Abstract:
A fastener driving tool comprising a tool nose through which a fastener is fired and a loading apparatus for introducing the fastener into the tool nose. The fastener is propelled by a gas combustion mechanism comprising a first priming cylinder having a first piston and an air intake fluidically connected via a first valve apparatus to a second delivery cylinder having a second piston. The first priming cylinder is fluidically connected to a fuel gas reservoir via a second valve apparatus. The first priming cylinder receives fuel from the reservoir and air through the air intake to form an air/fuel gas mixture therein. The first piston compresses the air/fuel gas mixture and transfers the air/fuel gas mixture to the second delivery cylinder via the first valve apparatus. The air/fuel mixture is ignited therein and urges the second piston towards the fastener and propels the fastener away from the tool nose.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage application of International Application No. PCT/AU2004/001836, filed on Dec. 30, 2004, which claims priority of Australian application number 2003907160, filed on Dec. 30, 2003 and Australian application number 2004900539, filed on Feb. 4, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to an internal combustion fastener driving tool. 
         [0003]    Fastener driving 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 tools is largely limited by 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 in the past have attempted to address these inefficiencies by making a larger tool and wasting larger volumes of fuel. 
         [0004]    One such prior art device is described in U.S. Pat. No. 5,213,247 (Gschwend et al). This device describes 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. Secondly, the device draws fuel and air into the combustion chamber with a 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. 
         [0005]    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 
       [0006]    In a first aspect the present invention consists in a fastener driving tool comprising: a tool nose through which a fastener is fired; loading means for introducing said fastener into said tool nose; said fastener being adapted to be propelled by a gas combustion mechanism, wherein said gas combustion mechanism comprises a first priming cylinder having a first piston and an air intake fluidically connected via a first valve means to a second delivery cylinder having a second piston, said first priming cylinder fluidically connected to a fuel gas reservoir via a second valve means, said first priming cylinder adapted to receive fuel gas from said fuel gas reservoir and air through said air intake thereby forming an air/fuel gas mixture therein, said first piston adapted to compress said air/fuel gas mixture and transfer said air/fuel gas mixture to said second delivery cylinder via said first valve means, said air/fuel mixture ignited therein and thereby urging said second piston towards said fastener and propelling the same away from said tool nose. 
         [0007]    Preferably in a first embodiment said first piston is mechanically actuated. Preferably said second valve means is opened and closed via mechanical actuation. 
         [0008]    Preferably in a second embodiment said first piston is electromagnetically actuated. Preferably said second valve means is opened and closed via electromagnetic actuation. 
         [0009]    Preferably said fastener driving tool is a nail gun. 
         [0010]    Preferably in a third embodiment a mechanism movable between a first and a second position along said tool nose includes a latching means for engaging said second position, such that said air/fuel gas mixture is further compressed by said second piston as said mechanism is moved from said first to said second position with said latching means engaged and wherein the downward force from the ignition of said air/fuel mixture overcomes said latching means and urges said second piston towards said fastener. 
         [0011]    Preferably a bumper is disposed near the bottom of said second delivery cylinder, such bumper adapted to be compressed by said second piston in the bottom of its travel and wherein the subsequent restoration of said bumper is further adapted to forcibly return said second piston back up said second delivery cylinder. 
         [0012]    Preferably the interior of said bumper forms a chamber adapted to port pressurised air via an outlet valve through a transfer channel to said first priming cylinder as said bumper is compressed. 
         [0013]    Preferably said first piston has an internal receiver for storing said pressurised air. 
         [0014]    Preferably a sealing ring having a semi-flexible lip is disposed around the periphery of said second piston. 
         [0015]    Preferably a mixing fan is rotatably mounted to the interior of said second delivery cylinder. 
         [0016]    Preferably an externally mounted motor drives said mixing fan via magnetic coupling. 
         [0017]    Preferably said second delivery cylinder is exhausted via a plate valve that fluidly connects said second delivery cylinder with an exhaust plenum when said plate valve is opened. 
