Patent Publication Number: US-10309636-B2

Title: Motor vehicle headlight lighting module with wavelength converter and separate air ducts for cooling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to the French application 1561525, filed Nov. 27, 2015, which application is incorporated herein by reference and made a part hereof. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a motor vehicle headlight lighting module of the type comprising: at least one first light source; a device for converting the wavelength of the light emitted by the first light source; and a fan able to generate a flow of air. 
     2. Description of the Related Art 
     It is known to provide headlights at the front of a motor vehicle able to form light beams to provide various lighting functions, for example of “high beam” or “low beam” type. 
     So-called adaptive lighting devices make it possible to adjust the beam intensity, dimensions and/or direction according to traffic conditions in order to provide these various functions. 
     Each headlight generally includes a plurality of lighting modules that make it possible to form a light beam of the headlight. The modules may be turned on and off independently of one another to vary the characteristics of the beam in real time. 
     By lighting module is meant a system containing at least one light source and a projection or reflection optical system. 
     Lighting modules as described in the document EP2690352, which is the equivalent of U.S. 2014/0029282, in the name of the Applicant notably comprise lighting devices including laser diode type light sources emitting blue light and a device able to convert the laser radiation into a beam of white light. A converter device of this kind consists of luminophore elements, for example. 
     The light sources and the converter device generate a considerable amount of heat when operating, and it is necessary to cool them. It is notably known to equip the lighting modules with fans that generate a flow of air able to cool the heating elements by convection. 
     The presence of a fan for each of the aforementioned elements makes optimum cooling possible. This solution is costly, however. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose an improvement to existing lighting modules notably optimizing the efficacy of the cooling of the various elements emitting heat. 
     To this end, the present invention relates to a lighting module of the aforementioned type including at least one first air duct and one second air duct that are separate, the fan being placed at the inlet of each of the first and second air ducts so as to distribute the flow of air between the ducts, the first light source and the wavelength converter device being disposed at the outlet of the first and second air ducts, respectively. 
     According to other advantageous aspects of the invention, the lighting module includes one or more of the following features, separately or in any technically possible combination: 
     the lighting module includes at least one second light source, the converter device being able to receive the light emitted by the second light source, the lighting module including at least one third air duct separate from the first and second air ducts, the fan being placed at the inlet of the third air duct so as to distribute the flow of air between the ducts, the second light source being disposed at the outlet of the third air duct; 
     the lighting module includes a support to which the fan, the wavelength converter device, the first light source and where applicable the second light source are fixed, the support comprising one or more internal walls defining the air ducts; 
     the air ducts are configured so as to direct onto the wavelength converter device a fraction between 10% and 40% inclusive, preferably between 15% and 25% inclusive, of the flow of air generated by the fan; 
     at least the first light source is in contact with a heatsink able to exchange heat with a flow of air, the heatsink being disposed in the air duct corresponding to the light source; 
     at least the first light source is a semiconductor light source, preferably a laser diode, emitting radiation the wavelength of which is preferably between 400 nm and 500 nm inclusive; 
     the wavelength converter device includes a plate able to reflect the laser radiation and a layer of luminophore covering the plate; 
     the lighting module further includes at least one reflector device able to deflect the light emitted by at least the first light source and to redirect the light onto the wavelength converter device; and 
     the lighting module further includes an imaging optical system able to project the light re-emitted by the wavelength converter device. 
     The invention further relates to a motor vehicle headlight including at least one lighting module as described above. 
     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 ACCOMPANYING DRAWINGS 
       The invention will be better understood on reading the following description, given by way of nonlimiting example only and with reference to the drawings, in which: 
         FIG. 1  is a view in section of a lighting module according to one embodiment of the invention; 
         FIG. 2  is an exploded perspective view of components of the lighting module from  FIG. 1 ; and 
         FIG. 3  is a back view of a component of the lighting module from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  represents in section a lighting module  10  according to a first embodiment of the invention. 
     The lighting module  10  is intended to be incorporated into a motor vehicle headlight, the headlight possibly including one or more other lighting modules. 
