TM 5-3805-290-23-1
THEORY OF OPERATION - CONTINUED
0003 00
BRAKE SYSTEM - CONTINUED
2.
Fan.
a.
When engine is in operation, fan rotates at a speed of 700 to 1,625 rpm. Fan speed is limited by fan flow control
valve, which is controlled by demand fan solenoid valve. Demand fan solenoid valve is controlled by machine
ECM. Fan motor speed depends on amount of flow allowed through fan flow control valve. Control of fan speed is
based on:
(1)
Inlet manifold temperature
(2)
Transmission oil temperature
(3)
Hydraulic oil temperature
(4)
Engine coolant temperature
b.
When machine ECM requires more air flow for cooling, it decreases amount of electric current sent to demand fan
solenoid valve to close it. When demand fan solenoid valve closes more, pilot oil pressure acting on fan flow con-
trol valve increases and pressure drop across orifice decreases. When pressure drop across orifice decreases, fan
flow control valve closes to restrict oil flow through fan flow control valve. When oil flow through fan flow con-
trol valve is restricted, oil flow from braking and hydraulic fan pump must flow through fan motor. This causes fan
motor to turn faster. Fan speed depends on amount of current sent to demand fan solenoid valve.
c.
When machine ECM does not require more air flow for cooling, it increases amount of electric current to demand
fan solenoid valve to shift demand fan solenoid valve more open. When demand fan solenoid valve opens more,
pilot oil acting on fan flow control valve is sent to tank. Pressure drop across orifice increases.
d.
When pressure drop across orifice increases, fan flow control valve will shift more open to increase oil flow
through fan flow control valve. When oil flow through fan flow control valve is increased, oil flow from braking
and hydraulic fan pump will flow through fan flow control valve instead of flowing to fan motor. This will cause
fan motor to turn more slowly. Fan speed depends on amount of current sent to demand fan solenoid valve.
e.
Makeup valve prevents fan motor cavitation dur-
ing deceleration.
f.
Hydraulic oil flows from fan motor to axle oil
cooler motor (if equipped). Hydraulic oil flows
from axle oil cooler motor to hydraulic oil
cooler. Bypass valve will open to allow hydraulic
oil to bypass oil cooler if pressure oil cooler inlet
rises because of a restriction in oil cooler. Bypass
valve will also open if hydraulic oil is cold.
g.
From hydraulic oil cooler, hydraulic oil flows to
hydraulic oil filter. Then, hydraulic oil flows to
hydraulic oil tank.
427-B1540
0003 00-104
