Description:FIELD OF INVENTION
[0001]Embodiments of a present disclosure relates to a motor assembly, and more particularly to a rotor assembly with unique arrangements of a plurality of permanent magnet segments for reducing torque ripples and a visible reduction of permanent magnet weight in the motor assembly.
BACKGROUND
[0002]A Brushless Direct Current (BLDC) electric motor is a normal synchronous motor using a direct current (DC). The BLDC motor includes two parts namely a stator and a rotor. The stator part is made up of a plurality of stacked steel laminations with axially cut slots for windings. The rotor part of the BLDC motor is made up of a plurality of permanent magnets.
[0003]The role of the stator is to provide a charge that will repel or attract the permanent magnets and make the BLDC motor rotate. The stator consists of a plurality of multiphase winding on a laminated core. The stator windings are provided with currents controlled in magnitude and sequence.
[0004]The rotor includes a plurality of permanent magnet segments or a moulded ring affixed to the inner surface of a steel cup-like component that is attached at one end to a shaft of the motor and directly transferring energy to the wheels.
[0005]The operation of the motor is based on magnetic locking between the stator and the rotor. The commutation is controlled electronically. An electronic controller replaces the commutator assembly of the brushed DC motor and an electronic sensor helps in detecting the angle of the rotor. With the help of a solid-state circuit, the electronic controller performs timed power distribution which continually switches the phase to the windings to maintain the motor rotating.
[0006]The motor includes an outer rotor design. The stator windings are connected to an integrated switching or inverter based control circuit which energizes proper winding at the proper time, in a particular pattern by sensing the position of the rotor around the stator. The permanent magnets on the rotor try to align with the energized electromagnets of the stator, and as soon as the permanent magnets align, the next electromagnets are energized. Thus, the rotor keeps moving.
[0007]A strong electromagnetic force exists between the permanent magnets of the rotor and the coils of the stator and hence an output torque is produced. Along with a useful torque, an undesirable component is also produced as a result of an interaction between the permanent magnets and poles of the stator. The undesirable component of the torque introduces ripple in the output torque.
Along with the useful torque, an undesirable component is also produced as a result of the interaction between the permanent magnets and the poles of the stator.
[0008]Torque ripple means a periodic increase or decrease in output torque as the motor shaft rotates. Torque ripple occurs due to change over of load current from one phase to the other. The torque ripple is also produced by the non-linear back EMF and the commutation torque ripple from the unbalanced outgoing phase and incoming phase current. Waveform of back-emf in combination with waveform of phase currents can lead to significant torque ripple. The torque ripple is divided in two parts: the torque pulsation due to current ripple and the torque pulsation due to commutation time.
[0009]Torque ripple is suppressed by at least one of: various construction changes, shift of permanent magnets, changing the width of the poles, and the like. The amount of torque ripple a motor produces depends on its construction and control methods.
[0010]Torque ripples are undesirable effect in BLDC motors. It is necessary to focus on the identification and reduction of sources of torque ripple in BLDC motor drives to reduce a noise and increase comfort in a vehicle. Pulsating torque is one of the most significant limitations and poses higher stress on the machine bearing and produces vibration. Therefore, reduction of the sharp change in attractive forces as the primary moves across the magnets to improve the smoothness of torque production is required.
[0011]Hence, there is a need for a rotor assembly with unique arrangements of a plurality of permanent magnet segments for reducing torque ripples and a visible reduction of permanent magnet weight to address the aforementioned issues.
SUMMARY
[0012]This summary is provided to introduce a selection of concepts, in a simple manner, which is further described in the detailed description of the disclosure. This summary is neither intended to identify key or essential inventive concepts of the subject matter nor to determine the scope of the disclosure.
[0013]In accordance with one embodiment of the disclosure, a rotor assembly with unique arrangements of a plurality of permanent magnet segments for reducing torque ripples of a motor assembly, is disclosed. The rotor assembly includes a rotor core, a wheel rim and a plurality of permanent magnet segments. The rotor core includes a plurality of grooves that are evenly spaced and placed axially at a circular outer surface of the rotor core. The wheel rim includes a plurality of bars that is evenly spaced and placed axially around an inner periphery of the wheel rim. The plurality of bars placed around the inner periphery of the wheel rim is slidably inserted through the plurality of grooves placed at the circular outer surface of the rotor core, which enables the rotor core to be inserted within the wheel rim.
[0014]The plurality of permanent magnet segments includes a first permanent magnet segment and a second permanent magnet segment. The first permanent magnet segment includes a plurality of permanent magnets. The second permanent magnet segment includes a plurality of permanent magnets. The first permanent magnet segment and the second permanent magnet segment are parallelly arranged at the circular inner surface of the rotor core of the rotor assembly.
[0015]The first permanent magnet segment is arranged slightly in advance to the second permanent magnet segment within the rotor core, which reduces harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment and the second permanent magnet segment to reduce the torque ripples in the motor assembly.
[0016]In an embodiment, reducing of the harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment and the second permanent magnet segment helps a stator to slide over the plurality of magnets of the first permanent magnet segment and the second permanent magnet segment of the rotor assembly without stress.
[0017]In another embodiment, reducing of the harmonic rich air gap between the plurality of magnets of the first permanent magnet segment and the second permanent magnet segment makes transition of the stator along magnetic poles of the plurality of permanent magnets smooth with low cross-over distortions.
[0018]In yet another embodiment, the transition of the stator along the magnetic poles of the plurality of permanent magnets generates a mutual magnetic flux, which provides smooth zero crossing for voltage and current waveforms to reduce the torque ripples in the motor assembly.
[0019]In yet another embodiment, the first permanent magnet segment includes 28 permanent magnets that are arranged in 30 slots, and the second permanent magnet segment includes 28 permanent magnets that are arranged in 30 slots.
[0020]To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will follow by reference to specific embodiments thereof, which are illustrated in the appended figures. It is to be appreciated that these figures depict only typical embodiments of the disclosure and are therefore not to be considered limiting in scope. The disclosure will be described and explained with additional specificity and detail with the appended figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021]The disclosure will be described and explained with additional specificity and detail with the accompanying figures in which:
[0022]FIG. 1 is a perspective view of a rotor assembly including a unique arrangement of a plurality of permanent magnet segments with a rotor core and a wheel rim, in accordance with an embodiment of the present disclosure;
[0023]FIG. 2 is a front view of the rotor assembly with the unique arrangement of the plurality of permanent magnet segments with the rotor core and the wheel rim, such as those shown in FIG. 1, in accordance with an embodiment of the present disclosure;
[0024]FIG. 3 is a cross sectional view of the rotor assembly showing the unique arrangement of the plurality of permanent magnet segments, such as those shown in FIG. 1, in accordance with an embodiment of the present disclosure; and
[0025]FIGS. 4A-4B are graphical representations depicting reduction of torque ripples in a motor assembly, based on one or more parameters, in accordance with an embodiment of the present disclosure.
[0026]Further, those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the benefit of the description herein.
DETAILED DESCRIPTION OF THE DRAWINGS
[0027]For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Such alterations and further modifications in the illustrated online platform, and such further applications of the principles of the disclosure as would normally occur to those skilled in the art are to be construed as being within the scope of the present disclosure.
[0028]The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more devices or subsystems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, subsystems, elements, structures, components, additional devices, additional subsystems, additional elements, additional structures or additional components. Appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.
[0029]Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. The system, methods, and examples provided herein are only illustrative and not intended to be limiting.
[0030]In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.
Definition:
[0031]Stator: A stator is the non-moving, fixed counterpart in a machine. Depending on the motor type and construction, the rotor or stator are designed as permanent magnets or copper windings.
[0032]Rotor: A rotor is the rotating part of a machine. In electrical motors or generators, the whole linear synchronously rotating part of the machine is termed the rotor. The rotor includes permanent magnets that help to rotate the rotor based on current applied to the stator.
[0033]FIG. 1 is a perspective view of a rotor assembly 100 including a unique arrangement of a plurality of permanent magnet segments 106 with a rotor core 102 and a wheel rim 104, in accordance with an embodiment of the present disclosure. A motor assembly generally includes a stator and a rotor. The stator includes a plurality of concentrated windings and forms an inner part of the motor assembly. The rotor of the motor assembly is external (i.e., the stator windings are located at a stator core while the rotor carrying the plurality of permanent magnet segments 106, surrounds the stator).
[0034]The rotor assembly 100 includes a unique arrangements of the plurality of permanent magnet segments 106 for reducing torque ripples and a visible reduction of permanent magnet weight in a motor assembly. In an embodiment, the unique arrangement of the plurality of permanent magnet segments 106 is achieved by providing spacing between each permanent magnet compared with the conventional continuous strip arrangement. In an embodiment, the plurality of permanent magnet segments 106 include at least two permanent magnet segments 106. In an embodiment, the motor assembly may be a Brushless Direct Current (BLDC) hub motor assembly.
[0035]The rotor assembly 100 includes the rotor core 102, the wheel rim 104, and the plurality of permanent magnet segments 106. The rotor core 102 includes a plurality of grooves that is evenly spaced and placed axially at a circular outer surface of the rotor core 102. The wheel rim 104 includes a plurality of bars that is evenly spaced and placed axially around an inner periphery of the wheel rim 104. The plurality of bars placed around the inner periphery of the wheel rim 104 is slidably inserted through the plurality of grooves placed at the circular outer surface of the rotor core 102, which enables the rotor core 102 to be inserted within the wheel rim 104.
[0036]The plurality of permanent magnet segments 106 includes a first permanent magnet segment 108 and a second permanent magnet segment 110. The first permanent magnet segment 108 includes a plurality of permanent magnets. The second permanent magnet segment 110 includes a plurality of permanent magnets. The first permanent magnet segment 108 and the second permanent magnet segment 110 are parallelly arranged at the circular inner surface of the rotor core 102 of the rotor assembly 100.
[0037]In other words, the plurality of permanent magnet segments 106 is arranged in an inner side of the rotor assembly 100 by slightly advancing an alignment of the one permanent magnet segment (e.g., the first permanent magnet segment 108) with respect to the other permanent magnet segment (e.g., the second permanent magnet segment 110), which provides the unique arrangement to a rotor permanent magnet assembly 100 (i.e., the rotor assembly 100).
[0038]The rotating field interacts with the magnetic field produces electromagnetic torque. Load torque includes two components such as a useful torque and a pulsation torque. An essential cause of torque ripples are based on harmonics of magnetic flux of air gap between the stator and the rotor. Improved performance and efficiency are achieved by adopting a higher winding factor, which results in the larger air gap that causes significant space harmonic rich field. The space harmonic rich air gap field has resulted in high torque ripple.
[0039]The first permanent magnet segment 108 is arranged slightly in advance to the second permanent magnet segment 110 within the rotor core 102, which reduces and optimizes harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment 108 and the second permanent magnet segment 110 to reduce the torque ripples in the motor assembly. The reduction of the harmonic rich air gap between the plurality of permanent magnets helps the stator to slide over plurality of magnets of the first permanent magnet segment 108 and the second permanent magnet segment 110 of the rotor assembly 100 without stress.
[0040]In an embodiment, the reduction of the harmonic rich air gap between the plurality of magnets of the first permanent magnet segment 108 and the second permanent magnet segment 110 makes transition of the stator along magnetic poles of the plurality of permanent magnets smooth with low cross-over distortions, and hence jerking of a vehicle is avoided. The transition of the stator along the magnetic poles of the plurality of permanent magnets generates a mutual magnetic flux, which provides smooth zero crossing for voltage and current waveforms to reduce the torque ripples to a large extent possible in the motor assembly. In an embodiment, the mutual magnetic flux producing the torque acts as a plain sailing when the stator is transitioned from one permanent magnet pole to another permanent magnet pole.
[0041] FIG. 2 is a front view of the rotor assembly 100 with the unique arrangement of the plurality of permanent magnet segments 106 with the rotor core 102 and the wheel rim 104, such as those shown in FIG. 1, in accordance with an embodiment of the present disclosure. The front view of the arrangement of the plurality of permanent magnet segments 106 with the plurality of magnets is visible as blocks in each permanent magnet of the plurality of permanent magnets. In an embodiment, the first permanent magnet segment 108 includes 28 permanent magnets that are arranged in 30 slots. In another embodiment, the second permanent magnet segment 110 includes 28 permanent magnets that are arranged in 30 slots. Hence, the plurality of permanent magnet segments 106 totally includes 56 permanent magnets arranged in 60 slots as the at least two permanent magnet segments 106 are arranged at the circular inner surface of the rotor core 102 of the rotor assembly 100.
[0042]In an embodiment, each permanent magnet of the plurality of permanent magnets in at least one of: the first plurality of permanent magnet segment 108 and the second plurality of permanent magnet segment 110 is equally spaced at 8.74 degree apart from another permanent magnet of the plurality of permanent magnets. In an embodiment, a first permanent magnet in the first permanent magnet segment 108 and a first permanent magnet in the second permanent magnet segment 110 are arranged as a first permanent magnet pair 202.
[0043]In an embodiment, an angle difference between the first permanent magnet in the first permanent magnet segment 108 and the first permanent magnet in the second permanent magnet segment 110 may be 1.5 degree. In an embodiment, an angle difference between each permanent magnet pair 202 of the plurality of permanent magnet segments 106 may be 2.06 degree.
[0044]In an embodiment, the plurality of permanent magnets of the plurality of permanent magnet segments 106 is fixed at the circular inner surface of the rotor core 102 using an adhesive material. In another embodiment, the first permanent magnet segment 108 and the second permanent magnet segment 110 are combined together using the adhesive material. In another embodiment, a thickness of the adhesive material may be 0.1 mm. In an embodiment, the diameter of the rotor core 102 after arranging the plurality of permanent magnet segments 106 may be 207.4 millimeter (mm). In an embodiment, the diameter of the wheel rim 104 may be 10 inches.
[0045]FIG. 3 is a cross sectional view of the rotor assembly 100 showing the unique arrangement of the plurality of permanent magnet segments 106, such as those shown in FIG. 1, in accordance with an embodiment of the present disclosure. The cross sectional view of the rotor assembly 100 includes the rotor core 102, the wheel rim 104, and the plurality of permanent magnet segments 106. The plurality of permanent magnet segments 106 includes the first permanent magnet segment 108 and the second permanent magnet segment 110.
[0046]The cross sectional view of the rotor assembly further shows that the first permanent magnet segment 108 is arranged in advance position with respect to the second permanent magnet segment 110 in order to reduce the harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment 108 and the second permanent magnet segment 110 for reducing the torque ripples in the motor assembly.
[0047]FIGS. 4A-4B are graphical representations (400A, 400B) depicting reduction of torque ripples in a motor assembly, based on one or more parameters, in accordance with an embodiment of the present disclosure. The graphical representation 400A depicts the computation of the torque ripples in the motor assembly based on one or more parameters including at least one of: torque, torque ripple, and output power, in continuous rating, as shown in a table of FIG. 4A. Further, the graphical representation 400B depicts the computation of the torque ripples being reduced in the motor assembly based on the one or more parameters including at least one of: the torque, the torque ripple, and the output power, in peak rating, as shown in a table of FIG. 4B.
[0048]The present invention provides the rotor assembly 100 that uniquely accommodates the plurality of permanent magnet segments 106 for reducing the torque ripples in the motor assembly. The present invention contemplates most practical way of which conspicuously reduces the torque ripples caused due to the space harmonic rich air gap field produced when a high winding factor for improved performance is implemented.
[0049]Further, the unique arrangement of the plurality of permanent magnet segments 106 of the rotor assembly 100 is provided in a specific correlation with the stator winging design. Due to the optimised spacing provided between each permanent magnet in the arrangement of the plurality of permanent magnet segments 106, the number of permanent magnets used in the contemplated hub motor assembly is reduced to a large visible extent compared to the conventional hub motors.
[0050]Further, saving of the permanent magnet weight itself is the most vital achievement of the proposed arrangement of the plurality of permanent magnet segments 106 in the rotor assembly 100 of the contemplated hub motor assembly, which in turn reduces cost and weight of the same.
[0051]Hence, the proposed arrangement of the plurality of permanent magnet segments 106 with the plurality of permanent magnets in the rotor assembly 100 helps in overriding of the most significant limitation of pulsating torque, which ensures a smooth driving force to the hub motor assembly. Further, the proposed arrangement of the plurality of permanent magnet segments 106 guarantees a smooth movement to the vehicle without any jerks, vibrations or noises, which increase vehicle comfort with a visible magnet weight reduction.
[0052]Furthermore, the permanent magnets are provided with a specific spacing in correlation to the stator winding design. This arrangement of the permanent magnets different from the conventional continuous strip arrangement provides a benefit of drastic reduction in the permanent magnet weight required for the motor assembly.
[0053]Further, the arrangement of the plurality of permanent magnet segments 106 conspicuously reduced the torque ripples caused due to the space harmonic rich air gap field. This arrangement further reduces the pulsating torque, which are the most significant limitations of the BLDC hub motors. Hence, there is an improved smoothness of torque production, reducing noise and vibration, thereby assuring more comfort to the vehicle.
[0054]While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person skilled in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
[0055]The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, order of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts need to be necessarily performed. Also, those acts that are not dependant on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.
, Claims:WE CLAIM:
1. A rotor assembly (100) with unique arrangements of a plurality of permanent magnet segments (106) for reducing torque ripples of a motor assembly, the rotor assembly (100) comprising:
a rotor core (102), wherein the rotor core (102) comprises a plurality of grooves that is evenly spaced and placed axially at a circular outer surface of the rotor core (102);
a wheel rim (104), wherein the wheel rim (104) comprises a plurality of bars that is evenly spaced and placed axially around an inner periphery of the wheel rim (104),
wherein the plurality of bars placed around the inner periphery of the wheel rim (104) is slidably inserted through the plurality of grooves placed at the circular outer surface of the rotor core (102), which enables the rotor core (102) to be inserted within the wheel rim (104); and
characterized in that
the plurality of permanent magnet segments (106), wherein the plurality of permanent magnet segments (106) comprises a first permanent magnet segment (108) and a second permanent magnet segment (110),
wherein the first permanent magnet segment (108) comprises a plurality of permanent magnets, and wherein the second permanent magnet (110) segment comprises a plurality of permanent magnets, characterized in that
the first permanent magnet segment (108) and the second permanent magnet segment (110) are parallelly arranged at the circular inner surface of the rotor core (102) of the rotor assembly (100), and
wherein the first permanent magnet segment (108) is arranged slightly in advance to the second permanent magnet segment (110) within the rotor core (102), which reduces harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment (108) and the second permanent magnet segment (110) to reduce the torque ripples in the motor assembly.

2. The rotor assembly (100) as claimed in claim 1, wherein reducing of the harmonic rich air gap between the plurality of permanent magnets of the first permanent magnet segment (108) and the second permanent magnet segment (110) helps a stator to slide over the plurality of magnets of the first permanent magnet segment (108) and the second permanent magnet segment (110) of the rotor assembly (100) without stress.

3. The rotor assembly (100) as claimed in claim 1, wherein reducing of the harmonic rich air gap between the plurality of magnets of the first permanent magnet segment (108) and the second permanent magnet segment (110) makes transition of the stator along magnetic poles of the plurality of permanent magnets smooth with low cross-over distortions.

4. The rotor assembly (100) as claimed in claim 3, wherein the transition of the stator along the magnetic poles of the plurality of permanent magnets generates a mutual magnetic flux, which provides smooth zero crossing for voltage and current waveforms to reduce the torque ripples in the motor assembly.

5. The rotor assembly (100) as claimed in claim 4, wherein the mutual magnetic flux producing torque acts as a plain sailing when the stator is transitioned from one permanent magnet pole to another permanent magnet pole.

6. The rotor assembly (100) as claimed in claim 1, wherein the first permanent magnet segment (108) comprises 28 permanent magnets that are arranged in 30 slots, and wherein the second permanent magnet segment (110) comprises 28 permanent magnets that are arranged in 30 slots.

7. The rotor assembly (100) as claimed in claim 1, wherein each permanent magnet of the plurality of permanent magnets in at least one of: the first plurality of permanent magnet segment (108) and the second plurality of permanent magnet segment (110) is equally spaced at 8.74 degree apart from another permanent magnet of the plurality of permanent magnets.

8. The rotor assembly (100) as claimed in claim 1, wherein a first permanent magnet in the first permanent magnet segment (108) and a first permanent magnet in the second permanent magnet segment (110) are arranged as a first permanent magnet pair (202).

9. The rotor assembly (100) as claimed in claim 8, wherein an angle difference between the first permanent magnet in the first permanent magnet segment (108) and the first permanent magnet in the second permanent magnet segment (110) is 1.5 degree.

10. The rotor assembly (100) as claimed in claim 8, wherein an angle difference between each permanent magnet pair (202) of the plurality of permanent magnet segments (106) is 2.06 degree.

11. The rotor assembly (100) as claimed in claim 1, wherein the plurality of permanent magnets of the plurality of permanent magnet segments (106) is fixed at the circular inner surface of the rotor core (102) using an adhesive material, and wherein a thickness of the adhesive material is 0.1 mm.

12. The rotor assembly (100) as claimed in claim 1, wherein the plurality of permanent magnet segments (106) comprises at least two permanent magnet segments (106) arranged parallelly at the circular inner surface of the rotor core (102) of the rotor assembly (100).

Dated this 30th day of October 2023

Vidya Bhaskar Singh Nandiyal
Patent Agent (IN/PA-2912)
Agent for applicant