Abstract:
A combustion-type power tool includes a cylinder, a piston, a head, a combustion chamber frame, an ignition unit, a trigger, a control member. The combustion chamber frame is abuttable on the head to provide a combustion chamber in cooperation with the head and the piston. The trigger is operated by a user for driving the fastener into a workpiece. The control member detects that the combustion chamber has been provided and the trigger has been operated, and allows the ignition unit to ignite the combustible gas only when the control member detects that both the combustion chamber has been provided and the trigger has been operated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field 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. 
     2. Description of Related Art 
     In a conventional combustion-type driving tool such as a nail gun, a combustion chamber is formed when a push member is pushed a predetermined distance. Then, a mixture of air and gaseous fuel injected into the 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. In U.S. Pat. No. 5,197,646, a man cannot turn on a trigger for turning on the ignition plug without pushing a push member. 
     SUMMARY OF THE INVENTION 
     However, in Japanese Patent Publication No. H07-36985, even if the push member is not pushed the predetermined distance, that is, the combustion chamber is not formed, a man can turn on the trigger. Thus, in Japanese Patent Publication No. H07-36985, spark and gaseous fuel is consumed in vain. 
     In view of the above-described drawbacks, it is an objective of the present invention to provide a combustion-type power tool in which the operation for the trigger is not valid if the combustion chamber frame has not been provided. 
     In order to attain the above and other objects, the present invention provides a combustion-type power tool includes a cylinder, a piston, a head, a combustion chamber frame, an ignition unit, a trigger, and a control member. 
     The combustion chamber frame is abuttable on the head to provide a combustion chamber in cooperation with the head and the piston. The trigger is operated by a user for driving the fastener into a workpiece. The control member detects that the combustion chamber has been provided and the trigger has been operated, and allows the ignition unit to ignite the combustible gas only when the control member detects that both the combustion chamber has been provided and the trigger has been operated. 
     Another aspect of the present invention provides a combustion-type power tool includes a striking member, an ignition unit, a trigger and a control member. 
     A combustion chamber can be provided in the striking member. The striking member provides a fastener with a striking force when the combustion chamber broadens in accordance with combustion of combustible gas injected into the combustion chamber. The ignition unit ignites combustible gas injected into the combustion chamber. The striking member provides the fastener with a striking force when the combustion chamber broadens in accordance with the combustion of the combustible gas injected into the combustion chamber. The trigger is operated by a user for driving the fastener into a workpiece. The control member detects that the combustion chamber has been provided and the trigger has been operated, and allows the ignition unit to ignite the combustible gas only when the control member detects that both the combustion chamber has been provided and the trigger has been operated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiments taken in connection with the accompanying drawings in which: 
         FIG. 1  shows a cross-section view of a combustion-type nail gun; 
         FIG. 2  shows a cross-section view of one part of the combustion-type nail gun before a combustion chamber is formed; 
         FIG. 3  shows a cross-section view of one part of the combustion-type nail gun after the combustion chamber has been formed; 
         FIG. 4  shows a cross-section view of one part of the combustion-type nail gun when a trigger is turned ON after the combustion chamber has been formed; 
         FIG. 5  shows a cross-section view when  FIG. 1  is cut at A-A line; 
         FIG. 6  shows a cross-section view of one part of a combustion-type nail gun before a combustion chamber has been formed; 
         FIG. 7  shows a cross-section view when  FIG. 6  is cut at B-B line; 
         FIG. 8  shows a cross-section view of one part of the combustion-type nail gun when the combustion chamber has been formed; 
         FIG. 9  shows a cross-section view of one part of the combustion-type nail gun when a trigger is turned ON after the combustion chamber has been formed; 
         FIG. 10  shows a cross-section view when  FIG. 9  is cut at C-C line; 
         FIG. 11  shows a cross-section view of one part of the combustion-type nail gun when the trigger is turned ON before the combustion chamber has been formed; and 
         FIG. 12  shows a cross-section view when  FIG. 11  is cut at D-D line. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A combustion-type power tool according to first embodiment of the present invention will be described with reference to  FIGS. 1 through 5 . The first embodiment pertains to a combustion-type nail gun  1 . Throughout the specification, the term “upper” and “lower” are used assuming that the combustion-type nail gun is oriented in a vertical direction. 
