Patent Publication Number: US-11644100-B2

Title: Seal ring

Description:
TECHNICAL FIELD 
     The present invention relates to a seal ring used for sealing a clearance between a rotary shaft and a housing, and specifically relates to a seal ring used in a state in which the seal ring is attached to an annular groove, i.e., a so-called stuffing box. 
     BACKGROUND ART 
     Typically, a seal ring is attached to the outer periphery of a rotary shaft. A sliding surface of the seal ring slides in close contact with a sliding surface formed at the rotary shaft, and accordingly, the seal ring seals a clearance between the rotary shaft and a housing to prevent leakage of sealed fluid (e.g., liquid). 
     For maintaining sealing properties in the seal ring for a long period of time, conflicting conditions of “sealing” and “lubrication” need to be satisfied. Particularly in recent years, while prevention of leakage of the sealed fluid has been made for, e.g., environmental measures, a demand for friction reduction has increased for reducing a mechanical loss. Friction reduction can be accomplished by the technique of generating a dynamic pressure between the sliding surfaces by rotation of the rotary shaft to slide the sliding surfaces with a fluid film of the sealed fluid being interposed. 
     For example, a seal ring as described in Patent Citation 1 has been known as the seal ring configured to generate the dynamic pressure between the sliding surfaces by rotation of the rotary shaft. The seal ring of Patent Citation 1 is attached to an annular groove provided at the outer periphery of a rotary shaft. The seal ring is pressed to a housing side and one side wall surface side of the annular groove by the pressure of high-pressure sealed fluid, and a sliding surface at one side surface of the seal ring slides in close contact with a sliding surface at one side wall surface of the annular groove. Moreover, at the sliding surface at one side surface of the seal ring, multiple dynamic pressure grooves opening on an inner diameter side are provided in a circumferential direction. The dynamic pressure groove includes a deep groove at the center in the circumferential direction and shallow grooves formed continuously to both sides of the deep groove in the circumferential direction, extending in the circumferential direction, and having bottom surfaces inclined such that the shallow grooves gradually become shallower toward terminal ends. When the rotary shaft and the seal ring rotate relative to each other, the sealed fluid is introduced from the inner diameter side of the sliding surface into the deep grooves. Moreover, a negative pressure is generated in each shallow groove of the seal ring on a side opposite to a rotation direction of the rotary shaft. Meanwhile, the sealed fluid introduced into the deep grooves is supplied to each shallow groove on the same side as the rotation direction, and therefore, a positive pressure is generated in such a shallow groove. Then, the positive pressure increases due to wedge action caused by the inclined bottom surface of the rotation-direction-side shallow groove, and is generated across the entirety of the dynamic pressure groove. Accordingly, the force of slightly separating the sliding surfaces from each other, i.e., so-called buoyancy, is obtained. The sliding surfaces are slightly separated from each other, and therefore, the high-pressure sealed fluid flows into a portion between the sliding surfaces from the inner diameter side of the sliding surface and the sealed fluid flows out of the rotation-direction-side shallow grooves generating the positive pressure to the portion between the sliding surfaces. Thus, a fluid film is formed between the sliding surfaces, and lubricity between the sliding surfaces is maintained. 
     CITATION LIST 
     Patent Literature 
     Patent Citation 1: JP 9-210211 A (third page, FIG. 3) 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the seal ring of Patent Citation 1, the sliding surface of the rotary shaft moves relative to the dynamic pressure grooves in the circumferential direction. The positive pressure increases as the number of rotations of the rotary shaft increases, and the fluid film is formed between the sliding surfaces to enhance the lubricity of the sliding surface. However, the dynamic pressure groove is configured such that both shallow grooves are positioned on the same circumference with respect to the deep groove. Thus, particularly upon high-speed rotation, cavitation is caused in a region where a great positive pressure and a great negative pressure are generated in the circumferential direction. Due to greater variation in the buoyancy generated across the circumferential direction of the sliding surface, there is a probability that an adverse effect on the fluid film, such as a non-uniform fluid film, is caused and the lubricity becomes unstable. 
     The present invention has been made in view of such a problem, and an object of the present invention is to provide a seal ring configured so that stable lubrication performance can be provided across a wide range of rotation speed. 
