Some Effects of Piston Friction and Crank or Gudgeon Pin Offset on Crankshaft Torsional Vibration

The varying inertia associated with reciprocating mechanisms leads to nonlinear frequency coupling between rotational speed and an engine system's average torsional natural frequencies. This coupling can cause secondary resonance problems. Recent work by the authors has shown that piston-to-cylinder friction and gudgeon pin or crank offset can modify coupling behavior. These effects can be demonstrated by analysis of an engine's receptance function and through time simulations. This paper presents the derivation of a single-cylinder engine receptance in the presence of piston-to-cylinder friction. Simulations are then used to investigate some of the effects of piston-to-cylinder friction, offset, and excitation phase on the frequency content of the crankshaft velocity. Simulations indicate that nonlinear coupling is affected by these variables, which has implications for secondary resonance detection and prevention. The most significant finding is that stronger coupling behavior can occur when piston-to-cylinder lubrication breaks down.