Abstract:
The purpose of the present invention is to provide a sealing device which has forward and reverse screw threads exhibiting a fluid-pumping action provided on a sliding portion of a seal lip, such that the pumping action is less susceptible to deterioration even with increasing wear on the screw threads and such that leakage of droplets from the screw threads is minimized. To achieve this, the forward and reverse screw threads which exhibit a pumping action on sealing fluid are arranged in a circle on the air-side lateral surface of the sliding portion of the seal lip. The forward and reverse screw threads each have a shape gradually increasing in thread height from the leading end of the lip to the air side. The forward screw threads and/or reverse screw threads are provided with seal protrusions for preventing leakage of droplets.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2014/076495, filed on Oct. 3, 2014 and published in Japanese as WO 2015/053170 A1 on Apr. 16, 2015. This application claims priority to Japanese Patent Application No. 2013-212658, filed on Oct. 10, 2013. The entire disclosures of the above applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a sealing device, and more particularly relates to a sealing device in which a screw achieving a fluid pumping action is provided in a sliding portion of a seal lip. The sealing device according to the present invention is used, for example, in an automobile-related field, or used in a field of a general purpose machine. 
         [0004]    2. Description of the Conventional Art 
         [0005]    There has been conventionally known a sealing device in which a screw achieving a pumping action applied to a sealed fluid is provided in an atmosphere side lateral face of a seal lip sliding portion for improving a sealing performance in relation to the sealed fluid such as an oil. In the case that the other sliding member (hereinafter, refer simply to a shaft) such as a rotary shaft rotates in both forward and reverse directions, a bidirectional screw  53  is provided in an atmosphere side lateral face  52  of a sliding portion of a seal lip  51 , as shown in  FIG. 5 . 
         [0006]    The bidirectional screw  53  is structured by circumferentially and alternately lining up and arranging forward direction screws  54  which achieve a sealing function based on a pumping action when the shaft rotates in a forward direction (an arrow C), and reverse direction screws  55  which achieve the sealing function based on the pumping action when the shaft rotates in a reverse direction, one by one, or several by several, or several tens by several tens. Each of the screws  54  and  55  is formed into a so-called parallel screw in which its longitudinally perpendicular cross sectional shape (including a screw height and a screw width) is formed uniformly over a whole length of the screw. 
         [0007]    The prior art described above can achieve an excellent sealing performance on the basis of the pumping action of each of the screws  54  and  55 , however, since each of the screws  54  and  55  is formed as the parallel screw as mentioned above, there is a problem that the pumping action is lowered in the case that wear caused by the sliding motion makes progress. 
         [0008]    In order to countermeasure the problem mentioned above, it can be thought that each of the forward direction screw  54  and the reverse direction screw  55  is formed into a ship bottom-like screw in place of the parallel screw, as shown in  FIG. 6  which shows a comparative example with the present invention. Since the ship bottom-like screw is provide with a shape that a screw height is enlarged little by little from a lip leading end  56  toward an atmosphere side B, the screw height thereof is hard to be lowered even if the wear makes progress. Accordingly, the pumping action is hard to be lowered. 
         [0009]    However, even in the case that each of the forward direction screw  54  and the reverse direction screw  55  is formed into the ship bottom-like screw as mentioned above, sealed fluid may leak by spray from the screws  54  and  55 . In order to suppress the leak by spray from the screws  54  and  55 , an additional countermeasure is necessary. 
       SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
       [0010]    The present invention is made by taking the above points into consideration, and an object of the present invention is to provide a sealing device having forward direction screws and reverse direction screws achieving a fluid pumping action provided in a sliding portion of a seal lip, wherein the pumping action is hard to be lowered even if wear of the screws makes progress, and leak by spray from the screws can be suppressed. 
