Brushless direct current motor system

Abstract

The invention relates to a brushless direct current motor system that includes an outer rotor receiving a load member such as a fan wheel having a plurality of blades. An axial extension of the rotor functions as a drive boss whose diameter is independent of the diameter of the motor stator core and is step-wise smaller in diameter at its outer closed end than at its inner opened end.

What is claimed is: 
     
       1. A brushless direct current motor system, said system including an outer rotor type motor comprising: a cup-shaped .Iadd.outer .Iaddend.rotor housing having .Iadd.inner and outer surfaces, an open and a closed end and .Iaddend.a shaft concentrically mounted therein extending internally thereof, the outer .[.portion.]. .Iadd.surface .Iaddend.of said housing being formed as a drive boss to receive .Iadd.and directly drive .Iaddend.at least one load member .[.for the direct driving thereof.]., the load member being a fan wheel having a plurality of blades, the fan wheel being a unitized assembly including a hub and radially extending fan blades mounted thereon uniformly .[.around the periphery.]. .Iadd.therearound .Iaddend.;   a bearing system in said motor receiving said shaft so as to rotate said .Iadd.outer .Iaddend.rotor housing;   stator means concentrically mounting said bearing system within said motor, said .Iadd.outer .Iaddend.rotor housing including permanent magnets on its .[.inside.]. .Iadd.inner .Iaddend.surface and being mounted to rotate around .[.the periphery of.]. said stator means .[.and.]. separated .Iadd.therefrom .Iaddend.by an air gap, the .[.outside.]. .Iadd.outer surface .Iaddend.of said .Iadd.outer .Iaddend.rotor housing at its closed end being provided with a step-wise reduction in its outer diameter to provide a reduced diameter hub portion .[.thereof, allowing the outside of this portion of the rotor housing.]. to mount and drive said unitized assembly; and   the hub of said unitized assembly being .[.dimensioned to be press fit over.]. .Iadd.fixed to .Iaddend.the reduced diameter hub portion of said outer rotor .Iadd.housing.Iaddend..   
     
     
       2. A system according to claim 1 wherein the diameter of the hub of said fan wheel is not greater than the diameter of the cup-shaped .Iadd.outer .Iaddend.rotor housing at its open end. 
     
     
       3. A system according to claim 2 wherein said system is part of an axial-flow fan .Iadd.having an air inlet side and an air exhaust side .Iaddend.and further comprising an outer fan housing of multi-corner profile, said .Iadd.outer fan .Iaddend.housing having a central cylindrical portion surrounding the fan .[.blade.]..Iadd.wheel.Iaddend., said .Iadd.outer fan .Iaddend.housing being broadened on the exhaust side of the .Iadd.central .Iaddend.cylindrical .[.central.]. portion by corner pockets into the .[.regular.]. multi-corner profile, said profile circumscribing .[.the outer diameter of.]. the fan wheel. 
     
     
       4. A system according to claim 3 wherein said corner pockets are formed by inclined .[.walls.]. .Iadd.wall sections .Iaddend.which extend from said central cylindrical portion. 
     
     
       5. A system according to claim 4 wherein the inclined wall .Iadd.sections also extend from the central cylindrical portion .Iaddend.on the air inlet side .[.is.]. .Iadd.and are .Iaddend.axially shorter than and at a different angle from the inclined wall .Iadd.sections .Iaddend.on the .[.outlet.]. .Iadd.exhaust .Iaddend.side of the central cylindrical portion, forming an asymmetrical cross section in the .Iadd.outer .Iaddend.fan housing. 
     
     
       6. A system according to claim 4 wherein the inclined .[.walls.]. .Iadd.wall sections also extend from the central cylindrical portion and these sections .Iaddend.on both the inlet and .[.outlet.]. .Iadd.exhaust .Iaddend.sides of the central cylindrical portion are of substantially .[.the.]. .Iadd.a .Iaddend.same angle and length .Iadd.with respect .Iaddend.to each other, forming a symmetrical cross section in the .Iadd.outer .Iaddend.fan housing.