Battery Module

Abstract

The present application relates to the technical field of energy storage devices, and in particular to a battery module. The battery module includes a plurality of battery cells, which are connected in series; an electrode output connecting piece, which is arranged at the output end of the battery module; a plurality of jumper electrode connecting pieces, which respectively connect the separated battery cells in the plurality of battery cells; an adjacent electrode connecting piece, which connects the adjacent battery cells in the plurality of battery cells, and forms a power supply path for the battery module through the electrode output connecting piece, the jumper electrode connecting piece and the adjacent electrode connecting piece; the plurality of jumper electrode connecting pieces are partially overlapped and attached in an insulating manner in a group of at least two. Through the above scheme, the application scenarios of the battery module are more diversified, which is conducive to providing the safety and energy density of the battery module.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage devices, and in particular to a battery module. Background Art

[0002] With the transformation of energy structure, sustainable electricity has gradually replaced traditional fossil fuels to become the mainstream energy. For example, electric vehicles are gradually replacing traditional fuel vehicles and becoming a new development trend, so rechargeable batteries are developing rapidly.

[0003] For current battery modules with multiple battery cells connected in series, the previous way of setting the electrode connecting sheets limits the diversity of battery module configurations, has deficiencies in heat dissipation and safety, and is not conducive to improving the energy density of the battery module. Summary of the invention

[0004] In order to solve the above problems, the present application provides a battery module.

[0005] A first aspect of the present application provides a battery module, comprising: a plurality of battery cells, the battery cells being connected in series;

[0006] An electrode output connecting piece, arranged at the output end of the battery module;

[0007] A plurality of jumper electrode connecting sheets, respectively connecting the separated battery cells in the plurality of battery cells;

[0008] Adjacent electrode connecting pieces, connecting adjacent battery cells among the plurality of battery cells, and forming a power supply path for the battery module through the electrode output connecting piece, the jumper electrode connecting piece and the adjacent electrode connecting piece;

[0009] The plurality of jumper electrode connecting sheets are arranged in groups of at least two and partially overlapped and attached in an insulating manner.

[0010] Preferably, the plurality of jumper electrode connecting sheets include an upper jumper sheet and a lower jumper sheet, and the upper jumper sheet and the lower jumper sheet are partially overlapped and arranged in an insulating manner.

[0011] Preferably, an insulating member is provided between the upper jumper and the lower jumper, and the periphery of the insulating member exceeds the periphery of the overlapping portion of the upper jumper and the lower jumper.

[0012] Preferably, the periphery of the insulating member exceeds the overlapping portion of the upper jumper piece and the lower jumper piece by 2-6 mm.

[0013] Preferably, the upper bridging piece includes an upper main body portion and a first upper connecting piece and a second upper connecting piece extending in parallel from the upper main body portion, and at least one of the first upper connecting piece and the second upper connecting piece is connected to the upper main body portion via an arc transition.

[0014] Preferably, the lower cross-piece includes a lower body portion and a first lower connecting piece and a second lower connecting piece extending in parallel from the lower body portion.

[0015] Preferably, the surfaces of the first upper connecting sheet, the second upper connecting sheet, the first lower connecting sheet and the second lower connecting sheet facing the battery unit are coplanar.

[0016] Preferably, positioning holes are respectively provided on the first upper connecting plate, the second upper connecting plate, the first lower connecting plate and the second lower connecting plate, and the hole spacing between the positioning holes of the first upper connecting plate and the positioning holes of the first lower connecting plate is D1, and the hole spacing between the positioning holes of the second upper connecting plate and the positioning holes of the second lower connecting plate is D2, and D1 is equal to D2.

[0017] Preferably, the hole spacing between the positioning holes of the first upper connecting piece and the positioning holes of the first lower connecting piece is D1, the spacing between the first upper connecting piece and the first lower connecting piece is P1, and D1 is 5 to 15 times of P1.

[0018] Preferably, the hole spacing between the positioning holes of the second upper connecting piece and the positioning holes of the second lower connecting piece is D2, the spacing between the second upper connecting piece and the second lower connecting piece is P2, and D2 is 5 to 15 times of P2.

