Patent Publication Number: US-2005116426-A1

Title: Seal ring

Description:
TECHNICAL FIELD  
      The present invention relates to a seal ring for sealing an annular clearance between two members which can rotate relative to each other.  
     BACKGROUND ART  
      In the related art, the seal ring of this kind is used in a hydraulic apparatus such as an automatic transmission of an automobile.  
      A seal ring according to the related art will be described with reference to  FIG. 10  to  FIG. 13 .  FIG. 10  is a schematic top plan view of a seal ring according to the related art.  FIG. 11  is a schematic section showing the state, in which the seal ring according to the related art is mounted.  
      On the other hand,  FIG. 12  presents schematic views of the seal ring according to the related art.  
      Moreover:  FIG. 12A  is a schematic, partial top plan view;  FIG. 12B  is a section b-b of  FIG. 12A ; and  FIG. 12C  is a side elevation taken in the direction of c of  FIG. 12A .  FIG. 13  is a perspective view of a cut portion of the seal ring according to the related art. This cut portion is a special step cut.  
      The shown seal ring  100  seals an annular clearance between a housing  200  that has a bore and a shaft  300  inserted in the bore. Moreover, the seal ring  100  is fitted for use in an annular groove  301  formed in the shaft  300 .  
      On the other hand, the seal ring  100  is formed of a resin material. This seal ring  100  is provided with a first seal face  101  for sealing the side wall face of the annular groove  301  formed in the shaft  300 , and a second seal face  102  for sealing the inner circumference of the bore formed in the housing  200 .  
      When a pressure is applied in the direction of arrow P in  FIG. 11 , the seal ring  100  is pushed to an unsealed fluid side A. Here, the arrow P direction is directed from a sealed fluid side O to the unsealed fluid side A.  
      As a result, the first seal face  101  pushes the side wall face of the annular groove  301 . On the other hand, the second seal face  102  pushes the inner circumference of the bore formed in the housing  200 . Thus, the individual seal faces seal at the individual positions.  
      As described above, the seal ring  100  prevents the leakage of the sealed fluid toward the unsealed fluid side A.  
      Here, the sealed fluid is exemplified by lubricating oil. The sealed fluid designates the ATF, especially in case it is utilized in the transmission of the automobile.  
      On the other hand, the ring body of the seal ring  100  is provided at its one circumferential portion with a cut portion S 0 , as shown in  FIG. 10 . One reason for providing the cut portion S 0  is to improve the assembling properties.  
      Various modes have been known for that cut portion S 0 . One mode is exemplified by a special step cut of two-step cuts, as shown in  FIG. 13 . The seal ring having this special step cut can properly respond to the change in the ambient temperature. This is reasoned in the following.  
      According to this special step cut, faces perpendicular to the circumferential direction form a clearance T 0  with respect to the circumferential direction. Moreover, the seal ring having that special step cut is constructed to block the sealed fluid side and the unsealed fluid side while keeping that clearance T 0 . As a result, the seal ring can absorb the change in the sizes by the clearance T 0  while keeping the sealing state, even if its body is expanded by the heat. Therefore, the seal ring having the special step cut can keep the sealing performance even with the change in the ambient temperature.  
      In the seal ring  100  thus far described, the seal ring  100  and the shaft  300  are individually abraded, when they rotate relative to each other, due to the friction to be caused between the first seal face  101  and the side wall face of the annular groove  301 . This phenomenon is serious especially in case the shaft  300  is made of a soft material such as an aluminum alloy.  
      One reason for that phenomenon is that a lubricating film of the lubricating oil is hardly formed between the first seal face  101  and the side wall face of the annular groove  301 . The abrasion is more serious especially in case the foreign substance in the lubricating oil is bitten between those faces or in case the abraded powder accumulates therebetween.  
      In case the seal ring  100  is used under a high pressure and at a high rotation, on the other hand, the first seal face  101  and the side wall face of the annular groove  301  are raised to a high temperature by the frictional heat resulting from the relative rotations of the seal ring  100  and the shaft  300 . This high temperature may melt the seal ring  100 .  
      A technique for reducing such abrasion is disclosed in JP-A-9-96363, for example. This technique provides a groove for feeding the lubricating oil as the sealed fluid to the clearance between the first seal face  101  and the side wall face of the annular groove  301 . This groove can form a lubricating film between those faces. Thus, the abrasion resistance is improved.  
