EP2410237A1 - Reflector of the corrected elliptical type - Google Patents

Abstract

The module has a dioptric element (4) provided with an optical axis (2), and receiving luminous rays reflected by reflectors (10). A transparent material bar (6) is arranged between the reflectors and the dioptric element. A reflective surface is formed such that the rays emitted by a light source and originated from a combustor (22) passes through another combustor (24) after reflexion on the reflective surface and refraction at the passage in the bar. An independent claim is also included for a method for optimizing a lighting module of a headlamp of a motor vehicle.

Description

The invention relates to a lighting module for a motor vehicle headlamp as well as to a method of optimizing such a module. More particularly, the lighting module comprises a reflector with a first and second focus, such as an elliptical reflector, a blade of transparent material disposed near the second focus, and a dioptric element such as a convergent lens.

To create cuts in the beams, it is known to use horizontal reflective covers called "folders", as for example in the patent document EP1357334 . It is known from the document FR 2 917 484 A1 to provide such a device with a reflective coating on the upper edge of a blade as a folder. This document indeed discloses an optical module comprising a double reflector of the elliptical type with a first focus where a light source is arranged, a second focus, a dioptric element of the biconvex lens type whose focus coincides with the second focus of the reflector, and a blade of transparent material disposed perpendicularly to the optical axis of the module. The slice or upper surface of the transparent blade is generally flat and aligned with the optical axis and covered with a reflective coating. The leading edge of the wafer, i.e., the edge of the wafer on the side of the lens is in the vicinity of the second focus. The reflective coating on the upper edge of the transparent strip consists for example of an aluminum deposit deposited under vacuum with a thickness ranging from less than a micron to a few tens of microns. The reflective coating constitutes a "folder" able to "fold" by reflection the rays coming from the upper reflector to ensure a cutoff of the "code" type beam thus generated. The rays from the lower reflector are added to those of the upper reflector to provide the "road" function. The bender thus formed has the advantage of being extremely thin which is particularly interesting in "road" function to avoid a dark area between the beams "code" and "road". Such fineness of bending is difficult to achieve by means of a reflective plate, at least in an industrial logic and at a reasonable price.

The blade serving as a support for the reflective coating, however, has the drawback of having a refractive index greater than 1 and hence of refracting the rays coming from the lower reflector. The use of a transparent support blade therefore generates a slight deviation of the rays that otherwise would pass through the second focus. This results in a loss of efficiency and lighting quality, the maximum intensity being lower than in the absence of blade. In addition, the lighting of the "code" type is provided by the establishment of a movable concealing cover between the folder and the lens. This construction leads to losses of efficiency since a portion of the lighting power is lost in the housing of the projector in lighting type "code".

The patent document FR 2 858 042 A1 discloses a lighting device comprising two elliptical reflectors arranged in opposition to a plane comprising the optical axis of the device. It differs from that of the preceding document essentially in that each reflector comprises its own light source, the lower reflector is inclined so that its optical axis forms an angle with the optical axis of the device and the upper reflector. This construction eliminates the cache of the previous teaching and allows a little room for cooling light sources. They are in fact preferably light sources of the light emitting diode type that generate a certain amount of heat and require suitable cooling. The device of this document differs from the previous teaching also in that the support of the coating forming the folder is no longer shaped blade but rounded part with a substantially flat upper face for the coating. The rounded surface of the support is generally spherical centered on the second focus. The rays from the lower reflector penetrate the transparent support to the normal of its outer surface so that the rays are not deflected by refraction. This part is ideally made of PMMA (polymethyl methacrylate). The production of this support piece is quite expensive on an industrial scale, especially when it is made of glass. The use of plastic material has indeed been problematic because of the presence of the lens that can cause overheating of this room by the outside light ("sun burn"). Glass is therefore preferred. In addition, this piece has a significant thickness in comparison with the blade of the previous teaching, which increases the intrinsic losses by absorption.

Patent Application No. FR09 / 56728 of the same applicant as the present application and not yet published at the filing date of the present application relates to a lighting module comprising a double blade consisting of two superimposed blades with a slight clearance so as to form two diopters between the transparent material and the thin layer of air trapped between the two blades, these dioptres to ensure a total reflection phenomenon and thus play the role of folder. The face of the blade facing the lower reflector ensuring the "road" function has a particular profile in order to recover some rays that would otherwise be lost. Just like teaching the document FR 2 917 484 A1 , the use of transparent blades generates a slight deviation of the rays that otherwise would pass through the second focus and, therefore, a loss of efficiency and lighting quality, including glassy reflections.

The object of the invention is to propose a lighting module that is more efficient than the modulators mentioned above.