[0019] The technical solution provided by this application can achieve the following beneficial effects:

[0020] In the battery module provided by the present application, multiple battery cells are connected in series via jumper electrode connecting plates and adjacent electrode connecting plates, which provides important technical support for improving the configuration diversity of the battery module.

[0021] For example, when the electrode output connecting pieces in the battery module are all arranged on the same side, the overall size of the entire battery module can be reduced to improve the energy density of the battery module, and the length of the jumper electrode connecting piece can be reduced, thereby reducing the heat generated by the jumper electrode connecting piece during the operation of the battery module, etc., thereby achieving the purpose of improving the safety of the battery module.

[0022] In addition, when the length of the jumper electrode connecting piece is small, the assembly error of the entire battery module is relatively small, and the assembly process of the battery module is convenient; at the same time, among the multiple jumper electrode connecting pieces, at least two are overlapped as a group and insulated and fitted, which can also prevent the installation of the jumper electrode connecting piece from occupying too much additional space in the battery module, thereby helping to improve the compactness of the structure, and then helping to improve the energy density of the battery module. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of a battery module provided in an embodiment of the present application;

[0024] Figure 2 for Figure 1 A top view of the structure shown;

[0025] Figure 3 A schematic diagram of a portion of the structure of a battery module provided in an embodiment of the present application;

[0026] Figure 4 A schematic diagram of the structure of a connecting sheet group in a battery module provided in an embodiment of the present application;

[0027] Figure 5 for Figure 4 An exploded schematic diagram of the structure shown;

[0028] Figure 6 Another structural schematic diagram of a battery module provided in an embodiment of the present application;

[0029] Figure 7 for Figure 6 Schematic diagram of the structure of the middle part;

[0030] Figure 8 This is a schematic diagram of the structure of a battery cell provided in an embodiment of the present application.

[0031] Reference numerals:

[0032] 1-Battery unit;

[0033] 11-battery monomer;

[0034] 111- pole;

[0035] 2-Electrode output connection piece;

[0036] 3-adjacent electrode connecting piece;

[0037] 4- jumper electrode connecting piece;

[0038] 41-upper jumper;

[0039] 410-Upper body part;

[0040] 411-first upper connecting piece;

[0041] 4111-positioning hole;

[0042] 412-second upper connecting piece;

[0043] 42-lower cross-piece;

[0044] 420-lower body;

[0045] 421-first lower connecting piece;

[0046] 422-second lower connecting piece;

[0047] 5-Insulation parts.

[0048] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application. DETAILED DESCRIPTION

[0049] The present application is further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0050] In the description of this application, unless otherwise clearly specified and limited, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to three or more; the terms "connected", "fixed", etc. should be understood in a broad sense, for example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] In the description of this specification, it should be understood that the directional words such as "upper", "lower", "left", and "right" described in the embodiments of the present application are described at the angles shown in the accompanying drawings and should not be understood as limitations on the embodiments of the present application. In addition, in the context, it should also be understood that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0052] The embodiments of the present application provide a battery module and a battery pack (not shown in the figure), wherein the battery pack includes the battery module. Of course, the battery pack may also be provided with a battery management system, a battery thermal management system, a battery system distribution box, a flexible connection and an electrical interface, etc., wherein the thermal management system may include an evaporator, a fan, an air duct and a temperature collection mechanism, etc.; for a single battery pack, one or more battery modules may be arranged inside it, which may be selected according to actual needs.

[0053] The following is a detailed description of the structure of the battery module: Figure 1 and Figure 6 As shown, a single battery module includes a frame (not shown in the figure) and a plurality of battery cells 1 arranged in the frame. Specifically, Figure 1 As shown, the battery unit 1 can be a single battery cell 11; or, the battery unit 1 can also be a battery pack formed by connecting a plurality of battery cells 11 in parallel, so as to increase the output current of the entire battery module.

[0054] For example, if Figure 6 As shown, the battery unit 1 in the battery module may include two battery cells 11. The two battery cells 11 are firstly Figure 7 The jumper electrode connecting piece 4 shown is connected in parallel and then connected in series with another battery unit 1. More specifically, as shown in FIG. Figure 8 As shown, the battery cell 11 may be a square structure, which includes two poles 111 with opposite polarities.

