Patent Description:
Pneumatic-powered-fastener-driving tools use a compressed air power source. To operate a typical pneumatic-powered-fastener-driving tool, an operator depresses a workpiece-contact element of the tool onto a workpiece to move the workpiece-contact element from an extended position to a retracted position and then pulls the trigger to actuate a control valve and start the fastener-driving cycle. Actuation of the control valve causes compressed air to act on the top of the piston and force the driving assembly to move through the cylinder from the pre-firing position to the firing position, thereby causing the driver blade to contact a fastener housed in the nosepiece and drive the fastener from the nosepiece into the workpiece.

As the driving assembly moves toward the firing position, the piston drives air inside the cylinder through several vents defined in the cylinder into a return chamber, thereby increasing the air pressure in the return chamber. As the driving assembly reaches the firing position, the volume above the piston is exposed to atmosphere, and the compressed air stops acting on the top of the piston. After the driving assembly reaches the firing position, the air in the return chamber reenters the cylinder through the vents and pushes on the bottom of the piston to force the driving assembly back to its pre-firing position. The piston forces any air above it out of the tool to atmosphere while the driving assembly returns to the pre-firing position. This completes the fastener-driving cycle.

Combustion-powered-fastener-driving tools use a small internal combustion assembly as their power source. To operate a typical combustion-powered-fastener-driving tool, an operator depresses a workpiece-contact element of the tool onto a workpiece. This moves the workpiece-contact element from an extended position to a retracted position, which causes one or more mechanical linkages to cause: (<NUM>) a valve sleeve to move to a sealed position to seal a combustion chamber that is in fluid communication with the cylinder; and (<NUM>) a fuel delivery system to dispense fuel from a fuel canister into the (now sealed) combustion chamber.

The operator then pulls the trigger to actuate a trigger switch, thereby causing a spark plug to deliver a spark and ignite the fuel/air mixture in the combustion chamber and start the fastener-driving cycle. This generates highpressure combustion gases that expand and act on the piston to force the driving assembly to move through the cylinder from the pre-firing position to the firing position, thereby causing the driver blade to contact a fastener housed in the nosepiece and drive the fastener from the nosepiece into the workpiece.

Just before the driving assembly reaches the firing position, the piston passes exhaust check valves defined through the cylinder, and some of the combustion gases that propel the cylinder exhaust through the check valves to atmosphere. This combined with heat exchange to the atmosphere and the fact that the combustion chamber remains sealed during the fastener-driving cycle generates a vacuum pressure above the piston, which causes the driving assembly to retract to the pre-firing position to complete the fastener-driving cycle. When the operator removes the workpiece-contact element from the workpiece, a spring biases the workpiece-contact element from the retracted position to the extended position, causing the one or more mechanical linkages to move the valve sleeve to an unsealed position to unseal the combustion chamber.

Some known or proposed combustion-powered-fastener-driving tools also include a return chamber similar to that of a pneumatic-powered-fastener-driving tool to help the piston return to the pre-firing position.

As explained below with respect to <FIG>, typical powered-fastener-driving tools that include a return chamber include a driver blade seal at the bottom of the cylinder. The driver blade seal operates with the driver blade to minimize air leakage through the nosepiece-and therefore maximize air flow into the return chamber-as the driving assembly moves from the pre-firing position to the firing position. The driver blade seal also operates with the driver blade to minimize air leakage through the nosepiece-and therefore maximize air pressure acting on the bottom of the piston-as the driving assembly moves from the firing position to the pre-firing position.

<FIG> shows an example prior art driving element <NUM> that includes: (<NUM>) an externally threaded connection element <NUM> threadably engageable to a piston (not shown); (<NUM>) a flange <NUM> attached to the bottom end of the connection element <NUM> and having an upper surface (not labeled) sized to engage an underside of the piston when the piston is threadably engaged to the connection element <NUM>; and (<NUM>) a driver blade <NUM> attached to and extending from a lower surface (not labeled) of the flange <NUM> and terminating in a free end 106a.

The driver blade <NUM> has a longitudinal axis APA and a length LPA. Moving from the flange <NUM> to the free end 106a along the longitudinal axis APA, the driver blade: (<NUM>) tapers toward the longitudinal axis APA to a width WPA1 along a distance DPA1; (<NUM>) maintains the width WPA1 along a distance DPA2; and (<NUM>) tapers toward the longitudinal axis APA to a width WPA3 along a distance DPA3. Although not shown, the transverse cross-section of the driver blade <NUM> (taken along a horizontal plane perpendicular to the longitudinal axis APA) along the distance DPA2 is generally rectangular shaped, and its size and shape do not change. Put differently, the transverse cross-section of the driver blade <NUM> is generally uniform along the distance DPA2.

<FIG> shows an example prior at driver blade seal <NUM> that defines a driver blade receiving opening 190a therethrough. The driver blade receiving opening 190a is shaped to correspond to and is sized just larger than the transverse cross-section of the driver blade <NUM> along the distance DPA2.

When installed, the driver blade <NUM> is slidably received in the driver blade receiving opening 190a of the driver blade seal <NUM>. The driver blade <NUM> and the driver blade seal <NUM> are positioned such that some part of the driver blade <NUM> along the distance DPA2 always occupies a portion of the driver blade receiving opening 190a when the driving assembly is in the firing position, the pre-firing position, or anywhere in between. Since the transverse cross-section of the driver blade <NUM> along the distance DPA2 is uniform, the driver blade <NUM> always occupies the same portion of the driver blade receiving opening 190a regardless of the position of the piston <NUM>.

<FIG> shows a transverse cross-section of the driver blade <NUM> just above the driver blade seal <NUM>. The driver blade <NUM> does not entirely fill the driver blade receiving opening 190a and engage the driver blade seal <NUM>. Rather, a small gap exists around the perimeter of the driver blade <NUM>. This gap is large enough to prevent the driver blade <NUM> from frictionally engaging the driver blade seal <NUM> during the fastener-driving cycle, as too much friction between the driver blade and the driver blade seal could undesirably slow driving assembly movement during the fastener-driving cycle and negatively affect tool operation. Yet the gap is small enough to minimize air leakage, as too much air leakage through the driver blade seal could reduce the air pressure in the return chamber so much as to negatively affect the driving assembly's return to the pre-firing position, such as by preventing the driving assembly from returning to the pre-firing position or returning the driving assembly to the pre-firing position too slowly.

If the air pressure in the return chamber is excessively high when the driving assembly reaches the firing position, the piston will impact the top of the cylinder with excessive force when the driving assembly reaches the pre-firing position. This could damage the piston, the cylinder, or other tool components, especially with repeated use. Also, if the piston impacts the top of the cylinder with too much force, it could bounce off of the cylinder and cause the driving assembly to end up between the pre-firing and the firing position upon completion of the fastener-driving cycle. Improper positioning of the driving assembly could result in a misfire the next time the operator tries to drive a fastener.

There is a need for a powered-fastener-driving tool that solves these problems.

<CIT> discloses a poppet valve having novel seal means for use in a pneumatic fastener apparatus of the kind having a cylinder, a piston slidably mounted for reciprocal movement in the cylinder, a fastener-driving hammer attached to the cylinder, and means including the poppet valve for controlling the application of pressurized air to the piston so as to cause it to execute a work stroke. The seal means comprises an O-ring disposed in a circumferentially-extending groove formed in the outer surface of the poppet valve member and arranged to make a sealing engagement with an end edge surface of the cylinder. More than half of the cross-sectional area of the O-ring is disposed within the groove so that as the poppet valve is driven into closing relation with the cylinder, the O-ring seal is clamped between an annular circumferentially-extending surface of the poppet valve member and the annular end edge surface of the cylinder, thereby providing a secure seal along the full perimeter of the cylinder.

<CIT>, which is prior art according to Article <NUM>(<NUM>) EPC, discloses a pneumatic or hydraulic mechanism having a housing defining a piston chamber and having a fluid inlet port. A piston is slidable in the piston chamber. The piston partitions the piston chamber into a front chamber and a rear chamber. The piston has one or more passages for fluid communication between the rear chamber and the front chamber, the one or more passages being sealed by a sealing mechanism. The sealing mechanism has a sealing state in which the sealing mechanism substantially inhibits fluid communication between the rear chamber and the front chamber, and a non-sealing state in which the sealing mechanism allows fluid communication between the rear chamber and the front chamber.

Various embodiments of the present disclosure provide a powered-fastener-driving tool including driver blade that has a varying cross-section that solves the above problems.

In one embodiment, the powered-fastener-driving tool includes a cylinder, a return chamber in fluid communication with the cylinder, a driver blade seal that defines a driver blade receiving opening, a driving element including a driver blade, and a piston within and movable relative to the cylinder and the driver blade seal. The piston is attached to the driving element such that the driver blade is slidably received in the driver blade receiving opening.

To drive a fastener, the piston is driven to move from a pre-firing position to a firing position. This movement forces air beneath the piston from the cylinder into the return chamber. Once the piston reaches the firing position and the air pressure in the return chamber has reached its maximum, the pressurized air flows from the return chamber back into the cylinder to force the piston from the firing position back to the pre-firing position.

The non-uniform cross-section of the driver blade is sized and shaped such that a portion of the driver blade receiving opening occupied by the driver blade changes as the piston moves between a pre-firing position and a firing position. This solves the above problems by reducing the impact force of the piston on the upper end of the cylinder when returning to the pre-firing position as compared to an identical prior art tool with a uniform cross-section driver blade. Specifically, since more air can leak through the driver blade receiving opening as the piston moves from the pre-firing position to the firing position, the return chamber is less pressurized following fastener driving than the return chamber of the prior art tool. This combined with the fact that more air can leak through the driver blade receiving opening as the piston moves from the firing position to the pre-firing position results in less force acting on the piston to return it to the pre-firing position as compared to the prior art tool. The varying cross-section of the driver blade thus precisely controls the amount of air leakage through the driver blade seal to achieve a desired piston return.

Other objects, features, and advantages of the present disclosure will be apparent from the detailed description and the drawings.

Various embodiments of the present disclosure provide a powered-fastener-driving tool including driver blade that has a varying cross-section. <FIG> illustrate part of one example embodiment of a combustion-powered-fastener-driving tool <NUM> of the present disclosure (sometimes called the "tool <NUM>" for brevity). Since certain portions of the tool <NUM>-such as a tool housing, a workpiece contact element and associated linkage(s), a fuel canister and associated fuel delivery system, and a trigger and associated trigger switch-are well-known in the art, they are generally described below but are not shown for clarity.

As best shown in <FIG>, the tool <NUM> generally includes: a cylinder <NUM> having an upper end <NUM> and a lower end <NUM>; a driving assembly <NUM> slidably disposed within the cylinder <NUM>; a bumper <NUM> at the bottom of the cylinder <NUM>; a driver blade seal <NUM> below the bumper <NUM>; a combustion chamber housing <NUM> partially surrounding and supported by the cylinder <NUM>; a cylinder head <NUM> supported by the combustion chamber housing <NUM>; a valve element <NUM> supported by, partially surrounding, and movable relative to the combustion chamber housing <NUM>; a return chamber <NUM> partially surrounding the cylinder <NUM>; and a nosepiece <NUM> depressible relative to the cylinder <NUM>, connected to and extending from the bottom of the return chamber <NUM>, sandwiching the bumper <NUM> between a nosepiece mounting plate 28a and the lower end <NUM> of the cylinder <NUM>, and sandwiching the driver blade seal <NUM> between the nosepiece mounting plate 28a and the bumper <NUM>.

One or more, and in this illustrated embodiment multiple, circumferentially spaced return ports <NUM> are defined through the cylinder <NUM> near an upper edge <NUM> of the bumper <NUM>. The quantity and location of the return ports <NUM> may vary. The portion of this example cylinder <NUM> that extends between the upper end <NUM> and the return ports <NUM> does not define any openings therethrough. But in other embodiments, the portion of the cylinder that extends between the upper end and the return ports defines one or more openings therethrough.

The driving assembly <NUM> includes a piston <NUM> threadably engaged to a driving element <NUM>. The piston <NUM> has an upper surface <NUM>, an underside <NUM>, and an outer cylindrical surface (not labeled). A sealing element (such as an o-ring) is attached to the outer surface and sealingly engages the inner cylindrical surface of the cylinder <NUM> to prevent the volume of the cylinder <NUM> below the piston <NUM> from fluidly communicating with the volume of the cylinder <NUM> above the piston <NUM>.

As best shown in <FIG>, the driving element <NUM> includes: (<NUM>) an externally threaded connection element <NUM> threadably engageable to the piston <NUM> (though the piston and driving element may be connectable in any other suitable manner); (<NUM>) a flange <NUM> attached to the bottom end of the connection element <NUM> and having an upper surface (not labeled) sized to engage the underside <NUM> of the piston <NUM> when the piston <NUM> is threadably engaged to the connection element <NUM>; and (<NUM>) a driver blade <NUM> attached to and extending from a lower surface (not labeled) of the flange <NUM> and terminating in a free end 206a.

The driver blade <NUM> has a longitudinal axis AA and a length LA. Moving from the flange <NUM> to the free end 206a along the longitudinal axis AA, the driver blade <NUM>: (<NUM>) tapers toward the longitudinal axis AA to a width WA1 along a distance DA1; (<NUM>) maintains the width WA1 along a distance DA2; (<NUM>) tapers toward the longitudinal axis AA to a width WA2 along a distance DA3; (<NUM>) maintains the width WA2 along a distance DA4; (<NUM>) tapers away from the longitudinal axis AA to a width WA3 along a distance DA5; (<NUM>) maintains the width WA3 along a distance DA6; and (<NUM>) tapers toward the longitudinal axis AA to a width WA4 along a distance DA7.

Although not shown, the transverse cross-section of the driver blade <NUM> (taken along a horizontal plane perpendicular to the longitudinal axis AA): (<NUM>) along the distance DA2 is generally rectangular shaped, and its size and shape do not change; (<NUM>) along the distance DA4 is generally rectangular shaped, and its size and shape do not change; and (<NUM>) along the distance DA6 is generally rectangular shaped, and its size and shape do not change. Put differently, the transverse cross-section of the driver blade <NUM> is generally uniform along the distance DA2, along the distance DA4, and along the distance DA6. The transverse cross-section of the driver blade <NUM> along the distance DA2 and the transverse cross-section of the driver blade <NUM> along the distance DA4 are different. The transverse cross-section of the driver blade <NUM> along the distance DA4 and the transverse cross-section of the driver blade <NUM> along the distance DA6 are different. The transverse cross-section of the driver blade <NUM> along the distance DA2 and the transverse cross-section of the driver blade <NUM> along the distance DA6 may be the same or different.

<FIG>, <FIG>, <FIG>, <FIG>, and <FIG> best show the driver blade seal <NUM>, which defines a driver blade receiving opening 90a therethrough. The driver blade receiving opening 90a is shaped to correspond to and is sized just larger than the transverse cross-section of the driver blade <NUM> along the distance DA2, as shown in <FIG>.

The driving assembly <NUM> is movable within and relative to the cylinder <NUM> between a pre-firing position (<FIG>, <FIG>, and <FIG>) and a firing position (<FIG>). When the driving assembly <NUM> is in the pre-firing position, part of the top surface <NUM> of the piston <NUM> engages the underside of the upper end <NUM> of the cylinder <NUM>. When the driving assembly <NUM> is in the firing position, part of the underside <NUM> of the piston <NUM> contacts the upper edge <NUM> of the bumper <NUM>.

When installed, the driver blade <NUM> is slidably received in the driver blade receiving opening 90a of the driver blade seal <NUM>. The driver blade <NUM> and the driver blade seal <NUM> are positioned such that: (<NUM>) when the driving assembly <NUM> is in the pre-firing position (<FIG>, <FIG>, and <FIG>), part of the driver blade <NUM> along the distance DA4 occupies a first portion of the driver blade receiving opening 90a; (<NUM>) when the driving assembly <NUM> is in the firing position (<FIG>), part of the driver blade <NUM> along the distance DA2 occupies a second larger portion of the driver blade receiving opening 90a; and (<NUM>) when the driving assembly <NUM> is in between the pre-firing and firing positions, the position of the driving assembly <NUM> controls which part of the driver blade <NUM> along the distance DA2, DA3, or DA4 occupies the driver blade receiving opening 90a and how much of the driver blade receiving opening 90a is occupied.

Since the transverse cross-section of the driver blade <NUM> differs along the distances DA2, DA3, and DA4, the driver blade <NUM> occupies different portions of the driver blade receiving opening 90a (depending on the position of the driving assembly <NUM>) throughout the fastener-driving cycle. Put differently, the unoccupied portion of the driver blade receiving opening 90a varies throughout the fastener-driving cycle. This means that the amount of air that can escape the cylinder <NUM> during the fastener-driving cycle through the portion of the driver blade receiving opening 90a unoccupied by the driver blade <NUM> changes as the driving assembly <NUM> moves, as described below with respect to <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

The following components of the tool <NUM> collectively define a combustion chamber: the cylinder head <NUM>, the combustion chamber housing <NUM> that includes a generally cylindrical outer wall <NUM> and a floor <NUM>, and the upper surface <NUM> of the piston <NUM> (when the driving assembly <NUM> is in the pre-firing position). This is merely one example combustion chamber, and in other embodiments the combustion chamber may be differently shaped and/or sized and may be defined by any suitable components.

The combustion chamber is in fluid communication with the cylinder <NUM> via an opening <NUM> defined through the combustion chamber housing <NUM> and an opening defined in the upper end <NUM> of the cylinder <NUM>. Unlike in conventional combustion-powered-fastener-driving tools, the outer wall <NUM> of the combustion chamber housing <NUM> is fixed relative to the cylinder <NUM> during the entire fastener-driving cycle.

As best shown in <FIG> and <FIG>, the valve element <NUM>, which defines multiple ports <NUM> therethrough, is supported by and partially surrounds the outer wall <NUM> of the combustion chamber housing <NUM>. The valve element <NUM> is movable relative to the outer wall <NUM> between: (<NUM>) an open position in which the ports <NUM> at least partially align with ports <NUM> defined through the outer wall <NUM>; and (<NUM>) a closed position in which the ports <NUM> are not aligned with and block the ports <NUM>, thereby sealing the combustion chamber. As best shown in <FIG>, at least some of the ports 38a of the outer wall <NUM> are located above an upper edge <NUM> of the valve element <NUM> and fluidically connect the combustion chamber to atmosphere outside of the tool <NUM> when the valve element <NUM> is in the open position. In various embodiments, the same ports <NUM> are used to intake air pre-ignition and to exhaust combustion gases post-ignition, as described further below.

One or more, and in this embodiment multiple, biasing elements <NUM> (such as springs) bias the valve element <NUM> to the open position. In this embodiment, to move the valve element <NUM> to the closed position, an operator depresses the nosepiece <NUM> of the tool <NUM>-and more particularly a workpiece contact element (not shown) at the end of the nosepiece <NUM> as is known in the art-against a workpiece with enough force to cause a linkage (not shown) that connects the nosepiece <NUM> to the valve element <NUM> to impose a force on the valve element <NUM> that overcomes the collective biasing force of the biasing elements <NUM>. This causes the valve <NUM> to move relative to the outer wall <NUM> and toward the cylinder head <NUM> to the closed position, thereby sealing the combustion chamber by blocking the ports <NUM>.