      This technique will be described with reference to  FIG. 12 . As shown in  FIG. 12 , the first seal face  101  is provided with a communication groove  101   a  for establishing the communication between the sealed fluid side O and the unsealed fluid side A. As a result, the lubricating oil on the sealed fluid side O leaks into the communication groove  101   a . When the first seal face  101  comes into sliding contact with the side wall face of the annular groove  301 , the lubricating film is formed between those faces. Thus, the lubricated state of the seal face is improved to improve the abrasion resistance.  
      On the other hand, the aforementioned communication groove  101   a  exhibits not only the function to form the lubricating film but also the following function. Specifically, the communication groove  101   a  exhibits the function to discharge the foreign substance existing in the lubricating oil or the abraded powder to the unsealed fluid side A. As a result, that foreign substance or abraded powder can be prevented from being bitten in the clearance between the first seal face  101  and the side wall face of the annular groove  301 . Moreover, it is effective to cool the seal face that the aforementioned lubricating film is formed. The provision of the communication groove  101   a  thus far described can improve the abrasion resistance.  
      Generally, the communication groove  101   a  has a sectional shape of a square (α=90 degrees). In JP-A-9-96363, however, the α is described to exceed 90 degrees but less than 180 degrees, preferably 120 degrees to 135 degrees, while considering removal of the burr which occurs at the molding time.  
     DISCLOSURE OF THE INVENTION  
      In the seal ring according to the related art thus far described, it is necessary for keeping the sealing performance to suppress the leakage of the lubricating oil from the communication groove  101   a  to some extent. For this suppression, it is necessary to make the width or depth of the groove as small as possible.  
      By forming the communication groove  101   a , therefore, the abrasion resistance can be improved, but the abrasion is not completely prevented. As the abrasion proceeds with the time, therefore, the communication groove  101   a  becomes gradually shallow. As a result, the ability to discharge the foreign substance (or the ability to discharge contaminants) or the ability to form the lubricating film lowers with the time.  
      As the abrasion further proceeds, the passage to the communication groove  101   a  is blocked. Then, the feed of the lubricating oil to the communication groove  101   a  is interrupted. Moreover, this interruption may cause a malfunction that an abnormal abrasion occurs.  
      This point will be described in more detail with reference to  FIG. 14 .  FIG. 14  is a schematic section showing the state, in which an abrasion has progressed due to a long use on the seal ring according to the related art.  
      As shown in  FIG. 14 , the side wall face of the annular groove  301  is abraded only at its portion in sliding contact with the first seal face  101 . Therefore, the seal ring  100  is pushed to the abraded extent toward the inner side than the initial position of the side wall face of the annular groove  301 .  
      When the bottom face of the communication groove  101   a  reaches the unabraded face of the side wall face of the annular groove  301 , therefore, the passage to the communication groove  101   a  is shut off, as indicated by arrow X in  FIG. 14 . Thus, the feed of the lubricating oil stops.  
      In order to solve this problem, the Applicant has proposed the technique which was disclosed in JP-A-2001-165322. In this technique, as shown in  FIG. 15 , a chamfered portion  101   b  is formed in the special step cut portion of the cut portion S 0  thereby to form a leakage passage of the lubricating oil. However, this technique may not discharge the foreign substance effectively. Here,  FIG. 15  schematically presents the position of a cut face A at its upper portion and a section at its lower portion.  
      An object of the invention is to keep the stable seal performance for a long time. Another object of the invention is to improve the ability to discharge contaminants. Still another object of the invention is to improve the qualification.  
      In order to achieve the aforementioned objects, according to the invention, there is provided a seal ring adapted to be so mounted in an annular groove, which is formed in one of two members to be assembled for concentric rotations relative to each other, that it may be brought into sliding contact with the side wall face of the annular groove on an unsealed fluid side and pushed into contact with the other member thereby to seal the annular clearance between those two members, 
          wherein the ring body is cut at one portion in the circumferential direction to form a cut portion, and     wherein the cut portion is provided at its one cut end portion with a projection and at its other cut end portion with a depression to engage with the projection, characterized:     in that a passage having an open end over the whole region in the annular groove depth direction in the sliding contact face against the side wall face of the annular groove and permitting leakage of a sealed fluid from the sealed fluid side to the side wall face of the annular groove on the unsealed fluid side is formed between confronting faces at the time when one cut end portion and the other cut end portion of the cut portion engage; and     in that a groove, which has a sectional shape taken generally perpendicular to an edge direction and having a polygonal shape of four or more angles or a general sector shape, is formed at intersecting angles of two adjoining ones of the outer wall faces of the projection, so that a clearance between the groove and the corresponding angle of the depression may form a portion of the passage.        

