Abstract:
To provide an easy-to-use electric chainsaw that uses, in place of a large battery pack with a high voltage rating that would have been used in conventional electric chainsaws, a battery power source composed of a set of small commonly used battery packs of the same rating. An electric chainsaw having a built-in electric motor that is powered by a rechargeable battery, wherein a set of commonly used battery packs of the same rating is used as the rechargeable battery. The set of battery packs is mounted at the back of the main housing so that the center of gravity (G) of the chainsaw is positioned within a range (R) of 1.5 time the width (W) of the grip section of a rear handle between the left and right sides of a center line that is centered in the horizontal direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric chainsaw that uses a rechargeable battery pack. 
       BACKGROUND ART 
       [0002]    Patent Literature 1 discloses an electric chainsaw. The electric chainsaw includes a main housing incorporating an electric motor to which power is supplied by a rechargeable battery, a guide bar projecting toward a front side with a basal end fixed to a side part of the main housing, a saw chain (saw teeth chain) stretched over an outer periphery of the guide bar and driven by the electric motor, a rear handle extending toward a back side from a back part of the main housing, and an arch-shaped front handle having left and right lower ends fixed to both sides of the main housing, where a trigger switch for starting up the electric motor is arranged on the rear handle. When using the chainsaw, an operator grips the rear handle with the right hand (or left hand), grips a side handle with the left hand (or right hand), and operates the trigger switch with a finger of the right hand (or left hand) to activate the electric motor. The saw chain thereby rotates around the outer periphery of the guide bar, enabling the operator to execute a wood cutting task. 
       CITATION LIST 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Publication No. 2010-201612 
       SUMMARY OF INVENTION 
     Technical Problems 
       [0004]    In the electric chainsaw described above, a large battery pack of high voltage standard (e.g., 36V) is incorporated to drive a high output electric motor. The application of the large battery pack of high voltage standard is limited to mainly the electric chainsaw and such battery pack is expensive, and furthermore, its general versatility is poor and in an actual situation, the financial strain on a user is large. In a technical field of electric tools, gardening tools, electric vacuum cleaners, and the like, a small commonly used battery pack of the same standard is being developed. 
         [0005]    Focusing on the actual situation described above, the present invention provides an electric chainsaw that uses a battery power source configured by a set of commonly used small battery packs of the same standard in place of a large battery pack of high voltage standard that has been used in the conventional electric chainsaw. In such electric chainsaw, the problem to be solved lies in incorporating a set of commonly used small batteries at an appropriate position in a main housing without affecting the operability of the saw chain. 
       Solutions to Problems 
       [0006]    In order to overcome the problem described above, the present invention provides an electric chainsaw including a main housing incorporating an electric motor to which power is supplied by a rechargeable battery; a guide bar projecting toward a front side with a basal end fixed to a side part of the main housing, a saw chain stretched over an outer periphery of the guide bar and driven by the electric motor, a rear handle gripped by an operator, the rear handle extending toward a back side from a back part of the main housing, and an arch-shaped front handle having left and right lower ends fixed to both sides of the main housing, the electric motor being started up by an operation of a trigger switch arranged on the rear handle; wherein a set of commonly used battery packs of a same standard is adopted for the rechargeable battery, the set of commonly used battery packs being assembled to the back part of the main housing so that a center of gravity G of the chainsaw is located within a range R of 1.5 times a width W (30 mm) on both left and right sides of a center line C extending perpendicularly at a center in a left and right direction of a grip section of the rear handle. 
         [0007]    In the electric chainsaw of the present invention configured as above, the set of battery packs are arranged at the back part of the main housing so that the center of gravity G of the chainsaw is located deviated in the left and right direction in the range R of 1.5 times the width W (30 mm) both left and right sides of the center line C extending perpendicularly at the center in the left and right direction of a grip section of the rear handle, whereby the main housing is slightly tilted in the left and right direction thus enhancing the operability of the saw chain. If the center of gravity of the set of battery packs is evenly deviated toward the left and right sides of the center line C extending perpendicularly at the center in the left and right direction of the grip section of the rear handle, a satisfactory left and right weight balance of the main housing can be realized. 
         [0008]    In the electric chainsaw of the present invention, the attachment/detachment task of each battery pack can be facilitated by arranging and assembling the set of battery packs in parallel in the main housing. 
         [0009]    In the electric chainsaw of the present invention, the electric motor an be used with high output when the set of battery packs are series-connected, whereas the electric motor can be used for a long period of time when the set of battery packs are parallel-connected. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a perspective view showing one embodiment of an electric chainsaw of the present invention. 
           [0011]      FIG. 2  is a plan view of the chainsaw shown in  FIG. 1 . 
           [0012]      FIG. 3  is a right side view of the chainsaw shown in  FIG. 1 . 
           [0013]      FIG. 4  is a rear view of the chainsaw shown in  FIG. 1 , and is a view showing a center of gravity of the chainsaw when seen from a back side. 
           [0014]      FIG. 5  is a right side view of a state in which a battery pack is detached. 
           [0015]      FIG. 6  is a perspective view showing the battery pack. 
