Patent Publication Number: US-2021190097-A1

Title: Filter retaining plug

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 16/379,983, filed Apr. 10, 2019, which claims priority to European Patent Application No. 18461547.4 filed Apr. 10, 2018, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to plugs which are used to retain a filter in, for example, a servovalve and to tools which may be used in removing such plugs. 
     BACKGROUND 
     Servovalves are used in a wide variety of aircraft control systems, for example in fuel and air management systems for operating engine fuel metering valves, active clearance control valves, bleed valves and so on. The operating medium of the servovalve will potentially be contaminated. Accordingly, servovalves are provided with filters. Such filters may include filter screens which are assembled in ports of the servovalve, for example in supply, control or return ports of the valve. These screens act to retain any particles which are large enough potentially to cause potential failure of the valve. For example in a flapper type servovalve, comprising two nozzles and a movable flapper element arranged between them, the total flapper operating total distance may be as small as about 0.2 mm. In such valves, the filter screen will typically act to filter out particles having a nominal size larger than 0.07 mm. Such filter screens can easily become blocked. This necessitates cleaning or removal and replacement of the filter screens. However, this may be difficult as the filter screen is typically retained by a press fitted plug. Removal of this plug is difficult and may cause damage to the servovalve body, requiring the servovalve itself then to require repair. 
     It would be desirable to provide a system which would mitigate these problems. 
     SUMMARY 
     From a first aspect, the present disclosure provides a plug for retaining a filter screen in a fluid port of a servovalve. The plug comprises an annular body. The annular body comprises opposed first and second axial end surfaces, a radially inner surface extending between the first and second axial end surfaces, a radially outer surface extending between the first and second axial end surfaces, and at least one recess formed in the radially inner surface for receiving a tool for removing the plug from the port. 
     The recess may be an annular recess extending circumferentially around the entire radially inner surface. 
     The at least one recess may extend perpendicularly to the radially inner surface. 
     The recess may extend radially into the plug body from the radially inner surface to a depth of from 30-50% of the thickness of the plug body measured between the radially inner and radially outer surfaces of the plug body. 
     The recess may have a height measured in a direction between the first and second axial end surfaces of 0.25 to 0.43 of the height of the plug body measured in the direction between the first and second axial end surfaces. 
     The plug body may be made from aluminium. 
     The disclosure also provides a servovalve comprising a port for receiving a working fluid, a filter screen mounted in the port and a plug in accordance with the disclosure interference fitted in the port to retain the filter screen in the port. 
     The disclosure also provides a tool for removing a plug in accordance with the disclosure from a port. The tool comprises a pair of handles pivotally mounted to one another about a pivot, each handle having a plug gripping portion extending therefrom beyond the pivot. Each plug gripping portion comprises an outwardly projecting tooth for engaging in the recess of the plug when the plug gripping portions are moved apart by operation of the handles. 
     The plug gripping portions may be configured such that as the handles are moved towards one another, the plug gripping portions are moved apart. 
     Each handle may further comprise a stop for limiting the movement of the handles and therefore the movement apart of the plug gripping portions. 
     Each stop may comprise an L-shaped element. 
     Each tooth may taper in an outward direction. 
     Each handle may comprise a first section arranged generally parallel to the first section of the other handle and an angled section extending therefrom to the pivot. 
     Each plug gripping portion may comprises a proximal portion attached to a respective handle and a distal portion comprising the outwardly projecting tooth, the proximal and distal portions of each plug gripping portion being offset laterally from one another whereby the distal portions of the gripping portions align. 
     The disclosure also provides a method of maintaining a servovalve comprising a fluid port and a filter screen retained in the fluid port by a plug in accordance with the disclosure interference fitted within the fluid port. The method comprises engaging a removal tool with the at least one recess of the plug body and pulling the plug out of the port using the tool. The removal tool may be a tool in accordance with the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a cross-section through a servovalve in accordance with the disclosure; 
         FIG. 2  shows an exploded view of the servovalve of  FIG. 1 ; 
         FIG. 3  shows a cross-sectional view of a plug in accordance with the disclosure; 
         FIG. 4  shows a perspective cross-sectional view of the plug of  FIG. 3 ; 
         FIG. 5  shows a plug removal tool in accordance with the disclosure; 
         FIG. 6  shows the tool of  FIG. 5  in a preliminary stage of removing a plug from a servovalve; 
         FIG. 7  shows a partial cross-sectional view of the tool in a removal configuration engaged with the plug; and 
         FIG. 8  shows the tool holding the removed plug. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , a servovalve  2  comprises a servovalve housing  4  which houses a pair of nozzles  6  and a flapper element  8 . As is known in the art, the flapper element  8  is deflected in a direction along the axes of the nozzles  6  by an actuator, not shown, in order to meter a working fluid which passes through the nozzles  6 . 
     The servovalve housing  4  comprises has three ports  10 , which allow communication of the working fluid to the nozzles  6 . The central port  10  is typically called a control port and its function is to communicate fluid to an actuator (not shown). This type of servovalve is well known in the art, being used in a wide variety of aircraft control systems, for example in fuel and air management systems for operating engine fuel metering valves, active clearance control valves, bleed valves and so on. 
