User's Manual

5
FIGURE 5 - WS-20
™
WHEEL SPEED SENSORS
HUB ASSEMBLY
WS-20
™
SPEED
SENSOR
WS-20
™
ANGLED
SENSOR
EXCITER RING
(100) TOOTH
WS-20
™
STRAIGHT
SENSOR
PACKARD
CONNECTOR
DEUTSCH
CONNECTOR
In the case of vehicles equipped with tandem rear axles
(6x2, 6x4), the wheel speed sensors are installed at the
wheels on the axle that is most likely to lose traction fi rst.
A single modulator controls both curb side brakes on the
tandem, and another modulator controls both brakes on the
driver’s side of the tandem. With this arrangement of the
speed sensors and modulators, both brakes on one side of
the tandem are treated as one since they will most likely be
on the same type of road surface. (Refer to fi gure 2)
NON-ANTILOCK BRAKE APPLICATION
During normal braking, air pressure from the brake valve
enters the control port of the service relay valve (either an
antilock or standard relay). The service relay delivers air
to, and through, the antilock modulator located near the
braked wheel, and into the brake actuator. The service
brakes are thus applied. If the wheel sensors do not detect
an impending wheel lock up, the EC-15
™
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 wheel speed
sensors detect an impending wheel lockup, the EC-15
™
controller will immediately begin modifi cation of the brake
application using the antilock modulator(s) at the affected
wheel(s).
Solenoid valves contained in the modulator are energized
and de-energized by the EC-15
™
controller in order to modify
the brake application. When a solenoid coil is energized
its shuttle moves, and depending upon the function of the
specifi c solenoid, it either opens or closes, thereby causing
the exhaust or reapplication of air pressure to the brake
actuator. The solenoids in each modulator are controlled
independently by the EC-15
™
controller. By opening and
closing the solenoid valves in the appropriate modulator,
the EC-15
™
controller is actually simulating what the driver
does when he “pumps the brakes”. It must be remembered
however that unlike the driver, the EC-15
™
controller is able
to “pump” each brake on the vehicle independently and
with far greater speed and accuracy.