      According to the construction of the invention, the passage has the open end over the whole region in the annular groove depth direction. As a result, the film of the sealed fluid is formed over the whole region in the sliding contact face against the side wall face of the annular groove. As a result, the seal ring is excellent in the abrasion resistance. Moreover, the passage is located at a position of no slide so that it does not change with the time. Therefore, it is possible to feed the sealed fluid stably.  
      Moreover, a portion of the passage is formed of the groove having a sectional shape of a polygonal shape of four or more angles or a general sector shape so that the effective sectional area can be enlarged. As a result, it is possible to improve the ability to discharge the foreign substance and the abraded powder in the lubricating oil. Moreover, the sliding face can be effectively cooled by leaking the sealed fluid effectively. These points can improve the abrasion resistance.  
      There is also provided a seal ring adapted to be so mounted in an annular groove, which is formed in one of two members to be assembled for concentric rotations relative to each other, that it may be brought into sliding contact with the side wall face of the annular groove on an unsealed fluid side and pushed into contact with the other member thereby to seal the annular clearance between those two members, 
          wherein the ring body is cut at one portion in the circumferential direction to form a cut portion, and     wherein the cut portion is provided at its one cut end portion with a projection and at its other cut end portion with a depression to engage with the projection, characterized:     in that a passage having an open end over the whole region in the annular groove depth direction in the sliding contact face against the side wall face of the annular groove and permitting leakage of a sealed fluid from the sealed fluid side to the side wall face of the annular groove on the unsealed fluid side is formed between confronting faces at the time when one cut end portion and the other cut end portion of the cut portion engage; and     in that grooves, which have a sectional shape taken generally perpendicular to an edge direction and having a polygonal shape of four or more angles or a general sector shape, are formed individually at intersecting angles of two adjoining ones of the outer wall faces of the projection and at corners confronting the angles in the depression, so that clearances formed by the grooves may form a portion of the passage.        

      According to the construction of the invention, the passage has the open end over the whole region in the annular groove depth direction. As a result, the film of the sealed fluid is formed over the whole region in the sliding contact face against the side wall face of the annular groove. As a result, the seal ring is excellent in the abrasion resistance. Moreover, the passage is located at a position of no slide so that it does not change with the time. Therefore, it is possible to feed the sealed fluid stably.  
      Moreover, a portion of the passage is formed by forming grooves having a polygonal shape of four or more angles or a general sector shape, individually at angles of the projection and at corners of the depression. Therefore, the effective sectional area can be enlarged. As a result, it is possible to improve the ability to discharge the foreign substance and the abraded powder in the lubricating oil. Moreover, the sliding face can be effectively cooled by leaking the sealed fluid effectively. These points can improve the abrasion resistance.  
      It is preferable that the other cut end portion is also provided with a projection having a construction identical to that formed at the one cut end portion whereas the one cut end portion is also provided with a depression having a construction identical to that formed at the other cut end portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic top plan view of a seal ring according to an embodiment of the invention.  
       FIG. 2  is a schematic section showing the state, in which the seal ring according to the embodiment of the invention is mounted.  
       FIG. 3  is a perspective, partially sectional view showing the state, in which the seal ring according to the embodiment of the invention is mounted.  
       FIG. 4  is a schematic perspective view showing a cut portion of the seal ring according to the first embodiment of the invention.  
       FIG. 5  presents schematic perspective views showing the state, in which the cut portions of the seal ring according to the first embodiment of the invention are individually separated.  
       FIG. 6  presents explanatory diagrams showing the sections of individual portions in the cut portions of the seal ring according to the first embodiment of the invention.  
       FIG. 7  is a diagram for comparing a groove having a triangular section and a groove having a square section.  
       FIG. 8  is a schematic section presenting a section in the cut portion of the seal ring according to the first embodiment of the invention.  
       FIG. 9  is a schematic section presenting a section in the cut portion of the seal ring according to a second embodiment of the invention.  
       FIG. 10  is a schematic top plan view of a seal ring according to the related art.  
       FIG. 11  is a schematic section showing the state, in which the seal ring according to the related art is mounted.  
       FIG. 12  presents schematic views of the seal ring according to the related art.  
       FIG. 13  is a perspective view showing a cut portion of the seal ring according to the related art.  
       FIG. 14  is a schematic section showing the state, in which an abrasion has progressed due to a long use on the seal ring according to the related art.  
