BENDIX MC-12 MODULATOR CONTROLLER ASSY Průvodce řešením problémů stáhnout pdf (Strana 21)

More info: visit www.bendix.com 1-800-AIR-BRAKE (1-800-247-2725)

The foundation brake is the actual braking mechanism

located at each end of the axle that provides the

primary retardation for controlling vehicle speeds.

It generally consists of an air service and/or spring

brake chamber, a mechanical brake mechanism and

friction material.

Cam Actuated Drum Brakes

In a cam type foundation drum brake, the pneumatic

system is linked by an air line to the air service and/or

spring brake chamber, which is then connected to the

arm of a slack adjuster by a push rod and clevis. The

slack adjuster is installed on the spline of the forged

brake cam shaft. The slack adjuster acts as a lever,

converting linear force of the chamber push rod into a

torsional force needed to apply the brakes.

When torque is applied to the cam shaft, the “S” shape

on one end of the cam spreads the brake shoes,

forcing the brake lining into contact with the brake

drum, therefore retarding and/or stopping the vehicle.

Cam brakes are offered in various drum diameters

to meet vehicle braking requirements, with the most

commonly encountered being the 16½ inch version.

The cam brake has a “leading-trailing” shoe design

with one or more ﬁ xed anchor points for the shoes,

opposite the cam end of the shoe.

The structure of cam actuated brakes generally

consists of stamped steel brake shoes and spiders

(torque plates) for standard duty applications, and

cast shoes and spiders for heavy duty applications.

S-Cam Brake Linings

When cam actuated drum brakes are applied, the

friction material contacts the brake drum. The friction

between the lining and drum effectively converts the

kinetic energy of the vehicle into thermal energy,

heating up the brake drum and lining. The friction

material used in the brake must have the capability

of withstanding the heat until dissipated. It takes the

right combination of ingredients to provide all the

desirable characteristics: including having a torque

output sufﬁ cient to stop the vehicle, long lining life,

long drum life, and noise reduction.

All friction material is identiﬁ ed by stenciled codes on its

edge. These codes consist of the name or brand of the

manufacturer, the formula identiﬁ cation, the speciﬁ c

part number, and usually two letters designating the

lining’s general friction level (examples: EF, FG).

It should be noted that these stenciled letters are

not considered to be accurate enough for choosing

replacement linings. Either genuine original equipment

linings should be used or an approved material with

direct performance comparison.

Selecting the ideal friction material also is dependent

upon how the driver uses the brakes, the terrain,

vehicle load, etc. The various formulations of material

are designed to meet the different needs of these

conditions. For example, a vehicle performing heavy

duty operations on rugged terrain may beneﬁ t by using

Foundation Brakes

Axle

Brake Chamber

Brake

Drum

Shoe

CAM

Automatic

Slack Adjuster

S-CAM BRAKE

Spider

Friction Material

Foundation Brakes: S-Cam and Air Disc

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