Electric drive axle assembly structure reliability evaluation method

Abstract

The invention discloses an electric drive axle assembly structure reliability evaluation method, and belongs to the technical field of new energy automobiles. The invention aims to solve the problem that the evaluation is one-sided because the calibration precision is low, the load is not associated with the road condition of a user and the dynamic influence of the load frequency on the structure is neglected when the reliability of the electric drive axle structure is evaluated, and the electric drive axle analysis model is subjected to test benchmarking adjustment, so that the simulation result has higher reference significance and higher reliability. According to the method, working conditions are analyzed, namely quasi-static structural strength and nominal stress fatigue analysis without considering frequency components and random vibration analysis considering the frequency components are included, the structural reliability of the electric drive system is comprehensively evaluated, establishment of a complex multi-body dynamic model for extracting the durable load is avoided, the load extraction precision can be improved through test calibration, and the reliability of the electric drive system is improved. Meanwhile, time and cost are saved, the actually measured load serves as a reference for simulating and calculating the working condition, and the analysis result is closer to the user working condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicles, and in particular relates to a method for evaluating the structural reliability of an electric drive axle assembly. Background Art

[0002] The electric drive axle assembly of new energy commercial vehicles integrates core components such as motors, transmissions, and bridge housings. It has a large and complex structure and must withstand multiple types of load excitations, including spring loads from the superstructure and frame, rotational loads from the transmission system, and uneven road surfaces. Therefore, it is necessary to focus on evaluating the structural reliability.

[0003] At present, there are many structural performance analysis methods for electric drive axles in the industry, but the load size is often judged only from engineering experience. The simulation model is not accurately calibrated, resulting in poor accuracy. The evaluation method often only considers quasi-static loading. Therefore, the evaluation of the reliability of the electric drive axle structure is relatively one-sided and has poor engineering reference significance. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for evaluating the structural reliability of an electric drive axle assembly to solve the problem of one-sided evaluation due to low calibration accuracy and only considering the influence of quasi-static loading when evaluating the structural reliability of an electric drive axle.

[0005] To solve the above technical problems, the present invention is implemented by adopting the following solutions: The present invention provides a method for evaluating the structural reliability of an electric drive axle assembly, comprising: Calibrate the simulation displacement and test displacement of the electric drive axle assembly to obtain the finite element analysis model of the electric drive axle assembly; Establish different working conditions on the finite element analysis model of the electric drive axle assembly, select stress calibration points, calibrate the test strains of the various loads and stress calibration points under different working conditions of the electric drive axle assembly, and obtain mathematical expressions of various loads and strains; Collect the test strain of the stress calibration point on the electric drive axle assembly under the user's road condition and the acceleration signal of the excitation position to obtain the strain spectrum and acceleration spectrum of the electric drive axle assembly under the user's road condition; According to the mathematical expression, strain spectrum, SN curve of the electric drive axle assembly material, and stress field of the electric drive axle assembly unit load in different directions under different working conditions, the quasi-static strength evaluation results and fatigue life evaluation results of the electric drive axle assembly are obtained; According to the acceleration spectrum and the finite element analysis model of the electric drive axle assembly, the random vibration evaluation results of the electric drive axle assembly are obtained; According to the quasi-static strength assessment results, fatigue life assessment results and random vibration assessment results of the electric drive axle assembly, the structural reliability assessment results of the electric drive axle assembly are obtained.

[0006] Optionally, calibrating the simulation displacement and the test displacement of the electric drive axle assembly to obtain a finite element analysis model of the electric drive axle assembly includes: A CAD analysis model of the electric drive axle assembly is established, and two circles of quadrilateral units are forcibly distributed around the mounting holes in the CAD analysis model of the electric drive axle assembly, and the diameter of the second circle of quadrilateral units is consistent with the diameter of the flange surface of the bolts / nuts, so as to obtain a finite element analysis model of the electric drive axle assembly to be optimized; In the finite element analysis model of the electric drive axle assembly to be optimized, a preload is established on the screw section of the solid bolt according to the preload of the bolt, a first rigid unit is established at the nodes on the inner and outer bearing mounting surfaces of the left and right wheel hubs, the main node of the first rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the first rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the first rigid unit on the left, the stress analysis result under the first preload condition is obtained by finite element solution, a second rigid unit is established at the nodes on the installation plane of the left and right leaf springs on the bridge housing, a vertical load of twice the dynamic load coefficient is established at the main nodes of the second rigid units on the left and right sides, the main node of the first rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the first rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the first rigid unit on the left, a load step of the bending condition is established, the stress analysis result under the first preload condition is brought into the load step of the bending condition, and the maximum vertical simulation displacement of the electric drive axle assembly under the bending condition is obtained by finite element solution; According to the goal that the difference between the maximum vertical simulation displacement and the vertical test displacement under the bending condition of the electric drive axle assembly is less than the set value, the mesh size in the finite element analysis model of the electric drive axle assembly to be optimized and the simplification method of the components in the electric drive axle assembly are adjusted to obtain the finite element analysis model of the electric drive axle assembly.