• un premier réflecteur avec une surface réfléchissante, avec au moins un premier foyer pour une source lumineuse et un second foyer;
• un élément dioptrique avec un axe optique, disposé de manière à recevoir les rayons lumineux réfléchis par le premier réflecteur et à transmettre les rayons lumineux l'atteignant en un faisceau lumineux ; cet élément dioptrique peut par exemple être une lentille convergente ;
• une lame en matériau transparent, disposée entre le premier réflecteur et l'élément dioptrique ;

la surface réfléchissante étant formée de manière à ce que des rayons émis par la source lumineuse et partant du premier foyer passent approximativement par le second foyer après réflexion sur la surface réfléchissante et réfraction au passage dans la lame.The object of the invention relates to a lighting module for a motor vehicle headlamp, comprising:

• a first reflector with a reflective surface, with at least a first focus for a light source and a second focus;
• a dioptric element with an optical axis, arranged to receive the light rays reflected by the first reflector and to transmit the light rays reaching it in a light beam; this dioptric element may for example be a convergent lens;
• a blade of transparent material disposed between the first reflector and the dioptric element;

the reflecting surface being formed in such a way that rays emitted by the light source and starting from the first focus pass approximately through the second focus after reflection on the reflective surface and refraction when passing through the blade.

Thus, the reflective surface according to the present invention is corrected compared to the two-focus reflective surfaces of the prior art. In the prior art the shape of the reflector is such that the light rays emitted by the light source and from the first focus are reflected to the second focus. Blade use with these systems of the prior art causes the deviation of the rays starting from the first focus before they reach the second focus. After refraction these rays, which initially left the first focus, no longer pass through the second focus. On the other hand, according to the invention, the surface is such that it is after refraction that these rays starting from the first focus pass through the second focus. Thus, according to the present invention, a corrected two-focus surface.

These measurements make it possible to simply optimize the reflector by correcting at least a portion of its reflective surface in order to compensate for the refractive effect of the blade. This improves the reflector photometry with a blade between the reflector and the lens. The use of a blade between the reflector and the lens can be done in different ways. The use of a blade, however, causes light losses of the order of a few percent, for example of the order of 10%, depending on the material and the thickness of the blade. It is therefore important for reasons of efficiency to optimize the optics of the module. The proposed correction provides a more concentrated beam and better photometry. This also makes it possible to optimize the use of a blade as a folder support, and thus to have a folder of particularly thin thickness, particularly in an application where the folder serves as a cutoff for a first cut-off beam adding to a second complementary beam cut, to avoid a dark area between the beams. For example, a dark zone is avoided between a code beam with an upper cut and a complementary beam with a lower cut, the complementary beam associated with the code beam forming a road beam.

The reflective surface may for example be a corrected ellipsoid portion surface, i.e., a surface modified with respect to an ellipsoid portion surface so as to compensate for the refraction of the blade.

According to an advantageous embodiment of the invention, the corrected reflecting surface is such that it transforms a spherical wave surface in the air coming from a given point of the light source into a spherical wave surface in the material of the blade centered approximately at the second focus. This given point is for example the center of the light source.

The corrected reflecting surface corresponds to a surface calculated on the basis of the Fermat principle of inverse light return and stationarity of the optical path followed by light along a path, starting from a beam of inverse rays passing through the second focus.

The calculated area is obtained by vector calculation of the inverse ray beam reflected by an imaginary surface corresponding to the area to be calculated, which is determined by imposing the constancy of the optical path along the calculated paths.

According to another advantageous embodiment of the invention, the blade is arranged to have a generally flat wafer and generally aligned with the optical axis of the dioptric element, said wafer forming a bender adapted to reflect a portion of the rays reflected by the reflective surface of the first reflector towards a portion of the dioptric element. Preferably, the edge of the blade is covered with a reflective coating. The upper surface of the blade thus forms a folder with a particularly thin thickness, for example in order to avoid a dark area between the "road" and "code" beams.

According to yet another advantageous embodiment of the invention, the edge of the edge of the blade on the side of the dioptric element is approximately at said second focus.

According to another advantageous embodiment of the invention, the optical axis of the first reflector forms an angle with the optical axis of the dioptric element, preferably an angle of more than 10 °, more preferably an angle of more than 20 °. , more preferably still an angle of more than 30 °. Preferentially, this angle is less than 50 °. These angles make it possible to optimize the yield.

According to yet another advantageous embodiment of the invention, the first reflector is arranged so that its reflecting surface moves away from the optical axis of the dioptric element when said reflective surface approaches its first focus. For example, when the optical axis of the dioptric element is horizontal, the first focus of the reflecting surface is located below the optical axis of the dioptric element.

The proposed reflective surface correction is particularly interesting for this configuration of the reflector, namely when it is inclined and moreover when it is "turned over". Indeed, in this configuration, the rays penetrate the blade with a greater angle of incidence and therefore undergo a greater deviation. The correction compensates for this deviation.

According to another advantageous embodiment of the invention, the module comprises a second reflector with a reflective surface, at least a first focus for a light source, a second focus, said reflecting surface being able to reflect the rays emitted by said light source. from said first focus to said second focus, said second focus being approximately coincident with the second focus of the first reflector, the optical axis of the second reflector forming an angle with the optical axis of the first reflector, the first and second reflectors being oriented by relative to their axes so that the reflecting surface of the second reflector is vis-à-vis the outer surface of the first reflector, this outer surface being the opposite surface to the reflecting surface of the first reflector. For example, the reflective face of the second reflector is facing the back of the second reflector.

Preferably, the light source or sources are electroluminescent diodes.

The invention also consists in a method for optimizing a lighting module of a motor vehicle headlamp, the module comprising: a first reflector with a reflective surface, with at least a first focus for a light source and a second home; a dioptric element with an optical axis, arranged to receive the light rays reflected by the first reflector and to transmit the light rays reaching it in a light beam; a blade of transparent material disposed near said second focus. This method comprises a step of producing the reflective surface of the first reflector. This embodiment comprises the correction of a reflective surface capable of reflecting the light rays emitted by the light source from the first focus to the second focus, this correction being performed so that rays emitted by said light source and starting of the first focus pass approximately through said second focus after reflection on said reflective surface and refraction when passing through said blade. For example, the correction of said reflective surface can be carried out by vector calculation of the optical path of a beam of inverse rays which, according to the principle of the inverse return of light, pass through the second focus then the blade, leave the blade with refraction and are then reflected by an imaginary surface corresponding to the surface to be calculated, the area to be calculated being obtained by applying the principle of Fermat reverse light reversal and stationarity of the optical path followed by light along a path .

According to an advantageous embodiment of the invention, the reflecting surface of the first reflector is obtained by vector calculation of the optical path of a beam of inverse rays reflected by an imaginary surface corresponding to the surface to be calculated.

According to another advantageous embodiment of the invention, the beam of inverse rays passes through the second focus then the blade, leaving the blade with refraction and then reflected by an imaginary surface corresponding to the surface to be calculated.

According to another advantageous embodiment of the invention, the module is a module according to the invention as defined above.

The first reflector and / or the second reflector is / are preferably in the form of a half-shell.

• La figure 1 est une vue en perspective d'un mode de réalisation d'un module d'éclairage selon l'invention.
• La figure 2 est une vue en coupe du mode de réalisation illustré en figure 1 avec tracé de rayons.
• La figure 3 est une vue schématisant le fonctionnement du réflecteur inférieur du module illustré en figure 2.
• La figure 4 est une vue agrandie de la lame d'un module d'éclairage selon l'invention.
• La figure 5 est une vue d'un module d'éclairage selon l'invention illustrant les points de référence, le référentiel et les vecteurs utilisés pour un exemple de calcul de la surface du réflecteur.
• La figure 6 est une première vue illustrant l'impact de la correction du réflecteur.
• La figure 7 est une seconde vue illustrant l'impact de la correction du réflecteur.

Other features and advantages of the present invention will be better understood from the description and the drawings, among which:

• The figure 1 is a perspective view of an embodiment of a lighting module according to the invention.
• The figure 2 is a sectional view of the embodiment illustrated in FIG. figure 1 with ray tracing.
• The figure 3 is a schematic view of the operation of the lower reflector of the module illustrated in figure 2 .
• The figure 4 is an enlarged view of the blade of a lighting module according to the invention.
• The figure 5 is a view of a lighting module according to the invention illustrating the reference points, the reference frame and the vectors used for an example of calculation of the surface of the reflector.
• The figure 6 is a first view illustrating the impact of reflector correction.
• The figure 7 is a second view illustrating the impact of reflector correction.

In the description of the invention, the terms "front", "back", "top", "bottom", "upper" or "bottom" are understood according to the position of the lighting module according to the figures and once integrated in a projector and mounted on a vehicle in conventional operating mode. It is recalled that the module could be mounted and used in other positions and / or orientations without departing from the invention. The terms mentioned above are therefore to be interpreted in a relative and not absolute manner.

It should also be noted that the optical elements are illustrated in the figures in a simplified manner with perfect matching of the focal points and optical axes for the sake of clarity of presentation. Such matches are not to be interpreted strictly, since in practice there may be slight deviations due to the imperfect nature of certain elements, mounting tolerance and / or to correct some effects related to imperfection of certain optical elements. The same applies to the light sources which are represented in a specific way, whereas it is clear that in practice these light sources are not perfectly punctual and have a light emission surface that has been chosen here. voluntarily not to represent.

To the figure 1 is schematically illustrated in perspective a lighting module according to the invention. It comprises a convergent lens 4 with a focus 24 and an optical axis 2 passing through the focus. A transparent plate 6 is disposed generally perpendicularly to the optical axis 2, or generally vertically in the half-space delimited by a horizontal median plane passing through the optical axis 2. The blade has a generally flat upper edge 26 comprising the axis optical 2 and at least approximately passing through the plane in question. The upper edge 26 is covered with a reflective coating. This coating is applied exclusively to the wafer 26, leaving the other faces transparent blade. The blade is arranged so that the front edge is at the focus 24. The wafer 26 has a projection at its median corresponding to the optical axis 2. The function of the jump will be explained further later. The blade is made of transparent material such as glass or any other transparent material, for example PMMA (polymethyl methacrylate).

