A graded control method for NVH of a commercial vehicle steering system

Abstract

This invention relates to the field of NVH (Noise, Vibration, and Harshness) technology for commercial vehicles, specifically providing a graded NVH control method for commercial vehicle steering systems. First, based on vehicles exhibiting idling vibration issues, real-vehicle modal and ODS (Operational Discharge Stress) tests are conducted to identify the target modes of interest. Then, for the base vehicle model, a first-level CAE (Computer-Aided Engineering) model including the interior and body, a second-level model including the steering wheel-column-CCB (Corner-Crossbeam), a third-level model including the steering wheel-column, and a fourth-level model for the steering wheel unit are sequentially established. After simulation and experimental benchmarking, system-level frequency avoidance targets are formulated, and based on the modal frequency differences between adjacent model levels, the first and second frequency avoidance sub-targets and component-level frequency avoidance targets are obtained. Finally, in the early stages of new vehicle development, based on the above-mentioned targets at each level, modal verification and structural optimization are performed on the corresponding CAE models sequentially from the fourth level to the first level until the targets are met. This invention improves development efficiency and reliability.

Description

Technical Field

[0001] This invention relates to the field of NVH (Noise, Vibration, and Harshness) technology for commercial vehicles, specifically to a graded control method for NVH in the steering system of commercial vehicles. Background Technology

[0002] The steering wheel of a commercial vehicle is crucial for the driver's interaction with the vehicle, and its vibration characteristics directly affect the driver's safety and comfort. Idle vibrations of the steering system exceeding a certain range can significantly impact the driver's subjective experience.

[0003] The first-order modal frequency of a steering system typically falls within the 20-40Hz range, which coincides with the excitation frequency of commercial vehicles under idling conditions. This makes the steering wheel more prone to resonance under idling conditions, leading to steering wheel vibration. Compared to passenger vehicles, commercial vehicle steering systems exhibit greater diversity: firstly, in terms of material selection, the steering wheel frame can be made of steel or aluminum-magnesium alloy; secondly, in terms of structural design, commercial vehicle steering systems come in two structural forms: with and without a CCB crossbeam. Due to this diversity in materials and structures, these issues make the steering system more susceptible to idling vibration. Therefore, evaluating and optimizing the modal characteristics of the steering system is crucial during product development. However, currently, in the early stages of commercial vehicle steering system design, designers and simulation engineers only perform strength analysis and simple individual modal analysis, failing to accurately reflect the NVH performance of the actual vehicle steering system. This can easily lead to low simulation accuracy due to incomplete model conditions or incorrect focus on modal identification. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a graded NVH control method for a commercial vehicle steering system, thereby improving development efficiency and vehicle performance.

[0005] The technical solution of the present invention provides a graded control method for NVH of a commercial vehicle steering system, comprising the following steps:

[0006] S1 identifies the target focus mode that causes steering wheel idling vibration through real vehicle modal testing and idle speed condition ODS testing;

[0007] S2. Establish a first-level CAE model including interior and body for the basic vehicle model, perform modal analysis, and verify the modal analysis results against the modal characteristics of the target mode of interest. After the verification is qualified, set the modal frequency avoidance target of the first-level CAE model based on the nth order excitation frequency under engine idling conditions, and denot it as the system-level frequency avoidance target.

[0008] S3 establishes a second-level CAE model including the steering wheel, column, and CCB crossbeam for the base vehicle, and a third-level CAE model including the steering wheel and column. After applying full constraints at their respective mounting points, constrained modal analysis is performed under the target interest mode to obtain their respective modal frequencies. Based on the modal frequencies of the second-level CAE model and the first-level CAE model, a first frequency avoidance sub-objective is formulated for the second-level CAE model. Based on the modal frequencies of the third-level CAE model and the second-level CAE model, a second frequency avoidance sub-objective is formulated for the third-level CAE model.

[0009] S4. A fourth-level CAE model of the steering wheel unit is established for the basic vehicle model. After applying full constraints to its mounting point, constrained modal analysis is performed under the target focus mode to obtain its modal frequency. Based on the modal frequency, a component-level frequency avoidance target is formulated.

[0010] S5, based on the component-level frequency avoidance target, the second frequency avoidance sub-target, the first frequency avoidance sub-target, and the system-level frequency avoidance target, sequentially verifies the modal frequencies obtained from the fourth-level, third-level, second-level, and first-level CAE models of the vehicle to be produced, and performs structural optimization on models that do not meet the corresponding targets until their modal frequencies meet their respective targets.

[0011] As can be seen from the above technical solutions, this application has the following advantages:

[0012] (1) Establishing a technical logic of basic vehicle model testing, multi-level CAE model benchmarking, target decomposition, and new vehicle model verification at each level, transforming the idling vibration problem exposed in traditional later testing into quantifiable and executable control targets at each level in the early design stage. Thus, before the physical prototype is manufactured, the resonance risk can be systematically identified and eliminated in a virtual environment, avoiding the steering wheel idling vibration problem from the source;

[0013] (2) By rigorously benchmarking the first-level CAE model against real vehicle test data, the authenticity and reliability of the simulation model were ensured. Furthermore, by scientifically decomposing complex vehicle-level targets into subsystem-level and component-level targets, when developing new vehicle models, it is not necessary to repeatedly build and calculate complex vehicle models. Instead, simplified subsystem and component models can be quickly analyzed and optimized, which greatly improves simulation efficiency and saves computing resources and development time.

[0014] (3) The proposed four-level CAE model and its corresponding four-level frequency avoidance target improve the comprehensiveness of the analysis model, can identify the difficult modes of key concern, and improve vehicle performance. Attached Figure Description

[0015] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of a graded NVH control method for a commercial vehicle steering system provided in an embodiment of the present invention.

[0017] Figure 2 A flowchart illustrating the process of setting control objectives for the initial stage.

[0018] Figure 3 A flowchart illustrating the process of evaluating and optimizing the steering system during the early design phase of a new vehicle model project. Detailed Implementation

[0019] To make the purpose, features, and advantages of this application more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solution protected by this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application and in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0021] The key terms used in this invention will be explained below.

[0022] ODS stands for "Operational Deflection Shapes." It is an experimental testing method used to measure the vibration mode and amplitude of a structure under actual working load excitation under specific operating conditions (such as engine idling). This invention uses ODS testing to obtain the actual vibration mode of the steering wheel under idling conditions in order to identify the dominant vibration mode causing vibration.

[0023] CAE stands for Computer-Aided Engineering. It is a technology that uses computer software to simulate, analyze, and optimize engineering products. In this invention, it refers to using Finite Element Analysis (FEA) software to create digital models of the steering system and vehicle body structure, and then performing modal and other NVH performance simulation calculations on them.

[0024] CCB: Refers to the "Cab Cross Beam," a structural beam at the bottom of the commercial vehicle cab that plays a primary supporting and connecting role. Its structure and stiffness have a significant impact on the overall modal characteristics of the steering system. In this invention, the CCB cross beam is one of the key components of the Level 2 CAE model.

[0025] Figure 1 This is a schematic flowchart of a graded NVH control method for a commercial vehicle steering system provided by an embodiment of the present invention, as shown below. Figure 1 As shown, the method includes the following steps.

[0026] S1 identifies the target mode of concern that causes steering wheel idling vibration through real vehicle modal testing and idle condition ODS testing.

[0027] S2. Establish a first-level CAE model including interior and body for the basic vehicle model, perform modal analysis, and verify the modal analysis results against the modal characteristics of the target mode of interest. After the verification is successful, set the modal frequency avoidance target of the first-level CAE model based on the nth order excitation frequency under engine idling conditions, and denot it as the system-level frequency avoidance target.

[0028] S3 establishes a second-level CAE model including the steering wheel, column, and CCB crossbeam for the base vehicle, and a third-level CAE model including the steering wheel and column. After applying full constraints at their respective mounting points, constrained modal analysis is performed under the target interest mode to obtain their respective modal frequencies. Based on the modal frequencies of the second-level CAE model and the first-level CAE model, a first frequency avoidance sub-objective is formulated for the second-level CAE model. Based on the modal frequencies of the third-level CAE model and the second-level CAE model, a second frequency avoidance sub-objective is formulated for the third-level CAE model.

[0029] S4. A fourth-level CAE model of the steering wheel unit is established for the basic vehicle model. After applying full constraints to its mounting point, constrained modal analysis is performed under the target focus mode to obtain its modal frequency. Based on the modal frequency, a component-level frequency avoidance target is formulated.

[0030] S5, based on the component-level frequency avoidance target, the second frequency avoidance sub-target, the first frequency avoidance sub-target, and the system-level frequency avoidance target, sequentially verifies the modal frequencies obtained from the fourth-level, third-level, second-level, and first-level CAE models of the vehicle to be produced, and performs structural optimization on models that do not meet the corresponding targets until their modal frequencies meet their respective targets.

[0031] It should be noted that steps S1 to S4 are performed in the initial stage to set control objectives, while step S5 is performed in the early design stage of a new vehicle model project to evaluate and optimize the steering system based on the control objectives set in the initial stage.

[0032] Figure 2 The flowchart for setting the initial control objectives is as follows: First, step S1 is executed to perform modal testing and idle condition ODS testing on vehicles exhibiting steering wheel idling vibration issues, identifying key modes affecting the steering system: the first-order yaw mode and the first-order vertical yaw mode. Then, step S2 is executed to establish an interior and body finite element model (Level 1 CAE model). This model undergoes modal analysis and testing for benchmarking, and is optimized to meet the requirement of avoiding the powertrain's idling excitation frequency. Next, steps S3 and S4 are executed to establish finite element models of the steering wheel and column with the CCB beam (Level 2 CAE model), the steering wheel and column (Level 3 CAE model), and the steering wheel unit finite element model (Level 4 CAE model), respectively, and target values ​​are set based on the differences between these and the previous level's modal characteristics.

[0033] Step S1 identifies the target mode of concern that causes steering wheel idling vibration through real vehicle modal testing and idle condition ODS testing, specifically including the following steps.

[0034] S11, define the X direction as the steering wheel face facing forward, the Y direction as the steering wheel face facing right, and the Z direction as the steering wheel face normal direction vertically upward.

[0035] This step defines a unified coordinate system to ensure that the directional references for subsequent test data descriptions, mode shape comparisons, and simulation analyses are consistent, thus avoiding errors introduced by inconsistent coordinate system definitions.

[0036] S12, based on multiple groups of vehicles with steering wheel idling vibration issues, the steering wheel was adjusted to the design position, and modal tests of the steering wheel and ODS tests of the engine under idling conditions were conducted.

[0037] This step involves collecting real-vehicle test data. Based on multiple sets of typical vehicles known to have steering wheel idling vibration issues (i.e., the base model), the steering wheel is adjusted to the commonly used driving position specified in the design. In this state, two tests are performed: first, an experimental modal test of the steering wheel is conducted to obtain the natural frequency, damping ratio, and mode shape of the steering system in a free state; second, the engine is started and kept at idle speed, while an ODS test is performed to obtain the actual vibration response mode of the steering wheel under this specific working excitation.

[0038] S13, extract the dominant vibration mode with the largest steering wheel vibration displacement from the ODS test results under idling conditions.

[0039] From the ODS test data collected under idling conditions, the dominant vibration mode with the largest steering wheel vibration displacement was extracted. This dominant vibration mode reflects the specific form of the steering wheel's actual severe vibration under idling excitation, and is the manifestation of the vibration problem in the time and frequency domains.

[0040] S14. Analyze the modal test results of the steering wheel, identify all inherent mode shapes within the ±3Hz frequency band of the engine idle speed, compare all identified inherent mode shapes with the dominant mode shape, and determine the inherent mode shape that is consistent with the dominant mode shape as the target mode of interest causing the steering wheel idle speed vibration.

[0041] This step involves modal identification and correlation confirmation. Specifically, the results of the aforementioned experimental modal tests are analyzed, with a focus on identifying all inherent mode shapes within the critical frequency band of ±3Hz (engine idle frequency). Subsequently, these identified inherent mode shapes are compared one by one with the dominant ODS mode shape determined in step S13. Through mode shape comparison, the inherent mode shape that is spatially consistent with the dominant ODS mode shape is identified. This inherent mode is the root cause of the steering wheel's resonant vibration under idling conditions, i.e., the target mode of concern to be controlled, typically the first-order yaw mode or the first-order vertical yaw mode of the steering system.

[0042] Step S2 establishes a first-level CAE model of the base vehicle, including the interior and body, performs modal analysis, and then sets a system-level frequency avoidance target, which specifically includes the following steps.

[0043] S21. Establish a first-level CAE model for the base vehicle. This model is a finite element model that includes the interior and body. Adjust the steering wheel to the same position as the actual vehicle test in step S1.

[0044] For the base vehicle model, a first-level CAE model is constructed using finite element analysis software. This model must completely include the finite element meshes of the interior system and the main body structure. The interior system must include key components such as the instrument panel assembly, seat mounting brackets, and steering system mounting base. The main body structure must include load-bearing structures such as the cab frame, floor beams, and pillars. The adjustment position of the steering wheel in the model (including height and angle) must be completely consistent with the steering wheel position tested on the actual vehicle in step S1, ensuring that the model boundary conditions are equivalent to the actual vehicle test conditions. The mesh size must meet the accuracy requirements of modal analysis. The mesh size of key areas such as the connection point between the steering column and the body, and the connection point between the CCB beam and the floor, should not exceed 8mm. The mesh size of non-critical areas can be controlled between 8-12mm. At the same time, the material parameters of the model must be accurately assigned, and the material parameters must be derived from the physical performance test reports of the actual parts.

[0045] S22, perform free mode calculations on the first-level CAE model within the first preset frequency range, and output its modal frequencies and mode shapes.

[0046] For the completed first-level CAE model, modal analysis solution parameters are set in the finite element analysis software: the analysis frequency range is set to a first preset frequency range, which can be 0-60Hz. This range covers the typical distribution range (20-40Hz) of the first-order yaw mode and the first-order vertical yaw mode of the commercial vehicle steering system, as well as the engine idle speed excitation frequency range. The Lanczos method is used to ensure the accuracy of modal calculations. The output parameters are set to the natural frequencies, mode shape contour maps, and modal participation coefficients of each mode. After starting the solution, the software will output the modal results of all orders of the model in the 0-60Hz range, including the frequency value of each mode and the corresponding mode shape, such as the steering wheel X-axis yaw, Y-axis yaw, and local vibration of the vehicle body.

[0047] S23, using the test results of the target mode of interest identified in step S1 as a benchmark, perform simulation and test comparison, including: from the modal calculation results in step S22, identify the first-level CAE model mode corresponding to the mode shape of the target mode of interest, compare the frequency of the mode with the test frequency, and when the error between the two is less than the preset error threshold, it is judged as qualified for comparison.

[0048] First, mode shape matching is performed. From the mode shape cloud map output by S22, simulation modes that are consistent with the mode shape of the target mode of interest are selected: For the first-order yaw mode (Y-axis yaw), it is necessary to confirm the yaw characteristics of the steering wheel around the X-axis in the simulation mode shape, and the area with the largest yaw amplitude is concentrated on the steering wheel surface; For the first-order vertical yaw mode (X-axis yaw), it is necessary to confirm the yaw characteristics of the steering wheel around the Y-axis in the simulation mode shape, and the area with the largest yaw amplitude is also concentrated on the steering wheel surface.

[0049] Then, frequency error verification is performed. The simulated modal frequencies of the above-mentioned mode shape matching are extracted and the difference between them and the target modes of interest obtained from the actual vehicle test is calculated. The preset error threshold is set to 5%. If the frequency error is ≤5%, the first-level CAE model is deemed to be qualified for calibration, and the model can be used for subsequent frequency avoidance target setting. If the frequency error is >5%, the problems in the model construction process need to be checked, including whether the stiffness assignment of the steering system and the body connection point is accurate (which can be corrected by adjusting the stiffness parameters of the spring unit at the connection point), whether the weight of the interior system components is consistent with the actual vehicle (which can be compensated by adding mass points to compensate for the mass deviation between the actual vehicle and the model), and whether there is distortion in the mesh (mesh with distortion rate >0.8 needs to be re-meshed). After correction, S22 is executed again until the calibration is qualified.

[0050] S24. For a qualified first-level CAE model, calculate its nth-order excitation frequency based on the engine idle speed, determine the excitation frequency range based on the calculation results, and set the modal frequency avoidance target of the steering system in the first-level CAE model based on the excitation frequency range, which is denoted as the system-level frequency avoidance target.

[0051] S241, Obtain the engine's idle speed range, and based on this speed range and the preset excitation order n, calculate the corresponding lower limit value of the nth order excitation frequency. With the upper limit of the nth order excitation frequency Thus, the excitation frequency range is determined as follows: .

[0052] S242, based on the excitation frequency range For the target focus mode of the steering system in the first-level CAE model, a modal frequency avoidance target is set, which is the modal frequency of the target focus mode of the first-level CAE model. Must meet or Modal frequency The conditions that need to be met are the system-level frequency avoidance targets, among which This is the preset safety margin frequency.

[0053] Extract the engine idle speed range from the engine technical specifications or actual vehicle test data of the base vehicle model, determine the order n used to calculate the excitation frequency, and then apply the excitation frequency calculation formula. ,in For each engine speed, calculate the lower limit of the nth-order excitation frequency corresponding to the lower limit of the idle speed. The upper limit of the nth-order excitation frequency corresponding to the upper limit of the idle speed. Thus, the excitation frequency range is determined as follows: .

[0054] Based on the above excitation frequency range, a preset safety margin frequency is introduced. The frequency is set to 3Hz, which effectively avoids the resonance risk caused by engine speed fluctuations. This value is used to set the modal frequency of the steering system's target mode of interest in the first-level CAE model. Must meet or Modal frequency The conditions that need to be met are system-level frequency avoidance targets.

[0055] S25, if the modal frequency of the target focus mode in the first-level CAE model does not meet the system-level frequency avoidance target, then by analyzing the strain energy distribution cloud map of the first-level CAE model under the target focus mode, the structural region where the strain energy is concentrated is identified, and the structure of the region is optimized; return to execute S22 to S24 until the first-level CAE model meets the requirements of the system-level frequency avoidance target.

[0056] If the modal frequencies of the target focus modes in the first-level CAE model do not meet the system-level frequency avoidance objective, then structural optimization is performed through the following steps.

[0057] S251, Analyze the strain energy distribution.

[0058] In finite element analysis software, the strain energy distribution cloud map corresponding to the target mode of interest is retrieved to identify the structural regions where strain energy is concentrated. For the first-order yaw mode, the strain energy concentration regions are usually the connecting bracket between the steering column and the vehicle body, and the middle region of the CCB crossbeam; for the first-order vertical yaw mode, the strain energy concentration regions are usually the lower support of the steering column and the reinforcing plate connecting the vehicle floor and the column.

[0059] S252, Develop an optimization plan.

[0060] For areas of concentrated strain energy, develop structural optimization schemes. If the strain energy is concentrated in the connecting brackets, the stiffness can be improved by increasing the bracket thickness and adding reinforcing ribs; if the strain energy is concentrated in the CCB beams or floor reinforcement plates, the stiffness can be improved by replacing them with higher strength materials and optimizing the cross-sectional shape.

[0061] S253, Iterative verification.

[0062] The optimization scheme is applied to the first-level CAE model. After updating the model structure parameters, the process returns to execute S22, S23, and S24 until the modal frequency of the target mode of interest in the model meets the system-level frequency avoidance target. The optimization process needs to record the structural parameters and modal frequency changes in each round of optimization to form an optimization iteration report.

[0063] Step S3 involves sequentially establishing a second-level CAE model and a third-level CAE model for the base vehicle, and setting corresponding frequency avoidance targets, specifically including the following steps.

[0064] S31. Establish a second-level CAE model for the base vehicle. This model is a finite element model that includes the steering wheel, steering column, and CCB beam. Apply full constraints at each mounting point of the steering column and the vehicle floor, the steering column and the CCB beam, and the CCB beam and the vehicle body.

[0065] For the base vehicle model, a second-level CAE model is constructed using finite element analysis software. This model must include the complete finite element structure of the steering wheel, steering column, and CCB beam.

[0066] The steering wheel model must include a skeleton, a foam layer, and a covering layer. The skeleton mesh uses tetrahedral or hexahedral elements with a mesh size of 5-8mm. The foam layer and the covering layer use solid elements with a mesh size of 8-12mm. The steering column model must include the column body, the telescopic mechanism, and the fixed support. The column body uses beam or shell elements, and the support uses shell elements with a mesh size of 8-12mm. The CCB beam model must include the beam body and the connecting supports at both ends, using shell elements with a mesh size of 8-10mm. The critical connection areas need to be meshed more precisely.

[0067] Based on the physical performance test reports of the actual components, material parameters, including elastic modulus, Poisson's ratio, and density, are assigned to each component.

[0068] The locations of each mounting point are clearly defined in the model. Full constraints are applied to the connection points between the column and the vehicle floor, the column and the CCB beam, and the CCB beam and the vehicle body. This means that the translational degrees of freedom in the X, Y, and Z directions and the rotational degrees of freedom about the X, Y, and Z axes are restricted. Fixed constraints are used to ensure that the constraint state is consistent with the fixing method of the parts in the actual vehicle, so as to avoid the modal calculation results being affected by the deviation of the constraint boundary conditions.

[0069] S32, Perform constrained modal analysis on the second-level CAE model, calculate its modal frequencies and mode shapes within a first preset frequency range, and identify the modal frequencies of the second-level CAE model corresponding to the target mode of interest from the calculation results, denoted as... .

[0070] In the finite element analysis software, the modal analysis frequency range of the second-level CAE model is set to the first preset frequency range (0-60Hz), which covers the typical distribution range of the first-order yaw mode and the first-order yaw mode of the steering system. The Lanczos method is selected as the solution method to ensure the accuracy and efficiency of the modal calculation. The output parameters are set as the natural frequency, mode shape contour map and modal participation coefficient of each mode, which facilitates subsequent mode shape identification and frequency extraction.

[0071] After initiating modal solving, the software outputs modal results for all orders within the 0-60Hz range. By examining the modal shape contour plots, modes consistent with the target modes of interest (first-order yaw mode and first-order vertical yaw mode) are identified. For the first-order yaw mode, it must be confirmed that the mode shape characteristic is the steering wheel oscillation in the Y direction around the Z-axis, with the maximum oscillation amplitude concentrated on the steering wheel surface. For the first-order vertical yaw mode, it must be confirmed that the mode shape characteristic is the steering wheel oscillation in the X direction around the Y-axis, with the maximum oscillation amplitude concentrated on the steering wheel surface. The natural frequencies corresponding to the identified target modes of interest are extracted and denoted as the target mode frequencies of the second-level CAE model. .

[0072] S33. Establish a third-level CAE model for the base vehicle model. This model is a finite element model that includes the steering wheel and steering column, and apply full constraints at the mounting points of the column and the vehicle floor, as well as the mounting points of the column and the CCB beam.

[0073] For the base vehicle model, a third-level CAE model is constructed. This model includes the steering wheel and steering column, but does not include the CCB crossbeam. The construction standards of the model components are consistent with those of the corresponding steering wheel and steering column in the second-level CAE model. That is, the mesh type, size, and material parameters of the steering wheel skeleton, foam layer, and covering layer remain unchanged; the mesh type, size, and material parameters of the steering column body, telescopic mechanism, and fixed bracket also remain unchanged, ensuring the consistency of the model components and avoiding deviations in modal results due to differences in component modeling.

[0074] Based on the fixing method of the steering column in the actual vehicle, full constraints are applied to the connection points between the column and the vehicle floor, and the connection points between the column and the CCB beam in the third-level CAE model (although the model does not contain the CCB beam, it is necessary to simulate the connection state between the column and the CCB beam in the actual vehicle). The constraint method is also fixed constraint, which restricts the translational degrees of freedom in the X, Y, and Z directions and the rotational degrees of freedom about the X, Y, and Z axes. This ensures that the constraint boundary conditions of the third-level CAE model are equivalent to the constraint state of the column in the second-level CAE model. The model is simplified only by removing the CCB beam, ensuring that the comparison benchmark between the two levels of models is consistent.

[0075] S34, Perform constrained modal analysis on the third-level CAE model, calculate its modal frequencies and mode shapes within a first preset frequency range, and identify the modal frequencies of the third-level CAE model corresponding to the target mode of interest from the calculation results, denoted as... .

[0076] The modal analysis parameters are consistent with those of the second-level CAE model. The frequency range is set to the first preset frequency range (0-60Hz). The solution method is Lanczos method. The output parameters include natural frequencies, mode shape contour plots and modal participation coefficients. This ensures that the modal analysis conditions of the two-level models are consistent and avoids the frequency comparison results being affected by differences in solution parameters.

[0077] After initiating modal solving, examine the output modal shape contour plots and identify modes that match the mode shapes of the target modes of interest (first-order yaw mode and first-order yaw mode). The mode shape characteristics must be consistent with the corresponding target mode shapes in the second-level CAE model. The first-order yaw mode is the Y-axis oscillation of the steering wheel about the Z-axis, and the first-order yaw mode is the X-axis oscillation of the steering wheel about the Y-axis. Extract the natural frequencies corresponding to these modes and denote them as the target mode frequencies of the third-level CAE model. .

[0078] S35, based on the modal frequencies of the second-level CAE model and the first-level CAE model, formulate the first frequency avoidance sub-objective for the second-level CAE model; based on the modal frequencies of the third-level CAE model and the first-level CAE model, formulate the second frequency avoidance sub-objective for the third-level CAE model.

[0079] After completing the modal analysis and frequency extraction of the second-level and third-level CAE models, the target modal frequencies of the two levels of models are summarized. Simultaneously, the target mode frequencies of interest of the first-level CAE model, which are determined after optimization in step S2, meet the benchmark requirements, and satisfy the system-level frequency avoidance target, are retrieved. A target modal frequency dataset for the three-level model is formed; the validity of this dataset is verified to ensure... All of these are modal frequencies that perfectly match the target mode shape in the corresponding model, and the frequency values ​​are within a reasonable range. If there are frequency anomalies, such as exceeding the range or not matching the mode shape, the modal analysis of the corresponding model must be returned to and the solution recalculated until the dataset is valid.

[0080] S351, Obtain the first-level CAE model that is finally determined after optimization in step S2 and meets the system-level frequency avoidance target. Read the modal frequencies of the target's focus modes in this model, and denote them as follows: .

[0081] From the first-level CAE model optimization report generated in step S2, retrieve the target interest mode frequencies that have been finally optimized and confirmed, and that meet the following conditions. :

[0082] The Level 1 CAE model has been verified through simulation and experimental benchmarking, with the simulation frequency and actual vehicle test frequency error of the target focus modes (first-order yaw mode and first-order vertical yaw mode) being ≤5%.

[0083] Target focus on modal frequencies To meet the system-level frequency avoidance objective, or ;

[0084] retrieved It must include the first-order yaw mode frequency and the first-order vertical yaw mode frequency of the first-level CAE model, denoted as , respectively. , The corresponding modal order, mode shape description, and optimized model structural parameters are recorded.

[0085] S352, Calculate the frequency difference between the second-level CAE model and the first-level CAE model in the target interest mode. ,Right now .

[0086] The target modal frequencies are based on the retrieved first-level CAE model. The modal frequencies of interest in the second-level CAE model. (Including the first-order yaw mode frequency of the second-level CAE model) First-order pendulum mode frequency of the second-level CAE model ), calculate the frequency difference between the two-stage models in the first-order yaw mode and the first-order yaw mode, respectively. :

[0087] First-order yaw mode frequency difference ;

[0088] First-order pendulum mode frequency difference .

[0089] S353, based on frequency difference In conjunction with the system-level frequency avoidance objective, the first frequency avoidance sub-objective is defined for the second-level CAE model, namely, the modal frequencies of the modes that the second-level CAE model focuses on. Must meet or The condition that must be met is the first frequency-avoidance sub-target.

[0090] Since the second-level CAE model is a simplified version of the first-level CAE model, its target modal frequencies differ from those of the first-level CAE model by a fixed value. To ensure that the physical subsystems corresponding to the second-level CAE model can still meet the system-level frequency avoidance requirements after being assembled into the vehicle, the frequency difference needs to be added to the system-level frequency avoidance target. This forms the frequency avoidance constraint conditions for the second-level CAE model.

[0091] For the first-order yaw mode, the second-level CAE model focuses on the modal frequencies. Must meet:

[0092] or

[0093] For the first-order pendulum mode, the second-level CAE model focuses on the modal frequencies. Must meet:

[0094] or

[0095] S354, Calculate the frequency difference between the third-level CAE model and the second-level CAE model in the target interest mode. ,Right now .

[0096] S355, based on frequency difference In conjunction with the system-level frequency avoidance objective, a second frequency avoidance sub-objective is defined for the third-level CAE model, namely, the modal frequencies of the modes that the third-level CAE model focuses on. Must meet or The condition that must be met is the second frequency avoidance sub-target.

[0097] The third-level CAE model is a further simplification of the second-level CAE model, and its target modal frequencies have a fixed difference from those of the second-level CAE model. To ensure that the physical subsystems (steering wheel + steering column) corresponding to the third-level CAE model, after being assembled with the CCB crossbeam, can meet the first frequency avoidance sub-objective of the second-level CAE model, and thus indirectly meet the system-level frequency avoidance objective, this frequency difference needs to be added on top of the system-level frequency avoidance objective. This forms the frequency avoidance constraint conditions for the third-level CAE model.

[0098] The derivation of the second frequency avoidance sub-target is similar to that of the first frequency avoidance sub-target, and will not be repeated here.

[0099] Step S4 involves establishing a Level 4 CAE model for the base vehicle and defining component-level frequency avoidance targets, which includes the following steps.

[0100] S41. Establish a fourth-level CAE model for the base vehicle model. This model is a finite element model of the steering wheel unit, and apply full constraints at the connection point between the steering wheel and the steering column.

[0101] For the base vehicle model, a fourth-level CAE model was constructed using finite element analysis software. This model is a finite element model of the steering wheel unit.

[0102] Using a 3D digital model of the base vehicle's steering wheel as input, the complete geometric features of the steering wheel skeleton, foam buffer layer, and outer skin covering layer are preserved, while unnecessary structures other than the connection between the steering wheel and the column are eliminated. A meshing strategy using hexahedrons as the primary element and tetrahedrons as secondary elements is adopted. The skeleton mesh size is controlled at 5-8mm, and the foam layer and covering layer mesh size is controlled at 8-12mm. The mesh quality must meet the following requirements: element distortion rate ≤0.8, warpage angle ≤15°, and AspectRatio ≤5, ensuring that the mesh accuracy meets the requirements of modal analysis.

[0103] Based on the physical performance test report of the steering wheel components of the base vehicle, precise material parameters, including elastic modulus, Poisson's ratio, and density, are assigned to each component of the model. Tie constraints are used to define the connection relationship between the skeleton and the foam layer, and between the foam layer and the covering layer, simulating the bonding process between layers in the real vehicle, and avoiding the influence of modeling deviations in connection methods on the modal results.

[0104] Apply full constraints at the connection flange between the steering wheel and the steering column. The constraint range is the circumferential area where all bolt holes of the connection flange are located. Restrict the translational degrees of freedom in the X, Y, and Z directions and the rotational degrees of freedom around the X, Y, and Z axes in this area to simulate the state of the steering wheel being rigidly connected to the column by bolts in a real vehicle. The constraint boundary conditions must be completely consistent with the installation state of the steering wheel in the real vehicle test in step S1.

[0105] S42, perform constrained modal analysis on the fourth-level CAE model, and calculate its modal frequencies and mode shapes within the second preset frequency range.

[0106] In the finite element analysis software, the frequency range for modal analysis is set to a second preset frequency range (0-100Hz). This range covers the typical distribution range (25-60Hz) of the first-order yaw and sway modes of the steering wheel unit, as well as the potential higher-order mode range, to avoid missing key modes. The solution method adopts the Lanczos method, and the modal extraction order is set to ≥20. The output parameters include the natural frequencies of each mode, mode shape contour plots, modal participation coefficients, and strain energy density distribution. The modal participation coefficients need to distinguish the contributions in the X, Y, and Z directions for subsequent target focus mode identification.

