Patent Publication Number: US-2013247753-A1

Title: Fluid Cylinder Assembly Having Automatic Stroke Shutoff

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/614,301 filed Mar. 22, 2012, which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to fluid cylinder assemblies, and more particularly to a fluid cylinder assembly incorporating automatic stroke shutoff. 
     Fluid cylinder assemblies are used in various applications to, for instance, raise and lower loads, extend and retract members, and provide general motion control. One problem common to most fluid cylinder assemblies is known as “overtravel.” Overtravel occurs when fluid pressure urges a plunger beyond its designed stroke range, such as when a control valve is maintained in an open position after the plunger is fully extended. Pressure spikes occur during overtravel that can induce additional stress causing damage to the fluid cylinder and degrade other components coupled to the system (e.g., valves, hoses, couplings, etc.). 
     Several attempts have been made to minimize the detrimental effects of overtravel. One approach involves strengthening portions of the fluid cylinder assembly that are impacted by overtravel. For instance, some cylinders include a “stopring” that is designed to withstand the force of a fully extended plunger that remains under fluid pressure. A stepped plunger is also typically required to engage the stopring. These stoprings and stepped plungers, however, increase the cost and complexity of the overall fluid cylinder assembly, while not reducing the undesirable stresses. Another approach involves a weep hole positioned in a pressure chamber. When a plunger nears the end of its stroke, a seal passes over the weep hole and pressurized fluid within the pressure chamber is vented through the weep hole, which reduces the forces and stresses of overtravel. However, in addition to the weep hole undesirably leaking fluid, this repeated movement of the seal across the weep hole damages the plunger seal and ultimately degrades operation of the overall fluid cylinder assembly. 
     In light of at least the above, a need exists for a fluid cylinder assembly incorporating an improved automatic stroke shutoff. 
     SUMMARY OF THE INVENTION 
     The fluid cylinder assembly concept includes a valve that automatically diverts fluid between pressure chambers when a plunger nears its end of stroke, thereby inhibiting the plunger from undesirable overtravel. 
     In one aspect, a fluid cylinder assembly comprises a cylinder base and a plunger bore that is defined by the cylinder base. A plunger is slidably seated within the plunger bore between a retracted position and an extended position, and a chamber bore is defined by the plunger. A chamber member has a first end coupled to the cylinder base and a second end slidably engaged with the chamber bore. An advance chamber is bounded by the plunger bore and the plunger, and a retract chamber is bounded by the chamber bore and the chamber member. A shunt passageway extends between the advance chamber and the retract chamber. A valve is seated in the shunt passageway and is moveable between a closed position at which fluid communication between the advance chamber and the retract chamber is inhibited, and an opened position at which fluid communication between the advance chamber and the retract chamber is established. The valve is positioned so that when the plunger is near the extended position the valve is in the opened position. 
     In another aspect, a fluid cylinder assembly comprises a cylinder base and a plunger bore that is defined by the cylinder base. A plunger is slidably seated within the plunger bore between a retracted position and an extended position, and a chamber bore is defined by the plunger. A chamber member has a first end coupled to the cylinder base and a second end slidably engaged with the chamber bore. A divider is coupled to the plunger and is slidably engaged about the chamber member. An advance chamber is bounded by the plunger bore, the plunger, the chamber member, and the divider. A retract chamber is bounded by the chamber bore, the chamber member, and the divider. A shunt passageway is formed through the divider to provide fluid communication between the advance chamber and the retract chamber. A valve is seated in the shunt passageway and coupled to the divider. The valve is moveable between a closed position at which fluid communication between the advance chamber and the retract chamber is inhibited, and an opened position at which fluid communication between the advance chamber and the retract chamber is established. The valve is positioned so that the valve engages the chamber member when the plunger is near the extended position to actuate the valve from the closed position to the opened position to establish fluid communication between the advance chamber and the retract chamber. 
