Motor

Abstract

A motor includes a stator and a rotor having magnets therein. The stator includes a stator core having a ring and a plurality of teeth extending from the ring; a plurality of coils wound on the plurality of teeth; and means for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hz (Hz) to 3500 Hz.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 581,762 filed on September 11, 2023 and U.S. Provisional Patent Application No. 63 / 467,454 filed on May 18, 2023, the entire contents of both provisional patent applications are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to motors, and more particularly to brushless DC electric motors. Background Art

[0004] The human ear perceives the loudness of sounds of different frequencies (Hz) at different loudness levels (phon). The human ear is susceptible to perceiving frequencies around 3,000 Hz. This is a phenomenon represented by the known equal loudness Fletcher-Munson curve. The natural frequency of an object is the frequency (Hz) at which the object tends to oscillate in the absence of a driving force. A vibrating object of a simple mass-spring system includes mass (kg) and stiffness (N / m). Stiffness is generally defined as the degree to which an object resists deformation in response to an applied force. The natural frequency of a mass-spring system is the frequency at which the system would oscillate if there were no driving force and no damping force. The natural frequency depends on both the mass of the object and the stiffness of the spring. Utility Model Content

[0005] In one aspect, the present disclosure provides a motor including a stator and a rotor having magnets therein. The stator includes a stator core having a ring and a plurality of teeth extending from the ring; a plurality of coils wound around the plurality of teeth; and a device for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz.

[0006] In other aspects, the present disclosure provides a motor comprising a stator and a rotor having a magnet therein. The stator comprises a stator core having a ring and a plurality of teeth extending from the ring; and a plurality of coils wound around the plurality of teeth. The motor comprises a device for adjusting a natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz. The device for adjusting is also configured to apply a compressive force to the ring of the stator core.

[0007] In other aspects, the present disclosure provides a motor including a stator and a rotor having magnets therein. The stator includes a stator core having a ring and a plurality of teeth extending from the ring; a plurality of coils wound around the plurality of teeth; and a first device for adjusting a natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz. The motor includes a second device for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hz to 3500 Hz, the second device for adjusting being configured to apply a compressive force to the ring of the stator core.

[0008] Other features and aspects of the present disclosure will become apparent by consideration of the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG1A is a reproduction of the Fletcher-Munson curves of equal loudness at various frequencies and sound pressure levels.

[0010] FIG. 1B is a cross-sectional view of a known brushless DC electric motor.

[0011] Figure 2 is an end view of a brushless DC electric motor including a material addition applied to a stator ring according to an embodiment of the present disclosure.

[0012] Figure 3 is an end view of a brushless DC electric motor including a material reduction portion removed from a stator ring according to an embodiment of the present disclosure.

[0013] Figure 4 is an end view of a brushless DC electric motor according to an embodiment of the present disclosure, wherein the stator includes circumferentially alternating rigid and flexible portions.

[0014] Figure 5 is an end view of a brushless DC electric motor according to an embodiment of the present disclosure wherein the stator includes teeth of increased thickness.

[0015] Figure 6 is an end view of a brushless DC electric motor including a trapezoidal material addition applied to a stator ring according to an embodiment of the present disclosure.

[0016] Figure 7 is an end view of a brushless DC electric motor including a rectangular material reduction portion removed from a stator ring according to an embodiment of the present disclosure.

[0017] Figure 8 is an end view of a brushless DC electric motor including a trapezoidal material reduction portion removed from a stator ring according to an embodiment of the present disclosure.

[0018] Fig.9A is an end view of a brushless DC electric motor including a ring surrounding a stator according to an embodiment of the present disclosure.

[0019] Fig. 9B is a stereoscopic view of a hose clamp that can be used to replace Fig.9A The ring surrounds the stator.

[0020] Other features and aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings. DETAILED DESCRIPTION

[0021] One consideration of the present disclosure is to reduce the human-perceptible sound produced when a motor resonates at its natural frequency. To this end, the mass and / or stiffness characteristics of the motor are adjusted to tune the motor's natural frequency away from frequencies to which the human ear is sensitive (e.g., about 2,500 Hz to about 3,500 Hz). In this way, even if the motor resonates at its natural frequency, its vibration is less perceptible to the human ear. Various arrangements for achieving this goal are described below.

[0022] FIG. 1A shows various equal loudness Fletcher-Munson curves. These curves are known in the field of acoustics and show equal loudness curves (in phons) over a range of sound pressure levels (in decibels (dB)) and frequencies (in Hertz (Hz)). The threshold Fletcher-Munson curve represents the lower threshold of human hearing. The 100phon Fletcher-Munson curve represents the threshold of human hearing, above which sounds are painful. The area between the threshold (i.e., 0phon) Fletcher-Munson curve and the 100phon Fletcher-Munson curve represents the hearing range of the human ear. Point A on the 100phon Fletcher-Munson curve shows that the human ear is most sensitive around 3,000 Hz.

[0023] FIG. 1B illustrates a cross-sectional view of a brushless DC electric motor 10 including a rotor 100 and a stator 200. The rotor 100 includes a rotor body 104 and a plurality of magnets 108 coupled to the rotor body 104. The illustrated rotor magnets 108 are arranged circumferentially around the rotor body 104 and may be magnetized alternately in the circumferential direction. The stator 200 includes a stator core 202 having a ring 204 and a plurality of teeth 208 extending radially inward from the ring 204. The stator 200 also includes a plurality of stator coils 212 wound around the teeth 208. The illustrated stator 200 is an outer stator configured for use with the inner rotor 100 in the motor 10. The ring 204 is annular and includes an inner surface 205 and an outer surface 206 opposite to the inner surface 205. Specifically, the outer surface 206 is radially outward relative to the inner surface 205. In the illustrated embodiment, the stator 200 is oriented about the longitudinal axis LA. The teeth 208 of the illustrated outer stator 200 extend inwardly from the inner surface 205 of the ring 204. In other words, the teeth 208 extend in a direction from the ring 204 toward the longitudinal axis LA. In the illustrated embodiment, the teeth 208 are oriented in a direction perpendicular to the longitudinal axis LA. However, inner stator motors (not shown) having teeth extending outwardly from the ring (i.e., the outer surface of the ring, away from the longitudinal axis LA) are well known. The stator teeth 208 are spaced apart from each other and are arranged circumferentially about the longitudinal axis LA. The stator teeth 208 each include a body portion 216 and a pair of end portions 220, which extend away from the body portion 216 and toward adjacent stator teeth 208 in a circumferential direction.

[0024] Rotor 100 and stator 200 may each be made of a single body (ie, one-piece rotor core, one-piece stator core) or multiple parts. In some cases, rotor 100 and / or stator 200 may include a plurality of laminations stacked one on another in an axial direction along longitudinal axis LA.

[0025] For comparison with the embodiments of the present application, some dimensions of the stator 200 are marked. As marked in FIG. 1B , the inner surface 205 defines an inner diameter D1 of the ring 204, and the outer surface 206 defines an outer diameter D2 of the ring 204. The ring 204 includes a substantially constant thickness T1 between the inner surface 205 and the outer surface 206 and around its circumference as measured in a radial direction relative to the longitudinal axis LA. The teeth 208 include a thickness T2 as measured in a direction tangential to the longitudinal axis LA. The teeth 208 include a length L1 as measured in a direction radially perpendicular to the longitudinal axis LA and between the ring 204 and the end portion 220.

[0026] Each of the embodiments described below is directed to providing a different arrangement of stators 300-600 to mitigate the perceived sound produced by the motor 10. Each stator 300-600 includes a sound mitigation feature 350-650 configured to adjust the natural frequency of the motor 10 away from frequencies to which the human ear is sensitive (e.g., about 2,500 Hz to about 3,500 Hz).

