Abstract:
A scroll-type compressor having a stationary scroll and a movable scroll is provided. A compression chamber is defined between a stationary scroll and a movable scroll. A refrigerant introducing passage formed in the movable scroll for introducing a refrigerant from the compression chamber to a driving mechanism. The compressed refrigerant including a lubricant introduced through the passage is affective to lubricate the driving mechanism. The compressor may also include a sump to collect the lubricant leaving the driving mechanism. Collected lubricant is reintroduced into the compression region via a suction region of the compressor.

Description:
BACK GROUND OF THE INVENTION 
     The present invention relates to a scroll-type compressor having movable and stationary scrolls and, in particular, to an improved lubrication arrangement and method for lubricating the components of a scroll-type compressor. 
     One type of scroll-type compressor to, which the present invention is applicable, has a compressed gas discharge port in the stationary scroll. Unexamined Japanese Patent Application No. 58-117380 discloses this type of compressor. The lubrication system of that compressor employs an oil sump at the bottom of a housing that accommodates an electric motor for driving the movable scroll. Oil in the oil sump is pumped by an oil pump through an oil passage that is eccentrically formed in the motor shaft (drive shaft of the movable scroll). The oil passage introduces the oil into a bearing located between the motor shaft and the movable scroll. Then, the oil in the bearing is radially introduced from the bearing to a thrust support member, which rotatably supports the movable scroll, and lubricates the support member. Finally, the oil is collected by a recovery hole and falls to the oil sump by gravity. 
     According to above application, it is necessary to install an oil pump in order to ensure a sufficient supply of oil to the sliding surfaces of the bearing. The requirement for an oil pump increases the cost of the compressor and introduces another component that may constitute a failure point. It therefore is desirable to achieve lubrication of the compressor without incorporating separate oil pump. 
     SUMMARY OF THE INVENTION 
     One object of the present invention, therefore, is to provide a scroll-type compressor and a method for lubricating the same, which obviates the need for an oil pump. Another object of the invention is to lubrication of a scroll compressor by introducing a refrigerant including a lubricant into the components to be lubricated through a pressure difference that exists between two or more regions of the compressor. 
     To achieve the foregoing, the present invention incorporates introducing passages for introducing lubricant-containing refrigerant from a compression chamber of a scroll-type compressor to a lower pressure region where the lubricant can lubricate components of the drive mechanism. At least part of the introducing passage is effective to restrict the rate of flow of refrigerant. The introducing passage may be located in the spiral wall of the movable scroll, or may be located in the movable scroll base plate. The preferred embodiment also includes a lubricant sump for collecting used lubricant in a lower pressure region of the compressor for re-introduction into a suction zone of the compressor via a lubricant passage interconnecting these two zones. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view of a scroll-type compressor according to a first embodiment of the present invention; 
     FIG. 2 is a perspective view of the stationary scroll and movable scroll, with the outline of the stationary scroll shown with fine lines, and the outline of the movable scroll shown with bold lines; 
     FIG. 3 is an end view of the stationary scroll, illustrating a orbital locus of a communicating hole through the movable scroll for introducing a refrigerant gas. 
     FIG. 4 is an enlarged cross-sectional view of a central portion of the stationary and movable scrolls of the compressor; 
     FIG. 5 is a cross-sectional view of a second embodiment of a scroll-type compressor according to the present invention; and 
     FIG. 6 is an enlarged partial sectional view of a central portion of the stationary and movable scrolls of a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of a motor driven scroll-type compressor (hereinafter, compressor) incorporating the improved lubricating method of the present invention is shown in FIGS. 1 to  4 . The compressor is typically employed to compress a refrigerant gas. 
     Referring to FIG. 1, an end surface of a stationary scroll  2  is jointed to an end surface of a center housing  4 . The opposite end of the center housing  4  is connected to a motor housing  6 . The stationary scroll  2 , the center housing  4  and the motor housing  6  comprise a compressor body  7 . A drive shaft  8  is rotatably supported by the center housing  4  and motor housing  6  through radial bearings  10 , 12 . An eccentric shaft  14  is integrally formed with the end of the drive shaft  8 . 
