Chapter 1 The Automobile 23
can energize the motor-generator to crank and
start the internal combustion engine. It can also
recharge the battery pack using electricity gen-
erated by the motor-generator. The HV power
cables connect all high-voltage components
together. Study Figure 1-26.
An internal combustion engine in a hybrid vehi-
cle must start up and propel the vehicle when the
HV battery becomes discharged from extended peri-
ods of driving. For example, if the hybrid has been
plugged into a home charger overnight, the hybrid
vehicle can be driven for over 50 miles (80 km) in
the all-electric mode, without the internal combus-
tion engine ever starting or running.
After the stored energy in the HV battery has been
depleted, the motor-generator will “fi re up” the gas
engine to spin the motor-generator’s armature. The
motor-generator will then produce enough elec-
tricity to help propel the vehicle and recharge the
battery pack while driving. By linking the running
engine crankshaft to the transmission input shaft,
the vehicle is propelled while the motor-generator is
spun by the engine to recharge the HV battery.
All hybrids use regenerative braking to convert the
kinetic energy of the vehicle into large amounts of
stored electrical energy. When the driver presses the
brake pedal, the vehicle’s drive axles rotate the motor-
generator. Since the large permanent magnet armature
shaft is diffi cult to turn, the “electrical/mechanical fric-
tion” inside the motor-generator helps slow the car
while also recharging the batteries. The conventional
hydraulic brake system has to do little or no work,
unless the brake pedal is suddenly pressed down hard.
In the Rearview Mirror
Early automobile manufacturers originated in vari-
ous ways. In many instances, they evolved from bicy-
cle makers, carriage and wagon makers, and other
types of industry. Early motorcars were similar to
horse-drawn carriages, but they were equipped with
noisy gasoline-powered engines, steam engines, or
electric motors and batteries. A single lever called
a tiller was used to steer the vehicle. Another hand
lever would apply “rawhide brake shoes” to rub on the
wagon wheels to slow the loud, self-propelled buggy!
Imagine driving one of these contraptions.
Wheel speed sensor
Hydraulic brake lines
Brake booster
Master cylinder
Brake caliper
Brake rotor
Figure 1-23. When the brake pedal is pressed, pressure is placed on a confi ned fl uid. The fl uid pressure transfers through the
system to operate the brake calipers. An emergency brake is a separate mechanical system that applies the rear wheel brakes
independent of the hydraulic brakes. (Mercedes-Benz)