# Patent

## Title
Method for determining when to replace a filter having a pressure relief valve

## Abstract

A fluid filter assembly having a relief valve for visually indicating when a filter element may be replaced. The fluid filter assembly of the present invention provides a vertical, transparent housing having a fluid inlet for communicating a fluid into the housing and a fluid outlet for communicating fluid downstream of the housing. A filter element is disposed within the housing between the fluid inlet and the fluid outlet for filtering the fluid.

## Background
The following patent application is a continuation of U.S. patent application Ser. No. 10/301,946, now U.S. Pat. No. 6,841,065, filed Nov. 22, 2002, which is a continuation of U.S. patent application Ser. No. 09/800,982, now U.S. Pat. No. 6,540,909, filed Mar. 7, 2001, which is a formalization of Provisional Patent Application Ser. No. 60/220,540, filed Jul. 25, 2000.


FIELD OF THE INVENTION
The present invention relates to fluid filters, and more particularly, a fluid filter having a pressure relief valve to provide an accurate visual indicator as to the remaining life of a filter element.
BACKGROUND OF THE INVENTION
It is well known to utilize fuel filter assemblies to filter fuel for a combustible engine of a motor vehicle. Such fuel filter assemblies comprise a variety of different orientations of the fuel filter assembly. For example, it is known to utilize sideways, downwardly, and upwardly mounted canisters having a paper filter media enclosed in the canister. With respect to upwardly mounted fuel assemblies, prior art filtration devices have been known to draw fuel into the filter assembly by use of a pump on the outlet side of the filter assembly. The fuel is directed downward into a lower chamber of the filter assembly wherein the fuel flow proceeds upward into an upper filter chamber of the filter assembly. The fuel may then be contained and sealed by a transparent filter cover or closure and a filter mount which may separate the lower chamber from the upper chamber.
Within the filter chamber of the filter assembly, the filter assembly may provide a filter canister comprised of a filter media circling a central filter tube that is contained by filter end caps at the top and bottom of the filter media. The end caps are sealed to the edges of the filter media to preclude any possible leak paths at the ends of the filter canister. The filter media typically comprises a porous paper material that may be pleated or concentrically wound so as to direct the fluid through the filter media. The filter media removes and retains undesirable contaminants within and on the media.
As fluid enters the filter chamber, the fuel level rises and passes through from the outside to the inside of the filter media. The fuel then flows downward into a central passage located along the central axis of the canister. The central passageway is in communication with a fuel outlet wherein the fuel passes outwardly from the filter assembly.
During the filtering process, the fuel is either drawn into the filter chamber by a vacuum or pushed into the filter chamber by pressure until the fuel finds a path through the filter media. As the fuel flows through the filter, dirt and other contaminants larger than the porous openings in the filter media, are trapped and retained by the filter media. These contaminants plug or clog the porous holes in the filter media and restrict or close the paths used by the flowing fuel. The fuel is then forced to seek other open and less restrictive flow openings which are available above the level of the fuel by climbing the height of the filter and accessing the clean areas of the filter media. This process of clogging and climbing continues until the filter media is completely immersed in the flowing fuel.
Even though the filter media may be completely immersed in the flowing fluid, the incoming fuel continues to pass through the filter media. It is not until the filter media becomes greatly clogged that the filter media needs to be replaced. This is a problem since the user generally views the height of the fuel in the filter chamber to see if the filter media is clogged. If the filter media is completely immersed in fuel, the user generally believes that the filter media needs to be replaced. Therefore, this type of system may lead to premature replacement of the filter media.
It would be desirable to provide a fuel filter assembly that provides an accurate indication as to the remaining usefulness of the filter media.
SUMMARY OF THE INVENTION
The present invention provides a fluid filter assembly that provides an accurate indication of the remaining usefulness of a filter element. The present invention provides a vertical, transparent housing having a fuel inlet for communicating fluid into the housing and a fluid outlet for communicating fluid downstream of said housing. A filter element is disposed within the housing between the fluid inlet and the fluid outlet for filtering the fluid. A means for maintaining and relieving a predetermined level of pressure across the filter element provides an accurate visual indicator as to whether the filter element needs replacement.
Preferably, the maintaining and relieving means provides a divider that is connected to the filter element and extends between a housing wall and an unfiltered side of the filter element. The divider divides the housing into an outer region and an inner region, wherein the outer and inner regions are in communication at a lower portion of the housing. A relief valve is in communication with a filtered side and the unfiltered side of the filter element and is located in the top of the filter element in the outer region of the housing. The relief valve opens when the pressure across the filter element exceeds the predetermined pressure level thereby raising the level of fluid in the outer region of the housing and indicating that the filter element needs replacement. A segment of filter media may be adjacently mounted to the relief valve to filter any unfiltered fluid that passes through the relief valve to the filtered side of the filter element.
Alternatively, the maintaining and relieving means may provide a restrictive filter media integrally connected to the filter element. The restrictive filter media prevents the flow of fluid through the restrictive filter media until the pressure across the filter element reaches the predetermined pressure level thereby causing the fluid in the housing to rise and indicating that the filter element needs replacement.



