Service Manual

ForwardDirection
WiththearmrestconsoleHI/LOWspeedswitchintheLOWspeed(mow)
position,solenoidvalve(S12)inthecombinationmanifoldisnotenergized
whichkeepsthefrontwheelmotorsandrearaxlemotorattheirmaximum
displacement.Withthemotorsatmaximumdisplacement,alowertractionspeed
isavailableformowingconditions.
WhentheHI/LOWswitchisintheLOWspeed(mow)positionandthetraction
pedalispushedintheforwarddirection,oilfromthepistonpumppassesthrough
thefronttractionmanifold.Oilowforthefrontwheelmotorsleavesfronttraction
manifoldportM1todrivethefrontwheelmotorsintheforwarddirectionand
thenreturnstothepistonpump.OilowfromfronttractionmanifoldportM2is
directedtodrivetherearaxlemotorintheforwarddirection.Oilreturningfrom
theaxlemotorentersthereartractionmanifoldattheM8port.Flowbypasses
thePRcartridgethroughtheCVcheckvalve,outmanifoldportP2andreturnsto
thepistonpump.
Whengoingdownahill,thetractorbecomesanover−runningloadthatdrives
thefrontwheelandrearaxlemotors.Inthiscondition,therearaxlemotorcould
lockupastheoilpumpedfromthemotorincreasespressureasitreturnstothe
pistonpump.T opreventrearwheellockup,anadjustablereliefvalve(RV)in
thereartractionmanifoldreducesrearaxlemotorpressurecreatedindownhill,
dynamicbrakingconditions.
ReverseDirection
ThetractioncircuitoperatesessentiallythesameinreverseLOWspeed(mow)
asitdoesintheforwarddirection.However,theowthroughthecircuitis
reversed.Oilowfromthepistonpumpisdirectedtothefrontwheelmotorsand
alsotothereartractionmanifold.Theoiltothefrontwheelmotorsdrivesthem
inthereversedirectionandthenreturnstothepistonpumpthroughthefront
tractionmanifold.Theoiltothereartractionmanifoldentersthemanifoldatport
P2andowsthroughpressurereducingvalve(PR)whichlimitsthedownstream
pressuretotherearaxlemotorto26bar(380PSI)sotherearwheelswillnot
scufftheturfduringreverseoperation.Thisreducedpressureowisdirected
outreartractionmanifoldportM8todrivetherearaxlemotorinreverse.Return
oilfromtherearmotorreturnstothepistonpump.
HydraulicSystem:HydraulicFlowDiagrams
Page5–16
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