[0055] During the assembly process of the battery module, multiple battery cells 1 can be connected in series through the jumper electrode connecting piece 4 and the adjacent electrode connecting piece 3; in order to output the electric energy of the entire battery module, an electrode output connecting piece 2 is also provided in the battery module, and the electrode output connecting piece 2 is arranged at the output end of the battery module. There are two electrode output connecting pieces 2, namely the total positive output electrode and the total negative output electrode.

[0056] By means of the jumper electrode connecting piece 4, the two electrode output connecting pieces 2 can be arranged on the same side of the entire battery module while shortening the electrode connecting piece, which is beneficial to improve the heat dissipation conditions, and obtain a higher energy density in the same assembly space while achieving high safety.

[0057] Specifically, in the process of connecting multiple battery cells 1 in a battery module, the battery cells 1 separated from each other in the multiple battery cells 1 are connected in series through the jumper electrode connecting piece 4, and the adjacent electrode connecting piece 3 can be used to connect two adjacent battery cells 1 in series. The remaining two battery cells 1 in the multiple battery cells 1 after being connected in series through the jumper electrode connecting piece 4 and the adjacent electrode connecting piece 3 are respectively connected to the two electrode output connecting pieces 2, thereby ensuring that the battery module can form a power supply circuit.

[0058] In order to further prevent the jumper electrode connecting piece 4 from occupying too much extra space in the frame of the battery module, as Figure 1 As shown, the plurality of jumper electrode connecting sheets 4 can be arranged in groups of two and partially overlapped and bonded in an insulating manner.

[0059] Specifically, if Figure 3 and Figure 4 As shown, the plurality of jumper electrode connecting pieces 4 may include an upper jumper piece 41 and a lower jumper piece 42, which are insulated and partially overlapped, so that the plurality of jumper electrode connecting pieces 4 can be located above the battery cell 1. In addition, since the jumper electrode connecting pieces 4 are overlapped and fitted, the space occupied by the jumper electrode connecting pieces 4 in the height direction of the battery module can be reduced to the maximum extent, so as to promote the development of the battery module towards high energy density. Through the above arrangement, while obtaining higher energy, better heat generation performance can also be obtained. Specifically, under the condition of ensuring the same flow area, the overall size of the jumper electrode connecting piece 4 of the above structure and arrangement is relatively smaller, so the heat generated during the operation of the battery module is also less. Moreover, on the basis of obtaining the above effect, due to the overlapping and fitting arrangement of the upper jumper piece 41 and the lower jumper piece 42, a very good structural property can also be obtained, which can prevent the displacement, deformation or even breakage of the upper jumper piece 41 and the lower jumper piece 42 caused by bumps, vibrations, etc. to the maximum extent.

[0060] In order to prevent the jumper electrode connecting piece 4 from contacting the jumped battery unit 1 and causing a short circuit in the battery module, preferably, Figure 7 As shown, a protective cover made of insulating material may be provided on the jumper electrode connecting piece 4; or, a safety interval may be provided between the jumper electrode connecting piece 4 and the battery unit 1 being jumped over to prevent the two from contacting and causing a short circuit in the battery module.

[0061] Specifically, the electrode output connection piece 2, the jumper electrode connection piece 4 and the adjacent electrode connection piece 3 can all be structures made of conductive materials such as metal. Preferably, the electrode output connection piece 2, the jumper electrode connection piece 4 and the adjacent electrode connection piece 3 can be formed of metal copper or aluminum. Figure 1 As shown, both the bridging electrode connecting sheet 4 and the adjacent electrode connecting sheet 3 can be in sheet-like structures, for example, and their thickness and length can be flexibly selected according to actual needs.

[0062] Furthermore, if Figure 3-5As shown, an insulating member 5 may be provided between the upper jumper 41 and the lower jumper 42, and the insulating member 5 may be made of insulating material to prevent the overlapping upper jumper 41 and the lower jumper 42 from being electrically connected, which can further reduce the space occupied by the jumper electrode connecting sheet 4. In order to further improve the reliability of the insulation relationship between the upper jumper 41 and the lower jumper 42.

