Turbocharger: Description and Operation

Turbocharger System Description




1 - Evaporative Emission (EVAP) Canister Vent Solenoid Valve
2 - EVAP Canister
3 - Non-Return Valve
4 - EVAP Canister Purge Solenoid Valve
5 - High Pressure Fuel Pump
6 - Camshaft Position (CMP) Actuator Solenoid
7 - Charge Air Bypass Valve Solenoid
8 - Turbocharger Bypass Valve
9 - Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
10 - Turbocharger Wastegate Actuator
11 - Turbocharger Wastegate Diaphragm Valve
12 - Camshaft Position (CMP) Sensor
13 - Ignition Coil/Module and Spark Plug
14 - Fuel Injector
15 - Charge Air Cooler (CAC)
16 - Intake Air Pressure and Temperature Sensor
17 - Throttle Body (TB)
18 - Manifold Absolute Pressure (MAP) Sensor
19 - Fuel Rail Pressure (FRP) Sensor
20 - Engine Coolant Temperature (ECT) Sensor
21 - Engine Exhaust Manifold
22 - Turbocharger
23 - Heated Oxygen Sensor (HO2S) 1 and 2
24 - Catalyst
25 - Crankshaft Position (CKP) Sensor
26 - Fuel Pump Module
27 - Accelerator Pedal
28 - Theft Deterrent
29 - Data Link Connector (DLC)
30 - Malfunction Indicator Lamp (MIL)
31 - GMLAN Serial Data
32 - Engine Control Module (ECM)

Turbocharger Description and Operation

A turbocharger (TC) is a compressor that is used to increase the power output of an engine by increasing the mass of the oxygen and therefore the fuel entering the engine. This BorgWarner(TM) dual-scroll turbocharger is mounted on the exhaust manifold and the lightweight turbine is driven by the waste energy generated by the flow of the exhaust gases. The turbine is connected by a shaft to the compressor which is mounted in the induction system of the engine. The compressor vanes compress the intake air above atmospheric pressure, thereby greatly increasing the density of the air entering the engine. The turbocharger is capable of producing up to 20 psi or 1.40 bar, of power-enhancing boost.

The TC incorporates a wastegate that is controlled by a pressure differential, that is determined by the engine control module (ECM) by means of a PWM solenoid, in order to regulate the pressure ratio of the compressor. A charge air bypass valve also controlled by the ECM by utilizing a remotely mounted solenoid is integrated into the unit to prevent compressor surging and damage from vibrations by opening during abrupt closed throttle conditions. When the bypass valve is open during closed throttle deceleration conditions, the bypass valve allows the air to recirculate in the turbocharger and maintain compressor speed. Within a calibrated range during the closed throttle event, or upon a wide open throttle command the bypass valve will then close to optimize turbo response.

The turbocharger is connected to the engine oiling system by a supply and drain tube and Mobil 1(TM) synthetic oil is installed at the factory. Synthetic oil is required for its friction-reducing capabilities and high-temperature performance. There is a cooling system circuit in the turbocharger that utilizes the engine coolant to further reduce operating temperatures.

Charge Air Cooler Description

The turbocharger is supported by an air-to-air charge air cooler (CAC) system, which uses fresh air drawn through a heat exchanger to reduce the temperature of the warmer compressed air forced through the intake system. Inlet air temperature can be reduced by up to 100°C (180°F), enhancing performance because cooler air is denser in oxygen and promotes optimal combustion. The CAC is connected to the turbocharger and to the throttle body by flexible ductwork that requires the use of special high torque fastening clamps. In order to prevent any type of air leak when servicing the ductwork, the tightening specifications and proper positioning of the clamps is critical, and must be strictly adhered to.

Benefits of Dual Cam Phasing

The camshafts of the Ecotec 2.0 liter turbocharged engine have camshaft position (CMP) sensors and CMP actuators that the ECM uses to accurately control the continuously variable intake and exhaust valve timing. This allows the combustion process to be optimized by the ECM to increase the response of the turbocharger, providing a more immediate feeling of power to the driver.

Benefits of Gasoline Direct Injection

In the Ecotec 2.0 liter turbocharged engine, the fuel is introduced directly into the combustion chamber during the intake stroke. As the piston approaches top-dead center, the mixture is ignited by the spark plug, thereby giving the name spark ignition direct injection (SIDI). SIDI allows the mixture to be leaner, with less fuel and more air at full power. SIDI also allows a slightly higher compression ratio, resulting in improved fuel consumption at part and full throttle.

The fact that the fuel is injected after the exhaust valve closes allows particularly high valve overlap values in certain engine operating ranges. This enhances the turbocharger response time. This would not be possible in a port fuel injection (PFI) engine due to the fact that unburned fuel would escape through the open exhaust valve.

Direct injection's precise fuel delivery enables more complete combustion which reduces emissions particularly on cold starts.

Electronic Vacuum Pump

The purpose of the electronic vacuum pump, if equipped, is to keep the vacuum in the brake booster at an acceptable level under various operating conditions. The ECM monitors the input signal from the brake booster pressure sensor. When the vacuum in the brake booster is not in an acceptable range the control module will command the relay ON that controls the vacuum pump.

Recommendations for Service

The turbocharger is designed so that it does not require any special maintenance, and inspection is limited to a few periodic procedures. To ensure that the turbocharger's lifetime corresponds to that of the engine, the following engine manufacturer's service instructions must be strictly adhered to:

* Oil and filter change intervals
* Maintaining the proper oil pressure
* Air filter change intervals
* Engine coolant change intervals
* Ignition system maintenance
* Injection system maintenance

The following causes are responsible for 90 percent of all turbocharger failures:

* Penetration of foreign bodies into the turbine or the compressor
* Dirt or contaminants in the oil
* Inadequate oil supply and/or pressure
* Higher than normal exhaust gas temperatures due to improper operation of the following:

- The ignition system
- The fuel injection system
- The exhaust system

These failures can be avoided by regular maintenance.