Battery pack and method for manufacturing the battery pack

Abstract

The present invention relates to a battery pack that houses a battery module and a method for manufacturing the battery pack. In the present invention, the first extension portion of the side frame together with the base plate forms a module mounting area, so that the load of the battery module mounted in the battery pack can be uniformly distributed, thereby simplifying the structure of the battery pack. The present invention may have an integrated cooling structure along with the load distribution structure described above.

Description

[Technical Field]

[0001] The present invention relates to a battery pack that houses a battery module and a method for manufacturing the battery pack.

[0002] More particularly, the present invention relates to a battery pack that can efficiently distribute the load of battery modules while simplifying the structure of the pack housing, and a method for manufacturing the battery pack.

[0003] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0083118, filed July 6, 2022, and Korean Patent Application No. 10-2003-0070867, filed June 1, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0004] A battery pack used in an electric vehicle or the like has a structure in which a number of battery modules, each including a plurality of secondary batteries, are connected in series or parallel to obtain high output. The secondary battery can be repeatedly charged and discharged through electrochemical reactions between components including positive and negative electrode current collectors, separators, active materials, and electrolytes.

[0005] Since a battery pack is equipped with multiple battery modules, it must be designed to have a structure that can stably support the load of these modules. In addition, to reduce energy consumption and improve energy efficiency, there is a demand for the development of technology that can reduce the weight of the battery pack while maintaining or improving its mechanical rigidity.

[0006] FIG. 1 is a schematic diagram showing a manufacturing process of a conventional battery pack proposed by the present applicant, and FIG. 2 is a schematic diagram showing the structure of the manufactured battery pack.

[0007] Referring to FIG. 1, in the past, a front frame 11, a rear frame 12, and side frames 13 and 14 were joined together to form a rectangular frame (FIG. 1(a)), and then a center frame 21 and a plurality of side beams 22 were joined to the rectangular frame to form a skeleton frame 20 of the battery pack (FIG. 1(b)). This skeleton frame 20 was then turned over (FIG. 1(c)), and a cooling panel 30 with a cooling channel formed therein was joined to the bottom of the skeleton frame 20 (FIG. 1(d)). A base plate 40 was then placed on the cooling panel, and the base plate 40 was joined to the skeleton frame 20 (FIG. 1(e)).

[0008] 2 shows a cross-sectional structure of the battery pack 1 manufactured in this manner. As shown in the figure, the base plate 40 is manufactured to a size capable of accommodating and supporting the entire lower surface area of ​​the battery module M, and the upper surface of the edge portion 41 of the base plate 40 is welded and joined to the lower end of the side frame to form a joint B.

[0009] However, the battery pack 1 having the above structure has the following drawbacks.

[0010] First, because the base plate 40 supports the entire load of the battery modules M, the load in the height direction, i.e., the Z-axis direction, is concentrated on the welded joint B between the base plate edge 41 and the side frame. Therefore, there is a risk that the load in the Z-axis direction during repeated use over a long period of time will cause the base plate edge 41 to sag below the welded joint between the side frames 13 and 14, or the joint B will widen.

[0011] Second, it is necessary to thicken the base plate 40 to withstand the load applied to the joint B, or to install a separate lower reinforcing structure 50 to distribute the load. However, thickening the base plate 40 increases the pack weight and reduces energy efficiency. Furthermore, it is undesirable because the load on the base plate 40 itself increases, which may actually act more heavily on the welded joint B. Furthermore, installing a lower reinforcing structure 50 increases the number of parts and requires a separate assembly process, raising manufacturing costs.

[0012] Third, since the cooling panel 30 and the base plate 40 are separately installed, the weight of the battery pack increases and the structure becomes complicated.

[0013] Therefore, there is a need to develop a technology that can effectively distribute the load applied to the joint between the base plate and the side frame and simplify the structure of the battery pack. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent Publication No. 10-2022-0031530 Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made to solve the above-mentioned problems, and aims to provide a battery pack that has a simple structure while effectively distributing the load of battery modules within the battery pack, and a manufacturing method thereof. [Means for solving the problem]

[0016] In order to solve the above problems, a battery pack according to one embodiment of the present invention is a battery pack having a module mounting area in which a plurality of battery modules are accommodated, and includes: a base plate on which the battery modules are mounted; a front frame coupled to a front end of the base plate; a rear frame coupled to a rear end of the base plate; and side frames coupled to both sides of the base plate, wherein the base plate has a size that forms only a portion of the module mounting area, and the side frames include side wall portions facing the battery modules, and first extension portions that extend from a lower portion of the side wall portions toward the base plate and are coupled to a side of the base plate, forming the module mounting area together with the base plate and supporting the load of the battery modules.

[0017] The first extension may be extended by a predetermined length to support at least a portion of a lower area of ​​the battery module.

[0018] Additionally, the upper surface of the base plate and the upper surface of the first extension may form a plane at the same height.

[0019] In this case, a step portion having a shape that engages with a side surface of the base plate and a side surface of the first extension portion coupled thereto may be provided.

[0020] The side frame may further include a second extension portion extending to the outside of the battery pack.

[0021] The second extension portion has a thickness greater than that of the first extension portion and can be fixed to and supported by a structure on which the battery pack is installed.

[0022] As one example, the vehicle may further include a center frame extending from the front frame to the rear frame and coupled to the base plate, and a module mounting area may be formed between the center frame and the side wall portion of the side frame, and the module mounting area may include an upper surface of at least a portion of a first extension portion of the side frame and an upper surface of the base plate.

[0023] The base plates may be disposed on both sides of the center frame, and side surfaces of the base plates on both sides may be coupled to both side surfaces of the center frame.

[0024] In this case, the center frame may include a vertical partition wall portion and a horizontal extension portion extending left and right from the lower portion of the vertical partition wall portion toward the base plate and coupled to the base plate, and the top surface of the horizontal extension portion and the top surface of the base plate may be located on the same plane.

[0025] The battery pack may further include a plurality of side beams extending between the vertical partition wall portion of the center frame and the side frames on both sides, and the side beams may be coupled to the vertical partition wall portion and the side frames, respectively, to divide the module mounting area into a plurality of areas.

[0026] The battery module may be fastened to a side wall of the side frame.

[0027] As another example, at least one of the base plate and the side frame may have an outer wall and an interior space surrounded by the outer wall, and the interior space may be divided by a plurality of partition walls extending from the outer wall to form a plurality of hollow channels.

