Patent Publication Number: US-2015076753-A1

Title: Overtravel Pressure Relief For A Gas Spring

Description:
TECHNICAL FIELD 
     This invention relates generally to gas springs and, more particularly, to overtravel pressure relief features for gas springs. 
     BACKGROUND 
     Gas springs are well known and have been used in dies of presses for sheet metal stamping operations. For example, gas springs can be used as press cushions, among many other types of applications. A conventional gas spring includes a casing, a piston rod carried in the casing, a bearing and sealing housing held in the casing by a retainer to guide and retain the piston rod within the casing, and a pressure chamber to hold pressurized gas, typically nitrogen at an operating pressure of, for example, 2,000 to 5,000 PSI in some applications. The housing includes one or more bearings to guide movement of the piston rod within the casing, and one or more seals to prevent leakage from the pressure chamber. The pressurized gas biases the piston rod to an extended position, and yieldably resists movement of the piston rod from the extended position to a retracted position. But the piston rod may overtravel beyond a design-intent retracted position, and overtravel may result in undesirable gas overpressure and other adverse conditions. 
     SUMMARY 
     In at least one implementation, a gas spring for forming equipment includes a casing including an axially extending side wall, an open end, a transversely extending closed end wall axially spaced from the open end, a pressure chamber established in part by the side and end walls to receive a gas under pressure, and a vent passage through the side wall. The gas spring also includes a piston rod received at least in part in the casing for reciprocation between extended and retracted positions, and a piston rod housing received at least in part in the casing between the piston rod and the casing. The gas spring further includes an overtravel pressure relief feature carried in the vent passage of the casing and having a through passage and an annular seal that seals against the piston rod housing. 
     In another implementation, a gas spring for forming equipment includes a casing including an axially extending side wall, an open end, a transversely extending closed end wall axially spaced from the open end, a pressure chamber established in part by the side and end walls to receive a gas under pressure, and an internal annular casing seal groove in the casing. The gas spring also includes an annular casing seal carried in the seal groove in the casing, and a piston rod received at least in part in the casing for reciprocation between extended and retracted positions. The gas spring further includes a piston rod housing received at least in part in the casing between the piston rod and the casing and having a cylindrical lower skirt in sealing engagement with the casing seal and having an overtravel pressure relief feature axially adjacent the casing seal, wherein displacement of the housing into the casing results in breach of the casing seal. 
     Some potential objects, features and advantages of the gas spring and/or its components set forth herein include providing a device that is readily usable with a wide range of forming equipment, readily permits use of common components among gas springs of different configuration and construction, can be easily serviced and its components replaced as needed, can be used in a wide range of applications having different size and force requirements, is readily adaptable to a wide range of press configurations, includes an overtravel pressure relief feature, and is of relatively simple design, economical manufacture and assembly, robust, durable, reliable and in service has a long useful life. Of course, an apparatus embodying the present invention may achieve, none, some, all or different objects, features or advantages than those set forth with regard to the illustrative embodiments disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of preferred embodiments and best mode will be set forth with regard to the accompanying drawings in which: 
         FIG. 1  is a fragmentary, sectional, perspective view of a presently preferred form of a gas spring with overtravel pressure relief features; 
         FIG. 2  is an enlarged, fragmentary, sectional view of the gas spring of  FIG. 1 , illustrating a piston in a normal retracted position with respect to a casing; 
         FIG. 3  is an enlarged, fragmentary, sectional view of the gas spring of  FIG. 1 , and, in contrast to  FIG. 2 , illustrates the piston in an overtravel position with respect to the casing; 
         FIG. 4  is a fragmentary, sectional, perspective view of another presently preferred form of a gas spring with an overtravel pressure relief feature, and with a multi-piece piston rod housing; 
         FIG. 5  is an enlarged, fragmentary, sectional view of the gas spring of  FIG. 4 , illustrating a coupling arrangement between upper and lower portions of the piston rod housing; 
         FIG. 6  is an enlarged, fragmentary, sectional view of the gas spring of  FIG. 4 , illustrating the piston rod housing; 
         FIG. 7  is a further enlarged, fragmentary, sectional view of the gas spring of  FIG. 4 , illustrating an overtravel condition thereof; 
         FIG. 8  is a cross-sectional, elevational view of an additional presently preferred form of a gas spring with an overtravel pressure relief feature, and with a multi-piece piston rod housing; 
         FIG. 9  is an enlarged, fragmentary, sectional view of the gas spring of  FIG. 8 , taken from oval  9  of  FIG. 8 , illustrating the piston rod housing; and 
         FIG. 10  is an enlarged, exploded view of the multi-piece piston rod housing of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIG. 1  illustrates a gas spring  10  that may be used in forming equipment, for example, sheet metal stamping dies and mechanical presses (not shown). In general, the gas spring  10  may include a casing  12 , a guide and seal assembly  14  carried by the casing  12 , a piston rod  16  carried by the casing  12  and extending through the guide and seal assembly  14  and having a piston plate  15  coupled thereto by fasteners, cooperating threads or other features, or in any suitable manner. The gas spring  10  also includes a pressure chamber  17  to hold a pressurized gas. An outer axial end of the piston rod  16  and/or the plate  15  may be engageable with a die member or another portion of a press or piece of forming equipment (not shown). 
