Patent Publication Number: US-2015061441-A1

Title: Electric machine and associated method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a non-provisional application and claims priority to U.S. Provisional Patent Application 61/871,518 filed Aug. 29, 2013 for “ELECTRIC MACHINE AND ASSOCIATED METHOD”, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The embodiments described herein relate generally to an electric machine, and more specifically, to a kit and method associated with motors having radially embedded permanent magnet rotors. 
     Various types of electric machines include permanent magnets. For example, a brushless direct current (BLDC) motor may include a plurality of permanent magnets coupled to an exterior surface of a rotor core. Typically, the permanent magnets are coupled to the exterior surface of the rotor core using an adhesive and/or an outer retaining covering. This coupling between the permanent magnets and the rotor core must resist forces exerted on the permanent magnets during high speed rotation tending to separate the permanent magnets from the motor. 
     Permanent magnets may also be positioned within a rotor core, commonly referred to as an interior permanent magnet rotor. Slots are formed within the rotor, and magnets are inserted into the slots. The magnet slots must be larger than the magnets to allow the magnets to be inserted. However, the magnets must be secured within the slots to prevent movement of the magnets during operation of the machine. The performance of the machine depends on maintaining the magnets in a known position within the rotor. An adhesive may be used to secure the magnets in a fixed position relative to the rotor. However, adhesives have a limited life due to factors such as temperature, temperature cycling, and environmental conditions. 
     Many known electric machines produce work by generating torque, which is the product of flux, stator current and other constants. In electric motors, flux is typically produced by permanent magnets positioned on a rotor within the motor. Some known rare earth permanent magnets, such as neodymium iron boron magnets, generate greater amounts of flux than typical ferrite permanent magnets. However, the cost of rare earth magnets has drastically risen in recent years, prompting the need for low-cost permanent magnet systems that generate similar amounts of flux and provide efficiencies similar to systems using rare earth magnets. 
     Positioning the permanent magnet in a radially extending orientation may enhance the magnetic field and enable the use of lower cost materials to replace rare earth magnets. 
     Positioning the permanent magnet in a radially extended orientation may necessitate constructions of the rotor that result in reduced cross sectional strength for the rotor which may tend to be more susceptible to the negative effects of vibrations. 
     Brushless motors are used in a wide variety of systems operating in a wide variety of industries. As such, the brushless motors are subject to many operating conditions. In such a brushless motor, a permanent magnet rotor and the produced torque may combine to result in cogging, as well as commutation torque pulses. The cogging and the torque pulses may get transmitted to the shaft of the motor, and then onto a fan or blower assembly that is attached to the shaft. In such applications these torque pulses and the effects of cogging may result in acoustical noise that can be objectionable to an end user of the motor. 
     To counter such operating conditions, introduction of a resiliency between the component that is producing these torque pulses and the shaft that transmits the torque to the fan or blower, which is attached to the shaft, would be desirable. However, the resilient rotor constructions that have been designed and produced are related to such motors where the permanent magnet structure is such that magnets are mounted on the surface of the rotor. In such systems, the resilient components are attached to a central core by metal rods or clips, spot welding, or by tig welding. However, in an interior permanent magnet rotor design, where magnets are interior to the rotor and a laminated structure is used for rotor core, it is difficult to attach a resilient component to rotor core by tig welding or spot welding without increasing a length of the rotor. 
     The present invention is directed to alleviate at least some of these problems with the prior art. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, an electric machine is provided. The electric machine includes a machine housing and a stator disposed at least partially within the housing. The electric machine also includes a radially embedded permanent magnet rotor disposed at least partially within the housing and an endcap. The rotor has at least one radially embedded permanent magnet that is configured to provide increased flux to reduce motor efficiency loss. The endcap is operably connected to a distal portion of the rotor. 
     In another aspect, the rotor of the electric machine has a portion thereof for interfering with the radially outward movement of the at least one radially embedded permanent magnet. 
     In another aspect, the electric machine further includes a resilient member configured for damping vibrations. 
     In another aspect, the resilient member of the electric machine includes an inner portion, an outer portion, and an intermediatary portion positioned at least partially between the inner portion and the outer portion. The intermediatary portion at least partially includes a resilient material. 
     In another aspect, the inner portion of the resilient member of the electric machine deflects when subjected to a radial load. 
     In another aspect, the rotor of the electric machine includes a central portion and a plurality of spokes extending outwardly from the central portion. 
     In another aspect, at least one of the plurality of spokes of the rotor of the electric machine defines a first feature and the endcap of the electric machine defines a second feature. 
     In another aspect, first feature of the rotor of the electric machine and the second feature of the rotor of the electric machine cooperate with each other to connect the endcap to the rotor 
     In another aspect, first feature of the rotor of the electric machine includes an internal wall defining an aperture and the second feature of the rotor of the electric machine includes a protrusion extending from the endcap. 
     In another aspect, the protrusion includes one of a pin, a post, and a threaded fastener. 
     In another aspect, the protrusion is integral with the endcap. 
     In another aspect, the protrusion has an interference fit with the aperture. 
     In another aspect, the protrusion has a radially extending rib. 
