Toro 08743 - Page 84

Thehydraulictractioncircuitisaclosedloopsystemconsistingofavariable
displacementpiston(traction)pump,threewheelmotors,andaremotemounted
reliefvalve.Thetractionpumpisdrivenbytheenginedirectlythrougharubber
drivecoupling.Thetractionpumpswashplateandtrunnionshaftismovedby
thetractionpedalthroughaneutraldetentlinkageassembly.
ForwardDirection
Withtheenginerunningandthetractionpedalintheneutralposition,thetraction
pump(P1)suppliesnoowtothewheelmotors.Whenthetractionpedalis
pressedtotheforwardposition,thelinkagefromthepedalpositionstheswash
plateinthetractionpumpsohydraulicuidowsouttheBport(rightsideofthe
pump).FluidowoutoftheBportgoesthroughthefrontwheelmotorrstand
thenthroughtherightandleftrearwheelmotors.Fluidfromtherearwheel
motorsreturnstothetractionpumpAport(leftsideofpump).Hydraulicuidis
continuouslypumpedthroughtheclosedlooptractioncircuitaslongasthe
tractionpedalispressedforward.Thetractionpumpincludesareliefvalve
(forwarddirection)thatlimitsforwardtractioncircuitpressureto22,063kPa
(3200psi)bar).
Theangleoftheswashplatedeterminesthestrokeofthepumppistonsand
thereforethevolumeofhydraulicuidowandultimatelytractionspeed.When
thetractionpedalispressedasmallamount,theswashplateangleisslight
resultinginlowpumpoutputandlowertractionspeed.Whenthetractionpedalis
pressedfully,thepumpswashplateangleisdramaticprovidingmaximumpump
outputandmaximumtractionspeed.
Aremotemountedreliefvalveexistsinthetractioncircuittopreventtherear
wheelmotorsfromengagingtooaggressivelyifthetractionpedalismovedinthe
forwarddirectionabruptly.Thereliefvalveissettoopenat15,858kPa(2300
psi).Thereliefvalveonlyoperatesintheforwarddirection.
Thepiston(traction)pumpusesasmallamountofhydraulicuidforinternal
lubricationduringoperation.Thepumpisequippedwithacasedraintoallow
thenormalinternalleakagetoberemovedfromthepump.Theleftrearwheel
motorincludesaushingvalvethatbleedsoffasmallamountofhydraulicuid
forcoolingtheclosedlooptractioncircuit.Theushingvalveonlyoperatesin
theforwarddirection.Thecasedrainandushingvalveareconnectedtothe
hydraulicreservoir.Thelossofhydraulicuidfromtheclosedloopsystemis
replenishedbythetractionpump’sinternalimplement/chargepump(P2).
Theimplement/chargepump(P2)isaxeddisplacementgerotorpumpthatis
partofthetractionpump.Theimplement/chargepumpreplenishestheclosed
looptractioncircuitwithhydraulicuidfromthetank.Thechargereliefvalve
suppliessufcientheadpressuresothatchargepumpowisguidedtothelow
pressuresideofthetractioncircuit.Chargepressureislimitedbythecharge
reliefvalvelocatedinthepiston(traction)pumpto689kPa(100psi).Charge
pumpowinexcessoftractioncircuitreplenishmentrequirementsisusedfor
thesteeringcircuitonSandPro5040machines,andtheliftcircuitforbothSand
Pro3040and5040machines.
Thefrontwheelmotorhasacheckvalveacrossitsportsthatallowsthemotorto
overrunduringtightturnsintheforwarddirection.
ReverseDirection
Thetractioncircuitoperatesessentiallythesameinreverseasitdoesinthe
forwarddirection.However,theowthroughthecircuitisreversed.Whenthe
tractionpedalispressedtothereverseposition,thelinkagefromthepedal
positionsthetractionpumpswashplatesouidowsoutoftheAport(leftside
ofpump).FluidowoutoftheAportgoestotherearwheelmotorsandturns
theminthereversedirection.Theuidowisthendirectedtothefrontwheel
HydraulicSystem:HydraulicFlowDiagrams
Page5–14
SandPro
®
3040and5040
20251SLRevA