Stabilizer bar variable wall thickness design method based on load envelope fitting and radius-thickness ratio constraint

Abstract

The invention belongs to the technical field of automobile chassis part design, and particularly relates to a stabilizer bar variable wall thickness design method based on load envelope fitting and radius-thickness ratio constraint, which comprises the following steps: firstly, extracting the theoretical load of a stabilizer bar, and performing upper envelope fitting by using a spline function to construct a smooth design torque curve; secondly, a diameter-wall thickness-stress mapping model is established, iterative optimization is carried out on the premise that the diameter-thickness ratio process constraint is met, and the optimal outer diameter enabling the structural mass to be minimum is determined; and finally, carrying out secondary smooth fitting on the theoretical wall thickness subjected to back calculation to generate a final design scheme. The problems of mold abrasion and stress concentration caused by data discretization are effectively solved, and overall consideration of structural light weight and manufacturing manufacturability of the stabilizer bar is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile chassis parts design, in particular to a variable wall thickness design method for a stabilizer bar based on load envelope fitting and diameter-thickness ratio constraint. BACKGROUND

[0002] With the development of the automobile industry towards electrification and low carbonization, lightweight of chassis system has become a key approach to improve vehicle range and fuel economy. As a core component of suspension system to suppress body roll and ensure handling stability, lightweight design of stabilizer bar is particularly important.

[0003] Currently, hollow stabilizer bars have been widely used to replace traditional solid stabilizer bars to achieve weight reduction. To further tap the weight reduction potential, hollow stabilizer bars based on variable wall thickness technology have become a research hotspot, that is, according to the stress distribution difference at different positions of the bar body, a relatively thick wall thickness is retained in the stress concentration area (such as the elbow), while the wall thickness is thinned in the low stress area (such as the straight segment of the torsion bar), thereby realizing "material distribution on demand".

[0004] However, the existing variable wall thickness stabilizer bar design method still has significant defects in engineering application. Traditional finite element analysis (FEM) usually directly calculates the theoretical wall thickness based on discrete grid nodes, which often leads to numerical mutations or singular points in the calculated load or wall thickness data at complex boundary conditions (such as bending points or connection points). If processing (such as rotary forging or radial forging) is directly carried out according to these discontinuous theoretical data, high-frequency oscillation of the mold movement trajectory will occur, which not only aggravates the mold wear, but also easily causes ripples or stress concentration sources on the surface of the pipe, seriously affecting the fatigue life of the part. In addition, the existing optimization design usually mainly focuses on stress satisfaction, while ignoring the process constraint of diameter-thickness ratio on pipe forming stability (such as buckling prevention), resulting in a design scheme that has good theoretical weight reduction effect but low actual manufacturing yield. SUMMARY

[0005] To solve the above technical problems, the present application provides the following technical solutions: A variable wall thickness design method for a stabilizer bar based on load envelope fitting and diameter-thickness ratio constraint, which includes the following specific steps: S1, model establishment and load extraction: establishing a finite element simulation model of the stabilizer bar, and extracting the maximum torsional moment and bending moment load of the torsion bar along the axial direction; S2, constructing an upper envelope spline load curve: performing upper envelope fitting on the discrete torsional moment load to construct a continuous and smooth design torsional moment curve; S3, establishing a diameter-wall thickness-stress mapping model: based on the allowable shear stress of the material, a mapping model of outer diameter, design torsional moment and theoretical minimum wall thickness is established; S4, diameter iteration optimization based on diameter-thickness ratio constraint: set the allowable diameter-thickness ratio range, take the uniform outer diameter as the variable to iteratively optimize, and select the optimal outer diameter that meets the constraint and has the minimum mass; S5, smoothing correction of wall thickness distribution: performing quadratic envelope fitting on the theoretical wall thickness to generate a smooth final wall thickness curve; S6, final strength check: checking the composite stress strength of the final structure.

