Abstract:
An apparatus and method for filtering a liquid utilize a filter apparatus including a bypass filter, a full flow filter, and a flow balancing element for dividing a total inlet flow of fluid to the filter apparatus into a bypass portion, passing through the bypass filter, and a full flow portion, passing through the full flow filter. The bypass filter has a lower filtering efficiency than the full flow filter element, so that a venturi tube is not required for causing the bypass portion to pass through the bypass filter. The flow balancing element divides the flow into a desired bypass portion and a desired full flow portion, at a predetermined operating temperature. Below the operating temperature, the bypass portion increases and the full flow portion decreases, the bypass portion becoming greater that the full flow portion at a second predetermined temperature below the operating temperature.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to an apparatus and method for filtering impurities from liquids, such as lubricating oil, hydraulic fluid and the like. More particularly, the invention relates to filtering impurities using a spin-on filter adapted to thread onto a filter mounting adaptor of, for example, a hydraulic system or a lubricating system.  
       BACKGROUND OF THE INVENTION  
       [0002]     spin-on filter is designed for a specified service life. The filter is then discarded and replaced with a new filter. Typically, more than one manufacturer produces filters which are interchangeable. As a disposable or throw-away type of item, the decision to purchase one brand of filter over a different brand is often based substantially on the price of the filter, and how often it must be replaced. For filters providing lubrication oil to an engine which will need to be started at cold ambient temperatures, it is also important to select a filter that has a low flow resistance during cold start conditions, so that an adequate flow of filtered lubricant can be supplied while the engine is coming up to operating temperature.  
         [0003]     In order to provide a high overall filtering efficiency of the filter, it is a common practice to incorporate two separate filtering elements within a common housing of the spin-on filter. Typically, one of these filters, known as the full flow filter, is used for filtering all or most of the fluid passing through the housing of the filter. The other filter element, known in the industry as a bypass filter, is used for performing additional filtration of a small portion, typically about 10 percent, of the fluid passing through the housing.  
         [0004]     In prior filters of this type, the full flow filter generally includes a full flow filter media having a rated efficiency for removing particles of a given size from the fluid passing through the full flow filter, and the bypass filter includes a bypass filter media having a higher rated efficiency for removing particles of the given size. Stated another way, the bypass filter media is essentially denser than the full flow filter media, making it capable of removing a higher percentage of particles of the given size from the smaller portion of fluid passing through the bypass filter. Theoretically, as the fluid is continuously circulated through the spin-on filter, in sequential passes through the filter housing, all of the fluid will eventually pass through the higher efficiency media of the bypass filter to receive additional filtration.  
         [0005]     Typically, prior filters of this type have included a venturi tube that is used to locally reduce the pressure in the fluid, at a strategic point within the housing, to aid in pulling a small portion (about 10%) of the fluid through the relatively dense bypass filter. The reduced pressure is created by directing most of the fluid flowing through the housing through a throat in the venturi tube, to thereby accelerate the fluid at the throat of the venturi tube. This acceleration of the fluid causes the fluid pressure at the throat of the venturi tube to drop, due to well known principles of fluid dynamics.  
         [0006]     In one prior approach to providing such a spin-on filter, the full flow and bypass filters are arranged in a parallel flow relationship to one another, with the flow through the full flow filter being accelerated in the venturi tube for dropping the pressure, in such a manner that a small portion of the total flow through the filter housing is induced to flow through the relatively dense bypass filter, rather than taking the path of lower resistance through the full flow filter. The small portion of fluid passing through the bypass filter is then reunited with the larger portion of fluid that was directed through the throat of the venturi tube, and the combined flow is returned to the system through the outlet of the spin-on filter. With this arrangement, the portion of the fluid receiving higher efficiency filtration in the bypass filter bypasses the full flow filter on that particular pass through the spin-on filter. This general approach is disclosed in U.S. Pat. No. 5,906,736 to Bounnakhom, et al.  
         [0007]     In another prior approach, the bypass filter is disposed within the filter housing in such a manner that all fluid passing through the housing of the spin-on filter, on a given pass, is first filtered by full flow filter. The filtered fluid then splits, with a larger portion being routed through the throat of a venturi tube, which is arranged for drawing a small portion of the fluid filtered by the full flow filter, on that particular pass, through a higher efficiency bypass filter element, to thereby provide a second stage of filtering for the small portion of fluid passing through both the full flow and bypass filters. This approach is disclosed in U.S. Pat. No. 6,478,958, to Beard, et al., which is assigned to the assignees of the present invention.  
