DE202017100639U1 - Headlight for motor vehicles with at least one laser light source - Google Patents

Abstract

Headlamp for motor vehicles with at least one laser light source (1) whose laser beam (3) is directed to at least one light conversion means having a phosphor (6) for light conversion, and with a projection system (8) for projecting the light generated at the at least one light conversion means (7) in the carriageway space, characterized in that at least two electrodes (10, 11) are arranged on the phosphor, which form the coverings of a capacitor (CP) with the phosphor as a dielectric, and a measuring device (12) is provided with to which the at least two electrodes are connected and which is arranged to measure the capacitance of the capacitor and to output a signal (s) if the determined capacitance lies outside a specified tolerance range around a desired value.

Description

The invention relates to a headlight for motor vehicles with at least one laser light source whose laser beam is directed to at least one light conversion means having a phosphor for light conversion, and with a projection system for projecting the light generated at the at least one light conversion means in the roadway space.

Laser light sources (e.g., semiconductor lasers, laser diodes) have a number of special advantageous properties, such as e.g. high radiation intensities and a small light-emitting surface. In addition, the emitted light beams are largely collimated.

This results in the use of laser light sources for lighting purposes, especially for vehicles, a number of advantages. For example, optical systems in which a laser light source is used as the light source can be realized with smaller focal lengths and more focused beam progressions. This is not possible with less strongly collimated light bundles - for example from incandescent lamps or LEDs. Thus, when using laser light sources, it is possible to realize optical systems for laser light with a small installation space.

Lasers typically emit monochromatic light or light in a narrow wavelength range. However, in a car headlamp, "white" mixed light is desired or prescribed by law for the radiated light, so that laser light sources in a vehicle headlamp can not be readily used and light conversion means are used. Such a light conversion agent contains a "phosphor" or phosphorus body, often in the form of a platelet, as described in more detail below.

The use of laser light sources poses the problem that they pose a high risk potential, in particular for the human eye. This is because lasers typically emit coherent and highly collimated light, which is potentially dangerous at the typical high radiation intensities of laser light sources. This is especially true at radiation powers of a few watts, as is desirable in the field of automotive lighting.

Therefore, in order to be able to use laser light sources in the motor vehicle sector, in particular for motor vehicle headlamps, safety regulations for the operation of laser devices must be observed. In particular, it must be ensured that light (laser light) escapes from a motor vehicle headlight only at an intensity below prescribed limits. In addition, dazzling or endangering road users must be avoided.

There is a particular risk in damage to the phosphor, such as a break or the occurrence of cracks or perforations. In such a case, at least a portion of the primary laser beam penetrates the phosphor, passes through the headlamp projection system on the road and can endanger people.

It is an object of the invention to provide a headlamp, in which a malfunction in the sense of partial or complete damage of the phosphor can be detected with little effort, so that measures can be taken to prevent the danger emanating from the laser interference radiation endangerment or minimal hold.

This object is achieved on the basis of a headlamp of the type described, according to the invention in that at least two electrodes are arranged on the phosphor, which form the linings of a capacitor with the phosphor as a dielectric, and a measuring device is provided, with which the at least two Electrodes are connected and which is adapted to measure the capacitance of the capacitor and to output a signal if the determined capacity is outside a specified tolerance range around a desired value.

An expedient and advantageously realizable development of the invention is characterized in that the measuring device is designed as an alternating voltage measuring bridge and the capacitor is connected to the phosphor as a dielectric in a bridge branch.

It may be particularly advantageous if the AC voltage bridge is a Vienna bridge.

Furthermore, it is expedient if in a further bridge branch, a reference capacitor, which is the same as the phosphor configured.

It can also be provided with advantage that the phosphor is cuboidal.

On the other hand, it is in many cases opportune if the phosphor is platelet-shaped.

In expedient embodiments of the invention, it is provided that the phosphor is transmissive.

It is very advantageous in many cases when the electrodes are transparent.

In this case, the electrodes can advantageously consist of vapor-deposited indium tin oxide.

Also, it may be useful for certain headlamp variants if the phosphor is reflective.

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

1 a schematic representation of an embodiment of a headlamp with the essential components of the invention

2 a detail of 1 in an enlarged view,

3 in a further enlarged perspective view of a phosphor with electrodes,

4 in side view a phosphor with damages and

5 a possible measuring bridge for determining a capacitance change

With reference to 1 Now, an embodiment of the invention will be explained in more detail. In particular, those are for a headlight according to the invention 1 It is clear that a motor vehicle headlight contains many other parts that allow its meaningful use in a motor vehicle, in particular a car or motorcycle. It should be noted at this point that the "headlight" shown and described here can also serve as a headlight module or as a lighting unit that sits in a headlight that has a plurality of modules. The term "headlight" is thus to be understood in this broader sense.

