A method for calculating the strength of a vehicle frame

Abstract

This invention provides a method for calculating vehicle frame strength, relating to the field of vehicle frame strength calculation. The method comprises the following steps: Simplifying the suspension by equating the front suspension leaf spring, rear suspension main spring, and rear suspension secondary spring to equal-width arc surfaces, ensuring that the contours and positions of the equivalent arc surfaces are consistent with the contours and positions of the upper surfaces of the corresponding first leaf springs. The equivalent surface of the secondary spring and the secondary spring are contacted to account for the piecewise linear nonlinear behavior of the rear suspension. The simplified models of the frame, suspension, and subframe assembly are imported into finite element analysis software. Calculations are performed by creating material and section properties, meshing, adding interactions, creating analysis steps, and defining boundary conditions. This invention improves the accuracy and efficiency of vehicle frame strength calculations.

Description

Technical Field

[0001] This invention relates to the field of frame strength calculation, and more particularly to a method for calculating frame strength. Background Technology

[0002] Truck frames are generally side-beam frames, as shown in the attached... Figure 1 As shown, the chassis includes two longitudinal beams and several crossbeams, and is generally equipped with a longitudinally mounted leaf spring suspension. Due to the large range of load variations on the truck rear axle, to avoid excessive differences in the deflection frequency between unloaded and fully loaded conditions, the rear axle suspension typically consists of a main leaf spring (referred to as the main spring) and a secondary leaf spring (referred to as the secondary spring). When the load is small, only the main spring is active. As the load increases, the gap between the secondary spring and its support gradually decreases. When they contact each other, the secondary spring begins to engage, working in conjunction with the main spring. Suspension treatment is one of the most critical steps in the strength calculation of the truck chassis, because the suspension stiffness directly determines the load distribution on the chassis.

[0003] Since longitudinal leaf springs consist of multiple leaf springs, and there is friction between adjacent leaves, a simplification is necessary when calculating frame strength, balancing computational complexity and accuracy. Generally, multiple leaf springs are treated as a single leaf spring of equal thickness. In some frame strength calculation methods, to simulate the piecewise linear nonlinear behavior of a primary and secondary spring rear suspension, a line constraint equation method is used, namely:

[0004] Vertical displacement of the auxiliary spring support - Vertical displacement of the auxiliary spring = Initial gap between the two.

[0005] The above calculation method shields the contact behavior between the auxiliary spring and the auxiliary spring support, reducing the amount of calculation. However, this method has obvious drawbacks, namely, the location where the auxiliary spring and the auxiliary spring support make contact cannot be defined with precision. It can only roughly estimate a point where contact may occur and apply the above constraint equation to this point. However, since the contact area between the auxiliary spring and the auxiliary spring support directly affects the overturning moment of the support on the frame, this method is not accurate enough to a certain extent. Summary of the Invention

[0006] To address the technical problem of low accuracy in frame strength calculation caused by shielding the contact behavior between the auxiliary spring and the auxiliary spring support in the prior art, this invention provides a frame strength calculation method that can improve the accuracy of frame strength calculation.

[0007] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a method for calculating the strength of a vehicle frame, comprising the following steps:

[0008] S01: The suspension is simplified by converting the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring into equivalent arc surfaces of equal width, ensuring that the contour and position of the equivalent arc surfaces are consistent with the contour and position of the upper surface of the first leaf spring of the corresponding leaf spring.

[0009] S02: Import the simplified models of the chassis, suspension, and subframe assembly into the 3D digital model into the finite element analysis software;

[0010] S03: Create material and section properties;

[0011] S04: Grid the components;

[0012] S05: Add interactions between components;

[0013] S06: Establish two static general analysis steps, the first for bending condition calculation and the second for bending-torsion combined condition calculation;

[0014] S07: Define boundary conditions for the two analysis steps respectively. The boundary conditions include load and displacement constraints. Apply a vertically downward concentrated force at the reference point of the center of mass of the cab, power system, superstructure and loaded cargo.

[0015] S08: Submit the analysis job for calculation.

[0016] By equating the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring to arc surfaces of equal width, the three-dimensional digital model of the suspension can be simplified, reducing the amount of calculation. On the other hand, the contact position between the auxiliary spring and the auxiliary spring support can be defined more accurately, improving the calculation accuracy and achieving a balance between the amount of calculation and the calculation accuracy.

