Geometrical Optimization of an Automotive Halfshaft 2017-01-1125

Halfshafts are very important components from vehicle powertrain. They are the element responsible to transmit torque and rotation from transmission to wheels. Its most basic design consists of a solid bar with joints at each extreme. Depending of bar length, the natural frequency of first bending mode might have a modal alignment with engine second order, resulting in undesired noise on vehicle interior. Many design alternatives are available to overpass this particular situation, like adding dampers, use tube shafts or use link-shafts, however, all of them are cost affected. This study proposes an investigation to obtain an optimal profile for a solid shaft, pursuing the lowest possible frequency for the first bending mode by changing its diameter at specific regions. The study is divided in four main stages: initially, a modal analysis of a halfshaft is done at vehicle to determinate its natural frequency when assembled on vehicle. Second, a CAE model is generated to reproduce results from modal analysis and validate the boundary conditions. On the next stage, the CAE model is submitted to an optimization routine through genetic algorithms, varying the diameter at different sections of the shaft and determining its natural frequency as a function of its profile. Finally, once an optimal design is achieved, a prototype is made to validate the results. The study has confirmed that it is possible to tune the bending natural frequency of the halfshaft by optimizing its profile, however, further investigation is recommended to determine the limits that this proposal can achieve.