Lichttechnischer starting point of the headlamp is a laser light source 2 , which, bundled by a focusing optics 3 a laser beam 4 emits. The laser light source is a laser driver 5 assigned, which serves for power supply and for monitoring the laser emission or eg for temperature control and can also be configured to modulate the intensity of the emitted laser beam. By "modulating" in the context of the present invention is meant that the intensity of the laser light source can be changed, be it continuous or pulsed, in the sense of switching on and off.

The laser light source 2 For example, there is blue or UV light in the form of the laser beam 4 which is on a phosphorus 6 a light conversion agent which serves in a known manner for light conversion. The phosphor 6 - One could also speak of a phosphorus body - converts blue or UV light, for example, into "white" light. In the context of the present invention, "phosphorus" is understood in general to mean a part of a substance or a mixture of substances which converts light of one wavelength into light of another wavelength or of a wavelength mixture, in particular "white" light, which is termed " Wavelength conversion "is subsumable.

One uses luminescent dyes, wherein the output wavelength is generally shorter and thus more energetic than the emitted wavelength mixture. The desired white light impression is created by additive color mixing. 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. For the light conversion agent - the "phosphor" - are for example optoceramics in question, these are transparent ceramics, such as YAG: Ce (an yttrium-aluminum garnet doped with cerium).

The phosphor usually has the shape of a small plate, whereby it is possible to work according to the reflected-light or the transmitted-light principle. In the first case ("reflective", incident light), the converted light is radiated on the same side on which the laser beam impinges, in the second, in 1 In the case shown ("transmissive", transmitted light), the converted light is radiated on the side opposite to the side irradiated by the laser. In both cases, the light used can also consist of a mixture of, for example, blue laser light with the converted light in order to obtain as "white" light as possible.

The phosphor 6 is in the present case cuboid, but it may, depending on the specific application, also be platelet-shaped, ie a body in which one dimension is very small compared to the other. The phosphorus does not have to be even, it can also have a curvature.

As mentioned above, in the present case, the phosphorus 6 transmissive, ie the outgoing on the opposite side of the laser beam incidence light is emitted over a large solid angle mixed light 7 the desired color. This mixed light emanating from the phosphor 7 becomes by means of a projection system 8th , which is designed here as a reflector, projected into the carriageway space.

If the phosphor 6 has damage, such as overheating or breakage, the laser beam 4 through the phosphor 6 pass through. In 1 is a passing through in an accident, compared to the mixed light strongly focused and correspond energy-dense interference beam 9 located. It is clear that such a relatively high-energy interfering beam can pose a potential danger to living beings, in particular to the eyesight of humans, since it passes through the projection system 8th the headlight 1 leave and do damage.

In order to recognize such an accident immediately, the invention now provides that on the phosphor 6 at least two electrodes, in 1 the electrodes 10 . 11 , are arranged, which form the coverings of a capacitor C _P with the phosphor as a dielectric, and a measuring device 12 is provided, with which the electrodes are connected and which is adapted to measure the capacitance of the capacitor C _P and for outputting a signal s, if the determined capacitance is outside a predetermined tolerance range around a desired value. In 1 are two lines 13 . 14 plotted the electrodes 10 . 11 with the measuring device 12 connect. The signal s can be the laser driver 5 be fed to this for immediate shutdown of the laser light source 2 to initiate, if there is an accident and also the signal s of a display device 15 be supplied for delivery, for example, an alarm signal.

In 2 which is an enlarged detail of the 1 represents, it can be seen also that the phosphor can optionally be encapsulated, for example by means of transparent or translucent Abdeckplättchen 16 . 17 , so that disturbing environmental influences, such as a condensate, on the phosphor can not occur or the capacity or the impedance of the phosphor 6 is not affected. On the other hand, it is also possible to provide no encapsulation and intentionally by a corresponding design of the electrodes, the capacity to make highly dependent on surface deposits. Thus, for example, a condensation on the surface of the phosphor can be detected, which is dangerous for the operation, as by a deflection, a deflection of the laser beam occurs and thus the risk of an unscheduled leakage of a laser interference beam 9 ,

In 3 is a further enlarged view of a cuboid phosphor 6 with two electrodes 10 . 11 shown from which lines 13 . 14 go out, wherein the phosphorus body has a dielectric constant ε at an electrode distance d. Of course, the electrodes could also be arranged on other, but preferably not necessarily opposite surfaces of the phosphor.

