Abstract:
Disclosed is a reciprocating pneumatic tool including first and second piston retaining mechanisms for preventing the piston from freely exiting the barrel of the tool when the retaining sleeve and workpiece are removed. The retaining mechanisms are located within the lower portion of the tool barrel, and do not interfere with normal operation of the tool.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to reciprocating power tools, and more particularly, to a piston retaining system in the barrel of a pneumatic tool.  
           [0003]    2. Description of the Prior Art  
           [0004]    Reciprocating power tools that hammer, chisel, and drill have been utilized in the construction industry for years, and will likely continue to play an important role on most job sites in the future. Pneumatically driven reciprocating tools have proven to be particularly effective in delivering high performance for relatively low cost. While ongoing design improvements have enhanced certain functional aspects of such tools, the basic design concept of a reciprocating pneumatic tool has not changed.  
           [0005]    An example of such a tool is the Chicago Pneumatic™ 4181™ “Rivet Buster.” Like most similar pneumatically driven tools, the 4181 includes an elongated barrel with a handle and trigger at one end and a retaining sleeve at the other end for holding a workpiece (e.g., a chisel or the like). Inside an upper portion of the barrel, proximate the handle, is a piston that reciprocates back and forth within the barrel, repeatedly striking the butt end of the workpiece within the lower portion of the barrel, thereby causing the workpiece head to reciprocate outside of the barrel.  
           [0006]    As noted above, such tools include a retaining sleeve, which may be removed to perform routine maintenance on the tool or to remove or replace the workpiece. In tool designs like the 4181, once the sleeve is removed, the piston can freely escape from the barrel. This feature promotes easy removal of the piston which may be desirable for maintenance purposes. Moreover, as long as the user takes basic precautionary steps, such as disengaging the tool from the air supply before removing the sleeve, the design presents no problem. However, if the worker fails to take such precautions, the piston could inadvertently exit the barrel. For example, if the sleeve is removed and the trigger is pressed while the tool is operable, the piston could be ejected from the barrel with a fair amount of force, causing damage.  
           [0007]    Thus, a need exists to provide a system that will prevent the free escape of the piston from the barrel when the retainer sleeve is removed. In addition, the system should not interfere with the existing functionality of the tool.  
         SUMMARY OF THE INVENTION  
         [0008]    In order to overcome the limitations of the prior art, the present invention provides a piston retaining system for preventing the free escape of the piston from the barrel of a reciprocating tool when the retaining sleeve and workpiece are removed. The improved tool comprises a barrel, a piston slidably placed within an upper portion of the barrel, a retaining sleeve mounted proximate a lower portion of the barrel, a workpiece slidably retained within the lower portion of the barrel by the retaining sleeve, and at least a first and a second piston retaining mechanism for preventing the free escape of the piston from the barrel when the retaining sleeve and workpiece are removed. Both retaining mechanisms are mounted within the lower portion of the barrel in such a manner that neither the piston nor the workpiece contacts the retaining mechanisms during the actual operation of the tool.  
           [0009]    The first piston retaining mechanism may comprise a retainer ring placeable within a circular groove cut into the inside diameter of the barrel. Specifically, the retainer ring is distally mounted around the butt of the workpiece. The retainer ring includes an opening with a diameter greater than the diameter of the butt of the workpiece, and a first end of a stepped piston, but less than the largest diameter of the piston. Therefore, the tool can operate without interference from the ring, yet the ring engages the upper portion of the piston to prevent the piston from exiting the barrel when the retaining sleeve and workpiece are removed. The ring may include a tapered inner surface to help trap the piston if required. The ring may be made of strong, yet flexible material, with a scarf cut so that it can be removed from the barrel and replaced if necessary.  
           [0010]    The second piston retaining mechanism may include a restricted area formed within the lower end of the barrel. The restricted area has a diameter greater than the diameter of the butt of the workpiece and the first stepped end of the piston, but less than the largest diameter of the piston. The restricted area prevents the inadvertent escape of the piston in the event the ring is worn, removed or in some other manner malfunctions while the retaining sleeve and workpiece are removed.  
