Abstract
Keywords - drive-by-wire, safety critical, steer-by-wire, torque vectoring, redundancy
The Drivewise program was designed to create a vehicle with two safety relevant "actuator" systems on it (Steer-by-wire and Torque-vectoringTM) is such a way that the combined system is both suitably safe and integrated from a drivers and cost perspective. This means that where practical from a safety viewpoint, sensors and electronic control units are shared by the 2 sub-systems and some faults in one subsystem are actually "covered" at a system level by the other sub-system. The design process used to develop the vehicle is an enhanced version of that proposed by the EU funded EASIS program (EASIS - Electronic Architecture and System Engineering for Integrated Safety Systems (1) ). This process has been heavily automated particularly by use of the AutoFMEATM tool (2) which allows a safety analysis to be conducted at an early stage in the program and progressively refined during the program. The speed and flexibility of this tool allowed exploration of various design trade-offs, allowing for example the safety impact of sharing a sensor to be easily investigated. The Steer-by-wire system fitted to the vehicle has a mechanical backup to allow driving on public roads but normally operates in a true steer by wire mode. The torque-vectoringTM system works on the two rear (driven) wheels and allows complete control of the torque split between the 2 wheels (even if the input torque from the gasoline engine is zero). This means that the torque-vectoringTM sub-system is able to generate a yaw motion on the vehicle which is normally used to competent the yaw introduced by the (front) steering. This capability for both systems to generate a yaw motion on the vehicle allows the use of one system as a backup for the other under some fault conditions. The system has been fitted to an Audi A6 vehicle.
The paper provides an overview of the design process used, focussing on the safety aspects of the design and the tools used. It then describes the final system and its implementation on the (Audi A6) vehicle. It will also include details of the validation work undertaken on the vehicle as well as some feedback on the performance of the complete system. Testing of the completed system is still ongoing and the latest results will be presented at the conference.