Abstract:
A dynamic seal advantageously utilizes a plurality of grooves on the active side or surface of the seal to capture a leaked lubricant and hydrodynamically pump the lubricant back into the lubricated side of the seal. The grooves are interrupted at an intermediate location by a continuous circumferential band that aids in preventing leakage past the band when the shaft is not rotating and the grooves on both sides of the band pump contaminants away from the sealing lip.

Description:
FIELD OF THE INVENTION 
     The present invention relates to dynamic shaft seals and, more particularly, to a dynamic shaft seal design with spiral grooves and a mid-lip band. 
     BACKGROUND OF THE INVENTION 
     Rotary shaft seals have been utilized in machinery, the automobile industry, as well as other industries. The seal has an air side and a lubricant side. The seal helps to maintain the lubricant (e.g. oil) on the lubricant side. Lubricant may, however, leak from the lubricated side to the non-lubricated (air) side through the interaction of the active surface of the seal with the shaft. Various arrangements have been devised to capture the leaked lubricant and deliver it back to the sealed side. In one, spiral grooves or built-up ribs (hereinafter collectively referred to as grooves) disposed on the active side of the seal capture the leaked lubricant and hydrodynamically pump the lubricant back into the lubricated side due to relative rotation between the seal and the shaft about which the seal is disposed. 
     The grooves used to hydrodynamically pump the lubricant are open at the oil side of the seal and communicate with the lubricant therein. Having the grooves open at the oil side of the seal creates potential problems. For example, static oil leaks can develop. Additionally, air leakage during pressurization testing of the machinery on which the seal is being used at the end of the assembly stage can also occur. In an attempt to address these drawbacks, the exit points of the spiral grooves on the oil side have been blocked. Blocking the exit point on the oil side, however, reduces the pump rate so significantly that the seal performance degrades and makes the use of such a seal impractical and/or impossible. Another attempt to address these drawbacks is to block the pumping groove not at the exit point on the inner side, but 2 to 3 loops of the groove toward the air side. Doing so reduces the pump rate also, but not to the extent where the seal performance degrades too much. This blockage, however, does lead to other difficulties. The most pronounced difficulty is oil stagnation close to the exit point. This in turn leads to oil coking in the groove and eventually to seal failure. Accordingly, it would be advantageous to provide a seal that effectively uses grooves to hydrodynamically pump lubricant back to the lubricant side while minimizing and/or eliminating the drawbacks mentioned above. 
     The seal with a controllable pump rate according to the principle of the present invention advantageously utilizes a groove on the active side or surface of the seal to capture leaked lubricant and hydrodynamically pump the lubricant back into the lubricated side. The groove extends along a portion of the active side of the seal. The groove, however, does not extend to the leading edge of the seal that faces the lubricant side. Rather, the groove stops short of the leading edge thereby forming a static dam or band between the groove and the sealing edge on the lubricant side of the seal. Lubricant that leaks past the sealing edge on the lubricant side is captured in the grooves and directed back toward the lubricant side due to relative rotation between the seal and the shaft on which the seal is disposed. The fluid pressure inside the groove grows until it reaches a critical value wherein the fluid pressure in the groove exceeds the seal lip opening pressure and the lubricant then escapes into the lubricant side of the seal. In some embodiments, the configuration of the groove is such that an induction zone is formed by a portion of the grooves and a booster zone is formed by a different portion of the grooves. The booster zone is adjacent the static dam. The fluid pressure growth is relatively slow in the induction zone and becomes relatively fast in the booster zone. 
     The use of a static dam in the seal of the present invention advantageously avoids static leakage and problems associated with insufficient fluid flow (coking, carbonization, etc.). Another advantage of the present invention is that some amount of lubricant is always present in the groove prior to the static dam liftoff. This lubricant provides improved seal lip lubrication thereby reducing wear and effectively removing coked lubricant and debris which in turn can extend the seal life. 
