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Most of you in the automotive electronics world have heard of or had some experience with ISO 26262 – the Functional Safety (FuSa) standard. It focuses on the safety aspects that need to be addressed in the development of automotive electronic systems. As part of this article, we will not go into details of describing or implementing the Functional Safety standard, but rather focus on importance of this standard in the automotive scenario.
Looking back, cars have been primarily mechanical in nature, but the past 20-30 years has seen proliferation of electronics content into it. Today, we are at a stage where electronics is defining and differentiating cars and seems like the trend will continue to make the car more of an electronic “device”. Primary goal of the automotive has been transportation and any malfunction in its operation could endanger human lives. With the increased complexity in electronics content, malfunctions can occur in electronics hardware or software. Thus, there is need to analyze these malfunctions – causes, effects, safety measures, etc. In this context, the ISO 26262 Functional Safety standard provides a systematic approach to perform the same.
For a better understanding of the importance of Functional Safety aspects, let us discuss a use case of the Electronic Parking Brake (EPB) system. Traditionally, parking brakes have been mechanical, i.e., a mechanical linkage actuating parking brakes in a vehicle at the rear wheels. Parking brakes are only actuated by pulling the mechanical linkage based on the driver’s need. With the advent of the EPB, there is an electronic switch that controls an electric motor system to actuate parking brakes at the rear wheels. So, the mechanical linkage has been replaced by an electronic switch and an electric motor. There could be changes in design and construction of the EPB between different suppliers and systems – we will not go into details of these.
Since mechanical linkage to the rear parking brakes is not present in an EPB, the electric motor, to actuate the rear parking brakes can be triggered independently based on certain conditions. Features such as automatic actuation (to prevent backward roll or when the vehicle becomes standstill) and release (based on forward vehicle motion) of the parking brakes can be implemented. Of course, the electric motor is also actuated or released based on the electronic switch input. Now, it becomes clear that EPB allows more flexibility in operation of the parking brake with introduction of electronics. Along with this, also comes the aspect of electronics malfunction which could lead to unintended operation of the electric motor and thus rear parking brakes.
As per the Functional Safety standard, we do a malfunction or hazard analysis to understand implications of electronics malfunction. Based on this an ASIL (Automotive Safety Integrity Level) is arrived at. ASIL A signifies the least safety criticality and ASIL D the highest. The derived ASIL and required safety goals to prevent the malfunction or hazard drives requirements to be implemented in hardware and software. Now, in the case of EPB, it might seem it’s only a parking brake and not so safety-critical, but this is not the case. Since electronics malfunction could cause unintended operation of the parking brake, it could so happen that the EPB gets actuated unintentionally at high vehicle speeds. This could lead to a dangerous scenario and the derived ASIL is D. Based on this, the EPB system needs to be implemented at an ASIL D level with the required functional safety mechanisms and process followed.
As we can see, mechanical systems when replaced with electronic systems in the vehicle can potentially lead to hazardous conditions and hence Functional Safety analysis is gaining importance. Understanding safety implications from a vehicle system perspective is important for hardware and software engineers implementing automotive electronic control units for safety-critical applications. Following the approach prescribed by ISO 26262, traceability can be shown from the implemented hardware and software safety mechanisms to the vehicle level hazard that has been addressed.
It is important for Functional Safety engineers to understand the vehicle system aspects in order to propose optimized safety mechanisms at the system, hardware, and software levels. Care should be taken to not over-engineer the safety mechanisms which could impact the cost and performance of the electronic systems.
As we discussed in this article, FuSa has become an essential attribute in the development of automotive electronic systems. It is required for engineers working on automotive electronics to imbibe this thinking and apply the standard into the design, development, and validation of systems.
Also, Read about AUTOSAR +FuSA – More power to automotive software
About the Author:
Principal Solution Architect
Functional Safety Leader for Powertrain and Vehicle Systems
Naveen Kalappa is Principal Solution Architect for automotive systems and software at KPIT Technologies. Naveen comes with very good implementation knowledge of automotive software and has performed a wide variety of technical roles at KPIT for over a decade. As part of his current role, he leads the Functional Safety Practice for Powertrain and Vehicle Systems.
Note : The opinions that may be presented in the article are of that of the author.
Reading Time: 4 mins