It should be noted that the edge 26 of the blade can perform the folding function without the presence of a reflective coating, and this by the use of the principle of total reflection on a diopter formed by the interface between two media index of different refraction. In this case, it will be necessary to ensure that the rays meet the diopter formed by the wafer with an angle of incidence greater than the limit angle of total reflection.

The module also comprises a first reflector 10 in the lower half-space. It is represented schematically by its reflective surface. This surface has an approximate elliptical profile, symmetrical in rotation about its optical axis 20. It comprises a first focus 22 intended to receive a light source and a second focus coinciding with the focus 24 of the lens 4. The optical axis 20 of the first reflector forms an angle with the optical axis 2 which is between 30 ° and 60 °, preferably between 40 ° and 50 °. The light source mainly illuminates in a half-space delimited by the transverse plane comprising the optical axis 20 of the reflector and is preferably of the type of diode electrolum inescente.

The module also comprises a second reflector 8 represented by its reflecting surface. It is composed of two reflecting sub-surfaces of symmetrical elliptical profile in revolution with respect to the respective optical axes 12 and 14. Each reflective sub-surface includes a first focus 16 or 18 for receiving a light source and a second focus coinciding with focus 24 of the lens and the second focus of the first reflector. The reflecting surface of the second reflector 8 consists of the juxtaposition of the two sub-surfaces in a half-space delimited by a plane passing through the respective optical axes 12 and 14 and the optical axis 2 of the lens 4, so as to form a doubly concave cavity able to reflect the light rays coming from the first The two respective optical axes 12 and 14 form an acute angle between them and each form an angle equal to the optical axis 2 of the lens and the module.

The lighting module also comprises a reflective plate 9 on its two faces and disposed approximately in the plane passing through the optical axes 12 and 14 of the second reflector and the reflecting edge 26 of the blade 6. It is disposed adjacent or almost -Adjacent to the rear edge of the wafer and extends to a distance from this rear edge. The rear edge of the plate 9 reaches approximately the height of the intersection of the reflecting surface of the first reflector 10 with said plane. More specifically, the profile of the rear edge of the reflective plate 9 is V-shaped whose tip is aligned with the optical axis and symmetry 2 of the module and directed rearwardly, so that the reflecting surface of the plate covers a major part of the area defined by the intersection of the reflective surface of the first reflector with the plane. The reflective plate 9 plays the role of complementary folder and will be explained later.

It should be noted that the optical axes 12 and 14 of the reflective sub-surfaces of the second reflector 8 need not be included in the horizontal median plane. Indeed, they can form a certain angle with this plane.

A sectional view and optical principle of the device of the figure 1 is illustrated in the figure 2 . For reasons of simplicity of exposition, it has been chosen to assimilate the second reflector to a single reflective surface with a single first focus and a single light source. This simplification does not alter the operating principle of the second reflector comprising two reflecting sub-surfaces and two light sources.

The second reflector 8 generates with its light source or sources 16 and 18 a cut-off beam ensuring for example a lighting function of the "code" type. Indeed, the majority of the rays emitted by the light source are reflected by the reflecting surface of the second reflector 8 to the second focus 24 and are transmitted by the lens in a beam of substantially parallel rays. Such a ray is illustrated by a solid line from the light source 16, 18 to the lens through the reflective surface and the second focus 24. Some rays, especially those emitted from a front lateral area of the light source, meet the folder 26 at the rear of the focus 24. They are reflected or "folded" towards an upper part of the lens with an angle of incidence such that they come out of the lens tilted slightly down. Such a ray is illustrated by a dashed line at the top of the figure. The folder thus plays the role of a cache in a conventional projection system and the projection of its edge forms the horizontal cut of the projected beam, this cutoff being useful in particular for a lighting function of the "code" type. It should be noted that, as previously mentioned, the folder comprises a projection at the front edge, so-called cutting edge, so that the cut is higher on one side than the other of the vertical median plane in order to project a cut. beam type "code" in accordance with the legislation.

Most of the rays emitted by the light source 22 of the first reflector 10 are reflected by the reflecting surface of the reflector, pass through the blade 6, pass through the focus 24, are projected by the upper part of the lens 4 and are added to the beam from the upper reflector to provide the "road" function. Such a radius is illustrated by a train interrupted at the bottom of the figure.

