Abstract:
A dynamoelectric machine constructed for speed and accuracy of manufacturing has a stator core constructed of 90° symmetrical stator laminations and the windings have differing numbers of poles which overlap in slots of the stator core are wound of the core formed by the laminations in unique fashion. The rotor bars of the machine are skewed to optimize performance of the machine when in the form of a single phase induction motor. Magnet wire leads of the windings are connected directly to terminals on a plug and terminal assembly which is formed for positive location on an end frame of the machine without welding or other fastening to the end frame. The end frames of the machine and stator laminations forming the stator core are formed so as to increase the precision of the final position of the stator relative to the rotor assembly of the dynamoelectric machine. The end frames are constructed for grounding without the use of fasteners or wire. The engagement of the end frames with the stator core is employed as the basis for alignment of the machine components.

Description:
This application is a Divisional Application of application Ser. No. 08/792,982, filed Feb. 3, 1997, which is now U.S. Pat. No. 5,852,338 which is a continuation of application Ser. No. 08/139,578 filed Oct. 20, 1993, abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to electrical apparatus and in particular to a dynamoelectric machine and a method of manufacturing the dynamoelectric machine. 
     BACKGROUND OF THE INVENTION 
     Competitive mass production of dynamoelectric machines in the form of electric motors such as those used in household appliances and other machines requires in the design and manufacture of the motor a simultaneous emphasis on speed and simplicity of manufacture, and the precision of the final motor construction. Moreover, any design or manufacturing process must not add costs out of proportion to the savings achieved through higher production. Thus, the present invention pertains to a motor which incorporates design features optimized for speed of manufacture and precision of the final product. 
     It is well established that the formation of the stator core of an electric motor may be most efficiently carried out by forming the core from a stack of laminations stamped from a sheet of highly magnetically permeable material. The laminations are frequently square because this shape wastes less of the sheet material from which the laminations are stamped. Each lamination is stamped with a central opening and radially extending slots which typically open into the central opening. The central openings of the stator laminations in the stack form the bore of the stator core and the slots define the teeth which extend the length of the stator bore and receive the wire windings of the motor. The slots are stamped symmetrically about the center of the central opening, leaving substantially equal amounts of material along each of the four edges of the lamination. Thus, the amount of magnetic flux which can be carried by the stator core is substantially the same along all four of its sides. 
     It is important that the stator bore be round and straight so that the rotor may freely rotate in the stator core bore while maintaining only a minimal separation between the rotor and the stator core. The straightness of the bore is adversely affected by the inherent presence of variations in thickness (called “gamma” variation) of the rolled sheet material from which the laminations are stamped, so that each lamination is not truly flat. If the laminations are stacked one on top of the other in the same orientation as when each lamination was stamped on the sheet material, the gamma variations will tend to add together rather than cancel out. Thus, the stator bore formed may be substantially curved and unsuitable for mating with the rotor in such a way which will permit the rotor to freely rotate in the stator bore. Punching the central openings of the laminations from the sheet material relieves certain stresses in the material, which tends to cause the material to elastically deform from the round shape struck by the punch, to an elliptical shape. Further deviations from round may be introduced by thermal stress as the stator core is annealed. Again, if the laminations are stacked together in such a way as to add the deviations from round, a bore which is too elliptical to receive the rotor may be produced. In a square lamination having substantially equal amounts of material remaining after punching on all four sides, deformations causing deviation from round can be expected to occur approximately equally along two perpendicular axes lying in the plane of the lamination. Accordingly, it is preferred to rotate each lamination 90° relative to the adjacent lamination in the stack so that gamma variations and deviations from round in the laminations tend to cancel each other out. 
     However, in the past 90° rotation of each lamination relative to the adjacent lamination in the stack has not been practical when constructing stator cores for certain two speed electric motors having two windings which have different numbers of poles. In a two speed motor having a four pole winding and a six pole winding, some of the turns of wire forming the poles must be placed in the same stator slots. In order to provide enough room, the slots where the windings will overlap must be deeper. This requirement introduces asymmetry in the arrangement of slots about the center of the central opening of each lamination, and reduces the amount of material on two of the sides of the lamination relative to the other sides. Equalizing the amount of material on all four sides may be accomplished by elongating the two sides having the deepest slots. However, the combination of the asymmetry of the slot arrangement and the rectangular shape of the lamination makes it impossible to rotate the laminations 90° relative to the adjacent lamination when stacking. The best that can be done presently is to rotate the laminations 180°, which does not permit cancellation of manufacturing tolerances as efficiently as 90° rotation, and thus adversely affects the roundness and straightness of the bore. 
     It is well known that in order to decouple stator slot order harmonics the rotor bars in the squirrel cage rotor of an induction motor should be skewed. Typically, skewing is accomplished by turning the rotor laminations making up the rotor slightly with respect to each other so that the passages formed by overlapping slots of the rotor laminations are generally helical in shape. Helical skewing can be carried out by hand using a jig, or automatically by machine. In the former instance, substantial labor costs are added to the production of the rotor, and in the latter instance it is difficult to reliably automate the delicate operation of turning the rotor laminations slightly relative to each other. Further, the helical passages have a stair-step configuration which can produce undesirable turbulence in the molten material poured into the passages to form the rotor bars. Significant savings can be realized by implementation of a “straight” skew, in which the rotor bar passage consists of two smooth, straight passages which overlap, but are skewed. The skewed passage is typically formed by making the rotor slots asymmetrical about a radial line of the rotor lamination, with the slots in one half of the stack of laminations forming the rotor being the mirror image of the slots in the other half. Although decoupling slot harmonics by using two straight passages which are skewed relative to one another is known, there is presently a need for such a straight skew which delivers better motor performance for single phase motors. 
     Once the rotor and stator have been constructed, it is necessary to assure that the rotor will be aligned with the stator core bore when the rotor is inserted into the bore. The rotor shaft is typically supported for free rotation at its ends in central openings in metal end frames which are connected to the stator core. Tolerances inherent in the formation of the central openings in the end frames and the stator core bore, and the absence of accurate location mechanism for the end frames on the stator core result in many rotor/stator core assemblies being out of alignment. Present practice calls for the introduction of shims in the central openings where the rotor shaft is received to bring the rotor and stator core into alignment. This procedure permits only a relatively coarse adjustment, and requires time and extra labor to accomplish. 
     The manufacturing step of mounting the rotor shaft on the end frames also presently requires significant labor and time to accomplish. The ends of the rotor shaft are mounted by bearings in the central openings of the end frames which permit free rotation of the rotor shaft about its longitudinal axis. Presently, the bearings include many parts and require substantial time to assemble and install in the end frames. 
     The inner raceways of the bearings held in the central openings of the end frames are typically fixed to the rotor shaft at predetermined locations. Thus, the relative location of the end frames is determined by the predetermined locations on the rotor shaft. The presence of tolerances in the dimensions of the rotor shaft, the end frames and the stator core occasionally results in the stator core and end frames not fitting together as they should in the assembly of the machine. A minor misalignment or structural irregularity of the rotor shaft may cause the shaft to wobble as it rotates. The wobble causes variations in the air gap (i.e., the distance separating the rotor and the stator core) which results in undesirable noise and vibration. 
     Another aspect of the assembly of the electric motor which is labor intensive is the electrical connection of the windings to a plug and terminal assembly used to connect the windings to a source of electricity and to control operation windings for starting the machine. Presently, there are at least four connections used to electrically connect the terminal end of each magnet wire to the plug and terminal assembly. The magnet wire is first connected to a terminal having sharp ridges which pierce the insulation on the wires to make electrical contact as the terminals are crimped against the magnet wire. The ridged terminal is connected to wire having plastic insulation, which is in turn connected to a terminal on the plug and terminal assembly. The terminal on the plug and terminal assembly is connected to the circuitry in the plug and terminal assembly. Typically, only two of these connections are made during assembly of the motor. However, each terminal connection is a more likely site for failure. Moreover, connection of the plug and terminal assembly to the end frames of the motor presently requires separate fasteners. The use of such fasteners, or alternative joining methods such as welding or soldering, adds the cost of the fasteners or joining material, and the cost of labor to connect the plug and terminal assembly by application of the fasteners or joining material. 
     In order to ground the motor end frames, a separate assembly step is required for ground connection. For instance, a screw may be received through an end frame and into the plug and terminal assembly, or the connection may be by insulated wire. The insulated wire is connected to the end frame by a screw or a clip, which are additional materials which require additional time to manipulate during assembly of the motor. 
     SUMMARY OF THE INVENTION 
     Among the several objects and features of the present invention may be noted the provision of a dynamoelectric machine capable of rapid production while maintaining quality at or above that of existing machines of the same type; the provision of such a machine which has fewer parts; the provision of such a machine which is secured together with fewer fasteners; the provision of such a machine which makes an economic use of materials in its construction; the provision of such a machine which has fewer internal electrical connections; the provision of such a machine which is grounded without requiring additional wiring or special ground connections; the provision of such a machine which is automatically connected to a ground remote from the machine when connected to a source of electrical power; the provision of such a machine in which the rotor and stator are accurately aligned; the provision of such a machine which accommodates misalignment or structural irregularity of the rotor without introducing substantial stresses to the machine during operation; and the provision of such a machine in which stator slot order harmonics are optimally decoupled. 
