EP2507545B2 - Light unit for vehicle - Google Patents

Description

Technical area

The present invention relates to a headlight module according to the preamble of claim 1.

State of the art

Such a headlight module is for example in the WO 2010/000610 A1 disclosed. This document describes a lighting unit for vehicle headlights, the lighting unit having light-emitting diode chips as a light source, which are provided with a fluorescent coating (chip layer coating) in order to convert the blue light generated by the light-emitting diode chips into white light. This lighting unit is designed as a component of a vehicle headlight and can therefore be viewed as a headlight module. In this patent application, the term headlight module refers to a module that is intended for use in a headlight or is designed as a component part of a headlight. In the sense of the invention, this module can be designed as a structural unit which is used as a whole in a headlight, or as a system of individual, interacting components of a headlight.

The EP 2 063 170 A2 discloses a lighting device for a vehicle with an optical imaging element arranged in the beam path of a light source, wherein a surface element is arranged between the light source and the imaging element and is designed to illuminate the focal plane of the imaging element.

The DE 101 61 177 A1 discloses a lighting unit for vehicles with a light source which is formed by an electron beam device in which an electron beam source for generating an electron beam and a conversion surface for converting the electron beam into a light beam are arranged.

The headlight module according to the invention is also primarily intended for use in a vehicle headlight, although other areas of use are also possible.
additional variable light distributions such as cornering lights and cornering lights based on the specifications of ECE regulation 123. In the near future, adaptive high beam will also be allowed. Parts of the high beam are masked out so as not to dazzle the traffic ahead or oncoming traffic. In addition, all current headlight systems must be designed to be pivotable about a horizontal axis, transverse to the direction of travel, in order to be able to ensure the range adjustment of the headlight. In very powerful headlights, this setting even has to be made automatically depending on the vehicle's load condition. In particular with the recently used LED headlights, this means that the entire system including a heavy cooling system has to be swiveled.

Mechanical systems with stepper motors are usually used for this purpose in order to pivot the headlight module about a horizontal axis. To implement dynamic cornering lights, it is also known to pivot the headlight module about a vertical axis.

For the adaptive high beam and other variable light distributions, mechanical systems with hinged screens or rollers are also used, by means of which the light from discharge lamps or halogen lamps is specifically blocked.

Also known are so-called matrix headlights based on discharge lamps which contain an imaging element and in which each pixel is responsible for a specific solid angle element. These headlights are known as pixel or matrix AFS (adaptive front lighting system) headlights. On the one hand, they need a high luminance to keep the optical components small, and on the other hand a high luminous flux, which - depending on the desired light distribution - is then largely faded out again so that only a small part of the high luminous flux is actually used.

The advantages of such an intensity-modulated matrix headlight are its high resolution and thus the possibility of doing without servomotors and moving components, while the disadvantage lies on the one hand in the high implementation costs and on the other hand in the low efficiency due to the type of light destruction.

Multi-LED headlights only switch light where it is needed and can therefore be more efficient in principle. However, due to the limited number of LEDs that can be switched at affordable costs, they do not offer enough resolution to fine-tune the headlight beam. You therefore still need servomotors and moving parts.

In summary, it can therefore be stated that all currently known systems represent a compromise between efficiency, costs and use of mechanical systems and thus inevitably reliability.

Presentation of the invention

The object of the present invention is therefore to provide a headlight module that enables dynamic light distribution for different driving situations at the lowest possible cost, high reliability and the highest possible efficiency, without the need to pivot the headlight module.

This task is solved by a headlight module with the features of claim 1.

The headlight module according to the invention has at least one phosphor or a phosphor mixture which can be excited to emit light by means of electromagnetic radiation and at least one radiation source for exciting the at least one phosphor or phosphor mixture. According to the invention, the headlight module additionally has at least one carrier device for the at least one phosphor and at least one beam steering device, the at least one beam steering device being arranged or designed in such a way that it emits electromagnetic radiation from the at least one radiation source onto the at least one phosphor or onto the phosphor mixture directs. The at least one beam steering device opens up the possibility of exciting the phosphor or the phosphor mixture only at the positions that correspond to a dynamic light distribution currently to be set in the driver's field of vision, for example on the roadway. In this case, similar to a scanning method of a scanner, the electromagnetic radiation emitted by the radiation source is guided by means of the beam steering device over all or only part of the surface of the carrier device provided with luminescent substance. Thus, only those areas of the phosphor or phosphor mixture are excited to emit light over which the electromagnetic radiation was guided. The beam is guided sufficiently quickly so that the human eye cannot follow it. In this way, a light distribution is generated on the surface of the carrier device provided with luminescent substance, which light distribution is projected, for example, onto the roadway to be illuminated by means of projection optics.