[0063] Preferably, if Figure 3 As shown, the periphery of the insulating member 5 can be arranged to extend beyond the periphery of the overlapping portion between the upper jumper 41 and the lower jumper 42, which can further prevent electrical connection problems caused by relative displacement between the upper jumper 41 and the lower jumper 42 due to factors such as battery module vibration during the operation of the battery module. As for the specific size of the peripheral edge of the insulating member 5 exceeding the overlapping portion of the upper jumper 41 and the lower jumper 42, it can be flexibly selected according to the specific sizes of the upper jumper 41 and the lower jumper 42. Specifically, the peripheral edge of the insulating member 5 can exceed the overlapping portion between the upper jumper 41 and the lower jumper 42 by 2-6 mm. More preferably, the aforementioned value can be 5 mm, which can not only ensure a good insulation effect between the upper jumper 41 and the lower jumper 42; at the same time, even if a certain amount of condensed water is generated due to temperature changes during the operation of the battery module, since the peripheral edge of the insulating member 5 exceeds the overlapping portion of the upper jumper 41 and the lower jumper 42 by 5 mm, the condensed water can condense, accumulate and flow down at the edge of the insulating member 5 without destroying the insulation state between the upper jumper 41 and the lower jumper 42.

[0064] Preferably, the upper jumper sheet 41 and the lower jumper sheet 42 can be attached to the insulating member 5 by hot pressing or bonding process to form an integrated jumper sheet group, which can avoid the position dislocation of the upper jumper sheet 41 and the lower jumper sheet 42 caused by the expansion of the battery cell 11, and drive the insulating member 5 to move, resulting in insulation failure between the upper jumper sheet 41 and the lower jumper sheet 42; at the same time, when assembling the battery module, the aforementioned integrated jumper sheet group can also improve the assembly efficiency of the battery module and reduce the probability of assembly errors in the battery module. More specifically, the insulating member 5 can be made of a flexible insulating material. Preferably, the elastic modulus of the insulating member 5 is ≥3000MPa, so that during the operation of the battery module, the insulating member 5 can also prevent the connection failure between the jumper electrode connecting sheet 4 and the pole 111 caused by the expansion of the battery unit 1. More specifically, the insulating member 5 can be formed by PET plastic by integral injection molding.

[0065] More specifically, the upper jumper 41 may include an upper body portion 410, a first upper connecting piece 411 and a second upper connecting piece 412, both of which are connected to the upper body portion 410, and the first upper connecting piece 411 and the second upper connecting piece 412 are respectively connected to the poles 111 of different battery cells 1, and the electrical connection between the two battery cells 1 is achieved through the upper body portion 410. In order to improve the consistency of the first upper connecting piece 411 and the second upper connecting piece 412, the two can extend in parallel from the same side of the upper body portion 410, and the two have different extension directions from the upper body portion 410, that is, the first upper connecting piece 411 and the second upper connecting piece 412 are bent relative to the upper body portion 410; considering that the battery module will inevitably experience vibration and expansion problems during operation, preferably, as Figure 3 As shown, the included angles between the first upper connecting piece 411 and the second upper connecting piece 412 and the upper main body 410 are set to form an arc transition, so that the adaptability of the two is stronger and the structural strength of the entire upper bridging piece 41 is stronger and not easy to break.

[0066] More specifically, at least one of the first upper connecting piece 411 and the second upper connecting piece 412 can extend from the upper main body portion 410 in the form of a circular arc bend, and the curvature and size of the arc can be flexibly changed according to actual conditions, which can not only further reduce the space occupied by the upper jumper piece 41, but also further enhance the bending resistance of the entire upper jumper piece 41; in addition, with the help of this structural feature, the upper jumper piece 41 and the lower jumper piece 42 can also be distinguished, thereby playing an anti-fool effect during the installation of the upper jumper piece 41 and the lower jumper piece 42.

