WO2023110655A1

WO2023110655A1 - Tyre designed for controlled flattening

Info

Publication number: WO2023110655A1
Application number: PCT/EP2022/085102
Authority: WO
Inventors: Rémi REYNAL DE ST-MICHEL; Michel Ahouanto; Sylvain MORIVAL; Olivier REIX
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2021-12-16
Filing date: 2022-12-09
Publication date: 2023-06-22
Also published as: FR3130692A1

Abstract

The invention relates to a tyre (1) designed to allow controlled flattening when the internal inflation pressure exceeds a certain threshold known in advance. Within each bead (50) is a layer of protective elastomeric material (80), positioned radially inside, having a first portion intended to be in contact with the rim hook (130) and a second portion intended to be in contact with the seat (110) of the rim (100). Channels (210) for discharging the inflation fluid are provided in the protective layer (80), running from the seat of the rim to the outside environment at the rim hook (130); in at least one bead (50), a circumferential collection channel (200) that does a complete wheel turn is arranged in the protective layer (80).

Description

Tire designed for controlled flattening

Field of invention

[OOOlJThe present invention relates to a tire for a motor vehicle designed for controlled flattening when the inflation pressure exceeds a certain threshold known in advance.

Definitions

[0002] By convention, a mark (O, OX, OY, OZ) is considered, the center O of which coincides with the center of the tire, the circumferential OX, axial OY and radial OZ directions respectively designate a direction tangent to the surface of rolling of the tire according to the direction of rotation, a direction parallel to the axis of rotation of the tire, and a direction orthogonal to the axis of rotation of the tire.

[0003] By radially inner, respectively radially outer, is meant closer to, respectively further from, the axis of rotation of the tire.

[0004] By axially inner, respectively axially outer, is meant closer to, respectively further from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tread of the tire and perpendicular to the axis rotation of the tire.

[0005] The constitution of the tire is usually described by a representation of its constituents in a meridian plane, that is to say a plane containing the axis of rotation of the tire. We will speak of a meridian section which corresponds to a section of the tire in a meridian plane.

[0006] A tire comprises a crown, intended to come into contact with the ground via a tread, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be fitted.

[0007] A radial tire further comprises a reinforcement reinforcement, consisting of a crown reinforcement, radially interior to the tread, and of a carcass reinforcement, radially interior to the crown reinforcement.

[0008] The crown reinforcement of a radial tire comprises a superposition of crown layers extending circumferentially, radially outside the carcass reinforcement. Each crown layer is made up of reinforcements parallel to each other and coated by a polymeric material of the elastomer type or elastomeric mixture. The assembly formed by the crown reinforcement and the tread is called the crown.

[0009] The carcass reinforcement of a radial tire usually comprises at least one carcass layer consisting of metallic or textile reinforcing elements coated in an elastomeric coating mixture. The reinforcing elements are substantially parallel to each other and make, with the circumferential direction, an angle of between 85° and 95°. The carcass layer comprises a main part, connecting the two beads together and wrapping, in each bead, around an annular reinforcement structure.

[OOlOJThe annular reinforcement structure considered here is a bead which, in the current state of the art, comprises a circumferential reinforcement element surrounded by at least one material, in a non-exhaustive manner, metallic, elastomeric or textile. The winding of the carcass layer around the bead runs from the inside to the outside of the tire to form a turn-up, including one end. The reversal, in each bead, allows the anchoring of the carcass reinforcement layer to the bead wire.

[OOllJLe Most often in this present patent application, the tire appears mounted on a rim. Said rim is chosen according to the specifications of the ETRTO standard (European Technical Organization for Tires and Rims) that, with a given tire size, combines recommended rims. In general, several rim widths can be suitable for the same tire size. The part of the rim which interacts with the tire in the context of the invention is axisymmetric with respect to the axis of rotation of the tire. To describe the rim, it suffices to describe the generating profile in a meridian plane.

[0012] In a meridian plane, the rim comprises at least one hook located at one axial end, and connected to a seat which is intended to receive a face of the bead located the most radially internally. Between the seat and the hook, takes place a rectilinear portion which connects the rim hook to the seat by fitting fillets. The hook of the rim extended by the straight portion axially limits the movement of the beads during inflation.

[0013] The bead embedded in the bead contributes to a plurality of functions of the tire mounted on a recommended rim.

[0014] The mountability of the beads on a rim during inflation is a performance which can be impacted by the invention. The fitability performance of the beads consists of evaluating the ability of the beads of a tire to be installed correctly on a rim during inflation. Means of observation, in particular radiographic, of the beads mounted on a rim make it possible to diagnose the quality of the assembly.

