Patent Publication Number: US-2016248287-A1

Title: Compressor

Description:
The present invention relates to a compressor according to the preamble of claim  1 , and to a method for producing a compressor, according to claim  5 . 
     Displacement compressors for compressing NH 3  are used in many areas of daily life and are nowadays the subject of increased interest due to the desired reduced use of halogenated hydrocarbons as coolant, which have been under debate in particular on account of their relatively high global warming potential. 
     Compressors of different constructions are available in order to be able to satisfactorily fulfill a respective use-specific object. Examples which may be named at this point are reciprocating piston compressors or screw compressors. 
     In the field of reciprocating piston compressors and also that of screw compressors, there exist semi-hermetic and hermetic embodiments having an electric motor which is at least partially NH 3 -cooled. That is to say that the electric motor of the NH 3  compressor in a refrigeration plant is at least partially cooled using NH 3 , cooling generally being carried out using intake gas, i.e. expanded NH 3  which is to be compressed or, in the case of two-stage compressors, also using intermediate-pressure gas, that is to say intake gas for a second compressor stage. 
     Due to the corrosive action of NH 3 , the motor windings of prior art NH 3  compressors are made of aluminum. As the conductivity of aluminum is relatively bad, this requires a relatively large cross-section for the windings. This increases the size of the motor and also that of the pressure-resistant motor housing, leading to high weight of the corresponding compressor. Moreover, in spite of the larger construction size, the efficiencies of aluminum windings remain below those of motors having windings made of more conductive materials. 
     Starting from this point, the present invention has the object of specifying a compressor, in particular a semi-hermetic or hermetic displacement compressor, for compressing NH 3 , which is as lightweight, as compact and as efficient as possible compared to the prior art compressors. The present invention also has the object of specifying a corresponding method for producing such a compressor. 
     This object is achieved, according to the invention, with a compressor according to claim  1  and, with respect to the method aspect, with a method having the features of claim  5 . 
     The object is achieved in terms of apparatus with a compressor, in particular a semi-hermetic or hermetic displacement compressor, for compressing NH 3 , having an at least partially NH 3 -cooled electric motor with motor windings, wherein the motor windings are made of copper and have an ammonia-resistant coating. The coating is optionally made of an extrudable material, or is extruded. The motor windings and the coating can be co-extruded, which ensures cost-effective and simple production. 
     It is to be noted, at this point, that a compressor according to the invention can be created in many different constructions, in particular as a semi-hermetic or hermetic NH 3  compressor with intake gas cooling or intermediate pressure cooling, moreover in particular as a semi-hermetic or hermetic screw compressor, as a semi-hermetic or hermetic compact screw compressor, or as a semi-hermetic or hermetic single-stage or two-stage piston compressor. 
     Furthermore, the concept of the present invention includes a corresponding method for producing a compressor, in particular a semi-hermetic or hermetic displacement compressor, for compressing NH 3 , having an at least partially NH 3 -cooled electric motor with motor windings, wherein the method has a step of producing the motor windings. The step of producing the motor windings has the following sub-steps:
         manufacturing the motor windings from the copper material;   coating the motor windings with an ammonia-resistant material.       

     In possible embodiments, both the motor windings and/or the ammonia-resistant coating can be produced by means of an extrusion method, it being also conceivable that the motor windings and the coating are extruded in immediate succession, wherein in this case the above-mentioned sub-steps are carried out in immediate succession. The ammonia-resistant coating can furthermore (optionally) be sprayed on or applied by means of a dipping method. 
     Furthermore, the basic concept of the present invention includes a corresponding use of motor windings which are made of copper and have an ammonia-resistant coating, for the production of an electric motor of a compressor, in particular a semi-hermetic or hermetic displacement compressor, for compressing NH 3 , having an at least partially NH 3 -cooled electric motor with motor windings. The motor windings and/or the coating can, in one possible embodiment, be extruded. Optionally, the motor windings and the coating can also be formed in two immediately successive extrusion steps, or the ammonia-resistant coating can be sprayed on or applied by means of a dipping method. 
    
    
     
       Further optional features of the invention are indicated in the subclaims and in the following description of the figures. The described respective features can be realized individually or in any combination. Accordingly, the invention is described in the following in relation to the appended drawings and with reference to exemplary embodiments. In the drawings: 
         FIG. 1  shows a schematic representation of an exemplary embodiment of a compressor according to the invention; 
         FIG. 2  shows a view of a motor winding of the compressor from  FIG. 1  in longitudinal section; and 
         FIG. 3  shows a view of a motor winding of the compressor from  FIG. 1  in cross section. 
     
    
    
       FIG. 1  shows, schematically as a section representation, a possible embodiment of a compressor  10  according to the invention. The compressor  10 , which in the described embodiment is designed as a semi-hermetic compact screw compressor and is intended to be used with NH 3  as coolant, has an electric motor  12  which drives a drive shaft  14 . The drive shaft  14  drives a compressor unit  16  for compressing the coolant (NH 3 ). 
     The compressor  10  also has a coolant inlet  18  and a coolant outlet  20 . In the embodiment described here, the coolant inlet  18  and the coolant outlet  20  are arranged such that incoming coolant flows through a motor space  22  of the compressor  10  in order to cool the electric motor  12 , before it enters the compressor unit  16  where it is compressed to a final pressure and is then fed to the coolant outlet  20 . 
     It is to be noted that, alternatively, it is also conceivable to cool the electric motor  12  using already-pressurized coolant, that is to say coolant which has already been compressed, by the compressor unit  16 , to an intermediate pressure or a final pressure. In particular, in this context, reference is made to multi-stage compressors in which the motor is cooled using coolant at an intermediate pressure, i.e. coolant which has been compressed to an intermediate pressure by means of a first compression stage and which is used to cool the electric motor  12  before it is fed to a second compression stage. 
     In order to withstand the NH 3  used as coolant, the electric motor  12  has windings  24  which have a conductor  26  made of copper and an ammonia-resistant coating  28  arranged on the conductor  26  (see, for this,  FIG. 2  and  FIG. 3 ). In the embodiment described here, the coating consists of an extrudable material, i.e. a material which can be worked by means of an extrusion method. Other materials may also be used in alternative embodiments. 
     During production of the possible embodiment described here, both the conductor  26  and the coating  28  are extruded in two immediately successive extruding steps, which ensures rapid, economical and cost-effective production. Also conceivable, however, are alternatively two, in particular temporally separated extrusion processes, or also coating the conductor by means of another method, for example a spray method or a dipping method. Furthermore, other materials may be located between the conductor  26  and the coating  28 , in particular materials provided in a layered arrangement. In the embodiment described, the coating has a thickness of a few hundred microns (μm). 
     Although the invention has been described with reference to embodiments with fixed feature combinations, it nonetheless also encompasses the conceivable further advantageous combinations as are indicated in particular, but not exhaustively, in the subclaims. All features disclosed in the application documents are claimed as essential to the invention insofar as they are novel over the prior art, whether individually or in combination. 
     LIST OF REFERENCE SIGNS 
     
         
           10  compressor 
           12  electric motor 
           14  drive shaft 
           16  compressor unit 
           18  coolant inlet 
           20  coolant outlet 
           22  motor space 
           24  winding 
           26  conductor 
           28  coating