Optoelectronic sensor for detecting moisture on a windshield with means to compensate for a metallic layer in the windshield

An optoelectronic sensor device for detecting the degree of wetting a multi-layer transparent pane by drop-shaped precipitation, the sensor device comprising:

• a beam guide element having a front surface connected to an inner surface of the pane not exposed to the precipitation in a region of a wiping area covered by a motor driven windscreen wiper device, the beam guide element having at least one measuring path with a beam entry window and a first beam exit window spatially separate therefrom and aligned at an angle of approximately 90.degree. thereto;
• a beam transmitter associated with the beam entry window;
• a first beam detector associated with the first beam exit window in such a manner that beams emitted by the beam transmitter are reflected in dependence upon the precipitation present on the pane and directed to the first beam detector, which in each case provides a first signal dependent upon the associated quantity of precipitation;
• and
• compensating means for correcting the first signal supplied by the first beam detector and resulting from a quantity of mixed beams, the correction being dependent upon a quantity of spurious beams reflected at a partially transparent metallic intermediate layer located in the pane;
• the beam guide element further comprising a second beam exit window, which is allocated to the measuring path and cooperates with a second beam detector, the second beam exit window being situated in a central region of a rear surface of the beam guide element facing away from the pane, said region being located between the two beam windows so that only those spurious beams reflected at the metallic intermediate layer in the pane exit from the second beam exit window and are detected by the second beam detector, which provides a second signal resulting from a quantity of the exiting spurious beams for use in correcting the first signal supplied by the first beam detector, the first signal resulting from a quantity of mixed beams composed of beams exiting the first beam exit window, and beams from a useful beam portion and a spurious beam portion, said quantity of mixed beams having a quasi clear geometrical relationship to the quantity exiting from the second beam exit window;
• wherein the second beam exit window has a width corresponding to the width extension of the beams in the measuring path, and a height dependent upon the spacing of the metallic intermediate layer relative to the inner surface the pane, a beam lens being allocated thereto and designed as a corresponding portion of an aspherical lens topography.

An optoelectronic sensor device for detecting the degree of wetting a multi-layer transparent pane by drop-shaped precipitation, the sensor device comprising:

• a beam guide element having a front surface connected to an inner surface of the pane not exposed to the precipitation in a region of a wiping area covered by a motor driven windscreen wiper device, the beam guide element having at least one measuring path with a beam entry window and a beam exit window spatially separate therefrom and aligned at an angle of approximately 90.degree. thereto;
• a beam transmitter associated with the beam entry window;
• a beam detector associated with the beam exit window in such a manner that beams emitted by the beam transmitter are reflected in dependence upon the precipitation present on the pane and directed to the beam detector, which in each case provides a signal dependent upon the associated quantity of precipitation;
• and
• compensating means for correcting the signal supplied by the beam detector and resulting from a quantity of mixed beams, the correction being dependent upon a quantity of spurious beams reflected at a partially transparent metallic intermediate layer located in the pane, the compensating means comprising a plurality of electrical components which produce an electrical correction signal, the correction signal, in contrast to the signal supplied by the beam detector, being phase-shifted and supplied to a current summation point located electrically behind the beam detector, the electrical components including a pulse-preparation stage and a phase-shifting stage as well as a correcting stage disposed electrically downstream thereof, the phase-shifting stage lying at the current summation point with its output over a capacitor provided for the purpose of suppressing a direct current portion, the pulse-preparation stage and phase-shifting stage being connected with the phase shifting stage input at the output of the pulse stage;
• the input of the pulse stage being connected to the output of a final stage associated with the beam detector.