[0017] Furthermore, in S01, when simplifying the suspension, the original three-dimensional digital models of the suspension supports, subframe, and other components directly connected to the frame are retained.

[0018] Since the suspension support is a component that is directly connected to the longitudinal beams of the chassis, it has a direct impact on the strength of the chassis. Preserving the original three-dimensional digital models of the suspension support, subframe, and other components that are directly connected to the chassis is beneficial to further improve the calculation accuracy.

[0019] Furthermore, in S02, when importing the three-dimensional model, the original three-dimensional model of the subframe longitudinal beam is retained, and bolts and rivets are replaced with line segments in the finite element analysis software.

[0020] Since the subframe longitudinal beams are in direct contact with the chassis longitudinal beams, preserving their complete model information helps improve the accuracy of strength calculations. Omitting the bolt and rivet models can further simplify the chassis model and reduce the amount of calculation.

[0021] Furthermore, in S03, bolts and rivets are meshed using Tmosinco beam elements, castings and complex welded parts on the frame are meshed using solid elements, sheet metal parts on the frame are meshed using shell elements, and equivalent curved surfaces are meshed using shell elements.

[0022] By using different unit division methods for different components, the accuracy of frame strength calculation can be further improved.

[0023] Furthermore, in S03, the shell element thickness value D of the equivalent arc-shaped surface is determined through a trial-and-error method, including the following steps:

[0024] S031: Import the curved surface separately into the finite element analysis software, assign corresponding material and section properties to the curved surface, mesh it using shell elements, and estimate a thickness value d1 and assign it to the shell elements.

[0025] S032: At the left edge of the curved surface, release only the rotational degree of freedom in the Z direction and constrain the other 5 degrees of freedom. At the right edge of the curved surface, release the translational degree of freedom in the X direction and the rotational degree of freedom in the Z direction and constrain the other 4 degrees of freedom.

[0026] S033: Apply a load F at the midpoint of the curved surface, in the negative Z-axis direction;

[0027] S034: After submitting the calculation, check the displacement δ of the midpoint of the arc surface along the load direction to obtain the stiffness value k1 = F / δ when the shell element thickness is d1. Compare k1 with the clamping stiffness K of the corresponding leaf spring. If k1 < K, increase the shell element thickness and recalculate. If k1 > K, decrease the shell element thickness and recalculate. When the calculated stiffness value is close to K, the corresponding shell element thickness value is the shell element thickness D of the equivalent arc surface.

[0028] By employing a trial-and-error algorithm, the shell element thickness value D of the equivalent arc surface can be determined simply and effectively, further improving the calculation accuracy of the frame strength.

[0029] Furthermore, when dividing the sheet metal parts on the chassis into shell units, the mid-surface extraction operation is performed first, followed by the shell unit division.

[0030] Furthermore, in S05, bolts and rivets on the frame are established with multi-point constraints to interact with bolt holes or rivet holes. For the load applied to the frame, distributed coupling constraints are established with the reference point of its center of mass and the connection area. Welds on the frame are bound. The subframe longitudinal beam and the frame longitudinal beam are established with face-to-face, limited slip soft contact. The frame longitudinal beam and the inner liner beam of the longitudinal beam are established with face-to-face, limited slip hard contact. The frame and the leaf spring support are established with face-to-face, limited slip hard contact. The equivalent arc surface of the auxiliary spring and the auxiliary spring support are established with face-to-face, limited slip contact. When there is a wear-resistant pad under the auxiliary spring support, the equivalent arc surface of the auxiliary spring and the auxiliary spring support are set to soft contact. When there is no wear-resistant pad, the equivalent arc surface of the auxiliary spring and the auxiliary spring support are set to hard contact. The equivalent arc surface is set to exclude its shell element thickness in the contact properties.

[0031] By considering the different working conditions of various components, the interaction between them can be defined more accurately. In the strength analysis process, the stress on the frame is closer to the actual situation, and the calculation is more accurate.

[0032] Furthermore, in S05, revolute pairs are added between the leaf spring and the leaf spring support, the leaf spring and the lug, and the lug and the leaf spring support. The revolute pairs are simulated by using join connection elements combined with distributed coupling constraints.

[0033] By using join connection elements and distributed coupling constraints to simulate rotating pairs, the motion and force transmission relationship between the interconnected elements can be reasonably simulated, thus improving the accuracy of calculations.

