Abstract:
A fluid activated cylinder assembly including an end cap having an annular protrusion and a hollow cylinder having an end zone. The cylinder applies compressive force to the annular protrusion in the end zone. The end zone having no accommodating cavity and no accommodating protrusion for the annular protrusion.

Description:
This application is a continuation of U.S. patent application Ser. No. 10/962,078 filed on Oct. 6, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a cylinder assembly, and, more particularly, to an end cap assembly of a cylinder assembly. 
   2. Description of the Related Art 
   Various techniques are employed to attach an end cap of a power cylinder to a cylindrical piston casing. Power cylinders that are metallic often use conventional threading, swaging or a welding technique to attach the end cap to the cylinder. In many instances, however, it is desirable to construct fluid power cylinders out of plastic materials in applications where strength-to-weight ratios are important considerations and in corrosive environments. Conventional techniques employed in the assembly of metallic cylinders do not apply to plastics. Additionally, it is desirable to construct fluid power cylinders that are disposable rather than repairable, since unskilled personnel may improperly replace fluid seals with disastrous consequences when the cylinder is put back into service. 
   What is needed in the art is an economic method of constructing a cylinder assembly. 
   SUMMARY OF THE INVENTION 
   The present invention provides an end cap that is assembled to a cylinder using a pressing operation. 
   The invention comprises, in one form thereof, a fluid activated cylinder assembly including an end cap having an annular protrusion and a hollow cylinder having an end zone. The cylinder applies compressive force to the annular protrusion in the end zone. The end zone having no accommodating cavity and no accommodating protrusion for the annular protrusion. 
   An advantage of the present invention is that the assembly of an end cap to a cylinder can be completed by a single pressing operation. 
   Another advantage of the present invention is that the cylinder does not require a machining operation to accommodate a protrusion from the end cap. 
   Another advantage is that the assembly can be assembled with very little time expenditure. 
   An even yet further advantage is the assembly of the present invention is a simple cost effective design. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an embodiment of the cylinder assembly of the present invention; 
       FIG. 2  is a partially section side view of the cylinder assembly of  FIG. 1 ; 
       FIG. 3  is a partially sectioned enlargement of an end cap of the cylinder assembly of  FIGS. 1 and 2 ; and 
       FIG. 4  is an exploded assembly view of an end cap and a portion of the cylinder of  FIGS. 1-3 . 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a cylinder assembly  10 , which generally includes a cylinder  12 , an end cap  14 , an end cap  16 , a piston  18 , a shaft  20 , and linkages  22  and  24 . End caps  14  and  16  are substantially similar except that end cap  16  has a hole through the middle, to accommodate shaft  20 . Shaft  20  is connected to linkage  24  and piston  18 . Piston  18  is slidably sealed within cylinder  12 . End caps  14  and  16  provide for the containment of a fluid within cylinder assembly  10 , which can be a gas or liquid that causes the displacement of piston  18 . Inlets are provided in both end caps  14  and  16  to provide for the movement of fluid therethrough. 
   Now, additionally referring to  FIG. 2 , cylinder  12  includes an outer surface  26  and an inner surface  28 . Cylinder  12  is substantially cylindrical having cylindrical inner and outer surfaces  26  and  28 . Cylinder  12  may be made of a resin material that is impregnated into layered fibers. The fibers have a “wet out” characteristic, which soaks up resin better than normal fibers, making cylinder  12  substantially translucent. The high wetting characteristic of the fibers prevent voids in the cylinder, which would lead to a less translucent appearance. The fibers may be wound, thereby orienting the fibers in at least one layer. Additionally, an epoxy may be utilized to wet the fibers and form surfaces  26  and  28 . 
   Cylinder  12  has no cavities, grooves, holes or protrusions in said end zone  30  for accommodating any feature on end caps  14  and  16 . End cap  14  is pressed into an end of cylinder  12 , and more particularly into an end zone  30  portion of cylinder  12 . Distal end  32  of cylinder  12  is positioned in an area in which, upon the insertion of end cap  14 , it can relax into a non-compressed mode. An end surface  34  of cylinder  12  interfaces with a boss of end cap  14 . 
