Abstract:
A hand-held power tool powered by a gas combustion mechanism comprising a first combustion chamber, a second chamber within a driving cylinder having aft and fore ends. The first combustion chamber in fluid communication with the second chamber via the aft end, a fan assembly, a driver assembly having a piston and driver movable therewithin between the aft and fore end, and a drive motor operably connected to the driver assembly. In use, whilst the piston is at or near the fore end of the driving cylinder, the fan assembly introduces air into the chambers thereby at least partially pressuring the air there within, fuel gas is introduced into the combustion chamber to form an air/fuel gas mixture therein, the drive motor operably moves the piston to a position at or near the aft end thereby compressing the air/fuel gas mixture within the combustion chamber so that the air/fuel mixture is ignited to impart motion onto the and to facilitate the operation of the tool.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an internal combustion fastener driving tool. 
       BACKGROUND 
       [0002]    Fastener driving tools, also known as impulse tools, have been developed that use internal combustion as a power source to drive fasteners such as nails into a work piece or substrate. The tools ignite a fuel/air mixture in a combustion chamber to forcibly drive a piston, which then ejects the fastener from the tool. The effectiveness of the prior art is largely limited to their efficiency in rapidly igniting the complete volume of fuel/air mixture. If insufficient volumes of fuel ignite, the device delivers unsuitable driving forces to the fastener. If the tool produces unreliable power outputs the fasteners may be driven to unsatisfactory depths or insufficiently seated. Prior art devices have attempted to address these inefficiencies by making a larger tool and wasting larger volumes of fuel. 
         [0003]    Some prior art tools also suffer from what is known as misfire or non-fire. This occurs when the tool is operated in low temperature conditions or at high altitude and hot conditions. The cause of the phenomenon is; (a) insufficient atomization and mixing of the air/fuel; (b) an insufficient fuel/air ratio; (c) low air density. 
         [0004]    One such prior art tool is described in U.S. Pat. No. 5,213,247 (Gschwend et al). This device includes a network of mechanisms that operate to measure a specific quantity of fuel and then draw that fuel, along with air, into a combustion chamber by mechanically expanding the combustion chamber volume. A drawback of this device is that the fuel and gas are not mixed sufficiently, which decreases the efficiency of combustion. 
         [0005]    A further disadvantage of such prior art tools is the tool mass (weight and physical size) required for a given output of energy. Furthermore, such tools draw fuel and air into the combustion chamber with partial vacuum. As a consequence the fuel/air mixture is ignited at a low pressure, which leads to a low burn rate and further inefficiency. This is particularly problematic in that the less efficient an internal combustion fastener driving tool is, the more susceptible the device is to output fluctuations that result in ignition failures and unsatisfactory driving forces to the fastener. 
         [0006]    Also prior art impulse tools such as those used in nail and fixing in the building industry have limitations in their use. Such tools have the capability of producing 70 to 100 joules of output energy. These tools will only produce their manufactured claimed output under optimal conditions ie; 24C @ sea level and a relevant humidity level of approximately 40%. If these optimum conditions change, so does the power output by as much as 25%, and in some cases they do not fire at all. This means that nails and fixers sometimes protrude and are only driven 80 to 90% of the manufactured depth, and thus the work piece may not meet building standards. This may also lead the operator to have to use a traditional hammer to finish the job. 
         [0007]    Some impulse tool manufactures have developed tools to produce in excess of 100 joules, but such tools have ended up being a far larger unit for consumers to reasonably expect to purchase. 
         [0008]    All prior art combustion tools used for fixing, suffer from gumming up and need to be cleaned regularly. This is caused by incomplete combustion in the tool. Carbon, lubricants and other bi-products of combustion and exhaust gases build up deposits within the combustion chamber, driver piston and head. 
         [0009]    The present invention seeks to provide a fastener driving tool that will ameliorate or overcome at least one of the deficiencies of the prior art. 
