Patent Publication Number: US-8123596-B2

Title: Power tools

Description:
This application claims priority to Japanese patent application serial number 2007-151437, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to power tools, such as disk grinders, and in particular, to power tools having an air introduction device for cooling a motor. 
     2. Description of the Related Art 
     A disk grinder is known that has a cylindrical body casing and an electric motor disposed within the body casing as a drive source. The body casing is adapted to be grasped by an operator. An output shaft of the electric motor is supported by a front casing that is disposed on the front side of the body casing. The rotation of the output shaft is transmitted to a spindle. A circular rotary grinding disk is attached to the front portion of the spindle. A rear casing is disposed on the rear side of the body casing. An inlet opening for introducing air is formed in the rear casing. A cooling fan is attached to the output shaft of the motor, so that a flow of the air from the rear side to the front side of the body casing is produced as the fan rotates. Therefore, the air can cool components of the motor. More specifically, the external air enters the rear casing via the inlet opening, flows into the body casing, and is then discharged from an outlet opening formed in the front portion of the body casing. 
     Techniques for channelling air into the body casing are disclosed in Japanese Laid-Open Patent Publications Nos. 9-272073 and 2002-18745. In these publications, the inlet opening is formed in a side portion of the rear casing. 
     It has been also known to attach a net-like filter to the inlet opening for preventing dust in the air from entering into the body casing through the inlet opening. However, the filter may increase resistance against flow of the air through the inlet opening and thus causes reduction in the flow rate of the cooling air. A proposed solution is to provide a plurality of guide plates  52  with respective shielding plates  53  as shown in  FIG. 4 . In the arrangement shown in  FIG. 4 , a plurality of inlet openings  51  are formed in opposite sides of a rear casing  50 . The guide plates  52  extend horizontally and inwardly from an inner wall of the rear casing  50  at positions adjacent to the inlet openings  51 . The shielding plates  53  are formed by upwardly bending the innermost ends of the guide plates  52 . With this configuration, the dust in the external air entering the inlet openings  51  may collide with the shielding plates  53 , so that the dust can be separated from the flow of the air. Hence, it is possible to introduce the external air into the rear casing  50  without substantial increase in the flow resistance, and therefore, a sufficient flow rate of the air containing a small amount of dust can be ensured. 
     However, according to the arrangement shown in  FIG. 4 , because all the shielding plates  53  extend upward toward the upper region of the rear casing  50 , the flow of the air entering the rear casing  50  from its left side and the flow of the air entering the rear casing  50  from its right side may collide with each other within the upper region of the rear casing  50 . In addition, some of the dust may not be shielded by the shielding plates  53  but may enter the upper region of the rear casing  50  with the flow of the air entering from both right and left sides of the rear casing  50  as shown in  FIG. 4 . Therefore, the dust carried by the flow of the air entering from the right side of the rear casing  50  and the dust carried by the flow of the air entering from the left side of the rear casing  50  may collide with each other, so that the dust may aggregate within the upper region of the rear casing  50  as indicated by a region D. 
     In general, functional elements of the motor, such as a commutator and carbon brushes are disposed within or near the upper region of the rear casing  50 . Therefore, if the amount of the aggregate dust within the upper region of the rear casing  50  increases, it is possible that the motor may malfunction because of the build-up of particulate. 
     Therefore, there has been a need for a power tool including an air introduction device that can introduce an external air into a casing without causing potential aggregation of dust within the casing. 
     SUMMARY OF THE INVENTION 
     One aspect according to the present invention includes a power tool having an air introduction device that can introduce an external air into the casing and produce a spiral flow of the air within the casing. This can prevent or minimize the deposition of dust, which may be carried by the air entering the casing, to components of a motor disposed within the casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a left side view of a power tool according to an embodiment of the present invention; 
         FIG. 2  is a cross sectional view taken along line ( 2 )-( 2 ) in  FIG. 1  and showing a vertical sectional view of a rear casino; 
         FIG. 3  is a cross sectional view similar to  FIG. 2  but showing a vertical sectional view of a rear casing of a power tool according to another embodiment of the present invention; and 
         FIG. 4  is a vertical sectional view of a rear casing of a known power tool. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved power tools. Representative examples of the present invention, which examples utilize many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings. 
