Turbocharger And Charge Air Cooler (CAC) Systems

TURBOCHARGER AND CHARGE AIR COOLER (CAC) SYSTEMS

Turbocharger System
A turbocharger is an exhaust gas driven device used to increase the power output of an engine by increasing the mass of air entering the engine. The increased mass of air is achieved by the compressor increasing the pressure of the air entering the engine. With the increased air pressure, comes temperature, which drives the need for a CAC. This reduces the air temperature prior to entering the engine. The turbocharger uses exhaust gas energy which would otherwise be lost, increasing the efficiency of the system.

The engine uses twin turbochargers in a parallel arrangement with one turbocharger connected to each cylinder bank. This configuration improves engine responsiveness due to the reduced inertia of 2 small rotating assemblies in the place of a single large one, and still meets power requirements. This allows improved turbocharger package and better utilization of heat energy from the more compact exhaust manifolds. The compact design of the system allows for the catalysts to be moved very close to the turbo outlet for improved emissions.

The engine has controls in place for both the compressor and turbine stages. Two electronically controlled bypass valves are used to bypass the compressors on heavy throttle releases to prevent an unwanted air rush noise from the turbocharger. The bypass valves provide a connection between the high pressure and low pressure sides of the compressor. When boost is not necessary, the wastegate on the turbine side is opened to reduce exhaust gas flow through the turbine. The wastegate is controlled by the powertrain control module (PCM) through a pulse width modulated (PWM) turbocharger (TC) wastegate regulating valve solenoid. This valve applies a percentage of boost pressure to the wastegate to open the poppet style wastegate valve. The wastegates are coupled by having one control output from the TC wastegate regulating valve solenoid that drives both turbocharger wastegate actuators.

Turbocharger System:

Charge Air Cooler (CAC) System
The CAC system is designed to cool the intake air which has been heated by the turbocharger. The removal of heat from the pressurized air going into the CAC increases the air density which improves combustion efficiency, engine horsepower, and torque. The system consists of a CAC radiator in the grille, and tubing to interconnect these components. The CAC is positioned after the turbocharger directly in the flow of the intake air. As the heated air flows through the CAC, it is cooled by the airflow through the grille. The PCM maintains a desirable intake air temperature by monitoring the TCBP/CACT (located at the throttle body) and the MAP/IAT2 (located at the intake manifold) sensors.

Turbocharger Airflow Diagram: