Jacobsen SLF 1880, Technical/Repair Manual

Page: 131 / 236

8E-29
TRACTION CIRCUIT—FORWARD
2WD SCHEMATIC AND THEORY OF
OPERATION
System Conditions:
• Operator in seat
• Engine running
• Park brake released
• Traction pedal in the FORWARD position
• 2WD/4WD switch in 2WD position
Charge Pressure Circuit
The charge pump and traction pump are both driven by
the engine. The charge pump supplies oil to the trac-
tion pump/circuit.
Hydraulic oil is drawn from the hydraulic tank and
enters the charge pump. Charge pressure oil is routed
to the 1160 psi (80 bar) relief valve in the traction pump
and to the “IN” port of the steering unit. Charge pres-
sure oil from the “OUT” port of the steering unit is
routed back to the traction pump (through charge filter
on 2011 and later units) against the combination check
valves/3045 psi (210 bar) relief valves and against the
58–102 psi (4–7 bar) (145-203 psi (10-14 bar) on 2011
& later units) charge relief valve. Charge pressure oil
will flow through the check valves into the return (low-
pressure) side of the closed-loop circuit. The charge
relief valve regulates the charge pressure applied to
the traction pump and traction circuit. When the incom-
ing charge oil reaches the relief valve setting, the relief
valve will open, releasing excess flow to the hydraulic
tank.
Traction Drive Circuit
When the traction pedal is moved to the FORWARD
position, operating pressure oil from the traction pump
rotating group is routed to the combination check
valves/3045 psi (210 bar) relief valves and the tow
valve, and exits the traction pump at port “A.” The oil is
then routed to the front wheel motors, driving the
motors. Oil exiting the front wheel motors is routed to
port “B” of the traction pump to replenish the intake
side of the traction pump rotating group.
Operating pressure oil is also supplied to port “A” of the
4WD valve. With the 2WD/4WD switch in the 2WD
position, oil flow is blocked by the 4WD solenoid and
does not flow to the rear wheel motors. The rear wheel
motors rotate freely as the mower travels forward.
Hydraulic oil is used to lubricate the internal compo-
nents of pumps and motors. This oil is returned via the
case drain lines back to the hydraulic tank.
Circuit Relief
The traction circuit is protected by relief valves. The
pilot-operated relief valve will open if the pressure rises
in the circuit to 3045 psi (210 bar), allowing oil to dump
to bypass to the charge side or low-pressure side of the
circuit. There is a relief valve for both forward and
reverse directions.
NOTICE
During the 2011 production year, the charge pres-
sure increased from 58-102 psi (4-7 bar) to 145-203
(10-14 bar) and the charge filter was added to the
system. The following information and schematics
reflect this change. Serial number information is on
page 8D-13.