Abstract:
A hydraulic device that includes a case, and a substantially hollow rod slidably extending from the case. The rod has a ram on a first end thereof that caps the rod to form a first hydraulic piston. The rod has a second hydraulic piston on a second end thereof, inside the case. The first and second pistons are at least partially radially coextensive, and a pressure barrier inhibits high pressure on the first piston inside the hollow rod from reaching a side of the second piston that faces the first piston.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of U.S. Provisional Patent Application No. 61/426,420 entitled “LIGHTWEIGHT CYLINDER,” filed Dec. 22, 2010, the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    This disclosure relates to hydraulic systems in general and, more particularly, to hydraulic actuators. 
       BACKGROUND 
       [0003]    Hydraulic systems are ubiquitous in the modern age. Nearly every machine in which a linear actuation or force is needed or can be used to produce a desired end can be constructed with hydraulics. Hydraulic systems are often more reliable, powerful, and versatile that electric based actuators. Additionally, hydraulic pumps can easily be driven from power take off (PTO) devices that are commonly built into industrial transmissions. 
         [0004]    Although hydraulic systems provide a good power to weight ratio, and are ultimately may be powered by the same engine that moves a vehicle, they are limited by the available pressure and the overall physical dimensions of the actuators and pistons. In order to make a more powerful hydraulic actuator, one has to increase the pressure to the actuator, or increase the size of the actuator. Naturally, application of pressure has an upper limit as pumps, seals, and gaskets can only operate within a limited range of specifications before part failure is imminent. The technique of increasing the size of the actuator also has limits as this increases the overall size and bulkiness of the completed system. 
         [0005]    What is needed is a device and method that addresses the above, and related, issues. 
       SUMMARY 
       [0006]    The invention of the present disclosure as disclosed and claimed herein, according to one aspect thereof, comprises a hydraulic device that includes a case, and a substantially hollow rod slidably extending from the case. The rod has a ram on a first end thereof that caps the rod to form a first hydraulic piston. The rod has a second hydraulic piston on a second end thereof, inside the case. The first and second pistons are at least partially radially coextensive, and a pressure barrier inhibits high pressure on the first piston inside the hollow rod from reaching a side of the second piston that faces the first piston. 
         [0007]    In one embodiment, the hydraulic device includes a rod guide inside the case and coaxial thereto, with the second piston slidably interposing the case and the rod guide. The pressure barrier may interpose the guide rod and the substantially hollow rod. A high-pressure, variable volume in the device may comprise a first volume inside the guide rod, a volume bound by the case and the second piston, and a volume between the first piston and the pressure barrier. In some embodiments, a low-pressure, variable volume inside the device comprises an area bound by the case, the guide rod, the second piston, and the pressure barrier. 
         [0008]    The case and ram may be urged apart by a relatively high pressure fluid inside the high pressure volume compared to the low pressure volume, and the case and ram may be urged together by a relatively high pressure fluid inside the low pressure volume relative to the high pressure volume. A high-pressure port may be provided on the case entering the high pressure volume, and a low pressure port may be provided on the case entering the low pressure volume. Some embodiments include at least one pressure equalizing port defined in the rod guide; some include at least one pressure equalizing port defined in the hollow rod. 
         [0009]    In some embodiments, the case and rod guide have a substantially circular cross-section. The rod guide may attach inside the case on a first end thereof, and may have a second tapered and threaded end that accepts the pressure barrier and retains the pressure barrier against the tapered end by an attached threaded cap. The device may also include a retainer on an open end of the case engaging the hollow rod and preventing the second cylinder from contacting the pressure barrier. 
         [0010]    The invention of the present disclosure, in another aspect thereof, comprises a device having a substantially cylindrical case with a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial. The device includes a fixed pressure barrier on an end of the guide member proximate the open end of the case. A first piston defines a hollow center and is located between the case and guide member, the piston being movable between the pressure barrier and the second end of the case. A hollow rod attaches on a first end to the first piston, encircles the pressure barrier, and attaches on a second end to a second piston. 
         [0011]    In some embodiments, the guide member defines a pressure equalizing port proximate the second end of the case such that a first single pressure volume of variable total size is defined by 1) the variable volume bound between the first piston, the case, and the guide member, 2) the volume inside the guide member, and 3) the volume between the pressure barrier, the second piston, and the hollow rod. A hydraulic port may be provided on the case accessing the first single pressure volume. 
         [0012]    The guide member may have a tapered portion and a threaded end, the guide member retaining the pressure barrier between the tapered portion and the threaded end by an attached threaded cap. Some embodiments will have a retainer attached to the open end of the case and abutting the hollow rod on a side opposite the pressure barrier such that the hollow rod slides into the retainer, the retainer sealing the second end of the case to prevent the first piston from leaving the case 
         [0013]    In some embodiments, the hollow rod defines a pressure equalizing port proximate the first piston such that a second single pressure volume of variable total size is defined by 1) the variable volume bound inside the hollow rod, outside the guide member, and between the first piston and pressure barrier, and 2) the variable volume bound outside the hollow rod, inside the case, and between the first piston and retainer. A hydraulic port may be provided on the case accessing the second single pressure volume. 
         [0014]    The invention of the present disclosure, in another aspect thereof, comprises a method including providing a substantially cylindrical case having a first, open end and a substantially cylindrical guide member inside thereof attached to a second end, the case and guide member being substantially coaxial, and inserting a piston that defines a hollow center between the case and guide member such that the guide member passes through the hollow center and the piston is movable along the guide member. The method includes attaching a fixed pressure barrier on and end of the guide member proximate the open end of the case such that the piston does not leave the case, attaching a first end of a hollow rod to the piston such that the hollow rod encircles the pressure barrier, and attaching a cap to a second end of the hollow rod, the cap being sized such that the cap and first piston are at least partially radially extensive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a side cutaway view of a hydraulic cylinder according to aspects of the present disclosure. 
           [0016]      FIG. 2  is an end-on cutaway view of the hydraulic cylinder of  FIG. 1 . 
           [0017]      FIG. 3  is a side view of the hydraulic cylinder of  FIG. 1  shown in an extended position. 
           [0018]      FIG. 4  is a side cutaway view corresponding to  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring now to  FIG. 1 , a side cutaway view of a hydraulic cylinder according to aspects of the present disclosure is shown. The hydraulic cylinder  100  has a case  102  having a closed end  103  and an opposite, open end  105 . In the present embodiment the case  102  is generally cylindrical in shape. The case  102  and other components described herein may be constructed from steel or another material suitable for use in hydraulics. A attachment point  104  may be provided on the closed end  103  to allow the cylinder  100  to be attached to machinery or other implements. On the open end  105  is a second attachment point  106 . In the present embodiment, the attachment points  104 ,  106  are simple loops but in other embodiments the attachment points  104 ,  106  may comprise clamps, knobs, threaded connections or other implements. The attachment points  104 ,  106  may also be considered hydraulic rams as explained in greater detail below. 
         [0020]    In the present embodiment the attachment point  106  attaches threadingly to a hollow rod  114  and forms a hydraulic piston with the piston face  108  inside the rod  114 . In some embodiments, the attachment point may be welded to the rod  114  or attached by other means. The piston face  108 , in response to hydraulic pressure, will tend to urge the attachments  104  and  106  away from one another. 
         [0021]    In the present embodiment a second piston  110  is provided inside the case  102 . The second piston  110  is toroidal in shape in the present embodiment. Since  FIG. 1  is a side cutaway view, the piston  110  may be seen at the top and bottom of the figure inside the case  102 . The piston  110  provides a piston face  112  that will also tend to urge the ends  104  and  106  apart in response to hydraulic pressure. 
         [0022]    A threaded cap or retainer  116  may thread into the case  102  in order to prevent the piston  110  from leaving the case  102  entirely. Various o-rings and seals are provided throughout the device  100  where needed to maintain proper hydraulic pressure. For example an o-ring seal is provided between the attachment point  106  and the hollow rod  114 . The retainer  116  provides two o-ring seals  118 ,  120  for the case  102  and rod  114 , respectively. In the present embodiment, an additional seal  122  is held by the retainer  116  and circumscribes the rod  114  and is held. 
         [0023]    In the present embodiment, inside the case  102  and attached in a fixed relationship to the closed end  103  of the case  102  is a guide rod  124 . In the present embodiment the guide rod is substantially cylindrical and hollow. The piston  110  may ride along the guide rod  124  as it moves within the case  102 . An o-ring  134  seals the piston  110  against the case  102 . A second o-ring  132  seals the piston  110  against the guide rod  124 . 
