Abstract:
In prior art scroll-type compressors, a cavity is formed in the interior of the compressor of a sufficient size to allow a misplaced or extra steel spherical ball to become lodged therein and cause seizure of the compressor. The present invention modifies a plate of the counterweight assembly or adds an additional component plate on the drive shaft of the compressor to prevent the introduction of an extra or misplaced steel spherical ball into this cavity during compressor assembly or repair.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of scroll-type compressors, and in particular to a device and method to prevent assembly error and improper functioning of a scroll-type compressor. 
     BACKGROUND OF THE INVENTION 
     Scroll-type compressors are well known in the prior art. They are used for compressing fluids of various types, for example, air conditioning refrigerant. U.S. Pat. Nos. 4,940,396 and 5,513,968 disclose scroll-type compressors that function by the interaction of two scroll members each having a circular end plate and a spiroidal or involute spiral element. The end plates of the scroll members face each other in parallel planes. One scroll member is connected to a drive shaft, rotated for example by an automotive engine, while the other scroll member is stationary, affixed in the compressor housing. The drive shaft is supported by bearings of typical design and is fitted with a counterweight assembly for the purpose of balancing the scroll member connected to the drive shaft during compressor activation. The scroll members maintain an angular and radial offset so that both spiral elements fit together at a plurality of line contacts between their curved surfaces and thereby seal off and define at least one pair of fluid pockets or chambers. The scroll member connected to the drive shaft is fixedly mounted by an eccentric bushing. In this manner, when the drive shaft rotates, the centerline axis of the moving scroll member is translated about the centerline axis of the stationary scroll member in an orbiting manner and is thus referred to as the orbiting scroll member. As the orbiting scroll member orbits around the stationary scroll member, the previously mentioned fluid chambers form between the spiral elements of the orbiting and stationary scroll members. Fluid is introduced into these chambers via intake ports in the compressor housing, is compressed when the volume in the chambers decreases as the orbiting scroll moves, and is expelled via discharge ports in the compressor housing. 
     The planar orbit of the orbiting scroll member is generated and controlled by numerous components with technology that has been available for some time. These same components prevent the orbiting scroll member from rotating. U.S. Pat. Nos. 4,439,118 and 5,938,418 disclose such components, known as ball coupling mechanisms or Oldham rings. The components of interest for the present invention are a plurality of steel spherical balls, an orbiting ball coupling ring, a fixed ball coupling ring, and a counterweight assembly. Each of the steel spherical balls is positioned in an associated one of a plurality of circular pockets formed in the fixed and orbiting ball coupling rings. During compressor assembly, the ball coupling mechanism is assembled by inserting the steel spherical balls into the pockets of the fixed ring, attaching the orbiting scroll member to the orbiting ring, aligning the circular pockets of the orbiting and fixed rings, and stacking the orbiting scroll and ring assembly to the fixed ring. The same process is followed when the compressor is repaired and reassembled. It is during this assembly or repair process that an extra or misplaced steel spherical ball may be intentionally or inadvertently placed in a counterweight cavity that is bounded by the front housing, the main drive bearing, the orbiting scroll member, the counterweight assembly, and the fixed ball coupling ring of the compressor. The prior art construction results in a path for the steel spherical balls to enter the aforementioned cavity. An extra or misplaced ball in this area will result in a catastrophic failure of the scroll compressor due to seizure of the compressor during operation. Restriction or prevention of the introduction of the steel spherical balls into the counterweight cavity, therefore, is imperative. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a device and a method for preventing a steel spherical ball from entering a counterweight cavity of a scroll compressor during compressor assembly or repair thereby avoiding compressor seizure during operation. The prior art compressor construction allows a misplaced and/or extra steel ball to enter the counterweight cavity through a clearance path between the eccentric bushing and the fixed ball coupling ring. The device according to the present invention solves this problem either by modifying a component of the counterweight assembly or by adding a component to the drive shaft. 
