The FlexRay protocol is a unique time-triggered protocol that provides options for deterministic data that arrives in a predictable time frame. FlexRay is a serial communication technology that is used in particular for data communication in very safety-critical use areas in the automobile such as brake-bye-wire and steer-by-wire. FlexRay was developed by the FlexRay consortium (including Bosch, BMW, Volkswagen, Daimler). FlexRay layouts include the Multi-drop Bus, the Star Network, and the Hybrid Network. The Multi-drop Bus topology is the same as in CAN and LIN systems, and it uses a single bus to connect multiple processors together. This system is helpful in implementing with other systems due to the similar layout of CAN and LIN networks. The Star Network topology consists of multiple ECUs connected to a central active node.

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Differential signaling on each pair of wires reduces the effects of external noise on the network without expensive shielding. FlexRay nodes typically also have power and ground wires available to power transceivers and microprocessors. FlexRay manages multiple nodes with a Time Division Multiple Access schemes. Every FlexRay node is synchronized to the same clock, and each node waits for its turn to write on the bus.  Because the timing is consistent in a TDMA scheme, FlexRay is able to guarantee determinism or the consistency of data delivered to nodes on the network. This provides many advantages for systems that depend on up-to-date data between nodes.

  1. Static Segment 
    Reserved slots for deterministic data that arrives at a fixed period.
  2. Dynamic Segment
    The dynamic segment behaves in a fashion similar to CAN and is used for a wider variety of event-based data that does not require determinism.

Key Features

Maximum Data Rates: 500 kbps – 10 Mbps
Communication Modes: Time-triggered, Event-triggered
Network Topology: Single-channel topologies, Dual-channel topologies

BMW X5 Vertical Dynamics Control Module

The E70 BMW X5 was the first production vehicle to have a FlexRay network fitted. It is implemented for the Vertical Dynamics Control module, which controls the suspension height for each individual suspension strut.

The network is configured in a Star Bus. This ensures the system can still operate if a satellite unit fails. Also, it is an advantageous setup when long lengths of wiring are required, as normal electrical interference will only affect one leg of the network due to this configuration. A satellite unit is located in each corner of the vehicle.

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