Finite Element Analysis and Optimization of Steering Axle Structure for New Energy Vehicles

Abstract

As the core component of new energy vehicles, the performance of the steering axle will directly affect the overall maneuverability, stability, and safety of vehicle driving. The structural performance indexes of the steering axle of the pure electric vehicle are analyzed by the finite element method, and a reasonable improvement plan is given according to its shortcomings. Firstly, the 3D model of the steering axle is established by SolidWorks (SOLIDWORKS 2023), and the details are simplified appropriately and then imported into the ANSYS (ANSYS2020R2 software) platform for static force analysis and modal analysis. Then, the stress distribution, deformation, and the first six orders of intrinsic frequency values of the steering axle are calculated and analyzed by using four working conditions, such as regular driving, emergency braking, lateral slip, and uneven road excitation, and it is concluded that the maximum stress of the original structure under each working condition is less than the requirement of the ultimate stress value. However, from the results, the maximum stress value is concentrated in the emergency braking condition and appears in the intermediate beam corner and the steering knuckle journal, which is also the most dangerous condition. In the modal analysis, it is concluded that the intrinsic frequency of this symmetry structure is much larger than the excitation frequency, and it can produce better dynamic effects under the working conditions, and the dynamic performance is better. Based on this, combined with the results of the static analysis of the proposed new increase in the thickness of the intermediate beam to improve the structural strength of the improvement measures, for this symmetry structure, through the re-simulation of the effect of the most critical conditions (emergency braking), the maximum deformation of the steering axle has been greatly reduced. In addition, the overall stiffness of the symmetry structure has been greatly improved, while the maximum stress is still less than the value of the permissible stress range, and the modal characteristics of the structure has not been affected. The finite element analysis software can effectively evaluate the performance and improve the optimization of the steering axle, which has certain theoretical significance and engineering reference value.

1. Introduction

1.1. Background and Significance of the Study

1.1.1. Background

In view of the increasingly severe situation of global climate change and the increasing attention of the whole society to environmental protection, the development of new energy vehicles has gradually become an important path for the global automobile industry to change in a new direction. New energy vehicles have the advantages of zero emissions, low noise, energy saving, and environmental protection, which can provide effective solutions to reduce environmental pollution and improve energy composition [1]. In the rapid progress of new energy vehicles, the performance improvement of its key parts is also more and more obvious, in which the optimization of the steering axle structure of new energy vehicles is particularly important [2].

The steering axle is one of the indispensable parts of new energy vehicles. Its function is to convey the instructions from the driver, keep the vehicle moving in a straight line or change the driving direction correctly, and ensure that the vehicle moves smoothly and safely, and its advantages and disadvantages largely affect the stability of the vehicle’s maneuvering, smoothness, and the comfort of the passengers [3]. In order to improve the overall performance and competitiveness of new energy vehicles, it is of great practical significance to strengthen the finite element analysis and optimization of the steering axle symmetry structure of new energy vehicles.

1.1.2. Research Significance

In the comprehensive and in-depth optimization study of steering axles for new energy vehicles, finite element analysis occupies an absolutely critical position, with its unique advantages. Through the use of this analytical method, it is possible to carry out extremely accurate simulations of stress distribution and deformation of steering axles under a variety of complex conditions, with the aim of providing highly supportive data for the subsequent design and optimization of the symmetry structure. It is worth mentioning that many scholars and engineers from different fields have actively carried out many valuable explorations and practical researches on the finite element analysis of steering axles of new energy vehicles [4].

With the help of building a complete vehicle dynamics model, the research conducted in-depth analysis of various influencing factors on the ride comfort of new energy vehicles, and gave targeted optimization proposals. These research methods and results are also useful for the optimization of steering bridges for new energy vehicles. In addition, another study focuses on the development and application of finite element software for forklift steering axles, which confirms the reliability and practicability of the software with the help of example analysis, and provides a powerful tool for the finite element analysis of steering axles for new energy vehicles [5].

Optimization research of new energy vehicle steering axle is not only limited to finite element analysis, specifically in the process of practical application, but also needs to be combined with the actual application of the situation, and the selection of suitable materials. Meanwhile, the processing technology to determine, and to do a good job of cost control, and these elements need to be applied to the relevant fields of multi-disciplinary technical knowledge and theory in order to complete the optimization of new energy vehicle steering axle research.

In this study, finite element analysis and optimization of the steering axle structure of new energy vehicles is very necessary and has important theoretical significance and practical value. Only through in-depth analysis and practical application can we better promote the development of new energy vehicle industry and enhance the manufacturing level of new energy vehicles. In addition, it can also provide a solution for the optimization and development of the steering axle of new energy vehicles, and it is very valuable to use them in the rapid development of technology in the future. The definitions of terms used in the article are presentsd in

Table 1. Abbreviations table.

Abbreviation	Meaning
ANSYS	Finite element analysis software
ABAQUS	Finite element analysis software
ISO	International organization for standardization
PSD	Power spectral density
DOE	Design of experiments
FEA	Finite element analysis
NVR	Network video recorder
NVH	Noise, vibration, harshness

.

1.2. Domestic and International Research Status

1.2.1. Construction of Basic Fatigue Life Prediction Model

Based on multi-body dynamics simulation, the load time history of key components of the steering bridge (universal joint, axle housing, steering joint) under standard operating conditions (full load, braking, steering) is obtained, and the Rain flow Counting method is used to extract the load spectrum feature values. Based on the material S-N curve database of ANSYS and Code Design Life or ABAQUS FEA, establish a high cycle fatigue (10⁵–10⁷ cycles) life prediction model, with a focus on the cumulative damage factor (Miner’s Rule) in stress concentration areas such as universal joint spline roots and steering joint arm transition corners. It is necessary to specifically integrate the simulation of “long-term use conditions” emphasized in the document, and extend the static strength analysis to durability evaluation in the time dimension by introducing road roughness levels (ISO 8608 standard [6]) and vehicle mileage coefficients (recommended to be equivalent to 100,000 km/5 years). For example, when conducting modal superposition fatigue analysis on bridge shells, the power spectral density (PSD) function containing random vibration characteristics should be input, rather than the ultimate load under a single operating condition.

1.2.2. Fatigue Strength Correction for Multi-Environment Coupling

A three-factor cross-validation experiment for the “harsh environment” conditions proposed was designed with the following:

Temperature effect: Test the fatigue limit changes of 20CrMnTi carburizing steel at −40 °C (extremely cold), 25 °C (normal temperature), and 80 °C (high temperature), and establish a temperature correction coefficient matrix based on the Arrhenius equation;

Corrosion aging: After conducting a neutral salt spray test (500 h) on the steering knuckle, observe the accelerating effect of corrosion pits on fatigue crack initiation through scanning electron microscopy, and introduce a corrosion fatigue reduction factor (recommended to be 0.75–0.85);

Assembly pre tightening force: Using the Design of Experiments (DOE) method to analyze the nonlinear relationship between the pre tightening torque of wheel hub bearings (recommended 25–35 N · m) and the fatigue life of bolt connections, in order to avoid micro-motion wear fatigue caused by over constraint.

1.2.3. Linkage Between Fatigue Optimization and Maintenance Strategies

The fatigue analysis results were directly converted into design improvement solutions as follows:

Structural optimization: Topology optimization reconstruction is adopted for areas with a lifespan lower than the target value (recommended ≥150,000 km), such as replacing the traditional solid steering knuckle arm with a biomimetic hollow structure, which can reduce weight by 12% and increase the fatigue life of dangerous points by 1.8 times.

Maintenance cycle definition: Based on the damage tolerance theory, a two-level warning threshold is set: when the accumulated damage reaches 0.3, the first endoscopic detection is triggered, and when it reaches 0.7, it is forcibly replaced (corresponding to the “reasonable maintenance and replacement cycle” required in the document).

The finite element analysis and optimization exploration of a new energy vehicle steering axle structure has aroused great concern and interest at home and abroad. By carrying out in-depth research and optimization of universal joints, bridge shells, steering knuckles, and other important components of the steering axle structure, the overall performance of the steering axle can be improved in a truly meaningful way to enhance the maneuverability, stability, and safety of the steering axle structure of the new energy vehicle. With the continuous progress and improvement of finite element analysis technology, coupled with the use of new materials and new technologies, the steering axle structure of new energy vehicles will be continuously improved and optimized, and its performance indexes will be even better.

1.2.4. Current Status of Foreign Research

Many famous foreign automobile companies and scientific research units have long used the finite element analysis method to decompose and observe the internal structure of the steering bridge in a thoughtful way. For example, there has been a case of steering drive axle ball cage universal joints as an experimental object. By establishing a reasonable model and detailed analysis results to explore the stress distribution and deformation state of the universal joint under complex loads, corresponding data support are provided for the optimization of the structure [7]. There is also some research focus on the tractor steering axle for vibration mechanics analysis and structural optimization, the use of the finite element method of the axle shell [8]. The vibration characteristics of the steering knuckle were analyzed in detail using the finite element method, and targeted measures were proposed to improve the service life and reliability of the steering axle.

Foreign scholars and others have designed and analyzed the steering axle of heavy commercial vehicles, applying torque to the wheels, in addition to maintaining the position of the wheels relative to each alternative and the body. The axle in the analysis has to carry the additional loads of the extra vehicle and the loaded items. The steering axle is one of the important components of the vehicle, involving the steering assembly, which occupies 35%–~40% of the total weight of the vehicle, from which it can be concluded that the structure of the steering axle plays an important role in influencing the driving performance of the vehicle. This study carries out a design study on the steering axle of a light minivan. In this study, it is mainly divided into two steps, one is to use the analytical method for modeling, and the second is to find the stresses and deformation in the axle [9]; foreign scholars K. Padma Raju used cast iron material model of the front axle of the heavy-duty truck, the literature points out that the cast iron material for the highway automotive market for the lightweight adaptation, but also to meet with the value of having the fuel economy of the effective vehicle needs.

1.2.5. Current Status of Domestic Research

Along with the rapid development of the domestic new energy automobile industry, the finite element analysis and optimization of the steering axle structure is also progressing, and many schools and research units have carried out in-depth research on it. For example, some literature has carried out relevant work on the steering knuckle arm using the finite element method, and some corresponding optimization methods have been proposed by the problem of insufficient loading capacity of the steering knuckle arm; i.e., changing the steering knuckle housing into a functional component that can act as a steering knuckle arm, and this can be used as the steering knuckle arm. This can simplify the steering device, make the force more uniform, and save the cost at the same time. Practice shows that this improvement measure fully meets the design requirements and improves the performance of the steering axle [10]. Researchers, used strength analysis and fatigue life evaluation of the front axle based on the finite element simulation technology to identify the key dangerous parts of the axle for the future structural optimization design to lay the foundation. In the process of adopting the new idea of multi-case joint fatigue simulation, the front axle of three typical conditions as the object of the simulation and the comprehensive consideration of the different operating parameters was used to obtain the fatigue characteristics of the front axle and the axle service life. The fatigue characteristics of the front axle [11] and the service life of the axle are obtained by considering different working condition parameters [12].

The finite element analysis and optimization of the steering axle structure of new energy vehicles in China have gained great results, but compared with foreign countries, there is still a certain degree of gap. This gap centers on the depth, breadth, and innovation of the research. Therefore, it is necessary for domestic scholars and research institutions to further strengthen the communication and collaboration with international personnel in the same field, to learn from cutting-edge research ideas and methods, and to continuously improve their own research standards. At the same time, attention should also be paid to the application of theoretical research results to actual production activities, with the help of practice to verify the accuracy and effectiveness of the theory, in order to promote the continuous development of the new energy automobile industry [13].

1.3. Research Content

The steering axle is an important part of the automobile under driving conditions, and its performance plays a decisive role in the driving quality of the whole vehicle. This part is rigidly connected to the frame with the help of the suspension system, and it has to withstand a variety of complex loads during the operation of the vehicle. There are the vertical dynamic loads caused by the unevenness of the road surface, and there are also the longitudinal braking forces generated by the braking conditions and the transverse forces under the side-slip conditions. Many experimental data and theoretical studies show that the loads borne by the steering axle during actual driving have multi-dimensional and dynamic characteristics. Since it is the weak part of the vehicle structure, the systematic research on the strength characteristics, stiffness, and structural stability of the steering axle has a key value in engineering practice.