[0015]Once the tire is mounted on a rim, the bead contributes to sealing, in particular of tubeless tires by preventing the escape of the internal inflation gas to the outside. The bead hoops a protective layer with a tightening that increases when mounting the tire on the rim. This sealing is carried out on the seat part and on the rim hook. A clamping pressure on the rim seat of approximately 1.4 MPa is expected and 2.5 MPa on the rim hook.

[0016]Furthermore, the tightening on the seat and on the rim hook must be sufficient to prevent the tire from becoming unseated during severe cornering.

[0017]Furthermore, the quality of the tightening of the tire on the rim also comes into play during the transmission of the driving and/or braking torques of the vehicle. High tightening of the bead on the rim is expected to prevent the beads from rotating on the rim, and to effectively transmit the motor/braking torques.

[0018]Finally, the rod contributes to the behavior of the vehicle. Changes of direction are initiated by a steering angle on the steering wheel which is transmitted to the wheels of the steering axle, then to the tires of this same axle thanks to the connection of the beads with the rim.

[0019] All the power of the vehicle is transmitted to the wheels of the driving axle then to the tires fitted to this same axle by the connection of the beads with the rim and finally to the four contact areas resulting from the crushing of the tires by the load of the vehicle on rolling ground. The quality of the behavior of the vehicle is therefore determined by these two contact zones, namely the contact of the tires with the rim and then the contact of the tires with the road surface.

Prior technique

[0020] Internal tire pressure monitoring systems have been a legal requirement since November 1, 2014 in the European Union. All vehicles registered from this date must be fitted with a TPMS (Tire Pressure Monitoring System) for countries which have incorporated this European law into their national legislation.

[0021] In accordance with European rules, the TPMS must notably comply with the following specifications: - A tire pressure loss at 20% below the operating pressure (Pwarm) of 1.5 bar must generate a TPMS alert within 10 minutes;

- a sudden or gradual loss of pressure in the four tires at 20% below the operating pressure (Pwarm) of 1.5 bar must generate a TPMS alert within 10 minutes;

- the TPMS must detect a drop in tire pressure in the speed range between 40 km/h and the maximum speed;

- the TPMS must have a data transfer rate of 434 MHz.

[0022] Thus, generally, the TPMS system checks the pressure downwards, but it is not designed to detect an abnormal increase in the inflation pressure of a tire above the operating pressure.

The relationship between the internal temperature of the inflation fluid and the pressure of this same fluid is known to those skilled in the art. A rise in internal temperature leads to an increase in inflation pressure. This rise continues as long as the temperature rises. In addition, above a certain temperature, various chemical reactions can occur in the tire under the effect of heat, such as thermo-oxidation and pyrolysis.

[0024] Pyrolysis is defined as the irreversible chemical decomposition of a material under the sole action of heat. In the case of a tire, it is the degradation of the rubber material that occurs. This phenomenon occurs when the temperature inside the tire reaches at least 185°C, and in the absence of oxygen (inflating with nitrogen does not eliminate the pyrolysis phenomenon).

[0025] The same indications prevail in the event of thermo-oxidation. On the other hand, this phenomenon, which occurs in the presence of oxygen, cannot occur if the tires are inflated with nitrogen.

[0026] The gases produced by pyrolysis and thermo-oxidation cause an increase in the pressure in the tire which can lead to it bursting, if the following three critical conditions are met simultaneously: sufficient concentration of flammable gas, temperature and pressure equal to or greater than the autoignition temperature and pressure of the gases, - oxygen concentration greater than 5.5%.

[0027JI1 followed by a violent explosion producing an instantaneous rise in pressure. At the time of the explosion, the pressure can reach 70 bars (7 MPa in SI unit) or more with the creation of shock waves.

[0028] The causes of overheating of the internal inflation fluid are numerous and may be linked in particular to the design of the tire or even to the conditions of use of the latter.

[0029] In a non-exhaustive manner, the causes of tire overheating include overheating of the brakes when complete or partial locking occurs, or even excessive use of the braking system. Using the vehicle with an overload beyond the load index provided for the tires fitted to it is also a cause of overheating of the internal inflation fluid. Similarly, use of the vehicle at excessive speed above that provided for by the speed index of the tires can lead to a rapid increase in the temperature of the inflation fluid.

[0030JI1 there is a need to detect an excessive increase in the internal inflation pressure of a tire while driving.

[0031] The inventors set themselves the objective of designing a tire allowing controlled flattening when the internal inflation pressure exceeds a pressure threshold known in advance.

