Abstract:
A sensor device for detecting moisture on a windscreen has a transmitter and a receiver and optics arranged between the transmitter and the receiver. The optics have an upper plane for connection to a windscreen, a decoupling region serving to decouple the electromagnetic rays from the optics into the windscreen, and a coupling region serving to couple the electromagnetic radiation from the windscreen into the optics, and which even for a small construction shall supply a usable signal. The decoupling region has at least one surface inclined relative to the upper plane of the optics.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a sensor device for detecting moisture on a windscreen comprising a transmitter and a receiver and optics arranged between the transmitter and the receiver, wherein the optics comprises an upper plane for connection to a windscreen, and wherein the optics comprises a decoupling region serving to decouple the electromagnetic rays from the optics into the windscreen, and a coupling region serving to couple the electromagnetic radiation from the windscreen into the optics. Furthermore the invention relates to optics for a sensor device of this kind and a motor vehicle with a windscreen and a sensor device arranged thereon. 
         [0003]    2. Brief Discussion of the Related Art 
         [0004]    The DE 40 06 174 C1 has disclosed a sensor device of the kind mentioned in the beginning. The windscreen has an optics arranged on it, which at one end has radiation introduced into it from a radiation transmitter. The radiation is reflected multiple times in the optics and in the plane supported against the topside of the optics. Decoupling of the rays from the windscreen depends upon the degree of wetting of the windscreen. The other end of the optics has a receiver arranged on it, which supplies a signal inversely proportional to the amount of precipitation. The sensor device operates according to the optical principle of total reflection. 
         [0005]    The basic problem consists in that the space available for the sensor device is becoming increasing smaller. This means that the surface of the optics forming the sensing region, is also reduced in size. As a result a signal of diminished accuracy is obtained. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is therefore based on the requirement to provide a sensor device of the kind mentioned in the beginning, which even for a small-size construction continues to supply a usable signal for detecting moisture on a windscreen. 
         [0007]    The solution to this requirement is a sensor device with the characteristics of patent claim  1 . As regards an optics the solution is supplied by the characteristics of patent claim  11  and as regards a motor vehicle the solution is supplied by the characteristics of patent claim  12 . 
         [0008]    A sensor device for detecting moisture on a windscreen with a transmitter and a receiver and an optics arranged between the transmitter and the receiver, the optics comprising an upper plane for connection to a windscreen and a decoupling region serving to decouple the electromagnetic rays from the optics into the windscreen and a coupling region serving to couple the electromagnetic radiation from the windscreen into the optics, is characterised in that according to the invention the decoupling region comprises at least one surface inclined relative to the upper plane of the optics, and in that the inclined surface comprises an angle of inclination between 2° and 20° relative to the upper plane. As a result the electromagnetic rays introduced by the transmitter into the optics are coupled particularly well into the windscreen. The upper plane of the optics is not a continuous plane in terms of a surface, but denotes the entire area adjoining the windscreen. This area is not continuously planar, but for example comprises, according to the invention, the inclined surfaces in the decoupling region. 
         [0009]    Preferably the inclined surface comprises an angle of inclination between 4° and 10° relative to the upper plane, in particular it comprises an angle of inclination between 4° and 7° relative to the upper plane. Especially preferred is an inclined surface of 5° relative to the upper plane. Preferably the inclined surface of the decoupling region is inclined in direction of the coupling region. Since the receiver transmits the electromagnetic radiation laterally into the optics, the angle at which the electromagnetic rays hit the inclined surface is larger relative to a non-inclined surface. Preferably the decoupling region comprises several inclined surfaces. In an especially preferred embodiment the decoupling region comprises four inclined surfaces. Of these four inclined surfaces at least two are inclined in direction of the coupling region. Preferably, however, one inclined surface, or two of the inclined surfaces in another embodiment, are inclined in direction of the transmitter. 
         [0010]    In another preferred embodiment of the invention the coupling region again comprises at least one surface inclined relative to the upper plane of the optics. The coupling region is the region, in which the light is coupled from the windscreen into the optics. This is arranged adjacent to the receiver of the sensor device. Due to this configuration of the geometry of the coupling region, an especially good decoupling of the light from the windscreen into the coupling region is achieved. The inclined surface of the coupling region preferably comprises an angle of inclination between 2° and 20° relative to the upper plane of the optics and especially preferably an angle of inclination between 4° and 10° relative to the upper plane of the optics. Especially preferably the inclined surface is at an angle of 5° relative to the upper plane of the optics. In a preferred design the coupling region comprises at least two inclined surfaces the inclined surfaces of which are aligned with each other in opposite directions, in particular such that they are inclined towards each other. In an alternative preferred embodiment the coupling region comprises two or more inclined surfaces which in their inclination extend in direction of the decoupling region. It is preferred if these are formed on the edge, i.e. particularly close to the receiver. The inclined surface most remote from the receiver or the inclined surfaces most remote and second most remote from the receiver are preferably inclined in direction of the receiver, i.e. inclined in opposite direction to the previously mentioned inclined surfaces. 
         [0011]    In another further development of the invention the optics comprises a convex shape between the decoupling region and the coupling region on its underside, i.e. opposite the upper plane. This especially adapted geometric shape on the underside of the optics ensures that inner total reflection is achieved thereby ensuring that the electromagnetic rays are reflected inside the optics virtually without any losses. This convex shape is arranged between the coupling region and the decoupling region. The inclined surfaces of the decoupling region are inclined in direction of the coupling region. Only the inclined surfaces which are completely above the intermediate region of the underside which comprises the convex shape, are inclined with their inclination in direction of the coupling region. The same applies vice versa to the inclined surfaces of the coupling region. Only the inclined surfaces in the coupling region which are completely above the intermediate region with the convex shape on the underside, are inclined in direction of the coupling region/the receiver. 
         [0012]    In another further development of the invention the optics, on its topside, comprises a central planar region between the decoupling region and the coupling region. This region ultimately separates the coupling region and the decoupling region from each other. On the underside there is the intermediate region which overlaps the respectively central portions of the coupling region and the decoupling region. According to another preferred further development of the invention the optics comprises a coupling optics opposite the transmitter, which is configured like a bowl with a convex outwardly protruding floor. This results in particularly good focussing and the collection of scattered light. This means that a maximum coupling of light into the optics is achieved. It is preferred if the sensor device including the transmitter and the receiver preferably configured as diodes, is tuned to wavelengths between 880 nm and 920 nm. 
         [0013]    Another aspect of the invention relates to the provision of an optics for the above mentioned sensor device, wherein the optics comprises an upper plane for connection to a windscreen and wherein the optics comprises a decoupling region serving to decouple the electromagnetic rays from the optics into the windscreen and a coupling region serving to couple the electromagnetic radiation from the windscreen into the optics. Furthermore the optics, in its decoupling region, comprises, according to the invention, at least one surface inclined relative to the upper plane of the optics. 
         [0014]    A further aspect of the invention consists in providing a motor vehicle with a windscreen and a sensor device arranged thereon for detecting moisture on a windscreen. The sensor device is configured corresponding to the above description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will now be explained in detail with reference to an embodiment shown in the drawing, which comprises three schematic illustrations, as follows: 
           [0016]      FIG. 1  shows a cross-section of a sensor device according to the invention, schematically drawn with a windscreen arranged thereon; 
           [0017]      FIG. 2  shows a perspective view of the optics of the sensor device of  FIG. 1 ; 
