Saab 1987 900 - Turbocharger and APC System

46 Technical description
III. Evaporative emission
control system
A sea l ed fuel system is us ed to pr event the
emission in to the atmosphere of vapors
from th e stored gasoline supply. Evapora-
ted fuel is vented from the fuel system to the
storage canister which is connected to the
throttle housing. The evaporated fu el is
purged from the storage canister a nd bur-
ned by the engine when it is running.
7
1 Fue l tank
2 Fue l tank vent
lines
3 Ventilation line to
storage canister
4 Inlet air
9
5 Storage canister
6 Inlet air a nd gas
vapors
7 Inlet manifold
8 Check valv e
9 Rollover valve
Turbocharger and APC
system with intercooler
Turbo models are equipp ed with a turbo-
charger , intercooler and Automatic Perfor-
mance Control (APC) system.
Turbocharger
The turbocharger is an exhaust dr iven com-
pressor that increases the flow a nd pressure
ofthe air ent er ing the cylinders. This allows
induction and burning of a larg er fuel
charge ther e by increasing power output
ov er that of a conventional engine. Being
driv en by the flow of exhaust gas es, the
speed of th e turboch a rger and, th erefore,
th e charging pr ess ur e, are proportional to
the speed and load of the en gine. A charge
pressure regulator (wast egate), which is
regulat ed by an electrically modulat ed
pressure signal from the APC sys tem, con -
trols the flow of ex haust gases to th e turbi-
ne. Turbocharg ed engines are equipped
with an engine oil cooler that is loc at ed at
the lower left of the radiator. The impeller
shaft b ea ring actually flo ats on a thin film
of engine oil circulated through the turboc-
harger housing by the engine oil pump.
Maintaining a cl ea n oil supply is therefore
important to the service lif e ofthe unit.
APe system
The APC system consists of simple electro-
nic components. A knock det ect or (1) on
the engine block senses the onset an d
degree of engine knock and transmits an
electronic signal to the control unit (3)
which also receives a signal from the inlet
manifold pr ess ur e transducer (2) and from
the ignition system (engine rpm). The data
IS processed by the control unit (3) which
transmits a signal to a solenoid valve (4)
that modulat es the control . pr ess ur e to the
1 APCKnock
detector
2 APC Pressure
transducer
3 APC Electrical
control unit
4 APC Solenoid valve
5 RPM signal from
ignition system
6 Turbocharger
7 Wastegate (Charge
Pressure
Regulator)
8 Wast eg ate
actuator
9 Overpressure
sa fety switch
10 Inlet air flow
11 Exhaust (to
catalytic converter
12 Bypass valve
13 Inter co oler
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