Textron JACOBSEN R-311 69166, Technical/Repair Manual

Page: 182 / 402

HYDROSTATIC POWER TRAIN
4203781 First Edition 5-19
5
Traction Circuit—Forward 4WD
Schematic and Theory of Operation
System Conditions:
• Engine running
• Park brake released
• Traction pedal in the FORWARD position
• 2WD/4WD switch in the 4WD 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 through port
“A.” Oil is then routed to the front axle drive motor, driving
the motor. Operating pressure oil is also routed to port
“A” of the 4WD valve. Oil exiting the front axle motor is
returned to the traction pump to replenish the intake side
of the pump.
When the 2WD/4WD switch is placed in the 4WD
position, the primary 4WD solenoid in the control valve
shifts, allowing oil to flow through the valve. Oil is then
routed to the pilot line of the secondary 4WD shuttle
valve in the 4WD valve, causing the valve to shift.
Operating pressure oil from port “A” flows through the
secondary 4WD shuttle valve through ports “R1” (right
motor) and “L1” (left motor) to the right and left rear
wheel motors, driving the rear wheels.
Oil exiting the rear wheel motors enters the 4WD valve at
ports “R2” (right motor) and “L2” (left motor), and flows
through the 4WD reverse solenoid valve, exiting the 4WD
valve at port “C.” A check valve will also open, allowing oil
to exit the 4WD valve at port “B.” Oil exiting the rear wheel
motors is returned to the traction pump to replenish the
intake side of the pump.
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.