Patent Publication Number: US-2021184538-A1

Title: Flinger with noise reduction structure and electric motor with the flinger

Description:
RELATED APPLICATIONS 
     This is a division of U.S. application Ser. No. 16/407,528, filed May 9, 2019, which claims priority to Japanese Application No. 2018-112633, filed Jun. 13, 2018, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flinger with a structure for reducing a noise caused during rotation and an electric motor with the flinger. 
     2. Description of the Related Art 
     In many cases, an electric motor (rotary electric machine) for rotating a spindle, etc., of a machine tool includes a component called a flinger including a plurality of tapped holes so that a weight such as a set screw is screwed into some of the tapped holes to enable balance adjustment during rotation. Thus, existence of the tapped hole without the weight screwed causes a noise when the electric motor (flinger) operates at a high-speed rotation. 
     It is known in the related arts to reduce this kind of noise as follows: a cover for covering an end face of a spindle (e.g., refer to JP 2000-218465 A) is provided; and a countersunk head screw is screwed into a tapped hole as a weight, and a face provided with the tapped hole is made substantially flat (e.g., refer to JP 2008-132579 A). 
     SUMMARY OF THE INVENTION 
     It is desirable a structure capable of effectively reducing a noise associated with rotation of an electric motor without requiring operation of mounting a cover, screwing a countersunk head screw, etc. 
     An aspect of the present disclosure is a flinger mounted in an electric motor including a stator, a rotor with a rotating shaft rotatable about an axis of the stator, and a front bearing and a rear bearing configured to rotatably support the rotating shaft, the flinger being mounted to one or both of a portion of the rotating shaft forward of the front bearing along the axis and a portion of the rotating shaft rearward of the rear bearing along the axis, the flinger having a plurality of tapped holes, and a cut-out cutting out a part of the respective tapped holes. 
     Another aspect of the present disclosure is a flinger mounted in an electric motor including a stator, a rotor with a rotating shaft rotatable about an axis of the stator, and a front bearing and a rear bearing configured to rotatably support the rotating shaft, the flinger being mounted to one or both of a portion of the rotating shaft forward of the front bearing along the axis and a portion of the rotating shaft rearward of the rear bearing along the axis, the flinger having a plurality of tapped holes, and partitions formed downstream of the respective tapped holes in a rotation direction of the rotating shaft. 
     Yet another aspect of the present disclosure is an electric motor including the flinger according to any one of the aspects described above of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be made more apparent by the following description of the preferred embodiments thereof with reference to the accompanying drawings wherein: 
         FIG. 1  illustrates a schematic structure of an electric motor according to a preferred embodiment of the present disclosure; 
         FIG. 2  illustrates a first example of a flinger provided in the electric motor of  FIG. 1 ; 
         FIG. 3  illustrates a structural example of a flinger in the related art; 
         FIG. 4  illustrates noise reduction action of the flinger of  FIG. 2 ; 
         FIG. 5  is a graph for illustrating noise reduction effect of the flinger of  FIG. 2 ; 
         FIG. 6  illustrates another structural example of the flinger according to the first example; 
         FIG. 7  illustrates yet another structural example of the flinger according to the first example; 
         FIG. 8  illustrates a second example of the flinger provided in the electric motor of  FIG. 1 ; 
         FIG. 9  is a partially enlarged view of a flinger in the related art; 
         FIG. 10  is a partially enlarged view of the flinger of  FIG. 8 ; 
         FIG. 11  illustrates an example of reducing an inflow of air into a tapped hole with a partition; 
         FIG. 12  is a graph for illustrating noise reduction action of the flinger of  FIG. 8 ; and 
         FIG. 13  illustrates another structural example of the flinger according to the second example. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a cross-sectional view in an axial direction illustrating a schematic structure of an electric motor (rotary electric machine)  10  according to a preferred embodiment of the present disclosure. The electric motor  10  includes a rotating shaft  18  rotatably supported about an axis  16  by a first bearing (front bearing)  12  and a second bearing (rear bearing)  14 , a rotor  20  rotating integrally with the rotating shaft  18  while fit to an outer circumferential surface of the rotating shaft  18 , and a stator  22  having a substantially cylindrical shape extending along the axis  16  to surround the rotor  20 . 
     The front bearing  12  is provided near a front end  18   a  of the rotating shaft  18  and supported by a front housing  26  fixed by screwing, etc., to a front end face  24   a  of a stator core  24 . The front housing  26  extends from the front end face  24   a  of the stator core  24  toward the front end  18   a  of the rotating shaft  18  and supports a part of the rotating shaft  18  and the front bearing  12  (an outer race thereof). The front housing  26  is also mounted with a front cover  28  having a substantially annular shape. The front end  18   a  of the rotating shaft  18  protrudes from the front housing  26  and the front cover  28 , and the rotating shaft  18  functions as an output shaft directly or indirectly connected to a spindle of a machine tool such as a lathe or a machining center, for example. Note that in the present specification, the output shaft side (left side in  FIG. 1 ) and the opposite side thereof (right side in  FIG. 1 ) are respectively referred to as “front” and “rear”, for convenience. 
     The rear bearing  14  is provided near a rear end  18   b  of the rotating shaft  18  opposing the front end  18   a  of the rotating shaft  18 . The stator core  24  is fixed at its rear end face  24   b  with a rear housing  30  by screwing etc., and the rear housing  30  is fixed with a support ring  32  by screwing etc., the support ring  32  supporting the rear bearing  14  (an outer race thereof). The rear end  18   b  of the rotating shaft  18  protruding from the rear housing  30  protrudes from a rear cover  34  mounted to the rear housing  30 . The rotating shaft  18  is also mounted at the rear end  18   b  with an encoder  36  configured to detect rotational position, rotation speed, etc., of the rotating shaft  18 . 
     The stator  22  includes the stator core  24  including a plurality of electromagnetic steel sheets that are laminated and a coil  38  wound around a protrusion (not illustrated) on an inner circumferential surface of the stator core  24 . The coil  38  is fixed to the stator core  24  by a resin, etc. The coil  38  extends along the rotational axis  16  so as to protrude from both ends of the stator core  24 , and is connected to a lead wire (not illustrated) led out of a terminal box  40 . The coil  38  generates a rotating magnetic field by using a current supplied through the lead wire, and the rotor  20  is rotated integrally with the rotating shaft  18  by the generated rotating magnetic field. 
     In the specification of the present application, the term, “radially outward” represents a direction away from the rotational axis  16  in a cross section, and the term, “radially inward” represents a direction approaching the rotational axis  16  in the cross section. In addition, the term, “axis direction”, or the term, “axial direction” represents a direction parallel to the rotational axis  16 . 
     The electric motor  10  includes at least one flinger (two in the example illustrated) that rotates integrally with the rotating shaft  18  to enable balance adjustment during rotation. More specifically, a flinger (labyrinth)  44  formed with a plurality of tapped holes  42  extending axially is fixed, by interference fit, etc., to a portion of rotating shaft  18  forward of the front bearing  12  along the axis  16  (the vicinity of the front cover  28  in the example illustrated) so that contamination of foreign materials into the electric motor can be prevented and balance adjustment during rotation can be performed by screwing a weight (not illustrated) such as a set screw into at least one of the tapped holes  42 . Likewise, a flinger  48  formed with a plurality of tapped holes  46  extending axially is fixed, by interference fit, etc., to a portion of rotating shaft  18  rearward of the rear bearing  14  along the axis  16  (the vicinity of the rear cover  34  in the example illustrated) so that contamination of foreign materials into the rear cover  34  can be prevented and balance adjustment during rotation can be performed by screwing a weight (not illustrated) such as a set screw into some of the tapped holes  46 . 
     While the flinger is provided on each of the front and rear sides the rotating shaft  18  in the example illustrated, the flinger may be provided only on any one of the sides. The flinger  44  and the flinger  48  each may have the same basic structure and function, so that only the flinger  48  on the rear side will be described below. 
     First Example 
       FIG. 2  is a perspective view illustrating a structural example of the flinger  48  according to a first example.  FIG. 3  is a perspective view illustrating a structural example of a flinger  49  in the related art as a comparative example. The flinger  48  includes the plurality of tapped holes  46  into which a weight for balance adjustment is detachable, and a cut-out  52  cutting out a part of each of the tapped holes  46  (female screw). The tapped holes  46  and the cut-out  52  are here formed in an end face  50  of the flinger  48  on an opposite side in an axial direction of the electric motor  10  to a side facing the inside of the electric motor  10 . More specifically, the cut-out  52  is formed as a recess cutting out each of the tapped holes from an open-end (here the end face  50 ) of each of the tapped holes  46  by a predetermined distance (less than a depth of each tapped hole), and is an annular groove in the example illustrated. However, the recess is not limited to this, and a recess such as a counterbored hole with a diameter more than that of each of the tapped holes  46  and an axial length less than that thereof may be formed concentrically with the corresponding one of the tapped holes  46 , for example. This kind of cut-out causes an air column formed in each of the tapped holes  46  to substantially have a length less than an air column formed in each of the tapped holes  47  of  FIG. 3 , as described above. 
       FIG. 4  illustrates noise reduction action of the flinger  48  illustrated in  FIG. 2 . Here, the tapped hole  47  (refer to  FIG. 3 ) provided in the flinger  49  in the related art illustrated in  FIG. 3  will be compared with the tapped hole  46  of the flinger  48 . 
     In each tapped hole formed in the flinger, rotation of the electric motor causes in- and outflow of air, so that each tapped hole serves as a kind of closed pipe during rotation. At this time, a natural frequency “f” of the closed pipe (air column) is expressed by Expression (1) below, where “V” is sonic velocity, and “L” is a length of the air column (n=1, 2, 3, . . . ). From Expression (1), it is found that as the length L of the air column decreases, the natural frequency f increases. 
         f   2n-1 =(2 n− 1)/4 L·V   (1)
 
     Here, the tapped hole  46  of the flinger  48  according to the first example has a depth (a length of an air column) less than a depth (a length of an air column) of the tapped hole  47  of the flinger  49  in the related art by a distance equivalent to a depth “d” of the groove  52 , so that the natural frequency increases. Thus, when the flinger  48  is used, rotation speed causing increase (maximization) in noise during rotation can be shifted to higher rotation speed than when the flinger  49  is used. 
       FIG. 5  is a graph for illustrating noise reduction effect when the flinger  48  illustrated in  FIG. 2  is mounted to the electric motor  10 . In  FIG. 5 , the horizontal axis represents a dimensionless number in proportion to rotation speed of the electric motor, and the vertical axis represents a dimensionless number in proportion to a level of sound caused by rotation of the electric motor. The level of sound was measured at a fixed position away from the flinger by a predetermined distance. Measurement results using the flinger  48  of  FIG. 2  are shown as a graph  54 , measurement results using the flinger  49  of  FIG. 3  are shown as a graph  56 , and measurement results using the flinger  49  of  FIG. 3  with the tapped holes  47  all of which were filled with respective set screws, etc., (almost equivalent to that without the tapped hole  47 ) are shown as a graph  58  as another (ideal) comparative example. 
     As can be seen from  FIG. 5 , when the flinger  49  was used, a level of sound at a rotation speed of about 170 became maximum (the graph  56 ). When the flinger  48  is used, the natural frequency increases more than the natural frequency of the flinger  49  as described above, and thus, it is conceivable that a level of sound becomes maximum in a range of a rotation speed more than 200. Thus, when the rotation speed of the electric motor is within a practical range (200 or less), using the flinger  48  enables a noise level to be greatly reduced from that of the flinger in the related art and to be nearly close to that of an ideal product (graph  58 ). 
     For  FIG. 4 , it is conceivable that a tapped hole may be simply reduced in length based on an idea that a shorter air column can reduce a noise more. However, in that case, a set screw, etc., needs to be reduced in length so as not to greatly protrude from an end face of a flinger (i.e., the set screw is reduced in weight). This is unfavorable because it is difficult to achieve an original function of balance adjustment. Then, in the first example, the cut-out is provided in the end face to reduce a depth affecting a noise level (a length of an air column) without changing a depth of the tapped hole from the end face, so that a set screw with the same length as that in the related art can be used and a noise can be prevented. 
       FIG. 6  illustrates a structural example of a flinger  48   a  as a modification of the first example. The flinger  48   a  includes the plurality of tapped holes  46   a  into which a weight for balance adjustment is detachable, and cut-outs  52   a  cutting out a part of the corresponding tapped holes  46   a  (female screw). The tapped holes  46   a  and the cut-outs  52   a  are here formed in an end face  50   a  of the flinger  48   a  on an opposite side in an axial direction of electric motor  10  to a side facing the inside of the electric motor  10 . The cut-outs  52   a  are each formed as a slit cutting out a part of a lateral portion of the corresponding one of the tapped holes  46   a  in a longitudinal direction of the tapped hole  46   a . In this case, each of the tapped holes  46   a  does not have a cylindrical column shape, so that the air column itself as illustrated in  FIG. 4  is not formed even by rotation of the electric motor. This enables a noise during rotation to be greatly reduced even when the flinger  48   a  is used as compared with that in the related art. 
       FIG. 7  illustrates a structural example of a flinger  48   b  as another modification of the first example. The flinger  48   b  includes the plurality of tapped holes  46   b  into which a weight for balance adjustment is detachable, and cut-outs  52   b  cutting out a part of the corresponding tapped holes  46   b  (female screw). The tapped holes  46   b  and the cut-outs  52   b  are here formed in an end face  50   b  of the flinger  48   b  on an opposite side in an axial direction of the electric motor  10  to a side facing the inside of the electric motor  10 . The cut-outs  52   b  are each formed as a slit cutting out a part of a lateral portion of the corresponding one of the tapped holes  46   b  in a longitudinal direction of the tapped hole  46   b  as with the cut-outs  52   a . However, while the cut-outs  52   a  are each opened in an outer lateral face of the flinger  48   a , the cut-outs  52   b  is formed so as not to be opened in an outer lateral face of the flinger  48   b . Thus, when the flinger  48   b  is used, it is expected not only noise reduction effect due to no formation of an air column as in the flinger  48   a , but also higher noise reduction effect due to a less turbulent flow of air in the periphery of the outer lateral face of the flinger  48   b  during rotation than that when the flinger  48   a  is used. 
     While the cut-out (slit) is formed through overall length of each tapped hole in each of  FIGS. 6 and 7 , even the cut-out formed in a part of each tapped hole in its longitudinal direction enables an air column to be substantially reduced more in length than that in the related art, thereby enabling a certain noise reduction effect to be acquired. In addition, the “longitudinal direction” (of a tapped hole) of the present disclosure is not limited to a direction strictly parallel to the axial direction of the tapped hole, and includes a direction with an angle 10° or less, 20° or less, or 30° or less, with respect to the axial direction, for example. The slit is also not limited to a linear shape, and may be a curved shape or a spiral shape, for example. 
     Second Example 
       FIG. 8  is a perspective view illustrating a structural example of a flinger  48   c  according to a second example. The flinger  48   c  includes a plurality of tapped holes  46   c  into which a weight for balance adjustment is detachable, and a partition  60  formed downward of each of the tapped holes  46   c  in a rotation direction of the rotating shaft  18 . The tapped holes  46   c  and the partition  60  are here formed in an end face  50   c  of the flinger  48   c  on an opposite side in an axial direction of the electric motor  10  to a side facing the inside of the electric motor  10 . The partition  60  is formed in a portion downstream of each of the tapped holes  46   c  on the end face  50   c . While the partition  60  is formed as a protrusion in a star shape formed both sides of each of the tapped holes  46   c  in the rotation direction in the example illustrated, the partition  60  is not limited to this. 
       FIGS. 9 to 11  each illustrate operation effect of the partition  60 . In the flinger  49  in the related art (refer to  FIG. 3 ), a flow of air in a substantially opposite direction to a rotation direction  62  (illustrated by an arrow  64 ) occurs in the vicinity of each of the tapped holes  47  when an electric motor is operated, as in  FIG. 9  illustrated as a comparative example. Then, a predetermined amount of air flows into and out from each of the tapped holes  47  to cause a noise. 
     In contrast, in the flinger  48   c  according to the second example, the partition  60  provided in the portion downstream of each of the tapped holes  46   c  in the rotation direction  62  on the end face  50   c  deflects a flow of air in a substantially opposite direction to the rotation direction  62  (illustrated by an arrow  66 ) as illustrated in  FIG. 10  (more specifically, the air is released in a direction away from the end face  50   c  as illustrated in  FIG. 11 ), so that an in- and outflow rate of air into and from each of the tapped holes  46  can be reduced more as compared with the flinger in the related art illustrated in  FIG. 9 . As a result, a noise during rotation can be reduced. 
       FIG. 12  is a graph for illustrating noise reduction effect when the flinger  48   c  illustrated in  FIG. 8  is mounted to the electric motor  10 . In  FIG. 12 , the horizontal axis represents a dimensionless number in proportion to rotation speed of the electric motor, and the vertical axis represents a dimensionless number in proportion to a level of sound caused by rotation of the electric motor. The level of sound was measured at a fixed position away from the flinger by a predetermined distance. Measurement results using the flinger  48   c  of  FIG. 8  are shown as a graph  68 , the measurement results using the flinger  49  of  FIG. 3  are shown as the graph  56 , and the measurement results using the flinger  49  of  FIG. 3  with the tapped holes  47  all of which were filled with respective set screws, etc., (almost equivalent to that without the tapped hole  47 ) are shown as the graph  58  as the other (ideal) comparative example. 
