Turbocharger - Operation
OPERATION
Exhaust gas pressure and energy drive 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.
Increasing air flow to the engine provides:
- Improved engine performance
- Improved operating economy
- Altitude compensation
The turbocharger also uses a wastegate, which regulates intake manifold air pressure and prevents over boosting at high engine speeds. When the wastegate valve is closed, all of the exhaust gases flow through the turbine wheel. As the intake manifold pressure increases, the wastegate actuator opens the valve, diverting some of the exhaust gases away from the turbine wheel. This limits turbine shaft speed and air output from the impeller.
The turbocharger is cooled by engine coolant. The coolant is delivered to the turbocharger by a supply line that connects from engine block to the after run pump, then to the turbocharger. A coolant return line connects the turbocharger to coolant adapter.
The turbocharger is lubricated by engine oil that is pressurized, cooled, and filtered. The oil is delivered to the turbocharger by a supply line that is tapped into the cylinder block. The oil travels into the bearing housing, where it lubricates the shaft and bearings. A return pipe at the bottom of the bearing housing, routes the engine oil back to the crankcase.
The most common turbocharger failure is bearing failure related to repeated hot shutdowns with inadequate "cool-down" periods. A sudden engine shut down after prolonged operation will result in the transfer of heat from the turbine section of the turbocharger to the bearing housing. This causes the oil to overheat and break down, which causes bearing and shaft damage the next time the vehicle is started.
Turbocharged engine uses an auxiliary after run coolant pump. Depending on operating conditions, the coolant pump will run for up to 10 minutes after the engine is shut down No cool down period is required and a light noise from the coolant pump is normal.