       SUMMARY OF INVENTION 
       [0010]    According to a first aspect the present invention consists in a hand-held power tool, the operational power of which is provided by a gas combustion mechanism, said gas combustion mechanism comprising a first combustion chamber, a second chamber within a driving cylinder having an aft end and a fore end, said first combustion chamber in fluid communication with said second chamber via said aft end, at least one fan assembly, a driver assembly having a piston and driver movable within said driving cylinder between said aft end and said fore end, and a drive motor operably connected to said driver assembly, wherein in use, whilst said piston is at or near said fore end of said driving cylinder, said fan assembly introduces air into said first combustion chamber and said second chamber thereby at least partially pressuring the air there within, fuel gas is introduced into said combustion chamber from a fuel supply port, the air and fuel gas being mixed to form an air/fuel gas mixture therein, said drive motor operably moves said piston to a position at or near said aft end thereby compressing said air/fuel gas mixture within said first combustion chamber so that said air/fuel mixture is ignited within the combustion chamber to impart motion onto said piston and to facilitate the operation of the tool. 
         [0011]    Preferably said fan assembly has a first external induction fan for introducing air into said first combustion chamber. 
         [0012]    Preferably said fan assembly has a second internal circulation fan disposed within said first combustion chamber. 
         [0013]    Preferably said second internal circulation fan is shrouded by a shroud having a free end portion that is frusto-conical in shape. 
         [0014]    Preferably said first combustion chamber is frusto-conically shaped in a region near where it adjoins said driving cylinder. 
         [0015]    Preferably said piston has an aft surface having a concave toroidal shape therein for redirecting air centrally forced thereon by said fan assembly. 
         [0016]    Preferably a separate exhaust cavity is at least partially disposed externally around said first combustion chamber and said driving cylinder, said exhaust cavity having an exhaust vent located near the fore end of said driving cylinder. 
         [0017]    Preferably a plurality of apertures interconnect said exhaust cavity with said first combustion chamber, and an air ducting shroud disposed near said apertures prevents air from passing there through when air is being introduced into said combustion chamber by said fan assembly. 
         [0018]    Preferably at least one exhaust port in communication with said exhaust cavity is located in said driving cylinder near its aft end, said exhaust port being closed by said piston when same has travelled to said aft end of said driving cylinder. 
         [0019]    Preferably said exhaust port closes prior to the air inlet side of said combustion chamber, thereby allowing supercharged air to be introduced into said combustion chamber. 
         [0020]    Preferably said tool further comprises a movable tool nose assembly and a trigger assembly both operably connected to an ECM for the control and actuation of the fan assembly, drive motor and gas supply port. 
         [0021]    Preferably said fan assembly and said drive motor are operably powered by a battery. 
         [0022]    Preferably said drive motor is adapted to act as a generator operably connected to ECM for charging of said battery. 
         [0023]    Preferably said air/fuel mixture is ignited by an ignition process initiated by multiple high tension sparks. 
         [0024]    Preferably said multiple high tension sparks are emitted from a plurality of igniters. 
         [0025]    Preferably in one embodiment the air is introduced into the combustion chamber and driver by a turbine/fan compressor. 
         [0026]    Preferably the air is introduced into the combustion chamber and driver by a positive displacement rotary vane compressor. 
         [0027]    Preferably the air introduced into the combustion chamber and driver is super-charged and a holding mechanism holds the driver assembly against super-charged air until ignition takes place. 
         [0028]    Preferably the increase in tool output energy is a result of supercharging. 
         [0029]    According to a second aspect the present invention consists in a hand-held power tool, operational power of which is provided by a gas combustion mechanism, said gas combustion mechanism comprising a first combustion chamber, and a second chamber within a driving cylinder having an aft end and a fore end, said first combustion chamber in fluid communication with said second chamber via said aft end, and a driver assembly having a piston and driver movable within said driving cylinder between said aft end and said fore end, and a drive motor operably connected to said driver assembly, wherein in use the volume of said first combustion chamber and said second chamber is fluidally pressurized in first and second stages, where said first stage comprises introducing supercharged air into said first combustion chamber and said second chamber via a fan whilst said piston is at or near said fore end of said driving cylinder and subsequently a fuel gas is introduced into said combustion chamber from a fuel supply port, the air and fuel gas being mixed to form an air/fuel gas mixture therein, and in said second stage said drive motor moves said piston to said aft end thereby compressing said fuel/gas mixture in said first combustion chamber so that said air/fuel mixture is ignited within the combustion chamber to impart motion onto said piston and to facilitate the operation of the tool. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  shows a schematic cross-sectional view of a hand held internal combustion nail fastener tool in accordance with a first embodiment of the present invention; 