     In one aspect of the present invention, a dynamic seal includes a lubricant side and a non-lubricant side. A sealing portion is operable to engage with and seal against a shaft. The sealing portion includes an active surface communicating with the non-lubricant side and a seal lip at an end thereof. The seal lip faces the lubricant side and defines an opening in which a shaft can be disposed. The active surface is operable to engage with and seal against a shaft disposed in the opening. There is at least one pumping element extending along the active surface and stopping short of the seal lip. The pumping element has a beginning point and a termination point. The pumping element is operable to capture lubricant that leaks past the seal lip and pump the lubricant toward the termination point and back into the lubricant side due to relative rotation between the active surface and a shaft. 
     In another aspect of the present invention, another dynamic seal is disclosed. The dynamic seal has both a lubricant side and a non-lubricant side. An active surface is operable to seal against a shaft. At least one groove extends along the active surface from the non-lubricant side toward the lubricant side with a portion of the active surface disposed between the groove and the lubricant side. The groove is operable to capture lubricant that leaks between the active surface and the shaft and pump captured lubricant into the lubricant side past the portion of the active surface. A first portion of the groove has a first characteristic. A second portion of the groove has a second characteristic different than the first characteristic. The second portion of the groove is closer to the lubricant side than the first portion of the groove. 
     In still another aspect of the present invention, a method of returning lubricant that leaks past a dynamic seal on a shaft back to a lubricant side of the seal is disclosed. The method includes: (1) capturing lubricant that leaks past the seal in a groove on an active surface of the seal, the groove stopping short of the lubricant side of the seal; (2) pumping the captured lubricant in the groove back toward the lubricant side of the seal; (3) increasing a fluid pressure in the groove as the groove approaches the lubricant side of the seal; (4) lifting a portion of the seal adjacent the lubricant side off of the shaft with the fluid pressure in the groove; and (5) returning captured lubricant in the groove back to the lubricant side of the seal through a gap between the lifted-off portion of the seal and the shaft. 
     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 simplified perspective view of the seal of the present invention; 
         FIG. 2  is a cross-sectional view of the seal of  FIG. 1  disposed around a shaft; 
         FIG. 3  is an enlarged fragmented cross-sectional view of the active side of the seal within circle  3  of  FIG. 2 ; 
         FIG. 4  is a graph of the hypothetical lubricant pressure in the groove as a function of distance for the seal configuration shown in  FIG. 3 ; 
         FIGS. 5A-5E  are fragmented representations of various alternate cross-sectional configurations or geometry for the grooves used in the seal according to the principle of the present invention; 
         FIG. 6  is a first alternate embodiment of the seal of  FIG. 1  showing a differing groove configuration; 
         FIG. 7  is a second alternate embodiment of the seal of  FIG. 1  showing a groove configuration wherein no booster zone is utilized; 
         FIG. 8  is a schematic simplified representation of a top plan view of the active surface of the seal of  FIG. 1  showing two distinct grooves extending along the active surface of the seal; 
         FIG. 9  is a cross-sectional view of an alternative seal design employing a plurality of spiral grooves and an intermediate circumferential band; 
         FIG. 10  is a cross-sectional view of an alternative seal design similar to  FIG. 9  with the circumferential band being shorter than the peaks defining opposite sides of the grooves; and 
         FIG. 11  is a cross-sectional view of an alternative seal design similar to  FIG. 9  with the circumferential band having a height taller than the peaks defining opposite sides of the grooves. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     With reference to  FIGS. 1-3 , a dynamic seal  20  according to the preferred embodiment of the present invention is shown. Seal  20  is mounted to a casing  22  which is disposed in a fixed housing  24  (best shown in  FIG. 2 ) in a manner which is well known in the art. Seal  20  engages a rotary shaft  28  and provides a sealed relationship between rotary shaft  28  and housing  24  in which casing  22  is disposed. With reference to  FIG. 2 , seal  20  includes a mounting portion  30  having an annular recess  32  therein. A mounting portion  22   a  of casing  22  resides within annular recess  32 . It should be noted that mounting portion  30  and casing  22  can take on many shapes and forms and are not considered to be particularly relevant to the present invention. Mounting portion  30  is mounted to casing  22  which can be made of plastic or metal and mounting portion  30  can be bonded thereto according to well known mounting techniques. 
