Patent Publication Number: US-7591236-B2

Title: Venting check valve for combustion nailer

Description:
RELATED APPLICATIONS 
   The present application claims priority under 35 USC § 119(e)(1) from U.S. Ser. No. 60/662,112 filed Mar. 15, 2005 and is a Continuation-In-Part of U.S. Ser. No. 11/182,208 filed Jul. 15, 2005 now U.S. Pat. No. 7,314,028. 

   TECHNICAL FIELD 
   The present invention relates generally to fastener-driving tools used for driving fasteners into workpieces, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools or combustion nailers. 
   BACKGROUND ART 
   Combustion-powered nailers are known in the art for driving fasteners into workpieces, and examples are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 5,713,313, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE® and PASLODE® brands. 
   Such nailers incorporate a housing enclosing a small internal combustion engine or power source. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: mixing the fuel and air within the chamber, turbulence to increase the combustion process, scavenging combustion by-products with fresh air, and cooling the engine. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body. 
   A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber. 
   Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or pre-firing position, through differential gas pressures created by cooling of residual combustion gases within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade. 
   As the piston is displaced in the cylinder, a swept volume of air is discharged through exhaust and vent ports. Following the drive stroke, the vent ports allow atmospheric air to enter the cylinder, on the non-combustion side of the piston, and facilitate the return of the piston via differential pressures. 
   An operational problem of conventional combustion nailers is that as air required for combustion enters the tool, due to the relatively dirty operational environment, dirt, dust and/or other debris, including but not limited to fragments of nail collation material, sawdust, wallboard particles and the like enters the tool, specifically the cylinder below the piston. This contaminated air enters mainly through the air vent ports located below the exhaust ports as the piston returns to its pre-firing position after combustion. These air ports are typically located below or in close proximity to a shock-absorbing bumper located within the cylinder. Air cannot reenter through the exhaust ports due to the presence of one-way petal valves. Thus, these ports do not contribute to the problem. Among other effects, through prolonged tool operation, these contaminants build up to cause piston malfunctions and deterioration of tool lubricants required for smooth operation of the piston and movement of the reciprocating valve sleeve, the component used to close the combustion chamber. Thus, more frequent cleaning and/or service is required. 
   Such nailers typically have an air filter located at an upper end of the tool near the combustion chamber fan air intake. However, this filter has been designed to filter air entering the tool and has no effect on the air located below the piston inside the cylinder, where contaminant-caused damage has been known to occur. To address this issue, manufacturers have incorporated a dust boot or shroud over the lower end of the tool. This feature reduces direct exposure of the engine to large contaminants, but is not effective to reduce fine contaminants that enter the cylinder during the piston return cycle. Additionally, such designs are bulky and restrict air flow through the tool. Alternatively, filter elements can be used, but the fine filtration properties of effective filters are prone to clogging when located at the lower end of the nailer, and are restrictive to air flow in and out of the cylinder. Also, the size of any such filter would necessarily be relatively large to permit the passage of sufficient air to maintain proper air circulation within the tool. As such, space, material and tool operational factors combine to discourage tool designers from placing a filter on the tool to filter the air in the cylinder below the piston. 
   Thus, there is a need for an improved combustion tool configured for reducing the harmful effects of contaminants drawn through the cylinder vent ports, while maintaining effective air flow between the inside and outside of the cylinder. 
   DISCLOSURE OF INVENTION 
   The above-listed need is met or exceeded by the present venting check valve for a combustion nailer, which features the ability to differentiate the volume of gases exhausted from the tool from the volume of air intake through the same ports. A greater volume of gases are permitted to be discharged from the cylinder than are allowed to be drawn into the cylinder on the return stroke. The variability in effective port size maintains tool power, facilitates piston return while preventing the entry of contaminants. 
