Abstract:
A two piston cylinder providing asymmetrical expansion and retraction capabilities is disclosed having two linked expansion chambers and a single chamber for retraction. The refraction chamber is situated between the two expansion chambers, and the expansion chambers are linked together by a tube passing through the piston that provides hydraulic fluid to both the retraction chamber and one of the expansion chambers.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to hydraulic cylinders, and more specifically to dual acting hydraulic cylinders that provide an asymmetrical power output during extension and retraction of a ram. 
     BACKGROUND OF THE INVENTION 
     Hydraulic cylinders typically consist of a cylinder barrel, in which a piston connected to a piston rod moves back and forth. The barrel is closed on each end by an end cap and by a gland where the piston rod comes out of the cylinder. The piston has sliding rings and seals. Typically, the piston divides the inside of the cylinder in two chambers, the expansion chamber and the retraction chamber. 
     In a single acting cylinder, hydraulic fluid is supplied to the expansion chamber, which applies a force against a first side of the piston causing it to move thereby increasing the size of the expansion chamber. To retract the cylinder, an external force is applied against the piston rod that causes the hydraulic fluid to exit from the expansion chamber. 
     In a dual acting cylinder, hydraulic fluid is supplied to the expansion chamber to extend the piston as with the single acting cylinder. For retraction, hydraulic fluid is supplied to the retraction chamber which applies a force against a second side of the piston causing it to retract. In a dual acting cylinder, the force supplied by the hydraulic fluid is dependent on the pressure of the hydraulic fluid and the surface area of the piston in contract with the hydraulic fluid. As a result of the two sides of the piston having similar surface areas and a common source typically being used to supply fluid for retraction and expansion, the ability of the cylinder to expand and contract against a load is often quite similar. 
     While the expansion and retraction abilities of a dual acting cylinder are often quite similar, it is common for substantially more power to be needed in the expansion direction as compared to retraction. When hydraulic cylinders are used on front end loaders, forces from gravity often assist in the retraction of the cylinder. 
     Attempts have been made by others to create hydraulic cylinders with asymmetric expansion and retraction power, however these designs typically involve a cumbersome additions to the cylinder and require a substantial increase in cylinder size. 
     U.S. Pat. No. 1,788,298 issued to Hottel in 1928 describes a fluid press or jack with an expansible chamber . . . a second expansible chamber between the inner face of the piston head and the ring or abutment . . . . For the purpose of simultaneously admitting fluid-pressure into the expansible chamber and the expansible chamber, a connection communicates with the chamber and a passageway is formed in the wall of the combined piston and cylinder structure. The Hottel design requires an extremely thick cylinder wall and is not practical for situations where the weight of the cylinder is a consideration. 
     U.S. Pat. No. 3,563,136 issued to Valente in 1971 describes a variable force hydraulic press with conduit means provided in said housing to achieve a fluid path from each said chamber to the exterior thereof, said fluid paths being associated with a source of fluid under pressure and control means. Accordingly, a selective application of fluid pressure to either or both said chambers may be attained, with the force exerted by said ram varying according to the total piston surface area subject to said fluid pressure. Like the Hottel patent, the Valente patent describes a press that requires a substantial amount of material and is not practical for situations where the weight of the hydraulic cylinder is a consideration. 
     SUMMARY OF THE INVENTION 
     A two piston cylinder providing asymmetrical expansion and retraction capabilities is disclosed having two linked expansion chambers and a single chamber for retraction. The refraction chamber is situated between the two expansion chambers, and the expansion chambers are linked together by a tube passing through the piston that provides hydraulic fluid to both the retraction chamber and one of the expansion chambers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a cross section of a two piston hydraulic cylinder. 
         FIG. 2  shows a cross section of a two piston hydraulic cylinder fully retracted. 
         FIG. 3  shows a cross section of a two piston hydraulic cylinder fully extended. 
         FIG. 4  shows a cross section of a two piston hydraulic cylinder with hydraulic fluid flowing in to extend the ram. 
         FIG. 5  shows a cross section of a two piston hydraulic cylinder with hydraulic fluid flowing in to retract the ram. 
         FIG. 6  shows a cross section of a two piston hydraulic cylinder with hydraulic fluid flowing in to retract the ram. 
         FIG. 7  shows an exploded perspective view of a two piston hydraulic cylinder. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention may be used with any fluid operable device. Although the preferred embodiment of the present invention is intended and adapted for use as a hydraulic cylinder on a loader and tractor, those of skill in the art will recognize that the present invention is equally adaptable for use with other fluid operable devices. However, for descriptive purposes, the present invention will be described in use of a hydraulic cylinder. 
       FIG. 1  illustrates an example of a two piston cylinder  10  having a hollow ram  15  passing through an outer gland  20  that is welded onto a barrel  25 . The ram  15  is threaded onto a piston  30  and encloses an inner gland  35  that is threaded onto a double walled concentric tube  40 . The concentric tube  40  passes through the piston  30  and is threaded into an oil inlet gland  45 . The ram  15  is substantially hollow to enclose the inner gland  35  and is of sufficient strength to withstand the pressure of hydraulic fluid radially pressing against the interior of the ram. In the wall of the ram  15 , a plurality of ram holes  50  are located between the concentric tube  40  and the barrel  25 . The ram holes  50  allow hydraulic fluid to pass from within the ram  15  to the gap between the ram  15  and the barrel  25 . A plurality of ram threads  55  are used to secure the ram  15  to the piston. Aside from the ram threads  55 , the piston is symmetrical about an axis of rotation  110 . 
     The outer gland  20  includes an outer o-ring  60  pressed against the ram  15 . The outer o-ring  60  prevents hydraulic fluid from exiting the retraction chamber  65  as the ram  15  retracts back into the barrel  25 . 
     The barrel  25  includes an expanded end  75  that accepts the oil inlet gland  45 , but does not allow the gland to pass further into the barrel. U.S. Pat. No. 7,455,010 issued to Westendorf and Langenfeld, herein incorporated by reference, describes the expanded barrel in more detail. 
     The piston  30  includes a first and second outer seal ( 80  and  85 ) between the piston  30  and the barrel  25  that acts to prevent hydraulic fluid from passing from the retraction chamber  65  to the inner expansion chamber  90 . The piston  30  also includes an inner seal  95  around a hole  100  through which the concentric tube  40  passes. As with the first and second outer seals ( 80  and  85 ), the inner seal  95  acts to prevent the flow of hydraulic fluid from the retraction chamber  65  to the main expansion chamber  90 . In the illustrated example, the hole  100  is a circular hole centrally located on the axis of the piston  30  while the concentric tube  40  is circular. The concentric nature of the hole and piston allows the ram  15  to rotate about the concentric tube  40  which allows the ram pin  105  to rotate if needed. For situations where rotation of the ram pin  105  is unwanted, the inventor contemplates using a piston  30  that has a hole  100  that is not aligned with the axis of rotation  110  of the two piston cylinder. Other designs, such as a rectangular concentric tube, may be used to limit the rotation of the ram  15 . 
     The piston  30  has an expansion face  81  upon which hydraulic fluid acts to move the piston and expel the ram  15  from the cylinder. The piston also has a first retraction face  82  and a second retraction face  83 . The first retraction face  82  is located within the ram  15  while the second retraction face  83  is located between the ram  15  and the barrel  20 . The ram holes  50  in the barrel allow hydraulic fluid to flow from the retraction chamber  65  to the outer retraction chamber  66  or auxiliary chamber and act upon the second retraction face  83  of the piston. While the ram holes  50  increase the retraction power of the cylinder  10  by allowing the hydraulic fluid to act upon the second retraction face  83  of the piston  30 , the inventor contemplates that the ram  15  may be constructed without ram holes  50 . Removing the ram holes  50 , would prevent hydraulic fluid from entering the second retraction chamber  66  which would decrease the retraction power of the cylinder, but would allow the cylinder to retract more quickly with a comparable flow rate of hydraulic fluid. 
     The inner gland  35  is enclosed by the ram  15  and substantially encircled by the outer gland  20 . Within the ram  15 , the inner gland  35  acts to separate the retraction chamber  65  from the outer expansion chamber  115 . An inner gland seal  117  presses against the ram  15  to prevent hydraulic fluid in the outer expansion chamber  115  from leaking into the retraction chamber  65 . In the illustrated example, the inner gland  35  is threaded onto the concentric tube  40  with inner gland threads  120 . The inner gland  35  is secured to the concentric tube  40  in such a way to receive hydraulic fluid from the tube for both expansion and retraction of the ram  15 . In the illustrated example, the inner gland  35  includes a retraction port  125  on the axis of rotation  110  that is adapted to receive hydraulic fluid for retraction of the ram  15 . From the retraction port  125  the fluid passes through a retraction path  130  and into the retraction chamber  65 . An expansion port  135  on the inner gland  35  receives hydraulic fluid from the concentric tube and passes it through an expansion path  140  to the outer expansion chamber  115 . In the illustrated example, the expansion port  135  is concentric around the axis of rotation  110 , however non-concentric designs are also contemplated. Two retraction and expansion paths  130  and  140  are shown, however more or less paths may be used. Additionally, the inner gland  35  may lack any retraction paths due to the concentric tube directly providing hydraulic fluid to the retraction chamber as seen in other figures. The inner gland  35  has a flat outer face  145  that matches the flat face  150  of the ram  15 . With matching faces, the minimum size of the outer expansion chamber  115  is reduced and the range of movement of the ram  15  through the cylinder may be increased. Although a small minimal size of the outer expansion chamber  115  is preferred, The flat face  150  of the ram  15  should not block the expansion paths  140  of the inner gland  35  when the ram  15  is fully retracted since the force exerted by the hydraulic fluid on the ram is related to the surface area of the flat face  150  upon which the hydraulic fluid presses. 
     The concentric tube  40  includes an inner tube  155  and an outer tube  160 . In the illustrated example, both the inner and outer tubes ( 155  and  160 ) are concentric around the axis of rotation  110 . The inner tube  155  is secured to, and receives hydraulic fluid directly from, the oil inlet gland  45 . The inner tube is also secured to the retraction port  125  in the inner gland  35 , and serves to transfer hydraulic fluid from the oil inlet gland  45  to the inner gland  35 . While the inventor contemplates a variation in which the outer tube  160  receives hydraulic fluid directly from the oil inlet gland  45 , in the illustrated example the outer tube includes tube holes  165  located adjacent to the oil inlet gland  45  that fluidly connects the inner expansion chamber  90  and the outer expansion chamber  115  by allowing hydraulic fluid to flow from the inner expansion chamber  90  into the outer tube  160 . The outer tube  160  serves to transfer the hydraulic fluid from the tube holes  165  to the expansion port  135  of the inner gland  35 . The inner and outer tubes ( 155  and  160 ) of the concentric tube  40  are preferably of robust construction as the concentric tube serves to transfer all of the expansion forces on the flat outer face  145  of the inner gland to the oil inlet gland  45 . Additionally, during retraction of the ram  15  the combination of the concentric tube  40  and the outer gland  20  experience a force equal to those experienced by the ram pin  105 . 
     The oil inlet gland  45  is secured in the expanded end  75  of the barrel  15  and includes a retraction fluid port  170 , an expansion fluid port  175 , and a gland pin  180 . In the illustrated example, a retraction fluid path  185  leads to a threaded region  190  on the oil inlet gland  45  that is secured to the concentric tube  40 . The retraction fluid path  185  feeds oil directly to the inner tube  155  from the retraction fluid port. An expansion fluid path  195  extends through the oil inlet gland  45  between the expansion fluid port  175  and the inner expansion chamber  90 . The retraction fluid port  170  and the expansion fluid port  175  are in close proximity on the oil inlet gland  45  which allows the expansion fluid line (not shown) and the retraction fluid line (not shown) to be run to approximately the same place. Standard dual acting cylinders require fluid lines to be run to opposite ends of the hydraulic cylinder which creates a messy appearance and increases the likelihood that the lines will become snagged on something. The risk of catching fluid lines on foreign objects is especially great when the hydraulic cylinders are used on agricultural machinery such as a front end loader. 
