hope this helps
Turbocharger System Description
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1394251&evc=sm&pubid=437&cellId=133229&mspsdsubkey=3243#oth1-1394244">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. In a conventional turbo, the turbine (4) spins as exhaust gas flows out of the engine and over the turbine blades. This spins the compressor wheel at the other end of the turbine shaft, pumping more air into the intake system.
The turbocharger for this system has vane position control by the engine control module (ECM). The vanes (5) can be opened and closed to vary the amount of boost pressure. Thus, the boost pressure can be controlled independent of engine speed. There are 9 controllable vanes in this turbocharger. The vanes mount to a unison ring (3) that can be rotated to change the vane angle. When the engine is not under load, the vanes are open to minimize boost and exhaust back pressure. To increase boost when the engine load requires it, the vanes are commanded closed. The ECM will vary 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 ECM may also close the turbocharger vanes under exhaust braking conditions.
The turbocharger control system utilizes the following components:
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1394251&evc=sm&pubid=437&cellId=133229&mspsdsubkey=3243#ss1-1394251">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 solenoid valve uses 2 circuits; a control circuit and a low reference circuit. The engine control module (ECM) uses a pulse width modulation on the HI control circuit to control the solenoid valve. The ECM will control the solenoid valve to allow the engine oil pressure (EOP) to move a piston (6). This piston rotates the unison ring, thus controlling the engine boost dependant upon engine load.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1394251&evc=sm&pubid=437&cellId=133229&mspsdsubkey=3243#ss2-1394251">Turbocharger Vane Position Sensor
The vane position sensor (1) uses 3 circuits: a 5-volt reference circuit, a low reference circuit, and a signal circuit. The engine control module (ECM) provides the sensor with 5 volts on the 5-volt reference circuit and a ground on the low reference circuit. Movement of the sensor from the open vane position to the closed vane position provides the ECM with a signal voltage through the position sensor signal circuit that ranges from 1 volt with the turbocharger vanes open to 3.5 volts with the turbocharger vanes completely closed.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1394251&evc=sm&pubid=437&cellId=133229&mspsdsubkey=3243#ss3-1394251">Engine Control Module (ECM)
The engine control module (ECM) controls all turbocharger control functions. The ECM monitors information from various sensor inputs that include the following:
• The accelerator pedal position (APP) sensor
• The engine coolant temperature (ECT) sensor
• The mass airflow (MAF) sensor
• The intake air temperature (IAT) sensor
• The vehicle speed sensor (VSS)
• The transmission gear position or range information sensors
• The boost pressure sensor