The Case for Urban Vehicles: Powertrain Optimization of a Power-Split Hybrid for Fuel Economy on Multiple Drive Cycles

Designing vehicles specifically for city use is a topic of increasing interest in the transportation community. Hybrid vehicle design typically seeks to maximize fuel economy subject to acceleration performance and other constraints, based upon the expected driving needs of the average user. Fuel economy predictions are inaccurate when the vehicle’s expected and actual uses are different. This paper studies the variation in design and fuel economy for a vehicle with a power-split hybrid electric powertrain optimized on a range of U.S. Environmental Protection Agency drive cycles, from the high-speed US-06 cycle to the low-speed New York City cycle. Results show variation of up to 9.8% in fuel economy and up to 41% in electric motor size. The vehicle designed for the dense urban environment has the largest variation in fuel economy, whereas the other vehicles have more similar performance. These results imply that the urban vehicle is the least robust and offers motivation for developing urban-specific vehicles. This analysis provides only a lower bound on potential performance because it does not consider possible vehicle downsizing or other design changes to meet customer expectations in urban use.