Abstract:
According to an aspect of the present invention, there is provided a power tool including: a housing; a fan rotatably supported by the housing so as to generate an air flow; a wall portion supported by the housing; and a heat generation portion supported by the wall portion, wherein the wall portion has an exposing hole to expose a part of the heat generation portion so that the exposed part of the heat generation portion is positioned within the air flow.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims a priority from prior Japanese Patent Application No. 2008-196093 filed on Jul. 30, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a power tool. 
         [0004]    2. Description of the Related Art 
         [0005]    In order to form holes in concrete etc. efficiently, vibration drills, which form holes while generating vibration, is used. In such the vibration drill, a motor is rotated in a state where a ratchet and a gear each having a convex-concave step portion are abutted to each other to thereby generate the vibration from the ratchet. The ratchet is covered by an inner cover formed by metal such as aluminum in order to secure the durability with respect to the vibration generated by the ratchet and heat generated by the vibration (see JP-H04-124870-A and JP-H05-318214-A, for example). 
         [0006]    However, in the vibration drills of the related art, since the inner cover is formed by metal such as aluminum, the material cost and the processing cost thereof are high. 
       SUMMARY OF THE INVENTION 
       [0007]    One of objects of the invention is to provide a power tool which is cheap, rigid and heat-resistant. 
         [0008]    According to an aspect of the present invention, there is provided a power tool including: a housing; a fan rotatably supported by the housing so as to generate an air flow; a wall portion supported by the housing; and a heat generation portion supported by the wall portion, wherein the wall portion has an exposing hole to expose a part of the heat generation portion so that the exposed part of the heat generation portion is positioned within the air flow. 
         [0009]    According to another aspect of the present invention, there is provided a power tool including: a housing; a fan rotatably supported by the housing so as to generate an air flow; a wall portion supported by the housing; a heat generation portion supported by the wall portion; and a heat dissipation portion formed to extend from the heat generation portion toward an inside of the air flow. 
         [0010]    According to still another aspect of the present invention, there is provided a power tool including: a housing; a fan rotatably supported by the housing so as to generate an air flow; a vibration generation portion that generates a vibration on a tip end tool; and a cover that is supported by the housing and receives a thrust transmitted from the tip end tool via the vibration generation portion, wherein the cover has an exposing hole to expose a part of the vibration generation portion so that the exposed part of the vibration generation portion is positioned within the air flow. 
         [0011]    The cover may be formed of a resin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic diagram of a vibration drill  1 . 
           [0013]      FIG. 2  is a sectional diagram showing the main portion of the vibration drill  1 . 
           [0014]      FIG. 3A  is a front view of a ratchet  71 ;  FIG. 3B  is a rear view of the ratchet  71 ;  FIG. 3C  is a top view of the ratchet  71 ;  FIG. 3D  is a side view of the ratchet  71 ; and  FIG. 3E  is a sectional view cut along a line IIIe-IIIe in  FIG. 3A . 
           [0015]      FIG. 4A  is a plan view of a change plate  72 ; and  FIG. 4B  is a sectional view cut along a line IVb-IVb in  FIG. 4A . 
           [0016]      FIG. 5A  is a diagram for explaining the position of a change lever  73  in a vibration mode; and  FIG. 5B  is a diagram for explaining the position of a change plate  72  in the vibration mode. 
           [0017]      FIG. 6A  is a diagram for explaining the position of the change lever  73  in a normal mode; and  FIG. 6B  is a diagram for explaining the position of the change plate  72  in the normal mode. 
           [0018]      FIG. 7A  is a front view of an inner cover  8 ;  FIG. 7B  is a rear view of the inner cover  8 ;  FIG. 7C  is a sectional view cut along a line VIIa-VIIa in  FIG. 7A ;  FIG. 7D  is a top view of the inner cover  8 ; and  FIG. 7E  is a side view of the inner cover  8 . 
           [0019]      FIG. 8  is a sectional view cut along a line VIII-VIII in  FIG. 2 . 
