A high-precision calculation method for thermal-fluid coupling of gear meshing transmission

Abstract

The present invention is applicable to the technical field of gear transmission system, and provides a high-precision calculation method for thermal-fluid coupling of gear meshing transmission. The method first builds a power loss and heat transfer distribution model of the gear transmission system based on the thermal network method, which is used to predict the temperature rise and system power loss of various parts of the gear transmission system under different working conditions. Then, a high-precision thermal-fluid coupling numerical simulation of the gear meshing transmission system is performed using fluid simulation software. The steps mainly include extracting the fluid calculation domain, dividing the fluid calculation domain grid, setting numerical simulation parameters, and coupling through UDF files to achieve high-precision gear system thermal-fluid coupling numerical simulation. This method uses UDF technology to apply the heat generation value obtained by the thermal network model to the gear meshing in the form of boundary conditions. In this way, the heat generation of the gear in the actual working process is simulated, and a higher-precision prediction is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of gear transmission systems, and in particular relates to a high-precision calculation method for thermal-fluid coupling of gear meshing transmission. Background Art

[0002] Gear transmission is widely used in the fields of engineering machinery, aerospace, rail transportation and new energy vehicles. As the most important basic component in mechanical transmission devices, gears are currently developing towards high reliability and long service life with the changes in the application requirements of transmission systems. With the advancement of mechanical technology, many fields have put forward higher requirements for the safety, reliability and stability of gear transmission systems. While ensuring transmission efficiency, gear transmission systems are also required to have a longer service life and lower failure rate. For example, under high-speed and heavy-load service conditions, the gear meshing surface presents various forms of damage failure modes due to the interaction of complex factors in multiple physical fields, especially the gear meshing friction heat generation, poor lubrication, and insufficient heat dissipation, which leads to tooth surface bonding failure. This will have an important impact on the reliable operation of the gear transmission device and the whole machine, causing the performance of the transmission system to drop sharply, and even causing serious safety accidents. At the same time, how to improve the efficiency and reliability of the gear transmission system, save energy, reduce emissions and reduce energy loss are also important issues that need to be solved urgently.

[0003] In order to meet the above-mentioned high requirements for gear transmission systems, it is necessary to conduct in-depth research on the evolution mechanism of multi-physical fields under the operating conditions of the gear transmission system, deeply analyze the cause mechanism of heat generation and heat dissipation in the gear transmission process and the temperature distribution law of the meshing tooth surface, establish the sensitivity mechanism of heat transfer and fluid dynamic lubrication characteristics, inhibit or avoid the reduction of gear transmission efficiency caused by bonding failure, and realize the forward design and optimization of high-reliability, high-stability and high-efficiency gear transmission system parameters.

[0004] Traditional calculation methods often ignore the complex interaction between thermal effects and fluid dynamic lubrication at the gear meshing point, resulting in a large deviation between the calculation results and the actual situation. Therefore, a high-precision prediction method that considers multi-physical field coupling is needed to provide more accurate thermal flow multi-field coupling calculation data to support the optimization design and fault prevention of the gear transmission system. However, the current method for studying the heat generation of gear transmission is to calculate the overall power loss of the transmission system, and then apply the overall power loss to the gear meshing surface without considering the gear meshing force. This is extremely inconsistent with the actual situation of friction heat generation and lubrication heat dissipation in the tooth surface meshing area under the service condition of the gear transmission, resulting in inaccurate calculation results. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a high-precision calculation method for thermal-fluid coupling of gear meshing transmission, aiming to solve the problems raised in the above-mentioned background technology.

[0006] The embodiment of the present invention is implemented as follows: a high-precision calculation method for thermal flow coupling of gear meshing transmission, comprising the following steps:

[0007] Step 1: Build a gear heat generation and heat dissipation model:

[0008] Based on AMEsim software, a heat generation and heat dissipation model of the gear system is built using the thermal network method. The model includes a power loss calculation module and a heat distribution module.

[0009] The power loss calculation module is used to calculate the power loss of each part of the gear system;

[0010] The heat distribution module distributes the heat generated by the system due to power loss to each component in a proportional relationship according to the spatial position relationship, the contact situation of each part and the heat exchange with the outside world;

[0011] After completing the construction of the power loss calculation module and the heat distribution module, connect the two modules to transfer heat. The power loss calculated by the power loss module is transferred to the heat distribution module to achieve heat transfer. Then, the heat is distributed to the entire system according to the thermal resistance and thermal conductivity.