         [0018]    Preferably in a second aspect the present invention consists in an apparatus utilising a gas combustion mechanism for propulsion of an object, said gas combustion mechanism comprises a first priming cylinder having a first piston and an air intake fluidically connected via a first valve means to a second delivery cylinder having a second piston, said first priming cylinder fluidically connected to a fuel gas reservoir via a second valve means, said first priming cylinder adapted to receive fuel gas from said fuel gas reservoir and air through said air intake thereby forming an air/fuel gas mixture therein, said first piston adapted to compress said air/fuel gas mixture and transfer said air/fuel gas mixture to said second delivery cylinder via said first valve means, said air/fuel mixture ignited therein and thereby urging said second piston towards said object thereby propelling the same. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective schematic view of a first embodiment of a nail gun in accordance with the fastener driving tool of the present invention. 
           [0020]      FIG. 2  is a cross-sectional schematic view of the nail gun of  FIG. 1 . 
           [0021]      FIG. 3  is a cut away end view of the nail gun of  FIG. 1 . 
           [0022]      FIG. 4  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 . 
           [0023]      FIG. 5  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as air and fuel enter the priming cylinder. 
           [0024]      FIG. 6  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as air/fuel mixture is compressed in the priming cylinder. 
           [0025]      FIG. 7  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as air/fuel mixture is transferred from the priming cylinder to the driving cylinder. 
           [0026]      FIG. 8  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as air/fuel mixture within the driving cylinder is compressed. 
           [0027]      FIG. 9  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as the ignited air/fuel mixture displaces the piston within the driving cylinder towards the nail to be fired. 
           [0028]      FIG. 10  is an enlarged view of the gas combustion mechanism shown in  FIG. 2 , as the driver connected to the piston propels the nail and the gas begins to be exhausted from the driving cylinder. 
           [0029]      FIGS. 11 and 12  are enlarged views of the gas combustion mechanism shown in  FIG. 2 , as piston is returned back up the driving cylinder and remaining exhaust gas is purged from the driving cylinder. 
           [0030]      FIG. 13  is an enlarged view of the cycle wheel arrangement used to control the tool cycle. 
           [0031]      FIG. 14  is an enlarged view of an alternative embodiment of the cycle wheel arrangement shown in  FIG. 13 . 
           [0032]      FIGS. 15   a  and  15   b  are enlarged elevation and cutaway views of the fuel gas cartridges. 
           [0033]      FIG. 16  is a cross-sectional schematic view of a second embodiment of a nail gun in accordance with the fastener driving tool of the present invention. 
           [0034]      FIG. 17  is a schematic view of a third embodiment of a nail gun in accordance with the fastener driving tool of the present invention. 
           [0035]      FIG. 18  is an enlarged schematic view of the internal receiver of the nail gun depicted in  FIG. 17 . 
           [0036]      FIG. 19  is an enlarged cutaway partial view of the sealing ring of the nail gun depicted in  FIG. 17 . 
           [0037]      FIG. 20  is an enlarged schematic view of the plate valve of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0038]      FIGS. 1 and 2  depict a combustion driven nail gun (tool) for firing nail fasteners. The nail gun comprises a priming cylinder A and a power driving cylinder B, housed within tool main body casing  62 . A tool support handle  7  having a pistol grip  5  extends from casing  62  and houses a fuel gas cartridge (reservoir)  3 . A battery  1  housed within removable battery casing  2  is attached to support handle  7 . A nail fastener cartridge (or magazine)  4  delivers nail fasteners  8  to tool nose (or barrel)  9 . 
         [0039]    The operation of the combustion nail gun will now be described. A user holds the combustion driven nail gun by tool support handle  7  and pistol grip  5 . The user&#39;s finger is placed on firing trigger  16 . Primary micro trigger  15  is activated. Electronic central processing unit (CPU)  18  is alerted that the tool is in operation. CPU  18  switches circuit on to a priming cylinder drive having a cycle sensor wheel  21  and main power feed slip ring  66  as shown in  FIG. 13 . Motor  35  is activated. Wheel  21  rotates causing first piston  24  to progress downward in priming cylinder A via connecting rod  23 , crank pin  22  and bearing  34 . A partial vacuum occurs above piston  24  in priming cylinder A causing transfer valve  32  to close and intake valve  31  to open. Air is drawn into priming cylinder A through intake port  30 . Fuel delivery striker segment  25  makes contact with pin  27  opening gas valve  26  in the head of gas cylinder  3  for a short duration. A given volume of atomised fuel is released from cylinder  3  and passes through gallery  28  to intake port  30 . Atomised fuel gas mixes with inward flowing air at intake port  30  through valve  31 , filling priming cylinder A with a mixture of fuel, gas and air, see  FIG. 5 . Piston  24  progresses back up priming cylinder A, and a pressure rise occurs closing valve  31 , see  FIG. 6 , and opening valve  32  transferring air/fuel mixture from priming cylinder A into driving cylinder B. Electro magnetic exhaust valves  42  and  45  are energised during the upward progression of piston  24  causing valve head  45  to open, allowing the inward flow of fuel/gas air mixture through valve  32  to purge residual exhaust gases from combustion space in cylinder B, see  FIG. 7 . When 50% of the fuel/gas air mixture phase has taken place slip ring  67  disengages electro magnetic valve  42  causing valve head  45  to close via a coil spring (not shown) and sealing exhaust port  43 . Piston  24  progresses to the top of priming cylinder A transferring fuel/gas air mixture into combustion area of driving cylinder B. Slip ring  69  disengages power circuit to motor. CPU  18  switches circuit on to cooling fan motor  41 . Tool is positioned and pressed onto a work piece, mechanism  61  is depressed alerting CPU  18  tool is safe to fire. CPU  18  switches circuit on to switch mechanism  17  allowing main firing trigger  16  to be fully depressed. Mechanism  17  alerts CPU  18  to activate igniter  48 . Fuel/air mixture in combustion area of driving cylinder B ignites and an explosion occurs, a rapid rise of pressure occurs causing valve  32  to seal close, see  FIG. 8 . Second piston  51  and driver  55  progress down bore  54  of cylinder B. Driver  55  drives fastener  8  down tool nose  9  into the work piece. As piston  51  progresses down cylinder B air under piston  51  escapes through exhaust port  60  and  12 . When piston  51  has traveled 90% of its travel the under side of piston  51  comes into contact with rubber bumper  58 . Bumper  58  absorbs energy and slows the progression of piston  51 . Exhaust port  60  is then uncovered allowing exhaust gases to escape from cylinder B into cavity  57  and then out through tool housing exhaust port  13 . At the end of travel piston  51 , piston  51  makes contact with power driver cylinder piston end of stroke sensor  59 . Sensor  59  alerts CPU  18  of the position of piston  51 . CPU  18  energises electro magnetic exhaust valve  42  to open allowing exhaust gases to be expelled from the top of cylinder B through exhaust port  43  into cavity  57  and out through cavity  13 . Stored energy in bumper  58  returns piston  51  and driver  55  back up bore  54  in driving cylinder B. Remaining exhaust gases in driving cylinder B are purged through exhaust port  43 . Air is allowed to be displaced to the underside of piston  51  in cylinder B through exhaust port  60  and  12  to prevent a partial vacuum inhibiting the return of piston  51  to top of bore  54  in cylinder B, see  FIGS. 11 and 12 . CPU  18  has an electronic timing mechanism built-in to operate electro magnetic valve  42  and cooling fan  41 . When piston  51  has reached the top of bore  54  of cylinder B, the CPU  18  switches the circuit to electro magnetic exhaust valve  42  off, allowing valve head  45  to close. CPU  18  allows cooling fan  41  to remain active for a period of approximately 10 seconds in one-shot use only, or for continuous application the cooling fan  41  may remain active. A temperature sensor (not shown) in cavity  57  in communication with CPU  18  may be incorporated. 
         [0040]      FIG. 13  depicts a mechanical brake/limiting mechanism (not shown) to ensure that only one revolution of cycle wheel  21  per tool cycle is required. 
