Patent Description:
A nail gun (nailer) is a tool which uses sudden application of a force to drive a nail or other fastener into a workpiece. A variety of mechanisms have been developed to supply the required force including the so-called "air spring". An air spring uses the compressibility of gas, which may be air, nitrogen, etc., (herein referred to simply as "air") to store energy which is released to forcefully move a driver which in turn forces the fastener into a workpiece. In particular, a motor is used to force a piston to compress the air within a cylinder. When a user presses a trigger on the nailer, the piston is released and the compressed gas forces the piston to move rapidly along a working axis of the nailer. A driver attached to the piston is thus driven into a fastener thereby driving the fastener into the workpiece.

In many air spring applications, a rack and pinion arrangement is used to compress and release the piston. In these devices a motor drives a pinion gear, and the pinion gear includes teeth extending from the periphery of the pinion gear which engage a rack fixed to the piston thereby forcing the piston to compress the gas. In order to release the piston, a portion of the pinion gear has a "tooth gap" wherein no teeth are provided along the periphery of the pinion gear. Consequently, when a user presses the trigger of the nailer with the pinion gear's last tooth before the tooth gap engaged with the rack, the motor rotates the pinion gear to a position whereat the teeth of the pinion gear no longer engage the rack, allowing the pressure of the gas in the cylinder to move the piston along the working axis.

This type of device is typically configured such that once the pinion gear is rotated by the motor to allow the piston to be moved by the compressed gas, the motor simply continues to rotate the pinion gear for one complete rotation of the pinion gear. Accordingly, the tooth gap of the pinion gear is selected such that the rack is engaged by a first tooth of the pinion gear only after the piston has completed its travel along the working axis. The continued rotation of the motor for one revolution of the pinion gear then drives the piston in the opposite direction along the working axis until the last tooth of the pinion gear before the tooth gap is engaged with the rack thereby compressing the gas with the piston. Thus, the pinion gear is moved in one complete rotation from the initiation of the sequence (pressing of the trigger) until the system is ready for the next pressing of the trigger.

The above described configuration works very well under normal operating conditions. Problems arrive, however, if the driver/piston do not travel to the designed extent along the working axis under the power of the compressed gas. Such situations can occur, for example, if a nail becomes jammed. In such situations, the motor continues to turn and the pinion gear is rotated for one complete turn. Because the piston is not fully extended along the working axis, however, as the first tooth of the pinion gear is rotated into contact with the rack, the tooth engages the rack at a midpoint of the rack rather than at the end of the rack. Consequently, the piston is fully retracted before the pinion gear has completed one full revolution.

Even though the piston is fully retracted in these situations before one complete rotation of the pinion gear, the motor continues to turn forcing the pinion gear toward a full rotation. The continued rotation of the motor forces the pinion gear teeth to momentarily disengage. Upon the disengagement, the compressed air in the cylinder forces the piston (and hence the rack) along the working axis. At the same time the motor rotates another tooth of the pinion gear into engagement with the rack which is now moving, resulting in a forceful impact between the pinion gear and the rack. Depending upon how much of the piston stroke was initially truncated, this can result in multiple shocks as the pinion gear is rotated until the pinion gear has completed one full rotation and the last tooth of the pinion gear is impacted by the rack.

The forceful collision(s) of the pinion gear and the rack is not only disconcerting to a user, it also creates a torsional shock load which propagates along the drive path from the pinion gear into drive gear of the nailer. The shock load, also referred to as a "jam shock", can lead to stress fractures within the main drive/gearing of the nailer resulting in catastrophic failure. While it is possible to provide materials which can withstand jam shock, such materials tend to be heavy which increases the weight of the portable tool which is undesired in a portable tool.

<CIT> discloses that in order to provide a driving machine which achieves reciprocating movements of a rack using a simple mechanism and is able to smoothly engage and disengage the rack by reducing the friction during engagement and disengagement of the rack, the driving machine is equipped with a nose that extends in a prescribed direction, a housing that has the nose, a blade that has an engaging section, is movably guided in the housing in the prescribed direction, and is capable of driving a fastener via the nose, and a transmission mechanism that has an engaged section for engaging with the engaging section in order to transmit a driving force, wherein the transmission mechanism has a roller mechanism for guiding the engaging section and engaged section to disengage from each other.

