Hollow shaft oil-spray cooled interior permanent magnet synchronous motor and its temperature field analysis method

Abstract

The present invention relates to a hollow shaft oil-spray-cooled interior permanent magnet synchronous motor. The hollow shaft oil-spray cooling structure comprises a hollow shaft and a hollow shaft oil passage disposed within the hollow shaft. The structure is characterized by a radial oil passage provided between the hollow shaft oil passage and the permanent magnet cavity of the rotor, and oil spray holes provided at the end caps at each end of the rotor, each of which communicates with the permanent magnet cavity of the rotor. The present invention also provides a temperature field analysis method for the hollow shaft oil-spray-cooled interior permanent magnet synchronous motor.

Description

Technical Field

[0001] The present invention belongs to the technical field of motors, and in particular relates to a built-in permanent magnet synchronous motor with a hollow shaft oil spray cooling structure. Background Art

[0002] Permanent magnet synchronous motors (PMSMs) are a popular choice for electric vehicle drive motors due to their high power density, high torque density, and wide speed range. However, their small size and high power and torque density can lead to a significant imbalance between heat generation and heat dissipation, resulting in excessive temperature rise. This can accelerate bearing aging, permanently demagnetize permanent magnets, and damage insulation materials, leading to motor failure and shortened service life. Therefore, it is crucial to design a suitable cooling structure, improve heat dissipation capabilities, and minimize motor temperature rise.

[0003] In actual operation, electric vehicle motors face complex and diverse operating conditions, resulting in varying losses and temperature rises in various components. For the same motor, under maximum torque conditions, high currents generate significant copper losses, making them the primary source of motor losses. Under maximum speed conditions, due to the high frequency of magnetic field alternation, iron losses are significant and account for a higher proportion. Furthermore, due to harmonics, eddy current losses in permanent magnets increase with increasing torque and speed. These variations in component losses under different operating conditions inevitably lead to differences in acoustic performance, necessitating a cooling structure design that takes these diverse operating conditions into account. Electric vehicle permanent magnet synchronous motors can be categorized as air-cooled, case-water-cooled, or oil-cooled, depending on the cooling fluid. For enclosed motors, air flow is limited, resulting in poor heat dissipation. Water-cooled motors, on the other hand, lack direct contact with heat-generating components, making them less effective at cooling the high eddy current losses in permanent magnets and the high temperature rise caused by rotor core losses. Because cooling oil is non-magnetic and has excellent insulation properties, it can be used to directly cool the rotor, permanent magnets, and windings within the motor.

[0004] Currently, direct oil cooling systems for motors are primarily divided into two types: case-based oil injection and hollow-shaft oil injection. Case-based oil injection only cools the end injection area, making it difficult to cool the center of the motor. Hollow-shaft oil injection often overlooks the uneven temperature rise caused by different oil injection volumes at both ends of the motor. By improving the hollow-shaft oil injection cooling structure, the oil injection volume can be more evenly distributed across the motor, thereby balancing the motor's temperature rise and achieving better cooling results.

[0005] The main calculation methods for the motor temperature field include the simplified formula method, the equivalent thermal network method, and the computational fluid dynamics method. The simplified formula method can no longer meet the current complex cooling structure analysis and motor temperature field calculation requirements because it only performs rough calculations. The equivalent thermal network method divides the various components of the motor into multiple units, has certain reliability and calculation accuracy, and is convenient to calculate. Due to the reliability and accuracy of the computational fluid dynamics method in analyzing the temperature field of complex models, most motor designs and research now require computational fluid dynamics analysis of the motor temperature field. However, since its early modeling and calculations require a lot of time and computing resources, in order to analyze the motor temperature field more comprehensively, quickly, and easily, the equivalent thermal network can be combined with the computational fluid dynamics method for joint analysis. Summary of the Invention

[0006] The purpose of the present invention is to improve the hollow shaft oil spray cooling structure of the built-in permanent magnet synchronous motor for electric vehicles and provide a temperature field analysis method thereof. The cooling structure proposed by the present invention redistributes the flow of cooling oil to both ends of the motor after the cooling oil enters the hollow shaft, so that the amount of cooling oil sprayed from both ends of the motor is more even, thereby improving the cooling oil utilization rate. In addition, the cooling oil first passes through the cooling structure in the rotating body to cool the rotor and permanent magnet with lower temperature rise, and then is sprayed through the oil spray hole of the end cover to cool the end winding with higher temperature rise, thereby improving the cooling effect. The present invention also establishes and analyzes an equivalent thermal network model for the structure. The technical solution is as follows:

[0007] A hollow shaft oil-spray cooled built-in permanent magnet synchronous motor, whose hollow shaft oil-spray cooling structure includes a hollow shaft and a hollow shaft oil channel arranged in the hollow shaft. It is characterized in that a radial oil channel is added between the hollow shaft oil channel and the permanent magnet cavity of the rotor, and end cover oil spray holes are respectively added to the end covers at both ends of the rotor, and the end cover oil spray holes are connected to the permanent magnet cavity of the rotor.