Although not shown, as is known in the art, depressing the nosepiece <NUM> of the tool against the workpiece also causes, such as via actuation of one or more mechanical or electromechanical switches: (<NUM>) a fuel canister (not shown) to dispense fuel into the combustion chamber via a fuel delivery system (not shown); and (<NUM>) a motor <NUM> attached to the cylinder head <NUM> to drive a fan blade <NUM> at least partially disposed within the combustion chamber for a designated period of time that spans the fastener-driving cycle and enables enhanced mixing of air and fuel within the combustion chamber before ignition and also facilitates exchanging combustion gases for fresh air after ignition.

As best shown in <FIG>, the return chamber <NUM> is in fluid communication with the cylinder <NUM> via the return ports <NUM>. The return chamber <NUM> is also in fluid communication with the atmosphere surrounding the tool <NUM> via the return ports <NUM>, the unoccupied portion of the driver blade receiving opening 90a of the driver blade seal <NUM>, and the nosepiece <NUM>. The return chamber <NUM> surrounds an exterior wall <NUM> of the cylinder <NUM>, and at an upper end <NUM> is defined in part by a radially inwardly projecting annular flange <NUM> with a seal <NUM> engaging the exterior wall <NUM>. Opposite the flange <NUM>, a lower return chamber end <NUM> is closed off. While the return chamber at least partially surrounds the cylinder in this illustrated embodiment, in other embodiments the return chamber may be shaped and/or located differently, such as within a handle of the tool <NUM>.

In operation, after ignition of the fuel/air mixture in the combustion chamber and movement of the driving assembly <NUM> to the firing position, the driving assembly <NUM> returns to the pre-firing position through action of pressurized air stored in the return chamber <NUM> simultaneously with exhaustion of the combustion gases from the combustion chamber. Specifically, as the driving assembly <NUM> moves relative to the cylinder <NUM> from the pre-firing position to the firing position under the force generated by ignition of the fuel/air mixture in the combustion chamber, the piston <NUM> compresses and forces the air below the underside <NUM> of the piston <NUM> through the return ports <NUM> and into the return chamber <NUM>.

Once the driving assembly <NUM> reaches the firing position, recoil forces created by the action of driving a fastener cause the nosepiece <NUM> of the tool <NUM>, which an operator is holding, to disengage the workpiece. This movement removes the forces opposing the collective biasing force of the biasing elements <NUM>, which causes the biasing elements <NUM> to move the valve element <NUM> to the open position. This unseals the combustion chamber and fluidically connects it to atmosphere outside tool <NUM> (via the ports <NUM> and <NUM>), enabling the combustion gases to exhaust from the combustion chamber and fresh air to enter the combustion chamber. This is contrary to conventional combustion-powered-fastener-driving tools in which the combustion chamber must remain closed until the piston returns to the pre-firing position to ensure that the differential pressure required to return the piston to the pre-firing position is maintained.

After the driving assembly <NUM> reaches the firing position and contacts the bumper <NUM>, the air pressure in the return chamber <NUM> is greater than the air pressure in the cylinder <NUM>. This causes the pressurized air in the return chamber <NUM> to flow back through the return ports <NUM> into the cylinder <NUM>. Some of that air acts on the underside <NUM> of the piston <NUM> to force the driving assembly <NUM> back to the pre-firing position while the remainder escapes through the unoccupied portion of the driver blade receiving opening 90a to atmosphere.

<FIG> show the tool <NUM> at different stages of the fastener-driving cycle. For the purposes of this example embodiment, the fastener-driving cycle starts following: (<NUM>) depression of the nosepiece <NUM> against a workpiece to move the valve element <NUM> to the closed position (thereby sealing the combustion chamber) and cause the fuel canister to dispense fuel into the combustion chamber; and (<NUM>) actuation of a trigger switch (not shown) via an operator pulling a trigger (not shown) as known in the art to cause a spark generator <NUM> attached to the cylinder head <NUM> to ignite the fuel/air mixture in the combustion chamber. This causes the driving assembly to travel from the pre-firing position to the firing position, thereby causing the driver blade <NUM> to drive a fastener from the nosepiece <NUM> into the workpiece. The fastener-driving cycle ends when the driving assembly <NUM> returns to the pre-firing position.

<FIG> shows the tool <NUM> before the nosepiece <NUM> (not shown) has been depressed against the workpiece (not shown). The valve element <NUM> is in the open position, the combustion chamber is unsealed, and the driving assembly <NUM> is in the pre-firing position. As shown in <FIG>, part of the driver blade <NUM> along the distance DA4 occupies a first portion of the driver blade receiving opening 90a of the driver blade seal <NUM>.

<FIG> shows the tool <NUM> after: (<NUM>) the nosepiece <NUM> has been pressed against the workpiece to move the valve element <NUM> to the closed position and seal the combustion chamber while also causing the fuel canister to dispense fuel into the combustion chamber; and (<NUM>) the operator pulled the trigger to actuate the trigger switch and cause the spark generator <NUM> to ignite the fuel/air mixture inside the combustion chamber. As shown in <FIG>, the same part of the driver blade <NUM> along the distance DA4 occupies the first portion of the driver blade receiving opening 90a of the driver blade seal <NUM>.

<FIG> shows the tool <NUM> after the combustion gases have forced the driving assembly <NUM> to begin moving from the pre-firing position to the firing position. The valve element <NUM> remains in the closed position and the combustion chamber remains sealed (with the valve element <NUM> blocking the ports <NUM>). As the driving assembly <NUM> travels toward the firing position, the piston <NUM> forces the air beneath it to flow: (<NUM>) through the return ports <NUM> into the return chamber <NUM>; and (<NUM>) through the part of the driver blade opening not occupied by the driver blade <NUM>. As shown in <FIG>, part of the driver blade <NUM> along the distance DA4 occupies the first portion of the driver blade receiving opening 90a of the driver blade seal <NUM>.

<FIG> shows the tool <NUM> as the driving assembly <NUM> reaches the firing position and after the driver blade <NUM> has driven a fastener (not shown) housed in the nosepiece <NUM>. The combustion chamber is unsealed by return of the valve element <NUM> to the open position through tool recoil (i.e., the nosepiece <NUM> disengaging the workpiece). Exhaust E flows through the openings <NUM> and <NUM> to atmosphere outside of the tool <NUM>. This relatively rapid exhaust of combustion gases significantly reduces heat buildup in the tool <NUM>. At this point, the air in the return chamber <NUM> has reached its maximum pressure during the fastener-driving cycle. As shown in <FIG>, part of the driver blade <NUM> along the distance DA2 now occupies a second portion of the driver blade receiving opening 90a of the driver blade seal <NUM>. The second portion of the driver blade receiving opening 90a is larger than the first portion of the driver blade receiving opening 90a. Specifically, in this illustrated example, the ratio of the first portion to the second portion is about <NUM>:<NUM>. In various embodiments, the first portion is about <NUM>% to <NUM>% smaller than the second portion.

So as the driving assembly <NUM> moves from the pre-firing position to the firing position, the driver blade <NUM> switches from occupying the first, smaller portion of the driver blade receiving opening 90a along the distance DA2 to the second, larger portion of the driver blade receiving opening 90a along the distance DA4. Since the first portion is smaller than the second portion, more air escapes to atmosphere through the unoccupied portion of the driver blade receiving opening 90a when the driver blade <NUM> occupies the first portion of the driver blade receiving opening 90a than when the driver blade <NUM> occupies the second portion of the driver blade receiving opening 90a.

Additionally, the varying cross-section of the driver blade <NUM> results in a lower maximum air pressure in the return chamber <NUM> as compared to a driver blade with a uniform cross-section identical to the cross-section along DA2. Since the portion of the driver blade <NUM> along the distance DA4 occupies less of the driver blade receiving opening 90a as compared to the cross-section along DA2, it enables comparatively more air to escape through the (larger) unoccupied portion of the driver blade receiving opening 90a to atmosphere and comparatively less air to enter the return chamber <NUM>.

<FIG> shows the tool <NUM> after the air stored in the return chamber <NUM> has acted on the piston <NUM> and begun forcing it from the firing position back toward the pre-firing position. As shown in <FIG>, part of the driver blade <NUM> along the distance DA4 now occupies the first portion of the driver blade receiving opening 90a of the driver blade seal <NUM>. Following piston return, the tool <NUM> resumes the position shown in <FIG>.

So as the driving assembly <NUM> moves from the firing position to the pre-firing position, the driver blade <NUM> switches from occupying the second, larger portion of the driver blade receiving opening 90a along the distance DA2 to the first, smaller portion of the driver blade receiving opening 90a along the distance DA4. Since the second portion is larger than the first portion, less air escapes to atmosphere through the unoccupied portion of the driver blade receiving opening 90a when the driver blade <NUM> occupies the second portion of the driver blade receiving opening 90a than when the driver blade <NUM> occupies the first portion of the driver blade receiving opening 90a. This means that the air entering the cylinder <NUM> from the return chamber <NUM> applies comparatively more force on the underside <NUM> of the piston <NUM> when the driver blade <NUM> occupies the second portion of the driver blade receiving opening 90a than when the driver blade <NUM> occupies the first portion of the driver blade receiving opening 90a.

Additionally, the varying cross-section of the driver blade <NUM> results in a reduced impact force of the piston <NUM> on the upper end <NUM> of the cylinder <NUM> upon return to the pre-firing position as compared to a driver blade with a uniform cross-section identical to the cross-section along DA2. Since the portion of the driver blade <NUM> along the distance DA4 occupies less of the driver blade receiving opening 90a as compared to the cross-section along DA2, more air to escape through the (larger) unoccupied portion of the driver blade receiving opening 90a to atmosphere and there is less air pressure forcing the piston <NUM> to the pre-firing position. The varying cross-section of the driver blade thus precisely controls the amount of air leakage through the driver blade seal to achieve a desired piston return.

