Abstract:
A pair of spaced apart radial shaft seals are held together by an interlocking pair of support members. The support members form an inner cavity which is in flow communication with the annulus between the shaft seals and the shaft. The inner cavity is vented to the atmosphere by means of a partial hole formed in the outer diameter portion of the support members. Any fluid that accumulates between the seals in the annulus is permitted to drain out through the inner cavity and the vent hole. The vent hole also prevents the formation of a vacuum in the annulus during operation. A channel between the support members is in flow communication with the annulus.

Description:
FIELD OF THE INVENTION 
     This invention relates to dynamic sealing of a shaft and more particularly to a pair of shaft seals with a vent to remove any accumulated fluid between the pair of shaft seals and to prevent the formation of vacuum between the seals and the shaft. 
     BACKGROUND OF THE INVENTION 
     A transfer case connects a transmission with a drive axle for four wheel drive applications or other applications requiring the separation of two fluids. One solution used to solve this problem involves using two different radial shaft seals which are installed around the shaft. If one of the seals fails, fluid accumulates in a cavity between the seals and vents out a hole placed between the seals in the outer periphery of the housing. This solution presents several problems. These include the need to correctly install both seals, the attendant time to install the two seals and the possibility of inconsistent seal depth which may block the vent hole in the housing. 
     Another solution uses a single metal support structure with a rubber shaft seal with two sprung lips and the outer periphery of the metal structure is partially coated with rubber or alternatively uncoated. This design is prone to cocking in assembly, the formation of a vacuum condition between the two sprung lips and the accumulation of the two fluids between the seals after the seals wear in, or the potential transfer of one fluid to the other fluid which may accelerate failure of the transfer case or the transmission. 
     Still another solution that has been proposed to solve this problem is to form a dual seal with a venting/drain capability. This design provides a cavity between two L-shaped support members each of which supports a sprung lip seal. The design is also prone to cocking and has a tendency for the seals to be pushed together, preventing the design from draining or venting. Also, this seal design is not compact which is a disadvantage when space is at a premium. 
     Thus, there remains a need to provide a compact, easily installed dual seal that can be installed in either direction, and that can provide for a controlled radial height to aid in the installation of the seal and assure flow communication between the seals to atmosphere. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to solve these problems by providing a pair of spaced apart shaft seals in a pair of support members that are connected to form a positive radial engagement surface. The pair of support members also form an internal cavity that is in flow communication with the annulus formed between the pair of seals and through a channel member and the shaft in order to vent to atmosphere. At least one hole at the interface between the pair of seals prevents blocking of the vent in the drain to atmosphere. 
     The present invention is directed to a dual seal for a shaft. The dual seal includes a first support member and a second support member. A first shaft seal member is adjacent to the first support member. The first and second support members having portions forming an inner cavity and at least one channel in flow communication with the cavity. The second shaft seal member is adjacent to the second support member. The first and second shaft members form an annulus between the first and second sealing members and the shaft. The annulus is in flow communication with at least one hole formed between the first and second seals so that at least one hole permits any accumulated fluid between the first and second shaft seal members to drain into the inner cavity, to prevent the formation of a vacuum in the annulus, and to prevent blocking at least one hole formed between the first shaft seal member and second shaft seal member. 
     It is an object of the present invention to provide a pair of shaft seal members with a hole between them to prevent the seals from restricting flow out of the annulus. 
     It is another object of the present invention to provide a compact and easily installed dual seal which keeps two fluids separated and vents vacuum and drains fluid in the annulus between the pair of seals to the atmosphere. 
     It is still a further object of the present invention to provide positive outer radial interlock of the two support members to maintain radial assembly height and to provide a positive stop for the dual seal during installation. 
     These and other features of the present invention will become apparent from the subsequent descriptions and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the dual seal according to the present invention; and 
     FIG. 2 is a side view of the dual seal according to the present invention; and 
     FIG. 3 is a cross sectional view along  3 — 3  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     It is customary in sealing technology to use the expression “axially inward” to mean the direction toward the sealed region. Additionally, the expressions “fluid” and “air” side of a seal mean the sides facing toward or away from the sealed or fluid containing area of the device. Typically, elastomeric sealing lips or radial shaft seals include a seal band which is formed along a generally circular path between the air and oil side. The sealed region generally contains oil, grease or the like lubricating fluid, either in liquid or vapor form or both, confined by the seal band. 
     The annular dual seal made according to the present invention seals against a shaft  16  in two locations, as shown in FIG.  3 . The shaft  16  is disposed in a housing  10  in a machine member  2  which is used to locate the dual seal  100 . Each of the sealing lips acts radially inwardly against a seal band on the shaft  16 . The first shaft seal  20  seals against a first fluid  4  and the second shaft seal  30  seals against a second fluid  6  which may be different than the first fluid  4 . 
