64 Auto Fundamentals
position. This reduces compression and increases
the size of the combustion chamber. At low
speeds, the head is positioned at 14:1 compression
ratio for best fuel economy. At higher speeds, the
compression is reduced to 8:1 to allow the super-
charger to force additional air into the cylinder
without causing knocking.
Experimental Engines
The search for better engines is never end-
ing. Many ideas have been tried and adopted,
others have failed. Currently, manufacturers are
experimenting with engines that can operate on
more than one type of fuel. Manufacturers are
also developing vehicles driven by electricity.
New Technologies
In addition to improving the operation and
effi ciency of traditional automotive engines,
many automakers are developing new tech-
nologies to achieve more-fuel-effi cient, cleaner-
running vehicles, including hybrid vehicles and
fuel cell vehicles. Hybrid vehicles are currently
being offered by several manufacturers. Fuel
cell vehicles are still in the experimental stages
but should be available in the near future.
Hybrid Vehicles
A hybrid vehicle uses two or more sources
of power. On most hybrid automobiles, the
power sources are an internal combustion
engine and at least one battery-operated motor-
generator. The two power sources are used in
combination or separately to reduce fuel con-
sumption. There are many variations in engine,
battery, and motor-generator layout. The fol-
lowing information is a general guide to hybrid
vehicle operation.
The engines in hybrid vehicles are simi-
lar to other automotive engines. Some gasoline
hybrids use Atkinson-cycle engines, which were
discussed earlier in this chapter. The hybrid
engine can be relatively small, and when extra
power is needed, the motor-generator assists the
engine in propelling the vehicle.
The motor-generator can propel the vehicle
and, when driven by the internal combustion
engine, can generate electricity to recharge the
hybrid battery. A hybrid vehicle can have as
many as three motor-generators, depending on
the design. They can be located between the
engine and the transmission or transaxle, inside
of the transmission or transaxle, or in the rear
axle or transfer case.
Hybrid batteries use much higher voltages
than a typical automotive vehicle battery. They
can produce between 200 to 600 volts. Their size
8:1
14:1
4°
4°
Figure 3-32.
This variable compression engine is shown in both
high and low compression modes. Note how the angle
between the upper and lower sections of the engine
changes to cause the change in compression.
Saab