Abstract:
An internal bypass filtration circuit including a microfine depth filtration cartridge, which operates in combination with the sump filter of an automatic transmission is disclosed. The present depth filtration cartridge functions to remove particulate matter as small as five microns to improve fluid cleanliness level without restricting fluid flow to the pump ensuring its volumetric efficiency. In one embodiment transmission fluid passes through a calibrated orifice in the bypass circuit to regulate flow to the depth filtration cartridge. In an alternate embodiment the depth filter media itself regulates filtration below a predetermined fluid pressure. The internal bypass circuit is installed by accessing a pressurized fluid circuit in the transmission valve body. A hydraulic bypass line interconnects such pressurized fluid circuit with the depth filtration cartridge, which is mounted internally of the transmission housing. The outlet of the depth filtration cartridge exhausts directly into the sump bypassing all other functional circuits.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 60/817,283 filed Jun. 28, 2006 entitled, Internal Bypass Filtration Circuit. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to automatic transmissions for land vehicles and, more particularly, to an internal bypass filtration circuit for such automatic transmissions. For purposes of this application the term “internal” refers to a physical location (i.e. a space or cavity) inside a transmission and is not be confused with terminology such as “filter with an internal by-pass”. The latter terminology refers to a common feature of a hydraulic filter element wherein if oil flow through the filter element becomes restricted, then an internal by-pass mechanism or passage within the filter opens and allows the oil to by-pass the filter element and keeps the oil circuit functioning. 
     Maintaining automatic transmission fluid (hereinafter “ATF”) in a clean condition free of particulates and contamination is critical to the proper function of an automatic transmission. Contamination of ATF is of particular concern to the automatic transmission rebuilding industry where there is a general trend toward achieving increased service longevity from remanufactured automatic transmissions. However, recent industry data is confirming exponentially higher contamination levels in remanufactured units due to various contributing factors and, accordingly, there is a need for increased filtration efficiency in such remanufactured transmissions. 
     Most automatic transmissions and transaxles use a standard wet sump system wherein ATF drains by gravity into the pan and the pump takes it up directly and discharges it to the hydraulic system. In a typical automotive application an ATF sump filter is submerged in the pan in fluid communication with the transmission pump. As the pump rotates ATF is drawn from the sump and through the filter by vacuum into the suction port of the pump. 
     Pumps in automatic transmission hydraulic systems are typically positive displacement pumps driven at engine speed. A positive displacement pump is one, which has the same output per revolution regardless of pump speed or pressure already developed in the system. Given the continuous flow requirements of the hydraulic system, a consistent flow of ATF through the filter to the pump is critical to proper lubrication and function of the transmission. 
     Because a sump filter is on the inlet side of the pump, it must not unduly restrict ATF uptake to the pump. This is a particular problem during cold start-up, hot idle and high volume/demand situations. Thus, it will be appreciated by those skilled in the art that the ATF filtration system has conflicting functions (i.e. ATF must flow freely to the pump without restriction, but must be filtered to remove harmful contaminants, which inherently restricts ATF flow). 
     The present internal bypass filtration system has been developed to resolve this problem and other shortcomings of the prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is an improved ATF filtration system for an automatic transmission that provides an internal bypass filtration circuit including a microfine depth filtration cartridge (i.e. ATF is passed through several layers of filter media), which operates in conjunction with the original equipment manufacture (hereinafter “OEM”) sump filter to increase ATF cleanliness level. 
     In accordance with a method of the present invention, the internal ATF bypass circuit is installed by drilling an access hole into an existing pressurized ATF circuit in the valve body or other access point within the transmission assembly. Thereafter, the access hole is threaded and a hydraulic bypass line with a mating threaded fitting is installed therein to deliver ATF to the depth filtration cartridge during pump operation. 
     ATF passes through a calibrated restriction (i.e. orifice) as it flows through the bypass line and is delivered to the depth filtration cartridge wherein ATF passes through the depth media. The outlet of the depth filtration cartridge exhausts directly into the sump/pan area bypassing all other functional circuits. The depth filtration cartridge includes a dedicated mounting bracket adaptable for a given transmission application. 
     The present depth filtration cartridge functions to remove a wide range of particulate matter (i.e. as small as 5 microns) from the ATF, but does not interfere with the unrestricted flow of ATF to the pump to ensure its volumetric efficiency and the proper function of the OEM filtration system. 
     The present bypass filtration circuit including the depth filtration cartridge is designed for installation in an open cavity or space within the transmission during remanufacturing operations using pre-existing fasteners from the transmission. By installing the present internal bypass filtration circuit as an upgrade during remanufacture, a local auto repair shop technician need not be relied upon to plumb and install such a depth filtration device externally of the transmission, which is the only option in current industry practice. Such practice often results in improper installation, ATF leakage, and pressure loss within the transmission system reducing the service longevity of such an externally installed device. 
