Variable cross-section trailing arm and torsion beam assembly

Abstract

The invention relates to the technical field of vehicle torsion beams, and particularly discloses a variable cross-section trailing arm which is sequentially provided with a first circumference shrinking section, a circumference expanding section, a second circumference shrinking section and an equal circumference section in the S-shaped streamline direction of a trailing arm body. The head end of the first circumference shrinking section is farther away from the center line of the torsion beam assembly than the tail end of the first circumference shrinking section, and the total relative change rate of the first circumference shrinking section is reduced by 5-18%; the circumference expanding section is bent towards the cross beam side of the torsion beam, and the total relative change rate of the circumference expanding section is expanded by 40-55%; the second circumference shrinking section is bent towards the outer side of the torsion beam assembly, the circumference of the section of the second circumference shrinking section is gradually reduced towards the equal-circumference section to be equal to that of the equal-circumference section, and the total relative change rate is reduced by 20-25%; wherein the tail end of the first circumference shrinking section is the minimum section circumference, and the tail end of the circumference expanding section is the maximum section circumference. The torsion beam assembly comprises a cross beam and variable-cross-section trailing arms installed at the two ends of the cross beam. According to the scheme, the rigidity and strength of the connecting area of the longitudinal arm and the cross beam are improved, and the lateral impact bearing capacity is improved.

Description

Technical Field

[0001] This invention relates to the field of vehicle torsion beam technology, specifically to a variable cross-section trailing arm and torsion beam assembly. Background Technology

[0002] With the deepening of automotive platform and modularization strategies, the requirements for the versatility of torsion beam suspension assemblies across various vehicle models and powertrains (such as gasoline, pure electric, and range-extended electric vehicles) are becoming increasingly stringent. This requires that the design of the same assembly must simultaneously meet continuously improving torsional stiffness, fatigue durability, and lightweighting targets within a strictly defined vehicle envelope. This systemic challenge permeates all components of the assembly, especially in the core load-bearing structure—the trailing arm—and its collaborative design with the crossbeam.

[0003] Firstly, for the trailing arm, as a key component directly connecting the vehicle body and wheels and transmitting complex loads, its structural design is crucial to the performance and reliability of the assembly. At the critical juncture of the connection design between the trailing arm and the crossbeam, existing technologies employ different design approaches. For example, the automotive torsion beam technology disclosed in patent publication number CN212555734U presents a typical design. In this design, except for the small cross-sectional area / perimeter at one end of the connecting sleeve, the cross-sectional area / perimeter of the trailing arm along the S-shaped streamline of the sleeve does not change significantly. This type of trailing arm ensures the connection strength with the crossbeam, spring disc, and wheel hub bracket through a small structural change rate. Furthermore, this type of torsion beam technology often does not place significant requirements on the design of the trailing arm, essentially operating on a dedicated design basis.

[0004] Another prior art, CN115837557B, discloses a closed torsion beam longitudinal arm with an S-shaped structure. In this type of longitudinal arm, the cross-sectional change, or perimeter change, of the S-shaped streamline varies significantly across different sections. The longitudinal arm has its minimum cross-sectional area / perimeter at a position very close to the sleeve installation point. From this minimum point, the perimeter rapidly increases along the S-shaped streamline direction, then the change in perimeter becomes very slow until it reaches its maximum, after which it decreases at a relatively rapid rate. Finally, the end of the longitudinal arm ends with a uniform perimeter. In this technology, the crossbeam overlaps the section of the longitudinal arm where the perimeter rapidly increases, while the sections where the perimeter increases slowly and decreases rapidly correspond to the spring tray. In the mounting area, the spring tray is welded to both the crossbeam and the trailing arm. This design ensures the strength and stiffness required for the torsion beam. However, for applications that need to accommodate multiple vehicle models and platforms, this means that the envelope space is severely limited, and the trailing arm design space is extremely limited. For example, the technology shown in CN115837557B has a small space for installing springs on the spring tray because the thickest part of the trailing arm is directly opposite the spring tray. This cannot meet the spring installation requirements of multiple vehicle models. Furthermore, the shock absorber mounting plate machined on the thickest part of the trailing arm also affects the strength and stress variation of the trailing arm. As a result, the torsion beam assembly formed by this type of trailing arm and the crossbeam cannot meet the requirements of both high stiffness (600 N·m / deg), high load-bearing capacity (high buckling), and noise reduction while satisfying the envelope space requirements. Currently, torsion beam assemblies with crossbeams and trailing arms are semi-independent suspensions and do not have requirements for high buckling.

[0005] In addition, another existing technology, such as a lightweight rear torsion beam with patent publication number CN210149420U, also discloses an S-shaped streamlined longitudinal arm. However, the longitudinal arm in this technology is made by stamping and welding the left and right separate parts separately. Moreover, the connection strength between the longitudinal arm and the crossbeam by the circumferential weld is still insufficient. A reinforcing plate needs to be welded between the top of the crossbeam and the top of the longitudinal arm to meet the connection strength requirements. All of these factors make it impossible for the rear torsion beam to meet the current requirements of high rigidity, high load-bearing capacity and lightweight. Summary of the Invention

[0006] The present invention aims to provide a variable cross-section longitudinal arm to improve the stiffness and strength of the connection area between the longitudinal arm and the crossbeam, and to improve the lateral impact bearing capacity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A variable cross-section longitudinal arm includes an S-shaped longitudinal arm body, and along the S-shaped streamline direction of the longitudinal arm body, starting from the mounting hole of the mounting sleeve, a first reduced perimeter section, an expanded perimeter section, a second reduced perimeter section, and an equal perimeter section are smoothly connected in sequence. The first end of the first shrinking section is farther from the centerline of the torsion beam assembly than its end, and its cross-sectional perimeter gradually decreases from the mounting hole toward the expanding section, with a total relative change rate of 5-18%. The expanding section bends toward the crossbeam side of the torsion beam, and its cross-sectional perimeter gradually increases toward the second contracting section, with a total relative change rate of 40-55%. The second reduced-perimeter section bends outward toward the torsion beam assembly, and its cross-sectional perimeter gradually decreases toward the equal-perimeter section until it is equal to the cross-sectional perimeter of the equal-perimeter section, with a total relative change rate of 20-25%. Wherein, the end of the first shrinking segment is the minimum cross-sectional perimeter, and the end of the expanding segment is the maximum cross-sectional perimeter.

[0008] Preferably, as an improvement, the total relative change rate of the cross-sectional perimeter of the first shrinking segment is reduced by 13-18%, and the total relative change rate of the cross-sectional perimeter of the expanding segment is increased by 45-50%.

[0009] Preferably, as an improvement, taking the outer closing edge of the longitudinal arm body as a reference, the arc length of the expanding section is 2.3-3 times the arc length of the first contracting section, the sum of the arc length of the first contracting section and the arc length of the expanding section is 40-50% of the total arc length, and the total arc length is the continuous outer arc length from the mounting hole on the longitudinal arm body to the end of the equal-circumference section.

[0010] Preferably, as an improvement, the circumference expansion section includes a rapid expansion section and a slow expansion section, the rapid expansion section being connected to the first circumference contraction section, and the slow expansion section being connected to the second circumference contraction section.

[0011] Preferably, as an improvement, the total relative change rate of the cross-sectional perimeter of the rapidly increasing segment and the slowly increasing segment is 20-25%, and the arc length corresponding to the slowly increasing segment is 2-2.5 times the arc length of the rapidly increasing segment.

[0012] Preferably, as an improvement, the lap weld between the crossbeam and the longitudinal arm body includes a top weld segment, a bottom weld segment, a front side weld segment, and a rear side weld segment. The top weld segment and the bottom weld segment are located on the top and bottom surfaces of the longitudinal arm body, respectively. The front side weld segment and the rear side weld segment connect the top weld segment and the bottom weld segment to form an annular weld. The front side weld segment is attached to the gradually increasing section, and the rear side weld segment is attached to the end of the gradually increasing section or the beginning of the second shrinking section. The front side weld segment is C-shaped or V-shaped, and the rear side weld segment is C-shaped or V-shaped. There is a rounded transition between adjacent weld segments.

[0013] Preferably, as an improvement, it further includes a hub bracket welded to the trailing arm body; the hub bracket includes a front side plate and a rear side plate; the front side plate is close to the crossbeam, and the front side plate is provided with a U-shaped opening, the U-shaped opening is fitted to a second shrinkage section, and the second shrinkage section is sandwiched between two wings of the U-shaped opening; the upper and lower wings of the U-shaped opening both extend from the side corner area of ​​the trailing arm body toward the crossbeam and toward the axis of the trailing arm body; the rear side plate is disposed opposite to the front side plate and is fixedly connected to the trailing arm body.

[0014] Preferably, as an improvement, the rear side plate is fixed to the end opening of the equicircular segment, and the rear side plate covers the end opening.