     As shown in FIGS. 1-3, the annular dual seal device according to the invention is designated by the numeral  100 . The dual seal device  100  fits into a bore  12  in a housing  10  and a shaft  16 . The housing  10  may optionally have a counterbore (not shown) to locate the dual seal  100  in the housing  10 . The dual seal  100  includes a first shaft seal  20 , a second shaft seal  30 , a first support member  40 , a second support member  50 , a cavity  60  between the first support member  40  and the second support member  50 , a channel  70  and a vent hole  80 . The shaft  16  is disposed in the bore  12 . The outer surface  17  of the shaft  16  has a first wear surface  18  adjacent to the first seal  20  and a second wear surface  19  adjacent to the second seal  50 . 
     The first shaft seal  20  includes an end portion of the first support member  40 , and a frusto-conical elastomeric seal body generally designated as  22 . The frusto-conical elastomeric seal body  22  is preferably formed with a generally air side surface portion  24 , a generally fluid side surface portion  26  and a seal band surface  27 . The surface  27  extends generally axially between the radially inner most edges of the surfaces and, depending on whether it is in a relaxed or installed condition, being either cylindrical or slightly frusto-conical. There is an annular groove  28  adjacent to the seal band surface  27  for receiving an annular garter spring  29 , as is conventional in the seal art. The frusto-conical seal surface&#39;s relatively steeply inclined fluid side surface  26  meets the less steeply inclined air side surface  24  to form the generally circular seal band  27 , which cooperates with the first wear surface  18  of the outer surface  17  of the shaft  16  to form a first dynamic shaft seal  20 . The first shaft seal  20  has a first radially extending portion adjacent to the fluid side surface portion  26 . The first fluid side is in the first fluid region  102  which contains the first fluid. 
     The second shaft seal  30  includes an end portion of the second support member  50  and an elastomeric seal body generally designated as  32 . The seal body  32  is similarly constructed as the first shaft seal  20  and has an air side surface portion  34 , a generally fluid side surface  36  and a circular seal band surface  37  with a groove  38 , for receiving an annular garter spring  39 . The frusto-conical fluid side surface  36  meets the less steeply inclined air side surface  34  to form the seal band  37  which cooperates with the second wear surface  19  of the outer surface of the shaft  16  to form a second dynamic shaft seal  30 . The second shaft seal  30  has a second radially extending portion which is adjacent to the fluid side surface portion  36 . The second fluid side is in the second fluid region  104  which contains the second fluid. The first fluid is separated from the second fluid. 
     Each seal  20 ,  30  preferably has a relatively circular inner surface on the seal band surfaces  27 ,  37 , respectively, to form a plain lip type seal that fits tightly around the shaft  16 . Alternatively, each seal  20 ,  30  may have a plurality of hydrodynamic vanes or ribs which are angularly formed on the air side surfaces  24 ,  34 , respectively. As the shaft  16  rotates, the seal band or the hydrodynamic action of the vanes creates a pumping action which is effective in returning any slight layer of fluid formed between the first seal band surface  27  and the first wear surface  18  into the interior of the first sealed region  102  and any slight layer of fluid formed between the second band surface  37  and the second wear surface  19  into the interior of the second sealed region  104 . With both seals  20 ,  30  pumping in such a manner, with or without the hydrodynamic vanes, and as rotation continues particularly after a finite duration of moderate to high speed operation, the ingestion of first fluid from the first sealed region  102  and the second fluid from the second sealed region  104  beneath the lip in the area between the seal band surfaces  27 ,  37 , respectively, creates a partial vacuum in the annulus  90 , as will be discussed later on. If this effect is allowed to continue to occur, it results in accelerated wear of the inner surface or the edge of the seal bands  27 ,  37 , or alternatively, the hydrodynamic vanes, because each is urged on to the wear surfaces  18 ,  19 , respectively, with greater force than is required. With time the inner surface of the seal bands of the plain lip type seal or, optionally, the hydrodynamic vanes wear and the seals  20 ,  30  are no longer capable of pumping as effectively as when the seals  20 ,  30  were new and ultimately some fluid leaks from either region  102  or region  104  into the annulus  90  which is formed between the first seal  20 , the second seal  30  and the shaft  16 . 
     The first support member  40  has a generally hook-like shape which includes a first radial portion  42  adjacent to the first seal  20 , a first radially and axially divergent portion  44  connected to the portion  42  on one end and to a radially and axially convergent portion  46  at the other end. The convergent portion  46  has a radially extending bump  47  for a purpose to be described later on and an axially extending portion  48 . 
