Abstract:
An electric power tool includes a tool body having a rotor, an inner cylindrical body and outer cylindrical body. The rotor is provided with a ventilation space therearound, a body part and a brush contact part, and housed in the inner cylindrical body. The inner cylindrical body is inserted in the outer cylindrical body which has a plurality of groove-like ventilation spaces on its inner face. The rotation of a fan fitted on the rotor circulates air within the tool body through the ventilation spaces so as to cool down the body part and the brush contact part of the rotor. The electric power tool has the rotor with which not only the body part but also other heated parts are fully cooled down. The electric power tool enhances heat dissipation efficiency from a motor case, enables efficient cooling of heated parts and has a long durability.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an electric power tool used for cutting and drilling in electric works, building works or the like. 
         [0003]    2. Description of the Related Art 
         [0004]    Heated parts in an electric power tool of this kind, such as a support bearing, a rotor body, and a brush contact part of a rotor, has been conventionally cooled in such a manner that outside air is introduced from a rear part of the tool by a fan provided within the tool body, applied to the heated part to absorb the heat thereof, and discharged from a front part of the tool. However, depending on the workpieces to be cut or drilled, while they are being cut or drilled, some kinds of cutting powders become powder dust and float therearound. As a result, the powder dust is contained in the outside air introduced into the tool body and adheres to the rotor and other parts to cause the breakdown of the electric power tool. 
         [0005]    Thus, a self-cooling motor applicable to this kind of electric power tool, in which an airflow is generated in a motor case by the rotation of a rotor which rotates within a stator and the motor case is cooled using this air flow, has been developed. One example of such a self-cooling motor is disclosed in Japanese Patent No. 3606841 (Pages 1 and 4, and FIG. 5). As shown in  FIG. 15 , for example, such a self-cooling motor  20  has a stator  21  and a rotor  22  rotating within this stator  21 . The rotor  22  has a cylindrical sleeve  23  attached to this rotor  22 , and this cylindrical sleeve  23  is provided with a spiral groove  23   a  on its outer surface to be hermetically fitted to the motor case  24 . A gap S is formed between a casing of this self-cooling motor  20  and the motor case  24 . The air flow generated between the stator  21  and the rotor  22  circulates as shown by arrows through the gap S so as to entrain the heat generated at the stator  21  to the outer side (the side of the gap S) of the stator  21  along with the rotation of the rotor  22 , and discharge it outside of the motor case  24 . In the drawing, reference numerals  25  and  26  denote hermetic seal parts, and reference numerals  27  and  28  denote bearings for rotatably supporting the rotor  22 . 
         [0006]    It is disclosed that this structure prevents the self-cooling motor  20  from entrapment of powder dust from the outside, and that this self-cooling motor  20  is suitable for operation for a long time in a place where a lot of powder dust floats. 
         [0007]    However, the foregoing self-cooling motor still has a problem. Although the body of the rotor  22  can be sufficiently cooled by the spiral groove  23   a  provided on the outer surface of the cylindrical sleeve  23  attached to the rotor  22 , heated parts other than the body of the rotor  22 , such as bearings  27  and  28  for supporting the rotor  22 , the brush contacting part (not shown) cannot be sufficiently cooled. 
         [0008]    Further, although the foregoing conventional self-cooling motor is designed to guide the heat generated at the stator  21  to the outer side (the side of the gap S) of the stator  21  along with the rotation of the rotor  22  and discharge the heat outside of the motor case  24 , heat dissipation efficiency is rather low and thereby the rotor  22  cannot be efficiently cooled off. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to dissolve the foregoing problems and provide an electric power tool which does not take powder dust in from outside. The electric power tool is provided with a rotor sufficiently cooling not only the body part but also other heated parts of the rotor, in which heat dissipation from the motor case is improved and efficient cooling of the heated parts is achieved, and thereby the tool has a long durability. 
         [0010]    For this purpose, the electric power tool according to the present invention includes a tool body having a rotor with a ventilation space therearound, a body part and a brush contact part, an inner cylindrical body housing the rotor therein, and an outer cylindrical body in which the inner cylindrical body is inserted and which has a plurality of groove-like ventilation spaces on its inner face. The rotation of a fan fitted on the rotor circulates air within the tool body through the ventilation spaces so as to cool down the body part and the brush contact part of the rotor. 
         [0011]    The outer cylindrical body may have a plurality of heat dissipation fins on its outer circumferential face. 
