Abstract:
The present invention provides a bearing sealing method for sealing a bearing member which is interposed between a first member and a second member and allows relative rotation between the first member and the second member. The method includes the steps of keeping the bearing member under a sealed state by interposing a seal between the first member and second member; and releasing the bearing member from the sealed state by bending a first seal element of the seal outward only upon pressure increase in the sealed bearing member. The first seal element is normally in contact with one of the first member and the second member.

Description:
BACKGROUND 
   The present invention relates to a method and a device for sealing, a bearing in which lubricant is used. 
   As to the method for sealing a bearing in which lubricant is used, a first example of prior art is shown in  FIGS. 9 and 10 . In this prior art regarding the connection of a rear-axle tie rod and a cylinder arm in a steering unit for a forklift truck, the cylinder arm  71  is held by upper and lower tie rods  72 ,  73  with a washer  75  of a disc spring interposed between the cylinder arm  71  and each of the tie rods  72 ,  73 , and a tie-rod pin  74  is inserted through the cylinder arm  71 , the tie rods  72 ,  73 , and the washers  75  to fasten them. A collar  77  that serves as a bearing member is fitted between the sliding surfaces of the cylinder arm  71  and the tie-rod pin  74 , thereby supporting the cylinder arm  71  pivotally around the tie-rod pin  74 . The tie-rod pin  74  is provided at the top thereof with a nipple  78  through which lubricating grease is supplied. The surface of the tie-rod pin  74  which slides over the collar  77  is formed with a supply port  74   a  which is opened to a circumferential groove  74   b  of the tie-rod pin  74 . The supply port  74   a  is connected to the nipple  78  through a communication passage  74   c  which is formed axially in the tie-rod pin  74 . Grease supplied from the nipple  78  to the sliding surfaces of the collar  77  and the tie-rod pin  74  smoothens the pivotal movement of the cylinder arm  71 . 
   A second example of prior art which is disclosed by Japanese Unexamined Patent Publication No. 10-338156 shows a structure for sealing a gear housing in a steering unit. In this prior art structure, washers are interposed between a dust boot and the inner ends of a pair of right and left tie rods, respectively. A lip made of an elastic material is baked to the inner peripheral edge of each washer in close contact with the outer peripheral surfaces, of bolts thereby to prevent the ingress of water. Therefore, when each washer is interposed between the dust boot and the inner ends of the tie rods to be firmly sandwiched therebetween, the lip is pressed in tight contact. With the flat surface of a bushing inserted in bolt holes of the inner ends of the tie rods and the outer peripheral surfaces of the bolts thereby to prevent the ingress of water from without. 
   In the above-mentioned first example of prior art, however, the rear-axle tie rod is firmly connected with the cylinder arm by only the washer  75  which is made of a disc spring and disposed between the cylinder arm  71  and the tie rod  72  ( 73 ) In this case, although the ingress of foreign matter is prevented, there is fear that liquid such as water may enter into sealing area through the paths C, D as shown in  FIG. 10 . When water enters into the sealing area, grease in a sliding portion is forced out of the sealing area, resulting in poor lubrication hence development of rust. 
   Although the lip seal washer which is disclosed by the above-mentioned second example of prior art solves the problem of the first example of prior art by preventing the ingress of water by having the lip which improves the sealing of the gear housing, it Is difficult to discharge or remove old lubricant out of the sealing area. Consequently, the lubricant supply from the nipple  78  of the first example of prior art cannot be performed. 
   SUMMARY 
   The present invention is directed to method and device for sealing a lubricated bearing, which prevent moisture and foreign matter from entering into the bearing and also permit replenishment or replacement of lubricant. 
   The present invention provides the bearing sealing method for sealing a bearing member which is interposed between a first member and a second member and allows relative rotation between the first member and the second member. The method includes the steps of: keeping the bearing member under a sealed state by interposing a seal between the first member and second member; and releasing the bearing member from the sealed state by bending a first seal element of the seal outward only upon pressure increase in the sealed bearing member. The first seal element is normally in contact with one of the first member and the second member. 
   The present invention also provides the bearing sealing device for sealing a bearing member which is interposed between a first member and a second member and allows relative rotation between the first member and the second member. The bearing sealing device includes a seal washer having a washer and a seal. The washer is located adjacent to the first member and the second member. The seal is combined with the washer and interposed between the first member and the second member for sealing the bearing member. The seal has a first seal element which is normally in contact with one of member surfaces of the first member and the second member and bendable outward only by increased pressure in the sealed bearing member. 
   Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments, together with the accompanying drawing, in which: 
       FIG. 1  is a plan view showing a steering unit for a rear axle according to a first preferred embodiment of the present invention; 
       FIG. 2  is a partially enlarged cross sectional view showing connections between, tie rods, cylinder arms and knuckle arms according to the first preferred, embodiment of the present invention; 
       FIG. 3  is a partially enlarged cross sectional view showing connection between the tie rods and the cylinder arms according to the first preferred embodiment of the present invention; 
       FIG. 4  is a detailed cross sectional view, showing the state of a seal washer, where it is free according to the first preferred embodiment of the present invention; 
       FIG. 5  is a detailed cross sectional view showing the state of the seal washer where it is combined according to the first preferred embodiment of the present invention; 
       FIG. 6  is a detailed cross sectional view showing the state of a seal washer where it is free according to a second preferred embodiment of the present invention; 
       FIG. 7  is a detailed cross sectional view showing the state of the seal washer where it is combined according to the second preferred embodiment of the present invention; 
       FIG. 8  is a detailed cross sectional view showing the state of a seal washer where it is free according to another embodiment of the present invention; 
       FIG. 9  is an enlarged cross sectional view showing a prior art connection between tie rods and a cylinder arm; and, 
       FIG. 10  is a partially enlarged cross sectional view showing the prior art a connection between the tie rod and the cylinder arm. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following will describe a bearing sealing device according to a first preferred embodiment of the present invention with reference to  FIGS. 1 through 5 . 
   FIG  1  shows a steering unit  1  for a forklift truck. The steering unit  1  includes a rear axle beam  2  which is swingably journaled at the rear of the forklift truck. Opposite ends of the rear axle beam  2  are provided with right and left wheels  3  respectively by knuckle arms  4  for rotation on their own axes and pivoting for steering operation. 
   A hydraulic cylinder  5  is mounted in the middle of the rear axle beam  2 , extending along the longitudinal direction of the rear axle beam  2  and right and left cylinder arms  6  each of which serves as a first member of the present invention, extend from the opposite ends of the hydraulic cylinder  51  respectively. The hydraulic cylinder  5  is operable in conjunction with a steering valve (not shown) whose operation is controlled by turning operation of a steering wheel (not shown) provided in driver&#39;s cabin, and the right and left cylinder arms  6  are moved reciprocally in the direction of vehicle width by oil under pressure fed into one chamber of the hydraulic cylinder  5  while oil in the others chamber is discharged in response to the operation of the steering valve. 
   The right and left knuckle arms  4 , each of which corresponds to the first member of the present invention, are rotatably supported by the respective king pins (not shown) which are in turn supported by the opposite ends of the rear axle beam  2  for pivotal movement about the king pins. The distal ends of the right and left cylinder arms  6 , each of which also corresponds to the first member of the present invention, are connected to the knuckle arms  4  through upper and lower tie-rods  7 ,  8 , respectively. The connection between each cylinder arm  6  and the tie rods  7 ,  8  and the connection between each knuckle arm  4  and the tie rods  7 ,  8  are pivoted by tie-rod pins  9 , each of which corresponds to a second member of the present invention. 
   The tie rods  7 ,  8  function to convert the reciprocating movement of the cylinder arm  6  into an arcuate motion of the knuckle arm  4 . According to the operation of the steering wheel the hydraulic cylinder  5  is operated to move the cylinder arms  6  in either direction depending on the direction in which the steering wheel is turned By such movement of the cylinder arms  6 , the knuckle arms  4  and the wheels  3  are pivoted or turned via the tie rods  7 ,  8  in the direction depending on the direction in which the cylinder arms  6  are moved. Specifically, when the cylinder arms  6  are moved toward the right wheel as seen in  FIG. 1 , the wheels  3  are turned in clockwise direction as seen in  FIG. 1  thereby to steer the forklift truck rightward, and vice versa. In  FIG. 1 , chain double-dashed lines show a state where the wheel  3  are steered leftward. 
