Abstract:
A lubricant supply tube for attachment to a drive shaft of a sealed reciprocating compressor comprising an elongated first portion adapted for extending downwardly from the drive shaft and inclined with respect to a rotational axis of the drive shaft for immersion into a lubricant in a lubricant sump of the compressor, and terminating in a substantially elliptical inlet orifice defining a first plane; and wherein the first plane is inclined with respect to a second plane extending perpendicular to a longitudinal axis of the elongated first portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates broadly to a lubricant supply tube for attachment to a drive shaft of a sealed reciprocating compressor and to a sealed reciprocating compressor. 
       BACKGROUND 
       [0002]    Sealed motor-driven compressors are used in many applications, and particularly in refrigeration and air conditioning systems. Such compressors are usually of the piston type and compress the gaseous refrigerant into liquid phase. Such sealed motor-compressors include a sump at the bottom of the sealed casing containing a liquid lubricant such as oil. Frequently, lubricant supply tubes are used in which one end of the tube extends downwardly into the sump at an angle with respect to the axis of rotation. The other end extends vertically upward toward the motor shaft to which it is connected. The motor shaft rotates the lubricant supply tube such that the liquid lubricant is forced upwardly in the tube by centrifugal force so as to be supplied to various moving components of the compressor. 
         [0003]      FIG. 1  illustrates a typical prior art supply tube which is more fully disclosed in detail in U.S. Pat. No. 5,088,579. Briefly, tube  1 , which is also referred to as an oil pickup tube, is rotated by a motor shaft  4  such that the oil flows upwardly through oil passage  6  which extends through knob  7 , crank shaft  5  and into shaft  4 . As clearly shown, the plane X defined by the inlet opening  2  of tube  1  is perpendicular to the longitudinal axis Y of the angled portion of the tube. 
         [0004]    In this design, the tube  1  is formed by folding a metal sheet into a cylindrical shape with a gap or fissure extending along the length of the tube where the folded portions meet. A vane portion extends across the fissure at about a mid point along the length of the tube, for structural integrity of the folded tube. While noise reduction may be achieved with such a design due to improve of gas release through the fissure, this design suffers from the higher cost of manufacturing the folded tube including the vane portion. 
         [0005]    A similar form of oil supply tube is disclosed in U.S. Pat. No. 3,858,685. In this design, the tube is also connected to the crankshaft, and extends downwardly therefrom at an angle with respect to the vertical axis of the motor shaft such that the inlet end of the tube is immersed in the liquid lubricant. The tube again includes a longitudinal fissure, a lower portion having a transversal section with a spinal shape, and the same portion includes a paddle extending radially outward of the tube for forming bubbles in the lubricant. However, again this design suffers from the higher cost of manufacturing the relatively complex design of the tube. 
         [0006]    As disclosed in U.S. Pat. No. 5,842,420, it has also been proposed to reduce the noise level of the compressor by providing an angled passage or duct within the crankshaft so as to draw the oil from the sump upwardly by centrifugal force. The lower end of the crankshaft is cut at an angle with respect to the rotational axis of the crankshaft in order to increase the inlet area of the duct, and thereby increase the oil pumping capacity of the duct, and this is said to also reduce the noise level. Integration of the oil pick up into the crankshaft represents a different design solution compared to designs using a separate tube for attachment to the crankshaft for drawing the oil from the sump. However, such integration can reduce the design flexibility as changes in the design require re-design of the entire crankshaft. 
         [0007]    While such prior art designs have been relatively effective in lubricating the compressor components which are adjacent to the outlet ports of lubricant passages, they have not been effective in reaching some of the compressor components, such as will be more fully described hereafter. 
       SUMMARY 
       [0008]    In accordance with a first aspect of the present invention there is provided a lubricant supply tube for attachment to a drive shaft of a sealed reciprocating compressor comprising an elongated first portion adapted for extending downwardly from the drive shaft and inclined with respect to a rotational axis of the drive shaft for immersion into a lubricant in a lubricant sump of the compressor, and terminating in a substantially elliptical inlet orifice defining a first plane; and wherein the first plane is inclined with respect to a second plane extending perpendicular to a longitudinal axis of the elongated first portion. 
         [0009]    An angle between the first and second planes may be in the order of about 15 to 50 degrees. 
         [0010]    An angle between the first and second planes may be in the order of about 30 to 45 degrees. 
         [0011]    The supply tube may include an elongated second portion inclined with respect to the first portion, and in use, the second portion is adapted for connection to the drive shaft. 
         [0012]    The elongated second portion may be adapted for connection to an eccentric portion of the drive shaft, and such that the inlet orifice rotates substantially on the rotational axis of the drive shaft. 
         [0013]    The elongated second portion may be provided with at least one degassing port on a side closer to the rotational axis of the drive shaft. 
         [0014]    The second portion may be adapted for an interference fit with a corresponding lubricant supply passage formed in the drive shaft. 
         [0015]    The second portion may be inclined with respect to the first portion, and in use, the second portion is adapted for connection to the drive shaft in a direction parallel to but offset from the rotational axis of the drive shaft. 
         [0016]    The lubricant supply tube may be adapted such that lubricant is provided to parts of the compressor due to splashing of the lubricant caused by rotation of the lubricant supply tube in the lubricant sump. 
         [0017]    In accordance with a second aspect of the present invention there is provided a sealed reciprocating compressor comprising a lubricant supply tube as defined in the first aspect. 
         [0018]    The compressor may be an induction compressor. 
