Battery pack liquid cooling plate based on rigid support mechanical connection structure

Abstract

This invention relates to the field of battery pack accessory technology, specifically to a battery pack liquid cooling plate based on a rigid support mechanical connection structure. The liquid cooling plate includes a liquid cooling structure with a connecting structure and a supporting structure installed at its top and bottom, respectively. The liquid cooling structure includes a flow channel plate and upper and lower substrates respectively installed on the upper and lower sides of the flow channel plate. Liquid flow channels are formed on both the upper and lower sides of the liquid cooling structure, with the liquid flowing in opposite directions on each side. This invention, by creating oppositely oriented cooling channels on the upper and lower sides of the flow channel plate, ensures that the liquid flows in opposite directions when cooling the battery pack. This allows the liquid flowing at the inlet of the upper cooling channel to exchange heat with the liquid flowing at the outlet of the lower cooling channel, reducing the temperature of the liquid at the outlet and decreasing the temperature difference between the liquid at the outlet and inlet, thereby improving the uniformity of cooling by the liquid cooling plate.

Description

Technical Field

[0001] This invention relates to the field of battery pack accessories technology, specifically to a battery pack liquid cooling plate based on a rigid support mechanical connection structure. Background Technology

[0002] The liquid cooling plate structure of the battery pack is a core component of the thermal management system for electric vehicle power batteries. Its main function is to quickly dissipate the heat generated during battery charging and discharging through contact between the internally circulating coolant and the battery module, maintaining the battery operating temperature within a reasonable range. The design of the liquid cooling plate structure directly affects heat dissipation efficiency, battery life, and overall vehicle safety.

[0003] In existing liquid cooling plates, the flow channels are generally S-shaped. The cooling liquid flows from the inlet to the outlet of the flow channel. During the flow, the liquid continuously exchanges heat with the batteries in the battery pack, causing the liquid temperature to gradually rise. The temperature of the liquid near the inlet is higher than that near the outlet. Since the heat exchange efficiency is closely related to the temperature difference, the cooling effect of the liquid at the outlet is worse than that at the inlet, affecting the uniformity of cooling by the liquid cooling plate and easily leading to localized overheating of the battery pack. Summary of the Invention

[0004] To address the aforementioned problems, the present invention provides a battery pack liquid cooling plate based on a rigid support mechanical connection structure, comprising a liquid cooling structure, wherein a connection structure and a support structure are respectively installed at the top and bottom of the liquid cooling structure.

[0005] The liquid cooling structure includes a flow channel plate and an upper substrate and a lower substrate respectively installed on the upper and lower sides of the flow channel plate. Liquid flow channels are opened on both the upper and lower sides of the liquid cooling structure, and the liquid flow directions in the upper and lower liquid flow channels are opposite. A turbulence unit for disturbing the liquid in the liquid flow channel is fixedly connected to the side of the upper substrate and the lower substrate near the flow channel plate.

[0006] The connection structure includes a fixing frame fixedly installed on the top of the upper substrate. The top of the fixing frame is threaded with a number of mounting bolts distributed front and back. The fixing frame is equipped with an anti-loosening unit to prevent the mounting bolts from loosening.

[0007] In one possible implementation, the upper liquid flow channel includes a plurality of cooling channels formed in a U-shape on the top of the flow channel plate. The plurality of cooling channels are distributed in parallel from the inside to the outside. The top of the flow channel plate is also provided with an inlet channel and an outlet channel. The inlet channel is connected to the rear end of the plurality of cooling channels, and the outlet channel is connected to the front end of the plurality of cooling channels.

[0008] In one possible implementation, the cross-sections of the plurality of cooling channels are all trapezoidal and the width of the side of the plurality of cooling channels communicating with the surface of the channel plate is the same, and the cross-sectional area of ​​the plurality of cooling channels gradually increases from the inside to the outside.

[0009] In one possible implementation, the lower liquid flow channel has the same structure as the upper liquid flow channel but in opposite directions, and the upper cooling channels and the lower cooling channels are distributed alternately.

[0010] In one possible implementation, an inlet and an outlet are fixedly connected to the top of the left end of the upper substrate. The outlet is located in front of the inlet. The inlet is connected to the left end of the upper inlet channel, and the outlet is connected to the left end of the upper outlet channel.

[0011] In one possible implementation, a second water inlet and a second water outlet are fixedly connected to the bottom of the left end of the lower substrate. The second water inlet is located in front of the second water outlet. The second water inlet is connected to the left end of the lower water inlet channel, and the second water outlet is connected to the left end of the lower water outlet channel.

[0012] In one possible implementation, the turbulence unit includes two turbulence blocks, namely, a first turbulence block and a second turbulence block, which are fixedly connected to the bottom of the upper substrate and located inside the corresponding cooling channel. The first turbulence block and the second turbulence block are tilted in opposite directions and are alternately distributed. The first turbulence block and the second turbulence block on the lower substrate have the same structure as the first turbulence block and the second turbulence block on the upper substrate.

[0013] In one possible implementation, the anti-loosening unit includes a U-shaped component detachably installed inside the fixing frame. Several spring pieces corresponding to the mounting bolts are fixedly connected to the left and right side walls of the U-shaped component. A ratchet post is integrally formed at the bottom of the mounting bolt. The spring pieces engage with the ratchet post. The bottom of the ratchet post is tapered. The fixing frame is threaded with fixing bolts for pressing and fixing the U-shaped component.

[0014] In one possible implementation, the support structure includes a support frame fixedly mounted on the bottom of the lower substrate, with a plurality of reinforcing beams equidistantly distributed on the bottom of the support frame, and a plurality of upwardly protruding reinforcing ribs stamped on the reinforcing beams, the tops of the reinforcing ribs being supported on the bottom of the lower substrate.

[0015] The beneficial effects of the present invention are as follows: 1. By opening cooling channels with opposite directions on the upper and lower sides of the flow channel plate, the liquid flows in opposite directions in the upper and lower cooling channels when cooling the battery pack. In this way, the liquid flowing at the inlet end of the upper cooling channel can exchange heat with the liquid flowing at the outlet end of the lower cooling channel, thereby reducing the temperature of the liquid at the outlet end, reducing the temperature difference between the liquid at the outlet end and the liquid at the inlet end, improving the uniformity of cooling of the liquid cooling plate, and avoiding local overheating of the battery pack.

[0016] 2. This invention sets cooling channels of different lengths with different cross-sectional areas. The longer the cooling channel, the larger the corresponding cross-sectional area, and the more liquid flows through the cooling channel, the more heat can be absorbed. While ensuring that the width of the cooling channel in contact with the battery pack is the same, the more liquid there is, the slower the temperature rises, and the longer the heat exchange distance can be achieved. This solves the problem that the liquid in a longer cooling channel has a larger heat exchange area, longer heat exchange time, and higher temperature than the liquid in a shorter cooling channel.

[0017] 3. The present invention turbulents the liquid flowing in the cooling channel by setting turbulence block one and turbulence block two on the upper and lower substrates. By continuously changing the flow direction of the liquid, the turbulence of the liquid is increased, so that the liquid in contact with the upper substrate leaves in time after heat exchange, avoiding the continuous contact of the high temperature part of the liquid with the upper substrate. At the same time, turbulence block one and turbulence block two can also increase the heat exchange area with the liquid and improve the heat exchange efficiency.

[0018] 4. When the liquid cooling plate is fixed to the battery pack housing using mounting bolts, after the bottom thread of the mounting bolt is installed into the fixing bracket, the ratchet column will enter between the spring plates on both sides. The ends of the spring plates will cooperate with the tooth grooves on the ratchet column, so that the mounting bolt can only be rotated in the tightening direction. When the mounting bolt is rotated in the loosening direction, the spring plates will block the ratchet column, preventing the mounting bolt from loosening. The spring plates limit the ratchet column, preventing the mounting bolt from loosening due to shaking when the battery pack moves, thus improving the firmness of the connection between the liquid cooling plate and the battery pack housing. Attached Figure Description

[0019] Figure 1 This is a three-dimensional structural schematic diagram of the first angle of the present invention.

[0020] Figure 2 This is a three-dimensional structural schematic diagram of the second angle of the present invention.

