Allison Transmission T 280

Thecapacityisreducedattherate/slopeprogrammedintothecalibrationand
maycontinuetobereducedatthisrateuntil:
•Theretarderisoperatingatapproximately27.5%ofitsmaximum
capacity.
•Theretarderisdeactivatedbytheoperatororbyvehicleoperating
conditionswhicheliminatetheneedforretardation.
•Enginewatertemperatureisreturnedtoalevelthatdoesnotinvokethe
capacityreduction.
NOTE:Fullretardationisrestorediftheoutputspeedincreases300
rpmabovethespeedatwhichwatercapacityreductionstarts.
4.3.2RETARDER/CRUISECONTROLINTERACTIONS.Twocontrol
featuresaffectretarderoperationwhenthevehicleisequippedwithcruise
control:
•Feature1:CruiseControlRetarderAutoOnDisable
Thisfeatureonlyappliestoelectronicenginesthatcommunicatewiththe
transmissionontheSAEJ1939.TheTCMcalibrationmustspecifythis
featuretobeeitheronoroff.Ifthefeatureisoninthecalibration,theTCM
prohibitsretarderoperationwhencruisecontrolisactivebutthethrottle
isclosed,whichimpliesdownhillcoastingoperation.Thisfeatureishighly
recommendediftheretarderapplysystemautomaticallyappliestheretarder
athighlevelsatclosedthrottle.
Ifthefeatureisoffinthecalibrationortheengineisnotelectronic,theTCM
commandsretarderoperationwheneverthecruisecontrolgoestozero
throttle.Thismodeofoperationisonlyacceptableifthesubsequentlevel
ofretarderapplyislessthan25%.
•Feature2:RetarderCancelCruiseControl
Thisfeatureprovidesforashortashoftheretarderindicatoroutputwhenever
therequestedretarderlevelisincreased.Theretarderindicatoroutputmust
bewiredtotheenginecruisecontroltoturnoffcruisecontrolwhenthelevel
ofretardationrequestedischanged.Thisoperationemulatestheeffectof
applyingtheservicebrakes.Feature2isanoptionalfeaturethatmustbe
speciedforthecontrolscalibration.
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