Patent Publication Number: US-2020300364-A1

Title: Sealing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2018/035964, filed Sep. 27, 2018 (now WO 2019/073808A1), which claims priority to Japanese Application No. 2017-199668, filed Oct. 13, 2017. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a sealing apparatus including a seal member made of polytetrafluoroethylene. 
     BACKGROUND 
     Further stabilization of sealing performance is desired in view of coping with environmental regulations and the like regarding sealing apparatuses for sealing an annular gap between a shaft and a housing which rotate relative to each other in an exhaust gas system such as EGR. In consideration thereof, the applicant has proposed a technique which relates to a sealing apparatus which uses a seal member made of polytetrafluoroethylene (PTFE) which has superior heat resistance and little sliding abrasion and which uses a leaf spring as measures to settling of the seal member due to a creep phenomenon which occurs over time (refer to PTL 1). A sealing apparatus according to a conventional example will now be described with reference to  FIGS. 8 to 10 . 
       FIG. 8  is a schematic sectional view of a sealing apparatus according to the conventional example.  FIGS. 9 and 10  are schematic sectional views of a sealing structure according to the conventional example. It should be noted that  FIG. 9  shows an initial state and  FIG. 10  shows a state after long-term use. Note that  FIGS. 8 to 10  show cross sections and depth lines have been omitted. 
     A sealing apparatus  800  according to this conventional example includes a metal ring  830 , a seal member  810  made of PTFE, a leaf spring  820 , and a metal fixing ring  840  fixed to an inner circumferential surface side of the metal ring  830 . The seal member  810  and the leaf spring  820  are fixed to the metal ring  830  by the fixing ring  840 . The seal member  810  is configured to be in close contact with and slide freely on an outer circumferential surface of a shaft  600  in a state in which its radially outward portion is fixed to the metal ring  830  and its radially inward portion is deformed to curve toward a fluid-to-be-sealed side (a high pressure side (H)). The leaf spring  820  is configured so that its radially outward portion is fixed to the metal ring  830  and its radially inward portion is deformed to curve along the seal member  810 , and the leaf spring  820  presses a vicinity of an end of a radially inward portion of the seal member  810  toward an outer circumferential surface of the shaft  600 . 
     The leaf spring  820  of the sealing apparatus  800  configured as described above can keep a vicinity of the end of the radially inward portion of the seal member  810  in close contact with the outer circumferential surface of the shaft  600  even if settling of the seal member  810  occurs. Thus, sealing performance is maintained over a long period of time. 
     However, the seal member  810  is subjected to pressure of the fluid to be sealed in a high-temperature environment over a long period of time. Then a creep phenomenon advances over time and a curved portion between a planar portion and a cylindrical portion of the seal member  810  has been deformed in a protruding direction toward a side opposite to the fluid-to-be-sealed side (a low-pressure side (L)) as shown in  FIG. 10 . Thus, a sliding area between the seal member  810  and the shaft  600  gradually increases. While a range of the sliding portion between the seal member  810  and the shaft  600  is S 1  in the initial state illustrated in  FIG. 9 , the range of the sliding portion between the seal member  810  and the shaft  600  has become S 2  (&gt;S 1 ) in a state after long-term use illustrated in  FIG. 10 . 
     As described above, the leaf spring  820  of the conventional sealing apparatus  800  causes a sliding area between the seal member  810  and the shaft  600  to increase over time, though it enables sealing performance to be maintained over a long period of time. This leads to increase in sliding resistance, which in turn increases torque. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Patent Application Laid-open No. 2015-203491 
       
    
     SUMMARY 
     Technical Problem 
     An object of the present disclosure is to provide a sealing apparatus capable of suppressing an increase in sliding resistance while sealing performance is maintained over a long period of time. 
     Solution to Problem 
     In order to achieve the object described above, the present disclosure adopts the following means. 