[0021] Figure 3 This is a breakdown diagram of the liquid cooling structure of the present invention.

[0022] Figure 4This is a top-view planar structural diagram of the liquid flow channel of the present invention.

[0023] Figure 5 This is a half-sectional view of the flow channel plate of the present invention.

[0024] Figure 6 This is a separate diagram of the connection structure of the present invention.

[0025] Figure 7 This is a three-dimensional structural diagram of the mounting bolt of the present invention.

[0026] Figure 8 This is a schematic diagram of the planar structure of the ratchet post and the spring plate of the present invention.

[0027] Figure 9 This is a three-dimensional structural diagram of the reinforcing beam of the present invention.

[0028] In the diagram: 1. Liquid cooling structure; 11. Flow channel plate; 12. Upper base plate; 121. Inlet 1; 122. Outlet 1; 13. Lower base plate; 131. Inlet 2; 132. Outlet 2; 14. Liquid flow channel; 141. Cooling flow channel; 142. Inlet flow channel; 143. Outlet flow channel; 15. Turbulence unit; 151. Turbulence block 1; 152. Turbulence block 2; 2. Connecting structure; 21. Fixing bracket; 22. Mounting bolt; 221. Ratchet post; 23. Anti-loosening unit; 231. U-shaped part; 232. Spring; 24. Fixing bolt; 3. Support structure; 31. Support frame; 32. Reinforcing beam; 321. Reinforcing rib. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described below, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] Please see Figure 1 - Figure 9 A battery pack liquid cooling plate based on a rigid support mechanical connection structure includes a liquid cooling structure 1, with a connection structure 2 and a support structure 3 installed at the top and bottom of the liquid cooling structure 1, respectively.

[0031] The liquid cooling structure 1 includes a flow channel plate 11 and an upper substrate 12 and a lower substrate 13 respectively installed on the upper and lower sides of the flow channel plate 11. Liquid flow channels 14 are provided on both the upper and lower sides of the liquid cooling structure 1, and the liquid flow directions in the upper and lower liquid flow channels 14 are opposite. The upper substrate 12 and the lower substrate 13 are fixedly connected to the side of the flow channel plate 11 with a turbulence unit 15 for disturbing the liquid in the liquid flow channel 14.

[0032] The connection structure 2 includes a fixing bracket 21 fixedly installed on the top of the upper base plate 12. The top of the fixing bracket 21 is threaded with a number of mounting bolts 22 distributed front and back. The fixing bracket 21 is equipped with an anti-loosening unit 23 for preventing the mounting bolts 22 from loosening.

[0033] In practical use, the mounting bracket 21 is fixed to the battery pack housing by using mounting bolts 22. The liquid cooling plate is installed at the bottom of the battery pack, and the upper base plate 12 contacts the bottom of the battery in the battery pack. The cooling liquid flows in the liquid flow channel 14. The liquid exchanges heat with the battery through the upper base plate 12 to prevent the battery temperature from getting too high. The anti-loosening unit 23 is used to restrict the rotation direction of the mounting bolts 22 to prevent the mounting bolts 22 from rotating in the direction of loosening, thereby improving the firmness of the connection between the liquid cooling plate and the battery pack housing and preventing the mounting bolts 22 from coming loose due to shaking when the battery pack moves.

[0034] As the liquid continuously exchanges heat, the temperature of the liquid closer to the outlet is higher. By setting a liquid flow channel 14 with opposite flow direction on the lower side of the flow channel plate 11, the liquid at the inlet end of the lower liquid flow channel 14 can exchange heat with the liquid at the outlet end of the upper liquid flow channel 14, thereby reducing the temperature difference between the liquid at the inlet end and the outlet end of the upper liquid flow channel 14, improving the uniformity of cooling of the liquid cooling plate, and avoiding local overheating of the battery pack.

[0035] When the liquid flows in the liquid channel 14, the turbulence unit 15 is used to turbulent the liquid, increase the degree of liquid turbulence, and allow the liquid in contact with the upper substrate 12 to leave in time after heat exchange, so as to avoid the high temperature part of the liquid from continuously contacting the upper substrate 12, and further improve the cooling efficiency.

