Abstract:
A fluid level indicator ( 22 ) indicating the level of a fluid ( 14 ) in a chamber ( 12 ) having a piston ( 16 ) is disclosed. The fluid level indicator ( 12 ) has a housing ( 24 ) that is positioned adjacent to the chamber ( 12 ). A plurality of magnetic pins ( 28, 38 ) are moveably disposed within the housing ( 24 ). The magnetic pins ( 28, 38 ) have a first position and a second position. At least one of the magnetic pins ( 38 ) shifts from the first position to the second position when the piston ( 16 ) is aligned therewith, thereby indicating the position of the piston ( 16 ) within the chamber ( 12 ) and indicating the level of fluid ( 14 ) within the chamber ( 12 ).

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to the field of fluid level indicating devices and, in particular to, a fluid level indicator that utilizes a plurality of magnetic pins to visually indicate fluid level in a fluid containing chamber having a piston. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the invention, its background will be described with reference to a hydraulic chamber in an aircraft as an example. 
     In an aircraft hydraulic system, hydraulic fluid supply and pressure is maintained using a hydraulic reservoir. The typical reservoir design incorporates a moving piston in a chamber to accommodate changes in reservoir volume. The reservoir volume will change as a result of temperature fluctuations, system leaks and differential actuator fluid exchange. The piston position in the chamber changes proportional with the change in reservoir fluid level. By measuring the position of the piston in the chamber, the fluid level in the reservoir can be measured. 
     In one system, fluid level may be indicated using a graduated rod attached to the piston that extends outwardly from the chamber. It has been found, however, that the rod must be equal in length to the entire piston travel in order to provide the required fluid level readings. Due to space limitations in many aircrafts, however, using a rod to indicate fluid level in the hydraulic reservoir is impractical. 
     To overcome these space constraints, attempts have been made to design a fluid level indicator for the hydraulic reservoir of an aircraft that does not require additional space next to the reservoir piston. For example, in one design, an indicator tube is mounted adjacent to the hydraulic reservoir that has a floating indicator disposed therein. The floating indicator is tied directly to the piston using a pulley and cabling system. It has been found, however, that like the graduated rod level indicator, having the level indicating device attached directly to the piston may induce failures in the reservoir piston if the level indicating device becomes restricted from moving or jammed. Additionally, it has been found that the accuracy of such devices may be affected by the high vibration, high shock loads and high g-forces experienced in certain aircraft. 
     Therefore, a need has arisen for a fluid level indicator for indicating the level of a fluid in a chamber having a piston. A need has also arisen for such a fluid level indicator that is not physically tied to the reservoir piston. Further, a need has arisen for a such a fluid level indicator that does not require substantial space next to the chamber. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein provides a fluid level indicator for indicating the level of a fluid in a chamber having a piston. The fluid level indicator of the present invention accurately indicates the level of the fluid in the chamber without being physically connected to the piston and without requiring substantial space next to the chamber. Additionally, the fluid level indicator of the present invention is unaffected by high vibration, high shock loads or high g-forces. 
     The fluid level indicator comprises a housing that is positioned adjacent to the chamber. Disposed within the housing are a plurality of magnetic pins. The magnetic pins move between a first position and a second position. Springs bias each of the magnetic pins toward the first position. To overcome the spring bias force, a metallic band is wrapped around the piston such that when the piston is aligned with one of the magnetic pins, that magnetic pin is shifted to the second position. A viewing window is attached to the housing such that the position of the magnetic pins may be viewed therethrough, thereby indicating the position of the piston within the chamber and indicating the level of fluid within the chamber. 
     The viewing window includes indicia specifying the level of fluid in the chamber. The viewing window may be frosted such that magnetic pins in the first position are seen through the viewing window and magnetic pins in the second position are not seen through the viewing window. Alternatively, the viewing window may be clear such that a first color is viewable when the magnetic pins are in the first position and a second color is viewable when the magnetic pins are in the second position. In this embodiment, the magnetic pins each have a polished button attached thereto. 
     In one embodiment, a booster magnet may be added that contacts the metallic band to increase the force attracting the magnetic pins toward the second position when piston is aligned therewith. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, including its features and advantages, reference is now made to the detailed description of the invention taken in conjunction with the accompanying drawings in which like numerals identify like parts and in which: 
     FIG. 1 is a cross sectional view of a fluid level indicator of the present invention attached to a hydraulic fluid chamber; 
     FIG. 2 is a top view of a fluid level indicator of the present invention; 
     FIG. 3 is a cross sectional view of a magnetic pin of a fluid level indicator of the present invention that is aligned with the piston of the hydraulic chamber; 
     FIG. 4 is a cross sectional view of a fluid level indicator of the present invention attached to a hydraulic fluid chamber; 
     FIG. 5 is a top view of a fluid level indicator of the present invention; and 
     FIG. 6 is a cross sectional view of a magnetic pin of a fluid level indicator of the present invention that is aligned with the piston of the hydraulic chamber. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     Referring now to FIG. 1, therein is depicted a reservoir chamber operating a fluid level indicator of the present invention that is generally designated  10 . Reservoir chamber  12  may be any typical chamber for containing a fluid  14  which may be a liquid or gas. As the volume of the fluid  14  changes within the chamber  12 , a piston  16  travels within the chamber  12  as indicated by the arrow  18 . Disposed between the piston  16  and the chamber  12  is a seal  20  that may be a conventional spring energized seal made from butyl rubber or silicon. The chamber  12  is made from a non-magnetic material such as aluminum or plastic and should be selected based upon the required service. Likewise, the piston  16  may be made from a non-magnetic material. 