     There has thus been outlined, rather broadly, the important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. 
     Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the present invention are set forth in the appended claims. The invention itself, however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein: 
         FIG. 1  is schematic representation of the sump of an automatic transmission showing the position of an OEM sump filter in the ATF pan and is labeled Prior Art; 
         FIG. 2  is a cutaway plan view of a fixed displacement, Gerotor type ATF pump installed within the pump body and is labeled Prior Art; 
         FIG. 3  is a schematic representation of an OEM filter housing and is labeled Prior Art; 
         FIG. 4A  is a partially cutaway elevation view of an embodiment of the depth filter assembly of the present invention; 
         FIG. 4B  is a partially cutaway elevation view of another embodiment of the depth filter assembly of the present invention; 
         FIG. 5  is a partial perspective view of a valve body of an automatic transmission illustrating the location of an access hole wherein the present depth filter assembly is installed; and 
         FIG. 6  is a partial bottom plan view of a transmission housing with the ATF pan removed illustrating the present internal bypass filtration circuit installed in its functional position within such housing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Prior to describing the present invention in detail, it may be beneficial to briefly discuss the structure and function of a so-called sump filter in an automatic transmission. With further reference to the drawings there is shown an illustration of such an ATF sump filter, indicated generally at  100 , within the sump or pan  120  of an automatic transmission. Such a sump filter  100  is comprised of a housing  105 , which is submerged below the ATF level as at  115  in the pan. Housing  105  is disposed in fluid communication via suction tube  102  with the transmission pump, indicated generally at  125  and shown in  FIG. 2 . 
     A positive displacement pump  125  of the Gerotor type is shown in  FIG. 2  for purposes of explanation. Of course, other types of positive displacement pumps such as gear pumps and vane pumps may be utilized with the present invention. In the Gerotor type pump  125  as the inner rotor  128  turns each of its teeth maintains continuous line contact with a tooth of the outer rotor  129 , the point of contact shifting from the flanks of the teeth  130  at full mesh to the tops of the teeth upon rotation as shown by the directional arrow  132 . In this way a pumping action is developed. 
     Passages or ports  126 ,  127  are required in the pump body  140  to carry ATF into the suction side and away from the discharge side respectively of the pump  125  to the hydraulic system. Rotation of the pump  125  at engine speed generates vacuum within the suction port  127 , which draws ATF from the pan  120  through primary inlet  135  and the sump filter element  110  via suction tube  102  as shown by directional arrows  150  ( FIG. 3 ). 
     As shown in  FIG. 3  the OEM sump filter  100  typically contains a filter element  110  that is rated in the range of 25-100 microns, through which ATF must pass en route to the pump  125 . A micron rating is a generalized way of indicating the ability of the filter element  110  to remove contaminants by the size of the particles. The importance of removing even the smallest particles to extend the operating life of ATF and components has been well established. But the micron rating does not properly and fully describe either the efficiency or the contaminant-holding capacity of the filter. 
     Component wear is directly related to the cleanliness level of the system (i.e. to the number of solid particles in the ATF). Thus, the cleaner the fluid, the less wear in the transmission. Not only large particles with diameters roughly equal to the micron rating, but also sludge particles smaller than 5 microns can cause significant damage, break downs, and generally degrade the ATF. 
     The media utilized in the OEM filter element  110  is the physical mechanism used for contamination control. The media utilized in OEM filter elements ranges from mesh screens to synthetic microfibers blended in various configurations. Media construction and filter configuration are used to determine the filter&#39;s efficiency for particle removal and must be balanced against the pressure drop, or resistance to flow, which are a normal consequence of filtration. 
     Because a sump filter  100  in an automatic transmission of the type shown in  FIG. 3  is disposed on the inlet side of the pump, it must guarantee a restriction-free flow of ATF to the hydraulic system. This is a particular problem during cold start-up, hot idle and high volume/demand situations. Thus, it will be appreciated that the ATF filtration system has conflicting functions (i.e. ATF must flow freely to the pump  125  without restriction, but must be filtered to remove harmful contaminants, which inherently restricts ATF flow). Accordingly, the present invention has been developed to balance this inherent effect of filtration with the desired cleanliness level and will now be described in detail. 
     The present internal bypass filtration system provides structures and functional features, which comprise microfine depth filtering means including, but not limited to, the following structures. Referring to  FIG. 4A , the present internal bypass filtration circuit, indicated generally at  10 , comprises a microfine depth filtration assembly, indicated generally at  25 , with an attached hydraulic bypass line  33  that functions independently of the OEM sump filter  100  to remove a wider range of particle sizes and contaminants from the ATF to improve cleanliness. 