Disclosure of Invention

[0032] This object has been achieved by a tire for a motor vehicle comprising, in a meridian plane: two beads intended to be mounted on a rim, two layers of sidewalls connected to the beads, a crown comprising a tread, the crown having a a first side connected to the radially outer end of one of the two sidewall layers and having a second side connected to the radially outer end of the other of the two sidewall layers; at least one carcass reinforcement extending from the two beads to the crown, the carcass reinforcement comprising a plurality of carcass reinforcement elements and being anchored in the two beads by turning around a bead wire, so as to form in each bead a main part and a reversal; the bead mounting rim comprising at least one hook located at one axial end, and connected to a substantially axial seat; between said seat and said hook, takes place a substantially radial rectilinear portion which connects the rim hook to the seat by a connecting fillet, in each bead, a layer of elastomeric protective material shrunk by the bead wire, and positioned radially internally having a first portion intended to be in contact with the hook of the rim and a second substantially axial portion intended to be in contact with the seat of the rim:

- inflation fluid evacuation channels are provided in the protective layer connecting the internal inflation cavity to the outside of the tire at the rim hooks;

- In at least one bead, a circumferential collector channel making a complete turn of the wheel is provided in the protective layer.

[0033]The principle of the invention is to allow the inflation fluid to be evacuated through channels arranged in the protective layer of the tire in contact with the rim, when the pressure of the inflation fluid exceeds a certain threshold. For this, the bead must be flexible enough to come off the seat of the rim when the inflation pressure increases beyond said threshold. The space freed up between the protective layer and the rim allows the inflation fluid to escape and cause the tire to flatten.

[0034] The inflation fluid evacuation channels are therefore positioned on the outer periphery of the tire. When the tire is mounted on a rim, only the radially outer end of the channel at the level of the rim hook is visible, the rest of the channel being hidden by the rim.

[0035] For a tire of the invention, the flattening occurs in complete safety without the tire detaching from the rim.

[0036] Indeed, the radial diameter of the point located at the end of the bead radially internally of a tire of the invention is less than the diameter of the rim measured at the seat. This difference in diameter is at the origin of a geometric tightening of the bead wire on a part of the protective layer located between the bead wire and the rim. This tightening is useful for keeping the tire in position on the rim when there is a drop in inflation pressure so as to prevent the tire from coming off the rim. The rod of the invention thanks to its large elastic elongation greater than or equal to 2% can absorb this stress without breaking the rod. [0037] The contour of the protective layer comprises a part which is axially the outermost which constitutes a portion of the outer periphery of the tire, intended to be in contact with the hook of the rim. Another radially innermost part is intended to be in contact with the seat of the rim. When the tire is mounted on the rim, the bead wire is positioned so as to end up substantially above the middle of the seat. EPTR is defined as the thickness of the protective layer measured along a radial straight line passing through the center of the rod. Therefore, EPTR is the radial distance between a first and a second point at the intersection of said radial straight line and a first and second contour of the protective layer passing under the rod. Equivalently, the thickness EPTA of the protective layer is measured along an axial straight line passing the center of the rod.

[0038JThe EPTR thickness of the protective layer plays a major role in tightening the bead on the rim. An EPTR thickness of approximately 2.5 mm is necessary for correct operation of the invention. As for the EPTA thickness, a minimum value of 2 mm is necessary to guarantee a suitable level of wear during carrying due to the friction of the protective layer on the rim.

[0039]The main characteristics of the invention, namely the presence of the inflation fluid evacuation channels and the ability of the bead wire to elongate up to 2% without breaking lead to the tire of the invention, that is to say a tire that can deflate mechanically when the inflation pressure exceeds a threshold.

[0040] The invention works just as well with a rod formed of an internal metal core surrounded by metallic threads, as for textile rods, for example in aramid with or without an internal core.

[0041] By way of illustration, for a dimension such as 245/45R18, the threshold pressure reached with a conventional metal rod is between 10 bars and 12 bars, whereas for an aramid textile rod, the threshold pressure is about 6 bar.

[0042] Other secondary characteristics related to the geometry of the channels, as well as the choice of rod materials or even different embodiments are presented below.

[0043] Advantageously, a circumferential collecting channel for the inflation fluid is arranged in the contact zone of the protective layer with the rim.

[0044]0n can realize the invention according to two main modes. In a first embodiment, the inflation fluid is evacuated only through the channels positioned on the outer periphery of the tire, described above, or according to a second embodiment, a circumferential manifold channel also provided in the protective layer supplies the channels positioned at the outer periphery.

[0045]Indeed, the contact of the rim with the protective layer is not uniform over one rotation of the wheel. In other words, the contact zones can differ from one meridian to another. The presence of the circumferential collecting channel in the protective layer makes a full revolution by crossing all the meridians. In this way, as soon as the bead has come off the rim seat, the pressurized internal air moves towards the circumferential collecting channel. It is then sufficient to have channels positioned on the outer periphery of the tire to recover the inflation fluid and expel it to the outside. For example, four diametrically opposed channels positioned on the outer periphery of the tire are sufficient for correct operation of the invention.

[0046] When the tire is mounted on a rim, the circumferential collecting channel for the inflation fluid is positioned opposite the connection fillet of the substantially radial rectilinear portion and the seat of the rim. In reality, there is no contact between the protective layer and the rim on the fillet when the tire is mounted on its rim. By positioning the circumferential collector channel at this location, the sealing of the tire is therefore not affected.

Advantageously, each inflation fluid evacuation channel has an axial width which is at most equal to 80% of EPTA.

[0048JI1 is to define a channel, that is to say an orifice in the protective layer of the bead of the tire which meets the need to evacuate the inflation fluid, but without being too intrusive to interfere with the correct operation of the bead, in particular in its ability to seal the tire. The inventors have proposed a width of the circumferential collecting channel consistent with the geometry of the bead and of the rim. The axial width of each evacuation channel must remain less than the thickness of the protective layer which is in contact with the upturn of the carcass reinforcement. It is necessary to avoid exposing the carcass reinforcement to external aggressions, such as oxidation, humidity which could arrive through the evacuation channel. The protective layer at the level of the connection fillet must limit any intrusions towards the inside of the bead.

[0049]Preferentially, the inflation fluid evacuation channels have rectilinear and parallel walls. This embodiment is the simplest to observe the operation of the invention on a prototype. But the simple geometry of the inflation fluid evacuation channels can cause problems with regard to external objects which can be inserted inside the tire. It is therefore possible to change the geometry of the evacuation channels by designing them as a succession of broken lines so as to oppose the intrusion of objects inside the tire, or even as a channel of zigzag shape.

[0050] Advantageously, the circumferential collector channel for the inflation fluid has a width which is at most equal to 80% of the thickness of the protective layer measured at the point situated in the middle of the connection fillet in the direction normal to this same leave.

[0051] Preferably, the outer edges of the circumferential collecting channel for the inflation fluid are rounded.

[0052] The presence of the circumferential channel must not interfere with the mounting of the bead on the rim. It is therefore necessary to avoid any geometric shape of the channel which could disturb the mounting on the rim. One solution is to have smooth geometry with rounded shapes.

[0053]Preferably, the protective layer comprises at least four channels for discharging the inflation fluid, evenly distributed circumferentially.

[0054] The circumferential collector channel is fed with the internal inflation fluid from each meridian where the bead has risen from the seat of the rim, thus allowing the inflation fluid to pass. The fluid is evacuated to the outside via one or more evacuation channels.

[0055]Additional characteristics are related not only to the choice of materials constituting the rods, but also to their structure.

[0056] In one embodiment, each rod consists of a central metal core, surrounded by layers of metal wires.

[0057] With a metal bead wire to obtain separation of the protective layer from the rim seat, the inflation pressure must reach a threshold level of between 10 bars and 12 bars. This relatively high pressure is lowered when using a textile bead.

[0058]Preferably, each rod is obtained by a stack of layers of aramid textile cords.

[0059] Aramid cords are obtained by twisting two aramid strands under a twist of 315 turns per meter. The strands themselves result from the overtwisting of two aramid yarns, also under a twist of 315 turns per meter. [0060] A spooling process is used to manufacture the rod from the textile cord. The rod is obtained by winding a turn around a support while moving laterally by a distance equal to the diameter of the cable. At the end of the process, the rod results from the assembly of several layers of cables which stick together, giving the rod its rigidity. The section of the assembly in a meridian plane can for example take the form of a hexagon, or any other polygonal or circular shape.

[0061] The elastic elongation of such a rod is greater than 5%. The threshold pressure for detaching the protective layer from the seat of the rim, and therefore allowing the tire to be flattened, falls to approximately 6 bars.

[0062] The use of the aramid bead is more practical than that of a metal bead, but has the disadvantage of having a bead with low circumferential bending stiffness.

To overcome this drawback, in a preferred embodiment, each rod comprises textile cables surrounded by a reinforcing material so as to form a sheath, the rod is obtained by a stack of layers of the textile cable thus sheathed.