[0034] Furthermore, based on the location of the tire contact point with the ground in the unloaded state of the actual vehicle, a tire contact point is established, and a rigid beam connection unit is directly established between the tire contact point and the middle area of ​​the corresponding equivalent arc surface of the leaf spring.

[0035] Furthermore, in S07, a vertically downward concentrated force is applied at the center of mass reference point of the load-applying body of the frame. The value of the concentrated force is equal to the weight value of the corresponding load-applying body. The displacement is applied at the tire contact point. In the bending condition, the vertical displacement of each wheel contact point is zero. In the bending-torsional combined condition, the frame is subjected to torsion by applying a vertical displacement e to some tire contact points.

[0036] As can be seen from the above technical solutions, the present invention has the following advantages:

[0037] This invention provides a method for calculating vehicle frame strength. By equating the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring to arc surfaces of equal width, the three-dimensional digital model of the suspension is simplified, reducing computational load. Furthermore, the contact position between the auxiliary spring and its support is more accurately defined, improving calculation precision and achieving a balance between computational load and accuracy. Retaining the original three-dimensional digital models of the suspension supports, subframe, and other components directly connected to the frame further enhances calculation accuracy. Preserving complete model information improves the accuracy of strength calculations, while omitting bolt and rivet models further simplifies the frame model and reduces computational load. Using different element subdivision forms for different components can further improve the accuracy of frame strength calculation; by adopting a trial-and-error algorithm, the shell element thickness value D of the equivalent arc surface can be determined simply and effectively, further improving the accuracy of frame strength calculation; by adding different action forms to consider the working conditions of different components, the interaction between each component can be defined more accurately, making the stress and other conditions of the frame closer to the actual situation during the strength analysis, and the calculation more accurate; by using join connection elements + distributed coupling constraints to simulate the rotating pair, the motion and force transmission relationship between the interconnected parts can be reasonably simulated, improving the calculation accuracy. Attached Figure Description

[0038] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the frame structure in the prior art.

[0040] Figure 2 This is a flowchart illustrating a specific embodiment of the present invention.

[0041] Figure 3 This is a partial model diagram of the vehicle frame after the equivalent arcuate surface of the main leaf spring and the auxiliary leaf spring of the rear suspension in a specific embodiment of the present invention.

[0042] Figure 4 This is a schematic diagram of finite element loading and boundary conditions for calculating the thickness of the equivalent arc-shaped curved shell element of the leaf spring in a specific embodiment of the present invention.

[0043] Figure 5 This is a flowchart illustrating the trial algorithm for calculating the thickness of the equivalent arc-shaped curved shell unit of the leaf spring in a specific embodiment of the present invention.

[0044] Figure 6 This is a stress cloud diagram showing the stress distribution when the auxiliary spring and the auxiliary spring support are not in contact during a bending condition in a specific embodiment of the present invention.

[0045] Figure 7 This is a stress cloud diagram showing the contact between the auxiliary spring and the auxiliary spring support in a bending condition according to a specific embodiment of the present invention.

[0046] Figure 8 This is a stress cloud diagram of a bending-torsional combined working condition in a specific embodiment of the present invention.

[0047] In the diagram, 1 is the longitudinal beam of the frame, 2 is the subframe, 3 is the front suspension leaf spring, 4 is the rear suspension main spring, and 5 is the rear suspension auxiliary spring. Detailed Implementation

[0048] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0049] like Figure 2 and Figure 3 As shown in the figure, this specific embodiment provides a method for calculating the strength of a vehicle frame, including the following steps:

[0050] S01: The suspension is simplified by converting the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring into equivalent arc surfaces of equal width, ensuring that the contour and position of the equivalent arc surfaces are consistent with the contour and position of the upper surface of the first leaf spring of the corresponding leaf spring.

[0051] S02: Import the simplified models of the chassis, suspension, and subframe assembly into the 3D digital model into the finite element analysis software;

[0052] S03: Create material and section properties;

[0053] S04: Grid the components;

[0054] S05: Add interactions between components;

[0055] S06: Establish two static general analysis steps, the first for bending condition calculation and the second for bending-torsion combined condition calculation;

[0056] S07: Define boundary conditions for the two analysis steps respectively. The boundary conditions include load and displacement constraints. Apply a vertically downward concentrated force at the reference point of the center of mass of the cab, power system, superstructure and loaded cargo.

[0057] S08: Submit the analysis job for calculation.

