The present invention relates generally to improvements
in portable combustion powered fastener driving tools, particularly to improvements
relating to the suspension of a motor for a combustion chamber fan for decreasing
the operationally-induced axial acceleration and oscillation of the motor to decrease
wear and tear on the motor, and specifically in applications where low-cost, iron
core fan motors are employed to power the combustion chamber fan motor.
More particularly, the present invention relates to a combustion
powered hand tool constructed and arranged for driving a driver blade to drive a
fastener into a work piece, said tool comprising
- a combustion chamber defined in part by a cylindrical head ;
- a combustion chamber fan ;
- a motor connected to said fan ; and
- a suspension mechanism connected to said motor.
Portable combustion powered, or so-called IMPULSE®
brand tools for use in driving fasteners into workpieces are described in commonly
assigned patents to
Nikolich U.S. Pat. Re. No. 32,452
U.S. Pat. Nos. 4,522,162
Similar combustion powered nail and staple driving tools
are available commercially from ITW-Paslode of Vernon Hills, Illinois under the
Such tools incorporate a generally pistol-shaped tool housing
enclosing a small internal combustion engine. The engine is powered by a canister
of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power
distribution unit produces the spark for ignition, and a fan located in the combustion
chamber provides for both an efficient combustion within the chamber, and facilitates
scavenging, including the exhaust of combustion by-products. The engine includes
a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder
A valve sleeve is axially reciprocable about the cylinder
and, through a linkage, moves to close the combustion chamber when a work contact
element at the end of the linkage is pressed against a workpiece. This pressing
action also triggers a fuel metering valve to introduce a specified volume of fuel
into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the
ignition of a charge of gas in the combustion chamber of the engine, the piston
and driver blade are shot downward to impact a positioned fastener and drive it
into the workpiece. The piston then returns to its original, or "ready" position,
through differential gas pressures within the cylinder. Fasteners are fed magazine-style
into the nosepiece, where they are held in a properly positioned orientation for
receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the
combustion in the chamber causes the acceleration of the piston/driver blade assembly
and the penetration of the fastener into the workpiece if the fastener is present.
This combined downward movement causes a reactive force or recoil of the tool body.
Hence, the fan motor, which is suspended in the tool body, is subjected to an acceleration
opposite the power stroke of the piston/driver blade and fastener.
Then, within milliseconds, the momentum of the piston/driver
blade assembly is stopped by the bumper at the opposite end of the cylinder and
the tool body is accelerated toward the workpiece. Therefore, the motor and shaft
are subjected to an acceleration force which is opposite the direction of the first
acceleration. These reciprocal accelerations cause the motor to oscillate with respect
to the tool. The magnitude of the accelerations, if left unmanaged, are detrimental
to the life and reliability of the motor.
Conventional combustion powered tools of the IMPULSE®
type require specially designed motors to withstand these reciprocal accelerations
of the shaft and motor, and the resulting motor oscillations. Among other things,
the motors are preferably of the ironless core type, and are equipped with internal
shock absorbing bushings, thrust and wear surfaces, and overall heavier duty construction.
Such custom modifications result in relatively expensive motors which increase the
production cost of the tools.
Thus, there is a need for a motor suspension mechanism
for a combustion powered tool which reduces operating demands on the motor, increases
reliability of the motor, and allows the use of closer to standard production fan
motors to reduce the tool's production cost. In an ongoing attempt to reduce manufacturing
costs, it is desirable to use the lowest cost fan motor possible for this application.
Accordingly, the instant case relates to a tool according
to claim 1.
