Patent Publication Number: US-7722051-B2

Title: Seal ring

Description:
This is a divisional application of application Ser. No. 10/515,917, filed Jul. 12, 2005, which in turn is a U.S. stage application under 35 U.S.C. 371 of PCT/JP03/06781, filed May 29, 2003 and published in Japanese. 

   TECHNICAL FIELD 
   This invention relates to a seal ring for sealing an annular clearance between two members which are made rotatable relative to each other. 
   BACKGROUND ART 
   In the conventional art, the seal ring of this kind is used in a variety of hydraulic apparatus such as an automatic transmission for an automobile. 
   A general seal ring will be described with reference to  FIG. 11  and  FIG. 12 .  FIG. 11  is a perspective view showing the mounted state of a seal ring according to the conventional art.  FIG. 12  is a schematic section showing the mounted state of the seal ring according to the conventional art. 
   The shown seal ring  100  seals the annular clearance between a housing  800  that has a bore and a shaft  700  inserted in the bore. This seal ring  100  is mounted for use in an annular groove  701  formed in the shaft  700 . 
   The seal ring  100  is made of a resin material. The seal ring  100  is provided with a first sealing face  100   a  for sealing the inner circumference  800   a  of the bore formed in the housing  800 , and a second sealing face  100   b  for sealing the side wall face  701   a  of the annular groove  701  formed in the shaft  700 . 
   When a pressure is applied in the direction of arrow P, as shown, from the sealing fluid to the unsealing fluid, the seal ring  100  is pushed to the side of the unsealing fluid. Therefore, the second sealing face  100   b  pushes the side wall face  701   a  of the annular groove  701 . On the other hand, the first sealing face  100   a  pushes the inner circumference  800   a  of the bore confronting the annular groove  701 . Thus, the first sealing face  100   a  and the second sealing face  100   b  seal at their respective positions. 
   Therefore, the seal ring  100  can prevent the sealing fluid from leaking to the side of the unsealing fluid. 
   Here, the sealing fluid is exemplified by lubricating oil, and indicates the ATF (Automatic Transmission Fluid) in case it is used in the transmission of an automobile. 
   On the other hand, the ring body of the seal ring  100  is provided with a separate portion  101  at one circumferential portion, as shown. One reason for this provision is to facilitate the work for mounting the seal ring  100  in position. 
   A variety of types have been known as that mode of the separate portion  101 . The example shown in  FIG. 11  and  FIG. 12  is a special step cut. This special step cut has a construction cut into two steps. By adopting this special step cut, the leakage can be reduced to properly match the change in the ambient temperature. 
   This special step cut is provided with a pair of a projection  101   a  and a depression  101   d  on one outer circumferential side across the separated portion and a pair of a depression  101   c  and a projection  101   b  on the other outer circumferential side. The construction is further made such that the projection  101   a  and the depression  101   c  fit each other whereas the depression  101   d  and the projection  101   b  fit each other. 
   The seal ring  100  adopting such special step cut can block the sealing fluid side and the unsealing fluid side such that the faces perpendicular to the circumferential direction form clearances with respect to the circumferential direction. As a result, even if the ring body is expanded or contracted by the ambient temperature, the seal ring  100  can absorb the changes in the sizes of the clearances while keeping the sealed state. As a result, the seal ring  100  can keep its sealing properties stably against the surrounding temperature change. 
   In recent years, the various hydraulic apparatus such as the automatic transmission for the automobile has needs of not only the leakage reduction but also the reduction of the friction of the sliding rotations for the seal ring used in the automatic transmission with a view to improving the fuel economy and the performance. 
   As shown in  FIG. 13  and  FIG. 14 , therefore, there is known a structure which is reduced in the pressure receiving area of the sealing faces.  FIG. 13  is a perspective view showing the mounted state of the seal ring according to the conventional art.  FIG. 14  is a schematic section showing the mounted state of the seal ring according to the conventional art. The seal ring, as shown in these Figures, according to the conventional art is constructed to reduce the friction of the sliding rotations from that of the seal ring according to the conventional art as shown in  FIG. 11  and  FIG. 12 . 
   This seal ring  200  is provided, like the aforementioned seal ring  100 , with a first sealing face  200   a , a second sealing face  200   b , and a separate portion  201  having a special step cut (including a projection  201   a , a depression  201   d , a depression  201   c  and a projection  201   b ). 
   In order to reduce the pressure receiving area (or the sliding area) on the sidewall face  701   a  of the annular groove  701 , moreover, this seal ring  200  is provided with a relief (as can also be called the “depression”, “notch” or “recess”). 
   Thus, this seal ring  200  contemplates to reduce the friction of the sliding rotations by reducing the pressure receiving area. 
   In case the side wall face  701   a  of the annular groove  701  is perpendicular to the groove bottom (that is, in case the second sealing faces  100   b  and  200   b  and the side wall face  701   a  are parallel to each other), the aforementioned seal rings  100  and  200  seal throughout their circumferences. Therefore, the problem of the leak does not arise. 
   However, the annular groove  701  may have its side wall face sloped such that its bottom is narrow and such that it becomes the wider as it comes the closer to its upper face. Generally, the slope occurs when the annular groove  701  is formed by the cutting work. In this case, there arises a problem that the sealing performance is not done throughout the circumference of the seal ring so that the leakage increases. This point will be described with reference to  FIG. 15  to  FIG. 18 . 
