Turbocharger System: Operation

Fig 1: Turbocharger Components - Typical

Courtesy of DAIMLERCHRYSLER CORP.

The exhaust gases of the engine are directed through the exhaust manifold, into the turbine housing, then onto the turbine wheel. See Fig 1. Exhaust gas flow energy drives the turbine, which in turn drives a centrifugal compressor that compresses the inlet air, and forces the air into the engine through the charge air cooler and plumbing. Since heat is a by-product of this compression, the air must pass through a charge air cooler to cool the incoming air and maintain power and efficiency.

The charge pressure is controlled by varying the position of the guide vanes. See Fig 1. The control linkage of the boost pressure actuator rotates the adjusting ring inside the turbine housing. See Fig 1. As a result, all the guide vanes meshed within the rotor ring, are also rotated to their appropriate position. See Fig 1.

Fig 2: Boost Pressure Solenoid

Courtesy of DAIMLERCHRYSLER CORP.

The boost pressure actuator is vacuum driven by the boost pressure solenoid. The boost pressure solenoid is electronically controlled by a pulse width modulated signal from the ECM. There is also a vacuum reservoir solenoid that closes and allows vacuum to the actuator or vents the vacuum to the atmosphere. See Fig 2.

Engine vacuum is supplied by the internal mechanical vacuum pump. Vacuum for the turbocharger actuator operation is supplied from the tee at the power brake booster. Vacuum is supplied to the boost pressure reservoir. The reservoir supples vacuum to the reservoir solenoid. The solenoid supplies vacuum to the booster solenoid, and the boost solenoid supplies vacuum to the actuator. When the engine is running battery positive voltage is supplied to the reservoir solenoid. The solenoid closes and allows vacuum to the boost pressure solenoid which modulates it's operation in accordance to the pulse width signal supplied by the ECM. The boost pressure solenoid supplies vacuum to the actuator or removes to atmosphere through the filter. Once the ignition is turned off, the reservoir solenoid closes to prevent vacuum reservoir bleed down.

Fig 3: Low RPM Operation

Courtesy of DAIMLERCHRYSLER CORP.

At low speeds, the flow cross-section is reduced by closing the guide vanes. The exhaust gas flow velocity through the turbine is the higher so the turbine turns at a higher speed. In addition, the exhaust gas flow is directed at the outer ends of the turbine blades. This generates more leverage and thus, the charge pressure rises. See Fig 3.

Fig 4: High RPM Operation

Courtesy of DAIMLERCHRYSLER CORP.

At high engine speeds the guide vanes are increasingly opened and the flow cross-section is thus enlarged, as a result of which the speed of the turbocharger reduces and the charge pressure drops. See Fig 4.