Design Optimization of Motor/Generator Full-load Characteristics in Two-mode Hybrid Vehicles

An important benefit in adopting multi-mode hybrid powertrains is the possibility of downsizing the electric motor/generator (M/G) units. This paper discusses design optimization of M/G full-load operation envelopes. A three-dimensional operation space analysis is introduced and the full-load speed-torque envelopes of M/G units appear as constraints in the powertrain operation space. The analysis shows how the change in the M/G characteristics affects the powertrain full-load performance and how the M/G units can be downsized by combining multiple modes. When the acceleration performance of a two-mode hybrid vehicle is estimated using this analysis method, the trade-off between enhancing performance and reducing M/G full-load capacities is formulated as an optimization problem. The results show significant improvement in dynamic performance at reduced M/G cost.