Abstract:
A hydraulic cylinder includes a cylinder assembly having a cylinder, defining an inner hydraulic chamber and being for reciprocating receipt of a piston and piston rod therein; a piston rod extending from the inner hydraulic chamber exteriorly of the cylinder; and a piston head assembly connected with the piston rod and disposed for reciprocation within the cylinder assembly. The piston head assembly includes a piston head and a valve assembly including a passageway defined in the piston head and a valve member having an outer surface and being sized and configured for reciprocation in the passageway between extended and retracted positions therein, the valve member defining at least one flat defined along the outer surface and at least one transition surface between the outer surface and the flat, the transition surface forming an angle with the flat of between about 40 and 50 degrees.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of patent application Ser. No. 12/861,809, filed Aug. 23, 2010, which application claims the benefit of the filing date of Provisional Application No. 61/235,879, filed Aug. 21, 2009, all of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of hydraulic cylinders, and more specifically, to a hydraulic cylinder with a piston valve assembly providing variable force output. 
     BACKGROUND OF THE INVENTION 
     In some hydraulic cylinders, the limit of stroke in at least one direction is defined when the piston head strikes the cylinder end cap or gland. Particularly in equipment where such cylinders are high pressure, double-acting cylinders cycled thousands of times, the resulting premature wear and damage to the cylinder is a problem. Improvements in such cylinders to lessen the wear and damage are continually being sought. 
     SUMMARY OF THE INVENTION 
     Generally speaking, a piston in a double acting hydraulic cylinder includes an automatic valve assembly for reducing the end stroke impact of the piston against the cylinder ends. 
     A hydraulic cylinder includes a cylinder assembly having a cylinder, defining an inner hydraulic chamber and being for reciprocating receipt of a piston and piston rod therein; a piston rod extending from the inner hydraulic chamber exteriorly of the cylinder; and a piston head assembly connected with the piston rod and disposed for reciprocation within the cylinder assembly. The piston head assembly includes a piston head and a valve assembly including a passageway defined in the piston head and a valve member having an outer surface and being sized and configured for reciprocation in the passageway between extended and retracted positions therein, the valve member defining at least one flat defined along the outer surface and at least one transition surface between the outer surface and the flat, the transition surface forming an angle with the flat of between about 40 and 50 degrees. 
     It is an object of the present invention to provide an improved bi-directional hydraulic cylinder. 
     Further objects and advantages of the present invention will become apparent from the following description of the preferred embodiment 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side, cross-sectional view of a hydraulic cylinder  10  with piston valve assembly in accordance with one embodiment of the present invention, and showing the hydraulic cylinder  10  in the forward biased condition  83 . 
         FIG. 2  is a side view of the shank  50  and rearward head  52  of the valve member  48  of valve assembly  22  of the apparatus  10   FIG. 1 . 
         FIG. 3  is a side view of the shank  50  and rearward head  52  of  FIG. 2 , and shown rotated 90 degrees about its axis  67 . 
         FIG. 3   a  is a cross-sectional view of the shank  50  of  FIG. 3  taken along the lines  3   a - 3   a  and viewed in the direction of the arrows. 
         FIG. 4  is side, cross-sectional view of the piston head  21  of  FIG. 5  viewed along the line  4 - 4  and viewed in the direction of the arrows. 
         FIG. 5  is a top view of the piston head  21  of the hydraulic cylinder  10  of  FIG. 1 . 
         FIG. 6  is a side, cross-sectional view of the hydraulic cylinder  10  of  FIG. 1  and shown biased forwardly with shank  50  just making contact with end cap  17 . 
         FIG. 7  is a side, cross-sectional view of the hydraulic cylinder  10  of  FIG. 1  and shown in the fully retracted (forward) condition  86 . 
         FIG. 8  is a side, cross-sectional view of the hydraulic cylinder  10  of  FIG. 1  and shown with piston head  21  piston rod  12  biased rearwardly and moved slightly away from end cap  17  and valve member  48  in the rearward, closed position  87 . 
         FIG. 9  is a side, cross-sectional view of the hydraulic cylinder  10  of  FIG. 7  and showing valve member  48  turned 90 degrees about its axis  67 . 
         FIG. 10  is a side, cross-sectional view of the hydraulic cylinder  10  of  FIG. 1  and shown in the fully extended (rearward) position  89 . 