         [0012]    The electric power tool according to the present invention includes a tool body having a rotor having a ventilation apace therearound, a body part, a brush contact part, a front bearing part and a rear bearing part, an inner cylindrical body housing the rotor therein, an outer cylindrical body in which the inner cylindrical body is inserted and which has a plurality of groove-like ventilation spaces on its inner face, a front cap attached to and covering the front end of the outer cylindrical body to provide a ventilation space between the front cap and the front end, and a rear cap attached to and covering the rear end of the outer cylindrical body to provide a ventilation space between the rear cap and the rear end. The rotation of a fan fitted to the rotor circulates the air within the tool body so as to cool the body part, the brush contact part, the front bearing part and the rear bearing parts. 
         [0013]    The outer cylindrical body may have a plurality of heat dissipation fins on its outer circumferential face. 
         [0014]    The electric power tool also has a support part for the front bearing part and a plurality of heat dissipation fin on the front cap, in which the circulating air through the ventilation spaces bumps against the heat dissipation fins, and a support part for the rear bearing part and a plurality of heat dissipation fins on the rear cap, in which the circulating air through the ventilation spaces bumps against the heat dissipation fins. 
         [0015]    The electric power tool according to the present invention sucks outside air into the tool body as part of the circulating air, and discharges part of the circulating air outside of the tool body. 
         [0016]    Being constructed as stated above, the electric power tool according to the present invention includes a rotor which enables to sufficiently cool not only the body part but also other heated parts of the rotor, and the electric power tool improves heat dissipation efficiency from the motor case, efficiently cools the heated parts, and has a long durability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a side view showing an embodiment of an electric power tool according to the present invention. 
           [0018]      FIG. 2  is a rear view showing the electric power tool according to the present invention shown in  FIG. 1 . 
           [0019]      FIG. 3  is a sectional view showing the electric power tool according to the present invention shown in  FIG. 1 . 
           [0020]      FIG. 4  is a side view showing another embodiment of an electric power tool according to the present invention. 
           [0021]      FIG. 5  is a rear view showing the electric power tool according to the present invention shown in  FIG. 4 . 
           [0022]      FIG. 6  is a sectional view showing the electric power tool according to the present invention shown in  FIG. 4 . 
           [0023]      FIG. 7  is a sectional view taken along line A-A in  FIG. 1  and line a-a in  FIG. 4 . 
           [0024]      FIG. 8  is a sectional view taken along line B-B in  FIG. 1  and line b-b in  FIG. 4 . 
           [0025]      FIG. 9  is a sectional view taken along line C-C in  FIG. 1  and line c-c in  FIG. 4 . 
           [0026]      FIG. 10  is a perspective view of a rotor of the electric power tool according to the present invention. 
           [0027]      FIG. 11  is a perspective view of a semi cylindrical body forming an inner cylindrical body of the electric power tool according to the present invention. 
           [0028]      FIG. 12  is a perspective view of an outer cylindrical body of the electric power tool according to the present invention. 
           [0029]      FIG. 13  is a perspective view of a front cap of the electric power tool according to the present invention. 
           [0030]      FIG. 14  is a perspective view of a rear cap of the electric power tool according to the present invention. 
           [0031]      FIG. 15  is a perspective view of a conventional self-cooling motor applicable to an electric power tool. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Preferable embodiments of an electric power tool according to the present invention will be described below in detail with reference to the drawings. 
         [0033]    Embodiments are shown in  FIGS. 1 to 3  or  FIGS. 4 to 6 . An electric power tool according to the present invention includes a tool body H having a rotor  1 , an inner cylindrical body  2  and an outer cylindrical body  3 . The inner cylindrical body  2  houses the rotor  1  with a ventilation space S 1  therearound, and is inserted into the outer cylindrical body  3  which has a plurality of groove-shaped ventilation spaces S 2  on its upper and lower parts of the inner face and a plurality of heat dissipation fins F 1  on its outer circumferential face. The outer cylindrical body  3  has, on its front end, a ventilation space S 3  covered with a front cap  4 , and, on its rear end, a ventilation space S 4  covered with a rear cap  5 . In the electric power tool according to the present invention, the rotation of a fan  6  which is attached to the rotor  1  circulates the air in the tool body H through the ventilation spaces S 1 , S 2 , S 3 , and S 4  so as to cool a body part  1   a , a brush contact part  1   b , a front bearing part  1   c  and a rear bearing part  1   d  of the rotor  1 . The air in the tool body H may be circulated by the rotation of the fan  6  through the ventilation spaces S 1  and S 2  so as to cool the body part  1   a  and the brush contact part  1   b  only. If the outer cylindrical body  3  has a plurality of groove-like ventilation spaces S 2  on its upper and lower parts of the inner face, the electric power tool according to the present invention can be carried out without a plurality of heat dissipation fins F 1  on its outer circumferential face. 
