Electricity: motive power systems – Periodic – repetitious or successive operations control of... – Variable periods or intervals between controlling operations
Patent
1990-01-03
1991-01-22
Ro, Bentsu
Electricity: motive power systems
Periodic, repetitious or successive operations control of...
Variable periods or intervals between controlling operations
318DIG2, 15250C, B60S 108
Patent
active
049873547
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a device for rain-induced switching on and off of an electric windshield wiper motor in vehicles.
In a known switching device of this type (DE-OS 22 39 359) the so-called rain sensor is constructed as a capacitive detector. Three electrodes are arranged on the inside of the windshield in the wiping area of the wiping blades. Two electrodes are connected to an alternating voltage and constitute a capacitor, so that an electric field is formed between them. The third electrode is arranged in such a way that only a small stray field of the electric field reaches it when the windshield is dry. The sensor signal is taken off at the third electrode and applied to an adder, to which the alternating voltage is fed so as to be out of phase by 180.degree.. The amplitude of the alternating voltage is dimensioned in such a way that the resultant output signal of the adder is zero when the windshield is dry.
The glass usually used to produce the windshields has a dielectric constant .epsilon. in the order of magnitude of 8. The moisture forming on the windshield during rain (water has a dielectric constant of .epsilon..apprxeq.80) changes the configuration of the lines of flux between the two capacitor electrodes in such a way that a large field component reaches the third, so-called measuring electrode. The signal amplitude of the sensor signal accordingly increases sharply. An output signal which reaches the switch for the windshield wiper motor as a closing signal occurs at the adder. The wiper motor is switched on. When the windshield is dry again, the output signal of the adder is absent and the wiper motor is switched off.
This known switching device has the problem that the rain sensor cannot distinguish between rain and water streaks which can remain on the windshield during wiping under certain circumstances. As a result of this, the wiper is often turned off too late and the wiper blades wipe in the dry state. The automatic wiper system accordingly works in an unsatisfactory manner.
SUMMARY OF THE INVENTION
The switching device, according to the invention, includes a control unit that generates a switch-on signal for the windshield wiper motor in response to increase in amplitude of the sensor signal above a predetermined threshold. The invention has the advantage that the wiper blades are switched off in a purposeful manner as soon as there is no additional moisture brought about by rain within the wiping area of the wiping blades on the windshield. Water remaining due to water streaks has no effect on the switching off, since the amplitude of the sensor signal remains constant when there are water streaks or decreases slowly and accordingly cannot contribute to maintaining the switch-on signal. The control unit required for the switching device can be integrated in an electronic wiper unit which is already present, e.g. for periodic wiping, at small additional expenditure.
BRIEF DESCRIPTION OF THE DRAWING
The invention is explained in more detail in the following description by means of an embodiment example shown in the drawing. The drawing shows a block wiring diagram of a device for rain-induced switching on and off of a windshield wiper motor.
DESCRIPTION OF THE EMBODIMENT PREFERRED
The switching device for the rain-induced switching on and off of an electric windshield wiper motor 10 shown in the wiring diagram comprises a switching relay 11 whose switching contact 12 is arranged in the electric circuit of the windshield wiper motor 10. The switching contact 12 can be arranged in series with the wiper switch 13 or the ignition switch which is to be actuated by hand and connects the windshield wiper motor 10 to the positive terminal U.sub.B of the vehicle battery.
The relay winding 14 of the switching relay 11 is connected to the output 15 of a control unit 16 whose input 17 is connected with the output of a so-called rain sensor 18. The rain sensor 18, which can be constructed in very different ways, supplies a sensor signal whose amplitud
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Ro Bentsu
Roberts Bosch GmbH
Striker Michael J.
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