Designing for safety affects every component of a product, and every automotive component supplier must implement best processes to ensure safe function. One frequently overlooked domain is the electrical system that implements signal connectivity among ECUs, sensors and actuators. This system can fail in ways that cannot be predicted by simply optimizing the individual component parts.
The increase in system complexity has caused an explosion in the number of operation states that a complete system can achieve. The electrical system must be designed to ensure system robustness in every state.
Failure modes and effects analysis (FMEA) is an effective tool for eliminating catastrophic failures caused by loss of component function. FMEA provides a numeric analysis of the consequences of a failure on each part in the system. The numeric results from FMEA highlight the most critical failures. This information can be used to identify which parts of the system should be redesigned and provide insight into how the redesign should be done to minimize the effects and consequences of component failure.
The major drawback of FMEA applied to electrical systems design is the effort required to collate the data that is processed into a numeric result. A further difficulty is that the result of a particular component failure is not always obvious. Each failure needs to be analyzed to understand its effects. In the case of electrical designs, that demands a detailed numeric analysis for every failure.
Developments in electrical systems design software have slashed the cost and effort of conducting FMEA on the electrical system. Modern ESD software can provide systems and wiring engineers with automated simulation facilities that provide rapid feedback on electrical continuity, voltages and currents as they create the electrical schematics. The automated simulation facilities then enable the use of advanced functions, such as FMEA, to ensure system safety and reliability.
Engineers place graphical symbols for each of the components and wires to create the schematic diagram. In addition to the graphical representation, there is an associated simulation model. The engineer thus can test the electrical behavior and integrity of the design at any time by simply invoking the “run simulation” command. This is a significant advance from the traditional design process, which required simulation specialists to assemble the simulation data, run the simulation and then process the results in context with the original circuit schematics.
Engineers can invoke a permutation processor on their electrical designs. The processor can be configured to permutate every state of the electrical system. The safety of the permutated system can be evaluated in several ways. It is the foundation of the FMEA analysis, but it is also used to provide sneak circuit analysis and component sizing analysis.
Component sizing analysis is used to calculate the appropriate specification of wires, fusing and circuit breakers by ensuring these components are correctly rated for the worst-case configuration of switches and controllers. The results can be back-annotated into the circuit schematics, speeding the design process and ensuring design quality.
Sneak circuit analysis, meanwhile, is used to detect unexpected system states that could potentially create an unsafe condition.
About the authors
John Wilson is a product marketing manager at Mentor Graphics’ Integrated Electrical Systems Division (IESD).
Muhammad Askar is a product marketing manager in the IESD.