Note: Descriptions are shown in the official language in which they were submitted.
CA 02531835 2002-04-29
VARIABLE VOLUME VALVE FOR
A COMBUSTION POWERED TOOL
This application is a divisional application of Canadian Patent File
No. 2,383,904 filed April 29, 2002.
BACKGROUND OF THE INVENTION
The present invention relates to a constant volume valve for a
combustion-powered tool, such as a power framing tool. More specifically, it
relates
to a constant volume valve assembly that measures a volume of a fluid before
allowing it to flow into a combustion chamber.
This invention also relates to a pneumatically powered, combustion-
powered, or other rapidly acting, fastener-driving tool of a type utilizing
collated
fasteners. Typically, as exemplified in Nikolich U.S. Pat. Re. 32,452,
Nikolich U.S.
Pat. No. 4,522,162; Nikolich U.S. Pat. No. 4,483,474; Nikolich U.S. Pat. No.
4,403,722 and Wagdy U.S. Pat. No. 4,483,473, which may be referred to for
further
details, a combustion-powered, fastener-driving tool comprises a combustion
chamber, which is defined by a cylinder body and by a valve sleeve arranged
for
opening and closing the combustion chamber. Generally, similar combustion-
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CA 02531835 2002-04-29
powered, nail- and staple- driving tools are available commercially from ITW-
Paslode (a unit of Illinois Tool Works Inc.) of Vernon Hills, IL,, under its
IMPULSE trademark.
In such a tool, it is beneficial to apply a constant force during the
driving stroke to each fastener as it is driven into the workpiece.
Measurement of
the amount of fuel to the combustion-powered tool, or the amount of compressed
gas to a pneumatically powered tool, helps provide a constant force. A
combustion powered fastening tool is described in U. S. Patent No. 4,721,240
to
Cotta that measures fuel by opening a valve for a length of time defined by
movement of a cam. Fuel passes through a fuel valve to a combustion chamber
conduit, the amount of which is equal to the volume that passes through a
needle
valve during the time the fuel valve is open. Measurement of the flow of a
fluid
by time allows the amount of fluid supplied to the tool to vary as flow rates
of the
fluid change. As a fuel cylinder is emptied, the flow rate of the fluid
changes as
the cylinder pressure drops. Similarly, pressure or flow variations in a
common
supply of pneumatic fluid will also result in differences in the amount of
power
supplied on each charge of the cylinder.
Control of fuel into a combustion chamber by valve assemblies is
shown in U. S. Patent Nos. 655,996 and 1,293,858. Both references disclose a
pressurized fluid inlet valve and fluid outlet valve that bracket a machine-
supply
passage. High-pressure fluid is fed to a machine to supply power via the inlet
valve, and is discharged through the outlet valve when it returns from the
machine
following expulsion of its power. Neitherireference teaches the use of such a
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CA 02531835 2002-04-29
system to supply a constant measurement of fluid. Further, following
combustion
of a fuel or expansion of a high-pressure fluid, the fluid is no longer useful
to
supply power to a tool and measurement at that point is ineffective.
U. S. Patent No. 4,913,331 to Utsumi describes an apparatus that
drives a piston with an internal combustion engine that utilizes a measuring
chamber to dispense a constant volume of fuel. A fuel piston containing the
measuring chamber is reciprocally moveable within a fuel cylinder. The fuel
inlet
channel and the fuel outlet channel are positioned such that the measuring
chamber is filled and emptied by movement of the piston between the inlet and
outlet channels. Seals are located on either side of the chamber between the
fuel
piston and the cylinder, preventing leakage of fuel from the pressurized fuel
supply to the combustion chamber. Steady movement of the piston would cause
rapid wear on these seals, since they are constantly in contact with the
cylinder
surface.
One operational drawback of conventional combustion-powered
tools, is that when operated at relatively low temperatures, such as below 32
°F ,
the pressure of the pressurized fuel falls, causing a greater pressure
differential
between the atmosphere and'the fuel. At this lower pressure, the fuel does not
dissipate as rapidly through the appropriate passageways and into the
combustion
chamber. This condition causes a delay in the combustion, which interferes
with
the operational efficiency of the tool.
Another operational drawback of conventional combustion powered
tools, is that when operated at relatively higher elevations or altitudes,
there is less
air for combustion. As a result, when used at such higher elevations,
conventional
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CA 02531835 2002-04-29
combustion-powered tools with constant volume fuel metering valves can have
overly
rich fuel/air mixtures in their combustion chambers, which can lead to fouling
of the
ignition system as well as other operational difficulties. As such, there is a
need for
a combustion-powered tool with a fuel metering valve which has the capability
of
adjusting the amount of fuel in the combustible fuel/air mixture.
Accordingly, this invention seeks to provide an improved constant
volume measurement of a fluid to an apparatus, such as a combustion-powered
tool,
to produce a constant driving force.
Further, this invention seeks to provide an improved constant volume
measurement of fluid in a compact space.
Further still, this invention seeks to provide an improved constant
volume valve assembly, whose seals are not constantly wearing against a
sealing
surface.
Still further, the present invention seeks to provide an improved
constant volume valve assembly that facilitates the movement of fuel even when
fuel
pressure drops, such as when the tool is exposed to low temperatures.
