Abstract:
A combustion-type power tool having a cooling arrangement for cooling a gas canister. The tool includes a housing having a gas canister accommodating section in which a gas canister is accommodated. An air passage is defined between the gas canister accommodating section and the gas canister accommodated therein. The gas canister accommodating section is formed with an air inlet port in communication with the air passage for introducing air into the air passage. Since air flows along the gas canister, the gas canister can be cooled. If the tool is provided with a fan, the rotation of the fan causes air suction passing through the air passage.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a combustion-type power tool, and more particularly, to such power tool capable of driving a fastener such as a nail, an anchor, and a staple into a workpiece. 
   In a conventional combustion-type driving tool such as a nail gun, a mixture of air and gaseous fuel injected into a combustion chamber is ignited by a spark at an ignition plug to cause gas expansion in the combustion chamber, which in turn causes a linear momentum of a piston. By the movement of the piston, a nail is driven into a workpiece. Such conventional combustion-type nail gun is described in U.S. Pat. No. 5,197,646 and Japanese Patent Publication No. H03-25307. 
   According to the conventional combustion-type power tool, a temperature of an entire tool including a gas canister is increased by heat generated upon combustion in a combustion chamber, particularly upon repeated operation, for example, continuous nail driving operation. As a result, an inner pressure of the gas canister will be increased thereby increasing an injection rate of the combustible gas. In the combustion-type power tool, air-fuel mixture can be ignited if gas density in the combustion chamber (amount of combustible gas per an entire inner volume of the combustion chamber) is within a predetermined range. If the injection amount of the combustible gas is increased, i.e., if density of the combustible gas is increased, ignition does not occur, or sufficient expansion capable of driving a nail into a workpiece cannot be provided due to insufficient ignition. 
   SUMMARY OF THE INVENTION 
   It is therefore, an object of the present invention to provide a combustion-type power tool capable of stabilizing a gas canister within a desirable temperature thereby providing injection with a constant amount of combustible gas, to thus realizing a stabilized ignition performance in a combustion chamber. 
   This and other object of the present invention will be attained by a combustion-type power tool including a housing, a cylinder head, a cylinder, a piston, a combustion chamber frame, a driver blade, and an ignition plug. 
   The housing includes a gas canister accommodating section and has one end and another end. The cylinder head is disposed at the one end and formed with a fuel passage allowing a combustible gas from the gas canister to pass therethrough. The cylinder is disposed in and fixed to the housing and defines an axial direction. The piston is slidably disposed in the cylinder and reciprocally movable in the axial direction. The piston divides the cylinder into an upper space above the piston and a lower space below the piston. The combustion chamber frame is disposed in the housing and movable in the axial direction. The combustion chamber frame is abuttable on the cylinder head to provide a combustion chamber in cooperation with the cylinder head and the piston. The driver blade extends in the axial direction from the piston in the lower space. The ignition plug is exposed to the combustion chamber for igniting a mixture of air and the combustible gas in the combustion chamber. 
   An air passage is defined between the gas canister accommodating section and the gas canister accommodated therein. The gas canister accommodates section being formed with an air inlet in communication with the air passage. 
   In another aspect of the invention, there is provided a gas canister cooling arrangement in a combustion-type power tool having a housing. The housing included a gas canister accommodating section for accommodating therein a gas canister. An air passage is defined between the gas canister accommodating section and the gas canister accommodated therein. An air inlet of the air passage is formed at the gas canister accommodating section. 
   In another aspect of the invention, there is provided a combustion-type power tool including an outer frame. The outer frame includes a gas canister accommodating section for accommodating a gas canister. The gas canister insertion opening is provided in the canister accommodating section. An air passage is defined between the gas canister accommodating section and the gas canister accommodated therein. The gas canister accommodating section is formed with an air inlet in communication with the air passage. The air inlet is independent of the canister insertion opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the single drawing; 
       FIG. 1  is a vertical cross-sectional side view showing a combustion-type nail gun embodying a combustion-type power tool according to an embodiment of the present invention, the nail gun being in an initial phase prior to nail driving operation. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A combustion-type power tool according to one embodiment of the present invention will be described with reference to  FIG. 1 . The embodiment pertains to a combustion-type nail gun. The combustion-type nail gun  1  has a housing  2  constituting an outer frame. The housing  2  is formed with an exhaust port  2   a . A head cover  3  formed with an intake port  3   a  is mounted on the top of the housing  2 . A handle  4  is attached to the housing  2  and extends from a side of the housing  2 . 
