Patent Publication Number: US-10309383-B2

Title: Bearing arrangement for a reciprocating compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/978,999 filed on Aug. 20, 2013, which claims priority to PCT/BR2011/000505 filed on Dec. 23, 2011, which claims priority to PI 1100652-8, a Brazilian application filed on Jan. 13, 2011. 
    
    
     FIELD OF THE INVENTION 
     The present invention refers to a constructive arrangement for providing a radial bearing for the crankshaft of a reciprocating refrigeration compressor, either hermetic or not, presenting smaller viscous friction losses in relation to the known bearing arrangements. 
     PRIOR ART 
     The refrigeration compressors of the reciprocating type, generally have a mechanical assembly composed by a crankcase, a crankshaft, at least one connecting rod and at least one piston, which elements are arranged so that the rotating movement of the crankshaft, provided by an electric motor of the compressor, is converted to a reciprocating linear movement of the piston. 
     A conventional construction of a reciprocating compressor, of the type illustrated in  FIG. 1 , presents, in the interior of a shell (not illustrated), a crankcase B which defines a cylinder  10 , inside which reciprocates a piston  20 . 
     The crankcase B is also provided with a bearing hub  30 , whose inner surface radially supports a crankshaft  40  which incorporates an eccentric end portion  45 , projecting outwardly from a first end  30   a  of the bearing hub  30  and operatively coupled to the piston  20 , by means of a connecting rod  50 , and a free end portion  46  which projects outwardly from a second end  30   b  of the bearing hub  30 . 
     In the present disclosure, the axis of the crankshaft  40  is considered to be coincident with the axis of the bearing hub  30 , independently of the operational condition of the compressor. 
     Around the eccentric end portion  45  of the crankshaft  40 , it is mounted a larger eye  51  of the connecting rod  50 , whose smaller eye  52  is coupled to the piston  20 , by a wrist pin  53 . The free end portion  46  of the crankshaft  40 , which projects outwards from the bearing hub  30 , is coupled to a rotor of an electric motor, not illustrated and which rotates the crankshaft  40 , impelling the piston  20 . Said free end portion  46  of the crankshaft  40  generally also carries, in this compressor construction, an oil pump not illustrated and which conducts oil from an oil reservoir, defined in a lower portion of the shell, to the compressor parts to be lubricated. The crankcase B generally supports, by an end portion  70 , a stator (not illustrated) of the electric motor. 
     In this known construction, during the compression of the gas in the cylinder  10 , the compression force F, which actuates against the eccentric end portion  45  of the crankshaft  40 , is transmitted to the crankcase B, by the crankshaft  40 , in the first and second end portions  30   a ,  30   b  of the bearing hub  30 , and on which there are applied a first and a second reaction forces F 1 , F 2 , derived from the compression force F. 
     The forces mentioned above, in the presence of the radial gaps between the crankshaft  40  and the bearing hub  30 , inherent to the sliding bearings, produce the so-called misalignment of the crankshaft  40 , whereby the two end portions  30   a ,  30   b  of the bearing hub  30  are those which support the load imposed to the bearing hub  30 , considering an ideal situation of high rigidity of the mechanism components. 
     Considering the deformable components and the presence of sliding (hydrodynamic) bearings, the reaction forces F 1 , F 2  are distributed in the regions of the end portions  30   a ,  30   b  of the bearing hub  30 , which regions effectively have the function of radially bearing the crankshaft  40 . There is a continuous search for constructive solutions which allow increasing the energy efficiency of these reciprocating refrigeration compressors, one of said solutions providing the reduction of the mechanical losses of the movable components, for example, the mechanical losses generated by the relative movement between the crankshaft  40  and the bearing hub  30 , generally as a function of the viscous friction generated by said lubricated parts, upon rotation of the crankshaft  40  in the interior of the bearing hub  30 . 
