Rotor balancing plate for rotating machines

Abstract

The present invention relates to the field of rotating machines and in particular to a balancing plate (100) utilized alongside the rotor of Permanent Magnet Synchronous Motor PMSM. The balancing plate (100) consists of a base (120) with multiple radially extending arms (140) forming a fan-like configuration, symmetrically spaced to create balanced pockets for weight reduction. Notably, the arms (140) of this balancing plate (100) feature a protruding profile facing the rotor. Crafted from stainless steel, this component enhances both the functionality and aesthetics of the PMSM, ensuring uniform weight distribution and bolstering stability. This balancing plate (100) plays a crucial role in optimizing the performance and design of PMSMs, offering a symmetrical approach to weight management and structural integrity.

Description

ROTOR BALANCING PLATE FOR ROTATING MACHINESTECHNICAL FIELD

[0001] The present invention rebates to the field of electrical motors and / or generators. In particular, the present invention particularly relates to a balancing plate utilized in the rotors of rotating machines.BACKGROUND

[0002] The motor functions as a crucial power source, generating rotational force through its primary components, namely the stator and rotor. Extended operation of the motor can result in increased heat production. Failure to dissipate this heat promptly can adversely affect the lifespan of the motor.

[0003] The previous designs featured an aluminum balancing plate whose outer circumferential diameter matched that of the core pack of the rotor. However, this design lacked any profile on the balancing plates. As a consequence, issues arose due to the generation of eddy currents within the balancing plate. Further issues included the rotation of the balancing plate rotating within the rotor, propelled by the flux created by the stator.

[0004] The rotation of the rotor resulted in the cutting of stator flux, inducing eddy currents within the balancing plate. These induced eddy currents, in turn, caused the plate to rotate. Consequently, the rotational movement of the balancing plate led to the conversion of the induced eddy currents into heat. This phenomenon further compounded the challenges associated with heat dissipation within the motor.

[0005] To tackle these challenges, several innovative solutions have been introduced. In CN212784925U, a spline is positioned on the outer surface of the main shaft, enabling the rotor to be securely affixed to the main shaft through precise matching with the spline. These splines arestrategically spaced along the main shaft, with multiple partition plates installed on the outer surface of the main shaft's middle section, aligning with the intervals between adjacent splines.

[0006] Moreover, centrifugal fans are mounted at both ends of the main shaft in a symmetrical arrangement. These fans are equipped with numerous radial air holes embedded within the rotor. This configuration enhances airflow and promotes efficient cooling of the motor components during operation.

[0007] CN114123636A discloses a motor balancing plate positioned at one end in the axial direction (A) of a motor rotor (11), featuring a disc-shaped configuration. The balancing plate's end face, oriented towards the rotor (11), exhibits partial protrusions forming a series of blades (21). These blades (21) are arranged circumferentially around the balancing plate and extend from its inner radial side to the outer radial side, forming centrifugal blades. Consequently, during rotation, the blades (21) agitate the air, generating an airflow that flows from the inner radial side to the outer radial side.

[0008] CN207459903U introduces a motor and its associated rotor balancing plate. This patent features fan blades positioned on the outer surface of the rotor balancing plate to enhance airflow in proximity to the rotor, aiding in heat dissipation. However, the effectiveness of heat dissipation achieved by the rotor balancing plate in this patent is constrained, and the structure of the rotor balancing plate is comparatively intricate, occupying significant space.

[0009] Several prior art references, such as those mentioned above, offer similar techniques and systems. However, there is still a need to develop an efficient system that can enhance and promote efficient cooling of the motor components during operation.OBJECTIVE OF THE INVENTION

[0010] A primary objective of the present invention is to provide a balancing plate for a rotor utilized in a rotating machine, specifically in a permanent magnet synchronous motor (PMSM).

[0011] Another objective of the present invention is to provide a balancing plate with a lesser outer circumferential diameter that of the magnetic core of the rotor.

[0012] Yet another objective of the present invention is wherein the balancing plate comprises protrusions in the form of fan blades arranged circumferentially.

[0013] Yet another objective of the present invention is to provide a balancing plate, wherein the protrusions are positioned on one side of the balancing plate.

[0014] Yet another objective of the present invention is to provide a balancing plate wherein the fan blades maintain symmetrical / laterally spaced air pockets between adjacent blades.

[0015] Another objective of the present invention is to provide a balancing plate made of stainless steel.

[0016] Yet another objective of the present invention is to a balancing plate for heat dissipation and cooling of core magnet temperature, irrespective of the direction of rotation of the plate.

[0017] Yet another objective of the present invention is to provide a balancing plate with higher resistivity to generation of eddy current.

[0018] Yet another objective of the present invention is to provide a balancing plate for improved dissipation of heat and reduction in core magnet temperature.

[0019] Yet another objective of the present invention is to provide a balancing plate that maintains heat dissipation and cooling of core magnet temperature, irrespective of the direction of rotation of the plate.SUMMARY OF THE INVENTION

[0020] The following summary is provided to facilitate a clear understanding of the new features in the disclosed embodiment and it is not intended to be a full, detailed description. A detaileddescription of all the aspects of the disclosed invention can be understood by reviewing the full specification, the drawing and the claims and the abstract, as a whole.

[0021] An aspect of the present invention discloses a balancing plate positioned beside the rotor in a Permanent Magnet Synchronous Motor (PMSM), wherein the balancing plate has a decreased outer circumferential diameter compared to that of the rotor. The balancing plate is equipped with multiple arms extending radially to this circumference, exhibiting a fan profile. These arms are evenly spaced apart, facilitating a symmetrical distribution of weight reduction pockets between adjacent arms.

[0022] Furthermore, another aspect of the invention discloses the arms of the balancing plate exhibiting a protruding profile on one side, the side facing the rotor. Furthermore, the balancing plate is constructed from stainless steel material. This characteristic contributes to the overall functionality and design of the balancing plate within the PMSM.BRIEF DESCRIPTION OF DRAWINGS

[0023] The detailed description is described with reference to the accompanying figures. Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements and features. The features and advantages of the present proposed system will become more apparent from the following detailed description a long with the accompanying figures, which forms a part of this application.

[0024] Fig.1 illustrates an exploded view of a rotor assembly and balancing plates according to prior art.

[0025] Fig.2 illustrates a front side of the balancing plate according to a preferred embodiment of the present invention.

[0026] Fig.3 illustrates a back side of the balancing plate according to a preferred embodiment of the present invention.

[0027] Fig.4 illustrates a side view of the balancing plate according to a preferred embodiment of the present invention.

[0028] It is to be noted, however, that the appended drawing illustrates only typical embodiments of this system and are therefore should not be considered limiting of its scope, for the system may admit to other equally effective embodiments.DETAILED DESCRIPTION OF THE INVENTION

[0029] The following is a detailed description of the present disclosure depicted in the accompanying drawings. However, it may be understood by a person having ordinary skill in the art that the present subject matter may be practiced without these specific details. The subject matter of the disclosure will be more clearly understood from the following description of the embodiments thereof, given by way of example only with reference to the accompanying drawings, which are not drawn to scale.

[0030] If the specification states that a component or a feature “may” or “can” be included, that particular component or feature is not required to be included or have the characteristic. The use of open-ended terms like “comprising” and variations herein is meant to encompass the steps listed thereafter and equivalents thereof as well as additional items. As used herein, the singular forms “a,” “an,” and “the” designate both the singular and the plural, unless expressly stated to designate the singular only.

[0031] The term ‘PMSM’ refers to Permanent Magnet Synchronous Motor. The term ‘SS’ refers to stainless stee. It is a type of synchronous motor in which permanent magnets are used to create the magnetic field required for the motor's operation. Ther term ‘balancing plate’ refers to a component in a Permanent Magnet Synchronous Motor (PMSM) designed to reduce vibrations and improve the overall performance of the motor.

[0032] In a PMSM, the stator surrounds the rotor and contains coils of wire. When electric current flows through these coils, it creates a magnetic field. The rotor, housing permanent magnets, interacts with this magnetic field, inducing rotation. However, imbalance in rotor mass distribution can cause vibrations. To counteract this, a balancing plate is strategically placed within the rotor. This plate adjusts the mass distribution, minimizing vibrations and ensuring smoother operation. As current flows through the stator coils, it generates a rotating magnetic field, which interacts with the fixed magnetic field of the rotor, producing torque and driving rotation. The balanced rotor, along with precise stator control, enables efficient performance in PMSMs, making them ideal for various applications, from industrial machinery to electric vehicles.

[0033] The rotor with a balancing plate in a PMSM significantly reduces vibrations, ensuring smoother operation and minimizing noise. By optimizing mass distribution, stability at high speeds is enhanced, leading to improved dynamic performance and precision control. This configuration extends the motor's lifespan by reducing mechanical stress on components, such as bearings. Additionally, it increases energy efficiency by mitigating losses associated with vibration. The balancing plate enables fine-tuning of the rotor's characteristics, enhancing torque production and speed control. Overall, this setup improves the reliability, efficiency, and performance of PMSMs across various applications.

[0034] The primary function of the balancing plate is to prevent axial movement of the magnets housed within the grooves of the magnetic plate located in the core of a PMSM rotor. Additionally, the balancing plate serves as a means for material removal during the balancing process. Typically, two balancing plates are employed in this setup. The side of the plate facing the magnets is denoted as the front side, while the side facing outward is termed the back side of the balancing plate, as described herein.

[0035] Fig.1 presents a prior art embodiment of a rotor assembly mounted on a shaft. In this depiction, the outer circumferential diameter of the balancing plate (20) aligns with that of the rotor (10). Moreover, the balancing plates lack any profile or protrusions. They are plain in design, as illustrated in Fig.1.

[0036] Referring back to Fig.l, the balancing plates in the PMSM are typically made of Aluminum, known for its conductivity of heat and electricity. However, the configuration depicted in Fig.l encountered issues due to the generation of eddy currents on the balancing plate. Eddy currents are induced within the balancing plate (20) by the flux generated by the stator of the PMSM, leading to the rotation of the balancing plate within the rotor. Subsequently, the induced eddy currents convert to heat.

[0037] Fig.2, 3, and 4 illustrate a balancing plate (100) mounted on a shaft (not shown here) according to a preferred embodiment of the present invention. According the Fig.2, the balancing plate (100) of a rotor in a PMSM is designed in a manner to overcome the limitations of the prior art. Referring back to Fig.2, the balancing plate (100) is initially designed out of Stainless Steel, hereinafter referred to as SS. SS has a higher resistivity to the conduction of eddies than Aluminum. Though Aluminum is a good conductor of heat and electricity, the Aluminium balancing plate encountered the limitation of generating eddy currents, which in turn results in heat generation in the Aluminium balancing plate. Thus, Aluminium has a low resistivity to the conduction of eddies, compared to stainless steel (SS).

[0038] However, simply changing the material alone does not significantly decrease the generation of eddy currents. Consequently, the profile of the balancing plate (100) has been altered to achieve the desired reduction in eddy currents. As depicted in Figs.2 and 3, the surface area of the balancing plate (100) is minimized by incorporating multiple pockets forming unique fan profile. This fan profile is positioned on the face of the balancing plate (100) that faces the rotor. Thus, the balancing plate (100) installed on the rotor shaft now features a fan profile on its front face, oriented towards the rotor. Moreover, the outer circumferential diameter of the balancing plate (100) is now constructed smaller compared to that of the rotor magnet.

[0039] Referring back to Fig.2, the balancing plate (100) comprises a base (120) featuring arms (140) of the fan profile extending radially. The arms (140) are symmetrically spaced apart laterally on the base (120), forming symmetrical weight reduction pockets (160) between the adjacent arms. During rotation, this configuration promotes effective cooling of the rotor magnets. Referring Figs.2 and 3, it is observed that the fan profile exhibits a slight protrusion from the base (120) only on one side, directed towards the front side facing the rotor. Additionally, the inclusion of the weight reduction pockets (160) between the arms (140) of the fan diminishes the surface area of the balancing plate (100), resulting in weight reduction.

[0040] Referring back to Figs 2 and 3, the presence of the weight reduction pockets (160) increases the airflow which helps to combat the heat generation in the magnet, thereby lowering the magnet temperature. Furthermore, due to less surface area on account of the pockets, the eddy generated in the balancing plate (100) is relatively less. Utilizing stainless steel for the balancing plate (100), along with weight reduction pockets, enhances resistance to eddy currents, reducing eddy current generation and increasing flux resistance in PMSM motors. This results in a significant reduction in eddy current generation within the SS balancing plate, up to 40% compared to aluminum.

[0041] Furthermore, by reducing the outer circumferential diameter (OD) of the balancing plate (100) when compared to the outer circumferential diameter of the rotor, the resistance to stator flux is heightened as flux from the stator traverses over the rotor too. This reduction in outer circumferential diameter of the balancing plate (100) strategically places the plate below the area affected by stator flux, underscoring the importance of dimensions in optimizing motor performance. Furthermore, as the profile on the plate adopts a protruding fan profile from the base (120), on the side facing the rotor, an airflow from the rotor to the magnet slots is facilitated, effectively cooling the magnets by inducing airflow within them. Additionally, the decreased outer circumferential diameter of the balancing plate (100) not only diminishes surface area but also ensures the secure positioning of magnets within the rotor core, preventing axial movement of the magnets. This balancing plate (100) is adeptly designed for both clockwise and anticlockwise rotations, ensuring consistent cooling efficiency regardless of rotational direction, with the fan- profiled area facing the magnets of the rotor.