Yet further, the present invention seeks to provide an improved constant
volume valve assembly that provides the capability of adjusting the fuel
mixture, such
as when the tool is operated at relatively high elevations.
SUMMARY OF THE INVENTION
These and other aspects are met or exceeded by the present device for
metering a constant volume of fluid to provide constant energy to a tool. This
apparatus is most useful in a portable fastening tool powered either
pneumatically
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CA 02531835 2002-04-29
or by an internal combustion engine. In the preferred embodiment,
configuration of
the valves and control mechanism also provides a delay between the closing of
one
valve and the opening of another, ensuring that fluid is metered before moving
downstream to the combustion chamber.
More particularly, in one aspect the invention provides a constant
volume metering chamber and valve assembly for use with a pressurized fluid
supply
containing a fluid in a combustion-powered tool, the assembly comprising a
housing
defining a metering chamber having a plurality of ports including an inlet and
an
outlet, a first spring-biased valve disposed in the housing to control fluid
flow through
the inlet, and a second spring-biased valve disposed in the housing to control
fluid
flow through the outlet. An actuator assembly is connected to the first and
second
spring-biased valves and is sequentially operable from a first position, in
which the
first spring-biased valve is open and the second spring-biased valve is
closed, to a
second position, in which the first and second spring-biased valves are both
closed,
and a third position, in which the first spring-biased valve is closed and the
second
spring-biased valve is open. The valve assembly is configured and arranged so
that
a volume of fluid entering the chamber from the inlet in the first position is
collected
in the metering chamber, sealed within the metering chamber in the second
position,
and released from the metering chamber in the third position to provide a
constant
volume of fluid for each sequential movement of the actuator from the first
position
to the third position.
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CA 02531835 2002-04-29
Further, the present invention provides a variable volume metering
chamber and valve assembly for a combustion-powered tool includes a housing
defining a metering chamber having an internal volume and including an inlet
and an
outlet, and a plunger configured for reciprocal movement relative to the
chamber for
adjusting the internal volume of the metering chamber. The plunger is
preferably
adjustable by the user to alter the volume of fuel retained in the metering
chamber.
In the housing, a first valve controls control fluid flow through the inlet, a
second
valve controls fluid flow through the outlet, and an actuator assembly,
connected to
the valves, is sequentially operable from a first position, in which the first
valve is
open and the second valve is closed, to a second position, in which the first
and
second valves are both closed, and a third position, in which the first valve
is closed
and the second valve is open.
The present metering valve also produces a constant driving force by
a fastener-driving tool because it provides a consistent quantity and quality
of fuel or
hydraulic fluid each time the tool is fired. The fluid supply to the power
tool of this
invention is measured by volume, not by time, providing a more accurate and
more
consistent supply of power to the tool. As pressure varies, the fluid density
changes
in either system because the molecules become more or less densely packed.
However, in a flow system, flow rates will also change if the pressure
SA
CA 02531835 2002-04-29
drop across the metering valve fluctuates. Change in flow rate will have no
effect
in a constant volume system as long as the constant volume chamber is filled
in the
time the inlet valve to the metering chamber is open.
Further, arrangement of the metering chamber and the spring-biased
valves in the present invention leads to compact use of space, as would be
useful
in a compact, portable tool. Collinear placement of the valves and the oblique
angle of the combustion chamber passageway features a shorter distance from
the
pressurized fluid supply to the combustion chamber, compared to other designs.
Using spring-biased valves to control fluid flow is also
advantageous. The seat of the valve that forms the seal with the inlet and
outlet of
the metering chamber is in contact with the walls of the chamber only for a
relatively short time. As the valves open and close, there is no
constantrubbing of
the seals with adjacent walls. This leads to longer life for the seals.
Another advantage of the present valve assembly is that a disk is
preferably provided to at least one of the spring-biased valves which
facilitates the
flow of fuel into a combustion chamber passageway even in operational
conditions
when fuel flow is impaired, as when outside operational temperatures fall
below
freeing.
Still another feature of the present valve assembly is that the actuator
assembly is configured to provide an inherent delay in the operation of the
upper
and lower spring-biased valves to ensure that a designated volume of fuel will
be
retained in the metering chamber before the lower valve releases the fuel to
the
combustion chamber. In the preferred embodiment, this delay is achieved in
part
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CA 02531835 2002-04-29
by a deliberately loose mating engagement between a tongue of an actuator
pivoting link arm and a notch in an actuator control arm. 'This loose
engagement
ensures that, while the pivoting link arm travels a continuous motion due to
the
engagement of the tool upon a workpiece, the actuator control arm is not
continuously moved, resulting in a slight "pause" in the operation of the
spring-
biased valves. In this manner, the consistency of the volume of fuel
temporarily
held in the metering chamber is maintained.
Yet another feature of the present valve assembly is that the valve
features an adjustment for changing the amount of fuel passed to the
combustion
chamber in each firing cycle. This is accomplished in the preferred embodiment
by providing an adjustable shaft which can be threadably advanced by the user
into the fuel metering chamber to reduce the volume of the chamber, and thus
reduce the space available for incoming fuel. Thus, as more fuel or a richer
mixture is desired, the shaft is backed off away from the fuel metering
chamber to
increase the chamber volume. A leaner fuel mixture is obtained by advancing
the
shaft into the fuel metering chamber.
A still further feature of the present valve assembly is that the
adjustable shaft described above can be replaced by an electric heating
element for
use when the tool is used in colder conditions of the type which induce lower
fuel
pressure. The heating element heats either the fuel metering chamber itself or
the
surrounding portion of the valve housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a back view of the present constant volume valve assembly
as attached to a fuel canister;
CA 02531835 2002-04-29
FIG. 2 is a front vertical sectional view of the present constant
volume valve assembly;
FIGS. 3A-3C are a series of fragmentary sectional views of the
present constant volume valve assembly depicting three valve positions as the
actuator assembly moves through an operational sequence;
FIG. 4 is a fragmentary sectional view of the present ~~constant
volume valve shown equipped with a disk for facilitating the movement of fuel
from the metering chamber into the combustion chamber;
FIG. 5 is a fragmentary sectional view of an alternate embodiment of
the present constant volume valve showing the sealing connection between the
valve and the interior nozzle of a pressurized fuel cartridge;
FIG. 6 is a partial cross-section taken along the line 6-6 of FIG. 4
and in the direction indicated generally, and depicts an alternate embodiment
of
the present valve assembly; and
1 S FIG. 7 is an alternate embodiment of the valve assembly depicted
in FIG. 6, in which the metering adjustment shaft is replaced with a heating
element.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2, a constant volume valve assembly and
metering chamber is, generally designated 10. In the following description,
the
terms "upper" and "lower" refer to the assembly in the orientation shown in
the
drawings. However, it is contemplated that the present assembly may be used in
a
variety of positions as is well known in the art. The present valve assembly
10 is
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CA 02531835 2002-04-29
particularly useful in a pneumatic or combustion powered tool (not shown),
having
a valve housing 12 in which the fluid to be metered is injected under
pressure.
The valve assembly 10 provides a fixed amount of fuel to the combustion
chamber
(not shown) of the tool. Alternatively, it is contemplated that the present
valve
assembly 10 may also meter pressurized air, which expands to provide power, to
the pneumatic tool. The present valve assembly 10 is usable in any tool or
device
that would benefit from a steady, uniform supply of a pressurized fluid.
The housing 12 of the valve assembly 10 includes at least two
spring-biased valves, a first spring-biased valve 16 and a second spring-
biased
valve 18 that respectively control the fluid flow to an inlet 20 and an outlet
22 of a
metering chamber 24. The metering chamber 24 is defined by the housing 12, and
optionally has one or more ports in addition to the inlet 20 and outlet 22, as
will be
discussed below. Neither the shape of the metering chamber 24, nor the
position
of the inlet 20 or outlet 22 is particularly important. However, it is
preferable to
place the inlet 20 and the outlet 22 at diametrically opposed ends of the
metering
chamber 24. In this configuration, the spring-biased valves 16, 18 are
preferably
approximately axially collinear, conserving space. In this preferred
configuration,
fluid flow through the metering chamber 24 will flow from the inlet 20 to the
outlet 22, generally parallel to the axes of the spring-biased valves 16, 18.
The metering chamber 24 may be any type of chamber capable of
providing a constant volume space for measurement of the fluid, meaning that
the
volume of fluid collected in the metering chamber is equal to the volume of
fluid
released from the metering chamber. While the fluid is sealed within the
metering
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CA 02531835 2002-04-29
chamber 24, the pressure remains constant. The metering chamber 24 may be a
separate vessel or it may simply be a cavity 24 within the housing 12. The
housing 12 will generally also be used to support other components of the
propulsion system, such as a pressurized fluid canister 28 (shown in F1G. 1)
and
the spring-biased valves 16, 18. Preferably, the metering chamber 24 is
stationary
relative to the housing 12.
The volume of the metering chamber 24 while preferably fixed, is
optionally adjustable by, for example, placement of a movable wall or opening
of
valves to additional chambers (not shown). However, its usefulness for
metering
purposes depends upon the ability of the chamber 24 to remain at a constant
volume until some setting, valve or adjustment is purposely changed.
The spring-biased valves 16, 18 each include a preferably conical
seat 30, 32, a rod 34, 36, and a spring 38, 40, respectively. Although
discussed in
terms of the first spring-biased valve 16, it is to be understood that the
following
1 S description also applies to the corresponding parts of the second spring-
biased
valve 18. The seat 30 is sized and configured to sealingly engagewith the
in1et20
of the metering chamber 24 when the spring-biased valve 16 is in a closed
position. Movement of the seat 30 between an open position and the closed
position, is controlled by the rod 34. Although the spring 38 is an economical
method of biasing the valve, use of other biasing devices is contemplated. The
spring 38 is used to bias the valve 16 toward the closed position. Each of the
springs 38, 40 has an anchored end 42, 44 end a movable end 46, 48,
respectively.