     Seal  20  includes a central opening  36  through which shaft  28  is disposed. The diameter of opening  36  is dimensioned to be less than the diameter of shaft  28  to provide a desired fit therebetween. That is, the portion of seal  20  proximate opening  36  will deform as seal  20  is positioned on shaft  28 . The deformation of seal  20  is resisted and a fluid-tight seal is formed against shaft  28 . 
     Seal  20  has a conically-shaped sealing portion  40  that extends axially and radially from mounting portion  30 . Opening  36  is located in sealing portion  40 . Sealing portion  40  has an active side/surface  44  that engages with shaft  28 . Sealing portion  40  also includes a non-active side/surface  48  that is opposite active surface  44 . Non-active surface  48  does not engage with shaft  28 . A leading seal edge or lip  52  separates active surface  44  and non-active surface  48 . Active surface  44  is exposed to air side  49  while non-active surface  48  and seal edge  52  are exposed to lubricant (e.g. oil) side  50 . 
     At least one groove  60  (two grooves are shown in  FIG. 8 ) is located on active surface  44  and spirals around shaft  28  with portions  62  of active surface  44  disposed therebetween. Groove  60  extends axially along active surface  44  as it wraps around shaft  28  with portions  62  of active surface  44  disposed therebetween. The pitch of groove  60  can vary and, if desired, may be uniform or constant. Groove  60  can be coined, cut into or otherwise formed along active surface  44 . 
     Groove  60  is a hydrodynamic pumping element. Groove  60  captures lubricant that seeps past seal edge  52  and pumps the captured lubricant back into lubricant side  50 . Relative rotation between active surface  44  and shaft  28  causes the lubricant captured within groove  60  to be directed toward lubricant side  50  and past seal edge  52 , as described below. 
     Referring now to  FIG. 3 , details of active surface  44  and groove  60  therein are shown. Groove  60  can be a single groove that extends helically or spirally along active surface  44  between a beginning point  64  and a termination point  68 . Alternatively, as shown in  FIG. 8 , seal  20  can have multiple grooves  60  that extend helically or spirally along active surface  44 . For example, as shown, a first groove  60   a  can extend from beginning point  64   a  to termination point  68   a  while a second groove  60   b  extends from beginning point  64   b  to termination point  68   b . Grooves  60   a ,  60   b  do not intersect one another. Additionally, grooves  60   a ,  60   b  spiral along active surface  44  in the same direction. The direction in which grooves  60   a ,  60   b  spiral determines the direction in which captured lubricant is routed due to relative rotation between seal  20  and shaft  28 . With both grooves  60   a ,  60   b  spiraling in the same direction, grooves  60   a ,  60   b  provide a unidirectional pumping action such that both grooves  60   a ,  60   b  pump lubricant therein in the same direction. While seal  20  is shown as having either one or two grooves  60 , it should be appreciated that more than two grooves can be utilized, if desired. 
     Groove  60  stops short of reaching seal edge  52 . Specifically, a static dam  70  is disposed between seal edge  52  and termination point  68 . Static dam  70  is adjacent seal edge  52  and is in direct contact with shaft  28  and forms a seal thereagainst. To facilitate the hydrodynamic pumping of leaked lubricant back into lubricant side  50 , groove  60  includes two distinct regions or sections  74 ,  76 . First region  74  is referred to as the induction zone while second region  76  is referred to as the booster zone. Induction zone  74  is characterized by groove  60  having a cross-sectional area that is substantially constant. In contrast, booster zone  76  is characterized by having a cross-sectional area that diminishes to zero as groove  60  approaches termination point  68  adjacent static dam  70 . In the preferred embodiment, the width W of groove  60  in both induction zone  74  and booster zone  76  is the same while the depth of groove  60  in induction zone  74  is different than the depth of groove  60  in booster zone  76 . Specifically, in induction zone  74  the depth of groove  60  is substantially constant while in booster zone  76  the depth of groove  60  diminishes as groove  60  approaches termination point  68 . Thus, the cross-sectional area of groove  60  in induction zone  74  is substantially constant while the cross-sectional area of groove  60  in booster zone  76  approaches zero as groove  60  approaches termination point  68 . The changing cross-sectional area of groove  60  in booster zone  76  advantageously facilitates the returning of lubricant from groove  60  back into lubricant side  50 , as described below. 
