Patent Publication Number: US-2013228978-A1

Title: Sealing device and sealing structure

Description:
TECHNICAL FIELD 
     The present invention relates to a sealing device and a sealing structure to seal an annular gap between a shaft and a housing rotating relative to each other. 
     BACKGROUND ART 
     Conventionally, there is known a sealing device including two seal lips sliding on a shaft and a grease filled in between the two seal lips so as to improve the sliding ability of the seal lip at a sealed fluid side (see Patent Literature 1). 
     Referring to  FIG. 6A  and  FIG. 6B , a sealing device according to the conventional example will be described.  FIG. 6A  is a schematic cross-sectional view illustrating a usage state of a sealing device according to the conventional example. Further,  FIG. 6B  illustrates a rotation direction (the arrow R in the drawing) of a rotary shaft when seen in the Z direction in  FIG. 6A . A sealing device  200  includes a rubber-made first seal lip  210  which is provided at a sealed fluid side (L) and a resin-made second seal lip  220  which is provided at an opposite side (A) of the sealed fluid side. Then, grease  230  is filled in between the first seal lip  210  and the second seal lip  220  in order to improve the sliding ability of the first seal lip  210  with respect to a shaft  300 . 
     Further, a tapered surface at the opposite side (A) of the sealed fluid side in relation to the lip tip of the first seal lip  210  is provided with screw thread protrusions (or screw thread grooves)  211  that exhibit a screw pump function. Accordingly, when the first seal lip  210  and the shaft  300  rotate relative to each other, the sealed fluid leaking to the opposite side (A) of the sealed fluid side in relation to the lip tip due to the sliding between the lip tip and the surface of the shaft  300  can be returned to the sealed fluid side (L). 
     However, in the conventional example, the grease  230  also moves to the sealed fluid side (L) by the screw pump effect of the screw thread protrusions (or screw thread grooves)  211  (see the arrow X in the drawing). Thus, the sliding ability of the first seal lip  210  may be degraded. Hence, an abnormal noise (squeaking) may occur when the first seal lip  210  slides on the surface of the shaft  300  and a sliding abrasion may be precipitated. Consequently, the durability of the sealing device is also degraded. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 10-73165 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     It is an object of the invention to provide a sealing device and a sealing structure in which sliding ability is stabilized. 
     Solution to Problem 
     The invention adopts the following means in order to solve the above-described problems. 
     That is, in the sealing device of the present invention to seal an annular gap between a shaft and a housing rotating relative to each other, the sealing device comprising: 
     a first seal lip which slides on a surface of the shaft; 
     a second seal lip which is provided at the opposite side of a sealed fluid side in relation to the first seal lip and slides on the surface of the shaft; and 
     a grease which is filled in between the first seal lip and the second seal lip, 
     wherein a lip tip of the first seal lip includes a first tapered surface which expands in diameter toward the sealed fluid side and a second tapered surface which expands in diameter toward the opposite side of the sealed fluid side, and 
     wherein the second tapered surface is provided with a plurality of screw thread protrusions or screw thread grooves which move the grease in the axial direction while rotating relative to the shaft, and each of the plurality of screw thread protrusions or screw thread grooves is disposed so as to move the grease toward the opposite side of the sealed fluid side. 
     Further, in the sealing structure of the present invention that includes: 
     a housing which has a shaft hole; 
     a shaft which is inserted into the shaft hole and rotates relative to the housing; and 
     a sealing device to seal an annular gap between the shaft and the housing, 
     wherein the sealing device includes 
     a first seal lip which slides on a surface of the shaft; 
     a second seal lip which is provided at the opposite side of a sealed fluid side in relation to the first seal lip and slides on the surface of the shaft; and 
     a grease which is filled in between the first seal lip and the second seal lip, 
     wherein a lip tip of the first seal lip includes a first tapered surface which expands in diameter toward the sealed fluid side and a second tapered surface which expands in diameter toward the opposite side of the sealed fluid side, and 
     wherein the second tapered surface is provided with a plurality of screw thread protrusions or screw thread grooves which move the grease in the axial direction while rotating relative to the shaft, and each of the plurality of screw thread protrusions or screw thread grooves is disposed so as to move the grease toward the opposite side of the sealed fluid side. 
