Abstract: An air filter is substantially made up of a filter element having a pleated filtering portion and a collar portion that extends on an outer periphery of the filtering portion and that has a sealing function, the filtering portion and the collar portion being integrally formed from the same material, and a cap and a case each of which has a flange for clamping the collar portion of the filter element. One of the flange of the cap and the flange of the case has a protruded portion that has an inclined portion. The collar portion of the filter element has a recess portion that contacts the inclined portion of the protruded portion and is guided by the inclined portion and fits to the protruded portion at a predetermined position so as to become set in position.

Abstract: An intake passage structure for an internal combustion engine has a first passage portion where a throttle valve is disposed and a second passage portion, downstream of the fist passage portion, where a mesh member is disposed. A relationship S.sub.1 .ltoreq..alpha.S.sub.2 holds between a cross-sectional area S.sub.1 of the first passage portion and a cross-sectional area S.sub.2 of the second passage portion where .alpha. is an open area rate of the mesh member. A clearance may be provided between a periphery of the mesh member and an inside surface of the intake pipe where the mesh member is disposed.

Abstract: A variable intake apparatus includes an intake manifold. The manifold has a surge tank and a plurality of branch pipes extending therefrom. The air in the surge tank is drawn into the combustion chambers of an engine via the branch pipes. The lengths of the branch pipes are different. A movable pipe is slidably located in each branch pipe. The movable pipes slides within the branch pipes for changing the effective passage length of the intake passages. The passage lengths of the movable pipes are determined such that the effective intake passage lengths are equalized. A motor actuates the movable pipes to slide within the branch pipes based on the engine speed. The movable pipes integrally move with respect to the branch pipes while keeping the passage lengths of the intake passages equalized.