Brake Lock Circuit; Warning Circuit - Komatsu 830E Shop Manual

BRAKE LOCK CIRCUIT

The primary function of the brake lock is to provide a
means for the operator to hold the vehicle while at the
shovel or dump. The brake lock only applies the rear
service brakes. It may also provide a second means
to stop the truck in the event the primary means
(treadle valve) malfunctions.

WARNING CIRCUIT

The brake warning circuit is equipped with a low brake
pressure warning light (on the overhead panel) and an
audible alarm (in the cab) to alert the operator of low
brake pressures. Several electrical sensors, a relay
and delay timer are used to detect brake system
problems.
• Pressure Sensor, system supply pressure
Located below the bleed down manifold on a tee
fitting is the low steering pressure switch. When
system supply pressure drops below 2300 psi
(15860 kPa), the low steering pressure light, low
brake pressure light and buzzer will turn on.
• Pressure Sensor, low accumulator pressure
(22)
Located on the brake manifold. When the accu-
mulator with the lower pressure falls below 2350
psi (16200 kPa), the low brake pressure light and
buzzer will turn on.
• Differential Pressure Switch
Located in the cab on the brake dual controller
(foot treadle) (12, Figure 3-2) is the Pressure
Differential Manifold. During brake application, if
the difference in brake apply pressure between
the front and rear circuits are greater than a preset
level, the low brake pressure light and buzzer will
turn on. The pressure differential switch com-
pletes a path to ground in order to turn on the low
brake pressure light and buzzer. Use of the differ-
ential pressure switch allows detection of faults
between the front and rear circuits, such as brake
line ruptures, poor brake valve tracking, line
blockage, and excessive air or brake displace-
ment.
J2-4
By turning on the dash mounted toggle switch, a
solenoid valve (15, Figure 2-1) and pressure reducing
valve (PR2, 14) will apply unmodulated pressure oil at
1500 ±75 psi (10343 ±517 kPa) to fully actuate the rear
brakes. A shuttle valve (13) in the rear brake line
provides the independence from the brake treadle
valve for brake application.
• Brake Lock Degradation Switch (9, Figure 2-1)
Located on the junction block (10) in the brake
cabinet. When the brake lock switch is turned on,
a pressure imbalance inside the differential pres-
sure manifold occurs (normal at this time) as only
the rear brakes are applied. The brake warning
light relay is energized and switches the electrical
connection from the differential pressure switch
to the low brake lock pressure switch. If the brake
lock apply pressure is less than 1000 psi (6900
kPa), a path to ground will be completed and the
low brake pressure light and buzzer will turn on.
• Brake Warning Relay (25)
Located in the brake cabinet. When the brake lock
switch is turned on, the brake warning light relay
is energized and switches the electrical connec-
tion from the differential pressure switch to the low
brake lock pressure switch. When the brake lock
switch is turned off, the relay is de-energized and
switches the connection from the low brake lock
apply pressure switch to the differential pressure
switch.
• Brake Delay Timer (24)
Located in the brake control cabinet. The delay
timer is connected in series between the low
brake pressure light/buzzer and the two switches,
the differential pressure switch and the low brake
lock apply pressure switch. If either switch com-
pletes a path to ground, the delay timer will not
complete the circuit for 1.2 seconds. This will
allow sufficient time for the hydraulic brake to
reach the proper pressures after actuation to
avoid false alarms.
Brake Circuit J02032