Abstract:
A constrained rotary vane compressor having a rotor-vane assembly within a stator often exhibits unwanted noise and vibration effects. The present invention offers a design and method to decrease noise and vibration effects of such compressors by the incorporation of an oil skive formed in the interior wall of the stator. The oil skive rids the vane tips of any excess liquid which may have collected on the rotating vanes, which otherwise may impact certain interior regions of the stator resulting in unwanted noise and vibration of the compressor.

Description:
BACKGROUND OF THE INVENTION 
     Constrained rotary vane compressors are known which utilize a rotor and an assembly of vanes rotating within a fixed, cylindrical stator housing. Such devices operate by the rotor having an axis of rotation offset from the axial centerline of the stator housing. Thus, compartments of varying volume are formed, defined by the regions between adjacent vanes, the stator interior, and the end walls of the stator. 
     Constrained rotary vane compressors differ from rotary vane compressors in that they include means for constraining the vanes from directly contacting the interior circumferential wall of the stator housing. Typically this is done by means of annular tracks formed in the stator end walls. The vanes include guide rollers projecting from either side and engaging said tracks. 
     The rollers and tracks constrain the vanes such that the distal edges of the vanes come in very close proximity to the interior wall of the stator housing, without actually contacting the wall, at particular points or regions to prevent the escape of fluid (i.e. gas or vapor) as the vanes rotate thereby performing the compression operation. There is a tendency for these vanes to vibrate and generate noise as they rotate, a characteristic rarely seen in unconstrained rotary vane compressors. In addition to the objectionable noise, the vibration increases wear and tear on the device. While many solutions to the noise/vibration problem in such devices have been employed with varying degrees of success, prior artisans have not heretofore satisfactorily solved the problem nor even appreciated at least one of the sources of the problem. 
     SUMMARY OF THE INVENTION 
     In the present invention, it has been discovered that noise and vibration problems arise in constrained rotary vane compressors when even slight amounts of liquid collect on the distal vane tips. Such liquid is typically lubricating oil that is intentionally circulated through the refrigeration system with the refrigerant. Additionally, under certain conditions slugs of refrigerant may enter the compressor still in their liquid state. Any such liquid that collects on the vane surface will tend to migrate to the distal vane tip by centrifugal action. As the vanes rotate throughout the interior of the stator past the inlet opening and into the compression region, liquid collected on the vanes apparently becomes trapped between a distal vane tip and the interior surface of the stator. In light of the high velocity of the vane relative to the stator, the fluid cannot flow fast enough to vacate the essentially instantaneous decrease in clearance between the vane tip and the interior surface of the stator, in the vicinity of the intake. Therefore, the liquid impacts the interior surface of the stator which imparts a force upon the vane assembly. This force then induces vibration of the compressor components and generates significant noise. 
     The present invention solves this problem through use of an oil skive comprising a depression formed in and across the width of the interior circumferential wall of the stator. The depression is located on the stator&#39;s interior between the inlet port of the compressor and the beginning of the compression region. The trailing wall of the depression, that is the wall of the depression which the rotating vanes pass last as they rotate, cuts across the interior wall of the stator at an angle to the axial centerline of the stator to provide a skiving action across the tip of a vane as it passes the trailing wall. 
     These and other objects, advantages and features of the invention can be more fully understood and appreciated by reference to the written specification and appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of a typical constrained rotary vane compressor taken along planes I--I of FIG. 3; 
     FIG. 2 is a sectional view of a typical constrained rotary vane compressor taken along plane II--II of FIG. 1, showing the rollers and constraining annular track in the stator end cap. 
