Patent Publication Number: US-2022213931-A1

Title: Sealing device

Description:
TECHNICAL FIELD 
     The present invention relates to sealing devices. 
     BACKGROUND ART 
     Rolling bearings, such as ball bearings are well known and are used, for example, in automotive vehicle hubs. Patent Document 1 discloses a sealing device that seals an inside of a rolling bearing. The sealing device includes a mounted ring press-fitted into the outer race of the rolling bearing, a seal ring integrally attached to the mounted ring, and a slinger mounted to the inner race, in which multiple lips formed at the seal ring are brought into contact with the slinger. The lips have a function of sealing lubricant (grease) inside the bearing and a function of sealing to prevent foreign matter, such as water and dust from ingress into the inside of the bearing. 
     BACKGROUND DOCUMENT(S) 
     Patent Document(s) 
     Patent Document 1: JP-A-2005-331002 
     SUMMARY OF THE INVENTION 
     For this type of sealing device, there is a demand to improve the function of protecting against water (including muddy water or salt water) from entering the inside of the sealed object (e.g., bearing) if the sealing device is used in an environment with a lot of water. It is also desirable for water to be discharged rapidly even if water does enter the sealing device. 
     Accordingly, the present invention provides a sealing device that has superior ability to discharge foreign matter and superior ability to protect the sealed object from foreign matter. 
     In accordance with an aspect of the present invention, there is provided a sealing device adapted to be disposed between an inner member and an outer member that rotate relative to each other, and adapted to act to seal a gap between the inner member and the outer member. The sealing device includes: a first sealing member including a cylindrical part adapted to be mounted to the outer member, and an annular part that extends radially inward from the cylindrical part toward the inner member; and a second sealing member including a sleeve adapted to be mounted to the inner member, and a flange that extends radially outward from the sleeve, the flange facing the annular part of the first sealing member. The first sealing member further includes at least one lip made of an elastic material that extends toward the flange of the second sealing member. An annular first clearance is provided between the flange and the cylindrical part of the first sealing member. The second sealing member further includes a labyrinth lip extending from the flange radially outward and extending toward the atmosphere side more than the cylindrical part of the first sealing member, and a second clearance is provided between the labyrinth lip and the outer member. The second clearance is radially outside the first clearance and communicates with the first clearance. 
     In this aspect, foreign matter may enter the space between the annular part of the first sealing member and the flange of the second sealing member through the first clearance between the flange and the cylindrical part. However, the labyrinth lip, which extends from the flange radially outward and extends toward the atmosphere side more than the cylindrical part of the first sealing member, covers the first clearance. Accordingly, the labyrinth lip prevents foreign matter from entering the space. Since the second clearance is provided between the labyrinth lip and the outer member, even if foreign matter enters the first clearance and/or space, the foreign matter will be discharged through the second clearance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional view of an example of a rolling bearing in which a sealing device according to an embodiment of the present invention is used; 
         FIG. 2  is a partial cross-sectional view of a sealing device according to an embodiment of the present invention; 
         FIG. 3  is a partial cross-sectional view of a sealing device according to a modification of the embodiment of the present invention; 
         FIG. 4  is a partial cross-sectional view of a sealing device according to another modification of the embodiment of the present invention; 
         FIG. 5  is a partial cross-sectional view of the sealing device of  FIG. 4  in a different orientation; 
         FIG. 6  is a partial cross-sectional view of a sealing device according to another modification of the embodiment of the present invention; 
         FIG. 7  is a perspective view of the sealing device of  FIG. 6  in which a part is cutaway; 
         FIG. 8  is a partial cross-sectional view of a sealing device according to another modification of the embodiment of the present invention; and 
         FIG. 9  is a partial cross-sectional view of a sealing device according to another modification of the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, with reference to the accompanying drawings, embodiments according to the present invention will be described. It is of note that the drawings are not necessarily to scale, and certain features may be exaggerated or omitted. 
       FIG. 1  shows an automotive vehicle hub bearing, which is an example of a rolling bearing in which a sealing device according to any one of the embodiments of the present invention is used. The present invention is not limited to hub bearings, and is applicable to other types of rolling bearings. In the following description, the hub bearing is a ball bearing. Again, the present invention is not limited to ball bearings, and is applicable to other types of rolling bearings, such as roller bearings and needle bearings, and other types of rolling elements. The present invention is also applicable to rolling bearings used in machines other than automotive vehicles. 
