TIRE COMPRISING A RADIOFREQUENCY TRANSPONDER

Abstract

A tire fitted with a transponder comprises: a crown comprising a crown reinforcement having an axial end at each of its edges, connected at each of its axial ends by a sidewall to a bead having an interior end; a carcass reinforcement layer formed of parallel metal reinforcers, which is anchored in each bead around a bead wire to form a main part and a turn-up; and the transponder comprising a dipole antenna consisting of a spring defined by a pitch P and a diameter D. A ratio between the pitch (P1) and the diameter (D1) for a loop of a first region of the spring is greater than 0.8, and the transponder is situated axially on the outside of an interior end of the bead and radially between the upper end of the bead wire and the axial end of the crown reinforcement.

Claims

1.-15. (canceled)

16. A tire casing (100) that is toroidal in shape about a reference axis and equipped with a passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) and comprises: a crown block (82) comprising a crown reinforcement (86) having an axial end (861) at each of its edges, and a tread (89), connected at each of its axial ends (821) to a bead (84) having an interior end (841) situated axially and radially on an inside of the bead (84) with respect to the reference axis, by a sidewall (83); a carcass reinforcement comprising at least one carcass reinforcement layer formed of mutually parallel metal reinforcing elements defining a direction of reinforcement, inserted between two skim layers of elastomer compound, the at least one carcass reinforcement layer being anchored in each of the beads (84) by being turned up around an annular bead wire (85) to form a main part of the at least one carcass reinforcement layer (87), extending from one bead wire (85) to the other and situated radially on an inside with respect to the crown block (82), and a turn-up of the at least one carcass reinforcement layer (88) in each of the beads (84), the turn-up of the at least one carcass reinforcement layer (88) being separated from the main part of the at least one carcass reinforcement layer (87) by a first layer of elastomer compound (91) extending radially externally from the bead wire (85); a second layer of elastomer compound (93) forming an exterior surface of the tire casing (100) in a region of the bead (84), the second layer of elastomer compound (93) being intended to come into contact with a rim; a third layer of elastomer compound (94) situated radially on an outside in contact with the second layer of elastomer compound (93) forming an exterior surface of the sidewall (83); the passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) comprising an electronic portion (20) and a radiating dipole antenna (10) consisting of a single-strand helicoidal spring defining a helix pitch P, a winding diameter D, a midplane (19) and a wire diameter defining an interior diameter (13) and an exterior diameter (15) of the radiating antenna (10), of which a length (L0) is designed to communicate on a frequency band with an external radiofrequency reader defining a first longitudinal axis (11), a central region and two lateral regions along the first longitudinal axis (11), the electronic portion (20) comprising an electronic chip and a primary antenna of coil type comprising at least one turn, and defining a second longitudinal axis and a midplane (21) perpendicular to the second longitudinal axis, the primary antenna being electrically connected to the electronic chip and electromagnetically coupled to the radiating dipole antenna (10), the primary antenna being circumscribed inside a cylinder of which an axis of revolution is parallel to the second longitudinal axis and in which the diameter is greater than or equal to one third of the interior diameter (13) of the radiating antenna (10) situated plumb with the primary antenna, and the passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) being arranged in such a way that the first (11) and second longitudinal axes are parallel and that the midplane of the primary antenna (21) is positioned in the central region of the helical spring (10), wherein, with the radiating dipole antenna (10) comprising a second region (102) in which the radiating dipole antenna (10) is situated plumb with the electronic portion (20) and a first region (101, 101a, 101b) in which the radiating dipole antenna (10) is not situated plumb with the electronic portion (20), a ratio between a helix pitch (P1) and a winding diameter (D1) for at least one loop of the helical spring in the first region (101, 101a, 101b) is greater than 0.8, wherein the ratio between the helix pitch (P1) and the winding diameter (D1) of each loop of the helical spring in the first region (101, 101a, 101b) of the radiating dipole antenna (10) is less than 3, wherein, with the passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) being situated plumb with the at least one carcass reinforcement layer, the first longitudinal axis (11) of the radiating antenna (10) of the passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) forms an angle of at least 45 degrees with the direction of reinforcement of the at least one carcass reinforcement layer, and wherein the passive radiofrequency transponder is situated axially on an outside of the interior end (841) of the bead (84) and radially between the radially outermost end (851) of the bead wire (85) and the axial end (861) of the crown reinforcement (86).

17. The tire casing (100) according to claim 16, wherein the tire casing (100) comprises at least a fourth layer of elastomer compound (92) situated axially on an outside of the main part of the at least one carcass reinforcement layer (87) with respect to the reference axis and axially on an inside of the second (93) and/or third (94) layer of elastomer compound with respect to the reference axis.

18. The tire casing (100) according to claim 16, wherein, with the tire casing (100) comprising at least one airtight layer of elastomer compound (90) situated furthest toward an inside of the tire casing (100) with respect to the reference axis, the tire casing (100) comprises at least a fifth layer of elastomer compound (96) axially on an inside of the main part of the at least one carcass reinforcement layer (87) with respect to the reference axis.

19. The tire casing (100) according to claim 16, wherein the tire casing (100) comprises at least one reinforcement layer which is formed of reinforcing elements inserted between two skim layers of elastomer compound.

20. The tire casing (100) according to claim 16, wherein the passive radiofrequency transponder (1, 1′, 1bis, 1bis′, 1ter, 1ter′, 1qua, 1qua′) is partially encapsulated in a mass of electrically insulating elastomer compound (3a, 3b).

21. The tire casing (100) according to claim 20, wherein a tensile elastic modulus of the encapsulating mass (3a, 3b) is lower than a tensile elastic modulus of at least one elastomer compound adjacent to the encasing mass (3a, 3b).

22. The tire casing (100) according to claim 20, wherein a relative dielectric constant of the encapsulating mass (3a, 3b) is lower than 10.

23. The tire casing (100) according to claim 16, wherein the passive radiofrequency transponder (1, 1′, 1ter, 1ter′) is situated at an interface defined by at least a surface of a layer of elastomer compound (91, 92, 93, 94, 96) of the tire casing (100).

24. The tire casing (100) according to claim 23, wherein, with the interface being defined by another layer of elastomer compound (91, 92, 93, 94, 96) or a reinforcement layer, the passive radiofrequency transponder (1, 1′, 1ter, 1ter′) is situated at a distance of at least 5 millimeters from the ends of the layers that make up the interface.

25. The tire casing (100) according to claim 16, wherein the passive radiofrequency transponder (1bis, 1bis′, 1qua, 1qua′) is situated on an inside of a layer of elastomer compound (91, 92, 93, 94, 96) of the tire casing (100).

26. The tire casing (100) according to claim 25, wherein the first longitudinal axis (11) of the radiating antenna (10) of the passive radiofrequency transponder (1bis, 1bis′, 1qua, 1qua′) is perpendicular to a thickness of the layer of elastomer compound (91, 92, 93, 94, 96).

27. The tire casing (100) according to claim 25, wherein the passive radiofrequency transponder (1bis, 1bis′, 1qua, 1qua′) is situated at a distance of at least 0.3 millimeters from the surfaces of the layer of elastomer compound (91, 92, 93, 94, 96).

28. The tire casing (100) according to claim 16, wherein a ratio between a helix pitch (P2) and a winding diameter (D2) for each loop of the second region (102) is less than or equal to 0.8.

29. The tire casing (100) according to claim 16, wherein the helix pitch (P1) of the radiating dipole antenna (10), which corresponds to the helix pitch of the radiating dipole antenna (10) in the first region (101,101a, 101b), is greater than a helix pitch (P2) of the radiating dipole antenna (10), which corresponds to the helix pitch of the radiating dipole antenna (10) in the second region (102).

30. The tire casing (100) according to claim 16, wherein, with the electronic portion (20) being placed inside the radiating dipole antenna (10), a first inside diameter D1′ of the radiating dipole antenna (10) in the first region (101, 101a, 101b) is smaller than a second inside diameter D2′ of the radiating dipole antenna (10) in a second region (102), and the electronic portion (20) is circumscribed by a cylinder of which an axis of revolution is parallel to the first longitudinal axis (11) and of which the diameter is larger than or equal to the first inside diameter D1′ of the radiating dipole antenna (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The invention will be better understood by means of the following detailed description. These applications are given solely by way of example and with reference to the appended figures, throughout which the same reference numerals denote identical parts, and in which:

[0085] FIG. 1 shows a perspective view of a radiofrequency transponder of the prior art;

[0086] FIG. 2 shows a perspective view of a radiofrequency transponder according to the invention;

[0087] FIGS. 3a and 3b are illustrations of the length of the wire of the radiating antenna depending on the ratio between the helix pitch and the winding diameter of the helical spring for a given elementary length of the radiating dipole antenna and depending on whether a constant pitch or constant winding diameter is employed;

[0088] FIG. 4 is one example of a radiofrequency transponder according to the invention, having certain particularities;

[0089] FIG. 5 is an exploded view of an identification tag according to the invention;

[0090] FIG. 6 shows a graph of the electrical power transmitted to two passive radiofrequency transponders incorporated into a tyre casing according to the invention, as a function of the observation frequency band;

[0091] FIG. 7 shows a view in meridian section of a tyre casing of the prior art;

[0092] FIG. 8 is a view in meridian section of the bead and of the sidewall of a tyre casing according to the invention when the passive radiofrequency transponder is located in the outer region of the tyre casing;

[0093] FIG. 9 is a view in meridian section of the bead and of the sidewall of a tyre casing according to the invention when the passive radiofrequency transponder is located in the inner region of the tyre casing;

[0094] FIG. 10 is a view in meridian section of a tyre casing comprising two carcass reinforcement layers;

[0095] FIG. 11 is a view in meridian section of a tyre casing comprising a sidewall insert for extended running and equipped with a passive radiofrequency transponder.

DETAILED DESCRIPTION OF EMBODIMENTS

[0096] Below, the terms “tyre” and “pneumatic tyre” are employed equivalently and refer to any type of pneumatic or non-pneumatic tyre.

[0097] FIG. 1 shows a prior-art radiofrequency transponder 1 in a configuration in which the electronic portion 20 is located inside the radiating antenna 10. The radiating antenna 10 consists of a steel wire 12 that has been plastically deformed in order to form a helical spring having an axis of revolution 11. The helical spring is defined primarily by a winding diameter of the coated wire and a helix pitch. These two geometric parameters of the helical spring are constant here. Thus, inside 13 and outside 15 diameters of the helical spring are precisely determined taking the diameter of the wire into account. The length L0 of the spring corresponds here to one half-wavelength of the radiofrequency transmission signal of the transponder 1 in a mass of elastomer compound. It is thus possible to define a median plane 19 of the helical spring perpendicular to the axis of revolution 11 separating the radiating antenna 10 into two equal parts. The geometric shape of the electronic portion 20 is circumscribed in a cylinder, the diameter of which is smaller than or equal to the inside diameter 13 of the helical spring. This makes it easier for the electronic portion 20 to be inserted into the radiating antenna 10. The median plane 21 of the primary antenna is located substantially superposed with the median plane 19 of the radiating antenna 10. Lastly, the axis of the primary antenna is substantially parallel to the axis of revolution 11 of the radiating antenna 10. The radiating antenna may be divided into two distinct regions: a first region 101 of the radiating antenna 10, in which the helical spring is not situated plumb with the electronic portion 20, and a second region 102 situated plumb with the electronic portion 20. The first region 101 of the radiating antenna 10 comprises two portions 101a and 101b of substantially equivalent lengths, these portions axially flanking the second region 102 of the radiating antenna 10.

[0098] FIG. 2 is a radiofrequency transponder 1 according to the invention, which has, with respect to the prior-art radiofrequency transponder, the distinctive feature that the ratio of the helix pitch to the winding diameter of at least one loop of the radiating antenna of the first region is higher than 0.8. In our case, all the loops of each of the regions 101a and 101b have had their ratio changed equivalently. This is achieved by decreasing the total number of loops in each of the sub-regions 101a and 101b. In this particular case, the winding diameter for the winding of the wire of the radiating antenna 10 is kept the same. However, it would also have been possible to modify the ratio of the helix pitch to the winding diameter of each loop of the first region 101 by increasing the winding diameter for the winding of the steel wire of the radiating antenna 10 in the first region 101 of this antenna. In our case, the helix pitch of the radiating antenna 10 in the second region 102 of the radiating antenna 10 has not been modified. Thus, the ratio between the helix pitch and the winding diameter in the second region 102 of the radiating antenna 10 is lower than 0.8.

[0099] FIGS. 3a and 3b are illustrations of the importance, with respect to the radioelectric and electromagnetic properties of the radiating antenna, of the ratio of the helix pitch to the winding diameter, for one loop of the helical spring.

[0100] FIG. 3a is an illustration of variations in the ratio of the helix pitch to the winding diameter of a loop when the helix pitch of the loop and the diameter of the wire from which the loop is formed remain constant. For an elementary length of the radiating antenna of length equal to the region occupied by a complete loop for a ratio equal to 1, the curvilinear distance of this loop is equal to 2*PI*PI elementary units. The curve 500 drawn with a solid line corresponds to this loop. Specifically, the radius of this loop is necessarily equal to PI elementary units. Considering now the curve 501 drawn in dotted line which corresponds to a ratio equal to 2, because the helix pitch is constant, the winding diameter of this loop must be a factor of two times smaller than the winding diameter of the previous loop, namely PI elementary units. Thus, the curvilinear distance of this loop illustrated by the dotted line 501 is equal to PI*PI elementary units. Therefore, the curvilinear length of a first loop, having a higher ratio of helix pitch to winding diameter than a second loop, is smaller than the curvilinear length of this second loop. The curve 502 drawn with the dashed line and the curve 503 drawn with the dash-dot line illustrate ratios of 0.8 and of 0.5, respectively. The curvilinear lengths of these two loops are equal to 2.5*PI*PI elementary units and 4*PI*PI elementary units, respectively.

[0101] FIG. 3b is an illustration of the variations in the ratio of the helix pitch to the winding diameter of a loop when the diameter of the loop and the diameter of the wire from which the loop is formed remain constant. For an elementary length of the radiating antenna of length equal to the region occupied by a complete loop for a ratio equal to 1, the curvilinear distance of this loop is equal to 2*PI*PI elementary units. The curve 505 drawn with a solid line corresponds to this loop. Specifically, the radius of this loop is necessarily equal to PI elementary units. Considering now the curve 506 which corresponds to a ratio equal to 2, because the winding diameter is constant, the helix pitch of this loop must be a factor of two times larger than the helix pitch of the previous loop, namely 4*PI elementary units. However, if the elementary length is limited to 2*PI elementary units, the curvilinear distance of this loop illustrated in dotted line is equal to PI*PI elementary units. Likewise, for curves 507 and 508 which correspond to ratios of 0.5 and 0.2 respectively, i.e. a doubling and a fivefold increase in the number of loops respectively, the curvilinear distance of the curve 507 illustrated in dotted line is equal to 4*PI*PI elementary units. Furthermore, the curvilinear distance of the curve 508 drawn in dash-dot-dot line is equal to 10*PI*PI elementary units.

[0102] Of course, instead of solely modifying the helix pitch or the winding diameter of each loop, it is possible to modify both parameters simultaneously. Only the ratio obtained via these two modifications will have an impact on the communication performance of the radiating antenna.

[0103] Specifically, the resistance of a conductive wire is proportional to the curvilinear length of the wire. The higher the ratio of the helix pitch to the winding diameter of the loop, the shorter the curvilinear length of the wire. Thus, the lower the electrical resistance of the loop. In conclusion, the radioelectric properties of the loops of the radiating antenna are improved by minimizing this electrical resistance. By minimizing the electrical resistance of the radiating antenna in the first region of the radiating antenna, the radiation efficiency of the antenna is improved both in transmission and in reception, the antenna mainly consisting of this first region. In addition, minimizing the electrical resistance of the antenna ensures a maximum electrical current is generated for a given electrical potential difference. Thus, the radioelectric performance and therefore the communication performance of the radiofrequency transponder are thereby improved.

[0104] As regards the second region of the radiating antenna, the radiation efficiency of this second region, which is smaller than the first region, is not essential. Specifically, the main function of this second region is to ensure electromagnetic coupling to the primary antenna of the electronic portion. This electromagnetic coupling is mainly due to inductive coupling if the primary antenna is a coil of a number of turns. For this coupling to occur, the radiating antenna must first generate a magnetic field. This magnetic field is in particular dependent on the inductance of the radiating antenna. To maximize the inductance of a coil, it is recommended to decrease the ratio of the helix pitch to the winding diameter of the coil or to increase the number of loops of the coil. By decreasing the ratio of the helix pitch to the winding diameter of the loops of the second region of the radiating antenna, the inductive coupling is maximized by increasing the inductance of the antenna. In addition, if this ratio is decreased by modifying only the helix pitch of the antenna, the number of turns making up the second region of the antenna is increased, this increasing the area of energy transfer between the two antennas. This increase in the area of energy transfer is of course favourable to the communication performance of the radiofrequency transponder.

[0105] FIG. 4 is an illustration of a radiofrequency transponder 1 operating in the frequency range between 860 and 960 MHz intended to be incorporated into a tyre casing. To improve the radiocommunication performance and the physical integrity of the radiofrequency transponder 1 within a tyre casing having a bead wire, without thereby impairing the endurance of the tyre casing, it will be preferable to arrange the axis of revolution of the radiating antenna 10 parallel to the axis U so that it rests on at least two reinforcing elements of the carcass reinforcement layer of the tyre casing. In particular, if the tyre casing has a single carcass reinforcement layer, for example a conventional tyre casing for a radial tyre, the axis of revolution of the radiating antenna 10 will be perpendicular to the direction of reinforcement defined by the radial reinforcing elements of the carcass reinforcement layer so that the mechanical anchor points for the passive radiofrequency transponder can be multiplied particularly if this transponder is incorporated during the course of manufacture of the tyre casing. As a result, the passive radiofrequency transponder 1 will be positioned circumferentially with respect to the reference axis of the tyre casing.

[0106] In addition, the radiofrequency transponder will be positioned axially on the outside with respect to the axially inner end of the bead. This is region that is mechanically stable as it does not experience sizeable unforeseen variations in thermomechanical deformation. Finally, the passive radiofrequency transponder 1 will be placed radially between the radially upper end of the bead wire and the axial end of the crown block of the tyre casing. This positioning in the radial direction makes it easier for the passive radiofrequency transponder incorporated into a tyre casing of a land vehicle to communicate with a radiofrequency reader situated outside the land vehicle as there are few conducting elements interposed between the radiofrequency reader and the passive radiofrequency transponder 1.

[0107] The radiofrequency transponder 1 here comprises a radiating antenna 10 and an electronic portion located inside the radiating antenna 10. The electronic portion comprises an electronic chip connected to a printed circuit board and a primary antenna consisting of a conducting wire comprising seventeen rectangular turns connected to the printed circuit board. The face of the printed circuit board opposite to the primary antenna comprises a galvanic circuit of meander shape forming a line of 10 millimetres length and of 1 millimetre width. Lastly, the diameter of the cylinder circumscribing the primary antenna is 0.8 millimetres.

[0108] The circuit board thus formed is embedded in a mass 30 of epoxy resin, ensuring the mechanical reliability of the electronic components and the electrical insulation of the circuit board. The cylinder circumscribing the stiff mass 30 has a diameter of 1.15 millimetres and a length of 6 millimetres.

[0109] The length L0 of the radiating antenna 10 is here 45 millimetres and corresponds to one half-wavelength of radioelectric waves at a frequency of 915 MHz in a medium of relative dielectric permittivity of about equal to 5. The radiating antenna 10 is produced using a steel wire 12 of 0.225 millimetre diameter the surface of which is coated with a layer of brass.

[0110] The radiating antenna 10 may be divided into two main regions. The first region 101 corresponds to the section of the radiating antenna that is not located plumb with the electronic portion. It comprises two sub-regions 101a and 101b flanking on either side the stiff and insulating mass 30.

[0111] Each sub-region 101a, 101b has a length L1 of 19 millimetres and comprises 12 circular turns of a constant winding diameter D1 of 1.275 millimetres. This defines inside and outside diameters of 1.05 and 1.5 millimetres, respectively. The helix pitch P1 of the circular turns is of 1.55 millimetres. Thus, the ratio of the helix pitch P1 to the winding diameter D1 of the turns is 1.21. The axially outer ends of each sub-region 101a and 101b ends in 2 adjoined turns. Thus, the high ratio ensures the efficacy of the radioelectric properties of the radiating antenna 10 is maximized in this region 101. In addition, the contact between the turns located outermost on the radiating antenna 10 prevents the helical springs from becoming interlaced with one another during handling of the radiofrequency transponders. As most of the turns of the first region 101 of the radiating antenna 10 have a ratio higher than 0.8, the radioelectric performance of the radiofrequency transponder 1 is clearly improved.

[0112] In the second region 102 of the radiating antenna 10, which corresponds to the section of the radiating antenna 10 located plumb with the electronic portion, the radiating antenna has a length of 7 millimetres. The helical spring has a constant helix pitch P2 of 1 millimetre and a constant winding diameter D2 of 1.575 millimetres. Thus, the inside diameter of the helical spring of the second region of the radiating antenna is 1.35 millimetres. This makes it possible to have a ratio of the helix pitch to the winding diameter that is constant of the order of 0.63. This ratio allows the inductance of the second region 102 of the radiating antenna 10 to be maximized with respect to the first region 101, this allowing the efficacy of the electromagnetic coupling to the electronic portion to be improved.

[0113] In this particular case, in the first region 101 the inside diameter of the radiating antenna 10, which is equal to 1.05 millimetres, is smaller than the diameter, equal to 1.15 millimetres, of the mass 30 as represented by the cylinder circumscribing the electronic portion. Thus, the sub-regions 101a and 101b of the first region 101 of the radiating antenna 10 form mechanical stops that limit the axial movement of the mass 30 inside the radiating antenna 10. The electronic portion is installed by inserting the stiff and insulating mass 30 into the radiating antenna 10.

[0114] In addition, the diameter of the cylinder circumscribing the primary antenna is much larger than one third of the inside diameter of the helical spring of the second region 102 of the radiating antenna. Although the cylinder circumscribing the primary antenna is not coaxial with the axis of revolution U of the radiating antenna 10, it is substantially parallel thereto. Furthermore, the minimum distance between the second region 102 of the radiating antenna 10 and the primary antenna is smaller than 0.3 millimetres, i.e. much smaller than one quarter of the inside diameter of the radiating antenna 10. This proximity of the antennas is permitted by the compressed pitch P2 applied in the second region 102 of the radiating antenna 10, which allows a lower tolerance to be obtained for the dimensions of the spring and in particular for the winding diameter D2. In addition, this proximity ensures better quality electromagnetic coupling between the two antennas. Of course, this electromagnetic coupling could have been improved by using turns of identical shape in the primary antenna and in the radiating antenna, such as circular turns for example. This coupling could also have been optimized by making the axes of the two antennas coaxial, this amounting to placing the circuit board inside the primary antenna in such a way as to minimize the axial dimension of the electronic portion. Thus, the quality of the area of transfer of electromagnetic energy between the two antennas would have been optimal.

[0115] Other specific embodiments, in particular in the case of variation of the winding diameter of the helical spring between the first and second regions of the radiating antenna, particularly in instances in which the inside diameter of the first region of the radiating antenna is smaller than the diameter of the cylinder circumscribing the electronic portion, may be employed.

[0116] FIG. 5 shows an identification tag 2 comprising a radiofrequency transponder 1 according to the invention embedded in a supple mass 3 made of electrically insulating elastomeric material, this mass being made up of the blocks 3a and 3b. The radiofrequency transponder 1 is generally placed in the middle of the tag 2 in order to maximize the smallest distance between the first region 101 of the radiating antenna 10 and the external surface of the identification tag 2.

[0117] In the case where the ratio between the helix pitch and the winding diameter of the loop of the first region 101 of the radiating antenna 10 is increased by decreasing the winding diameter of the steel wire, the volume occupied by the radiofrequency transponder 1 within the mass 3 of elastomeric material is decreased.

[0118] This allows, in a first application, the thickness of each of the blocks 3a and 3b of the identification tag 2 to be decreased while keeping the same distance between the external surface of the identification tag 2 and the first region 101 of the radiating antenna 10. This decrease in the thickness of the identification tag 2 will facilitate its introduction into an object to be identified, while preserving the same electrical-insulation potential. In a second application, this allows the distance between the first region 101 of the radiating antenna 10 and the external surface of the identification tag 2 to be increased. This second application allows radioelectric performance to be improved and therefore the communication performance of the radiofrequency transponder 1 placed in the identification tag 2. Specifically, the electrical insulation of the tag 2 is proportional to the distance between the first region 101 of the radiating antenna 10 and the external surface of the tag 2. The radioelectric operation of the radiofrequency transponder 1 is improved, or stays the same if this distance has reached its efficacy asymptote, by a better electrical insulation of the identification tag 2.

[0119] FIG. 6 is a graph of the electrical power transmitted by passive radiofrequency transponders, each located inside a XINCITY Michelin radial tyre tyre casing of 275/70 R22.5 dimension comprising a metal, in this case steel, carcass reinforcement layer, to an external radiofrequency reader. The passive radiofrequency transponders are situated in the bead region, radially on the outside of the radially upper end of the bead wire at a distance of 40 millimetres and bearing radially against the first layer of elastomer compound such that the first longitudinal axis of the radiating dipole antenna is perpendicular to the carcass reinforcement layer. The communication frequency of the radiofrequency transponders is centred on 915 MHz. The measurement protocol employed corresponds to that of standard ISO/IEC 18046-3 entitled “Identification Electromagnetic Field Threshold and Frequency Peaks”. Measurements were carried out at a wide range of scanned frequencies and not at a single frequency as conventionally is the case. The x-axis represents the frequency of the communication signal. The y-axis represents the electrical power received by the radiofrequency reader expressed in decibels relative to the maximum electrical power transmitted by a current state-of-the-art radiofrequency transponder. The dashed curve 1000 represents the response of a radiofrequency transponder according to the cited document. The continuous curve 2000 represents the response of a transponder according to the invention to the same signal transmitted by the radiofrequency reader. An improvement of about two decibels in favour of the radiofrequency transponder according to the invention at the communication frequency of the radiofrequency reader will be noted. The improvement remains of the order of at least one decibel over a wide frequency band about the communication frequency.

[0120] The circumferential direction of the tyre, or longitudinal direction, is the direction that corresponds to the periphery of the tyre and is defined by the direction of running of the tyre casing.

[0121] The transverse or axial direction of the tyre is parallel to the axis of rotation, or reference axis, of the tyre casing.

[0122] The radial direction is a direction which crosses the reference axis of the tyre casing and is perpendicular thereto.

[0123] The axis of rotation of the tyre casing is the axis about which it turns in normal use.

[0124] A radial or meridian plane is a plane that contains the axis of rotation of the tyre.

[0125] The circumferential median plane, or equatorial plane, is a plane that is perpendicular to the reference axis of the tyre casing and divides the latter into two halves.

[0126] FIG. 7 shows a meridian section of a tyre casing 100 including a crown 82 reinforced by a crown reinforcement or belt 86, two sidewalls 83 and two beads 84. The crown 82 is delimited axially by two axial ends 821 providing the connection with each sidewall 83 of the tyre casing 100. The crown reinforcement 86 made up of several reinforcement layers which are generally made of metal extends axially as far as an axial end 861 at each of its edges. The crown reinforcement 86 is surmounted radially on the outside by a tread 89 made of an elastomeric material. Each bead 84 is reinforced with a bead wire 85. A carcass reinforcement, in this case made up of a single carcass reinforcement layer, anchored in the beads 84comprising a main part 87 which is wound around the two bead wires 85 in each bead 84 and a turn-up 88 of this main part of the carcass reinforcement layer 87 which is arranged here towards the outside of the tyre casing 100, separates the tyre casing into two regions, which will respectively be called inner region, in the direction of the fluid cavity, and outer region, towards the outside of the wheel-tyre assembly. The carcass reinforcement is, in a manner known per se, made up of at least one layer reinforced with metal cords, for example in this instance steel cords, which is to say that these cords run practically parallel to one another. The main part 87 extends from one bead 84 to the other so as to form an angle of between 80° and 90° with the circumferential median plane EP. An airtight inner liner layer 90 extends from one bead 84 to the other radially internally with respect to the main part of the carcass reinforcement 87.

[0127] FIG. 8 shows a detailed view of the tyre casing 100 in the region of the bead 84 and the sidewall 83. This figure illustrates the positioning of the passive radiofrequency transponder 1 in the exterior region of the tyre casing 100 with respect to the main part 87 of the carcass reinforcement layer which, in the instance depicted, is made up of a single carcass layer.

[0128] The bead 84 consists of the bead wire 85, around which the main part of the carcass reinforcement layer 87 is wound, with a turn-up 88 situated in the outer region of the tyre casing 100. The turn-up 88 of the carcass layer ends with a free edge 881. A first layer of rubber compound 91, called bead wire filler, is situated radially externally and adjacent to the bead wire 85. It has a radially outer free edge 911 bearing on a face of the main part of the carcass reinforcement layer 87 (more precisely on the outer skim of the carcass reinforcement layer 87, without direct contact between the cords of the carcass layer and the electronic unit). A fourth layer of rubber compound 92, called “reinforcing filler”, is adjacent thereto. It has two free edges. The first free edge 921 is situated radially internally and bears on the turn-up 88 of the carcass reinforcement layer. The other free edge 922 is situated radially externally and ends on the face of the main part of the carcass reinforcement layer 87. Finally, the sidewall 83 is defined by means of a third layer of elastomer compound 94 covering both the fourth layer of elastomer compound 92 and the main part of the carcass reinforcement layer 87. The sidewall defined by the external surface of the third layer of elastomer compound 94 which has a free edge 941 situated radially on the inside ends in the turn-up 88 of the carcass reinforcement layer.

[0129] The airtight inner liner 90, which is adjacent to the main part of the carcass reinforcement layer 87 in this configuration, is located on the inner region of the tyre casing 100. It ends with a free edge 901 adjacent to the main part of the carcass layer 87. Finally, a second layer of elastomer compound 93, referred to as a bead protector, protects the carcass layer and the radially interior ends 901, 921 and 941 of the airtight inner liner 90, of the fourth layer of elastomer compound 92 and of the third layer of elastomer compound 94 respectively. The outer face of this second layer of elastomer compound 93 is able to be in direct contact with the rim flange during mounting of the tyre casing 100 on the wheel. This second layer of elastomer compound 93 has three radially outer free edges. The first free edge 931 is situated in the inner region of the tyre casing 100. The second free edge 932 is situated in the outer region of the tyre casing 100. Finally, the third free edge 933 constitutes the interior end 841 of the bead 84.

[0130] A bead 84 and its connected sidewall 83 of this tyre casing 100 is equipped with passive radiofrequency transponders, numbered 1, possibly with suffixes, which are situated in the exterior region of the tyre casing 100. The first passive radiofrequency transponder 1, having been encapsulated beforehand in an electrically insulating encapsulating rubber, is positioned on the outer face of the first layer of the bead wire filler 91. It is positioned at a distance of 20 millimetres from the free edge 881 of the turn-up 88 of the carcass layer that constitutes a mechanical singularity, that is to say beyond 10 millimetres away. This position ensures a region of mechanical stability for the radiofrequency transponder 1 that is beneficial to the mechanical endurance thereof In addition, embedding it within the very structure of the tyre casing 100 gives it good protection against mechanical attacks coming from outside the tyre casing 100. Finally, the first longitudinal axis of the passive radiofrequency transponder is in this case positioned circumferentially, which ensures an inclination perpendicular to the metal reinforcers of the main part 87 of the carcass reinforcement layer, favouring the radioelectric performance of the radiating dipole antenna and the positioning of the passive radiofrequency transponder within the structure of the tyre casing during manufacture of the tyre casing (tyre building and curing steps). Of course, this tyre 100 may be reinforced by a reinforcement layer, not depicted, situated, for example, between the fourth layer of elastomer compound 92 and the second 93 and/or third 94 layer(s) of elastomer compound. This reinforcement layer is generally made up of reinforcing elements which are oriented radially and, for example, sandwiched between two skim layers. This reinforcement layer has a radially outer end situated radially outside the end 881 of the turn-up 88 of the carcass reinforcement layer. The radiofrequency transponder 1 is spaced apart from the radially outer end of the reinforcement layer by at least 5 millimetres or even 10 millimetres if the reinforcing elements are metallic in nature.

[0131] In general, it is preferable for the passive radiofrequency transponder to be positioned at a radial distance of between 20 and 40 millimetres from the radially outer end of the bead wire 85 in order to be in a region of the tyre casing 100 that is mechanically stable during operation, as this guarantees the physical integrity of the radiofrequency transponder. In addition, this positioning is ensured to be radially on the outside of the rim flange, allowing good radiocommunication performance by limiting the disturbances associated with the, often metallic, nature of the wheel.

[0132] The second radiofrequency transponder 1bis, having optionally been encapsulated in an electrically insulating encapsulating rubber compatible with or similar to the material of the third layer of elastomer compound 94, is positioned on the inside of the third layer of elastomer compound 94. The material similarity between the third layer of elastomer compound 94 and the encapsulating rubber ensures that the radiofrequency transponder ibis is easily installed inside the sidewall 83 during the process of manufacturing the tyre casing. The radiofrequency transponder 1bis is simply placed within the material via a slit in the raw exterior face of the third layer of elastomer compound 94 during the building of the tyre casing 100 such that the first longitudinal axis of the radiating dipole antenna forms an angle of at least 45 degrees with respect to the radial direction of the tyre casing, this corresponding to the direction of reinforcement of the carcass reinforcement. Building the green tyre body and pressurizing it in the curing mould ensure that the radiofrequency transponder 1bis is, in the cured state, positioned as shown. This radiofrequency transponder 1bis is situated far from any free edge of any other constituent of the tyre casing 100 practically at the equator of the sidewall 83 providing the greatest radiofrequency communication distance. In particular, it is spaced from the free edge 932 of the bead protector, from the free edge 881 of the carcass reinforcement layer turn-up 88 and from the free edges 911 and 922 of the filler rubbers. Its positioning ensures improved communication performance with an external radiofrequency reader. Cyclic stress loadings during running will not be disruptive due to the mechanical decoupling between the radiating antenna and the electronic portion of the passive radiofrequency transponder 1bis. Of necessity, these two transponders are situated axially on the outside of the end 933 of the second layer of rubber compound 93 and therefore of the inner end of the bead 84. They are positioned radially between the radially outer end 851 of the bead wire 85 with respect to the reference axis of the tyre casing 100, and the axial ends 861 of the crown reinforcement 86.

[0133] FIG. 9 shows a detailed meridian section of a tyre casing 100 in the region of the bead 84 and of the sidewall 83. This FIG. 9 illustrates the position of the passive radiofrequency transponder in the inner region of the tyre casing 100 with respect to the main part of the carcass reinforcement layer 87, which is made of metal, in this case steel.

[0134] The tyre casing 100 comprises, in particular at the inner region, an airtight inner liner 90 and a layer of elastomer compound 96 interposed between the main part of the carcass layer 87 and the airtight inner liner 90. This component 96 has a radially interior free edge 961 located radially on the inside of the bead wire 85. This layer of elastomer compound 96 extends from one bead 84 to the other bead 84 of the tyre casing 100.

[0135] The location of the radiofrequency transponder at the interface between the airtight inner liner 90 and the layer of elastomer compound 96 allows the passive radiofrequency transponder 1 to be mechanically stabilized. It is approximately 40 millimetres radially on the outside of the free edge 931 of the bead protector 93, which means it can be situated radially on the outside of the rim flange when the tyre casing is in operation, mounted on a wheel. By contrast, in order to ensure improved radiocommunication performance, it is preferable to use an encapsulating rubber that is electrically insulating for encapsulating the radiofrequency transponder 1 and to orient the first longitudinal axis of the radiating dipole antenna of the radiofrequency transponder such that the inclination is at least 45 degrees, preferentially at least 60 degrees, with respect to the direction of the metal reinforcers of the carcass reinforcement layer. From the mechanical endurance point of view, this location is ideal for the passive radiofrequency transponder 1, which is protected from any external mechanical attack and from any internal thermomechanical attack. It ideally has a circumferential orientation given that it rests on at least two reinforcing elements of the carcass reinforcement layer 87. This ensures the radiofrequency transponder 1 has an axial position, with respect to the thickness of the tyre casing 100, that allows robust tuning of the resonance of the radiating dipole antenna of the passive radiofrequency transponder 1 when this transponder is incorporated in the tyre casing 100.

[0136] The second location of the radiofrequency transponder 1ter according to the invention allows improved radiocommunication performance by being radially further outwards in the tyre casing 100. However, it is advisable for it to be encapsulated in an electrically insulating rubber and for the first longitudinal axis of the radiating antenna to be positioned in such a way that the radiofrequency transponder 1ter is circumferential although an inclination of 45 degrees makes it possible to achieve the desired communication function. Here, in this example, the first longitudinal axis is placed circumferentially. It is preferable for the passive radiofrequency transponder 1ter to be positioned at the interface defined by at least two components of the tyre casing 100 during manufacture thereof. That means that the data contained in the electronic chip of the passive radiofrequency transponder cannot be falsified when this chip has been write-protected after the first writing to the memory associated with the electronic chip.

[0137] FIG. 10 illustrates an enlarged schematic depiction, in axial section, of the region of a bead 84 and of a sidewall 83 of a tyre casing mounted on its nominal rim J: the axially outermost point E of the main part of the carcass reinforcement layer is thus determined, with the tyre inflated to its nominal pressure, for example by tomography.

[0138] Again, there is part of the metal carcass reinforcement layer wrapped around a bead wire 85 to form a main part 87 and a turn-up 88 with a end 881.

[0139] The turn-up 88 of the carcass reinforcement layer is separated from the main part 87 of the carcass reinforcement layer by a first layer of elastomer compound 91, having a radially outer end 911.

[0140] The first layer of elastomer compound 91 is profiled so as to come to rest against the bead wire 85 and provide coupling and uncoupling between the turn-up 88 of the carcass reinforcement layer and the main part 87 of the carcass reinforcement layer.

[0141] The turn-up 88 and the main part 87 of the carcass reinforcement layer are said to be coupled if the reinforcing elements of each component are separated by a thickness of elastomer compound that is substantially constant and at most 5 millimetres over a length greater than 15% of the distance between the end 881 of the turn-up 88 of the carcass reinforcement layer and the radially outermost point B of the circle T circumscribing the bead wire 85. In addition, the turn-up 88 and the main part 87 of the carcass reinforcement layer are said to be uncoupled if, radially on the outside of the coupling zone, the thickness of the elastomer compound separating the respective reinforcing elements of the main part 87 and of the turn-up 88 of the carcass reinforcement layer is greater than that of the coupled region.

[0142] Depicted axially on the outside of the turn-up 88 of the carcass reinforcement layer is a fourth layer of elastomer compound 92 of which the radially outer end 922 is radially on the inside of the end 881 of the turn-up 88 of the carcass reinforcement layer. According to another embodiment which has not been depicted, the radially outer end 921 of the fourth layer of elastomer compound 92 is radially on the outside of the end 881 of the turn-up 88 of the carcass reinforcement layer.

[0143] The radially inner end 921 of the fourth layer of elastomer compound 92 is radially comprised between the points A and B, which are respectively the radially innermost and the radially outermost points of the circle T circumscribing the bead wire 85.

[0144] In contact with the fourth layer of elastomer compound 92 and radially below the bead wire 85, there is a second layer of elastomer compound 93 of which the axially outermost end 932 is radially on the inside of the end 922 of the fourth layer of elastomer compound 92. Finally, the radially and axially inner end 933 of the second layer of elastomer compound 93 constitutes the inner end 841 of the bead 84.

[0145] Axially in contact with the first layer of elastomer compound 91, with the fourth layer of elastomer compound 92, and with the second layer of elastomer compound 93, there is a third layer of elastomer compound 94. The radially inner end 941 of the third layer of elastomer compound 94 is radially on the inside of the end 922 of the fourth layer of elastomer compound 92.