[0058] In the frame strength calculation method of this specific embodiment, the front suspension leaf spring, the rear suspension main spring and the rear suspension auxiliary spring are equivalent to arc surfaces of equal width, which balances the amount of calculation and the calculation accuracy. On the one hand, it can simplify the three-dimensional digital model of the suspension and reduce the amount of calculation. On the other hand, it can also define the contact position between the auxiliary spring and the auxiliary spring support more accurately and improve the calculation accuracy.

[0059] In S01, since the suspension supports, subframe, and other components directly connected to the frame have a direct impact on the frame strength, when simplifying the suspension, the original three-dimensional models of the suspension supports, subframe, and other components directly connected to the frame are retained. The hangers, due to their simple shape, do not require much additional calculation and their original three-dimensional models are also retained.

[0060] In S02, since the subframe longitudinal beams are in direct contact with the frame longitudinal beams, when importing the 3D model, the original 3D model of the subframe longitudinal beams is retained. Bolts and rivets are replaced with line segments in the finite element analysis software and then assembled to their corresponding positions, which greatly reduces the amount of calculation. In this specific embodiment, as shown... Figure 1 As shown, the chassis is a 4×2 electric truck chassis, and the three-dimensional model of the power battery bracket assembly should also be imported into the software.

[0061] In S03, bolts and rivets are meshed using Temmosine beam elements, while castings and complex welded parts on the frame are meshed using solid elements. Sheet metal parts on the frame are meshed using shell elements, and equivalent curved surfaces are meshed using shell elements. In this specific embodiment, the sheet metal parts include frame longitudinal beams and inner lining beams, frame crossbeams, subframes, power battery pack bracket crossbeams, and power battery pack bracket longitudinal beams, etc. The shell elements are the versatile 4-node quadrilateral finite thin film strain linear reduced integral shell elements (S4). R), the five integration points are set by default to ensure the accuracy of the frame strength calculation. The integration rule is the default Simpson's rule. The thickness is taken as the thickness of the original sheet metal part. Since the leaf spring seat is in contact with the frame, it is divided using a modified 10-node quadratic tetrahedral element (C3D10M). There is no contact at the hanger, so it is divided using a 10-node quadratic tetrahedral element (C3D10). Since the quadratic element has high accuracy, the mesh can be slightly sparse. The equivalent arc surface of the leaf spring is also divided using S4R shell elements.

[0062] like Figure 4 and Figure 5 As shown, in S03, the shell element thickness value D of the equivalent arc-shaped surface is determined by a trial-and-error method, including the following steps:

[0063] S031: Import the curved surface separately into the finite element analysis software, assign the corresponding material and section properties to the curved surface, and use shell elements to generate the mesh, estimate a thickness value d1 and assign it to the shell element;

[0064] S032: At the left edge of the curved surface, release only the rotational degree of freedom in the Z direction and constrain the other 5 degrees of freedom. At the right edge of the curved surface, release the translational degree of freedom in the X direction and the rotational degree of freedom in the Z direction and constrain the other 4 degrees of freedom.

[0065] S033: Apply a load F at the midpoint of the arc-shaped surface, with the direction being the negative Z-axis. In this specific embodiment, the magnitude of F is 2000N.

[0066] S034: After submitting the calculation, check the displacement δ of the midpoint of the arc-shaped surface along the load direction to obtain the stiffness value k1 = F / δ when the shell element thickness is d1. Compare k1 with the clamping stiffness K of the corresponding leaf spring. If k1 < K, increase the shell element thickness and recalculate; if k1 > K, decrease the shell element thickness and recalculate. When the calculated stiffness value is close to K, the corresponding shell element thickness value is the shell element thickness D of the equivalent arc-shaped surface. This trial-and-error method can determine the shell element thickness D of the equivalent arc-shaped surface simply, quickly, and accurately.

[0067] By employing a trial-and-error algorithm, the shell element thickness value D of the equivalent arc surface can be determined simply and effectively.

[0068] To improve the accuracy of frame strength calculations, the interactions between components need to be considered. In S05, interactions between parts are added, including multi-point constraints, distributed coupling constraints, binding constraints, contact, join connection elements, and rigid beam connection elements. Bolts and rivets on the frame use multi-point constraints to establish interactions with bolt holes or rivet holes. For the load-bearing entities on the frame (including the cab, battery pack, superstructure, and loaded cargo), distributed coupling constraints are established between their center of mass reference points and the connection areas. Specifically, the cab's center of mass reference point is used to establish distributed coupling constraints with the cab mounting holes on the frame; the center of mass reference points of the engine, transmission, and other heavy components are used to establish distributed coupling constraints with the powertrain mounting holes on the frame; the center of mass reference points of the superstructure and loaded cargo are used to establish distributed coupling constraints with the upper surface of the subframe; binding constraints are used at welds on the frame; since there are wooden or rubber pads between the frame and subframe, considering both computational load and accuracy, these pads are ignored, and soft contact is used between the frame and subframe. A face-to-face, limited-slip soft contact is established between the subframe longitudinal beam and the frame longitudinal beam. The main surface is the lower flange of the subframe longitudinal beam, and the secondary surface is the upper flange of the frame longitudinal beam. A face-to-face, limited-slip hard contact is established between the frame longitudinal beam and the inner liner beam. The main surface is the frame longitudinal beam, and the secondary surface is the inner liner beam. A face-to-face, limited-slip hard contact is established between the frame and the leaf spring support. The main surface is the surface on the frame, and the secondary surface is the surface on the leaf spring support. A face-to-face, limited-slip hard contact is established between the power battery pack bracket longitudinal beam and the frame. The main surface is the surface on the frame, and the secondary surface is the surface on the power battery pack bracket. The equivalent arcuate surface of the secondary spring and the secondary... The spring support establishes a face-to-face, limited-slip contact. When there is an anti-wear pad under the secondary spring support, the equivalent arc surface of the secondary spring and the secondary spring support are set to soft contact. When there is no anti-wear pad, the equivalent arc surface of the secondary spring and the secondary spring support are set to hard contact. The main surface is the upper surface of the equivalent arc surface of the secondary spring, and the secondary surface is the surface of the secondary spring support and the secondary spring in contact. In order to ensure that the equivalent arc surface of the leaf spring participates in the contact with the upper surface of the actual leaf spring, the equivalent arc surface is set to exclude its shell unit thickness in the contact properties. The tangential behavior of the contact properties is defined according to the friction coefficient set according to the actual material.Revolute pairs are added between the leaf spring and leaf spring support, the leaf spring and the hanger, and the hanger and leaf spring support. These revolute pairs are simulated using join connection units combined with distributed coupling constraints. In this specific embodiment, when adding a revolute pair between the leaf spring and leaf spring support, two sets of coincident reference points, point1, pointA and point2, pointB, are established at the centers of the pin holes on both sides of the leaf spring support. Distributed coupling constraints are established between point1 and point2 and the inner surfaces of the pin holes on both sides of the leaf spring support, respectively. PointA and pointB are rigidly connected to the edges of the equivalent arc surface of the leaf spring. A join connection unit is established between point1 and pointA, and between point2 and pointB. In this way, the equivalent arc surface of the leaf spring can rotate around the central axis of the pin hole of the leaf spring support. The method for adding revolute pairs between the leaf spring and the hanger, and between the hanger and the leaf spring support, is the same and will not be repeated. The contact points of each tire and the middle area of ​​the equivalent arc surface of the leaf spring are respectively established... The rigid beam connection unit is established by creating a rigid beam connection unit in the finite element analysis software based on the position of the tire contact point with the ground under the actual vehicle's unloaded state. The rigid beam connection unit is then established between the tire contact point and the equivalent arc surface of the leaf spring. Specifically, the rigid beam connection unit is established between the left front wheel contact point and the equivalent arc surface of the left front leaf spring; the rigid beam connection unit is established between the right front wheel contact point and the equivalent arc surface of the right front leaf spring; the rigid beam connection unit is established between the left rear wheel contact point and the equivalent arc surface of the left rear main spring and auxiliary spring; and the rigid beam connection unit is established between the right rear wheel contact point and the equivalent arc surface of the right rear main spring and auxiliary spring. Additionally, rigid beam connection units are also established between the left and right front wheel contact points, and between the left and right rear wheel contact points. To more intuitively display the position of the tire contact point, in this specific embodiment, a beam model is created to represent the tire and the axle, and rigid body constraints are applied. The endpoints of the beam are the tire contact points. ;

[0069] In this specific embodiment, in S06, the initial increment step of the analysis step is appropriately reduced to ensure that the contact can be established smoothly. In this specific embodiment, the initial increment step is 0.02.

