Abstract:
A transmission oil filter is assembled from a filter element, a base, and a cover. Each of the three pieces extends beyond the filtration media to form an inlet channel. The inlet channel is low enough to fit under a valve body. Placing the inlet in this channel ensures that the inlet draws transmission fluid at road gradients and acceleration rates at which an inlet under the filtration media would draw air.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to the field of transmission systems. More particularly, the disclosure pertains to a filter assembly. 
       BACKGROUND 
       [0002]    Automatic transmission fluid serves many functions in a modern automatic transmission. Pressurized fluid may be used to engage friction clutches in order to establish a power flow path with a desired speed ratio. Fluid lubricates gears and bearings. Excess heat is removed by fluid flowing over various components. When the fluid contain contaminants, it may be less effective in these functions and may cause failures such as stuck valves. Therefore, transmissions often include fluid filters. 
         [0003]    Filters may be placed on either the inlet (low pressure) side of a transmission pump or on the outlet (high pressure) side of a transmission pump. Transmission oil filters typically contain a filtration media. The media may be pleated to increase the surface area in a limited space. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    A transmission includes a filter element, a filter cover, and a filter base. The filter element has a filtration portion and an extension. The filtration portion has side walls defining a top edge and supporting filtration media. The extension is joined to the filtration portion below the filtration media. The filtration portion and the extension define an element bottom edge. A height of the extension may be less than a distance between the filter element bottom edge and a top of the filtration media. The filter cover is in contact with the top edge. The filter cover defines a filter outlet adjacent to the filtration portion. The filter cover also defines a bottom cover edge. The filter base defines a filter inlet adjacent to the extension. The filter base is sealed against the element bottom edge and the cover bottom edge, for example by a single continuous weld. An interior height of the cover may be equal to a distance between the filter element top edge and the filter element bottom edge such that the filter element bottom edge and the cover bottom edge are coplanar. A valve body may extend over the inlet and extend lower than the top edge or lower that a top of the filtration media. The transmission may be filled with transmission fluid such that, when the transmission is inclined, the inlet is below the fluid surface and the filter base adjacent to the filtration portion is above the fluid surface. 
         [0005]    A transmission filter is assembled by placing a cover over an element and joining a base to bottom edges of the cover and of the element with a continuous sealing joint. The cover is placed over the element such that a surface of the cover defining an outlet contacts a top edge of the element to align the bottom edge of the element with a bottom edge of the cover. The element has filtration media extending a first distance above the element bottom edge. The element has an extension with a height relative to the element bottom edge less than the first distance. The base defines an inlet adjacent to the extension. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic diagram of a vehicle transmission. 
           [0007]      FIG. 2  is a cross section of a first oil filter in a transmission sump. 
           [0008]      FIG. 3  is a cross section of a second oil filter in a transmission sump. 
           [0009]      FIG. 4  is a cut-away pictorial view of the second oil filter. 
           [0010]      FIG. 5  is an exploded view of the second oil filter. 
           [0011]      FIG. 6  is a pictorial view of the second oil filter. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0013]      FIG. 1  schematically illustrates a transmission hydraulic system. Dash-dot lines indicate mechanical power flow. Solid lines indicate flow of hydraulic fluid. Dashed lines indicate electrical signals. Transmission input shaft  10  is connected to the vehicle crankshaft. Power from the engine is delivered to torque converter  12  which drives turbine shaft  14 . Clutches within gearbox  16  are engaged to establish a power flow path from turbine shaft  14  to output shaft  18 . Different power flow paths having different speed ratios may be established by engaging different clutches. In a rear wheel drive transmission, output shaft  18  is connected to a driveshaft which transmits the power to a rear differential and then to rear wheels. In a four wheel drive vehicle, a transfer case may be installed between the output shaft and the driveshaft to divert a portion of the power to a front differential and then to front wheels. In a front wheel drive vehicle, the output shaft may transmit power to a front differential via gears or a chain. 
