Patent Publication Number: US-2020292080-A1

Title: Annular dust seal

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application No. PCT/JP2019/011797, filed on Mar. 20, 2019, which claims priority to Japanese Patent Application No. 2018-053693, filed on Mar. 21, 2018. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to an annular dust seal, and particularly relates to an annular dust seal having an excellent dust seal function but not causing local wear, settling (deformation), and stick slip (squealing, vibration). 
     Background Art 
     Conventionally, as a dust seal used for a rod seal portion in a hydraulic cylinder or a suspension of a construction machinery, a shock absorber of an automobile, and the like, there is an annular dust seal  300  that is slidably in sealing contact with an outer peripheral surface of a reciprocating shaft (rod)  200  as shown in  FIG. 8  (Japanese Patent Application Publication No. 2014-214769). 
     The reciprocating shaft  200  is disposed in a housing (not shown), and is capable of reciprocating in an axial direction as indicated by an arrow A in  FIG. 8 . The reciprocating shaft  200  includes a base end side (a left side in  FIG. 8 ) located in the housing and a tip end side (a right side in  FIG. 8 ) protruding toward an outside in an axial direction from an opening end portion of the housing (hereinafter, referred to as “atmosphere side”). Although the housing is filled with oil, the hydraulic cylinder and the like are provided with both of a lip packing to prevent external oil leakage and a buffering for the purpose of hydraulic buffering and high-temperature oil cut at the time of high load on an inner side (hereinafter, referred to as “hydraulic side”) of the housing of the dust seal in many cases, and the dust seal is supplied with an oil film that has passed between the lip packing and the shaft. 
     The annular dust seal  300  is integrally formed in a circular annular shape from a rubber-like elastic material, and is attached with a metal ring  310  on an outer peripheral side. The annular dust seal  300  is disposed in an annular groove formed in the housing. The annular groove is formed to surround an outer peripheral surface of the reciprocating shaft  200 . 
     The annular dust seal  300  includes an oil lip  320 , which closely contacts with a peripheral surface of the reciprocating shaft  200 , on the hydraulic side. In addition, the annular dust seal  300  includes a circular annular dust lip  330 , which closely contacts with the peripheral surface of the reciprocating shaft  200 , on the atmosphere side. 
     The annular dust seal  300  brings the oil lip  320  into pressure-contact with the outer peripheral surface of the reciprocating shaft  200  with an elastic force of the rubber-like elastic material. In addition, the annular dust seal  300  brings the dust lip  330  into pressure-contact with the outer peripheral surface of the reciprocating shaft  200  with the elastic force of the rubber-like elastic material. When the oil lip  320  and the dust lip  330  are brought into pressure-contact with the outer peripheral surface of the reciprocating shaft  200 , the inside of the housing is sealed. 
     The annular dust seal  300  seals oil in the housing with the oil lip  320 . In addition, the annular dust seal  300  prevents earth and sand from entering the housing with the dust lip  330 . The annular dust seal  300  contributes to a longer service life of a device by maintaining a good lubrication state of a hydraulic holding component located closer to a hydraulic side than the dust lip  330  or a sliding component such as a bearing or a gear for a long period of time. The dust lip  330  is configured to form an appropriate oil film on the outer peripheral surface of the reciprocating shaft  200 . 
     The annular dust seal  300  is formed of an elastic material, for example, various rubbers, urethane, or PTFE capable of sealing a gap with the outer peripheral surface of the reciprocating shaft  200  in order to prevent external foreign substances from entering the housing by the dust lip  330 . In addition, since it is necessary to scrape off external foreign substances adhering to the outer peripheral surface of the reciprocating shaft  200 , the annular dust seal  300  is required to have a rigidity and is formed of a high-hardness synthetic resin material such as rubber or urethane. 
     Further, the annular dust seal  300  increases a seal contact pressure against the outer peripheral surface of the reciprocating shaft  200  to enhance seal properties against external foreign substances adhering to the outer peripheral surface of the reciprocating shaft  200 , and thus can contribute to a longer service life of a device. 
     However, since a surface pressure gradient is increased when the annular dust seal  300  increases the seal contact pressure against the outer peripheral surface of the reciprocating shaft  200 , an oil film passing through the dust lip may become thin and scraping leakage may increase when the shaft strokes toward the inner side of the housing. In addition, when the annular dust seal  300  is increased in a tightening force in order to increase the seal contact pressure, local wear, settling (deformation), stick slip (squealing, vibration), and the like may occur. 