   The case of the aforementioned seal ring  100  is shown in  FIG. 15  and  FIG. 16 . In case the side wall face  702   a  of an annular groove  702  is sloped, as shown, a sealing portion S is formed of only the lower end of the seal ring  100 . In short, the sealing action is performed in a substantially linear contact. 
   The reason for the expression of not merely the “linear contact” but the “substantially linear contact” is described in the following. This is because the contact is practically made through a face having a small width so that it is so grasped rather by the facial contact but not by the linear contact as to invite a misunderstanding. This expression also applies to the following description. 
   A clearance X usually exists in the seal ring  100  adopting the special step cut at the separate portion  101 , as shown. 
   This is because the seal ring  100  adopting the special step cut is constructed such that the clearance is formed between the faces perpendicular to the circumferential direction so as to correspond to the change in the ambient temperature. 
   In case the sealing action is performed by the substantially linear contact in the sealing portion S, as described above, it is apparent from the FIGS that an unsealed portion arises in the clearance X. Therefore, a leak occurs (at a leaking portion A). 
   On the other hand, the case of the aforementioned seal ring  200  is shown in  FIG. 17  and  FIG. 18 . 
   In this case, the sealing portion S is formed at the lower end of the seal ring  200  in the portion having no relief  202  and at the step portion over the relief in the portion having the relief  202 , as shown. In this case, too, the leak occurs (at leaking portion A) from the clearance X as in the case of the aforementioned seal ring  100 . 
   In the case of this seal ring  200 , on the other hand, the sealing portion S is formed of the stepped portion over the relief  202 , as shown, in the portion apart from the separate portion  201 . In the vicinity of the separate portion  201 , however, the sealing portion S is formed at the lower end of the seal ring  200 , as shown. At the stepped portion over the relief, as shown, the sealing portion cannot be sufficiently formed to make the sealing properties unstable (as indicated at portion Y). 
   This results in that the leak also occurs at this portion (i.e., a leaking portion B). 
   A seal ring  300  having a trapezoidal section is also known, as shown in  FIG. 19  to  FIG. 22 . 
   This seal ring  300  is given a trapezoidal shape for the sealing portion S of the substantially linear contact so as to reduce the sliding friction. Specifically, the seal ring  300  forms the sealing portion S at the upper end edge of the annular groove  701 . 
   In this case of the seal ring  300 , moreover, the sealing portion S is so formed at the upper end edge of the annular groove as to make the substantially linear contact not only in case the side wall face of the annular groove is perpendicular to the groove bottom, as shown in  FIG. 19  and  FIG. 20 , but also in case the side wall face is sloped with respect to the groove bottom, as shown in  FIG. 21  and  FIG. 22 . 
   In this case of the seal ring  300 , a leak occurs through a clearance Z between the projection and the depression in the special step cut no matter whether the side wall face of the annular groove might be inclined or not. The leakage is varied with the slope of the annular groove thereby to raise a problem that the stable leaking characteristics cannot be obtained. 
   If the side wall face  702   a  of the annular groove  702  is sloped in the aforementioned case of the seal ring  200 , moreover, the sealing portion S is formed of the lower end of the seal ring  200  and the step portion over the relief  202 , as shown in  FIG. 17 , so that a portion (as designated by Y in  FIG. 17 ) of unstable sealing properties is formed. 
   It is, therefore, conceivable to eliminate the step by forming the relief throughout the circumference, as shown in  FIG. 23  and  FIG. 24 .  FIG. 23  is a perspective view showing the mounted state of the seal ring according to a virtual art.  FIG. 24  is a schematic section showing the mounted state of the seal ring according to the virtual art. 
   In the case of this seal ring  400 , as shown, a relief  402  is formed throughout the circumference of the ring. Thus, no step is formed in the sealing portion. 
   Even in case the side wall face  702   a  of the annular groove  702  is sloped, therefore, only the upper portion of the relief  402  can provide the sealing portion S, as shown, to eliminate the portion of the unstable sealing properties. 
   In this case of the seal ring  400 , however, like the aforementioned case of the seal ring  300  of the trapezoidal section, the leak occurs through the clearance Z between the depression and the projection in a separate portion  401  adopting the special step cut, no matter whether the sidewall face of the annular groove might be vertical to or sloped with respect to the groove bottom. With the relief  402  being in the vicinity of the separate portion, moreover, the leakage may become more from that clearance Z. 
   DISCLOSURE OF THE INVENTION 
   The conventional art has found it difficult to reduce the leakage sufficiently, in case the side wall face of the annular groove is sloped with respect to the groove bottom. A demand is also made for reducing the friction of the sliding rotations. 
   An object to provide a seal ring which contemplates to reduce the leakage together with the friction of the sliding rotations. 
   The present invention is applied to a seal ring for sealing an annular clearance between two members which are assembled rotatably concentrically with and relative to each other. The seal ring comprises: a first sealing face for sealing the surface of one of the two members; and a second sealing face for sealing such a side wall face of the annular groove formed in the other member as is located on the side of an unsealing fluid. 
   The seal ring is provided with a separate portion separated at one circumferential portion. 
   In order to achieve the aforementioned object, in the invention, a relief kept out of abutment against the side wall face of the annular groove on the side of the unsealing fluid is formed throughout the circumference of the second sealing face. 