     A first embodiment of the present invention involves a modification of the counterweight assembly to occupy a portion of the counterweight cavity opposite the existing counterweight assembly. A plate component of the counterweight assembly is changed to restrict the clearance path sufficiently to prevent any extra and/or misplaced balls from gaining access to this cavity. This modification also prevents assembly of the counterweight assembly, the fixed ball coupling ring, and/or the orbiting scroll member if a misplaced or extra steel ball is present in the counterweight cavity. 
     A second embodiment of the present invention involves the addition of a component plate on the shaft to limit the available space for a misplaced/extra steel ball. This additional component is mounted directly on the shaft and occupies space opposite the counterweight assembly, in a manner similar to the modified counterweight assembly of the first embodiment. The additional component also prevents the assembly of the counterweight assembly, the fixed ball coupling ring, and/or the orbiting scroll member if a misplaced or extra steel ball is present in the counterweight cavity. 
     In each embodiment, the present invention provides these improvements while not degrading the performance or reliability of the scroll compressor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
     FIG. 1 is a cross-sectional elevation view of a prior art scroll-type compressor with an extra or misplaced steel spherical ball in the counterweight cavity. 
     FIG. 2 is an exploded view of the ball coupling mechanism and orbiting scroll member of FIG.  1 . 
     FIG. 3 is front elevation view of the counterweight assembly of FIG.  1 . 
     FIG. 4 is a cross-sectional view taken along the line  4 — 4  in FIG.  1 . 
     FIG. 5 is front elevation view of a counterweight assembly according to the present invention. 
     FIG. 6 is a cross-sectional view taken along the line  6 — 6  in FIG.  5 . 
     FIG. 7 is a fragmentary cross-sectional elevation view of the compressor shown in FIG. 1 including the counterweight assembly of FIG.  5 . 
     FIG. 8 is a fragmentary cross-sectional elevation view of the compressor shown in FIG. 1 including an alternate embodiment of the counterweight assembly according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a scroll-type compressor of prior art construction is indicated generally at  10  and includes a rear or main housing  12  attached to a front housing or cover  14  to form a hollow housing for the compressor working components. A crankshaft or drive shaft  16  extends through the front cover  14  and is rotatably supported on support bearings  24  and main drive bearings  26  mounted on the interior of the front cover. An eccentric bushing assembly  18  is attached to the drive shaft  16  and supports an orbiting scroll member  20 . The orbiting scroll member  20  cooperates with a fixed scroll member  22  attached to the main housing  12  to define fluid chambers  28 . As the drive shaft  16  is rotated, the centerline axis of the orbiting scroll member  20  orbits about the axis of rotation of the drive shaft  16  to alternately decrease and increase the volume of the fluid chambers  28 . Fluid is introduced into the increased volume chambers  28  via intake ports (not shown) and, as the orbiting scroll member  20  moves, the fluid chambers  28  decrease in volume to compress the fluid which is expelled from the fluid chambers  28  and out of the compressor  10  via discharge ports (not shown). 
     It is critical to the operation of the compressor that the radial offset relationship between the orbiting scroll member  20  and the stationary scroll member  22  is maintained. This offset relationship is accomplished by preventing the rotation of the orbiting scroll member. The orbiting scroll member is prevented from rotating by the use of a ball coupling mechanism  30 , shown in greater detail in FIG.  2 . The ball coupling mechanism  30  includes a fixed ball coupling ring  32  attached to the front cover  14 , an orbiting ball coupling ring  34  coupled to the orbiting scroll member  20 , and a plurality of steel spherical balls  36 . The ball coupling mechanism  30  is assembled with the front cover  14  detached from the main housing  12  and oriented with the drive shaft  16  pointed downwardly. The steel spherical balls  36  are inserted into associated pockets  38  formed in the fixed ring  32 . The orbiting scroll member  20  is coupled to the orbiting ring  34  and mounted on the eccentric bushing assembly  18  while aligning pockets  40  formed in the orbiting ring with the pockets  38  of the fixed ring  32 . The ball coupling mechanism  30  is assembled in this manner during initial manufacture and repair of the scroll-type compressor  10 . 
