Off-Road Chapter 3

Off-Road Chapter 3 - Chapter 3 Engine and Vehicle Testing...

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1 Chapter 3 Engine and Vehicle Testing Power Measurement Methods ± Power – the rate of doing work. A unit of power is a newton meter per second (watt). ± Brake power – the power output of the engine crankshaft. The engine may be stripped of part or all of its accessories. ± Power take-off power – the power delivered by a tractor through its pto shaft. Power Measurement Methods ± Drawbar power – the power of a tractor measured at the end of the drawbar. ± Friction power – the power required to run the engine at any given speed without production of useful work. It is usually measured with a suitable electric dynamometer that runs or “motors” the engine. It represents the friction and pumping losses of an engine.
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2 Power Measurement Methods ± Observed power – the power obtained at the dynamometer without any correction for atmospheric temperature, pressure, or water vapor. ± Corrected power – obtained by correcting observed power to standard conditions of sea-level pressure, 15.5 o C temperature, and zero vapor pressure. Power Measurement Methods ± Dynamometer – an instrument for determining power, usually by the independent measure of force, time, and the distance through which the force is moved. Dynamometers may be classified as brake, drawbar, or torsion, according to the manner in which the work is being applied. Also, they may be classed as absorption or transmission, depending on the disposition of the energy. Dynamometers ± A dynamometer for testing engines must include the following four essential elements: ± A means for controlling torque ± A means for measuring torque ± A means for measuring speed ± A means for dissipating power
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3 Prony brake ± It is the simplest type of dynamometer – an example of an absorption-type dynamometer. ± The rotor is connected to the crankshaft of the engine and rotates at engine speed. Surrounding the rotor are brake shoes that create torque drag on the rotor. The torque is controlled by tightening or loosening the hand lever. The torque is measured by a scale located at the end of the lever arm. A tachometer must be provided for measuring the rotor speed. After the torque and speed are measured, the power can be calculated. Prony Brake Dynamometer
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This document was uploaded on 11/21/2011.

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Off-Road Chapter 3 - Chapter 3 Engine and Vehicle Testing...

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