Principles Of Operation

Turbocharger

Principles of Operation

The variable geometry turbocharger is electronically controlled by the turbocharger actuator, via the PCM through the Controller Area Network (CAN). The 2-stage turbocharger consists of a low-pressure and high-pressure turbocharger mounted in series. The unison ring is moved by the turbocharger actuator and linkage. 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 reduces at the same rate. 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.

When the key is placed in the ON position, the turbocharger actuator enters the self-test mode. This causes the turbocharger actuator linkage to cycle through the complete range of motion. If the turbocharger linkage cycles more than once, the turbocharger vanes are sticking and the turbocharger actuator is attempting to clear them. The turbocharger actuator will cycle the linkage until full movement of the linkage is achieved, or until the actuator self-test times out. If the self-test times out, the key must be placed in the OFF position for a minimum of 30 seconds to reset the turbocharger actuator.