     These and still other aspects will be apparent from the description that follows. In the detailed description, preferred example embodiments will be described with reference to the accompanying drawings. These embodiments do not represent the full scope of the concept; rather the concept may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of an example fluid cylinder assembly in a retracted state. 
         FIG. 2  is a cross section along line  2 - 2  shown in  FIG. 1  of the example fluid cylinder assembly in a retracted state. 
         FIG. 3  is a cross section similar to  FIG. 2  showing the example fluid cylinder assembly in an extended state. 
         FIG. 4  is an isometric view of the example fluid cylinder assembly in the extended state. 
         FIG. 5  is a cross section along line  5 - 5  shown in  FIG. 4  of the example fluid cylinder assembly in the extended state. 
         FIG. 6  is a partial section view of the area circumscribed by arc  6 - 6  shown in  FIG. 5  of an example shunt valve assembly in a closed position. 
         FIG. 7  is a partial section view similar to  FIG. 6  showing the example shunt valve assembly in an opened position. 
         FIG. 8  is a partial exploded top isometric view showing the example shunt valve assembly. 
         FIG. 9  is a partial exploded bottom isometric view of the example shunt valve assembly. 
         FIG. 10  is a section view of an alternative example fluid cylinder assembly in an extended state. 
         FIG. 11  is a cross section along line  11 - 11  shown in  FIG. 10  of the alternative example fluid cylinder assembly in the extended state. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EXAMPLE EMBODIMENT 
     The fluid cylinder assembly concept that inhibits overtravel is described in the context of a hydraulic cylinder assembly (“cylinder assembly  10 ”) typically used as a lifting cylinder. However, as one skilled in the art will appreciate when given the benefit of this disclosure, the broader fluid cylinder assembly concept can be adapted to other applications and types of fluid cylinder assemblies, such as the various fluid cylinder assemblies manufactured by Enerpac of Menomonee Falls, Wis. The term fluid(s) includes pneumatic fluids, hydraulic fluids, and other types/forms of fluid that can be used in a cylinder assembly. Furthermore, throughout the description, terms such as front, back, side, top, bottom, up, down, upper, lower, inner, outer, above, below, and the like are used to describe the relative arrangement and/or operation of various components of the example embodiment; however, none of these relative terms are to be construed as limiting the construction or alternative arrangements that are within the scope of the claims. 
       FIG. 1  is an isometric view of the example cylinder assembly  10  in a retracted state. The cylinder assembly  10  includes a cylinder base  12  extending from a lower end  14  to an upper end  16 . A series of shackle assemblies  18 , which are used to manipulate the location of the cylinder assembly  10 , are mounted near the upper end  16  of the cylinder base  12 . Each shackle assembly  18  includes a ring  20  captured to a U-shaped bracket  22  that is in turn secured to the cylinder base  12 . The cylinder base  12  can be manufactured from AISI 4140 steel or any other material that meets the particular application requirements. 
     The example cylinder assembly  10  is a double-acting configuration, meaning that the cylinder assembly  10  can be urged to and between both the retracted state (shown, for instance, in  FIG. 1 ) and an extended state (shown, for instance, in  FIG. 4 ). The double-acting configuration incorporates an extend port  24  and a retract port  26 , both of which are formed near the lower end  14  of the cylinder base  12 . The extend port  24  and the retract port  26  are in fluid communication with a fluid source (e.g., a hydraulic pump and control valves) that selectively supplies pressurized fluid (e.g., hydraulic fluid) to one of the extend port  24  and the retract port  26  to ultimately extend and retract the cylinder assembly  10 . 
     With additional reference to  FIG. 2 , the cylinder assembly  10  includes a plunger  28  that is slidably seated within a plunger bore  30  defined by the cylinder base  12 . The plunger  28  is configured to move within the plunger bore  30  (relative to the cylinder base  12 ) between a retracted position shown, for instance, in  FIG. 2  and an extended position shown, for instance, in  FIG. 3 . The plunger  28  can be manufactured from AISI 1045 steel or any other material that meets the particular application requirements. An exterior surface  32  of the plunger  28  includes an annular recess  34  near a bottom end of the plunger  28  into which a bearing  36  is seated. The bearing  36  includes two half cylinders that are aligned and seated in the recess  34  to circumscribe the plunger  28 ; the bearing  36  can be manufactured from fabric polymer composite. The bearing  36  rides along an interior surface  38  of the plunger bore  30  as the plunger  28  extends and retracts. 
     In the example cylinder assembly  10 , the plunger  28  defines a central chamber bore  40  between an upper end cap  42  and a lower divider  44 . Specifically, the chamber bore  40  is generally cylindrical and the end cap  42  is in the form of a circular disk that is seated (e.g., press fit, threaded) near an upper end  46  of the plunger  28 . The end cap  42  can be manufactured from AISI 1045 steel. The end cap  42  also provides a mount for a saddle  48 , which can be made of AISI 1045 steel. The saddle  48  has a flat top surface  50  and a convex lower surface  52  that is seated in a mating concave dish  54  formed in the upper end  46  of the plunger  28 . A bolt  55  extends through an opening  56  in the saddle  48  and is engaged with a threaded bore  58  formed in the end cap  42 . The bolt  55  captures a flared retainer  60  and a helical spring  62  within a pocket  64  formed in the saddle  48 ; this configuration allows the orientation of the top surface  50  of the saddle  48  to be adjusted (e.g., skewed relative to the balance of the cylinder assembly  10 ). 
     The bottom of the chamber bore  40  is defined by the lower divider  44 , which can be manufactured from C95400 aluminum bronze. The lower divider  44  is also generally disc-shaped and is similarly seated (e.g., press fit, threaded) near a lower end  66  of the plunger  28 . An exterior radial surface  68  of the lower divider  44  includes an annular groove  70  into which an o-ring  72  is seated to seal with an interior surface  74  of the chamber bore  40 . The lower divider  44  is fixed to the plunger  28  such that the lower divider  44  translates with the plunger  28 . In other forms, the lower divider  44  can be integrally formed with the plunger  28 . The lower divider  44  also defines a central opening  76  that is sized to accommodate a tube portion  78  of a chamber member  80 . Specifically, the central opening  76  includes an internal, annular recess  82  into which a seal  84  having an E-shaped cross section is seated to seal with and wipe against the tube portion  78  (e.g., a generally cylindrical pipe) of the chamber member  80  as the plunger  28  extends and retracts. The chamber member  80  may be made of AISI 4040 steel or any other suitable materials. The chamber member  80  may also be integrally formed with the balance of the cylinder base  12 . 
     In the example embodiment, a lower end  86  of the chamber member  80  is fixed to the cylinder base  12 . The lower end  86  is seated (e.g., press fit, threaded) into a central opening  88  of a mounting plate  90 . The disc-shaped mounting plate  90 , which can be manufactured from AISI 1144 steel, is in turn bolted to the bottom  92  of the cylinder base  12  with several bolts. An upper end  94  of the chamber member  80  extends into the chamber bore  40  and has an upper disc  96  that is secured (e.g., press fit, threaded) to the tube portion  78 . The tube portion  78  includes an annular groove  98  near an upper end into which an o-ring  100  is seated to seal between the tube portion  78  and the upper disc  96 . The upper disc  96 , which can be made of AISI 4140 steel, includes an annular recess  102  into which a seal  104  having an E-shaped cross section is seated to seal with and wipe against the interior surface  74  of the chamber bore  40  as the plunger  28  extends and retracts relative to the stationary upper disc  96 . 
