Optical rain sensor device for a motor vehicle

Optical rain sensor device for a motor vehicle

State of the art

The invention relates to an optical rain sensor device for a motor vehicle according to the preamble of claim 1st

optical rain sensor or rain sensor devices are known for motor vehicles from the prior art, which are coupled in the vehicle interior via a coupling medium (eg., silicone) to the windshield. The optical rain sensor thereby derives a light beam of a transmitter and a radiation source through a lens system, ie, a sensor deroptikanordnung in the windshield. On the disc surface, the light is totally internally reflected and directed through another lens or a receiver optical assembly on a light detector or receiver. The more water that is on the disc surface of the windshield, the lower the reflection and thus also the temperature measured by the light detector signal. The optical rain sensor can control the wiper system of the motor vehicle as a function of the detected amount of rain and automatically select the most effective level of wiping speed.

Optical rain sensors of the embodiment described above are known for example from DE 102 61 244 Al.

The light detector should be shielded as possible of extraneous light (for. Example, sunlight) in order to avoid interference. In addition to the ambient light by sunlight from outside are also moisture and dirt inside the vehicle one of the disturbances in the rainfall provision. Under certain environmental conditions, there is on the inside of the windshield and the rain sensor, particularly at the rain sensor described sensitive optical or opto-electronic or electronic components, namely the lens systems, the radiation source and the light receiver to fitting, which influences the optical properties of the optical path between the radiation source and the light receiver in the rain sensor. Fitting manifests itself in a variety of water droplets of different size on the surfaces which influence the geometric and reflective properties of the components, especially the lens systems. An error occurring in the lens system fitting provides generally for a lower transmission of the optical path in the rain sensor, since the light beams can not be injected at the correct angle to the windshield by the large number of small water droplets which optically also act as small lenses. Therefore, only a part of the light hits in a necessary for total reflection angle of 45 ° to the surface of the windshield. This means that a significantly higher derivative for the disk cover of the rain sensor must be considered with respect to the transmission properties of the windscreen. Furthermore, the lens surface is given by the variety of water sertröpfchen other reflexive properties. The fact that in the presence of a fitting the light emitted by the rain sensor light no longer two (air - lens system - air), but three optical media (air - water - lens system - water - air) has to go through, the number of interfaces between optically different media, to which a certain portion of the light is reflected by two increased to four. This also leads to a loss of efficiency of the optical system. Furthermore, despite a dry windscreen initiated depending on the size of water droplets in connection with vibrations, which are caused in particular by the drive motor of the motor vehicle or by driving activity, mistakenly wipe cycles. In contrast to the radiation source is generated in the light receiver of the optical rain sensor barely power loss and heat, so that there also preferred fitting setting. For these reasons, a fog reducing the optical and optoelectronic components, in particular the lens system of the optical rain sensor is desirable. From the practice are known rain sensor systems in which the fitting is reduced electrically by a heating module. The lens system (especially at temperatures below 25 ° C) slightly heated in the presence of a risk of fogging to change the microclimate in the rain sensor in terms of the dew point and thus to prevent the emergence of the working stroke or reduce these.

Also, contamination can adversely affect the optical properties of the optical components. Contamination results regularly a filter effect or absorption of the light. Therefore in the known systems using closed housing for the rain sensors to keep the influence of particles from the vehicle interior air as low as possible.

ADVANTAGES OF THE INVENTION

The inventive optical rain sensor device for a motor vehicle, with several components, namely at least an electromagnetic radiation source, at least a receiving device, at least one transmitter optics assembly and at least one receiver optics arrangement, wherein by means of the at least one receiving means, a light emitted from the at least one radiation source of electromagnetic radiation is receivable, wherein the electromagnetic radiation from the at least one radiation source by means of passed at least one transmitter optics arrangement at an interface of the windshield window of the motor vehicle to the exterior of the vehicle, reflected there and by the one receiver optics arrangement further on the at least one receiving device is at least guided, wherein the surface of at least one of the components is at least partially provided with a nano-coating, which causes a photocatalytic self-cleaning of surfaces, has the advantage that fogging and contamination of the surfaces of the optical and opto-electronic and electronic components is largely avoided or reduced.

It is suggested to provide the particular optically effective surfaces of the optical components, in particular the transmitter optics assembly, the receiver optics arrangement, the electrical romagnetische radiation source and / or the receiving device, the optical rain sensor with a special coating, which can photocatalytic self-cleaning of surfaces cause. As "photocatalytic self-cleaning" one means the quality of surfaces which nopartikeln with a nano coating with sodium preferably made of titanium dioxide (TiO₂) Were coated, and thereby are capable upon irradiation with sunlight (specifically ultraviolet light) to decompose organic materials on the surface. Therefore, the surfaces remain clean. Further acts, such a coating antimicrobial. Moreover, such coating results in that no droplets forms on the surfaces of the water, but only a thin layer thereby misting of these surfaces is largely avoided. Derarti- ge surfaces are referred to as super hydrophilic.

By the photocatalytic self-cleaning of the devices, it is now possible to use optical rain sensors also open housing, which would in particular for the integration of additional functions in the rain sensor such as a Taupunktsensorik (also with a moisture measurement), an air quality sensor or the like is advantageous. For both functions, an air exchange with the environment is needed.