       Means for Solving the Problem 
       [0011]    In order to achieve the object mentioned above, in a sealing device according to claim  1  of the present invention, forward direction screws and reverse direction screws achieving a pumping action in relation to a sealed fluid are circumferentially provided in line in an atmosphere side lateral face of a seal lip sliding portion, each of the forward direction screws and the reverse direction screws has such a shape that a screw height is enlarged little by little from a lip leading end toward an atmosphere side, and a seal projection for preventing leak by spray is provided in any one or both of the forward direction screws and the reverse direction screws. 
         [0012]    Further, a sealing device according to claim  2  of the present invention is the sealing device described in claim  1  mentioned above, wherein the seal projection is provided associated with the reverse direction screw, and is extended from the reverse direction screw toward an opposite side to a forward rotating direction of the shaft. 
         [0013]    In the sealing device according to the present invention having the structure mentioned above, each of the forward direction screws and the reverse direction screws has such a shape that the screw height is enlarged little by little from the lip leading end toward the atmosphere side, that is, a corresponding to the ship bottom-like screw can be obtained. Accordingly, the screw height is hard to be lowered even if the wear makes progress. As a result, the pumping action is hard to be lowered. Further, the seal projection for preventing the leak by spray is provided in any one or both of the forward direction screws and the reverse direction screws. Therefore, the seal projection acts as a dam against the leak by spray of the seal fluid. As a result, it is possible to reduce an amount of the leak by spray. 
         [0014]    The seal projection for preventing the leak by spray is provided in any one or both of the forward direction screw and the reverse direction screw as mentioned above. However, in the case that the shaft normally rotates forward, the seal projection for preventing the leak by spray is preferably provided associated with the reverse direction screw. In this case, the seal projection is extended from the reverse direction screw toward an opposite side to the forward rotating direction of the shaft. 
       Effect of the Invention 
       [0015]    The present invention achieves the following effects. 
         [0016]    More specifically, in the present invention, each of the forward direction screws and the reverse direction screws has such a shape that the screw height is enlarged little by little from the lip leading end toward the atmosphere side, as mentioned above. Accordingly, the screw height is hard to be lowered even if the wear makes progress, and the pumping action is hard to be lowered. Further, the seal projection for preventing the leak by spray is provided in any one or both of the forward direction screws and the reverse direction screws. Therefore, the seal projection acts as a dam against the leak by spray of the seal fluid. As a result, it is possible to reduce an amount of the leak by spray. Therefore, it is possible to provide the sealing device in which the pumping action is hard to be lowered even if the wear of the screw makes progress, and the leak by spray from the screw can be suppressed. 
     
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         [0017]      FIG. 1  is a half cut cross sectional view of a sealing device according to a first embodiment of the present invention; 
           [0018]      FIG. 2  is an enlarged view of a substantial part in  FIG. 1 ; 
           [0019]      FIG. 3  is a front elevational view of a substantial part of a sealing device according to a second embodiment of the present invention 
           [0020]      FIG. 4  is a cross sectional view of a substantial part of a sealing device according to a third embodiment of the present invention 
           [0021]      FIG. 5  is a half cut cross sectional view of a sealing device according to the prior art; and 
           [0022]      FIG. 6  is a half cut cross sectional view of a sealing device according to a comparative example. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    The case that the forward direction screws and the reverse direction screws are circumferentially and alternately provided is included in “forward direction screws and reverse direction screws are circumferentially provided in line” described in claim  1  mentioned above in the present invention. Further, the case that forward direction screws and the reverse direction screws are circumferentially provided half circumference by half circumference (the forward direction screws are circumferentially provided over one half circumference and the reverse direction screws are circumferentially provided over the other half circumference is also included in “forward direction screws and reverse direction screws are circumferentially provided in line” described in claim  1  mentioned above in the present invention. 
       Embodiments 
       [0024]    Next, a description will be given of embodiments according to the present invention with reference to the accompanying drawings. 
       First Embodiment 
       [0025]      FIG. 1  shows a half cut cross section of a sealing device (an oil seal)  1  according to a first embodiment of the present invention.  FIG. 2  shows a substantial part in  FIG. 1  in an enlarged manner. The sealing device  1  according to the embodiment is a bidirectional rotation seal corresponding to rotation in both forward and reverse directions of a shaft (the other member which is not shown), and is structured as follows. 
