Service Manual

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g274972
Figure51
1.Piston(traction)pump
3.3
rd
gearpumpsection
2.4
th
gearpumpsection
Afoursectiongearpumpiscoupledtothepiston(traction)pump(Figure51).
Thefourthgearpumpsection(farthestfromthepistonpump)supplieshydraulic
owtothesteeringcircuit,theenginecoolingfancircuitandthetractioncharge
circuit.Thethirdgearpumpsectionsupplieshydraulicowtotheenginecooling
fancircuit,thelift/lowercircuitandthetractionchargecircuit.
Sothatthereissufcientoilowfortheenginecoolingfancircuit,oilowfrom
eitherorbothofthethirdorfourthgearpumpsectionisusedtodrivethe
hydrauliccoolingfanmotordependingonwhatothermachinefunctionsarebeing
used(steering,lift/lower).Ifadditionaloilowisneededforcoolingfanoperation
inextremeconditions(e.g.highambienttemperatures,cuttingveryheavygrass),
theTECcontrollercanallowowfromthetwopumpsectionstobecombined.
Oilowfromthethirdgearpumpsectionisroutedtothecombinationmanifold
(portP3)whereitisavailableeitherforthelift/lowercircuitortheenginecooling
fancircuit.Whenthelift/lowercircuitisnotbeingused(allliftswitchesinthe
neutralposition),solenoidvalve(S1)inthecombinationmanifoldisnotenergized
andgearpumpsectionoilowisdirectedtowardtheenginecoolingfanmotor.
Priorityoilowfromthefourthgearpumpsectionisprovidedtothesteering
circuit.Allexcessowfromthisgearpumpsectionisnormallyroutedtothe
tractionchargecircuitbyenergizedsolenoidvalve(S11).Thisvalveisenergized
bytheTECcontrolleraslongasthelift/lowerfunctionisnotbeingusedandthe
hydraulicoilandenginecoolanttemperaturesarewithinnormalranges.Ifinputs
totheTECcontrollersuggestadditionaloilowisnecessaryforthecoolingfan
(e.g.lift/lowercircuitisengagedorenginecoolanttemperatureiselevated),
solenoidvalve(S11)willbede−energizedallowingexcesspumpsectionoilow
tobedirectedtowardtheenginecoolingfanmotor.
Oilowfromthegearpumpsection(s)tothecoolingfanmotoriscontrolled
bytheproportionalreliefvalve(PRV)inthecombinationmanifold.Thisvalve
adjustsfancircuitpressureandowbasedonaPWM(PulseWidthModulation)
signalfromtheTECcontroller.Thecontrollerusesenginecoolantandhydraulic
oiltemperaturesasinputstodeterminetheproperPWMsignalforthe(PRV)
valve.Thefancircuitowdeterminesthespeedofthecoolingfanmotorand
thus,thespeedofthecoolingfan.
Ifthefanmotorisstalledforanyreasonduringmachineoperation,themanifold
proportionalreliefvalve(PRV)hasasecondaryfunctionasacircuitrelieftolimit
fanmotorpressureto224bar(3250PSI).
HydraulicSystem:HydraulicFlowDiagrams
Page5–34
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