   By forming the relief throughout the circumference, the sliding area (or the pressure receiving area) on the side wall face of the annular groove on the side of the unsealing fluid can be reduced to reduce the friction of the sliding rotations. 
   In the invention according to claim  1  or  2 , moreover, the relief is set to have a smaller radial width in the vicinity of the separate portion and a larger radial width at a position apart from the separate portion. 
   If a relief having an equal radial width is formed throughout the circumference so as to reduce the sliding area, the leakage of the sealing fluid in the vicinity of the separate portion may increase. 
   In the invention according to claim  1  or  2 , therefore, the radial width of the relief is narrowed in the vicinity of the separate portion to reduce the leakage of the sealing fluid. 
   In the invention according to claim  1 , moreover, the portion of the relief to transit from the narrower portion to the wider portion is set to have a gradually changing width. 
   In the case of the construction the relief portion quickly transits from the narrower portion to the wider portion, the unstable portion having no contact with the side wall face of the annular groove on the side of the unsealing fluid exists over a wide range, if the side wall face has a slope different from the second sealing face. 
   Therefore, the construction of the invention is intended to minimize the unstable portion having no contact with the side wall face. 
   This construction makes it possible to reduce the leakage of the sealing fluid. 
   However, the portion of the relief to transit from the narrower portion to the wider portion can achieves the object of the invention if it can reduce the leakage of the sealing fluid, even if it contains the portion other than the gradually width changing portion. 
   In the invention according to claim  2 , therefore, the portion of the relief to transit from the narrower portion to the wider portion contains a gradually width-changing portion. 
   In the invention according to claim  3 , on the other hand, a continuous annular sealing portion for sealing the side wall face of the annular groove is formed on the second sealing face even in the state where the slope of the side wall face of the annular groove on the side of the unsealing fluid and the slope of the second sealing face are different. 
   With this construction, the sealing portion is not interrupted by the annular sealing portion for the side wall face of the annular groove on the side of the unsealing fluid, so that the leakage of the sealing fluid can be reduced. 
   It is preferable that the annular sealing portion is kept in a state to continuously contact with the side wall face of the annular groove on the side of the unsealing fluid irrespective of a change in the size of a clearance between such faces of the separate portion as are substantially perpendicular to the circumferential direction. 
   With this construction, the stable sealing properties can be exhibited even in case the seal ring is expanded or contracted by the ambient temperature to change the size of the clearance between the faces in the separate portion perpendicular to the circumferential direction. 
   The aforementioned annular sealing portion can be realized by forming the aforementioned relief so that the formation of the sealing portion may not be obstructed. 
   The separate portion can contain a separating face concentric to the first sealing face, and such an end edge of the separating face as is located on the side of the annular groove on the side of the unsealing fluid forms a portion of the annular sealing portion. 
   In other words, the end edge of the separating face on the side of the side wall face of the annular groove on the side of the unsealing fluid is utilized as a portion of the annular sealing portion so that the continuous annular sealing portion for seating the side wall face can be formed without interrupting the sealing portion at the separate portion. 
   This separate portion can be exemplified by the special step cut or the step cut. 
   Here, the special step cut has a separate structure, in which the stepped separate portion is formed at each of the two sealing faces in the seal ring. 
   Moreover, the separate portion contains the separating face extending in the circumferential direction, and this separating end edge is formed as a portion of the stepped separate portion on the sealing face on the side wall face of the annular groove on the side of the unsealing fluid. 
   On the other hand, the step cut is a separate structure, in which a stepped separate portion is formed on that of two sealing faces in the seal ring, which is located on the side of the side wall face of the annular groove on the side of the unsealing fluid. 
   Moreover, the separate portion contains the separating face extending in the circumferential direction, and this separating end edge is formed as a portion of the stepped separate portion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a seal ring according to a first embodiment of the invention. 
       FIG. 2A  is a partially broken perspective view showing the state, in which the seal ring according to the first embodiment of the invention is mounted, and  FIG. 2B  is an enlarged view of a portion taken in a direction B of  FIG. 2A . 
       FIG. 3A  is a portion of a top plan view showing a modification of the seal ring according to the first embodiment of the invention;  FIG. 3B  is an enlarged view of a portion of  FIG. 3A ; and  FIG. 3C  is an enlarged view of a portion of the top plan view showing a modification of the seal ring according to the first embodiment of the invention. 
       FIG. 4  is a schematic section showing the state, in which the seal ring according to the first embodiment of the invention is mounted. 
       FIG. 5  is a top plan view of a seal ring according to a second embodiment of the invention. 
       FIG. 6  is a broken perspective view of a portion showing the state, in which the seal ring according to the second embodiment of the invention is mounted. 
       FIG. 7  is a schematic section showing the state, in which the seal ring according to the second embodiment of the invention is mounted. 
       FIG. 8  is a top plan view of a seal ring according to a third embodiment of the invention. 
       FIG. 9  is a broken perspective view of a portion showing the state, in which the seal ring according to the third embodiment of the invention is mounted. 
       FIG. 10  is a schematic section showing the state, in which the seal ring according to the third embodiment of the invention is mounted. 
       FIG. 11  is a perspective view showing the mounted state of the seal ring according to the conventional art. 
