Effect of the inertia variation on crankshaft vibration

Crankshaft vibration problem is always a major concern in the design of an internal combustion engine. Studies focusing on this problem have been carried out intensively over the past years. With the improvement on the engine, engine speed and gas pressures have increased. The engine crankshaft experiences greater and more serious vibrations. As most researches were done on pure torsional and bending vibration problem, this report aims to provide an insight to the coupled torsional-bending vibrations analysis. A mathematical model is used to analyse the effects of both the reciprocating parts and connecting rod on the coupled torsional and in-plane bending vibrations of the crankshaft. It is modelled using a (CAS) commercial algebraic system called Maple 16. The results show that the equivalent masses of the reciprocating parts and connecting rod and the crankshaft system will vary with respect to the crank angle. The peak to peak values and the spacing between the natural frequencies will also vary with different values of k_ipb. Significant coupling occurs at certain spacing |〖 ω ̅〗_n2-〖 ω ̅〗_n1 | between the natural frequencies of the crankshaft. The difference between the torsional and in-plane bending natural frequencies can be kept small to achieve a small difference in the peak to peak values and a small difference between the two natural frequencies in coupled free vibration problem. As the difference between ω_tor &〖 ω〗_ipb decreases, the dependency of the natural frequencies on the crank orientation decreases. A special case occurs when ω_tor/ω_ipb =1 where the dependency of the natural frequencies on the crank orientation becomes negligible.Bachelor of Engineering (Mechanical Engineering