[0027] Figure 2 A motor 10a and a stator 300 including a sound reduction feature 350 are shown according to a first embodiment of the present disclosure. The stator 300 further includes a structure similar to the stator 200, wherein similar features are labeled with similar numbers in the "300" series figure labels. The sound reduction feature 350 in this first embodiment is a plurality of material addition portions 350 disposed on a ring 304. In the illustrated embodiment, the material addition portions 350 are positioned on an outer surface 306. The material addition portions 350 are formed so that the outer surface 306 is wavy (e.g., an oscillating surface). The material addition portions 350 are circumferentially located between adjacent teeth 308 of the stator 300. In other words, the material addition portions 350 are circumferentially offset from the teeth 308. However, other shapes and positions of the material addition portions 350 are also possible. For example, Figure 6 Another motor 10e and a stator 300a including a material addition portion 351 shaped as a trapezoid are shown. The material addition portion 351 is at least partially radially aligned with the teeth 308 and at least partially offset from the teeth 308. Figure 6 As illustrated, the number of material addition portions 351 (eg, four) may be different than the number of teeth 308 (eg, six).

[0028] The thickness T3 measured between the outer surface 306 and the inner diameter D1 through the material addition portion 350 is greater than the thickness T1 measured between the inner surface 205 and the outer surface 206 of the ring 204 at a location not aligned with the material addition portion 350. In some embodiments, the thickness T3 is 50% or more greater than the thickness T1. In other embodiments, the thickness T3 is 30% or more greater than the thickness T1. In some embodiments, the thickness T3 may be greater than 30% and less than 50% greater than the thickness T1. In other embodiments, the thickness T3 may be 100% or more greater than the thickness T1. At the thickest portion of the material addition portion 350, the diameter D3 provided by the material addition portion 350 is greater than the outer diameter D2 of the stator ring 204. In some embodiments, the diameter D3 may be 2% to 50% greater than the outer diameter D2. In other embodiments, the diameter D3 may be 5% to 25% greater than the outer diameter D2. In the illustrated embodiment, the material addition portion 350 ( Figure 2 ) is approximately 8% larger than the outer diameter D2. Similarly, the material addition portion 351 ( Figure 6) is approximately 20% larger than the outer diameter D2.

[0029] Figure 3 A motor 10b and a stator 400 including a sound reduction feature 450 are shown according to a second embodiment of the present disclosure. The stator 400 further includes similar structure as the stator 200, wherein similar features are labeled with similar numbers in the "400" series reference numerals. The sound reduction feature 450 in this second embodiment is a material reduction portion 450 removed from the ring 404. The material reduction portion 450 shown is generally crescent-shaped. However, other shapes of material reduction portions 450 are also possible. For example, Figure 7 Another motor 10f and stator 400a are shown, which includes a rectangular material reduction portion 451. The material reduction portion 451 is radially aligned with the teeth 408. Similarly, Figure 8 Another motor 10g and a stator 400b are shown, the stator including a material reduction portion 452 that is shaped as a trapezoid. More specifically, the stator 400 includes a plurality of material reduction portions 450 that are circumferentially spaced from each other around the longitudinal axis LA. In the illustrated embodiment, the material reduction portions 450 are gaps in the ring 404 that position the outer surface 406 of the ring 404 closer to the longitudinal axis LA than the portion of the ring 404 that is aligned with the gap between adjacent stator teeth 408. In the illustrated embodiment, the diameter D4 measured at the circumferential position of the outer surface 406 of the ring 404 corresponding to the material reduction portion 450 is greater than the inner diameter D1 of the ring 204 and less than the outer diameter D2 of the ring 204. In some embodiments, the diameter D4 may be between the inner diameter D1 and the outer diameter D2, approximately 50% of the difference between the two. In some embodiments, the diameter D4 may be between the inner diameter D1 and the outer diameter D2, between 25% and 75% of the difference between the two.

