Abstract:
To reduce a shaft insertion load and prevent extrusion of a seal ring to the low pressure side, a sealing device has a seal ring in an installation groove formed on a shaft to have a tapered groove bottom section and a backup ring having a tapered section corresponding to the tapered groove bottom section, a gap is provided between a side wall surface at the low-pressure side of the mounting groove and a side end surface of the backup ring, a peripheral surface of the backup ring at the opposite side of the tapered section has a tapered surface which comes closer to a peripheral surface of a housing at the low-pressure side, and the tapered section is formed to have a two-staged taper.

Description:
This is a national stage of the International Application No. PCT/JP2006/322438 filed Nov. 10, 2006 and published in Japanese. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sealing device and, more particularly, a sealing device including a seal ring and a backup ring in a mounting groove to gasoline fuel, oil, water or the like of high-pressure fluid. 
     2. Description of the Conventional Art 
     A conventional sealing device includes a seal ring such as an O-ring made of a rubber-like elastic body and a back up ring made of a resin or the like and positioned at a low pressure side of the seal ring in a mounting groove having a tapered groove bottom inclined in such the direction that a distance between the tapered groove bottom and a housing expands from a side end surface at a low pressure side provided on the shaft toward a high pressure side, to seal a part between a shaft hole formed at the housing and a shaft. In the conventional sealing device, when pressure of fluid is applied from the high-pressure side, the backup ring is pressed toward the low pressure side from the high pressure side through the seal ring. The backup ring has an inner peripheral surface formed with a tapered part, which corresponds to the tapered groove bottom of the mounting groove and is inclined in the same direction as that of the groove bottom. Further, the back up ring has an outer peripheral surface formed with a parallel surface which is parallel to an inner peripheral surface of the housing. When the inner peripheral surface of the backup ring contacts the tapered groove bottom of the mounting groove by pressure from the high pressure side, the outer peripheral surface of the backup ring tightly contacts to the inner peripheral surface of the housing by radial directional component force. Accordingly, a gap between the backup ring and the inner peripheral surface of the housing is closed so as to prevent protruding of the seal ring toward the low pressure side. 
     According to such the constitution, there is no problem when the sealing device is subjected to a general fluid pressure or an eccentricity of the shaft is small. However, when the device is subjected to high-pressure fluid or has an eccentricity of the shaft is large, a gap may be generated between an outer peripheral surface of a backup ring and an inner peripheral surface of a housing so as to protrude a seal ring toward a low pressure side. Therefore, Japanese Patent Application Laid Open No. 11-315925 proposes a device in which a gap g is provided between a side end surface  101   a  at a low pressure side L of a backup ring  101  and a side wall surface  102   a  at a low pressure side L of a mounting groove  102 , as illustrated in  FIG. 12 . 
     Accordingly, when the device is subjected to high-pressure fluid, the backup ring  101  moves to the low pressure side L so as to generate radial directional component force. The radial directional component force reduces a gap between a tapered part of the backup ring  101  and the mounting groove  102  and a gap between an outer peripheral surface of the backup ring  101  and a housing  104 . Further, in order to obtain an effect to reduce a gap, a technique that an outer diameter of a backup ring  101  is set to be equal to or larger than an inner diameter of a housing  104  so as to fit those has been considered. 
     However, as illustrated in  FIG. 13 , when an outer diameter of a backup ring  101  is set to be equal to or larger than an inner diameter of a housing  104 , a side end surface  101   b  at a high pressure side H of the backup ring  101  contacts to a top end part  104 A of a housing  104  at the time of inserting a shaft into the housing  104 , so that a shaft insertion load increases. Further, since the shaft is inserted while the top end part  104 A is contacted with the side end surface  101   b , the backup ring  101  may be inclined and mounted in the state that inner and outer peripheral surfaces are not correctly in tight contact with opposite members. When being mounted in the above-described state, the backup ring  101  cannot realize the function of preventing protrusion of a seal ring  105 , and the seal ring  105  is protruded toward a low pressure side when being subjected to high-pressure fluid, so that a device may be damaged. Therefore, when the shaft is inserted while the top end part  104 A is contacted with the side end surface  101   b , a device cannot realize a seal function. 