   Since the steering unit  1  has a symmetric structure with respect to the longitudinal center of the axle beam  2  as appreciated from  FIG. 1 , the following will describe one side for the left wheel of the steering unit  1  with reference to  FIGS. 2 and 3 . The cylinder arm  6  has formed therethrough a hole  10  in which a collar  11  that serves as a bearing member is fitted. The collar  11  is formed in a ring shape and made of a ferrous metal. The collar  11  has an insertion hole  12  through which the tie-rod pin  9  is inserted. Meanwhile, the knuckle arm  4  has formed through the proximal end thereof a hole  13  in which a collar  14  that serves as the bearing member is fitted. The collar  14  is also formed in a ring shape and made of a ferrous metal. The collar  14  has an insertion hole  15  through which the tie-rod pin  9  is inserted. The collars  11 ,  14  are formed such that the axial length thereof is shorter than that of the holes  10 ,  13  respectively through which the collars  11 ,  14  are fitted, such that, with the collars  11 ,  14  fitted through the holes  10 ,  13 , respectively, a recess is formed at each of the top and bottom of each collar. 
   The upper and lower tie rods  7 ,  8  are plate-like members which are formed substantially the same in the outer peripheral shape thereof. The upper tie rod  7  is formed at the opposite ends thereof with hexagonal fitting holes  16  and the lower tie rod  8  is formed at the opposite ends thereof with through holes  17  The distance between the axial centers of the paired fitting holes  16  is substantially the same as that between the paired through holes  17 . The upper and lower tie rods  7 ,  8  are disposed such that the paired fitting holes  16  and the paired through holes  17  are axially aligned, respectively. 
   The tie rod pin  9  includes a head  18 , a fitting portion  19  that prevents rotation of the tie rod pin  9 , a shank portion  20  and an externally threaded portion,  21  which are disposed in this order from the top in axially aligned relation to each other. The head  18  is provided in the top face thereof with a grease nipple  24  for applying lubricating grease. The shank portion  20  has formed in the outer peripheral surface thereof two circumferential grooves  20   a.  One of the grooves.  20   a  has a supply port  20   b  extending toward the axial center of the groove  20   a.  The supply port  20   b  is in communication with a communication passage  25  which is formed in the tie-rod pin  9  along the central axis thereof and opened to the top face of the tie-rod, pin  9 . Therefore, grease is supplied from the grease nipple  24  to the groove  20   a  through the communication passage  25  and the supply port  20   b.    
   The cylinder arm  6  and the knuckle arm are arranged such that the distal end of the former and the proximal end of the latter are connected and held by the ends of the upper and lower tie rods  7 ,  8 , as shown in  FIG. 2 . Four seal washers  22 , each of which serves as a seal, are interposed between the cylinder arm  6  and the tie rods  7 ,  8  and between the knuckle arm  4  and the tie rods  7 ,  8 , respectively. In such arrangement, each tie-rod pin  9  is inserted through the aligned fitting hole  16 , insertion hole  12  and through hole  17  located at one end of the tie rods  7 ,  8  and through the aligned fitting hole  16 , insertion hole  15  and through hole  17  located at the other end of the tie rods  7 ,  8 . 
   In the inserted state of each tie-rod pin  9 , the fitting portion  19  is inserted in the hexagonal fitting hole  16  of the tie rod  7  to be fixedly positioned, the shank portion  20  is in contact with the inner peripheral surface of the insertion hole  12 ,  15  of the cylinder arm  6  or the knuckle arm  4  and inserted in the through hole  17  of the tie rod  8 , and a nut  23  is screwed on the externally threaded portion  21  via a washer  26  such that the tie-rod pin  9  is retained in the connected state. Therefore the cylinder arm  6  and the knuckle arm  4  are pivotally connected to each other by the tie-rod pins  9  and the tie rods  7 ,  8  for pivotal movement. 
   The seal washer  22  includes a washer  27  and a ring seal  28  which is made of a resilient material and fixed by baking to the inner peripheral surface  27   a  of the washer  27  and the inner peripheral portion  27   b  on the lower surface of the washer  27  as shown in  FIG. 4 . The washer  27  is provided by a metal disc spring and the seal  28  is made of any known resilient material such as nitrile rubber. The seal  28  of the seal washer  22  includes a first seal element  28   a  and a second seal element  28   b.  The first seal element  28   a  has a cross section of a protruding blade-like shape and is in contact with the surface of the cylinder arm  6  which corresponds to a member surface of the present invention. The second seal element  28   b  has a lip portion which is in contact with the surface of the tie-rod, pin  9  which also corresponds to the member surface of the present invention. The second seal element  28   b  is different from the first seal element  28   a.  The protruding blade-like portion of the first seal element  28   a  is formed with an outward slant with a predetermined angle of inclination α (0 degree&lt;α&lt;90 degrees) with respect to the central, axis O of the seal washer  22 . 