     In one embodiment, a power tool includes a casing, a motor disposed within the casing, and a first air introduction opening and a second air introduction opening formed in the casing on a first side and a second side opposite to the first side, respectively. The power tool further includes a first air introduction member and a second air introduction member extending inwardly from an inner wall of the casing at positions proximal to the first air introduction opening and the second air introduction opening, respectively. The first air introduction member is configured such that an external air flowing into inside of the casing via the first air introduction opening is directed in a first direction within the casing. The second air introduction member is configured such that an external air flowing into inside of the casing via the second air introduction opening is directed in a second direction within the casing. The first direction and the second direction are the same with respect to a circumferential direction of the casing. 
     With this arrangement, the air flowing into inside of the casing via the first air introduction opening may not collide with the air flowing into inside of the casing via the second air introduction opening but may merge therewith, so that the air flows in a spiral form within the casing. Therefore, any dust that may be contained in the air entering the casing can be prevented from aggregation within the casing and may not be deposited on components of the motor. With this configuration, it is possible to reduce or prevent malfunctions of the motor. 
     Further, any dust that may be contained in the air entering the casing can be smoothly discharged from the casing as it is carried by the spiral flow of the air. Therefore, it is possible to reduce the dust that may not be discharged from the casing but is remained within the casing. 
     The first side and the second side may be a left side and a right side of the casing, respectively, and the first direction and the second direction may be an upward direction and a downward direction, respectively. The first air introduction member may extend from an inner wall of the casing at a position proximal to the lower side of the first air introduction opening; and the second air introduction member may extend from the inner wall of the casing at a position proximal to the upper side of the second air introduction opening. 
     The first direction and the second direction may be determined such that the air entering the casing via the first and second air introduction openings flows in a spiral form within the casing in the same direction as a rotational direction of the motor. With this arrangement, the air can further smoothly flow through the casing. 
     The first air introduction member may include a first air introduction plate extending from the inner wall of the casing and inclined upward toward the inside of the casing. The second air introduction member may include a second air introduction plate extending from the inner wall of the casing and inclined downward toward the inside of the casing. 
     Alternatively, the first air introduction member may include a first air introduction plate extending substantially horizontally from the inner wall of the casing and a first shielding plate extending upward from an innermost end of the first air introduction plate. The second air introduction member may include a second air introduction plate extending substantially horizontally from the inner wall of the casing and a second shielding plate extending downward from an innermost end of the second air introduction plate. 
     In another embodiment, a power tool includes a casing, a motor disposed within the casing, and an air introduction device that can introduce an external air into the casing and can produce a spiral flow of the air within the casing. 
     The air introduction device may include a first air introduction device and a second air introduction device. The first air introduction device is disposed on a first side of the casing and is constructed to produce a flow of the air within the casing in a first direction with respect to a circumferential direction of the casing. The second air introduction device is disposed on a second side of the casing opposite to the first side and is constructed to produce a flow of the air within the casing in a second direction with respect to the circumferential direction of the casing. The first direction and the second direction are the same with each other, so that the flow of the air from the first air introduction device and the flow of the air from the second air introduction device are merged to produce the spiral flow. 
     The casing may include a first case and a second case coupled to each other and each defining a flow path therein. The motor is disposed within the first case, and the air introduction device is disposed at the second case 
     The air introduction device may further include a fan rotatably driven by the motor, so that the external air is drawn into the casing as the fan rotates. 
     An embodiment of the present invention will now be described with reference to  FIGS. 1 to 3 . Referring to  FIG. 1 , a disk grinder  1  is shown as an example of a power tool. The disk grinder  1  has a tool casing including a body casing  2 , a front casing  4  and a rear casing  10 . An electric motor  3  (as a drive source) is disposed within the body casing  2 . The front casing  4  is attached to the front portion of the body casing  2 . The rear casing  10  is attached to the rear portion of the body casing  2 . 
     A spindle (not shown) is supported within the front casing  4  and is rotatable about an axis perpendicular to the rotational axis of the motor  3 . A disk-like grinding wheel  5  is mounted to the front end of the spindle. 
     The body casing  2  has a substantially cylindrical tubular configuration. A main switch  7  is mounted to the upper portion of the body casing  2  and is operable to start and stop the motor  3 . A plurality of first air introduction openings  11  are formed in the left sidewall of the rear casing  10 . Similarly, a plurality of second air introduction openings  12  are formed in the right side wall of the rear casing  10 . 
     A cooling fan  6  is attached to an output shaft  3   a  of the motor  3 , so that the fan  6  rotates as the motor  3  is driven. The rotating fan  6  may produce a flow of air from the rear side to the front side (from the right side to the left side as viewed in  FIG. 1 ) within the body casing  2  and the rear casing  10 , so that that the motor  3  can be cooled by the flow of air. The air may enter the rear casing  10  from the outside via the first and second air introduction openings  11  and  12  formed in the rear casing  10 . 