[0015] Preferably, as an improvement, a shock absorber mounting bracket is fixed at the end of the isopleth segment.

[0016] The principles and advantages of this invention are: 1. This invention designs the longitudinal arm body with a cross-sectional perimeter that increases gradually from the minimum to the maximum, resulting in a maximum cross-sectional area in the middle of the longitudinal arm body. The crossbeam overlaps on this maximum cross-sectional area, improving the stiffness and strength of the overlap area between the crossbeam and the longitudinal arm. Because the crossbeam overlaps at this maximum cross-sectional area, the weld length at the crossbeam-to-longitudinal arm overlap is longer, allowing for a smoother weld transition and reducing sharp turns in the weld. This ensures that under different operating conditions (such as vertical runout, braking, starting, and lateral turning), the maximum weld damage or stress concentration point will appear in different sections of the weld in the torsion beam assembly due to different load directions. This avoids the problem in conventional designs where the maximum weld damage under different operating conditions occurs in the same weld section, thus dispersing the risk of fatigue damage and extending the service life of the weld and the torsion beam assembly.

[0017] 2. The variable cross-section longitudinal arm of the present invention utilizes an S-shaped streamlined structure, which ensures that the length of the crossbeam is shortened while achieving the same torsional stiffness. This contributes to the lightweight design of the torsion beam assembly, reducing the weight of the torsion beam assembly, which originally achieved a torsional stiffness of 600 N·m / deg, from approximately 24.2 kg to approximately 22.4 kg. The weight of the crossbeam is reduced from approximately 8.4 kg in the initial design to approximately 7 kg, greatly reducing the weight, especially the weight of the crossbeam, which has the highest material cost, thus meeting the current requirements for lightweight torsion beam assemblies.

[0018] 3. The S-shaped streamlined longitudinal arm guides the force on the torsion beam assembly. With its S-shaped structural design and control of the rate of change of the cross-sectional perimeter (the crossbeam overlaps on the area with the largest cross-sectional perimeter of the longitudinal arm, the connection strength between the crossbeam and the longitudinal arm is high, and the cross-sectional perimeter of the second shrinkage section after the maximum cross-sectional perimeter decreases slowly, ensuring the strength of the wheel hub bracket and spring tray after installation), the torsion beam assembly has excellent lateral stiffness. This ensures that the vehicle's Y-direction buckling limit reaches the level of the subframe, breaking the conventional setting that the performance of the torsion beam assembly in this aspect is far inferior to that of the subframe. In addition, the S-shaped streamlined design also meets the requirements of multiple models and platforms for the envelope space.

[0019] 4. The different bending directions and curvature centers of the expanded and contracted sections ensure that the longitudinal arm can be designed within the limited space required by multiple vehicle models and platforms. This provides sufficient space for the installation of spring trays, electric vehicle battery brackets, and installation tool locations for various vehicle models. The design of the longitudinal arm, which has a smooth transition within this limited space, ensures high torsional stiffness when in conjunction with the crossbeam, while also taking into account high load-bearing capacity and high comfort, and avoiding abnormal noises.

[0020] 5. By designing the U-shaped opening of the front side plate of the wheel hub bracket to start from the R-corner area of ​​the trailing arm and extend towards its axis, with the wing facing the crossbeam, the present invention increases the length of the connection weld between the wheel hub bracket and the trailing arm. This not only enhances the connection strength, but also actively guides and disperses the lateral impact force borne by the wheel from the corner area where stress concentration is likely to occur to other areas of the trailing arm, thereby effectively improving the impact resistance of the assembly.

[0021] 6. The rear side plate can not only increase the weld connection length with the longitudinal arm body, but also cover the end opening of the longitudinal arm body, saving the cost of having to install a separate cover on the end opening of the longitudinal arm body, and ensuring that external debris is not easily entered into the longitudinal arm body.

[0022] The present invention also provides a torsion beam assembly, including a crossbeam and the variable cross-section longitudinal arm.

[0023] Preferably, as an improvement, the cross-section of the beam is a closed section, and there is a gap between the cross-section lines of the closed section. The beam includes a first zone, a second zone and an overlapping zone arranged sequentially from the center of torsion to both ends. The overlapping zone is used to overlap with the longitudinal arm of the torsion beam assembly. The aspect ratio r of the first region's cross-section satisfies: 1.05 ≤ r ≤ 1.35. The cross-section of the first region has a closed inverted U-shaped structure, and the reduction rate of the cross-sectional perimeter of the first region does not exceed 14%. The cross-section of the second region gradually changes from a closed inverted U-shaped structure to a closed trapezoidal structure at the junction with the overlapping area, and the perimeter of the cross-section of the second region increases by 10%-27%. Based on the top closing edge of the crossbeam, the length of the second zone is 18-40% of the length of the first zone.

[0024] Preferably, as an improvement, the closer the first region is to the center of torsion, the smaller its cross-sectional perimeter; the closer the second region is to the center of torsion, the larger its cross-sectional perimeter; the minimum cross-sectional perimeter of the beam is located at the junction of the first and second regions; and the total reduction rate of the cross-sectional perimeter of the first region is 7-14%.

[0025] Preferably, as an improvement, the first region includes a torsion region and a transition region, the transition region connecting the second region, the length of the torsion region accounting for 75-90% of the length of the first region, and the reduction rate of the cross-sectional perimeter of the torsion region accounting for 80-90% of the total cross-sectional change rate of the first region.

[0026] Preferably, as an improvement, within the torsion zone, the rate of decrease in the cross-sectional perimeter gradually increases along the direction away from the torsion center, while within the transition zone, the rate of decrease in the cross-sectional perimeter gradually decreases.

[0027] Background of this invention: For crossbeams, under the dual constraints of space and performance, existing technical solutions face significant limitations in improving crossbeam performance, thus affecting the overall performance of the assembly. Existing approaches mainly fall into two categories: The first type of solution focuses on improving stiffness, but requires ample space. For example, the crossbeam in the "Production Process of Closed Torsion Beam Assembly" disclosed in patent publication number CN115722821A effectively improves stiffness by adopting an undulating structure, but its cross-sectional shape requires a lot of space in the Z-direction (height) and X-direction (width), making it difficult to adapt to platforms with strict space constraints.

[0028] The second type of solution focuses on adapting to space constraints, but performance improvement faces bottlenecks. For example, the "rear torsion beam structure" disclosed in patent publication number CN209208392U has a long and gentle torsion zone in its crossbeam to avoid top interference, but this usually limits its torsional stiffness to a low level (e.g., 430-450 N•m / deg), and its fatigue durability is mostly for medium-duty working conditions. If an attempt is made to improve its stiffness, conventional solutions such as proportional scaling up or increasing plate thickness will lead to dimensional overruns or conflicts with lightweighting goals, respectively.

[0029] When the width, length, and top space of the crossbeam are strictly constrained, extending downwards in the Z direction becomes the main direction. However, this will significantly reduce the width-to-height ratio of the crossbeam section, transforming it into a crossbeam with an extremely long and narrow "tall" structure in the middle. This fundamental change in cross-sectional shape will cause complex changes in the transmission path of force and moment and stress distribution. If combined with the use of an S-shaped streamlined trailing arm, the length of the crossbeam can be designed to be shorter, which helps with weight reduction. However, such a design will cause a high stress concentration area to form in the section of the crossbeam near the end of the trailing arm. Once high stress is formed, it will not meet the vehicle's durability requirements. On the other hand, if the trailing arm is relatively straight, the crossbeam will be longer. On the one hand, this will make the torsion beam assembly more rigid (good handling), but it will easily lead to substandard modal characteristics and resonance and abnormal noise problems. Moreover, it will not be able to meet the current mainstream of lightweight design.

[0030] The torsion beam assembly of this invention not only increases the torsional stiffness of the torsion beam assembly to 570 N.m / deg-630 Nm / deg under strict space constraints, but also enables the stress to be distributed more evenly. Thus, while meeting the requirements of space, torsional stiffness, durability and lightweight, the main vibration mode frequencies can be controlled within a safe range. Attached Figure Description

[0031] Figure 1 This is a three-dimensional structural schematic diagram of the variable cross-section longitudinal arm according to Embodiment 1 of the present invention.

[0032] Figure 2 for Figure 1 A three-dimensional structural diagram of the variable cross-section longitudinal arm after mirroring (i.e.) Figure 1 and Figure 2 The longitudinal arms are the two longitudinal arms in the torsion beam assembly that are connected to the crossbeam.

[0033] Figure 3 for Figure 2 Top view.

[0034] Figure 4 for Figure 2 The image only shows a three-dimensional structural diagram of the longitudinal arm body.

[0035] Figure 5 for Figure 4 Top view.

[0036] Figure 6 for Figure 1 A three-dimensional structural diagram of the wheel hub bracket.