     Referring now to  FIG. 4 , a hypothetical example of the fluid pressure (curve  82 ) within groove  60  as a function of the position within groove  60  is shown. As lubricant is captured by groove  60 , the relative rotation between seal  20  and shaft  28  drives the lubricant toward termination point  68 . As a result, the fluid pressure within groove  60  increases as termination point  68  is approached. In the groove design of the present invention, the fluid pressure growth (curve  82   a ) in induction zone  74  is at a lower (slower) rate than the fluid pressure growth (curve  82   b ) within booster zone  76 . Specifically, due to the substantially uniform cross-sectional area of groove  60  in induction zone  74 , the fluid pressure grows at a relatively slow rate which may or may not be a constant rate. When the lubricant enters into booster zone  76 , however, the reducing cross-sectional area of groove  60  therein causes the fluid pressure to increase more rapidly as groove  60  approaches termination point  68 . The rate of fluid pressure growth in booster zone  76  may be a constant or non-constant rate. Thus, the fluid pressure growth is relatively slow in induction zone  74  and becomes relatively fast in booster zone  76 . 
     Fluid pressure within groove  60  continues to grow until a critical value (the seal lip  52  opening pressure, as represented by line  84 ) is met or exceeded. As soon as the fluid pressure meets or exceeds the critical value, the fluid pressure build up in booster zone  76  exceeds the seal lip opening pressure and the lubricant is pumped into lubricant side  50 . That is, the pressure within booster zone  76  increases to a value which causes static dam  70  to lift off shaft  28  and allow the lubricant within groove  60  to flow back into lubricant side  50 . Once the fluid pressure within groove  60  drops below the critical pressure, static dam  70  moves back and seals against shaft  28  and the flow of lubricant from groove  60  into lubricant side  50  ceases. The lubricant will again begin to collect within groove  60  and cause the fluid pressure therein to increase. Once the fluid pressure exceeds the critical value again, static dam  70  will separate from shaft  28  and allow the lubricant within groove  60  to again flow into lubricant side  50  until such time as the fluid pressure drops below the critical value. This process continues throughout operation of seal  20 . 
     The physical shape and dimensions of groove  60  are chosen to provide a pump rate that is equal to or greater than the expected leakage rate of lubricant past seal lip  52  for the expected life of seal  20 . That is, during the life of seal  20 , the leakage rate past seal lip  52  may increase. The dimensions of groove  60  are chosen to provide a pumping rate that meets or exceeds the expected leakage rate of lubricant past seal lip  52  along with providing a fluid pressure rise that exceeds the critical value to enable the lubricant to be pumped back into the lubricant side of the seal. 
     Depending upon the leakage rate of lubricant past seal lip  52 , a steady state regime of groove  60  discharging lubricant back into lubricant side  50  is possible. That is, depending upon the design of groove  60 , the performance of seal lip  52  and the relative rotation between seal  20  and shaft  28 , it may be possible for a continuous flow of lubricant to leak past seal lip  52 , be captured by groove  60 , and transported back to lubricant side  50  by maintaining the pressure within groove  60  adjacent static dam  70  equal to or greater than the critical pressure. Thus, it should be appreciated that the returning of captured lubricant to lubricant side  50  can be a non-steady state occurrence or a steady state occurrence. 
