Turbocharger. Diesel engine
Turbocharger VTG
All diesel engines, as well as some petrol engines, of the AUDI A4 are equipped with a turbocharger. On the turbocharger shaft, two working wheels are located in two separate housings. The turbine wheels are driven by exhaust gases. They ensure the rotation of the turbocharger shaft and thus both turbine wheels at a speed of 300,000 rpm. The turbocharger is lubricated by the engine lubrication system.
In a gasoline engine, the turbocharger is additionally cooled by liquid.
Due to good filling of the cylinders with forced air, engine power increases up to 100%.
The turbocharger is designed to increase engine power (up to 100%) by increasing the air pressure in the intake manifold. Air does not simply enter the cylinders, but is supplied to them under pressure. Along with power, supercharging creates an increase in engine torque. The increase in power, among other things, depends on the pressure of the supercharged air, which is usually 0.4-0.8 atm. The pressure of the supercharged air is constantly monitored and regulated by the engine control unit. This eliminates the possibility of exceeding the pressure above the set value. In accordance with the increase in air supply, the high-pressure fuel pump increases the fuel supply.
The compressor turbine is driven by the exhaust gases. The gases pass through a special casing (compressor casing), are fed to the compressor turbine. The turbine rotates on a shaft, at the other end of which is a compressor wheel in a separate casing. It is this that feeds air under pressure into the pipeline.
The turbocharger with variable turbine geometry (VTG) has guide vanes whose position is controlled by the engine control unit via a solenoid valve and a vacuum actuator. This ensures optimum boost pressure across the entire speed range, resulting in higher torque and thus higher power, particularly at low speeds.
An air cooler is located between the turbocharger and the engine intake duct (intercooler), which cools the air pre-compressed by the turbocharger. This increases engine power because cold air, due to its higher density, has a higher oxygen content.
The air pressure in the pipeline is limited by a special sensor. When the maximum pressure is reached, the sensor opens the valve, thereby limiting the supply of exhaust gases to the turbine.
The compressor shaft is lubricated with engine oil, which is supplied through a specially designed hose. The shaft constantly "floats" in oil. From the compressor, the oil is discharged into the pan through the return hose.
Compared to a petrol engine, a diesel engine does not need to reduce the compression ratio due to turbocharging, which ensures that the injected fuel is fully utilised even at low revs.
The turbocharger is an integral part of the exhaust manifold and cannot be separated from it.
The turbocharger is a precision mechanism. Therefore, if a malfunction occurs, it must be completely replaced.
Precautionary measures
The rotation speed of the compressor turbines is enormous, and the operating temperature is very high. In order to avoid injury and damage to the turbocharger, please observe the following precautions.
- Do not start the engine after removing any turbocharger component. Foreign objects getting into the turbine blades can cause them to fail. You also risk injury from objects thrown from the turbine.
- After removing any turbocharger components or air intake hoses, cover it with a clean rag.
- Do not give gas immediately after starting the engine, especially if it is not warmed up. Oil cannot immediately lubricate the turbine shaft.
- Never turn off the ignition immediately after stopping the car. Do not press the accelerator pedal before stopping the engine. Immediately after turning off the ignition, oil is no longer supplied to the compressor shaft, and it will rotate for some time without lubrication.
- Before turning off the engine, let it idle for a few minutes, during which time the turbine speed will decrease significantly.
- Change the oil, oil filter and air cleaner regularly. Using old oil will cause deposits to form on the compressor shaft and cause it to fail. Before disconnecting the oil supply and return hoses from the compressor, thoroughly clean the surrounding surfaces. Store removed components in sealed containers.