       FIG. 1  shows the left side of the rear casing  10 . As shown in  FIG. 1 , in this embodiment, eight first air introduction openings  11  are formed in the rear casing  10  and each are configured as a through hole elongated in the forward and rearward directions (left and right directions in  FIG. 1 ), which is parallel to the motor axis or the output shaft  3   a  of the motor  3 . The first air introduction openings  11  are arranged in four rows in the vertical direction and each row includes two first air introduction openings  11  arranged in the forward and rearward directions. A plurality of first air introduction plates  11   a  are formed on the inner wall of the rear casing  10  at positions adjacent to the lower edges of the first air introduction openings  11  in first to third rows from above of the rear casing  10 . The first air introduction plates  11   a  extend inwardly of the rear casing  10  in a substantially horizontal direction and in parallel to each other. A first shielding plate  11   b  extends upward from the extended end or the innermost end of each of the first air introduction plates  11   a . Further, each shielding plate  11   b  has an outside edge that has an arc-shape configuration similar to the inner wall of the rear casing  10 . With this arrangement, the air introduced into the rear casing  10  via the first air introduction openings  11  flows upward (clockwise direction as viewed in  FIG. 2 ) along the inner wall of the rear casing  10  as indicated by outline arrows in  FIG. 2 . 
     In addition, in this embodiment, six second air introduction openings  12  are formed in the rear casing  10  and each are configured as a through hole elongated in the forward and rearward directions (left and right directions in  FIG. 1 ), which is parallel to the motor axis or the output shaft  3   a  of the motor  3 . The second air introduction openings  12  are arranged in three rows in the vertical direction and each row includes two second air introduction openings  12  arranged in the forward and rearward directions, so that the three rows of the second air introduction openings  12  are opposed to the first to third rows of the first air introduction openings  11 . A plurality of second air introduction plates  12   a  are formed on the inner wall of the rear casing  10  at positions adjacent to the lower edges of the second air introduction openings  12 . The second air introduction plates  12   a  extend inwardly of the rear casing  10  in a substantially horizontal direction and in parallel to each other. A second shielding plate  12   b  extends downward from the extended end or the innermost end of each of the second air introduction plates  12   a  and has an arc-shaped configuration along the inner wall of the rear casing  10 . With this arrangement, the air introduced into the rear casing  10  via the second air introduction openings  12  flows downward (clockwise direction as viewed in  FIG. 2 ) along the inner wall of the rear casing  10  as indicated by outline arrows in  FIG. 2 . 
     In this way, the air introduced from the left side of the rear casing  10  via the first air introduction openings  11  flows upward toward the upper region within the rear casing  10 , while the air introduced from the right side of the rear casing  10  via the second air introduction openings  12  flows downward toward the lower region within the rear casing  10 . Therefore, the air entering the first air introduction openings  11  and the air entering the second air introduction openings  12  flow within the rear casing  10  in the clockwise direction and may not collide with each other. As a result, even if the dust is conveyed within the rear casing  10  by the air entering the first and second air introduction openings  11  and  12 , the dust may be dispersed (and thus not aggregated) within the rear casing  10 . Therefore, it is possible to prevent the dust from building up or depositing onto the electrical components of the motor  3  and to eventually prevent potential electrical leakage or potential lock or burnout of the carbon brushes. 
     As described above, according to this embodiment, air (that may contain the dust) may enter from the outside to the inside of the rear casing  10  via the first and second air introduction openings  11  and  12 . The air may then be guided by the first and second air introduction plates  11   a  and  12   a  so as to collide with the first and second shielding plates  11   a  and  12   a , where the major part of the dust may be separated from the air. 
     The first shielding plates  11   a  are oriented upward while the second shielding plates  12   a  are oriented downward opposite to the orientation of the first shielding plates  11   a . Therefore, the air entering the first air introduction openings  11  flows upward after collision with the first shielding plates  11   a , while the air entering the second air introduction openings  12  flows downward after collision with the second shielding plates  12   a . Therefore, the air entering the first air introduction openings  11  and the air entering the second air introduction openings  12  may merge with each other and move toward the front side of the body casing  2  as a spiral or circulating flow of the air within the rear casing  10 . 
