Upper cover structure and application of upper cover structure on new energy automobile battery box

Abstract

The invention discloses an upper cover structure and application of the upper cover structure to a new energy automobile battery box. The upper cover structure is made of a continuous glass fiber reinforced PPS thermoplastic composite material. The top surface of the upper cover structure adopts a thin wall of which the thickness is less than or equal to 2.00 mm; radial reinforcing ribs are arranged on the upper cover structure; the flange edge of the upper cover structure is welded with a reinforcing strip through vibration friction; the upper cover structure is applied to the new energy automobile battery box. According to the upper cover structure and the application of the upper cover structure to the battery box of the new energy automobile, the novel battery box upper cover structure which can meet multiple requirements of light weight, high strength, high production efficiency, environmental protection, recyclability, thermal runaway safety performance and the like at the same time is provided through innovation of materials, structures and processes, and the upper cover structure has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile accessories, and in particular to an upper cover structure and its application in a battery box of a new energy vehicle. Background Art

[0002] In the new energy vehicle industry, energy storage batteries, such as lithium-ion batteries, are critical components. To ensure the safety of new energy vehicles, the battery box housing them places stringent structural requirements. In addition to meeting physical and mechanical requirements such as impact resistance, vibration resistance, and drop resistance, they must also meet stringent fire and flame retardancy testing conditions. For example, direct exposure of the battery pack to gasoline flames is crucial, requiring the box structure to remain intact. Currently, the components and covers housing energy storage batteries are mostly made of metal, which increases the overall weight of the battery pack and affects the range of new energy vehicles.

[0003] A battery pack typically consists of an upper cover and a lower case, which snap together to form a chamber to house the batteries. To improve the structural strength and airtightness of the connection between the upper and lower cases, the upper cover is typically thickened overall, but this approach struggles to meet lightweighting requirements.

[0004] Currently, composite battery box top covers are categorized into two types: thermoset composites and thermoplastic composites. Thermoset composites include SMC, PCM, and HP-RTM. SMC has been largely eliminated due to its low strength, while PCM and HP-RTM generally have low production efficiency, low yield, and limited potential for cost reduction. They also struggle to meet future environmental and recyclable regulatory requirements. Thermoplastic composite solutions primarily focus on PP and nylon injection molding. Injection moldings cannot be thinned and have low strength. PP and nylon require flame retardant modification for fire resistance, increasing material costs and posing a risk of flame retardant precipitation under prolonged ablation. Compared to other potential thermoplastic composites, such as PP and nylon, PPS-based thermoplastic composites offer superior strength and stiffness, deformation resistance, fire resistance, weather resistance, and chemical resistance.

[0005] Furthermore, existing battery pack thermal runaway safety redundancy designs are complex and costly. Therefore, a new battery case cover structure is urgently needed that can address existing issues such as excessive weight, low production efficiency, difficulty in recycling, and complex thermal runaway safety design, thereby meeting the lightweight, efficient manufacturing, and safety requirements of new energy vehicles.

[0006] Although there are some patents that address the problems of heavy metal battery box covers, low production efficiency, limited cost reduction space, difficulty in meeting future environmental protection and recycling regulations, and complex and high cost of thermal runaway safety redundancy design for battery packs, they all have certain limitations.

[0007] Patent CN109360919A discloses an all-composite battery box for new energy vehicles and its manufacturing method. The box is made entirely of fiber-reinforced composite materials, with the upper cover made of fast-curing prepreg and the lower box body using a sandwich structure of prepreg-core material-prepreg. This patent can effectively reduce the weight of the battery box, achieving the goal of lightweighting new energy vehicles. The integrated molding process avoids the connection problems and redundant weight caused by the separate preparation and splicing of components, thereby achieving further weight reduction. However, while meeting the performance requirements, this patent still faces the problem of achieving higher energy density.

