Prius+ and Volt-: Configuration Analysis of Power-Split Hybrid Vehicles With a Single Planetary Gear

—The majority of the hybrid electric vehicles (HEVs) available on the market are power-split hybrid vehicles with a single planetary gear (PG), including the popular Toyota Prius and Chevy Volt. Although both vehicles use a single PG, they have different configurations with different number of operating modes. The Prius has no clutch and has a single operating mode, whereas the Chevy Volt uses three clutches and has four modes. The goal of this paper is to present a thorough analysis on all possible configurations of power-split hybrid powertrain using a single planetary gear. The analysis includes: 1) search for all possible ways to connect powertrain elements to the PG, 2) identify all potential locations for clutch installations around the PG and examine the feasibility of additional operating modes introduced by the clutch installation; and, 3) optimize the fuel economy for performance comparison. The proposed analysis shows that a single PG can produce 12 different configurations, and each of which can have four feasible operating modes by adding three clutches to the PG. In case studies, we focus on the two configurations that are used in the Prius and Volt in order to find the impact of the additional (or removal of) clutches and modes on their fuel economy performance. Our results show that adding one clutch to the Prius transmission (which is named 'Prius+') can significantly improve the fuel economy in urban driving, while removing two clutch from the Volt transmission ('Volt-') will not significantly affect the fuel economy in both urban and highway driving. This multi-mode configuration analysis can be used to systematically design future power-split HEVs.