[0042] In terms of design specifics, the rotor balancing plate is crafted with reduced outer circumferential diameter in the range of 80 mm to 85 mm so as to minimize surface area and secure magnets against lateral movement within the rotor core. The fan profile, projecting approximately 0.3mm to 0.6mm from the base (120), optimizes cooling by facilitating airflow over the magnets during rotation. Furthermore, the thickness of the balancing plate ranges from 3mm to 8mm, witha preferred thickness of 5mm, balancing structural integrity and weight considerations. Additionally, incorporating depressions on the backside of the plate, up to 2mm deep, aids m weight reduction without compromising functionality, ensuring an optimal balance between performance and efficiency.Experimental data I

[0043] Table 1 shows a comparative study done between the rotors utilizing an aluminium balancing plate according to prior art, a stainless steel balancing plate and a stainless steel balancing plate with a fan profile according to the present invention. The rotors of all the three machines were run at an operational speed of 7000 RPM for 20 min.Table 1:

[0044] It is noticed that the temperature of the magnet utilizing the stainless steel balancing plate (100) with fan profile has a comparatively lesser temperature than the rotors utilizing the Aluminium balancing plate or stainless steel balancing plate without a fan profile.Experimental data II

[0045] Table II show a comparative study on how the features of the balancing plate utilized in the rotor affects the eddy current losses in watts faced by the magnet and the balancing plates.Table II:

[0046] When comparing the eddy current losses experienced in the rotor with an aluminum balancing plate versus a stainless steel balancing plate (100), it becomes apparent that the losses are relatively lower when the balancing plate is made of stainless steel.Experimental data III

[0047] Table III shows the temp experienced by the rotor magnet with the balancing plate over the rotor.

[0048] The rotor lamination, usually composed of laminated sheets of magnetic material like silicon steel, undergoes modification by integrating pockets or voids in specific regions to decrease the rotor’s overall weight. A laminated rotor with these weight reduction pockets experiences a magnet temperature of 144°C, whereas one without the pockets registers a magnet temperature of 136°C. Interestingly, when the weight reduction pocket (160) is positioned on the balancing plate over the V-slots of the magnet, it notably affects the magnet temperature, reducing it to 115°C.

[0049] The balancing plate in PMSM motors is therefore, engineered to address thermal issues and reduce eddy currents, enhancing overall efficiency. To achieve this, multiple design optimizations are implemented. Firstly, reducing the surface area of the balancing plate byincorporating pockets minimizes eddy current losses. Additionally, utilizing stainless steel, known for its lower conductivity compared to aluminum, further mitigates eddy currents while providing insulation against thermal changes. Moreover, a tailored fan profile integrated into the rotor cooling system ensures efficient heat dissipation regardless of rotational direction, contributing to improved thermal management and magnet longevity.

[0050] The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein; thus, the present invention is defined by the wording of the appended claims and the equivalents thereof. Thus, the equipment may be modified in all kinds of ways within the scope of the appended claims.

Claims

WE CLAIM:

1. A balancing plate (100) assembled on a shaft in an axial direction of a rotor of a Permanent magnet synchronous motor (PMSM), the balancing plate (100) comprising: an outer circumferential diameter relatively lesser than an outer circumferential diameter of the rotor; and a plurality of arms (140) extending radially to the outer circumferential diameter from a base (120); wherein the arms (140) are symmetrically spaced apart, thereby facilitating a symmetrical distribution of pockets (160) between adjacent arms (140).

2. The balancing plate (100) as claimed in claim 1, wherein the plate (100) has an outer circumferential diameter in the range of 80 - 85 mm.

3. The balancing plate (100) as claimed in claim 1, wherein the arms (140) have a protruding profile from the base (120) of the balancing plate (100).

4. The balancing plate (100) as claimed in claim 1, wherein the protruding profile projects in a range of 0.3mm to 0.6mm from the base (120) of the balancing plate (100).

5. The balancing plate (100) as claimed in claim 1, wherein a thickness of the balancing plate (100) lies in a range of 3mm to 8mm.

6. The balancing plate (100) as claimed in claim 1, wherein the balancing plate (100) is made of stainless steel.

7. The balancing plate (100) as claimed in claim 1, wherein the plate (100) can rotate in a clockwise or anticlockwise direction to provide a cooling effect.

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