Development of a Duty Cycle for the Design and Optimization of Advanced, Heavy-Duty Port Drayage Trucks

Abstract

Hybrid electric and electric trucks are potential technology solutions for reducing emissions at ports. However, developing an advanced, low-emission technology driveline entails thoroughly understanding typical truck operations in the real-world environment. This paper presents the work performed to develop a novel, more representative drayage duty cycle that characterizes drayage truck operations in the ports of San Pedro Bay in California. Unlike a conventional vehicle, an optimized hybrid driveline requires detailed understanding not only of torque requirements and vehicle speeds but also of the potential recovery of dynamic brake energy, charging opportunities, stopping and idling times, and many other operational requirements. Keeping this in mind, the duty cycle presented in this paper incorporated real-world, near-dock activities of Class 8 drayage trucks such as daily hours of operation, mileage, altitude profiles of routes, and idling and key-off patterns. The empirical duty cycle model was subsequently integrated with a complete vehicle simulation to explore the best solutions to minimize energy consumption for drayage applications in and around the ports. The analysis presented indicates that trucks spent most of the generated power in overcoming aerodynamic drag and rolling resistance of tires for a complete drayage shift and that electrical auxiliary loads dominated for near-dock operations because of idling and low-speed profiles. Therefore, achieving zero-emission near-dock operations entails focusing on auxiliary loads and rolling resistance. By using simulations, it was estimated that a hybrid truck with electrical power limited to about 100 kW could deliver a greenhouse gas emission reduction of about 30%.