The core content of this study is as follows: firstly, a finite element simulation model is constructed on the ANSYS platform, and the load boundary conditions are set for the steer axle under different constraints in four typical driving conditions. After, strength analysis and modal analysis, and then combined with the visual display of the simulation results, the optimal material selection scheme of the steer axle is determined to provide theoretical support for the optimal design of the structure. Then, in the simulation analysis, the structural stability of the 3D model is examined. In the simulation analysis, we focus on examining the structural rationality of the 3D model and paying attention to the influence of material characteristics and parts layout on stress distribution. Specifically, based on the demand for vibration damping performance and ductility, we select low-alloy high-strength structural steel with a yield strength of 420 MPa as the base material. Then, with the help of the stress cloud analysis technology, we systematically assess the phenomenon of stress concentration, find out the potentially dangerous cross-section, and the risk of overload failure, and comprehensively examine the characteristics of the deformation and stress distribution of the structure. The deformation and stress distribution characteristics of the structure are comprehensively examined [14].

2. Theoretical Foundation and Modeling, Static Analysis of Steering Axle for New Energy Vehicles

2.1. Basic Composition of Axle

The axle is a component that connects the wheels at both ends of the vehicle and is connected to the frame with the suspension as an intermediary. The vertical load and other loads on the frame are also transmitted to the wheels at both ends through the axle, and the various forces received on the wheels (rolling resistance, braking force, and lateral force, etc.) are also transmitted to the frame through the axle in the form of loads and torque and bending moments [15]. This shows that the axles play a role in transferring loads, bending moments and torques to each other in the traveling condition of the car.

The front axle is the most important component of the steering axle and is most commonly made of steel through die forging and heat treatment, which has excellent mechanical properties. It has a dotted cross-section, through holes at both ends of the axle and a thickened portion at both ends of the axle to provide good tensile strength. The center section is concave, forming a groove-like portion, which is designed to lower the center of mass of the vehicle. This achieves a 35%–~40% body weight capacity, and the entire center section of the axle is lowered in order to prevent interference due to the position of the front compartment. This also provides greater stability and safety by lowering the center of gravity of the road vehicle at high speeds [16].

The steering knuckle is the part that turns the wheels and is a forked piece. The steering knuckle connects the upper pin hole and the steering axle through the main pin, which in turn causes the steering knuckle to be angularly offset, allowing the car to produce good steering. In order to avoid collision between the tires and the steering longitudinal tie rod and other components during steering, the maximum steering angle of the steering wheel is determined by the steering limiting bolt screwed into the knuckle flange together with the front axle [17].

The steering knuckle thrust bearing not only carries the gravity of the body, but also bears the task of steering the front wheel smoothly. With the continuous progress and development of science and technology and industrial level, based on the driving condition of the car on different road surfaces, the impact loads are different, and the loads of each role are acted on the bearings. Therefore, the bearings are also gradually improving the requirements, and the enterprises are also pursuing the bearings with good rated static load capacity.

The steering knuckle main pin in the driving process load is huge, so in the design to ensure that it has good mechanical properties, this requires the surface to be hard and the axis to be tough. As such, the industrial main pin is mostly used in the manufacture of 20Cr, by nitriding treatment, with good mechanical properties [18].

2.2. Basic Parameters, Material Parameters, Structural Characteristics, and Modeling of the Axle

The steering axle is located in the front of the car, bearing about half of the load of the body, so it is also called the front axle. The steering axle transmits the load carried by the frame to the front wheels, so that the steering knuckle of the front wheels deflects the angle to realize the steering function of the car. The steering axle is subject to vertical and longitudinal loads under uneven road conditions, lateral forces under skidding conditions, and braking forces and moments under braking conditions.

According to its structural condition, the steering axle can be divided into two types of steering axles: integral type and disconnected type. A disconnected steering axle is mainly composed of steering knuckle, cantilever assembly, steering arm, trapezoidal arm, longitudinal tie rod, and other parts of the common composition. It is connected with the frame with the help of independent suspension; while the integral steering axle is composed of steering knuckles, brake drums, wheel hubs, and the direct push bearings of these parts of the combination of the non-independent suspension, the frame is connected, usually more often used in the field of trucks to bear the larger loads. The steering axle is usually used in the field of trucks, which are subject to large loads. In general, the structural characteristics of automotive steering axles are characterized by compactness, adjustability, and the use of self-suspension front axles. In view of these characteristics, in the design and manufacturing process, it is necessary to implement meticulous control and optimization to ensure that the steering axle can have stable and reliable performance and good driving performance [19].

SolidWorks modeling software is used to build the bridge shell model, which has powerful three-dimensional and two-dimensional modeling capabilities, as well as can easily and accurately establish complex geometric models. It can meet the accuracy requirements of the characteristics of a short period of time to quickly draw a three-dimensional model to meet the needs of the project and quickly modify or optimize the model. It is also conducive to the use of the work in the future [20]. In addition, it is easy to realize the seamless integration with simulation and analysis software such as stress analysis and fluid dynamics analysis. Therefore, SolidWorks is widely used in various industries such as aviation, aerospace, marine, automotive, electromechanical equipment, and other industries in the modeling of mechanical products, has great advantages.

The previous section describes the basic composition of the axle and structural characteristics of a full understanding of the use of SolidWorks software for 3D modeling of the axle system. First of all, according to the structural composition of the axle for the three-dimensional modeling of the components, modeling process with reference to the standard dimensions, tolerance requirements and engineering design specifications are required to ensure that the model has a high degree of engineering authenticity and assembly reasonableness.

According to the structural characteristics of the steering axle, in order to improve the efficiency of the finite element simulation when carrying out finite element modeling, it is necessary to carry out a reasonable simplification of the model. This simplification should ensure that it will not have an impact on the mechanical properties of the components and the dynamic characteristics, such as rounded corners, non-essential holes, transverse tie rods and tire hubs, and other non-critical components, as well as the removal of the peripheral components that do not have an effect or have a very small effect on the final model. The solid finite element model of the steering axle is established, and its solid model is shown in Figure 1.

The steering axle is also a part of the car. The structural performance of the axle directly affects the stability of the car handling and load capacity; in order to accurately do the finite element analysis of the performance of the axle, it is necessary to know the key geometric dimensions of the steering axle as well as the design load. The steering axle has the following roles: one is to support the frame and bear the vertical load from the frame; the second is to transfer the braking force and lateral force from the left and right half-shafts to the frame; and the third is to enable the car to realize the steering. Since the steering axle is generally on the front axle of the vehicle, the geometry of the steering axle mainly depends on the degree of steering flexibility, driving stability, and the center of gravity of the vehicle. The steering axle parameters in the following section are shown in

Table 2. Material properties of automobile axle.

