Turbocharger: Description and Operation

Fig. 1 Turbocharger assembly (Typical):

The turbocharger, Fig. 1, is used to increase engine power on a demand basis, therefore allowing a smaller, more economical engine to be used. The Buick turbocharged V6-231/3.8L is available with sequential port fuel injection.
As engine load increases and the throttle opens, more air-fuel mixture is drawn into the combustion chambers. As the increased volume is burned, a larger volume of high energy exhaust gases enters the engine exhaust system and is directed through the turbocharger turbine housing, Some of the exhaust gas energy is used to increase the speed of the turbine wheel which is connected to the compressor wheel. The increased speed of the compressor wheel compresses the air-fuel mixture and delivers the compressed air-fuel mixture to the intake manifold. The high pressure in the intake manifold allows a denser charge to enter the combustion chambers, in turn developing more engine power during the combustion cycle.
The intake manifold pressure (Boost) is controlled to a maximum value by an exhaust gas bypass valve (Wastegate). The wastegate, when necessary, allows a portion of the exhaust gas to bypass the turbine wheel, thereby not increasing turbine speed. An electronic wastegate is used. In this system, a pulse width modulated solenoid has been positioned between the manifold and wastegate diaphragm. Information regarding air flow, engine RPM, transmission gear and detonation is collected and analyzed by the Electronic Control Module. If the engine will tolerate additional boost, the solenoid signals the wastegate accordingly. Inside the wastegate, the exhaust divert valve is normally closed, allowing boost pressure to rise until the mass air flow called for by the ECM is satisfied. When air flow reaches this level, the exhaust divert valve opens, allowing the exhaust gas to divert around the turbine and flow directly into the exhaust system.
All fuel mixture changes are made by the Sequential Fuel Injection (SFI) system.
An Electronic Spark Control System is used to retard ignition timing up to 20° to minimize detonation. A piezoelectric sensor transforms engine detonation vibrations directly into an electrical signal which is fed to the Electronic Control Module. The ECM then adjusts the spark accordingly. An electronic filter with integrated circuitry is also used to filter out vibrations not associated to pre-ignition or detonation.
On some models an intercooler is added to the turbocharger intake side to cool the incoming pressurized air. This resulted in higher horsepower from the same displacement engine.
Do not attempt to start a turbocharged engine when the lubrication system is dry, such as after an oil change or after a prolonged storage period turbocharger damage may occur. To prevent turbocharger damage, crank engine without starting until a steady oil pressure reading is obtained, then start engine in a normal manner.