Car manufacturers have been able to enhance driving experiences by adding various interfaces to vehicle dashboards. So, when your screen flashes low tire pressure, it is in a way adding years to the tire’s life, maintaining fuel efficiency, and ensuring better ride quality. Timely and accurate display of tell tales like tire-pressure, seatbelt sign, door open/close warnings go a long way in ensuring that the driver and occupants are safe and are able to enjoy an enhanced ride quality.
The keywords to be noted in the previous paragraph are ‘timely’ and ‘accurate’. And it is due to these two very important factors that functional safety comes into the game. Automotive displays like Digital Instrument Cluster provide safety-critical information to the driver through visual alerts like flashing lights. If you add ADAS related warnings to the mix, you get an instrument cluster that is safety-critical to its highest limit, i.e., ASIL D. It is essential that such a cluster is highly reliable and displays warnings about safety-critical functionality with utmost accuracy. And in order to achieve such reliability, adherence to ISO 26262 standard is the way to go.
ISO 26262 for digital instrument clusters does not work differently. You have the same lifecycle to follow, beginning with item definition, HARA, various safety analyses like FMEA, FTA and testing. So why are we writing a whole new article stressing about FuSa for digital instrument cluster?
For one, as a technology provider, we have been fortunate to work on some really challenging ISO 26262 compliant digital instrument cluster projects. Another reason is that instrument clusters and other automotive displays are not usually considered safety critical. ASIL is assigned to them based on assumptions or industry norms. And that can prove to be a disaster in more ways than one can imagine.
A Closer Look into Digital Instrument Cluster to Understand Its Safety-Criticality
The first ever application of an instrument cluster in a passenger vehicle was in an Aston Martin vehicle in the year 1979. It was a basic instrument cluster showing vehicle speed, kilometers driven and fuel meter, to name a few. Fast forward to the era of e-cockpit*, digital instrument cluster is a goldmine of vehicle information.
*E-cockpit is a concept where an interactive multi-dimensional control center displays a wealth of vehicle related information on the screen and lets the vehicle occupant control a host of vehicle features with a few clicks. Usually, an e-cockpit comprises infotainment system, digital instrument cluster and head-up display.
A digital instrument cluster completely replaces a traditional analog instrument cluster. To make it truly digital, a combination of system-on-chip (SOC), display unit and software work in tandem. OEMs design instrument clusters in a very personalized manner; however, there are certain functionalities that most advanced clusters will have:
- Vehicle information (speed, tell tales, battery, etc.)
- Turn-by turn navigation system
- Call alert
- Weather information
- Music playback display
- Mechanism to upgrade the software/firmware
- On-board ambient light sensor
An instrument cluster system collects vehicle information from various ECUs and sensors through the vehicle network systems such as CAN, LIN, FlexRay and even Ethernet. There are interfaces such as communication interface and audio interface that make the data available to the instrument cluster display. The diagram below highlights all the elements that constitute a digital instrument cluster.
Whether a connected cluster is safety-critical is roughly decided by the kind of signals it is transmitting, processing and displaying. Obviously, a detailed HARA should be done to ascertain the ASIL value and safety goals.