Therefore, there is a need to reduce and/or eliminate the shock load of air spring systems.

According to one embodiment of the present disclosure, a power tool includes an air spring cylinder. A piston is movably positioned within the cylinder and a driver blade and a rack are attached to the piston. The power tool includes a lifter gear including a lifter gear wheel portion, and a plurality of teeth extending radially from the lifter gear wheel portion and configured to engage the rack. A hub includes a first end operably connected to a motor output and a second end including a hub wheel portion. A first receptacle is provided in one of the lifter gear and the hub and a first bearing element extends from the other of the lifter gear and the hub into the first receptacle. A first elastomeric damper is positioned within the first receptacle between the first bearing element and a bearing element defined portion of the first receptacle.

In one or more embodiments, the first bearing element extends completely through the first receptacle.

In one or more embodiments the bearing element defined portion of the first receptacle is defined by a second bearing element, and the second bearing element extends from the first receptacle in a first direction to a location within a second receptacle of the other of the lifter gear and the hub.

In one or more embodiments, the second bearing extends from the first receptacle, in a second direction opposite the first direction, to a first end portion.

In one or more embodiments, the power tool includes a lid extending orthogonally from the first end portion.

In one or more embodiments the second receptacle is a blind bore.

In one or more embodiments the first bearing element is one of a plurality of bearing elements extending from the hub, and the second bearing element is one of a plurality of bearing elements extending from the lifter gear.

In one or more embodiments, the first bearing element extends into a bearing element receiving portion of the first receptacle, the bearing element defined portion of the first receptacle has a first radius of curvature, the bearing element receiving portion of the first receptacle has a second radius of curvature, and the second radius of curvature is larger than the first radius of curvature.

In one or more embodiments, the power tool includes a one-way needle bearing clutch engaged with the hub.

In one embodiment, a method of assembling a power tool includes providing an air spring cylinder, and a piston movably positioned within the air spring cylinder. The method includes fixedly attaching a driver blade to the piston and fixedly attaching a rack to the piston. A first end of a hub is operably connected to a motor output, the hub including a second end including a hub wheel portion. An elastomeric damper is positioned within a receptacle of one of the hub and a lifter gear and the lifter gear is aligned with the hub. A bearing element extending from the other of the lifter gear and the hub is inserted into the receptacle such that the elastomeric damper is positioned within the first receptacle between the bearing element and a bearing element defined portion of the receptacle. The rack is then engaged with one of a plurality of teeth extending radially from a wheel portion of the lifter gear.

A method of operating a power tool includes actuating a motor having a motor output and rotating a hub including a first end operably connected to the motor output and a second end including a hub wheel portion. A lifter gear including a lifter gear wheel portion, and a plurality of teeth extending radially from the lifter gear wheel portion and engaged with a rack fixedly attached to a piston is rotated by passing torque from the hub to the lifter gear through an elastomeric damper positioned within a first receptacle between a first bearing element and a bearing element defined portion of the first receptacle, the first receptacle in one of the lifter gear and the hub and the first bearing element extending from the other of the lifter gear and the hub and into the first receptacle. Rotation of the lifter gear disengages the lifter gear from the rack. The method includes moving the piston within an air spring cylinder upon disengagement of the lifter gear from the rack using compressed air in the air spring cylinder thereby driving a fastener with a driver blade fixedly attached to the piston. The rack is reengaged with the plurality of teeth after moving the piston using the compressed air. Rotation of the lifter gear after re-engaging the rack continues by passing torque from the motor to the hub and from the hub to the lifter gear through the elastomeric damper positioned within the first receptacle between the first bearing element and the bearing element defined portion of the first receptacle.

In one or more embodiments, rotating the hub includes rotating the hub with the hub operably engaged with a one-way needle bearing clutch.

The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written description. It is to be understood that no limitation to the scope of the disclosure is thereby intended. It is further to be understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one skilled in the art to which this disclosure pertains.

