JP2020155340A - On-vehicle battery - Google Patents

Abstract

To provide an on-vehicle battery improving heat dissipation furthermore during charge and discharge of battery module, and guaranteeing safety by preventing electric leakage and short circuit due to dew condensation water.SOLUTION: An on-vehicle battery 10 includes multiple battery cells 11 in which external connection terminals are formed, an end plate 12 composed of a good heat conductor and placed on the end side in the arrangement direction of the battery cells 11, a bus bar 13 having one end side electrically connected with the battery cells 11, and the other end side placed above the end plate 12, a heat transfer plate placed between the end plate 12 and the bus bar 13, and conducting heat from the bus bar 13 to the end plate 12, a sheet 15 placed between the bus bar 13 and the end plate 12, and a holder 16 that is a frame-like component surrounding the heat transfer plate 14 from the surroundings. Furthermore, the crevice of the heat transfer plate 14 and the holder 16 is covered with the sheet 15.SELECTED DRAWING: Figure 3

Description

The present invention relates to an in-vehicle battery, and more particularly to an in-vehicle battery having a bus bar connecting a plurality of battery cells.

The in-vehicle battery has a large number of plate-shaped battery cells inside. Patent Document 1 describes this type of vehicle-mounted battery.

Specifically, in the battery module described in Patent Document 1, the external terminals of a plurality of cell cells are electrically connected to each other by a bus bar. It also has a heat transfer cover that is in direct contact with the busba and covers the busba. Further, the heat transfer cover is a heat conductive member having an insulating property, and is in direct contact with the battery container of the cell. As a result, the heat generated by the electrode group during charging and discharging is efficiently transferred to the surface of the battery container, so that the cell can be effectively cooled and the battery module can be miniaturized. Here, the busbar in Patent Document 1 corresponds to the bus bar of the present invention.

Japanese Unexamined Patent Publication No. 2013-80625

However, in the battery module according to the background technology described above, there is a problem that countermeasures against moisture are not always sufficient depending on the temperature condition and humidity condition of the atmosphere surrounding the battery module.

Specifically, when the external atmosphere surrounding the battery module is humid and a large temperature difference occurs between the bus bar of the battery module and the external atmosphere, the moisture contained in the external atmosphere is absorbed on the surface of the bus bar. Condensation. If this condensed water flows into the battery cell side, it may cause a short circuit or failure of the battery cell.

In addition, the bus bar generates heat when the battery module is charged and discharged. In particular, since the joint portion where the bus bar is joined to other members by bolts or the like is an interface between different materials having a high electric resistance value, a large amount of heat is generated when a large current flows through the joint portion. Therefore, in order to further improve the performance and life of the battery cell, it is desirable to have a configuration in which the heat dissipation of the bus bar can be further improved.

The present invention has been made in view of such problems, and an object of the present invention is to further improve heat dissipation during charging and discharging of the battery module, and to prevent electric leakage and short circuit due to condensed water. The purpose is to provide an in-vehicle battery that ensures safety.

The vehicle-mounted battery of the present invention has a plurality of battery cells in which external connection terminals are formed, an end plate arranged on the end side in the direction in which the battery cells are aligned, and an end plate made of a good thermal conductor, and one end side. A bus bar that is electrically connected to the external connection terminal and whose other end is arranged above the end plate and that is arranged between the end plate and the bus bar and conducts heat from the bus bar to the end plate. The heat transfer plate is provided with a heat transfer plate to be passed through, a sheet arranged between the bus bar and the heat transfer plate, and a holder which is a frame-shaped member surrounding the heat transfer plate from the surroundings. The gap with the holder is covered with the sheet.

Further, the vehicle-mounted battery of the present invention is characterized by having a wall-shaped portion formed on the outer peripheral portion of the holder.

Further, the vehicle-mounted battery of the present invention is characterized in that a groove is formed on the upper surface of the holder so as to surround the bus bar.

Further, the in-vehicle battery of the present invention is characterized in that a height difference is formed in the groove.

Further, the vehicle-mounted battery of the present invention is characterized in that the bottom surface of the groove is an inclined surface.

Further, the in-vehicle battery of the present invention is characterized in that a fin structure is formed on the end plate.

Further, the vehicle-mounted battery of the present invention is characterized in that the upper surface of the end plate is inclined downward toward the outside.

