Comprehensive Component On-Board Diagnostics: Systematic Transformation Approach to Malfunctions

Abstract

Exhaust emission standards for road vehicles require on-board diagnostics (OBD) of all comprehensive powertrain components (CCMs) impacting pollutant emissions. The legislation defines the generic malfunction criteria and pollutant threshold limits to trigger the component functional degradation. The electric drivetrain in xEV (more than one propulsion energy converter) applications substitutes or supports the internal combustion engine (ICE) operation with electric machine (EM) power. Malfunctions in the electric drivetrain will lead to an increase in ICE power demand. Hence, the electric drive system is classified as a comprehensive component in the OBD legislation. The regulation defines monitoring of the EM performance. The malfunctions that could prevent the EM(s) from properly operating emission control strategies, including any ICE control activation or electric drivetrain performance degradation, should be monitored by the OBD system. This work demonstrates an approach to systematically transform generic OBD legislation requirements into granular component malfunctions based on a simulation approach in the early development phase for an electric drivetrain. In the first step, the generic legislation requirements of properly functioning emission control strategies and performance degradation are transformed into electric drivetrain system element functional attributes. The malfunctions from different sources were collected as a potential malfunctions list including malfunction characterization. The impact on electric drivetrain system element functional attributes is determined for each of the malfunctions based on their characterization. Then, the matching set of malfunctions between the potential list and the OBD-derived system element functional impacts resulted in an optimized malfunction list. These optimized malfunctions are evaluated for their exhaust emission impact on a map-based one-dimensional vehicle longitudinal simulation model. The faults are also modeled to simulate their impact on ICE operation and their exhaust emissions when driven in the Worldwide harmonized Light-duty vehicles Test Cycle (WLTC). There are electric drivetrain faults that significantly increase the exhaust emissions of carbon monoxide (CO), non-methane hydrocarbons (NMHC), and oxides of nitrogen (NOx). Hence, it is important to note that even if the ICE is faultless, increased pollutant emissions can occur due to electric drivetrain malfunctions in an xEV vehicle.