The at least one radiation source is preferably a laser, for example a laser diode or an arrangement of several laser diodes or one or more light-emitting diodes, in particular super-light-emitting diodes. By means of these radiation sources, electromagnetic radiation from the spectral range of visible light and the ultraviolet and infrared range can be generated in a highly efficient manner and generated to excite the phosphor or phosphor mixture. An ultraviolet radiation or blue light emitting light-emitting diode arrangement and particularly preferably a laser diode arrangement is preferably used as the radiation source, and white light is generated therefrom by means of the luminescent material or the phosphor mixture, for example to enable a vehicle headlamp that emits white light.

• Dadurch, dass die Strahlung in der Anregungsstrahlungsquelle moduliert werden kann, wird über das oben angedeutete Abtastverfahren der Leuchtstoff nur dort angeregt, wo es benötigt wird. Dies resultiert in einer hohen Effizienz. Eine Effizienzverschlechterung, wie aus dem Stand der Technik bekannt, durch eine nachgeschaltete Modulation und Ausblendung von Strahlung ist nicht nötig. Dies trägt zur Reduktion des Benzinverbrauchs und der CO₂-Emission des Fahrzeugs bei.

A large number of advantages can be achieved on the basis of the present invention:

• Because the radiation in the excitation radiation source can be modulated, the above-indicated scanning method only excites the phosphor where it is needed. This results in high efficiency. A deterioration in efficiency, as known from the prior art, through a downstream modulation and masking out of radiation is not necessary. This contributes to a reduction in fuel consumption and CO ₂ emissions from the vehicle.

The present invention can achieve high resolution. The beam steering device, which can be implemented as a micromirror device (MEMS, MOEMS, DMD), for example, enables a resolution in the range of 1000 x 1000 pixels to be generated and thus the legally required setting of the light distribution without stepper motors. Furthermore, by dynamically changing the light distribution, cornering light, adaptive high beam and other variable light distributions according to ECE regulation 123 can be generated without moving the entire headlight module mechanically. The movement of the micromirrors is easy to implement due to their low mass.

Any aspect ratio can be set by means of the present invention. The surface of the luminescent material swept by the beam deflection device and the luminescent material itself can be produced in any length-to-width ratio (in one piece or in pieces) at low cost. This allows the special properties of a beam distribution of a headlight to be taken into account.

Another advantage of the present invention is its high flexibility. The desired light distribution can be programmed in any form using software. This means that the same headlight module can be used to produce highly functional headlights, but also simple light distributions. If a laser is used as the excitation radiation source, a light source for a frugal electric car can be generated by using a smaller laser class, i.e. with lower power consumption, while very complex and design-driven headlights are possible with higher laser powers or several exit surfaces, realized by lenses and reflectors are.

According to the invention, the at least one carrier device is transparent and applied to an optical filter device which is designed to at least partially reflect radiation emitted by the at least one phosphor. The at least one beam steering device is preferably arranged in such a way that radiation emitted by the at least one excitation radiation source passes through the optical filter device and the carrier device before it strikes the phosphor. As a result of this embodiment, radiation emitted by the excitation radiation source hits the phosphor at a small angle, as a result of which only extremely small distortions arise. The measures for distortion corrections are therefore very low. The space between the phosphor and the at least partially transparent optical device that may be provided can be kept free of further elements.