     The power dissipated, as a function of said viscous friction, is proportional to the axial extension of the radial bearing which supports the crankshaft  40 . Thus, it is known the provision of a radial recess in radial bearings of large axial extension, with the object of reducing the mechanical losses by viscous friction. Although the intermediary portion of the bearing hub  30  little contributes to the hydrodynamic support of the crankshaft  40 , it is responsible for a significant part of the viscous friction loss. On account of this fact, it is known in the art the provision of a circumferential recess  43 , in the median region of the crankshaft  40 , which is positioned between the end portions  30   a ,  30   b  of the bearing hub  30 , as illustrated in  FIG. 1  of the enclosed drawings. With the provision of the circumferential recess  43 , the crankshaft  40  presents a first support portion  41 , generally close to the eccentric end portion  45 , and a second support portion  42 , axially spaced from the first one and adjacent to the free end portion  46  of the crankshaft  40 . 
     The first and second support portions  41 ,  42  of the crankshaft  40  have their axial extensions dimensioned to provide the necessary and adequate hydrodynamic radial bearing of the shaft in relation to respective end portions of the bearing hub  30 , which define, respectively, a first and a second bearing portions  31 , which, in said prior art construction, present a constant diameter along the whole axial extension of the bearing hub  30 . Therefore, in said construction, the bearing hub  30  is not provided with any circumferential recess. 
     With the solution illustrated in  FIG. 1 , it is possible to reduce, through the axial dimensioning of the circumferential recess  43 , the axial extension of the first and second support portions  41 ,  42  of the crankshaft  40 , that is, of the axial extension of the radial bearing regions between the crankshaft  40  and the bearing hub  30  and, consequently, the levels of mechanical loss by viscous friction. However, the reduction of the axial extension of the first support portion  41  of the crankshaft  40 , allied to the unbalance produced by the eccentric end portion  45  and by the cast counterweight  44 , incorporated in the median region of the crankshaft  40 , impairs the grinding process of the shaft, mainly when produced by the centerless process, tending to increase shape errors (circularity and cylindricity) in the crankshaft  40 . The reduction of the useful bearing area and the natural unbalance of the crankshaft  40  make the grinding process of the crankshaft undesirably complex and costly, in case of using grinding processes other than the centerless. It should be noted that the second support portion  42  of the crankshaft  40  is adjacent to the free end portion  46 , the latter guaranteeing the axial extension of the second support portion  42  and an adequate support surface in the centerless grinding process of the crankshaft  40 . 
     In  FIG. 2  of the drawings, it is illustrated the construction described in document WO 03/098044, according to which it is provided not only one circumferential recess  43 , in the median region of the crankshaft  40 , but also a first, a second and, optionally, a third partial circumferential recesses  43   a ,  43   b  and  43   c  in the bearing regions of the crankshaft  40  and in the eccentric end portion  45 , which are submitted to lower loads during the operation of the compressor, that is, in the regions which generate low pressure in the oil film. The first partial circumferential recess  43   a  is provided in a shaft portion adjacent to the eccentric end portion  45 , in a region angularly aligned with the eccentric end portion  45 . The second partial circumferential recess  43   b  is provided in the eccentric end portion  45 , in a region angularly and diametrically opposite to the first partial circumferential recess  43   a . The third partial circumferential recess  43   c , which is optional, is provided in a region of the crankshaft  40 , adjacent to the free end portion of the latter and axially aligned with the second partial circumferential recess  43   b , provided in the eccentric end portion  45  of the crankshaft  40 . 
     Said second prior art solution presents some inconveniences associated with the production of said partial circumferential recesses  43   a ,  43   b  and  43   c.    
     One of the inconveniences results from the fact that the formation of said partial circumferential recesses requires more complex operations, including milling or the use of a cylindrical grinder. 
     Other negative aspect of said second previous solution results from the fact that the additional reduction of the viscous friction is limited to the region of the partial circumferential recesses  43   a ,  43   b  and  43   c  presenting a small circumferential extension and reduced axial width. 
