Abstract:
A motor stator is constructed from loose laminations which are aligned and secured to the compressor housing at the time of assembling the compressor unit. The loose lamination stator is first attached to the compressor housing to initially locate the stator. A solid sizing mandrel is pushed through the rotor accommodating bore to remove any burrs and initially size the bore. An expanding mandrel is then positioned within the rotor accommodating bore and expanded to finalize the sizing of the bore and the alignment with the compressor housing. Once the final size and alignment have been achieved, the stator is secured to the motor housing.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to motor stators created from packs of laminations. More particularly, the present invention relates to a motor stator created from packs of loose laminations where the center bore of the motor stator is drawn to size during the assembly of the motor.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hermetic refrigeration compressors normally incorporate a compressor and an associated electrically driven motor within a hermetically sealed shell. The electric motor will generally include a rotor secured to a drive shaft journaled in the compressor housing or other suitable bearing means and a stator secured to the compressor housing by means of bolts extending through the stator core.  
           [0003]    The stator core for these electric motors generally compress a plurality of stacked laminations bonded together by welding, varnishing or other means of bonding the individual laminations together. A set of windings is wound through the assembled stator core to produce the stator. The stator is mounted to a plurality of mounting pads or surfaces machined on the inner surface of the compressor housing. The stator is secured to the compressor housing using a plurality of bolts which are threadingly received by the compressor housing. The bonding of the laminations prior to assembly of the stator enables the correct alignment for the stator. The securing of the stator to the compressor housing results in a cantilever mounting arrangement for the stator in that only one end thereof is fastened to the compressor housing and the other end extends upwardly.  
           [0004]    It is important to have the plane defined by the machined surfaces on the compressor housing perpendicular to the axis of the rotor when the rotor is installed. In order to accomplish this, it is necessary that the rotor accommodating bore of the stator core be perpendicular to the lower surface of the stator core itself, since it is this lower surface which is supported on the machined surfaces of the compressor housing. The proper positioning of the rotor accommodating bore of the stator core ensures that the air gap between the stator and rotor of the electric motor will be very uniform along the entire axial length of the electric motor. In many hermetic compressor applications, the rotor is supported at only one end thereof, and normally at the same end where the stator is connected to the compressor housing. Because of this cantilevered supporting arrangement for the rotor, although it is relatively easy to maintain an accurate air gap at the end nearest the bearing, normal flexing and deflection of the rotor at the opposite end will result in a wider variance in the air gap, taking into consideration normal machining and bearing tolerances. Accordingly, in order to minimize as much as possible the error in the air gap at the stator core furthest from the mounting surface of the compressor housing, it is necessary that the rotor accommodating bore be very accurately aligned perpendicular to the reference plane defined by the mounting surfaces on the compressor housing.  
           [0005]    The plurality of laminations that make up the stator core can be a preassembled unit or they can be a plurality of loose individual laminations which are stacked up at the time of assembling the electric motor. When a preassembled unit is produced, the laminations are stacked together, aligned and then bonded together by welding, varnishing or by other means for bonding. The assembled units can have their rotor accommodating bore aligned during the assembling and securing operation or the rotor accommodating bore can be machined after assembly of the laminations. Once the stator core has been completed, the stator windings can be added to the core to produce the motor stator. The disadvantages to the preassembled stator cores include, but are not limited to, the relatively high costs associated with the alignment, the bonding and the subsequent machining of the rotor accommodating bore.  
           [0006]    In order to improve the quality of the electric motors and reduce their costs, the industry has turned to the assembling of loose individual stator laminations into the stator cone and then adding the stator winding to this assembly of loose stator laminations. The problem to be solved, when assembling loose laminations, is to align the individual stator core laminations in such a manner that a very accurate size and perpendicularity of the rotor accommodating bore is achieved, not only at the bottom of the stack, but also at the top of the stack.  
           [0007]    One prior art method for the assembling of stators having the loose individual stator laminations and the appropriate stator windings is to place the stator on the compressor body with the bolts extending through the loose stator laminations and loosely threadingly engaging the compressor body. An expanding mandrel is then placed through the center of the stator. The expanding mandrel is then expanded to form the final shape of the rotor accommodating bore. The expansion of the mandrel aligns the loose stack of stator laminations and the expansion of the mandrel will shear and/or crush any burrs which might be located within the bore. The individual bolts are then tightened to hold the stator laminations in place and to secure the stator.  