The vehicle-mounted battery of the present invention has a plurality of battery cells in which external connection terminals are formed, an end plate arranged on the end side in the direction in which the battery cells are aligned, and an end plate made of a good thermal conductor, and one end side. A bus bar that is electrically connected to the external connection terminal and whose other end is arranged above the end plate and that is arranged between the end plate and the bus bar and conducts heat from the bus bar to the end plate. The heat transfer plate is provided with a heat transfer plate to be passed through, a sheet arranged between the bus bar and the heat transfer plate, and a holder which is a frame-shaped member surrounding the heat transfer plate from the surroundings. The gap with the holder is covered with the sheet. As a result, according to the in-vehicle battery of the present invention, the heat generated from the bus bar can be positively conducted to the end plate by interposing the heat transfer plate between the end plate and the bus bar. It is possible to prevent overheating. Furthermore, since the holder is placed around the heat transfer plate and the gap between the heat transfer plate and the holder is covered with a sheet, even if dew condensation occurs on the surface of the bus bar, the dew condensation water passes through the upper surface of the sheet. And can be led to the holder. Therefore, it is possible to prevent the bus bar and the end plate from being inadvertently conducted by the condensed water.

Further, the vehicle-mounted battery of the present invention is characterized by having a wall-shaped portion formed on the outer peripheral portion of the holder. As a result, according to the in-vehicle battery of the present invention, by having the wall-shaped portion on the outer peripheral portion of the holder, it is possible to prevent the condensed water from flowing out to the outside at the wall-shaped portion.

Further, the vehicle-mounted battery of the present invention is characterized in that a groove is formed on the upper surface of the holder so as to surround the bus bar. As a result, according to the in-vehicle battery of the present invention, the dew condensation water can be stored in the groove of the holder and the dew condensation water can be prevented from flowing out to the outside.

Further, the in-vehicle battery of the present invention is characterized in that a height difference is formed in the groove. As a result, according to the in-vehicle battery of the present invention, by forming a height difference at the bottom of the groove, it is possible to prevent the condensed water stored in the groove from flowing to the battery side.

Further, the vehicle-mounted battery of the present invention is characterized in that the bottom surface of the groove is an inclined surface. As a result, according to the in-vehicle battery of the present invention, by making the bottom surface of the groove an inclined surface, it is possible to prevent the condensed water stored in the groove from flowing to the battery side.

Further, the in-vehicle battery of the present invention is characterized in that a fin structure is formed on the end plate. As a result, according to the in-vehicle battery of the present invention, heat dissipation from the end plate can be promoted by the fin structure of the end plate.

Further, the vehicle-mounted battery of the present invention is characterized in that the upper surface of the end plate is inclined downward toward the outside. As a result, according to the in-vehicle battery of the present invention, since the upper surface of the end plate is an inclined surface, the dew condensation water is guided outward by utilizing this inclination, and the dew condensation water enters the battery cell side. Can be prevented.

It is a figure which shows the vehicle with the vehicle-mounted battery which concerns on embodiment of this invention, (A) is a perspective view, (B) is a plan view. It is a perspective view which shows the vehicle-mounted battery which concerns on embodiment of this invention. It is an exploded perspective view which shows the vehicle-mounted battery which concerns on embodiment of this invention. It is a figure which shows the vehicle-mounted battery which concerns on embodiment of this invention, (A) is a front view, (B) is an enlarged cross-sectional view in the cut plane line AA of the vehicle-mounted battery shown in (A). It is a figure. It is an enlarged sectional view which shows the vehicle-mounted battery which concerns on other embodiment of this invention. It is an enlarged sectional view which shows the vehicle-mounted battery which concerns on other embodiment of this invention. It is an enlarged sectional view which shows the vehicle-mounted battery which concerns on other embodiment of this invention. It is an enlarged sectional view which shows the vehicle-mounted battery which concerns on other embodiment of this invention.

Hereinafter, the vehicle-mounted battery according to the embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the front-rear rear means the direction in which the battery cells 11 are stacked in the vehicle-mounted battery 10. The left-right direction is the left-right direction when the vehicle-mounted battery 10 is viewed from the front.

FIG. 1A is a perspective view illustrating a vehicle 30 equipped with an in-vehicle battery 10. FIG. 1B is a plan view illustrating an arrangement state of the vehicle-mounted battery 10.

As shown in FIG. 1 (A), a vehicle 30 such as an automobile or a train is equipped with an in-vehicle battery 10 (see FIG. 1 (B)) for supplying electric power to a motor and various electrical components. When the vehicle 30 is an automobile, an EV (Electrical Vehicle) vehicle, a HEV (Hybrid Electrical Vehicle) vehicle, a PHEV (Plug-in Hybrid Electrical Vehicle) vehicle, and the like have become widespread in recent years. Further, these vehicles 30 are also equipped with a plurality of in-vehicle batteries 10 having a high power storage function.

The vehicle 30 includes a vehicle body 31, a plurality of vehicle-mounted batteries 10 arranged in a battery arrangement area 32 defined in the vicinity of the bottom surface 33 of the vehicle, and a drive motor driven by electric power supplied from the vehicle-mounted battery 10. It has a tire (not shown) and a tire (not shown) that rotates by the driving force of a drive motor.

As shown in FIG. 1B, a plurality of vehicle-mounted batteries 10 are arranged in a matrix in the battery arrangement area 32 of the vehicle 30. The vehicle-mounted battery 10 has, for example, a rectangular parallelepiped shape, and its longitudinal direction is arranged along the front-rear direction of the vehicle 30. Then, a plurality of vehicle-mounted batteries 10 are efficiently arranged in the battery arrangement area 32, and many vehicle-mounted batteries 10 are mounted, so that the continuous mileage of the vehicle 30 can be extended.

Specifically, in the battery arrangement area 32 of the vehicle 30, two in-vehicle batteries 10 are arranged in the front row. On the other hand, in the second to fourth rows, four in-vehicle batteries 10 are arranged in each row. The vehicle-mounted batteries 10 are electrically connected to each other via a connection bus bar 28 described later.

FIG. 2 is a perspective view of the vehicle-mounted battery 10 as viewed from above on the front side. The vehicle-mounted battery 10 has a plurality of battery cells 11 arranged in the front-rear direction. As a whole, the vehicle-mounted battery 10 has a substantially rectangular parallelepiped shape formed elongated along the front-rear direction.

The battery cell 11 is a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery, and each battery cell 11 has a substantially plate shape.

The bus bar 13 is a connecting means for electrically connecting the battery cells 11 to each other. The bus bar 13 is a plate-shaped metal member made of a metal such as aluminum or copper and bent into a predetermined shape, and is arranged at the left end on the upper surface of the vehicle-mounted battery 10. The rear portion of the bus bar 13 is electrically connected to the connection terminal of each battery cell 11 via the cell bus bar 22. Here, two cell bus bars 22 are shown, but the cell bus bar 22 is provided corresponding to all the battery cells 11. The front portion of the bus bar 13 is arranged on the upper surface of the end plate 12.

The stud bolt 21 is a member that penetrates the front portion of the bus bar 13. The vehicle-mounted battery 10 is electrically connected to another vehicle-mounted battery 10 (not shown here) via a stud bolt 21.

The end plate 12 is a plate-shaped member arranged at both ends in the front-rear direction of the vehicle-mounted battery 10. Specifically, the end plate 12 is arranged on the front side of the battery cell 11 arranged at the foremost side and on the rear side of the battery cell 11 at the rearmost side. Here, the end plate 12 arranged behind the battery cell 11 is not shown. By arranging the end plates 12 at both ends in the front-rear direction, it is possible to prevent the dimensions of the vehicle-mounted battery 10 in the front-rear direction from changing due to the expansion of the battery cell 11 due to the temperature change. As the material of the end plate 12, a good thermal conductor having rigidity capable of suppressing expansion and deformation of the battery cell 11 and capable of satisfactorily conducting heat from the bus bar 13 can be adopted. As a specific material of the end plate 12, for example, a metal such as aluminum can be adopted.

A fin structure 20 is formed on the upper front portion of the end plate 12. The fin structure 20 is formed of a plurality of rib-shaped portions projecting forward from the front surface of the fin structure 20. By forming the fin structure 20, the surface area of the upper front surface portion of the end plate 12 can be increased, and heat exchange between the end plate 12 and the external atmosphere can be promoted. Further, although not shown here, the fin structure 20 is also formed in the upper portion of the outer surface of the end plate 12 arranged at the rear end of the vehicle-mounted battery 10.

The holder 16 is a substantially frame-shaped member arranged on the upper surface of the end plate 12. As the material of the holder 16, a resin having an insulating property or the like can be adopted.

FIG. 3 is an exploded perspective view showing the vehicle-mounted battery 10. With reference to this figure, a heat transfer plate 14, a holder 16, a sheet 15, and a bus bar 13 are arranged on the upper surface of the end plate 12 from the lower side.

The heat transfer plate 14 is a plate-shaped member made of a good heat conductor, and its lower surface is in contact with the upper surface of the end plate 12, and the upper surface thereof is in contact with the lower surface of the bus bar 13 via the sheet 15. As a specific material of the heat transfer plate 14, a synthetic resin such as metal or acrylic, rubber, a gel-like substance, or the like can be adopted. The upper surface of the heat transfer plate 14 is arranged on substantially the same plane as the upper surface of the inner edge portion of the holder 16.

The holder 16 is a member made of resin formed in a substantially frame shape, and a wall-shaped portion 17 is formed on the peripheral portion thereof. Further, the groove 18 shown in FIG. 4B is formed by denting the inside of the upper surface of the holder 16. When the holder 16 is viewed from above, a rectangular opening 26 is formed in the center of the holder 16. The heat transfer plate 14 is housed in the opening 26 (see FIG. 3).

The sheet 15 is a thin rectangular resin sheet made of a resin such as PP (polypropylene), which is arranged on the upper surface of the holder 16 and the heat transfer plate 14 and abuts on the lower surface of the bus bar 13. The sheet 15 has a substantially rectangular shape larger than the opening 26 of the holder 16. That is, in the front-rear direction and the left-right direction, the sheet 15 is formed to be slightly larger than the opening 26 of the holder 16. With the sheet 15 having such a configuration, the boundary between the heat transfer plate 14 and the holder 16 can be covered with the sheet 15. Further, on the lower surface of the sheet 15, an adhesive layer for adhering to the upper surfaces of the holder 16 and the heat transfer plate 14 is formed.

As described above, the bus bar 13 is a connecting means for connecting the battery cells 11 shown in FIG. 2 to each other. The front side portion of the bus bar 13 extends in the left-right direction along the upper surface of the end plate 12. As will be described later, the front portion of the bus bar 13 is thermally coupled to the end plate 12 via the sheet 15 and the heat transfer plate 14, and even if the bus bar 13 becomes hot during charging and discharging, the heat ends. Since the plate 12 is discharged to the outside, overheating of the bus bar 13 is prevented.

FIG. 4A is a front view showing the vehicle-mounted battery 10, and FIG. 4B is an enlarged cross-sectional view taken along the cutting surface line AA of the vehicle-mounted battery 10 shown in FIG. 4A.

With reference to FIG. 4A, the stud bolt 21 is inserted into the through hole penetrating the substantially central portion of the bus bar 13. The stud bolt 21 also penetrates the connecting bus bar 28 mounted on the upper surface of the bus bar 13. The connection bus bar 28 is a connection means for connecting the in-vehicle batteries 10 to each other. The stud bolt 21 is screwed into the nut 27. With this configuration, the bus bar 13 and the connecting bus bar 28 are fastened and electrically connected. By connecting the connecting bus bar 28 via the stud bolt 21 at the central portion of the bus bar 13, the connecting distance of the connecting bus bar 28 can be shortened.

Further, a bind bar 23 is arranged on the outside of the end plate 12 in the left-right direction. The bind bar 23 is a plate-shaped member for sandwiching and bundling the stacked battery cells 11 between the end plates 12. The end plate 12 and the bind bar 23 are fastened with a fixing bolt 24. Further, a module fixing bracket 25 for fixing the vehicle-mounted battery 10 to the housing of the battery pack (not shown here) is fixed to the lower part of the end plate 12.

With reference to FIG. 4B, the groove 18 is formed by recessing the inner portion of the upper surface of the holder 16. When the holder 16 is viewed from above, the groove 18 is formed in a frame shape. Further, the wall-shaped portion 17 is formed by projecting the outermost peripheral portion of the holder 16 upward in a wall shape. Here, the nut 27 and the connecting bus bar 28 shown in FIG. 4A are not shown.