[0028] The base plate may be an integrated cooling base plate in which a first cooling flow path is provided in the hollow channel.

[0029] In this case, the first extension of the side frame may have a hollow channel, and the hollow channel may be provided with a second cooling flow path.

[0030] In addition, the front frame and the rear frame each have a third cooling flow path that communicates with the first cooling flow path and the second cooling flow path, and one of the front frame and the rear frame may be formed with a coolant inlet and a coolant outlet that communicate with the third cooling flow path.

[0031] Alternatively, the front frame and the rear frame may each have a third cooling flow path that communicates with the first cooling flow path and the second cooling flow path, and one of the front frame and the rear frame may have a coolant inlet that communicates with the third cooling flow path, and the other may have a coolant outlet that communicates with the third cooling flow path.

[0032] The predetermined lengths of the first extension portions provided on both side frames may be the same, a single base plate may be positioned between both side frames, and the ratio of 1 / 2 of the length of the base plate extending between the both side frames to the predetermined length may be in the range of 6:4 to 9:1.

[0033] The predetermined lengths of the first extension portions provided on one side frame and the other side frame are the same, and two base plates of the same size are positioned between the one side frame and the other side frame and are coupled to the corresponding side frames, and the ratio of the length of each base plate extended to the corresponding side frame to the predetermined length may be in the range of 6:4 to 9:1.

[0034] The present invention also provides a method for manufacturing the battery pack, which has a module mounting area for accommodating a plurality of battery modules, and includes the steps of: coupling side surfaces of first extension portions of both side frames, the side frames extending toward the base plate and forming the module mounting area together with the base plate, to both side surfaces of a base plate having a size that forms only a portion of the module mounting area; coupling a front frame and a rear frame to front and rear ends of the base plate and the first extension portions, respectively; and mounting a plurality of battery modules in the module mounting area including upper surfaces of at least some of the first extension portions and the upper surface of the base plate.

[0035] A manufacturing method of a battery pack according to another embodiment of the present invention is a manufacturing method of a battery pack having a module mounting area in which a plurality of battery modules are accommodated, the method including the steps of: disposing base plates on both sides of a center frame, respectively, and coupling the base plates on both sides to the center frame; coupling a first extension portion of one side frame, which extends toward the base plate on one side of the center frame and forms a module mounting area together with the base plate on one side, to the base plate on one side; coupling a first extension portion of the other side frame, which extends toward the base plate on the other side of the center frame and forms a module mounting area together with the base plate on the other side, to the base plate on the other side; coupling a front frame and a rear frame to the first extension portions of the one and other side frames and front end portions and rear end portions of the base plates on both sides, respectively; and mounting a plurality of battery modules in the module mounting area including an upper surface of at least a portion of the first extension portion and an upper surface of the base plate. [Effects of the Invention]

[0036] According to the above various embodiments, the present invention can stably distribute the load of the battery module to the base plate and the side frame.

[0037] Furthermore, because the load distribution eliminates the need for additional reinforcing structures as in the past, the structure of the pack housing can be simplified.

[0038] In addition, because the load is effectively distributed between the base plate and the side frame, the thickness of the base plate can be reduced accordingly, thereby reducing the weight of the battery pack.

[0039] In addition, the lower structure of the battery pack can be made an integrated cooling structure, making the pack structure more compact. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a schematic diagram showing a manufacturing process of a conventional battery pack proposed by the present applicant; [Figure 2] FIG. 1 is a schematic diagram showing the structure of a conventional battery pack. [Figure 3] 1 is an exploded perspective view showing a battery pack according to an embodiment of the present invention; [Figure 4] 1 is an assembled perspective view showing a battery pack according to an embodiment of the present invention; [Figure 5] FIG. 2 is an assembled perspective view of the battery pack, excluding some components. [Figure 6] 3 is a schematic diagram showing an example of a joining structure between a base plate and a side frame according to the present invention. FIG. [Figure 7] 10 is a schematic view showing another example of the joining structure between the base plate and the side frame according to the present invention. FIG. [Figure 8] 1A to 1C are schematic diagrams illustrating a manufacturing process of a battery pack according to the present invention. [Figure 9] FIG. 10 is an exploded perspective view showing a battery pack according to another embodiment of the present invention. [Figure 10] FIG. 10 is an assembled perspective view showing a battery pack according to another embodiment of the present invention; [Figure 11] 10 is a schematic diagram showing an example of a joining structure between the base plate and the side frame according to the embodiment of FIG. 9. [Figure 12] FIG. 10 is a schematic diagram showing an example of a cooling path of the battery pack of the embodiment of FIG. 9. [Figure 13] FIG. 10 is a schematic diagram showing another example of a cooling path of a battery pack. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will become more apparent by describing in detail preferred embodiments of the present invention with reference to the accompanying drawings. The embodiments described herein are shown by way of example to facilitate understanding of the invention, and it should be understood that the present invention can be implemented in various forms different from the embodiments described herein. Furthermore, to facilitate understanding of the invention, the accompanying drawings are not drawn to scale, and the dimensions of some components may be exaggerated.

[0042] The present invention will be described in detail below.

[0043] A battery pack according to one embodiment of the present invention is a battery pack having a module mounting area in which a plurality of battery modules are accommodated, and includes: a base plate on which the battery modules are mounted; a front frame coupled to a front end of the base plate; a rear frame coupled to a rear end of the base plate; and side frames coupled to both sides of the base plate, wherein the base plate has a size that forms only a portion of the module mounting area, and the side frames include side wall portions facing the battery modules, and first extension portions that extend from a lower portion of the side wall portions toward the base plate and are coupled to a side of the base plate, forming the module mounting area together with the base plate and supporting the load of the battery modules.

[0044] The present invention also provides a method for manufacturing the battery pack, which has a module mounting area for accommodating a plurality of battery modules, and includes the steps of: coupling side surfaces of first extension portions of both side frames, the side frames extending toward the base plate and forming the module mounting area together with the base plate, to both side surfaces of a base plate having a size that forms only a portion of the module mounting area; coupling a front frame and a rear frame to front and rear ends of the base plate and the first extension portions, respectively; and mounting a plurality of battery modules in the module mounting area including an upper surface of at least a portion of the first extension portions and an upper surface of the base plate.

[0045] A manufacturing method of a battery pack according to another embodiment of the present invention is a manufacturing method of a battery pack having a module mounting area in which a plurality of battery modules are accommodated, the method including the steps of: disposing base plates on both sides of a center frame, respectively, and coupling the base plates on both sides to the center frame; coupling a first extension portion of one side frame, which extends toward the base plate on one side of the center frame and forms a module mounting area together with the base plate on one side, to the base plate on one side; coupling a first extension portion of the other side frame, which extends toward the base plate on the other side of the center frame and forms a module mounting area together with the base plate on the other side, to the base plate on the other side; coupling a front frame and a rear frame to the first extension portions of the one and other side frames and front end portions and rear end portions of the base plates on both sides, respectively; and mounting a plurality of battery modules in the module mounting area including an upper surface of at least a portion of the first extension portion and an upper surface of the base plate.

[0046] (First embodiment) FIG. 3 is an exploded perspective view showing a battery pack according to one embodiment of the present invention, FIG. 4 is an assembled perspective view showing a battery pack according to one embodiment of the present invention, FIG. 5 is an assembled perspective view showing some components of the battery pack excluding the battery pack, and FIG. 6 is a schematic view showing an example of a joining structure between a base plate and a side frame according to the present invention.

[0047] 3 to 6, a battery pack 100 of the present invention includes a base plate 110, a front frame 120, a rear frame 130, and side frames 140 and 150 on both sides.

[0048] A plurality of battery modules M are mounted on the base plate 110.

[0049] The battery module M may include a module housing that accommodates a plurality of battery cells. The battery cells may be secondary batteries, such as pouch-type secondary batteries, prismatic secondary batteries, or cylindrical secondary batteries. That is, various battery cells known at the time of filing of the present invention may be used as the battery cells.

[0050] The battery module M may include at least one bus bar (not shown) configured to electrically interconnect a plurality of battery cells. The plurality of battery modules M may be electrically connected to each other via a power cable or a bus bar. The detailed configuration of the battery module M may be a commonly known configuration. Therefore, a detailed description thereof will be omitted in this specification.

[0051] The battery pack 100 may also house an electrical component assembly (not shown). The electrical component assembly may house a relay device, a current sensor, a fuse, a BMS, an MSD (Manual Service Disconnector), etc. Such an electrical component assembly may be packaged together with the battery module within the battery pack 100 so as not to be exposed to the outside.

[0052] The base plate 110 may have a plate shape extending horizontally, where horizontal means the direction of a flat ground surface, and may be made of a metal material having excellent mechanical rigidity.

[0053] A front frame 120, a rear frame 130, and both side frames 140 and 150 are respectively coupled to the base plate 110. The coupling method may be, for example, friction stir welding.

[0054] When viewed from the front with reference to the arrow F in Figure 3, the front frame 120 can be connected to the front end of the base plate 110 to cover the front of the battery module M, and the rear frame 130 can be connected to the rear end of the base plate 110.

[0055] In this specification, terms indicating directions such as front, back, left, right, up, and down may vary depending on the position of the observer and the arrangement of the object. However, for the sake of convenience, in this specification, directions such as front, back, left, right, up, and down are indicated based on the view from the direction of arrow F in Figure 3.

[0056] A plurality of battery modules M may be positioned on the upper surface of the base plate 110. Therefore, the upper surface of the base plate 110 forms a module mounting area in which a plurality of battery modules are accommodated.

[0057] FIG. 5 shows the battery pack housing without the side beams, which will be described later, to more clearly show the module mounting area A. Referring to FIGS. 3 to 5, the width, i.e., the length in the X direction, of the base plate 110 of the present invention is smaller than the width (length in the X direction) of the entire battery pack. In particular, the base plate 110 of the present invention has both side widths that are smaller than the width of the module mounting area A in the battery pack. That is, the width of the base plate is smaller than the length of the module mounting area A in the X direction. Therefore, the base plate 110 has a size that forms only a portion of the module mounting area A. As a result, a portion of the lower area of ​​the plurality of battery modules is supported by the base plate 110, while the remaining area is located away from the base plate 110. This remaining lower area is supported by the side frames, as will be described later.

[0058] In this specification, the meaning that the base plate 110 has a size that forms only a portion of the module mounting area basically includes, first, that when one base plate 110 is installed under a battery pack, the width of the base plate is formed smaller than the width of the module mounting area A. It also includes the case where, as shown in Figures 3 and 4, when a center frame 160 is coupled between two base plates 110A and 110B and the module mounting area A is located between the center frame 160 and both side frames 140 and 150, each of the two base plates 110A and 110B has a small size (width) that forms only a portion of the module mounting area A. In other words, in this specification, the width of the base plate 110 that constitutes the battery pack does not constitute the entire width of the module mounting area A by itself, but only forms the entire module mounting area when combined with the width of other components (first extension portions of the side frames, which will be described later).

[0059] Meanwhile, the length (length in the Y direction) of the base plate 110 may be the same as the length of the battery pack 100 in the Y direction.

[0060] The front frame 120 may be elongated in the left-right direction (X direction) and erected in the height direction (Z direction). A lower surface of the front frame 120 may be coupled to an upper surface of the base plate 110. Also, lower surfaces of left and right end portions of the front frame 120 may be coupled to upper surfaces of first extension portions of side frames, which will be described later. The front frame 120 may include a front cover portion 121 extending in the height direction and a front plate portion 122 protruding forward from a lower portion of the front cover portion. The front plate portion 122 may be fixedly coupled to a structure such as a vehicle.

[0061] The rear frame 130 may be elongated in the left-right direction (X direction) and erected in the height direction (Z direction). The lower surface of the rear frame 130 may be coupled to the upper surface of the base plate 110, and the lower surfaces of the left and right end portions of the rear frame 130 may be coupled to the upper surfaces of first extension portions of the side frames (described later). The rear frame 130 may have the same or different shape as the front frame. In FIGS. 3 and 4, the rear frame 130 includes a rear cover portion 131 extending in the height direction and a rear plate portion 132 protruding rearward from a lower portion of the rear cover portion 131, and has the same shape as the front frame. The rear plate portion 132 may be fixedly coupled to a structure such as a vehicle.

[0062] The side frames 140 and 150 on both sides may have a shape that is elongated in the front-rear direction (Y direction). The side frames are composed of a first side frame 140 that covers the left side of the battery module and a second side frame 150 that covers the right side. When one base plate is provided under the battery pack, the first side frame 140 is coupled to the left end of the base plate, and the second side frame 150 is coupled to the right end of the base plate. That is, the side frames are coupled to both sides of the base plate.

[0063] Alternatively, as shown in Figures 3 to 5, when left and right base plates 110A and 110B are respectively coupled to both sides of the center frame 160, the first side frame 140 can be coupled to the left end of the left base plate 110A, and the second side frame 150 can be coupled to the right end of the right base plate 110B.

[0064] Therefore, the present invention includes a front frame 120, a rear frame 130, a first side frame 140, and a second side frame 150 so as to cover the front, rear, left, and right sides of the battery module.

[0065] The first side frame 140 includes a side wall 141 facing the battery module and a first extension 142 extending from a lower portion of the side wall toward the (left) base plate 110A. The second side frame 150 also includes a side wall 151 facing the battery module and a first extension 152 extending from a lower portion of the side wall toward the (right) base plate 110B. A characteristic feature of the present invention is that the first extensions 142 and 152 are coupled to the side surfaces of the left and right base plates, respectively, to form a module mounting area A together with the base plates. That is, the first extensions 142 and 152 of the first side frame 140 and the second side frame 150 extend a predetermined length toward the base plate 110 to support at least a portion of the lower area of ​​the battery module. As a result, at least a portion of the upper surfaces of the first extensions 142 and 152 and the upper surfaces of the base plates 110A and 110B together form the module mounting area A. As shown, the width of base plates 110A, 110B is greater than the width of first extensions 142, 152, so the area of ​​the lower part of the battery module supported by the base plates is greater than the area of ​​the lower part of the module supported by the first extensions. The first extensions 142, 152 support the lower surface of the module, which has a relatively smaller area than the base plates. However, since both the base plates and the side frames, specifically, the first extensions 142, 152 of the side frames and the base plates 110A, 110B, support the weight of the battery module, the battery module can be stably supported.

[0066] The first extension 142 provided on the first side frame 140 and the first extension 152 provided on the second side frame 150 may have the same length. That is, the extension lengths (predetermined lengths) of the first extensions 142, 152 extending from the lower portions of the side walls toward the base plate may be the same. In this case, a single base plate may be positioned between the first side frame 140 and the second side frame 150.

[0067] For optimal load distribution between the base plate and the first extensions, the ratio of half the length of the single base plate extending between the first side frame 140 and the second side frame 150 to the predetermined length of each of the first extensions 142, 152 may be in the range of 6:4 to 9:1. For example, if the length ratio is less than 6:4, the length of the first extensions may be too long, increasing the weight of the first side frames and complicating the welding work of the first side frames. Also, if the length ratio is greater than 9:1, the length of the first extensions may be too short, reducing the load distribution effect of the module by half.

[0068] 3 to 5, two base plates 110A, 110B of the same size may be positioned between the first side frame 140 and the second side frame 150. In this case, for optimal load distribution between each base plate and the first extension, the ratio of the length (X-direction length) of each base plate 110A, 110B extended to the corresponding side frame to the predetermined length may be in the range of 6:4 to 9:1.

[0069] The first side frame 140 and the second side frame 150 each include a second extension 143, 153 extending outward from the battery pack. The second extension 143, 153 is a portion fixed to a structure on which the battery pack 100 is installed, such as a vehicle. That is, the second extension 143, 153 includes a fastening point to the vehicle. Since the second extension 143, 153 is directly fastened to the vehicle, it receives a greater load than the first extension 142, 152. Therefore, in order to stably fasten and fix the battery pack to the vehicle, the second extension 143, 153 is formed to be thicker than the first extension 142, 152.

[0070] 6 shows the load distribution effect of the battery pack of the present invention. In FIG. 6, the right side surface of the right base plate 110B is coupled to one side surface of the first extension portion 152 of the second side frame 150. This coupling can be performed by, for example, welding. The second extension portion 153 of the second side frame 150 is fixedly coupled to a structure such as a vehicle.

[0071] The right side of the base plate 110B and the side of the first extension 152 are coupled together so that the upper surface of the base plate 110B and the upper surface of the first extension 152 form a plane at the same height. Therefore, the battery module can be stably supported on a flat plane at the same height. As shown in FIG. 6, most of the lower surface of the battery module M is supported by the upper surface of the base plate 110B, and one side of the lower surface is supported by the upper surface of the first extension 152. That is, since the lower surface of the battery module M is evenly supported across the upper surfaces of the base plate 110B and the first extension 152, the weight of the battery module is supported by both the base plate and the first extension. In addition, since the coupling portion between the base plate and the side frame is not concentrated toward the side end of the base plate as shown in FIG. 1, but is located toward the end of the first extension 152, which extends a predetermined length toward the inside of the base plate, the weight of the battery module can be evenly distributed. Therefore, the concentration of the load of the battery module as in the conventional battery module can be prevented. At this time, the second extension part 153 is fixed to the structure and receives stress in the opposite direction to the load of the battery module, but since it is formed to be thicker than the first extension part 152, it can sufficiently withstand the stress.

[0072] As described above, according to the present invention, the first extensions 142, 152 of the side frames 140, 150 and the base plate 110 together form the module mounting area A, thereby enabling the load of the battery module to be uniformly distributed. Therefore, there is no need to install a separate reinforcing structure to reinforce the base plate, as in the past. In addition, there is no need to make the width of the base plate long, as in the past, and the thickness of the base plate can be thinned so that the side frames can distribute and bear the load. This simplifies the structure of the battery pack, including the base plate. Furthermore, as will be described later, if the base plate is configured with an integrated cooling system, the battery pack structure can be made more compact.

[0073] Although FIG. 6 shows the coupling structure between the right base plate 110B and the second side frame 150, the coupling structure between the left base plate 110A and the first side frame 140 is the same.

[0074] FIG. 7 is a schematic diagram illustrating another example of a coupling structure between a base plate and a side frame according to the present invention. In FIG. 7, step portions 115, 155 are formed on the side of a base plate 110B and the side of a first extension portion 152 of a second side frame 150 coupled thereto, respectively, to interlock with each other. That is, the right side of the right base plate 110B has a step portion 115 formed of two vertical surfaces and a horizontal surface disposed between the two vertical surfaces. Similarly, the left side of the first extension portion 152 also has a step portion 155 formed of two vertical surfaces and a horizontal surface disposed therebetween, to interlock with the step portion 115 of the base plate. When the base plate 110B and the first extension portion 152 are coupled, the horizontal surface of the step portion 115 of the base plate and the horizontal surface of the step portion 155 of the first extension portion come into contact with each other and support the load, thereby distributing the load of the module more efficiently than the example of FIG. 5. In addition, when joining the opposing vertical surfaces of the step portions 115, 155, the base plate 110B and the first extension portion 152 of the second side frame 150 can be easily joined by welding the upper and lower ends of the vertical surfaces.

[0075] 6 and 7, the battery module M mounted on the base plate 110B and the first extension 152 may be fastened to the side wall 151 of the side frame by the fastening member 180. Fastening the module by the fastening member 180 has several technical significances. First, by fixing the battery module M to the side wall 151 by the fastening member 180, the battery module can be accurately positioned in the module mounting area A set in the battery pack 100. Second, by fastening the battery module M to the side wall 151 of the side frame, the battery module can be stably maintained without moving within the module mounting area A in the battery pack even when vibrations occur during vehicle operation. Finally, by fixing the battery module to the side wall with the fastening member 180, the load of the battery module M can be further distributed. In this case, the load of the battery module is distributed and supported by the base plate 110B, the side wall 151 of the side frame, and the first extension 152, which has the advantage of minimizing the problem of load concentration.

[0076] 3 to 5, the battery pack 100 of this embodiment further includes a center frame 160 between left and right base plates 110A and 110B. The center frame 160 serves to divide a plurality of battery modules M into left and right sections and is extended from the front frame 120 to the rear frame 130 and coupled to the base plate 110. The battery modules M are mounted between the center frame 160 and the side walls 141 and 151 of the side frames 140 and 150. That is, a module mounting area is formed between the center frame 160 and the side walls of the side frames. The left and right base plates 110A and 110B are coupled to first extensions 142 and 152 of the first and second side frames 140 and 150, respectively, and the module mounting area A corresponds to at least a portion of the upper surfaces of the first extensions 141 and 151 of the side frames and the upper surfaces of the base plates (see FIG. 5).

[0077] The center frame 160 may have vertical partition walls 161 and horizontal extensions 162 extending laterally from the lower portions of the vertical partition walls and coupled to the left and right base plates 110A and 110B, respectively. The center frame 160 and the left and right base plates 110A and 110B may be coupled by welding the horizontal extensions 162 to opposing sides of the base plates 110A and 110B. The top surfaces of the horizontal extensions 162 and the top surfaces of the base plates 110A and 110B are flush with each other. That is, the top surfaces of the horizontal extensions 162 and the base plates 110A and 110B form a flat surface, thereby stably supporting a battery module on the flat surface. In this case, the horizontal extensions 162, together with the base plates 110A and 110B and the first extensions 142 and 152, may form a module mounting area. As described above, the technical idea of ​​the present invention that "the base plate is sized to form only a portion of the module mounting area" also includes the cases of Figures 3 and 4 in which the horizontal extension of the center frame forms a portion of the module mounting area.

[0078] In this embodiment, the center frame 160 includes the horizontal extension 162, but it may not include the horizontal extension. That is, the center frame may be formed only with the vertical partition wall 161, and the left and right base plates may be connected to both side surfaces of the lower portion of the vertical partition wall.

[0079] The battery pack 100 of this embodiment further includes side beams 170 for separating the battery modules. The side beams 170 are installed to extend between the vertical partition wall portion 161 of the center frame 160 and the side frames 140 and 150 on both sides. That is, a plurality of side beams 170 are installed between the vertical partition wall portion 161 and the first side frame 140 and between the vertical partition wall portion 161 and the second side frame 150, respectively. The lower surface of the battery pack separated by the side beams 170 becomes a module mounting area A.

[0080] The arrangement of the battery modules in the battery pack is determined according to the arrangement of the center frame 160 and the side beams 170. In this embodiment, the battery modules are arranged in four rows facing each other. However, the arrangement of the battery modules is not limited thereto, and the battery modules may be arranged in other patterns depending on the arrangement of the center frame 160 and / or the side beams 170. In either case, a module mounting area A where the battery modules are mounted is formed on the base plate 110 and the first extension portions 142 and 152 of the side frames. As shown in FIG. 5, the upper surfaces of the horizontal extension portions of the center frame may also be included in the module mounting area. When the module M is closely positioned to the side wall portion 151 of the side frame, almost the entire upper surface of the first extension portion 152 is included in the module mounting area A. Typically, the module M and the side wall portion 151 are spaced apart by a predetermined distance to ensure an insulating distance, as shown in FIGS. 5 and 6. In this case, a portion of the upper surface of the first extension portion 152 where the module is placed is included in the module mounting area A. In either case, in the present invention, the first extension 152 stably supports a portion of the area of ​​the lower surface of the module, thereby enabling the weight of the module to be uniformly distributed.

[0081] In the embodiment of Figures 3 to 5, the side frames 140, 150 are disposed on the left and right sides of the battery module. However, depending on the design of the battery pack, the side frames may also be disposed on the front and rear sides of the battery module. In this case, frames corresponding to the front and rear frames of Figures 3 to 5 may be installed on the left and right sides of the battery module.

[0082] Also, in this embodiment, the side frames disposed on both sides of the battery pack have first extensions. However, in some cases, not only the side frames on both sides but also all frames forming the side walls of the battery pack, i.e., the front and rear frames in FIG. 3, may have first extensions extending toward the base plate. In this case, the base plate may be narrower in length as well as width by the extension length of the first extensions. In this case, the lengths of the first extensions of each frame may differ at corners where each side frame overlaps with the front frame or rear frame. For example, the first extension 142 of the first side frame 140 may extend long along the length direction (Y direction) of the battery pack, while the first extension formed on the front frame 120 may extend along the width direction (X direction) of the battery pack and not extend to the portion where the first extension 142 of the first side frame 140 is located.

[0083] In addition, an insulating pad or a thermally conductive resin layer such as thermal resin may be interposed between the base plate and the module.

[0084] FIG. 8 is a schematic diagram showing a manufacturing process of a battery pack according to the present invention.

[0085] In manufacturing a conventional battery pack as shown in Figure 1, a skeletal frame of the battery pack is created, and then a base plate is attached to the bottom of the skeletal frame. As a result, as mentioned above, a load is concentrated on the side edge of the battery pack where the base plate and the skeletal frame are joined. In addition, in the conventional battery pack, a separate cooling panel is attached before joining the base plate to the skeletal frame, which makes the structure complicated.

[0086] Meanwhile, a method for manufacturing a battery pack having a module mounting area in which a plurality of battery modules are accommodated according to one embodiment of the present invention includes the steps of: coupling the sides of first extension portions 142, 152 of both side frames 140, 150, which extend toward both sides of a base plate 110 having a size that forms only a portion of the module mounting area A and form the module mounting area A together with the base plate, respectively; coupling a front frame 120 and a rear frame 130 to front and rear ends of the base plate 110 and the first extension portions 142, 152, respectively; and mounting a plurality of battery modules M in the module mounting area A including at least a portion of the upper surfaces of the first extension portions 142, 152 and the upper surface of the base plate 110.

[0087] That is, in the method for manufacturing a battery pack according to an embodiment of the present invention, first, both side frames (first side frame 140, second side frame 150) are coupled to both sides of base plates 110A, 110B. When a single base plate is used, first extensions 142, 152 of the first side frame 140 and the second side frame 150 are coupled to both sides of the base plate 110, respectively. At this time, the base plate 110 has a size that forms only a part of the module mounting area A, and the first extensions 142, 152 form the module mounting area together with the base plate 110.

[0088] Next, the front frame 120 and the rear frame 130 are respectively coupled to the front end and rear end of the base plate 110. In this case, the first extensions 142, 152 of the first side frame 140 and the second side frame 150 are located at the left and right ends of the base plate, and the left and rear ends of the front frame 120 and the rear frame 130 are respectively coupled to the first extensions 142, 152 of the first side frame 140 and the second side frame 150.

[0089] Thereafter, a plurality of battery modules are mounted in module mounting area A including at least a portion of the upper surfaces of the first extensions 142 and 152 and the upper surface of the base plate. The battery module M is supported at a portion of its lower surface by the first extensions 142 and 152 in addition to the base plate, and the connection point between the base plate and the first extensions is located at the end of the first extensions 142 and 152, which are extended a predetermined length inside the battery pack, so that the load of the battery modules can be distributed evenly without being concentrated unevenly.

[0090] Furthermore, a manufacturing method of a battery pack according to another embodiment of the present invention is a manufacturing method of a battery pack having a module mounting area in which a plurality of battery modules are accommodated, and includes the steps of: arranging base plates 110A and 110B on both sides of a center frame 160, respectively, and coupling the both base plates 110A and 110B to the center frame 160; coupling a first extension 142 of one side frame 140, which extends toward the base plate 110A on one side of the center frame and forms a module mounting area together with the base plate 110A on one side, to the base plate 110A on one side; the first extension 152 of the other side frame 150 extending toward the base plate 110B on the other side of the frame and forming a module mounting area together with the other base plate 110B, connecting the front frame 120 and the rear frame 130 to the first extensions 142, 152 of the one and other side frames and the front and rear ends of the base plates 110A, 110B on both sides, respectively; and mounting a plurality of battery modules M in the module mounting area A including at least a portion of the upper surfaces of the first extensions 142, 152 and the upper surfaces of the base plates.

[0091] This embodiment is a manufacturing method for a center frame 160 having two base plates 110A, 110B on the left and right sides of the center frame. Therefore, the center frame 160 and the base plates 110A, 110B are joined together before the base plates 110A, 110B and the first extensions 142, 152 are joined together. That is, the (left and right) base plates 110A, 110B are placed on both sides of the center frame 160, and the base plates on both sides are joined to the center frame.

[0092] Then, the first extension 142 of the first side frame 140 is coupled to the left side surface of the base plate 110A on one side (left side) of the center frame 160.

[0093] Next, the first extension 152 of the second side frame 150 is coupled to the right side surface of the base plate 110B on the other side (right side) of the center frame 160.

[0094] The order of combining the first side frame, the second side frame and the base plate can be reversed.

[0095] After the base plate is joined to the first and second side frames, the front frame 120 and the rear frame 130 are joined to the front and rear ends of the first extensions 142 and 152 of the first and second side frames, and to the front and rear ends of the base plates 110A and 110B on both sides, respectively.

[0096] Finally, a plurality of battery modules are mounted in a module mounting area including at least a portion of the upper surfaces of the first extensions 142 and 152 and the upper surfaces of the base plates 110A and 110B.

[0097] Meanwhile, after the base plate and the first and second side frames have been joined, a plurality of side beams 170 may be fastened between the center frame and the first and second side frames. After the side beams are fastened, the front frame 120 and the rear frame 130 may be joined to the base plates 110A, 110B and the side frames 140, 150. Alternatively, the front frame and the rear frame may be first fastened to the base plate and the side frames to form a frame as shown in FIG. 5, and then the side beams may be joined.

[0098] (Second embodiment) FIG. 9 is an exploded perspective view showing a battery pack according to another embodiment of the present invention, FIG. 10 is an assembled perspective view showing a battery pack according to another embodiment of the present invention, and FIG. 11 is a schematic view showing an example of the joining structure of the base plate and the side frame according to the embodiment of FIG. 9.

[0099] In this embodiment, at least one of the base plates 210A, 210B and the side frames 240, 250 has an outer wall W and an internal space H surrounded by the outer wall. The internal space H may be divided by a plurality of partition walls P extending from the outer wall W to form a plurality of hollow channels.

[0100] For example, the base plates 210A, 210B and / or the side frames 240, 250 may be fabricated as hollow frames by extruding a metal material such as aluminum to form an empty space inside. By constructing the frame as hollow in this manner, it is possible to reduce the weight of the battery pack 200 and improve its energy efficiency. In addition, by forming rib-shaped partition walls P in the internal space, it is possible to maintain the mechanical rigidity of the frame at a reliable level.

[0101] The hollow channels may be formed in either or both of the side frames 240, 250 and the base plates 210A, 210B.

[0102] In this case, as shown in FIG. 11, hollow channels may be formed in any of the first extensions 242, 252, the side walls 241, 251, and the second extensions 243, 253 of the side frames 240, 250.

