Detroit Diesel 4000 Series, Руководство по обслуживанию, Страница: 1753 / 2706

SERIES 4000 12/16V SERVICE MANUAL
DDEC IV Engine Control System
If the fan clutch control system is incorporated into the system, fan clutch control may also be
regulated by numerous operational conditions built into that system’s design. See Figure 1049.
Figure 1049 DDEC IV Fan Clutch Control System
Regardless of the designed function of the specific fan clutch controls, the systems are calibrated
to respond within a specified range by sending an electrical signal to drive the solenoid. The
infinite slip ratios of (input) pulley speed to (output) fan speed in the fan clutch are controlled by
the thermal sensor or ECM’s sensitivity, and the solenoid valve’s response to that electrical signal,
by modulating the oil pressure being used to control the (modulated) engagement of the fan clutch.
Engine lubrication oil enters the solenoid through the inlet ("NO" or "INLET") port. The
pressure out ("COM" or "CLUTCH") opening of the solenoid valve is connected by a line to the
"CONTROL PRESSURE" port in the fan clutch bracket. The solenoid valve controls the speed of
the vehicle cooling fan by regulating the amount of oil pressure supplied to engage, modulate,
and allow release of the fan clutch. Oil exiting the fan clutch pressure cavity (and solenoid
valve) is directed to the engine oil reservoir (sump) through the ("NC" or "SUMP") port in the
solenoid valve.
Fully Released Mode
When engine coolant temperature is at or below the lower limit of the designed temperature range
of the thermal sensor (and none of the other thermal sensors or the ECM is sending a signal that
creates fan engagement), no oil pressure is directed into the pressure cavity.
All information subject to change without notice.
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C -1607