     Further among the objects and features of the present invention may be noted the provision of a method for manufacturing a dynamoelectric machine which requires fewer steps to secure the component parts together; the provision of such a method in which critical dimensions are held within closer tolerances to produce more accurate alignment of the stator and rotor; the provision of such a method which employs fewer individual fasteners; and the provision of such a method which can be carried out rapidly and at reasonable cost. 
     Generally, a two-speed dynamoelectric machine constructed according to the principles of the present invention comprises a stator, at least two windings on the stator, a rotor received in the stator and means supporting the rotor for rotation relative to the stator. A first of the two windings has a first number of poles and a second of the two windings has a second number of poles different from the first number of poles. A plurality of stator laminations stacked one on top of the other form the stator core. Each stator lamination comprises a sheet of highly magnetically permeable material having a generally central opening therein, and slots opening into the central opening and extending generally radially outwardly therefrom. The slots are disposed in an arrangement around the periphery of the central opening and receive turns of wire from the two windings of the dynamoelectric machine with at least some of the slots receiving turns of wire from both of the two windings. The arrangement of slots on each stator lamination is symmetrical about a pair of perpendicular lines lying generally in the plane of the stator lamination and intersecting generally at the center of the central opening, and about a diagonal line lying in the plane of the stator lamination, passing through the center of the central opening and making an angle of 45° with the perpendicular lines. Each stator lamination in the stack is rotated 90° relative to other stator laminations about a longitudinal axis of a central rotor-receiving bore of the stator core formed by the central openings of the stator laminations in the stack thereby forming a central bore which is straighter and more nearly cylindrical. 
     In another aspect of the present invention, a dynamoelectric machine comprises a stator including a stator core having a pair of opposing end faces, a bore through the stator core extending from one end face to the other end face, and windings including a start winding and at least one run winding on the stator, each winding having winding leads extending outwardly from the stator. First and second opposite end frames mounted on respective end faces of the stator core each have a generally central opening. A rotor assembly comprises a shaft received in bearing means associated with the central openings of the end frames, and a rotor fixedly mounted on the shaft for conjoint rotation therewith. The rotor is disposed at least in part in the stator core bore, and the rotor and the stator are adapted for magnetic coupling upon activation of the windings for rotating the shaft and rotor relative to the stator and end frames. A plug and terminal assembly includes a casing made of an insulator material, a plurality of lead terminals electrically connected to the winding leads and a plurality of electrical connectors protruding from the casing and electrically connected to the lead terminals. The electrical connectors are constructed for connecting the winding leads to a source of electrical power. A ground tab mounted on and in electrical contact with the second end frame is received in an opening in the casing with the ground tab being disposed for electrical connection to ground upon connection of the electrical connectors to ground. 
     In yet another aspect of the present invention, a dynamoelectric machine has a stator, windings, end frames, bearing means and a rotor assembly as described in the preceding paragraph. The dynamoelectric machine further comprises a plug and terminal assembly including a casing made of insulator material. A switch housed in the casing is operable between a first switch mode in which the start winding is activated and a second switch mode in which the start winding is deactivated. A plurality of electrical connectors are connected to the switch and adapted for connection to a power supply, and a plurality of magnet wire terminals are integrally connected to the switch and receive the terminal ends of the windings thereby providing direct connection of the windings to the switch. 
     In still another aspect of the present invention, a dynamoelectric machine comprises a stator, a rotor assembly, first and second end frames and first and second bearings. The first bearing is disposed in a central opening of the first end frame and fixedly mounted on a rotor shaft of the rotor assembly thereby to prevent axial movement of the rotor shaft relative to the first bearing. The second bearing, disposed in a central opening of the second end frame, comprises a housing and shaft bearing means supported by the housing in a shaft receiving passage. The shaft bearing means is constructed and arranged for rolling engagement with the rotor shaft in the shaft receiving passage for supporting the rotor shaft and permitting rotation of the rotor shaft about its longitudinal axis. The shaft bearing means is free of connection to the rotor shaft. 
     Methods of manufacturing a dynamoelectric machine are also disclosed. In one aspect of the method, end frames are each formed by simultaneously punching from sheet metal blank a generally central rotor shaft receiving opening and locator means spaced from the center of the central opening so as to precisely locate the center of the central opening relative to the locator means. 
     Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective of an electric motor; 
     FIG. 2 is a longitudinal section of the motor; 
     FIG. 3 is an exploded front perspective of the motor; 
     FIG. 4 is a perspective of the rear end frame of the motor, with a plug and terminal assembly illustrated as exploded away from the end frame; 
     FIG. 5 is an enlarged fragmentary perspective of the rear end frame showing the plug and terminal assembly as installed on the end frame; 
     FIG. 6 is an enlarged fragmentary section taken in the plane including line  6 — 6  of FIG. 5; 
     FIG. 7 is a front elevation of the plug and terminal assembly showing locating posts of the assembly as received in a stator slot (shown in phantom); 
     FIG. 8 is an end elevation of the plug and terminal assembly and a fragmentary portion of the stator core illustrating engagement of the locating posts therewith; 
     FIG. 9 is a an electrical schematic of the plug and terminal assembly, shown as plugged into a power source; 
     FIG. 10 is an enlarged fragmentary cross section of the motor illustrating the locator nubs of the end frames and locator openings of the stator core; 
     FIG. 11 is a section of the rear end frame taken in the plane including line  11 — 11  of FIG.  4  and showing a rotor shaft bearing mounted in the central opening of the rear end frame; 
     FIG. 12 is a longitudinal section of the rotor shaft bearing of FIG. 11; 
     FIG. 13 is an end elevation of a housing piece of the housing of the rotor shaft bearing; 
     FIG. 14 is a fragmentary elevation of the opposite end of the housing piece of FIG. 13; and 
     FIG. 15 is a plan of a stator lamination which forms the stator core; 
     FIG. 16 is a schematic illustrating the formation of stator laminations and the stator core; 
     FIG. 17 is a perspective of a rotor assembly of the motor, including a rotor shaft and a rotor core, with parts of the rotor core broken away to show details of construction; 
     FIG. 18 is a plan view of the rotor core with portions broken away to two levels to reveal the three different rotor slot orientations within the rotor core; 
     FIG. 19 is an enlarged fragmentary elevation of the rotor core showing a single rotor slot and illustrating in hidden lines the orientation of an underlying slot; 
     FIG. 20 is an enlarged fragmentary view of a rotor core having slots which are skewed accordingly to conventional mathematical prediction; and 
     FIG. 21 is a diagram illustrating two preferred windings of the motor and two other windings. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and in particular to FIGS. 1,  3  and  15 , a dynamoelectric machine in the form of a single phase, two speed induction motor  20  is shown to include a stator  22  having a core  24  made up of a stack of thin stator laminations  26 , and windings  27  on the stator core including a four pole start winding  28 , a four pole run winding  30  and a six pole run winding  32 . The stator  20 , stator core  24 , stator laminations  26  and windings  27  are indicated generally by their respective reference numerals. The windings illustrated are exemplary only, as the invention is applicable to dynamoelectric machines of other winding configurations. A rotor assembly indicated generally at  36  includes a rotor  38  received in a bore  40  of the stator core  24  and a rotor shaft  42  fixedly connected to the rotor. Opposite end portions of the rotor shaft  42  are received in a first bearing  44  and a second bearing (generally indicated at  46 ), respectively, for free rotation of the rotor assembly  36  about the longitudinal axis of the rotor shaft. As may be seen in FIG. 2, the first and second bearings  44 ,  46  are held in central openings  48  of first and second end frames (designated generally by reference numbers  50  and  52 , respectively) which support the rotor assembly  36 . A plug and terminal assembly, generally indicated at  56  is located on the second end frame  52 , and a centrifugal mechanism  58  of the type well known in the art is mounted on the rotor shaft  42  adjacent the second end frame. The end frames  50 ,  52  engage opposite end faces of the stator core  24  where they are positively located by locator nubs  60  associated with each end frame, which locator nubs are received in corresponding locator holes  62  in the end faces. The motor  20  is held together by keys  64  which are received in preformed channels  66  in the stator core  24  and bent over at their ends  68  (shown in phantom in FIG. 3) to hold the motor components together as shown in FIG.  1 . 
     One of the stator laminations  26  which is stacked together with a plurality of other stator laminations of identical construction to form the stator core  24  is shown in FIG.  15 . The lamination  26  has a generally central opening  72 , and a plurality of stator teeth  74  defining slots  76  therebetween opening into the central opening and extending generally radially outwardly from the central opening. Notches  78  at the four corners of the lamination  26  define the channel  66  of the stator core  24  (FIG.  3 ). As shown in FIG. 16, the laminations  26  are stamped from a strip W (from a roll R) of highly magnetically permeable material in a die D. All stator laminations  26  are preferably square in shape to permit maximum usage (and correspondingly less waste) of the material in the strip W. The slots  76  are shaped and arranged around the periphery of the central opening  72  so that the arrangement of slots is symmetrical about a pair of perpendicular lines L1 and L2 lying generally in the plane of the stator lamination  26  and intersecting generally at the center C of the central opening. The arrangement of slots  76  is also symmetrical about a diagonal line L3 lying in the plane of the stator lamination  26 , passing through the center C of the central opening  72  and making an angle of 45° with the perpendicular lines L1, L2. 
