Patent Publication Number: US-2019178384-A1

Title: Pressure-sensitive, frictionless seal ring design

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     Priority is claimed to German Patent Application No. DE 10 2017 011 438.2, filed on Dec. 12, 2017, the entire disclosure of which is hereby incorporated by reference herein. 
     FIELD 
     The invention relates to a seal arrangement as well as the use of such a seal arrangement in an actuator. 
     BACKGROUND 
     It is known from prior art to install O-rings as piston seals in a floating manner, e.g., in air pumps. When installed in a floating manner, the O-ring is not compacted but only slightly compressed, wherein its inner diameter does not rest against the groove bottom. The advantage of the floating installation of O-rings lies in the free movement and in the low wear of the O-ring under dynamic loads. 
     As an example of an actuator, AT 009827 U1 is mentioned, in which an actuation device with a cylinder-piston device is described, which briefly moves a piston at very high speed by means of compressed gas. Such an actuation device, which may be designed as a pyrotechnic actuator, is used for example to actuate safety devices in motorized vehicles. An example of such use is described in AT 511710 B1, from which emerges an apparatus for employing an engine hood, which is used for pedestrian protection. 
     The disadvantage of known piston-and-rod seals using the floating installation of O-rings is that for pistons at rest, moisture or contamination can get past the sealing point. This is due to the O-ring being insufficiently pressed in the groove. When pistons or rods are moved, O-rings tend primarily to twist locally or over the entire circumference due to the friction with the O-ring. Excessive leakage can result from this when a piston or rod moves. 
     SUMMARY 
     In an embodiment, the present invention a seal arrangement comprising: a housing; a machine element; a groove, which is placed in the housing or machine element; and a seal ring having a first seal lip configured to seal a sealing gap between the housing and the machine element, the seal ring being installed in the groove in a floating manner, wherein the seal ring has at least one additional seal lip, and wherein at least one additional seal lip is arranged as a lateral seal lip in a side surface of the seal ring and contacts lateral groove surfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  a seal arrangement without pressure applied in a construction as a rod seal 
         FIG. 2  the contact stress distribution of the three seal lips given a seal arrangement according to  FIG. 1  of the seal arrangement without pressure applied 
         FIG. 3  the seal arrangement from  FIG. 1  when pressure is applied 
         FIG. 4  the contact stress distribution of the seal arrangement according to  FIG. 3  when pressure is applied 
         FIG. 5  a seal arrangement without pressure applied in a construction as a piston seal 
         FIG. 6  a seal arrangement as a rod seal without pressure applied with a small seal lip radius 
         FIG. 7  a seal arrangement as a rod seal without pressure applied with a large seal lip radius 
         FIG. 8  a seal arrangement as a rod seal with pressure applied with a conical groove and a conical cross-section of the seal ring 
         FIG. 9  a seal arrangement as a rod seal without pressure applied with a seal ring having a rectangular cross-section and a tapering groove width 
         FIG. 10  a seal arrangement as a rod seal without pressure applied with spacers 
         FIG. 11  a seal arrangement as a rod seal without pressure applied with lateral lead-in bevels 
         FIG. 12  a seal arrangement as a rod seal without pressure applied with long lateral seal lips 
         FIG. 13  a seal arrangement as a rod seal without pressure applied with lateral lead-in bevels 
         FIG. 14  a seal arrangement as a rod seal without pressure applied with an x-shaped seal ring 
         FIG. 15  a seal arrangement as a rod seal without pressure applied with two initial seal lips 
         FIG. 16  a seal arrangement as a rod seal without pressure applied with four additional seal lips 
         FIG. 17  a seal arrangement as a rod seal without pressure applied with retaining collars 
         FIG. 18  a seal arrangement as a rod seal with pressure applied with retaining collars 
         FIG. 19  a seal arrangement as a rod seal without pressure applied with only one additional seal lip 
         FIG. 20  a seal arrangement as a rod seal with pressure applied with a through-passage to the groove bottom 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, the present invention provides a seal arrangement, which in a non-moved state reliably keeps away moisture and contamination, and simultaneously has only minimal friction when pressure is applied and the seal arrangement thus moves. An additional object of the invention is to create a seal arrangement, which is easy to install and has a simple structure. 
     The seal arrangement according to the invention has a housing which is designed as an outer part, as well as a machine element, particularly a piston or a rod able to move in relation to it, which is designed as an inner part. In the housing or machine element, there is placed a groove for holding a seal ring. The seal ring has a first seal lip for sealing a sealing gap between the housing and the machine element and is installed in a floating manner, i.e., the seal ring does not lie on the groove bottom, or in other words: the cross-sectional thickness of the seal ring is smaller than the seal surface clearance, i.e., the distance between the groove bottom and the rod or between the groove bottom and the housing. 
