4
ANTILOCK OPERATION
GENERAL
See Figure 6.
The first four rows of this table show normal vehicle braking
where the PMV does not intervene. In the case of a
rapid, non-antilock release of the brakes (e.g. if the driver
releases the brakes after a severe brake application), the
Bendix
®
M-40QR
™
PMV assists the quick release of the
brakes by being the point at which the air is exhausted.
The final four rows of the table show the actions taken
during an antilock braking event.
If equipped with a Bendix
®
EC-60
™
(or later) advanced
controller, following the completion of the second round
of PMV & TCV Chuff Tests, the controller (if configured to
do so) will perform a test to cross-check the trailer PMV
operation with the vehicle stop lamps. If the trailer
PMV circuit is mis-wired (including the steer axle TCV),
the PMV will exhaust a large amount of air, or none at all.
OPERATION
Mode
Modulator
Type
Hold
Solenoid
State
Exhaust
Solenoid
State
Description
Normal Braking
Normal,
Non-Antilock,
Brake Application
HF and QR
De-energized De-energized
Air pressure supplied to the modulator exits
the modulator delivery port and flows to the
service brake chambers.
Non-Antilock
Hold
HF and QR
De-energized De-energized
When the desired air pressure is attained in
the service brake chambers, the air pressure
in the system levels off.
Normal,
Non-Antilock,
Relatively “slow”
Brake Release
HF and QR
De-energized De-energized
Air from the brake chambers moves back
through the modulator in the reverse
direction as it flowed during application.
Simultaneously, a small amount of air will
generally be expelled from the modulator
exhaust port.
Rapid,
Non-Antilock,
Exhaust
(e.g., the driver
releases the
brakes after a
severe brake
application)
QR
De-energized De-energized
The internal bias piston blocks air from the
brake chamber from moving back through the
modulator. Instead, all the air is exhausted
out the modulator exhaust port.
HF
De-energized De-energized
Air from the brake chambers moves back
through the modulator in the reverse
direction as it flowed during application.
Simultaneously, air will be expelled from the
modulator exhaust port.
Antilock Braking
Antilock Apply
HF and QR
De-energized De-energized
Air pressure supplied to the modulator exits
the modulator delivery port and flows to the
service brake chambers.
Antilock Exhaust
HF and QR
Energized
Energized
Air from the brake chambers exhausts
through the modulator exhaust port.
Antilock Hold
HF and QR
Energized
De-energized
The modulator prevents supply air from
passing through the modulator and, at the
same time, prevents air from the brake
chambers from exhausting.
Antilock
"Reapply"
HF and QR
De-energized De-energized
The modulator re-applies air to the brakes in
the same manner it did during a non-antilock
event.
Figure 6 - Bendix
®
M-40QR
™
& M-40HF
™
Modulators: Operational Modes
