The present invention relates to securing a motor cover or cap to the stator of an electric motor, and particularly to the electric motor of a hermetic compressor. 
Hermetic compressors are provided with an electric motor which is operatively coupled to a compression mechanism, the motor and the compression mechanism both disposed within a sealed housing.  Typically, the motor has a generally cylindrical rotor through which a drive shaft longitudinally centrally extends.  The drive shaft rotates with the rotor and is typically provided with an eccentric portion for imparting working motion to the compression mechanism.  For example, the drive shaft may be the crankshaft of a reciprocating piston compressor, and drives the pistons in cylinders to compress the refrigerant during operation of the compressor in the well-known manner. 
Surroundingly disposed about the rotor is the generally annular motor stator having windings which are electrically connected to a source of power external to the compressor, as usual.  An electromagnetic force created in the stator drives the rotor, and thus the compressor mechanism. 
The rotor is radially supported by means of the drive shaft being supported in a bearing portion of the compressor mechanism crankcase or frame.  Initially, the stator is loosely attached to the crankcase or frame by means of a pair of bolts which extend through the length of the stator, in holes provided therein.  These two bolts may be located in holes on opposite radial sides of the stator. 
To provide proper operation of the motor, an air gap of constant width is established between the interfacing interior radial surface of the stator and the exterior radial surface of the rotor.  The radial position of the rotor, being supported by the drive shaft, is established by the journalled interface of the drive shaft and the crankcase or frame main bearing.  The radial position of the loosely attached stator is adjusted relative to the crankcase or frame to establish the proper air gap.  The air gap may be set by means of a jig temporarily placed between the interfacing radial surfaces of the rotor and stator.  The stator is then tightly secured to the crankcase, and thus radially fixed in place relative to the rotor, by tightening the two above-mentioned bolts.  The air gap having been set, the jig, if one is used, is then removed. 
Once the air gap has been set, and the jig removed, a motor cover or cap is placed over the axial ends of the stator and rotor located opposite the compression mechanism.  The cover has a periphery which is attached to the end of the stator, and encloses the interior of the stator within which the rotor is located.  The cover may be placed immediately after setting the air gap, or the compression mechanism and motor subassembly may undergo further processing toward assembly of the hermetic compressor before the cover is installed. 
The periphery of the cover is provided with a flange or an opposed pair of radially extending ears having apertures therein.  These apertures are aligned with a second pair of holes which longitudinally extend through the stator.  With the cover in place on the end of the stator, clearance is provided between the cover and the heads of the first pair of bolts.  A second pair of bolts, usually identical to the first pair of bolts, are then inserted through the aligned cover apertures and stator holes, and are threadedly engaged in the crankcase or frame.  Thus, the stator is further and finally secured to the compression mechanism by the bolts which secure the cover to the stator. 
A problem associated with such previous motor cover retention arrangements is that a change in the air gap may occur after the gap has been set.  Such changes may be the result of the compression mechanism and motor subassembly being bumped or jarred during assembly, causing the stator, which is secured to the crankcase or frame by only the first pair of tightened bolts, to move relative to the rotor; or the result of installation an tightening of the second pair of bolts, which retain the cover and further clamp the stator to the compression mechanism, after the jig is removed.  A way of better securing the stator so that the proper air gap can be maintained throughout the assembly process, and afterwards, is desirable. 
A further problem associated with such previous motor cover retention arrangements is that retaining the cover to the stator at only a pair of radially opposite locations may not adequately secure the cover.  The cover would be better secured if retained at more than only two locations. 
Another problem associated with such previous motor cover retention arrangements is that the second pair of bolts, which attach the cover to the stator end as well as to help secure the stator to the crankcase or frame, may not maintain proper torque after installation, and may lead to either post-assembly air gap variations or even bolts backing out of engagement with the crankcase or frame.  This result may stem from there being material or material thickness differences between the stator alone, which is clamped into place by the first pair of bolts, and the stator and cover, which are clamped into place by the second pair of bolts.  Further, consistent torquing of the first and second pairs of bolts may be difficult to easily achieve, for the setting of the air gap and the installation of the cover may be done at different assembly stations, by different operators, and with different tools.  To better ensure bolt clamping consistency, and reduce the risk of bolts becoming loosened, it is desirable eliminate clamped material or material thickness variations between all the stator-securing bolts, and to install all of these bolts at the same assembly station, by the same operator, and with the same tool. 
