Patent Publication Number: US-11045938-B2

Title: Power tool

Description:
CROSS-REFERENCE 
     This application claims priority to Japanese patent application serial number 2016-20898, filed on Feb. 5, 2016, the contents of which are herein incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention generally relates to a handheld power tool which may be used to perform various types of work, such as the cutting of materials. 
     BACKGROUND ART 
     A multifunction power tool, which is referred to as a multi-tool, can perform various kinds of work such as cutting work, peeling work, and grinding work, etc. by swinging a tip tool attached to an output axis of the power tool at a predetermined angle at high speed. The maximum swinging rate of the output axis may reach roughly 200,000 times per minute, which may cause microvibration. Owing to the microvibration, a problem of, for example, damaged operability and/or workability may occur in these types of power tools. Conventionally, in these types of power tools, various countermeasures have been taken to suppress such microvibration. Japanese Laid-Open Patent Publication No. 2015-229223 discloses a technique of suppressing microvibration in multifunction power tools such that a weight device is attached to one end of a motor shaft while an eccentric shaft for producing a swing movement is positioned at the other end of the motor shaft. Aside from this technique, Japanese Patent No. 4844409 discloses a technique of improving drop-impact strength by providing a thin wall part in a grip in pistol-type electric power tools. 
     Notwithstanding the aforementioned prior art, it is desirable to further suppress the microvibration occurring in multifunction power tools in which swing movement is performed at high speed. Some of the power tools may be configured such that their housing is integrally molded into a tubular body, or a half-split structure having left and right half-split housings made of resin. In the half-split structure, the microvibration caused by the high-speed swing movement can cause mating surfaces of the left and right half-split housings to vibrate at different phases (vibrate mutually) and/or to rub with each other. As a result, a heat generation problem may occur. Furthermore, in a case where a large amount of heat is generated, an additional problem of vibration welding, may occur. 
     Thus, due to these difficulties, there is a need in the art to solve the problem of heat generation by suppressing a mutual vibration of mating surfaces of the housing in multifunction power tools where the swing movement is performed at high speed. 
     SUMMARY 
     In one exemplary embodiment of the present disclosure, a power tool comprises a first half-split housing and a second half-split housing, and the first half-split housing is configured to be mated to the second half-split housing for screw connection. Furthermore, the first and the second half-split housings includes a relative displacement restriction means other than the screw connection for restricting a relative displacement of the first half-split housing with respect to the second half-split housing in a separating direction. 
     According to the embodiment, the power tool is provided with the relative displacement restriction means other than the screw connection for restricting the relative displacement of the half-split housings in the separating direction. Because of the relative displacement restriction means, a resistance to separation in the separating direction (separation resistance) is introduced between the half-split housings. Because of this element of construction, even if the screw connection is loosened, the half-split housings remain connected in an inseparable manner due to the separation resistance of the relative displacement restriction means. 
     Furthermore, the separation resistance which aids the half-split housings in remaining connected in a mating manner with each other dually functions as a resistance for restricting a displacement along the mating surfaces of the half-split housings in a longitudinal direction (a direction perpendicular to the separating direction). Thus, because of the separation resistance generated by the relative displacement restriction means, through the dual-function of the means, a relative displacement (vibration and/or rub) in a mating direction of the half-split housings can also be restricted. As a result, heat generation on the mating surface can be prevented and/or restricted. 
     In another exemplary embodiment of the disclosure, the first half-split housing includes a screw-boss part for fastening a screw, and the second half-split housing includes a boss-receiving part into which the screw-boss part of the first half is inserted. Furthermore, in this embodiment the relative displacement restriction means is configured by the screw-boss part being press-fitted to the boss-receiving part. 
     According to the embodiment, by press-fitting the screw-boss part to the boss-receiving part, separation resistance is introduced between the half-split housings. As a result, relative displacement (vibration and/or rub) in the mating direction of the half-split housings can be restricted and/or reduced. In the press-fitting structural configuration, an inner diameter of the boss-receiving part is configured to be sized with respect to an outer diameter of the screw-boss part such that the screw-boss part is press-fit to the boss-receiving part. In another structure, a protrusion is provided on an inner surface of the boss-receiving part such that the screw-boss part is press-fit to the boss-receiving part. 
     In another exemplary embodiment of the disclosure, the relative displacement restriction means is configured such that a press-fitting pin provided in the first half-split housing is press-fit to a press-fitting hole provided in the second half-split housing. 
     According to the embodiment, the press-fitting pin positioned between the half-split housings can generate the separation resistance. Because of the separation resistance, a relative displacement along the mating surface of the half-split housings in a longitudinal direction can be restricted. As a result, vibration and/or rub of the mating surface in a mating direction can be restricted, which can prevent and/or restrict heat generation. 
     In another exemplary embodiment of the disclosure, the first half-split housing includes a first mating surface, and the second half-split housing includes a second mating surface. A rib is provided on the first mating surface for restricting the relative displacement of the first half-split housing with respect to the second half-split housing in a mating direction, and a rib-receiving part into which the rib is inserted is provided on the second mating surface. In this manner, the relative displacement restriction means of this embodiment is structurally configured such that the rib is press-fit to the rib-receiving part. 
     According to the embodiment, the rib press-fit to the rib-receiving part can generate the separation resistance between the half-split housings. As a result, relative displacement (vibration and/or rub) along the mating surface of the half-split housings in a longitudinal direction can be restricted, which can prevent and/or restrict heat generation. 
     In another exemplary embodiment of the disclosure, a protrusion is provided on the rib, and the protrusion is configured to be elastically deformed such that the rib is press-fit to the rib-receiving part. 
     According to the embodiment, the protrusion is elastically deformed to be press-fit to the rib-receiving part. The press-fitting structural configuration of the rib with respect to the rib-receiving part is such that the protrusion is provided on a lateral side of the rib. In another structure, the rib is formed in a tapered manner to be press-fit to the rib-receiving part. In another structure, a groove width of the rib-receiving part is sized to be a little smaller than a thickness of the rib to be press-fit to the rib. Furthermore, in another structure, a elastic member such as a rubber sheet etc. is inserted between lateral sides of the rib and the rib-receiving part such that the rib is press-fit to the rib-receiving part. 
     In another exemplary embodiment of the disclosure, a plurality of ribs are provided on the first mating surface, and the relative displacement restriction means includes at least three ribs. 