       FIG. 15  is a section of the cut portion of the seal ring according to the related art. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the invention will be illustratively described in detail with reference to the accompanying drawings. However, the sizes, materials, shapes and relative arrangements of components described in the embodiment will not be intended to limit the scope of the invention thereto so long as they are not especially specified.  
     First Embodiment  
      A seal ring according to a first embodiment of the invention will be described with reference to  FIG. 1  to  FIG. 6 .  
      At first, a whole structure and soon of the seal ring according to the first embodiment of the invention will be described with reference to  FIG. 1  and  FIG. 2 .  
       FIG. 1  is a schematic top plan view of the seal ring according to the first embodiment of the invention.  FIG. 2  is a schematic section showing the state, in which the seal ring according to the first embodiment of the invention is mounted.  
      The seal ring  1  according to this embodiment seals an annular clearance between two members, which are assembled to turn freely and concentrically of each other, as shown in  FIG. 2 . Here, the annular clearance is formed between a housing  90  having a bore and a shaft  80  inserted in the bore. The seal ring  1  is mounted for use in an annular groove  81  formed in the shaft  80 .  
      The seal ring  1  is provided with a first seal face  2  and a second seal face  3 . The first seal face  2  seals the side wall face  81   a  of the annular groove  81  formed in the shaft  80  (or one member). On the other hand, the second seal face  3  seals the inner circumference  90   a  of the bore formed in the housing  90  (or the other member).  
      When a pressure is applied in the direction of arrow P of  FIG. 2 , the seal ring  1  is pushed toward an unsealed fluid side A. Here, the direction of the arrow P is directed from a sealed fluid side O to the unsealed fluid side A. As a result, the first seal face  2  pushes the side wall face  81   a  of the annular groove  81  (of the unsealed fluid side A). On the other hand, the second seal face  3  pushes the inner circumference surface of the bore formed in the housing  90 , i.e., the portion confronting the annular groove  81 . Thus, the individual seal faces seal at their individual positions.  
      As described above, the seal ring  1  prevents leakage of the sealed fluid to the unsealed fluid side A.  
      The sealed fluid in this embodiment means a fluid having lubricating properties. The following description will be made on the case, in which the sealed fluid is lubricating oil.  
      In the ring body of the seal ring  1  according to this embodiment, a cut portion S is formed at one circumferential portion, as shown in  FIG. 1 . One reason for providing that cut portion S is to improve the assembling properties.  
      This cut portion S is a special step cut having two steps. The seal ring having this special step cut can properly respond to the change in the ambient temperature.  
      This cut portion S will be described in detail with reference to  FIG. 3  to  FIG. 6 .  FIG. 3  is a perspective, partially broken section showing the mounting state of the seal ring according to the embodiment of the invention.  FIG. 3  shows the vicinity of the cut portion perspectively.  FIG. 4  is a schematic perspective view showing the cut portion of the seal ring according to this embodiment.  FIG. 5A  is a schematic perspective view showing the state, in which the cut portions are individually separated, and  FIG. 5B  is a schematic perspective view showing a groove to be formed in the cut portion.  FIG. 6A  to  FIG. 6C  are explanatory diagrams showing the sections of the individual portions in the cut portion. As a matter of fact, the individual cut end portions in the cut portion have curvatures, as shown in  FIG. 1 . For conveniences of the description, however, the cut end portions are schematically shown without any curvature in  FIG. 4  to  FIG. 6 .  
      In the cut portion S, the ring body is cut into one cut end portion and the other cut end portion. The one end portion will be called a first cut end portion  4 . The other cut end portion will be called a second cut end portion  5 . These first cut end portion  4  and second cut end portion  5  are constructed to engage with each other.  
      The first cut end portion  4  is provided with a projection  41  and a depression  42  adjacent to each other. On the other hand, the second cut end portion  5  is provided with a depression  51  to engage with the aforementioned projection  41  and a projection  52  to engage with the aforementioned depression  42  at adjacent positions.  
      For conveniences of the description, of the wall faces (or outer wall faces) to form the projection  41 , as shown in  FIG. 5 : the foremost end face will be called a first face  41   a ; the contact face in parallel with and on the inner side of the first seal face  2  will be called a second face  41   b ; and the contact face concentric to and on the inner side of the second seal face  3  will be called a third face  41   c.    
      Of the wall faces to form the depression  42 , on the other hand: the face perpendicular to the circumferential direction will be called a fourth face  42   a ; the contact face in parallel with and on the inner side of the first seal face  2  will be called a fifth face  42   b ; and the contact face concentric to and on the inner side of the second seal face  3  will be called a sixth face  42   c.    
