Hitachi ZW180 Technical Manual page 338

Operation
Modulation mechanism enables smoother gearshift
by changing the pressure increase waveform or
pressure decrease
depending on the vehicle condition (engine speed,
travel speed, and others).
Vehicle condition is judged by analyzing the
information (electric signal) sensed by the engine
speed sensor, travel speed sensor and shift lever
with the transmission controller. Therefore, the
electric signal depending on the gearshift is
transmitted from the controller to the proportional
solenoid valve.
Oil
Pressure
COMPONENT OPERATION / Drive Unit
waveform of each
Pressure
Decrease
Gearshift Point
The proportional solenoid valve supplies pressure oil
depending on the electric signal from the controller, to
clutch the modulation spool.
The modulation spool regulates the clutch oil
pressure depending on the oil pressure from the
proportional solenoid valve, and supplies pressure oil
to the clutch piston.
Time
Clutch Oil Pressure Waveform
T3-9-32
Pressure
Increase
T4GC-03-09-030