     It is a purpose of the present disclosure to provide an annular dust seal having an excellent dust seal function and improved in local wear, settling (deformation), and stick slip (squealing, vibration). 
     Other purposes of the present disclosure will become apparent from the following description. 
     SUMMARY 
     The above-described problems are solved by the following respective disclosures. 
     1. An annular dust seal including: 
     a circular annular dust lip, the annular dust seal being formed of an elastic material, supported by a housing, and bringing a surface of the dust lip into contact with an outer peripheral surface of a reciprocating shaft that is disposed in the housing and includes a tip end side protruding toward an atmosphere side, characterized in that 
     in a longitudinal section of the dust lip, an average radius of curvature of a surface having a convex curvature on an inner side of the housing from a top portion of the dust lip is larger than an average radius of curvature of a surface having a convex curvature on the atmosphere side from the top portion of the dust lip. 
     2. The annular dust seal according to 1 described above, characterized in that the average radius of curvature of the surface having the convex curvature on the inner side of the housing from the top portion of the dust lip is 1.5 to 4 times the average radius of curvature of the surface having the convex curvature on the atmosphere side from the top portion of the dust lip. 
     3. The annular dust seal according to 1 or 2 described above, characterized in that the average radius of curvature of the surface having the convex curvature on the inner side of the housing from the top portion of the dust lip is 2 to 3 times the average radius of curvature of the surface having the convex curvature on the atmosphere side from the top portion of the dust lip. 
     4. The annular dust seal according to 1, 2, or 3 described above, characterized in that, when the surface of the dust lip is brought into contact with the outer peripheral surface of the reciprocating shaft, 
     an end surface facing the atmosphere side forms an angle of 90° or more with respect to a generatrix of the outer peripheral surface at least in a vicinity of the outer peripheral surface of the reciprocating shaft. 
     5. The annular dust seal according to any one of 1 to 4 described above, characterized in that, when the surface of the dust lip is brought into contact with the outer peripheral surface of the reciprocating shaft, 
     an end surface facing the atmosphere side has a tapered shape protruding toward the atmosphere side as the end surface is closer to the outer peripheral surface of the reciprocating shaft. 
     According to the present disclosure, it is possible to provide an annular dust seal having an excellent dust seal function and improved in local wear, settling (deformation), and stick slip (squealing, vibration). 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A longitudinal sectional view showing a first embodiment (mounted state) of an annular dust seal of the present embodiment. 
         FIG. 2  A longitudinal sectional view showing the annular dust seal (unmounted state) shown in  FIG. 1 . 
         FIG. 3  An enlarged longitudinal sectional view showing a main portion of the annular dust seal shown in  FIG. 1 . 
         FIG. 4  A graph showing a contact pressure of the annular dust seal shown in  FIG. 1  with respect to the reciprocating shaft. 
         FIG. 5  A longitudinal sectional view showing a second embodiment (unmounted state) of the annular dust seal of the present disclosure. 
         FIG. 6  An enlarged longitudinal sectional view showing a main portion of the annular dust seal shown in  FIG. 5 . 
         FIG. 7  A graph showing a contact pressure of the annular dust seal shown in  FIG. 5  with respect to the reciprocating shaft. 
         FIG. 8  A longitudinal sectional view showing a conventional annular dust seal. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments for carrying out the present disclosure will be described. 
     First Embodiment 
       FIG. 1  is a longitudinal sectional view showing a first embodiment (mounted state) of an annular dust seal of the present embodiment. 
     The first embodiment of the annular dust seal  1  is used for a rod seal in a hydraulic cylinder or a suspension of a construction machinery, a shock absorber of an automobile, or the like. The present embodiment is an example of application to a rod sealing system employed in a hydraulic cylinder (not shown) to be used as an actuator of a construction machinery, a civil engineering machinery, a transport vehicle, or the like. 
     As shown in  FIG. 1 , a rod sealing system is provided between a piston rod  102  as a movable portion that reciprocates linearly and a cylinder housing  101  as a fixed portion that houses the piston rod  102 . The rod sealing system is supported by the housing  101 . The housing  101  has an opening portion  101   a  on an atmosphere side (a right side in  FIG. 1 ), and is in a lid-closed state on a hydraulic side (a left side and an inner side in  FIG. 1 ) (not shown). 
     A reciprocating shaft (rod)  102  is disposed in the housing  101 . One tip end side of the reciprocating shaft  102  is located on the hydraulic side inside the housing  101 , and the other tip end side thereof protrudes from the opening portion  101   a  of the housing  101 . The reciprocating shaft  102  can reciprocate in an axial direction as indicated by an arrow A in  FIG. 1 . A reciprocating speed in the axial direction of the reciprocating shaft  102  is regulated by fluid in the housing  101 . 
