Service Manual

Thehydraulictractioncircuitconsistsofabidirectionalvariabledisplacement
pistonpumpconnectedinaclosedlooptoahydraulicmotor.Thehydraulic
pumpisdrivenbytheenginethrougharubberdrivecoupling.
RightDirection
Pressingdowntherightmotioncontrolpedal,anglesthehydraulicpumpswash
platetocreateaowofuid.Thisuidowisdirectedtothehydraulicmotor
throughthe“A”porttorotatethedriverollerintherightdirection.Thetraction
pressureislimitedto16,000kPa(2,320psi)bytherighttractionreliefvalve
locatedinthehydraulicpump.
Theangleoftheswashplatedeterminespumpowandultimatelytraction
speed.Whenthemotioncontrolpedalispressedasmallamount,asmall
swashplateangleresultsinlowpumpoutputandlowertractionspeed.When
themotioncontrolpedalispressedfully,thepumpswashplateanglesfullyto
providemaximumpumpoutputandtractionspeed.
Theuidowingthroughthehydraulicmotorreturnstothevariabledisplacement
pumpandiscontinuouslypumpedthroughthetractioncircuitaslongasthe
motioncontrolpedalispressed.
Thehydraulicpumpisequippedwithacasedraintoallowinternalleakagetobe
removedfromthepump.Thecasedrainisconnectedtothehydraulictank.
Agerotorchargepumpinthepumpprovidesaconstantsupplyofchargeuidto
theclosedlooptractioncircuitforlubricationandtomakeupforuidthatislost
duetointernalleakageinthehydraulicpump.Thechargepumptakesitssuction
fromthehydraulictankthroughalter.Chargepressureislimitedto552kPa
(80psi)byacheckvalveinthechargecircuit.Thechargepumpowisdirected
tothelowpressuresideoftheclosedloopcircuit.
LeftDirection
Thetractioncircuitoperatesessentiallythesametomovethemachinetothe
leftdirectionasitdoestomovethemachineintherightdirection.However,
theowthroughthecircuitisreversed.Pushingdowntheleftmotioncontrol
pedalanglesthevariabledisplacementpumpswashplateinthehydraulicpump
intheoppositedirectiontocreateaowofuid.Thisuidisdirectedoutthe
pump“B”porttothemotorwhichturnsthedriverollerintheleftdirection.The
tractionpressureislimitedto16,000kPa(2,320psi)bytherighttractionrelief
valvelocatedinthehydraulicpump.
Theuidowingthroughthehydraulicmotorreturnstothevariabledisplacement
pumpandiscontinuouslypumpedthroughtheclosedtractioncircuitaslongas
themotioncontrolpedalispushed.
Thechargecircuitfunctionsthesameinleftdirectionasitdoesintheright
direction.
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HydraulicSystem:HydraulicFlowDiagrams
14211SLRevA