Abstract:
An actuator is provided. The actuator includes: a housing having an interior elongated hole; a rod dimensioned to fit in the elongated hole; a piston dimensioned to fit in and move along the elongated hole while connected to the rod; mating structure located on at least one of the piston and rod, the mating structure configured to allow the rod to attach to the piston in a manner to create clearance between the rod and the piston to allow the rod and piston to move with respect to each other. A method of attaching a piston to a rod in an actuator may also be provided. The method may include: fitting the piston to the rod; providing a clearance between the piston and the rod; fastening the piston to the rod in a loose manner as to preserve the clearance and allow the piston to move with respect to the rod.

Description:
[0001]    This application claims the benefit of a provisional U.S. patent application entitled Floating Piston, having a Ser. No. 62/027,289, filed Jul. 22, 2014. The disclosure of this application is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to piston and rod attachment systems and methods. More particularly, the present invention relates to a system and method of attaching a piston to a rod to reduce stress on the piston and rod resulting from side loads on the rod. 
       BACKGROUND OF THE INVENTION 
       [0003]    An actuator is a mechanism often used to lift or move an object or to clamp an object to prevent motion. An actuator may introduce linear or non-linear motion. Examples of actuators include hydraulic cylinders and/or pneumatic cylinders. Actuators are used in many applications, including construction equipment, engineering vehicles and manufacturing machinery. For example, the hydraulic cylinder is a mechanical actuator that may provide a unidirectional force through a unidirectional stroke. The hydraulic cylinder consists of a cylinder housing in which a piston connected to a rod moves back and forth. 
         [0004]    Actuators suffer from disadvantages or drawbacks associated with the misalignment of the rod. This misalignment may result when the longitudinal axis of the rod is not co-located with the longitudinal axis of the bore of the cylinder. This misalignment may be the result of setting poorly balanced or off-center loads on the cylinder. It is not uncommon for a load to be placed on the rod where the forces acting upon the rod are not acting in parallel to the longitudinal axis of the cylinder. These types of forces or loads are sometimes referred to as side loads or side loading. Side loads may occur, for example, when the rod contacts an uneven surface. Side loading may cause damage to the rod, piston, and other components of the cylinder, and cause the cylinder assembly to ultimately fail. 
         [0005]    Much effort has been made by manufacturers of hydraulic cylinders to reduce or eliminate the side loading of cylinders. It is almost impossible to achieve perfect alignment of a hydraulic cylinder, even though the alignment of the cylinder has a direct impact on the longevity of the hydraulic cylinder. Actuators for many applications are custom made and expensive so prolonging their life and operation can represent significant savings. 
         [0006]    These prior art methods and systems, however, have not sufficiently reduced or eliminated bending moments that cause stress on the rod and ultimately lead to rod failure. Therefore, there is a need for actuators that can operate to reduce bending moments that can potentially cause the cylinder assembly to fail. 
         [0007]    The presently disclosed system and method is directed at overcoming one or more of these disadvantages in currently available actuators. 
       SUMMARY OF THE INVENTION 
       [0008]    The foregoing needs are met, to a great extent, by the present invention, where one aspect an apparatus is provided that in some embodiments a rod is fitted to a piston in such a manner as to allow the piston to float or move with respect to the rod. In some embodiments, the float or movement of the piston allows displacement of the rod due to side loads. This results in a reduced stress level on the outer diameter of the piston. 
         [0009]    In accordance with an embodiment of the present disclosure, an actuator is provided. The actuator includes: a housing having an interior elongated hole; a rod dimensioned to fit in the elongated hole; a piston dimensioned to fit in and move along the elongated hole while connected to the rod; mating structure located on at least one of the piston and rod, the mating structure configured to allow the rod to attach to the piston in a manner to create clearance between the rod and the piston to allow the rod and piston to move with respect to each other. 
         [0010]    In accordance with another embodiment of the present disclosure, a method of attaching a piston to a rod in an actuator may also be provided. The method may include: fitting the piston to the rod; providing a clearance between the piston and the rod; fastening the piston to the rod in a loose manner as to preserve the clearance and allow the piston to move with respect to the rod. 
         [0011]    In accordance with yet another embodiment of the present invention, an actuator may be provided. The actuator may include: a housing having an interior elongated hole; a rod dimensioned to fit in the elongated hole; a piston dimensioned to fit in the elongated hole; means for connecting the piston and the rod located on at least one of the piston and rod, the means for connecting is configured to allow the rod to attach to the piston in a manner to create clearance between the rod and the piston to allow the rod and piston to move with respect to each other. 