     Solution to Problem 
     For solving the above-described problem, a seal ring according to the present invention is seal ring for sealing a clearance between a rotary shaft and a housing, including: inclined grooves formed at a sliding surface so as to be arranged in a circumferential direction, the inclined grooves being open on an outer diameter side of the seal ring to generate a drawing pressure; and supply grooves being open on a sealed fluid side of the seal ring and extending in a radially outward direction toward inner diameter sides of the inclined grooves. According to the aforesaid feature, high-pressure sealed fluid introduced through inner-diameter-side openings of the supply grooves is, on the outer diameter side, drawn by the drawing pressure due to a flow in the outer diameter direction in each inclined groove upon rotation of the rotary shaft, and the flow of sealed fluid in the radially outward direction is formed among the supply grooves and the inclined grooves. Thus, a fluid film can be formed with favorable balance in the circumferential direction among the supply grooves and the inclined grooves, and therefore, stable lubrication performance can be provided across a wide range of rotation speed. 
     It may be preferable that a seal portion is formed continuously in the circumferential direction and positioned between the supply grooves and the inclined grooves. According to this preferable configuration, the supply grooves and the inclined grooves between which the flow of sealed fluid in a radial direction is formed are separated from each other in the radial direction by the seal portion, and therefore, the fluid film is formed with favorable balance in the circumferential direction on the seal portion. 
     It may be preferable that the supply grooves are equally arranged in the circumferential direction. According to this preferable configuration, the flow of sealed fluid in the radial direction is formed with favorable balance in the circumferential direction on the seal portion. 
     It may be preferable that the supply grooves are communicated with each other through a communication groove which is positioned on the inner diameter side of the seal portion and extends in the circumferential direction. According to this preferable configuration, the high-pressure sealed fluid introduced through the inner-diameter-side openings of the supply grooves is supplied in the circumferential direction by the communication groove, and therefore, the flow of sealed fluid in the radial direction is reliably formed with favorable balance in the circumferential direction on the seal portion. 
     It may be preferable that the seal ring further comprise dynamic pressure grooves each formed at the sliding surface between adjacent two of the supply grooves in the circumferential direction and being open on the sealed fluid side of the seal ring. According to this preferable configuration, a negative pressure generated by the inclined grooves can be partially cancelled by a positive pressure generated in the dynamic pressure grooves, and therefore, the flow of sealed fluid in the radial direction is easily formed on the seal portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a seal ring according to a first embodiment of the present invention by partially-simplified illustration. 
         FIG.  2    is a sectional view illustrating a sealing structure for a clearance between a rotary shaft and a housing by the seal ring according to the first embodiment. 
         FIG.  3    is a partial side view of the seal ring according to the first embodiment. 
         FIGS.  4 A and  4 B  are partial side views and A-A sectional views of the seal ring according to the first embodiment for schematically illustrating a fluid film formation process in accordance with stages. 
         FIG.  5    is a partial side view and an A-A sectional view of the seal ring according to the first embodiment for schematically illustrating, following  FIGS.  4 A and  4 B , the fluid film formation process in accordance with stages. 
         FIG.  6    is a partial side view of a seal ring according to a second embodiment of the present invention. 
         FIG.  7    is a B-B sectional view of the seal ring of  FIG.  6   . 
         FIG.  8    is a partial side view of a seal ring according to a third embodiment of the present invention. 
         FIG.  9    is a partial side view of a seal ring according to a fourth embodiment of the present invention. 
         FIG.  10    is a partial side view of a seal ring according to a fifth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, modes for carrying out a seal ring according to the present invention will be described based on embodiments. 
     First Embodiment 
     A seal ring according to a first embodiment will be described with reference to  FIGS.  1  to  5   . Hereinafter, the right side in the plane of paper of  FIG.  2    will be described as a sealed fluid side L, and the left side in the plane of paper will be described as an atmosphere side A. Note that the fluid pressure of sealed fluid on the sealed fluid side L will be described as a higher pressure than an atmospheric pressure. Moreover, a sliding surface includes a flat surface and a groove recessed as compared to the flat surface. For the sake of convenience in description, the flat surface forming the sliding surface is, in the side views, indicated by the color of white, and the groove forming the sliding surface is indicated by dots. 