     According to the embodiment, due to the plurality of ribs, relative displacement (vibration and/or rub) along the mating surfaces of the half-split housings in a longitudinal direction can be restricted in a wider area. As a result, heat generation can be more simply and/or more reliably prevented and/or reduced. 
     In another exemplary embodiment of the disclosure, the power tool further comprises an output shaft that swings at a predetermined angle. Furthermore, the first half-split housing and the second half-split housing are configured to be located left and right with respect to a place including a swing axis of the output shaft. 
     According to the embodiment, the above-discussed effects can be applied to the half-split housings in the multifunction power tool having a fast swing output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall side view of a power tool according to an exemplary embodiment of the present disclosure. 
         FIG. 2  is an overall plan view of the power tool according to the exemplary embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional view taken along arrows (III)-(III) in  FIG. 2 , showing an overall internal structure of a half-split left housing. 
         FIG. 4  is a rear-to-front side view of the half-split left housing, as seen from an inner surface side (from a right side, according to the left-right orientation of  FIG. 2 ). 
         FIG. 5  is front-to-rear side view of the half-split right housing, as seen from an inner surface side (from a left side, according to the left-right orientation of  FIG. 2 ). 
         FIG. 6  is a figure showing a relative displacement restriction means of a first exemplary embodiment of the present disclosure, which is a cross-sectional view seen from arrows (VI)-(VI) in  FIG. 3 . 
         FIG. 7  is an exploded perspective view of  FIG. 6 , showing the housing in a sliced manner including the relative displacement restriction means of the first embodiment. 
         FIG. 8  is another figure showing a relative displacement restriction means of a second exemplary embodiment, which is a cross-sectional view seen from the same direction as from the arrows (VI)-(VI) in  FIG. 3 . 
         FIG. 9  is another figure showing a relative displacement restriction means of a third exemplary embodiment, which is a cross-sectional view seen from the same direction as from the arrows (VI)-(VI) in  FIG. 3 . 
         FIG. 10  is an exploded perspective view of  FIG. 9 , showing the housing in a sliced manner including the relative displacement restriction means of the third embodiment. 
         FIG. 11  is another figure showing a relative displacement restriction means of a fourth exemplary embodiment, which is a cross-sectional view seen from the same direction as from the arrows (VI)-(VI) in  FIG. 3 . 
         FIG. 12  is an enlarged view of (XII) in  FIG. 11 , showing a cross sectional view of a press-fitting state of a rib with respect to a rib-receiving part. 
         FIG. 13  is an exploded perspective view of  FIG. 11 , showing the housing in a sliced manner including the relative displacement restriction means of the fourth embodiment. 
         FIG. 14  is an enlarged perspective view of (XIV) in  FIG. 13 , showing a rib and its surroundings. 
         FIG. 15  is another figure showing a relative displacement restriction means of a fifth exemplary embodiment, which is a cross-sectional view seen from the same direction as from the arrows (VI)-(VI) in  FIG. 3 . 
         FIG. 16  is an exploded perspective view of  FIG. 15 , showing the housing in a sliced manner including the relative displacement restriction means of the fifth embodiment. 
         FIG. 17  is a perspective view of a press-fitting rib formed in a protruding shape and a rib-receiving part. 
         FIG. 18  is a perspective view of a press-fitting rib formed in an extending projection shape and a rib-receiving part. 
         FIG. 19  is a perspective view of a press-fitting rib formed in a tapered shape and a rib-receiving part. 
         FIG. 20  is a cross-sectional view of the housing, which is seen from arrows (XX)-(XX) in  FIG. 5 . 
         FIG. 21  is a cross-sectional view of the housing, which is seen from arrows (XXI)-(XXI) in  FIG. 5 . 
         FIG. 22  is a cross-sectional view of the housing, which is seen from arrows (XXII-(XXII) in  FIG. 5 . 
         FIG. 23  is a cross-sectional view of the housing, which is seen from arrows (XXIII)-(XXIII) in  FIG. 5 . 
         FIG. 24  is a cross-sectional view of the housing, which is seen from arrows (XXIV)-(XXIV) in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The detailed description set forth below, when considered with the appended drawings, is intended to be a description of exemplary embodiments of the present invention and is not intended to be restrictive and/or to represent the only embodiments in which the present invention can be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments of the invention. It will be apparent to those skilled in the art that the exemplary embodiments of the invention may be practiced without these specific details. In some instances, these specific details refer to well-known structures, components and/or devices that are shown in block diagram form in order to avoid obscuring significant aspects of the exemplary embodiments presented herein. 
     Hereinafter, exemplary embodiments of the present teachings will be described with reference to  FIGS. 1 to 24 . As shown in  FIGS. 1 to 3 , a multifunction electric power tool may be exemplified as a power tool  1  in each of exemplary embodiments. The power tool  1  may have a configuration in which a tip tool attached to an output shaft of a motor is swung at a predetermined angle at high speed. The power tool  1  may be used for various kinds of work such as, for example, a cutting work of plasterboards, a peeling work of tiles, and a grinding work of wooded materials, etc. Hereinafter, five embodiments will be described below. Each of the five embodiments may have differing features from each other with respect to a connection structure of half-split housings, and a basic structure of the housing, with the exception of the above feature may be common in the five embodiments. Because of this reason, only the embodiment 1 will be explained with regard to the basic structure of the power tool  1 , and the subsequent descriptions of the construction in the other four embodiments in common with the first embodiment may be omitted by using the same reference numerals. 
     The power tool  1  may be provided with a tool main body  10  in which an electric motor  11  is housed as a driving source, a mechanism section  20  that is located in front of the tool main body  10 , a grip  30  that is located at a rear part of the tool main body  10 , and a power supply section  40  that is located at a rear part of the grip  30 . In the power tool  1 , the mechanism section  20 , the tool main body  10 , the grip  30 , and the power supply section  40  may be successively arranged in this order from the front side, extending approximately in a straight line along the front-rear axis. The mechanism  20 , the tool main body  10 , the grip  30 , and the power supply section  40  may be housed in roughly a tubular housing  50  that extends along a motor axis M of the electric motor  11 . The housing  50  may include left and right half-split housings made from resin. Each of the five embodiments may have a feature in a connection structure of the half-split housings. The housing  50  may be described in detail later. 
     As shown in  FIG. 3 , the electric motor  11  of the tool main body  10  may be housed in a tubular motor case  11   a . A cooling fan  11   b  attached to a motor axis  11   c  may be housed in the motor case  11   a . An oval exhaust window  11   d  may be provided at a rear part of the motor case  11   a . In  FIG. 3 , the cooling fan  11   b  may be seen via the exhaust window  11   d . Furthermore, as shown in  FIGS. 1, 4, and 5 , a plurality of inlet ports  50   b  may be provided at a front side face, a center side face, and a rear side face in a longitudinal direction of the housing  50 . Furthermore, a plurality of exhaust ports  50   a  may be provided at approximately a center side-face in the longitudinal direction of the housing, which is located around the exhaust window  11   d . When the cooling fan  11   b  rotates by the running of the electric motor  11 , outside air may be introduced into an inside of the motor case  11   a  via the inlet ports  50   b  to cool the electric motor  11 . This air for cooling the electric motor  11  introduced into the inside of the motor case  11   a  may be exhausted from the exhaust window  11   d  to the outside of the housing  50  via the exhaust ports  50   a  by the continued rotation of the cooling fan  11   b.    
     The electric motor  11  may be powered by a battery pack  41  that is attached to the power supply section  40 . The mechanism section  20  may be connected to the motor shaft  11   c  of the electric motor  11 . The mechanism section  20  may include a driving shaft  22 , a swinging arm  23 , and a member that rotatably supports output shaft  24 , where the members of the mechanism section are inside a mechanism case  21 . The driving shaft  22  may be connected to the motor shaft  11   c  of the electric motor  11 . The driving shaft  22  may be rotatably supported by the mechanism case  21  via bearings  22   a  and  22   b . The driving shaft  22  may be rotatably supported around the motor axis M. Furthermore, an eccentric shaft  22   c  that is eccentrically located with respect to the motor axis M may be integrally formed with the driving shaft  22  at a front part thereof. A driving roller  25  may be attached to the eccentric shaft  22   c.    
     Operating parts  23   a  of the swinging arm  23  may be brought into slide contact with the driving roller  25  in both the left and right directions. The left and right operating parts  23   a  may be integrally formed with a rear part of the swinging arm  23 . The left and right operating parts  23   a  may extend in the rear direction in parallel at a predetermined space apart from each other. Furthermore, an output shaft  24  may be joined to a front part of the swinging arm  23 . The output shaft  24  may be rotatably supported around an output axis P that is perpendicular to the motor axis M. The output shaft  24  may be supported by the mechanism case  21  via an upper bearing  24   a  and a lower bearing  24   b.    
     When the electric motor  11  is run, the driving shaft  22  may rotate around the motor axis M. When the driving shaft  22  rotates around the motor axis M, the eccentric shaft  22   c  via its eccentric orientation revolves around the motor axis M. Consequently, displacement of the driving roller  25  in the left and right directions due to movement from the eccentric shaft  22   c  may be transferred to the swinging arm  23  via the left and right operating parts  23   a  while the driving roller  25  revolves around the motor axis M. Thus, the swinging arm  23  may swing about the output axis P in the left-right directions at a predetermined angle. Because of this movement, the output shaft  24  may rotate about the output axis P at the same predetermined angle. 
     A lower part of the output shaft  24  may protrude in a downward direction from a lower surface of the mechanism case  21 . A tool holder  26  may be provided at the lower part of the output shaft  24 . Furthermore, a tip tool T may be attached to the lower part of the output shaft  24  by inserting the tip tool T to the tool holder  26  and tightening a fixing screw  26   a  to fix the tip tool T. The tip tool T may be attached to the lower part of the output shaft  24 , extending from the lower part of the output shaft  24  in the front direction (a direction orthogonal to the output axis P). As shown in  FIGS. 1 and 2 , a band-shaped saw blade (cutting saw blade) may be attached to the output shaft  24  as the tip tool T. The tip tool T may be swung at high speed at the predetermined angle around the output axis P, and a cutting work may be performed by use of a tip of the tip tool T. For example, a wooden material can be cutout using the tip tool T in a rectangular shape. 
     A start switch  12  that is slidably operated in the forward and rearward directions may be provided on the upper peripheral surface of the main body housing  51  (corresponding to the tool main body  10 ) of the housing  50 . As shown in  FIG. 3 , an operation lever  13 , which is integrally formed with the start switch  12 , may be located below a lower surface of the start switch  12 . The operation lever  13  may extend in the rearward direction along an inner surface of the housing  50 . A rear portion of the operation lever  13  may be joined to a main switch  14  that is housed within the grip  30 . When the start switch  12  is slidably operated (moved) in the forward direction (the start switch  12  is turned on), through the movement of operation lever  13 , the main switch  14  may be switched on to run the electric motor  11 . On the other hand, when the start switch  12  is slidably operated (moved) in the rearward direction (the start switch  12  is turned off), through the movement of operation lever  13 , the main switch  14  may be switched off to stop the electric motor  11 . 
     The grip  30 , which can be held by a user with one hand, may be located proximate to the rear end of the tool main body  10 . A grip housing  53  (corresponding to the grip  30 ) of the housing  50  may have a thickness and shape such that the user can easily hold the grip  30  with one hand. A speed controller for adjusting a rotation speed of the electric motor  11  may be located at the rear part of the grip  30 . Furthermore, a rotary type adjustment dial  31   a  may be provided at the speed controller  31 . As shown in  FIGS. 2 and 3 , an upper part of the adjustment dial  31   a  may protrude from a window  53   a  provided at an upper surface of the grip housing  53 . A triangular indicator  53   b  for indicating an adjusted rotation speed of the electric motor  11  may be marked in front of the window  53   a . The window  53   a  may be provided at a bottom part of a rectangular convex flange  53   c  that is formed in an inverted cone shape, as seen from the plan view in  FIG. 2 . The upper part of the adjustment dial  31   a  may protrude from the window  53   a  in such a way so as to not protrude from the concave part  53   c . Because of this configuration, an inadvertent erroneous operation of the adjustment dial  31   a  may be prevented. 
     The power supply section  40  may be provided rearward of the grip  30 . A power supply section housing  54 , which houses the power supply section  40 , may be integrally formed with and protrude and tilt in a diagonally downward direction from the grip housing  53 . A main controller  43  for controlling the electric motor  11  may be housed in the power supply section housing  54 . Although not shown in  FIG. 3 , the main controller  43  may be configured such that a control circuit board of the main controller  43 , which molded with resin and is housed in a shallow rectangular case, comprises a motor control circuit and a power supply circuit. 
     A terminal stand  42  having positive and negative terminal plates  42   a  may be housed at the rear surface side of the main controller  43 . A pair of rail receiving sections  44  for guiding the battery pack  41  may be provided at the left and right side directions of the terminal stand  42 . The battery pack  41  which is slidably attached to the power supply section  40  may include a plurality of lithium ion cells housed in a case thereof. For example, the battery pack  41  may output 10.8 volts. A pair of guide rails  41   a  that engages with the pair of rail receiving sections  44  of the terminal stand  42  of the power supply section  40  may be provided on the front surface of the case comprising battery pack  41 . Furthermore, positive and negative terminal receiving parts may be arranged between the pair of guide rails  41   a  on the battery pack  41 . 
     The battery pack  41  may be attached to the power supply section  40  by sliding the battery pack  41  in the downward direction from an upward starting position relative to the terminal stand. On the other hand, from an attached position, the battery pack  41  may be removed from the power supply section  40  by sliding the battery pack  41  in the upward direction. Although not shown in the figures, a claw part for locking an attachment condition of the battery pack  41  with respect to the ten final stand of the power supply section  40  may be provided on the battery pack  41 . Furthermore, as shown in  FIG. 2 , an unlock button  41   b  may be provide on the upper surface of the battery pack  41  for releasing the attachment lock condition by displacing the claw part to an unlock position relative to the power supply section  40 . Subsequently, the battery pack  41  may be removed from the power supply section  41  and recharged for repeated use by a dedicated charger separately provided. 
     As discussed earlier, the power tool  1  may include the tubular housing  50  extending along the motor axis M, which comprises the left and right half-split housings. The housing  50  may be configured such that the left half-split housing  50 L and the right half-split housing  50 R are mated and screw-connected to each other. The front of the housing  50  may correspond to a mechanism section housing  52  of the mechanism section  20 . The rear of the mechanism section housing  52  may correspond to the front of main body housing  51  of the tool main body  10 . The rear of the main body housing  51  may correspond to the front of a grip housing  53  of the grip  30 . Furthermore, the rear of the grip housing  53  may correspond to the front of the power supply section housing  54  of the power supply section  40 . 
     As shown in  FIG. 2 , the left half-split housing  50 L and the right half-split housing  50 R of  FIGS. 4 and 5 , respectively, may be mated with each other on the mating surface J to form the tubular housing  50 .  FIGS. 4 and 5  show the left and right half-split housings  50 L,  50 R respectively seen from the right and left internal surface sides, respectively. Both the left and right half-split housings  50 L,  50 R may be provided with the mating surface J mainly along upper edge parts and lower edge parts thereof. 
     Outer circumferential surfaces of the left and right half-split housings  50 L,  50 R may be (partly or wholly) covered with elastic resin layer  55  in order to prevent slippage and/or reduce an impact of dropping etc. In  FIGS. 4 and 5 , the elastic resin layer  55  may be indicated by oblique lines in order to differentiate the elastic resin layer  55  from the mating surface J. Ribs  56  may be provided on the mating surface J in order to position the mating surface direction of the left and right half-split housings  50 L,  50 R (mainly in the upward and downward directions). As shown in  FIG. 4 , the ribs  56  may be provided on the mating surface J of the left half-split housing  50 L. Each of the ribs  56  may have a thin-plate shape, and a plurality of ribs  56  may be provided along the mating surface J at appropriate intervals. As shown in  FIG. 4 , five ribs  56  may be provided on the upper edge part and two ribs on the lower edge part of the left half-split housing  50 L (seven ribs  56  are provided in total). 
     Corresponding to the location of each of the ribs  56  on the left half-split housing  50 L, groove holes  58  may be respectively provided at corresponding locations on the mating surface J of the right half-split housing  50 R. Each of the groove holes  58  may have an appropriate groove width and length such that the opposing and/or corresponding ribs  56  can be inserted thereinto. As shown in  FIGS. 6, 8, and 9 , the left half-split housing  50 L may be mated with the right half-split housing  50 R by inserting the ribs  56  into the corresponding groove holes  58 . In this way, the left and right half-split housings  50 L,  50 R may be positioned in the mating direction and the mated housings  50 L and  50 R may be screw-connected to each other in the positioned state. Furthermore, the insertion of the ribs  56  into the corresponding groove holes  58  may restrict and/or prevent a positional displacement of the left and right half-split housings  50 L,  50 R in the mating surface direction, such that vibration etc. may not occur. 
     An auxiliary rib  57  may be provided at a lower end of the left half-split housing  50 L, and an auxiliary rib  59  at a lower end of the right half-split housing  50 R. As shown in  FIG. 4 , two auxiliary ribs  57  may be provided on the lower end of the mating surface J of the left half-split housing  50 L. Similarly, as shown in  FIG. 5 , two auxiliary ribs  59  may be provided on the lower end of the mating surface J of the right half-split housing  50 R. Each of the auxiliary ribs  57 ,  59  may be formed long along the mating surface J (extending in the longitudinal direction). The front auxiliary ribs  57  and  59  may be provided along the mating surface J of the main body housing  51 . The rear auxiliary ribs  57  and  59  may be provided along the mating surface J from the grip housing  53  to the power supply section housing  54 . 
     As shown in  FIGS. 6, 8, and 9 , the auxiliary ribs  57  of the left half-split housing  50 L and the corresponding auxiliary ribs  59  of the right half-split housing  50 R may be overlapped with each other in the left-right direction. Because of this overlapping construction, a positioning and/or a displacement prevention of the left half-split housing  50 L with respect to the right half-split housing  50 R may be performed in the upward and downward directions of the mating surface J. With regard to a structural configuration in which the auxiliary ribs  57  of the left half-split housing  50 L are overlapped with the auxiliary ribs  59  of the right half-split housing  50 R in the left-right direction, along the thickness of the tubular housing, the same configuration may be adopted in other embodiments discussed infra. 
     As shown in  FIG. 1 , the left and right half-split housings  50 L,  50 R may be screw-connected with each other where the components of the screw connection comprise screw-connection parts  60 , at nine locations in total. Each of the screw-connection parts  60  may comprise a screw-boss part  61  included on the left half-split housing  50 L, a boss-receiving part  62  included on the right half-split housing  50 R, and a screw  63  for screw-connecting the left and right half-split housings  50 L,  50 R. 