         [0008]     Although prior filters, using venturi tubes to draw a small percentage of the total fluid being filtered through a higher efficiency bypass filter, generally work well for their intended purpose, certain drawbacks have been noted. Only a small percentage of the total fluid flow is routed through the higher efficiency bypass filter on each pass of the fluid through the filter. It can thus take some time before all of the fluid passes through the bypass filter. Such filters often exhibit fairly high resistance to fluid flow through the filter during cold start operation. It has been noted that the media in such filters tends to capture contaminant particles in a non-uniform manner, which tends to reduce the amount of contaminant that the filter can remove and hold, before the pressure drop through the filter apparatus rises to a point that the filter should be replaced. The complexity of such filters also tends to undesirably drive up the cost of production and the price of the filter apparatus.  
         [0009]     It is desirable, therefore to provide an improved apparatus and method for fluid filtration that overcomes one or more of the drawbacks cited above, or other drawbacks, problems or deficiencies in prior art filters of the type addressed by the invention.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     The invention provides an improved apparatus and method for filtering a liquid, in a filter apparatus including a bypass filter and a full flow filter. In contrast to prior filter apparatuses of this type, however, the bypass filter of the present invention has a lower filtering efficiency for a particle of a given size than the full flow filter element, and a venturi tube is not required.  
         [0011]     A filter apparatus according to the invention may also include a flow balancing element for dividing a total inlet flow of fluid to the filter apparatus into a bypass portion, passing through the bypass filter, and a full flow portion, passing through the full flow filter. Because the bypass filter, in a filter apparatus according to the invention, has a lower filtering efficiency than the full flow filter element, a venturi tube is not required, as was the case in prior filter apparatuses, for causing the bypass portion to pass through the bypass filter. The flow balancing element causes the total inlet flow to divide into the desired bypass portion and the desired full flow portion, at a predetermined operating temperature. When the filter apparatus is operating at temperatures which are lower than the operating temperature, the bypass portion increases and the full flow portion decreases. In some forms of the invention, the bypass portion ultimately becomes greater that the full flow portion at a second predetermined temperature below the operating temperature.  
         [0012]     In one form of the invention, a filter apparatus includes a housing, a bypass filter, and a full flow filter. The housing has a closed end and an open end, joined by a cylindrical sidewall defining a longitudinal axis extending from the closed end to the open end of the housing.  
         [0013]     The bypass filter is disposed within the housing adjacent the open end of the housing, and includes an outer periphery thereof, spaced inward from the sidewall of the housing to form a space around the bypass filter for passage of fluid between the bypass filter and the sidewall. The bypass filter also includes an inner periphery thereof, which forms an axially oriented through-bore of the bypass filter. The bypass filter further includes a bypass filter media, which is disposed between the inner and outer peripheries of the bypass filter. The, bypass filter media has a bypass filter efficiency, for removing particles of a given size from a fluid flowing radially inward through the bypass filter media from the space around the bypass filter to the through-bore of the bypass filter.  
         [0014]     The full flow filter is disposed within the housing, adjacent the closed end of the housing, and includes an outer periphery thereof spaced inward from the sidewall of the housing to form a space around the full flow filter for passage of fluid between the full flow filter and the sidewall. The space between the full flow filter and the sidewall is connected in sealed fluid communication with the space between the bypass filter and the sidewall. The full flow filter also includes an inner periphery thereof, forming an axially oriented through-bore of the full flow filter, which is connected in sealed fluid communication with the through-bore of the bypass filter. The full flow filter further includes a full flow filter media, disposed between the inner and outer peripheries of the bypass filter.  
         [0015]     The full flow filter has a full flow filter efficiency, for removing particles of the given size from a fluid flowing radially inward through the full flow filter media from the annular space around the full flow filter to the through-bore of the full flow filter, which is generally higher than the bypass filter efficiency for removing particles of the given size.  
         [0016]     A filter apparatus, according to the invention, may also include a flow balancing element disposed in the through-bore of the bypass filter.  
         [0017]     In one form of the invention, a filter apparatus, having a filter inlet and a filter outlet, includes a flow balancing element, a housing, a bypass filter, a full flow filter, and a flow balancing element. The bypass filter includes a bypass filter media, having a bypass filter efficiency for removing a particle of a given size. The full flow filter includes a full flow filter media, having a full flow filter efficiency for removing a particle of a given size, with the full flow efficiency being higher than the bypass filter efficiency. The bypass filter and full flow filters each have a respective fluid inlet connected to one another in a parallel circuit relationship by the housing.  
         [0018]     The bypass filter and full flow filters each also have a respective fluid outlet connected to the flow balancing element. The flow balancing element has a full flow inlet, a bypass inlet, and an outlet, all connected to one another within the flow balancing element. The full flow inlet of the flow balancer is connected in fluid communication, in a series fluid circuit relationship, with the outlet of the full flow filter, and the bypass inlet of the flow balancer is connected in fluid communication in a series fluid circuit relationship with the outlet of the bypass filter. The outlet of the flow balancer is connected to the outlet of the filter apparatus.  
         [0019]     The bypass flow inlet of the flow balancing element defines an equivalent bypass flow restricting orifice, which is sized to restrict the flow through the bypass filter media to a desired bypass flow portion of a total inlet flow of fluid entering the filter inlet of the filter apparatus. The flow balancing element may also include a full flow restrictor that is sized to restrict the flow through the full flow media to a desired full flow portion of the total inlet flow of fluid to the filter apparatus. The equivalent bypass flow restricting orifice, and the full flow restrictor, may be sized to allow a larger portion of the inlet flow to pass through the bypass filter when the fluid is below a predetermined operating temperature of the filter apparatus, and to restrict the flow through the bypass filter to a smaller portion of the inlet flow fluid at the predetermined operating temperature of the filter apparatus.  
         [0020]     In one form of the invention, the full flow restrictor, full flow media, equivalent bypass orifice, and bypass filter media are cooperatively configured in such a manner that, at the operating temperature, the flow of fluid through the full flow filter will be larger than the flow of fluid through the bypass filter, and at a predetermined temperature below the operating temperature, the flow of fluid through the bypass filter will be larger than the flow of fluid through the full flow filter. Because the bypass filter media is less restrictive than the full flow filter media, this configuration results in less pressure drop through the filter apparatus, in comparison to prior filter apparatuses, during periods where the fluid is relatively cold, such as when an engine is first started and the engine lubricating oil has not yet come up to operating temperature.  
         [0021]     In some forms of the invention, the full flow filter includes a lower end plate thereof, which is located adjacent to the closed end of the housing and extends generally from the outer periphery to the inner periphery of the full flow filter. The lower end plate of the full flow filter also includes an imperforate section thereof, which blocks fluid flow from entering the through-bore of the full flow filter. The full flow filter also includes an upper end plate thereof, adjacent the bypass filter, extending generally inward from the outer periphery of the full flow filter, and defining an outlet of the through-bore of the full flow filter.  
         [0022]     The bypass filter includes a lower end plate thereof, adjacent the upper end plate of the full flow filter, extending generally inward from the outer periphery of the bypass filter, and defining a full flow inlet of the bypass filter in sealed fluid communication with the through-bore of the bypass filter. The bypass filter also includes an upper end plate thereof, adjacent the open end of the housing, extending generally inward from the outer periphery of the bypass filter, and defining an outlet of the through-bore of the bypass filter. The outlet of the full flow filter is sealingly connected to the full flow inlet of the bypass filter.  
         [0023]     The flow balancing element includes a generally imperforate wall thereof, spaced from the inner periphery of the bypass filter, and sealingly connecting the full flow inlet of the bypass filter to the outlet of the bypass filter. The wall of the balancing element may also define one or more through holes therein, that respectively form one or more bypass flow inlets to the flow balancing element for receiving the fluid flowing through the bypass filter media. The one or more bypass flow inlets in combination define an equivalent bypass flow restricting orifice, which may be sized to restrict the flow through the bypass filter media to a desired bypass flow portion of a total inlet flow of fluid to the filter apparatus. The wall of the balancing element may also include a section thereof that forms a full flow restrictor which may be sized to restrict the flow through the full flow media to a desired full flow portion of the total inlet flow of fluid to the filter apparatus. The section of the wall of the balancing element forming the full flow restrictor may also define at least one of the bypass flow inlets.  
         [0024]     A filter apparatus, according to the invention, may also include a baseplate and spacer apparatus operatively attached between the open end of the housing and the upper end plate of the bypass filter, for positioning the bypass and full flow filters within the housing, adapting the filter apparatus for spin-on attachment to a filter mounting structure, and defining a filter inlet of the filter apparatus. The baseplate may include an annular wall defining an upper edge and a lower edge of the baseplate, with the upper edge of the baseplate being joined to the open end of filter housing. The spacer may include an annular wall defining an upper and a lower end of the spacer, with the spacer extending between the lower edge of the base plate and the bypass filter element, with the upper end of the spacer, and the lower edge of the base plate being configured to form corresponding mating surfaces, that prevent fluid from flowing past the lower edge of the base plate. The annular wall of the baseplate may be imperforate, and the annular wall of the spacer may define one or more inlet flow passageways that provide fluid communication between inside and outside surfaces of the base plate and spacer.  
         [0025]     The invention may also take the form of a method for filtering a fluid, using a filter apparatus according to the invention.  
         [0026]     Other aspects, objectives and advantages of the invention will be apparent from the following detailed description and the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a cross section of a first exemplary embodiment of a filter apparatus, according to the invention.  
         [0028]      FIG. 2  is a cross section representation of the first exemplary embodiment of  FIG. 1 , installed on a filter mounting adapter, and having arrows superimposed to illustrate the manner in which fluid flows through the filter apparatus.  
         [0029]      FIG. 3  is an enlarged partial cross section of the first exemplary embodiment of  FIGS. 1 and 2 , showing an exemplary embodiment of a baseplate and spacer apparatus, according to the invention.  
         [0030]      FIG. 4  is a cross sectional view, of a second exemplary embodiment of the invention that is essentially identical to the first exemplary embodiment shown in  FIGS. 1-3 , except that a flow balancing element of the second exemplary embodiment is of a different shape than a corresponding flow balancing element of the first exemplary embodiment.  
         [0031]     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]      FIGS. 1 through 3  show a first exemplary embodiment of a filter apparatus, according to the invention, in the form of a spin-on filter  10 . As shown in  FIG. 1 , the spin on filter  10  includes, a housing  12 , enclosing a bypass filter  14 , a full flow filter  16 , a flow balancing element  18 , a baseplate and spacer apparatus  20 , an intermediate seal  22 , an outlet seal  24 , an inlet seal  26 , and a helical compression spring  28 . In general,  FIGS. 1 and 3  show structural details of the exemplary embodiment of the spin-on filter  10 , and  FIG. 2  shows the manner in which fluid flows through the exemplary embodiment of the spin-on filter  10 .  
         [0033]     The housing  12  has a closed end  30  and an open end  32 , joined by a cylindrical sidewall  34  defining a longitudinal axis  36  extending from the closed end  30  to the open end  32  of the housing  12 .  
         [0034]     The bypass filter  14  is disposed within the housing  12  at a point along the longitudinal axis  36  adjacent the open end  32  of the housing  12 . The bypass filter  14  has an outer periphery  38  that is spaced inward from the sidewall  34  of the housing  12 , to form a space  40  around the bypass filter  14 , for passage of fluid between the bypass filter  14  and the sidewall  34 . The bypass filter  14  also has an inner periphery  42  forming an axially oriented through-bore  44  of the bypass filter  14 , which is centered about the longitudinal axis  36 . A bypass filter media  46  is disposed between the inner and outer peripheries  42 ,  38  of the bypass filter  14 . The bypass filter media  46  has a rated bypass filter efficiency, for removing particles of a given size from a fluid flowing radially inward through the bypass filter media  46 , from the space  40  around the bypass filter  14  to the central through-bore  42  of the bypass filter  14 .  
         [0035]     The full flow filter  16  is disposed within the housing  12 , adjacent the closed end  30 , and has an outer periphery  48  that is spaced inward from the sidewall  34  of the housing  12 , to form a continuation of the space  40  around the bypass filter  14  and to thereby provide a space  40  around the full flow filter  16 , for passage of fluid between the full flow filter  16  and the sidewall  34  of the housing  12 . The space  40  between the full flow filter  16  and the sidewall  34  is connected in sealed fluid communication with the space  40  between the bypass filter  14  and the sidewall  34  of the housing  12 , by the sidewall  34  of the housing  12  in conjunction with other elements of the spin-on filter  10 , in a manner that will be understood from the following description and an examination of the drawings.  
         [0036]     The full flow filter  16  also has an inner periphery  50  thereof forming an axially oriented through-bore  52  of the full flow filter  16 . The through bore  52  of the full flow filter  16  is connected in sealed fluid communication with the through-bore  44  of the bypass filter  14  by an opening  54  the intermediate seal  22 , when the intermediate seal  22  is sandwiched between the bypass and full flow filters  14 ,  16 , in the manner shown in  FIGS. 1 and 2 . The full flow filter  16  further includes a full flow filter media  56  is disposed between the inner and outer peripheries  50 ,  48  of the full flow filter  16 , and has a rated full flow filter efficiency, for removing particles of the given size from a fluid flowing radially inward through the full flow filter media  56  from the annular space  40  around the full flow filter  16  to the through-bore  44  of the full flow filter  16 , with the full flow filter efficiency being higher than the bypass filter efficiency for removing particles of the given size.  
         [0037]     The flow balancing element  18  is disposed within the through-bore  44  of the bypass filter  16  for balancing the flows of fluid through the bypass filter  14  and full flow filter  16 .  
         [0038]     The full flow filter  16  includes a lower end plate  58  thereof, adjacent the closed end  30  of the housing  12 . The lower end plate  58  is attached to the lower end (as shown in the drawings) of the full flow media  56 , and extends generally from the outer periphery  48  to the inner periphery  50  of the full flow filter  16 . The lower end plate  58  also includes an imperforate center section  60  thereof, which blocks fluid flow from entering the through-bore  52  of the full flow filter  16 . The full flow filter  16  also includes an upper end plate  62  thereof, attached to the upper end of the full flow filter media  56  adjacent the bypass filter  14 , extending generally inward from the outer periphery  48  of the full flow filter  16 , and terminating in a centrally located, annular collar, defining an outlet  64  of the through-bore  52  of the full flow filter  16 .  
         [0039]     The bypass filter  14  includes a lower end plate  66  thereof, attached to the lower end of the bypass filter media adjacent the upper end plate  62  of the full flow filter  16 , extending generally inward from the outer periphery  38  of the bypass filter  14  and terminating in a centrally located annular collar that defines a full flow inlet  68  of the bypass filter  14  The juncture between the through-bores  52 ,  44  in the full flow and bypass filters  16 ,  14  is sealed by the intermediate seal  22 , which is clamped between the upper end plate  62  of the full flow filter  16 , and the lower end plate  66  of the bypass filter  14 . The intermediate seal  22  also engages the collars around the outlet  64  of the full flow filter  16  and the full flow inlet  68  of the bypass filter  14 , to provide sealed fluid communication between the outlet  64  of the full flow filter  16  and the full flow inlet  68  of the bypass filter  14 , through the opening  54  in the intermediate seal  22 .  
         [0040]     The bypass filter  14  also includes an upper end plate  70  thereof, attached to the end of the bypass filter media  46  adjacent the open end  32  of the housing  12 . The upper end plate  70  of the bypass filter  14  extends generally inward from the outer periphery  38  of the bypass filter  14  and terminates in an annular cup  72 , having a hole in the bottom thereof that defines an outlet  74  of the through-bore  44  of the bypass filter  14 . The outlet  74  of the through-bore  44  of the bypass filter  14  also serves as the filter outlet for the exemplary embodiments of the spin-on filter  10  disclosed herein.  
         [0041]     As shown in  FIGS. 1 and 2 , the outlet seal  24  is mounted in the annular cup  72 , and is held in place by a spacer  75  of the baseplate and spacer apparatus  20 , in a manner described in more detail below. As shown in  FIG. 2 , the outlet seal  24  is positioned by the annular cup  72  to seal against an outlet tube  76  extending from a filter mounting adapter  78 , when the spin-on filter  10  is installed on the mounting adapter  78 .  
         [0042]     As shown in  FIG. 1 , the flow balancing element  18 , in the first exemplary embodiment, includes a generally imperforate wall  80  thereof, that is spaced from the inner periphery  42  of the bypass filter  14  and extends between the lower and upper end plates  66 ,  70  of the bypass filter  14 . The ends of the wall  80  are sealingly connected to the full flow inlet  68  of the bypass filter  14  to the outlet  74  of the through bore  44  of the bypass filter  14 . The generally imperforate wall  80  of the flow balancing element  18  also defines a pair of through-holes therein, that respectively form a pair of bypass flow inlets  82 ,  84  to the flow balancing element  18  for receiving fluid flowing through the bypass filter media  46 , and into the through-bore  44  of the bypass filter  14 . The two bypass flow inlets  82 ,  84 , in combination, define an equivalent bypass flow restricting orifice of the flow balancing apparatus  18 , which is sized to restrict fluid flow through the bypass filter media  46  to a desired bypass flow portion of a total inlet flow of fluid to the filter apparatus  10 .  
         [0043]     The flow balancing element  18  also includes a full flow inlet  86  thereof, that mates with and receives fluid from the full flow inlet  68  of the bypass filter  14 . The flow balancing element  18  further includes an outlet  88  that mates with the outlet  74  of the through-bore  44  of the bypass filter  14 .  
         [0044]     An annular section  90  of the imperforate wall  80  of the flow balancing element  18 , disposed about the bypass flow inlets  82 ,  84  of the flow balancing element  18 , defines a full flow restrictor  90 . The full flow restrictor  90  is sized to restrict the portion of fluid flowing through the full flow media  56  and into the full flow inlets  68 ,  86  of the bypass filter  14  and flow balancing element  18 , to a desired full flow portion of a total inlet flow of fluid to the filter apparatus  10 .  
         [0045]     As best seen in  FIG. 3 , the baseplate and spacer apparatus  20 , of the spin-on filter  10 , includes a baseplate  92  and the spacer  75 . The baseplate and spacer apparatus  20  is operatively attached between the open end  32  of the housing  12  and the upper end plate  70  of the bypass filter  14  and performs several functions including positioning the bypass and full flow filters  14 ,  16  within the housing  12 , adapting the filter apparatus  10  for spin-on attachment to the filter mounting adapter  78 , and defining a filter inlet of the filter apparatus  10 , in a manner described in more detail below.  
         [0046]     The base plate  92 , in the exemplary embodiment, includes an annular wall  94  defining an upper edge  96  and a lower edge  98  of the baseplate  92 , with the upper edge  96  of the baseplate  92  being joined to the open end  32  of filter housing  12 . In the exemplary embodiment, a portion of the sidewall  34  of the housing  12 , adjacent the open end  32  of the housing  12 , is formed over the upper edge  96  of the baseplate  92 , to thereby join the baseplate  92  to the housing  12  with a so-called “J-lock” connection. In other embodiments of the invention, however, the baseplate  92  may be joined to the open end  32  of the housing  12  by other types of connections.  
         [0047]     The annular wall  94  of the baseplate  92  of the exemplary embodiment is also imperforate, but the baseplates of other embodiments of the invention may include holes for the passage of fluid. The annular wall  94  in the exemplary embodiment includes a first, a second, and a third wall section  100 ,  102 ,  103 . The first wall section  100  includes the upper edge  96  of the baseplate  92 , and has an outer diameter that is generally equal to an inner diameter of the sidewall  34  of the housing  12 . The second wall portion  102  has an inner surface that is somewhat smaller in diameter than the outer diameter of the first wall section  100 , and includes female threads  104  for engagement with mating male threads  106  on the filter mounting adapter  78 , for attaching the spin-on filter  10  to the filter mounting adapter  78  in the manner shown in  FIG. 2 . As shown in  FIG. 3 , the first and second sections  100 ,  102  of the annular wall  94  of the baseplate  92  are joined by the third wall section  103 .  
         [0048]     The inlet seal  26  seals the juncture of the open end  32  of the housing  12  with a seal surface  109  of the filter mounting adapter  78 , as shown in  FIG. 3 , when the spin-on filter  10  is attached to the mounting adapter  78 . When the spin-on filter  10  is properly tightened onto the threads  106  of the mounting adapter  78 , the inlet seal  26  and the outlet seal  24 , in conjunction with elements of the mounting adapter  78  and components of the filter  10  form an inlet plenum  107 , for directing a flow of fluid, supplied an annular groove  111  in the mounting adapter  78  that is attached to an inlet passage  113  of the mounting adapter  78 , in the manner shown in  FIG. 2   
         [0049]     The spacer  75 , in the exemplary embodiment, includes an annular wall  108  extending between the lower edge  98  of the base plate and the upper end plate  62  of bypass filter  14 , and defining an upper and a lower end  110 ,  112  of the spacer  75 . The upper end  110  of the spacer  75 , and the lower edge  98  of the base plate  75  are configured to form corresponding mating surfaces  114 ,  116 , of the baseplate  92  and the spacer  75  respectively, which fit together tightly enough to prevent fluid from flowing between the mating surfaces  114 ,  116  and past the lower edge  98  of the base plate  92 .  
         [0050]     The lower end  112  of the spacer  75  is attached to the upper end plate  62  of the bypass filter  14 , and defines an annular flange  118  that protrudes into the annular cup  72  in the upper end plate  62  of the bypass filter  14 , for retaining the outlet seal  24  within the annular cup  72 . The annular flange  118  forms a hole  120  in the lower end  112  of the spacer  75 , for passage therethrough of the outlet tube  76  of the filter mounting adapter  78 .  
         [0051]     The annular wall  108  of the exemplary embodiment of the spacer  75  also defines a plurality of circumferentially spaced inlet flow passageways  122  that provide fluid communication between inside and outside surfaces of the baseplate  92  and spacer  75 . The inlet flow passageways  122  in the spacer  75 , in combination, define a filter inlet that allows fluid to flow from the inlet groove  111  in the mounting adapter  78  into the filter housing  12 . In other embodiments of the invention, however, the annular wall  108  of the spacer  75  may be imperforate, and other provisions made for allowing entry fluid into the filter housing  12 .  
         [0052]     The spring  28  of the filter apparatus  10  is compressed between the closed end  30  of the housing  12 , and the lower end plate  58  of the full flow filter, to provide an axially directed force for axially positioning the bypass and full flow filters  14 ,  16 , with respect to the baseplate and spacer apparatus  20 , and to maintain the seal between the bypass and full flow filters  14 ,  16  provided by the intermediate seal  22 .  
         [0053]     By virtue of the construction described above, the spin-on filter  10  can be installed on the mounting adapter  78 , as described above, and operated in the manner illustrated by a number of illustrative arrows, indicating fluid flow, in  FIG. 2 .  
         [0054]     A total inlet flow of fluid to be filtered is supplied to the spin-on filter  10  by the inlet passage  113  in the mounting adapter  78 , via the annular groove  111  of the mounting adapter  78 . The total inlet flow enters into the inlet plenum area  107 , from the annular groove  111  in the mounting adapter  78 , and flows through the passageways  122  in the spacer  75  into the space  40  between the sidewall  34  of the housing  12  and the outer peripheries  38 ,  48  of the bypass and full flow filters  14 ,  16 . The incoming fluid also flows into and fills the space  124  adjacent the closed end  30  of the housing  12 , around the spring  28 , between the lower end plate  58  of the full flow filter  16  and the closed end  30  of the housing  12 , so that the entire volume within the housing  12  and outside of the bypass and full flow filters  14 ,  16  is filled with the incoming fluid to be filtered.  
         [0055]     As shown in  FIG. 2 , the inner peripheries  42 ,  50  of the bypass and full flow filters  14 ,  16  are perforated to allow the incoming fluid to flow radially inward through the medias  46 ,  56  of the bypass and full flow filters  14 ,  16  from the space  40 , around the outer peripheries  38 ,  48  of the bypass and full flow filters  14 ,  16 , into the through bores  44 ,  52  of the bypass and full flow filters  14 ,  16 . The portion of the fluid passing through the full flow filter  16 , exits the through-bore  52  of the full flow filter  16  through the outlet  64  of the full flow filter  16 , and enters the full flow inlet  86  of the flow balancing element. The portion of the fluid passing through the bypass filter  14 , exits the through-bore  44  of the bypass filter  14 , by flowing through the bypass flow inlets  82 ,  84  in the flow balancing element  18 . The combined portions of flow passing through the full flow filter  16  and the bypass filter  14  are then joined into a common total outlet flow of filtered fluid, that exits the spin-on filter  10  through a bore  126  in the outlet tube  76 .  
         [0056]     The proportions of the total inlet flow that pass through each of the bypass and full flow filters  14 ,  16  is primarily determined by the size of the bypass flow inlets  82 ,  84  and the flow restrictor  90  of the flow balancing element  18 , in conjunction with the operating characteristics of the medias  46 ,  56  of the bypass and full flow filters  14 ,  16 .  
         [0057]     In the exemplary embodiment of the spin on filter  10 , as described above, these components and features are selected in such a manner that, at a predetermined operating temperature, the portion of flow through full flow filter is approximately 75 percent of the total inlet flow, and the portion of flow through the bypass filter is approximately 25 percent. At cold temperatures, such as might be experienced by an engine lubrication system immediately upon starting the engine and until the engine warms up, and particularly where the temperature of the fluid is well below the operating temperature, most of the total inlet flow will pass through the bypass filter  14  rather than the full flow filter  16 . As the fluid warms up toward the operating temperature, the portions of flow passing respectively through the bypass and full flow filters will change proportionately, with the desired 25 percent bypass/75 percent full flow proportioning being established when operating temperature is reached.  
         [0058]     Specifically, in the exemplary embodiment of the spin-on filter  10 , the bypass media was selected to be 35% efficient at removing particles that are 10 microns in size, and the full flow filter media was selected to be 85% efficient at removing particles that are 10 microns in size. The bypass flow inlets  82 ,  84  in the flow balancing element, and the flow restrictor  90  of the flow balancing element  18  were then selected, through calculation and experimentation, to provide the desired division of the total inlet flow into the desired approximately 75 percent full flow portion and approximately 25 percent bypass portions of the total inlet flow, at operating temperature.  
         [0059]     The media efficiency ratings and desired proportions of the total inlet flow, described above in relation to the exemplary embodiment of the spin-on filter  10 , together with the particular configuration and arrangement of the components in the exemplary embodiment of the spin-on filter  10 , were judiciously and purposefully selected to provide a filter apparatus having lower resistance to fluid flow during cold-start operation than prior spin-on filter of this type, and to provide a larger capacity for holding removed contaminants than prior spin-on filters of this type, while still providing a high overall filtering efficiency. Having a lower resistance to fluid flow during cold-start operation, is advantageous in that, for an engine lubrication system, for example, better lubrication can be provided to the engine during cold-start operation. Having a higher capacity for holding removed contaminant is advantageous in that the interval between filter changes can be lengthened, thereby reducing operational costs for the system protected by the filter apparatus.  
         [0060]     Those skilled in the art will recognize, however, that in other embodiments of the invention it may be desirable to utilize bypass and full low medias having different efficiency ratings and/or change the configuration of the flow balancing element, or other components of the filter apparatus, to achieve different proportioning of the inlet fluid between the bypass and full flow filters.  
         [0061]     It should be noted that, although the shape of the wall  80  of the flow balancing element, in the exemplary embodiment described above, resembles a convergent/divergent nozzle, or the venturi tubes used in prior filters, the flow balancing element  18  of the present invention is both structurally and functionally very differently from such devices. The flow balancing element  18  of the present invention does not need to produce a lower pressure, to induce flow through the bypass filter, as was the case with venturis in prior filters having both a bypass and a full flow filtering element. The annular section of the wall  80  of the flow restrictor  18 , which forms the full flow restrictor  90  of the exemplary embodiment of the invention described above, does not restrict the flow through the flow balancing element  18  to a point that a significant reduction in pressure occurs at the flow restrictor  90 .  
         [0062]     As will be seen from an examination of  FIGS. 1 and 2 , the minimum diameter of the wall  80 , at the flow restrictor  90 , is approximately the same as the diameters of the inside surface  128  of the opening  54  in the intermediate seal  22 , and the bore  126  in the outlet tube  76  of the mounting adapter  78 . In order for the flow through the flow restrictor  90  to be accelerated to a degree significant enough to produce appreciable pressure drop at the bypass flow inlets  82 ,  84 , the full flow restrictor  90  would have to be considerably smaller in diameter than the diameters of the through hole in the intermediate seal  22  and the bore of the outlet tube  76 . In fact, in other embodiments of the invention, the full flow restrictor  90  may be separated from the bypass flow inlets  82 ,  84 , and might alternatively be provided by judicious sizing of the opening  54  in the intermediate seal  22 , the outlet  64  of the full flow filter  16 , the full flow inlet  68  of the bypass filter  14 , or other features located upstream from the bypass flow inlets  82 ,  84 . The bypass flow inlets may also have a very different configuration.  
         [0063]     In the exemplary embodiment of the spin-on filter  10 , shown in  FIGS. 1-3 , the annular wall  80  of the flow balancing element  18  has a conical shape on either side of the bypass flow inlets  82 ,  84 . This shape was selected for packaging reasons, to facilitate making connections to mating parts, and to form an outer surface that would direct and provide a smooth transition for the bypass portion of the fluid, as it changes direction from radial to axial, while moving along the outside of the wall  80  in the through bore  44  of the bypass filter  14 , prior to entering the bypass flow inlets  82 ,  84  in the flow balancing element  18 .  
         [0064]     To further emphasize this point,  FIG. 4  shows a second exemplary embodiment of a spin-on filter  130 , according to the invention, which is essentially identical, structurally and functionally, to the previously described spin-on filter  10 , except that the flow balancing element  18  of the first exemplary embodiment, having conical sections of the wall  80 , is replaced, in the second exemplary embodiment, with a flow balancing element  132  having a straight-sided annular wall  134 . The inner diameter of the straight-sided wall  134 , in the flow balancing element  132  of the second embodiment, is equal to the minimum diameter of the full flow restrictor  90  of the first embodiment. The entire inner surface  134  of the flow balancing element  132 , in the second embodiment, therefore, functions as the full flow restrictor in the second embodiment.  
         [0065]     From the disclosure provided herein, those having skill in the art will recognize that an apparatus or method, according to the invention, provides significant advantages in manufacturability and functionality, as compared to prior filters having a bypass element, a full flow element and a venturi tube for inducing flow through the bypass filter. It has also been found, that in a filter apparatus according to the invention, the filter media tends to be loaded more evenly with contaminants during its life. This results in the media of a filter apparatus according to the invention being able to hold more contaminant, before the filter needs to be replaced, thereby reducing operating costs of the system being served by the filter apparatus by reducing the frequency with which the filter apparatus needs to be replaced.  
         [0066]     Those having skill in the art will also recognize that, although invention has been described herein with reference to several exemplary embodiments, many other embodiments of the invention are possible. For example, although it is not necessary in practicing the invention to have the flow balancing element include a venturi, it is contemplated within the scope of the claimed invention that a flow balancing element in other embodiments of the invention might include a venturi.  
         [0067]     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0068]     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.