     For example, one or more of the gas springs  10  may be used in various implementations in forming equipment to provide a moveable component for support of a forming die or a workpiece with a yielding force or a return force. For example, in a binder ring implementation, the gas spring  10  may provide a yielding force against a binder ring of a forming die to hold a metal workpiece while another part of the forming die forms, cuts, stretches, or bends the workpiece. In a lifter implementation, the gas spring  10  may provide a yielding force and return force to lift a workpiece off a surface of the forming die or to otherwise maintain control of the workpiece. In a cam tool implementation, the gas spring  10  may apply a yielding force to return a cam-activated tool to its home position. Of course, the gas spring  10  may be used in a wide range of other implementations. 
     According to the present disclosure, the gas spring  10  may include an overstroke or overtravel pressure relief feature  18  in the event of an overtravel condition of a piece of forming equipment with which the gas spring  10  may be used. As will be discussed in greater detail below, the overtravel pressure relief feature  18  may be carried by the casing  12 . As an alternative, the gas spring  10  may include a different overtravel pressure relief feature  19  that may be carried by the assembly  14 . Although both features are illustrated in the drawings, it is contemplated that only one or the other may be implemented for any given gas spring. 
     Each of the features  18 ,  19  may be in fluid communication with the pressure chamber  17  during an overtravel condition and may function to allow pressurized gas to be communicated out of the pressure chamber  17 , to provide protection against overtravel conditions. The overtravel pressure relief features  18 ,  19  ordinarily do not allow gas in the pressure chamber  17  to exit the gas spring  10 , absent an overtravel condition associated with the gas spring  10 . But in the event of an overtravel condition, one or both of the overtravel pressure relief features  18 ,  19  may enable release of pressurized gas from within the pressure chamber  17  of the gas spring  10  to thereby significantly decrease the pressure of any gas remaining in the pressure chamber  17 . As used herein, the terminology “overtravel condition” includes a condition where a die member, or any other machine component with which the gas spring  10  interacts, travels beyond a design intent position with respect to the gas spring  10 . 
     With reference to  FIG. 2 , the casing  12  may include a side wall  20  that may terminate axially at a closed end  22  and at an open end  24  that receives the guide and seal assembly  14  and the piston rod  16  therein. The pressure chamber  17  is established at least in part by the side and end walls  20 ,  22  to receive a gas under pressure. The closed end  22  may be a separate component attached to the side wall  20 , for example by a weld joint, or may be integrally produced with the side wall  20 . The side wall  20  of the casing  12  has an inner surface  26  defining at least in part the pressure chamber  17 , and an outer surface  30 . The casing  12  may be of generally cylindrical shape, for example, wherein at least one of the inner or outer surfaces  26 ,  30  is cylindrical. The inner surface  26  of the side wall  20  may have a circumferential retainer groove  32  constructed for receipt of a retainer, shown here by way of example as a split ring  34 , to maintain the gas spring  10  in its assembled state. To facilitate mounting and locating the gas spring  10  within a press, a pair of longitudinally spaced circumferential grooves  36 ,  38  may be machined, formed, or otherwise provided in the outer surface  30  of the casing  12  adjacent its ends  22 ,  24 . To admit gas into the gas spring  10 , the casing  12  may include a passage or fill port  40  that may be provided through the closed end  22  of the casing  12  in any suitable manner. The fill port  40  may include a threaded passage  42  for coupling of a fill valve  41 , e.g., a Schrader valve, to the casing  12 . The closed end  22  of the casing  12  also may include a passage  39  in fluid communication between and with the pressure chamber  17  and the fill port  40 . 