     In another aspect, the rib is configured to at least one of compress or deform when positioned in the aperture. 
     In another aspect, at least one radially embedded permanent magnet of the rotor of the electric machine is positioned at least partially between two of the plurality of spokes of the rotor of the electric machine. 
     In another aspect, at least one radially embedded permanent magnet of the rotor of the electric machine defines a first part and the endcap defines a second part. The first part and the second part cooperate with each other to limit the movement of the at least one radially embedded permanent magnet relative to the endcap 
     In another aspect, at least one radially embedded permanent magnet of the rotor of the electric machine defines a first part and the endcap defines a second part. The first part and the second part cooperate with each other to limit the movement of the at least one radially embedded permanent magnet relative to the endcap. 
     In another aspect, at least one radially embedded permanent magnet of the rotor of the electric machine defines a first part and the endcap defines a second part. The first part and the second part cooperate with each other to limit the movement of the at least one radially embedded permanent magnet relative to the endcap. 
     In another aspect, at least one radially embedded permanent magnet of the rotor of the electric machine defines a proximate surface thereof proximate the central portion of the rotor and the proximate surface defines the first part. 
     In another aspect, the second part includes a member extending from the endcap. 
     In another aspect, the member comprises one of a pin, a post, a wedge and a threaded fastener. 
     In another aspect, the member is integral with the endcap. 
     In another aspect, the member has an inclined surface that increases the advances the member toward the proximate surface of the magnet as the endcap is advanced toward the rotor. 
     In another aspect, the at least one permanent magnet is a ferrite permanent magnet. 
     In another aspect, the electric motor further includes a second endcap. The second endcap is operably connected to the rotor and positioned opposed to the first endcap. 
     In another aspect, the at least one permanent magnet is fabricated from a magnetic material with remnance higher than 0.4 T, wherein the at least one permanent magnet is configured to provide increased flux to reduce motor efficiency loss compared to a copper winding. 
     In another aspect, the at least one permanent magnet is integral with the endcap. 
     In another aspect, the winding of the stator includes an aluminum winding. 
     In another aspect, an endcap for an electric machine is provided. The electric machine has a stator and a rotor including a permanent magnet. The endcap includes a feature cooperating with the rotor to secure the endcap to the rotor and a member cooperating with the magnet to limit the movement of the magnet relative to the rotor. 
     In yet another aspect, a method of manufacturing an electric machine is provided. The method includes the steps of providing a machine housing and disposing a stator at least partially within the housing. The stator includes a plurality of teeth. The method further includes the steps of winding a number of turns around at least one tooth of the plurality of teeth and disposing a rotor at least partially within the housing. The rotor has at least one permanent magnet and is configured to rotate with respect to the stator. The method further includes the step of disposing an endcap at a distal portion of the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a rotor subassembly for use in rotor assembly of the present invention; 
         FIG. 2  is a perspective view of the rotor assembly of the present invention including the rotor subassembly of  FIG. 1 ; 
         FIG. 3  is a perspective view of an end cap for use with the rotor subassembly of  FIG. 1  to be used to form the rotor assembly of  FIG. 2 ; 
         FIG. 3A  is a partial cross sectional view of the rotor assembly of  FIG. 2  along the line  3 A- 3 A in the direction of the arrows showing the interaction of the magnet, the rotor and the tabs of the end cap; 
         FIG. 3B  is a partial cross sectional view of the rotor assembly of  FIG. 2  along the line  3 B- 3 B in the direction of the arrows showing the interaction of the rotor apertures and the pins of the end cap; 
         FIG. 3C  is a enlarged partial perspective view of the end cap of  FIG. 3 , showing the pins and the tabs in greater detail; 
         FIG. 3D  is a enlarged partial perspective view of an alternate embodiment of a rotor assembly of the present invention having a alternate design for the pins of the end cap; 
         FIG. 3E  is a enlarged partial perspective view of an alternate embodiment of a rotor assembly of the present invention having a alternate design for the tabs of the end cap; 
         FIG. 4  is a perspective view the rotor assembly of  FIG. 3  assembled onto a shaft and having the resilient support of the present invention; 
         FIG. 5  is a plan view, partially in cross section, of an optional resilient end support for the rotor assembly of  FIG. 3 ; 
         FIG. 6  is a plan view of an end cap according to another aspect of the present invention; 
         FIG. 7  is an end view, partially in cross section, of the endcap of  FIG. 6 ; 
         FIG. 8  is a plan view of another end cap according to another aspect of the present invention; and 
         FIG. 9  is a flow chart of an exemplary method for assembling an electric motor according to another aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Due to increased costs of rare earth magnets and copper used for windings, lower cost alternative materials are desirable in the design and manufacture of electric motors. The methods, systems, and apparatus described herein facilitate the utilization of lower cost alternative materials within an electric machine. This disclosure provides designs and methods using material alternatives to rare earth magnets while reducing or recapturing the efficiency losses associated with those alternative materials and reducing or eliminating an increase of the length of the motor. This disclosure further provides designs and methods to reduce the vibration caused by torque by providing resilient rotor constructions. 
     Technical effects of the methods, systems, and apparatus described herein include at least one of improved performance and quality and reduced labor costs. 
       FIG. 1  is a perspective view of a rotatable assembly  12  for use in an electric motor  10  according to an embodiment of the present invention. The electric machine  10  may also include a machine assembly housing  14  and a stationary assembly  16 . The machine assembly housing defines an interior  18  and an exterior  20  of machine  10  and is configured to at least partially enclose and protect stationary assembly and rotatable assembly  12 . 
