Patent Publication Number: US-9850915-B2

Title: Power tool

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a power tool with a built-in fan. 
     Description of the Related Art 
     Power tools such as a screw fastening tool or a drilling tool have a built-in fan largely for cooling the electric motor which serves as the power source of the tool, and which is rotated by the same motor. In another aspect, electric tools such as a compact hand vacuum cleaner (known as a handy cleaner; see Japanese Laid-open Patent Application Publication No. 2003-111698) or a dust collector have a built-in fan for generating suction, which is rotated by an electric motor. As such, because a fan installed in a power tool causes vibration and noise as it rotates, some ideas have been proposed for reducing the vibration and noise. For example, Japanese Laid-open Patent Application Publication No. 2010-144530, Japanese Registered Utility Model No. 3148914, Japanese Patent No. 3071977 and Japanese Patent No. 3460350 disclose means for reducing noise and vibration caused by such fans. 
     Among the above documents, Publication No. 2010-144530 and Registered Utility Model No. 3148914 particularly disclose techniques that use what is known as uneven pitch fan to reduce wind noise or other undesired noise. The uneven pitch fan has angles between blades (i.e. circumferential positions or intervals about the rotation shaft) that are made uneven (i.e. uneven pitches) on a certain basis. For example, some angle may be the golden angle. With an uneven pitch fan, it is possible to reduce uncomfortable narrowband noise around the frequency of NZ/60 Hz (known as NZ noise), where N is the rotation frequency of the fan in 1/min, and Z is the number of blades. 
     SUMMARY OF INVENTION 
     In a power tool with a conventional uneven pitch fan installed, unstable outflow is caused because blades in the fan are arranged at uneven pitches. This unstable outflow is likely to cause vibration in the power tool. Thus, it is desired to reduce the vibration generated in the power tool. 
     In an aspect of the present invention, there is provided a power tool having a built-in dust suction fan, the dust suction fan having a plurality of blades at uneven pitches. The power tool, which may be a handy cleaner or a dust collector, has a built-in uneven pitch fan, which is effective for reducing uncomfortable NZ noise as described above. Thus, it is possible to achieve noise reduction in the power tool. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of the inside of a handy cleaner with a built-in fan, according to a first embodiment. 
         FIG. 2  is a front view of a dust suction fan with a shielding plate (a shroud) removed. 
         FIG. 3  is a perspective view of the dust suction fan with the shielding plate removed. 
         FIG. 4  is an axial cross-sectional view of the dust suction fan with a flattened blade. 
         FIG. 5  is a perspective view of a dust suction fan with blades of uneven thicknesses, according to a second embodiment. 
         FIG. 6  is a perspective view of a dust suction fan with blades of uneven skew angles, according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention will now be described with reference to  FIGS. 1 to 6 . In the following embodiments, a handy cleaner  1  is taken as an example of a power tool. The present embodiments are characterized largely by a dust suction fan  30  installed in the handy cleaner  1 . Since the basic structure of the handy cleaner  1  does not need to be changed in particular, its description will be briefly given. 
     The handy cleaner  1  comprises a front dust collecting case  10  and a back main body  20 . A dust suction nozzle  11  is provided on the front end of the dust collecting case  10 . Dust and dirt are sucked through the dust suction nozzle  11  into the dust collecting case  10 . A dust filter  12  is disposed behind the dust suction nozzle  11 . A filter frame  13  is installed in the front of the main body  20 , and the dust filter  12  is mounted on the filter frame  13  in a covering manner. The dust filter  12  is provided so as to protrude from the front of the main body  20  to the inside of the dust collecting case  10 . The dust filter  12  prevents dust collected in the case  10  from entering the main body  20 . The dust collecting case  10  can be removed from the main body  20  for discarding the dust collected in the case  10 . 
     The main body  20  is the functional part for generating the suction of dust into the dust collecting case  10 . The main body  20  includes an electric motor  22  as the power source, and a dust suction fan  30  rotated by the electric motor  22 , both of which are installed in a main body housing  21 . The dust suction fan  30  is disposed in the front of the main body  20  via a cylindrical fan case  24 . An elastic cover  23  for absorbing vibration covers the fan case  24 , particularly, its peripheral wall  24   d . The fan case  24  is supported in the main body housing  21  in the main body  20  via the elastic cover  23 . In an embodiment, a rubber cover may be used as the elastic cover  23  so as to function as a vibration absorber. The electric motor  22  is installed in a back base plate  24   c  of the fan case  24 . 
     The dust suction fan  30  used may comprise a centrifugal fan that blows out air in all radial directions. A front side of the fan case  24  is in communication with the inside of the dust filter  12  via an inlet port  24   a  which is provided in the center of the fan case  24 . Rotation of the suction fan  30  generates a radial airflow, which blows against the peripheral wall  24   d  of the fan case  24  and is thereby redirected backward. The air then flows to the back side through the outlet port  24   b  provided in the back base plate  24   c  of the fan case  24 . In this way, the airflow through the inlet port  24   a  (i.e. suction) is generated for sucking dust. The suction acts on the inside of the dust collecting case  10  through the dust filter  12 , and thus the dust is sucked into the collecting case  10  through the suction nozzle  11 . In addition, the air generated by rotation of the centrifugal dust suction fan  30  flows to the back side through the outlet port  24   b  provided in the back of the fan case  24 . The air does not directly blow against the main body housing  21 . Therefore, the vibration of the main body housing  21 , which is caused by the unstable outflow, is also reduced. 
     The upper side of the main body housing  21  is provided with an integrated loop-shaped handle  25  for users to grip. The front of the handle  25  has, on the inner side, a trigger-like switch lever  28 , which may be pulled by a user&#39;s finger to be operated. While holding the handle  25  by hand, the user may pull and operate (turn on) the switch lever  28  by his finger. When a main switch  29  is turned on, the electric motor  22  is started. Furthermore, when a user turns on the switch lever  28 , an LED light installed on the front of the handle  25  is turned on and illuminates the tip of the dust suction nozzle  11 . 
     A battery pack  26  serving as a power source, is mounted on the back of the main body  20  and below the handle  25 . The battery pack  26  may comprise, for example, a 14.4V lithium-ion battery, which is widely used as a main power source for hand electric tools, such as a screw fastening tool or cutting tool. The battery pack  26  can be repeatedly used. The battery pack  26  can be removed from a slide-type battery mount  27  and charged in a separately provided battery charger. 
     The dust suction fan  30  is provided with means for mainly the reduction of noise. The dust suction fan  30  may comprise what is known as an uneven pitch fan. Since the uneven pitch fan has irregular frequency with regard to its blade passing, the generation of the uncomfortable shrilling blade-passing noise characteristic of fans can be suppressed. The dust suction fan  30  includes a circular base plate or disk  31  which is fixed to an output shaft of the electric motor  22 , an annular shielding plate  32  which is disposed substantially parallel to the base plate  31  at a predetermined interval, and a plurality of blades  33  which are disposed between the shielding plate  32  and the base plate  31  at uneven pitches. The inlet port  24   a  of the fan case  24  is positioned with respect to the inlet hole  32   a  provided in the center of the shielding plate  32 .  FIG. 2  shows the dust suction fan  30  with the shielding plate  32  removed. 
     As shown in  FIG. 3 , the blades  33  are integrated with the base plate  31 . Each blade  33  has an inner end located near the center of the base plate  31  (where the rotation axis J passes), and extends radially from the inner end, while bending, to the outer end. The inner ends of the blades  33  are positioned substantially on the same circle with the center on the rotation axis J. The circumferential intervals (i.e. angles θ, or pitches) between inner ends of the adjacent blades  33  are not equal, and, as best shown in  FIG. 2 , are arranged in uneven angles in the circumference. Meanwhile, the curvatures of the bent blades  33  are matched with each other. Therefore, the intervals between the outer ends (on the outer circumference) of the circumferentially adjacent blades  33  are not equal and thus are uneven. 
     As shown in  FIG. 4 , each blade  33  has a portion on the inner end side which projects into the inlet hole  32   a  in the shielding plate  32 , where the height of the portion from the base plate  31  may be slanted, such that it gradually decreases towards the inner end. This height-varying inclined portion of the blade  33  will be hereinafter referred to as the inducer  33   a  of the blade  33 . The height of each blade  33  from the base plate  31  is substantially constant between the base plate  31  and the shielding plate  32 . This constant-height portion of the blade  33  will be hereinafter referred to as the body  33   b  of the blade  33 . Airflow generated by the rotation of the dust suction fan  30  passes through the inlet port  24   a  and through the inlet hole  32   a  in the shielding plate  32 , and then is directed radially outward. The inlet of each blade  33  is widely opened by the configuration of the inducer  33   a , and thereby air can be smoothly taken through the inlet hole  32   a  into the passages between the blades  33 . 
