EP3332168B1 - Laser lighting device for vehicle headlamps - Google Patents

Description

The invention relates to a laser illumination device for vehicles with two or more laser light sources, each adapted to produce a primary laser light beam, each assigned to each laser light source light guide, each primary laser light beam coupled to its first end and decoupled from its second end as a secondary laser light beam and each secondary Laser light beam is directed to a light conversion means to generate a predetermined luminous image on this, which is projected via a the light conversion means associated with the projection system as a light image on the road.

Moreover, the invention relates to a headlight with at least one such laser illumination device.

Furthermore, the invention relates to a vehicle with at least one such headlight.

Headlamps that work with laser beams scanning via a light conversion medium are known. They usually generate a light image on a light conversion medium, often called "phosphor" for short, on which the blue laser light, for example, is converted into essentially "white" light by fluorescence. The luminous image produced is then projected onto the roadway with the aid of the imaging system, for example a lens optic (see, for example, US Pat US 20150062943 A1 . JP 2013232390 A . US 20120051074 A1 . JP 2014010918 A . WO 2014121314 A1 and US 20130265561 A1 ). The problem with many such headlamps that the light image is often only light spots, that is generated in the form of so-called light spots and are moderately suitable for generating a law-compliant, such as dynamic light distribution. The microscanner is generally a beam deflection means, for example a micromirror, which can be moved about one or two axes, so that, for example, a row-by-row illumination image is "written". The modulation of the laser light source determines the desired luminance for each point or line of the luminous image, which on the one hand has to comply with legal specifications for the projected photograph and, on the other hand, can be adapted to the respective driving situation.

The use of the micro-scanner with one or more laser beams, which are modulated synchronously with the mirror oscillation, makes it possible to produce almost any light distribution. Such a method is also known in principle so-called Pico projectors and head-up displays, which also use micromirrors, which are designed as MEMS (micro-electro-mechanical systems). However, in contrast to such systems, which are often used in consumer electronics, significantly higher laser powers must be introduced for headlamps. However, it is not necessary to represent a colored light distribution. As mentioned above, working with blue laser light, which originates for example from laser diodes, is usually used. In view of the required high laser power in the order of 5 to 30 watts, it is important to make the best possible use of the laser power installed in a headlight.

In particular, the so-called 1D microscanner systems find their application in the headlamps. Several blue laser diodes are arranged so that the laser beams generated by them are directed to the phosphor via a single 1D microscanner. A "1D microscanner" is understood to mean a microscanner movable about a single axis. Each laser diode illuminates its own area on the phosphor so that separate lines are "written".

If the height of the lines in the far field is to be different (for example, to divide a light distribution as efficiently as possible on individual lines), the spot diameter of the laser diodes, i. the diameter of a light spot generated by the corresponding laser diode by the fluorescence, be correspondingly different on the phosphor. Depending on the application, these values can vary widely, e.g. if line heights between 0.2 mm and 0.9 mm are to be realized on a phosphor.

The light intensity in such a spot usually has a Gaussian shape, and decreases exponentially to spots edges (see, eg US 20150062943 A1 and US 20130265561 A1 ).

In addition, the laser beams generated by the conventional laser diodes have spatial asymmetries, which is why the spot is substantially elliptical, wherein the length of the ellipse main axis may differ greatly from the length of the ellipse axis. The limit of the spot is usually assumed to be the point at which the intensity has fallen to 1 / e or to 1 / e ² . The assumed value then defines the boundary to the next line in the luminous image.

The problem arises that the width of the Gaussian distribution does not make a sharp demarcation between the lines possible.

One way to counteract this problem, at least partially, is to vary the intensity value assumed for the determination of the line boundary (see eg EP 2690352 A1 ). However, there is another problem that if the values are set too low, dark streaks will appear between the lines in the light image and consequently also in the light image.

An object of the invention is to provide a laser illumination device in which a light image with improved photometric properties can be realized.
This object is achieved with a laser illumination device of the aforementioned type according to the invention that each primary laser light beam couples into a first end of the optical fiber and decouples from a second optical fiber end as a secondary laser light beam, wherein the second ends are arranged adjacent to each other in a row, and the light guide a different have a large cross-section.

