Automotive headlight light module

Abstract

Motor vehicle headlight light module (16), comprising a laser light source (18) with which laser light (20) can be emitted, a scanner unit (22) with which laser light (20) emitted by the laser light source (18) can be repeatedly reflected onto first sub-areas (38) of a wavelength converter (24), whereby for each first sub-area (38) a second sub-area (40) containing the first sub-area (38) is excited to emit fluorescent light by a first part of the laser light incident on the first sub-area (38), and wherein a second part of the laser light incident on the first sub-area (38) is scattered, and a projection optic (28) which collects fluorescent light emitted by the wavelength converter (24) and laser light scattered by the wavelength converter (24) and directs it into an illumination zone of the light module (16), characterized in thatthat the projection optics (28) consists of an achromat (30) and exactly one additional aspherical lens (32), wherein the achromat (30) is configured to correct chromatic aberrations, and the aspherical lens (32) has a lower refractive power than the achromat (30) and is configured to reduce spherical aberration, coma, and astigmatism.

Description

[0001] The present invention relates to a motor vehicle headlight light module for a motor vehicle according to the preamble of claim 1. Such a light module has a laser light source with which laser light can be emitted. The light module further has a scanner unit with which laser light emitted by the laser light source can be repeatedly reflected onto first subregions of a wavelength converter. For each first subregion, a second subregion results in which the first subregion is contained. A first part of the laser light incident on a first subregion of the wavelength converter excites the emission of fluorescent light from the associated second subregion. A second part of the laser light incident on the first subregion is scattered (without wavelength conversion).A projection optics unit collects the fluorescent light emitted by the wavelength converter and the laser light scattered by the wavelength converter and directs the light, which together produces a substantially white mixed light, into an illumination zone of the light module. The illumination zone is, for example, an area on a roadway illuminated by the light module.

[0002] Such a light module is assumed to be known per se.

[0003] Motor vehicle headlight light modules that operate with laser light sources and scanner units can be used to generate light distributions that can be dynamically adapted to traffic conditions. An example of such a light module is known from EP 3 139 082 A1. In these headlight light modules, a wavelength converter is scanned with, for example, blue laser light. With the controllable scanning movement of the laser light beam, whose light output is simultaneously modulated, a pre-image of a desired light distribution is written onto the wavelength converter. The wavelength converter converts the laser light into white light through scattering, fluorescence, and mixing of scattered light components and fluorescent light components. The projection optics project the pre-image as a light distribution of white light into the illumination zone.

[0004] The design of the projection optics significantly influences the lighting efficiency and cost of the headlight module. Projection optics are also of interest for other headlight systems equipped with matrix light sources. DE 10 009 782 A1 shows a matrix arrangement of semiconductor light sources in combination with a projection lens for generating variable light distributions.

[0005] Compact projection lens systems for mobile applications such as smartphones or projectors are known, for example, from US 2012 / 0275029 A1. They often consist of a large number of lenses (more than three lenses) and have a short working distance (distance between the original image and the projection optics). This makes them unsuitable for applications in headlights with reflective wavelength converters, as these require a large working distance to direct a laser light beam past the projection optics onto the wavelength converter. Furthermore, projection optics for a motor vehicle headlight requires a large numerical aperture (greater than 0.3) to achieve sufficient photometric efficiency (luminous flux of the emitted light distribution normalized to the luminous flux of the laser light source).

[0006] Various achromatic lenses are known from EP 2 306 074 A2. Spotlights with scanners and complex lenses are known from EP 3 018 004 A1. FR 3 044 743 A1 shows a spotlight with a lens comprising several lenses.

[0007] Against this background, the object of the invention is to provide a motor vehicle headlight light module of the type mentioned above, which consists of as few components as possible, is easy to manufacture, has a high light efficiency and has a large working distance in order to enable the use of reflective wavelength converters.

[0008] This object is achieved by the characterizing features of claim 1. The present invention differs from the prior art, which was initially assumed to be known per se, by the characterizing features of claim 1. According to this, the projection optics consist of an achromat and precisely one additional aspheric lens, wherein the achromat is designed to correct chromatic aberrations, and the aspheric lens has a lower refractive power than the achromat and is designed to reduce spherical aberration, coma, and astigmatism.