           [0008]    While the above procedure has worked well for small fractional horse power electric motors, it does not work that well for the larger electric motors required for refrigeration compressors. The main reason for the failure of the above procedure is due to the large forces required to expand the mandrel to align all the laminations at once including the removal of any burrs. The large forces required for the above procedure create the possibility that the assembled stator will deform which results in a defective electric motor.  
           [0009]    Thus, the continued development of the large motors needed for the refrigeration compressors includes the development of methods which will allow the use of the lower cost loose lamination electric motors for these large compressors.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides the art with a method which makes it possible to utilize the lower cost loose lamination electric motors for the larger horse power electric motors required for the refrigeration industry. Prior to this unique method, the use of loose lamination electric motors was not possible for the larger compressors. The method comprises first assembling the loose lamination stator with the appropriate wiring to the compressor body using the bolts that extend through the stator core and then loosely threading the bolts into the compressor body. A solid mandrel is then pushed through this assembly. The solid mandrel is the same size or slightly smaller than the rotor accommodating bore formed in the individual laminations. This solid mandrel aligns the laminations one at a time while simultaneously repositioning the copper wire and the plastic liners and the solid mandrel pre-forms the rotor accommodating bore by shearing off and/or deforming any burrs that may be located within the bore. The solid mandrel is removed, a positioning pin is inserted into one of the open bolt holes and an expanding mandrel is inserted and expanded to form the final shape of the rotor accommodating bore. The expanding mandrel is then collapsed and re-expanded to secure the laminations in place while the bolts are tightened. The bolts hold the laminations in place to maintain the final bore shape. This two step alignment and forming process significantly reduces the loads of any single forming process thus allowing the use of the loose lamination stators for the higher horse power electric motors required for refrigeration compressors.  
       
    
    
       [0011]    Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:  
         [0013]    [0013]FIG. 1 is a vertical sectional view of a hermetic refrigeration compressor which includes the loose lamination stator in accordance with the present invention;  
         [0014]    [0014]FIG. 2 is a top plan view of the motor cover, the loose laminated stator and rotor shown in FIG. 1;  
         [0015]    [0015]FIG. 3 is a fragmentary cross-sectional view of the compressor and electric motor taken in the direction of arrows  3 - 3  in FIG. 2;  
         [0016]    [0016]FIG. 4 is a cross-sectional view of the solid mandrel which aligns the loose laminations;  
         [0017]    [0017]FIG. 5 is a cross-sectional view of the expanding sleeve and arbor of the expanding mandrel;  
         [0018]    [0018]FIG. 6 is a cross-sectional view showing the assembly of the loose lamination stator and the compressor body;  
         [0019]    [0019]FIG. 7 is a cross-sectional view of the solid mandrel in the process of aligning the loose laminations; and  
         [0020]    [0020]FIG. 8 is a cross-sectional view of the expanding mandrel forming the rotor accommodating bore.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a refrigerant compressor which includes a loose lamination stator in accordance with the present invention and which is designated generally by the reference numeral  10 . Refrigerant compressor  10  comprises a hermetic shell  12 , a suction gas inlet  14 , a discharge tube  16  and a motor-compressor unit  18 . Motor compressor unit  18  is spring supported in the usual manner (not shown) and positioned at the upper end by means of a spring  20  located on a sheet metal projection  22 . Motor compressor unit  18  comprises a compressor housing  24  defining a plurality of pumping cylinders  26  (two parallel radially disposed cylinders in this case). A reciprocating pumping member is disposed in each cylinder  26  in the form of a piston  28  connected in the usual manner to a crankshaft  30  by a connecting rod  32 . Crankshaft  30  is rotationally journaled in a pair of bearings  34  disposed within housing  24 . The upper end of crankshaft  30  is affixed to a motor rotor  36  rotatively disposed within a bore  38  defined by a motor stator  40 . The upper end of motor stator  40  is provided with a motor cover  42  which has a recess  44  receiving spring  20  and an inlet opening  46 . Inlet opening  46  is positioned to receive suction gas entering through inlet  14  for the purposes of motor cooling prior to induction into the compressor. Each cylinder  26  in housing  24  is opened to an outer planar surface  48  on housing  24  to which is bolted the usual valve plate assembly  50  and cylinder head  52 , all in the usual manner.  