     SUMMARY OF THE INVENTION 
     Problems to be solved by the Invention 
     The present invention solves the above-described problems, and an objective of the present invention is to provide a sealing device capable of reducing a shaft insertion load and ensuring the function of preventing protrusion of a seal ring toward a low pressure side even when being subjected to high-pressure fluid. 
     Means for Solving the Problems 
     In order to obtain the above-described objectives, according to a first aspect of the present invention a sealing device, which is to seal a part between two members coaxially assembled, includes a seal ring made of a rubber-like elastic body and mounted in an annular mounting groove provided at one of the two members; a backup ring provided at a low pressure side in a width direction beyond the seal ring; a tapered part provided on a peripheral surface at a groove bottom side of the backup ring so as to incline in such direction that a distance between the peripheral surface of the backup ring and a peripheral surface of the other member is gradually reduced toward a low pressure side; a tapered groove bottom part provided on a groove bottom surface of the mounting groove so as to correspond to the tapered part of the backup ring; and a gap provided at a low pressure side of the backup ring in the mounting groove when a pressure is applied from a high pressure side, wherein the device further includes a tapered surface provided on a peripheral surface at the side opposite to the tapered part of the backup ring so as to approach a peripheral surface of the other member toward a low pressure side from a side end surface at a high pressure side. 
     Further, according to a second aspect of the present invention, the sealing device recited in the first aspect includes a tapered part of the backup ring which has a two-stage taper formed with a high pressure side tapered part and a low pressure side tapered part having a larger inclination angle than that of the high pressure side tapered part. 
     Effectiveness of the Invention 
     The present invention has the following effects. 
     A sealing device according to the first aspect of the present invention includes a tapered surface provided on a peripheral surface at the side opposite to the tapered part of the backup ring so as to approach a peripheral surface of the other member toward a low pressure side from a side end surface at a high pressure side. Thus, when one member is inserted, the other member is guided by the tapered surface without contacting to a side end surface at a high pressure side of the backup ring, so that the member can be accurately inserted while an insertion load being reduced. As a result of this, it can be prevented to decrease seal property due to faulty mounting of the backup ring. Further, when the device is subjected to high-pressure fluid, radial directional component force generated by moving of the backup ring in an axial direction is applied due to a gap being provided. The radial directional component force generates large compression force to eliminate a radial directional gap with the other member, where the gap is created due to the tapered surface being provided. That is, when a pressure is applied from a high pressure side, an outer peripheral surface and inner peripheral surface of the backup ring contact to respective opposite surfaces. However, since the gap is provided between a side wall surface at a low pressure side of the mounting groove and a side end surface at a low pressure side of the backup ring, the backup ring can move to a low pressure side as a high pressure being further applied thereafter. Accordingly, radial directional component force is generated so as to press further the outer surface and inner surface which have already contacted to the respective opposite surfaces. Therefore, the device has the function of preventing protrusion of a seal ring as in a conventional technique. 
     In addition, a sealing device according to the second aspect of the present invention has the tapered part of the backup ring formed in a two-stage tapered shape having a high pressure side tapered part and a low pressure side tapered part. The low pressure side tapered part has a larger inclination angle than that of the high pressure side tapered part. Thus, when the other member is guided by a tapered surface so as to be inserted, reaction force in the radially inside direction of the backup ring is reduced, so that an insertion load can be more reduced. 
     Since a backup ring is to prevent protrusion of a seal ring, a gap is not conventionally provided between a backup ring and a housing. Thus, a technique like the present application to positively change a shape of the device by providing a tapered surface so as to create a gap can not have been considered. However, in the present application, owing to a synergistic effect of high-pressure fluid and the gap at a shaft directional low pressure side, the gap becomes as small as possible when the device is subjected to high-pressure fluid, even though a tapered surface is provided, so that it becomes possible to keep “the function of preventing protrusion of a seal ring”. 
    