         FIG. 11  is a side, cross-sectional view of the piston head  121  of a hydraulic cylinder in accordance with an alternative embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and any alterations and modifications in the illustrated device, and further applications of the principles of the invention as illustrated therein are herein contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Referring to  FIG. 1 , there is shown a hydraulic cylinder  10  with piston valve assembly in accordance with one embodiment of the present invention. Hydraulic cylinder  10  is particularly adapted for use in bi-directional cylinders, but alternative embodiments are contemplated wherein the valve assembly is used in single acting hydraulic cylinders. Hydraulic cylinder  10  generally includes a cylinder assembly  11 , a piston rod  12  and a piston head assembly  13 . Cylinder assembly  11  includes a cylinder  16 , an end cap  17 , a gland  18  and various seals and wear rings (e.g. at  23  and  27 ) to provide fluid tight seals therein, as is known in the industry. Cylinder assembly  11  defines an inner hydraulic chamber  15  which is divided by the piston rod  12  and piston head assembly  13  into forward and rearward chambers  81  and  82 . Forward and rearward input ports  19  and  20  provide for the entry and exit of hydraulic fluid to the opposing forward and rearward chambers  81  and  82 , as described herein. 
     Referring to  FIGS. 1 ,  4  and  5 , piston head assembly  13  includes a piston head  21  and a valve assembly  22 . Piston head  21  has a round cross-section sized to be received and reciprocate within cylinder  16 . Piston head  21  has an outer cylindrical surface  24 , a front face  25 , and a rear face  26 . Defined in the outer cylindrical surface  24  of piston head  21  is a circumferential groove  29  for receiving a seal  30 . Piston head  21  also defines a central, axial bore  32  and a valve passageway  33  with an axis  34  which, in the present embodiment, is parallel to the axis  35  of piston head  21  and cylinder  16 . Extending inwardly from its front face  25 , piston head  21  also defines a forward counterbore  36 . The forward, reduced diameter end  37  of piston rod  12  extends through central bore  32  of piston head  21 , and a nut  38  is threadedly received thereon to tightly secure head  21  to the forward end of piston rod  12 . A portion of nut  38  sits within counterbore  36 , and a portion thereof extends forwardly of the front face  25  of head  21 . The limits of movement of rigidly connected piston head  21  and piston rod  12  are defined forwardly by nut  38  contacting end cap  17  and rearwardly by rear face  26  contacting gland  18 . From its rear face  26 , piston head  21  has a reduced diameter for a portion of its axial length, which forms a rear ledge  39  and a ledge cylindrical surface  40 . 
     Valve passageway  33  has a main bore  42  with a diameter X and, at its rear end, a counterbore  43  with a diameter Y. Counter bore  43  opens to both rear face  26  and rear ledge  39 . The bottom  44  of counter bore  43  is recessed forwardly of rear ledge  39  a distance M and forwardly of rear face  26  a distanced N. 
     Referring to  FIGS. 1-3 , valve assembly  22  includes a valve member  48  and the valve passageway  33 . Valve member  48  includes a central shank  50 , a forward head  51  and a rearward head  52 . Shank  50  has a generally round cross-section body  55  with a diameter T just slightly smaller (in one embodiment, about 0.005 inches in diameter) than the diameter X of valve passageway  33  so that shank  50  can freely slide therewithin. At its rearward end  53 , shank  50  is rigidly connected with rearward head  52 . The junction  54  between shank  50  and rearward head  52  forms not an abrupt 90 degree corner, but is instead slightly radiused, which contributes to a better seal between valve member  48  and piston head  21 . The forward end  57  of shank  50  is reduced in diameter and is threaded, and the junction  58  between the cylindrical body  55  and the threaded portion  57  forms a ledge  59 . Forward head  51  is a nut ( 51 ) threadedly received onto forward end  57  and securely against ledge  59 . In one embodiment, nut ( 51 ) is a 5/16″-18 UNF vinyl insert lock nut, shank diameter T is 0.370 inches, and main bore diameter X is 0.375 inches. Other dimensions are contemplated as would provide the desired variable piston force and cushioning characteristics. Also in this embodiment, shank  50  and rearward head  51 , in assembly, form a fixed unit with the forward head  51  comprising a separate element (nut  51 ) secured on the forward end  57  of shank  50  in a manner suitable to prevent the nut ( 51 ) from being vibrated loose or off shank  50  from the continual reciprocation of valve member  48 . Alternative embodiments are contemplated wherein the forward and rearward heads of valve member  48  include both heads  51  and  52  comprising separate pieces, such as a nut ( 51 ). 
     As shown in  FIGS. 2 ,  3  and  3   a , shank  50  is not entirely round in cross-section. A portion of shank  50  is removed (or shank  50  is formed) to define opposing flats  63  and  64  that extend from just rearwardly of forward junction  58  and to just forwardly of rearward junction  54 . Flats  63  and  64  are planar and parallel with each other and, in one embodiment, the shortest distance D between flats  63  and  64  is 0.28 inches; the shank diameter T is 0.37 inches; and, the resulting difference therebetween creates opposing pressure relief channels  65  each having a maximum depth W. This forms opposing gaps  66  ( FIG. 9 ) of about 0.047 inches between each flat  63 / 64  and main bore  42  (main bore diameter X (0.375 inches)-thickness D (0.28 inches). The gap distances W of relief channels  65  of flats  63  and  64  are identical; flats  63  and  64  are each planar; and flats  63  and  64  are symmetrical about a plane passing through the shank axis  67 . Alternative embodiments are contemplated wherein flats  63  and  64  may be non planar (e.g. curved) and/or not symmetrical about a plane passing through the shank axis  67 . 
     The junctions between each flat  63 / 64  and the cylindrical body  55  form forward and rearward transition surfaces  71  and  72  (flat  63 ) and  73  and  74  (flat  64 ). In one embodiment, each transition surface  71 - 74  forms a transition angle A between about 40 and 50 degrees with its adjacent flat ( 63 / 64 ), and preferably the transition angle A is about 45 degrees. Transition surfaces  71 - 74  (1) reduce impact stresses exerted upon valve member  48  from high force, repetitive impacts, thus reducing the incidence of mechanical failure at the junctions between shank  50  and heads  51  and  52 , and (2) soften the impact force, and thus force curve, particularly at the moment of valve closing. The distances Q and R of the transition surface from junctions  54  and ledge  59 , respectively, may be selected to be any value providing the desired force curve output. In one embodiment where the shank diameter T is about 0.37 inches, W is about 0.044 inches and the transition angle A is 45 degrees, Q and R are both about 0.07 inches. Alternative embodiments are contemplated wherein distances Q and R (or other companion parameters, such as the transition angles A at  71  and  72 ) may not be identical or symmetrical with each other), for example, to compensate for varying force applications for hydraulic cylinder  10 , that is, where the resistance to output force of piston rod  12  is greater in one direction than in the other. 
     It is noted that the relief channels created by flats  63  and  64  can be created by alternative configurations milled or defined in shank  50 . That is, the deviation from a round cross-section may be created in ways other than one or more flat surfaces. It is desired, however, that in one embodiment, the structure removed from or absent from a cylindrical profile of shank  50  be as near to cylindrical as possible so as to maintain as much structural integrity as possible. Also, the surfaces  63  and  64  need not be flat. Instead, they could have a convex, concave, rippled or other profile and still provide the desired gap  66  when assembled within main bore  42 . Also, there may be only one or more than two gaps  66  created. It is believed that the flat surfaces at  63  and  64  provide the optimum operating performance. 
     Alternative embodiments are contemplated wherein there are more than one valve assemblies  22  defined in the piston  21  to provide a different operating profile. 
     The length of each flat (i.e. between transition surfaces such as  71  and  72 ) can vary, but must be at least long enough to permit fluid flow through the corresponded gap  66  when the valve member  48  is between its extended and retracted positions. 
     In assembly, a forward hydraulic chamber  81  is defined by cylinder  16 , end cap  17 , piston head  21 , piston rod  12 , and valve member  48 . A rear hydraulic chamber  82  is defined by cylinder  16 , gland  18 , piston head  21 , piston rod  12 , and valve member  48 . 
     In  FIG. 1 , hydraulic cylinder  10  is shown in a forward biased condition  83  wherein the fluid pressure is higher in rear hydraulic chamber  82  than in forward hydraulic chamber  81 , which fluid pressure bears against head  52 , which seats against bottom  44  of counter bore  43 , and valve member  48  is thus biased to a forward closed position  84 . The greater pressure in chamber  82  also bears against piston head  21  and moves head  21 , rod  12  and valve member  48  toward end cap  17 .  FIG. 6  shows hydraulic cylinder  10  just as the leading end  85  of shank  50  contacts end cap  17  and can move forwardly no farther. The next infinitesimal forward movement of piston rod  12  and piston head  21  unseats rearward head  52  from piston head  21 , and fluid is permitted to flow through valve passageway  33 , thus greatly reducing the motive force against the rear face  26  of piston head  21  before it contacts end cap  17 , as shown with hydraulic cylinder  10  in the fully retracted (forward) condition  86  ( FIG. 7 ). The impact force of head  21  against end cap  17  is thus greatly reduced. 
