Abstract:
The present invention concerns a method of producing a lighting or signalling device comprising a light source ( 16 ), a reflector ( 14 ) reflecting the light rays emitted by the light source ( 16 ) towards a lens ( 18 ) so as to form along an optical axis (A—A) alighting or signalling beam, the lens ( 18 ) comprising a peripheral flange ( 24 ) and being held by a support ( 20 ), the support ( 20 ) comprising an annular surface ( 26, 26 ′) limited at its external periphery by a cylindrical rim ( 28, 34 ). According to the present invention, the method comprises the step consisting of deforming the cylindrical rim ( 28, 34 ) in the direction of the annular surface ( 26, 26 ′) in order to envelop the peripheral flange ( 24 ) of the lens ( 18 ) and hold it in place without play and without requiring an additional component, this deformation of the cylindrical rim ( 28, 34 ) being performed by applying on this rim a force parallel to the optical axis (A—A) of the lighting or signalling device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns a method of producing a lighting or signalling device, in particular for a motor vehicle, and more particularly a method of fixing the lens of such a lighting or signalling device. 
     There is known, for example from the document FR-A-2 696 528, a headlamp comprising an elliptical reflector, a light source at the first focus of the reflector, an intermediate component made from sheet metal comprising a part in the form of a holder with at the front a lip extending gradially towards the inside, a lens comprising a collar projecting towards the outside resting on the lip of the intermediate component, and a retaining ring mounted on the back lip of the lens under prestressing and on limit stops of the intermediate component in order to press the lens onto the front lip of the intermediate component. 
     In this headlamp, the lip of the intermediate component gets narrower towards the back towards its free end, is mounted with its internal edge receiving the lens on the collar thereof, is adjacent to the convex part of the lens, and the limit stops for the retaining ring are formed in tongues freely cut out in the lateral wall of the intermediate component, are oriented with their free end towards the reflector, are folded radially towards the inside, and extend at an acute angle towards the flat face of the lens. 
     Such a design has various drawbacks. First of all, it requires an additional component, the retaining ring, being interposed between the lens and the intermediate component, the retaining ring being put in place before the tongues are folded. This additional component has a non-negligible effect on the cost of the headlamp, as well as on the manufacturing time for this headlamp. Furthermore, if this retaining ring is omitted, the lens is not held in its optimum position with respect to the light source, and the headlamp must be rejected. Finally, during folding of the tongues, the lens is frequently broken, which leads to another source of rejects. 
     There is also known from the document U.S. Pat. No. 6,086,231 an elliptical headlamp in which the lens is held on the intermediate element by deformation of the circumferential part, radially towards the inside, in order to grip the lip of the lens. 
     The documents FR-A-2 459 938 and BE-A-508 945 describe parabolic headlamps comprising a reflector and a glass, the glass being held by folding over by thermoforming the lateral wall of a strut or by hot crimping the rim of the reflector against the back lip of the glass. 
     The application of radial forces, that is to say forces perpendicular to the optical axis of the headlamp, is difficult to control, so that it frequently happens that the lens or the glass breaks or cracks, the reject rate then being relatively high. 
     SUMMARY OF THE INVENTION 
     The present invention is situated in this context and its aim is to propose a method of manufacturing a lighting or signalling device which does not require an additional component between the lens and its support, which can easily be automated so as to reduce the cost of the lighting or signalling device, which is reliable so as to limit rejects, and which is inexpensive. 
     The object of the present invention is therefore a method of producing a lighting or signalling device comprising a light source, a reflector reflecting the light rays emitted by the light source towards a lens so as to form along an optical axis a lighting or signalling beam, the lens comprising a peripheral flange and being held by a support, the support comprising an annular surface limited at its external periphery by a cylindrical rim. 
     According to the present invention, this method comprises the step consisting of deforming the cylindrical rim in the direction of the annular surface in order to envelop the peripheral flange of the lens and hold it in place without play and without requiring an additional component, this deformation of the cylindrical rim being performed by applying on this rim a force parallel to the optical axis of the lighting or signalling device. 
     According to other advantageous and non-limiting characteristics of the invention:
         the support is made from a viscoelastic material;   the deformation of the cylindrical rim is the result of a plastic flow phenomenon;   the deformation of the cylindrical rim is performed at least three points on this rim;   the deformation of the cylindrical rim is performed over the whole of this rim;   the support consists of an injected and/or moulded material, and the force on the cylindrical rim is between 100 dN and 3000 dN;   the deformation of the cylindrical rim is performed by crimping this rim.       

     Another object of the present invention is a lighting or signalling device comprising a light source, a reflector reflecting the light rays emitted by the light source towards a lens so as to from along an optical axis a lighting or signalling beam, the lens comprising a peripheral flange and being held by a support, the support comprising an annular surface limited at its external periphery by a cylindrical rim, in which the lens is held on the support by a method in accordance with one of the above characteristics. 
     Other aims, characteristics and advantages of the present invention will emerge clearly from the description which now follows of an example embodiment given on a non-limiting basis with reference to the accompanying drawings in which: 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic sectional view of an elliptical headlamp produced in accordance with the teachings of the invention; 
         FIG. 2  depicts an enlarged view of a detail of  FIG. 1 , in a first step of the method according to the present invention; 
         FIG. 3  depicts an enlarged view of the same detail of  FIG. 1 , in a second step of the method according to the present invention; 
         FIG. 4  depicts a view of a machine enabling implementation of the method according to the present invention; 
         FIG. 5  depicts a detail of a first step of a second embodiment of the method according to the present invention; and 
         FIG. 6  depicts a detail of the second step of the second embodiment of the method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     By way of a preliminary, it should be noted that, from one figure to another, identical or similar elements are referenced as far as possible by the same reference signs. 
       FIG. 1  depicts a headlamp  10 , in particular for a motor vehicle, which comprises a bulb  12  mounted in the far end of a reflector  14  of the elliptical type so that the light source  16  provided by the bulb  12  is situated in the vicinity of a first focus of the reflector  14 . Such a light source  16  can be constituted by the filament of an incandescent bulb, or by the electric arc of a gaseous discharge lamp. 
     The remainder of the description will use non-limitatively an orientation from back to front, along the optical axis A—A of the headlamp  10 , which corresponds to the direction of propagation of the light beam emitted by the device. Thus, in  FIG. 1 , the “front” is situated at the right of the figure, whilst the “back” is situated at the left. 
     The optical axis A—A is generally parallel to the longitudinal axis of the vehicle equipped with the headlamp  10 . The optical axis A—A is substantially horizontal and can be defined for example by the two foci of the reflector  14 . 
     The headlamp  10  comprises a convergent lens  18  which is mounted, at the front, on a support which is formed in a framework part  20  of the headlamp  10  fixed on a front transverse surface  22  of the reflector  14 . The focal plane of the lens  18  passes in the vicinity of the second focus of the reflector  14 . In a variant, the framework part  20  can be produced in a single piece with the reflector  14 . 
     The assembly of the elements described above constitutes an optical headlamp unit  10  which is for example mounted conventionally in a housing (not depicted) closed by a glass. 
     In a known manner, the lens  18  is flat-convex, and comprises at its periphery a substantially cylindrical flange  24 . In a headlamp of the elliptical kind, the flat surface of the lens  18  is turned towards the back, whilst the convex surface is turned towards the front. The peripheral flange  24  prolongs the back flat surface, so that the radius of the back flat surface is smaller than the radius of curvature of the convex front surface of this lens. 
     As can be seen in  FIG. 1 , the lens  18 , or more exactly its peripheral flange  24 , is enveloped by the support  20 , so that the position of the lens along the optical axis A—A is defined accurately. 
     To do this, as can be seen better in  FIGS. 2 and 3 , the support  20  comprises an annular surface  26  limited at its external periphery by a cylindrical rim  28  extending towards the front. 
     The annular surface  26  is such that its internal diameter is smaller than that of the back flat surface of the lens  18 , whilst the internal diameter of the cylindrical rim  28  is slightly greater than that of this back flat surface of the lens  18 . 
     It is then possible to dispose the lens  18  from the front on the support  20 , so that its peripheral flange  24  rests on the annular surface  26  of the support  20 , as depicted in  FIG. 2 , and is surrounded by the peripheral rim  28 . 
     In accordance with the present invention, in this position, provision is made to deform the peripheral rim  28  so that it comes to envelop the flange  24  of the lens  18 . To do this, provision is made to apply a force on the front end of the rim  28 , in a direction substantially parallel to the optical axis A—A, so that it comes to envelop the flange  24  and hold it firmly in place. The material constituting the support  20  is chosen from the group of viscoelastic materials so that the application of a force or stress on this material causes a plastic flow phenomenon, this term being understood in the present description as meaning a cold flow of the material under the effect of a temporary stress. 
     According to this first embodiment of the method of the present invention, this force can be applied on the whole of the front end of the rim  28 , so that the flange  24  of the lens  18  is totally enveloped by this rim thus deformed. This variant is similar to crimping of the support  20  around the lens  18 . 
     According to a variant of this first embodiment, this force can be applied on the rim  28  locally, so that the lens  18  is held only at predetermined points of the flange  24 . Preferably, the points of application of this force will be situated symmetrically with respect to the optical axis A—A. There will for example be three of them, spaced apart by 120° with respect to the centre of the back flat face of the lens  18 . 
     There can for example be used for this purpose a crimping or *nap riveting machine, such as the one depicted schematically in  FIG. 4 . Such a machine comprises for example a base  100  on which the support  20  is immobilized, for example by means of jaws  102 . 
     The lens  18  is then disposed on the support  20 , so that its peripheral flange  24  rests on the annular surface  26  of the support  20  and is surrounded by the peripheral rim  28 , as depicted in  FIG. 2 . Next, a clamp  104 , provided with at least one roller  106 , two having been depicted in  FIG. 4 , is brought closer to the lens  18  so that this or these rollers come to engage the front surface of the peripheral rim  28 . 
     The clamp  104  is then rotated about an axis coincident with that of the lens  18 , so roller or rollers  106  roll on the rim  28 . 
     According to the viscoelastic material constituting the support  20  and the thickness of the rim  28 , the clamp  104 , and therefore the roller or rollers  106 , are applied on the rim  28  with a force or pressure sufficient to deform it so that it is flattened by plastic flow and forms a shoulder or a bead  30 , which comes to surround the flange  24 , in order to envelop or confine it permanently. 
     By way of example, if the support is made from injected aluminum, and if the rim  28  has a thickness of approximately 3 mm, a force of approximately 800 dN can be applied on the rim  28  without the rim thus deformed breaking the flange  24  or the lens  18 . 
     According to other example embodiments, if the support is made from injected magnesium, and if the rim  28  has a thickness of approximately 4 mm, a force of approximately 600 dN can be applied on the rim  28  to deform it, and if the support is made from an injected thermoplastic material, for example PBT (polybutylene terephthalate) with 30% glass fibres, and if the rim  28  has a thickness of approximately 5 mm, a force of approximately 300 dN can be applied on the rim  28  to deform it. 
     A fixing of the lens  18  is then obtained such as depicted in  FIG. 3 , where it can be seen that the front end of the support  20  confines or envelops without play the lens  18 , without it being necessary to use an additional component such as a retaining ring or a spring, as in the prior art. 
     Surprisingly, the Applicant noted that the method which has just been described is remarkably reliable, and that the reject rate is notably lower than with the methods of the prior art. 
       FIGS. 2 to 4  depict an embodiment in which the lens  18  is held by a deformation of its support from the front. It is of course possible to envisage that the lens  18  is held by a deformation of its support from the back. This is what is depicted in  FIGS. 5 and 6 . 
     It can be seen in these Figures that the support  20  comprises, as in the embodiment which has just been described, an annular surface  26 ′, but which this time faces the back of the support  20 . The annular surface  26 ′ is formed at the back of a radial rim or shoulder  32  of the internal surface of the support  20 , defining an internal cylindrical surface  34 . 
     The lens  18  is then disposed on the annular surface  26 ′ of the support  20 , so that its peripheral flange  24  rests on the annular surface  26 ′ of the support  20  and is surrounded by the Internal cylindrical surface  34 , as depicted in  FIG. 5 . As in the preceding embodiment, pressure is applied on the rim or the shoulder  32  in order to deform it so that it is flattened and comes to form a bead  30 ′ which surrounds or envelops without play the flange  24  of the lens  18 . 
     As in the preceding embodiment, according to a variant, this force can be applied on the shoulder  32  locally, so that the lens  18  is held only at predetermined points of the flange  24 . Preferably, the points of application of this force will be situated symmetrically with respect to the optical axis A—A. There will for example be three of them, spaced apart by 120° with respect to the centre of the back flat face of the lens  18 . 
     According to another variant of this second embodiment of the method of the invention, the force necessary for deformation of the shoulder  32  can be applied on the whole of the back face of this rim shoulder, so that the flange  24  of the lens  18  is totally enveloped by this rim thus deformed. Use will be made for this purpose of the same type of crimping or snap riveting machine as the one described in connection with  FIG. 4 , in order to obtain a fixing of the lens as depicted in  FIG. 6 . 
     There has therefore clearly been implemented according to the present invention a method of manufacturing a lighting or signalling device which does not require an additional component between the lens and its support, which can easily be automated so as to reduce the cost of the lighting or signalling device, which is particularly reliable as regards rejects, and which is inexpensive. 
     Of course, the present invention is not limited to the embodiments which have been described, but persons skilled in the art can on the contrary make many modifications thereto which fall within its scope. Thus the lens support can be added onto the reflector, or be in a single piece therewith. Likewise, although having been described in connection with the manufacture of an elliptical type headlamp, the present invention is applicable to the fixing of a glass of a lighting or signalling device onto the housing of this device.