[0007] Optionally, different operating conditions are established on the finite element analysis model of the electric drive axle assembly, including: In the finite element analysis model of the electric drive axle assembly, a preload is established on the screw section of the solid bolt according to the preload of the bolt, a third rigid unit is established at the nodes on the inner and outer bearing mounting surfaces of the left and right wheel hubs, the main node of the third rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the third rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the third rigid unit on the left, the stress analysis result under the second preload condition is obtained by finite element solution, a fourth rigid unit is established at the nodes on the installation plane of the left and right leaf springs on the bridge housing, a vertical load of one times the dynamic load coefficient is established at the main nodes of the fourth rigid units on the left and right sides, the main node of the third rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the third rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the third rigid unit on the left, the load step of the bending stiffness condition is established, the stress analysis result under the second preload condition is brought into the load step of the bending stiffness condition, and the stress analysis result under the bending stiffness condition of the electric drive axle assembly is obtained by finite element solution; In the finite element analysis model of the electric drive axle assembly, two fixing fixtures with a spacing equal to the actual vehicle leaf spring spacing are established to support the electric drive axle assembly, and a brake base plate is fixed to the electric drive axle shoulder by bolts. A preload is established on the screw cross section of the solid bolt according to the preload of the bolt, and all degrees of freedom of the bottom mounting surface of the fixing fixture are constrained. The stress analysis results under the third preload condition are obtained by finite element solution. Axle loads of set multiples are applied forward and backward at the load application hole position of the brake base plate, and all degrees of freedom of the bottom mounting surface of the fixing fixture are constrained. The load step of the braking condition is established, and the stress analysis results under the third preload condition are brought into the load step of the braking condition. The stress analysis results of the braking condition are obtained by finite element solution. In the finite element analysis model of the electric drive axle assembly, a fifth rigid unit is established at the nodes on the outer support surface of the inner and outer mounting bearings of the left wheel hub. The main node of the fifth rigid unit is the grounding point of the tire width center on one side of the axle. According to the preload of the bolt, a preload is established on the screw cross section of the solid bolt to constrain all degrees of freedom of the bottom mounting surface of the fixing fixture. The stress analysis result under the fourth preload condition is obtained by finite element solution. An axle load with a lateral setting multiple is applied at the main node of the fifth rigid unit to constrain all degrees of freedom of the bottom mounting surface of the fixing fixture, and a load step of the steering condition is established. The stress analysis result under the fourth preload condition is brought into the load step of the steering condition, and the stress analysis result of the steering condition is obtained by finite element solution.

[0008] Optionally, stress calibration points are selected to calibrate the axial loads and test strains of the stress calibration points under different working conditions of the electric drive axle assembly to obtain mathematical expressions of axial loads and strains, including: Select stress calibration points according to the stress analysis results of different working conditions of the electric drive axle assembly: select the first strain point that is only sensitive to the bending stiffness working condition, select the second strain point that is only sensitive to the braking working condition, and select the third strain point that is only sensitive to the steering working condition; The vertical load and the test strain of the first strain point under the bending stiffness condition of the electric drive axle assembly, the longitudinal load and the test strain of the second strain point under the braking condition, and the lateral load and the test strain of the third strain point under the steering condition are calibrated to obtain the functional expressions of the vertical load and strain, the longitudinal load and strain, and the lateral load and strain.

[0009] Optionally, collecting the test strain of the stress calibration point on the electric drive axle assembly under the user's road condition and the acceleration signal of the excitation position to obtain the strain spectrum and acceleration spectrum of the electric drive axle assembly under the user's road condition includes: The vehicle is loaded with user road condition loads, and the strains of three strain points on the electric drive axle assembly of the vehicle and the acceleration signals of the excitation positions are collected to obtain the strain spectrum and acceleration spectrum under the user road condition; The excitation position is the mounting surface of the fixing fixture and the electric drive axle.

[0010] Optionally, according to the mathematical expression, the strain spectrum, the SN curve of the electric drive axle assembly material, and the stress field of the electric drive axle assembly under unit loads in different directions under different working conditions, the quasi-static strength assessment result and fatigue life assessment result of the electric drive axle assembly are obtained, including: The axial load spectrum of the electric drive axle assembly is obtained according to the mathematical expression and the strain spectrum, and the extreme values ​​of the axial load spectrum of the electric drive axle assembly are extracted as the loads of different working conditions of the electric drive axle assembly to analyze and evaluate the quasi-static strength of the electric drive axle assembly under different working conditions based on the user's road conditions, and the quasi-static strength evaluation result of the electric drive axle assembly is obtained; The bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly are calculated based on the load spectrum of the electric drive axle assembly in all directions, the SN curve of the material of the electric drive axle assembly and the stress field of the unit load of the electric drive axle assembly in all directions under different working conditions. The fatigue life of the electric drive axle assembly is evaluated by comparing the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly with the design life, and the fatigue life evaluation result of the electric drive axle assembly is obtained; Among them, the method for obtaining the stress field of the unit load in each direction of the electric drive axle assembly under different working conditions is: taking the unit load in each direction as the load under different working conditions of the electric drive axle assembly, the constraints are equal to the constraints under each working condition, and the stress field of the unit load in each direction of the electric drive axle assembly is obtained by finite element solution.