The conventional iron core motor, also known as permanent
magnet, brushed DC motor of the instant case may be of the type produced by Canon
and Nidec Copal of Japan, as well as many other known motor manufacturers.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
- FIG. 1 is a fragmentary side view of a combustion powered fastener tool in accordance
with the present invention, the tool being partially cut away and in vertical section
for purposes of clarity;
- FIG. 2 is an exploded perspective view of the cylinder head of the tool depicted
in FIG. 1, with the suspension mechanism and combustion chamber fan motor according
to the present invention;
- FIG. 2A is a section taken along the line 2A of FIG. 2 and in the direction
- FIG. 3 is a cross-section of the cylinder head and suspension mechanism of the
present invention taken along the line 3-3 of FIG. 2 and in the direction generally
- FIG. 4 is an overhead plan view of the present suspension mechanism, with portions
omitted for clarity;
- FIG. 5 is an enlarged fragmentary view of the mechanism depicted in FIG. 4;
- FIG. 6 is a cross-section taken along the line 6-6 of FIG. 4 and in the direction
- FIG. 7 is an overhead plan view of a circuit board configured for mounting to
the present combustion fan motor;
- FIG. 8 is a graph showing the operationally-induced acceleration and oscillation
of a conventionally-suspended combustion chamber iron core fan motor in a combustion
powered hand tool. The X-axis represents time in milliseconds and the Y-axis represents
accelerations in g's measured by an accelerometer; and
- FIG. 9 is a graph of the type in FIG. 8 showing the performance of an iron core
fan motor in a combustion powered hand tool equipped with the improved motor suspension
of the present invention.
Referring now to FIG. 1, a combustion powered tool of the
type suitable for use with the present invention is generally designated 10. The
tool 10 has a housing 12 including a main power source chamber 14 dimensioned to
enclose a self-contained internal combustion power source 16, a fuel cell chamber
18 generally parallel with and adjacent to the main chamber 14, and a handle portion
20 extending from one side of the fuel cell chamber and opposite the main chamber.
In addition, a fastener magazine 22 is positioned to extend
generally parallel to the handle portion 20 from an engagement point with a nosepiece
26 depending from a lower end 28 of the main chamber 14. A battery (not shown) is
provided for providing electrical power to the tool 10, and is releasably housed
in a compartment (not shown) located on the opposite side of the housing 12 from
the fastener magazine 22. Opposite the lower end 28 of the main chamber is an upper
end 30. A cap 32 covers the upper end 30 and is releasably fastened to the housing
12 to protect the fan motor and spark plug. As used herein, "lower" and "upper"
are used to refer to the tool 10 in its operational orientation as depicted in FIG.
1; however it will be understood that this invention may be used in a variety of
orientations depending on the application.
A mechanically linked fuel metering valve (not shown),
such as that shown in
U.S. Patent No. 4,483,474
may be used. Alternatively, an electromagnetic, solenoid type fuel metering
valve (not shown) or an injector valve of the type described in commonly assigned
U.S. Patent No. 5,263,439
is provided to introduce fuel into the combustion chamber as is known
in the art. A pressurized liquid hydrocarbon fuel, such as MAPP, is contained within
a fuel cell located in the fuel cell chamber 18 and pressurized by a propellant
as is known in the art.
Referring now to FIGs. 1, 2, and 3, a cylinder head 34,
disposed at the upper end 30 of the main chamber 14, defines an upper end of a combustion
chamber 36, and provides a spark plug port (not shown) for a spark plug 38 (FIG.
4 only), an electric fan motor 40, and a sealing 0-ring 41. In the present invention,
the fan motor 40 is a conventional iron core motor, also known as permanent magnet,
brushed DC motor of the type produced by Nidec Copal of Tokyo, Japan, Canon of Japan,
as well as many other known motor manufacturers. The motor 40 has an armature shaft
end 42 with an armature (not shown); an armature shaft 43, and at least one mounting
aperture 44, which may be threaded depending on the application.
Referring to FIGs. 2, 2A and 3, the motor 40 includes a
brush end 45 opposite the armature shaft end 42. As is known in the art, the armature
shaft 43 (and the armature, not shown) is supported in the motor by bearings. A
bearing 46 at the brush end 45, and similarly at the armature shaft end 42, axially
supports the armature shaft 43 and the armature. A feature of the present motor
40 is that the bearing 46 has a flange 47 which is located inside a motor housing
48, rather than outside, as in many conventional motors. This disposition of the
bearing 46 and the flange 47 has been found to prevent unwanted unseating of conventional
bushings after exposure to repeated reciprocal forces of the type generated by combustion
tools and described above. Aside from the modifications recited above, a conventional
iron core motor is preferably beefed up to better withstand the challenging environment
of a combustion tool. For example, the commutator is preferably provided with plastic
tabs to prevent it from rotating relative to the armature shaft 43, additional adhesive
is applied to the commutator to increase axial and rotational load capacities and
the wire ends of the armature windings are wrapped around the insulalor additional
times to prevent their unwinding.