[0107] After starting the modal solver, the software generates a modal analysis result file. The post-processing module extracts the frequency values ​​and mode shape animations of each mode, sorts them from low to high frequency, and forms a fourth-level CAE model modal result table. The table must include the modal order, natural frequency, principal vibration direction, and mode shape description.

[0108] S43. From the analysis results of step S42, identify the fourth-level CAE model mode frequency corresponding to the target focus mode, and record this mode frequency as the frequency threshold.

[0109] S431, Extract all mode shapes calculated in step S42.

[0110] From the modal analysis results file output in step S42, extract all mode shapes within the second preset frequency range (0-100Hz). Using the "Mode Shape Animation Export" function of the finite element software's post-processing module, export each mode shape as an AVI format animation at 24 frames per second, and simultaneously generate displacement contour maps of each mode shape in the X, Y, and Z directions. Classify and label the extracted mode shapes according to the following rules:

[0111] The "potential yaw mode" is marked as follows: the mode shape is dominated by the yaw of the steering wheel around the Z-axis (normal to the wheel surface), and the yaw displacement accounts for ≥70%.

[0112] The "potential yaw mode" is marked as follows: the mode shape is dominated by the X-direction oscillation of the steering wheel around the Y-axis (the wheel surface is horizontal to the right), and the X-direction displacement accounts for ≥70%.

[0113] The mode marked "non-target mode" is dominated by radial contraction / expansion, spoke bending, or local vibration of the disc surface, with X / Y displacement accounting for less than 60%. Based on previous real vehicle test results, this type of mode has been confirmed to have no significant impact on idling vibration.

[0114] S432, compare the modal shape with the mode shape of the target mode of interest identified in step S1.

[0115] Using the target mode shape identified in the actual vehicle test in step S1 as a benchmark, the similarity between the mode shape extracted from the fourth-level CAE model and the benchmark mode shape is quantified and compared using the Modal Assurance Criterion (MAC).

[0116] From the vehicle modal test report in step S1, extract the mode shape data of the target modes of interest (first-order yaw and first-order vertical yaw), including the displacement values ​​in the X, Y, and Z directions of several feature points on the steering wheel surface, to form the reference mode shape displacement matrix. .

[0117] At the corresponding 12 feature points of the fourth-level CAE model, the displacement values ​​in the X, Y, and Z directions of the mode shape to be compared are extracted to form the CAE mode shape displacement matrix. .

[0118] According to the formula Calculate the similarity, where T represents matrix transpose. Set a MAC value ≥ 0.8 as the acceptable threshold for mode shape similarity. When the MAC value of a certain CAE mode shape is ≥ 0.8 with the reference mode shape, the two modes are considered to be identical.

[0119] S433: The mode with the highest similarity to the target mode of interest is identified as the mode corresponding to it in the fourth-level CAE model, and the natural frequency value of the mode is read. This frequency value is the fourth-level CAE model modal frequency corresponding to the identified target mode of interest.

[0120] For CAE mode shapes with a MAC value ≥ 0.8 in step S432, further verification is performed using mode shape animation: the first-order yaw mode should show the steering wheel oscillating around the Z-axis in the Y direction without significant spoke bending or local vibration; the first-order yaw mode should show the steering wheel oscillating around the Y-axis in the X direction without significant torsional deformation of the wheel surface. Modes that meet the MAC value requirement but have local mode shape interference are excluded.

[0121] From the CAE modes with confirmed consistent vibration modes, their natural frequency values ​​are read: the CAE mode frequency matching the first-order yaw reference mode is recorded as the yaw frequency threshold, and the CAE mode frequency matching the first-order sag reference mode is recorded as the sag frequency threshold; the two together constitute the frequency threshold. If multiple CAE modes have a MAC value ≥ 0.8 with the same reference mode, the mode with the lowest frequency is selected as the target mode, and the order and strain energy concentration region of this mode are recorded.

[0122] S44, define the component-level frequency avoidance target as the modal frequency of the target mode of the fourth-level CAE model. Not lower than the stated frequency threshold.

[0123] Based on the frequency threshold identified in step S43, and combined with the real-vehicle rectification experience of steering wheel idling vibration in the basic model, the component-level frequency avoidance target is formulated: in the fourth-level CAE model, the first-order yaw mode frequency of the steering wheel is ≥ the yaw frequency threshold, and the first-order yaw mode frequency is ≥ the yaw frequency threshold.

[0124] Figure 3 This is a flowchart illustrating the process of evaluating and optimizing the steering system during the early design phase of a new vehicle model project. In the early stages of project development, based on the target values ​​for each state established in the early stages, the steering system undergoes multi-level modal analysis and optimization control to avoid steering wheel idling vibration issues.

[0125] Specifically, step S5 includes the following steps.

[0126] For the S51 model, a fourth-level CAE model of the steering wheel unit is established, and after applying full constraints to its mounting point, constraint modal analysis is performed to obtain its modal frequencies.

[0127] S52, compare and verify the modal frequencies obtained in S51 with the component-level frequency avoidance target; if the target is not met, analyze the strain energy distribution of the fourth-level CAE model, identify the steering wheel structure that is sensitive to the mode and optimize it; after updating the model, return to S51 until its modal frequencies meet the component-level frequency avoidance target.

[0128] Using the finite element software's post-processing module, examine the strain energy distribution cloud map that does not meet the target mode, and identify areas of concentrated strain energy, typically at the connection between the frame spokes and the flange, or in the outer arc transition area of ​​the frame.

[0129] If the strain energy is concentrated at the root of the spoke, an optimized solution is to increase the thickness of the spoke and add reinforcing ribs on both sides of the spoke;

[0130] If the strain energy is concentrated in the outer ring of the skeleton, an optimization scheme is adopted that optimizes the cross-sectional shape of the outer ring and increases the wall thickness of the outer ring.

[0131] The optimized scheme is applied to the fourth-level CAE model of the vehicle to be produced, modal analysis is re-executed, the optimized modal frequencies are extracted, and then compared with the component-level frequency avoidance target again until the target requirements are met.

[0132] S53, based on the steering wheel design that meets the component-level frequency avoidance target, establishes a third-level CAE model of the vehicle to be produced, including the steering wheel and column, and performs constrained modal analysis after applying full constraints at its mounting points to obtain its modal frequencies.

[0133] S54, compare and verify the modal frequencies obtained in S53 with the second frequency avoidance sub-target; if the target is not met, analyze the strain energy distribution of the third-level CAE model, identify the modally sensitive structure and optimize it; after updating the model, return to S53 until its modal frequencies meet the second frequency avoidance sub-target.

[0134] Analyze the strain energy distribution that does not meet the target mode. If the strain energy is concentrated in the fixed support of the tube column, adopt the solution of adding support reinforcing ribs and optimizing the position of the support mounting holes; if the strain energy is concentrated in the tube column body, adopt the solution of increasing the tube column wall thickness and adding a damping ring in the middle of the tube column.

[0135] Based on the design of the steering wheel and column that meets the second frequency avoidance sub-objective, a second-level CAE model containing the steering wheel, column and CCB crossbeam is established for the production model. After applying full constraints to its mounting points, constrained modal analysis is performed to obtain its modal frequencies.

[0136] S56, compare and verify the modal frequencies obtained in S55 with the first frequency avoidance sub-target; if the target is not met, analyze the strain energy distribution of the second-level CAE model, identify the modally sensitive structure and optimize it; after updating the model, return to S55 until its modal frequencies meet the first frequency avoidance sub-target.

[0137] If the strain energy is concentrated in the CCB beam, the solution is to increase the beam cross-section height and add a support reinforcement plate in the middle of the beam; if the strain energy is concentrated at the connection between the column and the CCB beam, the solution is to increase the contact area of ​​the connecting bracket and use double bolts.

[0138] S57, based on the design of the steering system subsystem that meets the first frequency avoidance sub-objective, establishes a first-level CAE model of the vehicle to be produced, including the interior and body, and performs free modal analysis to obtain the modal frequencies of its steering system.

[0139] S58. Compare and verify the modal frequencies obtained in S57 with the system-level frequency avoidance target. If the target is met, the design is complete. If the target is not met, return to the corresponding steps in S51 to S56 to iteratively optimize the components or subsystems of the steering system until the first-level CAE model of the vehicle to be produced meets the system-level frequency avoidance target.

[0140] Analyze the reasons for not meeting the target. If the modal frequency falls into the excitation range due to insufficient body stiffness, the body structure needs to be optimized, such as increasing the number of floor crossbeams and thickening the column cross section. If it is caused by the coupling vibration between the steering system and the body, return to the corresponding steps in S52-S56 and adjust the structural parameters of the steering wheel, column or CCB crossbeam, such as further increasing the stiffness of the steering wheel frame and optimizing the column fixing method.

[0141] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A graded NVH control method for a commercial vehicle steering system, characterized in that, Includes the following steps: S1 identifies the target focus mode that causes steering wheel idling vibration through real vehicle modal testing and idle speed condition ODS testing; S2. Establish a first-level CAE model including interior and body for the basic vehicle model, perform modal analysis, and verify the modal analysis results against the modal characteristics of the target mode of interest. After the verification is qualified, set the modal frequency avoidance target of the first-level CAE model based on the nth order excitation frequency under engine idling conditions, and denot it as the system-level frequency avoidance target. S3 establishes a second-level CAE model containing the steering wheel, column and CCB crossbeam for the basic vehicle model, and a third-level CAE model containing the steering wheel and column. After applying full constraints at their respective mounting points, constrained modal analysis is performed under the target interest mode to obtain their respective modal frequencies. Based on the modal frequencies of the second-level CAE model and the first-level CAE model, the first frequency avoidance sub-objective is formulated for the second-level CAE model; Based on the modal frequencies of the third-level CAE model and the second-level CAE model, a second frequency avoidance sub-objective is formulated for the third-level CAE model; S4. A fourth-level CAE model of the steering wheel unit is established for the basic vehicle model. After applying full constraints to its mounting point, constrained modal analysis is performed under the target focus mode to obtain its modal frequency. Based on the modal frequency, a component-level frequency avoidance target is formulated. S5, based on the component-level frequency avoidance target, the second frequency avoidance sub-target, the first frequency avoidance sub-target, and the system-level frequency avoidance target, sequentially verifies the modal frequencies obtained from the fourth-level, third-level, second-level, and first-level CAE models of the vehicle to be produced, and performs structural optimization on models that do not meet the corresponding targets until their modal frequencies meet their respective targets.

2. The NVH graded control method for commercial vehicle steering systems according to claim 1, characterized in that, Step S1 specifically includes: S11, define the X direction as the steering wheel face direction forward, the Y direction as the steering wheel face direction to the right, and the Z direction as the steering wheel face normal direction vertically upward; S12, based on multiple groups of vehicles with steering wheel idling vibration issues, the steering wheel was adjusted to the design position, and the steering wheel modal test and the engine ODS test under idling conditions were carried out respectively. S13, extract the dominant vibration mode with the largest steering wheel vibration displacement from the ODS test results under idling conditions; S14. Analyze the modal test results of the steering wheel, identify all inherent mode shapes within the ±3Hz frequency band of the engine idle speed, compare all identified inherent mode shapes with the dominant mode shape, and determine the inherent mode shape that is consistent with the dominant mode shape as the target mode of interest causing the steering wheel idle speed vibration.

3. The NVH graded control method for commercial vehicle steering systems according to claim 2, characterized in that, The target modes of interest include the first-order yaw mode, which is dominated by oscillation in the Y direction, and the first-order pendulum mode, which is dominated by oscillation in the X direction.

4. The NVH graded control method for commercial vehicle steering systems according to claim 3, characterized in that, Step S2 specifically includes: S21. Establish a first-level CAE model for the base vehicle. This model is a finite element model that includes the interior and body. Adjust the steering wheel to the same position as the actual vehicle test in step S1. S22, perform free mode calculations on the first-level CAE model within the first preset frequency range, and output its modal frequencies and mode shapes; S23, using the test results of the target mode of interest identified in step S1 as a benchmark, perform simulation and test comparison, including: from the modal calculation results in step S22, identify the first-level CAE model mode corresponding to the mode shape of the target mode of interest, compare the frequency of the mode with the test frequency, and when the error between the two is less than the preset error threshold, it is judged as qualified for comparison; S24. For a qualified first-level CAE model, calculate its nth-order excitation frequency based on the engine idle speed, determine the excitation frequency range based on the calculation results, and set the modal frequency avoidance target of the steering system in the first-level CAE model based on the excitation frequency range, which is denoted as the system-level frequency avoidance target. S25, if the modal frequency of the target focus mode in the first-level CAE model does not meet the system-level frequency avoidance target, then by analyzing the strain energy distribution cloud map of the first-level CAE model under the target focus mode, the structural region where the strain energy is concentrated is identified, and the structure of the region is optimized; return to execute S22 to S24 until the first-level CAE model meets the requirements of the system-level frequency avoidance target.

5. The NVH graded control method for commercial vehicle steering systems according to claim 4, characterized in that, Step 24 specifically includes: S241, Obtain the engine's idle speed range, and based on this speed range and the preset excitation order n, calculate the corresponding lower limit value of the nth order excitation frequency. With the upper limit of the nth order excitation frequency Thus, the excitation frequency range is determined as follows: ; S242, based on the excitation frequency range For the target focus mode of the steering system in the first-level CAE model, a modal frequency avoidance target is set, which is the modal frequency of the target focus mode of the first-level CAE model. Must meet or Modal frequency The conditions that need to be met are the system-level frequency avoidance targets, among which This is the preset safety margin frequency.

6. The NVH graded control method for commercial vehicle steering systems according to claim 5, characterized in that, Step S3 specifically includes: S31. Establish a second-level CAE model for the basic vehicle model. This model is a finite element model that includes the steering wheel, steering column and CCB beam. Apply full constraints at each mounting point of the column and the vehicle floor, the column and the CCB beam, and the CCB beam and the vehicle body. S32, Perform constrained modal analysis on the second-level CAE model, calculate its modal frequencies and mode shapes within a first preset frequency range, and identify the modal frequencies of the second-level CAE model corresponding to the target mode of interest from the calculation results, denoted as... ; S33. Establish a third-level CAE model for the basic vehicle model. This model is a finite element model that includes the steering wheel and steering column, and apply full constraints at the mounting points of the column and the vehicle floor, as well as the mounting points of the column and the CCB beam. S34, Perform constrained modal analysis on the third-level CAE model, calculate its modal frequencies and mode shapes within a first preset frequency range, and identify the modal frequencies of the third-level CAE model corresponding to the target mode of interest from the calculation results, denoted as... ; S35, based on the modal frequencies of the second-level CAE model and the first-level CAE model, formulate the first frequency avoidance sub-objective for the second-level CAE model; based on the modal frequencies of the third-level CAE model and the first-level CAE model, formulate the second frequency avoidance sub-objective for the third-level CAE model.

7. The NVH graded control method for commercial vehicle steering systems according to claim 6, characterized in that, Step S35 specifically includes: S351, Obtain the first-level CAE model that is finally determined after optimization in step S2 and meets the system-level frequency avoidance target. Read the modal frequencies of the target's focus modes in this model, and denote them as follows: ; S352, Calculate the frequency difference between the second-level CAE model and the first-level CAE model in the target interest mode. ,Right now ; S353, based on frequency difference In conjunction with the system-level frequency avoidance objective, the first frequency avoidance sub-objective is defined for the second-level CAE model, namely, the modal frequencies of the modes that the second-level CAE model focuses on. Must meet or The condition that must be met is the first frequency-avoidance sub-target; S354, Calculate the frequency difference between the third-level CAE model and the second-level CAE model in the target interest mode. ,Right now ; S355, based on frequency difference In conjunction with the system-level frequency avoidance objective, a second frequency avoidance sub-objective is defined for the third-level CAE model, namely, the modal frequencies of the modes that the third-level CAE model focuses on. Must meet or The condition that must be met is the second frequency avoidance sub-target.

8. The NVH graded control method for commercial vehicle steering systems according to claim 7, characterized in that, Step S4 specifically includes: S41. Establish a fourth-level CAE model for the base vehicle model. This model is a finite element model of the steering wheel unit, and apply full constraints at the connection point between the steering wheel and the steering column. S42, Perform constrained modal analysis on the fourth-level CAE model and calculate its modal frequencies and mode shapes within the second preset frequency range; S43. From the analysis results of step S42, identify the fourth-level CAE model mode frequency corresponding to the target focus mode, and record the mode frequency as the frequency threshold. S44, define the component-level frequency avoidance target as the modal frequency of the target mode of the fourth-level CAE model. Not lower than the stated frequency threshold.

9. The NVH graded control method for commercial vehicle steering systems according to claim 8, characterized in that, Step S43 specifically includes: S431, Extract all mode shapes calculated in step S42; S432, compare the modal shape with the mode shape of the target mode of interest identified in step S1; S433: The mode with the highest similarity to the target mode of interest is identified as the mode corresponding to it in the fourth-level CAE model, and the natural frequency value of the mode is read. This frequency value is the fourth-level CAE model modal frequency corresponding to the identified target mode of interest.

10. The NVH graded control method for a commercial vehicle steering system according to claim 9, characterized in that, Step S5 specifically includes: S51. For the production model, a fourth-level CAE model of its steering wheel unit is established, and after applying full constraints to its mounting point, constraint modal analysis is performed to obtain its modal frequencies. S52, compare and verify the modal frequencies obtained in S51 with the component-level frequency avoidance target; if the target is not met, analyze the strain energy distribution of the fourth-level CAE model, identify the steering wheel structure that is sensitive to the modality and optimize it; after updating the model, return to S51 until its modal frequencies meet the component-level frequency avoidance target; S53, based on the steering wheel design that meets the component-level frequency avoidance target, establishes a third-level CAE model of the vehicle to be produced, including the steering wheel and the column, and performs constrained modal analysis after applying full constraints at its mounting points to obtain its modal frequencies. S54, compare and verify the modal frequencies obtained in S53 with the second frequency avoidance sub-target; if the target is not met, analyze the strain energy distribution of the third-level CAE model, identify the modally sensitive structure and optimize it; after updating the model, return to S53 until its modal frequencies meet the second frequency avoidance sub-target; S55, based on the design of the steering wheel and column that meets the second frequency avoidance sub-objective, establishes a second-level CAE model of the vehicle to be produced, including the steering wheel, column and CCB crossbeam, and performs constrained modal analysis after applying full constraints at its mounting points to obtain its modal frequencies. S56, compare and verify the modal frequencies obtained in S55 with the first frequency avoidance sub-target; if the target is not met, analyze the strain energy distribution of the second-level CAE model, identify the modally sensitive structure and optimize it; after updating the model, return to S55 until its modal frequencies meet the first frequency avoidance sub-target; S57, based on the design of the steering system subsystem that meets the first frequency avoidance sub-objective, establish a first-level CAE model of the vehicle to be produced, including the interior and body, and perform free modal analysis to obtain the modal frequency of its steering system. S58. Compare and verify the modal frequencies obtained in S57 with the system-level frequency avoidance target. If the target is met, the design is complete. If the target is not met, return to the corresponding steps in S51 to S56 to iteratively optimize the components or subsystems of the steering system until the first-level CAE model of the vehicle to be produced meets the system-level frequency avoidance target.

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