Hitachi ZW180, Technical Manual

Page: 74 / 374

SYSTEM / Control System
T2-1-32
Downshift Control
Purpose: To lower the speed shift by pushing the
switch installed at the right console.
Operation:
1. When traveling at speed 4 while the travel mode
switch is set in auto 1-4L mode, the signal is
transmitted to MC by pushing the downshift switch
once.
2. When the vehicle speed is faster than the allow-
able speed to shift down, MC cancels the signal
from the downshift switch. On the other hand, MC
transmits a signal to the speed shift solenoid valve
of speed 3 when the vehicle speed is slow
enough.
3. When the downshift switch is pushed while the
vehicle speed is slow enough to shift down, speed
2 is selected.
4. In case auto mode of the travel mode switch is
selected, auto speed shift control is recovered
three seconds after the speed shift has lowered,
and then the speed shift is automatically raised
once the vehicle speed increases.
5. When the downshift switch is continue to be
pushed, the speed shift is lowered to speed 2, and
speed 2 is kept during pushing.
6. At this time, when the downshift switch is released
and pushed again within three seconds while the
vehicle speed is slow enough to shift down, the
vehicle shifts to speed 1.
7. When the downshift switch is in the manual mode
of the travel mode switch, in case the vehicle
speed is slow enough to shift down, the speed
shift is lowered and the shifted speed is kept.
8. In case of the following, the downshift switch con-
trol is canceled.
•
Operation of the FNR lever or the FNR switch
•
Operation of the shift switch
•
Operation of the travel mode switch
•
Pushing the hold switch
(Only in auto mode of the travel mode switch)
NOTE: In case the vehicle speed sensor becomes
abnormal, MC receives the signal from the
transmission middle shaft sensor, and con-
trols by calculating the vehicle speed al-
lowable for the speed shift. In case both the
vehicle speed sensor and the transmission
middle shaft sensor are abnormal, lowering
the speed shift is possible as an emergency
measure only when the engine stops for
one reason or another but traveling is not
stopped.
NOTE: The shift switch has two switches, and their
combination of ON varies depending on
each speed shift. The controller judges
which speed shift has been selected by the
combination of the two input signals.
NOTE: The FNR switch does not transmit the neu-
tral signal. In case of no electric current
from the FNR switch, the controller judges
that the switch is neutral (N).
NOTE: Each mode switch of the travel mode switch
is supplied with respectively different volt-
ages from the monitor unit, and when the
switch selects a mode, MC judges which
mode has been selected by the input volt-
age.