Patent Publication Number: US-2019178382-A1

Title: Seal ring

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/JP2017/017978, filed May 12, 2017 (now WO 2017/195882A1), which claims priority to Japanese Application No. 2016-097005, filed May 13, 2016. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a seal ring configured to seal an annular gap between a shaft and a shaft hole in a housing. 
     BACKGROUND 
     An automatic transmission (AT) or a continuously variable transmission (CVT) of automobiles has a seal ring to seal an annular gap between a shaft and a housing which relatively rotates so as to maintain the hydraulic pressure. A known seal ring will be described with reference to  FIGS. 13 and 14 .  FIG. 13  is a schematic cross-sectional view of the known seal ring in a state when the hydraulic pressure is not maintained.  FIG. 14  is a schematic cross-sectional view of the known seal ring in a state when the hydraulic pressure is maintained. The known seal ring  500  is installed in an annular groove  310  disposed in an outer periphery of a shaft  300  and is slidably in contact with an inner peripheral surface of a shaft hole in a housing  400  through which the shaft  300  is inserted and a side wall surface of the annular groove  310 , respectively, whereby the annular gap between the shaft  300  and the shaft hole in the housing  400  is sealed. 
     The sliding torque of the seal ring  500  used for the above mentioned purpose is to be considerably lowered. An outer peripheral surface of the seal ring  500  is therefore configured to have a shorter perimeter as compared to the inner peripheral surface of the shaft hole of the housing  400 , so that interference is not generated. The diameter of the seal ring  500  increases in a state when the engine of the automobile is started and hydraulic pressure is high due to the hydraulic pressure, and the seal ring  500  is in contact with the inner peripheral surface of the shaft hole and the side wall surface of the annular groove  310 , and sufficiently exhibits the function to maintain the hydraulic pressure (see  FIG. 14 ). On the other hand, the seal ring  500  is out of contact with the inner peripheral surface of the shaft hole and the side wall surface of the annular groove  310  in a state when the engine is stopping and the hydraulic pressure is not applied to the seal ring  500  (see  FIG. 13 ). 
     The seal ring  500  configured as described above does not exhibit the sealing function in a state when the hydraulic pressure is not applied. Hence the oil having been sealed by the seal ring  500  becomes unsealed in a state with no load when, for example, a hydraulic pressure pump is stopped in an idle stopping state in such a configuration as in AT and CVT where a shift transmission is controlled using oil compressed and fed by the hydraulic pressure pump, and then the oil returns to the oil pan and no longer exists around the seal ring  500 . If the engine starts (restarts) in such state with no oil around the seal ring  500 , degradation of a response and operation property of the engine may occur due to lack of lubrication. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent Application Publication No. 2009-257439 
     SUMMARY 
     Technical Problem 
     One or more aspects of the present disclosure is to provide a seal ring that can perform a sealing function even in a state where a fluid pressure is low. 
     Solution to Problem 
     In response to the above issue, the present disclosure uses the following means. 
     The present disclosure provides a seal ring installed in an annular groove on an outer periphery of a shaft and configured to seal an annular gap between the shaft and a housing which rotate relative to each other to maintain a fluid pressure in a sealed region where the fluid pressure changes, the seal ring including: a seal ring main body made of resin; and an auxiliary seal ring made of rubbery elastic material and disposed on an outer peripheral surface of the seal ring main body at a position with the largest diameter, wherein, when the fluid pressure is not applied, the outer diameter of the auxiliary seal ring is larger than the inner diameter of an inner peripheral surface of a shaft hole of the housing through which the shaft is inserted. 
     The seal ring according to the present disclosure is configured so that, when the fluid pressure is not applied, the outer diameter of the auxiliary seal ring is larger than the inner diameter of the inner peripheral surface of the shaft hole in the housing through which the shaft is inserted. This allows the auxiliary seal ring to keep in close contact with the inner peripheral surface of the shaft hole regardless of whether the fluid pressure is being applied or not. This prevents the seal ring from moving in an axial direction upon changing from a state where the fluid pressure is applied to a state where the fluid pressure is not applied. Hence the sealing function is exhibited even in a state where little or no fluid pressure is applied (a state with little or no differential pressure). Thus, the fluid pressure can be maintained upon increasing of the fluid pressure in the sealed region. 
