Patent Publication Number: US-9844864-B2

Title: Sleeve for a pneumatic fastener-driving tool

Description:
BACKGROUND 
     The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to pneumatic-powered fastener-driving tools, also referred to as pneumatic tools or pneumatic nailers. 
     Fastening tools, and particularly those using compressed air as an energy source, incorporate a housing enclosing a cylinder. Slidably mounted within the cylinder is a piston assembly in communication on one side with a supply chamber and a return chamber on the opposite side thereof. The piston assembly includes a piston head and a rigid driver blade that is disposed within the cylinder. A movable valve plunger is oriented above the piston head. In its at-rest position this valve plunger prevents the drive chamber from communicating to the piston assembly and allows an air flow path to atmosphere above the piston assembly. In its actuated state, the valve plunger prevents or blocks the air flow path to atmosphere and allows an air flow path to the drive chamber 
     When a tool&#39;s actuation requirements have been met, the movable valve plunger opens and exposes one side of the piston assembly to a compressed gas energy source. The resulting pressure differential causes the piston and driver blade to be actuated downward to impact a positioned fastener and drive it into a workpiece. Fasteners are fed into the nosepiece from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade. 
     As the piston is actuated downward, it drives the air inside the cylinder through a series of vents into the return chamber increasing the pressure in this chamber. After the fastening event has taken place, the valve plunger moves back to the at-rest position, blocking the supply chamber&#39;s air flow path to the piston head and releasing the pressure above the piston head through the path to atmosphere. At this time, the pressure built in the return chamber pushes the piston assembly back up towards the top of the cylinder. The air above the piston head is forced through the valve plunger&#39;s air flow path to atmosphere. 
     The pressure available to drive the piston in pneumatic fastening tools varies based on the source. The variance in pressure causes fasteners to be driven to different depths in an underlying substrate or workpiece. Furthermore, the repeated, reciprocal motion of the piston and impact at the bottom of the cylinder reduces the working life of the tool. 
     SUMMARY 
     To overcome the above problems, the present fastener driving tool includes a cylinder or sleeve, and a piston movable within the cylinder where the cylinder and piston are configured to seal a volume of air at the bottom of the cylinder for reducing impact forces on the tool and improving the consistency of the driven depth of the fasteners. 
     In an embodiment, a fastener driving tool is provided and includes a housing enclosing a cylinder provided with a resilient bumper, a return air chamber in communication with the cylinder and a piston dimensioned for reciprocation within the cylinder to impact the bumper and having a driver blade depending therefrom. At least one inlet opening is disposed in the cylinder and in communication with the return air chamber and at least one outlet opening is disposed in the cylinder and spaced from the at least one inlet opening. The at least one outlet opening is in communication with the return air chamber and aligned with the piston so that each outlet opening is closed by the piston to seal the cylinder when the piston impacts the bumper and traps a residual volume of air in the sealed cylinder below the piston to damp impact of the piston upon the bumper. 
     In another embodiment, a fastener driving tool is provided and includes a cylinder provided with a resilient bumper, a return air chamber in communication with the cylinder and a piston dimensioned for reciprocation within the cylinder and having a driver blade depending therefrom, and a pair of spaced seal rings. A plurality of inlet openings are defined by the cylinder, where each of the inlet openings is in communication with the return air chamber. Also, a plurality of outlet openings are defined by the cylinder and spaced from the plurality of inlet openings. The plurality of outlet openings each having a height approximately less than or equal to a height of the piston, the piston configured to block each of the plurality of outlet openings to seal the cylinder when the piston impacts the bumper and retains a residual volume of air for providing damping to the piston. The plurality of outlet openings each having a height less than or equal to a distance between the rings so that at least one of an upper seal ring seals an upper margin of each of the plurality of outlet openings, and a lower seal ring seals a lower margin of each of the plurality of outlet openings when the piston impacts the bumper. 