         [0014]    Some engine power is diverted to drive transmission pump  20 . Transmission pump  20  draws fluid from sump  22 , through filter  24 , and delivers the fluid, at increased pressure, to valve body  26 . The pressure at which fluid enters the valve body may be called line pressure. Controller  28  commands a network of control valves within the valve body to deliver fluid to torque converter and gearbox components at desired pressures less than line pressure and at desired flow rates. Fluid drains from the control valves and from the gearbox back into sump  22 . 
         [0015]      FIG. 2  is a partial cross section of filter  24 , valve body  26  and sump  22 . When the vehicle is on level ground and either stationary or traveling at constant speed, the top of the fluid in the sump is represented by dotted line  30 . Pump  20  draws the fluid through filter inlet  32 , through filtration media  34 , and through filter outlet  36 . The filtration media may be pleated to increase the surface area within the constrained axial distance available. When the vehicle decelerates or is on a downhill incline, the fluid may move forward in the sump such that the top of the fluid follows dotted line  30 ′. This circumstance does not pose a problem with respect to filter  24 . However, when the vehicle accelerates or goes up a hill such that the top of the fluid follows dotted line  30 ″, the pump may draw air instead of fluid. If this occurs for a brief interval, the air may cause an unpleasant noise. If the situation persists, the transmission may cease to function or become damaged. Moving the filter farther rearward may not be possible due to the space required for the valve body or other transmission components. 
         [0016]      FIGS. 3 and 4  show a revised filter design  24 ′. Modified filter  24 ′ includes an extension channel  38 . The height h of the extension channel permits packaging the extension underneath the valve body  26 . The height h of the extension channel is less than the distance D between the bottom of the filter and the top of the filtration media. Therefore, the filtration media  34  does not extend into the extension channel  38 . Inlet  32 ′ is in the extension channel  38  as opposed to being under the filtration media  34 . In this location, inlet  32 ′ draws fluid regardless of the vehicle acceleration rate or the road incline. 
         [0017]      FIG. 5  illustrates a method of assembling filter  24 ′. The filter is assembled from three parts: a filter element  40 , a cover  42 , and a base  44 . Each of these parts may be made of plastic (except for the filtration media  34 ). Filter element  40  has side walls  46  that define a top edge  48  and a portion of a bottom edge  50 . Top edge  48  and bottom edge  50  are separated by a vertical distance H. The volume surrounded by the side walls is called the filtration portion. The filtration portion is open on both the top and on the bottom. The filtration media  34  is joined to the inner surface of the side walls between the top edge and the bottom edge. An extension extends from one of the side walls below the filtration media. The extension is open on the bottom but closed on the top. The bottom of the extension defines the remainder of the bottom edge of the filter element. The extension portion has a height h which is less than H. 
         [0018]    In a first assembly step, cover  42  is placed over filter element  40 . Cover  42  has side walls  54  which partially define a bottom edge  56  and an extension  58  which defines the remainder of the bottom edge  56 . The extension  58  is open on the bottom and closed on the top. Outlet channel  36  is formed into the top  60  of the cover. The bottom surface of the top  60  is separated from the bottom edge of the cover  56  by the distance H. Consequently, when the cover is placed over the filter element with the top edge  48  of the filter element in contact with the bottom surface of the top of the cover, the bottom edges  50  and  56  of the filter element and the cover respectively are aligned. 
         [0019]    In a second assembly step, the filter element and the cover are placed on the base  44 . The bottom edges  50  and  56  of the filter element and the cover respectively fit tightly against the flat top surface  62  of the base. In a third assembly step, heat is applied to a bottom surface of the base opposite the bottom edges  50  and  56  of the filter element and the cover. This heat momentarily melts the plastic. When the plastic re-hardens, the bottom edges of the filter element and the cover become welded to the base. The heat is applied around the full perimeter to form a continuous weld  64  (visible in  FIG. 3 ). In addition to fastening the components, this weld forms a seal which forces any fluid that enters inlet  32 ′to flow through filter media  34  before exiting outlet  36 . Alternatively, this continuous, sealing joint could be formed by adhesive. The completed filter is shown in  FIG. 6 . 
         [0020]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.