Air passage type silencer

An air passage type silencer comprising:

• an inlet-side ventilation pipe;
• an expansion portion that communicates with the inlet-side ventilation pipe and of which a cross-sectional area is larger than the cross-sectional area of the inlet-side ventilation pipe;
• an outlet-side ventilation pipe that communicates with the expansion portion and of which a cross-sectional area is smaller than a cross-sectional area of the expansion portion;
• an opening portion structure that is provided at at least one of a connection portion between the expansion portion and the inlet-side ventilation pipe or a connection portion between the expansion portion and the outlet-side ventilation pipe and of which a cross-sectional area gradually increases from the connection portion toward an inside of the expansion portion;
• and
• a sound absorbing material that is disposed at least between an inner peripheral surface of the expansion portion and a distal end of the opening portion structure,
• wherein the opening portion structure includes a cutout portion formed from the distal end to a root side at a portion of a peripheral surface,
• a width of the cutout portion gradually increases from the root side toward the distal end,
• a central axis of the inlet-side ventilation pipe and a central axis of the outlet-side ventilation pipe are disposed to be parallel to a vertical direction, and
• the opening portion structure including the cutout portion is disposed at a side surface of the expansion portion that is on a lower side in the vertical direction.