Abstract:
A telescoping housing for a single acting fluid actuator includes an outer actuator housing section and an inner actuator housing section mounted to reciprocate axially relative to the outer housing section while being surrounded thereby. The housing sections cooperate to form a chamber, and the housing is extended axially by supplying an actuator fluid under pressure to the chamber. A positive pressure is maintained in the chamber to avoid infiltration of outside contaminants into the chamber. Retraction is accomplished by reducing the fluid pressure sufficiently to allow the housing to retract under the influence of gravity, spring force, or other external force. The telescoping housing design eliminates the need for a reciprocating piston and piston rod.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to fluid actuators such as hydraulic and pneumatic cylinders and motive systems in which these cylinders are employed, and more particularly to the housings of these cylinders.  
         [0002]     In many industries, the need arises for localized applications of considerable force in areas that lack sufficient space to accommodate motors or engines capable of generating the required forces. Fluid actuators are well suited to meet these needs. A typical actuator construction includes an actuator housing composed of an elongate cylinder and two opposite end caps, a piston that reciprocates axially within the cylinder, and a piston rod mounted to reciprocate with the piston. One of the end caps has a central opening to accommodate the rod, while the other, known as a “blind” end cap, completely closes its end of the cylinder.  
         [0003]     Motive force is generated by providing a fluid to the housing between the piston and one of the end caps, to drive the piston toward the other end cap. In hydraulic systems, the actuator fluid is an incompressible fluid, such as oil. In pneumatic systems, the fluid is a compressible fluid such as air or another pneumatic gas.  
         [0004]     In either event, a broad range of new applications has increased the demand for actuators that are more reliable, yet produced at lower cost. In dusty or other more demanding environments, there is a need to reduce or eliminate infiltration during retraction of the piston. The desire to ensure that the housing cylinder, piston, rod, and end cap that accommodates the rod are concentric requires a high level of precision machining of these parts. Seals capable of accommodating relative motion are required at the piston/cylinder interface and the rod/end cap interface. Accordingly, there is a need for an improved fluid actuator design.  
         [0005]     Therefore, it is an object of the present invention to provide a fluid actuator that is less susceptible to infiltration during retraction and other stages of actuator operation.  
         [0006]     Another object is to provide a fluid actuator housing construction that requires fewer seals.  
         [0007]     A further object is to provide a fluid actuator of simpler design and having fewer essential components.  
         [0008]     Yet another object is to provide a lower cost, more efficient process for manufacturing housings for fluid actuators.  
       SUMMARY OF THE INVENTION  
       [0009]     To achieve these and other objects, there is provided a fluid actuator including a first actuator housing section having a first-section end wall, a first open end opposite the first-section end wall, and a first-section side wall extending in a longitudinal direction between the first-section end wall and the first open end. A second actuator housing section of the actuator has a second-section end wall, a second open end opposite the second-section end wall, and a second side wall extending in a longitudinal direction between the second-section end wall and the second open end. The second actuator housing section is disposed in opposition to the first actuator housing section with the second-section side wall surrounded by the first-section side wall and with the second open end confronting the first-section end wall. Thus, the first and second actuator housing sections cooperate to form an actuator housing with an enclosed chamber extending longitudinally between the first-section end wall and the second-section end wall. The second actuator housing section is adapted to reciprocate longitudinally with respect to the first actuator housing section, between an extended state in which the first-section end wall and second-section end wall are relatively remote from each other, and a retracted state in which the first-section end wall and the second-section end wall are relatively proximate to each other, thus to alternatively longitudinally expand and contract the actuator housing. A fluid supply component is fluid-coupled to the chamber and adapted to supply an actuator fluid under pressure to the chamber, to longitudinally expand the actuator housing.  
         [0010]     Thus, the reciprocating sections provide a telescoping actuator housing. A salient feature of this construction is that it eliminates the need for a piston and piston rod, since the motive force is generated through relative movement of the first and second actuator housing sections. Wipe-action seals at the piston/cylinder interface and rod/end cap interface of conventional cylinder constructions, are replaced functionally by a single seal at the interface of the first and second actuator housing sections, more particularly between the first and second side walls. The actuator housing sections preferably are an aluminum alloy and are formed by impact extrusion, thus to require relatively little precision machining. In any event, with only two components that need to be machined, production and assembly costs are reduced.  