[0012] Step 2: High-precision thermal-fluid coupling numerical simulation:

[0013] After building the gear heat generation and heat dissipation model, based on the ANSYS Fluent fluid simulation software platform, the UDF programming and thermal-fluid coupling numerical simulation method were used to analyze the flow field and temperature field inside the box during the gear meshing transmission process;

[0014] In the process of thermal-flux coupling numerical simulation, UDF technology is used to set the heat generation calculated by the constructed gear heat generation and heat dissipation model as the thermal boundary condition to the gear meshing point, so as to numerically simulate the heat generation and temperature rise of the gear surface during actual operation.

[0015] A further technical solution is that in step 1, building a power loss calculation module includes the following specific steps:

[0016] First, we need to identify the heat source generated by power loss during the operation of the gear system. Power loss includes gear oil churning loss, sliding loss, rolling loss and bearing loss. By setting parameters, we can calculate different bearing load conditions and the power loss of gears and bearings.

[0017] The power loss calculation module calculates the total power loss of the gear system according to the following formula and uses this as the basis for the heat distribution module:

[0018] 1) Calculation of gear oil stirring power loss:

[0019] (1);

[0020] (2);

[0021] (3);

[0022] in, P pad is the oil churning loss, unit: W; C md C is the calculation coefficient of gear side oil churning loss; ma is the calculation coefficient of gear surface oil churning loss; C side is the oil stirring loss on the tooth side, unit: W; C teeth is the oil churning loss on the tooth surface, unit: W; R 1 is the radius of the tooth tip circle, unit: mm; R 1 is the pitch circle radius, unit: mm; ω is the gear speed, unit: r / min; b is the tooth width, unit: mm; ρ is the density of lubricating oil, in g / mm 3 ;

[0023] Calculation of tooth side Reynolds number and Froude number:

[0024] (4);

[0025] (5);

[0026] in, g is the acceleration due to gravity, in m / s 2 ;

[0027] Calculation of tooth surface Reynolds number and Froude number:

[0028] (6);

[0029] (7);

[0030] in, ht is the tooth height, unit: mm;

[0031] When Re ≥ 2250:

[0032] (8);

[0033] When Re < 2250 and Re −0.6 ×Fro −0.25 < 8.7×10 −3 hour:

[0034] (9);

[0035] When Re < 2250 and Re −0.6 ×Fro −0.25 > 8.7×10 −3 hour:

[0036] (10);

[0037] When Re A 0.23 ×Fro A 0.32 ≥ 12:

[0038] (11);

[0039] When Re A 0.23 ×Fro A 0.32 < 12:00:

[0040] (12);

[0041] In the above formula, h is the gear oil immersion depth, unit: mm; V p Gear oil immersion volume, unit: mm 3 ; V 0 is the oil volume, unit: mm 3 ; ht 0 is the tooth addendum coefficient;

[0042] 2) Gear sliding loss:

[0043] (13);

[0044] in, F n is the normal force, unit is N; f g is the sliding coefficient; v g is the sliding speed, in m / s; L a is the meshing time, unit is s;

[0045] 3) Gear rolling loss:

[0046] (14);

[0047] in, F ris the rolling force, unit: N; v r is the rolling speed, unit: r / min;

[0048] 4) Bearing power loss:

[0049] (15);

[0050] (16);

[0051] (17);

[0052] in, P 0 is the friction power loss related to viscosity, unit: W; P f is the friction power loss related to the load, unit: W; P is the calculated load of the bearing friction torque, unit: N; d m is the bearing pitch diameter, unit: mm; f 0 is a coefficient related to the bearing type and lubrication method; f 1 is a factor related to bearing type and load; ω is the angular velocity of the inner ring of the bearing, unit: rad / s; n is the speed of the inner ring of the bearing, unit: r / min; v is the kinematic viscosity of the lubricating oil, unit: mm² / s; v n is the product of the kinematic viscosity of the lubricating oil and the speed of the inner ring of the bearing.

[0053] In the AEMsim simulation software, select the gear transmission components, set their corresponding geometric parameters and gear meshing parameters, then connect these modules, set the connection parameters, and input the power loss calculation formula; set the input shaft speed of the gear system, set the braking torque at the output end, and truly simulate the operating conditions of the gear reducer; then build a power loss calculation module based on AMEsim to calculate the power loss under the operating conditions of the gear system.

[0054] A further technical solution is to distribute the force of the gear transmission system before calculating the power loss, and accurately analyze the axial force, radial force, tangential force generated by the gear meshing and the force conditions of the bearings.