           [0020]      FIG. 9  is a sectional view cut along a line IX-IX in  FIG. 2 . 
           [0021]      FIG. 10A  is a front view of a bush  91 ; and  FIG. 10B  is a sectional view cut along a line Xa-Xa in  FIG. 10A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Hereinafter, an embodiment of the invention will be explained with reference to attached drawings. As the power tool according to the embodiment, where a vibration drill  1  is described.  FIG. 1  is a schematic diagram of the vibration drill  1 , and  FIG. 2  is a sectional diagram showing the main portion of the vibration drill  1 . Hereinafter, the left side, right side, upper side and lower side, inner side and nearer side of the drawing sheets in  FIGS. 1 and 2  will be explained as forward direction, backward direction, upper direction, lower direction, left side and right side, respectively. 
         [0023]    The vibration drill  1  includes a motor  2  for generating a rotation force, a gear portion  3  for reducing the speed of the rotation output from the motor  2 , a spindle  4  for transmitting the rotation force from the gear portion  3  to a not-shown tip end tool, a ball  5  disposed between the gear portion  3  and the spindle  4 , a chuck  6  for coupling the spindle  4  with the tip end tool, a vibration generation mechanism  7  for generating the vibration at the vibration drill  1 , an inner cover  8  for holding the vibration generation mechanism  7 , and a cooling mechanism  9 . 
         [0024]    The gear portion  3  includes a gear  31 , a bearing  32  for pivotally supporting the spindle  4  so as to be movable in a thrust direction, a spring  33  for urging the spindle  4  in the thrust direction, and a convex-concave gear step portion  34  for abutting against a ratchet step portion  71 A described later. The chuck  6  is fixed by left-hand screws in order to prevent the spindle  4  from loosing at the time of the reverse rotation. The vibration generation mechanism  7  includes a ratchet  7  for generating the vibration at the motor  2 , a change plate  72  disposed at a position corresponding to the mode of the vibration drill  1 , and a change lever  73  for allowing a user to move the position of the change plate  72 . 
         [0025]    The ratchet  71  will be explained by using  FIGS. 3A to 3E .  FIG. 3A  is a front view of the ratchet  71 ,  FIG. 3B  is a rear view of the ratchet  71 ,  FIG. 3C  is a top view of the ratchet  71 ,  FIG. 3D  is a side view of the ratchet  71 , and  FIG. 3E  is a sectional view cut along a line IIIe-IIIe in  FIG. 3A . The convex-concave ratchet step portion  71 A for abutting against the gear step portion  34  of the gear portion  3  is provided at the front surface of the ratchet  71 , and a plurality of bush attachment surfaces  71 B for attaching a bush  91  described later is provided at the rear surface of the ratchet  71 . As shown in  FIG. 3C , a space allowing the change plate  72  to slide in the left and right directions is formed between the left and right bush attachment surfaces  71 B. Further, the ratchet  71  is provided with an outer periphery  71 C to be fit in a fastened manner with the inner cover  8 , screw sheets  71 D for respectively receiving self tapping screws A for fixing with the inner cover  8 , and screw holes  71 E in which screws B are respectively inserted for fixing with the bushes  91 . The ratchet  71  is functioning as a heat generation portion and a vibration generation portion. 
         [0026]    Next, the explanation will be made as to the change plate  72  and the change lever  73  by using  FIG. 4A  to  FIG. 6B .  FIG. 5A  is a diagram for explaining the position of the change lever  73  in a vibration mode, and  FIG. 5B  is a diagram for explaining the position of the change plate  72  in the vibration mode.  FIG. 6A  is a diagram for explaining the position of the change lever  73  in a normal mode, and  FIG. 6B  is a diagram for explaining the position of the change plate  72  in the normal mode. 
