Digital Signal Processing Approach to Identify the Boundary of Vehicle Idle Status during Operation

Abstract

The MOVES is a tool to estimate on- and off-road emissions, in which 23 operating mode identification bins were defined based on vehicles’ specific power, speed, and acceleration. Bin 1 indicates an idling mode with the speed within 1.0 mph. However, the speed boundary in an earlier model of MOBILE 6.2 was 2.5 mph. Neither the change in the idling definition of the two models nor the speed boundary were investigated and discussed. This study proposed a method to theoretically redefine the idle boundary by characterizing vehicle emission rates. Vehicle speeds close to 0 mph were carefully studied based on 10,000-mile on-board emission tests in the state of Texas. A portable emission measurement system was used to detect real-time emissions from a 12-year-old gasoline light-duty vehicle, while the vehicle’s activity information was collected from an On-Board Diagnostic (OBD) II port. Power spectral density analysis was conducted on the collected emission and fuel consumption rates to identify a cut-off point that separates the frequency period with higher and lower energy. A Chebeshev I filter was designed to remove the high-frequency component to visualize the variables of emissions and fuel consumption on the vehicle’s moving trend lines. Based on observation and analysis results, 2.26 mph was identified as a boundary for an idle mode at an acceptance level of 95% significant change. It is recommended that the proposed method be applied to the emissions of more different types of vehicles with a wide range of mileages to validate the newly defined idle boundary.