Diagnosis on the FlexRay
FlexRay is a new bus system and communication system. FlexRay ensures reliable and very powerful data interchange in real time between the electrical and mechatronic components. FlexRay serves for networking innovative functions of today and of the future in the vehicle. FlexRay contains a powerful protocol for real-time-capable data transfer to different systems which are utilized in the vehicle. With a maximum data transfer rate of 10 MBit/s per channel, the FlexRay is very fast. The FlexRay is significantly faster than the data buses used to date in motor vehicles in the area of body as well as drive and chassis. FlexRay supports not only the higher bandwidth but also deterministic data interchange; its configuration is error-tolerant. This means that even after failure of individual components, reliable continued operation of the remaining communication systems is enabled. The central gateway module (ZGM) sets up the link between the various bus systems and the FlexRay.
Example F0x: FlexRay topology, maximum equipment
| Item | Explanation |
|---|---|
| SZL | Steering column switch cluster |
| EPS | electromechanical power steering |
| VTG | Transfer box |
| DME2 | Digital Engine Electronics 2 |
| DSC | Dynamic Stability Control |
| ICM | Integrated chassis management |
| DME/DDE | Digital Motor Electronics or Digital Diesel Electronics |
| EDCSVR | Damper satellite, front right |
| VDM | Vertical Dynamics Management |
| ZGM | Central gateway module |
| EDCSHR | Damper satellite, rear right |
| EME | Electrical machine electronics |
| HSR | Rear axle slip angle control |
| AL | Active front steering |
| SWW | Lane Change Warning |
| EDCSHL | Damper satellite, rear left |
| EDCSVL | Damper satellite, front left |
| PMA | Parking maneuvering assistant |
| R | Terminating resistor |
Example F2x: FlexRay topology, minimum equipment
| Item | Explanation |
|---|---|
| DSC | Dynamic Stability Control |
| DME/DDE | Digital Motor Electronics or Digital Diesel Electronics |
| EPS | electromechanical power steering |
| Front electronic module | Front Electronic Module |
| ICM | Integrated chassis management |
Depending on the vehicle equipment, the central gateway module (ZGM) is equipped with 2 star couplers each with 4 bus drivers. The bus drivers forward the data of the control units via the communication controller to the central gateway module (ZGM). Depending on the type of termination, the FlexRay control units are connected to these bus drivers in 2 different ways. Terminal resistors are used on both ends of the data lines on the FlexRay to prevent reflections. If only one control unit is connected to a bus driver (e.g. SZL on partial bus system 0, see wiring diagram), the connections at the bus driver and at the control unit are each fitted with a terminal resistor. If the connection to the control unit is not the physical end-node (e.g. DSC, ICM and DME on the 2nd partial bus system): The two components must be terminated at the ends of the respective paths with terminating resistors.
Bus signal
The deterministic data interchange ensures that each message is transferred in the time-controlled section in real time. Real time means that the transmission takes place in a specified time.
Bandwidth
The FlexRay bus system provides a maximum data transfer rate of up to 10 MBit/s per channel. The value corresponds to 20 times the data transfer rate of the PT-CAN2 (Powertrain CAN) or D-CAN (diagnosis-on CAN). This is why signal transmissions cannot be measured using the IMIB.
Waking and sleeping characteristics
The control units on the FlexRay can be woken by a bus signal. Despite this, the activation of most control units occurs on the FlexRay via an additional wake-up line from the Car Access System (CAS). The wake-up line has the same function as the wake-up line (terminal 15 WUP) used to date in the PT-CAN. The signal path corresponds to the signal path of the PT-CAN.
Synchronization
To implement synchronous execution of individual functions in networked control units, a common time base is necessary. As all the control units work internally with their own clock generator, time synchronization must take place via the bus. When starting up the Central Gateway Module, the control units (ZGM, DSC, ICM and DME/DDE) operate as synchronization nodes. For fault-free synchronization of the FlexRay bus system, communication from ZGM to at least 2 of the control units is required. If e.g. the DSC has failed, the control units ICM and DME/DDE are used as synchronization nodes. If the FlexRay is faulty, the bus lines of the control units ZGM, ICM, DSC and DME/DDE must be checked.
Troubleshooting
For faults on the bus system (e.g. short circuit to B+ or short circuit to ground) or at the control units on the FlexRay itself: Individual control units or entire paths from the bus communication can be excluded. Excluded from this is the path with the 4 control units authorized to perform wake up function on the FlexRay (ZGM, DME/DDE, DSC, ICM). No engine start is possible if an interruption of the communication between the control units occurs.
Resistance measurement on the FlexRay
The various termination options can lead to misinterpretations of the measurement results. A resistance measurement of the lines of the FlexRay is unable to provide a 100% true statement regarding the function of the wiring of the system. In the static state, the resistance value can be within the tolerance even if there is damage such as pinched locations or connector corrosion. It is possible to repair the FlexRay. In the event of damage, the cables can be joined with conventional cable connectors. Only special cables for FlexRay may be used! Various particularities must be observed during the installation. The wiring of the FlexRay is a twisted cable. This twist must be preserved during repair. Stripped sections in the repair area must be sealed with shrink-on hoses. Water ingress can affect the wave resistance (resistance for the spread of electromagnetic waves in a conductor) and thus the performance of the bus system.