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A speedometer is a vehicle instrument that measures the instantaneous speed. Image File history File links Download high resolution version (2048x1536, 1186 KB) From stock. ...
Image File history File links Download high resolution version (2048x1536, 1186 KB) From stock. ...
Look up Gauge in Wiktionary, the free dictionary. ...
Karl Benzs Velo (vélo means bicycle in French) model (1894) - entered into the first automobile race 2005 MINI Cooper S. An automobile (also motor car or simply car) is a wheeled passenger vehicle that carries its own motor. ...
This article or section does not cite its references or sources. ...
The Trikke is a Human Powered Vehicle (HPV) This article is about the means of transport. ...
Miles per hour is a unit of speed, expressing the number of international miles covered per hour. ...
Kilometres per hour (American spelling: kilometers per hour) is a unit of both speed (scalar) and velocity (vector). ...
Spur gears found on a piece of farm equipment A gear is a wheel with teeth around its circumference, the purpose of the teeth being to mesh with similar teeth on another mechanical device -- possibly another gear wheel -- so that force can be transmitted between the two devices in a...
An engine is something that produces an effect from a given input. ...
A sphere rotating around its axis. ...
This article or section does not cite its references or sources. ...
Traditional automotive speedometers are driven by a flexible, sleeved cable that is rotated by a set of small gears in the tail shaft of a transmission. The early Volkswagen Beetle and many motorcycles, however, use a cable driven from a front wheel. 6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ...
Spur gears found on a piece of farm equipment A gear is a wheel with teeth around its circumference, the purpose of the teeth being to mesh with similar teeth on another mechanical device -- possibly another gear wheel -- so that force can be transmitted between the two devices in a...
In mechanics, a transmission or gearbox is the system of gears and/or the hydraulic system (called variously hydrodynamic, fluid or automatic transmission) that transmits mechanical power from a prime mover—such as an engine or electric motor—to a typically rotary output device at a lower angular momentum but...
The most common form of speedometer relies on the interaction of a small permanent magnet affixed to the rotating cable with a small aluminum cup affixed to the shaft of the pointer. As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet 'drags' the cup--and thus the speedometer pointer--in the direction of its rotation with no mechanical connection between them. An eddy current is a phenomenon caused by a moving magnetic field intersecting a conductor or vice-versa. ...
The pointer shaft is held toward zero by a fine spring. The torque on the cup increases with the speed of rotation of the magnet (which, recall, is driven by the car's transmission.) Thus an increase in the speed of the car will twist the cup and speedometer pointer against the spring. When the torque due to the eddy currents in the cup equals that provided by the spring on the pointer shaft, the pointer will remain motionless and pointing to the appropriate number on the speedometer's dial.
The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires. The speedometer mechanism often also drives an odometer plus a small switch that sends pulses to the vehicle's engine computer. Calibration refers to the process of setting the magnitude of the output (or response) of a measuring instrument to the magnitude of the input property or attribute within specified accuracy and precision. ...
In an automobile and other four-wheeled vehicles, a differential is a device, usually consisting of gears, for allowing each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them. ...
Tires may refer to: the plural of tire the Italian name for Tiers, Italy, a town in South Tyrol, Italy Category: ...
A modern non-digital odometer A Smiths speedometer from the 1920s showing odometer and trip meter An odometer is a device used for indicating distance traveled by an automobile or other vehicle. ...
Another early form of mechanical speedometer relies upon the interaction between a precision watch mechanism and a mechanical pulsator driven by the car's wheel or transmission. The watch mechanism endeavors to push the speedometer pointer toward zero, while the vehicle-driven pulsator tries to push it toward infinity. The position of the speedometer pointer reflects the relative magnitudes of the outputs of the two mechanisms.
The speedometer was invented by Josip Belušić of Croatia in 1888. Modern speedometers are electronic. A rotation sensor, usually mounted on the rear of the transmission, delivers a series of electronic pulses whose frequency corresponds to the rotational speed of the driveshaft. A computer converts the pulses to a speed and displays this speed on an electronically-controlled, analog-style needle or a digital display, the latter of which is more common nowadays. Pulse counts may also be used to increment the odometer. Josip BeluÅ¡ić was a Croatian inventor. ...
