Abstract:
A filter assembly for a fluid flow system includes a filter housing, a housing inlet to allow the fluid flow into the filter housing and a housing outlet to allow the fluid flow to exit the filter housing. A filter element is located in the filter housing to collect contaminants from the fluid flow. A pressure sensor is located to measure a pressure drop across the filter element. The pressure sensor includes at least one sense line extending into an interior volume of the filter housing. A method of monitoring a filter assembly for a fluid flow system includes positioning a pressure sensor at a filter assembly, extending at least one sense line from the pressure sensor into an internal volume of a filter housing of the filter assembly, and measuring a pressure drop across a filter element of the filter assembly via the pressure sensor.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to fluid flow systems. More particularly, the present disclosure relates to fluid pressure detection in aircraft fuel and/or oil distribution systems. 
         [0002]    Aircraft fuel and oil distribution systems typically incorporate external gear pumps to urge flow of fuel or oil through the systems. The external gear pump, however, is often the source of a pressure ripple, an oscillation generated by the periodic meshing and unmeshing of the teeth of the external gear pump. An operating external gear pump can expose a fluid system to this oscillating pressure both on the inlet and outlet sides of the pump. Further, while discussed herein with regard to external gear pumps, pressure ripple effects often also exist in systems utilizing centrifugal pumps or positive displacement pumps. Both flow and pressure ripples exist with these pumps, but it is the pressure ripple that can be very problematic to components within a fluid system. 
         [0003]    Typically to protect a fluid system, and in particular the pump(s), a filtration system is employed to remove harmful contaminants from the fluid flow that could damage fluid system components. The filtration system usually incorporates a filter element that acts as a barrier to collect any contaminants that are blocked by the filter. A clean filter will cause a small pressure drop for fluid to pass through it. As the filter collects contaminants during the regular operation of the fluid system, this pressure drop will increase. If not monitored and actively managed, the filter could become sufficiently blocked to the point which it could block a significant amount of flow thus causing the pump to be too starved of fluid to properly function. 
         [0004]    Many conventional fluid systems include a bypass circuit function for this scenario, in which when flow through the filter is sufficiently blocked, fluid will bypass the filter entirely, so to not impede pump operation and system function. This solution, however, means allowing contaminated fluids to be passed into the system and this is typically undesirable for normal operation. Further, unwanted bypass events may occur when the fluid is at a low temperature (i.e. high viscosity) resulting in an increased pressure drop across the filter sufficient enough to actuate a bypass valve. Such events also allow unfiltered flow past the filter. 
         [0005]    To manage this, the pressure drop across the filter element is usually monitored. This is typically accomplished by use of a delta-pressure measurement from a single sensor as this arrangement tends to be more accurate than the use of two absolute pressure sensors. Managing the pressure drop when a filter element collects material and increases its pressure drop usually means that the filter element needs to be a maintainable/replaceable component. This service requirement drives the design of a filter bowl or manifold to allow quick and easy removal and replacement of the contaminated filter. 
         [0006]    A schematic view of a typical fluid flow system  100  is shown in  FIG. 1 . The fluid flow system  100  includes a pump element  102  and a filter assembly  104  located fluidly upstream of the pump element  102 . A fluid input line  106  directs a fluid flow into the filter assembly  104 , where the fluid flow passes through a filter element  108  and exits the filter assembly  104  at a fluid output line  110 . A delta pressure sensor  112  is utilized to measure the pressure drop across the filter assembly  104 . The delta pressure sensor  112  senses pressure of the fluid flow upstream of the filter assembly  104  via an upstream sense line  114 , located at the fluid input line  106 . Further, the delta pressure sensor  112  senses pressure of the fluid flow downstream of the filter assembly  104  via a downstream sense line  116 , located at the fluid output line  110 . Thus, the delta pressure sensor  112  measures the pressure drop across the filter assembly  104  indirectly via sense lines  114 ,  116  located remotely from the filter assembly  104 . 
         [0007]    Fluid pressure sensors are notoriously unreliable and as such these parts are designed to be accessible to be readily removed and replaced as needed. As a result the delta pressure sensor  112  may be located at a long distance away from the filter assembly  104 . As such, the sense lines  114 ,  116  are added to connect the remotely located delta pressure sensor  112  to the filter assembly  104 . These long sense lines  114 ,  116  between the fluid components couple the measurement of the pressure drop across the filter to a pressure that the sensor can measure in a remote location. These sense lines  114 ,  116  can prove problematic as they may be very long. An increase in the length of these sense lines  114 ,  116  may result in an undesirable system dynamic response that can result in physical damage to the sensor and signal distortion. 
         [0008]    Typical fluid filter design that allows the filter element  108  to be readily maintained drives the pressure sensor sense lines ports not to be located at the filter assembly  104 . Location of the delta pressure sensor&#39;s sense lines  114 ,  116  at the inlet or outlet port of fluid filter can also be problematic. The fluid filter inlet and outlet ports can contain physical features that can result in the sudden expansion or contraction of the flow. Pressure sensor sense lines  114 ,  116  located in the boundary layer or wake flow can result in the measurement of pressure that is not representative of the true pressure drop across the filter assembly  104 . This flow may also be turbulent and could also act as a cyclic pressure fluctuation similar to pressure ripple as mentioned from pump elements  102  within the fluid system  100 . Incorrect location of the sense lines  114 ,  116  may result in an inaccurate pressure drop measurement and also undesirable system dynamic response. 
       SUMMARY 
       [0009]    In one embodiment, a filter assembly for a fluid flow system includes a filter housing, a housing inlet to allow the fluid flow into the filter housing and a housing outlet to allow the fluid flow to exit the filter housing. A filter element is located in the filter housing to collect contaminants from the fluid flow. A pressure sensor is located to measure a pressure drop across the filter element. The pressure sensor includes at least one sense line extending into an interior volume of the filter housing. 
         [0010]    Additionally or alternatively, in this or other embodiments the measured pressure drop is indicative of an amount of blockage of the filter element due to contaminants collected at the filter element. 
         [0011]    Additionally or alternatively, in this or other embodiments the pressure sensor is located at the filter housing. 
         [0012]    Additionally or alternatively, in this or other embodiments the housing inlet and the housing outlet are located at a first end of the filter housing, and the at least one sense line extends into the interior volume at a second end of the filter housing opposite the first end. 
         [0013]    Additionally or alternatively, in this or other embodiments the pressure sensor includes a first half-bridge pressure sensor and a second half-bridge pressure sensor. The first half-bridge pressure sensor and the second half-bridge pressure sensor are operably connected to output a pressure drop across the filter element. 
         [0014]    Additionally or alternatively, in this or other embodiments the pressure sensor includes a first absolute pressure sensor and a second absolute pressure sensor. The first absolute pressure sensor and the second absolute pressure sensor are operably connected to output a pressure drop across the filter element. 
         [0015]    In another embodiment, a fluid flow system includes a fluid pathway, a pump element located at the fluid pathway to urge a fluid flow through the fluid pathway and a filter assembly located at the fluid pathway upstream of the pump element relative to a direction of fluid flow through the fluid pathway. The filter assembly includes a filter housing, a housing inlet connected to the fluid pathway to allow the fluid flow into the filter housing from the fluid pathway and a housing outlet connected to the fluid pathway to allow the fluid flow to exit the filter housing to the fluid pathway. A filter element is located in the filter housing to collect contaminants from the fluid flow. A pressure sensor is positioned to measure a pressure drop across the filter element. The pressure sensor includes one or more sense lines extending into an interior volume of the filter housing. 
         [0016]    Additionally or alternatively, in this or other embodiments the measured pressure drop is indicative of an amount of blockage of the filter element due to contaminants collected at the filter element. 
         [0017]    Additionally or alternatively, in this or other embodiments the pressure sensor is located at the filter housing. 
         [0018]    Additionally or alternatively, in this or other embodiments the housing inlet and the housing outlet are positioned at a first end of the filter housing, and the at least one sense line extends into the interior volume at a second end of the filter housing opposite the first end. 
