HYDROSTATIC POWER TRAIN
4203781 First Edition 5-11
5
Traction Circuit—Forward 2WD
Schematic and Theory of Operation
System Conditions:
• Engine running
• Park brake released
• Traction pedal in the FORWARD position
• 2WD/4WD switch in the 2WD position
Charge Pressure Circuit
The traction pump and gear pump are both driven by the
engine. One section of the gear pump provides operating
pressure oil for the steering and lift systems, and charge
pressure oil for the traction pump.
Oil is drawn from the hydraulic tank through a 100-mesh
screen, and enters the gear pump, supplying oil to all four
pump sections. Operating pressure oil from section 1 of
the gear pump is routed to port “P” of the control valve,
flows through the 4.5 gpm (17 lpm) priority valve, and out
port “ST” to the steering valve.
Oil flows through the steering valve to the charge filter.
The charge filter uses a 10-micron filter to remove debris
from the oil. In the event of the charge filter becoming
plugged, a 25 psi (1.7 bar) pressure switch will activate
the “Charge Filter” light on the control panel, and a
bypass valve will open to provide oil to the traction pump
and other systems. Charge pressure oil is then routed to
port “C” of the 4WD valve, port “F” of the control valve,
and the traction pump.
The control valve also incorporates a charge pressure
switch that will activate the “Charge Pressure” light on the
control panel if the charge oil pressure drops below 25
psi (1.7 bar). The control valve also includes a charge
relief valve that will open to dump oil to the hydraulic tank
when the charge pressure reaches 160 psi (11 bar).
Traction Drive Circuit
When the traction pedal is moved to FORWARD position,
the swash plate is moved, stroking the pump. This
change of the swash plate angle produces an increase of
oil flow on one side of the pump. Oil at operating pressure
is then routed against the check valve and 3500 psi (241
bar) relief valve, and exits the traction pump at Port “A.”
The oil is then routed to the front axle drive motor, driving
the motor. Oil exiting the front axle motor is returned to
the traction pump to replenish the intake side of the
pump.
Charge pressure oil is also supplied to port “C” of the
4WD valve. With the 2WD/4WD switch in the 2WD
position, oil flows through the 4WD reverse solenoid and
secondary 4WD shuttle valves, applying equal pressure
to both sides of the right and left rear wheel motors. This
provides no driving force to the rear wheel motors, but
allows the motors to rotate freely as the mower travels
forward.
Circuit Relief
The traction circuit is protected by a relief valve. The relief
valve will open if the pressure rises to 3500 psi (241 bar),
allowing oil to dump to the charge side of the circuit.
To Next Page
Loading...
Need help?
General
