FlexRay: Data Bus with a Future
Bosch researchers are working in an international consortium on the development of the FlexRay data bus, which will soon be used to reliably link electronic vehicle components with a very high data transfer rate.
If digital data traveling down a data line made noise, car passengers would be subjected to the constant babbling of dozens of sensors, actuators, and control units communicating uninterruptedly with one another as they seek attention and call out important information. There’s a lot going on, even if it’s happening in silence, which is why researchers are working to bring order to this flood of communication. This is how it’s done, using the established CAN data bus (CAN = Controller Area Network): One of the control units in the network “listens” to the data bus that links the electronic equipment; if everything is quiet, the unit in question can transmit information. The system works on a first-come, first-served basis. If more than one control unit wants to send simultaneously, a prioritizing mechanism determines which of them goes first. This ordered operation ensures extremely low lag times for data exchange. It’s only when too many control units want to transmit simultaneously and the data bus becomes overloaded that the devices begin to block each other, creating a data traffic jam. With the CAN system, it’s unclear exactly when each signal will run through the bus, because transmissions of other control units have to be waited on.
When implementing safety-related features in the future, however, it will be crucial to be able to precisely predict the time at which a message will be sent and the lag between transmission and arrival at the destination. The “x-by-wire” functions are an example of such features. They work by sensing the position of the brake pedal and steering wheel and electronically transferring the driver’s braking and steering commands to the corresponding actuators via a bus system. These, in turn, brake the vehicle or turn the front wheels as desired. Bosch researchers are working with industrial partners on the further development of the FlexRay bus system for use with such applications. With FlexRay, each control unit hooked up to the bus is given a precisely defined time slot. As a result, the control units transmit and receive data in an exactly predetermined sequence, within cycles that generally last just a few milliseconds. If the driving dynamics control unit has nothing to report, for example, its time slot remains empty. But if it needs to transmit data or commands, it will do so at the exact time specified by the bus clock, which makes the transmission procedure predictable. Researchers refer to this as a “deterministic” communication system with real-time capability — in other words, information on particular vehicle conditions is guaranteed at precisely defined intervals.
FlexRay also can transmit data at a rate of 10 MBit/s, which ensures there will be sufficient bus capacity available, even when vehicle networks become more complex in the future.
When implementing safety-related features in the future, however, it will be crucial to be able to precisely predict the time at which a message will be sent and the lag between transmission and arrival at the destination. The “x-by-wire” functions are an example of such features. They work by sensing the position of the brake pedal and steering wheel and electronically transferring the driver’s braking and steering commands to the corresponding actuators via a bus system. These, in turn, brake the vehicle or turn the front wheels as desired. Bosch researchers are working with industrial partners on the further development of the FlexRay bus system for use with such applications. With FlexRay, each control unit hooked up to the bus is given a precisely defined time slot. As a result, the control units transmit and receive data in an exactly predetermined sequence, within cycles that generally last just a few milliseconds. If the driving dynamics control unit has nothing to report, for example, its time slot remains empty. But if it needs to transmit data or commands, it will do so at the exact time specified by the bus clock, which makes the transmission procedure predictable. Researchers refer to this as a “deterministic” communication system with real-time capability — in other words, information on particular vehicle conditions is guaranteed at precisely defined intervals.
FlexRay also can transmit data at a rate of 10 MBit/s, which ensures there will be sufficient bus capacity available, even when vehicle networks become more complex in the future.
