How a turbocharger works

FUNCTION

The task of the turbocharger, also called exhaust gas turbocharger (ETC), is to compress the combustion air supplied by the engine.

The task of the turbocharger is to compress the combustion air that is supplied to the engine. Compared to naturally aspirated engines, this achieves a significantly better filling of the cylinders. This results in a higher engine output with lower consumption and better emissions.

With exhaust gas turbocharging, part of the exhaust gas energy is used to drive a turbine. Otherwise this would escape unused into the environment. A compressor is mounted on the shaft of the turbocharger opposite the turbine. This sucks in the combustion air and feeds it in compressed form to the engine. There is no mechanical coupling with the motor.

COMPONENTS OF THE EXHAUST GAS TURBOCHARGER

The exhaust gas turbocharger consists of a turbine and a compressor. These exhaust gas turbochargers are mechanically firmly connected to one another by a common shaft. The turbine is driven by the exhaust gases from the engine and provides the drive energy for the compressor. Most turbochargers use centripetal turbines and radial compressors.

RADIAL COMPRESSORS

A centrifugal compressor essentially consists of the following components:

• Compressor wheel

• Diffuser

• Volute casing

If the compressor wheel is rotated, it sucks in air axially (in the direction of the longitudinal axis) and accelerates it to a high speed. The air leaves the compressor wheel in a radial direction. In the diffuser, the speed of the air is reduced largely without loss. The consequence of this is that the pressure and the temperature rise. The diffuser is formed from the rear wall of the compressor and part of the volute casing. The air is collected in the spiral casing and the speed is further reduced until the compressor outlet.

CENTRIPETAL TURBINES

On the drive side, only radial turbines, which are also referred to as centripetal turbines, are used in exhaust gas turbochargers for passenger cars, commercial vehicles and industrial engines. These convert the pressure of the exhaust gas inside the volute into kinetic energy and feed the exhaust gas to the turbine wheel at a constant speed. Kinetic energy is the energy that an object contains due to its movement. In the turbine wheel, the kinetic energy of the exhaust gas is converted into rotational energy of the shaft. The turbine wheel is designed in such a way that almost all of the kinetic energy is converted at the outlet.

CHARGING PRESSURE CONTROL

In order for the turbo engine to function optimally, the charge pressure of the exhaust gas turbocharger must be adapted to the engine load and the engine speed. The simplest form of boost pressure control is the turbine-side bypass (bypass duct). The turbine is selected to be so small that the requirements for torque behavior at low speeds are met and the engine can be driven well. With this design, shortly before the maximum torque is reached, more exhaust gas is fed to the turbine than is necessary to generate the boost pressure. For this reason, after the required boost pressure has been reached, part of the exhaust gas volume is routed through a bypass around the turbine.

Diesel turbocharger The boost pressure control flap, which opens and closes the bypass, is actuated by a spring-loaded diaphragm depending on the boost pressure controlled. In modern passenger car diesel engines, the adjustable turbine geometry (VTG) with rotating guide vanes has meanwhile become the state of the art for boost pressure control. The adjustable turbine geometry makes it possible to adjust the flow cross section of the turbine depending on the engine operating point. As a result, the entire exhaust gas energy is used and the flow cross-section of the turbine can be set for each operating point. This improves the efficiency of the turbocharger and thus that of the engine compared to bypass control. The constant adaptation of the turbine cross-section to the driving condition of the engine also reduces fuel consumption and emissions. The engine's high torque even at low engine speeds and a carefully coordinated control strategy result in a noticeable improvement in dynamic driving behavior.

ENVIRONMENTAL PROTECTION

It was the use of turbocharging that made the triumphant advance of the diesel engine in cars possible. The advantages of the turbo-charged diesel engine, such as economy and torque, which have been valued in commercial vehicles for many years, have also increasingly convinced car buyers. Modern diesel engines today offer low consumption and emissions paired with high performance and driving pleasure.

ADVANTAGES OF THE TURBOCHARGER

The turbo engine has a lower consumption compared to an equally powerful naturally aspirated engine. The reason: some of the exhaust gas energy that would otherwise not be used contributes to increasing the engine's performance. A turbocharger can therefore be designed to be smaller than a naturally aspirated engine with the same output. The lower friction and heat losses of the smaller-displacement turbo engine bring further advantages.

In view of a further reduction in CO2 emissions in all drive concepts, turbocharging is also gaining in importance in Otto engines. Here the turbocharger is a key technology for so-called “downsizing” as a means of significantly reducing consumption without sacrificing performance or comfort. Downsizing describes the reduction of displacement and the number of cylinders.

VALUE RETENTION

The turbocharger is designed in such a way that it usually lasts for the life of the engine. It therefore does not require any special maintenance or care and is only checked as part of the inspection work. To ensure that the turbocharger lasts as long as the engine, the following service instructions from the vehicle or engine manufacturer must be strictly observed:

• Oil change intervals

• Maintenance of the oil filter system

• Check the oil pressure

• Cleaning the air filter system

CAUSE OF DAMAGE TO THE TURBOCHARGER

90 percent of all damage to the turbocharger is caused by the following causes, which can be avoided through regular maintenance:

• Penetration of foreign bodies into the turbine or the compressor

• Dirt in the oil

• Insufficient oil supply (oil pressure / filter system)

• Excessive exhaust gas temperatures (faults in ignition or injection systems)

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