Every car should have a turbocharger


Components of the exhaust gas turbocharger

The exhaust gas turbocharger consists of a turbine and a compressor. These 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. In most cases, turbochargers use centripetal turbines and radial compressors.

Centrifugal compressor

A centrifugal compressor essentially consists of the following components:

  • Compressor wheel
  • Diffuser
  • Volute casing

When 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 a 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 car, commercial vehicle and industrial engines. These convert the pressure of the exhaust gas inside the spiral housing 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.

Boost 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 the torque behavior at low speeds are met and the engine is easy to drive. 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.

The boost pressure control flap, which opens and closes the bypass, is controlled 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 conditions 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.