FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
AND
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
“IMPROVED STATOR FOR A FAN”
We, Bajaj Electricals Limited, an Indian National, of 45/47, Veer Nariman Road,
Fort Mumbai- 400001, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF INVENTION
The present invention relates to the field of consumer electronic goods. In particular, the present invention relates to fans with improved stator technology.
BACKGROUND OF THE INVENTION
Ceiling fans have been a staple in cooling and ventilation systems for decades, providing comfort to millions of households and commercial spaces worldwide. Over the years, various technological advancements have been made to improve the efficiency, durability, and user experience of ceiling fans. One notable development in this regard has been the adoption of high-energy-density Brushless Direct Current (BLDC) and Permanent Magnet Synchronous Motor (PMSM) technologies for ceiling fan applications.
Generally, the blades of the ceiling fans are rotated by a motor comprising a stator and a rotor. The stator is the static part of the motor whereas the rotor is the rotating part of the motor. A rotating magnetic flux is generated in the stator, which in turn induces the rotation of the rotor. The rotor, composed of magnetic materials, also produces its own magnetic field. In certain rotor and stator alignments, the magnetic fields of rotor and stator can interact. When this interaction happens, the rotor experiences resistance to motion. This phenomenon is commonly referred to as “cogging”.
Generally, an outer rotor 3-phase motor, for BLDC or PMSM designed for high energy density, is structured with three-phase windings on the stator. These windings can be connected in either a star or delta configuration, and they are positioned within an electrical angle of 120o between them. The torque produced by this motor is influenced by several key factors, including the specific characteristics of the windings (such as the number of turns), the amount of electrical current flowing through these windings, the quality and grade of the

magnets used in the rotor, and the thickness of those magnets. These factors collectively determine how much rotational force the motor can generate.
Generally, in high-energy-density BLDC/PMSM motors, rare earth magnets are the preferred choice. These magnets are favoured because they are exceptionally strong and provide a low air gap, which increases motor performance. However, this design choice can lead to elevated levels of vibrations and humming within the motor. The increased vibrations primarily stem from the presence of harmonics in the magnetic field at the air gap.
Traditionally, different methods have been employed to mitigate issues like cogging torque and torque fluctuations in motors. These methods include tweaking the air gap between components, altering the arrangement of slots and poles, adjusting the alignment of the stator and rotor, and shaping the magnets.
However, some of these techniques come with drawbacks. For instance, magnet shaping, while effective, can be expensive to implement. Similarly, approaches like skewing (changing the angle of the stator or rotor) and adjusting the air gap can significantly lower the motor's torque density. This reduction in torque density can negatively impact the motor's overall performance, making it less efficient or powerful.
In light of the above, there is a need in the art for improved stators which address at least one or more of the limitations in the art.
SUMMARY OF THE INVENTION
This summary is not intended to identify the essential features of the invention nor is it intended for use in determining or limiting the scope of the claimed subject matter.

In an aspect of the present invention, there is provided a stator comprising: a cylindrical core having a central axis; a plurality of teeth extending radially outwards from an inner surface of the cylindrical core, each tooth has a tooth face arc length (L), a tooth curvature radius (Rt), and any two adjacent tooth of the plurality of teeth defined by a slot opening; and a plurality of insulated conductive coils wound within the slot opening of the cylindrical core, wherein the stator diameter (D) is in the range of 80 mm to 105 mm.
In an aspect of the present invention, the stator is laminated using a material selected from the group comprising Cold Rolled Non-Grain Oriented (CRNGO) or semi-processed lamination steel
In an aspect of the present invention, in the stator, the slot opening is equal to ±10%
0.783(2r sinH^)
of � � cos � + 1.2 ), r is the radius of the stator, n is the number of pole
pairs in the stator, and C is the tooth width.
In an aspect of the present invention, in the stator, the tooth curvature radius (Rt) is in the range of 0.4r to 0.6r, and r is the radius of the stator.
In another aspect of the present invention, there is provided a fan motor comprising a stator, said stator comprising: a cylindrical core having a central axis; a plurality of teeth extending radially outwards from an inner surface of the cylindrical core, each tooth has a tooth face arc length (L), a tooth curvature radius (Rt), and any two adjacent tooth of the plurality of teeth defined by a slot opening; and a plurality of insulated conductive coils wound within the slot opening of the cylindrical core, wherein the stator diameter (D) is in the range of 80 mm to 105 mm.
In yet another aspect of the present invention, there is provided a fan comprising a fan motor, said fan motor comprising a stator, said stator comprising: a cylindrical

