Method for forming structural elements for vehicles

Abstract

Disclosed herein is a method for forming a reinforcing structural element for a vehicle, the method comprising the steps of: preparing a thin-walled hollow member (102); supporting at least a portion of the thin-walled hollow member (104); and overmolding a structural element material onto at least a portion of the thin-walled hollow member to form a reinforcing structural element (106).

Description

Technical Field

[0001] The present invention relates to a method for forming a vehicle structural element. More specifically, the present invention relates to a method for forming a vehicle structural element such as a structural housing for a high-voltage battery.

Background Art

[0002] Electric vehicles (EVs) carry heavy batteries that must be protected in case of destruction or collision that could cause penetration or damage to the battery pack.

[0003] A known technique for reducing the forces from a frontal or rear collision was to create a crumple zone in the vehicle to absorb the impact force and transmit the load of destruction across the front or rear of the vehicle. However, EV batteries or battery packs are particularly vulnerable to side-impact collisions. This is because there is limited lateral space in the vehicle to include a properly sized crumple zone for side collisions.

[0004] Battery box assemblies typically include molded plastic panels that are assembled together to hold the battery. The plastic material and molding processes such as compression molding or injection molding allow for the formation of various shapes for the overall battery pack assembly / electric vehicle and do not add significant weight. However, current molding methods are limited and produce battery box panels that do not provide weight-efficient protection from the load of destruction.

[0005] Solutions can be provided by strengthening the battery pack or battery box panels with stronger materials or additional layers, but the weight or overall size of the battery box / pack can increase significantly, which can then reduce the overall efficiency of the electric vehicle.

Summary of the Invention

[0006] The objective of the present invention is to address these problems and to achieve effective reinforcement of structural elements for vehicle assemblies. [Means for solving the problem]

[0007] According to an aspect of the present invention, a method for forming a vehicle reinforcement structural element is provided, the method comprising the steps of preparing a thin-walled hollow member, supporting at least a portion of the thin-walled hollow member, and overmolding a structural element material onto at least a portion of the thin-walled hollow member to form a reinforcement structural element.

[0008] In this method, structural elements can be effectively reinforced with lightweight components while also being able to be further overmolded into a desired shape. One or more thin-walled hollow members can be incorporated into the reinforced structural element. To reinforce the overmolded structural element, multiple thin-walled hollow members can be supported simultaneously or sequentially along different parts of the structural element. Thus, the reinforced overmolded structural element can achieve improved mechanical properties for safety requirements in the automotive industry, such as the European Economic Commission (ECE) regulations for lateral fracture impact behavior testing (e.g., 100 kN load). In particular, this reinforced structural element can be effectively used in battery box structures and battery covers to protect high-voltage batteries in electric vehicles.

[0009] Thin-walled hollow members include metallic or non-metallic tubes such as aluminum extrusions, steel tubes, or carbon fiber reinforced (CFRP) pultruded tubes, and typically exhibit exceptional mechanical properties (including high tensile or compressive strength and stiffness and high specific strength), allowing for the reinforcement of structural elements in a highly efficient manner. Thin-walled hollow members, such as CFRP pultruded tubes, do not significantly increase the volume or mass of the overall structure, but can enable the effective transfer of external forces onto structural elements into the thin-walled hollow members. This is particularly important in EVs, where the battery pack adds considerable weight to the vehicle, and it is desirable to control the weight of the battery pack and the overall weight of the electric vehicle within a target range.

[0010] As is understood, elongated, thin-walled hollow members, such as those formed by metal extrusion or tubing or fiber-reinforced pultrusion, exhibit improved mechanical properties along the main longitudinal axis of the elongated member (i.e., against axial forces applied along the walls of a tubular member), but are more susceptible to deformation, fracture, bending, or collapse against applied off-axis forces, particularly forces nearly perpendicular to the longitudinal axis.

[0011] In addition, thin-walled hollow members can be advantageously incorporated with structural elements in a way that realizes a multi-material configuration, where each layer or portion of the overmolded material can perform a specific function, such as allowing its internal surface to be used for running cables, wiring, or fluids through the structural element / entire assembly.