     The hub bearing  1  includes a hub  4  (inner member) that has a hole  2  into which a spindle (not shown) is inserted, an inner race  6  (inner member) mounted to the hub  4 , an outer race  8  (outer member) located outside the hub  4  and the inner race  6 , multiple balls  10  arranged in a row between the hub  4  and the outer race  8 , multiple balls  12  arranged in a row between the inner race  6  and the outer race  8 , and multiple retainers  14  and  15  that retain the balls in place. 
     Whereas the outer race  8  remains stationary, the hub  4  and the inner race  6  rotate with the spindle. 
     In  FIG. 1 , the central axis Ax common to the spindle and hub bearing  1  extends in a vertical direction. In  FIG. 1 , relative to the central axis Ax only the left part is shown; and although not shown in detail, in  FIG. 1  the upper side corresponds to the outer side (outboard side) of the automotive vehicle on which wheels are arranged, while the lower side corresponds to the inner side (inboard side) on which differential gears are arranged. In  FIG. 1 , the outer side and the inner side are shown in their respective radial directions. 
     The outer race  8  of the hub bearing  1  is mounted to the hub knuckle  16 . The hub  4  has an outboard side flange  18  that extends radially further outward than the outer race  8 . A wheel can be mounted to the outboard side flange  18  by hub bolts  19 . 
     A sealing device  20  that seals a gap between the outer race  8  and the hub  4  is located close to the end of the outer race  8  on the outboard side, and inside the end of the outer race  8  on the inboard side. Another sealing device  21  that seals a gap between the outer race  8  and the inner race  6  is located inside the end of the inner side of the outer race  8 . The sealing devices  20  and  21  prevent outflow of a lubricant in the form of grease from the interior of the hub bearing  1 , and prevent intrusion of foreign matter (water, including muddy water and salt water) into the interior of the hub bearing  1  from the outside. In  FIG. 1 , arrows F indicate an example direction of an exterior flow of foreign matter. 
     The sealing device  20  is located between the rotatable hub  4  and the cylindrical end portion  8 A on the outboard side of the stationary outer race  8  of the hub bearing  1 , and seals the gap between the outer race  8  and the hub  4 . The sealing device  21  is located between the rotatable inner race  6  and the end portion  8 B on the inboard side of the outer race  8  of the hub bearing  1 , and seals the gap between the outer race  8  and the inner race  6 . 
     As shown in  FIG. 2 , the sealing device  21  is provided in a gap between the end portion  8 B on the inboard side of the outer race  8  of the hub bearing  1  and the inner race  6  of the hub bearing  1 . The sealing device  21  is annular in shape; although, in  FIG. 2  only the left part of the sealing device  21  is shown. 
     The sealing device  21  has a composite structure that includes a first sealing member  24  and a second sealing member  26 . 
     The first sealing member  24  is a stationary sealing member that is mounted to the outer race  8  and does not rotate. The first sealing member  24  has a composite structure and includes an elastic ring  28  and a rigid ring  30 . The elastic ring  28  is made of an elastic material such as an elastomer. The rigid ring  30  is made of a rigid material such as a metal and reinforces the elastic ring  28 . As viewed in cross section, the rigid ring  30  is substantially L-shaped. A part of the rigid ring  30  is embedded in the elastic ring  28  and is in close contact with the elastic ring  28 . 
     The first sealing member  24  has a cylindrical part  24 A, an annular part  24 B, a radial lip  24 C, and axial lips  24 D and  24 E. The cylindrical part  24 A constitutes a mounted part that is to be mounted to the outer race  8 . More specifically, the cylindrical part  24 A is engaged by interference fit, namely, is press-fitted into the end portion  8 B of the outer race  8 . The annular part  24 B, which has a circular annular shape, is located radially inside the cylindrical part  24 A and extends from the cylindrical part  24 A radially inward toward the inner race  6 . The cylindrical part  24 A and the annular part  24 B are formed of the rigid ring  30  and the elastic ring  28 . 
     The radial lip  24 C and the axial lips  24 D and  24 E extend from the annular part  24 B toward the second sealing member  26 , and the distal ends of these lips are in contact with the second sealing member  26 . These lips are formed of the elastic ring  28 . 
     The second sealing member  26  may also be referred to as a slinger, that is, a rotational sealing member. The second sealing member  26  is mounted to the inner race  6 , rotates together with the inner race  6 , and acts to deflect exterior splashing of foreign matter. 