[0055] A further technical solution is that in step 1, building a heat distribution module includes the following specific steps:

[0056] The total power loss obtained by the power loss calculation module is regarded as the total heat generation of the gear system. When building the heat distribution module, the total heat generation is distributed to obtain the heat situation of each part, and the temperature of each part is calculated according to the loss power allocated to each part.

[0057] When building the heat distribution module, the shaft, bearings, gears, and gearboxes need to be divided into different mass blocks for model building;

[0058] When building a heat distribution module, it is necessary to calculate the thermal resistance and thermal conductivity of each part, and determine the specific distribution of heat based on the thermal resistance and thermal conductivity, and how much heat should be distributed to different parts; the thermal resistance and thermal conductivity of each part are calculated using the following formula:

[0059] 1) Thermal conductivity and thermal resistance between shaft mass blocks:

[0060] (18);

[0061] (19);

[0062] in, h 1 is the thermal conductivity between the shaft mass blocks, unit: W / K; S 1 is the cross-sectional area of ​​the shaft, unit: mm 2 ; t 2 and t 1 is the temperature of the adjacent mass blocks and the initial temperature, unit: K; R1 is the thermal resistance between the axial mass blocks, unit: K / W; l 1 is the characteristic length of the shaft mass block, unit: mm; λ 1 is the thermal conductivity of the shaft, unit: W / (mm·K).

[0063] 2) Thermal conductivity and thermal resistance of the shaft and the mass blocks of the components on the shaft:

[0064] (20);

[0065] (twenty one);

[0066] in, h 2. Thermal conductivity of the shaft and the mass block of the components on the shaft, unit: W / K; t 2 and t 1 is the temperature of the adjacent mass blocks and the initial temperature, respectively, in K; R2 is the thermal resistance between the shaft and the mass blocks of the components on the shaft, in K / W; l 2 is the characteristic contact length between the shaft and the mass block of the component on the shaft, unit: mm; λ 2 is the thermal conductivity of the components on the shaft, unit: W / (mm·K); d int is the inner diameter, in mm; dout It is the outer diameter in mm.

[0067] After completing the calculation of the thermal resistance and thermal conductivity between each mass block, it is necessary to correctly arrange the position of each mass block according to the positional relationship of the gears in the transmission process, and select different connection methods according to the relationship of heat conduction between each mass block and the different heat transfer methods.

[0068] A further technical solution is to divide the shaft into five mass blocks when dividing the mass blocks, namely the mass block connected to the gear, the mass block connected to the bearing, and the transition mass block in the middle; the bearings, gears, etc. are divided into individual mass blocks, and the box is divided into five mass blocks on all sides and up and down.

[0069] According to a further technical solution, in step 2, the numerical simulation process includes three contents, namely numerical simulation pre-processing, numerical simulation and UDF file writing;

[0070] Numerical simulation pre-processing includes operations such as computational fluid domain extraction, computational domain meshing, and simulation parameter setting;

[0071] In the process of meshing, it is necessary to encrypt the mesh boundary layer near the wall of the gear fluid domain, and at the same time, it is necessary to perform mesh independence analysis to eliminate the calculation errors caused by mesh factors;

[0072] When setting simulation parameters, it is necessary to assign initial temperatures to each surface of the calculation domain. The source of the initial temperature is the corresponding temperature obtained in the heat distribution module. The subsequent temperature rise changes are determined by the lost power through UDF programming to set boundary conditions for the meshing gears, determine whether the tooth surface is in the meshing process, and apply heat-generating power to the tooth surface in the meshing process to simulate the heat generated by power loss caused by friction during the actual meshing process, resulting in the temperature rise of the gears. After the heat-generating power is set for the tooth surface, the tooth surface generates a corresponding temperature rise, and then a thermal-fluid coupling numerical simulation is performed through the fluid, using the fluid as the medium for heat transfer to transfer heat from the meshing point to various parts of the gear system.

[0073] When performing numerical simulation, the AEMsim model and Fluent fluid numerical simulation are combined through UDF files. By applying heat-generating power to specific surfaces, the heat generation during actual operation is simulated. When writing UDF files, the power losses of different gears need to be applied to the relative gears respectively. During the writing process, the meshing condition of the gears during rotation needs to be intelligently identified. Heat can only be applied when the gears are in meshing state. The heat generation calculation formula for the tooth surface is:

[0074] (twenty two);

[0075] In the formula, t is the gear working time, unit: s; S g is the gear meshing area, unit: m 2 ; H is heat density, unit: W / (s·m 2 ).

