Abstract:
A dynamic shaft seal assembly is provided including a dynamic seal for engaging a rotary shaft. The dynamic seal includes a base portion that is mounted within a casing and has an axially extending barrel portion extending from a radially inner end of the base portion. The axially extending barrel portion terminates in a radially extending leg portion which extends inwardly from an end of the axially extending portion. A generally conically shaped seal portion extends from an end of the radially extending portion and the seal portion includes a radially inner face engaging the shaft and a radially outer face having a stiffening bead integrally formed thereon. The stiffening bead reduces the seal&#39;s propensity for “bell mouthing” while the axially extending barrel portion provides improved shaft followability for the dynamic seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/285,652, filed Nov. 22, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/065,023, filed on Feb. 24, 2005, the disclosures of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to “lay-down” dynamic shaft seals, and more particularly, to a dynamic shaft seal design to reduce the seal&#39;s torque, propensity for bell mouthing, and for providing improved shaft followability and improved ability to withstand internal excessive pressure or vacuum. The “lay-down” seal for their function rely on hydrodynamic pumping features as opposed to “standard” or “point-contact” seals that rely primarily on the intrinsic ability of some elastomers to pump in properly designed seals. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    Rotary shaft seals have been utilized in machinery, the automobile industry, as well as other industries. Three major problems associated with seals designed to have substantial contact areas between the shaft and the lip of the seal are “bell mouth,” the shaft followability at low temperatures, and oil carbonization in the pumping grooves due to local temperature rise causing increased torque. “Bell mouth” is a phenomenon associated with the lift of the edge of the lip from the shaft. The problem is extenuated for highly incompressible materials, like rubber and PTFE. The ability of the seal to follow the shaft when the shaft either wobbles or is misaligned is also important to a seal design. 
         [0004]    The present invention is designed to reduce seal torque, the propensity for “bell mouthing” and also provides for improved shaft followability at low temperatures. The dynamic seal includes an annular mounting portion which is capable of being mounted to a casing which surrounds a rotary shaft. The seal includes an axially extending portion extending from the radially inner end of the mounting portion, with a radially extending portion extending inwardly from an end of the axially extending portion. A generally conically shaped seal portion extends from an end of the radially extending portion with the seal portion including a radially inner face provided with a plurality of grooves or ribs and a radially outer face having a special bead defining a region of increased thickness. The bead acts as an integral spring to control the gap between the essentially conical portion of the seal and the shaft as well as a means for counteracting the “bell mouthing” propensity of the seal portion. The bead can have different shapes including a triangular-cross section or a rounded bead, as well as other configurations which are deemed to be appropriate. The bead is positioned slightly away from the edge of the lip to provide a sufficient lip “lay-down” to properly engage the hydrodynamic pumping features, which would normally be located on the lip contact are between the edge of the seal and the bead. The flexibility of the axially extending portion of the seal provides an improvement in the shaft followability due to the generally cylindrical shape of the axially extending portion having lower bending stiffness. Therefore, if the material of the seal does not have sufficient intrinsic elasticity, making the axially extending portion of the seal in a generally cylindrical shape improves the overall shaft followability. The length and the wall thickness of the cylindrical portion allow one to control the degree of flexibility to match the application requirements. 
         [0005]    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 
         [0006]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0007]      FIG. 1  is a detailed cross-sectional view of the dynamic seal according to the principles of the present invention; 
           [0008]      FIG. 2  is a cross-sectional view of the dynamic seal disposed against a shaft according to the principles of the present invention; 
           [0009]      FIG. 3  is a perspective view of the dynamic seal according to the principles of the present invention; 
           [0010]      FIG. 4  is a cross-sectional view of second embodiment of the dynamic seal according to the principles of the present invention; 
           [0011]      FIG. 5  is a cross-sectional view of the seal of  FIG. 4  shown under internal pressure; 
           [0012]      FIG. 6  is a cross-sectional view of the seal of  FIG. 4  shown under vacuum; 
           [0013]      FIG. 7  is a cross-sectional view of a dynamic seal according to the principles of the present invention, incorporating a deflection limiting retainer; 
           [0014]      FIG. 8  is a cross-sectional view of a dynamic seal according to the principles of the present invention including an interior shaft ring; 
           [0015]      FIG. 9  is a cross-sectional view of a dynamic seal according to the principles of the present invention including a dust lip integrally formed therewith; 
           [0016]      FIG. 10  is a cross-sectional view of a dynamic seal according to the principles of the present invention, including a support ring and casing; 
           [0017]      FIG. 11  is a detailed cross-sectional view of the dynamic seal according to the principles of the present invention with a support ring disposed therein; and 
           [0018]      FIG. 12  is a cross-sectional view of the dynamic seal disposed against a shaft according to the principles of the present invention with a support ring disposed therein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    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. 