The movable end 46 exerts a force against the seat 30 tending to move it in
the
CA 02531835 2002-04-29
direction of the metering chamber 24 by the force of the spring 40 pushing
against
the anchored end 42. Although the anchored end 42 may be anchored directly to
the housing 12, preferably, the anchored end is seated within a compartment
described in greater detail below.
Fluid is supplied to the housing 12 under pressure. It is generally
desirable that the tool is portable, and in such a case, the fluid is
delivered from
the pressurized canister 28 that fits within or attaches to the tool. In the
case
where the tool is to be used in a shop or other location where a large supply
of
pressurized fluid is available, the fluid is preferably available to the tool
through a
hose or similar device (not shown). The valve assembly 10 of the present
invention is useful in either of these situations, and use in either setting
is
contemplated. Since temperature and pressure affects the density of any fluid,
these factors should be kept as constant as possible to minimize variation in
the
amount of fluid supplied.
Before entering the valve assembly 10, the fluid preferably flows
through a filter 50 (FIG. 2) to minimize unwanted contaminants. The filter 50
is
preferably disposed at one end of a nipple 51, which matingly and sealingly
engages the canister 28. After passing the filter 50, the fuel travels into an
upper
passageway 52. The upper passageway 52 leads from the source of the
pressurized fluid, such as the pressurized canister 28, to the inlet 2Q of the
metering chamber 24. To achieve the most consistent amount of fluid, the upper
passageway 52 is preferably sufficiently wide to consistently achieve supply
pressure before closure of the first spring-biased valve 16.
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CA 02531835 2002-04-29
In some cases, it is desirable to provide an upper chamber 54 for
accumulation of pressurized fluid. Where, for example, the flow rate of the
fluid is
low, fluid accumulates in the upper chamber 54, providing a burst of fluid to
enter the
metering chamber 24 when the inlet 20 is opened. Fluid released from the
metering
chamber 24 flows into a lower chamber 56. Metering is accomplished through
opening and closing of the first and second spring-biased valves 16, 18 by an
actuator
assembly 60. The actuator assembly 60 is any mechanism capable of causing the
opening and closing of the first and second spring-biased valves 16, 18 in a
particular
sequence to allow measurement of the fluid in the metering chamber 24. While a
mechanical linkage is the preferred form of the actuator assembly 60, a
computer
controlling one or more cams is an example of an acceptable alternative
configuration.
In the preferred embodiment, the actuator assembly 60 includes a C-
shaped actuator arm with an upper arm 62, which is connected to the rod 34 of
the
first spring-biased valve 16, and a lower arm 64, which is connected to the
rod 36 of
the second spring-biased valve 18. The upper arm 62 and the lower arm 64 are
connected to each other by a control arm 66 (FIG. 1). A notch 67 in the
control arm
66 is engaged by a pivoting link arm 68 which is pivotally engaged to the
housing 12
at a point 68a. The specific engagement between the link arm 68 and the notch
67
is via a tongue 69. The control link arm 68 is operated through movement of
the
nosepiece valve linkage (not shown), the construction and operation of which
is
disclosed in the above referred to Nikolich patents.
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CA 02531835 2002-04-29
An important feature of the present actuator assembly 60 is that a
delay is created in the movement of the control arms 62, 64, 66 and their
actuation
of the upper and lower spring-biased valves 16, 18 so that a constant volume
of
pressurized fluid is momentarily retained in the metering chamber 24. This
delay
is created in part by a loose mating engagement between the tongue 69 and the
notch 67. In the preferred embodiment, the tongue 69 is provided with a
reduced
area compared to the notch 67, so that the control link arm 68 can move
slightly
along its arcuate travel path without causing movement of the control arms 62,
64,
and 66. The looseness or "sloppiness" of the engagement between the tongue 69
and the notch 67 can vary with the application, as can the specific
configuration of
the mating engagement, including having the notch on the arm and the tongue on
the control arm 66.
The actuator assembly 60 moves the first and second spring-biased
valves 16, 18 in either a first valve sequence or a second valve sequence,
depending on which valve is to be opened and which valve is to be closed. The
valve sequence is determined according to the combustion cycle, in the case of
a
combustion tool, or the impact cycle of a pneumatic tool.
Turning now to FIGS. 3A-3C, the valve sequences are described.
The beginning of the first valve sequence is defined when the tool is in
between
uses. In this position, the tool is powered up and ready to be used, but is
notyet in
contact with the workpiece into which a fastener is to be driven. At this
time, the
actuator assembly 60 is in the first position as depicted in FIG. 3A, the arm
62 is
spaced a maximum distance from an opposing wall of the housing 12. The first
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CA 02531835 2002-04-29
spring-biased valve 16 is in an open position and the second spring-biased
valve
18 is closed. The metering chamber 24 is thus filled with fuel or fluid due to
communication with the cartridge 28 through the passageway 52.
