Expanding the Use of Vehicle Specific Power in Analysis of Platoon Performance

Platooning is a coordinated driving strategy by which following trucks are placed into the wake of leading vehicles. Doing this leads to two primary benefits. First, the vehicles following are shielded from aerodynamic drag by a “pulling” effect. Secondly, by placing vehicles behind the leading truck, the leading vehicles experience a “pushing” effect. The reduction in aerodynamic drag leads to reduced fuel usage and, consequently, reduced greenhouse gas emissions. To maximize these effects, the inter-vehicle distance, or headway, needs to be minimized. In current platooning strategy iterations, Coordinated Adaptive Cruise Control (CACC) is used to maintain close following distances. Many of these strategies utilize the fuel rate signal as a controller cost function parameter. By using fuel rate, current control strategies have limited applicability to non-conventional powertrains.

Vehicle Specific Power (VSP) has shown promise as a metric by which the performance of such controllers can be measured. This study uses VSP to characterize the platooning performance of each vehicle participating in multiple testing campaigns. The data set includes a variety of platoon headway setpoints, two and four-truck platoon configurations, two different testing locations, and experimental results utilizing vastly different platooning control strategies. This effort validates the use of VSP as a platooning characterization metric through the inclusion of a larger data set than prior studies. Additionally, the current work illustrates the broad applicability of VSP as a platooning assessment metric by utilizing multiple vehicles operating in a variety of configurations.

VSP also has the potential to serve as a powertrain-independent replacement for the use of fuel rate in a CACC predictive control cost function. In exploration of this idea, several vehicles’ fuel rate and fuel consumption were compared to VSP results. VSP and fuel consumption are shown to possess a direct relationship; but a stronger correlation is found between fuel consumed and the sum of positive VSP. Recommendations for the adaptation of VSP to platoon performance and control are made.