Abstract:
A sensor device is described for detecting wetting of a windshield that has only one transmitter with which two measuring zones of the sensor device can be implemented on a wettable outside of the windshield. A light guidance body injecting transmitter radiation into the windshield has structures with which the transmitter radiation emitted by the transmitter is collected and parallelized in two different directions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sensor device for detecting wetting of a windshield. 
     German Patent 197 01 258 describes a sensor device that operates according to an optoelectronic principle for controlling wash/wipe systems for automotive windshields. The sensor device has multiple transmitters and at least one receiver for injecting and outputting via a coupling means a defined radiation into and out of the windshield whose wetting due to moisture or soiling is to be measured. The radiation is completely reflected at least once in the windshield on the (dry) surface of the windshield due to the injection angle and finally is outputted again to a receiver at a predetermined location. Total reflection is prevented by wetting of the surface of the windshield (air, water, ice, soiling, fog, etc.), resulting in wetting-dependent radiation losses due to output of a portion of the radiation from the original beam path, e.g., due to water droplets. The diminished radiation detected by the receiver is outputted as a sensor signal to a signal processing arrangement, where it is analyzed with regard to controlling a wash or wipe system for an automotive windshield, for example. A controller controls the wiper motor in continuous or interval wiping mode as a function of the sensor signal analyzed. 
     According to German Patent 197 01 258, the transmitters are arranged concentrically around the receiver on the coupling means or concentrically in sections, the coupling means having a circular or toroidal design, Thus, a circular base area is spanned by transmitters, receivers and coupling means. For this reason, the sensor, i.e., the sensor casing, is in the form of a round cylinder. 
     The sensitive area of the sensor is defined by the sum of the measuring ranges of the windshield between a transmitter and the respective receiver, i.e., the one receiving the radiation. The measuring range is understood to be the range on the wettable side of the windshield within which the transmitter radiation is completely reflected in the absence of wetting, and therefore the transmitter radiation can be outputted more or less in the measuring range because of wetting of the windshield. 
     One disadvantage here is that the same number of transmitters must be used for a given number of measuring ranges, i.e., sensitive area. However, a large number of transmitters and/or receivers leads to high manufacturing costs. 
     Another disadvantage is that the large number of transmitters and the circular arrangement of transmitters lead to a relatively great extent of the sensor and its contact area on the windshield and therefore make the sensor noticeable and cause interference for the driver of the vehicle when it is mounted within the wiping area on the windshield, as is customary today. 
     SUMMARY OF THE INVENTION 
     The sensor device according to the present invention has the advantage that two measuring ranges of the sensor can be achieved on the wettable outside of the windshield with only one transmitter, because a light guidance body that injects the transmitter radiation into the windshield has at least one structure with which the transmitter radiation emitted by the transmitter is collected and/or parallelized in two different directions. 
     It is especially advantageous that the light guidance body outputting the transmitter radiation from the windshield still has at least one structure with which the transmitter radiation from two different directions detected by the receiver is focused on the receiver. Thus, a sensor device with four measuring zones, i.e., sensitive areas, can be implemented with an arrangement of two transmitters and two receivers with the respective structures of the light guidance body, where the light guidance body also has a small extent and the sensor device has a small contact area on the windshield. 
     It is also advantageous that these structures have optical lenses or optical surfaces between the ambient medium and the light guidance body with the transmitter or receiver at the focal point. Thus, additional lenses or optical elements in the beam path are unnecessary, and thus the structural design of the light guidance body is simplified, and the overall size of the sensor device is greatly reduced. 
     For the purpose of optimization of the device, it is advantageous to set the beam angle of the two parallelized transmitter beams emitted by the transmitter at approx. 100° C. to 120°. Thus, the two optical surfaces of the structures can be arranged without any mutual overlap, so that resolution of the focused beams is high. 
     It is also especially advantageous to arrange two transmitters and two receivers so that their images in a plane parallel to the windshield form the corner points of a parallelogram, with the beam angle of the transmitter radiation bundled on the receiver from two different directions is approx. 60° to 80°. The structure focusing on the receiver thus has two overlapping optical surfaces, but they do not cause any interference in focusing the beams on the receiver. 
     In addition, the optical axes of the structures of the light guidance body are preferably aligned at an angle of inclination of approx. 45° to the windshield. Therefore, the transmitter radiation in the light guidance body can be injected into the windshield without further deflection, so that when the windshield is clean and dry, the light is completely reflected on the outside of the windshield and is relayed further in the windshield. 
     When the transmitter is arranged on a circuit board parallel to the windshield, the angle of inclination of approx. 45° also permits an optimal light yield of the transmitter, because when using a light emitting diode or a chip with a luminous surface parallel to the windshield as the transmitter, the radiation it emits in a solid angle is subject to Lambert&#39;s cosine law. 
     Due to the advantageous arrangement of the two transmitters and two receivers in the form of a parallelogram, the contact area of the sensor on the windshield is preferably rectangular or also a parallelogram. An oval contact area of the sensor with an oval light guidance body is also possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a through section of a transmitter and a receiver of a sensor device according to the present invention. 
     FIG. 2 shows a light guidance body of a sensor device according to the present invention. 
     FIG. 3 shows a view of the device shown in FIG.  2 . 