   The state of the seal washer  22  mounted in place shown in  FIG. 5 . The seal washer  22  is interposed between the tie rod  7  and the cylinder arm  6 , and is mounted over the shank portion  20  of the tie-rod pin  9 . The first seal element  28   a  is pressed in contact with an end face  11   a  of the collar  11  fitted in the cylinder arm  6  by a pressing force of a predetermined magnitude, and the second seal element  28   b  is in contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9  thereby to seal the bearing. Chain double-dashed lines in  FIG. 5  show the state of the seal  28  where it is free before being mounted. In the mounted state of the seal  28 , the first seal element  28   a  is in contact with the end face  11   a  of the collar  11  with an increased angle of inclination α of the protruding blade-like portion thereof. 
   It is noted that the seal washer  22  which is interpose between the tie rod  8  and the cylinder arm  6  is disposed in upside down relation to the above-described seal washer  22 . The first seal element  28   a  is in contact with the second seal element  28   b  is in contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9 . The same is true of the seal washer  22  which is interposed between the tie rods  7 ,  8  and the knuckle arm  4  and, therefore, the description thereof will be omitted. 
   The following will describe the operation for sealing the connection of the above described rear-axle tie rod Lubricating grease is supplied to the bearing from the grease nipple  24  on the top of the tie-rod pin  9  that serves as a shaft for connecting the cylinder arm  6  and the tie rod  7  (8). The grease reaches the grooves  20   b  in the circumferential surface of the shank portion  20  through the communication passage  25  formed in the tie-rod pin  9  and the supply port  20   b  and is then supplied to the sliding portion between the inner peripheral surface of the collar  11  that serves as the bearing and the outer peripheral surface of the shank portion  20 , thus smoothening the relative rotation between the cylinder arm  6  and the tie-rod pin  9 . 
   Meanwhile, the outer peripheral surface of the shank portion  20  is sealed by the second seal elements  28   b  of the upper and lower seal washers  22 . The end faces  11   a,    11   b  of the collar  11  are sealed by the first seal elements  28   a  of the upper and lower seal washers  22  which are in contact with the end faces  11   a,    11   b , respectively. That is, the outer peripheral surface of the shank portion  20 , the end faces  11   a,    11   b  of the collar  11 , the second seal elements  28   b  which are in contact with the outer peripheral surface of the shank portion  20  and the first seal elements  28   a  which are in contact with the respective end faces  11   a,    11   b  cooperate to form a sealed space  30 . 
   Replenishment of new grease will be described with reference to  FIG. 5 . When new grease is supplied from the grease nipple  24 , old grease which has been supplied to and used for lubricating the sliding surface is accumulated in the sealed space  30 . The grease applying pressure causes the pressure in the sealed space  30  to be increased and the first seal element  28   a  is subjected to a force (indicated by arrow P) which acts to push the first seal, element  28   a  away from the sealed space  30 . As a result, the first seal element  28   a  is moved in the direction which causes the first seal element  28   a  to be bent outwards making an opening between the first seal element  28   a  and the end face  11   a  thereby to allow the old grease to be discharged as indicated by arrow R. At the same time, the bearing of the collar  11  is filled with new grease. 
   On the Other hand, in the case of ingress of any foreign matter, the first seal element  28   a  receives external force indicated by arrow Q and the first seal element  28   a  is moved in the direction to be pressed against the end, faces  11   a  ( 11   b ). This causes the first seal element  28   a  to be strongly pressed in contact with the end face  11   a  ( 11   b ) thereby to prevent the ingress of foreign matter. The second seal element  28   b,  which is in contact with the outer peripheral surface of the shank portion  20 , does not allow its lip portion to move even if the pressure in the sealed space  30  is increased, so that the grease will not leak out of the sealed space  30  to flow along the outer peripheral surface of the shank portion  20 . In addition, even if the second seal element  28   b  receives an external force because of the ingress of any foreign matter, the lip portion of the second seal element  28   b  is not moved, which prevents the ingress of foreign matter along the outer peripheral surface of the shank portion  20 . 
