The Effect of Bearing Stiffnesses on Crankshaft Natural Frequencies

Crankshafts of internal combustion engines are torsionally soft; they are well known to get into resonance during engine operation. Also, fatigue due to operation under resonance conditions is the usual mode of their failure. Because of the presence of the webs and crank pins it could be expected that bearings play an important role in determining even the torsion dominated natural frequencies. However, there do not appear to be any systematic study which brings out the interaction between bearing design parameters and the life of crankshafts. It also appears from the literature that bearings are routinely designed without considering their influence on the crankshaft dynamics.

This study brings out the influence of radial and rotational stiffnesses of bearings on the torsion dominated natural frequencies. it obtains the threshold values for the stiffnesses below which the natural frequencies vary significantly with bearing stiffnesses. It also demonstrates that the effect of wear of bearings, during their life time, on crankshaft natural frequencies, could be taken into account. Such design procedures could facilitate the development of reliable crankshafts.

* Research Student

** Associate Professor