A look at accident statistics shows that despite the considerable growth in the number of motor vehicles, the number of accidents has declined. A sizable share of this improvement is due to active safety systems such as ABS and ESP. In the future, a whole series of intelligent driver assistance functions (e.g. lane keeping assistance and lane changing assistance) will produce another improvement in driving safety.
To satisfy these safety-critical driver assistance functions, a number of different electronic control modules need to be combined via a communication system to form an extremely challenging control engineering system network. The large number of signals to be transmitted, and the very strict latency time requirements (on the order of just a few milliseconds) and time deviations (Jitter) require not only a fast communication system, but one that is also time-triggered. There is a growing need for electronic interfaces to the chassis in order to implement these driver assistance functions (e.g. “steer by wire” and “brake by wire”).
Because by-wire systems belong to the class of fail-operational systems, a communication system is needed that can fulfill the most stringent reliability and availability requirements and can verify safety conformance. The realization that CAN could not satisfy these requirements led to the development of a number of time-triggered and fault-tolerant serial bus systems with higher data rates: TTP (Time Triggered Protocol), Byteflight, TTCAN (Time Triggered CAN) and FlexRay.
An important reason for the success of FlexRay was the founding of the FlexRay Consortium, under the auspices of which in the year 2000 the two automotive OEMs DaimlerChrysler and BMW and the two chip producers Motorola and Philips joined together. Based on the Byteflight bus system originally developed by BMW, the FlexRay consortium created the OEM-independent, time-triggered and fault-tolerant FlexRay communication standard with a data rate of up to 20 Mbit/s for extremely safety-critical and time-critical applications in the automobile.
Its extraordinarily high scalability of FlexRay communication (also with regard to topology and communications structure), and its comparatively high data rate, not only make FlexRay interesting for use in by-wire systems, but also for many other applications in the motor vehicle. In the new BMW X5, for example, FlexRay ensures transport of extraordinarily large quantities of data within the active chassis system (including steering angle, vehicle speed, longitudinal and transverse acceleration, body and wheel acceleration, ground clearance) in an extremely short period of time and reliably between the central control module and the four satellite ECUs, each of which is integrated in a bumper.
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