[0009] Achromats can be manufactured cost-effectively as standard products in the optics industry. They have the advantage of good and color-corrected imaging properties for image points close to the optical axis. However, they have the disadvantage that they can only sharply image small object fields (in this case: small areas of the wavelength converter). The additional asphere, which is arranged in the beam path between the wavelength converter and the achromat, significantly improves the imaging properties for image points far from the axis, i.e., points of the wavelength converter far from the axis. The asphere has a lower refractive power (the inverse of the focal length) than the achromat. For this reason, it only slightly influences the color properties of the achromat. The asphere enlarges the image field of the achromat.

[0010] A preferred embodiment is characterized in that the aspheric lens is a meniscus lens with a convex light entry surface facing the wavelength converter.

[0011] It is also preferred that a working distance of the motor vehicle headlight light module is greater than two thirds of the focal length of the projection optics.

[0012] Furthermore, it is preferred that the aspheric lens be made of plastic. The chromatic properties of the asphere material are not critical. Therefore, aspheres made of plastic, e.g., PMMA, can also be used, as they have a relatively small Abbe number (= high dispersion). The Abbe number characterizes the dependence of the refractive index of optical materials on the light wavelength (dispersion). The smaller the dispersion, the higher the Abbe number. Aspheres are easy to manufacture from plastic.

[0013] A further preferred embodiment is characterized in that the aspheric lens consists of polymethyl methacrylate.

[0014] It is also preferred that a focal length of the aspherical lens is at least three times greater than a total focal length of the projection optics or the achromat.

[0015] It is further preferred that the projection optics are configured to image fluorescent light emanating from a point of the wavelength converter located on an optical axis of the projection optics into a fluorescent light disc and to image scattered laser light emanating from the same point into a laser light disc.

[0016] It is also preferred that the projection optics be configured to generate the laser light disc with an associated laser light aperture angle that is greater than a fluorescent light aperture angle associated with the fluorescent light disc. This reduces unwanted color fringes.

[0017] A further preferred embodiment is characterized in that the projection optics are designed to generate laser light discs and fluorescent light discs in which the aperture angle belonging to the laser light disc is up to 1.5 times larger than the aperture angle belonging to the fluorescent light disc.

[0018] It is also preferred that the aspherical lens has an aspherical light entry surface and an aspherical light exit surface.

[0019] It is further preferred that the achromatic lens has a spherical light entrance surface and a spherical light exit surface. Achromatic lenses with spherical surfaces are standard products in the optics industry and are therefore available at low cost.

[0020] A further preferred embodiment is characterized in that the achromat consists of two spherical lenses glued together.

[0021] It is further preferred that a numerical aperture of the projection optics is greater than 0.3.

[0022] A further preferred embodiment is characterized in that the wavelength converter is a reflective wavelength converter.

[0023] A reflective wavelength converter has a mirrored back surface. This prevents backscatter losses, which occur with a transmissive wavelength converter. Another advantage is that good cooling is possible from the back without disturbing the optical properties.

[0024] Further advantages will become apparent from the following description, the drawings, and the dependent claims. It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the present invention.

[0025] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

[0026] Showing, in schematic form: Fig.1 shows an embodiment of a motor vehicle headlight module according to the invention; Fig. 2 a plan view of a wavelength converter from Fig. 1; Fig. 3 an embodiment of a projection optics consisting of an achromat and an aspherical lens; Fig. 4 an achromat from the Fig. 3 without an aspherical lens; Fig. 5 a dependence of the aperture angle of a light beam emanating from a point of the wavelength converter, after passing through a projection optics without an additional aspherical lens, on the distance of the point to the optical axis; Fig. 6 a dependence of the aperture angle of a light beam emanating from a point of the wavelength converter, after passing through a projection optics with an additional aspherical lens, on the distance of the point to the optical axis; Fig.7 a dependence of the aperture angle of a light beam emanating from a point or second sub-area of ​​the wavelength converter, after passing through a projection optics without an additional aspherical lens, on the wavelength; and Fig. 8 a dependence of the aperture angle of a light beam emanating from a point or second sub-area of ​​the wavelength converter, after passing through a projection optics with an additional aspherical lens, on the wavelength.

[0027] The same reference symbols in different figures designate the same or at least functionally comparable elements.

