Chevrolet Light Duty Truck 1973, Руководство по обслуживанию

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6 T - 2 6 E M I S S I O N C O N T R O L S Y S T E M S
THEORY OF OPERATION
The Air Injector Reactor (A.I.R.) system (Fig. 5f) is an
exhaust emission system that is used to actually burn the
unburned portion of the exhaust gases to reduce it’s
hydrocarbon and carbon monoxide content. The system
is primarily composed of an air pump, diverter valve,
check valve(s), combustion pipe assemblies and connect­
ing hoses and fittings.
Air is drawn into the air pump, where it is compressed.
The compressed air is fed out of the pump through the
diverter valve and check valve (operation of these valves
will be discussed in later paragraphs) into the
combustion pipe assemblies (Fig.
6
f). The combustion
pipes route the compressed air into the exhaust
manifolds (V
-8
engines) or cylinder head exhaust ports
(L
-6
engines). When this compressed air mixes with the
hot exhaust gases in the cylinder head or exhaust
manifold, combustion results. This combustion process
burns most of the un burned hydrocarbon and carbon
monoxide in the exhaust before it leaves the vehicle
through the exhaust system. Thus, the exhaust emitted at
the tail pipe is low in hydrocarbon and carbon monoxide
content.
Burning the unburned portion of the exhaust gases is
much like fanning dying embers. When the gases leave
the cylinders, they are extremely hot and still
inflammable if supplied with the other element of
combustion - namely oxygen. This oxygen is supplied in
the air being supplied by the pump (Fig. 7f). If oxygen is
not supplied to this mixture when it first leaves the
cylinders, the gases cool down to a non-inflammable
mixture by the time they enter the exhaust system.
One problem with such a system, however, is that during
engine overrun or deceleration, the exhaust gases in the
exhaust valve area are overly rich with fuel vapors. If
this system was allowed to operate under this condition,
a sizable backfire would result as soon as the fresh air
from the pump mixed with the overly rich vapor. To
Fig. 5f—Schematic of A.I.R. System
eliminate this possibility, a diverter valve has been
incorporated into the system.
The diverter valve is triggered by sharp rises in vacuum -
the vacuum signal is taken from just beneath the
carburetor throttle plate. When a sharp rise in vacuum is
sensed, as during engine overrun, the diverter valve
exhausts the air pump out-put into the atmosphere (Fig.
8
f). Since the compressed air from air pump never
reaches the air manifolds - no backfire occurs.
REAR COVER
DRIVE HUB ROTOR SHAFT
Fig. 7f—Air Injection Pump
LIGHT DUTY TRUCK SERVICE MANUAL