1
®
SD-13-4762
Bendix
®
MC-12
™
Modulator Controller Assembly
FIGURE 1 - MC-12
™
MODULATOR CONTROLLER ASSY.
wheel end send wheel speed information to the EC-12
™
controller through the 14 pin connector. The sensors are
actually AC. generators. They house magnets, which create
a magnetic field. When the field is interrupted by an irregular
surface, such as a tone ring, AC. voltage is produced. The
frequency of voltage increases or decreases as wheel speed
increases or decreases.
During normal, non antilock operation, the M-12
™
modulator's
inlet solenoid is open, and the exhaust solenoid is closed.
In this condition, the M-12
™
modulator functions as a regular
R-12
™
relay valve. It receives a control signal from the foot
valve, which passes through the open inlet solenoid and
causes the brakes to apply in proportion to the amount of
control pressure.
If wheel lock up is impending, the EC-12
™
controller
commands the solenoids to modulate brake chamber
pressure on the axle(s) in which the system is installed.
The MC-12
™
modulator/controller receives its power from
the vehicle's stop light circuit (pin 4 on the standard seven
pin connector—red). The power enters the EC-12
™
controller
at pin A and (optionally) pin B from the auxiliary terminal
(blue wire) of the trailer’s 7 pin connector.
DESCRIPTION
The Bendix
®
MC-12
™
modulator trailer antilock system is
designed to improve vehicle stability by reducing wheel lock
up during aggressive braking. Like Bendix's tractor antilock,
the trailer system can provide single or tandem axle control.
The main component is nipple mounted to a reservoir, so
the system requires no special trailer modifications.
The trailer antilock system consists of the following: MC-12
™
modulator/controller, WS-20
™
wheel speed sensors,
electrical connectors and wiring. The MC-12
™
modulator is
the main component. It houses the EC-12
™
electronic
controller and the M-12
™
modulator, which contains solenoids
and a standard relay valve.
The EC-12
™
controller houses the electronics that regulate
the trailer antilock system and also incorporates a diagnostic
display window and a 14 pin connector.
The EC-12
™
controller mounts to the M-12
™
modulator with
four bolts, and it is internally connected to the solenoids by
a four pin connector. The solenoids are the interface between
the EC-12
™
controller electronic signals and the
pneumatically operated modulator. Sensors mounted at the
DIAGNOSTIC
DISPLAY
DIAGNOSTIC
DISPLAY
DELIVERY
PORTS
(2 VERTICAL
2
HORIZONTAL)
CONTROL
PORT
14 PIN
CONNECTOR
EC-12
™
CONTROLLER
M-12
™
MODULATOR
DELIVERY
PORTS
(4 VERTICAL)