       FIG. 2  illustrates an example of a cylinder fully retracted while  FIG. 3  illustrates an example of a cylinder that has been fully extended. In  FIG. 2 , the flat outer face  145  of the inner gland  45  is in close proximity with the flat face  150  of the ram  15 . Further retraction of the cylinder is prevented by the contact of the two flat faces. The tube holes  165  are near the piston  30 , however they are still accessible so that the hydraulic fluid in the inner expansion chamber  90  may flow to the outer expansion chamber  115  (extremely small in  FIG. 2 ). In  FIG. 3 , the second retraction face  83  of the piston  30  is pressed against the outer gland  20  preventing further expansion of the cylinder. Alternatively, a small portion of hydraulic fluid may become trapped between the second retraction face  83  and the outer gland  20  after the ram holes  50  are fully blocked by the outer gland  20  and the inner gland  35 . The trapped fluid prevents the ram  15  from expanding. In the illustrated example, bore holes  200  pass through the ram adjacent to the second retraction face  83 . After the ram holes  50  are blocked, the bore holes  200  in the ram  15  allow the hydraulic fluid to slowly flow back into the retraction chamber  65 . The slowed movement of the hydraulic fluid acts as a shock absorber and prevents the piston  30  from forcefully striking the outer gland  20  during rapid expansion of the cylinder.  FIGS. 2 and 3  also illustrate alternate forms of the concentric tube  40  and inner gland  35 . In the illustrated example, an inner tube path  205  extends directly from the inner tube  155  to the retraction chamber  65 . Also, the inner gland  35  does not contain any retraction paths  130  because the hydraulic fluid for retraction is provided directly from the concentric tube  40 . 
       FIG. 4  illustrates the flow of hydraulic fluid into the cylinder to extend the ram. An expansion fluid line (not shown) supplies hydraulic fluid to the expansion fluid port  175  which then flows through the expansion fluid path  195  of the oil inlet gland  45  to the inner expansion chamber  90 . A portion of the hydraulic fluid in the inner expansion chamber acts upon the expansion face  81  of the piston  30  to move the ram  15  outward, while another portion of the hydraulic fluid passes through the tube holes  165  and enters the gap between the inner tube  155  and the outer tube  160 . The hydraulic fluid flows through the concentric tube  40  until it enters the inner gland  35  at the expansion port  135 . From the expansion port  135 , the hydraulic fluid moves through the expansion path  140  in the inner gland  35  until it reaches the outer expansion chamber  115  where it acts upon the face  150  of the ram  15  to assist in extension of the ram  15 . The hydraulic fluid is capable of extending the ram  15  until the second retraction face  83  of the piston  30  contacts the outer gland  20 . The combined volumes of the inner expansion chamber  90 , the refraction chamber  65 , and the outer expansion chamber  115  increases as the piston  30  moves away from the oil inlet gland  45 . 
       FIG. 5  illustrates the flow of hydraulic fluid into the hydraulic cylinder to retract the ram  15 . A retraction fluid line (not shown) supplies hydraulic fluid to the retraction fluid port  180  which then flows through the retraction fluid path  185  of the oil inlet gland  45  until it reaches the threaded region  190  of the gland. At the threaded region  190 , the hydraulic fluid enters the inner tube  155  of the concentric tube were it flows towards the inner gland  35 . In the illustrated example, the hydraulic fluid passes through an inner tube path  205  to reach the refraction chamber  65  where it acts upon the first retraction face  82  of the piston  30  to retract the ram  15 . A portion of the hydraulic fluid passes out of the retraction chamber  65  through the ram holes  50  in the ram  15  to reach the second retraction chamber  66  where it acts upon the second refraction face  83  of the piston to assist in the retraction of the ram. In another variation illustrated in  FIG. 6 , instead of passing through the inner tube path, the hydraulic fluid flows to a retraction port in the inner gland, where it then flows through a retraction path in the gland to reach the retraction chamber.  FIG. 7  illustrates an exploded three dimensional view of a two piston hydraulic cylinder. 
     Other alterations, variations, and combinations are possible that fall within the scope of the present invention. Although the preferred embodiments of the present invention have been described, those skilled in the art will recognize other modifications that may be made that would nonetheless fall within the scope of the present invention. Therefore, the present invention should not be limited to the apparatus and method described. Instead, the scope of the present invention should be consistent with the invention claimed below.