   The above bearing seal structure prevents the ingress of foreign matter while allowing the discharge of the grease. Since the old grease is appropriately discharged from the space new grease can be supplied into the space to constantly lubricate the sliding portion, which enhances the durability of the bearing. In addition, since the foreign matter such as moisture or dust is not permitted into the bearing, the shank portion  20  or the bearing members will not be affected by rust or abnormal wear. 
   Since the connections between the knuckle arm  4  and the ties rods  7 ,  8  have substantially the same operation as the above-described operation, the description thereof will be omitted. 
   The bearing sealing device according to the first preferred embodiment of the present invention has the following advantageous effects.
     (1) Since the first seal element  28   a  of the seal washer  22  has a blade-like protruding portion which is formed with an outward slant and set in contact at the tip end thereof with the end face  11   a  ( 11   b ) of the collar  11  of the cylinder arm  6 , the first seal element  28   a  is moved in the direction which causes the first seal element  28   a  to be bent outward by the grease pressure, thereby allowing the discharge of the grease. When an external pressure is applied to the first seal element  28   a,  the first seal element  28   a  is moved in the direction which causes the first seal element  28   a  to be pressed against the end faces  11   a  ( 11   b ). Thus, the first seal element  28   a  is then kept pressed against the end face  11   a  ( 11   b ) thereby to prevent the ingress of foreign matter   (2) Since the second seal element  28   b  of the seal washer  22  is kept in sealing contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9  that serves as the connecting shaft, the second seal element  28   b  prevents the lubricant retained by the bearing from leaking outward along the outer peripheral surface of the shank portion  20 . In addition the second seal element  28   b  prevents the ingress of foreign matter such as moisture into the sealed space  30  along the outer peripheral surface of the shank portion  20 . Therefore, no additional seal for the above sealing purposes will be needed.   (3) Since the seal washer  22  is constructed such that the washer  27  and the seal  28  are combined, failure to mount the seal in assembling of the bearing sealing device is avoided. In addition, inappropriate placement between the washer and the seal in assembling the bearing sealing device is prevented.   (4) Since the seal washer  22  is so constructed that the washer  27  and the seal  28  are combined and hence easy to assemble, the total cost for the bearing sealing device is reduced and, therefore the seal washer  22  is economical. The assembling process may dispense with some steps of operation and the number of parts for the device may be reduced and, therefore, the management of part numbers and quality inspection or verification may be facilitated.   (5) Since the first seal element  28   a  is made to have a long blade-like portion which can be bent to a large extent, variation in height dimension A of housing is absorbed thereby allowing the tolerance of the height dimension A to be increased. It is noted that the height dimension A of the housing corresponds to the distance between the lower surface of the tie rod  7  and the end face  11   a  of the collar  11  as shown in  FIG. 5 .   (6) The above effects (1) to (5) are achievable by the seal washer  22  which is interposed between the knuckle arm  4  and the tie rods  7 ,  8 .   

   The following will describe a bearing sealing device according to a second preferred embodiment of the present invention with reference to  FIGS. 6 and 7 . This second embodiment differs from the first embodiment in the shape of the first seal element of the seal washer. As a matter of explanatory convenience, the same reference numerals of the first embodiment are partially used for the second embodiment. The explanation for the common structure will be omitted and the modified structure only will be explained. 
   Referring to  FIG. 6 , the seal washer  50  which serves as a seal includes a washer  51  and a ring seal  52  which is made of a resilient material and fixed by baking to inner peripheral surface  51   a  of the insertion hole of the washer  51  and to inner peripheral portion  51   b  of the lower surface of the washer  51 . The washer  51  is provided by a metal disc spring and the seal  52  is made of any known resilient material such as nitrile rubber. The seal  52  of the seal washer  50  includes a first seal element  52   a  and a second seal element  52   b.  The first seal element  52   a  has a cross section of a protruding blade-like shape. The second seal element  52   b  has a lip portion which is contactable with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9 , as shown in  FIG. 7 . The blade-like protruding portion of the first seal element  52   a  has a lip shape protruding outward with respect to the central axis O of the seal washer  50 . 