[0037] Figure 7 This is a three-dimensional structural diagram of the torsion beam assembly of Embodiment 2 formed after the variable cross-section longitudinal arm, crossbeam, sleeve, hub bracket, spring tray, etc. of Embodiment 1 of the present invention are installed.

[0038] Figure 8for Figure 7 Top view.

[0039] Figure 9 for Figure 7 A three-dimensional structural diagram after rotation (to show the location of the lower weld).

[0040] Figure 10 for Figure 8 Section II in the diagram.

[0041] Figure 11 This is a three-dimensional structural diagram of the crossbeam in the torsion beam assembly of Embodiment 2 of the present invention (with a schematic diagram of the weld path).

[0042] Figure 12 for Figure 11 A three-dimensional structural diagram of the crossbeam before it is cut in the overlapping area.

[0043] Figure 13 for Figure 12 Top view.

[0044] Figure 14 for Figure 13 Cross-sectional views of oo, AA, BB, and CC.

[0045] Figure 15 This is a top view of Comparative 1 (the figure shows the inner and outer double inverted V-shaped structure of the section where the torsion center is located).

[0046] Figure 16 This is a schematic diagram of the three-dimensional structure of Comparative Example 1 at a specific angle.

[0047] Figure 17 The stress distribution diagram of the body under the vertical jump condition in Table 2 is shown (the left side of the figure is Sub-Example 1 of the present invention, and the right side is Comparative Example 1).

[0048] Figure 18 The stress distribution diagram of the weld seam under the jumping condition in Table 2 (the left side of the figure is Sub-Example 1 of the present invention, and the right side is Comparative Example 1).

[0049] Figure 19 The CAE analysis results of the buckling X-direction ultimate strength of Example 1 in Table 4 are shown.

[0050] Figure 20 The CAE analysis results of the buckling Y-direction ultimate strength of Example 1 in Table 4 are shown.

[0051] Figure 21 Table 4 shows the CAE analysis results of the ultimate strength in the buckling Z-direction of Example 1.

[0052] Figure 22 The results are from the bench fatigue simulation analysis of sub-example 1.

[0053] Figure 23 for Figure 22 A magnified view of a portion of the image.

[0054] Figure 24 The results of the bench fatigue simulation analysis are shown in Comparative Example 1-1.

[0055] Figure 25 for Figure 24 A magnified view of a portion of the image.

[0056] Figure 26 The simulation analysis results show that the torsion beam assembly formed by the crossbeam of sub-example 1 exhibits the first-order rigid body mode at 68.8 Hz.

[0057] Figure 27 The simulation analysis results for Sub-Example 1 show that the rigid body second-order mode appears at 90.7Hz.

[0058] Figure 28 The simulation analysis results of the first-order Z-direction bending mode appearing at 130.0 Hz are for example 1.

[0059] Figure 29 The simulation analysis results show that the first-order X-direction local bending mode appears at 199.7Hz in sub-example 1.

[0060] Figure 30 This is a schematic diagram of the longitudinal arm structure of Comparative Example I and Sub-Example 1.

[0061] Figure 31 for Figure 30 Top view.

[0062] Figure 32 The diagram shows the longitudinal arm structure of Comparative Examples I to III.

[0063] Figure 33 for Figure 32 Top view.

[0064] Figure 34 This is a schematic diagram of the longitudinal arm structure of Comparative Example IV, Comparative Example I, and Sub-Example 1.

[0065] Figure 35 for Figure 34 Top view.

[0066] Figure 36 This is a schematic diagram of the longitudinal arm structure of sub-example 2 and sub-example 1.

[0067] Figure 37 This is a stress distribution diagram of the weld in Comparative Example I under vertical jump conditions.

[0068] Figure 38 This is a stress distribution diagram of the weld in Comparative Example I under the condition of advancing over a ridge.

[0069] Figure 39 This is a stress distribution diagram of the weld seam under braking conditions, which is the comparison diagram II.

[0070] Figure 40 This is a stress distribution diagram of the weld seam under startup conditions, as shown in Comparative Example II.

[0071] Figure 41 This is a stress distribution diagram of the weld in Comparative Example III under vertical jumping conditions.

[0072] Figure 42 This is a stress distribution diagram of the weld seam in Comparative Example III under braking conditions.

[0073] Figure 43 This is a stress distribution diagram of the weld seam in Comparative Example III under startup conditions.

[0074] The reference numerals in the accompanying drawings include: crossbeam 10, torsion zone 11, transition zone 12, second zone 13, overlap zone 14, longitudinal arm 20, first shrinkage section 21, rapid increase section 22, slow increase section 23, second shrinkage section 24, equal circumference section 25, reference G, hub bracket 30, front side plate 31, wing 311, rear side plate 32, spring tray 40, sleeve 50, shock absorber mounting seat 60, weld 70, top seam section 71, bottom seam section 72, front side seam section 73, rear side seam section 74, and the abdominal inclination angle k of the second zone 13 (the angle k between the abdominal and the bottom surface of the overlap zone).

[0075] Figure 15 and Figure 16 The attached reference numerals are: torsion zone 81, transition zone 82, enlargement zone 83, overlap zone 84, and equal section segment 85. Detailed Implementation

[0076] The following detailed description illustrates the specific implementation method: Example 1 Combination Figures 1 to 7 A variable cross-section longitudinal arm 20 is manufactured using a plate rolling process. It includes an S-shaped longitudinal arm body and, along the S-shaped streamline direction of the longitudinal arm body, starting from the mounting hole of the longitudinal arm body mounting sleeve 50, it sequentially includes a smoothly connected first shrinkage section 21, a circumference expansion section (22, 23), a second shrinkage section 24, and an equal circumference section 25.

[0077] The cross-sectional perimeter of the first shrinkage section 21 gradually decreases from the mounting hole towards the expansion section. Starting from the mounting hole, the total relative change rate of the cross-sectional perimeter of the first shrinkage section 21 is 5-18% (preferably 13-18%). The distance between the beginning of the first shrinkage section 21 and the centerline of the torsion beam assembly is greater than the distance between the end of the first shrinkage section 21 and the centerline of the torsion beam assembly.

[0078] The perimeter of the cross section gradually increases towards the second shrinking section 24, and the total relative change rate of the perimeter of the cross section of the expanding section is 40-55% (preferred range is 45-55%). The expanding section bends toward the crossbeam 10 of the torsion beam.

[0079] The expanding segment includes a rapidly increasing segment 22 and a slowly increasing segment 23. The rapidly increasing segment 22 connects to the first shrinking segment 21, and the slowly increasing segment 23 connects to the second shrinking segment 24. The total relative change rate of the cross-sectional perimeter of both the rapidly increasing segment 22 and the slowly increasing segment 23 is 20-25%. The arc length corresponding to the slowly increasing segment 23 is 2-2.5 times the arc length of the rapidly increasing segment 22. Preferably, the difference between the total relative change rate of the cross-sectional perimeter of the rapidly increasing segment 22 and the slowly increasing segment 23 does not exceed 2%, that is, the total relative change rate of the cross-sectional perimeter of the rapidly increasing segment 22 and the slowly increasing segment 23 is basically the same.

[0080] The gradually enlarging section 23 is embedded in the end opening of the crossbeam 10, and the overlapping area of ​​the crossbeam 10 and the longitudinal arm 20 is located within the gradually enlarging section 23 or extends from the gradually enlarging section 23 to the head of the second shrinking section 24.

[0081] The lap weld 70 between the crossbeam 10 and the longitudinal arm body includes a top weld segment 71, a bottom weld segment 72, a front side weld segment 73, and a rear side weld segment 74. The top weld segment 71 and the bottom weld segment 72 are located on the top and bottom surfaces of the longitudinal arm body, respectively. The front side weld segment 73 and the rear side weld segment 74 connect the top weld segment 71 and the bottom weld segment 72 to form an annular weld 70. The front side weld segment 73 is attached to the gradually increasing section 23, and the rear side weld segment 74 is attached to the end of the gradually increasing section 23 or the head of the second shrinking section 24. The front side weld segment 73 is C-shaped or V-shaped, and the rear side weld segment 74 is C-shaped or V-shaped. There is a rounded transition between adjacent weld segments.

[0082] The cross-sectional perimeter of the second shrinking segment 24 gradually decreases towards the equal-perimeter segment 25 until it is equal to the cross-sectional perimeter of the equal-perimeter segment 25. The total relative change rate of the cross-sectional perimeter of the second shrinking segment 24 is reduced by 20-25%. The second shrinking segment 24 bends outward towards the torsion beam assembly.

[0083] The total relative rate of change is calculated as follows: (perimeter of the corresponding end section - perimeter of the corresponding beginning section) / perimeter of the corresponding beginning section.

[0084] The end of the first contraction segment 21 has a minimum cross-sectional perimeter, and the maximum cross-sectional perimeter is located at the end of the expansion segment. The maximum cross-sectional perimeter is 1.25-1.6 times the minimum cross-sectional perimeter, and the maximum cross-sectional perimeter is 1.23-1.35 times the cross-sectional perimeter of the equal-perimeter segment 25. Preferably, the maximum cross-sectional perimeter is 1.4-1.6 times the minimum cross-sectional perimeter, and the maximum cross-sectional perimeter is 1.27-1.32 times the cross-sectional perimeter of the equal-perimeter segment 25.

[0085] Taking the outer closing edge of the longitudinal arm body as the reference G, the arc length of the expansion segment is 2.3-3 times the arc length of the first contraction segment 21. The sum of the arc length of the first contraction segment 21 and the arc length of the expansion segment is 40-50% of the total arc length. The total arc length is the sum of the continuous arc lengths of the outer closing edge from the mounting hole on the longitudinal arm body to the end of the equal-circumference segment 25.

[0086] A hub bracket 30 is welded onto the longitudinal arm body; a front side plate 31 and a rear side plate 32 are formed on the hub bracket 30, and both the front side plate 31 and the rear side plate 32 are welded to the longitudinal arm body; the front side plate 31 is close to the crossbeam 10, and a U-shaped opening is machined on the front side plate 31. The U-shaped opening fits onto the second shrinkage section 24, and the second shrinkage section 24 is sandwiched between the two wings 311 of the U-shaped opening; the upper and lower wings 311 of the U-shaped opening both start from the corner area of ​​the outer side of the longitudinal arm body and extend towards the crossbeam 10 and towards the axis of the longitudinal arm body; this design can increase the weld length, enhance the connection strength, and disperse the lateral impact force from the stress concentration area to other areas of the longitudinal arm 20, thereby improving the impact resistance.

[0087] The rear side plate 32 is disposed opposite to the front side plate 31 and is fixedly connected to the longitudinal arm body. The rear side plate 32 is welded to the end of the longitudinal arm body away from the sleeve 50, that is, the rear side plate 32 is welded to the end opening of the second shrinkage section 24, and the rear side plate 32 faces and covers the end opening.

[0088] A shock absorber mounting base 60 is welded onto the rear side plate 32, and the position of the shock absorber mounting base 60 is directly opposite the end opening of the trailing arm body.

[0089] In this embodiment, considering the space constraints of multiple platforms and vehicle models, the maximum cross-sectional area of ​​the trailing arm body is set at the location where it connects to the crossbeam 10. This improves the stiffness and strength of the overlap area between the crossbeam 10 and the trailing arm 20. Because the crossbeam 10 overlaps at this maximum cross-sectional area, the weld length at the overlap between the crossbeam 10 and the trailing arm 20 is longer. Furthermore, the crossbeam 10 and the trailing arm 20 are connected by a circumferential weld on the thickest section of the trailing arm 20. This ensures that under different working conditions during bench testing (such as vertical runout and lateral turning), the maximum weld damage or stress concentration point will appear in different sections of the weld in the torsion beam assembly due to different load directions. This avoids the problem in conventional designs where the maximum weld damage under different working conditions occurs in the same weld section.

[0090] Furthermore, by using the S-shaped longitudinal arm 20 and the variable cross-section design, the length of the crossbeam 10 can be designed to be shorter while maintaining the torsion beam assembly at a high torsional stiffness of 600±30 N·m / deg. At this torsional stiffness, the weight of the torsion beam assembly is reduced from approximately 24.2 kg in the conventional design to 22.4 kg in this embodiment, and the weight of the crossbeam is reduced from 8.4 kg in the conventional design to 7 kg, significantly reducing material costs.

[0091] Furthermore, the S-shaped trailing arm 20, combined with the control of the cross-sectional perimeter, ensures that the crossbeam 10 overlaps at the thickest part of the trailing arm 20, guaranteeing the connection strength; the second shrinking section 24 gradually narrows, ensuring the strength of the mounting point between the wheel hub bracket 30 and the spring tray 40; and this embodiment enables the X-direction buckling to achieve an ultimate strength test exceeding 45KN, a Y-direction ultimate strength test approaching or even exceeding 22KN, and a Z-direction ultimate strength test exceeding 47KN. The buckling in all three directions meets or even exceeds the requirements of conventional torsion beam assemblies, breaking the situation where the Y-direction buckling in semi-independent suspension cannot reach 22KN, making it possible for a low-cost torsion beam assembly to replace the subframe with high component complexity and high manufacturing cost.

[0092] In addition, the curvature directions of the first shrinking section 21, the expanding section (22, 23) and the second shrinking section (24) change alternately, so that the longitudinal arm 20 can be smoothly arranged within the limited envelope space, reserving installation space for the spring tray 40, battery bracket and other components, taking into account high rigidity, high load-bearing capacity and high comfort, and avoiding abnormal noise.

[0093] In summary, this embodiment achieves a comprehensive breakthrough in lightweight, high strength, high stiffness, high load-bearing capacity, superior space utilization, and low cost through the coordinated design of S-shaped longitudinal arm geometry and variable cross-section. In particular, it surpasses traditional torsion beam designs in terms of high lateral stiffness, high load-bearing capacity (especially high buckling requirements), and multi-platform adaptability.

[0094] Example 2 Combination Figures 7 to 14 A torsion beam assembly includes a crossbeam 10 and variable cross-section longitudinal arms 20 of Embodiment 1, which are fixedly connected to both ends of the crossbeam 10. The axial ends of the crossbeam 10 are welded to the portions of the variable cross-section longitudinal arms 20 with the largest cross-sectional area, directly opposite to them. Both the crossbeam 10 and the variable cross-section longitudinal arms 20 are formed using a sheet metal rolling process.

[0095] I. Construction of crossbeam 10 and spring tray 40 The crossbeam 10 is made using a plate rolling process. The cross-section of the crossbeam 10 is a closed section with gaps between the cross-section lines. The crossbeam 10 has a first zone, a second zone 13, and an overlapping zone 14 in sequence from the center of torsion toward the longitudinal arm 20. The first zone, the second zone 13, and the overlapping zone 14 are integrated. The first zone is further divided into a torsion zone 11 and a transition zone 12 that are integrated from the center of torsion toward the end of the crossbeam 10. The adjacent zones transition smoothly.

[0096] The width-to-height ratio of the first section is r, and satisfies: 1.05≤r≤1.35. The cross-section of the first section has a closed inverted U-shaped structure, and the rate of change of the perimeter of the first section does not exceed 14%.

[0097] The cross-section of the second zone 13 gradually changes from a closed inverted U-shaped structure to a closed trapezoidal structure at the junction with the overlapping zone 14, and the perimeter of the cross-section of the second zone 13 increases by 10%-27%. With the top closing edge of the crossbeam 10 as a reference, the length of the second zone 13 is 18-40% of the length of the first zone. Preferably, the length of the second zone 13 is 37±3% of the length of the first zone.

[0098] The connection between the top U-shaped structure and the bottom U-shaped structure of the closed inverted U-shaped structure is a rounded transition connection, and the radius of the rounded corner R is not less than 2.5 times the wall thickness of the plate.

[0099] The further away from the center of torsion in the first zone (11, 12), the smaller the perimeter of its cross section. The further away from the center of torsion in the second zone (13), the larger the perimeter of its cross section. The minimum perimeter of the cross section of the beam 10 is located at the junction of the first zone and the second zone (13). The total reduction rate of the perimeter of the cross section in the first zone is 7-14% (preferably 7-10%), and the total increase rate of the perimeter of the cross section in the second zone (13) is 16%-23% (preferably 18-22%).

[0100] In the first region, the length of the torsion zone 11 accounts for 75-90% of the total length of the first region, and the reduction rate of the cross-sectional perimeter of the torsion zone 11 accounts for 80-90% of the total cross-sectional change rate of the first region. Within the torsion zone 11, the rate of decrease in the cross-sectional perimeter gradually increases along the direction away from the torsion center, while within the transition zone 12, the rate of decrease in the cross-sectional perimeter gradually decreases.

[0101] Define the width of the cross section at the center of torsion as W1, the width of the cross section at the end of the first zone as W2 (that is, the width of the end of the transition zone as W2), and the width of the cross section at the end of the second zone as W3. Then W1, W2, and W3 satisfy the proportional relationship: W1: W2: W3 = (0.75–0.9) : 1 : (1.3–1.45).

[0102] On the axial section of the crossbeam 10, the maximum angle k between the belly below the second zone 13 and the bottom surface of the overlapping zone 14 is less than 33°. The part below the transition zone 12 of the belly below the second zone 13 and the part below the overlapping zone 14 are smoothly connected. Furthermore, from the transition zone 12 to the overlapping zone 14, the distance between the belly below the second zone 13 and the top of the second zone 13 gradually increases.

[0103] As a preferred embodiment, the maximum angle k between the abdomen below the second zone 13 and the bottom surface of the overlapping zone 14 is less than 30°.