       FIG. 12  is a schematic section showing the mounted state of the seal ring according to the conventional art. 
       FIG. 13  is a perspective view showing the mounted state of the seal ring according to the conventional art. 
       FIG. 14  is a schematic section showing the mounted state of the seal ring according to the conventional art. 
       FIG. 15  is an explanatory view of a problem of the seal ring according to the conventional art. 
       FIG. 16  is an explanatory view of a problem of the seal ring according to the conventional art. 
       FIG. 17  is an explanatory view of the problem of the seal ring according to the conventional art. 
       FIG. 18  is an explanatory view of the problem of the seal ring according to the conventional art. 
       FIG. 19  is an explanatory view of a problem of the seal ring according to the conventional art. 
       FIG. 20  is an explanatory view of the problem of the seal ring according to the conventional art. 
       FIG. 21  is an explanatory view of the problem of the seal ring according to the conventional art. 
       FIG. 22  is an explanatory view of the problem of the seal ring according to the conventional art. 
       FIG. 23  is a perspective view showing the mounted state of the seal ring according to a virtual art. 
       FIG. 24  is a schematic section showing the mounted state of the seal ring according to the virtual 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. 4 .  FIG. 1  is a top plan view of a seal ring according to a first embodiment of the invention.  FIG. 2A  is a broken perspective view showing a portion of the state, in which the seal ring according to the first embodiment of the invention is mounted, and  FIG. 2B  is an enlarged view of a portion taken in a direction B of  FIG. 2A .  FIG. 3A  is a portion of a top plan view showing a modification of the seal ring according to the first embodiment of the invention;  FIG. 3B  is an enlarged view of a portion of  FIG. 3A  (i.e., an encircled portion of  FIG. 3A ); and  FIG. 3C  is an enlarged view of a portion of the top plan view showing a modification of the seal ring according to the first embodiment of the invention.  FIG. 4  is a schematic section showing the state, in which the seal ring according to the first embodiment of the invention is mounted. 
   As shown, the seal ring  1  seals the annular clearance between a housing  80  that has a bore and a shaft  70  inserted in the bore. This seal ring  1  is mounted for use in an annular groove  71  formed in the shaft  70 . 
   The seal ring  1  is made of a resin material. The seal ring  1  is provided with a first sealing face  3  for sealing the inner circumference  81  of the bore formed in the housing  80 , and a second sealing face  4  for sealing the side wall face  72  of the annular groove  71  formed in the shaft  70 . 
   When a pressure is applied in the direction of arrow P, as shown in  FIGS. 2 and 4 , from the sealing fluid to the unsealing fluid, the seal ring  1  is pushed to the side of the unsealing fluid. Therefore, the second sealing face  4  pushes the side wall face  72  of the annular groove  71 . 
   On the other hand, the first sealing face  3  pushes the inner circumference  81  of the bore confronting the annular groove  71 . Thus, the first sealing face  3  and the second sealing face  4  seal at their respective positions. 
   Therefore, the seal ring  1  can prevent the sealing fluid from leaking to the side of the unsealing fluid. 
   Here, the sealing fluid is exemplified by lubricating oil, and indicates the ATF (Automatic Transmission Fluid) in case it is used in the transmission of an automobile. 
   On the other hand, the ring body of the seal ring  1  is provided with a separate portion  2  at one circumferential portion, as shown. One reason for this provision is to facilitate the work for mounting the seal ring  1  in position. 
   A variety of types have been known as that mode of the separate portion  2 . In this embodiment, a special step cut is adopted as the separate portion  2 . This special step cut has a construction cut into two steps. Specifically, each of the first sealing face  3  and the second sealing face  4  is provided with the stepped separate portion, as shown. By adopting this special step cut, the leakage can be reduced to properly match the change in the ambient temperature. 
   This special step cut is provided with a pair of a projection  21  and a depression  22  on one outer circumferential side across the separated portion and a pair of a depression  24  and a projection  23  on the other outer circumferential side. The construction is further made such that the projection  21  and the depression  24  fit each other whereas the depression  22  and the projection  23  fit each other. 
   The seal ring  1  adopting such special step cut can block the sealing fluid side and the unsealing fluid side such that the faces perpendicular to the circumferential direction form clearances (i.e., a clearance  27  formed between the leading end face of the projection  21  and the confronting face of the depression  24 , a clearance  28  formed between the leading end face of the projection  23  and the confronting face of the depression  22 , and a clearance  29  on the inner circumferential side, as shown in  FIG. 2 ) with respect to the circumferential direction. 
   In other words, the projection  21  and the depression  24  are constructed to make sliding contact with not only a separating face  25  concentric with the first sealing face  3  but also a separating face  26  perpendicular to the axis. 
   This construction leaves any portion uninterrupted in the first sealing face  3  and in the second sealing face  4  by the separate portion  2 , even if the seal ring  1  has the clearance  27 , the clearance  28  and the clearance  29 , as described above. 
   Therefore, even if the seal ring  1  is expanded or contracted of its body by the ambient temperature to fluctuate the spacings of the clearance  27 , the clearance  28  and the clearance  29 , it can absorb the changes in the sizes of the clearances while keeping the sealed state. 
   As a result, the seal ring  1  can keep its sealing properties stably against the surrounding temperature change. 
