BYTEFLIGHT VEHICLE NETWORKS
Byteflight networks were first used in early 2000’s, and were primarily intended for safety systems such as Air-Bags systems. The Byteflight design was therefore dictated by the need for reliability, high fault tolerance and high data speed (the speed of the signals passing between different ECUs). Byteflight can however also be used for virtually any other vehicle system including the less safety critical systems (such as seat adjustments and central locking). One feature of Byteflight is that the signals passing between different electronic modules or ECUs are “Digital Light Beam” signals that pass through Fibre optic cables; and these pulsed light beam signals are effectively not affected by interference from other electrical sources (which can occur on conventional electrical signals passing through wires).
Fig 1 shows the Star Structure of the Byteflight system, which effectively has a Master ECU and many passive Slave ECUs. However, when Byteflight Star networks are (for example) used on the BMW safety systems, although there is a main controller or Master ECU, the other ECU’s (which could be regarded as Slave ECUs) do have some of their own control capability. The Master ECU is referred to as a “Safety Information Module” (or SIM), and the Slave ECUs are referred to as “Satellites”.
On the Byteflight networks, as well as the SIM transmitting signals to the Satellites, the Satellites can also transmit signals back to the SIM; so the signals can pass both ways (bi-directional) through the Fibre Optic Cables. The Star structure used on Byteflight networks does however provide the safety benefit that if one of the satellite ECU’s fails, then the other ECU’s can still function.
Note: In some versions of Byteflight, the Safety Information Module and the Gateway are separate modules; but for other Byteflight versions, the Safety Information Module and the “Gateway” are combined combine into a single module. However, with both arrangements, A Gateway is effectively a signal translator that enables the Byteflight network to receive or transmit data and information to or from other networks that use a different electronic signal language.
Safety Information Module
Note. As with other networks, there are detail variations of the Byteflight Networks for different vehicle applications; but the general principles of operation are the same across the different versions.
The Safety Information Module (or SIM) initially functions as a central “Communication Link” between all the other ECUs or Satellites; so all the information from the Satellites is passed back to the SIM, which can then re-distribute the information to the rest of the Satellites on the network.
Some of the Satellites contain “Crash Detection Sensors”; and the information from these “Crash Detection Sensors” is passed to the SIM. The SIM can then pass the information from each of the Satellite crash sensors to all the other Satellites; therefore ALL Satellites have access to the same information relating to the forces produced in a crash.
A second task for the SIM is to provide an “Alarm” signal to the Satellites when the information from the “Crash Detection Sensors” indicates that there are very high forces acting on the vehicle (that would occur during a vehicle crash). But at this stage, the SIM has yet to establish exactly where on the vehicle these high level forces will have a major effect. The “alarm” signal therefore provides a warning to the Satellites so that they are “ready” to activate an air bag or Seat-Belt pre-tensioner. When all of the information is gathered from the Crash Detection sensors, the decision is then made as to which parts of the safety system should be activated (such as which of the Air-Bags should be activated to best protect the occupants).
Satellites and Crash sensors
The crash sensors contained in some of the Satellites are positioned at strategic locations around the vehicle. The sensors are usually acceleration sensors (or “Accelerometers”) that can detect left and right forces as well as forward and backward forces (Lateral and Longitudinal forces); but note that sensors might only detect forces in one direction (either Lateral or Longitudinal). Satellites with crash sensors can be located in the region of the doors and door pillars to monitor the forces acting on the side of the vehicle.
A Centrally located Satellite with a crash sensor (which can be located within the SIM assembly) is then usually fitted in the region of the interior centre console; and this Centrally located sensor provides an indication of the Lateral and Longitudinal forces that are being applied to the whole vehicle. But the Satellite sensors in the doors or door pillars then indicate which part of the vehicle the forces are acting against.
Other sensors are then connected to the Seat-Belt buckles to detect whether a Seat-Belt is fastened, and Pressure sensors are then also fitted to the seats to detect whether a seat is occupied. The information from these sensors is then passed via a Satellite module to the SIM to enable the SIM to decide which parts of the safety system are activated; and it also allows the SIM to decide the timings for the activations (which can also be dependent on vehicle speed).
Some of the Satellite modules are then used to directly provide the trigger signal for activation of specific Air-Bags or Seat-Belt Pre-tensioners; so by using separate Satellites and Crash Sensors it is then easier to be selective of which Air-Bags are activated.
Light Beam DIGITAL Signals
The Digital Signals used in the Byteflight networks, are pulsed or Digital Light beams. The Digital Light-Beams pass through Fibre Optic cables, at around 10 million data bits / sec (10 Mbits/sec), which means that there can be 10 million individual signal pulses every second; and this is typically 20 times faster than the signals used in CAN-Bus networks that are used for powertrain systems.
As a brief description, a conventional “electronic” digital signal is created within either the SIM or a Satellite module (depending on what information is being transmitted around the network); but the electronic digital signal is then converted into a pulsed infra-red Light-Beam that is transmitted through Fibre Optic Cables. When the receiving Satellite or the SIM receives the Light-Beam signal, it then converts it back to an electronic digital signal for use internally; but when the SIM converts a Light Beam signal that has been received from a Satellite
into a conventional electrical signal, the signal can then be re-converted back to a light beam signal for re-distribution to the other Satellites on the rest of the network.
The information is small part of the full Learnguistics On-Line “Vehicle Network” Training course that is available from Ryans Automotive.
The information is provided by Peter Coombes (author of Learnguistics training courses)”.