     Stated another way, the size and arrangement of slots  76  of the stator laminations  26  are “90° symmetrical”, i.e., any stator lamination superposed with another stator lamination may be rotated relative to the other stator lamination 90°, or any multiple thereof, about an axis perpendicular to the plane of the laminations and passing through the center C of the laminations, and the slots  76  will be substantially superposed and coextensive. However, it is to be understood that the rotational symmetry of the slots  76  could be other than 90° and still fall within the scope of the present invention. Generally speaking, rotational symmetry of the slots  76  of N°, where N is less than 180, will permit at least incremental improvement in the roundness and straightness of the stator bore  40 . 
     As is known, the 90° symmetry of the stator laminations  26  permits the construction of a stator core  24  having a straighter and more nearly cylindrical bore  40 . In the final assembly of the motor  20 , the rotor  38  and the periphery of the stator core bore  40  should preferably have the minimum possible separation, while permitting free rotation of the rotor in the bore. Deviations of the stator core bore  40  from being straight and cylindrical typically occur because of non-uniform thickness of individual stator laminations  26  (“gamma variations”), and elliptical deformation of the central openings  72  caused by stress relief in the material after punching the central opening. It has been found that these errors tend to occur equally along the lines L1, L2 shown in FIG.  15 . All of the stator laminations  26  have the same original orientation when they are stamped from the highly magnetically permeable material and fed one after another in a forward direction to a stacking station. Rotation of each stator lamination  26  from its original orientation 90° relative to the adjacent stator lamination in the stack forming the stator core  24  results in the aforementioned errors tending to cancel each other out. As shown in FIG. 16, rotation of the stator laminations  26  is carried out in a revolving barrel B (the “stacking station”) into which the stator laminations are received after they are stamped. Prior to each stator lamination being driven into the barrel B, it rotates 90° so that adjacent stator laminations  26  in the stack forming the stator core  24  are rotated relative to each other 90° from their original orientations. The stacking and rotating of the stator laminations  26  continues until the stack reaches a predetermined height corresponding to the size of the stator core  24 . 
     The four pole start winding  28 , four pole run winding  30  and six pole run winding  32  are schematically illustrated on the stator lamination  26  shown in FIG.  15 . Each winding  27  has a pair of magnet wire leads  80  at opposite ends of the winding which are connected to a source of power as described in detail hereinafter. It is to be understood that the precise arrangement of the windings  27  may be other than shown in FIG.  15  and still fall within the scope of the present invention. As may be seen from the winding diagram, turns of magnet wire from different windings will lie in the same slots  76 . 
     Difficulty in exploiting the advantage derived from 90° rotation of each stator lamination  26  arises when the stator core  24  is wound for a two speed motor of the type disclosed herein having two windings each with a different number of poles (e.g., a four pole winding  30  and a six pole winding  32 ). More specifically, the difficulty occurs when one of the windings has a rotational symmetry which differs from and is not a whole number factor of the rotational symmetry of the stator laminations  26 . Rotational symmetry of a winding is equal to the angular spacing of the poles of the winding around the periphery of the stator core bore  40 . In the six pole winding  32 , the poles are spaced at 60° intervals around the stator core bore  40 , and no two poles of the six poles are spaced apart by 90°. If the six pole winding  32  is rotated 90° from an initial position, its appearance is not the same as it was in the initial position. Difficulty in winding a 90° symmetric stator occurs generally when two of the windings have a different number of poles, and the number of one of the poles is an even number which is greater than two and not a multiple of four. 
     Accordingly, when the six pole winding  32  and four pole winding  30  (or four pole start winding  28 ) are wound on the stator  22 , some of the slots  76  adjacent two sides of the lamination will be required to receive substantially more turns of magnet wire than others. In the past, accommodation has been made by making the lamination slots which receive extra turns of wire deeper. However, this introduces asymmetry in the arrangement of slots, making them no longer 90° symmetric. Moreover, the amount of material to carry the magnetic flux produced by the windings is reduced along two of the edges of the lamination. The amount of material along each side of the lamination  26  is referred to as the “yoke” of the lamination. Preferably, the yoke should be nearly the same along all four edges of the lamination  26 . The decrease in material caused by the depth of the slots can be remedied by making the lamination with an elongated rectangular shape. However, these rectangular laminations (not shown) are only symmetrical when rotated 180° relative to each other. Less effective cancellation of gamma deviations and elliptical deformations of the central openings  72  occurs with 180° rotation of the stator laminations  26  when forming the stator core  24 . 
     The stator lamination  26  of the present invention has been constructed to receive magnet wire from the four and six poles windings  28 ,  30 ,  32  of a two speed motor in a 90° symmetrical arrangement of the slots  76 . The yoke along the four peripheral edges of the lamination  26  is substantially the same, with the minimum distance y separating the bottom of any of the slots  76  and the nearest edge of the stator lamination  26  being approximately equal along all four edges of the lamination. However, a sinusoidal distribution of the turns of magnet wire at each pole of each winding  27  would result in certain slots  76  being overfilled and other slots being under-filled. The amount a slot  76  is filled with wire is commonly expressed in terms of “slot fill percentage”, which corresponds to a ratio of the cross sectional area of the magnet wire times the number of turns in the slot, divided by the area of the slot. The slot fill percentage of each slot  76  should be greater than about 30% and less than about 70%, and more preferably be greater than about 40% and less than about 60%. To achieve slot fill percentages in this range in a stator  22  made up of 90° symmetrical stator laminations  26 , the spatial distribution of turns of magnet wire among the slots  76  at least some of the poles of some of the windings is distorted from an ideal sinusoidal distribution of turns for the particular number of slots of the stator. More turns of wire are placed in some slots  76  and fewer in others than would be called for in an ideal sinusoidal distribution of turns. Further, the distortion of the turns from the sinusoidal distribution is dissimilar at least two of the poles of one of the windings  27  resulting in the introduction of a controlled amount of even harmonics upon energizing the winding. Preferably, the distortion should occur in the run winding (i.e., the four pole winding  30  or six pole winding  32 ) which is used least in ordinary operation of the motor  20 . Distortion is carried out so as to bring the slot fill percentages within the preferred ranges. Another, lesser preferred way of bringing slot fill percentages within an acceptable range is to remove turns from one or more of the poles of one of the windings  27 . The precise arrangement of the turns will depend upon the size of the stator  22 , the number of windings  27  and poles in each winding, as well as the desired operating characteristics of the motor  20 . 
     Two preferred winding configurations for the motor  20  of the present invention, having a stator  22  with  36  slots wound with a four pole start winding (designated “4P START”), four pole main winding (designated “4P MAIN”) and six pole winding (designated “6”) are diagrammatically illustrated in FIG. 21, and compared with a sinusoidal winding and another winding. The lettered columns represent slots in the stator  22 , as indicated on the stator lamination  26  shown in FIG. 15, and the lines between the columns represent the teeth  74  of the stator. The numbers in the columns are the number of turns received in the slot for a particular winding, and each row of numbers represents the distribution of turns for the winding designated at the right hand side of the row. The rows are arranged in four vertically spaced groups of three rows, each group representing all windings on a given stator. At the bottom of FIG. 21, the location and span of the coils of each pole for each of the windings are schematically indicated by nested brackets. The brackets illustrate generally the possible spans of the coils, but in fact the designer may chose not to include one of the spans shown by the brackets. In winding groups where it has been chosen not to include particular spans, the number “0” has been placed in the slots where turns of wire making up that span would ordinarily be received. The instance where a particular slot or slots  76  lie at the interior of the pole, and no wire is placed them, the absence of wire is indicated by dashed lines “ - - - ”. 
     The top group of windings is a sinusoidal distribution of turns for the  36  slot stator  22  illustrated herein. A sinusoidal winding configuration is ordinarily preferred for best motor performance. However, in this instance, some of the slots are too full and others relatively empty, making it completely impractical to manufacture. The winding group second from the top in the diagram of FIG. 21 is a first attempt to reduce the disparity in the number of turns received in respective slots  76 . Although this second winding configuration makes better use of the slots by distorting the turns from the sinusoidal configuration, it is also impractical to manufacture. The third and fourth groups from the top are manufacturable winding configurations and are believed to operate within acceptable parameters. 
     The completed stator  22  is supported together with the rotor assembly  36  in the final assembly of the motor  20  by the first and second end frames  50 ,  52 . The rotor  38  is received inside the stator bore  40  and is in a closely spaced relation with the stator core  24  in the stator core bore. The end frames  50 ,  52  are each formed from sheet metal blank which is formed into a cup-shaped configuration including generally square, flat interior and exterior faces (designated  90  and  92 , respectively) and a skirt  94  projecting outwardly from the interior face  90  of the end frame. Four feet  96  extend laterally outwardly from the outer edges of the skirt  94  at the corners of the end frames  50 ,  52 . The central opening  48  of each end frame is generally tubular in shape, and an inwardly projecting retaining lip  98  narrowing the central opening at its axially outer end is disposed for engaging the bearing ( 44  or  46 ) received in the opening. Referring now to FIGS. 4 and 5, material is removed from the end frames  50 ,  52  at circumferentially spaced locations around their respective central openings  48  leaving vents  100  permitting circulation of cooling air through the motor. However, not all of the material at the location of the vents  100  is removed from the end frames  50 ,  52 . At each vent  100 , material is left forming a retaining tab  102  which extends axially inwardly from the inner end of the central opening  48  at the periphery of the opening. 
     The first bearing  44  includes an inner race  106 , an outer race  108  and ball bearings  109  received in the races (FIGS.  1  and  3 ). The inner race  106  is fixedly connected to the rotor shaft  42  of the rotor assembly  36  adjacent one end, and the shaft and first bearing  44  are located in the central opening  48  in the first end frame  50  with the outer race of the first bearing engaging the retaining lip  98 . The retaining tabs  102  are deformed inwardly against the outer ring  108  of the first bearing  44  so that the first bearing is captured in the central opening  48  between the retaining lip  98  and retaining tabs (FIG.  2 ). Thus, the first end frame  50  is positively located relative to the first bearing  44  and the rotor  38 . The second bearing  46 , described in more detail below, and the opposite end of the rotor shaft  42  are located in the central opening  48  of the second end frame  52 . The second bearing  46  is captured in the central opening  48  between the retaining tabs  102  and retaining lip  98  of the second end frame  52  in the same way as the first bearing  44  (FIG.  5 ). 
