TM 5-3895-382-24
The propel brake interlock performs two functions. It prevents
the operator from propelling the machine while the parking
brake is applied and it also provides for controlled propelling
when the parking button is released.
The main components of the propel brake interlock are:
parking brake fuse (3), neutral start relay #2 (NSR2)(5), neutral
start relay #1 (NSR1)(6), brake relay #1 (BR1)(7), brake relay
#2 (BR2)(8), parking brake switch (9), parking brake solenoid
(11), front propel pump neutralizer valve (14), rear propel pump
neutralizer valve (15) and neutral start switch (16).
Parking brake solenoid (11), front propel pump neutralizer
valve (14) and rear propel pump neutralizer valve (15) receive
electrical power from brake relay #2 (BR2)(8). This allows
parking brake solenoid (11) to move the two-position brake
valve, sending non-filtered charge pressure oil to the parking
brake in the front propel motor. In order for this to be
accomplished, the following three conditions must be met:
First, key start switch (17) must be in the ON position. This
provides electrical power to parking brake switch (9) from main
relay (2) and parking brake fuse (3).
Second, the propel control lever must be in the neutral
position. With the propel control lever in this position, neutral
start relay #2 NSR2 (5) is energized, breaking continuity from
neutral start relay #2 (NSR2)(5) to brake relay #2 (BR2)(8).
Third, parking brake switch (9) must be released. When this is
done and with the propel control lever in the neutral position,
electrical power to the brake relay #1 (BR1)(7) and brake relay
#2 (BR2)(8) is interrupted and electrical power is supplied to
parking brake solenoid (11), front propel pump neutralizer vale
(14) and rear propel pump neutralizer vale (15).
This in turn allows both propel pumps to go on stroke when the
propel control lever is moved forward or reversed and allows
unfiltered charge pressure oil to flow to the parking brake in the
front propel motor. The charge pressure works against the
applied spring pressure, releasing the parking brake.
If an operator would try to release the parking brake with the
propel control lever in the forward or reverse position, the
machine would not move. With the propel control lever not in
the neutral position, neutral start relay #2 (NSR2)(5) is not
energized. Electrical power is sent from neutral star relay #2
(NSR2)(5) to brake relay #2 (BR2)(8). Due to the electrical
logic of brake relay #2 (BR2)(8), this would continue to supply
the coils of brake relay #1 (BR1)(7) and brake relay #2
(BR2)(8) with electrical power even if parking brake switch (9)
is released. This prevents electrical power from being supplied
to parking brake solenoid (11), front propel pump neutralizer
valve (14) and rear propel pump neutralizer valve (15). This
provides a latching mechanism and prevents an operator from
propelling the machine until the propel control lever is brought
back to the neutral position. With the propel control lever in the
neutral position, the latching mechanism is eliminated and the
operator is allowed to operate and propel the machine.
11-27
