longitudinal grooves (SC) 7 and 12 in the outer longitudinal grooves (SE) 9 of the four tires 1.

For the four tires, a first notation of the leaks at this temperature θι is carried out, the nails being in place, notation at T0. Then, for the first two tires, it performs a second rating of the leaks, nails in place at T0 + 1 hour.

At T1, the nails are torn from the first two tires, still at the temperature θι of 0 ° C and a first notation is made, then a second at Tl + 10 minutes minimum.

The temperature of the refrigerated container is then lowered to a temperature θ ₂ of -10 ° C. and the last two tires are left in place at this temperature for at least four hours.

Then, T2, a log of leaks, nails in place. At T3, the nails are torn off and a log of the leaks is made at T3 and preferably a second at T3 + 10 minutes minimum.

The result of the test is a qualitative observation of the leaks of each perforation, before extraction, after extraction and about 10 minutes after extraction.

Leaks are evaluated with the aid of a surfactant, for example an aerosol can of the brand "1000 bubbles". The product is projected on the perforation and the observer notes the presence, the size and the number of the bubbles with the aid of a magnifying glass and under a strong lighting.

Figures 4 to 7 illustrate the various cases observed with the perforating objects in place (Fig. 4, 5 (a), 6 and 7 (a)) and after its extraction or ejection (Fig. 5 (b), 7 (b)). In FIG. 4, we see a nail 21 passing through a perforation 41 disposed in the longitudinal groove 9 of the tire. We do not see any bubbles, there is no leak, the perforation is noted 10 or 100%.

In Figure 5 (a), there is a perforating object 21 through a perforation 51 disposed in the longitudinal groove 9 of the tire. The application of the surfactant product makes it possible to display a large number of very very small bubbles 51, only visible with a magnifying glass and with a diameter of less than 0.1 mm. This is a very low leak, rated 8 or 80%.

In Figure 5 (b), there is a perforation 52 made by a perforating object that has been expelled or extracted. The perforation 52 is also located in the outer longitudinal groove 9 of the tire. The application of surfactant product also allows to visualize a large number of very very small bubbles 51, visible with the magnifying glass and of diameter less than 0.1 mm. We give the same notation 8 or 80%.

In Figure 6, there is a perforating object 21 through a perforation 61 disposed in the outer longitudinal groove 9 of the tire. There the application of the surfactant product makes it possible to visualize a set of small bubbles 63 of diameter substantially between 0.1 mm and 1 mm. This is a low leak rated 6 or 60%.

In Figure 7 (a), there is a perforating object 21 through a perforation 71 always disposed in a longitudinal groove of the tire. The application of the surfactant product makes it possible to display a single large bubble 73 with a diameter greater than 1 mm. We are in the presence of a leak rated 0 or 0%>.

In Figure 7 (b), we see in the longitudinal groove of the tire perforation 72 donations perforating object was expelled during taxiing or extracted after stopping. In the same way, we see only one large bubble 73 with a diameter greater than 1 mm. This is a leak rated 0 or 0%.

The following tables present the results of the protocol nails.

Table 1: protocol nails before rolling

With:

- SE: nail placed in the outer groove 9;

- SC: nail placed in the central groove 7; and

- CT: nail placed in a transverse hollow 11.

No leak is observed for the 12 nails incorporated in the half of the top block of the tire 1, the performance is 100%>.

Table 2: protocol nails after rolling

Nails in place after rolling

0 3 mm 0 4 mm 0 5 mm 0 3 mm

Positions SC SE CT SC SE CT SC SE CT SC SE CT

Notes 10 10 10 10 8 6 10 6 6 10 10 8 After six hours of driving at 100 km / h, it is found that none of the twelve nails was ejected. A very low leakage is observed for a nail with a diameter of 3 mm; a low leak noted 6 and a very low leak noted 8 for nails 4 mm in diameter and two low leakage noted 6 for nails 5 mm diameter. The performance thus decreases by 97% for nails with a diameter of 3 mm to 80% for those with a diameter of 4 mm and 73% for those with a diameter of 5 mm.

Table 3: Post-extraction nail protocol

[00101] Table 3 above shows the results observed after tearing nails. Two phases of notations are performed: immediately after tearing (T0) and 10 minutes later (T10). Note that some notes can evolve between T0 and T10. The results are good between 80 and 90%.

An overall score "nails in place" can be calculated from the results of Table 2, by weighting the different nail diameters with a frequency curve appearance of nails customers. Similarly, an overall rating of "torn nails" can be calculated from the results in Table 3.

The following tables present the results of the screw test.

