Coreless Axial Flux Motor with Ferrofluid Filled Air Gap and Its Design Method

Abstract

This invention discloses a coreless axial flux motor with a ferrofluid-filled air gap and its design method. The coreless axial flux motor includes a stator with stator windings and a rotor with permanent magnets, with an air gap formed between the stator and rotor filled with ferrofluid. The design method includes generating a current motor design scheme based on the structural parameters of the coreless axial flux motor; establishing a motor model of the coreless axial flux motor based on the current motor design scheme and calculating the power required to overcome the ferrofluid friction loss during rotor rotation; if the power does not meet preset constraints, adjusting the structural parameters of the coreless axial flux motor and repeating the above steps until the optimal current motor design scheme is obtained. This invention aims to solve the problem of low air gap flux density in traditional coreless axial flux motors and improve the heat dissipation performance of coreless axial flux motors.

Description

Technical Field

[0001] This invention relates to the field of motor design and manufacturing technology, specifically to a coreless axial flux motor with ferrofluid filling the air gap and its design method. Background Technology

[0002] A coreless axial flux motor is a special type of permanent magnet synchronous motor. Its key characteristic is the absence of a core (i.e., the stator or rotor does not contain magnetic materials such as silicon steel sheets) found in traditional motors, and the magnetic flux direction is axial (the magnetic field flows along the motor's rotation axis, unlike the radial flux structure of traditional permanent magnet motors). Compared to cored motors, coreless motors reduce iron losses, lighten the motor weight, and eliminate cogging torque (which causes motor vibration and noise). Their high overload capacity and high power density make them highly valuable. However, coreless axial flux motors suffer from low air gap magnetic flux density, low phase inductance, weak field weakening capability, and susceptibility to eddy current and circulating current losses. Under the same size and operating current conditions, the output torque of a coreless motor is typically lower than that of a cored motor, requiring a larger amount of permanent magnets to achieve the same performance. Summary of the Invention

[0003] The technical problem to be solved by the present invention is as follows: In view of the above-mentioned problems of the prior art, the present invention provides a coreless axial flux motor with ferrofluid filling the air gap and its design method. The present invention aims to solve the problem of low air gap magnetic flux density in traditional coreless axial flux motors, and achieve the same output torque performance as cored motors without the need to increase the amount of permanent magnets, while improving the heat dissipation performance of coreless axial flux motors.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A coreless axial flux motor with a ferrofluid-filled air gap includes a stator with stator windings and a rotor with permanent magnets, and an air gap is formed between the stator and the rotor. The air gap is filled with a ferrofluid, which is a liquid with oil as a base and containing nanoscale ferromagnetic particles.

[0006] Optionally, the number of rotors is two, and the two rotors are distributed symmetrically on the upper and lower sides of the stator winding, and the two rotors are exactly the same in size and material.

[0007] Optionally, the gain flux generated by the ferrofluid filling the air gap for the coreless axial flux motor is:

[0008] ;

[0009] in, For gain flux, The inner radius of the motor. The outer radius of the motor. The permeability of free space, Radial position Local magnetization function at radial position .

[0010] Optionally, the calculation function expression for the local magnetization intensity function is:

[0011] ;

[0012] in, The saturation magnetization is It is a hyperbolic cotangent function. , is the magnetic energy coefficient Radial position The radial magnetic field intensity distribution at that location.

[0013] Optionally, the gain flux density generated by the ferrofluid filling the air gap for the coreless axial flux motor is:

[0014] ;

[0015] in, Radial position Gain flux density at the point, The permeability of free space, Radial position Local magnetization function at radial position The inner radius of the motor. Let be the outer radius of the motor.

[0016] A design method for a coreless axial flux motor with a ferrofluid-filled air gap includes the following steps:

[0017] S101, Generate the current motor design scheme based on the structural parameters of the coreless axial flux motor;

[0018] S102, Establish a motor model of a coreless axial flux motor based on the current motor design scheme;

[0019] S103, using the motor model to calculate the power required to overcome the ferrohydrodynamic friction loss for rotor rotation;

[0020] S104, determine whether the power required to overcome the ferrofluid friction loss of the rotor rotation meets the preset constraint conditions with the input power of the motor. If it does not meet the preset constraint conditions, adjust the structural parameters of the coreless axial flux motor and jump to step S101; otherwise, output the current motor design scheme.