         [0011]     In preferred constructions, the first and second side walls are cylindrical and concentric on a longitudinal axis. To enhance stability and ensure a more effective seal, the first side wall is crimped or otherwise radially reduced along an annular end region near the open end for a contiguous, sliding engagement with the outside surface of the second side wall. A wear ring is advantageously disposed between the end region and second side wall. To further stabilize the arrangement, a second wear ring is positioned between the second side wall near its open end and an inside surface of the first side wall. The wear ring is formed with a break to allow passage of air (or oil in hydraulic versions) between the chamber and a narrow, annular gap between the first and second side walls with a maximum length when the housing is retracted. This eliminates the need for the housing to “breathe,” thus to minimize the chance for contamination from the environment outside the housing.  
         [0012]     Another aspect of the invention is a process for assembling a fluid actuator housing, including the following steps:  
         [0013]     (a) providing a first actuator housing section having a first-section end wall, a first open end opposite the first-section end wall, and a first-section side wall extending in an axial direction between the first-section end wall and the first open end;  
         [0014]     (b) providing a second actuator housing section having a second-section end wall, a second open end opposite the second-section end wall, and a second-section side wall extending in an axial direction between the second-section end wall and second open end, wherein an outside diameter of the second-section side wall is less than an inside diameter of the first-section side wall;  
         [0015]     (c) inserting the second actuator housing section axially into the first actuator housing section such that the first-section side wall surrounds the second-section side wall and the second open end confronts the first-section end wall;  
         [0016]     (d) with the second actuator housing section so inserted, permanently radially reducing an end region of the first-section side wall proximate the first open end, to secure the second actuator housing section against removal from the first actuator housing section while permitting the second actuator housing section to travel axially relative to the first actuator housing section.  
         [0017]     A salient advantage of this process is the absence of a piston and piston rod, and the resulting elimination of the need to concentrically align the piston, the rod, the cylinder surrounding the piston, and the end cap or other end structure designed to accommodate the rod.  
         [0018]     Further in accordance with the present invention, there is provided a fluid actuator system including an actuator housing comprising a first actuator housing section having a first end wall and an axially extending first side wall, and a second actuator housing section having a second end wall and an axially extending second side wall. The second actuator housing section is mounted to reciprocate axially relative to the first actuator housing section between extended and retracted states with the first side wall in surrounding relation to the second side wall. The first and second actuator housing sections cooperate to define a chamber with the first and second end walls disposed at opposite ends of the actuator housing to determine opposite ends of the chamber. The system further includes a fluid source containing a fluid. A fluid supply path extends from the fluid source to the chamber. A fluid pump is disposed along the fluid supply path, and is operable to convey the fluid from the fluid source into the chamber under pressure to cause the second actuator housing section to travel axially toward the extended state.  
         [0019]     When the actuator housing is retracted under an external force, a positive pressure is maintained while the fluid is evacuated from the chamber. This further reduces the potential for infiltration from the environment outside the housing. In most applications, the first housing section remains substantially fixed while the second housing section axially reciprocates. In such cases and in others, the fluid supply path includes a passage through the end wall of the first actuator housing section.  
         [0020]     Thus in accordance with the present invention, a fluid actuator housing is formed with telescoping sections to eliminate the need for the reciprocating piston and piston rod found in conventional fluid actuators. This reduces the number of required parts, and along with it the manufacturing costs and complexity. Further, the reciprocating sections virtually eliminate the potential for contamination due to infiltration from the ambient environment, during actuator extension and retraction.  
     
    
     IN THE DRAWINGS  
       [0021]     Further features and advantages will become apparent upon consideration of the following detailed description and the drawings, in which:  
         [0022]      FIG. 1  is a side elevation of a fluid actuator housing constructed in accordance with the present invention;  
         [0023]      FIG. 2  is a sectional view taken along the line  2 - 2  in  FIG. 1 , showing the housing in a retracted position;  
         [0024]      FIG. 3  is a partially sectioned side elevation of an alternative embodiment fluid actuator housing;  
         [0025]      FIG. 4  is a sectional view taken along the line  4 - 4  in  FIG. 3 , showing the housing retracted;  
         [0026]      FIG. 5  is an exploded parts view of a further alternative embodiment fluid actuator housing;  
         [0027]      FIGS. 6 and 7  are sectional views of the housing of  FIG. 5 , retracted and extended, respectively;  
         [0028]      FIG. 8  is a partial sectional view of the housing, taken along the line  8 - 8  in  FIG. 6 ;  
         [0029]      FIG. 9  is a partially sectioned view of yet another alternative embodiment fluid actuator housing; and  
         [0030]      FIG. 10  schematically illustrates a system incorporating a fluid actuator, constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     Turning now to the drawings, there is shown in  FIGS. 1 and 2  a fluid actuator  16 , which can be either a hydraulic cylinder or a pneumatic cylinder. Actuator  16  has an elongate, telescoping cylindrical housing, including an outer actuator housing section  18  and an inner actuator housing section  20  mounted for longitudinal (axial) reciprocation relative to housing section  18  to alternatively extend and retract the housing.  
         [0032]     Outer housing section  18  has an elongate, axially extending annular side wall  22 , an end wall  24 , and an open end  26  opposite the end wall. Near the open end, side wall  22  is inclined radially inwardly as indicated at  28  to form a reduced-diameter end region  30 . As best seen in  FIG. 2 , end wall  24  has a width in the axial direction sufficient to accommodate a fluid passage  32  and a centered, axially extending opening  34  to facilitate mounting actuator  16  in a desired operating environment. Opening  34  typically has internal threads.  
         [0033]     Inner housing section  20  includes a longitudinally extending side wall  36  and an end wall  38 . As seen in  FIG. 2 , inner housing section  20  has an open end  40  opposite the end wall. Near open end  40 , side wall  36  is inclined radially outward to provide an enlarged-diameter end region  42 . End wall  38  has an axial width sufficient to accommodate an opening  44  which, like opening  34  of opposite end wall  24 , is internally threaded and facilitates the mounting of actuator  16  in the working environment. Actuator housing sections  18  and  20  preferably are formed of aluminum.  
         [0034]     Actuator  16  further includes components that guide and facilitate axial reciprocation of the housing sections. An annular bearing or wear ring  46  surrounds inner housing section  20  along end region  42 , retained against axial movement with respect to housing section  20 . Bearing  46  is contiguous with and slidable relative to an inside surface  48  of side wall  22 . Similarly, an annular bearing or wear ring  50  is disposed between end region  30  and side wall  36 , constrained against axial movement relative to side wall  22  while being contiguous with and slidable relative to an outside surface  52  of side wall  36 . Bearings  46  and  50  preferably are formed of brass, impregnated or coated with polytetrafluoroethylene (PTFE) at least along their sliding surfaces.  
         [0035]     An annular seal  54  is mounted integrally with outer housing section  18  near open end  26 , and surrounds inner housing section  20  in a slidable sealing/wiping engagement with outside surface  52  of side wall  20 . Seal  54  is formed of a suitable polymer such as polyurethane.  
         [0036]     Housing sections  18  and  20  cooperate to form a substantially enclosed chamber  56  inside the housing. With side wall  22  in surrounding relation to side wall  36 , inner housing section  20  is mounted to reciprocate axially relative to outer housing section  18  between an extended state ( FIG. 1 ) in which end walls  24  and  38  are relatively remote from one another, and a retracted state ( FIG. 2 ) in which the end walls are relatively proximate each other. The retracted state is determined by the engagement of side wall  36  at open end  40  with end wall  24 .  
         [0037]     As seen in  FIG. 2 , the bearings and side wall end regions determine a narrow annular gap  57  between side walls  22  and  36  when actuator  16  is retracted. As the actuator is extended, gap  57  is progressively reduced in volume as its axial length shortens. To ensure against a pressure buildup in the gap, bearing  46  is configured to allow passage of air (or oil) between gap  57  and chamber  56 . This avoids a pressure buildup in gap  57  during housing extension, which if present would work against extension.  
         [0038]     Actuator  16  is operated by supplying an actuator fluid through fluid passage  32  into chamber  56 , extending the housing in opposition to a force represented by arrows  58  that tends to maintain the actuator housing in the retracted state. The force may be a spring force, or may be due to gravity from the weight of a component supported by the actuator. In any event, outer housing section  18  typically is held stationary or mounted pivotally relative to a fixed location, while the inner housing section reciprocates.  
         [0039]     The actuator fluid can be a substantially incompressible fluid such as oil in a hydraulic system, or a compressible fluid such as air in a pneumatic system. In either event, pressure to the fluid can be applied in a controlled manner to determine both the rate and the amount of housing extension. One advantage of the telescoping housing construction is reduced potential for contamination from the environment surrounding the housing. In conventional actuators, retraction temporarily develops a relative vacuum in the chamber upstream of the piston, which may cause ambient air including entrained particles to be drawn into the chamber. Retraction of actuator  16 , in contrast, does not create a relative vacuum in the chamber. Instead, a positive pressure is present throughout the chamber during retraction. The capacity to resist infiltration is particularly beneficial for actuators used in environments with high concentrations of particulates or corrosive elements.  
         [0040]     Another advantage of actuator  16  is that it requires only one sealing interface, namely seal  54  between side walls  22  and  36 . Conventional piston/rod actuator housings require up to five sealing interfaces, one between the housing wall and piston, one between the blind end wall or cap and the housing, one between rod end wall or cap and the housing, another between the piston rod and the end wall or cap that accommodates the rod, and sometimes one between the rod and piston.  
         [0041]      FIGS. 3 and 4  illustrate an alternative embodiment fluid actuator  60  with a housing formed by telescoping inner and outer housing sections  62  and  64  having respective end walls  66  and  68  and side walls  70  and  72 . As before, each of the housing sections has an open end opposite its end wall.  
         [0042]     Side wall  72  of the. outer housing section includes a reduced-diameter end region  74  near its open end. End wall  68  accommodates an opening  76  for mounting the actuator in a working environment, and a fluid passage  78  that is inclined and linear, as compared to the “L” shape of passage  32 .  
         [0043]     Side wall  70  includes an enlarged-diameter end region  80  near its open end. End wall  66  accommodates an opening  82  for mounting the actuator. Annular bearings  84  and  86 , and an annular seal  88 , are positioned and function in the manner described in connection with actuator  16 .  
         [0044]     A portion of  FIG. 3  is cut away to reveal the manner in which end region  74  of side wall  72  and end region  80  of side wall  70  function as limiting features, by engaging one another when inner housing section reaches the extended state, to prevent any further extension of the housing.  
         [0045]      FIGS. 5-8  illustrate another alternative fluid actuator  90  with a telescoping housing and related components including an outer actuator housing section  92 , an inner actuator housing section  94 , bearings  96  and  98 , and an annular seal  100 . Outer housing section  92  includes a side wall  102 , an end wall  104 , an open end  106  opposite the end wall—and in the finished actuator ( FIGS. 6 and 7 ), an annular end region  108  having a reduced diameter. End wall  104  accommodates a centered axially extending opening  110  to mount the actuator, and a radial (vertical in  FIGS. 6 and 7 ) fluid passage  112 . An annular depression  114  in the end wall is fluid-coupled to passage  112 , and thus cooperates with the passage to admit fluid into a chamber  116  of the housing.  
         [0046]     Inner housing section  94  includes a side wall  118 , an end wall  120  accommodating an axial opening  122  used to mount the actuator, and an end region  124  near an open end  126  of the housing section. End region  124 , in contrast to end regions  42  and  80  of the previous embodiments, is not formed by radially enlarging the side wall. Consequently, the inside diameter of the inner housing section is uniform, although the outside diameter is larger at the end region.  
         [0047]     An advantage of the telescoping cylinder housing is the relative ease and low cost of its manufacture. With reference to  FIG. 5 , manufacturing begins with forming housing sections  92  and  94 , by impact extrusion of an aluminum alloy. The housing sections are machined to provide certain features to facilitate assembly, e.g. an annular groove  128  near the open end of housing section  92  to accommodate bearing  96 , and an annular groove  130  shaped to accommodate seal  100 . Similarly, an annular groove  132  is formed along the outside surface of housing section  94  to accommodate bearing  98 .  
         [0048]     After machining, the bearings are installed into their respective grooves. Bearings  96  and  98  are formed with breaks or scarf cuts as indicated at  134  and  136 , respectively. This facilitates radial expansion and contraction of each bearing into a close, conforming fit against its associated side wall. With respect to bearing  96 , scarf cut  134  facilitates a radial reduction of the bearing when end region  108  is radially reduced during actuator assembly. In connection with bearing  98 , scarf cut  136  provides a passage between the side walls that allows movement of oil or air across the wear surface between the chamber and an annular gap  138  between the side walls.  
