Battery pack lower box and battery pack

Abstract

The application relates to the technical field of batteries, in particular to a battery pack lower box and a battery pack. The battery pack lower box comprises a bottom plate, a frame and a side beam, the frame is arranged along the circumference of the bottom plate, a containing space is formed between the frame and the bottom plate, and the containing space is suitable for mounting a module; the side beam is fixedly arranged on the outer side of the frame, the inside of the side beam is provided with a reinforcing rib, the reinforcing rib comprises a negative Poisson's ratio structure, the negative Poisson's ratio structure comprises a plurality of concave polygonal monomers which are sequentially connected along a first direction; and / or the reinforcing rib comprises a triangular rib and a first horizontal rib, the first horizontal rib extends along a second direction, and the triangular rib is arranged at an angle with the second direction, wherein the second direction is perpendicular to the first direction. By arranging the side beam on the outer side of the frame and arranging the reinforcing rib in the inside of the side beam, the strength is improved, and the weight can be relatively reduced; the negative Poisson's ratio structure or the structure in cooperation of the triangular rib and the first horizontal rib has a good buffering and energy-absorbing effect, and the extrusion resistance is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a lower housing for a battery pack and a battery pack. Background Technology

[0002] During electric vehicle operation, various complex conditions may arise, and the battery pack installed on the vehicle may be subjected to impacts, compression, and other incidents. The lower casing of the battery pack is the main part of the battery pack used to install and support the battery modules, playing a role in protecting the battery modules. The structural strength of the lower casing has a significant impact on the overall safety performance of the battery pack.

[0003] In existing technologies, the lower casing of battery packs is typically made of steel or aluminum alloy, with the strength increased by increasing the thickness of the steel or aluminum. However, increasing the thickness increases the weight of the lower casing, which is detrimental to battery pack lightweighting and results in a lower overall energy density. Furthermore, to maintain a lightweight design, it is difficult to achieve the required strength thickness for the lower casing, leading to poor compression resistance and compromised battery pack safety. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor compression resistance and heavy weight of the lower casing of the battery pack in the prior art, thereby providing a lower casing of the battery pack and the battery pack with good compression resistance and light weight.

[0005] To address the aforementioned problems, the present invention provides a battery pack lower housing, comprising: a base plate; a frame arranged circumferentially along the base plate, wherein a receiving space formed between the frame and the base plate is suitable for installing a module; a side beam fixedly disposed on the outer side of the frame, wherein a reinforcing rib is provided inside the side beam, the reinforcing rib including a negative Poisson's ratio structure, the negative Poisson's ratio structure including a plurality of concave polygonal units connected sequentially along a first direction; and / or, the reinforcing rib including a triangular rib and a first horizontal rib, the first horizontal rib extending along a second direction, the triangular rib being angled to the second direction, wherein the second direction is perpendicular to the first direction.

[0006] Optionally, the concave polygonal unit is composed of a first trapezoid, a concave hexagon, and a second trapezoid arranged sequentially along the second direction. The lower base of the first trapezoid is equal in length to and coincides with the first base of the concave hexagon. The second base of the concave hexagon is equal in length to and coincides with the lower base of the second trapezoid. The concave hexagon also includes a first folded edge group and a second folded edge group arranged opposite to each other and concave inward. The line connecting the first fold point of the first folded edge group and the second fold point of the second folded edge group is shorter than the length of the first base and the second base. The second fold point is connected to the first fold point of the adjacent concave polygonal unit by a connecting rib.

[0007] Optionally, the two endpoints of the upper base of the first trapezoid are the first endpoint and the sixth endpoint, and the two endpoints of the upper base of the second trapezoid are the fifth endpoint and the tenth endpoint; the projections of the first inflection point and the fifth endpoint on the upper base of the first trapezoid coincide with the first endpoint, and the projections of the second inflection point and the tenth endpoint on the upper base of the first trapezoid coincide with the sixth endpoint and are a distance of b3 from the sixth endpoint; or, the projections of the second inflection point and the tenth endpoint on the upper base of the first trapezoid coincide with the sixth endpoint, and the projections of the first inflection point and the fifth endpoint on the upper base of the first trapezoid coincide with the first endpoint and are a distance of b3 from the first endpoint, so as to form an eccentric negative Poisson's ratio structure.

[0008] Optionally, the first trapezoid is an isosceles trapezoid, the line connecting the first inflection point and the second inflection point is parallel to the first base, the first folded edge group includes a first folded edge and a second folded edge, the second folded edge group includes a third folded edge and a fourth folded edge, the first folded edge and the third folded edge are respectively connected to the first trapezoid, the length of the first folded edge is a5, the length of the third folded edge is b2, where a5 > b2 or a5 < b2; the length of the upper base of the first trapezoid is a1, and the projection length of the distance between the first inflection point and the second inflection point in the first direction is a6, where a6 > a1.

[0009] Optionally, the module includes several battery cells, the thickness of the battery cells is H, the length of the upper base of the first trapezoid is a1, the height of the first trapezoid is a3, and the angle between the first side of the first trapezoid and the second direction is α1, wherein 0.8≤a1 / H≤1.5, 0.2≤a3 / H≤0.5, and 0°≤α1≤60°;

[0010] And / or, the length of the first side is a2, and the length of the first folded edge is a5, where 0.6≤a5 / a2≤0.85; 0.2≤b3 / H≤0.5.

[0011] Optionally, the base plate is constructed as a honeycomb structure, comprising several honeycomb units, each of which is surrounded by honeycomb ribs with a thickness of c4, wherein 1 / 7≤c4 / H≤1 / 4.

[0012] Optionally, a sleeve is provided on the side beam that runs through the side beam. The triangular rib and the first horizontal rib are both connected to the outer wall of the sleeve. The angle between the triangular rib and the second direction is θ, where 30°≤θ≤60°.

[0013] Optionally, the reinforcing rib also includes a second transverse rib area. The second transverse rib area is constructed as a strip-shaped area extending along the first direction and located between the first transverse rib and the bottom plate. The second transverse rib area includes a plurality of second transverse ribs, which extend along the second direction. The height of the second transverse rib is c, the height of the first transverse rib is b, and the height of the frame is d, where 1 / 4≤b / c≤1 / 2, 1 / 3≤c / d≤3 / 5.

[0014] Optionally, the lower housing of the battery pack also includes a crossbeam and a longitudinal beam disposed on the upper side of the base plate. The crossbeam extends along a second direction, and the longitudinal beam extends along a first direction. The crossbeam and the longitudinal beam are provided with beam reinforcing ribs inside.

[0015] The present invention also provides a battery pack, comprising: the aforementioned lower housing of the battery pack; a module installed inside the lower housing of the battery pack; and a cover plate disposed at the upper end of the lower housing of the battery pack to close the lower housing of the battery pack.

[0016] The present invention has the following advantages:

[0017] 1. By setting the base plate and frame below and around the module, the module is supported and protected, reducing damage from external impacts. Side beams are installed on the outer side of the frame, with reinforcing ribs inside, increasing the strength of the side beams and improving the battery pack's lower housing's ability to withstand lateral impacts and compression, thus protecting the entire module. Compared to traditional methods that increase strength by adding thickness, the reinforcing rib structure can relatively reduce the weight of the side beams, contributing to a lighter battery pack and increasing its overall energy density. Furthermore, the negative Poisson's ratio reinforcing ribs or the reinforcing rib structure combining triangular ribs and the first horizontal rib have good buffering and energy absorption effects, further improving the battery pack's lower housing's resistance to compression and providing better safety protection.