core having a central axis; a plurality of teeth extending radially outwards from an inner surface of the cylindrical core, each tooth has a tooth face arc length (L), a tooth curvature radius (Rt), and any two adjacent tooth of the plurality of teeth defined by a slot opening; and a plurality of insulated conductive coils wound within the slot opening of the cylindrical core, wherein the stator diameter (D) is in the range of 80 mm to 105 mm.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein
Figure 1 depicts a cross-sectional view of a stator, in accordance with an embodiment of the present invention.
Figures 2a-2b depicts cogging plots showing comparison between cogging torque in a conventional motor and a motor equipped with the stator of the present invention, in accordance with an embodiment of the present invention.
Figures 3a-3b depicts cogging plots showing comparison between FFT analysis of air gap flux in a conventional motor and the motor equipped with the stator of the present invention, in accordance with an embodiment of the present invention.
Figures 4a-4b depicts graphs showing comparison between current-time curve for a motor equipped with a conventional stator and the motor equipped with the stator of the present invention, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION

Those skilled in the art will be aware that the invention described herein is subject to variations and modifications other than those specifically described. It is to be understood that the invention described herein includes all such variations and modifications. The invention also includes all such features referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said features.
For convenience, before further description of the present invention, certain terms employed in the specification, examples are collected here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art. The terms used throughout this specification are defined as follows, unless otherwise limited in specific instances.
As used in the specification and the claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.
Generally, cogging torque occurs in BLDC/PMSM fan motors due to the magnetic interaction between the permanent magnets or coils in the stator and the magnets or magnetic poles in the rotor. When the magnets of the rotor are not precisely aligned with the magnetic elements of the stator, particularly at low speeds during startup, magnetic reluctance creates resistance to rotation, resulting in “cogging torque”. In general, cogging torque is most noticeable at low speeds because the rotor lacks the rotational momentum to overcome this resistance, leading to uneven startup and potential performance issues in BLDC fans, such as noise and vibration.
The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only.

The present invention provides a stator 100 comprising: a cylindrical core 102 having a central axis; a plurality of teeth 104 extending radially outwards from an inner surface of the cylindrical core 102, wherein each tooth 104 has a tooth face arc length L, a tooth curvature radius Rt, and any two adjacent tooth of the plurality of teeth 104 are defined by a slot opening 106; and a plurality of insulated conductive coils wound within the slot opening 106 of the cylindrical core 102, wherein the stator diameter (D) is in the range of 80 mm to 105 mm.
The stator 100 is laminated using a material selected from the group comprising Cold Rolled Non-Grain Oriented (CRNGO) steel or semi-processed lamination steel.
In an embodiment, the slot opening 106 of the stator 100 is equal to ±10% of
0.783(2r sinH^)
( � � cos � + 1.2 ), where r is the radius of the stator 100, n is the number
of pole pairs in the stator 100, and C is the teeth width.
In an embodiment, r is in the range of 40 mm to 52.5 mm. In a preferred embodiment, r is 46.55 mm. In some exemplary embodiments, the number of pole pairs n may include 7 pole pair combination, 8 pole pair combination, 10 pole pair combination, and the like. In a preferred embodiment, the number of pole pairs n is 8. In an embodiment, teeth width C may vary. In a preferred embodiment, teeth width C is 3.5 mm.
In an embodiment, the slot opening 106 depends at least on the teeth width C, the number of pole pairs n, and the radius r of the stator 100. In a preferred embodiment, the slot opening 106 is 3.5 mm ± 10%.
The slot opening 106 of the stator 100 is an air gap throughout the pole pitch, which, as per the present invention, reduces the harmonics in air gap flux, thereby

improving torque characteristics and reducing cogging torque. Improvement in the slot opening 106 characteristics is economically cheaper than shaping the magnet without compromising the torque density of the motor.
In an embodiment, the tooth curvature radius Rt is in the range of 0.2r to 0.6r, where r is the radius of the stator 100. In a preferred embodiment, Rt is 0.38r or 17.86 mm. In one implementation, the tooth curvature radius Rt also contributes in the reduction of the cogging torque.
In an embodiment, the stator 100 has reduced cogging effect. For example, a motor equipped with the stator 100 has around 10 times less cogging effect than a conventional motor. In another embodiment, the stator 100 has reduced vibration torque. For example, a motor equipped with the stator 100 has around 10 times less vibration torque than a conventional motor. In yet another embodiment, the stator 100 has reduced humming noise upon operation. In a preferred embodiment, the stator 100 has reduced cogging torque, reduced vibration torque, and reduced humming noise upon operation.
In an embodiment, the stator 100 of the present invention facilitates reduction in nth harmonic in air gap flux. In an example, the stator 100 of the present invention facilitates reduction in 3rd harmonic in air gap flux. In another example, the stator 100 of the present invention facilitates reduction in 5th harmonic in air gap flux.
It is emphasized that wherever range of values is specified, a value up to 10% below and above the lowest and highest numerical value of the specified range respectively, is included in the scope of the disclosure.
Figure 1 depicts a sectional view of the stator 100, in accordance with an embodiment of the present invention.

The stator 100 comprises a cylindrical core 102. The stator 100 is laminated with
electrical grade steel or magnetic steel. In an embodiment, the electrical grade steel
is Cold Rolled Non-Grain Oriented (CRNGO) steel. The cylindrical core 102 has a
central axis. The stator 100 further comprises a plurality of teeth 104 extending
5 radially outwards from an inner surface of the cylindrical core 102, wherein each
tooth 104 has a tooth face arc length L, a tooth curvature radius Rt, and any two adjacent tooth 104 of the plurality of teeth 104 are defined by a slot opening 106.
Figures 2a-2b depicts cogging plots 200a-200b showing comparison between
0 cogging torque in a conventional motor and a motor equipped with the stator 100
of the present invention, in accordance with an embodiment of the present invention.
Figure 2a is a cogging plot 200a showing moving torque (represented on y-axis)
5 of a conventional stator in a conventional motor as a function of time (x-axis). The
cogging plots 200a-b depicts the amplitude values indicating the intensity of the cogging torque in each case. It can be observed from the graph 200a that over a period of 50ms, the maximum amplitude value is found to be about 87mNm.
0 Figure 2b is a cogging plot 200b showing moving torque (represented on y-axis) of
the stator 100 of the present invention as a function of time (x-axis). It can be observed from the cogging plot 200b that over a period of 21.3ms, the maximum amplitude value is found to be about 35.27mNm, that indicates a reduction of around 60% as compared to the cogging plot 200a.
5
Figures 3a-3b depicts cogging plots 300a-300b showing comparison between FFT analysis of air gap flux in a conventional motor and the motor equipped with the stator 100 of the present invention, in accordance with an embodiment of the present invention. 0

Figure 3a depicts a cogging plot 300a showing the FFT analysis of air gap flux in a conventional motor. Figure 3b depicts a cogging plot 300b showing the FFT analysis of air gap flux in the motor with the stator 100 of the present invention. The FFT (Fast Fourier Transform) analysis of the air gap flux may refer to a graphical representation of the frequency components present in the magnetic flux generated by the motor.
The cogging plots 300a-b depicts amplitude vs frequency plots for the conventional motor and the motor with the stator 100, respectively. The amplitude is represented on the X-axis and the frequency is represented on the Y-axis in the cogging plots
300a-300b.
The comparison is focused on the presence of the 3rd harmonic in the motor flux. Generally, harmonics in the context of electrical systems refer to multiples of the fundamental frequency, and they can often lead to issues such as increased noise, vibrations, and inefficiencies in the motor's operation.
The cogging plots 300a-b depicts that the value of 3rd harmonic present in the motor flux of the conventional motor is 0.07, whereas the value of 3rd harmonic present in the motor flux of the motor with the stator 100 is 0.01. The M3 point in the cogging plot 300b signifies the frequency point where the 3rd harmonic is most pronounced, leading to a higher dB level in the plot.
The stator 100 of the present invention facilitates reduction in the value of 3rd harmonic in the motor flux in which the stator 100 is installed.
Figures 4a-4b depicts graphs 400a-b showing comparison between current-time curve for a motor equipped with a conventional stator and the motor equipped with the stator 100 of the present invention, in accordance with an embodiment of the present invention.