     A bushing  16  is fitted on the eccentric shaft  14  to rotate therewith integrally. A balance weight  18  is fitted on the end of the bushing  16  so that the balance weight  18  integrally rotates with the bushing  16 . A movable scroll  20  is mounted on the bushing  16  through a needle bearing  22  so that the movable scroll  20  faces the stationary scroll  2 . A cylindrical boss  24   a  extends toward the rear (right hand side in FIG. 1) of a movable scroll base plate  24 , and accommodates the needle bearing  22 . It will be seen that rotation of the motor shaft  8  causes the eccentric shaft  14  to trace an orbital motion that is transmitted to the movable scroll  20  in a conventional manner. 
     The stationary scroll  2  includes a stationary spiral wall  28  formed on one side of a stationary scroll base plate  26 . Similarly, the movable scroll  20  has a movable spiral wall  30  formed on one side of a movable scroll base plate  24 . The stationary scroll  2  and the movable scroll  20  are arranged so that the stationary spiral wall  28  and the movable spiral wall  30  are engaged each other. A tip seal  28   a  is fitted on the end surface of the stationary spiral wall  28 , while a tip seal  30   a  is fitted on the end surface of the movable spiral wall  30 . As shown in FIG. 2, crescent-shaped compression chambers (closed spaces)  32  are formed between the stationary spiral wall  28  and the movable spiral wall  30 . These two walls contact each other along lines that move from the outer periphery to the inner part of the stationary spiral wall as the movable scroll follows an orbital motion during operation of the motor. As noted above, the orbital movement of the eccentric shaft  14  brings the orbital motion of the movable scroll  20 . The balance weight  18  cancels the centrifugal force caused by the orbital motion of the movable scroll  20 . 
     A driving mechanism  23 , which transmits rotating force of the drive shaft  8  to the movable scroll  20  as the orbital motion, comprises the eccentric shaft  14 , the bushing  16 , the needle bearing  22  and the radial bearings  10 ,  12 . 
     As shown in FIG. 1, plural equidistant holes  34  (e.g. four holes) are located in the forward end of the center housing  4  about its periphery. (Only one hole  34  is visible in FIG.  1 ). Stationary pins  36  of smaller diameter are supported in the center housing  4  and extend into the holes  34 . Similarly, pins  38  fixed on the movable scroll base plate  24  also extend into the holes  34 , but from the opposite direction. While the eccentric shaft  14  rotates, the movable scroll  20  tends to rotate about the axis of the bushing  16 . The pins  36  and  38  prevent the movable scroll  20  from self-rotating during rotation of the eccentric shaft  14 . Thus, the holes  34  and pins  36  and  38  constitute a rotation preventing mechanism for restricting rotation of the orbiting movable scroll  20  during operation of the compressor. 
     A thrust plate  25  is fixed to the movable scroll  24 , and interposed between the rear of the movable scroll base plate  24  and the opposed forward end surface of the center housing  4 . The thrust plate  25  maintains the appropriate clearance between the scroll base plates  24 ,  26  and spiral walls  28 ,  30 . The movable spiral wall  30  is sealed against the top surface of the stationary scroll base plate  26  through the tip seal  30   a,  which resides in a groove in end surface of the movable spiral wall  30 . The contact pressure of the movable spiral wall  30  is adjusted by the thickness of above-mentioned thrust plate  25 . 
     The compressor is driven by an electric motor  46 , of which the motor stator  44  is secured in a closed motor chamber  48  of the motor housing  6 , the motor rotor  45  being fixed on the drive shaft  8 . 