     In this embodiment, the second sealing member  26  also has a composite structure that includes an elastic ring  32  and a rigid ring  34 . The rigid ring  34  is made of a rigid material such as a metal. 
     As viewed in cross section, the rigid ring  34  is substantially L-shaped. The rigid ring  34  includes a cylindrical sleeve  34 A and an annular flange  34 B that extends radially outward from the sleeve  34 A. The sleeve  34 A constitutes a mounted part that is to be mounted to the inner race  6 . More specifically, an end portion of the inner race  6  is engaged by interference fit, namely, is press-fitted into the sleeve  34 A. 
     The flange  34 B is located radially outside the sleeve  34 A, extends radially outward, and faces the annular part  24 B of the first sealing member  24 . In this embodiment, the flange  34 B is a flat plate and lies on a plane that is perpendicular to the axis of the sleeve  34 A. 
     The elastic ring  32  is in close contact with the flange  34 B of the rigid ring  34 . In another point of view, the second sealing member  26  includes the sleeve  34 A made of only a rigid material, and a flange  35  that extends radially outward from the sleeve  34 A and faces the annular part  24 B of the first sealing member  24 , in which the flange  35  is made of a rigid material and an elastic material. 
     The flange  35  includes the flange  34 B of the rigid ring  34  (rigid portion of the flange  35 ) and flange portions  32 A and  32 B of the elastic ring  32  (elastic portions of the flange  35 ). The elastic portion  32 A of the flange  35  is fixedly adhered to the entirety of the surface of the rigid portion  34 B that is opposite to the sleeve  34 A (inboard side surface), and the elastic portion  32 B of the flange  35  extends from the elastic portion  32 A to the outboard side and is fixedly adhered to the entirety of the outer peripheral surface of the rigid portion  34 B. 
     The flange portion  32 A of the elastic ring  32  is used to measure a rotational speed of the inner race  6 . More specifically, the elastic ring  32  is formed of a resin material that contains a magnetic metal powder and a ceramic powder, or an elastomer material that contains a magnetic metal powder and a ceramic powder, and has a large number of S poles and N poles provided by the magnetic metal powder. In the flange portion  32 A of the elastic ring  32 , a large number of S poles and N poles are alternately arranged at equiangular intervals in a circumferential direction. The angle of rotation of the flange portion  32 A of the elastic ring  32  is measured by use of a magnetic rotary encoder (not shown). Since the material of the elastic ring  32  contains a metal powder, it has a higher degree of hardness than that of usual resin materials or elastomer materials and thus is not readily susceptible to damage by foreign matter. 
     The radial lip (grease lip)  24 C of the first sealing member  24  extends radially inward from the inner end of the annular part  24 B. The radial lip  24 C extends toward the sleeve  34 A of the second sealing member  26 , and the distal end of the radial lip  24 C is in contact with the sleeve  34 A. The radial lip  24 C extends radially inward and toward the outboard side, and has a primary role in preventing outflow of the lubricant from the inside of the hub bearing  1 . 
     The axial lips (side lips)  24 D and  24 E of the first sealing member  24  extend laterally from the annular part  24 B. The distal ends of the axial lips  24 D and  24 E extend radially outward toward the inboard side and are in contact with the rigid portion  34 B of the flange  35  of the second sealing member  26 . Each of the axial lips  24 D and  24 E has a primary role in preventing exterior intrusion of foreign matter into the hub bearing  1 . 
     The first sealing member  24  is mounted to the stationary outer race  8 . On the other hand, the inner race  6  and the second sealing member  26  rotate, and the radial lip  24 C and the axial lips  24 D and  24 E slide on the second sealing member  26 . 
     An annular first clearance  36  is provided between the distal end on the inboard side of the cylindrical part  24 A of the first sealing member  24  and the flange  35  of the second sealing member  26 . Foreign matter may enter through the first clearance  36  into a space  38  between the annular part  24 B of the first sealing member  24  and the flange  35  of the second sealing member  26 . Conversely, foreign matter in the space  38  can also be discharged through the first clearance  36 . 
     The second sealing member  26  further has two labyrinth lips  40  and  42 . 
     The labyrinth lip  40  is a truncated-cone shaped ring that extends radially outward and toward the inboard side (atmosphere side) from the flange  35  (especially, the elastic portions  32 A and  32 B) of second sealing member  26 . The labyrinth lip  40  extends more toward the inboard side than the cylindrical part  24 A of the first sealing member  24 , and an annular second clearance  44  is provided between the labyrinth lip  40  and the outer race  8 . The second clearance  44  communicates with the first clearance  36 . The second clearance  44  is located radial outside the first clearance  36 . In other words, the labyrinth lip  40  covers the first clearance  36  at least partially. 
