SAE 2011, Detroit

A Comparison of CAN, FlexRay, and Ethernet Architectures for the Design of Automotive ABS systems

Using Model Based Systems Engineering to Optimize  Vehicle Electronics Architectures:

Today’s automotive design engineers are harnessing the latest computer and communications technology to extend the drivers experience to a unprecedented level. Progress in drive, safety, comfort, security, and entertainment systems requires today over 100 electronic control units (ECUs) communicating via bus systems. Furthering the complexity is the future proof readiness that must be built in to accommodate advances in driver assist systems, automated driving systems, voice recognition, intelligent maintenance and diagnostics. smart web., etc.

One of the most fundamental design criteria challenges concerns the overall vehicle electronics architecture. Within that scope, selecting a robust network architecture requires the vetting of complex combinations of systems behavior amongst dynamic internal and external environmental considerations. These systems will dynamically couple subsystems in automobiles and demand visual information processing with significant increased requirements for signal processing and communications. Current options include the use of CAN, MOST, and FlexRay bus systems. With current design methodologies being stressed coping with the complexity of current networked electronics in automobiles, how can the upcoming systems with significantly higher complexity + dynamic coupling be developed? What are possible solutions to this design and security challenge?

In design of avionics engineers have been confronted for more than two decades with networked systems of 50 times higher complexities than in automobiles. Airbus A380 aircraft contain more >5000 electronic control units (ECUs) connected by switched Ethernet, made deterministic and protected by high security AFDX protocols. Safe virtual channels avoid all unwanted coupling between subsystems (one of the major challenges in automobiles.) Executable specifications that include architecture (HW), function (SW), application/mission/use cases + usabilty are used during concept development to permit architecture optimization and avoid redesigns during system integration. Can this technology also be a solution to the rapidly increasing requirements of automobiles?

Available Ethernet technologies of up to 100GHz could easily meet the bandwidth requirements of planned automobiles. In this paper it is investigated whether Ethernet with AFDX protocols can also meet requirements of safety critical systems in automobiles. A vehicle dynamic model with longitudinal and lateral dynamics is developed to investigate ABS longitudinal control and Electronic Stability Control (ESC). Using the simulation tool MLDesigner, a virtual prototype of a vehicle is developed that includes this dynamics model, and architecture and function of ABS systems using CAN, FlexRay, and Ethernet bus systems with AFDX protocols. The breaking performance of this virtual prototype is investigated for constant and dynamically changing friction coefficients.

It is shown that 100MHz switched Ethernet buses with AFDX protocols achieve identical performance to ABS systems with FlexRay buses. With MLDesigner the virtual prototype can easily be extended to design and validate tightly coupled networked driver assist systems with high bandwidth requirements for visual information processing.