Vehicle Weight kg	Wheelbase m	Distance from Front Axle to Center of Gravity m	Distance from Rear Axle to Center of Gravity m	Height of Center of Gravity
1600	2.7	1.3	1.4	0.5

.

In this study, low alloy high strength structural steel with a yield strength of 420 MPa is selected as the material for finite element simulation analysis of the steering axle, which has high strength, excellent fatigue resistance, good toughness, wear resistance, and corrosion resistance. It is widely used in the field of mechanical components, and it can obtain more excellent comprehensive mechanical properties after heat treatment. Material parameters are shown in

Table 3. Material properties of automobile axle.

Material	Density (kg/m3)	Young’s Modulus (MPa)	Poisson’s Ratio	Yield Strength (MPa)
Alloy structural steel	7900	2.1 × 105	0.3	420

. A comparative analysis of different materials is presented in

Table 4. Comparative analysis of different materials.

Evaluation Dimension	Existing 420 MPa Low Alloy Steel	700 MPa Grade Ultra-High Strength Steel	SiC/Al Composites
Yield strength (MPa)	420	700	550
Density (kg/m3)	7900	7850	2800
Fatigue life (10 10 times)	180	240	160
Cost index (steel = 1)	1.0	1.5	3.5
Applicable scenarios	Conventional load vehicle type	Heavy duty new energy commercial vehicles	Lightweight oriented passenger car

.

2.3. Application of Finite Element Analysis in Steering Axle Structure

The core gap between domestic and foreign research is reflected in three levels of research depth is as follows:

Basic theory: The research on micro-damage mechanism of materials is insufficient in China, and the correlation model between crystal defect evolution and macro-fatigue performance has been established in the world; Technical method level: The linear finite element assumption is mostly adopted in China, and the international mainstream software has integrated geometric nonlinearity and contact nonlinearity algorithms; Engineering application layer: Domestic verification mostly relies on bench test, while international verification realizes the digital thread integration of virtual test and physical test.

This study intends to achieve a breakthrough in two aspects: one is the data dimension, which integrates the 500,000 km real vehicle load data of 10 main engine factories in China for the first time, and constructs a load spectrum database in line with the characteristics of Chinese roads; the other is the method dimension. This innovatively introduces the multi-physical field analysis of temperature–load coupling, and revises the assumption of constant material parameters in traditional simulation. This research path of “based on Chinese data and integrating international methods” can not only make up for the “lack of research depth and breadth” pointed out, but also avoid the problem of blindly copying foreign models.

Through quantitative comparison (such as stress concentration factor, cost reduction, and other specific data) and methodology traceability (evolution logic from single-point optimization to system modeling), the previous research comparison is more three-dimensional.

Finite element analysis is applied in the design and optimization of steering axle structure of new energy vehicles. The use of the finite element analysis method for new energy vehicle steering axle structure mechanical analysis research can effectively grasp the new energy vehicle steering axle structure in the complex working conditions, the force distribution law, deformation and fatigue life, and other relevant parameter information, for the optimization of the design of the structure to provide an effective reference basis.

In the design process of new energy vehicle steering axle structure, with the help of finite element analysis, it can be realized to simulate and analyze the force of the structure under various working conditions and loading conditions, and put forward the problems of defects and hidden dangers in the design process in a timely manner. Through the continuous debugging and improvement of structural dimensions and material selection, researchers can solve problems such as failures and defects in advance, which is also conducive to reducing the cost of improving or repairing the steering axle structure at a later stage [21].

When optimizing the steering axle structure, finite element analysis can also be used. After the finite element analysis of the existing structure, the analysis can be used to find out the stress concentration area and deformation of the structure, and then optimize the structure according to the actual situation. Specifically, including changing the original shape, adding reinforcement, adjusting the connection method to improve the structure’s strength, stiffness and fatigue life and other key performance [22].

Finite element analysis can be used to realize the reliability and durability of the steering axle structure of new energy vehicles, through the establishment of models for different working conditions and harsh environments, to study the working status of the steering axle structure under long-term use. This provides new energy vehicles with a reference basis for designing a reasonable maintenance and replacement cycle.

Finite element analysis (FEA) plays a great role in the structural design and optimization of steering axles for new energy vehicles, as well as in reliability evaluation. As the finite element analysis technology is constantly improving and developing, it is believed that more and more new energy enterprises will be able to use the finite element analysis technology for their own products in the future, which will help to promote the development of China’s new energy automobile industry.

2.4. Finite Element Model Meshing

In the process of finite element analysis, meshing is a very critical pre-processing step, the quality of which has a direct impact on the accuracy of the results of static analysis. In this study, the pre-processing model is imported into the ANSYS software platform, for large and complex structural systems, the use of scientific and reasonable mesh delineation strategy can improve the computational efficiency, but also for the subsequent numerical simulation to provide a reliable basis for the analysis of the results of a more visualized effect. The default cell size is set to 7 mm during meshing, and adopts an automatic method for preliminary mesh generation of the overall structure to ensure the continuity of the mesh division of each part as well as the computational efficiency. A 5 mm geometry adjustment is set for the fixed pin and spacer, which are small-sized parts in the steering axle model, and a 3 mm geometry control is set for the link pin. Mesh encryption is used for the shutdown components to better capture the detailed features in the localized stress concentration areas. The cell statistics of the steering axle finite element model after mesh discretization shows that the model contains 401,388 nodes and 252,009 cells, as shown in Figure 2. The overall quality of the mesh is good, which meets the accuracy and stability requirements of the subsequent static analysis [23].

2.5. Static Working Condition Analysis

According to vehicle dynamics, the load analysis of the steering axle is divided into four typical working conditions: emergency braking, lateral slip, uneven road surface excitation, and regular driving conditions. From the static point of view, the load distribution of the steering axle can be divided into three categories according to the direction of the action: vertical load, transverse load, and longitudinal load, and the dynamics analysis shows that there are differences in the characteristics of the load under different driving conditions; only the vertical load is borne in regular driving, and only the vertical load is borne in emergency braking. Only the vertical load is borne, the emergency braking condition presents the vertical and longitudinal composite load characteristics, the sideslip condition shows the superposition of vertical and transverse loads, and when the vehicle is on the uneven road surface, it only generates the dynamic load effect in the vertical direction [24].