[0008] Patent CN112582730A discloses a lightweight battery pack for new energy vehicles and a new energy vehicle, comprising a tray with at least one opening for accommodating the new energy vehicle battery pack and a cover for closing and opening the tray opening. The tray and cover each consist of two layers of CFRP sheeting with a foam layer in between, forming a "sandwich structure." This provides the battery pack with excellent strength and rigidity, while significantly reducing weight. Furthermore, the foam layer in the middle prevents temperature fluctuations from affecting the battery pack within the pack, thereby improving the range of the new energy vehicle. However, while ensuring lightweight and stable performance, this patent still faces challenges in optimizing materials and structure.

[0009] Therefore, it is of great practical significance to develop a new type of new energy vehicle battery box cover structure to solve the above technical problems. Summary of the Invention

[0010] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide a top cover structure and its application in the battery box of new energy vehicles. Through the innovation of materials, structure and process, a new type of battery box top cover structure is provided which can simultaneously meet multiple requirements such as lightweight, high strength, high production efficiency, environmental protection and recyclability, and thermal runaway safety performance, and has broad application prospects.

[0011] Technical solution: A top cover structure, which is made of continuous glass fiber reinforced PPS thermoplastic composite material; the top surface of the top cover structure adopts a thin wall with a thickness of ≤2.00mm; the top cover structure is provided with radial reinforcement ribs; the flange edge of the top cover structure is welded with reinforcement strips by vibration friction welding.

[0012] Furthermore, radial reinforcement ribs are provided on the upper and lower sides of the upper cover structure.

[0013] Furthermore, the above-mentioned upper cover structure, the continuous glass fiber reinforced PPS thermoplastic composite material has V-0 flame retardant performance (test standard UL-94), and there is no risk of flame retardant precipitation during long-term ablation in the uncontrolled state of the battery cell.

[0014] Continuous glass fiber reinforced PPS thermoplastic composite is a high-performance composite material that combines the excellent properties of polyphenylene sulfide (PPS) with the reinforcement of continuous glass fiber. PPS itself is V-0 flame retardant, and no flame retardant is required to create it. A top cover structure constructed with this composite material can sustain combustion at 1200°C for over 10 minutes. Existing top cover materials typically achieve V0 flame retardancy by adding small molecule flame retardants to a matrix such as epoxy resin. However, under actual operating conditions (e.g., during battery cell runaway), this can lead to flame retardant precipitation, spontaneous combustion, or excessive smoke generation.

[0015] Compared with other thermoplastic composites such as PP and nylon base materials, continuous glass fiber reinforced PPS thermoplastic composites have better strength and stiffness, deformation resistance, fire resistance, weather resistance, and chemical resistance, and have high production efficiency, high yield, and are environmentally friendly and recyclable.

[0016] Furthermore, the top surface of the upper cover structure is made of a thin wall with a thickness of 1.5 mm.

[0017] The top surface of the upper cover structure adopts a 1.5mm thin-wall design, which reduces the weight of the battery box cover and meets the needs of lightweighting and increasing the driving range of new energy vehicles.

[0018] Furthermore, in the above-mentioned upper cover structure, the layout of the radial reinforcement ribs on the upper cover structure is based on the thermal runaway probability density function as a weight factor, and the Voronoi diagram algorithm is used to generate the initial path, in which the main path is set in the area with a probability density ≥0.65.

[0019] Furthermore, in the above-mentioned upper cover structure, the rib height of the central area of ​​the radial reinforcement rib is 3.5mm, and the shape is set to be elliptical, and the rib height gradually changes to 3.5mm and the width is 3.4mm in the edge area according to the quadratic curve; the main ribs of the radial reinforcement ribs are arranged at 70.5° and 110°, and 2 to 3 secondary ribs are inserted in the interval according to the stress gradient.

[0020] Specifically: when simulating thermal runaway of the battery pack, the top surface of the upper cover structure is subjected to a maximum internal pressure of 15kPa (corresponding to the GB38031-2020 standard). The deformation of the original flat-plate structure of the upper cover structure (the top surface uses a thin wall with a thickness of 1.5mm) is 41mm (without tooling). After optimization, the upper cover structure with a radial reinforcement rib structure (the top surface also uses a thin wall with a thickness of 1.5mm) has a maximum deformation reduced to 29mm (without tooling), and the stress distribution is uniform (the peak stress is reduced from 320MPa to 196MPa).

[0021] Simulating the extreme operating conditions (-40℃~150℃) under battery usage scenarios, the maximum deformation of the optimized upper cover structure with radial reinforcement rib structure (the top surface also uses a thin wall with a thickness of 1.5mm) is significantly better than that of the original flat plate structure upper cover structure (the top surface uses a thin wall with a thickness of 1.5mm), and the maximum stress is less than the material stress.

[0022] The radial reinforcement ribs guide the flame to flow outward along the channels between the ribs, which can significantly suppress the risk of backflow. Compared with the grid-type, annular, and wavy reinforcement rib designs, its flow diversion efficiency is as high as 89%, and its specific stiffness is 168. It can effectively prevent the battery cells from backflowing into the interior during thermal runaway of the battery pack, thereby improving the thermal runaway safety performance of the battery pack.

[0023] Furthermore, in the above-mentioned upper cover structure, the reinforcement strip is made of continuous glass fiber reinforced PPS thermoplastic composite material.

[0024] The reinforcement strip connected to the flange edge is made of the same material as the upper cover structure, both of which are continuous glass fiber reinforced PPS thermoplastic composite materials, and are welded by vibration friction welding to ensure welding strength, uniformity and consistency, saving bolt fixing or gluing processes and improving production efficiency.

[0025] Furthermore, the above-mentioned upper cover structure adopts an ultrasonic vibration friction welding machine, uses phase control welding technology according to the rheological properties of continuous glass fiber reinforced PPS thermoplastic composite materials, and selects three-stage vibration control in the frequency range to match the "high-low-high" pressure mode.

[0026] Furthermore, the three-stage vibration control of the above-mentioned upper cover structure is specifically as follows: the amplitude of the startup period is 1.8~2.2mm, the frequency is 80~100Hz, and the time accounts for 20%, which is used to break through the surface roughness; the amplitude of the plasticization period is 1.2~1.5mm, the frequency is 120~150Hz, and the time accounts for 60%, which is used to stabilize the material melt flow; the amplitude of the fusion period is 0.5~0.8mm, the frequency is 180~200Hz, and the time accounts for 20%, which is used to achieve grain refinement and exhaust.

[0027] Furthermore, in the above-mentioned upper cover structure, the joint surfaces of the reinforcement strips are pre-processed and interlocked; the roughness of the flange edge welding surface of the upper cover structure is controlled to Ra 2.5μm, and after pre-processing by belt grinding, the shear strength of the welding surface reaches 45MPa. After 3h of random vibration test at 20~2000Hz, the post-weld structure has no cracks and the displacement is ≤0.1mm.

[0028] Specifically: the joint surface of the reinforcement strip is pre-processed and interlocked (depth 0.5mm, angle 60°) to increase the melting area. The single-sided welding width is expanded from 23mm to 28mm, and the effective bonding area is increased by 20~30% through mechanical bite, forcing the material to flow and fill, eliminating unmelted dead corners, improving welding reliability, and reducing the possibility of stress concentration during welding.

[0029] The present invention also relates to the application of the upper cover structure, which is applied to a battery box of a new energy vehicle.

[0030] The beneficial effects of the present invention are: (1) Lightweight advantage: The battery box cover is lightweight in design. The top surface of the cover structure adopts a 1.5mm thin-wall design, and radial reinforcement ribs are used to enhance the strength of the top surface of the cover structure, effectively reducing the weight of the battery box cover and meeting the requirements of lightweighting and improving the driving range of new energy vehicles. (2) Material performance advantages: Made of continuous glass fiber reinforced PPS thermoplastic composite material, the material is V-0 flame retardant, and there is no risk of flame retardant precipitation in the long-term ablation of the battery cell in an uncontrolled state. It has high production efficiency and high yield, and is environmentally friendly and recyclable. It solves the problems of low production efficiency, low yield, limited cost reduction space, and difficulty in meeting future environmental protection and recyclable regulations for existing thermosetting composite materials; (3) Process advantages: The flange edge adopts the design of the reinforcement strip of continuous glass fiber reinforced PPS thermoplastic composite material by vibration friction welding. The reinforcement strip is made of the same material as the upper cover structure, which ensures the welding strength, uniformity and consistency, saves the gluing process and does not require the use of metal nesting, thereby improving production efficiency; (4) Safety performance advantage: The radial reinforcement rib layout design can effectively prevent the battery cells from flowing back into the battery pack when the battery pack is in thermal runaway, thereby improving the thermal runaway safety performance of the battery pack and solving the problem of the existing metal solution requiring the addition of mica paper or mica board, which is a complex and costly safety redundancy design. Through optimized design, the stability and safety of the battery box cover can be guaranteed under various working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the upper cover structure of the present invention; Figure 2 A top view of the upper cover structure of the present invention; Figure 3 A bottom view of the upper cover structure of the present invention; Figure 4 Schematic diagram of the local structure of the upper cover structure of the present invention Figure 1 ; Figure 5 A schematic diagram of friction welding of the flange strip and the reinforcement strip of the upper cover structure of the present invention; In the picture: Upper cover structure 1, radial reinforcement ribs 2, reinforcement strips 3. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1 、 2 , 3, 4, 5 and Examples further illustrate the present invention. Example

[0033] like Figure 1 、 2 As shown in Figures 3 and 3, the top surface of the upper cover structure 1 of the present invention adopts a 1.5mm thin-wall design to further achieve the purpose of lightweighting. At the same time, radial reinforcement ribs 2 are provided on the upper and lower sides of the upper cover structure 1 to effectively enhance the top surface strength of the upper cover structure 1.

[0034] In the top surface design of the upper cover structure 1, the layout of the radial reinforcement ribs 2 is based on the random non-fixedness of thermal runaway of the battery pack. The path size that diffuses from the center to the surrounding area increases from small to large, causing a pressure difference, preventing the edge cells from losing control and flowing back to the interior, thereby improving the thermal runaway safety performance of the battery pack.

[0035] The design of radial reinforcement rib 2 is as follows: 1. Simulation parameter input: Based on the thermal runaway flow field simulation (using ANSYS Fluent to establish a field thermo-mechanical coupling model, considering the interaction between heat conduction and internal pressure), the topology optimization design rules for radial stiffener 2 are established: (1) Path planning algorithm: Generate the initial path through the Voronoi diagram algorithm, and use the thermal runaway probability density function as the weight factor (the main path is set in the area with probability density ≥ 0.65); (2) Size gradient rule: The center area (within a radius of 150 mm) has a rib height of 3.5 mm and an elliptical shape, which gradually changes to the edge (at a radius of 600 mm) with a rib height of 3.5 mm and a width of 34 mm according to a quadratic curve; (3) Angle distribution: The main reinforcement is arranged at intervals of 70.5° and 110°, and 2-3 secondary reinforcements are inserted within the interval according to the stress gradient; (4) When simulating thermal runaway of the battery pack, the top surface of the upper cover structure 1 is subjected to a maximum internal pressure of 15 kPa (corresponding to the GB38031-2020 standard). The deformation of the original flat-plate structure 1 (with a thin wall of 1.5 mm thickness on the top surface) is 41 mm (without tooling). The maximum deformation of the upper cover structure 1 (with a thin wall of 1.5 mm thickness on the top surface) of the present invention (with the optimized radial reinforcement structure 2) is reduced to 29 mm (without tooling), and the stress distribution is uniform (the peak stress is reduced from 320 MPa to 196 MPa), as shown in Table 1. (5) Simulating the extreme working conditions (-40℃~150℃) under the battery usage scenario, the maximum deformation of the upper cover structure 1 (the top surface also uses a thin wall with a thickness of 1.5mm) of the present invention (the optimized structure with radial reinforcement ribs 2) is significantly better than that of the upper cover structure 1 of the original flat plate structure (the top surface uses a thin wall with a thickness of 1.5mm), and the maximum stress is less than the material stress, as shown in Table 1.