     Advantageous Effects of the Disclosure 
     As described above, according to the present disclosure, the sealing function can be exhibited even in a state where the fluid pressure is low. 
    
    
     
       DRAWINGS 
         FIG. 1  is a side view of a seal ring according to Example 1. 
         FIG. 2  is an enlarged view of a part of the side view of the seal ring according to Example 1. 
         FIG. 3  is an enlarged view of a part of the side view of the seal ring according to Example 1. 
         FIG. 4  is an enlarged view of a part of the seal ring according to Example 1 when viewed from the outer peripheral surface side. 
         FIG. 5  is an enlarged view of a part of the seal ring according to Example 1 when viewed from the inner peripheral surface side. 
         FIG. 6  is a schematic cross-sectional view depicting a state of using the seal ring according to Example 1. 
         FIG. 7  is a schematic cross-sectional view depicting a state of using the seal ring according to Example 1. 
         FIG. 8  is a schematic cross-sectional view depicting Modification  1  of the auxiliary seal ring of the seal ring according to Example 1. 
         FIG. 9  is a schematic cross-sectional view depicting Modification  2  of the auxiliary seal ring of the seal ring according to Example 1. 
         FIG. 10  is a schematic cross-sectional view depicting Modification  3  of the auxiliary seal ring of the seal ring according to Example 1. 
         FIG. 11  is a schematic cross-sectional view depicting Modification  4  of the auxiliary seal ring of the seal ring according to Example 1. 
         FIG. 12  is a schematic cross-sectional view depicting Modification  5  of the auxiliary seal ring of the seal ring according to Example 1. 
         FIG. 13  is a schematic cross-sectional view depicting a state of using a known seal ring. 
         FIG. 14  is a schematic cross-sectional view depicting a state of using a known seal ring. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present disclosure will be described in detail with reference to the drawings using the following example. The dimensions, materials, shapes and relative positions of the components described in the example are not intended to limit the scope of the disclosure unless otherwise specified. A seal ring according to Example 1 is used for maintaining hydraulic pressure in a transmission, as in AT and CVT, of an automobile, and seals the annular gap between a shaft and a housing which rotate relative to each other. When differential pressure is generated between both sides of the seal ring, a side where pressure is higher will be referred to as “high pressure side” a side where pressure is lower will be referred to as “low pressure side” in the following description. 
     Example 
     A seal ring according to Example 1 will be described with reference to  FIGS. 1 to 7 .  FIG. 1  is a side view (schematic side view) of the seal ring according to Example 1.  FIG. 2  is an enlarged view of the side view of the seal ring according to Example 1 at a part indicated by a circle in  FIG. 1 .  FIG. 3  is an enlarged view of the side view of the seal ring according to Example 1 at the part indicated by the circle in  FIG. 1  when viewed from the opposite side.  FIG. 4  is an enlarged view depicting the seal ring according to Example 1 at the part indicated by the circle in  FIG. 1  when viewed from an outer peripheral surface side of the seal ring.  FIG. 5  is an enlarged view depicting the seal ring according to Example 1 at the part indicated by the circle in  FIG. 1  when viewed from an inner peripheral surface side of the seal ring.  FIGS. 6 and 7  are schematic cross-sectional views by A-A section indicated in  FIG. 1  depicting a sealing structure (state of using the seal ring) according to Example 1.  FIG. 6  depicts the sealing structure in a state at no load, and  FIG. 7  depicts the sealing structure in a state where differential pressure is generated. 