[0018] 2. The structure of sequentially splicing the first trapezoid, the concave hexagon, and the second trapezoid is a negative Poisson's ratio structure. This structure can achieve the following: when subjected to a force along the second direction, the dimensions of the concave polygonal unit become shorter along both the second and first directions, thereby absorbing more energy and reducing the force transmitted to the module. The structure is compact and has high rigidity, thus better protecting the module and reducing damage.

[0019] 3. For a negative Poisson's ratio structure composed of concave polygonal units, the deformation of the folds on both sides along the first direction will be different during the actual compression process along the second direction. However, the lengths of the folds on both sides along the first direction of the eccentric negative Poisson's ratio structure are different, so they can compensate for the difference in the actual deformation of the folds on both sides. This makes the deformation of the side beam as a whole in all parts of the first direction equal, thereby avoiding uneven deformation, improving the strength and stability of the side beam structure, and enabling better force transmission and energy absorption, thus better protecting the internal structure of the battery pack's lower casing.

[0020] 4. By setting a certain angle θ between the triangular rib and the first horizontal rib, when the side beam is subjected to external force, the force transmission path of the triangular rib is longer, and a triangular area is formed between the triangular rib and the first horizontal rib, making the structure more stable and the buffering effect stronger. Thus, by setting the reinforcing rib to connect the triangular rib and the first horizontal rib, the same buffering and energy absorption function can be achieved, as well as the protection of the modules and other structures inside the battery pack. In addition, the side beam structure is compact, has high rigidity, and is relatively lightweight. The process is simple, achieving a balance between performance and weight, which has a positive effect on reducing the weight of the entire battery pack and improving energy density. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the structure of the lower housing of the battery pack according to an embodiment of the present invention is shown;

[0023] Figure 2 A bottom view of the lower battery pack housing with a side beam employing a negative Poisson's ratio structure is shown.

[0024] Figure 3 It shows Figure 2 A three-dimensional structural diagram;

[0025] Figure 4 It shows Figure 3 A partially enlarged structural diagram;

[0026] Figure 5 It shows Figure 3 A schematic diagram of the structure of the lower casing of the battery pack after it has been subjected to stress and deformation;

[0027] Figure 6 A schematic diagram of the lower casing of the battery pack, which uses a triangular rib and a first horizontal rib connection structure, is shown.

[0028] Figure 7 It shows Figure 6 A partially enlarged structural diagram;

[0029] Figure 8 It shows Figure 6 A bottom view of the lower casing of the battery pack;

[0030] Figure 9 It shows Figure 8 A partially enlarged structural diagram;

[0031] Figure 10 An exploded structural diagram of the battery pack according to an embodiment of the present invention is shown;

[0032] Figure 11 A schematic diagram illustrating the definition of positive Poisson's ratio is shown.

[0033] Figure 12 A schematic diagram of the structure defining negative Poisson's ratio is shown;

[0034] Figure 13 A schematic diagram of a concave polygonal monomer with an eccentric negative Poisson's ratio structure is shown.

[0035] Figure 14 A schematic diagram of the connection structure between the honeycomb-structured bottom protective plate and the side beam of the eccentric negative Poisson's ratio structure is shown.

[0036] Figure 15 A model diagram of the battery pack is shown;

[0037] Figure 16 The modal analysis results of the battery pack with a conventional aluminum structure before the improvement are shown in the figure.

[0038] Figure 17 The modal analysis results of the battery pack with a negative Poisson's ratio structure according to an embodiment of the present invention are shown in the figure.

[0039] Figure 18 The diagram shows the Z-axis vibration intensity results of the battery pack with the negative Poisson's ratio structure according to an embodiment of the present invention.

[0040] Figure 19 The diagram shows the Y-axis vibration intensity results of the battery pack with the negative Poisson's ratio structure according to an embodiment of the present invention;

[0041] Figure 20 The diagram shows the X-axis vibration intensity results of the battery pack with a negative Poisson's ratio structure according to an embodiment of the present invention.

[0042] Figure 21 A schematic diagram of the force transmission path of a negative Poisson's ratio structure is shown.

[0043] Figure 22 A schematic diagram of the symmetrical negative Poisson's ratio structure before deformation is shown.

[0044] Figure 23 It shows Figure 22 A schematic diagram of the deformed symmetrical negative Poisson's ratio structure;

[0045] Figure 24 A schematic diagram of strain simulation results for a battery pack with an eccentric negative Poisson's ratio structure according to an embodiment of the present invention is shown.

[0046] Figure 25 It shows Figure 24 The diagram shows a magnified view of a region containing the maximum strain.

[0047] Explanation of reference numerals in the attached figures:

[0048] 10. Base plate; 20. Frame; 30. Side beam; 31. Sleeve; 32. Reinforcing part; 40. Reinforcing rib; 41. Triangular rib; 421. First horizontal rib; 422. Second horizontal rib; 423. Third horizontal rib; 43. Longitudinal rib; 44. Cross rib; 50. Concave polygonal single unit; 5001. First end point; 5002. Second end point; 5003. First inflection point; 5004. Fourth end point; 5005. Fifth end point; 5006. Sixth endpoint; 5007, Seventh endpoint; 5008, Second inflection point; 5009, Ninth endpoint; 5010, Tenth endpoint; 51, First trapezoid; 52, Second trapezoid; 53, Concave hexagon; 531, First base edge; 532, Second base edge; 54, Connecting rib; 61, Crossbeam; 62, Longitudinal beam; 621, Middle longitudinal beam; 622, Side longitudinal beam; 71, Module; 72, Cover plate; 73, Thermally conductive structural adhesive; 80, Bottom protective plate. Detailed Implementation

[0049] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0051] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0053] like Figures 1 to 9 As shown, the lower housing of the battery pack in this embodiment includes: a base plate 10, a frame 20, and a side beam 30. The frame 20 is arranged circumferentially along the base plate 10, and the space formed between the frame 20 and the base plate 10 is suitable for installing the module 71. The side beam 30 is fixedly arranged on the outside of the frame 20, and a reinforcing rib 40 is provided inside the side beam 30. The reinforcing rib 40 includes a negative Poisson's ratio structure, which includes a plurality of concave polygonal units 50 connected sequentially along a first direction. And / or, the reinforcing rib 40 includes a triangular rib 41 and a first horizontal rib 421. The first horizontal rib 421 extends along a second direction, and the triangular rib 41 is angled to the second direction, wherein the second direction is perpendicular to the first direction. The first direction refers to... Figure 1 The middle arrow points to the "first direction"; the second direction refers to... Figure 1 The middle arrow points to the "second direction"; the outer side of the border 20 refers to the side of the border 20 that is away from the accommodating space.

