Turbocharger: Description and Operation

Turbocharger System Description





Variable Vane Turbocharger Overview




1 - Turbocharger Vane Position Sensor
2 - Turbocharger Vane Position Control Solenoid Valve
3 - Turbocharger Vane Position Unison Ring
4 - Turbine Wheel
5 - Turbocharger Vanes
6 - Hydraulic Piston
7 - Cam

The turbocharger increases engine power by pumping compressed air into the combustion chambers, allowing a greater quantity of fuel to combust at the optimal air/fuel ratio. The turbine spins as exhaust gas flows out of the engine and over the turbine blades, and turns the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.

The ECM controls the turbocharger vanes. The vanes are used to vary the amount of boost pressure and can control the boost pressure independent of engine speed. The vanes mount to a unison ring which is rotated to change the vane angle. The ECM will vary the vane angle which adjusts the boost dependent upon the load requirements of the engine.

The turbocharger vanes are normally open when the engine is not under load. However, the ECM will often close the turbocharger vanes to create back pressure to drive exhaust gas through the Exhaust Gas Recirculation (EGR) valve as required. At extreme cold temperatures, the ECM may close the vanes at low load conditions in order to accelerate engine coolant heating.

The turbocharger is also utilized as a component of the exhaust brake system, if equipped. Under certain conditions, the ECM will automatically close the turbocharger vanes to build back pressure in the exhaust, which reduces engine speed and slows the vehicle without applying the brakes.

During regeneration, the ECM will vary the turbocharger vanes to assist with the exhaust system warm-up, and to maintain proper engine exhaust temperatures needed to properly regenerate the Diesel Exhaust Particulate Filter (DPF).

The turbocharger control system utilizes the following components:

Turbocharger Vane Position Control Solenoid Valve

The vane position control solenoid valve (2) works in conjunction with oil pressure to control the turbocharger vanes. The ECM uses a pulse width modulation on both control circuits to control the solenoid valve. The solenoid valve allows the engine oil pressure to move a piston. This piston rotates the unison ring, thus controlling the engine boost dependent upon engine load.

Turbocharger Vane Position Sensor

The ECM uses the turbocharger vane position sensor to monitor the turbocharger vane angle. The voltage is low when the vanes are open and high when the vanes are closed.