     The seal ring  1  according to the present embodiment seals a portion between a rotary shaft  2  and a housing  3  of a rotary machine, the rotary shaft  2  and the housing  3  rotating relative to each other. In this manner, the seal ring  1  partitions the inside of the housing  3  into the sealed fluid side L and the atmosphere side A (see  FIG.  2   ), and prevents leakage of the sealed fluid from the sealed fluid side L to the atmosphere side A. Note that the rotary shaft  2  and the housing  3  are made of a metal material such as stainless steel. Moreover, the sealed fluid is one used for the purpose of cooling and lubricating, e.g., a not-shown gear and a not-shown bearing provided in a machine chamber of the rotary machine, such as oil. 
     As illustrated in  FIGS.  1  to  3   , the seal ring  1  is a component molded with resin such as PTFE, and is provided with a joint portion  1   a  at one spot in a circumferential direction to form a C-shape. The seal ring  1  is used with the seal ring  1  being attached to an annular groove  20 , the annular groove  20  being provided along the outer periphery of the rotary shaft  2  and having a rectangular sectional shape. The rotary shaft  2  rotates clockwise as indicated by a white arrow in  FIG.  3   , and the seal ring  1  rotates counterclockwise relative to the annular groove  20  of the rotary shaft  2 . Note that in  FIG.  2   , the section of the seal ring  1  along a radial direction is schematically illustrated. 
     Moreover, the seal ring  1  has a rectangular sectional shape. The seal ring  1  is pressed to the atmosphere side A by the fluid pressure of the sealed fluid acting on a side surface on the sealed fluid side L, and accordingly, a sliding surface S 1  formed on a side surface  10  (hereinafter sometimes merely referred to as a “side surface  10 ”) side on the atmosphere side A slidably closely contacts a sliding surface S 2  on a side wall surface  21  (hereinafter sometimes merely referred to as a “side wall surface  21 ”) side of the annular groove  20  on the atmosphere side A. Further, in response to stress in an expansion direction due to the fluid pressure of the sealed fluid acting on an inner circumferential surface, the seal ring  1  is pressed in a radially outward direction, and accordingly, an outer circumferential surface  11  closely contacts an inner circumferential surface  31  of a shaft hole  30  of the housing  3 . 
     Note that the sliding surfaces S 1 , S 2  form a substantial sliding region between the side surface  10  of the seal ring  1  and the side wall surface  21  of the annular groove  20  of the rotary shaft  2 . Moreover, a non-sliding surface S 1 ′ is formed continuously to an outer diameter side of the sliding surface S 1  on the side surface  10  side, and a non-sliding surface S 2 ′ is formed continuously to an inner diameter side of the sliding surface S 2  on the side wall surface  21  side (see  FIG.  2   ). 
     As illustrated in  FIGS.  1  to  4   , the sliding surface S 1  formed on the side surface  10  side of the seal ring  1  includes a flat surface  16 , multiple supply grooves  13  extending in the radial direction from an inner-diameter-side end portion of the side surface  10 , a communication groove  14  communicated with outer-diameter-side end portions of the supply grooves  13  and formed continuously in a substantially annular shape across the joint portion  1   a , and multiple inclined grooves  15  formed inclined to the direction of rotation of the rotary shaft  2  from the vicinity of an outer-diameter-side end portion of the communication groove  14  (i.e., an outer-diameter-side end portion of a later-described seal portion  16   a ) and communicated with an outer-diameter-side end portion of the side surface  10  (on the atmosphere side A). Note that the supply grooves  13  are arranged at equal intervals in the circumferential direction of the sliding surface S 1 , except for the vicinity of the joint portion  1   a . Moreover, the inclined grooves  15  extend from the sliding surface S 1  to the non-sliding surface S 1 ′, and are arranged at equal intervals in the circumferential direction, except for the vicinity of the joint portion  1   a.    
     The flat surface  16  includes the seal portion  16   a  positioned between the outer-diameter-side end portion of the communication groove  14  and an inner-diameter-side end portion of each of the multiple inclined grooves  15  and formed continuously in a substantially annular shape across the joint portion  1   a , an inner-diameter-side lubrication portion  16   b  sandwiched by adjacent ones of the supply grooves  13  in the circumferential direction, and an outer-diameter-side lubrication portion  16   c  sandwiched by adjacent ones of the inclined grooves  15  in the circumferential direction (see  FIG.  3   ). The dimension of the seal portion  16   a  in the radial direction is 1/20 (preferably ⅕ to 1/50) of the dimension of the sliding surface S 1  in the radial direction, and is the substantially same dimension as the dimension of the outer-diameter-side lubrication portion  16   c  in the circumferential direction. Note that the dimension of the seal portion  16   a  in the radial direction is preferably short, considering that the sealed fluid easily moves over the seal portion  16   a.    