         [0024]    The guide rod  124  provides a tapered end  125  that is also threaded. In the present embodiment, a pressure barrier  126  is retained on the tapered end  125  of guide rod  124  by a threaded cap  128 . In some embodiments the end  125  may stepped rather than tapered. The pressure barrier  126  is thus held in fixed relationship to the guide rod  124  and case  102 . In some embodiments, the pressure barrier  126  threads directly to the guide rod  124 . In order to effectively block high pressure from reaching a back side  113  of the piston  110  the pressure barrier may seal against the hollow rod  114 . O-ring seals  128 ,  130  are provided for sealing the pressure barrier  126  against the hollow rod  114  and the guide rod  124 , respectively. 
         [0025]    One or more pressure equalization ports  123  may be defined in the guide rod  124  proximate the end  103  of the case  102 . This allows a single high pressure volume  302  to be defined that includes: the variable volume bound by the piston  110 , the case  102  and the guide rod  124 ; the volume bound by the interior of the guide rod  124 ; and the variable volume bound by the pressure barrier  126  and the piston  108 . A high pressure hydraulic port  136  may be installed in the case  102  near the end  103 . In response to hydraulic pressure supplies at the port  136 , the volume  302  will expand forcing the attachment points  104 ,  106  apart. Due to the pistons  108 ,  110 , having at least partial overlap in their radii, and the presence of the pressure barrier  126  on the guide rod  124 , the expansive force of the attachment points  104 ,  106  will be increased. Depending upon the diameter of the guide rod  124  and the retainer  116 , and the thickness of various components, the output of the cylinder  100  could approach twice the output of a traditional hydraulic cylinder at a given pressure. 
         [0026]    The hollow rod  114  may have one or more pressure equalization ports  115  defined therein proximate the piston  110 . This allows a single variable low pressure volume  304  to be defined by the two variable volumes including: the volume bound by the rod  114  and the guide rod  124  between the piston  110  and the pressure barrier  126 ; and the volume bound by the case  102  and rod  114  between the piston  110  and the retainer  116 . In the present embodiment, the case  102  provides a low pressure hydraulic port  138  proximate the retainer  116 . 
         [0027]    In operation, any time a greater hydraulic pressure exists in the high pressure volume  302  than the low pressure volume  304 , the ends  104  and  106  will be urged apart. If the low pressure volume  304  is pressurized to a greater degree than the high pressure volume  302 , the ends  104  and  106  will be urged back together. (It is understood that under various operating conditions, it may be necessary for the pressure in the low pressure volume  304  to actually be higher than that of the high pressure volume  302 .) 
         [0028]    Referring now to  FIG. 2  an end-on cutaway view of the hydraulic cylinder of  FIG. 1  is shown (e.g., taken along line AA in  FIG. 1 ). As previously described, the general shape of the case  102  may be that of a cylinder. Therefore when viewed as an end-on cutaway, the case  102  will appear circular. Here it can be seen how the piston face  108  is bound circumferentially by the hollow rod  114  (shown in ghost) behind piston  110 . And the interior piston  110  is retained between the case  102  and the guide rod  124 . From this view it can also be appreciated how, depending upon the thickness and diameter of various components, the amount of force available with a hydraulic cylinder of the present design can approach double that of a traditional design. 
         [0029]    Referring now to  FIG. 3 , a side view of the hydraulic cylinder of  FIG. 1  is shown. This view illustrates the cylinder  100  in an extended position. Here the hollow rod  114  is substantially fully extended and the first end  104  and second end  106  are further apart then shown in  FIG. 1 . 
         [0030]    Referring now to  FIG. 4 , a side cutaway view corresponding to  FIG. 3  is shown. As a result of a higher pressure in the volume  302  than in the volume  304 , the piston  110 , the piston  108 , and the rod  114 , have all extended away from the first end  103  of the case  102  forcing the ends  104 ,  106  apart. Because at least one pressure point  123  is defined in the guide member  124 , high pressure can exist throughout the volume  302 . Also, because the pressure barrier  126  prevents the high pressure from reaching both sides of the piston  110 , at least a portion of the hydraulic forced input on port  136  is doubled within the cylinder  100  by the two pistons  110 ,  108 . 
         [0031]    Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.