     With reference to  FIG. 2 , the guide and seal assembly  14  may be disposed in the open end  24  of the casing  12  and may be sealingly coupled to the casing  12 . The assembly  14  may include a piston rod housing  44 , a guide bushing  46 , a rod seal  48 , a rod wiper  50 , a dust cover (not shown), all of which may be carried by the housing  44 , and a casing seal  54  that may be carried by the casing  12  in a seal groove  53 . The guide bushing  46  may be composed of any suitable low friction material, and may be sized to slidably engage the piston rod  16  to guide the piston rod  16  for axial reciprocation within the casing  12 . The housing  44  may include a shoulder  45  in an outer surface thereof to cooperate with the split ring  34 , which may removably retain the housing  44  in the casing  12 . 
     The piston rod  16  is disposed at least in part in the casing  12  and through the guide and seal assembly  14  for reciprocation along an axis A between extended and retracted positions over a cycle of the gas spring  10  including a retraction stroke and an extension or return stroke. The piston rod  16  is acted on by gas in the pressure chamber  17  to bias the piston rod  16  toward the extended position, and away from the retracted position. The piston rod  16  extends out of the casing  12  through the guide and seal assembly housing  44 , and includes an outer axial end, and an inner axial end disposed in the casing  12  and that may be radially enlarged and engageable with a portion of the piston rod housing  44  to retain the piston rod  16  in the casing  12 . The piston rod  16  is in sealing engagement with the rod seal  48  and in sliding engagement with the piston rod bushing  46  for guided relative movement between the extended and retracted positions. 
     The overtravel pressure relief feature  18  may be a vent plug including a plug body  60  and a plug seal  62  carried by the body  60 . The feature  18  may be carried in a vent passage  63  of the sidewall  20  of the casing  12 . The plug body  60  may include a threaded outer diameter  61  for threading into the corresponding vent passage  63 , which may be threaded. Accordingly, the plug body  60  also may have a through passage  64  with a counterbore, which may have tool features to cooperate with a tool (not shown), for example, internal flats, for instance, hex flats for cooperation with an Allen wrench or the like for installing and/or removing the plug body  60 . The plug body  60  further may include a stepped down end  65  to carry the plug seal  62 . The plug seal  62  may be an annular seal for sealing engagement with a lower portion or skirt  66  of the piston rod housing  44 . The plug seal  62  may engage a smooth cylindrical portion of the housing  44 , or any other suitable geometric portion of the housing  44  that provides a good seal. Additionally, the axial face of the stepped down end  65  of the plug body  60  may be in full circumferential contact with the housing  44 . In any case, the vent plug establishes a fully circumferential, annular seal with the housing  44  that is ordinarily completely closed, absent an overtravel condition. The seal  62  may be composed of a urethane, nitrile, or any other suitable sealing material, and may be of 70-90 durometer on the Shore A scale. 
     The alternative overtravel pressure relief feature  19  may be a groove, notch, flattening, reduced diameter, or any other relief in an outer diameter of the piston rod housing  44 . The feature  19  may include a lower end  68  that may be axially adjacent and/or overlapping a portion of the seal  54 , and an upper end  69  axially spaced from the lower end  68 . One or both of the ends  68 ,  69  may be conical or otherwise tapered surfaces. 
     With reference now to  FIG. 3 , when the piston  16  has travelled past a design-intent fully retracted position, such that the piston  16  has overtravelled, one or both of the relief features  18 ,  19  enable desired depressurization of the pressure chamber  17 . When the piston  16  overtravels, the piston plate  15  strikes an upper end  43  of the housing  44  to displace the housing  44  into the casing  12 . 
