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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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