Control concept for the partial admission of a turbocharger turbine

One of the main challenges in turbocharging an internal combustion engine (ICE) is the controlling of the turbocharger. Through the power balance of the turbine and compressor mounted on the same shaft, both components run dependently from each other. Further the operation of the turbocharger depends on the operation of the ICE. At low engine speeds, the turbocharger should produce a steep and large pressure increase in the compressor to reach a fast power increase of the ICE. At this state however, the ICE delivers low exhaust gas mass flow to drive the turbocharger turbine, which results in low rotational speed of the turbocharger and consequently low pressure increase. On the other hand, there is a surplus of exhaust gas energy at high ICE speeds because of high temperatures and large mass flow rates of the exhaust gases resulting in excessive turbine power. State-of-the-art to solve this problem is using a Waste-Gate turbocharger. As a part of the exhaust gas mass flow is bypassed around the turbine, a smaller turbine is utilized to drive the compressor. This leads to a reduced inertia of the rotor allowing a more rapid speed-up of the turbocharger and as a consequence more engine power output at low engine speeds. However, the energy of the bypassed mass flow is wasted at high ICE speeds.