         [0020]    With reference to  FIGS. 1-3 , the dynamic seal  10 , according to the principles of the present invention, will now be described. The dynamic seal  10  is mounted to a casing  12  which is disposed in a fixed housing  16  (best shown in  FIG. 2 ) in a manner which is well known in the art. The dynamic seal  10  engages a rotary shaft  14  so that the dynamic seal  10  provides a sealed relationship between the rotary shaft  14  and the housing  16  in which the casing  12  is disposed. With reference to  FIG. 1 , the dynamic seal  10  includes a mounting portion  20  which is designed to be engaged between first and second portions  12 A,  12 B of casing  12 . It should be noted that the mounting portion  20  can take on many shapes and forms and is not considered to be particularly relevant to the present invention. The mounting portion  20  is mounted to the casing  12  which can be made of plastic or metal and the mounting portion  20  can be clamped or bonded thereto according to well known mounting techniques. 
         [0021]    The dynamic seal  10  includes an axially extending barrel portion  22  extending from a radially inner end  20 A of the mounting portion  20 . The axially extending barrel portion  22  is preferably generally cylindrical in shape although other shapes, such as conical or a convoluted curve shape, can also be utilized. The dynamic seal  10  includes a radially extending portion  24  extending inwardly from a distal end  22 B of the axially extending barrel portion  22 . A generally conically shaped seal portion  26  extends from a radially innermost end  24 A of the radially extending portion  24 . The seal portion  26  includes a radially inner face  28  which may be provided with a plurality of grooves  30 . The grooves  30  can be helical in shape or can take other known forms. The grooves  30  provided in the radially inner surface  28  of the seal portion  26  are capable of retaining oil therein in order to provide lubrication between the dynamic shaft seal  10  and rotary shaft  14  and also can provide a pumping function for returning leaked oil to the oil side of the seal. A radially outer face  32  of the conically shaped seal portion  26  is provided with a stiffening bead  34  defining a region of increased thickness. The stiffening bead  34  can have different shapes, including a triangular shape, as shown, or can have rounded or other shape configurations. The stiffening bead  34  is positioned slightly away from the end edge  26 A of the lip  26  to allow a proper contact area to develop. The bead  34  serves as an integrally formed spring for biasing the sealing lip  26  against the rotary shaft  14  for counteracting bell mouthing of the sealing lip  26 . Normally, the seal lip-free edge faces the oil side. However, reverse mounting is also possible. In that case, the design of the spiral grooves have to be accommodated appropriately to pump in the direction of the oil sump. 
         [0022]    The improvement in the shaft followability of the dynamic seal  10  is provided by the axially extending barrel portion  22 . The generally cylindrical shape of the barrel portion  22  has a lower bending stiffness than other structures; therefore, the axially extending barrel portion  22  is able to readily account for a wobbling shaft or a shaft that is out of center relative to the housing  16 . 
         [0023]    It should be noted that if desired or advantageous in a particular application, the dynamic shaft seal  10  of the present invention can optionally include one or more axial or radial dirt protective lips  38  as are known in the art, one of which is shown, for example, in  FIG. 2 . The optional dirt protective lip  38  can be formed integrally with the dynamic shaft seal, or can be formed separately therefrom and attached thereto, and can have any of a number of shapes or configurations, as is also known in the art. In addition, the lip  38  can protrude transversely from the dynamic shaft seal in any of a number of directions, including, but not limited to, the exemplary angular relationship protruding generally radially away and axially away from the shaft-engaging sealing components, as shown, for example, in  FIG. 2 . 
         [0024]    The radially extending leg portion  24  can be straight, as shown, or alternatively, can be provided with a convoluted shape. The outer diameter of the shaft is specifically designed to have a larger diameter than the inner diameter of the radially inwardly extending leg portion  24 . As illustrated in  FIG. 2 , the generally conically shaped seal portion  26  is designed to take on a generally cylindrical form when deformed by the rotary shaft  14  and the leg  24  is designed to apply pressure to the heel portion  36  of the seal portion  26 . The leg portion  24  acts radially on the end  22 A of the barrel portion  22  which has a length sufficient to allow the barrel portion  22  to flex radially inwardly and outwardly to accommodate for shaft wobble or shaft misalignment. The length of the leg portion is derivative from the length of the seal portion, the amount of the seal-to-shaft interference, and the distance between the casing and the shaft. 