         [0034]    As clearly shown in  FIG. 10 , the rotor  1  has a rotor shaft R, the body part  1   a  provided on the shaft R, the fan  6  fitted to the part of the rotor shaft R in front of the body part  1   a , the brush contact part  1   b  fitted to the part of the rotor shaft R in back of the body part  1   a , the front bearing part  1   c  attached to the front part of the rotor shaft R, and the rear bearing part  1   d  attached to the rear end of the rotor shaft R, and a tool  7  for cutting and drilling is to be mounted on the front end of the rotor shaft R. As clearly shown in  FIGS. 3 and 6 , the rotor  1  is assembled into the electric power tool in the manner that the body part  1   a  is disposed on a bobbin  8 , the brush contact part  1   b  is disposed on a brush table  9 , the front bearing part  1   c  is disposed on the front cap  4 , and the rear bearing part  1   d  is disposed on the rear cap  5 . 
         [0035]    The inner cylindrical body  2  may be made of materials with high heat conductance such as an aluminum alloy. However, in order to decrease the heat conductance to the outer cylindrical body  3 , it is rather preferable that the inner cylindrical body  2  is made of materials with low heat conductance such as a synthetic resin. The inner cylindrical body  2  according to the present invention is formed in a cylindrical shape by combining two semi cylindrical bodies as shown in  FIG. 11 , which holds the bobbin  8  and the brush table  9 , and communicates with the ventilation spaces S 3  and S 4  at its front and rear ends respectively. 
         [0036]    The outer cylindrical body  3  may be made of, for example, metal materials or complex materials including a metal and a synthetic resin. However, it is preferable that the outer cylindrical body  3  is made of materials with high heat conductance such as an aluminum alloy. In the cylindrical body  3  of the present invention, the outer circumferential part has an elliptical cylindrical shape, while the inner circumferential part has a cylindrical shape. And, as described above, a plurality of groove-like ventilation spaces S 2  are formed on its upper and lower parts of the inner face and a plurality of heat dissipation fins F 1  are formed on the other circumferential face. Alternatively, both of the inner and outer circumferential parts may be formed in an elliptical cylindrical shape, or both in a cylindrical shape. The electric power tool with the outer circumferential part in an elliptical cylindrical shape may be easily held and enhances workability while performing cutting and drilling operations. The groove-like ventilation spaces S 2 , which are formed on the upper and lower parts of the inner faces, may be formed on the right and left parts of the inner face or on the upper, lower, right, and left parts of the entire inner face. 
         [0037]    The front cap  4  is made of material with high heat conductance such as an aluminum alloy. The front cap  4  includes a support part  4   a  for the front bearing part  1   c  at its front part and a plurality of heat dissipation fins F 2  therein. The fins receive the air circulating within the tool body H through the ventilation space S 3 . Further, if necessary, the front end of this front cap  4  is provided with a guide frame body  10  for cutting and drilling of the tool  7  attached to the front end of the rotor shaft R. 
         [0038]    The rear cap  5  is made of material with high heat conductance such as an aluminum alloy. The rear cap  5  has a support part  5   a  for the rear bearing part  1   d  at its front part and a plurality of heat dissipation fins F 3  on the outer circumference of this support part  5   a . The heat dissipation fins  3  receive the air circulating within the tool body H through the ventilation space S 4 . Further, a seal cap  11   a  is attached behind the rear cap  5 , so as to prevent outside air from being sucked into the tool body H. 
         [0039]    In the embodiment shown in  FIGS. 4 to 6 , the electric power tool of the present invention sucks outside air into the tool body H and makes it part of the circulating air and discharges part of the circulating air outside of the tool body H. In other words, in place of the seal cap  11   a  of the foregoing embodiment, the electric power tool includes an incomplete seal cap  11   b  having a plurality of small ventilating holes and a filter  13 . This incomplete seal cap  11   b  enables to suck outside air to be part of the circulating air (about 5 to 10% of the circulating air) through the ventilating holes  13  and the filter  13 . When the incomplete seal cap  11   b  is attached, an air intake  5   b  is provided at the rear cap  5  so as to take outside air into the tool body H through this air intake  5   b , and an air outlet  4   b  is provided at the front cap  4  so as to exhaust part of the circulating air through this air outlet  4   b.    
