Patent Publication Number: US-2023147598-A1

Title: Working device

Description:
TECHNICAL FIELD 
     The present invention relates to a working device having a cover that covers at least a part of an outer surface of an enclosure portion. 
     BACKGROUND ART 
     A working device, which has a drive unit generating a drive force, an energy supply unit supplying energy such as electric power, and a power transmission unit driven by the drive unit, is configurated so that the drive unit, the energy supply unit, and the power transmission unit are accommodated in an enclosure and cannot contact with an interior of the enclosure. The enclosure is often made of a synthetic resin or metal as a material. In addition, when a mechanism inside the enclosure is accompanied by heat generation, a cooling mechanism by a cooling fan may be provided or a protective cover may be attached outside a heat generating portion of the enclosure so that an operator does not feel uncomfortable in touching an exterior of the enclosure. Such a known technique is disclosed in, for example, Patent Document 1. Patent Document 1 discloses that cooling air, which is sucked into a main body by a fan for cooling a motor, flows between a case and a cover, thereby cooling the case. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: International Publication No. WO 2016/121463 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In recent years, as an output of a drive unit of a working device is increased, it has become important to take measures against heat generation. For example, a working device such as an impact device has a main housing made of a synthetic resin and a metal case, but a problem arises about taking measures against a temperature rise in a metal case portion as an output of a motor increases. In particular, when some kind of electronic component such as an LED (light emitting diode) is mounted in the vicinity of the case of the heat generating portion, heat countermeasures against the electronic components becomes also an important problem. In Patent Document 1, cooling air for cooling a motor is used to cool the metal case and the vicinity of the LED. That is, the cooling fan rotated by the motor cools the motor by the cooling air sucked from a rear end portion of the enclosure, and the subsequent cooling air is used to cool a metal case portion. However, such a cooling method cannot obtain a sufficient cooling effect since a flow rate of the cooling air flowing a periphery of the case decreases when the metal case and the fan separate from each other. 
     The present invention has been made in view of the above background, and an object of the present invention is to provide a working device capable of suppressing an excessive temperature rise of an enclosure portion with a simple configuration. Another object of the present invention is to provide a working device in which a cooling mechanism is provided outside a metal portion on the enclosure portion. 
     Still another object of the present invention is to provide a working device in which a cover added outside the enclosure portion is used and the enclosure portion is cooled by utilizing vibration of the working device during an operation. 
     Means for Solving the Problems 
     The following is a description of typical features of the invention disclosed in the present application. 
     According to one feature of the present invention, a working device includes: a drive unit that generates a driving force; an energy supply unit that supplies energy to the drive unit; a power transmission unit that is driven by the drive unit; an enclosure portion accommodating the drive unit, the energy supply unit, and the power transmission unit; and a cover portion that covers at least a part of an outer surface of the enclosure portion, and the working device has an airflow passage configured to allow an inflow and an outflow of outside air by being opened and closed between the outer surface of the housing portion and the cover portion. Also, the airflow passage has: first and second vents that open outside the working device; and a passage portion that connects the first and second vents between an outer surface of the enclosure portion and an inner surface of the cover portion. At least one of the first and second vents is configured by a gap formed between the outer surface of the enclosure portion and the cover portion or is configured by a through hole penetrating inner and outer surfaces of the cover portion. Incidentally, the cover portion and the airflow passage are provided at least one of a position corresponding to the power transmission unit, a position corresponding to the energy supply unit, or a position corresponding to the drive unit. 
     According to another feature of the present invention, in a working device having a housing accommodating the drive unit, and a case connected to a front of the housing and accommodating the power transmission unit, the cover portion is configured to cover the case, a first vent and a second vent that communicate with an outer portion of the enclosure portion are provided between the cover portion and the enclosure portion or at at least one of the cover portion and the enclosure portion, and air sucked from the first vent passes between the cover portion and the enclosure portion and is exhausted from the second vent. The housing accommodates a fan driven by the drive unit, the fan sucks fan air (outside air) from a third vent provided in the housing, and the fan air is exhausted from a fourth vent provided in the enclosure portion. The cover portion is supported so as to be movable at least in an axial direction of the drive unit with respect to the case and, by the cover portion moving in the axial direction, air is sucked from the first vent. 
     According to sill another feature of the present invention, in the case of the working device, a board provided with an LED element is supported so as to be movable at least in an axial direction of the drive unit with respect to the case and, by the board moving in the axial direction, air is sucked from the first vent. An energizing member for energizing the board on a side of the case is provided between the case and the board and, by movement of the energizing member due to vibration generated during a working operation, air is sucked from the first vent. Incidentally, the drive unit of such a working device may be configured by an electric motor using electric power as an energy source, and the energy supply unit may be configured as a power supplying unit for supplying electric power to the electric motor. The power supplying unit is supplied with power from a detachable battery pack. The drive unit may be configured by using compressed air as an energy source, and the energy supply unit may be configured as a compressed air supply unit for supplying the compressed air. The drive unit may be configured by an internal combustion engine using fuel as an energy source, and the energy supply unit may be configured as a fuel supply unit for supplying the fuel to the internal combustion engine. 
     Effects of the Invention 
     According to the present invention, an airflow passage is formed between the outer surface of the enclosure portion and the cover portion of the working device, and the volume of the airflow passage is increased or decreased by the cover portion moved by the reaction or vibration during the operation of the working device, and outside air is configured to flow in or out the working device, so that an excessive temperature rise of the enclosure portion can be suppressed. Further, since the airflow passage for cooling the case does not communicate with the inside of the enclosure, there is no concern that grease may leak from the enclosure portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a vertical sectional view showing an internal structure of an impact device  1  according to an embodiment of the present invention; 
         FIG.  2    is a developed perspective view of an enclosure ( 2 ,  5 ,  20 ) and a cover  50  in the impact device  1  of  FIG.  1   ; 
         FIG.  3    is a perspective view of a hammer case  5  alone of  FIG.  2   ; 
         FIG.  4    is a partial sectional view of a neighborhood of a striking mechanism  30  of  FIG.  1   ; 
         FIG.  5    is a partially enlarged view of a neighborhood of a hammer case  5  and the cover  50  of  FIG.  3    during an exhaust operation; 
         FIG.  6    is a partially enlarged view a neighborhood of the hammer case  5  and the cover  50  of  FIG.  3    during a suction operation; 
         FIG.  7    is a partial sectional view of a neighborhood of a striking mechanism  30  according to a modification example of the present embodiment; and 
         FIG.  8    is a vertical sectional view showing an internal structure of a nail driver  101  according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Embodiment 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. Incidentally, in the following figures, the same components are denoted by the same reference numerals, and a repetitive description thereof will be omitted. Further, in the present specification, front-back and up-down directions will be described as directions shown in the figures. 
       FIG.  1    is a vertical sectional view showing an internal structure of an impact device  1  according to an embodiment of the present invention. An impact device  1 : uses a rechargeable battery  90  as a power source; drives a striking mechanism  30  using a motor  4  as a drive source; converts rotation of a rotating member into an intermittent striking force in a rotational direction by the striking mechanism  30 ; and rotates a tip tool holding unit  70  coupled to the striking mechanism  30 . An enclosure (housing) of the impact device  1  is configured by a main body housing  2  ( 2   a ,  2   b ,  2   c ) made of a synthetic resin, a metal hammer case  5  for accommodating the striking mechanism  30 , and a rear cover  10 . 
     The main body housing  2  is composed of three parts, that is, a body part  2   a  formed in a cylindrical shape, a handle part  2   b  which is a part held by an operator with one hand, and a battery attaching part  2   c  for attaching a detachable battery  90 . The handle part  2   b  extends downward so as to be substantially orthogonal to a central axis (rotational axis A 1 ) of the body part  2   a , and an operation lever (trigger lever  7   a ) of a trigger switch  7  for controlling an ON-state or OFF-state of a motor is provided at a position of an index finger of the operator gripping the main body housing. A forward/reverse switching lever  8  for switching the rotational direction of the motor is provided above a rear of the trigger lever  7   a . The trigger switch  7  turns on the rotation of the motor  4  by an operation of pulling the trigger lever  7   a  with a finger, that is, by an operation of moving the trigger lever  7   a  to a rear side, and turns off the rotation of the motor by releasing a pulling operation of the trigger lever  7   a . Incidentally, a type and structure of the trigger switch  7  are arbitrary, and not only a working device having the slide-type trigger lever  7   a  but also any switch mechanism such as a switch having a swing-type trigger lever that swings around a swing axis or a touch button type switch may be used. 
     The hammer case  5  has a tapered cup shape, which forms a large opening on a rear side (opening  5   f  described later in  FIG.  4   ) and a small opening (through hole  5   a ) through which an anvil  40  penetrates at a center of a front end side, the small opening becoming a bottom. The hammer case  5  is fixed by being sandwiched by the body part  2   a  of the left-right split type main body housing  2 . The motor  4 , a speed reduction mechanism  24  using planetary gears, and the striking mechanism  30  are arranged alongside in the cylindrical body part  2   a  on an axis coaxial with a rotational axis A 1 . The speed reduction mechanism  24  and the striking mechanism  30  serve as a power transmission unit of the present embodiment. 
     The battery attaching part  2   c  for attaching the battery  90  is formed at a lower portion inside the handle part  2   b . The battery attaching part  2   c  is a diameter-expanded portion formed so as to extend in a radial direction (orthogonal direction) from a central axis in a longitudinal direction of the handle part  2   b , and the battery  90  is attached on the lower side of the battery attaching part  2   c . The battery  90  is a secondary battery using a lithium-ion battery widely used in power tools. That is, the working device (impact device  1 ) of the present embodiment uses electric power from the battery  90  as an energy source. 
     A type and shape of the battery  90  are arbitrary. The battery  90  can be removed from the main body housing  2  by relatively moving the battery  90  on a front side with respect to the main body housing  2  while a release button  91  is pushed in the main body housing from a state shown in  FIG.  1   . Incidentally, a power source of the impact device  1  of the present embodiment is arbitrary and, instead of using the battery  90  as a power source, electric power from a commercial power source may be used as an energy source via an AC power cable. 
     The main body housing  2  is made of a synthetic resin manufactured in a two-part division format rightward and leftward, and is fixed by using a plurality of screws. A plurality of screw bosses  19   a  to  19   g  for screwing are formed on one side (left side) of the main body housing  2 , and a plurality of screw holes (not shown) for passing the screws are formed on the other side (right side). 
     Inside the battery attaching part  2   c  of the main body housing  2  and on an upper side of the battery  90 , a control circuit board  48  on which a circuit for controlling a speed of the motor  4  by a pulling operation of the trigger lever  7   a  is mounted is accommodated. The control circuit board  48  is arranged in a direction substantially perpendicular to a longitudinal central axis of the handle part  2   b , and mounts a unshown microcomputer. Further, a switch holder  49  is provided on an upper surface of the battery attaching part  2   c , and various operation buttons such as a striking strength setting button and a remaining amount check button of the battery  90 , and indicator lamps corresponding to them are arranged on the switch holder  49 . 
     A brushless DC motor is used for the motor  4 , and is driven by an exciting current generated by an inverter circuit. The rotating shaft  4   d  of the motor  4  is arranged so that a rotational axis A 1  extends in the longitudinal direction of the body part  2   a . A stator of the motor  4  is configured by: a stator core  4   b  which is formed of a laminated iron core(s) and in which a plurality of magnetic pole pieces are formed; and a coil  4   c  wound around each tooth of the stator core  4   b . The rotor  4   a  forms a magnetic path(s) by a permanent magnet(s) accommodated inside the laminated iron core. 
     A cooling fan  15  is provided on a rear side in an axial direction of the motor  4  and coaxially with a rotating shaft  4   d . The cooling fan  15  rotates in synchronization with the motor  4  to suck outside air from an air intake port  17  (see  FIG.  2    for reference numerals) near a center of the body part  2   a  of the main body housing  2 , and cools the motor  4  to then discharge it from an unshown air outlet port  18  (see  FIG.  2    for reference numerals) formed on an outer circumferential side of the cooling fan  15 . The rotating shaft  4   d  of the motor  4  is pivotally supported by a bearing  21   a  on a front side of the stator core  4   b  and a bearing  21   b  on a rear side thereof. 
     A drive circuit board  45  is arranged in front of the motor  4  in the axial direction and between the stator core  4   b  and an inner cover  29 . The drive circuit board  45  mounts an inverter circuit composed of: three magnetic detection means  47  for detecting a magnetic field of a permanent magnet included in the rotor; and six semiconductor switching elements  46  such as an FET (Field effect transistor), and is formed of an annular printed circuit board. A commercially available Hall IC can be used as the magnetic detection means  47 , and a plurality (for example, three) Hall ICs are mounted at predetermined intervals at positions opposing the permanent magnets of the rotor. 
     The speed reduction mechanism  24  decelerates an output of the motor  4  at a predetermined reduction ratio and transmits it to a spindle  31 . The speed reduction mechanism  24  is configured to include: a sun gear  25  fixed to a tip of the rotating shaft  4   d  of the motor  4 ; a ring gear  28  provided on an outer circumferential side of the sun gear  25  so as to surround the sun gear  25  at a distance; and a plurality (for example, three) of planetary gears  26  that are arranged in a space between the sun gear  25  and the ring gear  28 . The sun gear  25  is a spur gear that serves as an input unit for the speed reduction mechanism  24 . The ring gear  28  is also called an outer gear, which forms a gear(s) on an inner circumferential surface of a ring-shaped outer cylinder portion. An outer circumferential surface of the ring gear  28  is inserted inside an inner cover  29 , and the inner cover  29  is held non-rotatably with respect to the main body housing  2 . 
     The planetary gear  26  rotates so as to be meshed with an outer circumferential side gear surface of the sun gear  25  and an inner circumferential side gear surface of the ring gear  28 . The planetary gear  26  is pivotally supported by a disk-shaped portion at a rear end of the spindle  31 , and the planetary gear  26  revolves around the sun gear  25  while rotating around a shaft  27  pivotally supported by the spindle  31 . That is, when the rotating shaft  4   d  of the motor  4  rotates, the sun gear  25  rotates in synchronization with the rotation and a rotational force of the sun gear  25  is decelerated at a predetermined ratio and transmitted to the spindle  31 . 
     The inner cover  29  is a part manufactured by integrally molding a synthetic resin, and is held by the body part  2   a  of the main body housing  2  so as to be sandwiched from a right-left direction. The inner cover  29  holds two bearings  21   a  and  22   b , and is centered so that the rotating shaft  4   d  of the motor  4  and a rotational center of the spindle  31  are coaxial. The bearing  21   a  held by the inner cover  29  is for pivotally supporting the rotating shaft  4   d  of the motor  4 , so that, for example, a ball bearing is used. The bearing  22   b  held by the inner cover  29  is for pivotally supporting a rear end of the spindle  31 , so that, for example, a ball bearing is used. 
     The hammer  33  is arranged on an outer circumferential side of a shaft part of the spindle  31 , and a unshown hammer cam groove  34  is formed on the inner circumferential surface. The hammer  33  is held by a cam mechanism using a steel ball  36 , and the outer circumferential surface of the spindle  31  and a part of the inner circumferential surface of the hammer  33  touch each other. A hammer spring  35  is provided on a front side of a rear-side disk part of the spindle  31  and between the front side of the rear-side disk part and the hammer  33 . Further, a spindle cam groove  32  is formed on the outer circumferential surface of the spindle  31 . The spindle  31  is manufactured by integral molding of metal due to a relationship with its strength. A rotating body of the spindle  31  and the anvil  40  is pivotally supported at an inner wall of the hammer case  5  by the needle type bearing  22   a  on the front side and is pivotally supported at the hammer case  5  by the ball type bearing  22   b  on the rear side. 