     The lighting module  10  includes a first lighting device  12  and a second lighting device  14 , a wavelength converter device  16  and an imaging optical system  18 . 
     The lighting module  10  further includes a fan  20  able to generate a flow of air. 
     The lighting module  10  further includes a support  22  to which the first lighting device  12  and the second lighting device  14 , the wavelength converter device  16 , the imaging optical system  18  and the fan  20  are fixed. 
     An orthonomic frame of reference (X, Y, Z) represented in  FIGS. 1, 2 and 3  is considered. The horizontal axes X and Y are respectively parallel and perpendicular to an optical axis  23  of the imaging optical system  18 ; the axis Z is vertical. 
     In the example from  FIG. 1 , the first lighting device  12  and the second lighting device  14  are substantially identical and correspond to the same description given hereinafter. 
     The first lighting device  12  and the second lighting device  14  include a light source  24  disposed on an emission axis substantially parallel to X. The light source  24  is preferably a semiconductor light source, more preferably a laser diode. In the example from  FIG. 1 , the light source  24  of the first lighting device  12  and the second lighting device  14  is a laser diode. 
     The light source or laser diode  24  emits for example a visible beam the wavelength of which is between 400 nm and 500 nm inclusive, preferably between 440 nm and 470 nm inclusive. 
     The first lighting device  12  and the second lighting device  14  further include an optical device able to concentrate the beam emitted by the laser diode  24 . 
     The first lighting device  12  and the second lighting device  14  further include a reflector  26  able to direct towards the wavelength converter device  16  a light ray emitted by the laser diode  24  and concentrated by the optical device. The reflector  26  is preferably mobile in one or two directions so as to form a scanning system. In the example from  FIG. 1 , the reflector  26  is formed of a plurality of mirrors that are mobile independently. The movement of the mirrors of the reflector is notably controlled by an electronic circuit card  28 . 
     The first lighting device  12  and the second lighting device  14  further include: an enclosure  30  enclosing the laser diode  24 , the optical device and the reflector  26 , and a heat exchanger or heatsink  32  assembled to the laser diode  24 . The heat exchanger  32  is preferably a finned heatsink made from a material of good thermal conductivity such as aluminum. 
     The enclosure  30  includes a lateral orifice  34  allowing the light ray emitted by the laser diode  24  and deflected by the reflector  26  to exit towards the wavelength converter device  16 . 
     The wavelength converter device  16  is for example formed of a substrate in the form of a plate  36  able to reflect the laser radiation onto which is deposited a continuous layer  38  of luminophore. The plate  36  is for example made of aluminum. 
     The continuous layer  38  of luminophore is disposed in a plane (Y, Z). The first lighting device  12  and the second lighting device  14  are respectively disposed above and below the continuous layer  38  along Z. 
     The plane (Y, Z) of the continuous layer  38  is close to a focal plane of the imaging optical system  18 . The imaging optical system  18  includes for example one or more lenses  40 . 
     In the example from  FIG. 1 , the support  22  of the lighting module  10  includes two separate components, to be more precise a lens assembly  42  and a casing  44 . The lens assembly  42 , the casing  44  and the wavelength converter device  16  are represented in an exploded perspective view in  FIG. 2 . The casing  44  is represented from behind in  FIG. 3 . 
     The lens assembly  42  and the casing  44  are assembled to each other, for example screwed together. The plate  36  of the wavelength converter device  16  is held between the lens assembly  42  and the casing  44  along the axis  23 , the continuous layer  38  of luminophore being oriented towards the lens assembly  42 . 
     The lens assembly  42  has a substantially parallelepiped shape with respective walls disposed in planes (X, Y), (X, Z) and (Y, Z). 
     The lens assembly  42  notably includes a front opening  48  and a rear opening  50  in respective walls disposed in the plane (Y, Z). The lens assembly  42  is assembled to the imaging optical system  18  at the level of the front opening  48 . The lens assembly  42  is further assembled to the plate  36  of the wavelength converter device  16  at the level of the rear opening  50 . 
