•  When the VBC solenoid valve is operated according to the duty signal from the PCM, the vacuum passage is opened and vacuum is applied to the guide blade actuator of the turbocharger. Due to this, the rod of the guide blade actuator is pulled and the opening angle of the guide blades changes.

•  When the duty signal is on for a long time, the vacuum that acts on the guide blade actuator is reduced and the guide blades move in the closing direction.

•  When the duty signal is off for a long time, the vacuum that acts on the guide blade actuator is reduced and the guide blades move in the opening direction.

•  When the guide blades are moved in the closing direction, the passages that lead the exhaust gas to the turbine impellers become narrow and the flow rate of the exhaust gas increases. Due to this, the exhaust gas pressure is increased and the boost pressure is also increased. On the other hand, when the guide blades are moved in the opening direction, the passages that lead the exhaust gas to the turbine impellers become wide. Due to this, the exhaust gas pressure is reduced and the boost pressure is also reduced.