Abstract:
A connection for a tube is formed by placing a coiled spring around an end of a tube and inserting a barbed tubular portion from a connection into the tube. The connection forces the tube to expand applying pressure against the coil spring and forcing it to expand and exert radial pressure against the tube towards the inserted tubular portion.

Description:
[0001]    Plastic hose and tubing is used to transport a variety of different gases and liquids. The plastic tubing must be connected at either end using some type of fitting. A hard fitting such as a metal fitting is particularly useful and preferred. Generally these have a barbed tubular portion which slides into the hose or tubing and a coupling such as a threaded section or the like at the opposite end. The tubular portion is preferably barbed and is larger than the internal diameter of the tube. The barbed portion is forced into the end of the tube stretching it and is held by compression.  
           [0002]    In many applications compression fitment is not adequate over the long term. Thermal cycles allow the tubing to expand. Also, internal pressures tend to act upon the tubing causing it to expand. Such barbed-style compression fittings rely on the elastic properties of the material to maintain sealing compressions. These designs are prone to leakage with temperature cycling as the plastic material relaxes.  
           [0003]    There are spring-type clamps that can be installed after the assembly is made which cause compression pressure in a narrow area under the clamp. These require a secondary operation to install. Unless several of the clamps are applied, only a very small portion of the barb is actually affected.  
           [0004]    Other types of fittings form a seal from the deformation of a metal sealing ring or ferrule compressed around the tubing by tightening a threaded nut. The sealing force relies on the elastic properties of the plastic material retaining compression when deformed. This fitting design is common and gives adequate performance. However if the assembly is exposed to cycling temperature or the plastic material relaxes and the sealing compression is reduced, leakage may occur. An exemplary such device is shown in FIG. 4. This device also employs a spiral spring to prevent the end of the tube from kinking. Such a spiral spring does not actually engage the plastic tubing holding it in position. The spring itself is used purely for prevention of kinking of the end of the hose as is commonly used.  
           [0005]    Another such device is shown in U.S. Pat. No. 5,286,068 which actually uses a multi-component fitting to force the spring against the tubing itself and the tubing itself simply is marginally engaged by the spring itself. Other spring-type clamps are disclosed for example in Sweger, U.S. Pat. No. 3,941,254 and Assenheimer, U.S. Pat. No. 6,193,382 B1.  
           [0006]    The present invention is premised upon the realization that an extremely secure tight connection can be formed between the end of a coupling and plastic tubing wherein the exterior of the plastic tubing is engaged by a coil spring. More particularly, such a coupling is formed by placing a coiled spring around a distal end of a plastic tube and inserting a barbed tubular member into the interior of the tube. The barbed tubular member causes the plastic tubing to expand causing the coil spring to likewise expand and at the same time apply compressive force against the exterior of the tube.  
           [0007]    This coupling finds particular application in automotive environments particularly air brake tubing. However, it can be used in virtually any application in which a plastic tube is fitted with a hard or metal coupling. The particular metal coupling can be either a male or female coupling. Further it can be a threaded or bayonet-type fitment or other snap-on fitment or the like.  
           [0008]    The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a fragmentary perspective view of the present invention.  
         [0010]    [0010]FIG. 2 is cross-sectional view taken at lines  2 - 2  of FIG. 1.  
         [0011]    [0011]FIG. 3 is a perspective view of the present invention prior to assembly.  
         [0012]    [0012]FIG. 4 is a cross-sectional view of the present invention prior to assembly.  
         [0013]    [0013]FIG. 5 is a perspective view partially in cross-section showing the assembly of the present invention.  
         [0014]    [0014]FIG. 6 is a cross-sectional view of a prior art hose fitment. 
     
    
     DETAILED DESCRIPTION  
       [0015]    As shown in FIG. 1, the present invention  11  is plastic tubing  14  fitted with one or more end couplings  12  (one end shown). Tubing  14  can be used to transport a variety of different fluids including various gases including air, liquids and the like. It has particularly valuable application as air brake tubing. However, the present invention is certainly not limited to such an application.  
         [0016]    Coupling or fitting  12  has a connecting portion  18  and a tubular portion  20 . The connecting portion  18  can be any of a variety of different connecting members. It is shown with external threading however it could have internal threading, it could be a snap on or bayonet-type fitment or any other type of connection. The tubular portion  20  is shown with barbs  22  which facilitate connecting the tube  14  to the fitting  12 . However, the barbs are not absolutely essential but are preferred.  
         [0017]    As shown in FIG. 2, the end portion  16  of tube  14  surrounds the tubular portion  20  with the distal end  24  of the tube  14  abutted against a shoulder  26  connecting portion  18 . The tube  14  has an internal surface  28  which forms an air-tight seal between the tubular portion  20  of fitting  12  and the tube end  16 . The tube  14  has an unstretched internal diameter D 1  and an external surface  30  having an external diameter when it is unstretched of D 2  and when it is stretched over the tube portion  20 , a larger diameter of D 3 .  
         [0018]    Surrounding the tube end  16  and particularly the portion of the tube that is covering tube portion  20  is a coil spring  32 . The coil spring  32  has a tightly coiled forward portion  34  and a more loosely coiled rear portion  36 . It likewise has an internal surface  38  which in an unstretched state has a diameter approximately equal to the external diameter D 2  of the tube when in an unstretched position.  
         [0019]    As shown in FIG. 2, the portion of the coil spring  32  surrounding the tube end  16  which covers tubular portion  20  is in a stretched condition and has a diameter less than the diameter of the external surface of the tube D 3  and is embedded into the external surface  30  of the tube end  16 . The coiled spring is in a stretched tensional state around tube end  16  applying radial pressure against surface  30  maintaining an air tight seal.  
         [0020]    As shown in FIG. 5, the fitting  12  of the present invention is assembled in a single step. The spring  32  is simply slipped over the tubing  14  so that the end  40  of spring  32  is immediately adjacent the end of tube end  24 .  
         [0021]    The spring  32  is held by clamp  42  which presses spring  32  against tube  14 . The tubular portion  20  of fitting  12  is forced into the interior  44  of the tube as the spring  32  is held in position. The fitting  12  engaged by a hydraulic ram diagrammatically shown as  46  in FIG. 5. The ram includes a guide rod  48  which extends through the connector  12  and through tubular portion  20 . Rod  48  is inserted into the tube end  16  which guides the tube portion  20  into the end of the tube. Tube portion  20  is tapered as at  21  to facilitate entry into the tube. The hydraulic pressure is then applied as shown by arrow  50  which will force the tubular portion  20  into end  16  of tube  14 .  
         [0022]    As the tubular portion  20  is inserted into the tube end  16 , it will cause the tube to expand outwardly so that the outer surface  30  of the tube  15   14  expands from diameter D 2  to diameter D 3 . This in turn will force the coil spring  32  to expand. Since this is held in position by clamp  42 , tube  14  does not initially move. As the tube portion  20  is inserted inwardly and the tube  14  expands, the spring  32  actually holds itself in position engaging the tube wall  30 . The pressure from the expansion of the tube wall will cause the coil spring  32  to expand radially. The hydraulic ram continues to insert the tubular portion  20  into the tube end  16  until the distal end  24  engages the fitment  12 . The hydraulic ram is then withdrawn and the fitment is in place. The spring applies radial force against the tube wall which holds the tube in position. In this condition, the spring is in a stretched condition which applies continual radial force against the tub and thus against the tubular portion  20  of the fitment  12 .  
         [0023]    Although much less preferred, the tubular portion  20  could be forced into said tube end  16  first and the coiled spring  32  forced over said tube end. But this is a two-step process and therefore more expensive and would also tend to damage the tubing.  
         [0024]    The relative dimensions of the outside diameter of the tubular portion  20  relatively to the inside diameter of the tubing  14  and the internal diameter of the spring  32  in an unstretched position combine to form a tight fitment. The inside diameter of the coil spring  32  should be approximately equal to the external diameter of the tubing  14  when both are in an unstretched condition. The spring should be able to be placed over the tube easily without significant mechanical assistance and preferably by hand. This allows the spring to be easily inserted over the tubing without prior stretching of the spring. The internal diameter of the spring can be slightly greater than the external diameter of the tubing. However, this is less preferred. A snug fit wherein the spring is equal to or perhaps a millimeter smaller than the external diameter of the tubing allows the spring to be easily inserted over the tube end without sliding in an uncontrolled manner.  
         [0025]    The tubular portion  20  of the fitting  12  is larger than the internal diameter of the tubing  14  causing the tubing to expand when the tubular portion  20  is inserted into tube  14 . As an example, tubing  14  may have an internal diameter of 0.375″. The outside diameter of tubular portion  20  measured from barb to barb (if barbs are present) may be 0.470″. This causes an expansion of the internal diameter of the tube of slightly greater than 25%. The tubing outside diameter may have an exemplary diameter of 0.530″ when in an unstretched position and an exterior diameter of 0.590″ with the tubular portion  20  of fitting  12  inserted. This would provide for an expansion of 11.3%. The spring, on the other hand, will have an unstretched outside diameter of about 0.678″ with an internal diameter of from approximately 0.52″ to 0.54″. The external diameter of the spring when inserted over the fitting expands to about 0.7″ providing a spring expansion of about 3% whereas the outside expansion of the tube is approximately 11%. This indicates that the spring actually imbeds itself into the surface of the plastic tubing. Although not critical, the spring should expand about 1% to 5%.  
         [0026]    The tubing  14  can be formed from a wide variety of different plastics depending upon the particular application. It can be fiber reinforced nylon, fiber reinforced laminated tubing such as a nylon/polyurethane/nylon laminate and can be formed from polyolefins, polyvinyl alcohols and the like. Generally it will be flexible at room temperature and meet any other application requirements. The fitting and spring can be formed for hard plastic or any suitable metal such as copper, stainless steel or brass. The spring may be galvanized if desired.  
         [0027]    The connection of the present invention along with the method of forming this connection provides many different advantages. From an assembly point of view, the process requires only one step. The spring and the fitting are inserted in one quick operation. Further, the spring itself will remain in a tensioned condition applying kinetic energy to the connection.  
         [0028]    As expansion and contraction, the spring will compensate for any changes maintaining radial compressive force against the fitment.  
         [0029]    Thus, the present invention provides a significantly improved fitment which is not significantly greater in cost than standard prior art fitment. This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims wherein we claim: