Dynamometer

In addition to being used to determine the torque or power characteristics of a machine under test, dynamometers are employed in a number of other roles.

In the rehabilitation, kinesiology, and ergonomics realms, force dynamometers are used for measuring the back, grip, arm, and/or leg strength of athletes, patients, and workers to evaluate physical status, performance, and task demands.

The dynamometer has a "braking" torque regulator - the power absorption unit is configured to provide a set braking force torque load, while the prime mover is configured to operate at whatever throttle opening, fuel delivery rate, or any other variable it is desired to test.

Constant force test routines require the PAU to be set slightly torque deficient as referenced to prime mover output to allow some rate of acceleration.

A load cell transducer can be substituted for the scales in order to provide an electrical signal that is proportional to torque.

Eddy current dynamometers require an electrically conductive core, shaft, or disc moving across a magnetic field to produce resistance to movement.

The electromagnet voltage is usually controlled by a computer, using changes in the magnetic field to match the power output being applied.

Powder dynamometers are typically limited to lower RPM due to heat dissipation problems.

The magnetisation of the rotor is thus cycled around its B-H characteristic, dissipating energy proportional to the area between the lines of that graph as it does so.

Unlike eddy current brakes, which develop no torque at standstill, the hysteresis brake develops largely constant torque, proportional to its magnetising current (or magnet strength in the case of permanent magnet units) over its entire speed range.

[2] Units often incorporate ventilation slots, though some have provision for forced air cooling from an external supply.

Where permitted, the operator of the dynamometer can receive payment (or credit) from the utility for the returned power via net metering.

Due to the low viscosity of air, this variety of dynamometer is inherently limited in the amount of torque that it can absorb.

An oil shear brake has a series of friction discs and steel plates similar to the clutches in an automobile automatic transmission.

Loads up to hundreds of thermal horsepower can be absorbed through the required force lubrication and cooling unit.

Most often, the brake is kinetically grounded through a torque arm anchored by a strain gauge which produces a current under load fed to the dynamometer control.

Hydraulic dynos are renowned for having the quickest load change ability, just slightly surpassing eddy current absorbers.

An eddy-current or waterbrake dynamometer, with electronic control combined with a variable frequency drive and AC induction motor, is a commonly used configuration of this type.

Disadvantages include requiring a second set of test cell services (electrical power and cooling), and a slightly more complicated control system.

It is usually connected to a computer that records applied braking torque and calculates engine power output based on information from a "load cell" or "strain gauge" and a speed sensor.

The engine is generally tested from somewhat above idle to its maximum RPM and the output is measured and plotted on a graph.

A 'motoring' dynamometer provides the features of a brake dyno system, but in addition, can "power" (usually with an AC or DC motor) the PM and allow testing of very small power outputs (for example, duplicating speeds and loads that are experienced when operating a vehicle traveling downhill or during on/off throttle operations).

Many modern computer-controlled brake dyno systems are capable of deriving that "inertial mass" value, so as to eliminate this error.

With modern electronics and quick reacting, low inertia dyno systems, it is now possible to tune to best power and the smoothest runs in real time.

Motor vehicle emissions development and homologation dynamometer test systems often integrate emissions sampling, measurement, engine speed and load control, data acquisition, and safety monitoring into a complete test cell system.

In retail settings it is also common to tune the air-fuel ratio using a wideband oxygen sensor that is graphed along with the RPM.

The Regnier dynamometer was invented and made public in 1798 by Edmé Régnier, a French rifle maker and engineer.

[10] A patent was issued (dated June 1817)[11][12] to Siebe and Marriot of Fleet Street, London for an improved weighing machine.

A company founded by the Winthers brothers, Dynamatic Corporation, manufactured dynamometers in Kenosha, Wisconsin until 2002.

Starting in 1938, Heenan & Froude manufactured eddy current dynamometers for many years under license from Dynamatic and Eaton.