A New Approach of Multi-objective System Optimization Supporting Automotive Electric Powertrain Layout

Propulsion systems of electric and hybrid-electric vehicles include battery, inverter, electric motor and gearbox. The design process of such propulsion systems involves a wide range of parameters according to different requirements and boundary conditions, e.g. performance, efficiency, packaging and costs. Powertrain conception and layout are performed on system level under consideration of specific component properties and represent multi-dimensional optimization problems. In traditional system design development processes, the involvement of a large number of technical and economic factors leads to suboptimal solutions since the complex relations between different, partially conflicting domains involved are not sufficiently considered. With the target to solve this problem, the present publication introduces an integrated multi-objective optimization strategy supporting an effective conception of electric propulsion systems. The strategy contains a holistic consideration of all components and requirements in a multi-objective manner. It is based on a comprehensive system design synthesis, which is based on component-specific Pareto-optimal designs to handle performance, efficiency, package and costs for given system requirements. By consideration of the complex interactions between inverter, electric machine and gearbox, a number of optimal electric powertrain system layouts is generated by means of evolutionary algorithms. In this way, the applied multi-objective optimization creates design variants, which are evaluated by analysis models and rated according to defined design objectives. The pre-defined objectives include specific criteria of potential conflicts in the design process, e.g. costs, energy efficiency and package integration. The result is a Pareto-front of possible e-drive designs, indicating the best possible trade-off between the conflicting objectives. Based on this Pareto front, promising design variants can be selected by engineers and further investigated in the course of detailed development. In addition, requirements that are defined on full-vehicle level can be considered and given boundary conditions can be implemented effectively. In this way, the presented system design approach for the development of electrically driven axles enables a multi-objective optimization considering efficiency, performance, costs and package. It is capable to reduce development time and to improve overall system quality at the same time.