     &lt;Sealing Structure and Configuration of Seal Ring&gt; 
     The sealing structure and the configuration of the seal ring according to Example 1 will be described with reference to, in particular,  FIGS. 1, 6 and 7 . The sealing structure according to Example 1 includes a shaft  300  and a housing  400  which rotate relative to each other, and a seal ring  10  which seals an annular gap between the shaft  300  and the housing  400 , that is, between the shaft  300  and the inner peripheral surface of a shaft hole in the housing  400  through which the shaft  300  is inserted. The seal ring  10  according to Example 1 is installed in an annular groove  310  disposed on the outer periphery of the shaft  300 , and seals the annular gap between the shaft  300  and the housing  400  which rotate relative to each other. Thereby the seal ring  10  maintains the fluid pressure in the sealed region where the fluid pressure (hydraulic pressure in Example 1) changes. Example 1 assumes that the fluid pressure in the right side region in  FIGS. 6 and 7  changes, and the seal ring  10  maintains the fluid pressure in the sealed region on the right side in  FIGS. 6 and 7 . When the engine of the automobile is stopping, the fluid pressure in the sealed region is low and in a state at no load, but when the engine starts, the fluid pressure in the sealed region becomes high. 
     The seal ring  10  according to Example 1 includes a seal ring main body  100  made of resin and an auxiliary seal ring  200  made of rubbery elastic material disposed on the outer peripheral surface of the seal ring main body  100 . Such materials as polyether ether ketone (PEEK), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE) may be used for the seal ring main body  100  and acrylic rubber (ACM), fluoro rubber (FKM), and hydrogenated nitrile butadiene rubber (HNBR) may be used for the auxiliary seal ring  200 . 
     The auxiliary seal ring  200  of the seal ring  10  according to Example 1 is configured to have a larger outer diameter as compared to the inner diameter of the inner peripheral surface of the shaft hole in the housing  400 , when the external force (fluid pressure) is not being applied. 
     &lt;Seal Ring Main Body&gt; 
     The seal ring main body  100  of Example 1 will be described in detail. The seal ring main body  100  has a joining portion  110  disposed at one location in the circumferential direction. This configuration of the joining portion  110  in the seal ring main body  100  may be described in such a way that a joining portion is formed in an annular member having a rectangle cross-section. This description, however, only gives an expression on the shape of the joining portion  110  and is not intended to limit the forming process of the joining portion to processing an annular member having a rectangle cross-section. That is, the joining portion  110  may be formed by molding annular member having a rectangle cross-section and then cutting it, or by molding an annular member having a joining portion if an appropriate resin material is used. The manufacturing method of the seal ring main body is not limited. 
     The joining portion  110  is formed by a so-called special step cut having joining surfaces (cut surfaces), which give a step-like appearance when viewed even from the outer peripheral surface side and both side wall surface sides. Specifically, the seal ring main body  100  has, on one side with respect to the joining surfaces, a first fitting convex  111 X and a first fitting concave  112 X, and, on the other side with respect to the joining surfaces and on the outer periphery side, a second fitting concave  112 Y, into which the first fitting convex  111 X is fitted, and a second fitting convex  111 Y, which is fitted into the first fitting concave  112 X. The end face  113 X on the one side with respect to the joining surface and on the inner peripheral surface side faces the end face  113 Y on the other side with respect to the joining surface and on the inner peripheral surface side. The special step cut allows the seal ring to stably maintain air tightness even if the perimeter of the seal ring main body  100  changes due to thermal expansion or thermal contraction. The joining surfaces (cut surfaces) may be formed not only by cutting but also by molding. The special step cut is a known technology, hence the details thereof are omitted. 
     &lt;Auxiliary Seal Ring&gt; 
     The auxiliary seal ring  200  according to Example 1 will be described in detail. The auxiliary seal ring  200  is disposed on the outer peripheral surface of the seal ring main body  100  at a position with the largest diameter. The outer peripheral surface of the seal ring main body  100  has a cylindrical surface. “The auxiliary seal ring  200  is disposed on the outer peripheral surface of the seal ring main body  100  at a position with the largest” implies that the auxiliary seal ring  200  is formed on the seal ring main body  100  not by being inserted in a groove formed on the outer peripheral surface of the seal ring main body  100 , but by being fixed using adhesion, monolithic molding or the like. Nevertheless, the auxiliary seal ring  200  may be disposed on the outer peripheral surface of the seal ring main body  100  by insertion on the condition that the auxiliary seal ring  200  can be fixed to the seal ring main body  100  with adequate positioning accuracy. The auxiliary seal ring  200  is disposed at two locations on both sides with respect to the central surface of the seal ring main body  100  in the width direction (see  FIGS. 4, 6 and 7 ). Each auxiliary seal ring  200  is disposed along the entire periphery of the outer peripheral surface of the seal ring main body  100 , except for the joining portion  110  (see  FIG. 4 ). The auxiliary seal ring  200  has a triangle shaped cross-section when sectioned by a plane including the central axis of the shaft  300  (see  FIGS. 6 and 7 ). 
