Toro Groundsmaster 4500-D Series - Page 120

Thetractioncircuitpistonpumpisavariabledisplacementpumpthatisdirectly
coupledtotheengineywheel.Thispumputilizesanintegralelectro-hydraulic
servopistonassemblythatcontrolstherateanddirectionofhydraulicow.
Pressingthetractionpedalrotatesapotentiometerthatprovidesaninputtothe
machineTECcontroller.ThecontrollerinturnsendsacorrespondingPWM
(PulseWidthModulation)outputtotheelectronicpumpcontroltorotatethe
pumpswashplateaccordinglytocontrolpumpoutputanddirection.Theswash
plateanglesensorisattachedtothepumptoprovidethepositionoftheswash
plate.Tractioncircuitoilisdirectedtothedualdisplacementfrontwheelandrear
axlemotors.Operatingpressureonthehighpressuresideoftheclosedtraction
circuitloopisdeterminedbytheamountofloaddevelopedatthewheelandaxle
motors.Asthetractionloadincreases,circuitpressurecanincreasetorelief
valvesettings:350bar(5075PSI)inforwardand360bar(5225PSI)inreverse.
Iftractioncircuitpressureexceedsthereliefsetting,oilowsthroughthepiston
pumpreliefvalvetothelowpressuresideoftheclosedlooptractioncircuit.
Frontwheelandrearaxlemotorsarepositivedisplacement,twospeedvariable
motors.Thedualdisplacementwheelandaxlemotorsallowoperationineither
LOWorHIrange.Themotorsarespringbiasedtomaximumdisplacementfor
LOWspeedandarehydraulicallyshiftedtominimumdisplacementforHIrange.
Therearaxlemotorincludesaushingvalvethatbleedsoffasmallamountof
hydraulicoilforcoolingoftheclosedlooptractioncircuit.Thechargecircuit
replenishesoilthatisbledfromthetractioncircuitbytheushingvalve.
Anoptionaltractioncircuitowdividerisavailablethatequallysplitstraction
pumpowbetweenthefrontwheelmotorsandrearaxlemotortoprevent
excessivecircuitowgoingtoaspinningwheel.Ifequipped,thefronttraction
manifoldwhichincludestheowdividerismountedtotheright,rearsideofthe
frontframe.
Thepistonpump,frontwheelmotorsandrearaxlemotorusesmallamountsof
hydraulicuidforinternallubrication.Fluidisdesignedtoleakacrosstraction
pumpandmotorcomponentsintothecasedrain.Thisleakageresultsintheloss
ofhydraulicuidfromtheclosedlooptractioncircuitthatmustbereplaced.The
chargecircuitisdesignedtoreplacethistractioncircuitleakage.Thegearpump
sectionthatsuppliesoiltothesteeringandlift/lowercircuitsalsoprovidesoil
forthechargecircuit.
Gearpumpowforthechargecircuitisdirectedthroughtheoillterandtothe
lowpressuresideoftheclosedlooptractioncircuit.Chargepressureislimitedto
18bar(260PSI)byareliefvalvelocatedinthepistonpump.
ForwardDirection
WiththearmrestconsoleAutoandLowmodecontrolswitchintheAutomode
position,theTECcontrollercontrolstwospeedshiftmanifoldsolenoid.The
solenoidvalveinthetwospeedshiftmanifoldisenergizedbytheTECcontroller
forHIrange.Thisenergizedsolenoidvalvedirectschargepressuretoshiftthe
frontwheelmotorsandrearaxlemotortotheirminimumdisplacement.With
themotorsattheirminimumdisplacements,afastertractionspeedisavailable
fortransport.
WhenAutomodeisinHIrangepositionwiththetractionpedalpushedinthe
forwarddirection,oilfromthepistonpumpoilisdirectedtothefrontwheel
motorsandrearaxlemotorthroughaparallelsystem.Oilowtothefrontwheel
motorsdrivesthemotorsintheforwarddirectionandthenreturnstothepiston
pump.Oilowtotherearaxlemotordrivesthemotorintheforwarddirection.
OilreturningfromtheaxlemotorentersthereartractionmanifoldattheM8
port.FlowbypassesthePRcartridgethroughtheCVcheckvalve,outmanifold
portP2andreturnstothepistonpump.
HydraulicSystem:HydraulicFlowDiagrams
Page5–18
Groundsmaster
®
4500-D/4700-D
19245SLRevA