EP1766444A1 - Night vision system for vehicles - Google Patents

Abstract

A filter transmits white light of a partial beam from the radiation source at one angle, and transmits white light of another partial beam from the radiation source at another angle.

Description

 Night vision system for vehicles

The present invention relates to night vision auxiliary systems for vehicles. Such systems are known, which comprise an infrared headlight which emits radiation directed outwards in front of the vehicle, and an infrared camera and a system for transmitting an image recorded by the camera in visible form to the driver , The headlamp has a white light source and a filter, which suppresses the visible part of the radiation of the radiation source and transmits the part located in the infrared region.

However, in practice, such a filter often leaves part of the visible, especially in the red color range

Radiation happen. However, in the case of a headlight, such red transmission radiations, irrespective of how intense they are, are troublesome since they can lead to a confusion between the front and rear of the vehicle for other drivers. The improvement of the filters with regard to the suppression of the red

Light while retaining the useful portion of the infrared radiation, i. The radiation range between 800nm and 100nm is expensive. The problem here is that the (red) area to be suppressed adjoins directly to the useful, pass-through infrared range. For this purpose, it would be necessary for the transmission characteristic of the filter to have steep edges, since a necessary very good suppression in the red region contrasts with a necessary very good transmission in the IR range.

In order to solve this problem, DE 699 03 076 discloses an infrared illuminating device which comprises a filter whose transmittance is designed to emit white and infrared radiation along an axis of the device, the intensity of the white radiation indeed being quite high Zero can be different, but carries less than 2000 Cd be¬. This is achieved by the fact that the filter transmits infrared rays (IR rays), ultraviolet rays (UV rays) and visible, blue and red near-rays and visible Grund¬ rays with yellow-green color between them. FIG. 1 schematically shows the transmittance T of a notch filter as it can be used as a function of the wavelength λ according to an embodiment in DE 699 03 076. The visible residual radiation transmitted in this case then adds to a white color impression.

Such notch filters can be realized by means of a multilayer system. Their reflection and transmission characteristics are based essentially on interference effects. According to the prior art, the filter should then be realized in such a way that it can transmit the visible radiation of a radiation source in such a way that the synthesis of the transmitted visible part produces white light (see claim 3 of DE 69903 076). , Since interference filters show an angle-dependent transmission behavior, the filter must, however, be adapted to the respective illumination geometry of the headlight. For example, FIG. 3 a shows a headlamp 2 with a lighting geometry in which the filter 10 is acted upon essentially vertically. In contrast, the illumination geometry of the headlight in FIG. 3b leads to a loading geometry in which the vertical action essentially plays no role. However, such an adaptation of the filter to a respective new geometry is complex and therefore expensive.

It is therefore the object of the present invention to specify a filter whose transmission characteristic has a great tolerance to variations in the illumination geometry.

Another problem is the signal fluctuations which are difficult to avoid associated with the production of such interference filters. Among the key parameters that determine the transmission characteristics are the opti- layer thicknesses and the refractive indices of the layers. Small variations in these parameters during the coating process or, much more likely, from one coating to the next, can influence which parts of the visible light are transmitted. It is difficult to observe that only a small part of the visible radiation is to be transmitted (for example in the range of 0.5%) and therefore even small uncertainties in the transmission can lead to large changes in the color impression.

It is therefore a further object of the present invention to provide a method according to which the interference filters required for the illumination devices can be produced in high yield without the need for cost-intensive measures for reducing the manufacturing variations.

Solution according to the invention

As the person skilled in the art knows, the color impression is determined by essentially three influencing factors: a) the emission characteristic of the light source (typical light sources have their maximum in the green or yellow-green spectral range), b) a physiological factor which depends on the wavelength-dependent light inc - sensitivity of the human visual system is related, where the photosensitivity in the yellow is highest and c) the transmission characteristic of the optical system used Sys¬. Technically, the color impression can be specified by means of the so-called color coordinates. FIG. 2 shows a schematic diagram of how blue (B), green (G), red (R) and yellow (Y) color impressions are to be assigned to a corresponding diagram. In addition, in Fig. 2, the area is framed by a broken line in which a white color impression prevails.

The hatched area shown in FIG. 2 indicates the legally permissible range currently prescribed for a system in accordance with the so-called ECE standard, which are fulfilled here. that should. This permitted range is shown enlarged again in FIG. 4.

The radiation emanating from a lighting device has to be legally admitted within this

ECE area lie. The object is then to realize this simultaneously for different application geometries. As a rule, the typical radiation sources radiate in each direction in which they actually emit, with essentially the same spectral characteristic. In order to achieve the desired tolerance to the loading geometry, a filter according to the invention has the property of transmitting a portion of the visible radiation for a wide range of angles of incidence, such that for each of the angles of incidence of the area white light is transmitted.

This can be realized by the fact that the transmitted radiation leads to the same color coordinates for each angle of the range immediately after exiting the filter. However, such a restrictive condition is not necessary at all. As the inventor has stated, it suffices to ensure that color coordinates which are within the legally permitted range are respectively realized for the angle of incidence range. As the inventor also found, it is particularly advantageous to allow a variation along the blue-yellow axis (Figure 4 along the axis AA ^v ). In the production of the interference filter, particular care is taken during the design phase as well as during the production phase that the transmission characteristic of the filter in the green region is particularly stable. This both in terms of manufacturing tolerances as well as with respect to angle dependence. By contrast, lower requirements are placed on the stability in the blue and yellow-red areas. This has the consequence that, although there are variations of the color coordinates with respect to angles of incidence and / or manufacturing tolerances. However, these variations are essentially along the axis AA ¹ in FIG Figure 4 from. This makes it easier and better to comply with legal requirements than was previously possible according to the prior art.

The production of a filter according to the invention will now be described in detail by way of example, which leads to color coordinates for an angle range from 0 ° to 40 °, all of which lie within the ECE white range.

The filter is to be used in a night vision auxiliary system equipped with a halogen headlamp from the company HRS (12V, 55W, 64211SUP). The corresponding spectral profile is shown in FIG. The schematic structure of such a headlamp is shown in FIG. 6a.

The substrate material used for the filter is a Corning glass substrate

In the example, the coating materials niobium oxide are used as high refractive index material and SiO2 as low refractive index material for the filter. Alternative coating materials would be possible, for example, titanium oxide / silicon oxide or tantalum oxide / silicon oxide.

To determine the required layer thicknesses of the multilayer system, a commercial thin film calculation program was used (OptiLayer for Windows by Messrs A. Tikhonravov and M. Trubetskov).

By means of a so-called RayTrace program (ASAP, commercial software), ie with a software which allows to simulate optical paths of beams in complex optical systems, it is determined which angles of incidence are relevant. For the example to be described here, the calculation with ASAP shows that the centroid angle of incidence on the filter is 20 °. However, to be largely independent of the exact system layout, the design will additionally be for 0 to 40 ° optimized so that the variation along the ^s ' ECE white area axis''(Figure 4 along the axis AA ^v ).

For this purpose, the design is optimized step by step for an angle. First, a design is determined, which transmits on average less than 0.5% for 20 ° incidence angle in the visible range. The design should also have a steep edge whose T = 50% point in the example is 780nm and which transmits more than 75% for the infrared range (wavelength 800-100nm). In addition, in order to protect the human eye in the application, the design is designed such that less than 60% are transmitted from about 1040 nm to a width of at least 25 nm in the near infrared range.

Thereafter, for the angle of incidence of 20 ° while maintaining the spectral characteristic, the color locus is optimized in such a way that it comes as close as possible to the ECE standard (ie, as close as possible and preferably exactly to the coordinates: x = 0.375 and y = 0.375). Subsequently, the color coordinates for the angles of incidence 0 °, 30 ° and 40 ° are optimized so that they come within the range of the ECE standard. For these angles of incidence, however, it is not necessary to realize the same color coordinates as for the angle of incidence of 20 °. It is only required that the angle shift as far as possible within the ECE white area along an axis which is indicated in Figure 4 with the references AA ^x . This is achieved particularly easily if it is ensured that the spectra of the different angles for the green region (480-580 nm) have the smallest possible change. The result of such an optimization is shown in FIG. 6b for 0 °, 10 °, 20 °, 30 ° and 40 ° angle of incidence. The AA ¹ axis can be defined using the linear equation y = 0.695 * x + 0.1. In FIG. 6b, it is noticeable that the x coordinate increases monotonously as the angle of incidence increases. The y coordinate should, at an x-coordinate, which lies in the interval 0.31 <x <0.45, be maximally 0.025 of the defined deviating straight lines. For smaller x, the color locus is no longer in the ECE region, for larger x, a more horizontal course is desirable, since here the ECE region has the corresponding course.