           [0016]      FIG. 7  is a cross-sectional view taken along line A-A of  FIG. 6 . 
           [0017]      FIG. 8  is a rear view of a first alternative embodiment. 
           [0018]      FIG. 9  is a rear view of a second alternative embodiment. 
           [0019]      FIG. 10  is a right side view of a third alternative embodiment. 
           [0020]      FIG. 11  is a right side view of a fourth alternative embodiment. 
           [0021]      FIG. 12  is a right side view of a fifth alternative embodiment. 
           [0022]      FIG. 13  is a right side view of a sixth alternative embodiment. 
           [0023]      FIG. 14  is a right side view (a) of a seventh alternative embodiment, and is a right side view (a) of when a back part of a main housing is turned. 
           [0024]      FIG. 15  is a right side view (a) of an eighth alternative embodiment, and is a right side view (a) of when a back part of a main housing is turned. 
           [0025]      FIG. 16  is a right side view of a ninth alternative embodiment. 
           [0026]      FIG. 17  is a right side view of a tenth alternative embodiment. 
           [0027]      FIG. 18  is a right side view of an eleventh alternative embodiment. 
           [0028]      FIG. 19  is a right side view of a twelfth alternative embodiment. 
           [0029]      FIG. 20  is a right side view of a thirteenth alternative embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    One embodiment of an electric chainsaw according to the present invention will be hereinafter described with reference to the drawings. As shown in  FIGS. 1 to 3 , an electric chainsaw  10  includes a main housing  11 , where a longitudinal guide bar  21  is arranged to project out toward a front side at a front part of a right side surface of the main housing  11 . A back part of the guide bar  21  is covered by a sprocket cover  12  arranged at the front part of the right side surface of the main housing  11 , and a portion of the guide bar  21  excluding the back part is projected out toward a front side of the main housing  11 . A loop-like saw chain  22  is rotatably attached to an outer periphery of the guide bar  21 . The saw chain  22  is rotatably stretched between the guide bar  21  and a sprocket  24  rotatably supported on an immediate back side of the guide bar  21 . A plurality of saw-like blades are continuously provided on the saw chain  22 , so that the saw-like blades continuously travel at the outer periphery of the guide bar  21  when the saw chain  22  is rotated at the outer periphery of the guide bar  21 . 
         [0031]    As shown in  FIGS. 2 and 3 , an electric motor  23  is accommodated at a front part of the main housing  11 , and the electric motor  23  causes the saw chain  22  to rotate along the outer periphery of the guide bar  21 . An output shaft  23   a  of the electric motor  23  is projected into the sprocket cover  12 , and the sprocket  24  is fixed to the output shaft  23   a . When the sprocket  24  is rotated by the drive of the electric motor  23 , the saw chain  22  rotates along the outer periphery of the guide bar  21  by the rotating sprocket  24 . 
         [0032]    As shown in  FIGS. 1 to 4 , a rear handle  13  extending toward a back side is arranged at the back part of the main housing  11 , and a front handle  15  is arranged at an intermediate part in a front and back direction of the main housing  11 . When seen from a side surface, the rear handle  13  has a substantially U shape laid in a direction in which the back side is closed, and an upper part of the rear handle  13  serves as a grip section  13   a  to be gripped by an operator. The grip section  13   a  of the rear handle  13  has a substantially circular cross-sectional shape in a direction orthogonal to a longitudinal direction, where a horizontal width W of the grip section  13   a  is set to 30 mm, a width suited to a size for being gripped with a hand. A range suited for gripping a horizontal length of the grip section  13   a  with the hand is 25 mm to 40 mm. A trigger switch  14  is arranged on a lower surface side at the front part of the grip section  13   a  of the rear handle  13 , and the electric motor  23  is driven by push operating the trigger switch  14 . 
         [0033]    As shown in  FIGS. 1 to 4 , the front handle  15  has a substantially U shape which a lower side is opened to cross the intermediate part in the front and back direction of the main housing  11 , where both ends in the longitudinal direction of the front handle  15  are fixed to both side parts of the main housing  11 . In the front handle  15 , the intermediate part, which becomes the upper side of the main housing  11 , is assumed as a grip section  15   a  to be gripped by the operator. The front handle  15  has a substantially U shape in which the lower side is opened, but this is not the sole case, and may be an O shape forming a loop form. 
         [0034]    As shown in  FIGS. 1 to 4 , a battery power source  30  that supplies power to the electric motor  23  is removably attached to the back part of the main housing  11 , and the battery power source  30  of the embodiment includes a pair of battery packs  31  arranged side by side on both left and right sides at the back part of the main housing  11 .  FIG. 5  is a right side view of the main housing  11  with the battery pack  31  detached, where two attachment sections  25  for attaching the pair of battery packs  31  are arranged at a central part of the back part of the main housing  11  (in  FIG. 5 , only the attachment section on the right side is shown, and the illustration of the attachment section on the left side, which is symmetric to the attachment section on the right side, is omitted). The two attachment sections  25  are arranged at positions adjacent to each other at the central part of the back part of the main housing  11 . The attachment section  25  is arranged by the same number as the battery pack  31 . 
         [0035]    The attachment section  25  includes a connector portion  25   a  removably connected to an electric connector  34  of the battery pack  31 . The connector portion  25   a  is electrically connected to the electric motor  23 , where when the electric connector  34  of the battery pack  31  is electrically connected to the connector portion  25   a , the electric motor  23  is electrically connected to the battery pack  31 . A pair of left and right guide rails  25   b  extending in an up and down direction are arranged on both left and right sides of the connector portion  25   a , and the battery pack  31  is attached to be slidably movable in the up and down direction along the guide rails  25   b . A locking portion  25   c  formed to recess toward an inner side is formed at the upper part of the attachment section  25 , so that a hook  36  provided on the battery pack  31  can be locked to the locking portion  25   c.  When the hook  36  of the battery pack  31  is locked to the locking portion  25   c  of the attachment section  25 , the battery pack  31  is regulated from moving along the guide rails  25   b  on the attachment section  25 . 
         [0036]    The battery pack  31  is used as a battery power source of the electric motor  23 , and can be charged using a charger (not shown). Furthermore, the battery pack  31  is a power source having high versatility that can be used as a power source for various types of electric tools and electric gardening tools. The battery pack.  31  of the embodiment has a nominal voltage of 18V, and is widely used in various types of electric tools and gardening tools. In the embodiment, two battery packs  31  are series-connected with respect to the electric motor  23  to be used as a 36V power source. 
         [0037]    As shown in  FIGS. 6 and 7 , the battery pack  31  includes a substantially cuboid shaped housing  32 , and ten battery cells  33  having a circular column shape are accommodated in the housing  32 . In the battery pack  31 , a longitudinal direction of the housing  32  is assumed as a direction of slidably moving to and attaching to the attachment section  25 , and the battery cells  33  are accommodated with an axis line direction thereof lying in a direction orthogonal to the direction of slidably moving to and attaching to the attachment section  25 . In the battery pack  31 , a substantially center position of the housing  32  is a center of gravity G 1 . 
         [0038]    An upper wall (peripheral wall) shown in  FIG. 6  of the housing  32  is a wall surface facing the attachment section  25 , and the electric connector  34  removably connected to the connector portion  25   a  of the attachment section  25  is arranged on the upper wall of the housing  32 . As described above, the electric motor  23  and the battery pack  31  are electrically connected by electrically connecting the connector portion  25   a  of the attachment section  25  to the electric connector  34 . A pair of rails  35  extending in the longitudinal direction are integrally formed at the upper wall, shown in  FIG. 6 , of the housing  32 . The pair of rails  35  are arranged on both sides of the electric connector  34  in a direction orthogonal to the longitudinal direction of the housing  32 . The hook  36  projecting out toward the upper side (toward the attachment section  25 ) is arranged on the upper wall, shown in  FIG. 6 , of the housing  32 , and this hook  36  is biased toward the upper side (toward the locking portion  25   c  of the attachment section  25 ) shown in  FIG. 6  by a spring member  37 . 
         [0039]    When the hook  36  is locked to the locking portion  25   c  of the attachment section  25  with the battery pack  31  attached to the attachment section  25 , the electric connector  34  of the battery pack  31  is electrically connected to the connector portion  25   a  of the attachment section  25 , and the battery pack  31  is regulated from moving along the guide rail  25   b . When the hook  36  is retreated from the locking portion  25   c  against the biasing force of the spring member  37  with a release button  36   a , the battery pack  31  becomes slidably movable along the guide rails  25   b . If the battery pack  31  is slidably moved along the guide rails  25   b  in this state, the electric connection of the electric connector  34  of the battery pack  31  and the connector portion  25   a  of the attachment section  25  is released, and the battery pack  31  is detached from the attachment section  25 . 
         [0040]    As shown in  FIGS. 2 and 3 , a controller  26  that controls the power supply from the battery pack  31  to the electric motor  23  and the drive of the electric motor  23  is arranged inside the main housing  11 , and the controller  26  is arranged on a lower side of the attachment section  25  at a position proximate to a position where the attachment section  25  is arranged. 
         [0041]    In the chainsaw  10  configured as above, when the grip section  13   a  of the rear handle  13  is gripped with the right hand, the grip section  15   a  of the front handle  15  is gripped with the left hand, and the trigger switch  14  at the front part of the grip section  13   a  is push operated with a forefinger of the right hand, the electric motor  23  is driven by the power supply from the two battery packs  31 . The saw chain  22  rotates along the outer periphery of the guide bar  21  when the sprocket  24  is rotated by the drive of the electric motor  23 . When the saw chain  22  rotating along the outer periphery of the guide bar  21  makes contact with lumber such as a log in such a state, the lumber such as the log is cut by the saw chain  22  rotating along the outer periphery of the guide bar  21 . 
         [0042]    In the chainsaw  10  configured as above, the pair of rechargeable battery packs  31  that can be used in various types of electric tools and gardening tools are used for the battery power source  30  that supplies power to the electric motor  23 . A user does not need to possess a battery pack of a variety of standards (e.g., different voltages) with the chainsaw  10 , and the electric tool, the gardening tool since the battery pack  31  of high versatility that can be used even for electric tools and gardening tools is used for the battery power source of the chainsaw  10 , thus enhancing the usability of the user. 
         [0043]    A center of gravity G of the chainsaw  10  is mainly defined by a position of the electric motor  23 , which is a heavy load, a position of the guide bar  21 , and a position of the pair of battery packs  31 , which are also heavy loads. The operability may lower the position of the center of gravity G of the chainsaw  10  is inappropriate. As shown in  FIG. 4 , the pair of battery packs  31  are arranged at the back part of the main housing  11  such that the center of gravity G of when seen from the back side of the chainsaw  10  is located deviated in the left and right direction in a range R of 1.5 times a width W (30 mm) on both left and right sides of a center line C extending perpendicularly at a center in the left and right direction of the grip section  13   a . Thus, the main housing of the chainsaw  10  is less likely to tilt in the left and right direction when the grip section  13   a  of the rear handle  13  of the chainsaw  10  is gripped, whereby the grip section  1 . 3   a  does not need to be strongly gripped and the operator is less likely,to get tired. Furthermore, the center of gravity G of when seen from the back side of the chainsaw  10  is slightly deviated toward a right side from the center line C within the range R of 1.5 times a length width W (30 mm) on both left and right sides of the center line C extending perpendicularly at the center in the left and right direction of the grip section  13   a . The main housing of the chainsaw  10  is thereby slightly tilted toward the right side (left and right direction), and the operability of the chainsaw  10  can be improved. 
         [0044]    Each center of gravity G 1  of the pair of battery packs  31  is located in the range R of 1.5 times the width W (30 mm) of the grip section  13   a  on both left and right sides of the center line C extending perpendicularly at the center in the left and right direction of the grip section  13   a . Furthermore, the pair of battery packs  31  are arranged such that each center of gravity G 1  is divided to both left and right sides from the center line C extending perpendicularly at the center in the left and right direction of the grip section  13   a . The weight balance in the left and right direction of the chainsaw  10  thus improves when the operator grips the grip section  13   a  of the rear handle  13 , and hence the operator does not need to strongly grip the grip section  13   a  and the operator is more unlikely to get tired. 
         [0045]    In such electric chainsaw  10 , the pair of battery packs  31  are arranged at positions juxtaposed on the left and right at the back part of the main housing  11 . The attachment/detachment task of the battery pack  31  by the user is thus facilitated compared to when the pair of battery packs  31  are arranged at positions spaced apart from each other. 
         [0046]    Furthermore, in such chainsaw  10 , the main housing  11  includes two attachment sections  25  corresponding to the two battery packs  31  at the back part thereof to attach the pair of battery packs  31 . The battery pack  31  includes the electric connector  34  and the pair of rails  35  arranged on both sides of the electric connector  34  at the peripheral wall of the housing  32  incorporating the plurality of battery cells  33  and the attachment section  25  includes the connector portion  25   a  electrically connected to the electric connector  34  of the battery pack  31  and the pair of guide rails  25   b  that engage the pair of rails  35  in a freely slidably moving manner. The battery pack  31  can be attached while being electrically connected with respect to the attachment section.  25  by slidably moving the pair of rails  35  of the battery pack  31  along the guide rails  25   b  of the attachment section  25 , that is, by slidably moving the battery pack  31  with respect to the attachment section  25 , whereby the operability of the attachment task of the battery pack  31  with respect to the attachment section  25  is enhanced. 
         [0047]    Moreover, the battery pack  31  includes the hook  36  that projects out so as to be able to advance/retreat with respect to the attachment section  25 , and the attachment section  25  includes the locking portion  25   c  that locks with the hook  36 , where the hook  36  is biased by the spring member  37  to lock with the locking portion  25   c . Since the hook  36  is biased by the spring member  37  to lock with the locking portion  25   c,  the battery pack  31  is regulated from slidably moving from the attachment section  25 , so that the battery pack  31  is prevented from separating from the attachment section  25 . The battery pack  31  can be slidably moved from the attachment section  25 , and the battery pack  31  can be detached from the attachment section  25  by releasing the hook  36  from the locking portion  25   c  against the biasing force of the spring member  37 . Thus, the battery pack  31  can be regulated from slidably moving or can be slidably moved with respect to the attachment section  25  by simply operating the hook  36 , whereby the operability of the attachment task of the battery pack  31  with respect to the attachment section  25  is enhanced. 
         [0048]    The guide rail  25   b  of the attachment section  25  is inclined approximately 10° toward the back side from a vertical direction, and the battery pack  31  is attached to the attachment sections  25  on both left and right sides while being inclined approximately 10° toward the back side at the back part of the main housing  11 . As the battery pack  31  is attached while being inclined toward the back side, the operator can easily detach the battery pack  31  from the attachment section  25  by gripping the side handle  15  of the chainsaw  10  placed on the ground and the like with one hand and holding it down toward the ground side, and grabbing the battery pack  31  with the other hand and pulling out the battery pack  31  toward the diagonally upper back side, which is the side opposite to the side handle  15 . 
         [0049]    Next, other alternative embodiments using a pair of battery packs  31  in the electric chainsaw  10  will be described. In the following description, aspects different from the chainsaw  10  of the embodiment described above will be mainly described, and description on operation effects described above will be omitted unless otherwise stated. In regards to each figure of the alternative embodiment, the guide bar  21 , the saw chain  22 , and the electric motor  23  are similar to those described in the above embodiment, and hence will not be illustrated and will be omitted. 
       First Alternative Embodiment 
       [0050]    As shown in the rear view of  FIG. 4 , the attachment section  25  is arranged in a standing manner without tilting toward the left or right outer sides in the electric chainsaw  10  of the embodiment described above, whereas the left and right attachment sections  25  are arranged on both left and right sides of the back part of the main housing  11  such that an upper part side tilts toward the outer side, and the battery pack  31  is attached such that the upper part side tilts toward the outer side at both left and right sides of the back part of the main housing  11  in a chainsaw  10  of a first alternative embodiment, as shown in a rear view of  FIG. 8 . 
       Second Alternative Embodiment 
       [0051]    As shown in the right side view of  FIG. 3  and the rear view of  FIG. 4 , the battery pack  31  is attached by being slidably moved from the upper side at both left and right sides of the back part of the main housing  11  in the electric chainsaw  10  of the embodiment described above, whereas the battery pack  31  is attached by being slidably moved from the lower side at both left and right sides of the back part of the main housing  11  with the attachment section  25  turned upside down in a chainsaw  10  of a second alternative embodiment, as shown in a rear view of  FIG. 9 . 
       Third Alternative Embodiment 
       [0052]    As shown in the right side view of  FIG. 3 , the attachment section  25  is inclined approximately 10° toward the back side from a vertical direction and the battery pack.  31  is attached while being inclined approximately 10° toward the back side at both left and right sides of the back part of the main housing  11  in the electric chainsaw  10  of the embodiment described above, whereas the attachment section  25  is arranged standing in the vertical direction and the battery pack  31  is attached standing in the vertical direction at both left and right sides of the back part of the main housing  11  in a chainsaw  10  of a third alternative embodiment, as shown in a right side view of  FIG. 10 . In such a case, the operator can easily detach the battery pack  31  from the attachment section  25  by gripping the rear handle  13  or the front handle  15  of the chainsaw  10  placed on the ground and the like with one hand and holding it down toward the ground side, and grabbing the battery pack  31  with the other hand and pulling it out toward the upper side. 
       Fourth Alternative Embodiment 
       [0053]    As shown in the right side view of  FIG. 3 , the attachment section  25  is inclined approximately 10° toward the back side from a vertical direction and the battery pack  31  is attached while being inclined approximately 10° toward the back side at both left and right sides of the back part of the main housing  11  in the electric chainsaw  10  of the embodiment described above, whereas the attachment section  25  is inclined approximately 10° toward the front side from the vertical direction and the battery pack  31  is attached while being inclined approximately 10° toward the front side at both left and right sides of the back part of the main housing  11  in a chainsaw  10  of a fourth alternative embodiment, as shown in a right side view of  FIG. 11 . In such a case, the operator can easily detach the battery pack  31  from the attachment section  25  by gripping the rear handle  13  of the chainsaw  10  placed on the ground and the like with one hand and holding it down toward the ground side, and grabbing the battery pack  31  with the other hand and pulling it out toward the diagonally upper front side, which is the side opposite to the rear handle  13 . 
       Fifth Alternative Embodiment 
       [0054]    As shown in a right side view of  FIG. 12 , in an electric chainsaw  10  of a fifth alternative embodiment, two attachment sections  25  are juxtaposed on the left and right at an upper surface of the back part of the main housing  11 , and a pair of battery packs  31  are attached side by side on the left and right in each of the two attachment sections  25  at the upper surface of the back part of the main housing  11 . The two attachment sections  25  and the two battery packs  31  are arranged on both left and right sides of the center line C extending in an up and down direction at a center in a left and right direction of the grip section  13   a  of the rear handle  13  (rear view is omitted), and the center of gravity when seen from the back side of the chainsaw  10  is located in the range R of 1.5 times the horizontal width of the grip section  13   a  from the center line C. An interval of the wall surfaces adjacent to each other of the two battery packs  31  attached side by side on the left and right is 5 mm, so that an occupying space by the two battery packs  31  is narrowed. The occupying space by the pair of battery packs  31  can be sufficiently narrowed if the interval of the wall surfaces adjacent to each other of the pair of battery packs  31  is smaller than 15 mm. 
         [0055]    The attachment section  25  is inclined such that the back part becomes the upper side at the upper surface of the back part of the main housing  11 , and the battery pack  31  is attached while being inclined such that the back part becomes the upper side at the upper surface of the back part of the main housing  11 . In such a case, the operator can easily detach the battery pack  31  from the attachment section  25  by gripping the side handle  15  of the chainsaw  10  placed on the ground and the like with one hand and holding it down toward the ground side, and grabbing the battery pack  31  with the other hand and pulling it out toward the diagonally upper back side, which is the side opposite to the front handle  15 . 
       Sixth Alternative Embodiment 
       [0056]    As shown in a right side view of  FIG. 13 , in an electric chainsaw  10  of a sixth alternative embodiment, a battery pack accommodation cover  16  in which an upper surface is opened is arranged at a periphery of each attachment section  25  of the main housing  11  in the chainsaw  10  of the embodiment described above. The battery pack accommodation cover  16  covers the battery pack  31  other than an upper end portion thereof. Since the battery pack accommodation cover  16  covers a majority of the battery pack  31 , the battery pack  31  is less likely to be scratched during the operation. The spring member  17  including a plate spring is arranged at a bottom part of the battery pack accommodation cover  16 , and the battery pack  31  is biased toward the upper side by the spring member  17 . When the hook  36  of the battery pack  31  is released from the locking portion  25   c  of the attachment section  25  from a state in which the battery pack  31  is attached to the attachment section  25  in the battery pack accommodation cover  16 , the battery pack  31  is pushed out toward the upper side by the biasing force of the spring member  17 . The upper part of the battery pack  31  thus projects out from the opening at the upper surface of the battery pack accommodation cover  16 , and hence the battery pack  31  can be easily detached by grabbing the upper part of the battery pack  31  and pulling out the battery pack toward the upper side from the battery pack accommodation cover  16 . 
       Seventh Alternative Embodiment 
       [0057]    As shown in a right side view of  FIG. 14 , in an electric chainsaw  10  of a seventh alternative embodiment, a battery pack accommodating portion  11   c  is arranged inside the main housing  11 . The main housing  11  is divided to a main part  11   a  excluding the back part and a back part  11   b  including the rear handle  13 , where an upper end on the front side of the back part  11   b  is supported to be turnable about a horizontal axis line at an upper end on the back side of the main part  11   a.  Two battery pack accommodating portions  11   c  are arranged one above the other in the main part  11   a  of the main housing  11 , and the battery pack accommodating portion  11   c  has the back side opened when the back part  11   b  is turned. The battery pack  31  is removably accommodated in each upper and lower battery pack accommodating portion  11   c  from the opening on the back side. The attachment section  25  described above is arranged in each battery pack accommodating portion  11   c,  and the battery pack  31  accommodated in each battery pack accommodating portion  11   c  is removably attached to the attachment section  25 . The attachment section  25  of the upper stage is arranged at a lower part of the battery pack accommodating portion  11   c,  and the attachment section  25  of the lower stage is arranged at an upper part of the battery pack accommodating portion  11   c,  where the attachment sections  25  of the upper stage and the lower stage are arranged at positions adjacent to each other. 
         [0058]    The spring member  17  including the plate spring is arranged at the back, which becomes the front part of each battery pack accommodating portion  11   c , and the battery pack  31  is biased toward the back side by the spring member  17 . When the back part  11   b  of the main housing  11  is turned toward the upper side to release the hook  36  of the battery pack  31  from the locking portion  25   c  of the attachment section  25  with the battery pack  31  attached to the attachment section  25  in the battery pack accommodating portion  11   c , the battery pack  31  is pushed out toward the back side by the biasing force of the spring member  17 . The back part of the battery pack  31  thus projects out from the opening on the back side of the battery pack accommodating portion  11   c,  and hence the battery pack  31  can be easily detached by grabbing the back part of the battery pack  31  and pulling out the battery pack toward the back side from the battery pack accommodating portion  11   c.    
       Eighth Alternative Embodiment 
       [0059]    As shown in a right side view of  FIG. 15 , in an electric chainsaw  10  of an eighth alternative embodiment, the battery pack accommodating portion  11   c  is arranged inside the main housing  11 . The main housing  11  is divided to a main part  11   a  excluding the back part, and a back part  11   b  including the rear handle  13 , where the upper end on the front side of the back part  11   b  is supported to be turnable about the horizontal axis line at the upper end on the back side of the main part  11   a.  Two battery pack accommodating portions  11   c  are arranged on the left and right in the main part  11   a  of the main housing  11  (only the battery pack accommodating portion  11   c  on the right side is shown in  FIG. 15 , and the illustration of the battery pack accommodating portion  11   c  on the left side, which is symmetric to the right side, is omitted), and the battery pack accommodating portion  11   c  has the back side opened when the back part  11   b  is turned. The battery pack  31  is removably accommodated in each battery pack accommodating portion  11   c  on the left and right from the opening on the back side. The attachment section  25  described above is arranged in each battery pack accommodating portion  11   c , and the battery pack  31  accommodated in each battery pack accommodating portion  11   c  is removably attached to the attachment section  25 . The attachment section  25  on the left side is arranged on the right side of the battery pack accommodating portion  11   c , and the attachment section  25  on the right side is arranged on the left side in the battery pack accommodating portion  11   c , and the left and right attachment sections  25  are arranged at positions adjacent to each other at the central part in the left and right direction of the main housing  11 . 
         [0060]    Similar to the seventh alternative embodiment, the spring member  17  including the plate spring is arranged at the back, which becomes the front part of each battery pack accommodating portion  11   c , and the battery pack  31  is biased toward the back side by the spring member  17 . When the back part  11   b  of the main housing  11  is turned toward the upper side to release the hook  36  of the battery pack  31  from the locking portion  25   c  of the attachment section  25  with the battery pack  31  attached to the attachment section  25  in the battery pack accommodating portion  11   c , the battery pack  31  is pushed out toward the back side by the biasing force of the spring member  17 . The back part of the battery pack  31  thus projects out from the opening on the back side of the battery pack accommodating portion  11   c , and hence the battery pack  31  can be easily detached by grabbing the back part of the battery pack  31  and pulling out the battery pack toward the back side from the battery pack accommodating portion  11   c.    
       Ninth Alternative Embodiment 
       [0061]    As shown in a right side view of  FIG. 16 , in an electric chainsaw  10  of a ninth alternative embodiment, the battery pack accommodating portion  11   c  is arranged in two stages, upper and lower, at the back part of the main housing  11 . The battery pack accommodating portion  11   c  has the right side surface side opened, and the battery pack  31  is accommodated in the battery pack accommodating portion  11   c  from such opening. The attachment section  25 , described above, is arranged in the battery pack accommodating portion  11   c , and the battery pack  31  accommodated in each battery pack accommodating portion  11   c  is removably attached to the attachment section  25 . The attachment section  25  of the upper stage is arranged at a lower part of the battery pack accommodating portion  11   c , and the attachment section of the lower stage is arranged at an upper part of the battery pack accommodating portion  11   c , where the attachment sections  25  of the upper stage and the lower stage are arranged at positions adjacent to each other. 
         [0062]    A spring member (not shown) including the plate spring is arranged as shown in the seventh alternative embodiment at the back, which becomes the left side part of the battery pack accommodating portion  11   c , and the battery pack  31  is biased toward the right side by the spring member. When the hook  36  of the battery pack  31  is released from the locking portion  25   c  of the attachment section  25  with the battery pack  31  attached to the attachment section  25  in the battery pack accommodating portion  11   c , the battery pack  31  is pushed out toward the right side by the biasing force of the spring member. The right side part of the battery pack  31  thus projects out from the opening on the right side of the battery pack accommodating portion  11   c,  and hence the battery pack  31  can be easily detached by grabbing the right side part of the battery pack  31  and pulling out the battery pack toward the right side from the battery pack accommodating portion  11   c.    
       Tenth Alternative Embodiment 
       [0063]    As shown in  FIG. 17 , an electric chainsaw  10  of a tenth alternative embodiment has two battery pack accommodating portions  11   c  arranged on the front and back at the back part on the lower side of the main housing  11 . The battery pack accommodating portion  11   c  has the right side surface side opened, and the battery pack  31  is accommodated in the battery pack accommodating portion  11   c  from such opening. An interval of the wall surfaces adjacent to each other of the two battery packs  31  attached side by side to the front and back is 5 mm, and an occupying space by the two battery packs  31  is narrowed. The occupying space by the two battery packs  31  can be sufficiently narrowed if the interval of the wall surfaces adjacent to each other of the two battery packs  31  is smaller than 15 mm. The attachment section  25  described above is arranged at the upper part of the battery pack accommodating portion  11   c , and the battery pack  31  accommodated in each battery pack accommodating portion  11   c  is removably attached to the attachment section  25 . 
         [0064]    A plate spring member (not shown) is arranged as shown in the seventh and eighth alternative embodiment at the back, which becomes the left side part of the battery pack accommodating portion  11   c , and the battery pack  31  is biased toward the right side by the spring member. When the hook  36  of the battery pack  31  is released from the locking portion  25   c  of the attachment section  25  with the battery pack  31  attached to the attachment section  25  in the battery pack accommodating portion  11   c , the battery pack  31  is pushed out toward the right side by the biasing force of the spring member. The right side part of the battery pack  31  thus projects out from the opening on the right side of the battery pack accommodating portion  11   c , and hence the battery pack  31  can be easily detached by grabbing the right side part of the battery pack  31  and pulling out the battery pack toward the right side from the battery pack accommodating portion  11   c.    