     &lt;Mechanism when Seal Ring is in Use&gt; 
     The mechanism when the seal ring  10  according to Example 1 is in use will be described with reference to  FIGS. 6 and 7 .  FIG. 6  shows the sealing structure in a state at no load and with little or no differential pressure between the left and right region with respect to the seal ring  10  when the engine has stopped.  FIG. 6  shows a cross-sectional view of the seal ring  10  by A-A section indicated in  FIG. 1 .  FIG. 7  shows the sealing structure in a state where the fluid pressure in the right region is higher than that in the left region with respect to the seal ring  10  when the engine has started.  FIG. 7  shows a cross-sectional view of the seal ring  10  by A-A section indicated in  FIG. 1 . 
     As described above, the outer diameter of the auxiliary seal ring  200  is set larger than the inner diameter of the inner peripheral surface of the shaft hole in the housing  400  when the fluid pressure is not applied to the seal ring  10  of Example 1. This enables the outer peripheral surface of the seal ring  10  (more specifically, the outer peripheral surface of the auxiliary seal ring  200 ) to keep in contact with the inner peripheral surface of the shaft hole of the housing  400  even when in the state at no load and with no differential pressure between the left and right regions (see  FIG. 6 ). 
     When the engine starts and differential pressure is generated, the seal ring  10  comes in contact with the side wall surface of the annular groove  310  on the lower pressure side (L) due to the fluid pressure from the higher pressure side (H). The seal ring  10  keeps in contact with the inner peripheral surface of the shaft hole in the housing  400 . Thus the side face of the seal ring main body  100  and the side wall surface of the annular groove  310  keep in contact and sliding on with each other while the shaft  300  and the housing  400  rotate relative to each other. The frictional force between the auxiliary seal ring  200  made of rubbery elastic material and the inner peripheral surface of the shaft hole of the housing  400  is set high so as to prevent sliding. Hence the sliding abrasion of the auxiliary seal ring  200  can be prevented. Thereby the annular gap between the shaft  300  and the housing  400  is sealed. When the engine stops and no load is applied thereafter, the outer peripheral surface of the seal ring  10  is in contact with the inner peripheral surface of the shaft hole of the housing  400 , and the seal ring  10  hardly moves in the axial direction of the shaft  300 . Thus, the seal ring  10  keeps in contact with the side wall surface of the annular groove  310  on the lower pressure side (L). This enables the annular gap between the shaft  300  and the housing  400  to be kept sealed even in a state at no load. 
     &lt;Advantages of Seal Ring of Example 1&gt; 
     The auxiliary seal ring  200  of the seal ring  10  according to Example 1 is configured to have a larger outer diameter as compared to the inner diameter of the inner peripheral surface of the shaft hole in the housing  400 , when the fluid pressure is not being applied. This allows the auxiliary seal ring  200  to keep in close contact with the inner peripheral surface of the shaft hole regardless of whether the fluid pressure is being applied or not. This prevents the seal ring  10  from moving in an axial direction upon changing from a state where the fluid pressure is applied to a state where the fluid pressure is not applied. Hence the sealing function is exhibited even in a state where little or no fluid pressure is applied (a state with little or no differential pressure). Thus, the fluid pressure can be maintained upon increasing of the fluid pressure in the sealed region. 
     Specifically in an engine having an idling stop function, the hydraulic pressure can be maintained upon beginning of increase in the hydraulic pressure in the sealed region when the engine having been in a stopped state restarts in response to pressing of an accelerator. A known seal ring made of resin may have function to prevent the leakage of fluid to some extent. The seal ring  10  of Example 1, by contrast, can sufficiently prevent the leakage of fluid because the annular gap between the shaft  300  and the housing  400  is continuously sealed even in a state at no load. This allows the differential pressure across the seal ring  10  to be maintained for a certain time after the engine stops and pumping action ceases. This means that the differential pressure of the engine having the idling stop function can be sufficiently maintained especially if duration of the state where the engine stops is not too long and the fluid pressure can be sufficiently maintained upon restarting of the engine. 
     The seal ring  10  according to Example 1 has a symmetric shape with respect to the central surface in the width direction. This allows the seal ring  10  to be installed in the annular groove  310  regardless of installation direction, thus installation is very easy. Further, the seal ring  10  can be used even in a configuration where the higher pressure side and the lower pressure side switch. 
     (Other) 
     Although the cross-sectional shape of the auxiliary seal ring  200  in Example 1 is a triangle, the shape of the auxiliary seal ring according to the present disclosure is not limited to this example and may have various configurations. For example, as illustrated in Modification  1  in  FIG. 8 , an auxiliary seal ring  210  may have an approximate triangle shaped cross-section with an inclined line curved. Further, as illustrated in Modification  2  in  FIG. 9 , an auxiliary seal ring  220  may have a semicircle shaped cross-section. Further, as illustrated in Modification  3  in  FIG. 10 , an auxiliary seal ring  230  may have a trapezoid shaped cross-section. Furthermore, as illustrated in Modification  4  in  FIG. 11 , an auxiliary seal ring  240  may have a rectangle shaped cross-section. 
     Although the auxiliary seal ring  200  in Example 1 is disposed at two locations on both sides with respect to the central surface of the seal ring main body  100  in the width direction, the positions and a number of auxiliary seal rings according to the present disclosure are not limited to this. For example, as illustrated in Modification  5  in  FIG. 12 , an auxiliary seal ring  250  may have a rectangle shaped cross-section and be disposed so as to cover the entire outer peripheral surface of the seal ring main body  100 . 
     Although the cross-sectional shape of the seal ring main body  100  in Example 1 is a rectangle, the shape of the seal ring main body according to this disclosure is not limited to this, but may have various shapes. For example, the seal main body may be formed by providing an annular cutting having a rectangle shaped cross-section on both side faces of an annular member having a rectangle shaped cross-section. The annular cutting on the side faces may be disposed on the inner peripheral surface side or on the outer peripheral surface side. In either case, the seal ring main body has a T-shaped cross-section. The seal ring main body may be an annular member having a rectangle cross-section with a dynamic pressure generating groove disposed on both side faces of the annular member. 
     Although the joining portion  110  in Example 1 is formed by the special step cut, various known techniques may be used for forming the joining portion. For example, a straight cut, a bias cut, a step cut and the like can be used. Since these are known techniques, a detailed description thereof is omitted. The straight cut is a structure where the annular member is cut linearly in the radial direction. The bias cut is a structure where the annular member is cut diagonally with respect to the radial direction. The step cut is a structure where the annular member is cut stepwise when viewed even from the outer peripheral surface and the inner peripheral surface, and is cut linearly when viewed from both side faces, or a structure where the annular member is cut stepwise when viewed from both side faces, and is cut linearly when viewed from the outer peripheral surface and the inner peripheral surface. The cutting structure may be formed by cutting or by molding. An endless seal ring without a joining portion may be used. 
     REFERENCE SIGNS LIST 
     
         
           10  Seal ring 
           100  Seal ring main body 
           110  Joining portion 
           111 X Fitting convex 
           111 Y Fitting convex 
           112 X Fitting concave 
           112 Y Fitting concave 
           113 X End face 
           113 Y End face 
           200 ,  210 ,  220 ,  230 ,  240 ,  250  Auxiliary seal ring 
           300  Shaft 
           310  Annular groove 
           400  Housing