         [0025]    The dynamic shaft seal  10  of the present invention can be utilized for isolating an oil environment from an air environment disposed on either side of the dynamic seal  10 . In order to optimize the seal design, the length of the seal portion  26  and the stiffness of the bead  34  (geometry, thickness, material, etc.) are specifically chosen for particular applications. Furthermore, the thickness of the radially extending leg portion  24  is also specifically designed to provide sufficient pressure on the heel  36  of the seal portion  26 . The thickness and length of the barrel portion  22  should also be specifically designed to accommodate the requisite flexibility of a particular application. The seal material composition for the dynamic seal can include plastic, rubber, or any of a wide variety of known elastomers, such as PTFE, TPE (thermoplastic elastomers), TPV (thermoplastic vulcanizates), and Flouroprene™ material, a composition described in U.S. Pat. No. 6,806,306. An additional embedded spring in the bead may be utilized in order to extend the life of the seal due to the fact that creep can occur in thermoplastic or elastomeric materials which prevents the material from regaining its original properties. The spring would then provide an additional radial load on the seal surface that the thermoplastic material is incapable of maintaining over a long life. The spring can also improve the robustness of the seal required in contaminated environments. Instead of imbedding, the spring can be placed in a specially designed and manufactured spring groove after completion of the molding operation (as is normal with other radial lip seals). 
         [0026]    With reference to  FIGS. 4-6 , a dynamic seal according to a second embodiment of the present invention will now be described. The dynamic seal  100  includes a mounting portion  102  which is designed to be engaged between first and second portions of a casing. It should be noted that the mounting portion  102  can take on many shapes and forms and is not considered to be particularly relevant to the present invention. The mounting portion  102  is mounted to a casing which can be made of plastic or metal and the mounting portion  102  can be clamped, bonded or otherwise secured thereto according to well-known mounting techniques. 
         [0027]    The dynamic seal  100  includes an axially extending barrel portion  104  extending from a radially inner end  102 A of the mounting portion  102 . The axially extending barrel portion  104  is preferably generally cylinder shaped although other shapes, such as conical or a convoluted curve shape, can also be utilized. The dynamic seal  100  includes a radially extending portion  106  extending inwardly from a distal end  104 A of the axially extending barrel portion  104 . A generally conically shaped seal portion  108  extends from a radially innermost end  106 A of the radially extending portion  106 . 
         [0028]    The axially extending barrel portion  104  extends in a first axial direction from mounting portion  102 , while the generally conically shaped seal portion  108  extends from the radially innermost end  106 A of radially extending portion  106  in an axial direction opposite to the first axial direction. 
         [0029]    The seal portion  108  includes a radially inner face  110  which may be provided with at least one groove or a plurality of grooves. The grooves can be helical in shape or can take other known forms. The grooves provided in the radially inner surface  110  of the seal portion  108  are capable of retaining oil therein in order to provide lubrication between the dynamic shaft seal  100  and rotary shaft  14  and also can provide a pumping function for returning leaked oil to the oil side of the seal. 
         [0030]    A radially outer face  112  of the conically shaped seal portion  108  is provided with a stiffening bead  114  defining a region of increased thickness. The stiffening bead  114  can have different shapes, including a triangular shape as shown, or can have rounded or other shaped configurations. The stiffening bead  114  is positioned slightly away from the end edge  108 A of the lip  108  to allow a proper contact area to develop. The bead  114  serves as an integrally formed spring for biasing the sealing lip  108  against the rotary shaft  114  for counteracting bell mounting of the sealing lip  108 . The location and shape of the bead  114  is dependent upon the specific application and the desired spring force. 
         [0031]    Normally, the seal lip-free edge  108 A faces the oil side. However, reverse mounting is also possible. In that case, the design of the spiral grooves has to be accommodated appropriately to pump in the direction of the oil side. 
         [0032]    With the design of the present invention, the dynamic seal  100  is capable of withstanding excessive internal pressure or vacuum.  FIG. 5  illustrates a cross-sectional view of the dynamic seal  100  disposed against a shaft  14  and under a pressure of 170 MBAR.  FIG. 6  illustrates the dynamic seal  100  disposed against a shaft  14  and exposed to a vacuum pressure of −50 MBAR. In the case of excessive internal pressure being applied to the dynamic seal  100 , the axially extending barrel portion  22  which radially overlaps the seal portion  108  provides a radial spring acting upon the radially extending portion  106  to limit the deformation in the seal portion  108 . 
         [0033]    In the case of an excessive vacuum being applied, the axially extending barrel portion  104  limits the axial movement of radially extending portion  106 , thus limiting the axial movement of the seal portion  108 . 
