Textron JACOBSEN GP400, Technical/Repair Manual

Page: 125 / 354

HYDROSTATIC POWER TRAIN
4252490-Rev A 5-7
5
Theory of Operation and
Sub-Circuit Schematics
Traction Circuit—Neutral Schematic
and Theory of Operation
(2WD Models)
System Conditions:
• Engine running
• Park brake released
• Traction pedal in the neutral position
Charge Pressure Circuit
The charge pump and traction pump are both driven by
the engine. The charge pump is mounted between the
rotating group and rear valve plate assembly in the
traction pump housing. It supplies oil to the traction
pump/circuit. Oil is drawn from the hydraulic tank through
the charge filter and enters the charge pump.
The charge filter uses a 10-micron filter to remove debris
from the oil. If the charge filter becomes plugged, a 29 psi
(2.0 bar) pressure switch will activate the “Filter Blocked”
LED on the instrument panel. The charge filter will be
bypassed when the pressure exceeds 51 psi (3.5 bar).
Oil from the charge pump is routed to the 150–210 psi
(10–15 bar) charge relief valve, the 800 psi (55 bar)
implement relief valve, and the two check valves.
The charge relief valve regulates the charge pressure
applied to the traction pump/circuit. When the incoming
charge pressure oil reaches 150–210 psi (10–15 bar),
the charge pressure relief valve will open, venting excess
flow back to the hydraulic tank via the steering unit and
oil cooler.
The excess charge pump supply is used to operate the
steering circuit. The 800 psi (55 bar) implement relief
valve is used to allow intermittent operation of the charge
pump at 800 psi (55 bar).
Traction Pump Circuit
The traction pedal is linked to the traction pump by cable.
Movement of the traction pedal results directly in a
corresponding movement of the traction pump
swashplate. With the traction pedal in the neutral
position, the swashplate is centered in the neutral
position and there is no oil flow through the traction
pump.
The charge oil is supplied to the closed-loop traction
circuit via the check valves and exits the traction pump at
ports “A” and “B.” Oil from port “A” is routed in parallel to
the front wheel motors. Since pressure is equal on each
side of the front wheel motors, no movement occurs.
With the closed-loop circuit charged with oil, the 150–210
psi (10–15 bar) charge pressure relief valve opens and
vents excess oil to the hydraulic tank via the steering unit
and oil cooler.