[0146] The bead 84 also comprises a passive radiofrequency transponder 1bis positioned axially on the outside relative to the interface between the turn-up 88 of the carcass reinforcement and the fourth layer of elastomer compound 92. This passive radiofrequency transponder 1bis is placed radially in the region of coupling between the main part 87 of the carcass reinforcement layer and the turn-up 88 of this carcass reinforcement layer, namely between the two points C and D of FIG. 10. The passive radiofrequency transponder ibis is preferably positioned substantially in the middle of this coupled region, between C and D. The radiofrequency transponder 1bis is embedded inside the fourth layer of elastomer compound 92 at a distance greater than 2 mm and preferably greater than 3 mm from the exterior surfaces of the fourth layer of elastomer compound 92.

[0147] This position affords the passive radiofrequency transponder 1bis good mechanical protection and the applicant has discovered experimentally that a distance greater than 2 mm from the metal reinforcing elements of the turn-up 88 of the carcass reinforcement layer provides good robustness of communication with an external reader even if the reading distances are practically identical or very similar compared with a passive radiofrequency transponder positioned at the interface between the turn-up 88 and the fourth layer of elastomer compound 92. The reading distance is thus less susceptible to the unpredictabilities of industrial scale manufacture than when the passive radiofrequency transponder is placed directly at the interface between the fourth layer of elastomer compound 92 and the skim coating of the layer of metal reinforcers of the turn-up 88.

[0148] FIG. 10 also depicts passive radiofrequency transponders 1bis′, aqua and 1qua′ placed in alternative positions. The passive radiofrequency transponder 1bis′ is embedded inside the fourth layer of elastomer compound 92 radially on the outside relative to the point B; the passive transponders 1qua and 1qua′ are both embedded in the third layer of elastomer compound 94, this layer constituting the surface of the sidewall 83 of the tyre casing. These last two positions are highly favourable from the point of view of communication between the radiofrequency transponder and an external reader. Further, the very good mechanical strength of the radiofrequency transponder allows it to withstand the particularly harsh in-service mechanical stresses in the vicinity of the point E of the sidewall 83 in particular.

[0149] FIG. 11 illustrates a partial axial section through the tyre casing described in FIG. 10.

[0150] The tyre casing comprises, in the region of the bead 84, a first passive radiofrequency transponder 1 positioned at the interface between the turn-up 88 of the carcass reinforcement layer and the fourth layer of elastomer compound 92. Preferentially, the passive radiofrequency transponder 1 is embedded in an electrically insulating encapsulating mass having a relative dielectric permittivity of less than 10 and of which the extension modulus is lower than the extension modulus of the fourth layer of elastomer compound 92. It is laid out in such a way that the first longitudinal axis of the radiating dipole antenna forms an angle of at least 45 degrees between this first longitudinal axis and the direction of reinforcement of the main part 87 and of the turn-up 88 of the carcass reinforcement layer.

[0151] The radiofrequency transponder placed in the region of coupling between the main part 87 and the turn-up 88 of the carcass reinforcement layer, namely between the points C and D, preferentially in the central region. This position is easily delimited by the profiled shape of the first layer of elastomer compound 91 against which the turn-up 88 of the carcass reinforcement layer rests.

[0152] A second passive radiofrequency transponder 1′ is placed in the region of the bead 84 at the interface between the second layer of elastomer compound 93 and the fourth layer of elastomer compound 92. Optionally, this radiofrequency transponder 1′ will be placed inside an encapsulating mass. However, this passive radiofrequency transponder 1′ will be kept away from the ends 932 and 921 of the second 93 and of the fourth 92 layers of elastomer compound so as to preserve the endurance of the tyre casing and the physical integrity of the radiofrequency transponder 1′. Keeping it away from the metal reinforcers of the carcass reinforcement layer improves the communication performance of the passive radiofrequency transponder 1′.

[0153] The tyre casing is also equipped with two passive radiofrequency transponders 1ter and 1ter′ in the region of the sidewall 83 of the tyre casing. The first radiofrequency transponder 1ter is positioned at the interface formed by the turn-up 88 of the carcass reinforcement layer and the third layer of elastomer compound 94. The more radially outward positioning of this transponder by comparison with the first two passive radiofrequency transponders 1 and 1′ provides a longer distance for communication with a reader external to the tyre casing, particularly when in service on a vehicle. This first passive radiofrequency transponder 1ter is positioned at least 10 millimetres from the end 881 of the turn-up 88 of the carcass reinforcement layer and at least 5 millimetres from the end 922 of the fourth layer of elastomer compound 92 so as to preserve the endurance of the tyre casing and the physical integrity of the passive radiofrequency transponder 1ter.

[0154] Finally, the second passive radiofrequency transponder 1ter′ in the sidewall 83 of the tyre casing is positioned at the interface between the main part 87 of the carcass reinforcement layer and the third layer of elastomer compound 94. This is the best position for the distance for communication between the radiofrequency transponder and an external reader. The distancing of the radiofrequency transponder 1ter′ from the end 911 of the first layer of elastomer compound is 20 millimetres, which is easily enough in this configuration to ensure the endurance of the tyre casing and the physical integrity of the passive radiofrequency transponder 1ter′.

[0155] It is preferable to encapsulate the passive radiofrequency transponders 1ter, 1ter′ in an electrically insulating encapsulating mass having a relative dielectric permittivity of less than 10 and of which the extension modulus is less than the extension modulus of the third layer of elastomer compound 94.

[0156] In these examples, the first longitudinal axis of the radiating dipole antenna is positioned circumferentially, which for casings of radial tyres ensures that the angle between the first longitudinal axis and the direction of reinforcement of the main part 87 and of the turn-up 88 of the carcass reinforcement layer is at least 60 degrees.