Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
2001-08-15
2003-01-14
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
C029S888023, C384S126000, C384S537000, C384S903000
Reexamination Certificate
active
06506038
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to screw compressors, and more particularly to bearing arrangements for screw compressors.
BACKGROUND OF THE INVENTION
The rotors of a screw compressor are supported by bearings at both the suction end and the discharge end of the compressor. In a typical bearing arrangement, there is one radial bearing supporting each end of the rotor and at least one axial bearing supporting the discharge end of the rotor. This arrangement is used for both rotors.
FIG. 1
illustrates a typical prior art bearing arrangement for a screw compressor
10
.
As shown in
FIG. 1
, the compressor
10
includes two rotors
14
and
18
mounted for rotation between a suction end
22
and a discharge end
26
. At the suction end
22
, the first and second rotors
14
,
18
are housed in a suction housing
30
and are supported by radial bearings
34
and
38
. The suction housing
30
is connected to one end of a rotor housing
42
that surrounds portions of the rotors
14
,
18
. A discharge housing
46
is connected to the other end of the rotor housing
42
. Radial bearings
50
and
54
support the discharge ends of the rotors
14
,
18
inside the discharge housing
46
.
Typically, each of the radial bearings
34
,
38
,
50
, and
54
are rolling element bearings. When mounted, the separable inner race of each bearing
34
,
38
,
50
, and
54
is pressed onto the ends of the respective rotor shafts, while the outer race with the rollers is retained in the respective suction housing
30
or discharge housing
46
. Due to the tolerances, the fit between the outer race of the bearings
34
and
38
and the suction housing
30
is often a transition fit (slip fit and press fit), so it is common to axially fix each outer race between a shoulder
58
of the suction housing
30
on one end, and a snap ring
59
on the other end.
Likewise, the fit between the outer race of the bearings
50
and
54
and the discharge housing
46
is often a slip fit, so each outer race is axially fixed between a shoulder
60
on one end, and a snap ring
61
on the other end. The snap rings
59
and
61
are retained in grooves that are cast or machined in the respective suction housing
30
and discharge housing
46
.
To accommodate the axial movement of the rotors
14
,
18
, axial bearings
66
,
70
, and
74
are used at the discharge end
26
. Two of the axial bearings
66
and
70
are mounted in tandem relation on the first rotor
14
, while the second rotor
18
has only one of the axial bearing
74
mounted thereon. Just as with the radial bearings
50
,
54
, the inner races of the axial bearings
66
,
70
, and
74
are pushed onto the respective rotor shafts, and the outer races are free to rotate. The axial bearings
66
and
70
are axially fixed between an end surface
78
of the discharge housing
46
on one end, and a thrust collar
82
on the other end. The thrust collar
82
is shrunk onto the rotor shaft, as is understood by those skilled in the art. Likewise, the axial bearing
74
is axially fixed between the end surface
78
on one end, and a thrust collar
86
on the other end.
The compressor
10
can also include a pair of reverse-thrust or backup bearings
90
. The backup bearings
90
each have a spring-loaded outer race, in the form of a spring
91
that is retained between the bearing
90
and a cup
92
, that biases the backup bearings
90
into engagement with a step in the respective rotors
14
,
18
. This spring bias is intended to keep the outer races of the axial bearings
66
and
74
securely seated against the end surface
78
during startup of the compressor
10
, thereby substantially preventing any relative rotation or movement between the outer races of the axial bearings
66
and
74
and the end surface
78
. While also serving other purposes, this backup bearing arrangement eliminates the need to mechanically anti-rotate the outer races of the axial bearings
66
and
74
with pins, keys, or other known anti-rotation devices. An axial bearing cover
94
is mounted to the end surface
78
of the discharge housing
46
to cover and protect the axial bearings
66
,
70
,
74
, and
90
and to provide a fixed engagement surface for the spring-loaded backup bearings
90
.
SUMMARY OF THE INVENTION
The prior-art bearing arrangement described above has some drawbacks. For example, when the compressor
10
is started, the spring bias of the backup bearings
90
is often not enough to keep the outer races of the bearings
66
and
74
seated securely against the end surface
78
of the discharge housing
46
. This allows the outer races of the bearings
66
and
74
to rotate or vibrate relative to the end surface
78
of the discharge housing
46
. Because the end surface
78
is typically a softer material (e.g., cast iron) than the material used for the outer race of the bearings
66
and
74
(e.g., steel), the rotation and vibration of the bearings
66
and
74
results in wearing and grooving in the end surface
78
. The wearing and grooving can be further accentuated by non-perfect parallel seating of the bearings
66
and
74
against the end surface
78
. Testing has shown wear rates on the order of one micrometer per one-thousand hours of compressor operation.
Large amounts of wearing and grooving result in increased axial rotor endplay with respect to the end surface
78
of the discharge housing
46
. The increased axial end-play results in a loss of compressor performance and increased discharge temperatures, both of which decrease the overall efficiency of the compressor
10
.
Using backup bearings
90
also creates other disadvantages. For example, the compressor
10
must be larger to accommodate the backup bearings
90
, and the backup bearings
90
add to the overall cost of the compressor
10
. These disadvantages, while tolerable if the backup bearings
90
perform as intended, are exacerbated when the backup bearings
90
fail to prevent the wearing and grooving that causes increased axial rotor end-play. Of course, the size of the backup bearings
90
can be increased to include a larger spring force to eliminate wearing and grooving, however, such larger backup bearings would reduce the life of the axial bearings
66
,
70
, and
74
due to the larger thrust force.
The present invention overcomes these and other problems by providing a wear-preventing and positioning device for combined axial and radial bearing arrangements in the discharge end of a compressor. The device substantially eliminates wearing and grooving on the discharge housing without the use of spring-loaded backup bearings or other anti-rotation devices coupled to the outer races of the axial bearings. Therefore, the overall size and cost of the compressor is greatly reduced. The single device also axially positions the radial bearings and the axial bearings on the discharge side. Therefore, the snap rings are also eliminated, further reducing the size and cost of the compressor.
The device is a thin, hard, specially-configured and flattened strip of material that fits over both rotor shafts and abuts the end surface of the discharge housing. One face of the strip axially fixes the radial bearings while the opposing face axially fixes the axial bearings. The strip is sandwiched between the outer race of the axial bearings and the end surface of the discharge housing to eliminate direct contact between the axial bearings and the discharge housing. Because the strip is approximately the same hardness as the material used for the outer races of the axial bearings, rotation or vibration of the axial bearings will not create significant wearing or grooving in the strip. The need for spring-loaded backup bearings to prevent rotation of the axial bearings is therefore eliminated.
Additionally, the special configuration of the strip substantially fixes the strip with respect to the discharge housing so that any movement or vibration of the axial bearings will not cause relative movement between the strip and the discharge housing. This substantially eliminat
Erickson Lee John
Sjoholm Lars Ivan
Michael & Best & Friedrich LLP
Thermo King Corporation
Vrablik John J.
LandOfFree
Wear-preventing and positioning device for a screw compressor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wear-preventing and positioning device for a screw compressor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wear-preventing and positioning device for a screw compressor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3068572