The development of Motor Vehicle Technology has responded to the consumer need
for safe , comfortable and reliable transport
that can meet the demands of environmental
policies, economy and efficiency required in modern society through the use of advanced electronic systems
with computerised control.
A top of the range luxury vehicle may have over eleven thousand electrical and electronic components forming a networked
control and operation system.
CONTROLLER AREA NETWORK
A computerised vehicle control network consists of
a series of electronic control units linked
to each other . Data is transmitted digitally around the network on a "bus" system.
Modules referred to as Nodes are connected
together by a "physical layer". The physical
layer can be a single cable , twisted pair or
even an optical cable.
Sensors provide input data to the control units which process this information to command
actuators which respond to the outputs of the control system.
The vehicle CAN ( Controller Area Network)
databus system may utilise a signal from one sensor for several functions, for example
a speed sensor signal may be used for not only the speedometer reading but also linked to traction control, anti lock braking,
engine management , speed related audio volume, rolling door locks and satellite navigation systems .
In the past this may have required individual sensors and wiring for each function but by using a network the number of
wires and sensors can be reduced resulting in cost benefits for the manufacturer which may be passed onto the consumer.
Multiple signals may be sent as a stream of
information data on a bus wire.
A benefit of a vehicle data bus control
system is that control units can "talk" to
each other , for example when the brake pedal
is depressed the brakes are applied, the
brake lights switched on , and a signal sent
to the engine management to reduce fuelling,
and antilock braking function activated. This
can reduce the quantity of cables inf vehicle
Network communication means that all data is
available to all control units on the
network. This multiplexed system can be used
in diagnostics to identify faults.
Future vehicle network systems may be developed to communicate with external systems by telematics , in a similar
way to a model aircraft being controlled at distance by a handheld transmitter, or your computer being linked to a wireless
network. A telematics system fitted to a vehicle with diagnostics would theoretically be capable of informing the manufacturer
that the vehicle is about to breakdown before the inevitable occurred. Or if a traffic signal was on stop, it could transmit
a signal to the vehicle to hold the brakes on until a go signal occurred.
The Nodes of a network system may be linked together in Star, Line, or Ring formation.
The "Star" network has a central hub to which all nodes are connected, if this fails the whole network fails.
The "Line" network has spurs branched off a main communication line. If the main line is interrupted a secondary
system is normally in place as backup so it can continue to function.
The "Ring " network links nodes in a ring (similar to the ring main electric supply in a house)
CAN uses a Line Network.
The nodes are normally linked by a twisted pair cable (ISO 11898) though a single wire standard (SAE J2411) has been developed.
The twin line system is favoured by the majority of manufacturers as it offers greater reliability , lower rate of failure,
and faster data transmission speed. The two data lines are known as CAN-H (CAN High ) and CAN-L (CAN Low).
If a fault exists it can be diagnosed by
connection of diagnostic equipment to a further line known as the "K-line " (ISO 9141)
Standardisation allows one manufacturer to link its system to work with that of another manufacturer , for example auxiliary
body equipment fitted to a commercial vehicle enabled with a CANbus system could communicate with the vehicle engine.
Several CAN systems may exist in a modern vehicle.
Different vehicle networks may run at
different data transfer speeds, the
individual networks may be linked at a
specific node referred to as the "gateway".
Seperation of networks can be employed by use
of bus cut relays built in to control units
to prevent one failed network interfering
with another working network.
The structure of the CAN system and its data transmission has been defined by the International Standardisation Organisation
(ISO) and the Society of Automotive Engineers (SAE)
Other Vehicle Network Systems
Other systems of networking data from control units in a vehicle exist including :
LINbus ( Local Interconnect Network) ;this is a secondary system to the CANbus.
MOST (Media Orientated Systems Transport) ;used for multimedia.
The "MOST" network uses optical transmission methods such as Photo diodes and fibre optic cable for high speed
data transmission . This may be used for Audio,TV,and computer multimedia applications.
Byteflight (a BMW system)
D2B Optical (a Daimler Chrysler system)
Bluetooth ; used for wireless transmission of speech signals and data processing.
Power Line Communication ; This system integrates power supply and data lines.
The integration of electronic control to mechanical components is known as Mechatronics.
Mechatronics can be used for such repetative actions as control of the clutch enabling smooth gear changes and increased
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