   Now, additionally referring to  FIGS. 3 and 4 , end cap  14  is illustrated, however, end cap  16  has substantially the same features as end cap  14 . End cap  14  includes annular protrusion  36  that is of a larger diameter than the diameter of inner surface  28  of cylinder  12 . The pressing of end cap  14  into cylinder  12  causes the material of cylinder  12  to be at least temporarily forced outward as end cap  14  is pressed into cylinder  12 . A portion of cylinder  12  at distal end  32  relaxes around annular protrusion  36 , thereby holding end cap  14  in position within cylinder  12 . The insertion force of end cap  14 , as it is slid into cylinder  12 , is less than the force required to remove end cap  14  from cylinder  12 . This property is arrived at by the shape of annular protrusion  36 . Annular protrusion  36  may be partially curved or have ramped portions as illustrated in the figures. 
   End cap  14  has a lead-in portion  38  which may be slightly smaller in diameter than the interior diameter of surface  28 . Additionally, lead-in surface  38  may have a radiused portion to aid in the insertion of end cap  14  into cylinder  12 . Following lead-in portion  38  is first ramped portion  40 . The surface of ramped portion  40  is an inclined surface when seen in a cross-sectional view. As distal end  32  of cylinder  12  encounters ramped portion  40 , the resilient nature of cylinder  12  allows for the flexing outward of the wall of cylinder  12  as end cap  14  is pressed into end zone  30 . Following first ramped portion  40  is first raised portion  42  which is substantially flat and parallel to surface  28 . Following raised portion  42  is a second ramped portion  44  that places further outward force on cylinder  12 . Following second ramped surface  44  is a second raised portion  46 . Following second raised portion  46  is an abrupt reduction portion  48 , where the diameter of annular protrusion  36  is reduced to substantially the inner diameter of cylinder  12  in its relaxed stated. Following abrupt portion  48  is reduced diameter portion  50 , which allows for a relaxed area of cylinder  12  to reposition itself as shown in  FIG. 3 . End cap  14  is inserted until end surface  34  contacts boss  52 , thereby controlling the depth of insertion of end cap  14  into cylinder  12 . The material of cylinder  12  places a compressive force on annular protrusion  36  and abrupt section  48  serves to substantially increase the force required to remove end cap  14  from cylinder  12 . It is the resilient nature of cylinder  12  that coacts with the shape of annular protrusion  36  of end cap  14  to advantageously serve to secure end cap  14  in cylinder  12 . 
   During the insertion of end cap  14  into cylinder  12 , cylinder  12  is stressed, without severing the fibers therein. Preferably the stress to the wall of cylinder  12 , at the point of insertion is about 65% to 70% of the ultimate burst strength of cylinder  12 . The inherent elasticity of the material of cylinder  12  maintains a constant external radial pressure on end cap  14 , with minimal long term creep that would allow relaxation of pressure therefrom. The constant external radial pressure is due to the non-creep characteristic of the fibers in cylinder  12 . This pressure obviates the need to incorporate a seal, such as an O-ring, to prevent leakage from assembly  10 . 
   It is the nature of abrupt section  48  to resist the removal of end cap  14  from cylinder  12 , since it takes more force to expand the material of cylinder  12  over an abrupt edge than over an inclined ramp. Further, the hardness of the material of end cap  14  also alters the removal force, in that abrupt section  48  will serve to shear part of the inner filaments of cylinder  12 , if an attempt is made to remove end cap  14  from cylinder  12 . 
   Advantageously, cylinder  12  can be a hollow cylindrical resin and fiber construct that is cut to a required length and without further preparation of cylinder  12 , end caps  14  and  16  may be inserted to produce cylinder assembly  10 . As can be seen in  FIG. 3 , end cap  14  is positioned in cylinder  12 , where, at distal end  32 , inner surface  28  is relaxed to be a substantially similar diameter as that portion of cylinder  12  that is outside of end zone  30 . The relaxed portion at distal end  32  is an important feature since the end of cylinder  12  is cut, thereby exposing fibers from the material of cylinder  12  and the cut fibers will have a tendency to potentially ravel and unwind over time if distal end  32  is not in a relaxed state. 
   Advantageously, compressive force applied by cylinder  12  against end cap  14  causes material of cylinder  12  to seal around annular protrusion  36 , thereby sealing fluid contained within cylinder assembly  10 . 
   While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.