         [0040]    Further, as shown in the drawings, the electric power tool according to the present invention includes a front engaging part  14   a  for a handle at the front end of the upper part of the outer cylindrical body  3  and a rear engaging part  14   b  for the handle is provided at the rear end of the upper part of the rear cap  5 . A handle  15  is connected to these engaging parts so as to provide the handle  15  on the tool body H. Furthermore, a boundary between the rear cap  5  and the seal cap  11   a  or the incomplete seal cap  11   b  is provided with a penetration hole  16  through which a power code C is brought into the tool body H. 
         [0041]    Being constructed as stated above, the electric power tool according to the present invention can cool the body part  1   a , the brush contact part  1   b , the front bearing part  1   c  and the rear bearing part  1   d  of the rotor  1  as follows. 
         [0042]    First, in the electric power tool according to the present invention, when the rotor  1  is driven to rotate for performing cutting and drilling operations, the fan  6  attached to this rotor  1  rotates. Then, in the electric power tool according to the embodiment shown in  FIGS. 1 to 3 , along with the rotation of the fan  6 , air within the tool body H flows forward and bumps against the fins F 2  provided at the front cap  4  and turns around to the ventilation space S 3  and then to the ventilation spaces S 2  provided in the outer cylindrical body  3 . Subsequently the air further moves through the ventilation space S 4 , bumps against the fin  3  provided on the rear cap  5 , turns around to the ventilation space S 1  provided around the rotor  1 , reaches the fan  6 , and here the air has come full circle. On the other hand, in the electric power tool according to the embodiment shown in  FIGS. 4 to 6 , along with the rotation of the fan  6 , air within the tool body H flows forward and bumps against the fins F 2  provided at the front cap  4 . Part of the air discharges from the air outlet  4   b  provided at the front cap  4 , and the remaining air turns around to the ventilation space S 3  and then the ventilation spaces S 2  provided the outer cylindrical body  3 . Then, the air further moves through the ventilation space S 4 , bumps against the fin  3  provided at the rear cap  5  to turn around. Due to a negative pressure generated by the air turning around, outside air is taken in through an air intake  12  of the incomplete seal cap  11   b  and further sucked into the tool body H through the air intake  5   b  provided at the rear cap  5 . The air newly taken in moves forward together with the air having turned around to the ventilation space S 1  around the rotor  1  and then reaches the fan  6 , where the air has come full circle. 
         [0043]    In both embodiments, during the air circulation through the ventilating spaces within the electric power tool, circulating air comes into contact with the body part  1   a , the brush contact part  1   b , the front bearing part  1   c  and the rear bearing part  1   d  of the rotor  1 . Heat generated at the body part  1   a  and the brush contact part  1   b  of the rotor  1  may be dissipated into the circulating air, and thereby the body part  1   a  and the brush contact part  1   b  are cooled. Heat generated at the front bearing part  1   c  is conducted to the front cap  4  by which the front bearing part  1   c  is supported, and efficiently released to the circulating air which bumps against the fins F 2  provided at this front cap  4 , and thereby the front bearing part  1   c  can be sufficiently cooled. On the other hand, the heat generated at the rear bearing part  1   d  is conducted to the rear cap  5  by which the rear bearing part  1   d  is supported, and efficiently released to the circulating air which bumps against the fins F 3  provided at this rear cap  5 , and thereby the rear bearing part  1   d  can be sufficiently cooled. 
         [0044]    Then, the heat in the circulating air the temperature of which is increased while cooling the body part  1   a , the brush contact part  1   b , the front bearing part  1   c  and the rear bearing part  1   d  of the rotor  1  is efficiently conducted to the outer cylindrical body  3  while the circulating air passes through a plurality of groove-like ventilation spaces S 2  formed on the outer cylindrical body  3 , and efficiently dissipated by a plurality of heat dissipation fins F 1  formed on the outer circumferential face of this outer cylindrical body  3 . Thus, the circulating air can be sufficiently cooled. Further, even if there is no heat dissipation fin F 1  on the outer circumferential face of the outer cylindrical body  3 , the heat in the circulating air is dissipated from the outer circumferential face of this outer cylindrical body  3  and thereby the circulating air is cooled off. 
         [0045]    Further, according to the embodiment shown in  FIGS. 4 to 6 , in the electric power tool of the present invention, part of the circulating air is discharged through the air outlet  4   b  at the front cap  4 , and outside air is taken in through the air intake  5   b  at the rear cap  5 . Therefore, rise of the temperature of the circulating air can be suppressed compared to the embodiment shown in  FIGS. 1 to 3 , and the respective heated parts can be more sufficiently cooled.