Referring to <FIG>, there is depicted a power tool <NUM> with an air spring as described below. The power tool in the embodiment of <FIG> is a nailer <NUM>. The nailer <NUM> includes a housing <NUM> that defines a drive section <NUM> and a grip section <NUM>. A trigger <NUM> is provided in the grip section <NUM> and a battery receptacle <NUM> is configured to removably couple with a battery <NUM> at the grip section <NUM>. In other embodiments, the power tool is a corded tool. The nailer further includes a removable nail magazine <NUM>. A work contact element (WCE) assembly <NUM> extends out of the housing <NUM>.

As shown in <FIG>, within the drive section <NUM> a cylinder <NUM> and accumulator <NUM> are provided. A cap <NUM> is used to seal the cylinder <NUM> and the accumulator <NUM> and defines a headspace <NUM> above the cylinder <NUM> and the accumulator <NUM> (see <FIG>). A PCBA <NUM> is operably connected to the trigger <NUM>, the battery <NUM>, and a DC brushless motor <NUM>.

With reference to <FIG>, a piston <NUM> is provided within the cylinder <NUM>. A driver <NUM> is fixedly attached to the piston <NUM> as is a rack <NUM>. The rack <NUM> includes a number of rollers <NUM> which are configured to be engaged by teeth <NUM> of a lifter gear <NUM>. As shown more clearly in the simplified depiction of <FIG>, the lifter gear <NUM>, which functions as a pinion gear, includes a toothed section <NUM> and a tooth gap section <NUM>. The tooth gap section <NUM> is bounded by a first tooth <NUM>F and a last tooth <NUM>L. The lifter gear <NUM> is operably connected to the motor <NUM> through a hub <NUM> (see <FIG>) and a planetary gearbox <NUM> (see <FIG>). Continuing with <FIG>, the hub <NUM> is supported by a one-way needle bearing clutch <NUM>.

Additional details regarding the structure of the lifter gear <NUM> and the hub <NUM> are provided with further reference to <FIG>. The hub <NUM> includes a geared motor side end portion <NUM> which is operably connected to the planetary gearbox <NUM>. A body portion <NUM> is fixedly connected to an inner race of the one-way needle bearing clutch <NUM> which is not shown herein in further detail. The body portion <NUM> is oversized to provide for increased torque capacity with the one-way needle bearing clutch <NUM>. A wheel portion <NUM> is positioned at the non-motor facing side of the hub <NUM>. A central bore <NUM> extends inwardly from the wheel portion <NUM> into the body portion <NUM>. The central bore is provided not only for coupling with the lifter gear as described below, but also to reduce the weight of the hub <NUM>. A plurality of damper holders in the form of receptacles <NUM> are located about the periphery of the wheel portion <NUM>. The receptacles <NUM> in this embodiment are closed on the motor facing side, but in other embodiments are at least partially open.

Additional damper holders in the form of bearing elements <NUM> are provided on the wheel portion <NUM> and extend in a direction away from the motor side toward the lifter gear <NUM>. In some embodiments the hub is provided only with receptacles and in other embodiments the hub is provided only with bearing elements.

Within the wheel portion <NUM>, the bearing elements <NUM> define one wall portion of the receptacles <NUM>. The bearing elements <NUM> are sized to extend into damper holders <NUM> which are in the form of receptacles in a wheel portion <NUM> of the lifter gear <NUM>. In the embodiment of <FIG>, the bearing elements <NUM> of the hub <NUM> are sized to extend completely through the wheel portion <NUM> of the lifter gear <NUM>. In other embodiments, the bearing elements <NUM> are sized to terminate within the wheel portion <NUM>.

The lifter gear <NUM> is also provided with damper holders in the form of bearing elements <NUM> which are sized to extend into the receptacles <NUM> of the hub <NUM>. Bearing elements <NUM> in this embodiment extend both in the direction toward the hub <NUM> as well as in a direction away from the hub <NUM> and each bearing element <NUM> defines a portion of the wall of an associated receptacle <NUM>. A lip <NUM> (see also <FIG>) is provided on the non-motor facing side of the bearing elements <NUM>. The hub <NUM> further includes a shaft <NUM> with an internal bore <NUM> which lightens the weight of the lifter gear <NUM>.

In the embodiment of <FIG>, the receptacles <NUM> and <NUM> are similarly shaped and described with respect to a receptacle <NUM>. As most clearly seen in <FIG>, the receptacles <NUM> include a bearing element receiving portion <NUM> and a bearing element defined portion <NUM>. The bearing element receiving portion <NUM> has an inner diameter which is selected to receive a bearing element <NUM> from the hub <NUM>. The bearing element defined portion <NUM> has an inner diameter that is sized and shaped to be complimentary to an elastomeric damper <NUM>. The bearing element defined portion <NUM> is thus a portion of the bearing element <NUM> within the wheel portion <NUM>.

Elastomeric dampers <NUM> (see <FIG>) are arranged in the damper holders <NUM>/<NUM>/<NUM>/<NUM> as described in detail with respect to <FIG>. Each elastomeric damper <NUM> extends from within a hub receptacle <NUM> to within a lifter gear receptacle <NUM>. Within the receptacles <NUM> and the receptacles <NUM>, the elastomeric dampers are located between the bearing elements <NUM>/ <NUM> and the bearing element defined portion of the receptacles <NUM>/<NUM> (i.e., bearing element defined portion <NUM> for the receptacle <NUM> and bearing element defined portion <NUM> for the receptacle <NUM>).

Accordingly, while the bearing elements <NUM> can contact the receptacles <NUM> along the bearing element receiving portion <NUM>, the elastomeric dampers <NUM> preclude contact between the bearing element defined portion <NUM> and the bearing elements <NUM>. Likewise, the bearing elements <NUM> can contact the receptacles <NUM> along the bearing element receiving portion <NUM>, but the elastomeric dampers <NUM> preclude contact between the bearing element defined portion <NUM> and the bearing elements <NUM>.

In the embodiment of <FIG>, the elastomeric damper <NUM> has a substantially circular cross section with a maximum radius of curvature RD. The various components are sized to provide for a tight fit when the unit is assembled which is described with reference to the components shown in <FIG>. In <FIG>, the bearing element <NUM> has an inner radius of curvature RBE1i which is substantially the same as an inner radius of curvature RBE2i of the bearing element <NUM>. The radii of curvature RBE1i and RBE2i are selected to provide a friction fit with the elastomeric damper <NUM>. The bearing element <NUM> has an outer radius of curvature RBE1o which is substantially the same as an inner radius of curvature RBERP of the bearing element receiving portion <NUM>. Thus, when assembled the hub <NUM> and lifter gear <NUM> are tightly rotationally coupled.

The configuration of the hub <NUM>, lifter gear <NUM>, and elastomeric pads <NUM> provides for ease of assembly. In particular, the elastomeric pads can be loaded into the receptacles <NUM>, the receptacles <NUM>, or a combination of receptacles <NUM> and <NUM> as desired. The shaft <NUM> is then aligned with the central bore <NUM>, and inserted into (or received by) the central bore <NUM>. As the shaft <NUM> is positioned within the bore <NUM>, the bearing elements <NUM> are positioned in the receptacles <NUM> and the bearing elements <NUM> are positioned in the receptacles <NUM>. The elastomeric pads are likewise positioned within the receptacles <NUM>, the receptacles <NUM>, or a combination of receptacles <NUM> and <NUM> into which they were not previously loaded. The lips <NUM> and the blind bore receptacles <NUM> (or optionally lips in some embodiments) maintain the elastomeric pads <NUM> within the hub <NUM> and lifter gear <NUM> during the assembly. The bolt <NUM> is then used to secure the assembly with the elastomeric pads <NUM> precluding contact between the inner wall portions <NUM> and the inner wall portions <NUM>.

Continuing with <FIG>, as noted above, the bolt <NUM> secures the lifter gear <NUM> to the hub <NUM>. Consequently, the shaft <NUM> of the lifter gear <NUM> is maintained within the central bore <NUM> thereby aligning the hub <NUM> and the lifter gear <NUM> while entrapping the elastomeric dampers <NUM> between the hub <NUM> and the lips <NUM>.

While one variation of the hub/lifter gear/damper arrangement has been depicted, a variety of modifications are available. Thus, in some embodiments, one of the hub and the lifter gear includes damper holders only in the form of receptacles and the other of the hub and the lifter gear includes damper holders only in the form of bearing elements. In some embodiments neither bearing elements of the hub nor bearing elements of the lifter gear extend beyond the receptacles into which they are inserted. In some embodiments, both the bearing elements of the hub and the bearing elements of the lifter gear extend beyond the receptacles into which they are inserted. In some embodiments, bearing elements are provided which define a bearing element defined portion of a receptacle and do not extend outwardly of the receptacle.

