Abstract:
The present invention concerns a method of measuring the wear on at least one tire ( 20 ) mounted on a wheel ( 10 ) and comprising tread pattern elements ( 27, 28 ), and a tire ( 20 ), wheel ( 10 ), and a tire/wheel assembly ( 1 ) for implementing this method. According to the invention, the wear measurement method includes detecting electromagnetic energy transmitted through a transmission element disposed in at least one tire tread element to an internal space of the tire, the energy detected representative of a wear condition of the tread element or elements ( 27, 28 ). A tire ( 20 ) according to the invention comprises at least one device for transmitting electromagnetic radiation ( 50, 60 ), which device is disposed in at least one of tread element ( 27, 28 ) to conduct incident radiation striking the external surface to the tire ( 20 ) to the internal space, the transmission devices ( 50, 60 ) becoming exposed to the external surface upon a predetermined amount of wear of the tread element ( 27, 28 ).

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
       [0001]     The present invention concerns a method of measuring, the wear, when stopped or running, on at least one tire mounted on a wheel, a tire and a wheel provided separately for implementing this method, and a tire/wheel assembly for a motor vehicle comprising the tire and the wheel. The invention also concerns methods of manufacturing the tire and a motor vehicle comprising at least one such tire/wheel assembly.  
         [0002]     It is known how to provide wear detectors on the tread pattern elements of a tire tread for motor vehicles.  
         [0003]     The British patent publications GB-A-2 330 808 and GB-A-2 268 715 disclose visual wear detectors consisting of layers of colored rubber reflecting light, which are disposed over the entire circumference of the tire, in the mass of the tread, and which are visible following a given amount of wear on the tire.  
         [0004]     A major drawback of these detectors lies in the precarious nature of the wear information obtained, which can only be noted visually and possibly much after the critical wear threshold of the tire has been exceeded.  
         [0005]     One aim of the present invention is to propose a method of measuring the wear on at least one tire comprising tread pattern elements and mounted on a wheel, which makes it possible to remedy this drawback.  
         [0006]     To this end, the wear measuring method according to the invention comprises the step of assigning a wear variable representing the wear on the element or elements to an energy variable representing the energy of electromagnetic radiation transmitted from the external space to the internal space of the or each tire through at least one of the elements.  
         [0007]     Tread pattern element, in the present description, means any element in relief which is intended to be in contact at one time or another with the ground, i.e. as soon as running starts, or after wear on this element has begun. This element can thus consist of a block, for example substantially parallelepipedal or cylindrical in shape, or a circumferential rib with a variable transverse section (i.e. extending over all or part of the circumference of the tread).  
         [0008]     It should be noted that the tread pattern element according to the invention can advantageously consist of a “wear indicator,” for example in the form of a block or rib with a height substantially less than that of the tread patterns intended to be in contact with the ground during ground contact.  
         [0009]     According to another characteristic of the invention, the energy variable itself represents the fact that an electromagnetic radiation transmission means is flush with the top surface of the top of the element, the top surface of the tread pattern elements being intended to be in contact with the ground right from the start or at a subsequent time during running.  
         [0010]     According to another characteristic of the invention, the method comprises assigning, to a value of the energy variable less than at least one predetermined energy threshold, of a value of the wear variable corresponding to wear on the element which does not extend as far as at least one predetermined wear threshold.  
         [0011]     According to one embodiment of the invention, the method comprises the allocation, to a value of the energy variable equal to or greater than the predetermined energy threshold, of a value of the wear variable corresponding to a wear on the element which has reached or exceeded the predetermined wear threshold.  
         [0012]     According to another embodiment of the invention, the method comprises the allocation, to a plurality of values of the energy variable reaching or exceeding the predetermined energy threshold, of the same number of values of the wear variable corresponding respectively to levels of wear on the element reaching or exceeding the predetermined wear threshold, so that the increase in wear on the element is measured continuously between the wear threshold and a maximum wear level.  
         [0013]     Advantageously, the electromagnetic radiation transmitted from the external space to the internal space consists of visible light, the tire or tires equipping the same motor vehicle.  
         [0014]     Another aim of the present invention is to propose a tire for implementing this wear measurement method, the tire being delimited radially by an internal face and by tread pattern elements intended to be in contact with the ground by means of their respective tops from the very beginning or at a given moment in the running.  
         [0015]     According to the invention, the tire comprises in its mass at least one electromagnetic radiation transmission means which is designed to be able to transmit, through at least one of the elements, incident radiation issuing from the space external to the tire to the space internal thereto, as from the time when the transmission means is flush with the surface of the top of the element.  
         [0016]     The or each transmission means is preferably permeable to visible light (i.e. being translucent or transparent) and can be formed from one or more mineral or organic materials.  
         [0017]     Tests carried out show that the rigidity and the area of the axial section (i.e. in the axial plane of the tire perpendicular to its median circumferential plane) of the transmission means determine the ability of the latter to remain in place during running in the course of the life of the tire. This is because a transmission means will have all the more tendency to be ejected from the tire when any local discontinuities of rigidity with the adjacent compositions of the tire are higher (i.e. this means will be more rigid), for the same area of the axial section characterizing it.  
         [0018]     According to a first example embodiment of the invention, the or each transmission means consist of one or more relatively rigid materials each having a modulus of elasticity MA10 (at 10% deformation), measured in accordance with ASTM D 412 of 1998, which is between 1 GPa and 10 GPa (this material advantageously being based on glass, quartz or a plastic comprising a choice of a thermoplastic polymer such as a polystyrene, a methyl polymethacrylate, a polycarbonate, a polyamide, a polyvinyl chloride, a polyester or a thermosetting polymer).  
         [0019]     It is possible for example to use one or more optical fibers opening out in the internal space, which are each formed by a core based on glass, silica or quartz and a sheath based on a thermoplastic polymer or a glass, silica or quartz with a refractive index less than that of the core.  
         [0020]     It is also possible to use one or more optical fibers which are each formed from plastics such as those mentioned (the sheath of the optical fiber or fibers being formed from a plastic with a refractive index less than that of the core).  
         [0021]     It is also possible to use as transmission means one or more assemblies, rectilinear or not, of optical fibers with a very small cross-section (diameter between 50 μm and 100 μm) which are each embedded in a sheath consisting of a rubber composition designed to mechanically decouple each optical fiber assembly from the adjacent rubber compositions in the tire.  
         [0022]     Each optical fiber assembly is advantageously of the same type as those used for producing the cables used as metallic or textile reinforcements in tires (i.e. twisted cables or cables with layers with a finite or infinite winding pitch), and each assembly has an increased resistance to breakage caused by the deformations in running on the crown of the tire. It is possible for example to use assemblies or bundles of fibers each comprising from around ten to around a hundred optical fibers.  
         [0023]     It should be noted that these optical fiber assemblies are particularly advantageous for implementing the wear measurement method according to the invention, because on the one hand of the excellent light transmission coefficient of this type of material, which makes it possible to use assemblies with a diameter of less than 1 mm, and on the other hand the absence of changes in these assemblies over time and under the thermomechanical stresses caused during the life of the tire.  
         [0024]     Preferably, the or each transmission means consisting of this relatively rigid material or materials will have an axial section with a very much reduced area (for example like that of an optical fiber), so as to minimize any discontinuities in rigidity with the adjacent compositions and thus remain durably in place, following prolonged running.  
         [0025]     It should be noted that this minimization of the area of the axial section of the or each transmission means can be compensated for by the use of a very high radiation transmission coefficient for this transmission means and/or by providing a plurality of such transmission means in the tire, for a given quantity of energy transmitted.  
         [0026]     According to a second preferential example embodiment of the invention, the or each transmission means consists of at least one rubber composition based on at least one elastomer having a modulus of elasticity MA10 (at 10% deformation), measured in accordance with ASTM D 412 of 1998, which is between 1 MPa and 20 MPa (this elastomer advantageously belonging to the family consisting of cross-linkable elastomers, thermoplastic elastomers, true polyurethanes and polyurethane derivatives, such as polyurethane/urea, polyureas, polyurea/urethane, polyurethane/isocyanurate, polyurea/isocyanurate or polyurethane/urea/isocyanurate).  
