Abstract:
A motor includes ( 1 ) a rotor including a permanent magnet fixed to a rotor shaft, ( 2 ) a stator including a rotor insertion hole and an inner periphery, where the inner periphery of the stator is oppositely disposed to the permanent magnet of the rotor and where the rotor insertion hole has a prescribed space and the rotor is inserted into the rotor insertion hole, ( 3 ) a bearing supporting one end of the rotor shaft, and ( 4 ) a bearing holder including a bearing insertion hole into which the bearing is inserted. In this motor, when an outer diameter of the permanent magnet of the rotor is set to be “A”, an inner diameter of the bearing insertion hole of the bearing holder is set to be “B”, and an inner diameter of the rotor insertion hole of the stator is set to be “C”, a relationship of “A&lt;B&lt;C” is satisfied.

Description:
[0001]     The present invention is based on Japanese Patent Application No. 2005-299026 filed Oct. 13, 2005, the contents of which are incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a motor, specifically to a motor which is suitable to reduce its size.  
         [0004]     2. Description of the Related Art  
         [0005]     A PM type stepping motor has been conventionally known as a motor which is rotationally driven in proportion to an inputted number of pulses. For example, in a PM type stepping motor provided with pole teeth, a permanent magnet is fixed to a rotor shaft of a rotor and ring-shaped coils are wound around a stator. When a pulsed current is supplied to the ring-shaped coils, a magnetic field is generated in the pole teeth of the stator and the rotor is rotationally driven in proportion to an inputted number of pulses.  
         [0006]      FIG. 4  is a sectional view showing a conventional structure of a PM type stepping motor  100  provided with the pole teeth.  
         [0007]     In  FIG. 4 , a PM type stepping motor  100  includes a rotor  110  provided with a permanent magnet  102  fixed to a rotor shaft  101  and a stator  120  provided with a rotor insertion hole  103  within which the rotor  110  is inserted. A bottom end of the rotor shaft  101  is supported with a bearing  130  through a steel ball  104 . Further, the rotor shaft  101  is supported with a bearing  130  through a steel ball  104 . Further, the bearing  130  is supported so as to be capable of being displaced in an axial direction “L” of the rotor shaft  101  by a bearing holder  140  provided with a bearing insertion hole  105 . A flat spring  106  for applying a pressurization to the rotor  110  in the axial direction “L” of the rotor shaft  101  is abutted against an under face of the bearing  130 .  
         [0008]     In this conventional structure of a PM type stepping motor  100 , the dimensions of the rotor  110 , the stator  120  and the bearing  130  are set as follows. In other words, when the outer diameter of the rotor  110  (permanent magnet  102 ) is set to be φA2 (mm), the inner diameter of the bearing insertion hole  105  (outer diameter of the bearing  130 ) is set to be φB2 (mm), and the inner diameter of the stator  120  (rotor insertion hole  103 ) is set to be φC2 (mm), the relationship of A 2 , B 2  and C 2  is satisfied as follows: A 2 &lt;B 2 =C 2  (see  FIG. 4 ). The conventional PM type stepping motor  100  satisfying this relationship is assembled as follows. In other words, first, a thrust bearing  108  is fixed to a frame  107  and the stator  120  is fixed to the frame  107 . Next, a bearing holder  140  is attached to the under face of the stator  120 . Next, the rotor shaft  101  (rotor  110 ) to which the permanent magnet  102  is fixed is inserted into the rotor insertion hole  103  of the stator  120  from a bearing insertion hole  105  of the bearing holder  140  and a front end of the rotor shaft  101  is set to be engaged with the thrust bearing  108 . Finally, the bearing  130  is assembled into the bearing insertion hole  105  of the bearing holder  140  from the rear side such that the steel ball  104  is held between the rotor shaft  101  and the bearing  130 , and then the under face of the bearing  130  is urged by the flat spring  106 .  
         [0009]     As described above, when the conventional stepping motor  100  is assembled, the rotor  110  is inserted into the rotor insertion hole  103  of the stator  120  through the bearing insertion hole  105  of the bearing holder  140  and, for this purpose, the relationship of “A2&lt;B2=C2” is satisfied.  
         [0010]     In the above-mentioned stepping motor  100 , it is conceivable that the relationship of “C2&lt;B2” is satisfied. For example, in a stepping motor described in Japanese Patent Laid-Open No. Hei 9-135562, it may be structured such that the relationship of “C2&lt;B2” is satisfied to prevent the bearing  130  from protruding into the rotor insertion hole  103 . However, in this case, the bearing  130  may protrude into the rotor insertion hole  103 , and the bearing  130  may be brought into contact with the stator  120  (specifically, pole teeth). In order to prevent this problem, as shown in  FIG. 4 , a protruded part in an axial direction may be provided at a center portion of the bearing  130 .  
         [0011]     Recently miniaturization of a motor itself is strongly required as the length and size of an electronic apparatus such as a digital camera has been reduced. However, in the conventional stepping motor ( FIG. 4  and the above-mentioned reference), the size of the motor cannot be sufficiently reduced.  
         [0012]     In other words, in the conventional stepping motor  100  in  FIG. 4 , for example, whose outer diameter is about φ8 mm, the length “E2” of the bearing holder  140  is set to be larger than the length “D2” of the bearing  130  that is designed in consideration of securing its strength, and the length “E2” is set to be sufficiently small (about ⅕) in comparison with the length “H2” of the stator  120 . However, for example, when the outer diameter of the stepping motor  100  is set to be about φ6 mm and, as a result, when the length “H2” of the stator  120  is modified to be a shorter length “H2′”, the length “E2” of the bearing holder  140  is required to be shorter but may not be sufficiently smaller in comparison with the length “H2′” (&lt;H 2 ) of the stator  120 . This is because, as described above, the length “E2” of the bearing holder  140  is required to be at least larger than the length “D2” of the bearing  130  which designed in consideration of securing the strength of the bearing  130  itself. As a result, the total length of the motor cannot be shorter (smaller) and thus the bearing holder  140  causes a trouble when the stepping motor  100  is mounted on a device such as a digital camera. Further, as shown in  FIG. 4 , formation of the protruded part at the center portion of the bearing  130  obstructs the miniaturization of the stepping motor.  
         [0013]     Further, as shown in the stepping motor described in the above-mentioned reference, in the case that the motor is structured such that the relationship of “A2&lt;C2&lt;B2” is satisfied to reduce the damage of the motor in  FIG. 4 , when the outer diameter of the stepping motor is set to be, for example, about φ6 mm, the length “E2” of the bearing holder ( 140  in  FIG. 4 ) cannot be sufficiently reduced as similarly to the stepping motor  100 , and thus the miniaturization of a stepping motor cannot be sufficiently attained.  
       SUMMARY OF THE INVENTION  
       [0014]     An object of the present invention is to reduce the size of a motor, while maintaining a sufficient strength of a bearing.  
         [0015]     In view of the problems described above, the present invention may advantageously provide a motor which is capable of reducing its size while securing a sufficient strength of the bearing.  
         [0016]     In order to solve the above-mentioned problems, the present invention provides a motor including (1) a rotor having a permanent magnet which is fixed to a rotor shaft, (2) a stator having a rotor insertion hole and an inner periphery, where the inner periphery of the stator is oppositely disposed to the permanent magnet of the rotor and where the rotor insertion hole has a prescribed space and the rotor is inserted into the rotor insertion hole, (3) a bearing which supports one end of the rotor shaft, and (4) a bearing holder having a bearing insertion hole into which the bearing is inserted. In the motor, when an outer diameter of the permanent magnet of the rotor is set to be “A”, an inner diameter of the bearing insertion hole of the bearing holder is set to be “B”, and an inner diameter of the rotor insertion hole of the stator is set to be “C”, a relationship of “A&lt;B&lt;C” is satisfied.  
         [0017]     According to this invention, in a motor which includes a rotor, a stator, a bearing and a bearing holder, an inner diameter of a bearing insertion hole provided in the bearing holder is set to be larger than an outer diameter of a permanent magnet of the rotor and set to be smaller than an inner diameter of a rotor insertion hole provided in the stator.  
         [0018]     In the motor in accordance with the present invention, the inner diameter “B” of the bearing insertion hole, i.e., the outer diameter “B” of the bearing is set to be smaller than the inner diameter “C” of the rotor insertion hole and thus the bearing is capable of protruding into the rotor insertion hole. When the bearing is capable of protruding into the rotor insertion hole, the length in an axial direction of the bearing holder (protruded portion on the rear side of the stator) can be reduced while the length in the axial direction of the bearing remains unchanged. In addition, even when the bearing is protruded into the rotor insertion hole, since the relationship of “B&lt;C” is satisfied, the bearing is prevented from abutting with the stator (specifically, the pole teeth).  
         [0019]     Accordingly, downsizing of the motor itself can be attained while considering to secure a sufficient strength of the bearing and to reduce possibility of the motor damage.  
         [0020]     In accordance with the present invention, it is required that the relationship of “A&lt;B&lt;C” is satisfied but it is not required that the bearing is actually protruded into the rotor insertion hole. Further, in accordance with an embodiment of the present invention, the outer diameter “A” of the permanent magnet is the largest outer diameter of the permanent magnet of the rotor, the inner diameter “B” of the bearing insertion hole is the smallest inner diameter of the bearing insertion hole of the bearing holder, and the inner diameter “C” of the rotor insertion hole of the stator is the smallest inner diameter of the rotor insertion hole, specifically, the smallest inner diameter of the inner circumference of the pole teeth which structures the stator.  
         [0021]     In accordance with an embodiment of the present invention, a part of the bearing is protruded on the rotor insertion hole side from the bearing holder.  
         [0022]     According to this embodiment of the present invention, a part of the bearing is protruded on the rotor insertion hole side from the bearing holder. Therefore, the length of the bearing holder can be reduced while the length of the bearing remains as it is, and thus further downsizing of the motor can be attained while securing a sufficient strength of the bearing.  
         [0023]     In other words, according to this embodiment, the length of the bearing holder can be made smaller by permitting the bearing to protrude into the rotor insertion hole and thus the length of the motor can be also made smaller. Further, according to this embodiment having the above-mentioned structure, the protruded bearing does not abut with the stator and the function as a bearing is not damaged while the strength as a bearing is secured. Further, according to the present invention, even when the bearing holder is made of a blank material such as a sintered body which is not provided with elasticity or plasticity and thus which is not deformable, the length in the axial direction of the bearing holder can be shortened while the length of the bearing remains unchanged. Specifically, the bearing may be preferably structured of one piece of a circular plate-shaped member which includes a side circumferential face, a first flat face, and a second flat face, the two flat faces sandwiching the side circumferential face. The side circumferential face of the bearing is formed with a slide face for the bearing insertion hole of the bearing holder and a recessed part for receiving a steel ball is formed in the first flat face. The second flat face is used as an abutting face with a flat spring for applying pressurization to the bearing so that the first flat face of the bearing is urged to protrude to the rotor insertion hole side by the flat spring. When the bearing is structured as described above, where one piece of a circular plate-shaped member can be used as the bearing, for example, the bearing does not need to be structured such that a center portion of one face of the bearing is protruded and a recessed part for receiving a steel ball is formed in the protruded center portion as shown in  FIG. 4 . As such, the bearing is formed with a simple structure and thus the strength as a bearing is secured.  
         [0024]     In accordance with an embodiment of the present invention, the bearing insertion hole provided in the bearing holder is formed as a hole for inserting the rotor into the rotor insertion hole of the stator.  
         [0025]     According to this embodiment, since the bearing insertion hole provided in the bearing holder is used as a hole (entrance) through which the rotor is inserted to the inside of the stator, the whole length of the motor can be shortened.  
         [0026]     In other words, according to this embodiment, the bearing holder can be shortened, and thus the whole length of the motor can be also shortened. Furthermore, even when the bearing holder is shortened, the function of bearing is sufficiently performed while strength is maintained.  
         [0027]     In the conventional PM type stepping motor  100  (see  FIG. 4 ), an inner diameter “B2” of the bearing insertion hole  105  of the bearing holder  140  is set to be equal to an inner diameter “C 2 ” of the rotor insertion hole  103  of the stator  120  from a viewpoint of simplification of manufacturing (assembling) step. Therefore, at the time of assembling a motor, when the rotor  110  is inserted into the stator  120 , the permanent magnet  102  may come into contact with the stator  120  (especially, with the pole teeth) to cause a motor damage. However, according to the present invention, for example, in  FIG. 4 , since the bearing insertion hole  105  whose inner diameter is smaller than the rotor insertion hole  103  of the stator  120  is used as a hole for inserting the rotor  110 , the rotor  110  is inserted into the rotor insertion hole  103  in the state where the center of rotor shaft  101  is accurately coincided with the center of the rotor insertion hole  103  and thus the rotor shaft  101  of the rotor  110  is prevented from being eccentrically inserted into the rotor insertion hole  103 . Accordingly, possibility of the motor damage can be reduced.  
         [0028]     Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a cross-sectional view showing a mechanical structure of a PM type stepping motor in accordance with an embodiment of the present invention.  
         [0030]      FIG. 2  is an enlarged explanatory view showing a portion around a bearing in the PM type stepping motor shown in  FIG. 1 .  
         [0031]      FIG. 3  is an exploded perspective view for explaining a method for assembling a PM type stepping motor in accordance with an embodiment of the present invention.  
         [0032]      FIG. 4  is a cross-sectional view showing a conventional structure of a PM type stepping motor provided with pole teeth.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     An embodiment of the present invention will be described below with reference to the accompanying drawings.  
         [0034]      FIG. 1  is a cross-sectional view showing a mechanical structure of a PM type stepping motor  1  in accordance with an embodiment of the present invention. The PM type stepping motor  1  is mounted, for example, on an electronic apparatus such as a digital camera, a digital video camera, an FDD, or an ODD.  
         [0035]     In  FIG. 1 , the PM type stepping motor  1  includes a rotor  10  provided with a permanent magnet  12  which is fixed to a rotor shaft  11 , a stator  20  provided with a rotor insertion hole  13  into which the rotor  10  is inserted, a bearing  30  supporting a bottom end of the rotor shaft  11  through a steel ball  14 , and a bearing holder  40  provided with a bearing insertion hole  15  for supporting the bearing  30  so as to be displaceable in an axial direction “L” of the rotor shaft  11 . A flat spring  16  for applying pressurization in the axial direction “L” to the rotor  10  is abutted with an under face of the bearing  30 .  
         [0036]     In the stator  20 , a first annular bobbin  22 A around which a coil  21  is wound and a second annular bobbin  22 B around which another coil  21  is wound are disposed so as to be superposed each other in the axial direction “L” of the rotor shaft  11 . An inner ring-shaped stator core  23 A and an outer ring-shaped stator core  24 A are disposed on both sides of the first bobbin  22 A in the axial direction “L” of the rotor shaft  11  in an superposed manner. Further, an inner ring-shaped stator core  23 B and an outer ring-shaped stator core  24 B are disposed on both sides of the second bobbin  22 B in the axial direction “L” of the rotor shaft  11  in an superposed manner. A plurality of pole teeth  25 A of the inner stator core  23 A and a plurality of pole teeth  26 A of the outer stator core  24 A are disposed on the inner peripheral face of the first bobbin  22 A such that respective pole teeth  25 A are alternately disposed with respective pole teeth  26 A in a circumferential direction. Further, a plurality of pole teeth  25 B of the inner stator core  23 B and a plurality of pole teeth  26 B of the outer stator core  24 B are disposed on the inner peripheral face of the second bobbin  22 B such that respective pole teeth  25 B are alternately disposed with respective pole teeth  26 B in a circumferential direction. In accordance with an embodiment, the first bobbin  22 A and the second bobbin  22 B are made of a resin member, and the inner stator cores  23 A,  23 B and the outer stator cores  24 A,  24 B are made of a magnetic metal member.  
         [0037]     As described above, the stator  20  is structured so as to have the rotor insertion hole  13  into which the rotor  10  is inserted. A base end side of the rotor  10  is disposed on an inner side of the rotor insertion hole  13  coaxially. A permanent magnet  12  is fixed to the rotor shaft  11  on the base end side, i.e., a rear side of the rotor  10 . The permanent magnet  12  is disposed so as to face the pole teeth  25 A,  26 A,  25 B and  26 B of the stator  20  with a predetermined space.  
         [0038]     A U-shaped frame (metal frame)  17  is fixed to a front end face of the outer stator core  24 A. The rotor shaft  11  of the rotor  10  is supported by a thrust bearing  19  that is fixed to a bent portion on the front side of the frame  17 . In other words, the front end of the rotor shaft  11  of the rotor  10  is pivotally supported by the frame  17 . A lead screw part  11 A is formed on the outer periphery of a portion of the rotor shaft  11  which protrudes on the frame  17  side. A screw part of a head member in an electronic apparatus such as a digital camera (not shown) to which this motor is mounted is threadedly engaged with the lead screw part  11 A. When the lead screw part  11 A is rotated, a head section arranged in the electronic apparatus on which this motor is mounted is vertically moved in the axial direction “L” of the rotor shaft  11  in  FIG. 1 .  
         [0039]     The shaft end  18  on the rear side in the axial direction “L” of the rotor shaft  11  of the rotor  10  is supported by a bearing  30  through a steel ball  14 . The bearing  30  is formed in a circular plate shape with one diameter in the axial direction “L” of the rotor shaft  11 . A front face of the bearing  30  is provided with a recessed part  30 A which is formed with a conical recessed face for receiving the steel ball  14 . The steel ball  14  is held between a recessed part  18 A formed of a conical recessed face in the shaft end portion  18  and the recessed part  30 A formed of the conical recessed face in the bearing  30 . Specifically, the bearing  30  is structured of one piece of a circular plate-shaped member having a side circumferential face for abutting with, and sliding on, the bearing insertion hole  15  of the bearing holder  40 , and two upper and lower flat faces, one face at each end of the side circumferential face of the bearing  30  in the axial direction “L” of the rotor shaft  11 . The side circumferential face of the bearing  30 , formed of one piece of a circular plate-shaped member, is formed as a sliding face for the bearing insertion hole  15  of the bearing holder  40 . The recessed part  30 A, for receiving the steel ball  14 , is formed on one of the two flat faces, i.e., the upper flat face in  FIG. 2 . Further, the other of the two flat faces, i.e., the lower flat face in  FIG. 2  is formed as an abutting face with the flat spring  16  which applies pressurization to the bearing  30 . The bearing  30  is arranged such that the upper face in  FIG. 2  is protruded on the rotor insertion hole  13  side.  
         [0040]     As described above, the bearing holder  40 , which is provided with the bearing insertion hole  15  and made of a sintered body, is disposed under the stator  20 . The bearing  30  is mounted in the inside of the bearing insertion hole  15  in a state that the bearing  30  can be displaced in the axial direction “L” of the rotor shaft  11 .  
         [0041]     In accordance with an embodiment, an inside diameter “B1” of the bearing insertion hole  15  formed in the bearing holder  40  in the PM type stepping motor  1  is set to be larger than an outer diameter “A1” of the rotor  10 . In addition, both the outer diameter “A1” of the rotor  10  and the inside diameter “B1” are set to be smaller than the inside diameter “C1” of the rotor insertion hole  13  formed in the stator  20 . Further, the upper flat face of the bearing  30  protrudes from the upper end (end of the rotor  10  side) of the bearing holder  40  by an amount of “F1” and thus the bearing  30  protrudes on the rotor insertion hole  13  side in the stator  20 . These dimensions will be described in detail below with reference to  FIG. 2 .  
         [0042]      FIG. 2  is an enlarged explanatory view showing a portion around the bearing  30  in the PM type stepping motor  1  shown in  FIG. 1 .  
         [0043]     As shown in  FIG. 2 , in the PM type stepping motor  1 , the smallest inside diameter “B1” of the bearing insertion hole  15  is the same size as the largest outer diameter “B1” of the circular plate-shaped bearing  30 . The diameter “B1” is set to be smaller than the smallest inside diameter “C1” of the rotor insertion hole  13 , and the bearing  30  protrudes into the rotor insertion hole  13 . In this embodiment, the pole teeth  25 A,  26 A,  25 B, and  26 B of the stator  20  are disposed so as to face the permanent magnet  12 . Therefore, the inside diameter formed by these pole teeth  25 A,  26 A,  25 B, and  26 B corresponds to the above-mentioned smallest inside diameter “C1” of the rotor insertion hole  13 . As described above, this embodiment is structured such that the outer diameter “B1” of the circular plate-shaped bearing  30  is set to be smaller than the inside diameter “C1” of the rotor insertion hole  13 , and the bearing  30  protrudes into the rotor insertion hole  13 . Therefore, even when the length “D1” of the bearing  30  is equal to that of the conventional bearing (for example, even when the length “D1” is equal to the length “D2” shown in  FIG. 4 ), the length “E1” of the bearing holder  40  can be made smaller (the length “E1” can be made smaller than the length “E2” shown in  FIG. 4 ). Accordingly, in the case that the outer diameter of the PM type stepping motor  1  is set to be, for example, about φ6 mm, even when the length “E1” of the bearing holder  40  is also set to be relatively sufficiently smaller in comparison with the length of the stator  20 , the length “D1” of the bearing  30  can be secured. Thus the total length of the motor can be made shorter (smaller) to cause to be capable of being mounted on a device such as a digital camera.  
         [0044]     Further, even when the bearing  30  protrudes into the rotor insertion hole  13 , the outer diameter “B1” of the bearing  30  is smaller than the inside diameter “C1” of the rotor insertion hole  13 . Therefore, the bearing  30  is not brought into contact with the stator  20  (especially, not contact with the pole teeth  25 B and  26 B).  
         [0045]     As described above, in the PM type stepping motor  1  in accordance with an embodiment of the present invention, the bearing  30  is structured as a circular plate-shaped bearing with one diameter in the axial direction of the rotor shaft  11 . Further, the outer diameter “B1” of the bearing  30  is set to be smaller than the inside diameter “C1” of the rotor insertion hole  13  such that the circular plate-shaped bearing  30 , with only one outer diameter along the axial direction, is capable of protruding into the rotor insertion hole  13 . Therefore, the strength of the bearing  30  is sufficiently secured, the possibility of motor damage is reduced, and the size of the motor can be reduced.  
         [0046]      FIG. 3  is an exploded perspective view for explaining a method for assembling a PM type stepping motor  1  in accordance with an embodiment of the present invention.  FIG. 3  is a view for describing an assembling method of the bearing  30  and the like in the PM type stepping motor  1 . The frame  17 , on which the thrust bearing  19  is mounted, is previously fixed to the front end face of the outer stator core  24 A.  
         [0047]     In  FIG. 3 , firstly, the bearing holder  40  is attached to the under face of the outer stator core  24 B. More specifically, four protruded parts  51  for welding are formed on the under face of the outer stator core  24 B, and the bearing holder  40  is positioned and abutted with the protruded parts  51 . After that, an electric current is supplied to the protruded parts  51  to perform spot-welding and the bearing holder  40  is fixed to the outer stator core  24 B.  
         [0048]     Next, the bearing insertion hole  15  of the bearing holder  40  is used as a hole (entrance) for inserting the rotor  10  (not shown in  FIG. 3  but see  FIG. 1 ). More specifically, the rotor  10  is inserted from the bearing insertion hole  15  and its front end is engaged with the thrust bearing  19  (see  FIG. 1 ).  
         [0049]     In the PM type stepping motor  1  in accordance with an embodiment of the present embodiment, the inside diameter “B1” of the bearing insertion hole  15  is set to be smaller than the inside diameter “C1” of the rotor insertion hole  13  of the outer stator core  24 B. Therefore, the bearing holder  40  can be made smaller while retaining its strength. Thus, the total length of the motor can be shortened. Further, when the rotor  10  is inserted into the stator  20 , the rotor  10  can be inserted in a state where the center of the rotor shaft  11  accurately coincides with the center of the rotor insertion hole  13 . Thus a situation is prevented where the rotor shaft  11  is inserted into the stator  20  in an eccentrically shifted manner. Therefore, possibility of the motor damage is reduced.  
         [0050]     After the rotor  10  has been inserted into the stator  20 , the bearing  30  is inserted into the bearing insertion hole  15  of the bearing holder  40 . At this time, the steel ball  14  is held between the recessed part  18 A (not shown in  FIG. 3 ; see  FIG. 1 ), formed at the shaft end  18  of the rotor shaft  11 , and the recessed part  30 A, formed in the bearing  30 . Finally, a flat spring pressing cap member  60 , having the flat spring  16 , is attached to the bearing holder  40 . More specifically, four pawl parts  60 A which are extended from its outer peripheral edge part to the bearing holder  40  side are formed in the flat spring pressing cap member  60 . The flat spring pressing cap member  60  is attached to the bearing holder  40  by these pawl parts  60 A engaging with the outer peripheral edge part of the bearing holder  40 . The under face (rear face) of the bearing  30  is urged by the flat spring  60  to prevent from generating a noise caused by shaking of the rotor shaft  11 .  
         [0051]     In accordance with an embodiment of the present invention, the bearing holder  40  is made of a member such as a sintered body. However, the bearing holder  40  is not so limited, and may be made of, for example, resin or the like.  
         [0052]     A motor in accordance with the present invention is effective as a motor which is required to retain the strength of the bearing and reduce its size.  
         [0053]     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.  
         [0054]     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.