       FIG. 3  illustrates an arrangement described in patent document JP 62-118074 (publication number). In this third prior art solution, the reduction of the viscous friction is obtained by means of a circumferential recess  33 , in the inner surface of the bearing hub  30 , which defines a first and a second bearing portion  31 ,  32 , in the respective first and second ends  30   a ,  30   b  of said bearing hub  30 . In this construction, only the bearing hub  30  is configured to provide, with its circumferential recess  33 , a reduction in the median region of reduced radial load, reducing the viscous friction between the crankshaft  40  and the bearing hub  30 , in a magnitude similar to that of the first solution presented in  FIG. 1 . 
     This third known construction has the inconvenience of presenting cylindricity deviations upon using very small axial extensions of the first and the second bearing portions  31 ,  32 . Moreover, the second bearing portion  32  generally presents a minimum axial extension, as a function of the low loads to which it is submitted. 
     This third construction does not permit obtaining a maximum reduction of the axial extension of the radial bearing regions and, consequently, of the viscous friction. Therefore, it is more advantageous and usual to use the first solution, presented in  FIG. 1 , with the first and the second support portion  41 ,  42  of the crankshaft  40  presenting an axial extension sufficient to guarantee simple and reliable grinding operations for the crankshaft  40 . 
     SUMMARY OF THE INVENTION 
     In the face of the inconveniences of the known constructive solutions, the present invention has the object of providing a bearing arrangement for a reciprocating refrigeration compressor, of the type discussed above, which allows minimizing the power dissipated by viscous friction between the crankshaft and the bearing hub, maintaining the surfaces of the crankshaft and bearing hub reliable and adequate to more simple surface finishing operations as, for example, grinding, superfinishing and burnishing processes. 
     The present bearing arrangement is applied to a compressor of the type commented above and which includes a crankcase defining a bearing hub, in which is housed a crankshaft incorporating an end portion, projecting outwards from a first end of the bearing hub, and a free end portion, projecting outwards from a second end of the bearing hub. 
     According to the invention, the bearing hub comprises a first and a second bearing portion, spaced from each other by a circumferential recess, the crankshaft comprising a first and a second support portion, spaced from each other by a circumferential recess which is axially offset in relation to the circumferential recess of the bearing hub. 
     The bearing and support portions present axial extensions superior to those required for axially bearing the crankshaft, part of the axial extension of the first support portion and of the second bearing portion defining, with a confronting axial extension of the first bearing portion and of the second support portion, respectively, a first and a second radial bearing region for the crankshaft. 
     Considering the present bearing arrangement as being applied to reciprocating compressors, for small household and commercial refrigeration systems, with the crankshaft presenting diameters smaller than 21.0 millimeters, said radial bearing regions are dimensioned to present a radial gap of about 5.0-15.0 micrometers. 
     The construction proposed by the invention allows obtaining, simultaneously, radial bearing regions, with axial dimensions relatively reduced in relation to the known constructions, achieving minimum values of viscous dissipation (mechanical loss), with the support and bearing portions presenting axial extensions sufficient for the surface finishing operations of the shaft and of the bearing hub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described below, with reference to the enclosed drawings, given by way of example and in which: 
         FIG. 1  represents, schematically, a longitudinal sectional view of a crankcase with its bearing hub housing a crankshaft provided with a circumferential recess, disposed between two support end portions, according to a first prior art constructive arrangement; 
         FIG. 2  represents a view similar to that of  FIG. 1 , but illustrating the crankshaft provided with three partial circumferential recesses, which are positioned in the crankshaft and in its eccentric end portion, but only in the regions less required in terms of radial bearing, according to a second prior art constructive arrangement; 
         FIG. 3  represents a view similar to that of  FIG. 1 , but illustrating a crankcase with its bearing hub housing a crankshaft and being provided with a circumferential recess, defined between the first and the second bearing portions, according to a third prior art constructive arrangement; 
         FIG. 4  represents a view similar to that of  FIGS. 1 and 3 , but illustrating the same compressor crankcase, partially cut and having its bearing hub and the respective crankshaft provided with respective circumferential recesses, formed according to a first embodiment of the present invention; 
         FIG. 5  represents a view similar to that of  FIG. 4 , but illustrating the crankshaft and the bearing hub provided with respective circumferential recesses, formed according to a second embodiment of the present invention; and 
         FIG. 6  represents a view similar to that of  FIG. 5 , but illustrating the crankshaft and the bearing hub provided with respective circumferential recesses and defining, besides the first and the second radial bearing regions, a third radial bearing region, intermediary to the first two, according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As already previously described, the bearing arrangement of the present invention is applied to a refrigeration compressor of the type partially illustrated in the enclosed drawings and which includes, in the interior of a shell (not illustrated), a crankcase B which comprises cylinder  10 , at least, and one bearing hub  30  having a first end  30   a  and a second end  30   b.    