     As shown in a solid line and a two-dot chain line in  FIG. 4  (also see  FIG. 3 ), the inducers  33   a  of the blades  33  may have different configurations. The configurations of the inducers  33   a  may be changed as desired so that their face areas differ from each other. It is possible to control the inflow of air into the body  33   b  of each blade  33  by changing the dimensions or face area of the inducer  33   a . The greater the dimensions or face area of the inducer  33   a , the larger the volume of air introduced there. On the other hand, the larger the interval θ between the adjacent blades  33 , the larger the volume of air that flows out of there. This will result in a possibility that vibration may be generated due to the unstable volume (or unstable volume) of outflow. 
     Considering this, for the blades  33  with a large interval θ, their inducer  33   a  can be configured to have a small face area to reduce the volume of air introduced there. The radial outflow from between the blade bodies  33   b  is reduced, and thus it is possible to reduce or eliminate the unstableness of outflow in the entirety of the dust suction fan  30 . As described above, in this first embodiment, to deal with the vibration caused by unstable outflow, the configuration or the face area of the inducer  33   a  may be properly changed so as to offset the unstable outflow caused by the uneven intervals θ (the uneven pitches) and reduce the vibration. 
     As described above, in the present embodiments, the handy cleaner  1  (or other power tools) may include a dust suction fan  30  installed in it; the fan having a plurality of blades  33  with uneven pitches between the blades  33 . In this way, an uneven pitch fan which has a reduction effect of an uncomfortable noise, such as NZ noise, is installed in the power tool, such as the handy cleaner  1  or a dust collector, as a dust suction fan. Thus, it is possible to achieve noise reduction in the power tool. 
     The dust suction fan  30  may comprise a centrifugal fan which blows out air in all radial directions. The centrifugal uneven pitch fan allows for preventing the uncomfortable shrilling blade-passing noise (as called NZ noise) generated in the centrifugal fan. 
     The dust suction fan  30  may be provided with means for correcting the unstable outflow which can be caused by the uneven pitches between the blades  33 . The unstable outflow caused by the dust suction fan  30  being an uneven pitch fan is corrected by the means for correcting unstable outflow. As a result, vibration caused by the unstable outflow is reduced. In summary, it is possible to reduce the NZ noise or other uncomfortable noise that is caused due to the dust suction fan  30  being an uneven pitch fan. At the same time, vibration caused by the unstable outflow is reduced by the means for correcting unstable outflow applied in the dust suction fan  30 . This allows improved user-friendliness of the handy cleaner  1 . 
     The blades  33  may have inducers of uneven face areas for correcting unstable outflow. In addition to the face area, the inducers of blades  33  may be designed to have uneven configuration in terms of shape, dimension or any other, which changes the outflow of air from between the blades  33 . In this manner, it is possible to correct the unstable outflow caused by the uneven pitches and reduce the vibration of the power tool. 
     Instead of properly changing the configuration of the inducer  33   a , other means can be taken for correcting unstable outflow, for example, as described below. 
     In a second embodiment, as shown in  FIG. 5 , the blades  41  may have uneven thicknesses for correcting unstable outflow. Specifically, a dust suction fan  40  may include some blades of a thickness d 1  and other blades of a thickness d 2 . Thickness d 2  is greater than the thickness d 1 . The larger the thickness of the blade, the smaller the outflow from there. For this reason, the blade at a larger pitch can be designed to have a greater thickness than the thickness of the blade at a smaller pitch. This is done so that the outflow from the larger pitched blade can be adjusted and generally matched with the outflow from the smaller pitched blade. In this way, making use of the fact that the outflow from between the blades varies when the thicknesses of the blades are uneven, it is possible to reduce the vibration of the dust suction fan  30  by correcting the unstable outflow caused by the uneven pitches. 
     In a third embodiment, as shown in  FIG. 6 , the blades may have uneven skew angles (which are the angles of blades  51  with respect to the surface of the base plate  52 ) for correcting unstable outflow. This dust suction fan  50  also allows for a reduction in vibration by correcting the unstable outflow caused by the uneven pitches of the blades  51 . In the fan shown in  FIG. 6 , all skew angles α, β and γ of the blades  51  are different from each other. Different skew angles α, β and γ of the blades  51  allows for controlling the outflow from between the blades  51 . Making use of the fact that the outflow from between the blades varies when the skew angles of the blades are uneven, it is possible to reduce the vibration of the dust suction fan  50  by correcting the unstable outflow caused by the uneven pitches. 
