Calculation method for heat balance temperature of new energy automobile speed reducer

Abstract

The invention belongs to the technical field of new energy automobiles, and relates to a new energy automobile speed reducer heat balance temperature calculation method, which is realized by the following steps: step 1, analyzing and calculating a heat source in a speed reducer; 2, analyzing a transmission path of heat in the speed reducer; 3, temperature node division is conducted on parts in the speed reducer; 4, constructing a thermal network model of the speed reducer; 5, the convective heat transfer coefficient between the components is calculated; step 6, analyzing the type of the thermal resistance between the parts and calculating the size of the thermal resistance; 7, listing a heat balance equation of each node; and 8, solving the heat balance equation set to obtain the steady-state temperature value of the speed reducer under the working condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicles and relates to a method for calculating the thermal equilibrium temperature of a reducer of a new energy vehicle, which is used to accurately calculate the steady-state temperature field of the reducer and can provide a reference for thermal analysis and optimization of the reducer. Background Art

[0002] The reducer of new energy vehicles has a compact structure and small heat dissipation space. A large amount of heat will be generated during operation due to various losses. High temperature will not only affect the lubrication effect of the transmission system, causing gear wear and bonding, but also cause thermal deformation of the box body, which will have a huge impact on the precision of the reducer.

[0003] At present, there are two main methods for calculating the thermal equilibrium temperature of the reducer, namely the finite element method and the experimental method. The finite element method analyzes the temperature field of the gear body in the gearbox. The finite element method is relatively complex and time-consuming for the entire system, and some boundary conditions are difficult to determine. The experimental method requires high cost of related experimental equipment, high manpower and material resources, long time period, and cannot measure the temperature change trend of the internal parts of the transmission device.

[0004] In summary, there is still a lack of a fast and accurate method for calculating the thermal equilibrium temperature of the reducer of new energy vehicles. Summary of the invention

[0005] Purpose of the present invention: In view of the defects of the prior art, the present invention provides a method for calculating the thermal equilibrium temperature of a new energy vehicle reducer, which is used to accurately calculate the steady-state temperature field of the reducer and provide a reference for thermal analysis and optimization of the reducer.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] According to the structure and working principle of the reducer, the various heat sources and heat transfer paths of the reducer are first analyzed; then the thermal network model and thermal balance equation of the reducer are established based on the thermal network method, and the thermal resistance and convection heat transfer coefficient of various types of reducers are analyzed and calculated; Matlab software is used to perform a first-order steady-state iterative solution to the thermal balance equation, and finally the steady-state temperature value of each node in the reducer under different working conditions of thermal balance is obtained. The specific steps are as follows:

[0008] Step 1: Analyze the structure and working principle of the reducer, and find out the causes of heat generation, which are gear meshing friction power loss, bearing friction power loss, oil stirring power loss and wind resistance power loss. Calculate the heat loss of each part of the reducer.

[0009] After step 1, proceed to step 2.

[0010] Step 2: Analyze the heat transfer path in the reducer. Heat transfer includes three ways: heat conduction, heat convection, and heat radiation. Since heat radiation requires a considerable temperature difference between two components, but the internal space of the reducer is compact and the temperature difference of the components under study is relatively low, heat radiation between internal components is not considered.

[0011] After step 2, proceed to step 3.

[0012] Step 3: Simplify the reducer based on its characteristics. According to the distribution position of gears and transmission shafts and the geometry of the housing, divide and number the main parts of the reducer such as gears, bearings, housings, support shafts and lubricating oil, oil-gas mixture in the housing, and external ambient air into nodes.

[0013] After step 3, proceed to step 4.

[0014] Step 4: Construct the thermal network model of the new energy vehicle reducer based on the divided temperature nodes.

[0015] After step 4, proceed to step 5.

[0016] Step 5: Calculate the convective heat transfer coefficients between the gears, bearings, housing and lubricating oil respectively.

[0017] After step 6, proceed to step 7.

[0018] Step 7: Establish the heat balance equation for each node.

[0019] After step 7, proceed to step 8.

[0020] Step 8: Iteratively solve the node heat balance equation to obtain the steady-state temperature value of each node under different working conditions.

[0021] The beneficial effects of the present invention are: Based on the thermal network method, the reducer of new energy vehicles is calculated and analyzed. The influence of wind resistance power loss is taken into account to make the calculation closer to reality. The thermal network model of the reducer is quickly established, and a more accurate steady-state temperature field of the reducer is obtained through calculation and solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a calculation flow chart of the present invention.

[0023] Figure 2 This is the heat transfer route map inside the reducer.

[0024] Figure 3 Node partition diagram for reducer temperature.

[0025] Figure 4 This is the thermal network model diagram of the reducer. DETAILED DESCRIPTION

[0026] The following are specific embodiments of the present invention. Figure 1 The solution of the present invention is further described by calculating the steady-state temperature of a certain new energy vehicle reducer, but the present invention is not limited to these examples.

[0027] Step 1: The heat loss calculation formula is as follows: (1) The friction power loss during gear meshing mainly includes the sliding friction power loss between the tooth surfaces. and rolling friction power loss , the parameters of lubricating oil, speed and torque determine the magnitude of gear meshing friction power loss; (2) The total power loss can be expressed as ,in, M 0 is the friction torque caused by the load, M 1 is the viscous friction torque caused by lubricating oil; (3) The power loss caused by oil stirring is the oil stirring power loss of the gear end face Oil stirring power loss at gear meshing surface sum; (4) Wind resistance loss It is the energy loss of the oil-gas mixture in the gearbox when the gears run at high speed.