         [0034]    The improvement in the shaft followability of the dynamic seal  100  is provided by the axially extending barrel portion  104 . The generally cylindrical shape of the barrel portion  104  has a lower bending stiffness than other structures. Therefore, the axially extending barrel portion  104  is able to readily account for a wobbling shaft or a shaft that is out of center relative to the housing. 
         [0035]    It should be noted that if desired or advantageous in a particular application, the dynamic seal shaft  100  of the present invention can optionally include one or more axial or radial dirt protective lips  120  as illustrated in  FIG. 9 . The optional dirt protective lip  120  can be formed integrally with the dynamic shaft seal, or it can be formed separately therefrom and attached thereto and can have any of a number of shapes or configurations, as is also known in the art. The radially extending leg portion  106  can be straight, as shown, or alternatively, can be provided with an angled or convoluted shape. As illustrated in  FIGS. 5 and 6 , the generally conically shaped seal portion  108  is designed to take on a generally cylindrical form when deformed by the rotary shaft  14  and the leg  106  is designed to apply pressure to the heel portion of the seal portion  108 . The leg portion  106  acts radially on the end  104 A of the barrel portion  104  which has a length sufficient to allow the barrel portion  104  to flex radially inwardly and outwardly to accommodate for shaft wobble or shaft misalignment. The length of the leg portion  106  is derivative from the length of the seal portion  108 , the amount of the seal-to-shaft interference, and the distance between the casing and the shaft. 
         [0036]    The dynamic shaft seal  100  can be utilized for isolating an oil environment from an air environment disposed on either side of the dynamic seal  100 . In order to optimize the seal design, the length of the seal portion  108  and the stiffness of the bead  114  (geometry, thickness, material, etc.) are specifically chosen for particular applications. Furthermore, the thickness of the radially extending leg portion  106  is also specifically designed to provide sufficient pressure on the heel of the seal portion  108 . The thickness and length of the barrel portion  104  should also be specifically designed to accommodate the requisite flexibility of a particular application. The seal material composition for the dynamic seal can include plastic, rubber, or any of a variety of known elastomers, such as PTFE, TPE (thermoplastic elastomers), TPV (thermoplastic vulcanizates) and Flouroprene™ material. 
         [0037]    With reference to  FIG. 7 , the dynamic seal  100  according to the principles of the present invention is shown mounted to a retainer ring  130 . The retainer ring  130  is designed to be press fit within a bore of a housing and includes an axially extending portion  130 A, a first radially extending mounting portion  130 B to which the dynamic seal  100  is mounted, and a retaining flange  130 C disposed at an opposite end of the axially extending portion  130 A. A support ring  132  includes an axially extending arm portion  132 A and a radially inwardly extending arm portion  132 B. The axially extending arm portion  132 A is designed to be retained by the retainer  130  and can include an inwardly angled exterior surface  134  which facilitates the support ring  132  to being press fit within retaining flange  130 C. The radially inwardly extending arm portion  132 B is disposed adjacent to the radially extending portion  106  of dynamic seal  100  with an axial gap extending therebetween. The gap  136  permits axial movement of the radially extending portion  106 , but limits the axial movement thereof relative to the mounting portion  102 . 
         [0038]    With reference to  FIG. 8 , a dynamic seal  100 , according to the principles of the present invention is shown utilized in a cassette-type seal including a running sleeve  150  adapted to be mounted to a shaft and to be rotated therewith. The running sleeve  150  includes a finished exterior surface  152  that is engaged by the seal portion  108  of dynamic seal  100 . The running sleeve  150  also includes a radial wall portion  150 A extending adjacent to the radially extending portion  106  of the dynamic seal  100 . The radial wall portion  150 A limits the axial movement of the radially extending portion  106  of dynamic seal  100  in the rightward direction as illustrated in  FIG. 8 . The radially extending portion  106  of the dynamic seal  100  may also include a protruding portion  154  that can come in contact with the radially extending wall portion  150 A of running sleeve  150 . The protruding portion  154  limits the contact surface that engages the radial wall portion  150 A so as to limit the friction contact between the dynamic seal  100  and running sleeve  150 . 
         [0039]    The running sleeve  150  also includes a radial flange portion  150 B provided at a second end thereof that provides a barrier for limiting axial movement of the seal portion  108  in the leftward direction as illustrated in  FIG. 8 . Thus, the retaining flange  150 B prevents the seal portion  108  from being dislodged from the exterior finished surface  152  of running sleeve  150 . The running sleeve  150  can be connected to the retainer  130  so that the seal assembly can be assembled as a cassette-type seal or can be separate, as shown. 