In an embodiment which is expedient with regard to the control-related expenditure, provision can be made for the micro-scanner to be pivotable about exactly one axis. Such a 1D microscanner can also be used to deal with EMC problems (EMC stands for electromagnetic compatibility). Compared to the 1D microscanners, with the two-axis swiveling microscanners - in short 2D microscanners - the beam deflection means (such as a micromirror) must oscillate a lot faster, so that a uniformly illuminated light image can be realized as the path through which the image is scanned will be much longer. As a result, one must be able to turn on and off the laser light sources themselves very quickly. Thus, extremely short switching times and extremely steep switching edges of the laser light sources must be realized in order to efficiently modulate laser light sources. This is especially important in skimming scenarios, ie when given areas of the lane are to be hidden due to beispielswese the oncoming traffic or the close-ahead traffic or objects at a roadside.
With regard to the reduction of the light losses when coupling the primary laser beams into the optical waveguides, it is advantageous if each laser light source is followed by an optical attachment which couples the primary laser light beam into the first end of the optical waveguide associated with this laser light source.

With regard to a compact structure and a well-controlled heat dissipation, it is expedient if the secondary laser light beams are subdivided into two or more laser light beam groups, each laser light beam group being guided by a respective micro scanner.

With regard to the divergence of the laser beam, it may be advantageous if the optical fibers of at least a subset of the optical fibers are arranged as a cone tapering in the direction of light propagation. The light guides (for example, glass rods) can be used without bending. Use of curved optical fibers (eg fibers) can contribute to increasing the divergence of the laser beam in one or both of its axes (major ellipse axis, ellipse minor axis) and affect the tuning of the laser beam profile size to the size of the micro-scanner.

With regard to the collimation of the secondary light beams, it may be advantageous for the second ends to be arranged and / or formed such that the secondary light beams extend substantially parallel to one another.

In order to produce a luminous image subdivided in lines, it is expedient for the second ends to be arranged adjacent to one another in a row.

With regard to focusing or collimation, it can be advantageous if each optical scanner is preceded by an optical imaging system.

It is expedient for the optical imaging system to have one, two or more lenses and / or one, two or more diaphragms and / or one, two or more reflectors.

With regard to the compact arrangement of the light guides, it can be provided that the primary laser light beams couple at least a subset of the primary laser light beams into the first ends via at least one beam deflection means, for example a mirror or a prism.

With regard to an efficient shaping of the intensity profile of the light beams, it is expedient for the light guides to have a substantially rectangular cross section.

In order to vary the spot size, the light guides have a different sized cross-section.

With regard to the quality and the resolution of the light image, it is of particular advantage if the first intensity profile in each spatial direction substantially Gaussian shape and the second intensity profile in each spatial direction substantially flat-top shape (even in top hat shape or Top Hat intensity profile known).

Moreover, it may be advantageous if the second intensity profile in each spatial direction has a substantially flat top shape and the beam cross section of the secondary light beams is substantially rectangular.

• Fig. 1 die für die Erfindung wesentlichen Komponenten einer Laserbeleuchtungsvorrichtung herkömmlicher Art ( AT 514834 A2 ) und deren Zusammenhang in schematischer Darstellung,
• Fig. 1a zwei überlagernde durch die Laserbeleuchtungsvorrichtung herkömmlicher Art erzeugte Leuchtflecken und ihre Intensitätsprofile,
• Fig. 2 die wesentlichen Komponenten einer erfindungsgemäßen Laserbeleuchtungsvorrichtung und deren Zusammenhang in schematischer Darstellung,
• Fig. 2a die erfindungsgemäße Laserbeleuchtungsvorrichtung mit konusförmig angeordneten starren Lichtleitern und einem schematisch dargestellten Abbildungssystem,
• Fig. 2b die erfindungsgemäße Laserbeleuchtungsvorrichtung mit gekrümmten Lichtleitern und einem schematisch dargestellten Abbildungssystem,
• Fig. 2c zwei durch die erfindungsgemäße Laserbeleuchtungsvorrichtung erzeugte Leuchtflecken und ihre Intensitätsprofile,
• Fig. 3 ein stationäres durch die Laserbeleuchtungsvorrichtung erzeugte Leuchtbild,
• Fig. 4 eine beispielhafte Anordnung der Lichtleiterenden aus der Fig. 2a, und
• Fig. 5 eine schematische Darstellung einer Einkoppelung der primären Strahlen in die Lichtleiter über Umlenkspiegel.

