Copyright by Goodheart-Willcox Co., Inc.
336 Auto Engine Repair
Open
17 psi (120 kPa)
Move
Disconnect
Plug
Pressure
gauge
Figure 16-11. To check the waste gate for proper operation,
disconnect the pressure hose from the waste gate. Then, apply
the specified pressure to the waste gate. The lever arm and
valve should move. (Toyota)
Intercoolers are relatively easy to service. Figure 16-12
shows how to replace an air-to-air intercooler on a
turbocharged engine. Simply remove covers to gain access
to the intercooler. Then, remove hoses and mounting bolts.
Avoid hitting and damaging the intercooler during
installation. They are often made of aluminum and can be
dented and damaged easily.
Supercharger Construction
A supercharger for a passenger vehicle is a small
unit mounted on the top of the engine intake manifold,
Figure 16-13. It is usually belt driven off of the engine crank-
shaft pulley. Some superchargers have an electromagnetic
clutch, similar to the clutch on an air conditioning compres-
sor. This allows the supercharger to be turned on and off.
However, most superchargers are direct drive without an
electromagnetic clutch. A supercharger normally consists of:
Housing.
Rotors.
Timing gears.
Extension housing.
Drive pulley.
The supercharger housing is the large aluminum enclo-
sure for the rotors, rotor bearings, and drive gears. The inside
of the housing is precision machined to form airflow cham-
bers of equal size. The supercharger housing is normally
bolted to the intake manifold. The throttle body is mounted
at the inlet of the supercharger, as shown in Figure 16-13.
The supercharger rotors are meshing, twisted blades
or fans that spin to produce pressure inside the supercharger
housing. The rotors fit precisely in the supercharger housing
and are supported by sealed ball or needle bearings. Refer
to Figure 16-14.
Supercharger timing gears keep the two rotors timed
and spinning at the same speed. The timing gears are
attached to the rotors and are enclosed in the gear case,
which is formed as part of the supercharger housing. One
timing gear is driven by the drive pulley; the other is driven
by the first timing gear. The rotor gears operate in a bath of
oil. A small reservoir is formed into the front of the super-
charger housing. As the timing gears spin, they are splash
lubricated to prevent wear on the gear teeth.
The supercharger extension housing is bolted to the
front of the supercharger housing. It encloses a shaft that
connects one of the supercharger timing gears to the drive
pulley. It also contains a large, sealed bearing for the drive
pulley. See Figure 16-14.
The supercharger drive pulley is connected to one
of the timing gears by the shaft, which is inside the super-
charger extension housing. The drive pulley draws power
from the crankshaft through a large serpentine belt.
Supercharger Bypass Valve
A supercharger bypass valve is used to improve
engine efficiency by only providing maximum boost when
needed. Figure 16-15A shows a schematic for a typical
supercharger bypass circuit.
Under normal cruising conditions (low load), the
bypass valve is held open to allow boost pressure to flow
back up into the intake air. See Figure 16-15B. This reduc-
es boost pressure and parasitic pumping losses to improve
fuel economy.
When the driver presses on the accelerator pedal
for full power and rapid acceleration, the bypass valve
closes. All boost pressure flows into the engine. See
Figure 16-15C.
Supercharger Operation
When the accelerator pedal is pushed to the floor
for passing or getting up to highway speed, the super-
charger spins faster to provide more boost. If equipped
with an electromagnetic clutch, a switch sends power to
the electro magnetic clutch on the supercharger pulley.
This engages the supercharger and the rotors spin. Engine
power is instantly increased.
Most superchargers used on production vehicles
provide 4 psi to 10 psi (30 kPa to 70 kPa) of boost. Larger
units that provide much more boost are used on racing
engines and diesel trucks. The supercharger normally
uses two rotors that compress air entering the engine. This
pressurized air is fed into the intake manifold where it is
mixed with fuel before being pulled into the combustion
chamber.
Supercharging has the advantage of instant air pressure
increase on demand. With a turbocharger, there is a slight
delay in pressure and power increase (turbo lag) as the unit
builds up speed. This delay does not occur with a super-
charger since it is driven by the crankshaft.