Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
2000-03-21
2001-08-28
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Electric or magnetic motor
Reexamination Certificate
active
06280155
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to hermetic compressors for use in cooling, refrigeration or air-conditioning systems, and more particularly to hermetic scroll compressors.
Well known to those having skill in the art are hermetic scroll compressors such as compressor
10
of
FIG. 1
, having a closed hermetic housing
12
comprised of cylindrical section
14
with end cap
16
welded at the upper end thereof and base
18
at the lower end thereof. Base
18
includes a plurality of mounting feet
20
. Compressor
10
has electric motor
22
, which comprises stator
24
fixed inside cylindrical section
14
by, for example, shrink-fitting. Surrounded by stator
24
is rotor
26
, which is attached to shaft
28
by, for example, press-fit. Counterweight
27
is attached to an upper end of shaft
28
and counterweight
31
is attached to rotor
26
, as is customary, to provide substantially balanced rotation of shaft
28
. Shaft
28
is coupled to orbiting scroll
30
through eccentric
29
. Shaft
28
is supported, at opposing ends thereof, by bushing
32
and auxiliary bearing
34
. Bushing
32
is fixed within main bearing
48
by, for example, press-fit. Main bearing
48
and auxiliary bearing
34
are rigidly affixed to an internal surface
33
of cylindrical section
14
of housing
12
typically by press-fit or spot weld methods. Generally, auxiliary bearing
34
includes a plurality of outwardly extended legs
36
secured to internal surface
33
of cylindrical section
14
.
Those having skill in the art of compressor construction readily appreciate that spot welding, although a preferable manufacturing process to attach the bearings to the housing, may cause heat generated distortion which can lead to misalignment of stator-rotor air gap
38
. To facilitate this process, radially directed holes
40
are provided in an end portion of each leg
36
to accommodate a steel pin
42
in each hole. This process further requires each pin
42
to be aligned with each corresponding hole
44
provided in a lower part of cylindrical section
14
. Finally, each pin
42
is spot welded to cylindrical housing section
14
at hole
44
.
Turning now to the construction of the scroll compressor mechanism
57
, in the upper part of housing
12
, is non-orbiting scroll member
46
axially fixed to main bearing
48
by a plurality of bolts
50
in such a manner that orbiting wrap
52
, integral with orbiting scroll member
30
, and non-orbiting wrap
54
, integral with non-orbiting scroll member
46
, combine to form compression cavities or chambers
56
. Orbiting scroll member
30
, non-orbiting scroll member
46
and main bearing
48
comprise compressor mechanism
57
which is positioned in an upper part of cylindrical housing section
14
. A typical procedure associated with assembly of compressor
10
includes request for concentricity of inner radial surface
59
of stator
24
respective of inner radial surface
61
of main bearing
48
. Annular bushing
32
attached to main bearing
48
, by typical means such as press-fit, is substantially concentric with main bearing
48
. Main bearing
48
and bushing
32
must also properly align shaft
28
to provide suitable clearance between orbiting and non-orbiting wraps
52
and
54
, respectively, so proper compression in compression chambers
56
may be attained. After alignment is achieved, main bearing
48
and/or non-orbiting scroll member
46
is welded to housing
12
.
Discharge gas compressed by compressor mechanism
57
flows through discharge port
64
provided with check valve
62
, and into first discharge chamber
66
. First discharge chamber
66
is defined in part by a volume formed between planar surface
68
of non-orbiting scroll
46
and end cap
16
. Thereafter, the discharge gas flows from first discharge chamber
66
to second discharge chamber
70
and exits through discharge tube
72
. Discharge chamber
70
is defined by axial surface
78
of compressor mechanism
57
, internal surface
33
of a portion of housing
14
, generally below compressor mechanism
57
, and external surface
55
of the compressor motor
22
. Discharge chambers
66
and
70
are in fluid communication through narrow (e.g., 0.035″-0.040″wide) passage
74
formed by internal surface
33
of cylindrical section
14
and peripheral surface
69
of compressor mechanism
57
. Discharge tube
72
extends through the wall of cylindrical section
14
of housing
12
and into chamber
70
to transfer refrigerant gas away from compressor assembly
10
.
A problem associated with scroll compressors heretofore, is one of excessive noise caused by refrigerant gas turbulently flowing over the compressor mechanism prior to being discharged from the compressor housing. Compressed refrigerant gas exiting discharge port
64
enters first discharge chamber
66
, and is thereafter forced over peripheral surface
69
of compressor mechanism
57
and into second discharge chamber
70
. Narrow passage
74
, disposed between first discharge chamber
66
and second discharge chamber
70
, is substantially flow-restrictive and consists of a thin ring or annular shaped passage between cylindrical section
14
of housing
12
and compressor mechanism
57
. An outer profile of compressor mechanism
57
, exposed to the refrigerant gas flowing thereover, is generally cylindrical, and includes a pair of axially opposed and generally planar surfaces
76
,
78
, respectively, which are connected by cylindrical surface
80
. The transition of discharge gas flow from axial planar surfaces
76
,
78
, respectively to cylindrical surface
80
generally includes moderately sharp edges which generate turbulence when refrigerant gas flows over compressor mechanism
57
. An increase in noise is attributable to an increase in energy of the gas as gas molecules transition from a substantially ordered state to a substantially unorganized and chaotic state. The noise is transmitted through housing
12
of compressor assembly
10
and into the surrounding area.
Another problem associated with compressor assembly
10
arises during operation wherein localized heating occurs between the rotating rotor
26
and the stationary stator
24
. Region
25
, positioned extending radially through outer peripheral margins of rotor
26
and inner peripheral margins of stator
24
, becomes heated which detrimentally affects motor efficiency.
Yet another problem associated with scroll compressors heretofore, is the costly and laborious procedure of aligning the main bearing, auxiliary bearing and stator within the housing to preserve proper scroll wrap and shaft bearing clearances; typically the clearances required are a few ten thousandths of an inch. This procedure is often referred to as “mounting” the compressor.
Mounting of scroll compressors typically requires the diameter of the cylindrical part of the housing to be machined to provide a reference location to concentrically align the main bearing with the auxiliary bearing and to eliminate uneven stator-rotor gap during assembly. Aligning each bearing relative to the housing requires the bearing support structures to include an outer diameter smaller than that of the inner diameter of the cylindrical section of the housing so that a gap is formed between the structure and the inner surface of the housing. The gap must be uniform and somewhat small to facilitate favorable conditions for alignment and spot welding. Further, as mentioned above, typical scroll compressor design mandates precise radial placement of each bearing, thus, a typical scroll compressor exhibits a supporting bearing structure larger than necessary and/or a plurality of special arms attached to the bearing support to allow for radial adjustability. Unfortunately, these design requirements add to the weight of the compressor, complicate assembly and further add to machining time, which in turn, increases the per unit cost to the manufacturer.
Once the bearings and scroll are suitably aligned, the problem of weldability between metal
Baker & Daniels
Patel Vinod D
Tecumseh Products Company
Walberg Teresa
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