[0012] The inclusion of thin-walled hollow members during the molding process has not been previously considered. This is because overmolding techniques such as compression molding, injection molding, vacuum injection, resin transfer molding, or liquid injection typically require the application of considerable internal mold pressure to the structural elements, which can crush thin-walled hollow members that are attached to or integrated into the structural elements during the overmolding process. For example, the internal mold pressure in injection molding can easily exceed 150 MPa. When this pressure is applied to an overmolded configuration for CFRP pultruded molds where the fibers are positioned approximately along the main longitudinal axis, the material wall thickness is less than 1 mm, and the outer dimensions are greater than 20 mm, it can easily lead to the collapse of the pultruded member and failure of the overmolding process. However, the present invention makes it possible to effectively incorporate thin-walled hollow members into the molding process and realize reinforced structural elements.

[0013] Preferably, the step of supporting at least a portion of the thin-walled hollow member includes the step of inserting a solid support into the thin-walled hollow member or injecting a fluid. In this method, the solid support or fluid can provide mechanical support to the thin-walled hollow member because it offsets any external pressure on the thin-walled hollow member during the overmolding process. At least a portion of the supported thin-walled hollow member experiences overmolding pressure during the overmolding step.

[0014] The solid support may be in the form of a mandrel or rod that fills the hollow space in at least a portion of the thin-walled hollow member. Importantly, the solid support makes sufficient contact with the inner surface of the thin-walled hollow member to ensure that external pressure (from the overmolding process) can be transmitted to the solid support through the walls of the thin-walled hollow member. As you would understand, the solid support must be robust enough to withstand and "absorb" external pressure / force.

[0015] The supporting fluid may be a gas or liquid, or even a foamy substance or foam, injected into the hollow space within at least a portion of the thin-walled hollow member. In this method, the walls of the thin-walled hollow member can be supported from within by air pressure, hydraulic pressure, or physically during the overmolding process, preventing the walls from bending or collapsing. The fluid can fill the space within the hollow member and be injected into the hollow member to provide variable hydraulic pressure to actively counteract any external pressure from the overmolding process. During the overmolding process, the fluid pressure is controlled to prevent the thin-walled hollow member from damage such as deformation, strain, breakage, or rupture from within, by controlling the pressure difference between the inside and outside of the thin walls of the hollow member. A similar technique is used in gas-assisted injection molds to create hollow polymer components.

[0016] Preferably, the fluid is a high-pressure gas. In this method, once the overmolding process is completed and the structural elements are formed, the support can be easily removed from inside the thin-walled hollow member.

[0017] The use of a solid support allows for easy removal of the solid support from the structural element after the overmolding step, thereby leaving the structural element reinforced by the thin-walled hollow member. Similarly, fluid injection can be stopped after the overmolding step to realize the reinforced structural element. As understood, the fluid in the thin-walled hollow member can be discharged from the hollow member.

[0018] The step of supporting at least a portion of the thin-walled hollow member may include the step of positioning at least a portion of the thin-walled hollow member within a connecting component. The thin-walled hollow member may be positioned or placed within the connecting component in a manner that allows external pressure during the overmolding process to be applied to the connecting component rather than to the thin-walled hollow member. In this manner, the connecting component prevents any distortion, deformation, or collapse of the thin-walled hollow member.

[0019] The connecting components may be made of a different material from the material of the thin-walled hollow member and / or the material of the structural element. The material of the connecting components may be selected to help overcome / avoid any chemical incompatibility between the materials of the thin-walled hollow member and / or the structural element, thereby improving the bonding process, insulation, and / or corrosion resistance of the reinforced structural element.

[0020] The connecting component may include a material having a significantly lower Young's modulus than that of the thin-walled hollow member. This method can reduce residual stresses resulting from the manufacturing process (including the overmolding process) when the assembly is subjected to temperature changes, or any stresses arising from the difference in the respective coefficients of thermal expansion (CTE) between the structural element and the thin-walled hollow member. The method may further include the step of joining the thin-walled hollow member to the connecting component, preferably by bonding, fastening, or welding.

[0021] Alternatively, at least a portion of the thin-walled hollow member can be placed within the connecting component by overmolding the connecting component material onto at least a portion of the thin-walled hollow member. In this method, the method effectively utilizes multiple overmolding steps to form a reinforced structural element. As understood, the method may include at least two separate and consecutive overmolding steps, in which the connecting component is overmolded onto the thin-walled hollow member in a first overmolding step, and in a second step, the structural element material is overmolded onto the connecting component-thin-walled hollow member combination to form a reinforced structural element (e.g., a final reinforced battery housing).

[0022] The connecting component may have a geometric feature or reference that provides the position of the thin-walled element or the positioning component itself when it is inside the overmolding mold tool. The connecting component may further realize that such a geometric feature or reference is configured to position an array of thin-walled elements which are conveniently configured to give them the structural performance and functionality described previously.

[0023] The connecting component can cover the opening of the thin-walled hollow member. In this method, the connecting component can act as one of the end components of the thin-walled hollow member. Thus, the thin-walled hollow member can be positioned within the connecting component in different configurations or angles, which in turn allows for different connection configurations between the structural element and the connecting component. For example, the reinforcing structural element may be in the shape of a panel with an upward projection (e.g., an upward flange), and the connecting component can be suitably shaped to join or connect to the upward projection to achieve the corner arrangement of the structural element for the overall structural assembly. Advantageously, the connecting component can be positioned at the corner or edge of the structural assembly, which in turn allows the thin-walled hollow member to achieve effective reinforcement in different directions.

[0024] Thin-walled hollow members can have an elongated shape with a main axis. Elongated thin-walled hollow members, such as those formed by metal extrusion, pipe, or fiber-reinforced pultrusion, have a main longitudinal axis along which effective reinforcement is achieved in a direction parallel to the main axis. As understood, structural assemblies can be designed so that energy / forces applied to the structural elements of the assembly are transmitted into the elongated thin-walled hollow member along its main axis. Thin-walled hollow members of other shapes and cross-sections, such as rectangular or round members, or cross-sections with multiple cavities or protruding flanges, can also be used.

[0025] The main axis of the thin-walled hollow member may be parallel to the plane of the reinforcing structural element. The main axis of the thin-walled hollow member may be at an angle to the plane of the reinforcing structural element. In this method, one or more thin-walled hollow members can be arranged in different configurations, as the structural element material is overmolded onto the thin-walled hollow member, resulting in effective reinforcement of the final reinforcing structural element / structural element assembly. Arranging the thin-walled hollow member in this way can also provide space-efficient reinforcement to the structural element, which can be particularly advantageous for battery box designs where the "free space" around the battery is typically limited and highly restricted. For example, the gap between the outer surface of the battery and the inner surface of the structural element (i.e., the battery box panel / cover) may be about 20 millimeters.

[0026] The thin-walled hollow member can include a retractable core. A thin-walled hollow member having a retractable core can be extended or retracted during the manufacturing process. For example, the core can be extended to support the hollow member in order to overmold a connecting component or a structural element onto the thin-walled hollow member. After the connecting component or the structural element has been overmolded for further connection (e.g., by adhesion, welding, or fastening) to another connecting component or structural element or a connecting component within the entire assembly, the retractable core of the thin-walled hollow member can then be retracted. After the connecting component or the structural element has been overmolded for further connection (e.g., by adhesion, welding, or fastening) to another connecting component or structural element or a connecting component within the entire assembly, the retractable core of the thin-walled hollow member can then remain in its extended configuration. The retractable core can then be retracted. The retractable core can be metallic or non-metallic. The metallic core can be solid or hollow, or can include fluid passages to facilitate thermal regulation of the core and the subsequent overmolding process. The metallic core can be made from a single piece or multiple pieces to facilitate the retraction process. The core can be made from an aggregated mass, such as the sand cores commonly used in metalworking factories. The core can be made from a ceramic compound. The aggregated mass or the ceramic core can be retracted by simple extraction through an aperture or mechanical fragmentation or dissolution through a solvent such as water. The core can be made from a material that expands favorably at a temperature, and thus can be extended into the thin-walled member at a low temperature and then expanded, thus achieving a close mechanical support inside the thin-walled member. The core can include an expandable structure that extends when inflated, thus achieving a close mechanical support inside the thin-walled membrane.

[0027] Preferably, the step of supporting the thin-walled hollow member includes providing that the retractable core is in a retracted position for the overmolding step.

