Abstract:
An assembly for filtering contaminants from automatic transmission fluid includes a housing including a first inlet and a second inlet, through which fluid enters the housing, and an outlet, through which fluid exits the housing; a first media filter located within the housing in a first fluid flow path between the first inlet and the outlet; and a second media filter located within the housing in a second fluid flow path between the second inlet and the outlet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a suction filter with multiple filtration elements that are fed from multiple inlets for an automatic transmission. 
     2. Description of the Prior Art 
     A simple transmission suction filter has a single media layer that is crimped on the edges between the housing flanges. This design has an inherit weaknesses: its overall capacity balanced against its efficiency and pressure drop. As more efficient media have higher flow resistance, i.e., lower permeability, a single media layer filter must be quite larger to handle the required transmission flow without having an excessive pressure drop at cold temperatures when the viscosity of the transmission fluid is highest. 
     Most transmission suction filters use a bag filter media arrangement, which provide higher media packaging density. This allows an increased area for fluid flow, which results in a lower pressure drop and higher dirt holding capacity while maintaining high efficiency. Furthermore, bag filters can be designed to take up less overall area due to their multiple layers of contact. They do, however, require a greater thickness to support the bag arrangement. 
     Bag filters have been further refined to improve performance, as U.S. Pat. No. 5,049,274 discloses. There the filter element was changed to an impregnated felt that was folded into a bag and crimped on the edges between two flanges. A hole in the lower portion of the folded bag was sealed on the edges and connected to the filter suction inlet. 
     An alternative used in a few transmissions employs a pleated, non-planar filter element design described in European Patent EP1588753A1. A pleated design provides an increased filter media packaging density. The tradeoff, however, is two fold: a pleated filter is more expensive to manufacture, but pleated technology allows only a rectangular housing configuration. 
     A need exists in the industry for a suction filter that provides high media packaging density, high dirt holding capacity, high filtration efficiency, packaging flexibility for irregular shaped housings, and low cost 
     SUMMARY OF THE INVENTION 
     A suction assembly for filtering contaminants from automatic transmission fluid includes a housing including a first inlet and a second inlet, through which fluid enters the housing, and an outlet, through which fluid exits the housing; a first media filter located within the housing in a first fluid flow path between the first inlet and the outlet; and a second media filter located within the housing in a second fluid flow path between the second inlet and the outlet. 
     The suction filter that provides high media packaging density, high dirt holding capacity, high filtration efficiency, packaging flexibility for irregular shaped housings, and low cost 
     A coarse filtering media is created with a bag filter, which communicates with a centrally located fluid inlet. A high efficiency filtering media comprises a single media layer, which is located between the bag filter and the bottom of the filter housing and is supplied through a series of smaller inlet holes arranged around the circumference of the bag filter inlet. 
     A molded separator grid, located between the bag filter and the single layer, comprises vertical ribs connected by narrow horizontal ribs, which support the two filtering layers and provide as flow channels for fluid that passes through the high efficiency single layer. 
     The bag filter is connected to the top of the main central inlet and the single layer is connected to a middle platform on the main central inlet. With a proper balance of inlet areas, fluid will flow through the central inlet into the bag filter and through the smaller inlet holes into the single layer filter. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a cross sectional view of a suction filter; 
         FIG. 2  is bottom view of the suction filter of  FIG. 1 ; 
         FIG. 3  is a schematic diagram that illustrates parallel fluid flow paths through the fine media filter and coarse media filter in the suction filter of  FIG. 1 ; 
         FIG. 4  is a cross sectional view of a suction filter that includes two filter bags; 
         FIG. 5  is a cross sectional view of a suction filter that includes two layers of fine filtration media; and 
         FIG. 6  is a cross sectional view of a suction filter in which the separator grid is formed with the first inlet. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  a suction filter  10  that includes an upper housing  12  provided with internal supporting ribs  13 , a lower housing  14  secured to the upper housing at peripheral flanges  16 ,  18 , a separator grid  20  located in the lower housing between a coarse media bag  22 , located in the upper housing between an outlet  24  and the separator grid, and a fine media  26  located in the lower housing between a passageway  28  and the separator grid. 
     Preferably, the separator grid  20  is a molded component comprising canted ribs  32  connected by narrow horizontal ribs  32 ,  36 , which support the two filtering layers and provide flow channels for fluid that passes through the high efficiency, fine media layer  26 . A lower surface of the coarse media bag  22  contacts a surface of the upper ribs  32  of the separator grid  20 , and an upper surface of the coarse media contacts the lower surface of internal supporting ribs  13 . An upper surface  34  of the fine media  26  contacts the surface of the lower ribs  32  of the separator grid  20 . 
     A first inlet  40 , aligned with passageway  28 , directs incoming fluid through an opening  42  in the coarse media bag  22  and inlet  40  to the interior of the coarse media bag. 
     Fluid flow through passageway  28  enters the first inlet  40  and a second inlet  44 . One flow path is through inlet  40  and the coarse media bag  22 . A second flow path is through inlet  44  and the fine media  26 . The separator grid  20 , which maintains a flow passageway between the fine media  26  and the bag media  22 , provides support for both media  22  and  26 . Flow passage to outlet  24  is maintained open by passages between the upper surface of coarse media bag  22  and internal supporting ribs  13 . 
       FIG. 2  shows that passageway  28  leads to the first inlet  40 , which directs fluid into the bag media  22 , and the a second inlet  44 , which comprises a series of angularly spaced holes, which direct incoming fluid to the fine media  26 . Although  FIG. 2  illustrates an arrangement with eight secondary inlet holes  44 , any number of holes can be used to feed the fine media  26 . 
     In the embodiment of  FIGS. 1 and 2 , the fine media  26  and separator grid  20  are both supported on a ledge  46  formed on a fitting  47  in which the inlet  40  is formed. A ledge  48  formed on the lower housing  14  also supports the fine media  26  and separator grid  20  on the housing  14 . 
     Preferably fine media  26  and bag media  22  are secured to separator grid  20  by ultrasonic welding around the periphery of the opening  42  and the separator grid opening where fitting  47  is located. 
       FIG. 3  is a schematic diagram illustrating parallel fluid flow paths through the fine media filter  34  and coarse media filter  22  in suction filter  10 , which draws fluid from a fluid sump  47  and returns fluid through a transmission  49  to sump. The flow resistance between the flow paths R CROSS  is negligible and can be disregarded. 
     The variables of filtration hydraulic circuits are analogous to electrical variables of an electric circuit, and their relationships can be expressed in equations that correspond to the equations of Kirchhoff&#39;s voltage laws when considering the following analogies: 
     Voltage and Pressure Drop (PD) 
     Current and Flow Rate (Q) 
     Electric Resistance and Flow Resistance 
     In the schematic diagram of  FIG. 3 , formulas (1) and (2) can be used to express flow through the fine media filter  34 . 
                                           PD   system     +       (     R   1     )     ⁢     (     I   1     )         =   0             Subtract             PD   system     +       (     R   2     )     ⁢     (     I   2     )         =   0                                                 (     R   1     )     ⁢     (     I   1     )       -       (     R   2     )     ⁢     (     I   2     )         =   0                                           (     R   1     )     ⁢     (     I   1     )       =       (     R   2     )     ⁢     (     I   2     )                       (   1   )               
Substituting hydraulic circuit variables for their corresponding electric variables in equation (1)
 
( R   FINE )( Q   FINE )=( R   COARSE )( Q   COARSE )  (2)
 
     In the dual-inlet, dual-media filter  10 , the fine filter  26  has a resistance between 4× and 10× the resistance of the coarse media filter  22 , depending on the media selected. If the flow resistance of the fine filter  26  is large, flow will always be present through the fine filter, provided its resistance does not approach infinity. Note that a new factor, defined as Media Resistance Factor (K MR ) has been defined and is simply a ratio of the flow resistance of the coarse media  22  and fine media  26 . Values for K MR  range between 0, when the coarse media is relatively restrictive or clogged, and 1 when the flow resistance of the porous media  26  is similar to that of the coarse media  22 .
 
( Q   FINE )=( R   COARSE )( Q   COARSE )/( R   FINE )
 
( Q   FINE )=[( R   COARSE )/( R   FINE )]( Q   COARSE )
 
( Q   FINE )=( K   MR )( Q   COARSE )
 
       FIG. 4  illustrates a suction filter  50  that includes two filter bags, the coarse medial bag  22  and a fine media bag  52 , instead of the single layer filter  26 . While suction filter  50  provides additional media packaging density for the high efficiency option, it also requires additional thickness. Preferably fine media bag  52  and bag media  22  are secured to separator grid  20  by ultrasonic welding around the periphery of opening  42  and the opening of the separator grid  20  where fitting  47  is located. 
       FIG. 5  illustrates a suction filter  60  that adds a second, upper layer of fine filtration media  62  between the coarse media bag  22  and upper housing  12 . An additional upper separation grid  64  is supported on a fitting  66 , which engages the edges of the lower separation grid  20  and the upper separation grid  64 , and provides a wall of a channel  68 . 
     Much like the two bag filter  50 , suction filter  60  requires additional thickness and also requires an additional channel  68 , which directs and carries incoming fluid to the upper layer of fine filtration media  62 . Preferably fine media  26  and bag media  22  are secured to separator grid  20  by ultrasonic welding around the periphery of opening  42  and the opening of the separator grid  20  where fitting  47  is located. 
       FIG. 6  is a cross sectional view of a suction filter in which the separator grid  70  is formed with a first inlet  72  that carries fluid through the separator grid  70  into the bag media  22 . Fitting  47  of the embodiment of  FIG. 1  is deleted. Fluid also flows through a second opening  74  to the fine media  26 . Passageway  28  communicates with first and second inlets  72 ,  74 . Fluid flows through inlet  74  and separator grid  70  and along the outside of bag media  22  to outlet  24 . Fluid flows through inlet  72  into and through bag media  22  to the outlet  24 . 
     Preferably, fine media  26  and bag media  22  are secured to separator grid  70  by ultrasonic welding around the periphery of the first inlet  72 . 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.