Abstract:
A combustion-powered fastener-driving tool includes a combustion-powered power source; at least one fan associated with the power source during operation; and a control system operationally associated with the power source and connected to the at least one fan for adjusting the length of time for energizing the at least one fan as a function of the number of combustion firings by the power source.

Description:
RELATED APPLICATION 
   This is a divisional of application Ser. No. 11/028,020, filed Jan. 3, 2005, and Applicants claim priority under 35 USC § 120 from the above-identified parent application, and from U.S. Ser. No. 60/543,053 filed Feb. 9, 2004. 

   BACKGROUND 
   The present invention relates generally to fastener-driving tools used for driving fasteners into workpieces, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools. 
   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, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 5,713,313, 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, Ill. under the IMPULSE® and PASLODE® brands. 
   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 position. 
   BRIEF SUMMARY 
   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 a combustion-powered power source, at least one fan associated with the power source, at least one temperature sensing device in operational proximity to the power source, and a control system operationally associated with the power source and connected to the at least one fan and the at least one temperature sensing device for adjusting the length of operational time of the at least one fan as a function of power source temperature sensed by the at least one temperature sensing device. 
   In another embodiment, a combustion-powered fastener-driving tool includes a combustion-powered power source, at least one fan associated with the power source during operation, and a control system operationally associated with the power source and connected to the at least one fan for adjusting the length of time of fan operation as a function of a rate of combustion firings by the power source. 

   
     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. 
   

   DETAILED DESCRIPTION 
   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  40 U 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  40 L 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, U.S. Pat. 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 F of the tool  10  ( FIG. 2 ). 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 fan overdrive. 
   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 at  71 . 
   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 ΔT value. At step  130 , the resulting difference ΔT 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 ΔT, 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 ΔT 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 at  71 . 
   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.