BRIEF DESCRIPTION OF THE DRAWINGS
The description herein makes reference to the accompanying drawings wherein like referenced numerals refer to like parts throughout several views and wherein:
FIG. 1 is a schematic drawing showing the fluid flow path and the normal rising fluid path of a prior art fuel filter assembly.
FIG. 2 is a schematic drawing showing the rising fluid level in the fluid filter assembly of the present invention.
FIG. 3 is a schematic drawing showing a segment of filter media being utilized above a relief valve of the present invention.
FIG. 4 is a schematic drawing showing a segment of filter media being utilized underneath the relief valve of the present invention.
FIG. 5 is a schematic drawing of a hang down fluid filter assembly of the present invention.
FIG. 6 is a schematic drawing showing a restrictive media being utilized as a relief valve in the fluid filter assembly of the present invention.
FIG. 7 is a bottom view of the filter element of the present invention.
FIG. 8 is a sectional view of the filter element of the present invention taken in the direction of arrows 9—9 in FIG. 8.
FIG. 9 is an exploded view of the relief valve shown in the top of the filter element of the present invention.
FIG. 10 is a sectioned perspective view of the relief valve shown in the top of the filter element of the present invention.



DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the present invention will now be described in detail with reference to the preferred embodiment.
FIG. 2 shows a fluid filter assembly 10 of the present invention in its preferred form. The fluid filter assembly 10 is best suited for filtering and processing diesel fuel, but the fluid filter assembly 10 may also be utilized with other fluids, such as gasoline, oil, water, antifreeze, etc. The fluid filter assembly 10 is mounted vertically upright and provides a closed housing 12, a lower fluid storage chamber 16, and an upper filter chamber 17. A fluid inlet 14 is in communication with the lower fluid storage chamber 16, which is in communication with the upper chamber 17 through a passageway 15. A filter element 20 is housed within the upper chamber 17 of the housing 12 for filtering a fluid 19 to a fluid outlet 18. The fluid inlet 14 delivers fluid 19 into the housing 12 so that the fluid 19 may pass through the filter element 20 and out the fluid outlet 18. A relief valve 38 mounted in the top of the filter element 20 opens when the pressure level across the filter element 20 reaches a predetermined level. A relief valve filter 40 filters fluid 19 that passes through the relief valve 38. Preferably, the relief valve filter 40 is mounted below the relief valve 38, as shown in FIG. 4, but alternatively, the relief valve filter may be mounted above the relief valve 38, as shown in FIG. 3.
To filter contaminants from the fluid 19, the filter element 20 is fabricated from a pleated porous paper material. The filter element 20 encircles a central filter tube 22 and is contained by a top and bottom end cap 24, 26, respectively, as seen in FIGS. 2 and 7–11. The top and bottom end caps, 24, 26 are sealed to the edges of the filter element 20 to preclude any possible leak paths at the ends of the filter element 20. A flexible seal 28 is provided on the bottom end cap 26 of the filter element 20 to create a seal between the central filter tube 22 and an inner core 43 of the filter element 20 and ensure that unfiltered fluid 19 does not leak into or escape through the fluid outlet 18. The filter element 20 is preferably pleated or concentrically wound but may also be arranged in any of the ways known to one familiar with filtration construction so as to direct the fluid 19 through the filter element 20. In addition, the filter element 20 may be fabricated from a hydrophobic filter material to filter out water from the fluid 19.
The portion of the housing 12 between the filter element 20 and an outer wall 37 of the upper filter chamber 17 of the housing 12 is preferably divided by a substantially frusto-conical divider 30. The divider 30 has a top portion 32 that is either integrally or sealingly connected to the top end cap 24 of the filter element 20. The divider 30 also has a bottom portion 33 that extends downward toward the bottom of the filter element 20, while also tapering or flaring outward away from the filter element 20. It should be noted that the present invention is not limited to a frusto-conical divider 30, but rather, the divider may also be substantially cylindrical wherein the bottom portion of the divider may extend downward substantially parallel to the filter element 20. In both embodiments, the divider 30 essentially divides the upper chamber 17 of the housing 12 into an inner portion or region 34 and an outer portion or region 36. The inner portion 34 is the space contained between the outside or unfiltered side of the filter element 20 and the inner surface of the divider 30. The outer portion 36 is the space contained between the outer surface of the divider 30 and the inner surface of the outer wall 37 of the upper chamber 17 of the housing 12. The inner and outer portions 34, 36 remain in fluid communication at the bottom portion of the upper filter chamber 17 of the housing 12.
In order to maintain and relieve the pressure in the upper chamber 17 of the housing 12, a relief valve 38 is mounted in the top end cap 24 of the filter element 20. The top end cap 24 is fabricated from a thin metallic material having a shape complementary to the top of the filter element 20. The top end cap 24 has a substantially circular configuration with sidewalls 39 that extend downward from its periphery to sealingly connect to and cover the top of the filter element 20. The top end cap 24 also has a centrally located recessed portion 41 which is received by and complementarily engages the inner core 43 of the filter element 20.
The recessed portion 41 of the top end cap 24 is formed by two layers of thin metallic material. A first inner layer 45 is integrally connected to the sidewalls 39 and the portion of the top end cap 24 that extends over the top of the filter element 20. A second outer layer of the recessed portion 41 is formed by a substantially cylindrical cup that is connected to and complementarily engages the inner layer 45 of the recessed portion 41. The inner layer 45 of the recessed portion 41 has a raised portion 49 relative to the outer layer 47. The outer layer 47 has four apertures 51 that extend therethrough and align directly under the raised portion 49 of the inner layer 45 of the recessed portion 41. A sheet of filter media 53 lies between the inner layer 45 and the outer layer 47 of the recessed portion 41 so as to cover the four apertures 51 extending through the outer layer 47.
The raised portion 49 of the inner layer 45 provides two apertures 55, 57 extending therethrough. The larger of the two apertures 55 receives a flexible valve member 58 having an inverted mushroom-shaped configuration. The stem portion 59 of the mushroom-shaped, configuration is disposed within the larger aperture 55. The head portion 61 of the flexible member 58 extends across the underside of the raised portion 49 of the inner layer 45 such that the head portion 61 of the flexible member 58 covers the smaller aperture 57. The smaller aperture 57 acts as a port such that when the pressure level across the filter element 20 reaches a predetermined level, the head portion 61 of the flexible member 58 flexes away from the smaller aperture 57 thereby allowing fluid 19 and/or air/vapor from the unfiltered side of the filter element 20 to pass through the smaller aperture 57. Fluid 19 will only pass through the smaller aperture 57 after all of the air/vapor has first passed through the smaller aperture 57. The fluid 19 and/or air/vapor passes through the sheet of filter media 53 and through the four apertures 51 in the outer layer 47 of the recessed portion 41 to the filtered side of the filter element 20. Although the patentable subject matter may be limited to a relief valve 38 having the structure defined above, Applicants consider the invention to include any relief valve 38 having a structure that provides for the release of fluid 19 and/or air/vapor at a predetermined pressure level.
The relief valve 38 is normally closed until the pressure level across the filter element 20 exceeds a predetermined level. When the relief valve 38 is closed, the air/vapor within the outer portion 36 of the housing 12 is trapped thereby forcing the fluid level in the outer portion 36 to be lower than the fluid level in the inner portion 34. This occurs because as long as the filter element 20 is not clogged, air/vapor and fluid 19 within the inner portion 34 will pass through the filter element 20 at a pressure less than the pressure level in which the relief valve 38 is to open. Once the pressure across the filter element 20 exceeds the predetermined level due to the filter element being sufficiently clogged, the relief valve 38 opens and allows air/vapor and/or fluid 19 to pass from the outer portion 36 of the housing 12 to the inner core 43 of the filter element 20.
In a secondary embodiment of the fluid filter assembly 10′, a restrictive filter media section 42 of the filter media 20′ is either integrally formed on the top of the filter media 20′ or is attached to the upper portion of the filter media 20′, as shown in FIG. 6. The restrictive section 42 of the filter media 20′ acts in the same manner as the relief valve 38 and the relief valve filter 40 of the preferred embodiment, but the secondary embodiment does not require the divider 30. The restrictive section 42 of the filter media 20′ only allows air/vapor and/or fluid 19 to pass through the restrictive section 42 once the pressure level across the filter element 20 exceeds a predetermined level. This ensures that the fluid level within the housing 12 will remain at a level below the restrictive filter media 42. Once the predetermined pressure level is reached, air/vapor and/or fluid is allowed to pass through the restrictive filter media 42 thereby raising the fluid level and providing a visual indicator that the filter element 20′ needs replacement.
In yet another embodiment of the present invention, a divider 30′′ and a relief valve 38′′ may be utilized in conjunction with a hang down fluid filter assembly 10′′, as shown in FIG. 5. The structure in this embodiment is similar to that of the preferred embodiment in that the divider 30′′ is sealingly connected to a top end cap 24′′. The divider 30′′ extends downward along the bottom portion of the filter element 20 while flaring outward from the filter element 20. A relief valve filter (although not shown in FIG. 5 but similar to that shown in FIGS. 3 and 4) is mounted in a portion of the central filter tube 22. The relief valve filter is incorporated with the relief valve 38′′ to prevent any unfiltered fluid 19 from entering fluid outlet 18′′. The relief valve 38′′ in the hang down fluid filter assembly 10′′ works in the same manner as the preferred embodiment. The divider 30′′ forms an outer portion 34′′ and an inner portion 32′′ of the housing 12′′ wherein the trapped air in the outer portion 34′′ forces the fluid level in the outer portion 34′′ to be lower than the fluid level in the inner portion 32′′. This allows the filter element 20 to become completely clogged before reaching the predetermined pressure level that will open the relief valve 38′′. Once the relief valve 38′′ opens, air/vapor passes through the relief valve 38′′ thereby allowing the fluid level in the outer portion 34′′ to rise and provide a visual indicator that the filter element 20 needs replacement.
In operation, the prior art device functions as depicted in FIG. 1. Fluid 19 enters the fluid inlet 14 of the fluid filter assembly 10 and accumulates within the lower chamber 16 of the housing 12. Fluid flows through the passageway 15 leading to the upper filter chamber 17 wherein an unfiltered fluid level is established within the upper filter chamber 17. The fluid 19 is drawn into the filter chamber 17 by vacuum (as most commonly occurs in diesel fuel filters) or forced by low pressure (as seen in oil, antifreeze or many other filters) until it finds a path through the filter element 20. As the filter element 20 becomes partially clogged, the restriction increases temporarily overcoming the surface tension of fluid covering the unused pores of the filter 20 element and causing a temporary flow of air/vapor through the filter element 20. As the air/vapor passes, it creates a void on the outside of the filter element 20, and the fluid level rises to fill the void. The new fluid level allows flow through clean and unused pores of the filter element 20, and the restriction through the filter element 20 reestablishes itself at a fluid level as previously described. Once the fluid level establishes itself, the surface tension of the fluid 19 across the remaining pores of the filter media 20 prevents the flow of air/vapor through the filter element 20 until, once again, the restriction increases to a level in which air/vapor is forced through the filter element 20. This process continues as dirt and other contaminants in the fluid 19, larger than the openings in the filter element 20, are trapped and retained by the filter element 20 as the fluid 19 passes through the filter element 20. These contaminants plug or clog the holes in the filter media 20 and restrict and/or close the paths used by the flowing fluid 19. The fluid 19 is forced to seek other open and less restrictive fluid openings that are above the level of the fluid 19, and therefore, the fluid 19 climbs up the height of the filter element 20 and uses the clean areas of the filter element 20. The process of clogging and climbing continues until the filter element 20 is completely immersed in the flowing fluid 19. When the fluid level reaches the top of the upper filter chamber 17, this has generally been a visible indication to the user to change the filter element 20. The problem with changing the filter element 20 at this point is that the filter element 20 still allows for the passage of fluid 19 through the filter element 20 even when the fluid level has risen to the top of the filter chamber 17. Therefore, if the filter element 20 is changed immediately upon the fluid level rising to the top of the filter chamber 17, then the filter element 20 is being replaced prematurely.
During the operation of the preferred embodiment of the present invention, fluid 19 enters the fluid filter assembly 10 and the upper filter chamber 17 in the same way as described in the prior art. However, by employing the divider 30 and incorporating the preset relief valve 38 in the top end cap 24, the fluid level can be made to rise approximately in proportion to the plugging rate of the fuel element 20. This gives an accurate visual indicator as to the remaining life of the filter element 20. In so doing, the incoming fluid 19 and air/vapor initially behave as similarly described in the prior art. When the fluid level approaches the bottom of the divider 30, the fluid 19 continues to rise between the filter element 20 and the inside surface of the divider 30, which was previously defined as the inner portion of the housing 12, but the fluid 19 does not rise between the outer surface of the divider 30 and the outer wall of the housing 12, which was previously defined as the outer portion of the housing 12. This is because the trapped air/vapor in the outer portion 36 of the housing 12 prevents the rise of fluid 19 into the outer portion of the housing 12.