The sheet 15 is arranged between the heat transfer plate 14 and the bus bar 13. Further, the lower surface of the sheet 15 covers not only the upper surface of the heat transfer plate 14 but also the upper surface of the holder 16 and the portion inside the groove 18. Further, the sheet 15 is made of a flexible material such as a resin having excellent waterproofness. Therefore, the sheet 15 is deformed following the shapes of the upper surfaces of the heat transfer plate 14 and the holder 16. Further, the lower surface of the sheet 15 is adhered to the upper surface of the heat transfer plate 14 and the upper surface of the holder 16 via an adhesive or the like.

On the upper surface of the end plate 12, the heat transfer plate 14 is surrounded by the holder 16, and there is a slight gap between the heat transfer plate 14 and the holder 16. The sheet 15 closes this gap from above. Therefore, the dew condensation water formed on the surface of the bus bar 13 under the usage conditions is guided to the groove 18 of the holder 16 along the upper surface of the sheet 15. The condensed water is stored in the groove 18 of the holder 16 and then evaporated. Therefore, it is possible to prevent the condensed water from entering between the heat transfer plate 14 and the holder 16.

According to the vehicle-mounted battery 10 of the present embodiment, overheating of the bus bar 13 and its peripheral members can be prevented. Specifically, when the vehicle-mounted battery 10 is charged and discharged, a large current passes through the bus bar 13, so that the bus bar 13 and its peripheral portion where the interface between different materials exists generates heat. In this embodiment, the bus bar 13 is thermally coupled to the end plate 12 via the heat transfer plate 14. Further, since the end plate 12 is a plate-shaped member arranged at the end of the vehicle-mounted battery 10, it has a sufficient surface area. Therefore, the heat generated by energizing the bus bar 13 is conducted to the end plate 12 via the heat transfer plate 14 and then released to the outside atmosphere. Therefore, heating of the bus bar 13 during charging / discharging is prevented, and further, performance deterioration and life deterioration due to overheating of the battery cell 11 are prevented.

Further, referring to FIG. 4A, the entire lower surface of the portion extending along the left-right direction of the bus bar 13 is in contact with the upper surface of the heat transfer plate 14. With such a configuration, the area where the bus bar 13 and the end plate 12 come into contact with each other via the heat transfer plate 14 can be increased, and the heat dissipation of the bus bar 13 can be improved.

Further, in the present embodiment, the holder 16 is arranged above the end plate 12 so as to surround the heat transfer plate 14, and the gap between the heat transfer plate 14 and the holder 16 is covered with the sheet 15. With this configuration, the condensed water adhering to the surface of the bus bar 13 is transmitted through the upper surface of the sheet 15 and stored in the groove 18 of the holder 16. Therefore, since the condensed water does not enter the gap between the heat transfer plate 14 and the holder 16, it is possible to prevent the heat transfer plate 14 and the end plate 12 from being inadvertently conducted with each other.

Other forms of the vehicle-mounted battery 10 will be described with reference to the drawings after FIG.

FIG. 5 is an enlarged cross-sectional view showing the vehicle-mounted battery 10 according to another embodiment. Here, the wall-shaped portion 17 of the holder 16 is formed higher than that of the vehicle-mounted battery 10 shown in FIG. 4 and the like. Specifically, the upper end portion of the wall-shaped portion 17 is arranged above the upper end portion of the battery cell 11. By doing so, a large amount of dew condensation water can be stored inside the holder 16, and the effect of preventing the dew condensation water from entering the battery cell 11 side can be remarkable.

FIG. 6 is an enlarged cross-sectional view of the vehicle-mounted battery 10 according to still another embodiment. In the following description, the groove 18 arranged in the front is referred to as a groove 181 and the groove 18 arranged in the rear is referred to as a groove 182. Further, the groove 181 has a bottom surface 191 and the groove 182 has a bottom surface 192.

Here, a height difference is formed between the bottom surface 191 and the bottom surface 192. Specifically, the bottom surface 191 of the groove 181 arranged in the front is arranged below the bottom surface 192 of the groove 182 arranged in the rear. The height difference L1 between the bottom surface 191 and the bottom surface 192 is, for example, 1 mm.