     The upper end  16  of the cylinder base  12  also includes a bearing  106  seated on a ledge  108  and configured to slidably engage the exterior surface  32  of the plunger  28 . The bearing  106  can be made of C95400 aluminum bronze or any other suitable material. A lower seal  110  having an inverted U-shaped cross section is seated beneath the bearing  106  on a lower ledge  112  that is formed in the interior surface  38  of the plunger bore  30 . One arm of the lower seal  110  wipes against the exterior surface  32  of the plunger  28 , and the other arm is urged into engagement with the cylinder base  12 . An upper seal  114  is seated atop the bearing  106  and is secured in place by an annular retainer  116  that is engaged (e.g., press fit, spring fit) with a notch  118  at the top of the cylinder base  12 . Specifically, a lip  120  of the retainer  116  covers a top portion of the upper seal  114  to axially restrain the upper seal  114  relative to the cylinder base  12 . The upper seal  114  defines a rim  122  extending radially inward to wipe against the exterior surface  32  of the plunger  28 . The lower seal  110  and the upper seal  114  inhibit contaminants from entering the plunger bore  30  and prevent fluid within the plunger bore  30  from leaking, and can be made of polyurethane. The various seals and bearings described are for illustrative purposes and, as one skilled in the art will appreciate, may be modified to accommodate specific application requirements. 
     With specific reference to  FIGS. 2 and 3 , the position of the plunger  28  can be adjusted between the retracted state (e.g., shown in  FIG. 2 ) and the extended state (e.g., shown in  FIG. 3 ) by selectively directing a pressurized fluid into one of the extend port  24  (via an extend coupling  24 A) and the retract port  26  (via a retract coupling  26 A). Directing fluid into an advance chamber  124  urges the plunger  28  toward the extended position. As best shown in  FIG. 3 , the advance chamber  124  is generally defined and bounded by the plunger bore  30  and the lower end  66  of the plunger  28 , including the divider  44  seated near the lower end  66 . The tube portion  78  of the chamber member  80  extends through the advance chamber  124  and therefore also defines the volumetric bounds of the example advance chamber  124 . Specifically, with reference to  FIG. 3 , pressurized fluid is directed into the extend port  24  that is in fluid communication with a horizontal extend passageway  126  formed in the lower end  14  of the cylinder base  12 . A vertical extend passageway  128  intersects the horizontal extend passageway  126  and is in fluid communication with the advance chamber  124 . Under typical circumstances, the inflow of pressurized fluid into the advance chamber  124  will be reduced or stopped manually by an operator prior to the plunger  28  reaching an end of stroke or fully extended position. 
     Given that the example cylinder assembly  10  is a double-acting cylinder, the plunger  28  can be forcibly retracted from an extended state to a retracted state via selective introduction of pressurized fluid. Directing fluid into a retract chamber  130  urges the plunger  28  toward the retracted position. As best shown in  FIGS. 2 and 5 , the retract chamber  130  is generally defined and bounded by the chamber bore  40  (including the divider  44 ) and the chamber member  80  (including the upper disc  96 ). To retract the plunger  28 , pressurized fluid is directed into the retract port  26  that is in fluid communication with a horizontal retract passageway  132  formed in the lower end  14  of the cylinder base  12 . The horizontal retract passageway  132  abuts the lower end  86  of the chamber member  80 , which includes an annular recess  134  and a cross passage  136 . Fluid flows from the horizontal retract passageway  132 , into the annular recess  134 , and into the cross passage  136 . The cross passage  136  intersects a vertical retract passageway  138  formed along the length of the chamber member  80 . The vertical retract passageway  138  of the example chamber member  80  includes plugs  140  at top and bottom ends to define the ends of the vertical retract passageway  138 . An upper horizontal retract passageway  142  extends radially outward from the vertical retract passageway  138  to provide fluid communication between the vertical retract passageway  138  and the retract chamber  130 . 
     If the pressure within the retract chamber  130  exceeds a predetermined level (e.g., above approximately three thousand pounds per square inch in the example embodiment), a check valve  144  will open to allow fluid communication between the retract chamber  130  and the advance chamber  124 . As best illustrated in  FIGS. 5 ,  6 , and  7 , the check valve  144  is seated in a check passageway  146  that is formed through the divider  44  of the plunger  28 . A valve seat  147  is formed at a conical portion  148  and a ball  150  (made of AISI 1080 steel) is sized to seal with the valve seat  147 . The ball  150  is engaged with a ball guide  152  having a notched head  154  and a post  156  extending form the head  154 . The ball guide  152  may be formed of AISI 12L14 steel. A spring  158  is fit about the post  156  and is captured between the back side of the head  154  and an insert  160  secured (e.g., threaded) into the check passageway  146 . The spring  158  is preferably made of music wire steel and the insert  160  can be made of AISI 12L14 steel. If the pressure within the retract chamber  130  becomes excessive, the ball  150  will be urged against the ball guide  152  to compress the spring  158 , ultimately unseating the ball  150  from the valve seat  147  allowing fluid communication between the retract chamber  130  and the advance chamber  124  via the check passageway  146 . 
     The cylinder assembly  10  also includes automatic stroke shutoff to inhibit the plunger  28  from being urged beyond its predefined end of stroke position, and therefore inhibiting excess stress on the cylinder assembly  10  and associated components. As illustrated in  FIGS. 5 ,  6 ,  7 ,  8 , and  9 , a shunt passageway  162  is formed in and extends through the divider  44  that is coupled to the plunger  28 . The shunt passageway  162 , when unobstructed, provides fluid communication between the advance chamber  124  and the retract chamber  130 . As best shown in  FIGS. 8 and 9 , the shunt passageway  162  defies a series of aligned, stepped cylindrical portions that taper from a larger opening  166  adjacent the advance chamber  124  to a smaller opening  168  adjacent the retract chamber  130 . Specifically, the shunt passageway  162  tapers from a bottom end cylindrical portion  170 , to a lower cylindrical portion  172 , to an upper cylindrical portion  174 , and to a top end cylindrical portion  176 . Additionally, the shunt passageway  162  includes a shunt port  163  that is skewed relative to and intersects the upper cylindrical portion  174 ; the shunt port  163  provides an unimpeded pathway for fluid to flow between the retract chamber  130  and the shunt passageway  162  when a shunt valve assembly  178  is in the opened position. 
     While the overall dynamic operation of the shunt valve assembly  178  is dependent on a variety of application specific factors (e.g., the present load being supported by the cylinder assembly  10 ), in one form the shunt valve assembly  178  is configured such that more fluid flows through an open shunt valve assembly  178  (i.e., from the shunt port  163 ) than is being introduced into the advance chamber  124  (e.g., via a piston pump). This configuration reduces or eliminates excessive stress that can result from overtravel and the accompanying increased pressure within the advance chamber  124 . In other applications, for instance, the shunt valve assembly  178  can be configured to flow slightly less fluid than is being introduced and may operate in conjunction with a weep hole (discussed below) to slow the application of excess stress caused by overtravel. In the aspirational configuration, the inflow of fluid is exactly balanced with the outflow of fluid such that the plunger  28  stops extending once the shunt valve assembly  178  has been actuated; this configuration further minimizes the retraction of the plunger  28  once the pressurized fluid is no longer being introduced into the advance chamber  124 . 
     In some situations the shunt valve assembly  178  may cycle or reciprocate between the opened position and the closed position. For instance, if pressurized fluid is continuously introduced into the advance chamber  124  when the shunt valve assembly  178  is in the opened position, the shunt valve assembly  178  will expel sufficient fluid into the retract chamber  130  to allow the plunger  28  to retract far enough to disengage or deactivate the shunt valve assembly  178  (i.e., the shunt valve assembly  178  returns to the closed position). Continuing to supply pressurized fluid into the advance chamber  124  will result in the plunger  28  extending toward a fully extended position, which will again actuate the shunt valve assembly  178  from the closed position to the opened position. This cycle can be repeated until the operator ceases the inflow of fluid (e.g., deactivates a pump). Additionally, the dynamic pulsing introduced into the flow of fluid (e.g., by the repetitive pulsing of a piston pump) can result in cycling of the shunt valve assembly  178 , especially when the ball  192  is only slightly unseated from the valve seat  196 . 
     In the example cylinder assembly  10 , the shunt valve assembly  178  is seated in the shunt passageway  162 . The shunt valve assembly  178  is normally closed and can be selectively opened as the plunger  28  reaches its end of stroke. Specifically, the shunt valve assembly  178  can be moved between a closed position (shown in  FIG. 6 ) at which fluid communication between the advance chamber  124  and the retract chamber  130  is inhibited and an opened position (shown in  FIG. 7 ) at which fluid communication between the advance chamber  124  and the retract chamber  130  is established. 
     With specific reference to  FIGS. 6 ,  7 ,  8 , and  9 , the shunt valve assembly  178  is positioned so that when the plunger  28  is near the extended position (or at the fully extended position or end of stroke) the shunt valve assembly  178  is urged to the opened position. In the opened position, the shunt valve assembly  178  allows pressurized fluid to flow from the advance chamber  124  into the retract chamber  130 , thus reducing or eliminating excessive pressure within the advance chamber  124  until the flow of pressurized fluid into the advance chamber  124  is stopped, at which time the shunt valve assembly  178  will close and the plunger  28  is held in the extended position (i.e., absent excessive pressure in the retract chamber  130 , a fluid leak, etc.). 
     The shunt valve assembly  178  includes several components to control the flow of fluid between the advance chamber  124  and the retract chamber  130 . An actuator pin  180  includes a larger diameter portion  182  that extends through the top end cylindrical portion  176 . A conical flange  184  is formed on the actuator pin  180  between the larger diameter portion  182  and a smaller diameter portion  186 . The conical flange  184  is sized to engage a tapered or conical stop surface  188  (shown best in  FIG. 9 ) formed in the shunt passageway  162  between the top end cylindrical portion  176  and the upper cylindrical portion  174  when the shunt valve assembly  178  is in the fully closed position (shown in  FIG. 6 ). The actuator pin  180  may be made of AISI 4340 steel or any other suitable material. An end face  190  of the smaller diameter portion  186  is adjacent to a ball  192 , which is urged upward toward the end face  190  by an upper spring  194  that is seated in the lower cylindrical portion  172  with the ball  192 . The ball  192  can be made of AISI 1080 steel and the spring  194  can be made from music wire steel. In the closed position, the ball  192  is seated against a conical valve seat  196  (shown best in  FIG. 9 ) formed between the upper cylindrical portion  174  and the lower cylindrical portion  172  to inhibit fluid communication between the advance chamber  124  and the retract chamber  130 . The actuator pin  180 , the ball  192 , and the upper spring  194  are captured in the shunt passageway  162  by an upper cylindrical retainer  198  that is secured (e.g., press fit, threaded) into a lower end  200  of the lower cylindrical portion  172 . The retainer  198  defines a central opening  202  to allow fluid to flow through the retainer  198  and can be made from AISI 12L14 steel. 
     The example shunt valve assembly  178  further includes a lower cylindrical retainer  204  seated in the bottom end cylindrical portion  170 . An upper rim  206  of the lower cylindrical retainer  204  defines a generally V-shaped groove  208  into which a seal  210  is seated to abut with and seal against a beveled surface  212  positioned between the bottom end cylindrical portion  170  and the lower cylindrical portion  172 . The lower cylindrical retainer  204  includes a contoured interior passage  214  (shown in cross section in  FIGS. 8 and 9 ). A hexagonal opening  216  extends from a bottom of the interior passage  214  toward an inwardly tapering portion  218 . A ledge  220  is formed at an upper end of the tapering portion  218  and provides a seat  222  for a disc  224  that is sized to slidably move within a cylindrical portion  226 . The disc  224  is engaged by the lower end  228  of a spring  230  and urged toward the seat  222  by the spring  230 . Specifically, an upper end  232  of the spring  230  is captured between the disc  224  and an inverted castellated cage  234 . The castellated cage  234  is secured in a radially expanded cylindrical portion  236  with ends of legs  238  of the castellated cage  234  engaged with a lower ledge  240 . An upper hub  242  of the castellated cage  234  abuts an inwardly beveled surface  244  of the interior passage  214 . The legs  238  of the castellated cage  234  extend from the upper hub  242  and are circumferentially spaced. The upper hub  242  includes a central opening  246  and arcuate cutouts  248  to allow and meter the selective flow of fluid along the interior passage  214  when the disc  224  is unseated from the seat  222 . In the example embodiment, the lower cylindrical retainer  204 , the disc  224 , the spring  230 , and the castellated cage  234  can be those manufactured by Hawe North America, Inc. of Charlotte, N.C. 
     During an example operational cycle of the cylinder assembly  10 , with the plunger  28  beginning in the retracted position shown in  FIG. 2 , a pressurized fluid (e.g., hydraulic fluid) is directed into the advance chamber  124  via the extend port  24 , the horizontal extend passageway  126 , and the vertical extend passageway  128  to ultimately urge the plunger  28  toward the extended position shown in  FIGS. 3 and 5 . As the plunger  28  approaches the fully extended position or the end of stroke, the shunt valve assembly  178  embedded in the divider  44  of the plunger  28  approaches the upper disc  96  of the chamber member  80 . As best shown in  FIG. 6 , pressurized fluid within the advance chamber  124  unseats the disc  224  from the seat  222  against the urging of the spring  230 . The disc  224  is moved upward into the castellated cage  234  such that fluid from the advance chamber  124  flows between the legs  238 , through the central opening  246  of the upper hub  242 , and past the arcuate cutouts  248 . The fluid is inhibited, at this point, from flowing completely through the shunt passageway  162  because the ball  192  remains seated by the upper spring  194  against the valve seat  196 . 
     As shown in  FIG. 7 , continuing to extend the plunger  28  toward or to the fully extended position results in the larger diameter portion  182  of the actuator pin  180  engaging the upper disc  96  of the chamber member  80 , thereby unseating the ball  192  from the valve seat  196  against the urging of the upper spring  194 . In other words, the shunt valve assembly  178  is moved or actuated from the closed position to the opened position as a result of the engagement with the chamber member  80 , thereby establishing fluid communication between the advance chamber  124  and the retract chamber  130 . Fluid in the advance chamber  124  flows through the shunt passageway  162  and along the shunt port  163  into the retract chamber  130 . With the shunt valve assembly  178  opened, the fluid enters the retract chamber  130 , is directed to the upper horizontal retract passageway  142 , into the vertical retract passageway  138 , downward to the cross passage  136 , outward into the annular recess  134 , along the horizontal retract passageway  132 , and ultimately to the retract port  26 . 
     The flow of fluid through the opened shunt port  163  can be tailored to various applications by, for instance, altering the size and contours of the shunt port  163 . Furthermore, varying the form factor of, for example, the overall shunt passageway  162 , the valve seat  196 , the ball  192 , and/or the upper spring  194  can influence both the dynamic response and the fluid throughput of the shunt valve assembly  178 . The dynamic nature of the fluid being introduced into the advance chamber  124  also impacts the dynamics of the shunt valve assembly  178 , influencing the ultimate operation (e.g., opening, closing, cycling, etc.) of the shunt valve assembly  178  during use in any particular application. 
     The example shunt valve assembly  178  configuration reduces the overall stress on the cylinder assembly  10  and associated components (e.g., hoses, pumps, seals, etc.) by reducing or eliminating the pressure spike that typically occurs if a plunger is allowed to overtravel. Given the benefit of this disclosure, one skilled in the art will appreciate the various control options (e.g., valves) that can implement the fluid cylinder assembly concept. For instance, in one form, when the plunger  28  is being extended, the retract chamber  130  must be allowed to drain to accommodate fluid traveling through the shunt port  163  into the retract chamber  130 . 