[0030] Figure 4A motor 10c and a stator 500 including a sound mitigation feature 550 according to a third embodiment of the present disclosure are shown. The stator 500 further includes a structure similar to the stator 200, wherein similar features are labeled with similar numbers in the "500" series reference numerals. The sound mitigation feature 550 in this third embodiment includes circumferentially alternating rigid portions 554 and flexible portions 558. In the illustrated embodiment, the stator 500 includes rigid portions 554 that are radially aligned with the stator teeth 508 and radially aligned with respect to the longitudinal axis LA. The stator 500 includes flexible portions 558 that are radially aligned with the gaps between adjacent stator teeth 508. The rigid portions 554 have a higher stiffness than the flexible portions 558. The sound mitigation feature 550 adjusts the stiffness of the stator 500, and therefore the stiffness of the motor 10c. Optionally, the materials forming the rigid portions 554 and the materials forming the flexible portions 558 are different. In other embodiments, stator 500 may include other structural differences (e.g., the presence of a lattice structure, a solid body, etc.) to distinguish rigid portion 554 from flexible portion 558. Optionally, the mass of stator 500 is different from the mass of stator 200. Figure 4 In the illustrated embodiment, radially extending dashed lines define the separation between the rigid portion 554 and the flexible portion 558. In some embodiments, these boundaries may be visible. In other embodiments, the boundary between the rigid portion 554 and the flexible portion 558 may not be visible.

[0031] Figure 5A motor 10d and a stator 600 including a sound mitigation feature 650 are shown according to a fourth embodiment of the present disclosure. The stator 600 further includes a structure similar to the stator 200, wherein similar features are labeled with similar numbers in the "600" series reference numerals. The sound mitigation feature 650 in this fourth embodiment is an increased thickness stator tooth 650. As measured in a direction tangential to the longitudinal axis LA, these increased thickness stator teeth 650 include a thickness T4 that is greater than the thickness T2 of the stator teeth 208. In the illustrated embodiment, the stator core 602 is a single piece (i.e., a unitary construction). In some embodiments, the thickness T4 of the increased thickness stator teeth 650 can be approximately 1 mm greater than the thickness T2 of the stator teeth 208. In other embodiments, the thickness T4 of the increased thickness stator teeth 650 can be approximately 2 mm greater than the thickness T2 of the stator teeth 208. In other embodiments, the thickness T4 of the increased thickness stator tooth 650 can be approximately 4 millimeters greater than the thickness T2 of the stator tooth 208. In other embodiments, the thickness T4 of the increased thickness stator tooth 650 can be greater than the thickness T2 of the stator tooth 208 and 50% or less thicker than the stator tooth 208. In other embodiments, the thickness T4 of the increased thickness stator tooth 650 can be 10% to 60% greater than the thickness T2 of the stator tooth 208. The stator tooth 650 has a similar length L1 as compared to the stator tooth 208. Thus, the thickness ratio (T4) per unit length (L1) of the stator tooth 650 of the illustrated stator 600 is greater than the thickness ratio (T2) per unit length (L1) of the stator 200.

[0032] Fig.9AA motor 10h is shown that includes, for example, a stator 400 and a ring 700 (e.g., a shrink ring) surrounding the stator 400. The ring 700 itself serves as a sound mitigation feature of the motor 10h. The motor 10h can be constructed from the stator 400 or any other suitable stator (e.g., any one of the stators 200, 300, 400, 500, 600, etc.). The stator 400 is circumferentially positioned within the ring 700. The ring 700 provides circumferential support to the stator 400 in a direction extending radially inward, which extends from the ring 700 and toward the longitudinal axis LA. The ring 700 is generally annular. The ring 700 includes a radial outer surface 704 and a radial inner surface 708. As described above, the stator 400 includes an outer surface 406 that defines an outer diameter D2. The radial inner surface 708 of the ring 700 defines an inner diameter D5. The radial outer surface 704 of the ring 700 defines an outer diameter D6. The ring 700 may be made of a hardened (e.g., rigid) material (e.g., steel) that is shrink-fitted around the outer surface 406 of the stator 400. The ring 700 and / or the stator 400 may be heated to a temperature above room temperature (i.e., a pressing temperature) to expand the inner diameter D5 of the ring 700 until the outer diameter D2 of the stator 400 is less than the inner diameter D5 of the ring 700, at which point the stator 400 may be pressed into the ring 700. When the temperature of the ring 700 and the stator 400 returns to room temperature, the inner diameter of the ring 700 may shrink to establish a press fit between the radial inner surface 708 of the ring 700 and the outer surface 40 of the stator 400. Thus, a compressive force is applied to the stator 400 from the ring 700 in a radially inward direction. The compressive force may adjust the resonant mode frequency of the motor 10h to a ring compression frequency outside the range of 2500 Hz to 3500 Hz. In some embodiments, the ring compression frequency may be greater than 10,000 Hz (10 kHz). In some embodiments, the ring may be compressed at a frequency greater than 30,000 Hz (30 kHz).

[0033] Fig. 9BAn adjustable ring clamp 800 is shown including a radial outer surface 804 and a radial inner surface 808. The adjustable ring clamp 800 further includes an adjustment mechanism 812, which is configured to adjust the size of the inner diameter D5 of the radial inner surface 808. When the adjustment mechanism 812 is actuated, the adjustable ring clamp 800 can be compressed onto the stator 400 or loosened from the stator in a manner similar to the ring 700. The adjustment mechanism 812 can be actuatable throughout the life of the motor 10h. One or more hose clamps 800 can replace the ring 700 in the motor 10h. Alternatively, one or more hose clamps 800 can be tightened on the radial outer surface 704 of the ring 700. The adjustable ring clamp 800 itself, or the adjustable ring clamp 800 and the ring 700 can be used as a sound reduction feature of the motor 10h. In other words, both the ring 700 and the adjustable ring clamp 800 are compression sound reduction features. In either arrangement, the one or more hose clamps 800 provide a similar radially inwardly extending compressive force to the outer surface 406 of the stator 400, such that the hose clamp(s) 800 adjust the resonant mode frequency of the motor 10h to a clamp compression frequency outside the range of 2500 Hz to 3500 Hz. In some embodiments, the clamp compression frequency is greater than 10 kHz. In some embodiments, the clamp compression frequency is greater than 30 kHz.

[0034] It should be understood that the stators 300-600 are shown for use with the rotor 100. The stators 300-600 and the sound mitigation features 350-650 may be modified (ie, flipped, inverted) accordingly to accommodate an outer rotor (not shown).

[0035] By including the sound mitigation features 350 to 650, 700, 800 in the stators 300 to 600, at least one of the mass of the motors 10a to 10h and the stiffness of the motors 10a to 10h is adjusted compared to the motor 10. In this way, the natural frequency of the motor 10a to 10h including one of the stators 300 to 600 is different from the natural frequency of the motor 10 including the stator 200.

[0036] During operation of the motor 10, the stator coils 212 are energized, and the electromagnetic field emanating from the stator coils 212 is implemented by the magnets 108 of the rotor 100, which causes the rotor 100 to rotate about the longitudinal axis LA and relative to the stator 200. The rotation of the rotor 100 and / or other operational vibrations caused by the rotor 100 may cause induced vibrations of the stator 200 and the motor 10 as a whole. In some cases, the stator 200 may be caused to vibrate at its natural frequency, at which the stator 200 may undesirably vibrate near the frequency to which the human ear is most sensitive (e.g., 3,000 Hz).

[0037] The sound mitigation features 350-650, 351, 451, 452 of the stators 300-600, 300a, 400a, 400b, as well as the ring 700, hose clamp(s) 800, effectively adjust (i.e., tune) the natural frequency of the motors 10a-10h to a frequency other than the frequency to which the human ear is most sensitive (e.g., between 2500 Hz and 3500 Hz). In some embodiments, by replacing the stator 200 with one of the stators 300-600 that includes the sound mitigation features 350-650, the natural frequency of the motors 10a-10g is adjusted to about 4300 Hz. In some embodiments, the natural frequency of the motors 10a-10g is adjusted to between 3800 Hz and 4800 Hz. In other embodiments, the natural frequency of the motors 10a-10g is adjusted to between 4000 Hz and 4600 Hz. In other embodiments, the natural frequency of the motors 10a to 10h is adjusted to a frequency greater than 10kHz. In other embodiments, the natural frequency of the motors 10a to 10h is adjusted to a frequency greater than 30kHz. In other embodiments, by replacing the stator 200 with one of the stators 300 to 600, 300a, 400a, 400b including the sound mitigation features 350 to 650, 351, 451, 452, and / or by further providing a ring 700 or an adjustable ring clamp 800, the natural frequency of the motors 10a to 10h is adjusted to about 4300Hz. In other embodiments, by replacing the stator 200 with one of the stators 300 to 600, 300a, 400a, 400b, the resonant frequency of the motor 10 can be adjusted to a natural frequency less than the frequency to which the human ear is most sensitive (e.g., less than 2500Hz). Thus, a perceived sound reduction of approximately 5dB is possible.

[0038] Although the present application has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the present application described.

[0039] Various features of the invention are set forth in the appended claims.

Claims

1. A motor, characterized in that: The motor includes: a rotor including magnets therein; and A stator, the stator comprising a stator core having a ring and a plurality of teeth extending from the ring, a plurality of coils wound around the plurality of teeth, and A device is provided for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz.

2. The motor according to claim 1, characterized in that The means for adjusting comprises a material addition applied to the ring.

3. The motor according to claim 2, characterized in that The material addition portions are circumferentially offset from the plurality of teeth.

4. The motor according to claim 2, characterized in that These material additions are trapezoidal in shape.

5. The motor according to claim 1, characterized in that The means for adjusting comprises a reduced portion of material removed from the ring.

6. The motor according to claim 5, characterized in that The material reduction portions are radially aligned with the plurality of teeth.

7. The motor according to claim 5, characterized in that These material reduction sections are crescent-shaped.

8. The motor according to claim 1, wherein: The means for adjusting comprises rigid and flexible portions alternating circumferentially in the stator core.

9. The motor according to claim 8, characterized in that The rigid portions are radially aligned with the plurality of teeth, and wherein the flexible portions are radially aligned with gaps defined between adjacent teeth.

10. The motor according to claim 8, characterized in that The rigidity of the rigid parts is higher than the rigidity of the flexible parts.

11. The motor according to claim 1, characterized in that The means for adjustment include stator teeth of increased thickness.

12. A motor, characterized in that: The motor includes: a rotor including magnets therein; A stator, the stator comprising a stator core having a ring and a plurality of teeth extending from the ring, a plurality of coils wound around the plurality of teeth; and A device for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz, the device for adjusting being configured to apply a compressive force to the rings of the stator core.

13. The motor according to claim 12, characterized in that The means for adjusting comprises a shrink ring shrink-fitted onto the stator.

14. The motor according to claim 12, wherein: The means for adjusting comprises a ring clamp configured to be tightened onto the stator.

15. The motor according to claim 14, characterized in that The ring clamp includes an adjustment mechanism configured to be actuated to adjust an amount of compressive force applied to the stator by the clamp.

16. A motor, characterized in that: The motor includes: a rotor including magnets therein; A stator, the stator comprising a stator core having a ring and a plurality of teeth extending from the ring, a plurality of coils, the plurality of coils being wound around the plurality of teeth, a first device for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hertz (Hz) to 3500 Hz; and Second means for adjusting the natural frequency of the motor to a frequency value outside the range of 2500 Hz to 3500 Hz, the second means for adjusting being configured to apply a compressive force to the ring of the stator core.

17. The motor according to claim 16, characterized in that The first means for adjusting comprises a reduced portion of material removed from the ring.

18. The motor according to claim 17, characterized in that The material reduction portions are radially aligned with the plurality of teeth, and wherein the material reduction portions are rectangular.

19. The motor according to claim 18, characterized in that The second means for adjusting comprises a shrink ring shrink-fitted onto the stator.

20. The motor according to claim 19, wherein This frequency value is greater than 10,000 Hz.

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