Some diesel engines use an intake shutter. The intake shutter has following functions.
(1) Stops vibration immediately after engine is turned off. In diesel engines, air continues to be drawn into the cylinder and compressed even after the ignition switch is turned off. To prevent vibration from occurring immediately after engine is turned off, the intake shutter is closed immediately after the ignition switch is turned off in order to shut the intake air off and stop the engine smoothly.
(2) Reduces intake air noise. During deceleration, or low speed and light load, the amount of the intake air is reduced by the intake shutter. The intake air noise is reduced without drawing unnecessary air into the intake manifold.
(3) Improves EGR performance. The intake shutter opening angle is controlled to attain the proper EGR effect, depending on the engine running condition.
The intake shutter is also called throttle valve.