     The substantially-constant cross-sectional area of groove  60  in induction zone  74  and the decreasing cross-sectional area of groove  60  in booster zone  76  advantageously facilitate the return of captured lubricant to lubricant side  50 . The substantially constant cross-sectional area in induction zone  74  allows the fluid pressure within induction zone  74  to gradually increase as the lubricant approaches booster zone  76 . The induction zone  74  can be configured so that during nominal operation of seal  20  (that is, with seal  20  experiencing normal anticipated maximum leakage of lubricant past seal lip  52 ) the critical pressure is not reached. By not reaching the critical pressure within induction zone  74 , a greater portion (that portion between induction zone  74  and seal lip  52 ) of active surface  44  can maintain contact with shaft  28  thereby helping to prevent lubricant from leaking through seal  20 . The reducing cross-sectional area of groove  60  in booster zone  76  advantageously increases the fluid pressure within booster zone  76  above the critical pressure  84  in a location that is adjacent static dam  70 . The disruption of the contact between static dam  70  and shaft  28  at this location reduces the amount of active surface  44  that is dislodged from intimate contact with shaft  28  during the returning of captured lubricant to lubricant side  50 . It should be appreciated that while it is preferred that the cross-sectional area of groove  60  within induction zone  74  be substantially constant, variation in the cross-sectional area is possible. That is, variation in the cross-sectional area that causes a slower rate of fluid pressure increase than in booster zone  76  and/or avoids or minimizes the potential for the fluid pressure therein to exceed the critical pressure can be employed, although all the advantages of the present invention may not be realized. 
     The cross-sectional shape of groove  60  can vary. For example, as shown in  FIG. 3 , the cross-sectional shape or geometry of groove  60  can be triangular. However, as shown in  FIGS. 5A-5E , other geometries or cross-sectional shapes can be employed. For example, the cross-sectional shape can be square or rectangular, as shown in  FIG. 5A , curved or rounded, as shown in  FIG. 5B , trapezoidal, as shown in  FIG. 5C , and/or skewed toward or away from seal lip  52 , as shown in  FIGS. 5D and 5E , respectively. It should be appreciated that, while it is preferred to keep the cross-sectional area of groove  60  substantially constant in induction zone  74 , the geometry of groove  60  can change while maintaining the cross-sectional area substantially constant. That is, if desired, the geometry of groove  60  can change (e.g. triangular to rectangular), while maintaining the cross-sectional area substantially constant and still resulting in a gradual buildup of fluid pressure within induction zone  74 . The geometry of groove  60  can also change in booster zone  76  so long as a reduction in the cross-sectional area is achieved and approaches zero at the termination point. Thus, the geometry of groove  60  can change so long as the requirements regarding the cross-sectional area are met. 
     Referring now to  FIG. 6 , a first alternate embodiment of a seal  120  according to the principle of the present invention is shown. In seal  120 , the decreasing cross-sectional area of booster zone  176  is different than that in the preferred embodiment. Specifically, the depth D of groove  160  in both induction zone  174  and booster zone  176  remains substantially constant. To decrease the cross-sectional area of groove  160  within booster zone  176 , the width of groove  160  at the contact plane of active surface  144  decreases as groove  160  approaches termination point  168 . The decreasing cross-sectional area of groove  160  in booster zone  176  causes the fluid pressure to increase rapidly in booster zone  176 , allowing operation of seal  120  along the same principles discussed above with reference to seal  20 . It should be appreciated that the manner in which the cross-sectional area of groove  160  is decreased within booster zone  176  can vary from that shown. For example, a combination of a decreasing depth and a decreasing width of groove  160  can be employed to reduce the cross-sectional area of groove  160  in booster zone  176  as groove  160  approaches termination point  168 . Additionally, a changing geometry for groove  160  can also be utilized, as discussed above. 
     Referring now to  FIG. 7 , a second alternate embodiment of a seal  220  according to the principles of the present invention is shown. In this embodiment, a booster zone is not utilized. Rather, groove  260  ends at termination point  268  with static dam  270  disposed between termination point  268  and seal lip  252 . The cross-sectional area of groove  260  is generally uniform throughout its length. As a result, the fluid pressure within groove  260  builds at a gradual pace until eventually overcoming the critical pressure (the opening pressure of seal lip  252 ) and directing the captured lubricant back to the lubricant side  50 . The design of groove  260  is configured to ensure that the fluid pressure within groove  260  at termination point  268  exceeds the critical pressure while maintaining a sufficient pump rate to route captured lubricant back to lubricant side  50 . Thus, in this embodiment, the active surface  244  includes a groove  260  that has a termination point  268  that stops short of reaching seal lip  252 , thus forming a static dam  270  therebetween. It should be appreciated that while the second alternate embodiment is operable to return lubricant to the lubricant side  50  of seal  220 , all the benefits of using the preferred embodiment may not be realized. 