     When a reaction force received from the tip tool is low, the hammer  33  rotates in conjunction with the rotation of the spindle  31 . However, when the reaction force received from the tip tool becomes large, the steel ball  36  of the unshown cam mechanism moves and a relative position of the hammer  33  and the spindle  31  in a rotational direction fluctuate slightly, so that the hammer  33  moves largely to the rear side. Since the hammer  33  is always energized to the front side with respect to the spindle  31  by the hammer spring  35 , the movement of the hammer  33  to the rear side is made while the hammer spring  35  is compressed. When the hammer  33  retracts, a contact length between a hitting claw of the hammer  33  and a blade part (hit claw) of the anvil  40  in a front-rear direction becomes smaller. When the contact length reaches a position of 0, engagement of the hammer  33  with the anvil  40  leads to being released. 
     When the engagement of the hammer  33  with the anvil  40  becomes disengaged, the hammer  33  is pushed out on the front side by a compressive force of the hammer spring  35  and leads to being engaged (or colliding) with the next hit claw of the anvil  40  when viewed in the rotational direction. At this time, the hammer  33  is rapidly accelerated in the rotational direction and on the front side by actions of elastic energy accumulated in the hammer spring  35  and the cam mechanism in addition to the rotational force of the spindle  31 , moves forward by an energizing force of the hammer spring  35 , and begins to rotate integrally by the striking claw of the hammer  33  being reengaged with the blade part of the anvil  40 . At this time, since a strong rotational striking force is applied to the anvil  40 , the rotational striking force is transmitted to the screw via a unshown tip tool attached in the attaching hole  42  of the anvil  40 . Subsequently, the same operation is repeated, and the disengagement and engagement operations are repeated (striking operation) until the tightening of a tightening target is completed. 
     The tip tool holding unit  70  can apply to a known configuration, that is, is configured to include: an attaching hole  42  that has a hexagonal cross-sectional shape extending axially rearward from a front end portion of the anvil  40 ; steel balls  74  formed at two locations in a circumferential direction; and a sleeve  71  provided on an outer circumference side. A coil spring  72  that energizes the sleeve  71  to the rear side is attached inside the sleeve  71 . The coil spring  72  is held by a washer  73  held by a C-shaped ring so as not to come off to the front side. 
       FIG.  2    is a developed perspective view of an enclosure and a cover  50  of the impact device  1  of  FIG.  1   . An enclosure of the impact device  1  is composed of a synthetic resin part (main body housing  2 , rear cover  10 ) and a metal part (hammer case  5 ). The main body housing  2  is configured to be capable of being divided into two rightward and leftward in a vertical plane including the rotational axis A 1 . The body part  2   a  of the main body housing  2  has such a substantially cylindrical shape that the rotational axis A 1  becomes a central axis thereof, has openings on the front side and the rear side of a cylindrical portion, and the metal hammer case  5  is connected to the front-side opening portion  3 . A rear cover  10  manufactured by integral molding of a synthetic resin is attached to the rear-side opening of the body part  2   a . The rear cover  10  uses screw bosses  11  formed on both left and right sides (right-side screw boss  11  cannot be seen in  FIG.  2   ), and is fixed to the body part  2   a  by two unshown screws arranged in a direction parallel to the rotational axis A 1 . A plurality of air intake ports (third vents)  17  dispersed in a circumferential direction are formed in the vicinity of a divided surface (surface perpendicular to rotational axis A 1 ) of the body part  2   a  with the rear cover  10 . Further, air outlet ports (fourth vents)  18  formed in a slit shape are formed on right and left side surfaces of the cylindrical portion of the rear cover  10 . 
     The hammer case  5  has a bell shape having an opening  5   f  (see  FIG.  4    described later for reference numerals) on the rear side, and is fixed so that the vicinity of a rear end thereof is sandwiched by the main body housing  2 . A front side of the body part  2   a  becomes an opening  3 , but a line connecting an outer edge of the opening  3  is not a circular opening surface orthogonal to the rotational axis A 1 . Both the left and right sides of the opening  3  are formed so that a front extending portion  3   b  whose contour is formed by an edge of a side wall of a triangle toward the front side, and constitute features on design. Since the front extending portions  3   b  are located in the right and left directions of the hammer case  5 , the hammer case  5  can be held more stably. An upper side portion  3   a  of the opening  3  extends rightward and leftward, and an abutment surface that abuts on a rear edge upper portion  54   a  of the cover  50  is formed at the upper side portion. An abutment surface of the upper side portion  3   a  has such a slope as to recede as it goes radially outward with respect to the rotational axis A 1 , so that a gap between the rear edge upper portion  54   a  and the upper side portion  3   a  forms a part (upper side part) of a second vent. A lower side portion  3   c  of the opening  3  becomes a gap portion for inserting a rear edge lower portion  54   c  of the cover  50  between the lower side portion  3   c  and a holding portion of the trigger lever  7   a  of the main body housing  2 . 
     A through hole  5   a  is formed on the front side of the hammer case  5 . A part of the through hole  5   a  is formed into a short cylindrical shape (cylindrical portion  5   b ), and a circumferential groove  5   c  continuous in the circumferential direction is formed on an outer peripheral surface thereof. The circumferential groove  5   c  is a groove for attaching a retaining ring  56 . A convex portion  5   d  for positioning a rotational direction using the rotational axis A 1  of the cover  50  as an axial line is formed on the rear side of the circumferential groove  5   c . The anvil  40  penetrates on the front side from the through hole  5   a  of the hammer case  5 , and the tip tool holding unit is fixed to a tip portion of the anvil  40 . 
