Torsional vibration of powertrains

The recent introduction of stringent emissionrequirements together with economic pressure has ledto a particular focus on increasing powertrainefficiency. This has seen the incorporation ofreal-time measurements to predict system behaviourand engine condition. Accurate models for allcomponents are thus important. This work investigatesthe consequences of some common assumptions made inlow frequency torsional powertrain models andproposes improved models where appropriate. Inparticular piston-to-cylinder friction(crank/gudgeon) offset and tyre torsional behaviourwere studied. It was found that piston-to-cylinderfriction can increase the inertia variation of anengine mechanism. Offset also modifies its nonlinearbehaviour. For small (gudgeon) values these effectsare minimal. However for large (crank) values theeffects should not be ignored. The low frequencytorsional damping properties of a small pneumatictyre were found to be more accurately represented ashysteretic rather than viscous. Time DomainReceptance modelling was used to extend the resultsto a multicylinder engine powertrain. The findingsshould be of interest to both industry and academiaalike.