Toro Groundsmaster 4500-D Series - Page 121

ForwardDirection(continued)
Whengoingdownahill,thetractorbecomesanover-runningloadthatdrives
thefrontwheelandrearaxlemotors.Inthiscondition,therearaxlemotorcould
lockupastheoilpumpedfromthemotorincreasespressureasitreturnstothe
pistonpump.T opreventrearwheellockup,anadjustablereliefvalve(RV)in
thereartractionmanifoldreducesrearaxlemotorpressurecreatedindownhill,
dynamicbrakingconditions.
ReverseDirection
ThetractioncircuitoperatesessentiallythesameinreverseHIrangeasitdoesin
theforwarddirection.However,theowthroughthecircuitisreversed.Oilow
fromthepistonpumpisdirectedtothefrontwheelmotorsandalsototherear
tractionmanifold.Theoiltothefrontwheelmotorsdrivestheminthereverse
directionandthenreturnstothepistonpump.Theoiltothereartractionmanifold
entersthemanifoldatportP2andowsthroughpressurereducingvalve(PR)
whichlimitsthedownstreampressuretotherearaxlemotorto27.6bar(400PSI)
sotherearwheelswillnotscufftheturfduringreverseoperation.Thisreduced
pressureowisdirectedoutreartractionmanifoldportM8todrivetherearaxle
motorinreverse.Returnoilfromtherearmotorreturnstothepistonpump.
Groundsmaster
®
4500-D/4700-D
Page5–19
HydraulicSystem:HydraulicFlowDiagrams
19245SLRevA