[0036] Please see Figure 3 and Figure 4 The upper liquid flow channel 14 includes several cooling channels 141 formed in a U-shape on the top of the flow channel plate 11. The cooling channels 141 are distributed in parallel from the inside to the outside. The top of the flow channel plate 11 is also provided with an inlet channel 142 and an outlet channel 143. The inlet channel 142 is connected to the rear end of the cooling channels 141, and the outlet channel 143 is connected to the front end of the cooling channels 141.

[0037] Please see Figure 3- Figure 5 The cross-sections of several cooling channels 141 are all trapezoidal, and the width of the side of several cooling channels 141 that is connected to the surface of the channel plate 11 is the same. The cross-sectional area of ​​several cooling channels 141 gradually increases from the inside to the outside.

[0038] In practical use, the liquid flows sequentially into several cooling channels 141 through the inlet channel 142. After passing through the cooling channels 141, the liquid flows into the outlet channel 143, where it is discharged after merging with the flow. Because the cooling channels 141 are U-shaped and parallel from the inside to the outside, the outer cooling channels 141 are longer than the inner ones, resulting in a longer cooling area and heat exchange time. Since the cross-sectional area of ​​the outer cooling channels 141 is larger than that of the inner ones, the outer... The side cooling channel 141 has a larger volume of liquid flowing through it. Given that the top width of several cooling channels 141 is the same, the heat exchange efficiency per unit time is the same. The more liquid flows through the cooling channel 141, the more heat can be absorbed. The more liquid there is, the slower the temperature rises, and the longer the heat exchange distance can be achieved. This solves the problem that the liquid in the longer cooling channel 141 has a larger heat exchange area, longer heat exchange time, and higher temperature than the liquid in the shorter cooling channel 141. It further improves the uniformity of liquid cooling plate cooling and avoids local overheating.

[0039] Please see Figure 3 - Figure 5 The lower liquid flow channel 14 has the same structure as the upper liquid flow channel 14 but the directions are opposite. Several cooling channels 141 on the upper side and several cooling channels 141 on the lower side are distributed alternately.

[0040] Please see Figure 1 and Figure 3 The top left end of the upper substrate 12 is fixedly connected to an inlet 121 and an outlet 122. The outlet 122 is located in front of the inlet 121. The inlet 121 is connected to the left end of the upper inlet channel 142, and the outlet 122 is connected to the left end of the upper outlet channel 143.

[0041] Please see Figure 2 and Figure 3 The bottom left end of the lower substrate 13 is fixedly connected to a water inlet 131 and a water outlet 132. The water inlet 131 is located in front of the water outlet 132. The water inlet 131 is connected to the left end of the lower water inlet channel 142, and the water outlet 132 is connected to the left end of the lower water outlet channel 143.

[0042] In practical use, the liquid on the upper side flows into the upper inlet channel 142 from inlet 121, and then flows out from outlet 122 after being transported by the upper cooling channel 141 and outlet channel 143. The liquid on the lower side flows into the lower inlet channel 142 from inlet 131, and then flows out from outlet 132 after being transported by the lower cooling channel 141 and outlet channel 143. By transporting the liquid on the upper and lower sides of the flow channel plate 11 from opposite directions, the liquid flow directions in the upper and lower cooling channels 141 are reversed. In this way, the liquid flowing at the inlet end of the upper cooling channel 141 can exchange heat with the liquid flowing at the outlet end of the lower cooling channel 141, reducing the temperature of the liquid at the outlet end, reducing the temperature difference between the liquid at the outlet end and the liquid at the inlet end, and improving the uniformity of cooling of the liquid cooling plate.

[0043] Please see Figure 3 and Figure 4 The turbulence unit 15 includes two turbulence blocks: a first turbulence block 151 and a second turbulence block 152, which are fixedly connected to the bottom of the upper substrate 12 and located inside the corresponding cooling channel 141. The first turbulence block 151 and the second turbulence block 152 are tilted in opposite directions and are alternately distributed. The first turbulence block 151 and the second turbulence block 152 on the lower substrate 13 have the same structure as the first turbulence block 151 and the second turbulence block 152 on the upper substrate 12.