         [0012]    There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0013]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0014]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of a cylinder assembly where the rod is in an extended position in accordance with an embodiment; 
           [0016]      FIG. 2  is a cross-sectional view of a cylinder assembly where the rod is in a retracted position in accordance with an embodiment; 
           [0017]      FIG. 3  is a partial cross-sectional view of a cylinder assembly showing additional detail; 
           [0018]      FIG. 4  is a partial cross-sectional view of a cylinder assembly; 
           [0019]      FIG. 5  is a partial cross-sectional view of a cylinder assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Example embodiments in accordance with the present disclosure will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present disclosure is found in the accompanying figures. And actuator may include a piston and cylinder assembly similar to that shown. While the example described herein is a hydraulic cylinder, it will be understood principles of the present disclosure are not limited to hydraulic cylinders but may be used with pneumatic cylinders, gas filled cylinders, or any other type of cylinder or actuator. 
         [0021]    An embodiment of the present inventive apparatus is illustrated in  FIGS. 1 and 2 .  FIGS. 1 and 2  illustrate a cross-sectional view of a hydraulic cylinder assembly  111 . The hydraulic cylinder assembly  111  includes a hydraulic cylinder  112  having a housing  113 . The hydraulic cylinder housing  113  defines an interior space  114 . The hydraulic cylinder  112  contains a plug  120  and a retainer  122  to define a substantially fluid tight interior  114 . A first port  116  and a second port  118  provide inlet/outlets for hydraulic fluid to enter or leave the interior  114  of the hydraulic cylinder  112 . 
         [0022]    When hydraulic fluid enters the second port  118  and exits the first port  116 , the piston  124  is pushed upward as shown in  FIG. 1 . This causes the rod or shaft  126  to move out of the hydraulic cylinder  112 . When hydraulic fluid enters the first port  116  and exits the second port  118 , the piston is pushed inward as shown in  FIG. 2 . This causes the rod or shaft  126  to move into the hydraulic cylinder  112 . 
         [0023]    As the rod or shaft  126  moves in and out of the hydraulic cylinder  112 , the rod  126  slides against the retainer  122 . Often, the rod  126  is subjected to side loads or, in other words, loads that are not in line with the longitudinal axis of the cylinder  112 . Side loads cause the rod  126  to urge against the retainer  122 . Wear of the surface  128  of the rod  126  against the retainer  122  can cause damage to the surface  128  of the rod  126  and/or retainer  122 . 
         [0024]      FIG. 3  is an enlarged detailed partial cross-sectional view similar to that shown in  FIG. 2 . The rod  126  is seated in a socket portion  250  of the piston  124 . The piston  124  may include various voids  252 ,  254 , and  256 . These voids  252 ,  254 , and  256  may be used for various inserts such as piston seals or any other inserts. In other embodiments they may be left as voids or not be present. In still other embodiments, there may be more or fewer voids  252 ,  254  and  256  than as shown. 
         [0025]    The piston  124  when seated against the plug  120  may also form a gap or clearance  272  between the piston  124  and the plug  120 . This gap or clearance  272  may be a result of the projection  274  on the piston  124 . The projection  274  prevents the piston  124  from moving completely against the plug  120 . As a result, hydraulic fluid coming into the port  118  can fill into the gap  272  and exert force upwardly (as shown in  FIG. 3 ) to move the piston  124  in an upward direction. If there were no gap  272 , it would be difficult for fluid to urge against the piston  124  to lift the piston  124 . In some embodiments, the projection  274  may cover about 10% of the surface area of the piston  124 . In other embodiments the projection  274  may have different dimensions. After reviewing this disclosure, one of ordinary skill in the art will understand that the projection  274  could also be located on the plug  120  and achieve a similar result. 
         [0026]    The socket portion  250  of the piston  124  may contain a seat void  258 . The rod seat  260  may form the bottom of the socket portion  250 . The piston end  262  of the rod  126  is fit with in the socket portion  250 . The piston end  262  of the rod  126  may be chamfered as shown at sides  264  and  266  in  FIGS. 3 and 5 . When the piston end  262  of the rod  126  is fit with in the socket portion  250  of the piston  124 , there is a clearance or void  268  between the seat  260  in the socket portion  250  of the piston  124  and the end  262  of the rod  126 . The clearance void  268  extends to both seat corners  270  and  273 . The clearance void  268  may be a result of loosely attaching the piston  124  to the rod  126 . 
         [0027]    As shown in  FIG. 3 , the piston  124  is attached to the rod  126  with fasteners  280  fit into fastener holes  276  in the piston  124  and fastener holes  278  located in the rod  126 . In some embodiments, only the fasteners  280  and the fastener holes  278  in the rod  126  are threaded. The fasteners  280  are adjusted so that the gap  268  is at a desired amount. In some embodiments, the gap  268  may be about 0.015 inches. In other embodiments larger or smaller gaps may be used. In some embodiments, when attaching the piston  124  to the rod  126 , the fasteners  280  are turned so that the piston  124  just contacts the rod  126  and then the fasteners  280  are backed out about a half turn to create a desired gap  268 . 
         [0028]      FIG. 4  shows a piston assembly  111  not in accordance with the present disclosure. The piston assembly  111  shown in  FIG. 4  represents a piston  124  and rod  126  that are unified together. The piston  124  and rod  126  may be unified because they are made of a single unitary part or they are unified because the piston  124  is attached to the rod  126  in a snug manner so that no gap  268  (as shown in  FIGS. 3 and 5 ) exists. 
         [0029]    The rod  126  will encounter a side load or, in other words a load that is not completely parallel with the axis E of the cylinder  112 , causing the rod  126  and the piston  124  to be displaced. In  FIG. 4 , the side load force is represented by arrow F. The angle of arrow F is exaggerated to better illustrate the side load. The force of arrow F, causes the rod  126  to be displaced so that the axis D the of the rod  126  and the axis G of the piston  124  are not parallel to the axis E of the interior  114  of the cylinder. Because the rod  126  and piston  124  are unified, it is assumed for the sake of this discussion that the axis D of the Rod  126  and the axis G of the piston  124  are coaxial. Theoretically, if there were no side load force F and the hydraulic piston assembly  111  was manufactured to perfect dimensions, the axis D of the rod  126  the axis G of the piston  124  and the axis E of the interior  114  of the cylinder would be perfectly aligned. However this is never the case so a misalignment of the three axes D, G, and E is the rule rather than the exception. 
         [0030]    Displacement of the rod  126  as a result of force F causes the surface  128  of the rod  126  to bear against the bearing surface  142  of the retainer  122 . The bearing of the surface  128  of the rod  126  against the bearing surface  142  in the retainer  122  results in a retainer high stress area  284 . As the rod  126  moves in or out and bears against the retainer  122 , the surface  128  of the rod  126  may become scored, worn, or damaged as well as the surface  142  of the retainer  122 . 
         [0031]    On the opposite side of the rod  126  there is a gap  294  between the rod  126  and the bearing surface  142  of the retainer  122 . In addition the piston  124  may also have a high stress area  286 . In the piston high stress area  286 , the wall  288  of the cylinder housing rubs against the bearing surface  290  on the piston  124 . This may result in wear and scoring on either or both of the piston  124  and the wall  288  of the cylinder housing. Not only does this condition create undesirable wear, it can also reduce the efficiency and effectiveness of the cylinder assembly  111  due to energy being wasted in overcoming friction to move the piston  124  or rod  126  in the high stress areas  284 ,  286 . 
         [0032]      FIG. 5  is a partial enlarged cross-sectional view of a cylinder assembly  111  in accordance with the present disclosure. The rod  126  is loosely connected to the piston  124 . This loose connection may sometimes be referred to as a floating piston  124 . Arrow F represents a force acting in a direction not parallel to the cylinder axis E. The rod  126  is displaced by the side load of force F so that the exterior surface  128  of the rod  126  is pressed against the bearing surface  142  of the retainer  122  at the high stress area  284 . On the opposite side of the rod  126  a gap  294  exists between the rod  126  and the retainer  122 . 
         [0033]    The piston  124  is squarely within the interior  114  of the cylinder  112  in contrast to what was shown in  FIG. 4 . As a result, the axis G of the piston is substantially parallel with the axis E of the cylinder  112 . This is different than what was shown in  FIG. 4 . In  FIG. 4  the rod axis D and the piston axis G were substantially coaxial. However in the embodiment shown in  FIG. 5 , the piston axis G is substantially parallel with the bore axis E. Making the piston axis G substantially parallel with the bore axis D allows the piston  124  to move in the interior  114  of the cylinder  112  without creating undue stress, wear, or have increased friction to move the piston  124  along the side wall  288 . 