   The state of the seal washer  50  mounted in place is shown in  FIG. 7 . The seal washer  50  is interposed between the tie rod  7  and the cylinder arm  6 , and is mounted over the shank portion  20  of the tie-rod pin  9 . The first seal element  52   a  is pressed in contact with the inner peripheral surface of the through hole  10  of the cylinder arm  6  on which the collar  11  is mounted by a pressing force of a predetermined magnitude, and the second seal element  52   b  is in contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9  thereby to seal the bearing. Chain double-dashed lines in  FIG. 7  show the state of the seal  52  where it is free before being mounted. 
   It is noted that the seal washer  50  which is interposed between the tie rod  8  and the cylinder arm  6  is disposed in upside down relation (not shown) to the above-described seal washer  50 . The first seal element  52   a  is in contact with the inner peripheral surface of the through hole  10  of the, cylinder arm  6  on which the collar  11  is mounted, and the second seal element  52   b  is in contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9 . The same is true of the seal washer  50  which is interposed between the tie rods  7 ,  8  and the knuckle arm  4  and, therefore, the description thereof will be omitted. 
   The following will describe the operation for sealing the connection of the above-described rear-axle tie rod. Lubricating grease is supplied to the bearing from the grease nipple  24  on the top of the tie-rod pin  9  that serves as a shaft for connecting the cylinder arm  6  and the tie rod  7  (8). The grease reaches the grooves  20   b  in the circumferential surface of the shank portion  20  through the communication passage  25  formed in the tie-rod pin  9  and the supply port  20   b  and is then supplied to the sliding portion between the inner peripheral surface of the collar  11  that serves as the bearing and the outer peripheral surface of the shank portion  20 , thus smoothening the relative rotation between the cylinder arm  6  and the tie-rod pin  9 . 
   Meanwhile, the outer peripheral surface of the shank portion  20  is sealed by the second seal elements  52   b  of the upper and lower seal washers  50 . The end face of the cylinder arm  6  is sealed by the first seal elements  52   a  of the seal washers  50  which are in contact with the respective upper and lower sides of the inner peripheral surface of the through hole  10  of the cylinder arm  6  on which the collar  11  is mounted. That is, the outer peripheral surface of the shank portion  20 , the inner peripheral surface of the, through hole  10  of the cylinder arm  6 , the second seal elements  52   b  which are in contact with the outer peripherial surface of the shank portion  20 , and the first seal elements  52   a  which are in contact with the inner peripheral surface of the through hole  10  of the cylinder arm  6  cooperate to form a sealed space  53 . 
   Replenishment of new grease will be described with reference to  FIG. 7 . When new grease is supplied from the grease nipple  24 , old grease which has been supplied to and used for lubricating the sliding surface is accumulated in the sealed space  53 . The grease applying pressure causes the pressure in the sealed space  53  to be increased and the first seal element  52   a  is subjected to a force (indicated by arrow S) which acts to push the first seal element  52   a  away from the sealed space  53 . As a result, the first seal, element  52   a  is moved in the direction which causes the first seal element  52   a  to be bent outward, making an opening between the first seal element  52   a  and the inner peripheral surface of the through hole  10  thereby to allow the old grease to be discharged as indicated by arrow U. At the same time, the bearing of the collar  11  is filled with new grease. 
   On the other hand, in the case of ingress of any foreign matter, the first seal element  52   a  receives external force indicated by arrow T and the first seal element  52   a  is moved in the direction which causes the first seal element  52   a  to be pressed against the inner peripheral surface of the through hole  10  of the cylinder arm  6 . This causes the first seal element  52   a  to be strongly pressed in contact with the inner peripheral surface of the through hole  10  thereby to prevent the ingress of foreign matter into the sealed space  53 . The second seal element  52   b,  which is in contact with the outer peripheral surface of the shank portion  20 , does not allow its lip portion to move even if the pressure in the sealed space  53  is increased, so that the grease will not leak out of the sealed space  53  to flow along the outer peripheral surface of the shank portion  20 . In addition even if the second seal element  52   b  receives an external force because of the ingress of any foreign matter, the lip portion of the second seal element  52   b  is not moved, which prevents the ingress of foreign matter along, the outer peripheral surface of the shank portion  20 . 