   In order to satisfy the needs for reducing the friction of the sliding rotations, moreover, the seal ring  1  according to this embodiment is provided throughout its circumference with a relief (e.g., a depression, a notch or a lighting portion)  5  for reducing the pressure receiving area of the sliding face of the annular groove  71  against the side wall face  72 . 
   Thus, the seal ring  1  according to this embodiment contemplates to reduce the friction of the sliding rotations by reducing the pressure receiving area. 
   In this embodiment, moreover, the step is formed in the boundary between the second sealing face  4  and the relief  5  in the vicinity of the separate portion  2 . 
   As a result, the relief  5  is radially narrowed near the separate potion  2  and radially widened at the portion apart from the separate portion  2 . Specifically, a step is formed between a boundary  51  at a position apart from the separate portion  2  and a boundary  52  and  53  in the vicinity of the separate portion  2 , as shown in  FIG. 1  and  FIG. 2 . Moreover, the boundaries  52  and  53  are arranged on the inner circumference side of the separating face  25 . 
   Thus in the vicinity of the separate portion  2 , the leakage of the sealing fluid can be reduced by narrowing the relief radially of the relief  5 , while satisfying the needs for reducing the friction of the sliding rotations. 
   In this embodiment, on the other hand, the potion of the relief  5  to transit from the narrow portion to the wide portion is set to have gradually changing width. Specifically, the relief  5  is provided with a slope  54  between the boundary  51  and the boundary  52  and a slope  55  between the boundary  51  and the boundary  53 . 
   The sloping angle (i.e., the angle with respect to the boundary  51 , as shown in  FIG. 2B ) θ of those slopes  54  and  55  is set to 10 degrees or less, preferably about 5 degrees. 
   In case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4  are made substantially equal to each other by the construction thus far described, the substantial entirety of the second sealing face  4  makes sliding contact with the side wall face  72  so that the construction sufficiently exhibits the sealing properties. 
   In case the annular groove  71  is formed into such a shape due to shortage of the working precision as is narrowed toward the groove bottom, on the other hand, a deviation arises between the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4 , as shown in  FIG. 2  or  FIG. 4 . 
   With the relief  5  being formed, the step portion between the relief  5  and the second sealing face  4 , that is, the individual end edge portions of the boundary  51 , the boundary  52  and the boundary  53  act as the sealing portions to make substantially linear sliding contact with the side wall face  72 . 
   Here, the depth of the aforementioned relief  5  has to be set so that the individual end edge portions of the boundary  51 , the boundary  52  and the boundary  53  may sufficiently function as the sealing portions. In short, the depth of the relief  5  has to be set by considering the relation to the angle (i.e., the angle which can be conceived in consideration of errors or the like) of the side wall face  72  of the annular groove  71 . 
   More specifically, the depth of the relief  5  has to be set so that the end edge of the seal ring  1  on the inner circumference side may not abut against the side wall face  72  of the annular groove  71 . 
   Moreover, the aforementioned step is formed at the joining portion between the boundary  51  and the boundary  52  and at the joining portion between the boundary  51  and the boundary  53 , as described above. 
   However, these joining portions are made to join through the slope  54  and the slope  55  so that they can form relatively stable sealing portions. In other words, it is possible to substantially eliminate the leak (at a leaking portion B) from a portion Y of the aforementioned conventional art, as shown in  FIG. 17 . 
   In the construction, the boundaries  52  and  53  are arranged on the inner circumference side of the separating face  25 . Therefore, the leakage from the clearance  29  on the inner circumference side of the separate portion  2  is reduced to some extent. By the seal ring  1  according to the embodiment of the invention thus far described, the leakage can be reduced together with the friction of the sliding rotations. 
   Even in case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4  deviate from each other, moreover, it is possible to reduce the leakage as much as possible. 
   As a result, the working precision of the annular groove can be relaxed to lead to the reduction in the cost. By intentionally deviating the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4 , moreover, the sealing portion can be made of not a facial contact but a substantially linear contact thereby to reduce the friction of the sliding rotations. 
   Here, it is desired from the viewpoint of sealing properties that the joining portion between the boundary  51  and the boundary  52  and the joining portion between the boundary  51  and the boundary  53  are gradually changed in width. Therefore, it is desired that the joining portions are made exclusively of the slope  54  and the slope  55 , as described above. 
   As a matter of fact, however, a manufacturing problem may make it difficult to make those joining portions exclusively of the slopes, for example. Therefore, portions other than the slopes may exist within as far as the sealing properties are not substantially affected adversely. 
   One example is shown in  FIG. 3 . 
   As in the seal ring  1  shown in  FIGS. 1 and 2 , the slope  54  is formed at the joining portion between the boundary  51  and the boundary  52 , as shown in  FIGS. 3A and 3B . The slope  55  is also formed at the joining portion between the boundary  51  and the boundary  53 . 
   In this example shown in  FIGS. 3A and 3B , moreover, a perpendicular face  54   a  perpendicular to the boundary  52  is interposed between one end of the slope  54  and the boundary  52 . 
   A perpendicular face  55   a  perpendicular to the boundary  53  is also likewise interposed between one end of the slope  55  and the boundary  53 . These perpendicular face  54   a  and perpendicular face  55   a  are formed for a manufacturing problem of the seal ring. 