[0064] The same spooling process described above is used to manufacture the bead, which therefore has a circumferential bending rigidity which facilitates the manufacture of the tire blank as well as the mountability performance on the rim.

Still in this preferred embodiment, the sheath around the textile cable is made of a 6-6 polyamide, or a polylactic polymer, or even a vinyl-esther.

[0066] In another embodiment, each bead comprises an internal core, surrounded by aramid textile cords.

The core may consist of a polylactic polymer (in English: PLA, PolyLactic Acid). PLA can have a Young's modulus between 3 and 3.5 GPa, a tensile strength between can have a Young's modulus of 50 to 70 MPa, an elongation at break varying from 2 to 10%, and a flexural modulus of 4 to 5 GPa.

[0068] One of the advantages of PLA is that it is a natural, bio-sourced alternative to conventional petroleum-based materials.

[0069] Indeed, PLA can be obtained from corn starch. It is a product resulting from the fermentation of sugars or starch under the effect of bacteria synthesizing lactic acid. In a second step, the lactic acid is polymerized by a fermentation process, to become polylactic acid.

[0070]Another possible choice for the core of each rod is polyamide (Nylon) 66. It is composed of two monomers which each contain 6 carbon atoms, hexamethylenediamine and adipic acid, which give its name to the nylon 66. Nylon 66 is used where high strength, stiffness, good heat stability and/or chemical resistance are required, as is the case here. Its elastic modulus is 3.5 GPa, and its compression modulus is 2.7 GPa. Its elongation at break is 70%.

Brief description of the drawings

[0071] Other advantageous details and characteristics of the invention will emerge below from the description of the embodiments of the invention with reference to the figures which represent schematic views of a tire, and bead wires according to modes of realization of the invention. Figures are not drawn to scale for ease of understanding.

[0072] Figure 1-A shows a section of a tire of the invention in a meridian plane. Figure 1-B is a magnification of a portion of Figure 1-A surrounded by a dashed circle showing a magnification of the area of the bead containing a bead of a tire of the invention.

[0073] Figures 2 -A, 2-B, 2-C illustrate the operation of the invention in three phases, at the bead of the tire.

[0074] Figures 3-A, 3-B, and 3-C are views in a circumferential plane showing the evacuation channels and circumferential collector of the inflation fluid.

Figure 4-A is a metal rod, and Figures 4-B and 4-D are embodiments of the invention with textile rods shown in a meridian plane. In these embodiments, the textile cables of the rod are sheathed by a reinforcing material (4-B). Figure 4-C is a magnification of two cables each surrounded by a sheath. Figure 4-D is another embodiment where yarns of a textile are embedded in an elastomeric matrix to form a bead wire.

[0076] Figures 5-A, 5-B, 5-C, 5-D and 5-E represent other embodiments of the invention with textile cables associated with an internal core made of a material homogeneous rigid variable geometric shape around which the textile cables are wound. Figure 5-F is a view in the circumferential direction of a rod.

[0077] Figure 5-G is an embodiment where the rod does not have an internal core, and are not sheathed either. The rod is obtained by the spooling of aramid cords in several superimposed layers.

Detailed description of the invention

The invention was implemented on a passenger tire of size 245/45R18, according to the ETRTO (European Technical Organization for Rims and Tires) specification standard. Such a tire can carry a load of 800 kilos, inflated to a pressure of 250 kPa.

In FIG. 1-A, the general reference tire 1 comprises a carcass reinforcement 90 consisting of reinforcements coated with a rubber composition, and two beads 50 in contact with a rim 100. A zone 49 delimited by a dotted circle defines a lower zone of the tire, a magnification of which is proposed in Figure 1-B. The carcass reinforcement 90 is anchored in each of the beads 50. The tire further comprises a crown reinforcement 20 comprising two working layers 21, 22, and a hooping layer 23. Each of the working layers 21 and 22 is reinforced by wire reinforcement elements which are parallel in each layer and crossed from one layer to another, forming with the circumferential direction angles equal to 27°. The hooping layer 23, arranged radially outside the crown reinforcement 20, is formed of reinforcement elements oriented circumferentially and wound in a spiral. A tread 10 is placed radially externally on the hooping layer 23; it is this tread 10 which ensures the contact of the tire 1 with the ground. The tire 1 shown is a “tubeless” tire: it comprises an “inner rubber” 95 of rubber composition impermeable to the inflation gas, covering the inner surface of the tire.

[0080] The part of the rim 100 which interacts with the tire in the context of the invention is axisymmetric with respect to the axis of rotation of the tire.

In a meridian plane, the rim 100 comprises at least one hook 120 located at one axial end, and connected to a seat 110 which is intended to receive a face of the bead located the most radially internally. Between the seat 110 and the hook 120, takes place a rectilinear portion 130, called the cliff of the rim, which connects the rim hook 120 to the seat 110 by a connecting fillet 140. The hook of the rim 120 extended by the rectilinear portion 130 axially limits the movement of the beads during inflation.

In FIG. 1-B, a general reference lower zone 55 is shown containing the sidewall layer 30 and the bead 50. The contour of the lower zone repeats the outer contours of the sidewall layer 30 at least in part. and the outer contour of the bead 50.

[0083]Said bead 50 partly comprises a carcass reinforcement 90 which comprises a main part 52, then wraps around a bead wire 51 to form a turn-up 53. A padding layer 70 is positioned between the main part 52 of the carcass reinforcement 90 and its upturn 53. According to the embodiments, the bead 50 may comprise a lateral reinforcement layer 60, positioned axially outside the upturn 53, and axially inside the sidewall layer 30. Axially the most inside the bead 50, a sealed layer 95 forms the inner wall in contact with the internal inflation air.

Said bead 50 also comprises a protective layer 80 which is in axial contact on the outside with a rectilinear portion 130 of the rim so as to limit the axial displacement of the bead. Said protective layer 80 also comprises a portion intended to be in contact with the rim at the level of the rim seat 110. A sidewall layer 30 of the bead 50 partly constitutes an outer side wall.

Still in FIG. 1-A, and/or 1-B, opposite fillet 140, a circumferential collecting channel 200 for the inflation fluid is arranged.

[0086] Figure 2 -A shows a bead of a tire of the invention where the circumferential collecting channel 200 of the inflation fluid is represented. FIG. 2-B shows the separation of the protective layer 80 from the rim seat 110 of the rim when the pressure of the inflation fluid reaches a threshold pressure. A space 220 is thus created, then fills with the inflation fluid. Finally, FIG. 2-C shows the inflation fluid evacuation channel 210, in contact with the circumferential collecting channel 200 of the inflation fluid.

[0087] Figures 3-A, 3-B, and 3-C are views of the tire in a circumferential plane. The reference 300 is a circumference at one of the ends of the tread and a radially outer sidewall layer. The circumferences 310 and 320 determine the area of contact of the protective layer 80 with the rim 100. The inflation fluid evacuation channels 210 are arranged in the protective layer 80. The evacuation channels 210 have rectilinear walls in Figure 3-A, while the walls are zigzagged in Figure 3-B. Figure 3-C shows circumferential inflation fluid collection channel 200 in communication with exhaust channels 210.

[0088] In Figure 4-A, there is shown a meridian section of a rod 51 consisting of a central steel core 520, surrounded by metal cables 510.

In Figure 4-B, there is shown a rod of hexagonal section. The 560 textile cables are surrounded by a sheath made of a second 550 material. A sheathing process is used to manufacture the bead from the sheathed cable. The rod is obtained by winding a coil around a support while moving laterally a distance equal to the diameter of the sheathed cable. At the end of the process, the rod results from the assembly of several layers of sheathed cables which stick together, giving the rod a certain rigidity.

[0090] Figure 4-C shows a magnification of the sheathed cable. The 550 sheath surrounds the 560 textile cable.

[0091] Figure 4-D shows a bead of a tire of the invention where the cords are actually yarns of textile dispersed in a matrix made up of a material. The matrix can be made of a polylactic polymer (PLA), or a nylon (Polyamide 6-6: PA66) or vinyl ester.

[0092] Figures 5-A, 5-B, 5-C, 5-D and 5-E are embodiments where the rod has a web of variable geometry in a meridian section. The core is referenced 555, and the textile cables 560. Figure 3-F is a view in the circumferential direction showing the winding of the textile cables around an internal core.

[0093] Tire configurations of the invention have been tested in order to clearly highlight the performance provided by the invention. The results of these tests are compared with each other and positioned in relation to the threshold pressure required for flattening the tire.

[0094]Each of the rods of witness T comprises a mild steel core with 0.1% carbon, and a layer of twisted metal cables around said core. The wires of the cables are made of steel with 0.7% carbon. The core has a diameter of 215 hundredths of a millimeter and each wire rope around the core has a diameter of 130 hundredths of a millimeter. The total diameter of the rod, (core + layers of cables included) is 4.79 mm. The mass of such a rod is 169 g. It is illustrated in Figure 4-A. The first tire P1 according to the invention comprises a pair of bead wires composed of textile cords. The cable is obtained after twisting two aramid strands each having a linear mass of 167 tex. Each strand comes from the overtwisting of a yarn at 315 turns per meter. The twist during the twisting phase is also 315 turns per meter. Then, the aramid cable is coated with a thin layer of rubber to help the cables stick together.

[0096] A spooling process is used to manufacture the rod from the textile cord. The rod is obtained by winding a turn around a support while moving laterally a distance equal to the diameter of the cable. At the end of the process, the rod results from the assembly of several layers of sheathed cables which stick together, giving the rod its rigidity. The section of the assembly in a meridian plane takes the form in this example of a hexagon. The bead of the tire PI is shown in Figure 5-G.

The second tire P2 of the invention comprises bead wires consisting of sheathed cables. Starting from the same textile cable of the tire PI, a sheath made of a reinforcing material surrounds the textile cable. The rod is obtained by the same shearing process this time with the sheathed cable.

[0098] The sheath of the cable is made of polyamide 6-6, and the geometry of the rod is hexagonal in shape as shown in Figure 4-B. The section of the sheathed cable is 0.55 mm2, and the total section of the rod is 24 mm2. The rod is obtained after a spooling of 45 turns. The mass of this rod is 35 grams.

Finally, the third tire P3 in accordance with the invention contains a pair of bead wires, each consisting of several layers of aramid textile cords wound around an inner core consisting of a PLA polymer. The cables are identical to those used for PI, and the inner core of the PLA rod has a diameter of 5.5 mm. The rod is shown in Figure 5-E.

[OOlOOJThe section of the central core is 24 mm2, and the total section of the rod is 41 mm2. In a meridian plane, a section of the rod is hexagonal in shape, as shown in Figure 3-E. The core is extruded in a continuous process, then cut, bent and glued to itself to form a ring. The mass of the rod is 60 grams. [OOlOlJU circumferential collector channel has been provided in the tires of the invention (PI, P2, P3), and for each tire at least four inflation fluid evacuation channels are connected to the collector channel.

[00102]The following table summarizes the different configurations tested:

[00103] [Table 1]

[00104] The control tire T, and those of the invention (PI, P2, P3) were tested and were compared for the level of the threshold pressure necessary for flattening. [00105] For this, the first test carried out is that of mounting the tire on the associated rim. The tires were inflated with ambient air as the internal inflation fluid, with a pressure of 250 kPa.

[00106] The rim mountability test consists in giving a result on the overall mountability from the breakdown of an assembly into elementary operations which include in particular: passing the rim hooks, taking pressure, crossing humps of the rim, fitting the bead by compression, sealing under the rim seat, bead breaking and dismantling. To carry out this test, means are necessary such as for example a semi-automatic mounting machine, or even means of observation, in particular radiographic, of the beads mounted on a rim making it possible to diagnose the quality of the mounting.

[00107] The presence of the internal inflation fluid evacuation channel for the tires of the invention (PI, P2, P3) in the protective layer did not disturb the mounting on the rim thanks to the adopted geometry of the channel manifold with rounded shapes.

[00108] The leak tests did not reveal any unwanted pressure leaks.

[00109] By continuing to inflate beyond 250 kPa, the tires (PI, P2, P3) hold the pressure up to 600 kPa. Above 600 kPa, the protective layer peels off the rim seat, then the inflation fluid enters through the circumferential collector channel and escapes through the evacuation channels until the tires are flattened.

[00110] On the control tire T which is not equipped with evacuation channels, the inflation pressure reached a pressure of 1.5 MPa causing the metal bead wire to break.

[OOlllJThis result shows the advantage of the invention which causes the tire to be flattened before the bead wire breaks.

[00112] The tire PI corresponds to an embodiment where each bead wire is obtained by only a stack of textile cords. The great advantage of such an embodiment is to have a rod that meets the dimensioning requirements while having a minimum mass of around 20 grams. However, the major drawback is the low circumferential bending stiffness which causes the bead wire to collapse under its own weight or under the weight of the carcass layer, which constitutes a real hindrance for the method used. [00113] The bead wires of the tire P2 provide a solution to this lack of circumferential bending rigidity. Indeed, aramid cables are sheathed by a polymer with a compression modulus greater than 3 GPa.

[00114] The beads of the P3 tire are designed with another solution to provide circumferential bending stiffness. Indeed, these rods have a central core in polyamide 6-6. Aramid cords are wrapped around the central core.

|00115|A result higher (respectively lower) than 100% means an improvement (respectively a deterioration) of the performance considered.