[0076] The present invention provides a high-precision calculation method for thermal-fluid coupling of gear meshing transmission, which is mainly divided into two parts: the first part uses the thermal network method to build a heat generation and heat dissipation model of the gear system, and builds a power loss and heat transfer distribution model of the gear transmission system based on the thermal network method, which is used to predict the temperature rise and system power loss of each part of the gear transmission system under different working conditions, which serves as the basis for the next part; the second part uses fluid simulation software to perform high-precision thermal-fluid coupling numerical simulation, which mainly includes extracting the fluid calculation domain, dividing the fluid calculation domain grid, setting numerical simulation parameters, and connecting the content of the first part with it through the UDF file, so as to achieve high-precision gear system thermal-fluid coupling numerical simulation. The two parts of this method are coupled through UDF technology, and the heat generation value obtained by the thermal network model is applied to the gear meshing in the form of boundary conditions. In this way, the heat generation of the gear in the actual working process is simulated, and a higher-precision temperature distribution and fluid dynamic behavior prediction are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 It is a partial schematic diagram of the heat generation and heat dissipation model of the gear transmission system based on AMEsim;

[0078] Figure 2 Another partial schematic diagram of the heat generation and heat dissipation model of the gear transmission system based on AMEsim;

[0079] Figure 3 It is another partial schematic diagram of the heat generation and heat dissipation model of the gear transmission system based on AMEsim;

[0080] Figure 4 It is a three-dimensional model and a mesh model;

[0081] Figure 5 Calculate the heat distribution at the gear meshing point based on UDF programming;

[0082] Figure 6 The calculation flow chart is shown in Figure 2. DETAILED DESCRIPTION

[0083] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0084] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0085] like Figure 6 As shown, a high-precision calculation method for thermal flow coupling of gear meshing transmission provided by an embodiment of the invention includes the following steps:

[0086] Step 1: Build a gear heat generation and heat dissipation model:

[0087] Based on AMEsim software, the heat network method is used to build a heat generation and heat dissipation model of the gear system. The model includes a power loss calculation module and a heat distribution module. The power loss calculation module mainly calculates the power loss of each part of the gear system through a formula. Power loss is the direct cause of the temperature rise of the gear system. Accurately calculating the total power loss of the gear system is the premise for predicting the temperature rise of each part of the gear system in the heat distribution module; the main function of the heat distribution module is to distribute the heat generated by the system due to power loss to each component in a certain proportional relationship according to the spatial position relationship, the contact situation of each part and the heat exchange with the outside world. This proportional relationship is determined by parameters such as the mass, thermal resistance and thermal conductivity of each component.

[0088] Step 1.1: Build the power loss calculation module:

[0089] In order to accurately build the power loss calculation module, we must first clarify the heat source during the working process of the gear system. Here we choose a gear system containing a pair of meshing gears for demonstration. Power loss includes gear oil stirring loss, sliding loss, rolling loss and bearing loss. By setting parameters such as speed and load torque, we can calculate different bearing load conditions and the power loss of gears and bearings.

[0090] Before calculating power loss, it is necessary to distribute the force of the gear transmission system and accurately analyze the axial force, radial force, tangential force generated by gear meshing and the force conditions of the bearings. In the subsequent process of power loss calculation, there are many places where force conditions are needed, so correct force analysis is the basis for successfully building a power loss calculation module. The content of this part is sufficient to be solved by existing technology, and no further explanation is given here.

[0091] The power loss calculation module calculates the total power loss of the gear system according to the following formula and uses this as the basis for the heat distribution module.

[0092] 1) Calculation of gear oil stirring power loss:

[0093] (1);

[0094] (2);

[0095] (3);

[0096] in, P pad is the oil churning loss, unit: W; C md C is the calculation coefficient of gear side oil churning loss; ma is the calculation coefficient of gear surface oil churning loss; C side is the oil stirring loss on the tooth side, unit: W; C teeth is the oil churning loss on the tooth surface, unit: W; R 1 is the radius of the tooth tip circle, unit: mm; R 1 is the pitch circle radius, unit: mm; ω is the gear speed , unit: r / min; b is the tooth width, unit: mm; ρ is the density of lubricating oil, in g / mm 3 .

[0097] Calculation of tooth side Reynolds number and Froude number:

[0098] (4);

[0099] (5);

[0100] in, g is the acceleration due to gravity, in m / s 2 ; The same parameter symbols are not repeated here.

[0101] Calculation of tooth surface Reynolds number and Froude number:

[0102] (6);

[0103] (7);

[0104] in, ht is the tooth height, unit: mm.