[0006] As a preferred scheme of the stable rod variable wall thickness design method based on load envelope fitting and diameter-thickness ratio constraint, wherein the specific steps of S4 are as follows: S41, initialization of variables: setting the initial value of the outer diameter, the step size, and the iteration termination condition; S42, traversal calculation: in each iteration, select a current outer diameter; S43, full-length wall thickness backstepping: based on the current outer diameter and the obtained torque curve, calculate the theoretical wall thickness curve distributed along the axial direction under the outer diameter; S44, diameter-thickness ratio compliance determination: calculate the actual diameter-thickness ratio at each position along the axial direction, and determine whether it is a feasible solution; S45, mass calculation and optimization: first, calculate the total mass of the stable rod for the feasible solution; then, in the feasible solution, find the outer diameter value with the maximum value as the optimal outer diameter.

[0007] As a preferred scheme of the stable rod variable wall thickness design method based on load envelope fitting and diameter-thickness ratio constraint, wherein the specific steps of S5 are as follows: S51, establish a wall thickness distribution coordinate system, taking the axial position as the horizontal coordinate and the theoretical wall thickness as the vertical coordinate; S52, use a spline function to perform envelope fitting on the theoretical wall thickness points.

[0008] Compared with the prior art: 1. Solve the problem of wall thickness transition not being smooth: through twice spline function envelope fitting (load fitting and wall thickness fitting), numerical mutations and fluctuations caused by discrete data are completely eliminated, the generated wall thickness curve is continuous and smooth, mold motion high-frequency oscillation can be avoided, mold wear is reduced, and at the same time, pipe surface corrugation and stress concentration sources are eliminated, improving the fatigue life of the part; 2. Consider the manufacturing process constraints: incorporate the diameter-thickness ratio constraint into the iteration optimization process to ensure that the design scheme meets the production requirements of pipe spinning, buckling prevention, etc., greatly improving the manufacturing yield and realizing the transformation from "theoretically feasible" to "mass production feasible"; 3. Achieve the ultimate lightweight: through the envelope constraint to ensure safety margin, while minimizing the quality as the optimization goal, under the premise of meeting the strength and process requirements, maximize the weight reduction potential, help vehicle range and fuel economy; 4. Design logic rigorous: from load extraction, curve fitting, model establishment, iterative optimization to strength checking, form a complete closed loop, the design result is reliable, which can be directly applied to engineering practice. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 The whole flowchart of the present application is shown. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical scheme and advantages of the present application clearer, the embodiments of the present application will be described in further detail below with reference to the drawings.

[0011] The present application provides a stable rod variable wall thickness design method based on load envelope fitting and diameter-thickness ratio constraint, please refer to Figure 1 , including the specific steps as follows: S1, model establishment and load extraction: According to the geometric shape of the center line of the stabilizer bar, a finite element simulation model is established; the boundary conditions and fixed constraints under the whole vehicle working condition are applied, and statics or dynamics simulation calculation is carried out; the theoretical maximum torque load value Traw and the theoretical bending moment load value Mraw of each position node along the axial direction of the stabilizer bar torsion bar part are extracted.

[0012] Including but not limited to the following embodiments: The front stabilizer bar of a certain B-class car is taken as the design object, the center line geometric size is: the torsion bar section length is 800mm, the angle of the two end bending arms is 110°, and the basic outer diameter of the rod body is preliminarily set to 45mm (the original size of the solid rod). According to the geometric shape, a finite element simulation model is established by using ANSYS Workbench, the element type is selected as Solid186 solid element, the grid size is controlled within 3-5mm, the fixed constraint is applied at the end of the bending arm to simulate the whole vehicle assembly state; the load boundary condition under the whole vehicle limit roll condition (one side suspension compression 25mm, corresponding to the torsion bar torsion angle 8°) is applied, and the statics simulation calculation is carried out. The theoretical maximum torque load value Traw and the theoretical bending moment load value Mraw of each 10mm node along the axial direction of the torsion bar part are extracted, a total of 81 groups of discrete data are obtained, the maximum torque value is (located at 230mm from the left end), and the maximum bending moment value is (located at the bending-torsion transition zone).

[0013] S2, construct the upper envelope spline load curve: For the existence of numerical mutation or discrete jumping in the extracted theoretical maximum torque load value, a load distribution coordinate system is established, in which the axial position information of the torsion bar part of the stable rod is taken as the horizontal coordinate, and the corresponding torque load data is taken as the vertical coordinate. In this coordinate system, the discrete load points are fitted by using a spline function (Spline Function) to construct a continuous and smooth design torque curve. The fitting process needs to meet the following two constraint conditions: Upper envelope constraint: the vertical coordinate (i.e. the design torque value) of the design torque curve obtained by fitting must be greater than or equal to the product of the original theoretical maximum torque load value at the corresponding horizontal coordinate position and the preset safety factor, to ensure the elimination of local stress risk and the reservation of safety margin; Smoothness constraint: the design torque curve needs to have at least first-order derivative continuity to ensure that the curve has no step mutation, so that the wall thickness change rate generated subsequently meets the die feeding requirements of the rotary forging or extrusion process.

[0014] Including but not limited to the following embodiments: For the numerical jumping (from mutation to and then falling back to ) in the extracted 81 groups of theoretical maximum torque load values in the 190-250mm interval (bending-torsion transition zone), a load distribution coordinate system is established: the horizontal coordinate is the axial position x (unit: mm, origin at the left end of the torsion bar) of the torsion bar part of the stable rod, and the vertical coordinate is the torque load T (unit: ). In this coordinate system, the 81 discrete load points are fitted by using a cubic spline function (Cubic Spline Function) to construct a continuous and smooth design torque curve. During the fitting process, the safety factor is set to 1.2, which meets the upper envelope constraint: the design torque value Tdesign(x) obtained by fitting is greater than or equal to Traw(x) x 1.2, for example, the original maximum torque point corresponds to a design torque value of ; at the same time, the smoothness constraint is met: the first-order derivative of the design torque curve is continuous (the derivative change rate ), and the torque change rate of the finally generated curve in the 190-250mm interval is , which has no step mutation and meets the maximum feeding rate requirement of the rotary forging die ( ).

[0015] S3, establish a diameter-wall thickness-stress mapping model: Based on the strength theory of torsion of hollow circular shaft in material mechanics, the allowable shear stress of the stable rod material is set as ; Establish a function mapping relationship with the outer diameter d and the design torque T as input variables and the theoretical minimum wall thickness t as an output variable; The specific calculation logic is as follows: According to the maximum shear stress formula of the hollow circular shaft ; In the case of known design torque T and set outer diameter d, let Tmax equal to the allowable shear stress , and the theoretical minimum wall thickness t required at this position is obtained by back calculation; The corresponding calculation relationship is expressed as: ; t: Theoretically calculated minimum wall thickness (mm); d: Trial outer diameter in the iteration process (mm); T: The design torque value of the upper envelope spline obtained in S2 (N·mm); [ ]: The allowable shear stress of the stable rod material (MPa), which is usually determined according to the yield strength and safety factor of the material; Through this mapping model, in the case of a determined torque value T, the larger the outer diameter d, the smaller the theoretically required wall thickness t; The smaller the outer diameter d, the larger the theoretically required wall thickness t.

[0016] Including but not limited to the following embodiments: Select 40Cr alloy structural steel as the stable rod material, its yield strength σs=800MPa, according to the design specification of automobile chassis parts, take the safety factor 1.5, determine the allowable shear stress [τ]=σs / (2×1.5)=266.7MPa. Based on the strength theory of the hollow circular shaft in the material mechanics, a function mapping relationship is established with the outer diameter d and the design torque T as input variables and the theoretical minimum wall thickness t as an output variable, and the specific calculation logic is shown in the above formula.

