Cooling fan and cooling fan module

A cooling fan, comprising

• a fan shroud having a shroud upper side and having a shroud underside and being formed with a fan wheel recess which is surrounded by a shroud ring;
• a fan wheel rotatably arranged in the fan wheel recess for conveying an air flow along a conveying direction from the shroud upper side to the shroud underside;
• said fan wheel having a central hub cup, a plurality of radially oriented blades, and an outer ring connecting said blades to one another at blade tip ends thereof;
• wherein a circumferential ring gap is formed between said outer ring and said shroud ring;
• said shroud ring on the shroud underside extending axially beyond said outer ring with a shroud ring section;
• said shroud ring section being oriented parallel or at an angle of inclination and radially inwards relative to the conveying direction, so that the shroud ring section engages radially behind said outer ring, at least in some sections thereof;
• a connecting line being inclined at an acute angle relative to the conveying direction from a radially outermost edge of an outer ring end surface of said outer ring to a radially innermost edge of a shroud ring end surface of said shroud ring section;
• a rib structure introduced into the ring gap in order to reduce swirl in a gap flow oriented against the conveying direction;
• and
• said rib structure having a number of ribs which protrude into the ring gap at least in some sections and extend beyond an axial outer ring end surface of said outer ring toward said inclined shroud ring section.