Toro GroundsmasterR 4300-D Service Manual page 43

Traction Circuit
The hydraulic traction circuit consists of a variable dis-
placement piston pump (P5) connected in a closed loop,
parallel circuit to four (4) orbital roller vane wheel mo-
tors. The traction pump input shaft is rotated by a drive
shaft that is driven from the engine flywheel.
Forward traction circuit pressure can be measured at a
test port located in the hydraulic tube that connects the
front wheel motors. Reverse traction circuit pressure
can be measured at test ports in the AWD control man-
ifold.
Forward Direction (Fig. 10)
Pushing the top of the traction pedal angles the traction
pump swash plate to create a flow of oil. This oil flow is
directed to the wheel motors via hydraulic hoses and
tubes to drive the wheels in the forward direction. Trac-
tion pump flow is directed to the front wheel motors and
then to the opposite rear wheel motors to maximize trac-
tion. To reduce tire scuffing when turning, traction sys-
tem pressure is equalized in the AWD control manifold
with an orifice and a bi--directional relief valve. Check
valves in the AWD manifold allow the rear wheel motors
to over--run during tight turns. Forward traction pressure
is limited to 3625 PSI (250 bar) by the forward traction
relief valve (R3) located in the traction pump.
Oil flowing from the wheel motors returns to the variable
displacement pump and is continuously pumped
through the traction circuit as long as the traction pedal
is pushed.
The angle of the swash plate determines pump flow and
ultimately traction speed. When the traction pedal is de-
pressed a small amount, a small swash plate rotation re-
sults in low pump output and lower traction speed. When
the traction pedal is depressed fully, the pump swash
plate rotates fully to provide maximum pump output and
traction speed.
Groundsmaster 4300--D
Gear pump section (P3) supplies oil flow for the steering
circuit and also provides a constant supply of charge oil
to the closed loop traction circuit. This charge oil pro-
vides lubrication for traction circuit components and also
replenishes traction circuit oil that is lost due to internal
leakage in the traction circuit.
Gear pump section (P3) takes its suction from the hy-
draulic reservoir. Charge pump flow is directed to the low
pressure side of the closed loop traction circuit. Charge
relief valve (R5) located in the traction pump limits the
charge relief pressure to 200 PSI (14 bar).
The piston pump is equipped with a case drain to allow
internal leakage to be removed from the pump. The
case drain is connected to the gear pump inlet.
The piston pump (P5) includes a flushing valve that
bleeds off a small amount of hydraulic fluid for cooling
of the closed loop traction circuit. The charge system re-
plenishes oil that is bled from the traction circuit by the
flushing valve.
Reverse Direction
The traction circuit operates essentially the same in re-
verse as it does in the forward direction. However, the
flow through the circuit is reversed. Pushing the bottom
of the traction pedal rotates the traction pump swash
plate to create a flow of oil. This oil is directed to the
wheel motors to drive the wheels in the reverse direc-
tion. Reverse traction pressure is limited to 3625 PSI
(250 bar) by the reverse traction relief valve (R4) located
in the traction pump.
Oil flowing from the wheel motors returns to the traction
pump and is continuously pumped through the closed
loop traction circuit as long as the traction pedal is
pushed.
The charge circuit and flushing valve function the same
in reverse as they do in the forward direction.
Page 4 - - 11 Hydraulic System