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//-->IntroductionThe requirements relating to driving safety,driving comfort, exhaust emissions and fueleconomy are are becoming ever morestringent.This entails more intensive informationexchange between control units.A well-engineered solution is necessary toensure that the electrics/electronics in thevehicle still remain manageable and do nottake up too much space.TheCAN data busby Bosch is such a solution.It was developed specially for automobiles andis used by both Volkswagen and Audi.CAN stands for Controller Area Network andmeans that control units are networked andinterchange data.JJJSSP 186/01A CAN data bus can be compared to anomnibus.Whilst the omnibus transports a largenumber of persons, the CAN data bustransports a large volume ofinformation.In this Self-study Programme we will explainto you the design and function of theCAN databus.2The contents at a glancePageIntroduction ______________________________________________CAN data bus ____________________________________________Data transfer _____________________________________________Function _________________________________________________CAN data bus in the convenience system __________________CAN data bus in the drive train_____________________________Test your knowledge ______________________________________241012172430Important/NoteNewThe Self-study Programme is not a Workshop Manual!Precise instructions for testing, adjustment and repair can be found in the appropriate WorkshopManual.3CAN data busData transferWhat are the possible options for data trans-fer in vehicles at present?·Option No. 1:Each item of information is exchanged overa separate wire.·Option No. 2:All information is exchanged betweencontrol units along a maximum of twowires: the CAN data bus.The figure below shows you option No. 1,where each item of information is transferredalong a separate wire.A total of five wires are required for datatransfer in this case.Motronic control unitJ220Engine speedAutomatic gearbox control unitJ217Fuel consumptionThrottle valve positionEngine interventionUpshift/downshiftSSP 186/04Conclusion:A separate wire is required for each item ofinformation.As the volume of additional informationincreases, so does the number of wires andthe number of pins on the control units.Therefore, this data transfer mode is onlysuitable for exchanging a limited volume ofinformation.4In contrast to option No. 1, all information istransferred along two wires in the CAN databus.The same data is transferred along the twobidirectional wires of the CAN data bus.You will find further information in this Self-study Programme.Motronic control unitJ220Engine speedFuel consumptionThrottle valve positionEngine interventionUpshift/downshiftAutomatic gearbox control unitJ217SSP 186/05Conclusion:With this data transfer mode, all information istransferred along two wires regardless of thenumber of participating control units and thevolume of information involved.Data transfer with the CAN data bus wouldtherefore make sense if a large volume ofinformation is exchanged between controlunits.5CAN data busThe CAN data busis a type of data transfer between controlunits. It links the individual control units toform an integrated system.The more information a control unit hasregarding the state of the overall system, thebetter it can co-ordinate the individualfunctions.The following components in the drive trainform an integrated system:···the engine control unit,the automatic gearbox control unit andthe ABS control unitThe following components in the conveniencesystem form an integrated system:··the central control unit andthe door control unitsDoor control unitABS control unitCentral control unitSSP 186/02Engine control unitAutomatic gearbox control unitBenefits of the data bus:··If the data protocol is extended to includeadditional information, only softwaremodifications are necessary.Low error rate through continuousverification of the transmitted informationby the control units as well as additionalsafeguards in the data protocols.Fewer sensors and signal lines through themultiple use of a sensor signal.···High-speed data transfer is possiblebetween control units.More space available through smallercontrol units and smaller control unitplugs.The CAN data bus conforms tointernational standards and thereforefacilitates data interchange betweendifferent makes of control unit.·6 [ Pobierz całość w formacie PDF ]