         [0022]    Referring now to FIGS. 2 and 3, motor cover  42  is generally cup-shaped and it includes a peripheral flange portion  54  adapted to seat on the upper end of stator  40 . Flange portion  54  includes a pair of diametrically opposed extensions  56  and  58  which serve to accommodate openings for a pair of bolts  60  and  62 , respectively. Also, a pair of diametrically opposed recesses or cut out portions  64  and  66  are provided on flange portion  54  offset approximately 90° from respective extensions  56  and  58 . Recesses  64  and  66  serve to provide a clearance for stator securing bolts  68  and  70 , respectfully.  
         [0023]    The assembling of motor-compressor unit  18  includes positioning motor stator  40  on housing  24  and centering stator  40  so that a uniform gap is provided between bore  38  and rotor  36 . Thereafter, stator securing bolts  68  and  70  are tightened thereby locking stator  40  in position so as to assure the above noted uniform air gap is maintained. Next, motor cover  42  may be positioned in overlying relationship to the upper end of stator  40  with recess portions  64  and  66  aligned with previously tightened stator securing bolts  68  and  70 . Thereafter, stator securing bolts  60  and  62  are inserted through openings provided in extensions  56  and  58  of motor cover  42 , through holes in stator  40  and into threaded engagement with compressor housing  24  to secure motor cover  42  and stator  40  to housing  24 .  
         [0024]    The present invention is directed towards a unique apparatus and method for providing the uniform gap discussed above when a loose lamination stator  40  is used. Stator  40  comprises a plurality of loose stator laminations  80  and stator windings  82 . In the prior art, laminations  80  of stator  40  are aligned at the time of assembly of windings  82  and are bonded in alignment by welding, varnishing or other bonding means. The bonding of laminations  80  defined bore  38 . Thus, the prior art method used to provide the uniform air gap was to set the position of bore  38  in relation to bearing  34  which journals crankshaft  30  and thus motor rotor  36 . The present invention utilizes motor stator  40  having the plurality of laminations  80  loose thus requiring both the creation and alignment of bore  38 .  
         [0025]    Referring now to FIG. 4, a non-adjustable or solid mandrel  90  is disclosed. Solid mandrel  90  includes a body  92  which is sized to be the same size or just slightly smaller than the diameter needed for bore  38 . Preferably, a clearance of one-thousandth (0.001) of an inch is provided between the outside diameter of body  92  and the inside diameter of bore  38 . A lead-in chamfer  94  is provided at one end of mandrel  90  and a connecting flange  96  is provided at the opposite end. Body  92  defines an internal bore within which is positioned a bushing  98 . Bushing  98  is designed to engage the end of crankshaft  30  which aligns mandrel  90  with crankshaft  30  to properly align stator  40  as detailed below.  
         [0026]    Referring now to FIG. 5, an expanding mandrel  100  is disclosed. Mandrel  100  includes an expandable sleeve  102  and an arbor  104 . Sleeve  102  includes a body  106  which is sized to be slightly smaller than the diameter of bore  38 . A lead in chamfer  108  is provided at one end of sleeve  102  and a connecting flange  110  is provided at the opposite end. Body  106  defines an internal bore which defines a frusto-conical shaped surface  112  which interfaces with arbor  104  as described below. Body  106  also defines a plurality of axial extending slots  114  which extend from the chamfered end of body  106  towards the flanged end. Interleaved with slots  114  are a plurality of axially extending slots  116  which extend from the flanged end of body  106  towards the chamfered end. Slots  114  and  116  provide for the expansion of sleeve  102  due to the engagement with arbor  104 .  
         [0027]    Arbor  104  includes a body  118  which is designed to be inserted into the internal bore of sleeve  102 . The exterior surface of body  118  defines a frusto-conical surface  120  which is designed to engage frusto-conical shaped surface  112  of body  106  of sleeve  102 . The engagement between surfaces  120  and  112  expands body  106  of sleeve  102  due to the presence of slots  114  and  116 . Body  118  defines an internal bore within which another bushing  98  is disposed. Bushing  98  is designed to engage the end of crankshaft  30  which aligns mandrel  100  with crankshaft  30  to properly align stator  40  as detailed below.  