     The cover  50  is a molded product of a synthetic resin having higher elasticity than the main body housing  2 , and covers an outer portion of the hammer case  5  located on the front side of the main body housing  2 . On both the left and right sides of the cover  50 , such rear edge V-shaped portions  54   b  as to recede rearward in a V-shape are formed, and oppose the front extending portions  3   b  formed in the main body housing  2 . By providing the cover  50  in this way, a metal portion having high thermal conductivity (outer circumferential side exposed surface on the outer circumferential side of the hammer case  5 ) can be covered, so that the present embodiment is configured for the operator to be unable to directly touch the hammer case  5  located on an outer circumferential side of a heat generating portion. A shape of the cover  50  is set to a shape corresponding to the outer circumferential side exposed surface of the hammer case  5 , and an opening  53  is formed on the front side. The opening  53  is a hole for penetrating the cylindrical portion  5   b  of the hammer case  5 , and two rotation-stop concave portions  53   a  are formed above and below the opening  53  so as to be prevented from rotating in the rotational direction using the rotational axis A 1  as the axial line. The concave portion  53   a  engages with a convex portion  5   d  of the hammer case  5 . An annular portion  51  formed in a plane is formed on an outer circumferential side of the opening  53  of the cover  50 , and three through holes  55   a  to  55   c  are formed in a circumferential direction of the annular portion  51 . A part of the annular portion  51  is located on an inner circumferential side of the through holes  55   a  to  55   c , and the annular portion abuts on a retaining ring  56  to be provided on a front side thereof. 
     A lighting device  60  is configured by an inverted horseshoe-shaped (U-shaped) lighting board  61  and LEDs (light emitting diodes)  62   a  to  62   c  soldered onto the lighting board  61 . For the LEDs  62   a  to  62   c , it is preferable to use a chip LED surface emitting type for surface mounting. The lighting board  61  is called a printed circuit board, and is obtained by forming conductor wirings on a board made of an insulator. Although not shown in  FIG.  2   , a wiring  63  (see  FIG.  1   ) extending from a control circuit board  48  is connected to a rear side of the lighting board  61 , and electric power is supplied to the LEDs (light emitting diodes)  62   a  to  62   c  from the control circuit board  48  via the wiring  63 . An upper side of the lighting board  61  becomes an opening end  61   a , and a lower side thereof has a protruding portion  61   b  formed for positioning the lighting board at the concave portion  3   e  formed in the inner wall portion of the main body housing  2 . 
     The board holder  65  is a transparent or translucent synthetic resin member. The board holder  65  is configured based on an annular surface  66  and a cylindrical surface  67  connected to an outer circumferential side thereof. The annular surface  66  abuts on a front side surface of the lighting board  61  except for the vicinity of the LEDs  62   a  to  62   c , and the cylindrical surface  67  abuts on an outer edge of the board holder  65 , thereby accommodating the lighting board  61  inside it. Irradiation windows  68   a  to  68   c  formed so as to project forward are formed on portions of the board holder  65  opposing the LEDs  62   a  to  62   c . The irradiation windows  68   a  to  68   c  are located so as to be separated from the LEDs  62   a  to  62   c  by a predetermined distance, and causes light from the LEDs  62   a  to  62   c  to pass in a predetermined direction (here, in a direction substantially parallel to the rotational axis A 1 ). Here, the irradiation windows  68   a  to  68   c  are formed as simple transparent plate-shaped windows, but they may each be formed in a lens shape so that transmitted light is directed in a predetermined direction or is diffused. 
     To assemble the impact device from a developed state of  FIG.  2   , first, the lighting board  61  is fitted into the board holder  65 , and they are fitted inside the cover  50  for assembly. Next, the convex irradiation windows  68   a  to  68   c  of the board holder  65  are fitted into the through holes  55   a  to  55   c  of the cover  50 , and they are positioned inside the cover  50 . After an assembly of the cover  50 , the board holder  65 , and the lighting board  61  is completed in this way, the assembly is moved on a rear side along the rotational axis A 1  while interposing the elastic body  64  behind them, and the cover  50  is positioned so as to be caused to adhere tightly to the hammer case  5 . Under such a state, the C-shaped metal retaining ring  56  is attached into a circumferential direction groove  5   c  of the hammer case  5 , and the cover  50  is held so as not to slip from the front side of the rotational axis A 1 . At this time, by making the elastic body  64  slightly compressed, a slight energizing force has acted on the front side with respect to the cover  50 . The elastic body  64  as an energizing member may use an annular rubber, a foamed member, or the like. Incidentally, a shape of the elastic body  64  does not have to be an annular shape, and may be a shape stepped in the circumferential direction, a C-shape, or the like. Further, a known spring means may be used as the elastic body  64 . Furthermore, the elastic body  64  may be composed of a plurality of parts. In this way, the cover  50  is supported by the hammer case  5  in a state of being slightly moveably in a rotational axis A 1  direction of the drive unit (motor  4 ). 