     According to the invention, the seal ring has at least one additional seal lip, wherein the seal ring may have in particular two additional seal lips or four seal lips. The at least one additional seal lip is arranged as a lateral seal lip in a side surface of the seal ring and contacts the associated lateral groove surfaces, i.e., the side surfaces of the groove. The lateral groove surfaces can also be referred to as groove end surfaces. The seal arrangement is configured according to the invention in such a manner that the contact stress in the region of the first seal lip is always less than the contact stress in the region of the at least one other seal lip, regardless of whether the seal arrangement is subjected to pressure. By retaining the floating installation of the seal ring, it is advantageously ensured that when pressure is applied and if a certain pressure of the seal arrangement is exceeded, the seal ring is moved into the groove and the relative motion between the housing and machine element can occur without frictional influences of the seal arrangement. By providing at least one additional seal lip, the seal ring is axially pressed into the groove during installation and at the contact surface of the at least one additional seal lip with the at lateral groove surface, a barrier is created, which does not let moisture and contamination pass through when the seal arrangement is at rest. 
     In an advantageous further development of the seal arrangement according to the invention, lead-in bevels are provided on the seal ring. According to a first variant, the lead-in bevels may be arranged only at the transition from the side surfaces to the groove bottom-side surface. According to a second variant, the lead-in bevels extend over most of the side surfaces. In the third variant, the lead-in bevels extend over all the side surfaces of the seal ring so that a wedge-shaped or trapezoidal design of the seal ring results. All three variants ensure simplified installation of the seal ring. 
     In another design variant of the seal arrangement considered to be advantageous, the groove is designed conically and the seal ring has a conical cross-section. In an alternative construction variant, the groove has a groove width that tapers toward the groove bottom and the seal ring has a rectangular cross-section. Both design variants have the advantage that the seal ring first moves into the groove when a higher pressure is applied. 
     In an advantageous manner, this is also achieved by a seal arrangement in another variant, according to which the seal ring has on its side facing the groove bottom at least one projection as a spacer. In particular, two spacers may be provided to achieve symmetrical force distribution. 
     In a particularly advantageous and thus preferred further development of the seal arrangement according to the invention, the at least one additional seal lip is arranged on the slot-side end of the side surfaces of the seal ring. When there are multiple seal lips per side surface, one seal lip each is arranged at least on the respective slot-side end of the side surface. 
     It was recognized that the seal ring may also be designed in an x-shaped manner, i.e., it can have an x-shaped cross-section. Improved installation and a reproducible deformation behavior can thereby be achieved. 
     In an advantageous further development of the seal arrangement according to the invention, the lateral groove surfaces are each provided with an undercut and the side surfaces of the seal ring are each provided with a complementary projection, to form a retaining collar each. By providing such retaining collars, it is advantageously achieved that after pressure has been applied and after the seal ring has moved into the groove, it can no longer move in the sealing gap. The reason is that when using the seal arrangement in an actuator, the pressure can slowly escape out of the actuator. If the actuator is used for example as a pyrotechnic actuator to raise the engine hood of a motorized vehicle for pedestrian protection, an achievement is that the engine hood is lowered again after a defined period of time. 
     In an advantageous further development of the seal arrangement according to the invention, the region of the groove bottom of the groove is connected by means of at least one narrow through-passage, e.g., a bore hole, to a pressure chamber to generate a time-delayed pressure in the region of the groove bottom when pressure is applied. In other words, one or more small bore holes are made in the groove bottom, i.e., in the groove toward the pressure chamber. If designed as a piston seal, a time-delayed pressing of the seal ring to the piston is thereby achieved so that the leakage is minimal when the piston is extended and after the piston is extended, the seal ring is pressed back against the piston. If designed as a rod seal, a time-delayed pressing of the seal ring to the rod is achieved so that leakage is minimal when the rod is extended and after the rod is extended, the seal ring is pressed against the rod again. Holding the pressure when the actuator is extended is important so that a component to be moved by the actuator, e.g., an engine hood, does not drop again immediately after the actuator is extended. 
     In a first embodiment of the seal arrangement, the groove is arranged in the housing and the seal arrangement is designed as a rod seal. By contrast in a second embodiment of the seal arrangement, the groove is arranged in the machine element and the seal arrangement is designed as a piston seal. 
     The invention also relates to the use of a seal arrangement as described above in an actuator, particularly in a very fast-acting actuator, such as a pyrotechnic actuator for example, wherein when the actuator is subjected to pressure the seal ring plunges deeper into the groove. The contact pressure of the seal ring is thereby less than the pressure in the chamber to be sealed when the operating pressure is greater in relation to the ambient pressure. 