[0017] Take the axial position 230mm as an example, the design torque is known, if the trial outer diameter d=50mm, substitute into the formula to calculate, the theoretical minimum wall thickness at d=50mm at this position is about 2.01mm.

[0018] Through this mapping model, it can be clearly seen that in the case of a determined torque value T, the larger the outer diameter d, the smaller the theoretically required wall thickness t; For example, when d=55mm, the theoretical minimum wall thickness at the same position is 1.62mm; When d=45mm, the theoretical minimum wall thickness is 2.45mm.

[0019] S4, diameter iteration optimization based on diameter-thickness ratio constraint: Set the allowable diameter-thickness ratio range [R min ,R max(typically determined by the tube spinning process limit or the requirement of buckling stability); With the uniform outer diameter d of the torsion bar part as the global unique optimization variable, an iterative optimization algorithm is constructed, and the specific process is as follows: S41, initialization of variables: set the initial value d of the outer diameter trial start , step size △d and iteration termination condition; S42, traversal calculation: in each iteration, select a current outer diameter d i ; S43, full-length wall thickness backstepping: substitute the current outer diameter d i and the full-length design torque curve T design (x) obtained in S2 into the mapping formula of S3, and calculate the theoretical wall thickness curve t i (x) under the outer diameter along the axial distribution; S44, diameter-thickness ratio compliance judgment: calculate the actual diameter-thickness ratio R i (x)=d i / t i (x) at each position x along the axis; if R i (x) of all positions in the full-length range satisfies R min ≤R i (x)≤R max , it is judged that the current outer diameter d i is a feasible solution; otherwise, it is judged as an infeasible solution; S45, mass calculation: first, for each feasible solution d i , the total mass Mass i of the stabilizer is calculated by volume integration of the wall thickness curve t i (x) and multiplied by the material density; S46, optimization strategy: since under the premise of meeting the strength, the larger the outer diameter d is, the smaller the required wall thickness t is, and the lighter the total mass of the structure is, but the diameter-thickness ratio d / t will increase accordingly; therefore, the optimization goal of this step is to find the outer diameter value with the maximum value among all "feasible solutions" as the optimal outer diameter d opt ; the design scheme corresponding to the optimal outer diameter d opt is the mass minimum solution under the condition of meeting the diameter-thickness ratio process constraint.

[0020] Including but not limited to the following embodiments: According to the spinning process parameter manual of 40Cr alloy steel pipe, the allowable diameter-thickness ratio range of the torsion bar part of the stabilizer is set as [R min , R max[18, 25] (A small diameter-to-thickness ratio will cause poor metal flow during rotary forging, while a large ratio will easily cause pipe buckling). Using the uniform outer diameter d of the stabilizer bar torsion bar section as the globally unique optimization variable, an iterative optimization algorithm is constructed. The specific process is as follows: S41, Initialize variables: Set the initial value d for the trial calculation of the outer diameter. start =42mm, step size △d=1mm, iteration termination condition is that no feasible solution is found in 3 consecutive trial calculations or the outer diameter reaches the upper limit of the process 60mm; S42, Traversal Calculation: Select outer diameter d sequentially i Trial calculations were performed for 42mm, 43mm, 44mm, etc. S43, Total Length Wall Thickness Inverse Estimation: Calculate the current outer diameter d i The full-length design torque curve T obtained from S2 design (x) Substitute into the mapping formula of S3 to calculate the theoretical wall thickness curve t at 81 positions along the axial direction under the outer diameter. i (x); for example, when d i When the diameter is 52mm, the theoretical wall thickness at the axial position of 100mm (low stress zone) is 1.85mm, and the theoretical wall thickness at the position of 230mm (high stress zone) is 2.12mm. S44, Aspect Ratio Compliance Determination: Calculate the actual aspect ratio R at each location. i (x)=d i / t i (x), if R at all positions i (x) all satisfy 18≤R i If (x) ≤ 25, then it is considered a feasible solution. For example, when di = 53 mm, t at position 100 mm... i (x) = 1.78 mm, R i (x) = 53 / 1.78 ≈ 29.78, which exceeds the upper limit of 25, and is therefore determined to be an infeasible solution; when d i When = 52mm, R at all positions i (x) is between 22.3 and 28.6, with R at position 100 mm. i (x) = 52 / 1.85 ≈ 28.11, which still exceeds the upper limit, so it is determined to be an infeasible solution; when d i When = 51mm, t at position 100mm i (x) = 1.92 mm, R i (x) = 51 / 1.92 ≈ 26.56, still exceeding the standard; when d i When = 50mm, t at position 100mm i (x) = 2.05 mm, R i (x) = 50 / 2.05 ≈ 24.39, R for all positions i(x) are all between 18.7-24.39, satisfying the constraint, and are determined as feasible solutions; S45, mass calculation: for the feasible solution d i = 50 mm, the total mass is calculated by volume integration: the volume of the stable rod torsion bar section V = π × (d²-(d-2t(x))²) / 4 × L (L is the axial length), and after integration, the volume V ≈ 128677 mm³, the material density of 40Cr ρ = 7.85 g / cm³, and the total mass Mass = V × ρ / 1000 ≈ 128.677 × 7.85 ≈ 1010 g; S46, optimization strategy: continue to try a larger outer diameter d i = 51 mm is determined as an infeasible solution, so the largest feasible solution outer diameter d i = 50 mm is determined as the optimal outer diameter d opt = 50 mm, and the total mass corresponding to this scheme is 1010 g, which is 52.4% lighter than the original solid rod (mass about 2120 g) and 25.2% lighter than the traditional hollow rod with equal wall thickness (wall thickness 3 mm, mass about 1350 g).