     Upon application of fluid pressure to the forward hydraulic chamber  81  through forward input port  19 , piston head  21  and piston rod  12  are biased rearwardly (to the right in  FIG. 8 ), as is shank  50  and rearward head  52 , whereby valve member  48  nearly instantaneously moves rearwardly, and head  51  seals against front face  25  and blocks further fluid flow through valve passageway  33 . The angled, forward transition surfaces  71  and  73  cooperate to smooth (lessen) the abrupt impact force of valve member  48  closing against front face  25 . In similar fashion, with greater hydraulic pressure applied to forward hydraulic chamber  81  than to rear hydraulic chamber  82 , piston rod  12  and piston head  21  move rearwardly until rearward head  52  contacts and is stopped by gland  18 . Further rearward movement of rod  12  and head  21  unseats forward head  51  from piston head  21 , and the higher fluid pressure in rear hydraulic chamber  82  is relieved into forward hydraulic chamber  81 . The impact of piston head  21  against gland  18  is consequently lessened. Shown in  FIG. 10  is hydraulic cylinder  10  in the fully extended (rearward) position  89 . 
     Referring to  FIG. 11 , there is shown a piston head  121  in accordance with an alternative embodiment of the present invention. Piston head  121  is identical to the piston head  21  of  FIG. 4 , except as described herein, and like reference numbers are used for identical elements. Referring to the piston head  21  ( FIG. 4 ), the transitional rim  123  at the junction between the cylindrical wall  125  of main bore  42  and the annular bottom surface  44  is shown as being radiused to closely match and mate with the radiused junction  54  of valve member  48 . Such closely mating profiles of rim  123  and junction  54  provide desirable sealing engagement between piston head  21  and valve member  48  and a desirable output force curve at the region corresponding to the closing of valve passageway  33  by rearward head  52 . 
     In the embodiment of  FIG. 11 , the transitional rim  127  at the junction between the cylindrical wall  128  of main bore  130  and annular bottom surface  131  is chamfered instead of radiused. The curved surface  134  of the radiused junction  54  is sized sufficiently less than the chamfer profile (at  127 ) so that the rearward, annular surface  135  of head  52  can seat flat against annular bottom surface  131  without the any of the curved surface  134  contacting any of the piston  21  proximal the chamfered, transitional rim  127 , thus avoiding mushrooming or other damage to either transitional rim  127  or curved surface  134 . In one embodiment, the diameter X of main bore  130  is 0.375 inches; the chamfer of rim  127  is at a 45 degree angle to cylindrical wall  128 ; the short side dimension B of the isosceles triangle for which transitional rim  127  is the hypotenuse is between about 0.088 and 0.100 inches (and preferably about 0.090 inches); and, the radius of the curved surface  134  is 0.086 inches. Alternative embodiments are contemplated wherein the dimensions of chamfered surface (transitional rim)  127  and curved surface  134  vary from the foregoing example, but a close tolerance between chamfered surface  127  and curved surface  134  is desired. 
     Alternative embodiments are contemplated wherein passageway  33  does not have a circular cross-section, as shown in  FIG. 5 , but instead has a non-circular cross-section. The corresponding valve member has a complementary configuration to freely reciprocate therein between fluid-flow sealing extended and retracted positions, and has flats creating relief channels, as with the valve member  48  herein, to permit relief of hydraulic pressure from one of chambers  81 / 82  to the other when the piston head nears one of the end cap  17  and gland  18 . 
     Alternative embodiments are contemplated wherein the nut  38  has a smaller profile—that is, it does not extend as far forward from the front face  25  of piston  21 —or is non-existent (piston rod  12  is threaded connected directly into piston  21 ). In this configuration, the leading end  85  of valve member  48 , when in the rearward closed position  87 , bottoms out against end cap  17  instead of the nut  38 , which can result in damage or failure to valve member  48 . In this embodiment, piston  21  is provided with a counterbore (not shown) defined in the front face  25  and at the opposite, forward end of, and coaxial with valve passageway  33 . The leading end  85  of valve member  48  can then seat within that counterbore to provide clearance for and allow piston  21  to bottom out against end cap  17  instead of valve member  48 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.