Model Based Fault Diagnosis For Automotive Functional Safety
Functional safety is an important element for future automobile development. To ensure functional safety, the automotive industry has adopted a functional safety standard ISO26262 to standardize the design and implementation of functional safety requirements during different phases of an automobile's safety lifecycle. This dissertation proposes a model based approach for achieving some aspects of automotive functional safety through model based diagnosis. After using hazard analysis and risk assessment to define functional safety and diagnostic requirements, the method developed in this dissertation consists of a systematic approach for the design of diagnostic strategies that leads to implementation of the algorithms to satisfy the functional safety goals. In particular, this dissertation exploits the mathematical tools of structural analysis to detect and isolate various faults in a complex system. The advantage of using the structural analysis approach for fault detection and isolation lies in the ability to efficiently analyze the analytic redundancy of a system and systematically design structured residual generators to satisfy given diagnostic requirements. The effectiveness of this approach is demonstrated by designing diagnostic algorithms for sensor fault detection and isolation in a permanent magnet synchronous machine electric drive system for an electrified powertrain. The diagnostic strategy is proven to be effective in detecting and isolating various sensor faults in a PMSM drive system. ii The structural analysis approach systematically generates the options of designing residual generators, whose number may be quit large in a complex system. This dissertation also introduces a novel approach for selecting residual generators to downsize the solution sets, considering the feasibility, diagnosability and computational complexity of residual generators, as well as their sensitivity and robustness. Based on these criteria, the optimal diagnostic test could be extracted from a large number of candidate equation sets to achieve the most desirable performance. The same diagnostic approach can be integrated into the functional safety lifecycle to provide solutions to functional safety problems. This dissertation illustrates this concept by developing a safety case torque functional safety of pedal by wire systems. The case study starts with investigating the problem by hazard analysis and risk assessment. Then, quantitative fault modeling is used to conduct a quantitative analysis on the effect of the faults. The fault modeling method can be used to assist hazard analysis and risk assessment in defining the risk level of each potential hazard, so as to help define the functional safety requirements. Next, the structural fault detection and isolation approach is used to analyze the diagnosability of various faults in a pedal by wire system and to systematically design diagnostic tests to detect and isolate pedal mechanical stiction fault and pedal sensor faults. Finally, fault mitigation strategies are designed to mitigate the effect of these faults on torque functional safety.