Abstract:
A filter for a fluid system is designed to capture and retain large debris. The filter includes a structure that captures the debris, and due to the design, configuration, or conformation of the structure, the structure makes it difficult for the captured debris to break loose and thereby prevents repeated impact of the debris with a filter surface. Different embodiments form regions of reduced turbulence such as an angled annular wall, angled wall, or baffles, or a contoured basket in an inlet region that captures large debris, and retains the debris in the structure of the filter.

Description:
BACKGROUND 
       [0001]    This application claims the priority benefit of U.S. provisional application Ser. No. 61/993,690, filed May 15, 2014, the disclosure of which is expressly incorporated herein by reference. 
     
    
       [0002]    The present disclosure relates to an apparatus, filter, or strainer (hereinafter referred to as a filter). The disclosure finds particular application as a filter for fluid flow, such as filtering fuel in a fuel pump environment, and is directed to entrapping or retaining large debris that enters the filter to minimize the potential for damage to the filter and/or downstream of the filter. It may find application in related environments and applications that encounter similar conditions. 
         [0003]    Many main fuel pumps contain a filter to protect the high pressure stage, typically referred to as an interstage strainer. The purpose of the filter is to collect and retain large debris. Often the filtration level is fairly course as the main fuel filter in the system is designed to collect small particulates. The design of these filters is usually a large cylindrical screen with significant internal volume to hold large debris, e.g., a bolt, a nut, a washer, etc. When a large item is introduced into the filter, the flow velocity, engine vibration, and pump vibration cause the item to move within the filter and potentially could eventually wear through as result of repeated impact with the filter surface. 
         [0004]    Consequently, a need exists for an improved filter that captures and immobilizes the debris, thus preventing motion that could potentially lead to wear through of the filter screen. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    There is provided a filter for a fluid system that is designed to capture and retain large debris. 
         [0006]    The filter includes a structure that captures the debris, and due to the design, configuration, or conformation of the structure, the structure makes it difficult for the captured debris to break loose and thereby prevents repeated impact of the debris with a filter surface. 
         [0007]    A primary advantage of the present disclosure is the ability to not only capture but retain debris and thereby subsequently limit movement of the debris. 
         [0008]    Another benefit resides in the ability to tune the structure. 
         [0009]    Still another advantage is found in accommodating the improved filter in the same footprint of existing filters. 
         [0010]    Additional benefits and advantages of the present disclosure will become more apparent from reading and understanding the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a longitudinal cross-sectional view of a first embodiment of the present disclosure. 
           [0012]      FIG. 2  is a view taken generally along the lines  2 - 2  of  FIG. 1 . 
           [0013]      FIG. 3  is a longitudinal cross-sectional view of a second embodiment of the present disclosure. 
           [0014]      FIG. 4  is a view taken generally along the lines  4 - 4  of  FIG. 3 . 
           [0015]      FIG. 5  is a longitudinal cross-sectional view of a third embodiment of the present disclosure. 
           [0016]      FIG. 6  is a longitudinal cross-sectional view of a fourth embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The use of interstage filters or strainers is common in aircraft engine fuel systems as a last chance filter upstream of a positive displacement high-pressure pump stage and that protects the pump stage from large debris. These filters are typically a high micron rated screen or mesh formed in a cylindrical shape with significant internal volume to capture large debris such as bolts, washers, etc. Fluid flow typically enters through one end of the cylinder and exits in a generally radial direction through the screen. When an item enters the filter, the item will continue to move due to flow stream currents and vibration due to the engine and pump. This motion could cause the item to repeatedly impact the screen causing wear and permanent damage. Eventually, this wear could lead to potential failure of the screen. Although it has been proposed to make the screen more durable, e.g., thicker, it is believed that such a solution would only extend the time for wear to occur. 
         [0018]    The present disclosure proposes to resolve the problem of large debris in connection with a filter of this type by preventing the debris or item from moving once the debris has entered the filter. One design as shown in  FIGS. 1 and 2  employs a design intended to isolate large debris from a highly motivating turbulent flow field so that the large debris becomes immobile. More specifically, a filter  100  is typically used to capture large debris (not shown). A hollow housing or screen  102  is shown as a generally hollow cylindrical screen that is open at first and second ends  104 ,  106 , and forms a significant internal volume or internal cavity  108  to hold large debris. The housing  102  has openings  110  that extend radially therethrough to provide a high micron rate cylindrical screen or mesh. The openings  110  are of a predetermined size and typically uniformly spaced along the housing  102 . 
         [0019]    A generally annular, partially conical or frusto-conical wall  120  is positioned in the internal volume  108 , preferably nearer the outlet end  106  and spaced from the inlet end  104 . The precise location of the wall  120  may vary, but the wall is intended to separate the internal volume  108  into first and second portions  108   a ,  108   b  shown upstream and downstream of the wall  120 . Preferably the wall  120  is secured about an outer periphery or outer circumference  122  to an inner surface of the screen  102 . Any conventional manner of securing the wall  120  and screen  102  may be used. A through opening  124  is provided in the wall  120  located at a generally central location in this arrangement and the through opening is also axially spaced downstream from the outer circumference  122  and thereby the wall is generally configured as a symmetrical, generally frusto-conical shape, although one skilled in the art will recognize that other shapes or conformations may be used without departing from the scope and intent of the present disclosure. For instance, the opening  124  need not be centered in the wall  120 , and the opening need not be located downstream of the remainder of the wall. 
         [0020]    The internal volume/cavity first portion  108   a  receives flow directly from inlet end or inlet passage  130 . The flow at the inlet end  130  generally proceeds axially into the cavity  108  and then exits radially through the screen  102 , the flow is generally turbulent and thus creates the issues associated with large debris as described above. In an effort to limit the impact of the flow on large debris that enters the cavity  108 , the wall  120  creates a cavity portion  108   b  downstream of the wall (and likewise downstream of the cavity first portion  108   a ) that has a reduced level of turbulence. In this manner, past experience with large debris (not shown) helps to determine a suitable dimension of the opening  124  to receive the potential large debris therethrough and allow the debris to become entrapped/retained/isolated in the cavity portion  108   b . The orientation of the opening  124  downstream of the outer periphery of the wall  120  also aids in directing the debris through the opening, and creates a cavity portion  108   b  of reduced turbulence that reduces the possibility that the debris, once the debris has entered into the cavity portion  108   b , is able to re-enter the cavity portion  108   a.    
         [0021]      FIGS. 3 and 4  use many of the same design principles in filter  200  that receives flow from the inlet end  230  and cavity portion  208   a , and subsequently prevents or limits the movement of the debris once the debris has entered into cavity portion  208   b . Here, wall  220  creates first and second cavity portions  208   a ,  208   b  and the wall has a different conformation than that shown and described in connection with  FIGS. 1 and 2 . Specifically, the wall  220  has the general shape of a truncated circle, i.e., the substantially circular shape is cut off along a chord, that forms an opening  224  that is offset from the central portion of the cavity and instead is positioned along one edge region of the inner periphery of the screen  202  (to the right-hand side as illustrated in  FIG. 3 ). Likewise, the wall  220  is inclined or disposed at an angle relative to the longitudinal axis of the housing  202  so that a connection region of the wall along an outer peripheral portion thereof with the screen is upstream of the opening  224 . Again, this angular positioning of the wall  220  aids in directing the debris through the opening  224 , and creates a cavity portion  208   b  of reduced turbulence that reduces the possibility that the debris, once the debris has entered into the cavity portion  208   b , is able to re-enter the cavity portion  208   a.    
         [0022]    Another embodiment is shown in  FIG. 5 . Particularly, filter  300  uses baffles  320  that extend or project inwardly from an inner surface of the screen or housing  302  to reduce the motivating turbulent flow field by the incorporation of the baffle plates in the screen body  302 . In  FIG. 5 , the baffles  320  extend radially inward from an inner surface of the screen  302 , and more particularly in this arrangement, the baffles extend substantially perpendicular to the inner surface of the screen. Moreover, the baffles  320  are circumferentially continuous or discontinuous and each extend radially inward into the cavity  308  approximately the same dimension, and are equally spaced in an axial direction (i.e., in an axial direction defined between the inlet end  304  and the outlet end  306 ), although it is also contemplated that the baffles can be oriented at a non-perpendicular angle, may extend inwardly into the cavity by different dimensions, and may have variable axial spacing as desired for a particular set of flow parameters. The baffles  320  create regions of decreased turbulence in the regions of the baffles so that debris entering into the lower turbulent regions will have a tendency to remain in such regions. 
         [0023]      FIG. 6  illustrates yet another design in which a basket  420  is disposed in the inlet region  404  of the filter  400 . The flow in the inlet region  404  is generally uniform (i.e., not turbulent or at least less turbulent than the flow in the cavity  408  where the fluid transitions between axial to radial flow, and even recirculates through the openings  410  in the screen  402 ). Preferably the basket  420  has a contoured shape that does not adversely impact the generally laminar flow in this region. As a result, large debris captured in the basket  420  does not have the same tendency to repeatedly bounce against the inner surface of the basket and cause undesired wear as the debris might encounter when captured in a turbulent flow region. 
         [0024]    This written description uses examples to describe the disclosure, including the best mode, and also to enable any person skilled in the art to make and use the disclosure. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Moreover, this disclosure is intended to seek protection for a combination of components and/or steps and a combination of claims as originally presented for examination, as well as seek potential protection for other combinations of components and/or steps and combinations of claims during prosecution.