Method for simulating winding process of high-speed permanent magnet motor rotor carbon fiber sheath

Abstract

The invention discloses a simulation method for a high-speed permanent magnet motor rotor carbon fiber sheath winding process. According to the method, a carbon fiber sheath with a continuous spiral structure is discretized, and the winding process is simulated through an activation scaling method or an activation scaling method and is realized based on finite element simulation. According to the invention, the mechanical energy change of the carbon fiber layer in the winding process is compared with the chemical energy change in the chemical reaction, and the activation force is introduced to realize the simulation of the carbon fiber winding process. According to the method, the real physical attributes of all parts of the rotor are reserved, and the stretching effect of winding tension on the carbon fiber layer is simulated. On the basis of simulating the carbon fiber winding process by using the method disclosed by the invention, the stress of the rotor bound by the carbon fibers under various working conditions can be accurately calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed motor rotor strength analysis, and more specifically, relates to a simulation method and a stress calculation method for the winding process of a carbon fiber sleeve of a high-speed permanent magnet motor rotor. Background Art

[0002] High-speed permanent magnet motors have characteristics such as high efficiency, high power density, and high-speed direct drive, and have received extensive attention in the modern industrial community. However, under the action of the centrifugal force generated by high-speed rotation, permanent magnets have a very high risk of damage. In order to provide sufficient pre-tightening force for the rotor, composite carbon fibers with high tensile strength, low density, and low electrical conductivity are required to bind the rotor. At the design stage of high-speed permanent magnet motors, it is necessary to check the strength of the rotor bound by carbon fibers under different working conditions to ensure the safety of rotor operation. Currently, the commonly used method for simulating the actual winding process of carbon fibers is the equivalent temperature field method, which applies a false thermal expansion coefficient or temperature rise to the carbon fiber layer, so that the thermal stress of the carbon fiber layer is equal to the stress generated by the winding tension. However, this method sacrifices the thermal expansion coefficient or temperature rise of the carbon fiber layer and cannot accurately calculate the rotor stress under high-temperature working conditions after winding is completed.

[0003] Therefore, there is an urgent need for a new calculation method to simulate the winding process of the carbon fiber sleeve in order to accurately calculate the rotor stress under different working conditions after winding is completed. Summary of the Invention

[0004] Aiming at the defects existing in the existing methods for simulating the winding process of carbon fiber sleeves, the purpose of the present invention is to propose a simulation method for the winding process of a carbon fiber sleeve of a high-speed permanent magnet motor rotor, and use the activation scaling method or the activation scaling method to simulate the winding process of the carbon fiber sleeve of the rotor. The proposed method is based on finite element simulation, retains the true physical properties of each component of the rotor, and calculates the rotor stress under different working conditions. The technical solution of the present invention is as follows:

[0005] A simulation method for the winding process of a carbon fiber sleeve of a high-speed permanent magnet motor rotor, discretizes the carbon fiber sleeve with a continuous spiral structure, and the winding process is simulated by the activation scaling method or the activation scaling method.

[0006] Further, the activation scaling method is implemented based on the three-dimensional motion unit method, and its steps include:

[0007] A1. Construct an initial finite element model, requiring that the outer diameter of the permanent magnet rotor is greater than the inner diameter of the first layer of carbon fiber, and the outer diameter of the i-th layer of carbon fiber is greater than the inner diameter of the (i + 1)-th layer of carbon fiber;

[0008] A2. Apply a compressive activation force pointing inward to the permanent magnet rotor, so that the radius of the permanent magnet rotor decreases until it is less than the inner diameter of the first layer of carbon fiber;

[0009] A3. The first layer of carbon fiber moves to the surface of the permanent magnet rotor, the activation force is removed, and the permanent magnet rotor spreads the carbon fiber layer outward to complete the winding of the first layer of carbon fiber;

[0010] A4. Repeat steps A2 and A3 until all layers of carbon fiber winding are completed.