         [0026]    More specifically, as shown in  FIG. 1 , there is provided a seal lip (a main lip)  7  which slidably comes into close contact with a peripheral surface of the shaft together with an outer peripheral seal portion  4 , an end face cover portion  5  and a dust lip (a sub lip)  6  by a rubber-like elastic body  3  attached (vulcanization bonded) to a metal ring  2 , and a leading end sliding portion of the seal lip  7  is provided with a sealed fluid side lateral face (an inclined surface)  8  and an atmosphere side lateral face (an inclined surface)  9 . Reference numeral  10  denotes a lip leading end where both the lateral faces  8  and  9  intersect, and is formed as a pointed end. 
         [0027]    The atmosphere side lateral face  9  in both the lateral faces  8  and  9  of the seal lip  7  is provided with a forward direction screw (a forward screw portion)  11  which achieves a sealing function by pushing back sealed fluid to a sealed fluid side A on the basis of a pumping action when the shaft rotates in a forward direction (rotates forward as shown by an arrow C), and is provided with a reverse direction screw (a reverse screw portion)  21  which achieves the sealing function by pushing back the sealed fluid to the sealed fluid side A on the basis of the pumping action when the shaft rotates in a reverse direction (rotates reverse). The forward direction screws  11  and the reverse direction screws  21  are circumferentially provided half circumference by half circumference, and a changing portion between the forward direction screws  11  and the reverse direction screws  21  is shown in the drawing. 
         [0028]    As shown in  FIG. 2  in an enlarged manner, the forward direction screw  11  is constructed by a spiral projection. A direction of the spiral is set to a direction which is inclined forward in a forward rotating direction C of the shaft from its atmosphere side end portion  11   a  toward a sealed fluid side end portion  11   b.  Further, the forward direction screw  11  is structured such that a parallel screw  12  starting from the lip leading end  10  and a ship bottom-like screw  13  connecting thereto are integrally provided. 
         [0029]    The parallel screw  12  is formed so that a longitudinally perpendicular cross sectional shape thereof (including a screw height and a screw width) is uniform over a whole length of the screw, and the ship bottom-like screw  13  is provided with such a shape that a longitudinally perpendicular cross section thereof (including a screw height and a screw width) is enlarged little by little from the lip leading end  10  side (the sealed fluid side A) toward the atmosphere side B. Since the minimum height of the ship bottom-like screw  13  is set to be identical to the height of the parallel screw  12 , the maximum height of the ship bottom-like screw  13  is set to be larger than the height of the parallel screw  12 . Each of the longitudinally perpendicular cross sections of the parallel screw  12  and the ship bottom-like screw  13  is formed into a triangular shape or an approximately triangular shape. 
         [0030]    On the other hand, the reverse direction screw  21  is also constructed by a spiral projection. A direction of the spiral is set to a direction which is inclined rearward in the forward rotating direction C of the shaft from its atmosphere side end portion  21   a  toward a sealed fluid side end portion  21   b . Further, the reverse direction screw  21  is structured such that a parallel screw  22  starting from the lip leading end  10  and a ship bottom-like screw  23  connecting thereto are integrally provided. 
         [0031]    The parallel screw  22  is formed so that a longitudinally perpendicular cross sectional shape thereof (including a screw height and a screw width) is uniform over a whole length of the screw, and the ship bottom-like screw  23  is provided with such a shape that a longitudinally perpendicular cross section thereof (including a screw height and a screw width) is enlarged little by little from the lip leading end  10  side (the sealed fluid side A) toward the atmosphere side B. Since the minimum height of the ship bottom-like screw  23  is set to be identical to the height of the parallel screw  22 , the maximum height of the ship bottom-like screw  23  is set to be larger than the height of the parallel screw  22 . Each of the longitudinally perpendicular cross sections of the parallel screw  22  and the ship bottom-like screw  23  is formed into a triangular shape or an approximately triangular shape. 
