JP2014099961A - Electric motor and ventilation fan - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric motor capable of suppressing a clearance between a rear bearing and a rear bearing holding part and suppressing generation of abnormal sound.SOLUTION: The electric motor comprises: a metallic frame with which a front bearing holding part is formed in the center of a front end plate and a frame flange is formed in the outer circumference of a rear end of a cylindrical trunk; a stator which is fitted into the cylindrical trunk of the frame; a resin bracket with which a rear bearing holding part is formed in the center and an outer cylinder part and a through hole are formed in the outer circumference; a rotor of which the front bearing is held by the front bearing holding part of the frame, the rear bearing is held by the rear bearing holding part of the bracket and which is disposed within the stator; and a metallic cover with which a cover flange coupled with the frame flange is formed in the outer circumference of the front end thereof and the cylindrical trunk is externally fitted to an outer cylinder of the bracket and coupled to the frame. In the rear bearing holding part of the resin bracket, a ring which is made of a porous metal material and to which the rear bearing is fitted is insert-molded at an inner circumferential side.

Description

  The present invention relates to an electric motor used for a fan, a ventilation fan, or the like.

  Conventionally, a metal frame in which a front bearing holding part is formed at the center of the front end plate and a frame flange is formed on the outer peripheral part of the rear end of the cylindrical body, and a coil is wound and fitted into the cylindrical body of the frame. A stator, a pin erected on the rear side of the stator and entangled with the end of the coil, a rear bearing holding portion formed in the center, and an outer cylinder portion and a through hole formed in the outer peripheral portion. A resin-made bracket in which the outer cylinder portion is press-fitted into the cylindrical body portion of the frame and the pin is inserted into the through-hole, a moisture-proof seal that closes the through-hole through which the pin is inserted, and a front bearing is the frame The rear bearing held by the front bearing holding portion of the bracket is held by the rear bearing holding portion of the bracket and disposed in the stator, and the electronic components constituting the power supply circuit and the drive circuit are mounted on the rear side of the bracket. Placed A circuit board that is conductively connected to the pin, and a cover flange that is fastened to the frame flange is formed on the outer periphery of the front end, and a cylindrical body portion is externally fitted to the outer cylindrical portion of the bracket, and is fastened to the frame. An electric motor is disclosed that includes a metal cover that contacts and dissipates heat from the electronic component (see, for example, Patent Document 1).

JP 2011-066980 A

  However, according to the above conventional technique, since the rear bearing holding portion of the bracket that holds the rear bearing is made of resin, when the motor becomes high temperature due to high load operation, the difference between the linear expansion coefficient of the resin and the metal causes the rear bearing holding portion. There is a problem that a gap is formed between the bearing and the rear bearing holding portion, and abnormal noise is likely to occur due to deterioration of the rear bearing holding portion due to creep or fretting and vibration of the rotor shaft.

  If a thermosetting resin such as BMC is used as the material for the bracket, the linear expansion coefficient is close to that of the metal and is not easily deformed by heat, the molding cycle time is longer than that of thermoplastic resin. There is a problem that the processing cost increases. Further, when a thermosetting resin such as BMC is used, it is difficult to reduce the thickness of a bracket having a complicated shape with unevenness, and there is a problem that the size of the electric motor increases due to the large size of the bracket.

  In addition, since thermosetting resins such as BMC are large due to poor moldability, the distance between the rotor and the rotational speed detection means (Hall IC) of the drive circuit is increased, and the position detection accuracy of the rotor is deteriorated. There is a problem that a deviation occurs between the induced voltage phase of the electric motor and the motor phase current phase generated from the drive circuit, the efficiency of the electric motor is deteriorated, and abnormal noise is generated.

  The present invention has been made in view of the above, and can suppress the gap between the rear bearing and the rear bearing holding portion, is low-cost and small, has high rotor position detection accuracy, and generates abnormal noise. It aims at obtaining the electric motor which can suppress this.

  In order to solve the above-described problems and achieve the object, the present invention includes a metal frame in which a front bearing holding portion is formed in the center of the front end plate and a frame flange is formed in the rear end outer peripheral portion of the cylindrical body portion. A stator in which a coil is wound and fitted in the cylindrical body portion of the frame, a resin-made bracket in which a rear bearing holding portion is formed in the center and an outer cylinder portion and a through hole are formed in the outer peripheral portion; A bracket in which a bearing is held in a front bearing holding portion of the frame and a rear bearing is held in a rear bearing holding portion of the bracket and disposed in the stator, and an electronic component constituting a power supply circuit and a drive circuit is mounted on the bracket A metal circuit board disposed on the rear side, a cover flange that is fastened to the frame flange is formed on the outer periphery of the front end, and a cylindrical body portion is externally fitted to the outer cylindrical portion of the bracket and fastened to the frame Made Comprising a cover, a bearing holder after the resin bracket, porous metal material made of a ring the rear bearing is fitted to the inner peripheral side, characterized in that the insert molded.

  According to the present invention, it is possible to obtain an electric motor that can suppress a gap between the rear bearing and the rear bearing holding portion, is small in cost, has high rotor position detection accuracy, and can suppress occurrence of abnormal noise. There is an effect that it is.

FIG. 1 is a partial sectional view showing an embodiment of an electric motor according to the present invention. FIG. 2 is an enlarged view of part A in FIG. FIG. 3 is a rear view showing a state in which the bracket is assembled in the frame. FIG. 4 is a rear view of the circuit board. FIG. 5A is a front view of the bracket. FIG. 5B is an enlarged view of a portion B in FIG. FIG. 5C is a view on arrow C in FIG. FIG. 6 is a circuit block diagram of the electric motor according to the embodiment. FIG. 7 is a rear view of the stator. FIG. 8 is an enlarged sectional view of a rear bearing holding portion of the bracket according to the first embodiment. FIG. 9 is a cross-sectional view of a ventilation fan equipped with the electric motor of the embodiment. FIG. 10 is an enlarged cross-sectional view of a rear bearing holding portion of the bracket according to the second embodiment. FIG. 11 is an enlarged sectional view of a rear bearing holding portion of the bracket according to the third embodiment.

  Embodiments of an electric motor according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
1 is a partial cross-sectional view showing an embodiment of an electric motor according to the present invention, FIG. 2 is an enlarged view of a part A in FIG. 1, and FIG. 3 is a rear view showing a state in which a bracket is incorporated in a frame. 4 is a rear view of the circuit board, FIG. 5-1 is a front view of the bracket, FIG. 5-2 is an enlarged view of a portion B in FIG. 5-1, and FIG. 3 is a view in the direction of arrow C in FIG. 5-2, FIG. 6 is a circuit block diagram of the electric motor of the embodiment, FIG. 7 is a rear view of the stator, and FIG. 8 is the first embodiment. It is an expanded sectional view of the rear bearing holding part of the bracket.

  As shown in FIGS. 1 and 2, the electric motor 90 of the embodiment has a front bearing holding portion 1a formed at the center of the front end plate 1t, and a frame flange 1b formed at the rear end outer peripheral portion of the cylindrical body portion 1d. A metal frame 1 formed in a cap shape as a whole, an iron core 2b on which an insulator 2d is mounted and a coil 2a is wound, and a stator 2 fitted in a cylindrical body 1d of the frame 1, The shaft 3a is fitted, the front bearing 3b and the rear bearing 3c are mounted, the front bearing 3b is held by the front bearing holding portion 1a of the frame 1, and the rotor 3 disposed in the stator 2 is held, and the rear bearing 3c is held in the center. The rear bearing holding portion 4a is formed, the outer cylindrical portion 4b is formed on the outer periphery, and the outer cylindrical portion 4b is press-fitted into the cylindrical barrel portion 1d of the frame 1 from the rear of the stator 2; It is equipped with.

  A bracket flange 4f is provided on the outer peripheral portion of the outer cylindrical portion 4b of the bracket 4, and the bracket flange 4f is sandwiched between a frame flange 1b and a cover flange 8b described later, thereby positioning the bracket 4 in the axial direction. By sandwiching and fixing the bracket flange 4f between the frame flange 1b and the cover flange 8b, it is possible to prevent the bracket 4 press-fitted into the frame 1 from being displaced in the axial direction due to a difference in thermal expansion coefficient between resin and metal. Can do.

  The outer diameter of the outer cylindrical portion 4 b of the bracket 4 is formed to be a size that is a squeeze to the inner diameter of the frame 1. Moreover, the outer peripheral surface of the outer cylinder part 4b of the bracket 4 is in contact with the inner peripheral surface of the frame 1 over the entire periphery. As described above, the center of the frame 1 and the center of the bracket 4 can be precisely aligned. The front bearing 3 b is held by the front bearing holding portion 1 a of the frame 1, and the rear bearing 3 c is held by the rear bearing holding portion 4 a of the bracket 4.

On the outer edge portion of the bracket 4 (inside the outer cylinder portion 4b), four axial through holes 4c are formed. The through hole 4c, a pin 2c erected on the rear side of the outer flange 2d ₁ of the insulator 2d mounted on the iron core 2b of the stator 2 is inserted. The characteristic structure of the bracket 4 will be described later.

  The through-hole 4c is a tapered hole so that the inner diameter on the stator 2 side (motor section 11 side) is large and the inner diameter on the circuit board 5 side (circuit section 12 side) is small so that the gap with the pin 2c is small. After the pin 2c is inserted into the through hole 4c, a quick-drying moisture-proof seal 6 is provided so as to close the gap with the pin 2c in order to prevent air from entering from the motor unit 11 side to the circuit unit 12 side.

  The circuit board 5 is attached (arranged) on the circuit part 12 side of the bracket 4 so that the pins 2c are inserted, and the pins 2c and the circuit board 5 are conductively connected by solder 2e or the like. As shown in FIGS. 1, 4 and 6, the circuit board 5 has electronic components 7 such as a Hall IC 7b for detecting the position of the rotor 3, a drive circuit 7c for rotating the rotor 3, a microcomputer 7d, and a power supply circuit 7e. Has been implemented.

  As shown in FIG. 1, aluminum radiation fins 9 for radiating heat generated from the electronic component 7 are attached to the circuit board 5. A heat radiating sheet 9a having a cushioning property and an insulating sheet 9b having an electrical insulating property are bonded to the heat radiating fins 9, and the insulating sheet 9b is pressed by a rear end plate 8t of a metal cover 8 that covers the circuit board 5, Heat is radiated from the surface of the cover 8.

  The cylindrical body portion 8d of the cover 8 is fitted on the outer cylinder portion 4b of the bracket 4, and the cover flange 8b formed on the outer peripheral portion of the front end of the cover 8 is overlapped with the frame flange 1b via the bracket flange 4f. The frame 1 and the cover 8 are fixed by inserting (press-fitting) the cover protrusion 8c into the frame hole 1c of 1 and bending the cover protrusion 8c.

  As shown in FIG. 3, the frame flange 1b, the bracket flange 4f, and the cover flange 8b are provided with four fastening holes 10. The fastening holes 10 are used to screw the electric motor 90 to a product such as a ventilation fan.

  Since the bracket 4 is made of resin such as PPS and has an insulating property, a creeping distance in the radial direction between the coil 2a, the pin 2c and the circuit board 5, the frame 1 and the cover 8 can be secured. Further, the space between the coil 2a and the bracket 4 and the space between the circuit board 5 and the bracket 4 are unnecessary (may be brought into contact with each other), and the axial dimension of the electric motor 90 can be reduced. .

  Since the bracket 4 is positioned in the axial direction so that the bracket flange 4f is sandwiched between the frame flange 1b and the cover flange 8b, the bracket 4 does not tilt with respect to the axis. Further, since the bracket 4 is press-fitted into the frame 1, the degree of coaxiality between the front bearing holding portion 1a of the frame 1 and the rear bearing holding portion 4a of the bracket 4 is high, and the shaft 3a and the rotor 3 can be assembled with high accuracy. Can do.

  By sandwiching the bracket flange 4f between the frame flange 1b and the cover flange 8b, the bracket 4 can be easily fixed, and the stress of the transportation vibration in the axial direction or the drop impact is applied to the circuit board 5 or the circuit board 5 and the pin. It can prevent joining to the junction part of 2c, and can maintain the quality of the junction part of the circuit board 5, the circuit board 5, and the pin 2c in a favorable state.

  Since the through hole 4c is a tapered hole having a large inner diameter on the motor unit 11 side, a space for tying the end of the coil 2a to the pin 2c is secured, and when the bracket 4 is press-fitted into the frame 1, There is no fear that the connected terminal will break.

  Since the bracket 4 is press-fitted into the frame 1 and the moisture-proof seal 6 is provided in the through hole 4c so as to close the gap with the pin 2c, the motor part 11 and the circuit part 12 can be separated in an airtight manner. And adverse effects such as moisture and condensation in the circuit section 12 can be avoided. Since the moisture resistance performance of the circuit unit 12 is high, it is possible to reduce the working time and the number of processes for molding and potting.

  Since the heat generated by the electronic component 7 is radiated from the entire surface of the cover 8 through the radiation fins 9, the radiation sheet 9a, and the insulating sheet 9b, the temperature rise of the electronic component 7 can be suppressed. The cover protrusion 8c is press-fitted into the frame hole 1c of the frame 1, and the cover protrusion 8c is bent to fix the frame 1 and the cover 8, so that the frame 1 and the cover 8 are securely conductively connected, and the electric motor 90 Can be provided anywhere on the frame 1 and the cover 8, and the assembly workability of the electric motor 90 is good. Further, a fixing screw for the frame 1 and the cover 8 is not necessary.

  Further, even when the electric motor 90 is abnormal (failure due to a temperature rise or the like of the electronic component 7), the electronic component 7 or the like is covered with the metal cover 8, so that it can be safely stopped.

  As shown in FIG. 6, a commercial AC power supply 7f is input to the circuit unit 12 from the outside, converted into a DC voltage by the power supply circuit 7e, and a voltage corresponding to the element is supplied to each element. The drive circuit 7c generates an AC voltage so that a current in a predetermined direction flows through the coil 2a wound around the stator 2 through the pin 2c, and the rotor 3 is rotated by the current flowing through the coil 2a.

  The microcomputer 7d detects the induced voltage phase of the electric motor 90 based on the signal from the Hall IC 7b, and controls the induced voltage phase and the motor phase current phase generated by the drive circuit 7c to be in phase. By making the induced voltage phase and the motor phase current phase the same phase, the efficiency of the electric motor 90 can be maximized.

  The drive circuit 7c performs sine wave drive so that the motor phase current becomes a sine wave. By performing sine wave driving, vibration of the electric motor 90 is reduced, and even when the motor 90 is used as a fan motor such as a duct ventilation fan, it is not necessary to provide a vibration-proof structure in the product, and the product can be produced at low cost.

  Since the motor phase current output from the drive circuit 7c is controlled based on the output signal of the Hall IC 7b as the rotor position detecting means, if the relative position of the stator 2 and the Hall IC 7b deviates from the assumed position, A shift occurs between the induced voltage phase and the motor phase current phase, leading to deterioration in motor efficiency, and distortion occurs in the waveform of the motor phase current output from the drive circuit 7c, causing abnormal noise.

  As shown in FIG. 7, in the stator 2, a resin molded insulator 2d is mounted on an iron core 2b for the purpose of insulation from the coil 2a, and the coil 2a is wound around the insulator 2d. The terminal of the coil 2a is electrically connected to the pin 2c. A groove 2f is provided on the outer peripheral portion of the iron core 2b.

  As shown in FIGS. 5A to 5C, the bracket 4 is provided with a positioning projection 4h that fits in the groove 2f of the iron core 2b on the stator 2 side of the outer cylinder portion 4b. The tip of the positioning protrusion 4h has a tapered shape in order to improve the insertability into the groove 2f.

  As shown in FIG. 4, notches 5 a are provided at two locations on the outer edge of the circuit board 5. As shown in FIG. 3, a plurality of support bases 4 i that support the circuit board 5 are provided on the circuit part 12 side of the bracket 4. A screw hole 4j for fixing the circuit board 5 is provided in a part of the plurality of support bases 4i, and a board positioning protrusion 4k that fits into the notch 5a of the circuit board 5 is provided in the vicinity of the screw hole 4j. It has been. The groove 2f of the iron core 2b and the notch 5a of the circuit board 5 may be holes.

  By fitting the groove 2f of the iron core 2b of the stator 2 and the positioning projection 4h of the bracket 4 and fitting the board positioning projection 4k of the bracket 4 and the notch portion 5a of the circuit board 5, the stator 2 and the circuit board 5 are fitted. The position detection accuracy of the rotor 3 by the Hall IC 7b is improved, and the efficiency of the electric motor 90 is improved, by minimizing the positional deviation between the stator 2 and the Hall IC 7b mounted on the circuit board 5. Low noise is achieved.

  Next, a characteristic structure of the bracket 4 according to the first embodiment will be described with reference to FIGS. 1 and 8. The bracket 4 is molded into a thin and small shape by a thermoplastic resin such as PPS. On the inner peripheral side of the rear bearing holding portion 4a of the bracket 4, a short cylindrical metal ring 15 that fits and holds the rear bearing 3c (see FIG. 1) is insert-molded. The ring 15 is made of a porous metal material such as a sintered metal. The wall thickness t of the ring 15 is t = 0.8 to 2.0 mm. In order to improve the insertability of the rear bearing 3c, a chamfered portion 15a is formed in the front inner peripheral portion.

  If the wall thickness t of the metal ring 15 is t = 0.8 to 2.0 mm and a porous metal having a low compressive strength such as a sintered metal is used, the ring 15 is compressed by the molding pressure at the time of insert molding. It is deformed to follow the shape of the core of the molding die. Therefore, it is not necessary to manufacture the roundness and inner diameter of the ring 15 with high precision (if the core of the molding die is made with high precision, the accuracy of the ring 15 itself may be poor), and the ring 15 processing costs can be reduced. Further, since the clearance between the ring 15 and the core of the molding die can be increased, the insertability of the ring 15 at the time of insert molding is good.

  According to the electric motor 90 of the embodiment described above, the porous structure in which the rear bearing 3c is fitted to the inner peripheral side of the rear bearing holding portion 4a of the bracket 4 which is thinly molded with a thermoplastic resin such as PPS. Since the ring 15 made of a metal material is insert-molded, the gap generated between the rear bearing 3c and the rear bearing holding portion 4a (ring 15) can be suppressed, and the generation of abnormal noise can be suppressed. It is small and the position detection accuracy of the rotor 3 is high.

  FIG. 9 is a cross-sectional view of a ventilation fan equipped with the electric motor of the embodiment. As shown in FIG. 9, the electric motor 90 of the embodiment is mounted on the body 41 of the ventilation fan 100, and the blower fan 42 is attached to the shaft 3a. The body 41 is installed on the ceiling plate 43 and the grille 44 is attached to the body 41 from below.

  When the electric motor 90 is rotated and the blower fan 42 is rotated, an air flow indicated by an arrow in FIG. 9 is generated. In the electric motor 90, the circuit unit 12 and the motor unit 11 are partitioned by the bracket 4 (see FIG. 1), and the motor unit 11 is exposed to the air flow, but the circuit unit 12 is blocked from the air flow. Therefore, it can be used for ventilation in a high humidity atmosphere such as a bathroom. Moreover, since the electric motor 90 can be reduced in size, the ventilation fan 100 can be reduced in size and it is easy to install in the back of a ceiling.

  In addition, the electric motor 90 has a built-in power supply circuit 7e and a drive circuit 7c (see FIG. 6), so that AC power can be directly input to the electric motor 90, and there is no need to provide a space for mounting the circuit board on the ventilation fan 100. The body can be shared with the ventilation fan equipped with the AC motor.

  Furthermore, since the drive circuit 7c of the electric motor 90 performs sine wave drive, the distortion rate of the current flowing through the coil 2a is small and abnormal noise is unlikely to occur. Therefore, a noise reduction mechanism such as a floating structure is provided on the blower fan 42. There is no need to provide it, and the cost can be reduced. In addition, it is possible to share with the blower fan attached to the AC motor.

Embodiment 2. FIG.
FIG. 10 is an enlarged cross-sectional view of a rear bearing holding portion of the bracket according to the second embodiment. In insert molding, not only molding pressure at the time of resin molding of the bracket 4 but also contraction force due to post-contraction of the resin after molding is applied to the ring 15 (see FIG. 8). The contraction force due to the rear contraction is stronger on the rear side of the rear bearing holding part 4a close to the wall part of the bracket 4 that contracts in the radial direction than on the front side of the rear bearing holding part 4a that projects and opens in a cylindrical shape. . Therefore, there is a problem that the rear side of the ring 15 contracts in the radial direction.

The outer diameter of the ring 25 of the second embodiment is larger on the rear side than on the front side, and the wall thickness t ₂ on the rear side of the ring 25 is larger than the wall thickness t ₁ on the front side (t ₁ and t ₂ is in the range of 0.8 to 2.0 mm), the outer peripheral surface of the ring 25, the diameter of the rear side is a large conical surface. By thicker than the front wall thickness t ₁ of the wall thickness t ₂ of the rear side of the ring 25, it is possible to reduce the amount of shrinkage due to shrinkage after the rear side of the ring 25. In the ring 25, a chamfered portion 25a is formed on the front inner peripheral portion in order to improve the insertability of the rear bearing 3c.

Embodiment 3 FIG.
FIG. 11 is an enlarged sectional view of a rear bearing holding portion of the bracket according to the third embodiment. As shown in FIG. 11, the outer diameter of the ring 35 of the third embodiment, towards the rear than the front side have been increased, the thickness t ₂ of the large-diameter portion 35b of the rear side of the ring 35, the front side thicker than the thickness _{t 1 (t 1} and _{t 2} is in the range of 0.8 to 2.0 mm), the outer peripheral surface of the ring 35 has a stepped cylindrical surface. By thicker than the front wall thickness t ₁ of the wall thickness t ₂ of the large-diameter portion 36b of the rear side of the ring 35, it is possible to reduce the amount of shrinkage due to shrinkage after the rear side of the ring 35. The ring 35 has a chamfered portion 35a formed on the front inner peripheral portion in order to improve the insertability of the rear bearing 3c.

1 frame, 1a front bearing holding portion, 1b frame flange, 1c frame hole, 1d cylindrical body, 1t front end plate, 2 stator, 2a coil, 2b iron core, 2c pin, 2d insulator, 2d ₁ outer flange, 2e solder, 2f groove, 3 rotor, 3a shaft, 3b front bearing, 3c rear bearing, 4 bracket, 4a rear bearing holding part, 4b outer cylinder part, 4c through hole, 4f bracket flange, 4h positioning projection, 4i support base, 4j screw hole 4k board positioning protrusion, 5 circuit board, 5a notch, 6 moisture-proof seal, 7 electronic component, 7b Hall IC, 7c drive circuit, 7d microcomputer, 7e power circuit, 7f commercial AC power supply, 8 cover, 8b cover flange, 8c cover protrusion, 8d cylindrical body, 8t rear end plate, 9 heat radiating fin, 9a heat radiating sheet, 9b insulating sheet, 1 Fastening hole, 11 motor part, 12 circuit part, 15, 25, 35 ring, 15a, 25a, 35a chamfered part, 35b large diameter part, 41 body, 42 blower fan, 43 ceiling plate, 44 grille, 90 electric motor, 100 ventilator .

Claims (9)

A metal frame in which a front bearing holding portion is formed in the center of the front end plate and a frame flange is formed on the outer peripheral portion of the rear end of the cylindrical body portion;
A stator wound with a coil and fitted into the cylindrical body of the frame;
A resin-made bracket in which a rear bearing holding portion is formed in the center and an outer cylindrical portion and a through hole are formed in the outer peripheral portion;
A rotor in which a front bearing is held in a front bearing holding portion of the frame and a rear bearing is held in a rear bearing holding portion of the bracket and disposed in the stator;
A circuit board on which electronic components constituting a power supply circuit and a drive circuit are mounted and disposed on the rear side of the bracket;
A cover flange that is fastened to the frame flange is formed on the outer periphery of the front end, and a metal cover that is fastened to the frame by fitting a cylindrical body portion to the outer tube portion of the bracket, and
The electric motor characterized in that the rear bearing holding portion of the resin bracket is insert-molded with a ring made of a porous metal material into which the rear bearing is fitted on the inner peripheral side.   The electric motor according to claim 1, wherein a resin material of the bracket is a thermoplastic resin.   The electric motor according to claim 1, wherein the porous metal material of the ring is a sintered metal.   The electric motor according to claim 1, wherein a chamfered portion is formed on a front inner peripheral portion of the ring.   The electric motor according to claim 1, wherein the outer diameter of the ring is larger on the rear side than on the front side.   The electric motor according to claim 5, wherein an outer peripheral surface of the ring is a conical surface.   The electric motor according to claim 5, wherein an outer peripheral surface of the ring is a stepped cylindrical surface.   The electric motor according to claim 1, wherein a thickness of the ring is in a range of 0.7 mm to 2.0 mm.   A ventilation fan in which a blower fan is driven by the electric motor according to claim 1.