Windscreen wiper
From Wikipedia, the free encyclopedia
A windscreen wiper (windshield wiper in North America) is a device used to wipe rain and dirt from a windscreen. Almost all automobiles are equipped with windscreen wipers, often by legal requirement.
Wipers can also be fitted to other vehicles, such as buses, trams, locomotives, aircraft and ships.
A wiper generally consists of an arm, pivoting at one end and with a long rubber blade attached to the other. The blade is swung back and forth over the glass, pushing water from its surface. The speed is normally adjustable, with several continuous speeds and often one or more "intermittent" settings. Most automobiles use two synchronized radial type arms, while many commercial vehicles use one or more pantograph arms. Mercedes-Benz pioneered a system called the Monoblade in which a single wiper extends outward to get closer to the top corners, and pulls in at the ends and middle of the stroke, sweeping out a somewhat 'W'-shaped path.
Some larger cars are equipped with "hidden" (or "depressed-park") wipers. When wipers are switched off, a "parking" mechanism or circuit moves the wipers to the lower extreme of the wiped area, near the bottom of the windshield, but still in sight. To hide the wipers, the windshield extends below the rear edge of the hood, and the wipers park themselves below the wiping range at the bottom of the windshield, but out of sight.
Wipers may be powered by a variety of means, although most in existence 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 air operated wipers, run by bleeding a small amount of air pressure from the brake system to a small air operated motor mounted just above the windscreen. These wipers are activated by opening a valve which allows pressurized air to enter the motor.
Early wipers were often powered by manifold vacuum, but this had the drawback that manifold vacuum alters depending on throttle position and is almost non-existent under wide-open throttle; 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 powered also the speedometer. The wipers' speed was therefore variable with car speed. When the car was waiting at a crossroad, the wipers were not powered, thus a handle under the speedometer allowed to power them by hand.
Most windscreen wipers operate together with a windscreen washer; a pump that supplies water and detergent (usually a blend called windscreen wiper fluid) from a tank to the windscreen through small nozzles, mounted on the hood or on the wipers, known as a 'wet-arm' system.
Some automobiles have small 'windscreen' wipers/washers on the headlights. In more modern vehicles, these have been replaced with a powerful jet spray, without wipers.
Some vehicles are fitted with wipers (with or without washers) on the back window as well. Rear-window wipers are typically found on hatchbacks, station wagons, sport utility vehicles, minivans, and some sports cars. They were first implemented in the 1970s, but SUVs did not use them until the 1980s.
Nowadays some cars include intelligent (automatic) windscreen wipers that detect the presence and amount of rain using a rain sensor, and automatically adjusts the speed of the blades according to the amount of rain detected.
[edit] History
Inventor J. H. Apjohn came up with a method of moving two brushes up and down on a vertical plate glass windshield in 1903.
Mary Anderson is said to have invented the windshield wiper swinging arm in the United States, where she patented the idea in 1903. The idea was initially met with resistance, but was a standard feature on all American cars by 1916.
In April 1911, a patent for windscreen wipers was registered by Sloan & Lloyd Barnes, patent agents of Liverpool, England, for Gladstone Adams of Whitley Bay. The first designs for the windscreen wiper are also credited to Józef Hofmann, the world-famous concert pianist and Mills Munitions, Birmingham who also claimed to have been the first to patent windscreen wipers in England.
Inventor William M. Folberth, in 1919, applied for a patent for an automatic windshield wiper apparatus. The patent was granted in 1922. It was the first automatic mechanism. Trico later settled a in a patent dispute with Folberth and purchased Folberth's Cleveland company, the Folberth Auto Specialty Co. The new vacuum-powered system quickly became standard equipment on automobiles, and the vacuum principle was in use until about 1960.
In the late 1950s, a feature common on modern vehicles first appeared, operating the wipers automatically for two or three passes when the washer button was pressed, making it unnecessary to manually turn them on as well. Today, a simple electronic timing circuit is used, but originally a small vacuum cylinder mechanically linked to a switch provided the delay as the vacuum leaked off.
In 1969, the first intermittent wipers were introduced with an adjustable delay between wipes, making it possible to select the degree of wiping action required. Robert Kearns is the recognized inventor of this system although it took years of concerted effort and legal action before he was eventually compensated.
In 1970. Saab Automobile introduced headlight wipers across the product range. These operated on a horizontal reciprocating mechanism, with a single motor. They were later superseded by a radial spindle action wiper mechanism, with individual motors on each headlamp.
In March 1970, Citroën introduced rain-sensitive intermittent windshield wipers on the SM model. When the intermittent function was selected, the wiper would make one swipe. If the windshield was relatively dry, the wiper motor drew high current. This caused the delay device to delay the next wipe longest. If the motor drew little current, it indicated that the glass was wet, causing the delay device to minimize the delay.
In the late 20th century, rain-sensing windshield wipers appeared on various models, one of the first being Buick's Park Avenue Ultra. As of early 2006, rain-sensing wipers are standard on all Cadillacs, and are available on many other GM, Chrysler, Jeep, Peugeot, Citroën, Toyota, Mercedes, Honda and Renault as well as many other main-stream manufacturers.
[edit] See also
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[edit] External link and references
- Howstuffworks - [1]