As to the inner portion 34 of the housing 12, fluid 19 and air/vapor move through the filter element 20 in a usual manner. The fluid level continues to rise between the filter element 20 and the inside surface of the divider 30 as the filter element 20 becomes more clogged. This continues until the fluid 19 has risen to the full or nearly full height of the filter element 20, as previously described. Once the filter element 20 is completely saturated, the pressure differential across the filter element 20 begins to increase with the increased clogging of the filter element 20. Once this pressure differential reaches a predetermined level, preferably 5′′ Hg, the relief valve 38 may open, and vapor/air may flow through the relief valve 38 while fluid flows through the filter element 20 since both present the same amount of resistance to flow. As the pressure differential across the filter media 22 begins to exceed the 5′′ Hg point, the relief valve 38 becomes the preferred flow path since its pressure differential is fixed at 5′′ Hg. Since air/vapor is closest to the relief valve 38, the air/vapor flows through the relief valve 38 first, and the fluid 19 follows. The fluid level begins to rise in the outer portion 36 of the housing 12, thereby providing a visual indicator to the operator that the filter element 22 is plugged. The relief valve filter 40 provided in the fluid path of the relief valve 38 ensures that the fluid 19 that passes through the relief valve 38 is filtered. Once the user sees that the fluid level in the outer portion 36 of the housing 12 has risen to the top of the upper filter chamber 17, the user knows to replace the filter element 20.
In operation, the secondary embodiment, as depicted in FIG. 4, works in a similar manner as described in the preferred embodiment. The fluid level rises within the filter chamber 17, until it reaches the restrictive filter media 42 on the filter media 20. When the fluid level reaches the restrictive media 42, the pressure differential across the filter media 20′ must rise to a preferred level of 5′′ Hg in order for the air/vapor and fluid 19 to pass through the restrictive media 42. The fluid level stops at a point just below the restrictive media 42 until the filter media 20′ becomes so clogged that the pressure differential reaches the 5′′ Hg level. At that point, air/vapor and fluid 19 pass through the restrictive media 42, thus allowing the fluid level to rise within the filter chamber 17 of the fluid filter assembly 10′. The user may then use the risen fluid level as an indicator that the filter media 20′ needs to be replaced.
In operation, the alternative embodiment depicted in FIG. 5 works in exactly the same manner as described in the preferred embodiment. The only difference in the embodiment depicted in FIG. 5 is that the housing 12′′ is upside down, but the fluid level responds in the same manner as described in the preferred embodiment.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, the scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

## Claims

1. A method for determining when to replace a filter element of a fluid filter assembly, comprising the steps of:
providing a vertical housing having a fluid inlet adaptable to receive a fluid into said housing and a fluid outlet adaptable to communicate said fluid downstream of said housing;
providing a filter element within said housing between said fluid inlet and said fluid outlet for filtering said fluid;
connecting a divider to said filter element and having said divider extend between a wall of said housing and an unfiltered side of said filter element to divide said housing into an outer region and an inner region, wherein said outer and inner regions are in communication at a lower portion of said housing;
maintaining and relieving a predetermined level of pressure across said filter element;
monitoring the fluid level in said outer region of said housing by viewing said fluid level through a transparent wall of said housing; and
replacing said filter element when said fluid level reaches the top of said filter element in said outer region of said housing.

2. The method as stated in claim 1, further comprising the steps of:
providing a relief valve in said filter element to maintain and relieve a predetermined level of pressure across said filter element.

3. The method stated in claim 2, further comprising the steps of:
filtering said fluid that passes through said relief valve.