     The lens assembly  42  also includes a top opening  52  and a bottom opening  54  in respective walls in the plane (X, Y). The lens assembly  42  is assembled to the first lighting device  12  and the second lighting device  14  at the level of the top opening  52  and the bottom opening  54 , respectively. The top opening  52  and the bottom opening  54  each face the lateral orifice  34  of the enclosure  30  of the first lighting device  12  and the second lighting device  14 . 
     The casing  44  also has a substantially parallelepiped shape. The casing  44  notably includes a back  60 , disposed in the plane (Y, Z), and lateral external walls in the plane (X, Y) and (X, Z), respectively. 
     Moreover, the casing  44  includes two internal walls  62 ,  64  disposed on respective opposite sides of a plane of symmetry (X, Y) of the casing, the plane of symmetry passing through the optical axis  23 . The internal walls  62 ,  64  bear on the lateral external walls in the plane (X, Z) of the casing  44 . 
     The internal walls  62 ,  64  divide the interior of the casing  44  into three separate ducts  66 ,  68  and  70  isolated from one another and contiguous along Z. In particular, the casing  44  includes a central duct  68  and two lateral ducts  66  and  70 . 
     The back  60  of the casing  44  includes three openings  72 ,  74  and  76  contiguous along Z. Each of the openings forms an inlet of a respective one of the ducts  66 ,  68  and  70 . The fan  20  is assembled to the back  60  so as to cover the openings  72 ,  74  and  76 . A flow of air generated by the fan  20  is therefore divided between the three separate ducts  66 ,  68  and  70 . 
     The heatsink  32  of each of the first lighting device  12  and the second lighting device  14  is disposed inside the casing  44  in one of the two lateral ducts  66  and  70 . A flow of air passing through each lateral duct  66 ,  70  is therefore able to cool a laser diode  24  via the corresponding heatsink  32 . 
     The plate  36  of the wavelength converter device  16  is disposed at the outlet of the central duct  68  in contact with the edges of the internal walls  62 ,  64  and opposite the opening  74 . The casing  44  preferably includes holes  80  in the vicinity of the plate  36  to form an air outlet of the central duct  68 . 
     A flow of air passing through the central duct  68  is therefore able to cool the plate  36 . 
     The position of the internal walls  62 ,  64  is configured so as to direct onto the plate  36  of the wavelength converter device  16  a fraction between 10% and 40% inclusive, preferably between 15% and 25% inclusive, of the flow of air generated by the fan  20 . Each heatsink  32  therefore receives between 30% and 45% inclusive of the flow of air. 
     A method of operating the lighting module  10  will now be described. When each of the laser diodes  24  is fed with electricity, it emits laser radiation that is directed towards the wavelength converter device  16  by the reflector  26  that forms a scanning system. A number of points of the continuous layer  38  of luminophore therefore receive the laser radiation from the laser diode  24  successively. 
     In known manner, each point of the continuous layer  38  receiving the monochromatic and coherent “blue” laser radiation re-emits light considered “white”, i.e. including a plurality of wavelengths between approximately 400 nm and approximately 800 nm inclusive. 
     The imaging optical system  18  then forms an image at infinity of the light spots of the continuous layer  38  of luminophore in the form of a light beam able to illuminate the road in front of a vehicle. 
     The wavelength conversion process heats the plate  36  of the wavelength converter device  16 . Moreover, the heat diffused by each laser diode  24  is dissipated in the corresponding heatsink  32 . 
     The fan  20  generates a flow of air divided into three separate flows, one in each of the ducts  66 ,  68  and  70 . Each of the flows of air cools the plate  36  or one of the heatsinks  32 , preventing overheating of the lighting module  10 . 
     The shape of the casing  44  enables the formation in parallel of three separate flows of air from a single fan  20 . It is therefore possible to modulate the quantity of air directed onto each of the components of the lighting module  10  liable to become heated in operation. 
     While the system, apparatus, process and method herein described constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise system, apparatus, process and method, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.