Measuring and testing – Meteorology – Precipitation
Reexamination Certificate
2001-12-17
2003-10-21
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Meteorology
Precipitation
C073S170210, C073S170160, C073S863000, C340S602000
Reexamination Certificate
active
06634225
ABSTRACT:
BACKGROUND
The present invention relates to a rain sensor to detect humidity drops inside an area on a transparent window, with at least one transmitting element to emit optical rays into the window and with at least one receiving element to receive at least one part of the emitted optical rays, where the intensity of the optical rays received is dependent on the number of humidity drops in the area of the window observed by the rain sensor.
The invention also relates to a procedure for operating a rain sensor to detect humidity drops inside an area on a transparent window, with at least one transmitting element to emit optical rays into the window and with at least one receiving element to receive at least one part of the emitted optical rays, where the intensity of the optical rays received is dependent on the number of humidity drops in the area of the window observed by the rain sensor.
Rain sensors of the type described above are known from the prior art in different embodiments. They are normally used in motor vehicles to permit automatic control of windshield wiper activation depending on the intensity of a rainfall. The rain sensors usually observe a specific area of the windshield and determine the intensity of the rainfall in this area.
The known rain sensors have one or more transmitting elements which emit optical rays in the observed areas of the window. The transmitting elements are configured, for example, as luminescent diodes (light-emitting diodes or LEDs). The optical rays emitted can be in the visible or the invisible wave length range. At least one part of the optical rays emitted is reflected from the observed area onto one or more receiving elements in the rain sensor. The receiving elements are configured, for example, as inversely operated luminescent diodes (LEDs). The receiving elements generate a signal which is dependent on the intensity of the optical rays received. The intensity of the optical rays received is in turn dependent on the number of humidity drops in the area of the window observed by the rain sensor. Examples of humidity drops which can be detected are raindrops, dewdrops, drops of fog, melted snowflakes or melting hailstones.
The receiving elements can, for example, receive the optical rays reflected from the window without humidity drops and register a decrease in the intensity of the optical rays received when humidity drops appear. The receiving elements can also receive only the optical rays reflected from the humidity drops and register an increase in the intensity of the optical rays received when humidity drops appear.
Rain sensors are known which are located at a distance from the observed window. The optical rays pass across an air gap from the transmitting elements to the window or from the window to the receiving elements respectively. Rain sensors of this type have the advantage that they can monitor a relatively large area and that the observed area can be selected to be exactly in the field of vision of the driver without the rain sensor interfering with the driver's view.
Another embodiment of rain sensors is attached directly to the window in the area to be observed with the assistance of a flexible adhesive layer. The adhesive layer has firstly a mounting function, attaching the rain sensor securely to the window and, secondly, a compensating function, offsetting irregularities on the window or the rain sensor and locating the rain sensor on the window without entrapped air.
The adhesive layer consists preferably of silicone and has almost the same refractive index as the window being observed. The optical rays emitted at a specific angle by the transmitting elements into the adhesive layer are almost not deflected at all at the transition from the adhesive layer into the window being observed. However, at the transition from the window to the outside air there exists a relatively large difference in the refractive indices, so that the optical rays for the most part are totally reflected in the direction of the receiving elements at the transition of window/air. The receiving elements receive the totally reflected optical rays and generate a signal which is dependent on the intensity of the optical rays received.
If humidity drops are present on the window, the result in the area of the drops is a transition of window/drops instead of a transition of window/air, which results in a change in the difference in the refractive indices in the area of the drops. At the transition of window/drops, the optical rays are no longer totally reflected in the direction of the receiving elements, but totally reflected in other directions, or they even pass out of the window into the humidity drops. With this type of rain sensor, if there are humidity drops on the window, optical rays with a lower intensity are received and the signal from the receiving elements changes accordingly.
The known rain sensors are operated with a supply voltage, usually a DC voltage, which is converted in the rain sensor by an oscillator into a square-wave signal with a specific frequency to power the transmitting elements. The frequency is in the range of several kHz, for example, 30 kHz. The transmitting elements powered by the square-wave signal emit optical rays with the frequency of the square-wave signal. The receiving elements receive optical rays and generate a signal which also has this frequency. The effect of humidity drops on the window being observed is a change in amplitude in the signal from the receiving elements. A determination is made concerning the number of humidity drops on the window from the change in amplitude of the signal. The square-wave signal powering the transmitting elements can therefore be described as a carrier signal, to which a signal dependent on the number of humidity drops on the window can be up modulated by changing the amplitude.
Finally, rain sensors are also known from the prior art which have two signal paths, each having one or several transmitting elements. The transmitting elements for the two signal paths emit optical rays alternately. The receiving element(s) alternately receive(s) optical rays which were emitted by the transmitting elements of the one and the other signal path. The signals from the receiving elements are fed to a comparator which creates an output signal from the difference between the signals. The output signal is dependent on the change in amplitude of the signal of one signal path relative to the amplitude of the signal of the other signal path. If no humidity drops are present on the window in the area being observed, the output signal of the comparator is, so to speak, a signal with the same frequency as the square-wave signal powering the transmitting elements, but with an amplitude of zero, in other words, a DC signal.
The rain sensors known from the prior art have the disadvantage that they radiate electromagnetic waves during operation, specifically in the long-wave range, that is to say, harmonics in a frequency range of up to several hundred kHz. This causes interference in radio broadcasts, particularly in this frequency range. The interference affects radio broadcasts particularly when the rain sensor is located in the proximity of a receiving antenna which is being used for the radio broadcast, so that the disruptive electromagnetic waves from the rain sensor affect the antenna directly. The disruptive electromagnetic waves from the known rain sensor can be heard as a continuous whistling in an automobile radio. Similarly, strong external electromagnetic fields which are created in the vehicle interior, for example, by the use of mobile telephones, can result in a disruption in the operation of the known rain sensor.
SUMMARY
It is therefore desirable for the present invention to design and develop a rain sensor of the type described above with the purpose of effectively reducing interference from the rain sensor with radio broadcasts, if possible even preventing interference completely.
The invention proposes using the rain sensor described above as a starting point
Ellington Alandra
Lefkowitz Edward
Lewis J. Gordon
Valeo Auto-Electric Wischer und Motoren GmbH
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