Hitachi ZW180 Technical Manual page 84

Hydraulic Fan Cooling Control
Purpose: To improve fuel consumption rate and noise
reduction by restricting the hydraulic fan
speed in response to each oil temperature
and coolant temperature.
Operation:
1. When the engine is started, the fan pump rotates
and delivers oil to the fan motor.
2. MC receives the signals from the hydraulic oil
temperature sensor, engine coolant temperature
sensor and torque converter oil temperature
sensor at the same time, and calculates three
target hydraulic fan speeds.
3. MC selects the fastest speed, and transmits the
signal to the flow rate control solenoid valve.
4. The flow rate control solenoid valve is operated.
As pressure oil from the flow rate control solenoid
valve flows into the right end of the flow rate con-
trol valve, the flow rate control valve spool moves
to the left.
5. When the flow rate control valve spool moves to
the left, as a part of pressure oil to the fan motor
flows to the tank port, the fan motor speed is low-
ered accordingly.
6. In case either oil temperature or coolant tem-
perature is above the set temperature, the hy-
draulic fan speed is maximum when the engine
speed is maximum.
7. In case either oil temperature or coolant tem-
perature is below the set temperature, the hy-
draulic fan speed is lowered in response to the
data of the highest temperature.
8. As, the signal from the fresh air temperature
sensor also enters MC, the fan is always rotated
at the maximum speed while disregarding the
controls in 2 to 7 in case the air conditioner switch
is ON at the fresh air temperature of 35 °C (95 °F)
and above.
NOTE: In case any of the engine speed sensor,
hydraulic oil temperature sensor, engine
coolant temperature sensor, torque con-
verter oil temperature sensor or fresh air
temperature sensor is abnormal, hydraulic
fan cooling control is always made at the
maximum speed.
SYSTEM / Control System
T2-1-42