Abstract:
A refrigeration motor compressor assembly has a housing including a lubricant sump in the bottom thereof into which the lower end of the drive shaft and associated rotor extend. A shield is provided which is positioned by the drive shaft and extends above the oil level in the sump in surrounding spaced relationship to the lower end of the rotor. As the rotor rotates within the shield, lubricant contained therein is thrown out of the surrounding shield and a close fit between the shield and the shaft restricts return flow of lubricant into the area occupied by the rotating rotor.

Description:
This application is a continuation of U.S. patent application Ser. No.  07 / 824 , 069  filed Jan.  23 ,  1992 , now Reissue Pat. No. RE.  34 , 297  which is a reissue of U.S. Pat. No.  4 , 895 , 496 , issued Jan.  23 ,  1990 . 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to refrigeration compressors and more specifically to such compressors incorporating shields for reducing the lubricating oil level in the area surrounding the rotating rotor. 
     Typical refrigeration compressors incorporate a lubricant sump in the lower or bottom portion of the housing into which the drive shaft extends so as to pump lubricant therefrom to the various portions requiring lubrication. In addition, the lubricant also often acts to aid in removal of heat from the various components. In order to insure sufficient lubricating oil is contained within the sump to assure adequate lubrication and/or cooling of the moving parts while also minimizing the overall height of the housing, it is sometimes necessary that the oil level extend above the rotating lower end of the rotor. However, the higher viscosity of the oil as compared to refrigerant gas creates an increased drag on rotation of the rotor resulting in increased power consumption. This problem is further aggravated in scroll type compressors which typically employ a counterweight secured to the lower end of the rotor. 
     The present invention, however, provides a shield which projects above the oil level in the sump and is positioned in surrounding relationship to the lower end of the rotor via a close fit with the drive shaft whereby the oil level in the area within the shield is reduced by the initial rotation of the rotor upon startup and return oil flow into this area is greatly restricted. Thus, the oil induced drag on the rotor and resulting increased power consumption of the motor is greatly reduced. In one embodiment, a rotation inhibiting projection is provided on the shield while in another embodiment the shield is allowed to rotate with the drive shaft although the speed of rotation thereof will be substantially less than that of the drive shaft due to the drag exerted thereon by the lubricant. In both embodiments, however, the power consumption of the motor is greatly reduced thus resulting in significant improvement in the operating efficiency of the compressor. 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view of a refrigeration compressor of the scroll type incorporating a shield surrounding the lower end of the motor rotor in accordance with the present invention, the section being taken along a radial plane extending along the axis of rotation of the drive shaft; 
     FIG. 2 is a section view of the compressor of FIG. 1, the section being taken along line  2 — 2  thereof; 
     FIG. 3 is a perspective view of the shield shown in FIGS. 1 and 2; and 
     FIG. 4 is a fragmentary section view similar to FIG. 1 but showing only a portion of the oil sump and an alternative embodiment of the shield, all in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and more specifically to FIG. 1, there is shown a hermetic refrigeration compressor  10  incorporating a shield  12  all in accordance with the present invention. 
     Compressor  10  comprises an outer shell or housing  14  within the lower portion of which is disposed an electric motor  16  including a stator  20  and a rotor  22 . Motor  16  is operative to drive a compressor assembly  24  disposed in the upper portion of shell  14  via a drive shaft  26  extending therebetween and to which rotor  22  is secured adjacent the lower end. As shown, compressor assembly  24  is of the scroll type and incorporates an upper fixed scroll member  28  and a lower scroll member  30  which is driven by drive shaft  26  in orbiting motion relative to the fixed scroll member  28 . Drive shaft  26  is rotatably supported within shell  14  by means of upper and lower bearing assemblies  32  and  34  respectively each of which are fixedly secured to shell  14 . Compressor  10  is described in greater detail in presently pending application Ser. No. 899,003 filed Aug. 22, 1986 entitled “Scroll Type Machine With Axially Compliant Mounting” assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference. 
     The lower portion of shell  14  defines a lubricant sump  36  containing a supply of oil for lubrication of the various components of compressor  10  as well as augmenting cooling thereof. In order to both minimize the overall height of compressor  10  as well as to assure an adequate supply of lubricant is contained within the sump, oil level  38  extends above the lower ends of the end turns  40  of stator  20  and both a counterweight  42  and the lower end portion  44  of rotor  22  to which counterweight  42  is secured. 