         [0028]    Referring now to FIG. 3 and  6 - 8 , the assembly of stator  40  to compressor housing  24  will be described. Stator  40  is provided with laminations  80  being loose or in an unbonded condition. Each lamination  80  is manufactured using a stamping press or a piece of similar equipment. Thus, when producing laminations  80 , any distortion and/or thickness variation in laminations  80  will be relatively consistent. If all of laminations  80  are stacked in the same orientation, the distortion and/or thickness variation will become additive adding to the misalignment of laminations  80 . The present invention reduces and/or eliminates the build-up of distortion and/or thickness variation by dividing the total number of laminations  80  into four groups identified as A, B, C and D in FIG. 6. By keeping track of the orientation of each lamination  80  coming from the stamping press, Group B can be orientated 180° with respect to Group A, Group C can be orientated 180° with respect to Group B (the same orientation as Group A) and Group D can be orientated 180° with respect to Group C (180° with respect to Group A). In this manner, any distortion and/or thickness variation in laminations  80  is circumferentially spread out over the entire stack of laminations  80  providing a more uniform stack of laminations  80 . While the present application is being described with four groups of laminations, it is within the scope of the present invention to have more than four groups, if desired. Once circumferentially stacked, laminations  80  are loosely held by windings  82 . Loose laminate stator  40  is placed on compressor housing  24  and bolts  68  and  70  are inserted through stator  40  and loosely threaded into compressor housing  24  as shown in FIG. 6. Bolts  60  and  62  are not assembled at this time. A “dummy” rotor  130  is inserted into bore  38  and it engages the end of crankshaft  30  extending through bearing  34 . Dummy rotor  130  positions loose laminate stator  40  with respect to compressor housing  24  and crankshaft  30 .  
         [0029]    Next, as shown in FIG. 7, solid mandrel  90  is pushed through bore  38  of stator  40 . Chamfer  94  guides mandrel  90  into bore  38  which aligns laminations  80  one at a time while simultaneously repositioning windings  82  and the plastic liners (not shown) disposed between laminations  80  and windings  82 . Because body  92  of mandrel  90  is sized to be just slightly smaller than bore  38 , burrs on laminations  80  are forced to either shear off or they ride up on top of each other one at a time. As mandrel  90  finishes its stroke and thus its alignment, bushing  98  engages the end of crankshaft  30  to again align stator  40  at a position where bore  38  is concentric with the end of crankshaft  30 .  
         [0030]    Next, as shown in FIG. 8, expanding mandrel  100  is inserted into bore  38  in a collapsed or unexpanded condition and a locating pin  30  is inserted into one of the open bolt bores extending through laminations  80  of stator  40 . Locating pin  130  is designed to be slightly larger in diameter than the diameter of bolts  60  and  62  and will thus provide a pivoting point for laminations  80  during the sizing process described below. Sleeve  102  extends entirely through bore  38  and arbor  104  is disposed within the central bore of sleeve  102 . Arbor  104  is then moved axially with respect to sleeve  102  causing surface  120  to engage surface  112  causing the expansion of sleeve  102 . Sleeve  102  expands due to slots  114  and  116 . Sleeve  102  expands until the final bore shape for bore  38  is achieved. As arbor  104  extends axially into sleeve  102 , its bushing  98  engages the end of crankshaft  30  to again align stator  40  at a position where bore  38  is concentric with the end of crankshaft  30 .  
         [0031]    Expanding mandrel  100  is then collapsed by reversing arbor  104  and then expanding mandrel  100  is re-expanded by again reversing arbor  104 . During the re-expansion of mandrel  100 , a lower pressure is used to move arbor  104 . As arbor  104  extends axially into sleeve  102  the second time, its bushing  98  again engages the end of crankshaft  30  to finalize the alignment of stator  40  at a position where finished bore  38  is concentric with the end of crankshaft  30 .  
         [0032]    Bolts  68  and  70  are then tightened to hold laminations  80  in place. Expanding mandrel  100  and locating pin  130  are removed. Motor rotor  36  is heated and shrunk fit onto the end of crankshaft  30 . Finally, motor cover  42  is installed over stator  40  and bolts  60  and  62  are inserted through cover  42 , through stator  40  and threaded into compressor housing  24 . Bolts  60  and  62  are tightened to complete the assembly as shown in FIG. 3.  
         [0033]    The above method provides a system for utilizing loose lamination stators in the higher horse power electric motors without generating the typical prior art large forces which have the capability of deforming the stator which resulted in a defective electric motor.  
         [0034]    While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.