Under normal driving conditions, the steering axle mainly bears the vertical static load transmitted by the vehicle body through the suspension system. At this time, there is no significant longitudinal or lateral force involved, belonging to the most basic type of working conditions.

The formula for calculating the load under normal driving conditions is shown in (1):

$$F_z={\displaystyle \frac{m\cdot g\cdot L_1}{L}}$$

(1)

where m vehicle weight (unit: kg), g gravity acceleration, L 1 front axle to the center of gravity distance, and L wheelbase (unit: m).

Setting load constraints: for the movement of the X, Y, Z direction of the support position of the wheel hub of the bearing link at both ends of the steering axle, the fixed support is simulated so that the end point cannot be shifted and turned to.

Setting the loading load: after bringing the parameters into the formula calculation, it is learned that in this particular case, a force of 8139 N vertically downward is to be applied in the positive direction of the Y-axis of the suspension support seat. This is shown in Figure 3.

With the help of finite element analysis of the equivalent stress distribution of the steering bridge results can be illustrated, the extreme value of the structural stress appeared in the steering bridge at the corner of the region, the specific number of 17.05 MPa, significantly lower than the threshold value of the yield strength of the material. This is completely in line with the requirements of the structural strength design specification. The results of the displacement analysis show that the maximum deformation of the steering bridge reached 0.1 mm, the deformation is in the range of the engineering license. This deformation is within the permissible range of the project, as shown in Figure 4.

When the vehicle is under emergency braking, the body is tilted forward and the center of gravity is shifted forward, resulting in an increase in the vertical load on the front axle. At the same time, there is a significant longitudinal inertia force, and the steering axle is subjected to the composite effect of vertical load and longitudinal braking force at the same time [25].

Emergency braking condition vertical load calculation, the formula is shown in (2):

$$F_z^{\prime }=F_Z+{\displaystyle \frac{G\cdot h\cdot a}{g\cdot L}}$$

(2)

Calculation of longitudinal load under emergency braking condition, the formula is shown in (3):

$$F_X=m\cdot a\cdot \frac{L_2}{L}$$

(3)

where h is the height of the center of gravity (unit: m), a is the acceleration of the vehicle (unit: 8 m/s²), and L(2) the distance from the rear axle to the center of gravity (unit: m).

Setting load constraints: for the movement of the X, Y, Z direction of the support position of the wheel hub of the bearing link at both ends of the steering axle, simulate the fixed support, so that the end point can not be shifted and turned to.

Setting the loading load: after bringing the parameters into the formula calculation, it is learned that in this particular case, a force of 10,509 N vertically downward is to be applied in the positive Y-axis direction of the suspension support seat and a force of 6636.92 N in the positive Z-axis direction is to be applied at the suspension support location. This is shown in Figure 5.

The stress distribution cloud diagram and displacement distribution cloud diagram of the steering axle under emergency braking are shown in Figure 6. From the equivalent stress map, the maximum stress is 69.4 MPa, the maximum stress occurs at the steering knuckle journal, the stress is much less than the yield limit of the material, which meets the strength requirements. The maximum displacement of the steering axle is 0.53 mm as shown in Figure 6.

When the vehicle undergoes a sharp turn or side slip, a significant lateral load is generated on the steering axle, while there is still a vertical static load on the body. The steering axle force under such conditions is the superposition of vertical load and lateral centrifugal force.

Lateral slip condition vertical load calculation, the formula is shown in (4):

$$F_Z={\displaystyle \frac{m\cdot g\cdot L_1}{L}}$$

(4)

Lateral load calculation for lateral slip condition, the formula is shown in (5):

$$F_y={\displaystyle \frac{m\cdot v^2\cdot h}{R\cdot L}}$$

(5)

where v is the vehicle speed (take 16.67 m/s), and R is the turning radius (take 25 m).

Setting load constraints: for the movement of the X, Y, Z direction of the support position of the wheel hub of the bearing link at both ends of the steering axle, simulate the fixed support, so that the end point cannot be shifted [26].

Setting the loading load: after bringing the parameters into the formula calculation, it is learned that in this particular working condition, a force of 7557 N vertically downward is to be applied in the Y-axis positive direction of the suspension support seat and a force of 9221.7 N in the X-axis positive direction is to be applied at the suspension support location as shown in Figure 7.

As shown in the stress cloud analysis, the maximum equivalent stress value of the steering axle in the side-slip condition is 26.27 MPa. This stress concentration area mainly appears in the journal part, and its cause can be attributed to the composite lateral force and torque produced in the process of side-slip. This is lower than the yield strength of the material, which can fit the requirements of the design of the structural strength, and the results of the displacement analysis show that the maximum deformation of the steering axle is only 0.5 mm, and the maximum deformation of the steering axle is only 0.5 mm. The result of displacement analysis shows that the maximum deformation of the steering axle is only 0.09 mm, which verifies its structural reliability. The displacement distribution of the steering axle under side-slip condition is shown in Figure 8.

When the vehicle is driving on an unpaved road or undulating road, the tires and the ground produce periodic contact impacts, and the steering axle is mainly subjected to changing vertical dynamic loads. This kind of load fluctuates frequently, which is easy to cause fatigue damage.

Uneven road surface excitation load calculation formula, the formula is shown in (6):

$$F_b=m\cdot k\cdot {\omega }^2\cdot h_1+F_Z$$

(6)

where k for the road surface excitation coefficient (take 0.3), $\omega$ road surface excitation angular frequency (take 12.57 rad/s), and h 1road surface undulation height (take 0.02 m).

Setting load constraints: for the movement of the X, Y, Z direction of the hub support position of the bearing links at both ends of the steering axle, simulate the fixed support, so that the end point cannot be shifted.

Setting the loading load: after bringing the parameters into the calculation of Equation (6), it is learned that in this particular case, a force of 9654.2 N vertically downward is to be applied in the positive direction of the Y-axis of the suspension support seat, as shown in Figure 9.

From Figure 10, the stress distribution of the steering axle under the uneven road condition can be seen. From the equivalent stress cloud diagram, the maximum stress is 20.13 MPa which is less than the yield limit of the material, and meets the design requirements of the structural strength; from the displacement cloud diagram, the maximum deformation of the steering axle is 0.11 mm, which can meet the use of the stiffness requirements. From the displacement map, it can also be seen that the steering axle does not have excessive deformation in the working condition, which shows that the steering axle has good rigidity.

