Toro 10176SL Service Manual Models 30448 30446 Groundsmaster 4000 4010 D D Preface

Traction Circuit: Low Speed (4WD)
The traction circuit piston pump is a variable displace-
ment pump  that is directly  coupled to  the engine fly-
wheel. Pushing the traction pedal engages a hydraulic
servo valve  which controls the  variable displacement
piston pump swash plate to create a flow of oil. This oil
isdirectedtothefrontwheelandrearaxlemotors.Oper-
ating pressure on the high pressure side of the closed
traction circuit loop is determined by the amount of load
developedatthefixeddisplacementwheelandaxlemo-
tors.  As the  load increases,  circuit  pressure can  in-
crease to  relief valve settings:  4000 PSI (274  bar) in
forward and 5000 PSI (343 bar) in reverse. If pressure
exceeds the relief setting,  oil flows through the piston
pump relief valve to the low pressure side of the closed
loop traction circuit. The traction circuit provides opera-
tion in either Hi speed (2WD) or Low speed (4WD).
Forward Direction
WhentheHi/LowswitchisintheLowspeed(4WD)posi-
tionandthetractionpedalispushedintheforwarddirec-
tion,  oil  from  the  piston  pump  passes  through  the
traction manifold. Oil flow from traction manifold port M1
drives the front  wheel motors in  the forward direction
and then returns to the piston pump. Oil flow from trac-
tion manifold port M2 is routed to the P1 port of the 4WD
manifoldwhereitisdirectedtothePD1cartridgeandout
ofthe manifold to drivethe rearaxle motor in theforward
direction. Oilreturning fromthe rearmotor re--entersthe
4WD manifold at the M2 port. Flow passes through the
PD2cartridge,throughtheCVcheckvalve,outmanifold
port P2 and back to the piston pump.
When going down a hill, the tractor becomes an over--
running load that drives the wheel and axle motors. In
this condition, the rear axle motor could lock up as the
oil pumped from the motor increases pressure as it re-
turns to the piston pump. To prevent rear wheel lock up,
an adjustable relief valve (RV) in the 4WD manifold re-
duces rear axle motor pressure created in down hill, dy-
namic braking conditions.
Traction circuit pressure (forward and reverse) can be
measured at test ports in hydraulic tubes. The forward
traction port is on the left side of the machine and the re-
verse traction port is on the right side of the machine.
The  traction  circuit  pump  and  motors  use  a  small
amount of hydraulic 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
that must be replaced. The charge circuit is designed to
replace this traction circuit leakage.
Reverse Direction
The traction circuit operates essentially the same in re-
verse Low speed (4WD) as it does in the forward direc-
tion. However, the flow through the circuit is reversed.
Oil flow  from the piston  pump is directed  to the front
wheel motors and also to the 4WD manifold. The oil to
the front wheel motors drives them in the reverse direc-
tion and  then returns to  the piston pump through  the
traction manifold.Theoiltothe4WDmanifold    entersthe
manifoldatportP2andflowsthrough    pressurereducing
valve (PR) which limits the down stream pressure to the
rear axle motor to 650 PSI (45 bar) so the rear wheels
will not scuff the turf during reverse operation. This re-
duced pressure flows through the PD2cartridge andout
port M2 to the rear axle motor. Return oil from the rear
motor re--enters  the 4WD  manifold at port  M1, flows
through the PD1 cartridge, exits the manifold at port P1
and returns to the piston pump.
The gear pump section that supplies oil to the steering
and lift/lower circuits also provides oil for the charge cir-
cuit. This gear  pump is driven  directly off the traction
pump. It  provides a  constant supply  of charge  oil to
make up for oil that is lost due to internal leakage in the
traction pump and motors.
Pump flow for the charge circuit is directed through the
oil filter and to the low pressure side of the closed loop
traction circuit. A  filter bypass valve allows  charge oil
flow to  the closed loop  if the filter  becomes plugged.
Charge pressure is limited to 250 PSI (17 bar) by a relief
valve located in the oil filter manifold. Charge pressure
can be measured at the charge circuit pressure test port
on the oil filter manifold.
A flow divider is incorporated into the traction circuit and
is located in the traction manifold. When in Low speed
(4WD),
the operator can momentarily engage this flow
divider when low traction situations could lead to wheel
spin. Depressing the flow divider switch energizes the
solenoid valve in the traction manifold. This energized
solenoid valve causes traction  pump hydraulic flow to
split between  the  front wheel  motors (approximately
45%)
and rear axle  motor (approximately 55%) to re-
duce the chance  that excessive circuit flow goes  to a
spinning wheel.
Groundsmaster 4000--D/4010--D
Page 4 -- 11
Hydraulic System
Product Specification
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