Design method for local structural strength of power battery lower box body integrated with BMS support

Abstract

The invention discloses a local structural strength design method of a power battery lower box integrated with a BMS support. The method comprises the following steps: S1, designing the position and basic size of a longitudinal stiffening beam; s2, according to the BMS structure connection form and the size of a connecting piece, a lower box body reinforcing longitudinal beam mounting hole is designed, and meanwhile a wire harness fixing position is set; the structural shape of the reinforced longitudinal beam is optimized according to the stress deformation and the force transfer path of the cross beam under the module expansion working condition; according to the stress deformation and the force transfer path of the cross beam under the module expansion working condition, the welding seam position of the reinforced longitudinal beam and the cross beam is optimized; establishing a finite element model of the expansion working condition of the power battery module, and defining material attributes; establishing a connection relationship between parts of the power battery; applying constraint conditions to the finite element model, and constraining the degree of freedom in six directions by a power battery fixed point; static strength analysis is conducted under the expansive force load working condition, and static strength safety coefficient calculation is conducted on the structure; evaluating the structure of the lower box body and locking the model structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of power battery module structural strength design, and in particular relates to a method for designing the local structural strength of a power battery lower box with an integrated BMS bracket. Background Art

[0002] At present, the power battery management system (BMS) is generally designed on the top of the battery or inside the battery box. Since the design on the top of the battery is not conducive to saving Z-direction space and affects the vehicle's passability, some power batteries fix the BMS inside the power battery box, generally separated from the module or single body by structures such as beams, such as Figure 1 shown.

[0003] The current traditional design is to weld a bracket on the upper part of the liquid cooling plate to fix the BMS. The advantage is that it is easy to install and change the design of the BMS bracket. Once the BMS design is changed, the installation bracket can be redesigned. The only disadvantage is that if the BMS bracket design is too weak, there will be strength and durability risks, and if it is too thick, there may be a reduction in energy density. In addition, the mechanical properties of the liquid cooling plate material are weak, and the welding process and subsequent vibration damage will bring the risk of damage to the liquid cooling plate.

[0004] At the same time, if it is verified that the lower box crossbeam cannot withstand the strength risk caused by the expansion of the battery cell, it is necessary to add a separate crossbeam support structure to reduce the local strength problem caused by the deformation of the crossbeam.

[0005] Therefore, in order to integrate the above requirements, it is necessary to provide a power battery lower box design method that integrates the BSM bracket function and comprehensively considers the strength performance. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a local structural strength design method for the lower box of a power battery with an integrated BMS bracket, which is a standardized finite element operation process integrating finite element modeling, optimization, process combination, etc., reduces the design problems caused by the lack of experience of design engineers, solves the problem of large discreteness of calculation results caused by the subjective judgment of simulation engineers, unifies the judgment criteria, and improves the simulation efficiency.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for designing the local structural strength of a lower box of a power battery integrated with a BMS bracket, comprising the following steps:

[0009] Step 1: Local structure and size design:

[0010] S1. Design of the position and basic dimensions of the longitudinal reinforcement beam;

[0011] S2. BMS mounting hole design: According to the BMS structural connection form and connector size, design the mounting hole of the lower box reinforcement longitudinal beam, and set the wiring harness fixing position at the same time;

[0012] S3. Optimize and strengthen the structural shape of the longitudinal beam according to the stress deformation and force transmission path of the cross beam under the module expansion condition;

[0013] S4. According to the stress deformation and force transmission path of the cross beam under the module expansion condition, optimize and strengthen the weld position of the longitudinal beam and the cross beam;

[0014] Step 2: Finite element verification:

[0015] S5. Establish a finite element model of the power battery module expansion condition and define material properties;

[0016] S6. Establishing the connection relationship between the components of the power battery;

[0017] S7. Apply constraints to the finite element model, and constrain the power battery fixed point to have 6 degrees of freedom in all directions;

[0018] S8. Conduct static strength analysis under expansion force load conditions and calculate the static strength safety factor of the structure;

[0019] S9. Evaluate the lower box structure and lock the model structure.

[0020] Furthermore, in step S1, according to the proposed integrated BMS structural dimensions, the position and width of the local lower box reinforcement longitudinal beam are designed to ensure that the longitudinal reinforcement beam is in the middle position, and the process feasibility, load-bearing capacity and structural weight are comprehensively considered to determine that the width of the reinforcement beam is greater than or equal to 35 mm, and ensure that the gap with the through longitudinal beam is greater than 15 mm.

[0021] Furthermore, in step S2, if the mounting hole opening is for bolt connection, a smooth through hole is opened; if it is for rivet connection, the opening corresponds to the size of the rivet part.

[0022] Furthermore, in step S3, by increasing the contact area between the reinforcing longitudinal beam and the cross beam and gradually reducing it toward the frame, local stress concentration is reduced and the load is effectively directed to the frame.

[0023] Furthermore, in step S4, the upper weld of the reinforcing beam is welded inwards with about 5 mm on both sides, and the weld length is 20 to 30 mm. The lower weld is welded in the middle position, and the weld length is 20 to 30 mm.

[0024] Furthermore, in step S5, the power battery lower box, liquid cooling plate, module / cell, and aluminum bar are divided by finite element method. The longitudinal reinforcement beam, the lower box transverse and longitudinal beams, and the weld are required to be divided by first-order hexahedral units, and the unit size is not greater than 1.5 mm. The aluminum bar is defined by elastic-plastic material, and the compression curve of the return frame and the buffer pad between the cells is defined by superelastic material.

[0025] Furthermore, in step S6, the longitudinal reinforcing beam and the cross beam are defined as a contact relationship, and the contact attribute is limited slip; the modules are defined as limited slip; and the remaining positions are defined as small slip and Tie connection according to the real connection relationship.

[0026] Furthermore, in step S7, if the overall power battery model is used, the 1 to 6 directional degrees of freedom of the constrained fixed points are defined; if the 1 / 2 or 1 / 4 model is used, in addition to the 1 to 6 directional degrees of freedom of the constrained fixed points, the cut section must also define symmetry constraints.

[0027] Furthermore, in step S9, the lower box structure, including beams, welds, and reinforcing beams, is evaluated to see whether they meet the strength requirements; if they do, the structural design is locked and output; if they do not, steps S3 to S4 are repeated, and finite element verification is performed again.

[0028] Furthermore, in step S9, if the static strength safety factor of the longitudinal reinforcing beam is less than 1, and the area less than 1 is large, consider thickening or widening the longitudinal reinforcing beam; if the position where the safety factor is less than 1 is relatively concentrated and only involves local stress concentration, then adjust the local position structure; if the static strength safety factor of the weld structure is less than 1, move the weld structure 1 to 3 mm away from the BMS side.

[0029] The present invention has the following advantages:

[0030] The present invention provides a standardized and process-based strength design method for the local structure of the lower box of a power battery, which reduces the design problems caused by the lack of experience of design engineers, reduces the problem of large discreteness of calculation results caused by the subjective judgment of simulation engineers, unifies the judgment criteria, and improves the simulation efficiency.

[0031] The present invention effectively takes into account the BSM fixation and local structural strength and durability, which not only saves space for layout, but also saves materials and processes, and is conducive to achieving product cost reduction.

[0032] The present invention fully considers the structural mechanics transmission path, optimizes processes such as weld position and length, and proposes a standardized design method, which can effectively guide subsequent similar designs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the contents of the embodiments of the present invention and these drawings without paying any creative work.

[0034] Figure 1 It is a schematic diagram of the local structure of the lower box of the power battery;

[0035] Figure 2 This is a flow chart of a method for designing the local structural strength of a power battery lower box with an integrated BMS bracket according to an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of the optimized lower box reinforcement longitudinal beam with integrated BMS bracket function. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0038] Example

[0039] like Figure 1 As shown, this embodiment is a method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket, comprising the following steps:

[0040] Step 1: Local structure and size design:

[0041] S1. Design of the position and basic dimensions of the longitudinal reinforcement beam: According to the proposed integrated BMS structural dimensions, the position and width of the local lower box reinforcement longitudinal beam are designed. Combined with aesthetic design, the longitudinal reinforcement beam is ensured to be in the middle position, and the process feasibility, load-bearing capacity and structural weight are comprehensively considered to determine that the width of the reinforcement beam is greater than or equal to 35mm, and ensure that the gap with the through longitudinal beam is greater than 15mm.

[0042] In this embodiment, according to the proposed integrated BMS structural dimensions, the width is 40mm, the installation width is 45mm, and the aesthetic design is combined to ensure that it is in the middle position. The position of the local lower box reinforcement longitudinal beam is designed, and the process feasibility, load-bearing capacity and structural weight are comprehensively considered to determine the width of the reinforcement beam to be 35mm.

[0043] S2. BMS mounting hole design: According to the BMS structural connection form and connector size, design the lower box reinforcement longitudinal beam mounting hole and set the wiring harness fixing position at the same time.

[0044] Specifically, if the opening is a bolt connection, a smooth through hole is opened, and the size is slightly larger than the bolt diameter; if it is a rivet connection, the opening corresponds to the size of the rivet part.

[0045] In this embodiment, the BMS structure is fixed with bolts, the nominal diameter of the bolts is 5 mm, the diameter of the BMS mounting hole on the lower box reinforcement longitudinal beam is determined to be 5.5 mm, and nuts are welded on the lower surface of the mounting surface.

[0046] S3. According to the stress deformation and force transmission path of the cross beam under the module expansion condition, the structural shape of the longitudinal beam is optimized and strengthened.

[0047] Specifically, the contact area between the reinforced longitudinal beam and the cross beam is increased and gradually reduced toward the frame, thereby reducing local stress concentration and effectively directing the load to the frame.

[0048] S4. According to the stress deformation and force transmission path of the cross beam under the module expansion condition, optimize and strengthen the weld positions of the longitudinal beam and the cross beam.

[0049] Specifically, the upper weld position of the reinforcing beam is selected to be welded inward with about 5mm on both sides, and the weld length is 20 to 30mm. The lower weld is selected to be welded in the middle position, and the weld length is 20 to 30mm.

[0050] In this embodiment, the upper weld position of the reinforcing beam is selected to be welded inwards with about 5mm on both sides, and the weld length is 20mm. The lower weld is selected to be welded in the middle position, and the weld length is 20mm.

[0051] Step 2: Finite element verification:

[0052] S5. The finite element model of the expansion condition of the power battery module is established, and the material properties are defined.

[0053] Specifically, finite element division is performed on the power battery lower box, liquid cooling plate, module / cell, aluminum bar and other structures, and the material properties of each component are defined.

[0054] Among them, the longitudinal reinforcement beam, the lower box transverse and longitudinal beams and the welds are required to be divided by first-order hexahedral units, and the unit size is not greater than 1.5mm. The aluminum bar is defined by elastic-plastic materials, and the compression curve of the return frame and buffer pad between the battery cells is defined by hyperelastic materials.

[0055] S6. Establish the connection relationship between the various components of the power battery.

[0056] Specifically, the longitudinal reinforcement beam and the cross beam are defined as a contact relationship with limited slip as the contact property; the modules are defined as limited slip; the remaining positions are defined as small slip and Tie connection according to the real connection relationship.

[0057] S7. Apply constraints to the finite element model, and constrain the power battery fixing point to have 6 degrees of freedom.

[0058] Specifically, if the overall model of the power battery is used, define the 1 to 6 degrees of freedom in the directions of the constraint fixed point; if the 1 / 2 or 1 / 4 model is used, in addition to the 1 to 6 degrees of freedom in the directions of the constraint fixed point, the cut section must also define symmetry constraints.

[0059] S8. Perform static strength analysis under expansion force load conditions and calculate the static strength safety factor of the structure.

[0060] The expansion force load is defined as the maximum expansion force corresponding to a single battery cell at 65% SOC.

[0061] S9. Evaluate the lower box structure and lock the model structure.

[0062] Specifically, evaluate whether the lower box structure, including beams, welds, reinforcing beams and other structures, meets the strength requirements; if they meet the requirements, lock and output the structural design; if they do not meet the requirements, repeat steps S3 to S4 and re-perform finite element verification.