     As shown in  FIG. 4 , nine screw-boss parts  61  each having a screw hole  61   a  for fastening the screws  63  may be provided on the inner surface of the left half-split housing  50 L as seen from the right side. Each of the screw-boss parts  61  may be provided in a protruding direction from the inner surface of the left half-split housing  50 L toward the right half-split housing  50 R, with which the left half-split housing  50 L mates. Furthermore, the screw hole  61   a  has a predetermined depth and may be provided on the protruding side. Three screw-boss parts  61  may be provided on the inner surface of the mechanism section housing  52  of the left half-split housing  50 L. Two screw-boss parts  61  may be provided on the inner surface of the main body housing  51  of the left half-split housing  50 L. Two screw-boss parts  61  may be provided on the inner surface of the grip housing  53  of the left half-split housing  50 L. Furthermore, two screw-boss parts  61  may be provided on the inner surface of the power supply section housing  54  of the left half-split housing  50 L. Furthermore, in addition to the three screw-boss parts  61  provided on the mechanism section housing  52 , three case-fixing parts  64  each having a screw hole  64   a  for fixing the mechanism section case  21  may be provided on the inner surface of the mechanism section housing  52  of the left half-split housing  50 L. 
     As shown in  FIG. 5 , nine boss-receiving parts  62  in total may be provided on the inner surface of the right half-split housing  50 R, corresponding to the nine screw-boss parts  61  of the left half-split housing  50 L. Each of the boss-receiving parts  62  may have a cylindrical shape such that the screw-boss part  61  can be inserted thereinto. An insertion hole  62   a  for inserting the screw  63  may be provided at a bottom center of each boss-receiving part  62 . By inserting the screw  63  into the insertion hole  62   a  from the right half-split housing  50 R and fastening the screw  63  to the screw hole  61   a  of the left half-split housing  50 L, the left half-split housing  50 L may be firmly connected to the right half-split housing  50 R in a mating manner to jointly form the tubular housing  50 . Conversely, when all of the screws  63  are removed from the nine screw-connection parts  60 , the left half-split housing  50 L may be separated from the right half-split housing  50 R. 
     A means for restricting a displacement in a mutual separation direction (hereinafter, referred to as a relative displacement restriction means  70 ) may be provided between the left half-split housing  50 L and the right half-split housing  50 R. Hereinafter, several embodiments with respect to the relative displacement restriction means  70  may be described below. As shown in  FIGS. 5 to 7 , a relative displacement restriction means  71  of the first embodiment may be configured such that a press-fitting protrusion  71   a  may be provided on an inner surface of the boss-receiving part  62 . The press-fitting protrusion  71   a  may be provided at an upper screw-connection part  60  of the two screw-connection parts  60  that are located in the grip housing  53  of the right half-split housing  50 R. A degree of rub and/or vibration, which may potentially occur without the displacement restriction means between the mating surface J of the left and right half-split housings  50 L,  50 R, would be presumed to be larger in the vicinity of the upper screw-connection part  60 . As a result, the relative displacement restriction means  71  is provided at this place in the first embodiment. 
     In the upper screw-connection part  60  of grip housing  53  of the right half-split housing  50 R, four press-fitting protrusions  71   a  may be provided on the outer periphery of the inner circumferential surface of the boss-receiving part  62  at equal intervals (four protrusions equally spaced in the circumferential direction). Due to the presence of the press-fitting protrusions  71   a  on the outer periphery of the inner circumferential surface, an (actual) inner diameter of the upper boss-receiving part  62  may become smaller than that of the other eight boss-receiving parts  62 . Hence, the inner diameter of the upper boss-receiving part  62  may be appropriately sized such that the protruding tip part of the screw-boss part  61  of the left half-split housing  50 L can be inserted thereinto. 
     Because of this configuration, in a state where the left and right half-split housings  50 L,  50 R are connected to each other, the screw-boss part  61  may be press-fit to an inner peripheral hole of the boss-receiving part  62  in the upper screw-connection part  60  located in the grip housing  53 . On the other hand, for the other eight screw-connection parts  60 , each of the corresponding screw-boss parts  61  may be inserted into the corresponding inner peripheral holes of the corresponding boss-receiving part  62  without any resistance. In this way, in one of the nine screw-connection parts  60  (the upper screw-connection part  60  located in the grip housing  53 ), the screw-boss part  61  may be press-fit to the screw-receiving part  61  because of the press-fitting protrusions  71   a . In this manner, a resistance in the separating direction (separation resistance) may be generated between the left and right half-split housings  50 L,  50 R. Thus, even if all of the screws  63  are loosened in the screw-connection parts  60 , the left and right half-split housings  50 L,  50 R may still be kept in a mating configuration with respect to each other, with the retaining force of the separation resistance of the upper screw-connection part  60  located in grip housing  53  present. In the first embodiment, the separation resistance by the press-fitting protrusions  71   a  (a retaining force for retaining the housings in the mating manner) may be configured such that when, for example, the housing  50  is held in a horizontal left-to-right direction with only one of the half-split housings being held by the user, the other of the half-split housings may not be separated (may not fall) due to its own weight by gravity. In the first embodiment, a protruding size of the four press-fitting protrusions  71   a  in the direction of the inner diameter from the outer periphery of the inner circumferential surface of the boss receiving part  62  may be appropriately set in order to generate the separation resistance desired. 
     The separation resistance for retaining the left and right half-split housings  50 L,  50 R in the mating configuration (with press-fit separation resistance present) with respect to each other may also dually serve as a resistance for restricting a displacement of the left and right half-split housings  50 L,  50 R in the mating surface direction J (in a direction perpendicular to the separation direction). Due to the nature of the separation resistance obtained by the press-fitting protrusions  71   a  (relative displacement restriction means  70 ) via the press fit structural configuration as described, a relative displacement (rub and/or vibration) of the left and right half-split housings  50 L,  50 R may be restricted in the direction of the mating surface J, which effectively prevents and/or restricts heat from generating on the mating surface J. 
