Toro Groundsmaster 4500-D Series - Page 118

ForwardDirection(continued)
WheninLOWmodepositionwiththetractionpedalpushedintheforward
direction,oilfromthepistonpumpisdirectedtothefrontwheelmotorsandrear
axlemotorthroughaparallelsystem.Oilowtothefrontwheelmotorsdrives
themotorsintheforwarddirectionandthenreturnstothepistonpump.Oilow
totherearaxlemotordrivesthemotorintheforwarddirection.Oilreturningfrom
theaxlemotorentersthereartractionmanifoldattheM8port.Flowbypasses
thePRcartridgethroughtheCVcheckvalve,outmanifoldportP2andreturnsto
thepistonpump.
Whengoingdownahill,thetractorbecomesanover-runningloadthatdrives
thefrontwheelandrearaxlemotors.Inthiscondition,therearaxlemotorcould
lockupastheoilpumpedfromthemotorincreasespressureasitreturnstothe
pistonpump.T opreventrearwheellockup,anadjustablereliefvalve(RV)in
thereartractionmanifoldreducesrearaxlemotorpressurecreatedindownhill,
dynamicbrakingconditions.
ReverseDirection
ThetractioncircuitoperatesessentiallythesameinreverseLOWmodeasit
doesintheforwarddirection.However,theowthroughthecircuitisreversed.
Oilowfromthepistonpumpisdirectedtothefrontwheelmotorsandalsoto
thereartractionmanifold.Theoiltothefrontwheelmotorsdrivestheminthe
reversedirectionandthenreturnstothepistonpump.Theoiltothereartraction
manifoldentersthemanifoldatportP2andowsthroughpressurereducing
valve(PR)whichlimitsthedownstreampressuretotherearaxlemotorto27.6
bar(400PSI)sotherearwheelswillnotscufftheturfduringreverseoperation.
ThisreducedpressureowisdirectedoutreartractionmanifoldportM8to
drivetherearaxlemotorinreverse.Returnoilfromtherearmotorreturnsto
thepistonpump.
HydraulicSystem:HydraulicFlowDiagrams
Page5–16
Groundsmaster
®
4500-D/4700-D
19245SLRevA