Method of Producing an Infrared Lamp

Abstract

A description is given of a method of producing an infrared lamp (1) for a vehicle night vision system (12), in which a tube (2) which surrounds a radiation source (3) that emits infrared radiation and light radiation is provided with an infrared-transmitting coating (10). It is ensured, by setting specific process parameters in the coating process and/or by post-treating the coated tube (2), that holes (11) form in an irregular arrangement in the coating (10), which holes have at least in some areas a defined average size and a defined average surface density. A description is furthermore given of a corresponding infrared lamp (1) and of a headlamp comprising such an infrared lamp (1) for a vehicle night vision system (12).

Description

FIG. 1 shows a schematic diagram of a halogen lamp according to the prior art.

FIG. 2 shows a schematic diagram of the halogen lamp of FIG. 1, but with the coating according to the invention.

FIG. 3 shows a microscope image of a coating according to the invention on a lamp surface, according to a first example of embodiment.

FIG. 4 shows a microscope image of a coating according to the invention on a lamp surface, according to a second example of embodiment.

FIG. 5 shows a schematic diagram of a process for producing the infrared lamp according to the invention.

FIG. 6 shows a highly schematic diagram of a motor vehicle night vision system.

FIG. 1 shows a schematic diagram of a conventional halogen lamp according to the prior art. By way of example, the so-called H7 bulbs are constructed in this way. The radiation source used here is a coil 3 which is held by two electrodes 4, 5. The coil 3 with the electrodes 4, 5 is surrounded by a glass tube 2 which is filled with a conventional halogen gas. Located at the end of this tube 2 is the so-called lamp tip or sealed tip 9 which is caused by the manufacturing process. The electrodes 4, 5 are fixed to thin metal foils 6 in a so-called pinch area 8. Fixed to these metal foils 6 are supply lines 7 which at the other end pass towards the outside. This line transfer via the metal foils 6 takes place for sealing reasons. Using its pinch area 8 as a base, the lamp 7 can be inserted in a holder provided for such bulbs, wherein the supply lines 7 are pushed into suitable connector contacts. During operation, a voltage of around 12-14 V is usually applied to the coil 3, and as a result the coil 3 begins to glow. Both infrared radiation and visible light are then emitted from the lamp.

According to the invention, such a lamp 1 is provided with a coating 10 as shown in FIG. 2. This coating 10 has holes 11 in an irregular, random arrangement, for example irregularly shaped defects or cracks. In the illustrated example of embodiment, only the central region of the lamp tube 2 is provided with the coating 10. The sealed tip 9 and the pinch 8 have not been coated.

FIGS. 3 and 4 in each case show microscope images of part of the coating 10, on which the holes 11 can clearly be seen. It can also be seen here that these holes 11 occur in an irregular manner, are irregularly shaped and are of different size.

These holes 11 are produced by setting specific process parameters during the coating operation or in a post-treatment process following the coating operation, wherein the surface density and/or average size are precisely defined by selecting suitable parameters. FIG. 3 shows part of a coating 10 with a surface density and average size of the holes 11 distributed relatively uniformly over the entire surface. FIG. 4 on the other hand shows part of a coating 10 in which, by suitably selecting the process parameters and/or by virtue of the type of post-treatment process, it has been ensured that a higher surface density and greater average size of the holes 11 occurs in certain regions, whereas in other regions there is a lower hole density and smaller average size of the holes 11.

In both cases, these are multilayer coatings with alternating Si and SiO₂ layers. The layers have in each case been applied in a so-called MicroDyn sputtering process. This process is a sputtering process in which the plasma is produced not by particle bombardment but rather by microwaves. As a result, even higher densities and higher refractive indices can be achieved than in the conventional ion-assisted vapor-deposition of layers. In particular, there is no diffusion between the individual layers. These lamps coated in this way have then been exposed to a defined thermal post-treatment process.

The process of producing such a lamp 1 is shown once again in FIG. 5 in the form of a flow chart. In a first process step I, a bulb is produced in a conventional manner, for example an H7 halogen bulb as shown in FIG. 1. In process step II, this bulb is then coated. Regions of the lamp which are to be left free of the coating are preferably covered by the lamp holder during the coating operation. In a further process step III, the desired holes are then produced with the defined average surface density and with a defined average size.

