Patent Application
20070231170
The present disclosure relates to compressors, and more specifically to a drive shaft for a compressor.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
During scroll compressor operation, a drive shaft experiences loads from a variety of sources including a compression mechanism being driven, counterweights, and rotor torque, as well as reaction loads from bearings. These loads cause bending of the drive shaft during operation of the compressor. The shaft operating loads in scroll compressors rotate with the drive shaft. As such, the drive shaft typically has a first radial side in tension and a second radial side in compression during each revolution of the drive shaft. The stress at a specific location may vary, but there is not a reversal of tension and compression. The bending of the drive shaft under load causes shaft ends housed in bearings to cause excessive bearing wear due to an angular orientation within the bearing, which may result in compressor failure. In order to protect against this bending, drive shafts are often constructed with increased diameters to account for high load conditions.
A compressor drive shaft may include a first journal portion, a second journal portion, and an intermediate portion disposed therebetween. The first journal portion, second journal portion, and intermediate portion may form a non-linear body portion. The non-linearity may be defined by the first journal portion extending at an angle relative to the rotational axis of the drive shaft.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present claims.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present teachings in any way.
The following description is merely exemplary in nature and is not intended to limit the present teachings, application, or uses.
The present teachings are suitable for incorporation in many different types of scroll and rotary compressors, including hermetic machines, open drive machines and non-hermetic machines. For exemplary purposes, a compressor 10 is shown as a hermetic scroll refrigerant-compressor of the low-side type, i.e., where the motor and compressor are cooled by suction gas in the hermetic shell, as illustrated in the vertical section shown in
Compressor 10 may include a cylindrical hermetic shell 16, a compression mechanism 18, a main bearing housing 20, a motor assembly 22, a refrigerant discharge fitting 24, and a suction gas inlet fitting 26. The hermetic shell 16 may house the compression mechanism 18, main bearing housing 20, and motor assembly 22. Shell 16 may include an end cap 28 at the upper end thereof. The refrigerant discharge fitting 24 may be attached to shell 16 at opening 30 in end cap 28. The suction gas inlet fitting 26 may be attached to shell 16 at opening 32. The compression mechanism 18 may be driven by motor assembly 22 and supported by main bearing housing 20. The main bearing housing 20 may be affixed to shell 16 at a plurality of points in any desirable manner.
The motor assembly 22 may generally include a motor 34, a frame 36 and a drive shaft 38. The motor 34 may include a motor stator 40 and a rotor 42. The motor stator 40 may be press fit into frame 36, which may in turn be press fit into shell 16. Drive shaft 38 may be rotatably driven by rotor 42. Windings 44 may pass through stator 40. Rotor 42 may be press fit on drive shaft 38. A motor protector 46 may be provided in close proximity to windings 44 so that motor protector 46 will de-energize motor 34 if windings 44 exceed their normal temperature range.
Drive shaft 38 may include an eccentric crank pin 48 having a flat 49 thereon and one or more counter-weights 50 at an upper end 52. Drive shaft 38 may include a first journal portion 53 rotatably journaled in a first bearing 54 in main bearing housing 20 and a second journal portion 55 rotatably journaled in a second bearing 56 in frame 36. Drive shaft 38 may include an oil-pumping concentric bore 58 at a lower end 60. Concentric bore 58 may communicate with a radially outwardly inclined and relatively smaller diameter bore 62 extending to the upper end 52 of drive shaft 38. The lower interior portion of shell 16 may be filled with lubricating oil. Concentric bore 58 may provide pump action in conjunction with bore 62 to distribute lubricating fluid to various portions of compressor 10. Drive shaft 38 may have a pre-bent configuration, as discussed below.
Compression mechanism 18 may generally include an orbiting scroll 64 and a non-orbiting scroll 66. Orbiting scroll 64 may include an end plate 68 having a spiral vane or wrap 70 on the upper surface thereof and an annular flat thrust surface 72 on the lower surface. Thrust surface 72 may interface with an annular flat thrust bearing surface 74 on an upper surface of main bearing housing 20. A cylindrical hub 76 may project downwardly from thrust surface 72 and may include a journal bearing 78 having a drive bushing 80 rotatively disposed therein. Drive bushing 80 may include an inner bore in which crank pin 48 is drivingly disposed. Crank pin flat 49 may drivingly engage a flat surface in a portion of the inner bore of drive bushing 80 to provide a radially compliant driving arrangement, such as shown in assignee's U.S. Pat. No. 4,877,382, the disclosure of which is herein incorporated by reference.
Non-orbiting scroll member 66 may include an end plate 82 having a non-orbiting spiral wrap 84 on lower surface 86 thereof. Non-orbiting spiral wrap 84 may form a meshing engagement with wrap 70 of orbiting scroll member 64, thereby creating an inlet pocket 88, intermediate pockets 90, 92, 94, 96, and outlet pocket 98. Non-orbiting scroll 66 may have a centrally disposed discharge passageway 100 in communication with outlet pocket 98 and upwardly open recess 102 which may be in fluid communication with discharge fitting 24. A flip seal 104 may be located around recess 102 and abut shell 16, thereby providing sealed communication between discharge passageway 100 and discharge fitting 24, while allowing axial displacement of non-orbiting scroll 66 relative to shell 16.
Non-orbiting scroll 66 may be mounted to main bearing housing 20 in any manner that will provide limited axial movement of non-orbiting scroll member 66. For a more detailed description of the non-orbiting scroll suspension system, see assignee's U.S. Pat. No. 5,055,010, the disclosure of which is hereby incorporated herein by reference. A variety of seals may also be included for sealing between the end cap 28 and non-orbiting scroll 66.
Axial pressure biasing may be included in compressor 10, as disclosed in Assignee's aforesaid U.S. Pat. No. 4,877,328, the disclosure of which is herein incorporated by reference. A capacity modulation system may also be included in the system, as described in assignee's aforesaid U.S. Pat. No. 6,821,092.
Relative rotation of the scroll members 64, 66 may be prevented by an Oldham coupling, which may generally include a ring 108 having a first pair of keys 110 (one of which is shown) slidably disposed in diametrically opposed slots 112 (one of which is shown) in non-orbiting scroll 66 and a second pair of keys (not shown) slidably disposed in diametrically opposed slots in orbiting scroll 64.
With additional reference to
During operation, deflection of drive shaft 138 may occur at a similar location throughout a complete rotation. This deflection is due to the applied loads acting on drive shaft 138, and therefore bearing reaction loads, rotating with drive shaft 138. These loads may include loads from a compression mechanism, counterweights, and rotor torque, as well as reaction loads from bearings. As such, a first radial side 122 of drive shaft 138 may always be under tension and a second radial side 124 of drive shaft 138 may always be under compression during operation of compressor 10. First radial side 122 may be generally opposite second radial side 124. More specifically, when drive shaft 138 is used in a scroll compressor similar to that in
As noted above, and shown in
As described above regarding drive shaft 138 in
In order to compensate for the deflection described above, drive shaft 38 may be bent in a direction generally opposite the direction of deflection during operation. Specifically, drive shaft 38 may be bent in such a manner that first journal portion 53 may be disposed at an angle that generally proximates angle β relative to first bearing wall 120 when compressor 10 is in a non-operating state. Specifically, angle β may generally be between 0 and −α degrees. More specifically, angle β may generally be equal to −α/2 degrees. While described in terms of −α, angle β may also be described in terms of +α, with the understanding that angle β may extend generally opposite angle α.
More specifically, in the example of scroll compressor 10, shown in
As a result, the net bending of drive shaft 38 under loading during operation may be reduced. For example, if drive shaft 38 has a pre-bend of −α/2, the tilt angle under load may be reduced from α to α/2.
Maximum tilt angle α may be determined in a number of ways including advanced methods such as Finite Element Analysis (FEA). An alternative way to determine maximum tilt angle α is to build hardware and test to find the maximum tilt angle. Once maximum tilt angle α has been determined, or at least approximated, angle β may be determined. Angle α may generally be between 0.21 and 0.35 degrees, depending on compressor operation. More specifically, angle α may be approximately 0.28 degrees. As such, angle β may be between 0.1 and −0.18 degrees. More specifically, angle β may be approximately −0.14 degrees. Angle β may be more or less depending on the application, as loads may vary depending on the compressor application.
While drive shaft 38 has been described in a scroll compressor environment, the application of a pre-bent drive shaft extends to other areas as well. For example, a pre-bent drive shaft may be beneficial for use in a vane-type compressor, various turbine machines, or any other apparatus having loads rotating together with a drive shaft.
Pre-bent drive shaft 38 may be formed in a variety of ways. Drive shaft 38 may be initially formed as linear and then bent into non-linear by applying a press load in a middle portion of drive shaft 38 while drive shaft 38 is supported at both ends. The press load may be sufficient to press drive shaft 38 beyond its yield point. Alternatively, drive shaft 38 may be initially formed as a generally cylindrical member and may be ground to a desired shape. Alternatively, drive shaft 38 may be formed as a bent or curved structure using a process such as powdered metal (PM) forming. Yet another method of forming the pre-bent structure may include the assembly of two or more pieces together.