         [0019]    The compressor may be an inverter compressor. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]    Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which: 
           [0021]      FIG. 1  is an illustration of an oil supply tube of the prior art; 
           [0022]      FIG. 2  is a cross-sectional view of a sealed motor-compressor unit incorporating the lubricant supply tube according to one embodiment of the invention; 
           [0023]      FIG. 3  shows a detail of  FIG. 2 ; 
           [0024]      FIG. 4  shows another detail of  FIG. 2 ; and 
           [0025]      FIG. 5  is a Table showing one example of the reduction of the compressor noise level achieved by the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to  FIGS. 2 and 3 , a motor-driven piston type compressor is illustrated, and it will be readily understood by those skilled in this art that such units include a sealed casing  10  enclosing a motor  12 . A cylinder block  37  including the cylinder  20  and a bearing  39  for supporting the drive shaft  18  is provided. Motor  12  includes a stator  14 , a rotor  16 , and the output drive., shaft  18 , configured as an induction compressor supplied with typically either a 50 Hz or 60 Hz power supply. 
         [0027]    As also shown in  FIG. 2 , and in more detail in  FIG. 3 , shaft  18  comprises an off-set or eccentric portion  24 , which in turn, drives connecting rod  26  and piston  28  within cylinder  20 . Connecting rod  26  is connected to piston  28  by a bearing in the form of a piston pin  32 , which is hollow and secured to the piston  28  by way of a locking pin  25  in this example embodiment. The legs of a U-shaped washer  34  extend between the interior wall of the piston  28  and the outer side surface of rod  26 . 
         [0028]    As shown in more detail in  FIG. 4 , a lubricant supply tube  40  is connected by a vertical straight portion  40   b  to the lower end of the eccentric portion  24  of the shaft  18  so as to rotate with the tip  42  at the open end of an inclined portion  40   a  of the tube  40  substantially on the rotational axis  44  of shaft  18 . In this example embodiment, the straight portion  40   b  is attached to the eccentric portion  24  by an interference fit into a corresponding oil supply passage  41  internal to the eccentric portion  24 , and extending into the shaft  18 . 
         [0029]    The inclined portion  40   a  of the tube  40  extends at an angle, B, with respect to the axis  44  such that a lubricant such as oil from the sump is drawn upwardly within the tube  40  as illustrated in  FIG. 4 . Preferably the angle, B, of inclination of portion  40   a  is in the order of about 140 degrees to 170 degrees with respect to the axis  44 , and the vertical straight portion  40   b  includes at least one degassing port  43 , on a side closer to the rotational axis  44  of shaft  18 . 
         [0030]    A lubricant outlet port  35  is formed in a recess or groove  45  on the eccentric portion  24 , allowing provision of lubricant via the internal passage  38  formed in the connecting rod  26  and to the piston  28  and piston pin  32  (see  FIGS. 2 ,  3 ). Another lubricant outlet port  47  is formed at the bottom of the drive shaft  18  and in fluid communication with a helical lubricant passage  49  formed on the surface of the drive shaft  18 . The passage  49  terminates above an upper end of the bearing  39  for lubrication during operation of the compressor. 
         [0031]    In the example embodiment, parts of the compressor such as U-washer  34  and the sliding surfaces of the piston  28  and connecting rod  26  (see  FIGS. 2 ,  3 ) are advantageously additionally lubricated by the splashing created by the rapid rotation of the inclined portion  40   a  of the tube  40 . 
         [0032]    Referring more specifically to  FIG. 4 , and contrary to the prior art oil supply tubes shown in  FIG. 1 , the plane “X” defined by the inlet orifice  42  of the tube  40  extends at an angle, A, with respect to a plane “Y” which extends perpendicular to the longitudinal axis  48  of portion  40   a  of the tube  40 . Because of terminating the tube  40  with the inlet orifice  42  at an angle A, it has been found that the noise level of the compressor can be substantially reduced. For example, as shown in Table  1  of  FIG. 5 , at both 50 Hz &amp; 60 Hz power supply the-decibel levels can be substantially reduced, and a maximum reduction can be achieved with angle A being in the range of about 30 to 45 degrees, measured at the high frequency band. 
         [0033]    It has been recognized by the inventors that by selecting the angle A in a range from about 15 to 50 degrees and preferably from about 30 to 45 degrees, the height of the vortex  51  can be increased to an extent sufficient for causing splashing of lubricant to adjacent components, including the U-washer  34  and the sliding surfaces of the piston  28  and connecting rod  26  (see  FIGS. 2 ,  3 ). It has further been recognized by the inventors that this additional lubrication facilitates noise reduction in the operation of the compressor. This noise reduction is in addition to noise reduction facilitated by foaming of the oil in the sump  36  (see  FIG. 2 ) as a result of the rotation of the tube  40 , which improves the sound insulating properties of the oil. 
         [0034]    The tube  40  in an example embodiment is made from carbon steel, and advantageously fabricated by tube forming. However, it will be appreciated that the tube can be fabricated from other suitable materials and using different fabrication techniques, in different embodiments. 
         [0035]    From the foregoing description of one embodiment of the present invention, it will be apparent that the foregoing objects are achieved regarding both improved lubrication and noise reduction of compressors which are lubricated by the use of lubricant supply tubes drawing lubricant from sumps. It will also be understood that the foregoing description of one embodiment is purely illustrative of the principles of the invention, rather than exhaustive thereof, and that numerous variations of the illustrated embodiment will become apparent to those skilled in the art of compressors. 
         [0036]    For example, it will be appreciated that the present invention can be equally applied to inverter compressors in which the speed of the motor can be controlled using signals from a control box, as is understood in the art.