CA 02507896 2007-05-22
COMBUSTION POWERED TOOL SUSPENSION
FOR IRON CORE FAN MOTOR
This application is a division of Canadian Patent File No. 2,357,877
filed September 26, 2001, issued June 3, 2006.
BACKGROUND OF THE INVENTION
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.
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, and U.S. Pat. Nos. 4,522,162; 4,483,473;
4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which may be referred to
CA 02507896 2001-09-26
for further details. Similar combustion powered nail and staple driving tools
are
available commercially from ITW-Paslode of Vemon Hills, Illinois under the
IMPULSE brand.
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
praduces 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 body.
A valve sleeve is axially reciprocable about the cylinder and, through a
linkage, moves to close the combustion chamber when a work contact element at
the
end of the linkage is pressed against a workpiece. This pressing action also
triggers
a fuel metering valve to introduce a specified volume of fuel into the closed
combustion chamber.
Upon the pulling of a trigger switch, which causes the 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.
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CA 02507896 2001-09-26 ~
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
t 0 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
.0 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
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A <a". CA 02507896 2001-09-26
._xe 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. At
this time,
such a motor is a conventional iron core motor, also known as permanent
magnet,
brushed DC motor of the type produced by Canon and Nidec Copal of Japan, as
well
as many other known motor manufacturers. When iron core motors were employed
as combustion tool fan motors, the conventional suspension was found to result
in an
underdampened condition, wherein the motor oscillated excessively and out of
tune
relative to the operational oscillation of the combustion tool, as described
above. In
other words, there is a mechanical impedance mismatch between the combustion
tool
and the combustion chamber fan motor. This is due in large part to the greatly
reduced
weight of the iron core motors as compared to conventional motors. The iron
core
motors weigh only about 1/3 as mucti as conventional ironless core combustion
chamber fan motors. The iron core motors are less durable, and are incapable
of
5 withstanding the degree of 50g forces or higher which are generated through
combustion.
As a result, in operation, the conventional combustion tool motor
suspensions underdampen the iron core motor. This underdampening significantly
reduces the effectiveness of the suspension, and subjects the motor to
damaging axial
~ forces. Instead, the goal is to achieve critical dampening, in which there
is just enough
dampening to receive the combustion-generated motion and prevent oscillation
past
equilibrium.
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CA 02507896 2001-09-26
One way to achieve critical dampening between the fan motor and the
combustion toot is to increase its flexibility, as by reducing the mass of the
resilient
suspension member which circumscribes and projects radially from the motor and
the
motor container to fasten those conlponents to the combustion head of the
tool. It has
been found that increasing the flexibility in this way, to a degree which will
satisfactorily suspend the iron core motor, also results in the unsatisfactory
situation
wherein the suspension member loses its resiliency and, upon the generation of
the
forces initiated by combustion, is unable to return the motor to the
designated start
position.
Another design parameter of combustion tools is that, while capacitors
are known for reducing voltage spikes and transients for brushed motors, and
it is
advantageous to place the capacitor closer to the source of the spikes and
transients,
capacitors were not able to survive the inipact forces generated in a
combustion tool
at the fan motor. Thus, such noise suppression capacitors had to be mounted in
more
remote, and less effective locations on the tool.
Thus, there is a need for a combustion tool fan motor suspension which
can accommodate an iron core motor and provide sufficient dainpeningto protect
the
motor from combustion-generated impact forces. There is also a need for a
combustion tool fan motor suspension which allows the mounting of a noise
suppression capacitor on or near the fan motor.
Accordingly, the present invention seeks to provide an
improved combustion powered tool with an improved suspension mechanism for an
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CA 02507896 2001-09-26
iron core combustion chamber fan motor, in which the suspension reduces
operationally-
induced reciprocal accelerations of the motor while keeping the oscillations
of the motor
within an acceptable range.
Another aspect of the present invention seeks to provide an improved
combustion powered tool which features a mechanism for dampening operationally-
induced
oscillation of the combustion chamber fan motor, especially when the motor is
of the iron
core type.
A further aspect of -the present invention seeks to provide an improved
combustion powered tool having a suspension which is mounted to the tool to
"float" relative
to the combustion chamber and thus dampen combustion induced vibrations.
A still further aspect of the present invention seeks to provide an improved
an
iunproved combustion powered tool having a suspension mechanism for a
combustion
chamber fan motor which increases the life of the motor.
Further still, another aspect of the present invention seeks to provide an
improved combustion powered tool having a suspension mechanism for a
combustion
chamber fan motor which can accommodate the mounting of a noise suppression
capacitor
on or near the fan motor.
