The variable nozzle vane changes the flow speed and direction of the exhaust gas to optimize boost pressure from low speeds to high speeds using the engine ECU to control the pitch of the nozzle vane, which is mounted on the circumference of the turbine.
At low speed
As the nozzle vane passage becomes narrow (closes), the flow speed of the exhaust gas flowing into the turbine wheel becomes faster and the turbine wheel operates more efficiently. In this way, as the exhaust gas pressure applied to the turbine wheel is increased, the increase of boost pressure becomes faster, and engine output is increase even at low speeds.
At high speed/heavy load
As the nozzle vane passage becomes wide (opens), the boost pressure is controlled because the flow direction of the exhaust gas changes and the efficiency rate of the exhaust gas, which is activated on the turbine wheel, decreases. However, the excess rotation of the turbine wheel is prevented with improvement of the fuel consumption and engine output because the boost pressure is controlled to the specified pressure.