           [0031]      FIG. 2  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  with the driver and piston in a fully retracted position and the air flow paths as air is introduced into the combustion chamber; 
           [0032]      FIG. 3  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  with the driver and piston in a fully extended position where the piston abuts and compresses the bumper as a result of the firing trigger being fully depressed and air/fuel mixture being ignited; 
           [0033]      FIG. 4  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  in the mode when a user has touched the trigger, thereby causing external air to be force fed (supercharged) into the combustion and drive cylinder chambers and the piston has been driven to a positioning abuting the bumper and blocking the exhaust port; 
           [0034]      FIG. 5  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  placed against the substrate and ten percent travel of the movable tool nose has occurred; 
           [0035]      FIG. 6  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  placed against the substrate and one hundred percent travel of the movable tool nose has occurred; 
           [0036]      FIG. 7  shows a schematic cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  placed against the substrate and the firing trigger been activated about ten percent of its travel; 
           [0037]      FIG. 8  shows a schematic internal partial cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1 ; 
           [0038]      FIG. 9  shows a schematic partial cross-sectional view of the hand held internal combustion nail fastener tool of  FIG. 1  with depicting an external portion of the tool; 
           [0039]      FIG. 10  is shows an enlarged schematic of the drive motor, gear, rack, driver and piston that form the drive assembly; 
           [0040]      FIG. 11  shows a schematic cross-sectional view of a hand held internal combustion nail fastener tool in accordance with a second embodiment of the present invention; and 
           [0041]      FIG. 12  shows a schematic internal view of a positive displacement rotary vane air pump that may replace turbine/fan utilised in the tool shown in  FIG. 11 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0042]      FIGS. 1-10  depict a hand held internal combustion nail fastener tool  100 , comprising a driver motor  101 , an induction/circulation motor  102 , an external induction fan  103 , an internal circulation fan  104 , a twenty-four volt battery pack  105 , a combustion space volume (chamber)  106 , a driver cylinder chamber  107  within cylinder  13 , an exhaust (cooling) cavity  108 , a fuel cell cartridge  109 , and igniters  110   a  and  110   b . The combustion chamber  106  has a frusto-conical shape in the vicinity where it joins with driver cylinder chamber  107 . 
         [0043]    The operation of tool  100  will now be described. A user (not shown) holds tool  100  by support handle (pistol grip)  34 . Preferably the user&#39;s index finger is placed on firing trigger  3 . The touch sensor  35  alerts the Electronic Control Module (ECM)  27  that tool  100  is to be operated. ECM  27  actuates the electrical circuit to the induction and circulation fan motor  102  to operate at twelve volts. This results in the external induction fan  103  and internal circulation fan  104  to drive air from external of tool  100  in through air intake filter  21 . External air is force fed into the combustion chamber  106  and driver cylinder chamber  107  as charged air. Simultaneously ECM  27  checks the position of drive motor  101 , which is in communication with driver  14  and piston  15  via drive motor gear  7  and driver gear rack  11 . The drive motor  101  repositions driver  14  and piston  15  so that the underside of piston  15  is resting on bumper  8 , see  FIG. 4 . In this position the piston  15  is blocking the exhaust port  10  and seals chambers  106  and  107 . Also at this same point of the tool cycle the combustion chamber housing  17  is in the one hundred percent (100%) open mode in communication with movable tool nose portion  5 . As external air is drawn in via fan  103 , an air duct  20  prevents the air now under pressure from fan  103  from entering cavity  108 , so one hundred percent (100%) of external air is directed into the combustion chamber  106 . Upon entering combustion chamber  106 , the incoming air is further accelerated by the internal circulation fan  104 . As the air passes through fan  104 , the air is forced to flow through frusto-conically shaped circulation shroud  25 , which further speeds up the air flow. Air is then directed down the centre of driver chamber  107  via shroud  25 . At the base of chamber  107  (within cylinder  13 ), the air flow is split and redirected back up chamber  107  into the combustion chamber  106 , via the “toroidally” shaped concave aft surface of piston  15 , where the air flow splits and approximately 70% exits chamber  106  via exhaust port  16 , flowing into and along cavity  108  and exiting tool  100  via exhaust vent  9 . The remaining air flow in chamber  106  (approximately 30%) flows up to the top of the chamber  106  where it rejoins the incoming air flow through a plurality of holes/vents arranged around the base of circulation shroud  25  as seen in  FIG. 4 . 