The results obtained are summarized in Table 2 below:

[00117] [Table 2]

[00118] The tires of the invention have a burst pressure comparable to that of the control. The flexibility of the rods of the invention has little effect on their resistance to bursting. The mass of the rods of the invention is significantly less than that of control T.

[00119] The inventors have designed a tire equipped with a pair of bead wires with a significantly reduced mass while performing the plurality of functions expected of the bead wires. The inventors have also proposed rods whose industrial cost remains under control compared to the state of the art. The beads of the invention allow the tire to be flattened via evacuation channels when the inflation pressure exceeds the threshold of 600 kPa.

Claims

[Claim 1] Tire (1) for a motor vehicle comprising, in a meridian plane: two beads (50) intended to be mounted on a rim (100), two layers of sidewalls (30) connected to the beads (50), a crown ( 20) comprising a tread (10), the crown (20) having a first side connected to the radially outer end of one of the two sidewall layers (30) and having a second side connected to the radially outer end exterior of the other of the two sidewall layers (30); at least one carcass reinforcement (90) extending from the two beads (50) to the crown (20), the carcass reinforcement (90) comprising a plurality of carcass reinforcement elements and being anchored in the two beads (50) by turning around a rod (51), so as to form in each bead a main part (52) and a turning (53); the mounting rim (100) of the bead (50) comprising at least one hook (120) located at one axial end, and connected to a substantially axial seat (110); between said seat (110) and said hook (120), takes place a rectilinear portion (130), substantially radial, which connects the rim hook (120) to the seat (110) by a connecting fillet (140), in each bead , a layer of protective elastomeric material (80) shrunk by the bead wire (51), and positioned radially internally having a first portion intended to be in contact with the hook of the rim (120) and a second substantially axial portion intended to be contact with the seat of the rim (110), characterized in that:

- inflation fluid evacuation channels (210) oriented in the radial direction are arranged in the protective layer (80), said channels connecting the internal inflation cavity to the outside of the tire (1) at the level of the zone of said protective layer (80) intended to be in contact with the hooks of the rim (120);

- In at least one bead (50), a circumferential collector channel (200) making a complete turn of the wheel is arranged in the protective layer (80).

[Claim 2] Tire (1) according to the preceding claim, the axial width of the protective layer (80), EPTA, being measured along an axial axis passing through the center of the rod (51) in which each radial channel (210) for discharging the inflation fluid has an axial width which is at most equal to 80% of EPTA.

[Claim 3] A tire (1) according to claim 2, wherein the axial width of the protective layer (80) has an axial width, EPTA, of greater than or equal to 2 mm.

[Claim 4] Tire (1) according to one of the preceding claims, in which the inflation fluid evacuation channels (210) have straight parallel walls.

[Claim 5] Tire (1) according to one of Claims 1 to 3, in which the walls of the evacuation channels (210) have a direction of broken lines so as to oppose the intrusion of objects to the inside of the tire (1).

[Claim 6] Tire (1) according to one of Claims 1 to 3, in which the evacuation channels have a zigzag shape.

[Claim 7] Tire (1) according to one of Claims 2 to 6, in which the circumferential collecting channel for the inflation fluid (200) has an axial width which is at most equal to 80% of the thickness of the protective layer (80) measured at the point located in the middle of the connection fillet (140) in the direction normal to this same fillet.

[Claim 8] A tire (1) according to one of Claims 2 to 7, in which in each meridian the outer edges of the circumferential collecting channel (200) for the inflation fluid are rounded.

[Claim 9] Tire (1) according to one of the preceding claims, in which the protective layer (80) comprises at least four channels (210) for discharging the inflation fluid, evenly distributed circumferentially.

[Claim 10] Tire (1) according to one of the preceding claims, in which each bead wire consists of a central metal core, surrounded by layers of metal wires.

[Claim 11] Tire (1) according to one of Claims 1 to 9, in which each bead wire is obtained by a stack of layers of textile cords.

[Claim 12] Tire (1) according to one of Claims 1 to 9, each bead comprising textile cords surrounded by a reinforcing material so as to constitute a sheath, in which the bead is obtained by a stack of layers of the textile cord thus sheathed.

[Claim 13] A tire (1) according to claim 12, in which the sheath around the textile cord consists either of a 6-6 polyamide, or of a polylactic polymer, or else of a vinyl esther.

[Claim 14] Tire (1) according to one of Claims 1 to 9, in which each bead comprises an internal core made of a polymer surrounded by textile cords.