     Since, as is discussed above, the distances moved by the flapper element  8  may be relatively small, in order to prevent operation of the flapper element  8  being compromised by contamination, particle filters  14  are arranged in one or more of the ports  10 . As can be seen in  FIG. 1 , in an embodiment of the disclosure, the filters  14  are received within a bore  16  of the respective ports  10  and are received on an annular shoulder  18  at the base of each bore  16 . 
     The filter  14  may be a screen or mesh structure as is known in the art, with an appropriate mesh size. For example, in some embodiments the filter  14  may be configured to filter particles having a nominal size larger than 0.07 mm. The filter  14  may be made from any suitable material, for example a metal or a plastics material. 
     The filter  14  is retained on the shoulder  18  within the bore  16  by a plug  20  which is press fitted into the bore  16 . As can be seen in  FIGS. 3 and 4 , the plug  20  has an annular body  22  having opposed first and second axial end surfaces  24 ,  26 , a radially inner surface  28  extending between the first and second axial end surfaces  24 ,  26  and a radially outer surface  30  extending between the first and second axial end surfaces  24 . The first and second axial end surfaces  24 ,  26  are generally parallel to one another and perpendicular to the central axis A of the plug  20 . The radially inner and outer surfaces  28 ,  30  are also generally parallel to one another and extend parallel to the central axis A of the plug  20 . 
     An annular recess  36  is formed in the radially inner surface  28 . In this embodiment, the recess  36  extends entirely around the circumference of the inner surface  28 . In other embodiments, however, one or more pairs of diametrically opposed recesses may be provided instead. However, an annular recess  36  may be more easily manufactured and may facilitate removal of the plug  20 . 
     The recess  36  extends into the plug body  22  generally perpendicularly to the radially inner surface  28 . In the disclosed embodiment, the recess  36  has opposed axial surfaces  38 ,  40  and a base surface  42 . The axial surfaces  38 ,  40  may, as shown, be parallel to the axial end surfaces  24 ,  26  of the plug body  22 . The base surface  42  may be parallel to the radially inner and outer surfaces  28 ,  30  of the plug body  22 . 
     The recess  36  may extend radially into the plug body  22  from the radially inner surface  28  to a depth D of from 30-50% of the thickness T of the plug body  22  measured between the radially inner and radially outer surfaces  28 ,  30  of the plug body  22 . 
     The recess  36  may have a height HR measured in the direction between its opposed axial surfaces  38 ,  40  of from 0.25 to 0.43 of the height HP of the plug body  22  measured between the first and second axial end surfaces  28 ,  30  of the plug body  22 . 
     In a typical embodiment, the plug body  22  may have an outer diameter DPO of 7.5 mm and an inner diameter DPI of 4.7 mm and the recess  36  have an outer diameter DR of 6 mm. The inner diameter DPI of the plug body  22  will need to be large enough to allow the flow of working fluid through the respective ports  10 ,  12 . The height HP of the plug body  22  may typically be 2.7 mm and the height HR of the recess  36   22  may typically be 1 mm. 
     As can be seen, for example  FIG. 3 , in embodiments, the plug  20  may be symmetrical about an axial centreline B defined equidistant between the first and second axial end surfaces  24 ,  26  of the plug  20  such that it may be inserted into the bore  16  in either orientation, thereby facilitating assembly. Also, as can be seen in  FIG. 3 , the corners  32 ,  34  between the first and second axial end surfaces  24 ,  26  and the radially outer surface  30  may be chamfered or rounded in order to facilitate insertion of the plug  20  into the bore  16 . 
     The plug body  22  may be made from any suitable material. In certain embodiments, the plug body  22  may be made from aluminium for example. This will provide sufficient rigidity and strength for the plug body  22 . 
     As discussed above, the plug body  22  is press fitted into the bore  16  in order to retain the filter  14  in position. The recess  36  facilitates removal of the plug  20  from the bore  16  as will be discussed further below. 
       FIG. 5  illustrates a tool  50  which may be used in removing the plug  20  from a bore  16 . 
     The tool  50  comprises a pair of handles  52   a ,  52   b  pivotally mounted to one another about a pivot  54 . The pivot  54  may take any suitable form, for example a pin extending through respective openings (not shown) on the handles  52   a ,  52   b . Each handle  52   a ,  52   b  has a respective plug gripping portion  56   a ,  56   b  extending therefrom beyond the pivot  54 . 
     Each plug gripping portion  56   a ,  56   b  comprises an outwardly projecting tooth  58   a ,  58   b  at its distal end for engaging in the recess  36  of the plug  20  when the plug gripping portions  56   a ,  56   b  are moved apart by operation of the handles  52   a ,  52   b.    
