Power
Wipers may be powered by a variety of means, although most in use today are powered by an electric motor through a series of mechanical components, typically two 4-bar linkages in series or parallel.
Vehicles with air operated brakes sometimes use pneumatic wipers, powered by tapping a small amount of pressurized air from the brake system to a small air operated motor mounted on or just above the windscreen. These wipers are activated by opening a valve which allows pressurized air to enter the motor.
Early wipers were often driven by a vacuum motor powered by manifold vacuum. This had the drawback that manifold vacuum varies depending on throttle position, and is almost non-existent under wide-open throttle, when the wipers would slow down or even stop. This problem was overcome somewhat by using a combined fuel/vacuum booster pump.
Some cars, mostly from the 1960s and 1970s, had hydraulically driven wipers.
On the earlier Citroën 2CV, the windscreen wipers were powered by a purely mechanical system, a cable connected to the transmission; to reduce cost, this cable also powered the speedometer. The wipers' speed was therefore variable with car speed. When the car was waiting at an intersection, the wipers were not powered, but a handle under the speedometer allowed the driver to power them by hand.
Read more about this topic: Windscreen Wiper
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