The figure 3 is a view similar to that of the figure 2 where among the two reflectors, only the lower reflector, namely the first reflector, is illustrated. This view is enlarged and illustrates certain optical features of the module according to the invention. A first ray interrupted and corresponding to that of the figure 2 is illustrated. It is emitted by the light source 22, is reflected by the reflective surface, penetrates the transparent plate 6 and undergoes a first refraction, passes through the blade, passes through the focus 24, leaves the blade and undergoes a second refraction before meeting the lens in its upper half. A second ray is shown in solid lines. It is emitted by an off-center zone of the light source 22 and is reflected towards an area of the folder slightly behind the second focal point 24. Like the first ray, it penetrates the blade, undergoes a first refraction, passes through the blade until to meet the folder 26, is reflected down, crosses the rest of the thickness of the blade, leaves the blade, undergoes a second refraction downwards and meets the lens in its lower half. This ray will then be transmitted and deflected by the lens towards the upper part of the illumination beam. An enlarged view from the top of the blade illustrates the phenomena of refraction and reflection of these two typical rays.

The upper edge of the blade forming the folder is ideally inclined from the cutoff edge to the bottom of the module to further concentrate the rays reflected by the folder. The figure 4 is an enlarged view of the top of the blade. The upper edge 26 included in the horizontal median plane is illustrated in solid lines. The inclined upper edge 36 is shown in broken lines. It has a clearance angle 13 with respect to the horizontal median plane. This angle corresponds to a clearance of height d at the rear face of the blade. A ray 28 from the first reflector 10 and penetrating the blade is illustrated. It is refracted and undergoes a first deflection 30. It is then reflected by the non-inclined folder into a radius 32 traversing the remainder of the thickness of the blade and then out by undergoing a second refraction 34. The point of emergence of the radius is at a distance e from the cutoff edge. This ray comes out of the blade at an angle with the normal to the front face of the blade. The same incident ray of the blade will be reflected by the inclined bender 36 in a radius 38 less inclined than the corresponding radius 32. This ray 38 will then leave the blade at an emergence point at a distance e 'of the cutting edge this distance e 'being less than the distance e. The outgoing ray 40 undergoes a second refraction and forms an angle α 'with the normal to the front face of the blade which is less than the value α of the same incident ray reflected by the inclined bender 36. Because of these two effects, the Outgoing ray 40 will meet the lens at a lower incident angle and at a point closer to the optical axis. The projected beam from such rays will therefore be closer to the horizontal and provide higher photometric illumination due to lower losses by glassy reflections, especially on the front face of the blade and on the faces of the lens.

It should be noted that the material of the blade will preferably be glass as opposed to plastic materials for reasons of temperature resistance. Indeed, the presence of the lens has the effect that the external sunlight can concentrate via the lens at the focus 24 and overheat the material of the blade. The edge of the blade opposite the edge serving as a folder may also be similarly inclined, and this symmetrically so as to reduce the height of the rear face of a given value. Although this slice of the blade does play no role from the point of view of optics, such inclination or clearance angle simplifies the shaping of the blade by simplifying demolding in a direction perpendicular to the front and rear faces. The optical faces can then be surfaced to ensure flatness and optical qualities.

The reflective surface of the first reflector is corrected to compensate for the first refraction to which the rays are subjected upon entry into the blade. The calculation of the correction of the surface will be described below in relation to the figure 5 .

The calculation is based on the application of the Huygens principle and Fermat's optical path principle.

Indeed, according to the principle of Huygens, the light spreads from one to the next, the set of points of equal light disturbance being called the wave surface. Each point of this surface reached by light behaves like a secondary source that emits spherical wavelets in an isotropic medium. The envelope surface of these wavelets forms a new wave surface.

Light propagates more difficultly or more slowly in environments other than vacuum. The middle index n is defined by
n = c / v
where c and v are the speed of light in the vacuum and in the medium, respectively.

où s désigne l'abscisse curviligne le long du chemin parcouru dans le milieu entre les points A et B, et AB la longueur du chemin parcouru entre A et B. Le principe de Fermat s'énonce : entre deux points A et B, atteints par la lumière, le chemin optique suivi le long du trajet est stationnaire. Il résulte notamment: $$L\left(\mathit{AB}\right)={\displaystyle {\int }_A^B}{}_{}\mathit{nds}={\displaystyle {\int }_B^A}n\left(-\mathit{ds}\right)={\displaystyle {\int }_B^A}\mathit{nds}ʹ$$

en considérant que ds'=-ds est l'élément de coordonnée curviligne de B vers A, on peut alors écrire que $$L\left(\mathit{AB}\right)=L\left(\mathit{BA}\right)$$