     The teeth  58   a ,  58   b  may have any suitable profile as long as they can be received within the recess  36 . In this embodiment, each tooth  58   a ,  58   b  tapers in an outward direction. Thus, as shown, the upper surface  59  of each tooth  58   a ,  58   b  may be angled. This may facilitate positioning of the tooth  58   a ,  58   b  in the recess  36 , as can be seen from  FIG. 7  for example. Of course other shapes of tooth  58   a ,  58   b  are possible within the scope of the disclosure. 
     In the disclosed embodiment, the plug gripping portions  56   a ,  56   b  are configured such that as the handles  52   a ,  52   b  are moved towards one another the plug gripping portions  56   a ,  56   b  are moved apart. This facilitates removal of the plug  20  as it is possible to engage the tool  50  with the plug  20  using just one hand. 
     Each handle  52   a ,  52   b  further comprises a stop  60   a ,  60   b  for limiting the movement of the handles  52   a ,  52   b  and therefore the movement apart of the plug gripping portions  56   a ,  56   b . The stops  60   a ,  60   b  therefore determine how far the teeth  58   a ,  58   b  will extend into the recess  36  and indicate to a user that the teeth  58   a ,  58   b  are properly located in the recess  36  when the stops  60   a ,  60   b  engage. 
     In the embodiment described, each stop  60   a ,  60   b  is generally L-shaped, having opposed distal surfaces  62   a ,  62   b  which will engage with each other in the closed position. Of course, different forms of stop may be provided. In this embodiment, both stops  60   a ,  60   b  extend from a respective handle  52   a ,  52   b . In other embodiments, only one stop may extend from a handle  52   a ,  52   b , the other stop being formed as a stop surface on the handle  52   a ,  52   b.    
     As can be seen from  FIG. 5 , in this embodiment each handle  52   a ,  52   b  comprises a first section  64   a ,  64   b  arranged generally parallel to the first section  64   a ,  64   b  of the other handle  52   a ,  52   b  and an angled section  66   a ,  66   b  extending therefrom to the pivot  54 . The stops  60   a ,  60   b  extend from the angle sections  66   a ,  66   b  and are cranked such that the stop surfaces  62   a ,  62   b  thereof are generally parallel when they engage one another. 
     As can also be seen from  FIG. 5 , each plug gripping portion  56   a ,  56   b  comprises a proximal portion  68   a ,  68   b  attached to its respective handle  52   a ,  52   b  at the pivot  54  and a distal portion  70   a ,  70   b  comprising the outwardly projecting tooth  58   a ,  58   b . As the handles  52   a ,  52   b  are spaced laterally along the pivot axis P, the plug gripping portions  56   a ,  56   b  are shaped such that the proximal portions  68   a ,  68   b  and distal portions  70   a ,  70   b  are offset laterally from one another in the opposite direction so that the distal portions  70   a ,  70   b  of the plug gripping portions  56   a ,  56   b  align back to back when the handles  52   a ,  52   b  are spaced apart, thereby assuring that the teeth  58   a ,  58   b  are aligned. The proximal portions  68   a ,  68   b  and  70   a ,  70   b  may therefore, as shown, be joined by an angled section  72   a ,  72   b.    
     Having described the plug  20  and tool  50 , removal of a plug  20  from a bore  16  will now be described. 
     Firstly, with the tool  50  in the “closed” position shown in  FIG. 5 , the plug engaging portions  56   a ,  56   b  are inserted into the plug  20  as shown in  FIG. 6 . The tool  50  is inserted to such a depth that the teeth  58   a ,  58   b  lie opposite the recess  36 . 
     The handles  52   a ,  52   b  are then moved together as indicated by arrow A in  FIG. 6 . This will cause the plug gripping portions  56   a ,  56   b  to pivot apart from one another, as shown schematically by the arrow B in  FIG. 7 . This moves the teeth  58   a ,  58   b  into the recess  36  as shown in  FIG. 7 . The movement of the teeth  58   a ,  58   b  is limited by the stops  60   a ,  60   b  coming into engagement with each other. This will indicate to the user that the teeth  58   a ,  58   b  are fully engaged in the recess  36  and that the plug  20  may then be removed. 
     To remove the plug  20 , the user pulls on the handles  52   a ,  52   b , and possibly also twists the tool to loosen the plug  20 . Once the plug  20  has been removed (as shown in  FIG. 8 ) it may be discarded. The filter  14  may then be removed, for example using a hook-like tool and the relevant port  10 ,  12  cleaned if necessary. A new filter  14  may then be placed in the bore  16  and a new plug  20  press fitted into the bore  16  to retain the filter  14 . 
     The above described embodiments arrangement offers significant advantages. Firstly, they may allow easy replacement of a filter  14  without the need to return the servovalve  2  to the manufacturer. This is both attractive in terms of time and cost. The tool  50  also allows easy and consistent gripping of a plug  20  to facilitate its removal. The use of an annular recess  36  is potentially advantageous as it will allow the tool  50  to be engaged in the recess in any angular orientation, facilitating removal of the plug  20 . 
     It will be appreciated that the above embodiments are exemplary only and that modifications thereto may be made within the scope of the disclosure.