         [0044]      FIG. 5  depicts tool  100  placed onto a substrate where ten percent (10%) travel of movable tool nose portion  5  has occurred. Tool nose portion  5 , which is in communication with housing  17 , has caused housing  17  to shut off the exhaust port  16  allowing one hundred percent(100%) of air flow to circulate around chambers  106  and  107 . At this same point the ECM  27  has switched motor  102  to twenty-four volts, 200% of the normal manufacturer duty-cycle voltage for motor  102 . This causes motor  102  to greatly increase its rotation (rpm) thus increasing the volume and speed of air flow into chambers  106  and  107 , as exhaust port  16  is closed the increase in air flow into chambers  106  and  107  causes an increase in air pressure there within. In prior art impulse tools the exhaust port and air inlet would close off simultaneously, however in this embodiment of the invention, after exhaust port  16  closes, the increased rotation of motor  102  continues to introduce “supercharged” air into chambers  106  and  107 . This is because the closure of exhaust port  16  is in or near the first ten percent (10%) of travel of housing  17 , leaving the inlet side open to receive charged air. 
         [0045]      FIG. 6  depicts tool nose  5 , in communication with the housing  17 , has operated (travelled) at one hundred percent (100%). At this point of the tool cycle, air flow from fan  103  has been redirected into cavity  108  via a plurality of holes/vents now revealed in air ducting shroud  20 . During the last say five percent (5%) of travel of chamber housing  17 , seals  17 A and  17 B cause chambers  106  and  107  to be sealed. When chamber housing  17 , has operated (travelled) at one hundred percent (100%) and therefore chambers  106  and  107  are sealed, a metered amount of gas from fuel cell  109  via gas regulator valve head  23  and gas regulator valve actuator  24 , in communication with 17, has entered chamber  106  through jet  33 . 
         [0046]    Gas delivery jet  33  is extended into chamber  106  in close proximity to rear of fan  104 . As the fuel exits jet  33  the rapidly rotating blades of fan  104  accelerate the vaporization and expansion reaction of the fuel gas as well as rapidly circulating and mixing the air and fuel together in chambers  106  and  107 . 
         [0047]      FIG. 7  also depicts that the firing trigger  3  has been actuated ten percent (10%) of its travel. At this point the ECM  27  in communication with trigger  3  switches electrical circuit on to driver motor  101 , causing piston  15  and driver  14  in conjunction with rack  11  and gear  7 , to travel one hundred percent (100%) to the top of driver cylinder  13 . As chamber  106  is sealed all the air mass in chamber  107  is compressed in to chamber  106 , creating a pressure greater than ambient (pressure difference). Also, as the driver assembly  14  and piston  15  achieve one hundred percent (100%) of travel up to the top of cylinder  13 , a nail  40  has been placed into the fixed tool nose  6  from fastener magazine  4 . Air and fuel now contained in chamber  106  circulates rapidly, shroud  25  directs the fuel/air mixture across the igniters  110   a  and  110   b , by means of vents/holes (not shown) at the base of shroud  25 . 
         [0048]      FIG. 4  depicts that firing trigger  3  has operated 100% of its travel. ECM  27  switches circuit on to high tension ignition coil  1 , thereby operating same very rapidly, at approximately twenty-five to fifty applications. The resulting pulses of high voltage created by the ignition coil  1  are in communication with igniters  110   a  and  110   b . The resulting multiple high-tension sparks from igniters  110   a  and  110   b  ignite the fuel/air mixture in combustion chamber  106  simultaneously. ECM  27  switches driver motor  101  to a separate electrical circuit converting driver motor  101  to a generator. As the fuel/air mixture ignites in chamber  106 , a rapid rise in pressure occurs forcing the driver assembly  14  and piston  15  down cylinder  13  ejecting nail  40  into the substrate (or work piece). As the driver assembly  14  and piston  15  progress down the cylinder  13 , motor  101  now acting as a generator is in communication with driver assembly  14 , via rack  11  and gear  7 . The resulting charge is sent back into the battery pack  105 , increasing battery/tool cycles between charges. As the driver assembly (driver  14  and piston  15 ) reach 90% of travel, the underside of piston  15  comes into contact with bumper shock absorber  8 , which reduces the kinetic energy of driver  14  and piston  15 , bringing them to a steady controlled stop in cylinder  13 . At this stage of the tool/combustion cycle the exhaust ports  10  configured in plurality at the base of cylinder  13 , are uncovered by piston  15 . The exhaust gases in chambers  106  and  107  escape/evacuate through exhaust ports  10 , reducing the gas pressure in chambers  106  and  107  to a partial vacuum (lower pressure) than ambient. The stored energy in bumper  8  then repels the driver assembly (driver  14  and piston  15 ) approximately thirty percent (30%) back up bore  13 . ECM  27  then switches fan motor  102  back to normal running mode at 12V. Simultaneously ECM  27  in communication with driver motor  101  checks the position of the driver assembly (driver  14  and piston  15 ) and adjusts as required, at the bottom of the bore  13  with underside of piston  15  resting on bumper  8  also “closing off” the exhaust ports  10 . 