     As earlier noted, rotation of the shaft  8  results the rotation of the eccentric shaft  14 , which translates into the orbital motion of the movable scroll  20 . The gas to be compressed, a refrigerant, for example, enters at an inlet  42  formed in the stationary scroll  2  and flows from the periphery of the scrolls  2 ,  20  into a recess defined between the base plates  24 ,  26  and spiral walls  28 ,  30 . Then, the orbital motion of the movable scroll  20  seals the spiral walls  28 ,  30  so as to form into compression chambers  32  to compress the refrigerant. The compression chambers  32  move progressively inwardly toward the center of the scrolls  2 ,  20 , thereby progressively reducing the volume of the gas trapped therein and effecting a consequent compression of the gas. 
     A discharge port  50  formed at the center portion of the stationary scroll base plate  26  communicates with the compression chamber  32  at the center of the scroll. A discharge chamber  52  is formed on the rear of the stationary scroll base plate  26 , and a discharge valve  54  for opening and closing the discharge port  50  is disposed in the discharge chamber  52 . The discharge valve  54  comprises a reed valve  56  and a retainer  58 . An outlet  51   a  in the rear cover  51  of the discharge chamber  52  will be connected to an external refrigerant discharge conduit (not shown in the drawings). 
     A compression mechanism  21 , which includes the scrolls  2 ,  20 , and the motor chamber  48  are partitioned by the center housing  4 . A communication passage  49  in the center housing  4  connects a suction region in the refrigerant flow with the motor chamber  48 . To that end, the inlet  42  is connected with a space  49   a  around the periphery of the movable scroll  20 , which in turn communicates with the motor chamber  48  through a communication hole  49   b  in the center housing  4 . The space  49   a  and the communication hole  49   b  together constitute the communication passage  49 , which remain open regardless the orbital position of the movable scroll  20 . 
     A flat mounting surface  7   a  is formed on the outer peripheral surface of the compressor body  7  for mounting an inverter housing  70 . Control elements, including an inverter  60  for controlling the electric motor  46  is contained within the housing  70 . High temperature elements of the inverter  60 , such as switching devices  62  are separated from low temperature parts such as capacitors  64 . The switching devices  62  are located in a cylindrical portion  70   a  of the housing  70 , and supported by an outer surface of a cylindrical body  63  in the cylindrical portion  70   a.    
     The cylindrical body  63  has an inlet passage  63   a  that connects to the inlet  42 , and further the passage  63   a  will be connected to an external refrigerant suction conduit (not shown in the drawings). Preferably the inverter housing  70  is made of heat insulating material, such as synthetic resin. The bottom plate  70   b  of the inverter housing  70  is mounted on the flat mounting surface  7   a  through a leg portion  70   c  with a clearance C, which functions as a heat insulating area. 
     Electrical power for the motor is supplied from the switching devices  62 , which are connected to the electric motor  46  via lead wires  67 ,  68  through three conducting pins  66  that extend through the walls of the motor housing  6  and the inverter housing  70 . 
     In accordance with the invention, and as shown in FIGS. 1 and 2, a refrigerant introducing passage  80  extends through the movable spiral wall  30  and the movable scroll base plate  24 . During operation of the compressor, it introduces a small amount of compressed refrigerant from the innermost compression chamber  32  into a space  81  formed generally at the rear of the movable scroll base plate  24  in the vicinity of the boss  24   a.  The introducing passage  80 , which is bored through the movable spiral wall  30 , has one opening end in the end surface of the movable spiral wall  30  and the other opening end in the rear surface of the scroll base plate  24  to connect to the space  81 . 
     As best seen in FIG. 4, the tip seal  30   a  protrudes slightly beyond the end of the movable spiral wall  30 . Accordingly, an clearance C 1  is established between the end surface of the movable spiral wall  30  where the tip seal  30   a  does not exist and the surface of the stationary scroll base plate  26 . 
     Accordingly, the refrigerant introducing passage  80  includes the clearance C 1  and always communicates with the compression chamber  32  to enable compressed refrigerant to flow into the space  81 . The clearance C 1  principally restricts the flow-rate of the introduced refrigerant from the compression chamber  32  to the space  81 . 
     The thrust plate  25  adjusts the contact pressure of the movable spiral wall  30  through the tip seal  30   a.    