During the first valve sequence, the first spring-biased valve 16
moves from an open position to a closed position and the second spring-biased
valve 18 opens, but the second valve does not begin to open until firsf valve
is
completely closed. This first valve sequence will generally be triggered by
some
stimulus in preparation for firing of the tool. To have power to drive a
fastener,
the metered fluid is moved into position to deliver that power; i.e., fuel is
moved
into the combustion chamber or air into an expanding cylinder. The sequence is
preferably initiated by any preparatory mechanism, such as contact ofthe tool
with
a workpiece, beginning to squeeze the trigger mechanism and the like. if a
combustion powered framing tool is used, priming of the combustion chamber
preferably takes place when a workpiece contact element comes in contact with
the workpiece, allowing the fuel to flow from the metering chamber 24, through
the lower chamber 56, into a combustion chamber passageway 70 and ultimately
to the combustion chamber (not shown). In the depicted and preferred
embodiment, the sequence is initiated by contacting the tool with a workpiece,
which causes the pivoting link arm 68 to begin its arcuate path of travel
represented by the arrow A (FIG. 1).
It is important to note that the metering chamber 24 is used solely for
measurement of the fluid, and that there are no physical or chemical changes
to the
fluid while it is sealed in the chamber. To provide constant power, the fluid
is
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CA 02531835 2002-04-29
preferably delivered at the same volume, temperature and pressure for each
cycle.
Fluids cannot be accurately measured while chemical or physical reactions are
taking place, thus it is preferred that the fluid have the same chemical
composition
when it is released from the metering chamber 24 as when it entered the
metering
chamber.
Referring now to FIG. 3A, which corresponds to the first position in
the preferred embodiment shown, in this position, fluid freely enters the
metering
chamber 24. As the pivoting link arm 68 moves in an arc defined by the arrow A
(FIG. 1), the tongue 67 moves in a reverse arcuate direction. As such, the
former
upward pressure exerted upon the first rod 34 by the upper arm 62 is released,
allowing the spring 38 to bias the first seat 30 of the first valve 16 into
engagement
with the inlet 20 of the metering chamber 24.
At this point, both spring-biased valves 16, 18 are closed, preventing
flow of the fluid from the fluid supply canister 28 into and out of the
metering
1 S chamber 24. This position is depicted in FIG. 3B, and corresponds to the
second
position of the actuator assembly 60. The metering chamber 24 is closed at
both
the inlet 20 and the outlet 22, sealing the fluid within it and providing a
measured
volume of fluid within the chamber.
The loose mating engagement between the tongue 69 and the notch
67 described above results in a temporary delay in the opening of the secornl
valve
18 while the pivoting link arm 68 continues its arcuate path defined by the
arrow
A (FIG. 1 ). Due to the loose engagement, as the pivoting link arm 68 moves,
there
is a delay while the upward bias opening the first valve 16 is released, and
the
CA 02531835 2002-04-29
control arm 66 has not been moved sufficiently to open the second valve 18.
This
delay ensures that the volume of fuel in the metering chamber 24 will remain
constant, and that unwanted additional amounts cannot enter the chamber, or
that
premature leakage from the outlet 22 into the lower chamber 56 cannot occur.
The third position of the actuator assembly 60 is shown in FIG. 3 C,
which is attained after the first valve 16 has completely closed and the
second
spring-biased valve 18 is opened. In this position, the fluid is released from
the
metering chamber 24. In the preferred embodiment, the entire first valve
sequence
takes place as the actuator arm 60 moves continuously from the first position
through the second position to the third position.
Following firing of the tool 12, the second valve sequence is
initiated, in which the lifting of the tool from the workpiece causes the
pivoting
linking arm 68 to move the actuator assembly 60 from the third position,
through
the second position, to the first position. This sequence closes off the
outlet 22 of
the metering chamber 24 from flow downstream, and reopens the inlet 20 to
again
allow flow of fluid into the metering chamber 24. Any stimulus that follows
firing
of the tool 12 but precedes the first valve sequence may be used to start this
sequence.
The second valve sequence moves the first and second spring-biased
valves through the same steps as the first valve sequence, but in the reverse
order.
Starting with the third actuator assembly 60 position shown inFIG. 3C, the
second
spring-biased valve 18 is disengaged from the outlet 22, preventing flow of
the
fluid from the metering chamber 24. After the second valve 18 is completely
16
CA 02531835 2002-04-29
closed, the second actuator assembly 60 position is obtained, as shown in FIG.
3B.
Here both valves 16, 18 are closed to prevent backflow of the fluid, and the
metering chamber 24 contains only a residual amount of fluid. Finally, the
first
spring-biased valve 16 is disengaged from the inlet 20, allowing free flow of
the
fluid from the fluid supply 28 into the metering chamber 24, but that fluid is
prevented from flowing freely from the pressurized fluid supply 28 through the
inlet 20 and the outlet 22 of the metering chamber 24 to the combustion
chamber
passageway 70.
In the preferred embodiment, this operation or valve sequence is
controlled by the pivoting action of the link arm 68 which moves the actuator
assembly 60 from a position where the upper arm 62 has a maximum spacing from
the housing 12 (FIG 3A), to a position where the lower arm 64 has a maximum
spacing from the housing 12 (FIG 3C). In the preferred embodiment, in addition
to the loose mating engagement between the notch 67 and the tongue 69, the
actuator assembly 60 also includes a delay mechanism also operating betweenthe
closing of one of the valves 16, 18 and the closing of the other valve 18, 16.