     The labyrinth lip  42  is a cylindrical ring that projects from the flange  35  toward the annular part  24 B of the first sealing member  24 . In this embodiment, the labyrinth lip  42  is located at the outermost edge of the second sealing member  26 . 
     In this embodiment, the labyrinth lip  40  is integrally attached to the elastic portions  32 A and  32 B of the flange  35 , whereas the labyrinth lip  42  is integrally attached to the elastic portion  32 B of the flange  35 . In other words, the labyrinth lips  40  and  42  are parts of the elastic ring  32 . Therefore, the labyrinth lips  40  and  42  are made of the same material as the elastic ring  32 , i.e., a resin material containing a magnetic metal powder and a ceramic powder, or an elastomer material containing a magnetic metal powder and a ceramic powder. Since the labyrinth lips  40  and  42  contain a metal powder and a ceramic powder, they have superior durability against impact of hard foreign matter and a superior wear resistance. 
     In the sealing device  21 , foreign matter may enter into the space  38  between the annular part  24 B of the first sealing member  24  and the flange  35  of the second sealing member  26  through the first clearance  36  between the flange  35  and the cylindrical part  24 A. However, since the first clearance  36  is covered with the labyrinth lip  40 , which extends from the flange  35  radially outward and toward the atmosphere side more than the cylindrical part  24 A, the ingress of foreign matter into the space  38  is inhibited. Since the second clearance  44  is provided between the labyrinth lip  40  and the outer race  8 , even if foreign matter enters the first clearance  36  and/or the space  38 , the foreign matter will be discharged through the second clearance  44 . In particular, in this embodiment, the second sealing member  26  rotates along with the inner race  6 , so that the foreign matter is easily discharged through the second clearance  44  by a centrifugal force. 
     In addition, the annular labyrinth lip  42  protrudes from the flange  35  toward the annular part  24 B of the first sealing member  24 . Although the labyrinth lip  42  is not in contact with the first sealing member  24 , the labyrinth lip  42  complicates and elongates the path of entry of foreign matter from the first clearance  36  to the space  38 . Thus, the ingress of foreign matter into the space  38  is inhibited. The labyrinth lip  42  overlaps the distal ends of the axial lips  24 D and  24 E in radial directions. Therefore, it is difficult for foreign matter to penetrate between the distal ends of the axial lips  24 D and  24 E and the rigid portion  34 B of the flange  35 . 
     The sealing device  21  is mounted to the gap between the outer race  8  and the inner race  6  by, for example, a mounting jig  50 . The arrow depicted by the phantom line in the figure indicates the direction of movement of the mounting jig  50 . 
     The mounting jig  50  is formed of a metal such as a steel, and has coaxial circular annular portions  52  and  54 . The end surface of the circular annular portion  52  can be brought into contact with the end surface of the cylindrical part  24 A of the first sealing member  24 , and the end surface of the circular annular portion  54  can be brought into contact with the elastic portion  32 A of the flange  35  of the second sealing member  26 . 
     By means of the mounting jig  50 , the first sealing member  24  and the second sealing member  26  of the sealing device  21  are attached, in combination, simultaneously to the gap between the outer race  8  and the inner race  6 . By pressing the mounting jig  50  from the inboard side to the outboard side, as indicated by the arrow of the phantom line, the circular annular portion  52  of the mounting jig  50  presses the cylindrical part  24 A of the first sealing member  24 , and thus the entirety of the first sealing member  24  toward the outboard side, and the circular annular portion  54  of the mounting jig  50  presses the flange  35  of the second sealing member  26 , and thus the entirety of the second sealing member  26  toward the outboard side. 
     The maximum outer diameter DL of the labyrinth lip  40  is less than the outer diameter DO of the cylindrical part  24 A of the first sealing member  24  and equal to or less than the inner diameter DI of the cylindrical part  24 A. The inner diameter of the circular annular portion  52  of the mounting jig  50  is greater than or equal to the inner diameter DI of the cylindrical part  24 A. Therefore, when mounting the cylindrical part  24 A of the first sealing member  24  to the outer race  8  with use of the mounting jig  50 , the labyrinth lip  40  does not get in the way and the cylindrical part  24 A can be easily pushed into the outer race  8 . 