Returning to <FIG>, the WCE assembly <NUM> includes a nose piece <NUM>, which in this embodiment is the WCE, that is fixedly attached to a WCE stamping <NUM>. A WCE extension <NUM>, also shown in <FIG>, is attached to the WCE stamping <NUM> at one end and at the other end includes a bearing portion <NUM>. The WCE extension <NUM> further includes shoulders <NUM>. The WCE extension <NUM> is maintained in alignment with a plunger <NUM> by a pair of guides <NUM> (also shown in <FIG>). A WCE spring <NUM> biases the WCE stamping <NUM> along a work or drive axis <NUM> in a direction away from the WCE extension <NUM>. The shoulders <NUM> of the WCE extension <NUM> act as stops with the lower of the two guides <NUM> to limit downward travel of the nose piece/WCE <NUM>, WCE stamping <NUM>, and WCE extension <NUM>.

As used, herein, "downward" refers to the direction in which a nail (not shown) is driven by the nailer <NUM> along the drive axis <NUM>, which is in the downward direction in theconfiguration depicted in <FIG>. Additionally, for ease of discussion, "movement" of the various components is described herein with reference to the housing <NUM> of the nailer. In particular, under normal operating conditions the WCE <NUM>, the WCE stamping <NUM>, and the WCE extension <NUM> do not actually move since the WCE <NUM> is positioned against a work piece. Rather the rest of the nailer <NUM> is moved to compress the WCE spring <NUM>. Nonetheless, the WCE <NUM>, the WCE stamping <NUM>, and the WCE extension <NUM>, along with other components, will be described as "moving" for ease of discussion, it being understood that the "movement" simply refers to movement relative to the housing <NUM>.

Returning to <FIG>, a portion of the housing <NUM> is removed as is the cap <NUM> (see <FIG> and <FIG>) to reveal a head valve assembly <NUM> which is also shown in <FIG>. The head valve assembly <NUM> includes a flapper valve <NUM> which has a seal <NUM>, the plunger <NUM>, and a pivot <NUM>. The pivot <NUM> includes a circular pin <NUM> that fits within an oval pivot bore <NUM> of the flapper valve <NUM>. The flapper valve <NUM>, which can seal the headspace <NUM>, and thus the accumulator <NUM>, from the cylinder <NUM>, includes a pair of fingers <NUM> that receive a neck portion <NUM> of the plunger <NUM>.

The neck portion <NUM> is located between a head <NUM> and shoulder <NUM> of the plunger <NUM>. The neck portion <NUM> is configured to slide between the fingers <NUM> from the side (i.e., in a direction orthogonal to the drive axis <NUM>), while the head <NUM> and the shoulder <NUM> are sized to not pass through the fingers <NUM> in directions along the drive axis <NUM>. In some embodiments the neck portion is circular in cross section. In other embodiments the neck portion is configured to allow insertion into the fingers in one orientation, while preventing insertion (or removal) when rotated to a different orientation.

A shaft portion <NUM> of the plunger <NUM> extends outwardly of the headspace <NUM> in an airtight but slidable manner through an insert <NUM>. The shoulder <NUM> of the plunger <NUM> is configured to abut the insert <NUM>, which is fixedly positioned in the nailer <NUM>, in a non-firing configuration as depicted in <FIG>.

Operation of the nailer <NUM> is described with initial reference to <FIG>. In the configuration of <FIG>, the piston <NUM> is at is full upward position within the air cylinder <NUM>, and is held at this position by the last tooth <NUM>L of the lifter gear <NUM> (see <FIG>). In this configuration the air within the upper portion of the air cylinder <NUM>, the headspace <NUM>, and the air accumulator <NUM> is fully pressurized. The pressure differential between the headspace <NUM> and atmosphere acts across the plunger <NUM> biasing the plunger <NUM> downwardly along the drive axis <NUM> thereby forcing the shoulder <NUM> of the plunger <NUM> against the insert <NUM>.