[0067] Further, the lower cross-connecting piece 42 may include a lower body portion 420, a first lower connecting piece 421 and a second lower connecting piece 422. The first lower connecting piece 421 and the second lower connecting piece 422 may both extend in parallel from the same side of the lower body portion 420, so that under the condition of equal size, the flow area of ​​the first lower connecting piece 421 and the second lower connecting piece 422 can be maximized. The first lower connecting piece 421 and the second lower connecting piece 422 are also respectively connected to the poles 111 of different battery cells 1, and the electrical connection of the two battery cells is realized by means of the lower body portion 420.

[0068] In order to ensure that the portion of the jumper electrode connecting piece 4 used for connecting with the pole 111 can have a good bonding effect with the pole, preferably, the first upper connecting piece 411, the second upper connecting piece 412, the first lower connecting piece 421 and the second lower connecting piece 422 can be made coplanar with the surface of the battery unit 1, so as to ensure that the above four can have a larger bonding area with the surface of the pole 111. Specifically, the surfaces of the above four facing the pole 111 can be placed in the same plane by bending. Since the upper jumper 41 is located above the lower jumper 42, the first upper connecting piece 411 and the second upper connecting piece 412 can be bent, such as the first upper connecting piece 411 and the second upper connecting piece 412 can be extended from the upper body part 410 in parallel in a circular arc bending manner. It should be noted that after the battery module has been working for a period of time, due to the vibration of the battery module and the expansion of the battery cell 11 and other factors, one or more of the first upper connecting piece 411, the second upper connecting piece 412, the first lower connecting piece 421 and the second lower connecting piece 422 in the battery module may be displaced or bent, which does not conflict with the design concept of the present application and is also within the protection scope of the present application; at the same time, taking into account factors such as processing accuracy and errors of measuring instruments, during the production and processing of the battery module, the flatness among the first upper connecting piece 411, the second upper connecting piece 412, the first lower connecting piece 421 and the second lower connecting piece 422 is ≤1mm, then the aforementioned four can be considered to be coplanar.

[0069] Furthermore, when the two electrode output connecting pieces 2 of the battery module are arranged on the same side of the battery module, Figure 1 As shown, the two electrode output connecting pieces 2 are arranged on the same side in the length direction of the battery module. During the assembly process of the battery module, it is only necessary to reserve installation space at the positions where the two electrode output connecting pieces 2 are located. The reserved space can be formed with the help of the frame structure of the original module (such as the end plate). Compared with the arrangement of the electrode output connecting pieces 2 on the same side in the height direction or the width direction, this can reduce the space required for installing the battery module; at the same time, when the size of the frame of the battery module remains unchanged, the two electrode output connecting pieces 2 of the battery module are located on the same side, which can also prevent the problem of short circuit of the battery module due to the contact between the electrode output connecting pieces 2 and the frame when the battery module is squeezed. It should be noted that the length direction of the battery module can be as follows: Figure 1 In the direction X, the width and height directions of the battery module are Figure 1 The directions Y and Z in the .

[0070] At the same time, when the two electrode output connecting pieces 2 in the battery module are arranged on the same side of the battery module, the overall size of the entire battery module can be reduced to improve the energy density of the battery module, and the length of the jumper electrode connecting piece 4 can be reduced, thereby reducing the heat generated by the jumper electrode connecting piece 4 during the operation of the battery module, thereby achieving the purpose of improving the safety of the battery module; in addition, when the length of the jumper electrode connecting piece 4 is small, the assembly error of the entire battery module is relatively small, and the assembly process of the battery module is convenient.

[0071] In the process of connecting the battery cells 1 through the jumper electrode connecting piece 4, the jumper electrode connecting piece 4 can cross over one battery cell 1, or can cross over two, three or more battery cells 1, which is not limited here. Optionally, in the process of grouping the battery module, the jumper electrode connecting piece 4 can connect multiple battery cells 1 together with the adjacent electrode connecting piece 3 in a manner of crossing over an odd number of battery cells 1; or, the jumper electrode connecting piece 4 can also connect multiple battery cells 1 together with the adjacent electrode connecting piece 3 in a manner of crossing over an even number of battery cells 1. In this regard, in the production process of the battery module, the actual connection method selected can be determined according to demand.

