Patent Application
20200148011
The present invention relates to a tyre suitable for running flat and equipped with an electronic device.
For several years, tyre manufacturers have sought to eliminate the need for the presence of a spare wheel on board the vehicle while at the same time guaranteeing that the vehicle will be able to continue its journey despite a significant or complete loss of pressure from one or more of the tyres. This, for example, allows a service centre to be reached without the need to stop, under circumstances that are often hazardous, in order to fit the spare wheel.
One envisaged solution is the use of run-flat tyres which are provided with self-supporting sidewalls (sometimes referred to by their trade designations “ZP” for “zero pressure” or “SST” for “self supporting tyre”).
A run-flat tyre comprising a crown comprising a crown reinforcement, which reinforcement is formed of two crown plies of reinforcing elements and surmounted by a tread, is known from the prior art. Two sidewalls extend the crown radially inwards. These sidewalls are reinforced by rubber inserts that are able to support a load at reduced pressure or even with no pressure.
The tyre further comprises two beads each one comprising a bead wire and a carcass reinforcement extending from the beads through the sidewalls to the crown and comprising at least one carcass ply of reinforcing elements. The carcass ply is anchored to each of the beads via a turn-up about the bead wire.
When the inflation pressure is significantly reduced in comparison with the service pressure, or is even zero (this is then referred to as “run-flat” mode), the tyre must make it possible to cover a given distance at a given speed. This performance, referred to as “ERM” (extended running mode) performance, is required by legislation or by motor vehicle manufacturers in order to allow the producer to advertise the tyre as being a run-flat tyre.
When the inflation pressure is close to the service pressure (this is then referred to as “normal running” mode), it is desirable for the tyre to exhibit performance, referred to as “IRM” (inflated running mode) performance, that is as high as possible. This IRM running performance includes, amongst other things, the mass, the rolling resistance or even the comfort.
Furthermore, it is advantageous to equip tyres with electronic identification devices that allow them to be identified and tracked during the manufacture thereof, the storage thereof, the entirety of the lifetime thereof and also during retreading thereof.
The tyres in question are tyres for heavy goods vehicles, passenger vehicles, construction equipment, agricultural machinery, and aeroplanes.
Such electrical devices may be radiofrequency transponders or radiofrequency identification (RFID) transponders.
These electronic devices must be placed very precisely in order to guarantee good radiofrequency communication, an acceptable device lifetime and in order not to penalize the operation or the endurance of the tyres.
The particular conditions of use of tyres able to run flat when running flat makes it particularly difficult to introduce such electronic devices into these types of tyres.
The subject of the invention is a tyre suitable for running flat, the tyre comprising a crown, two sidewalls and two beads, a carcass reinforcement anchored in each bead and a sidewall insert placed in each of the two sidewalls axially internally relative to the carcass reinforcement. This tyre is characterized in that it is equipped with an electronic device comprising at least one radiofrequency transponder and in that the electronic device is placed axially internally relative to the outer rubber layer of the sidewall and externally relative to the carass reinforcement and radially at above 55% of the section height of the tyre.
Preferentially, the electronic device is placed radially at above 65% of the section height of said tyre.
The electronic device may be placed at the interface between the outer rubber layer of the sidewall and the carass reinforcement.
In this zone the mechanical stresses are low during running in inflated mode due to the high rigidity of the rubber from which the sidewall insert is made. This allows the electronic device to have a good fatigue resistance.
This position makes it possible to guarantee that quality of the electromagnetic communication between the electronic device and a receiver external to the tyre is optimal. The wheel on which the tyre is mounted is in general made of metal and a position too close thereto could disrupt the communication.
Another undeniable advantage is that during the life of the tyre in normal, inflated, mode the latter is able to undergo many curb scrapes. In the most severe cases (taxis, etc.) the outer rubber layer of the sidewall my even wear down to 80% of its thickness as-new. These scrapes are observed to occur around the zone that is axially the outermost of the tyre, and that is off-centred toward the rim flange. Such a position, at above 55% and preferably above 65% of the section height of the tyre is therefore very advantageous, because little worn by curb scrapes.
