Functional Safety of an Embedded Automotive System Measured by Fault Tree Birnbaum Importance – Applied for a Steering Angle Sensor with Intrinsic Redundancy

Functional safety, required e.g. by IEC 61508 [1], encounters rising recognition in the development of automotive electronic systems. Sufficient protection against safety-critical faults has to be approved. Guidelines for corresponding metrics exist but apply either for parallel redundant architectures or for on-board diagnosis. But in automotive embedded systems, often hybrid solutions are implemented.

In this context, the determination of safety metrics may be obstructed using the conventional methods. The underlying FMEA cannot treat failure combinations with sufficient stringency.

An alternative approach, based on Fault Tree Analysis (FTA) is described. A new safety metric was developed using the Birnbaum Importance and is called Protection against Fault Propagation (PFP). It considers both fault diagnosis, and redundancy.

It was applied for the embedded steering angle sensor system from Valeo. The results provide the necessary arguments for functional safety of this system.