The optical path is the path traveled by the light traveled in a vacuum during the propagation time in the medium: $$\mathrm{The}\left(\mathit{AB}\right)={\displaystyle {\int }_{t_{\mathrm{AT}}}^{t_B}}\mathit{cdt}={\displaystyle {\int }_{\mathrm{AT}}^B}\mathit{nds}=\mathrm{vs}\left(t_B-t_{\mathrm{AT}}\right)=\mathrm{not}\cdot \mathit{AB}$$

where s denotes the curvilinear abscissa along the path traveled in the middle between points A and B, and AB the length of the path traveled between A and B. The Fermat principle is stated: between two points A and B, reached by the light, the optical path followed along the path is stationary. It results in particular: $$\mathrm{The}\left(\mathit{AB}\right)={\displaystyle {\int }_{\mathrm{AT}}^B}{}_{}\mathit{nds}={\displaystyle {\int }_B^{\mathrm{AT}}}\mathrm{not}\left(-\mathit{ds}\right)={\displaystyle {\int }_B^{\mathrm{AT}}}\mathit{nds}\text{'}$$

considering that ds' = - ds is the curvilinear coordinate element from B to A, we can then write that $$\mathrm{The}\left(\mathit{AB}\right)=\mathrm{The}\left(\mathit{BA}\right)$$

This is the reverse principle of light: the path followed by the light to go from one point to another does not depend on the direction of propagation of light.

• Un référentiel x-y-z centré en O est illustré à la figure. Un vecteur
  
  de longueur égale à 1, originaire du point O et orienté selon le chemin inverse de la lumière dans la lame depuis le point O où ϕ est le complément de l'angle avec l'axe z et θ le complément de l'ange avec l'axe y et s'écrit : $$\overrightarrow{r}=\left(\begin{array}{c}\mathit{-}\mathit{cos\; \phi }\cdot \mathit{cos\; \theta }\\ \mathit{cos\; \phi }\cdot \sin \theta \\ \sin \mathit{\phi }\end{array}\right)$$
  

The reverse optical path from an emergence point O corresponding to the focus 24 to the light source F is calculated as follows:

• An xyz repository centered at O is shown in the figure. A vector
  
  of length equal to 1, originating from the point O and oriented along the inverse path of the light in the plate from the point O where φ is the complement of the angle with the axis z and θ the complement of the angel with the axis y and is written: $$\overrightarrow{r}=\left(\begin{array}{c}\mathit{-}\mathit{cos\; \phi }\cdot \mathit{cos\; \theta }\\ \mathit{cos\; \phi }\cdot \sin \theta \\ \sin \mathit{\phi }\end{array}\right)$$
  

$$\mathit{\lambda }\sin \mathit{\phi }=\epsilon$$

où ε est l'épaisseur de la lame.
Il s'ensuit : $$O=P+\frac{\epsilon }{\sin \mathit{\phi }}\overrightarrow{r}$$

The first optical path section OP is written: $$O+\mathit{\lambda }\overrightarrow{r}=\mathit{OP}$$

$$\mathit{\lambda }\sin \mathit{\phi }=\epsilon$$

where ε is the thickness of the blade.
It follows: $$O=P+\frac{\epsilon }{\sin \mathit{\phi }}\overrightarrow{r}$$

où

est le vecteur normé originaire du point P orienté selon le rayon inverse vers le réflecteur, il s'ensuit que i_x = n_rx et i_y = nr_y Etant donné que le module de

est égal à 1, il s'ensuit que $$n^2\left(r_x^2+r_y^2\right)+i_z^2=1$$

et $$i_z=\sqrt{1-n^2{\left(\cos {}_{}\mathit{\phi }\right)}^2}$$

d'où on peut calculer

. Le point M est un point de la surface réfléchissante à calculer, d'où $$P+\mu \overrightarrow{\iota }=M$$

$$\mathit{PM}+\mu +n\mathit{\lambda }=K$$

où K, qui est le chemin optique de O à F est une constante en application du principe de Fermat. Il s'ensuit $${\left(\overrightarrow{\mathit{FP}}+\mu \overrightarrow{\iota }\right)}^2={\left(K-n\lambda -\mu \right)}^2$$

$$\to {\mathit{FP}}^2+{\mu }^2+2\mu \overrightarrow{\mathit{FP}}\cdot \overrightarrow{\iota }={\left(K-n\mathit{\lambda }\right)}^2+{\mu }^2-2\left(K-n\lambda \right)\mu$$

$$\to 2\mu \left(\overrightarrow{\mathit{FP}}\cdot \overrightarrow{\iota }+K-n\lambda \right)={\left(K-n\lambda \right)}^2-{\mathit{FP}}^2$$

However, in the application of the law of Snell-Descartes only the angle φ changes with the passage of the diopter, so that $\mathrm{not}\cdot \overrightarrow{r}-\overrightarrow{i}\alpha \overrightarrow{z},$

or

is the normalized vector originating from the point P oriented according to the inverse radius towards the reflector, it follows that i _x = n _rx and i _y = nr _y Given that the modulus of

is equal to 1, it follows that $${\mathrm{not}}^2\left(r_x^2+r_{\mathrm{there}}^2\right)+i_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">z</figure-callout>}}^2=1$$

and $$i_z=\sqrt{1-{\mathrm{not}}^2{\left(\cos {}_{}\mathit{\phi }\right)}^2}$$

from where we can calculate

. Point M is a point on the reflecting surface to be calculated, hence $$P+\mu \overrightarrow{\iota }=M$$