     The relative radial position of the stator  22  and rotor assembly  36  is controlled by the locator nubs  60  and locator holes  62  associated with the first and second end frames  50 ,  52  and the stator core  24 . The end frames  50 ,  52  each include four of the locator nubs  60 , one on each of the four feet  96  of the end frame. As best seen in FIG. 10, each locator nub  60  is received in a corresponding locator hole  62  formed in the end face of the stator core  24 , thereby positively radially locating the stator core and the end frames  50 ,  52 . The nubs  60  are preferably formed by punching through the end frames  50 ,  52  at the feet  96  so that the nubs extend outwardly from the feet a substantial distance into the holes  60  upon assembly of the end frames with the stator  22 . Positive location of the end frames  50 ,  52  and stator core  24  also produces positive location of the rotor assembly  36  and stator core  24  by virtue of the first and second bearings  44 ,  46  being captured in the central openings  48  of respective end frames. In the preferred embodiment, the locator nubs  60  and the central openings  48  of the end frames  50 ,  52  are punched from the sheet metal blank during the same stroke of the die, which permits a close tolerance to be maintained on the distance from the center of the central openings  48  and the center of the locator nubs  60 . Likewise, the locator holes  62  in each stator lamination  26  are formed during the same stroke of the press which forms the central opening  72  of the lamination so that the distance between the center of the stator bore  40  formed by the stacked stator laminations  26  and the center of the locator holes  62  is maintained within a close tolerance. The maintenance of these close tolerances in turn allows the relative radial position of the rotor assembly  36  and stator core  24  to be maintained within a tight range for each motor  20  manufactured. 
     The locator nubs  60  of the end frames  50 ,  52  are disposed on an embossment  112  formed on each foot  96  of the end frames and protruding inwardly from an inwardly facing surface  114  of the foot (FIG.  4 ). As shown in FIG. 10, the embossments  112  are the portions of the feet  96  of each end frame  50 ,  52  which engage a respective end face of the stator core  24 . All of the embossments  112  on each end frame  50 ,  52  are formed at the same time in the die so that their relative location is very precise, more so particularly than the relative location of the inwardly facing surfaces  114  of the feet  96 . The embossments  112  on each end frame  50 ,  52  are generally located in a plane so that when they engage the stator core  24  the end frame is not undesirably pitched or cocked with respect to the stator core. As a direct consequence, the longitudinal axis of the rotor shaft  42  is better aligned with the centerline of the stator core bore  40 . 
     Referring now to FIGS.  3  and  11 - 14 , the second bearing  46  includes a plastic, tubular housing formed from first and second pieces (generally indicated at  116  and  118 , respectively) and having a shaft receiving passage  120 . An annular raceway defining member  122  is disposed in the shaft receiving passage  120  and extends around the shaft receiving passage. A plurality of long, thin needle bearings  124  (broadly, “shaft bearing means”) are disposed in the raceway of the raceway defining member  122  and engage the rotor shaft  42  in the shaft receiving passage  120 . The rotor shaft  42  is received through the shaft receiving passage  120  of the second bearing  46  and is supported for rotation by engagement with the needle bearings  124 , but is free of any fixed connection to the second bearing. Thus, the shaft  42  and second bearing  46  are free to slide lengthwise of each other such that the location of the second bearing on the rotor shaft is determined by the engagement of the second end frame  52  with the stator core  24 . 
     The first and second pieces  116 ,  118  of the second bearing housing are substantially identical, each having a cylindrical outer wall  126  sized for close fitting reception in the central opening  48  of the second end frame  52  and a generally cylindrical inner wall  128  which is concentric with and spaced radially inwardly of the outer wall. As shown in FIG. 13, the outer and inner walls  126 ,  128  are joined by three generally thin, arcuate diaphragm portions  130  extending between the inner and outer walls. The arcuate diaphragm portions  130  are spaced angularly of each other around the shaft receiving passage  120  by arcuate voids  132 . The arrangement of arcuate diaphragm portions  130  and voids  132  is such that the relative location of diaphragm portions and voids is exactly reversed about a transverse line L4. Thus, when the second piece  118  is rotated about the line L4 and brought into engagement with the first piece  116 , the diaphragm portions  130  of the first piece are received in the voids  132  of the second piece and vice versa. The diaphragm portions  130  of the first and second pieces  116 ,  118  form a continuous annular diaphragm  134  when the first and second pieces are mated together. 
     Preassembly of the second bearing  46  is carried out by installing the raceway defining member  122  in the first piece  116  of the housing. The raceway defining member  122  engages a locating shoulder  136  formed in the first piece  116  and projects out of the first piece. The second piece  118  slides over the exposed portion of the raceway defining member  122  and into engagement with the first piece  116 . The raceway defining member engages another locating shoulder  138  in the second piece  118 , and the diaphragm portions  130  of the first and second pieces mate in the way described above to form the continuous diaphragm  134 . The first and second pieces  116 ,  118  are temporarily held on the raceway defining member  122  by friction fits, and there is preferably no separate connection of the pieces to one another. Upon installation of the second bearing  46  in the central opening  48  of the second end frame  52 , and bending of the retaining tabs  102  against the second piece  118 , the first and second pieces are held together by engagement with the retaining tabs and the retaining lip  98  of the central opening  48 . It is to be understood that the second bearing  46  may be formed as one piece or otherwise than precisely described herein and still fall within the scope of the present invention. 
     The rotor shaft  42  may extend through the shaft receiving passage  120  of the second bearing  46  at an angle to the longitudinal axis L5 of the shaft receiving passage in the undeformed configuration of the second bearing housing. In that event, the diaphragm  134  deforms by deflecting out of its plane to permit the shaft receiving passage  120  to be pivoted to generally align itself with the longitudinal axis LA of the rotor shaft  42 . However, the diaphragm  134  has sufficient strength of resist translational movement of the rotor shaft  42  in directions perpendicular to its longitudinal axis LA so that the shaft does not wobble as it rotates in operation. The plastic material of the second bearing housing pieces  116 ,  118  has a preferred modulus of elasticity in the range of 400,000 to 800,000 psi. It is believed that a modulus of elasticity of the plastic as high as 2,500,000 would still permit the second bearing  46  to function properly. Steel and other materials having far greater moduli of elasticity could be used if made sufficiently thin. 
     To reduce noise in operation, the clearance between the needle bearings  124  and the rotor shaft  42  is taken up by intentionally canting the second bearing  46  relative to the longitudinal axis LA of the rotor shaft  42 . Canting is accomplished by an asymmetrical formation (broadly “canting means”) on the housing, which in the illustrated embodiment comprises a pair of longitudinally and radially opposite bumps  140  on the outer walls  126  of the first and second housing pieces  116 ,  118  (see FIGS.  12  and  14 ). The bump  140  associated with the first housing piece  116  engages the retaining lip  98  in the central opening  48  of the second end frame  52 , causing the second bearing  46  to be tilted relative to the second end frame in the central opening. As illustrated in FIG. 2, the bump  140  is sized so that the longitudinal axis L5 of the shaft receiving passage  120  makes an angle of approximately 1° with the longitudinal axis LA of the rotor shaft  42 . The angle shown in FIG. 2 has been greatly exaggerated for purposes of illustration. The intentional misalignment of the axes of the shaft receiving opening  120  and the rotor shaft  42  causes the shaft to bear against the needle bearings  124  and to elastically deform the diaphragm  134 . The elasticity of the diaphragm material provides a reaction force against the rotor shaft  42  so that the needle bearings  124  are held against the shaft. This constant, forced engagement of the rotor shaft  42  and the needle bearings  124  significantly reduces noise during operation. 
     The bump  140  on the second housing piece  118  is not necessary to produce the desired cant of the second bearing  46  relative to the longitudinal axis of the rotor shaft  42 . Of course, the bump  140  is present on the second piece  118  because it is identical to the first piece  116 . To do away with the bump  140  on one of the housing pieces would require completely separate molds for the two pieces  116 ,  118  which is undesirable from the stand-point of cost and simplicity of assembly. However, the bump  140  on the second piece  118  also facilitates installation of the second bearing  46  in the central opening  48  of the second end frame  52  with the desired cant. More specifically, the bump on the second piece is constructed for engagement with an installing tool (not shown) having a flat face which engages the radially inner end of the second piece  118  for pushing the second bearing  46  into the central opening  48  of the second end frame  52 . The bump  140  on the second piece  118  causes the second piece, and hence the entire second bearing  46  to be canted in the same direction as the engagement of the bump  140  on the first piece  116  with the retaining lip  98 . Thus, the desired misalignment is achieved even when, as will occur from time to time, the bump  140  on the first piece  116  is not fully seated against the retaining lip  98  in the central opening  48 . 
     The windings  27  may be connected to a source of electrical power via the plug and terminal assembly  56  mounted on the second end frame  52  of the motor  20 . As shown in FIG. 7, the plug and terminal assembly  56  includes a two-piece casing, generally indicated at  150 , made of insulator material, and a plurality of lead terminals  152  which receive the magnet wire leads  80  extending from the windings  27 . The lead terminals  152  each have a serrated formation  154  including a plurality of sharpened ridges so that when the lead terminals  152  are crimped onto the magnet wire leads (as shown for the top terminal in FIG.  7 ), the insulation of the magnet wire is penetrated by the ridges to provide electrical connection. In the preferred embodiment, the lead terminals  152  are Amplivar® terminals manufactured by Amp, Inc. of Harrisburg, Pa. Referring to FIG. 9, a switch  157  forming part of a switch circuit (generally indicated at  155 ) housed in the casing  150  is operable between a first switch mode (shown in solid lines) in which the start winding  28  is activated and a second switch mode (shown in phantom) in which the start winding is deactivated. The switch  154  is operated by the centrifugal mechanism  58  in a way which is well known in the art. Generally, the centrifugal mechanism  58  rotates with the rotor shaft  42 , and extends as the revolutions of the shaft reach a predetermined level to actuate a lever arm  159  which opens the switch  157 . As shown in FIG. 5, a plurality of electrical connectors (designated sequentially by reference numerals  156   a - 156   f ) protruding from casing  150  are electrically connected to lead terminals  152  through the switch circuit. The electrical connectors  156   a - 156   f  are constructed as plugs for plug-in connection to a source of electrical power. 