   The handle  4  has a trigger switch  5  and accommodates therein a battery (not shown). The battery is detachably disposed in the handle  4 . A canister housing  29  is provided in the housing  2  at a position immediately beside the handle  4 . In the depicted embodiment shown in  FIG. 1 , a right side part of the housing  2  is made integrally with the handle  4 . Therefore, the canister housing  29  is defined by a material of the handle  4  and a material of the housing  2 . 
   The canister housing  29  is formed with an air inlet port  2   b  at a position near one end of a gas canister  30 . The gas canister  30  is detachably disposed in the canister housing  29 . The canister housing  29  has a canister insertion opening through which the gas canister  30  is inserted into the canister housing  29 . A pivot shaft  2 B protrudes from the canister housing  29 , and a cover  2 A is pivotally supported to the pivot shaft  2 B for opening and closing the canister insertion opening. The gas canister  30  includes an accumulating section  30 A for accumulating therein a combustible liquidized gas, and a gauging section  30 B provided at an end of the accumulating section  30 A for allowing the liquidized gas to pass therethrough at a constant amount. The gauging section  30 B is provided with an injection rod  30 C connected to a gas canister connecting portion  25 A provided in a cylinder head  11  (described later). An air passage  30   a  for allowing air to pass therethrough is defined between a wall surface of the canister housing  29  and an outer surface of the gas canister  30 . A magazine  6  for containing therein nails (not shown) is provided at a lower side of the handle  4 . 
   A nose  7  extends from an end of the housing  2 , the end being opposite to the head cover  3 . The nose  7  is formed integrally with a cylinder  20  (described later) and has a tip end in confrontation with a workpiece  28 . The nose  7  is adapted for guiding sliding movement of a drive blade  23 A (described later) and the nail. A push lever  9  is movably provided and has a lower portion slidable with respect to a lower end portion  7 A of the nose  7 . The push lever  9  has a tip end adapted to be pressed against the workpiece  28 , and has an upper end portion associated with an arm member  8  fixed to a base section  10 A of a combustion-chamber frame  10  which will be described later. 
   A compression coil spring  22  is interposed between the arm member  8  and the cylinder  20  for normally urging the push lever  9  in a protruding direction away from the head cover  3 . When the housing  2  is pressed toward the workpiece  28  while the push lever  9  is in abutment with the workpiece  28  against a biasing force of the compression coil spring  22 , an upper portion of the push lever  9  is retractable into the housing  2 . 
   A cylinder head  11  is secured to the top of the housing  2  for closing the open top end of the housing  2 . The cylinder head  11  supports a motor  18  at a position opposite to a combustion chamber  26  described later. Further, an ignition plug  12  is also supported to the cylinder head  11  at a position adjacent to the motor  18 . The ignition plug  12  has an ignition spot exposed to the combustion chamber  26 . The ignition plug  12  is ignitable upon manipulation to the trigger switch  5  and upon movement of the combustion chamber frame  10  to its predetermined position because of the pressing of the push lever  9  against the workpiece  28 . The motor  18  has a rotation shaft  18 A to which a fan  19  positioned in the combustion chamber  26  is fixed. 
   The cylinder head  11  has a handle side in which is formed a fuel injection passage  25  which allows a combustible gas to pass therethrough. One end of the fuel injection passage  25  serves as an injection port that opens at the lower surface of the cylinder head  11 . Another end of the fuel injection passage  25  is engaged with the gas canister connecting portion  25 A in communication with the injection rod  30 C. The combustion-chamber frame  10  is provided in the housing  2  and is movable in the lengthwise direction of the housing  2 . The combustion chamber frame  10  includes the base section  10 A and a head section  10 B extending from the base section  10 A at a position opposite to the push lever  9 . 
   A head switch (not shown) is provided in the housing  2  for detecting an uppermost stroke end position of the combustion chamber frame  10  when the nail gun  1  is pressed against the workpiece  28 . The head switch can be turned ON when the push lever  9  is elevated to a predetermined position for starting rotation of the motor  18 . 