The placement at the interface between the sidewall rubber and the carcass reinforcement is advantageous because it is easy to position the electronic device during the manufacture of the tyre at this interface.
According to another embodiment, the outer rubber layer of the sidewall having a radially outer end P, the electronic device is placed radially internally at a distance D larger than 5 mm and preferably larger than 10 mm from this radially outer end of the rubber layer of the sidewall.
This allows the electronic device to be positioned away from the zone that is mechanically most stressed in service.
According to another feature of the tyre that is the subject of the invention, the sidewall insert has a maximum thickness comprised between 6 and 16 mm.
The electronic device may consist of a radiofrequency transponder. It may also consist of a radiofrequency transponder encapsulated in an electrically insulating encapsulating rubber mass.
It is necessary for correct radiofrequency operation of the radiating antenna of the electronic device, for said antenna to be embedded in a mass of electrically insulating encapsulating rubber. It is thus possible to use a semi-finished element consisting of a radiofrequency transponder embedded in a mass of electrically insulating rubber to place it into the structure of the tyre during its manufacture in the chosen place.
However, it is also possible to directly place the radiofrequency transponder between two blends of the tyre when said blends, because of their formulation, are electrically insulating.
Preferably, the elastic modulus of the encapsulating rubber mass is lower than or equal to the elastic modulus of the adjacent rubber blends.
According to another aspect, the relative dielectric constant of the encapsulating rubber mass is lower than the relative dielectric constant of the adjacent rubber blends.
The radiofrequency transponders conventionally comprise an electronic chip and a radiating antenna able to communicate with an external radiofrequency reader.
According to a first embodiment, the radiating antenna comprising two helical antenna segments, and the electronic chip is galvanically connected to the two helical antenna segments.
According to another embodiment, the radiofrequency transponder in addition comprises a primary antenna electrically connected to the electronic chip, wherein the primary antenna is inductively coupled to the radiating antenna, and wherein the radiating antenna is a dipole antenna consisting of a single-strand helical spring.
This second embodiment has the advantage of mechanically disassociating the radiating antenna from the electronic components of the transponder and thus of avoiding the weak point of conventional transponders, namely the zone in which the antenna segments are fastened to the carrier of the electronic chip. The integration of such an electronic device into a tyre allows the risk of deterioration of the device, because of its structure, to be decreased while improving radiocommunication performance and minimizing the related risks to the physical integrity of the tyre.
Specifically, deterioration of the electronic device is generally caused by failures in the electrical connections that exist between the communication radiating antenna and the electronic portion of the device. Here, no mechanical connection is required since the transfer of energy between the communication antenna and the electronic chip is achieved with an electromagnetic field, via a primary antenna. However, although the size of the radiating antenna, which is related to the frequency band of communication and to its far-field operation, is by nature large, the primary antenna is not subjected to this constraint. Thus it is of smaller size, in general allowing the deformations of the tyre to be easily endured without generation of excessively high mechanical stresses within the galvanic junction between it and the electronic chip. Lastly, the supple nature of the radiating antenna limits the risks of the deterioration of the zone of the tyre close to the transponder.
Secondly, the introduction of the primary antenna makes it possible to disassociate contradictory constraints on the size of the radiating antenna and the electrical impedance of the electronic portion of the device. Thus, it is possible to dimension the primary antenna in order to match its electrical impedance to that of the chip in order to minimize losses and to therefore improve the performance of the electronic device in terms of power consumption. The dimensions of the radiating antenna are then chosen solely with respect to the criterion of the communication frequency of the electronic device. All of this tends to improve the radiocommunication performance of the electronic device.
According to one preferred embodiment, the radiating antenna defining a first longitudinal axis, the primary antenna is a coil having at least one turn defining a second longitudinal axis that is circumscribed in a cylinder the axis of revolution of which is parallel to the second longitudinal axis and the diameter of which is comprised between one third and three times, and preferably between half and two times, the average diameter of the helical spring of the radiating antenna.