Figure 4a is a graph 400a depicting the current-time curve for a motor equipped with a conventional stator and Figure 4b is a graph 400b depicting the current-time curve for a motor equipped with the stator 100 of the present invention. In each of the graphs, current is represented on the y-axis and time on the x-axis. The red curve represents current level in Phase A, the green curve represents current level in Phase B, and the blue curve represents current level in Phase C of a three-phase motor.
The graph 400a indicates that more harmonics are present in motor phase currents, whereas the graph 400b indicates that high frequency fluctuations in current levels are minimal in the case of the motor equipped with the stator 100 of the present invention, thereby resulting in reduction of harmonics.
Moreover, an experiment was performed to observe the vibration levels in a conventional fan motor and a fan with a motor equipped with the stator 100 of the present invention were recorded. To perform the experiment, a sensor was mounted on a down rod of a fan with conventional motor and a sensor was mounted on a down rod of a fan with motor equipped with the stator 100; and a constant motor speed of both the fans was maintained during the measurement process.
In general, cogging vibrations are more dominant at lower speed. Hence, motor vibrations were measured at 100 rotations per minute (RPM). It was observed that the fan motor with the conventional stator exhibit vibration levels of 5.286 mm/s whereas the motor equipped with the stator 100 exhibit a much lower vibration level of 0.359 mm/s (nearing almost 17 times reduction).
ADVANTAGES OF THE PRESENT INVENTION
The stator of the present invention exhibits reduced cogging torque, reduced vibration levels, and lower humming noise at lower rotations per minute (RPM) in high energy density BLDC/PMSM motors. Further, the stator of the present invention achieves lower nth harmonic in the fan motor of the present invention. In

the stator of the present invention, the slot opening parameter results in an air gap throughout pole pitch such that the harmonics in air gap flux are reduced, cogging torque is reduced and load torque ripple (periodic increase or decrease in torque as the rotor rotates) is reduced, thereby improving overall torque characteristics.
The stator characteristics of the present invention are also economically cheaper to implement as compared to shaping the magnet without deterioration in the torque density of the motor. All of the above, results in lower mechanical wear of bearings and improved bearing life.

I/We Claim:
1. A stator (100) comprising:
a cylindrical core (102) having a central axis;
a plurality of teeth (104) extending radially outwards from an inner surface of the cylindrical core (102), each tooth having a tooth face arc length (L), a tooth curvature radius (Rt), and any two adjacent tooth of the plurality of teeth (104) defined by a slot opening (106); and
a plurality of insulated conductive coils wound within the slot opening (106) of the cylindrical core (102),
wherein the stator (100) diameter (D) is in the range of 80 mm to 105 mm.
2. The stator (100) as claimed in claim 1, wherein the stator (100) is laminated using a material selected from the group comprising Cold Rolled Non-Grain Oriented (CRNGO) steel or semi-processed lamination steel.
3. The stator (100) as claimed in claim 1, wherein the slot opening (106) is
0.783(2r sinH^)
equal to ±10% of ,() � cos � + 1.2 , wherein r is the radius of the stator
(100), n is the number of pole pairs in the stator (100), and C is the tooth (104) width.
4. The stator (100) as claimed in claim 1, wherein the tooth curvature radius (Rt) is in the range of 0.4r to 0.6r, and r is the radius of the stator (100).
5. A fan motor comprising a stator (100) as claimed in claim 1.

6. A fan comprising a fan motor as claimed in claim 5.