Powered nailer with positive piston return

Abstract

A powered nailer includes a power source including a driving element reciprocating within a cylinder between a prefiring position and a fastener driving position, the latter occurring when the driving element engages a bumper disposed at the bottom of the cylinder. A reciprocating valve element defines a combustion chamber in fluid communication with the cylinder, and is configured for receiving a dose of fuel and air prior to a user-generated ignition. A return chamber at least partially surrounds the cylinder and is in fluid communication with the cylinder, being configured for receiving a supply of pressurized air generated by the driving element as it moves from the prefiring position to the fastener driving position, the pressurized air acting on an underside of the driving element for returning it to the pre-firing position.

Claims

1. A method of operating a powered nailer including a cylinder having a first volume, a driving element reciprocatable within the cylinder between a pre-firing position and a fastener driving position, an outer wall partially defining a combustion chamber, a reciprocating valve element exterior to and surrounding the outer wall, a return chamber having a second volume, the ratio of the second volume to the first volume being at least 1:1, said method comprising: causing a valve opening defined by the reciprocating valve element to align with a port of the outer wall when the reciprocating valve element is in an open position; causing the valve opening defined by the reciprocating valve element to be unaligned with the port of the outer wall when the reciprocating valve element is in a closed position; receiving in the return chamber a supply of pressurized air through a plurality of openings, the pressurized air generated by the driving element as the driving element moves from the pre-firing position to the fastener driving position; and releasing from the return chamber the pressurized air through the plurality of openings into the cylinder to act on an underside of the driving element to return the driving element to the pre-firing position.

2. The method of operating a powered nailer of claim 1, wherein the ratio is 2:1.

3. A method of operating a powered nailer a power source including a driving element reciprocatable within a cylinder between a pre-firing position and a fastener driving position, the driving element being in the fastener driving position when the driving element engages a bumper disposed at a bottom of the cylinder, an outer wall partially defining a combustion chamber in fluid communication with the cylinder, the combustion chamber configured to receive a dose of fuel and air prior to a user-generated ignition, a reciprocating valve element exterior to and surrounding the outer wall, wherein the reciprocating valve element defines a valve opening that is in registry with a port of the outer wall when the reciprocating valve element is in an open position, and wherein the valve opening is unaligned with the port of the outer wall when the reciprocating valve element is in a closed position, and a return chamber in fluid communication with the cylinder via a plurality of openings between the return chamber and the cylinder, wherein the plurality of openings are circumferentially-spaced about the cylinder, said method comprising: receiving a supply of pressurized air in the return chamber through the plurality of openings, wherein the pressurized air is generated by the driving element as the driving element moves from the pre-firing position to the fastener driving position; and releasing the pressurized air from the return chamber into the cylinder through the same plurality of openings through which the supply of pressurized air was received, to act on an underside of the driving element to return the driving element to the pre-firing position.

4. The method of operating a power nailer of claim 3, which includes, after an ignition in the combustion chamber, returning the driving element to the pre-firing position through action of the pressurized air stored in the return chamber and simultaneously exhausting the combustion chamber.

5. The method of operating a power nailer of claim 3, wherein the return chamber is defined in part by an annular, radially-inwardly projecting flange with a sealing relationship to an exterior wall of the cylinder.

6. The method of operating a power nailer of claim 3, which includes opening the combustion chamber to atmosphere upon the driving element reaching the bumper.

7. The method of operating a power nailer of claim 6, which includes causing the return chamber to store sufficient pressurized air to push the driving element to the pre-firing position, and which includes causing the post fastener-driving tool recoil to automatically open the combustion chamber post firing.

8. The method of operating a power nailer of claim 3, which includes delaying opening of the combustion chamber post-ignition and opening the combustion chamber before return of the driving element to the pre-firing position.

9. The method of operating a power nailer of claim 3, which includes causing the return chamber to have a pressure of 8 psi when the driving element is in the fastener driving position.

10. The method of operating a power nailer of claim 3, wherein the cylinder is continuous from an upper end adjacent the pre-firing position to a bumper area at an opposite end from the upper end.

11. A method of operating a powered nailer including a cylinder, a driving element reciprocatable within the cylinder, an outer wall partially defining a combustion chamber in fluid communication with the cylinder, the outer wall defining a port in fluid communication with the combustion chamber, a reciprocating valve element exterior to and surrounding the outer wall, said method comprising: causing a valve opening defined by the reciprocating valve element exterior to align with the port of the outer wall when the reciprocating valve element is in an open position; and causing the valve opening defined by the reciprocating valve element exterior to be unaligned with the port of the outer wall when the reciprocating valve element is in a closed position, such that the port enables both intaking of air before combustion occurs in the combustion chamber and exhausting of gases after combustion occurs in the combustion chamber, while the reciprocating valve element is in the open position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a fragmentary front view of the present tool, featuring the power source;

(2) FIG. 2 is a cross-section taken along the line 2-2 of FIG. 1 and in the direction generally indicated;

(3) FIG. 3 is an enlarged fragmentary portion of the tool depicted in FIG. 2;

(4) FIG. 4 is a fragmentary vertical cross-section of the present tool, shown in the rest position;

(5) FIG. 5 is a fragmentary vertical cross-section of the present tool, shown in the ignition position;

(6) FIG. 6 is a fragmentary vertical cross-section of the present tool, shown in the fastener driving position;

(7) FIG. 7 is a fragmentary vertical cross-section of the present tool shown where the nail has been driven and the combustion chamber opens; and

(8) FIG. 8 is a fragmentary vertical cross-section of the present tool shown with the piston returning via pressure in the return chamber.