Table 4 - vis-notes protocol before rolling

[00104] Table 4 above shows the results observed during the introduction of 40 mm long screws in the crown of the tire. Twelve screws were inserted on a ½ tire. Hot notations are carried out ("hot tire" line) then after cooling of the tire ("cold tire" line). It is noted that the insertion of the screws leads in this example the systematic appearance of more or less important leaks. The performance index is 25% hot tire and 30% after cooling the tire. All or part of these leaks will disappear during taxiing.

Table 5: vis-notes protocol after driving at 70 km / h

[00105] Table 5 shows the results observed at the end of the first rolling of the screw protocol at 70 km / h. The index obtained is very close to the two preceding before the rolling: 32%.

Table 6: vis-notes protocol after driving at 130 km / h

Table 6 above shows the results observed at the end of the second run at 130 km / h. Note on this case that the notes have increased significantly between the ^1st and the second rolling with the screws in place: I _M = 60%.

Table 6 also shows the results observed at the end of the tearing of the screws. As for nails, two phases of notations are performed: immediately after tearing (T0) and 10 minutes later (T10). The scores obtained after tearing of the screws are 72% for T0 and 90% for T 10.

[00108] The following tables present the results of the plugs test Table 7: protocol caps - notes after setting up and tearing

[00109] Table 7 above shows the results observed after the phases of setting up and tearing nails. If a note is 0, the hole is wicked and a new insertion is made a little further on the top of the tire. Table 8: traffic jam protocol - notes after driving at 150 km / h

Notes after rolling

It is mainly 5mm diameter nails which are used: it is desired to reveal the possible weaknesses of the tested product on the most unfavorable cases.

[00111] Table 8 above shows the results observed at the end of rolling. Two phases of notations are performed: immediately after tearing (T0) and 10 minutes later (T10). We notice that the majority of the notes are at 10.

Table 9 below shows the results of the second part of the puncture resistance test at a temperature of 0 ° C.

The notes are average scores obtained for the first two tires at a temperature θι of 0 ° C. As, surprisingly, no clear influence of the nail diameter was observed, this table does not detail the results obtained as a function of this nail diameter. Table 9: Second Part Test at 0 ° C

After the nails were put in place, only a nano-leak was noted for one of the nails with a diameter of 3 mm. An hour later, there were 8 nano-leaks distributed according to the three diameters of the nails, hence the lowest score of 93%.

Immediately after tearing the nails, Tl, there were two leaks noted 0, seven nano-leaks noted 8 and 15 perforations well closed, hence the score of 86%.

Finally, 10 minutes after tearing away the nails (Tl + 10 min), only a leak rated 0, a micro-leak noted 6, two nano-leaks noted 8 and twenty perforations well closed, were observed. where the rating of 93%>. One of the leaks had become a micro-leak and seven nano-leaks had closed on their own.

The combination gives a mean resistance index at 0 ° C. of 94%.

Table 10 below shows the results of the second part of the puncture resistance test, at a temperature of -10 ° C.

The notes are average scores obtained for the last two tires at a temperature θ ₂ of -10 ° C. As, surprisingly, no clear influence of the nail diameter was observed, this table does not detail the results obtained as a function of this nail diameter. Table 10: Second Part Test at -10 ° C

Average rating at Θ2 = -10 ° C 96%

Note after placement of nails (T0) at θι 99%

Note 4 hours after implementation (T2 + 4) of θ ₂ 99%

Note after removal of nails (T3) at θ ₂ 89%

Note 10 mm after removal of nails (T3 + lOmn) at Θ2 89% After the establishment of nails, we only noted a nano-leak for one of the nails diameter 3 mm, note: 99%.

After lowering the temperature to θ ₂ as described earlier and expected the thermal stabilization, no change was observed hence the identical score of 99%.

Immediately after the tearing of the nails, at T3, there was observed a leak noted 0, eight nano-leaks noted 8 and 15 perforations well closed, hence the rating of 89%>.

Finally, 10 minutes after tearing of the nails (T3 + 10 min), the same leak noted 0 was observed, the same eight nano-leaks noted 8 and the same twenty perforations well closed, hence the same rating of 89%>.

The assembly gives an average resistance index at -10 ° C. of 96%.

As there is no rolling, this second part of the test gives high average resistance indices but can track the influence of temperature on this resistance and thus characterize the performance of these tires in a wide range. range of uses.

The test described concerned a tire equipped during its manufacture of a layer of self-sealing product. As already indicated, the described test also makes it possible to test other solutions such as puncture-resistant bombs and repair kits.

[00128] Tests have been carried out with these other solutions. It can be seen that the shutter performance is practically 100% for all the solutions during a puncture with instantaneous removal of the perforating object. On the other hand, during a rolling with perforating object in place, from 200 to 300 km of rolling, the performance of the puncture-resistant bombs becomes null, the product leaves by the perforations. As far as the repair kits are concerned, their performance is better but they also decrease very strongly with the length of the rolling carried out with the perforating objects in place.

