TURBOCHARGER FUNCTION AND CONTROL

It is no coincidence that a turbocharger is also called an exhaust gas turbocharger: the turbocharger function consists in compressing the combustion air supplied by the engine - that is, the exhaust gases.

Unlike naturally aspirated engines, this advantage allows a much better filling of the cylinders. The result: higher engine output, while fuel consumption remains low and emission levels improve.

TURBOCHARGER COMPONENTS AND THEIR FUNCTION

During exhaust gas turbocharging, part of the exhaust gas energy is used to drive the turbine. Otherwise, this energy from the exhaust gases would escape unused into the environment.

The turbocharger function can be explained as follows: a shaft connects two turbine wheels located in two separate chambers. The engine's exhaust gas flows through one chamber, setting them spinning at tremendous speed (over 200,000 rpm). This also drives the second impeller, which blows fresh air under pressure into the engine's combustion chamber. This considerably increases the engine's output. For example, a Golf TSI with a small displacement of 1.4 litres delivers a strong 122-160 HP.

Turbochargers in passenger cars

It was turbocharging alone that made it possible for the diesel engine to find its way into passenger cars. The advantages of the turbocharged diesel engine, such as high economy and strong torque, have been successfully established in commercial vehicles for many years and are winning over more and more car drivers too.

With its low fuel consumption and low emissions, high output and great driving pleasure, a modern diesel engine has now become very attractive to motorists.

Other exhaust gas turbocharger components

In addition to the turbine, the turbocharger also contains a compressor. The two components are rigidly connected to each other by a common shaft. The compressor is mounted on the turbocharger shaft opposite the turbine. It draws in the combustion air and delivers it to the engine in compressed form. In general, turbochargers mostly use centripetal turbines and radial compressors.

The radial compressor in the turbocharger function

A radial compressor usually consists of the following components:

Compressor wheel
Diffuser
Volute housing

As the compressor wheel rotates, it draws in air along the longitudinal axis and accelerates it to a high speed. The air then leaves the compressor wheel again in a radial direction.

From there it passes into the diffuser, which reduces the speed of the air with almost no losses. Pressure and temperature rise. The diffuser is formed by the compressor back plate and part of the volute housing.

The volute housing collects the air and reduces its speed further up to the compressor outlet.

Centripetal turbine

In exhaust gas turbochargers for passenger car engines, commercial vehicle engines and industrial engines, only radial turbines are used on the drive side. These turbines are also known as centripetal turbines.

The centripetal turbine works by converting the pressure of the exhaust gas inside the volute housing into kinetic energy and feeding the exhaust gas to the turbine wheel at a constant speed.

Kinetic energy here means the energy an object possesses due to its motion. This kinetic energy of the moving exhaust gas is converted in the turbine wheel into rotational energy of the shaft. The turbocharger's turbine wheel is designed so that almost all of the kinetic energy built up has been converted by the time it reaches the outlet.

Boost pressure control

To guarantee optimum operation of the turbo engine, the boost pressure of the exhaust gas turbocharger must be adapted to the engine load and engine speed. The simplest way to control the boost pressure is with a bypass valve on the turbine side (also called a wastegate) using a vacuum actuator or an electronic actuator.

The turbine is chosen small enough that the expected torque characteristics are met even at low engine speeds and the engine offers good driveability. With an ideally designed turbine, more exhaust gas is supplied shortly before maximum torque is reached than is needed to generate the boost pressure. Once the required boost pressure has been reached, the bypass diverts part of the exhaust gas flow around the turbine.

In diesel engines, especially for passenger cars, boost pressure control is now handled as standard by variable turbine geometry (VTG) with adjustable guide vanes.

Advantages of the exhaust gas turbocharger over a naturally aspirated engine

Compared with a naturally aspirated engine of equal power, a turbo engine of the same output has lower fuel consumption. After all, the exhaust gas energy contributes in part to increasing the engine's output and would otherwise not be used at all.

For this reason, a turbo engine can be designed smaller than a naturally aspirated engine for the same output. Further advantages of the turbocharged engine with its smaller displacement also result from its lower friction and heat losses. With CO2 emissions being reduced across all powertrain concepts, turbocharging is also gaining importance in petrol engines. Here the turbocharger serves as the technology for so-called “downsizing”, which significantly reduces fuel consumption without sacrificing performance or comfort. The term downsizing therefore describes reducing the engine displacement and the number of cylinders.

A long engine life

When you buy a turbocharger, it is designed so that, with correct use and compliance with the service instructions of the vehicle or engine manufacturer, it will normally last as long as the engine.

No maintenance or special care is required; its operation is only checked as part of routine inspection work. The following points are important:

Regular oil changes
Maintenance of the oil filter system
Checking the oil pressure
Cleaning the air filter system

Turbocharger damage

Should a turbocharger repair become necessary after all, in 90% of cases the reason is a lack of regular maintenance - so it could have been avoided. At Turboservice24 you can also buy diesel particulate filters and order your new turbocharger at a low price as an exchange unit or brand new. The causes of damage are usually:

Foreign objects in the turbine or compressor
Dirt in the oil
Insufficient oil supply (oil pressure/filter system)
Excessive exhaust gas temperatures due to faults in the ignition or injection systems