The fan motor 40 is slidingly suspended by a fan motor
suspension mechanism, generally designated 50, within a depending cavity 52 in the
center of the cylinder head 34 to allow for some longitudinal movement of the motor.
As is best seen in FIG. 3, the motor 40 is preferably retained in the cavity 52
so that an air gap 54 is created between the lower or armature shaft end 42 of the
motor (enclosed by a protective cap as will be described below) and a floor 56 of
the cavity 52. The function of the air gap 54 is to provide operating dynamic clearance,
i.e., to provide clearance for the motor during oscillations occurring in the course
Referring now to FIGS. 2, 3 and 6, in a preferred embodiment,
the mechanism 50 includes a rigid, circular motor retaining cup 58 having an outer
annular lip 59, a generally cylindrical sidewall 60 and a floor 62. In the preferred
embodiment, the motor retaining cup 58 is made by drawing a flat disk of sheet metal
or equivalent material, and is dimensioned to circumscribe and enclose the motor
40, however it can be appreciated that other shapes for the cup 58 may be used in
tools having different combustion chamber head shapes. An advantage of this structure
of the cup 58 is that it provides a heat and dirt barrier for protecting the motor
40. Further, the cup 58 provides the attachment point for the motor 40, since the
floor 62 is provided with a central armature shaft aperture 64 (FIG. 6.) for accommodating
the armature shaft 43, and apertures 65 through which fasteners 66 secure the armature
shaft end 42 to the floor 62.
Thus, a feature of the present suspension 50 is that the
motor 40 is secured to the cup 58 only at the armature shaft end 42. Yet another
feature of the motor retaining cup 58 is that once the motor 40 is secured thereto,
it serves as a linear bearing journal for axial movement of the motor relative to
the cavity 52 in the cylinder head 34.
The suspension mechanism 50 also includes a mounting bracket
68 which is secured to the cylinder head 34 with a plurality of, and preferably
three openings 70 through which are passed threaded fasteners 71. As best seen in
FIGs. 3 and 6, the bracket 68 includes an inner radiused shoulder 72 and a depending
sidewall 74. The shoulder 72 and the sidewall 74 of the bracket 68 are concentric
with, and radially spaced from, a radial lip 76 of the motor retaining cup 58. In
the preferred embodiment, the motor retaining cup 58 is provided with a resilient
"C"-shaped bumper 75 (FIG. 4) vulcanized or bonded to the outer annular lip 59 of
the cup 58. The bumper 75 prevents the motor retaining cup 58 from contacting a
circuit board 116 if the tool is dropped.
Between and integrally secured to the depending sidewall
74 and the radial lip 76 is a resilient web 78 having an inner portion 80 secured
to the sidewall lip 76, a middle portion 82, and an outer portion 84 secured to
the sidewall 74 (best seen in FIG. 6). In the preferred embodiment, the web 78 is
a neoprene rubber with a durometer of 25-30 hardness which is vulcanized both to
the cup 58 and the bracket 68. However, it is contemplated that other materials
and bonding methods as are known in the art will provide the necessary adhesion
and flexibility properties similar to those of rubber.
As best shown in FIG. 6, the web 78 is secured to the sidewall
74 and the lip 76 such that an upper surface 86 of the web forms an annular dish-like
groove or recessed area. It will be seen that the web 78 is the only structure provided
for securing the head mounting bracket 68 to the motor retaining cup 58. Also, in
the preferred embodiment, the upper surface 86 preferably has a plurality of equidistantly
spaced, descending bores 88 extending at least partially through the middle portion
82. In the preferred embodiment, the bores 88 are blind, in that they do not extend
entirely through the middle portion 82. This construction is preferred as a manufacturing
technique to prevent rubber flashings created by molding throughbores from becoming
detached from the web 78 and falling into the engine. A lower surface 90 of the
web 78 has an annular groove 92 which is configured such that the groove does not
communicate with the bores 88. As shown in FIG. 4, the web 78 and a part of the
mounting bracket 68 are interrupted, and do not form complete circles, to allow
for a space for installing the spark plug 38.