     The bearing hub  30  houses a crankshaft  40  which incorporates an eccentric end portion  45 , projecting axially outwards from the first end  30   a  of the bearing hub  30 , and a free end portion  46 , which projects axially outwards from the second end  30   b  of the bearing hub  30 . Although  FIGS. 4 and 5  do not illustrate the cylinder, the piston and the connecting rod, it should be understood that such parts were suppressed only by reasons of simplification of said figures, since they are already part of the type of compressor to which the present bearing arrangement is applied. 
     The parts of crankcase B and crankshaft  40  can be constructed in any adequate well known prior art material as, for example, aluminum or cast iron alloys for the crankcase B, and steel or cast iron alloys for the crankshaft  40 . 
     As illustrated in  FIG. 4  of the enclosed drawings, the present bearing arrangement includes a bearing hub  30  which comprises a first bearing portion  31  and a second bearing portion  32 , axially spaced from each other by a circumferential recess  33 , which is provided around the median region of the bearing hub  30 . 
     The circumferential recess  33  should present a radial depth only sufficient to prevent its bottom cylindrical face  33   a  from having any bearing function, that is, from producing losses by viscous friction jointly with the confronting surface of the crankshaft  40 . However, said radial depth should not reach values which can impair the adequate lubrication of any of the regions of the bearing hub  30  in which the effective bearing of the crankshaft  40  occurs, as described ahead. 
     In like manner, the crankshaft  40  comprises a first support portion  41  and a second support portion  42 , which are spaced from each other by a circumferential recess  43 , provided around the median region of the crankshaft and whose radial depth is defined in a manner only sufficient to prevent its bottom cylindrical face  43   a  from having any bearing function, that is, from producing losses by viscous friction jointly with the confronting surface of the bearing hub  30 . However, as already mentioned above, said radial depth must not reach values which can impair the adequate lubrication of any of the regions in which the effective bearing of the crankshaft  40  occurs. 
     In the refrigeration compressors considered in the present invention, the radial depth of the circumferential recesses  33 ,  43  is preferably defined between about 0.03 and 0.10 millimeters. 
     According to the present invention, the first and second bearing portions  31 ,  32  of the bearing hub  30 , and the first and second support portions  41 ,  42  of the crankshaft  40  present respective axial extensions, which are predetermined to guarantee the formation, on the bearing hub  30  and in the crankshaft  40 , of support surfaces for effecting the surface finishing operations required for the support portions  41 ,  42  of the crankshaft  40  and for the bearing portions  31 ,  32  of the bearing hub  30 . 
     As already commented in relation to the prior art, in case the bearing portions  31 ,  32  of the bearing hub  30 , or the support portions  41 ,  42  of the crankshaft  40 , have their axial extensions individually reduced to minimum values, but still capable of guaranteeing an adequate radial bearing of the crankshaft  40 , said reduced bearing portions  31 ,  32  and support portions  41 ,  42  will not be capable of providing surface extensions which allow simple, reliable and relatively uncostly surface finishing operations of the bearing hub  30  and of the crankshaft  40 . 
     A particular aspect of the present invention refers to the determination of the axial extension of said bearing portions  31 ,  32  and support portions  41 ,  42 , since this dimensioning is made independently of the axial extensions required for the radial bearing regions of the crankshaft  40  which are formed by the radially confronting axial extensions of said support portions  41 ,  42  of the crankshaft  40  and of the bearing portions  31 ,  31  of the bearing hub  30 . 
