Bendix Commercial Vehicle Systems EC-17 ANTILOCK TRACTION CONTROL4/10 - Manual (Page 6)

6
If the EC-17 ™ controller is programmed for traction control,
it contains the following outputs:
- A connection to the engine's electronic control module
allows the EC-17
™ controller to reduce engine torque under
certain circumstances.
- A traction dash light is connected to and controlled by
the EC-17
™ controller and serves as a means of advising
the driver of the condition of the traction control system.
- A connection to the traction solenoid (located in the
upper portion of the antilock traction relay valve (see Figure
3) is provided via a 2 pin Deutsch connector.
OPERATION - ANTILOCK (ABS)
PHILOSOPHY
The Bendix ® EC-17 ™ antilock system uses individual
sensors, modulators and an electronic controller to control
the four vehicle wheel ends. By monitoring the deceleration
rate during braking, and subsequently adjusting the brake
application pressure at each wheel, the EC-17
™ controller
is able to improve braking between the vehicle tire and the
road surface it is on, while maintaining vehicle stability.
The rear axle brakes are controlled independently; therefore
brake application pressure at an individual wheel is adjusted
solely on the basis of its behavior on the road surface on
which it is traveling.
While each steering axle brake is under the control of an
individual modulator, the EC-17
™ controller does not treat
these brakes independently. The EC-17 ™ controller uses a
modified individual control philosophy for the steering axle
brakes. This is done in order to minimize "steering wheel
pull" in the event each wheel is traveling on a different road
surface (for example, ice close to the curb and a dry crown).
Essentially the EC-17
™ controller controls the braking force
differences between the two brakes.
The wheel on dry pavement is initially given less braking
force and is brought up to optimum during the stop, while
the wheel on ice attempts to maintain optimum braking
during the entire stop.
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 lock first. 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 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.
NON ANTILOCK BRAKE APPLICATION
During normal braking, air pressure from the brake valve
enters the control port of the service relay valve. 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-17
™ controller
does not initiate any corrective action and the vehicle comes
to a stop in a normal fashion.
ANTILOCK BRAKE APPLICATION
If a service brake application is made and the wheel speed
sensors detect an impending wheel lockup, the EC-17
™
controller will immediately begin modification of the brake
application using the antilock modulator(s) at the affected
wheel(s). Solenoid valves contained in the modulator (hold
and exhaust) are energized and de-energized by the
EC-17
™ controller in order to modify the brake application.
When a solenoid coil is energized, its shuttle moves.
Depending upon the function of the specific 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-17
™ controller. By opening and closing the
solenoid valves in the appropriate modulator, the EC-17 ™
controller is actually simulating what drivers do when they
"pump the brakes". It must be remembered however that
unlike the driver, the EC-17
™ controller is able to "pump"
each brake on the vehicle independently and with far greater
speed and accuracy.
OPERATION - TRACTION CONTROL (ATC)
PHILOSOPHY
Traction control is a natural extension of antilock. Just as
antilock helps vehicle control and stability during braking,
traction control helps during vehicle acceleration. The wheel
speed sensors not only detect rapid decreases in wheel
speed for antilock but also detect unreasonably high
increases for traction control. With traction control, a
spinning wheel is instantly detected and compared with the
other wheels on the vehicle, both front and rear. Two methods
are used to control wheel spin, torque limiting and differential
braking. Both methods could be configured within the ECU
independently or together. On units manufactured after mid-
year 2000, only torque limiting can be configured
independently. On units manufactured after mid-year 2000
it will also be necessary that the J1922 or J1939 serial link
protocol communicate the vehicle throttle position or the
ATC will not function.
With traction control, a spinning wheel is instantly detected
and compared with the other wheels on the vehicle, both
front and rear. Two different methods are used to control
wheel spin; torque limiting and differential braking. Depending
upon vehicle type, speed and road (surface) condition, each