Frame pre-bent longitudinal beam preparation method, pre-bent longitudinal beam and motor home frame

Abstract

The invention relates to the technical field of motor home frame manufacturing, in particular to a preparation method of a pre-bent longitudinal beam of a frame, the pre-bent longitudinal beam and the motor home frame. The preparation method comprises the following steps: continuously rolling and forming a strip-shaped metal raw material to form an integrated longitudinal beam with a target section; accumulative plastic bending in the length direction of the longitudinal beam is applied to the longitudinal beam through the adjustable eccentric bending roller, so that the longitudinal beam synchronously forms continuous upward arch-shaped pre-bending; enabling the longitudinal beam to pass through a shaping roller frame to stabilize an arch-shaped pre-bent curve; the arch height of the arch-shaped pre-bending is detected in real time, the eccentricity of the adjustable eccentric bending roller or the roller gap of the shaping roller frame is adjusted according to the detected arch height deviation, and springback is compensated; and performing fixed-length cutting on the longitudinal beam. Quantitative controllable pre-bending is synchronously completed in the one-time forming process of the longitudinal beam, follow-up shape correction and welding finishing are not needed, the shape line consistency and the material performance integrity of the left longitudinal beam and the right longitudinal beam are guaranteed, and the vehicle driving stability and the structure durability are improved.

Description

Technical Field

[0001] This invention relates to the field of RV frame manufacturing technology, and in particular to a method for preparing a pre-bent longitudinal beam, the pre-bent longitudinal beam, and an RV frame. Background Technology

[0002] As a core load-bearing component of the vehicle chassis, the longitudinal beams, together with the crossbeams, suspension connectors, and traction connection structure, form the complete chassis. Their primary function is to withstand various loads generated during vehicle operation, transmit forces under traction, braking, and bumpy conditions, and ensure the overall structural stability and smooth driving posture of the vehicle. The longitudinal beams resist external forces through their own structural strength, and with pre-bending design, they counteract sagging deformation under full load, maintaining the vehicle's level posture. Therefore, the structural form and forming process of the longitudinal beams directly affect the chassis's load-bearing capacity, mechanical properties, and service life.

[0003] Currently, there are three main technical solutions in the industry for forming the longitudinal beams of vehicle frames. The first is a straight beam bending and welding shaping structure. This solution typically uses channel steel or rectangular steel pipes as the raw material for the longitudinal beams. The raw material is first bent to form a rough shape, then spliced ​​and welded to achieve structural closure. Finally, manual straightening is performed based on experience to meet basic installation and usage requirements. The second is a three-section longitudinal beam structure, where both left and right longitudinal beams consist of three sections of steel: a front section, a middle section, and a rear section. These three sections are connected and fixed using bolts or clamping plates to form a complete longitudinal beam for load-bearing function. The third is an I-beam hot-bending or mechanical bending process. This process artificially imparts the required pre-bending shape to the longitudinal beam through high-temperature heating or mechanical forced bending to counteract the sagging deformation caused by suspension compression and load bending when the vehicle is fully loaded.

