Minggu, 21 November 2010

How dynamometers work

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

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