Rain sensor

In a rain sensor, a sensor field is arranged between two windshield wiper blades which lie one above the other on a windshield. The sensor field is thus located outside of the field of view of the driver and is wiped by the lower windshield wiper blade. The sensor field is connected to an evaluation circuit arranged on a wiper motor by connecting lines which pass around the lower wiper blade.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to a rain sensor having a sensor field on a 
car windshield against which, in a position of rest, two windshield wiper 
blades rest one above the other in the plane of the windshield, a 
windshield wiper motor which drives the windshield wiper blades being 
controlled by an evaluation circuit as a function of a signal given off by 
the sensor. 
Such rain sensors are used in modern motor vehicles in order automatically 
to turn the windshield wiper motor on when raindrops or splattered water 
strike the windshield. Since the sensor field generally has conductive 
paths made of a material which is non-transparent which are generally 
applied to the windshield, it is arranged outside the field of view of the 
driver. In the case of the windshield, the rain sensor is therefore 
frequently located in a region which is covered by the rear view mirror. 
In order that the windshield wiper be turned off after the elimination of 
raindrops or of splattered water, the sensor field must be arranged in the 
wiping region of the windshield wiper blades. In the case of motor 
vehicles which have two windshield wiper blades arranged in their basic 
position one above the other on the windshield, the windshield, however, 
is not wiped in the region of the rear view mirror. 
SUMMARY OF THE INVENTION 
It is an object of the invention so to develop a rain sensor of the 
aforementioned type that it does not impair the view of the driver and 
that moisture present on the sensor field is removed upon each operation 
of the wiper motor. 
According to the invention, the sensor field (7) is arranged at a place 
between the two windshield wiper blades (2, 3) in their position of rest. 
By this arrangement of the rain sensor, the sensor field is necessarily 
wiped by the lower wiper blade upon each wiping process. Furthermore, a 
short-circuiting of the sensor field such as could be caused by the 
conductor paths being bridged over by a wet wiper blade is excluded. 
Since, as a benefit of the invention, the sensor field is arranged on the 
windshield outside the field of view of the driver, impairing of his 
vision is reliably excluded. 
After a wiping of the windshield by the wiper blades, a slight film of 
moisture as a rule remains on the sensor field. This film of moisture 
could lead to the wiper motor remaining in operation even though rain 
drops are no longer impinging on the windshield. The wiper motor is 
reliably turned off if, in accordance with an advantageous further 
development of the invention, the evaluation circuit is developed so as to 
establish, after each wiping process, a zero point of the signals of the 
sensor field (7) which leads to the turning off of the wiper motor (4). 
The sensor field, which is arranged on the outside of the windshield, is 
contacted in simple manner with the evaluation circuit arranged within the 
vehicle if the sensor field (7)--in accordance with another advantageous 
further embodiment of the invention--is connected to the evaluation 
circuit (8) by connecting lines (9, 10) which extend through openings 
developed in the windshield (1). Such openings can be produced, for 
instance, by a laser beam. 
The sensor field is contacted in simple manner with the evaluation circuit 
without having to fear that the connecting lines of the sensor field will 
be bridged over by a wet windshield wiper blade if the connecting lines 
(9, 10), in accordance with another advantageous further development of 
the invention, extend laterally around the lower windshield wiper blade 
(2) and around the lower edge of the windshield (1). 
The invention permits of numerous embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawing shows a windshield 1 on which, in their position of rest shown, 
two windshield wiper blades 2, 3 lie one above the other. The windshield 
wiper blades 2, 3 are driven by a common wiper motor 4. For greater 
clarity, the wiping regions 5, 6 of the windshield wiper blades 2, 3 are 
shown in dashed line in the drawing. An elongated sensor field 7 is 
arranged between the windshield wiper blades 2, 3 on the windshield 1. 
Upon the commencement of rain or in the case of splattered water, this 
sensor field 7 sends a signal to an evaluation circuit 8 which is 
connected to the windshield wiper motor 4. This evaluation circuit 8 is 
developed to control the wiper motor 4. Upon the commencement of rain, the 
windshield 1 and the sensor field 7 are wiped by the wiper blades 2, 3. 
Thereupon, the wiper motor 4 is turned off. Connecting lines 9, 10 leading 
from the sensor field to the wiper motor 4 pass laterally around the lower 
wiper blade 2 so as to avoid a short circuit by a wet wiper blade 2, 3.