[0011] The implementation process of the activation scaling method based on the three-dimensional motion unit method is described as follows: at the initial moment, there is a permanent magnet rotor (for the convenience of description, it is called the 0th layer) and N carbon fiber layers in the space, where the outer diameter of the i-th (i≥0) layer is larger than the inner diameter of the i+1 layer; when winding the i-th (i≥1) layer, the condition for winding to occur is that the inner diameter of the i-th layer is larger than the outer diameter of the i-1 layer. Therefore, in order to enable winding to occur, the activation force of compressive nature is applied to the i-1th layer, driving the outer diameter of the i-1th layer to be smaller than the inner diameter of the i-th layer; after the i-th carbon fiber layer moves to the surface of the i-1th carbon fiber layer, the activation force is removed, and the internal components will stretch the i-th carbon fiber layer outward to complete the winding of the i-th layer; from the inside to the outside, the winding of all carbon fiber layers is completed. Under the action of the activation force, each layer of carbon fiber completes a process of "contraction" and "expansion" in two time steps, realizing the simulation of the actual winding process.

[0012] Furthermore, the activation scaling method is implemented based on a two-dimensional birth-death unit method, and the steps include:

[0013] B1. Construct an initial finite element model, requiring that the outer diameter of the permanent magnet rotor is larger than the inner diameter of the first layer of carbon fiber, and the outer diameter of the i-th layer of carbon fiber is larger than the inner diameter of the i+1-th layer of carbon fiber;

[0014] B2, the activation force starts to act from the outermost carbon fiber layer, causing the carbon fiber layer to expand outward and increase in radius until the inner diameter of the i-th carbon fiber layer is larger than the outer diameter of the i-1-th carbon fiber layer, at which time the i-1-th layer is activated;

[0015] B3, repeat step B2 until the permanent magnet rotor is activated, during which the activation force on each layer of carbon fiber continues to act;

[0016] B4. Starting from the first layer of carbon fiber, remove the activation force layer by layer, and the carbon fiber layer shrinks to complete the winding of all layers of carbon fiber.

[0017] The implementation process of the activation scaling method based on the two-dimensional birth and death element method is described as follows: At the initial moment, there is a permanent magnet rotor (for the convenience of narration, called the 0th layer) and N layers of carbon fiber in the "dead" space, where the outer diameter of the i-th (i≥0) layer is greater than the inner diameter of the (i + 1)-th layer; to meet the winding conditions of the carbon fiber layer, starting from the Nth layer, the carbon fiber layers are activated layer by layer inward, and an activation force with an expansion property is applied to drive the outer diameter of the i-th (i≥1) layer of carbon fiber to be greater than the inner diameter of the (i - 1)-th (i≥1) layer; before activating the permanent magnet rotor, all activation forces need to act continuously; after activating all components, starting from the 1st layer, the activation forces acting on the carbon fiber layers are removed layer by layer; removing the activation force will cause the carbon fiber layer to contract inward, producing a binding effect on the inner components and realizing the simulation of the actual winding process.

[0018] In the present invention, the main differences between the activation scaling method and the activation expansion and contraction method lie in the acting direction and duration of the activation force. In the method, the activation force only serves to change the radius of the carbon fiber layer to meet the winding conditions. Within the range of elastic deformation, the magnitude and nature of the activation force do not affect the stress calculation result, as long as it is large enough to enable winding to occur; the role of the activation force is the same as that of the activation energy in a chemical reaction.

[0019] When using the method to simulate the winding process of the carbon fiber layer, before and after winding, the radius of each layer of carbon fiber increases, resulting in an increase in its elastic potential energy. Therefore, each layer of carbon fiber has a tendency to contract inward to the equilibrium position, which generates circumferential stress on the carbon fiber layer and radial pressure on the inner components; the change in the elastic potential energy of the carbon fiber layer before and after winding can be analogized to the change in the chemical energy of a substance before and after a chemical reaction. The method uses the circumferential stress generated by this contraction tendency to simulate the stress generated by the winding tension. The winding tension is controlled by changing the initial radius of each layer of carbon fiber, where the radius refers to the radius at the middle position of the carbon fiber layer. The solution method for the initial radius of the carbon fiber layer is described as follows:

[0020] The circumferential stress of the carbon fiber layer generated by the contraction tendency is an explicit function of the radius of the carbon fiber layer, that is, σ θ =f(r). At r = R0, its Taylor expansion can be expressed as,

[0021] σ θ =f(R0)+f'(R0)(r - R0)+f”(R0)(r - R0) 2 / 2+… (1)

[0022] Furthermore, only retaining the linear main part, Equation (1) can be simplified to,

[0023] σ θ =f(R0)+f'(R0)(r - R0) (2)

[0024] Equation (2) is a linear unary function with respect to R0. Therefore, through two iterations, the initial radius of the carbon fiber layer under a given winding tension can be determined.

[0025] Furthermore, after winding, the carbon fiber layers are closely attached together, and its radius R c is known. The initial radius R1 of the first iteration satisfies

[0026] σ T =(R c -R1) / R1×E / / (3)

[0027] where σ T is the stress generated by the winding tension, calculated as σ T =F t / (ab), F t is the winding tension, a and b are the width and thickness of the carbon fiber layer respectively; E ∥ is the Young's modulus along the parallel direction of the carbon fiber. The circumferential stress σ θ1 corresponding to the initial radius R1 of the carbon fiber layer can be calculated by the proposed method. The initial radius of the second iteration is R1+ΔR, and the corresponding circumferential stress obtained is σ θ2 . Substituting (R1,σ θ1 ) and (R1+ΔR,σ θ2 ) into (2) can solve the initial radius of the carbon fiber layer under a given winding tension.

[0028] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0029] The method provided by the present invention, on the premise of retaining the true physical properties of each material of the rotor, realizes the simulation of the carbon fiber sheath winding process by using the circumferential stress generated by the shrinkage trend caused by the change in the radius of the carbon fiber layer before and after winding to equivalently represent the action of the winding tension. After the winding process simulation is completed, applying the rotational speed and temperature rise conditions to the rotor can check the rotor stress under various working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Those skilled in the art will understand the above and other objects, advantages and features of the present application more clearly according to the following detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings.

[0031] Figure 1 is a schematic diagram for implementing the activation scaling method based on the three-dimensional motion element method;

[0032] Figure 2 is a schematic diagram for implementing the activation scaling method based on the two-dimensional birth and death element method;

[0033] Figure 3Schematic diagram of interference fit between preformed carbon fiber sleeve and permanent magnet rotor;

[0034] Figure 4 Relationship between radius and temperature of permanent magnet rotor in the embodiment of the present invention when using liquid nitrogen cooling for interference fit;

[0035] Figure 5 Maximum value of the first principal stress of the permanent magnet in the rotor with a preformed carbon fiber sleeve under high-speed and high-temperature conditions calculated by the proposed method;

[0036] Figure 6 Maximum value of the circumferential stress of the carbon fiber sleeve in the rotor with a preformed carbon fiber sleeve under high-speed and high-temperature conditions calculated by the proposed method;

[0037] Figure 7 Schematic diagram of simplifying the continuous spiral structure carbon fiber sleeve into a multi-layer discrete circular ring structure;

[0038] Figure 8 Schematic diagram of the surface-mounted permanent magnet motor rotor structure with a multi-layer carbon fiber sleeve;

[0039] Figure 9 Change of circumferential stress of carbon fiber layers during carbon fiber winding calculated by the proposed activation scaling method and activation scaling method in the embodiment of the present invention;

[0040] Figure 10 Circumferential stress of carbon fiber layers calculated by the activation scaling method under different working conditions;

[0041] Figure 11 Stress between the permanent magnet and the rotating shaft calculated by the activation scaling method under different working conditions;

[0042] In all the figures, working condition A - normal temperature (22 °C) stationary condition; working condition B - normal temperature overspeed (1.2 times the rated speed) condition; working condition C - hot state (150 °C) overspeed condition; working condition D - hot state stationary condition.

[0043] Among them, 1 - rotating shaft, 2 - permanent magnet, 3 - first layer of carbon fiber, 4 - Nth layer of carbon fiber, 5 - preformed carbon fiber sleeve, 6 - permanent magnet rotor, 7 - activation force. Detailed implementation manners

[0044] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are only for the purpose of describing specific embodiments and are not intended to limit the invention.

[0046] In order to solve the problem that the existing method for winding the carbon fiber maintenance sleeve of the rotor of an analog high-speed permanent magnet motor sacrifices the true physical properties of carbon fiber, starting from the law of change of the mechanical energy of the carbon fiber layer during the winding process, the present invention proposes an activation scaling method and an activation scaling method that retain the true physical properties of each material based on finite element simulation. The implementation processes are as follows Figure 1 、 Figure 2 shown. Driven by the activation force 7, the winding process can occur. The method controls the circumferential stress after the winding layer is wound by changing the initial radius of the carbon fiber layer, and uses this circumferential stress to equivalently simulate the stress generated by the winding tension. Compared with the traditional method of using thermal stress to equivalently simulate the stress generated by the winding tension, the method retains the true physical properties and temperature rise of each material, and can accurately check the stress of the rotor tied by carbon fiber under various working conditions after winding.

[0047] The technical solutions of the present application are further described below with reference to embodiments.

[0048] Embodiment 1

[0049] For the preformed carbon fiber maintenance sleeve 5, it is first wound and cured on the core mold, and then the permanent magnet rotor 6 is press-fitted with the preformed carbon fiber maintenance sleeve 5 by the cold fitting method. The assembly schematic diagram is as Figure 3 shown. The conventional method is: soak the permanent magnet rotor 6 in liquid nitrogen to cool it down, reduce its outer diameter, so that the permanent magnet rotor 6 can penetrate into the preformed carbon fiber maintenance sleeve 5, and after returning to room temperature, the press-fitting is completed.

[0050] According to the implementation process of the press-fitting, the preformed carbon fiber maintenance sleeve 5 is regarded as a generalized layer of carbon fiber. Therefore, the activation scaling method is used to simulate its assembly process. The compressive activation force 7 acts on the permanent magnet rotor to simulate the cooling effect of liquid nitrogen, and removing the activation force simulates heating up to room temperature.

[0051] Among them, the initial radius of the carbon fiber layer is determined by the interference amount and the interference method. As Figure 4As shown, when the rotor of this embodiment is cooled from room temperature to liquid nitrogen temperature, the reduction in the radius of the permanent magnet rotor 6 does not exceed 0.1 mm. Therefore, its interference amount can be determined to be 0.09 mm. When the tolerance acts on the sheath, it is called external interference; when the tolerance acts on the permanent magnet, it is called internal interference. Therefore, for the rotor of this embodiment, when the interference method is external interference, the initial inner diameter of the sheath is 38.11 mm and the outer diameter of the permanent magnet is 38.2 mm; when the interference method is internal interference, the initial inner diameter of the sheath is 38.2 mm and the outer diameter of the permanent magnet is 38.29 mm.

[0052] After assembly, the maximum value of the first principal stress of the calculated permanent magnet is as Figure 5 shown, and the maximum value of the circumferential stress of the preformed carbon fiber sheath is as Figure 6 shown. The results show that the stress calculation results of the interference fit between the preformed carbon fiber sheath 5 and the permanent magnet rotor 6 using the two proposed methods are very close.

[0053] Embodiment 2

[0054] When manufacturing a carbon fiber rotor using the large-tension winding method, the carbon fiber is directly tied to the surface of the rotor. As Figure 7 shown, since the thickness of the carbon fiber is relatively thin, for the convenience of calculation, the continuous spiral structure is simplified into a discrete ring structure.

[0055] For Figure 8 the multi-layer carbon fiber rotor structure shown, the key to simulating the winding process using the activation scaling method and the activation scaling method lies in determining the initial radius of each layer of carbon fiber. In this embodiment, the constant-tension dry winding method is used, the winding tension is 700 N, and the corresponding winding stress is 882 MPa. Taking the initial radius of the first layer of carbon fiber as an example, it is illustrated how to determine the initial radius of the carbon fiber layer.

[0056] After the first layer of carbon fiber in this embodiment is wound, its radius is 38.2625 mm, that is, it is closely attached to the surface of the permanent magnet rotor. The elastic modulus in the parallel direction of the carbon fiber is 130 GPa. From formula (3) in the specification, the initial radius of the first iteration can be obtained as 38.0047 mm. Using the proposed method, the circumferential stress of the carbon fiber layer obtained by finite element calculation for the first iteration is 875.7122 MPa. Since formula (2) in the specification is a linear function, its expression can be determined with only two sets of data. The initial radius of the second iteration is selected as (38.0047 + ΔR) mm, where ΔR is a very small value, and the stress of the second iteration can be calculated. Thus, the expression of formula (2) is obtained, and by inverse solution, the initial radius of the carbon fiber with the required circumferential stress of 882 MPa can be obtained. The solution method for the radii of the carbon fibers in the remaining layers is the same.

[0057] The winding processes of the carbon fiber sheaths of this embodiment are respectively simulated using the activation scaling method and the activation scaling method. Figure 9(a) and 9(b) are the circumferential stress variations of the carbon fiber layer during the winding process. The results show that the results obtained by the two methods are almost the same, and the stress variations of the carbon fiber layer during the winding process have the same trend. The proposed method realizes the simulation of the binding effect on the carbon fiber layer, and the stress relaxation phenomenon during winding can be observed.

[0058] After winding, different rotational speeds and temperature rise conditions were applied to the rotor, and the rotor stresses under four typical working conditions were verified: static at room temperature (working condition A), overspeed at room temperature (working condition B), overspeed at high temperature (working condition C), and static at high temperature (working condition D). The circumferential stresses of the carbon fiber layer under different working conditions are as Figure 10 shown. Figure 11 (a) is the maximum value of the first principal stress of the permanent magnet under different working conditions, Figure 11 (b) is the maximum value of the von Mises stress of the shaft under different working conditions.

[0059] The proposed method is used to simulate the winding process of the carbon fiber sleeve in this embodiment. After winding, the stresses of the carbon fiber rotor under different working conditions can be accurately calculated. The proposed method provides strong support for checking the rotor strength of such high-speed motors in the design stage.

[0060] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for simulating the winding process of a carbon fiber sheath of a high-speed permanent magnet motor rotor, characterized in that: The carbon fiber sheath with a continuous spiral structure is discretized, and the winding process is simulated by constructing a finite element model through an activation scaling method or an activation expansion and contraction method. When constructing the initial finite element model, the initial radius of the carbon fiber layer needs to be determined, and the steps include: The circumferential stress of the carbon fiber layer generated by the shrinkage tendency is an explicit function of the radius of the carbon fiber layer, that is, σ θ =f(r), at r = R0, its Taylor expansion can be expressed as, σθ＝f ( R0 ) +f '( R0 )( r-R0 ) +f ”( R0 )( r-R0 ) 2 / 2+" (1) Keeping only the linear main part, equation (1) can be simplified to: σ θ =f(R0)+f'(R0)(r-R0) (2) Formula (2) is a linear one-variable function about R0, so the initial radius of the carbon fiber layer under a given winding tension can be determined through two iterations; Since the carbon fiber layers are tightly together after winding, the radius R c It is known that the initial radius R1 of the first iteration satisfies σT=(Rc-R1) / R1×E& (3) Among them, σ T is the stress generated by the winding tension, calculated as σ T =F t / (ab),F t is the winding tension, a and b are the width and thickness of the carbon fiber layer respectively; E ∥ is the Young’s modulus along the direction parallel to the carbon fiber; The initial radius of the second iteration is R1+ΔR, and the corresponding circumferential stress is σ θ2 , convert (R1,σ θ1 ) and (R1+ΔR,σ θ2 ) is substituted into (2) to solve the initial radius of the carbon fiber layer under a given winding tension.

2. The simulation method according to claim 1, characterized in that: The activation scaling method is implemented based on the three-dimensional motion unit method, and its steps include: A1. Construct an initial finite element model, requiring that the outer diameter of the permanent magnet rotor is larger than the inner diameter of the first layer of carbon fiber, and the outer diameter of the i-th layer of carbon fiber is larger than the inner diameter of the i+1-th layer of carbon fiber; A2. The inward compressive activation force acts on the permanent magnet rotor, so that the radius of the permanent magnet rotor decreases until it is smaller than the inner diameter of the first layer of carbon fiber; A3. The first layer of carbon fiber moves to the surface of the permanent magnet rotor, the activation force is removed, and the permanent magnet rotor spreads the carbon fiber layer outward to complete the winding of the first layer of carbon fiber; A4. Repeat steps A2 and A3 until all layers of carbon fiber winding are completed.

3. The simulation method according to claim 1, characterized in that: The activation scaling method is implemented based on a two-dimensional birth-death unit method, and the steps include: B1. Construct an initial finite element model, requiring that the outer diameter of the permanent magnet rotor is larger than the inner diameter of the first layer of carbon fiber, and the outer diameter of the i-th layer of carbon fiber is larger than the inner diameter of the i+1-th layer of carbon fiber; B2, the activation force starts to act from the outermost carbon fiber layer, causing the carbon fiber layer to expand outward and increase in radius until the inner diameter of the i-th carbon fiber layer is larger than the outer diameter of the i-1-th carbon fiber layer, at which time the i-1-th layer is activated; B3, repeat step B2 until the permanent magnet rotor is activated, during which the activation force on each layer of carbon fiber continues to act; B4. Starting from the first layer of carbon fiber, remove the activation force layer by layer, and the carbon fiber layer shrinks to complete the winding of all layers of carbon fiber.

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