     In a further embodiment, a method for generating a residual air volume in a pneumatic fastening tool is provided where the tool includes a cylinder provided with a resilient bumper, a piston dimensioned for reciprocation within the cylinder, a driver blade depending from the piston, and at least one outlet opening. The method includes positioning the at least one outlet opening to correspond with a position of the piston when it impacts the bumper, wherein each of the outlet openings is blocked by the piston to seal the cylinder upon the impact of the bumper; and reducing a volume defined between the piston and the lower end of the cylinder by increasing at least one of piston profile and bumper profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pneumatic fastening tool; 
         FIG. 2  is a fragmentary side vertical section of the present pneumatic fastening tool of  FIG. 1 ; 
         FIG. 3  is a fragmentary vertical section of the present pneumatic fastening tool provided with outlet ports adjacent the point where the piston engages the bumper; 
         FIG. 4  is a fragmentary vertical section of an alternate embodiment of the present pneumatic fastening tool provided with a modified piston configuration; 
         FIG. 5  is a fragmentary vertical section of another alternate embodiment of the present pneumatic fastening tool provided with a modified bumper; and 
         FIG. 6  is a fragmentary vertical section of still another alternate embodiment of the present pneumatic fastening tool provided with a modified piston. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1 and 2 , there is fragmentarily illustrated a fastener driving tool, generally illustrated as  10 , which embodies the control valve assembly and bumper arrangement according to the present invention. The tool  10  may be of known construction, and, as illustrated, comprises a housing  12  including a generally vertically extending head or forward portion and a rearwardly extending hollow handle  14  having a cavity defining a fluid reservoir  16 . Pressurized fluid, such as compressed air, is supplied to the fluid reservoir  16  of the tool by a suitable flexible line. The drive system for the tool  10  includes a main or power cylinder  18  mounted within the head portion of the housing  12  and having an open upper end  18   a  that is adapted to be selectively connected to the reservoir  16 . The open upper end of the cylinder  18  is in engagement with a main or cylinder valve assembly  20  of a known type, under the control of a control valve assembly  22  according to the present invention. A fastener driving assembly  24  slidably mounted in the cylinder  18  includes a main or drive piston  26  and has connected thereto a depending drive blade member  28 . The fastener driving assembly  24  is normally biased to a position with the piston  26  adjacent the cylinder valve assembly  20 . An exhaust valve assembly indicated generally as  32  is provided for controlling the selective connection of the upper end  18   a  of the cylinder  18  to the atmosphere. 
     When the tool  10  is to be operated, compressed fluid from the reservoir  16  enters the upper open end  18   a  of the cylinder  18  and drives the fastener driving assembly  24  downwardly to engage and set a fastener or nail  34  supplied to a drive track  36  in a nosepiece or nosepiece structure  38 . The flow of compressed fluid in the upper end of the cylinder  18  is controlled by the main valve assembly  20 , which includes a vertically movable ring member  40  defining a valve element. The cylinder side of the ring member  40  is continuously in communication with the fluid reservoir  16  through a suitable passageway  44  so that pressurized fluid continuously acts against the cylinder side of the ring member  40  tending to displace the ring member  40  from the edge  18   a  of the cylinder  18 . However pressurized fluid is also introduced to the opposite side of the ring member  40  through a passageway while the fastener driving tool  10  is in a static or at rest position. The differential pressure acting on the ring member  40  is effective to maintain the ring member  40  down, in a closed position. However, if the pressurized fluid above the ring member  40  is discharged, the pressurized fluid acting through the passageway  44  is effective to unseat the ring member  40  from the edge  18   a  of the cylinder  18  to dump pressurized fluid into the top of the main cylinder  18  and to drive the drive piston  26  through the drive stroke. 
     When the fastener driving tool  10  is at rest, or during the return stroke of the drive piston  26 , the upper open end of the cylinder  18  is exhausted to the atmosphere through the exhaust valve assembly  32 . In the illustrated embodiment, the exhaust valve assembly  32  includes a valve member  50  spaced below an inner surface of a downwardly projecting boss  54  defined in a cap  56  of the tool  10 . The cap  56  has a plurality of exhaust passageways  58  providing for the exhaust of the fluid when the ring member  40  is in its downward position. 
     To provide for the return stroke of the fastener driving assembly  24 , there is provided a return air chamber  60  communicating with the lower end of the cylinder  18  through a plurality of fluid inlet openings or ports  62  and a plurality of fluid outlet openings or ports  64 . An annular band  63 , made of rubber or other suitable material, is positioned on the periphery of the cylinder  18  and over the inlet ports  62 . The band  63  includes a slit or other suitable closable opening that is aligned with each inlet port  62  so that the inlet ports each act as a one-way check valve that allows a pressurized fluid, such as pressurized air, to flow through the inlet ports into the return air chamber  60  but not from the return air chamber to the cylinder. The cylinder  18  includes a pair of spaced annular protrusions  65  that are positioned adjacent to each end of the band  63  to help secure the band&#39;s position on the cylinder. The outlet ports  64  are generally larger in size than the inlet ports  62  and are configured to allow air to flow between the cylinder  18  and the return air chamber  60 . 