       FIG. 1  shows a cross-section view of a combustion-type nail gun  1 . The combustion-type nail gun  1  has a housing  2  constituting an outer frame and including a main housing  2 A and a canister housing  2 B juxtaposed thereto. An exhaust port (not shown) is formed on main housing  2 A. A head cover  3  is mounted on the top of the main housing  2 A. An intake port (not shown) is formed on the head cover  3 . A gas canister  4  is detachably accommodated in the canister housing  2 B. The gas canister  4  contains therein combustible liquidized gas. 
     A handle  5  extends from a side of the canister housing  2 B. The handle  5  has a trigger  6 , and accommodates therein a battery (not shown). The trigger  6  will be described later in detail. A magazine  7  and a tail cover  8  are disposed below the housing  2 . The magazine  7  is adapted for containing therein nails (not shown), and the tail cover  8  is adapted for feeding the nail in the magazine  7  and setting the nail to a predetermined position. 
     A combustion chamber frame  9  is provided in the main housing  2 A. The combustion chamber frame  9  is movable in the lengthwise direction thereof in the main housing  2 A interlockingly in accordance with the movement of a push member  14  (described later), since the lower portion of the combustion chamber frame  9  is connected to the push member  14  via a link member (not shown). The combustion chamber frame  9  is provided with an engage piece  91  extending from an outer surface of the combustion chamber frame  9  in a radial direction of the combustion chamber frame  9 . The engage piece  91  will be described later in detail. 
     A cylinder  10  is fixed to the main housing  2 A and has an inner space. An outer surface of the cylinder  10  is in sliding contact with the combustion chamber frame  9 . Thus, the cylinder  10  guides movement of the combustion chamber frame  9 . An exhaust hole  10   a  is formed on the cylinder  10 . An exhaust-gas check valve  10   b  is also provided at the cylinder  10  in order to selectively close the exhaust hole  10   a.    
     A piston  11  is slidably and reciprocally provided in the cylinder  10 . The piston  11  divides an inner space of the cylinder  10  into an upper space above the piston  11  and a lower space below the piston  11 . 
     A driver blade  12  extends downwards from one surface of the piston  11 , the surface being at the cylinder space below the piston  11 . The driver blade  12  is positioned coaxially with the nail setting position where the tail cover  8  sets the nail, so that the driver blade  12  can strike against the nail during movement of the piston  11  toward its bottom dead point. 
     A bumper  13  is provided on the bottom of the cylinder  10 . The bumper  13  is made from a resilient material. When the piston  11  moves to its bottom dead point, the piston  11  is abuttable on the bumper  13 . 
     The push member  14  is movably provided at a lower portion of the main housing  2 A. The push member  14  has a tip portion adapted to be pressed against a workpiece  40 , and has an upper portion associated with the combustion chamber frame  9  via the link member (not shown). 
     A compression coil spring  15  is interposed between the link member and the cylinder  10  for normally urging the push member  14  in a protruding direction away from the head cover  3 . When the housing  2  is pressed toward the workpiece  40  while the push member  14  being in abutment with the workpiece  40  against a biasing force of the compression coil spring  15 , an upper portion of the push member  14  is retractable into the main housing  2 A. 
     A cylinder head  16  is secured to the top of the main housing  2 A for closing the open top portion of the main housing  2 A. A fuel injection passage  16 A that allows the combustible gas from the gas canister  4  to pass therethrough is formed the cylinder head  16 . One portion of the fuel injection passage  16 A is connected to an opened space  30  formed between the upper surface of the piston  11  and the lower surface of the cylinder head  16 . Another portion of the fuel injection passage  16 A is connected to the gas canister  4 . Further, the cylinder head  16  has sealing members  16 B that seals a combustion chamber  20  described later while engaging with the combustion chamber frame  9 . 
     A motor  17  and an ignition plug  18  are supported to the cylinder head  16 . The ignition plug  18  has an ignition spot exposed to the opened space  30 . The ignition plug  18  is ignitable upon manipulation to the trigger  6  and upon the upward movement of the combustion chamber frame  9  in accordance with the pressing of the push member  14  against the workpiece  40 . A fan  19  is disposed in the opened space  30 , and is connected to the motor  17 . 
     A head switch (not shown) is provided in the main housing  2 A for detecting an uppermost stroke portion position of the combustion chamber frame  9  when the push member  14  is pressed against the workpiece  40 . The head switch can be turned ON when the push member  14  is elevated to a predetermined position for starting rotation of the motor  17 . 
     When the upper portion of the combustion chamber frame  9  abuts on the cylinder head  16 , the lower surface of the cylinder head  16 , the inner surface of the combustion chamber frame  9 , and the upper surface of the piston  11  define the combustion chamber  20  in combustion. 
     When the upper portion of the combustion chamber frame  9  is separated from the cylinder head  16 , a first flow passage  31  as shown in  FIG. 2  in communication with an atmosphere is provided between the combustion chamber frame  9  and the cylinder head  16 , and a second flow passage  32  in communication with the first flow passage  31  is also provided between the combustion chamber frame  9  and the upper portion of the cylinder  10 . These flow passages  31  and  32  allow a combustion gas and a fresh air to pass along the outer peripheral surface of the cylinder  10  for discharging these gas through the exhaust port (not shown) of the main housing  2 A. Further, the above-described intake port (not shown) of the head cover  3  is formed for supplying a fresh air into the combustion chamber  20 , and the exhaust hole  10   a  is adapted for discharging combustion gas generated in the combustion chamber  20 . 
     In accordance with the movement of the push member  14 , the gas canister  4  is tiltingly moved toward the cylinder head  16  by way of a cam mechanism (not shown), and a gauging section (not shown) of the gas canister  4  is pressed. Then, the gas canister  4  injects the combustible liquidized gas into the combustion chamber  20  through the fuel injection passage  16 A. 
     The fan  19  stirs and mixes the air with the combustible gas as long as the combustion chamber frame  9  remains in abutment with the cylinder head  16 . Further, 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  20 . Furthermore, the fan  19  performs scavenging such that the exhaust gas in the combustion chamber  20  can be scavenged therefrom and also performs cooling to the combustion chamber frame  9  and the cylinder  10  when the combustion chamber frame  9  moves away from the cylinder head  16 . 
     When the piston  11  moves to its bottom dead point, the tip portion of the driver blade  12  strikes against the nail, and the piston  11  abuts on the bumper  13  and stops. In this case, the bumper  13  absorbs a surplus energy of the piston  11 . 
     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 member  14  is biased away from the cylinder head  16  as shown in  FIG. 1  by the biasing force of the compression coil spring  15 , so that the push member  14  protrudes from the lower portion of the tail cover  8 . 
     Thus, the uppermost portion of the combustion chamber frame  9  is spaced away from the cylinder head  16  as shown in  FIG. 2 . Further, a part of the combustion chamber frame  9  that defines the combustion chamber  20  is also spaced away from the top portion of the cylinder  10 . Hence, the first flow passage  31  and the second flow passage  32  are provided. In this condition, the piston  11  stays at its top dead point in the cylinder  10 . 
     If a user pushes the push member  14  onto the workpiece  40 , the push member  14  is moved toward the cylinder head  16  against the biasing force of the compression coil spring  15 . At the same time, the combustion chamber frame  9  that is associated with the push member  14  is also moved toward the cylinder head  16 , closing the first flow passage  31  and the second flow passage  32 . Thus, the sealed combustion chamber  20  is provided. 
     When the combustion chamber  20  is provided in accordance with the movement of the push member  14 , the combustible liquidized gas in the gas canister  4  is injected into the combustion chamber  20  through the fuel injection passage  16 A. 
     Further, when the combustion chamber  20  is provided in accordance with the movement of the push member  14 , the head switch is turned ON to energize the motor  17  for starting rotation of the fan  19 . Rotation of the fan  19  stirs and mixes the combustible gas with air in the combustion chamber  20 . 
     In this state, if the trigger  6  provided at the handle  5  is turned ON, spark is generated at the ignition plug  18  to ignite the combustible gas. The combusted and expanded gas pushes the piston  11  to its bottom dead point. Therefore, the nail in the tail cover  8  is driven into the workpiece  40  by the driver blade  12 . 
     After the nail driving, the cylinder space above the piston  11  becomes communicated with the exhaust hole  10   a  of the cylinder  10 . Thus, the high pressure and high temperature combustion gas is discharged out of the cylinder  10  through the exhaust hole  10   a  to the atmosphere to lower the pressure in the combustion chamber  20 . When the pressure of the inner space of the cylinder  10  and the combustion chamber  20  becomes same as the atmospheric pressure, the exhaust-gas check valve  10   b  is closed. 
     Combustion gas still remaining in the cylinder  10  and the combustion chamber  20  has a high temperature at a phase immediately after the combustion. However, the high temperature can be absorbed into the walls of the cylinder  10  and the combustion chamber frame  9 . Absorption of the heat into the cylinder  10  etc. causes rapid cooling to the combustion gas. Thus, the pressure in the sealed space in the cylinder  10  above the piston  11  further drops to less than the atmospheric pressure creating a so-called “thermal vacuum”. Accordingly, the piston  11  can be moved back to the initial top dead point position. 
     Then, the trigger  6  is turned OFF, and the user lifts the combustion-type nail gun  1  from the workpiece  40  for separating the push member  14  from the workpiece  40 . As a result, the push member  14  and the combustion chamber frame  9  move away from the cylinder head  16  because of the biasing force of the compression coil spring  15 . Thus, the first flow passage  31  and the second flow passage  32  are provided. 
     In the present embodiment, the fan  19  is configured to keep rotating for a predetermined period of time after the detection of the predetermined position of the combustion chamber frame  9  by the head switch in spite of OFF state of the trigger  6 . Thus, fresh air is sucked into the combustion chamber  20  through the intake port formed at the head cover  3  by the rotation of the fan  19 . Thus, the combustion gas is urged to flow through the first flow passage  31  and the second flow passage  32 , and is discharged to the atmosphere through the exhaust port formed in the main housing  2 A. Thus, the combustion chamber  20  is scavenged. 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. 
     Next, the trigger  6  will be described in detail referring to  FIGS. 2 through 5 .  FIG. 2  shows a cross-section view of one part of the combustion-type nail gun  1  before the combustion chamber  20  is formed.  FIG. 3  shows a cross-section view of one part of the combustion-type nail gun  1  after the combustion chamber  20  has been formed.  FIG. 4  shows a cross-section view of one part of the combustion-type nail gun  1  when the trigger  6  is turned ON after the combustion chamber  20  has been formed.  FIG. 5  shows a cross-section view when  FIG. 1  is cut at A-A line. 
     The trigger  6  is provided with a spark switch  61 , an actuator  62 , a switch lever  63 , a support shaft  64  and a spring  65 . The spark switch  61  has a junction (not shown) between the spark switch  61  and the ignition plug  18 , and is connected to a drive circuit (not shown). The drive circuit drives the ignition plug  18  to spark when the junction is connected. The actuator  62  protrudes from the spark switch  61  upward. When the actuator  62  is pushed, the junction of the spark switch  61  is connected. When the trigger  6  is turned ON, the spark switch  61  and the actuator  62  is moved upward. 
     The support shaft  64  is fixed to the handle  5 . The switch lever  63  is supported to the support shaft  64  rotatably. The switch lever  63  has a first portion  63 A positioned at the combustion chamber frame  9  side, and a second portion  63 B positioned at the spark switch  61  side. A portion of the switch lever  63  positioned at the combustion chamber frame  9  side than the support shaft  64  has a curved shape as shown in  FIG. 5  in order to keep the support shaft  64  from contacting with the gas canister  4 . 
     The first portion  63 A is positioned above the engage piece  91  of the combustion chamber frame  9 , and engagable with the engage piece  91  when the engage piece  91  is moved upward in accordance with the movement of the push member  14 . The second portion  63 B is positioned above the actuator  62 . 
     The spring  65  is provided below a portion of the switch lever  63  positioned at the spark switch  61  side than the support shaft  64 . Thus, the switch lever  63  is biased in an anticlockwise direction in  FIGS. 2  though  4 . 
     Here, a positional relation between the first portion  63 A and the actuator  62  is set so that a bottommost of the second portion  63 B contacts with a topmost portion of the actuator  62  only when the second portion  63 B is moved downward in accordance with the rotation of the switch lever  63  and the actuator  62  is moved upward in accordance with the ON of the trigger  6  as shown  FIG. 4 . 
     Accordingly, when the combustion chamber  20  has not formed, the spark switch  63  is not turned ON even if the trigger  6  is turned ON. Thus, the combustion-type nail gun  1  can prevents the ignition plug  18  from sparking in the opened space  30  in vain. 
     Note that the push member  14  may be turned ON after the trigger  6  is turned ON, though the trigger  6  is turned ON after the push member  14  is turned ON in the present embodiment. Thus, it is possible to drive the nail into the workpiece  40  regardless of order of operating the push member  14  and trigger  6 . 