     FIG. 3 is a sectional view of a typical constrained rotary vane compressor utilizing an oil skive of the present invention, taken along plane III--III of FIG. 1; 
     FIG. 4 is a side view of a typical stator housing to more clearly show the oil skive of the present invention; 
     FIG. 5 is a cross section of the stator housing taken along plane V--V of FIG. 4, which allows fuller appreciation of the details of the oil skive; and 
     FIG. 6 is a sectional view of a typical constrained rotary vane compressor utilizing a plurality of oil skives of the present invention, taken along plane III--III of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the preferred embodiment, a constrained rotary vane-type compressor (FIGS. 1, 2 and 3), has a central rotor 10 having a plurality of vanes 20 slideably extending radially outward from rotor 10, residing within a stator 30. Stator 30 has end caps 40 formed or attached at both ends. The axis of rotation 11 of rotor 10 is offset from, but parallel to, the axialcenterline 32 of stator 30 so as to form vaned compartments of varying volume throughout the cycle of rotation. The distal vane tips 21 of vane 20 &#34;engage&#34; the interior surface 31 of stator 30, thereby forming a properseal between vane compartments throughout the region of compression. Otherwise, fluid in a particular compartment undergoing compression may escape to other regions within the stator, thereby lowering the overall efficiency of the compressor. By &#34;engage&#34; it is meant that the distal vanetips come into very near proximity to the surface of the stator interior Innormal operation the interior surface 31 of the stator will become coated with lubricating oil which will act to seal this gap. In the preferred embodiment, the gap between the vane tip and the interior surface of the stator is in the range of 0.025 to 0.127 mm, (0.001 to 0.005 inches). To assist such engagement, the vanes may be further guided by tracks 50 in end caps 40 of stator 30. Thus, each vane 20 is equipped with at least oneroller 51 which runs in tracks 50. Track 50 provides a cam surface for roller 51 contacting it, such that as the rollers progress about a track, vanes 20 are guided as they rotate within the interior of stator 30. 
     Since the vane tip 21 does not actually touch the interior surface 31 of the stator 30 and the vane 20 does not rely on the interior surface 31 to arrest its centrifugal acceleration, it is possible to relieve certain portions of the stator interior substantially from the circumferential profile which the vane tip traces. (This is not possible with a conventional, unconstrained, rotary vane compressor.) Creating such relieved areas is, in fact, quite desirable in the vicinity of the inlet 90 and outlet 93 inasmuch as it allows a more gradual transition of the fluid flow and reduces energy losses in these areas. In FIGS. 3 and 4 it can be seen that the inlet port surface 91 and outlet port surface 92 are both relieved in this manner. 
     Throughout the operation of most conventional constrained rotary vane compressors, various liquids may collect on the exposed surfaces of the vanes. Indeed, as previously noted, lubricating oil is purposely circulated with the refrigerant to aid in sealing and as a lubricant. In addition, under certain conditions slugs of refrigerant still in their liquid state may be encountered. As the vanes rapidly rotate, centrifugal force directs the liquids collected on the vane surfaces to the distal ends of the vanes. When the vane tip clearance is increased, as in the region near inlet port surface 91, a ridge of liquid may form on the tip of the vane. This ridge of liquid may have a height such that when situated on the end of a rotating vane, the effective radial dimension of the vane exceeds the radial dimension of the stator interior. Thus, upon avane entering the region of compression, the liquid may become trapped between the interior surface of the stator and the distal vane tip. The essentially instantaneous decrease in clearance above the tip of the vane does not allow sufficient time for the relatively viscous liquid to be displaced from the vane tip. The result is that liquid then impacts the interior surface of the stator which imparts a force upon the vane assembly. Occurrence of this is often exhibited as noise and vibration of the compressor. 
     FIGS. 4 and 5 clearly show the preferred embodiment of the oil skive 60 of the present invention. Oil skive 60 is essentially an angular depression in the generally cylindrical stator wall 31 comprising a depression bottomwall 80 and a trailing wall or step 70 formed in the interior wall 31 of stator 30. Step 70 is referred to as the trailing wall of oil skive 60 because it is the last wall of oil skive 60 which vanes 20 pass as they rotate. The formation, (typically by machining) results in depression bottom wall 80 formed on one side of trailing wall 70. Skive 60 (trailing wall 70 and accompanying depression bottom wall 80) is located between inlet port 90 of the compressor and region 100 where compression begins. The oil skive must be machined at the intersection point of inlet port surface 91 and stator interior 31 such that the oil skive 60 is the first point of engagement for a vane entering compression region 100 of stator 30. 