       FIG.  3    is a perspective view of a hammer case  5  alone of  FIG.  2   . The hammer case  5  is a member that constitutes a part of the enclosure of the impact device  1  connected to the front-side opening  3  of the body part  2   a  of the main body housing  2 . The hammer case  5  in the impact device  1  accommodates a speed reduction mechanism  24  (see  FIG.  1   ) and a striking mechanism  30  (see  FIG.  1   ), holds a bearing  22   a  that pivotally supports an anvil  40  as an output shaft, and accommodates a bearing  22   b  for pivotally supporting a spindle  31 , so that it is manufactured with sufficient rigidity by integral molding. The cylindrical portion  5   b  serves as a base portion for sliding the cover  50 , and the circumferential groove  5   c  and the retaining ring  56  serve as a fixing tool for fixing the cover  50 . An internal space between the speed reduction mechanism  24  and the striking mechanism  30  is filled with grease. Although the hammer case  5  of the present embodiment is made of metal with an aluminum alloy, it may be made of other materials. The hammer case  5  has a bell shape, its front side forming a cylindrical through hole  5   a  that penetrates through the anvil  40 , and its rear side being a circular opening  5   f  connected to the front-side opening  3  of the main body housing  2 . The vicinity of the opening  5   f  of the hammer case  5  is sandwiched from right and left by the main body housing  2 . In order to facilitate clamping of the hammer case  5 , a stepped portion  5   e  is formed in the vicinity of the opening  5   f  and, further, a protruding portion  6  for preventing relative movement with the main body housing  2  is formed. Ribs extending from rightward and leftward are formed on an inner wall portion of the main body housing  2 , and the protruding portion  6  is configured to be suppressed from right and left by the ribs. 
       FIG.  4    is a partial sectional view of the vicinity of the striking mechanism  30  of  FIG.  1   . The striking mechanism  30  is accommodated inside the hammer case  5 . Since the main body housing  2  is made of a synthetic resin, thermal conductivity of the metal hammer case  5  is higher and heat generated by the motor  4  is easily transmitted to the hammer case  5 . Therefore, the synthetic resin cover  50  is attached so that the operator cannot directly touch the outer surface of the hammer case  5 . Only if the operator does not directly touch the hammer case  5 , the cover  50  may be caused to adhere tightly outside the hammer case  5 . However, the present embodiment has been configured to have a slight gap  9  between the cover  50  and the hammer case  5 . As a result, formed has been an airflow passage in which a passage portion is formed (second vent) between the through holes  55   a  to  55   c  on the front side of the cover  50  (first vents:  55   c ,  55   b  are shown so as to be visible in the figure) and the rear edge  54  ( 54   a  to  54   c :  54   b  is invisible in the figure) of the cover  50 . As shown in a developed perspective view of  FIG.  2   , the cover  50  is attached so as to cover an outside of the hammer case  5  from the front side in a rotational axis A 1  direction, and is fixed by the retaining ring  56 . At this time, instead of causing an inner portion of the cylindrical wall  52  of the cover  50  to adhere tightly to the hammer case  5 , the opening  53  (for example, the concave portion  53   a ) of the cover  50  has mainly contacted with the cylindrical portion  5   b  and the convex portion  5   d  of the hammer case  5  (see  FIG.  3   ). That is, the relative movement with respect to the cover  50  and the hammer case  5  is not completely restrained. As a result, the cover  50  slightly moves in a front-rear direction during an operation of the impact device  1  and in other directions due to recoil or vibration. If a material of the cover  50  is configured to have flexibility enough to allow such movement, a size of the gap  9  will greatly fluctuate during the operation of the impact device  1 . As a result, a volume in the airflow passage formed by the gap  9  fluctuates, so that air in the airflow passage is sucked in or exhausted from the outside. 
       FIG.  5    is a partially enlarged view of a neighborhood of the hammer case  5  and the cover  50  of  FIG.  3    during an exhaust operation. During the operation of the impact device  1 , the cover  50  is in a state of being moved on a rear side as shown by an arrow  57   a . A retreat of the cover  50  causes the lighting board  61  and the board holder  65  to retreat in the same manner. A retreat of the lighting board  61  is made while the elastic body  64  is compressed. When the cover  50  is retracted, the annular portion  51  is separated from a rear surface of the retaining ring  56  and becomes such a state as to generate the gap  56   a  and the gap  9   a  is narrowed above such a state, so that the volume in the airflow passage is reduced and air existing inside is exhausted to the outside as shown by the arrows  58   a  to  58   c . Incidentally, in the sectional view of  FIG.  5   , an exhaust state at a point indicated by the arrow  58   a  is typically shown, but the same air exhaust is performed at the opening  3  of the hammer case  5  in the circumferential direction and at the entire portion of the rear edge  54  of the cover  50 . 
     The arrow  58   a  is a flow of air discharged outside from the gap portion between the upper side portion  3   a  of the opening  3  of the body part  2   a  and the rear edge upper portion  54   a  of the cover  50 . Further, the arrows  58   b ,  58   c  are flows of air discharged outside from respective gaps between the through holes  55   a  to  55   c  of the cover  50  and the board holder  65 . In the configuration of the present embodiment, the lighting board  61  and the board holder  65  also move altogether with the movement of the cover  50  rearward in the rotational axis A 1  direction, so that the lighting board  61  and the board holder  65  move like blades for discharging air. 
       FIG.  6    is a partially enlarged view of a neighborhood of the hammer case  5  and the cover  50  of  FIG.  3    during an air intake operation. After the cover  50  is retracted as shown in  FIG.  5   , the cover  50  moves forward as shown by the arrow  57   b  due to a restoring force of the elastic body  64  and returns to an original position (position shown in  FIG.  4   ). As the cover  50  advances, the lighting board  61  and the board holder  65  also advance in the same manner. An advanced position of the cover  50  is limited to a position where the annular portion  51  contacts the rear surface of the retaining ring  56 . Since the volume in the airflow passage reduced due to the advancement of the cover  50  increases again, air is sucked from the outside into the inside as shown by the arrows  59   a  to  59   c . That is, the same air suction as that of the arrow  59   a  is performed at the opening  3  of the hammer case  5  and the entire portion of the rear edge  54  of the cover  50 . The arrows  59   b ,  59   c  are flows of air sucked from the respective gaps between the through holes  55   a  to  55   c  of the cover  50  and the board holder  65 . 