     As can be seen from  FIG. 12 , when the flinger  49  was used, a level of sound at a rotation speed of about 170 became maximum (the graph  56 ). Even when the flinger  48   c  was used, a level of sound at a rotation speed of about 170 tended to become maximum. However, an in- and outflow rate of air into and from each of the tapped holes  46   c  is greatly reduced by the partition  60  as described above, so that a noise level in the second example can be greatly reduced as compared with that in the related art to be brought nearly close to that of the ideal product (graph  58 ). 
     In the measurement of  FIG. 12 , the partition  60  had a height h of 0.5 mm (refer to  FIG. 11 ). However, the height is an example, and can be appropriately changed to 1 mm or less, 2 mm or less, 3 mm or less, etc., according to rotation speed and a level of noise. 
       FIG. 13  illustrates a structural example of a flinger  48   d  as a modification of the second example. The flinger  48   d  includes a plurality of tapped holes  46   d  into which a weight for balance adjustment is detachable, and partitions  70  formed downward of the corresponding tapped holes  46   d  in a rotation direction of the rotating shaft  18 . The tapped holes  46   d  and the partitions  70  are here formed in an end face  50   d  of the flinger  48   d  on an opposite side in an axial direction of the electric motor to a side facing the inside of the electric motor  10 . The partitions  70  are each formed in a portion downstream of the corresponding one of the tapped holes  46   d  on the end face  50   d . While the partitions  70  are each formed as a protrusion radially extending from the rotation center in an intermediate portion between adjacent tapped holes  46   d  on the end face  50   d  in the example illustrated, the partitions  70  are not limited to this. Even when the flinger  48   d  of  FIG. 13  is used, as in when the flinger  48   c  of  FIG. 8  is used, an in- and outflow rate of air into and from each of the tapped holes  46   d  is greatly reduced by the corresponding partitions  70 . This enables a noise level to be greatly reduced as compared with that in the related art. 
     While twelve tapped holes are formed in the end face of the flinger, at an equal interval of 30° in a circumferential direction about the axis  16 , in each of the examples described above, the present disclosure is not limited to this. For example, four tapped holes may be formed in the end face of the flinger, at an equal interval of 90° in the circumferential direction, six tapped holes may be formed in the end face of the flinger, at an equal interval of 60° in the circumferential direction, or eight tapped holes may be formed in the end face of the flinger, at an equal interval of 45° in the circumferential direction. While an interval between a pair of tapped holes of a plurality of tapped holes may not be equal, it is preferable that tapped holes each with the same size be formed in the circumferential direction at an equal interval on a circle concentric with the rotation center in consideration of balance and eccentricity associated with rotation of a spindle. In addition, a tapped hole does not typically pass through a flinger (a tapped hole has a depth shorter than an axial length of a flinger). Further, the tapped hole may be provided in a face of the flinger other than an end face thereof (e.g., an outer lateral face). 
     It is preferable that the cut-outs and partitions in the examples described above be formed so as not to impair rotational symmetry of the flinger. This is because when the flinger itself is rotational asymmetric, it is very difficult to adjust rotation balance by inserting a set screw, etc., into the tapped hole. 
     When the flinger according to the present disclosure is applied to an electric motor (rotary electric machine), a noise associated with rotation of the electric motor can be greatly reduced without using a cover for preventing a noise or filling the tapped hole for a purpose other than balance adjustment. The flingers according to the examples described above each can be relatively easily manufactured by only modifying a die, so that there is also not much difference in cost from the flinger in the related art. In addition, when an electric motor with any one of the flingers according to the present disclosure is applied to a machine tool such as a NC lathe or a machining center, in which a spindle is typically rotated at high speed, a work environment with less noise can be achieved. 
     According to the present disclosure, a level of a sound generated during rotation of an electric motor, due to existence of a tapped hole, can be greatly reduced as compared with that in the related art. 
     While the invention has been described with reference to specific embodiments chosen for the purpose of illustration, it should be apparent that numerous modifications could be made thereto, by a person skilled in the art, without departing from the basic concept and scope of the invention.