         [0019]    Additionally or alternatively, in this or other embodiments the pressure sensor includes a first half-bridge pressure sensor and a second half-bridge pressure sensor. The first half-bridge pressure sensor and the second half-bridge pressure sensor are operably connected to output a pressure drop across the filter element. 
         [0020]    Additionally or alternatively, in this or other embodiments the pressure sensor includes a first absolute pressure sensor and a second absolute pressure sensor. The first absolute pressure sensor and the second absolute pressure sensor are operably connected to output a pressure drop across the filter element. 
         [0021]    Additionally or alternatively, in this or other embodiments the pump element is an external gear pump. 
         [0022]    Additionally or alternatively, in this or other embodiments the fluid flow system is a fuel system for an aircraft. 
         [0023]    Additionally or alternatively, in this or other embodiments the fluid pathway extends from a fuel tank to an aircraft engine. 
         [0024]    In yet another embodiment, a method of monitoring a filter assembly for a fluid flow system includes positioning a pressure sensor at a filter assembly, extending at least one sense line from the pressure sensor into an internal volume of a filter housing of the filter assembly, and measuring a pressure drop across a filter element of the filter assembly via the pressure sensor. The measured pressure drop is indicative of an amount of blockage of the filter element due to contaminants collected at the filter element. 
         [0025]    Additionally or alternatively, in this or other embodiments the measured pressure drop is compared to a selected threshold, and maintenance or replacement operations are performed on the filter assembly if the measured pressure drop exceeds the threshold. 
         [0026]    Additionally or alternatively, in this or other embodiments a first pressure is measured via a first half-bridge pressure sensor disposed at the filter housing, and a second pressure is measured via a second half-bridge pressure sensor disposed at the filter housing. A difference between the first pressure and the second pressure define the pressure drop across the filter element. The first half-bridge pressure sensor and the second half-bridge pressure sensor together define the pressure sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0028]      FIG. 1  is a schematic view of a typical fluid flow system; 
           [0029]      FIG. 2  is a schematic view of an embodiment of a filter and pressure monitor system for a fluid flow system of an aircraft; 
           [0030]      FIG. 3 a    is a graphical representation of pressure ripple effects of the typical prior art system; 
           [0031]      FIG. 3 b    is a graphical representation of effects of the presently disclosed system; 
           [0032]      FIG. 4  is a schematic view of another embodiment of a filter and pressure monitor system for a fluid flow system of an aircraft; and 
           [0033]      FIG. 5  is a schematic view of yet another embodiment of a filter and pressure monitor system for a fluid flow system of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Referring now to  FIG. 2 , illustrated is a portion of a fluid flow system  10 , for example, a fuel system or oil system for an aircraft or other application. The fluid flow system  10  includes a fluid pathway  12  and a pump element  14  disposed at the fluid pathway  12  to urge a fluid, for example, fuel or oil, along the fluid pathway  12 . In some embodiments, such as shown, the pump element  14  is an external gear pump, while in other embodiments the pump element  14  may be, for example, a centrifugal pump or a positive displacement pump. The fluid pathway  12  may, for example, convey a flow of fuel from a fuel tank  16  to an aircraft engine  18 . 
         [0035]    A filter assembly  20  is located along the fluid pathway  12  upstream of the pump element  14 , relative to a direction of fluid flow through the fluid pathway  12 . The filter assembly  20  is utilized to remove contaminants from the fluid flow to protect the pump element  14  and other downstream components, for example, aircraft engine  18  components from damage caused by contaminants in the fluid flow. The filter assembly  20  includes a filter housing  22  having a housing inlet  24  and a housing outlet  26 . The housing inlet  24  and the housing outlet  26  are connected to the fluid pathway  12  to allow the fluid flow to flow into and out of the filter housing  22  via the housing inlet  24  and the housing outlet  26 . In some embodiments, the filter housing  22  includes a housing sidewall  28  and further includes a housing end cover  30  located at an end of the housing sidewall  28 . In some embodiments, the filter housing  22  is substantially cylindrical in shape. The end cover  30  is removable from the housing sidewall  28  via, for example, a threaded interface  32  between the housing sidewall  28  and the end cover  30 . Removing the end cover  30  allows for access to an interior of the filter housing  22  for maintenance or replacement of a filter element  34  located in the filter housing  22 . In operation, fluid flow enters the filter housing  22  via the housing inlet  24  and flows across the filter element  34 , which captures contaminants in the fluid flow and removes them from the fluid flow. The fluid flow proceeds out of the filter housing  22  via the housing outlet  26  and toward the pump element  14 . 