[0011] Optionally, the extreme values ​​of the load spectrum of the electric drive axle assembly in all directions are extracted as the loads of the electric drive axle assembly in different working conditions to analyze and evaluate the quasi-static strength of the electric drive axle assembly in all directions under different working conditions based on the user's road conditions, and the quasi-static strength evaluation results of the electric drive axle assembly are obtained, including: The extreme values ​​of the load spectrum of the electric drive axle assembly in all directions are used as the loads of the electric drive axle assembly in different working conditions, and the constraints are equal to the constraints under each working condition. The quasi-static strength of the electric drive axle assembly in all directions under different working conditions based on the user's road condition limit load is obtained through finite element solution; If the quasi-static strength of the electric drive axle assembly in different working conditions based on the user's road condition limit load is less than the yield strength of the electric drive axle assembly and the bending stiffness value is less than the preset value, then the electric drive axle assembly is evaluated to meet the quasi-static strength performance requirements, otherwise the electric drive axle assembly is evaluated to not meet the quasi-static strength performance requirements; The bending stiffness value is equal to the ratio of the maximum vertical simulated displacement of the electric drive axle assembly under the bending stiffness condition to the wheelbase.

[0012] Optionally, the fatigue life of the electric drive axle assembly is evaluated by comparing the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly with the design life to obtain a fatigue life evaluation result of the electric drive axle assembly, including: if the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly all meet the design life requirements, then the electric drive axle assembly is evaluated to meet the fatigue life performance requirements; otherwise, the electric drive axle assembly is evaluated to not meet the fatigue life performance requirements.

[0013] Optionally, according to the acceleration spectrum and the finite element analysis model of the electric drive axle assembly, a random vibration evaluation result of the electric drive axle assembly is obtained, including: The acceleration spectrum is converted into power spectrum density in all directions, and the random vibration analysis of the electric drive assembly is performed after setting the modal extraction range and system damping to obtain the maximum 3σ stress of the electric drive axle assembly in all directions; If the maximum 3σ stress of the electric drive axle assembly in each direction is not greater than the yield strength of the components in the electric drive axle assembly, the electric drive axle assembly is evaluated to meet the random vibration performance requirements, otherwise the electric drive axle assembly is evaluated to not meet the random vibration performance requirements.

[0014] Optionally, a structural reliability assessment result of the electric drive axle assembly is obtained based on the quasi-static strength assessment result, fatigue life assessment result, and random vibration assessment result of the electric drive axle assembly, including: if the quasi-static strength assessment result, fatigue life assessment result, and random vibration assessment result of the electric drive axle assembly all meet preset performance requirements, then it is assessed that the electric drive axle assembly meets the structural reliability requirements; otherwise, the electric drive axle assembly does not meet the structural reliability requirements.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the electric drive axle analysis model of the present invention has been adjusted through experimental benchmarking, and the simulation results have a higher reference significance; the analysis conditions include both quasi-static structural strength and nominal stress fatigue analysis that does not consider frequency components, and random vibration analysis that considers frequency components, which can more comprehensively evaluate the structural reliability of the electric drive system; it avoids establishing a complex multi-body dynamics model to extract endurance loads, and the load extraction accuracy can be improved through experimental calibration, while saving time and cost; the measured load is used as a reference for simulation calculation conditions, and the analysis results are closer to user conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flow chart of a method for evaluating the structural reliability of an electric drive axle assembly provided by an embodiment of the present invention; Figure 2 is a schematic diagram of an electric drive axle assembly under a bending condition in a method for evaluating the structural reliability of an electric drive axle assembly provided by an embodiment of the present invention; Figure 3 It is a front view schematic diagram of an electric drive axle assembly under a braking condition in a method for evaluating the structural reliability of an electric drive axle assembly provided by an embodiment of the present invention; Figure 4 It is a schematic side view of an electric drive axle assembly under a braking condition in a method for evaluating the structural reliability of an electric drive axle assembly provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of a steering condition in a method for evaluating the structural reliability of an electric drive axle assembly provided by an embodiment of the present invention; In the figure: 1, fixing fixture; 2, brake base plate; 3, wheel hub; L1, wheelbase; L2, leaf spring distance; a, brake base plate load application hole; R, rolling radius; F1, 0.3 times the forward axle load; F2, 0.3 times the rearward axle load; F3, 0.3 times the lateral axle load. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention. Embodiment 1:

[0018] like Figure 1 As shown, this embodiment provides a method for evaluating the structural reliability of an electric drive axle assembly, comprising the following steps: A. Establish the finite element analysis model of the electric drive axle assembly.

[0019] Specifically, a CAD analysis model of the electric drive axle assembly including core components such as the motor assembly, transmission housing, bridge housing, gears, bearings, and half shafts is established. Check the CAD analysis model, adjust basic data problems such as interference and misalignment of mounting holes, and ensure that the data is free of interference, the mounting holes are aligned, and the data is consistent with the actual object. For components with non-uniform thickness such as bridge housings, transmission housings, and gears, second-order tetrahedral units are used for mesh discretization, with a mesh size of 3mm. Appropriate encryption is used at the fillet to ensure the integrity of data features. For other bracket-like structures with uniform plate thickness, two-dimensional shell units are used for mesh discretization, with a mesh size of 5mm. For mounting holes, two circles of quadrilateral units are forcibly distributed around the mounting holes, and the diameter of the second circle of quadrilateral units is consistent with the flange diameter of the bolts / nuts. Bolts are divided using hexahedral units, and sliding contact is set between the bolts and their connected parts and between the connected parts, considering the friction between the components. Sliding contact is established between the inner and outer bearings of the wheel hub 3 and the electric drive axle. Considering the contact friction, the initial value of the friction coefficient is set to 0.15. The weld is simulated by solid units and the nodes are coupled to the connected parts of the weld to ensure the consistency of the mass and center of mass of the analysis model and the actual object. In this way, the finite element analysis model of the electric drive axle assembly to be optimized is obtained.

[0020] B. Calibrate the simulation displacement and test displacement of the electric drive axle assembly to adjust the finite element analysis model of the electric drive axle assembly to obtain a high-precision finite element analysis model of the electric drive axle assembly.

[0021] Specifically, for the finite element analysis model of the electric drive axle assembly in A, the bolt preload is first solved: according to the calculation formula of the bolt preload and the tightening torque: F=T*1000 / (K*d), where F is the bolt preload, in N, T is the bolt tightening torque, in N•m, K is the torque coefficient, and the initial value here is 0.2, d is the diameter of the bolt, in mm, and according to the calculation formula of the tightening torque T and the above bolt preload and tightening torque in the actual process assembly of the electric drive axle, the bolt preload can be obtained; then, according to the bolt preload, a preload load is established on the screw cross section of the solid bolt, and a rigid unit is established with the nodes of the mounting surfaces of the inner and outer bearings of the left and right wheel hubs 3 to ensure that the main nodes of the rigid units on the left and right sides are symmetrical and the spacing is the actual wheel spacing L1, refer to Figure 2Perform bending condition constraints. The main node of the left rigid unit is a simply supported beam constraint. All movement degrees of freedom are constrained and all rotation degrees of freedom are released. The main node of the right rigid unit releases one more lateral movement degree of freedom than the left side. Establish a load step with only bolt preload, perform nonlinear solution calculation, and obtain the stress analysis results under the preload condition; then establish a rigid unit with the nodes on the left and right leaf spring installation planes on the bridge shell to ensure that the main nodes of the left and right rigid units are symmetrical and the spacing is the actual vehicle leaf spring spacing L2. Establish vertical loads at the main nodes of the left and right rigid units. Both the left and right sides are the axle loads of the drive axle assembly. This completes the load setting of the electric drive axle bending condition (2 times the dynamic load coefficient), refer to Figure 2 The bending working condition constraint is performed. The main node of the left rigid unit established by the node of the mounting surface of the inner and outer bearings of the left wheel hub 3 is a simply supported beam constraint, which constrains all degrees of freedom of movement and releases all degrees of freedom of rotation. The main node of the right rigid unit established by the node of the mounting surface of the inner and outer bearings of the right wheel hub 3 releases one more degree of freedom of lateral movement than the left side, thereby establishing the load step of the bending working condition. The stress analysis result of the preload working condition is brought into the load step of the bending working condition. The bending working condition stress and displacement analysis results of the electric drive axle assembly are obtained by finite element solution. According to the bending working condition stress and displacement analysis results of the electric drive axle assembly, the maximum vertical simulation displacement of the electric drive axle assembly under the bending working condition is obtained; finally, the bench test displacement results of the electric drive axle assembly with the same load and boundary conditions are compared. According to the goal that the maximum vertical displacement of the bending working condition of the electric drive axle assembly differs by <2% from the test displacement result, the mesh size in the finite element analysis model of the electric drive axle assembly, the simplified method of the components in the electric drive axle assembly, etc. are adjusted to obtain a high-precision finite element analysis model of the electric drive axle assembly.

[0022] C. Establish bending stiffness conditions, braking conditions and steering conditions, calculate the stress analysis results, and select stress calibration points based on the analysis results.

[0023] Specifically, for the high-precision finite element analysis model obtained in B, a rigid unit is established at the nodes of the mounting surfaces of the inner and outer bearings of the left and right wheel hubs 3 to ensure that the main nodes of the rigid units on the left and right sides are symmetrical and the spacing is the actual wheel spacing L1. Figure 2Perform bending stiffness working condition constraints (bending stiffness working condition constraints are the same as bending stiffness working condition constraints). The main node of the left rigid unit is a simply supported beam constraint. All movement degrees of freedom are constrained and all rotation degrees of freedom are released. The main node of the right rigid unit releases one more lateral movement degree of freedom than the left side. According to the preload of the bolt solved in B, a preload load is established on the screw cross section of the solid bolt, and then a load step with only the bolt preload is established. Nonlinear solution calculation is performed to obtain the stress analysis results under the preload condition; then rigid units are established at the nodes on the left and right leaf spring installation planes on the bridge housing to ensure that the main nodes of the rigid units on the left and right sides are symmetrical and the spacing is the actual vehicle leaf spring spacing L2. Vertical loads are established at the main nodes of the rigid units on the left and right sides (the load is halved compared to step B). Both the left and right sides are the axle loads of the drive axle assembly. In this way, the load setting of the bending stiffness working condition (1 times the dynamic load coefficient) of the electric drive axle is completed. Refer to Figure 2 The bending stiffness working condition constraint is performed. The main node of the left rigid unit established by the node of the mounting surface of the inner and outer bearings of the left wheel hub 3 is a simply supported beam constraint, which constrains all movement degrees of freedom and releases all rotational degrees of freedom. The main node of the right rigid unit established by the node of the mounting surface of the inner and outer bearings of the right wheel hub 3 releases one more lateral movement degree of freedom than the left side, thereby establishing the load step of the bending stiffness working condition. The stress analysis result of the above-mentioned preload working condition is brought into the load step of the bending stiffness working condition. The stress and displacement analysis results of the bending stiffness working condition of the electric drive axle assembly are calculated by finite element nonlinear solution. The ratio of the maximum vertical displacement of the electric drive axle assembly to the wheelbase L1 under this condition is the maximum deformation of the tire per meter, also known as the bending stiffness value.

