Fuel Charging and Controls - Turbocharger

TURBOCHARGER

The 2-stage turbocharger assembly consists of the following components:
- Low-pressure turbocharger
- High-pressure turbocharger
- Turbocharger actuator

The 2-stage turbocharger assembly is an exhaust-driven centrifugal compressor. Its purpose is to increase power output by supplying compressed air to the engine. The internal components are oil and air cooled. Engine oil is circulated through the housings, which acts as a heat barrier between the hot turbine and the cold compressor. Sleeve-type bearings are lubricated by engine oil. Oil is pumped directly from the oil filter module, then circulated to each turbocharger housing and returned to the sump through the oil drains in the turbocharger pedestal. The 2-stage turbocharger assembly consists of a low-pressure and high-pressure turbocharger mounted in series.

The variable geometry turbocharger is electronically controlled by the turbocharger actuator, via the PCM through the controller area network (CAN). The turbocharger actuator controls intake manifold pressure. The high-pressure turbocharger uses a set of moveable vanes in the turbine housing to change the flow of the exhaust gases throughout the turbocharger. These vanes can be positioned to change the angle or direction and the velocity of flow to the turbine wheel, depending upon the conditions in which the engine is operating. As power demand increases, exhaust gas velocity increases in direct relation, as does intake manifold boost pressure. Conversely, as the flow of exhaust gas diminishes, intake manifold boost pressure also reduce at the same rate.

Vanes mounted around the internal circumference of the high-pressure turbine housing are connected to a unison ring. The unison ring links all the vanes together and when the unison ring moves, all the vanes move. The unison ring is moved by the turbocharger actuator and linkage. Turbocharger control is a closed-loop system using the exhaust pressure (EP) sensor to provide feedback to the PCM. In response to engine speed, engine load, manifold pressure and barometric pressure, the PCM controls the turbocharger actuator position to match manifold boost to the requirements of the engine.

Expanding exhaust gases drive the turbine shaft assembly to speeds over 100,000 rpm. Filtered air entering the low-pressure turbocharger compressor side of the turbocharger is compressed and delivered to the high-pressure turbocharger. The air entering the high-pressure turbocharger compressor side of the turbocharger is compressed and delivered to a charge air cooler (CAC). The very hot compressed air is cooled by the CAC, and then continues on to fill the intake manifold at a pressure higher than atmospheric pressure. Because considerably more air is forced into the intake manifold, the results are increased power, fuel efficiency and the ability to maintain power at higher altitudes.