Page 36 - Understanding Automotive Electronics

2735 | CH 1 Page 23 Tuesday, March 10, 1998 10:52 AM

AUTOMOTIVE FUNDAMENTALS 1

BRAKES

Brakes are as basic to the automobile as the engine drivetrain system and
are responsible for slowing and stopping the vehicle. Most of the kinetic energy
of the car is dissipated by the brakes during deceleration and stopping (with the
other contributions coming from aerodynamic drag and tire rolling resistance).
There are two major types of automotive brakes: drum and disk brakes.
Drum brakes are an extension of the type of brakes used on early cars and
horsedrawn wagons. Increasingly, automobile manufacturers are using disk
brakes. Consequently, it is this type that we discuss here.
Disk brakes are illustrated in Figure 1.16. A flat disk is attached to each
wheel and rotates with it as the car moves. A wheel cylinder assembly (often
called a caliper) is connected to the axle assembly. A pair of pistons having
brakepad material are mounted in the caliper assembly and are close to the
disk.
Under normal driving conditions, the pads are not in contact with the
disk, and the disk is free to rotate. When the brake pedal is depressed, hydraulic
pressure is applied through the brake fluid to force the brake pads against the
disk. The braking force that decelerates the car results from friction between the
disk and the pads.

Figure 1.16
Disk Brake System

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 23