     Stationary assembly  16  typically includes a stator core  26 , which includes a plurality of stator teeth or projections  22 . End caps (not shown) are positioned over opposed end teeth of the plurality of stator teeth  22 . Wire  28  is wound around stator teeth  22  and the end caps to form each of a plurality of windings  24 . In an exemplary embodiment, stationary assembly is a three phase salient pole stator assembly. Stator core is formed from a stack of laminations made of a highly magnetically permeable material, and windings are wound on stator core in a manner known to those of ordinary skill in the art. Laminations are stacked such that stator core reaches a predefined length. In the exemplary embodiment, the plurality of laminations that form the stator core may be either interlocked or loose laminations. In an alternative embodiment, stator core is a solid core. For example, stator core may be formed from a soft magnetic composite (SMC) material, a soft magnetic alloy (SMA) material, and/or a powdered ferrite material using a sintering process. In another alternate embodiment, the windings are wound around a plurality of spools (not shown), each of which is removably fitted to one of the stator teeth. 
     As shown in the embodiment of  FIG. 1 , rotatable assembly  12  includes a permanent magnet rotor core or rotor  36  and a shaft  38  and is configured to rotate around an axis of rotation  34 . In the exemplary embodiment, rotor core  36  is formed from a stack of laminations made of a magnetically permeable material and is substantially received in a central bore of stator core. While  FIG. 1  is an illustration of a three phase electric motor, the methods and apparatus described herein may be included within machines having any number of phases, including single phase and multiple phase electric machines. 
     In the exemplary embodiment, electric machine  10  is coupled to a fan (not shown) for moving air through an air handling system, for blowing air over cooling coils, and/or for driving a compressor within an air conditioning/refrigeration system. More specifically, machine  10  may be used in air moving applications used in the heating, ventilation, and air conditioning (HVAC) industry, for example, in residential applications using ⅓ horsepower (hp) to 1 hp motors or greater and/or in commercial and industrial applications and hermetic compressor motors used in air conditioning applications using higher horsepower motors, for example, but not limited to using ⅓ hp to 7.5 hp motor or greater. Although described herein in the context of an air handling system, electric machine  10  may engage any suitable work component and be configured to drive such a work component. Alternatively, electric machine  10  may be coupled to a power conversion component, for example, an engine, a wind turbine rotor, and/or any other component configured to rotate rotatable assembly  12  to generate electricity using electric machine  10 . 
     Continuing to refer to  FIG. 1 , the rotatable assembly  12 , also referred to as a radially embedded permanent magnet rotor, includes the rotor core  36  and the shaft  38 . Examples of motors that may include the radially embedded permanent magnet rotors include, but are not limited to, electronically commutated motors (ECM&#39;s). ECM&#39;s may include, but are not limited to, brushless direct current (BLDC) motors, brushless alternating current (BLAC) motors, and variable reluctance motors. Furthermore, rotatable assembly  12  is driven by an electronic control (not shown), for example, a sinusoidal or trapezoidal electronic control. 
     Rotor core  36  is substantially cylindrical and includes an outer edge  40  and a shaft central opening or inner edge  42  having a diameter corresponding to the diameter of shaft  38 . Rotor core  36  and shaft  38  are concentric and are configured to rotate about axis of rotation  34 . In the exemplary embodiment, rotor core  36  includes a plurality of laminations  44  that are either interlocked or loose. For example, laminations  44  are fabricated from multiple punched layers of stamped metal such as steel. In an alternative embodiment, rotor core  36  is a solid core. For example, rotor core  36  may be fabricated using a sintering process from a soft magnetic composite (SMC) material, a soft magnetic alloy (SMA) material, and/or a powdered ferrite material. 
     In the exemplary embodiment, rotor core  36  includes a plurality of radial apertures  46 . For example, a first wall  48 , a second wall  50  and a third wall  52  define a first radial aperture  54  of the plurality of radial apertures  46 . Each radial aperture  46  includes a depth d and thickness t and extends axially through rotor core  36  from first end  30  (shown in  FIG. 1 ) to second end  32  (also shown in  FIG. 1 ). Each radial aperture  46  is configured to receive one or more permanent magnets  56  such that each magnet  56  is radially embedded in rotor core  36  and extends at least partially from rotor first end  30  to rotor second end  32 . In the exemplary embodiment, permanent magnets  56  are hard ferrite magnets magnetized in a direction tangent to axis of rotation  34 . However, magnet  56  may be fabricated from any suitable material that enables motor  10  to function as described herein, for example, bonded neodymium, sintered neodymium, and/or samarium cobalt. 
     In the exemplary embodiment, rotor core  36  includes a plurality of rotor poles  58 , each having an outer wall  60  along rotor outer edge  40  and an inner wall  62  (shown in  FIG. 1 ). In the exemplary embodiment, the number of radial apertures  46  is equal to the number of rotor poles  58 , and one magnet  56  is positioned within each radial aperture  46  between a pair of rotor poles  58 . Although illustrated as including ten rotor poles  58 , rotor core  36  may have any number of poles that allows motor  10  to function as described herein, for example, six, eight or twelve poles. 
     In the exemplary embodiment, the design of radially embedded permanent magnet rotor core  36  utilizes lower-cost magnets, yet achieves the power densities and high efficiency of machines using higher-cost magnets, such as neodymium magnets. In the exemplary embodiment, increased efficiency and power density of motor  10  is obtained by increasing the flux produced by rotor core  36 . Increased flux generation is facilitated by magnets  56  positioned in radial apertures  46  at depth d, between a minimum magnet depth and a maximum magnet depth. The minimum magnet depth is defined by the equation: 
     
       
         
           
             
               
                 D 
                 
                   m 
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                   i 
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               = 
               
                 
                   ( 
                   
                     π 
                     * 
                     R 
                   
                   ) 
                 
                 n 
               
             
             , 
           
         
       
     
     wherein D min  represents the minimum depth variable, R represents the rotor radius, and n represents the number of rotor poles. The maximum magnet depth is defined by the equation: 
     
       
         
           
             
               
                 D 
                 
                   ma 
                    
                   
                       
                   
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                   x 
                 
               
               = 
               
                 R 
                 - 
                 
                   
                     0.5 
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                     t 
                   
                   
                     tan 
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                       ( 
                       
                         180 
                         n 
                       
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     wherein D max  represents the maximum depth variable, R represents the rotor radius, t represents the magnet thickness in the direction of magnetization, and n represents the number of rotor poles. In the exemplary embodiment, rotor core  36  facilitates increased flux production resulting in optimum efficiency and power density when magnets  56  extend into radial aperture at a depth between D min  and D max . 
     Continuing to refer to  FIG. 1 , the radial apertures  46  may, as shown, be generally rectangular. Alternatively, radial apertures  46  may have any suitable shape corresponding to the shape of the permanent magnets that enables electric motor to function as described herein. For example, radial apertures  46  may be tapered, as described in more detail below. 
     In the exemplary embodiment of  FIG. 1 , radial aperture  46  includes one or more permanent magnet retention members or tabs  66 . For example, a first pair of tabs  66  is located proximate pole outer wall  60  along rotor outer edge  40  and extends into radial aperture  46  from first and second walls  48  and  50 . Each tab  66  of the first pair of tabs  66  is configured to facilitate retention of magnet  56  within radial aperture  46  by substantially preventing movement of magnet  56  in a radial direction towards outer edge  40 . Further, a second pair of tabs  68  is located along pole inner wall  62  and extends into radial aperture  46  from first and second walls  48  and  50 . Each tab  66  of the second pair of tabs  68  is configured to facilitate retention of magnet  56  within radial aperture  46  by substantially preventing movement of magnet  56  in a radial direction towards shaft  38 . Alternatively, rotor core  36  may have any number and location of tabs  66  that enable rotor core  36  to function as described herein. 
     Alternatively, it should be appreciated that the radial apertures and magnet may be matingly generally tapered. First and second walls of the radial aperture may converge as they extend from rotor inner wall  62  to rotor outer wall  60  and are configured to engage the tapered walls of magnet to facilitate retention of magnet within radial aperture by substantially preventing movement of magnet in a radial direction towards rotor outer edge. Furthermore, each tapered radial aperture may include a pair of protrusions located along pole inner wall  62  to facilitate retention of magnet within radial aperture by substantially preventing movement of magnet in a radial direction. 
     As shown in  FIG. 1 , the rotor core  36  is positioned relative to stationary assembly  16 , and rotor outer edge  40  and an inner edge  74  of stationary assembly  16  define a small air gap  72 . Air gap  72  allows for relatively free rotation of rotor core  36  within stationary assembly  16 . Radially embedded magnets  56  of rotor core  36  are configured to facilitate increased flux to air gap  72 , resulting in increased motor torque generation. The radial orientation of radially embedded magnets  56  results in the magnet flux only crossing the magnet once, as opposed to the flux produced by surface-mounted magnets, which must cross the magnets twice. Crossing magnet  56  only once significantly reduces the path of the flux through material of low permeability (i.e. air and magnet  56 ), resulting in increased flux delivery and torque. Increased flux delivery and torque also result from radial magnets  56  of the same polarity positioned on opposite edges  48  and  50  of each rotor pole  58 , which focuses flux toward rotor outer edge  40 . However, any magnetic support structure above or below magnet  56  in a radial direction provides a path for flux to flow without crossing air gap  72 , resulting in torque losses. In the exemplary embodiment of  FIG. 5 , only a small or limited amount of magnetic material (i.e. tabs  66 ) is positioned above or below magnet  56 . Alternatively, rotor core  36  does not include any magnetic material immediately above or below magnet  56  such that no magnetic material is positioned between permanent magnet  56  and rotor outer edge  40 . 
     In the exemplary embodiment, rotor poles  58  are spaced from each other a distance f to reduce flux loss through magnetic support structure (e.g. rotor poles  58 ). In the exemplary embodiment, distance f is greater than or equal to five times the length of air gap  72  (the gap between rotor outer edge  40  and stator inner edge  74 ), facilitating high flux generation. Alternatively, distance f is greater than or equal to three times the length of air gap  72 . Alternatively still, distance f is greater than or equal to ten times the length of air gap  72 . In the exemplary embodiment, distance f is maintained between tabs  66 . Alternatively, distance f is maintained between radial aperture walls  48  and  50  if no tabs  66  are present, or between tab  66  and wall  48  or  50  if tab  66  is present on only one of walls  48  and  50 . 
     As shown in  FIG. 1 , rotor core  36  may include a plurality of laminations  44  as mentioned herein, and, for simplicity, each lamination may be similar or identical and include a plurality of pie shaped portions  80  extending by spoke portions  82  from a central tubular shape hub portion  84 . 