Because the head <NUM> of the plunger is larger than the opening defined by the fingers <NUM> of the flapper valve <NUM> (in a plane orthogonal to the drive axis <NUM>), the flapper valve <NUM> is maintained in a non-firing position, and hence the seal <NUM>, is held firmly against the upper portion of the air cylinder <NUM> thus sealing the air cylinder <NUM> from the headspace <NUM>. In some embodiments, the pivot bore <NUM> is circular, which creates a tight seal around the entire circumference of the seal <NUM>. In the embodiment of <FIG>, the pivot bore <NUM> is oval with the major axis extending along the drive axis <NUM>, and positioned to have the pin <NUM> centrally located when the shoulder <NUM> is resting against the insert <NUM>. Consequently, the force of the seal <NUM> against the air cylinder <NUM> is reduced at locations proximate the pivot <NUM>. The reduced force reduces frictional forces introduced between the seal <NUM> and the air cylinder <NUM> which must be overcome when actuating the WCE assembly, allowing the WCE actuating force (described below) to be dominated by forces from the WCE spring <NUM> and forces resulting from the pressurized air in the headspace acting against the plunger <NUM> as discussed in further detail below.

The reduced force of the seal <NUM> against the air cylinder <NUM> may result in some initial leakage past the seal <NUM> in the event the air in the headspace <NUM> is at a higher pressure than the air in the air cylinder <NUM>, but such leakage does not significantly affect the safety performance of the head valve assembly <NUM>. In particular, in the event the piston <NUM> is inadvertently released from the last tooth <NUM>L, for example, due to a mechanical or electrical fault, the compressed air in the volume of the air cylinder <NUM> above the piston <NUM> will force the piston <NUM> to begin to move downwardly. The area in the air cylinder <NUM> above the piston thus depressurizes rapidly.

The pressure in the headspace <NUM> does not, however, depressurize as rapidly (if at all) since the flapper valve <NUM> is in a non-firing position which hinders passage of air from the headspace <NUM> to the air cylinder <NUM>. Thus, the pressure differential across the flapper valve <NUM> quickly fully seals the flapper valve <NUM> even if some leakage initially occurs. Thus, the air in the headspace <NUM>, and the air in the air accumulator <NUM> is not allowed to pass freely into the air cylinder <NUM>. Accordingly, the piston <NUM> is driven with a substantially lesser force than during normal operation. This safety feature is provided by flapper valves which are initially tightly seated, flapper valves which are initially not tightly seated, and flapper valves which allow some leakage even when tightly seated. In all instances, because the passage of air into the air cylinder is obstructed, the force applied to a fastener is substantially reduced in the event of an inadvertent firing of the nailer <NUM>.

Continuing with the description of normal operation of the nailer <NUM>, with the piston and flapper valve in the configuration of <FIG>, a user presses the WCE/nosepiece <NUM> (see <FIG>) against a workpiece (not shown) thereby compressing the WCE spring <NUM> as the WCE stamping <NUM> and WCE extension <NUM> move upwardly, with respect to the housing <NUM>, along the drive axis <NUM>. This movement continues until the bearing portion <NUM> of the WCE extension <NUM> contacts the lower end of the shaft <NUM> of the plunger <NUM>. At this point, additional force must be applied to provide continued upward movement of the WCE <NUM>, WCE stamping <NUM>, WCE extension <NUM>, and plunger <NUM>.

Specifically, the force required to move the WCE <NUM> is referred to as the "WCE actuation force". The WCE actuation force is a design choice which takes into account the weight of the tool and provides a safety factor to ensure the operator is actively pressing the WCE against a workpiece to prevent inadvertent firing of the nailer. In some instances the WCE actuation force is desired to be the amount of force provided by the tool (the weight of the tool at the nose of the tool) plus about <NUM>% of the total weight of the tool. Thus, for a power tool of <NUM> pounds with an even weight distribution between the nose and the rear of the tool, the force provided by the tool is about <NUM> pounds force and the additional <NUM>% requires another <NUM> pounds force for a total of <NUM> pounds force.

