Abstract:
A lighting or signalling device for a motor vehicle, comprising a light source and a light guide associated with the light source, the light rays issuing from the light source entering the light guide through an entry face and propagating in the light guide in order to emerge therefrom substantially parallel to a general direction of emission through an exit face. The guide comprises at least one internal intermediate wall or a lateral wall on which the light rays undergo at least one total reflection.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention concerns lighting or signalling devices for motor vehicles.  
         [0003]     2. Description of the Related Art  
         [0004]     It is normal to connect together, in a single housing, several lighting or signalling functions, so as to simplify the electric wiring for these various functions in a motor vehicle. Each function comprises a light source, in general a reflector and possibly a lens, these various elements being arranged so as to provide a lighting or signalling beam whose geometric and photometric characteristics must be in accordance with various regulations.  
         [0005]     Each function thus requires a minimum volume for its installation in a particular lighting or signalling device. However, the volume available for installing lighting or signalling devices is becoming smaller and smaller both at the front and at the rear of a modern motor vehicle. This is because the constraints of aerodynamics and the ideas of the designers result in shapes that are often very different from those resulting solely from technical considerations. As a result, in many cases, the space available for grouping together these functions in the same housing is insufficient and it is then necessary to distribute various functions in different housings, and hence a rise in the cost and an increase in the wiring and assembly time.  
         [0006]     It has already been attempted to resolve this problem by using light guides. FIGS.  1  to  4  depict an example of a device using such a solution. It can be seen in  FIG. 1  that a lamp  1  is intended to be mounted in a reflector  2  so as to concentrate the light rays issuing from the lamp  1  on the entry face  3  of optical fibres or groups of optical fibres  4 . The reflector  2  is for example is of the elliptical type, the light source of the lamp  1  being placed in the vicinity of a first focus of the reflector  2 , the faces  3  being available in the vicinity of the second focus of the reflector  2 . The exit faces  5  of the optical fibres  4  are coupled to the entry faces  6  of the light guides  7 .  
         [0007]     The light guides  7 , in the example shown, are configured so as to extend in a circular pattern, and are disposed for example so as to surround the front perimeter of a dipped beam headlight. The light guides  7  are for example in accordance with those described in the document DE-A-41 29 094. They comprise, as can be seen better in  FIG. 2 , a face  8  formed from a succession of prisms or serrations and an exit face  9 , cylindrical or toric. The prisms or serrations on the face  8  return the light rays propagating in the light guide  7  towards the face  9  ( FIG. 3 ), which supplies an exit beam from them, which can for example fulfil the function of a town lamp in a headlight.  
         [0008]     Such a solution is particularly costly, since it requires a light source such as a halogen lamp, an elliptical reflector, a flexible cluster of optical fibres and a rigid light guide made from glass or plastics material, where one of the faces is machined so as to form prisms or serrations on it. In addition, it has as a drawback the fact that the light rays propagating in the guide are diverted by the serrations or prisms in an uncontrolled fashion, which causes numerous losses of light. Moreover, the periodic structure of the serrations or prisms is found in the emerging beam, so that the light guide has a greatly non-homogeneous appearance. Finally, this solution has the drawback of being very bulky so as to be able to house the light source, the reflector, the optical fibres and the light guides.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is placed in this context and its purpose is to propose a lighting or signalling device that makes it possible easily to dispose a supplementary lighting and signalling function in a headlight, such a lighting or signalling device also having to be simple to assemble, reliable in its functioning and compact, the photometric performance complying with current regulations, such a device also having to be inexpensive.  
         [0010]     The object of the invention is therefore a lighting or signalling device for a motor vehicle. In one aspect, one embodiment comprises a light source and a light guide associated with the light source, the light rays issuing from the light source entering the light guide through an entry face and propagating in the light guide in order to emerge therefrom substantially parallel to a general direction of emission by an exit face, the guide comprising at least one internal intermediate wall or a lateral wall on which the light rays undergo at least one total reflection.  
         [0011]     According to one embodiment, the light source is associated with an optical system such that the light rays are emitted over 360° around the axis of this source, in an angle of approximately ±30° with respect to the horizontal plane perpendicular to an optical axis of the source.  
         [0012]     According to other characteristics, other embodiments may include one or more of the following features: 
        the guide comprises a central section and at least one lateral section separated by at least one internal intermediate wall;     a direction of the light rays emitted by the light source passing through the central section is modified only by refractions on the entry and exit faces;     a direction of the light rays emitted by the light source passing through a lateral section is modified by at least one total reflection on at least one internal intermediate wall or a lateral wall;     a light source consists of at least one light emitting diode;     a light source associated with a light engine having an entry face, a rear reflection face, a front reflection face and an exit face, the light engine emitting radially outwards the rays that it receives from the light source;     a guide having a thickness that is small compared with its width;     a guide having an exit face of that has the form of a very elongate rectangle;     a guide having an exit face that extends over a portion of a circumference.        
 
         [0021]     These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     Other aims, characteristics and advantages of the present invention will emerge clearly from the following description that will now be made of an example embodiment given non-limitingly with reference to the accompanying drawings, in which:  
         [0023]      FIG. 1 , already commented on, depicts a schematic view in perspective of an embodiment of the prior art;  
         [0024]      FIG. 2  depicts a view to a larger scale of detail  11  in  FIG. 1 ;  
         [0025]      FIG. 3  depicts a view in longitudinal section of the light guide in  FIG. 1  and  2 ;  
         [0026]      FIG. 4  depicts a view in transverse section of the light guide in  FIGS. 1 and 2 ;  
         [0027]      FIG. 5  depicts a ¾ rear view in isometric perspective of half of the light guide according to the present invention;  
         [0028]      FIG. 6  depicts a ¾ front view in isometric perspective of a first variant embodiment of a light guide according to the present invention;  
         [0029]      FIG. 7  depicts a ¾ front view in isometric perspective of a second variant embodiment of a light guide according to the present invention;  
         [0030]      FIG. 8  depicts a ¾ front view in isometric perspective of a third variant embodiment of a light guide according to the present invention;  
         [0031]      FIG. 9  depicts the radiation diagram of a light emitting diode that can be used with light guide of one of FIGS.  5  to  8 ;  
         [0032]      FIG. 10  depicts a variant light source that can be used with the light guide of one of FIGS.  5  to  8 ;, and  
         [0033]      FIG. 11  depicts in exploded view a fourth variant embodiment of a light guide according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     By convention, in the present description, “front” means the direction in which the final light beam is emitted, and “rear” the opposite direction.  
         [0035]     For reasons of clarity,  FIG. 5  depicts only half of a light guide, produced in accordance with the present invention, and designated overall by the reference  10 . The complete guide is formed by joining the half depicted and another half symmetrical with respect to a vertical mid-plane M, as variants of a guide have been depicted for example in  FIGS. 6, 7 ,  8  and  11 .  
         [0036]     The guide  10  is associated with a light source  12 , consisting of example of a light emitting diode. The light rays emitted by this source  12  enter the guide  10  through an entry face  14  and emerge therefrom by an exit face  16 , their direction after the exit face  16  being substantially parallel to a general direction X-X oriented from rear to front.  
         [0037]     In accordance with the present invention, the guide  10  consists of a block  20  of transparent material whose thickness E is much smaller than its width L. By way of non-limiting example, the width L can be twenty times greater than the thickness E. The exit face  16  thus has the form of a very elongate rectangle. Such a guide can be produced from a thermoplastic material such as polycarbonate (PC), or polymethyl methacrylate (PMMA) or any other transparent material, for example glass. In the example embodiments depicted in  FIGS. 5, 6  and  11 , the thickness is counted in the vertical direction, so that the guide  10  has its top and bottom faces substantially horizontal. In the example embodiments depicted in  FIGS. 7 and 8 , the exit face  16  of the guide  10  has a curved shape, the thickness is counted in the radial direction and the width in the circumferential direction.  