     Further according to the present invention and as illustrated in  FIG. 4 , the circumferential recesses  33 ,  43 , of the bearing hub  30  and of the crankshaft  40 , respectively, are axially and partially offset from each other and also axially dimensioned so that the first and second bearing portions  31 ,  32  of the bearing hub  30 , define, respectively, with the first and second support portions  41 ,  42  of the crankshaft  40 : [0044] a first radial bearing region M 1 , having an axial extension equal to the axial extension of the first bearing portion  31  and smaller than the axial extension of the first support portion  41 ; and [0045] a second radial bearing region M 2 , having an axial extension smaller than the axial extensions of the second bearing portion  32 , and of the second support portion  42  (which defines the free end portion  46 ). 
     As can be noted, the bearing arrangement proposed by the present invention allows the first and second radial bearing regions M 1 , M 2  to be dimensioned in the axial direction, considering only the bearing requirements for the crankshaft  40 , without said axial dimensioning, which is reduced in the radial bearing regions M 1 , M 2  and capable of minimizing the losses by viscous friction in the operation of the crankshaft  40 , undesirably reducing the axial extensions of the bearing portions  31 ,  32  and support portions  41 ,  42  and, thus, impairing the surface finishing operations of the bearing hub  30  and of the crankshaft  40 . 
     According to the proposed arrangement, the axial dimensioning of the first and second radial bearing regions M 1 , M 2  is made so as not to interfere, at least in a relevant manner, with the axial dimensioning of the bearing portions  31 , 32  and of the support portions  41 , 42 . Thus, it is possible, with the present invention, to provide the first and second radial bearing regions M 1 , M 2  with dimensions that are relatively reduced in relation to those required in the prior art solutions. 
     In the shaft construction illustrated in the enclosed drawings, the second support portion  42 , of the crankshaft  40 , extends through the free end portion  46  of the latter, allowing the axial extension of the second radial bearing region M 2  to be defined only by determination of the positioning of the adjacent end of the circumferential recess  43  of the crankshaft  40 . It should be noted that the free end portion  46  of the crankshaft  40  guarantees an adequate axial extension for the second support portion  42  of the crankshaft  40 , even though said portion projects only slightly inwardly the bearing hub  30 , so as to define therein the second radial bearing region M 2 , with an axial extension which is very reduced due to the smaller load to which this second radial bearing region is submitted upon the compressor operation. 
     Further according to the enclosed drawings, the first and the second bearing portions  31 ,  32  are respectively positioned adjacent to the first and second ends  30   a ,  30   b  of the bearing hub  30 . Thus, the axial extensions of the first and second radial bearing regions M 1 , M 2  are limited by the ends of the circumferential recesses  33 ,  43 , respectively provided in the bearing hub  30  and in the crankshaft  40 . 
     In the construction illustrated in  FIG. 4 , the circumferential recess  43  of the crankshaft  40  is made so as to provide a first support portion  41  with an axial extension superior to that required for the respective radial bearing region M 1 . This radial bearing region M 1  is defined by the minimum axial extension required for the first bearing portion  31  necessary for an adequate and reliable surface finishing operation of the bearing hub  30 . In this case, the axial extension of the first radial bearing region M 1  can be over-dimensioned in relation to the value required for an adequate bearing of the crankshaft  40 , the priority of said dimensioning being determined by the minimum extension required for the first bearing portion  31 , as a function of the requirements of the surface finishing process of the bearing hub  30 . 
     However, as illustrated in the embodiment of  FIG. 5 , the first support portion  41  of the crankshaft  40  can be provided with at least one relief circumferential recess  47 , which is at least partially confronting with a respective axial extension of the first bearing portion  31 . Thus, this relief circumferential recess  47 , which confronts an extension of the first bearing portion  31 , diminishes the axial extension of the first radial bearing region M 1 , reducing it to the minimum values required for the provision of an adequate radial bearing region for the crankshaft, reducing to the minimum the energy losses by viscous friction, maintaining the entire axial extension of the first support portion  41 , which is thus composed by a first axial extension  41   a  and a second axial extension  41   b , with an adequate dimensioning for a correct and reliable grinding operation of the crankshaft  40 . 
