HIL Simulation for an Airbag ECU

Task

When a vehicle crashes into something, the electronic control unit (ECU) for the airbag system reacts in milliseconds. The airbag ECU evaluates the data from the vehicle’s acceleration and pressure sensors and if necessary activates the appropriate airbag. To test this ECU by hardware-in-the-loop (HIL) simulation, it has to be fed various sensor signals that are undistinguishable from the real ones.

Challenge

The airbag ECU itself contains several internal acceleration sensors. Access to these sensors is provided by the OEM to enable sensor simulation directly on the ECU circuit board, either in analog form or via SPI protocol. The external vehicle sensors are simulated via current-based protocols such as PSI5, PEGASUS, or PAS.

To simulate a crash, up to 500 input signals have to be provided. Over several hundred FlexRay signals, up to 100 CAN signals, and 12 PSI channels with up to 3 sensors and 4 SPI interfaces are first recorded during a real crash and then replayed time-synchronously during the HIL simulation. As the airbag is a safety-critical application, its ECU evaluates the signals. If any signal differs from what the airbag ECU expects, the system does not deploy an airbag.

Solution

A dSPACE HIL simulator based on SCALEXIO with numerous I/O boards offers all the necessary input and output interfaces. The airbag ECU is connected to the HIL simulator via Hypertac connectors for the external sensors and via custom connectors for the internal sensors. The ignition tablet for the airbag is simulated by using ceramic resistors. The simulation is controlled from dSPACE ControlDesk. A special library based on RTT was implemented for time- synchronized data replay.