[0028] In detail, the Fig.1 shows a motor vehicle headlight 10 with a housing 12, the light exit opening of which is covered by a transparent cover plate 14. A motor vehicle headlight light module 16 is arranged in the housing. The light module 16 has a laser light source 18 with which laser light 20 can be emitted. The laser light 20 is, for example, but not necessarily, light from the blue part of the visible light spectrum. The laser light 20 has, for example, a wavelength of 460 nm. The laser light source 18 preferably has a collimator 18.1.

[0029] The light module 16 has a scanner unit 22. The scanner unit 22 has at least one controllably movable micromirror 22.1 and a mirror actuator 22.2. The micromirror 22.1 is arranged with a reflective surface in the beam path of the collimated laser light 20. A wavelength converter 24 can be illuminated with the reflected laser light emanating from the micromirror 22.1. Depending on the mirror position, either a portion of the wavelength converter 24 is illuminated with the reflected laser light, or the reflected laser light is directed past the wavelength converter. Such light is lost for generating a light distribution. Both the mirror position and the laser light source are controlled by a control unit 25.

[0030] The wavelength converter 24 is a reflective wavelength converter. The reflective wavelength converter 24 has, for example, a mirrored rear side 24.1 and a heat sink 26 arranged in thermal contact therewith.

[0031] The light module has projection optics 28. The projection optics 28 are configured, by their nature and arrangement, to collect fluorescent light emitted by the wavelength converter 24 and laser light scattered by the wavelength converter 24 and to direct them through the transparent cover plate 14 and out of the headlight 10 into an illumination zone of the light module 16.

[0032] The projection optics 28 are characterized in that they consist of an achromat 30 and exactly one additional aspherical lens 32.

[0033] The achromat 30 is designed to correct chromatic aberrations. The additional aspherical lens 32 has a lower refractive power than the achromat 30 and is designed to reduce spherical aberration, coma, and astigmatism.

[0034] A working distance 34 of the light module 16, which here is understood to be a distance of the wavelength converter 24 from a light entry surface of the projection optics 28 facing the wavelength converter 24, is preferably greater than two-thirds of the wavelength converter-side focal length of the projection optics 28.

[0035] The working distance 34 is particularly preferably large enough to allow the reflected laser light to be incident on the wavelength converter 24 from the side. This lateral irradiation has the advantage of allowing the use of a reflective wavelength converter, which has further advantages such as good cooling and the avoidance of backscatter losses. The angle of incidence 36 of the reflected laser beam onto the wavelength converter 24 is preferably less than 60°.

[0036] Fig.2 shows a plan view of a section of the surface 24.2 of the wavelength converter 24, which faces the micromirror 22.1 and the projection optics 28. Laser light 20 reflected and collided by the micromirror 22.1 falls onto a first partial region 38 of the wavelength converter 24. The diameter of the first partial region 38 illuminated by this laser light is, for example, 50 micrometers. As a result of the illumination of the first partial region 38, a second partial region 40 is excited to fluorescence, i.e., to emit fluorescent light. The second partial region 40 is larger than the first partial region 38, and the first partial region 38 is contained within the second partial region 40. The diameter of the second partial region 40 is, for example, 200 micrometers. The fluorescent light has longer wavelengths than the exciting laser light.The wavelengths of fluorescent light, for example, lie in a yellow-red spectral range of visible light (500 - 650nm).

[0037] A third subregion 42 contains the first subregion 38 and is contained within the second subregion 40. The diameter of the third subregion 42 is larger than the diameter of the first subregion 38. At the same time, the diameter of the third subregion 42 is smaller than the diameter of the second subregion 40. The diameter of the third subregion 42 is, for example, 100 micrometers. The third subregion 42 is a subregion from which scattered laser radiation, whose wavelength has not changed, emanates. The mixing of the scattered laser light with the fluorescent light produces the desired white light.

[0038] Fig.3 shows an embodiment of a projection optics system 20 consisting of an achromatic lens 30 and an aspheric lens 32. The aspheric lens 32 is characterized by having an aspheric light entry surface 32.1 and an aspheric light exit surface 32.2. The aspheric lens 32 is a meniscus lens with a convex light entry surface 32.1 facing the wavelength converter 24. The light exit surface 32.2 is concave. The aspheric lens 32 is made of plastic, for example, polymethyl methacrylate (PMMA). A wavelength converter-side focal length of the aspheric lens 32 is at least three times greater than a total focal length of the projection optics system 28 comprising the aspheric lens 32 and the achromatic lens 30.

[0039] Fig. 4 shows the achromat 30 from the Fig.3 without the aspherical lens. The achromat 30 is characterized by having a spherical light entry surface 30.1 and a spherical light exit surface 30.2. In the example shown, the achromat 30 consists of two spherical lenses 30.3 and 30.4 bonded together.

[0040] Fig. Figure 5 shows the dependence of the aperture angle of a light beam emanating from a point or second subregion of the wavelength converter 24, which is illuminated with collimated laser light emanating from the micromirror 22, after passing through the projection optics 28, on the distance of the point from the optical axis of the projection optics. This considers a situation in which the laser beam is not moved and in which the projection optics 28 has only the achromatic lens 30, but not the additional aspherical lens 32.

[0041] Fig.Figure 6 shows the dependence of the aperture angle of a light beam emanating from a point or second sub-area of ​​the wavelength converter, which is illuminated with collimated laser light emanating from the micromirror, after passing through the projection optics, on the distance of the point from the optical axis of the projection optics. This considers a situation in which the laser beam is not moved and in which the projection optics consists of the achromat and only one additional aspherical lens arranged in the light path between the wavelength converter and the achromat.

[0042] On the abscissa are in the Fig. 5 and the Fig. 6 The distances of these points from the optical axis of the projection optics are plotted.

[0043] A comparison of the Fig. 5 and Fig.6 illustrates the influence of exactly one additional asphere 32: The aperture angles are significantly smaller for the projection optics 28 having exactly one additional aspherical optics 32 and also vary much less.

[0044] Each aperture angle corresponds at a certain distance to the size of a disc of light resulting from the point image.

[0045] The following table shows optical parameters of a projection optics that only has the achromatic lens compared to optical parameters of a projection optics that also has exactly one aspherical lens. Without asphere With asphere Spherical aberration 0,53 0,38 Coma -0,029 -0,017 astigmatism 0, 17 0, 10 Petzval field curvature 0, 14 0,14 color, tangential color 0,0013 -0,011

[0046] With the exception of the chromatic aberration (5th line), which is slightly worse in the projection optics with exactly one aspherical lens than in the projection optics that only consists of the achromat, all values ​​are improved by the addition of exactly one aspherical lens.

[0047] Fig.Figure 7 shows the wavelength dependence of the aperture angle of a light beam emanating from a point or second sub-area of ​​the wavelength converter, which is illuminated with collimated laser light emanating from the micromirror, after passing through the projection optics. This considers a situation in which the laser beam is not moving, in which the projection optics only has the achromatic lens but not the additional aspherical lens, and in which the points or second sub-areas lie on the optical axis.

[0048] Fig.Figure 8 shows the wavelength dependence of the aperture angle of a light beam emanating from a point or second sub-area of ​​the wavelength converter, which is illuminated with collimated laser light emanating from the micromirror, after passing through the projection optics. This considers a situation in which the laser beam is not moving and in which the projection optics incorporate not only the achromatic lens but also exactly one additional aspherical lens, and in which the points or second sub-areas lie on the optical axis.

[0049] The wavelengths of the light emanating from the respective point or second sub-area are plotted on the abscissa.

[0050] A comparison of the Fig. 7 and Fig.Figure 8 illustrates the influence of the one additional asphere: The aperture angles are significantly smaller for the projection optics with one additional aspherical lens. In the case of a point image, each aperture angle corresponds to the size of a disc of light at a certain distance.

[0051] Fig. Figure 8 additionally shows that the size of such a light disk increases with shortening wavelength.

[0052] This effect can advantageously be used to compensate for a chromatic aberration by the projection optics 28 being configured to image fluorescent light emanating from a point of the wavelength converter lying on an optical axis of the projection optics 28 into a fluorescent light disk and to image scattered laser light emanating from the same point into a laser light disk, wherein the projection optics is configured by the additional aspherical optics to generate the laser light disk with an associated laser light aperture angle that is greater than a fluorescent light aperture angle associated with the fluorescent light disk.

[0053] Advantageously, the projection optics 28 are configured to generate laser light discs and fluorescent light discs in which the aperture angle belonging to the laser light disc is up to 1.5 times larger than the aperture angle belonging to the fluorescent light disc.

