Highly Fuel-Efficient Transmission and Propulsion Concepts

Abstract

The integration of one or more electric machines into the drivetrain has resulted in many different powertrain concepts in recent years, ranging from the P2 hybrid to dedicated hybrid transmission (DHT). Two types of DHT with different characteristics are investigated. The first type is the power split hybrid (PS-DHT), which has very low mechanical complexity but needs high electrical effort in the transmission. The second type is multi-mode DHT (MM-DHT), which has a slightly higher mechanical complexity but much less electrical effort when compared with the PS-DHT. A transmission synthesis is used to determine the concept of the MM-DHT. The three different powertrain concepts (i.e., P2, PS-DHT, and MM-DHT) are analyzed and evaluated regarding fuel economy and performance. Legal driving cycles (e.g., Worldwide Harmonized Light vehicles Test Procedure) and the 3D method (driver, driven vehicle, driving environs) are used to investigate the drivetrain in the context of real driving operation. Results show that the two DHT concepts offer better fuel economy than the P2 hybrid drivetrain while still providing the same or even better driving performance. The study also shows that new hybrid concepts created with transmission synthesis can lead to further improvements in hybrid powertrains.