Toro Groundsmaster 7210 - Traction Circuits

TractionCircuits
ThetractionsystemoftheGroundsmasterconsistsofatransmissionthatis
directlyconnectedto,anddrivenby,theengineywheel.Thetransmission
provides2identicalandindependentclosedlooptractioncircuits:onefor
therightwheelmotorandtheotherfortheleftwheelmotor.Eachofthese
transmissioncircuitsincludesavariabledisplacement,slipperfootdesignpiston
pumpwhichprovideshydraulicowforawheelmotor.Theswashplateineach
ofthesepistonpumpsiscontrolledby1oftheoperatortractionlevers.
Theangleoftheswashplatedeterminesthepumpowandultimatelytraction
speed.Whenatractionleverismovedasmallamount,asmallswashplate
rotationresultsinlowpumpoutputandlowertractionspeed.Whenthetraction
leverismovedfully,thepumpswashplaterotatesfullytoprovidemaximum
pumpoutputowandtractionspeed.
Becausehydraulicuidowtoeachrearwheelisdeterminedbythetraction
levermovementandsubsequentswashplateposition,steeringisaccomplished
bymovingthe2tractionleversadifferentamountordirection.
WiththeenginerunningandthetractionleversintheNEUTRALposition,the
swashplatesofthepistonpumpareheldintheverticalposition,providingno
owtoeitherwheelmotorandthemachineremainsstationary.Thetransmission
reversecheckvalvesincludeanoricewhichmakesiteasiertolocatethe
transmissionNEUTRALposition.
ForwardDirection
Whenatractionleverispushedforward,therodconnectedtothetractionlever
positionstheswashplateinthepistonpumptoprovidehydraulicuidowfrom
thetransmission(portAfortherightsideorCfortheleftside).Thisuidowsto
thewheelmotorandturnsthemotorintheforwarddirection.Theuidowfrom
thewheelmotorreturnstothetransmission(portBorD)andiscontinuously
pumpedwhilethetractionleverispushedforward.
Asthetractionloadincreases,theforwardtractioncircuitpressurecanincrease
totherelief-valvesettingof27,600kPa(4,000psi).Ifthecircuitpressureismore
thantherelief-valvesetting,uidowsthroughtheforwardreliefvalveinthe
transmissiontothelow-pressuresideoftheclosedlooptractioncircuit.
Thepistonpumpsuseasmallamountofhydraulicuidforinternallubrication.
Theuidisdesignedtoleakacrossthepumppartsintothetransmissioncase
drain.Thisleakageresultsinthelossofhydraulicuidfromtheclosedloop
tractioncircuitsthatmustbereplaced.
Achargepumpinthetransmissionsupplieshydraulicowformaintaining480to
690kPa(70to100psi)tothelow-pressuresideofthe2tractioncircuits.The
chargepumpalsoprovidespressureforthetransmissionPTOdrivesystem.The
chargepumpreplenishestheclosedlooptractioncircuitswithuidfromthe
hydraulictank.Thecharge-reliefvalveinthetransmissionmaintainssufcient
pressuresothatthecharge-pumpowisguidedpastcheckvalvestothe
low-pressuresideofeachtractioncircuit.Thecharge-pumpowinexcessof
systemrequirementsisreleasedthroughthecharge-reliefvalvebacktothe
hydraulictank.
The2transmissiontractioncircuitsincludeaushingvalvethatbleedsoffa
smallamountofhydraulicuidforcoolingoftheclosedlooptractioncircuits.
Theushingvalvesareopenedonlyduringforwarddirectionoperation.When
theushingvalvesareunseated,someuidfromthelow-pressuresideofthe
tractionloopisreturnedtothehydraulictank.Theuidlossfromtheclosedloop
duetotheushingvalveisreplacedbythechargepump.
Groundsmaster7210
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HydraulicSystem:HydraulicSchematics
16222SLRevC