[0024] Reference Figure 3 and Figure 4 The braking condition constraints and loading are performed. Two fixing fixtures 1 with a spacing equal to the actual vehicle leaf spring spacing L2 are used to support the electric drive axle assembly. The brake base plate 2 is fixed to the electric drive axle shoulder by bolts to constrain all degrees of freedom of the bottom mounting surface of the fixing fixture 1. According to the preload force of the bolt obtained by solving B, a preload load is established on the screw section of the physical bolt, and then a load step with only the preload force of the bolt is established. Nonlinear solution calculation is performed to obtain the stress analysis results under the preload condition; then Figure 3 and Figure 4 0.3 times the forward axle load F1 and 0.3 times the backward axle load F2 are applied to the load application hole a of the brake base plate 2 respectively. The forward axle load F1 and the backward axle load F2 are located at a vertical position offset by a rolling radius R downward from the axis of the electric drive axle assembly, constraining all degrees of freedom of the bottom mounting surface of the fixing fixture 1, thereby establishing the load step of the braking condition, bringing the stress analysis results under the above-mentioned preload condition into the load step of the braking condition, and obtaining the stress analysis results of the braking condition through finite element nonlinear solution calculation.

[0025] Reference Figure 5 Steering condition constraints and loading are performed, and a rigid unit is established at the nodes on the outer support surface of the inner and outer bearings of the left wheel hub 3. The main node of the rigid unit is the grounding point at the tire width center on one side of the axle. All degrees of freedom of the bottom mounting surface of the fixing fixture 1 are constrained. According to the preload force of the bolt solved in B, a preload load is established on the screw cross section of the solid bolt, and then a load step with only the bolt preload force is established, and a nonlinear solution calculation is performed to obtain the stress analysis result under the preload condition; then, a lateral axle load F3 of 0.3 times is applied to the main node of the rigid unit of the left wheel hub 3 bearing. The lateral axle load F3 of 0.3 times is located at a vertical position offset downward by a rolling radius R from the axis of the electric drive axle assembly, and all degrees of freedom of the bottom mounting surface of the fixing fixture 1 are constrained, thereby establishing a load step of the steering condition, and the stress analysis result of the steering condition is obtained by finite element nonlinear solution calculation.

[0026] Looking at the finite element stress analysis results of the bending stiffness condition, the braking condition, and the steering condition, a strain point is selected on the electric drive axle assembly, which has a certain strain value only in the bending stiffness condition, and the strain values ​​of the braking and steering conditions are close to 0, that is, it is only sensitive to the bending stiffness condition, and is recorded as the first strain point; a strain point is selected on the electric drive axle assembly, which has a certain strain value only in the braking condition, and the strain values ​​of the bending stiffness and the steering condition are close to 0, that is, it is only sensitive to the braking condition, and is recorded as the second strain point; a strain point is selected on the electric drive axle assembly, which has a certain strain value only in the steering condition, and the strain values ​​of the bending stiffness and the braking condition are close to 0, that is, it is only sensitive to the steering condition, and is recorded as the third strain point.

[0027] D. Calibrate the vertical, longitudinal, and lateral loads and test strains of the stress calibration points under the bending stiffness, braking, and steering conditions of the electric drive axle assembly, and obtain the mathematical expressions of the vertical load and strain, longitudinal load and strain, and lateral load and strain.

[0028] Specifically, the vertical load and the strain of the first strain point in C under the bending stiffness condition of the electric drive axle assembly, the longitudinal load and the strain of the second strain point in C under the braking condition, and the lateral load and the strain of the third strain point in C under the steering condition are calibrated on the test bench to obtain the function expression of the vertical load and the strain of the first strain point under the bending stiffness condition, the function expression of the longitudinal load and the strain of the second strain point under the braking condition, and the function expression of the lateral load and the strain of the third strain point under the steering condition.

[0029] E. Collect the strain and acceleration signals of the electric drive axle assembly under the user's road conditions of the whole vehicle, and obtain the strain spectrum and acceleration spectrum of the electric drive axle assembly under the user's road conditions.

[0030] Specifically, the vehicle is loaded with the user road condition load, and the strains of three strain points on the electric drive axle assembly in the vehicle and the acceleration signals of the excitation positions (i.e., the mounting surfaces of the fixing fixture 1 and the electric drive axle in C) are collected to obtain the strain spectrum and acceleration spectrum under the user road condition.

[0031] F. Based on the functional expression of load and strain in D and the strain spectrum under the user road condition in E, the vertical, longitudinal and lateral load spectra of the electric drive axle assembly are obtained, and the extreme values ​​of the load spectrum are extracted as the quasi-static strength analysis load of the electric drive axle assembly to perform strength analysis of bending stiffness condition, braking condition and steering condition, evaluate the analysis results, and obtain the quasi-static strength assessment results.

