Turbocharger (G2006270): Operation: Turbocharger

The turbine wheel of the turbocharger uses the exhaust gases from the engine to drive the compressor wheel. The compressor wheel draws in fresh air which is supplied to the engine cylinders in a compressed form.

The Variable Geometry Turbocharger (VGT) - primary turbocharger allows the optimum inlet geometry (inlet area and flow angle) to be used over a wide range of engine operating conditions. This allows a rapid speed of response and higher boost pressures at low engine speeds. The variable vane angle determines both the inlet area as well as the flow angle, as controlled by the Powertrain Control Module (PCM). The variable vanes allow efficient use of the exhaust gas energy which in turn improves turbocharger and engine efficiency.

Principles of Variable Vane Operation 

The variable vanes in the primary turbocharger are controlled by the Powertrain Control Module (PCM). The PCM controls the Variable Geometry Turbocharger (VGT) vane actuator attached to the primary turbocharger. The VGT vane actuator is used to adjust the pitch angle of the vanes by rotating the turbine housing. The VGT vane actuator also provides the PCM with a feedback signal to determine the pitch angle of the vanes.

The variable vanes in the primary turbocharger improve the exhaust gas power transfer to the turbine wheel which in turn drives the compressor wheel. At low engine speeds this greatly assists the increase in turbocharger boost pressure.

As engine speed, and therefore the exhaust gas velocity increases, the vanes are opened. The amount of opening is determined by the PCM to make sure that the power transfer from the turbine wheel to the compressor wheel is within the turbocharger speed and boost pressure requirements.

At high engine speed and exhaust gas flow, the PCM increases the vane opening to avoid overspeed of the turbines and provide a smooth high speed operation. At this point the dual mode boosting system comes into effect by utilizing the secondary turbocharger.