5-4 4181383 First Edition
HYDROSTATIC POWER TRAIN
5
Theory of Operation and
Sub-Circuit Schematics
Traction Circuit Forward Schematic
and Theory of Operation
See Figure 5-3.
System Conditions:
• Engine running
• Park brake released
• Traction pedal depressed (forward 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 a 100 mesh screen, and enters the charge
pump. Oil is then routed to the charge pressure relief
valve, the traction pump, and the displacement control
valve. The charge pressure relief valve regulates the
charge pressure applied to the traction pump/circuit.
When the incoming charge pressure oil reaches 285 psi
(20 bar), the charge pressure relief valve will open,
venting excess flow to the hydraulic tank.
Traction Pump Circuit
When the traction pedal is moved to the forward position,
the displacement control valve is moved to the forward
position. Charge oil is supplied through 0.28” orifice,
displacement control valve, and to the traction pump,
moving the swash plate, stroking the pump, and
producing oil flow to port “A.” Operating pressure oil from
port “A” of the traction pump is supplied in parallel to the
front wheel motors and in series to the rear wheel
motors, resulting in full-time four-wheel drive. Oil from the
rear wheel motors returns to the traction pump, entering
through port “B.” The 0.28” orifice meters the amount of
oil to servo piston which dampens the flow of oil,
reducing the chance of wheel spin. The 0.31” office
dampens the flow of oil to tank. The traction circuit is
protected by a circuit relief valve. This valve will open,
venting excess oil flow to the return side of loop when the
pressure rises above 3625 psi (250 bar).
Hot Oil Shuttle
The hot oil shuttle is located in the 4WD valve. The hot oil
shuttle is held open when there is operating pressure oil
in the forward direction. This allows a small amount of
charge pressure oil to drain to the hydraulic tank for oil
cooling.
To Next Page
Loading...
Need help?
General
