 torsional vibration is angular vibration of an objectâcommonly a shaft along its axis of rotation. torsional vibration is often a concern in power transmission systems using rotating shafts or couplings where it can cause failures if not controlled. a second effect of torsional vibrations applies to passenger cars. torsional vibrations can lead to seat vibrations or noise at certain speeds. both reduce the comfort. in ideal power generation, or transmission, systems using rotating parts, not only the torques applied or reacted are "smooth" leading to constant speeds, but also the rotating plane where the power is generated (or input) and the plane it is taken out (output) are the same. in reality this is not the case. the torques generated may not be smooth (e.g., internal combustion engines) or the component being driven may not react to the torque smoothly (e.g., reciprocating compressors), and the power generating plane is normally at some distance to the power takeoff plane. also, the components transmitting the torque can generate non-smooth or alternating torques (e.g., elastic drive belts, worn gears, misaligned shafts). because no material can be infinitely stiff, these alternating torques applied at some distance on a shaft cause twisting vibration about the axis of rotation. == sources of torsional vibration == torsional vibration can be introduced into a drive train by the power source. but even a drive train with a very smooth rotational input can develop torsional vibrations through internal components. common sources are: * internal combustion engine: the torsional vibrations of the not continuous combustion and the crank shaft geometry itself cause torsional vibrations * reciprocating compressor: the pistons experience discontinuous forces from the compression. * universal joint: the geometry of this joint causes torsional vibrations if the shafts are not parallel. * stick slip: during the engagement of a friction element, stick slip situations create torsional vibrations. * lash: lash in a drive train can cause torsional vibrations if the direction of rotation is change ==crankshaft torsional vibration== torsional vibration is a concern in the crankshafts of internal combustion engines because it could break the crankshaft itself; shear-off the flywheel; or cause driven belts, gears and attached components to fail, especially when the frequency of the vibration matches the torsional resonant frequency of the crankshaft. 
Mechanical_vibrations