     The refrigerant introducing passage  80  orbits with the movable scroll  20 , its orbital locus shown in FIG. 3 by the phantom circular line. It will also be noted from FIG. 3 that the passage  80  is positioned so as not to communicate with the discharge port  50 . Accordingly, high-pressure refrigerant in the discharge chamber  52  cannot flow directly into the space  81  through the refrigerant introducing passage  80 . 
     An oil sump  82  is formed at the bottom of the motor chamber  48 . The oil sump  82  connects to a suction region (a space between the outer periphery of the spiral walls  28 ,  30 ) through an oil passage  83 . 
     In operation of the compressor, it will be understood that refrigerant introduced into the inlet  42  is compressed in the compression chamber  32 , and the high-pressure gas is discharged through the discharge valve  54  into the discharge chamber  52 . Referring to FIG. 4, the refrigerant in the innermost compression chamber  32  flows into the space  81  through the clearance C 1  and the refrigerant introducing passage  80  as a result of the differential pressure between the low pressure in the space  81  and high pressure in the compression chamber  32 . 
     Referring to FIG. 1, the refrigerant with entrained oil introduced into the space  81  flows into the motor chamber  48  through the spaces between the sliding surfaces of the elements of the orbital driving mechanism  23 , such as the needle bearing  22  and radial bearing  10 , so that the oil lubricates those surfaces. In this embodiment, the opening of the refrigerant introducing passage  80  in the moveable scroll base plate  24  may be located, formed or angled in a particular manner to supply oil directly to the necessary parts for lubrication, such as the needle bearing  22 . 
     The entrained oil in the refrigerant blown into the space  81  separates from the refrigerant and descends to the oil sump  82  at the bottom of the motor chamber  48 . Because the suction region at the periphery of the spiral walls  28  and  30  is at a lower pressure than the motor chamber  48 , oil stored in the oil sump  82  flows into the suction region through the oil passage  83  and there joins with the refrigerant and transported into compression chamber  32 . As earlier stated, some of the compressed refrigerant in the innermost compression chamber  32  is forced through the passage  80  into the space  81  as a result of the differential pressure. Since oil is contained in the flow through the passage, this oil lubricates the needle bearing  22  and the radial bearing  10  of the driving mechanism  23 . By utilizing the differential pressure to supply lubricating oil, the compressor lubrication system can be simplified driven pumps are no longer essential. The clearance C 1  between the stationary scroll base plate  26  and the movable spiral wall  30  is preferably selected to restrict the rate of refrigerant flow to the minimum necessary to achieve sufficient lubrication of the bearings so as to prevent decreasing efficiency due to the outflow of the refrigerant from the compression chamber  32 . 
     It may be mentioned that, when the refrigerant enters the passage  63   a  of the cylindrical body  63  in the inverter housing  70  from an evaporator in the external conduit (not shown in the drawings) to the compressor, the refrigerant cools the inverter  60  in the inverter housing  70 , especially the switching devices  62  adjacent to the cylindrical body  63 . 
     Additionally, during the operation of the compressor, both the compression process and the electric motor  46  generate heat in the compressor body  7 . For that reason, the inverter housing  70  accommodating the inverter  60  is spaced from the compressor body  7  with the clearance C in order to improve thermal isolation of the housing  70  from the compressor body  7  both during the operation and stop of the compressor. 
     During the operation of the compressor, the motor chamber  48  is always connected to the suction region of the refrigerant through the communication passage  49 , as well as through the oil passage  83  at a bottom of the center housing  4 . The heat is transmitted between the refrigerant in the suction region and the refrigerant in the motor chamber  48  through the passages  49 , 83 , that is high heat in the refrigerant in the motor chamber  48  is transmitted to the refrigerant in the suction region, and the heat transmission cools the electric motor  46 . Additionally, the refrigerant flows between the motor chamber  48  and the suction region through the communication passage  49  and the oil passage  83 , since the pressure in the motor chamber  48  is higher than the suction region. Therefore, heat is transmitted from the motor chamber  48  to the suction region through the communication passage  49  or the oil passage  83  with the refrigerant. Accordingly, the refrigerant flow contributes to electric motor  46  cooling. 