         [0032]    Further, a seal projection  31  for preventing leak by spray is provided as a particularly characteristic structure of the present invention, and the seal projection  31  is provided associated with the reverse direction screw  21  in the embodiment, and is extended toward an opposite side to the forward rotating direction C of the shaft from the reverse direction screw  21 . 
         [0033]    The seal projection  31  is structured as follows. 
         [0034]    In the seal projection  31 , a base end portion  31   a  thereof is connected to the ship bottom-like screw  23  of the reverse direction screw  21 , that is, is connected to a halfway position in a longitudinal direction of the ship bottom-like screw  23 . 
         [0035]    The seal projection  31  is constructed by a spiral projection, and a direction of the spiral is set to a direction which is inclined rearward in the forward rotating direction C of the shaft from its base end portion  31   a  toward a leading end portion  31   b.  Therefore, the seal projection  31  is inclined in the same direction as the ship bottom-like screw  23  or the reverse direction screw  21  to which the seal projection  31  is connected, however, an angle of incline in relation to the lip leading end  10  is set to be smaller than the ship bottom-like screw  23  or the reverse direction screw  21 . The seal projection  31  may be extended in a circumferential direction of the sealing device  1 , and the direction of the spiral may be a direction which is inclined forward in the forward rotating direction C of the shaft from the leading end portion  31   b  toward the base end portion  31   a  a little. 
         [0036]    The seal projection  31  is formed so that a longitudinally perpendicular cross sectional shape (including a projection height and a projection width) thereof is uniform over a whole length of the projection, in the same manner as the parallel screw  22 . Further, a height thereof is formed to be smaller than the height (the maximum height) of the ship bottom-like screw  23 , and is set to be identical or approximately identical to the height of the parallel screw  22  and the minimum height of the ship bottom-like screw  23 . Further, the longitudinally perpendicular cross sectional shape is formed into a triangular shape or an approximately triangular shape. 
         [0037]    The height of the seal projection  31  is formed to be smaller than the height (the maximum height) of the ship bottom-like screw  23  because the ship bottom-like screw  23  does not come into contact with the surface of the shaft if the height of the seal projection  31  is made larger than the ship bottom-like screw  23 , whereby the pumping function can not be achieved. Thus, the ship bottom-like screw  23  can be brought into contact with the shaft surface by forming the height of the seal projection  31  smaller than the height (the maximum height) of the ship bottom-like screw  23 . As a result, it is possible to make the ship bottom-like screw  23  achieve the pumping function. 
         [0038]    Further, the height of the seal projection  31  is set to be identical or approximately identical to the height of the parallel screw  22  because the parallel screw  22  does not come into contact with the shaft surface if the height of the seal projection  31  is made larger than the parallel screw  22 , whereby the pumping function can not be achieved. On the contrary, in the case that the height is made smaller than the parallel screw  22 , the pumping function of the parallel screw  22  is not obstructed, however, the effect of suppressing the leak by spray by the seal projection  31  becomes small. Thus, the parallel screw  22  can be brought into contact with the shaft surface by setting the height of the seal projection  31  to be identical or approximately identical to the height of the parallel screw  22 . As a result, it is possible to make the parallel screw  22  achieve the pumping function, and it is possible to achieve the effect of suppressing the leak by spray by the seal projection  31 . 
         [0039]    Two seal projections  31  are provided in parallel each other to every one reverse direction screw  21 . However, the number of the seal projection  31  may be one or plural number equal to or more than three. 
         [0040]    The sealing device  1  having the structure mentioned above is installed, for example, to an inner periphery of a shaft hole of a housing, and is structured such as to seal the sealed fluid within the machine so as to prevent the sealed fluid from leaking out to an outside of the machine by the seal lip  7  slidably coming into close contact with the peripheral surface of the shaft inserting into the shaft hole. The sealing device is structured as both rotation seal in correspondence to the rotation of the shaft in both the forward and reverse directions as mentioned above, and is characterized by a point that the following operations and effects can be achieved by the structure mentioned above. 