[0054] The battery pack lower housing of this embodiment supports and protects the module 71 by setting the base plate 10 and the frame 20 below and around the module 71, reducing damage to the module 71 from external impacts. By setting the side beam 30 on the outside of the frame 20 and the reinforcing rib 40 inside the side beam 30, the strength of the side beam 30 is improved, enhancing the battery pack lower housing's ability to withstand lateral impact and compression, thus protecting the entire module 71. Compared with the traditional method of increasing strength by increasing thickness, the reinforcing rib structure can relatively reduce the weight of the side beam 30, which is beneficial for achieving battery pack lightweighting and thus improving the energy density of the entire battery pack. In addition, the reinforcing rib 40 with a negative Poisson's ratio structure or the reinforcing rib 40 structure that combines the triangular rib 41 with the first horizontal rib 421 has a good buffering and energy absorption effect, further improving the compression resistance of the battery pack lower housing and providing better safety protection.

[0055] It should be noted that, as Figure 10 As shown, the lower housing of the battery pack is part of the battery pack structure, used to support and protect module 71. The frame 20 of the lower housing is located on the upper side of the base plate 10 and extends upward, thus forming an accommodating space between the frame 20 and the base plate 10. Here, "upper" refers to... Figure 1 The direction indicated by the middle arrow is "up". Specifically, the base plate 10 and the frame 20 are integrally formed, or the base plate 10 and the frame 20 can also be connected as one piece by welding or bolting.

[0056] It should be noted that Poisson's ratio refers to the ratio of the transverse normal strain to the axial normal strain of a material under uniaxial tension or compression. It is an elastic constant reflecting the transverse deformation of the material and describes its deformation characteristics under external forces. Most structures in practical applications are positive Poisson's ratio structures, and their deformation modes under external forces can be simplified as follows: Figure 11 The diagram shown represents the definition of Poisson's ratio. The structural Poisson's ratio is: Poisson's ratio δ0 = (x 01 -x0) / (y0-y 01 When Poisson's ratio is positive, its effect is that when subjected to external force, the length y0 shortens and the width x0 increases accordingly. Correspondingly, when the side beam 30 of the battery pack's lower casing is compressed by a force along the second direction, the dimension of the side beam 30 along the second direction shortens and the dimension along the first direction increases, thus resulting in a relatively large compressive force transmitted to the module 71. However, in this embodiment, the side beam 30 adopts a negative Poisson's ratio structure. When the side beam 30 is subjected to an external force along the second direction, its deformation can be simplified as follows: Figure 12 The diagram shown represents the definition of negative Poisson's ratio. In this case, Poisson's ratio δ1 = (x 11 -x1) / (y1-y 11 When the value is negative, the length y1 becomes shorter and the width x1 becomes shorter when subjected to external force. This structure has good resistance to compression and impact energy absorption, which can reduce the force transmitted to the lower box body and thus better protect the internal structure of the battery pack, such as module 71.

[0057] Preferably, there are two side beams 30, which are respectively arranged on both sides of the frame 20 along the second direction, so that both sides of the battery pack lower box have good anti-compression ability, thereby providing protection for the internal modules 71 and other structures from different directions.

[0058] It is understandable that the reinforcing rib 40 can be configured to include only a negative Poisson's ratio structure, or it can be configured to include only a structure in which the triangular rib 41 and the first transverse rib 421 are connected, or it can be configured to be a structure in which the negative Poisson's ratio structure is combined with the triangular rib 41 and the first transverse rib 421. All of these can play the role of buffering and absorbing energy and reducing weight.

[0059] For negative Poisson's ratio structures, further combining Figures 2 to 5 and Figure 13As shown, the concave polygonal unit 50 is formed by splicing together a first trapezoid 51, a concave hexagon 53, and a second trapezoid 52 arranged sequentially along the second direction. The lower base of the first trapezoid 51 is equal in length to and coincides with the first base 531 of the concave hexagon 53. The second base 532 of the concave hexagon 53 is equal in length to and coincides with the lower base of the second trapezoid 52. The concave hexagon 53 also includes a first folded edge group and a second folded edge group arranged opposite to each other and concave inward. The line connecting the first fold point 5003 of the first folded edge group and the second fold point 5008 of the second folded edge group is shorter than the length of the first base 531 and the second base 532. The second fold point 5008 is connected to the first fold point 5003 of the adjacent concave polygonal unit 50 by a connecting rib 54. In this design, the lower base of the trapezoid refers to the relatively longer base, and the lower base is the relatively shorter base. The upper and lower bases are parallel. The first trapezoid 51 is connected to the base plate 10 through its upper base. The first base 531 of the concave hexagon 53 is parallel to the second base 532. The inward concavity refers to the indentation towards the center of the area enclosed by the six sides of the concave hexagon 53. The structure formed by the sequential splicing of the first trapezoid 51, the concave hexagon 53, and the second trapezoid is a negative Poisson's ratio structure. This structure ensures that when subjected to a force along the second direction, the dimensions of the concave polygonal unit 50 become shorter in both the second and first directions, thereby absorbing more energy and reducing the force transmitted to the module 71. This results in a compact and rigid structure, better protecting the module 71 and reducing damage.

[0060] In this embodiment, the two endpoints of the upper base of the first trapezoid 51 are the first endpoint 5001 and the sixth endpoint 5006, and the two endpoints of the upper base of the second trapezoid 52 are the fifth endpoint 5005 and the tenth endpoint 5010, respectively. The projections of the first inflection point 5003 and the fifth endpoint 5005 on the upper base of the first trapezoid 51 coincide with the first endpoint 5001, and the projections of the second inflection point 5008 and the tenth endpoint 5010 on the upper base of the first trapezoid 51 coincide with the sixth endpoint 5006 and are a distance of b3, so as to form an eccentric negative Poisson's ratio structure. That is, the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 are on the same straight line and the straight line is perpendicular to the upper base of the first trapezoid 51. The line connecting the second inflection point 5008 and the tenth endpoint 5010 is perpendicular to the upper base of the first trapezoid 51. However, the sixth endpoint 5006 is not on the same straight line as the second inflection point 5008 and the tenth endpoint 5010, thus forming an eccentric structure. That is, the two sides of the concave polygonal single unit 50 in the first direction are not symmetrical to each other, thus making the concave polygonal single unit 50 an eccentric negative Poisson's ratio structure. It is understood that, as an alternative implementation, the projections of the second inflection point 5008 and the tenth endpoint 5010 on the upper base of the first trapezoid 51 may coincide with the sixth endpoint 5006, and the projections of the first inflection point 5003 and the fifth endpoint 5005 on the upper base of the first trapezoid 51 may coincide with the first endpoint 5001 and the distance between them and the first endpoint 5001 may be b3. That is, the line connecting the sixth endpoint 5006, the second inflection point 5008, and the tenth endpoint 5010 may be a straight line perpendicular to the upper base of the first trapezoid 51, while the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 may not be on the same straight line. This can also form an eccentric structure, thereby making the concave polygonal unit 50 an eccentric negative Poisson's ratio structure. For the negative Poisson's ratio structure composed of the concave polygonal unit 50 in this embodiment, during the actual compression process along the second direction, the deformation of the folded edges on both sides along the first direction will be different. Since the lengths of the folded edges on both sides along the first direction of the eccentric negative Poisson's ratio structure are different, this difference can compensate for the different actual deformation of the folded edges on both sides, making the overall deformation of the side beam 30 equal at all points in the first direction. This avoids uneven deformation, improves the strength and stability of the side beam 30 structure, and enables better force transmission and energy absorption, thus better protecting the internal structure of the battery pack's lower casing. When the battery pack is impacted or compressed, the lower casing of the battery pack is subjected to... Figure 5 The crushing damage shown absorbs the energy of external forces, thus protecting the internal structures of module 71. The explanation and performance verification of the eccentric negative Poisson's ratio structure are specifically combined... Figures 21-23 As shown below, and described in the "Explanation of the Eccentric Negative Poisson's Ratio Structure" section, it will not be repeated here.

[0061] Specifically, the first trapezoid 51 includes an upper base, a lower base, and a first side and a second side arranged opposite to each other; the second trapezoid 52 includes an upper base, a lower base, and a third side and a fourth side arranged opposite to each other; the concave hexagon 53 includes a first base 531, a second base 532, and a first folded edge group and a second folded edge group arranged opposite to each other. The first folded edge group includes a first folded edge and a second folded edge, and the second folded edge group includes a third folded edge and a fourth folded edge. The first side, the first folded edge, the second folded edge, and the third side are connected in sequence, and the endpoints of each line segment are connected in sequence along the second direction to form a first endpoint 5001, a second endpoint 5002, a first fold point 5003 (which is also the third endpoint), a fourth endpoint 5004, and a fifth endpoint 5005. The second side, the third folded edge, the fourth folded edge, and the fourth side are connected in sequence, and the endpoints of each line segment are connected in sequence along the second direction to form a sixth endpoint 5006, a seventh endpoint 5007, a second fold point 5008 (which is also the eighth endpoint), a ninth endpoint 5009, and a tenth endpoint 5010. For the eccentric negative Poisson's ratio structure, the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 are collinear, and the line connecting them is a straight line perpendicular to the base of the first trapezoid 51. The line connecting the second endpoint 5002 and the fourth endpoint 5004 is a straight line perpendicular to the base of the first trapezoid 51. The line connecting the seventh endpoint 5007 and the ninth endpoint 5009 is a straight line perpendicular to the base of the first trapezoid 51. The line connecting the second inflection point 5008 and the tenth endpoint 5010 is a straight line perpendicular to the base of the first trapezoid 51. The sixth endpoint 5006 is not collinear with the second inflection point 5008 and the tenth endpoint 5010, and the line connecting them is perpendicular to the base of the first trapezoid 51. The first direction has a dimensional distance of b3; it can be understood that, as an alternative implementation, the eccentric negative Poisson's ratio structure can also swap the two side groups of the concave polygonal monomer 50 along the first direction, that is, the sixth endpoint 5006, the second inflection point 5008 and the tenth endpoint 5010 are collinear and the line connecting them is a straight line perpendicular to the bottom edge of the first trapezoid 51, the line connecting the first inflection point 5003 and the fifth endpoint 5005 is a straight line perpendicular to the bottom edge of the first trapezoid 51, and the first endpoint 5001 is not collinear with the first inflection point 5003 and the fifth endpoint 5005 and has a dimensional distance of b3 along the first direction.

[0062] In this embodiment, the first trapezoid 51 is an isosceles trapezoid. The line connecting the first inflection point 5003 and the second inflection point 5008 is parallel to the first base 531. The first folded edge group includes a first folded edge and a second folded edge, and the second folded edge group includes a third folded edge and a fourth folded edge. The first folded edge is opposite to the third folded edge, and the second folded edge is opposite to the fourth folded edge. The first folded edge and the third folded edge are respectively connected to the first trapezoid. The length of the first folded edge is a5, the length of the third folded edge is b2, and the length of the upper base of the first trapezoid 51 is a1. The distance between inflection point 5003 and the second inflection point 5008 is projected as a6 in the first direction, where a6 > a1 and a6 = a1 + b3, a5 > b2, so that the concave polygonal unit 50 is an eccentric structure with the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 collinear, and the sixth endpoint 5006 not collinear with the second inflection point 5008 and the tenth endpoint 5010. In this case, a6 is the length of the line connecting the first inflection point 5003 and the second inflection point 5008. By setting a6 > a1 and a5 > b2, the first set of broken lines is shifted away from the center of the concave polygonal unit 50 along the first direction, thereby obtaining an eccentric negative Poisson's ratio structure. It is understood that, as an alternative implementation, when the concave polygonal monomer 50 is an eccentric structure in which the sixth endpoint 5006 is collinear with the second inflection point 5008 and the tenth endpoint 5010, and the first endpoint 5001, the first inflection point 5003 and the fifth endpoint 5005 are not collinear, a5 < b2. In this case, the first folded edge group is offset along the first direction away from the center of the concave polygonal monomer 50, and an eccentric negative Poisson's ratio structure can also be obtained.

[0063] It is understandable that, as an alternative implementation, a5 = b2 can also be set. Taking the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 as collinear, and the sixth endpoint 5006 as not collinear with the second inflection point 5008 and the tenth endpoint 5010 as an example of an eccentric structure, in this case, the line connecting the first inflection point 5003 and the second inflection point 5008 is not parallel to the first bottom edge 531 (i.e., not parallel to the first direction), and the distance from the second inflection point 5008 to the lower base of the second trapezoid 52 is less than or greater than the distance from the first inflection point 5003 to the lower base of the second trapezoid 52. It is only necessary to ensure that the projections of the second inflection point 5008 and the tenth endpoint 5010 on the upper base of the first trapezoid 51 coincide and the distance from the sixth endpoint 5006 is b3. In this case, the length of the line connecting the first inflection point 5003 and the second inflection point 5008 is greater than a6, and an eccentric negative Poisson's ratio structure can also be constructed. The design of the eccentric negative Poisson's ratio structure, in which the sixth endpoint 5006, the second inflection point 5008, and the tenth endpoint 5010 are collinear and the first endpoint 5001 is not collinear with the first inflection point 5003 and the fifth endpoint 5005, is the same as described above and will not be repeated here.

[0064] The following explanation uses an eccentric negative Poisson's ratio structure as an example, where the first endpoint 5001, the first inflection point 5003, and the fifth endpoint 5005 are collinear, and the sixth endpoint 5006 is not collinear with the second inflection point 5008 and the tenth endpoint 5010.

[0065] In this embodiment, module 71 includes a plurality of battery cells, the thickness of which (i.e., along) Figure 1 The dimension in the "height direction" indicated by the middle arrow is H, the length of the upper base of the first trapezoid 51 is a1, the height of the first trapezoid 51 (i.e. the dimension of the first trapezoid 51 along the second direction) is a3, and the angle between the first side and the second direction is α1, where 0.8≤a1 / H≤1.5, 0.2≤a3 / H≤0.5, and 0°≤α1≤60°. That is, the length a1 of the upper base of the first trapezoid 51 is 0.8-1.5 times the cell thickness H, ensuring that the size of the concave polygonal cell 50 along the first direction is within a reasonable range. This avoids excessive density and increased mass due to the size of the concave polygonal cell 50 being too small, while also ensuring that the buffering energy absorption effect is not reduced due to the size of the concave polygonal cell 50 being too large. The height a3 of the first trapezoid 51 is 0.2-0.5 times the cell thickness H, ensuring that the size of the concave polygonal cell 50 along the second direction is within a reasonable range. This provides sufficient distance for force transmission and sufficient deformation space, while avoiding excessive mass increase due to the size of the side beam 30 along the second direction. This achieves a balanced design of performance and strength, reducing the weight of the entire battery pack undercarriage while ensuring structural strength, and improving energy density. The angle α1 between the first side and the second direction varies from 0° to 60°, and is determined according to the needs. The angle α2 between the first side and the lower base of the first trapezoid 51 is 90° - α1. The angle β1 between the second side and the second direction is α1. The angle β2 between the second side and the lower base of the first trapezoid 51 is α2. The length of the first side is a2 = a3 / cosα1. The length of the second side is b1 = a2. That is, the first trapezoid 51 is guaranteed to be an isosceles trapezoid. Correspondingly, the length of the lower base of the first trapezoid 51 is a4 = a2*cosα2 + b1*cosβ2 + a1. Then, a4 = a1 + 2*a2*cosα2 can be solved.

[0066] In this embodiment, the length of the first side is a2, and the length of the first folded edge is a5, where 0.6≤a5 / a2≤0.85. By setting the length of the first folded edge a5 to be 0.6-0.85 times the length of the first side a2, it can satisfy the deformation margin of the negative Poisson's ratio structure during the deformation process under stress, provide sufficient connection strength, and avoid the side beam 30 from being too large in the second direction due to the excessive length of the first folded edge, thereby reducing the weight of the lower box of the battery pack. Correspondingly, the angle α3 between the first folded edge and the first bottom edge 531 is arcos((a2*cosα2) / a5), the angle α4 between the first folded edge and the second direction is 90°-α3, and the angle α5 between the first folded edge and the first direction is α3; the angle β3 between the third folded edge and the first bottom edge 531 is arcos(((b1*cosβ1)-b3) / b2), where b3 is the angle between the second folding point 5008 and the tenth endpoint 5010 in the first trapezoid 51. The projection on the upper bottom coincides with the distance to the sixth endpoint 5006, which is also the distance between the projection of the second inflection point 5008 and the sixth endpoint 5006 in the first direction. 0.2≤b3 / H≤0.5, that is, b3 is generally 0.2-0.5 times the cell thickness H. This can provide sufficient eccentricity so that the overall deformation of the concave polygonal single unit 50 is uniform during the stress process, and can also avoid the negative Poisson's ratio structural density in the side beam 30 being too small due to excessive eccentricity, thereby ensuring structural strength.

[0067] Correspondingly, two adjacent concave polygonal units 50 are connected by connecting ribs 54. One end of the connecting rib 54 is connected to the second inflection point 5008 of one concave polygonal unit 50, and the other end is connected to the first inflection point 5003 of the adjacent concave polygonal unit 50. The length of the connecting rib 54 is a7, where a7 = a4, ensuring the uniformity of the distribution of each concave polygonal unit 50 along the first direction, thereby enhancing the stability of the side beam 30 structure. The triangle formed by the extension of the first side, the first inflection point, and the connecting rib 54 is usually an isosceles triangle. The angle between the extension of the first side and the connecting rib 54 is equal to the angle α5 between the first inflection point and the connecting rib 54, and is generally 30°-60°.

[0068] Specifically, the concave hexagon 53 can generally be designed as a symmetrical structure with respect to the line connecting the first inflection point 5003 and the second inflection point 5008. The line connecting the first inflection point 5003 and the second inflection point 5008 is parallel to the first direction. Then, the second bottom edge 532 is parallel to the first bottom edge 531, the length of the first folded edge is equal to the length of the second folded edge, and the length of the third folded edge is equal to the length of the fourth folded edge. The structure design is simple and easy to process. In particular, when the line connecting the first inflection point 5003 and the second inflection point 5008 is not parallel to the first direction, the concave hexagon 53 is no longer designed as a symmetrical structure with respect to the line connecting the first inflection point 5003 and the second inflection point 5008. In this case, the second bottom edge 532 is still parallel to the first bottom edge 531, the first folded edge is equal to the second folded edge, and the fourth folded edge is not equal to the third folded edge. It is understandable that, as an alternative implementation, when the line connecting the first fold point 5003 and the second fold point 5008 is parallel to the first direction, the length of the first fold edge can be set to be unequal to the length of the second fold edge, and the length of the third fold edge can be set to be unequal to the length of the fourth fold edge, as long as the second bottom edge 532 is parallel to the first bottom edge 531.

[0069] Specifically, the lower base of the second trapezoid 52 coincides with the second base edge 532, and its length is equal to a4. The length of the upper base of the second trapezoid 52 is equal to a1 + b3, which is 1 / 2 - 3 / 4 of the length of the lower base a4 of the second trapezoid 52. The fourth side and the fourth folded edge are symmetrical about the second base edge 532. The length of the third side and the angle between it and the base edge of the trapezoid are consistent with those of the first trapezoid 51. It can be understood that when the concave polygonal single unit 50 is not an eccentric structure, but has a left-right symmetrical structure along the first direction, the second trapezoid 52 can be designed to have the same dimensions as the first trapezoid 51.

[0070] Preferably, the base plate 10 is provided with base plate reinforcing ribs. The base plate 10 can be constructed as a polygonal structure, or it can be based on a flat plate structure with added intersecting cross ribs 44, or it can be set as a combination of polygonal structure and cross ribs 44. All of these can enhance the structural strength of the base plate 10. When the battery pack is subjected to external impact force, the base plate 10 can effectively absorb the impact energy and improve the bottom safety protection, thereby providing protection for the internal modules 71 and other structures from the bottom of the battery pack housing.

[0071] In this embodiment, the bottom plate reinforcing ribs are constructed as a honeycomb structure, comprising several honeycomb cells, each formed by honeycomb ribs. The honeycomb structure offers good stability, high strength, and a certain degree of cushioning, protecting the internal structure of the battery pack's lower casing from below and reducing damage to modules 71 and the like. The thickness of the honeycomb ribs is c4, where 1 / 7 ≤ c4 / H ≤ 1 / 4, meaning the thickness of the honeycomb ribs is generally 1 / 7 to 1 / 4 of the cell thickness H. This ensures the structural strength of the honeycomb structure while preventing excessive weight on the bottom plate 10, thus providing sufficient protection for the internal structure of modules 71 and achieving overall battery pack lightweighting.

[0072] Specifically, the negative Poisson's ratio structure in the side beam 30 is misaligned with the honeycomb structure of the base plate 10, such as... Figure 14 As shown, along the first direction, the size of the honeycomb cell is larger than the size of the concave polygonal cell 50. The size of the honeycomb cell along the first direction is c1 = c4 + a4 + c2, where c4 is the thickness of the honeycomb reinforcement, a4 is the length of the lower base of the first trapezoid 51 (also the length of the connecting reinforcement 54), and c2 is the distance along the first direction between the inner wall of a concave polygonal cell 50 and its corresponding honeycomb cell. The distance between two adjacent concave polygonal cells 50 is c2 + c3 + c4, where c2 is the distance from the first concave polygonal cell to the honeycomb reinforcement along the first direction, c3 is the distance from the second polygonal cell to the honeycomb reinforcement along the first direction, c3 is approximately 0.5-0.8 times the cell thickness H, and c2 is approximately half of c3. Further combining... Figure 4 As shown, the dimension of the side beam 30 along the height direction is f, and the dimension of the frame 20 along the height direction is d, where f is 1 / 3 to 3 / 5 of d. Through the above dimensional design, the negative Poisson's ratio structure and the honeycomb structure can effectively absorb impact forces, thereby further enhancing the protection of the internal structures such as module 71.

[0073] In this embodiment, the side beam 30 is provided with a through mounting hole for connecting the battery pack to the vehicle when it is installed. The mounting hole and its surrounding area are critical stress areas. A sleeve 31 is circumferentially arranged around the mounting hole, and a reinforcing rib 40 is connected to the outer side of the sleeve 31 to ensure the strength and reliability requirements of the mounting hole. There are multiple sleeves 31, preferably six, three on each of the two side beams 30. Specifically, a concave polygonal unit 50 surrounds the circumference of the sleeve 31, thereby strengthening the sleeve 31.

[0074] Preferably, the side beam 30 is further provided with a reinforcing part 32 extending along the first direction. The reinforcing part 32 has an L-shaped cross-section and is fastened to the side beam 30. Specifically, it is located at the corner of the upper side of the side beam 30 and the side away from the frame 20, to further enhance the strength of the side beam 30 when connected to external structures such as vehicles. Correspondingly, the reinforcing part 32 is also provided with an opening corresponding to the sleeve 31. Here, "upper side" refers to the side beam 30 extending along the first direction. Figure 1 The direction indicated by the middle arrow is "up".

[0075] For the structure where the triangular rib 41 and the first horizontal rib 421 are connected, both the triangular rib 41 and the first horizontal rib 421 are connected to the outer wall of the sleeve 31. The angle between the triangular rib 41 and the second direction is θ, that is, the angle between the triangular rib 41 and the first horizontal rib 421 is θ, 30°≤θ≤60°, which is specifically designed and determined according to the lateral compressive force. The lateral compressive force refers to the force applied to the side beam 30 along the second direction. By setting a certain angle θ between the triangular rib 41 and the first horizontal rib 421, when the side beam 30 is subjected to external force, the force transmission path of the triangular rib 41 is longer, and a triangular area is formed between the triangular rib 41 and the first horizontal rib 421, making the structure more stable and the buffering effect stronger. Thus, by setting the reinforcing rib 40 to connect the triangular rib 41 and the first horizontal rib 421, the same buffering and energy absorption function can be achieved, as well as the protection of the module 71 and other structures inside the lower box of the battery pack. Furthermore, the side beam 30 has a compact structure, high rigidity, relatively light weight, and simple manufacturing process, achieving a balance between performance and weight, which has a positive effect on reducing the weight of the entire battery pack and improving energy density.

[0076] In this embodiment, the reinforcing rib 40 further includes a second transverse rib area. The second transverse rib area is constructed as a strip-shaped region extending along the first direction and located between the first transverse rib 421 and the base plate 10. The second transverse rib area includes a plurality of second transverse ribs 422, which extend along the second direction. The height of the second transverse rib 422 is c, the height of the first transverse rib 421 is b, and the height of the frame 20 is d, wherein 1 / 4 ≤ b / c ≤ 1 / 2, that is, the height of the first transverse rib 421 is 1 / 4 to 1 / 2 of the height of the frame 20, which ensures that the first transverse rib 421 has the characteristics of... Sufficient strength is required to achieve the supporting and force-transmitting effect of the first horizontal rib 421, while also reducing the overall weight of the reinforcing rib 40, thereby reducing the weight of the entire battery pack; 1 / 3≤c / d≤3 / 5, meaning the height of the side beam 30 is 1 / 3-3 / 5 of the height of the frame 20. Similarly, this ensures the structural strength of the side beam 30, enabling it to withstand external compressive forces, while avoiding an increase in weight due to excessive height of the side beam 30. This achieves both protection of the internal structure of the battery pack and helps to improve the energy density of the battery pack. Here, height refers to the height along the frame 20. Figure 1 The dimension in the "height direction" indicated by the middle arrow.

[0077] Preferably, the reinforcing rib 40 further includes a third transverse rib area, which is constructed as a strip-shaped region extending along the first direction and connecting the second transverse rib area and the base plate 10. The third transverse rib area includes a plurality of third transverse ribs 423, which extend along the second direction. The height of the third transverse ribs 423 is equal to the height of the second transverse ribs 422. One end of the third transverse rib 423 is connected to the second transverse rib 422 and the other end is connected to the base plate 10 to further enhance the structural strength of the side beam 30. The triangular rib 41, the first transverse rib 421, the second transverse rib 422, and the third transverse rib 423 are connected by ribs to ensure effective force transmission. More preferably, the reinforcing rib 40 also includes longitudinal ribs 43 extending along the first direction. The longitudinal ribs 43 can be set at both ends of the second transverse rib 422 along the second direction to increase the strength of the reinforcing rib 40 and improve the reliability of the side beam 30.

[0078] Preferably, the frame 20 is also provided with longitudinal ribs 43 to increase the strength of the frame 20 and further increase the impact resistance of the battery pack lower housing.

[0079] In this embodiment, the lower battery pack housing also includes a crossbeam 61 and a longitudinal beam 62 disposed on the upper side of the base plate 10. The crossbeam 61 extends along a second direction, and the longitudinal beam 62 extends along a first direction to further enhance the strength and stability of the lower battery pack housing. The longitudinal beam 62 includes a central longitudinal beam 621 and an edge longitudinal beam 622 disposed at intervals. The central longitudinal beam 621 is disposed near the center of the lower battery pack housing, and the edge longitudinal beam 622 is disposed near the edge frame 20 of the lower battery pack housing. The crossbeam 61 and the longitudinal beam 62 are internally reinforced with beam stiffeners. These stiffeners can be configured as one or a combination of crossbeams, longitudinal beams, triangular beams, and negative Poisson's ratio structures to increase the structural strength of the crossbeams 61 and the longitudinal beam 62, further enhancing the overall lateral compressive strength of the lower battery pack housing and improving its stability. The term "upper side" refers to... Figure 1 The side in the direction indicated by the middle arrow, where "up" is located.

[0080] Preferably, the lower casing of the battery pack is made of a new type of composite high-compression-resistant material, which can be made of nylon and glass fiber mixture, such as PA6 as the base material with 45% glass fiber added, and continuous glass fiber composite board is used for local reinforcement to improve local stiffness and strength. The material has a small mass, which helps to reduce the overall weight of the lower casing of the battery pack, thereby further improving the energy density of the battery pack. At the same time, the material has good overall thermal insulation and insulation performance, which improves economic benefits and reduces costs.

[0081] Preferably, the novel high-compression-resistant box molding process can adopt the LFT-D process, specifically using long glass fiber reinforced thermoplastic material and direct mixing compression molding. The specific steps are as follows: raw materials → mixer → raw material glass fiber → mixer screw → heating → conveying → mold pressing → head and tail cutting, sample taking → roller straightening → inspection → cutting finished product → finished product inspection → packaging → warehousing.

[0082] like Figure 10 As shown, the present invention also provides a battery pack, which includes: the lower housing of the battery pack, a module 71 and a cover plate 72, wherein the module 71 is installed inside the lower housing of the battery pack; the cover plate 72 is disposed at the upper end of the lower housing of the battery pack to close the lower housing of the battery pack.

[0083] In this embodiment, the battery pack also includes a bottom protective plate 80 disposed at the bottom of the lower casing of the battery pack. The bottom protective plate 80 is located at the bottom of the entire battery pack and is used to protect the battery pack from the bottom. Specifically, the bottom protective plate 80 is bolted to the frame 20, which facilitates operation and provides high connection strength. Preferably, the bottom protective plate 80 is made of steel plate with a PVC coating to prevent rust and conductivity; it can be understood that, as an alternative implementation, the bottom protective plate 80 can also be made of composite material, which is lighter in weight. Here, "bottom" refers to... Figure 10 The end of the direction indicated by the middle arrow, which points to "down".

[0084] In this embodiment, an adhesive is provided between the module 71 and the cover plate 72. The module 71 and the cover plate 72 are bonded together by the adhesive to reduce the relative shaking between the module 71 and the cover plate 72, increase the stability of the structure, and improve the safety performance of the battery pack. Preferably, the module 71 is composed of a module top cover, a module body, and a module bottom plate. The module top cover is located on the upper side of the module body, and the module bottom plate is located on the lower side of the module to protect the module body. Preferably, the cover plate 72 is a liquid cooling plate with flow channels suitable for guiding liquid. The liquid flow carries away the temperature of the module. The liquid cooling plate has functions such as cooling the module 71, equalizing the temperature, and providing support, ensuring that the module 71 operates within the normal temperature range, thereby improving the electrical performance of the battery pack. Correspondingly, the adhesive is a thermally conductive structural adhesive 73, which provides thermal conductivity and connection, and can transfer the temperature of the module 71 to the liquid cooling plate.

[0085] Specifically, the cover plate 72 is bolted to the frame 20 of the lower battery pack housing, the module base plate is bolted to the longitudinal beam 62, and the reinforcing rib 40 is glued to its surrounding structure to improve overall rigidity.

[0086] The following is a modeling and simulation analysis of a battery pack with a negative Poisson's ratio structure:

[0087] 1. Modal Analysis Boundary: To verify the battery pack's stress performance, modal analysis was performed. The analysis boundary constrained the six sleeves connected to the vehicle (DOFs 1-6, simulating the battery pack's installation state with the vehicle), and their modal frequencies were extracted. The battery pack model diagram and its analysis boundary are shown below. Figure 15 As shown.

[0088] The formula for calculating the modal frequency of the battery pack is as follows:

[0089] Typically, for a battery pack as a multi-degree-of-freedom mechanical system, and neglecting the influence of external forces, its modal analysis dynamic equations can be expressed as follows:

[0090]

[0091] Where [M] is the system mass matrix, [C] is the system damping matrix, and [K] is the system stiffness matrix. For nodal acceleration vectors, Let {u} be the nodal velocity vector, and {u} be the nodal displacement vector.

[0092] If we neglect system damping, equation (1) can be transformed into the following form:

[0093]

[0094] Assuming the system's free vibration is a sinusoidal response motion, i.e., u = u0sin(ωt), then equation (2) can be expressed as follows:

[0095] -[M]ω 2 {u}sin(ωt)+[K]{u}sin(ωt)=0 (3)

[0096] ([K]-ω 2 [M]){u}=0 (4),

[0097] Solving equation (4) above, we can obtain the roots of the equation. That is, eigenvalues, i.e. Then, using ω = 2πf, the modal natural frequencies of the system can be solved. That is Figures 16 to 17 The modal frequencies in

[0098] The obtained {u} is a certain order modal vector in the battery pack system, which can be represented by a column vector composed of the vibration values ​​of all measuring points on that order, as follows:

[0099]

[0100] That is, equation (5) represents the mode shape of the battery pack system, such as Figures 16 to 17 The color cloud map is shown in the image.

[0101] 2. Modal analysis is performed on the assembly. The purpose of modal analysis is to obtain the frequency of the battery pack's installation in the vehicle, and then assess whether it resonates with other systems in the vehicle. For example... Figure 16 The modal analysis results are for the battery pack with a traditional aluminum structure before the improvement. Figure 17 For the battery pack with negative Poisson's ratio structure in this embodiment (using composite materials), based on the vibration analysis results in Table 1, the first-order overall mode of the battery pack before the improvement was 52.7Hz, while the first-order overall mode of the battery pack with negative Poisson's ratio structure in this embodiment was 39.6Hz, which is better than the target requirement of 35Hz and meets the overall vibration performance requirements of the battery pack. Furthermore, the weight of the lower housing of the battery pack in this embodiment is reduced by 12.9% compared with the weight of the lower housing before the improvement, which is a significant effect.

[0102] Table 1 Comparison of Vibration Analysis Results

[0103]

[0104] 3. Vibration analysis boundary: In order to verify the stress performance of the battery pack, random vibration analysis is performed. The analysis boundary is the 1-6 degrees of freedom of the 6 sleeves constrained at the vehicle body mounting position. Random vibration loads are applied, considering the main force direction Z, and the vibration results of each component are extracted.

[0105] The vibration stress calculation process is as follows:

[0106] Based on solving for the model stiffness matrix, the deformation is then calculated under external forces (acceleration excitation force in this example, which can be calculated using F=ma).

[0107] {x} = [K]-1{F} (6),

[0108] Where {x} is the displacement matrix of the node, F is the external force, and K is the stiffness matrix;

[0109] Then, based on the definition of strain, the strain of the system structure can be solved.

[0110] {ε}={Δx} / {x} (7)

[0111] Where Δx is the relative deformation of the structure;

[0112] Then, the stress is solved using Hooke's Law.

[0113] {σ}=[E]{ε} (8),

[0114] Where [E] is the elastic modulus of the structural component.

[0115] Combination Figures 18 to 20The vibration intensity results of this embodiment and the random vibration analysis results shown in Table 2 show that the maximum stress in the Z direction under random vibration conditions is 5.44 MPa, the maximum stress in the Y direction is 1.09 MPa, and the maximum stress in the X direction is 1.91 MPa, all of which are less than the reference 13 MPa and meet the vibration intensity requirements.

[0116] Table 2 Results of random vibration analysis

[0117]

[0118] The following explains the eccentric negative Poisson's ratio structure:

[0119] Apply such as to the battery pack Figure 21 As shown, a lateral force F along the second direction causes the battery pack to deform under the action of force F. For a symmetrical negative Poisson's ratio structure, Figures 22 to 23 The diagram shows the structure before and after deformation. Specifically, it shows the relative sides of two adjacent concave polygonal units 50 (hereinafter referred to as the first concave polygonal unit and the second concave polygonal unit) on the side of the side beam 30 away from the frame 20. Further, it compares the length data of each line segment in Table 3 for the negative Poisson's ratio structure before and after deformation. Specifically, X1 is the distance between the fifth endpoint 5005 of the first concave polygonal unit and the tenth endpoint 5010 of the second concave polygonal unit; X2 is the distance between the fourth endpoint 5004 of the first concave polygonal unit and the ninth endpoint 5009 of the second concave polygonal unit; X3 is the distance between the first inflection point 5003 of the first concave polygonal unit and the second inflection point 5008 of the second concave polygonal unit (i.e., the length of the connecting rib 54); Y1 is the length of the third side of the first concave polygonal unit; Y2 is the length of the fourth side of the second concave polygonal unit; and Y3 is the length of the first concave polygonal unit. The second fold edge of the body and Y4 are the fourth fold edge of the second concave polygonal unit. It can be seen that the deformation of Y1 (-0.784mm) is greater than that of Y2 (-0.497mm), and the deformation of Y3 (-2.149mm) is greater than that of Y4 (-1.281mm). This indicates that the deformation of the third and fourth sides of the concave polygonal unit 50 is not equal, and the deformation of the second and fourth fold edges is not equal. That is, the deformation of the two sides of the concave polygonal unit 50 along the first direction is different. Therefore, designing the concave polygonal unit 50 as an eccentric structure, with the length of the second fold edge greater than the length of the fourth fold edge and the length of the third side greater than the length of the fourth side, can compensate for the above-mentioned problem of different deformation. The length of the first fold edge is greater than the length of the second fold edge for the same reason. This further shows that the eccentric negative Poisson's ratio structure has better performance, can ensure the uniformity of structural deformation before and after the overall structure is subjected to force, and improve the stability of the structure.