With respect to the nailer <NUM>, the WCE actuation force is initially established primarily by the counter force of the WCE spring <NUM> with some negligible friction forces, and is thus a function of the spring constant of the WCE spring <NUM>. Thus, the WCE actuation force is initially simply the force needed to overcome the WCE counter-force of the WCE spring <NUM>. Once the bearing portion <NUM> contacts the plunger <NUM>, however, the force of the pressurized air in the headspace <NUM> against the plunger <NUM> must also be overcome. This force is a function of the pressure in the headspace <NUM> along with the diameter of the plunger. By forming the pivot bore <NUM> as an oval as described above, frictional forces associated with the seal <NUM> and air cylinder <NUM> are significantly reduced. Moreover, because the frictional forces between the seal <NUM> and the air cylinder <NUM> are significantly reduced, moving the flapper valve <NUM> does not introduce significant torque on the plunger <NUM>, thereby minimizing friction associated with movement of the plunger <NUM>.

Therefore, since the pressure in the head valve is a design parameter which is determined based upon the force needed to drive the fastener, the main determinants of the actuation counter-force are the spring constant of the WCE spring <NUM> and the diameter of the of the plunger <NUM>.

Thus, the WCE spring <NUM> spring constant and the diameter of the plunger <NUM> can be selected to provide a desired WCE actuation force profile. In one embodiment, the spring constant and the plunger diameter are selected such that the WCE spring <NUM> and movement of the plunger <NUM> each account for about <NUM>% of the actuation counterforce as the flapper valve <NUM> moves into a firing position. In other embodiments, different actuation counter-force profiles are provided.

Continued application of the WCE actuation force moves the plunger <NUM> to a firing position as depicted in <FIG>. In the configuration of <FIG>, a continuous air path is provided between the air accumulator <NUM> and the air cylinder <NUM> through the headspace <NUM>. As shown in <FIG>, the opening defined by the fingers <NUM> is larger than the diameter of the neck portion <NUM>, allowing the flapper valve <NUM> to pivot about the pivot pin <NUM> without torqueing the plunger <NUM> and/or creating significant friction.

A sensor (not shown, typically a Hall sensor) senses the position of the WCE <NUM>, either directly or indirectly, such as by sensing the WCE stamping <NUM> or the WCE extension <NUM>, and sends a signal to the PCBA <NUM> indicating that the WCE <NUM> has been depressed sufficiently to allow for firing of the nailer <NUM>. A signal indicating depression of the trigger is also sent to the PCBA <NUM>. With the flapper valve in the firing position and the trigger depressed, the PCBA <NUM> "fires" the nailer by energizing the motor <NUM> thereby rotating the hub <NUM> in the direction of the arrow <NUM> in <FIG>. The rotation indicated by the arrow <NUM> in <FIG> corresponds to rotation in the direction of the arrows <NUM> and <NUM> in <FIG>.

As evidenced by <FIG>, as the hub <NUM> rotates, the inner wall <NUM> which is defined by the bearing element <NUM>, and which extends from the bearing element defined portion <NUM> into a bearing element receiving portion <NUM> of the receptacle <NUM>, is forced against the elastomeric pad <NUM> and thus the elastomeric pad <NUM> is forced against the inner wall <NUM> which is defined by the bearing element <NUM>, and which extends from above (as depicted in <FIG>) the bearing element defined portion <NUM>, through the bearing element defined portion <NUM>, and into the bearing element receiving portion <NUM> of the receptacle <NUM>. The motor <NUM> thus causes the lifter gear <NUM> to rotate. There is, however, no direct transfer of torque from the hub <NUM> to the lifter gear <NUM>.

Returning to <FIG>, as the lifter gear <NUM> rotates in the direction of the arrow <NUM>, the last tooth <NUM>L is forced out of engagement with the bottom roller <NUM> in the rack <NUM> allowing compressed air entrapped in the cylinder <NUM> above the piston <NUM>, as well as compressed air in the headspace <NUM> and accumulator <NUM>, to expand thereby forcing the piston <NUM> along the drive axis <NUM>. The driver <NUM> is then forced against a nail (not shown) forcing the nail into a workpiece (not shown).

Once the driver <NUM> has been fully extended, the motor <NUM> will have rotated the lifter gear <NUM> so that the first tooth <NUM>F is positioned to engage the first (top) roller as shown in <FIG>. Continued rotation of the motor <NUM> results in continued rotation of the lifter gear <NUM> resulting in the piston <NUM>, and hence the driver <NUM>, being lifted to the ready position shown in <FIG> by time the motor <NUM> effects one complete rotation of the lifter gear <NUM>.

