Abstract:
An optical system for a motor vehicle, the optical system performing at least one main optical function and including in particular a diffusion screen, at least one light source of the LED type, each LED of the optical system producing a set of rays of light to be propagated in the diffusion screen wherein the screen is in the form of a curved sheet, with an upper lateral flange and a lower lateral flange which meet at a periphery which has in particular a rear face and a front edge and the principal function is performed essentially via an output face constituted by the front edge of the diffusion screen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to French Application No. 0801168 filed Mar. 3, 2008, which application is incorporated herein by reference and made a part hereof. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject of the present invention is an optical system for a motor vehicle having a stylized main function, performed by means of at least one light source, in particular of the light-emitting diode type. The essential purpose of the invention is to propose, on the basis of a limited number of light sources, preferably LEDs, an optical system performing a main optical function by means of a transmission screen, the visible surface of which is sufficient to satisfy the regulatory requirements of the optical function under consideration. The term optical system refers to an element forming part or all of a headlamp device, exhibiting at least one light source and means of performing at least one optical function; optical function refers to the production of a regulatory light beam for the production of certain of the lights mentioned below. 
     The domain of the invention is, in general, that of the lights or lamps of motor vehicles. In this domain, various types of lights are known, among which are included essentially:
         tail lights, or position lights, of low intensity and range;   low beam lights, or dipped lights, of higher intensity and with a range on the road in the vicinity of 70 meters;   long-range high-beam headlamps, and additional lights of the long-range type, with a zone of vision on the road in the vicinity of 200 meters;   advanced headlamps, known as dual-mode, which combine the functions of dipped headlights and full beam headlights by incorporating a detachable mask;   fog lamps;   signalling lights, in particular front and rear turn indicators, reverse lights, or tail lights;   signalling devices of the position light type for daytime use, known as DRL (Daytime Running Light) devices.       

     The domain of application of the invention is essentially that relating to brake lights, turn indicators, position lights or DRL. 
     2. Description of the Related Art 
     For all of these headlamps and lights, the light sources traditionally used are of the halogen lamp type, or discharge lamps. But for some years now, automotive equipment suppliers have proposed the utilization of light-emitting diodes, or LEDs; this utilization concerns, for example, indicator lights or rear lights. 
     Light-emitting diodes present a certain number of advantages:
         first of all, for a long time, it has been known that this type of diode does not send out beams omnidirectionally, but radiates in a half space opposite a substrate which supports the P-N junction of the diode considered; thus, by using radiation more directionally than halogen or discharge lamps, from the state of the art, the quantity of energy wasted is less than with discharge or halogen lamps;   further, these diodes have recently been improved in terms of the intensity of radiated power. Moreover, manufactured diodes have for a long time emitted radiation in red, but now also in white, which expands the field of their potential uses. The amount of heat which they give off is relatively limited, and a certain number of constraints, in connection with the dissipation of heat in state of the art headlamp devices, no longer apply; the problem of heat dissipation, however, remains important for power LEDs;   finally, diodes consume less energy than discharge or halogen lamps, even at the same radiation intensity; they take up little space, and their particular shape offers new possibilities for the creation and the configuration of the complex surfaces associated with them, in particular by arranging them on electronic supports of the flexboard type.       

     The use of LEDs has become more and more widespread, in particular to respond to the aesthetic criteria desired by vehicle manufacturers. This use especially enables the production of headlamps presenting original volumes, for example by arranging LEDs three-dimensionally, i.e. on a non-plane support substrate, within the headlamp devices in question, or again, by using light guide type elements. 
     Furthermore, an optical system has recently been proposed in which different LEDs were specifically used to create a curtain of light by means of a screen inside the optical system, in which the light produced by the diode or diodes is propagated, the optical system also performing an optical function, known as the main optical function by comparison with any other optical function which may be performed by the optical system in question, in the form of a light beam generated by a third light source. In this optical system, it is necessary to make use of a plurality of light sources, as the LEDs used are not involved in the performance of the main optical function. The cost of such an optical system is therefore high, due to the large number of light sources it requires, and, for the same reasons, it takes up a lot of space. 
     The term curtain of light refers to a surface illuminated by part of an optical system, the illumination being produced by light beams circulating inside a volume, in particular delimited by the illuminated surface, the illumination having until then a purely decorative function, not executing, or not contributing to—or only insignificantly—the performance of the main optical function. Advantageously, the illumination produced is as continuous as possible, with no pixelization effect. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to propose a solution to the problems and disadvantages which have just been explained. In one aspect of the invention, an optical system is proposed in which the number of light sources involved is limited, preferably by limiting the utilization of LEDs to the performance of a main function. Moreover, in another aspect of the invention, a screen is disposed in which are diffused the signals, or beams, of light produced by the light sources, in particular LEDs, in such a way that, due to the positioning of the diffusion screen, it is essentially an output edge of the screen which contributes to the performance of the desired main function; the visible illuminated surface is increased by the shape of the screen considered, a lateral flange of the screen diffusing light so as to contribute to the performance of the desired main function. Advantageously, the positioning of the diffusion screen is such that it contributes to the performance of a second optical function of the lateral marking type, this function being known in English as a “side marker”. 
     The invention thus essentially concerns an optical system for a motor vehicle, the optical system performing at least one main optical function and comprising in particular:
         a diffusion screen, also known as a light guide;   at least one light source, notably of the LED type, each light source of the optical system producing a set of rays of light which are propagated in the diffusion screen.       

     In one aspect, the invention comprises a system in which:
         the screen is in the form of a sheet, notably curved or substantially plane, with an upper lateral flange and a lower lateral flange which are joined by means of a periphery having a rear face, a front edge, the periphery can also comprise a first lateral face and a second lateral face;   the main function is performed essentially via an output face constituted by the front edge of the diffusion screen; and   at least one part of the upper lateral flange diffuses a light beam contributing notably to the performance of the main function and/or performing a complementary optical function.       

     The optical system according to the invention may comprise, in addition to the main characteristics which have just been mentioned in the preceding paragraph, one or more supplementary characteristics including the following:
         the front edge has a thickness of between 3 and 5 millimeters, notably 4 millimeters;   a first part of the upper lateral flange diffuses a light beam contributing to the performance of the main function;   at least one part of the upper lateral flange diffuses a light beam and is oriented in such a way as to increase the visible illuminated surface of the optical system in the direction of emission of the main function;   the main optical function performed is of the brake light type, or of the position light type, or of the turn indicator type;   a second part of the upper lateral flange diffuses a light beam performing a complementary optical function;   the complementary optical function performed is of the lateral marking type;   the upper lateral flange diffuses a light beam via a plurality of micro-roughnesses suitable to disperse to the exterior of the diffusion screen some of the rays of light propagating in the diffusion screen, these micro-roughnesses forming notably a plurality ( 110 ) of minidiscs;   the micro-roughnesses form minidiscs having a diameter substantially between two tenths of a millimeter and six tenths of a millimeter, typically four tenths of a millimeter;   the light sources, in particular LEDs, are arranged opposite the rear face of the diffusion screen;   it comprises at least one lateral face, the light sources, in particular the LEDs, being arranged opposite at least one of the lateral faces of the diffusion screen;   the light sources, in particular LEDs, are arranged opposite a single lateral face of the diffusion screen;   the rear face of the periphery comprises a plurality of reflecting prisms suitable to direct the light beams produced by the light sources, in particular LEDs, to the front edge of the diffusion screen.       

     The supplementary characteristics are associated, according to all possible combinations and to the extent that these supplementary characteristics are not mutually exclusive, in different embodiments of the subject matter of the invention. 
     The present invention also relates to a headlamp or to a signalling light for a motor vehicle equipped with an optical system according to the invention, with its main characteristics, and possibly one or more supplementary characteristics which have just been mentioned. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
       The invention and its different applications will be better understood by reading the following description and examining the accompanying figures. 
       These figures are shown only by way of indication and do not in any way limit the invention. The figures show: 
         FIGS. 1A ,  1 B and  1 C are different perspectival views of a first embodiment of an optical system according to the invention; 
         FIG. 2  is a perspective view of a second embodiment of an optical system according to the invention; 
         FIG. 3  is a perspective view of a third embodiment of an optical system according to the invention; 
         FIG. 4  is a top view of the third embodiment shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The different elements appearing in several figures, unless otherwise stated, have retained the same reference numbers. 
       FIGS. 1A ,  1 B and  1 C show a first embodiment of an optical system according to the invention in, respectively, a first position, a second position and a third position. A three-dimensional orthogonal marker is shown in these figures, with an axis of abscissas X corresponding to the axis of displacement of the reversing vehicle, and a normal Z axis corresponding to the vertical. 
     In these figures, the optical system  100  according to the invention consists of a diffusion screen  113  and of a plurality of LEDs  101  producing the rays of light  102  which are intended to be propagated in the diffusion screen  113 . The screen  113  is made from a transparent plastic material, in particular of the type PMMA (for PolyMethyl MethAcrylate) or PC (for superfluid high transmission PolyCarbonate). 
     Advantageously, the LEDs  101  is all arranged on a single plane substrate, not shown, which holds them in position and controls them. 
     The diffusion screen  113  takes the form of a curved sheet. A term of this type refers to the fact that the screen  113 , if it were flattened, would constitute an element of homogeneous thickness, of approximately four millimeters, said thickness being small in size in relation to the other dimensions of the flattened shape; which is of the quadrilateral type in the example shown. 
     The diffusion screen  113  is thus characterized by an upper lateral flange  108 , a lower lateral flange  109 , these two parts being linked by a periphery  103 , having a front edge—i.e. a linear face— 104 , a first lateral face  105 , a second lateral face  106  and a rear face  107 . The front edge  104  is the face of the optical system which is directly visible to an observer positioned at the rear of the vehicle equipped with the optical system considered. In the examples shown, the diffusion screen is curved such that an observer positioned at the rear of the vehicle sees at least part of the upper lateral flange  108 . Such a characteristic is expressed by the fact that at least one of the lateral faces  105  or  106  of the periphery  103  constitutes a curved, or at least inclined, segment. 
     In the first example shown, the diodes  101  are arranged opposite the rear face  107 , at the level of which the rays of light  102  which they produce enter the diffusion screen  113 . The rays of light  102  are thus propagated in the volume defined by the diffusion screen  113 , possibly after reflection from the lateral faces  105  and  106 , to exit from the diffusion screen  113  at the front edge  104  in the form of a light beam  111 , where a main optical function is at least partially performed, for example of the sidelight type. 
     Advantageously, the upper lateral flange  108  consists of a plurality of minidiscs with a diameter of between 2 and 6 tenths of a millimeter, which make it possible, with the aid of the micro-roughnesses which they exhibit, to diffuse to the exterior of the diffusion screen  113 , through a first part  115  of the upper lateral flange  108 , some of the rays of light  102  in the form of a light beam  112 . The term micro-optic surface is often used to describe such a diffusion surface. In  FIG. 1B , the minidiscs are represented by points inside a zone  110  surrounded by a circle, shown enlarged at the top right of the illustration of the diffusion screen  113 . In the enlarged illustration, a light beam  112  generated by one of the minidiscs has been represented by a set of arrows. Obviously, most if not all of the minidiscs generate a light beam  112 . Two other zones  110  have been shown in diagram form on the diffusion screen  113 . The minidiscs may preferably be distributed over the entire lateral flange  108 . The light beams  112 , corresponding to the light diffused by the minidiscs, contribute to the performance of the main optical function by increasing the visible illuminated surface of the optical system  100 . The visible illuminated surface may thus be made larger to a greater or lesser degree by inclining the optical system  100  more or less. 
     The front edge  104  is rendered homogeneous with the aid of a surface which is either perfectly diffusing to conceal the hot points and to distribute the beams spatially, or covered in optical patterns (equivalent to pseudo-toric surfaces of small dimensions to match the surface) to distribute the beams spatially, or perfectly polished to reveal the hot points corresponding to the position of the origin of the emitters, the LEDs. 
     Advantageously, part  114  of the upper lateral flange  108  is used to perform a complementary function of the lateral marking type (side marker in English): to this end, provision is made that the part  114  is substantially vertical, and that it projects at least partially beyond the body of the vehicle so as to be visible when the vehicle is viewed from the side. 
       FIG. 2  shows a second embodiment  200  of an optical system according to the invention. The second embodiment differs from the first embodiment by the following characteristics:
         the LEDs  201 , producing light beams  202 , are arranged opposite the first lateral face  105 , and not opposite the rear face  107 ;   the rear face  107 , which was plane in the first embodiment  100 , has been replaced by a rear face  207 , consisting of a succession of reflecting prisms  208 , which use total reflection to redirect the light beams  202  to the front edge  104 , over the entire length necessary to the performance of the main function, as in the first embodiment described.       

     The other elements which appeared in the first embodiment are still present, and fulfill the same function. 
       FIGS. 3 and 4  show a third embodiment  300  of an optical system according to the invention. It differs from the first embodiment in that the diffusion screen  313  is substantially plane, thus in the form of a substantially plane sheet. The lower  309  and upper  308  lateral flanges are substantially plane. Preferably, the rear edge  307  and the lateral edges  305  and  306  are also substantially plane. The output face  304  preferably forms, with the upper lateral flange  308 , an angle of over 90 degrees and the diffusion screen  313  is oriented such that:
         the output face  304  is substantially perpendicular to the X-axis, this X-axis corresponding to the direction of emission of the light of the main function; and   the upper lateral flange forms an acute angle in relation to the transverse Y-axis, the front edge  304  and the lateral flange  308  are directly visible to an observer positioned facing the direction of the X-axis.       

     In this third embodiment, the orientation thus makes it possible firstly to have part of the main function essentially or mainly performed by the output edge  304  according to the X-axis, i.e. towards the rear of the vehicle when the device is situated in a rear light of the vehicle, and secondly, by means of the light diffused by the upper lateral flange  308 , to have an increase in the visible surface according to the X-axis of this main function, and a repeat function along the Y-axis, that is, on the side of the vehicle when the device is situated at the rear of the vehicle. 
     The other elements, for example the micro-roughnesses which appeared in the first embodiment, are still present in this third embodiment and fulfill the same function. 
     To explain the present invention, the expression “upper lateral flange” generally refers to the lateral flange which is oriented towards the exterior of the vehicle and thus visible to an observer. In particular, it could be applied to a diffusion screen which, once mounted on the vehicle, would show a visible lateral flange which is vertical, or even inclined towards the ground. 
     While the forms of apparatus herein described constitutes preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.