         [0036]    A relatively clean filter element  34  will cause a relatively small pressure drop across the filter element  34 , while as the filter element  34  collects contaminants the pressure drop across the filter element  34  will increase. If not monitored and actively managed, the filter element  34  may block a significant amount of the fluid flow thus starving the pump element  14  of fluid. The pressure drop across the filter element  34  is monitored by a delta pressure sensor  36  located at the filter housing  22 , in some embodiments, embedded in the housing sidewall  28  or the end cover  30 . The pressure drop signal detected by the delta pressure sensor  36  is output via an output harness  48 . The delta pressure sensor  36  includes sense lines  44  which extend into an interior volume  50  of the filter assembly  20  to directly measure the pressure drop across the filter element  34 . The delta pressure sensor  36  senses a pressure drop of the fluid flow across the filter element  34 , with a pressure drop exceeding a preselected threshold indicative of the need to perform maintenance on or replacement of the filter element  34 . It is desired to locate the sense lines  44  within the interior volume  50  and as far away from the turbulent flow of the housing inlet  24  and the housing outlet  26  as possible. Further, the relatively large volume of fluid in the interior volume  50  attenuates any pressure ripple typically observed when the sense lines are located elsewhere. Locating the delta pressure sensor  36  at the filter housing  22  allows for direct measurement of the pressure drop across the filter element  34 , compared to indirect measurement schemes of the prior art, and eliminates long sense lines and sense lines at the inlet and outlet ports of the filter assembly of such indirect measurement schemes. 
         [0037]    Further, as shown in  FIG. 2 , locating the delta pressure sensor  36  at the filter housing  22  shields the measurement of pressure drop across the filter element  34  from pressure ripples in the fluid flow caused by the pump element  14  as shown in  FIGS. 3 a    and  3   b.    
         [0038]    Pump elements  14 , such as external gear fuel pumps can create both flow and pressure oscillations. These oscillations are typically related to the pump element  14  shaft rotational speed, thus varying the forced oscillation frequency within the fluid system. Flow lines, such as fluid pathway  12 , as well as sense lines can have dynamics that react adversely to these perturbations, corrupting the sensed signal due to nonlinear effects of the flow passages and sense lines, and sense line/sensor volume combination, as well as frequency resonances and their unwanted effects. As a consequence, one or more sense lines may be affected over the entire fluid system&#39;s operating range. 
         [0039]    Oscillation can couple with the natural frequency of the sense line thus leading to amplified cyclic pressures within a sense line. This can result in erroneous pressure readings that can skew the detected pressure signal. Peak pressures due to spikes, and in particular, the resulting amplification by system dynamics, can damage parts in the fluid flow system  10 . 
         [0040]    Locating delta pressure sensor  36  at the filter housing  22 , can optimize flow path dynamics and also can provide the means to measure pressures that have much reduced levels of signal perturbations. 