         [0027]     Preferably, use is made of dienic elastomers which can either be vulcanized or cross-linked with peroxides. It is possible to cite for example polybutadienes, polyisoprenes or styrene/butadiene copolymers. It is also possible to use elastomers with a reduced number of double bonds such as EPDMs (ethylene, propylene and diene terpolymers) or butyl rubbers (isoprene and isobutylene copolymers), halogenated or not.  
         [0028]     Even more preferentially, use is made of polyisoprenes, styrene/butadiene copolymers, isoprene/styrene copolymers or polybutadienes.  
         [0029]     By way of translucent rubber composition which can be used in these transmission means consisting of rubber, use is advantageously made of compositions with no staining element and strong ingredients which are not soluble or dissolve only with difficulty in the translucent composition, which comprise: 
        paraffin oils by way of plasticizing oil, instead of the usual aromatic or even naphthenic oils,     non-staining phenolic antioxidants as an antioxidant, instead of the usual antiozonants which result in significant browning of the composition,     a reinforcing inorganic filler such as silica, in reduced quantities, by way of reinforcing filler instead of carbon black (which is excluded in these translucent compositions).        
 
         [0033]     In the present application, “reinforcing inorganic filler”, in known manner, is understood to mean an inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also referred to as “white” filler or sometimes “clear” filler in contrast to carbon black, this inorganic filler being capable, on its own, without any other means than an intermediate coupling agent, of reinforcing a rubber composition intended for the manufacture of tires, in other words being capable of replacing a conventional tire-grade carbon black filler in its reinforcement function.  
         [0034]     Advantageously, the entirety or at the very least a majority proportion of said reinforcing inorganic filler is silica. The silica used may be any reinforcing silica known to persons skilled in the art, in particular any precipitated or fumed silica having a BET surface area and a CTAB specific surface area both of which are less than 450 m 2 /g, even if highly dispersible precipitated silicas are preferred. Silica having BET or CTAB specific surfaces in the range of 80 m 2 /g to 260 m 2 /g are preferably used.  
         [0035]     In the present specification, the BET specific surface area is determined in known manner, in accordance with the method of Brunauer, Emmet and Teller described in “The Journal of the American Chemical Society”, vol. 60, page 309, February 1938, and corresponding to AFNOR-NFT-45007 (November 1987); the CTAB specific surface area is the external surface area determined in accordance with the same AFNOR-NFT-45007 of 1987.  
         [0036]     “Highly dispersible silica” is understood to mean any silica having a very substantial ability to disagglomerate and to disperse in an elastomeric matrix, which can be observed in known manner by electron or optical microscopy on thin sections. As non-limitative examples of such preferred highly dispersible silicas, mention may be made of the silicas Ultrasil 7000 and Ultrasil 7005 from Degussa, the silicas Zeosil 1165MP, 1135MP and 1115MP from Rhodia, the silica Hi-Sil EZ150G from PPG, the silicas Zeopol 8715, 8745 and 8755 from Huber, and treated precipitated silicas such as, for example, the silicas “doped” with aluminum described in application EP-A-735 088.  
         [0037]     The physical state of the reinforcing inorganic filler is immaterial, whether it be in the form of a powder, microbeads, granules or alternatively balls. Of course, “reinforcing inorganic filler” is also understood to mean mixtures of different reinforcing inorganic fillers, in particular of highly dispersible silicas as described above.  
         [0038]     As reinforcing inorganic filler, there may also be used for example: 
        aluminas (of formula Al 2 O 3 ), such as the high-dispersibility aluminas which are described in the European patent document EP-A-810 258, or alternatively,     aluminum hydroxides, such as those described in the international patent document WO-A-99/28376.        
 
         [0041]     Also suitable are reinforcing inorganic fillers comprising carbon blacks modified by silica such as, for example, the fillers sold by CABOT under the name “CRX 2000”, which are described in the international patent document WO-A-96/37547.  
         [0042]     The translucent rubber composition according to the invention furthermore comprises, in conventional manner, a reinforcing inorganic filler/elastomeric matrix bonding agent (also referred to as coupling agent), the function of which is to ensure sufficient chemical and/or physical bonding (or coupling) between said inorganic filler and the matrix, while facilitating the dispersion of this inorganic filler within the matrix.  
         [0043]     Advantageously, the or each transmission means based on this elastomer or elastomers can have an axial cross-section with a relatively large area, because of the fairly insignificant difference in rigidity compared with the adjacent rubber compositions, and can on the other hand have a relatively small coefficient of transmission for a given quantity of energy transmitted.  
         [0044]     According to a preferential embodiment of the invention in accordance with this second example, the tire is such that all the rubber compositions situated radially inside the wear indicator or indicators (i.e. including the or each transmission means) are translucent, comprising neither carbon black nor darkening agent.  
         [0045]     According to a third example embodiment of the invention, the or each transmission means can advantageously comprise a core intended to transmit radiation, based on at least one relatively rigid material, as defined above in the first example embodiment, which is enveloped with a compressible deformable sheath designed to mechanically decouple the core from the adjacent rubber compositions in the tire. This sheath is preferably based on a cellular rubber and has a modulus of elasticity MA10, measured in accordance with ASTM D 412 of 1998, of between 0.1 MPa and 1 MPa.  
         [0046]     This transmission means comprising the core and the sheath has for example the form of a bar whose side surface (consisting of the sheath) can advantageously be cylindrical, prismatic, conical or pyramidal in shape.  
         [0047]     It should be noted that this core can advantageously have both a high coefficient of transmission and an also large axial section area, like the second example embodiment.  
         [0048]     The sheath is preferably based on a cellular rubber with closed cells in order to prevent the absorption of water and in particular the diffusion of inflation gas in the structure of the tire (in particular in the plies and cables of the carcass reinforcement).  
         [0049]     By way of example, it is possible to use glass for the core and, for the sheath, butyl foam, polychloroprene, a butadiene and acrylonitrile copolymer (NBR), an ethylene, propylene and diene terpolymer (EPDM), or a rubber composition used in the tire which has been expanded.  
         [0050]     The tires according to the invention can be manufactured as follows.  
         [0051]     According to a first embodiment of the invention, each radiation transmission means is formed in the tire during manufacture, before the curing of the corresponding cover (“cover” means in the present invention the uncured tire, sometimes referred to as the “blank”). It is in this case necessary for the material or materials making up each transmission means to be able to withstand the curing temperature of the tire (typically around 170° C.) without damage.  
         [0052]     According to a second preferred embodiment of the invention, each transmission means is formed in the tire after the operation of curing the corresponding cover, preferably by the insertion and possibly adhesive bonding of the or each transmission means in a recess formed in the cured tire.  
         [0053]     In accordance with this last preferred embodiment, the or each transmission means has substantially the shape of a drawing pin comprising a head provided with a stem at its center, the stem being contained in a radial recess formed from the internal face to the top of the corresponding tread pattern element, so that the head is in contact with the internal face and the free end of the stem is practically flush with the surface of the top, the head and part of the stem extending from the head being formed from the translucent rubber composition whilst the other part of the stem contained in the free end is formed from at least one opaque rubber composition, the interface radial height between the translucent composition and the opaque composition being designed to correspond to a wear threshold to be detected in the tread pattern element.  
         [0054]     According to one advantageous embodiment of the invention, the tire comprises several radiation transmission means which have respectively different colors in the spectrum of the visible range.  
         [0055]     Advantageously, the or each transmission means has a cross-section in the axial direction of the tire whose area increases continuously over a given wear height radially towards the inside of the tire, so that the quantity of energy of the radiation transmitted in the internal space increases continuously with the area of the section flush with the surface of the top of the element, when the latter wears.  
         [0056]     According to one advantageous embodiment of the invention, the or each transmission means extends over the entire circumference of the tire.  
         [0057]     Advantageously, the tire can comprise a plurality of transmission means whose respective heights, in the radial direction of the tire, correspond to various predetermined wear thresholds to be detected for the element.  
         [0058]     In the aforementioned case in which the or each radiation transmission means comprises an optical fiber opening out in the internal space, the tire can be provided with at least one wear detection unit which contains: 
        in a radially uppermost upstream part passing through the internal face and ending in one of the tread pattern elements recessed from its top, the transmission means, which comprise one or more optical fibers parallel to each other which are each designed so as to be able to transmit incident radiation issuing from the space external to the tire to the space internal thereto and whose radial height or heights correspond respectively to one or various predetermined wear thresholds to be detected for the element, and     in a radially lower downstream part mounted in the space internal to the tire, a detection means connected to the optical fiber or fibers which is designed to detect the energy of the radiation transmitted to it by the fiber or fibers, from the time when at least one of the fibers is flush with the surface of the top of the tread pattern element.        
 
         [0061]     According to another characteristic of the invention, the wear detection unit comprises, in the downstream part, a transmitter coupled to an antenna for transmitting electrical signals representing measurements of radiated energy and a microprocessor for processing the radiated energy measurements.  
         [0062]     Another aim of the present invention is to propose a wheel comprising a rim intended to receive a tire as defined previously, for implementing the also aforementioned wear measurement method.  
         [0063]     According to the invention, the wheel rim is provided with a means of detecting the energy of the radiation transmitted by the or each transmission means in the space internal to the tire, as from the time when the or each transmission means are flush with the surface of the top of the tread pattern element because of wear on the latter.  
         [0064]     Advantageously, the wheel rim is also provided with a means of quantifying the energy of the radiation transmitted in the space internal to the tire and/or means of locating in the tire each radiation transmission means.  
         [0065]     Also advantageously, the wheel rim is also provided with a means of discriminating the colors of the visible radiation transmitted.  
         [0066]     According to a preferential embodiment of the invention, the detection means is contained in a wheel module which is mounted on the wheel rim and which is intended to monitor the operating parameters of the tire/wheel assembly, such as its internal pressure and temperature, the wheel module also comprising a transmitter coupled to an antenna for transmitting electrical signals representing measurements of radiated energy, temperature and pressure, and a microprocessor intended to process all the measurements of radiated energy, temperature and pressure.  
         [0067]     According to one advantageous example embodiment of the invention, the wheel rim is also provided with means for picking up the radiation received at the surface of the rim in radial directions with respect to the rim surface, and for concentrating this radiation picked up by directing it practically along the rim surface to the radiation detector.  
         [0068]     To this end, the rim is for example provided at its bottom with a collar for holding the wheel module, the radially uppermost face of the collar comprising the means for picking up and concentrating the radiation.  
         [0069]     Another aim of the present invention is to propose a tire/wheel assembly for implementing the aforementioned wear measurement method, comprising a wheel and a tire mounted on the wheel.  
         [0070]     According to the invention, the tire/wheel assembly is such that the tire and the wheel are as defined previously.  
         [0071]     Another aim of the invention is to propose a motor vehicle which comprises at least one tire/wheel assembly according to the invention, this vehicle being provided with a receiver intended to receive the signals from the transmitter, a computer connected to the receiver which is intended to process these signals and a display installed in the vehicle cabin which is connected to the computer and which is intended to inform the vehicle driver of the state of wear of the tread pattern elements on the tire or tires. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0072]     The aforementioned characteristics of the present invention, as well as others, will be understood better from a reading of the following description of example embodiments of the invention, given by way of illustration and non-limitingly, the description being made in relation to the accompanying drawings, in which:  
         [0073]      FIG. 1  is a schematic view in meridian section of a tire/wheel assembly according to a first embodiment of the invention;  
         [0074]      FIG. 2  is a schematic view in meridian section of a tire/wheel assembly according to a second embodiment of the invention;  
         [0075]      FIG. 3  is a schematic view in meridian section of a tire/wheel assembly according to a third embodiment of the invention;  
         [0076]      FIG. 4  is an enlargement showing an exploded view of the wear measurement means with which the tire according to the invention in  FIG. 3  is provided;  
         [0077]      FIG. 5  is a schematic view in section along the circumferential mid-plane V-V of  FIG. 1  of a variant embodiment of the tire/wheel assembly of  FIG. 2 ;  
         [0078]      FIG. 6  illustrates schematically and partially the mounting of a tire/wheel assembly according to the invention on the chassis of a motor vehicle according to the invention, as well as the transmission of information from the tire/wheel assembly to the interior of the vehicle;  
         [0079]      FIG. 7  is a view in axial section of a radiation transmission means according to an example embodiment of the invention for measuring wear;  
         [0080]      FIG. 8  is a schematic view in axial section, according to an example embodiment of the invention, of an introduction means which can be used for introducing into the tire a transmission means according to the invention such as the one in  FIG. 7 , through the radially internal face of the tire;  
         [0081]      FIG. 9  is a schematic view in meridian section of a tire showing the transmission means of  FIG. 7  having been introduced into the mass of the tire by the introduction means of  FIG. 8 ;  
         [0082]      FIG. 10  is a schematic view in meridian section of portion of a tire in which there has been formed, through the radially external face of the tire and during the curing thereof, a recess intended to allow the introduction into the tire of a transmission means according to the invention;  
         [0083]      FIG. 11  is a view in axial section of a transmission means according to another example embodiment of the invention which is intended to be introduced into the tire of  FIG. 10  through the radially external face;  
         [0084]      FIG. 12  is a view in axial section of a transmission means according to a variant embodiment of  FIG. 11 , also intended to be introduced into the tire of  FIG. 10  through the radially external face;  
         [0085]      FIG. 13  is a view in axial section of an example of means according to the invention for producing a recess in a tire through its radially external face before the curing of the tire;  
         [0086]      FIG. 14  is a schematic view in axial section of another example of means according to the invention for producing a recess which is adjustable for depth in a tire through its radially external face during the curing of the tire;  
         [0087]      FIG. 15  is a schematic view in axial section of a variant of  FIG. 14  of means according to the invention for producing a recess adjustable for depth in a tire through its radially external face during the curing of the tire;  
         [0088]      FIG. 16  is a schematic view in axial section of another variant of  FIG. 14  of means according to the invention for producing a recess adjustable for depth in a tire through its radially external face during the curing of the tire;  
         [0089]      FIG. 17  is a schematic view in meridian section of a tire/wheel assembly according to the invention in accordance with a variant embodiment of  FIG. 1 , in which several radiation transmission means each comprise assemblies of non-rectilinear optical fibers; and,  
         [0090]      FIG. 18  is a schematic view in partial section along the circumferential mid-plane of  FIG. 1  of a wheel rim according to a variant embodiment of the invention which is provided with a wheel module according to the invention comprising in particular the radiation detection means and means for concentrating the radiation towards the detection means. 
     
    
     DETAILED DESCRIPTION  
       [0091]     The tire/wheel assembly  1  depicted in  FIG. 1  comprises a wheel  10 , a tire  20  which is mounted on the wheel  10  and a wheel module  30  which is also mounted on the wheel  10  between the wheel and the tire  20  and which is in particular intended to monitor operating parameters of the tire/wheel assembly  1 , such as its internal pressure and temperature.  
         [0092]     For reasons of clarity, only the rim  11  of wheel  10  is illustrated in  FIG. 1 . This rim  11  comprises, as from its peripheral projections  12  and  13 , two rim seats  14  and  15  intended to receive respectively beads  21  and  22  of the tire  20 , and a surface  16  which connects these seats together.  
         [0093]     It should be noted that the rim  11  of a tire/wheel assembly according to the invention could have any form known in the prior art, in particular comprising seats  14  and  15  more or less inclined towards the inside or towards the outside of the rim  11  and a surface  16  having a non-linear geometry in meridian section, for example comprising one or more grooves or channels.  
         [0094]     In the usual fashion, the tire  20  comprises essentially a carcass reinforcement (shown by a carcass ply  23  in  FIG. 1 ) which is radially surmounted by a crown reinforcement (shown by working crown plies  24   a  and  24   b  in  FIG. 1 ). The carcass reinforcement  23  is extended laterally from the crown by side walls  25 , which terminate in beads  21  and  22  reinforced by bead wires  21   a  and  22   a.  A tread  26  comprising tread pattern elements  27 ,  28  radially surmounts the crown reinforcement.  
         [0095]     The tire  20  can also comprise a so-called wrapping ply  29  which for example radially surmounts the crown reinforcement, so as to cover the working crown plies  24   a,    24   b,  and which is in particular characterized in that the cables which reinforce it are disposed in a spiral at an angle of 0° or close to 0° to the circumferential mid-plane P of the tire (it is also known how to dispose relatively narrow strips or plies at an angle of approximately 0° in place of the aforementioned cables, to fulfill a function of wrapping of the crown reinforcement).  
         [0096]     It should be noted that the tire  20  of the tire/wheel assembly  1  according to the invention could have a different architecture from that mentioned above, though it must necessarily comprise a tread  26  surmounting carcass and crown reinforcements which comprise composite plies  23 ,  24   a,    24   b  reinforced by cables.  
         [0097]     By way of tread pattern elements  27 ,  28 ,  FIG. 1  depicts on the one hand first tread pattern elements  27  consisting for example of blocks or circumferential ribs which are intended, when the motor vehicle  40  (depicted symbolically in  FIG. 6 ) comprising the tire/wheel assembly  1  is running, to change by means of their respective tops  27   a  in contact with the ground as soon as running begins, and on the other hand a second tread pattern element  28  consisting of a “wear indicator” which may have a form similar to that of the first tread pattern elements  27  but having a height substantially less than these elements  27 .  
         [0098]     In the example in  FIG. 1 , the tire  20  is provided with a plurality of transmission means  50 ,  60  which are each designed to be able to transmit incident electromagnetic radiation external to the tire  22 , such as visible light, from a radially uppermost upstream end  51 ,  61  to a radially lower downstream end  52 ,  62  of these transmission means  50 ,  60 .  
         [0099]     There can be seen firstly in  FIG. 1  the transmission means  50  which are each disposed in the tire  20 , so that their end  51  opens out in a first tread pattern element  27  on the tread  26  whilst facing the top  27   a  thereof, at a given distance from this top  27   a  corresponding to a predetermined wear height of this tread pattern element  27 , and so that their end  52  opens out on the radially internal face  20   a  (represented by the internal rubber compound) of the tire  20  and thus communicates with the internal space thereof (i.e. the space included between the tire  20  and the rim  10 ).  
         [0100]     There can also be seen in  FIG. 1  the transmission means  60  which is disposed in the tire  20 , so that its radially uppermost end  61  opens out in a second tread pattern element  28  or “wear indicator” on the tread  26  whilst being situated radially just below the top  28   a  thereof, and so that its radially lower end  62  opens out on the radially internal face  20   a  of the tire  20  and thus communicates with the internal space thereof.  
         [0101]     Each radiation transmission means  50 ,  60  passes through firstly part of the tread  26  and secondly the wrapping ply  29 , the working crown plies  24   a  and  24   b  and the carcass ply  23 .  
         [0102]     It should be noted that each transmission means  50  or  60  can consist of any means transparent to one or more electromagnetic radiations (i.e. which allows such radiation to pass) and, preferentially, a means which allows at least visible light to pass.  
         [0103]     In the embodiment in  FIG. 1 , the radiation transmission means  50 ,  60  each have a cylinder shape whose diameter is for example around 0.5 mm, and are respectively disposed opposite the tops  27   a,    28   a  of the tread pattern elements  27 ,  28  occupying different positions in the axial direction of the tire  20 . One of the transmission means  50  occupies for example a location centered on the circumferential mid-plane P of the tire  20 , whilst others occupy axially adjacent positions on each side of this plane P (including the “wear indicator”  28 ), which may go as far as the shoulder  26   a  of the tire  20 .  
         [0104]     The wheel module  30  is provided according to the invention with detection means  31  designed to detect at one or more points in the internal space of the tire  20  the energy of light radiation transmitted by each transmission means  50  or  60 . The detection means  31  can consist of an electrically passive detector, such as a photovoltaic cell, or an electrically active detector such as a photoelectric detector advantageously consisting of a photodiode (a semiconductor diode producing an electric current by absorption of the light radiation).  
         [0105]     Optionally, the radiation detection means  31  is coupled to a means of quantifying the transmitted radiation (not shown) which is designed to quantify the energy of the radiation transmitted in the space internal to the tire  20 .  
         [0106]     It should be noted that the transmission means  50 ,  60  can be formed respectively from materials of different colors in the visible range spectrum, for example based on translucent and colored rubber compositions, for modulating the quantities of light energy transmitted by these means  50 ,  60  inside the tire  20  (for example blue light conveys approximately twice as much energy as red light).  
         [0107]     It should also be noted that different radial heights for the radially uppermost ends  51 ,  61  of the transmission means  50 ,  60  (corresponding to more or less critical wear heights of the tread pattern elements  27 ,  28 ) can be respectively associated with different colors for the means  50 ,  60 .  
         [0108]     Also optionally, the wheel module  30  can be provided with means for locating in the tire  20  each radiation transmission means  50 ,  60 , and/or means of discriminating the colors of the transmitted radiation (these location and discrimination means are not shown).  
         [0109]     The locating means can for example consist of n-i separating flaps which are impermeable to the transmitted radiation in question and whose function is to practically divide the internal space of the tire  20  into n zones respectively situated opposite the n_ transmission means  50 ,  60 . It is also possible to use locating means consisting of lenses, reflective surfaces of the mirror type, or a combination of several of these elements, including separating flaps.  
         [0110]     The means of discriminating the colors of the transmitted radiation can for example consist of a filter or a prism.  
         [0111]     Still optionally, the wheel module  30  can be provided, upstream of the detection means  31  and/or means of quantifying the transmitted radiation, with means, such as a lens, for focusing the radiation transmitted by each or all of the transmission means  50 ,  60  (i.e. for concentrating it at a focus), or on the other hand for diffracting this transmitted radiation.  
         [0112]     The wheel module  30  in particular also comprises: 
        sensors  32  intended to measure the pressure and temperature in the space internal to the tire  20 ,     a high-frequency radio transmitter  33  coupled to an antenna  34  for transmitting, in the direction of a radio receiver  41  which is mounted on the vehicle  40  (see  FIG. 6 ) outside the tire/wheel assembly  1 , electrical signals representing measurements of radiated energy, temperature and pressure,     a battery  35  for the electrical supply to the wheel module  30 , and     a microprocessor  36  intended to provide the preparation and a first processing of all the measurements of radiated energy, temperature and pressure, as well as management of the frequency of communications with the vehicle  40  (battery economizer function  35 ) and intended to provide control of the radio transmissions (it should be noted that this microprocessor  36  could integrate the aforementioned sensors  32 ).        
 
         [0117]     For the description of the following figures, the numerical references in  FIG. 1  have been kept for elements having identical structural characteristics and have been increased by  100  as from  FIG. 2  for elements or means having identical functional, if not structural, characteristics.  
         [0118]     The tire/wheel assembly  101  of  FIG. 2  is differentiated from that of  FIG. 1  solely in that each radiation transmission means  150  with which it is provided is formed from a material transparent at least to visible radiation (preferably a translucent rubber composition) and in that it has a given geometry formed by two distinct parts ( 153  and  155 ) which can be formed from identical or different materials.  
         [0119]     Each radiation transmission means  150  is delimited radially by a radially upper upstream end  151  opening out in a tread pattern element  127  on the tread  126  whilst facing the top  127   a  thereof, at a given distance from this top  127   a  corresponding to a predetermined wear height of this tread pattern element  127 , and by a radially lower downstream end  152  opening out on the radially internal face  120   a  of the tire  120  and thus communicating with the internal space of the latter.  
         [0120]     More precisely, each transmission means  150  comprises an upstream part  153  which is delimited radially by the radially uppermost end  151  and by a radially lower base  154  surmounting the wrapping crown ply  29  which is radially uppermost, so that the cross-section of the upstream part  153  increases radially from the end  151  to the base  154 .  
         [0121]     In the example in  FIG. 2 , this upstream part  153  has a conical shape. It should be noted that it could also have a pyramidal or prismatic shape or a frustoconical or truncated pyramid shape, provided that its section increases in the radially lower direction of the tire  120 .  
         [0122]     Each transmission means  150  also comprises a downstream part  155  which extends radially from the base  154  to the radially lower end  152 , and which passes through the cap ply  29 , the working crown plies  24   a  and  24   b  and the carcass ply  23  of the tire  120 . As can be seen in  FIG. 2 , this downstream part has a constant cross-section in the radial direction of the tire  120  and has for example a cylinder shape whose diameter is similar to that of each transmission means  50 ,  60  in  FIG. 1 .  
         [0123]     The tire/wheel assembly  101  in this  FIG. 2  comprises a wheel module  30  having all the characteristics mentioned above in relation to  FIG. 1 , this module  30  being in particular provided with the detection means  31  designed to detect the energy of transmitted radiation and possibly the quantification means designed to quantify the energy of this transmitted radiation, the means of locating each transmission means  150 , the means of discriminating the colors of the transmitted radiation and the focusing or diffraction means.  
         [0124]     The tire/wheel assembly  201  depicted in  FIG. 5  shows a variant of the embodiment illustrated in  FIG. 2 . This tire/wheel assembly  201  is differentiated from those in  FIGS. 1 and 2  solely by the geometry of transmission means  250  with which the tire  220  is provided in its mass.  
         [0125]     Transmission means  250  extends over the entire circumference of the tire  220  and is delimited radially by a radially uppermost upstream perimeter  251  opening out in a tread pattern element  227  of the tread  226  whilst facing the top  227   a  of the latter, at a given distance from this top  227   a  corresponding to a predetermined wear height of this tread pattern element  227 , and by a plurality of radially lower downstream ends  252  opening out on the radially internal face  220   a  of the tire  220  and thus communicating with the space internal to the latter.  
         [0126]     More precisely, transmission means  250  comprises an upstream part in the form of a ring  253  with a reduced thickness in the axial direction of the tire  220  (i.e. a practically flat ring in the form of a circumferential groove), which is delimited radially by the radially uppermost perimeter  251  and by a radially lower perimeter  254  surmounting the cap ply  29  which is radially uppermost, so that the cross-section of the upstream part  253  is constant in the radial direction of the tire  220 .  
         [0127]     It should be noted that this upstream part  253  could have a more significant axial thickness, for example an elliptic (in particular circular) or polygonal (in particular rectangular) shape in the axial direction of the tire  220 , conferring on it for example a substantially torus or annular volume shape. In this case, the upstream part  253  could be delimited by radially upper and lower surfaces  251  and  254 , instead of the aforementioned perimeters.  
         [0128]     Transmission means  250  also comprises a plurality of downstream parts  255  regularly spaced apart over the circumference of the tire  220 , which each extend radially from the radially lower perimeter or surface  254  to one of the corresponding radially lower ends  252 , and which pass through the cap ply  29 , the working crown plies  24   a  and  24   b  and the carcass ply  23  of the tire  220 . Like the downstream part  155  in  FIG. 2 , this downstream part  255  has for example a constant cross-section in the radial direction of the tire  220  and has for example a cylinder shape whose diameter is similar to that of the downstream part  155 .  
         [0129]     It should be noted that the tire  220  in  FIG. 5  can be provided with several radiation transmission means  250  distributed over the width (axial dimension) of the tire  220 .  
         [0130]     The tire/wheel assembly  201  in this  FIG. 5  comprises a wheel module  30  also having all the characteristics mentioned above in relation to  FIG. 1 .  
         [0131]     The tire/wheel assembly  301  in  FIG. 3  is differentiated essentially from the one in  FIGS. 1, 2  or  5  in that the tire  320  which it has is provided in its mass with at least one wear detection unit  370  which incorporates: 
        in a radially uppermost upstream part  371 , radiation transmission means  350  comprising optical fibers  372  to  377  (see the insert in  FIG. 4 ), and     in a radially lower downstream part  378 , a detection means or photodetector  331  (electrically active or passive, used in this case in photovoltaic mode) fixed to these optical fibers  372  to  377 , which is provided for detecting the radiation energy specifically transmitted by each fiber  372  to  377 , and an electronic unit  333  comprising a radio transmitter coupled to an antenna for transmitting electrical signals representing the measurements of radiated energy in the direction of the radio receiver  41  mounted on the vehicle  40  ( FIG. 6 ), and a microprocessor for processing the measurements of radiated energy, as well as management of the frequency of the communications with the vehicle  40 .        
 
         [0134]      FIG. 3  depicts a tread pattern element  327  consisting of a parallelepipedal-shaped “block” or a rib which is provided in its mass with the detection unit  370 , which extends radially through the tire  320  from the radially internal face  320   a  thereof and as far as the inside of the element  327 .  
         [0135]     As can be seen in  FIG. 3 , the unit  370  has substantially the shape of a drawing pin (i.e. a head forming the downstream part  378  on which there is mounted a point forming the upstream part  371 ).  
         [0136]     Inside the unit  370 , the optical fibers  372  to  377  and the detection means  331  are covered with a coating composition  379  which is identical to that of the tread  326  or compatible therewith.  
         [0137]     As can be seen in  FIG. 4 , the optical fibers  372  to  377  are mounted in a specific manner on the photodetector  331 , which comprises locations  331   a  respectively intended to receive them.  
         [0138]     The photodetector  331  has a circular shape and at its center there is mounted a reference optical fiber  372  of maximum height amongst the set of fibers  372  to  377  (this maximum height corresponding to a predetermined wear threshold of the tread pattern element  327 ). Around this reference fiber  372  there are mounted in a circle and at equal distances from each other the optical fibers  373  to  377  (measurement optical fibers) comprising a fiber  373  with a height equal to that of the reference fiber  372  followed by the fibers  374  to  377  whose height decreases in a regular fashion over the circumference of the photodetector  331 , so that the fiber  377  of minimum height is adjacent to the fiber  373  of maximum height.  
         [0139]     The locations  331   a  of the photodetector  331  are connected by cables  331   b  to the electronic unit  333  for the processing of the signals generated by this photodetector  331 .  
         [0140]     It should be noted that these various heights of the measurement optical fibers  373  to  377  correspond respectively to wear thresholds to be detected for the tread pattern element  327  and that the wear measurements could be refined further by providing an increased number of measurement optical fibers where the differences in height are lesser over the circumference of the photodetector  331 .  
         [0141]     As can be seen in  FIG. 3 , the downstream part  378  of the unit  370  is mounted in contact with the radially internal face  320   a  of the tire  320  by means of a shoulder which its internal fixing face forms with the upstream part  371 .  
         [0142]     It should be noted that the downstream part  378  can have any suitable geometry (circular or rectangular cross-section etc), provided that it matches the shape of this internal face  320   a  at the location provided for its fixing. This downstream part  378  can advantageously have a broadening of its cross-section in the direction of its internal fixing face (a frustoconical or prismatic shape for example).  
         [0143]     As for the upstream part  371  of the detection unit  370 , this can also have various geometries, for example parallelepipedal or cylindrical shapes.  
         [0144]     The unit  370  was incorporated in the tire  320  when the latter was manufactured, by fixing the shoulder of the downstream part  378  and the upstream part  371  to a location of the tire  320  which is provided for this purpose. This location has for example the shape of a cavity with a rectangular cross-section which is intended to receive the upstream part  371 .  
         [0145]     This incorporation of the unit  370  in the tire  320  is preferably carried out after the curing of the latter, by insertion and adhesive bonding of the unit  370  in a recess formed in the cured tire  320 .  
         [0146]      FIG. 6  depicts schematically the motor vehicle  40  equipped with mounted assemblies  1 ,  101 ,  201 ,  301 , at least one of which (depicted in cross-section as well as the wheel stub axle  42  on which it is mounted) is in accordance with the present invention (for example as described with reference to one of FIGS.  1  to  5 ).  
         [0147]     There are shown on this tire/wheel assembly  1 ,  101 ,  201 ,  301 , on the one hand the means  50 ,  60 ,  150 ,  250 ,  350  of transmitting radiation from the external space (ambient air) to the internal space of the tire/wheel assembly  1 ,  101 ,  201 ,  301  (including inside the detection box  370 , in the case of the transmission means  350  of  FIG. 3 ). In addition, the tire/wheel assembly  1 ,  101 ,  201 ,  301  includes the wheel module  30  incorporating the pressure and temperature sensors, the radio transmitter coupled to an antenna  34  for transmitting electrical signals representing measurements of radiated energy, pressure and temperature in the direction of the radio receiver  41  mounted on the vehicle  40 , and the microprocessor for processing the radiated energy measurements, as well as management of the frequency of the communications with the radio receiver  41  (the sensors, the radio transmitter and the microprocessor not being shown for reasons of clarity).  