         [0041]      FIG. 14  is an alternate embodiment to the mechanical mechanism  21  of  FIG. 13 . In this alternate embodiment electronic crank angle mechanisms  70 ,  19   a , stepper motor  35  and high-tension spark mechanisms maybe incorporated into and in communication with CPU  18 . 
         [0042]      FIG. 15  depicts high pressure liquid fuel cylinders containing for example methanol as a fuel medium and liquid/gaseous CO 2  as a pressurizing medium as opposed to a conventional MAPP gas. Storing fuel in this matter typically at 850 psi allows more efficient atomization of the fuel gas medium and combining with air mass in a combustion cylinder process more energy is extracted. Hydrogen may also be utilised as a fuel gas medium. 
         [0043]      FIG. 16  depicts a second embodiment of a nail gun in accordance with the present invention. The nail gun of this second embodiment is similar to that of the first embodiment and like reference numerals have been used to depict similar components. The main difference is that the first embodiment shown in  FIG. 2  has an actuation mechanism in the form of a connecting rod  23 , crank pin  22  and bearing  34  for mechanically actuating the piston  24  within priming cylinder A. However, in this second embodiment the actuation mechanism is replaced by an electromagnetic actuation mechanism. A solenoid cylinder (or coil)  102  actuates piston  24  to transfer gas/fuel air mixture into driving cylinder B. A piston return spring  103  is connected to piston  24  to urge the piston upwardly when solenoid cylinder  102  is deactivated. Furthermore, gas release solenoid  104  replaces the mechanical means (of the first embodiment) of fuel delivery to intake port  30 . The priming cylinder A also has exhaust ports  105 . Solenoids  102  and  104  are both in communication with CPU  18  and are both electronically actuated. 
         [0044]      FIG. 17  depicts a third embodiment of a nail gun in accordance with the present invention. This embodiment is similar to that of the previous embodiments and like reference numerals have been used to denote similar components. This embodiment shows a number of preferable features, each of which may replace or compliment corresponding components of the previous embodiments. The preferable features are described individually in the following paragraphs. 
         [0045]    The nail gun depicted in  FIG. 17  comprises first and second spring biased balls  201  and  202  that are disposed on mechanism  61  and engage the bottom of driver  55  to retain second piston  51  near the top of driving cylinder B. Balls  201  and  202  move inwardly towards each other by spring force, once driver  55  passes above them on the return stroke of the tool. In alternative arrangements, balls  201  and  202  engage location indentations in driver  55 , which advantageously provides positive control of driver  55 . In use, balls  201  and  202  retain second piston  51  and driver  55  high in driving cylinder B, even as the compressed fuel/air gas mixture is introduced. When the tool is subsequently positioned and pressed onto the work piece, mechanism  61  is depressed from a first to a second position, alerting CPU  18  that the tool is safe to fire. As mechanism  61  is depressed, second piston  51  also moves higher, further compressing the air/fuel gas mixture in driving cylinder B just prior to ignition. Upon ignition, second piston  51  and driver  55  are forcibly driven down, overcoming the spring force of first and second spring biased ball  201  and  202 . When second piston  51  and driver  55  complete their return stroke, first and second spring biased balls  201  and  202  again engage the bottom of driver  55 . This arrangement enables high pre-ignition gas pressures to be achieved due to the extra 10% or so of upward travel imparted to second piston  51 . 
         [0046]    The third embodiment of the nail gun depicted in  FIG. 17  depicts a chamber  203  that exists in the interior of bumper  58 . Bumper  58  is preferably constructed of high-grade durable rubber and layered fabric to provide durability and high resilience. In this configuration, bumper  58  still slows the progression of piston  51  and then returns piston  51  and driver  55  back up bore  54  in driving cylinder B. For those purposes, a spring may also supplement bumper  58 . In use, as bumper  58  is compressed by piston  51 , chamber  203  compresses, sending pressurised air out outlet valve  204 , through transfer channel  205  and into internal receiver  206  of piston  24 . Bumper  58  and chamber  203  resiliently restore from their compressed state, forcibly returning piston  51  back up bore  54 . The expanding volume of chamber  203  causes a pressure drop that closes outlet valve  204  and opens fill valve  209 , drawing fresh air into chamber  203  while sealing transfer channel  205  at pressure. In this way, wasted energy is recovered by pumping pressurised air back to priming cylinder A for subsequent use. The pressure of the air/fuel mixture is also increased, which in turn increases the efficiency of its combustion. 
         [0047]      FIG. 18  will now be used to describe how piston  24  and internal receiver  206  interact to utilise the air pressurised by chamber  203 . The motion of piston  24  occurs as explained in the previous embodiments. Whenever piston  24  is at the top of priming cylinder A, inlet aperture  207  is aligned with transfer channel  205 . Piston  24  is in this top position when the downward motion of piston  51  compresses bumper  58  and thus pressurises the air in transfer channel  205  through to internal receiver  206 . As explained above, when piston  51  returns up bore  54 , outlet valve  204  closes, keeping transfer channel  205  and internal receiver  206  pressurised. Upon the next use, piston  24  travels downward, sealing internal receiver  206 . The same downward motion simultaneously creates a partial vacuum above piston  24  in priming cylinder A, causing transfer valve  32  to close and intake valve  31  to open. Air and fuel are drawn into priming cylinder A through intake port  30  and valve  31 . When piston  24  nears the bottom of its travel, bypass  208  aligns with bypass aperture  210  allowing pressurised air from internal receiver  206  to pressurise the air/fuel mixture above piston  24 . The consequential pressure rise closes intake valve  31 . Piston  24  then progresses back up priming cylinder A and a further pressure rise occurs, opening valve  32  and transferring the air/fuel mixture from priming cylinder A into driving cylinder B. This arrangement advantageously allows the pressurised air from chamber  203  to be stored for use at a later time. 
         [0048]      FIG. 19  is an enlarged partial view of second piston  51  depicting a preferable configuration of sealing ring  52 . In this configuration, sealing ring  52  is fabricated from carbon impregnated Teflon and has the cross-sectional shape shown in  FIG. 19 . The material of sealing ring  52  and its small contact area with bore  54  results in minimal frictional resistance, which advantageously results in a smaller upward force required to return second piston  51  back up driving cylinder B. A semi flexible lip  211  extends upward from sealing ring  52  and is spaced apart from bore  54  when lip  211  is at rest. Upon ignition, high pressure acts on the top of second piston  51  and sealing ring  52 , causing lip  211  to flex outward against bore  54  from its rest position, thereby providing a greater gas seal and minimising losses. Once the gas pressure is relieved, the sealing lip  211  returns to its rest position off of bore  54  thus minimising resistance during the return stroke. 
         [0049]      FIG. 20  is an enlarged schematic view of a preferable alternative configuration of power driver cylinder head  47 . In this configuration, mixing fan  212  is rotatably mounted to the interior of power driving cylinder B. Mixing fan  212  is magnetically coupled to cooling fan motor  41 , which is mounted to the exterior of driving cylinder B. Structural components between mixing fan  212  and cooling fan motor  41  are preferably made of aluminium. Mixing fan  212  agitates the air/fuel gas mixtures to obtain more complete combustion, raising the reliability of the tool&#39;s power output. 
         [0050]      FIG. 20  also depicts electro magnetic valve  42  being replaced by plate valve  213 , which is preferably also electro magnetically actuated. When plate valve coil  215  is de-energised, plate valve spring  214  biases plate valve  213  to the open position. When CPU  18  energises plate valve coil  215 , electro magnetic force overcomes plate valve spring  214  to close plate valve  213 . When plate valve  213  is open, power driving cylinder B is in fluid communication with exhaust plenum  216 , allowing rapid purging of residual exhaust gases from the combustion space in cylinder B. 
         [0051]    Whilst the abovementioned embodiment of the present invention is described with reference to a nail gun for driving nails, it should be understood that the present invention in other not shown embodiments can be used to fire other fasteners, but is limited thereto. Also, in other not shown embodiments the gas combustion mechanism of the abovementioned embodiment may be used in some other apparatus where an object is propelled. Such drive apparatus may have a tool or drive application different to the nail gun of the abovementioned embodiments. 
         [0052]    The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of”.