     According to the relative displacement restriction means  71  in the first embodiment discussed above, the screw-boss part  61  may be press-fit to the inner circumferential surface of the boss-receiving part  62  in one of the nine screw-connection parts  60  as described above, by which the left and right half-split housings  50 L,  50 R are connected with each other (are not easily separated from each other). Under the press-fitting condition, the appropriate resistance (separation resistance) may be obtained between the left and right half-split housings  50 L,  50 R through configuration of the press-fit configuration and sizing of protrusions  71   a  as described above. Because of the presence of the separation resistance, the relative displacement of the left and right half-split housings  50 L,  50 R may be restricted in the direction of the mating surface J. Thus, rub and/or vibration on the mating surface J can be restricted, which may restrict heat generation. 
       FIG. 8  shows a relative displacement restriction means  72  of a second embodiment. The relative displacement restriction means  72  of the second embodiment may be configured such that instead of the four press-fitting protrusions  71   a , a tubular rubber bush  72   a  is inserted into and/or fittedly mounted to the outer periphery of the inner circumferential surface of the boss-receiving part  62 . The tip end of the screw-boss part  61  may then be press-fit to the inner circumferential surface of the rubber bush  72   a . In this way, as with the first embodiment, separation resistance may be generated in one of the screw-connection parts  60  of the left and right half-split housings  50 L,  50 R. 
     As discussed above, because of the relative displacement restriction means  72  (the rubber bush  72   a ) of the second embodiment, the separation resistance may be generated between the left and right half-split housings  50 L,  50 R. Because of this separation resistance, the relative displacement of the left and right half-split housings  50 L,  50 R may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the longitudinal direction of the mating surface J. Thus, rub and/or vibration of the mating surface J can be restricted, which may restrict heat generation. 
       FIGS. 9 and 10  show a relative displacement restriction means  73  of a third embodiment. The relative displacement restriction means  73  of the third embodiment may be configured such that the separation resistance can be generated between the left and right half-split housings  50 L,  50 R by use of a press-fitting pin  73   a . In the third embodiment, the press-fitting pin  73   a  may be press-fitted between the mating surface J of the left and right half-split housings  50 L,  50 R along and/or in the vicinity of the upper screw-connection part  60  located in the grip housing  53 . Because of the press-fitting pin  73   a , the separation resistance, as present in the other embodiments above, may be obtained between the left and right half-split housings  50 L,  50 R. As a result, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where rub and/or vibration between the mating surface J of the left and right half-split housings  50 L,  50 R can be restricted, which may restrict heat generation. 
       FIGS. 11 to 14  shows a relative displacement restriction means  74  of a fourth embodiment. The relative displacement restriction means  74  of the fourth embodiment may be configured such that instead of the press-fitting pin  73   a , a rib  56  of the left half-split housing  50 L may be press-fit to a groove hole  58  of the right half-split housing  50 R, which generates separation resistance between the left and right half-split housings  50 L,  50 R. In the fourth embodiment, a rubber sheet  74   a  may be attached to the rib  56  to obtain a necessary press-fitting margin to contact the inner peripheral surface of the groove hole  58 . The rubber sheet  74   a  may be attached to both the outside and inside surfaces of the rib  56  (upside and downside surfaces of the rib  56  as shown in  FIG. 12 ). As shown in  FIGS. 11 and 12 , the rubber sheet  74   a  may be attached to the both sides of the rib  56 , and the rib  56  with the rubber sheet  74   a  may be press-fit to the groove hole  58 . By press-fitting the rib  56  with the rubber sheet  74   a  to the groove hole  58 , the separation resistance may be generated between the left and right half-split housings  50 L,  50 R. As a result, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where rub and/or vibration (relative displacement) between the mating surface J of the left and right half-split housings  50 L,  50 R may be restricted, and thus heat generated in this area may be restricted. 
       FIGS. 15 and 16  show a relative displacement restriction means  75  of the fifth embodiment. The relative displacement restriction  75  of the fifth embodiment may be configured such that a thickness of the rib  56  of the left half-split housing  50 L in the grip housing  53 , relative to the rib  56  of the fourth embodiment described above, is increased to obtain a necessary a press-fitting margin. In  FIGS. 15 and 16 , a symbol W may be added to the rib  56  whose thickness is increased to add the press-fitting margin. In the fifth embodiment, the rubber sheet  74   a  may not be attached to the rib  56  to obtain the press-fitting margin unlike in the fourth embodiment, but the thickness of the rib  56  itself may be increased (the rib  56  having an increased thickness may be formed by molding) to obtain the press-fitting margin to contact the inner peripheral surface of groove hole  58  on its own. By press-fitting the rib  56 W to the groove hole  58 , the relative displacement restriction may be obtained between the left and right half-split housings  50 L,  50 R. As a result, in the fifth embodiment, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where rub and/or vibration (relative displacement) between the mating surface J of the left and right half-split housings  50 L,  50 R may be restricted, and thus heat generation may be restricted. 
     As discussed above, the rubber sheet  74  may be attached to the rib  56  in the fourth embodiment and the thickness of the rib  56  itself may be increased in the fifth embodiment in order to press-fit the (positioning) rib  56  provided on the mating surface J to the groove hole  58 . Other than the aforementioned embodiments, an additional relative displacement restriction means (press-fitting structure) embodiment may be adopted as shown in  FIGS. 17 to 19 . The press-fitting structure shown in  FIG. 17  may be such that a plurality of protrusions  56   a  are provided on a surface of the rib  56  or both surfaces of the ribs  56  to obtain the necessary press-fitting margin. By press-fitting the rib  56  having the protrusions  56   a  to the groove hole  58 , the separation resistance may be generated between the left and right half-split housings  50 L,  50 R. As a result, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where rub and/or vibration on the mating surface J may be restricted, and eventually heat generation in this area may be restricted.  FIG. 17  shows four protrusions  56   a , but more than four protrusions may be provided to obtain the press-fitting margin. Other than this configuration, for example, another configuration in which only one protrusion is provided on either one surface of the rib  56  may be adopted. 
     Furthermore, as shown in  FIG. 18 , instead of the protrusion(s)  56   a  discussed above, the necessary press-fitting margin may be obtained by providing a projection  56   b  extending in a longitudinal direction of the rib  56  on a surface or both surfaces of the rib thereof.  FIG. 18  shows one projection  56   b  on one surface of the rib  56 , but the projection  56   b  may be provided on the opposite side as well, thus being present on both surfaces of the rib  56 . Furthermore, other constructions in which a plurality of projections are provided on one surface of the rib  56  in order to obtain the necessary press-fitting margin may be contemplated. 
       FIG. 19  shows another press-fitting structure (an additional relative displacement restriction means embodiment). The press-fitting structure shown in  FIG. 19  may be configured such that a rib  56 T formed in a tapered shape is press-fitted to the groove hole  58  to generate the separation resistance between the left and right half-split housings SOL,  50 R. A thickness of the rib  56 T may be continuously reduced (i.e. may be tapered) toward its extending tip side. By press-fitting the tapered rib  56  to the groove hole  58 , the separation resistance may be generated between the left and right half-split housings  50 L,  50 R. As a result, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where rub and/or vibration on the mating surfaces J may be restricted, and eventually heat generation may be restricted. 
     As discussed above, the relative displacement restriction means  71 ,  72 ,  73 ,  74 , and  75  may provide the separation resistance in the left and right half-split housings SOL,  50 R in order to restrict not only relative displacement in the horizontal left-to-right direction, but also relative displacement (rib and/or vibration) between the mating surface J, which eventually restricts heat from being generated. In the press-fitting configurations of the second to fifth embodiments and those shown in  FIGS. 17 to 19 , the separation resistance between the left and right half-split housing  50   l ,  50 R (the retaining force for retaining the housings in the mating manner) may be configured such that when, for example, the housing  50  is held in a horizontal direction with only one of the half-split housings being held, the other of the half-split housings may not be separated (may not fall) due to its own weight. In addition, the relative displacement may not only be restricted in the horizontal left-to-right direction, but may also be restricted in the direction of mating surface J, where because of this configuration, rub and/or vibration between the mating surfaces J may be effectively reduced, which can restrict heat from being generated. 
     In the first embodiment, the relative displacement restriction means  71  may be provided in the upper boss-receiving part  62  of the grip housing  53 . However, the relative displacement restriction means  71  of the first embodiment may be provided in another boss-receiving part  62  or in a plurality of boss-receiving parts  62  selected from the nine boss-receiving parts  62  in total such that the separation resistance can be generated. Similarly, this alternate or plural placement of the means may also be applied to the press-fitting structure of the second to fifth embodiments. In the second to fifth embodiments, the press-fitting margin may be provided in the upper edge side rib  56  of the grip housing  53 , or the press-fitting pin  73   a  may be inserted in the vicinity of the rib  56 . However, the exemplified press-fitting structure may be applied to the other rib  56  or a plurality of ribs  56  selected from the seven ribs  56  in total. 
     In the above-discussed embodiments, the press-fitting margin may be provided in the rib  56 . However, instead of the ribs  56 , the press-fitting margin may be provided in the groove hole  58  into which the rib  56  is inserted. 
     In addition to the above discussed relative displacement restriction means, countermeasures against vibration and/or countermeasures for absorbing impacts at the time of falling etc. may be taken in the embodiments of the power tool  1 .  FIG. 20  shows a means for restricting vibration of the housing  50  transferred from the mechanism section  20 . A first impact absorption member  81  may be provided on the internal surface of the left and right half-split housings  50 L,  50 R. In more detail, the first impact absorption member  81  may be provided on the front side of the mechanism section housing  52  of the housing  50 . As shown in  FIG. 20 , the first impact absorption member  81  may be provided in a substantially bilaterally symmetrical manner around the mechanism section housing  21  of the left and right half-split housings  50 L,  50 R. As shown in  FIGS. 5 and 20 , the first impact absorption member  81  may include four absorbing protrusions  81   a  on each side, for the left and right sides. The four absorbing protrusions  81   a  may be arranged at appropriate angular intervals and in a parallel configuration relative to each other in a circumferential direction, each extending in the forward and rearward directions. The four absorbing protrusions  81   a  may be formed integrally with an outer-surface-side elastic resin layer  55  by double molding at the time of molding of the half-split housings. The same elastic resin as used in the outer-surface-side elastic resin layer  55  may also be used in the four absorbing protrusions  81   a.    
     In assembling of the mechanism section  20  with regard to the housing  50 , each of the absorbing protrusions  81   a  at the front side  52  of the mechanism section housing may be pressed against an outer surface of the mechanism case  21 . In this configuration, the mechanism case  21  may thus support the housing  50  via the left and right first impact absorption member  81 . Because of the first impact absorption member  81 , vibration generated in the mechanism section  20 , and in particular vibration caused by swing movement of the swinging arm  23 , may be absorbed, and eventually vibration of the housing  50  may be reduced. Furthermore, because of the first impact absorption member  81 , vibration of the left and right half-split housings  50 L,  50 R may be reduced, and thus rub and/or vibration on the mating surface J may be reduced. As a result, heat generated in this area may be restricted. 
     Furthermore, as shown in  FIG. 21 , a second impact absorption member  82  for absorbing vibration of the electric motor  11  may be provided on the inner surface of the left and right half-split housings  50 L,  50 R. The second impact absorption member  82  may be provided in the main body housing  51  of the housing  50 . The second impact absorption member  82  may comprise a pair of rubber sheets  82   a  provided along the inner surface of left and right half-split housings  50 L,  50 R. In assembling of the electric motor  11  with regard to the housing  50 , the pair of rubber sheets  82   a  having appropriate elasticity may be pressed against the outer circumferential surface of the motor case  11   a . Because of this construction, vibration occurring in the electric motor  11  may be absorbed, and eventually vibration of the housing  50  may be reduced. By reducing vibration of the left and right half-split housings  50 L,  50 R through the absorption by the second impact absorption member  82 , rub and/or vibration on the mating surface J may be reduced, and eventually heat generated in this area may be restricted. 
     As shown in  FIG. 22 , a pair of ventilation seals  83  for closing a gap between an outer surface of the motor case  11   a  and the internal surface of the right and left half-split housings  50 L,  50 R may be provided in the main body housing  51  of the housing  50 . The ventilation seal  83  may be circumferentially provided along the inner periphery of the left and right half-split housings  50 L,  50 R. 
     Because of the pair of ventilation seals  83 , the gap between the outer surface of the motor case  11   a  and the internal surface of the right and left half-split housings  50 L,  50 R may be closed in front of the exhaust window  11   d . As a result, because the gap is closed in front of the exhaust window  11   d , the air that is exhausted from the exhaust window  11   d  cannot flow in the forward direction, which thereby prevents the exhaust air from entering again into the motor case  11   a . In this respect, due to the presence of the ventilation seals  83 , exhaust efficiency of the electric motor  11  can be improved, and further cooling efficiency of the electric motor  11  can be improved. Furthermore, by arranging similar ventilation seals to  83  at the back of the exhaust window  11   d , exhaust and/or cooling efficiency of the electric motor  11  may be further improved. 
