Abstract:
A fuel filter restriction indicating device communicating with the supply of fuel passing from a fuel tank to an internal combustion engine. The indicating device senses a decrease in the supply of fuel drawn through the fuel filter by the engine based upon changes in the amount of vacuum in the negative side of the fuel supply, the amount of restriction being indicated by the movement of an indicating device. A mechanism included in the indicating device senses the movement of the indicating device and progressively locks the indicating device into various indicating positions as the vacuum increases due to an increased restriction of the filter, so that the maximum reading of restriction achieved during engine operation remains visible to the operator or maintenance personnel even after the engine is turned off.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a mechanical filter gauge for determining the filtering capability of a vehicle filter, and in particular to a mechanical gauge for measuring and displaying the functionality of a vehicle&#39;s fuel filter. 
     The improved device of the present invention is used in connection with a fuel filter for internal combustion engines. It is particularly useful for application to trucks, particularly fleet trucks where a reduction in fuel filter changes can lead to significant cost savings. Formerly, to save costs, preexisting air filter gauges, such as those disclosed in U.S. Pat. Nos. 4,369,728 and 4,445,456, were modified to serve as fuel filter gauges, in order to minimize tooling costs and to utilize familiar technology. However, these gauges proved relatively costly, due to the materials needed to withstand fuels. 
     Prior art fuel filter gauges are also larger than necessary. The vacuum range of a plugged fuel filter is about five times higher than for an air filter. This translates into piston forces which are five times higher in the larger size prior art fuel gauge. The additional requirement of handling 20 psi back pressure creates excessive forces in the existing gauge causing damage. 
     Prior art fuel filter gauges also required felt filters in the base in the area of the reset button. However, these felt filters can be inadvertently mispositioned, resulting in leaks. The felt filters could also leak and freeze if the fuel filter gauge was mounted with the push button reset gauge in an upward position. 
     Certain fuel systems include two fuel filters, thereby requiring two fuel filter gauges. These systems have the first filter located prior to a ten psi electric in-line fuel pump, for example, with the second filter positioned between this electric pump and the engine driven pump located adjacent to the engine. The fuel filter gauge located after the first filter but before the first pump will be exposed to suction vacuum only, typically up to 10 in.Hg as the first filter plugs. The second fuel filter gauge attached to the fuel system after the second fuel filter will be exposed to pressure up to 10 psi or the pressure level the in-line electric pump is capable of producing. The second gauge will eventually respond to vacuum created by the engine driven pump when filter restriction due to plugging is great enough to block flow from the in-line pump. Thus the fuel filter gauges must withstand both pressure and vacuum, which has proven problematic for prior art fuel filter gauges. Back pressure can occur in two pump fuel systems and during initial pressurization testing for leaks in the fuel system at the assembly plant. The lock pin mechanism of prior art fuel filter gauges had difficulty withstanding the back pressure force and the prior art diaphragm could reverse fold against the edges of the metal diaphragm retainer causing a cut therefrom and a resulting leak. 
     A gauge of this type preferably indicates the condition of the fuel filter and locks itself in position, permitting determination of the condition of the fuel gauge even when the vehicle engine is not running. In the prior art, however, lock pin forces were concentrated at points that were prone to overload, distortion and breakage at high operating temperatures. 
     Additionally, prior art indicators have not always been easy to fully reset, due in part to poor leverage, high lock force, and high reset spring force, sometimes resulting in a gauge that may give a false, premature signal that a filter requires replacement. This may in turn result in unnecessary filter maintenance. 
     The fuel filter gauge of the present invention overcomes difficulties described above and affords other features and advantages heretofore not available. 
     SUMMARY OF THE INVENTION 
     The fuel filter gauge of the present invention indicates when the fuel filter of an internal combustion engine requires replacement by measuring the performance of the filter by measuring the vacuum in the fuel system of the vehicle. The device gives a gradual reading from a clean filter condition to a dirty filter condition and automatically locks into the highest clogged fuel flow condition experienced during engine operation so that it may be read after shutdown and may also be monitored during engine operation. 
     An object of the invention is to provide a gauge for indicating that a fuel filter for a vehicle with an internal combustion engine requires replacement. It is a further object of this invention to provide such a gauge that is reliable over a long period of time despite constant exposure to engine fuel. 
     It is a further object of the invention to provide such a gauge that is relatively smaller in size, thereby reducing material costs. Reduction in size also results in a smaller diameter diaphragm which greatly reduces the piston effective area and the associated calibration spring force by the square of the diameter. 
     It is a further object of the invention to provide such a gauge that is easily reset after each filter change. It is a further object that this fuel filter gauge be relatively small in size, and made of relatively inexpensive materials to minimize manufacturing costs. It is an important operating objective of this invention that the fuel filter gauge be capable of handling at least 20 psi back pressure. 
     It is a further object of the invention that a breather filter design be employed that eliminates the need for a felt filter. It is also an object of the invention that the fuel filter gauge be positionable with the push button reset switch in an upward position without risk of damage from outside contaminants entering the lock mechanism of the fuel filter gauge. 
     It is yet a further object of the invention that the fuel filter gauge be capable of locking itself in position when the engine is turned off, indicating the status of the fuel filter even after the engine has stopped running. An additional objective of this invention is to provide a fuel filter gauge that is easy to reset when a used filter has been replaced. 
     It is yet a further object of this invention to provide a fuel filter gauge capable of withstanding both pressure and vacuum forces. It is also an object that the internal locking mechanism and diaphragm assembly of the gauge must be able to withstand the pressure reversals and forces encountered in the fuel system. 
     Other objects and advantages of the invention will become apparent from the following detailed description and from the appended drawings in which like numbers have been used to describe like parts throughout the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a fuel intake system for an internal combustion engine incorporating the fuel filter gauge of the present invention; 
     FIG. 2 is a perspective view of the fuel filter gauge of the present invention; 
     FIG. 3 is an exploded view of the indicating device illustrated in FIG. 2; 
     FIG. 4 is a vertical section view of the indicating device taken along line  4 — 4  of FIG. 2; 
     FIG. 5 is a partial section view similar to FIG. 4, showing the lockpin and lock fingers in the locking position; 
     FIG. 6 is a partial section view similar to FIG. 5, showing the interaction between the lockpin, lock fingers and the reset push-button; 
     FIG. 7 is a detailed partial side view of the lockpin; and 
     FIG. 8 is a bottom perspective view of the base cap. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to the drawings, and in particular to FIGS. 1 and 2, the fuel filter gauge is generally indicated by reference numeral  10 . As shown schematically in FIG. 1, in a typical fuel system, including a water separator filter F 1  and a main fuel filter F 2 , it is preferable to include two fuel filter gauges  10 . The fuel system also preferably includes fuel tank T, fuel heater H, a 10 psi electric in-line fuel pump P 1 , and an engine having a fuel pump P 2  driven thereby. Fuel travels through a fuel line L from fuel tank T to the engine. 
     Fuel filter gauge  10  includes a preferably transparent housing  12 , a base cap  14 , a calibration spring  16  and an indicator cup  18 , a preferably generally cup-shaped member. Housing  12  is preferably sonic welded to base cap  14 , although the use of adhesives, heat, and threaded attachment means may also be envisioned for achieving fixed attachment between the two components. Other main components include the indicator/lock pin  20 , the diaphragm  22 , the reset cover  24  and the reset button  26 . A label liner  28  having delineations  30  is positioned within housing  12 . As indicator cup  18  changes position, as shall be shown, its position relative to delineations  30  indicates the condition of the fuel filter that is being monitored. As shown in FIG. 4, housing  12  preferably includes a female thread portion  13  for threaded engagement with a fitting connecting fuel filter gauge  10  to fuel line L. Threaded portion  13  is preferably a ½-20 UNF thread, which is very robust and difficult to strip. 
     Referring to FIG. 4, indicator cup  18  preferably includes a guide stem  32  that is slidably received within housing guide bore  34 . Guide stem  32  includes an angled or rounded tip  36  that aids entry into guide bore  34  of housing  12 . Guide stem  32  helps prevent tilt of indicator cup  18  and the potential for lockpin  20  to become disengaged from base cap  14 , as shall be seen. Indicator cup  18  preferably also includes a shoulder  38  that contacts the end of housing guide bore  34  to limit movement of indicator cup  18 . Calibration spring  16  bears against the end surface  15  of housing  12  on one end, and against indicator cup  18  on the other. Calibration spring  16  preferably bears against the calibration spring seat  40  of indicator cup  18 . The outer edge  42  of indicator cup  18  is positioned with respect to delineations  30  of label liner  28  to give a clear, visual indication of the condition of the fuel filter being monitored, by indicating the vacuum level of fuel line L. 
     Diaphragm  22  includes inner and outer bead seals  44 ,  46 , respectively, for retaining diaphragm  22  in position. Inner bead seal  44  is positioned between indicator cup  18  and lockpin  20 , and outer bead seal  46  is positioned between housing  12  and base cap  14 . Additionally, base cap  14  also includes a diaphragm antireversal wall  47 , which supports the underside of diaphragm  22  when indicator cup  18  is in the lower, reset position indicated in FIG.  4 . This configuration results in diaphragm  22  being supported on all surfaces during back pressure, minimizing failure due to reversal. Diaphragm  22  is preferably made of cloth lined flourosilicon to control durometer throughout the temperature range, to handle fuels and other chemicals, and to minimize cuts. 
     Of particular interest is lockpin  20 , as shown in FIGS. 4,  5  and  7 . Lockpin  20  includes a retention stem  48  for retaining indicator cup  18 . Retention stem  48  frictionally engages indicator bore  50  of indicator cup  18 . Retention stem  48  preferably includes retention ribs  52  to ensure a secure fit between lockpin  20  and indicator cup  18 . Lockpin  20  also preferably includes an integral lock ring  54  to help retain diaphragm  22  in proper position with respect to housing  12  and indicator cup  18 . It is preferred that lock ring  54  include a raised, rounded circumferential edge  56 , as best shown in FIG.  4 . Rounded edge  56  helps prevent cutting into diaphragm  22  when indicator cup  18  is in the fully extended, upper lock position, as shown in FIG. 5, and provides anti-reversal support for diaphragm  22  when back pressure is being applied to gauge  10 . 
     Of particular significance on lockpin  20  is lock stem  58 . Lock stem  58  preferably is configured with several angled stops  60  for engagement with lock fingers  62  of base cap  14 . The latch angle  64 , as shown in FIG. 7, may vary depending on the design criteria specified for specific applications of fuel filter gauge  10 . A relatively large latch angle  64  allows lock fingers  62  to slip off latch stops  60  when excessive force is applied to indicator cup  18 . A relatively shallow latch angle  64  makes the latching mechanism resist slippage when high forces are applied to indicator cup  18 . It is preferable that angle  64  fall within the range of approximately 22.5° to approximately 30°. The use of a relatively large latch angle  64  may be significant in the situation when, for example, a dirty fuel filter F 1  is replaced with a new fuel filter F 1 , and the service technician forgets to reset fuel filter gauge  10 , as shall be discussed. With a relatively large latch angle  64 , gauge  10  would then auto reset when sufficient backpressure is applied and yet operate normally holding peak vacuum levels as fuel filter F 1  again becomes plugged. It is the purpose of angled stops  60  to permit indicator cup  18  to snap back to the initial, reset position shown in FIG. 4 without having to use reset button  26  when high backpressure puts excessive load on lock fingers  62  to prevent breakage of lock fingers  62 . 
     Base cap  14 , as illustrated in FIGS. 4-6 and  8 , preferably includes three lock fingers  62  molded therein. Base cap  4  also preferably includes three push button retention fingers  66  for maintaining the position of reset button  26 . Reinforcing ribs  68  preferably spaced between lock fingers  62  and pushbutton retention fingers  66  provide additional support for indicator support shoulder  70 , against which lock ring  54  bears during backpressure. As may be seen in FIGS. 4-6, reset cover  24  includes a peripheral engagement member  72  for frictional engagement with a corresponding engagement channel  74  formed in base cap  14 . Base cap  14  also preferably includes flow ports  76  staggered throughout to form an integral, molded-in labyrinth filter. This labryrinth filter serves to prevent water and dirt from entering the region of lockpin  20 , lock fingers  62 , and diaphragm  22 . Under normal operating conditions, water and dirt can enter this region around reset spring  24  and reset button  26 . However, water is undesirable because it may freeze the mechanism in the winter, and dirt may result in abrasion and ensuing damage to the mechanism. The geometry of flow ports  76  results in dirt being trapped within the labyrinth, and water being expunged therefrom, regardless of the orientation of fuel filter gauge  10 . The labyrinth seal eliminates the need for a felt filter as used in the prior art, which if even slightly improperly positioned could result in admission of damaging dirt and water directly into the indicating mechanism, and allows the reset button to be mounted in an upward position without leakage. 
     Reset pushbutton  26  extends through and projects from reset cover  24 , as shown in FIGS. 2,  5  and  6 . Reset button  26  overlies and surrounds a substantial portion of lock stem  58  of lockpin  20 , and includes a circumferential rib  78  for engagement with pushbutton retention fingers  66  of base cap  14 . Reset button  26  also includes an angled face  79  for engagement with lock fingers  62  of base cap  14 . 
     In use, fuel filter gauges  10  are installed as shown in FIG.  1 . With a clean fuel filter F 1 , F 2 , the position of indicator cup  18  is as shown in FIG.  4 . As the fuel filter F 1 , F 2  with which fuel filter gauge  10  is associated becomes clogged with contaminants, a vacuum is formed that gradually overcomes the force of calibration spring  16 . As calibration spring  16  compresses, indicator cup  18  is drawn towards the end of housing  12  having threaded portion  13 , until it reaches the position shown in FIG.  5 . As indicator cup  18  is drawn towards the position shown in FIG. 5, it is retained in intermittent positions by engagement of base cap lock fingers  62  with angled lock stem stops  60  of lock stem  58 . Thus, when the vehicle engine is turned off, gauge  10  continues to indicate the condition of fuel filter F 1 , F 2  by the position of indicator cup outer edge  42  relative to delineations  30  of label liner  28 . Preferably, when indicator cup  18  reaches the position indicated in FIG. 5, label liner  28  clearly indicates that it is time for fuel filter F 1 , F 2  to be replaced. 
     Once a dirty fuel filter F 1 , F 2  has been replaced, fuel filter gauge  10  may be reset very simply by pressing reset button  26  in the direction of arrow  80  of FIG.  6 . Upon depressing reset button  26 , angled face  79  thereof engages and forces aside lock fingers  62 , previously engaged with lock stem stops  60 , permitting calibration spring  16  to bias lockpin  20  toward reset cover  24 , resulting in lock ring  54  bearing against indicator support shoulder  70 , as generally shown in FIG.  4 . 
     Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are contemplated as being within the scope of the present invention. Accordingly, the present invention is not limited in the particular embodiments which have been described in detail therein. Rather, reference should be made to the appended claims as indicative of the scope and content of the present invention.