     Disposed adjacent to the cylinder  12  is the fluid level indicator  22 . The fluid level indicator  22  may be attached to cylinder  12  in a variety of methods. For example, the fluid level indicator  22  may be adhered to the chamber  12  using adhesive. The fluid level indicator  22  has a non-magnetic housing  24  that is preferably a plastic. The housing  24  has a plurality of bores formed therein such as the bore  26 . Disposed within each of the bores is a magnetic pin such as the magnetic pin  28  disposed in the bore  26 . Also disposed within the bores are springs, such as the spring  30  that biases the magnetic pin  28  in the direction away from the cylinder  12  and against a cover  32 . 
     The cover  32  serves as a viewing window through which the user of the fluid level indicator  22  may visually determine the position of the magnetic pins relative to the cover  32 . For example, as best seen in FIG. 2, when the magnetic pins, such as magnetic pin  34 , are biased against the cover  32 , the user would see a dark area  36  indicating contact between the magnetic pin  34  and the cover  32 . Conversely, if a magnetic pin such as the magnetic pin  38  is in the retracted position, the user of the fluid level indicator  22  would see the opened area as indicated at  40 . This may be achieved using a cover  32  that comprises a frosted, transparent material such as a frosted plexiglass. In this case, when a magnetic pin is against the cover  32 , the ambient light is reflected off the upper surface of the magnetic pin  28 , thus allowing the user to view the color of the upper surface of the magnetic pin  28 . Because the frosted cover  32  scatters ambient light, the magnetic pins disappear from view if they are moved away from the cover  32 . 
     Now referring to FIG. 3, the magnetic pin  28  is shown in the retracted position within the bore  26  with the spring  30  in a fully compressed position between the surfaces  42 ,  44 . The magnetic pin  28  is placed in the retracted position due to the magnetic attraction between the magnetic pin  28  and a band  46  that is wrapped around the piston  16 . The band  46  comprises a material that has a suitable attraction to the magnetic pin  28  such as steel. In addition, a booster magnet  48  may be added to piston  16  to boost the attraction between the band  46  and the magnetic pin  28 . 
     In operation, as the piston  16  moves along the path indicated by the arrow  18 , the band  46  becomes aligned with the various magnetic pins. When the band  46  is in alignment with one of the magnetic pins such as magnetic pin  28 , the magnetic pin  28  is attracted to the band  46  and shifts from the extended position against the surface  50  of the cover  32  to the retracted position against surface  52  of the housing  22 . As such, as the piston  16  moves within the chamber  12 , the various magnetic pins are retracted to indicate the level of fluid  14  within the chamber  12  as best seen in FIG.  2 . 
     The cover  32  includes indicia  54  specifying the level of the fluid  14  within the chamber  12 . While FIG. 2 depicts ten percent increments between the indicia  54 , the fluid level indicator  22  actually provides an indication the level of the fluid  14  within the chamber  12  down to five percent increments. Specifically, as the piston  16  moves between two magnetic pins such as the magnetic pin  38  and the magnetic pin  28 , the band  46  along with the booster magnet  48  attract both the magnetic pin  28  and the magnetic pin  38  such that both are retracted. In this case, there would be two open areas such as the open area  40  and the user would average the two values to obtain the accurate reading. For example, if the magnetic pin  28  and the magnetic pin  38  were both retracted, the level of the fluid  14  within the chamber  12  should be read as fifty-five percent. 
     Turning now to FIG. 4, therein is depicted another embodiment of a fluid level indicator coupled to a reservoir chamber that is generally designated  70 . The reservoir chamber  72  has a fluid  74  contained therein and includes a piston  76 . A seal is provided between the chamber  72  and the piston  76  by the seal  78 . The piston  76  has a band  80  wrapped therearound. Attached to the outer surface of the chamber  72  is a fluid level indicator  82 . The fluid level indicator  82  has a housing  84  with a plurality of bores, such as the bore  86 . Disposed within the bores are a plurality of magnetic pins, such as the magnetic pin  88 . The fluid level indicator  82  includes a cover  90  that is preferably a clear plastic. In addition, the fluid level indicator  82  has a fluorescent plastic layer  92  that is disposed beneath the cover  90 . A spring, such as the spring  94 , is disposed within each of the bores to bias the magnetic pins toward the cover  90 . Each of the magnetic pins includes a domed surface such as domed surface  96  of the magnetic pin  88 . The domed surface may be constructed from a polished stainless steel. 
     As best seen in FIG. 5, when a magnetic pin, such as the magnetic pin  98 , is in the extended position, light reflects off of the domed surface  100  as indicated at  102 . When a magnetic pin such as the magnetic pin  88  is in the retracted position, however, light reflects off of the domed surface  96  into the fluorescent plastic layer  92  giving an indication as seen at  104 . Using fluid level indicator  82 , the user may easily view the level of the fluid  74  within the chamber  72  at any angle with respect to the fluid level indicator  82 . 
     As the level of the fluid  74  within the chamber  72  changes and the piston  76  moves in the directions indicated by the arrow  106 , the various magnetic pins are retracted as they become aligned with the band  80  as best seen in FIG.  6 . As such, when band  80  is in alignment with the magnetic pin  88 , the spring  94  is compressed between the surfaces  108  and  110  until the magnetic pin  88  contacts the surface  112  of the housing  84 . When the band  80  moves out of alignment with the magnetic pin  88 , the spring  94  biases the magnetic  88  toward the cover  90  until the domed surface  96  contacts the surface  114  of the cover  90 . As such, the level of the fluid  74  within the chamber  72  is indicated using the fluid level indicator  82 . Using the indicia  116 , as best seen in FIG. 5, the user is quickly able to determine that level. Even though the indicia  116  are shown in increments of ten percent, the fluid level indicator  82  provides resolution down to five percent as the band  80  will attract two magnetic pins when the band  80  is positioned between adjacent magnetic pins. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.