Patent ID: 8091177

Claim:
An axial-flow fan comprising: a hub including an open end and a substantially closed end, the hub defining a central axis; a plurality of blades coupled to the hub and extending radially outwardly from the hub, each blade having a root coupled to the hub, a tip spaced from the hub, a first edge proximate the open end of the hub and interconnecting the root and the tip, the first edge defining one of a leading edge and a trailing edge with respect to a rotational direction of the hub about the central axis, and a second edge proximate the substantially closed end of the hub and interconnecting the root and the tip, the second edge defining the other of the leading edge and the trailing edge; and a plurality of ribs coupled to the hub, including a first rib substantially aligned with a first plane intersecting the central axis and an intersection of the first edge of a first of the plurality of blades with the hub, at the root of the first blade, wherein an angular spacing between the first plane and a reference plane intersecting the central axis and an intersection of the first edge of a second of the plurality of blades with the hub, at the root of the second blade, defines one sector, and a second rib substantially aligned with a second plane angularly positioned between the first plane and the reference plane, at a location less than or equal to about (1/nR−0.05) sectors from the first plane in which nR equals the number of ribs divided by the number of blades; wherein the entire root of the first blade is positioned on a first side of the second plane, and wherein the entire root of the second blade is positioned on a second side of the second plane opposite the first side.