     Seals  20 ,  120 ,  220  can be made from a variety of material compositions. For example, the dynamic seal can include plastic, rubber, or any of a wide variety of known elastomers, such as PTFE, TPE (thermoplastic elastomers), TPV (thermoplastic volcanizates), and Flouroprene™ material, a composition described in U.S. Pat. No. 6,806,306, among others. 
     The seal according to the principles of the present invention has many advantages. Firstly, static leakage and problems associated with insufficient fluid flow (coking, carbonization, etc.) are easily controlled by appropriately adjusting the design parameters, and, therefore, providing a reliable sealing function. Another advantage is that some amount of lubricant is always present in the groove prior to liftoff of the static dam from the shaft. This lubricant provides improved seal lip lubrication thereby reducing wear, effectively removing coked lubricant and the wear debris, which in turn extends seal life. Thus, the seal according to the principle of the present invention provides many advantages. 
     While the present invention has been described and illustrated with reference to specific embodiments, it should be appreciated that these embodiments are merely exemplary in nature and that variations that depart from the embodiment shown are intended to be within the scope of the present invention. For example, while a variety of geometries are shown for the cross-sectional configuration of the groove, it should be appreciated that these cross-sectional geometries are merely exemplary and that other cross-sectional geometries can be employed. The shape of portions  62 ,  162 ,  262  of active surface  44 ,  144 ,  244  can vary. For example, portions  62 ,  162 ,  262  can have a width that varies and may be reduced to, or be, a point, if desired. Additionally, while the seal has been shown with reference to a particular sealing portion  40 , mounting portion  30  and casing  22 , it should be appreciated that these are merely exemplary and that other configurations that allow an active surface of a seal to engage with a shaft can be employed. Moreover, seal  20 ,  120 ,  220  does not need to seal against the outer diameter of shaft  28 . Rather, seal  20 ,  120 ,  220  can have an active surface  44 ,  144 ,  244  that seals against a component attached to shaft  28 , such as a flat area or surface of an axial slinger or flange. Such applications may provide a pumping action in the radial direction. Furthermore, while the depiction of multiple grooves in  FIG. 8  shows that the termination and ending points for the respective grooves are directly across from one another, it should be appreciated that they do not need to have such relative positioning and can be skewed from one another. Moreover, it should be appreciated that the dimensions shown herein for seal  20 , are merely exemplary to facilitate an understanding of the principles and functionality of the present invention. As such, the dimensions shown herein can vary without deviating from the spirit and scope of the present invention. Additionally, while particular materials of construction have been disclosed as being suitable for use in the seal, it should be appreciated that such a list is merely illustrative and not exhaustive of the types of materials that can be used to form a seal according to the principle of the present invention. Furthermore, it should be appreciated that while the pumping element is described as grooves, the use of raised ribs on the active surface of the seal may also be utilized in lieu of the grooves although all of the benefits of the present invention may not be realized. Moreover, it should be appreciated that while shaft  28  is described as being a rotary shaft, shaft  28  could be stationary and seal  20  could rotate about shaft  28 . 
     According to a further embodiment as shown in  FIG. 9 , a seal lip  300  includes plural spiral grooves  302  that extend axially through the end  304  of the seal lip  300  facing the oil side. The grooves  302  are defined by a valley portion  306  disposed between opposite peaks  308 . The seal is provided with a continuous circumferential band  310  that interrupts the spiral grooves  302  such that the spiral grooves  302  extend on both sides of the continuous circumferential band  310 . By having grooves  302  on both sides of the circumferential band  310 , internal contamination is pumped away from the sealing lip  300 . The band  310  prevents leakage past the band  310  when the shaft is not rotating. 
     As shown in  FIG. 9 , the continuous circumferential band  310  can be of equal height to the peaks  308 . Alternatively, the circumferential band  310 ′ can be of smaller height than the peaks  308 , as illustrated in  FIG. 10 , or the band  310 ″ can be taller than the peaks  308 , as illustrated in  FIG. 11 . 
     Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.