   In the absence of these perpendicular face  54   a  and perpendicular face  55   a , a strong force is applied at a parting time of the mold for the seal ring to the boundary portion between the boundary  52  and the slope  54  and to the boundary portion between the boundary  53  and the slope  55 . 
   This strong force raises a cause for shortening the lifetime of the mold. 
   In order to solve this drawback, therefore, the perpendicular face  54   a  and the perpendicular face  55   a  are provided. Considering only the viewpoint of the sealing properties, it is desired to make the joining portion between the boundary  51  and the boundary  52  and the joining portion between the boundary  51  and the boundary  53  exclusively of the slope  54  and the slope  55 , as has been described hereinbefore. 
   In comparison with another advantage, however, some portion other than the slope may be contained within such a range as not to affect the sealing properties adversely. 
   For example, the slope  54  may contain a stepped portion  54   b , as shown in  FIG. 3C . 
   Second Embodiment 
   A seal ring according to a second embodiment of the invention will be described with reference to  FIG. 5  to  FIG. 7 .  FIG. 5  is a top plan view of a seal ring according to a second embodiment of the invention.  FIG. 6  is a broken perspective view of a portion showing the state, in which the seal ring according to the second embodiment of the invention is mounted.  FIG. 7  is a schematic section showing the state, in which the seal ring according to the second embodiment of the invention is mounted. 
   As shown, the seal ring  1   a  seals the annular clearance between a housing  80  that has a bore and a shaft  70  inserted in the bore. This seal ring  1   a  is mounted for use in an annular groove  71  formed in the shaft  70 . 
   The seal ring  1   a  is made of a resin material. The seal ring  1   a  is provided with a first sealing face  3   a  for sealing the inner circumference  81  of the bore formed in the housing  80 , and a second sealing face  4   a  for sealing the side wall face  72  of the annular groove  71  formed in the shaft  70 . 
   When a pressure is applied in the direction of arrow P, as shown in  FIGS. 6 and 7 , from the sealing fluid to the unsealing fluid, the seal ring  1   a  is pushed to the side of the unsealing fluid. Therefore, the second sealing face  4   a  pushes the side wall face  72  of the annular groove  71 . 
   On the other hand, the first sealing face  3   a  pushes the inner circumference  81  of the bore confronting the annular groove  71 . Thus, the first sealing face  3   a  and the second sealing face  4   a  seal at their respective positions. 
   Therefore, the seal ring  1   a  can prevent the sealing fluid from leaking to the side of the unsealing fluid. 
   Here, the sealing fluid is exemplified by lubricating oil, and indicates the ATF (Automatic Transmission Fluid) in case it is used in the transmission of an automobile. 
   On the other hand, the ring body of the seal ring  1  is provided with a separate portion  2   a  at one circumferential portion, as shown. One reason for this provision is to facilitate the work for mounting the seal ring  1  in position. 
   A variety of types have been known as that mode of the separate portion  2   a . In this embodiment, a special step cut is adopted as the separate portion  2   a . This special step cut has a construction cut into two steps. 
   Specifically, each of the first sealing face  3   a  and the second sealing face  4   a  is provided with the stepped separate portion, as shown. 
   By adopting this special step cut, the leakage can be reduced to properly match the change in the ambient temperature. 
   This special step cut is provided with a pair of a projection  21   a  and a depression  22   a  on one outer circumferential side across the separated portion and a pair of a depression  24   a  and a projection  23   a  on the other outer circumferential side. The construction is further made such that the projection  21   a  and the depression  24   a  fit each other whereas the depression  22   a  and the projection  23   a  fit each other. 
   The seal ring  1   a  adopting such special step cut can block the sealing fluid side and the unsealing fluid side such that the faces perpendicular to the circumferential direction form clearances (i.e., a clearance  27   a  formed between the leading end face of the projection  21   a  and the confronting face of the depression  24   a , a clearance  28   a  formed between the leading end face of the projection  23   a  and the confronting face of the depression  22   a , and a clearance  29   a  on the inner circumferential side, as shown in  FIG. 6 ) with respect to the circumferential direction. 
   In other words, the projection  21   a  and the depression  24   a  are constructed to make sliding contact with not only a separating face  25   a  concentric with the first sealing face  3   a  but also a separating face  26   a  perpendicular to the axis. 
   This construction leaves any portion uninterrupted in the first sealing face  3   a  and in the second sealing face  4   a  by the separate portion  2   a , even if the seal ring  1   a  has the clearance  27   a , the clearance  28   a  and the clearance  29   a , as described above. 
   Therefore, even if the seal ring  1   a  is expanded or contracted of its body by the ambient temperature to fluctuate the spacings of the clearance  27   a , the clearance  28   a  and the clearance  29   a , it can absorb the changes in the sizes of the clearances while keeping the sealed state. 
   As a result, the seal ring  1   a  can keep its sealing properties stably against the surrounding temperature change. 
   In order to satisfy the needs for reducing the friction of the sliding rotations, moreover, the seal ring  1   a  according to this embodiment is provided throughout its circumference with a relief (e.g., a depression, a notch or a lighting portion)  5   a  for reducing the pressure receiving area of the sliding face of the annular groove  71  against the side wall face  72 . 
   Thus, the seal ring  1   a  according to this embodiment contemplates to reduce the friction of the sliding rotations by reducing the pressure receiving area. 
