Hitachi ZW180, Technical Manual

Page: 104 / 374

SYSTEM / Control System
T2-1-62
Lift Arm Auto-Leveler Downward Control (Op-
tional)
Purpose: To locate the lift arm between the horizon
and the lowest position.
Operation:
1. If the SET position of the lift arm auto-leveler
downward set switch is selected after the lift arm
is located within the allowable location of the lift
arm auto-leveler (b’ in the illustration), the signal
from the lift arm angle sensor is memorized by
MC, and that is the lift arm auto-leveler downward
stop position.
NOTE: When the lift arm is outside b’, although the
SET position of the lift arm auto-leveler
downward set switch is selected, the lift
arm auto-leveler downward stop position
cannot be set. In case setting was thus
unsuccessful, or setting in a different posi-
tion is needed, set the lift arm auto-leveler
downward stop position again.
2. When the lift arm auto-leveler downward switch is
turned ON, terminal B-22 of MC is grounded, and
excites the electromagnet on the lift arm down-
ward side of the pilot valve. When the lift arm
control lever is moved to the lift arm lowering de-
tent position (position farther than the lowering
position), the lift arm operation lever is retained by
the electromagnet on the lift arm lowering side,
and pressure oil from the pilot valve is supplied to
the control valve.
3. Pressure oil from the main pump flows to the rod
side port of the lift cylinder through the lift arm
spool in the control valve, and lowers the lift arm.
4. When the lift arm angle sensor moves to the lift
arm auto-leveler downward stop position, terminal
B-22 of MC is not grounded, and the electro-
magnet on the lift arm lowering side is unexcited
for a while until it is excited again soon after.
5. Thus the lift arm control lever returns to the neu-
tral position, and pilot pressure from the pilot
valve stops flowing to the control valve.
6. As the lift arm spool in the control valve also re-
turns to neutral, the lift arm stops at the lift arm
auto-leveler downward stop position.
NOTE: In case the lift arm angle sensor is abnor-
mal, the lift arm auto-leveler downward
control is not made.
IMPORTANT: In case either the lift arm angle sen-
sor or MC has been replaced, make
learning control of the lift arm angle
sensor. (Refer to the OPERATIONAL
PERFORMANCE TEST/Adjustment.)
b (Lift Arm Downward
Work Range)
Position of
Lift Arm Tip Pin
Position of
Lift Arm Foot Pin
b’ (Lift Arm
Auto-Leveler
Downward
Allowable Set-
ting Range)