Air filter apparatus in the intake system of an internal combustion engine

Unfiltered air (2) enters a fixed housing (1) and passes through a flat filter element (4), sealed (10) round the edges (5b), to a filtered air outlet (3). Projecting catches (5,5a) on opposite edges of the filter cassette (5) engage a catch element (7,8) on the fixed housing and on a swiveling and removable lid (9) with an electronic control circuit (6). The lid has a seal (15) and is held by a fastening screw (14) and an axle (12) engaging on a claw (13) on the fixed housing. The lid covers an aperture (11) through which the filter element may be removed.