[0044] In practical use, when the liquid flows from the cooling channel 141, when the liquid passes through the first turbulence block 151 and the second turbulence block 152, the turbulence block 151 and the second turbulence block 152 will divert the liquid. At the same time, the turbulence block 151 and the second turbulence block 152 with different inclination directions can continuously change the direction of liquid flow, play a turbulent role, and increase the degree of liquid turbulence. Compared with the liquid flowing smoothly in the straight channel, the turbulent liquid can leave in time after contacting the upper substrate 12 for heat exchange, avoiding the high temperature part of the liquid from continuously contacting the upper substrate 12. At the same time, the turbulence block 151 and the second turbulence block 152 can also increase the heat exchange area with the liquid and improve the heat exchange efficiency.

[0045] Please see Figure 1 , Figure 6 , Figure 7 and Figure 8 The anti-loosening unit 23 includes a U-shaped part 231 that can be detachably installed inside the fixing frame 21. Several spring pieces 232 corresponding to the mounting bolts 22 are fixedly connected to the left and right side walls of the U-shaped part 231. A ratchet post 221 is integrally formed at the bottom of the mounting bolts 22. The spring pieces 232 are engaged with the ratchet post 221. The bottom of the ratchet post 221 is conical. The fixing frame 21 is threaded with fixing bolts 24 for pressing and fixing the U-shaped part 231.

[0046] In practical use, when installing the liquid cooling plate and the battery pack housing together, align the mounting bracket 21 with the mounting part on the battery pack housing, and then use the mounting bolt 22 to thread the mounting bracket 21 and the battery pack housing together. The bottom end of the mounting bolt 22 enters the interior of the mounting bracket 21, and the ratchet post 221 at the bottom of the mounting bolt 22 is inserted between the two spring pieces 232 on the left and right. When the mounting bolt 22 is tightened, the inclined edge of the ratchet tooth on the ratchet post 221 will push the spring piece 232, causing the spring piece 232 to deflect away from the center of the ratchet post 221, without hindering the rotation of the ratchet post 221. After installation, the spring piece 232 and the ratchet tooth on the ratchet post 221 abut together, preventing the mounting bolt 22 from rotating in the loosening direction, improving the firmness of the mounting bolt 22 connection, and avoiding the situation where the mounting bolt 22 becomes loose due to shaking when the battery pack moves.

[0047] Please see Figure 2 and Figure 9 The support structure 3 includes a support frame 31 fixedly installed at the bottom of the lower substrate 13. Several reinforcing beams 32 are riveted to the bottom of the support frame 31 and are distributed equidistantly on the left and right. Several reinforcing ribs 321 are stamped on the reinforcing beams 32 and protrude upwards. The top of the reinforcing ribs 321 is supported at the bottom of the lower substrate 13. The flow channel plate 11, the upper substrate 12 and the lower substrate 13 are made of aluminum alloy, and the support frame 31 and the reinforcing beams 32 are made of stainless steel.

[0048] In practical use, in order to ensure that the liquid cooling plate has sufficient support, traditional liquid cooling plates require the use of thicker aluminum alloy materials to process the flow channel plate 11, upper substrate 12 and lower substrate 13 when supporting the battery pack, which results in high production costs. In this invention, a stainless steel support frame 31 and reinforcing beams 32 are installed at the bottom of the lower substrate 13 for support. The spaced reinforcing beams 32 require less material and have lower production costs.

[0049] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "connected," "installed," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, an integral connection, or a sliding connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0050] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made based on the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A battery pack liquid cooling plate based on a rigid support mechanical connection structure, characterized by: The liquid cooling structure (1) is provided with a connecting structure (2) and a supporting structure (3) on the top and bottom respectively; The liquid cooling structure (1) comprises a flow channel plate (11) and an upper base plate (12) and a lower base plate (13) installed on the upper and lower sides of the flow channel plate (11) respectively, liquid flow channels (14) are formed on the upper and lower sides of the liquid cooling structure (1), the directions of liquid flowing in the upper and lower liquid flow channels (14) are opposite, and the upper base plate (12) and the lower base plate (13) are fixedly connected with turbulence units (15) for disturbing the liquid in the liquid flow channels (14) on the sides close to the flow channel plate (11). The connecting structure (2) comprises a fixed frame (21) fixedly installed on the top of the upper base plate (12), a plurality of mounting bolts (22) are threadedly installed on the top of the fixed frame (21) in front and back distribution, and an anti-loosening unit (23) for limiting the loosening of the plurality of mounting bolts (22) is installed in the fixed frame (21). The upper liquid flow channel (14) comprises a plurality of cooling flow channels (141) in U-shaped form formed on the top of the flow channel plate (11), the plurality of cooling flow channels (141) are distributed in parallel from inside to outside, and the top of the flow channel plate (11) is further provided with a water inlet flow channel (142) and a water outlet flow channel (143), the water inlet flow channel (142) is communicated with one end of the plurality of cooling flow channels (141) on the rear side, and the water outlet flow channel (143) is communicated with one end of the plurality of cooling flow channels (141) on the front side. The cross sections of the plurality of cooling flow channels (141) are all trapezoidal, the widths of the sides of the plurality of cooling flow channels (141) communicated with the surface of the flow channel plate (11) are the same, and the cross sectional areas of the plurality of cooling flow channels (141) gradually increase from inside to outside. The turbulence unit (15) comprises a plurality of turbulence blocks one (151) and turbulence blocks two (152) fixedly connected to the bottom of the upper base plate (12) and located in the corresponding cooling flow channels (141), the inclination directions of the plurality of turbulence blocks one (151) and turbulence blocks two (152) are opposite and they are alternately distributed, and the turbulence blocks one (151) and turbulence blocks two (152) on the lower base plate (13) and the upper turbulence blocks one (151) and turbulence blocks two (152) on the upper base plate (12) have the same structure.

2. The battery pack liquid cooling plate based on rigid support mechanical connection structure according to claim 1, characterized in that: The lower liquid flow channel (14) has the same structure as the upper liquid flow channel (14) but the direction is opposite, and the plurality of cooling flow channels (141) on the upper side and the plurality of cooling flow channels (141) on the lower side are alternately distributed.

3. The battery pack liquid cooling plate based on rigid support mechanical connection structure according to claim 1, characterized in that: The top of the left end of the upper base plate (12) is fixedly connected with a water inlet one (121) and a water outlet one (122), the water outlet one (122) is located on the front side of the water inlet one (121), the water inlet one (121) is communicated with the left end of the upper water inlet flow channel (142), and the water outlet one (122) is communicated with the left end of the upper water outlet flow channel (143).

4. The battery pack liquid cooling plate based on rigid support mechanical connection structure according to claim 1, characterized in that: The bottom of the left end of the lower substrate (13) is fixedly connected with a second water inlet (131) and a second water outlet (132), the second water inlet (131) is located in front of the second water outlet (132), the second water inlet (131) is communicated with the left end of the lower water inlet flow channel (142), and the second water outlet (132) is communicated with the left end of the lower water outlet flow channel (143).

5. The battery pack liquid cooling plate based on rigid support mechanical connection structure according to claim 1, characterized in that: The anti-loosening unit (23) comprises a U-shaped piece (231) detachably mounted in the fixed frame (21), a plurality of elastic sheets (232) corresponding to the mounting bolts (22) are fixedly connected to the left and right side walls of the U-shaped piece (231), a ratchet column (221) is integrally formed at the bottom of the mounting bolt (22), the elastic sheet (232) is in clamping connection with the ratchet column (221), the bottom of the ratchet column (221) is tapered, and the fixed frame (21) is in threaded connection with a fixing bolt (24) for pressing and fixing the U-shaped piece (231).

6. The battery pack liquid cooling plate based on rigid support mechanical connection structure according to claim 1, characterized in that: The support structure (3) comprises a support frame (31) fixedly installed at the bottom of the lower substrate (13), a plurality of reinforcing cross beams (32) equally distributed leftward and rightward are riveted to the bottom of the support frame (31), a plurality of reinforcing convex ribs (321) protruding upward are punched on the reinforcing cross beams (32), and the top of the reinforcing convex rib (321) is supported on the bottom of the lower substrate (13).

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