     In the present internal bypass circuit  10  ATF is forced under pressure through depth filter assembly  25  independently of ATF taken up directly by the pump  125  bypassing all other functional hydraulic circuits within the transmission system. The filtered ATF output of the depth filtration assembly  25  exhausts via outlet port  32  directly into the sump  120  to be recirculated by the pump  125 . 
     Depth filtration assembly  25  comprises a filter canister  27  containing depth filtration media  30  designed to capture particles as small as 5 microns in size, which are not visible without magnification. It has been determined that particulates in this size range can be damaging to the transmission hydraulic system and that removing such contaminants will prevent early system failure and/or continuing hydraulic system leakage. 
     Still referring to  FIG. 4A , depth filtration media  30  contained in the present filter canister  27  comprises microfine mesh, synthetic fibers, cellulose fibers, and/or multi-layer media in various configurations for a given transmission application. In one embodiment an orifice block  37  defining a calibrated restriction or orifice  45  is attached to a first end of bypass line  33 . Orifice block  37  includes a fitting  37   a  having an external #10-32 thread for engagement in a threaded access hole  35  ( FIG. 5 ) formed in the valve body in accordance with a method of the present invention, which is described hereinafter in further detail. 
     In an alternative embodiment of the present internal bypass filtration circuit  10 ′ shown in  FIG. 4B , orifice block  37  is omitted and the filter media  30  within the canister  27  is designed such that the filter media itself regulates and will not permit any appreciable ATF flow through the canister  27  below a predetermined fluid pressure to ensure the volumetric efficiency of the pump  125  and that sufficient fluid pressure is maintained within the transmission system. In this embodiment a first end of hydraulic bypass line  33  is provided with a flare nut  34  that connects the bypass line directly to the threaded access hole  35  formed in the valve body  40 . An opposite end of hydraulic bypass line  33  is also provided with a flare nut  34  that connects the bypass line to a threaded coupling  38  which, in turn, engages a mating fitting  39  attached to the canister  27 . 
     In a method of the present invention, the internal ATF bypass circuit  10 ,  10 ′ is installed for operation in conjunction with an OEM filtration system described hereinabove by drilling an access hole  35  into a pressurized hydraulic circuit contained within the valve body  40  at a predetermined location as shown in  FIG. 5 . Next, access hole  35  is tapped to provide threads of a desired size. In the embodiment shown a #10-32 threaded hole  35  is utilized to attach the bypass line  33  to the valve body  40 . 
     Alternatively, any other suitable access point on the valve body  40  or transmission housing  200  ( FIG. 6 ) providing access to a pressurized ATF circuit within the hydraulic system can be utilized to locate such access hole  35 . Of course, such location varies for each installation and detailed instructions are provided to the technician for a given transmission application. 
     Next, an orifice block  37  defining a calibrated restriction or orifice  45  is attached to a first end of bypass line  33 . Orifice block  37  includes a fitting  37   a  having a matching external #10-32 thread for engagement in the threaded access hole  35 . Orifice  45  functions to restrict ATF flow by controlling the volume of fluid delivered to the depth filtration assembly  25  to a calculated level based on the pump capacity and the requirements of the hydraulic system. An opposite end of hydraulic bypass line  33  is provided with a flare nut  34  that connects the bypass line to a threaded coupling  38  which, in turn, engages a mating fitting  39  attached to the canister  27 . 
     The present internal bypass filtration system provides structures and functional features, which comprise mounting means including, but not limited to, the following structures. The present depth filtration assembly  25  also includes a dedicated mounting bracket  42  for installation of canister  27  at a suitable position within the transmission housing  200  using pre-existing machine screws  50  installed within the housing as shown in  FIG. 6 . 
     It will be understood that the present bypass filtration circuit  10  including depth filtration assembly  25  is designed primarily for installation in proximity to the sump pan  120  or other space within the transmission housing  200  ( FIG. 6 ) as an upgrade during industry remanufacture operations. By installing the present bypass filtration circuit  10  during remanufacturing operations, a transmission shop technician need not be relied upon to plumb and install an alternative filtration device externally of the transmission as is the present industry practice. Such practice can result in improper installation, ATF leakage, and pressure loss reducing the service longevity of such an external filtration device. 
     However, it is contemplated that the present internal bypass filtration circuit  10  will also be provided in an aftermarket kit including a depth filtration assembly  25 , bypass line  33 , orifice block  37 , fittings  38 ,  39 , installation tools, and instructions for internal installation by a qualified service technician. 
     Although not specifically illustrated in the drawings, it should be understood that additional equipment and structural components will be provided as necessary and that all of the components described above are arranged and supported in an appropriate fashion to form a complete and operative Internal Bypass Filtration System incorporating features of the present invention. 
     Moreover, although illustrative embodiments of the invention have been described, a latitude of modification, change, and substitution is intended in the foregoing disclosure, and in certain instances some features of the invention will be employed without a corresponding use of other features. 
     Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.