BRTEF SUMMARY OF THE INVENTION
The invention in one broad aspect provides a suspension mechanism for a
motor of a combustion chamber fan in a combustion powered hand tool
constructed and
arranged for driving a driver blade to drive a fastener into a work piece, the
tool having a
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CA 02507896 2001-09-26
cylinder head and generating an upward axial acceleration of the motor or fan
upon a
combustion in the chamber, a subsequent reciprocal axial acceleration of the
motor when a
piston connected to the driver blade bottoms out on a bumper, at least one of
the
accelerations causing the motor to oscillate relative to the tool. The
suspension mechanism
comprises means for suspending the motor or fan, the suspending means
configured for
providing progressive dampening to the motor or fan upon the generation of
said axial
accelerations. The suspending means is configured for providing at least one
stop defining
an amount of axial travel of the motor relative to the cylinder head- induced
by the axial
accelerations, and wherein said progressive dampening increases as the axial
travel of the
motor or fan increases relative to the cylinder head and toward said at least
one stop.
More particularly, the present improved combustion powered fastener tool
features a mechanism for suspending a combustion chamber fan motor that
reduces the
effects of the reciprocal axial acceleration of the motor, and the resulting
oscillation of the
motor, during operation of the tool. In the preferred embodiment, the assembly
includes a
flexible rubber web vulcanized to a motor retaining ring. The web is also
vulcanized to a
cylinder head mounting bracket so that only the web secures the ring to the
bracket. In
addition, the bracket is mounted via threaded fasteners and bushings to the
cylinder head so
that it will "float" relative to the movement of the combustion chamber. To
this end, the
bracket features resilient standoffs located at the cylinder head mounting
points which provide
progressive dampening. As the motor changes position, dampening increases. As
such, the
present motor suspension mechanism provides more accurately tuned dampening to
iron core
-
fan motors than conventional suspensions. Another feature of the present motor
suspension
is that is permits the mounting of a noise suppression capacitor on the fan
motor.
7
CA 02507896 2001-09-26
More specifically, the present invention provides a suspension mechanism for
a motor of a combustion chamber fan in a combustion powered hand tool
constructed and
arranged for driving a driver blade to drive a fastener into a work piece, the
tool generating
an upward axial acceleration of the motor upon combustion in the chamber, a
subsequent
reciprocal axial acceleration of the motor when the piston bottoms out on a
bumper, at least
one of the accelerations causing the motor to oscillate relative to the tool,
the suspension
mechanism includes a suspending portion- configured for providing progressive
dampening
to the motor upon the generation of the axial accelerations.
In addition, the present invention also provides a combustion powered hand
tool constructed and arranged for driving a driver blade to drive a fastener
into a work piece.
The tool includes a combustion chamber defined in part by a cylinder head, a
combustion
chamber fan, a motor connected to said fan and a suspension mechanism for the
motor
configured for regulating the relative axial movement of the motor relative to
the cylinder
head. The suspension mechanism includes a suspending portion configured for
providing
progressive dampening to the motor upon the initiation of axial acceleration
of the cylinder
head.
8
CA 02507896 2001-09-26
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
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 generally indicated;
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 indicated;
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 generally indicated;
FIG. 7 is an overhead plan view of a circuit board configured for
mounting to the present combustion fan motor;
9
CA 02507896 2001-09-26
õ a a
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 perforrriance of an
iron core fan motor in a combustion powered hand tool equipped with the
improved
motor suspension of the present invention.
DETAILED DESCRIPTION OF THE 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 cliamber 14 dimensioned to enclose a
self-
contained internal combustion power source 16, a fuet 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
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CA 02507896 2001-09-26
protect the fan motor and spark plug. As used herein, g IowereB andaupper
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 clianiber 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
11
CA 02507896 2001-09-26
Jhe 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 insulator 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 arnlature 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 of
operation.
12
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CA 02507896 2001-09-26
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,
hovvever 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 ~i
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
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CA 02507896 2001-09-26
. adially 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 rnethods 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
14
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CA 02507896 2001-09-26
aetached 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'atso 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 ordinaiy 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.
CA 02507896 2001-09-26
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 rnounting 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 96.
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
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CA 02507896 2001-09-26
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
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CA 02507896 2001-09-26
o a
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.
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CA 02507896 2001-09-26
More specifically, the capacitor 120, which is preferably of the 1 uf 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 0-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 0-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
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CA 02507896 2001-09-26
ciie cylinder body defines a seat 148 for a bumper 150 which defines the lower
limit
of travel of the piston 144e 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
CA 02507896 2001-09-26
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 SO
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 ar-d 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
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CA 02507896 2001-09-26
a suspension incorporatdng 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 tlhe 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 9dditional 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.
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CA 02507896 2001-09-26
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
S suspension mechanism 50 decreases acceleration and also dampens oscillation
and
dynamically operates without detrimental contact within the positive
constra.ints 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
acconunodate
the severe acceleration forces generated by the too110.
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.
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