     The switch circuit  155  is of conventional construction and is schematically shown in FIG. 9 as part of the electrical circuit including the windings  27 , a plug  160  from the power source and control switches associated with the power source. A pair of leads  162 ,  164  are respectively interposed between electrical connectors  156   b  and  156   c  and a pair of terminal posts  166 ,  168  of a single pole double throw speed selector switch  170 . Speed selector switch  170  has a movable arm  172  for selective circuit making engagement with its cooperating posts  166 ,  168 , and the switch arm  172  is connected in circuit relation with a line terminal LT1. A switch  173  located in the circuit between the electrical connector  156   a  and the six pole (low speed) winding  32  is shown in its motor start position in which the four pole (high speed) winding  30  will be activated even of the arm  172  of the selector switch  170  has been moved to post  168  for low speed operation of the motor  20 . The switch  173  is moved as a result of actuation of the lever arm  159  by the centrifugal mechanism  58  to de-energize the four pole winding  30  and energize the six pole winding  32  when the motor reaches the predetermined speed. Of course, when high speed (i.e., the four pole winding  30 ) is selected by moving the arm  172  into engagement with post  166 , movement of the switch  173  out of electrical contact with the four pole winding does not result in energization of the six pole winding  32  or de-energization of the four pole winding  30 . 
     Another line terminal LT2 is connected by a lead  174  with electrical connector  156   f , the line terminals LT1, LT2 defining the power source. A double pole double throw reversing switch  176  of the type well known in the art is used for controlling the direction of current through start winding  28  and, consequently, the direction of rotation of the motor  20 . A lead  178  connects the reversing switch  176  to a terminal post  166  of speed selector switch  170 . Other leads, designated  180   a - 180   c , connect the reversing switch  176  to electric connectors  156   d ,  156   e  and  156   a , respectively. A ground lead  182  connects the second end frame  52  to ground, as described in more detail below. 
     The casing  150  of the plug and terminal assembly  56  is formed with an integral stall  186  for receiving a thermal protector indicated generally at  188  (shown exploded from the stall in FIG. 3) which protects the motor  20  from overloads. The thermal protector  188  has a housing  189  and two contacts  190  projecting from it for connection to the switch circuit  155 . The thermal protector  188  may be inserted into the stall  186  with the contacts  190  extending further into the casing  150  generally in registration with contacts  192  of the switch circuit  155  (FIG.  9 ). As shown in FIG. 7, two openings  194  on each side of the casing  150  are located at the junction of the thermal protector contacts  190  and switch circuit contacts  192  (not seen in FIG.  7 ). A joining tool (not shown) is extended through the openings  194  to join (as by soldering) the thermal protector contacts  190  to the switch circuit contacts  192 . 
     As shown in FIGS. 4 and 5, the plug and terminal assembly  56  is supported in a cutout  200  formed in the skirt  94  of the second end frame  52  without fixed connection to the end frame or other part of the motor  20 . Slot defining formations, generally indicated at  202 , on each side of the plug and terminal casing  150  define slots  204  which receive respective edge margins  206  of the second end frame  52  bounding the cutout  200 . The slots  204  are sized so that the slot defining formations  202  grip the second end frame edge margins  206  in the slots to facilitate holding the plug and terminal assembly  56  in position. However, the slot defining formations  202  do not grip the edge margins  206  of the second end frame  52  so tightly as to prevent the plug and terminal assembly  56  from being manually slid into and out of the cutout  200 . The plug and terminal assembly  56  is further secured in position in the cutout  200  by locating post means comprising in this embodiment a single generally triangular locating post  208  generally adjacent one end of the plug and terminal assembly, and a pair of flat end surfaces  210  of the slot defining formations  202  located adjacent the opposite end of the plug and terminal assembly. The locating post  208  and the flat end surfaces  210  are formed as one piece with the casing  150 . As shown in FIG. 8, the locating post  208  and flat end surfaces  210  engage one end face of the stator core  24  and urge the plug and terminal assembly  56  against the second end frame  52  at the closed end of the cutout  200 . A cylindrical projection  212  at the axially inner end of the locating post  208  is received in one of the slots  76  of the stator. Thus, it may be seen that the plug and terminal assembly  56  is mounted on the motor  20  without welding and without any nuts, bolts or other fastening devices. 
     The first and second end frames  50 ,  52  of the motor are grounded by connection to the ground associated with the power source (e.g., the frame of a washing machine) by a ground tab (designated generally by reference numeral  218 ) formed as one piece with the second end frame. As shown in FIGS. 4 and 5, the ground tab  218  is located at the bottom of the cutout  200  in the second end frame  52 . The cutout  200  is formed in the sheet metal blank at a location correspond-ing to one side of the skirt  94  of the second end frame  52 . However, the metal is not completely removed and a portion remains as a flap  220  extending laterally outwardly from the second end frame  52  at the bottom of the cutout  200 . The ground tab  218  is stamped out of the material in the flap  220  and bent to project axially inwardly from the flap. An electrical connector portion  222  of the ground tab  218  projects radially outwardly of the remainder of the tab, and a stabilizing finger  224  extends axially inwardly of the electrical connector portion. 
     The plug and terminal assembly casing  150  is formed with an opening  228  which receives the ground tab  218  upon insertion of the plug and terminal assembly  56  into the cutout  200 . As shown in FIG. 5, the electrical connector portion  222  of ground tab  218  as received in casing  150  is aligned with the other electrical connectors  156   a - 156   f  which are adapted to be connected to the plug  160  associated with the power source (FIG.  9 ). The stabilizing finger  224  is received in a recess  230  at the end of the opening  228  defined in part by an overhang portion  232  of the casing  150  (FIG.  6 ). In the recess  230 , the stabilizing finger  224  is held by engagement with the overhang portion  232  and the portion of the casing  150  opposite the overhang portion from substantial movement transverse to the lengthwise extension of the finger as shown in FIG.  6 . Thus, the stabilizing finger  224  aids in holding the plug and terminal assembly  56  in place in the cutout  200  in the second end frame  52  by resisting tilting movement of the plug and terminal assembly casing  150 . 
     Referring now to FIGS. 17-19, the rotor assembly  36  of the present invention is made up of a stack of generally thin, circular rotor laminations  240  made of highly magnetically permeable material. Slots  242  in the rotor laminations  240  are spaced circumferentially around the periphery of the rotor laminations. As shown in FIG. 19, each slot  242  includes a radially inner portion  244  and a radially outer skew portion  246  extending outwardly and laterally (e.g., circumferentially), from the radially inner portion toward the circumference of the rotor lamination  240 . The radially inner portion  244  of each slot  242  at least partially overlies corresponding radially inner portions of slots on the other rotor laminations in the stack forming the rotor  38 . The overlying slots  242  define axially extending passages in which rotor bars  248  are disposed. The rotor bars  248  are formed by pouring molten aluminum or another suitable conductor into the passages formed by the overlying slots (FIG.  17 ). However, it is to be understood that rotor bars may be placed in the rotor  38  by other methods, such as press fitting, and still fall within the scope of the present invention. The rotor bars  248  are not shown in FIGS. 18 and 19 for clarity, but are connected at the ends thereof by end rings (not shown) to form a squirrel cage rotor conductor arrangement as will be understood by persons skilled in the art. 
     The rotor laminations  240  in the stack defining the rotor  28  are arranged in three adjacent sets, designated  250 ,  252  and  254 , respectively. The slots  242  in the first set of laminations  250  have their skew portions  246  extending laterally in a first direction, the slots in the second set of laminations  252  have their skew portions extending laterally in a second direction opposite the first, and the slots in the third set of laminations  254  have their skew portions extending laterally in the first direction. All of the rotor laminations  240  are virtually identical. Thus, the slots  242  are of substantially the same size and shape, and thus the slots in the second set of laminations  252  (as arranged in the stack) appear to be mirror images of the slots in the first set  250  and third set  254  of laminations. As shown in FIG. 19, the radially inner portions  244  of partially overlying slots of the first set  250  and second set  252  of laminations generally overlie each other. However, the skew portions  246  of the first set  250  and second set  252  of laminations have no portions which are overlying. The skewed condition of the skew portions  246  of the slots  242  of the second set  252  of laminations relative to the skew portions of the first set  250  and third set  254  of laminations facilitates decoupling from the rotor bars  248  of stator slot order winding harmonics and stator slot opening permeance harmonics. The first set  250  and third set  254  of rotor laminations have slots  242  which are oriented the same way, and the second set of laminations  252  is interposed between the first and third sets. The dimension of each of the first set  250  and third set  254  of rotor laminations parallel to the longitudinal axis LA of the rotor shaft  42  is preferably approximately equal to ¼ the total axial dimension of the rotor, and the dimension of the second set of laminations  252  is preferably approximately equal to ½ the total axial dimension of the rotor. The arrangement of the sets  250 ,  252 ,  254  of rotor laminations produces a more balanced rotor which reduces mechanical noise in operation of the motor  20 . Moreover, the arrangement of laminations  240  into the three sets  250 ,  252  and  254  reduces current loss due to leakage from the rotor bars into the laminations  240 . It is to be understood that the rotor  38  may be formed from two sets of rotor laminations  240  having slots  242  which are skewed, or more than three sets of rotor laminations and still fall within the scope of the present invention. The skew of the present design is easily manufactured and provides particularly good performance for single phase motors. 
     Referring to FIGS. 17 and 19, the laterally outermost points L of the skew portions  246  of the overlying slots  242  in said first set of rotor laminations  250  lie generally along a first axially extending line A1 and the laterally outermost points of said skew portions of the corresponding slots in said second set of rotor laminations  252  lie generally along a second axially extending line A2. The skew of the slots  242  in the first and second sets may be represented by the distance d between the first line A1 and the second line A2. In the preferred embodiment, the distance d falls within a range expressed by the following equation, 
     
