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Crankshafts developed wide applications even before methods to design them got evolved. Initially, they were assumed to be made up of beam segments. Since, the length to width ratios of the segments are of the order of one, these methods were not effective. Therefore, till recently they were designed based mostly on in-house experience and by using empirical formulae. Of late, with the advent of powerful computers, analysis based on finite element method has come into use for crankshaft design. In this work, we generate, from fundamentals, a systematic procedure to design crankshafts for finite life. Our method uses the advantages of both the classical method and the finite element technique. For the initial and the approximate results, we use the classical method. A software developed, TVAL, based on this method, quickly gives the natural frequencies, critical modes, displacements and stresses. For more accurate results, we model the crankshaft using solid finite elements.

Identification of natural frequencies is a fundamental step in crankshaft design. For satisfactory operation they should be well separated from the operating speed range and several of its harmonics. These frequencies depend on crankshaft's mounting conditions, its geometry and material properties. In this work ten crankshaft parameters are identified besides the bearing stiffness which can bring about changes in natural frequencies. The effect of variation of each of these parameters is studied. Also, the feasibility of using geometrically identical spheroidal graphite iron crankshaft in place of a forged one is examined from the point of view of natural frequencies. Three crankshafts are considered for the intended study.

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.