Parking Brake Circuit - Hitachi ZW180 Technical Manual

PARKING BRAKE CIRCUIT

•
When the key switch is turned to the ON position,
the power from terminal M excites the battery
relay through fuse #8 of fuse box A.
•
The battery power flows to parking brake relay 1
through fuse #2 of fuse box B.
•
The power flows to terminal D of parking brake
relay 1 through terminal B of parking brake relay 1.
The power flows to terminal B of parking brake
relay 2 and terminal B of the parking brake switch.
•
The parking brake switch consists of three circuits
of ON, NEUTRAL and OFF, and it is kept ON
when turned ON, and it is automatically returned
to NEUTRAL when turned OFF.
•
When the parking brake switch is turned to the
OFF position, current flows from terminal E of the
parking brake switch to terminal A of parking
brake relay 2 and the parking brake solenoid
valve.
•
At this time, if the engine is not running, parking
brake relay 1 is excited as terminal 2-18 of the
monitor unit is grounded.
•
Therefore, the parking brake cannot be released
as the power between parking brake relay 1 and
terminal B of the parking brake switch and
terminal B of the parking brake relay is blocked.
•
If the engine is running, parking brake relay 2 is
excited as current from terminal L of the alternator
enters terminal 2-2 of the monitor unit and
releases grounded terminal 2-18 of the monitor
unit.
•
Consequently, a circuit in which electricity flows
from terminal C of parking brake relay 2 to
terminal A of parking brake relay 2 and the
parking brake solenoid valve (self-exciting circuit)
is formed. Therefore, the parking brake solenoid
valve is activated and the parking brake is
released.
•
As the parking brake switch automatically returns
to neutral, the circuit from terminal E of the
parking brake switch to parking brake relay 2 is
blocked.
SYSTEM / Electrical System
T2-4-30
•
However, as a self-exciting circuit is formed in
parking brake relay 2, current keeps flowing to the
parking brake solenoid valve, and keeps the
released condition of the parking brake until the
key switch is turned to the OFF position or the
parking brake switch is turned to the ON position.
IMPORTANT: The
released
running.
•
When the parking brake switch is turned to the
ON position, terminal A of the parking brake
switch is grounded, and parking brake relay 1 is
excited.
•
The power to terminal B of parking brake relay 2
and terminal B of the parking brake switch
through terminal D of parking brake relay 1 is
blocked.
•
Consequently, the parking brake is applied as
parking brake relay 2 and the parking brake
solenoid valve are unexcited.
parking brake cannot
unless the engine
be
is