chinalie: Dynamometer

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Not to be confused with dynameter.

For the dynamometer used in railroading, see dynamometer car.

A dynamometer or "dyno" for short, is a machine used to measure torque and rotational speed (rpm) from which power produced by an engine, motor or other rotating prime mover can be calculated.

A dynamometer can also be used to determine the torque and power required to operate a driven machine such as a pump. In that case, a motoring or driving dynamometer is used. A dynamometer that is designed to be driven is called an absorption or passive Dynamometer. A dynamometer that can either drive or absorb is called a universal or active dynamometer.

In addition to being used to determine the torque or power characteristics of a machine under test (MUT), Dynamometers are employed in a number of other roles. In standard emissions testing cycles such as those defined by the US Environmental Protection Agency (US EPA), dynamometers are used to provide simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer). In fact, beyond simple power and torque measurements, dynamometers can be used as part of a testbed for a variety of engine development activities such as the calibration of engine management controllers, detailed investigations into combustion behavior and tribology.

In the medical realm, hand dynamometers are used for surgery routine screening of grip strength and initial and ongoing evaluation of patients with hand trauma and dysfunction.

Contents

1 Principles of operation

2 Detailed dynamometer description

3 Types of dynamometers

3.1 Types of absorption/driver units

3.2 Eddy Current type absorber

4 Powder Dynamometer

5 Hysteresis Dynamometers

5.1 Electric motor/generator dynamometer

5.2 Fan Brake

5.3 Hydraulic brake

5.4 Water brake type absorber

6 How dynamometers are used for engine testing

6.1 General testing methods with types of dynamometer systems

6.2 Engine dynamometer

6.3 Chassis dynamometer

6.4 Common misconceptions about dynos

7 History

8 See also

9 References

9.1 Citations

9.2 General references

10 External links

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Principles of operation

An absorbing dynamometer acts as a load that is driven by the prime mover that is under test. The dyno must be able to operate at any speed, and load the prime mover to any level of torque that the test requires. A dynamometer is usually equipped with some means of measuring the operating torque and speed.

The dynamometer must absorb the power developed by the prime mover. The power absorbed by the dynamometer must generally be dissipated to the ambient air or transferred to cooling water. Regenerative dynamometers transfer the power to electrical power lines.

Dynamometers can be equipped with a variety of control systems. If the dynamometer has a torque regulator, it operates at a set torque while the prime mover operates at whatever speed it can attain while developing the torque that has been set. If the dynamometer has a speed regulator, it develops whatever torque is necessary to force the prime mover to operate at the set speed.

A motoring dynamometer acts as a motor that drives the equipment under test. It must be able to drive the equipment at any speed and develop any level of torque that the test requires.

Only torque and speed can be measured; Power must be calculated from the torque and speed figures according to the formula:

Where K is determined by the units of measure used as can be seen below:

To calculate power in horsepower (hp) use:

where:

Torque is in pound-feet (lbft)

Rotational speed is in revolutions per minute (rpm)

To calculate power in kilowatts use:

where:

Torque is in newton-metres (N)

Rotational speed is in revolutions per minute (rpm)

(On graphs of torque vs. rpm the numerical values of torque and power are always equal when the rpm value is equal to the constant, K. The numerical values of horsepower and lbft of torque are always equal at 5252 rpm because 5252 rpm in the numerator cancels out the constant, 5252, in the denominator leaving only the torque figure equal to the power figure.)

See also internal combustion engine (performance section).

Detailed dynamometer description

Electrical dynamometer setup showing engine, torque measurement arrangement and tachometer

A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in a housing. The rotor is coupled to the engine or other equipment under test and is free to rotate at whatever speed is required for the test. Some means is...(and so on)