     Thus it will be understood that in the normal operation of the fastener driving tool  10 , the working fluid above the piston  26  will flow through the fluid inlet ports  62  into the return air chamber  60 , and will thereafter flow through the fluid outlet ports  64  below the piston  26  to drive the piston  26  back through its return stroke. The fluid pressure drop should be less through the port beneath the piston than above, otherwise it will not be displaced sufficiently, blocking ports  62  and allowing the full return stroke. A greater volume of fluid will exit from chamber  60  to the bottom of the driver thus shifting it upwardly and closing off flow from inlet ports  62  to above the driver and to atmosphere. Residual return fluid below the piston  26  will be dissipated to atmosphere by bleeding through a bleed opening  70  formed between the drive blade  28  and a bumper assembly  72  (air also allowed to escape passed the piston seal through gaps in the upper-most section of the sleeve). The bumper assembly  72  includes at one resilient cushioning member or bumper  74  in the lower end of the cylinder  18 . The bumper  74  acts as a stop for the piston  26  when it is at the end of its drive stroke. 
     The control valve assembly  22  includes a trigger valve  76 . The trigger valve  76  includes a trigger  78 , which may be depressed to a first position to provide for single actuation of the tool  10 , and further depressible to a second position to provide contact actuation of the tool  10  so long as the trigger is held in the depressed position. 
     Referring now to  FIG. 3 , an important feature of the present fastener driving tool  10  is that at least one, and preferably a plurality of the outlet ports  64  defined by the cylinder  18 , are placed generally coplanar with, or in alignment with the piston  26  when it reaches the bottom of its travel and strikes the bumper  74 . Thus, as the piston  26  passes the inlet ports  62 , some of the back pressure (pressure of the compressed air under the piston) is released to the return air chamber  60  ( FIG. 2 ) through the outlet ports  64 . However, as the piston  26  impacts the bumper  74 , the piston temporarily closes, and preferably, seals the outlet ports  64 , thus trapping a residual amount of air in a volume ‘V’ below the piston  26  to provide a damping effect. The compressed damping volume ‘V’ is sufficient to damp the impact of the piston  26  upon the bumper  74 , and is considered sufficient to prevent premature tool failure due to impact forces generated from repeated reciprocal impact of the piston on the bumper. 
     In the preferred embodiment, the outlet ports  64  are provided in a spaced array around the cylinder  18  at the point where the piston  26  impacts the bumper  74 . The shape of the outlet ports  64  may vary to suit the situation, and are preferably oval. It should be appreciated that the outlet ports  64  may also be rectangular, circular or may be any suitable size or shape. The piston  26  is typically provided with at least one seal ring  80 . In an embodiment shown in  FIGS. 3-6 , the piston  26  includes a pair of seal rings  80  that are made of metal. It should be appreciated that each seal ring  80  may be made of a metal, a polymer, such as an injection molded polymer, or any suitable material or combination of materials. 
     As the piston  26  moves downward within the cylinder  18 , the fluid under the piston  26  moves through the outlet ports  64  and into the return air chamber  60 . Additionally, when an upper piston ring  80   a  moves past the inlet ports, pressurized fluid, which is in the cylinder  18  above the piston  26  and driving the piston downward within the cylinder, flows through the inlet ports and into the return air chamber  60 . As stated above, the inlet ports  62  are configured to allow fluid flow in one direction (from the cylinder to the return air chamber) but not in a second, opposite direction (from the return air chamber to the cylinder). As the piston  26 , and more specifically, a lower piston ring  80   b  moves past the outlet ports  64 , the lower piston ring seals the area of the cylinder below the piston  26  and thereby prevents escape of residual air located between the piston  26  and bottom end  82  of the cylinder. The residual volume of air “V” between the piston  26  and the bottom end  82  of the cylinder  18  has a fluid pressure that increases as the piston compresses the fluid. The pressure of the residual fluid significantly decreases the downward velocity of the piston  26  and lessens the impact of the piston on the bumper  74  thereby limiting the compression of the bumper. By limiting the compression of the bumper, the present fastener driving tool  10  controls the depth of the drive of the tool, i.e., the depth that a fastener penetrates a substrate or workpiece, regardless of the pressure of the incoming fluid source. 
     For example, in conventional fastener driving tools, if the pressure of fluid, such as air, supplied to the tool is 80 psi, the piston will impact the bumper and compress it a designated amount, which causes the driven fastener to further penetrate an underlying substrate or workpiece by a depth or distance equal to that designated amount. Using air that is at a higher pressure, such as 120 psi, causes the piston  26  to move at a greater downward velocity within the cylinder  18  than the 80 psi fluid. Thus, the impact of the piston  26  on the bumper  74  is greater thereby further compressing the bumper and causing the fastener to be driven into the substrate or workpiece at a depth that is greater than the fastener depth using the air at 80 psi. As a result, the depth of the fasteners driven into a substrate or workpiece using conventional fastener driving tools, and more specifically, conventional pneumatic fastener driving tools varies based on the pressure of the fluid source being used to power the tool. 