[0036] Table 1 Working condition type Temperature range Internal pressure range Maximum deformation of radial reinforcement Pressure uniformity index Standard working conditions 25℃ 15kpa 29mm 0.82 Low temperature limit -40℃ 10kpa 27mm 0.78 High temperature limit 150℃ 15kpa 33mm 0.75 2. Density Adjustment The radial ribs of radial reinforcement 2 are designed with a rib width of 34 mm, creating localized high-rigidity supports. The number of ribs is appropriately reduced in low-stress areas to maintain structural stability. Radial reinforcement 2 guides flames outward along the channels between the ribs, significantly reducing the risk of backflow. Table 2 compares different rib designs.

[0037] Table 2 type Diversion efficiency (%) Specific stiffness Advantages Defects (for thermal runaway scenarios) Grid type 48 120 Good isotropy Hinders the directional diffusion of high-pressure flames and easily causes local pressure accumulation Ring 52 135 Strong resistance to radial deformation Unable to form an effective pressure gradient, low backflow suppression efficiency wavy 57 110 Improve out-of-plane stiffness Uneven flow resistance, risk of stress concentration Radial 89 168 Directional flow guidance + gradient stiffness Need to accurately match the thermal runaway probability distribution like Figure 1 、 2 As shown in Tables 3, 4, and 5, the flange edge of the upper cover structure 1 utilizes a vibration-friction-welded reinforcement strip 3. The reinforcement strip 3 is made of the same material as the upper cover structure 1: a continuous glass-fiber-reinforced PPS thermoplastic composite. This ensures weld strength, uniformity, and consistency, eliminating the need for bolting or gluing, and improving production efficiency. The continuous glass-fiber-reinforced PPS thermoplastic composite is manufactured in-house, and its performance data is shown in Tables 3, 4, 5, and 6.

[0038] Table 3 Physical properties unit Test standards Test results density <![CDATA[g / cm 3 ]]> ASTM D792 1.85 Fiber mass fraction % ASTM D3171 63.52 Fiber surface density <![CDATA[g / m 2 ]]> ISO 10352 320 flame retardancy - UL-94 V-0 Table 4 Mechanical properties unit Test standards Test results tensile strength Mpa ASTM D3039 430 Tensile modulus Gpa ASTM D3039 23 Poisson's ratio - ASTM D3039 0.215 Bending strength Mpa ASTM D7264 340 flexural modulus Gpa ASTM D7264 21 Table 5 *The leakage current test conditions are: AC 3000V, increase the voltage for 10s, maintain it for 60s, then decrease the voltage for 10s, repeat 5 times; the insulation resistance test conditions are: AC 1000V.

[0039] Table 6 * Fire resistance test conditions: gas source is propane and oxygen, flame pressure is about 1Mpa, material is 20cm away from flame, and no alumina powder is sprayed.

[0040] Furthermore, the flange edge of the upper cover structure 1 uses a 2mm thick molding structure, which replaces the metal molding fixed with traditional bolts through ultrasonic vibration friction welding. There is no insulation and corrosion protection problem of using metal molding, no need for electrophoresis, and the number of parts is reduced, further reducing weight.

[0041] The welding of the reinforcement strip 3 is specifically as follows: 1. Welding process An ultrasonic vibration friction welder employs phase-controlled welding technology based on the rheological properties of continuous glass fiber-reinforced PPS thermoplastic composites. Unlike traditional fixed-frequency vibration, a three-stage vibration control system is used, coupled with a "high-low-high" pressure pattern. This achieves the process goals of reducing surface roughness, promoting plastic flow, and achieving weld compaction in stages. A dynamic gap of 0.05-0.1mm (calculated based on material thermal expansion technology) is preset during welding to absorb thermal deformation and prevent microcracks caused by residual stress. The vibration control parameters are shown in Table 7.

[0042] Table 7 stage Amplitude (mm) Frequency (Hz) Time proportion Functional Goal Start-up period 1.8-2.2 80-100 20% Breakthrough in surface roughness Plasticization period 1.2-1.5 120-150 60% Stable material melt flow Fusion period 0.5-0.8 180-200 20% Grain refinement and degassing 2. Structural Adaptation Design like Figure 5 As shown in the figure, the joint surface of the reinforcement strip 3 is pre-processed and interlocked (depth 0.5mm, angle 60°) to increase the melting area. The single-side welding width is expanded from 23mm to 28mm. The effective bonding area is increased by 20%-30% through mechanical bite, forcing the material to flow and fill, eliminating unmelted dead corners, improving welding reliability, and reducing the possibility of stress concentration during welding.

[0043] Furthermore, the flange weld surface roughness was controlled to Ra 2.5μm (pre-processed by belt grinding). The weld surface shear strength reached 45MPa. After a 3-hour random vibration test at 20Hz to 2000Hz, the welded structure showed no cracks and a displacement of ≤0.1mm.

[0044] The upper cover structure of the present invention manufactured by the above process has a product yield of 98.5%, and the HP-RTM process yield is about 85%.

[0045] To sum up: The upper cover structure described in the present invention, through innovations in materials, structures and processes, provides a new battery box upper cover structure that can simultaneously meet multiple requirements such as lightweight, high strength, high production efficiency, environmental protection and recyclability, and thermal runaway safety performance.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A cover structure, characterized in that: The upper cover structure (1) is made of continuous glass fiber reinforced PPS thermoplastic composite material; the top surface of the upper cover structure (1) adopts a thin wall with a thickness of ≤2.00 mm; radial reinforcement ribs (2) are provided on the upper cover structure (1); and the flange edge of the upper cover structure (1) is welded with reinforcement strips (3) by vibration friction welding.

2. The upper cover structure according to claim 1, characterized in that: The continuous glass fiber reinforced PPS thermoplastic composite material has V-0 grade flame retardancy.

3. The upper cover structure according to claim 1, characterized in that: The top surface of the upper cover structure (1) adopts a thin wall with a thickness of 1.5 mm.

4. The upper cover structure according to claim 1, characterized in that: The layout of the radial reinforcement ribs (2) on the upper cover structure (1) is designed based on the thermal runaway probability density function as a weight factor, using a Voronoi diagram algorithm to generate an initial path, wherein the area with a probability density ≥ 0.65 is set as the main path.

5. The upper cover structure according to claim 4, characterized in that: The radial reinforcing ribs (2) have a central region with a rib height of 3.5 mm and an elliptical shape, and gradually change to an edge region with a rib height of 3.5 mm and a width of 3.4 mm according to a quadratic curve; the main ribs of the radial reinforcing ribs (2) are arranged at intervals of 70.5° and 110°, and 2 to 3 secondary ribs are inserted within the interval according to the stress gradient.

6. The upper cover structure according to claim 1, characterized in that: The reinforcing strip (3) is made of continuous glass fiber reinforced PPS thermoplastic composite material.

7. The upper cover structure according to claim 1, characterized in that: An ultrasonic vibration friction welding machine is used, and phase-controlled welding technology is used according to the rheological properties of continuous glass fiber reinforced PPS thermoplastic composite materials. Three-stage vibration control is selected for the frequency range to match the "high-low-high" pressure mode.

8. The upper cover structure according to claim 7, characterized in that: The three-stage vibration control is specifically as follows: the amplitude of the startup period is 1.8~2.2mm, the frequency is 80~100Hz, and the time accounts for 20%, which is used to break through the surface roughness; the amplitude of the plasticization period is 1.2~1.5mm, the frequency is 120~150Hz, and the time accounts for 60%, which is used to stabilize the material melt flow; the amplitude of the fusion period is 0.5~0.8mm, the frequency is 180~200Hz, and the time accounts for 20%, which is used to achieve grain refinement and exhaust.

9. The upper cover structure according to claim 1, characterized in that: The joint surface of the reinforcing strip (3) is pre-processed and interlocked; the roughness of the flange edge welding surface of the upper cover structure (1) is controlled to be Ra 2.5μm, and the shear strength of the welding surface reaches 45MPa after pre-processing by belt grinding. After 3 hours of random vibration test at 20~2000Hz, the welded structure has no cracks and the displacement is ≤0.1mm.

10. Application of the upper cover structure according to any one of claims 1 to 9, characterized in that: The upper cover structure (1) is applied to a battery box of a new energy vehicle.

Images