Abstract:
A hybrid piston rod having an outer metallic jacket bonded to a pultruded composite core. The composite core formed of fibrous strands coupled together by a binder material. The hybrid piston rod includes couplers that permit the hybrid piston rod to be coupled to a piston and positioned with a hydraulic cylinder. The resultant hydraulic cylinder can be used for construction equipment or in other applications where hydraulic cylinders are used.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/044,522 that was filed on Apr. 14, 2008 and is incorporated in its entirety by reference herein. 
     
    
     BACKGROUND 
       [0002]    A piston rod is used in combination with a piston and is positioned within a cylinder. The piston rod and piston move in a linear motion within the cylinder in response to a hydraulic force being applied to the piston. There is a need in the fluid power industry to reduce the weight of the piston rod in hydraulic cylinders to make the systems, in which they are used, lighter and more energy efficient. The primary criterion for determining diameter of the piston rod for a given hydraulic application is the column buckling requirements for the rod. While it is possible to manufacture a hollow piston rod, the resultant rod would sacrifice in buckling resistance. As an example, a hollow steel piston rod would reduce overall rod weight by forty percent but would reduce column buckling resistance by thirty percent as compared to a solid steel piston rod. 
       SUMMARY 
       [0003]    The present disclosure relates to piston rods for use in hydraulic applications. The piston rod is coupled to a piston and positioned within a hydraulic cylinder. The piston rods and piston move in reaction to a hydraulic pressure being applied to the piston. The force of the piston rod can be used in various hydraulic operations. 
         [0004]    In illustrative embodiments, the hybrid piston rod includes an outer metallic jacket or sleeve bonded to a pultruded composite core. The hybrid piston rod is coupled to a piston and is positioned with a hydraulic cylinder. The resultant hydraulic cylinder can be used for construction equipment or in other applications where hydraulic cylinders are used. The weight savings achieved by using the hybrid piston rod is approximately thirty percent with only a twelve percent reduction in buckling properties. The ratio of weight reduction to column buckling is significantly greater with the hybrid piston shaft. Since the piston rod weight often represents half the weight of the complete hydraulic cylinder, a reduction in rod weight is a significant factor in reducing the overall cylinder weight. 
         [0005]    Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The detailed description particularly refers to the accompanying figures in which: 
           [0007]      FIG. 1  is a sectional view of a hydraulic cylinder having a cylinder wall, a pair of end caps and also showing a piston and hybrid piston rod positioned within the cylinder wall; 
           [0008]      FIG. 2  is a perspective view of the hybrid piston rod showing a metal jacket surrounding a fiberglass pultruded rod; 
           [0009]      FIG. 3  is a perspective view of the hybrid piston rod showing the metal jacket adhered to the pultruded core; 
           [0010]      FIG. 4  is a graph of unsupported piston shaft length per factor of safety; and 
           [0011]      FIG. 5  is a graph of shaft weight per unsupported shaft length. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    A hybrid piston rod  10  is adapted to be used in a hydraulic cylinder  12 , as shown, in  FIG. 1 . The hydraulic cylinder  12  includes a tubular cylinder wall  14 , and first and second end caps  16 ,  18 . The hybrid piston rod  10  is coupled to a piston  20 , which is adapted to move within the cylinder  12 . The hybrid piston rod  10  consists of an outer metallic jacket or sleeve  22  bonded to a pultruded composite core  24  by use of an adhesive  26 , as shown in  FIGS. 2 and 3 . As an example, chrome plated and polished DOM 1026 tubing can be used as a jacket around a fiberglass pultruded rod core. Both the DOM 1026 tubing and pultruded rod core are bonded together by use of adhesive  26 . Other material may be used for the jacket  22  such as stainless steel. Other materials can also be used for the core  24  including pultruded graphite. Fiberglass with a thermoset plastic such as polyvinylesters can also be used, as an example. The adhesive can include epoxies and other adhesive known to have high bond characteristic between metal and composite materials. 
         [0013]    The core  24  of the hybrid piston rod  10  is manufactured by using a pultrusion process in one embodiment. To manufacture the core using the pultrusion process, strands of fiberglass material, that are pre-coated with a thermoset resin, are passed through heated curing dies that shape and cure the rod core  24 . The forming dies can control the dimension of the outer diameter of the core  24 . Alternatively, the outer surface of the core  24  can be machined to a desired diameter. While thermoset resins are preferred, it may be possible to use thermoplastics, however the resultant structure would not be as resistant to buckling. 
         [0014]    Alternatively, the fiberglass or carbon fiber strands can be dipped into a resin bath to coat the fibers before pulling them through the forming dies. The use of resin acts as a substitute to the thermoset plastic material being used to form the core  24 . The outer diameter of the core is either the same diameter or slightly less than the inner diameter of the sleeve if an adhesive is used or slightly oversized if a resistance fit is to be used to secure the components together. While graphite and fiberglass strands are described, it is contemplated that other types of fibers could also be used to form the core. Also, it is contemplated that the core could be manufactured using a unidirectional molding process as opposed to a pultrusion process. 
         [0015]    The weight savings by using hybrid piston rod  10  is 30% with only a 12% reduction in buckling properties. The ratio of weight reduction to column buckling is significantly greater with the hybrid piston rod  10  than a hollow metal piston rod. Since the piston rod weight often represents half the weight of the complete hydraulic cylinder  12 , a reduction in rod weight is a significant factor is reducing the overall cylinder weight. Listed below are several analytical scenarios for samples of the hybrid piston rod  10 . 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Reference Cylinder 
               
             
          
           
               
                   
                 1 
                 2 
                 3 
                 4 
               
               
                   
                   
               
             
          
           
               
                 Input: 
               
             
          
           
               
                 Cylinder Bore Size (in) 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
               
               
                 Operating Pressure (psi) 
                 3000 
                 3000 
                 3000 
                 3000 
               
               
                 Factor of Safety 
                 4 
                 4 
                 4 
                 4 
               
               
                 Unsupported Length (in) 
                 12 
                 24 
                 36 
                 48 
               
               
                 Clevis Pin Hole Diameter (in) 
                 0.64 
                 0.64 
                 0.64 
                 0.64 
               
               
                 Metal Type 
                 DOM 1026 
                 DOM 1026 
                 DOM 1026 
                 DOM 1026 
               
               
                 ldm 
                 0.625 
                 0.625 
                 0.625 
                 0.625 
               
               
                 ldm, tolerance 
                 −0.006 
                 −0.006 
                 −0.006 
                 −0.006 
               
               
                 Odm 
                 1.000 
                 1.000 
                 1.000 
                 1.000 
               
               
                 Emx 
                 30000000 
                 30000000 
                 30000000 
                 30000000 
               
               
                 Tm yield 
                 65000 
                 65000 
                 65000 
                 65000 
               
               
                 Tm, ultimate 
                 75000 
                 75000 
                 75000 
                 75000 
               
               
                 Density −m, lb/in{circumflex over ( )}3 
                 0.282 
                 0.282 
                 0.282 
                 0.282 
               
               
                 Composite Type 
                 Pultruded 
                 Pultruded 
                 Pultruded 
                 Pultruded 
               
               
                 ODc 
                 0.615 
                 0.615 
                 0.615 
                 0.615 
               
               
                 Ecx 
                 6000000 
                 6000000 
                 6000000 
                 6000000 
               
               
                 Tcx 
                 100000 
                 100000 
                 100000 
                 100000 
               
               
                 Ccx 
                 100000 
                 100000 
                 100000 
                 100000 
               
               
                 Density −c, lb/in{circumflex over ( )}3 
                 0.074 
                 0.074 
                 0.074 
                 0.074 
               
             
          
           
               
                 Results: 
               
             
          
           
               
                 Compression Force (Full face) 
                 5301 
                 5301 
                 5301 
                 5301 
               
               
                 Tensile Force (Rod face) 
                 4410 
                 4410 
                 4410 
                 4410 
               
               
                 C/S area metal 
                 0.478602 
                 0.478602 
                 0.478602 
                 0.478602 
               
               
                 C/S area composite 
                 0.297057 
                 0.297057 
                 0.297057 
                 0.297057 
               
               
                 C/S area total 
                 0.775659 
                 0.775659 
                 0.775659 
                 0.775659 
               
               
                 “I” metal 
                 0.041597 
                 0.041597 
                 0.041597 
                 0.041597 
               
               
                 “Ix” composite 
                 0.007022 
                 0.007022 
                 0.007022 
                 0.007022 
               
               
                 “I” total 
                 0.048619 
                 0.048619 
                 0.048619 
                 0.048619 
               
               
                 Ex hybrid 
                 26533701 
                 26533701 
                 26533701 
                 26533701 
               
               
                 Jo hybrid, polar moment of 
                 0.098175 
                 0.098175 
                 0.098175 
                 0.098175 
               
               
                 inertia 
               
               
                 ko, hybrid, radius of gyration 
                 0.355766 
                 0.355766 
                 0.355766 
                 0.355766 
               
               
                 C, coefficent of constraint 
                 1 
                 1 
                 1 
                 1 
               
               
                 Critical column buckling stress, 
                 230178 
                 57545 
                 25575 
                 14386 
               
               
                 hybrid 
               
               
                 Compression stress in hybrid 
                 6834 
                 6834 
                 6834 
                 6834 
               
               
                 piston rod 
               
               
                 Colume Buckling Factor of 
                 33.7 
                 8.4 
                 3.7 
                 2.1 
               
               
                 Safety, Hybrid 
               
               
                 Compression Strain, hybrid 
                 0.003091 
                 0.006182 
                 0.009272 
                 0.012363 
               
               
                 Compression stress in metal 
                 7728 
                 7728 
                 7727 
                 7727 
               
               
                 jacket 
               
               
                 Compression stress in 
                 1546 
                 1546 
                 1545 
                 1545 
               
               
                 composite core 
               
               
                 Compression Yield Factor of Safety - 
                 8.4 
                 8.4 
                 8.4 
                 8.4 
               
               
                 Metal Jacket 
               
               
                 Compresion Factor of Safety - 
                 64.7 
                 64.7 
                 64.7 
                 64.7 
               
               
                 Compoiste 
               
               
                 Jo, metal jacket, polar moment 
                 0.068214 
                 0.068214 
                 0.068214 
                 0.068214 
               
               
                 of inertia 
               
               
                 ko, metal jacket, radius of 
                 0.377528 
                 0.377528 
                 0.377528 
                 0.377528 
               
               
                 gyration 
               
               
                 Critical column buckling stress, 
                 293060 
                 73265 
                 32562 
                 18316 
               
               
                 metal jacket (only) 
               
               
                 Compresion stress in metal 
                 11076 
                 11076 
                 11076 
                 11076 
               
               
                 jacket (only) 
               
               
                 Column Buckling Factor of Safety, 
                 26.5 
                 6.6 
                 2.9 
                 1.7 
               
               
                 metal jacket (only) 
               
               
                 Jo, Metal (solid shaft), polar 
                 0.098175 
                 0.098175 
                 0.098175 
                 0.098175 
               
               
                 moment of inertia 
               
               
                 ko, metal shaft, radius of 
                 0.355766 
                 0.355766 
                 0.355766 
                 0.355766 
               
               
                 gyration 
               
               
                 Critical column buckling stress, 
                 260248 
                 65062 
                 28916 
                 16265 
               
               
                 metal shaft (solid) 
               
               
                 Compresion stress in metal shaft 
                 6834 
                 6834 
                 6834 
                 6834 
               
               
                 (solid) 
               
               
                 Column Buckling Factor of Safety, 
                 38.1 
                 9.5 
                 4.2 
                 2.4 
               
               
                 metal shaft only 
               
               
                 Wt/Length Metal Jacket 
                 1.6196 
                 3.2392 
                 4.8588 
                 6.4784 
               
               
                 Wt/Length Composite Core 
                 0.2638 
                 0.5276 
                 0.7914 
                 1.0551 
               
               
                 Wt/Length Hybrid piston shaft 
                 1.8834 
                 3.7668 
                 5.6502 
                 7.5335 
               
               
                 Wt/Length Solid Metal Shaft 
                 2.6578 
                 5.3156 
                 7.9734 
                 10.6311 
               
               
                   
               
             
          
         
       
     
         [0016]      FIG. 4  is a graph of several piston rods with unsupported shaft length on the x-axis and factor of safety on the y-axis. As can be seen, the hybrid piston rod has characteristics that are very similar to the solid metal shaft with respect to column buckling. While having similar characteristics to a solid metallic rod, the weight savings are substantial. 
         [0017]      FIG. 5  is a graph of both metal and hybrid piston rods regarding the weight of the piston rod per unsupported shaft length. The shaft length is positioned on the x-axis and the weight per unsupported shaft length is positioned on the y-axis. As can be seen the characteristics of the hybrid piston rod are very similar to the solid metal piston shaft. Data for the graph is set forth in the table. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
             
               
               
             
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Factors of Safety, Piston Rods 
               
             
          
           
               
                   
                 Shaft Unsupported Length (in) 
               
             
          
           
               
                   
                 12 
                 24 
                 36 
                 48 
               
               
                   
               
               
                 Hybrid, Column Buckling 
                 33.7 
                 8.4 
                 3.7 
                 2.1 
               
               
                 Solid Metal Shaft, Column Buckling 
                 38.1 
                 9.5 
                 4.2 
                 2.4 
               
               
                 Metal Jacket (only), Column 
                 26.5 
                 6.6 
                 2.9 
                 1.7 
               
               
                 Buckling 
               
               
                 Metal Jacket (Hybrid), Compression 
                 8.4 
                 8.4 
                 8.4 
                 8.4 
               
               
                 (Yield) 
               
               
                 Composite Core (Hybrid), 
                 64.7 
                 64.7 
                 64.7 
                 64.7 
               
               
                 Compression 
               
               
                   
               
             
          
           
               
                 Shaft Weights per Unsupported 
               
               
                 Length 
               
             
          
           
               
                   
                 Shaft Length (in) 
               
             
          
           
               
                   
                 12 
                 24 
                 36 
                 48 
               
               
                   
               
               
                 Solid Metal Piston Shaft 
                 2.6578 
                 5.3156 
                 7.9734 
                 10.6311 
               
               
                 Hybrid Piston Shaft 
                 1.8834 
                 3.7668 
                 5.6502 
                 7.5335 
               
               
                   
               
             
          
         
       
     
         [0018]    The hybrid piston rod  10  can be used in place of traditional all steel piston rods to provide for a significant savings in weight but provide for similar strength properties. The ends of the piston rod  10  can be finished with couplings to allow the rod  10  to be coupled to the piston on one end and to other components on the second end. The couplings can be either welded to the jacket  22  of piston rod  10  or secured by threading, pinning, adhesive, or resistance fit. The couplings can be either butted up to the end of the position rod  10  or positioned within the jacket  22 . If positioned within the jacket  22 , the core  24  would be positioned to lie against the coupling. 
         [0019]    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.