[0028] After step 1, proceed to step 2.

[0029] Step 2: The heat transfer route diagram in the reducer is as shown in the attached figure. Figure 2 As shown, when the reducer is working, part of the heat generated when the gears are meshing is transferred to the shaft and the housing through gear heat conduction, and the other part is brought into the oil pool by the lubricating oil through thermal convection, and finally transferred to the housing to exchange heat with the outside air by thermal convection, so that the temperature field of the reducer is in a balanced state.

[0030] After step 2, proceed to step 3.

[0031] Step 3: Temperature node division as shown in the attached Figure 3 , divided into 24 nodes in total. 1, 7, 13, 14 are the temperatures of the gears, 3, 5, 9, 11, 17, 19 are the temperatures of the bearings, 2, 8 are the temperatures of the input shaft and the intermediate shaft, 16, 20 are the temperatures of the output shaft, 4, 6, 10, 12, 18, 21 are the temperatures of the housing outside the bearings, and 15 is the temperature of the differential housing; among them, A is the temperature of the air outside the housing, O is the temperature of the lubricating oil, and M is the temperature of the oil-gas mixture.

[0032] After step 3, proceed to step 4.

[0033] Step 4: By analyzing the heat transfer path of the reducer and dividing the temperature nodes in detail, the attached Figure 4 Thermal network model of the reducer. Here, represents the thermal resistance of heat conduction between two nodes, and represents the thermal resistance of heat convection between two nodes.

[0034] After step 4, proceed to step 5.

[0035] Step 5: Calculation of convection heat transfer coefficient: (1) The forced convection heat transfer coefficient between gear and lubricating oil is: ; (2) The convective heat transfer coefficient between lubricating oil and bearing is: ; (3) The convection heat transfer coefficient between the inner wall of the box and the lubricating oil is: ; (4) The convective heat transfer coefficient between the outer surface of the box and the ambient air is: .

[0036] After step 5, proceed to step 6.

[0037] Step 6: The formula for calculating the conduction thermal resistance of gears, bearings, housings, etc. is: ,The calculation formula of convection thermal resistance between each component and lubricating oil or air is: .

[0038] After step 6, proceed to step 7.

[0039] Step 7: List the thermal balance equations. When the entire reducer system reaches thermal balance, the temperature of the parts in the box tends to be stable, and the temperature of each node no longer changes with time. The temperature solution formula when the node reaches steady state is: .

[0040] After step 7, proceed to step 8.

[0041] Step 8: Calculate and solve the problem by programming with the first-order steady-state iterative method in MATLAB. The initial temperature of the lubricating oil is 25°C, and the initial temperature of the ambient air is 20°C. The thermal equilibrium temperatures of each node under the working conditions of rated speed of 8000r / min and rated power of 70kW are shown in the following table:

[0042] In the above description, the present invention is described through specific embodiments, but those skilled in the art should understand that various modifications and variations can be made without departing from the concept and field of the invention within the scope of the claims.

Claims

1. A method for calculating the thermal equilibrium temperature of a new energy vehicle reducer, characterized in that: This method is based on the thermal network method, takes temperature as the target value, starts from the reducer heat source, analyzes the heat transfer path in the reducer and divides the detailed temperature nodes, builds a thermal network model, calculates the thermal resistance and convection heat transfer coefficient, lists the thermal balance equation of each node, and solves the steady-state temperature value of each node of the reducer; the specific steps are as follows: Step 1: The heat source takes into account the gear meshing friction power loss, bearing friction power loss, oil stirring power loss and windage power loss; After step 1, proceed to step 2; Step 2: The heat transfer path is that part of the heat generated when the gears are meshing is transferred to the shaft and the housing through heat conduction of the gears, and the other part is brought into the oil pool by the lubricating oil through heat convection, and finally transferred to the housing to exchange heat with the outside air by heat convection; After step 2, proceed to step 3; Step 3: The temperature nodes are divided into 24 nodes, mainly including parts such as gears, bearings, housings, support shafts and lubricating oil, oil-gas mixture in the housing, and external ambient air; After step 3, proceed to step 4; Step 4: The thermal network model is based on the law of conservation of energy, and the heat flowing into each temperature node is equal to the heat flowing out; After step 4, proceed to step 5; Step 5: Calculate the convection heat transfer coefficient between the gear, bearing, housing and lubricating oil, and transform the gear convection heat transfer problem into a problem of fluid sweeping across a flat plate; After step 5, proceed to step 6; Step 6: Thermal resistance calculation includes conduction thermal resistance and convection thermal resistance. The convection heat transfer coefficient determines the convection thermal resistance. After step 6, proceed to step 7; Step 7: Based on the law of conservation of energy, the heat flowing into each temperature node is equal to the heat flowing out, and the heat balance equation for each node is listed; After step 7, proceed to step 8; Step 8: Solve to obtain the steady-state temperature value of each node of the reducer. Use MATLAB to program the first-order steady-state iterative method to calculate and solve. The initial temperature of the lubricating oil is 25°C, and the initial temperature of the ambient air is 20°C. Get the steady-state temperature value of each node of the reducer.

2. The method for calculating the thermal equilibrium temperature of a new energy vehicle reducer according to claim 1 is characterized in that: The calculation of windage power loss is added in step 1, and the calculation formula is: 。

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