         [0148]      FIG. 6  shows a computer  43  with which the vehicle  40  is provided, which integrates the operating laws of the tire  20 ,  120 ,  220 ,  320 , this computer  43  being connected to the radio receiver  41  and being intended to manage the display of the results of measurements made, from the use which is made thereof upstream.  
         [0149]     There is also depicted a display  44  which is connected to the computer  43  and which is for example installed on the dashboard of the vehicle  41 , this display being for example intended to continuously inform the driver of the vehicle  40  of the state of wear of the tread pattern elements  27 ,  28 ,  127 ,  227 ,  327  of the tire or tires  20  to  320 .  
         [0150]      FIG. 7  is a view in axial section of a radiation transmission means  450  according to one example embodiment of the invention. This transmission means  450  having in the example in  FIG. 7 a  symmetry of revolution, the cutting plane considered here contains the axis of symmetry of the means  450 .  
         [0151]     This transmission means  450  has substantially the shape of a thumb tack, comprising a head  51  practically in the form of a thin disc which is provided with a cylindrical stem  452  at its center. The means  450  is intended to be introduced through the radially internal face  420   a  of the tire  420  (i.e. the internal layer) after the curing thereof, in a radial cylindrical recess  480  previously formed in the outer casing before it is cured or during its curing (this radial recess  480 , formed from the internal face  420   a  to the external face of the casing  427   a,  is visible in  FIG. 9 , so that the head  451  of the means  450  is in close contact with the internal face  420   a  and the free end  452   a  of the stem  452  is practically flush with the radially external surface  427   a  of the tread pattern element  427  whose wear is to be measured (see  FIG. 9 ).  
         [0152]     As can be seen in  FIG. 7 , the means  450  is formed by a translucent rubber composition part  453  and an opaque rubber composition part  454  which are respectively situated to form a border at a predetermined interface height  455  of the stem  452 , which height is designed to correspond to a wear threshold to be detected in the tread pattern element  427  of the tire  420  (see  FIG. 9 ).  
         [0153]     In the example in  FIG. 7 , the head  451  and the translucent rubber composition part  453  of the stem  452  extending from the head  451  containing are formed from the same translucent composition, which is obtained by molding or injection, whilst the opaque rubber composition part  454  of the stem  452 , ending in the free end  452   a,  is formed from the opaque composition, which may be chosen, for example, to be identical to the rubber composition used for the tread.  
         [0154]     The translucent composition  453  comprises an elastomer matrix consisting for example of a polyisoprene, a styrene/butadiene copolymer, an isoprene/styrene copolymer or a polybutadiene, and also comprises: 
        a paraffin oil instead of the aromatic or naphthenic oils,     non-staining phenolic antioxidants instead of the antiozonants which result in significant browning of the composition,     silica by way of reinforcing filler instead of carbon black.        
 
         [0158]     It will be understood that the interface  455  between these two compositions  453  and  454  can be provided closer to the head  451  or the free end  452   a,  according to the selected wear threshold.  
         [0159]     Two methods, which may be used separately or in combination, of introducing and holding the transmission means  450  in the recess  480  in the tire  420  are described.  
         [0160]     A first method consists of mechanically clamping the stem  452  by the rubber wall of the recess  480 , obtained by the choice of a diameter of the stem  452  which is greater than that of the recess  480  and by housing this stem  452  inside an insertion means  490  consisting of a metallic sheath in the form of a needle (shown in axial section in  FIG. 8 ) intended to allow the insertion of the stem  452  in the tire  420 , so that the head  451  and the free end  452   a  are disposed in the aforementioned manner.  
         [0161]     As can be seen in  FIG. 8 , the sheath  490  comprises, at one of its ends, an opening  491  to allow the axial insertion of the stem  452 , and at its other end, a frustoconical tip  492  intended to facilitate the insertion of the sheath  490  in the recess  480  of smaller diameter. The sheath  490  comprises, between the opening  491  and the tip  492 , a cylindrical portion  493  hollow over at least part of its length, which forms a tubular housing intended to contain at least part of the stem extending from its free end  452   a  (the length of the housing being less than that of the stem  452 ).  
         [0162]     By way of example, the inventors have made use of transmission means  450  in which the diameter of the head  451  is  20  mm and the diameter of the stem  452  between 1 mm and 5 mm. A coefficient of clamping of the stem  452  by the recess  480  ranging from 0% to 30% has been used (this coefficient of clamping being defined as being the ratio of the difference between the diameters of the recess  480  and of the stem  452  to the diameter of the recess  480 ). The diameter of the recess  480  for this transmission means can vary from 1 mm to 4 mm.  
         [0163]     Use has also been made of sheaths  490  with a total length L ranging from 40 to 60 mm and whose hollow cylindrical portion  493  is delimited by an annular wall  494  with a thickness of 0.3 mm. As for the inside diameter of this wall  494 , this is slightly greater than the diameter of the stem  452  which it is intended to contain.  
         [0164]      FIG. 9  illustrates the insertion of the sheath  490  in the recess  480 , through the internal face  420   a  of the tire  420  (for reasons of clarity, the various cable plies are not shown). It can be seen that the head  451  of the means  450  remains outside the opening  491  of the sheath  490  when the stem  452  is housed in the latter.  
         [0165]     In a first step of this insertion (see arrow A), the sheath  490  is pressed into the recess  480 , which has the effect of expanding the latter by increasing its diameter, until the tip  492  and an adjacent part of the cylindrical portion  493  project radially outside the external face  427   a.    
         [0166]     In a second step (illustrated by the arrow B), a traction is exerted, for example via a clamp (not shown), on the part  493  of the sheath  490  projecting outside the tire  420 , which allows the radial passage of the stem  452  in the recess  480  because of the elasticity of the adjacent rubber compositions and brings the head  451  of the means  450  precisely under the internal face  420   a.    
         [0167]     In a third step consisting of the complete extraction of the sheath  490  radially outside the tire  420  because of the aforementioned traction, the recess  480  regains its initial diameter and its wall clamps the stem  452  radially, which keeps the means  450  securely in this position during the subsequent running of the tire  420 .  
         [0168]     A second method of inserting and holding the transmission means  450  of  FIG. 7  in the recess  480  in the tire  420  depicted in  FIG. 9  consists of fixing this means  450  to the wall of the recess  480  by means of an adhesive of the dual component type, without necessarily having to carry out a mechanical clamping of the stem  452  by the wall of the recess  480 .  
         [0169]     A first component C of this adhesive (shown in  FIG. 7 ) comprising ultra-accelerators and vulcanization activators is deposited on the means  450  by soaking the latter in a solution based on this first component, or by depositing a film of this first component on the stem  452  and on the head  451  by a method of the coextrusion type. This first component C covers the cylindrical surface of the stem  452  and the adjacent surface, in the form of a circular ring, of the head  451 .  
         [0170]     A second component of this adhesive (not shown) in the form of a solution comprising sulphur is deposited at the time of insertion of the means  490  in the form of a needle in the recess  480 , on the external wall of the means  490 , on the wall of the recess  480  and on the internal layer  420   a  of the tire  420  to which the head  451  is intended to be applied. The solution based on this second component facilitates the passage of the insertion means  490  in the recess  480 , by lubrication.  
         [0171]     After the insertion means  490  has been extracted from the tire  420 , the first C and second components of the adhesive come in contact with each other and interact. It should be noted that this interaction is all the more effective, the greater the degree of mechanical clamping of the stem  452  by the wall of the recess  480 .  
         [0172]     It should also be noted that the bonding of the head  451  to the internal layer  420   a  of the tire  420  holds the means  450  against the wall of the recess  480  without the necessity of mechanical clamping of the stem  452  by the wall  480 .  
         [0173]     The adhesive used for fixing the stem  452  to the wall of the recess  480  is sold by the company Schrader under the name “Saphir”, and is based on natural rubber and carbon black.  
         [0174]     According to a variant embodiment (not shown), the transmission means  450  comprises the head  451  and the aforementioned translucent rubber composition part  453  only, which may be introduced and held in the recess  480  in the tire  420  according to the aforementioned methods.  