$$\mathit{PM}+\mu +\mathrm{not}\mathit{\lambda }=K$$

where K, which is the optical path from O to F, is a constant in application of the Fermat principle. It follows $${\left(\overrightarrow{\mathit{FP}}+\mu \overrightarrow{\iota }\right)}^2={\left(K-\mathrm{not}\lambda -\mathrm{<figure-callout\; id="2"\; label="\mu "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\mu </figure-callout>}\right)}^2$$

$$\to {\mathit{<figure-callout\; id="2"\; label="FP"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">FP</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="\mu "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\mu </figure-callout>}}^2+2\mu \overrightarrow{\mathit{FP}}\cdot \overrightarrow{\iota }={\left(K-\mathrm{not}\mathit{<figure-callout\; id="2"\; label="\lambda "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\lambda </figure-callout>}\right)}^2+{\mu }^2-2\left(K-\mathrm{not}\lambda \right)\mu$$

$$\to 2\mu \left(\overrightarrow{\mathit{FP}}\cdot \overrightarrow{\iota }+K-\mathrm{not}\lambda \right)={\left(K-\mathrm{not}\lambda \right)}^2-{\mathit{<figure-callout\; id="2"\; label="FP"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">FP</figure-callout>}}^2$$

est connu étant donné que les points F et P sont connus, le vecteur

a été calculé sur base du calcul sus mentionné et λ est connu, il suffit alors de poser une constante K qui convient pour alors calculer la valeur de p et en déduire un point de la surface pour un vecteur

donné. On peut ensuite itérer sur base d'un faisceau de rayons inverses et en déduire les coordonnées de la surface réfléchissante. L'homme de métier n'aura aucune difficulté à mettre en oeuvre un pareil calcul notamment par des méthodes de calcul numérique itératives.The vector

is known since the points F and P are known, the vector

has been calculated on the basis of the above-mentioned calculation and λ is known, it is then sufficient to set a constant K which is suitable for then calculating the value of p and deducing a point from the surface for a vector

given. We can then iterate on the basis of a beam of inverse rays and deduce the coordinates of the reflecting surface. The skilled person will have no difficulty in implementing such a calculation including numerical iterative calculation methods.

In other words more physical, the reflector is corrected so as to transform a spherical wave surface from a source point F to the surface of the emitter into a spherical wave surface in the material of the blade, centering the second focus 24, this second focus being located in the material of the blade in the vicinity of its front exit face and its upper face (slice).

The elliptical reflective surface correction is applicable to various configurations, including the configuration of the reflector 10 of the present invention, as well as to a conventional configuration as shown in broken line at the end of FIG. figure 5 .

It should be noted that the correction does not necessarily have to be made on the entire reflective surface but essentially on the area reflecting the rays that will form the central part of the beam.

The figure 6 illustrates an elliptical reflector configuration in a half-space and whose surface is generally oriented towards the optical axis of the module, showing in particular the effect of the reflective surface correction. Specifically, it illustrates a lighting module configuration with two elliptical reflectors 8 and 42 in opposite half-spaces and whose reflective surfaces are both directed towards the optical axis 2 of the module. The optical axes of the reflectors are slightly inclined to provide a space for cooling the light sources 16, 18 and 44. A first ray from the light source 44 and reflected at a point A is shown in solid lines. The broken line associated with the solid line illustrates the optical path that would follow the ray if the reflecting surface was not corrected according to the transparent blade 6; namely, this ray would be refracted as it enters the blade and would be deflected from the second focus 24. A second ray from the light source 44 and reflected at a point B closer to the optical axis of the reflecting surface is shown in a line. full. This grazing ray and directed towards the hearth 24 will meet the space dedicated to cooling and get lost instead of penetrating the blade. In this configuration, some of the rays will be lost in the cooling radiator of the light sources. This situation is all the more true as the surface of the reflector is corrected. Indeed, this correction has the effect of reflecting the rays from the light source so as to have a deviation from the second focus, this deviation being such that the rays are oriented towards a point at the rear of the second focus, which intensifies the problem of loss of rays in the space needed to cool the light sources.

The figure 7 illustrates the effect of reflective surface correction for an elliptical reflector configuration in a half-space and whose surface is generally opposite to the optical axis of the module. A first ray coming from the light source 22 and reflected at a point A of the corrected reflecting surface is shown in solid lines. In the absence of correction of the surface, this ray would point to the second focus 24 but would be deflected when it enters the blade and would pass below the focus. This line is illustrated in broken lines. Having "Turned" the reflector about 180 ° on its optical axis has on the one hand to minimize or even eliminate the thickness of the dead volume adjacent to the rear edge of the folder, and secondly tilt the rays reflected by the reflector so that most of them do not get lost in building elements of the module. The correction of the reflective surface is all the more interesting in this configuration that the average angle of incidence on the rear face of the blade is important. A second ray coming from the light source and reflected by a point B further from the optical axis of the reflector is also illustrated. This spoke will meet the complementary folder 9 so as to be returned to the blade and participate in the production of ambient light beam. It should be noted that the preferred light source is of the electroluminescence diode type. Such a source illuminates in a half-space but concentrates a major part of the lighting power in a cone centered on its main illumination axis (that is to say a perpendicular to the optical axis of the reflector), so that the configuration of the figure 7 will allow the spokes forming most of the lighting power to work optimally.