4 shows a side view of a damaged phosphor 6 which is damage in the form of cracks 18 shows. Such cracks lead to a change in the capacitance of the capacitor C _P , that of the electrodes 10 . 11 and the phosphorus 6 is formed.

What the measuring device 12 As should be apparent to those skilled in the art, there are innumerable measurement techniques and devices for capacity measurement. In particular, alternating current measuring bridges are suitable, of which in 5 the Messtechnik Wien known bridge is shown. The bridge includes four pointing, with two branches having resistors R ₂ and R ₃ , and the other two branches having impedances consisting of a capacitor and a shunt resistor in the equivalent circuit shown. In an impedance branch is to be measured, here variable capacitor C _{P of} the phosphor 6 and the parallel resistance R _P , which is also represented by the phosphor. In the other impedance branch is a reference capacitor C ₁ and its associated resistor R ₁ . The bridge lies with two bridge nodes at an AC voltage U _W. If the bridge is in a balanced state, then the voltage U ₀ between the other two bridge nodes is equal to zero. Applied to the invention, it makes sense to make the reference capacitor C _{1 the} same in electrical terms as that of the phosphor 6 formed capacitor C _P.

In undisturbed operation of the headlamp, namely undamaged phosphorus, the bridge is balanced. For example, if a crack occurs 18 ( 4 ) in the phosphor 6 on, the capacitance of the capacitor C _{P changes} , the bridge is detuned and a voltage U ₀ occurs in the measuring device 12 detected and can be recycled accordingly.

It should again be emphasized that this method of detecting a change in capacity is only one of many possibilities which are available to the person skilled in the art. In principle, furthermore, with a corresponding design of the measuring device, a change of the parallel resistance R _P could additionally or alternatively be evaluated as a criterion for a fault condition of the phosphor.

Furthermore, it is often useful if the electrodes are transparent and consist for example of vapor-deposited indium tin oxide. Such Of course, solution can be used to advantage with a transmissive phosphor.

In principle, it is possible to use both reflective and transmissive beam paths for the headlight, with a mixture of reflective and transmissive beam paths ultimately not being ruled out.

The headlight may also be one with a scanning laser system in which an image is "written" on the phosphor by a laser beam deflected by micromirrors, which image is then projected onto the road via an imaging system. An example of such a headlamp for generating an image by a scanning laser beam is as in the published Austrian patent application AT 514 633 A1 the applicant described.

LIST OF REFERENCE NUMBERS

1

 headlights

2

 Laser light source

3

 focusing optics

4

 laser beam

5

 laser driver

6

 phosphorus

7

 mixed light

8th

 projection system

9

 spurious

10

 electrode

11

 electrode

12

 measuring device

13

 management

14

 management

15

 display

16

 cover plates

17

 cover plates

18

 cracks

ε

permittivity

C _P

 capacitor

C ₁

 capacitor

R ₁

 resistance

R ₂

 resistance

R ₃

 resistance

R _P

 resistance

U _W

 AC

U ₀

 tension

d

 distance

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• AT 514633 A1 [0042]

Claims (10)

Headlight for motor vehicles with at least one laser light source ( 1 ), whose laser beam ( 3 ) is directed to at least one light conversion agent comprising a phosphorus ( 6 ) for light conversion, and with a projection system ( 8th ) for projecting the light generated at the at least one light conversion means ( 7 ) in the carriageway space, characterized in that at least two electrodes ( 10 . 11 ) are arranged, which form the coverings of a capacitor (C _P ) with the phosphor as a dielectric, and a measuring device ( 12 ) is provided, with which the at least two electrodes are connected and which is adapted for measuring the capacitance of the capacitor and for outputting a signal (s), if the determined capacitance is outside a specified tolerance range around a desired value. Headlamp according to claim 1, characterized in that the measuring device is designed as an alternating voltage measuring bridge and the capacitor is connected to the phosphor as a dielectric in a bridge branch. Headlight according to claim 2, characterized in that the AC voltage bridge is a Vienna bridge. Headlamp according to claim 2 or 3, characterized in that in a further bridge branch, a reference capacitor is the same as the phosphor is configured. Headlamp according to one of claims 1 to 4, characterized in that the phosphor is cuboidal. Headlamp according to one of claims 1 to 4, characterized in that the phosphor is platelet-shaped. Headlight according to one of claims 1 to 6, characterized in that the phosphorus is transmissive. Headlamp according to one of claims 1 to 7, characterized in that the electrodes are transparent. Headlight according to claim 8, characterized in that the electrodes consist of vapor-deposited indium tin oxide. Headlamp according to one of claims 1 to 9, characterized in that the phosphor is reflective.

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