[0004] The aforementioned existing technologies have several technical problems in practical applications: In the straight beam bending and welding shaping scheme, the heat input generated during the welding process can lead to local coarsening of metal grains, resulting in uneven distribution of the mechanical properties of the longitudinal beams and residual stress accumulation, which can easily lead to irregular deformation or crack propagation during long-term use; while the shaping and straightening rely on manual operation, it is difficult to ensure that the pre-bending lines of the left and right longitudinal beams are consistent, resulting in poor product consistency during mass production. The force transmission path of the three-segment longitudinal beam structure is manually segmented, and bending moment and shear force are prone to abrupt changes in the connection area, forming stress concentration; under long-term vibration, temperature change and other working conditions, the preload of bolted connections will gradually decrease, and even loosening may occur, which not only increases the risk of deformation and noise, but also reduces the durability of the entire vehicle. Moreover, when the structure is fully loaded or traveling at high speed, the rear section of the longitudinal beam is prone to sinking, affecting traction stability and vehicle posture. Hot bending process will destroy the original rolling streamline structure of steel, resulting in a decrease in the yield strength and fatigue limit of the material; mechanical bending will cause the strain to concentrate in local section, causing local buckling of web plate and twisting of flange, and the rebound is unstable, making it difficult to ensure the accuracy of pre-bending arc. Under long-term fatigue cycle, it is easy to produce permanent deformation or cracking, which is difficult to meet the needs of scenarios such as RVs with high requirements for vibration durability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing pre-bent longitudinal beams, the pre-bent longitudinal beams, and a motorhome frame. This method solves problems such as poor continuity of longitudinal beam structure, insufficient pre-bending accuracy, impaired mechanical properties, and poor batch consistency in existing technologies. It enables quantitative and controllable pre-bending to be completed simultaneously during the one-time forming process of the longitudinal beams, eliminating the need for subsequent straightening and welding adjustments. This ensures the consistency of the left and right longitudinal beam profiles and the integrity of material properties, thereby ensuring that the frame maintains good horizontal posture and overall rigidity under both preparation and full-load conditions, improving vehicle driving stability and structural durability.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A method for preparing a pre-bent longitudinal beam for a vehicle frame includes: continuously roll forming a strip of metal raw material to form an integral longitudinal beam with a target cross-section; during the roll forming process, applying cumulative plastic bending along the length direction of the longitudinal beam to an adjustable eccentric bending roller, so that the longitudinal beam synchronously forms a continuous upward arched pre-bend; passing the longitudinal beam with the arched pre-bend through a shaping roller frame to stabilize the curve of the arched pre-bend; detecting the arch height of the arched pre-bend in real time, and adjusting the eccentricity of the adjustable eccentric bending roller or the roll gap of the shaping roller frame according to the detected arch height deviation to compensate for springback; and cutting the longitudinal beam to a fixed length.

[0007] Optionally, real-time detection of the arch height and adjustment based on the deviation includes: calculating the difference between the measured arch height and the target arch height; if the difference is positive, increasing the eccentricity of the bending roller or decreasing the gap of the shaping roller; if the difference is negative, decreasing the eccentricity of the bending roller or increasing the gap of the shaping roller.

[0008] Optionally, the arch height of the pre-bent arch is based on the line connecting the support points at both ends of the longitudinal beam, where the arch height h satisfies the relationship h=k·L, where L is the distance between the support ends of the longitudinal beam and k is a proportionality coefficient.

[0009] Optionally, the value of the midpoint arch height h ranges from 6mm to 18mm.

[0010] This invention also provides a pre-bent longitudinal beam, which is an integrally formed component manufactured using the preparation method described above; The pre-bent longitudinal beam has a continuous and gradually changing upward arched pre-bent line along its length. The arch height at the midpoint of the pre-bent longitudinal beam is between 6 mm and 18 mm, with the line connecting the support points at both ends as the reference.

[0011] Optionally, the cross-sectional shape of the pre-bent longitudinal beam is one of C-shaped, Z-shaped, L-shaped, U-shaped, cap-shaped, or I-shaped.

[0012] Optionally, the cross-section of the pre-bent longitudinal beam is a composite thin-walled cross-section with reinforcing ribs, flanges, or inner folds.

[0013] This invention also provides a motorhome frame, comprising: A pair of pre-bent longitudinal beams, which are arranged parallel to each other along the longitudinal direction of the vehicle; A crossbeam is positioned between a pair of pre-bent longitudinal beams; A suspension connector is provided on the pre-bent longitudinal beam; The traction connection structure is installed on the pre-bent longitudinal beam.

[0014] Optionally, the crossbeam and the pre-bent longitudinal beam are connected by bolts, rivets, or partial structural welding.