     Alternatively, the rotor core may include a first half-core, a second half-core, a center lamination, and first and second end laminations. The half-cores each include a plurality of independent rotor poles positioned radially about a sleeve. A plurality of radial apertures are defined between rotor poles and are configured to receive one or more permanent magnets. Each rotor pole is held in spaced relation to sleeve by at least one of center lamination and end laminations. In this exemplary embodiment, laminations also referred to as shorting laminations, are structurally similar, and each includes a plurality of connected rotor poles positioned radially about a central hub. Rotor poles each include an outer edge and an inner edge. Adjacent pairs of rotor poles are connected at inner edges by a bridge, which is connected to central hub. 
     In this exemplary embodiment, the center lamination is positioned between half-cores, and end laminations are positioned on opposite ends of rotor core. In this exemplary embodiment, half-cores are solid cores. Alternatively, half-cores are formed as a whole core and/or are fabricated from a plurality of lamination layers. Although rotor core is described with a single center lamination and two end laminations, rotor core may have any number of center and end laminations that enables motor to function as described herein. Connected rotor poles support rotor poles at a distance from sleeve to prevent flux losses in half-cores, since little or no magnetic material is located above or below magnets positioned therein. A portion of flux generated by rotor core is lost, however, due at least in part to connected rotor poles of laminations. In order to minimize flux losses, in the exemplary embodiment, the sum of the thicknesses of laminations having connected rotor poles is less than or equal to 12% of the total length of rotor core. Alternatively, the sum of the thicknesses of laminations having connected rotor poles is less than or equal to 2% of the total length of rotor core. Alternatively still, the sum of the thicknesses of laminations having connected rotor poles is less than or equal to 1% of the total length of rotor core. 
     Referring now to  FIG. 2  and according to an embodiment of the present invention, endcaps  100  are shown in position on opposed ends  102  of the rotor core  36 . As shown, the endcaps  100  are operably connected to the rotor core  36 . The endcaps may be used to assist in the securing of the components that form the rotor core  36  together and to improve the rigidity of the rotor core  36 . 
     Referring now to  FIG. 3 , one of the endcaps  100  is shown in greater detail. The endcap  100  may have any suitable size and shape and for simplicity and as shown, the endcap  100  may have a generally cylindrical shape. For example, the endcap  100  may have an outside diameter EOD (see  FIG. 3 ) defined by outer periphery  104  of the endcap  100  and the outside diameter EOD may be similar to outside diameter OD (see  FIG. 2 ) of rotor core  36 . 
     The endcap  100  may have opposed inner face  106  and outer face  108 . The opposed faces  106  and  108  may be parallel and spaced apart defining an end cap thickness CT. The thickness CT is selected to provide sufficient strength and rigidity to the endcap  100 . As shown in  FIG. 2 , the inner face  106  of endcaps  100  may mate against opposed ends  102  (see  FIG. 2 ) of rotor core  36 . 
     Referring now to  FIG. 3  and  FIG. 3B , the endcap  100  may include a rotor engaging feature  110  for engaging rotor core  36 . As shown in  FIG. 3B , the rotor engaging feature may be in the form of a protrusion  110  extending outwardly in a normal direction from inner face  106  of endcap  100 . The protrusion  110  may have any suitable shape and preferably has a shape that cooperates with rotor endcap engaging feature  112  on rotor core  36  (see  FIG. 1 ). 
     As shown in  FIG. 3 ,  FIG. 3B  and  FIG. 3C , the protrusion  110  may be in the form a cylindrical post  110 . The post  110  may define a post diameter PD and post length PL. The post  110  may include one or more lands  114  which define one or more grooves  116  spaced therebetween. The lands  114  and grooves  116  may extend in a longitudinal direction along the post  110 . The lands  114  of the post  110  may be configured to be conformable to fit matingly with the rotor endcap engaging feature  112  on rotor core  36 . The lands  114  may be elastically or deformably conformable. 
     While the endcap  100  may include a solitary post  110 , it should be appreciated and as shown in  FIG. 3 , the endcap  100  may include a plurality of posts  110 . Each of the posts  110  may be identical or some may be different. The posts  110  may be equally spaced apart or may be spaced apart in any fashion. 
     Continuing to refer to  FIG. 3 ,  FIG. 3B  and  FIG. 3C , the post  110  may be narrowed at tip  118  of the post  110  to assist assembly onto the rotor core  36 . For example the post may be stepped, have a radius or, as shown, have a chamfer  120  at the tip  118 . To add durability and strength to the posts and to assist manufacturing base  122  of post  110 , the endcap  110  adjacent the post  110  at the base  122  may be have a recess  124 . The recess may serve to provide for a transition from the face of end cap  110  to the post  100  to assure that sharp corners are avoided and that there is no interference between the endcap  110  and the laminations  44  of rotor core  36  (see  FIG. 1 ). 
     Referring again to  FIG. 3B  and  FIG. 2 , the rotor endcap engaging feature  112  on rotor core  36  may have any suitable configuration to cooperate with the rotor engaging feature  110  of endcap  100 . For example and as shown in  FIG. 3B  and  FIG. 2 , the rotor endcap engaging feature  112  may be in the form of an aperture  112 , for example, a cylindrical shaped opening formed in at least some of the laminations  44  that form the rotor core  36 . 
     Referring again to  FIG. 3 , the rotor engaging feature  110  of endcap  100  may be in the form of an aperture or opening  126  formed in the endcap  100 . A single or a plurality of openings  126  may be used. The rotor engaging feature  110  of endcap  100  may include either posts  110  or openings  126 , or as shown in  FIG. 3 , may include both posts  110  and openings  126 . The openings  126  may be positioned in alignment with the apertures  112  in the laminations  44  of the rotor core  36 . Fasteners (not shown), in the form of rivets or threaded fasteners may be matingly inserted into the openings  126  and the apertures  112 , The fasteners may extend from one endcap  100  to the opposed endcap  100 , securing the endcaps  100  to the laminations  44  that form the rotor core  36  to each other. The fasteners further improve the rigidity of the rotor core  36 . 
     Referring to  FIG. 3 ,  FIG. 3A  and  FIG. 3C , the endcap  100  may include a magnet engaging feature  128  for cooperation with the magnets  56  positioned in rotor core  36 . The magnet engaging feature  128  may serve to limit the movement of the magnets  56  relative to the rotor core  36 . 