In a preferred embodiment, the headlight module furthermore comprises at least one at least partially transparent optical device which is arranged in the beam path of the radiation emitted by the at least one phosphor or phosphor mixture. This can preferably be an aspherical lens and / or a free-form lens. This allows the intermediate image to be enlarged or projected to infinity on the phosphor - this is typically the case for automobile headlights from a distance greater than 25 m. A desired distortion can be achieved by means of freeform lenses, for example in order to produce a stretching of the light distribution in peripheral areas. As a result, the fluorescent surface can be kept small and the light distribution can still be expanded to larger areas

The at least one carrier device is preferably thermally connected to a cooling device, the cooling device representing a heat sink. Alternatively, the heat sink can represent the at least one carrier device. If the heat sink is designed to be reflective, for example by coating with aluminum, aluminum oxide or titanium oxide, the phosphor can be applied directly to the heat sink in a particularly cost-effective manner.

The surface of the carrier device provided with the at least one luminescent substance or luminescent mixture can be planar or curved, at least in regions. Through these measures, a higher image sharpness can be achieved, since an optional curvature of the surface of the at least one phosphor can ensure that almost all areas of the phosphor lie in the focal point of the at least partially transparent optical device that may be provided. This can be achieved by appropriately designing the surface of the phosphor or by designing the carrier device.

The headlight module preferably comprises at least one beam splitter device which is arranged between the at least one excitation radiation source and the at least one beam steering device. This opens up the possibility of optimally illuminating a plurality of phosphor areas, which can be arranged spatially separated from one another, by means of a respective beam steering device. A separate optical device can be provided for each of the fluorescent areas, so that the light that leaves the headlight module is composed of the light of several superimposed individual light distributions.

In a further embodiment, several phosphor areas with different phosphors are present, the phosphors being selected such that they produce different secondary colors. The latter are preferably chosen such that they result in white when they are subsequently superimposed. Such a combination of phosphors can preferably be based on red-green-blue (RGB) color coordinates; however, other color systems known in the art are also possible.

The at least one beam steering device comprises a micromirror device. The micromirror device preferably comprises at least one micromirror which can be pivoted about two axes.

The headlight module furthermore comprises a control device for the at least one excitation radiation source and for the at least one beam steering device.

The control device is designed to control at least one micromirror of the micromirror arrangement in such a way that it assumes predeterminable spatial positions and orientations, the control device also being designed to switch the radiation source on or off depending on the position or orientation of the at least one micromirror. In particular, the control device can be designed such that the electromagnetic radiation emitted by the radiation source is guided by means of the at least one micromirror line by line or column by column over the surface of the carrier device provided with luminescent material.

The electromagnetic radiation emitted by the radiation source can be guided by means of the at least one micromirror over the entire surface of the support device provided with luminescent material and the radiation source can be switched off or switched on when certain positions or positions of the microscopic mirror are reached in order to excite only a section of the area provided with luminescent material and thus to generate the desired light distribution.

Alternatively, the electromagnetic radiation emitted by the radiation source can be guided by means of the at least one micromirror only over part of the surface of the carrier device provided with luminescent material, in which case the radiation source remains switched on constantly in order to also excite only a section of the area provided with luminescent material and to generate a desired light distribution.

In the first case, the modulation capability of the excitation radiation source is used, whereby a high level of efficiency can be achieved, since light does not have to be unnecessarily destroyed or masked out. In the second case, radiation from the excitation radiation source is available longer for the solid angle in which light emission is desired. As a result, the excitation radiation source can be dimensioned weaker, which is also reflected in an increase in efficiency and in a reduction in implementation costs. In addition, a more homogeneous use of the excitation radiation source is thereby achieved.

The optical device can comprise at least one reflection device which is arranged in such a way that at least radiation emitted by the at least one phosphor strikes the at least one reflection device. In this way, a deliberate distortion to achieve a desired light distribution can be implemented in a simple manner. In addition, enlargement effects can be achieved. Reflection devices offer the advantage that the orientation of the fluorescent material in the direction of travel of the motor vehicle can take place above, below or to the side, which enables a greater degree of freedom in the implementation of a headlight module according to the invention. In addition, different length-to-width ratios of the exit surface can be implemented, as a result of which the design of a headlight with a headlight module according to the invention can be adapted in a simple manner to the specifications of end customers.

Further advantageous embodiments emerge from the subclaims.