The limitation of the change in the green range is achieved by heavily weighting this range in the optimization. This is not only necessary to ensure that the filter design for incidence angles of 0 ° to 40 ° run along the ECE white area, but also to keep the Lichtstärkeän¬ tion small, since in this case the green area has the largest th influence.

Table 1 lists the optical layer thickness distribution of the design and the index of refraction used.

The refractive index of the material used niobium oxide is 2.34 and silicon oxide is 1.47.

For the production of the filter, sputtering technology was used in the example (more precisely: reactive DC magnetron sputtering ring). In situ, the optical spectra are continuously determined during the process (monitoring) and the sputtering process is corrected for measured deviations from the calculated target spectrum. This ensures that the realized

Filter actually, especially in the green area, the gefor¬ derten optical characteristics have. In other words, in order for the color locus to pass into the ECE white, the monitoring is most heavily weighted during the production of the product, especially in the wavelength range of 480-580 nm.

Alternatively, other coating techniques can also be used. These include, among others, the PVD and CVD processes. As PVD processes, for example, thermal evaporation can be used in particular when this process is plasma-assisted (IAD). If such a filter is incorporated into the beam path of a headlamp, an infrared illumination device for motor vehicles, for example a headlamp, can be realized with at least one radiation source and a filter, wherein the device has a white line in one axis of the device And infrared radiation in a wavelength range which is between 800 and 1200 nm, the infrared radiation having an intensity of more than 25 W / sr and the white radiation having a non-zero intensity of less than 2000 Cd Has. The filter is capable of transmitting a first visible part of a first partial beam of the radiation source at a first angle and a second visible part of a second partial beam of the radiation source at a second angle different from the first one. It is characteristic that the transmitted first visible part forms white light and the transmitted second visible part forms white light.

Table 1

Claims

claims 1. Infrared illumination device for motor vehicles, for example a headlamp, with at least one Strahlungs¬ source (2) and a filter (10), wherein the device emit in one axis, a white and infrared radiation in a wavelength range between 800 and 1200nm ver¬ where the infrared radiation has an intensity of more than 25 W / sr and the white radiation has an intensity equal to zero of less than 2000 Cd and the filter has at a first angle a first visible part of a first partial beam Radiation source is able to transmit and the filter is able to transmit a second visible part of a second partial beam of the radiation source at a second angle different from the first one, characterized in that the second angle differs considerably from the first one and the transmitted first visible part white light forms and the transmitted second visible part forms white light. 2. Infrared illumination device according to claim 1, characterized in that the greater of the two angles leads to an x-coordinate of the color locus of the corresponding transmitted visible part, which is greater than the x-coordinate of the color locus of the transmitted visible part to the smaller Angle leads. 3. Infrared illumination device, for motor vehicles, for example, a headlamp, with at least one Strahlungs¬ source (2) and a filter (10), the device in one axis emit a white and infrared radiation in a wavelength range between 800 and 1200nm ver ¬ mag, wherein the infrared radiation has an intensity of more than 25 W / sr and the white radiation has an intensity equal to zero of less than 2000 Cd characterized gekennzeich¬ net that for any angle pair within the Win¬ kelbereichs of 0 ° to 40 ° with a first angle and a second angle defines the filter under the first Angle is able to transmit a first visible part of a first partial beam of the radiation source and the filter is able to transmit a second visible part of a second partial beam of the radiation source below the second angle different from the first one, and the transmitted first visible part is white light forms and the transmitted zwei¬ te visible part forms white light. 4. Infrared illumination device according to one of claims 2 or 3, characterized in that the respective y-coordinate of the color locus of the angles corresponding to the transferred visible part deviates by no more than 0.025 from the equation defined by the equation y = 0.695 * x + 0.1 lines , for x-coordinates in the interval 0.31 <x <0.45.