Turbocharger: Description and Operation

Turbocharger:

PURPOSE AND LOCATION
The turbo charger, bolted to the exhaust manifold, provides an effective way of boosting the power output of an engine without increasing its cubic capacity.

CONSTRUCTION AND OPERATION
The turbo charger consists two bladed rotors mounted on a shaft. The first of these (the turbine) is propelled by the exhaust gases exiting the cylinders, while the second (compressor) is used to compress the intake air.

Since compressed air contains more oxygen per unit of volume (higher air density), it can fill the cylinder to a higher degree, increasing engine horse power.
The maximum speed of the turbo charger rotors is approx. 120,000 RPM. This requires that the rotors are carefully balanced.

To regulate the maximum charge pressure, the turbo charger uses a wastegate valve. When the intake manifold pressure gets too high, the wastegate valve opens a by-pass around the turbine wheel, reducing the exhaust gas pressure in the manifold. This results in lower turbo rotor speed and as a result, lowers the boost pressure in the intake manifold.

The turbo charger is lubricated by the normal engine lubrication system. A supply line feeds the turbo charger with pressurized oil from the engine lubrication system. The engine oil lubricates the floating bearings where the charger shaft floats on a film of oil. Engine oil returns into the crankcase via the return pipe.

The charger utilizes the engine cooling system to control bearing temperature. A supply and return line route coolant through the turbo charger bearing housing. The coolant, together with the engine oil, reduce the turbo temperatures by approximately 50% over engine oil cooled units. This reduces the overall thermal load and increases turbo charger reliability and service life.

CAUTION: 1. The engine oil (amount and purity) is an important factor in the service life of the turbo charger. Always change the engine oil/filter as often as Volvo recommends and refill with the correct oil quality/grade.
2. Never race the engine immediately after start-up. Allow the engine to idle for a while so the turbo charger can be properly lubricated.
3. Allow the engine to idle before shut-down. If the engine is turned off at high RPM, the turbo will rotate without lubrication for a long time. This can ruin the turbo charger shaft and bearings under extreme conditions. By letting the engine idle for a while before turning off, the turbo charger has time to slow down and reduce its temperature.