BENDIX SD-13-4788 Manual de usuario descargar pdf (Pagina 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

modiﬁ ed 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 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 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 modiﬁ cation 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 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-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 conﬁ gured

within the ECU independently or together. On units

manufactured after mid-year 2000, only torque limiting can

be conﬁ gured 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)

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