Any
type of delay mechanism is suitable, such as an electrical delay, electronic
means
of a mechanical delay mechanism. In the most preferred mechanical delay
mechanism, the actuator assembly 60 is slidably connected to each of the rods
34,
36. The first rod 34 has a first opener 71 such as a 'C'-clip secured to the
rod 34
and the second rod 36 has a second opener 72. Spacing of the openers 71, 72 on
the rods 34, 36 are preferably used to create a delay in the closing of one
valve 16,
18 before the opening of the other valve 18, 16.
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CA 02531835 2002-04-29
In the preferred delaying mechanism, the control arm 66 of the
actuator assembly 60 is longer than the housing 26 in which the valve assembly
resides. The excess length is sufficient to allow the upper arm 62 and the
lower
arm 64 to sandwich the housing 12 between them with excess space between the
housing, and the actuator arms 62, 64. In response to the stimulus that
triggers the
valve sequences, the control arm 66 moves up and down (directions relate to
the
tool, as oriented in FIG. 3).
Refernng now to FIG. 3A, as the actuator assembly 60 moves
through the first valve sequence, the upper arm 62 begins in contact with the
first
opener 71. As the control arm 66 moves downward, release or expansion of the
first spring 3 8 holds the first opener 71 against the upper arm 62 until the
first seat
30 comes into contact with the inlet 20 of the metering chamber, closing the
first
spring-biased valve. Once the control arm 66 moves sufficiently so that the
upper
arm 62 is disengaged from the first opener 71 (as shown in FIG. 3B), the first
spring 38 biases the valve 16 into the closed position. During this movement
from
the first position (FIG. 3A) to the second position (FIG. 3B) of the control
arrn 66,
the lower arm 64 has slid along the second rod 36, partially, but not totally
decompressing the second spring 40. Next, in moving from the second position
(FIG. 3B) to the third position (FIG. 3 C) of the control arm 66, the lower
arm 64
slides along the second rod 36 and finally contacts the second opener 72,
compressing the second spring 40, and opening the second spring-biased valve
18.
The second valve sequence similarly reverses the above steps, introducing a
delay
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CA 02531835 2002-04-29
between the closing of the second spring-biased valve 18 and the opening of
the
first spring-biased valve 16.
Seals are used where suitable to prevent flow of the fluid into the
area outside the valve assembly 10, the metering chamber 24, and the housing
12.
The exact number, shape and placement of such seals depend on the exact
configuration of the valve assembly 10 for a specific application. In the
preferred
embodiment shown, a removable insert 74 is optionally used to surround the rod
34, 36 of each of the spring-biased valves 16, 18 as the rod passes through
the
housing 26 and contacts actuator assembly 60, 0-rings 76, gaskets or similar
devices, are preferably used to prevent leakage between the removable insert
74
and the housing 12 or the rods 34, 36. In some applications, it will be
preferable
for the length of the spring 38, 40 to exceed the dimensions of the upper
chamber
54 or the lower chamber 56, When this is desirable, the removable insert 74
includes a hollow compartment 78 that is sized and configured to receive a
portion
of the length of the spring 38, 40, and to receive the anchored end 42. The
removable insert 74 also provides easy access to the spring-biased valves 16,
18
and their component parts when replacements are installed.
Referring now to FIG. 4, it is preferred that the present valve
assembly 10 be provided with a mechanism for facilitating the movement or
evacuation of fuel from the metering chamber 24 through the outlet 22 and
ultimately into the passageway 70 leading to the combustion chamber. As
described above, it has been found that when combustion-powered tools of this
type are operated at cold temperatures, such as below 32° F, the fuel
pressure
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CA 02531835 2002-04-29
drops and it becomes more difficult to move the fuel into the combustion
chamber.
To address this problem, the present valve assembly 10 is preferably provided
with a disk 80 secured to the valve 18, specifically at the end of the rod 36
disposed in the metering chamber 24. The disk 80 is preferably located closer
to
the inlet 20 when the valve 18 is closed. To that end, the disk 80 is secured
to a
pedestal 82 which in turn is secured to the conical seat 32. In the preferred
embodiment, the disk 80 is made of brass or equivalent rigid, heat resistant
material, and the pedestal 82 is made of rubber or similar resilient polymeric
or
plastic material. However, other materials are contemplated. Preferably, the
disk
80 is friction fit to the pedestal 82 through a frictional mating engagement
between
a lug 84 on the pedestal and an axial bore 86 in the disk. However, other ways
of
fastening the disk 80 to the pedestal 82 are contemplated, including but not
limited
to ultrasonic welding, insert molding, adhesives or other mechanical
fasteners.
The disk 80 is dimensioned to have a diameter which approximates, but is less
than the diameter of the metering chamber 24.
In operation, as the valve 18 opens, as described above in relation to
FIG. 3 C, the disk 80 moves with the seat 32 from its rest position near the
inlet 20
of the metering chamber 24, (best seen in FIG. 4) to a location closer to the
outlet
22. This movement will push any residual fuel from the metering chamber 24
through the outlet 22 and ultimately into the passageway 70 leading to the
combustion chamber. Tn this manner, the fuel is mechanically moved from the
metering chamber 24. However, since the problem of low fuel pressure is
temperature-related, an alternate solution would be to provide a supplemental
CA 02531835 2002-04-29
exhaust passageway 88 through which hot exhaust from the combustion chamber
heats
up the metering chamber during operation of the tool. An equivalent
arrangement is
the provision of an electric heating element powered by a resistor or other
known
arrangement which maintains a satisfactory temperature in the metering chamber
24
to maintain fuel pressure.
Referring now to FIG. 5, the connection between the valve 10 and the
fuel canister 28 is shown in greater detail. It is important that a sealing
relationship
be established between the valve 10 and the fuel canister 28 to prevent loss
of fuel,
as well as avoid unwanted combustion. The fuel canister 28 is provided with an
internal stem 90 which defines an outlet for the fuel contained in the
canister under
pressure, as is known in the art. As is well known in the art, and exemplified
by U.S.
Patent No. 5,115,944 which may be referred to for further details, the stem 90
is
secured to, and is circumscribed by an endcap 92 which encloses the end of the
canister 28 and forms a rolled seam 94 thereover.
An adapter 96 frictionally engages the endcap 92 and circumscribes and
protects the projecting stem 90. An axial passageway 98 is defined by the
adapter 96
and accommodates the stem 90. In the preferred embodiment, the adapter also
includes a frangible end membrane 100 which blocks the passageway 98, and
provides
a visible indication of whether or not the canister 28 has been used. The
membrane
100 is configured to be pierced upon mating engagement with the nipple 51.
Accordingly, the passageway 98 is dimensioned for accommodating the nipple 51.
21
CA 02531835 2002-04-29
ri
By the same token, the nipple 51 is preferably generally cylindrical
in shape, and has a diameter or cross-sectional parameter dimensioned to
slidably
and matingly engage the passageway 98, and a length dimensioned to engage an
end 102 of the stem 90 to effect fluid communication between the canister 28
and
the valve 10. In the preferred embodiment, the nipple 51 is cylindrical,
however,
other non-circular cross-sectional shapes are contemplated depending on the
application, and including oval, square, rectangular and polygonal shapes.
1n the preferred embodiment, the nipple 51 and the stem 90 are
configured so that, upon operational engagement as depicted in FIG. 5, a
sealing
relationship is achieved. This relationship, designed to prevent unwanted loss
of
fuel, may be achieved through frictional contact between the end 102 of the
stem
90 and an-end 104 of the nipple 51. However, it is preferred that some sort of
sealing formation be provided to at least one of the nipple 51 and the stem
90. In
the preferred embodiment, the sealing formation is a resilient O-ring 106
provided
to the nipple 51. However, other known types of sealing formations are
contemplated, including but not limited to ring seals, molded seals and flat
washers.
Also, the present nipple end 104 defines a chamber 108 for receiving
or capturing a resilient sealing member such as the 0-ring 106. More
specifically,
the end 104 is tapered or chamfered for both retaining the 0-ring 106 and also
for
facilitating insertion of the nipple 51 into the adapter passageway 98. The
tapered
end 104 more easily pierces the membrane 100, especially when the nipple 51 is
22
CA 02531835 2002-04-29
r.
fabricated of metal such as brass, which is preferred, however other suitably
rigid
and durable materials are contemplated.
To further enhance the sealed relationship of the engaged nipple 51
and the stem 90, the end 102 of the stem is configured for matingly engaging
or
S accommodating the O-ring 106. As such, the end 102 is preferably provided
with
an annular groove 110. Naturally, it is contemplated that the O-ring 106 or
other
resilient sealing member may be alternately mounted to the stem 90, or
thatitmay
be attached to the nipple end 104 by adhesive, in a groove (not shown) or
other
known type of O-ring attachment technology.
It is also contemplated that, depending on the application, if fluid
communication with the canister 28 is required for any reason, a connector may
be
provided in the form of the nipple 51 which, at the end opposite to the end
104, is
in fluid communication with a fluid container or reservoir as desired.
In use, the canister 28 is inserted into the combustion tool so that the
nipple 51 matingly engages the adapter 96. The canister 28 is pressed upon the
nipple S 1 so that the membrane 100 is pierced and the nipple end 104 enters
the
passageway 98 until contact is made with the stem end 102. As described above,
as sealing relationship is preferably obtained, and it is contemplated that
other
locking apparatus may be employed to secure the canister 28 in this position.
Thus, it will be seen by those skilled in the art that the present valve
assembly and metering changer provide a simple method of providing a constant
volume of fluid to a power fastening tool. The two spring-biased valves 16, 18
control the inlet and the outlet to the constant volume metering chamber 24,
23
CA 02531835 2002-04-29
measuring a constant amount of fluid, independent of in fluctuations in the
fluid
flow rate. The actuator assembly 60 manipulates opening and closing of the
valves 16, 18, receiving the fluid from the pressurized source 28 and metering
it
before it flows downstream to a combustion or expansion chamber. This
arrangement of the valves 16, 18 minimizes wear on the seals, reducing
maintenance.