       
         (2π r )/(2 S−P )&lt; d≦ (2π r )/(2 S−P )+δ+ρ  (1)  
       
     
     The variable r is the radial distance between the center of the rotor lamination  240  and the either line A1 or A2 (FIG.  18 ). S is the number of slots in the stator core, and P is the number of poles of a selected one of the windings (the harmonics of which are to be decoupled from the rotor). As explained in more detail below, ρ/2 corresponds to the distance between the laterally outermost point L of the slot  242  and its radially outermost point R (FIG.  19 ), and δ/2 generally corresponds to the distance δ/2 between a first magnetic saturation region M1 and a second magnetic saturation region M2 (FIG.  20 ). 
     More specifically, ρ/2 is the distance between first and second parallel planes (which are seen on edge in FIG.  19  and appear as lines A3 and A4, respectively) in a third plane (which is also seen on edge in FIG.  19  and appears as line A5) which includes the lines A1 and A2. The first plane A3 includes the radially outermost point R of the skew portion  246  of the slot, and the second plane A4 includes the line A1 or A2. The first plane A3 and second plane A4 intersect the third plane A5 at right angles, and all three planes (A3, A4, A5) are perpendicular to the plane in which FIG. 19 lies. 
     The distance δ/2 is explained with reference to FIG. 20 showing two sets of rotor laminations  258  having slots  260  with skew portions  246  which extend laterally in opposite directions. The illustrated skewed slots  260  do not have the same shape as the slots  242  shown in FIG.  19 . Generally, the rotor laminations  240  having slots  242  have more material between the slot and the circumference of the rotor lamination  240  than the rotor laminations  258  having slots  260 . The configuration of the slots  260  is an initial configuration chosen on the assumption that, for each slot  260 , the sole location of magnetic saturation is region Ml adjacent the radially outermost point R of each slot which corresponds to the slot bridge (i.e., the narrowest strip of material surrounding the slot). However, as explained below, we have found and unexpected result that a second saturation region M2 occurs at a location spaced from the first saturation region M1. The distance δ/2 corresponds to the distance between parallel lines, designated A6 and A7, respectively. Line A6 is perpendicular to the plane AS and intersects the first saturation region M1 (and radially outermost point R). Line A7 is also perpendicular to plane A5 and intersects the second saturation region M2. 
     The stator slot order harmonics which are decoupled by the skew of the rotor bars  248  are represented by: 
     