     The second support member  50  also has a generally hook-like shape but oppositely configured (that is substantially a mirror image) to that of the first support member  40 . Thus the second support member  50  has a second radial portion  52  adjacent to the second seal  30  and spaced apart from the first radial portion  42 . A first radially and axially divergent portion  54  connected at one end to the portion  52  and to a radially and axially convergent portion  56  at the other end. The convergent portion  56  has an axially extending portion  59  which overlaps the axially extending portion  48  of the first support member. The axially extending portion  58  forms the outer diameter  59 . 
     Between the first support member  40  and the second support member  50 , an internal cavity  60  is formed. The cavity  60  has a lower diverging section formed by radially and axially divergent portions  44 ,  54 ,and an upper converging section formed by radial and axially convergent portions  46 ,  56  to form a divergent and convergent shaped cavity  60 . A vent hole  80  is formed in the housing  10  which is in flow communication with a hole  49  in the first axially extending flat portion  48 . Optionally, the portion  48  may be partially closed off but not completely closed off by the portion  59  to prevent the migration of dirt into the cavity  60 . The vent hole  80  is in flow communication with the cavity  60  through the hole  49  and the atmosphere A. The outside surface of the first support member  40  is covered with an elastomeric layer  21  except over portion  48  and the bump  47 . Optionally, the bump may be partially covered with rubber. Similarly, the outside surface of the second support member  50  is covered with an elastomeric layer  31  except for portion  58  and the outer diameter  58 . 
     Between the first radial portion  42  and the second radial portion  52  a channel  70  is formed. The channel  70  is formed by at least one partial hole in the first shaft seal  30  and at least one partial hole in the adjacent second shaft seal  40 . Preferably, one to eight channels  70  are formed between the seal band surfaces  27 ,  37 , respectively. The channel  70  is in flow communication with the cavity  60 . Optionally, the channel  70  may be formed by locking the first support member  40  and the second support member  50  together in an axial predetermined distance by forming an undercut or positive stop  57  in the bottom surface of the first seal  20  which creates a gap between the seals  20 ,  30 . 
     As stated earlier, the first shaft seal  20  and the second shaft seal  30  are normally spaced apart axially along the shaft  16  to form the annulus  90 . The annulus  90  is in flow communication with the channel  70  which in turn is in flow communication with the cavity  60 , hole  49  and the vent hole  80  and in flow communication with the atmosphere A. This is called the “flow function” which includes both the venting and draining modes. Thus, when the seals  20 ,  30  are new, a vacuum condition in the annulus  90  is prevented from forming by the flow function. When the seal band surfaces  27 ,  37  or the hydrodynamic vanes wear away and fluid leaks past the seals  20 ,  30 , respectively, the flow function drains any fluid that accumulates in the annulus  90  between the seal band surfaces  27 ,  37  and the shaft  16 . 
     The elastomeric seals  20 ,  30  and elastomeric layers  21 ,  31  are preferably made from the same polymeric material such as fluorocarbon, nitrile, ethylene acrylate, polyacrylate, nitride, hydrogenated nitrile, silicone, fluoropolymer, fluorosilicone, TPV and TPE or any other similar material that is suitable for the application. Optionally, the elastomeric seals  20 ,  30  and the elastomeric layers  21 ,  31  may each be made of different polymeric materials listed above. Further optionally, each of the elastomeric seals  20 ,  30  may be made of different polymeric material listed above, such as, for example, PTFE lips with a rubber outer diameter. 
     Only portions  46 ,  56 , respectively, of the support members  40 ,  50  are covered with an elastomeric layers  21 ,  31 . Thus, the outer diameters of the second support member, the portions  48 ,  59  and the bump  47  may be partially covered with an elastomeric layer or optionally, not covered with an elastomeric layer. The axial portion  59  is contiguous to the bore  12  and the housing  10 . The elastomeric layers on the outer diameter of the portions  46 ,  56 , respectively, form static seals with the bore  12  to prevent the migration of fluid from the first fluid region  102  to the vent hole  80  and the migration of fluid from the second fluid region  104  to the vent hole  80 . The bump  47  and the overlapping axial portion  58  and axial portion  48  function to assist the dual seal  100  in retention in the bore  12  and to reduce spring back of the dual seal  100  in the housing  10 . 
     Typical fluids used in the application are gear oil, automatic transmission fluid (ATF), ATF type  1 , ATF type  2 , gear oil type  2  or, alternatively, the same fluid on both sides of the dual seal  100  where separation is needed because of the application or contamination requirements. 
     The height of the dual seal  100  above the surface of the shaft  16  is designated the radial distance R and the axial distance or width of the dual seal  100 , which includes the elastomeric layers  21 ,  31 , is designated the axial distance d. The ratio of Rid is less than 1.5 and preferably less than 1.0. 
     While the present invention has been described in connection with a preferred embodiment, it is not intended to limit the invention to that embodiment only. On the contrary, it is intended to cover all alternative modifications and equivalents that may be included within the spirit and scope of the invention as defined by the drawings and the appended claims.