[0054] By this design, the aperture angle of a light beam emanating from a pre-image point located on the optical axis of the projection optics 28 is optimized for the wavelength range of the fluorescent light, and at the laser wavelength, an aperture angle up to 1.5 times larger is permitted.

[0055] As explained above, illuminating the wavelength converter with laser light results in different sized sub-areas on the wavelength converter. A second sub-area, from which fluorescent light emanates, is larger than a third sub-area, from which scattered laser light emanates. The scattered laser light is, for example, blue light. The fluorescent light then has wavelengths from the yellow-red spectral range. The different sizes of the second sub-areas and the third sub-areas can then lead to the appearance of undesirable yellow-red color fringes in the illumination zone.

[0056] This undesirable effect is reduced and thus partially or completely compensated by the fact that, as Fig.As shown in Figure 8, pre-image points on the wavelength converter emitting blue light are imaged into larger light discs than pre-image points on the wavelength converter emitting fluorescent light. Because the imaging (point imaging) is better for the wavelength range of fluorescent light than for the wavelength(s) of laser light, the two wavelength components overlap in the illumination zone, reducing unwanted color effects.

Claims

[1] A motor vehicle headlight light module (16), comprising a laser light source (18) with which laser light (20) can be emitted, a scanner unit (22) with which laser light (20) emitted by the laser light source (18) can be repeatedly reflected onto first partial regions (38) of a wavelength converter (24), whereby for each first partial region (38), a second partial region (40) containing the first partial region (38) is excited to emit fluorescent light by a first part of the laser light incident on the first partial region (38), and wherein a second part of the laser light incident on the first partial region (38) is scattered, and projection optics (28) which collect fluorescent light emitted by the wavelength converter (24) and laser light scattered by the wavelength converter (24) and direct them into an illumination zone of the light module (16), characterized byin that the projection optics (28) consists of an achromat (30) and exactly one additional aspherical lens (32), wherein the achromat (30) is designed to correct chromatic aberrations, and the aspherical lens (32) has a lower refractive power than the achromat (30) and is designed to reduce spherical aberration, coma and astigmatism. [2] Motor vehicle headlight light module (16) according to claim 1, characterized by that the aspherical lens (32) is a meniscus lens with a convex light entry surface (32.1) facing the wavelength converter (24). [3] Motor vehicle headlight light module (16) according to claim 1 or 2, characterized by that a working distance (34) of the motor vehicle headlight light module (16) is greater than two thirds of the focal length of the projection optics (28). [4] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized bythat the aspherical lens (32) is made of plastic. [5] Motor vehicle headlight light module (16) according to claim 4, characterized by that the aspheric lens (32) is made of polymethyl methacrylate. [6] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized by that a focal length of the aspherical lens (32) is at least three times greater than a total focal length of the projection optics (28) or the achromat (30). [7] Motor vehicle headlight light module (16) according to one of the preceding claims, wherein the projection optics (28) are configured to image fluorescent light emanating from a point of the wavelength converter lying on an optical axis of the projection optics (28) into a fluorescent light disc and to image scattered laser light emanating from the same point into a laser light disc, characterized bythat the projection optics (28) are configured to generate the laser light disc with an associated laser light aperture angle that is greater than a fluorescent light aperture angle associated with the fluorescent light disc. [8] Motor vehicle headlight light module (16) according to claim 7, characterized by that the projection optics (28) are designed to generate laser light discs and fluorescent light discs in which the opening angle belonging to the laser light disc is up to 1.5 times larger than the opening angle belonging to the fluorescent light disc. [9] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized by that the aspherical lens (32) has an aspherical light entry surface (32.1) and an aspherical light exit surface (32.2). [10] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized bythat the achromat (30) has a spherical light entry surface (30.1) and a spherical light exit surface (30.2). [11] Motor vehicle headlight light module (16) according to claim 10, characterized by that the achromat (30) consists of two spherical lenses (30.3, 30.4) glued together. [12] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized by that a numerical aperture of the projection optics (28) is greater than 0.

3. [13] Motor vehicle headlight light module (16) according to one of the preceding claims, characterized by that the wavelength converter (24) is a reflective wavelength converter.

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