Abstract:
A bidirectional valve comprising a flexible member with an aperture formed therein. The flexible member reacts to differential pressure thereacross by deforming, thereby causing the inside surfaces of the aperture to separate and create a vent path. The bidirectional valve can be tuned to open the aperture in reaction to varied differential pressures thereacross, thereby allowing a fluid to pass through the aperture.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/393,388, filed on Jul. 2, 2002. The disclosure of the above application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to bidirectional relief valves, and more specifically to an automatic transmission vent/relief valve. 
   BACKGROUND OF THE INVENTION 
   A conventional automatic transmission for a vehicle includes rotating shafts that penetrate a housing. These shafts typically have bearings that rotatably support the shafts within the housing and seals are incorporated on the outside of the bearings in order to retain the transmission fluid within the housing and to keep dirt and contamination out of the housing. During operation, a conventional automatic transmission generates heat which is dissipated by the transmission fluid. A typical transmission can exceed 200° F. during normal operation. As the internal housing of the transmission is heated, the air within the housing absorbs some of the heat. As this air is heated, it undergoes a volumetric expansion and/or increase in pressure. In a sealed transmission, an increase in internal air pressure within a fluid chamber may be relieved through the shaft seals. As air escapes past the seals, it pushes some transmission fluid out through the bearings and seals to the outside of the transmission housing. This leaking of transmission fluid is undesirable, in part, because it would require additional transmission fluid to be added periodically. 
   Additionally, a transmission housing that has relieved air by pushing air and transmission fluid out past the bearings, will draw or suck air back in through the bearings as the air within the transmission housing cools and contracts. As air is drawn in past the seals, dirt and other contaminants can be pulled past the seals and into the bearings and fluid chamber. This contamination can shorten the life of the bearings and internal moving parts. 
   Therefore, to prevent an unwanted air pressure increase, air is typically vented to the outside of the transmission housing to relieve the volumetric expansion of air. Typically a vent or breather assembly is incorporated into a transmission housing in order to relieve the pressure due to this expansion of the heated air. This vent includes an elongated body inserted through an aperture in the transmission housing having a cap and a filter assembly inserted therein. The vent assemblies involve multiple machined components and typically regulate the internal pressure of the transmission equal to that of the ambient pressure outside of the transmission. 
   One drawback associated with this design is the inability of these vent assemblies to limit the amount of ambient air allowed into the transmission fluid chamber. As the transmission cools and air is drawn back into the transmission housing, the moisture, or humidity, within the ambient air is also drawn into the housing. As the transmission cools further, this moisture condenses within the transmission housing and mixes or stratifies within the transmission fluid. The operation of the automatic transmission can be adversely affected if an undesirable amount of water is pulled into the transmission through the vent assembly. 
   Another drawback associated with typical vent assemblies involves fill tube overflow. Transmission fluid is typically added to an automatic transmission through a fill tube. As fluid is added, some vent assemblies may not allow for adequate pressure relief of air to account for the volume of fluid added. When this occurs, fluid flow down the fill tube will slow and/or stop due to an air pressure increase within the transmission that exceeds the pressure exerted by the level of fluid in the fill tube. As more fluid is poured into the tube, the rate of fluid being poured can exceed the rate of fluid flow through the fill tube, causing the fluid to undesirably overflow the fill tube and spill onto the components located adjacent the fill tube. 
   What is needed is a transmission vent assembly that will allow an adequate amount of air pressure to be relieved and that also incorporates a relief assembly that will actuate when a pre-selected differential pressure across the transmission housing is reached. 
   SUMMARY OF THE INVENTION 
   In accordance with the teachings of the present invention, a method and apparatus for venting an automatic transmission is disclosed. In one form, the present invention provides a bidirectional vent valve for an automatic transmission that includes a flexible member defining a slit therein. The flexible member is configured to seal the transmission housing and to relieve pressure bi-directionally once a pre-selected pressure differential across the flexible member is experienced. 
   In another form, the present invention provides a method for venting an automotive component including coupling a flexible member to a housing of an automotive component wherein the flexible member defines a slit therein. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an automatic transmission in accordance with the teachings of the present invention; 
       FIG. 2  is a perspective view of the vent valve illustrated in  FIG. 1 ; 
       FIG. 3  is a sectional view of the vent valve of  FIG. 2 ; and 
       FIG. 4  is a perspective of the vent of  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments of a method and apparatus for venting an automatic transmission are merely exemplary in nature and is no way intended to limit the invention, its application, or uses. Moreover, while the present invention is described in detail with a reference to an automatic transmission, it will be appreciated by those skilled in the art that the present invention is not limited to an automatic transmission but may also be used with any other housing that requires a vent valve. With initial reference to  FIG. 1 , an automatic transmission in accordance with the teachings of the present invention is illustrated and referred to generally by the numeral  10 . Automatic transmission  10  includes a top portion  12 , and a bottom portion  14  defining a chamber  18 . Top portion  12  defines a vent aperture  16  that provides a passageway between chamber  18  and an external surface of top portion  12 . A valve  20  is interposed within vent aperture  16 . 
   With specific reference to  FIGS. 2 and 3 , valve  20  includes a body  22 , a cap  24 , a sleeve  26 , and a flexible member, or vent,  28 . Body  22  is illustrated to include a connecting portion  30  at a first end  32 , and a venting portion  34  at a second end  36 . Connecting portion  30  includes a ridged surface  38  for engaging the valve aperture  16 . Venting portion  32  includes an inside bore  40 , and a shoulder  46  that extends about the circumference of body  22 . Connecting portion  30  further includes an internal bore  48  that extends from first end  32  to inside bore  40 . Body  22  further includes a collar  50  formed about the circumference of body  22  wherein ridged surface  38  extends from collar  50  to first end  32 . As presently preferred, body  22  is turned from AISI 12L14 steel. 
   Referring now to  FIG. 4 , vent  28  includes an annular retaining collar  58  connected to a flexible, hollow dome  60  having a slit  62  formed therein. Dome  60  is defined by an inner surface  64  and an outer surface  66 . Retaining collar  58  includes a circular outer surface  70 , a top surface  72 , and a bottom surface  74 . Slit  62  is defined by an inside surface  76  and an inside surface  78 . Inside surfaces  76 ,  78  extend from the inner surface  64  to the outer surface  66 . Vent  28  is configured to be interposed within inside bore  40  such that dome  60  extends away from first end  32 , as best seen in  FIG. 3 . As presently preferred, vent  28  is constructed of fluoro-silicon. It will become apparent below that dome  60  could be formed to any shape, including a flat or curved, that provides a flexible portion. When the air pressure acting on inner surface  64  exceeds the air pressure acting on outer surface  66 , a first pressure differential condition is created. When the air pressure acting on outer surface  66  exceeds the air pressure acting on inner surface  64 , a second pressure differential condition is created. 
   As illustrated in  FIG. 3 , sleeve  26  includes a cylindrical mating surface  80  disposed between a lower end  82  and an upper end  84 . Sleeve  26  is configured to be inserted into body  22  wherein mating surface  80  is in interference with inside bore  40 . In this manner, sleeve  26  retains vent  28  within body  22 . 
   Cap  24  includes a cylindrical wall  90 , intersecting an end member  92  at a first end  94 , and a second end  96 . When assembled, cap  24  is superposed about venting portion  34  and second end  96  is crimped in at least two places such that cylindrical wall  90  contacts shoulder  46 . In this manner, cap  24  is retained on body  22  while providing a vent path  100  therebetween. As presently preferred, cap  24  is stamped from AISI 1010 steel. 
   Valve  20  is inserted into valve aperture  16  and driven into valve aperture  16  with a rubber hammer. As valve  20  is inserted into vent aperture  16 , ridge surface  38  engages the internal surface of vent aperture  16  thereby retaining valve  20  within vent aperture  16 . 
   During operation of transmission  10 , heat from the internal rotating members of transmission  10  is transferred to the fluid within transmission  10  and also to the air within chamber  18 . As the air is heated within the chamber  18 , air pressure within transmission  10  increases to a pressure greater than ambient. This increase in air pressure produces a first differential pressure as the pressure on inner surface  64  acts to deform dome  60 . The first differential pressure is the amount that the internal air pressure within transmission  10  exceeds an ambient air pressure outside of transmission  10 . As the air pressure within chamber  18  increases, dome  60  is deformed such that inside surfaces  76 ,  78  of slit  62  are forced apart, thereby providing an opening, or vent path, for the air to be expelled from the chamber  18 . When air is vented out of chamber  18 , the air pressure within chamber  18  is reduced, thereby allowing dome  60  to deform such that inside surfaces  76 ,  78  of slit  62  come together to reestablish a seal therebetween. 
   As will be appreciated by one skilled in the art, the shape of dome  60 , the length of slit  62 , and the thickness of vent  28  are factors that determine a minimum first differential pressure across vent  28  that will open slit  62 . As presently preferred, slit  62  opens when the first differential pressure reaches a range of greater than 0.0 to about 1.0 psid, and more preferably, about 0.25 psid. Thus provided, valve  20  allows a portion of the air pressure within transmission  10  to be reduced by venting air within chamber  18  to a location outside of transmission  10  when the first differential pressure exceeds a predetermined value. 
   As transmission  10  begins to cool, the air within the chamber  18  will cool and contract. This contraction of air within transmission  10  will decrease the internal air pressure within the chamber  18 . As the air pressure within the chamber  18  decreases below the ambient air pressure outside of transmission housing  10 , the second pressure differential condition is produced. When the second pressure differential condition is produced, the ambient air pressure begins to push on outside surface  66  of vent  28 . This decrease in air pressure within chamber  18  produces a second differential pressure as the greater pressure on outer surface  66  acts to deform dome  60 . The second differential pressure is the amount that the ambient air pressure outside of transmission  10  exceeds the internal air pressure within transmission  10 . As the air within the chamber  18  cools further, the second differential pressure increases, causing the dome  60  of vent  28  to deform until inside surfaces  76 ,  78  are forced apart, thereby allowing air to enter the chamber  18 . As presently preferred, vent  28  will allow air to enter the chamber  18  when the second differential pressure reaches a range of greater than 0.0 to about 3.0 psid, and more preferably, about 1.25 psid. In this manner, vent  28  provides a bidirectional relief/vent valve  20  for transmission  10 . The curvature of dome  60  is predetermined in order to cause valve  20  to actuate in response to both the first differential pressure and the second differential pressure. The cap  24  provides a protective device for vent  28  by inhibiting contact with water, dirt and other contaminants. 
   It is envisioned that while vent  28  is described as being comprised or constructed of fluorosilicon, that the vent  28  could be constructed of other flexible materials that would allow slit  62  to open and close in reaction to pressure differentials thereacross. By maintaining a pressure of about 1.25 psi within transmission housing  18 , valve  20  limits the amount of ambient air that is drawn into the transmission  10  as the air within the chamber  18  cools. Thus provided, the valve  20  limits the amount of moisture that is drawn into the chamber  18  during heating and cooling cycles. It would also be anticipated that slit  62  could be a single slit, as illustrated, or could comprise a series of parallel or perpendicular slits or a circular piercing arranged within vent  28  to open when a desired first and/or second pressure differential is met. 
   While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope, thereof. Therefore, it is intended that the invention not be limited to a particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.