How is the speed of the turbine in a turbo-charger controlled?

The speed of the turbine in a turbocharger is primarily controlled by the diversion of exhaust gases. This mechanism allows the system to manage how much exhaust flow is directed towards the turbine wheel, influencing its rotational speed. When more exhaust gas is directed to the turbine, it results in increased turbine speed, which consequently boosts the intake air pressure. Conversely, if the exhaust gases are restricted or diverted away, the turbine slows down. This method effectively harnesses the energy from the engine’s exhaust to optimize performance without requiring additional complex mechanisms.

Controlling the exit of exhaust gas passing out of the eye of the impeller, while it does affect the efficiency of the turbocharger, primarily pertains to how well the system performs rather than directly controlling turbine speed. The use of a variable controller may also imply a method of managing speed but isn't a standard component as it would be in other parts of the engine. Lastly, having an automatic gearbox between the turbine and the impeller is not a typical design feature in turbochargers, as there is a direct coupling between the two components for effective energy transfer.