   More specifically, a combustion nailer configured for reducing intake of contaminated air during operation includes a combustion engine having a cylinder with a piston reciprocating between a prefiring position and a fully extended position, and at least one air port in the cylinder below the fully extended position. The at least one air port is provided with a venting check valve configured so that the discharge or outflow volume from the cylinder out the at least one air port is greater than the inflow. 
   In another embodiment, a combustion nailer includes a combustion-powered power source having an air intake end and an opposite bumper end, defining a cylinder encircling a reciprocating piston associated with a driver blade, and having at least one air port located at the bumper end below the piston. At least one air intake is provided with an air filter, and an air passageway is in fluid communication with at least one air port and in fluid communication with the air filter for creating a bi-directional air flow between the at least one air port and the at least one air intake during tool operation. A venting check valve is provided and is configured so that the discharge volume from the cylinder out the at least one air port is greater than the inflow, the venting check valve being in fluid communication with the passageway. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a front perspective view of a fastener-driving tool incorporating the present venting check valve; 
       FIG. 2  is a fragmentary vertical cross-section of the tool of  FIG. 1  shown in the rest position; 
       FIG. 2A  is a fragmentary vertical cross-section of the tool of  FIG. 2  depicting a modified venting check valve; 
       FIG. 3  is a fragmentary vertical cross-section of an alternate embodiment of the tool depicted in of  FIG. 2 ; and 
       FIG. 4  is a fragmentary vertical cross-section of another alternate embodiment of the tool depicted in  FIG. 2 . 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Referring now to  FIGS. 1 and 2 , a combustion-powered fastener-driving tool, also known as a combustion nailer, incorporating the present venting check valve is generally designated  10  and preferably is of the general type described in detail in the patents listed above and incorporated by reference in the present application. A housing  12  of the tool  10  encloses a self-contained internal power source  14  ( FIG. 2 ) within a housing main chamber  16 . As in conventional combustion tools, the power source or combustion engine  14  is powered by internal combustion and includes a combustion chamber  18  that communicates with a cylinder  20 . A piston  22  reciprocally disposed within the cylinder  20  is connected to the upper end of a driver blade  24 . As shown in  FIG. 2 , an upper limit of the reciprocal travel of the piston  22  is referred to as a pre-firing position, which occurs just prior to firing, where ignition of the combustion gases initiates the downward driving of the driver blade  24  to impact a fastener (not shown). 
   Through depression of a trigger  26  associated with trigger switch  27  the terms trigger and trigger switch are used here interchangeably), an operator induces combustion within the combustion chamber  18 , causing the driver blade  24  to be forcefully driven downward through a nosepiece  28  ( FIG. 1 ). The nosepiece  28  guides the driver blade  24  to strike a fastener that had been delivered into the nosepiece via a fastener magazine  30 . 
   Adjacent to the nosepiece  28  is a workpiece contact element  32 , which is connected, through a linkage  34  to a reciprocating valve sleeve  36 , an upper end of which partially defines the combustion chamber  18 . Depression of the tool housing  12  against the workpiece contact element  32  in a downward direction as seen in  FIG. 1  (other operational orientations are contemplated as are known in the art), causes the workpiece contact element to move from a rest position to a pre-firing position. This movement overcomes the normally downward biased orientation of the workpiece contact element  32  caused by a spring  38  (shown hidden in  FIG. 1 ). Other locations for the spring  38  are contemplated. 
   Through the linkage  34 , the workpiece contact element  32  is connected to and reciprocally moves with, the valve sleeve  36 . In the rest position ( FIG. 2 ), the combustion chamber  18  is not sealed, since there is an annular gap  40  including an upper gap  40 U separating the valve sleeve  36  and a cylinder head  42 , which accommodates a spark plug  46 , and a lower gap  40 L separating the valve sleeve  36  and the cylinder  20 . A chamber switch  44  is located in proximity to the valve sleeve  36  to monitor its positioning. In the preferred embodiment of the present tool  10 , the cylinder head  42  also is the mounting point for at least one cooling fan  48  and an associated fan motor  49  which extends into the combustion chamber  18  as is known in the art and described in the patents which have been incorporated by reference above. In the rest position depicted in  FIG. 2 , the tool  10  is disabled from firing because the combustion chamber  18  is not sealed with the cylinder head  42  and the cylinder  20 , and the chamber switch  44  is open. 
