Multifunction Vehicle Bus

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The Multifunction Vehicle Bus (MVB, for example “multi- purpose vehicle bus ”) is a field bus for data communication within a rail vehicle . It is mostly used as part of the Train Communication Network (TCN) and has been standardized with this by the IEC in IEC 61375. Another part of the TCN is the Wire Train Bus (WTB) across multiple vehicles. The MVB-M was specified in 1999 for several firmly coupled vehicles, which means that underground trains and trams in particular can do without a WTB. Especially new train suppliers entering the market rely on Ethernet.

History of origin

Computer-controlled components are also being used more and more in railway vehicles. These are, for example, heating with air conditioning, on-board power converters and the closed toilet facilities. Initially, these were not linked to one another, so that the train crew could only read malfunctions from control lamps. In the workshop, too, the exact cause of the malfunction could usually only be read off on the control itself, but this involved opening the switch boxes . For this reason, the desire for a vehicle-wide diagnostic system was expressed. This is how this vehicle bus was created. The MVB was developed in a consortium of ABB, AEG, Firema and Siemens in the 1990s. The technical basis of the MVB is the process bus P215 from ABB .

technology

The MVB is a real data bus single master - multi slave; several bus connections can be connected to one line. Only one of these interfaces is allowed to send data at a time. The MVB master specifies the timeslot with its master frame, the slave then sends its slave frame, this is comparable to the CAN -RTR procedure. As with FlexRay , the operating system as well as the application must be synchronous with the MVB bus, if this is not the case, data loss also occurs in the event of oversampling because the MVB cluster and CPU drift, the CPU and MVB master controller have their own clock supplies . Real-time operating systems based on the AUTOSAR standard have such synchronization mechanisms. The data is then received by everyone else. The data is sent in a synchronous time division multiplex process with a gross transmission rate of 1.5 Mbit / s. The signal levels on the line are RS485 levels.

There are three different transmission media:

• EMD ( English electrical bus middle distance ): twisted pair cable with electrical isolation of the bus circuits by transformers.
• ESD ( electrical short distance bus ): twisted two-wire line with additional ground line and either no potential separation or potential separation through optocouplers . Due to the limited input voltage range of the optocouplers, a compensating line is necessary. It connects the masses of the optocoupler modules.
• OGF ( optical glass fiber ): fiber optic cable. Point-to-point connections with so-called star couplers.

The simplest bus physics is EMD; it is used by Siemens and other manufacturers. ESD is still used by Bombardier. Bombardier uses OGF primarily in high-performance locomotives.

application

Practically all railway vehicles supplied by the manufacturers Siemens and AEG / ABB / Adtranz / Bombardier since 1995 were and will be equipped with MVB as a fieldbus. The MVB connects the most important components of the control technology with one another. These are mostly drive control, train protection, driver's cab displays, central control devices, decentralized inputs / outputs, door controls, air conditioning systems, auxiliary converters, recorders and more.

The MVB transfers the short but time-critical control and status signals for automating the train (such as time or speed) in real time (cycles typically 16 ms to 512 ms) in its " process data ". It is also used to transmit diagnostic messages, etc. The "message data" of the MVB are used for this.