3/15/2011 1 Crank Effort Diagrams The torque on an engine crankshaft varies considerably throughout the working cycle, due to variations in the crank position, the pressure in the cylinder and the inertia of the moving parts. Variation of torque of an engine crankshaft If the crankshaft torque is plotted against the crank angle, a turning moment or crank effort diagram is obtained. Crank Effort Diagram Crank effort diagram for a single-cylinder four-stroke engine. The net area of the diagram, shown shaded, represents the work done during the cycle and the average height represents the mean torque exerted (line AE). Mean Torque Mean Torque If the resisting torque is uniform, this is equal to the mean engine torque if the mean speed is to remain constant. Mean Torque Engine torque > resisting torque (AB) Engine speeds up; Engine torque < resisting torque (BC) Engine slows down; At points of intersection (A, B C etc), Engine torque = resisting torque no accelerationor deceleration: speed is max. or min. at these points
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