     With specific reference to  FIG. 5 , the cylinder assembly  10  may incorporate a weep passageway  149  (shown with dashed lines in  FIG. 5 ) that allows fluid within the advance chamber  124  to flow from the advance chamber  124  if, for instance, the shunt valve assembly  178  malfunctions (e.g., becomes clogged, etc.). The weep passageway  149  is formed in the plunger  28  and extends from a lower opening  151  that is in fluid communication with the advance chamber  124  to an upper opening  153  extending through the exterior surface  32  of the plunger  28 . The upper opening  153  is positioned to be slightly below the lower ledge  112  that supports the lower seal  110  when the plunger  28  is near its end of stroke position. In use, if the shunt valve assembly  178  is operational, the stroke of the plunger  28  will be limited prior to the upper opening  153  sliding past the lower seal  110 . However, if the shunt valve assembly  178  malfunctions and the plunger  28  moves to a fully extended end of stroke position, the upper opening  153  of the weep passageway  149  will move past the lower seal  110  and thus allow pressurized fluid to flow from the advance chamber  124 , into the lower opening  151 , through the weep passageway  149 , and out through the upper opening  153  to atmosphere, thus reducing the pressure within the advance chamber  124 . The location and configuration of the weep passageway  149  can be modified to accommodate any application specific requirements. 
     An alternative example fluid cylinder assembly (“cylinder assembly  500 ”) is shown in  FIGS. 10 and 11 . Many of the components are similar to those illustrated and described in  FIGS. 1-9  and will therefore not be repeated in detail. For instance, the cylinder assembly  500  includes a shunt valve assembly  502  coupled to a plunger  504 . As the plunger  504  approaches the extended position, the shunt valve assembly  502  can be engaged to actuate the shunt valve assembly  502  from a closed position (at which fluid is inhibited from flowing between an advance chamber  506  and a retract chamber  508 ) and an opened position (at which fluid communication between the advance chamber  506  and the retract chamber  508  is established). 
     Several distinctions from the cylinder assembly  10  are illustrated in  FIG. 11 . Specifically, a lower end  510  of the plunger  504  includes an annular recess  512  into which a ring  514  is stacked atop an inverted U-shaped annular seal  516 . The seal  516  includes a radially inward lip  518  that engages with the annular recess  512  and a radially outward lip  520  that engages with and wipes against an interior surface  522  of a plunger bore  524 , which is defined by a cylinder base  526 . The cylinder base  526  also includes a weep hole  528  (which is shown plugged in  FIG. 5  illustrating the cylinder assembly  10 ) extending through a vertical wall  530  of the cylinder base  526  that provides further overtravel protection, in addition to the shunt valve assembly  502 . Fluid within the advance chamber  506  can escape through the weep hole  528  should the shunt valve assembly  502  malfunction or be unable to accommodate the necessary fluid flow. 
     Once the plunger  504  has been extended to the desired position, a locknut  532  having internal threads  534  can be engaged with mating external threads  536  formed along the exterior of the plunger  504 . The locknut  532  is threaded downward along the plunger  504  to bring a bottom surface  538  of the locknut  532  into engagement with an end face  540  of the cylinder base  526 . The locknut  532  can be incorporated as a secondary support to maintain the plunger  504  in the desired position and/or can be configured such that pressurized fluid need not be continually urged into the advance chamber  506  to maintain the position of the plunger  504 . 
     While there has been shown and described what is at present considered the preferred embodiments, it will be appreciated by those skilled in the art, when given the benefit of this disclosure, that various changes and modifications can be made without departing from the scope of the invention defined by the following claims. For instance, while the example shunt valve assemblies are mechanically actuated, the shunt valve assembly can be adapted to be electrically actuated. In one example, the actuator pin  180  can be replaced by an electrical contact. When the electrical contact is actuated (e.g., due to engagement with the chamber member  80 ), an electrical circuit can be triggered to energize a normally closed solenoid valve, which would allow for fluid communication between the advance chamber  124  and the retract chamber  130 . Other various modifications to the broader concept are also within the skill of one of ordinary skill in the art.