In the examples of embodiments shown in FIGS. 3 and 4, the coatings have in each case been heated for 100 hours by a heating device, wherein the temperature is above 600° C. It has been found that at a temperature of 650° C. the number of holes no longer significantly increases after 100 hours. Since the temperature of 650° C. is also above the maximum temperature which can be reached on the tube during operation of the lamp, with these parameters it is also ensured that the holes do not inadvertently expand or the number of holes does not increase during subsequent operation.

For most use purposes, it is sufficient to produce a uniform density distribution and average size as shown in FIG. 3. In principle, however, it is also possible to produce different hole densities and average sizes in some areas, as shown in FIG. 4. For example, a higher hole density may be achieved in the region of the coil than in the other regions if, in addition or as an alternative to external heating, the coil itself is made to glow and thus the temperature of the tube is increased in a targeted manner at this location. FIG. 4 shows the effect after 100 hours of heating by the coil, wherein a temperature of on average 650° C. has likewise been reached in the tube. Since, however, glowing of the coil in the post-treatment process would automatically also lead to a reduction in the service life of the subsequent lamp, purely external heating in a heating device is the preferred measure.

It has been found that the thermal post-treatment of the coating does not have any negative effects on the reflection spectrum. The filter edge is merely shifted towards lower wavelengths.

The coating should therefore preferably be built up such that the filter edge of the coating lies in the range from 830 to 880 nm at an operating temperature of the lamp. The number and size of the holes made is then sufficient to compensate the residual red light in the run-up phase of the lamp. Preferably, the filter edge should lie in the range from 730 to 780 nm in the “cold” state of the lamp. The coating on the lamp reaches a temperature of 600-700° C. approximately three minutes after switch-on. In the process, the filter edge is shifted by 100 nm into the desired range of 830 to 880 nm.

FIG. 6 shows in a highly schematic manner a motor vehicle night vision system 12 in which an infrared lamp according to the invention can be used. The front part of a motor vehicle 13 is schematically shown here. The IR lamp 1 according to the invention is placed in a conventional reflector 14 within a headlamp 15. Of course, the vehicle 13 also has other conventional lamps and headlamp systems such as full beam, low beam, fog lights, etc.

The IR light IR exiting from the infrared lamp 1 according to the invention is emitted via the reflector 14 out of the headlamp 15 in the emission direction A into the traffic space and strikes any object O located in said traffic space. This object O reflects the IR radiation. The reflected IR radiation IR_R is detected by an infrared-sensitive camera system 16 which is located in the vehicle 13 for example at the top behind the windscreen. In principle, the IR-sensitive detector used may be a normal CCD or CMOS camera. Such cameras are IR-sensitive anyway, and for use in normal cameras have an IR filter which need only be removed for use in a night vision system. Preferably, a camera system 16 comprising two cameras at a distance from one another may be used in order to be better able to detect spatial information. After suitable processing, the images recorded by the IR camera system 16 can then be displayed to the driver of the motor vehicle 13 on a display (not shown). Automatic evaluation of the data is also possible, so that the driver is notified about objects O located on the road for example by means of acoustic signals or light signals.

In one particularly preferred example of embodiment, in such a motor vehicle night vision system use is made of a lamp 1—as shown in FIG. 2—which does not have any coating in the pinch area 8 and in the region of the sealed tip 9 but is provided with the coating 10 on all of the rest of its surface, said coating having the holes 11 according to the invention. The average surface density of the irregularly occurring holes and the average size thereof are set such that the visible light passing through the holes and the pinch and the sealed tip, together with the amount of visible red light passing through the infrared-transmitting coating, has a spectrum which essentially has a color in the ECE white region. Moreover, the hole size and hole density and the regions left free of the coating in the pinch area and at the sealed tip are selected such that the white light L emitted into the traffic space in the emission direction A is less than 60 candela, particularly preferably less than 50 candela.