Brief description of the drawings

Fig. 1

in schematischer Darstellung ein erstes Ausführungsbeispiel eines erfindungsgemäßen Scheinwerfermoduls;

Fig. 2

eine detailliertere Darstellung eines Ausführungsbeispiels der vorliegenden Erfindung mit einem gekrümmten Leuchtstoffträger und einer optischen Vorrichtung;

Fig. 3

eine detailliertere Darstellung eines Ausführungsbeispiels der vorliegenden Erfindung mit einem planen Leuchtstoffträger und einer Reflexionsvorrichtung; und

Fig. 4

eine CIE-Normfarbtafel zur Bestimmung der in einem erfindungsgemäßen Scheinwerfermodul einzusetzenden Anregungsstrahlungsquellen und Leuchtstoffe.

In the following, exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of a first embodiment of a headlight module according to the invention;

Fig. 2

a more detailed illustration of an embodiment of the present invention with a curved fluorescent support and an optical device;

Fig. 3

a more detailed illustration of an embodiment of the present invention with a planar fluorescent substrate and a reflection device; and

Fig. 4

a CIE standard color table for determining the excitation radiation sources and phosphors to be used in a headlight module according to the invention.

Preferred embodiment of the invention

In the different figures, the same reference symbols are used for identical and identically acting components. These are therefore only introduced once.

Fig. 1 shows a schematic representation of a first embodiment of a headlight module 10 according to the invention. This comprises at least one radiation source 12, which is preferably designed as a blue light emitting laser, in particular as a blue light emitting laser diode. Radiation from the excitation radiation source 12 hits a beam steering device 14, which is preferably designed as a micromirror device. The radiation emitted by the beam steering device 14 first passes through an optical filter device 16, then a carrier device 18 for the at least one phosphor and finally the at least one phosphor 20. The carrier device 18 is preferably made of highly thermally conductive material. The optical filter device 16 is designed in such a way that it allows radiation from the radiation source 12 to pass while it reflects radiation emitted by the phosphor 20. The beam steering device 14 is designed to deflect the radiation emitted by the radiation source 12 in such a way that regions of the phosphor 20 that differ in time are excited. The carrier device 18 is preferably made of ceramic, for example of polycrystalline aluminum oxide ceramic (PCA) or of sapphire.

The phosphor 20 can be composed of several different phosphor components which convert the electromagnetic radiation from the radiation source 12 into light of different wavelengths or colors. Furthermore, the phosphor 20 can also be a phosphor mixture. Since around 20% of the energy in the phosphor 20 is lost through the Stokes shift and is converted into heat, the phosphor 20 is cooled by means of a cooling device 22. This can be a fan, for example. An optical device 24, for example a projection lens with a focal length of 20 mm to 100 mm, enables the luminance distribution to be mapped into the far field without distortion.

In the Fig. 1 The illustrated embodiment of a headlight module according to the invention is characterized in that the radiation from the radiation source 12 hits the phosphor 20 at a small angle of incidence, whereby the spot size, i.e. the beam diameter of the beam striking the phosphor 20, is kept small and ensures optimal excitation of the phosphor becomes. Typical spot sizes are 0.1 mm to 0.2 mm in order to ensure the necessary resolution for the generation of different light distributions. The luminescent material 20 and the radiation source 12 are matched to one another in such a way that the light emitted by the headlight module 10 is white with a color temperature in the range of 3000-6500 Kelvin.

Fig. 2 shows in greater detail a combination of phosphor 20 and optical device 24 of a headlight module 10 according to the invention. This can be achieved by appropriate design of the phosphor surface itself or by appropriate design of the carrier device 18 Optical device 24 can be an aspherical lens in order to achieve a magnification and thereby project the intermediate image onto the phosphor 20 into infinity. This is the case with automobile headlights from a distance greater than 25 m. The focal plane of such aspherical lenses, that is to say the plane from which the image is sharply focused, is not planar, but typically a curved surface. It is therefore particularly preferred to design the surface of the phosphor 20, or the carrier device 18 for the phosphor 20, preferably as a sphere or, more generally, as a conic section.

The optical device 24 can also represent a free-form lens in order to deliberately distort the image. In this way, for example, the light distribution can be stretched into peripheral areas in order to keep the actual phosphor matrix, i.e. the rows and columns on the phosphor 20 to be set by the control device 34, but nevertheless an expansion of the light distribution to larger areas to enable.