DETAILED DESCRIPTION

(9) Referring to FIGS. 1 and 2, a powered nailer is generally designated 10, and the basic structure of which is well known in the art, described in the patents incorporated by reference above. Such tools incorporate a tool housing enclosing a small internal combustion engine, also referred to as a power source 12. The engine 12 is powered by a canister of pressurized fuel gas, also called a fuel cell.

(10) The power source 12 includes a cylinder 14 and a driving element 16 reciprocating within the cylinder between a prefiring position at an upper end 18 of the cylinder as seen in FIG. 2, and fastener driving position. The fastener driving position occurs when the driving element 16 engages a bumper 20 disposed at a lower end 22 or bottom of the cylinder 14. Preferably, the driving element 16 includes a radially projecting piston 24 and a depending driver blade 26, which sequentially engages fasteners (not shown) into a nosepiece 28, which depends from the lower end 22 of the cylinder 14. However, the driving element 16 may be provided in a variety of configurations besides that depicted here.

(11) A combustion chamber 30 is in fluid communication with the cylinder 14 and is defined at a lower end by the piston 24 in the prefiring position, and also in a lateral or radial direction by a generally cylindrical outer wall 32 connected to a floor 34 defining an opening 36 communicating with the cylinder 14. Unlike conventional combustion tools, the present combustion chamber wall 32 is fixed during the entire fastener driving operational cycle. A plurality of ports 38 are formed in the wall 32.

(12) Referring now to FIGS. 2 and 3, a vertically reciprocating valve element 40 surrounds the wall 32 and is biased to an open position by at least one biasing element 42 such as a spring. The biasing force of the spring 42 is overcome by the user pressing the tool nosepiece 28 against a workpiece, which causes a mechanical linkage, such as a probe connected to a workpiece contact element (not shown) or any other suitable mechanical linkage, to move the valve element 40 to a closed position. In FIGS. 2 and 3, the valve element 40 is shown in the open position.

(13) A cylinder head 44 defines an upper end of the combustion chamber 30, and as is known in the art, includes a spark generator or spark plug 46 as well as a fan blade 48 powered by a motor 50. Alternative configurations are contemplated for forming the upper end of the combustion chamber. The fan blade 48 projects into the combustion chamber 30 for enhancing the mixing of air and fuel vapor which are deposited into the chamber prior to a user-generated ignition caused by the spark generator 46. The fan blade 48 also facilitates the exchange of spent gases after ignition.

(14) Referring now to FIGS. 2 and 3, a return chamber 52 is in fluid communication with the cylinder 14. The return chamber 52 is configured for receiving a supply of pressurized air generated by the driving element 16 as it moves from the prefiring position to the fastener driving position. While in the illustrated embodiment, the return chamber 52 at least partially surrounds the cylinder 14, other locations are contemplated within the tool housing, including, but not limited to a handle portion. During tool operation, after the fastener is driven into the workpiece by the driver blade, 26, the pressurized air in the return chamber 52 acts on an underside 54 of the piston 24 portion of the driving element 16 for returning the element to the pre-firing position.

(15) Pressurized air is forced into the return chamber 52 through a plurality of circumferentially-spaced openings 56 (FIG. 2) located near the lower end 22 of the cylinder 14, preferably near an upper edge 58 of the bumper 20. The location of the openings 56 may vary to suit the application. As the piston 24 travels down the cylinder 14 under the force generated by the ignition of fuel and air in the combustion chamber 30, air caught below the underside 54 of the piston is compressed and forced through the openings 56 and into the return chamber 52.

(16) As seen in FIGS. 2 and 3, the return chamber 52 surrounds an exterior wall 60 of the cylinder 14, and at an upper end 62, is defined in part by an annular, radially-inwardly projecting flange 64 with a seal 66 engaging the exterior wall 60. Opposite the flange 64, a lower return chamber end 68 is closed off (FIG. 2). It will be appreciated that, through the return openings 56, the return chamber 52 is also in fluid communication with atmosphere through the nosepiece 28.

(17) After an ignition in the combustion chamber 30, the driving element 16 returns to the pre-firing position through action of pressurized air stored in the return chamber 52 simultaneously with the exhausting of the combustion chamber 30. Once the driving element 16, and specifically the piston 24 reaches the bumper 20, recoil forces created by the action of driving a nail cause the tool 10, held by a user, to move away from the workpiece. This movement allows the springs 42 to open the valve element 40, opening the chamber 30 to ambient and allowing entry of a new charge of fresh air. This operation is contrary to conventional combustion tools, where differential pressure must be maintained in the combustion chamber after combustion until the piston reaches the pre-firing position.