   Firing is enabled when an operator presses the workpiece contact element  32  against a workpiece. This action overcomes the biasing force of the spring  38 , causes the valve sleeve  36  to move upward relative to the housing  12 , closing the gaps  40 U and  40 L, sealing the combustion chamber  18  and activating the chamber switch  44 . This action also induces a measured amount of fuel to be released into the combustion chamber  18  from a fuel canister  50  (shown in fragment). 
   Upon pulling the trigger  26 , the spark plug  46  is energized, igniting the fuel and air mixture in the combustion chamber  18  and sending the piston  22  and the driver blade  24  downward toward the waiting fastener for entry into the workpiece. As the piston  22  travels down the cylinder  20 , it pushes a rush of air which is exhausted through at least one petal, reed or check valve  52  and at least one venting port or hole  54 , hereafter referred to as ports, located beyond the piston displacement ( FIG. 2 ). At the bottom of the piston stroke or the maximum piston travel distance, the piston  22  impacts a resilient bumper  56  as is known in the art. With the piston  22  beyond the exhaust check valve  52 , high pressure gasses vent from the cylinder  20 . Due to cooling of the residual gases, internal pressure differentials created in the cylinder  20  cause the piston  22  to be forced back to the pre-firing position shown in  FIG. 2 . 
   For combustion nailers that use differential pressures for piston return, atmospheric pressure acts on the non-combustion side of the piston  22 . The ports  54  allow air communication between the inside and outside of the tool  10 . For some nailers, the ports  54  are sized to assure proper power performance during the drive stroke. This reduces the swept volume air brake that acts on the piston  22 , causing power losses. The area of the ports  54  is often larger than the minimum required to effectively return the piston  22 . The larger the port area is, the greater the tendency for dirt and contaminants to infiltrate the tool  10 . 
   A feature of the present nailer  10  is that since the air flow required during the drive cycle of the tool  10  is greater than for piston return, a venting check valve or restrictive flow valve, generally designated  60  is placed over the ports  54  for regulating the flow. As the piston  22  reaches the end of its stroke and impacts the bumper  56 , the check valve  60  allows the air to discharge out of the cylinder  20  once the inherent offset check valve pressure is overcome. An important feature of the check valve  60  is that it is constructed and arranged to not be a total check to return air flow, but instead to allow a restricted inflow which is less than the piston power stroke discharge described above. The amount of restricted inflow may vary with the application, but preferably is the minimum required for effective piston return. The minimum area can be a single or multiple ports that can be connected or plumbed to another area of the tool. 
   As seen in  FIG. 2 , the check valve  60  preferably surrounds the cylinder  20  adjacent the ports  54 , and is preferably a rubber-like flap or a spring steel band which is radially expandable upon exposure to sufficient air pressure. Other means of creating one-way flow are also contemplated, such as a reed petal or spring biased plate or ball valves. While other types of attachment are contemplated, the check valve  60  is preferably secured at an upper end  62  to the cylinder  20 , such as by a radially inwardly projecting lip  64  engaging an annular groove  66 . 
   To permit the restricted inflow of ambient air, a web portion  68  is provided with at least one aperture  70  in fluid communication with ports  54 , however it is contemplated that the aperture need not be in direct registry with the corresponding port, as long as internally directed airflow is permitted. Additionally, the sectional areas of the apertures  70  may be larger or smaller than the sectional areas of ports  54 . As shown in  FIG. 2 , the apertures  70  are smaller in sectional area than the associated ports  54 . The number of apertures  70  may vary to suit the application, and it is contemplated that the number of apertures may be more or less than the number of ports  54 . It is also contemplated that at least one port  54  is not covered or obstructed by any portion of the check valve  60  (See  FIG. 2A ). 
   Referring now to  FIG. 3 , a combustion nailer provided with an alternate embodiment of the present venting check valve is generally designated  80 . Shared components with the nailer  10  are designated with the same reference number. Also, it is contemplated that the nailer  80  preferably be constructed and arranged to include all of the features of the nailer  10 . 
   Included on the housing  12  is a cap  82  that closes an upper end  84  of the housing and defines an air intake end  86  with an air intake  88  in the cap. An air filter  90  is associated with the cap  82  as is known in the art and is supported by a protective grille  92 . As is well known in the art, the air filter  90  is releasably secured to the cap  82 . The air filter  90  is made of a porous material such as plastic or metal mesh, foam or the like that is designed to allow the passage of air into the housing  12 , but prevent the ingress of construction debris, dirt and other operational contaminants. 
   Opposite the upper end  84 , a lower end  96  of the tool  80  has a driver blade passageway  98  in the nosepiece  28  that slidingly accommodates the driver blade  24 . An endplate  100  defines a central aperture  102  through which the driver blade  24  passes, as well as air when the piston  22  reciprocates during operation. Thus, the central aperture  102  may also be termed an air port, however it is also contemplated that the port  54  is such an air port or that other air ports may be provided in the end plate  100  or in lower portions of the cylinder  20 . 
   A grommet or wiping seal  104  is located at a lower end of the cylinder  20  just above an upper end of the nosepiece  28  for preventing air from escaping from the air port towards the nosepiece, while permitting relative sliding action of the driver blade  24  in the passageway  98 . 
   An important feature of the nailer  80  is the provision of at least one air passageway, generally designated  106 , in fluid communication with the at least one air port  54 ,  102  and in operational relationship with the air filter  90 . The at least one air passageway  106  creates fluid communication (the preferable fluid being air) between the lower end of the cylinder  20  and the air filter  90 , as well as the air intake  88 . While in the preferred embodiment the air filter  90  is provided for filtering air entering the tool  10 , it is also contemplated that additional or dedicated air filters and associated air intakes may be provided which are provided specifically for connection to the passageway  106 . For clarity, only the filter  90  will be presently described. 
   Thus, air entering the cylinder  20  as the piston  22  returns to the pre-firing position shown in  FIG. 2  must first pass through the filter  90 . Also, during the combustion cycle, air is forced out of the air port  54 , as well as the venting check valve  60 . 
   In the preferred embodiment, the passageway  106  is provided in the form of at least one tube, also referred to as an interconnection tube, having a central section  108  generally parallel with an operational axis of the piston  22 , and upper and lower ends  110 ,  112  preferably projecting at generally right angles to the central section formed as radiused bends for effecting connection respectively to the air intake and the at least one air port  54 . The specific angular orientation of the upper and lower ends  110 ,  112  may vary to suit the situation. While depicted as at least one continuous tube, it is also contemplated that the passageway  106  be defined by tubular segments joined by fixed angle fittings, or individual component configurations that create a passageway in a finished assembly. 
   More specifically, the upper end  110  is preferably secured within an air chamber  114  defined by the cap  82  below the air filter  90 . Conventional techniques for securing the upper end  110  are contemplated, including but not limited to friction fit, chemical adhesives, clips, rigid fittings or the like. It is also considered that the upper end  110  is in fluid communication with the housing main chamber  16  that is downstream of the air filter  90 . 
   It is preferred that the central section  108 , and at least a majority of the upper and lower ends  110 ,  112  of the passageway  106  extends inside the main housing  12  along the combustion engine  14 . If necessary, the main housing  12  can be radially extended to encompass the passageway  106 . As a further alternate embodiment, the passageway  106  can be integrally molded with the housing  12 . It is also contemplated that the passageway  106  may be disposed externally of the housing  12 . The passageway  106  is preferably manufactured of a tubing of sufficient durability to withstand the potential impacts and temperatures typically experienced by combustion nailers. 