     The rod sealing system includes a rod packing (not shown), a buffering (not shown) disposed on the hydraulic side of the rod packing, and a dust seal  1  disposed on the atmosphere side of the rod packing. Accordingly, the buffering, the rod packing, and the dust seal  1  are arranged in this order from the hydraulic side to the atmosphere side. 
     The rod packing serves as a main seal for preventing leakage of hydraulic oil to the outside, and has a structure in which a circular annular U-packing is mainly used and a flat washer-shaped backup ring is adjacent to the U-packing. Both the U-packing and the backup ring are housed in a mounting groove provided on an inner peripheral surface of the cylinder housing  101 . 
     The buffering plays a role of maintaining durability of the rod packing by buffering shock pressure and fluctuation pressure at the time of high load and preventing high-temperature hydraulic oil from flowing into a side of the rod packing. Such a buffering has a structure in which a circular annular U-packing is mainly used and a backup ring is fitted into a heel portion of the U-packing. Both the U-packing and the backup ring are housed in the mounting groove provided on an inner peripheral surface of the cylinder housing  101 . 
       FIG. 2  is a longitudinal sectional view showing the annular dust seal (unmounted state) shown in  FIG. 1 . 
     As shown in  FIG. 2 , the annular dust seal  1  is integrally formed of an elastic material into a circular annular shape. As a material forming the annular dust seal  1 , a synthetic resin material such as various rubbers, urethane, or PTFE is preferable as an elastic material capable of sealing a gap with an outer peripheral surface  102   a  of the reciprocating shaft  102 . 
     The annular dust seal  1  is provided with a metal ring  2  on the outer peripheral side. The metal ring  2  includes a circular annular plate portion  2   a  and a circular tubular portion  2   b  formed by bending an outer peripheral part of the circular annular plate portion  2   a.  The metal ring  2  is attached to the annular dust seal  1  in such a manner that the circular tubular portion  2   b  is arranged along the outer peripheral surface of the annular dust seal  1  and the circular annular plate portion  2   a  is buried in the annular dust seal  1 . 
     The annular dust seal  1  is disposed in an annular groove  103  formed in the housing  101  as shown in  FIG. 1 . The annular groove  103  is located near the opening portion  101   a  of the housing  101 , surrounds the outer peripheral surface  102   a  of the reciprocating shaft  102 , and is formed coaxially with the reciprocating shaft  102 . 
     As shown in  FIGS. 1 and 2 , the annular dust seal  1  includes a circular annular oil lip  3 , which contacts with the outer peripheral surface of the reciprocating shaft  102 , on the hydraulic side (inner side). In addition, the annular dust seal  1  includes a circular annular dust lip  4 , which contacts with the outer peripheral surface of the reciprocating shaft  102 , on the atmosphere side. 
     The annular dust seal  1  brings a surface of the oil lip  3  into pressure-contact with the outer peripheral surface  102   a  of the reciprocating shaft  102  with an elastic force of the elastic material. Further, the annular dust seal  1  brings a surface of the dust lip  4  into pressure-contact with the outer peripheral surface  102   a  of the reciprocating shaft  102  with the elastic force of the elastic material. When the oil lip  3  and the dust lip  4  are brought into pressure-contact with the outer peripheral surface  102   a  of the reciprocating shaft  102 , the inside of the housing  101  is sealed. 
       FIG. 3  is an enlarged longitudinal sectional view showing a main portion of the annular dust seal shown in  FIG. 1 . 
     The surface of the dust lip  4  is formed in a torus shape, and has a circular arc shape in longitudinal section as shown in  FIG. 3 . In the longitudinal section of the dust lip  4 , an average radius of curvature (≈(R 1 +R 2 )/2) of a surface  4   b  having a convex curvature on the hydraulic side from a top portion  4   c  of the dust lip  4  becomes larger than an average radius of curvature (=R 2 ) of a surface  4   a  having a convex curvature on the atmosphere side from the top portion  4   c  of the dust lip  4 . 
     In the longitudinal section of the dust lip  4 , the average radius of curvature (≈(R 1 +R 2 )/2) of the surface  4   b  having the convex curvature on the hydraulic side from the top portion  4   c  of the dust lip  4  is preferably 1.5 to 4 times the average radius of curvature (R 2 ) of the surface  4   a  having the convex curvature on the atmosphere side from the top portion  4   c  of the dust lip  4 . 