   The above bearing seal structure prevents the ingress of foreign matter into the sealed space  53  while allowing the discharge of the grease therefrom. Since the old grease is appropriately discharged from the sealed space  53 , new grease can be supplied into the sealed space  53  to constantly lubricate the sliding portion, which enhances the durability of the bearing. In addition, since the foreign matter such as moisture or dust is not permitted into the bearing from without, the shank portion  20  or the bearing members will not be affected by rust or abnormal wear. Since the connections between the knuckle arm  4  and the tie rods  7 ,  8  have substantially the same operation as the above-described operation, the description thereof will be omitted. 
   The bearing sealing device according to the second preferred embodiment of the present invention has the following advantageous effects (7) to (9) in addition to the aforementioned (2) to (4).
     (7) Since the first seal element  52   a  of the seal washer  50  has a blade-like protruding portion which is in contact with the inner peripheral surface of the through hole  10  of the cylinder arm  6  in which the collar  11  is fitted, the first seal element  52   a  is moved in the direction which causes the first seal element  52   a  to be bent outward by the grease pressure in the sealed space  30 , thereby making an opening between the first seal element  52   a  and the inner peripheral surface of the through hole  10  through which the grease is allowed to be discharged. When the external pressure is applied to the first seal element  52   a,  the first seal element  52   a  is moved in the direction which causes the first seal element  52   a  to be pressed against the inner peripheral surface of the through hole  10 . Thus, the first seal element  52   a  is then kept pressed against the inner peripheral surface of the through hole  10  thereby to prevent the ingress of foreign matter.   (8) Since the sealing is accomplished by the first seal element  52   a  which is in contact with the inner peripheral surface of the through hole  10  in which the collar  11  is fitted, variation in transverse dimension B for seal housing is relatively small thereby to stabilize the sealing. It is noted that the transverse dimension B of the housing corresponds to the distance between the inner peripheral surface of the through hole  10  and the outer peripheral surface of the shank portion  20  as shown in  FIG. 7 .   (9) The above effects (7) and (8), as well as the aforementioned (2) to (4) are achievable by the seal washer  50  which is interposed between the knuckle arm  4  and the tie rods  7 ,  8 .   

   The present invention is not limited to the, above-described embodiments but may be variously modified within the scope of the purpose of the invention, as exemplified below. 
   In modified embodiments to the first and second embodiments, the second seal element  62   b  which is in contact with the outer peripheral surface of the shank portion  20  of the tie-rod pin  9  has a lengthened and straight-shaped lip portion, as shown in  FIG. 8 , so that the contact length or area between the lip portion and the outer peripheral surface of the shank portion  20  is enlarged. 
   In the first and second embodiments, the ring seal is so arranged that its first seal element is in contact with the end face of the bearing member or the inner wall surface of the fitting hole on which the bearing member is mounted and the first seal element is bendable outward only by the grease pressure in the sealed space, and that the second seal element is in contact with the outer peripheral surface of the shank portion of the tie-rod pin and it is not bendable by pressure. In modified embodiments to the first and second embodiments, however, the first seal element is formed so as not to be bent by any pressure, and the second seal element is formed so as to be bent outward only by the pressure in the sealed space. In this case, grease can be discharged to the outside flowing along the outer peripheral surface of the shank portion which is in contact with the second seal element. Alternatively, both of the first and second seal elements may be formed so as to be bent outward by the internal pressure only. In this case, grease can be discharged to the outside flowing along both of the inner peripheral surface of the through hole  10  of the cylinder arm  6  which is in contact with the first seal element and the outer peripheral surface of the shank portion which is in contact with the second seal element. 
   Although in the first and second embodiments a resilient disc spring is used for the washer of the seal washer, a ring-shaped flat washer having no resilient force may be used. Alternatively, when resilient force is needed for the washer, a resilient member such as spring washer may be used with the flat washer. 
   Although In the first and second embodiments the collar is used for the bearing member and grease is supplied to the sliding portion between the collar and the shaft, a sliding bearing other than the collar may be used for the bearing member. Alternatively, a rolling bearing such as ball bearing or roller bearing may be used. Grease supply is not necessarily needed when oilless bearing or sealed type bearing is used. 
   Although in the first and second embodiments a bearing sealing device is used for the steering unit mounted on a forklift truck, the bearing sealing device is not limited to the use for an industrial vehicle such as forklift truck. The bearing sealing device of the present invention is applicable to any product having the bearing of the above structure such as vehicles other than forklift truck or machine tools. 
   Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope and equivalence of the appended claims.