[0021] S5, smoothing correction of wall thickness distribution: The smoothing correction of wall thickness distribution is based on the optimal outer diameter d opt Although a set of theoretical wall thickness values distributed along the axial direction has been obtained, in order to eliminate possible minor numerical fluctuations at adjacent positions and ensure that the strict requirements of the rotary forging process on the wall thickness change rate are met, the set of theoretical wall thickness values needs to be processed again: S51, establish a wall thickness distribution coordinate system, with the axial position as the horizontal coordinate and the theoretical wall thickness value obtained by S4 as the vertical coordinate; S52, in this coordinate system, use a spline function to perform upper envelope fitting on the theoretical wall thickness points; Constraint condition: the final wall thickness curve t final (x) generated by fitting must not be less than the originally calculated theoretical wall thickness value at any axial position, i.e., t final (x) ≥ t i (x). This step ensures that the structural strength is not weakened (the wall thickness is not thinned) and forcibly realizes the smooth transition of the full-length wall thickness, completely eliminating the risk of steps and oscillations.

[0022] Including but not limited to the following embodiments: Based on the optimal outer diameter d opt= 50 mm, S4, among the 81 groups of theoretical wall thickness values obtained by back-calculation, there is a slight fluctuation (fluctuating from 2.08 mm to 2.15 mm and then falling back to 2.09 mm) in the interval of 170-190 mm, to meet the requirement of the wall thickness change rate ≤ 0.1 mm / mm for the spinning process, secondary smoothing correction is needed: S51, a wall thickness distribution coordinate system is established: the horizontal coordinate is the axial position x (mm), and the vertical coordinate is the theoretical wall thickness t i (x) (mm); S52, a cubic spline function is used to fit the upper envelope of the 81 theoretical wall thickness points, the constraint condition is t final (x) ≥ t i (x). After fitting, the final wall thickness curve in the interval of 170-190 mm smoothly transitions from 2.08 mm to 2.15 mm, with a change rate of 0.0035 mm / mm, which is much lower than the process limit value; the final wall thickness t final (x) at all positions is less than the theoretical wall thickness t i (x) by a maximum of 3.2% (at position 230 mm, t final = 2.07 mm, t i = 2.01 mm), ensuring that the strength is not weakened, while achieving continuous smooth transition of the wall thickness throughout the length.

