Speedometer
A speedometer is a type of gauge that shows the speed a vehicle is moving. It usually shows the speed in miles per hour (mph) for countries that use the statute mile for distances or kilometres per hour (km/h) for countries that use the metric system. Originally, a speedometer was an option that car owners could buy to put on their car. Beginning about 1910 it was built into all cars.[1]
History
The electric speedometer was invented by the Croatian Josip Belušić[2] in 1888, and was originally called a velocimeter. Charles Babbage is credited with creating an early type of a speedometer. These were usually fitted to locomotives.[3][4]
A speedometer was patented by a German, Otto Schulze on October 7, 1902,[5] it uses a rotating flexible cable usually driven by gearing linked to the output of the vehicle's transmission. The early Volkswagen Beetle and many motorcycles, however, use a cable driven from a front wheel.
Speedometer accuracy
Most speedometers have tolerances of some ±10%, mainly due to variations in tire diameter.[6] Sources of error due to tire diameter variations are wear, temperature, pressure, vehicle load, and nominal tire size. Vehicle manufacturers usually calibrate speedometers to show the vehicle is going faster.[6]
Underinflation
When a tire has less air pressure than it should, it is underinflated. Underinflation causes excessive heat and reduces the diameter of the tires.[7] This causes it to rotate faster than the speedometer shows it is. Tires underinflated by only 10 psi can mean a car or truck reading 70 mph on the speedometer is actually traveling at 72 mph.[7]
Speedometer Media
An animation of an electronic Aston Martin speedometer's self-test routine, showing how an analogue speedometer hand may indicate the vehicle's speed
A digital, LCD speedometer in a Honda Insight
A speedometer showing mph and km/h along with an odometer and a separate "trip" odometer (both showing distance traveled in miles)
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References
- ↑ William Harris. How Speedometers WorkHowStuffWorks/InfoSpace LLC. Retrieved 10 September 2015.
- ↑ Sobey, Ed. A Field Guide to Automotive Technology (2009)Chicago Review Press. p. 78. ISBN 978-1-55652-812-5. Retrieved 30 January 2015.
- ↑ Charles Babbage and the Difference Engine - NewMyths.com. google.com. Retrieved 30 January 2015.
- ↑ Udini → Flow. proquest.com. Retrieved 30 January 2015.
- ↑ Speedometer (26 April 2005)Siemens. Retrieved 30 January 2015.
- ↑ 6.0 6.1 Ask the experts: Speedometers and speed cameras (13 August 2012)Fairfax Media. Retrieved 10 September 2015.
- ↑ 7.0 7.1 Frank Markus. Speedometer Scandal! (April 2002)Car and Driver/Hearst Communications, Inc.. Retrieved 10 September 2015.
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