[0028] The thin-walled hollow member can be provided with fiber-reinforced plastic drawing forming. The thin-walled hollow member can be provided with metal extrusion or a tube. The thin-walled hollow member can have a cross-section that varies along its main axis. This can create thin-walled structural elements made of metal or non-metal materials including fiber materials and other composite materials, which can be achieved through a number of manufacturing processes, such as hydroforming or autoclave molding or 3D printing or injection molding or other existing processes.

[0029] Preferably, the step of overmolding the structural element material onto at least a part of the thin-walled hollow member includes one or more of compression molding, injection molding, vacuum injection, resin transfer molding, and / or liquid injection. Injection molding can include the step of injecting a fiber-reinforced or non-reinforced resin into the mold. Compression molding can include a fiber-reinforced compound.

[0030] Preferably, the structural element material includes a fiber reinforcement agent. For example, the structural element material can include fibers having a predefined length and / or a range of different lengths in order to achieve reinforcement of the structural element from forces or pressures in different directions. The length or range of lengths of the fibers can be selected based on the dimensions of the final reinforced structural member (e.g., the designed thickness of the reinforced structural member). The length of the fiber can be longer than 0.1 mm or 1 mm, or preferably longer than 25 mm. Also, the structural element material formulation can include fibers of different lengths used in combination.

[0031] The use of fiber-reinforced structural element materials or structural element materials containing fiber reinforcing agents can be carried out using thermosetting resins such as epoxy, polyester, or vinyl ester, or thermoplastic resins such as nylon or polypropylene. Different resin combinations can be used in this method. For example, a thermosetting resin for thin-walled hollow members can be combined with a thermoplastic resin for overmolding materials (i.e., connecting parts or structural elements).

[0032] According to another aspect of the present invention, a vehicle reinforcement structural element formed using the disclosed method is provided.

[0033] Embodiments of the present invention are described herein by reference to the figures. [Brief explanation of the drawing]

[0034] [Figure 1] This is a flowchart illustrating a method for forming a vehicle structural element according to an embodiment of the present invention. [Figure 2] This is a perspective view of a vehicle structural element in an embodiment of the present invention. [Figure 3A] This is a perspective view of a vehicle structural element in an embodiment of the present invention. [Figure 3B] This is a perspective view of a vehicle structural element in an embodiment of the present invention. [Figure 4] This is a schematic diagram of a battery box including a vehicle reinforcement structural element according to an embodiment of the present invention. [Modes for carrying out the invention]

[0035] The methods provided herein improve the mechanical properties of structural elements for molded and overmolded assemblies for vehicles by reinforcing structural elements with lightweight hollow members, such as elongated carbon fiber reinforced plastic pultrusions. Supporting thin-walled hollow members during the overmolding process allows for effective integration of the hollow members into the final shape of the structural element, as determined by design or manufacturing requirements.

[0036] Figure 1 illustrates a method 100 for forming a reinforced structural element according to the present invention.

[0037] In step 102, thin-walled hollow members are prepared, such as by metal extrusion or fiber-reinforced plastic pultrusion. As can be understood, multiple thin-walled hollow members may be prepared.

[0038] In step 104, the thin-walled hollow member is supported by one or more portions of the hollow member. For example, a tubular or rod-shaped hollow member can be supported along portions of its length. The steps of supporting the thin-walled hollow member portion include one or more of the steps of inserting a solid support (rod or mandrel), injecting fluid, and / or positioning the portion within a connecting component. As will be understood by those skilled in the art, the insertion of a solid support and the injection of fluid provide support to the inner surface of the hollow member's wall, and the positioning of the portion within a connecting component provides external support to the hollow member that shields it from any excessive overmolding pressure / force. Thus, at least a portion of the thin-walled hollow member can be supported from either surface (inner and outer) or both surfaces of the hollow member's wall.

[0039] In step 106, the structural element material is overmolded onto the support portion of the thin-walled hollow member. The overmolding step may include a compression molding step in which the structural element material having at least a portion of the thin-walled hollow member is placed in a mold / molding tool and mold cavity pressure is applied to the two components so that the structural element material is overmolded into the shape around the hollow member component. Alternatively, the overmolding process may include an injection molding step in which the hollow member component is placed in a mold and the structural element material is injected into the mold under mold cavity pressure to form the structural element. As will be understood by those skilled in the art, other overmolding processes such as vacuum injection, resin transfer molding, and / or liquid injection may also be used.

[0040] The overmolding step 106 may include multiple overmolding cycles using different overmolding techniques to form a multilayer and / or multi-material structure. Each layer in the structural element may perform a different function for the overall structural assembly or provide different features / properties. Importantly, in each overmolding process, at least a portion of the thin-walled hollow member is supported internally and / or externally to offset the overmolding pressure (e.g., excessive mold cavity pressure) to prevent damage to the thin-walled hollow member.

[0041] Figure 2 shows the arrangement configuration 200 of the thin-walled hollow member 202 and the structural element material 204.

[0042] The thin-walled hollow member 202 has a fluid, i.e., gas or liquid, injected into its hollow core, providing hydraulic pressure against the inner surface of the hollow member's walls. The pressure of the injected fluid can be adjusted to offset and compensate for the mold cavity pressure during the overmolding process. In this particular example, the thin-walled hollow member 202 is in the shape of a rod with a square cross-section. However, different shapes and cross-sections will become apparent to those skilled in the art. Support from its inner surface to the thin-walled hollow member can also be achieved by using a solid rod or mandrel inserted into the hollow core.

[0043] The structural element material 204 is overmolded into the shape of a panel into a thin-walled hollow member during the overmolding process.

[0044] Figure 3A shows another arrangement configuration 300 of the thin-walled hollow member 302 and the structural element material 304.

[0045] A thin-walled hollow member 302 is placed inside a connecting part 306. Optionally, the thin-walled hollow member 302 can be connected to the connecting part 306 by adhesive bonding, welding, fastening, overmolding, or a combination of the above. Alternatively, the thin-walled hollow member 302 can be held in place within the connecting part 306 by a design-defined press mechanism. As understood, when the connecting part 306 is overmolded onto the thin-walled hollow member 302, the thin-walled hollow member 302 is suitably supported to prevent it from being deformed or collapsing. For example, a solid or fluid support can be provided in the manner described above, or the thin-walled hollow member 302 can include a retractable core that is maintained in its retracted position to support the thin walls of the hollow member 302 during the overmolding process.

[0046] Similar to the specific example in Figure 2, the structural element material 304 is overmolded into a thin-walled hollow member during the overmolding process.

[0047] The connecting component 306 connects the thin-walled hollow member 302 to the structural element panel 304 and acts as a shield to prevent the mold cavity pressure of the overmolding process from damaging the thin-walled hollow member 302.

[0048] When the structural element material 304 is overmolded onto the connecting component 306, the preparatory assembly of the connecting component 306 onto the thin-walled hollow member 302 allows for the removal of any "undercut" areas in the thin-walled hollow member 302 that would otherwise not conform to the main molding (drafting) direction for overmolding the structural element material 304. The undercut areas in the thin-walled hollow member 302 allow for an optimal cross-sectional design, independent of the drafting requirements of the overmolding process.

[0049] Figure 3B shows another arrangement configuration 350 of the thin-walled hollow member 352 and structural element material 354 in the connecting component 356.

[0050] In this arrangement configuration 350, the structural element material 354 was overmolded into the shape of a panel having a projection 358 that extends perpendicularly from the main surface of the panel, in order to create a corner between the panel and the projection 358.

[0051] The connecting component 356 is positioned at the corner, and the thin-walled hollow member 352 is received within the connecting component 356, so that the receiving open end of the hollow member 352 is covered by the connecting component 356. As can be understood, this allows the thin-walled hollow member 352 to be positioned at different angles relative to the structural panel 354, that is, at an angle where the main longitudinal axis of the hollow member 352 is in the plane of the panel 354.

[0052] This "off-axis" arrangement of hollow members allows thin-walled hollow members to be connected to structural panels or elements in numerous different ways, thereby improving the versatility and flexibility of the reinforced structural element assembly.

[0053] Figure 4 is a schematic cross-sectional view of a battery box 400 having multiple thin-walled hollow members. For ease of understanding, Figure 4 shows only the rear panel 402, base panel 404, side panel 406, and curved panel 408 of the battery box 400.

[0054] The base panel 404 is reinforced by a thin-walled hollow member 410, which is spaced across the base panel 404 to achieve reinforcement. The thin-walled hollow member 410 is positioned parallel to the plane of the base panel 404. Because the hollow member 410 can effectively withstand axial loads, it can be positioned horizontally and perpendicular to the vehicle's driving direction 420 to achieve reinforcement to the battery box 400 from lateral impact forces.

[0055] The rear panel 402 and side panels 406 are reinforced by thin-walled hollow members 412, providing vertical reinforcement to the battery box 400 (i.e., perpendicular to the base panel 404). This can protect the housed battery (not shown) from crushing forces resulting from the vehicle hitting uneven surfaces or speed bumps on the drive surface.

[0056] The curved panel 408 extends upward from the base panel 404 and outward from the side panel 406 (i.e., away from the battery (not shown) housed in the battery box 400). The curved panel 408 is reinforced against lateral impact forces by a thin, hollow member 414 extending between the side panel 406 and the curved panel 408.

[0057] As those skilled in the art will understand, battery boxes or other structural element assemblies have a variety of different shapes and sizes, and this disclosure makes it possible for structural elements, such as panels or covers, to be effectively reinforced against pressure or force from different directions. The present invention makes it possible to provide effective reinforcement to a structural element by positioning thin-walled hollow members parallel to the main plane or main axis of the structural element, or at an angle / off-axis to the main plane. [Explanation of Symbols]

[0058] 100 ways 200 configuration 202 Thin-walled hollow member 204 Structural element materials 300 configuration 302 Thin-walled hollow member 304 Structural element materials, structural element panels 306 Connecting parts 350 configuration 352 Thin-walled hollow member 354 Structural element materials, panels 356 Connecting parts 358 Protrusion 400 Battery Box 402 Rear Panel 404 Base Panel 406 Side Panel 408 curved panel 410 Thin-walled hollow member 412 Thin-walled hollow member 414 Thin-walled hollow member

Claims

1. A method for forming a reinforced structural element for a vehicle, The steps include preparing a thin-walled hollow member, The steps include supporting at least a portion of the thin-walled hollow member, The steps include: forming the reinforcing structural element by overmolding a structural element material onto at least a portion of the thin-walled hollow member; Methods that include...

2. The method according to claim 1, wherein the step of supporting at least a portion of the thin-walled hollow member includes the step of inserting a solid support into the thin-walled hollow member or injecting a fluid.

3. The method according to claim 1 or 2, wherein the step of supporting the thin-walled hollow member includes the step of placing the thin-walled hollow member in a connecting component.

4. The method according to claim 3, further comprising the step of connecting the thin-walled hollow member to the connecting part, preferably by bonding, fastening, or welding.

5. The method according to claim 3, wherein at least a portion of the thin-walled hollow member is disposed within the connecting component by overmolding a connecting component material onto at least a portion of the thin-walled hollow member.

6. The method according to claim 3, 4, or 5, wherein the connecting component covers the opening of the thin-walled hollow member.

7. The method according to any one of claims 1 to 6, wherein the thin-walled hollow member includes an elongated shape having a main axis.

8. The method according to claim 7, wherein the main axis of the thin-walled hollow member is parallel to the plane of the reinforcing structural element.

9. The method according to claim 7, wherein the main axis of the thin-walled hollow member is at a certain angle with respect to the plane of the reinforcing structural element.

10. The method according to any one of claims 1 to 9, wherein the thin-walled hollow member comprises a retractable core.

11. The method according to claim 10, wherein the step of supporting the thin-walled hollow member includes the step of providing that the retractable core is in a retracted position for the step of overmolding.

12. The method according to any one of claims 1 to 11, wherein the thin-walled hollow member comprises fiber-reinforced plastic pultrusion.

13. The method according to any one of claims 1 to 11, wherein the thin-walled hollow member comprises metal extrusion.

14. The method according to any one of claims 1 to 13, wherein the step of overmolding the structural element material onto at least a portion of the thin-walled hollow member includes one or more of compression molding, injection molding, vacuum injection, resin transfer molding, and / or liquid injection.

15. The method according to any one of claims 1 to 14, wherein the structural element material includes a fiber reinforcing agent.

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