Patent Publication Number: US-2017356483-A1

Title: Cold-worked riveted piston/rod assembly and method of making same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 62/349,971, filed on Jun. 14, 2017, and incorporates by reference the disclosure thereof in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Hydraulic and pneumatic actuators typically include a cylinder and a piston and piston rod assembly displaceable within the cylinder. The piston and piston rod typically are formed separately and then connected together. For example, the piston rod may be formed with a threaded end, and the piston may be formed with a threaded receptacle opposite its working face. The piston rod and piston may be joined by threading the threaded end of the piston rod into the threaded receptacle of the piston. This assembly method, however, is imperfect in that the piston and piston rod may become unthreaded and disconnected during use, thereby rendering the actuator unusable. 
     Alternatively, the piston rod may be formed with a deformable end and the piston may be formed with a hole extending through its face for receiving the deformable end of the piston rod. The piston and piston rod may be joined by inserting the deformable end of the piston rod through the hole in the piston and peening the end of the deformable end of the piston rod into secure engagement with the piston. This method of assembly also is imperfect in that some form of seal is required between the piston rod/piston interface to preclude working fluid from bypassing the piston while the actuator is in use and further because the working face of the piston is prone to damage during the peening process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a piston and piston rod assembly according to the present disclosure; 
         FIG. 2  is a side view of the piston and piston rod assembly of  FIG. 1 ; 
         FIG. 3  is a perspective view of an end of the piston rod of  FIG. 1 ; 
         FIGS. 4A-4D  are views of the piston and piston rod assembly of  FIG. 1  showing details thereof; 
         FIGS. 5A-5C  are views of the piston rod of  FIG. 1  showing details thereof; 
         FIGS. 6A-6C  are drawings of the piston of  FIG. 1  showing details thereof; 
         FIG. 7  is a perspective cutaway view of the piston and piston rod assembly of  FIG. 1 ; and 
         FIG. 8  is a perspective view of the piston of  FIG. 1  assembled to the piston rod of  FIG. 1  and installed in an orbital riveting machine prior to a peening operation that secures the piston to the piston rod. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The drawings show an illustrative embodiment of a piston and piston rod assembly  20  including a piston  22  and a piston rod  24  according to the present disclosure. The piston rod  24  is shown as stepped cylindrical, having a first (or main) portion  26  of a first diameter and a second (or protruding) portion  28  of a second diameter lesser than the first diameter. In other embodiments, the main portion  26  and the protruding portion  28  may have forms other than cylindrical. For example, the main portion  26  and the protruding portion  28  may have rectangular, oval, or other cross sections. In such embodiments, the cross-sectional area of the main portion  26  typically would completely or at least partially bound or overlap the cross-section of the protruding portion  28 . The piston rod  24  may be made of aluminum or another material such as steel, plastic, or another material capable of being selectively plastically deformed, as discussed further below, and able to withstand the stresses to which the piston rod may be subjected in use. The piston rod  24  may be formed in any suitable manner For example, the piston rod  24  may be machined from solid bar stock. 
     As best shown in  FIGS. 4A and 5B , the protruding portion  28  extends from the main portion  26  and is concentric therewith. A ledge (or land)  30  is defined by the exposed end surface of the main portion  26  at the junction of the main portion  26  and the protruding portion  28 , as shown in  FIGS. 6A and 6B . The protruding portion  28  has a free end  32  opposite the end thereof connected to the main portion  26 . In addition, the protruding portion  28  defines a circumferential groove  34  extending inwardly from the periphery of the cylindrical body of the protruding portion  28 , as best shown in  FIG. 5B . The groove  34  may house one or more seal rings  40 , for example O-rings, and one or more optional back-up rings  36 ,  38  adjacent the seal ring. For example, the seal ring  40  may be sandwiched between a pair of back-up rings  36 ,  38 . The back-up rings  36 ,  38  or one of them may have a convex surface facing the seal ring  40 . This arrangement of seal ring  40  and back-up rings  36 ,  38  may mitigate or preclude working fluid from leaking past the interface between the protruding portion  28  and the piston  22 , as will become evident from the discussion below. Such leakage could adversely affect the ability of an actuator including the piston and piston rod assembly  20  to retain pressure in a working chamber of the actuator and could thereby adversely affect the actuator&#39;s operating efficiency. 
     As shown in  FIG. 4 , the main portion  26  of the piston rod  24  includes a free end having a surface  42 . The surface  42  may be concave, as best shown in  FIG. 5D . The surface  42  and the main portion  26  may cooperate to define a hole  44  for receiving an end of a foot pad (not shown). The hole  44  may be internally threaded, as shown in  FIG. 6D . 
     As shown in  FIGS. 4C, 6A-6C, and 7 , the piston  22  may have a generally annular body having a first end  46  and a second end  48  and defining a bore  50  extending there through from the first end to the second end. In other embodiments, the piston could be a body of another suitable shape or cross-section having a first end and a second end and defining a bore extending there through from the first end to the second end. The bore  50  of the piston  22  may be of a single continuous diameter from the first end to the second end. Alternatively, as shown, the bore  50  may have a first diameter over at least a central portion of its length and define a counter bore  47  extending inwardly from the first end  46  of the piston  22  and/or a countersink  49  extending inwardly from the second end  48  of the piston. The counter bore  47  may have a second diameter greater than the first diameter of the bore  50 , and the counter sink  49  may have a major diameter greater than the first diameter of the bore  50 . 
     In any event, the bore  50  is sized to slidingly receive the protruding portion  28  of the piston rod  24  through the piston  22  without excessive lateral play. The bore  50  also is sized to slidingly receive the protruding portion  28  of the piston rod  24  and the seal ring  40  (and the back-up rings  46 ,  48 , if provided) within the groove  34  of the protruding portion and sufficiently compress or otherwise engage the seal ring to effect a seal between the piston  22  and the piston rod  24 , as best shown in  FIGS. 4D and 7 . 
     As best shown in  FIGS. 6C and 7 , the exterior circumferential surface of the piston  22  defines first and second circumferential ring grooves,  54 ,  56 . The ring grooves  54 ,  56  are configured to receive respective piston rings, for example, at least one wear ring  58  and one seal ring  60 . As best shown in  FIGS. 1 and 2 , a wear ring  58  may be received in the first ring groove  54  and a seal ring  60  may be received in the second ring groove  56 . The seal ring  60  may be provided to block transmission or leakage of working fluid across the interface between the piston  22  and a corresponding cylinder (not shown). The wear ring  58  may be provided to mitigate or reduce wear on the piston and/or the corresponding cylinder. In other embodiments, the positions of the seal and wear rings could be reversed. Other embodiments could include more or fewer ring grooves and corresponding piston rings. 
     In the illustrated embodiment, the exterior circumferential surface of the piston  22  is tapered inwardly proximate the second end  48  of the piston. In other embodiments, the exterior circumferential surface of the piston could be right cylindrical (except for the regions defining the piston ring grooves). 
     As shown in  FIG. 8 , the protruding portion  28  and the piston  22  are configured so that the free end  32  of the protruding portion may extend beyond the end of the bore  50  proximate the first end of the piston when the protruding portion is fully inserted in the piston from the second end  48  of the piston, that is, when the ledge  30  abuts the second end of the piston. With the piston  22  and the piston rod  24  so assembled, the free end  32  of the protruding portion  28  of the piston rod  24  may be cold-worked to form a head of a rivet, thereby securing the piston to the piston rod. More specifically, the free end  32  of the protruding portion  28  of the piston rod  24  may be flattened or otherwise deformed to form a lip  64  that is larger in diameter than the diameter of the bore  50  at the first end  46  of the piston  22  to thereby secure the piston to the piston rod. The securement may be, but need not be, sufficient to eliminate play between the piston  22  and piston rod  24  and/or preclude rotation of the piston relative to the piston rod. 
     The cold-working may be performed using any suitable process, for example, orbital riveting, peening, crushing, or another process that deforms the free end  32  of the protruding portion  28 . For example,  FIG. 8  shows the unworked piston  22  and piston rod  24  assembly installed in an orbital riveting machine. The orbital riveting machine may be used to perform an orbital riveting process on the free end  32  of the protruding portion  28  of the piston rod of the unworked assembly, the orbital riveting process flattening or otherwise deforming the free end of the protruding portion to form a lip  64  that is larger in diameter than the diameter of the bore  50  at the first end  46  of the piston  22 , thereby securing the piston to the piston rod. 
     The free end  32  of the protruding portion  28  of the piston rod  24  may be cold worked to be recessed from, flush with, or proud of a top rim  66  of the piston  22 . The free end  32  of the protruding portion  28  of the piston rod  24  may be cold worked to yield a substantially continuous and planar surface. 
     In any event, the bore  50  and counter bore  47  of the piston  22  and the protruding portion  28  of the piston rod  24  may be sized so that the cold working process can be accomplished without the cold working tool or the lip  64  coming into contact with either the face of the piston  22  or the inner wall of the counter bore  47 . For example, as shown in  FIG. 1 , the inner wall of the counter bore  47  defined by the top rim  66  of the piston  22  and the lip  64  resulting from cold working the protruding portion  28  cooperate to define a groove  70  there between. 
     The embodiment shown in the drawings is illustrative and not limiting. The scope of the invention is defined only by the claims below.