Abstract:
A rain sensor and a method for installing a rain sensor are provided for a motor vehicle. The rain sensor includes a housing in which at least one printed circuit board is located and which has a light-conducting member, which at least partially closes the housing in the manner of a lid. A plate is located between the light-conducting member and the printed circuit board. During installation, the plate is partially punched through.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a rain sensor, in particular for a motor vehicle, and a method for installing a rain sensor. 
   BACKGROUND INFORMATION 
   There are numerous rain sensors for motor vehicles, for instance, as recited in German Published Patent Application No. 198 46 968. Essentially, the rain sensors consist of a housing in which a printed-circuit board having a transmitter and a receiver are located as optical components, and which is closed off by a light-conducting member mounted on the windshield of a motor vehicle. When in operation, the transmitter emits infrared radiation, which is coupled into the windshield by the light-conducting member mounted on the windshield of the motor vehicle. If moisture is present on the outside of the windshield, the radiation of the transmitter at this boundary surface is scattered toward the outside. If there is no moisture on this boundary surface, the radiation of the transmitter is completely reflected at this glass-air boundary surface. This completely reflected radiation is concentrated by the light-conducting member and focused on the receiver, which then emits a signal that may be taken as the degree of the moisture present on the windshield. 
   However, in the manufacture of motor vehicles, the light-conducting member is often already mounted on the windshield when the window is produced. In the final production phase, the housing with the printed-circuit board is then attached to the light-conducting member, by a clip-on connection, for instance, so that the light-conducting member closes the housing like a lid. 
   SUMMARY OF THE INVENTION 
   The rain sensor according to the present invention reduces potential damage to the electronic system on the printed circuit board resulting from electrostatic discharge (ESD)by the mounting of a plate between the light-conducting member and the printed circuit board. This has the advantageous result that no ESD-protected work areas are necessary in the manufacture or for required spare-parts. 
   The plate may have a design that has a cut-out in the area where a transmitter or a receiver, as an optical component, interacts with the light-conducting member. This ensures that the plate does not dampen or even inhibit the interaction of the optical component with the light-conducting member. 
   The plate may be very thin and thus configured as a foil and, at least in part, provided with a perforation in the coupling region. Since the light-conducting member is to be pierced by the housing only when it is mounted directly on the light-conducting member, the installation requires no additional tools. 
   The light-conducting member may be provided with separation aids for the through-punching of the plate, so that a reliable through-punching of the plate in the coupling region is ensured in series production. 
   A subcarrier having a cut-out in the coupling areas, that is, in the regions of the optical components, may be situated between the printed-circuit board and the light-conducting member. This allows the plate to be designed as a thin foil, without any loss in stability of the system. 
   If the plate is in the form of a paper foil, a metal-coated paper foil or plastic film, the electronics of the rain sensor may be protected from ESD damage in a simple and inexpensive manner. 
   Moreover, the plate may be of a foil-type, optically transparent and stretchable and clings to the light-conducting member in the coupling regions, since no through-punching of the foil will be necessary in that case. 
   Furthermore, contact devices may extend from the housing through the plate. These may be used, for example, for contacting a heating device. 
   A simple possibility of ESD protection is given, especially in the spare-part trade, if the plate is in the form of a foil and is able to be peeled off from the housing or the subcarrier. The subcarrier may have a cut-out only in the areas of the optical components, so that adequate protection is ensured even after the foil has been peeled off. 
   The method also may provide that the plate that protects the printed-circuit board from ESD damage is pierced only during installation of the housing on the light-conducting member. In this way, ESD damage during installation of the housing on the light-conducting member is avoided and ESD-protected work areas may be saved. 
   An electrical component, which is operatively connected to a mechanical or optical component, may be protected from damage stemming from electrostatic discharge (ESD) by a simple plate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic sectional view of a rain sensor according to the present invention, prior to installation. 
       FIG. 2  is a rain sensor according to  FIG. 1 , after installation. 
       FIG. 3  is a plan view of a foil of a rain sensor according to the present invention. 
       FIG. 4  is a plan view showing a variation of the foil from FIG.  3 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a rain sensor  10  according to the present invention, prior to the final installation. A light-conducting member  14 , over which a housing  16  with a printed-circuit board  18  may be slipped, is glued onto a window  12 . A coupling medium may be disposed between window  12  and light-conducting member  14  as well. Printed-circuit board  18 , on which electronic and optical components are affixed in SMD technology, is clipped into housing  16 . The optical components are transmitter  20  and receiver  21  of rain sensor  10  and are used to transmit and receive IR-radiation. Transmitter  20  and receiver  21  are implemented as semiconductor components. Located between printed-circuit board  18  and light-conducting member  14 , is a foil-type plate  22 , which is supported by a subcarrier  24 . Subcarrier  24  is a plastic plate, which has cut-outs in the regions of optical components  20 ,  21 . Prior to installation, housing  16  is thus closed off by plate  22 . 
   Light-conducting member  14  has lens-type projections  26  which are provided to couple the radiation of transmitters  20  or to focus the radiation to receivers  21 . 
   When housing  16  is slid onto light-conducting member  14 , foil-type plate  22  is pierced by separation aids  28 . These separation aids  28  are, for example, circular structures extending around protrusions  26  and projecting beyond them. When housing  16  is slid on, separation aids  28 , therefore, cut through plate  22  in the region of protrusions  26  and, thus, in coupling region  30  ( FIG. 2 ) between optical components  20 ,  21  and protrusions  26 . A perforation in foil-type plate  22  may aid this process. 
   In  FIG. 2 , a rain sensor  10  according to the present invention is illustrated in the mounted position on window  12 . Separation aids  28  have cut through foil  22  in coupling areas  30 , so that foil  22  is cut out between protrusions  26  and associated optical components  20 ,  21 . 
     FIG. 3  illustrates a plate  22  in a plan view. Plate  22  has the same outer contour as housing  16  and seals the housing from electrostatic discharge. Plate  22  is made of a metal-plated paper foil, for instance. Expediently, the metal-coating is on the outside of housing  16 , i.e. on the side facing away from printed-circuit board  18 , so as to prevent inadvertent short-circuits in response to plate  22  making contact with the printed-circuit board. 
   In coupling regions  30 , where optical components  20 ,  21  are located, plate  22  has a circular perforation  32  which facilitates the through-punching of plate  22  by separation aids  28  when it is slid onto light-conducting member  14  (FIG.  1 ). 
   In  FIG. 4 , a variation of the foil from  FIG. 3  is illustrated. In this case, the perforation is not implemented in a completely circular shape, but approximately in a U-shape. When housing  16  is slid onto light-conducting member  14 , the plate sections are not detached but merely displaced such that a coupling between optical components  20 ,  21  and protrusions  26  in coupling region  30  is made possible. This prevents pieces of plate  22  from remaining inside the housing in an undefined manner following installation, thereby possibly causing malfunctions. To that end, light-conductor  14  may also have additional formations that keep the punched-out pieces in a defined position. 
   In a variant of the present invention, it is possible, for example, to provide separation aids  28  at subcarrier  24  or on printed-circuit board  18 . 
   In another exemplary embodiment of the present invention, plate  22  is implemented as a peel-off foil. Subcarrier  24  covers printed-circuit board  18  in the direction of light-conducting member  14 , leaving uncovered only the coupling regions  30  of optical components  20 ,  21 . Foil-type plate  22  is glued to subcarrier  24  or to the edge of housing  12  and is peeled off just before housing  12  and light-conducting member  14  are joined. 
   In a further simplification, subcarrier  24  may be omitted and only a plate  22  with recesses in coupling regions  30  be provided. In this case, optical components  20 ,  21  may also be protected with the aid of a simple protective cap, which is removed prior to installation. 
   As a rule, the method is also implementable for other control devices, such as control devices of wiper motors or ABS in which optical or mechanical components are separable from electrical components. In the case of a wiper motor, protrusions  26  or pins, for example, may be used as contact points on the outside of the housing of the wiper motor, the control electronics being accommodated in a separate housing. This separate housing is then closed off by a plate  22 . When the separate housing with the control electronics is slid over the housing of the wiper motor, plate  22  is punched through by protrusions  26  and the wiper motor thereby contacts the control electronics.