     The described invention and the described advantageous further developments of the invention also represent advantageous further developments when combined with each other—to the extent it is technically reasonable. 
       FIGS. 1 and 2  depict a seal arrangement  100 , with a housing  5  and a machine element moveable in relation to it, designed as piston  4 . Dashed-dotted line  6  indicates the center line and axis of symmetry of seal arrangement  100 . A groove  13  is made in housing  5 . Groove  13  has a groove end surface facing away from pressure as groove side  1 , a groove bottom  2  and a pressure-facing groove end surface as groove side  3 . A seal ring  20  is inserted in groove  13 . Seal ring  20  is installed in a floating manner in groove  13 , i.e., groove ring  20  has no contact with groove bottom  2 . This is the condition of seal arrangement  100  when there is only ambient pressure and thus P=0. Seal ring  20  is constructed in such a manner that it has a seal lip  26  in the seal region between the machine element and the housing, in other words here between piston  4  and housing  5 , said seal lip contacting piston  4 . In addition, seal ring  20  has a first additional lateral seal lip  21 , specifically on the side, facing away from pressure, of seal ring  20  near the contact surface of seal lip  26  and a second additional lateral seal  23 , which is arranged on the pressure-facing side of seal ring  20  also near the contact surface of seal lip  26 . These two additional lateral seal lips  21 ,  23  contact lateral groove surfaces  1  and  3  respectively and represent a barrier to moisture and contamination, so that these cannot get past seal arrangement  100 . 
     If seal arrangement  100  is subject to a pressure  9  that is above atmospheric pressure and if a certain pressure is exceeded, seal ring  20  is pressed into groove  13 . As one can see in  FIG. 3 , seal ring  20  is pushed so far into groove  13  until seal ring  20  lies on groove bottom  2 . Then a motion  10  of piston  4  is possible without seal ring  20  having a frictional influence. 
     Seal ring  20  moves in groove  13  or detaches from the piston or rod  4  when a certain pressure P_x is reached. Certain pressure P_x may be 7 bar, for example. Seal ring  20  then first detaches at P&gt;P_x from the piston or rod  4  and not at a lower pressure P. 
     Required pressure P_x to move seal ring  20  thereby depends on the following parameters: 
     the friction coefficient and the surface size between seal ring  20  and the two lateral groove end surfaces 
     the axial pressing height 
     the hardness of the seal 
     the groove shape or the angle of the two front surfaces (groove tapering). 
     For a conical groove shape, the necessary pressure P is larger primarily due to the incompressibility of the material 
     the presence of spacer nubs  12  as depicted in  FIG. 10  and the design of spacer nubs  12   
     the construction variant of seal arrangement  100 , i.e., as a rod or piston seal. For example, for a rod seal, seal ring  20  is expanded, wherein low pressure is needed. For a piston seal, seal ring  20  is compressed, wherein a higher pressure is needed. 
     For easier installation, seal ring  20  may be provided with lead-in bevels  25  as one can see in  FIGS. 1 and 2 . 
     In the depicted embodiment, seal ring  20  is dimensioned in such a manner that an axial compression of seal ring  20  in groove  13  occurs.  FIG. 2  depicts the contact stress of the seal lips for the seal arrangement according to  FIG. 1 , i.e., without pressure applied at P=0. Contact stress  31  of lateral seal lip  21  facing away from pressure as well as contact stress  33  of pressure-facing lateral seal lip  23  are greater than contact stress  32  of the first seal lip on the piston or rod  4 . 
     If a pressure P&gt;0 is applied to seal arrangement  100 , seal ring  20  will then move into groove  13 , as depicted in  FIG. 3 . As one can see in  FIG. 4 , there is no contact stress  32  any more of the first seal lip on the piston or the rod. However, contact stresses  31 ,  32  of lateral seal lips  21 ,  23  are maintained. 
     While  FIGS. 1 and 3  as well as the other drawings depicting seal arrangements  100  each portray a rod seal,  FIG. 5  shows a piston seal. Seal arrangement  100  has a housing  5 , a piston  4  that can move relative to it, and a seal ring  20 . Piston  4  has a groove  13 , in which seal ring  20  is located. 
       FIGS. 6 and 7  depict seal arrangements  100 , which have a seal ring  20  with various radii R of first seal lip  26 . According to  FIG. 6 , seal lip radius R of first seal lip  26  is significantly smaller than seal lip radius R according to  FIG. 7 . 
       FIGS. 8 to 10  described below show seal arrangements in which seal ring  20  first moves into groove  13  at a higher applied pressure P. 
     According to  FIG. 8 , seal ring  20  has a conical cross-section and groove  13  is also constructed in a conical manner. 