[00129] The test thus described has the advantage of being very selective and complete. It also has the advantage of being based on the analysis of the leak rates of each perforation and not on a loss of pressure which allows to obtain many results with a single tire or with a very small number of similar tires. .

Claims

1. Method for testing the resistance of a tire to a loss of pressure following perforation, characterized in that:

in a first part carried out at an ambient temperature above 10 ° C:

• creating in the wall of said tire a plurality of perforations by inserting through said wall a plurality of piercing objects;

• stop driving; and

For each perforation, a pressure loss resistance index based on an estimate of the leakage rate of said perforation is determined;

said first part comprising two phases such as:

in the first phase, the plurality of piercing objects is composed of tapered and smooth-walled objects such as nails and the rolling is carried out in such a way that the objects are not ejected during the rolling; and

- In the second phase, the plurality of piercing objects is composed of tapered objects but walls with a thread such as screws and rolling is performed at speeds below 80 km / h;

in a second part carried out at an ambient temperature below 10 ° C:

A plurality of perforations are created in the wall of said tire or similar tire by inserting through said wall a plurality of tapered perforating objects with smooth walls such as nails;

For each perforation, a cold resistance pre-index is determined for the loss of pressure based on an estimation of the flow rate of said perforation;

The plurality of piercing objects is extracted from the wall of said tire; and

For each perforation, a cold resistance index is determined for the loss of pressure based on an estimate of the leakage rate of said perforation.

2. Test method according to claim 1, wherein the whole of the second part is performed when the tire is at a temperature between -20 ° C and + 10 ° C.

3. Test method according to any one of the preceding claims, wherein the insertion of the piercing objects of the second phase of the first part is performed when the tire is at a temperature of the order of 50 to 60 degrees Celsius.

4. Test method according to one of the preceding claims, wherein the rolling of the first phase of the first part is performed at a fixed speed Vi between

90 and 120 km / h.

5. Test method according to one of the preceding claims, wherein the rolling of the second phase of the first part is performed at a fixed speed V ₂ between 50 and 75 km h.

6. Test method according to any one of the preceding claims, wherein the second phase of the first part further comprises a second test at a fixed speed V ₂ -2 greater than 80 km / h.

7. Test method according to any one of the preceding claims, further comprising in the first part a third phase with the following steps:

- creating in the wall of said tire a plurality of perforations by inserting through said wall a plurality of piercing objects;

extracting from the wall of said tire the plurality of piercing objects;

- Roll the tire after extraction of perforating objects at a speed V ₃ greater than 120 km / h for a given distance with a regulated inflation pressure;

- stop taxiing; and

8. Test method according to claim 7, wherein the speed V ₃ is fixed and less than 180 km / h.

9. Test method according to any one of the preceding claims, wherein, the tire having no self-extinguishing product, in the first part, at stopping the rolling and before determining the indices of resistance to loss. pressure, is placed in the internal cavity of the tire a sealing product.

10. Test method according to any one of the preceding claims, wherein, the tire having no self-sealing product, in the second part, after inserting and tearing the perforating objects, it is put in place in the internal cavity. of the tire a sealing product, it brings, if necessary, the tire to the test temperature of the second part, and the index of resistance to pressure loss is determined.

11. Test method according to any one of the preceding claims, wherein in the first part, the rolling distance of the tire having a plurality of perforations through its wall is greater than 200 km and preferably greater than 500 km.

12. Test method according to any one of the preceding claims, wherein in the first part, the rolling of said tire is performed on a steering wheel.

A test method according to any one of the preceding claims, wherein the tire is inflated prior to inserting the plurality of piercing objects through the wall of said tire.

14. Test method according to any one of the preceding claims, wherein the inflation pressure during the different parts of the test is regulated at a pressure of between 1.8 and 5 bar depending on the type of tire.

15. Test method according to any one of the preceding claims, wherein the plurality of piercing objects comprises screws and nails of various diameters and / or lengths.

16. Test method according to any one of the preceding claims, wherein the plurality of piercing objects comprises from 10 to 50 piercing objects, preferably between 20 and 40.

17. Test method according to any one of the preceding claims, wherein the diameter of the perforating object or objects is 3 to 5 mm.

18. Test method according to any one of the preceding claims, wherein the perforating object or objects are inserted into the crown of the tire.

19. A test method according to any one of the preceding claims, wherein a surfactant is used to visualize and qualitatively assess the leakage rate of each perforation.

20. The test method according to claim 19, wherein the following scale is used to assess the leakage rate of a perforation:

- 100: no bubble is visible, no leak;

- 80: nano-leakage, very small bubbles less than 0.1 mm in diameter, visible only by magnifying glass;