Centrifugal fan having main blade with axially upper end projecting upward

1. A centrifugal fan comprising:

an impeller arranged to rotate about a rotation axis;

an impeller case arranged to accommodate the impeller;

a motor arranged to rotate the impeller; and

a motor case joined to the impeller case and arranged to accommodate the motor; wherein

the impeller comprises:

a boss portion joined to a shaft arranged to rotate about the rotation axis;

a hub arranged to extend radially outward from an outer circumferential surface of the boss portion; and

a plurality of blades arranged on an upper surface of the hub;

each blade is arranged to extend radially outward away from the rotation axis;

an inner wall of the impeller case is arranged to cover the blades, and comprises an inside surface extending radially outward along an upper end portion of each blade; and

the impeller case comprises an air inlet defined in a central portion thereof, with a side end portion of the air inlet comprising a curved surface projecting radially inward;

wherein the curved surface of the air inlet is arranged to have an axial dimension smaller than a radial dimension thereof, the radial dimension being a dimension in a radial direction from a most radially inner point of the curved surface to a point where the curved surface extends furthest away from the impeller in an axial direction;

wherein the blades comprise:

a main blade arranged to extend radially outward from a point radially inward of a radially innermost end of the curved surface of the air inlet; and

an auxiliary blade arranged to extend radially outward from a point radially outward of the radially innermost end of the curved surface of the air inlet;

the main blade has an axially upper end projecting upward and positioned radially outward of the radially innermost end of the curved surface of the air inlet;

a distance between the main blade and the inside surface of the impeller case is arranged to be shortest at the axially upper end of the main blade; and

wherein a plurality of auxiliary blades is equidistantly located between the two adjacent main blades.

2. The centrifugal fan according to claim 1 , wherein an upper end portion of the boss portion is arranged at a level lower than that of a radially innermost end of the curved surface of the air inlet.

3. The centrifugal fan according to claim 1 , wherein an upper end portion of the boss portion is arranged radially inward of a radially innermost end of the curved surface of the air inlet.

4. The centrifugal fan according to claim 1 , wherein the upper surface of the hub comprises a slanting surface arranged to extend from the outer circumferential surface of the boss portion obliquely downward and radially outward.

5. The centrifugal fan according to claim 4 , wherein the slanting surface of the hub comprises a curved surface concaved radially inwardly and downwardly.

6. The centrifugal fan according to claim 4 , wherein

the upper surface of the hub further comprises a flat surface arranged to extend from a radially outer end of the slanting surface substantially perpendicularly to the rotation axis; and

a periphery of the flat surface is arranged to project radially outwardly relative to a periphery of each blade.

7. The centrifugal fan according to claim 6 , wherein the hub comprises a slanting surface radially outside the periphery of the flat surface, the slanting surface extending obliquely downward and radially outward.

8. The centrifugal fan according to claim 1 , wherein the curved surface of the air inlet is arranged to project upwardly relative to a radially innermost end of the curved surface of the air inlet.

9. The centrifugal fan according to claim 1 , wherein

the auxiliary blade has a radially outer end at a radially outermost point of an upper end portion thereof; and

a distance between the auxiliary blade and the inside surface of the impeller case is arranged to be shortest in an axial direction at the radially outer end of the auxiliary blade.

10. The centrifugal fan according to claim 1 , further comprising an annular shroud arranged on the upper end portion of each blade, wherein a radially inner end of the shroud is arranged radially outward of a radially outer end of the hub.

11. A centrifugal fan comprising:

an impeller arranged to rotate about a rotation axis;

an impeller case arranged to accommodate the impeller;

wherein the impeller comprises:

a boss portion joined to a shaft arranged to rotate about the rotation axis;

a hub arranged to extend radially outward from an outer circumferential surface of the boss portion; and

a plurality of blades arranged on an upper surface of the hub;

each blade is arranged to extend radially outward away from the rotation axis;

an inner wall of the impeller case is arranged to cover the blades, and comprises an inside surface extending radially outward along an upper end portion of each blade; and

the impeller case comprises an air inlet defined in a central portion thereof, with a side end portion of the air inlet comprising a curved surface projecting radially inward;

wherein the curved surface of the air inlet is arranged to have an axial dimension smaller than a radial dimension thereof, the radial dimension being a dimension in a radial direction from a most radially inner point of the curved surface to a point where the curved surface extends furthest away from the impeller in an axial direction;

wherein the blades comprise:

a main blade arranged to extend radially outward from a point radially inward of a radially innermost end of the curved surface of the air inlet; and

an auxiliary blade arranged to extend radially outward from a point radially outward of the radially innermost end of the curved surface of the air inlet;

the main blade has an axially upper end projecting upward and positioned radially outward of the radially innermost end of the curved surface of the air inlet; and

a distance between the main blade and the inside surface of the impeller case is arranged to be shortest at the axially upper end of the main blade; and

wherein a plurality of auxiliary blades is equidistantly located between the two adjacent main blades.

12. A centrifugal fan comprising:

an impeller arranged to rotate about a rotation axis;

an impeller case arranged to accommodate the impeller;

wherein the impeller comprises:

a boss portion joined to a shaft arranged to rotate about the rotation axis;

a hub arranged to extend radially outward from an outer circumferential surface of the boss portion; and

a plurality of blades arranged on an upper surface of the hub;

each blade is arranged to extend radially outward away from the rotation axis;

an inner wall of the impeller case is arranged to cover the blades, and comprises an inside surface extending radially outward along an upper end portion of each blade; and

the impeller case comprises an air inlet defined in a central portion thereof, with a side end portion of the air inlet comprising a curved surface projecting radially inward

wherein the blades comprise:

a main blade arranged to extend radially outward from a point radially

inward of a radially innermost end of the curved surface of the air inlet; and an auxiliary blade arranged to extend radially outward from a point radially outward of the radially innermost end of the curved surface of the air inlet;

the main blade has an axially upper end projecting upward and positioned radially outward of the radially innermost end of the curved surface of the air inlet;

a distance between the main blade and the inside surface of the impeller case is arranged to be shortest at the axially upper end of the main blade; and

wherein a plurality of auxiliary blades is equidistantly located between the two adjacent main blades.