MG MG6 Series 2011 - Operation

Engine
EngineElectricalSystem
Operation
StarterMotor
Whenthehandsetisdocked,theimmobilisationunit,located
withintheinstrumentpack,comparesthecodestoredwithin
thehandsetwiththatstoredintheunit.Ifthesecodesmatch,
asignalissent,viathe
BCMtothestarterrelaylocatedinthe
enginecompartmentfusebox.Thestarterrelayenergisesthe
startersolenoid.Thesolenoidwindingsbecomeenergised
drivingthepinionintoengagementwiththeringgearonthe
ywheel.Thepinionisforcedintomeshontheywheelring
gearviaanengaginglever.Ifthegearsdonotfullymesh,
aexiblelinkageallowsthesolenoidtoclosethecontacts
connectingthemotortothebatteryfeed.Thisallowsahigh
currenttoowtothemotorwhichcreepsthegearsinto
mesh.Thepinionrotatesviaaunidirectionalclutchturning
thestarterringgearontheywheel/driveplate.
Oncetheenginehasstarted,thepinionspeedwillexceedthe
motorspeed.Ifthehandsetisheldinthecrankposition,
theunidirectionalclutchwillslipprotectingthemotor.When
thehandsetisreleased,thesolenoiddeenergises,theswitch
contactsareopenedandthespringforcewithdrawsthepinion
fromtheywheelringgear.
T oallowthestartermotortodrawthemaximumcurrent
whencrankingtheengine,certainloadsarepowereddown
whenthehandsetismovedtotheCRANKposition.The
headlampmainbeam,HeatedRearWindow
HRWand
Heating,VentilationandAirConditioningHVACblower
motorallpowereddown.Whencrankingiscompletethe
loadsarere-enabledindividuallytolimitthecurrentdraw
fromthebattery.
Theloadsarere-enabledafterthefollowingtimedelays:
•HVACblowerafter1second
•
HRWafter1.5seconds
Ifcrankingtakesmorethan45seconds,thestartermotoris
disengagedandallloadsarere-enabledimmediately.
Alternator
Thealternatorusesaselfexcitedsysteminwhichanumberof
diodessupplytherotorwithaportionofthecurrentgenerated
bythealternator.Thealternatorcannotsupplytheinitial
currentrequiredtostartthechargingprocess.
Thisinitialcurrentisprovidedbyabatteryfeedfromthe
ignitionswitchandexcitestheeldwindingstostartthe
chargingprocess.Whentheignitionisswitchedon,battery
voltageisalsosuppliedthroughthechargewarninglightand
isconnectedtoearthviathealternatoreldwindings,causing
thewarninglighttoilluminateandsupplyingthealternator
withtheinitialcurrent.
Whentheengineisstartedtherotorrotateswithinthe
stator,generating3-phaseAlternatingCurrentAC.TheAC
producedisunsuitableforusebythevehicle'selectricalsystem
andpassesthroughtherectiersemiconductordiodes.The
diodesonlyallowowofcurrentonewayensuringthatthe
outputcurrentis'rectied'.Thediodesintherectieralso
preventcurrentowfromthebatterytothealternatorwhen
thealternatoroutputvoltageislessthanthebatteryvoltage.
Theregulatorhaspowertransistors,connectedtotheearth
sideoftheeld,whichrapidlyswitchonandoffactingasaeld
switchingdevice.Thisregulatesthevoltageoutputaccording
tothevoltagesensedinternallytopreventoverchargingand
damagetothevehicle'selectricalcomponents.Theoutput
islimitedtoapproximately14.2Vandisprotectedbyasurge
protectiondiode.Thisvaluewillallowthealternatortovary
theoutputvoltagedependingonthestateofchargeofthe
batteryandchargethebatteryquicklywheninalowstate
ofcharge,forexampleoperatingthestartermotorandwill
reducethechargingratetozeroasthebatteryreachesafully
chargedstatepreventingovercharging.Theregulatorprovides
analternatorloadsignaltothe
ECM.Thesignalisa12volts
digitalPulseWaveModulatedPWMfrequencywheretheduty
cyclevariesfrom0-100%accordingtoalternatorloadallowing
theECMtoadjustidlespeedundervaryingelectricalloads.
Theregulatoralsohasachargewarninglightoutputwhich
controlsthewarninglightoperation.Ifthealternatoroutput
fallstobelowthebatteryvoltagethechargewarninglight
isilluminated.Outputvoltagerisesrapidlyastherotational
speedoftherotorincreases,increasingthepotentialdifference
ontheoutputsideofthediodes.Asthevoltageincreasesthe
chargewarninglightisextinguishedwhenthealternatoroutput
voltageequalsthebatteryvoltage.Atthispointthealternator
generatesenoughcurrentfromtheelddiodestoselfexcite
andchargingofthebatterywillstart.
Failure
Thealternatorcouldfail,orprovideanincorrectsignal,inthe
followingways:
•Internalregulatorfailure
•Diodepackfailure
•Statorwindingopencircuit
•Statorwindingshortcircuittoearth
•Fieldwindingshortcircuit
•Fieldwindingopencircuit
•Mechanicaldefect
•Externalwiringshortcircuit
•Externalwiringopencircuit
Version2.0340