Through the anti-fogging effect of the nanocoating can be entirely dispensed with a heating module in the rain sensor. The optical properties are only slightly affected by a thin (almost invisible) film of water in fogging. A coating of titanium dioxide nanoparticles causes a cost savings and reduces the space requirement on the circuit board, since the heating module is no longer needed. Thus, the space requirement of the rain sensor is reduced, or the functionality of the rain sensor - at constant space - be extended.

An exemplary embodiment of the invention is described in principle with reference to the drawing.

Brief Description of Drawings

The single figure of the drawing shows a simplified representation of an optical rain sensor device according to the invention.

Description of embodiments

In the figure, an inventive optical rain sensor device is shown, which operates on the principle described below.

A source of electromagnetic radiation 6, such as an infrared LED or the like sends (the so-called useful light) from a certain angle of the inside of a pane or windshield 1 fro, ie Usually, (not shown) from the passenger compartment of a motor vehicle electromagnetic radiation 4, in the direction of the windshield 1. the radiation 4 passes through the interface between the interior and windshield 1 and is directed against the formed of the windshield 1 and the vehicle exterior interface 10, which is referred to in this field as a sensitive surface. In general, then, the light rays are parallel to the windshield first The angle of incidence of the electromagnetic radiation 4 from the interface 10 is chosen such that the electromagnetic radiation 4 in a non-for example, by rain drops 11 wetted windshield 1 at the interface 10 according to the laws of the optics in the direction of the inside of the windshield 1 as reflected radiation 5 is totalreflek- Animal T and a close to the disk inner side which is arranged for example embodied as an infrared LRD receiver 7 and a receiving device is detected. In a wetting of the pane 1 with the raindrops 11, this total reflection is as due to the changed refractive index ratios disturbed seen from the figure at the boundary surface 10 or removed so that a part is coupled out 4a of the electromagnetic radiation 4 to the outside, and less at the receiver 7 radiation 5 as in the case of total reflection arrives. From the onset of the incident light (or the signal differences) includes one ne of the radiation source 6 and the receiver 7 assigned, z. B. arranged on a circuit board evaluation unit 8 to the present degree of wetting and controlled accordingly wiping operations of the wiper. To realize this basic principle, the radiation source 6, the receiver 7 and the evaluation unit 8, together with a control unit, not shown, are housed in a casing 9 for the effective light beam guide with one of the radiation source 6 associated transmitter optics arrangement or coupling optics 3a and the receiver 7 associated receiver optics arrangement or output optical system is equipped 3b and for the purpose of undisturbed light line and input coupling of the radiation 4 or 5 into and out of the windshield 1 with an optical coupling medium as an intermediate layer 2, z. B. silicone, free of air bubbles to the windshield 1 is docked. The coupling-mentioned or Auskoppeloptiken 3a, 3b typically consist of lenses or lens systems, one side convex and their other side is flat. The transmitter optics assembly 3a, the receiver optics assembly 3b, the electromagnetic radiation source 6 and the receiver 7 are 3a to the optical components, 3b, 6, 7 of the optical rain sensor device, wherein the electromagnetic see radiation source 6 and the receiver 7, because of their function, of course, as optoelectronic and electronic components can be referred to.

In the present embodiment, the invention now the surfaces of the electrical netic radiation source 6, the receiver 7, the receiver optical assembly 3b and transmitter optics arrangement 3a or lens systems provided with a nano coating 12, which causes a photocatalytic self-cleaning surfaces. This fogging and contamination of these surfaces is very largely prevented or reduced in an advantageous manner. The nanocoating 12 has to nanoparticles of titanium dioxide (TiO₂) on.

In further embodiments, not shown, of course, only the surfaces of selected optical elements can 3a, 3b, 6, 7, in particular only partially (eg. As only the optically active part of the surface), be provided with a nano coating 12, which a photocatalytic self-cleaning of the surface causes.

Basis of the self-cleaning is the so-called photocatalysis. Titanium dioxide is a semiconductor in which sunlight coming light generates electron-hole pairs when the energy of the photons is greater than the band gap (internal photoelectric effect). The electrons or holes can in titanium dioxide diffuse to the surface, where they produce free radicals, which lead to the decomposition of organic substances. In particular, the holes have a high oxidative effect. OH radicals are formed from water. Organic substances are decomposed thereby. End products are often CO₂ and water. The super hydrophilic properties of surfaces shanks come about by oxygen vacancies on the titanium dioxide surface. At these locations, OH groups are bound to lead to good wetting with water.

There are products to be available with which produces nano coatings of titanium dioxide. An example of this is the VP TiO prepared by the method AERO SIL®-₂ P90 (hydrophilic fumed titanium dioxide).

The coating with titanium dioxide nanoparticles to the Optikanordnun- gene 3a, 3b and the light guide should preferably be performed while the sensor assembly, if the optics assemblies 3 a, 3b is composed of several individual parts. If the optics assemblies 3a, 3b executed as in the present embodiment, one piece, so the coating operation can also be performed in advance.