SUPERCHARGERS
A supercharger
is an air pump that increases engine power by pushing a denser air charge into the
combustion chamber. With more air and fuel, combustion produces more heat energy and
pressure to push the piston down in the cylinder. There are three basic types of
superchargers:
- Centrifugal
supercharger (fig. 5-39). The centrifugal
supercharger has an impeller equipped with curved vanes. As the engine drives the
impeller, it draws air into its center and throws it off at its rim. The air then is
pushed along the inside of the circular housing. The diameter of the housing gradually
increases to the outlet where the air is pushed out.
- Rotor
(Rootes) supercharger (fig. 5-40). The Rootes supercharger is of the
positive displacement type and consists of two rotors inside a housing. As the engine
drives the rotors, air is trapped between them and the housing. Air is then carried to the
outlet where it is discharged. The rotors and the housing in this type of supercharger
must maintain tight clearances and therefore are sensitive to dirt.
- Vane-type
supercharger (fig. 5-41). The vane-type
supercharger has an integral steel rotor and shaft, one end supported in the pump flange
and the other end in the cover, and revolves in the body, the bore of which is eccentric
to the rotor. Two sliding vanes are placed 180 degrees apart in slots in the rotor and are
pressed against the body bore by springs in the slots. When the shaft rotates, the vanes
pick up a charge of air at the inlet port, and it is carried around the body to the outlet
where the air is discharged. Pressure is produced by the wedging action of the air, as it
is forced toward the outlet port by the vane.
The term supercharger
generally refers to a blower driven by a belt, chain, or gears. Superchargers
are used on large diesel and racing engines.
The
supercharger raises the air pressure in the engine intake manifold. Then, when the intake
valves open, more air-fuel mixture (gasoline engine) or air (diesel engine) can flow into
the cylinders. An intercooler is used between the supercharger outlet and the engine to
cool the air and to increase power (cool charge of air carries more oxygen needed for
combustion).
A
supercharger will instantly produce increased pressure at low engine speed because it is
mechanically linked to the engine crankshaft. This low-speed power and instant throttle
response is desirable for passing and entering interstate highways. |
Figure
5-39.—Centrifugal supercharger.
Figure
5-40.—Rootes supercharger.
Figure
5-41.—Vane-type supercharger. |