     As shown in FIG. 1, a counterweight cavity  42  is formed inside the front cover  14  on the opposite side of the drive shaft  16  from a counterweight assembly  44  attached to the drive shaft. This counterweight cavity  42  is bounded by the front cover  14 , the main drive bearing  26 , the drive shaft  16 , the counterweight assembly  44 , the orbiting scroll member  20 , and the ball coupling mechanism  30 . The counterweight cavity  42  is large enough so that an extra or misplaced steel spherical ball  36 ′ could be introduced into the cavity during compressor assembly or repair without preventing the compressor  10  from being assembled or reassembled. If the extra or misplaced ball  36 ′ is situated in the cavity  42  and not removed prior to assembly, the result is a catastrophic failure upon startup of the compressor  10  due to seizure since the extra ball  36 ′ will prevent proper rotation of the shaft  16  by contact with the counterweight assembly  44 . 
     The device and method according to the present invention, in two preferred embodiments outlined below, prevents the introduction of extra or misplaced steel spherical balls  36 ′ into the counterweight cavity  42  during compressor assembly or repair, which in turn prevents compressor seizure. A first preferred embodiment of the present invention includes a modified counterweight assembly. A prior art counterweight assembly  44  is shown in more detail in FIG.  3  and FIG.  4 . The counterweight assembly  44  includes five plates  44   a,    44   b,    44   c,    44   d,  and  44   e  held together in stacked orientation by a plurality of fasteners such as rivets  46 . The plates  44   a  and  44   c  through  44   e  are generally arcuate while the plate  44   b  is formed as slightly more than a half circle. The plate  44   b  has a pair of apertures  48  formed therein for attachment to the drive shaft  16  by fasteners (not shown). A central aperture  50  is formed in the plate  44   b  for receiving a compliance pin (not shown) of the eccentric bushing  18 . 
     A first preferred embodiment of the present invention includes a modified counterweight assembly  52  shown in FIG.  5  and FIG.  6 . The assembly  52  includes the plates  44   a,    44   b,    44   d  and  44   e  from the prior art assembly  44 . However, the plate  44   c  has been replaced by two plates  52   c  and  52   f.  The plate  52   c  is similar in shape to the plate  44   c,  but is thinner. The plate  52   f  has a thickness corresponding to the difference in thickness between the plates  44   c  and  52   c  and a suitable mass such that overall thickness and weight of the counterweight assembly  52  remains unchanged from the counterweight assembly  44 . However, the plate  52   c  has an annular shape including an arcuate portion  54  that extends into the counterweight cavity  42  when the compressor is assembled. 
     As shown in FIG. 7, the modified counterweight assembly  52  will not allow the assembly of the orbiting scroll member  20  with misplaced or extra steel spherical ball  36 ′. When the extra ball  36 ′ is misplaced into the counterweight cavity  42 , the ball is supported by the arcuate portion  54  at an elevated level making it impossible for the orbiting scroll  20  (not shown) to be placed on top of the eccentric bushing  18 . In addition, the elevated ball  36 ′ will be more visible to the operator during the assembly or repair process, reducing the possibility that the operator will attempt to assemble the compressor  10  with an extra ball in place. 
     A second preferred embodiment of the present invention is shown in FIG.  8 . An additional component in the form of a thin plate  56  is mounted between an end of the drive shaft  16  and the bushing  18 . The prior art counterweight assembly  44  remains unchanged. A portion  58  of the plate  56  extends into the counterweight cavity  42 . When the ball  36 ′ is misplaced in the counterweight cavity  42 , the ball is supported by the portion  58  at an elevated level making it impossible for the orbiting scroll  20  (not shown) to be placed on top of the eccentric bushing  18 . 
     In both of the embodiments described above, a plate portion is positioned in the counterweight cavity  42  to elevate the misplaced ball  36 ′ making it impossible to continue assembly of the compressor. 
     In accordance with the provisions of the patent statues, the present invention has been described in what is considered to be its preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.