Torsional vibration responses of the engine crankshaft-gearbox coupled system with misfire and breathing slant crack based on instantaneous angular speed

Torsional vibration responses of an engine crankshaft-gearbox coupled system with misfire and breathing slant crack are investigated in this paper. The crankshaft is modelled by lumped mass method and its dynamic equations are deduced based on Lagrange equation. Both the time varying mesh stiffness of the gearbox composing of a pinion and a gear and the response-dependent stiffness of a shaft element with a breathing slant crack are evaluated. Natural frequencies of the healthy and cracked systems are analysed respectively. Torsional vibrations based on the instantaneous angular speed (IAS) of the flywheel and the driven shaft are compared among the operating conditions of normal, misfire and breathing slant crack on the driven shaft. Simulation results are validated by experiments, which show that the encoder on the driven shaft is better because it can monitor the IAS of the flywheel and the driven shaft simultaneously and the signals are more prominent here.