Rotor assembly and electrodynamic machine with axial vents for heat transfer

A rotor assembly for an electrodynamic machine includes a lamination section with rotor laminations formed to define annular arrays of axial vents and rotor slots, with rotor conductor bars being disposed in the rotor slots, an end connector supported by the rotor conductor bars, wherein an axial space is formed between the end connector and the lamination section, and an annular guiding element arranged in the axial space between the end connector and the lamination section for guiding a cooling fluid flow in an axial direction.

BACKGROUND

Aspects of the present invention generally relate to electrodynamic machines, which include for example electric motors, such as AC asynchronous motors, for example induction motors, and AC synchronous motors, as well as electric generators, and more particularly to rotor assemblies of induction machines with axial vents for heat transfer.

2. Description of the Related Art

Electrodynamic machines typically generate a large amount of heat during operation. Excessive heat can damage internal components, limit the amount of power that can be provided by the machine, and/or adversely affect the longevity of the machine. Electrodynamic machines may have fans or radial and/or axial vents that can remove at least some heat from the machine by drawing cooling air through various passageways in the machine.

Air cooled or gas cooled induction machines, including induction motors and generators, typically employ axial vents for cooling purposes formed in a rotor assembly of the machine. The rotor assembly of an induction machine can be designed as a squirrel cage rotor, such as for example a fabricated copper squirrel cage rotor. The squirrel cage rotor may comprise rotor laminations including rotor conductor bars embedded in the laminations, wherein the axial vents are formed in the rotor laminations. The rotor conductor bars are connected, for example welded or brazed, to end connectors, also referred to short circuit rings. Squirrel cage rotors typically comprise one or more axial spaces between the rotor laminations (or a pressure plate) and the end connectors. But the axial spaces allow the rotor conductor bars to behave like a fan, which draws air away from the intended cooling path of the axial vents, which can be considered a parasitic air flow path. Therefore, a need exists to improve the cooling efficiency of induction machines without adversely affecting the performance of the machine.

SUMMARY

Briefly described, aspects of the present invention generally relate to electrodynamic machines, which include for example electric motors, such as AC asynchronous motors, for example induction motors, and AC synchronous motors, as well as electric generators, and more particularly to rotors of induction machines with axial vents for heat transfer.

A first aspect of the present invention provides a rotor assembly for an electrodynamic machine comprising a lamination section comprising rotor laminations formed to define annular arrays of axial vents and rotor slots, with rotor conductor bars being disposed in the rotor slots, an end connector supported by the rotor conductor bars, wherein an axial space is formed between the end connector and the lamination section, and an annular guiding element arranged at least in the axial space between the end connector and the lamination section for guiding a cooling fluid flow in an axial direction.

A second aspect of the present invention provides an electrodynamic machine comprising a rotor assembly comprising a lamination section with rotor laminations formed to define annular arrays of axial vents and rotor slots, with rotor conductor bars being disposed in the rotor slots, a stator assembly defining an annular core receiving the rotor assembly, the rotor assembly rotating within the stator assembly based on electromagnetic fields generated by the stator assembly and the rotor assembly, a first end connector supported by the rotor conductor bars, wherein a first axial space is formed between the end connector and the lamination section, and a first annular guiding element arranged at least in the first axial space between the end connector and the lamination section for guiding a cooling fluid flow in an axial direction of the rotor assembly.

DETAILED DESCRIPTION

To facilitate an understanding of embodiments, principles, and features of the present invention, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of being electrodynamic machines and rotor assemblies of induction machines. Embodiments of the present invention, however, are not limited to use in the described devices or methods.

FIG. 1illustrates schematically a partial cut away elevational view of an exemplary induction machine100, which can be an induction motor or an induction generator, in accordance with embodiments disclosed herein. The exemplary machine100is a totally enclosed fan cooled alternating current motor, it being understood that the present invention may be applied to other types of electrodynamic machines and electric motors that have a rotating mass. The machine100comprises a housing110and a stator120circumferentially oriented therein. The stator120forms a generally annular core into which is axially inserted a rotor assembly130, which shall hereafter generally be referred to as a rotor. The rotor130has a shaft140onto which are affixed a stack of abutting rotor laminations150. The rotor laminations150, which are flat sheets of insulation coated ferromagnetic metal, e.g., pressed steel, are abutted to form the rotor core. For simplicity, motor components that are not deemed necessary for one skilled in the art to make and use the present invention are not included in the figures.

FIG. 2illustrates a perspective view of an example squirrel cage rotor assembly200of an induction machine in accordance with embodiments disclosed herein. The rotor assembly200, hereafter generally referred to as squirrel cage rotor or simply rotor, may be used in an induction machine100as illustrated inFIG. 1. The rotor200may also be used in other suitable types of electric motors or machines.