     According to  FIG. 9 , seal ring  20  has an essentially rectangular cross-section, while the groove width of groove  13  tapers over a non-continuous bevel  8 . 
     In the variant according to  FIG. 10 , seal ring  20  is constructed with two spacers arranged on the side of the groove bottom, as spacer nubs  12 . Spacer nubs  12  result in seal ring  20  not lying in a planar manner on groove bottom  2  when no pressure is applied. When a pressure P&gt;0 is applied, a groove bottom-side deformation of seal  20  is possible so that seal ring  20  can plunge deeper into groove  13 . A corresponding construction of spacer nubs  12  enables one to set a pressure P at which seal ring  20  plunges into groove  13 . 
     In the construction variants of seal arrangement  100  described below and depicted in  FIGS. 11 to 13 , possible designs of seal ring  20  are shown which allow better and simpler installation as well as a reproducible deformation behavior of seal ring  20 . 
     In the variant according to  FIG. 11 , seal ring  20  has a lead-in bevel  25  which extends over most of the side surface of seal ring  20 . 
     In the variant according to  FIG. 13 , lead-in bevel  25  extends in each case over the entire side surface of seal ring  20 . 
     In the variant according to  FIG. 12 , seal ring  20  has particularly wide additional lateral seal lips  21 ,  23 . As a result, the risk of tilting of seal ring  20  is decreased. 
     In the variant according to  FIG. 14 , a seal ring  20  having an x-shaped cross-section is used. This seal ring  20  has two groove bottom-side lateral support lips  22  in addition to lateral seal lips  21 ,  23 . 
     In the variant according to  FIG. 15 , seal lip  26  of seal ring  20  is designed in a two-part manner by a first pressure-facing seal lip  27  to the piston or rod, and by a second seal lip  28 , facing away from pressure, to the piston or rod. 
     In the variant of seal ring  20  depicted in  FIG. 16 , said seal ring has an essentially rectangular cross-section and lateral support lips  22  in addition to lateral seal lips  21 ,  23 . This construction variant can also prevent a tilting motion of seal ring  20 . 
     In the variants of seal arrangement  100  shown in  FIGS. 17 and 18 , a construction is selected in which, after pressure is applied, seal ring  20  remains in groove  13  and no longer moves back into the sealing gap. While  FIG. 17  shows a rectangular configuration of seal ring  20  and groove  13 ,  FIG. 18  reveals a conical construction of seal ring  20  and groove  13 . In both cases, lateral groove undercuts  7  are provided, which function as retaining collars. The situation is depicted in  FIG. 17 , with seal arrangement  100  not yet subjected to pressure.  FIG. 18  shows that after pressure P&gt;0 is applied, seal ring  20  plunges into groove  13 , is retained there by retaining collars in groove undercuts  7 , and can no longer move back. 
       FIG. 19  shows an alternative embodiment of seal arrangement  100 . Contrary to the previously described seal arrangements  100  depicted in the other drawings, according to  FIG. 19  seal ring  20  has only a lateral seal lip  23  on the pressure-facing side of seal ring  20 , which is also arranged near the contact surface of first seal lip  26 . 
       FIG. 20  depicts an additional embodiment of seal arrangement  100 , in which, after pressure is applied, seal ring  20  is displaced into groove  13  and moves back into the sealing gap. To do so, a narrow through-passage  14  is provided, which connects groove bottom  2  of groove  13  to a pressure chamber, where there is a pressure p&gt;0. This is used to generate a time-delayed pressure  9  in the region of groove bottom  2  when pressure is applied. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Groove side (groove end surface facing away from pressure) 
           2  Groove bottom 
           3  Groove side (pressure-facing groove end surface) 
           4  Piston or rod 
           5  Housing 
           6  Center line and axis of symmetry 
           7  Lateral groove undercut 
           8  Groove bevel 
           9  Pressure 
           10  Piston/rod movement direction 
           11  Plastic shell (concave on one side) 
           12  Spacer nub 
           13  Groove 
           14  Passage 
           20  Seal ring 
           21  Lateral seal lip, facing away from pressure, near contact surface 
           22  Lateral support lip 
           23  Pressure-facing lateral seal lip near contact surface 
           25  Lead-in bevel on ring 
           26  Seal lip to piston/rod 
           27  Pressure-facing seal lip to piston/rod 
           28  Seal lip, facing away from pressure, to piston/rod 
           31  Contact stress of lateral seal lip facing away from pressure 
           32  Contact stress of first seal lip to piston/rod 
           33  Contact stress of pressure-facing lateral seal lip 
           100  Seal arrangement 
         P Pressure 
         F Contact stress 
         R Seal lip radius