[0105] When Re ≥ 2250:

[0106] (8);

[0107] When Re < 2250 and Re −0.6 ×Fro −0.25 < 8.7×10 −3 hour:

[0108] (9);

[0109] When Re < 2250 and Re −0.6 ×Fro −0.25 > 8.7×10 −3 hour:

[0110] (10);

[0111] When Re A 0.23 ×Fro A 0.32 ≥ 12:

[0112] (11);

[0113] When Re A 0.23 ×Fro A 0.32 < 12:00:

[0114] (12);

[0115] In the above formula, h is the oil immersion depth, unit: mm; V p is the immersion oil volume, unit: mm 3 ; V 0 is the oil volume, unit: mm 3 ; ht 0 is the tooth addendum coefficient;

[0116] 2) Gear sliding loss:

[0117] (13);

[0118] in, F n is the normal force, unit is N; f g is the sliding coefficient; v g is the sliding speed, in m / s; L a is the meshing time, unit is s.

[0119] 3) Gear rolling loss:

[0120] (14);

[0121] in, F r is the rolling force, unit: N; v ris the rolling speed, unit: r / min;

[0122] 4) Bearing power loss:

[0123] (15);

[0124] (16);

[0125] (17);

[0126] in, P 0 is the friction power loss related to viscosity (not related to load), unit: W; P f is the friction power loss related to the load, unit: W; P is the calculated load of the bearing friction torque, unit: N; d m is the bearing pitch diameter, unit: mm; f 0 is a coefficient related to the bearing type and lubrication method; f 1 is a factor related to bearing type and load; ω is the angular velocity of the inner ring of the bearing, unit: rad / s; n is the speed of the inner ring of the bearing, unit: r / min; v is the kinematic viscosity of the lubricating oil, unit: mm² / s; v n is the product of the kinematic viscosity of the lubricating oil and the speed of the inner ring of the bearing.

[0127] In the AEMsim simulation software, select the gear transmission component and set its corresponding geometric parameters, such as the number of teeth, helix angle, pressure angle, tooth width, tooth thickness and other basic parameters, as well as gear meshing parameters, such as the number of teeth of the mating gear, center distance, gear oil immersion depth, etc. The corresponding modules for this part can be found in the transmission model library provided by AMEsim, and then these modules are connected, the connection parameters are set, and the power loss calculation formula is entered. Set the input shaft speed of the gear system, set the braking torque at the output end, and truly simulate the operating conditions of the gear reducer. Build a power loss calculation module (heat generation module) based on AMEsim to calculate the power loss and total heat generation under the operating conditions of the gear system.

[0128] Step 1.2: Build the heat distribution module:

[0129] The total power loss obtained by the power loss calculation module can be regarded as the total heat generation of the gear system. When building the heat distribution module, the total heat generation needs to be reasonably distributed to obtain the heat situation of each part, and the temperature of each part is calculated according to the power loss allocated to each part. Figure 1-Figure 3When building the heat distribution module, the shaft, bearings, gears and gearboxes need to be divided into different mass blocks. The more mass blocks are divided, the more accurate the prediction of the gear temperature will be. However, dividing the mass blocks too much will make the model extremely complicated. In order to meet the prediction accuracy requirements of the model building, the shaft is divided into 5 mass blocks, namely the mass block connected to the gear, the mass block connected to the bearing and the transition mass block in the middle; the bearings, gears, etc. are divided into single mass blocks respectively, and the box is divided into 5 mass blocks around and up and down to build the model.

[0130] When building a heat distribution module, you need to calculate the thermal resistance and thermal conductivity of each part, and determine the specific distribution of heat based on the thermal resistance and thermal conductivity, and how much heat should be distributed to different parts. The thermal resistance and thermal conductivity of each part are calculated using the following formula.

[0131] 1) Thermal conductivity and thermal resistance between shaft mass blocks:

[0132] (18);

[0133] (19);

[0134] in, h 1 is the thermal conductivity between the shaft mass blocks, unit: W / K; S 1 is the cross-sectional area of ​​the shaft, unit: mm 2 ; t 2 and t 1 are the adjacent mass block temperature and initial temperature, unit: K; R 1 is the thermal resistance between the shaft mass blocks, unit: K / W; l 1 is the characteristic length of the shaft mass block, unit: mm; λ 1 is the thermal conductivity of the shaft, unit: W / (mm·K).

[0135] 2) Thermal conductivity and thermal resistance of the shaft and the mass blocks of the components on the shaft:

[0136] (20);

[0137] (twenty one);

[0138] in, h 2. Thermal conductivity of the shaft and the mass block of the components on the shaft, unit: W / K; t 2 and t 1 are the adjacent mass block temperature and initial temperature, unit: K; R 2 is the thermal resistance between the shaft and the mass block of the components on the shaft, unit: K / W; l 2 is the characteristic contact length between the shaft and the mass block of the component on the shaft, unit: mm; λ 2 is the thermal conductivity of the components on the shaft, unit: W / (mm·K); d int is the inner diameter, in mm; d out It is the outer diameter in mm.

[0139] After completing the calculation of the thermal resistance and thermal conductivity between each mass block, it is necessary to correctly arrange the position of each mass block according to the position relationship of the gear in the transmission process. Different connection methods should be selected between each mass block according to the relationship of heat conduction, such as: heat conduction connection between shaft mass blocks, between gear mass blocks and shaft mass blocks, between bearings and shaft mass blocks, and heat radiation between the box and air. Correctly selecting the heat transfer method is the prerequisite for the correct construction of the model.

[0140] After completing the construction of the power loss calculation module and the heat distribution module, they need to be connected for heat transfer. The power loss calculated by the power loss module is transferred to the heat distribution module to achieve heat transfer, and then the heat is distributed to the entire system based on the thermal resistance and thermal conductivity.

[0141] Step 2: High-precision thermal-fluid coupling numerical simulation:

[0142] The gear heat generation and heat dissipation model has been built. Based on the ANSYS Fluent fluid simulation software platform, UDF programming and thermal-fluid coupling numerical simulation methods are used to analyze the internal flow field and temperature field of each part of the box during the gear meshing transmission process. In the process of thermal-fluid coupling numerical simulation, the UDF technology is used to set the heat generation calculated by the first part of the gear system heat generation and heat dissipation model as the thermal boundary condition to the gear meshing, and then simulate the heat generation and temperature rise of the gear surface in actual operation to achieve high-precision numerical simulation. The numerical simulation process includes three main contents, namely numerical simulation pre-processing, numerical simulation and UDF file writing. There are some precautions for all three parts.

[0143] The pre-processing of numerical simulation mainly includes computational fluid domain extraction, computational domain meshing, simulation parameter setting and other operations. It should be noted that in the process of meshing, the boundary layer of the mesh near the wall of the gear fluid domain needs to be encrypted, because too large a difference in the boundary layer mesh will cause a large velocity gradient in the boundary layer, which will cause a large deviation when analyzing the flow field, resulting in a large error in the numerical simulation results. In addition to boundary layer encryption, it is also necessary to perform a mesh independence analysis to eliminate the computational errors caused by mesh factors. Figure 4 Shown are the computational domain model, mesh model, and local boundary layer refinement.

[0144] When setting simulation parameters, it is necessary to assign initial temperatures to each surface of the calculation domain. The source of the initial temperature is the corresponding temperature obtained in the AMEsim heat distribution module. The subsequent temperature rise changes are determined by the lost power through UDF programming to set boundary conditions for the meshing gears, determine whether the tooth surface is in the meshing process, and apply heat-generating power to the tooth surface in the meshing process to simulate the heat generated by power loss caused by friction during the actual meshing process, resulting in the temperature rise of the gears. After the heat-generating power is set for the tooth surface, the tooth surface generates a corresponding temperature rise, and then a thermal-fluid coupling numerical simulation is performed through the fluid, using the fluid as the medium for heat transfer to transfer heat from the meshing point to various parts of the gear system. Correctly setting the temperature parameters, calculation step size, gear speed, and number of iterations is the key content of this part.

[0145] After numerical simulation pre-processing, parameter setting and other steps, the next step is numerical simulation. This part is one of the key points of this method, mainly involving the loading of UDF files and the use of UDF files in Fluent simulation software. In the user-defined module of Fluent simulation software, select complied under the functions list to import the written UDF file and select compile import to apply the UDF file to the grid.

[0146] The core of this method is to write UDF program files, combine the AEMsim model and Fluent fluid numerical simulation through UDF files, and simulate the heat generation during actual operation by applying heat generation power to specific surfaces, so as to achieve a high-precision thermal-fluid coupling numerical simulation that is more in line with the actual situation. When writing UDF files, the power loss of different gears needs to be applied to the relative gears separately, instead of applying the total power loss together. The most important point in the writing process is to intelligently identify the meshing condition of the gears during rotation. Only when the gears are in meshing state can heat be applied, so as to better simulate the heat generation of the actual operating conditions of the gears. Figure 5 The numerical simulation results of heat generation distribution at the gear meshing point based on UDF programming are shown. The formula for calculating the heat generation on the tooth surface is:

[0147] (twenty two);

[0148] In the formula, t is the gear working time, unit: s; S g is the meshing area of ​​the gears, and the meshing area of ​​the active gear (pinion) is 0.000041m 2 , the meshing area of ​​the driven gear (large gear) is 0.000036m 2 , H is the heat density, unit is W / (s·m2 ).

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-precision calculation method for thermal-fluid coupling of gear meshing transmission, characterized in that: The following steps are involved: Step 1: Build a heat generation and heat dissipation model for the gear system: Based on AMEsim software, a heat generation and heat dissipation model of the gear system is built using the thermal network method. The model includes a power loss calculation module and a heat distribution module. The power loss calculation module is used to calculate the power loss of each part of the gear system; The heat distribution module distributes the heat generated by the system due to power loss to each component in proportion according to the spatial position relationship, the contact situation of each part and the heat exchange with the outside world; After completing the construction of the power loss calculation module and the heat distribution module, connect the two modules to transfer heat. The power loss calculated by the power loss module is transferred to the heat distribution module to achieve heat transfer. Then, the heat is distributed to the entire system according to the thermal resistance and thermal conductivity. Step 2: High-precision thermal-fluid coupling numerical simulation: After building the gear heat generation and heat dissipation model, based on the ANSYS Fluent fluid simulation software platform, the UDF programming and thermal-fluid coupling numerical simulation method were used to analyze the flow field and temperature field inside the box during the gear meshing transmission process; In the process of thermal-fluid coupling numerical simulation, the UDF technology is used to set the heat generation calculated by the built gear heat generation and heat dissipation model as the thermal boundary condition to the gear meshing point, so as to numerically simulate the heat generation and temperature rise of the gear surface in actual operation; In step 1, building a power loss calculation module includes the following specific steps: First, we need to identify the heat source generated by power loss during the operation of the gear system. Power loss includes gear oil churning loss, sliding loss, rolling loss and bearing loss. By setting parameters, we can calculate different bearing load conditions and the power loss of gears and bearings. The power loss calculation module calculates the total power loss of the gear system according to the following formula and uses this as the basis for the heat distribution module: 1) Calculation of gear oil stirring power loss: （1）； （2）； （3）； in, P pad is the oil churning loss, unit: W; C md C is the calculation coefficient of gear side oil churning loss; ma is the calculation coefficient of gear surface oil churning loss; C side is the oil stirring loss on the tooth side, unit: W; C teeth is the oil churning loss on the tooth surface, unit: W; R 1 is the radius of the tooth tip circle, unit: mm; R 1 is the pitch circle radius, unit: mm; ω is the gear speed, unit: r / min; b is the tooth width, unit: mm; ρ is the density of lubricating oil, in g / mm 3 ; Calculation of tooth side Reynolds number and Froude number: （4）； （5）； in, g is the acceleration due to gravity, in m / s 2 ; Calculation of tooth surface Reynolds number and Froude number: （6）； （7）； in, ht is the tooth height, unit: mm; When Re ≥ 2250: （8）； When Re < 2250 and Re −0.6 ×Fro −0.25 < 8.7×10 −3 hour: （9）； When Re < 2250 and Re −0.6 ×Fro −0.25 > 8.7×10 −3 hour: （10）； When Re A 0.23 ×Fro A 0.32 ≥ 12: （11）； When Re A 0.23 ×Fro A 0.32 < 12:00: （12）； In the above formula, h is the gear oil immersion depth, unit: mm; V p Gear oil immersion volume, unit: mm 3 ; V 0 is the oil volume, unit: mm 3 ; ht 0 is the tooth addendum coefficient; 2) Gear sliding loss: （13）； in, F n is the normal force, unit: N; f g is the sliding coefficient; v g is the sliding speed, unit: m / s; L a is the meshing time, unit: s; 3) Gear rolling loss: （14）； in, F r is the rolling force, unit: N; v r is the rolling speed, unit: r / min; 4) Bearing power loss: （15）； （16）； （17）； in, P 0 is the friction power loss related to viscosity, unit: W; P f is the friction power loss related to the load, unit: W; P is the calculated load of the bearing friction torque, unit: N; d m is the bearing pitch diameter, unit: mm; f 0 is a coefficient related to the bearing type and lubrication method; f 1 is a factor related to bearing type and load; ω is the angular velocity of the inner ring of the bearing, unit: rad / s; n is the speed of the inner ring of the bearing, unit: r / min; v is the kinematic viscosity of the lubricating oil, unit: mm² / s; v n is the product of the kinematic viscosity of the lubricating oil and the speed of the inner ring of the bearing; In the AEMsim simulation software, select the gear transmission components, set the corresponding geometric parameters and gear meshing parameters, then connect these modules, set the connection parameters, and input the power loss calculation formula; set the input shaft speed of the gear system, set the braking torque at the output end, and truly simulate the operating conditions of the gear reducer; then build a power loss calculation module based on AMEsim to calculate the power loss and total heat generation under the operating conditions of the gear system; In step 1, building a heat distribution module includes the following specific steps: The total power loss obtained by the power loss calculation module is regarded as the total heat generation of the gear system. When building the heat distribution module, the total heat generation is distributed to obtain the heat situation of each part, and the temperature of each part is calculated according to the loss power allocated to each part. When building the heat distribution module, the shaft, bearings, gears, and gearboxes need to be divided into different mass blocks for model building; When building a heat distribution module, it is necessary to calculate the thermal resistance and thermal conductivity of each part, and determine the specific distribution of heat based on the thermal resistance and thermal conductivity, and how much heat should be distributed to different parts; the thermal resistance and thermal conductivity of each part are calculated using the following formula: 1) Thermal conductivity and thermal resistance between shaft mass blocks: （18）； （19）； in, h 1 is the thermal conductivity between the shaft mass blocks, unit: W / K; S 1 is the cross-sectional area of ​​the shaft, unit: mm 2 ; t 2 and t 1 are the adjacent mass block temperature and initial temperature, unit: K; R 1 is the thermal resistance between the shaft mass blocks, unit: K / W; l 1 is the characteristic length of the shaft mass block, unit: mm; λ 1 is the thermal conductivity of the shaft, unit: W / (mm·K); 2) Thermal conductivity and thermal resistance of the shaft and the mass blocks of the components on the shaft: （20）； （21）； in, h 2. Thermal conductivity of the shaft and the mass block of the components on the shaft, unit: W / K; t 2 and t 1 is the temperature of the adjacent mass blocks and the initial temperature, respectively, in K; R2 is the thermal resistance between the shaft and the mass blocks of the components on the shaft, in K / W; l 2 is the characteristic contact length between the shaft and the mass block of the component on the shaft, unit: mm; λ 2 is the thermal conductivity of the components on the shaft, unit: W / (mm·K); d int is the inner diameter, in mm; d out is the outer diameter, in mm; After completing the calculation of the thermal resistance and thermal conductivity between each mass block, it is necessary to correctly arrange the position of each mass block according to the positional relationship of the gears in the transmission process, and select different connection methods according to the relationship of heat conduction between each mass block and the different heat transfer methods.