         [0049]     After its insertion into groove  128 , bearing  96  retains a diameter larger than that of bearing  98 . This permits insertion of inner housing section  94 , with bearing  98  surrounding end region  124 , axially into outer housing section  92  to locate end region  124  inwardly of end region  108  such that open end  126  confronts end wall  104 . After insertion of inner housing section  94 , seal  100  is inserted into groove  130 . The seal is retained, although somewhat loosely, since at this stage the groove has a diameter larger than the seal diameter.  
         [0050]     With housing section  94  thus inserted, outer housing section  92  is crimped along end region  108 . This is a cold working stage in which the aluminum side wall is permanently (i.e. plastically) deformed to reduce the diameter along the end region. Crimping also radially compresses bearing  96 , by narrowing scarf cut  134 . Finally, crimping reduces groove  130  more closely about seal  100 , to positively retain the seal.  
         [0051]     The assembly of actuators  16  and  60  is substantially the same, with an additional plastic deformation step. Specifically, side wall  36 / 70  of inner housing section  20 / 62  is plastically deformed along end region  42 / 80  to increase the side wall diameter. The side wall is enlarged in this fashion before the inside housing section is machined or inserted into the outside housing section, either before or after placement of the bearing into the groove.  
         [0052]     As shown in  FIG. 8 , scarf cut  136  forms a gap between side walls  102  and  1   18  in the finished actuator. This permits air, or oil in hydraulic versions, to pass freely between chamber  116  and gap  138 . Thus, as inner housing section  94  moves axially from the retracted state ( FIG. 6 ) toward the extended state ( FIG. 7 ), the actuator fluid flows from the gap into the chamber, avoiding a pressure buildup that otherwise would resist housing extension. As best seen in  FIG. 7 , end regions  108  and  124  encounter each other when the housing is extended to a predetermined point, preventing further extension and reducing gap  138  to its minimum size. Subsequent retraction of the housing causes air or oil to flow from the chamber into the gap.  
         [0053]      FIG. 9  shows an alternative embodiment fluid actuator  140  in which an outer actuator housing section  142  and an inner actuator housing section  144  are each composed of several parts. Outer housing section  142  includes a side wall  146 , an end cap  148  threadedly coupled to the side wall, and an annular retaining feature  150  threadedly coupled to the other end of the side wall. Inside housing section  144  includes a side wall  152 , and an end cap  154  threadedly coupled to the side wall. An annular bearing  156  surrounds the side wall near the end opposite from end cap  154 .  
         [0054]     An opening through retaining feature  150  accommodates longitudinal sliding of inner housing section  144 . Annular grooves in feature  150  accommodate a bearing  158  maintained in sliding engagement with side wall  152 , and an annular seal  160  maintained in sliding, wiping engagement with the side wall.  
         [0055]     Actuator  140  avoids the need to crimp either of the side walls, but requires considerably more precision machining.  
         [0056]      FIG. 10  schematically illustrates a system  162  configured according to the present invention. The system includes a fluid actuator  164  similar to actuator  90 , although any of the previously discussed embodiments would suffice. An actuator fluid supply  166  is coupled to the fluid actuator through a supply line  168 , a bidirectional valve  170  and a line  172 . Line  172  is coupled to a fluid passage through the end wall similar to passage  112 , to complete a fluid supply path to the chamber inside actuator  164 . A fluid pump  174  along line  168  is operable to supply the fluid under pressure to the chamber, to extend actuator  164  against a force that tends to keep the actuator retracted, represented by the arrow at  176 . In conjunction with the telescoping section design, when valve  170  is operated to direct fluid from line  172  to line  178 , the fluid is evacuated from actuator  164  by action of force  176 . The positive pressure created in actuator  164  by the action of force  176  further minimizes the chance for infiltration of environmental particulates and contaminants near the actuator even during the retraction of actuator  164 .  
         [0057]     Line  172 , valve  170  and a return line  178  from the valve to fluid supply  166  form a fluid return path from the chamber to the fluid supply. Valve  170  is operable in concert with pump  174  to direct the actuator fluid from line  168  to line  172  when the pump is applying a positive pressure, and alternatively to direct fluid from line  172  to return line  178  when the pump is not active.  
         [0058]     Thus in accordance with the present invention, fluid actuators and systems employing fluid actuators can be manufactured and configured more quickly, require fewer component parts, and are more resistant to infiltration of particles and other contaminants suspended in the surrounding air. Elimination of the piston and piston rod found in conventional actuators also reduces the number of seals required. As a result, fluid actuators and systems are produced at lower cost, yet afford long-term, reliable performance.