The present application claims priority under 35 USC §
120 from US Serial No. 60/543,053 filed February 9,2004.
The present invention relates generally to a combustion-powered
fastener-driving tool according to the preamble of claim 1 and to a method for operating
it according to claim 16.
Such a tool is known from
EP-A-1 459 850
. Temperature elevation of a combustion chamber frame is detected by a
temperature sensor. If the detected temperature exceeds a preset temperature, ignition
of an ignition plug is prohibited, alarming is performed by a display to notify
the user of inoperable state of the tool and cooling is performed by rotating a
fan until the temperature again reaches a predetermined value.
Combustion-powered tools are known in the art for use in
driving fasteners into workpieces, and examples are described in commonly assigned
patents to Nikolich
U.S. Pat. Re. No. 32,452
U.S. Pat. Nos. 4,522,162
, all of which are incorporated by reference herein. Similar combustion-powered
nail and staple driving tools are available commercially from ITW-Paslode of Vernon
Hills, Illinois under the IMPULSE®
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 a spark for ignition, and a fan located in a combustion
chamber provides for both an efficient combustion within the chamber, while facilitating
processes ancillary to the combustion operation of the device. Such ancillary processes
include: inserting the fuel into the combustion chamber; mixing the fuel and air
within the chamber; and removing, or scavenging, combustion by-products. The engine
includes a reciprocating piston with an elongated, rigid driver blade disposed within
a single 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
spark to ignite a charge of gas in the combustion chamber of the engine, the combined
piston and driver blade is forced downward to impact a positioned fastener and drive
it into the workpiece. The piston then returns to its original or pre-firing 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.
The above-identified combustion tools incorporate a fan
in the combustion chamber. This fan performs many functions, one of which is cooling.
The fan performs cooling by drawing air though the tool between firing cycles. This
fan is driven by power supplied by an onboard battery and, to prolong battery life,
it is common practice to minimizing the run time of the motor. Also, short fan run
time reduces fan motor wear (bearings and brushes), limits sound emitting from the
tool due to air flow, and most importantly limits dirt infiltration into the tool.
To manage fan 'on time', combustion tools typically incorporate a control program
that limits fan 'on time' to 10 seconds or less.
Combustion tool applications that demand high cycle rates
or require the tool to operate in elevated ambient temperatures often cause tool
component temperatures to rise. This leads to a number of performance issues. The
most common is an overheated condition that is evidenced by the tool firing but
no fastener driven. This is often referred to as a "skip" or "blank fire." As previously
discussed, the vacuum return function of a piston is dependent on the rate of cooling
of the residual combustion gases. As component temperatures rise, the differential
temperature between the combustion gas and the engine walls is reduced. This increases
the duration for the piston return cycle to such an extent that the user can open
the combustion chamber before the piston has returned, even with a lockout mechanism
installed. The result is the driver blade remains in the nosepiece of the tool and
prevents advancement of the fasteners. Consequently, a subsequent firing event of
the tool does not drive a fastener.
Another disadvantage of high tool operating temperature
is that there are heat-related stresses on tool components. Among other things,
battery life is reduced, and internal lubricating oil has been found to have reduced
lubricating capacity with extended high temperature tool operation.
Thus, there is a need for a combustion-powered fastener-driving
tool which reduces fan on time. In addition, there is a need for a combustion-powered
fastener-driving tool which manages tool operating temperatures within accepted
limits to prolong performance and maintain relatively fast piston return to pre-firing
The above-listed needs are met or exceeded by the present
combustion-powered fastener-driving tool which overcomes the limitations of the
current technology. The present tool is provided with a temperature sensing system
which more effectively controls running time of the fan. Fan run time may be determined
by monitoring tool temperature, by comparing power source temperature against ambient
temperature, or by controlling fan run time as a function of tool firing rate.
More specifically, a combustion-powered fastener-driving
tool includes the features of claim 1.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
- FIG. 1 is a front perspective view of a fastener-driving tool incorporating
the present temperature control system;
- FIG. 2 is a fragmentary vertical cross-section of the tool of FIG. 1
shown in the rest position;
- FIG. 3 is a fragmentary vertical cross-section of the tool of FIG. 2 shown in
the pre-firing position;
- FIGs. 4A-C are an operational flowchart illustrating a control program wherein
the tool temperature is monitored for fan energization when needed; and
- FIG. 4D is an operational flowchart illustrating a control program subroutine
wherein tool firing rate is monitored for fan energization.