     As shown in  FIG. 1  features, in the form of, for example, outer tabs  66  and inner tabs  68 , may be used to limit the motion of the magnets  56  within the pockets  46  formed in rotor core  36 . Even with such limiting motion features  66  and  68 , manufacturing tolerances and need for assembly clearances may permit the magnets  56  to move within the pockets  46 , particularly at high rotational speeds of the rotor core  36 . Such movement of the magnets may contribute to vibration and/or noise. The magnet engaging feature  128  is intended to serve to limit the movement of the magnets  56  relative to the rotor core  36  and to reduce such vibration and/or noise. 
     As shown in  FIG. 3 ,  FIG. 3A  and  FIG. 3C , the magnet engaging feature  128  may be in the form of a protrusion  128 . Note that there may be, as shown, a solitary protrusion  128  defining the magnet engaging feature  128  or a plurality of protrusions. The protrusions  128  cooperates with the magnets  56  and, as such, the protrusions  128  may have a one to one relationship with the magnets  56  and may, like the magnets  56 , be uniformly positioned in the rotor core  36 . As shown in  FIG. 2 , the protrusions  128  may, when the endcaps  100  are positioned on rotor core  36 , be matingly fitted into the pockets  46  of the rotor core  36 . 
     While, as shown in  FIG. 3 ,  FIG. 3A  and  FIG. 3C , the protrusions  128  engage inner face  130  of the magnets  56 , it should be appreciated that the protrusions  128  may be positioned relative to the magnets such that the protrusions  128  engage any other portion of the magnets, for example the outer face  132  of the magnets  56 . 
     The protrusions  128  may have any suitable shape and may, since the endcaps  100  are assembled onto the opposed ends  102  of the rotor core  36 , extend normally from inner face  106  of endcap  100 . The protrusions  128  may have a simple shape such as rectangular or cylindrical shape. As shown the protrusions have a generally rectangular shape. While the protrusions may be rectangular, as shown the protrusions  128  may include an inclined face  134  for engagement with inner face  130  of the magnets  56 . 
     The inclined face  134  of the protrusion  128  serves to urge the magnet  56  toward the outer tab  68  of rotor core  36  as the endcap  100  is assembled onto the rotor core  36 . Preferably the endcap  100  is made of a resilient material and is integral such that the protrusion  128  keeps an outwardly force on the magnet, keeping it securely against the outer tabs  68  of rotor core  36 , reducing vibration and noise. 
     While the inclined face  134  of the protrusion  128  may be planar, as shown in  FIG. 3 , the inclined face  134  may have a centrally located raised portion  136  centrally positioned between relieved portions  138 . The centrally located raised portion  136  guide the magnet  56  outwardly and the relieved portions  138  provides added resiliency to the protrusion  128 . 
     While the rotor engaging features  110  in the form of conformable posts  110  may be sufficient to provide the rotor core  36  with sufficient rigidity with or without the fasteners positioned in the openings  126  and in the apertures  112  and while the magnet engaging features  128  in the form of protrusions  128  may be sufficient to rigidly secure the magnets  56 , it should be appreciated that to obtain further rigidity for the rotor core  36 , including improved rigidity for the magnets  56 , the rotor core  36  may further include a material, for example a fluid or otherwise conformable material that may dry, form, harden or cure around the posts  110  and/or around the protrusions  128  and other portions of the rotor core  36  to add further rigidity to the rotor core  36 . Such a fluid or conformable material may be a sealant, an adhesive, a coating, a varnish, a paint or a polymer in liquid or solid form. 
     Referring now to  FIG. 2 , the endcaps  100  are shown positioned on opposed ends  102  of rotor core  36 . The outer face  108  of endcap  100  may include an outer circular rib  142  and axial ribs  144  to provide rigidity for the endcap  100 . 
     The Endcap  100  may be made of any suitable durable material. For example the endcap  100  may be made of a non-electrically conductive, non-magnetically conductive material. For example, the endcap  100  may be made of a polymer. If made of a polymer, the endcap  100  may be molded into an integral piece. 
     Referring now to  FIG. 3D  and according to another embodiment of the present invention, endcap  200  is shown. Endcap  200  is similar to endcap  100  except endcap  200  includes a protrusion, pin or post  210  different than post  110  of the endcap  100  of  FIG. 3 . 
     As shown in  FIG. 3D , the protrusion  210  may be in the form a cylindrical post  110 . The post  210  may include one or more lands  214  which define one or more grooves  216  spaced therebetween. The lands  214  and grooves  216  may extend in a longitudinal direction along the post  210 . The lands  214  of the post  210  may be configured to be conformable to fit matingly with the rotor endcap engaging feature  112  on rotor core  36 . The lands  214  may be elastically or deformably conformable. 
     While the endcap  200  may include a solitary post  210 , it should be appreciated and as shown in  FIG. 3 , the endcap  200  may include a plurality of posts  210 . Each of the posts  210  may be identical or some may be different. The posts  210  may be equally spaced apart or may be spaced apart in any fashion. 
     The post  210  may be narrowed at tip  218  of the post  210  to assist assembly onto the rotor core  36 . For example the post may be stepped, have a radius or, as shown, have a chamfer  220  at the tip  218 . To add durability and strength to the posts and to assist manufacturing base  222  of post  210 , the post at the base  222  may have a chamfer or as shown, a radius  224 . 
     Referring now to  FIG. 3E  and according to an embodiment of the present invention, endcap  200 A is shown. Endcap  200 A is similar to endcap  100  except endcap  200 A includes a magnet engaging feature  228 A different than magnet engaging feature  128  of the endcap  100  of  FIG. 3 . 
     Referring to  FIG. 3E , the endcap  200 A may include a magnet engaging feature  228 A for cooperation with the magnets  56  positioned in rotor core  36 . The magnet engaging feature  228 A may serve to limit the movement of the magnets  56  relative to the rotor core  36 . 
     As shown in  FIG. 3E , the magnet engaging feature  228 A may be in the form of a protrusion  228 A. Note that there may be a solitary protrusion  228 A or a plurality of protrusions  228 A. The protrusions  228 A cooperate with the magnets  56  and, as such, the protrusions  228 A may have a one to one relationship with the magnets and may, like the magnets  56 , be uniformly positioned in the rotor core  36 . As shown in  FIG. 2 , the protrusions  228 A may, when the endcaps  200 A are positioned on rotor core  36 , be matingly fitted into the pockets  46  of the rotor core  36 . 
     While, as shown in  FIG. 3E , the protrusions  228 A engage inner face  130  of the magnets  56 , it should be appreciated that the protrusions  228 A may be positioned relative to the magnets such that the protrusions  228 A engage any other portion of the magnets, for example the outer face  132  of the magnets  56 . 
     The protrusions  228 A may have any suitable shape and may, since the endcaps  200 A are assembled onto the opposed ends  102  of the rotor core  36 , extend normally from inner face of endcap  200 A. The protrusions  228 A may have a simple shape such as rectangular or cylindrical shape. As shown the protrusions have a generally rectangular shape. While the protrusions may be rectangular, as shown the protrusions  228 A may include an inclined face  234 A for engagement with inner face  130  of the magnets  56 . 
     The inclined face  234 A of the protrusion  228 A serves to urge the magnet  56  toward the outer tab  68  of rotor core  36  as the endcap  200 A is assembled onto the rotor core  36 . Preferably the endcap  200 A is made of a resilient material and is integral such that the protrusion  228 A keeps a outwardly force on the magnet, keeping it securely against the outer tabs  68  of rotor core  36 , reducing vibration and noise. 
     While the inclined face  234 A of the protrusion  228 A may be planar, as shown in  FIG. 3E , the inclined face  234 A may have spaced apart end portions  236 A separated by a relieved portion  238 A. The end portions  236 A guide the magnet  56  outwardly and the relieved portion  238 A provides added resiliency to the protrusion  228 A. 
     As shown in  FIG. 4 , the rotor assembly  12  may include a resilient structure  146  positioned between the rotor core  36  and the shaft  38 . The resilient structure  146  in the rotor assembly  12  is beneficial in the suppression of vibration transmissibility from the motor. 
     Referring now to  FIG. 5 , the resilient structure of  FIG. 4  is shown in greater detail. In the illustrated embodiment, the rotor assembly  12  includes the resilient structure  146  that includes an outer rigid structure  148 , an inner rigid structure  150 , and a resilient component  152  that is in the annular space between the inner rigid structure  150  and the outer rigid structure  148 . 
     As shown in  FIGS. 4 and 5 , these three components are located proximate a endcap  100  of rotor assembly  12  such that inner rigid structure  150  engages shaft  38  and outer rigid structure  148  engages, for example, a endcap  100  that engages rotor core  36  that contains the various interior permanent magnets  56  therein. In embodiments, an interior surface  154  of inner rigid structure  150  is attached to the corresponding portion  156  of shaft  38  to provide rotation of shaft  38 . In specific embodiments, interior surface  154  of inner rigid structure  150  as well as the corresponding portion  156  of shaft  38  are keyed such that rotation of rotor core  36  ensures rotation of shaft  38 . It should be appreciated that the shaft  38  may be in clearance with the opening  42  formed in rotor core  36  such that vibrations between core  36  and shaft  38  are isolated from each other. 
     In various embodiments, the three components (outer rigid structure  148 , inner rigid structure  150 , and resilient component  152 ) are fabricated as separate components or are molded together as a single component. Fabrication includes placing inner rigid structure  150  within a bore extending through the resilient component. In various implementations, two resilient structures  146  are utilized in a motor configuration, for example, one on each end of a rotor. Alternatively, a single resilient structure  146  may be utilized proximate the axial center of rotor core  36 . 
     In various embodiments resilient component  152  is a thermoset material or a thermoplastic material, for example rubber, or other elastomeric, low modulus material of between about 30 and about 70 MPa (MegaPascals), which is either preformed or formed in place. In one embodiment, resilient component  152  is formed in place such that it is attached to the inner rigid structure  150 . Resilient structure  146  can be attached to the endcaps  100  and central rotor core  36  (laminations  44 ) using various mechanical devices, including, but not limited to, rivets, bolts and nuts, keyways, adhesives, and columns that are inserted, injected or cast. Alternatively, resilient structure  146  may be press fit within the rotor core  36  in a fashion similar to the seating of a bearing. 
     Since the resilient component  152  is quite pliable, securing the resilient component  152  to the outer rigid structure  148  and to the inner rigid structure  150  is preferred, as mechanical connections, such as interference fits and even mechanical interlock of components may not be sufficient to prevent motion between the resilient component and the outer rigid structure  148  and/or the inner rigid structure  150 . Surface treatments to the outer rigid structure  148  and/or the inner rigid structure  150  may reduce such motion. Alternatively or in addition, a material such as an adhesive may be applied between the resilient component  152  and the outer rigid structure  148  and/or the inner rigid structure  150  to further reduce such motion. 
     Referring now to  FIGS. 6 and 7 , another embodiment of an endcap for use in a rotor assembly according to an embodiment of the present invention is shown as endcap  300 . Endcap  300  is similar to endcap  100  of  FIGS. 2-4 , except endcap  300  may include a resilient structure  346  that includes an outer rigid structure  348  that is integral with end cap housing  302 . 
     The endcap  300 , as shown in  FIG. 6 , includes an outer rigid structure  348  that, unlike the outer rigid structure  148  of resilient structure  146  of  FIG. 4 , is integral with end cap housing  302 . The outer rigid structure  348  serves as a portion of a resilient structure  346  that functions similarly to the resilient structure  146  of  FIG. 4 . The resilient structure  346  further includes an inner rigid structure  350  and a resilient component  352 . The inner rigid structure  350  may be similar or identical to inner rigid structure  150  of  FIG. 5 . The resilient component  352  may be similar or identical to the resilient component  152  of  FIG. 5 . 
     Similarly to the resilient component  152  of the resilient structure  146  of the motor  10  of  FIGS. 1-5 , the resilient component  352  is quite pliable. Securing the resilient component  352  to the outer rigid structure  348  and to the inner rigid structure  350  is preferred, as mechanical connections, such as interference fits and even mechanical interlock of components may not be sufficient to prevent motion between the resilient component and the outer rigid structure  348  and/or the inner rigid structure  350 . 