   In this embodiment, moreover, the relief  5   a  and the second sealing face  4   a  are joined to each other by a tapered face  51   a .  32 . On the other hand, the end edge of the separating face  25   a  is aligned to the outer circumference end edge of the tapered face  51   a.    
   This construction forms such a continuous annular sealing portion with the outer circumference end edge of the tapered face  51   a  and the end edge of the separating face  25   a  as to seal the side wall face  72  of the annular groove  71 . 
   In case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a  are made substantially equal to each other by the construction thus far described, the substantial entirety of the second sealing face  4   a  makes sliding contact with the side wall face  72  so that the construction sufficiently exhibits the sealing properties. 
   In the separate portion  2   a , moreover, the end edge of the separating face  25   a  forms the sealing portion which can also prevent the leak of the sealing fluid from the clearance  27   a  or the clearance  29   a.    
   In case the annular groove  71  is formed into such a shape due to shortage of the working precision as is narrowed toward the groove bottom, on the other hand, a deviation arises between the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a , as shown in  FIG. 6  or  FIG. 7 . 
   In this case, this embodiment is provided with the relief  5   a  and the tapered face  51   a  so that the upper end edge of the tapered face  51   a  and the end edge of the separating face  25   a  form the continuous annular sealing portion for sealing the side wall face  72  of the annular groove  71 . 
   Here, the depth of the aforementioned relief  5   a  and the tapering angle of the tapered face  51   a  have to be set so that the annular sealing portion may sufficiently function as the sealing portion. In short, these depth and angle have to be set by considering the relation to the angle (i.e., the angle which can be conceived in consideration of errors or the like) of the side wall face  72  of the annular groove  71 . 
   More specifically, the depth of the relief  5   a  and the tapering angle of the tapered face  51   a  have to be set so that the end edge of the seal ring  1   a  on the inner circumference side may not abut against the side wall face  72  of the annular groove  71 . 
   Thus in this embodiment, independently of whether the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a  are equal or different, the outer circumference end edge of the tapered face  51   a  and the end edge of the separating face  25   a  form the continuous annular sealing portion for sealing the side wall face  72  of the annular groove  71 . 
   As a result, the sealing portion is formed without any interruption throughout the whole circumference. 
   Independently of whether the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a  are equal or different, therefore, it is possible to prevent the sealing fluid from leaking from the clearance  27   a  or the clearance  29   a.    
   Moreover, the sealing properties are excellent because no portion is unstable in the sealing properties. 
   By the seal ring  1   a  according to the embodiment of the invention thus far described, the leakage can be reduced together with the friction of the sliding rotations. 
   Even in case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a  deviate from each other, moreover, it is possible to reduce the leakage as much as possible. 
   As a result, the working precision of the annular groove can be relaxed to lead to the reduction in the cost. 
   By intentionally deviating the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   a , moreover, the sealing portion can be made of not a facial contact but a substantially linear contact thereby to reduce the friction of the sliding rotations. 
   Third Embodiment 
   A seal ring according to a third embodiment of the invention will be described with reference to  FIG. 8  to  FIG. 10 .  FIG. 8  is a top plan view of the seal ring according to a third embodiment of the invention.  FIG. 9  is a broken perspective view of a portion showing the state, in which the seal ring according to the third embodiment of the invention is mounted.  FIG. 10  is a schematic section showing the state, in which the seal ring according to the third embodiment of the invention is mounted. 
   As shown, the seal ring  1   b  seals the annular clearance between a housing  80  that has a bore and a shaft  70  inserted in the bore. This seal ring  1   b  is mounted for use in an annular groove  71  formed in the shaft  70 . 
   The seal ring  1   b  is made of a resin material. The seal ring  1   b  is provided with a first sealing face  3   b  for sealing the inner circumference  81  of the bore formed in the housing  80 , and a second sealing face  4   b  for sealing the side wall face  72  of the annular groove  71  formed in the shaft  70 . 
   When a pressure is applied in the direction of arrow P, as shown in  FIGS. 9 and 10 , from the sealing fluid to the unsealing fluid, the seal ring  1   b  is pushed to the side of the unsealing fluid. Therefore, the second sealing face  4   b  pushes the side wall face  72  of the annular groove  71 . 
   On the other hand, the first sealing face  3   b  pushes the inner circumference  81  of the bore confronting the annular groove  71 . Thus, the first sealing face  3   b  and the second sealing face  4   b  seal at their respective positions. Therefore, the seal ring  1   b  can prevent the sealing fluid from leaking to the side of the unsealing fluid. 
   Here, the sealing fluid is exemplified by lubricating oil, and indicates the ATF (Automatic Transmission Fluid) in case it is used in the transmission of an automobile. 
   On the other hand, the ring body of the seal ring  1   b  is provided with a separate portion  2   b  at one circumferential portion, as shown. One reason for this provision is to facilitate the work for mounting the seal ring  1   b  in position. A variety of types have been known as that mode of the separate portion  2   b.    
   In this embodiment, a special step cut is adopted as the separate portion  2   b . This special step cut has a construction cut into two steps. Specifically, each of the first sealing face  3   b  and the second sealing face  4   b  is provided with the stepped separate portion, as shown. By adopting this special step cut, the leakage can be reduced to properly match the change in the ambient temperature. 