Referring now to FIGS. 1 -3, a combustion-powered fastener-driving
tool incorporating the present control system is generally designated 10 and preferably
is of the general type described in detail in the patents listed above and incorporated
by reference in the present application. A housing 12 of the tool 10 encloses a
self-contained internal power source 14 (FIG. 2) within a housing main chamber 16.
As in conventional combustion tools, the power source 14 is powered by internal
combustion and includes a combustion chamber 18 that communicates with a cylinder
20. A piston 22 reciprocally disposed within the cylinder 20 is connected to the
upper end of a driver blade 24. As shown in FIG. 2, an upper limit of the reciprocal
travel of the piston 22 is referred to as a top dead center or pre-firing position,
which occurs just prior to firing, or the ignition of the combustion gases which
initiates the downward driving of the driver blade 24 to impact a fastener (not
shown) to drive it into a workpiece.
Through depression of a trigger 26 associated with a trigger
switch 27(shown hidden), an operator induces combustion within the combustion chamber
18, causing the driver blade 24 to be forcefully driven downward through a nosepiece
28 (FIG. 1). The nosepiece 28 guides the driver blade 24 to strike a fastener that
had been delivered into the nosepiece via a fastener magazine 30.
Included in the nosepiece 28 is a workpiece contact element
32, which is connected, through a linkage 34 to a reciprocating valve sleeve 36,
an upper end of which partially defines the combustion chamber 18. Depression of
the tool housing 12 against the workpiece contact element 32 in a downward direction
as seen in FIG. 1 (other operational orientations are contemplated as are known
in the art), causes the workpiece contact element to move from a rest position to
a pre-firing position. This movement overcomes the normally downward biased orientation
of the workpiece contact element 32 caused by a spring 38 (shown hidden in FIG.
1). Other locations for the spring 38 are contemplated.
Through the linkage 34, the workpiece contact element 32
is connected to and reciprocally moves with, the valve sleeve 36. In the rest position
(FIG. 2), the combustion chamber 18 is not sealed, since there is an annular gap
40 including an upper gap 40U separating the valve sleeve 36 and a cylinder head
42, which accommodates a chamber switch 44 and a spark plug 46, and a lower gap
40L separating the valve sleeve 36 and the cylinder 20. In the preferred embodiment
of the present tool 10, the cylinder head 42 also is the mounting point for at least
one cooling fan 48 and the associated fan motor 49 which extends into the combustion
chamber 18 as is known in the art and described in the patents which have been incorporated
by reference above. In addition,
US Patent No. 5,713,313
also incorporated by reference, discloses the use of multiple cooling
fans in a combustion-powered tool. In the rest position depicted in FIG. 2, the
tool 10 is disabled from firing because the combustion chamber 18 is not sealed
at the top with the cylinder head 42 and the chamber switch 44 is open.
Firing is enabled when an operator presses the workpiece
contact element 32 against a workpiece. This action overcomes the biasing force
of the spring 38, causes the valve sleeve 36 to move upward relative to the housing
12, closing the gap 40, sealing the combustion chamber 18 and activating the chamber
switch 44. This operation also induces a measured amount of fuel to be released
into the combustion chamber 18 from a fuel canister 50 (shown in fragment).
In a mode of operation known as sequential operation, upon
a pulling of the trigger 26, the spark plug 46 is energized, igniting the fuel and
air mixture in the combustion chamber 18 and sending the piston 22 and the driver
blade 24 downward toward the waiting fastener for entry into the workpiece. As the
piston 22 travels down the cylinder 20, it pushes a rush of air which is exhausted
through at least one petal, reed or check valve 52 and at least one vent hole 53
located beyond the piston displacement (FIG. 2). At the bottom of the piston stroke
or the maximum piston travel distance, the piston 22 impacts a resilient bumper
54 as is known in the art. With the piston 22 beyond the exhaust check valve 52,
high pressure gasses vent from the cylinder 20. Due to internal pressure differentials
in the cylinder 20, the piston 22 is drawn back to the pre-firing position shown
in FIG. 3.
As described above, one of the issues confronting designers
of combustion-powered tools of this type is the need for a rapid return of the piston
22 to pre-firing position prior to the next cycle. This need is especially critical
if the tool is to be fired in a repetitive cycle mode, where an ignition occurs
each time the workpiece contact element 32 is retracted, and during which time the
trigger 26 is continually held in the pulled or squeezed position. During repetitive
cycle operation, ignition of the tool is triggered upon the chamber switch 44 being
closed as the valve sleeve 36 reaches its uppermost position (FIG. 3). Such repetitive
cycle operation often leads to elevated tool operating temperatures, which extend
the piston return time.
To manage those cases where extended tool cycling and/or
elevated ambient temperatures induce high tool temperature, at least one temperature
sensing device 60 such as a thermistor (shown hidden in FIG. 1) is preferably located
at a lower end of the cylinder 20 and is preferably disposed to be in or in operational
relationship to, a forced convection flow stream of the tool 10. Other types of
temperature sensing devices are contemplated. Also, other locations on the tool
10 are contemplated depending on the application. The temperature sensing device
60 is connected to a control program 66 associated with a central processing unit
(CPU) 67 (shown hidden in FIG. 1) and is configured to extend 'on time' of the at
least one cooling fan 48 until the temperature is lowered to the preferred "normal"
operating range. Alternately, the program 66 is configured to hold the fan 48 on
for a fixed time, for example 90 seconds, which is long enough to assure that the
combustion chamber temperature has returned to the "normal" operating range. In
the preferred embodiment, the program 66 and the CPU 67 are located in a handle
portion 68 of the tool 10.
The temperature threshold is selected based upon the proximity
of the temperature sensing device 60 to the components of the power source 14, the
internal forced convection flow stream, and desired cooling effects to avoid nuisance
fan operation. Excessive fan run time unnecessarily draws contaminants into the
tool 10 and depletes battery power. Other drawbacks of excessive fan run time include
premature failure of fan components and less fan-induced operational noise of the
tool 10. For demanding high cycle rate applications and/or when elevated ambient
temperatures present overheating issues, temperature controlled forced convection
will yield more reliable combustion-powered nail performance and will also reduce
thermal stress on the tool.
Referring now to FIG. 4A and considering a sequential firing
mode, although the present program can be applied to a repetitive firing mode as
well, a portion of the control program 66 associated with monitoring tool temperature
is generally designated 70. Beginning at the START prompt 71, the program 70 determines
at 72 if the chamber switch 44 (designated HEAD) is open or not. A closed HEAD signifies
that the combustion chamber 18 is closed and ready for combustion. If the HEAD is
closed, the program cycles. If the HEAD is open, the program 70 checks whether the
trigger 26 is open at 74. If the trigger 26 is closed with the HEAD open, the program
cycles. At step 76, once the HEAD is closed, the fan 48 is turned on at step 78,
which circulates fuel and air mixed in the combustion chamber 18.
Next, the program 70 checks whether to activate the ignition
process by determining whether the trigger 26 is closed at 80 or the HEAD is open
at 82. If the trigger 26 has not been closed, and the HEAD 44 reopened, as if the
operator was interrupted in using the tool 10 or decided to put it down unused,
the program 70 checks at 84 whether the 90 second fan signal is on. If not, that
indicates that the tool has not been used, and the fan 48 is turned on at 86 for
5 seconds, and then is turned off. If the 90 second fan signal has been turned on,
the program 70 returns to START at 71, and the extended cooling cycle continues.
Returning to the trigger closed 80-HEAD open 82 loop, once
the trigger 26 is closed, indicating a combustion is desired, the program 70 activates
a spark at 90, which may also be performed in conjunction with the control circuit
66. After ignition, the program 70 determines whether the HEAD 44 is open at 92,
and if not, the program cycles. If the HEAD 44 is open, the program 70 checks to
see if the trigger 26 is open at 94. If not, the program 70 cycles until the trigger
does open, at which time the program goes to TEMP at 96, or COMPARE TEMP at 98,
or to RATE at 100, depending on which of the present embodiments is employed. The
TEMP 96 subroutine uses one temperature sensor 60 to monitor tool temperature and
turn on the fan 48 into extended operation, also known as "overdrive" when tool
temperature exceeds a preset value. The COMPARE TEMP 98 subroutine uses a calculated
value based on readings of two temperature sensors to activate the fan 48 into overdrive,
and the RATE 100 subroutine monitors the firing rate of the tool 10 to activate
Referring now to FIG. 4B, the TEMP subroutine 96 first
determines whether the HEAD 44 is open at 102. Once the HEAD 44 is determined to
be opened, the trigger 26 is checked at 104. If the trigger 26 is closed, indicating
that the operator is actively using the tool, the program 70 cycles until the trigger
is open. At that time, at step 106, the program 70 monitors the temperature from
the temperature sensor 60. At step 108, the program 70 determines whether the sensed
temperature is greater than 60°C. If the temperature is not greater than 60°C,
at 108, the program 70 determines if the 90 second fan timer has been activated
at 110, which would also indicate that the fan 48 had been energized for that period.