         [0038]     In one embodiment, entry face  14  of the block  20  completely surrounds the source  12  so that a majority of the light rays emitted by the source enter this block.  
         [0039]     Advantageously, use will be made of a light source  12  having a radiation diagram like the one depicted in  FIG. 9  and such that the light rays are emitted over 360° around the axis A-A of this source, situated in the mid-plane M, in an angle of approximately ±30° C with respect to the horizontal plane perpendicular to the optical axis A-A of the source. Such a light source  12  with light emitted diode is for example described in the document U.S. Pat. No. 6,679,621 and comprises a primary lens S procuring such a radiation diagram.  
         [0040]     It is also possible to use a suitable optical system in association with a light emitting diode provided with a conventional primary lens, as depicted in  FIG. 10 . Such an optical system is similar to the light engine described for example in the document EP-A-1 416 220.  
         [0041]     The light engine  22  depicted in  FIG. 10  comprises an entry face  24  that is arranged axially opposite the diode  12 . The profile of the entry face  24 , in axial section, is such that the majority of the light rays emitted by the diode  12  enter the light engine  22 .  
         [0042]     The entry face  24  comprises a coaxial central portion forming a collimator that has a roughly hemispherical shape convex towards the rear, and a coaxial annular peripheral portion that has a roughly hemispherical shape concave towards the front.  
         [0043]     The hemispherical profile of the central portion of the entry face  24  is such that the majority of the light rays received, coming from the diode  12 , are refracted inside the light engine  22  whilst being diverted, so that these light rays enter the light engine  22  following a direction substantially parallel to the optical axis A-A.  
         [0044]     The peripheral hemispherical portion of the entry face  24  is centred on the diode  12 , so that the majority of the light rays received by the peripheral hemispherical portion, coming from the diode  12 , are refracted inside the light engine  22  without being diverted.  
         [0045]     The light engine  22  comprises a rear reflection face  20  with a concave parabolic annular shape. The rear reflection face  30  is designed to reflect axially towards the front, according to the principle of total reflection, the light rays that enter the light engine  22  through the peripheral portion of the entry face  24 . To this end, the focus of the parabola forming the rear reflection face  30  is substantially merged with the light source  12 .  
         [0046]     The light engine  22  has a front reflection face  32  with a roughly convex and coaxial conical shape. The front reflection face  32  is designed so as to reflect, according to the principle of total reflection, the light rays travelling inside the light engine  22 , towards a cylindrical exit face  34 .  
         [0047]     The front reflection face  32  comprises a conical central portion that is arranged axially opposite the entry face  24  and axially opposite a part of the rear reflection face  30 .  
         [0048]     The angle at the vertex of the conical portion is approximately 90°, so that the light rays that reach this conical portion and that are parallel to the optical axis A-A are reflected radially outwards.  
         [0049]     The rays emitted by the source  12  thus strike the entry face  24  of the guide  12  at a predetermined angle of incidence, the entry face  24  making them undergo a refraction imposing a first deviation on them. The rays then propagate in the guide  10 , able to undergo therein total reflections on the top and bottom faces of this guide.  
         [0050]     Referring back to  FIGS. 5-7 , the guide  10  is divided into several sections by intermediate walls  17 . The guide  10  thus comprises for example a central section C, situated in front of the light source  12 , and in which the light rays such as RI undergo only a refraction on passing through the entry and exit faces  14  and  16 , and possibly total reflections on the top and bottom faces of the central section C. The entry and exit faces  14  and  16  are configured so that the emerging light rays are substantially parallel to the general direction X-X. The exit face of the central section C can, as depicted in  FIG. 5 , be slightly convex. Any total reflections on the top and bottom faces do not modify the direction of propagation in the general plane of the guide.  