In one example embodiment: WA1 and WA3 are <NUM> inches (~<NUM>), WA2 is <NUM> inches (~<NUM>), WA4 is <NUM> inches (~ <NUM>), DA1 is <NUM> inches (~ <NUM>); DA2 is <NUM> inches (~ <NUM>); DA3 and DA5 are <NUM> inches (~ <NUM>), DA4 is <NUM> inches (~ <NUM>), DA6 is <NUM> inches (~ <NUM>), DA7 is <NUM> inches (~ <NUM>), the thickness of the driver blade <NUM> along its length LA is <NUM> inches (~ <NUM>). In one example embodiment, the cylinder volume is about <NUM> cubic inches (~ <NUM><NUM>) and the return chamber volume is about <NUM> cubic inches (~ <NUM><NUM>), though these may vary in other embodiments.

<FIG> shows another example driving element <NUM>, which includes: (<NUM>) an externally threaded connection element <NUM> threadably engageable to the piston <NUM>; (<NUM>) a flange <NUM> attached to the bottom end of the connection element <NUM> and having an upper surface (not labeled) sized to engage the underside of the piston when the piston is threadably engaged to the connection element <NUM>; and (<NUM>) a driver blade <NUM> attached to and extending from a lower surface (not labeled) of the flange <NUM> and terminating in a free end 306a.

The driver blade <NUM> has a longitudinal axis AB and a length LB. Moving from the flange <NUM> to the free end 306a along the longitudinal axis AB, the driver blade <NUM>: (<NUM>) tapers toward the longitudinal axis AB to a width WB1 along a distance DB1; (<NUM>) maintains the width WB1 along a distance DB2; (<NUM>) tapers toward the longitudinal axis AB to a width WB2 along a distance DB3; and (<NUM>) maintains the width WB2 along a distance DB4.

Although not shown, the transverse cross-section of the driver blade <NUM> (taken along a horizontal plane perpendicular to the longitudinal axis AB): (<NUM>) along the distance DB2 is generally rectangular shaped, and its size and shape do not change; and (<NUM>) along the distance DB4 is generally rectangular shaped, and its size and shape do not change. Put differently, the transverse cross-section of the driver blade <NUM> is generally uniform along the distance DB2 and along the distance DB4. The transverse cross-section of the driver blade <NUM> along the distance DB2 and the transverse cross-section of the driver blade <NUM> along the distance DB4 are different.

Since DB2 is larger than DA2, assuming all other factors are held constant, the pressure in the return chamber would be higher for the driving element <NUM> than for the driving element <NUM>.

<FIG> shows another example driving element <NUM>, which includes: (<NUM>) an externally threaded connection element <NUM> threadably engageable to the piston <NUM>; (<NUM>) a flange <NUM> attached to the bottom end of the connection element <NUM> and having an upper surface (not labeled) sized to engage the underside of the piston when the piston is threadably engaged to the connection element <NUM>; and (<NUM>) a driver blade <NUM> attached to and extending from a lower surface (not labeled) of the flange <NUM> and terminating in a free end 406a.

The driver blade <NUM> has a longitudinal axis AC and a length LC. Moving from the flange <NUM> to the free end 406a along the longitudinal axis AC, the driver blade <NUM>: (<NUM>) tapers toward the longitudinal axis AC to a width WC1 along a distance DC1; (<NUM>) maintains the width WC1 along a distance DC2; (<NUM>) tapers toward the longitudinal axis AC to a width WC2 along a distance DC3; and (<NUM>) maintains the width WC2 along a distance DC4.

Although not shown, the transverse cross-section of the driver blade <NUM> (taken along a horizontal plane perpendicular to the longitudinal axis AC): (<NUM>) along the distance DC2 is generally rectangular shaped, and its size and shape do not change; and (<NUM>) along the distance DC4 is generally rectangular shaped, and its size and shape do not change. Put differently, the transverse cross-section of the driver blade <NUM> is generally uniform along the distance DC2 and along the distance DC4. The transverse cross-section of the driver blade <NUM> along the distance DC2 and the transverse cross-section of the driver blade <NUM> along the distance DC4 are different.

Since DC2 is the same as DA2, assuming all other factors are held constant, the pressure in the return chamber would be the same for the driving elements <NUM> and <NUM>.

<FIG> shows another example driving element <NUM>, which includes: (<NUM>) an externally threaded connection element <NUM> threadably engageable to the piston <NUM>; (<NUM>) a flange <NUM> attached to the bottom end of the connection element <NUM> and having an upper surface (not labeled) sized to engage the underside of the piston when the piston is threadably engaged to the connection element <NUM>; and (<NUM>) a driver blade <NUM> attached to and extending from a lower surface (not labeled) of the flange <NUM> and terminating in a free end 506a.

The driver blade <NUM> has a longitudinal axis AD and a length LD. Moving from the flange <NUM> to the free end 506a along the longitudinal axis AD, the driver blade <NUM>: (<NUM>) tapers toward the longitudinal axis AD to a width WD1 along a distance DD1; (<NUM>) maintains the width WD1 along a distance DD2; (<NUM>) tapers toward the longitudinal axis AD to a width WD2 along a distance DD3; (<NUM>) maintains the width WD2 along a distance DD4; (<NUM>) tapers away from the longitudinal axis AD to a width WD3 along a distance DD5; (<NUM>) maintains the width WD3 along a distance DD6; (<NUM>) tapers toward the longitudinal axis AD to a width WD4 along a distance DD7; (<NUM>) maintains the width WD4 along a distance DD8; (<NUM>) tapers away from the longitudinal axis AD to a width WD5 along a distance DD9; (<NUM>) maintains the width WD5 along a distance DD<NUM>; (<NUM>) tapers toward the longitudinal axis AD to a width WD6 along a distance DD11; and (<NUM>) maintains the width WD6 along a distance DD12.