     As illustrated in  FIGS.  2  to  5   , the supply groove  13  supplies, regardless of rotation/stop of the rotary shaft  2 , the sealed fluid to a portion between the sliding surfaces S 1 , S 2  when the sealed fluid has a higher pressure than that of atmospheric air. The supply groove  13  has a rectangular shape as viewed from the side. The supply groove  13  opens on the inner diameter side (i.e., the sealed fluid side) of the sliding surface S 1 , and is communicated with the communication groove  14  on the outer diameter side. Moreover, a bottom surface  13   d  (see  FIG.  4 A ) of the supply groove  13  is formed flat, and is parallel with the flat surface  16 . The depth of the supply groove  13  is several tens to several hundreds of μm and preferably 100 to 200 μm. Note that the depth of the supply groove  13  may be much deeper (e.g., up to about a depth of 1 mm). 
     The communication groove  14  is formed to extend in the circumferential direction at a position on the outer diameter side with respect to the center of the sliding surface S 1  in the radial direction, has an arc shape as viewed from the side, and has a shorter dimension in the radial direction than the dimension of the supply groove  13  in the circumferential direction. Moreover, a bottom surface  14   d  of the communication groove  14  is formed flat, is parallel with the flat surface  16 , and is formed continuously to the bottom surface  13   d  of the supply groove  13 . The depth of the communication groove  14  is substantially the same as that of the supply groove  13  (see  FIG.  4 A ). 
     As illustrated in  FIGS.  2  to  5   , the inclined groove  15  extends to the outer diameter side in the rotation direction of the rotary shaft  2  from the seal portion  16   a , i.e., extends inclined with respect to the radial direction, and has the function of generating a drawing pressure in the inclined grooves  15  due to a flow in the radially outward direction upon rotation of the rotary shaft  2 . The inclined groove  15  is configured such that a closed portion  15   d  extending along the outer-diameter-side end portion of the seal portion  16   a , a planar outer inclined wall portion  15   b  positioned on an opposite rotation side of the rotary shaft  2  and formed perpendicularly to a bottom surface  15   e , a planar inner inclined wall portion  15   c  positioned on a rotation side of the rotary shaft  2  and formed perpendicularly to the bottom surface  15   e , and an opening  15   a  crossing the outer inclined wall portion  15   b  and the inner inclined wall portion  15   c  and communicated with a non-sliding surface S 1 ′ side (i.e., the atmosphere side A) form a parallelogram shape as viewed from the side. The inclined groove  15  has the substantially same dimension in the circumferential direction as the dimension of the communication groove  14  in the radial direction, and has a longer dimension in an extension direction than the dimension in the circumferential direction. Moreover, the bottom surface  15   e  of the inclined groove  15  is formed flat, and is parallel with the flat surface  16 . The depth of the inclined groove  15  is shallower than those of the supply groove  13  and the communication groove  14 . 
     Further, the outer-diameter-side lubrication portion  16   c  having a shorter dimension in the circumferential direction than the dimension of the inclined groove  15  in the circumferential direction is interposed between adjacent ones of the inclined grooves  15  in the circumferential direction. Note that the dimensions of these portions may be the same as each other, or the outer-diameter-side lubrication portion  16   c  may have a longer dimension. Moreover, the multiple inclined grooves  15  may be formed with a curvature such that the outer-diameter-side lubrication portions  16   c  are formed to the outer diameter side with the substantially equal width. 
     Next, fluid film formation between the sliding surface S 1  of the seal ring  1  and the sliding surface S 2  of the side wall surface  21  of the annular groove  20  (hereinafter sometimes merely referred to as “between the sliding surfaces S 1 , S 2 ”) will be described with reference to  FIGS.  4 A,  4 B, and  5   . Note that a case where the rotary shaft  2  rotates clockwise as indicated by the white arrow in  FIG.  3   , i.e., a case where the seal ring  1  rotates counterclockwise relative to the annular groove  20  of the rotary shaft  2  in  FIG.  3   , will be described herein by way of example. Further, note that each of  FIGS.  4 A,  4 B, and  5    schematically illustrates an association between an enlarged partial side view of the seal ring  1  as viewed from the side and an A-A sectional view cut along the supply groove  13 , the communication groove  14 , and the inclined groove  15  of the enlarged partial side view. 
     First, as illustrated in  FIG.  4 A , when the rotary shaft  2  stands still, the supply grooves  13  and the communication groove  14  are filled with the sealed fluid due to the fluid pressure. Moreover, the high-pressure sealed fluid is supplied to the supply grooves  13  and the communication groove  14 , and due to a resting pressure, the force of separating the sliding surfaces S 1 , S 2  acts on the supply grooves  13  and the communication groove  14 . 
     Next, as illustrated in  FIG.  4 B , upon rotation of the rotary shaft  2 , the sliding surface S 1  on the side surface  10  side slides on the sliding surface S 2  on the side wall surface  21  (see  FIG.  2   ) side. Accordingly, the sealed fluid in the communication groove  14  generates a clockwise flow along the communication groove  14 . Moreover, although not shown in the figure, the sliding surface S 2  passes over the supply grooves  13 , and therefore, the sealed fluid flows out of the supply grooves  13  to follow the rotation direction of the rotary shaft  2 . 
     Meanwhile, on the outer diameter side with respect to the seal portion  16   a , the sealed fluid and air in the inclined grooves  15  move from a closed portion  15   d  side to an opening  15   a  side of the inclined groove  15 , and accordingly, the drawing pressure is generated from the closed portion  15   d  side to the opening  15   a  side of the inclined groove  15 . Thus, a negative pressure is generated on the closed portion  15   d  side. 
     The sealed fluid forming a fluid film on the seal portion  16   a  is drawn into the inclined grooves  15  by such a negative pressure. Accordingly, the sealed fluid in the communication groove  14  leaks out to a seal portion  16   a  side, and the flow F of moving the sealed fluid over the seal portion  16   a  from the communication groove  14  and drawing the sealed fluid into the inclined grooves  15  is formed (see  FIG.  5   ). The fluid film is reliably formed on the seal portion  16   a , and lubricity is enhanced. The fluid film of the sealed fluid is formed between the sliding surfaces S 1 , S 2  due to, e.g., the flow F and the resting pressure, and the lubricity is enhanced. 
     Moreover, the multiple inclined grooves  15  are formed at equal intervals across the circumferential direction, and therefore, a dynamic pressure is substantially uniformly generated across the outer diameter side of the sliding surface S 1  (i.e., the seal portion  16   a ). Thus, stable buoyancy can be obtained across the circumferential direction. 
     Further, as described above, not only the sealed fluid is mainly supplied from the communication groove  14  to a portion between the sliding surface S 2  and the seal portion  16   a , but also the high-pressure sealed fluid is supplied from the inclined grooves  15  and the communication groove  14  to the outer-diameter-side lubrication portion  16   c  interposed between adjacent ones of the inclined grooves  15  in the circumferential direction and is supplied from the inner diameter side of the sliding surface S 1  and the supply grooves  13  to the inner-diameter-side lubrication portion  16   b  defined by adjacent ones of the supply grooves  13  and the communication groove  14 . Thus, the fluid film of the sealed fluid having a substantially equal thickness is formed between the sliding surfaces S 1 , S 2 . 
     As described above, the high-pressure sealed fluid introduced through inner-diameter-side openings of the supply grooves  13  moves over the seal portion  16   a , and on the outer diameter side, is drawn by the drawing pressure due to the flow in the radially outward direction in the inclined grooves  15  upon rotation of the rotary shaft  2 . Accordingly, the flow F of sealed fluid in the radially outward direction is formed among the supply grooves  13 , the communication groove  14 , and the inclined grooves  15 . Thus, the fluid film can be formed with favorable balance in the circumferential direction among the supply grooves  13 , the communication groove  14 , and the inclined grooves  15 , and therefore, stable lubrication performance can be provided across a wide range of rotation speed. 
     Moreover, the sealed fluid is sufficiently supplied as described above, and therefore, the fluid film can be reliably formed between the sliding surfaces S 1 , S 2  across a wide range of rotation speed. Thus, the lubricity of the seal ring  1  can be enhanced. 
     Further, the supply grooves  13 , the communication groove  14 , and the inclined grooves  15  among which the flow of sealed fluid in the radial direction is formed are separated in the radial direction by the seal portion  16   a , and therefore, the fluid film is formed with favorable balance in the circumferential direction on the seal portion  16   a . With this configuration, the lubricity of the seal portion  16   a  can be enhanced. 
     In addition, the multiple supply grooves  13  are equally arranged in the circumferential direction, and therefore, the flow of sealed fluid in the radial direction is formed with favorable balance in the circumferential direction on the seal portion  16   a.    
     Moreover, the multiple supply grooves  13  are, on the inner diameter side of the seal portion  16   a , communicated with each other through the communication groove  14  extending in the circumferential direction, and therefore, the high-pressure sealed fluid introduced through the inner-diameter-side openings of the supply grooves  13  is supplied in the circumferential direction by the communication groove  14 . Thus, the flow of sealed fluid in the radial direction is reliably formed with favorable balance in the circumferential direction on the seal portion  16   a.    
     Further, the seal ring  1  is in the C-shape, and therefore, seal performance can be stably maintained even when the circumferential length of the seal ring  1  changes due to thermal expansion/contraction. 
     Second Embodiment 
     Next, a seal ring according to a second embodiment will be described with reference to  FIGS.  6  and  7   . Note that the same reference numerals are used to represent the same components as those described in the above-described embodiment, and overlapping description thereof will be omitted. 
     The seal ring  101  in the second embodiment will be described. As illustrated in  FIG.  6   , in the present embodiment, a sliding surface S 1  (see  FIG.  2   ) formed at a side surface  110  of the seal ring  101  includes a flat surface  16 , multiple supply grooves  13 , a communication groove  14 , multiple inclined grooves  15 , and a dynamic pressure groove  12  provided between adjacent ones of the supply grooves  13  in a circumferential direction. 
     The dynamic pressure groove  12  has the function of generating a dynamic pressure according to rotation of a rotary shaft  2 . The dynamic pressure groove  12  includes a deep groove  120  opening on an inner diameter side (i.e., the sealed fluid side) of the seal ring  101  and provided at the center in the circumferential direction and a pair of shallow grooves  121 ,  122  (i.e., positive pressure generators and negative pressure generators) formed continuously from both sides of the deep groove  120  in the circumferential direction and extending in the circumferential direction. An inner-diameter-side lubrication portion  16   b  in an inverted U-shape as viewed from the side is arranged between the dynamic pressure groove  12  and each of the supply grooves  13  adjacent to such a dynamic pressure groove  12  in the circumferential direction and the communication groove  14 . Note that in  FIGS.  6  and  7   , the right side with respect to the deep groove  120  in the plane of paper is the shallow groove  121  (i.e., the positive pressure generator), and the left side in the plane of paper is the shallow groove  122  (i.e., the negative pressure generator). 
     Specifically, as illustrated in  FIG.  7   , the deep groove  120  has a bottom surface formed flat, and the shallow grooves  121 ,  122  have bottom surfaces as inclined surfaces formed such that the shallow grooves  121 ,  122  gradually become shallower from a deep groove  120  side to terminal ends in the circumferential direction. Moreover, the bottom surface of the deep groove  120  is formed much deeper than deepest portions of the shallow grooves  121 ,  122 , and the depth of the deep groove  120  is several tens to several hundreds of μm and preferably 100 to 200 μm. 
     According to such a configuration, in fluid film formation between the sliding surfaces S 1 , S 2 , a negative pressure is generated in each shallow groove  122  (hereinafter merely referred to as a “shallow groove  122 ”) of the seal ring  101  on a side (i.e., the left side in the plane of paper of  FIG.  6   ) opposite to a rotation direction of the rotary shaft  2 . Meanwhile, sealed fluid introduced into the deep grooves  120  is supplied to each shallow groove  121  (hereinafter merely referred to as a “shallow groove  121 ”) of the seal ring  101  on the same side (i.e., the right side in the plane of paper of  FIG.  6   ) as the rotation direction, and a positive pressure is generated in such a shallow groove  121  due to wedge action caused by the inclined surface. Then, the positive pressure is generated across the entirety of the dynamic pressure grooves  12 , and accordingly, the force of slightly separating the sliding surfaces S 1 , S 2  from each other, i.e., so-called buoyancy, is obtained. That is, the positive pressure (i.e., the buoyancy) can be generated not only on an outer diameter side of the sliding surfaces S 1 , S 2  but also on an inner diameter side by the dynamic pressure grooves  12 . Thus, responsiveness of fluid film formation to rotation of the rotary shaft  2  can be enhanced. 
     Moreover, the force of sucking the sealed fluid present between the sliding surfaces S 1 , S 2  around the shallow groove  122  generating the negative pressure acts on such a shallow groove  122 . Thus, the sealed fluid is supplied to the shallow groove  122  and a surrounding inner-diameter-side lubrication portion  16   b  thereof from the supply groove  13  adjacent to such a shallow groove  122  in the circumferential direction. Further, the shallow groove  122  as the negative pressure generator in the dynamic pressure groove  12  opens on the inner diameter side (i.e., the sealed fluid side), and the sealed fluid is also introduced from the inner diameter side of the sliding surface S 1 . Thus, the sealed fluid is easily held on the shallow groove  122 . 
     Further, the negative pressure generated by the inclined grooves  15  can be partially cancelled by the positive pressure generated on the outer diameter side of the sliding surface S 1 , and the sliding surfaces S 1 , S 2  can be easily separated from each other by the dynamic pressure generated across the entirety of the dynamic pressure grooves  12 . Thus, the flow of sealed fluid in a radial direction is easily formed on a seal portion  16   a.    
     In addition, the dynamic pressure groove  12  arranged on the inner diameter side of the sliding surface S 1  may be freely formed, and may be formed as, e.g., a T-shaped groove, a Rayleigh step, or a spiral groove. 
     Third Embodiment 
     Next, a seal ring according to a third embodiment will be described with reference to  FIG.  8   . Note that the same reference numerals are used to represent the same components as those described in the above-described embodiments, and overlapping description thereof will be omitted. 
     The seal ring  201  in the third embodiment will be described. As illustrated in  FIG.  8   , in the present embodiment, a sliding surface S 1  (see  FIG.  2   ) formed at a side surface  210  of the seal ring  201  includes a flat surface  16 , multiple supply grooves  13 , a communication groove  14 , multiple inclined grooves  15 , and a dynamic pressure groove  112  provided between adjacent ones of the supply grooves  13  in a circumferential direction. 
     The dynamic pressure groove  112  includes a deep groove  220  opening on an inner diameter side (i.e., the sealed fluid side) of the seal ring  201 , provided at the center in the circumferential direction, and communicated with the communication groove at an outer-diameter-side end portion and a pair of shallow grooves  121 ,  122  formed continuously from both sides of the deep groove  220  in the circumferential direction and extending in the circumferential direction. An inner-diameter-side lubrication portion  16   b  in an L-shape as viewed from the side is arranged between the dynamic pressure groove  112  and each of the supply grooves  13  adjacent to such a dynamic pressure groove  112  and the communication groove  14 . 
     According to such a configuration, in fluid film formation between the sliding surfaces S 1 , S 2 , sealed fluid can be supplied to the communication groove  14  not only from the supply grooves  13  but also from the deep grooves  220  of the dynamic pressure grooves  112 . Thus, a fluid film can be more reliably formed between the sliding surfaces S 1 , S 2  across a wide range of rotation speed, and lubricity of the seal ring  201  can be enhanced. 
     Fourth Embodiment 
     Next, a seal ring according to a fourth embodiment will be described with reference to  FIG.  9   . Note that the same reference numerals are used to represent the same components as those described in the above-described embodiments, and overlapping description thereof will be omitted. 
     The seal ring  301  in the fourth embodiment will be described. As illustrated in  FIG.  9   , in the present embodiment, a sliding surface S 1  (see  FIG.  2   ) formed at a side surface  310  of the seal ring  301  includes a flat surface  16 , multiple supply grooves  113 , and a single inclined groove  115  inclined to a rotation direction of a rotary shaft  2  from the vicinity of an outer-diameter-side end portion of each supply groove  113  (e.g., an outer-diameter-side end portion of a seal portion  16   a ) to an outer-diameter-side end portion of the side surface  310 . According to such a configuration, a flow F (see  FIG.  5   ) moving over the seal portion  16   a  at outermost diameter portions of the sliding surfaces S 1 , S 2  can be formed with a simple configuration. 