Thus, the primary antenna being a loop antenna, energy is mainly transferred between the radiating antenna and the primary antenna by inductive coupling. This requires a certain proximity (in order to limit the gap between the two antennas) between the two antennas, requiring the coil of the primary antenna to be dimensioned, with respect to the radiating antenna, in order to ensure a transfer of energy that is sufficiently effective to obtain the desired radiocommunication quality. Concretely, the primary antenna may advantageously be of diameter smaller than that of the radiating antenna; in this case the entirety of the electronic portion of the transponder is inserted into the radiating antenna and the assembly is then particularly robust in an environment such as that of a tyre.
The antenna may also be of diameter larger than that of the radiating antenna; this case is particularly advantageous when it is desired to add, to the radiofrequency transponder, other, active or passive, electronic components in order to allow additional functions, such as for example surveillance of the state of the tyre, to be added.
According to one advantageous embodiment, the radiating antenna having a central zone between two lateral zones and the primary antenna having a median plane perpendicular to the second longitudinal axis, the first and second longitudinal axes are parallel to each other and the median plane of the primary antenna is placed in the central zone of the radiating antenna.
Thus, it is ensured that the distance between the radiating and primary antennas is constant along the longitudinal axes of these antennas, thus optimizing level with each element of length of the primary antenna an equivalent transfer of energy. In addition, the magnetic field created by a coil through which an electric current flows being maximum at the centre of the length of the coil (in the case of a λ/2 antenna), it is preferable to place the median plane of the primary antenna in the central zone of the radiating antenna and more preferably at the centre thereof in order to maximize the magnetic field that is the origin of the inductive coupling.
Preferably, in the case of a tyre able to run flat, the primary antenna is placed in the interior of the single-strand helical spring of the radiating antenna.
It is advantageous, when the tyre has a preferential running direction, to place an electronic device in each of the two sidewalls.
Conversely, when the tyre has an outer side and an inner side for mounting on a vehicle, the electronic device is advantageously placed in the sidewall on the outer side of the tyre.
In both cases, after mounting, an electronic device is always placed in the sidewall placed towards the outside of the vehicle, this makes it possible to facilitate communication between this electronic device and its radiofrequency transponder and an external receiver.
The various subjects of the present invention will be better understood by means of the following detailed description and the attached drawings, the same reference numbers having been used in all the drawings to reference identical parts, and in which drawings:
Hereinafter, the terms “rubber blend”, “rubber” and “blend” are used in an equivalent manner to identify rubber constituents of the tyre.
This figure also indicates the section height SH of the tyre, i.e. the radial distance between the nominal diameter of the mounting rim of the tyre NRD and the radially outermost part of the tread of the tyre. In the context of this invention, the nominal diameter of the mounting rim of the tyre is taken to be the diameter of the tyre as indicated by its size.
In all the figures, the tyre is shown free, not mounted on a rim and such that the width between the two beads is decreased to the width of the nominal ETRTO rim.
As regards the axial direction, what is meant by “axially external” is an axial direction directed toward the exterior of the tyre and by “axially internal” what is meant is an axial direction directed toward the median plane EP of the tyre.
This run-flat tyre 30 comprises a crown 32 reinforced by a crown reinforcement or belt 36, a sidewall 33 and a bead 34, the bead 34 being reinforced with a bead wire 35. The crown reinforcement 36 is surmounted radially externally by a rubber tread 39. A carcass reinforcement 37 is wound around the bead wire 35 in the bead 34, the turn-up 38 of this reinforcement 37 being, for example, arranged towards the exterior of the tyre 30. In a manner known per se, the carcass reinforcement 37 is made up of at least one ply reinforced by what are known as “radial” cords, for example here of textile, that is to say that these cords are disposed virtually parallel to one another and extend from one bead to the other so as to form an angle of between 80° and 90° with the median circumferential plane EP. An airtight inner liner 40 extends from one bead to the other radially internally with respect to the carcass reinforcement 37. The bead 34 comprises a protective rubber (or “protector”) 42 able to make contact with the surface of a rim. It also comprises a first filling rubber 46 extending radially externally relative to the bead wire 35.
