Composite power metal stator sleeve

#This invention relates generally to electric machines, and more particularly, to the manufacture of stator sleeves for use with stators and stator cores in electric machines.

#It is to be understood that the present invention is equally applicable in the context of generators as well as motors. However, to simplify the description that follows, reference to a motor should also be understood to include generators, and reference to an electric machine should be understood to include both motors and generators.

#Alternating current generators and electric motors typically incorporate a fixed stator assembly for inductively producing magnetic fields that interact with an adjacent rotating component or rotor. A stator assembly incorporates a magnetic stator core fabricated traditionally from thin laminates of an iron-based material such as a silicon-iron alloy. Individual laminations are punched from flat sheets of the ferrous material using specialized dies with the required shape and number of slots and teeth. The individual laminations are coated with a thin insulating layer to reduce eddy current losses, carefully aligned in a stack, and secured to form a stator core. Conductors are wound in the slots to complete the stator assembly for incorporation into a generator or motor. Topsticks or slot wedges may also be added after the conductors are wound in the slots to enclose the winding in the slot. Most production electric machines incorporate side-extending tooth tips integrally fashioned during the stamping process. Some electric machines utilize fully open slots to increase the conductor content in the slot. However, fully open slots may result in excessive rotor losses due to relatively large air gap flux/reluctance variations caused by the low reluctance of the large slot opening as compared to the high reluctance of the body of the stator tooth. One option for maintaining open slots during the winding process followed by a methodology for providing tooth tips during machine operation involves forming the laminations such that the tooth tips extend into the air gap, and subsequently bending the tips into the proper position after winding of the conductors.

#The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.

#FIG. 1 is a perspective view of a composite powder metal stator sleeve of the present invention having alternating magnetically conducting segments and magnetically non-conducting segments, the sleeve in surrounding relation to a rotor assembly.

#FIG. 2 is a plan view of the stator sleeve of FIG. 1 positioned over the teeth of a stator core to provide stator tooth tips with radii.

#The present invention provides composite powder metal stator sleeves for stator assemblies in electric machines, such as belt-driven alternators, starter-motor alternators, propulsion motors, machine tools, centrifuges, and automotive and non-automotive motors and generators. The composite powder metal sleeves enable use of conventional laminated stator cores with a simple, tip-less tooth configuration, while providing high or maximum slot fill to thereby provide high thermal heat dissipation and low current density. To this end, a sintered powder metal sleeve is fabricated to comprise alternating magnetically conducting segments and magnetically non-conducting segments. The two powder materials are joined together via a press and sinter operation, an injection molding operation or a sinterbonding operation into an annulus, thus forming a cylindrical shape that fits over the stator's teeth. The sleeve not only provides a magnetically conducting (permeable) material as an extension of the stator teeth, it also provides the tooth tips and topsticks thereby allowing for an unparalleled ease of winding insertion and the highest possible slot fill while retaining traditional stator performance. The tooth tip portions of the sleeve can be patterned exactly after standard tooth tips or any other desired shape, and can be varied to provide different stator assemblies while using a single tip-less stator core configuration. Also, grooves may be slit into the sleeve surface so as to face the air gap to reduce eddy currents formed by air gap fluctuations, if necessary.

#The magnetically conducting segments comprise a sintered ferromagnetic powder metal, also referred to as a permeable or magnetic material. The ferromagnetic material may be soft ferromagnetic powder metal. In an embodiment of the present invention, the ferromagnetic powder metal is nickel, iron, cobalt or an alloy thereof. In another embodiment of the present invention, this ferromagnetic metal is a low carbon steel, a high purity iron powder with a minor addition of phosphorus, such as covered by MPIF (Metal Powder Industry Federation) Standard 35 F-0000, which contains approximately 0.27% phosphorus, or a silicon-iron powder, such as covered by MPIF Standard FS-0300, which is essentially Fe-3% Si. In general, AISI 400 series stainless steels are magnetically conducting, and may be used in the present invention.

#The magnetically non-conducting segments comprise a sintered non-ferromagnetic powder metal, also referred to as non-permeable or non-magnetic material. In an embodiment of the present invention, the non-ferromagnetic powder metal is austenitic stainless steel, such as SS316. In general, the AISI 300 series stainless steels are non-magnetic and may be used in the present invention. Also, the AISI 8000 series steels are non-magnetic and may be used.