The web 78 provides a shock absorbing and isolating system
to minimize the operational dynamics of the main chamber 14 caused by the combustion
on the motor and also to protect the motor from axial acceleration and large oscillations.
Although the preferred embodiment includes the bores 88 in the upper surface 86
and the annular groove 92 in the lower surface 90, it is contemplated that the bores
and the groove could be in either surface 86, 90, and that the depth of the groove
92 may vary. The depth and orientation of the bores 88 may vary with the application.
For example, a second set of bores may also be provided to the web 78 so that they
open toward the lower surface 90. Also, the depth of the groove 92 may vary with
the application. Further, it is contemplated that several other patterns or other
durometers for the rubber for the web 78 would provide similar shock absorbing characteristics.
Therefore, the bores 88, and the groove 92 do not necessarily need to be present,
and if present, do not necessarily need to be round, nor the grooves or recessed
areas 86, 92 annular, nor do all of the bores need to be in the upper surface 86
characterized by rounded corners to prevent tearing. It is contemplated that one
of ordinary skill in the art will be able to vary the number, spacing, disposition
and/or configuration of the bores 88 and/or the groove 92 to suit a particular application.
Referring now to FIGs. 4-6, an important feature of the
present suspension mechanism 50 is that it provides progressive dampening to the
motor 40 upon the generation of impact forces by combustion in the tool 10. In the
present application, "progressive dampening" means that the suspension mechanism
50 provides increased energy absorption as the motor 40 moves axially relative to
the cylinder head 34. This progressive dampening reduces operationally-induced acceleration
and oscillation of the motor 40 and allows the use of more conventional motors to
drive the fan.
One aspect of the present suspension mechanism 50 which
provides this advantage is that the mounting bracket 68 is partially de-coupled
relative to the cylinder head 34. Rather than being rigidly secured to the cylinder
head 34, the mounting bracket 68 is fastened to the cylinder head with a plurality
(preferably three) of the threaded fasteners 71 and plurality of bushings described
below, but is retained in an axially spaced relationship relative to the cylinder
head by a like plurality of resilient spacer members 94 at each attachment point.
Each of the spacer members 94 has a base 96 which, in the preferred embodiment is
generally circular, however other shapes are contemplated. A central aperture 98
is provided for accommodating the bushing and the fastener 71. In addition, each
spacer member 94 has a plurality, and preferably three, peripherally spaced rubber
or otherwise resilient standoffs 100 projecting generally axially from the base
When viewed from the side, the rubber standoffs 100 are
tapered and form a generally pointed upper end or tip 102 as they extend from a
lower end 104 adjoining the base 96. It is this tapered or triangular configuration
which provides the progressive dampening. It is also contemplated that the number
and precise configuration of the standoffs 100 may vary to suit the application.
It should be noted that the spacer members 94 are preferably made of the same rubber-like
material which forms the resilient web 78, and are preferably vulcanized to the
mounting bracket 68 when the web 78 is formed.
Referring now to FIGs. 2 and 6, the upward travel of the
mounting bracket 68 and the spacer members 94 is restrained by a rigid mounting
bushing 106 associated with each spacer member. Each of the mounting bushings 106
is configured for matingly engaging the resilient spacer member 94 and has a radially
projecting lip 108 for providing a stop to axial movement of the head mounting bracket
68. The lip 108 is provided with a diameter sufficient to engage the standoffs 100.
In addition, the bushings 106 engage the cylinder head 34 at their lower ends, and
are provided with a sufficient axial length to accommodate vertical travel of the
mounting bracket 68 during operation. At their upper ends 110, the bushings 106
have a nipple 112 dimensioned to matingly engage a corresponding opening 114 in
a circuit board 116 (FIG. 6). At each attachment point, once the fastener 71, with
the assistance of a lockwasher 118, secures the circuit board 116 and the bushing
106 to the cylinder head 34, the mounting bracket 68, and the suspension 50, actually
"float", or are movable independently of, and relative to the cylinder head.
Due to the construction of the standoffs 100, when operational
forces cause the suspension 50 to move upward relative to the cylinder head 34,
the standoffs 100 compress, and their tapered configuration provides progressively
more dampening with increased axial movement of the mounting bracket 68. Accordingly,
with more axial travel of the mounting bracket 68, there will be more energy absorbed
by the resilient spacer members 94 to decelerate the motor 40. The dampening is
limited by the radial lip 108 and the circuit board 116. If necessary, additional
energy is absorbed by the resilient web 78, which allows the motor retaining cup
58 to move relative to the mounting bracket 68.
Referring now to FIGs. 2 and 7, another feature of the
present tool 10 is that the increased effectiveness of the suspension mechanism
50 allows for the mounting of a noise suppression capacitor 120 directly upon the
motor 40. As indicated above, noise suppression capacitors are known for the purpose
of reducing voltage spikes and transients. In conventional combustion tools of the
type sold under the IMPULSE® brand, the relatively heavy duty ironless core
motors did not generate voltage spikes to the extent where a noise suppression capacitor
was needed. However, the present tool 10 employs the typically lighter duty iron
core motors 40 with which such suppression is advisable, especially to protect the
electronic control unit (ECU) which generates the signal for the spark plug 38.
By the same token, these types of capacitors cannot normally survive the significant
"g" forces generated in a combustion tool. Thus, the present suspension mechanism
50 provides another benefit in that the capacitor 120 can be mounted directly on
the motor 40, for increased suppressive qualities.
More specifically, the capacitor 120, which is preferably
of the luf size, although other sizes are contemplated depending on the application,
is connected to a circuit board 122 having a conventional noise suppression circuit
124, as is known in the art. The circuit board 122 and the capacitor 120 are mounted
adjacent the brush end 45 of the motor 40. To withstand the impacts experienced
by the motor 40, the circuit board 122 is secured by chemical adhesive to the brush
end 45 of the motor, in addition to solder points 126. A protective cap 128 covers
the circuit board 122 and snapingly engages the edge of circuit board 122.
Referring now to FIG. 1, the generally cylindrical combustion
chamber 36 opens and closes by sliding motion valve member 130 which is moved within
the main chamber 14 by a workpiece contacting element 132 on the nosepiece 26 using
a linkage in a known manner. The valve member 130 serves as a gas control device
in the combustion chamber 36, and sidewalls of the combustion chamber are defined
by the valve member 130, the upper end of which sealingly engages an O-ring 41 to
seal the upper end of the combustion chamber. A lower portion 136 of the valve member
130 circumscribes a generally cylindrical cylinder body or cylinder 138. An upper
end of the cylinder body 138 is provided with an exterior O-ring (not shown) which
engages a corresponding portion of the valve member 130 to seal a lower end of the
combustion chamber 36.
Within the cylinder body 138 is a reciprocally disposed
piston 144 to which is attached a rigid, elongate driver blade 146 used to drive
fasteners (not shown), suitably positioned in the nosepiece 26, into a workpiece
(not shown). A lower end of the cylinder body defines a seat 148 for a bumper 150
which defines the lower limit of travel of the piston 144. At the opposite end of
the cylinder body 138, a piston stop retaining ring 152 is affixed to limit the
upward travel of the piston 144.
Located in the handle portion 20 of the housing 12 are
the controls for operating the tool 10. A trigger switch assembly 154 includes a
trigger switch 156, a trigger 158 and a biased trigger return member 160. The ECU
162 under the control of the trigger switch 156 activates the spark plug 38.
As the trigger 158 is pulled, a signal is generated from
the ECU 160 to cause a discharge at the spark gap of the spark plug 38, which ignites
the fuel which has been injected into the combustion chamber 36 and vaporized or
fragmented by a fan 164. The fan 164 is driven by the armature shaft 43, and is
located within the combustion chamber 36 to enhance the combustion process and to
facilitate cooling and scavenging. The fan motor 40 is preferably controlled by
a head switch and/or the trigger switch 156, as disclosed in more detail in the
prior patents incorporated by reference.