A motor cover retention arrangement which avoids the above-mentioned problems associated with previous arrangements is desirable, particularly in hermetic compressor applications, for once installed, the motor is then sealed inside the housing and is thereafter practically inaccessible for service or repair. 
The present invention provides a motor cover retention means which is of particular use in hermetic compressors and solves the problems associated with prior motor cover retention arrangements.  Through use of the present invention, the quality and reliability of hermetic compressors can be realized vis-a-vis previous compressor utilizing the above described motor cover retention means. 
In accordance with the present invention, the stator is secured to the compressor crankcase or frame with a plurality, e.g., four, bolts, which may all tightened simultaneously, or at least at the same assembly station, by the same operator, with the same tool once the air gap is set and with the air gap jig in place.  The bolts have a circumferential groove defined in the heads thereof, or located between the heads and a flange which abuts the end of the stator.  The periphery of motor cover is provided with a flange provided with the same number of apertures as there are stator-securing bolts, e.g., four.  These cover apertures are positioned such that are each aligned with the bolt heads, and are sized to be slightly greater than the bolt heads.  The cover is installed onto the end of the stator, which is already firmly secured to the compression mechanism by all of the bolts, with the heads of the bolts projecting through the cover apertures; the groove provided in or adjacent to the bolt head located on the side of the cover opposite the stator.  Once in place on the end of the stator, the motor cover is secured by forcing E-clips into the grooves of the bolts.  The cover is thus retained onto the stator end by the clips. 
The cover or the clips may be placed in an elastically deformed state through the interface therebetween, and held in this elastically deformed state after installation of the cover and clips, the elastic deformation urging the cover into tight abutting contact with the end of the stator, to better secure the cover in its installed position.  The cover may further be provided, adjacent its bolt head-receiving apertures, with one or more projections which bear against the installed E-clip, the cover urged into tight abutting contact with the stator end through the resilience of the clips and/or the cover. 
The present invention provides a hermetic compressor including a housing, a compression mechanism disposed in the housing, and a motor disposed in the housing and operatively coupled to the compression mechanism, the motor comprising a stator, the stator having, relative to the compression mechanism, a proximal end and a distal end.  At least one fastener extends through the stator, and the stator is fixed, relative to the compression mechanism, by the fastener.  A motor cover is disposed over the distal end of the fixed stator, a portion of the fastener extending through the cover, and a clip engages the portion of each fastener, the cover being retained to the fixed stator by the clip. 
The present invention also provides a method of assembling a hermetic compressor which includes the steps of: providing a compression mechanism, a motor including a rotor and a substantially annular stator, a plurality of fasteners, a motor cover provided with a plurality of apertures, and a plurality of clips; surrounding the rotor with the stator; placing the fasteners longitudinally through the stator; loosely attaching the stator and the compression mechanism with the fasteners; aligning the stator relative to the rotor, whereby an air gap therebetween is set; tightening the fasteners and fixing the stator relative to the compression mechanism after the air gap is set; aligning the cover apertures with the fasteners and fitting the cover over the stator and rotor such that portions of the fasteners extend through the cover apertures, whereby the fastener portions protrude through the cover; and engaging the clips onto the protruding fastener portions, whereby the cover is retained in a position between the stator and the clips. 
The present invention also provides a method of assembling a hermetic compressor which includes the steps of: providing a compression mechanism, a rotor, a stator having a plurality of holes therethrough, a plurality of bolts having heads, a motor cover having a plurality of apertures, and a plurality of clips; positioning the stator relative to the compression mechanism; placing the plurality of bolts into the stator holes; loosely attaching the stator and the compression mechanism with the bolts; radially positioning the rotor relative to the compression mechanism; radially positioning the stator relative to the rotor, whereby a desired air gap therebetween is set; after the air gap is set, tightening the plurality of bolts to securely attach the stator and the compression mechanism, whereby the radial position of the stator relative to the rotor is fixed; placing the cover over the stator and rotor and fitting the bolt heads through the cover apertures; and engaging a clip onto each bolt adjacent its head, whereby the cover is retained between the stator and the clips.