         [0175]     It should be noted that an entirely translucent transmission means improves the precision of positioning of the wear detection threshold in the tire  420  with respect to the internal layer  420   a  thereof under which the head of the transmission means is applied. This is because the end of the stem of the means is adjusted after insertion of the latter in the recess  480  (the head then being applied under the internal layer  420   a ), so as to exactly position this end at the wear threshold to be detected using the tread pattern bottom as the reference surface.  
         [0176]     The remaining volume of the recess  480  is entirely filled in with an opaque rubber composition like that of the tread, or with an opaque rubber cylinder which is deposited on the surface of this translucent stem.  
         [0177]      FIG. 10  shows a tire  520  in which there has been formed, through the radially external face  527   a  thereof (forming the top of the corresponding tread pattern element  527 ) and during curing thereof, a recess  580  according to another embodiment of the invention which is intended to allow the insertion in the tire  520  of another transmission means  550  according to the invention (depicted in  FIG. 11 ).  
         [0178]     This recess  580  was formed from the external face  527   a  and extends as far as the internal face  520   a  of the tire  520 . The recess  580  also has a symmetry of revolution but consists of a first cylindrical portion  581  of reduced height opening out on the external face  527   a  and a second concentric cylindrical portion  582  of greater height but lesser diameter, which opens out on the internal face  520   a  and which is connected to the first by a shoulder  583  corresponding to the wear threshold to be detected.  
         [0179]     The diameter of the first portion  581  is, for example, 5 mm, whilst the diameter of the second portion  582  is, for example, 2.5 mm.  
         [0180]      FIG. 11  illustrates the structure of this other transmission means  550  according to the invention which is intended to be inserted in the recess  580  of  FIG. 10 , this means  550  consequently comprising first portion  551  and second portion  552  and including a shoulder  553 .  
         [0181]     The second portion  552  of the means  550  is formed by a translucent rubber composition such as the one mentioned above with reference to  FIG. 7 , and the first portion  551  is formed by an opaque rubber cylinder (this rubber being, for example, identical to the one forming the tread) which is introduced radially outside the tire  520  in the recess  580 .  
         [0182]      FIG. 12  illustrates the structure of a variant embodiment according to the invention of this transmission means  650  (the recess intended to receive it not being shown, but being understood to have a similar profile).  
         [0183]     As can be seen in  FIG. 12 , this means  650  comprises, from the external face to the internal face of the tire intended to receive it, a first cylindrical portion  651  which is formed from the opaque rubber composition and which is connected by a first shoulder  652  to a second concentric cylindrical portion  653  also formed from the opaque composition but with a diameter greater than the first portion  651 , and a third cylindrical portion  654  concentric with the previous ones, which is formed from the translucent rubber composition and which is connected to the second portion  653  by a second shoulder  655 .  
         [0184]     It should be noted that the transmission means  550 ,  650  of FIGS.  11  or  12  associated with the recess  580  of  FIG. 10  allows the precise adjustment of the interface  553  between the translucent and opaque compositions at the shoulder  583  (or the second shoulder  655 , in the example in  FIG. 12 ), which corresponds to the wear threshold to be detected and is itself exactly positioned with respect to the tread pattern bottom, since it issues directly from the molding.  
         [0185]     For the insertion and holding in the corresponding recesses of the transmission means  550 ,  650  according to FIGS.  11  or  12 , it is also possible to use (separately or in combination) the above described methods of mechanical clamping of the means by the wall of the recess  580  or of adhesive bonding via the adhesive of the two-component type.  
         [0186]     In general terms, the recesses  480 ,  580  mentioned above in relation to  FIGS. 9 and 10  were produced according to two distinct methods and via distinct piercing means, as indicated below.  
         [0187]     According to a first method used, applicable to the recesses  480  in  FIG. 9 , before curing of the outer tire casing, one or more metallic piercing means  700  are used, such as the one depicted in  FIG. 13 , which has in this example a symmetry of revolution, the cutting plane in question here containing the axis of symmetry of the means  700 .  
         [0188]     This piercing means  700  has substantially the shape of a thumb tack, comprising a head  701  having a rounded cap shape of slight thickness, which is provided with a cylindrical stem  702  at its center which is the diameter of the recess  480  to be produced and whose free end  703  is also shaped as rounded cap. This means piercing  700  is intended to be introduced into the outer casing  420  through the radially external face  427   a  of its tread. The length of this stem  702  is designed to be greater than the distance separating the internal layer  420   a  of the tire  420  from the radially uppermost surface of the last reinforcement of the crown reinforcement which the tire  420  has.  
         [0189]     The piercing means  700  is advantageously formed from a metal covered with a low friction coating, for example, Teflon® brand coating material, and has for example a total height varying from 6 mm to 10 mm, the head  701  having a diameter varying from 20 mm to 40 mm and the stem  702  having a diameter varying from 1 mm to 5 mm.  
         [0190]     The piercing means  700  may be introduced into the casing  420  at the desired location or locations for the recess or recesses  480 . The casing is then cured and is positioned in the curing press (not shown) so as to place the piercing means  700  in the tread pattern element or elements of the mold which correspond to the one or ones  427  chosen to be provided with the transmission means  450 .  
         [0191]     After curing, this piercing means  700  are withdrawn from the tire  420  and in this way a passage  480  is formed through the cable plies of the tire  420 , such as the working crown plies. The rubber remaining radially inside these plies is then perforated in order to ensure that the recess  480  opens out on the internal layer  420   a  of the tire  420 .  
         [0192]     According to a second embodiment of the recesses  480 ,  580  used during the curing of the casing (this method is applicable to the recesses  480  and  580  in  FIGS. 9 and 10 ), the casing  420 ,  520  to be cured is placed in a curing mold provided with one or more metallic piercing means  800 ,  810 ,  820  like the ones depicted in  FIGS. 14, 15  or  16 . These piercing means  800 ,  810 , and  820  have diameters corresponding to those of the recess or recesses  480 ,  580  to be produced, which, in turn, correspond to those for the transmission means  450 ,  550 . Then, before curing, the casing  420 ,  520  is pierced by piercing means  800 ,  810 ,  820 , and the piercing means are held in the casing  420 ,  520  during curing to keep in the separated position the cables of the various plies through which the piercing means  800 ,  810 ,  820  pass, without cables being cut or damaged.  
         [0193]     The piercing means  800  shown in  FIG. 14  comprises a cylindrical stem  801  the free end of which is for example in a shape of a rounded cap and which is provided with a means  803  of controlling its position along its axis of symmetry X′X. In the example in  FIG. 14 , this control means  803  is screw threads (i.e. a transmission screw).  
         [0194]     The piercing means  810  shown in  FIG. 15  comprises a cylindrical stem  811  such as the one in  FIG. 14  which is connected to a means  813  of controlling its position along its axis of symmetry X′X, by means of a concentric portion  814  forming a shoulder  815  intended to constitute the wear threshold. In the example in  FIG. 14 , this control means  813  is also a transmission screw.  
         [0195]     The piercing means  820  in  FIG. 16  comprises a cylindrical stem  821  as mentioned previously which is provided with a screw  822  controlling its translation on the axis X′X, this screw  822  being mounted inside a concentric portion  823  which forms a shoulder  824  with the stem  821  and which is itself adjustable in translation via another control screw  825 .  
         [0196]     It should be noted that this shoulder  824  is designed to determine the wear threshold to be detected in the tread pattern element  527  in question.  
         [0197]     With reference to the examples shown in FIGS.  14  to  16 , it should also be noted that the stem  801 ,  811 ,  821  of each piercing means  800 ,  810 ,  820  has a diameter between 1 mm to 3 mm, and a length between from about 10 to 20 mm.  
         [0198]     In addition, it should be noted that the slightly rounded shape of the free end  802 ,  812 ,  822  of each piercing means is designed so as to allow the formation of a recess  480 ,  580  in the cable plies without these cables being pushed radially or cut.  
         [0199]     It should also be noted that the length of the piercing means  800 ,  810 ,  820  according to this second method is chosen so as to obtain a recess  480 ,  580  opening out in the radially internal layer  420   a,    520   a  of the tire  420 ,  520 , without piercing the curing membrane.  
         [0200]     Thus there is formed in the cured tire  420 ,  520  a passage with a predetermined diameter through the cable plies without damaging the latter, particularly with regard to the crown plies. This method of producing the recesses  480 ,  580  during curing makes it possible in particular to subsequently introduce transmission means  450 ,  550  having a diameter greater than the pitch of the cables in the crown plies.  
