The use of a CAN bus system in a car makes it possible to network electronic modules such as control units or intelligent sensors such as the wheel angle sensor.
The abbreviation "CAN" means Controller Area Network.
The CAN bus system provides the following advantages for the car as an overall system:
• Data exchange between control units take place on a uniform platform.
This platform is call a protocol. The CAN bus acts as a so-called data highway.
• Systems involving several control units, e.g. ESP, can be implemented efficiently.
• System expansions are easier to implement in the form of optional extras.
• The CAN bus is an open system which permits adaptation to various transmission media
such as copper or optical fibre cables.
• Control units are diagnosed via the K-wire. Inside the car, diagnosis already takes place
via the CAN bus in some cases (for example the airbag and the door control unit).
In this context, this is called a "virtual K-wire" . In future cars, there will be no K-wire.
•A cross-system diagnosis is possible across several control units.
Many individual modules are connected in parallel to the CAN bus system.
This results in the following requirements for the design of the overall system:
•High level of error protection: transmission interference caused by internal or external sources must
be detected with a high degree of certainty.
•High availability: if a control unit fails, the rest of the system must continue to be functional as far as
possible in order to exchange information.
•High data density: all control units have the same information status at all times.
This means there is no difference in data between the control units.
In case of faults anywhere in the system, all the connected users can be informed
with equal certainty.
•High data transmission rate: data exchange between networked users must be very fast
in order to meet real time requirements.
Signals are sent over the CAN bus system digitally, at present over copper wires.
Secure transmission is possible at a maximum rate of 1000 kbps (1 Mbps).
The maximum data rate at VOLKSWAGEN and AUDI has been fixed at 500 kbps.
The CAN bus system is divided into 3 special systems due to the different requirements regarding signal
repetition rate and the large data volume:
•Drive train CAN bus (high-speed) at 500 kbps with almost real time requirements
•Convenience CAN bus(low-speed) at 100 kbps with low time requirements
•Infotainment CAN bus(low-speed) at 100 kbps with low time requirements
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