     Shield  12  is preferably formed as a one piece structure from a suitable polymeric composition such as a nylon material for example. It should be noted that other materials may be utilized so long as they are able to resist degradation from both the oil and refrigerant utilized in the system as well as the heat generated during operation of compressor  10 . It should also be noted that the use of a dielectric non-magnetic material is believed preferable due to the proximity of the shield to the motor rotor and stator and the desire to avoid any interference with the operation thereof. 
     As best seen with reference to FIGS. 1 and 3, shield  12  incorporates a first generally cylindrically shaped portion  46  open at the upper end thereof and positioned in surrounding relationship to lower end portion  44  of rotor  22  and associated counterweight  42 . Cylindrical portion  46  extends axially upwardly between rotor  22  and the end turns  40  of stator  20  to a height just slightly above maximum normal oil level  38 . A lower hollow generally cylindrically shaped portion  48  extends axially downwardly therefrom in relatively closely spaced relationship to shaft  26  and includes an annular radially inwardly extending flange portion  50  which is received within a reduced diameter portion  51  of shaft  26 . A radially extending annular flange portion  52  extends between and interconnects cylindrical portions  46  and  48 . In order to restrict rotation of shield  12 , a generally flat flange portion  54  is integrally formed on shield  12  extending axially downwardly from the lower surface of flange portion  52  and generally radially outwardly from cylindrical portion  48 . Leg  56  extends axially downwardly from flange portion  54  and is received between a pair of support legs  58 ,  60  forming a part of lower bearing assembly  34  and cooperates therewith to restrict rotational movement of shield  12 . 
     In operation, the rotational movement of the lower end portion  44  of rotor  22  and the associated counterweight  42  will operate to throw oil which has accumulated within the hollow shield  12  radially outwardly and over the top edge of shield  12  through the open spaces in the stator end turns as well as between shield  12  and these end turns and into sump  36  thereby lowering the oil level in the area surrounding the rotating rotor. Because the lower cylindrical portion  48  of shield  12  is closely fitted to the shaft  26 , only a very small amount of oil will flow upwardly therebetween. Further, once a substantial amount of the oil within shield  12  has been expelled, shield  12  will become buoyant and float upwardly in the oil sump. As this occurs, flange portion  50  will move into engagement with the annular shoulder  62  on crankshaft  26  thus limiting further axial movement so as to thereby prevent shield  12  from moving upwardly into engagement with the spinning rotor  22 . This engagement will also operate to establish a further restriction or seal against oil flow into the interior of shield  12 . Thus, shield  12  will operate to effectively reduce the drag on rotor rotation due to its partial immersion into the oil in the lubricant sump and thereby eliminate the resulting power consumption. In this regard, it should be noted that the clearance between cylindrical portion  48  and shaft  26  is sufficient to avoid any excessive wear or drag on shield  12  but yet small enough to enable shaft  26  to effectively maintain shield  12  and particularly upper cylindrical portion  46  thereof the desired substantially coaxial position with respect to rotor  22  so as to avoid the possibility of contact therebetween. When compressor  10  is de-energized, shield  12  will slowly settle axially downwardly as lubricating oil gradually flows back into the interior thereof until such time as it comes to rest on lower bearing assembly  34  as shown in FIG.  1 . 
     Referring now to FIG. 4, a modified embodiment of a shield  64  in accordance with the present invention is shown in operative relationship to a motor assembly  66  and associated drive shaft  68  of a refrigeration compressor  70 . Shield  64  is virtually identical to shield  12  with the exception that flange portion  54  and associated leg  56  have been deleted therefrom. Accordingly, corresponding portions of shield  64  have been indicated by like numbers primed. Because shield  64  does not incorporate any means to prevent relative rotation thereof, the viscous drag resulting from the oil disposed between cylindrical portion  48 ′ and shaft  66  will result in rotational movement thereof. However, this rotation will be substantially slower than the speed of rotation of drive shaft  66  because of the viscous drag exerted on shield  64  by the oil within sump  36 ′. Hence, it is believed only a slight stirring of the oil within sump  36 ′ will occur as shield  64  is allowed to rotate which stirring may be beneficial to aid in cooling of the lower end turns of stator  20 ′. 
     Thus, as may now be appreciated, substantial improvements in operating efficiency are achieved by incorporation of either shield  12  or  64  due to the reduced motor power consumption. These longlasting benefits are achieved at a relatively low cost as shields  12  and  64  may be easily and inexpensively formed in any suitable manner such as injection molding or the like and further enable the overall height of the motor compressor to be kept to a minimum. 
     While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to provide the advantages and features above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.