     According to these inventions, the screw thread protrusions or the screw thread grooves can exhibit the function to move the grease toward the opposite side of the sealed fluid side in relation to the lip tip of the first seal lip. Thus, it is possible to suppress leaking of the grease to the sealed fluid side. Accordingly, it is possible to stably maintain a state where the grease is filled in between the first seal lip and the second seal lip and hence to maintain the sliding ability of the first seal lip for a long period of time. 
     Further, the plurality of screw thread protrusions or screw thread grooves are preferably provided up to a position of reaching an edge portion between the first tapered surface and the second tapered surface of the lip tip of the first seal lip. 
     Accordingly, it is possible to exhibit a function (a screw pump function) to move the grease toward the opposite side of the sealed fluid side from the initial stage where the screw thread protrusions and the like are not abraded due to sliding. 
     Advantageous Effects of Invention 
     As described above, according to the present invention, the sliding ability can be stabilized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating an application example of a sealing device according to an example of the present invention. 
         FIG. 2  is a schematic cross-sectional view of a sealing device according to Example 1 of the present invention. 
         FIG. 3A  is a schematic cross-sectional view illustrating a usage state of the sealing device according to Example 1 of the present invention. 
         FIGS. 4A to 4D  are process diagrams illustrating an assembling procedure of the sealing device according to Example 1 of the present invention. 
         FIG. 5  is a schematic cross-sectional view of a sealing device according to Example 2 of the present invention. 
         FIG. 6A  is a schematic cross-sectional view illustrating a usage state of a sealing device according to the conventional example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a mode for carrying out this invention will be exemplarily described in detail with reference to the drawings. Note that, the dimensions, the materials, the shapes, the relative arrangements, and the like of the constituents described in the embodiments do not limit the scope of the invention unless otherwise specified. 
     EXAMPLE 1 
     Referring to  FIGS. 1 to 4D , a sealing device according to Example 1 of the present invention will be described. 
     Application Example of Sealing Device  
     Referring to  FIG. 1 , an application example of a sealing device  100  according to this Example of the present invention will be described.  FIG. 1  is a schematic cross-sectional view of a water pump  10  for a vehicle. The water pump  10  includes a rotary shaft  21  and a housing  30  having a shaft hole into which the rotary shaft  21  is inserted. A bearing  22  which smoothens the rotation of the rotary shaft  21  is mounted to the rotary shaft  21 . Further, a pulley  23  which receives a rotational driving force by a belt or the like (not illustrated) is mounted to one end side of the rotary shaft  21 , and an impeller  24  which pressure-feeds cooling water (LLC) is mounted to the other end side thereof. Then, the sealing device  100  according to this Example is disposed in an annular gap between the rotary shaft  21  and the housing  30  so as to suppress the leaking of the cooling water to the outside (that is, the opposite side (A) of the sealed fluid side (L)) . Namely, in this Example, the sealed fluid is cooling water. 
     Configuration of Sealing Device  
     Referring to  FIGS. 2 to 3B , the sealing device  100  according to this Example of the present invention will be described. Here,  FIGS. 2 and 3A  are cross-sectional views obtained by cutting the plane passing through the center of the rotary shaft  21 ,  FIG. 2  illustrates a cross section of the sealing device  100  itself, and  FIG. 3A  illustrates a cross section in a usage state of the sealing device  100 .  FIG. 3B  illustrates the rotation direction (indicated by the arrow R in the drawing) of the rotary shaft when seen from the Z direction in  FIG. 3A . Note that, the sealing device  100  has a rotationally symmetric shape. 
     The sealing device  100  includes a metal-made cartridge  110 , a rubber-made first seal lip  120 , a metal-made casing  130 , a synthetic resin-made second seal lip  140 , a metal-made backup ring  150 , a metal-made adapter  160 , and a grease  170  as lubricant. 
     The cartridge  110  is formed as an annular member, and is fitted to the inner peripheral surface of the shaft hole of the housing  30 . The first seal lip  120  includes a substantially cylindrical fixed portion  121 , an inward portion  122  which extends inward from the end portion of the fixed portion  121 , and a lip portion  123  which extends from the inner tip of the inward portion  122  toward the sealed fluid side (L) and is further configured to be directed inward. The annular casing  130  is fitted into the fixed portion  121  of the first seal lip  120 . Accordingly, the fixed portion  121  is sandwiched between the outer peripheral surface of the casing  130  and the inner peripheral surface of the cartridge  110 , thereby positioning the first seal lip  120  in the radial direction with respect to the cartridge  110 . 
     The second seal lip  140  includes a plate-like fixed portion  141  and a lip portion  142  which is configured to be directed further inward from the inner tip of the fixed portion  141  and to be directed toward the sealed fluid side (L) . The annular backup ring  150  is provided at the opposite side (A) of the sealed fluid side of the second seal lip  140 . Accordingly, the fixed portion  141  of the second seal lip  140  is sandwiched between the backup ring  150  and an inward flange portion  131  of the casing  130 , thereby fixing the second seal lip  140  to the cartridge  110 . 
     Then, the annular adapter  160  is provided at the sealed fluid side (L) of the fixed portion  121  of the first seal lip  120 . Accordingly, the first seal lip  120  is also positioned in the axial direction with respect to the cartridge  110 . 
     Further, the grease  170  is filled in a spatial region which is formed between the first seal lip  120  and the second seal lip  140  (see  FIG. 2 ) . Here, the filling amount of the grease  170  is set to an amount to fill up a space formed between the first seal lip  120  and the second seal lip  140  when the rotary shaft  21  is mounted to the sealing device  100  (the state illustrated in  FIG. 3A ) with the grease  170 . 
     Here, particularly, an assembling procedure of the sealing device  100  will be described by referring to  FIGS. 4A to 4D . First, the fixed portion  141  of the second seal lip  140  is placed in the casing  130 . Subsequently, the backup ring  150  is fitted (see  FIG. 4A ). Next, the left end portion of the casing  130  in the drawings is bent inward (see the arrow in the drawings). Then, the first seal lip  120  is placed onto this integrated combination of the casing  130 , the second seal lip  140 , and the backup ring  150  (see  FIG. 4B ). Subsequently, the integrated combination of these is press-inserted in the axial direction along the inner peripheral surface of the cartridge  110 , and the fixed portion  121  of the first seal lip  120  is fitted to the inner peripheral surface of the cartridge  110  (see  FIG. 4C ). Then, the adapter  160  is press-inserted into the inner peripheral surface of the cartridge  110 . In this state, the grease  170  is filled into a spatial region formed between the first seal lip  120  and the second seal lip  140 . 
     With the above-described configuration, each of the above-described members is integrally formed into one cartridge. That is, the sealing device  100  including the cartridge  110 , the first seal lip  120 , the casing  130 , the second seal lip  140 , the backup ring  150 , the adapter  160 , and the grease  170  can be handled as a single part. 
     Then, in the sealing device  100  according to this Example, the tip of the lip portion  123  of the first seal lip  120  is configured to include a first tapered surface  123   a  which expands toward the sealed fluid side (L) and a second tapered surface  123   b  which expands toward the opposite side (A) of the sealed fluid side. Note that, an edge portion E is formed between the first tapered surface  123   a  and the second tapered surface  123   b.    
     Further, the second tapered surface  123   b  is provided with a plurality of screw thread protrusions (or screw thread grooves)  124  which move the grease  170  in the axial direction while rotating relative to the rotary shaft  21 . Then, each of the plurality of screw thread protrusions  124  is disposed so as to move the grease  170  toward the opposite side (A) of the sealed fluid side. That is, when the rotary shaft  21  rotates (see  FIG. 3B ), the lip portion  123  slides on the surface of the rotary shaft  21 , and the grease  170  moves toward the opposite side (A) of the sealed fluid side in relation to the edge portion E of the tip of the lip portion  123  due to the screw pump effect of the screw thread protrusions  124  (see the arrows Y of  FIG. 3A ) . Here, from the opposite side (A) of the sealed fluid side on the second tapered surface  123   b,  the screw thread protrusions  124  are provided up to the position of reaching the edge portion E of the tip of the lip portion  123 . Accordingly, it is possible to exhibit the function (the screw pump function) to move the grease  170  toward the opposite side (A) of the sealed fluid side from the initial stage where the screw thread protrusions  124  are not abraded due to sliding. 
     Advantage of Sealing Device  100  of this Example  
     According to the sealing device  100  of this Example, it is possible to exhibit the function to move the grease  170  toward the opposite side (A) of the sealed fluid side in relation to the tip of the lip portion  123  of the first seal lip  120  by the screw thread protrusions (or the screw thread grooves)  124 . For this reason, it is possible to suppress the leaking of the grease  170  to the sealed fluid side (L) . Accordingly, it is possible to stably maintain a state where the grease  170  is filled in between the first seal lip  120  and the second seal lip  140  and hence to maintain the sliding ability of the first seal lip  120  for a long period of time. Consequently, it is possible to suppress the occurrence of abnormal noise (squeaking) and to improve the durability of the sealing device  100  due to a decrease in sliding abrasion. 
     Further, since a coat of the grease  170  is stably formed between the first seal lip  120  and the surface of the rotary shaft  21 , it is possible to effectively suppress the leaking of the cooling water (LLC), namely the sealed fluid, toward the opposite side (A) of the sealed fluid side. Further, for this reason, even when the screw thread protrusions (or the screw thread grooves)  124  that exhibit the function to move a fluid toward the opposite side (A) of the sealed fluid side are provided, the leaking of the cooling water is not precipitated. 
     EXAMPLE 2 
       FIG. 5  illustrates Example 2 of the present invention. In this Example, a modified example of the cartridge of Example 1 will be described. Since the other configurations and effects are the same as those of the Example 1, the same reference numerals will be given to the same constituents, and the description thereof will not be repeated. 
     The annular gap to be sealed by the sealing device may be larger depending on the relation between the diameter of the shaft (the rotary shaft  21 ) and the diameter of the shaft hole of the housing  30 . For this reason, in a sealing device  100   a  according to this Example, the cartridge  110   a  is provided with an S-shaped cross-sectional portion so as to have elasticity in the radial direction, and hence exhibits a sufficient sealing performance without degrading the attaching ability with respect to a large annular gap. Since the configurations other than the cartridge  110   a  are the same as those of Example 1, the description thereof will not be repeated. 
     Others 
     In above-described Examples, a case has been described in which the present invention is used in the water pump  10  for the vehicle as an application example of the sealing device, but the present invention may be applied to various devices that need to seal an annular gap between a shaft and a housing rotating relative to each other. In particular, the present invention can be appropriately used as a sealing device or a sealing structure to seal a shaft hole of devices for home appliances or industrial water pumps with small load. 
     REFERENCE SIGNS LIST 
     
         
           10 : WATER PUMP 
           21 : ROTARY SHAFT 
           22 : BEARING 
           23 : PULLEY 
           24 : IMPELLER 
           30 : HOUSING 
           100 ,  100   a : SEALING DEVICE 
           110 ,  110   a : CARTRIDGE 
           120 : FIRST SEAL LIP 
           121 : FIXED PORTION 
           122 : INWARD PORTION 
           123 : LIP PORTION 
           123   a : FIRST TAPERED SURFACE 
           123   b : SECOND TAPERED SURFACE 
           124 : SCREW THREAD PROTRUSION 
           130 : CASING 
           131 : INWARD FLANGE PORTION 
           140 : SECOND SEAL LIP 
           141 : FIXED PORTION 
           142 : LIP PORTION 
           150 : BACKUP RING 
           160 : ADAPTER 
           170 : GREASE