      Here, the second face  41   b  and the fifth face  42   b  are located on the common face but will be described to have different names for conveniences of the description. Moreover, a face for reference of the first cut end portion  4  will be called a reference face  43 .  
      On the side of the second cut end portion  5 , too, of the wall faces (or outer wall faces) to form the projection  52 : the foremost end face will be called an eleventh face  52   a ; the contact face in parallel with and on the inner side of the first seal face  2  will be called a twelfth face  52   b ; and the contact face concentric to and on the inner side of the second seal face  3  will be called a thirteenth face  52   c.    
      Of the wall faces to form the depression  51 , moreover: the face perpendicular to the circumferential direction will be called a fourteenth face  51   a ; the contact face in parallel with and on the inner side of the first seal face  2  will be called a fifteenth face  51   b ; and the contact face concentric to and on the inner side of the second seal face  3  will be called a sixteenth face  51   c.    
      Here, the twelfth face  52   b  and the fifteenth face  51   b  are located on the common face but will be described to have different names for conveniences of the description. Moreover, a face for reference of the second cut end portion  5  will be called a reference face  53 .  
      In the state having the seal ring  1  mounted, moreover, the wall faces in the circumferential direction closely contact with each other. Here, the wall faces in the circumferential direction are: the second face  41   b  and the fifteenth face  51   b ; the fifth face  42   b  and the twelfth face  52   b ; the third face  41   c  and the sixteenth face  51   c ; and the sixth face  42   c  and the thirteenth face  52   c.    
      On the other hand, the wall faces in the direction perpendicular to the circumferential direction, that is, the confronting wall faces are arranged to confront each other individually through clearances T 1 , T 2  and T 3 . Here, the confronting wall faces are: the fourth face  42   a  and the eleventh face  52   a ; the first face  41   a  and the fourteenth face  51   a ; and the reference face  43  and the reference face  53 .  
      Thus, the seal ring  1  having the special step cut can prevent the leakage of the sealed fluid in the mounted state because its wall faces in the circumferential direction closely contact with each other.  
      Moreover, the wall faces in the direction perpendicular to the circumferential direction confront each other to form the clearances. Even if the seal ring  1  expands or contracts relative to the housing  90 , therefore, their changes can be absorbed to extents of the clearances. Here, the expansion or contraction of the seal ring  1  relative to the housing  90  is caused by the difference in a linear expansion coefficient between the materials of those members. From the discussion thus far made, the seal ring  1  can keep the sealing performance properly even against the change in the ambient temperature.  
      Generally, the material for the seal ring  1  is a resin, and the material for the housing  90  is a metal. Due to the difference between their linear expansion coefficients, therefore, the thermal expansion of the seal ring  1  becomes larger as the temperature becomes higher, thereby to reduce the clearances T 1 , T 2  and T 3 .  
      On the other hand, these clearances T 1 , T 2  and T 3  are so set on principle that they may not disappear. The clearances T 1  and T 2  are further set to become smaller than the clearance T 3  (T 1 =T 2 &lt;T 3 ). This setting is made to retain the clearance T 3  without fail even if the clearances T 1  and T 2  disappear.  
      As one feature of the seal ring  1  according to this embodiment, moreover, there is enumerated a construction, in which the leakage of the sealed fluid is not completely prevented at the cut portion S. In this construction, more specifically, when the individual cut end portions are brought into contact with each other, there is formed such a passage between the confronting faces of those cut end portions as allows the leakage of the sealed fluid from the sealed fluid side O to the side wall face  81   a  of the annular groove  81  on the unsealed fluid side A.  
      The construction or the like to form that passage will be described in detail.  
      As shown in  FIG. 5A , rectangular grooves M 1 , M 2  and M 3  are formed individually at the angles, where the first face  41   a  and the first seal face  2 , the first face  41   a  and the third face  41   c , and the second face  41   b  and the third face  41   c  at the projection  41  formed at the first cut end portion  4  intersect. These rectangular grooves are cut out generally in the rectangular shapes at sections generally perpendicular to the edge directions. Here,  FIG. 5B  shows the edge line N or the intersecting angle, at which the first face  41   a  and the first seal face  2  intersect. Here, the aforementioned rectangular groove is located at the intersecting angle of the adjoining faces, that is, either the face confronting the depression  51  engaging the projection  41  and formed in the second cut end portion  5  or the face (i.e., the first seal face  2 ) confronting the side wall face  81   a  of the annular groove  81 .  
      Likewise, rectangular grooves M 4 , M 5  and M 6  are formed at angles, where the eleventh face  52   a  on the projection  52  formed at the second cut end portion  5  and the face confronting the first seal face  2 , the eleventh face  52   a  and the thirteenth face  52   c , and the twelfth face  52   b  and the thirteenth face  52   c  intersect. These rectangular grooves are cut out generally in the rectangular shapes at the sections generally perpendicular to the edge direction. Here, the aforementioned rectangular groove is located at the intersecting angle of the adjoining faces, that is, either the face confronting the depression  42  engaging the projection  52  and formed in the first cut end portion  4  or the face (i.e., the face confronting the first seal face  2 ) confronting the side wall face  81   a  of the annular groove  81 .  
      By thus forming the rectangular grooves, the clearances are formed between the angles of the depressions corresponding to the individual rectangular grooves. These clearances form the passage.  
      This point will be described in more detail with reference to  FIG. 6 .  FIG. 6A  to  FIG. 6C  present sections taken in three directions at the engaging portion between the projection  41  and the depression  51 . The engaging portion between the projection  52  and the depression  42  is similar so that its description is omitted.  
      Here,  FIG. 6A  schematically presents the location of the cut face A at its upper portion and the section at its lower portion.  FIG. 6B  and  FIG. 6C  schematically present perspective views at their individual upper portions and views taken in directions B and C at their individual lower portions.  
      At first,  FIG. 6A  presents a section perpendicular to the circumferential direction in the engaging portion between the projection  41  and the depression  51 .  
      As shown, the clearance is formed between the rectangular groove M 3  and the corresponding angle, at which the fifteenth face  51   b  and the sixteenth face  51   c  intersect. Thus, a first passage R 1  is formed.  
      Moreover,  FIG. 6B  presents a section parallel to the first seal face  2  in the engaging portion between the projection  41  and the depression  51 .  
      As shown, the clearance is formed between the rectangular groove M 2  and the corresponding angle, at which the fourteenth face  51   a  and the sixteenth face  51   c  intersect. Thus, a second passage R 2  is formed.  
      Moreover,  FIG. 6C  presents a section concentric to the second seal face  3  in the engaging portion between the projection  41  and the depression  51 .  
      As shown, the clearance is formed between the rectangular groove M 1  and the corresponding angle, at which the fourteenth face  51   a  and the side wall face  81   a  (not shown in  FIG. 6 ) of the annular groove  81  intersect. Thus, a third passage R 3  is formed.  
      Moreover, the aforementioned first passage R 1 , second passage R 2  and third passage R 3  are connected with each other. A similar passage is also formed in the engaging portion between the projection  52  and the depression  42 . These individual passages form a 0-th passage R 0 .  
      At the engaging portions between the projection  52  and the depression  42 , there are individually formed passages corresponding to the aforementioned first passage R 1 , second passage R 2  and third passage R 3 . With the clearance T 3  being between the reference face  43  and the reference face  53 , on the other hand, there is also formed a passage leading from the clearance T 3  directly to the first passage R 1 , as shown in  FIG. 4 .  
      A fourth passage R 4  is also formed by the clearance T 3  between the reference face  43  and the reference face  53 .  
      Here, the 0-th passage R 0  has an open end K 1  for the first seal face  2 , and the fourth passage R 4  has an open end K 2  for the first seal face  2 .  
      Moreover, the region of the open end K 1  in the depth direction of the annular groove is designated by La in  FIG. 4  and  FIG. 6 , and the region of the open end K 2  in the depth direction of the annular groove is designated by Lb in  FIG. 4  and  FIG. 6 . Thus, the open ends of the passages are formed all over the first seal face  2  in the annular groove depth direction.  
      As a result, the open ends of the passages are formed over the whole region (indicated at Lo in  FIG. 2 ) in the annular groove depth direction in the sliding contact face of the first seal face  2  against the side wall face  81   a  of the annular groove  81 .  
      With the construction thus far described, the lubricating oil as the sealed fluid leaks from the sealed fluid side O via the 0-th passage R 0  and the fourth passage R 4 . At this time, the open ends of the passages are formed in the annular groove depth direction in the sliding contact face against the side wall face  81   a  of the annular groove  81  throughout the annular groove depth direction. As a result, a film of the lubricating oil is formed all over the sliding contact face by the sliding contact between the first seal face  2  and the side wall face  81   a . Therefore, the oil film can lower the frictional force at the sliding contact time and can cool the whole sliding face.  
      As a result, the sliding performance can be improved, and a foreign substance or abraded powder in the lubricating oil can be discharged via those passages so that the abrasion resistance is improved.  
      In the related art, there is a construction, in which the passage for causing the leakage of the sealed fluid is formed at the sliding position, as described above. In the seal ring  1  according to this embodiment, on the contrary, the passage for permitting the leakage of the sealed fluid is formed in the unsliding cut portion S. In this embodiment, therefore, the shape (e.g., the sectional shape or the size) of the passages does not change with the time. Therefore, it is possible to feed the sealed fluid stably for a long time. Moreover, it is possible to keep the function stably to discharge the foreign substance or abraded powder in the lubricating oil.  
      As a result, the stable sealing performance can be kept for a long time to improve the qualification. Moreover, a shaft can be properly used even if it is made of a soft metal material such as an aluminum alloy. Moreover, the seal ring can be used under higher PV conditions than those (i.e., 25 to 30 MPa·m/s) for the resin seal ring of the related art.  
      In this embodiment, on the other hand, the second passage R 2  is formed by providing the rectangular groove M 2 . Even if the seal ring  1  is thermally expanded to bring the first face  41   a  as the leading end face of the projection  41  into abutment against the fourteenth face  51   a  thereby to reduce the clearance T 2  to zero, the second passage R 2  can be retained to feed the sealed fluid stably.  
      Likewise, the third passage R 3  is formed by providing the rectangular groove M 1 . Even if the seal ring  1  is thermally expanded to bring the first face  41   a  as the leading end face of the projection  41  into abutment against the fourteenth face  51   a  thereby to reduce the clearance T 2  to zero, the third passage R 3  can be retained.  
      At the portions of the second passage R 2  and the third passage R 3 , on the other hand, the size of the clearance T 2  fluctuates so that the flow rate does not become stable. In this embodiment, therefore, the flow rate is set by the first passage R 1 .  
      Specifically, the necessary flow rate is set by the size of the rectangular groove M 3 . Here, the rectangular groove M 1  and the rectangular groove M 2  are set larger than the rectangular groove M 3  so that they may not be influenced by the flow rates of the second passage R 2  and the third passage R 3 . As a result, it is possible to keep the smallest sectional area of the leakage passage constant. Therefore, the flow rate is determined exclusively by the size of the rectangular groove M 3 .  
      Here, as shown in  FIG. 6A  to  FIG. 6C  it is assumed that the areas of the rectangular grooves M 1 , M 2  and M 3  are L 1 ×L 2 , L 3 ×L 4  and L 5 ×L 6 , respectively. At this time, the value of L 1 ×L 2  is set smaller than the values of L 3 ×L 4  and L 5 ×L 6 . Here, the magnitudes of the values L 1  and L 2  are restricted by the size of the cut portion S and the quantity of leakage demanded for the using conditions or the like. These magnitudes are desirably about 0.2 to 0.5 mm.  
      In case (of JP-A-2001-165322) the leakage passage of the lubricating oil is formed by forming the chamfer, the chamfered portion has the triangular section. As a result, the portion capable of discharging the foreign substance is restricted within the generally central region of the triangle. Therefore, the area is seriously lost to reduce the effective area. It seems to follow that the discharge of the foreign substance is not effective. In this embodiment, on the contrary, the leakage passage of the lubricating oil is formed into the rectangular groove. Therefore, the areal loss is reduced to enlarge the effective area so that the foreign substance can be discharged generally all over the groove.  
       FIG. 7  is a diagram for comparing a triangle C 1  and a square D 1  having equal sectional areas. The region of the triangle C 1  to pass the largest foreign substance is C 2 , and the region of the square D 1  to pass the largest foreign substance is D 2 . It is understood from the diagram that the region D 2  is larger than the region C 2 .  
      Thus in the case of equal sectional areas, the square section has a larger effective area than that of the triangular section for discharging the foreign substance. Therefore, the square section can discharge a larger foreign substance so that it has a superior ability to discharge the contaminants in the lubricating oil. In respect of the leakage of the lubricating oil, moreover, the square section can leak the sealed fluid more efficiently. Therefore, the square section can cool the seal face more effectively. Therefore, the abrasion resistance is improved the better to improve the sliding performance the better.  