[0015] Optionally, the suspension connector includes a suspension lug disposed on the outside of the pre-bent longitudinal beam, the vertical installation position of the suspension lug matching the pre-bending profile of the pre-bent longitudinal beam.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: 1. The pre-bent longitudinal beam preparation method of this invention uses continuous roll forming of strip metal raw materials to form an integral longitudinal beam, avoiding the damage to the material rolling flow line caused by traditional segmented splicing or welding processes. This ensures uniform distribution of the mechanical properties of the longitudinal beam and solves the problems of grain coarsening and residual stress accumulation caused by welding heat input in traditional processes. During the roll forming process, cumulative plastic bending is applied through adjustable eccentric bending rolls. The method of superimposing multiple small plastic deformations, unlike traditional single-pass forced bending, avoids local strain concentration and makes the upward arched pre-bending of the longitudinal beam continuous and gradual. This effectively solves the problems of web buckling, flange twisting, and unstable springback caused by mechanical bending. The shaping roll frame processes the pre-bent longitudinal beam to prevent local curvature abrupt changes in the pre-bent line, making the arc transition smoother, while suppressing springback and further improving the stability of the pre-bent shape. By detecting the arch height in real time and adjusting the eccentricity or roll gap according to the deviation, a closed-loop control is formed to compensate for the springback differences under different materials, plate thicknesses, or forming speeds, solving the problems of insufficient pre-bending accuracy and poor batch consistency in traditional processes. Fixed-length cutting allows for the production of longitudinal beams of the required length based on the wheelbase requirements of different vehicle models. The entire manufacturing process eliminates the need for subsequent straightening and welding, simplifying the process steps and improving production efficiency. This manufacturing process ensures the structural continuity of the longitudinal beams through continuous rolling, achieves precise pre-bending through cumulative plastic bending, stabilizes the curve shape through shaping rollers, controls accuracy through real-time compensation, and adapts to different application requirements through fixed-length cutting. Together, these technologies ensure that the longitudinal beams maintain the integrity of material properties while possessing a stable pre-bending profile and good batch consistency. This improves the overall structural performance of the vehicle frame, batch production consistency, and long-term reliability, demonstrating promising prospects for industrial application and significant promotional value.

[0017] 2. Compared to traditional straight beam welded frame structures, this invention achieves integrated forming and quantitative pre-bending of longitudinal beams through continuous cold bending roll forming, avoiding material property degradation caused by welding heat-affected zones and shape deviations caused by manual shaping. Verification through equivalent static load deflection testing and finite element simulation shows that, under the same frame size and load conditions, the maximum deflection of the frame structure of this invention is reduced by 12%–25%, the peak stress of the longitudinal beams is reduced by 18%–35%, the consistency of bending springback is improved by more than 30%, and the pre-bending deviation of the left and right beams can be stably controlled within ≤0.8mm (the typical mass production deviation in the industry is 3.5–7mm). Therefore, this invention can significantly improve the vehicle's full-load posture stability and traction smoothness, increase frame fatigue life, and enhance the durability and reliability of the living quarters connection structure.

[0018] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In addition, the dimensions or spacing between the components are exaggerated to show the position of each component, and the schematic diagrams are for illustrative purposes only.

[0020] Figure 1 This is a flowchart of the longitudinal beam preparation method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the longitudinal beam provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the manufacturing principle of the longitudinal beam provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the longitudinal beam manufacturing production line provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the roller-pressed display plate provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the roller pressing process provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the roll pressing and pre-bending forming process provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the rolled product provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the pre-bending process provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of the longitudinal beam cross-section provided in an embodiment of the present invention; Figure 11 This is a schematic diagram of a motorhome frame provided in an embodiment of the present invention; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, it should be understood that when the terms include and / or encompass are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Example 1 like Figure 1 As shown, this embodiment proposes a pre-bent longitudinal beam for the vehicle frame (such as...). Figure 2 The preparation method of (shown) includes: Strip metal raw materials are continuously roll-formed to form an integral longitudinal beam with a target cross-section; During the roll forming process, an adjustable eccentric bending roller applies cumulative plastic bending along the length of the longitudinal beam, causing the longitudinal beam to synchronously form a continuous upward arched pre-bending. The longitudinal beam with an arched pre-bend is passed through a shaping roller frame to stabilize the curve of the arched pre-bend; The arch height of the pre-bent arch is detected in real time, and the eccentricity of the adjustable eccentric bending roller or the roller gap of the shaping roller frame is adjusted according to the detected arch height deviation to compensate for the springback. The longitudinal beams are cut to a fixed length.

[0022] like Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 As shown, this method uses a continuous roll forming process to directly process strip metal raw materials, forming a longitudinal beam body with the required closed or open cross-section in one step. This is fundamentally different from the traditional process of first processing straight beams and then bending or splicing them in subsequent processes. An adjustable eccentric bending roller device is integrated into this continuous forming process. When the longitudinal beam material passes through this device, the eccentric bending roller applies a continuous bending moment distributed longitudinally. Because the material is in a continuous plastic deformation state, this bending effect gradually accumulates from the feeding end, eventually forming a smooth, continuous, and upward-facing arched curve along the entire length of the longitudinal beam, i.e., the required pre-bending.

[0023] Subsequently, the longitudinal beam with initial pre-bending is passed through a set of shaping rollers. The function of these rollers is to constrain and shape the pre-bent line. Through the progressive pressing and straightening of multiple rollers, local unevenness or distortion is eliminated, the entire arch curve tends to be stable, and some elastic recovery is suppressed.

[0024] To achieve high-precision control of the pre-bending dimensions, this method also includes an online detection and feedback adjustment process. Immediately after shaping, an arc-measuring device (such as a laser profilometer) is used to perform real-time non-contact measurement of the arch height of the formed longitudinal beam, and the measured data is compared with a preset target value. Once a deviation is detected, the control system automatically fine-tunes the eccentricity of the upstream eccentric bending roller or the gap between the forming rollers, thereby changing the amount of plastic deformation applied to the material and dynamically compensating for springback caused by fluctuations in material properties or minor changes in process parameters.

[0025] Finally, the longitudinal beams that meet the accuracy requirements are cut to a fixed length to obtain the finished product, such as... Figure 9 As shown.

[0026] This method abandons the traditional approach that relies on welding or post-bending straightening, avoiding the material strength reduction, uneven microstructure, and residual stress problems caused by the heat-affected zone of welding from the source of the process. It also eliminates the springback instability and localized stress concentration caused by forced bending in the later stages. By combining simultaneous forming and pre-bending with online detection and real-time compensation, precise and stable control of the pre-bending shape and dimensions can be achieved while ensuring the continuity of the longitudinal beam structure and the integrity of the material, providing a technological foundation for obtaining consistently high-quality products in mass production.

[0027] Continuous roll forming is a well-known technology in the cold bending of metal strips. The unit typically includes an uncoiler, a guide and leveling mechanism, a multi-pass forming stand, and a length-cutting device. The adjustable eccentric bending roll refers to a roll in the roll forming stand whose bearing seat position can be adjusted via a servo motor or hydraulic mechanism, causing a controllable offset of its central axis relative to the standard forming line. This alters the distribution of the roll gap in the material width direction, introducing bending moment. The online arc measuring device can employ a sensor array based on the laser triangulation principle, calculating the real-time arch height by scanning the contour of the upper surface of the longitudinal beam and comparing it with a baseline.

[0028] This process offers high forming precision, controllable pre-bending value, good consistency between left and right profiles, and allows for rapid switching between different cross-sections by changing the roller type. It boasts high production efficiency, wide applicability, and significantly improved overall manufacturing quality and durability.

[0029] Real-time detection of the arch height and adjustment based on the deviation includes: calculating the difference between the measured arch height and the target arch height; if the difference is positive, increasing the eccentricity of the bending roller or decreasing the gap of the shaping roller; if the difference is negative, decreasing the eccentricity of the bending roller or increasing the gap of the shaping roller.

[0030] The system first calculates the algebraic difference between the measured arch height and the target arch height. When the difference is positive, it indicates that the actual arch height exceeds the target value, meaning the material springback is less than expected or over-bending has occurred. In this case, the control system issues a command to reduce the eccentricity of the eccentric bending roller or increase the gap between the forming rollers to weaken the applied plastic bending. Conversely, when the difference is negative, it indicates that the actual arch height is insufficient, meaning the springback is too large or the pre-bending is insufficient. In this case, the eccentricity is increased or the roller gap is decreased to enhance the bending.

[0031] Specific process for controllable pre-bending of longitudinal beams: Raw material roll → guiding device → preforming roller frame → eccentric upper bending roller / lower bending roller (pre-bending formation) → shaping roller frame (arc stabilization) → online laser arc measuring device → automatic compensation adjustment → finished product (with upward arched pre-bent longitudinal beam).

[0032] 1. Raw material introduction and initial shaping: The coil or flat sheet is fed into the roll forming line through the uncoiler; the material is kept centered in the width direction by the guiding device to avoid deviation; through 2 to 3 pre-forming roller frames, the steel strip is initially formed into the basic shape of the target cross section (Z / L / C / U / cap shape, which provides the cross section stiffness basis for subsequent longitudinal bending).

[0033] 2. Controllable longitudinal plastic bending using eccentric upper / lower bending rollers: The upper bending roller is an adjustable eccentric roller, its center offset from the standard roller line by a controllable eccentricity e; the lower bending roller also has eccentricity adjustment capability, forming an upper and lower eccentric bending roller pair; when the material passes through this roller pair, the upper bending roller applies a downward pressing force, while the lower bending roller lifts the material upward, generating localized cumulative plastic deformation, causing the longitudinal beam to gradually form an upward arching trend; by adjusting the eccentricities e1 and e2 of the upper and lower bending rollers, the pre-bending amount h can be precisely controlled. Its core principle is the accumulation of small plastic deformations over multiple passes, thereby forming a continuous arc along the entire longitudinal beam instead of the traditional single-pass forced bending.

[0034] 3. The shaping rollers stabilize the curve, ensuring a continuous pre-bending line: After passing through the pre-bending station, the material enters 2-4 shaping rollers. These rollers stabilize the newly formed pre-bending line, preventing abrupt changes in local curvature; through multi-roller wrapping pressing, they smooth the curve transition; suppress springback, making the pre-bending dimensions more stable; and ensure the consistency of the curves of the left and right longitudinal beams (deviation ≤ 0.8mm). The shaping rollers do not alter the pre-bending, but rather ensure that the pre-bending is uniform, smooth, without springback, and without deviation.

[0035] 4. Online laser arc measurement: After shaping, a laser arc measuring instrument is set up to measure in real time: the midpoint arch height h, the consistency of the arc curve, the springback compensation value, the symmetry deviation of the left / right beam, and the system automatically adjusts the eccentric roller e value in a closed loop.

[0036] 5. Unloading → One-time forming of pre-bent longitudinal beams: After the above process, the longitudinal beams have a continuous upward arch shape, the arc accuracy h is controlled within ±1.0mm, the left and right deviation is ≤0.8mm, and no further welding or heating is required.

[0037] Springback compensation adjustment ensures a stable and consistent h (arch height), suitable for different materials, plate thicknesses, and speeds. Detailed process of springback compensation adjustment: 1. Real-time measurement of longitudinal beam curvature: A laser arc measuring instrument (laser triangulation) is installed at the exit of the shaping section. The contour data of the upper surface of the longitudinal beam is continuously collected, and the current h value is calculated. This is then compared in real time with the target h0 (e.g., 9.5 mm).

[0038] 2. Calculate the rebound deviation Δh: When a deviation is detected in the actual measured value h (Δh = measured h – target h), the system judges the trend of rebound or bending. If Δh > 0 → excessive rebound. If Δh < 0 → insufficient pre-bending.

[0039] 3. Automatic compensation and adjustment of eccentricity or roll gap: The control system automatically adjusts the following based on Δh: upper bending roll eccentricity e1, lower bending roll eccentricity e2, and forming roll gap δ. Small-range fine adjustments (typically 0.05–0.20 mm) are sufficient to compensate for springback. The adjustments take effect immediately on the next section of material, forming a closed-loop control system.

[0040] 4. Stable and consistent output h (arch height): Through continuous compensation, h is kept stable at the target value ±1.0mm.

[0041] The process involves passing the rolled material sequentially through a guide section, a pre-forming section, an eccentric bending roller section, and a shaping roller frame section. Under the adjustable pressing force of the eccentric upper and lower bending rollers, the longitudinal beam forms a continuous upward pre-bent line. After the arc is stabilized by the shaping roller frame, the arch height is collected and automatically compensated by an online arc measuring device, thus achieving one-time forming of the pre-bent longitudinal beam.

[0042] For RV chassis with a wheelbase of 3.0m-7.0m, the arch height h satisfies: Preferred fixed value scheme: standard 4.5m–5.5m wheelbase platform, h=9.5mm (3 / 8″) ±1.0mm; Proportionalization scheme: h = k·L, where L is the spacing between the support ends of the longitudinal beams, and k is the proportionality coefficient, taken as (1.5–3.0)×10. - ³. The midpoint camber height h refers to the vertical distance from the center point of the longitudinal beam along its length to the chord line connecting its two theoretical support endpoints. This formula transforms the setting of the pre-bending amount from a fixed empirical value into a variable related to the basic structural dimensions of the chassis. For vehicle platforms with different wheelbases, a suitable pre-bending camber height can be calculated based on the same proportional coefficient. This allows the upward camber provided by the pre-bending to more reasonably and scientifically match the expected deflection deformation of the specific chassis under full load, thereby optimizing the compensation effect.

[0043] The value of the midpoint arch height h ranges from 6mm to 18mm. Limiting h within this range ensures the practicality and effectiveness of the pre-bending design. Furthermore, the arch height deviation between the left and right longitudinal beams does not exceed 0.8mm, thereby ensuring that the frame maintains good horizontal posture and overall rigidity under both preparation and full-load conditions.

[0044] Example 2 This embodiment provides a pre-bent longitudinal beam, which is an integrally formed component manufactured using the preparation method described above; The pre-bent longitudinal beam has a continuous and gradually changing upward arched pre-bent line along its length. The arch height at the midpoint of the pre-bent longitudinal beam is between 6 mm and 18 mm, with the line connecting the support points at both ends as the reference.

[0045] As the core load-bearing component of the frame, the integrated and continuous structure provides higher overall stiffness and bending strength; the precise and controllable pre-bending enables it to actively and accurately compensate for load deformation after being assembled into the frame, helping the frame maintain a stable posture under different loads; good geometric consistency lays the foundation for the frame's left-right symmetry, driving stability, and reliable connection with other components.

[0046] like Figure 10 As shown, the cross-sectional shape of the pre-bent longitudinal beam is one of C-shaped, Z-shaped, L-shaped, U-shaped, cap-shaped, or I-shaped. These cross-sections are formed by bending different sheet metals and have their own specific bending and torsional properties and ease of connection. For example, the C-shaped cross-section is simple to manufacture and the opening facilitates connection with other cross beams; the cap-shaped cross-section (or channel-shaped) has a high bending moment of inertia; and the I-shaped cross-section provides excellent bending efficiency. By changing the forming die combination on the roller press, longitudinal beams with different cross-sectional shapes can be flexibly produced on a single production line. Those skilled in the art can select the most suitable cross-sectional shape according to specific mechanical performance requirements and installation interfaces without changing the basic process principle of pre-bending.

[0047] The pre-bent longitudinal beam has a composite thin-walled section with reinforcing ribs, flanges, or inward folds. Reinforcing ribs are raised ridges stamped onto the web or flanges of the section, effectively improving the local stiffness of the plate and preventing buckling under pressure. Flanges pointing outwards or inwards at small angles enhance edge stiffness, improve connection conditions, or increase safety. Inward folds form more complex closed or semi-closed section structures. These features can be achieved through special roll forming processes or subsequent auxiliary forming stations. Using this type of composite section allows for improved moment of inertia and bending and torsional stiffness of the longitudinal beam section through structural optimization without significantly increasing material usage. This results in less deformation and lower material stress levels under the same load, further improving the frame's load-bearing capacity, stiffness, and durability, achieving a balance between lightweight and high performance.

[0048] Example 3 This embodiment proposes a caravan frame applicable to the structural frames of towable caravans, recreational trailers, flatbed freight trailers, vehicle transport trailers, garbage transfer trailers, small engineering equipment transport vehicles, light commercial vehicles, vending truck modified chassis, agricultural operation trailers, forestry operation trailers, light commercial vehicle chassis, small freight trailers, container mini chassis vehicles, and light construction equipment chassis.

[0049] like Figure 11 As shown, the RV frame includes: A pair of pre-bent longitudinal beams, which are arranged parallel to each other along the longitudinal direction of the vehicle; A crossbeam is positioned between a pair of pre-bent longitudinal beams; A suspension connector is provided on the pre-bent longitudinal beam; The traction connection structure is installed on the pre-bent longitudinal beam.

[0050] Between the main longitudinal beams, multiple crossbeams are used for lateral connection, forming a basic frame grid that provides lateral stability and torsional stiffness to the chassis. Suspension connectors are also installed on the longitudinal beams for mounting suspension systems, such as leaf springs or air suspension, and traction connection structures (such as tow pin seats or trailer hitch mounting plates).

[0051] The one-piece pre-bendable frame can counteract the sagging tendency caused by suspension compression and load bending moment when the caravan is towed on the road, so that the frame maintains a stable geometric posture during driving. This effectively reduces phenomena such as braking nose-dive, rear-end sinking, vehicle body swaying and loosening of the connecting parts of the living cabin, thereby improving vehicle safety and passenger comfort.

[0052] The crossbeam and the pre-bent longitudinal beam are connected by bolts, riveting, or partial structural welding. Bolts use high-strength bolts, which are convenient for installation and subsequent maintenance; riveting provides a permanent connection with high reliability; partial structural welding is welding performed at specific points and is usually used in areas requiring extremely high connection strength.

[0053] The suspension connector includes a suspension lug disposed on the outside of the pre-bent longitudinal beam, and the vertical installation position of the suspension lug matches the pre-bending profile of the pre-bent longitudinal beam.

[0054] Suspension lugs are raised structures used to mount suspension hangers or directly connect suspension components (such as leaf springs). Matching the vertical installation position to the pre-bending line means that during design and installation, the specific installation point of the lug in the longitudinal beam height direction is determined based on the actual spatial curve of the longitudinal beam under pre-bending conditions. This ensures that after the suspension system is installed, when the frame is under target load, the load-bearing plane of the entire frame can reach or approach an ideal horizontal state, thereby optimizing the suspension's stress angle and the vehicle's driving posture. By actively aligning the suspension connection point with the pre-bending line, the design intent of the pre-bending is accurately executed, fully utilizing the pre-bending's compensatory adjustment effect on the frame's posture and avoiding the cancellation of the pre-bending effect or the generation of new torque interference due to improper connection point positioning, ultimately ensuring the vehicle's driving stability and ride comfort.

[0055] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method of manufacturing a pre-bent rail longitudinal beam, characterized in that, The application comprises: continuous roll forming of a strip-shaped metal raw material to form an integral longitudinal beam with a target cross section; during the roll forming, applying cumulative plastic bending along the length direction of the longitudinal beam by an adjustable eccentric bending roll to synchronously form a continuous upward arch-shaped pre-bend in the longitudinal beam; passing the longitudinal beam with the arch-shaped pre-bend through a shaping roll stand to stabilize the curve of the arch-shaped pre-bend; real-time detection of the arch height of the arch-shaped pre-bend and adjustment of the eccentricity of the adjustable eccentric bending roll or the roll gap of the shaping roll stand according to the detected arch height deviation to compensate for springback; cutting the longitudinal beam to a fixed length.

2. The production method according to claim 1, wherein The real-time detection of the arch height and the adjustment according to the deviation comprise: calculating the difference between the measured arch height and the target arch height; if the difference is positive, increasing the eccentricity of the bending roll or decreasing the shaping roll gap; if the difference is negative, decreasing the eccentricity of the bending roll or increasing the shaping roll gap.

3. The production method according to claim 1, wherein The arch height of the arch-shaped pre-bend is measured from the line connecting the support points at both ends of the longitudinal beam, wherein the midpoint arch height h satisfies the relationship h=k·L, where L is the distance between the support ends of the longitudinal beam, and k is a proportionality coefficient.

4. The production method according to claim 3, wherein The value of the midpoint arch height h is in the range of 6mm to 18mm.

5. A pre-bent longitudinal beam, characterized by The pre-bent longitudinal beam is an integrally formed component made by the preparation method of any one of claims 1 to 4; The pre-bent longitudinal beam has a continuous and gradually changing upward arch-shaped pre-bend line along its length direction. The midpoint arch height is in the range of 6mm to 18mm.

6. The pre-bent rail of claim 5, wherein, The cross-sectional shape of the pre-bent longitudinal beam is one of C-shaped, Z-shaped, L-shaped, U-shaped, hat-shaped or I-shaped.

7. The pre-bent rail of claim 5, wherein, The cross section of the pre-bent longitudinal beam is a composite thin-walled cross section with stiffeners, flanges or inner flanges.

8. A recreational vehicle frame characterized by, The application comprises: a pair of pre-bent longitudinal beams as claimed in any one of claims 5 to 7, arranged in parallel along the longitudinal direction of the vehicle; a cross beam arranged between the pair of pre-bent longitudinal beams; a suspension connecting piece arranged on the pre-bent longitudinal beam; a traction connecting structure arranged on the pre-bent longitudinal beam.

9. The recreational vehicle frame of claim 8, wherein, The cross beam and the pre-bent longitudinal beam are connected by screwing, riveting or local structural welding.

10. The recreational vehicle frame of claim 8, wherein, The suspension connecting piece comprises a suspension lug arranged on the outer side of the pre-bent longitudinal beam, and the vertical mounting position of the suspension lug matches the pre-bend line of the pre-bent longitudinal beam.

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