         [0041]    More specifically, in the sealing device  1  having the structure mentioned above, since the forward direction screw  11  and the reverse direction screw  21  are respectively provided with the ship bottom-like screws  13  and  23  which are formed into the shapes that the screw heights are enlarged little by little from the lip leading end  10  toward the atmosphere side B, the screw height is hard to be lowered even if the wear makes progress together with the sliding motion with the shaft. Accordingly, the pumping action is hard to be lowered. 
         [0042]    Further, since the seal projection  31  is extended from the reverse direction screw  21  toward the opposite side to the forward rotating direction C of the shaft associated with the reverse direction screw  21 , the seal projection  31  acts as a damp against the leak by spray of the sealed fluid. As a result, it is possible to reduce an amount of the leak by spray. The spray of the sealed fluid is created, for example, by a part of the fluid which is pushed back to the lip leading end  10  by the forward direction screw  11  achieving the pumping action, the part of the fluid flying in all directions to the atmosphere side B due to a centrifugal force when the shaft forward rotates (an arrow D). Since the seal projection  31  is provided at a position receiving the spray, it is possible to effectively suppress generation of the leak by spray. Further, since the seal projection  31  acts as the dam, an effect of inhibiting the dusts from entering from the atmosphere side B can be expected. 
         [0043]    In the embodiment mentioned above, the seal projection  31  is extended from the reverse direction screw  21  toward the opposite side to the forward rotating direction C of the shaft associated with the reverse direction screw  21  so that the seal projection  31  acts as the damp when the shaft forward rotates. However, in the case of making the seal projection  31  act as the dam when the shaft reverse rotates, the seal projection  31  may be provided so as to extend from the forward direction screw  11  toward the forward rotating direction C associated with the forward direction screw. Further, the structure may be made such as to be provided with both the seal projection  31  which is extended from the reverse direction screw  21  toward the opposite side to the forward rotating direction C associated with the reverse direction screw  21 , and the seal projection  31  which is extended from the forward direction screw  11  toward the forward rotating direction C of the shaft associated with the forward direction screw  11 , so as to respectively correspond to the bidirectional rotation of the shaft. 
         [0044]    Further, in the embodiment mentioned above, the seal projection  31  is provided to be branched from the reverse direction screw  21  or the forward direction screw  11 , however, it can be thought that the seal projection  31  is provided so as to be embedded at a halfway position in the longitudinal direction of the reverse direction screw  21  or the forward direction screw  11 . 
       Second Embodiment 
       [0045]      FIG. 3  shows an example in which the seal projection  31  is provided so as to be embedded at the halfway position in the longitudinal direction of the reverse direction screw  21 , that is, the seal projection  31  is provided between the parallel screw  22  and the ship bottom-like screw  23  in the reverse direction screw  21 . 
       Third Embodiment 
       [0046]    Further,  FIG. 4  shows an example in which the seal projection  31  is provided so as to be embedded at the halfway position in the longitudinal direction of the reverse direction screw  21 , that is, the seal projection  31  is provided between the parallel screw  22  and the ship bottom-like screw  23  in the reverse direction screw  21 . Further, at the same time, the seal projection  31  is provided so as to be embedded at the halfway position in the longitudinal direction of the forward direction screw  11 , that is, the seal projection  31  is provided between the parallel screw  12  and the ship bottom-like screw  13  in the forward direction screw  11 . 
         [0047]    According to the second and third embodiments mentioned above, each of the screws  11  and  21  is formed into a crank-like bent shape as well as the same operations and effects as those of the first embodiment can be achieved. Therefore, a circumferential space per one screw can be made smaller. As a result, more number of screws can be lined up circumferentially at this degree, and it is possible to enhance the pumping action and the sealing function achieved by the screws. Further, since the seal projection  31  acts as the dam as mentioned above, the dam can inhibit the dusts from entering from the atmosphere side B.