Hitachi ZW180 Technical Manual page 341

•
At End of Clutch Connection
(Refer to Pressure Oil Waveform B on T3-9-32.)
Finally, pressures in oil chamber (e) and oil
chamber (g) become equal.
Spring (3) is installed in oil chamber (g). As the
force pushing leftward of oil chamber (e) is larger
than the force pushing rightward of oil chamber
(g) and spring (3) force, modulation spool (2) is
pushed to the left end. Therefore, oil passage (b)
and oil passage (d) are completely open. (Refer
to the illustration below.)
Consequently, the clutch pressure and the
regulator pressure become equal and constant.
1 - Modulation Spool
2 - Modulation Spring
COMPONENT OPERATION / Drive Unit
•
During Shift Down Condition from Forward 2nd
Speed to 1st Speed [at DSS]
Pressure increase of the 1st speed clutch
pressure is similar to "Clutch Connection from
Neutral".
Pressure decrease of the 2nd speed clutch
pressure is operated reversely against pressure
increase. The clutch pressure is gradually
decreased by gradually decreasing the electric
signal (electric current value) from the high
condition.
Both clutch pressures overlap by gradually
increasing the 1st speed clutch pressure and
gradually decreasing the 2nd speed clutch
pressure. Therefore, lack of torque at shift down
during digging is prevented and the operation can
be done smooth.
The proportional solenoid valve and modulation
spool (2) organize a set in terms of construction,
and are installed to each clutch. Therefore, the
best modulation pressure waveform can be
always obtained by combining the pressure
increase
decrease characteristics. (Refer to Clutch Oil
Pressure Waveform on T3-9-32.)
To Clutch
3 g
b
T3-9-35
characteristics and
Piston
d
the pressure
2 e
T4GD-03-09-015