Abstract:
The amount of wear on the vanes of a sliding vane rotary pump is determined by inserting a wear inspection dip stick into a wear inspection port providing in a housing of the sliding vane rotary pump. The wear dipstick includes one or more mark providing an indication of the amount of wear on the vanes, and a marking member which provides an indication of current vane length and allows a maintenance person to easily determine when a pump replacement is required.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of provisional application Ser. No. 60/475,290, filed Jun. 3, 2003, hereby incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       FIELD OF THE INVENTION  
       [0003]     The present invention relates to dry air sliding vane rotary pumps, and more particularly to a method and apparatus for evaluating wear in the vanes without disassembling the pump housing.  
       BACKGROUND OF THE INVENTION  
       [0004]     Sliding vane rotary pumps are well known for use in a variety of applications, and are particularly common in aeronautical and aviation applications. These devices are commonly used, for example, in powering gyroscopically controlled flight instruments in airplanes. Proper maintenance to prevent the failure of these devices is therefore very important.  
         [0005]     Sliding vane rotary pumps typically comprise a rotor, a housing or stator, and a plurality of vanes. The rotor includes radial slots which receive the vanes, and can be constructed of either carbon, carbon composite, or hardened metal materials. The stator is typically constructed of a hardened metal material and the interior comprises an ellipsoidal cavity which receives the rotor. The vanes are typically constructed of carbon or carbon composites, and, as the rotor rotates, are caused by gravity to slide in and out of the slots as the rotor moves within the cavity, extending and retracting synchronously with the relative rotation of the rotor to provide compression and expansion of the air and therefore to produce a pumping pressure.  
         [0006]     The sliding motion of the vanes, however, results in a significant degree of friction which is exacerbated by the atmospheric pressures induced when used in aviation applications. While a number of efforts have been made to mitigate the frictional wear from the sliding vanes, including, for example, employing various coatings on both the vanes and the rotor, wear and breakage of the vanes remains problematic, as the friction developed between the vane and the rotor is eventually destructive to the pump. As the vanes reciprocate in the rotor slots, friction causes the vanes to wear, eventually shortening the vanes until they no longer reciprocate in the slots properly. Eventually, the shortened vanes lead to pump failure. Although the wear on the vanes can be monitored to some extent on the aircraft&#39;s vacuum gauge, which provides an indication if the pump is not operating correctly, there is generally little warning of a pending failure, as pump performance and efficiency are generally unaffected by wear on the vanes until a total or near total failure occurs.  
         [0007]     To prevent such failures, the operation time of the pump is monitored and the number of hours of operation is used as a benchmark for determining when to replace the pump. While generally effective in preventing pump failure, replacing the pump based entirely on hours of operation is expensive, resulting in premature pump replacement even when no significant wear has occurred, and further incurring costs in the form of maintenance time, down time for the vehicle and equipment expense. To reduce the equipment costs, the pump can be removed from the equipment and disassembled to evaluate the amount of wear. Again, however, this operation requires a high degree of maintenance activity, significant vehicle down time, and is highly dependent on the opinion of the evaluator.  
         [0008]     Another alternative, in which the length of the vanes are visually monitored, has been proposed in U.S. Pat. No. 6,450,789. Here, a “view port” is provided in a back of the housing of the pump. Through the view port, a maintenance person can examine the length of the vanes with reference to the width of the port and/or an associated calibration hole. While providing a means for viewing the rear on the vane, the view port can be difficult to access in the vehicle, and further requires a judgment call on the part of the maintenance personnel examining the pump.  
         [0009]     There remains a need, therefore, for an easy, consistent and effective way to gauge the wear on a vane in a dry air sliding vane pump without requiring removal or disassembly of the pump.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     One object of the invention is to provide a dipstick for determining wear on a vane in a sliding vane rotary pump. The dipstick comprises an elongated member, sized and dimensioned for insertion into an inspection port provided in a side of the sliding vane rotary pump which selectively provides access to at least one vane in the pump. A wear indicator mark is located on the elongated member in a position selected to indicate that the sliding vane rotary pump is worn when the elongated member is inserted into the inspection port. A marking device is slideably mounted on the elongated member, wherein when the elongated member is inserted into the inspection port, the marking device is slidable along the elongated member to contact the housing. In this position, the marking device provides a comparator for visually comparing the wear of the vane to the wear indicator mark.  