If not, indicating the tool 10 has not been extensively used or use has been discontinued,
the fan 48 is turned on for 5 seconds at 112 and then is turned off, following which
the program 70 reverts to the START routine 71.
If the temperature is greater than 60°C at 108 and
the 90 second fan timer, as well as the fan 48, has been turned on at 110, then
the temperature sensor 60 is checked at 114 to determine if the monitored temperature
is less than or equal to 40°C. If not, indicating the tool is still at operational
temperature, the program 70 begins the START routine at 71. If the sensed tool temperature
has been reduced to less than or equal to 40°C after operation of the 90 second
fan timer and the fan 48, even if the 90 seconds has not expired, the 90 second
timer reverts to a 5 second fan timer, which is turned on at 116. After 5 seconds,
the fan 48, and an optional indicator, such as a light and/or audible alarm 115
(FIG. 1) which was turned on in conjunction with the energization of the 90 second
fan timer (discussed below at 118) is turned off. Next, the program 70 goes to START
If the monitored tool temperature is greater than or equal
to 60°C at 108, then the fan 48, the fan timer, as well as the optional indicator
115 is turned on for 90 seconds at 118, then both are turned off, following which
the program 70 goes to START at 71. It is preferred that the fan running for 90
seconds is sufficient to cool the tool 10 during operation and prevent overheating.
However, it will be understood that the temperature levels and fan run times discussed
herein may be modified to suit the particular application.
Referring now to FIG. 4C, the COMPARE TEMP subroutine 98
is provided. In this embodiment, the tool 10 is provided with a first temperature
sensor 60 near the power source 14, such as the cylinder 20 or the combustion chamber
18. A second temperature sensor 120 (shown hidden in FIG. 1) is also located on
the tool 10, but further from the power source 14 such that it is not significantly
affected by the power source 14. One potential location is on the tool housing 12
in the handle portion 68, however other locations are contemplated.
Initially, at step 124, the program 70 determines the ambient,
or close to ambient reference temperature value from reading the second temperature
sensor 120. Next, at step 126, the program 70 determines the tool reference temperature
from the first temperature sensor 60 located closer to the power source 14. At step
128, the readings from the sensors 120 and 60 are compared, obtaining a &Dgr;T
value. At step 130, the resulting difference &Dgr;T is compared against a predetermined
value, such as a conventional "look-up" table developed to suit the application.
If the resulting difference is greater than the predetermined value, then at step
132 the fan 48 is turned on for 90 seconds, then is turned off. If the resulting
difference is less than the predetermined value, then at step 134 the fan 48 is
turned on for 5 seconds, then off. It is also contemplated that the subroutine 98
is configurable so that the greater the difference &Dgr;T, the longer the fan
run time. At the conclusion of either activation of the fan, the program returns
to START at 71. It is also contemplated that the &Dgr;T can be compared to the
ambient reference temperature to determine fan run time.
Referring now to FIG. 4D, the RATE subroutine 100 is described.
A tool cycle rate, or the number of firings per minute, or the number of combustions
or ignitions of the spark plug 46 over time, is determined by the program 70 at
step 136, and then that value is compared against a predetermined rate at step 138
as in a "look-up" table. This data is preferably monitored by the CPU 67. Depending
on the application, a threshold firing rate is established and added to the program
70 which is considered sufficient to cause an excessive tool temperature, for example
60°C. The program 70 then checks at step 140 to determine whether the firing
rate exceeds the predetermined rate, and if so, the tool 10 is likely overheating
or has a raised operating temperature. As such, at step 142, the fan is turned on
for 90 seconds, then is turned off. If the tool 10 is so equipped, the indicator
115 is temporarily energized, as described above in relation to FIG. 4B. If the
calculated firing rate is less than the predetermined rate, indicating that tool
temperature is acceptable, the fan 48 is turned on for 5 seconds at step 144, then
is turned off, again optionally with periodic energization of the indicator 115.
Upon the execution of either of steps 142 or 144, the program 70 returns to start
Note that it is contemplated that the program 70 may be
configured so that GO TO TEMP 96, GO TO COMPARE TEMP 98 and GO TO RATE 100 may be
used in combination with each other, and are not required to be exclusively used
as a fan control.
While a particular embodiment of the present temperature
monitoring for fan control for combustion-powered fastener-driving tool has been
described herein, 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.