Year 1888 (MDCCCLXXXVIII) was a leap year starting on Sunday (click on link for calendar) of the Gregorian calendar (or a leap year starting on Tuesday of the 12-day slower Julian calendar). ...
Electronics is the study of the flow of charge through various materials and devices such as, semiconductors, resistors, inductors, capacitors, nano-structures, and vacuum tubes. ...
Cardan driveshaft with universal joints A driveshaft or driving shaft or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. ...
A display device is a device for visual presentation of images (including text) acquired, stored, or transmitted in various forms. ...
A modern non-digital odometer A Smiths speedometer from the 1920s showing odometer and trip meter An odometer is a device used for indicating distance traveled by an automobile or other vehicle. ...
As of 1997, federal standards in the United States allowed a maximum 5% error on speedometer readings (per "Auto Tutor", American Automobile Association of California magazine, Oct. 17, 1997). Aftermarket modifications, such as different tire and wheel sizes or different differential gearing, can cause speedometer inaccuracy.
In the United States during the 1980s a federal law was passed mandating that speedometers on newly manufactured vehicles could not display speeds higher than 85 mph. This law is no longer in effect.
Speedometers for other craft have specific names and use other means of sensing speed. For a boat, this is a pit log. For an aircraft, this is a Pitot Tube. Image File history File links Commons-logo. ...
The Wikimedia Commons (also called Wikicommons) is a repository of free content images, sound and other multimedia files. ...
Figure 1: Photo of World War II US Navy submarine pitometer. ...
A Pitot tube is a measuring instrument used to measure fluid flow. ...
Error
Speedometer error can come from several causes but most commonly is due to nonstandard tire diameter, in which case the - percent error = 100("standard diameter"/"new diameter" - 1).
Nearly all tires now have their size shown as "T/A_W" on the side of the tire, and the tire's - diameter in inches = TxA/1270 + W.
For example, a standard tire is "185/70R14" with diameter = 185x70/1270 + 14 = 24.196850 in. Another is "195/50R15" with 195x50/1270 + 15 = 22.677165 in. Replacing the first tire (and wheels) with the second (on 15" wheels), a speedometer reads 24.19../22.67..=1.0670139 times the correct speed or 6.7% too high.
GPS -
GPS devices may indicate the true speed of travel on the user interface. Unlike instrumental speedometers which provide a continious reading, the GPS speed readouts have a one second update interval. A taxi in Kyoto, equipped with GPS navigation system An automotive navigation system is a satellite navigation system designed for use in automobiles. ...
Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
The reading is based on reception of data from the satellites in orbit, and is therefore independent of the car's transmission components. Discrepancies between the two readings may be caused by instrument error (on the vehicle), or by changing directly influencial factors, such as tire sizes.
See also Airspeed Indicator The airspeed indicator is an instrument used in an aircraft to display the crafts airspeed, typically in knots, to the pilot. ...
A modern non-digital odometer A Smiths speedometer from the 1920s showing odometer and trip meter An odometer is a device used for indicating distance traveled by an automobile or other vehicle. ...
A hubometer (hub, center of a wheel + -ometer, measure of), or hubodometer, is a device mounted on the axle of an automobile or other vehicle that measures distance traveled. ...
Figure 1: Photo of World War II US Navy submarine pitometer. ...
Tachometer showing engine RPM (rotations per minute), and a redline from 6000 and 7000 RPM. A tachometer gauges the speed of rotation of a shaft or disk (from Greek: tachos = speed, metron = measure), as in a motor or other machine. ...
A taximeter is a mechanical or electronic device installed in taxicabs, similar to an odometer, which calculates passenger fares based on a combination of distance travelled and waiting time. ...
Vehicle instrument is an instrument that measures some parameters in the vehicle. ...
External links - Autoblog: Gauging changes
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