Toro Greensmaster 3120 - Hydraulic Flow Diagrams; Traction Circuit

HydraulicFlowDiagrams
TractionCircuit
Thepiston(traction)pumpisdrivendirectlybytheengine.Thetractioncircuitof
thehydraulicsystemactsessentiallyasaclosedloop.Withtheenginerunning
andthetractionpedalintheneutralposition,theswashplateofthepiston
pumpisheldintheverticalposition,providingnoowineitherdirectionandthe
machineremainsstationary.Apairof0.031inchoricesinthetraction(piston)
pump(oneoneachsideoftheswashplate)helpkeepthesysteminneutral.
ForwardDirection
Whenthetractionpedalispressedtotheforwardposition,thelinkagefromthe
pedalpositionstheswashplateinthepistonpumpsouidowsouttheupper
port(A)ofthepump;refertoFigure19.Fluidowoutoftheupperportgoesto
thewheelmotorsandturnsthemintheforwarddirection.Theuidowoutof
thewheelmotorsreturnstothepistonpumplowerport(B)andiscontinuously
pumpedwhilethetractionleverisintheforwardposition.
Asthetractionloadincreases,theforwardtractioncircuitpressurecanincrease
totherelief-valvesettingof19,994kPa(2,900psi).Ifthecircuitpressureismore
thantherelief-valvesetting,uidowsthroughtheforwardreliefvalveinthe
transmissiontothelow-pressuresideoftheclosed-looptractioncircuit.
Thepistonpumpusesasmallamountofhydraulicuidforinternallubrication.
Theuidisdesignedtoleakacrossthepumppartsintothepumpcasedrain.
Thisleakageresultsinthelossofhydraulicuidfromtheclosed-looptraction
circuitthatmustbereplacedbythetractionchargecircuit.Hydraulicuidis
suppliedtothetractionpumpchargecircuitfromthegearpumpsection(P3)after
servicingthedemandsofthesteeringandliftcircuits.Chargecircuitpressure
ismaintainedbya276kPa(40psi)checkvalve(CV)locatedinthemower
manifold.Apairofcheckvalvesinthetraction(piston)pumpcontroltherelease
ofchargecircuitowwhenuidreplacementisrequiredbytheclosed-loop
system.Chargecircuitowinexcessofclosed-loopsystemrequirements
returnstothehydraulictankviathetraction(piston)pumpcasedrain.
ReverseDirection
Thetractioncircuitoperatesessentiallythesameinreverseasitdoesinthe
forwarddirection.
Whenthetractionpedalispressedtothereverseposition,thelinkagefromthe
pedalpositionstheswashplateinthepistonpumpsouidowsoutthelower
port(B)ofthepump.Fluidowoutofthelowerportgoestothewheelmotors
andturnstheminthereversedirection.Theuidowoutofthewheelmotors
returnstothepistonpumpupperport(A)andiscontinuouslypumpedwhilethe
tractionleverisintheforwardposition
Asthetractionloadincreases,thereversetractioncircuitpressurecanincrease
totherelief-valvesettingof19,994kPa(2,900psi).Ifthecircuitpressureismore
thantherelief-valvesetting,uidowsthroughthereversereliefvalveinthe
transmissiontothelow-pressuresideoftheclosed-looptractioncircuit.
Thechargecircuitfunctionsthesameinreverseasitdoesintheforward
direction.
Greensmaster3120
Page4–15
HydraulicSystem:HydraulicFlowDiagrams
17230SLRevC