[0063] Among them: if the static strength safety factor of the longitudinal reinforcing beam and other structures is less than 1, and the area less than 1 is large, consider thickening or widening the longitudinal reinforcing beam; if the position where the safety factor is less than 1 is relatively concentrated, it only involves local stress concentration, and the local position structure is adjusted, such as adding chamfers, etc.; if the static strength safety factor of the weld structure is less than 1, consider moving the weld structure 1 to 3 mm away from the BMS side. Although the embodiments of the present invention have been shown and described, it can be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for designing the local structural strength of the lower box of a power battery with an integrated BMS bracket, characterized in that: The following steps are involved: Step 1: Local structure and size design: S1. Design of the position and basic dimensions of the longitudinal reinforcement beam; S2. BMS mounting hole design: According to the BMS structural connection form and connector size, design the mounting hole of the lower box reinforcement longitudinal beam, and set the wiring harness fixing position at the same time; S3. Optimize and strengthen the structural shape of the longitudinal beam according to the stress deformation and force transmission path of the cross beam under the module expansion condition; S4. According to the stress deformation and force transmission path of the cross beam under the module expansion condition, optimize and strengthen the weld position of the longitudinal beam and the cross beam; Step 2: Finite element verification: S5. Establish a finite element model of the power battery module expansion condition and define material properties; S6. Establishing the connection relationship between the components of the power battery; S7. Apply constraints to the finite element model, and constrain the power battery fixed point to have 6 degrees of freedom in all directions; S8. Conduct static strength analysis under expansion force load conditions and calculate the static strength safety factor of the structure; S9. Evaluate the lower box structure and lock the model structure.

2. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In step S1, the position and width of the local lower box reinforcement longitudinal beam are designed according to the proposed integrated BMS structural dimensions to ensure that the longitudinal reinforcement beam is in the middle position, and the process feasibility, load-bearing capacity and structural weight are comprehensively considered to determine that the width of the reinforcement beam is greater than or equal to 35 mm, and ensure that the gap with the through longitudinal beam is greater than 15 mm.

3. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In step S2, if the mounting hole opening is for bolt connection, a smooth through hole is opened; if it is for rivet connection, the opening corresponds to the size of the rivet part.

4. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket according to claim 1, characterized in that: In step S3, by increasing the contact area between the reinforcing longitudinal beam and the cross beam and gradually reducing it toward the frame, local stress concentration is reduced and the load is effectively directed to the frame.

5. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In step S4, the upper weld of the reinforcing beam is welded inwards with about 5 mm on both sides, and the weld length is 20 to 30 mm. The lower weld is welded in the middle position, and the weld length is 20 to 30 mm.

6. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In the step S5, the lower box of the power battery, the liquid cooling plate, the module / cell, and the aluminum bar are divided by finite element. The longitudinal reinforcement beam, the lower box transverse and longitudinal beams, and the weld are required to be divided by first-order hexahedral units, and the unit size is not greater than 1.5 mm; the aluminum bar is defined by elastic-plastic material, and the return frame and buffer pad between the cells are defined by superelastic material to define their compression curves.

7. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In the step S6, the longitudinal reinforcing beam and the cross beam are defined as a contact relationship, and the contact attribute is limited slip; the modules are defined as limited slip; and the remaining positions are defined as small slip and Tie connection according to the real connection relationship.

8. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In step S7, if the overall power battery model is used, the 1-6 directional degrees of freedom of the constrained fixed points are defined; if the 1 / 2 or 1 / 4 model is used, in addition to the 1-6 directional degrees of freedom of the constrained fixed points, the cut section must also define symmetry constraints.

9. The method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 1, characterized in that: In step S9, the lower box structure, including the cross beam, welds, and reinforcing beams, is evaluated to see whether they meet the strength requirements; if they do, the structural design is locked and output; if they do not, steps S3 to S4 are repeated, and finite element verification is performed again.

10. A method for designing the local structural strength of the lower box of a power battery integrated with a BMS bracket as claimed in claim 9, characterized in that: In step S9, if the static strength safety factor of the longitudinal reinforcing beam is less than 1 and the area less than 1 is large, consider thickening or widening the longitudinal reinforcing beam; if the position where the safety factor is less than 1 is relatively concentrated and only involves local stress concentration, then adjust the local position structure; if the static strength safety factor of the weld structure is less than 1, move the weld structure 1 to 3 mm away from the BMS side.

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