How Dynamometers Work

eters or dyno systems seem complicated but onceUnlike transmission dynos, absorption dynamometers
you understand the basics it all becomes clear! Aproduce the torque that they measure by creating a
dynamometer is basically just a measuring tool, in theconstant restraint to the turning of a shaft, by applying
same way as voltmeters, scales or speedometersmechanical friction, fluid friction, or electromagnetic
are.induction.
Among force-measuring devices, dynamometers areA Prony brake develops mechanical friction on the
a flexible metallic ring that bends when a force isedges of a rotating pulley by the means of a few
applied in such a manner as to tend to collapse it (thebrake blocks that are squeezed against the wheel by
amount of bending being a measure of the appliedtightening the bolts until the friction torque FR balances
force) and a hydraulic “load cell” that measuresthe torque WL.
compressive loads in terms of fluid pressure.A water brake creates a resistance by circulating the
Once you have built your new motor, or fitted anywater flow between a rotating impeller and a
tuning parts, it is very important to visit a goodstationary shell, while an electric dynamometer
automotive Dynamometer or rolling road. If you don't,generates and absorbs direct-current electricity or
then you will never be able to properly set up youreddy currents. In each case, the element that exerts
engine.the restraining influence is freely cradled so that its
A good dynamometer allows you to use a gastendency to rotate with the rotating body can be
analyzer while under load so you can see the real airrestricted and the restricted force is measured at a
fuel mixture at all RPM's while driving.known distance from the axis of rotation.
Power-measuring dynamometers may be eitherTorque is the product of the spring load or weight and
transmission dynamometers or absorptionthe distance from the axis of rotation. Dynamometers
dynamometers. The former utilize devices thatalso measure the torque produced by an engine in
measure torque, in terms of the elastic twist of theorder to reveal important information about its
shaft or of a special torquemeter inserted betweenperformance.
some sections of the shaft. The torque is produced byA diagnose is then presented in performance graphs,
the useful load that the prime mover, motor, orwhich can be easily printed and interpreted.
machine is carrying.