     Specifically, a sealing apparatus according to the present disclosure is a sealing apparatus configured to seal an annular gap between a shaft and a housing which rotate relative to each other, the sealing apparatus including: a metal ring configured to be fixed to a shaft hole provided in the housing; a seal member having a planar and annular member made of polytetrafluoroethylene and configured so that a radially outward portion thereof is fixed to the metal ring and a radially inward portion thereof is in close contact with and slide freely on an outer circumferential surface of the shaft in a state being deformed to curve toward a fluid-to-be-sealed side on which a fluid to be sealed is sealed; and a leaf spring having a planar and annular metal member, a radially outward portion thereof being fixed to the metal ring and a radially inward portion thereof being configured to be deformed to curve along the seal member, the leaf spring pressing the seal member radially inwardly toward the outer circumferential surface of the shaft, wherein the leaf spring is provided with, at intervals in a circumferential direction, a plurality of projections configured to dig into the seal member as, in accordance with the shaft being inserted into the shaft hole, the radially inward portion of the seal member is deformed to curve toward the fluid-to-be-sealed side and the radially inward portion of the leaf spring is deformed to curve along the seal member. 
     Note that the “fluid-to-be-sealed side” refers to a side on which a fluid to be sealed is configured to be sealed. Thus, the side configured to have a fluid to be sealed is the “fluid-to-be-sealed side” though in a state where a fluid to be sealed is not actually sealed. 
     Since the seal member of the sealing apparatus according to the present disclosure is constituted by the planar and annular member made of polytetrafluoroethylene and configured to be in close contact with and slide freely on the outer circumferential surface of the shaft in a state in which the radially outward portion thereof is fixed to the metal ring and the radially inward portion is deformed to curve toward the fluid-to-be-sealed side, superior heat resistance and the like can be realized and sliding abrasion can be reduced as compared to a sealing apparatus having a seal member made of a rubber-like elastic body. In addition, since the sealing apparatus according to the present disclosure includes the leaf spring which presses the seal member radially inwardly toward the outer circumferential surface of the shaft, stable sealing performance can be maintained over a long period of time even if settling of the seal member itself occurs. 
     Since the leaf spring of the sealing apparatus according to the present disclosure is provided with, at intervals in the circumferential direction, a plurality of projections configured to dig into the seal member, the seal member can be prevented from moving relative to the leaf spring in portions where the plurality of projections have dug into the seal member. This prevents the seal member from being deformed in a protruding direction toward a side opposite to the fluid-to-be-sealed side even when subjected to pressure of the fluid to be sealed. This suppresses an increase in a sliding area between the seal member and the shaft. 
     Further, since the projections are configured to dig into the seal member as, in accordance with the shaft being inserted into the shaft hole, the radially inward portion of the seal member is deformed to curve toward the fluid-to-be-sealed side and the radially inward portion of the leaf spring is deformed to curve along the seal member, the seal member and the leaf spring can be deformed not forcedly, thus an occurrence of distortion in any one of the seal member and the leaf spring is suppressed, and detachment of the projections having dug into the seal member is suppressed. 
     The projections may be configured to dig into positions on the reverse side of portions in the seal member which are configured to be in close contact with and slide freely on the outer circumferential surface of the shaft. 
     This ensures the projections to dig into the seal member. 
     The projections may extend radially inwardly toward the fluid-to-be-sealed side. 
     This prevents the projections having dug into the seal member from coming off even when the seal member is subjected to pressure of the fluid to be sealed. 
     Note that the respective configurations described above can be adopted in combination with each other to the greatest extent feasible. 
     Advantageous Effects of the Disclosure 
     As described above, according to the present disclosure, an increase in sliding resistance can be suppressed while sealing performance is maintained over a long period of time. 
    
    
     
       DRAWINGS 
         FIG. 1  is a front view of a sealing apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a rear view of the sealing apparatus according to the embodiment. 
         FIG. 3  is a rear view of a leaf spring according to the embodiment. 
         FIG. 4  is a schematic sectional view of the leaf spring according to the embodiment. 
         FIG. 5  is a schematic sectional view of the sealing apparatus according to the embodiment. 
         FIG. 6  is a schematic sectional view of a sealing structure according to the embodiment. 
         FIG. 7  is a partly sectional perspective view of the sealing apparatus according to the embodiment. 
         FIG. 8  is a schematic sectional view of a sealing apparatus according to a conventional example. 
         FIG. 9  is a schematic sectional view of a sealing structure according to the conventional example. 