       
           n= 2 mS/P± 1  (2)  
       
     
     where n is the harmonic order number, m is the mode number (typically m=1), S is the number of slots in the stator core  24 , and P is the fundamental number of magnetic poles of the motor  20 . In order to decouple a particular stator slot order harmonic, the mutual reactance X of the slot should go to zero. Mutual reactance X may be expressed by the following equation for the skew geometry of the rotor bars  248  of rotors embodying the present invention: 
     
       
           X=X   m   X   α , where X α =cos( nα/ 4)  (3)  
       
     
     X α  is the component of mutual reactance attributable to the angle α of skew of the rotor bar in “electrical” degrees. In order to decouple a particular harmonic X αn : 
     
       
         α n /4=π/2  (4)  
       
     
     Substituting for n in equation (2), the angle of skew a needed to decouple the stator slot order harmonics can be expressed as: 
     
       
         α/2=π(2 S/P± 1)  (5)  
       
     
     The conversion to mechanical degrees of skew is made by substituting α=α mech P/2, or: 
     
       
         α mech /2=2π/(2 S±P )  (6)  
       
     
     Thus, the predicted distance d′ in plane A5 between the lines A1 and A2, defined above, may be found by substituting for α mech  in equation (6): 
     
       
         α mech =2π d′ /(2π r )  (7)  
       
     
     or, after simplification: 
     
       
           d′= (2π r )/(2 S±P )  (8)  
       
