Rapid Configuration Design of Multiple-Planetary-Gear Power-Split Hybrid Powertrain via Mode Combination

Hybrid powertrain technologies must be applied to sports utility vehicles (SUV) and light trucks (LT) in the near future to meet the new corporate average fuel economy standards. For SUV and LT, multimode hybrid powertrains using multiple planetary gears (PGs) help to deliver the required torque while achieving better fuel economy. Compared with single and double PG systems, three-PG system can provide more design flexibility. However, it is not practical to search through all possible three-PG designs using exhaustive search methods because of the enormous size of the design space. In this paper, a rapid structure optimization method is proposed. Fuel-saving (FS) modes and high launching performance (HLP) modes are first identified through normalized efficiency analysis and maximum output torque analysis. Then, a constrained optimization problem is defined to limit the mode candidates (FS and HLP modes). Following this approach, the design space is reduced by a factor of 1000. Three clutch designs are obtained from the designs with fewer clutches (one or two) by using the design-extension technique. Finally, a case study demonstrates how the proposed method is applied to the optimal design of three-PG hybrids.