     At the time of molding elastic resin layer  55  covered on the outer surface of the housing  50 , the pair of ventilation seals  83   a  may be formed (molded) by pouring molten resin material via resin casting ports  50   c  provided in the left and right half-split housings  50 L,  50 R to the inner face side thereof. In this manner of molding construction, the pair of ventilation seals  83   a  may be simultaneously formed by the same material as the elastic resin layer  55  located outside the ventilation seals  83   a.    
     As shown in  FIG. 23 , a fourth impact absorption member  84  for reducing vibration of the speed controller  31  and reducing impact of dropping the housing  50  may be provided on the inner side of the left and right half-split housings  50 L,  50 R at the rear of the main body housing  51  of the housing  50 . The fourth impact absorption member  84  may be provided with a pair of cushioning elements  84   a  that are in contact with the left and right sides of the speed controller  31 . The speed controller  31  may be cushioned against the inner periphery of the housing  50  and supported by the cushioning elements  84   a  that are in contact with the left and right sides of the speed controller  31 . Because of this construction of cushioning elements, the vibration attributed to and/or of the speed controller  31  may be reduced, and in case the device is dropped, an impact of the dropping of the housing  50  upon the speed controller  31  may also be reduced. As a result, durability and/or reliability of the speed controller  31  can be improved and also malfunction of the speed controller  31  can be prevented. 
     Similar to the molding formation of the ventilation seals  83  as described above, at the time of molding elastic resin layer  55  covered on the outer surface of the housing  50 , the cushioning elements  84   a  of the fourth impact absorption member  84  may be formed (molded) by pouring molten resin material via resin casting ports  50   d  provided in the left and right half-split housings  50 L,  50 R to the inner face side thereof. In this manner, the cushioning elements  84   a  may be simultaneously formed by the same material as the elastic resin layer  55  located outside the cushioning elements  84   a.    
     As shown in  FIG. 24 , a fifth impact absorption member  85  for reducing vibration of the main controller  43  may be provided on the inner surface of the left and right half-split housings  50 L,  50 R of the power supply section housing  54  of the housing  50 . The fifth impact absorption member  85  may be provided with four cushioning elements  85   a  in total that are in the vicinity of and in contact with each corner of the main controller  43 . Each of the cushioning members  85   a  may be formed in a block shape. Similar to the ventilation seals  83  and the fourth impact absorption member  84 , the cushioning elements  85   a  of the fifth impact absorption member  85  may be simultaneously formed by pouring molten resin material via resin casting ports at the time of molding elastic resin layer  55 . The main controller  43  may be cushioned against the inner periphery of the housing  50  and supported by the cushioning elements  85   a  that are in contact with the left and right sides of the main controller  43 . Because of this construction, vibration of the main controller  43  may be reduced, and in case the device is dropped, an impact of dropping the housing  50  on the main controller  43  may also be reduced. As a result, durability and/or reliability of the main controller  43  can be improved and also malfunction of the main controller  43  can be prevented. 
     The present invention is not limited to the embodiments discussed above and may be further modified without departing from the scope and spirit of the present teachings. In the first and second embodiments of the present disclosure, the screw-boss part  61  may be configured to be press-fit into the insertion hole  62   a  of the boss-receiving part  62  in the upper screw-connection part  60  of the grip housing  53 . However, the press-fit construction discussed above is not limited to this configuration and may be applied to another screw-connection part  60  as well. Furthermore, the press-fit construction may be applied to a plurality of screw-connection parts  60 , for example, three screw-connection parts  60 . 
     In the first embodiment of the present disclosure, the press-fitting protrusion  71   a  may be provided in the insertion hole  62   a  of the boss-receiving part  62 , and in the second embodiment, the rubber bush  72   a  may be inserted into the insertion hole  62   a , in order to press-fit the screw-boss part  61  into the insertion hole  62  of the boss-receiving part  62 . However, the screw-boss part  61  may instead be configured to have the press-fitting margin to press-fit into the insertion hole  62   a  of the boss-receiving part  62 . Furthermore, the screw-boss part  61  may be configured to be formed in a tapered shape to press-fit into the insertion hole  62   a  of the boss-receiving part  62 . 
     In the third embodiment, the press-fitting pin  73   a  may be press-fit between the left and right half-split housings  50 L,  50 R in the vicinity of the upper screw-connection part  60  of the grip housing  53 . However, the press-fitting pin  73   a  is not limited to this configuration, and may instead be located in the vicinity of another screw-connection part  60 , and furthermore a plurality of press-fitting pins formed in a similar shape to the pin  73   a  may be press-fit between the left and right half-split housings  50 L,  50 R. 
     In the fourth and fifth embodiments, the upper edge side rib  56  of the grip housing  53  may be press-fit to the groove-hole  58 . However, instead of this figuration, the rib  56  located in another portion of the device may be press-fit to its respective groove hole, and furthermore a plurality of the ribs  56  may be press-fit to the groove-holes, in order to generate separation resistance between the left and right half-split housings  50 L,  50 R. The point is that the relative displacement restriction means  70  may be applied to the mating surface J where large degree of rub and/or vibration might occur, such that an adequate separation resistance can be generated between the left and right half-split housings  50 L.  50 R, whereby rub and/or vibration may be reduced on the mating surface direction of the mating surface J to restrict heat generation. 
     In the embodiments, the multifunction power tool described may represent an exemplary embodiment of the power tool. However, the present teaching is not limited to this embodiment, and may also be applied to vibration drills, screw fastening devices, cutting devices, and any other electric power tools. Furthermore, instead of the battery pack, the present teaching may be applied to the power tool in a case where power may be supplied to the power tool by a mains AC power source such as a 100V commercial power source. 
     In the embodiments, the half-split structure represented by the described left and right half-split housings  50 L,  50 R may represent an exemplary embodiment of the housing  50  of the power tool  1 . However, the relative displacement restriction means  70  may be applied to another case where a front housing is mated to a front portion of a tubular main body housing, a main body housing is mated to a rear portion of the rear housing, or left and right half-split housings of a grip housing are mated with each other, whereby rub and/or vibration on the mating surface may be reduced and heat generation may be prevented.