Abstract:
A sealed compressor is provided with a spray lubricant that will provide lubricant at various bearing surfaces during initial start-up of the compressor. The lubricant will wear away quickly after initial run-in, but liquid lubricant will be provided by that time.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT Application No. PCT/IB2008/001318, which was filed on Jan. 30, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to a temporary coating for a sealed compressor, to provide lubricant at bearing surfaces for start-up. 
     Refrigerant compressors are typically mounted in a sealed container. An electric motor is provided in the sealed container and drives a rotating shaft. The rotating shaft drives a pump unit to compress the refrigerant. 
     One known type of compressor pump unit is a scroll compressor. In a scroll compressor, the rotating shaft has an eccentric pin that works in combination with a rotation prevention mechanism, typically an Oldham coupling, to cause orbiting movement of an orbiting scroll member. The orbiting scroll member has a base with a generally spiral wrap extending from the base. The wrap interfits with a wrap from a non-orbiting scroll member, and compression chambers are defined between the two wraps. As the orbiting scroll member orbits, the size of the compression chambers decreases and an entrapped refrigerant is compressed. 
     In scroll compressors, and in other types of compressors, a liquid lubricant is typically pulled upwardly through passages in the shaft to lubricate sliding surfaces in the compressor pump unit. The lubricant serves to lubricate the surfaces, and prevent wear or other damage to the components sliding or rotating relative to each other. 
     However, at start-up, it may be the case that sufficient liquid lubricant will not be at those surfaces. Thus, there may sometimes be damage to the surfaces before the lubricant can reach the sliding surfaces. This is especially true at initial run-in of the compressor, when it is initially started. 
     In particular, at initial run-in of the compressor, a problem called “edge loading” can occur, since there is typically some small misalignment between the rotating shaft and several bearings that mount the shaft. This misalignment can result in edges of the bearing contacting the shaft over a limited surface, rather than providing support over a larger surface area. Seizure and undue wear of portions of the components can occur, which is undesirable. This problem is made more acute if there is insufficient lubricant during the initial run-in. 
     Also, modern refrigerants, which may include mixtures of R32 and R125, or a mixture of R143a and R125 can have some undesirable interaction in compressors utilizing ester oil or ether oil as a lubricant. In such compressors, the refrigerant which circulates over the bearing surfaces, can pull the lubricant away from the bearing surfaces back downwardly into the sump. When this occurs, there is even less lubricant during the initial start-up. 
     It is known in the prior art to provide various types of bearings having self-lubricating properties. As an example, any number of prior art patents have proposed utilizing bearings having impregnated polytetrafluoroethylene (“PTFE”) material. In general, these proposals could be characterized as somewhat complex and expensive. 
     In addition, these bearings do not address the lack of liquid lubricant at the sliding surfaces at initial start-up of the compressor. 
     SUMMARY OF THE INVENTION 
     In a disclosed embodiment of this invention, a self-lubricating material is sprayed onto components that will be part of the relatively sliding surfaces. The spray only provides lubricant for a short period of time after initial start-up of the compressor, however, it is this run-in period which is most problematic. In a disclosed embodiment, the self-lubricating material is a dry material. In one proposed embodiment, it is a PTFE spray material. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view through a scroll compressor incorporating the present invention. 
         FIG. 2  shows a shaft from the  FIG. 1  compressor. 
         FIG. 3A  shows a first bearing surface. 
         FIG. 3B  shows a second bearing surface. 
         FIG. 3C  shows a third bearing surface. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A compressor  20  is shown in  FIG. 1  as a scroll compressor. The scroll compressor has an orbiting scroll member  22 , and a non-orbiting scroll member  24 . An electric motor  26  drives a rotating shaft  28 . The components sit within a sealed shell  21 . An oil sump  30  is defined at the bottom of the shell  21 . A first bearing  32  mounts a lower end  34  of the shaft  28 . Crankcase  35  includes another bearing  36  supporting an intermediate portion  38  of the shaft  28 . An upper bearing  40  is formed within the orbiting scroll  22 , and supports an eccentric pin  42  from the shaft  28 . 
     As is known, an inlet or suction tube  44  delivers refrigerant into a chamber  46  surrounding the motor  26 . That refrigerant circulates to cool the motor, and is delivered to compression chambers between the scroll members  22  and  24 . This refrigerant is allowed to circulate over the bearing surfaces. As mentioned above, when particular refrigerants such as mixtures of R32 and R125, or a mixture of R143a and R125 are utilized in a compressor utilizing ester oil or ether oil as its lubricant, the problem mentioned above can occur. 
     The refrigerant is compressed between the scroll members  22  and  24  and delivered into a discharge chamber  48 , and through a discharge tube  50  to a downstream location, such as to a condenser in an air conditioning unit. 
     As mentioned above, in the prior art, there has sometimes been a lack of lubricant at sliding surfaces, such as the bearings  40 ,  36 , and  32 . This often occurs at initial run-in or start-up of the compressor. 
       FIG. 2  shows a shaft  28  in which a PTFE spray, shown schematically by box  51 , is sprayed onto surfaces  34 ,  38  and  42 . The shaft  28  can now be mounted within the motor, the shell sealed, and the compressor charged with refrigerant. At initial start-up of the compressor, the PTFE coated shaft will provide lubricant. 
     The sprayed locations  34 ,  38  and  42  corresponding to the locations of the bearings  40 ,  36 , and  32  as shown in  FIGS. 3A-3C . On the other hand, the spray material could be sprayed on the bearing locations  40 ,  36 , and  32 . However, it may be simpler to spray the self-lubricating material onto the shaft as shown in  FIG. 2 . 
     The spray coating can be applied in a very thin layer, and may be less than 50 micrometers, and preferably between 5 and 10 micrometers. Such thicknesses are sufficient to fill up any microscopic grooves on the shaft surface. Any wear during run-in to accommodate misalignment will occur in parallel with the removal of the sprayed layer, but while the sprayed layer will prevent undue wear and seizure of the bearing material. 
     While any number of self-lubricating material may be utilized, a dry self-lubricating material is preferred. The dry material will not fall back downwardly into the oil sump, even if the compressor is shipped and stored for long periods of time, and will not interact with the above mentioned particular refrigerants. Even more preferably, a polytetrafluoroethylene material, typically known as Teflon® may be utilized. One potential material is available under the trade name Lubrifiant A Sec, from Ront Production. See www.ront.com. However, other materials may be utilized. While spray materials are disclosed, other methods of depositing the layer can be used. 
     While embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.