Referring now to FIG. 6, an alternate embodiment of the present
valve assembly is generally designated 120. Shared components ofthe assemblies
and 120 are identified with identical reference numbers. The main difference
10 between the assemblies 10 and 120 is that the valve assembly 120 includes a
mechanism for varying the volume of the fuel metering chamber 24, so that the
user can selectively adjust the volume of fuel sent by the valve-assembly to
the
combustion chamber of the tool. This adjustability is especially useful when
the
tool is used at higher altitudes or elevations, where the air is thinner and
less fuel
is needed for efficient combustion.
In the preferred embodiment, the mechanism for varying the volume
of the fuel metering chamber is a dosage plunger 122, referred to here as a
plunger, which is an elongate member oriented to linearly reciprocate relative
to
the metering chamber 24. It is preferred that the plunger reciprocates along a
longitudinal axis which is generally normal to an axis of operation defined by
the
valves 16, 18.
The plunger 122 is contemplated as having any configuration which
can withstand the operational environment of the combustion tool, and take up
space in the metering chamber 24 which would otherwise be taken up by fuel. In
the preferred embodiment, the plunger 122 is an elongate metal shaft or rod,
having a valve end 124 and an adjustment end 126.. As stated previously, the
valve
end 124 is configured for reducing the volume of the metering chamber 24 by
taking up a certain amount of space otherwise occupied by fuel prior to each
firing
cycle of the tool. As depicted here, the valve end 124 is generally
cylindrical in
24
CA 02531835 2002-04-29
shape with a truncated end, however the end is alternately contemplated as
having
a complementary shape to a wall 128 of the metering chamber 24.
Opposite the valve end 124, the adjustment end 126 is configured for
selective manipulation, here axial rotation, which is accomplished in the
preferred
embodiment by a screwdriver slot 130. Any conventional shape of driver slot is
considered suitable, including but not limited to slotted, Phillips, Tor-x,
etc., as
well as hex-shaped for an Allen wrench or a conventional socket. Custom-made
adjustment configurations are also contemplated for use in applications where
only
certain qualified service personnel are permitted to adjust the tool.
Between the valve end 124 and the adjustrrient end 126, the plunger
122 is preferably provided with threads so that the axial reciprocation of the
valve
end 124 into and out of the metering chamber 24 may be positively controlled.
Any equivalent structure for achieving this goal is also contemplated. Also;
the
plunger 122 is provided with a sufficient length so that adjustment can be
made
externally of the valve housing 12.
A sleeve 132 is configured for mounting in operational relationship
to the valve housing 12 and reciprocally accommodates the plunger 122. More
specifically, the sleeve 132 circumscribes and thus supports the plunger 122,
and
is fixed to the housing 12, preferably by being press-fit into a bore 134. The
bore
134 is in communication with the metering chamber 24. Other ways to fix the
sleeve 132 to the housing 12 are contemplated, including welding, chemical
adhesives and the like. The sleeve 132 is provided with a central, axial
throughbore 136 which is in communication with the metering chamber 24 and
which is dimensioned to accommodate the plunger 122. To adequately support the
plunger 122, the sleeve 132 has a sufficient length, which extends generally
normally to the valve housing 12. However, the plunger 122 is preferably
longer
than the sleeve 132. An outer end 138 of the sleeve 132 is preferably threaded
to
engage threads 140 of the plunger 122. The specific location of the
corresponding
threaded portions of the plunger 122 and the sleeve 132 may vary to suit the
application.
CA 02531835 2002-04-29
Since the bore 134, as well as the throughbore 136, are in fluid
communication with the metering chamber 24, it is important that they be
sealed to
prevent the unwanted leakage of fuel. Accordingly, the sleeve 132 is
preferably
provided with a seal 142 in the form of an O-ring located in a suitably-
dimensioned O-ring groove 144. Depending on the application, the groove 144
may be positioned either on the sleeve 132 or in the bore 134. In addition, a
plunger seal 146, also preferably an 0-ring, seals the throughbore 136 and is
disposed in a groove 148, either in the throughbore 136 or the plunger 122.
So that the operation of the valves 16, 18 is not impaired, it is
preferred that the plunger 122 be disposed in the metering chamber in an
offset
position. In other words, the longitudinal axis of the plunger 122 is offset
from a
vertical plane bisecting the metering chamber 24 in the direction of
reciprocal
movement of the plunger. Practically speaking, and referring now to FIG. 6,
the
plunger 122 is located behind the axis of movement of the valves 16, 18.
Referring now to FIG. 7, another feature of the present system 120 is
that the plunger 122 or the sleeve 132 is heated so that the tool can be used
in
relatively low temperatures (below 32°F) when the fuel pressure
decreases as
described above. The heat can be provided electrically by connecting live
leads
150 powered by the battery (not shown) of the tool.
Alternately, replacing the plunger 122 with a stationary heating
element 152 can provide heat. The heating element 152 may be reciprocated
within the sleeve 132 through a friction fit, and is also contemplated as
being
connectable to the battery as is well known in the art. As described above in
relation to the supplemental exhaust passageway 88 (FIG. 4), additional heat
can
be provided from the combustion chamber.
While a particular embodiment of the constant volume valve
assembly and metering chamber has been shown and described, it will be
appreciated by those skilled in the art that changes and modifications may be
made
26
CA 02531835 2002-04-29
thereto without departing from the invention in its broader aspects and as set
forth
in the following claims.
27