         [0040]    With reference to  FIG. 10 , a dynamic seal  200 , according to the principles of the present invention, is shown. The dynamic seal  200  is mounted to a metal casing  202  and is also provided with a support ring  204  which can be made from plastic, metal, or other materials. The dynamic seal  200  is mounted to the casing  202  which is adapted to be disposed in a fixed housing in a manner which is well known in the art. The dynamic seal  200  engages a rotary shaft or other member so that the dynamic seal  200  provides a sealed relationship between the rotary member and the housing in which the casing  202  is disposed. The dynamic seal  200  includes a mounting portion  206 A,  206 B with the portion  206 B of the mounting portion overlapping the metal casing  202  on at least one face thereof. A mounting portion  206 B defines a bead portion  208  extending radially outward away from casing  202 . The mounting portion  206 B can also extend radially beyond metal casing  202  so as to provide a friction engagement with the housing in which the seal assembly is inserted. The mounting portion  206 A,  206 B can take on many shapes and forms. The dynamic seal  200  includes an axially extending barrel portion  212  extending from a radially inner end of the mounting portion  206 A,  206 B, the axially extending barrel portion  212  is preferably general cylindrical in shape, although other shapes, such as conical or a convoluted curve shape, can also be utilized. The dynamic seal  200  includes a radially extending portion  214  extending inwardly from a distal end  212 B of the axially extending barrel portion  212 . A generally conically shaped seal portion  216  extends from a radially innermost end  214 A of the radially extending portion  214 . The seal portion  216  includes a radially inner face  218  which may be provided with a plurality of grooves  220 . The grooves  220  can be helical in shape or can take other known forms. The grooves  220  provided in the radially inner surface  218  of the seal portion  216  are capable of retaining oil therein in order to provide lubrication between the dynamic shaft seal  200  and a rotary member, and also can provide a pumping function for returning leaked oil to the oil side of the seal. A radially outer face  222  of the conically shaped seal portion  216  is provided with a stiffening bead  224  defining a region of increased thickness. The stiffening bead  224  can have different shapes, including a triangular shape, as shown, or can have rounded or other shaped configurations. The stiffening bead of  224  is provided to allow a proper contact area to develop on the sealing lip  216 . The bead  224  serves as an integrally formed spring for biasing the sealing lip  216  against the rotary shaft for counteracting bell mouthing of the sealing lip  216 . Normally, the seal lip-free edge faces the oil side. However, reverse mounting is also possible. A dirt protective lip  226  extends from the end portion  214 A of radially extending leg portion  214 . 
         [0041]    The support ring  204  includes an outer ring portion  204 A which engages the bead  208  of mounting portion  206 B in order to provide an axial restrain on the support ring  204 . A radially extending portion  204 B extends radially inward from the outer ring portion  204 A and a second inner ring portion  204 C extends axially from an innermost end portion of radial portion  204 B. The inner ring  204 C extends axially and parallel to the axially extending barrel portion  212  of dynamic seal  200 . The inner ring  204 C limits the radial movement of the axially extending barrel portion  212 . The inner ring portion  204 C includes a radially inwardly extending leg portion  204 D which is generally parallel to the radially extending portion  214  of the dynamic seal  200 . The radially extending leg portion  204 D limits the axial movement of the radially extending portion  214  of the dynamic seal. 
         [0042]    The casing  202  includes an outer ring portion  202 A adapted to be received in a bore of a housing. A first radially inward step portion  202 B extends radially inward from the outer ring portion  202 A. A intermediate ring portion  202 C extends axially from the radially inwardly extending portion  202 B. A mounting arm  202 D extends radially inward from the intermediate axial portion  202 C. The dynamic seal  200  is mounted to the radially inwardly extending arm  202 D. 
         [0043]    With reference to  FIG. 11 , a free floating support ring  300  is shown for use with the dynamic seal  10  which is shown in  FIG. 1 . The support ring  300  can be formed from plastic, metal, or other materials. The support ring  300  extends axially and parallel to the axially extending barrel portion  22  of the dynamic seal  10  and limits the radial movement of the axially extending barrel portion  22 . The support ring  300  includes a radially extending end surface  300   a  which is generally parallel to the radially extending portion  24  of the dynamic seal  10 . The radially extending end surface  300   a  limits the axial movement of the radially extending portion  24  of the dynamic seal. The support ring  300  is restrained from axial movement by radially extending portion  24  and by the exterior housing  302 , or can be otherwise restrained by other members such as a dust lip  38 , as shown in  FIG. 12 , or by other means either attached to or separate from the seal assembly. 
         [0044]    The description of the invention is merely exemplary in nature and, 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.