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A dynamometer, or '''"dyno"''' for short, is a device used to measure RPM and Torque from which Power produced by an Engine or other rotating device can be calculated. It is said to have been created by the "Father of Computing" Charles Babbage . There are two types of dynos: one that is bolted directly to an engine, known as an engine dyno, or a dyno that can measure power and torque without removing the engine from the frame of the vehicle, known as a chassis dyno. A dynamometer works by absorbing the power developed by the test engine and measuring the torque required to do so. Power is then calculated from the torque and RPM figures and proportioned to a standard horsepower according to this formula :
A dynamometer actually only measures torque and RPM, and power is calculated from those measurements. (''This is the reason that horsepower and torque are always equal at 5252 RPM on horsepower graphs — when RPM in the formula becomes 5252, it cancels out the divisor of 5252 leaving only the torque figure as the power figure''.) ''See also Internal Combustion Engine (performance section)''. Types of absorption units There are several types of power absorption units :
The most common type is the water brake, due to its high power capability, controllability, and lower cost. The schematic above shows the most common type of water brake, the variable level type. Water is added until the engine is held at a steady rpm against the load. Water is then kept at that level and replaced by constant draining and refilling, which is needed to carry away the heat created by absorbing the horsepower (which in itself is a measure of power output of the engine). The Housing attempts to rotate in response to the torque produced but is restrained by the scale or torque metering cell which measures the torque. Dynamometers are useful in the development and refinement of modern day engine technology. The concept is to use a dyno to measure and compare power transfer at different points on a vehicle, thus allowing the engine or drivetrain to be modified to get more efficient power transfer. For example, if an engine dynamo shows that a particular engine achieves 400 N·m (300 lbf·ft) of torque, and a chassis dynamo shows only 350 N·m (260 lbf·ft), one would know to look to the drivetrain for the major improvements. Dynamometers are typically very expensive pieces of equipment, reserved for certain fields that rely on them for a particular purpose. GENERAL WORKINGS The dynamometer applies various loads on the engine and measures the engine's ability to move the load. The dynamometer may be connected to a Computer which calculates the output of the engine. The engine is run from idle to its maximum RPM and the output is measured and plotted on a Graph . Nearly all aspects of engine operation are measured during a dyno run. ENGINE DYNAMOMETER An engine dynamometer measures power and torque directly from the engine's Crankshaft (or Flywheel ), when the engine is removed from the vehicle. These dynos do not account for power losses in the drivetrain, such as the Gearbox , Transmission or Differential Etc . CHASSIS DYNAMOMETER A Chassis dynamometer measures power from the engine through the Wheel s. The vehicle is parked on rollers which the car then turns and the output is measured. These dynos can be fixed or portable. Because of frictional and mechanical losses in the various drivetrain components, the measured horsepower is generally 15-20 percent less than the brake horsepower measured at the crankshaft or flywheel on an engine dynamometer.John Dinkel, "Chassis Dynamometer", ''Road and Track Illustrated Automotive Dictionary,'' (Bentley Publishers, 2000) p. 46. SEE ALSO
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