         [0051]     The guide  10  also comprises lateral sections L 1 , L 2  and L 3  in the examples depicted, the exit faces  16  of which are coplanar in the example in  FIG. 5  and parallel in the example in  FIG. 6 , and perpendicular to the general direction X-X. The exit faces  16  can even be continuous or merged, as depicted in  FIGS. 7, 8  and  11 .  
         [0052]     Each lateral section receives the light rays that have entered the guide  10  through the entry face  14 , in the part of this section closest to the light source  12 , and comprises at least one intermediate wall making the light rays undergo at least one total reflection, so as to make them emerge through the exit face  16 , in a direction substantially parallel to the general direction X-X.  
         [0053]     As can be seen in  FIGS. 5 and 6 , the first lateral section L 1  is delimited by a part of the entry  14 , an exit face  16  and an intermediate wall  17  imposing a total reflection on the rays such as R 2  ( FIG. 5 ), whilst the other sections L 2  and L 3  comprise two such intermediate walls  17 , at least one of these intermediate walls interposing a total reflection on rays such as R 3  and R 4 . The intermediate walls  17  separate the volume of the guide into distinct sections, each guiding part of the light flux emitted by the source  12  towards the exit faces  16 .  
         [0054]     The end lateral section, in this case the section L 3 , is delimited by part of the entry face  14 , an exit face  16 , an intermediate wall  17  and a lateral wall  18 , imposing a total reflection on rays such as R 4 .  
         [0055]     Through an appropriate choice of the angles made by the intermediate  17  or lateral faces  18  with the general direction X-X, the light rays can be distributed substantially uniformly on the exit faces  16 . In the lateral sections as in the central section, any total reflections on the top and bottom faces do not modify the direction of propagation in the general plane of the guide.  
         [0056]     It is thus possible to distribute all the light flux emitted by the light source  12  on the exit faces  16 , using only the total reflection on the intermediate walls  17  of the guide  10 , and possibly on the top and bottom walls, so that the illumination of the exit faces is even.  
         [0057]     So as to perfect the evenness of the light beam emerging from the guide  10 , or to confer a particular photometric pattern on it with regard to geometry, or even to confer a particular style on it, it will be possible to provide the exit face with optical arrangements  50 , as depicted in  FIG. 11 .  
         [0058]     Likewise it will be possible to confer on the exit face  16  a shape other than rectangular. As depicted in  FIGS. 7 and 8 , the guide  10  can be curved, so that its largest dimension, in this case its width L, is measured over an arc of a circle, and its smallest dimension, the thickness E, is measured radially.  
         [0059]     It will then be possible to produce a guide  10  whose exit face  16  extends over a portion of a circumference, for example over approximately a quarter of a circle, as depicted in  FIG. 7 . It will thus be possible to join four guides  10  like the one depicted in  FIG. 7  in order to obtain an assembly like the one depicted in  FIG. 8 , whose exit face  16  extends practically continuously in a full circle.  
         [0060]     A lighting or signalling device has therefore indeed been produced that makes it possible to easily dispose a supplementary lighting and signalling function in a headlight. This is because the invention makes it possible to give the exit faces  16  a relatively small thickness E, for example less than 20 mm. The size of such a guide is therefore minimal, which enables it to be installed in a small volume.  
         [0061]     Such a lighting or signalling device is also particularly simple to produce since it consists of a single piece, no adjustment being necessary. In addition the light beam obtained is extremely homogeneous, which makes it possible to easily obtain photometric performance meeting the regulations in force.  
         [0062]     Naturally, the present invention is not limited to the embodiments described, but a person skilled in the art will on the contrary make many modifications to it which come within its scope. Thus the exit face can be disposed so that its largest dimension is vertical. Likewise the exit faces can have a shape other than planar, for example convex or concave.  
         [0063]     While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that this 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.