Design of Power Split Hybrid Powertrains with Multiple Planetary Gears and Clutches.

Abstract

Fuel economy standards for automobiles have become much tighter in many countries in the past decades. Hybrid electric vehicles (HEVs), as one of the most promising solutions to take on these challenging standards, have been successful in the US market. In the last few years, an observed trend is to use multiple planetary gears with multiple operating modes to further improve vehicle fuel economy and driving performance. Most work in existing literature on HEV design and optimization has been based on specific configurations, rather than exhaustively searching through all possible configurations. This limitation arises from the large size of the design space–millions to trillions of possible topological candidates. In this dissertation, a systematic design methodology is presented, which enables the exhaustive search of multi-mode powertrain systems. As a first step, a systematic analysis has been performed for all 12 single PG configurations with multiple operating modes enabled by clutch operation. The Dynamic Programming (DP) technique is used to solve the optimal energy management problems for each design candidate. For multi-mode HEVs with multiple PGs, an automated modeling and mode classification methodology is developed, which makes it possible to exhaustively search all possible designs. General mode shift mechanisms are studied, while mode shift cost is evaluated using Dijkstra’s algorithm, which identifies the optimal mode shift path. For each candidate, the optimal control problem needs to be solved so that all designs can be compared based on their best possible execution. A fast and near-optimal energy management strategy is proposed. The comparison results show that it is up to 10,000 times faster than DP while achieving similar performance. To ensure acceptable launching performance of the design candidates, a fast and optimal acceleration performance test procedure is developed, which can be used to determine optimal control inputs and mode shift schedule. Combining all proposed methodologies produces a systematic and optimal design procedure. Optimization results show that the exhaustive search design method is able to identify dozens of better designs than the production hybrid vehicle models available in today’s market.