Copyright by Goodheart-Willcox Co., Inc.
Chapter 16 Turbocharging and Supercharging Systems 331
Bypass
valve
closed
Bypass
valve
open
Spring
holds
valve closed
Diaphragm
flexed
down
Sensor line
feeds
moderate
pressure to
diaphragm
Airflow
Airflow
Boost not
limited
Intercooler
Exhaust gasses Induction air
A
Intercooler
Exhaust gasses Induction air
B
Boost
pressure
limited
Figure 16-5. Waste gate operation. A—As long as boost
pressure is not too high, the waste gate remains closed and
all exhaust gasses are directed against the turbine wheel
blades. B—When boost reaches a preset level, the waste gate
is opened and some of the exhaust gasses are diverted from
the turbine wheel blades. (Saab)
Figure 16-6. A—An intercooler cools the air charge entering
the engine for increased horsepower. B—This is an air-to-
air intercooler unit used on a small-displacement, 4-cylinder
engine. (Saab, Ford)
Turbocharger
Intercooler
Hot air in
Airflow
Cool
air out
Engine intake
manifold
A
B
A turbocharger intercooler is an air-to-air or air-
to-liquid heat exchanger that cools the air entering the
engine. It is a radiator-like device mounted at the pressure
outlet of the turbocharger. See Figure 16-6. Turbocharged
engines often use an air-to-air intercooler. The intercooler
is mounted near the front of the engine compartment so
fresh outside air can flow through the intercooler fins.
In an air-to-air intercooler design, outside air flows
over and cools the fins and tubes of the intercooler. The
hot, compressed air from the turbocharger flows through
the intercooler. Heat from the compressed air is transferred
to the intercooler tubes and fins, and then to the outside air.
An air-to-liquid design works in the same way except a cool-
ant is used to cool the fins and tubes instead of outside air.
Computer-Controlled Turbocharging
In a computer-controlled turbocharging system, the
electronic control module (ECM) operates the waste gate
based on sensor signals, Figure 16-7. Several sensors, espe-
cially the knock sensor, speed sensor, and oxygen sensor,
provide data to the computer. The ECM output is sent to a