The tyre 30 is able to run flat because of the presence of a sidewall insert 44 placed axially internally relative to the carcass reinforcement 37. This insert comprises two circumferential adjacent rubber masses 441 and 442. This insert 44 allows the structure of the tyre to withstand the load thereon at zero pressure. The order of magnitude of the elastic modulus of the rubber of a sidewall insert is of the order of twice the value of the modulus of the sidewall rubber or greater.
The sidewall 33 of
This zone Z is preferentially limited radially to a distance D of 5 mm from the radially outer end P of the outer sidewall rubber layer 48. This radial distance D is very preferentially larger than 10 mm so that the service lifetime of the electronic device is not negatively affected.
On account of the high modulus of the rubber from which the sidewall insert is made, which is necessary to ensure the bearing capacity of the tyre and of the vehicle when running flat, the electronic device is, in the zone Z, much less mechanically stressed in inflated running mode than is the case with a conventional tyre without sidewall insert, and thus has an acceptable service lifetime.
In
A third favourable position for an electronic device is also shown in
The three positions illustrated are located in the zone Z, which zone is favourable in the case of a tyre comprising sidewall inserts.
The encapsulating elastomer blend contains 100 phr (parts per 100 parts of elastomer by mass) of a polymer such as EPDM (ethylene propylene diene monomer rubber), butyl rubber, neoprene or a diene elastomer such as SBR (styrene-butadiene rubber), polybutadiene, natural rubber or polyisoprene.
The blend may contain fillers such as fillers of silica, carbon black, chalk and kaolin type:
Such amounts and types of fillers make it possible to guarantee a relative permittivity lower than 6.5, in particular at a frequency of 915 MHz.
The stiffness in the cured state of the encapsulating blend is preferably lower than or close to those of the adjacent blends.
In a first embodiment shown in
The radiofrequency transponder 1 of the electronic device 2 such as shown in
The radiofrequency transponder 1 according to the second embodiment of the electronic device 2 comprises an electronic chip 22 and a radiating antenna 10 able to communicate with an external radiofrequency reader. It in addition comprises a primary antenna 24 electrically connected to the electronic chip 22 and inductively coupled to the radiating antenna 10. The radiating antenna is a dipole antenna consisting of a single-strand helical spring defining a first longitudinal axis.
The electromagnetic conduction of such an antenna occurs mainly via a skin effect, i.e. it mainly occurs in the exterior layers of the antenna. This thickness of skin is in particular dependent on the frequency of the radiation and of the material from which the conduction layer is made. By way of example, for a UHF frequency (for example 915 MHz), the skin thickness is about 2.1 μm for silver, 2.2 μm for copper, and 4.4 μm for brass.
The steel wire may be coated with these layers then formed; alternatively it may also be formed then coated.
The helical spring is primarily defined by a winding diameter of the coated wire and by a helix pitch. Thus, given the diameter of the wire, the inside diameter 13 and outside diameter 15 of the helical spring may be precisely determined. The length 17 of the spring 10 here corresponds to one half-wavelength of the transmission signal of the radiofrequency transponder 1 in a rubber mass. It is furthermore possible to define a median plane 19 of the helical spring 10 perpendicular to the axis of revolution 11 separating the radiating antenna into two equal portions. This plane is in the middle of the central zone 16 of the radiating antenna, this central zone 16 corresponding to about 25% of the total length of the antenna and preferably 15%.
This radiofrequency transponder 1 has the advantage of being much more mechanically resistant than conventional transponders and thus is particularly suitable for a hostile use such as encountered with run-flat tyres.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1755690 | Jun 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/051259 | 5/31/2018 | WO | 00 |