[0070] In S07, a vertically downward concentrated force is applied at the center-of-mass reference point of the load-applying body of the chassis. The value of the concentrated force is equal to the weight value of the corresponding load-applying body. The load value is set in the first analysis step and continues to the second analysis step. The displacement is applied at the tire contact point. In the bending condition, the vertical displacement of each wheel contact point is zero. In the bending-torsional combined condition, the chassis is subjected to torsion by applying a vertical displacement e to some tire contact points. In this specific embodiment, the overall coordinate system is as follows: the positive direction of the Z-axis is perpendicular to the upper wing surface of the chassis and upward; the positive direction of the X-axis is parallel to the wing surface of the chassis and towards the rear of the vehicle; and the positive direction of the Y-axis is perpendicular to the belly surface of the chassis and towards the right side of the vehicle.

[0071] The displacement constraint at the tire contact point under bending conditions is:

[0072] Left front wheel X=0, Z=0 Right front wheel X=Y=Z=0

[0073] Left rear wheel Z=0 Right rear wheel Z=0

[0074] The displacement constraint at the tire contact point under combined bending and torsion conditions is as follows:

[0075] Left front wheel X=0, Z=e; Right front wheel X=Y=Z=0

[0076] Left rear wheel Z = 0, Right rear wheel Z = e

[0077] In this specific embodiment, e is 120 mm.

[0078] In S08, within the finite element software, multiple CPUs are configured for parallel processing based on the computer configuration, and analysis jobs are submitted for calculation.

[0079] Since the load and displacement are applied in a linear manner to a given value, in this specific embodiment, the historical process of a certain physical quantity from zero to a given value can be looked up in increments.

[0080] In this specific embodiment, stress concentration will inevitably occur at the midpoint of the equivalent arc surface that is rigidly connected to the tire contact point. However, since the stiffness of the equivalent arc surface is consistent with the clamping stiffness of the actual leaf spring, it will not have too much impact on the accuracy of stress and strain calculation of the frame.

[0081] Figure 6 This is the stress cloud diagram of the process where the auxiliary spring is not in contact during the bending condition in this calculation example (the subframe is hidden). At this time, the load is small and the stress in various parts of the frame is small. Figure 7 This is the final stress cloud diagram of the auxiliary spring in contact during the bending condition in this calculation example (the subframe is hidden); Figure 8 This is the final stress cloud diagram of the combined bending and torsion condition in this calculation example (the subframe is hidden). It can be seen that the frame as a whole has undergone relatively obvious torsional deformation.

[0082] In this specific embodiment, the finite element analysis software used is ABAQUS.

[0083] As can be seen from the above specific embodiments, the present invention has the following beneficial effects:

[0084] 1. By equating the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring to arc surfaces of equal width, the three-dimensional digital model of the suspension can be simplified, reducing the amount of calculation. On the other hand, the contact position between the auxiliary spring and the auxiliary spring support can be defined more accurately, improving the calculation accuracy and achieving a balance between the amount of calculation and the calculation accuracy.

[0085] 2. Retaining the original three-dimensional models of suspension supports, subframes, and other components directly connected to the chassis is beneficial for further improving calculation accuracy;

[0086] 3. Retaining complete model information helps improve the accuracy of strength calculations, while omitting bolt and rivet models can further simplify the chassis model and reduce the amount of calculation.

[0087] 4. By using different unit division methods for different components, the accuracy of frame strength calculation can be further improved;

[0088] 5. By adopting the trial-and-error method, the shell element thickness value D of the equivalent arc surface can be determined simply and effectively, further improving the calculation accuracy of the frame strength;

[0089] 6. By adding different action modes that take into account the actual working conditions of different components, the interaction between each component can be defined more accurately. In the strength analysis process, the stress on the frame and other conditions are closer to the actual situation, and the calculation is more accurate.

[0090] 7. By using join connection elements and distributed coupling constraints to simulate rotating pairs, the motion and force transmission relationship between the two connected elements can be reasonably simulated, thus improving the accuracy of calculation.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of calculating the strength of a vehicle frame, characterized by, Includes the following steps: S01: The suspension is simplified by converting the front suspension leaf spring, rear suspension main spring, and rear suspension auxiliary spring into equivalent arc surfaces of equal width. This ensures that the contour and position of the equivalent arc surfaces are consistent with the contour and position of the upper surface of the first leaf spring of the corresponding leaf spring. When simplifying the suspension, the original three-dimensional models of the suspension support, subframe, and other components directly connected to the frame are retained. S02: Import the simplified models of the chassis, suspension, and subframe assembly into the 3D digital model into the finite element analysis software; S03: Create material and section properties. Bolts and rivets are meshed using Timoshenko beam elements. Castings and complex welded parts on the frame are meshed using solid elements. Sheet metal parts on the frame are meshed using shell elements. Equivalent curved surfaces are meshed using shell elements. S04: Grid division for each component; S05: Add interactions between components. Bolts and rivets on the frame are established with multi-point constraints to interact with bolt holes or rivet holes. For loads applied to the frame, distributed coupling constraints are established with reference points at the center of mass and the connection area. Welds on the frame are bound. Subframe longitudinal beams and frame longitudinal beams are established with face-to-face, limited-slip soft contact. Frame longitudinal beams and longitudinal beam inner liner beams are established with face-to-face, limited-slip hard contact. Frames and leaf spring supports are established with face-to-face, limited-slip hard contact. The equivalent arc surface of the auxiliary spring and the auxiliary spring support are established with face-to-face, limited-slip contact. When there is a wear-resistant pad under the auxiliary spring support, the equivalent arc surface of the auxiliary spring and the auxiliary spring support are set to soft contact. When there is no wear-resistant pad, the equivalent arc surface of the auxiliary spring and the auxiliary spring support are set to hard contact. The equivalent arc surface is set to exclude its shell element thickness in the contact properties. Add rotating pairs between leaf springs and leaf spring supports, leaf springs and lugs, and lugs and leaf spring supports. S06: Establish two static general analysis steps, the first for bending condition calculation and the second for bending-torsion combined condition calculation; S07: Define boundary conditions for the two analysis steps respectively. The boundary conditions include load and displacement constraints. Apply a vertically downward concentrated force at the reference point of the center of mass of the cab, power system, superstructure and loaded cargo. S08: Submit the analysis job for calculation.

2. The method of claim 1, wherein, In S02, when importing the 3D model, the original 3D model of the subframe longitudinal beam is retained, and bolts and rivets are replaced with line segments in the finite element analysis software.

3. The method of claim 2, wherein, In S03, the shell element thickness value D of the equivalent arc-shaped surface is determined through a trial-and-error method, including the following steps: S031: Import the curved surface separately into the finite element analysis software, assign corresponding material and section properties to the curved surface, mesh it using shell elements, and estimate a thickness value d1 and assign it to the shell elements. S032: At the left edge of the curved surface, release only the rotational degree of freedom in the Z direction and constrain the other 5 degrees of freedom. At the right edge of the curved surface, release the translational degree of freedom in the X direction and the rotational degree of freedom in the Z direction and constrain the other 4 degrees of freedom. S033: Apply a load F at the midpoint of the curved surface, in the negative Z-axis direction; S034: After submitting the calculation, check the displacement δ of the midpoint of the arc surface along the load direction to obtain the stiffness value k1=F / δ when the shell element thickness is d1. Compare k1 with the corresponding clamping stiffness K of the leaf spring. If k1<K, increase the shell element thickness and recalculate. If k1>K, decrease the shell element thickness and recalculate. When the calculated stiffness value is close to K, the corresponding shell element thickness value is the shell element thickness D of the equivalent arc surface.

4. The method of claim 3, wherein, In S04, when dividing the sheet metal parts on the chassis into shell units, the mid-surface extraction operation is performed first, followed by the shell unit division.

5. The method of claim 4, wherein, In S05, a revolute joint is simulated by using join connection elements combined with distributed coupling constraints.

6. The method of claim 5, wherein, Based on the location of the tire contact point with the ground under the actual vehicle's unloaded state, establish the tire contact point, and directly establish a rigid beam connection unit between the tire contact point and the middle area of ​​the corresponding leaf spring equivalent arc surface.

7. The method of claim 1, wherein, In S07, a vertically downward concentrated force is applied at the center of mass reference point of the load-applying body of the frame. The value of the concentrated force is equal to the weight value of the corresponding load-applying body. The displacement is applied at the tire contact point. In the bending condition, the vertical displacement of each wheel contact point is zero. In the bending-torsional combined condition, the frame is subjected to torsion by applying a vertical displacement e to some tire contact points.

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