    
     
       BRIEF EXPLANATION OF DRAWINGS 
         FIG. 1  is a structural explanation view of a sealing device according to embodiment 1 of the present invention, 
         FIG. 2  is an explanation view to illustrate a size of a backup ring part in  FIG. 1 , 
         FIG. 3  is an explanation view to illustrate a state in which a pressure is applied while the device of embodiment 1 is mounted, 
         FIG. 4  is an explanation view to illustrate a state in which a pressure is applied while the device of embodiment 1 is mounted, 
         FIG. 5  is a structural explanation view of a sealing device according to embodiment 2 of the present invention, 
         FIG. 6  is a structural explanation view of a sealing device according to embodiment 3 of the present invention, 
         FIG. 7  is a structural explanation view of a sealing device according to embodiment 4 of the present invention, 
         FIG. 8  is an explanation view to illustrate a state at the time of inserting a shaft in embodiment 4, 
         FIG. 9  is an explanation view to illustrate a state at the time of inserting a shaft in embodiment 4, 
         FIG. 10  is an explanation view to illustrate a state in which a pressure is applied while the device of embodiment 4 is mounted, 
         FIG. 11  is an explanation view to illustrate a state in which a pressure is applied while the device of embodiment 4 is mounted, 
         FIG. 12  is a structural explanation view of a sealing device according to a conventional example, and 
         FIG. 13  is an explanation view to illustrate a state in which a conventional example has a problem. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to drawings. However, the present invention is not limited to the contents described in the embodiments if there is no limitative description. 
       FIG. 1  is a cross sectional view of main parts of a sealing device according to embodiment 1 of the present invention. This sealing device is mounted in an annular space between a shaft hole provided at a housing and a shaft inserted into an inner periphery of the shaft hole. 
     The sealing device  1  includes a seal ring  20  mounted in a mounting groove  10  provided on an outer peripheral surface of shaft  2 , and a backup ring  30 . 
     The mounting groove  10  includes a tapered groove bottom part  12  inclined in such the direction that a distance between the tapered groove bottom part  12  and an inner peripheral surface  3   a  of a housing  3  expands from a side wall surface  11  at a low pressure side L toward a high pressure side H, and a parallel bottom surface  13  which is in parallel to an inner peripheral surface  3   a  of the housing  3  from an end part at a high pressure side H of the tapered groove bottom part  12  toward a high pressure side H. 
     A seal ring  20  is formed with a rubber-like elastic body, and is an O-ring having an approximately circular cross section in a free state. When the seal ring  20  is mounted in a mounting groove  10 , the seal ring  20  is compressed in a radial direction by the inner peripheral surface  3   a  of the housing  3  and the parallel bottom surface  13  of the mounting groove  10  so as to be in an ellipse shape, and the high pressure side H and the low pressure side L are separated by reaction force of the compressed seal ring  20 . 
     A backup ring  30  is made of a resin such as PTFE, or nylon or a compound material of these resins, and is in a cylindrical shape. Side end surfaces  31  and  32  are formed as surfaces which rectangularly cross the inner peripheral surface  3   a  of the housing  3  at both the high pressure side H and the low pressure side L. A predetermined gap g is provided between a low pressure side end surface  32  and a side wall surface  11  at the low pressure side L of the mounting groove  10 . The size in a radial direction of the low pressure side end surface  32  of the backup ring  30  is set to be larger than a distance from the tapered groove bottom part  12  at the side wall surface  11  at the low pressure side L of the mounting groove  10  to the inner peripheral surface  3   a  of the housing  3 . 
     Further, an inner peripheral surface  33  of the backup ring  30  is formed with a tapered part  35 , which opposites to the tapered groove bottom part  12  of the mounting groove  10 , has an approximately same inclination angle as that of the tapered groove bottom part  12 , and inclines in the same direction. An outer peripheral surface  34  includes tapered surface  36 , which opposites to the inner peripheral surface  3   a  of the housing  3  and approaches the inner peripheral surface  3   a  of the housing  3  from the high pressure side end surface  31  toward the low pressure side L, and a parallel surface  37  which is in parallel to the inner peripheral surface  3   a  of the housing  3  from an end part at the low pressure side L of the tapered surface  36  toward the low pressure side L. 
     As illustrated in  FIG. 2 , it is proper that the tapered surface  36  has a shape represented by the following formulas, where an inner diameter of the housing  3  is φD, an outer diameter of the backup ring  30  is φd1, and an outer diameter of an angle part at a high pressure side of the tapered surface  36  of the backup ring  30  is φd2.
 