[0103] Forming a plurality of hollow channels in the base plates 210A and 210B not only reduces the weight but also allows the space to be used as a cooling channel installation area. That is, instead of installing a cooling panel separate from the base plate as in the conventional case, the cooling channel is integrated into the base plate to form an integrated cooling base plate, which further simplifies the lower structure of the battery pack.

[0104] 9 and 11, a plurality of hollow channels in the left and right base plates 210A and 210B extend in the longitudinal direction (Y direction), and each hollow channel is provided with a first cooling flow path 214. The direction and arrangement of the first cooling flow paths 214 are determined by the direction and arrangement of the hollow channels. Therefore, if the hollow channels are formed in the width direction (X direction), the first cooling flow paths 214 are also provided in the width direction.

[0105] In this case, the first extension portions 242, 252 of the side frames may also have hollow channels, and the second cooling channels 244, 254 may be installed in the hollow channels. Referring to Figure 11, similar to the first cooling channel 214 of the base plate 210B, the second cooling channel 254 is also installed in the hollow channel of the first extension portion 252, extending along the longitudinal direction. That is, the first cooling channel 214 and the second cooling channels 244, 254 all form refrigerant flow paths that extend in the longitudinal direction of the battery pack.

[0106] In this embodiment, the load distribution effect achieved by the first extensions 242 and 252 is also achieved. That is, as shown in FIG. 11 , the first extension 252 of the side frame 250, which extends toward one side of the base plate 210B, is coupled to the base plate 210B. In this embodiment, interlocking stepped portions 215 and 255 are formed on the coupling sides of the base plate 210B and the first extension 252, respectively. This allows for more uniform distribution of the load of the battery module. Furthermore, in this embodiment, the base plate 210B and the side frame 250 are both lightweight extruded frames with hollow channels, which reduces the load of the battery pack. Furthermore, the integrated cooling structure, which includes first and second cooling channels within the hollow channels of the base plate and side frame, eliminates the need for a separate cooling panel.

[0107] 9 again, the front frame 220 and the rear frame 230 of this embodiment include third cooling channels 224, 234 that communicate with the first cooling channel 214 and the second cooling channels 244, 254. Specifically, the front frame 220 includes a front cover 221 and a front plate 222 that is installed below the front cover 221 and includes the third cooling channel 224. A communication hole 225 that communicates with the first and second cooling channels is formed in the rear surface of the front plate 222 so that the third cooling channel 224 of the front plate 222 can communicate with the first and second cooling channels. In addition, coupling protrusions 226 for coupling to the base plates 210A, 210B and the first extensions 242, 252 may be formed at upper and lower ends of the rear surface of the front plate 222. The front frame 220 can be joined to the base plates 210A, 210B and the first extensions 242, 252 by contacting and welding the joining protrusions 226 to the upper and lower surfaces of the base plates 210A, 210B and the first extensions 242, 252.

[0108] The rear frame 230 also includes a rear cover portion 231 and a rear plate portion 232 installed below the rear cover portion and including a third cooling channel 234. Communication holes 235 communicating with the first and second cooling channels are formed in the front surface of the rear plate portion 232 so that the third cooling channel 234 of the rear plate portion can communicate with the first and second cooling channels. Furthermore, coupling protrusions 236 for coupling with the base plate and the first extension portion may be formed on the upper and lower ends of the front surface of the rear plate portion 232. The coupling protrusions 236 may be brought into contact with and welded to the upper and lower surfaces of the base plates 210A, 210B and the first extension portions 242, 252, respectively, to couple the rear frame 230 to the base plate and the first extension portion.

[0109] The third cooling channels 224, 234 provided in the front plate and the rear plate, respectively, are connected to the first cooling channel 214 installed in the hollow channel of the base plate and the second cooling channels 244, 254 installed in the hollow channel of the first extension portion, respectively.

[0110] Fig. 12 is a schematic diagram showing an example of a cooling path of the battery pack of Fig. 10. As shown in Fig. 12, a refrigerant inlet I and a refrigerant outlet O may be formed on the front surface of the front plate 220. That is, both the refrigerant inlet I and the refrigerant outlet O may be formed on the front side of the battery pack 200. Alternatively, the refrigerant inlet I and the refrigerant outlet O may be formed on the rear surface of the rear plate 230.

[0111] As shown in the figure, a coolant (e.g., water) injected into the coolant inlet I is introduced into the first cooling channel 214 on one side of the base plate and the second cooling channel 254 in the first extension portion 252 of the second side frame 250 via the third cooling channel 224 and the communication hole 225 of the front frame 220. The coolant flows along the longitudinal direction of the battery pack and reaches the third cooling channel 234 via the communication hole 235 of the rear frame 230. The coolant then returns from the third cooling channel in the rear frame 230, forms a cooling path that returns to the coolant outlet O of the front frame 220 via the first cooling channel 214 on the other side of the base plate and the second cooling channel 244 in the first extension portion 242 of the first side frame 240.

[0112] FIG. 13 is a schematic diagram showing another example of a cooling path of a battery pack.

[0113] In this example, a coolant inlet I is provided in the front frame 220, and a coolant outlet O is provided in the rear frame 230.

[0114] In this case, a cooling path can be formed from the refrigerant inlet I of the forward frame 220 - the third cooling channel 224 of the forward frame 220 - the second cooling channel 254 of the first cooling channel 214 and the first extension 252 of the base plate - the third cooling channel 234 of the aft frame 230 - the first cooling channel 214 of the base plate - the third cooling channel 224 of the forward frame - the second cooling channel 244 of the first cooling channel 214 and the first extension 242 of the base plate - the third cooling channel 234 of the aft frame 230 - the refrigerant outlet O.

[0115] As described above, the present invention can form cooling paths in various ways by providing cooling channels in the base plate and the first extensions of the side frames.

[0116] Meanwhile, the battery pack may include a pack cover (not shown) that covers an upper portion of the battery module and is coupled to the side frame.

[0117] The above description merely exemplifies the technical concept of the present invention, and various modifications and variations may be made by a person skilled in the art without departing from the essential characteristics of the present invention. Therefore, the drawings disclosed in the present invention are intended to explain, not to limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such drawings. The scope of protection of the present invention should be interpreted by the scope of the claims, and all technical concepts within the equivalent range should be interpreted as being included in the scope of the present invention. [Explanation of symbols]

[0118] 100, 200: Battery pack 110, 210: Base plate 110A, 210A: Left side base plate 110B, 210B: Right side base plate 120, 220: Front frame 121, 221: Front cover 122, 222: Front plate section 130, 230: Rear frame 131, 231: Rear cover 132, 232: Rear plate section 140, 240: First side frame 141, 241: Side wall 142, 242: 1st extension 143, 243: 2nd extension 150, 250: Second side frame 151, 251: Side wall 152, 252: 1st extension 153, 253: 2nd extension 160, 260: Center frame 161, 261: Vertical partition wall 162, 262: Horizontal extension 170, 270: Side beam M: Battery module A: Module mounting area 214: First cooling channel 244, 254: Second cooling channel 224, 234: Third cooling channel

Claims

1. A battery pack having a module mounting area in which a plurality of battery modules are accommodated, a base plate on which the battery module is mounted; a front frame coupled to a front end of the base plate; a rear frame coupled to a rear end of the base plate; side frames coupled to both sides of the base plate, the base plate has a size that forms only a part of the module mounting area, the side frame includes: a side wall portion facing the battery module; and a first extension portion extending from a lower portion of the side wall portion toward the base plate and coupled to a side surface of the base plate, forming the module mounting area together with the base plate and supporting a load of the battery module; the base plate includes a first cooling channel; The first extension of the side frame includes a second cooling channel.

2. The battery pack of claim 1 , wherein the first extension extends from a lower portion of the side wall toward the base plate by a predetermined length to support at least a portion of a lower area of ​​the battery module.

3. The battery pack according to claim 1 , wherein an upper surface of the base plate and an upper surface of the first extension form a plane having the same height.

4. The battery pack according to claim 1 , wherein a step portion having a shape that interlocks with a side surface of the base plate and a side surface of the first extension portion coupled thereto is provided.

5. The battery pack of claim 1 , wherein the side frame further comprises a second extension extending outward from the battery pack.

6. The battery pack according to claim 5 , wherein the second extension portion has a thickness greater than that of the first extension portion and is fixed to and supported by a structure on which the battery pack is installed.

7. a center frame extending from the front frame to the rear frame and coupled to the base plate; a module mounting area is formed between the center frame and the side wall portions of the side frames; The battery pack according to claim 1 , wherein the module mounting area includes an upper surface of at least a portion of the first extension portion of the side frame and an upper surface of the base plate.

8. The battery pack of claim 7 , wherein the base plates are disposed on both sides of the center frame, and side surfaces of the base plates on both sides are coupled to both side surfaces of the center frame.

9. the center frame includes a vertical partition wall portion and a horizontal extension portion extending from a lower portion of the vertical partition wall portion to the left and right toward the base plate and coupled to the base plate; The battery pack according to claim 8 , wherein an upper surface of the horizontal extension and an upper surface of the base plate are located on the same plane.

10. The vehicle further includes a plurality of side beams extending between the vertical partition wall of the center frame and the side frames on both sides, The battery pack of claim 9 , wherein the side beams are coupled to the vertical partition wall and the side frames, respectively, and divide the module mounting area into a plurality of areas.

11. The battery pack according to claim 1 , wherein the battery module is fastened to a side wall portion of the side frame.

12. At least one of the base plate and the side frame is An outer wall and an internal space surrounded by the outer wall, The battery pack according to claim 1 , wherein the interior space is divided by a plurality of partition walls extending from the outer wall to form a plurality of hollow channels.

13. The battery pack according to claim 12 , wherein the base plate is an integrated cooling base plate in which the first cooling flow path is provided in the hollow channel.

14. the first extension of the side frame has a hollow channel; The battery pack according to claim 13 , wherein the hollow channel is provided with the second cooling flow path.

15. the front frame and the rear frame each include a third cooling passage communicating with the first cooling passage and the second cooling passage; The battery pack according to claim 14 , wherein one of the front frame and the rear frame is formed with a coolant inlet and a coolant outlet that communicate with the third cooling channel.

16. the front frame and the rear frame each include a third cooling passage communicating with the first cooling passage and the second cooling passage; 15. The battery pack according to claim 14, wherein one of the front frame and the rear frame is formed with a coolant inlet communicating with the third cooling channel, and the other is formed with a coolant outlet communicating with the third cooling channel.

17. A method for manufacturing a battery pack having a module mounting area in which a plurality of battery modules are accommodated, a step of coupling side surfaces of first extension portions of side frames on both sides of a base plate having a size that forms only a portion of the module mounting area, the side frames extending toward the base plate and forming the module mounting area together with the base plate, the base plate including a first cooling channel, and the first extension portions of the side frames including a second cooling channel; coupling a front frame and a rear frame to the front end and rear end of the base plate and the first extension portion, respectively; and mounting a plurality of battery modules in a module mounting area including an upper surface of at least a portion of the first extension and an upper surface of the base plate.

18. A method for manufacturing a battery pack having a module mounting area in which a plurality of battery modules are accommodated, disposing base plates on both sides of a center frame and coupling the both base plates to the center frame, wherein the both base plates each have a cooling channel; coupling a first extension portion of a side frame on one side to the base plate on one side of the center frame, the first extension portion of the side frame on one side extending toward the base plate on one side of the center frame and forming a module mounting area together with the base plate on one side, the first extension portion of the side frame on one side having a cooling channel; connecting a first extension portion of an other side frame to the other base plate of the center frame, the first extension portion of the other side frame extending toward the other base plate of the center frame and forming a module mounting area together with the other base plate, the first extension portion of the other side frame having a cooling channel; coupling a front frame and a rear frame to the first extension portions of the one and other side frames and the front and rear ends of the base plates on both sides, respectively; and mounting a plurality of battery modules in a module mounting area including an upper surface of at least a portion of the first extension and an upper surface of the base plate.

19. The predetermined lengths of the first extension portions provided on the side frames on both sides are the same, A single base plate is located between the side frames on both sides. The battery pack of claim 2, wherein a ratio of half the length of the base plate extending between the side frames on both sides to the predetermined length is in the range of 6:4 to 9:

1.

20. The predetermined lengths of the first extension portions provided on one side of the side frame and the other side of the side frame are the same, Two base plates of the same size are positioned between the side frames on one side and the side frames on the other side, and are coupled to the corresponding side frames, 3. The battery pack according to claim 2, wherein a ratio of the length of each base plate extended to the corresponding side frame to the predetermined length ranges from 6:4 to 9:1.

Images