   At the lower end  112 , the passageway  106  is placed in fluid communication with the interior of the cylinder  20  through the exhaust opening or air port  54 . It is preferred that the lower end  112  not protrude into the cylinder  20  to avoid interference with the piston  22 , however a protruding tube is acceptable if the entrance point in the cylinder is located below the lowermost point of piston travel. The lower end  112  is ultimately secured to a bottom portion of the cylinder  20  and passes through the venting check valve  60  and at least one of the apertures  70  to maintain this fluid communication. Similar fastening techniques described above relative to the upper end  110  are employable for securing the lower end  112  in position. It will be understood that all such apertures  70  will be in communication with the air passageway  106 , such as by a manifold (not shown) or other suitable connector fitting known in the art. However, it is also contemplated that there are additional exhaust openings  54  not provided with apertures  70  and not in communication with the passageway  106  in view of the larger volume of discharge gases upon combustion compared to the intake volume needed for piston return. 
   The sectional area of the passageway  106  is determined so that only sufficient volume of air is admitted for effecting piston return. This area will vary depending on the type of nailer  80  and the size of the combustion power source  14 . 
   Referring again to  FIG. 2 , it will be seen that instead of the grommet or wiping seal  104 , a replaceable plug  118  is provided which is fixable in the driver blade passageway  98  and includes an opening  120  for slidingly accommodating the driver blade  24 . 
   Referring now to  FIG. 4 , another embodiment of the present nailer is generally designated  130 , and shared components with the tools  10  and  80  are designated with identical reference numbers. The nailers  80  and  130  are very similar in construction. In the tool  130  a passageway is generally designated  132  and is formed externally on the housing  12 . 
   A main difference between the tools  130  and the tool  80  is that an upper end  134  of the passageway  132  is not in communication with the air intake  88 , but is in fluid communication with at least one supplemental air intake  136  located in a specially reconfigured upper end  138  of the main housing  12 . However, both the air intake  88  and the supplemental air intake  136  are preferably located at or adjacent the air intake end  86 . The supplemental air intake  136  is preferably provided with its own filter  140 , protective grille  142  and a supplemental air chamber  144  with which the upper end  134  is in fluid communication. In some applications, it is contemplated that the filter  140 , the protective grille  142  and the supplemental air chamber  144  would be eliminated. It is also contemplated that the at least one supplemental air intake  136  may be located on the main housing in any suitable location which is satisfactorily remote from the relatively high operational temperatures of the combustion power source  14 . 
   While the upper end  134  of the passageway  132  is shown as a vertically projecting extension of a central portion  146 , other angular orientations or other configurations are contemplated as long as fluid communication with the air port  54  is maintained. Also, as is the case with the nailers  10  and  80 , while the passageway  132  is shown on a periphery of the housing  12 , an internal disposition is also contemplated. The operation of the embodiment  130  is substantially the same as described above in relation to the embodiment  80 , with the primary difference being that the chamber  144  does not also supply air to the combustion power source  14 , more specifically combustion chamber  18 . 
   Another feature of the nailer  130  is that, as is shown in  FIG. 3 , the lower end  112  of the passageway  132  optionally passes through the venting check valve  60  and the associated aperture  70 . It is also contemplated that the passageway  132  could enter the cylinder  20  in dependently of the venting check valve  60  as shown at  148 , passing directly through the cylinder wall and the associated air port  54   a . Such an arrangement is also contemplated for the tool  80  shown in  FIG. 3 . In the embodiment of  FIG. 4 , it is contemplated that the venting check valve  60  would be designed to accommodate the direct engagement of the passageway  132  with the port  54   a  without interfering with operation of the check valve. 
   Thus, it will be seen that the present nailer features a venting check valve for providing selective intake of return air once combustion has occurred. Once implemented, the present venting check valve system provides for reduced tool maintenance, a reduction in required lubrication, reduced wear and more regulated flow communication between the inside and outside of the sleeve. 
   While particular embodiments of the present venting check valve for a combustion nailer have 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.