       FIG. 3  is a partial cross-sectional view of a sealing device according to a modification of the embodiment. In this modification, the labyrinth lip  42  is not formed, and the shape of the labyrinth lip  40  is different from that of the labyrinth lip  40  in  FIG. 2 . 
     In this modification, the first clearance  36  is also covered with the labyrinth lip  40 , which prevents the ingress of foreign matter into the space  38 . Since the second clearance  44  is provided between the labyrinth lip  40  and the outer race  8 , even if foreign matter enters the first clearance  36  and/or the space  38 , the foreign matter will be discharged through the second clearance  44 . 
     The maximum outer diameter DL of the labyrinth lip  40  is less than the outer diameter DO of the cylindrical part  24 A of the first sealing member  24  and equal to or less than the inner diameter DI of the cylindrical part  24 A. Therefore, when mounting the cylindrical part  24 A of the first sealing member  24  to the outer race  8  with use of the mounting jig  50 , the labyrinth lip  40  does not get in the way and the cylindrical part  24 A can be easily pushed into the outer race  8 . 
       FIG. 4  is a partial cross-sectional view of a sealing device according to another modification of the embodiment, in which the labyrinth lip  42  is not formed and the shape and position of the labyrinth lip  40  are different from those of the labyrinth lip  40  in  FIG. 2 . 
     In this modification, the first clearance  36  is also covered with the labyrinth lip  40 , which prevents the ingress of foreign matter into the space  38 . Since the second clearance  44  is provided between the labyrinth lip  40  and the outer race  8 , even if foreign matter enters the first clearance  36  and/or the space  38 , the foreign matter will be discharged through the second clearance  44 . 
     The maximum outer diameter DL of the labyrinth lip  40  is less than the outer diameter DO of the cylindrical part  24 A of the first sealing member  24  and equal to or less than the inner diameter DI of the cylindrical part  24 A. Therefore, when mounting the cylindrical part  24 A of the first sealing member  24  to the outer race  8  with use of the mounting jig  50 , the labyrinth lip  40  does not get in the way and the cylindrical part  24 A can be easily pushed into the outer race  8 . 
     In this modification, an annular protrusion  60  is formed on the inner peripheral surface of the elastic portion  32 A of the flange  35 . The annular protrusion  60  protrudes radially inward from the sleeve  34 A. Once the end of inner race  6  is fitted into sleeve  34 A, the annular protrusion  60  is compressed by the outer peripheral surface of the end of inner race  6  to prevent or reduce penetration of foreign matter between the end of inner race  6  and sleeve  34 A. 
     In this modification, the flange  35  does not have an elastic portion  32 B that covers the outer peripheral surface of rigid portion  34 B. A circumferential groove  62  is formed on the outer peripheral surface of the boundary portion between the labyrinth lip  40  and the flange  35 . In this modification, the outer peripheral surface of the elastic portion  32 A of the flange  35  forms the bottom surface of the circumferential groove  62 , and the rigid portion  34 B of the flange  35  forms a partition wall of the circumferential groove  62 . 
     Thus, the circumferential groove  62  is disposed on the atmosphere side (i.e., outside the space  38  between the annular part  24 B and the flange  35 ) for the first clearance  36 . External foreign matter that is on the point of entering the first clearance  36 , but is blocked by the outer edge of the rigid portion  34 B of the flange  35 , will enter the circumferential groove  62 . Since the circumferential groove  62  is formed on the outer peripheral surface of the boundary portion between the labyrinth lip  40  and the flange  35 , foreign matter that has entered the circumferential groove  62  is restricted from entering the space  38  through the first clearance  36  by means of the rigid portion  34 B of the flange  35 . 
       FIG. 5  is a partial cross-sectional view of the sealing device of  FIG. 4  in a different orientation.  FIG. 5  shows that water drops WD, which have been prevented from entering the space  38  by the rigid portion  34 B of the flange  35 , have entered the circumferential groove  62 . Since the flange  35  is circular and annular, the water drops WD that have entered the circumferential groove  62  fell down through the outer peripheral surface of the elastic portion  32 A of the flange  35 , as shown by the arrow of the phantom line. Thereafter, they do not enter the space  38 . Although the water drops WD may contain dust, damage to the axial lips  24 D and  24 E is prevented or reduced by preventing the water drops WD from entering the space  38 . 
       FIG. 6  is a partial cross-sectional view of a sealing device according to another modification of the embodiment. This modification is a variant of the modification in  FIG. 4 . In this modification, labyrinth lips  40  are disposed intermittently in a circumferential direction. 
     More specifically, in this modification, as shown in  FIG. 7 , the labyrinth lip  40  has an annular proximal portion  64  and multiple distal portions  66  that are intermittently provided. The proximal portion  64  is a truncated-cone shaped ring that extends radially outward and toward the inboard side (atmosphere side) from the flange  35  of the second sealing member  26  (especially, the elastic portions  32 A and  32 B). The multiple distal portions  66  extend radially outward and toward the inboard side (atmosphere side) from the proximal portion  64 , and are spaced apart from one another in a circumferential direction. The inner peripheral surfaces of the distal portions  66  are flush with the inner peripheral surface of proximal portion  64 , and the outer peripheral surfaces of distal portions  66  are flush with the outer peripheral surface of proximal portion  64 . 
     As shown in  FIG. 6 , the maximum outer diameter DN of the proximal portion  64  of the labyrinth lip  40  is less than the inner diameter DI of the cylindrical part  24 A of the first sealing member  24 . The maximum outer diameter DM of the distal portions  66  of the labyrinth lip  40  is less than the outer diameter DO of the cylindrical part  24 A and greater than the inner diameter DI of the cylindrical part  24 A. 
     According to this modification, since the maximum outer diameter DM of the distal portions of the labyrinth lip  40  is greater than the outer diameter DI of the first clearance  36 , ingress of foreign matter into the space  38  between annular part  24 B and flange  35  through the first clearance  36  may further be reduced. 
     The sealing device  21  is mounted to the gap between the outer race  8  and the inner race  6  by, for example, a mounting jig  70 . The arrow depicted by the phantom line in the figure indicates the direction of movement of the mounting jig  70 . 
     The mounting jig  70  is formed of a metal such as a steel, and has multiple projections  72  intermittently formed and a circular annular portion  74 . The end surfaces of the projections  72  can be brought into contact with the end surface of the cylindrical part  24 A of the first sealing member  24 , and the end surface of the circular annular portion  74  can be brought into contact with the elastic portion  32 A of the flange  35  of the second sealing member  26 . The projections  72  are spaced apart from each other in a circumferential direction. 
     By means of the mounting jig  70 , the first sealing member  24  and the second sealing member  26  of the sealing device  21  are attached, in combination, simultaneously to the gap between the outer race  8  and the inner race  6 . By pressing the mounting jig  70  from the inboard side to the outboard side, as indicated by the arrow of the phantom line, the projections  72  of the mounting jig  70  press the cylindrical part  24 A of the first sealing member  24 , and thus the entirety of the first sealing member  26  toward the outboard side, and the circular annular portion  74  of the mounting jig  70  presses the flange  35  of the second sealing member, and thus the entirety of the second sealing member  26 , toward the outboard side. 
     The maximum outer diameter DM of the distal portions  66  of the labyrinth lip  40  is greater than the inner diameter DI of the cylindrical part  24 A of the first sealing member  24 . However, the distal portions  66  are intermittently provided in a circumferential direction, and when pressing on the cylindrical part  24 A of the first sealing member  24 , the projections  72  are located between the intermittently arranged distal portions  66 , so that the distal portions  66  do not get in the way. Since the maximum outer diameter DN of the proximal portion  64  of the labyrinth lip  40  is less than the inner diameter DI of the cylindrical part  24 A of the first sealing member  24 , the proximal portion  64  is also not obstructive. Therefore, when mounting the cylindrical part  24 A of the first sealing member  24  to the outer race  8  with use of the mounting jig  70 , the labyrinth lip  40  does not get in the way and the cylindrical part  24 A can be easily pushed into the outer race  8 . 
       FIG. 8  is a partial cross-sectional view of a sealing device according to another modification of the embodiment. In this modification, the axial lip  24 E is not provided. In this modification, the second sealing member  26  has multiple water discharge protrusions (fins)  80  located in the space  38 . The water discharge protrusions  80  protrudes from the flange  35  toward the annular part  24 B of the first sealing member  24 . The water discharge protrusions  40  are of the same shape and size, and are arranged at equiangular intervals in a circumferential direction. 
     In this modification, the flange  35  further includes an elastic portion  32 C, which is fixedly attached to a portion (outer portion) of a surface (outboard side surface) of the sleeve portion  34 A of the rigid portion  34 B. Multiple water discharge protrusions  80  are integrally attached to the elastic portion  32 C of the flange portion  35 . In other words, the water discharge protrusions  80  comprise portions of the elastic ring  32 . 
     In this modification, together with relative rotation of the inner race  6  and the outer race  8 , the water in the space  38  flows along the water discharge protrusions  80  and is rapidly discharged from the space  38  through the first clearance  36  and the second clearance  44 . Accordingly, the sealing device  21  provides a superior protective effect for the hub bearing  1 , which is to be sealed, against water. For the sealing device  21  itself, deterioration, which is accelerated in the presence of water (including muddy water or salt water), is reduced. 
       FIG. 9  is a partial cross-sectional view of a sealing device according to another modification of the embodiment. In this modification, instead of the labyrinth lip  40  made of an elastic material, there is provided a labyrinth lip  90  made of a rigid material such as a metal. 
     The labyrinth lip  90  is a truncated-cone shaped ring that extends radially outward and toward the inboard side (atmosphere side) from the flange  35  (especially, the rigid portion  34 B) of the second sealing member  26 . The labyrinth lip  90  extends more toward the inboard side than the cylindrical part  24 A of the first sealing member  24 , and an annular second clearance  44  is provided between the labyrinth lip  90  and the outer race  8 . The second clearance  44  communicates with the first clearance. The second clearance  44  is located radial outside the first clearance  36 . In other words, the labyrinth lip  90  covers the first clearance  36  at least partially. 
     The labyrinth lip  90  is integrally attached to the rigid portion  34 B of the flange  35 . In other words, the labyrinth lip  90  is a part of the rigid ring  34 . Therefore, the labyrinth lip  90  is made of the same material as the rigid ring  34 , i.e., a metal, and has superior durability against impact of hard foreign matter and a superior wear resistance. 
     In this modification, the first clearance  36  is also covered with the labyrinth lip  90 , which prevents foreign matter from entering the space  38 . Since the second clearance  44  is provided between the labyrinth lip  90  and the outer race  8 , even if foreign matter enters the first clearance  36  and/or the space  38 , the foreign matter will be discharged through the second clearance  44 . 
     The maximum outer diameter DL of the labyrinth lip  90  is less than the outer diameter DO of the cylindrical part  24 A of the first sealing member  24  and equal to or less than the inner diameter DI of the cylindrical part  24 A of the cylindrical part  24 A. Therefore, when mounting the cylindrical part  24 A of the first sealing member  24  to the outer race  8  with use of the mounting jig  50 , the labyrinth lip  90  does not get in the way and the cylindrical part  24 A can be easily pushed into the outer race  8 . 
     Other Modifications 
     The present invention has been shown and described with reference to preferred embodiments thereof. However, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the claims. Such variations, alterations, and modifications are intended to be encompassed in the scope of the present invention. 
     For example, in the above-described embodiment, the hub  4  and the inner race  6 , which are inner members, are rotatable members, while the outer race  8 , which is an outer member, is a stationary member. However, the present invention is not limited thereto, and may be configured such that multiple sealed members rotate relative to each other. For example, inner members may be stationary while an outer member may be rotatable, or all of the members may be rotatable. 
     The present invention is not limited to sealing the hub bearing  1 . For example, the sealing device or the sealing structure according to the present invention may be applied to a differential gear mechanism or other power transmission mechanism of an automotive vehicle, to a bearing or other support mechanism for a drive shaft of an automotive vehicle, or to a bearing or other support mechanism of a rotary shaft of a pump. 
     Although the rigid ring  30  of the sealing device  21  in the embodiment and modifications consists of a single component, in place of the rigid ring  30 , there may be employed multiple rigid rings that are provided radially apart from each other. 
     Although the sealing device  21  in the embodiment and modifications includes at least one axial lip, the axial lip may be omitted. 
     The labyrinth lip  40  made of an elastic material may be formed of a resin material that does not contain a metal powder and/or a ceramic powder, or an elastomer material that does not contain a metal powder and/or a ceramic powder. 
     Featured of the embodiment and the modifications may be combined as long as no contradiction arises thereby. 
     Aspects of the present invention are also set out in the following numbered clauses: 
     Clause 1. A sealing device adapted to be disposed between an inner member and an outer member that rotate relative to each other, and adapted to act to seal a gap between the inner member and the outer member, the sealing device including: 
     a first sealing member including a cylindrical part adapted to be mounted to the outer member, and an annular part that extends radially inward from the cylindrical part toward the inner member; and 
     a second sealing member including a sleeve adapted to be mounted to the inner member, and a flange that extends radially outward from the sleeve, the flange facing the annular part of the first sealing member, 
     the first sealing member further including at least one lip made of an elastic material that extends toward the flange of the second sealing member, 
     an annular first clearance being provided between the flange and the cylindrical part of the first sealing member, 
     the second sealing member further including a labyrinth lip extending from the flange radially outward and extending toward the atmosphere side more than the cylindrical part of the first sealing member, a second clearance being provided between the labyrinth lip and the outer member, the second clearance being radially outside the first clearance and communicating with the first clearance. 
     Clause 2. The sealing device according to clause 1, wherein a maximum outer diameter of the labyrinth lip is equal to or less than the inner diameter of the cylindrical part of the first sealing member. 
     According to this clause, since the maximum outer diameter of the labyrinth lip is equal to or less than the inner diameter of the cylindrical part of the first sealing member, when the cylindrical part of the first sealing member is mounted to the outer member, the cylindrical part can be easily pushed into the outer member. 
     Clause 3. The sealing device according to clause 1, wherein the labyrinth lips are disposed intermittently in a circumferential direction, 
     a maximum outer diameter of a proximal portion of the labyrinth lip being less than an inner diameter of the cylindrical part of the first sealing member, 
     a maximum outer diameter of distal portions of the labyrinth lip being greater than an inner diameter of the cylindrical part. 
     According to this clause, since the maximum outer diameter of the distal portions of the labyrinth lip is greater than the size of the first clearance, ingress of foreign matter into the space between annular part and flange through the first clearance may further be reduced. On the other hand, since the labyrinth lips are disposed intermittently in a circumferential direction and the maximum outer diameter of the proximal portion of the labyrinth lip is less than the inner diameter of the cylindrical part of the first sealing member, when the cylindrical part of the first sealing member is mounted to the outer member, the cylindrical part can be easily pushed into the outer member. 
     Clause 4. The sealing device according to any one of clauses 1-3, wherein a circumferential groove is formed on an outer peripheral surface of a boundary portion between the labyrinth lip and the flange. 
     According to this clause, the circumferential groove is disposed on the atmosphere side (i.e., outside the space between the annular part and the flange) for the first clearance. External foreign matter that is on the point of entering the first clearance, but is blocked by the outer edge of the flange, will enter the circumferential groove. Since the circumferential groove is formed on the outer peripheral surface of the boundary portion between the labyrinth lip and the flange, foreign matter that has entered the circumferential groove is restricted from entering the space through the first clearance by means of the flange. 
     Clause 5. The sealing device according to any one of clauses 1-4, wherein the flange includes a rigid portion made of a rigid material and an elastic portion made of an elastic material that is adhered to a surface of the rigid portion opposite to the sleeve, 
     the labyrinth lip being integrally formed with the elastic portion. 
     Clause 6. The sealing device according to clause 5, wherein the elastic portion of the flange is made of a resin material containing a metal powder and/or a ceramic powder, or an elastomer material containing a metal powder and/or a ceramic powder 
     According to this clause, the labyrinth lip has superior durability against impact of hard foreign matter and a superior wear resistance. 
     Clause 7. The sealing device according to clause 1, wherein the flange includes a portion made of a rigid material, 
     the labyrinth lip being integrally formed with the portion made of the rigid material. 
     According to this clause, the labyrinth lip has superior durability against impact of hard foreign matter and a superior wear resistance. 
     REFERENCE SYMBOLS 
       1 : Hub bearing 
       6 : Inner race (inner member) 
       8 : Outer race (outer member) 
       21 : Sealing device 
       24 : First sealing member 
       26 : Second sealing member 
       28 : Elastic ring 
       30 : Rigid ring 
       24 A: Cylindrical part 
       24 B: Annular part 
       24 C: Radial lip 
       24 D,  24 E: Axial lip 
       32 : Elastic ring 
       34 : Rigid ring 
       34 A: Sleeve 
       34 B: Flange (rigid portion of flange  35 ) 
       35 : Flange 
       32 A: Elastic portion of flange  35   
       32 B: Elastic portion of flange  35   
       36 : First clearance 
       38 : Space 
       40 : Labyrinth lip 
       44 : Second clearance 
       50 ,  70 : Mounting jig 
       62 : Circumferential groove 
       64 : Proximal portion 
       66 : Distal portion 
       90 : Labyrinth lip