     FIG. 4 a  shows a section along line Iva-IVa through a transmitter and a receiver of the light guidance body shown in FIG.  2 . 
     FIG. 4 b  shows a section along line Ivb-IVb through a transmitter of the fiber optic light guidance body shown in FIG.  3 . 
     FIG. 5 shows another embodiment of a light guidance body according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a sectional diagram of an optoelectronic sensor device mounted on an automotive windshield  14  to detect wetting with moisture or soiling of windshield  14 . The sensor device has a casing  20  which is mounted on windshield  14 , in particular by gluing or pressing. A light guidance body  10  having two structures  22  projecting on a top side  18  of light guidance body  10  facing the interior of the sensor is also in direct contact with windshield  14  light guidance body  10  is pressed against windshield  14  by casing  20  with a clamping spring, for example, or is glued to it. Structures  22  have lens-like optical surfaces  24 . A transmitter  6  and a receiver  8  are located at the focal point of optical surfaces  24 . Both are mounted on and parallel to a circuit board  4  which is in turn arranged parallel to windshield  14  inside sensor device casing  20 . 
     The beam path of transmitter radiation  30  is depicted along optical axes  28  of optical surfaces  24 . Transmitter radiation  30  is aligned in parallel to optical surface  24  of structure  22  assigned to transmitter  6  and is sent in a light guide  26  to the base of fiber optic light guidance body  10 . Beam path  30 , aligned in parallel, is first inputted into windshield  14  by light guidance body  10  and is subject to at least total reflection on outside  32  of clean and unwetted windshield  14 , and it is outputted from windshield  14  by light guidance body  10  and refractive surface  24  of additional structure  22  provided for receiver  8  and then it is focused on receiver  8 . 
     FIG. 2 shows a perspective view of light guidance body  10  having a rectangular contact area  12  aligned with windshield  14  and top side  18  having a peripheral web  16 . Structures  22 . 1  and  22 . 2  integrally molded on light guidance body  10  are arranged in pairs and project out of top side  18  of light guidance body  10 . A total of four structures  22  each have two lense-shaped curved optical surfaces  24  and each have two cylindrical light guides  26 , with optical surfaces  24  extending into the troughs  27  of light guidance body  10  in front of them. 
     Both light guidance body  10  and structures  22  are made of the same material which is essentially transparent for the transmitter radiation. For example, plexiglass materials, which are pigmented or left transparent according to transmitter radiation  30  used (infrared or visible light), are suitable for this purpose. Pigmenting fiber optic light guidance body  10 , e.g., in black, makes it possible to filter out some of the interfering light, i.e., ambient light  34 , striking light guidance body  10  through windshield  14  in an unwanted manner. 
     Fiber optic Light guidance body  10 , shown in a perspective view in FIG. 2, is illustrated with a view of top side  18  in FIG.  3 . Structures  22  are connected by dash-dot lines  28   a  which correspond to the, projection of optical axes  28  of optical surfaces  24  on top side  18  parallel to windshield  14 . Dash-dot lines  28   a  form a parallelogram. A transmitter  6  or a receiver  8  is arranged at each corner point of the parallelogram. Inside angles and of the parallelogram correspond to beam angle of the two bundled beams emitted by one of two transmitters  6  along optical axes  28 , i.e., lines  28   a , and beam angle corresponds to transmitter radiation  30  bundled on one of the two receivers  8  from the two different directions. Beam angle of transmitter  6  is approximately 110°, and beam angle of receiver  8  is approximately 70° 
     It can also be seen on the basis of FIG. 3 that structures  22 . 1  and  22 . 2  are different. Structures  22 . 1  assigned to beam angle of transmitters  6  are characterized by complete circular optical surfaces  24  and light guides  26 . Structures  22 . 2  assigned to beam angle of receivers  8  have optical surfaces  24  and light guides  26  that are interlinked and merge into one another. 
     FIG. 4a shows a section through light guidance body  10  and two structures  22 . 1  and  22 . 2  along line IVa—IVa according to FIG.  3 . Optical axes  28  of optical surfaces  24  and a transmitter  6  and a receiver  8  are shown here. Angle of inclination of optical axes  28  relative to contact area  12 , i.e., to outside  32  of the windshield, is approximately 45° and thus permits total reflection of incident transmitter radiation  30  on outside  32  of the windshield. 
     FIG. 4 b  shows a section along line IVb—IVb, according to FIG. 3, through light guidance body  10  and a structure  22 . 1  assigned to a transmitter  6 . Optical axes  28  of optical surfaces  24  of structure  22 . 1  and transmitter  6  are shown here. This illustrates the parallelization of the transmitter radiation in two directions X 1 , X 2  in a section perpendicular to windshield  14 . 
     FIG. 5 illustrates another embodiment, depicting the arrangement of transmitters  6  and receivers  8  in a parallelogram. Structures  22  have not been shown for the sake of simplicity. Light guide  10  is now also shaped like a parallelogram, but otherwise it has the same properties and features as light guidance body  10  in the first embodiment according to FIGS. 1 through 4. A feature common to both embodiments is, for example, the parallelization of the transmitter radiation of one transmitter  6  in two directions X 1 , X 2  as seen in the view parallel to windshield  14  along dotted lines  28   a  and the focusing of the transmitter radiation from two directions X 1 , X 2  on one receiver  8 .