   This special step cut is provided with a pair of a projection  21   b  and a depression  22   b  on one outer circumferential side across the separated portion and a pair of a depression  24   b  and a projection  23   b  on the other outer circumferential side. 
   The construction is further made such that the projection  21   b  and the depression  24   b  fit each other whereas the depression  22   b  and the projection  23   b  fit each other. 
   The seal ring  1   b  adopting such special step cut can block the sealing fluid side and the unsealing fluid side such that the faces perpendicular to the circumferential direction form clearances (i.e., a clearance  27   b  formed between the leading end face of the projection  21   b  and the confronting face of the depression  24   b , a clearance  28   b  formed between the leading end face of the projection  23   b  and the confronting face of the depression  22   b , and a clearance  29   b  on the inner circumferential side, as shown in  FIG. 9 ) with respect to the circumferential direction. 
   In other words, the projection  21   b  and the depression  24   b  are constructed to make sliding contact with not only a separating face  25   b  concentric with the first sealing face  3   b  but also a separating face  26   b  perpendicular to the axis. 
   This construction leaves any portion uninterrupted in the first sealing face  3   b  and in the second sealing face  4   b  by the separate portion  2   b , even if the seal ring  1   a  has the clearance  27   b , the clearance  28   b  and the clearance  29   b , as described above. 
   Therefore, even if the seal ring  1   b  is expanded or contracted of its body by the ambient temperature to fluctuate the spacings of the clearance  27   b , the clearance  28   b  and the clearance  29   b , it can absorb the changes in the sizes of the clearances while keeping the sealed state. 
   As a result, the seal ring  1   b  can keep its sealing properties stably against the surrounding temperature change. 
   In order to satisfy the needs for reducing the friction of the sliding rotations, moreover, the seal ring  1   b  according to this embodiment is provided throughout its circumference with a relief (e.g., a depression, a notch or a lighting portion)  5   b  for reducing the pressure receiving area of the sliding face of the annular groove  71  against the side wall face  72 . 
   Thus, the seal ring  1   b  according to this embodiment contemplates to reduce the friction of the sliding rotations by reducing the pressure receiving area. 
   In this embodiment, moreover, a tapered face  51   b  is formed at the position having the depression  24   b.    
   On the other hand, the end edge of the separating ace  25   b  is aligned to the outer circumference end edge of the tapered face  51   b.    
   This construction forms such a continuous annular sealing portion with the end edge of a boundary  52   b  between the relief  5   b  and the second sealing face  4   b  and the end edge of the separating face  25   b  as to seal the side wall face  72  of the annular groove  71 . 
   In case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b  are made substantially equal to each other by the construction thus far described, the substantial entirety of the second sealing face  4   b  makes sliding contact with the side wall face  72  so that the construction sufficiently exhibits the sealing properties. 
   In the separate portion  2   b , moreover, the end edge of the separating face  25   b  forms the sealing portion which can also prevent the leak of the sealing fluid from the clearance  27   b  or the clearance  29   b.    
   In case the annular groove  71  is formed into such a shape due to shortage of the working precision as is narrowed toward the groove bottom, on the other hand, a deviation arises between the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b , as shown in  FIG. 9  or  FIG. 10 . 
   In this case, this embodiment is provided with the relief  5   b  and the tapered face  51   b  so that the end edge of the boundary  52   b  between the relief  5   b  and the second sealing face  4   b  and the end edge of the separating face  25   b  form the continuous annular sealing portion for sealing the side wall face  72  of the annular groove  71 . 
   Here, the depth of the aforementioned relief  5   b  and the tapering angle of the tapered face  51   b  have to be set so that the annular sealing portion may sufficiently function as the sealing portion. In short, these depth and angle have to be set by considering the relation to the angle (i.e., the angle which can be conceived in consideration of errors or the like) of the side wall face  72  of the annular groove  71 . 
   More specifically, the depth of the relief  5   b  and the tapering angle of the tapered face  51   b  have to be set so that the end edge of the seal ring  1   b  on the inner circumference side may not abut against the side wall face  72  of the annular groove  71 . 
   Thus in this embodiment, independently of whether the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b  are equal or different, the end edge of the boundary  52   b  between relief  5   b  and the second sealing face  4   b  and the end edge of the separating face  25   b  form the continuous annular sealing portion for sealing the side wall face  72  of the annular groove  71 . 
   As a result, the sealing portion is formed without any interruption throughout the whole circumference. Independently of whether the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b  are equal or different, therefore, it is possible to prevent the sealing fluid from leaking from the clearance  27   b  or the clearance  29   b.    
   Moreover, the sealing properties are excellent because no portion is unstable in the sealing properties. 
   By the seal ring  1   b  according to the embodiment of the invention thus far described, the leakage can be reduced together with the friction of the sliding rotations. 
   Even in case the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b  deviate from each other, moreover, it is possible to reduce the leakage as much as possible. 
   As a result, the working precision of the annular groove can be relaxed to lead to the reduction in the cost. 
   By intentionally deviating the slope of the side wall face  72  of the annular groove  71  and the slope of the second sealing face  4   b , moreover, the sealing portion can be made of not a facial contact but a substantially linear contact thereby to reduce the friction of the sliding rotations. 
   INDUSTRIAL APPLICABILITY 
   According to the invention, as has been described hereinbefore, the leakage can be reduced together with the friction of the sliding rotations.