NUMERICAL FATIGUE LIFE EVALUATION OF AN INNOVATIVE INTERNAL COMBUSTION ENGINE SHAFT

A novel self-balanced internal combustion engine is presented. The new engine has a modular structure composed of two cylinders arranged in opposite way. It is characterized by an innovative system of linking between the pistons and the shaft, which has three toggles. One of these is on the middle of the shaft, whereas the others two are placed symmetrically. Thanks to this particular shape of the shaft, the pistons can rotate with the same timing and so the new engine comes back to be perfectly auto-balanced. Moreover, the fatigue life prediction of the shaft has been studied through numerical methods. In particular, two different approaches have been compared to estimate the maximum number of working cycles: the first is based on a “static” resistance criterion, the second consider the multiaxial nature of the stress and is based on the maximum shear stress (critical) plane criterion. The stress distribution on the shaft during the usual working conditions, has been evaluated by a FEM package. Results highlight that the critical plane approach is more conservative than “static” one.