In the event the driver <NUM> does not fully extend, resulting in the configuration of <FIG>, then the first tooth <NUM>F will engage a roller <NUM> other than the first (top) roller <NUM>. In <FIG>, the first tooth <NUM>F is shown engaging the third roller <NUM>. Continued rotation of the motor <NUM> in this scenario results in continued rotation of the lifter gear <NUM> resulting in the piston <NUM>, and hence the driver <NUM>, being lifted to the ready position before the motor <NUM> effects one complete rotation of the lifter gear <NUM>. Consequently, jam shock will occur as the motor <NUM> continues rotating the lifter gear <NUM> with the piston <NUM> at the ready position shown in <FIG>.

In particular, as the motor <NUM> continues rotating the lifter gear <NUM> with the piston <NUM> at the ready position, the teeth <NUM> are forced out of engagement with the rack <NUM>. The flapper valve <NUM> will still be in the firing position, accordingly, the air in the accumulator <NUM> is not yet isolated from the air in the cylinder <NUM>. Thus, the compressed air in the cylinder <NUM>, the headspace <NUM>, and the accumulator <NUM> will force the piston <NUM>, and hence the rack <NUM>, along the drive axis <NUM> as a following tooth <NUM> rotates into the path of a roller <NUM> of the rack <NUM>.

A portion of the force of the impact of the engagement of the tooth <NUM> with a roller <NUM> of the moving rack <NUM> is transferred to the bearing elements <NUM> of the lifter gear <NUM> and transferred to the elastomeric pads <NUM> through the contacting portions of the bearing elements <NUM> and the elastomeric pads <NUM>. The elastomeric pads <NUM> thus absorb at least a portion of the force of the impact.

In some embodiments, some of the force of the impact is further transferred from the elastomeric pads <NUM> to the bearing elements <NUM> of the hub <NUM>. Any such force is precluded from reversing the rotation of the hub <NUM>, however, by the one-way needle bearing clutch <NUM>. Thus, the planetary gearbox <NUM> is protected from the jam shock.

In any event, once the last tooth <NUM>L has engaged the lowest roller, rotation of the motor <NUM> is stopped. Upon lifting the nailer <NUM> off of the workpiece, the WCE spring <NUM> forces the WCE <NUM>, the WCE stamping <NUM>, and the WCE extension <NUM> downwardly along the drive axis <NUM> until the shoulders <NUM> of the WCE extension <NUM> contact the lower guide <NUM>.

The downward movement of the WCE extension <NUM> allows the compressed air within the headspace <NUM> to force the plunger <NUM> outwardly from the headspace <NUM> in a downward direction along the drive axis <NUM>. The plunger <NUM> continues to move along the drive axis <NUM> until the shoulder <NUM> once again contacts the insert <NUM>. As the plunger <NUM> moves downwardly, the head <NUM> contacts the fingers <NUM> and forces the flapper valve <NUM> to move from the firing position of <FIG> to the non-firing position of <FIG>. The nailer <NUM> is thus configured for a subsequent firing operation.

Claim 1:
A power tool (<NUM>), comprising:
an air spring cylinder (<NUM>);
a piston (<NUM>) movably positioned within the air spring cylinder (<NUM>);
a driver blade (<NUM>) fixedly attached to the piston (<NUM>);
a rack (<NUM>) fixedly attached to the piston (<NUM>);
a lifter gear (<NUM>) including a lifter gear wheel portion (<NUM>), and a plurality of teeth (<NUM>) extending radially from the lifter gear wheel portion (<NUM>) and configured to engage the rack (<NUM>);
a motor (<NUM>) including a motor output;
a hub (<NUM>) including a first end (<NUM>) operably connected to the motor output and a second end including a hub wheel portion;
a first receptacle (<NUM>) in one of the lifter gear (<NUM>) and the hub (<NUM>);
a first bearing element (<NUM>) extending from the other of the lifter gear (<NUM>) and the hub (<NUM>) and into the first receptacle (<NUM>); and
a first elastomeric damper (<NUM>) positioned within the first receptacle (<NUM>) between the first bearing element (<NUM>) and a bearing element defined portion (<NUM>) of the first receptacle (<NUM>).