           [0018]      FIG. 3  shows a cross-section through the sensor device according to the invention in a housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  shows a cross-section through the sensor device according to the invention in a housing with a windscreen  4  arranged thereon. Essentially the sensor device comprises an optics  1 , a transmitter  2  and a receiver  3 . The optics is arranged supported against a windscreen  4 . The optics comprises an upper plane  13  for connection to the windscreen. The optics  1  does not comprise a continuous upper plane, but is shaped only partially in the upper area in a planar manner. The term upper plane denotes the topside, which is provided for connection to the windscreen  4 . The transmitter  2  is typically configured as a diode and radiates electromagnetic rays into the optics  1 . To this end the optics  1  comprises a coupling optics  5  opposite the transmitter  2 , which is configured in the shape of a bowl  7  with a convex outwardly protruding floor  6 . From the optics  1  the electromagnetic rays then reach the windscreen  4  via a decoupling region  8 . The electromagnetic rays are reflected from the topside of the windscreen  4  and are ultimately reflected several times between the optics  1 /its underside  21  and the topside of the windscreen  4 . When the windscreen  4  is wetted with water or rain, electromagnetic rays are decoupled from this system and the intensity decreases. The decrease in intensity at the receiver  3  which typically is also a diode, then is a measure for the wetting of the windscreen  4  on the topside. The decoupling region  8  in the embodiment shown comprises three inclined surfaces  9 ,  10  and  11 , which have an inclination in direction of the receiver  3  or a coupling region  16  arranged in the vicinity of the receiver  3 . The angle α is between 2° and 20°, preferably between 4° and 10° and in particular between 5° and 8°. Due to this geometry on the topside of the light conductor a particularly good coupling of the light from the optics  1  and a particularly good coupling of the light into the windscreen  4  is achieved. Furthermore a surface  14  is provided which lies mirror-symmetrically opposite one of the inclined surfaces  11 , which is inclined in the opposite direction, i.e. in direction of the receiver of the transmitter  2 . The inclined surfaces  11  and  14  are separated from each other by a point  12  triangular in cross-section. The surface  14  inclined towards the transmitter  2  lies completely above the underside  21  insofar as this has a convex shape and lies between the decoupling region  16  and the coupling region  8 . Approximately in the middle of the optics  1  a central planar region  13  is provided. This is indeed planar and configured so as to be supported against the windscreen. In the right-hand area of  FIG. 1 , i.e. adjacent to the receiver  3  a coupling region  16  is provided, in which a maximum of electromagnetic rays from the windscreen  4  is coupled into the optics  1 /decoupled from the windscreen  4 . Here again several inclined surfaces are provided. These are in particular the surfaces  17  and  20 , which are directly adjacent to the receiver  3  and are inclined in direction of the transmitter  2  or in direction of the decoupling region  8 . The surfaces  17  and  20  are inclined at an angle β relative to the upper plane  13 . The angle of inclination is between 2° and 20°, in particular between 4° and 10° and especially preferred between 5° and 8°. In a direction adjoining the transmitter  2  a further inclined surface  18  is provided which is inclined in direction of the receiver  3 . The surfaces  18  and  17  are arranged symmetrically to each other to the right and left of a structure  19  triangular in cross-section. The surface  18  is completely above the convex underside  21  of the optics  1 . In direction of the transmitter  2  next to it there is a further inclined surface  15  which is also inclined in direction of the receiver  3 , i.e. comprises the same inclination as the inclined surface  18 . The surfaces  15 ,  17 ,  18  and  20  are all inclined at the same angle, in particular at an angle between 4° and 8°. The surfaces  15  and  18  have an inclination in direction of the receiver  3 , whilst the surfaces  17  and  20  have an inclination in direction of the transmitter  2 . These two groups of surfaces are therefore inclined in opposite directions towards each other. 
         [0020]      FIG. 2  shows an optics  1  in a perspective view. In contrast to  FIG. 1  neither the windscreen  4  nor the transmitter  2  nor the receiver  3  are shown. What is clearly visible is the coupling optics  5  which is shaped in form of a bowl  7  and which comprises a floor  6  protruding convexly outwardly in direction of transmitter  2 . The upper plane provided for contacting the windscreen  4 , is formed in a central region  13  and is configured as a plane in a circumferential frame  23 . In the remaining regions provision is made essentially for the inclined surfaces  9 ,  10 ,  11  and  14  of the decoupling region  8  and the inclined surfaces  15 ,  17 ,  18  and  20  of the coupling region  16 . A decoupling optics  22  is provided adjacently to the receiver  3 . This is configured essentially as a convexly shaped spherical surface. 
         [0021]      FIG. 3 , in comparison to  FIG. 1 , shows the device according to the invention in cross-section. In contrast to  FIG. 1  this shows the device laterally reversed, i.e. the transmitter  2  is arranged on the right-hand side and the receiver  3  is arranged on the left. Identical parts are marked with the same reference symbols. A housing  30  is provided, in which the transmitter  2  is arranged on a printed circuit board  31  and in which the receiver  3  is arranged on a printed circuit board  32 . Transmitter and receiver are preferably diodes, which operate in the infrared range between 880 nm and 920 nm. 
         [0022]    On the inclined surfaces the angles are shown. These are 5° for the incline and 47° for the short inclined surface. The convexly shaped underside  21  is configured as part of the circumference of a circle. 
         [0023]    All features mentioned in the above description and the claims can be combined at random with any of the features of the independent claim. The disclosure of the invention is therefore not limited to the described/claimed feature combinations, rather all feature combinations which are meaningful in terms of the invention are to be considered as disclosed.