It should be noted that providing a draft angle to the edge of the blade forming the folder and as described above in connection with the figure 4 is particularly meaningful with the "upside-down" arrangement of the reflector because the rays there meet the transparent blade with a larger angle of incidence.

Claims (14)

Lighting module for a motor vehicle headlamp, comprising: a first reflector (10) with a reflective surface, with at least a first focus (22) for a light source and a second focus (24); a dioptric element (4) with an optical axis (2), arranged to receive the light rays reflected by the first reflector and to transmit the light rays reaching it in a light beam; a transparent material blade (6) disposed between said first reflector (10) and said dioptric element (4); characterized in that said reflective surface is formed in such a way that rays emitted by said light source and from the first focus (22) pass approximately through said second focus (24) after reflection on said reflective surface and refraction when passing through said blade (6) . Lighting module according to the preceding claim, characterized in that the corrected reflecting surface is such that it transforms a spherical wave surface in the air from a given point of the light source into a spherical wave surface in the material of the blade centered approximately at the second focus. Lighting module according to one of the preceding claims, characterized in that the corrected reflecting surface corresponds to a surface calculated on the basis of Fermat principle of reverse light return and stationarity of the optical path followed by light along a path, starting from a beam of inverse rays passing through the second focus. Lighting module according to the preceding claim, characterized in that the calculated area is obtained by vector calculation of the optical path of the beam of inverse rays reflected by an imaginary surface corresponding to the surface to be calculated, which is determined by imposing the constancy of the path optical along the calculated paths. Lighting module according to one of the preceding claims, characterized in that the blade (6) is arranged to have a generally flat wafer (26) which is generally aligned with the optical axis (2) of the dioptric element. (4), said wafer (26) being able to reflect a portion of the rays reflected by said reflecting surface to a portion of the dioptric element (4). Lighting module according to the preceding claim, characterized in that the edge of the edge (26) of the blade (6) on the side of the dioptric element (4) is approximately at said second focus (24). Lighting module according to one of Claims 5 and 6, characterized in that the optical axis (22) of the first reflector (10) forms an angle with the optical axis (2) of the dioptric element (4) , preferably an angle of more than 10 °, more preferably an angle of more than 20 °, more preferably still an angle of more than 30 °. Lighting module according to one of the preceding claims, characterized in that the first reflector (10) is arranged in such a way that the reflecting surface moves away from the optical axis (2) of the dioptric element (4). ) when said reflective surface approaches its first focus. Lighting module according to one of the preceding claims, characterized in that it comprises a second reflector (8) with a reflective surface, at least a first focus (16, 18) for a light source, a second focus (24). ), said reflective surface being adapted to reflect light rays emitted from said light source from said first focus (16, 18) to said second focus (24), said second focus being approximately coincident with the second focus (24) of the first reflector (10), the optical axis (12, 14) of the second reflector (8) forming an angle with the optical axis (20) of the first reflector (10), the first and second reflectors (10, 8) being oriented by relative to their respective optical axes (20; 12, 14) so that the reflective surface of the second reflector is opposite the outer surface of the first reflector; outer surface being the surface opposite to the reflecting surface of the first reflector. Lighting module according to one of the preceding claims, wherein the one or more light sources are light emitting diodes. A method of optimizing a lighting module of a motor vehicle headlamp, the module comprising: a first reflector (10) with a reflective surface, with at least a first focus (22) for a light source and a second focus (24),; a dioptric element (4) with an optical axis (2), arranged to receive the light rays reflected by the first reflector and to transmit the light rays reaching it in a light beam; a blade (6) of transparent material disposed near said second focus (24); characterized in that the method comprises a step of producing the reflective surface of the first reflector, said manufacturing step comprising the correction of a reflective surface able to reflect the light rays emitted by said light source from said first focus (22) to said second focus (24), this correction being carried out so that rays emitted by said light source and from the first focus (22) pass approximately through said second focus (24) after reflection on said reflective surface and refraction to the passage in said blade (6). . Method according to claim 11, characterized in that the reflecting surface of the first reflector (10) is obtained by vector calculation of the optical path of a beam of inverse rays reflected by an imaginary surface corresponding to the surface to be calculated. Method according to claim 12, characterized in that the reverse beam passes through the second focus (24) and then the blade (6), coming out of the blade (6) with refraction and then reflected by an imaginary surface corresponding to the surface to calculate. Method according to one of Claims 11 to 13, characterized in that the module is a module according to one of Claims 1 to 10.

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