         [0041]    A simulation of the effects of the location of the delta pressure sensor is shown in  FIGS. 3 a  and 3 b   . In  FIG. 3 a   , the data show delta-pressure signals from a typical pressure sensor with sense lines located remotely from the filter assembly and represented at  38 . In  FIG. 3 b   , delta pressure signals from a delta pressure sensor with sense lines extending into the interior volume  50  of the filter assembly  20 , are represented at  40 . The delta-pressure signals  38 ,  40  (arbitrary units) are plotted along the respective ordinates with identical scaling. Both delta-pressure signal curves are plotted with respect to fuel pump speed (arbitrary units) along the respective abcissas with identical scaling for a true comparison. The advantages of the location of the pressure filter and sense lines  44  at the filter housing  22  (as shown in  FIG. 2 ) indicate that most of the unwanted pressure ripple effects have been effectively attenuated by the presence of the large volume of fluid present at the filter housing  22 . The analysis shows that in essence this added volume acts as a “settling chamber” allowing clear pressure signal detection by the delta pressure sensor  36  located in the filter housing  22  as shown in  FIG. 2 . Additionally, the analysis shows that minimized sense line length decouples the response of the sense lines from matching the pressure ripple frequency resulting in no amplification of the attenuated pressure ripple in the filter housing volume. 
         [0042]    Referring now to  FIG. 4  another embodiment of a fluid flow system  10  is shown. In this embodiment, delta pressure sensor  36  includes two half-bridge pressure sensors  42   a ,  42   b . First half-bridge pressure sensor  42   a  is located at housing end  52 , with a first sense line  44   a  extending through housing end  52  to the interior volume  50  of the filter housing  22 . Similarly, second half-bridge pressure sensor  42   b  is located at the housing sidewall  28 , with a second sense line  44   b  extending through the housing sidewall  28  into the interior volume  50  of the filter housing  22 . The two half-bridge pressure sensors  42   a ,  42   b  are connected via a pigtail harness  46  and the measured pressures are summed at pressure sensor  42   a  to arrive at a delta pressure measurement across the filter element  34 . The half-bridge pressure sensors  42   a ,  42   b  are further connected to an electronic engine control (not shown) to which the delta pressure across the filter element  34 , the difference between the pressures measured by the two half-bridge pressure sensors  42   a ,  42   b , is output via an output harness  48  connected to either of the two half-bridge pressure sensors  42   a ,  42   b . This approach minimizes the length of both sense lines  44   a ,  44   b , while in embodiments utilizing a single delta pressure sensor  36 , one sense line will necessarily be longer than the other sense line. As an alternative to utilizing two half-bridge pressure sensors  42   a  and  42   b , two absolute pressure sensors may be utilized in a similar way. In operation, fluid flow enters the filter housing  22  via the housing inlet  24  and flows across the filter element  34 , which captures contaminants in the fluid flow and removes them from the fluid flow. The fluid flow proceeds out of the filter housing  22  via the housing outlet  26  and toward the pump element  14 . 
         [0043]    Referring now to the embodiment of  FIG. 5 , it is proposed to locate the delta pressure sensor  36  at a location of the filter housing  22  as far away as practicable from the filter housing inlet  24  and the housing outlet  26 . Thus the delta pressure sensor&#39;s  36  associated sense lines  44   a ,  44   b  will be far away from forced flow disturbances present at the housing inlet  24  and the housing outlet  26  due to sudden contraction and expansion, respectively, of the fluid flow at these locations, thus improving accuracy of the delta pressure measurement. As shown in  FIG. 5 , in an embodiment, the housing outlet  26  is located at end cover  30 , and the filter housing inlet  24  is located at the filter housing sidewall  28 , at a location nearer to the end cover  30  than to the housing end  52 . The delta pressure sensor  36  is located at the housing end  52 , with the associated sense lines  44   a  and  44   b  located at the housing end  52  and the housing sidewall  28  nearer to the housing end  52  than to the end cover  30 . 
         [0044]    Benefits of the delta pressure sensor arrangement disclosed herein include, but are not limited to, allowing direct measurement of delta pressure across the filter element  34 , reducing sense line length compared to prior systems, reducing inaccuracies by avoiding measurement at or near the inlet port  24  and outlet port  26 , and reducing pressure signal distortion due to the pressure ripples in the operation of the pump element  14 . Further, the arrangement reduces the potential for damage to pressure sensors as they are now isolated from pressure ripple effects. 
         [0045]    While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate in spirit and/or scope. Additionally, while various embodiments have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.