The invention together with further advantages is explained in more detail below by way of example embodiments, which are illustrated in the drawing. In this show

• Fig. 1 the essential components of the invention for a laser illumination device of a conventional type ( AT 514834 A2 ) and their context in a schematic representation,
• Fig. 1a two overlapping spots produced by the laser illumination device of conventional type and their intensity profiles,
• Fig. 2 the essential components of a laser illumination device according to the invention and their context in a schematic representation,
• Fig. 2a the laser illumination device according to the invention with conically arranged rigid optical fibers and a schematically illustrated imaging system,
• Fig. 2b the laser illumination device according to the invention with curved optical fibers and a schematically illustrated imaging system,
• Fig. 2c two light spots produced by the laser illumination device according to the invention and their intensity profiles,
• Fig. 3 a stationary light image generated by the laser illumination device,
• Fig. 4 an exemplary arrangement of the optical fiber ends of the Fig. 2a , and
• Fig. 5 a schematic representation of a coupling of the primary rays in the light guide via deflecting mirror.

Based on Fig. 1 and Fig. 1a Now, the problem to be solved by the present invention will be explained. Photometric starting point of the laser illumination device shown here are two, here superimposed groups 1 and 2 of four laser light sources 11, 12, 13, 14 and 21, 22, 23, 24, which can each emit a denoted by 11p to 18p laser beam. The laser light sources 11 to 18 are associated with a laser driver 3, wherein this driver 3 is used for power supply and is also set up to modulate the beam intensity of the individual lasers. By "modulating" in the context of the present invention is meant that the intensity of a laser light source can be changed, be it continuous or pulsed, in the sense of switching on and off, pulsed. It is essential that the light output can be changed dynamically analogously, depending on where the beams are directed. In addition, there is the possibility of switching on and off for a certain time in order not to illuminate defined places

The laser driver 3 in turn contains signals from a central headlight driver 4, which sensor signals s1 ... si ... sn can be supplied. On the one hand, these control and sensor signals can be, for example, switching commands for switching from high beam to low beam or, on the other hand, signals received by light sensors or cameras which detect the lighting conditions on the road and, for example, hide or attenuate certain areas in the light screen. The laser light sources 11 to 18, which are preferably designed as laser diodes, emit for example blue or UV light.

Each laser light source 11 to 18 is followed by its own collimator optics 21 to 28, which bundles the initially highly divergent laser beam 11p to 18p. Subsequently, the distance of the laser beams of the first group 1 and the second group 2 is each reduced by a common converging lens 31 and 32 and with subsequent diverging lenses 41 and 42, the exit angle of the laser beams is kept as low as possible.

The four laser beams 11p, 12p, 13p and 14p of the first group 1 "bundled" in the described manner strike a first microscanner 51 and analogously the laser beams 15p, 16p, 16p and 18p of the second group 2 strike a second microscanner 52 and are reflected together on a formed in the present case as a luminous surface light conversion means 60. The term "microscanner" is understood here to mean a universal beam deflecting device which can be pivoted about one or two spatial axes, which is usually designed as a micromirror, does not necessarily have to be designed as such, but is designed as e.g. a prism can be formed. The light conversion means 60 comprises, in a known manner, a phosphor for light conversion, which, for example, converts blue or UV light into "white" light. In the context of the present invention, "phosphorus" is generally understood to mean a substance or a substance mixture which converts light of one wavelength into light of another wavelength or of a wavelength mixture, in particular into "white" light, which can be subsumed under the term "wavelength conversion" is. In this case, "white light" is understood as meaning light of such a spectral composition which causes the color impression "white" in humans. Of course, the term "light" is not limited to radiation visible to the human eye. Also suitable for the light conversion agent are optoceramics, ie transparent ceramics, such as, for example, YAG-Ce (an yttrium-aluminum garnet doped with cerium).

