Connected and automated driving technology is known to improve real-world vehicle efficiency by considering information about the vehicle’s environment such as traffic conditions, traffic lights or road grade. This study shows how the powertrain of a hybrid-electric vehicle realizes those efficiency benefits by developing methods to directly measure real-time transient power losses of the vehicle’s powertrain components through chassis-dynamometer testing.
This study is a follow-on to SAE Technical Paper 2019-01-0116, Test Methodology to Quantify and Analyze Energy Consumption of Connected and Automated Vehicles [1], to understand the sources of efficiency gains resulting from connected and automated vehicle driving. A 2017 Toyota Prius Prime was instrumented to collect power measurements throughout its powertrain and driven over a specific driving schedule on a chassis dynamometer. The same driving schedule was then modified to simulate a connected and automated vehicle driving profile, and the sources of vehicle efficiency improvements were analyzed. While conventional powertrain components typically only have two sources and sinks of power, e.g. an input and output shaft, the components of modern hybrid-electric vehicles are tightly integrated and have multiple sources and sinks of energy. This study describes the methods used to calculate transient power losses of the vehicle’s powertrain components while considering all sources and sinks, and results of chassis-dynamometer testing are presented.
Results of this study showed higher efficiency and lower power losses at the vehicle-level and lower overall power demand over a connected and automated vehicle (CAV)-simulated drive cycle. Despite higher losses and lower efficiency of the power electronics over the CAV drive cycle, the engine operated in a lower area of its brake-specific fuel consumption (BSFC) map, resulting in lower engine losses. This showed that the engine operating regime was the dominant factor driving overall vehicle efficiency.