     The height of trailing wall 70 is preferably between about 0.5 mm to about 2.0 mm; such height is more or less constant as the trailing wall extends across the width of the interior wall of stator 30. Oil skive 60 (trailingwall 70 and depression bottom wall 80) preferably extends substantially across the width of stator 30, and most preferably entirely so as this maximizes the benefits and advantages of the present invention. It is crucial to the function of the oil skive 60 that the intersection of trailing wall 70 and stator interior 31 be essentially a sharp edge. 
     FIG. 5 shows clearly that the trailing wall 70 extends across the width of stator 30 at a slight angle to the axial centerline of stator 30 projectedonto stator wall 31. In the preferred embodiment, trailing wall 70 is oriented such that as the vane 20 approaches the oil skive 60, the liquid-covered distal tip of the vane will make contact first at point 71.As the vane movement progresses the point of contact (where oil is being skived off the vane tip) will shift from 71 to the opposite end 72 of the trailing wall 70. The projected length 73 of skive trailing wall 70 is equal to the distance that the vane travels during this skiving action and, with the rpm, determines the amount of time during which the oil can be displaced from the vane tip. If distance 73 is zero, there is essentially no time for oil displacement and large hydraulic forces, vibration, etc. ensue. In the preferred embodiment distance 73 is approximately the same as the thickness of one vane 20 used in the compressor, resulting in an angular orientation of trailing wall 70 to theaxial centerline of stator 30 of approximately 10°. In the broader aspects of the invention, this angle can be from about 1° to 30°. 
     Liquid which has been wiped off a passing vane 20 collects on trailing wall70 and on depression bottom wall 80 existing on one side of trailing wall 70. The surface of depression bottom wall 80 extends from trailing wall 70to its intersection with inlet port surface 91. As trailing wall 70 is oriented at some angle to the vane 20 edge, the liquid collected on depression bottom wall 80 is further directed towards that end of trailingwall 70 which last engages a passing vane 20. This collected liquid is thenswept into the general compression region after the vane 20 has passed the trailing wall 70, and before the next vane 20 approaches. 
     The trailing wall 70, as seen in FIG. 4, should be oriented approximately perpendicular to the path of the tip of passing vane 20, or even undercut,to ensure that the skiving action will not generate a radial force onto thevane 20. As shown in FIGS. 3-4, the trailing wall 70 is generally radially oriented with respect to stator 30, substantially in the same plane as a vane 20 having reached its point of closest approach to wall 70 while sweeping past oil skive 60. Furthermore, the surface of depression bottom wall 80 intersects trailing wall 70 face surface at an angle of 90°in the preferred embodiment. However, it is envisioned that a range of trailing wall face angles may be utilized, greater or lesser than 90°. 
     In the foregoing, skive 60 has been shown positioned just &#34;downstream&#34; (in the direction of rotation of rotor 10 and vanes 20) from inlet port 90. Inthe broader aspects of the invention, the skive, or multiple skives, could be located at different points throughout the stator. A logical location for such a skive is any point at which vane tips 21 move from an area where they are not in close proximity to the interior surface 31 of stator30 to a point where they re-approach close proximity to the interior surface 31. Thus a logical location for a second oil skive 60A in the preferred embodiment shown would be just on the downstream side of the exhaust port 93 as illustrated in FIG. 6. 
     Of course, it is understood that the foregoing is merely a preferred embodiment of the invention and that various changes and alterations can be made without departing from the spirit and broader aspects thereof as set forth in the appended claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents.