Abstract:
A hydraulic cylinder includes piston and plunger assemblies fitted together with a retention ring. This design allows finish-machined pistons to be assembled without welding of semi-finished machine components.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of hydraulic cylinders and, in particular, to piston and plunger assemblies in hydraulic cylinders.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hydraulic cylinders are well known in the art. Conventional hydraulic cylinders include an outer cylinder capped at both ends. A piston is movably disposed in the cylinder. A hollow piston rod, or a plunger tube, in also movably disposed within the cylinder. As hydraulic pressure builds, the piston is moved, which in turn moves the plunger tube.  
           [0003]    The connection between the piston and the plunger tube can be made in a variety of ways known in the art. Welding is the most common connection means in telescopic hydraulic cylinders. The working efficiency of welding is low and it is difficult to remove spatter resulting from welding. Residual spatter may give rise to serious defects in the operation of the hydraulic cylinder. U.S. Pat. No. 5,960,696, issued to Niwa et al., addresses this concern, disclosing a device that includes a pipe in a spigot portion of the piston. The pipe is press fit into the interior of the spigot portion rather than welded. The press-fit pipe is included in the spigot portion to allow oil to flow through the pipe into a reservoir from an oil passage in the piston. It is intended to dispense with the pipe welding work and prevent contamination that results from welding. However, the patent does not address the connection between the piston and the plunger tube.  
           [0004]    The normal process for plunger assemblies is to weld semi-finished machined components and follow up with a finish operation. This process is not only inefficient because of the welding, but also extra time is required by the finish operation. The problem is magnified in multi-stage telescopic cylinders. Ideally, an assembly process would allow for finish-machined parts to be assembled without separate assembly (welding) and finishing steps.  
           [0005]    Therefore, what is needed is a hydraulic cylinder assembly that does not utilize welding in the assembly process. An improved connection between the piston and the plunger tube is also required. A process for assembling hydraulic cylinders that reduces time and cost is also needed.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is a hydraulic cylinder with a close fitted piston over a plunger tube. The close fitting replaces any welding needed to connect the piston and the plunger tube. A retention ring is used in conjunction with the close fitting to retain the piston.  
           [0007]    Each cylinder can include several plunger tube assemblies of varying diameters and lengths to make up a complete hydraulic cylinder. A piston is pre-machined to size, to match the corresponding plunger, and locked into position about the plunger. A spring tension split ring is incorporated to retain the piston. This retaining ring also helps carry the load placed on the piston. The plunger tube is provided with an oil hole to allow oil to pass from plunger to plunger for normal cylinder operation.  
           [0008]    Therefore, it is an aspect of this invention to provide a hydraulic cylinder that does not use welds to attach the piston to the plunger tube.  
           [0009]    It is another aspect of the invention to provide an improved connection between a piston and a plunger tube.  
           [0010]    It is yet another aspect of the invention to utilize a close fit with a retaining ring between the piston and the plunger tube.  
           [0011]    It is a further aspect of the invention to provide an assembly for a hydraulic cylinder with a substantially reduced process time.  
           [0012]    It is a further aspect of the invention to allow machine finished pistons to be assembled and substantially eliminate the need for a follow up machine finish operation.  
           [0013]    These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the appended claims and accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a cross sectional view of a plunger tube assembly used in the present invention.  
         [0015]    [0015]FIG. 2 is an isometric view of the plunger tube assembly shown in FIG. 1 detailing the insertion slot in use with the present invention.  
         [0016]    [0016]FIG. 3 is an isometric view of a telescopic hydraulic cylinder, a preferred embodiment of the present invention.  
         [0017]    [0017]FIG. 4 is a side view of a telescopic hydraulic cylinder in use with a dump body. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    [0018]FIG. 1 shows plunger tube assembly  10 . Plunger tube assembly  10  is selected from a variety of diameters and lengths to be movably inserted into the telescopic hydraulic cylinder shown in FIG. 3. A telescoping hydraulic cylinder will use several plunger tube assemblies  10 , each of differing diameter, in normal operation. The different diameters allow the telescoping cylinder to collapse upon itself when not in use.  
         [0019]    Piston  14  is pre-machined to size, specifically dimensioned to slide over plunger tube  12 . Piston  14  is close fitted over plunger tube  12 . In this manner, plunger tube  12  and piston  14  fit together to form plunger assembly  10 . Piston  14  includes piston locating surface  15 , which is a close sliding fit incorporated to align piston  14  on plunger tube  12 . Because of the close fitted piston, retained by retention ring  16 , no welds are required in the assembly process.  
         [0020]    After piston  14  is slid into position, retention ring  16  is inserted between piston  14  and plunger tube  12  through slotted opening  18  in piston  14 . Retention ring  16  maintains the position of piston  14  about plunger tube  12 . Retention ring  16  carries loads placed on piston  14  at piston centering surface  20 . Loads at piston locating surface  22  are carried by the end of plunger tube  12 . Piston surface  38  carries the thrust of plunger assembly  10  during extension. As each plunger is fully extended the load shifts to piston centering surface  20 . This surface locates plunger assembly  10  in a center position when fully extended from one plunger to another. The load on this surface is carried by retention ring  16 .  
         [0021]    In the preferred embodiment, piston  14  includes slotted opening  18 , as seen in FIG. 2. Slotted opening  18  is located directly over retention ring  16 . When installing piston  14  over plunger tube  12 , slotted opening  18  is used to insert retention ring  16  in its correct location.  
         [0022]    To assist in the installation of piston  14 , piston chamfer  26  is included. Piston chamfer  26  is an angular chamfer located near piston centering surface  20 . The angular chamfer is incorporated to assist in installing piston  14  about plunger tube  12 .  
         [0023]    Multiple plunger assemblies  10  with plunger tubes  12  of varying diameters can be incorporated into a telescopic hydraulic cylinder  30 , as shown in FIG. 3. FIG. 3 demonstrates the exterior of telescopic hydraulic cylinder  30  when extended. Plunger assembly  10  is located in cylinder  32 . Plunger assemblies of smaller diameters (not shown) are located in cylinders  34 . FIG. 4 demonstrates extended telescopic hydraulic cylinder  30  in use with dump body  36 .  
         [0024]    To extend telescopic hydraulic cylinder  30 , oil is introduced in to cylinder  32 . Hydraulic pressure is built up and pushes against piston end  38 , shown in FIG. 1. The hydraulic pressure pushes against this surface when extending each plunger. When closed, each plunger assembly  10  rests on piston end  38 . Piston stop  40  receives piston end  38  of the succeeding plunger. When closed, each succeeding plunger assembly  10  will rest against piston stop  40 .  
         [0025]    In a telescopic hydraulic cylinder with multiple plunger assemblies, plunger tube  12  includes plunger oil hole  42 . Plunger oil hole  42  allows oil to pass from plunger to plunger for normal cylinder operation. Once plunger tube assembly  10  is fully extended, oil (not shown) passes through plunger oil hole  42  to reach the next plunger assembly (not shown). Hydraulic pressure then pushes on the piston end (not shown) of the succeeding plunger, extending the succeeding plunger.  
         [0026]    Wear guide groove  44  is also included in the preferred embodiment. A non-metallic wear ring (not shown) is installed in wear guide groove  44 . The wear ring prevents metal-to-metal scoring between plunger tube assemblies as hydraulic pressure extends each plunger tube assembly  10 .  
         [0027]    Because of the close fit of piston  14  and retention ring  16  about plunger tube  12 , no welding steps are needed to assemble plunger assembly  10 . In the preferred embodiment, machine finished pistons are used for piston  14  so that no additional finishing step is required. The process time for a typical 6″ three stage cylinder using the present invention is reduced by approximately 30% over traditional methods of welding and including an additional finishing step.  
         [0028]    Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.