Auto Electronics

Under the Hood of the 2008 BMW X6

Expanding on its pioneering application of FlexRay in the X5, the BMW X6 xDrive35i and X6 xDrive50i models also include FlexRay, as well as CAN, LIN and MOST. BMW was the first carmaker to offer the Bluetooth wireless protocol on its vehicle and the X6 includes Bluetooth, too. The X6, called a Sports Activity Coupe, exemplifies the variety of networks used in modern vehicles.

While CAN continues to be the main vehicle bus, other protocols are expanding based on requirements of various systems or subsystems (Table). High speed CAN's capability of 500 kbps to 1 Mbps meets the requirements of powertrain and provides a main bus for body electronics. However, this is more performance than many subsystems require, especially those in body electronics. In addition, the twisted pair and 5V supply requirements can add unnecessary cost to the subsystem. For these applications, the single-wire, master-slave LIN (Local Interconnect Network) bus with a maximum 20 kbps speed provides a lower cost alternative. With many of these systems in its vehicles, BMW recognized the need for this type of vehicle bus and was one of the founding members of the LIN Consortium.

Applications with streaming data, such as high-performance audio and infotainment systems require more bandwidth than CAN. The MOST (Media Oriented Systems Transport) protocol operates at 25 Mbps. To keep noise to minimum, a fiber-optic physical layer is used. With a need for high performance audio and leading-edge infotainment systems, BMW was one of the founding members of the MOST Cooperation.

The newest vehicle bus, FlexRay, was initially proposed as a fault tolerant high-speed protocol for safety systems and x-by-wire applications. Today, FlexRay may have other appeal for some OEMs. “They are running too many nodes on the electrical architecture of the vehicle and they are running out of bandwidth,” said Kay Stepper, Director of Marketing, Robert Bosch GmbH. “Manufacturers need the additional bandwidth and speed to realize these functions.” BMW has taken the lead in applying FlexRay to production vehicles.

EXPANDING FLEXRAY

The BMW X6 has essentially the same network as the X5.

Adaptive Drive controls the interaction of the X6's anti-roll bars and dampers for improved driving behavior. By monitoring and/or calculating a number of vehicle parameters including road speed, steering angle, longitudinal and lateral acceleration, body and wheel velocity, as well as ride and damper position, the system determines the appropriate reaction. Using the 10 Mbps speed and time-triggered design of the FlexRay bus, fast and reliable data transmission occurs in the network. Applying this information, swivel motors on the anti-roll bar and electromagnetic valves in the Electronic Damping Control (EDC) dampers respond to minimize body roll and provide the optimum suspension damping. The driver determines whether a sporting or comfortable setting is maintained by pressing a button.

Later this year, the BMW Group will launch a vehicle with up to 16 Flex-Ray nodes. In this application, FlexRay will network powertrain, driver assistance and chassis systems. Previous information indicates that the system will use a single channel, single star and linear bus topology with un-shielded twisted pairs installed in a conventional wiring harness.

REFERENCE:

Auto Electronics Protocol Chart http://autoelectronics.com/2008-in-vehicle-data-buses.pdf.

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