2. The high-precision calculation method for thermal-fluid coupling of gear meshing transmission according to claim 1 is characterized in that: In step 2, the numerical simulation process includes three contents, namely numerical simulation pre-processing, numerical simulation and UDF file writing; Numerical simulation pre-processing includes computational fluid domain extraction, computational domain meshing, and simulation parameter setting; In the process of meshing, it is necessary to encrypt the mesh boundary layer near the wall of the gear fluid domain, and at the same time, it is necessary to perform mesh independence analysis to eliminate the calculation errors caused by mesh factors; When setting simulation parameters, it is necessary to assign initial temperatures to each surface of the calculation domain. The source of the initial temperature is the corresponding temperature obtained in the heat distribution module. The subsequent temperature rise changes are determined by the lost power through UDF programming to set boundary conditions for the meshing gears, determine whether the tooth surface is in the meshing process, and apply heat-generating power to the tooth surface in the meshing process to simulate the heat generated by the gears during the actual meshing process due to power loss, resulting in the temperature rise of the gears. After the heat generation power is set for the tooth surface, the tooth surface generates a corresponding temperature rise, and then the thermal-fluid coupling numerical simulation is performed through the fluid, using the fluid as the medium for heat transfer to transfer heat from the meshing point to various parts of the gear system; When performing numerical simulation, the AEMsim model and Fluent fluid numerical simulation are combined through UDF files. By applying heat generation power to the specified surface, the heat generation during actual operation is simulated. When writing UDF files, the power losses of different gears need to be applied to the corresponding gears respectively. During the writing process, the meshing condition of the gears during rotation needs to be intelligently identified. Heat can only be applied when the gears are in meshing state. The heat generation calculation formula for the tooth surface is: （22）； In the formula, t is the gear working time, unit: s; S g is the gear meshing area, m 2 ; H is heat density, unit: W / (s·m 2 ).

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