Automated topology optimisation of hybrid electric vehicle powertrains

Abstract

Abstract:Hybrid Electric powertrains are comprised of gasoline and electric powertrains components. These components can be connected in numerous configurations; as the number of components increase, the number of configurations increase exponentially. In this research, an algorithm was developed to automatically assemble and compare all possible hybrid electric powertrain configurations. Combinatorics was used to discover all possible combinations of: an internal combustion engine, high-torque low-speed electric motor, low-torque high-speed electric motor, planetary gearset, five-speed discrete gearbox, and battery. The Graph Theoretic Method was used to generate the powertrain models. The steadystate system models were solved symbolically, and Dynamic Programming was used to determine the optimal control law that minimized fuel consumption. To save computation time, topologies were evaluated using a multi-stage screening process. The component sizes of the top 24 topologies were optimized and ranked by fuel consumption. It was found that the Parallel and Powersplit-like topologies with discrete gearboxes were most efficient. The best performing topology is a Powersplit Hybrid type, with a discrete gearbox connected to the final drive and the output gear of the planetary carrier and electric motor in parallel.Keywords: hybrid electric vehicles; hybrid electric powertrains; topology optimization; linear graph theory; Graph Theoretic Method; design automation Biographical notes: IntroductionConventional transportation vehicles use combustion engines for propulsion because fossil fuels are energy dense and relatively inexpensive. Rising fuel prices, depletion of fossil fuels, and public environmental awareness have made electric vehicles an attractive alternative. Electric vehicles use electricity instead of gas for propulsion. They are more efficient, quieter, and do not create tailpipe emissions. Unfortunately, conventional electric vehicles are heavily reliant on batteries for energy storage. Batteries are expensive, heavy, and require charging equipment. Fuel cells have been proposed as an alternative to batteries, but hydrogen fuelling infrastructure is not widely available, and high pressure hydrogen storage technology is not mature. As an intermittent step from gasoline to electric vehicles, Hybrid Electric Vehicles (HEVs) have emerged in the marketplace.Hybrid Electric powertrains combine elements from traditional gasoline powertrains and electric powertrains. This is advantageous because they operate 10-20% more efficiently, and can refuel at any gasoline station (Chen et al., 2009;del Re et al., 2010;Chan, 2007). Including additional powertrain components create challenges. Complex controllers are required to ensure the system is operating efficiently. Cost and weight also increase with the number of components.The number of potential powertrain configurations increase exponentially as more components are included. Novel powertrain architectures can be identified through human