Evaluation of Constant Speed Assumption for Determining Cylinder Excitation Torque

Order based torsional vibration analysis codes require a separate, non-linear model to compute single cylinder excitation torque for input. The slider crank mechanism model is typically derived using a crankshaft constant angular velocity assumption. Additionally, the equation describing this constant speed mechanism is derived in an approximate form. An exact model for the slider crank mechanism turning at non-constant speed is used in an iterative procedure with an order based impedance model torsional analysis code to quantify the effects of these assumptions. Results are presented for an in-line six diesel engine, and generalized where possible.