         [0201]      FIG. 17  is a schematic view in meridian section of a tire/wheel assembly  1  according to the invention in accordance with a variant embodiment of  FIG. 1 , in which several radiation transmission means  50 ,  50 ′,  60  each comprise assemblies of optical fibers with a diameter of between 50 μm and 100 μm which are embedded in a rubber sheath (not shown for reasons of clarity) in order to decouple them mechanically from the adjacent tread composition.  
         [0202]     Each assembly illustrated in  FIG. 17  is of the same type as those used for producing the metallic or textile cables in tires (i.e. twisted cables or layered cables with a finite or infinite winding pitch), and has increased resistance to the breakage caused by the deformations in running of the crown of the tire  20 . It is, for example, possible to use assemblies each comprising around ten to a hundred optical fibers.  
         [0203]     It should be noted that each of these assemblies can be introduced into the tire  20  after it is cured without prior piercing of the tire  20 , by inserting through the radially external face  20   a  of the tire  20  a needle of the “medical needle” type, because of the reduced diameter of each assembly which allows its passage between the cables of the crown plies without imposing any significant local deformation on these cables.  
         [0204]     This type of introduction allows the use of any tire, without prior discrimination between the tires  20  provided with transmission means  50 ,  50 ′,  60  according to the invention and tires working normally.  
         [0205]     As can be seen in  FIG. 17 , one or more assemblies of optical fibers  50 ,  50 ′,  60  are installed in tire with the respective radially uppermost ends  51 ,  61  disposed in tread pattern elements  27 ′ off center with respect to the circumferential mid-plane P of the tire/wheel assembly  1 . Radiation detection means  30  is centered with the circumferential mid-plane P. The assemblies of optical fibers  50 ′ can be non-rectilinear overall (i.e. consisting of a succession of rectilinear segments connected together by elbows), so that the radially lower end  52  of each assembly which is intended to transmit the radiation to the radiation detection means  30  opens out on the radially internal face  20   a  of the tire  20  whilst being practically opposite the detection means  30 .  
         [0206]     It should be noted that this non-rectilinear geometry for the assembly of optical fibers makes it possible to dissociate the positioning of the upstream end  51  (for example situated in the “shoulder” area of the tire  20  of each transmission means  50 ′, from the positioning of the remaining part of the means  50 ′ which passes at right angles through the cable plies, without any risk of degrading the functioning of these cables, by positioning the passage of the transmission means  50 ′ in line with these cables at the least detrimental locations, for example at one third of the width of the tread.  
         [0207]      FIG. 18  is a schematic view in partial section along the circumferential mid-plane P of  FIG. 1  of a rim  11  of a wheel  10  according to a variant embodiment of the invention. The rim  11  is provided with a wheel module  30  according to the invention comprising, in particular, means of detecting the radiation transmitted by a transmission means according to the invention (the detection means and the transmission means not being shown), and means  17  for picking up and concentrating this radiation towards the detection means.  
         [0208]     The rim  11  shown in  FIG. 18  has a “collar”  18  for holding the wheel module  30 , which is for example as defined in relation to  FIG. 1 . This holding collar  18  in a known manner matches the cylindrical geometry of the rim  11 . According to one example embodiment of the invention, the collar  18  comprises, on its radially outermost face, means  17  for picking up the radiation received on its surface in radial directions (see arrows F 1 ) with respect to the cylindrical surface of the rim  11  and for concentrating this picked-up radiation by directing it practically along the cylindrical surface of the rim  11  (see arrows F 2 ) towards at least one surface  38  of the wheel module  30  containing the radiation detector.  
         [0209]     It should be noted that the means  17  for picking up and concentrating the radiation can be formed using the material or materials precisely constituting the holding collar  18  and that it can thus advantageously have a reduced cost per unit surface area.  
         [0210]     This dissociation of the means  17  for picking up the radiation and the wheel module  30  makes it possible not to have to carry out a precise “azimuthing” of the transmission means with respect to the radiation detection means (i.e. ensuring that the transmitted radiation detection means is situated precisely opposite the or each transmission means or at least in the “cone” of the radiation transmitted by the latter).  
         [0211]     With reference to any one of the embodiments in  FIGS. 1, 2 ,  5  or  18 , the method according to the invention for measuring the wear on a tire  20 ,  120 ,  220  comprises the following steps. Non-limitingly, it will be considered below for reasons of clarity of the disclosure that the incident radiation external to the tire  20 ,  120 ,  220  consists of visible light.  
         [0212]     As long as the wear on one of the tread pattern elements  27 ,  127 ,  227  of the tire  20 ,  120 ,  220  has not reached the perimeter or the radially uppermost upstream surface  51 ,  151 ,  251  of the light transmission means  50 ,  150 ,  250  situated in the tread pattern element, this transmission means does not open out on the top  27   a  ,  127   a  ,  227   a  of the tread pattern element. As a result, the detection means  31  does not detect transmitted light in the space internal to the tire  20 ,  120 ,  220 , which results in the fact that the radio receiver  41  mounted on the vehicle  40  receives no light signal from the transmitter  33 . Consequently the display  44  signals no alert information to the driver of the vehicle  40  concerning wear on the tire  20 ,  120 ,  220 .  
         [0213]     After the wear on a tread pattern element  27 ,  127 ,  227  has reached the perimeter or the radially outermost surface  51 ,  151 ,  251  of the corresponding light transmission means  50 ,  150 ,  250 , the transmission means is uncovered and opens on the surface of the tread element top  27   a,    127   a,    227   a.  The transmission means now transmits, to the space internal to the tire  20 ,  120 ,  220 , light coming from outside the tire, and this transmitted light is detected by the detection means  31 . The transmitter  33  then transmits a signal representing the detected light to the receiver  41  via the antenna  34 , and the driver is informed by the display  44  that a wear threshold has been reached for the tread pattern element  27 ,  127 ,  227  (critical or not, according to the predetermined height initially separating the transmission means  50 ,  150 ,  250  from the top  27   a,    127   a,    227   a  of the tread pattern element).  
         [0214]     In the example in  FIG. 2  where the radially outermost part  153  has a cross-section increasing in the direction radially opposite to the top  127   a  of the tread pattern element  127 , it should be noted that the accentuation of the wear on the tread pattern results in a continuous increase in the quantity of transmitted light which is detected by the detection and quantification means  31 , and therefore in the signal representing this detected quantity which is received by the receiver  41  and, consequently, delivered continuously in the form of alert messages to the driver of the vehicle  40 .  
         [0215]     In the case of a light transmission means  60  which is situated in a “wear indicator” or wear bar  28 , it should be noted that there is practically zero initial distance separating the radially outermost end  61  of this transmission means  60  from the top  28   a  of the wear bar  28 . This small distance leads to the result that, when the wear on the tire  20  is such that the wear bar  28  makes wear contact with the ground, the transmission means  60   a  little time afterwards is flush with the surface of the top  28   a  and then transmits the external light to the internal space of the tire  20 . The result is the detection of this light and the transmission to the receiver  41  of a representative signal which is delivered to the driver of the vehicle  40  in the form of an alert message signifying that the wear threshold has been exceeded.  
         [0216]     It should be noted that the embodiment in  FIG. 5  is particularly advantageous, since it takes account of an average wear over the entire circumference of the tire  220 , with consequently increased reliability for the detection of the fact that the light transmission means  250  is flush with the circumference.  
         [0217]     With reference to the embodiment in  FIGS. 3 and 4 , the method according to the invention for measuring the wear on a tire  320  is differentiated from what has just been stated solely in that the detection means  331  can detect several stages of wear via a single light transmission means  350 , because the latter contains a plurality of measuring optical fibers  373  to  378  which, as the tire wears, become successively flush with the surface of the top  327   a  of the tread pattern element  327 .  
         [0218]     In conclusion, it should be noted that provision could also be made for installing a radio receiver on a terminal fixed to the ground (instead of the receiver  41  mounted on the vehicle  40 ) placed in a route where the vehicle  40  passes.  
         [0219]     It should also be noted that the display  44  could serve as an interface vis-à-vis users other than solely the driver of the vehicle  40 .