Fig. 3 shows a schematic representation of an embodiment in which the optical device 24 is designed as a reflection device. The reflection device can be parabolic in shape and then fulfills a similar purpose as an aspherical lens, that is to say rays emanating from a point are imaged into infinity, that is to say made parallel. Since the luminescent material 20 only emits into a half-space, a maximum of a quarter reflector shell is required.

Freeform reflectors can, in turn, deliberately distort the light distribution, that is to say one can work with different magnification and distortion factors in the different areas of the reflection device.

Reflection devices also have the advantage that the fluorescent material 20 can be attached above, below or to the side in the direction of travel, whereby a greater degree of freedom can be achieved in the design of a system equipped with a headlight module 10 according to the invention. At the same time, different length-to-width ratios of the exit surface can be realized, whereby a great freedom of choice can be achieved for the design of a headlight equipped with a headlight module 10 according to the invention.

Fig. 4 shows a CIE standard color table in which combinations of excitation radiation sources 12 and phosphors 20, such as can be used for a headlight module according to the invention, are shown by way of example. The curve line 36 represents the spectral color line. Curve line 38 encloses a field that is considered white according to the ECE regulations. The white point 40 is also drawn in. The curve 42 reproduces the Planck curve.

An application of a headlight module 10 according to the invention in a vehicle headlight requires white light, with "white" being defined by the ECE regulations and the CIE standard. The color location is preferably placed in the vicinity of the white point 40 (approx. 5500 K or even up to 6500 K) in order to generate light colors similar to daylight. Depending on the pump wavelength of the laser used as radiation source 12, which can be between 400 and 480 nm, the phosphor 20 must therefore have its center of gravity between 570 and 590 nm. 590 nm produces warm white light and 570 nm with a pump wavelength of around 410 nm produces cold white light. Some combinations are shown as examples in FIG. 6. The straight connecting line goes through the white field 38 and the color location can be set there.

The most efficient solution is a phosphor with 570 nm, as this is at the maximum of V (λ) and can be achieved with a pump wavelength of the laser of 405 nm.

Phosphors 20 are used as they are already used today for light-emitting diodes for generating white light. For example, the phosphor 20 is yttrium aluminum garnet doped with cerium (YAG: Ce) or related garnets with doping in different concentrations. Various embodiments of such phosphors 20 can be EP 1 471 775 can be removed. Further typical phosphors are calsine, phosphors of the SCAP type, nitridosilicates and chlorosilicates, oxynitrides and silicates, in particular orthosilicates, as they are already known per se and are used for mixing in order to generate white light. Typical examples of this are given in the laid-open documents DE 10 2006 036577 , DE 201 15 914 U1 , US 2003/146690 , WO 2001/040403 , WO 2004/030109 , DE 10 2007 060 199 , DE 103 19 091 and DE 10 2005 017 510 disclosed. The light colors warm white, cold white and daylight-like white can be set by means of these phosphors and, in particular, white light with a desired color temperature in the range from 3000 Kelvin to 6500 Kelvin can also be generated with these phosphors. Examples of this can be found in the DE 10 2004 038 199 , the WO 00/33389 and the EP 1 878 063 .

The use of phosphors that emit red light, such as nitrides, in the phosphor mixture 20 also ensures that the white light contains more than 5% of the red content required by law for vehicle headlights. A laser or a laser diode which emits ultraviolet radiation or blue light is used as the radiation source 12 for exciting the phosphor mixture 20.

In principle, in a headlight module 10 according to the invention, a UV radiation source can also be used as the radiation source 12 instead of the laser emitting blue light. In this case, at least two different phosphors are required for generating white light, the color locations of which are diametrically opposite to the white point 40. This results in an increased color quality because of the spectrum of light can be controlled independently of the pump wavelength of the excitation radiation source 12.

In a headlight module 10 according to the invention, the light emitted by the headlight module 10 is preferably composed of two color components, in particular the radiation from the radiation source 12 and the radiation emitted by one or more phosphors. This allows the wavelength of the emitted light to be controlled very well, which makes color control much easier than with today's white LEDs.

With a 3-color system, for example red, green and blue (RGB), the color quality, i.e. the color rendering index, can be significantly improved and the entire color space spanned by the phosphors can be represented by different modulation of the different colors.

Legal requirements require the possibility of range adjustment for the approval of headlights in a motor vehicle. In the prior art, the cut-off line HDG of the headlight is specifically tilted downwards by 1%, corresponding to 0.57 °, towards the horizon, which means that electric servomotors, in some cases even very complex stepper motors, are required in the prior art headlight will. In the case of a headlight module 10 according to the invention, these servomotors can be omitted, since the HDG can be precisely controlled in the range of 0.1 °. This can be achieved by a correspondingly fine setting of the line signal for the beam steering device. Since the latter is an analog signal, there are in principle no limits with regard to the resolution of the HDG in a headlight module 10 according to the invention. Via a corresponding control of the control device 34, for example by connection to a bus system of the motor vehicle that is coupled to inclination sensors of the motor vehicle, or by manual input in the driver's control panel, an effect can be achieved by appropriate control of the beam steering device 14 in a headlight module 10 according to the invention corresponding to a tilt.

The control device 34 is also designed to set the range setting to a predetermined value if communication with the motor vehicle fails. At the same time, the control of the beam steering device 14 is preferably switched to normal low beam by means of a permanently stored light distribution in order to protect the phosphor 20.

If the radiation source 12 fails or works incorrectly or at low power, provision is also made to signal the driver that there is a defect, typically by means of a corresponding warning lamp on the dashboard. This informs the driver of the restricted functionality and the need to visit a workshop.

If the beam steering device 14 fails, a warning signal is also generated for the driver and the radiation source 12 is switched off. Finally, provision is made to deactivate the radiation source 12 if the vehicle is in a workshop for maintenance and the headlight module 10 has to be opened. This reliably protects the maintenance personnel. Likewise, a safety device can also be provided which switches off the radiation source 12 in the event of an open headlight housing or in the event of an accident, in particular if the headlight housing is broken.

The power of the excitation radiation source 12 is preferably between 5 and 20 W.

Claims (10)

1. Headlight module (10) comprising

   - at least one phosphor (20) which can be excited to emit light by means of electromagnetic radiation, and

   - at least one radiation source (12) for exciting the at least one phosphor (20);

   wherein the headlight module (10) furthermore comprises:

   - at least one carrier device (18) for the at least one phosphor (20) and

   - at least one beam directing device (14) which is arranged in such a way that it directs electromagnetic radiation emitted by the at least one radiation source (12) onto the at least one phosphor (20),

   characterized in that the at least one carrier device (18) is embodied as transparent and is applied on an optical filter device (16) designed to at least partly reflect radiation emitted by the at least one phosphor (20), wherein the headlight module (10) furthermore comprises a control device (34) for the at least one beam directing device (14) and the at least one radiation source (12), wherein the at least one beam directing device (14) comprises a micromirror device, and wherein the control device (34) is designed to switch the radiation source (12) on or off in dependence on the position or orientation of at least one micromirror of the micromirror device.
2. Headlight module (10) according to Claim 1, wherein the headlight module 10 furthermore comprises at least one at least partly transparent optical device (24) arranged in the beam path of the radiation emitted by the at least one phosphor (20).
3. Headlight module (10) according to Claim 1, wherein the at least one beam directing device (14) is arranged in such a way that radiation emitted by the at least one radiation source (12) passes through the optical filter device (16) and the carrier device (18) before it impinges on the phosphor (20).
4. Headlight module (10) according to any of the preceding claims, wherein the at least one phosphor (20) is applied as a coating on a surface of the carrier device (22).
5. Headlight module (10) according to any of the preceding claims, wherein the headlight module (10) comprises at least one beam splitter device (30) arranged between the at least one radiation source (12) and the at least one beam directing device (14) .
6. Headlight module (10) according to any of the preceding claims, wherein the optical device (24) comprises at least one reflection device arranged in such a way that at least radiation emitted by the at least one phosphor (20) impinges on the at least one reflection device.
7. Headlight module (10) according to any of the preceding claims, wherein the optical device (24) comprises at least one aspherical lens or/and a freeform lens.
8. Headlight module (10) according to any of the preceding claims, wherein the radiation source (12) is at least one laser diode or a laser diode arrangement.
9. Headlight module (10) according to any of the preceding claims, wherein provision is made of a safety device for automatically switching off the radiation source (12) in the case of an open headlight housing.
10. Vehicle headlight comprising a headlight module according to one or more of Claims 1 to 9.

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