[0021] Optionally, the functional expression for calculating the ferrohydrodynamic friction loss that the rotor needs to overcome to rotate using a simplified model in step S103 is as follows:

[0022] ;

[0023] in, The power required to overcome ferrofluid friction losses for rotor rotation. For ferromagnetic fluid viscosity, The thickness of the air gap. ω is the angular velocity of the rotor. The inner radius of the motor. Let be the outer radius of the motor.

[0024] Optionally, step S103, which uses a simplified model to calculate the ferrohydrodynamic friction loss that the rotor needs to overcome to rotate, includes:

[0025] S201, assuming that the rotor wall rotates while the stator wall remains stationary during the flow of the ferrofluid in the air gap, the radial position of the ferrofluid is determined. Axial position Tangential velocity at the point :

[0026] ;

[0027] in, The angular velocity of the rotor, The thickness of the air gap and its axial position. The value is 0 at the stator wall and 0 at the rotor wall. radial position , The inner radius of the motor. The outer radius of the motor;

[0028] S202, based on the radial position of the ferrofluid Axial position Tangential velocity at the point The gradient was calculated to determine the radial position of the ferrofluid. Shear stress at:

[0029] ;

[0030] in, For ferrofluid in radial position Shear stress at the point, For ferromagnetic fluid viscosity, For ferrofluid in radial position Axial position Tangential velocity at the point The gradient;

[0031] S203, based on the radial position of the ferrofluid Calculation of the total drag torque caused by shear stress at the location:

[0032] ;

[0033] in, The total drag torque caused by ferrofluid shear;

[0034] S204, Calculate the ferrofluid friction loss that the rotor needs to overcome to rotate based on the total resistance torque caused by ferrofluid shear:

[0035] ;

[0036] in, The power required to overcome the ferrofluid friction loss for the rotor to rotate.

[0037] Optionally, in step S104, when determining whether the power required to overcome the ferrofluid friction loss for rotor rotation meets the preset constraint condition with respect to the input power of the motor, the preset constraint condition means that the ratio between the power required to overcome the ferrofluid friction loss for rotor rotation and the input power of the motor is less than or equal to a preset percentage parameter.

[0038] Optionally, in step S102, when establishing the motor model of the coreless axial flux motor according to the current motor design scheme, it includes constructing a half-model for the stator and a rotor as the motor model for a coreless axial flux motor in which two rotors are distributed symmetrically on the upper and lower sides of the stator winding; and in step S103, after calculating the power required to overcome the ferrofluid friction loss for rotor rotation using the motor model, it includes multiplying the power required to overcome the ferrofluid friction loss for rotor rotation calculated using the half-model by 2 to obtain the final power required to overcome the ferrofluid friction loss for all rotor rotations.

[0039] Compared with existing technologies, the present invention mainly achieves the following beneficial effects: Ferrofluid is a stable colloidal dispersion system formed by the combination of nanoscale magnetic particles and a carrier liquid. It can be magnetized under an applied magnetic field and exhibit a significant magnetic response while maintaining liquid fluidity. In a static state, the ferrofluid behaves as a flowable liquid, adaptable to any container shape; under a magnetic field, it exhibits strong magnetism similar to a solid magnet, allowing for precise control and actuation. Its magnetic nanoparticles are extremely small in size and exhibit superparamagnetism at room temperature. This means that it is strongly magnetized in the presence of an external magnetic field, but the magnetism immediately disappears once the magnetic field is removed, leaving no residual magnetism, which enables precise control and actuation. The present invention relates to a coreless axial flux motor with a ferrofluid-filled air gap. The air gap between the stator and rotor is filled with ferrofluid. On the one hand, by using ferrofluid, the magnetic field distribution can be improved, thereby increasing the air gap flux density and solving the problem of low air gap flux density in traditional coreless axial flux motors. It can achieve the same output torque performance as a cored motor without the need to increase the amount of permanent magnets. On the other hand, the ferrofluid-filled structure is in direct contact with the stator winding, which can improve the motor's heat dissipation capacity, thereby increasing the torque density. Good thermal management can improve insulation life and enable the motor to operate reliably. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a coreless axial flux motor in an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the basic process of the method in the embodiments of the present invention.

[0042] Figure 3 This is a schematic diagram of the structure of the motor model (semi-model) in an embodiment of the present invention.

[0043] Explanation of reference numerals in the attached diagram: 1. Stator; 10. Stator winding; 2. Rotor; 20. Permanent magnet; 3. Air gap. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0045] like Figure 1 As shown, this embodiment provides a coreless axial flux motor with a ferrofluid-filled air gap, including a stator 1 with stator windings 10 and a rotor 2 with permanent magnets 20, and an air gap 3 is formed between the stator 1 and the rotor 2. The air gap 3 is filled with ferrofluid, which is a liquid with oil as the base and containing nanoscale ferromagnetic particles. By injecting ferrofluid into the air gap 3, the ferrofluid becomes an ideal magnetic conductor and cooling material due to its unique magnetism and fluidity.

[0046] As an optional implementation, the coreless axial flux motor with ferrofluid-filled air gap in this embodiment is a dual-rotor structure, such as... Figure 1 As shown, in this embodiment, there are two rotors 2, which are distributed symmetrically on the upper and lower sides of the stator winding 10, and the two rotors 2 are exactly the same in size and material.

[0047] The air gap 3 is filled with ferrofluid, and the magnetic flux is calculated by superimposing the linear part of the air gap magnetic flux and the nonlinear part of the ferrofluid:

[0048] ;

[0049] in, Defined as total magnetic flux; Defined as fundamental magnetic flux; the magnetic flux generated in the absence of a ferrofluid. Defined as gain flux; the additional magnetic flux generated by the filled ferrofluid after excitation. Specifically, the gain flux generated by the ferrofluid filling the air gap 3 for the coreless axial flux motor is:

[0050] ;

[0051] in, For gain flux, The inner radius of the motor. The outer radius of the motor. The permeability of free space, Radial position Local magnetization function at radial position .

[0052] In this embodiment, the Langevin function is used to simulate the magnetization vector of the ferrofluid. Therefore, the expression for calculating the local magnetization intensity function is as follows:

[0053] ;

[0054] in, Saturation magnetization (refers to the limit value of magnetization reached by a ferrofluid when all its internal magnetic particles are oriented in a sufficiently strong external magnetic field). It is a hyperbolic cotangent function. , which is the magnetic energy coefficient (characterizing the degree of coupling between the magnetic moment of a ferrofluid particle and an external magnetic field, and is related to temperature and the magnitude of the particle's magnetic moment). Radial position Radial magnetic field strength distribution at a radial distance of (referring to the radial distance of) The strength of the external magnetic field generated by the permanent magnet or stator current at that location.

[0055] This embodiment assumes that the ferrofluid is an incompressible Newtonian fluid with constant viscosity; it satisfies the no-slip boundary condition, i.e., the fluid velocity at the wall is equal to the wall velocity; and the size of air gap 3 is... ,in When considering the radius of the motor and relatively smooth flow, the circumferential velocity distribution of the liquid is primarily taken into account, while radial and axial backflow are ignored. Total magnetic flux density in the air gap. It is composed of two superimposed parts:

[0056] ;

[0057] in, Defined as the total magnetic flux density in the air gap; represents the total magnetic field strength in the air gap. Defined as the basic magnetic flux density; for the original excitation at a radius of... The original magnetic induction intensity generated at that location; Defined as gain flux density; is the additional magnetic flux density increment generated after the ferrofluid is magnetized; whereby the gain flux density (the additional magnetic flux density increment generated after the ferrofluid is magnetized) generated by the ferrofluid filling the air gap 3 for the coreless axial flux motor is:

[0058] ;

[0059] in, Radial position Gain flux density at the point, The permeability of free space, Radial position Local magnetization function at radial position The inner radius of the motor. Let be the outer radius of the motor.