         [0027]    As shown in  FIGS. 4A and 4B , the change plate  72  is provided with a plane portion  72 A, a hole portion  72 B and a coupling portion  72 C. The change lever  73  is coupled to the coupling portion  72 C, and the change plate  72  slides in accordance with the movement of the change lever  73 . When the tip end tool is pushed against a processing object member in a state that the change lever  73  locates at the position of the vibration mode shown in  FIG. 5A , the ball  5  fits in the hole portion  72 B of the change plate  72  as shown in  FIG. 5B , whereby the gear step portion  34  abuts against the ratchet step portion  71 A. When the motor  2  rotates in this state, the gear step portion  34  also rotates. Thus, a striking action arises between the gear step portion  34  and the ratchet step portion  71 A in accordance with the rotation of the gear step portion  34  to thereby generate vibration. Due to this vibration, the vibration drill  1  can efficiently form holes concrete, mortar, stone etc. 
         [0028]    In contrast, when the tip end tool is pushed against the processing object member in a state that the change lever  73  locates at the position of the normal mode shown in  FIG. 6A , the ball  5  abuts against the plane portion  72 A of the change plate  72  as shown in  FIG. 6B , whereby the gear step portion  34  does not contact with the ratchet step portion  71 A. In this case, since the vibration is not generated even if the motor  2  rotates, the vibration drill  1  can efficiently form holes in steel, wood etc. like a normal drill. 
         [0029]    Next, the explanation will be made as to the inner cover  8  by using  FIG. 7A  to  FIG. 9 .  FIG. 7A  is a front view of the inner cover  8 ,  FIG. 7B  is a rear view of the inner cover  8 ,  FIG. 7C  is a sectional view cut along a line VIIa-VIIa in  FIG. 7A ,  FIG. 7D  is a top view of the inner cover  8 , and  FIG. 7E  is a side view of the inner cover  8 .  FIG. 8  is a sectional view cut along a line VIII-VIII in  FIG. 2 , and  FIG. 9  is a sectional view cut along a line IX-IX in  FIG. 2 . 
         [0030]    The inner cover  8  is formed by resin. The inner cover  8  is provided with a seat surface  81  for supporting the ratchet  71  in the thrust direction, an inner periphery  82  to be fit in a fastened manner with the outer periphery  71 C of the ratchet  71 , an exposing hole portion  83  for exposing the rear end of the ratchet  71 , screw holes  84  in which the self tapping screws A received by the screw sheets  71 D of the ratchet  71  are respectively inserted, and a slide hole  85  for enabling the sliding operation of the change lever  73 . The seat surface  81  is formed to have an area and a thickness sufficient for securing a sufficient rigidity for supporting a thrust and a torque transmitted to the ratchet  71  from the tip end tool. In this embodiment, the seat surface  81  has the thickness of 5 mm and the area of the seat surface  81  is set so as to be in proportional to the area of the exposing hole portion  83 . The inner cover  8  corresponds to a wall portion and a cover of the invention. 
         [0031]    As shown in  FIGS. 8 and 9 , when the ratchet  71  is attached to the inner cover  8  thus configured, the rear end portion of the ratchet  71  is exposed from the exposing hole portion  83  of the inner cover  8 . In this manner, according to the vibration drill  1  of the embodiment, since the rear end portion of the ratchet  71  for generating the vibration is exposed from the exposing hole portion  83  of the inner cover  8 , the heat generated due to the vibration can be dissipated. The inner cover of the vibration drill of the related art is formed by metal having a thickness of about 2.5 mm in order to support a thrust and a torque transmitted to the ratchet from the tip end tool. In contrast, although the inner cover  8  of the vibration drill  1  according to the embodiment is formed by resin, since it is formed to have the thickness of 5 mm, the thrust transmitted to the ratchet  71  from the tip end tool can be securely supported. The inventors of the invention experimentally found that the inner cover  8  of the embodiment has improved rigidity as compared with the aluminum inner cover having the thickness of about 2.5 mm of the related art. Further, since the ratchet  71  and the inner cover  8  are fixed to each other by means of the self tapping screws A, these members are combined more firmly. 
         [0032]    Next, the explanation will be made as to the cooling mechanism  9  by using  FIGS. 1 ,  2 ,  10 A and  10 B. The cooling mechanism  9  includes a bush  91 , a fan  92 , a fan guide  93 , a housing  94 , an exhaust port  95  and a suction port  96 . The inner cover  8  and the fan  92  are supported by the housing  94 . 
         [0033]      FIG. 10A  is a front view of the bush  91  and  FIG. 10B  is a sectional view cut along a line Xa-Xa in FIG.  10 A. The bush  91  has rigidity with respect to the thrust and torque transmitted from the tip end tool and is formed by material with high thermal conductivity, for example, a sintered part such as a metal pressed part of steel. As shown in  FIGS. 10A and 10B , the bush is provided with an attachment portion  91 A attached to the bush attachment surfaces  71 B of the ratchet  71  by means of the screws B, screw holes  91 B for receiving the screws for fixing to the ratchet  71 , a slide portion  91 C for enabling the sliding operation of the change plate  72 , and an extended portion  91 D acting as a cooling fin. 
         [0034]    An air flow is generated by the rotation of the fan  92 , and flows toward the exhaust port  95  form the suction port  96  through an air passage formed by the fan guide  92  and the housing  94 . In the vibration drill  1  according the embodiment, the rear end portion of the ratchet  71  exposed from the exposing hole portion  83  of the inner cover  8  is exposed in the air flow. Thus, the heat generated at the ratchet  71  in accordance with the vibration can be dissipated efficiently. 
         [0035]    Further, since the bush  91  is attached to the rear end portion of the ratchet  71 , the bush  91  is also exposed in the air flow. Since the bush  91  is formed by the metal press processing with high thermal conductivity, the heat generated at the ratchet  71  in accordance with the vibration can be dissipated more efficiently. Further, although the thrust and torque transmitted from the tip end tool to the ratchet  71  is finally applied to the bush, since the bush  91  is formed by the metal press processing, the bush has also durability with respect to the thrust and torque transmitted from the tip end tool. 
         [0036]    Further, in this embodiment, the bush  91  is provided with the extended portion  91 D in a manner of being bent from the attachment portion  91 A and the extended portion  91 D is exposed in the air flow. Since the extended portion  91 D is also formed by the metal pressing process and has high thermal conductivity, the extended portion also acts as a cooling fin, so that the heat generated at the ratchet  71  in accordance with the vibration can be dissipated further efficiently. The size of the extended portion  91 D is adjusted in accordance with a desired heat dissipation amount. Further, since the extended portion is bent from the attachment portion  91 A, the entire rigidity of the bush is further improved and further the durability with respect to the thrust and torque transmitted from the tip end tool is also improved. The bush  91  and the extended portion  91 D correspond to a heat dissipation member of the invention. 
         [0037]    In this manner, according to the vibration drill  1  of the embodiment, since the fixing operation is performed by the seat surface  81  that is formed to have the area and thickness for securing the sufficient rigidity and the self tapping screws A, the cheap resin inner cover  8  can be employed without causing a problem relating to the rigidity even in the vibration mode. Further, according to the vibration drill  1  of the embodiment, since the rear end portion of the ratchet  71  exposed from the exposing hole portion  83  of the inner cover  8 , the bush  91  fixed by the ratchet  71  and the screws B, and the extended portion  91 D are exposed in the air flow, the heat generated at the ratchet  71  in accordance with the vibration can be dissipated efficiently. Thus, although resin is disadvantageous in the heat durability, it becomes possible to form the inner cover  8  by using resin. 
         [0038]    The power tool according to the invention is not limited to the aforesaid embodiment and various modification may be made within a scope not departing from the gist of the invention. For example, the invention is applicable to the other kinds of power tools having a heat generation portion or a vibration generation portion as well as the vibration tool. A member which generates heat due to a rubbing or a striking is considered as the heat generation portion or the vibration generation. 
         [0039]    According to the invention, a power tool which is cheap, rigid and heat-resistant can be provided.