     As described above, since the cover  50  swings back and forth with respect to the hammer case  5  during the operation of the impact device  1 , an airflow is generated in the gap  9  between the hammer case  5  and the cover  50  by repeating the states of  FIGS.  5  and  6    and heat can be taken from an outer surface of the hammer case  5 , so that a cooling effect of the hammer case  5  can be enhanced. 
       FIG.  7    is a partial sectional view of a neighborhood of a striking mechanism  30  according to a modification example of the present embodiment. In the embodiment shown in  FIGS.  1  to  6   , the lighting device (lighting board  61 , board holder  65 , etc.) is provided between the cover  50  and the hammer case  5 . However, it is not essential to provide the lighting device to obtain the effect of the present invention.  FIG.  7    is a partial sectional view of an neighborhood of a striking mechanism  30  of an impact device  1 A without providing the lighting device. A shape of a hammer case  5 A is the same as that of the hammer case  5  shown in  FIG.  3    except that a position of a circumferential-directional groove  5 C in a rotational axis A 1  direction is different. 
     A shape of a cover  80  is almost the same as that of the cover  50  of the first embodiment, but a space for accommodating the lighting device (lighting board  61 , board holder  65 , etc.) needs not to be provided inside, so that the front side position (position of the annular portion  81 ) is formed slightly rearward. Vent holes  85   a ,  85   b  which the rotational axis A 1  penetrates are formed in the annular portion  81  of the cover  80 . That is, the vent holes  85   a ,  85   b  allow outside air to flow in and out between the outer surface of the housing portion (hammer case  5 ) and the cover  50 . The number of vent holes  85   a ,  85   b  to be provided is two or more in the circumferential direction, and an inflow and an outflow of the air to the airflow passage by the gap  89  are possible. The elastic body  64  is interposed on the rear side of the annular portion  81  of the cover  80 , thereby being held on the front side by the retaining ring  56  so as not to slip from the hammer case  5 A. As described above, when the impact device  1  is operated, the cover  80  swings back and forth and radially, etc. with respect to the hammer case  5 A and the airflow in the airflow passage due to the gap  89  is generated, so that the hammer case  5 A can be cooled effectively. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIG.  8   .  FIG.  8    is a vertical sectional view showing an internal structure of a nail driver  101  according to a second embodiment of the present invention. The present invention is configured so that a slightly movable flexible cover  150  is provided outside a metal housing portion (cylinder case  102 , injection path case  105 ) of a working device so as to separate a slight gap and that an airflow between the metal housing and the cover  150  during an operation of the working device is generated. The principle of this configuration is the same as that of the first embodiment, and the present invention can similarly be applied not only to the impact device  1  as described in the first embodiment but also to other working devices whose power sources are other than the motor. 
     An outer-shell shape of the nail driver  101  is determined by a main body part that includes: a cylinder case  102  having a cylindrical shape; a handle  103  protruding in a direction substantially orthogonal from an axial direction of the cylindrical shape of the cylinder case  102 ; a head cover  104  for closing a lid of an upper side opening of the cylinder case  102 ; and a projection path case  105  fixed to a lower side opening of the cylinder case  102 . A trigger lever  109  for injecting a fastener is provided on a lower side near a base of the handle  103 , and an accumulator  117  is formed inside the handle  103 . The accumulator  117  is provided over from the inside of the handle  103  to the inside of the cylinder case  102 , and is a space for accumulating compressed air supplied by a unshown air hose attached to and detached from a plug  118 . A trigger valve mechanism  121  is provided in the vicinity of the cylinder case  102  of the handle  103 . The trigger valve mechanism  121  controls an on-off valve of an air passage passing through the trigger valve mechanism  121  from the accumulator  117 . The injection path case  105  is composed of a nose portion  105   b  having a through hole in a center as well as a closing portion  105   a  that closes the lower side of the cylinder case  102 . 
     A push lever  113  having an injection passage formed therein is provided below the nose portion  105   b  of the injection path case  105 . A magazine  116 , which is a means for supplying a fastener, is provided behind a guide passage of the injection path case  105 . The magazine  116  accommodates a plurality of nails (not shown) as fasteners, and sequentially feeds the nails to be hit into the injection path. 
     A cylinder  125  is provided over in the cylinder case  102  and in the head cover  104 . The piston  135  is accommodated inside the cylinder  125 , and a driver blade  136  is connected to a lower side of the piston  135  so as to extend. 
     When the operator pulls the trigger lever  109 , the accumulator  117  and a upper side space of the piston  135  communicate with each other, so that compressed air flows into the upper side space of the piston  135  and thereby the piston  135  moves toward a bottom dead center side at once. When the piston  135  moves to a bottom dead center, it collides with a piston bumper  140 . The piston bumper  140  is formed by molding an elastic body such as a synthetic rubber into a substantially cylindrical shape, and has a shaft hole at a center. Since the piston  135  stops downward movement of the piston  135 , continuous use of the nail driver  101  causes a large amount of heat generation. 
     In the second embodiment, a synthetic resin cover  150  is provided so as to cover an outer circumferential surface of a portion, which closes the lower side opening of the cylinder case  102  (closed portion  105   a ), on the metal injection path case  105 . The cover  150  is attached so as to cover the closing portion  105   a  of the injection path case  105  from below with the elastic body  164  interposed therebetween, and is fixed by the retaining ring  156 . An upper end  154  of the cover  150  serves as a vent (second vent), and a plurality of vents  155  (first vent) are further formed on a lower side thereof. 
     In the second embodiment, a drive unit of the working device (from the trigger valve mechanism  121 , which is opened by the trigger operation, to the piston  135 ) uses compressed air as an energy source, and an energy supply unit (flow path by the plug  118  and the accumulator  117 ) is configured as a compressed air supply unit that supplies compressed air. However, even in the working device (nail driving device  101 ) using such compressed air, providing the cover  150  outside the housing makes it possible to effectively cool the closed portion  105   a  of the injection path case  105  and the vicinity of the lower end of the cylinder case  102 . 
     Although the present invention has been described above based on two embodiments, the present invention is not limited to the above-mentioned embodiments and can be variously modified within a range not departing from the scope of the present invention. For example, an internal combustion engine using fuel as an energy source may be configured as a drive source for the working device. In that case, an energy supply unit is configured as a fuel supply unit that supplies fuel to the internal combustion engine. As an example, a gas type nail driver using gas fuel as an energy supply source of the nail driver  101 , which is the second embodiment, can be considered. 
     EXPLANATION OF REFERENCE NUMERALS 
       1 ,  1 A . . . Impact device;  2  . . . Main body housing;  2   a  . . . Body part;  2   b  . . . Handle part;  2   c  . . . Battery attaching part;  3  . . . Opening;  3   a  . . . (Opening) upper side part;  3   b  . . . (opening) front extending portion;  3   c  . . . (Opening) lower side part;  3   e  . . . Concave portion;  3   f  . . . Opening;  4  . . . Motor;  4   a  . . . Rotor;  4   b  . . . Stator core;  4   c  . . . Coil;  4   d  . . . Rotating shaft;  5 ,  5 A . . . Hammer case;  5   a  . . . Through hole;  5   b  . . . Cylindrical portion;  5   c ,  5 C . . . Circumferential groove;  5   d  . . . Convex portion;  5   e  . . . Step portion;  5   f  . . . Opening;  6  . . . Protruding portion;  7  . . . Trigger switch;  7   a  . . . Trigger lever;  8  . . . Forward/reverse switching lever;  9 ,  9   a  . . . Gap;  10  . . . Rear cover;  11  . . . Screw boss;  15  . . . Cooling fan;  17  . . . Air intake port (third vent);  18  . . . Air outlet port (fourth vent);  19   a  to  19   g  . . . Screw boss;  21   a ,  21   b  . . . Bearing;  22   a ,  22   b  . . . Bearing;  24  . . . Speed reduction mechanism;  25  . . . Sun gear;  26  . . . Planetary gear;  27  . . . Shaft;  28  . . . Ring gear;  29  . . . Inner cover;  30  . . . Striking mechanism;  31  . . . Spindle;  32  . . . Spindle cam groove;  33  . . . Hammer;  34  . . . Hammer cam groove;  35  . . . Hammer spring;  36  . . . Steel ball;  40  . . . Anvil;  42  . . . Attaching hole;  45  . . . Drive circuit board;  46  . . . Semiconductor switching element;  47  . . . Magnetic detection means;  48  . . . Control circuit board;  49  . . . Switch holder;  50  . . . Cover;  51  . . . Annular portion;  52  . . . Cylindrical wall;  53  . . . Opening,  53   a  . . . Concave portion;  54  . . . Rear edge;  54   a  . . . Rear edge upper portion;  54   b  . . . Rear edge V-shaped portion;  54   c  . . . Rear edge lower portion;  55   a  to  55   c  . . . Through hole;  56  . . . Retaining ring;  56   a  . . . Gap (on rear surface side of retaining ring);  58   a  to  58   c  . . . Exhaust direction;  59   a  to  59   c  . . . Suction direction;  60  . . . Lighting device;  61  . . . Lighting board;  61   a  . . . Opening end;  61   b  . . . Protruding portion;  62   a  to  62   c  . . . LED;  63  . . . Wiring;  64  . . . Elastic body;  65  . . . Board holder;  66  . . . Annular surface;  67  . . . Cylindrical surface;  68   a  to  68   c  . . . Irradiation window;  70  . . . Tip tool holding unit;  71  . . . Sleeve;  72  . . . Coil spring;  73  . . . Washer;  74  . . . Steel ball;  80  . . . Cover;  81  . . . Annular portion:  85   a ,  85   b  . . . Vent hole;  89  . . . Gap;  90  . . . Battery;  91  . . . Release button;  101  . . . Nail driver;  102  . . . Cylinder case;  103  . . . Handle;  104  . . . Head cover;  105  . . . Injection path case;  105   a  . . . Closing portion;  105   b  . . . Nose portion;  109  . . . Trigger lever;  113  . . . Push lever;  116  . . . Magazine;  117  . . . Accumulator;  118  . . . Plug;  121  . . . Trigger valve mechanism;  125  . . . Cylinder;  135  . . . Piston;  136  . . . Driver blade;  140  . . . Piston bumper;  150  . . . Cover;  154  . . . Upper end;  155  . . . Vent;  156  . . . Retaining ring;  164  . . . Elastic body; and A 1  . . . (Motor) rotational axis.