With the help of ANSYS software to conduct simulation analysis of the four conditions, the results show that in the emergency braking conditions under the structure response, the maximum stress value is 69.4 MPa, and the maximum deformation is 0.53 mm. Due to the vehicle in the emergency braking process, the vehicle body tilted forward and the center of gravity shifted forward, resulting in the front axle needing to withstand the vertical load at the same time and significant longitudinal braking force, causing the formation of a composite effect of the bending and torsion of coupled stress state. This mechanical characteristic triggers the stress concentration in the local area of the steering axle, which reduces the overall safety margin and poses a certain structural risk. Although the maximum stress value has not yet exceeded the yield strength of the material, which meets the current use requirements, it is still necessary to optimize the design of the structure in consideration of the extreme load superposition that may exist under actual road conditions.

3. Modal Analysis of New Energy Vehicle Steering Axle

3.1. Theory of Modal Analysis

Modal analysis as a coordinate transformation method. Its core function is to transform the response vectors described in the physical coordinate system to the modal coordinate system, which is a new reference system. It should be noted that the solid model and finite element analysis used in this analysis method are exactly the same as those used in the modal analysis of steering bridges, because only the intrinsic frequency and vibration characteristics need to be obtained and these parameters have no relationship with external loads and do not need to be applied to the steering bridge. There is no relationship between these parameters and the external loads and no external loading conditions need to be imposed. Considering that the effect of structural damping on the results of intrinsic frequency calculation can be ignored, only the undamped free vibration equations need to be established in the solution process to complete the analysis [27].

3.2. Modal Analysis Working Condition

When the modal analysis of a steered axle is carried out, the imposition of constraints can help to obtain more accurate results of the dynamic characteristics of the working conditions. However, the loads and constraints of the steered axle in the actual working conditions have a high degree of complexity, and the imposition of constraints when the boundary conditions are not clear may lead to pathological problems in the stiffness matrix, which will reduce the accuracy of the modal analysis results. Considering these factors, this study finally adopts the free modal analysis method to carry out the modal characterization of the steered bridge.

3.3. Analysis of Modal Calculation Results

When carrying out modal analysis, the modal order is set to sixth-order in the modal analysis parameter setting interface, which is mainly based on the following considerations: the low-order intrinsic frequency of the mechanical system is generally characterized by lower values, and this kind of frequency component has a greater impact on the system vibration characteristics. Its frequency range and the intrinsic frequency interval of human tissues have a relatively large overlap. Therefore, in the modal analysis, only the first six orders of intrinsic frequencies and their corresponding vibration patterns can be extracted to meet the engineering needs. In the finite element analysis and optimization of the steering axle structure of new energy vehicles, the core purpose of analyzing the first six modes is to systematically evaluate the dynamic characteristics of the structure and avoid potential risks.

The steering axle equipped with new energy vehicles will inevitably be subjected to high-frequency excitation from the motor in the process of actual operation, the influence of transmission system vibration and random loads on the road surface, etc. If its own intrinsic frequency coincides with the frequency of external excitation, it is very likely to cause resonance phenomenon, which may lead to structural fatigue or NVR of the steering axle. This phenomenon may cause structural fatigue of the steering axle or deteriorate the NVH performance of the vehicle; with the help of the extraction of the first six modes, it is possible to effectively identify the resonance risk interval, such as the interaction between the operating frequency of the electric motor in the operating state and the low-order modes. It is also important to identify the modes that exhibit various vibration patterns such as overall bending, local torsion, or joint vibration, which reflect the dynamic weaknesses of the structure in a more direct way, such as one of the modes, which corresponds to the stiffness of the steering axle as a whole, and the other modes, which are from the first to the sixth-order. However, the other first to sixth-order modes will most likely expose the problems of local vibration in the battery pack mounting area or suspension pivot points, and ultimately these reflections and exposures provide the basis for subsequent optimization design work such as topology weight reduction or reinforcement arrangement. In addition, the load distribution of the steering axle in new energy vehicles is significantly different from that of conventional vehicles due to the centralized distribution of the battery pack mass and the high torque characteristics of the motor, and the first six orders of modal analysis can verify whether it is adapted to such special working conditions. From the perspective of computational efficiency, the low-frequency modes have a greater impact on the actual working conditions, and the higher-order modes have a faster energy decay and high analysis cost, so the selection of the sixth-order is the result of a balance between engineering experience and computational resources. Finally, the analysis results lay the foundation for the subsequent harmonic response, random vibration, and fatigue life prediction, to ensure that the optimized steer axle achieves the comprehensive optimum between light weight, strength, and dynamic stability. The results of the first six orders of modal analysis of the steer axle are shown in Figure 11.

The results of the modal analysis show that in the absence of constraints and under zero load condition, the steered axle system exhibits sixth-order intrinsic vibration with modal frequencies of 134.25 Hz, 285.69 Hz, 315.5 Hz, 324.161 Hz, 454.08 Hz, and 528.86 Hz, respectively. In the field of structural dynamics, rigid-body modes as a key concept to describe the free vibration of a system without deformation, are characterized by the synchronous movement of the various components of the system, and have the same frequency and vibration pattern. The theory has a key role in guiding the design of the stability of engineering structures and vibration response prediction. The steering bridge second-order and second-order and higher modal frequencies exceed 100 Hz, of which first-order modes are more than 100 Hz. The second-order and higher modal frequencies of the steering bridge exceed 100 Hz, and the minimum intrinsic frequency of the first-order modes reaches 134.76 Hz, which indicates that the structure has high dynamic stiffness characteristics.

According to the data obtained from the vehicle dynamics study, in typical driving conditions, the vertical excitation frequency of the road surface shows a multi-band distribution: the excitation frequency of the smooth road surface is concentrated around 3 Hz, the excitation frequency of the ordinary road surface is about 11 Hz, the excitation frequency of the rugged road surface can be up to 20 Hz, the frequency of the excitation triggered by the unbalance of the wheels is in the range of 11 Hz, and the intrinsic frequency of the frame structure is also in the range of 11 Hz, which shows that the structure has high dynamic stiffness characteristics. Based on the above vibration characteristic analysis, the steering axle structure design needs to focus on avoiding the resonance risk of the human body and the vehicle system. With the help of optimizing the vibration damping system parameter configurations to reach the vibration isolation of the human body’s sensitive frequency bands, the results of the modal analysis show that the steering axle’s first six orders of intrinsic frequency is significantly higher than the human body’s sensitive frequency range and the typical roadway excitation spectra, and the structural design can effectively avoid vibration with human body parts. This structural design can effectively avoid resonance with various parts of the human body, and guarantee the smoothness of driving and the comfort of riding [28,29].

4. Optimization and Analysis of Steering Axle for New Energy Vehicles

4.1. Optimization Programming

According to the finite element simulation analysis of the steering axle under four typical working conditions, it can be seen that the greatest structural stress is caused by the emergency braking condition, which produces the greatest deformation and, therefore, has the greatest impact on the safety of the vehicle driving. The results of the modal analysis show that the intrinsic frequency of the structure under the low-order modes is within a reasonable range, and there is no risk of resonance, which indicates that the dynamic stability of the whole structure is good. The simulation analysis shows that the maximum stress and deformation are concentrated in the middle beam area of the steering bridge, mainly due to the insufficient strength and stiffness of the middle beam, for which the optimization measure of thickening the wall thickness of the middle beam is proposed to improve the load capacity of the middle beam as well as the safety margin of the overall structure, i.e., to increase the thickness of the wall of the middle beam by 3 mm on the basis of the original structure to improve the bending and torsion stiffness of the middle beam of the steering bridge and reduce the concentration of stress. After formulating the optimization scheme, the optimized steered axle structure is subjected to finite element analysis under the same boundary conditions and loads, and the results are compared with the original structure to examine the structural performance improvement of the optimized structure compared with the original structure, so as to check the effectiveness of the optimization measures.

4.2. Post-Optimization Simulation

Using the same loads and boundary conditions as those before optimization, the optimized steer axle model is subjected to static analysis to evaluate its mechanical properties under typical working conditions. The focus of the analysis includes stress distribution, displacement change, and safety factor, especially focusing on the performance in the high load region [30].

4.2.1. Static Analysis

From the equivalent stress distribution of the finite element analysis of the steering bridge after optimization in Figure 12, it can be seen that the maximum value of the structural stress occurs in the area at the corner of the steering bridge, i.e., 15.93 MPa, which is smaller than the limit value of the yield strength of the material, and it is within the design specification of structural strength. From the results of displacement analysis, the maximum displacement of the steering bridge is 0.08 mm, which is within the engineering range.

The stress distribution cloud diagram of the optimized steering axle under emergency braking is shown in Figure 13. From the equivalent stress map, the maximum stress is 70.021 MPa, the maximum stress occurs at the steering knuckle journal, the stress is far less than the yield limit of the material, which meets the strength requirements. The maximum displacement of the steering axle is 0.42 mm, which is within the permissible range. The displacement distribution cloud diagram under emergency braking condition is shown in Figure 13.

As shown in Figure 14, the stress cloud analysis shows that the maximum equivalent stress value of the optimized steering axle under the lateral slip condition is 21.48 MPa, and this stress concentration area mainly appears in the journal part. This can be attributed to the composite lateral force and torque produced in the process of the lateral slip, and the stress value is lower than the yield strength of the material, which can meet the requirements of the design of structural strength, and the results of the displacement analysis show that the maximum deformation of the steering axle is 21.48 MPa. The result of displacement analysis shows that the maximum deformation of the steering axle is only 0.08 mm, which verifies its structural reliability. The displacement distribution of the steering axle under side-slip condition is shown in Figure 14.

Figure 15 presents the stress distribution of the optimized steering axle under uneven road conditions. The equivalent stress analysis shows that the maximum stress value is 18.3 MPa, which is lower than the yield limit of the material and conforms to the design standard of structural strength, and the displacement cloud analysis shows that the maximum deformation of the steering axle is 0.1 mm, which verifies that its stiffness performance meets the usage requirements. The displacement distribution through the uneven road conditions is shown in Figure 15.

4.2.2. Modal Analysis

The results of the first six-order modal analysis of the optimized model show that in the absence of constraints and at zero load, the steered axle system exhibits sixth-order intrinsic vibration characteristics with modal frequencies of 133.78 Hz, 288.5 Hz, 315.58 Hz, 355.511 Hz, 438.42 Hz, and 550.42 Hz, respectively. From the results of the first six levels of modal analysis, it can be seen that the frequency changes before and after optimization are minimal. In the field of structural dynamics, the rigid body modes as a key concept to describe the free vibration of the system without deformation, which is characterized by the various components of the system to maintain synchronous motion and have the same frequency and vibration pattern. The theory has a key role in guiding the design of the stability of the engineering structure and the prediction of the vibration response. The steering bridge of the second-order and the second-order and above the modal frequency exceeds 100 Hz, of which the first-order modal frequency is 438 Hz and 550.22 Hz. The second-order and higher modal frequencies of the steering bridge exceed 100 Hz, and the minimum intrinsic frequency of the first-order modes reaches 134.76 Hz, which indicates that the structure has high dynamic stiffness characteristics.

The results of the first six-order modal analysis of the optimized model in Figure 16 indicate that the structure has high dynamic stiffness characteristics. The finite element analysis results of the steering axle structure of the new energy vehicle show that there are certain problems of large deformation under extreme working conditions such as emergency braking. In order to address these weaknesses, this study proposes an optimization scheme with the wall thickness of the intermediate beam thickened by 3 mm as the core, and uses ANSYS to carry out static and modal analysis of the model before and after optimization under the same boundary conditions and load conditions. Comparison of the analysis results in

Table 5. Comparison of finite element analysis results before and after optimization.

Working Condition Type	Comparison Item	Before Optimization	After Optimization	Trend	Percentage
Regular driving	Maximum stress	17.05 MPa	15.93 MPa	Reduction	6.6%
	Maximum displacement	0.10 mm	0.08 mm	Reduction	20% reduction
Emergency braking	Maximum stress	69.40 MPa	70.02 MPa	Increase	0.9% increase
	Maximum displacement	0.53 mm	0.42 mm	Decrease	20.8% lateral slip
Lateral slip	Maximum stress	26.27 MPa	21.48 MPa	Reduction	18.2% of
	Maximum displacement	0.09 mm	0.08 mm	Reduction	11.1%
Pavement excitation	Maximum stress	20.13 MPa	18.30 MPa	Decrease	9.1%
	Maximum displacement	0.11 mm	0.10 mm	Decrease	9.1% of the maximum displacement
Modal frequency	First-order frequency	134.25 Hz	133.78 Hz	Decrease	0.4%
	Second-order frequency	528.86 Hz	550.22 Hz	Increase	4% increase

shows that the optimized structure has lower stress levels, reduced deformation, and enhanced structural stiffness under most working conditions. Moreover, the frequency change of the modal analysis is small, which does not have a negative impact on the dynamic performance and still effectively avoids the risk of resonance. Therefore, the optimized steering axle improves the safety margin of the structure on the basis of meeting the requirements of strength and stiffness, and has better engineering application value. There are certain contribution results in the development history of new energy vehicles. In the context of the rapid development of new energy vehicle technology, the optimization and innovation of the steering axle structure not only provides key support for the improvement of vehicle performance, but also lays a solid foundation for the subsequent lightweight design, application of new materials, and other cutting-edge research.

5. Comparative Analyses with Relevant Studies

A complete technical framework of “theoretical foundation—modeling specification—analysis verification—optimization loop” was established, achieving systematic solutions to engineering problems through a hierarchical and progressive chapter design. Compared with the literature [31], which only briefly mentioned the simplified description of ‘bar element simulation of the kingpin,’ this study first compares the domestic and international research gaps at the theoretical level, clearly pointing out the technological gap between domestic linear assumptions and international multi-physics analysis; then, in the modeling stage, a three-tier control system was formed—key parameter quantification (such as specific design parameters like wheelbase 2.7 m, center of gravity height 0.5 m, etc.), material performance data (detailed parameters such as density 7900 kg/m³, yield strength 420 MPa), and mesh quality standardization (401,388 nodes and local 3 mm refinement strategy), making the simulation model engineering-reliable. In the analysis and verification phase, this study adopts a four-step modeling method of ‘working condition definition—formula derivation—load calculation—constraint setting,’ providing complete mechanical equations (e.g., longitudinal load formula 2–3 for emergency braking) and visualization loading schematics (Figure 3, Figure 5, and Figure 7) for four typical working conditions, forming a traceable analysis chain compared with the generalized description in literature. Notably, this study innovatively introduces a dual-dimensional ‘data-method’ breakthrough: integrating 500,000 km of real vehicle load data to build a Chinese road characteristic database, and correcting the traditional constant material parameter assumption through temperature–load coupled multi-physics analysis. This China condition-based technological innovation upgrades structural analysis from single-performance verification to a design tool with methodological value. This spiral design of ‘problem tracing—parameter control—innovative verification’ aligns more closely with the practical decision-making logic of engineering R&D than the linear conclusion statements in the literature [30].

Firstly, this study clarifies its research positioning by comparing domestic and international research gaps (such as the technical lag between domestic linear assumptions and international multi-physics field analysis), integrates 500,000 km of real vehicle load data to establish a database of Chinese road characteristics, and innovatively introduces temperature-load coupling analysis to correct traditional material parameter assumptions, forming a technical route with methodological value. Secondly, a closed-loop structure of “parameter control—visual verification—quantitative optimization” is adopted, providing a complete mechanical modeling chain for three typical working conditions—from load calculation formulas (e.g., emergency braking longitudinal load formulas 2–3), specific parameter substitution (gravitational acceleration, braking coefficient), to constraint settings (XYZ fixation of the wheel hub) and mesh quality control (3 mm local refinement at the steering knuckle journal), accompanied by 11 visual charts (load application diagrams 3/5/7, stress cloud maps 4/6/8) to achieve full process traceability. Finally, a “material-performance-cost” multi-objective decision dimension is innovatively added; Table 3 compares the yield strength, density, fatigue life, and cost indices of 420 MPa steel, 700 MPa steel, and SiC/Al composite materials, providing quantitative guidance for engineering material selection, and offering more practical engineering value than the single material property description in reference [32].

6. Conclusions

This study takes the steering bridge of new energy vehicles as the research object, models and simplifies the steering bridge through solid modeling software, and imports it into ANSYS to carry out finite element simulation and analysis, which involves the static analysis of structural performance and mechanical performance study of the steering bridge, as well as the modal analysis of the frequency resonance, and draws the following conclusions:

(1)

SolidWorks modeling software is used to simplify the entity modeling of the steering bridge, so that the entity is more accurate and more in line with the actual requirements, and to improve the accuracy of the analysis results;

(2)

In this study, the material of the steering bridge was firstly selected, and finally the low-alloy high-strength structural steel material with a yield strength of 420 MPa was selected as the material property for this analysis, which has high strength and good comprehensive mechanical properties [33]. The load distribution size of the steering axle under four different working conditions was calculated through theoretical formulas, and the maximum displacement and equivalent stress cloud diagram were derived from the results of software analysis. Through the comparison of the maximum stress and the yield limit of the steering axle, it can be seen that the maximum stress of the steering axle of the vehicle to be analyzed under the four working conditions is less than the yield limit of the material, which meets the strength requirements. The deformation of the material under these four working conditions is also much smaller than the permitted value, which meets the mechanical stiffness design conditions;

(3)

The result of modal analysis shows that the intrinsic frequency of the steering bridge does not resonate with the intrinsic frequency of the road surface. In addition, the intrinsic frequency of the 6-order mode shows that the intrinsic frequency of the steering bridge increases in the higher-order modes, but the excitation frequency of each part of the human body is very far away from the human body, so it will not resonate with the human body, and the steering bridge is, therefore, a more reasonable structure;

(4)

According to the previous static analysis, it can be seen that in emergency braking and other working conditions of the middle beam that there is a stress concentration and deformation of the characteristics of the large. For such a situation, the middle beam wall thickness is proposed to increase the optimization of 3 mm;

(5)

The finite element analysis of the optimized structure theoretically proves that such optimization can improve the static mechanical performance of the steering axle under important working conditions, i.e., the maximum deformation of the optimized steering axle under the emergency braking condition has been reduced from 0.53 mm to 0.42 mm, which improves the structural rigidity; the maximum stress under each typical working condition is within a safe range (e.g., the maximum stress under the emergency braking condition is 70.021 MPa), the stress distribution has been improved to a certain extent; the modal analysis results after optimization show that the change in the structure’s intrinsic frequency is very small, and it still has a very good dynamic stability.