           [0011]    It is therefore an object of the present invention to provide a piston retaining system that will prevent the free escape of the piston from the barrel of a reciprocal tool when the retaining sleeve and workpiece are removed.  
           [0012]    It is therefore a further object of the present invention to provide a piston retaining system that will not interfere with, or contact, the piston or workpiece during normal operation of the tool. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 depicts a cross-sectional side view of a pneumatic tool that includes a piston retaining system in accordance with the present invention;  
         [0014]    [0014]FIG. 2 depicts a cross-sectional side view of the lower barrel portion of a pneumatic tool with a workpiece in a neutral position in accordance with the present invention;  
         [0015]    [0015]FIG. 3 depicts a cross-sectional side view of the lower barrel portion of a pneumatic tool with a workpiece in an extended position in accordance with the present invention;  
         [0016]    [0016]FIG. 4 depicts a cross-sectional side view of a lower barrel portion of a pneumatic tool with the retaining sleeve and workpiece removed, the view depicting the piston being blocked by the first piston retaining mechanism in accordance with the present invention;  
         [0017]    [0017]FIG. 5 depicts a front view of the first piston retaining mechanism in accordance with the present invention;  
         [0018]    [0018]FIG. 6 depicts a cross-sectional side view of the first piston retaining mechanism in accordance with the present invention; and  
         [0019]    [0019]FIG. 7 depicts a cross-sectional side view of a lower barrel portion of a pneumatic tool with the retaining sleeve and workpiece removed, the view depicting the piston being blocked by the second piston retaining mechanism in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Although certain embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc. Although the drawings are intended to illustrate the present invention, the drawings are not necessarily drawn to scale.  
         [0021]    Referring to the drawings, FIG. 1 depicts a side view of a pneumatic tool  10  that includes a piston retaining system in accordance with the present invention. The tool  10  generally comprises a handle  11 , a barrel  17 , a retaining sleeve  26 , and a workpiece  18 . The handle  11  includes an air intake port  9  and a trigger  13 . To generally operate the tool  10 , pneumatic air is supplied into the air intake port  9 . Pressing the trigger  13  then causes the workpiece  18  to reciprocate thereby causing a hammering, chiseling or drilling motion.  
         [0022]    The barrel  17  includes a proximal portion  14  and a distal portion  12 . During operation, a piston  16  reciprocates within the proximal portion  14  of the barrel  17  and repeatedly strikes a first end  30  of the workpiece  18  causing the workpiece  18  to reciprocate within the distal portion  12  of the barrel  17 . The piston  16  is generally cylindrical at an upper end or portion  19  having a stepped or tapered lower end or portion  15 . The piston  16  has a maximum diameter at the upper end  19 , which is approximately equal to the inner diameter of the proximal portion  14  of the barrel  17 . The piston  16  has a stepped decreased diameter at the lower end  15 .  
         [0023]    The retaining sleeve  26  slidably retains the workpiece  18  in place such that a second end of the work piece  18  (e.g., a chisel head) can extend and reciprocate outside of the tool  10 . The second end of the workpiece  18  may include a chisel, drill, hammer, or any other commonly used tool. As noted, the retaining sleeve  26  provides a system for allowing the workpiece  18  to slidably move within the distal portion  12  of the barrel  17  during operation of the tool  10 . In addition, the retaining sleeve  26  can be removed from the tool  10  in order to remove and replace the workpiece  18  when the tool  10  is not in operation.  
         [0024]    The retaining sleeve  26  includes an outer sleeve  25 , a first inner sleeve  24 , a second inner sleeve  22  and a bumper  28 . The first inner sleeve  24  and the second inner sleeve  22  hold and lock onto the workpiece  18  and are slidable within the retainer sleeve  26 . The motion of workpiece  18  is limited by the longitudinal space within which the first inner sleeve  24  and the second inner sleeve  22  can travel. In particular, the inner sleeves  22 ,  24  are limited in a first direction by the end of distal portion  12  of the barrel  17  and are limited in a second direction by the outer sleeve  25  and the bumper  28  which also acts as a spring for returning the work piece  18  to a neutral position.  
         [0025]    The tool  10  further includes a first piston retaining mechanism  20 , in this example a retainer ring, that prevents the piston  16  from escaping the distal portion  12  of the barrel  17  when the retaining sleeve  26  and the workpiece  18  are removed from the tool  10 . As is discussed with respect to FIGS.  2 - 4 , the retainer ring  20  does not interfere with the piston  16  or the workpiece  18  while the tool  10  is being operated. While this embodiment generally describes the first piston retaining mechanism as a ring, it is understood that any device that is similarly situated to provide the same functionality falls within the scope of this invention. For example, a star shaped ring, a semi-circular ring, a nub shaped protrusion, or similar device could likewise be used.  
         [0026]    [0026]FIGS. 2 and 3 depict the placement of the retainer ring  20  during operation of the tool  10 . The retainer ring  20  is placeable in a groove  46  cut out of the inside of the distal portion  12  of the barrel  17 . It can be seen in both FIG. 2 and FIG. 3 that the retainer ring  20  is mounted in such a position that it is circumferentially outside (i.e., distally spaced from) the cross-sectional area of the butt portion  32  of the workpiece  18 . The butt  32 , as used herein, defines that portion of the workpiece  18  that reciprocates within or through the retainer ring  20  during operation of the tool  10 .  
         [0027]    [0027]FIG. 2 depicts the workpiece  18  in a retracted or “neutral” position such that the workpiece  18  is retracted into the distal portion  12  of the barrel  17  as far as possible. As can be seen, the first inner sleeve  24  is flush with the end of the barrel  17  thereby limiting the inward travel of the workpiece  18  to the point shown. Conversely, FIG. 3 depicts the workpiece  18  in an extended or “impact” position such that the workpiece  18  is extended out of the barrel  17  as far as possible. As illustrated, the second inner sleeve  22  is prevented from further outward motion by the outer sleeve  25  of the retainer sleeve  26 . The bumper  28  provides a spring means for returning the workpiece  18  to the retracted position shown in FIG. 2.  
         [0028]    During operation, the piston  16  reciprocates along a longitudinal axis  34  and repeatedly strikes the end  30  of the workpiece  18  to drive the workpiece  18  from a retracted position, shown in FIG. 2, to an extended position, shown in FIG. 3. The result is a continuous reciprocating motion of the workpiece  18  back and forth along the longitudinal axis  36 .  
         [0029]    The motion of the piston  16  is limited in the direction toward the workpiece  18  by the end  30  of the workpiece  18  in the extended position as shown in FIG. 2. Furthermore, because the stepped lower end  15  of the piston  16  has a diameter less than the diameter of the opening  42  in the retainer ring  20  (see FIG. 6), the retainer ring  20  does not interfere with the motion of the piston  16  while the tool  10  is operating.  
         [0030]    Similarly, the butt  32  of the workpiece  18  reciprocates within the opening  42  of the retainer ring  20 . Therefore, the butt  32  does not contact the retainer ring  20  during operation of the tool  10  because the retainer ring opening  42  (see FIG. 6) has a diameter that is greater than the maximum cross-sectional diameter of the butt  32  of the workpiece  18 . Thus, the retainer ring  20  does not interfere with the functional operation of either the piston  16  or the workpiece  18  during the actual operation of the tool  10 .  
         [0031]    The functional purpose of retainer ring  20  is depicted in FIG. 4, which depicts the distal portion  12  of the barrel  17  with the retaining sleeve  26  and the workpiece  18  removed therefrom. As noted above, the retaining sleeve  26  may frequently be removed on a job site to perform maintenance on, to remove or replace the workpiece  18 . If the tool  10  happened to be connected to an air supply while the sleeve  26  was removed, pressing the trigger would cause the piston  16  to be forced outward without being limited in its outward travel by the end  30  of the workpiece  18 . In this case, the pneumatic force on the piston  16  would cause the piston  16  to be forced toward the opening in the distal portion  12  of the barrel  17 . However, the retainer ring  20 , which has an opening  42  with a diameter that is less than the maximum diameter of the piston  16 , will act to block the free escape of the piston  16  from the distal portion  12  of the barrel  17 .  
         [0032]    It should be noted that upon impact of the piston  16  with the ring  20 , the ring  20  will maintain its relative position in the barrel  17 . In particular, the ring  20  will be jammed circumferentially outward into the groove  46  in the distal portion  12  of the barrel  17 , thereby ensuring that the piston  16  is trapped in position. Therefore, because the ring  20  expands into the groove  46  in the distal portion  12  of the barrel  17 , there is no chance for the ring  20  to be dislodged and pushed out ahead of the piston  16 . The expansion of the ring  20  is facilitated by including a ring profile, such as a taper, that causes the ring to expand (see FIGS. 5 and 6).  
         [0033]    [0033]FIGS. 5 and 6 depict a front view and cross-sectional side view of the retainer ring  20 , respectively. The retainer ring  20  includes an outer radial surface  48  and an inner radial surface  50 . The retainer ring  20  has a minimum opening  42  that is greater in diameter than the butt  32  of the workpiece  18  and the lower end  15  of the piston  16 , but smaller in diameter than the maximum diameter of the piston  16 , namely at the upper end  19  of the piston  16 . The ring  20  has a width  44  and outer diameter  46 , which together define the cylindrical cross sectional area or space of the ring  20 .  
         [0034]    The opening  42  of the ring  20  may include a tapered edge  40  to better handle the impact of the piston  16 , should the piston  16  be caused to contact the ring  20 . The tapered edge  40  will cause a wedging effect which will cause the ring  20  to be jammed into groove  46  and the piston  16  to become trapped in the barrel  17 , rather than bounce back and forth within the barrel  17 . It should be recognized that alternate ring profiles, other than a taper, could likewise be utilized to provide a similar result. For example, a concave or rounded profile could possibly provide the same functionality.  
         [0035]    The ring  20  may also include a scarf cut  38  which allows the ring  20  to be easily removed or inserted into the barrel  17  of the tool  10 . Because of the likely damage caused during an impact of the piston  16  with the ring  20 , it is envisioned that the ring  20  should be easily replaceable. In addition, removal of the ring  20  should be relatively easy in the event access to the piston  16 , for maintenance purposes or the like, is required.  
         [0036]    The ring  20  may be manufactured from a strong, flexible material such as synthetic rubber, plastic, fibre or polyurethane, that is also extremely rugged and hard to shear, such as Dupont&#39;s Hytrel 55D™. Recent advances in the ability to manufacture polyurethane to very specific and demanding specifications, however, may provide unexpectedly good characteristics in terms of strength and durability for this type of retaining device. Nonetheless, other ring materials and designs could provide adequate functionality and are therefore considered to fall within the scope of this invention. For example, a metal snap-ring or spring like device could be substituted for the ring as described herein.  
         [0037]    The tool  10  further includes a second piston retaining mechanism  31 , in this example a restricted area or neck within the distal portion  12  of the barrel  17 . As illustrated more clearly in FIG. 7, the restricted area  31  at the distal portion  12  of the barrel  17  prevents the piston  16  from escaping the end of the barrel  17  when the retaining sleeve  26  and the workpiece  18  are removed, and the retainer ring  20  is either removed, worn or in some other manner fails to stop the piston  16  from advancing. The restricted area  31  of the barrel  17  has a diameter greater than the diameter of the lower end  15  of the piston  16 , but a smaller diameter than the diameter of the upper end  19  of the piston  16 . Accordingly, if the retainer ring  20  fails to prevent to escape of the piston  16 , the restricted area  31  of the barrel  17  will compensate and stop the forward movement and escape of the piston  16 .  
         [0038]    The restricted area  31  may be formed within the distal portion  12  of the barrel  17  via a conventional machining process, or other similarly used processes. Alternatively, the restricted area  31  may formed outside the tool  10  and mounted within the distal portion  12  of the barrel  17  using known attachment methods, such as welding, etc.  
         [0039]    The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and use the invention. However, those skilled in the art will recognize that the foregoing descriptions and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims.