Turbochargers used to work like this, which was totally unexpected.
 

People often refer to the term "turbine intervention". For example, when the maximum torque and speed of an engine is 1700-4000, many people will say that the turbine is involved at 1700. In fact, this is a wrong view. Let's take a detailed analysis of this problem today.
 

If there is a turbocharger now, the maximum engine torque speed is 1500-3500, let's see how the turbocharger moves from the start of small throttle to the rapid speed increase.

When the engine starts to idle, there is little exhaust gas, which is not enough to meet the normal operation of the supercharger, so the exhaust bypass valve on the supercharger opens to let the exhaust gas enter the exhaust pipe directly from here. The engine at this time is actually a naturally aspirated engine. But the bypass valve is next to the turbine blade, so even if the bypass valve is fully opened, some exhaust gas will drive the turbine blade to rotate.
 

Suppose the car is parked on the downhill road, then we start with a light step on the throttle, because the engine hardly needs any effort to ensure the start, ECU does not think that there is a need for boosting, because boosting will inevitably lead to greater fuel injection, so at this time the turbine bypass valves are still open, or equivalent to self-priming. When we continue to step on the throttle to keep the speed and gear unchanged, the engine power is bigger, but the car still does not need so much power, ECU will still think that the power is enough, do not need to boost, so at this time the bypass valve will continue to be fully open, even if your speed reaches 2000 ECU still does not intend to let the turbine work. It's just that the exhaust is larger and the turbine may turn faster on its own.
 

Then we start to see when the turbine works. If we park on the flat ground and get a floor oil acceleration, the car starts to rush forward when you push the throttle to the bottom, then ECU knows it's time for the supercharger to perform the real technology, immediately shut down the bypass valve completely, the engine starts to increase speed uniformly from idle speed, and the supercharger also increases with the increase of exhaust gas. Add and speed up the rotation. Even if the engine speed is less than 1500 rpm, the turbocharger is providing turbocharging for the engine.
 

From the above, we can draw the conclusion that as long as the engine is running the supercharger, it will turn, but the speed is very low, so the effective supercharger pressure can not be formed. When you don't need a lot of power, the supercharger doesn't work either, in order to save fuel. When you need more power, ECU will adjust throttle opening and exhaust bypass valve opening according to power demand to give different turbocharging values to the engine in order to obtain the required power.
 

Usually some so-called turbine intervening speed is not rigorous, it is easy to make people mistakenly think that the turbine works only when the maximum torque speed is reached. In fact, this is not the case. If you need more power, even if the speed is only 1000 turbines, it will pressurize you. However, if you want to output the maximum torque, you must have enough exhaust gas to ensure the pressurization pressure, and the maximum torque speed can just meet the requirements. That's just the amount of exhaust gas. Generally speaking, the depth and speed of your throttle pedal determine your acceleration requirements, and ECU will calculate how much power you need according to your requirements, and then control the throttle and bypass valve switches to provide the corresponding boost pressure so that the engine can output the required power.