0 ≦φd 1 −φD  and 0 &lt;φD−φd 2≦0.6
 
Preferably,
 
0 ≦φd 1 −φD≦ 0.3 and 0 &lt;φD−φd 2≦0.6
 
In addition, when a backup ring is otherwise mounted in a mounting groove provided at a housing, not like the embodiment of the present invention, the tapered surface  36  has a shape represented by the formula “Inner diameter of a backup ring≦Outer diameter of a shaft”. Further, the inclination angle θ of the tapered surface is properly within the following range from viewpoints of insertability.
 
5≦θ≦30°
 
     In the above-described structure, when a shaft  2  is inserted into the housing  3 , a top end part  3 A of the housing  3  contacts to the backup ring  30 . However, since the backup ring  30  includes the tapered surface  36 , the top end part  3 A is guided by the tapered surface  36  without contacting to the high pressure side end surface  31  of the backup ring  30 . Thus, the shaft  2  can be accurately inserted while an insertion load being reduced. 
     Further, since the top end part  3 A of the housing  3  does not contact to the high pressure side end surface  31 , it can be prevented to decrease sealing property by faulty setting of the backup ring  30 . 
     Furthermore, when the device is subjected to low-temperature and low-pressure fluid (25° C.×5 MPa) from the high pressure side H toward the low pressure side L, a radial directional gap  41  between the backup ring  30  and the housing  3  remains as illustrated in  FIG. 3 . However, since the fluid has a low pressure, the seal ring  20  is not protruded to a low pressure side L, and thus the seal ring  20  is not damaged. Further, when the device is subjected to high-temperature and high-pressure fluid (80° C.×15 MPa) radial directional component force generated by moving of the backup ring  30  in the axial direction is applied since the gap g is provided between a low pressure side end surface  32  of the backup ring  30  and the side wall surface  11  at the low pressure side L of the mounting groove  10 . This radial directional component force generates as large compression force as to eliminate a radial directional gap  41  between the backup ring  30  and the housing  3 , which is created due to providing of the tapered surface  36 , as illustrated in  FIG. 4 . Therefore, protrusion of the seal ring  20  to the low pressure side L, and deterioration of sealing property caused due to damage of the seal ring  20  can be prevented. 
     An insertion load of embodiment 1 was measured to compare with that of a conventional product. As a result of this, the load was a 5 to 10% level with respect to the conventional product, so that the load could be reduced by 90% or more comparing with the conventional product. Further, the device is subjected to high-pressure fluid under the conditions of (1) 5 MPa at an ordinary temperature and (2) 15 MPa at 80° C. after insertion of the shaft. As a result of this, it could be confirmed that the device could keep the function to prevent protrusion of an O-ring under the both conditions. 
     In addition, this embodiment 1 discloses a case that the tapered surface  36  is formed at a part of the outer peripheral surface  34  of the backup ring  30 . However, as illustrated in embodiment 2 of  FIG. 5 , the tapered surface  36  can be formed on the whole surface of an outer peripheral surface  34 . 
     Further, the tapered surface  36  can be not only an inclined plane surface but also an inclined curved surface as illustrated in embodiment 3 of  FIG. 6 . Of course, the inclined curved surface can be formed at a part of the outer peripheral surface  34  although this case is not illustrated. 
     Furthermore, in embodiment 4 illustrated in  FIG. 7 , an inner peripheral surface  33  of the backup ring  30  is formed as a two-stage tapered part with a high pressure side tapered part  35   a  having an inclination angle α which is approximately equal to an inclination angle of the tapered groove bottom part  12  of the mounting groove  10 , and a low pressure side tapered part  35   b  having an inclination angle β which is larger than the inclination angle α of the high pressure side tapered part  35   a.    