     Next, a combustion-type power tool according to second embodiment of the present invention will be described with reference to  FIGS. 6 through 12  wherein like parts and components as the first embodiment are designated by the same reference numerals to avoid duplicating description and description with respect the like parts and components as the first embodiment are omitted. The second embodiment pertains to a combustion-type nail gun  100 . The combustion-type nail gun  100  is provided with a trigger  60  instead of the trigger  6  of the first embodiment. 
       FIG. 6  shows a cross-section view of one part of the combustion-type nail gun  100  before the combustion chamber  20  has been formed.  FIG. 7  shows a cross-section view when  FIG. 6  is cut at B-B line. The trigger  60  is provided with a spark switch  61 , an actuator  62 , a switch lever  603 , a support shaft  64  and a spring  65 . Description with respect to the spark switch  61 , the actuator  62 , the support shaft  64  and the spring  65  is omitted, since they have same constructs as the first embodiment respectively. 
     The switch lever  603  has a first portion  603 A positioned at the combustion chamber frame  9  side, a second portion  603 B positioned at the spark switch  601  side, and a plate spring  70 . The first portion  603 A is not positioned above the engage piece  91  of the combustion chamber frame  9 . A U-shape groove  80  is formed in the first portion  603 A. The plate spring  70  has a U-shape portion  70 A and an extending portion  70 B that extends from one portion of the U-shape portion  70 A. The U-shape portion  70 A is fit into the U-shape hole  80 . When the U-shape portion  70 A is fit into the U-shape hole  70 , the extending portion  70 B is positioned above the engage piece  91 , and engagable with the engage piece  91  when the engage piece  91  is moved upward in accordance with the movement of the push member  14 . 
     The second portion  603 B is positioned above the actuator  62 . An groove  90  is formed in the  603 B. The handle  5  includes a restrain member formed as a V-shape plate spring therein as shown in  FIG. 7 . The V-shape spring has a fixed portion  51 A fixed to the inner surface of the handle  5  and a free portion  51 B opposite to the groove  90 . 
       FIG. 8  shows a cross-section view of one part of the combustion-type nail gun  100  when the combustion chamber  20  has been formed.  FIG. 9  shows a cross-section view of one part of the combustion-type nail gun  100  when the trigger  60  is turned ON after the combustion chamber  20  has been formed.  FIG. 10  shows a cross-section view when  FIG. 9  is cut at C-C line. 
     In the states as shown in  FIGS. 8 through 10 , the trigger  60  is not turned ON, that is, the trigger  60  is not moved upward though the second portion  603 B is moved downward. Accordingly, in the state of  FIG. 9 , the free portion  51 B is inserted into the groove  90  in accordance with the movement of the trigger  60  downward. Then, if the trigger  60  is turned ON, that is, the trigger  60  is moved upward, the free portion  51 B deforms while keeping being inserted into the groove  90  as shown in  FIG. 10 . Thus, the second portion  63 B contacts with the actuator  62  in accordance with the movement of the trigger  60  upward when the trigger  60  is turned ON. 
       FIG. 11  shows a cross-section view of one part of the combustion-type nail gun  100  when the trigger  60  is turned ON before the combustion chamber  20  has been formed.  FIG. 12  shows a cross-section view when  FIG. 11  is cut at D-D line. 
     When the trigger  60  is turned ON before the combustion chamber  20  has been formed, the free portion  51 B moves a position not opposite to the groove  90  in accordance with the movement of the trigger  60  upward as shown in  FIG. 12 . Therefore, the free portion  51 B does not inserted into the groove  90  even if the second portion  603 B is moved downward in accordance with the movement of the push member  14 . 
     At this time, the switch lever  603  cannot rotates, since the free portion  51 B obstructs the rotation of the switch lever  603 . Therefore, a great impact is applied to the first portion  603 A from the engage piece  91 . However, the U-shape portion  70 A deforms in accordance with the movement of the engage piece  91  upward while keeping the extending portion  70 B contacting with the engage piece  91  as shown in  FIG. 11 . Since the plate spring  70  reduces an impact applied to the first portion  603 A, it prevents the first portion  603 A and the engage piece  91  from damaging. 
     Accordingly, when the combustion chamber  20  has not formed, the spark switch  63  is not turned ON even if the trigger  6  is turned ON. Thus, the combustion-type nail gun  100  can prevents the ignition plug  18  from sparking in the opened space  30  in vain. 
     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.