Automotive Mechatronic Safety Argument Framework

A modern vehicle uses mechanical components under software control, referred to as mechatronic systems, to deliver its features. The software for these, and its supporting hardware, are typically developed according to the functional safety standard ISO 26262:2011. This standard requires that a safety argument is created that demonstrates that the safety requirements for an item are complete and satisfied by evidence. However, this argument only addresses the software and electronic hardware aspects of the mechatronic system, although safety requirements derived for these can also be allocated to the mechanical part of the mechatronic system. The safety requirements allocated to hardware and software also have a value of integrity assigned to them based on an assessment of the unmitigated risk. The concept of risk and integrity is expressed differently in the development of the mechanical components. In this thesis, we address the challenge of extending the safety argument required by ISO 26262 to include the mechanical components being controlled, so creating a safety argument pattern that encompasses the complete mechatronic system. The approach is based on a generic model for engineering which can be applied to the development of the hardware, software and mechanical components. From this, a safety argument pattern has been derived which consequently can be applied to all three engineering disciplines of the mechatronic system. The harmonisation of the concept of integrity is addressed through the use of special characteristics. The result is a model-based assurance approach which allows an argument to be constructed for the mitigation of risk associated with a mechatronic system that encompasses the three engineering disciplines of the system. This approach is evaluated through interview-based case studies and the retrospective application of the approach to an existing four corner air suspension system.