Service Manual

TractionCircuit:LOWSpeed(Mow)
Thetractioncircuitpistonpumpisavariabledisplacementpumpthatisdirectly
coupledtotheengineywheel.Thispumputilizesanintegralelectro−hydraulic
servopistonassemblythatcontrolstherateanddirectionofhydraulicow.
Pressingthetractionpedalrotatesapotentiometerthatprovidesaninputtothe
machineTECcontroller.ThecontrollerinturnsendsacorrespondingPWM
(PulseWidthModulation)outputtotheelectronicpumpcontroltorotatethe
pumpswashplateaccordinglytocontrolpumpoutputanddirection.Traction
circuitoilisdirectedtothedualdisplacementfrontwheelandrearaxlemotors.
Operatingpressureonthehighpressuresideoftheclosedtractioncircuitloopis
determinedbytheamountofloaddevelopedatthewheelandaxlemotors.As
thetractionloadincreases,circuitpressurecanincreasetoreliefvalvesettings:
300bar(4350PSI)inforwardand345bar(5000PSI)inreverse.Iftraction
circuitpressureexceedsthereliefsetting,oilowsthroughthepistonpump
reliefvalvetothelowpressuresideoftheclosedlooptractioncircuit.Traction
circuitpressurecanbemeasuredattestportsattachedtothesidesofthepiston
pump.Theforwardtractionportisontherightsideofthepumpandthereverse
tractionportisontheleftside.
Frontwheelandrearaxlemotorsarepositivedisplacement,twospeedvariable
motorsthatallowoperationineitherLOW(mow)orHI(transport)speed.The
motorsarespringbiasedtomaximumdisplacementforLOWspeedandare
hydraulicallyshiftedtominimumdisplacementforHIspeed.Therearaxlemotor
includesaushingvalvethatbleedsoffasmallamountofhydraulicoilfor
coolingoftheclosedlooptractioncircuit.Thechargecircuitreplacesoilthatis
bledfromthecircuitbytheushingvalve.
TheSmartPower
TM
featurepreventstheenginefromslowingdowninheavyload
conditions(e.g.cuttingtallgrass)byautomaticallydecreasingthetractionspeed
ifnecessary.Withareducedtractionspeed,thecuttingbladescancontinueto
beatoptimumspeed.
Atractioncircuitowdividersplitstractionpumphydraulicowbetweenthefront
wheelmotors(approximately45%)andrearaxlemotor(approximately55%)
topreventexcessivecircuitowgoingtoaspinningwheel.Theowdivider
islocatedinthefronttractionmanifoldmountedtotheright,rearsideofthe
frontframe.
Tractioncircuitcomponentsusesmallamountsofhydraulicoilforinternal
lubrication.Fluidisdesignedtoleakacrosstractionpumpandmotorcomponents
intothecasedrain.Thisleakageresultsinthelossofhydraulicoilfromthe
closedlooptractioncircuitthatisreplacedbythechargecircuit.Thegearpump
sectionsthatsupplythesteering,coolingfanandlift/lowercircuitsalsoprovide
chargecircuitoil.
Gearpumpowforthechargecircuitisdirectedthroughtheoillterandtothe
lowpressuresideoftheclosedlooptractioncircuit.Chargepressureislimitedto
17bar(250PSI)byareliefvalvelocatedinthepistonpump.
ForwardDirection
WiththearmrestconsoleHI/LOWspeedswitchintheLOWspeed(mow)
position,solenoidvalve(S12)inthecombinationmanifoldisnotenergized
whichkeepsthefrontwheelmotorsandrearaxlemotorattheirmaximum
displacement.Withthemotorsatmaximumdisplacement,alowertractionspeed
isavailableformowingconditions.
WhentheHI/LOWswitchisintheLOWspeed(mow)positionandthetraction
pedalispushedintheforwarddirection,oilfromthepistonpumppassesthrough
thefronttractionmanifold.Oilowforthefrontwheelmotorsleavesfronttraction
manifoldportM1todrivethefrontwheelmotorsintheforwarddirectionand
Groundsmaster
®
4000-D&4010-D
Page5–15
HydraulicSystem:HydraulicFlowDiagrams
13202SLRevF