The rotor200includes a plurality of stacked rotor lamination sections210, wherein each lamination section210comprises one or more rotor laminations which may be laminated steel plates or sheets. Each rotor lamination has a central bore and is configured to be received over a rotor shaft205. Each lamination is formed from a relatively thin piece of sheet metal that is punched, stamped or otherwise cut into shape and then consolidated with one or more adjacent and substantially similarly shaped and sized laminations to form the lamination sections210. The consolidation is performed in accordance with various known methods. With enough laminations consolidated together, the laminations may form multiple lamination sections210. The lamination sections210are arranged in an axial direction A on the rotor shaft205, wherein gaps220formed between the lamination sections210provide radial vents for guiding cooling fluid, such as for example air or cooling gas, through the rotor200for cooling purposes.

Further, the rotor200includes a plurality of rotor conductor bars230radially distributed around the periphery of the lamination sections210and received through a respective plurality of outer periphery slots in the rotor laminations. The rotor conductor bars230define a pair of opposing bar end regions240. The rotor200further includes end connectors250, herein referred to as short circuit rings250on opposing axial ends, arranged within the bar end regions240. The rotor conductor bars230and/or short circuit rings250may be made of, e.g., copper or aluminum. Other suitable conductive material(s) may alternatively be used for rotor conductor bars230and/or short circuit rings250. The short circuit rings250are each supported by ends of the rotor conductor bars230, wherein the rotor conductor bars230can be for example welded or brazed to the short circuit rings250.

As illustrated inFIG. 2, the squirrel cage rotor200comprises axial spaces260between end lamination sections215and the short circuit rings250, which allow the rotor conductor bars230, specifically the ends of the bars230to behave like a fan, which draws air away from an intended cooling path of axial vents270(seeFIG. 3).

FIG. 3illustrates a front view of the example squirrel cage rotor200as illustrated inFIG. 2in accordance with embodiments disclosed herein.FIG. 3illustrates one of the end connectors250, the rotor shaft205and rotor lamination section210supported by the shaft205. As described before, the rotor lamination section210comprises one or more rotor laminations, each lamination comprising a plurality of axial vents270and a plurality of slots. The slots are arranged about radial periphery and are each configured to receive there through a rotor conductor bar230of the rotor200(seeFIG. 2). The axial vents270may be arranged in a ring around a central bore275, which receives the shaft205, and may be openings that pass axially through a plurality of stacked rotor laminations and lamination sections210to provide a passageway for cooling air and/or cooling gas to be received through the rotor200.

FIG. 4illustrates a perspective view of a guiding element400for an induction machine in accordance with an exemplary embodiment of the present invention. The guiding element400, which is an annular guiding element, provides a designated flow path for a cooling fluid, such as for example air or cooling gas, flowing through an induction machine rotor, for example in the squirrel cage rotor200as shown inFIG. 2(see alsoFIG. 5). Thus, the guiding element400may also be referred to as baffle or air baffle.

In an exemplary embodiment, the guiding element400is non-magnetic and/or comprises material(s) that is/are non-magnetic. Further, the guiding element400is designed as electrically non-conductive or at least less electrically conductive than other electric parts of the rotor200, in particular less electrically conductive than the end connectors250and the rotor conductor bars230of the rotor200. The end connectors250and the rotor conductor bars230can comprise for example copper, wherein the guiding element400does not comprise copper, but a material or combination of materials that is less conductive than copper and non-magnetic.

In an exemplary embodiment, the guiding element400can comprise metal, for example steel or stainless steel, and can be a sheet metal ring or sheet metal hollow cylinder, wherein the ring or hollow cylinder can comprise one or more segments. In an alternative embodiment, the guiding element400can comprise plastics or a composite. The guiding element400can be a monolithic component, andFIG. 3shows the hollow cylinder made of one integral piece as a monolithic component. But the guiding element400may comprise multiple segments, for example two or four ring sections. Two ring sections can form the annular guiding element400, wherein each ring section extends for example over 180°. Also, four ring sections can form the annular or circular guiding element400, wherein each ring section can extend for example over 90°.

The annular guiding element400configured as hollow cylinder as shown inFIG. 4comprises a cylindrical section410and two parallel annular bases430and440perpendicular to the cylinder's axis C. The guiding element400comprises a plurality of tabs450for mounting the guiding element400to another part of the rotor200, in particular to the short circuit ring250. The guiding element400can comprise different numbers of tabs450. The exemplary guiding element400ofFIG. 4comprises twelve tabs450, but can comprise more or less than twelve tabs450, for example eight tabs450. The tabs450are arranged about one of the annular bases430,440and are equidistant from each other, i.e. arranged with equal distances to each other. Each tab450can comprise many different shapes or forms, for example rectangular, square, triangular or polygonal, with or without rounded corners. Further, each tab450can be configured to comprise an opening or mounting hole460for mounting the guiding element400to the short circuit ring250.

FIG. 5illustrates a perspective view of a squirrel cage rotor assembly500of an induction machine including the guiding element400as illustrated inFIG. 4in accordance with an exemplary embodiment of the present invention. The squirrel cage rotor assembly500corresponds essentially to the rotor assembly200previously described with reference toFIG. 2.

AsFIG. 5illustrates, the squirrel cage rotor assembly500, herein also referred to as rotor500, comprises two guiding elements400, each arranged in the opposing bar end regions240defined by the rotor conductor bars230. As noted before, because of the design/construction of the rotor500, the rotor500comprises axial spaces260between the end lamination sections215and the short circuit rings250, which allow the rotor conductor bars230, specifically the ends of the bars230to behave like a fan, which draws air away from an intended cooling path of axial vents270(seeFIG. 3).

According to an exemplary embodiment, the guiding elements400are arranged at least in the axial spaces260for guiding a cooling fluid flow in the axial direction A of the rotor500. In other words, each guiding element400is arranged to bypass or bridge the axial space260between the short circuit ring250and the end lamination section215so that cooling fluid, such as air or cooling gas, cannot flow from the axial vents270in a radial direction through the spaces260to an outside of the rotor assembly500. The cooling fluid flows through the axial vents270within the lamination sections210and outwards of the rotor500in the axial direction A and thereby provides improved cooling of the rotor500because the cooling fluid cannot escape radially through the spaces260and away from the rotor500. The parasitic air flow path is effectively eliminated. The guiding elements400support and further define the cooling path of the axial vents270.

An outer diameter of the annular guiding element400is configured such that it can be positioned on an inner diameter surface of each short circuit ring250. Thus, the outer diameter of the guiding element400corresponds essentially to an inner diameter of the short circuit rings250. When assembled, the annular guiding element400abuts upon the inner diameter surface of the short circuit ring250as well as the ends of the rotor conductor bars230. A width W of the guiding element400(which may also referred to as height, for example when the guiding element400is referred to as hollow cylinder) is such that the guiding element400extends over the axial space260as well as the width (height) of the short circuit ring250. The guiding element400bypasses and bridges the axial space260. The guiding element400is coupled to an annular outer surface255of the short circuit ring250, for example bolted or screwed, via the tabs450and mounting holes460. Thus, the short circuit ring250comprises corresponding mounting holes which may also be used for balancing of the short circuit ring250.

The annular guiding element400provides an easy and cost-effective solution for providing a designated cooling path of the axial vents270. The guiding element400can be mounted during an assembly of the induction machine or later in the field, for example during a service of a machine, without other modifications. Material strength requirements of the guiding element400can be minimized since the guiding element400is mostly retained by the rotor conductor bars230and the short circuit rings250. The guiding element400can be constructed in two or more pieces to easily fit around fans or other shaft mounted components, as well as minimize fabrication cost of a full cylinder.

FIG. 6andFIG. 7illustrate perspective views of further embodiments of guiding elements600,700for an induction machine in accordance with exemplary embodiments of the present invention. The guiding elements600,700comprise essentially the same characteristics and construction as the guiding element400described inFIG. 4with exception of the tabs450. The guiding elements600,700comprise different tab configurations.

With reference toFIG. 6, the guiding element600can comprise a circular or annular mounting element650which is coupled to one of the annular bases430or440(seeFIG. 4). The mounting element650is in form of a flattened ring or cylinder and comprises the same material(s) as the guiding element600since the mounting element650is a feature of the guiding element600. The guiding element600does not comprise individual tabs for mounting to the short circuit ring250. Instead, the guiding element600comprises the mounting element650with mounting holes660provided about the annular mounting element650, the mounting holes660being equidistant from each other. The mounting element650can comprise for example twelve mounting holes660, but can of course also comprise more or less than twelve mounting holes660. When assembled, the mounting element650abuts upon the annular outer surface255of the end connector250(seeFIG. 5). The guiding element700ofFIG. 7is similar to the guiding element600as shown inFIG. 6and comprises an annular mounting element750with equidistant mounting holes760. In an embodiment, the mounting element750further comprises cut-outs770, for example to reduce material costs. As noted before with reference to the guiding element400, the guiding elements600,700can be integrated components, i.e. monolithic components or one-piece components, or can be multiple-piece components comprising one or more segments. The guiding elements600,700can comprise plastics or a composite, and can be formed integrally for example by moulding. In other embodiments, the guiding elements600,700can comprise metal.