     As shown in  FIG. 1 , the handy cleaner  1  (or other power tool) may include a main body housing  21 , a fan case  24  with a built-in dust suction fan  30 , and a handle  25  provided in the main body housing  21  for users to grip. The handy cleaner  1  may further include a vibration absorber provided between the fan case  24  and the handle  25 . The vibration absorber absorbs vibration caused by the unstable outflow from the dust suction fan  30 . In the first embodiment above, the handy cleaner  1  includes, as the vibration absorber, the elastic cover  23  which covers the fan case  24 . The main body housing  21  supports the fan case  24  via the elastic cover  23 . Therefore, the elastic cover  23  (or the vibration absorber) absorbs the vibration which is caused by the unstable outflow, and thus the vibration is prevented from being transmitted to the handle  25 . In this manner, the vibration on the handy cleaner  1  user&#39;s hand which grips the handle  25  is reduced. This allows improved user-friendliness of the handy cleaner  1 . 
     The dust suction fan  30  may be shielded by the fan case  24  in radial directions so that the radial airflow from the dust suction fan  30  may be prevented from directly blowing against the main body housing  21 . In this manner, the airflow is redirected into the axial direction of the dust suction fan  30 . Therefore, the vibration of the main body housing  21  is reduced from being caused by the unstable outflow from the uneven pitch fan. In other words, the fan case  24  (or particularly its peripheral wall  24   d ) functions as the vibration absorber. The vibration on the handy cleaner  1  user&#39;s hand which grips the handle  25  is reduced because the vibration of the main body housing  21  is reduced by the fan case  24  as the vibration absorber. This allows improved user-friendliness of the handy cleaner  1 . 
     Although embodiments of the present invention are described with reference to the structures above, it should be understood by those skilled in the art that various alterations, improvements, or modifications may be applied insofar as they are within the scope of the present invention. Thus, embodiments of the present invention may include all such alterations, improvements, and modifications without departing from the spirit and the scope of the appended claims. Embodiments of the present invention are not limited to the specific structures described above and can be modified as described below for example. 
     In addition to what is described above, the deflection angle or inclination of each blade with respect to the radial direction may be changed for correcting or reducing unevenness of outflow caused by the uneven pitch fan (means for correcting unstable outflow M). When the dust suction fan  30  is seen in a plan view as shown in  FIG. 2 , the deflection angle is, in other words, the circumferential position of the blade on the base plate face (see void arrow in  FIG. 2 ) with respect to a radial line (see dashed lines in  FIG. 2 ) passes through the inner end of the blade. The deflection angles may be changed to control the airflow from between the blades  33 . In this way, it is possible to compensate for the unstable outflow caused by the uneven pitches, and reduce the vibration of the fan. 
     The blades may have uneven deflection angles (or inclination) with respect to radial directions for correcting unstable outflow from the fan. The outflow from between the blades varies when the deflection angles of the blades with respect to radial directions are uneven. 
     The various means for correcting unstable outflow M described above can be used either alone or in combination. In this way, the unstable outflow caused by the uneven pitches is reduced, and thus can achieve both noise reduction, which is realized by the uneven pitch blades, and vibration reduction of the power tool, which is realized by correcting the unstable outflow. 
     Even when the blades  41  have no inducers as shown in  FIG. 5 , unstable outflow can be corrected by other means that do not involve inducers. This allows for the reduction of vibration in power tools. 
     The means for correcting unstable outflow M can be applied not only to the dust suction fan  30  of a handy cleaner  1 , but also to a fan installed in other power tools, such as a motor cooling fan, a blowing fan used in a dust collector, or an engine-powered blower. 
     For absorbing the vibration caused by the unstable outflow from the dust suction fan  30 , the outer surface of the peripheral wall  24   d  may, for example, be covered with a sponge or subjected to raising process, rather than using the elastic cover  23  as a vibration absorber. 
     Instead of the peripheral wall  24   d  of the fan case  24 , a peripheral wall comparable to the peripheral wall  24   d  may be provided, as the vibration absorber, on the main body housing  21  side via an elastic member, and thus radial airflow from the dust suction fan may be prevented from directly blowing against the main body housing  21 . 
     The vibration absorber which is interposed between the handle  25  and the dust suction fan  30  may also be embodied as follows. First, a floating handle structure (an anti-vibration handle) may be applied in which the main body housing supports the handle  25  via an elastic member. Second, the main body housing may be provided with a dual structure. Third, the airflow can be stabilized by arranging a number of dust suction fans in series in the axial direction in such a manner that their phases of uneven pitches are mutually offset. Fourth, the main body housing may support the dust suction fan and fan case via an electric motor. It should be noted that these structures can be applied in combination as desired. Such vibration absorbers also prevent the vibration, which is caused by the unstable outflow from the uneven pitch fan, from being transmitted to the handle  25 .