A turbocharged engine provides the following advantages over a conventional direct-induction engine:
- Higher volumetric efficiency.
- Increased engine power and torque
- Reduced fuel consumption
- Reducing exhaust toxicity
- Use of exhaust gas energy
- No dependence on altitude above sea level
- Limited periods of increased boost for immediate engine demand
A typical turbocharger driven by a rotating electronic actuator:
| Pos. | Spare part number | Name |
| A | - | Low engine crankshaft speed |
| B | - | Average engine crankshaft speed |
| C | - | Maximum engine speed |
| 1 | - | ECM |
| 2 | - | Rotary electronic actuator |
| 3 | - | Rotating adjustment ring |
| 4 | - | Adjustable paddles |
| 5 | - | Turbine wheel |
In response to signals from various sensors, the ECM controls the REA to operate a rotating adjustment ring. Moving the adjustment ring changes the angle of the adjustable vanes to divert the exhaust gas flow toward the inner center or outer edge of the turbine wheel.
The maximum position of the variable turbocharger vanes (fully open position) is also the default emergency position in the event of an electrical problem. REA will move the variable vanes to the fully open position to prevent engine damage due to increased boost pressure.
A - low engine crankshaft speed
At low engine speeds, the volume of exhaust gases leaving the engine is low. The vanes move to the closed position to direct the flow of exhaust gases to the outer edge of the turbine wheel. The closed position of the vanes reduces the flow capacity of the gases and increases the velocity of the gases going to the turbine wheel. The speed of the turbine wheel increases, correspondingly increasing the amount of charge air (boost pressure) supplied by the compressor.
B - Average engine crankshaft speed
As the engine speed and exhaust gas volume increase, the vanes move to an open position to direct the exhaust gas flow toward the center of the turbine wheel. The vanes do not restrict the exhaust gas flow and therefore the velocity of the gases depends on the engine speed. The turbine wheel speed is maintained by increasing the velocity of the gases leaving the engine and directed toward the center of the turbine wheel.
C - Maximum engine speed
At maximum engine speed, the volume of exhaust gas leaving the engine is high. The vanes move toward the fully open position and do not affect the gas velocity. The exhaust gas flow contacts the central area of the turbine wheel to maintain the turbine wheel speed and the boost pressure from the compressor.
Increased boost pressure
During moderate to hard acceleration, the turbocharger must produce higher boost pressure for a limited period of time to meet the current fuel delivery needs of the engine. The ECM will request REA to move the variable vanes to the closed position to increase the speed of the turbine wheel, which is already spinning at high speed. The high boost pressure condition is tolerated by the ECM for a limited period.
Barometric pressure sensor
At high altitude, the turbocharger will operate normally, but due to the lower ambient pressure, the turbine and compressor may have a tendency to overspeed. The ECM contains a barometric pressure sensor to prevent excessive boost pressure and possible engine damage under these conditions. The ECM opens the variable vanes earlier in the opening phase to suit the vehicle altitude.
Turbocharger lubrication
Rapid acceleration and deceleration demands of the turbocharger depend on the stability of the flow of clean oil. The oil supplied by the engine lubrication system provides lubrication to the shaft and bearings of the turbocharger, while also acting as a coolant for the central housing of the turbocharger.
To maintain the expected service life of the turbocharger, the engine oil should be changed at regular service intervals using the recommended quality oil in the required quantity. The oil should have a free passage through the turbocharger and be able to return unrestricted to the oil sump.
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