     Above-mentioned cooling effects are so called “stagnation cooling” that involves a little refrigerant. This is different from the conventional designs wherein the entire motor chamber may serve as a refrigerant passage where a large amount of refrigerant flows. Because only a small amount of the refrigerant in the suction region contributes to the “stagnation cooling”, the temperature rise in the suction refrigerant is limited. Accordingly, the temperature limitation prevents the specific volume of the suction refrigerant being increased so as to solve the problem of less compression efficiency. 
     It may also be noted that the thermal load of the inverter  60  is generally much less than that of the electric motor  46 . Therefore, the thermal energy extracted from the inverter  60  by the refrigerant affects only a slight rise of the refrigerant temperature, as compared with cooling systems in which the entire refrigerant traverses the motor chamber  48 . Therefore, arrangement of the present invention does not have less compression efficiency. 
     The illustrated embodiment gains high cooling efficiency because the suction refrigerant for cooling the electric motor  46  is at a lower temperature than that of the discharge refrigerant. Additionally, sealing material around the drive shaft  8  to seal the motor chamber  48  can be omitted, since some refrigerant flow from the discharge region into the motor chamber  48  is utilized for lubrication and therefore not a disadvantage. The invention therefore has simple structure and reduces the manufacturing cost. 
     The second embodiment will be now described with reference to FIG.  5 . In this embodiment, the needle bearing  22  between the bushing  16  and the boss  24   a  of the movable scroll base plate  24  is replaced by a plain bearing  27  (sliding bearing), in order to have the sealing function of the plain bearing  27 . The other members of this embodiment that are similar to the first embodiment have same reference numbers. 
     The plain cylindrical bearing  27  is press-fitted into the inner cavity of the boss  24   a,  and rotatably receives the bushing  16 . The clearance between the sliding surface of the plane bearing  27  and the bushing  16  is sufficiently close to perform a sealing effect. The sealing performance depends on the axial length of the plain bearing  27 . The longer the axial length, the better the sealing efficiency. In this embodiment, the plain bearing  27  extends the axial length of the sliding surface of the eccentric shaft  14 . During the operation of the compressor, the refrigerant entering the space  81  from the compression chamber  32  flows to the radial bearing  10  through the clearance of the sliding surface of the plain bearing  27  in order to lubricate the sliding surface with the oil in the refrigerant. The oil film formed on the sliding surfaces prevents the leakage of the refrigerant into the motor chamber  48 . Consequently, the refrigerant in the space  81  will be in a high-pressure state that is close to the pressure in the compression chamber  32 . 
     One benefit of the embodiment of FIG. 5 is that the high pressure (backpressure) in the space  81  applies a force to rear of the movable scroll base plate  24  in the axial direction toward the stationary scroll  2 . This improves the sealing performance at the tip seals  28   a  and  30   a.  Furthermore, due to this backpressure against the movable scroll  20 , a thrust plate for adjusting the clearance such as illustrated in the first embodiment can, in many instances, be eliminated. 
     A third embodiment will be now described with reference to FIG.  6 . This embodiment has a narrow passage  85  with small diameter hole (pinhole), through the movable scroll base plate  24 . The diameter of the narrow passage  85  is determined to obtain a necessary and sufficient flow of the refrigerant from the compressor chamber  32  into the space  81  to lubricate the driving mechanism  23 . The narrow passage  85  itself therefore serves as the restriction passage in this embodiment. 
     In the above-described embodiments, the refrigerant introducing passage  80  and narrow passage  85  are formed in the movable spiral wall  30  or base plate  24 , respectively. However, provision of the restricting passage is not limited to any specific locations within the movable scroll  20  or base plate  24 , but it may be determined based on the efficiency regarding the outflow of the refrigerant. Moreover, although the scroll-type compressor has been disclosed as driven by an electric motor, the invention is not limited to an electric motor as the driving force, but can be adapted to other power sources such as an engine or other mechanical power source. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.