     The overtravel pressure relief feature  18  enables depressurization when the piston rod housing  44  is displaced into the casing  12  to an extent that some recessed feature of the housing  44  axially overlaps the seal  62  so as weaken, interrupt, or otherwise breach the seal between the seal  62  and the housing  44  to allow gas to escape therebetween and out of the side of the gas spring  10  as indicated by horizontal arrows. In the illustrated embodiment, the recessed feature includes at least the lower portion  68  of the alternative feature  19 . In other embodiments, the recessed feature may include some lower portion or extension of the seal groove  53 , or any other suitable shallow groove, relief, or recess. 
     The alternative feature  19  enables depressurization when the piston rod housing  44  is displaced into the casing  12  to an extent that the lower portion of the feature  19  is displaced past a lower portion of the seal  54  so as to weaken or interrupt sealing between the seal  62  and the housing  44  to allow gas to escape therebetween and out of the open end of the gas spring  10  as indicated by vertical arrows in  FIG. 3 . 
     The gas spring  10  may be assembled in any suitable manner and its various components may be manufactured in any suitable manner and composed of any suitable materials. For example, the casing  12  may be turned, bored, drilled, tapped, and/or otherwise machined from tube and/or solid bar stock. In another example, the vent plug body  60  may be constructed from, for example, steel, brass, copper, carbon fiber, and/or any other suitable material(s). 
     In assembly, the guide and seal assembly  14  may be pre-assembled, and the piston rod  16  may be assembled through the housing  44 , and the assembly  14  with the rod  16  therein may be assembled into the casing  12  and retained therein in any suitable manner, for example via assembly of the split ring  34  into the groove  32 . Thereafter, the vent plug may be threaded or otherwise coupled to the casing  12  until the seal  62  seals with the housing  44 . 
     In operation, and with respect to  FIG. 1 , any suitable pressurizing device (not shown) may be coupled to the port  40  to open the valve  41  and introduce pressurized gas through the port  40  into the chamber  17 . Once a desired pressure is reached, the pressurizing device may be retracted to allow the valve  41  to seat and thereby seal the pressurized gas within the pressure chamber  17 . 
     Thereafter, the gas spring  10  may be used for any suitable purpose and, in the event of an overtravel condition where a machine component travels beyond a design intent position with respect to the gas spring  10 , the piston plate  15  strikes the exterior end of the housing  44 , thereby displacing the housing  44  axially into the casing  12 , and thereby resulting in breach or unseating of one or more of the seals  54 ,  62 . Such unseating will allow pressurized gas in the chamber  17  to escape through one or both of the features  18 ,  19 . 
       FIGS. 4-7  illustrate another presently preferred form of a gas spring  110 . This form is similar in many respects to the form of  FIGS. 1-3  and like numerals between the forms generally designate like or corresponding elements throughout the several views of the drawing figures. Accordingly, the description of the embodiments are incorporated by reference into one another in their entireties, and a description of the common subject matter generally may not be repeated here. 
     The gas spring  110  includes a guide and seal assembly  114  including an annular housing cap  152  coupled to an upper end  143  of a piston rod housing  144  and trapping a wiper  150  therebetween. The cap  152  extends the length of the housing  144  so that the housing  144  projects beyond the open end of the casing  112  and may allow for partial travel of the housing  144  axially into the casing  112  in that the cap  152  may be stopped by the retaining ring  134 . The cap  152  may be coupled to the housing  144  by fasteners, threading or other integral fastening, welding, or in any suitable manner. 
     For example, and with respect to  FIGS. 5 and 6 , a retention ring  170  may be carried between corresponding radially outwardly and inwardly extending shoulders  171 ,  173  of the housing  144  and the cap  152 , respectively. Also, set screws  172  may be threaded into the cap  152  and into engagement with the retention ring  170  to seat the retention ring  170  to the corresponding housing shoulder  171 . The retention ring  170  may be a C-shaped ring. Additionally, the cap  152  may carry an annular seal  174  for sealing the assembly  114  to the casing  112 . 
     With reference to  FIG. 6 , the assembly  114  also may include a piston rod housing seal  154  and a seal backup  156  that may be carried by the housing  144  in a seal groove  153 . Also, the housing  144  may include a step, turned down annulus, notch, circumferential groove, spiral groove, flattening, or any other suitable recessed feature  167 , which may be axially adjacent to and in recessed communication with the seal groove  153 . 
     Accordingly, as illustrated in  FIG. 7 , when the piston  116  has travelled past a design-intent fully retracted position, such that the piston  116  has overtravelled, the relief feature  118  enables desired depressurization of the gas spring  110 . When a die plate or other machine component and the piston  116  overtravel, the machine component strikes the cap  152  to displace the housing  144  axially into the casing  112 . 
     The relief feature  118  enables depressurization when the piston rod housing  144  is axially displaced into the casing  112  to an extent that the recessed feature  167  of the housing  144  axially overlaps the plug seal  162  so as to weaken, interrupt, or otherwise breach the seal between the seal  162  and the housing  144  to allow gas to escape therebetween and out of the side of the gas spring  110  via the passage through the plug  160  as indicated by the horizontal arrows in  FIG. 7 . 
       FIGS. 8-10  illustrate another presently preferred form of a gas spring  210 . This form is similar in many respects to the form of  FIGS. 1-7  and like numerals between the forms generally designate like or corresponding elements throughout the several views of the drawing figures. Accordingly, the description of the embodiments are incorporated by reference into one another in their entireties, and a description of the common subject matter generally may not be repeated here. 
     The gas spring  210  includes a casing  212 , a guide and seal assembly  214  carried by the casing  12 , a piston rod  216  carried by the casing  212  and extending through the guide and seal assembly  214 , and a pressure chamber  217  to hold a pressurized gas. Also, the gas spring  210  includes an overtravel pressure relief feature  218 . The guide and seal assembly  214  includes a housing cap  252  that is coupled to an upper end  243  of a piston rod housing  244  and traps a wiper  250  therebetween. 
     With respect to  FIGS. 9 and 10 , the cap  252  may be coupled to the housing  244  by an integral coupling configuration, for example, a bayonet connection. More specifically, the cap  252  may be of generally cylindrical configuration and may include a plurality of radially inwardly extending bayonet lugs  272 . Likewise, the upper end  243  of the piston rod housing  244  may be of generally cylindrical configuration and may include a plurality of radially outwardly extending bayonet lugs  270  for cooperation with the cap lugs  272 . In assembly, the cap  252  is lowered over the housing upper end  243  so that the cap lugs  272  register in spaces between the housing lugs  270 . Then, the cap  252  is rotated so that the cap lugs  272  underlie and engage the housing lugs  270  to lock the cap  252  onto the housing  244 . 
     The overtravel pressure relief feature  218  may be a vent plug including a plug body  260  and a plug seal  262  carried by the body  260 . The feature  218  is in a vent passage  263  of a sidewall  220  of the casing  212 . The plug body  260  may be coupled into the corresponding vent passage  263  by threading or in any other suitable manner. The plug body  260  has a through passage  264  and a sealing end  265  carrying a plug seal  262  that engages the housing  244 . As indicated in  FIG. 9 , the axial end face of the end  265  of the plug body  260  is in full circumferential contact with the housing  244 . Also, the housing  244  includes a recessed feature  267 , which may be a fully circumferential groove as shown, or a step, turned down annulus, notch, spiral groove, flattening, or any other suitable recessed feature axially adjacent to and normally downstream of the plug body  260  and seal  262 . 
     In the event of an overtravel condition where a machine component travels beyond a design intent position with respect to the gas spring  110 , the machine component strikes the cap  252 , thereby axially displacing the housing  244  further into the casing  212 , and thereby moving the recessed feature  267  into fluid communication with the through passage  264  of the plug  260  to allow pressurized gas in the chamber  217  to escape through the overtravel feature  218 . 
     In one or more of the forms disclosed above, the overtravel pressure relief features do not fail during normal use from pressure fluctuations, for example, over 150-300 bar. Also, the features are retained during an overtravel condition to prevent any secondary hazard. Moreover, the overtravel pressure relief feature is configured to discharge pressure with overtravel on the order of 0.5 to 1.5 mm, for example. The overtravel pressure relief feature allows for normal operation of a gas spring and is configured for retrofit of existing products, which also can be serviced by an existing product repair kit and procedure. 
     It should be appreciated that one of ordinary skill in the art will recognize other embodiments encompassed within the scope of this invention. The plurality of arrangements shown and described above are merely illustrative and not a complete or exhaustive list or representation. Of course, still other embodiments and implementations can be achieved in view of this disclosure. The embodiments described above are intended to be illustrative and not limiting. The scope of the invention is defined by the claims that follow.