[0072] A preferred embodiment is as follows Figure 1 As shown, the jumper electrode connecting piece 4 connects multiple battery cells 1 together with the adjacent electrode connecting piece 3 in a manner of separating one battery cell 1 to form a power supply circuit. When this connection method is used to group battery modules, the operation is simple, and the structure of each jumper electrode connecting piece 4 and each adjacent electrode connecting piece 3 is relatively simple, which is convenient for production and assembly.

[0073] Furthermore, the lengths or shapes of the multiple jumper electrode connecting pieces 4 are the same, which can improve the standardization of the components in the battery module, thereby further reducing the difficulty of processing the jumper electrode connecting pieces 4 and the difficulty of assembling the jumper electrode connecting pieces 4 and the battery unit 1.

[0074] Preferably, the two electrode output connecting pieces 2 can be arranged to extend in the same direction, such as Figure 1 As shown, both electrode output connecting pieces 2 can extend along the length direction of the battery module. Therefore, during the use of the battery module, even if the battery module is squeezed from multiple directions other than the aforementioned length direction, the electrode output connecting pieces 2 in the battery module of this structure will not contact the frame of the battery module, causing a short circuit in the battery module.

[0075] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery module, characterized in that: include: A plurality of battery cells, wherein the battery cells are connected in series; An electrode output connecting piece, arranged at the output end of the battery module; A plurality of jumper electrode connecting sheets, respectively connecting the separated battery cells in the plurality of battery cells; Adjacent electrode connecting pieces, connecting adjacent battery cells among the plurality of battery cells, and forming a power supply path for the battery module through the electrode output connecting piece, the jumper electrode connecting piece and the adjacent electrode connecting piece; The plurality of jumper electrode connecting sheets are arranged in groups of at least two and partially overlapped and bonded in an insulating manner; The electrode output connecting pieces include more than two, and the two or more electrode output connecting pieces are arranged on the same side of the battery module; The plurality of jumper electrode connecting pieces include an upper jumper piece and a lower jumper piece, wherein the upper jumper piece and the lower jumper piece are partially overlapped and configured in an insulated manner; The upper cross-piece includes an upper body portion and a first upper connecting piece and a second upper connecting piece extending in parallel from the upper body portion, and the lower cross-piece includes a lower body portion and a first lower connecting piece and a second lower connecting piece extending in parallel from the lower body portion; The first upper connecting piece and the first lower connecting piece are respectively provided with positioning holes, the hole spacing between the positioning holes of the first upper connecting piece and the positioning holes of the first lower connecting piece is D1, the spacing between the first upper connecting piece and the first lower connecting piece is P1, and D1 is 5 to 15 times of P1.

2. The battery module according to claim 1, characterized in that: An insulating member is provided between the upper jumper and the lower jumper, and the periphery of the insulating member exceeds the periphery of the overlapping portion of the upper jumper and the lower jumper.

3. The battery module according to claim 2, characterized in that: The periphery of the insulating member exceeds the overlapping portion of the upper jumper piece and the lower jumper piece by 2-6 mm.

4. The battery module according to claim 1, characterized in that: At least one of the first upper connecting piece and the second upper connecting piece is connected to the upper main body portion via an arc transition.

5. The battery module according to claim 1, characterized in that: The first upper connecting sheet, the second upper connecting sheet, the first lower connecting sheet, and the second lower connecting sheet are coplanar with surfaces facing the battery unit.

6. The battery module according to claim 1, characterized in that: The first upper connecting piece, the second upper connecting piece, the first lower connecting piece, and the second lower connecting piece are respectively provided with positioning holes, and the hole spacing between the positioning holes of the first upper connecting piece and the positioning holes of the first lower connecting piece is D1, and the hole spacing between the positioning holes of the second upper connecting piece and the positioning holes of the second lower connecting piece is D2, and D1 is equal to D2.

7. The battery module according to claim 1, characterized in that: The hole spacing between the positioning holes of the second upper connecting piece and the positioning holes of the second lower connecting piece is D2, the spacing between the second upper connecting piece and the second lower connecting piece is P2, and D2 is 5 to 15 times of P2.

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