     In the longitudinal section of the dust lip  4 , the average radius of curvature (≈(R 1 +R 2 )/2) of the surface  4   b  having the convex curvature on the hydraulic side from the top portion  4   c  of the dust lip  4  is more preferably 2 to 3 times the average radius of curvature (R 2 ) of the surface  4   a  having the convex curvature on the atmosphere side from the top portion  4   c  of the dust lip  4 . 
     As in the embodiment, in general materials, temperature conditions, and types of dust when used for the rod seal in the hydraulic cylinder or suspension of the construction machinery and the shock absorber of the automobile, the radius of curvature R 1  on the hydraulic side is preferably about 0.4 mm to 0.5 mm, and the radius of curvature R 2  on the atmosphere side is preferably about 0.15 mm to 0.2 mm. However, optimum values of these specific numerical values vary depending on the materials forming the annular dust seal  1 , the temperature conditions, the types of dust, and the like. 
       FIG. 4  is a graph showing a contact pressure of the annular dust seal shown in  FIG. 1  with respect to the reciprocating shaft. 
     In  FIG. 4 , a region where the contact pressure is positive is a region where the dust lip  4  is crushed due to elastic deformation and contacts with the outer peripheral surface  102   a  of the reciprocating shaft  102 . The atmosphere side of the contact region is a right end of a horizontal axis, and a left side of the horizontal axis indicates a distance to the hydraulic side. 
     In a conventional product in  FIG. 4 , a position having a maximum contact pressure is the top portion of the dust lip. In the annular dust seal  1  of the present embodiment, a position of the top portion  4   c  is the same as that of the conventional product, but the contact pressure may not be maximum at the top portion  4   c  due to the difference in the radius of curvature of the surface of the dust lip  4 . 
     As shown in  FIG. 4 , the contact pressure of the dust lip  4  with respect to the outer peripheral surface  102   a  of the reciprocating shaft  102  has a lower peak value than that of the above-described conventional product, and a length in the axial direction of the portion having the peak value is longer on the hydraulic side. A required surface pressure width w 1  in which the contact pressure exceeds a required surface pressure p is wider than that of the conventional product. This is because the radius of curvature R 1  on the hydraulic side is increased. The conventional product and the annular dust seal  1  of the present embodiment shown in  FIG. 4  have the same material, overall shape, temperature conditions, and the like. 
     Since the contact pressure of the dust lip  4  with respect to the outer peripheral surface  102   a  of the reciprocating shaft  102  is reduced due to a large radius of curvature R 1  on the hydraulic side, local wear, settling (deformation) and stick slip (squealing, vibration) are prevented, and scraping leakage of a liquid (oil) is prevented. Further, a liquid film (for example, an oil film) adhering to the outer peripheral surface  102   a  of the reciprocating shaft  102  has an appropriate thickness. Since the contact pressure of the dust lip  4  is sufficiently applied to the outer peripheral surface  102   a  of the reciprocating shaft  102  due to a small radius of curvature R 2  on the atmosphere side, an excellent dust seal function is realized. 
     In other words, the annular dust seal  1  has an excellent dust seal function of preventing external foreign substances (such as earth and sand, ore, oil, water, ice, and sap) from entering the housing  101 , and brings hydraulic holding components located closer to the hydraulic side than the annular dust seal  1  and sliding components such as bearings and gears into a good lubricating state. The annular dust seal  1  can maintain the excellent dust seal function for a long period of time, and can contribute to a longer service life of a device. 
     Second Embodiment 
       FIG. 5  is a longitudinal sectional view showing a second embodiment (unmounted state) of the annular dust seal of the present disclosure, and  FIG. 6  is an enlarged longitudinal sectional view of a main portion of the annular dust seal shown in  FIG. 5 . In  FIGS. 5 and 6 , the portions having the same reference numerals as those in  FIGS. 1 to 3  are the portions having the same configuration, the description of such portions will not be presented with reference to the description of the above-described embodiment. 
     As shown in  FIGS. 5 and 6 , in the annular dust seal  1 , it is preferable that an atmosphere-side end surface  1   a  facing the atmosphere side has a tapered shape protruding toward the atmosphere side as the end surface  1   a  is closer to the outer peripheral surface  102   a  of the reciprocating shaft  102  in a mounted state. 
     As described above, since the shape of the atmosphere-side end surface  1   a  has the tapered shape protruding toward the atmosphere side as the end surface  1   a  is closer to the outer peripheral surface  102   a  of the reciprocating shaft  102 , foreign substances adhering to the outer peripheral surface  102   a  can be satisfactorily scraped off with the atmosphere-side end surface  1   a.    
