Design and analysis of a novel multi-speed automatic transmission with four degrees-of-freedom

With the pressing demand of reducing fuel consumption and improving driving performance, automatic transmissions (ATs) tend to have a wider ratio spread and more speeds. However, it is difficult to achieve a compact design by using only planetary gear sets (PGSs) or only parallel-axis gear pairs (PGPs). In this paper, we propose a novel multi-speed AT characterized by a combination of PGSs and PGPs on two parallel axes. All feasible clutching sequences are synthesized through a systematic procedure. Results reveal that we can obtain a nine, eleven or thirteen-speed clutching sequence by tuning the stationary ratios of PGPs. A computational model based on genetic algorithm (GA) is established to optimize the gear ratios. Within the constraints of stationary ratios and single transition shift, an optimal solution is found with a wide ratio spread. Furthermore, a matrix method is developed to analyze transmission kinematics and kinetics, which is especially suitable for computer-aided analysis of complex four degrees-of-freedom (DOFs) transmissions. Key parameters such as power flow, efficiency and clutching sequence of the proposed AT are evaluated and compared. This research may shed light upon synthesis, design and analysis of complex ATs with a wider ratio spread and more speeds.