Chapter 3 Engine Classifi cation, Parts Identifi cation 65
and power output create extra heat, which may
need to be removed by an external fan system.
Figure 3-33 shows the layout of a typical hybrid
vehicle with a single motor-generator and battery.
Most motor-generators operate on alter-
nating current (ac), while the hybrid batteries
deliver direct current (dc). Various devices are
used in a hybrid vehicle to convert dc to ac and
ac to dc, as well as to raise and lower system volt-
age. The vehicle’s drivetrain computer operates
these devices. Many hybrid accessories, such as
the power steering pump, coolant pump, and air
conditioner compressor, are driven by electric
motors instead of drive belts.
Hybrid vehicles can be full or mild types.
On a full hybrid, the motor-generator moves the
vehicle as long as the battery is charged above
a certain level. If the battery charge falls below
this level, the engine starts and recharges the
battery through the motor-generator. In some
designs, the engine can also move the vehicle
during heavy acceleration or when the vehicle is
traveling at cruising speeds.
In a mild hybrid, the internal combustion
engine moves the vehicle and operates to motor-
generator to recharge the battery. In this type
of hybrid, the engine shuts off when the vehicle
is coasting, braking, or stopped. Then, when
the driver presses the accelerator or releases
the brake pedal, motor-generator restarts the
engine. In some mild hybrids, the motor-gener-
ator assists the engine in propelling the vehicle
when extra power is needed.
Many vehicle hybrid systems have a
regenerative braking system. A regenerative
braking system converts vehicle motion into
electricity when the vehicle’s brakes are applied.
This electricity is directed to the battery to help
recharge it.
Some hybrid vehicles can be recharged from
the home electrical system or at charging stations
found in many cities. These are called plug-in
hybrids. Recharging the battery with household
current is more economical than recharging
with the vehicle engine. Fully recharging a plug-
in hybrid using 120-volt household current takes
about 12 hours. A transformer can be used to
raise charging voltage to 240 volts. 240-volt cur-
rent recharges the battery in as little as 4 hours.
All-Electric Vehicles
All-electric vehicles have a motor and
battery. They do not have an internal combus-
tion engine. The battery is recharged when the
vehicle is parked, either at home or at a charg-
ing station. The battery is partially recharged
by regenerative braking. All-electric vehicles
have a relatively short range of about 100 miles
(160 km). They may become more common as
the number of charging stations increases and
recharging times become shorter.
Fuel Cell Vehicles
Several manufacturers are working to
develop fuel cell vehicles. A fuel cell is a chemi-
cal device in which hydrogen and oxygen gases
are combined to form water. This chemical reac-
tion produces electrons. Enough electrons are
produced to supply the voltage that operates an
electric motor to move the vehicle. A fuel cell
vehicle must be refueled with hydrogen in the
same way current vehicles are refueled with
gasoline. A supercharger is used to pull the
hydrogen-oxygen mixture through the fuel cell.
An on-board computer controls the entire pro-
cess. See Figure 3-34. Future fuel cells may pro-
duce hydrogen by a reaction between water and
sodium borhydride, a common and inexpensive
ingredient commonly found in laundry detergents.
12-volt battery
Engine
Electric
motor
300-volt
battery pack
Transmission
Figure 3-33.
A hybrid vehicle uses both an internal combustion engine
and an electric motor for power. Note that this particular
hybrid uses a four-cylinder engine.
Ford Motor Co.