         [0011]     Another object of the invention is to provide a sliding vane rotary pump and a wear calibration device, in combination. The wear calibration device comprises an elongated wear calibration member including a wear indicator mark, and a marking device is slideably mounted on the elongated wear calibration member. The rotary vane pump comprises a housing including an inspection port, wherein the interior of the housing defining a bore for receiving a rotor. The rotor includes a plurality of radially-extending slots, and a plurality of vanes corresponding to the plurality of slots in the rotor are slideably received in the slots. To check the wear on the vanes, the elongated member is inserted into the inspection port when the slots in the rotor are selectively aligned with the inspection port, until the elongated member contacts a vane. The marking member is slid to a position contacting the outer surface of the housing to provide a mark which is then comparable to the wear indicator mark on the elongated member to indicate an amount of wear on the vane.  
         [0012]     Another object of the invention is to provide a method for determining the amount of wear on a vane in a sliding vane rotary pump including a housing defining an interior wall, a rotor provided within the interior wall and comprising a plurality of radially-extending slots, and a plurality of vanes, the number of vanes corresponding to the number of slots. The method comprises providing an inspection port in the housing of the sliding vane rotary pump to provide access to the slots in the rotor, calibrating an elongated member sized and dimensioned to be insertable in the inspection port to include a calibration mark indicating a length at which the vanes are worn and the pump should be replaced, rotating the rotor until the inspection port aligns with a slot in the rotor, and inserting the elongated member into the inspection port until it contacts the vane in the rotor. After the elongated member is inserted into the inspection port, the insertion length is compared versus the calibrated wear indicator mark to determine whether to replace the pump.  
         [0013]     These and other aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefore, to the claims herein for interpreting the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of a sliding vane rotary pump;  
         [0015]      FIG. 2  is an exploded view of the sliding vane rotary pump of  FIG. 1 ;  
         [0016]      FIG. 3  is a perspective view of a wear inspection dipstick;  
         [0017]      FIG. 4  is a cutaway view of the pump of  FIG. 1 , illustrating the insertion of the dipstick of  FIG. 2  in the wear inspection port.  
         [0018]      FIG. 5  is a perspective view of the dipstick illustrating an incorrect installation;  
         [0019]      FIG. 6  is a perspective view of the dipstick illustrating normal pump wear; and  
         [0020]      FIG. 7  is a perspective view of the dipstick illustrating a worn pump. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Referring now to the figures and more particularly to  FIG. 1 , a sliding vane rotary vacuum pump  10  is shown. The vacuum pump  10  comprises a housing  20  including an inspection port  14  for receiving a wear inspection dipstick  12 . The housing  20  is enclosed by a rear end  16  and front end  18  each of which includes a threaded aperture for receiving a pipe (not shown) for circulating air through the pump  10 .  
         [0022]     Referring now to  FIG. 2  an exploded view of the vacuum pump  10  of  FIG. 1  is shown. The housing  20  comprises an ellipsoidal pump cavity  58  which receives a rotor  22  comprising a plurality of slots  24  extending radially inward towards the center of the rotor from the outer edge of the rotor  22 . Each of the slots  24  receives a rotary vane  26  which is slidably engaged in the corresponding slot  24 . The rotor  22  further comprises a plurality of apertures extending longitudinally through the rotor  22  for receiving the fingers of a three-finger drive  26  and a central aperture  63  for receiving a central cylindrical member  61  in the rear end plate  60 , as described below. Each of the fingers of the three finger drive  26  is associated with a cushion  28 , the cushions  28  being provided between the apertures  30  and the drive  26  minimizing wear of the rotor  22 .  