[0120] Further integration such as Figure 21The force transmission path in the negative Poisson's ratio structure indicated by the middle arrow shows that after the side beam 30 of the battery pack is compressed by the force F indicated by the arrow in the figure, the waist of the negative Poisson's ratio structure contracts inward, which is consistent with the deformation result of X2 shown in Table 3. This indicates that the negative Poisson's ratio structure absorbs a certain force, thereby reducing the force transmitted to the inside of the battery pack and making the compression deformation inside the battery pack smaller. Therefore, the negative Poisson's ratio structure has a better energy absorption effect and can better protect the module 71.

[0121] Table 3 Results of negative Poisson's ratio structure before and after deformation

[0122] raw / mm After deformation / mm Difference / mm X1 43.782 43.727 -0.055 Y1 28.535 27.751 -0.784 Y2 28.535 28.039 -0.496 X2 18.453 16.304 -2.149 Y3 26.168 24.887 -1.281 Y4 26.168 25.760 -0.408 X3 42.203 42.395 0.192

[0123] like Figures 24 to 25 The figure shows the strain simulation results after applying a lateral force F along the second direction to a battery pack with an eccentric negative Poisson's ratio structure. It can be seen that the maximum strain on the lower housing of the battery pack is 16.9%, the critical value for structural failure is 4.5%, and there is local failure on the side beam 30 of the lower housing of the battery pack. However, the failure range is small (only the bottom of the frame 20 is partially cracked). The eccentric negative Poisson's ratio structure absorbs more energy through local failure, which greatly reduces the force transmitted to the inside of the battery pack. It can effectively improve the lateral compression resistance of the battery pack, make full use of the energy absorption and compression impact energy of the structure, and better protect the module 71.

[0124] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A battery pack lower housing, characterized in that, include: Base plate; A frame is provided along the circumference of the base plate, and the receiving space formed between the frame and the base plate is suitable for installing the module; A side beam is fixedly installed on the outside of the frame. The side beam is provided with a reinforcing rib inside. The reinforcing rib includes a negative Poisson's ratio structure, which includes a plurality of concave polygonal units connected sequentially along a first direction. The concave polygonal unit is composed of a first trapezoid, a concave hexagon, and a second trapezoid arranged sequentially along a second direction. The lower base of the first trapezoid is equal in length to and coincides with the first base of the concave hexagon. The second base of the concave hexagon is equal in length to and coincides with the lower base of the second trapezoid. The concave hexagon also includes a first folded edge group and a second folded edge group arranged opposite to each other and concave inward. The line connecting the first fold point of the first folded edge group and the second fold point of the second folded edge group is less than the length of the first base and the second base. The second fold point is connected to the first fold point of the adjacent concave polygonal unit by a connecting rib. The two endpoints of the upper base of the first trapezoid are the first endpoint and the sixth endpoint, and the two endpoints of the upper base of the second trapezoid are the fifth endpoint and the tenth endpoint, respectively; The projections of the first inflection point and the fifth endpoint onto the upper base of the first trapezoid coincide with the first endpoint; the projections of the second inflection point and the tenth endpoint onto the upper base of the first trapezoid coincide with the sixth endpoint and are at a distance of b3; or, the projections of the second inflection point and the tenth endpoint onto the upper base of the first trapezoid coincide with the sixth endpoint; the projections of the first inflection point and the fifth endpoint onto the upper base of the first trapezoid coincide with the first endpoint and are at a distance of b3, to form an eccentric negative Poisson's ratio structure.

2. The lower housing of the battery pack according to claim 1, characterized in that, The first trapezoid is an isosceles trapezoid. The line connecting the first inflection point and the second inflection point is parallel to the first base. The first folded edge group includes a first folded edge and a second folded edge. The second folded edge group includes a third folded edge and a fourth folded edge. The first folded edge and the third folded edge are respectively connected to the first trapezoid. The length of the first folded edge is a5, and the length of the third folded edge is b2, wherein a5 > b2 or a5 < b2. The length of the upper base of the first trapezoid is a1, and the projected length of the distance between the first inflection point and the second inflection point in the first direction is a6, where a6 > a1.

3. The lower housing of the battery pack according to claim 2, characterized in that, The module includes several battery cells, the thickness of the battery cells is H, the length of the upper base of the first trapezoid is a1, the height of the first trapezoid is a3, and the angle between the first side of the first trapezoid and the second direction is α1, wherein 0.8≤a1 / H≤1.5, 0.2≤a3 / H≤0.5, and 0°≤α1≤60°; And / or, the length of the first side is a2, and the length of the first folded edge is a5, wherein 0.6≤a5 / a2≤0.85; 0.2≤b3 / H≤0.

5.

4. The lower housing of the battery pack according to claim 3, characterized in that, The base plate is constructed as a honeycomb structure, comprising several honeycomb units, each of which is surrounded by honeycomb ribs, the thickness of which is c4, wherein 1 / 7≤c4 / H≤1 / 4.

5. The lower housing of the battery pack according to claim 4, characterized in that, The reinforcing rib further includes a triangular rib and a first transverse rib. The first transverse rib extends along a second direction, and the triangular rib is set at an angle to the second direction, wherein the second direction is perpendicular to the first direction. A sleeve is provided on the side beam, and the triangular rib and the first transverse rib are both connected to the outer wall of the sleeve. The angle between the triangular rib and the second direction is θ, where 30° ≤ θ ≤ 60°.

6. The lower housing of the battery pack according to claim 5, characterized in that, The reinforcing rib also includes a second transverse rib area, which is constructed as a strip-shaped area extending along the first direction and located between the first transverse rib and the base plate. The second transverse rib area includes a plurality of second transverse ribs, which extend along the second direction. The height of the second transverse rib is c, the height of the first transverse rib is b, and the height of the frame is d, wherein 1 / 4≤b / c≤1 / 2, 1 / 3≤c / d≤3 / 5.

7. The lower casing of the battery pack according to any one of claims 1 to 6, characterized in that, The lower housing of the battery pack also includes a crossbeam and a longitudinal beam disposed on the upper side of the base plate. The crossbeam extends along the second direction, and the longitudinal beam extends along the first direction. The crossbeam and the longitudinal beam are provided with beam reinforcing ribs inside.

8. A battery pack, characterized in that, include: The lower housing of the battery pack as described in any one of claims 1-7; The module is installed inside the lower housing of the battery pack; A cover plate is provided at the upper end of the lower housing of the battery pack to close the lower housing of the battery pack.

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