     Fifth Embodiment 
     Next, a seal ring according to a fifth embodiment will be described with reference to  FIG.  10   . Note that the same reference numerals are used to represent the same components as those described in the above-described embodiments, and overlapping description thereof will be omitted. 
     The seal ring  401  in the fifth embodiment will be described. As illustrated in  FIG.  10   , in the present embodiment, a sliding surface S 1  (see  FIG.  2   ) formed at a side surface  410  of the seal ring  401  includes a flat surface  16 , multiple supply grooves  213 , multiple communication paths  214  each communicated with adjacent two of the supply grooves  213 , and multiple inclined grooves  215  inclined to a relative turning direction from the vicinity of an outer-diameter-side end portion of each communication path  214  (e.g., an outer-diameter-side end portion of the seal portion  16   a ) to an outer-diameter-side end portion of the side surface  410 . According to such a configuration, a flow F (see  FIG.  5   ) moving over the seal portion  16   a  at outermost diameter portions of the sliding surfaces S 1 , S 2  can be formed with a simpler configuration than those of the first to third embodiments. 
     The embodiments of the present invention have been described above with reference to the drawings, but specific configurations are not limited to these embodiments. The present invention also includes even changes and additions made without departing from the scope of the present invention. 
     For example, the configuration of the dynamic pressure groove of the second embodiment or the third embodiment may be applied to the fourth and fifth embodiments. 
     Moreover, the form in which the rotary shaft  2  is turned clockwise to generate the dynamic pressure in the inclined grooves  15  has been described. However, the rotary shaft  2  is rotated counterclockwise to move the sealed fluid from the opening  15   a  side to the closed portion  15   d  side of the inclined groove  15 , and therefore, outflow of the sealed fluid can be reduced with favorable responsiveness. 
     Further, the number and shape of dynamic pressure grooves, supply grooves, communication paths, or inclined grooves provided at the sliding surface S 1  or the non-sliding surface S 1 ′ of the seal ring may be changed as necessary such that a desired dynamic pressure effect is obtained. Note that the location and shape of the deep groove of the dynamic pressure groove to which the sealed fluid is introduced, the location and shape of the supply groove to which the sealed fluid is introduced, the location and shape of the communication path to which the sealed fluid is introduced, and the location and shape of the inclined groove to which the sealed fluid is introduced may be changed as necessary according to the assumed degree of abrasion of the sliding surface. 
     In addition, the inclined groove may have a bottom surface as an inclined surface formed such that the inclined groove gradually becomes shallower from the opening side to the closed portion. With such a form, the drawing pressure is more easily generated due to taper action. 
     Moreover, the seal ring may be formed in an annular shape without the joint portion  1   a , and the outer shape thereof is not limited to a circular shape as viewed from the side. The seal ring may be formed in a polygonal shape. 
     Further, the seal ring is not limited to the rectangular sectional shape, and for example, may have a trapezoidal sectional shape or a polygonal sectional shape. The seal ring may be configured such that the side surface forming the sliding surface S 1  is inclined. 
     In addition, the grooves described in the above-described embodiments may be formed at the sliding surface S 2  of the annular groove  20  of the rotary shaft  2 . 
     Moreover, the oil has been described as the example of the sealed fluid, but the sealed fluid may be liquid such as water or coolant or gas such as air or nitrogen. 
     REFERENCE SIGNS LIST 
       1  to  401  Seal ring 
       2  Rotary shaft 
       3  Housing 
       10  Side surface 
       12  Dynamic pressure groove 
       13  Supply groove 
       14  Communication groove 
       15  Inclined groove 
       16  Flat surface 
       16   a  Seal portion 
       16   b  Inner-diameter-side lubrication portion 
       16   c  Outer-diameter-side lubrication portion 
       20  Annular groove 
       21  Side wall surface 
       110  Side surface 
       112  Dynamic pressure groove 
       113  Supply groove 
       214  Communication path 
       115  Inclined groove 
       210  Side surface 
       213  Supply groove 
       215  Inclined groove 
       310  Side surface 
       410  Side surface 
     S 1 , S 2  Sliding surface 
     S 1 ′, S 2 ′ Non-sliding surface