flap rests against a wall portion of the inlet duct from where it can be swiveled into the intake duct into a flow directing turbulence generating position application_number US 21821702 A description an intake system 1 of an internal combustion engine not shown with an inlet duct 2 and a control flap 3 is shown schematically in fig1 the intake system 1 has a flange surface 4 and a mounting structure 5 for a fuel injection valve not shown the intake system 1 is connected at the flange surface 4 to a cylinder head not shown which includes passages extending up to the inlet valves of the respective cylinder in an open position the control flap 3 rests in a niche 6 in the wall 7 of the inlet duct 2 the niche 6 has an arcuate contour to ensure that the air gap 8 between the niche and the control flap 3 is minimal the axis of the pivot shaft 9 of the control flap is disposed in the center of the inlet duct 2 the control flap 3 is connected to the pivot shaft 9 by means of side arms 10 and has a cross section area in the form of a circular segment in an open position the control flap 3 does not pose any significant resistance to the flow in the inlet duct 2 0026 fig2 shows schematically the intake system 1 of an internal combustion.