[0104] The torsion beam assembly also includes a spring tray 40 fixed in the area of ​​the angle between the crossbeam 10 and the longitudinal arm 20. The spring tray 40 is welded to both the crossbeam 10 and the longitudinal arm 20.

[0105] The torsion beam assembly in this embodiment not only increases the torsional stiffness of the torsion beam assembly to 570 N.m / deg-630 Nm / deg under stringent space constraints, but also enables more uniform stress distribution. This is particularly evident in the most challenging vertical and extreme torsional conditions for this type of narrow-height beam. Figure 17 Under the condition of foundation vertical jump, the maximum stress value of the crossbeam can be kept below 428MPa; combined with Figure 22 and Figure 23 Under ultimate torsion conditions, the crossbeam no longer exhibits a narrow, high-stress zone near the corner R of the inner and outer plates on one side. Instead, the highest stress occurs at non-corner positions (the maximum stress under ultimate torsion conditions is 491.1 MPa), and there are multiple lower stress zones on both sides of the crossbeam axis, resulting in a more uniform stress distribution. Ultimately, the fatigue damage of the body under torsion conditions is as low as 0.192. Furthermore, while meeting space requirements, torsional stiffness requirements, durability requirements, and extreme lightweight requirements, the main vibration mode frequencies can be controlled within a safe range.

[0106] II. Stiffness Analysis To demonstrate the above performance advantages, the following sub-example 1 and comparative example 1 are provided: Sub-example 1: The length of the first section of the crossbeam 10 is 380±5mm. The length of the torsion zone 11 in the first section accounts for 80±5% of the total length of the first section. The perimeter of the cross-section at the torsion center of the crossbeam 10 (i.e., the starting end of the first section) is 335±5mm. The width-to-height ratio of the starting end of the first section is 1.1. The width W1 of the starting end of the first section is 78.5±2mm, the width W2 of the ending end of the first section is 95.7±2mm, and the cross-sectional width W3 of the ending end of the second section is 130±2mm. The ratio of W1:W2:W3 is (0.76~0.86):1:(1.31~1.41); the minimum cross-sectional perimeter formed by the junction of the first zone and the second zone 13 is 306±5mm, the reduction rate of the cross-sectional perimeter of the first zone is 8.5±0.5%, and the reduction rate of the cross-sectional perimeter of the torsion zone 11 accounts for 80-90% of the total cross-sectional change rate of the first zone; the length of the second zone 13 is 140±5mm, the growth rate of the cross-sectional perimeter of the second zone 13 is 21.5±0.5%, the width-to-height ratio of the cross-section at the junction of the second zone 13 and the overlapping zone 14 is 1.6±0.1 times, and the length of the overlapping zone 14 is 60±2mm. On the axial section of the second zone 13, the maximum included angle between the web of the second zone 13 and the bottom surface of the overlapping zone 14 is 30±1°. The plate thickness of the beam 10 is 2.6mm, and the plate material is CP800 steel.

[0107] In the longitudinal arm of Sub-Example 1: the perimeter of the first reduced-perimeter section 21 is 232mm±5mm, the minimum perimeter is 195±5mm, the maximum perimeter is 1.48±0.1 times the minimum perimeter, and the maximum perimeter is 1.3±0.1 times the perimeter of the equal-perimeter section 25. Using the projected arc length of the longitudinal arm body as a reference G, the total arc length of the longitudinal arm body from the mounting hole of the sleeve 50 to the end of the equal-perimeter section 25 is 477±10mm. The arc length of the expanded-perimeter sections (22, 23) is 2.48±0.1 times the arc length of the first reduced-perimeter section 21. The sum of the arc length of the first reduced-perimeter section 21 and the arc length of the expanded-perimeter sections (22, 23) is 44.6±2% of the total arc length. The total relative change rate of the perimeter of the rapidly increasing section 22 and the slowly increasing section 23 is 21±2%. The arc length corresponding to the slowly increasing section 23 is... The arc length of the rapidly increasing segment 22 is 2.25 ± 0.1 times; the total relative change rate of the cross-sectional perimeter of the second shrinking segment 24 is reduced by 23.2%; the projected arc length of the equal-perimeter segment 25 on the outer side of the longitudinal arm body is 58 mm ± 5 mm; the projected arc length of the equal-perimeter segment 25 on the inner side of the longitudinal arm body is 29.3 m ± 2 mm; the length of the circumferential weld between the crossbeam 10 and the longitudinal arm 20 is 464 ± 10 mm; the wheel center distance of sub-example 1 is 1590 mm, the deflection angle is 3.6°, and the torsional stiffness is 600 ± 15 N.m / deg.

[0108] Comparative Example 1, combined with Figures 15 to 16The difference between Comparative Example 1 and Sub-Example 1 is that the torsional stiffness of the torsion beam assembly is 430±15 Nm / deg. The crossbeam of Comparative Example 1 includes a torsion zone 81, a transition zone 82, an enlargement zone 83 and an overlap zone 84 from the torsion center to both ends. The torsion zone 81 has an inner and outer double inverted V-shaped structure, and the inner and outer inverted V-shapes are attached to each other in the area near the top. The transition zone 82 transitions from a double inverted V-shape to a double inverted U-shape, and the inner and outer layers of the double inverted U-shape structure are not attached. The enlargement zone 83 transitions from a double inverted U-shape to a trapezoidal structure. The cross-sectional perimeter of the torsion zone 81 remains basically unchanged, with a cross-sectional perimeter of 330±5mm and a length of 305±5mm. The cross-sectional perimeter of the transition zone 82 gradually increases by 3.6%, and the length of the transition zone 82 is 185±5mm. The cross-sectional perimeter of the enlarging zone 83 decreases by 5.2±0.1%, and the length of the enlarging zone 83 is 51.5±2mm. The length of the overlapping zone 84 is 57±2mm. The width of the beam at the center of torsion in this comparative example 1 is 85±2mm, and the cross-sectional perimeter is 330±5mm. The maximum cross-sectional perimeter of 342±5mm is located at the junction of the transition zone 82 and the enlarging zone 83. The longitudinal arm of the torsion beam assembly is also S-shaped, but the longitudinal arm only shows a slight decrease in cross-sectional perimeter near the sleeve, followed by a slight increase in cross-sectional perimeter. However, a constant cross-sectional segment 85 with an unchanged cross-sectional perimeter is formed before the crossbeam. This constant cross-sectional segment 85 accounts for 70±3% of the total length of the longitudinal arm. The cross-sectional perimeter near the sleeve mounting hole is 220mm, the minimum cross-sectional perimeter is 215±2mm, and the cross-sectional perimeter of the constant cross-sectional segment 85 is also 220mm. The length of the circumferential weld at the overlap between the crossbeam and the longitudinal arm is 408±10mm.

[0109] First, stiffness analysis was performed on Sub-Example 1 and Comparative Example 1. The analysis results are shown in Table 1 below.

[0110] Table 1 Stiffness analysis of Sub-Example 1 and Comparative Example 1

[0111] As can be seen from Table 1, the stiffness of Example 1 is superior to that of Comparative Example 1.

[0112] III. Strength and bench fatigue analysis Referring to Table 2, CAE strength analysis was performed on Sub-Example 1 and Comparative Example 1. Since Comparative Example 1 is based on the current conventional rear axle load requirement of 700-1000Kg, the rear axle load used in this analysis is 900Kg; while Sub-Example 1 needs to take into account the application of fuel, pure electric and range-extended vehicles, so the load requirement during testing is higher, and the rear axle load requirement is 1150Kg.

[0113] Table 3 shows the bench fatigue tests of Sub-Example 1 and Comparative Example 1.

[0114] Table 2 CAE intensity analysis of Sub-Example 1 and Comparative Example 1

[0115] Table 3. Bench fatigue analysis of Sub-Example 1 and Comparative Example 1

[0116] Explanation of Table 3: Torsional conditions: The test conditions of sub-example 1 and comparative example 1 are also different. The test conditions of sub-example 1 are: multi-level load spectrum accelerated life test. The test first uses a medium intensity displacement (±40mm) for 300,000 cycles to simulate long-term use; then it uses a high intensity displacement (±67mm) for 50,000 cycles. After no failure, it is tested with ultimate load until failure. This test is to verify the fatigue strength of the torsion beam assembly throughout its entire life cycle and the remaining load-bearing capacity after damage. The test conditions for the torsional condition in Comparative Example 1 in Table 3 are as follows: single-stage ultimate load durability test, which directly applies a high-intensity displacement (±67mm) for 50,000 cycles or until the specimen fails. This test is to verify the crack resistance under ultimate conditions (belonging to the basic standard). In the parallel runout conditions in Table 3, the maximum test load of Sub-Example 1 is 12.3 kN, while the maximum test load of Comparative Example 1 is only 9.8 kN; In the lateral force conditions in Table 3, both Sub-Example 1 and Comparative Example 1 use two-stage load cycles. The difference is that the maximum lateral force experienced by Sub-Example 1 in the second stage reaches 5.3 kN, while the maximum lateral force in the same stage of Comparative Example 1 is only 3.5 kN.

[0117] Based on the test results, all tests in Table 2 of Sub-Example 1 meet the requirements of range-extended, fuel, and pure electric vehicles, especially in vertical jump conditions (weld seams) and left / right turning conditions, where they are superior to Comparative Example 1.

[0118] Combination Figure 17 It can be seen that under the basic vertical jump condition, the maximum stress of the torsion beam in sub-example 1 occurs in the second zone 13 of the crossbeam 10, near the top of the outer layer of the weld. This confirms that the second zone 13 is a design challenge for the crossbeam 10 with its narrow and high torsion zone 11, which requires sufficient enveloping space. However, the maximum stress of 428 MPa under a test load 1.28 times that of comparative example 1 is sufficient to meet the requirements of range-extended, fuel, and pure electric vehicles. Figure 17Similarly, it can be observed that the maximum stress in Comparative Example 1 occurs at the corner area where the crossbeam and longitudinal arm overlap, which is also the location of the weld. Therefore, fatigue cracks are more likely to occur in this area compared to other parts of the crossbeam. This demonstrates the rationality of the design of overlapping the longitudinal arm and crossbeam at the maximum cross-sectional area of ​​the longitudinal arm in this embodiment.

[0119] from Figure 18 It can be clearly seen that the weld quality of the scheme in Example 1 under the basic working condition of vertical jump is higher than that of Comparative Example 1. Moreover, the location of the maximum stress in the vertical jump-weld and vertical jump-body of Comparative Example 1 is in the same area of ​​the torsion beam assembly, indicating that this location is most prone to failure under the vertical jump condition.

[0120] As shown in Table 3, the overall damage of Sub-Example 1 is better than that of Comparative Example 1. Sub-Example 1 only has a weld damage of 1.572 in the CAE analysis of the lateral force condition. In response to this, an actual bench fatigue test was conducted. The weld damage in the actual test was much less than the CAE value of 1.6, so it can fully meet the high fatigue durability requirements while taking into account torsional stiffness. Moreover, under the lateral force condition shown in Table 3, even though the maximum lateral force (5.3 kN) borne by Sub-Example 1 is much higher than the maximum lateral force (3.5 kN) borne by Comparative Example 1, the overall damage of the torsion beam is still much lower than that of Comparative Example 1. This shows that the scheme of this embodiment can withstand higher impacts and has good lateral stiffness.

[0121] Furthermore, in existing technologies, such as the semi-independent suspension torsion beam assembly in Comparative Example 1, which is a typical representative of existing products, the products are used in vehicles with low requirements for corresponding test conditions, such as rear axle load of 700-1000Kg. Therefore, the ultimate strength requirement of the torsion beam assembly is low. For this type of semi-independent suspension torsion beam assembly, the buckling limit strength is not analyzed in conventional design. The buckling limit strength analysis is usually only performed on independent suspensions (such as subframes). Referring to Table 4 below, the design of the embodiment of the present invention needs to be usable in multiple vehicle types (fuel, pure electric, and range-extended vehicles) and, based on the narrow and tall crossbeam design, can take into account fatigue performance, vibration performance, and also meet the ultimate strength requirements of the subframe.

[0122] IV. Buckling Limit Strength Analysis Table 4 below and Figures 19 to 21 This is the buckling analysis result of Sub-Example 1 of the present invention.

[0123] Table 4. Buckling analysis results of sub-example 1

[0124] As shown in Table 4 above, the torsion beam assembly of this embodiment can achieve the subframe level in buckling performance tests in the X, Y, and Z directions. This ensures that the torsion beam assembly of this embodiment can achieve the subframe's ability to resist multidimensional deformation under extreme working conditions, and ensures that the torsion beam assembly of this embodiment can have high torsional stiffness, high load-bearing capacity, high NVH requirements, high lateral stiffness, and extreme lightweight under extremely demanding spatial envelope requirements.

[0125] V. Comparative Analysis of Beam Design To demonstrate the performance advantages of the beam in Sub-Example 1, the following comparative examples are provided: Comparative Example 1-1: Compared with Sub-Example 1, the difference lies in the plate thickness being 2.5mm, the plate material being FB780 steel, the torsion zone length in the first zone accounting for 86±5% of the total length of the first zone, the perimeter of the cross-section at the torsion center of the beam (i.e., the starting end of the first zone) being 345mm, the width-to-height ratio at the starting end of the first zone being 1.11, where the width W1 at the starting end of the first zone is 82±2mm, the width W2 at the end of the first zone is 94.5±2mm, and the ratio of W1:W2:W3 is (0.83~0.91):1 (1.33~1.43); the minimum cross-sectional perimeter formed by the junction of the first and second zones is 314±5mm, the reduction rate of the cross-sectional perimeter of the first zone is 9±0.5%, and the reduction rate of the cross-sectional perimeter of the torsion zone accounts for 80-90% of the total cross-sectional change rate of the first zone; the growth rate of the cross-sectional perimeter of the second zone is 18±0.5%. On the axial section of the second zone, the maximum angle between the web of the second zone and the bottom surface of the overlapping area is 33°.

[0126] Comparative Examples 1-2: Compared with Sub-Example 1, the difference between Comparative Examples 1-2 is that the thickness of the plate is 2.5mm and the plate material is FB780 steel.

[0127] Comparative Examples 1-3: Compared with Sub-Example 1, the only difference between Comparative Examples 1-2 is that the material of the sheet is FB780.

[0128] Sub-Example 1 and Comparative Examples 1-1, 1-2, and 1-3 were tested under the same ultimate torsional conditions. The maximum stress of the crossbeam body during the test is shown in Table 5.

[0129] Table 5. Maximum stress of the body under the same ultimate torsional condition for Sub-Example 1 and 3 comparative examples.

[0130] Since the torsional stiffness of the beam is determined by the minimum cross-sectional area of ​​the torsional zone, when the torsional zone of Sub-Example 1 and the three comparative examples are the same, the torsional stiffness of Sub-Example 1 and the comparative examples can also reach a high torsional stiffness of 600±15N·m / deg.

[0131] From Table 5 and Appendix Figures 22 to 25 It can be seen that the maximum stress in Sub-Example 1 designed according to the embodiments of the present invention is reduced by about 80 MPa compared with Comparative Example 1-1, and from the attached... Figure 22 It can be seen that the maximum stress in Sub-Example 1 is not at the corner R, but rather at the inner plate near the axis of the corner R. In this weaker area at the corner R, the maximum stress is only 475.5 MPa. Compared to Comparative Examples 1-1, the maximum stress in Sub-Example 1 of the present invention has shifted from the weak area at the corner R to the web of the inner plate, which significantly reduces the damage caused by the maximum stress. According to the SN curve of the reactive material properties, in the high-stress area, a stress reduction of 30 MPa can significantly improve fatigue life, or even double it. In comparison, the 80 MPa reduction in maximum stress in Sub-Example 1 can significantly improve fatigue life, reducing the damage to the beam body under torsional conditions that were originally difficult to achieve to 0.192.

[0132] Furthermore, as can be seen from Comparative Examples 1-2 and 1-3, changes in the cross-section and the thickness of the plate both affect the stress.

[0133] When performing installation modal simulation using this sub-example 1 (in conjunction with...) Figures 26 to 29 This allows the torsion beam to exhibit a rigid body first-order mode at around 68.8 Hz, a rigid body second-order mode at around 90.7 Hz, a first-order Z-direction bending mode at around 130.0 Hz, and a first-order X-direction local bending mode at around 199.7 Hz, thus keeping the modal frequencies within a safe range.

[0134] VI. Comparative Analysis of Designs Under Variations in Both Longitudinal Arm and Crossbeam To demonstrate the performance advantages of the present invention, the following comparative examples and sub-example 2 are provided for comparison. The following comparative examples and examples can meet the requirement of torsional stiffness of 600±15N.m / deg after the crossbeam and longitudinal arm are matched.

[0135] Comparative Example I: Combination Figure 30 and Figure 31Compared with the longitudinal arm of Sub-Example 1, the difference is that the S-shaped streamline of this comparative example is basically the same as that of Sub-Example 1, but the difference is that the perimeter of the head section of the first shrinking section is 237±5mm, the minimum perimeter of the section is 225±5mm, that is, the perimeter change rate of the section of the first shrinking section is about 5.1%, the maximum perimeter of the section is 1.3±0.1 times the minimum perimeter of the section, the maximum perimeter of the section is 1.25±0.1 times the perimeter of the equal perimeter section, the total perimeter change rate of the section of the expanding section is 30%, and the perimeter change rate of the section of the second shrinking section is about 21.4%. Based on the projected arc length of the longitudinal arm body on the outer side, the total arc length of the longitudinal arm body from the mounting hole to the end of the equicircular section is 482±10mm. The arc length of the expanded circumference section is 2.8±0.1 times the arc length of the first contracted circumference section. The sum of the arc length of the first contracted circumference section and the arc length of the expanded circumference section is 44±2% of the total arc length. The length of the equicircular section is about 14mm shorter than that of the equicircular section in sub-example 1. The projected arc length of the equicircular section on the outer side of the longitudinal arm body is 98mm±5mm, and the projected arc length of the equicircular section on the inner side of the longitudinal arm body is 15.5mm±2mm. The length of the circumferential weld between the crossbeam and the longitudinal arm is 472±10mm.

[0136] In addition, the longitudinal arm of Comparative Example I is thicker and heavier than that of Sub-Example 1. However, in order to meet the envelope requirements of multiple models and multiple platforms, a small recess of about 7mm is provided at the top of the rapidly increasing section.

[0137] Compared with the beam of sub-example 1, the beam of Comparative Example I differs in that: the first zone is not divided into a torsion zone and a transition zone; the formed plate material is 2.5mm thick FB780 plate; the length of the first zone of the beam is 440±5mm; the perimeter of the cross section at the torsion center of the beam (i.e., the starting end of the first zone) is 368±5mm; the width-to-height ratio of the starting end of the first zone is 1.12; the width W1 of the starting end of the first zone is 87±2mm; the width W2 of the end of the first zone is 98.4±2mm; and the width of the end of the second zone is... The cross-sectional width W3 is 130±2mm, and the ratio of W1:W2:W3 is (0.85~0.92):1:(1.28~1.37). The minimum cross-sectional perimeter formed by the boundary between the first and second zones is 333±5mm, and the perimeter reduction rate of the first zone is 9.5±0.5%. The length of the second zone is 80±5mm, and the perimeter increase rate of the second zone is 12±0.5%. The width-to-height ratio of the cross-section at the boundary between the second zone and the overlapping zone is 1.51±0.1, with a width of 130±5mm. On the axial section of the second zone, the maximum angle between the web of the second zone and the bottom surface of the overlapping zone is 32°.

[0138] Comparative Example II: The shape and structure of the longitudinal arm are as follows Figure 32 and Figure 33As shown, the longitudinal arm exhibits a smaller cross-sectional perimeter only in the area with the smallest cross-sectional size. The minimum cross-sectional perimeter is 232±5mm, the maximum cross-sectional perimeter is 255±5mm, and the length of the circumferential weld connecting the crossbeam and the longitudinal arm is 403±10mm.

[0139] The difference between the beam in Comparative Example II and the beam in Sub-Example 1 is as follows: the plate thickness is 2.6mm, the plate material is FB780 steel, the length of the first section of the beam is 390±5mm, the perimeter of the cross section at the torsion center of the beam (i.e., the starting end of the first section) is 376.5±5mm, the width-to-height ratio of the starting end of the first section is 1.1, the width of the starting end of the first section is 87.4±2mm, and the width of the cross section at the end of the first section is 106.6±2mm; the minimum cross section perimeter formed by the junction of the first and second sections is 355±5mm, and the reduction rate of the cross section perimeter of the first section is 5.7±0.5%; the length of the second section is 150±5mm, the growth rate of the cross section perimeter of the second section is 2.4±0.5%, and the width-to-height ratio of the cross section at the junction of the second section and the overlapping section is 1.4±0.1 times, with a width of 123±5mm. On the axial section of the second section, the maximum angle between the web of the second section and the bottom surface of the overlapping section is 21°. Comparative Example III: The shape and structure of the longitudinal arm are as follows Figure 32 and Figure 33 As shown, the longitudinal arm structure shows a trend of gradually increasing cross-sectional area towards the hub bracket mounting end. The minimum cross-sectional perimeter is 232±5mm, and the maximum cross-sectional perimeter is 290±5mm. The length of the circumferential weld between the crossbeam and the longitudinal arm is 380±10mm. The crossbeam of Comparative Example III has the same structure as the crossbeam of Comparative Example II. The difference lies in the adaptive change of the cut shape in the overlapping area due to the different longitudinal arms.

[0140] Comparative Example IV: Combination Figure 34 and Figure 35Because Comparative Example I has a 7mm concave pit on the front segment 21, which easily leads to stress concentration, Comparative Example IV no longer has a pit. However, to meet the envelope requirements, the first perimeter reduction segment is reduced in size, resulting in a difference from Comparative Example I: In Comparative Example IV, The perimeter of the first shrinking section is 230±5mm at the head end, and the minimum perimeter is 202±5mm. The total relative change rate of the perimeter of the first shrinking section is about 12% smaller. The maximum perimeter is 1.43±0.1 times the minimum perimeter, and the maximum perimeter is 1.25±0.1 times the perimeter of the equal-perimeter section. The total relative change rate of the perimeter of the expanding section is about 44% larger. The total relative change rate of the perimeter of the second shrinking section is about 21% smaller. Based on the projected arc length of the longitudinal arm body on the outer side, the total arc length of the longitudinal arm body from the mounting hole to the end of the equal-perimeter section is 479±10mm. The length of the circumferential weld between the crossbeam and the longitudinal arm is 463±10mm. In addition, surface undulations appeared in the rapidly increasing section, and the surface transition was not as smooth as in sub-example 1.

[0141] Compared with the beam of sub-example 1, the beam in Comparative Example IV differs in the following ways: the plate thickness is 2.5mm, the plate material is FB780 steel, the length of the torsion zone in the first zone accounts for 86±5% of the total length of the first zone, the perimeter of the cross-section at the torsion center of the beam (i.e., the starting end of the first zone) is 345±5mm, the width-to-height ratio at the starting end of the first zone is 1.13, the width W1 at the starting end of the first zone is 82±2mm, the width W2 at the end of the first zone is 95±2mm, and the cross-sectional width W3 at the end of the second zone is 131±2mm. The ratio of W1:W2:W3 is (0.82~0.9):1:(1.33~1.43); the minimum cross-sectional perimeter formed by the boundary between the first and second zones is 298±5mm; the reduction rate of the cross-sectional perimeter in the first zone is 13.4±0.5%; the reduction rate of the cross-sectional perimeter in the torsion zone accounts for 55-65% of the total cross-sectional change rate in the first zone; the growth rate of the cross-sectional perimeter in the second zone is 26.7±0.5%; the width-to-height ratio of the cross-section at the boundary between the second zone and the overlapping zone is 1.51±0.1, with a width of 131±5mm. On the axial section of the second zone, the maximum angle between the web of the second zone and the bottom surface of the overlapping zone is 32°.

[0142] Sub-example 2: Combination Figure 36 Compared with the longitudinal arm of Sub-Example 1, the difference of this longitudinal arm is that: the longitudinal arm of this Comparative Example V is slightly smaller than the corresponding part of Sub-Example 1 in the first shrinking section and the rapid increasing section. The perimeter of the first shrinking section of Sub-Example 2 is 222.5±5mm, the minimum perimeter is 188.6±5mm, the maximum perimeter is 287.3±5mm, and the total relative change rate of the perimeter of the expanding section is about 52%. Both Sub-Example 2 and Sub-Example 1 show a smooth transition on the surface of the longitudinal arm. Compared with the beam in sub-example 1, the beam used in sub-example 2 differs in the following ways: the plate thickness is 2.5mm, the plate material is FB780 steel, the length of the torsion zone in the first zone accounts for 86±5% of the total length of the first zone, the perimeter of the cross-section at the torsion center of the beam (i.e., the starting end of the first zone) is 345mm, the width-to-height ratio at the starting end of the first zone is 1.11, the width W1 at the starting end of the first zone is 82±2mm, the width W2 at the end of the first zone is 94.5±2mm, and the ratio of W1:W2:W3 is (0.83~0.91):1 (1.33~1.43); the minimum cross-sectional perimeter formed by the junction of the first and second zones is 314±5mm, the reduction rate of the cross-sectional perimeter of the first zone is 9±0.5%, the reduction rate of the cross-sectional perimeter of the torsion zone accounts for 80-90% of the total cross-sectional change rate of the first zone; and the increase rate of the cross-sectional perimeter of the second zone is 18±0.5%. On the axial section of the second zone, the maximum angle between the web of the second zone and the bottom surface of the overlapping zone is 33°.

[0143] Under the same test conditions, the strength analysis of Comparative Examples 1 to Sub-Example 2 is shown in Table 6 below.

[0144] Table 6 Strength analysis of Comparative Examples 1 to Sub-Example 2

[0145] In the above sub-example 1, the maximum plastic strain under vertical impact in extreme working conditions is 0.07%, the maximum plastic strain under longitudinal impact is 0.05%, and the maximum plastic strain under lateral impact of the left wheel / right wheel is 1%.

[0146] Under the same test conditions, the wheel center stiffness analysis of Comparative Example 1 to Sub-Example 2 is shown in Table 7 below.

[0147] Table 7. Wheel center stiffness analysis of Comparative Examples 1 to Sub-Example 2

[0148] Under the same test conditions, the ultimate strength test results of Comparative Example I, Comparative Example IV, and Sub-Example 2 are shown in Table 8 below.

[0149] Table 8. Ultimate strength test results for Comparative Example I, Comparative Example IV, and Sub-Example 2

[0150] from Figures 37 to 38 The maximum weld stress analysis diagrams shown in Comparative Example I for the vertical jump and forward crossing conditions reveal that the maximum stress values ​​under both conditions occur at different weld locations where the crossbeam and longitudinal arm overlap.

[0151] And from Figures 39 to 40In Comparative Example II, the maximum weld stress occurs at the weld joint between the crossbeam and the longitudinal arm under both braking and starting conditions, and the maximum weld stress occurs on the same weld segment under both conditions. Figures 41 to 43 In Comparative Example III, the maximum weld stress occurs on the weld where the crossbeam and longitudinal arm overlap under various working conditions, including the jumping condition, braking condition, and starting condition. Furthermore, the maximum weld stress occurs on the same weld segment under both the jumping condition and the braking condition.

[0152] In Sub-Example 1, under various working conditions, the maximum stress distribution of the weld was only on the lap weld between the crossbeam and the longitudinal arm under the vertical jump and forward obstacle crossing conditions, and at different locations on this lap weld. This comparison shows that the S-shaped longitudinal arm structure, represented by Sub-Example 1 and Comparative Example I, can disperse the risk of fatigue damage and extend the service life of the weld and torsion beam assembly. Referring to Table 6, the extreme working conditions in Table 6 show that under the design structure of Comparative Example I, the maximum plastic strain of the left and right wheels under lateral impact is significantly higher than that of Comparative Examples II and III (0.69% and 0.83%, respectively). This indicates that although the longitudinal arm adopts an S-shaped streamlined structure, it still has a good ability to withstand lateral impact.

[0153] Combining Tables 6 and 8, the analysis of Comparative Example I, Comparative Example IV, and Sub-Example 2 shows that the overall performance of Comparative Example IV and Sub-Example 2 under basic working conditions is not significantly different. Although they are not as good as the effect of Sub-Example 1 of the present invention, they are very close to the effect of Sub-Example 1 under basic working conditions. However, because Comparative Example IV can only reduce the local cross-section of the longitudinal arm to avoid the space of the battery pack, the transition of the longitudinal arm structure of Comparative Example IV is not as smooth as that of Sub-Example 2 and Comparative Example I. It performs slightly worse in the left and right wheel impact conditions, as well as in the X-direction ultimate strength test and the Y-direction ultimate strength test under extreme working conditions. Sub-Example 2, on the other hand, shows significant optimization of the maximum stress of the body under multiple basic working conditions.

[0154] Comparing Comparative Example I with Sub-Example 1, it can be seen that the crossbeam and longitudinal arm of Comparative Example I are larger than those of Sub-Example 1. The advantage of this larger size is that it helps to increase the lateral impact on the left and right wheels. However, with its relatively larger structure, Comparative Example I is more rigid overall, and the torsion beam assembly is not as lightweight as that of Sub-Example 1.

[0155] Referring to Tables 1 and 7, the S-shaped trailing arm structures of Sub-Example 1, Comparative Example I, Comparative Example IV, and Sub-Example 2 have a wheel center stiffness of 4.5-5.5 N / m in the X direction, 6.5-7.5 N / m in the Y direction, and 2.0-2.5 N / m in the X direction, which are within a suitable stiffness range. However, Comparative Example II has a very large stiffness in the Y direction.

[0156] In summary, the variable cross-section longitudinal arm of the present invention, with its S-shaped streamline structure and cross-sectional variation design, enables the longitudinal arm to have high lateral stiffness and high load-bearing capacity (especially high buckling ultimate strength). At the same time, due to the S-shaped design, the length of the crossbeam is greatly shortened, which helps to reduce the weight of the torsion beam assembly. Furthermore, in conjunction with the crossbeam, it achieves a long weld design and smooth corner transition, ensuring the fatigue performance of the torsion beam assembly.

[0157] The torsion beam assembly formed by the longitudinal arm 20 and the crossbeam 10 of the present invention, under strict spatial constraints and with the crossbeam 10 having an extremely long, narrow, and high cross-sectional structure, still achieves a balance of high torsional stiffness, high load-bearing capacity, extreme lightweight, and high NHV performance. Moreover, its load-bearing capacity and NHV performance are comparable to those of the subframe, but its cost is far lower than that of the subframe, making it possible for a semi-independent torsion beam assembly to replace the high-cost subframe.

[0158] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A variable cross-section longitudinal arm, comprising an S-shaped longitudinal arm body, characterized in that: Along the S-shaped streamline direction of the longitudinal arm body, starting from the mounting hole of the mounting sleeve, a first shrinking section, an expanding section, a second shrinking section, and an equal-circumference section are smoothly connected in sequence. The first end of the first shrinking section is farther from the centerline of the torsion beam assembly than its end, and its cross-sectional perimeter gradually decreases from the mounting hole toward the expanding section, with a total relative change rate of 5-18%. The expanding section bends toward the crossbeam side of the torsion beam, and its cross-sectional perimeter gradually increases toward the second contracting section, with a total relative change rate of 40-55%. The second reduced-perimeter section bends outward toward the torsion beam assembly, and its cross-sectional perimeter gradually decreases toward the equal-perimeter section until it is equal to the cross-sectional perimeter of the equal-perimeter section, with a total relative change rate of 20-25%. Wherein, the end of the first shrinking segment is the minimum cross-sectional perimeter, and the end of the expanding segment is the maximum cross-sectional perimeter.

2. The variable cross-section longitudinal arm according to claim 1, characterized in that: The total relative change rate of the cross-sectional perimeter of the first shrinking segment is 13-18%, and the total relative change rate of the cross-sectional perimeter of the expanding segment is 45-50%.

3. The variable cross-section longitudinal arm according to claim 1, characterized in that: Based on the outer closing edge of the longitudinal arm body, the arc length of the expanding section is 2.3-3 times the arc length of the first contracting section. The sum of the arc length of the first contracting section and the arc length of the expanding section is 40-50% of the total arc length. The total arc length is the continuous outer arc length from the mounting hole on the longitudinal arm body to the end of the equal-circumference section.

4. A variable cross-section longitudinal arm according to claim 1, characterized in that: The expansion section includes a rapid expansion section and a slow expansion section. The rapid expansion section is connected to the first contraction section, and the slow expansion section is connected to the second contraction section.

5. A variable cross-section longitudinal arm according to claim 4, characterized in that: The total relative change rate of the cross-sectional perimeter of both the rapidly increasing segment and the slowly increasing segment is 20-25%, and the arc length corresponding to the slowly increasing segment is 2-2.5 times the arc length of the rapidly increasing segment.

6. A variable cross-section longitudinal arm according to claim 4, characterized in that: The lap weld between the crossbeam and the longitudinal arm body includes a top weld section, a bottom weld section, a front side weld section, and a rear side weld section. The top weld section and the bottom weld section are located on the top and bottom surfaces of the longitudinal arm body, respectively. The front side weld section and the rear side weld section connect the top weld section and the bottom weld section to form a circumferential weld. The front side weld section is attached to the gradually increasing section, and the rear side weld section is attached to the end of the gradually increasing section or the head of the second shrinking section. The front side weld section is C-shaped or V-shaped, and the rear side weld section is C-shaped or V-shaped. There is a rounded transition between adjacent weld sections.

7. A variable cross-section longitudinal arm according to claim 1, characterized in that: It also includes a hub bracket welded to the trailing arm body; the hub bracket includes a front side plate and a rear side plate; the front side plate is close to the crossbeam, and the front side plate is provided with a U-shaped opening, the U-shaped opening fits into the second shrinkage section, and the second shrinkage section is sandwiched between the two wings of the U-shaped opening; the upper and lower wings of the U-shaped opening both extend from the side corner area of ​​the trailing arm body toward the crossbeam and toward the axis of the trailing arm body; the rear side plate is arranged opposite to the front side plate and is fixedly connected to the trailing arm body.

8. A variable cross-section longitudinal arm according to claim 7, characterized in that: The rear side plate is fixed to the end opening of the equicircular segment, and the rear side plate covers the end opening.

9. A variable cross-section longitudinal arm according to claim 7, characterized in that: The end of the isopleth segment is fixed with a shock absorber mounting base.

10. A torsion beam assembly, comprising a crossbeam, characterized in that: It also includes the variable cross-section longitudinal arm as described in any one of claims 1-9. The expanding section is embedded in the end opening of the crossbeam, and the overlapping area of ​​the crossbeam and the longitudinal arm is located within the expanding section or extends from the expanding section to the head of the second contracting section.

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