(18) At the same time, the pressure of the air compressed into the return chamber 52 is greater than the pressure of the cylinder 14, which causes the air in the return chamber to push the piston 24 back up the cylinder to the pre-firing position. A portion of the compressed air from the return chamber 52 also escapes to ambient or atmosphere through the nosepiece 28. While different volumes are contemplated depending on the application, in an illustrated embodiment, the return chamber 52 is dimensioned for storing a sufficient volume of compressed air to reach approximately 8 psi.

(19) It should be noted that, unlike conventional pneumatic nailers, in an illustrated embodiment, the cylinder 14 is continuous and aperture-free from the return openings 56 near the bumper 20 to the opening 36. Also, the valve element 40 is provided with openings 70 that are in registry with at least some of the ports 38 in the wall 32 when the valve element is in the open position shown in FIGS. 2 and 3, and out of registry when the valve element is in the closed position. The closed position is reached after vertical movement of the valve element 40 towards the cylinder head 44 just prior to combustion, as the user presses the tool 10 against a workpiece. In an illustrated embodiment, at least some of the ports 38a are open to ambient and are located above an upper edge 72 of the valve element 40 when the valve element is in the open position. In various embodiments, the same ports 38 are used for intake of air and pre-combustion and exhaust of gases post-combustion.

(20) Referring now to FIG. 2, the cylinder 14 has a first volume V.sub.1, and the return chamber 52 has a second volume V.sub.2, the ratio of the second volume to the first volume being at least 1:1. In the preferred embodiment, the ratio is approximately 2:1.

(21) Referring again to FIG. 3, in the illustrated embodiment, the combustion chamber 30 has a portion 74 extending below a line “L” defined by an upper edge 76 of the piston 24 of the driving element 16 at the pre-firing position. During tool operation, the floor 34 of the combustion chamber 30 is in contact with the annular flange 64, and both components remain fixed during the fastener driving cycle. Alternate configurations are contemplated for the connection between, and the relative positions of, the combustion chamber 30 and the return chamber 52.

(22) As an option, a mechanical or electro-mechanical delay mechanism 80 (FIG. 1), such as a solenoid with plunger under control of a tool control program (not shown), is disposed in operational relationship to the valve element 40 for delaying the opening of the combustion chamber 30 post-ignition. Specifically, the delay mechanism 80 is configured for opening the combustion chamber 30 before return of the driving element 16 to the prefiring position.

(23) Referring now to FIGS. 4-8, the sequential operation of the tool 10 of the present disclosure is depicted. FIG. 4 shows the tool in its rest state or position, similar to FIGS. 2 and 3 discussed above. The valve element 40 is in the open position, allowing exchange of air within the combustion chamber 30. Also, the driving element 16, including the piston 24 is in the prefiring position.

(24) Referring to FIG. 5, the tool 10 has been pressed against a workpiece, and the valve element 40 is in the closed position, sealing the combustion chamber 30. Fuel is introduced into the combustion chamber, and a spark ignites the air-fuel mixture. The return pressure 52 is open to atmosphere.

(25) Referring now to FIG. 6, the combustion gases urge the driving element 16 down to begin driving a fastener. The combustion chamber 30 remains sealed by the valve element 40. Air volume beneath the piston 24 is reduced, increasing the pressure of air in this space. The increase of air pressure forces air into the return chamber 52 via the return openings 56. At this point, about 4 msec has transpired since ignition.

(26) Referring now to FIG. 7, the driving element 16 has completed its stroke, and the driving of the nail is completed. Thus, the combustion chamber 30 is opened by return of the valve element 40 to the rest position through tool recoil. Exhaust E passes through the openings 38, 70. This relatively rapid exhaust of gases significantly reduces heat buildup in the tool 10, allowing use of unconventional materials in tool construction. In the return chamber 52, the air has reached the maximum pressure, preferably 8 psi, and volume is at a minimum for the tool size. At this point in the cycle 8 msec have elapsed since ignition.

(27) Referring now to FIG. 8, as the relatively high pressure exhaust gases leave the still open combustion chamber 30, the stored air in the return chamber 52 pushes the driving element 16 back to the prefiring position seen in FIG. 4. Approximately 4 psi of air pressure is needed for achieving piston return. At this point, approximately 20 msec have transpired since ignition. Following piston return, the tool 10 resumes the rest position seen in FIG. 4. While the focus of the present disclosure is on combustion powered fastener tools, it is contemplated that features described above are applicable in other types of powered fastener driving tools, including but not limited to tools powered pneumatically, electrically, and/or by powder cartridges.

(28) While a particular embodiment of the present powered nailer with positive piston return has been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the disclosure in its broader aspects and as set forth in the following claims.