Electrified powertrain configurations are critical to the fuel economy and
performance of hybrid vehicles. While single planetary gear (PG) configurations
- such as the Toyota Prius - have the advantage of simple control and excellent
fuel economy, the generator1 is unable to participate in the drive, resulting in
poor acceleration. To overcome these problems, we propose a new multi-gear
electronically controlled continuously variable transmission (ECVT) due to its
high efficiency and excellent acceleration performance. It requires only one PG
and two synchronizers. For this type of multi-gear ECVT hybrid vehicle, this
paper describes in detail the synchronizer-based shift logic of the new
configuration. Furthermore, the power flow and dynamics modeling process in
different operating modes are systematically analyzed. In addition, the global
optimal Dynamic Programming (DP) algorithm is presented and a new near-optimal
energy management strategy, Rapid-DP, is employed to evaluate the acceleration
and fuel consumption of the new design, respectively. The newly proposed design
is also qualitatively and quantitatively analyzed under Federal Test Procedure
72 (FTP72), Highway Fuel Economy Test Cycle (HWFET) and Worldwide Harmonized
Light Vehicles Test Cycle (WLTC) driving cycles. The case results show that
compared with the original Toyota Prius, the proposed multi-gear ECVT
configuration can effectively improve the overall performance, with a fuel
economy improvement of 4.01%-4.96%, a power improvement of 50% on average, and a
shift smoothness comparable to that of the Prius under different driving cycles,
which verifies the validity of the new configuration proposed in this study.
Meanwhile, this study provides a new theoretical basis for optimizing and
modifying the technology path of multi-gear power-split hybrid vehicles.