Diagnosis on the FlexRay

Diagnosis On The FlexRay

FlexRay is a new bus and communication system. FlexRay ensures reliable and very powerful data interchange in real time between the electrical and mechatronic components. The purpose of FlexRay is to network the innovative functions in the vehicle today and in the future.

FlexRay contains a powerful protocol for real-time data interchange in the distributed systems deployed 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 fault-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.







Depending on the level of equipment of the vehicle, the central gateway module (ZGM) contains one or two so-called star connectors, each with 4 bus drivers.

The bus drivers forward the data of the control modules via the controller for communication to the ZGM. Depending on the type of termination, the FlexRay control modules 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 module is connected to a bus driver (e.g. SZL on bus driver BD0, see circuit diagram), the connections at the bus driver and at the control module are each fitted with a terminal resistor. If the connection at the control module is not the physical end node (e.g. DSC, ICM and DME at the bus driver BD2, see circuit diagram), the two components must be terminated at the ends of each bus path with terminal 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).

Waking and sleeping characteristics
FlexRay control modules can be wakened by a bus signal.

Despite this, most FlexRay control modules are wakened across an additional wake-up line by 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 modules, a joint time basis is necessary. As all the control modules work internally with their own cycle generator, time synchronization must take place via the bus. When the central gateway module is powered up, the control modules ZGM, DSC, ICM and DME/DDE function as synchronization nodes.

Communication from the ZGM to at least 2 of the control modules is necessary for fault-free synchronization of the FlexRay bus system. If e.g. the DSC has failed, the control modules ICM and DME/DDE are used as synchronization nodes. If the FlexRay is faulty, the bus lines of the control modules ZGM, ICM, DSC and DME/DDE must be checked.

Troubleshooting
In the event of faults on the bus lines (e.g. short circuit to positive or short circuit to ground) or on the FlexRay control modules themselves, individual control modules or entire paths can be excluded from bus communication.

This does not include the path with the 4 FlexRay control modules (ZGM, DME/DDE, DSC, ICM) that are authorized to wake the system.

If communication between these control modules is interrupted, no engine start is possible.

Wiring
The wiring of the FlexRay bus system is designed as two-wire, twisted cable (partially clad).

Some of the terminal resistors are located in the central gateway module and in the user devices.

Measurements 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 may be used for FlexRay.

During installation, various special features must be borne in mind. 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. If moisture enters, this can affect the wave resistance (resistance for the spread of electromagnetic waves in a conductor) and thus the performance of the bus system.