Powertrain Hybridization for Autonomous Vehicles

TL;DR

This paper investigates how autonomous vehicles can optimize hybrid powertrain design, showing that AVs can operate efficiently with smaller motors than traditional HEVs due to precise velocity control and energy management.

Contribution

It demonstrates that AVs require smaller hybrid motors for optimal energy efficiency, highlighting the importance of velocity control and energy management in hybrid vehicle design.

Findings

AVs can use smaller motors (~12 kW) for similar hybrid benefits as larger motors (~30 kW) in human-driven vehicles.

Velocity smoothing significantly improves fuel efficiency, especially in small-motor HEVs.

Optimal torque request in AVs enhances regenerative braking and engine efficiency.

Abstract

The powertrains of today's hybrid electric vehicles (HEVs) are developed for human drivers and, therefore, may not be the optimum choice for future Autonomous vehicles (AVs), given that AVs can accurately manipulate their velocity profile to avoid unnecessary energy loss. In this work, we closely examine the necessary degree of hybridization for AVs compared to human drivers by deploying real-world urban driving profiles and generating equivalent AV drive cycles in a mixed autonomy scenario. We solve the optimal energy management problem for HEVs with various motor sizes from the automotive market, and demonstrate that while human drivers typically require a motor size of around 30 kW to fully benefit from hybridization, AVs can achieve similar gains with only a 12 kW motor. This greater benefit from a smaller motor size can be attributed to a more optimal torque request, allowing for higher gains from regenerative braking and a more efficient engine operation. Furthermore, We investigate the benefits of velocity smoothing for both traditional cars and HEVs and explore the role of different mechanisms contributing to fuel consumption reduction. Our analysis reveals that velocity smoothing provides greater benefits to HEVs equipped with small motors compared to non-hybrid vehicles and HEVs with larger motors.