With this configuration, the condensed water generated on the surface of the bus bar 13 flows toward the holder 16. Specifically, the condensed water flowing into the groove 181 from the bus bar 13 stays in the groove 181. Further, since the bottom surface 191 is lower than the bottom surface 192, the condensed water flowing into the groove 182 from the bus bar 13 moves to the groove 181. As a result, the dew condensation water can flow in the direction away from the battery cell 11, and the dew condensation water can be prevented from coming into contact with the battery cell 11.

FIG. 7 is an enlarged cross-sectional view of the vehicle-mounted battery 10 according to still another embodiment. Here, the bottom surface 191 and the bottom surface 192 exhibit an inclined surface that inclines downward toward the front. The angle θ1 at which the bottom surface 191 and the bottom surface 192 are inclined from the horizontal plane is, for example, about 2 degrees. Further, the bottom surface 191 and the bottom surface 192 are arranged on the same plane.

With this configuration, the condensed water generated on the surface of the bus bar 13 flows forward inside the holder 16. Specifically, the condensed water flowing into the groove 181 from the bus bar 13 stays in the groove 181. Further, since the bottom surface 191 and the bottom surface 192 are inclined surfaces, the condensed water flowing into the groove 182 from the bus bar 13 moves to the groove 181. As a result, the dew condensation water can flow in the direction away from the battery cell 11, and the dew condensation water can be prevented from coming into contact with the battery cell 11.

FIG. 8 is an enlarged cross-sectional view of the vehicle-mounted battery 10 according to still another embodiment. Here, the upper surface of the end plate 12 exhibits an inclined surface that inclines downward toward the front. Further, the bottom surface 191 and the bottom surface 192 of the holder 16 also exhibit an inclined surface that inclines downward toward the front. The angle θ2 at which the upper surface, the bottom surface 191 and the bottom surface 192 of the end plate 12 are inclined from the horizontal plane is, for example, about 5 degrees.

With this configuration, the condensed water generated on the surface of the bus bar 13 flows forward inside the holder 16. Specifically, the condensed water flowing into the groove 181 from the bus bar 13 stays in the groove 181. Further, since the bottom surface 191 and the bottom surface 192 are inclined surfaces, the condensed water flowing into the groove 182 from the bus bar 13 moves to the groove 181. As a result, the dew condensation water can flow in the direction away from the battery cell 11, and the dew condensation water can be prevented from coming into contact with the battery cell 11.

Although the embodiments of the present invention have been described above, the present invention is not limited to this, and changes can be made without departing from the gist of the present invention. In addition, the above-mentioned forms can be combined with each other.

10 In-vehicle battery 11 Battery cell 12 End plate 13 Bus bar 14 Heat transfer plate 15 Sheet 16 Holder 17 Wall-shaped parts 18, 181, 182 Grooves 191, 192 Bottom surface 20 Fin structure 21 Stud bolt 22 Cell bus bar 23 Bind bar 24 Fixing bolt 25 Module Fixed bracket 26 Opening 27 Nut 28 Connection bus bar 30 Vehicle 31 Body 32 Battery placement area 33 Bottom

Claims (7)

Multiple battery cells with external connection terminals and
An end plate arranged on the end side in the direction in which the battery cells are aligned and made of a good heat conductor,
A bus bar whose one end side is electrically connected to the external connection terminal and whose other end side is arranged above the end plate.
A heat transfer plate that is arranged between the end plate and the bus bar and allows heat conducted from the bus bar to the end plate to pass through.
A sheet arranged between the bus bar and the heat transfer plate,
A holder, which is a frame-shaped member surrounding the heat transfer plate from the surroundings, is provided.
An in-vehicle battery characterized in that the gap between the heat transfer plate and the holder is covered with the sheet. The vehicle-mounted battery according to claim 1, further comprising a wall-shaped portion formed on the outer peripheral portion of the holder. The vehicle-mounted battery according to claim 1 or 2, wherein a groove is formed on the upper surface of the holder so as to surround the bus bar. The vehicle-mounted battery according to claim 3, wherein a height difference is formed in the groove. The vehicle-mounted battery according to claim 3, wherein the bottom surface of the groove is an inclined surface. The vehicle-mounted battery according to any one of claims 1 to 5, wherein a fin structure is formed on the end plate. The vehicle-mounted battery according to any one of claims 1 to 6, wherein the upper surface of the end plate is inclined downward toward the outside.

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