Although not shown, the transverse cross-section of the driver blade <NUM> (taken along a horizontal plane perpendicular to the longitudinal axis AD): (<NUM>) along the distance DD2 is generally rectangular shaped, and its size and shape do not change; (<NUM>) along the distance DD4 is generally rectangular shaped, and its size and shape do not change; (<NUM>) along the distance DD6 is generally rectangular shaped, and its size and shape do not change; (<NUM>) along the distance DD8 is generally rectangular shaped, and its size and shape do not change; (<NUM>) along the distance DD10 is generally rectangular shaped, and its size and shape do not change; and (<NUM>) along the distance DD12 is generally rectangular shaped, and its size and shape do not change. Put differently, the transverse cross-section of the driver blade <NUM> is generally uniform along the distances DD2, DD4, DD6, DD8, DD10, and DD12. The transverse cross-sections of the driver blade <NUM> along the distances DD2, DD6, and DD10 are different form the transverse cross-sections of the driver blade <NUM> along the distance distances DD4, DD8, and DD12. The transverse cross-sections of the driver blade <NUM> along the distances DD2, DD6, and DD10 may be the same or different. The transverse cross-sections of the driver blade <NUM> along the distances DD4, DD8, and DD12 may be the same or different.

These are merely example driver blades with cross-sections that vary in terms of their width to ensure the unoccupied portion of the driver blade receiving opening changes during the fastener-driving cycle. The cross-section of the driver blade may vary in any suitable manner to ensure the unoccupied portion of the driver blade receiving opening changes during the fastener-driving cycle. For instance, in another embodiment the driver blade's width remains constant along its length but its thickness varies to ensure the unoccupied portion of the driver blade receiving opening changes during the fastener-driving cycle. In another embodiment the driver blade's width and thickness change along its length to ensure the unoccupied portion of the driver blade receiving opening changes during the fastener-driving cycle. In another embodiment the shape of the driver blade's transverse cross-section changes along its length to ensure the unoccupied portion of the driver blade receiving opening changes during the fastener-driving cycle.

While the above-described example tool is a combustion-powered-fastener-driving tool, the features described above can apply to other types of powered-fastener-driving tools, including tools powered pneumatically, electrically, or by powder cartridges.

In various embodiments of the fastener-driving tool, the first position is a pre-firing position near an upper end of the cylinder and the second position is a firing position near a lower end of the cylinder.

In various such embodiments of the fastener-driving tool, an interior volume of the cylinder between the piston and the driver blade seal is in fluid communication with atmosphere at least in part via a portion of the driver blade receiving opening not occupied by the driver blade.

In various such embodiments of the fastener-driving tool, a first unoccupied portion of the driver blade receiving opening is not occupied by the driver blade when the driver blade is in the first position and a second unoccupied portion of the driver blade receiving opening that is smaller than the first unoccupied portion is not occupied by the driver blade when the driver blade is in the second position.

In various such embodiments of the fastener-driving tool, the first part of the driver blade has a first width and the second part of the driver blade has a second width that is larger than the first width.

In various such embodiments of the fastener-driving tool, the first part of the driver blade has a first thickness and the second part of the driver blade has a second thickness that is larger than the first thickness.

In various such embodiments of the fastener-driving tool, the return chamber is in fluid communication with atmosphere at least in part via the one or more openings and via a portion of the driver blade receiving opening not occupied by the driver blade.

In various such embodiments, the fastener-driving tool further comprises one of: (<NUM>) an internal combustion engine assembly; and (<NUM>) an air inlet attachable to a compressed air source.

Claim 1:
A fastener-driving tool (<NUM>) comprising:
a cylinder (<NUM>) defining one or more openings (<NUM>) therethrough;
a return chamber (<NUM>) in fluid communication with the cylinder via the one or more openings;
a driver blade receiving opening (90a);
a driving element (<NUM>) including a driver blade (<NUM>) having a non-uniform cross-section; and
a piston (<NUM>) within the cylinder and attached to the driving element such that the driver blade is slidably received in the driver blade receiving opening,
characterised in that the fastener-driving tool further comprises a driver blade seal (<NUM>) defining the driver blade receiving opening (90a),
and in that the non-uniform cross-section is such that the piston is movable relative to the cylinder and the driver blade seal between: (<NUM>) a first position in which a first part of the driver blade occupies a first portion of the driver blade receiving opening; and (<NUM>) a second position in which a second part of the driver blade occupies a second portion of the driver blade receiving opening that is larger than the first portion.