     Further, the atmosphere-side end surface  1   a  of the annular dust seal  1  does not need to be a conical surface (a longitudinal section is a straight line), and may form an angle of 90° or more in the mounted state with respect to a generatrix of the outer peripheral surface  102   a  at least in the vicinity of the outer peripheral surface  102   a  of the reciprocating shaft  102 . 
     Since the atmosphere-side end surface  1   a  forms an angle of 90° or more with respect to the generatrix of the outer peripheral surface  102   a  in the vicinity of the outer peripheral surface  102   a,  the annular dust seal  1  can satisfactorily scrape off the foreign substances adhering to the outer peripheral surface  102   a.  When the atmosphere-side end surface  1   a  forms an angle of less than 90° with respect to the generatrix of the outer peripheral surface  102   a  in the vicinity of the outer peripheral surface  102   a,  the foreign substances adhering to the outer peripheral surface  102   a  may enter the space between the reciprocating shaft  102  and the annular dust seal  1  without being satisfactorily scraped off with a reciprocating motion of the reciprocating shaft  102 . 
     When the annular dust seal  1  is in a state of not being mounted around the reciprocating shaft  102  as shown in  FIG. 5 , the atmosphere-side end surface  1   a  forms an angle of less than 90° with respect to the generatrix of the outer peripheral surface  102   a  of the reciprocating shaft  102  to be mounted, and may have a tapered shape protruding toward the atmosphere side as being away from the outer peripheral surface  102   a.  In other words, when being mounted around the reciprocating shaft  102  as shown in  FIG. 6 , the annular dust seal  1  is displaced by being pressed against the outer peripheral surface  102   a  of the reciprocating shaft  102 , and the atmosphere-side end surface  1   a  forms an angle of 90° or more with respect to the generatrix of the outer peripheral surface  102   a  of the reciprocating shaft  102  and has a tapered shape protruding toward the atmosphere side as the end surface  1   a  is closer to the outer peripheral surface  102   a.  The amount of the annular dust seal  1  to be displaced becomes a tightening margin. 
       FIG. 7  is a graph showing a contact pressure of the annular dust seal shown in  FIG. 5  with respect to the reciprocating shaft. 
     In  FIG. 7 , a region where the contact pressure is positive is a region where the dust lip  4  is crushed due to elastic deformation and contacts with the outer peripheral surface  102   a  of the reciprocating shaft  102 . The atmosphere side of the contact region is a right end of a horizontal axis, and a left side of the horizontal axis indicates a distance to the hydraulic side. 
     In a conventional product in  FIG. 7 , a position having a maximum contact pressure is the top portion of the dust lip. In the annular dust seal  1  of the present embodiment, a position of the top portion  4   c  is the same as that of the conventional product, but the contact pressure may not be maximum at the top portion  4   c  due to the difference in the radius of curvature of the surface of the dust lip  4 . 
     Even in this embodiment, as shown in  FIG. 7 , the contact pressure of the dust lip  4  with respect to the outer peripheral surface  102   a  of the reciprocating shaft  102  has a lower peak value than that of the above-described conventional product, and a length in the axial direction of the portion having the peak value is longer on the hydraulic side. A required surface pressure width w 2  in which the contact pressure exceeds a required surface pressure p is wider than that of the conventional product. This is because the radius of curvature R 1  on the hydraulic side is increased. The conventional product and the annular dust seal  1  of the present embodiment shown in  FIG. 7  have the same material, overall shape, temperature conditions, and the like. 
     Accordingly, the annular dust seal  1  has an excellent dust seal function, can maintain the excellent dust seal function for a long period of time, and can contribute to a longer service life of a device. Further, the annular dust seal  1  of the present embodiment can satisfactorily scrape off foreign substances adhering to the outer peripheral surface  102   a  of the reciprocating shaft  102  with the atmosphere-side end surface  1   a.    
     Specific configuration, shapes, materials, operations, numerical values, etc. in the description of the above-described embodiments are merely examples for describing the present disclosure, and is not intended to restrictively interpret the present disclosure. 
     The annular dust seal described above is used in the rod sealing system of the hydraulic cylinder to be used as an actuator of the construction machinery, the civil engineering machinery, the transport vehicle, or the like. However, the annular dust seal is not limited to the rod sealing system of the hydraulic cylinder, and is applicable to any devices that needs to seal the inside of the housing around the shaft from the atmosphere.