         [0049]    Tool  101  is then raised off the substrate allowing movable tool nose portion  5  to extend. Tool nose portion  5  in communication with housing  17  slides forward, allowing air to circulate around  106  and  107  and exit through exhaust ports  16 . The firing trigger  3  is then released resetting the ECM  27  back to the start cycle status. 
         [0050]    A hand-held power tool as described in the abovementioned embodiment overcomes the disadvantages of the prior art prior by achieving:
       Higher output energy   more consistent energy production   Reduced exhaust emissions   Reduction in tool overall size for a given energy output   Increases the range of “impulse tool” capability into 4 inch (100 mm) nails and concrete pins       
 
         [0056]    The above mentioned embodiment of the present invention overcomes the disadvantages and difficulties of the prior art by:
       Reconfiguring the combustion cycle/process.   Supercharging the induction process.   Improving the working fluid air/fuel mixture, mass by adding a secondary stage of compression prior to ignition.   Improving the fuel atomization process.   Improving the ignition process.   Improving the combustion chamber dynamics.   Improving the gas flow across the driver piston surface.   Redefine the gas flow and mixing process within the combustion chamber.   Improving the ignition and flame front progress.       
 
         [0066]    In a modification of the first embodiment not shown, motor  101  is replaced by a coil spring assembly positioned inside cylinder  13  acing upon the underside of driver piston  15 . A locking mechanism in mechanical communication with driver  14  will also be necessary to achieve driver piston and driver assembly return when chambers  106  and  107  are under pressure resulting in a charged air system. 
         [0067]    In a second embodiment,  FIG. 11  shows alternative methods of pre-charging or super-charging an internal gas combustion nail/fastening tool  100  of the first embodiment. In this embodiment turbine/fan (compressor)  201  replaces conventional fan blade  103 . Fan motor  102  drives both internal circulation fan  104  and centrifugal turbine/fan  201 . Turbine/fan  201  is capable of delivering much higher air pressure than conventional fan blade  103 . With this type of super-charging arrangement utilizing turbine/fan  201 , it is necessary to extend the rear tool housing  202  to provide appropriate ducting. 
         [0068]      FIG. 12  shows an arrangement of a positive displacement rotary vane air pump (compressor)  203  with inlet port  204  and outlet port  205 . Rotary vane air pump  203  device can replace turbine/fan  201  of the second embodiment and achieve even higher air pressure delivery to tool  100  of the first embodiment. 
         [0069]    It should be understood that although various air pump (compressor) mechanisms such as external induction fan  103 , turbine/fan  201  and rotary vane air pump  203  have been described in the abovementioned embodiments for the super-charging of tool  100 , it is not limited to these particular mechanisms, and other air pump mechanisms may be utilised. 
         [0070]    Where higher efficiency pump mechanisms, such as turbine/fan  201  or rotary vane air pump  203  are used in a hand held internal combustion nail fastener tool  100  utilizing a super-charging combustion process as described, it is possible to dispense with driver motor  101 , drive motor gear  7  and driver gear rack  11 . To combat the charged air effect in combustion chamber  106  it would be necessary to incorporate a driver piston locking holding mechanism (not shown), to hold the driver mechanism  14  and  15  in place at the top of the driver cylinder  13  until ignition has taken place. As combustion pressure rises in combustion chamber  106 , typically in excess of 10 bar, the gas combustion pressure acting upon driver piston  15  will overcome the driver assembly locking mechanism (not shown) and eject a nail at high velocity from tool  100 . The driver assembly locking mechanism may be configured so that the driver assembly  14  and  15  is held at the top of the cylinder  13  until a pressure of typically say 1.5 bar exists in combustion chamber  106 . 
         [0071]    The terms “comprising” and “including” (and their grammatical variations) as used herein are used in inclusive sense and not in the exclusive sense of “consisting only of”.