An application under the pressure to succeed

Bayrische Motoren Werke Aktiengesellschaft is generally known as BMW. Because of the continuous progress and the increasing demands of technology, setting up industrial communication and use of high-power information technology has become more and more important in the automobile industry. After all, the competition for the top producer requires the ability to produce increasingly large series increasingly faster. However, this requires automation of the machines and installations, so that their processes can be replicated without prior processing, thus establishing a flowing and unimpaired work process. The task to find a suitable way to reach this target, in addition to the aspect of gained time and the aspect of cost reduction and increased turnover. However, safety also is a criterion that is the focus of development. After all, the designed vehicles should reach ever higher speeds without compromising safety. To be able to reach such a combination, the installed devices must be able to communicate with each other in order to expose problems and to carry out sequences according to a specified pattern. For this, BMW has developed its own application known as “ByteFlight”. This bus system arose out of cooperation with the companies Motorola, Elmos, and Infineon. The main attention of this application is precisely the aspect of safety.

The purpose of ByteFlight

Various expectations are connected with the project created by BMW. After all, the increasing requirements and the ever increasing number of sensors and actuators requires considerably more electronically operated systems. With this, the conventionally used mechanical components are upstaged as they cannot be operated in connection with a central control computer. At this point, networking of the different electronic components via a high-performance data bus such as ByteFlight is required. Here, the functions of the application refer to the reduction of the wiring costs the multiple use of the collected sensor data.

How ByteFlight works

The application operates on the basis of a transmission protocol which is oriented around messages. These telegrams consist of a start frequency which contains a data quantity of 6 bit, one byte for the identification and as a length 12 data bytes (max.) and two CRC bytes. This way, all stations within the bus unit can have all of the existing messages at their disposal within the system. The purpose is to expose real-time behavior that can be predicted, so that required actions can be initialized in advance in order to maintain the level of safety at a high level. For this, ByteFlight uses the deterministic access procedure TDMA, where the incoming and the outgoing signals always are the same and the intermediate results also show the same value. This makes the process reproducible and ultimately predictable. For this, each of the coupled bus stations is simply provided with a strictly specified time interval with a defined time span, the so-called time slot.

The special characteristics of ByteFlight

Optical polymer fibers were installed to transmit the data within the vehicle and between its devices. These are fiber optics made of plastic which serve the task of data transmission. Thanks to their structure, a data rate of 10 Mbps can be achieved through their use. However, the really special feature of ByteFlight is its topology of a star, wherein this network maintains the characteristics of an “intelligent star coupler”. With this topology, any number of subscribers connect to a centrally located subscriber, so that a star-shaped arrangement is created. With this, it is practical that the central device does not necessarily require a higher level of control intelligence and the failure of any one subscriber does not cause a crash of the entire network. The system can also be expanded to incorporate as many subscribers as is required.

The future of ByteFlight

Until approximately five years ago, ByteFlight could be found in the models of the 7, 6, and 5 series of BMW cars. Here, the system was responsible for transmission of near real-time data pertaining to the airbag system and the electronics of the body. Information related to the chassis also was transmitted by means of the application. However, the general overhaul of the 5 BMWs and the 6 BMWs also led to removal of ByteFlight. The successor is a time-controlled CAN. In the 7 series models, the application will also be replaced in the near future as here the FlexRay bus system will be used instead. However, the usefulness of ByteFlight is not being questioned. Namely, thanks to the quality and the level of performance of the data bus system, basic use is possible in all those real-time applications where extremely short latency times, a very high data throughput and strong interference endanger the safety of the driver in handling the vehicle and impair quick and easy communication between the devices.