         [0023]     Referring still to  FIG. 2 , as described above, the three-fingered drive  26  is coupled at a first end to the rotor  22 . At the opposing end, the three-fingered drive  26  is coupled to a drive shaft  32  comprising an external spline  34 , a shear shaft  36 , and an internal spline  38 . The external spline  34  can be coupled to an external drive mechanism for rotating the drive shift  32 , the three-fingered drive  26 , and therefore to rotate the rotor  22 . The drive shaft  32  extends outside of a front end mounting plate  48  which is coupled to the internal spline  38  of the drive shift  32  through a gasket  44 , a ceramic drive plate  42 , and a sponge  40 . The front end mounting plate  48  is further coupled to the housing  20  of the pump  10  through first and second rubber seals  50  and  54  and a metal ring  52 .  
         [0024]     At the opposing end of the pump  10 , the housing  20  is enclosed by the rear end  16 . The rear end  16  includes a rear end plate  60  which is coupled to the housing  20  with first and second rubber seals  62  and  66  and a metal ring  64 . A clockwise/counterclockwise adaptor plate  70 , selectively activated to reverse the direction of air flow from clockwise to counterclockwise, is also coupled to the housing  20  via retainer clips  72 . A spring  68  is provided between the clockwise/counterclockwise adaptor plate  70  and the rear end plate  60 . The rear end plate  60  further comprises a central cylindrical member  61  extending from the center of the rear end plate toward the rotor  22  which is received in the central aperture  63  in the rotor  22 , as described above.  
         [0025]     Referring still to  FIG. 2 , in operation an external drive system is coupled to the drive shaft  32  of the front end  18  of the housing  20 . As described above, the external drive system drives the drive shaft  32  which causes the three-finger drive  26  to rotate in the rotor  22 , thereby rotating the rotor  22  within the ellipsoidal pump cavity  58 . As the rotor  22  rotates within the ellipsoidal cavity  58  the vanes  26  are forced by centrifugal forces to slide into and out of the slots  24  when rotated. As the vanes  26  slide in and out of the rotor  22 , air is compressed in the pump cavity  58  such that a pump pressure develops as is known in the art and is described, for example, in U.S. Pat. Nos. 6,450,789 B1; 4820,140; 3,191,852; and 4,804,317, each of which describe a sliding vane rotary device and which are incorporated herein by reference for their description of such devices.  
         [0026]     Referring now to  FIG. 3 , the wear inspection dipstick  12  comprises an elongated member  82  extending from a handle portion  84 . The handle portion  84  comprises a wide handle section  86  which is sized and dimensioned to allow for easy handling by an operator, and a mounting section  88  coupled to the handle section  86  through a tapered section  87 . The elongated member  82  extends from a central portion of the mounting section  88  and includes first and second wear indicator marks  90  and  92 , respectively, which are located on the elongated member  82  to provide a visual comparison point when testing the wear of the vanes  26  in the pump  10 . The elongated member  82  is in turn sized and dimensioned to extend into the wear inspection port  14  in the housing  20  of the vacuum pump  10 .  
         [0027]     Referring still to  FIG. 3 , a marking member, here shown as a collar  80 , is sized and dimensioned to be slidably received on the elongated member  82 , and is provided to “mark” wear on the wear inspection dipstick  12  in use. As shown, the collar  80  is preferably ring-shaped, the inner diameter being selected to be slidably received on the elongated member  82 , and the outer diameter selected to be greater than the outer diameter of the inspection port  14  in the housing  20 , such that the collar  80  is stopped consistently when it is slid into the housing  20 , thereby consistently marking a position on the elongated member  82 .  
         [0028]     Referring now to  FIG. 4 , in use a cap (not shown) is removed from the wear inspection port  14  when the magnetos used to ignite the engine are turned off. The rotor  72  is rotated, typically by rotating a propeller coupled to the vacuum pump  10 , until the wear inspection port  14  is aligned with a slot  24  in the rotor  22 . The wear inspection port  14  is located in the housing  20  and extends through the pump cavity  58  through the ellipsoidal interior wall. The alignment of the wear inspection port  14  and the slot  24  can be checked, for example, by shining a flashlight in the inspection port  14  and visually gauging the alignment. As can be seen from  FIG. 4 , the inspection port  14  is preferably positioned at the upper portion of the pump such that the vane  26  in the slot  24  located adjacent the wear inspection port  14  is forced by gravity into the slot  24 . In this position, the length of the vane  26  can be determined as a function of the distance between the top end of the vane  26  and the housing  20  through the wear inspection port  14 .  
         [0029]     When the wear inspection port  14  is aligned with the slot  24 , the collar  80  is slid onto the elongated member  82  and the wear inspection dipstick  12  is inserted into the wear inspection port  14 . The collar  80  is slid into contact with the housing  20 , wherein the collar  80  provides a mark indicating the distance that the elongated member  82  was inserted into the wear inspection port  14 . The collar  80 , therefore, provides a measure of the length of the vane  26 , as a function of its position on the elongated member  82 , and the position of the collar  80  can be compared against the positions of the wear marks  92  and  94  to determine the amount of wear on the vanes  26 .  
         [0030]     Referring now to  FIGS. 5-7 , the position of the collar  80  on the wear inspection dipstick  12  is shown in three wear measurement situations. In  FIG. 5  the collar  80  is shown at the wear indicator mark  92  which is located on the elongated member  82  to indicate that the elongated member  82  has contacted the outer surface of the rotor  22  rather than the slot  24 . Therefore, the mark  92  indicates that the wear inspection port  14  is not aligned with the slot  24  in the rotor  20 . In  FIG. 6  the collar  80  is shown marking a position between the wear marks  90  and  92 . This position indicates that the wear of the vanes  26  in pump  10  is normal and that the pump need not be replaced at this time.  
         [0031]     Referring now to  FIG. 7 , here the collar  80  is positioned over the wear indicator mark  90 . When the collar  80  appears in this position the length of the vane  26  is less than desirable, indicating significant wear. Therefore, the pump  10  needs to be replaced.  
         [0032]     In alternative embodiments, a wear indicator port  14  could be provided in alternate locations in the housing  20 . For example, a wear indicator port  14  could be provided in an end of the housing  20 , such as in the rear end plate  60 . Here, the dipstick  12  is not be calibrated to check the distance to the vane  26  from the housing  20 , as described above. Rather, the position of the wear indicator port  14  is selected to be positioned at a location in which, when the dipstick  12  is inserted, the absence of a vane  26  indicates that the pump needs to be replaced, and the presence of the vane  26  indicates that the vane  26  has not worn to the point at which it needs to be replaced. Appropriate wear marks, positioned on the elongated member  82  as described as described above, would be included to provide a comparator for visualizing the results of the inspection. Other alternative embodiments, in which, for example, the wear inspection port is provided on the front mounting plate  48 , or positioned in a bottom portion of the housing  20  wherein the vanes  26  are slid out of the rotor, and the position is verified by inspecting the position of the back end of the vane  26  as opposed to the tip end, are also possible.  
         [0033]     It should be understood that the methods and apparatuses described above are only exemplary and do not limit the scope of the invention, and that various modifications could be made by those skilled in the art that would fall under the scope of the invention. For example, although a specific embodiment of a sliding vane rotary pump has been shown and described, it will be apparent that the method and apparatus for determining wear in the vanes described above could be used in a number of similar devices, including those described in the patents incorporated by reference above. Furthermore, although a specific ring-shaped collar  80  has been described for marking the wear on the dipstick  12 , it will be apparent that a number of different sliding or moving markers could also be used. Additionally, although a specific dipstick configuration and associated handle has been described, various other handle and member configurations could also be employed. To apprise the public of the scope of this invention, therefore, the following claims are made: