Bendix Commercial Vehicle Systems EC-14 ANTILOCK CONTROLLER 5/04 - Manual (Page 6)

6
Rear Axle Brakes - The vehicle’s rear axle brakes are
controlled by the MC-14
™ modulator controller (EC-14 ™
controller and M-12 ™ modulator). Like the standard service
relay valve it replaces, the M-12 ™ modulator delivers brake
application pressure to the service chambers on the rear
axle equally. Two speed sensors on the rear axle “report”
changes in acceleration and deceleration to the EC-14
™
controller. If required, the EC-14 ™ controller adjusts the
application pressure to the rear axle service brakes, via the
M-12
™ modulator, based on the wheel behavior “reported”
to it by the speed sensors. In the case of vehicles equipped
with tandem rear axles (6x2, 6x4), the speed sensors are
installed on the axle that is most likely to lose traction first.
The MC-14
™ modulator controller controls all service brakes
on the tandem equally.
The EC-14 ™ controller utilizes a “Select Smart” brake control
philosophy for the rear axle brakes. This means that the
EC-14
™ controller will initially adjust application pressure to
all rear axle service chambers based on the speed information
from the first wheel to approach a locked condition. The
initial pressure adjustment will attempt to prevent all wheels
on the axle(s) from locking. If a substantial braking difference
is detected between the two wheels on the axle equipped
with the speed sensors, the EC-14
™ controller will override
the first air pressure adjustment and allow one wheel to
lock. Both wheels including the locked wheel will continue
to be monitored for speed and braking difference changes
that would require pressure adjustments.
Steering Axle Brakes - The steering axle brakes are
controlled by the EC-14
™ controller and the M-21 ™ or M-22 ™
modulator. Although connected to the EC-14 ™ controller via
a wire harness, the M-21 ™ or M-22 ™ modulator is not an
integral part of the MC-14 ™ modulator controller assembly.
Brake application air passes through the M-21 ™ or M-22 ™
modulator on its way to the front axle service chambers
from the foot valve.
Two speed sensors on the front axle “report” changes in
acceleration and deceleration to the EC-14
™ controller.
The EC-14 ™ controller uses a “Select Low” brake control
philosophy for the front axle brakes. It will attempt to prevent
wheel lock by adjusting application pressure to both front
axle service chambers based on the speed information from
the first wheel to approach a locked condition. The M-21
™ or
M-22 ™ modulator provides the EC-14 ™ controller with the
means of adjusting front axle service application pressure
when required.
NON-ANTILOCK BRAKE APPLICATION
During normal braking, the brake valve simultaneously
delivers air to the control port of the M-12
™ modulator on the
rear axle(s) as well as to and through the M-21 ™ or M-22 ™
modulator on the front axle. The M-12 ™ modulator functions
the same as standard service relay valve and applies air to
the rear axle service brakes. Because the M-21
™ or M-22 ™
modulator does not have a relay valve function, service air
passes through it to a quick release valve and from there to
the front axle service chambers. The service brakes are thus
applied.
If the speed sensors do not detect an impending wheel lock
up, the EC-14
™ controller does not initiate any corrective
action and the vehicle comes to a stop in a normal fashion.
ANTILOCK CONTROLLED BRAKE
APPLICATION - SYSTEM FULLY OPERATIONAL
If a service brake application is made and the speed sensors
detect an impending wheel lockup on an axle, the EC-14
™
controller will immediately begin modification of the brake
application using the antilock modulator(s) at the affected
axle(s).
Solenoid valves contained in the modulator are energized
and de energized by the EC-14
™ controller in order to modify
the brake application. When a solenoid coil is energized its
shuttle moves, and depending upon the function of the specific
solenoid, it either opens or closes, thereby causing the
exhaust or re-application of air pressure to the brake chamber.
The solenoids in either the M-12
™ or M-21 ™ modulator are
controlled independently by the EC-14 ™ controller. By
opening and closing the solenoid valves in the appropriate
modulator, the EC-14
™ controller is actually simulating what
the driver does when he “pumps the brakes”.
It must be remembered however that unlike the driver, the
EC-14
™ controller is able to “pump” brakes on either the
front or rear axle(s), or both, independently and with far greater
speed and accuracy.
ANTILOCK SYSTEM OPERATION -
COMPONENT FAULT STRATEGY
The Bendix ® EC-14 ™ controller handles equipment faults
using a conservative fail-safe philosophy. Any single electrical
problem with a component devoted to antilock braking,
results in simultaneous illumination of the antilock condition
lamp on the dash and a troubleshooting LED on the EC-14
™
controller. Depending upon the type of problem and its
position of occurrence the EC-14
™ controller can continue
antilock function at a lower performance level, disable all of
the antilock on the vehicle or only a portion. When antilock
is disabled, the brakes on the affected axle(s) revert to
standard air braking.
Complete antilock system shut down will occur if:
•
Electrical power is below or above the 10 to 17 volt
operating range.
•
A controller fault is detected.
•
Two or more faults, regardless of where, are detected.