         FIG. 10  is a schematic sectional view of the sealing structure according to the conventional example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a mode for implementing the present disclosure will be described in detail by way of example of an embodiment with reference to the drawings. However, it is to be understood that dimensions, materials, shapes, relative arrangements, and the like of components described in the embodiment are not intended to limit the scope of the disclosure thereto unless specifically noted otherwise. 
     Embodiment 
     A sealing apparatus according to an embodiment of the present disclosure will be described with reference to  FIGS. 1 to 7 . A sealing apparatus  10  according to the present embodiment is used in, for example, an exhaust gas system such as EGR in order to seal an annular gap between a shaft  600  and a housing  700  which rotate relative to each other. Thus, the sealing apparatus  10  may be used in a high-temperature environment. Hereinafter, a “fluid-to-be-sealed side” refers to a side on which a fluid-to-be-sealed is configured to be sealed. Thus, the side configured to have a fluid to be sealed is “fluid-to-be-sealed side” though in a state where a fluid to be sealed is not actually sealed. Pressure on the fluid-to-be-sealed side reaches higher than that on a side opposite thereto. Thus, in the following description, the fluid-to-be-sealed side may be referred to as a high-pressure side (H) and a side opposite thereto may be referred to as a low-pressure side (L). 
     &lt;Sealing Apparatus&gt; 
     A configuration of the sealing apparatus  10  will be described.  FIG. 1  is a front view of a sealing apparatus according to the embodiment.  FIG. 2  is a rear view of the sealing apparatus.  FIG. 3  is a rear view of a leaf spring according to the embodiment.  FIG. 4  is a schematic sectional view of the leaf spring along the line B-B in  FIG. 3 .  FIG. 5  is a schematic sectional view of the sealing apparatus along the line A-A in  FIG. 2 .  FIG. 6  is a schematic sectional view of a sealing structure. Note that  FIGS. 5 and 6  show cross sections and depth lines have been omitted.  FIG. 7  is a partly sectional perspective view of the sealing apparatus. Note that  FIG. 7  is a perspective view of a vicinity of a section of the sealing apparatus in the sealing structure according to the embodiment seen in an oblique direction and that a shaft and a housing are omitted in the drawing. 
     The sealing apparatus  10  includes a metal ring  300 , a seal member  100 , a leaf spring  200 , and a metal fixing ring  400  fixed to an inner circumferential surface side of the metal ring  300 . The metal ring  300  includes a cylindrical part  310 , an inward flange part  320  which extends radially inwardly from one end side of the cylindrical part  310 , and a swaging part  330  which is formed on the other end side of the cylindrical part  310  by being bent radially inwardly. The cylindrical part  310  is fitted in a state in close contact with an inner circumferential surface of a shaft hole provided in the housing  700 . Thus, sufficient sealing performance can be achieved between an outer circumferential surface of the metal ring  300  and the inner circumferential surface of the shaft hole of the housing  700  when the housing  700  is made of cast metal (for example, cast aluminum). This ensures sealing performance even if a plurality of minute depression such as blowholes exist on the inner circumferential surface of the shaft hole of the housing  700 . Note that the “one end side” described above corresponds to the “low-pressure side (L)” and the “other end side” described above corresponds to the “high-pressure side (H)” in the sealing structure. 
     The seal member  100  includes a planar and annular member made of polytetrafluoroethylene (PTFE). Characteristics of PTFE include superior heat resistance, pressure resistance, and chemical resistance as well as low sliding abrasion. The seal member  100  is configured so that a radially outward portion thereof is fixed to the metal ring  300  and a radially inward portion thereof is in close contact with and slide freely on an outer circumferential surface of the shaft  600  in a state being deformed to curve toward the high-pressure side (H). 
     The leaf spring  200  includes a planar and annular metal member. The leaf spring  200  is configured so that a radially outward portion thereof is fixed to the metal ring  300  and a radially inward portion thereof is deformed to curve along the seal member  100  and presses the radially inward side of the seal member  100  toward the outer circumferential surface of the shaft  600 . The leaf spring  200  is provided with, at intervals in the circumferential direction, a plurality of inner slits  220  which extend from an end on an inner circumferential surface side toward an end on an outer circumferential surface side. The leaf spring  200  is provided with, at intervals in the circumferential direction, a plurality of outer slits  230  which extend from the end on the outer circumferential surface side toward the end on the inner circumferential surface side. The inner slits  220  and the outer slits  230  are alternately provided in the circumferential direction. The leaf spring  200  is provided with, at intervals in the circumferential direction, a plurality of projections  210  configured to dig into the seal member  100 . 
     The fixing ring  400  includes a cylindrical part  410 , which is fixed to an inner circumferential surface side of the metal ring  300 , and an inward flange part  420 , which extends radially inwardly from one end side of the cylindrical part  410 . The swaging part  330  is formed by bending an end portion on the other end side in the metal ring  300  radially inwardly so as to abut against an end of the fixing ring  400  in a state in which the seal member  100 , the leaf spring  200 , and the fixing ring  400  are arranged on the inner circumferential surface side of the metal ring  300 . The radially outward side end of the seal member  100  and the radially outward side end of the leaf spring  200  are fixed to the metal ring  300  by being compressed between the inward flange part  320  and the fixing ring  400 . 
     &lt;Mounting Method and State in Use of Sealing Apparatus&gt; 
     A mounting method and a sealing structure of the sealing apparatus  10  will now be described with reference to  FIGS. 5 to 7 . The sealing apparatus  10  configured as described above is inserted into a shaft hole provided in the housing  700  and fitted into the shaft hole. The outer circumferential surface of the cylindrical part  310  of the metal ring  300  in the sealing apparatus  10  comes into close contact with an inner circumferential surface of the shaft hole. The shaft  600  is inserted from a left side in  FIG. 6  (the low-pressure side (L) in use) toward a right side in  FIG. 6  (the high-pressure side (H) in use). Thus, radially inward side ends of the seal member  100  and the leaf spring  200  are pushed by the shaft  600 . Then the seal member  100  and the leaf spring  200  deform so that the radially inward side portions relative to portions compressed between the inward flange part  320  and the fixing ring  400  curve toward the fluid-to-be-sealed side. Thus, an inner circumferential surface in a vicinity of a distal end in a curved portion of the seal member  100  comes into close contact with the outer circumferential surface of the shaft  600 . In addition, an inner circumferential surface in a vicinity of a distal end in a curved portion of the leaf spring  200  comes into close contact with an outer circumferential surface in a vicinity of the distal end in the curved portion of the seal member  100 . Due to elastic restoring force of the leaf spring  200 , a vicinity of the distal end in the curved portion of the seal member  100  is pressed toward the outer circumferential surface of the shaft  600  by a portion of the leaf spring  200  near the distal end. 
     &lt;Projections of Leaf Spring&gt; 
     The projections  210  provided on the leaf spring  200  will now be described in greater detail. The projections  210  are configured not to dig into the seal member  100  in a state where the sealing apparatus  10  is assembled, that is, a state prior to insertion of the shaft  600 . The elastic force of the leaf spring  200  is set so that, in this state, distal ends of the projections  210  abut against the seal member  100  while a radially inward portion of the leaf spring  200  is slightly deflected, and the projections  210  are prevented from digging into the seal member  100  as illustrated in  FIG. 5 . 
     In addition, the projections  210  are configured to dig into the seal member  100  as, in accordance with the shaft  600  being inserted into the shaft hole of the housing  700 , the radially inward portion of the seal member  100  is deformed to curve toward the fluid-to-be-sealed side and the radially inward portion of the leaf spring  200  is deformed to curve along the seal member  100 . 
     When the radially inward portion of the seal member  100  deforms and the radially inward portion of the leaf spring  200  deforms in accordance with insertion of the shaft  600 , a radially inward portion of the seal member  100  becomes sandwiched between the shaft  600  and the leaf spring  200 . Thus, pressing force of the projections  210  provided on the leaf spring  200  on the seal member  100  increases as compared to that in a state prior to the insertion of the shaft  600 , and then the projections  210  dig into the seal member  100 . 
     Note that the projections  210  are configured to dig into positions on the reverse side of portions in the seal member  100  which are configured to be in close contact with and slide freely on the outer circumferential surface of the shaft  600 . In addition, the projections  210  are configured to extend radially inwardly toward the fluid-to-be-sealed side as illustrated in  FIG. 5 . 
     Advantages of Sealing Apparatus According to Present Embodiment 
     Since the seal member  100  of the sealing apparatus  10  includes the planar and annular member made of PTFE and configured to be in close contact with and slide freely on the outer circumferential surface of the shaft  600  in a state in which the radially outward portion thereof is fixed to the metal ring  300  and the radially inward portion is deformed to curve toward the fluid-to-be-sealed side, superior heat resistance and the like can be realized and sliding abrasion can be reduced as compared to a sealing apparatus having a seal member made of a rubber-like elastic body. In addition, since the sealing apparatus  10  includes the leaf spring  200  which presses the seal member  100  radially inwardly toward the outer circumferential surface of the shaft  600 , stable sealing performance can be maintained over a long period of time even if settling of the seal member  100  itself occurs. 
     Since the leaf spring  200  is provided with, at intervals in the circumferential direction, a plurality of projections  210  configured to dig into the seal member  100 , the seal member  100  can be prevented from moving relative to the leaf spring  200  in portions where the plurality of projections  210  have dug into the seal member  100 . This prevents the seal member  100  from being deformed in a protruding direction toward the low-pressure side (L) even when subjected to pressure of the fluid to be sealed. Assuming that a seal member is solely pressed by a leaf spring toward an outer circumferential surface of a shaft, the seal member would be gradually deformed to protrude toward a low-pressure side due to a creep phenomenon under a high-temperature environment and sustained pressure of a fluid to be sealed. Further, the seal member would gradually slide toward the low-pressure side (L) relative to the leaf spring in a pressed portion of the seal member by the leaf spring. 
     In contrast, the seal member  100  of the sealing apparatus  10  according to the present embodiment can be prevented from moving relative to the leaf spring  200  in portions where the plurality of projections  210  have dug into the seal member  100  as described above. This prevents the seal member  100  from being deformed in a protruding direction toward the low-pressure side (L). This suppresses an increase in a sliding area between the seal member  100  and the shaft  600 . Thus, an increase in sliding resistance between the seal member  100  and the shaft  600  can be suppressed. 
     Further, since the projections  210  are configured to dig into the seal member  100  as, in accordance with the shaft  600  being inserted into the shaft hole, the radially inward portion of the seal member  100  is deformed to curve toward the fluid-to-be-sealed side and the radially inward portion of the leaf spring  200  is deformed to curve along the seal member  100 , the seal member  100  and the leaf spring  200  can be deformed not forcedly, thus an occurrence of distortion in any one of the seal member  100  and the leaf spring  200  is suppressed, and detachment of the projections  210  having dug into the seal member  100  is suppressed. 
     Specifically, the seal member  100  and the leaf spring  200  are deformed with different degrees of bending. Thus, assuming that the projections  210  are configured to dig into the seal member  100  in a state prior to deformation, distortion would occur in any one of the seal member  100  and the leaf spring  200  during deformation, and hence the projections  210  which had dug into the seal member  100  would come off easily. In contrast, in the present embodiment, since the projections  210  are configured to dig into the seal member  100  during the deformation process of the seal member  100  and the leaf spring  200 , an occurrence of distortion in any one of the seal member  100  and the leaf spring  200  can be suppressed. 
     In addition, since the projections  210  are configured to dig into positions on the reverse side of portions in the seal member  100  which are configured to be in close contact with and slide freely on the outer circumferential surface of the shaft  600 , the seal member  100  is directly sandwiched by the projections  210  and the shaft  600  from both surfaces&#39; sides. This ensures the projections  210  to dig into the seal member  100 . 
     Further, since the projections  210  are configured to extend radially inwardly toward the fluid-to-be-sealed side, the projections  210  having dug into the seal member  100  can be prevented from coming off even when the seal member  100  is subjected to pressure of the fluid to be sealed. 
     (Other) 
     Positions where the projections  210  are provided on the leaf spring  200  are not limited to the positions shown in the embodiment described above. 
     REFERENCE SIGNS LIST 
     
         
           10  Sealing apparatus 
           100  Seal member 
           200  Leaf spring 
           210  Projection 
           220  Inner slit 
           230  Outer slit 
           300  Metal ring 
           310  Cylindrical part 
           320  Inward flange part 
           330  Swaging part 
           400  Fixing ring 
           410  Cylindrical part 
           420  Inward flange part 
           600  Shaft 
           700  Housing