[0008] Furthermore, cooling oil flows in from one end of the hollow shaft.

[0009] Furthermore, the radial oil channel is located at the axial center of the motor rotor.

[0010] Furthermore, the cooling oil flows from the hollow shaft through the radial oil passage into the permanent magnet cavity of the rotor, and is then sprayed out from the oil spray holes on the end covers at both ends of the rotor.

[0011] Furthermore, the permanent magnet synchronous motor adopts a "V" type permanent magnet structure.

[0012] Furthermore, the built-in permanent magnet synchronous motor has three typical operating conditions: rated operating condition, maximum torque operating condition, and maximum speed operating condition.

[0013] The present invention also provides a temperature field analysis method for the hollow shaft oil-spray cooled internal permanent magnet synchronous motor, which is implemented based on the equivalent thermal network method and includes the following steps:

[0014] (1) Simplify the motor model according to the initial motor structure and parameters, and assign several nodes to the stator yoke, winding, stator teeth, rotor shoes, permanent magnets, rotor yoke, shaft, bearings, end cover, housing, and air cavity;

[0015] (2) Construct an equivalent thermal network based on the simplified motor model;

[0016] (3) Calculate the thermal conduction and convection resistances between the nodes of the simplified motor model as follows:

[0017] a. According to the different component positions of the nodes, the thermal conduction resistance is divided into a flat plate thermal conduction model and a cylindrical thermal conduction model. Among them, the nodes in the axial direction of the motor are plate-type thermal conduction, and the mutual thermal resistance is calculated using formula (1); the nodes in the radial direction of the motor are cylindrical-type thermal conduction, and the mutual thermal resistance can be calculated using formula (2):

[0018]

[0019] Where L is the material thickness, S is the contact area, and λ 平板 is the thermal conductivity of the material, l is the equivalent length of the cylindrical thermal conduction model, R 平板 is the mutual thermal resistance between the two nodes on the flat plate heat conduction model; λ1 is the thermal conductivity of the material inside the cylinder, λ2 is the thermal conductivity of the material outside the cylinder, r1 is the inner diameter of the cylinder, r2 is the radius of the interface between the two parts of the cylinder, r3 is the outer diameter of the cylinder, R 圆筒 is the mutual thermal resistance between the inner and outer diameters of the cylinder;

[0020] b. The convective heat transfer coefficient between the fluid and the solid, excluding the end windings, is calculated using equations (3)-(5). The convective heat transfer coefficient of the end windings is obtained by simulation fitting based on the computational fluid dynamics method. The convective heat transfer thermal resistance is calculated using equation (6):

[0021]

[0022] Where D is the equivalent length of the air gap, υ is the kinematic viscosity coefficient of the fluid, u is the fluid velocity, Nu is the Nusselt number of the fluid, Re is the Reynolds number of the fluid. Pr is the Prandtl number, α is the convective heat transfer coefficient, λ 流体 is the thermal conductivity of the fluid, and S is the heat exchange area.

[0023] (4) Due to the law of energy conservation, the energy flowing out of each node in the motor is equal to the energy flowing into it. By analogy with Kirchhoff's current law in the circuit, the heat balance equation for any node is obtained, as shown in formula (7):

[0024] -G(i,1)T(1)-…+G(i,i)T(i)-…-G(i,n)T(n)=P(i) (7)

[0025] Where G(i,i) is the self-heat conductance of node i, G(i,n) is the mutual heat conductance between node i and node n, P(i) is the loss of node i, and T(i) is the temperature rise of node i. Combining the heat balance equations listed for each node establishes the cooling matrix of the motor, as shown in formula (8)

[0026]

[0027] (5) According to the motor cooling matrix established in step (4), the average temperature rise of each motor component under three typical operating conditions, namely, rated speed condition, maximum torque condition, and maximum speed condition, is calculated respectively.

[0028] Furthermore, the motor end is modeled by obtaining the convective heat transfer coefficient of the winding end through simulation fitting based on the computational fluid dynamics method. The motor speed range is evenly divided into sub-intervals, and the VOF multiphase flow model in the Fluent software is used for computational fluid dynamics analysis. The results obtained in each sub-interval are fitted to obtain the convective heat transfer coefficient curve of the winding end as the speed changes. The results of the equivalent thermal network method and the computational fluid dynamics method are compared under three typical working conditions for the main components of the motor: stator, winding, rotor and permanent magnet for verification.

[0029] Compared with the prior art, the effective benefits brought by the technical solution of the present invention are:

[0030] 1. This structure allows the cooling oil to come into direct contact with the main heat-generating components in the motor, namely the permanent magnets and windings, thereby improving the cooling effect.

[0031] 2. This structure allows the cooling oil to first cool the rotor and permanent magnets with lower temperature rise, and then cool the windings with higher temperature rise, so that the cooling oil can be fully utilized.

[0032] 3. This structure adds radial oil channels to redistribute the cooling oil flowing to both ends of the motor through the permanent magnet cavity, making the flow more even, thereby allowing the cooling oil to come into more complete contact with the end windings and improving the cooling effect.

[0033] 4. This structure reduces the overall temperature rise of the motor while ensuring that the electromagnetic performance of the motor remains basically unchanged.

[0034] 5. The present invention provides a temperature field analysis method for the built-in permanent magnet synchronous motor with a hollow shaft oil-spray cooling structure. This temperature field analysis method combines the advantages of the computational fluid dynamics method and the equivalent thermal network method, can effectively reduce the computing time and resources required for temperature field calculation and analysis, and has a very high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the motor rotor structure.

[0036] Figure 2 This is a cross-sectional view of the motor rotating body.

[0037] Figure 3 It is an overall cross-sectional view of the motor of the present invention.

[0038] Figure 4 Simplify the model for the motor.

[0039] Figure 5 It is the equivalent thermal network model of the motor.

[0040] Reference numerals:

[0041] 101-motor rotor, 102-permanent magnet, 103-hollow shaft, 104-end cover, 105-hollow shaft oil channel, 106-radial oil channel, 107-permanent magnet cavity, 108-end cover oil injection hole, 109 oil outlet DETAILED DESCRIPTION

[0042] The present invention will be described below with reference to the accompanying drawings and embodiments.

[0043] When using water cooling, the housing cannot directly contact the heat-generating components, and the traditional hollow shaft oil spray cooling method ignores the different distances between the oil spray ports and the oil inlet at both ends of the motor, which leads to different oil spray volumes. To overcome the shortcomings of the existing technology, the present invention provides a new hollow shaft oil spray cooling structure. After the cooling oil enters the hollow shaft, the flow rate to the two ends of the motor is redistributed, making the amount of cooling oil sprayed from both ends of the motor more even, improving the cooling oil utilization rate. The cooling oil first passes through the cooling structure in the rotating body to cool the rotor and permanent magnets with lower temperature rise, and then is sprayed through the oil spray holes in the end cover to cool the end windings with higher temperature rise, thereby improving the cooling effect.

[0044] The hollow shaft oil spray cooling structure of the permanent magnet synchronous motor of an electric vehicle of the present invention uses the original oil inlet 109 set at one end of the hollow shaft and the oil outlet 109 set at the bottom of the casing, utilizes the permanent magnet cavity 107 of the rotor as part of the oil circuit, adds a radial oil channel 106 at the axial center position of the motor rotor between the hollow shaft oil channel 105 and the permanent magnet cavity 107 of the rotor, and adds an end cover oil spray hole 108 on the rotor end cover 104, so that the cooling oil flows from the hollow shaft through the radial oil channel 106 into the permanent magnet cavity 107 and is then sprayed out from both ends of the rotor.

[0045] Equivalent thermal network analysis method for the hollow shaft oil-injection cooling structure of a permanent magnet synchronous motor in an electric vehicle. The following describes the embodiments of the present invention in detail using an 8p / 48s motor as an example. The motor parameters are shown in Table 1.

[0046] Table 1 Motor parameters

[0047] parameter symbol Numerical unit Rated speed <![CDATA[n N ]]> 5300 r / min Rated torque <![CDATA[T N ]]> 72 Nm Pole pairs P 8 -- Number of slots Q 48 -- Stator outer diameter <![CDATA[D sw ]]> 168 mm Stator inner diameter <![CDATA[D sn ]]> 102 mm Air gap length δ 0.8 mm Rotor outer diameter <![CDATA[D rw ]]> 100.4 mm Core length l 140 mm

[0048] (6) First, the motor end is modeled, and the speed range of 4500 r / min-14100 r / min is evenly divided into 17 nodes. The VOF multiphase flow model in Fluent software is used for computational fluid dynamics analysis. The 17 sets of results are fitted to obtain the convective heat transfer coefficient curve of the winding end as the speed changes, as shown in formula (1):

[0049] α 油 =588.83+0.0177r+3.89×10 -6 r 2 -1.5265×10 -10 r 3 (1)

[0050] Where, α 油 is the convection heat transfer coefficient of the winding end, and r is the motor speed.

[0051] (7) Simplify the motor model according to the initial motor structure and parameters, such as Figure 4 The motor is divided into several nodes, where nodes 1-3 are the stator yoke, nodes 4-8 are the windings, nodes 9-11 are the stator teeth, nodes 12-14 are the rotor shoes, nodes 15-17 are the permanent magnets, nodes 18-20 are the rotor yoke, node 21 is the shaft, nodes 22-23 are the bearings, nodes 24-25 are the end covers, node 26 is the housing, and nodes 27-29 are the air cavity.

[0052] (8) Construct an equivalent thermal network based on the simplified motor model, such as Figure 5 shown.

[0053] (9) Calculate the thermal resistance of heat conduction and heat convection between each node. The thermal conduction resistance is mainly divided into a flat plate heat conduction model and a cylindrical heat conduction model. The nodes in the axial direction of the motor are plate heat conduction, and the mutual thermal resistance can be calculated using formula (2), such as the thermal resistance between node 1 and node 2; the nodes in the radial direction are cylindrical heat conduction, and the mutual thermal resistance can be calculated using formula (3), such as the thermal resistance between node 1 and node 4:

[0054]

[0055] Where L is the material thickness, S is the contact area, and λ 平板 is the thermal conductivity of the material, l is the equivalent length of the cylindrical thermal conduction model, R 平板is the mutual thermal resistance between the two nodes on the flat plate heat conduction model; λ1 is the thermal conductivity of material 1 on the inner side of the cylinder, λ2 is the thermal conductivity of material 2 on the outer side of the cylinder, r1 is the inner diameter of the cylinder, r2 is the radius of the interface between the two parts of the cylinder, r3 is the outer diameter of the cylinder, R 圆筒 is the mutual thermal resistance between the inner and outer diameters of the cylinder. The convective heat transfer coefficient between the fluid and the solid, excluding the end windings, can be calculated using equations (4)-(6). For a more detailed derivation of the convective heat transfer coefficient calculation formula, see Ming Kang, Huimin Wang, Liyan Guo. Self-circulation cooling structure design of permanent magnet machines for electric vehicle [J]. Applied Thermal Engineering, 2020, 165. The convective heat transfer thermal resistance can be calculated using equation (7), such as the convective heat transfer thermal resistance between node 1 and node 27:

[0056]

[0057]

[0058] Where D is the equivalent length of the air gap, υ is the fluid's kinematic viscosity coefficient, u is the fluid flow rate, Nu is the fluid's Nusselt number, Re is the fluid's Reynolds number. Pr is the Prandtl number, α is the convective heat transfer coefficient, λ 流体 is the thermal conductivity of the fluid, and S is the heat exchange area.

[0059] (10) Due to the law of conservation of energy, the energy flowing out of each node in the motor is equal to the energy flowing into it. Therefore, by analogy with Kirchhoff's current law in the circuit, the heat balance equation for any node can be obtained, as shown in formula (8):

[0060] -G(i,1)T(1)-…+G(i,i)T(i)-…-G(i,n)T(n)=P(i) (8)

[0061] Where G(i,i) is the self-heat conductance of node i, G(i,n) is the mutual heat conductance between node i and node n, P(i) is the loss of node i, and T(i) is the temperature rise of node i. The heat balance equations listed for each node are combined to establish the cooling matrix of the motor, as shown in formula (9):

[0062]

[0063] (11) According to the motor cooling matrix established in step (5), the average temperature rise of each motor component under three typical working conditions, namely, rated speed condition, maximum torque condition, and maximum speed condition, can be calculated respectively, as shown in Table 2.

[0064] Table 2 Temperature rise of motor components under three working conditions

[0065]

[0066]

[0067] Table 3 Temperature rise of motor components under three working conditions

[0068]

[0069] (12) The results of the thermal network method and the computational fluid dynamics method are compared under three typical working conditions for the main components of the motor: stator, winding, rotor and permanent magnet. As shown in Table 3, the maximum error does not exceed 1%, which meets the requirements.

Claims

1. A temperature field analysis method for a hollow shaft oil-spray cooled interior permanent magnet synchronous motor. The applicable hollow shaft oil-spray cooled interior permanent magnet synchronous motor has a hollow shaft oil-spray cooling structure. The hollow shaft oil-spray cooling structure includes a hollow shaft and a hollow shaft oil passage disposed within the hollow shaft. A radial oil passage is provided between the hollow shaft oil passage and the permanent magnet cavity of the rotor. End cap oil spray holes are provided at each end of the rotor, and the end cap oil spray holes are connected to the permanent magnet cavity of the rotor. The temperature field analysis method for this motor is implemented based on the equivalent thermal network method and includes the following steps: (1) Simplify the motor model according to the initial motor structure and parameters, and assign several nodes to the stator yoke, winding, stator teeth, rotor shoes, permanent magnets, rotor yoke, shaft, bearings, end cover, housing, and air cavity; (2) Construct an equivalent thermal network based on the simplified motor model; (3) Calculate the thermal conduction and convection resistances between the nodes of the simplified motor model as follows: a. According to the different component positions of the nodes, the thermal conduction resistance is divided into a flat plate thermal conduction model and a cylindrical thermal conduction model, where: The nodes in the axial direction of the motor are flat plate heat conduction, and the mutual thermal resistance is expressed by formula (1): Calculation: The heat conduction between the nodes in the radial direction of the motor is cylindrical, and the mutual thermal resistance can be calculated using formula (2): Where L is the material thickness, S is the contact area, and λ 平板 is the thermal conductivity of the material, l is the equivalent length of the cylindrical thermal conduction model, R 平板 is the mutual thermal resistance between the two nodes on the flat plate heat conduction model; λ1 is the thermal conductivity of the material inside the cylinder, λ2 is the thermal conductivity of the material outside the cylinder, r1 is the inner diameter of the cylinder, r2 is the radius of the interface between the two parts of the cylinder, r3 is the outer diameter of the cylinder, R 圆筒 is the mutual thermal resistance between the inner and outer diameters of the cylinder; b. The convective heat transfer coefficient between the fluid and the solid, excluding the end windings, is calculated using equations (3)-(5). The convective heat transfer coefficient of the end windings is obtained by simulation fitting based on the computational fluid dynamics method. The convective heat transfer thermal resistance is calculated using equation (6): Where D is the equivalent length of the air gap, υ is the kinematic viscosity coefficient of the fluid, u is the fluid flow rate, Nu is the Nusselt number of the fluid, Re is the Reynolds number of the fluid, Pr is the Prandtl number, α is the convective heat transfer coefficient, and λ is the 流体 is the thermal conductivity of the fluid, S is the heat exchange area; (4) Due to the law of energy conservation, the energy flowing out of each node in the motor is equal to the energy flowing into it. By analogy with Kirchhoff's current law in the circuit, the heat balance equation for any node is obtained, as shown in formula (7): -G(i,1)T(1)-…+G(i,i)T(i)-…-G(i,n)T(n)=P(i) (7) Where G(i,i) is the self-thermal conductance of node i, G(i,n) is the mutual thermal conductance between node i and node n, P(i) is the loss of node i, and T(i) is the temperature rise of node i. The heat balance equations listed for each node are combined to establish the cooling matrix of the motor, as shown in formula (8): (5) According to the motor cooling matrix established in step (4), the average temperature rise of each motor component under three typical operating conditions, namely, rated speed condition, maximum torque condition, and maximum speed condition, is calculated respectively.

2. The temperature field analysis method of the hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: The motor end is modeled by obtaining the convective heat transfer coefficient of the winding end through simulation fitting based on computational fluid dynamics. The motor speed range is evenly divided into sub-intervals. The VOF multiphase flow model in Fluent software is used for computational fluid dynamics analysis. The results obtained in each sub-interval are fitted to obtain the convective heat transfer coefficient curve of the winding end as the speed changes. The results of the equivalent thermal network method and the computational fluid dynamics method are compared under three typical working conditions for the main components of the motor: stator, winding, rotor and permanent magnet for verification.

3. The temperature field analysis method of the hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: Cooling oil flows in from one end of the hollow shaft.

4. The temperature field analysis method of the hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: The radial oil channel is located at the axial center of the motor rotor.

5. The temperature field analysis method of the hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: The cooling oil flows from the hollow shaft through the radial oil channel into the permanent magnet cavity of the rotor, and then sprays out from the oil spray holes on the end covers at both ends of the rotor.

6. The temperature field analysis method of the hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: The permanent magnet synchronous motor adopts a "V" type permanent magnet structure.

7. The temperature field analysis method of a hollow shaft oil-spray cooled interior permanent magnet synchronous motor according to claim 1, characterized in that: The built-in permanent magnet synchronous motor has three typical operating conditions: rated operating condition, maximum torque operating condition, and maximum speed operating condition.

Images