The microscanner 51 is driven by a micro scanner drive 5 and set in oscillations of constant frequency, whereby these vibrations can correspond in particular to the mechanical natural frequency of the micro scanner. The microscanner drive 5 is in turn controlled by the headlight drive 4 in order to adjust the oscillation amplitude of the microscanners 51, 52, whereby asymmetric oscillation about the axis can be adjustable. The control of microscanners is known and can be done in many ways, eg electromagnetic, electrostatic, thermoelectric and piezoelectric. In proven embodiments of the invention, the microscanners 51, 52 vibrate, for example, with a frequency of a few hundred Hz and their maximum deflection is a few degrees to 60 °, depending on their control. The position of the microscanners 51, 52 is expediently reported back to the micro scanner control 5 and / or to the headlight driver 4. The two microscanners can oscillate synchronously, but it is also a non-synchronous Swing applicable, for example, to make the thermal load of the luminous surface or the light conversion medium uniform.

In the still, ie not vibrated, microscanners produce the focused laser beams 11p to 18p on the light conversion means 60, namely the luminous surface, which is generally flat, but need not be flat, light spots, each having a luminous flux distribution, the Intensity profile of the relevant laser light beam correspond. In Fig. 1a For example, two spots 71p and 72p are schematically shown by a laser illumination device of FIG Fig. 1 be generated. In this case, each luminous flux distribution is essentially Gaussian and corresponds to the intensity profile of the two "adjacent" laser beams, for example 11p and 12p. A section along the line AA represents a luminous flux course 73 and is of high relevance for the luminous image to be imaged on the carriageway by means of a projection system PS. The luminous flux profile 73 described here does not allow a sharp demarcation between the light spots and leads to large fluctuations in light intensity in the light image.

The term "road surface" is used here for a simplified representation, because of course it depends on the local conditions, whether the photo is actually on the road or even beyond. For example, In order to test the radiated light distributions, a projection of the light image on a vertical surface in accordance with the relevant standards, which relate to the automotive lighting technology.

According to the invention, this problem is solved by shaping the beam profile of the laser light beams. The essential components of a laser illumination device according to the invention, which has technical means with which the solution is implemented, are based on a non-limiting embodiment in FIG Fig. 2 shown. Here, for the sake of simplicity, only one of the two laser light sources groups of Fig. 1 taken into consideration. Each laser light source 11 to 14 is followed by its own intent optics 81 to 84, which bundles the initially highly divergent primary laser beam 11p to 18p and then focused on the first ends 91e to 94e of the optical fibers 91 to 94 so that the primary laser light beams substantially without losses couple into the light guides. The laser light beams are advantageously coupled into the light guide in such a way that, for example, in a rectangular light guide the Longitudinal axis of, emitted by the laser light source, typically elliptical beam cross-section having, laser beam, parallel to the cross-sectional longitudinal axis of the rectangular light guide runs. In general, the type of coupling depends on which axis (major ellipse axis or ellipse minor axis) the laser light beams are to have less divergence on coupling out (the secondary laser light beams).

It should be noted at this point that the term "light guide" also all technical means are subsumed, which are suitable for shaping the beam profile (intensity profile and the cross section of the laser beams). Thus, all "beam profile shapers" are applicable to a specific technical embodiment of the present invention. For example, multimode fibers or glass rods of various types can be used. The type of beamformer refers to the behavior of its refractive index. One differentiates between e.g. Step index fibers, gradient index fibers or homogeneous beam profile shapers (with a constant refractive index). In addition, the beam profile formers may have different cross-sectional sizes (from a few to hundreds of microns to a few millimeters). Thereby, the size of the light spots on the light conversion means and consequently the resolution of the light image can be varied. Furthermore, such a beam profiler may be used, for example, as an array of optics, e.g. Lenses, mirrors and diaphragms, be realized.

The term "attachment optics" in the context of the present invention is understood to mean an optical system which is suitable for focusing the originally diverging primary laser light beams 11p to 14p onto the associated first ends 91e to 94e. This attachment optics, as in the illustrated embodiment, may include a collimator lens and a condenser lens, but may alternatively include other optical means available to those skilled in the art that are suitable for focusing the primary laser light beams.

In the propagation of the primary laser light beams 11p to 14p in the optical fibers 91 to 94, these are multiply totally reflected. This causes the light to "fill in" the entire cross section of the light guide. In this case, the beam profile of the light beams emerging from the light guides as secondary light beams 11s to 14s essentially assumes the shape of the cross section of the light guides. In connection with the present invention used optical fibers have a substantially rectangular shape of the cross section. Accordingly, the secondary light beams 11s to 14s have a substantially rectangular intensity profile. In the Fig. 2c For example, two rectangular spots 71s and 72s formed on the light conversion means 60 by two of the secondary beams, for example, 11s and 12s, have a substantially rectangular beam cross section and a substantially rectangular intensity profile, also referred to in the literature as a flat top or top -Hat form or simply called top hat, the secondary laser beams correspond and have a substantially rectangular luminous flux profile 73 a and 73 b along the section BB. The size of the cross section may vary from optical fiber to optical fiber and, as a result, lead to differently sized spots on the light conversion means 60. As a result, the luminous flux density (illuminance) in a light spot and consequently the light intensity of this light spot can be adjusted. This is in the Fig. 3 thematized, which shows eight differently sized and differently bright luminous spots 100 to 107. Such spots occur when the microscanners 51, 52 do not vibrate. If these are set in vibration by the microscanner drive 5, so that the microscanners 51, 52 are pivoted about an axis, light bands z0 to z8 are formed on the light conversion means.

Although the preferred embodiment shows microscanners that vibrate only about one axis, it is also possible to use microscanners that oscillate about two axes. In this case, a plurality of laser beams may be directed to such a micro-scanner, directly generated adjacent light bands. Embodiments with only a single micro-scanner are also conceivable, in which, for example, the secondary laser beams impinge against the main emission direction of the headlight directly onto the micro-scanner, which then directs the laser beams to a phosphorescent phosphor.

Fig. 2a and Fig. 2b show two embodiments of the present invention, in which the secondary laser light beams 11 s to 14 s reach the micro scanner 51 via an optical imaging system 6. The imaging system 6 is shown schematically as a converging lens. In general, it is an optical system comprising one, two or more lenses, which are arranged one behind the other and / or each associated with a light guide, and / or reflectors, and which optical system the secondary light beams 11s to 14s via the micro scanner 51 on the light conversion means 60 collimated / focused.

It shows Fig. 2a Light guides 91 to 94, which are arranged as a converging in the light propagation direction cone. In this arrangement, the light guides 91 to 94 can be "rigid".

Fig. 2b shows a light guide assembly, which is particularly suitable for formed as a multimode fiber light guide 91 to 94. In this case, the optical fibers can be curved and arranged such that the second ends 91z to 94z are arranged adjacent to each other in a row. As a result, the secondary laser light beams 11s to 14s are substantially parallel, and the distance between the light spots on the light conversion means 60 by the imaging optical system 6 can be minimized.

Fig. 4 shows an arrangement of the optical fiber ends of the Fig. 2a , Although the optical fibers 91 to 94 converge in a cone shape at an opening angle α, the second ends 91z to 94z are formed, eg, by grinding, so that the secondary light beams 11s to 14s are substantially parallel to each other. In this case, the opening angle α must not be arbitrarily large, since this would require the corresponding grinding of the second ends 91z to 94z and would lead to undesirable distortions in the light and thus in the light image.

It should be noted at this point that it is in the in Fig. 4 represented arrangement is a special case. In practice, it may well happen that the second ends 91z to 94z are not in one plane. The grinding angle is given by the law of refraction and by the opening angle α. The configuration of the second ends 91z to 94z (by grinding) serves as a technical means for the secondary laser light beams, which generate the light spots on the light conversion means, to strike the light conversion means at a predetermined angle, preferably parallel to each other.