     Because the air entering the rear casing  10  from the left side and the air entering the rear casing  10  from the right side flow vertically in opposite directions, the flow from the left side and the flow from the right side do not collide with each other. Hence, the dust contained in the air may be dispersed within the rear casing  10  and not deposited on the electrical components of the motor  3 . Therefore, this configuration reduces or prevents malfunctioning of the motor  3 . 
     In addition, according to this embodiment, the air entering the rear casing  10  from the left side and the air entering the rear casing  10  from the right side flow is guided in the same direction with respect to the circumferential direction of the rear casing  10  (clockwise direction in  FIGS. 2 and 3 ). Therefore, the air entering the rear casing  10  can smoothly flow within the rear casing  10  and the body casing  2  toward the front side of the body casing  2  as a spiral or circulating flow. 
     The above embodiment may be modified in various ways. For example, although one shielding plate  11   b  ( 12   b ) is provided for each air introduction opening  11  ( 12 ), two or more shielding plates may be provided.  FIG. 3  shows an alternative embodiment in which two shielding plates are provided for each of the second air introduction openings  12 . Thus, in this embodiment, the second air introduction plate  12   a  for each of the second air introduction openings  12  extends from a position offset upward by a predetermined distance from the lower edge of the corresponding second air introduction opening  12 . More specifically, the second introduction plates  12   a  for the second row of the second air introduction openings  12  and those for the third row of the air introduction openings  12  extend from the lower edges of the first row of the air introduction openings  12  and the second row of the air introduction openings  1 Z, respectively. An auxiliary shielding plate  12   c  extends upward (i.e., in opposite direction from the second shielding plates  12   b ) from an intermediate position of each of the air introduction plates  12   a  of the second and third rows. In addition, an additional air introduction plate  12   a   1  extends from the lower edge of each of the air introduction plates  12   a  in the third row. An additional auxiliary shielding plate  12   c   1  extends upward from the extended end or the innermost end of the additional introduction plate  12   a   1 . 
     Because the auxiliary shielding plates  12   c  and  12   c   1  extend upward in opposite direction from the second shielding plates  12   b , the auxiliary shielding plates  12   c  and  12   c   1  serve to initially separate the dust from the air before the air collides with the second shielding plates  12   b  for separation of the dust there. 
     Also with this embodiment, the air entering the second air introduction openings  12  is directed downward by the second shielding plates  12   b  after collision with the auxiliary shielding plates  12   c  and  12   c   1 . Therefore, the flow of the air entering the first air introduction openings  11  and the flow of the air entering the second air introduction openings  12  merge with each other to produce a spiral or circulating flow of the air. Because the auxiliary shielding plates  12   c  and  12   c   1  are provided, it is possible to further reliably separate the dust from the air. Therefore, the potential improper operation of the motor  3  can be further minimized. 
     Although the auxiliary shielding plates  12   c  and  12   c   1  are provided for the second air introduction holes  12  in the above embodiment, it is possible to provide similar auxiliary shielding plates for the first air introduction holes  11  in addition to or in place of the auxiliary shielding plates  12   c  and  12   c   1 . 
     The above embodiments may be further modified. For example, although the shielding plates  11   b  ( 12   b ) extend from the extended ends or the innermost ends of the substantially horizontal air introduction plates  11   a  ( 12   a ), each shielding plate  11   b  ( 12   b ) may extend directly from the inner wall of the rear casing  10 . More specifically, each shielding plate  11   b  may extend obliquely upward from a position adjacent to the lower edge of the corresponding air introduction opening  11 , and each shielding plate  12   b  may extend obliquely downward from a position adjacent to the upper edge of the corresponding air introduction opening  12 . 
     Although the air entering the rear casing  10  from the left side is directed upward and the air entering the rear casing  10  from the right side is direction downward, it is possible to reverse the directions, so that the air may flow or circulate within the rear casing  10  in a counterclockwise direction as viewed in  FIG. 2  or  FIG. 3 . 
     In addition, although the first and second air introduction openings  11  and  12  are formed in the right and left side portions of the rear casing  10 , it is possible to form the first and second air introduction openings  11  and  12  in the upper and lower portions of the rear casing  10 . Furthermore, the configuration of the rear casing  10  may have any other configuration than the cylindrical tubular configuration. For example, the rear casing  10  may have a polygonal configuration in cross section. Further, although the first and second air introduction openings  11  and  12  are formed in the rear casing  10 , they may be formed in the body casing  2 . 
     Further, the present invention can be applied to any other power tools than the disk grinder as long as they have a tubular case with openings from which the air enters for cooling a motor. For example, the present invention can be applied to drills, screwdrivers and cutting devices that have electric motors as driver sources.