     
     It is apparent from equation (7) that distance d′ is the length of an arcuate segment of a circle having a radius r. The arcuate segment corresponding to d′ would be defined by the intersection of radial lines (not shown) passing through the laterally outermost points L of the skew portions  246  with the circle of radius r. However, the difference between the linear distance between end points of the arcuate segment of length d′ and the length d′ is so small that it has been represented as a linear distance in the drawings. Likewise, the distances  6  and ρ, which are actually lengths of arcuate segments of a circle having a radius r, are shown for simplicity as linear distances in a plane AS. The distances δ/2 and ρ/2 are large relative to the difference between the arcuate distance and the linear distance between end points of the corresponding arcuate segments. The arcuate segment of length δ/2 would be defined by the intersection of radial lines (not shown) passing through the first and second saturation regions M1 and M2, respectively, with the circle of radius r. The arcuate segment of length ρ/2 would be defined by the intersection of radial lines (not shown) passing through the radially outermost point R and laterally outermost point L of a slot  242  with the circle of radius r. 
     The predicted distance d′ (which is actually a range due to the presence of ±P) does not in fact equate to the distance d between laterally outermost points of the skew portions  246  of the slots  242  of the rotor laminations of the first set  250  and second set  252 . The predicted distance d′ must be first corrected by adding ρ/2 for both the slots of the first set  250  of rotor laminations and the slots of the second set  252  of rotor laminations to account for the distance (ρ/2) in the plane line A5 between the radially outermost point R and the laterally outermost point L intersecting line A1 of the first set slot, and the distance (ρ/2) in the plane A5 between the radially outermost point R and the laterally outermost point L intersecting line A2 of the second set slot. Ideally, ρ would equal zero and the radially outermost point R would coincide with the laterally outermost point L. However, the slot  242  should preferably have a finite radius of curvature at the radially outermost point R to accommodate manufacture so the two points L and R do not actually coincide. 
     However, even when the distance d′ has been modified to account for the noncoincidence of the radially outermost point R and the laterally outermost point L, the optimum skewing for single phase motors has not been acheived. The equations (3)-(8), used to predict the necessary skew distance d′, clearly assume that the location of magnetic flux saturation (M1) will be in the narrowest strip of rotor lamination material between the slot  260  and the outer circumference of the lamination  258  (i.e., generally at the radially outermost point R of the slot). Referring to FIG. 20, the predicted distance between laterally outermost points L of the slots  260  having oppositely extending skew portions is d′+ρ. In FIG. 20, ρ/2 is the distance between a first plane (seen on edge in FIG.  20  and represented by line A6) and a second plane (also seen on edge in FIG.  20  and represented by line A8). The first plane A6 intersects the radially outermost point R and is perpendicular to a third plane seen on edge in FIG.  20  and represented by line A5. The second plane A9 is parallel to the first plane A6 and intersects a line including the laterally outermost points L of the axially aligned slots of a respective set of rotor laminations  258 . 
     However, we have surprisingly found that for single phase motors there is a second saturation region M2 spaced from the first region M1, as discussed above (FIG.  20 ). In order to compensate for this unexpected anomaly, the skew distance d is further increased from the predicted distance d′+ρ by δ, where δ/2 corresponds to the distance between the narrow strip (i.e., first magnetic saturation region M1) and the second saturation region M2, as stated above. The skew distance d will always be greater than the predicted distance d′. Accordingly, the lower limit for the skew distance d will be greater than the upper predicted distance d′ (i.e., d&gt;πD/(2S−P)+ρ). The amount δ varies from slot-to-slot and with the rotational position of the rotor  38  relative to the stator  22 . Therefore, δ is actually an averaged value of the actual δ associated with each slot  242 . Presently, we have determined δ both experimentally, and by use of a finite element analysis of the rotor  38 . In view of the foregoing, d would preferably be chosen as: 
     
       
           d=πD/ 2 S+ρ+δ   (9)  
       
     
     where the quantity ρ+δ is sufficiently large so that the distance d still exceeds the predicted distance d′, or: 
     
       
         ρ+δ&gt;π D /(2 S−P )−π D /(2 S )  ( 10 )  
       
     
     The dynamoelectric machine (induction motor  20 ) of the present invention is constructed for ease, speed and precision of assembly. The component parts of the motor shown in FIG. 3 may be assembled without the used of fasteners other than the keys  64 . Nut and bolt fasteners may be completely eliminated. As discussed above, many of the component parts, in particular the stator  22  and the end frames  50 ,  52 , have been constructed to achieve greater precision and to facilitate the final assembly of the motor  20 . The following is an example of one way in which the motor components shown in FIG. 3 might be assembled together. However, this example is not exclusive of other possible methods of assembly, particularly in the order of assembly. 
     The first bearing  44  is press fit onto the rotor shaft  42  of the rotor assembly  36  at a predetermined location. The centrifugal mechanism  58  is fixed to the rotor shaft  42  on the opposite side of the rotor  38  from the first bearing  44 . The end of the rotor shaft  42  mounting the first bearing  44  is inserted into the central opening  48  of the first end frame  50  with the first bearing engaging the retaining lip  98  of the central opening to terminate further movement of the rotor shaft and first bearing through the opening. The retaining tabs  102  are bent over against the first bearing  44  to capture the first bearing in the central opening  48  of the first end frame  50 . 
     The stator  22  is placed over the rotor assembly  36  with the rotor  38  being received in the stator core bore  40 . One end face of the stator core  24  engages the embossments  112  on the feet  96  of the first end frame  50 , and the locator nubs  60  are received in corresponding locator holes  62  of the stator core  24 . The stator windings  27  are connected to the plug and terminal assembly  56  by placing the magnet wire leads  80  into respective lead terminals  152  and crimping the terminals against the magnet wire (FIG.  7 ). The ridges of the serrated formation  154  of the lead terminals  152  penetrate the magnet wire insulation and bring the lead terminals into electrical connection with the magnet wires. 
     The second bearing  46 , assembled as previously described, is secured in the central opening  48  of the second end frame  52  by bending over the retaining tabs  102  against the bearing. The second end frame  52  is placed over the end of the rotor shaft  42  opposite the first end frame  50  and the rotor shaft is received in the shaft receiving passage  120  of the second bearing  46 . The plug and terminal assembly  56  is mounted on the second end frame  52  by pushing it into the cutout  200 . The slots  204  of the slot defining formations  202  have flared mouths  234  at one end to facilitate entry of the edge margins  206  bordering the cutout  200  into the slots (FIGS.  4  and  5 ). The ground tab  218  is received into the opening  228  in the casing  150  as the plug and terminal assembly  56  is pushed into the cutout  200 , and the stabilizing finger  224  enters the recess  230 . The electrical connector portion  222  of the ground tab  218  is aligned with the electrical connectors  156   a - 156   f  of the plug and terminal assembly  56  so that it is prepared to be plugged into the ground lead  182  when the motor  20  is connected to a source of electrical power. 
     The second end frame  52  is pushed toward the end face of the stator core  24  with the rotor shaft  42  sliding through the shaft receiving passage  120  until the embossments  112  on the feet  96  of the second end frame  52  engage the end face of the stator core with the locator nubs  60  received in the locator holes  62  in the stator core. The motor components are secured together by placing the keys  64  into the channels  66  in the stator core  24  and deforming the ends  68  of the keys over onto the feet  96  of respective end frames  50 ,  52 . The intentional misalignment of the axis L5 of the shaft receiving passage  120  of the second bearing  46  with the longitudinal axis LA of the rotor shaft  42  causes the diaphragm  134  of the second bearing to be elastically deformed and hold the needle bearings  124  against the rotor shaft. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.