     Therefore, in this embodiment 4, when the shaft  2  is inserted, the high pressure side tapered part  35   a  contacts to the tapered groove bottom part  12  as illustrated in  FIG. 8 , and thus a top end part  3 A of a housing  3  is guided by a tapered surface  36  having the inclination angle α so as to move to the low pressure side L. As illustrated in  FIG. 9 , when the top end part  3 A moves from a position shown with a broken line to a position shown with a solid line toward a low pressure side in an arrow m direction so as to increase an insertion load, the backup ring  30  is deformed so as to escape from the insertion load since a clearance  42  is exists between the low pressure side tapered part  35   b  and the tapered groove bottom part  12 . That is, the backup ring  30  is deformed from a shape shown with a broken line to a shape shown with a solid line in  FIG. 9 . As a result of this, since the low pressure side tapered part  35   b  contacts to the tapered groove bottom part  12 , the top end part  3 A is guided by the tapered surface  36  having the smaller inclination angle β than an inclination angle α so as to move to the low pressure side L. Therefore, the insertion load can be more reduced than that in embodiment 1. 
     Under a condition that the collapse margin of the backup ring  30  when the backup ring  30  is fitted to the housing  3  is set to about 0.1 mm (Outer diameter of the backup ring  30 −Inner diameter of the housing  3 =about 0.2 mm), an insertion load of the shaft  2  in embodiment 4 is measured to compare with that of the above-described embodiment 1, as a result of which, the insertion load is a 25 to 30% level with respect to embodiment 1, and thus the insertion load can be reduced by about 75% comparing with embodiment 1. 
     Further, when the device is subjected to low-temperature and low-pressure fluid (25° C.×5 MPa) from the high pressure side H toward the low pressure side L, a radial directional gap  41  remains between the backup ring  30  and the housing  3  as illustrated in  FIG. 10 , and a radial directional gap  43  also remains between the backup ring  30  and the shaft  2 . However, since the fluid has a low pressure, the seal ring  20  is not protruded to the low pressure side L, so that the seal ring  20  is not damaged. Furthermore, when the device is subjected to high-temperature and high-pressure fluid (80° C.×15 MPa), radial directional component force generated by moving of the backup ring  30  in the axial direction is applied since a gap g is provided between the low pressure side end surface  32  of the backup ring  30  and the side wall surface  11  at the low pressure side L of the mounting groove  10 . Thus, the backup ring  30  is deformed so as to eliminate the radial direction gaps ( 41 ,  43 ) as illustrated in  FIG. 11 . Therefore, protrusion of the seal ring  20  to the low pressure side L and deterioration of sealing property by damaging of the seal ring  20  can be prevented. 
     In addition, the low pressure side tapered part  35   b  is an inclined plane surface in this example. However, the low pressure side tapered part  35   b  can be an inclined curved surface. In this case, the low pressure side tapered part  35   b  is formed in the state of having a gap between the low pressure side tapered part  35   b  and the tapered groove bottom part  12  of the mounting groove  10 , when the high pressure side tapered part  35   a  contacts to the tapered groove bottom part  12  of the mounting groove  10  before insertion of the shaft. 
     Furthermore, the backup ring  30  can have a collapse margin which is compressed at the time of being fitted.