The ignition forces the piston 144 and the driver blade
146 down the cylinder body 138, until the driver blade contacts a fastener and drives
it into the substrate as is well known in the art. The piston then returns to its
original, or "ready" position through differential gas pressures within the cylinder,
which are maintained in part by the sealed condition of the combustion chamber 36.
The fan motor 40 experiences two primary accelerations
during this cycle. First, when the ignition of combustible gases in the chamber
36 forces the piston 144 downwardly toward the workpiece, and preferably a fastener
into the workpiece, the tool 10 experiences an opposing upward force, or a recoil
force, in the opposite direction. The fan motor 40, which is suspended by the mechanism
50 in the tool, is accelerated upwardly in the direction of the recoil of the tool
by a force transmitted through the suspension mechanism. Further, the armature shaft
43 is accelerated in the same direction by having constrained movement relative
to the motor within limits of axial play. Then, in less than approximately: 10 milliseconds,
the piston 144 bottoms-out in the cylinder 138 against the bumper 150. This action
changes the acceleration of the tool 10 towards the workpiece. Therefore, the motor
and shaft are now accelerated in this new, opposite direction.
These reciprocal accelerations are repeatable and the suspension
mechanism 50 must be tuned so that the motor does not oscillate excessively with
respect to the tool and either bottom out or top out as discussed earlier. By "tuned"
it is meant that the resilience of the suspension mechanism is adjusted to prevent
a particular motor from excessive oscillation within predetermined, application-specific
limits, depending on the combustion-induced force generated by the particular power
source 16. The present tuned suspension mechanism 50 anticipates the two opposite
accelerations separated by a predetermined fairly repeatable time and resiliently
constrains the motor within the bounds of the cap and the floor of the cavity to
minimize the acceleration force of "g's" witnessed by the motor.
FIGs. 8 and 9 show the acceleration and oscillation experienced
by the motor during operation of the tool. The results shown in FIG. 8 are from
a tool having a suspension incorporating the resilient web 78 disposed between the
cup 58 and the bracket 68, and incorporating an iron core motor 40, which is lighter
than the motor for which the suspension was designed. As shown, at about 4 milliseconds
after ignition (which occurs at about the 5 millisecond point on the graph), shown
at 170, the motor experienced an acceleration force of about or 40g from
the acceleration of the tool due to the recoil force which was immediately transmitted
to the motor through the suspension mechanism. At about 9 milliseconds after ignition,
shown at 172, the motor experienced an acceleration in the opposite direction of
about 135g following when the piston 144 bottomed-out in the cylinder 138
which was again transmitted to the motor. Thereafter, the motor experienced an oscillation
of approximately two additional accelerations greater, labeled as 174 (40g's)
and 176 (25g's) caused by its lack of tuning of the suspension mechanism.
Note that this suspension did not have the present "floating" mounting bracket 68
and the standoffs 100.
FIG. 9 shows the acceleration and oscillation experienced
by the motor 40 in a tool 10 equipped with the present improved fan motor suspension
mechanism 50. After ignition, the first acceleration 170 of the motor 40 was about
30g and the reciprocal acceleration 172 was only about 35g. Thereafter,
the motor 40 experienced no additional accelerations above 30g's. The "floating"
progressive dampening provided by the present suspension mechanism 50 causes less
immediately transmitted acceleration, while also not allowing excessive amplitude
of oscillation so there is no bottoming out or topping out.
The result of the present invention is that the improved
fan motor suspension mechanism 50 not only decreases acceleration of the motor 40,
but also decreases the overall travel or displacement of the motor and the amount
of oscillation of the motor. As shown in FIGs. 8 and 9, due to proper tuning, the
improved motor suspension mechanism 50 decreases acceleration and also dampens oscillation
and dynamically operates without detrimental contact within the positive constraints
of the tool 10 (bottoming or topping out). A major benefit of this discovery is
that the motor 40 may be of the inexpensive, lightweight iron core type and may
still accommodate the severe acceleration forces generated by the tool 10.
While a particular embodiment of the combustion tool suspension
for iron core fan motor of the invention 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 invention in its broader aspects and as set forth
in the following claims.