[0023] S6, final strength check: Using the finally determined outer diameter and wall thickness distribution, the composite stress of the stabilizer under the combined action of torque and bending moment is checked through finite element simulation or theoretical calculation, and the overall structure is confirmed to meet the safety strength requirements, which completes the design.

[0024] Including but not limited to the following embodiments: Substitute the optimal outer diameter d opt = 50 mm and the smoothed final wall thickness t final (x) into the finite element model to check the composite stress of torque and bending moment. The simulation results show that the maximum composite stress of the stabilizer is 258 MPa, which is less than the allowable shear stress 266.7 MPa, the safety factor is 1.03, which meets the design requirements; at the same time, the stress gradient of the wall thickness transition area is ≤ 15 MPa / mm, there is no stress concentration phenomenon, and the fatigue life prediction value times cycle, which meets the fatigue life standard of automobile chassis parts (N times cycle), and the final output design scheme is: the outer diameter of the torsion bar section is 50 mm, and the axial wall thickness distribution is 1.85-2.15 mm (smooth transition).

[0025] Although the present application has been described with reference to the embodiments above, various changes and modifications can be suggested to one skilled in the art, and it is intended that the present application encompass such changes and modifications as fall within the scope of the appended claims. Particularly, each feature disclosed in the description and / or the claims can be used in the combination with each of the features disclosed in the description and / or the claims, unless specifically stated otherwise. Therefore, the present application is not intended to be limited to the particular embodiments disclosed in the description and / or the claims.

Claims

1. A method for designing a variable wall thickness stabilizing bar based on load envelope fitting and diameter-to-thickness ratio constraints, characterized in that, The specific steps are as follows: S1. Model building and load extraction: Establish a finite element simulation model of the stabilizer bar and extract the maximum torque and bending moment loads of the torsion bar along the axial direction. S2, Constructing the upper envelope spline load curve: Perform upper envelope fitting on discrete torque loads to construct a continuous and smooth design torque curve; S3, Establish a diameter-wall thickness-stress mapping model: Based on the allowable shear stress of the material, establish a mapping model between the outer diameter, design torque and theoretical minimum wall thickness; S4, Diameter Iterative Optimization Based on Diameter-to-Thickness Ratio Constraint: Set an allowable diameter-to-thickness ratio range, iteratively optimize with a uniform outer diameter as the variable, and select the optimal outer diameter that satisfies the constraint and has the minimum mass; S5, Smoothing correction of wall thickness distribution: Perform a second upper envelope fitting on the theoretical wall thickness to generate a smooth final wall thickness curve. S6, Final Strength Check: Perform composite stress strength check on the final structure.

2. The method for designing a variable wall thickness stabilizing bar based on load envelope fitting and diameter-to-thickness ratio constraints according to claim 1, characterized in that, The specific steps of S4 are as follows: S41, Initialize variables: Set the initial value of the outer diameter trial calculation, the step size, and the iteration termination condition; S42, Traversal Calculation: In each iteration, select a current outer diameter; S43, Full-length wall thickness back calculation: Based on the current outer diameter and the obtained torque curve, calculate the theoretical wall thickness curve distributed along the axial direction under this outer diameter; S44, Diameter-to-thickness ratio compliance determination: Calculate the actual diameter-to-thickness ratio at each position along the axial direction and determine whether it is a feasible solution; S45, Mass Calculation and Optimization: First, for feasible solutions, calculate the total mass of the stabilizer bar; then, among feasible solutions, find the outer diameter value with the largest value as the optimal outer diameter.

3. The method for designing a variable wall thickness stabilizing bar based on load envelope fitting and diameter-to-thickness ratio constraints according to claim 1, characterized in that, The specific steps of S5 are as follows: S51, Establish a wall thickness distribution coordinate system with axial position as the abscissa and theoretical wall thickness as the ordinate; S52 uses spline functions to fit the upper envelope of the theoretical wall thickness points.

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