     As illustrated in  FIG. 5 , the relief circumferential recess  47  is provided in a median region of the first support portion  41  of the crankshaft  40 , and confronting with a respective axial extension of the first bearing portion  31 , adjacent to the circumferential recess  33  of the bearing hub  30 . 
     The positioning of the relief circumferential recess  47 , in a median region of the first support portion  41  and confronting with the first bearing portion  31 , allows the extension of the first radial bearing region M 1  to be defined by subtracting the axial extension portion of said relief circumferential recess  47  which confronts the first bearing portion  31 , without causing decrease in the whole axial extension of the first support portion  41 . It should be noted that the radial depth of the relief circumferential recess  47  is dimensioned according to the same criteria already commented in relation to the dimensioning of the radial depth of the other circumferential recesses  33 ,  43  of the bearing hub  30  and of the crankshaft  40 . 
     As illustrated in  FIG. 6  of the enclosed drawings, the bearing hub  30  can have its circumferential recess  33  defined by at least two recess portions  33   b ,  33   c , which are separated apart by a third bearing portion  35 , radially confronting with the first support portion  41  (according to the embodiment of  FIG. 4 ) or with the second axial extension  41   b  of the first support portion  41  (according to the embodiment of  FIG. 5 ), in order to define, with said first support portion  41  or second axial extension  41   b , a third radial bearing region M 3 , disposed between the first and the second radial bearing region Ml, M 2 . The circumferential recess portion  33   b , of the bearing hub  30 , juxtaposed with the relief circumferential recess  47 , of the crankshaft  40 , defines a cooperative recess  100 ,  100   a , which has length defined by both the axial length of the circumferential recess portion  33   b  and the axial length of the relief circumferential recess  47 . Additionally, the circumferential recess portion  33   c , of the bearing hub  30 , juxtaposed with the relief circumferential recess  43 ,  43   a , of the crankshaft  40 , defines a cooperative recess  100 ,  100   b , which has length defined by both the axial length of the circumferential recess portion  33   c  and the axial length of the relief circumferential recess  43 ,  43   a.    
     The third radial bearing region M 3  occupies a positioning intermediate to the first and second radial bearing regions M 1 , M 2 , allowing to improve the alignment of the crankshaft  40  in its lower end (region of the rotor), so as to provide a rotor operation which is more centralized in relation to the hole of the stator. 
     Thus, even though the provision of the third radial bearing region M 3  causes an increase in the sum of the axial extensions of the multiple radial bearing regions, in relation to the sum of the axial extensions of only two radial bearing regions, said provision will be determined as a function of the project features of the compressor, mainly of the levels of deformation of the shaft, and/or of the diametrical gap values used in the project. 
     If it is necessary or convenient to provide a higher bearing degree for the crankshaft  40 , the constructive solution, suggested in  FIG. 6  of the drawings, allows complying with the requirement for a greater extension for the radial bearing, maintaining the sum of the axial extensions of the multiple bearing regions in values which are reduced in relation to the solutions suggested by the prior art. 
     It should be understood that the circumferential recess  33  of the bearing hub  30  may be defined by more than two recess portions, which are separated apart by bearing portions. The number of circumferential recesses, provided in the crankshaft  40  and in the bearing hub  30 , can vary according to the project features of the compressor and, more specifically, according to the bearing requirements for the crankshaft. 
     It should be noted that the radial depth of the recess portions  33   b ,  33   c  is dimensioned according to the same criteria already commented in relation to the dimensioning of the radial depth of the other circumferential recesses  33 ,  43  and  47  of the bearing hub  30  and of the crankshaft  40 . 
     While only some embodiments for the present invention have been described herein with reference to the embodiments of the enclosed drawings, it should be understood that other possible constructions can be presented, without departing from the inventive concept defined in the claims that accompany the present specification.