[0060] like Figure 2 As shown, this embodiment also provides a design method for a coreless axial flux motor with a ferrofluid-filled air gap, comprising the following steps:

[0061] S101, Generate the current motor design scheme based on the structural parameters of the coreless axial flux motor;

[0062] S102, Establish a motor model of a coreless axial flux motor based on the current motor design scheme;

[0063] S103, using the motor model to calculate the power required to overcome the ferrohydrodynamic friction loss for rotor 2 to rotate;

[0064] S104, determine whether the power required to overcome the ferrofluid friction loss of rotor 2 and the input power of the motor meet the preset constraints. If they do not meet the preset constraints, adjust the structural parameters of the coreless axial flux motor and jump to step S101; otherwise, output the current motor design scheme.

[0065] In step S101, when generating the current motor design scheme based on the structural parameters of the coreless axial flux motor, the structural parameters of the coreless axial flux motor include the dimensional parameters of the stator 1 and rotor 2, the dimensional parameters of the stator winding 10 and permanent magnet 20, and the dimensional parameters of the air gap 3. For example... Figure 1 As shown, the motor topology in this embodiment is a dual-rotor single-stator structure, with stator winding 10 and stator 1 located in the middle, and two rotors 2 distributed symmetrically on the upper and lower sides of stator winding 10, with the corresponding parts having completely identical dimensions and materials.

[0066] In step S102, when establishing the motor model of the coreless axial flux motor based on the current motor design scheme, this includes a coreless axial flux motor with two rotors 2 mirror-symmetrically distributed on the upper and lower sides of the stator winding 10. A half-model is constructed for the stator 1 and one rotor 2 as the motor model. To establish the mathematical model, the coordinate system to be used must first be defined. Generally, a cylindrical coordinate system can be used for the motor model. ,in Radial coordinates, Circumferential coordinates Let be the axial coordinate. Assuming the structure and boundary conditions are axisymmetric, then the flow of the ferrofluid with respect to the circumferential coordinate... Since it is not sensitive, the circumferential coordinates are ignored in the analysis in this embodiment to simplify the analysis. The circumferential direction is transmitted through the tangential velocity component. This can be represented, thus a planar coordinate system was adopted. To construct a semi-model for stator 1 and rotor 2 as the motor model, the final motor model (semi-model) is as follows: Figure 3 As shown. In step S103, after calculating the power required to overcome the ferrofluid friction loss of rotor 2 rotation using the motor model, the power required to overcome the ferrofluid friction loss of rotor 2 rotation calculated using the semi-model is multiplied by 2 to obtain the final power required to overcome the ferrofluid friction loss of all rotor 2 rotations.

[0067] As an optional implementation, the functional expression for calculating the ferrohydrodynamic friction loss that the rotor 2 needs to overcome to rotate using a simplified model in step S103 is as follows:

[0068] ;

[0069] in, The power required to overcome the ferrofluid friction loss for rotor 2 to rotate. For ferromagnetic fluid viscosity, The thickness of air gap 3, Let be the angular velocity of rotor 2. The inner radius of the motor. Let be the outer radius of the motor.

[0070] To quickly estimate the ferrofluid loss within the air gap, the Torsional Couette Approximation theory was employed. The ferrofluid flows within the gap, with the rotor wall rotating and the stator wall stationary. Based on these assumptions, the fluid's radial position... Axial position Tangential velocity at the point ,unit The gap can be approximated as along Linear distribution of directions:

[0071] ;

[0072] The stator end face is stationary. The rotor end face rotates. ;exist The velocity transitions linearly between the two directions; radial direction Boundary conditions , ; The thickness of the gap between the rotor and the stator; ω is the angular velocity of the rotor.

[0073] As an optional implementation, step S103, which uses a simplified model to calculate the ferrohydrodynamic friction loss that the rotor 2 needs to overcome to rotate, includes:

[0074] S201, assuming that when the ferrofluid flows in the air gap 3, the rotor 2 wall rotates while the stator 1 wall remains stationary, thus determining the radial position of the ferrofluid. Axial position Tangential velocity at the point :

[0075] ;

[0076] in, Let be the angular velocity of rotor 2. The thickness of air gap 3 and its axial position The value is 0 at the stator 1 wall and the value is [value missing] at the rotor 2 wall. radial position , The inner radius of the motor. The outer radius of the motor;

[0077] S202, according to Newton's fluid shear formula, shear stress The circumferential friction force per unit area can be derived from the velocity gradient. Therefore, it can be determined based on the radial position of the ferrofluid. Axial position Tangential velocity at the point The gradient was calculated to determine the radial position of the ferrofluid. Shear stress at:

[0078] ;

[0079] in, For ferrofluid in radial position Shear stress at the point, For ferromagnetic fluid viscosity, For ferrofluid in radial position Axial position Tangential velocity at the point The gradient;

[0080] S203, within the effective radius of action Based on the radial position of the ferrofluid Calculation of the total drag torque caused by shear stress at the location:

[0081] ;

[0082] in, The total drag torque caused by ferrofluid shear;

[0083] S204, Calculate the ferrofluid friction loss that rotor 2 needs to overcome to rotate based on the total resistance torque caused by ferrofluid shear:

[0084] ;

[0085] in, The power required to overcome the ferrofluid friction loss for the rotor 2 to rotate.

[0086] The total drag torque caused by ferrofluid shear can be expressed as:

[0087] ;

[0088] Therefore, the ferrohydrodynamic friction loss that rotor 2 needs to overcome to rotate can be expressed as:

[0089] .

[0090] In step S104, when determining whether the power required to overcome the ferrofluid friction loss for rotor 2 to rotate meets the preset constraint condition with respect to the motor's input power, the preset constraint condition refers to a ratio between the power required to overcome the ferrofluid friction loss for rotor 2 to rotate and the motor's input power being less than or equal to a preset percentage parameter. Ferrofluid entering the motor's air gap will cause friction loss. As an optional implementation, if the loss ratio exceeds 3% of the rated output during design, the concentration of nanoparticles should be adjusted or the filling amount reduced. Therefore, the preset constraint condition can be expressed as:

[0091] ;

[0092] in, Defined as the input power of the motor.

[0093] In summary, the design method of the coreless axial flux motor with ferrofluid-filled air gap in this embodiment is based on the Langevin function, which explicitly decomposes the air gap flux into a basic flux term and a ferrofluid magnetization gain term. This is used to calculate and optimize the effect of the ferrofluid on the air gap magnetic field during the design phase. Based on the torsional Cueter approximation, the complex three-dimensional problem is simplified into a single-air gap equivalent model. Only the loss of ferrofluid filling on one side of the air gap is calculated, and the calculation results are mapped to the other side of the air gap according to the symmetry relationship, realizing rapid prediction of losses during the design phase. When the proportion of ferrofluid friction loss to input power exceeds a threshold, the loss is controlled by adjusting the particle concentration or filling amount, thereby achieving a quantifiable trade-off between magnetic flux density gain and friction loss. This method can optimize the structural parameters of the coreless axial flux motor with ferrofluid-filled air gap by addressing the ferrofluid friction loss that needs to be overcome for rotor 2 rotation.