         [0034]    As shown in  FIG. 5 , the piston  124  is squarely located within the interior  114  of the cylinder  112 , and there is no undue binding in the area  286  between the bearing surface  290  on the piston  124  and the wall  288  of the cylinder  113 . Instead, the rod  126  urges against an interior of the socket portion  250  of the piston  124 . The side  264  of the rod  126  is pressed against the sidewall  296  of the socket portion  250  at stress area  298  as a result of force F. However the urging of the side  264  of the rod  126  against the sidewall  296  of the piston  124  does not create unnecessary wear binding because there is relatively little movement of the rod  126  with respect the piston  124  compared to the movement of the piston  124  against the sidewall  288  of the cylinder housing  113  such as that shown in  FIG. 4 . As a result, the wear on the sidewall  288  of the cylinder housing  113  is much reduced in  FIG. 5  compared to the embodiment shown in  FIG. 4 . Furthermore, it requires less force or energy to move the piston  124  and rod  126  in and out through the interior  114  of the cylinder  112  then in the embodiment shown in  FIG. 4 . 
         [0035]    The rod  126  still may have a clearance void  268  but the shape of that void  268  may be different or change depending upon the direction and amount of force F. One of ordinary skill the art would understand that the orientation of the rod  126  would change if the direction and/or amount of the force F also changed. 
         [0036]    The chamfer at either side  266  and  264  or anywhere else around the circumference of the rod  126  may, in some embodiments, provide relief to allow the rod  126  to slightly pivot or otherwise move in the socket portion  250  of the piston  124 . In some embodiments, a point identified in  FIG. 5  is point D, E, G may exist where the rod axis D, the cylinder axis E, and the piston axis G intersect. In some embodiments this may be a point about which the rod  126  pivots as a result of force F. 
         [0037]    One of ordinary skill in the art may understand after reviewing this disclosure that if force F is significant enough the rod  126  will pivot or move within the piston  124  and also cause the piston  124  to pivot or move within the interior  114  of the cylinder housing  113 . 
         [0038]    In some embodiments, the fasteners  280  may only be threadably attached to the rod  126  in the fastener holes  278  and not threadably attached to the faster holes  276  in the piston  124  to better facilitate pivoting movement of the rod  126  with respect to the piston  124 . 
         [0039]    Forces F 1 , F 2 , and F 3  illustrated in  FIG. 5  are reactionary forces resulting from the force F placed on the rod  126 . As discussed above, when force F is applied to the rod  126 , the rod  126  will pivot about point D,E,G. This movement will cause the rod  126  to contact the retainer  122  at stress area  284 . Furthermore, the bottom of the rod  126  may slide to the right as shown in  FIG. 5  toward corner  270 . The rod  126  will also contact the piston  124  at stress area  298 . This contact will result in reactionary forces acting upon the rod  126 . For example force F 1  is a reactionary force that the retainer  122  will impart upon the rod  126 . Force F 2  is a reactionary force the piston  124  will impart upon the side of the rod  126 . Force F 3  represents a force that the piston  124  will impart to the rod  126 . One of ordinary skill in the art will understand that the reactionary forces as illustrated as F 1 , F 2 , and F 3  are mere representations of forces which are distributed along an area and not only at discrete points as shown. The reactionary forces F 1 , F 2 , and F 3  will create a bending moment to counteract the force F imparted to the rod  126 . One advantage of the floating piston design is that due to the relative movement between the piston  124  and the rod  126  reactionary force F 3  is created in reaction to force F. The presence of F 3  results in the magnitude of F 1  and F 2  being smaller to react to force F than if F 3  was not present. 
         [0040]    In particular, reactionary force F 3  will create a bending moment which will result in a lower stress in stress areas  284 ,  286 , and  296  between the rod  126  and the retainer  122 , the rod  126  and the piston  124 , and the piston  124  and the housing  113 , then would be found in an embodiment shown in  FIG. 4  operating under a similar side load F. As a result, the embodiment shown in  FIG. 5  provides certain advantages compared to the embodiment of  FIG. 4 . 
         [0041]    In addition to reducing stress, the embodiment of  FIG. 5  also reduces wear between the piston  124  and the housing  113 . The wear is reduced because the high stress contact area is static between the rod  126  and the piston  124  which is in contrast, to the embodiment of  FIG. 4  where the high stress area is dynamic between the piston  124  and the housing  113  of the cylinder  112 . In the embodiment of  FIG. 5 , at the dynamic surface between the piston  124  and the housing  113  of the cylinder  112  the stress is reduced due to the piston  124  being able to better align within the cylinder  112  even when the rod  126  is out of alignment due to a side load F. 
         [0042]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.