At an in Fig. 5 schematically illustrated embodiment couple the primary laser light beams via mirrors 200 to 207 (via a so-called "mirror staircase") in the first ends. As a result, both the opening angle α reduced as well as a optimized cooling of the laser diodes can be realized, since they can be arranged in one plane and thereby realize a simpler connection to a common heat sink. Although a mirror staircase has been used in this embodiment, it may be replaced by other technical means, generally beam deflection means, which are suitable for deflecting light. For example, the mirrors 200 to 207 can be partially or entirely replaced by prisms. Likewise, arrangements are conceivable in which two or more primary laser beams are deflected via one and the same beam deflection means.

In the illustrated embodiments of the present invention, the overlapping of the light bands on a light surface or a light conversion means does not take place, and the light image thus generated is projected onto the road surface. However, it is also possible for two or more separate laser illumination devices according to the invention to be provided in a headlight, with these being aligned with one another such that the overlapping of the light images takes place. Although one or two groups each with four laser light sources are described in the exemplary embodiments shown, it should be clear to the person skilled in the art that several groups with different and different numbers of laser light sources are also conceivable according to the respective application.

Claims (14)

1. A laser lighting device for vehicles, said device having two or more laser light sources (11 to 18), wherein each is designed to generate a primary laser light beam (11p to 18p), and having optical fibres (91 to 94) associated with each respective laser light source, wherein each primary laser light beam is injected into the first end (91e to 94e) of said fibre and is ejected from its second end (91z to 94z) as a secondary laser light beam (11s to 14s), and wherein each secondary laser light beam is directed onto a light conversion means (60) to generate a defined lighting pattern on the same, which is projected onto the roadway as an illumination pattern by means of a projection system (PS) associated with the light conversion means, wherein each primary laser light beam has a first intensity profile (71p, 72p), characterized in that each secondary laser light beam has a second intensity profile (73a, 73b), which differs from the first intensity profile, that each secondary laser light beam is directed onto the light conversion means by means of a micro scanner (51, 52), that the second ends (91z to 94z) of the optical fibres (91 to 94) are arranged adjacent to each other in a row, and that the optical fibres have diameters of differing sizes.
2. The laser lighting device according to Claim 1, characterized in that the micro scanner (51, 52) can be swivelled about exactly one axis.
3. The laser lighting device according to Claim 1 or 2, characterized in that each laser light source is connected to a downstream optical head (81 to 84), which injects the primary laser light beam into the first end (91e to 94e) of the optical fibre (91 to 94) associated with the respective laser light source.
4. The laser lighting device according to any one of Claims 1 to 3, characterized in that the secondary laser light beams are divided into two or more laser light beam groups, wherein each laser light beam group is directed by means of one respective micro scanner (51, 52).
5. The laser lighting device according to any one of Claims 1 to 4, characterized in that the optical fibres (91 to 94) of at least a subset of the optical fibres are arranged in a conical shape tapering toward the direction of the light propagation.
6. The laser lighting device according to any one of Claims 1 to 5, characterized in that the two ends are arranged and/or designed in such a manner that the secondary light beams essentially extend parallel to each other.
7. The laser lighting device according to any one of Claims 1 to 6, characterized in that each micro scanner is connected to a downstream optical imaging system (6).
8. The laser lighting device according to Claim 7, characterized in that the optical imaging system (6) has one, two or more lenses and/or one, two or more apertures and/or one, two or more reflectors.
9. The laser lighting device according to any one of Claims 1 to 8, characterized in that the primary laser light beams of at least a subset of the primary laser light beams are injected into the first ends by means of at least one beam deflection means (200 to 207), for example a mirror or a prism.
10. The laser lighting device according to any one of Claims 1 to 9, characterized in that the optical fibres have an essentially rectangular cross section.
11. The laser lighting device according to any one of Claims 1 to 10, characterized in that the first intensity profile has an essentially Gaussian form in every spatial direction and the second intensity profile has an essentially flat-top form (73a, 73b) in every spatial direction.
12. The laser lighting device according to any one of Claims 1 to 11, characterized in that the second intensity profile has an essentially flat-top form (73a, 73b) in every spatial direction and that the beam cross section of the secondary light beams is essentially rectangular (71s, 72s).
13. A headlamp with at least one laser lighting device according to any one of Claims 1 to 12.
14. A vehicle with at least one headlamp according Claim 13.

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