Finally, it should be pointed out once again that the methods and lamps shown in the figures and in the description are merely examples of embodiments which can be widely varied by the person skilled in the art without departing from the scope of the invention. For example, further method steps may be added to the method sequence described in detail. Moreover, it should be pointed out for the sake of completeness that the use of the indefinite article “a” or “an” does not rule out the fact that the relevant features may also be present a number of times and that the use of the term “comprise” does not rule out the existence of further elements or steps.

Claims

1. A method of producing an infrared lamp (1) for a vehicle night vision system (12), in which a tube (2) which surrounds a radiation source (3) that emits infrared radiation and light radiation is provided with an infrared-transmitting coating (10), wherein, by setting specific process parameters in the coating process and/or by post-treating the coated tube (2), it is ensured that holes (11) form in an irregular arrangement in the coating (10), which holes have at least in some areas a defined average size and a defined average surface density.

2. A method as claimed in claim 1, characterized in that the average size and the average surface density are essentially selected such that the light radiation passing through the holes (11) during operation of the lamp (1) has a sufficient intensity to mask an amount of visible red light which is transmitted through the infrared-transmitting coating (10).

3. A method as claimed in claim 1, characterized in that certain part-regions (8, 9) of the tube (2) remain without an infrared-transmitting coating (10) and the average size and average surface density of the holes (11) in the coating (10) are essentially selected such that the light radiation passing through the holes (11) during operation of the lamp (1), together with the light radiation passing through the coating-free part-regions (8, 9) of the tube (2), has a sufficient intensity to mask an amount of visible red light which is transmitted through the infrared-transmitting coating (10).

4. A method as claimed in claim 3, characterized in that the holes (11) have an average size of between 1 and 20 μm, preferably between 2 and 8 μm, and in that the average surface density is approximately 10 to 40 holes per mm2, preferably 15 to 25 holes per mm2.

5. A method as claimed in claim 1, characterized in that the average size and average surface density of the holes (11) in the coating (10) and possibly the coating-free part-regions (8, 9) of the tube (2) are essentially designed and/or arranged such that the light radiation exiting through the holes (11) and possibly the uncoated part-regions (8, 9) during operation of the lamp (1), mixed with the amount of visible red light which is transmitted through the infrared-transmitting coating (10), results overall in light which essentially has a color in the ECE white region.

6. A method as claimed in claim 1, characterized in that, in order to form the infrared-transmitting coating (10) on the tube (2), a number of coating layers are applied on top of one another.

7. A method as claimed in claim 1, characterized in that the coating layers are applied by means of a sputtering process (II).

8. A method as claimed in claim 1, characterized in that the coated tube (2) is subjected to a defined heating process (III) until holes (11) having the defined average size and average surface density have formed in the coating (10).

9. A method as claimed in claim 8, characterized in that the coated tube (2) is kept at a given minimum temperature at least until the number and average size of the holes (11) no longer changes significantly.

10. A method as claimed in claim 1, characterized in that, during the coating process, a defined vacuum is set such that holes (11) having the defined average size and average surface density form in the coating (10).

11. A method as claimed in claim 1, characterized in that the coating (10) is built up such that a filter edge of the coating lies in the range from 830 to 880 nm at an operating temperature of the lamp.

12. An infrared lamp (1) for a vehicle night vision system (12), comprising a radiation source (3) which emits infrared radiation and light radiation,comprising a tube (2) which surrounds the radiation source (3),and comprising an infrared-transmitting coating (10) which is applied to the tube (2) and which has an irregular arrangement of holes (11) having at least in some areas a defined average size and a defined average surface density.

13. A headlamp (15) for a vehicle night vision system (12), comprising an infrared lamp (1) as claimed in claim 12.

14. A headlamp as claimed in claim 13, characterized in that the average size and the average surface density of the holes (11) in the coating (10) and possibly the uncoated part-regions (8, 9) of the tube (2) are essentially designed such that the light radiation exiting through the holes (11) and possibly the uncoated part-regions (8, 9) during operation of the lamp (1), mixed with the amount of visible red light which is transmitted through the infrared-transmitting coating (10), results overall in light (L) having a color which essentially lies in the ECE white region, wherein the light intensity when the light is emitted from the vehicle headlamp (15) in emission direction (R) is less than approximately 60 candela.

15. The use of an infrared lamp (1) as claimed in claim 12 for a motor vehicle night vision system (12).