Turbocharger: Description and Operation

Fig. 1 Turbocharger assembly (Typical):

Fig. 16 Turbocharger system schematic. V6-231:

TURBOCHARGER
The turbocharger, Fig. 15, is used to increase engine power on a demand basis, therefore allowing a smaller, more economical engine to be used. The turbocharged V6-231 is available with either two or four barrel carburetion on 1982-83 models and with sequential port fuel injection on 1984-87 models.
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 gasses enters the engine exhaust system and is directed through the turbocharger turbine housing, Fig. 16. 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, Fig. 16. 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 allows a portion of the exhaust gas to bypass the turbine wheel, thereby not increasing turbine speed. On 1982-83 models, the wastegate is operated by a spring loaded diaphragm device sensing the pressure differential across the compressor. When intake manifold pressure reaches a set value above ambient pressure, the wastegate begins to bypass the exhaust gas. On 1984-87 models, 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.