BENDIX MC-12 MODULATOR CONTROLLER ASSY Guia de Resolução de Problemas descarregar pdf (Página 58)

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FIGURE 16 - BRAKING FORCES-EFFECT OF SLACK

ADJUSTER ARM LENGTH

Torque On Brake

Camshaft 4000 Inch

Pounds With Slack

Adjuster Arm 4

Inches Long.

Torque On Brake

Camshaft 6000 Inch

Pounds With Slack

Adjuster Arm 6

Inches Long.

S-Cam and Air Disc Brakes

Braking Forces - Effect of Slack Adjuster Arm

Length

Figure 16 illustrates how the principles of leverage

apply when a brake chamber and slack adjuster

combination is being selected to meet specific

requirements.

With the same brake chamber force of 1,000 pounds,

the torque on the brake camshaft can be increased

from 4,000 inch pounds to 6,000 inch pounds merely

by using a slack adjuster with a 6” arm instead of one

with a 4” arm.

In an S-Cam foundation brake, the full range of braking

forces for any vehicle is provided by the use of different

sizes of brake chambers and slack adjusters.

A term which is used to express the relation of the

brake chamber size and slack adjuster arm length

is “AL” factor. The “AL” factor differs from torque or

turning moment in that only the variable factors which

determine the force are expressed. The reason for

this is that an air pressure of 60 pounds is generally

used in calculating air braking forces and therefore, is

considered constant. The length of the slack adjuster

lever arm and the size or effective area of the brake

chamber acting on the slack adjuster are the two

variables altered to meet braking requirements. The

product of the effective area of the brake chamber

and the length of the slack adjuster arm is expressed

as the “AL” factor, which, when multiplied by the 60

pounds air pressure used in making brake calculations,

determines the torque on the brake camshaft. As an

example: If a brake chamber having an effective area

of 16 square inches is acting on a slack adjuster having

an arm length of ﬁ ve inches, the “AL” factor is 80. The

actual torque on the brake camshaft is therefore the

“AL” factor (80) multiplied by the air pressure used in

making brake calculations (60), or 4,800 inch pounds.

Bendix Air Disc Brakes

Bendix Air Disc Brakes (ADB) are “ﬂ oating caliper”

pneumatic disc brakes for use as the foundation

braking on all axles of heavy commercial vehicles

and trailers. Air Disc Brakes are easier to service

than traditional S-Cam brakes. Air Disc Brakes are

available in models with or without spring brakes.

The function of the ADB is to convert the air pressure

applied when the driver applies the brakes into braking

force against the rotor on the vehicle wheel. This is

done by the application of air from the foot brake or

relay valve entering the brake chamber causing the

plate to move the push rod outwards. The push rod

exerts force on the lever (see Figure 17) and this

force is transferred and multiplied as it turns around

the eccentric bearing. The bearing and the connected

actuating beam move outward, overcoming the force

of the two return springs. The force is then transferred

to the two threaded tubes, tappets and ﬁ nally to the

inner and outer brake pads.

FIGURE 17 - AIR DISC BRAKE - CUT-AWAY VIEW

Lever

Rotor

Eccentric

Bearing

Inner Brake Pad

Outer

Brake

Pad

Actuating

Beam

Return Springs

Actuator Push Rod

Supply

Port

Diaphragm

Brake

Chamber

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 69 70

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