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The megatrends "reduction of emissions" and "fuel consumption reduction" play a predominant role in the development of powertrains. For transit buses this implies both the reduction of emissions and pollutions of the internal combustion engine, and, on the other hand, a further reduction of noise and brake dust. Also very important is the reduction of both fuel consumption and CO₂ emissions. For all these targets the actual developments on the engine side have led to great improvements in the last decades, but what can be mentioned for the other components of the powertrain, especially looking for transmissions? First of all the relevant trends for transit buses have to be considered: A large increase of the torque of the combustion engines during the last years has a big impact on the development of transmissions for buses.

In a collaborative investigation of ZF Friedrichshafen AG and the Fraunhofer-Institut für Betriebsfestigkeit LBF [1], both constant and variable amplitude fatigue tests were performed on induction-hardened automatic transmission shafts made from Ck 35 mod. steel. The objectives of the project were to evaluate the safety reserves of the shafts and to apply several selected methods to assess fatigue life, to compare these methods and to gain insights for future component developments.