       Eleventh Alternative Embodiment 
       [0065]    As shown in  FIG. 18 , in an electric chainsaw  10  of an eleventh alternative embodiment, two attachment sections  25  are arranged juxtaposed to the front and back on the lower side of the rear handle  13  at the back part of the main housing  11 , and two battery packs  31  are attached side by side to the front and back on the lower side of the rear handle  13  at the back part of the main housing  11 . The interval of the wall surfaces adjacent to each other of the two battery packs  31  attached side by side to the front and back is 5 mm, so that the occupying space by the two battery packs  31  is narrowed. The occupying space by the two battery packs  31  can be sufficiently narrowed if the interval of the wall surfaces adjacent to each other of the two battery packs  31  is smaller than 15 mm. The respective center of gravity of the two battery packs  31  when seen from the back side is located in the range R of 1.5 times the horizontal width of the grip section  13   a  at both left and right sides of the center line C extending perpendicularly at the center in the left and right direction of the grip section  13   a  of the rear handle  13 , and the center of gravity when seen from the back side of the chainsaw  10  is located within the range R of 1.5 times the horizontal width of the grip section  13   a  at both left and right sides of the center line C extending in the up and down direction of the grip section  13   a  of the rear handle  13 . In the example described above, the interval of the wall surfaces adjacent to each other of the pair of battery packs  31  is 5 mm, but if the interval of the wall surfaces adjacent to each other of the two battery packs  31  is greater than or equal to 15 mm, a finger can be inserted between the two battery packs  31  to facilitate the attachment/detachment operation. 
       Twelfth Alternative Embodiment 
       [0066]    As shown in  FIG. 19 , in an electric chainsaw  10  of a twelfth alternative embodiment, two attachment sections  25  are arranged juxtaposed to the left and right on the lower side of the rear handle  13  at the back part of the main housing  11 , and two battery packs  31  are attached side by side to the left and right on the lower side of the rear handle  13  at the back part of the main housing  11  (in  FIG. 19 , the attachment section  25  on the right side and the battery pack  31  on the right side are shown, and the illustration of the attachment section  25  on the left side and the battery pack  31  on the left side, which are symmetric to the right side, is omitted). The interval of the wall surfaces adjacent to each other of the two battery packs  31  attached side by side to the left and right is 5 mm, so that the occupying space by the two battery packs  31  is narrowed. The occupying space by the two battery packs  31  can be sufficiently narrowed if the interval of the wall surfaces adjacent to each other of the two battery packs  31  is smaller than 15 mm. The respective center of gravity of the two battery packs  31  when seen from the back side is located in the range R of 1.5 times the horizontal width of the grip section  13   a  at both left and right sides of the center line C extending in the up and down direction of the grip section  13   a  of the rear handle  13 , and the center of gravity when seen from the back side of the chainsaw  10  is located within the range R of 1.5 times the horizontal length of the grip section  13   a  at both left and right sides of the center line C in the left and right direction extending in the up and down direction of the grip section  13   a  of the rear handle  13 . Furthermore, the two battery packs  31  are arranged such that each center of gravity G 1  is divided to both left and right sides of the center line C extending in the up and down direction of the grip section  13   a . In the example described above, the interval of the wall surfaces adjacent to each other of the two battery packs  31  is 5 mm, but if the interval of the wall surfaces adjacent to each other of the two battery packs  31  is greater than or equal to 15 mm, a finger can be inserted between the two battery packs  31  to facilitate the attachment/detachment operation. 
       Thirteenth Alternative Embodiment 
       [0067]    As shown in  FIG. 20 , in an electric chainsaw  10  of a thirteenth alternative embodiment, two attachment sections  25  are arranged at a central part in the left and right direction on the lower side of the rear handle  13  at the back part of the main housing  11 , and two battery packs  31  are attached to both left and right sides on the lower side of the rear handle  13  at the back part of the main housing  11  (in  FIG. 20 , the attachment section  25  on the right side and the battery pack  31  on the right side are shown, and the illustration of the attachment section  25  on the left side and the battery pack  31  on the left side, which are symmetric to the right side, is omitted). The respective center of gravity G of the two battery packs  31  when seen from the back side is located in the range R of 1.5 times the width of the grip section  13   a  at both left and right sides of the center line C extending in the up and down direction of the grip section  13   a  of the rear handle  13 , and the center of gravity when seen from the back side of the chainsaw  10  is located within the range R of 1.5 times, the width of the grip section  13   a  at both left and right sides of the center line C extending in the up and down direction of the grip section  13   a  of the rear handle  13 . Furthermore, the two battery packs  31  are arranged such that each center of gravity G 1  is divided to both left and right sides of the center line C extending in the up and down direction of the grip section  13   a.    
         [0068]    In the chainsaws  10  configured as above, description has been made that the two battery packs  31  are series-connected with respect to the electric motor  23 , but the present invention is not limited thereto. The electric motor  23  can be used with high output when the pair of battery packs  31  are series-connected with respect to the electric motor  23 , whereas the electric motor  23  can be used for a long period of time when the pair of battery packs  31  are parallel-connected with respect to the electric motor  23 . The series connection and the parallel connection can be selected by a control circuit. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  chainsaw 
           11  main housing 
           21  guide bar 
           22  saw chain 
           23  electric motor 
           25  attachment section 
           25   a  connector portion 
           25   b  guide rail 
           25   c  locking portion 
           30  power source 
           31  battery pack 
           32  housing 
           33  battery cell 
           34  electric connector 
           35  rail 
           36  hook 
         G center of gravity of chainsaw 
         G 1  center of gravity of battery pack 
         C center line (center line in left and right direction extending in up and down direction when grip section is seen from back side) 
         R range (range of 1.5 times horizontal length of grip section at both left and right sides from center line C of grip section)