Patent ID: 8678785

Claim:
A ventilation fan comprising: a rotor holder having a substantially cylindrical shape, the rotor holder being arranged to rotate around a rotation axis; a field magnet fixed to an inner circumference of the rotor holder; an impeller cup having a substantially cylindrical shape fixed to an outer circumference of the rotor holder, the impeller cup including a plurality of blades defined on an outer circumference thereof; a base portion arranged to rotatably support the rotor holder through a bearing portion and a bearing holding portion; a stator portion arranged to be supported by the bearing holding portion; and a circuit board; wherein the base portion includes an outer circumferential wall extending upwards in an axial direction from an outer circumferential edge portion thereof, an inner circumferential portion of the outer circumferential wall being directly opposed to an outer circumferential portion of the circuit board in a radial direction without any intervening elements arranged therebetween; a gap defining a labyrinth structure is provided between an upper end portion of the outer circumferential wall of the base portion and a lower end portion of an outer circumferential portion of the impeller cup; the impeller cup includes a cylindrical portion which is arranged to extend in the axial direction inside the outer circumferential portion thereof; and a lower end portion of the cylindrical portion is located axially lower than the upper end portion of the outer circumferential wall of the base portion and an outer circumferential portion of the cylindrical portion is directly opposed to the inner circumferential portion of the outer circumferential wall in the radial direction without any intervening elements arranged therebetween.