   Since the arm member  8  is fixed to the base section  10 A, the combustion chamber frame  10  is moved in accordance with the movement of the push lever  9 . The cylinder  20  is fixed to the housing  2 . The combustion chamber frame  10  has an inner surface in sliding contact with the cylinder  20 . Thus, the cylinder  20  guides movement of the combustion chamber frame  10 . The cylinder  20  has an axially intermediate portion formed with an exhaust hole  21 . An exhaust-gas check valve (not shown) is provided to selectively close the exhaust hole  21 . 
   A piston  23  is slidably and reciprocally provided in the cylinder  20 . The piston  23  divides an inner space of the cylinder  20  into an upper space above the piston  23  and a lower space below the piston  23 . The driver blade  23 A extends downwards from a side of the piston  23 , the side being at the cylinder space below the piston  23 , to the nose  7 . The driver blade  23 A is positioned coaxially with the nail setting position in the nose  7 , so that the driver blade  23 A can strike against the nail during movement of the piston  23  toward its bottom dead center. Further, a bumper  24  is provided on the bottom of the cylinder  20 . The bumper  24  is made from a resilient material. When the piston  23  moves to its bottom dead center, the piston  23  abuts on the bumper  24  and stops. In this case, the bumper  24  absorbs a surplus energy of the piston  23 . 
   When the upper end of the combustion-chamber frame  10  abuts on the cylinder head  11 , the cylinder head  11 , the combustion-chamber frame  10 , and the upper cylinder space above the piston  23  define in combustion the combustion chamber  26 . When the combustion-chamber frame  10  is separated from the cylinder head  11 , a first flow passage  31  in communication with an atmosphere is provided between the cylinder head  11  and the upper end portion of the combustion-chamber frame  10 , and a second flow passage  32  in communication with the first flow passage  31  is provided between the lower end portion of the combustion-chamber frame  10  and the upper end portion of the cylinder  20 . These flow passages  31 ,  32  allow a combustion gas and a fresh air to pass along the outer peripheral surface of the cylinder  20  for discharging these gas through the exhaust port  2   a  of the housing  2 . Further, the above-described intake port  3   a  is formed for supplying a fresh air into the combustion chamber  26 , and the exhaust hole  21  is adapted for discharging combustion gas generated in the combustion chamber  26 . 
   Rotation of the fan  19  performs the following three functions. First, the fan  19  stirs and mixes the air with the combustible gas as long as the combustion chamber frame  10  remains in abutment with the cylinder head  11 . Second, after the mixed gas has been ignited, the fan  19  causes turbulent combustion of the air-fuel mixture, thus promoting the combustion of the air-fuel mixture in the combustion chamber  26 . Third, the fan  19  performs scavenging such that the exhaust gas in the combustion chamber  26  can be scavenged therefrom and also performs cooling to the combustion chamber frame  10  and the cylinder  20  when the combustion chamber frame  10  moves away from the cylinder head  11  and when the first and second flow passages  31 ,  32  are provided. 
   Next, operation of the combustion-type nail gun  1  will be described. In the non-operational state of the combustion-type nail gun  1 , the push lever  9  is biased away from the cylinder head  11  as shown in  FIG. 1  by the biasing force of the compression coil spring  22 , so that the push lever  9  protrudes from the lower end of the nose  7 . Thus, the uppermost end portion of the head section  10 B is spaced away from the cylinder head  11  because the arm member  8  connects the combustion chamber frame  10  to the push lever  9 . Further, a part of the combustion chamber frame  10  which part defines the combustion chamber  26  is also spaced away from the top portion of the cylinder  20 . Hence, the first and second flow passages  31  and  32  are provided. In this condition, the piston  23  stays at its top dead center in the cylinder  20 . 
   With this state, if the push lever  9  is pushed onto the workpiece  28  while holding the handle  4  by a user, the push lever  9  is moved toward the cylinder head  11  against the biasing force of the compression coil spring  22 . At the same time, the combustion chamber frame  10  which is associated with the push lever  9  through the arm member  8  is also moved toward the cylinder head  11 , closing the above-described flow passages  31  and  32 . Thus, the sealed combustion chamber  26  is provided. 
   In accordance with the movement of the push lever  9 , the liquidized gas in the gas canister  30  is injected into the combustion chamber  26  through the gas canister connecting portion  25 A and through the fuel injection passage  25 . 
   Further, in accordance with the movement of the push lever  9 , the combustion-chamber frame  10  reaches its uppermost stroke end whereupon the head switch is turned ON to energize the motor  18  for starting rotation of the fan  19 . Rotation of the fan  19  stirs and mixes the combustible gas with air in the combustion chamber  26 . 
   In this state, when the trigger switch  5  provided at the handle  4  is turned ON, spark is generated at the ignition plug  12  to ignite the combustible gas. The combusted and expanded gas pushes the piston  23  to its bottom dead center. Therefore, a nail in the nose  7  is driven into the workpiece  28  by the driver blade  23 A until the piston  23  abuts on the bumper  24 . 
   After the nail driving, the piston  23  strikes against the bumper  24 , the cylinder space above the piston  23  becomes communicated with the exhaust hole  21 . Thus, the high pressure and high temperature combustion gas is discharged out of the cylinder  20  through the exhaust hole  21  of the cylinder  20  and through the check valve (not shown) provided at the exhaust hole  21  to the atmosphere to lower the pressure in the combustion chamber  26 . When the inner space of the cylinder  20  and the combustion chamber  26  becomes the atmospheric pressure, the check valve is closed. 
   Combustion gas still remaining in the cylinder  20  and the combustion chamber  26  has a high temperature at a phase immediately after the combustion. However, the high temperature can be absorbed into the walls of the cylinder  20  and the combustion chamber frame  10 . Thus, temperature of the cylinder  20  and the gas canister  30  will be elevated. The absorbed heat is diffused to the atmosphere from the cylinder  20  and the combustion chamber frame  10 . 
   Absorption of the heat into the cylinder  20  etc. causes rapid cooling to the combustion gas. Thus, the pressure in the sealed space in the cylinder  20  above the piston  23  further drops to less than the atmospheric pressure (creating a so-called “thermal vacuum”). Accordingly, the piston  23  can be moved back to the initial top dead center position. 
   Then, the trigger switch  5  is turned OFF, and the user lifts the combustion-type nail gun  1  from the workpiece  28  for separating the push lever  9  from the workpiece  28 . As a result, the push lever  9  and the combustion chamber frame  10  move away from the cylinder head  11  because of the biasing force of the compression coil spring  22  to restore a state shown in  FIG. 1 . Thus, the first and second flow passages  31  and  32  are provided. In this case, the fan  19  is configured to keep rotating for a predetermined period of time in spite of OFF state of the trigger switch  5 . In the state shown in  FIG. 1 , fresh air flows into the combustion chamber  26  through the intake port  3   a  formed at the head cover  3  and through the flow passages  31 ,  32  as shown by an arrow “a 1 ”˜“a 4 ”, expelling the residual combustion gas out of the exhaust port  2   a . Thus, the combustion chamber  26  is scavenged. 
   At the same time, air is sucked into the housing  2  through the air inlet port  2   b  as shown by an arrow “b 1 ” by the rotation of the fan  19 . The sucked air flows through the air passage  30   a  and passes along the outer side of the gauging  30 B and is directed toward the fan  19  as shown by an arrow “b 2 ”. Then, the air flows radially outwardly of the fan  19  as shown by an arrow “b 3 ”, and then passes through the second flow passage  32  as indicated by an arrow “a 4 ” and is discharged through the exhaust port  2   a.    
   In this way, the air flow “b 1 ” and “b 2 ” cools the gas canister  30 . Accordingly, even if the temperature of the cylinder  20  etc. is elevated due to the repeated operation of the tool  1 , temperature increase of the gas canister  30  can be restrained to maintain the internal pressure of the gas canister  30  at approximately constant level. As a result, a constant amount of combustible gas can be supplied into the combustion chamber  26  to provide a stabilized ignition. Further, since the air inlet port  2   b  in the housing  2  is positioned near the end of the gas canister  30 , the end being opposite to the gauging section  30 B, an entirety of the gas canister  30  can be subjected to cooling. 
   The above-described advantage can be provided by forming the air inlet port  2   b  at the proper region of the housing  2 . Thus, the temperature increase of the gas canister  30  can be restrained, thereby providing a constant amount of combustible gas, to thus realize the stabilized ignition performance. Then, the rotation of the fan  19  is stopped to restore an initial stationary state. Thereafter, subsequent nail driving operation can be performed by repeating the above described operation process. 
   While the invention has been described in detail and with reference to specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modification may be made therein without departing from the scope of the invention. For example, the present invention is not limited to the nail gun but is available for any kind of power tools in which a combustion chamber and a piston are provided, and as long as expansion of gas as a result of combustion of air-fuel mixture in the combustion chamber causes reciprocal motion of the piston.