Method and system for analyzing integrated fatigue durability of power assembly suspension bracket

Abstract

The invention relates to an integrated fatigue durability analysis method and system for a power assembly suspension bracket. The method comprises the following steps: establishing a rigid body dynamic model of a 19-degree-of-freedom power assembly suspension system of a commercial vehicle based on a whole vehicle; establishing a finite element model of the suspension bracket, and solving and outputting a modal neutral file and a modal stress file of the suspension bracket; establishing a rigid-flexible coupling dynamic model of the power assembly suspension system to consider the influence of the flexibility of the bracket; solving the rigid-flexible coupling dynamic model, and outputting modal displacement files of the suspension bracket under different road excitation; based on a modal stress recovery theory, the modal stress and the modal displacement of the suspension bracket are superposed, and the fatigue life of each node of the suspension bracket is calculated by using a Goodman corrected S-N method; the invention provides a method for analyzing the fatigue durability of a structure under the conditions of long driving mileage and complex road conditions, which is used for efficiently predicting the fatigue durability of a bracket after a vehicle runs for hundreds of thousands of kilometers under the complex road conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of automobiles, and particularly to a method and system for analyzing the integrated fatigue durability performance of a powertrain mounting bracket. Background Art

[0002] As a key component connecting the powertrain and the vehicle frame, the powertrain mounting system of commercial vehicles plays roles such as supporting the powertrain and attenuating the transmission of engine vibrations to the vehicle frame and cab, directly affecting the vehicle's NVH level, the driving experience of the driver, and the fatigue life of structural components. Among them, the mounting bracket is subject to complex forces, and its anti-fatigue durability performance is crucial, directly related to the driving safety of the vehicle. Therefore, it is of great importance to accurately and efficiently analyze the fatigue durability performance of the powertrain mounting bracket, which can provide theoretical guidance for the structural design and improvement of the mounting bracket, and enhance the product quality and market competitiveness of commercial vehicles.

[0003] The commonly used structural fatigue analysis methods in engineering mainly include the quasi-static method, the PSD method, and the transient method. The quasi-static method is characterized by high efficiency and can meet the cracking risk identification of high-frequency parts such as brackets, but it ignores the influence of load frequency and damping, cannot consider the resonance of certain frequency structures, and can only be used for components whose natural frequency is much higher than the load excitation frequency; the fatigue analysis speed of the PSD method is much faster than that of the time domain method, and the load can be graded and standardized loads can be defined, but generally, the accuracy of frequency domain fatigue analysis is considered to be lower than that of time domain fatigue analysis. The transient fatigue analysis is characterized by high accuracy and can identify the cracking risk caused by resonance. The transient method often uses the linear modal superposition method, including two processes: stress analysis and fatigue calculation. Its analysis process is generally as follows: in the finite element software, the load obtained from multi-body dynamics analysis or experimental testing is directly applied to the structural component, and after solving to obtain the modal displacement time history, the modal stress is superimposed to obtain the actual stress time history of the structure, and then the structural fatigue life is solved according to the S-N method modified by Goodman. In this process, the modal displacement is solved according to the full-degree-of-freedom model, and the efficiency is low, especially when applying long driving mileage load data. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for analyzing the integrated fatigue durability performance of a powertrain mounting bracket in view of the deficiencies of the prior art. By solving the rigid-flexible coupling dynamics model with reduced structural degrees of freedom, the modal displacement file of the flexible body is obtained, and then combined with the modal stress file, the fatigue life of the bracket can be quickly solved; at the same time, the concept of the structural unit damage value is proposed to solve the structural fatigue damage value corresponding to the unit mileage, which can be used for the efficient prediction of the fatigue durability performance of the bracket after the vehicle has traveled hundreds of thousands of kilometers under complex road conditions, effectively shortening the development cycle and reducing the development cost.

[0005] The present invention is implemented by adopting the following technical solutions:

[0006] Integrated fatigue durability performance analysis method for powertrain mounting brackets, comprising the following steps:

[0007] S1. For the structural characteristics of commercial vehicles, apply the ADAMS / View module to establish a multi-rigid body dynamics model of a 19-degree-of-freedom powertrain mounting system based on the vehicle body;

[0008] S2. Apply HyperMesh software to establish finite element models of the upper and lower brackets of the engine mounts, and solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the brackets;

[0009] S3. Based on the multi-rigid body dynamics model established in step S1 and the modal neutral file obtained in step S2, establish a rigid-flexible coupling dynamics model of the powertrain mounting system that can consider the flexibility of the brackets;

[0010] S4. Based on the ADAMS / View rigid-flexible coupling dynamics model, apply engine excitation and road surface excitation simultaneously, solve for the dynamic response and output the modal displacement file of the mounting brackets;

[0011] S5. According to the modal stress and modal displacement, calculate the stress time history of the mounting brackets based on the modal stress recovery theory, and calculate the fatigue life of the mounting brackets using the S-N method;

[0012] S6. By statistically analyzing the actual driving conditions of the vehicle, obtain the proportional relationship of different road conditions, vehicle speeds, and loading conditions during the total driving process, and propose the concept and calculation method of the structural unit damage value, which can be used for the fatigue durability performance analysis of the mounting brackets after driving hundreds of thousands of kilometers and the system.

[0013] Furthermore, step S1 includes:

[0014] The multi-rigid body dynamics model consists of 5 rigid bodies: the powertrain, the cab, the frame, and the front and rear suspension sub-assemblies. Among them, the powertrain and the cab consider six degrees of freedom in the longitudinal x, transverse y, vertical z, roll Rx, pitch Ry, and yaw Rz directions, the frame considers three degrees of freedom in the z, Rx, and Ry directions, and the front and rear suspension sub-assemblies consider two degrees of freedom in the z and Rx directions respectively;

[0015] The connection relationship between rigid bodies is connected by a spring / damper parallel force element, and the stiffness and damping values are obtained by equivalent according to the actual connection relationship; the front and rear suspension sub-assemblies are composed of axles, wheels, and 3 / 4 leaf springs.

[0016] Furthermore, step S2 includes:

[0017] According to the geometric model of the powertrain mount bracket, use HyperMesh software to establish the finite element model of the mount bracket; define ASET as the reduced boundary of the super element degrees of freedom at the connection positions between the mount bracket and other components, and at the same time as the external connection points for transmitting forces, so as to apply corresponding loads and constraints in the subsequent dynamic simulation; solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the bracket.

[0018] Further, step S3 includes:

[0019] In the ADAMS / View module, import the modal neutral file of the mount bracket obtained by solving in step S2 into the 19-degree-of-freedom model and replace the original rigid body component, set the damping ratio of each order of vibration mode and the modal truncation order of the flexible body, and complete the establishment of the rigid-flexible coupling dynamic model.

[0020] Further, step S4 includes:

[0021] Apply vertical displacement excitations corresponding to different road surface conditions on the left and right sides of the front and rear suspension spring lower assemblies of the dynamic model, set the solver parameters and solve, and output the modal displacement files of each mount bracket under different conditions as the input for the fatigue analysis of the mount bracket.

[0022] Further, step S5 includes:

[0023] Based on the modal stress recovery theory, superimpose the modal stress obtained in step S2 and the modal displacement obtained in step S4 to obtain the stress time history of the bracket;

[0024] Use the rainflow counting method to count the number of stress cycles, calculate the fatigue life of each node of the bracket according to the Goodman-corrected S-N method, and output it in the form of a cloud diagram, where the minimum value of the life among all nodes is the fatigue life of the bracket.

[0025] Further, step S6 includes:

[0026] Set a group of typical road surfaces, vehicle speeds and loading conditions to represent the actual driving conditions of the vehicle, and the proportion of each condition is obtained according to the statistics of the actual driving conditions of the vehicle;

[0027] Decompose different road conditions, driving speeds and loading conditions into multiple independent simulation conditions, and use the parallel analysis method to conduct fatigue reliability analysis;

[0028] The fatigue durability analysis method of the mount bracket under long driving mileage and complex road conditions is as follows: First, define the road surface condition set R = {R i}, i = 1, …, N R , where R i represents the i-th road surface condition, and N RThe number of road surface conditions considered for fatigue durability performance analysis. Assume that for each road surface condition, the vehicle travels at different speeds {V ij}, j = 1, …, N vi through, where V ij represents the vehicle passing through the i-th road surface condition at the j-th speed; assume that for the same road surface and the same speed, the vehicle travels with different loading states {L ijk}, k = 1, …, N lij and L ijk represents the vehicle passing through the i-th road surface with the k-th loading condition and the j-th speed. Introduce the dimensionless weight coefficient α i to represent the proportion of each road condition length s i in the total driving mileage S of the vehicle, that is and there is Similarly, for different speeds in the same road condition R i there also correspond different weights β ij , and there is For different loading conditions under the same road condition R i and the same speed V ij there correspond different weights γ ijk , and there is The weights α i , β ij and γ ijk are all statistically obtained according to the actual operation of the vehicle;

[0029] Then define the structural unit damage value to represent the structural fatigue damage value corresponding to the unit mileage. In the formula, e ijk represents the fatigue damage value when the vehicle passes through the i-th road surface condition with the k-th loading condition and the j-th speed, then the structural fatigue damage value e w corresponding to the total driving mileage S can be expressed as: e w = e u ·S.

[0030] The integrated fatigue durability performance analysis system for the powertrain mount bracket includes the integrated fatigue durability performance analysis method for the powertrain mount bracket described in any one of the above;

[0031] The system includes:

[0032] A rigid body dynamics model establishment module for establishing a multi-rigid body dynamics model of a 19-degree-of-freedom powertrain mount system based on the whole vehicle;

[0033] The modal response solving module is used to solve and output the modal stress file and modal neutral file of the mounting bracket; establish a finite element model of the powertrain mounting bracket using HyperMesh, and solve and output the modal neutral file and modal stress file of the mounting bracket based on the modal synthesis method; after establishing the finite element model of the mounting bracket, write a batch bat file and a HyperMesh / TCL command script to complete the solution and output of the modal neutral file and modal stress file of each finite element model of the mounting bracket.

[0034] The rigid-flexible coupling dynamics model establishment module is used to establish a rigid-flexible coupling dynamics model of the powertrain mounting system that can consider the influence of the bracket flexibility. By calling the ADAMS / cmd command through a batch bat file, complete the reading of the modal neutral file, the replacement of the original rigid body parts, and the connection between the flexible bracket and the powertrain and the vehicle frame, and realize the automatic establishment of the rigid-flexible coupling dynamics model.

[0035] The modal displacement solving module is used to solve and output the modal displacement file of the mounting bracket under different road conditions; write a bat file and an ADAMS / cmd command script to complete the vertical road surface displacement excitation loading on the left and right sides of the front and rear suspension spring lower assemblies of the rigid-flexible coupling dynamics model; solve and output the modal displacement file of each mounting bracket as the load input for the fatigue analysis of the mounting bracket.

[0036] The fatigue life calculation module is used to obtain the stress time history of the mounting bracket, and then calculate the structural fatigue life using the S-N method modified by Goodman; write a bat file and an nCode fatigue analysis software script command to realize the automatic input of the modal stress file and modal displacement file of the mounting bracket and the automatic solution of the structural dynamic stress; call the SN CAE Fatigue module to solve the structural fatigue life and output the fatigue result file in HyperMesh format; write a bat file and a HyperView / TCL command script to read the fatigue result file and output the minimum fatigue life of the bracket in text format.

[0037] The fatigue durability performance prediction module gives a fatigue durability performance analysis method for the mounting bracket under long driving mileage and complex road conditions by defining and solving the structural unit damage value; set a group of typical road conditions, vehicle speeds and loading conditions to represent the actual driving conditions of the vehicle, and the proportion of each condition can be obtained according to the actual driving conditions of the vehicle; decompose different roads, driving speeds and loading conditions into multiple independent simulation conditions, and use the parallel analysis method to calculate the fatigue life.

[0038] The fatigue durability performance analysis of the powertrain mounting bracket under long driving mileage and complex road conditions is as follows: define the structural unit damage value Used to represent the structural fatigue damage value corresponding to the unit mileage, then the structural fatigue damage value e corresponding to the total driving mileage S w Can be expressed as e w = e u ·S. In the formula, e ijk Represents the fatigue damage value when the vehicle passes through the i-th road condition at the k-th loading condition and the j-th speed. The weight coefficient α i Used to represent the proportion of each road condition length s i In the total driving mileage S of the vehicle, that is Under the same road condition, different speeds also correspond to different weights β ij , for the same road condition R i , the same speed V ij Under different loading conditions, different weights γ ijk ; The weights α i , β ij And γ ijk Can be obtained by statistical analysis of the actual driving conditions of the vehicle.

[0039] Compared with the prior art, the present invention has the following beneficial technical effects:

[0040] (1) In view of the non-negligible coupling effect between the commercial vehicle cab and other systems, the present invention establishes a 19-degree-of-freedom dynamic model of the powertrain mount system based on the whole vehicle, while taking into account both simulation accuracy and calculation efficiency;

[0041] (2) By defining the unit damage value of the structure, the present invention can comprehensively consider various external conditions such as multiple road conditions, different speeds and loadings, and can adopt a parallel analysis method for fatigue analysis to improve the analysis efficiency;

[0042] (3) The present invention realizes the automation of simulation from modal response solution, rigid-flexible coupling dynamic model establishment, modal displacement output and structural fatigue durability performance analysis by writing script commands, laying a foundation for the parameter optimization work of the mount system;

[0043] (4) The present invention is applicable to the powertrain mount systems of commercial vehicles in various layout forms. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Is the flow chart of the integrated fatigue durability performance analysis method for the powertrain mount bracket of the present invention;

[0045] Figure 2 Is the schematic diagram of the integrated fatigue durability performance analysis system for the powertrain mount bracket of the present invention;

[0046] Figure 3 Is the simplified schematic diagram of the 19-degree-of-freedom multi-rigid-body dynamic model of the powertrain mount system of the present invention;

[0047] Figure 4 It is the excitation diagram of Class B road surface for the third embodiment of the present invention;

[0048] Figure 5 It is the excitation diagram of washboard road surface for the third embodiment of the present invention;

[0049] Figure 6 It is the calculation result diagram of the quasi-static analysis method in the third embodiment of the present invention;

[0050] Figure 7 It is the calculation result diagram of the modal transient method in the third embodiment of the present invention;

[0051] Figure 8 It is the calculation result diagram of the frequency response analysis method in the third embodiment of the present invention;

[0052] Figure 9 It is the calculation result diagram of the integrated fatigue analysis method in the third embodiment of the present invention. Detailed implementation manners

[0053] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] Premise description:

[0055] The ADAMS / View module provides a basic operation dialogue environment directly facing users and the pre-processing function of virtual prototype analysis. It is convenient to establish relevant objects in the model in a man-machine interaction manner, such as defining moving parts, defining the constraint relationships or force connection relationships between parts, and applying forced drives or external load excitations. It supports a command input window, where commands of Adams / View can be directly input, and at the same time provides the ability to quickly establish parametric models, facilitating design improvement;

[0056] HyperMesh software is a prior art and has a powerful pre-processing function for finite element mesh generation;

[0057] Goodman is for fatigue damage calculation;

[0058] The rain-flow counting method is an existing technology, and its main function is to simplify the measured load history into several load cycles for fatigue life estimation and the compilation of fatigue test load spectra. Based on the two-parameter method, it takes into account two variables, dynamic strength (amplitude) and static strength (mean value), which conforms to the inherent characteristics of fatigue loads. The rain-flow counting method is mainly used in the engineering field and is particularly widely used in fatigue life calculations.

[0059] The bat file is an existing technology and is a batch processing file under DOS. The batch processing file is a text file without formatting, which contains one or more commands; its file extension is.bat or.cmd;

[0060] The nCode (Ansys nCode) fatigue analysis software is a well-known international fatigue durability simulation analysis software;

[0061] The SN CAE Fatigue module is a sub-module in the nCode fatigue analysis software, namely high-cycle fatigue life analysis;

[0062] The script files of HyperView are all TCL command scripts;

[0063] Embodiment 1

[0064] As Figure 1-2 shown, the integrated fatigue durability performance analysis method for the powertrain mount bracket includes the following steps:

[0065] S1. According to the structural characteristics of commercial vehicles, use the ADAMS / View module to establish a multi-rigid-body dynamics model of the 19-degree-of-freedom powertrain mount system based on the vehicle body;

[0066] S2. Use the HyperMesh software to establish a finite element model of the upper and lower brackets of the dynamic mount, and solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the bracket;

[0067] S3. Based on the multi-rigid-body dynamics model established in step S1 and the modal neutral file obtained in step S2, establish a rigid-flexible coupling dynamics model of the powertrain mount system that can consider the flexibility of the bracket;

[0068] S4. Based on the ADAMS / View rigid-flexible coupling dynamics model, apply engine excitation and road surface excitation simultaneously, solve the dynamic response and output the modal displacement file of the mount bracket;

[0069] S5. According to the modal stress and modal displacement, calculate the stress time history of the mount bracket based on the modal stress recovery theory, and calculate the fatigue life of the mount bracket using the S-N method;

[0070] S6. By statistically analyzing the actual driving conditions of the vehicle, the proportional relationships of different road conditions, vehicle speeds, and loading conditions in the total driving process are obtained. The concept and calculation method of the structural unit damage value are proposed, which can be used for the fatigue durability performance analysis and system of the mount bracket after driving hundreds of thousands of kilometers.

[0071] As Figure 3 shown, step S1 includes:

[0072] The multi-rigid body dynamics model consists of five rigid bodies: the powertrain 200, the cab 100, the frame 300, the front lower suspension spring 400, and the rear lower suspension spring assembly 500. The powertrain mount bracket 600 is considered as a flexible body. Among them, the powertrain and the cab consider six degrees of freedom in the longitudinal x, transverse y, vertical z, roll Rx, pitch Ry, and yaw Rz directions, the frame considers three degrees of freedom in the z, Rx, and Ry directions, and the front and rear lower suspension spring assemblies consider two degrees of freedom in the z and Rx directions respectively.

[0073] The connection relationship between rigid bodies is connected by a spring / damper parallel force element, and the stiffness and damping values are obtained by equivalent according to the actual connection relationship. The front and rear lower suspension spring assemblies are composed of axles, wheels, and 3 / 4 leaf springs.

[0074] Step S2 includes:

[0075] According to the geometric model of the powertrain mount bracket, the finite element model of the mount bracket is established by using HyperMesh software. Define ASET as the reduced boundary of the super element degrees of freedom at the connection positions between the mount bracket and other components, and at the same time as the external connection points for transmitting forces, so as to apply corresponding loads and constraints in the subsequent dynamic simulation. Solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the bracket.

[0076] Step S3 includes:

[0077] In the ADAMS / View module, import the modal neutral file of the mount bracket obtained by solving step S2 into the 19-degree-of-freedom model and replace the original rigid body components. Set the damping ratio of each order of vibration mode and the modal truncation order of the flexible body to complete the establishment of the rigid-flexible coupling dynamics model.

[0078] Step S4 includes:

[0079] Apply vertical displacement excitations corresponding to different road surface conditions on the left and right sides of the front and rear lower suspension spring assemblies of the dynamic model, set the solver parameters and solve, and output the modal displacement files of each mount bracket under different conditions as the input for the fatigue analysis of the mount bracket.

[0080] Step S5 includes:

[0081] Based on the modal stress recovery theory, the modal stress obtained in step S2 and the modal displacement obtained in step S4 are superimposed to obtain the stress time history of the bracket;

[0082] The rain flow counting method is used to count the number of stress cycles. According to the Goodman-modified S-N method, the fatigue life of each node of the bracket is calculated and output in the form of a cloud map. The minimum value of the life among all nodes is the fatigue life of the bracket.

[0083] Step S6 includes:

[0084] Set a group of typical road conditions, vehicle speeds, and loading conditions to represent the actual driving conditions of the vehicle. The proportion of each condition is obtained according to the statistical results of the actual driving conditions of the vehicle;

[0085] Decompose different road conditions, driving speeds, and loading conditions into multiple independent simulation conditions, and use the parallel analysis method for fatigue reliability analysis;

[0086] The fatigue durability analysis method of the suspension bracket under long driving mileage and complex road conditions is as follows: First, define the set of road conditions R = {R i}, i = 1, …, N R , where R i represents the i-th road condition, and N R is the number of road conditions considered in the fatigue durability analysis. Assume that under each road condition, the vehicle passes through at different speeds {V ij}, j = 1, …, N vi , where V ij represents the vehicle passing through the i-th road condition at the j-th speed; assume that under the same road surface and the same speed, the vehicle travels at different loading states {L ijk}, k = 1, …, N lij , where L ijk represents the vehicle passing through the i-th road surface at the k-th loading condition and the j-th speed. Introduce the dimensionless weight coefficient α i to represent the proportion of the length s i of each road condition in the total driving mileage S of the vehicle, that is and there is Similarly, different speeds in the same road condition R i also correspond to different weights β ij , and there is Different loading conditions under the same road condition R i and the same speed V ij correspond to different weights γ ijk , and there is The weights α i β ij and γ ijkAll are obtained by statistics based on the actual operating conditions of the vehicle;

[0087] Then define the structural unit damage value to represent the structural fatigue damage value corresponding to the unit mileage. In the formula, e ijk represents the fatigue damage value when the vehicle passes through the i-th road condition at the k-th loading condition and the j-th speed. Then the structural fatigue damage value e corresponding to the total driving mileage S w can be expressed as: e w = e u ·S.

[0088] Embodiment 2

[0089] Integrated fatigue durability performance analysis system for the powertrain mounting bracket: including any one of the above integrated fatigue durability performance analysis methods for the powertrain mounting bracket;

[0090] The system includes:

[0091] A rigid body dynamics model establishment module, used to establish a multi-rigid body dynamics model of the 19-degree-of-freedom powertrain mounting system based on the whole vehicle;

[0092] A modal response solution module, used to solve and output the modal stress file and modal neutral file of the mounting bracket; apply HyperMesh to establish a finite element model of the powertrain mounting bracket, and solve and output the modal neutral file and modal stress file of the mounting bracket based on the modal synthesis method; after establishing the finite element model of the mounting bracket, write a batch bat file and a HyperMesh / TCL command script to complete the solution and output of the modal neutral file and modal stress file of each finite element model of the mounting bracket;

[0093] A rigid-flexible coupling dynamics model establishment module, used to establish a rigid-flexible coupling dynamics model of the powertrain mounting system that can consider the influence of the bracket flexibility, and complete the reading of the modal neutral file, the replacement of the original rigid body parts, and the connection between the flexible bracket and the powertrain and the vehicle frame through a batch bat file calling the ADAMS / cmd command, so as to realize the automatic establishment of the rigid-flexible coupling dynamics model;

[0094] A modal displacement solution module, used to solve and output the modal displacement file of the mounting bracket under different road conditions; write a bat file and an ADAMS / cmd command script to complete the vertical road surface displacement excitation loading on the left and right sides of the front and rear suspension spring lower assemblies in the rigid-flexible coupling dynamics model; solve and output the modal displacement file of each mounting bracket as the load input for the fatigue analysis of the mounting bracket;

[0095] The fatigue life calculation module is used to obtain the stress time history of the mounting bracket, and then calculate the structural fatigue life by applying the Goodman-corrected S-N method; write a bat file and nCode fatigue analysis software script commands to realize the automatic input of the modal stress file and modal displacement file of the mounting bracket and the automatic solution of the structural dynamic stress; call the SN CAE Fatigue module to solve the structural fatigue life and output the fatigue result file in HyperMesh format; write a bat file and HyperView / TCL command script to read the fatigue result file and output the minimum fatigue life of the bracket in text format.

[0096] The fatigue durability performance prediction module gives a fatigue durability performance analysis method for the mounting bracket under long driving mileage and complex road conditions by defining and solving the unit damage value of the structure; set a group of typical road conditions, vehicle speeds and loading conditions to represent the actual driving conditions of the vehicle, and the proportion of each condition can be obtained according to the statistical results of the actual driving conditions of the vehicle; decompose different roads, driving speeds and loading conditions into multiple independent simulation conditions and use the parallel analysis method to calculate the fatigue life.

[0097] The fatigue durability performance analysis of the powertrain mounting bracket under long driving mileage and complex road conditions is as follows: Define the unit damage value of the structure to represent the structural fatigue damage value corresponding to the unit mileage, then the structural fatigue damage value e corresponding to the total driving mileage S w can be expressed as e w = e u ·S. In the formula, e ijk represents the fatigue damage value when the vehicle passes the i-th road surface condition at the k-th loading condition and the j-th speed, and the weight coefficient α i is used to represent the proportion of the length s of each road condition i in the total driving mileage S of the vehicle, that is Different speeds under the same road surface condition also correspond to different weights β ij , and different loading conditions under the same road condition R i and the same speed V ij correspond to different weights γ ijk ; the weights α i , β ij and γ ijk can be obtained according to the statistical results of the actual driving conditions of the vehicle.

[0098] Example 3

[0099] For a certain model of light truck with an in-line four-cylinder four-stroke engine, a rigid-flexible coupling dynamics model of the powertrain mounting system based on the whole vehicle is established, considering the influence of the flexibility of the mounting bracket, as Figure 3 shown.

[0100] When the vehicle is running, there are mainly two kinds of excitations acting on the powertrain mounting system. One is the road surface excitation that is transmitted to the powertrain through the tires and suspension system and induces its low-frequency vibration, and the other is the excitation force and torque with periodic characteristics generated by the engine itself. In the dynamic model, both the engine excitation and the road surface excitation are applied simultaneously.

[0101] The main excitations of an in-line four-cylinder four-stroke engine are the second-order torque at low speed and the second-order inertia force at high speed. Therefore, F x = 0, and its excitation force and excitation torque are simplified as:

[0102]

[0103] In the formula: m is the mass of the single-cylinder piston and the reciprocating motion part; θ is the engine layout inclination angle (usually referring to the angle between the crank and the horizontal plane); r is the crank radius; λ is the ratio of the crank radius to the connecting rod length; ω is the angular velocity of the engine crankshaft rotation; A is the distance from the center line of the second and third cylinders to the center of mass; M0 is the average output torque of the engine.

[0104] The class road surface excitation is generated by inverting according to the corresponding power spectral density function, and excitations such as washboard road surface are generated according to specific geometric parameters. The generation tools are all self-written Matlab programs. Some of the generated road surface excitations are shown in Figure 4-Figure 5 ;

[0105] The distribution weight α i of the road surface condition, the distribution weight β ij of the vehicle speed, and the distribution weight γ ijk of the loading state are shown in Table 1:

[0106]

[0107] Then the unit damage value of the mounting bracket can ensure that the bracket does not undergo fatigue failure within the driving mileage of ten thousand kilometers.

[0108] Figure 6-Figure 9 , the comparison results of the fatigue life of the mounting bracket under the combined action of the class B road surface and the engine excitation calculated by different methods are given, verifying the accuracy of the integrated fatigue analysis method, and at the same time having an advantage in calculation efficiency.

[0109] The comparison of the calculation results and accuracy of the fatigue analysis method is shown in Table 2:

[0110]

[0111] Table 2

[0112] The integrated fatigue analysis method can be efficiently used for predicting and improving the fatigue durability performance of brackets after a vehicle has traveled hundreds of thousands of kilometers under complex road conditions, significantly shortening the development cycle and reducing the development cost.

[0113] Although the present invention has been described in detail by referring to the accompanying drawings and in conjunction with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An analysis method for the integrated fatigue durability performance of a powertrain mounting bracket, characterized in that, It includes the following steps: S1. According to the structural characteristics of commercial vehicles, use the ADAMS / View module to establish a multi-rigid-body dynamics model of a 19-degree-of-freedom powertrain mounting system for the whole vehicle. S2. Use the HyperMesh software to establish finite element models of the upper and lower brackets of the dynamic mount, and solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the brackets. S3. Based on the multi-rigid-body dynamics model established in step S1 and the modal neutral file obtained in step S2, establish a rigid-flexible coupling dynamics model of the powertrain mounting system that can consider the flexibility of the brackets. S4. Based on ADAMS / View, establish a rigid-flexible coupling dynamics model, apply engine excitation and road surface excitation at the same time, solve the dynamic response, and output the modal displacement file of the mounting bracket. S5. According to the modal stress and modal displacement, calculate the stress time history of the mounting bracket based on the modal stress recovery theory, and calculate the fatigue life of the mounting bracket using the S-N method. S6. By statistically analyzing the actual driving conditions of the vehicle, obtain the proportional relationship of different road conditions, vehicle speeds, and loading conditions in the total driving process, and propose the concept and calculation method of the structural unit damage value, which can be used for fatigue durability analysis of the mounting bracket after driving hundreds of thousands of kilometers.

2. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 1, characterized in that, Step S1 includes: The multi-rigid-body dynamics model consists of 5 rigid bodies: the powertrain, the cab, the frame, and the front and rear suspension lower assemblies. Among them, the powertrain and the cab consider six degrees of freedom in the longitudinal x, transverse y, vertical z, roll Rx, pitch Ry, and yaw Rz directions, the frame considers three degrees of freedom in the z, Rx, and Ry directions, and the front and rear suspension lower assemblies respectively consider two degrees of freedom in the z and Rx directions. The connection relationship between rigid bodies is connected by a spring / damper parallel force element, and the stiffness and damping values are obtained by equivalent according to the actual connection relationship; the front and rear suspension lower assemblies are composed of axles, wheels, and 3 / 4 leaf springs.

3. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 2, characterized in that, Step S2 includes: According to the geometric model of the powertrain mounting bracket, use the HyperMesh software to establish a finite element model of the mounting bracket; define ASET at the connection positions between the mounting bracket and other components as the reduced boundary of the super element degrees of freedom and at the same time as the external connection points for transmitting forces, so as to apply corresponding loads and constraints in the subsequent dynamic simulation; solve based on the modal synthesis method to obtain the modal neutral file and modal stress file of the bracket.

4. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 3, characterized in that, Step S3 includes: In the ADAMS / View module, import the modal neutral file of the mounting bracket obtained by solving in step S2 into the 19-degree-of-freedom model and replace the original rigid body components, and set the damping ratio of each order of vibration mode and the modal truncation order of the flexible body to complete the establishment of the rigid-flexible coupling dynamics model.

5. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 4, characterized in that, Step S4 includes: Apply vertical displacement excitation corresponding to different road conditions on the left and right sides of the front and rear suspension lower assemblies of the dynamic model, set the solver parameters and solve, and output the modal displacement files of each mounting bracket under different conditions as the input for the fatigue analysis of the mounting bracket.

6. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 5, characterized in that, Step S5 includes: Based on the modal stress recovery theory, superimpose the modal stress obtained in step S2 and the modal displacement obtained in step S4 to obtain the stress time history of the bracket; The stress cycle times are counted by the rain - flow counting method. The fatigue life of each node of the bracket is calculated according to the S - N method modified by Goodman and output in the form of a contour map. The minimum value of the life among all nodes is the fatigue life of the bracket.

7. The analysis method for the integrated fatigue durability performance of a powertrain mounting bracket according to claim 6, characterized in that, Step S6 includes: Set a group of typical road surfaces, vehicle speeds, and loading conditions to represent the actual driving conditions of the vehicle. The proportion of each condition is obtained according to the statistical results of the actual driving conditions of the vehicle; Decompose different road conditions, driving speeds, and loading conditions into multiple independent simulation conditions, and use the parallel analysis method for fatigue reliability analysis; Analysis method for fatigue durability performance of the mounting bracket under long driving mileage and complex road conditions is as follows: First, define the set of road surface conditions R = {R i}, i = 1, …, N R , where R i represents the i-th road surface condition, and N R is the number of road surface conditions considered for fatigue durability analysis. Assume that under each road surface condition, the vehicle passes at different speeds {V ij}, j = 1, …, N vi , where V ij represents the vehicle passing the i-th road surface condition at the j-th speed. Assume that under the same road surface and the same speed, the vehicle travels at different loading states {L ijk}, k = 1, …, N lij , where L ijk represents the vehicle passing the i-th road surface at the k-th loading condition and the j-th speed. Introduce the dimensionless weight coefficient α i to represent the proportion of the length s i of each road condition in the total driving mileage S of the vehicle, that is and there is Similarly, different speeds in the same road condition R i also correspond to different weights β ij , and there is Different loading conditions under the same road condition R i and the same speed V ij correspond to different weights γ ijk , and there is Weights α i , β ij and γ ijk are all obtained by statistics according to the actual operation of the vehicle; Then define the structural unit damage value which is used to represent the structural fatigue damage value corresponding to the unit mileage. In the formula, e ijk represents the fatigue damage value when the vehicle passes through the i-th road condition at the k-th loading condition and the j-th speed. Then the structural fatigue damage value e w corresponding to the total driving mileage S can be expressed as: e w = e u ·S.

8. An analysis system for the integrated fatigue durability performance of a powertrain mounting bracket: characterized in that, It includes the integrated fatigue durability performance analysis method of the powertrain mount bracket described in any one of claims 1 - 7; The system includes: A rigid - body dynamics model establishment module, which is used to establish a multi - rigid - body dynamics model of a 19 - degree - of - freedom powertrain mount system based on the whole vehicle; A modal response solution module, which is used to solve and output the modal stress file and modal neutral file of the mount bracket. Use HyperMesh to establish a finite - element model of the powertrain mount bracket, and solve and output the modal neutral file and modal stress file of the mount bracket based on the modal synthesis method. After establishing the finite - element model of the mount bracket, write a batch bat file and HyperMesh / TCL command script to complete the solution and output of the modal neutral file and modal stress file of each finite - element model of the mount bracket; A rigid - flexible coupling dynamics model establishment module, which is used to establish a rigid - flexible coupling dynamics model of the powertrain mount system that can consider the influence of the bracket flexibility. Call the ADAMS / cmd command through a batch bat file to complete the reading of the modal neutral file, the replacement of the original rigid body parts, and the connection between the flexible bracket and the powertrain and the vehicle frame, so as to realize the automatic establishment of the rigid - flexible coupling dynamics model; A modal displacement solution module, which is used to solve and output the modal displacement file of the mount bracket under different road conditions. Write a bat file and an ADAMS / cmd command script to complete the vertical road surface displacement excitation loading on the left and right sides of the front and rear suspension spring lower assemblies of the rigid - flexible coupling dynamics model. Solve and output the modal displacement file of each mount bracket as the load input for the fatigue analysis of the mount bracket; A fatigue life calculation module, which is used to obtain the stress time - history of the mount bracket, and then calculate the structural fatigue life by applying the S - N method modified by Goodman. Write a bat file and an nCode fatigue analysis software script command to realize the automatic input of the modal stress file and modal displacement file of the mount bracket and the automatic solution of the structural dynamic stress. Call the SN CAE Fatigue module to solve the structural fatigue life and output the fatigue result file in HyperMesh format. Write a bat file and a HyperView / TCL command script to read the fatigue result file and output the minimum fatigue life of the bracket in text format; The fatigue durability performance prediction module provides a fatigue durability performance analysis method for the mounting bracket under long driving mileage and complex road conditions by defining and solving the structural unit damage value; a set of typical road conditions, vehicle speeds, and loading conditions are set to represent the actual driving conditions of the vehicle, and the proportion of each condition can be obtained according to the statistics of the actual driving conditions of the vehicle; different roads, driving speeds, and loading conditions are decomposed into multiple independent simulation conditions, and a parallel analysis method is used for fatigue life calculation; Analysis of the fatigue durability performance of the powertrain mounting bracket under long driving mileage and complex road conditions is as follows: Define the structural unit damage value to represent the structural fatigue damage value corresponding to the unit mileage. Then, the structural fatigue damage value e w corresponding to the total driving mileage S can be expressed as e w = e u ·S. In the formula, e ijk represents the fatigue damage value when the vehicle passes the i-th road condition at the k-th loading condition and the j-th speed. The weight coefficient α i is used to represent the proportion of each road condition length s i in the total driving mileage S of the vehicle, that is Under the same road condition, different speeds also correspond to different weights β ij . For the same road condition R i and the same speed V ij , different loading conditions correspond to different weights γ ijk ; The weights α i , β ij and γ ijk can be obtained by statistics according to the actual driving conditions of the vehicle.

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