     To overcome the above variable depth of drive problem, the present fastener driving tool  10  seals and retains a residual amount of fluid between the piston  26  and the bottom end  82  of the cylinder  18  to significantly decrease the downward velocity of the piston and thereby reduce the impact of the piston on the bumper  74 . Controlling the impact of the piston  18  on the bumper  74 , significantly decreases the compression of the bumper thereby decreasing the differences in the drive depths of the fasteners due to the varying pressures of fluid sources. Additionally, lessening the impact of the piston  26  on the bumper  74  reduces the impact shock on the tool  10  which extends the working life of the tool. 
     Referring now to  FIG. 4 , an alternate embodiment of the present tool is generally designated  83 . Components shared with the tool  10  discussed above are designated with the same reference numbers. The main distinction of the tool  83  is that a piston  26  is provided having an annular damping formation  84  depending from a lower face  86  of the piston. A main purpose of the damping formation  84  is to reduce the volume ‘V’ and accordingly generate increased damping action. As such, the specific shape of the formation  84  may change to suit the situation. However, it is preferred that the damping formation  84  is provided with an angled leading edge  88  configured to complement the opposing profile  90  of the bumper  74 . 
     As shown in  FIG. 4 , as the piston  26  reaches its lowest travel limit, the compressed volume ‘V 2 ’ is reduced compared to the volume ‘V’ ( FIG. 3 ), thus increasing the pressure and the damping action. Also, it will be seen that a lower seal ring  80   b  on the piston  26  is engaged with the cylinder  18 , sealing the volume ‘V 2 ’ from the return air chamber  60  ( FIG. 2 ). 
     Referring now to  FIG. 5 , another alternate embodiment of the present tool is generally designated  91 . Components shared with the embodiments  10  and  83  discussed above are designated with identical reference numbers. The main distinction of the tool  91  is that a bumper  74  is provided having an increased volume compared to conventional bumpers. More specifically, an outer profile  92  of the bumper  74  defines a general normal or right angle profile along an upper exterior edge that increases the overall profile of the bumper over the profile of conventional bumpers. Also, an upper edge  94  is generally parallel with the opposing piston lower face  86 . As is the case with the tool  83  ( FIG. 4 ), this enlarged bumper profile  92  decreases the trapped volume below the piston  26 , creating a volume ‘V 3 ’ that has a higher compression and provides increased damping force. In view of the embodiments  83  and  91 , it will be understood that the volume ‘V’ can be reduced by increasing piston profile, bumper profile, or combinations of the two. 
     Referring now to  FIG. 6 , it will be seen that as the piston  26  passes the outlet ports  64 , the lower piston seal ring  80   b  is in sealing contact with the cylinder  18 , however the upper piston seal ring  80   a  has passed an upper edge of the outlet ports, and as such has allowed the cylinder above the piston to be exposed to ambient. While only a temporary condition, in some cases such exposure may interfere with the creation and maintenance of the fluid pressure above the piston  26  and the residual volume of fluid sealed under the piston to ensure sufficient damping of the piston and the return of the piston to its initial position after a drive stroke. 
     To maintain a sealing relationship above and below the piston as the piston impacts the bumper  74 , an alternate embodiment of the present tool is provided and is generally designated  96 . In the embodiment of tool  96 , components shared with the previous embodiments are designated with identical reference numbers. A main distinction of the tool  96  is that a piston  98  is provided with an increased thickness or height “P”. While the piston  98  depicted is somewhat exaggerated for purposes of explanation, the height “P” is sufficient to maintain a sealing relationship between the upper piston seal ring  80   a  and the cylinder  18  during the travel cycle of the piston, regardless of whether it is against or away from the bumper  74  in the vicinity of the outlet ports  64 . As such, it will be appreciated that the height “P” of the piston  96  may vary to suit the application, provided the sealing relationship is maintained between the upper seal ring  80   a  and the cylinder  18  at an upper margin of the outlet ports  64 . As shown in  FIG. 6 , the piston  96  has just contacted the bumper  74  and as such has not compressed the bumper, and the lower piston ring  80   b  seals the volume ‘V’ as it progresses past the outlet ports  64  to reach and seal a lower margin of the outlet ports as seen in  FIG. 3 . Once the volume V is sealed to create the residual volume under the piston  96  and the vacuum is maintained above the piston  96 , the piston returns to the top of the cylinder. 
     While a particular embodiment of a pneumatic-powered fastener-driving tool has been described herein, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.