[0094] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method of designing a coreless axial flux motor with ferrofluid filled air gap, characterized by, The coreless axial flux motor includes a stator (1) with stator windings (10) and a rotor (2) with permanent magnets (20), and an air gap (3) is formed between the stator (1) and the rotor (2). The air gap (3) is filled with a ferrofluid, which is a liquid with oil as a base and containing nanoscale ferromagnetic particles. The design method includes the following steps: S101, Generate the current motor design scheme based on the structural parameters of the coreless axial flux motor; S102, Establish a motor model of a coreless axial flux motor based on the current motor design scheme; S103, using the motor model to calculate the power required to overcome the ferrofluid friction loss of the rotor (2) to rotate; The calculation function expression for the power required for the ferrofluid friction loss is as follows: ； in, The power required to overcome the ferrofluid friction loss for the rotor (2) to rotate. For ferromagnetic fluid viscosity, The thickness of the air gap (3) is... Let be the angular velocity of rotor (2). The inner radius of the motor. The calculation of the power required for the friction loss of the ferrofluid includes: S201, assuming that when the ferrofluid flows in the air gap (3), the rotor (2) wall rotates and the stator (1) wall is stationary, thus determining the radial position of the ferrofluid. Axial position Tangential velocity at the point : ； in, Let be the angular velocity of rotor (2). The thickness of the air gap (3) and its axial position The value is 0 at the stator (1) wall and the value is 0 at the rotor (2) wall. radial position , The inner radius of the motor. Where S202 is the outer radius of the motor; S202 is determined by the radial position of the ferrofluid. Axial position Tangential velocity at the point The gradient was calculated to determine the radial position of the ferrofluid. Shear stress at: ； in, For ferrofluid in radial position Shear stress at the point, For ferromagnetic fluid viscosity, For ferrofluid in radial position Axial position Tangential velocity at the point The gradient; S203, based on the radial position of the ferrofluid. Calculation of the total drag torque caused by shear stress at the location: ； in, S204, the total resistance torque caused by ferrofluid shear; based on the total resistance torque caused by ferrofluid shear, calculate the ferrofluid friction loss that the rotor (2) needs to overcome to rotate: ； in, The power required to overcome the ferrofluid friction loss required for the rotor (2) to rotate; S104, determine whether the power required to overcome the ferrofluid friction loss of the rotor (2) and the input power of the motor meet the preset constraint conditions. If they do not meet the preset constraint conditions, adjust the structural parameters of the coreless axial flux motor and jump to step S101; otherwise, output the current motor design scheme. The preset constraint conditions refer to the ratio between the power required to overcome the ferrofluid friction loss of the rotor (2) and the input power of the motor being less than or equal to the preset percentage parameter.

2. The design method of a coreless axial flux motor with ferrofluid-filled air gap according to claim 1, characterized in that, The number of rotors (2) is two. The two rotors (2) are distributed symmetrically on the upper and lower sides of the stator winding (10), and the two rotors (2) are completely identical in size and material.

3. The design method of a coreless axial flux motor with ferrofluid-filled air gap according to claim 1, characterized in that, The gain flux generated by the ferrofluid filling the air gap (3) on the coreless axial flux motor is: ； in, For gain flux, The inner radius of the motor. The outer radius of the motor. The permeability of free space, Radial position Local magnetization function at radial position .

4. The design method of a coreless axial flux motor with ferrofluid-filled air gap according to claim 3, characterized in that, The expression for calculating the local magnetization intensity function is as follows: ； in, The saturation magnetization is It is a hyperbolic cotangent function. , is the magnetic energy coefficient Radial position The radial magnetic field intensity distribution at that location.

5. The design method of a coreless axial flux motor with ferrofluid-filled air gap according to claim 1, characterized in that, The gain flux density generated by the ferrofluid filling the air gap (3) for the coreless axial flux motor is: ； in, Radial position Gain flux density at the point, The permeability of free space, Radial position Local magnetization function at radial position The inner radius of the motor. Let be the outer radius of the motor.

6. The design method of a coreless axial flux motor with ferrofluid-filled air gap according to claim 1, characterized in that, In step S102, when establishing the motor model of the coreless axial flux motor according to the current motor design scheme, it includes constructing a half-model for the stator (1) and a rotor (2) as the motor model for the coreless axial flux motor in which the two rotors (2) are distributed symmetrically on the upper and lower sides of the stator winding (10). In step S103, after calculating the power required to overcome the ferrofluid friction loss of the rotor (2) to rotate using the motor model, it includes multiplying the power required to overcome the ferrofluid friction loss of the rotor (2) to rotate using the half-model by 2 to obtain the final power required to overcome the ferrofluid friction loss of all rotors (2) to rotate.

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