Greensmaster 3300/3400 Hydraulic SystemPage 5 -- 13
Traction Circuit
The traction circuit piston pump is a variable displace-
ment pump that is directly coupledtotheengine. Push-
ingthetractionpedalcontrolsthevariabledisplacement
piston pump swash plate to create a flow of oil. This oil
is directed to the wheel motors. Operating pressure on
the high pressuresideof the closed traction circuitloop
is determined by the amount of load developed at the
fixed displacement wheel motors. As the load in-
creases,circuitpressurecanincreasetoreliefvalveset-
tings: 3000 PSI (207 bar) in both forward and reverse.
If pressure exceeds the relief setting, oil flows through
the r elief valve to the low pressure side of the closed
loop traction circuit.
The tractioncircuitpump and wheel motorsuse a small
amount ofhydraulic fluid for internal lubrication.Fluid is
designed to leak across traction pump and motor com-
ponents into the case drain. This leakage results in the
lossofhydraulicfluidfromtheclosedlooptractioncircuit
thatmust bereplaced. Thecharge circuitis designedto
replace this traction circuit leakage.
The gear pump section that supplies oil to the steering
andliftcircuitsalsoprovidescharge circuitoil.Thisgear
pump is driven directly off the piston (traction) pump. It
provides a constant supply of charge oil to the traction
circuit to make up for oil that is lost due to internal leak-
age in the traction pump and wheel motors.
Charge pump flow is directed to the low pressure side
of the closed loop traction circuit. Charge circuit pres-
sure (110 to 150 PSI / 7.6 to 10.3 bar) is maintained by
the charge relief valve that is attached to the piston
pump back plate.
The functional control lever on TriFlex Greensmaster
machines has positions for neutral, mow and transport.
When the functional control lever is in the neutral posi-
tion,thetractionpedalissecuredintheneutralposition.
The mow position allows traction pedal inputs that are
appropriateformowspeedsbylimitingthemovementof
the piston pump swash plate. The transport position al-
lows full movement of the traction pedal so complete
pump swash rotation is possible.
Forward
The piston (traction) pump is driven directly by the en-
gine. The hydraulic traction circuit acts essentially as a
closed loop. Taking its suction directly from the return
sideofthewheelmotorsofthetractioncircuit,thepiston
pump supplies oil flow to the wheel motors through the
supply side of the traction circuit.
Withtheenginerunningandtractionpedalintheneutral
position, the piston pump supplies no flow to the wheel
motors. When the traction pedal is pressed to the for-
ward position, the linkage from the pedal positions the
swash plate in the piston pump so oil flows out the top
port of the pump. Oil flow out of the top port goes to the
wheel motors and turns them in the forward direction.
Oilflowingoutofthe wheelmotorsreturnsto thebottom
portof thepiston pumpand iscontinuouslypumped out
the top port.
Reverse
The traction circuit operates essentially the same in re-
verse as it does in the forward direction. However, the
flow through the c ircuit is reversed.
Withtheenginerunningandtractionpedalintheneutral
position, the piston pump supplies no flow to the wheel
motors. When the traction pedal is pressed to the re-
verse position, the linkage from the pedal positions the
swash plate in the piston pump so oil flows out the bot-
tomportofthepump.Oilflowoutofthebottomportgoes
tothewheelmotorsand turnstheminthereversedirec-
tion.
Oilflowingoutofthewheelmotorsreturnstothetopport
of the piston pump and is continuously pumped out the
bottom port.
Traction Circuit Cooling
Thepiston pumpincludes ashuttle valvethat bleedsoff
asmallamountofhydraulicfluidforcoolingoftheclosed
looptraction circuit.This valveallowsasmallamountof
hydraulic oil to pass from the low pressure side of the
traction circuit while operating the traction unit in either
direction. A relief valve in the piston pump back plate
prevents shuttle valve bleed off until the relief valve
opens(70to100PSI/ 4.9to6.8bar).Thechargecircuit
replenishesoilthatisbledfromthetractioncircuitbythe
shuttle valve.
NOTE: Theshuttlev alveassemblyislocatedinthepis-
ton pump back plate. Access to the shuttle valve re-
quires removal of the back plate from the piston pump.
Hydraulic
System
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