[0032] Specifically, according to the strain spectrum in E and the functional expression of load and strain in D, the vertical load spectrum, longitudinal load spectrum and lateral load spectrum of the electric drive axle assembly are obtained, and the extreme values ​​of the vertical load spectrum, longitudinal load spectrum and lateral load spectrum are extracted to carry out quasi-static strength analysis of the electric drive axle assembly bending, braking and steering conditions based on user road conditions, respectively. The extreme value of the vertical load spectrum is used as the load of the bending stiffness condition, the extreme value of the longitudinal load spectrum is used as the load of the braking condition, and the extreme value of the lateral load spectrum is used as the load of the steering condition. The constraints under the three conditions are equivalent to the corresponding settings in C, and the three-way quasi-static strength analysis results based on the user road condition limit load are obtained. The maximum stress values ​​of the three conditions are all less than the yield strength of the electric drive axle assembly and the bending stiffness value is <1.4mm / m, which is determined to meet the quasi-static strength performance. If one condition does not meet the requirements, the quasi-static strength performance is not met.

[0033] G. Calculate the stress field of the vertical, longitudinal and lateral unit loads of the electric drive axle assembly.

[0034] Specifically, the loads of the bending stiffness condition, braking condition and steering condition in C are replaced with unit loads, and the corresponding constraints of each condition in C are used as constraints to carry out the strength calculation of the three-dimensional (i.e. vertical, longitudinal and lateral) unit load to obtain the three-dimensional unit load stress field of the electric drive axle assembly.

[0035] H. According to the three-dimensional load spectrum of the electric drive axle assembly in F, the SN curve of the material and the unit load stress field in G, the three-dimensional fatigue life of the electric drive axle assembly is obtained. According to the product design life, the analysis results are evaluated and the fatigue life assessment results are obtained.

[0036] Specifically, according to the vertical load spectrum, longitudinal load spectrum, lateral load spectrum of the electric drive axle assembly in F, the three-dimensional unit load stress field of the electric drive axle assembly in G and the SN fatigue characteristic curve of the electric drive axle assembly material, the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly are calculated and analyzed. Only when the bending fatigue life, braking fatigue life and steering fatigue life meet the design life requirements at the same time, the electric drive axle assembly is judged to meet the fatigue life performance requirements. If one working condition does not meet the requirements, the fatigue life performance requirements are not met.

[0037] I. Perform random vibration analysis of the electric drive axle assembly according to the acceleration spectrum under the user road condition in E, evaluate the analysis results, and obtain random vibration assessment results.

[0038] Specifically, the acceleration spectrum under the user road condition in E is converted into a three-way PSD (Power Spectral Density) spectrum, the modal extraction range is set to 0-500Hz, the system damping is set to 0.05, and the random vibration analysis of the electric drive axle assembly is performed to obtain the 1σ stress of the electric drive axle in three directions (i.e., vertical, longitudinal, and lateral). The maximum value of the 3σ stress, which is three times the maximum 1σ stress of the electric drive axle assembly, should not exceed the yield strength of the components in the electric drive axle assembly. If it exceeds, the random vibration performance requirements are not met. If it does not exceed, the random vibration performance requirements are met.

[0039] J. Comprehensively evaluate the quasi-static strength assessment results, fatigue life assessment results, and random vibration assessment results to assess whether the electric drive axle assembly meets the structural reliability requirements.

[0040] Specifically, based on the quasi-static strength assessment results in F, the fatigue life assessment results in H, and the random vibration assessment results in I, if any one of them does not meet the performance requirements, the electric drive axle assembly does not meet the structural reliability requirements. Only when all three meet the performance requirements can the electric drive axle assembly meet the structural reliability requirements.

[0041] In summary, the electric drive axle analysis model in the electric drive axle assembly structural reliability assessment method described in this embodiment has been adjusted through experimental benchmarking, and the simulation results have a higher reference significance; the analysis conditions include both quasi-static structural strength and nominal stress fatigue analysis that does not consider frequency components, and random vibration analysis that considers frequency components, which more comprehensively assesses the structural reliability of the electric drive system; it avoids establishing a complex multi-body dynamics model to extract endurance loads, and the load extraction accuracy can be improved through experimental calibration, while saving time and cost; the measured load is used as a reference for simulation calculation conditions, and the analysis results are closer to user conditions. Embodiment 2:

[0042] This embodiment provides a new energy vehicle, which is equipped with an electric drive axle assembly evaluated by the electric drive axle assembly structure reliability evaluation method described in the first embodiment.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for evaluating the structural reliability of an electric drive axle assembly, characterized in that: include: Calibrate the simulation displacement and test displacement of the electric drive axle assembly to obtain the finite element analysis model of the electric drive axle assembly; Establish different working conditions on the finite element analysis model of the electric drive axle assembly, select stress calibration points, calibrate the test strains of the various loads and stress calibration points under different working conditions of the electric drive axle assembly, and obtain mathematical expressions of various loads and strains; Collect the test strain of the stress calibration point on the electric drive axle assembly under the user's road condition and the acceleration signal of the excitation position to obtain the strain spectrum and acceleration spectrum of the electric drive axle assembly under the user's road condition; According to the mathematical expression, strain spectrum, SN curve of the electric drive axle assembly material, and stress field of the electric drive axle assembly unit load in different directions under different working conditions, the quasi-static strength evaluation results and fatigue life evaluation results of the electric drive axle assembly are obtained; According to the acceleration spectrum and the finite element analysis model of the electric drive axle assembly, the random vibration evaluation results of the electric drive axle assembly are obtained; According to the quasi-static strength assessment results, fatigue life assessment results and random vibration assessment results of the electric drive axle assembly, the structural reliability assessment results of the electric drive axle assembly are obtained.

2. The electric drive axle assembly structural reliability assessment method according to claim 1, characterized in that: Calibrate the simulation displacement and test displacement of the electric drive axle assembly to obtain the finite element analysis model of the electric drive axle assembly, including: A CAD analysis model of the electric drive axle assembly is established, and two circles of quadrilateral units are forcibly distributed around the mounting holes in the CAD analysis model of the electric drive axle assembly, and the diameter of the second circle of quadrilateral units is consistent with the diameter of the flange surface of the bolts / nuts, so as to obtain a finite element analysis model of the electric drive axle assembly to be optimized; In the finite element analysis model of the electric drive axle assembly to be optimized, a preload is established on the screw section of the solid bolt according to the preload of the bolt, a first rigid unit is established at the nodes on the inner and outer bearing mounting surfaces of the left and right wheel hubs, the main node of the first rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the first rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the first rigid unit on the left, the stress analysis result under the first preload condition is obtained by finite element solution, a second rigid unit is established at the nodes on the installation plane of the left and right leaf springs on the bridge housing, a vertical load of twice the dynamic load coefficient is established at the main nodes of the left and right second rigid units, the main node of the first rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the first rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the first rigid unit on the left, a load step of the bending condition is established, the stress analysis result under the first preload condition is brought into the load step of the bending condition, and the maximum vertical simulation displacement of the electric drive axle assembly under the bending condition is obtained by finite element solution; According to the goal that the difference between the maximum vertical simulation displacement and the vertical test displacement under the bending condition of the electric drive axle assembly is less than the set value, the mesh size in the finite element analysis model of the electric drive axle assembly to be optimized and the simplification method of the components in the electric drive axle assembly are adjusted to obtain the finite element analysis model of the electric drive axle assembly.

3. The electric drive axle assembly structure reliability assessment method according to claim 1, characterized in that: Different working conditions are established on the finite element analysis model of the electric drive axle assembly, including: In the finite element analysis model of the electric drive axle assembly, a preload is established on the screw section of the solid bolt according to the preload of the bolt, a third rigid unit is established at the nodes on the inner and outer bearing mounting surfaces of the left and right wheel hubs, the main node of the third rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the third rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the third rigid unit on the left, the stress analysis result under the second preload condition is obtained by finite element solution, a fourth rigid unit is established at the nodes on the installation plane of the left and right leaf springs on the bridge housing, a vertical load of one times the dynamic load coefficient is established at the main nodes of the fourth rigid units on the left and right sides, the main node of the third rigid unit on the left constrains all movement degrees of freedom and releases all rotational degrees of freedom, the main node of the third rigid unit on the right releases one more degree of freedom of lateral movement than the main node of the third rigid unit on the left, the load step of the bending stiffness condition is established, the stress analysis result under the second preload condition is brought into the load step of the bending stiffness condition, and the stress analysis result under the bending stiffness condition of the electric drive axle assembly is obtained by finite element solution; In the finite element analysis model of the electric drive axle assembly, two fixing fixtures with a spacing equal to the actual vehicle leaf spring spacing are established to support the electric drive axle assembly, and a brake base plate is fixed to the electric drive axle shoulder by bolts. A preload is established on the screw cross section of the solid bolt according to the preload of the bolt, and all degrees of freedom of the bottom mounting surface of the fixing fixture are constrained. The stress analysis results under the third preload condition are obtained by finite element solution. Axle loads of set multiples are applied forward and backward at the load application hole position of the brake base plate, and all degrees of freedom of the bottom mounting surface of the fixing fixture are constrained. The load step of the braking condition is established, and the stress analysis results under the third preload condition are brought into the load step of the braking condition. The stress analysis results of the braking condition are obtained by finite element solution. In the finite element analysis model of the electric drive axle assembly, a fifth rigid unit is established at the nodes on the outer support surface of the inner and outer mounting bearings of the left wheel hub. The main node of the fifth rigid unit is the grounding point of the tire width center on one side of the axle. According to the preload of the bolt, a preload is established on the screw cross section of the solid bolt to constrain all degrees of freedom of the bottom mounting surface of the fixing fixture. The stress analysis result under the fourth preload condition is obtained by finite element solution. An axle load with a lateral setting multiple is applied at the main node of the fifth rigid unit to constrain all degrees of freedom of the bottom mounting surface of the fixing fixture, and a load step of the steering condition is established. The stress analysis result under the fourth preload condition is brought into the load step of the steering condition, and the stress analysis result of the steering condition is obtained by finite element solution.

4. The electric drive axle assembly structural reliability assessment method according to claim 3 is characterized in that: Select stress calibration points, calibrate the axial loads and test strains of the stress calibration points under different working conditions of the electric drive axle assembly, and obtain mathematical expressions of axial loads and strains, including: Select stress calibration points according to the stress analysis results of different working conditions of the electric drive axle assembly: select the first strain point that is only sensitive to the bending stiffness working condition, select the second strain point that is only sensitive to the braking working condition, and select the third strain point that is only sensitive to the steering working condition; The vertical load and the test strain of the first strain point under the bending stiffness condition of the electric drive axle assembly, the longitudinal load and the test strain of the second strain point under the braking condition, and the lateral load and the test strain of the third strain point under the steering condition are calibrated to obtain the functional expressions of the vertical load and strain, the longitudinal load and strain, and the lateral load and strain.

5. The electric drive axle assembly structural reliability assessment method according to claim 4, characterized in that: Collect the test strain of the stress calibration point on the electric drive axle assembly under the user's road conditions and the acceleration signal of the excitation position to obtain the strain spectrum and acceleration spectrum of the electric drive axle assembly under the user's road conditions, including: The vehicle is loaded with user road condition loads, and the strains of three strain points on the electric drive axle assembly of the vehicle and the acceleration signals of the excitation positions are collected to obtain the strain spectrum and acceleration spectrum under the user road condition; The excitation position is the mounting surface of the fixing fixture and the electric drive axle.

6. The electric drive axle assembly structural reliability assessment method according to claim 1, characterized in that: Based on mathematical expressions, strain spectra, SN curves of electric drive axle assembly materials, and stress fields of unit loads in different directions of electric drive axle assemblies under different working conditions, the quasi-static strength assessment results and fatigue life assessment results of the electric drive axle assembly are obtained, including: The axial load spectrum of the electric drive axle assembly is obtained according to the mathematical expression and the strain spectrum, and the extreme values ​​of the axial load spectrum of the electric drive axle assembly are extracted as the loads of different working conditions of the electric drive axle assembly to analyze and evaluate the quasi-static strength of the electric drive axle assembly under different working conditions based on the user's road conditions, and the quasi-static strength evaluation result of the electric drive axle assembly is obtained; The bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly are calculated based on the load spectrum of the electric drive axle assembly in all directions, the SN curve of the material of the electric drive axle assembly and the stress field of the unit load of the electric drive axle assembly in all directions under different working conditions. The fatigue life of the electric drive axle assembly is evaluated by comparing the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly with the design life, and the fatigue life evaluation result of the electric drive axle assembly is obtained; Among them, the method for obtaining the stress field of the unit load in each direction of the electric drive axle assembly under different working conditions is: taking the unit load in each direction as the load under different working conditions of the electric drive axle assembly, the constraints are equal to the constraints under each working condition, and the stress field of the unit load in each direction of the electric drive axle assembly is obtained by finite element solution.

7. The electric drive axle assembly structural reliability assessment method according to claim 6, characterized in that: The extreme values ​​of the load spectrum of the electric drive axle assembly in all directions are extracted as the loads of the electric drive axle assembly in different working conditions to analyze and evaluate the quasi-static strength of the electric drive axle assembly in all directions under different working conditions based on the user's road conditions, and the quasi-static strength evaluation results of the electric drive axle assembly are obtained, including: The extreme values ​​of the load spectrum of the electric drive axle assembly in all directions are used as the loads of the electric drive axle assembly in different working conditions, and the constraints are equal to the constraints under each working condition. The quasi-static strength of the electric drive axle assembly in all directions under different working conditions based on the user's road condition limit load is obtained through finite element solution; If the quasi-static strength of the electric drive axle assembly in different working conditions based on the user's road condition limit load is less than the yield strength of the electric drive axle assembly and the bending stiffness value is less than the preset value, then the electric drive axle assembly is evaluated to meet the quasi-static strength performance requirements, otherwise the electric drive axle assembly is evaluated to not meet the quasi-static strength performance requirements; The bending stiffness value is equal to the ratio of the maximum vertical simulated displacement of the electric drive axle assembly under the bending stiffness condition to the wheelbase.

8. The electric drive axle assembly structural reliability assessment method according to claim 6, characterized in that: The fatigue life of the electric drive axle assembly is evaluated by comparing the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly with the design life, and a fatigue life evaluation result of the electric drive axle assembly is obtained, including: if the bending fatigue life, braking fatigue life and steering fatigue life of the electric drive axle assembly all meet the design life requirements, then the electric drive axle assembly is evaluated to meet the fatigue life performance requirements; otherwise, the electric drive axle assembly is evaluated to not meet the fatigue life performance requirements.

9. The electric drive axle assembly structural reliability assessment method according to claim 1, characterized in that: Based on the acceleration spectrum and the finite element analysis model of the electric drive axle assembly, the random vibration evaluation results of the electric drive axle assembly are obtained, including: The acceleration spectrum is converted into power spectrum density in all directions, and the random vibration analysis of the electric drive assembly is performed after setting the modal extraction range and system damping to obtain the maximum 3σ stress of the electric drive axle assembly in all directions; If the maximum 3σ stress of the electric drive axle assembly in each direction is not greater than the yield strength of the components in the electric drive axle assembly, the electric drive axle assembly is evaluated to meet the random vibration performance requirements, otherwise the electric drive axle assembly is evaluated to not meet the random vibration performance requirements.

10. The electric drive axle assembly structural reliability assessment method according to claim 1, characterized in that: According to the quasi-static strength assessment results, fatigue life assessment results, and random vibration assessment results of the electric drive axle assembly, a structural reliability assessment result of the electric drive axle assembly is obtained, including: if the quasi-static strength assessment results, fatigue life assessment results, and random vibration assessment results of the electric drive axle assembly all meet the preset performance requirements, then it is assessed that the electric drive axle assembly meets the structural reliability requirements; otherwise, the electric drive axle assembly does not meet the structural reliability requirements.

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