Brake System
The brake system produces friction to slow or stop the
vehicle. When the driver presses the brake pedal, fluid pres-
sure actuates a brake mechanism at each wheel. These
mechanisms force friction material (brake pads or shoes)
against metal discs or drums to slow wheel rotation.
Figure 1-25 shows the fundamental parts of a brake
system.
Accessory and Safety Systems
Common accessory systems include the air condi-
tioner, sound system, power seats, power windows, and
rear window defogger. Common safety systems include
seat belts, air bags, and security systems. See Figure 1-26.
Hybrid Vehicle
Most auto manufacturers now build and sell hybrid
vehicles. A hybrid vehicle uses two methods of propul-
sion—an internal combustion engine and a large electric
motor-generator—to help improve vehicle performance
(acceleration), increase fuel economy (gas mileage), and
reduce emissions (air pollution). See Figure 1-27.
The fundamental parts of a hybrid vehicle include:
• Motor-generator—device that can propel the
vehicle like a motor or produce electrical energy
like an alternator.
• High voltage cables—large diameter, insulated
conductors that carry voltage between the motor-
generator, hybrid control module, and battery
pack.
• Hybrid control module—high power electrical-
electronic circuits that manage the flow of electrical
energy through a vehicle’s electrical-mechanical
drive train.
• Hybrid battery pack—large set of battery cells
that can store huge amounts of electrical energy
and output high current and voltage to help propel
the vehicle.
• Internal combustion engine—gasoline or diesel
engine that propels the vehicle at cruising speeds
and drives the motor-generator.
During acceleration, hybrid vehicles rely on the
motor-generator for propulsion. Then, when the vehicle
reaches a specific speed (or the battery pack becomes dis-
charged), the internal combustion engine takes over. In
addition to propelling the vehicle, the engine also spins
the motor-generator’s armature. This causes the motor-
generator to produce electricity to recharge the battery
pack for the next vehicle acceleration cycle.
During braking, the rotational force of the vehicle’s
drive axles spins the motor-generator’s armature, causing
the motor-generator to produce electrical energy to
recharge the battery. This is known as regenerative
18 Section 1 Introduction to Automotive Technology
Figure 1-25. When the brake pedal is pressed, pressure is placed on a confined fluid. The fluid pressure transfers through the
system to operate the brakes. An emergency brake is a mechanical system that applies the rear wheel brakes. A—Complete system.
B—Close-up. (Cadillac, Nissan)
Master
cylinder
Brake booster
Emergency brake
Hydraulic
unit
Caliper
Rotor
or disc
Brake
pedal
Brake
lines
A B
Brake rotor
or disc
Wheel
Wheel
hub
Tire
Brake
caliper