Audi A4 B6 - the Repair manual and operation

6.4.6. A turbocompressor - the general information and precautionary measures

Turbocompressor. Diesel engine

VTG turbocompressor

All diesel engines as well as some petrol engines, the AUDI A4 car are equipped with a turbocompressor. On a turbocompressor shaft in two separate cases two driving wheels are located. The drive of turbine wheels is carried out from the fulfilled gases. They provide rotation of a shaft of a turbocompressor and by that both turbine wheels with a speed of 300 000 rpm. Lubricant of a turbocompressor is carried out from the engine lubrication system.

At the petrol engine the turbocompressor is in addition cooled with liquid.

Owing to good filling of cylinders with the forced air engine capacity increases up to 100%.

The turbocompressor is intended for increase in engine capacity (to 100%) by increase in pressure of air in the inlet pipeline. Air not just comes to cylinders, and moves in them under pressure. Along with power pressurization creates increase in torque of the engine. Growth of power, among other things, depends on pressure of the forced air which as a rule, makes 0.4-0.8 atm. Pressure of the forced air is constantly controlled and regulated by the control unit of the engine. It excludes a possibility of excess of pressure over the established value. According to increase in air supply, TNVD increases fuel supply.

The turbine of the compressor is given to rotation by the fulfilled gases. Gases, passing through a special casing (a compressor casing), move to the compressor turbine. The turbine rotates on a shaft on which other end there is a compressor wheel in a separate casing. It gives air under pressure to the pipeline.

The turbocompressor with variable geometry of the turbine (VTG) has the directing shovels which position is regulated by the control unit of the engine by means of the electromagnetic valve and the vacuum drive. It provides the optimum pressure of pressurization in all range of turns that results in higher torque and, thereby, to higher power, in particular, at low numbers of turns.

Between a turbocompressor and the inlet channel of the engine the air cooler is located (intercooler) which cools the air which is previously compressed a turbocompressor. It increases engine capacity since cold air thanks to its higher density has higher content of oxygen.

Air pressure in the pipeline is limited to the special sensor. At achievement of extreme pressure the sensor opens the gate, limiting to that supply of the fulfilled gases to the turbine.

The shaft of the compressor is oiled motive which moves on specially intended hose. The shaft constantly "floats" in oil. From the compressor oil is taken away in the pallet on a returnable hose.

In comparison with the petrol engine the diesel engine has no need to reduce extent of compression because of pressurization that provides even on low turns full use of injectable fuel.

The turbocompressor is a component of a final collector and cannot be separated from it.

The turbocompressor represents the precision mechanism. Therefore at emergence of malfunction it has to be completely replaced.

Precautionary measures

Speed of rotation of turbines of the compressor is huge, and working temperature is very big. To avoid getting injured and also not to damage a turbocompressor, observe the following precautionary measures.

• Do not start the engine after removal of any component of a turbocompressor. Hit of foreign objects on shovels of turbines can lead to an exit of the last out of operation. You also risk to be traumatized from the objects which are thrown out from the turbine.
• After removal any a component of a turbocompressor or hoses of an air inlet cover it with pure rags.
• Do not give gas at once after start of the engine, especially if it is not heated-up. Oil cannot instantly grease a turbine shaft.
• Never switch off ignition at once after a car stop. Do not press an accelerator pedal before an engine stop. At once after switching off of ignition oil ceases to move to a compressor shaft, and some time it will rotate without lubricant.
• Before killing the engine, let's it work on single turns several minutes during which the speed of rotation of the turbine considerably will decrease.
• Regularly change oil, an oil filter and the air cleaner. Use of old oil will lead to formation of deposits on a shaft of the compressor and to its exit out of operation. Before disconnecting hoses of giving and return of oil from the compressor, carefully clear nearby surfaces. You store the removed components in tight containers.