      The shown example thus far described has been exemplified by the case, the groove for forming the passage is given a generally square sectional shape. However, this sectional shape may be a rectangular shape, a trapezoidal shape or a polygonal shape having four or more angles. This is because these sectional shapes can make the effective area larger than that of the triangular section. Moreover, a groove M 7  having a sectional shape of a general sector may also be formed, as shown in  FIG. 8  schematically presenting a section corresponding to the position of the cut face of the upper portion of  FIG. 6A . In this case, too, the effective area can be made larger than that of the triangular section.  
      Here, a resin composite of a heat-resisting resin and a filler can be applied as the material making the seal ring  1 .  
      As the heat-resisting resin, there can be enumerated a polycyanoacryle-ether resin (PEN), an aromatic polyether-ketone resin such as polyether-ether ketone (PEEK) resin, an aromatic thermoplastic polyimide resin, a 4-6 polyamide resin, a polyphenylene sulfide resin, a polytetrafluoroethylene resin and so on. These resins are excellent in heat resistance, flame resistance and chemical resistance, and exhibit excellent mechanical properties.  
      Here, the filler is blended with a view to improving the mechanical strength and the wear resistance of the material and to give low-friction properties and so on. The material for the filler should not be especially restricted.  
     Second Embodiment  
       FIG. 9  shows a second embodiment of the invention. In the aforementioned first embodiment, a portion of the passage is constructed by forming the groove only in the projection side disposed in the cut end portion. In this embodiment, a portion of the passage is constructed by forming a groove in the depression side, too.  
      The remaining constructions and actions are identical to those of the first embodiment so that their descriptions are omitted by designating the identical components by the common reference numerals.  
       FIG. 9  is a schematic section presenting a section in the cut portion of the seal ring according to the second embodiment of the invention.  FIG. 9  schematically presents a section corresponding to the cut face of the upper portion of  FIG. 6A .  
      In this embodiment, as shown, there is formed a groove M 8  having a trapezoidal section generally perpendicular in the edge direction to the angle, at which the two adjoining outer wall faces (i.e., the second face  41   b  and the third face  41   c , and the twelfth face  52   b  and the thirteenth face  52   c ) on the projection ( 41 ,  52 ) intersect.  
      There is also formed a groove M 9  having a trapezoidal section generally perpendicular in the edge direction to the corner (i.e., the corner formed by the fifteenth face  51   b  and the sixteenth face  51   c , and the corner formed by the fifth face  42   b  and the sixth face  42   c ) which confronts that angle in the depression ( 51 ,  42 ).  
      Moreover, those grooves M 8  and M 9  form a portion of the passage.  
      Thus, the grooves are formed individually on the projection side and on the depression side so that a portion of the passage is formed by the clearances of those grooves. As a result, the passage area can be made larger than that of the aforementioned first embodiment. Thus, the flow rate can be made higher to find an effective application to the case, in which the lubrication has to be enhanced for the using conditions. Moreover, the effective area for discharging the foreign substance can be made larger than that of the construction of the first embodiment. Therefore, it is possible to improve the contaminant discharging ability better.  
      With the grooves being formed in the projection or the depression, the shearing strength becomes the lower as the sectional area of the projection or the depression is the less. Here in this embodiment, however, the groove is formed in both the projection and the depression. Therefore, the area of the groove formed on the projection side or the depression side for acquiring the effective sectional area of the necessary passage can be smaller than that of the case, in which the groove is formed in one of the projection or the depression. Thus, this embodiment is effective, too, for suppressing the reduction in the shearing strength.  
      Here, the shown embodiment has been described on the case, in which the sectional shape is trapezoidal. However, the sectional shape should not be limited to the trapezoidal shape but may be a polygonal shape having four or more angles, or a sector shape. In the shown embodiment, the grooves to be formed on the projection side and the depression side have the identical sizes and shapes, but may also have different sizes and shapes.  
      In the description thus far made, moreover, the grooves are formed individually in the angles and corners of the arcuate portions of the projection and the depression thereby to form the passages. On the contrary, the passages can also be formed by forming the grooves individually in the angles and corners (e.g., the angle between the first face  41   a  and the third face  41   c  and the corner between the fourteenth face  51   a  and the sixteenth face  51   c ) of the radially cut portions of the projection and the depression.  
      There can also be conceived a construction, in which the grooves are formed not on the projection side but exclusively on the depression side.  
     INDUSTRIAL APPLICABILITY  
      According to the invention, as has been described hereinbefore, it is possible to keep the sealing performance stably for a long time. Moreover, the ability to discharge contaminants is improved. Still moreover, the qualification is improved.