Toro Groundsmaster 4300-D - Traction Circuits

TractionCircuits
Thehydraulictractioncircuitconsistsofavariabledisplacementpistonpump
(P5)connectedinaclosedloop,parallelcircuitto4orbitalrollervanewheel
motors.Thetractionpumpinputshaftisrotatedbyadriveshaftthatisdriven
fromtheengineywheel.
Theforwardtractioncircuitpressurecanbemeasuredatthetestportlocatedin
thehydraulictubethatconnectsthefrontwheelmotors.Thereversetraction
circuitpressurecanbemeasuredatthetestportsinthecrosstraxmanifold.
ForwardDirection
Pressingthetopoftractionpedal,anglesthetractionpumpswashplateto
createaowofuid.Thisuidowisdirectedtothewheelmotorsviahydraulic
hosesandtubestodrivethewheelsinforwarddirection.Thetractionpump
owisdirectedtothefrontwheelmotorsandthentotheoppositerearwheel
motorstomaximizethetraction.Toreducethetirescufngwhenturning,the
tractionsystempressureisequalizedinthecrosstraxmanifoldwithanorice
andabi-directionalreliefvalve.Thebi-directionalreliefvalveinthecrosstrax
manifoldallowrearwheelmotorstoover-runduringtightturns.Theforward
tractionpressureislimitedto25,000kPa(3,625psi)bytheforwardtractionrelief
valve(R3)locatedinthetractionpump.
Theuidowingfromthewheelmotorsreturnstothevariabledisplacement
pumpandiscontinuouslypumpedthroughthetractioncircuitaslongasthe
tractionpedalispressed.
Theangleoftheswashplatedeterminespumpowandultimatelytraction
speed.Whenthetractionpedalispressedasmallamount,asmallswashplate
rotationresultsinlowpumpoutputandlowertractionspeed.Whenthetraction
pedalispressedfully,thepumpswashplaterotatesfullytoprovidemaximum
pumpoutputandtractionspeed.
Thegearpumpsection(P3)suppliesuidowforthesteeringcircuitandalso
providesaconstantsupplyofchargeuidtotheclosedlooptractioncircuit.
Thischargeuidprovideslubricationfortractioncircuitcomponentsandalso
replenishestractioncircuituidthatislostduetointernalleakageinthetraction
circuit.
Thegearpumpsection(P3)takesitssuctionfromthehydraulicreservoir.The
chargepumpowisdirectedtothelowpressuresideoftheclosedlooptraction
circuit.Chargereliefvalve(R5)locatedinthetractionpumplimitsthecharge
reliefpressureto1,400kPa(200psi).
Thepistonpumpisequippedwithacasedraintoallowinternalleakagetobe
removedfromthepump.Thecasedrainisconnectedtothegearpumpinlet.
Thepistonpump(P5)includesaushingvalvethatbleedsoffasmallamountof
hydraulicuidforcoolingoftheclosedlooptractioncircuit.Thechargesystem
replenishesuidthatisbledfromthetractioncircuitbytheushingvalve.
ReverseDirection
Thetractioncircuitoperatesessentiallythesameinreverseasitdoesinthe
forwarddirection.However,inthereversedirectiontherearwheelmotors
arebypassedfromthecircuittopreventrearwheelspinandimprovesteering
control.Pressingthebottomofthetractionpedal,rotatesthetractionpump
swashplatetocreateaowofuid.Theuidowisdirectedtothecrosstrax
manifoldwherethe2internalcheckvalveallowsthehydraulicuidtobypassthe
rearwheelmotors.Thentheuidowstothefrontwheelmotors,turningthem
inthereversedirection.Thereversetractionpressureislimitedto25,000kPa
(3,625psi)bythereversetractionreliefvalve(R4)locatedinthetractionpump.
Groundsmaster
®
4300-D
Page4–17
HydraulicSystem:HydraulicFlowDiagrams
16226SLRevC