     The endcap  300  may include one or more rotor engaging features  310  for engaging rotor core  36 . The rotor engaging features  310  may be in the form of protrusions  310  similar to protrusions  110  of the endcap  100  of  FIG. 3 . The protrusions  310  may be in the form of posts  310  similar to posts  110  of the endcap  100  of  FIG. 3 . Similarly, the endcap  300  may further include openings  326  similar to openings  126  of the endcap  100  of  FIG. 3 . 
     The endcap  300  may further include one or more magnet engaging features  328  for cooperation with the magnets  56  positioned in rotor core  36 . The magnet engaging feature  328  may be in the form of protrusions  328  similar to protrusions  128  of the endcap  100  of  FIG. 3 . The protrusions  328  may include an inclined face  334  similar to protrusions  128  of the endcap  100  of  FIG. 3  for engagement with inner face  130  of the magnets  56 . 
     The Endcap  300  may be made of any suitable durable material. For example the endcap  300  may be made of a non-electrically conductive, non-magnetically conductive material. For example, the endcap  300  may be made of a polymer. If made of a polymer, the endcap  300  may be molded into an integral piece. 
     Referring now to  FIG. 8 , another embodiment of an endcap for use in a rotor assembly according to an embodiment of the present invention is shown as endcap  400 . The endcap  400  includes an endcap housing  402 . The endcap housing  402  is similar to endcap housing  302  of  FIGS. 6 and 7  and may include the magnet engaging features (not shown), the openings (not shown), and the rotor engaging features (not shown) of the endcap housing  302  of  FIGS. 6 and 7 . Endcap  400  includes a resilient structure  446  that includes an outer rigid structure  448  that, like the outer rigid structure  348  of the resilient structure  346  of  FIGS. 6 and 7 , is integral with end cap housing  402 . The resilient structure  446  further includes an inner rigid structure  450 . The inner rigid structure  450  may be similar or identical to inner rigid structure  350  of the resilient structure  346  of  FIGS. 6 and 7 . The resilient structure  446  further includes an resilient component  452 . The resilient component  452  may be similar or identical to resilient component  352  of the resilient structure  346  of  FIGS. 6 and 7 . 
     Similarly to the resilient component  352  of the resilient structure  346  of  FIGS. 6 and 7 , the resilient component  452  is quite pliable. Securing the resilient component  452  to the outer rigid structure  448  and to the inner rigid structure  450  is preferred, as mechanical connections, such as interference fits and even mechanical interlock of components may not be sufficient to prevent motion between the resilient component and the outer rigid structure  448  and/or the inner rigid structure  450 . 
     Since the endcap housing  402  is preferably molded from a polymer material, materials that may serve to provide adherence of the resilient component  152  to the outer rigid structure  148  and/or to the inner rigid structure  150 , when made of a metal, such as in the outer rigid structure  148  and/or the inner rigid structure  150  of the resilient structure  146  of  FIGS. 1-5 , may not serve to adhere the resilient component  452  to the outer rigid structure  448  and/or to the inner rigid structure  450  of the resilient structure  446  of  FIG. 8 . 
     While, as stated earlier, mechanical interference between the resilient component and a rigid component may not be sufficient, providing mechanical interference between two rigid components, the outer rigid structure  448  and the inner rigid structure  450  may be sufficient. As shown in  FIG. 8 , the outer rigid structure  448 , as shown, includes protrusions  466  that cooperate with pockets  468  formed in the inner rigid structure  450 . The resilient component  452  is positioned between the outer rigid structure  448  and the inner rigid structure  450  to provide the needed resiliency. 
     The above described embodiments are associated with a resilient rotor construction for an interior permanent magnet rotor used, for example, in a brushless motor. The resilient rotor assembly helps to suppress the cogging and commutation torque pulses known to occur in a permanent magnet rotor which does not incorporate a resilient rotor assembly. 
     Referring now to  FIG. 9 , a flow chart of an exemplary method  500  for manufacturing an electric machine  10  (see  FIG. 1 ). The method  500  includes the step  502  of the step of providing a machine housing  14  (see  FIG. 1 ). The method  500  further includes the step  504  of disposing a stator  16  (see  FIG. 1 ) at least partially within the housing  14  (see  FIG. 1 ). The method  500  further includes the step  506  of disposing a rotor  12  (see  FIG. 1 ) at least partially within the housing  14  (see  FIG. 1 ). The rotor  12  (see  FIG. 1 ) has at least one permanent magnet  56  (see  FIG. 1 ) and is configured to rotate with respect to the stator. The method  500  further includes the step  508  of disposing an endcap  100  (see  FIG. 2 ) at a distal portion of the rotor  12  (see  FIG. 1 ). 
     The methods, systems, and apparatus described herein facilitate efficient and economical assembly of an electric motor. Exemplary embodiments of methods, systems, and apparatus are described and/or illustrated herein in detail. The methods, systems, and apparatus are not limited to the specific embodiments described herein, but rather, components of each apparatus and system, as well as steps of each method, may be utilized independently and separately from other components and steps described herein. Each component, and each method step, can also be used in combination with other components and/or method steps. 
     When introducing elements/components/etc. of the methods and apparatus described and/or illustrated herein, the articles “a”, “an”, “the”, and “the” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
     Described herein are exemplary methods, systems and apparatus utilizing lower cost materials in a permanent magnet motor that reduces or eliminates the efficiency loss caused by the lower cost material. Furthermore, the exemplary methods system and apparatus achieve increased efficiency while reducing or eliminating an increase of the length of the motor. The methods, system and apparatus described herein may be used in any suitable application. However, they are particularly suited for HVAC and pump applications. 
     Exemplary embodiments of the electric motor assembly are described above in detail. The electric motor and its components are not limited to the specific embodiments described herein, but rather, components of the systems may be utilized independently and separately from other components described herein. For example, the components may also be used in combination with other motor systems, methods, and apparatuses, and are not limited to practice with only the systems and apparatus as described herein. Rather, the exemplary embodiments can be implemented and utilized in connection with many other applications. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.