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Windscreen wiper







Assignment

40 of the traffic licencing regulation deals with windows, wipers, washers, defrosting and drying equipment for windscreens. Apart from the regulation, that only security glass may be used, it specifies the use of windscreen wipers, which provide the driver with an adequate field of vision. An efficient heating system against misting or icing, must also be present.
Since 1926 , the conventional wiper system has been improved to cope better with the changing weather conditions (e.g., very heavy rain- and snowfall). Another very important point is also the protection against the freezing of the wipers onto the windscreen e.g., through having certain windscreen heating zones. The most modern, electronically controlled wipers still have difficulty with the strongly domed front- and very broad, shallow rear windscreens.

Function

In the above picture, the fairly complicated, classical system with the wiper motor, reduction gear and linkage to the two wiper arms can be seen. As a rule, the shaft at the output of the reduction gear, turns with a relatively small lever-arm and provides the wiper, with it's much longer arm, with a back-and -forth movement. The relationship of the levers to each other, decides the area which will be wiped by the blades. There are also systems, where the lever on the motor only carries out a reversing movement.
Electrically, the wiper motor is connected to earth, the switch and also to terminal 15 (ignition plus). This connection is only broken in the end-positions, e.g., by a cam operated contact. This is where the plus connection of the wiper-switch becomes effective. If it is switched off, the wiper motor stops running at this point, and only at this point.

Not long ago, the Daimler-Benz concern involved itself, at great expense, in the mechanics. The aim was, to clean an enormous windscreen, right up to the extreme corners, using only one wiper arm. To achieve this, the length of the wiper-arm was varied during operation. In the meantime they are no longer quite so strict, two wipers are allowed again.

Electronic wiper control drastically reduces the amount of mechanics. Each arm now has it's own wiper-motor and is thus controlled, so that it changes direction when a certain angle is reached, avoiding a collision with the other one. By using sensors, the attempt is made, to ensure a constant wiper speed, regardless of the varying friction values, or to reduce the speed shortly before the direction is changed, making them quieter when they reach the extremes. Further software solutions are also possible, e.g., the controlling of both wipers with as little disturbance for the driver as possible.

The operation of the equipment, with wiper-motor and linkage, may not be interrupted by force, e.g., through snow. In this case, there is the danger of the brushes burning out, the breaking off of gearwheels or - after a max. of 15 minutes - the motor burning out. This is completely different in modern equipment with stepper-motors. If the wiper blade is blocked, it will try to continue it's operation a few times, then automatically switch itself off. One can also twist one arm alone on it's axle by hand. With the renewed switching on, both wipers will sort themselves out, and take up the correct operation once again. The wipers stop finally, after switching off, sometimes before - and sometimes after the direction change, so that the rubber wiper-blades are not forced into a certain curvature when not in use for longer periods. However, this also prevents one from stopping the wipers in any particular position by switching off the ignition, e.g., to more easily change the wiper blades. In this case, one should read the instructions. 11/10




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Translator: Don Leslie - Email: lesdon@t-online.de

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