WO2006093010A1

WO2006093010A1 - Casing for module and casing for battery pack

Info

Publication number: WO2006093010A1
Application number: PCT/JP2006/303246
Authority: WO
Inventors: Toshizo Hosoya
Original assignee: Nec Corporation; Fuji Jukogyo Kabushiki Kaisha
Priority date: 2005-03-01
Filing date: 2006-02-23
Publication date: 2006-09-08
Also published as: JP5270915B2; JP5949608B2; JP2013118195A; JPWO2006093010A1

Abstract

A casing for a module and a casing for a battery pack. The casing (20) for the module comprises holding faces (42), a supporting part (40), duct side faces (31) and a duct end face (33), a duct bottom face (32), and a cooling duct (30). The holding faces (42) hold the module (14). The supporting part (40) comprises the side face portion of a frame shape raised from the holding faces (42), namely, side faces (43), an abutting part (44), and an L-shaped fixture (45). The duct side faces (31) and the duct end face (33) are formed by raising from the duct bottom face (32). The cooling duct (30) comprises an opening part (34) for leading cooling water therein.

Description

Specification

Module housing and battery pack housing

Technical field

The present invention relates to a module housing for fixing and holding a module formed by connecting a plurality of laminate batteries, and an assembled battery housing for fixing and holding an assembled battery formed by connecting a plurality of modules. About.

Background art

[0002] Since the battery itself has low rigidity, when the battery is modularized, a box-shaped casing that covers the entire surface of the module 214 that is configured by electrically connecting a predetermined number of laminated batteries. In some cases, a configuration in which the module 214 is accommodated in the 200 is employed (see Japanese Patent Application Laid-Open No. 2004-14317 and FIG. 1).

[0003] The modularized battery is a battery that is assembled into a battery by electrically connecting a plurality of modules 214, and finally obtains the required voltage value. It is stored in the case 300 and handled (see Fig. 2).

Disclosure of the invention

[0004] When housed in a box-shaped module housing that covers a battery, the rigidity of the housing itself is low in a box-shaped housing surrounded by a simple plane. For this reason, a method is generally adopted in which a rib is provided on the wall surface of the casing to increase rigidity. On the other hand, since the battery generates heat, if a force rib that needs to introduce cooling air into the case is provided on the inner wall surface of the case, the flow of the cooling air is obstructed and the desired cooling characteristics can be obtained. It may not be possible. Therefore, it is preferable for the flow of the cooling air to add a smooth plate member covering the ribs so as not to obstruct the flow of the cooling air to the wall surface of the module casing. The configuration in which the ribbed wall surface is covered with a smoother wall surface increases the rigidity and does not hinder the flow of cooling air, but increases the weight and costs. In addition, if the module case with a structure in which the ribbed wall surface is covered with a smoother wall surface in a limited space in the assembled battery case, the cross section of the cooling air flow path is narrowed, and eventually Therefore, it may be difficult to obtain good cooling characteristics. [0005] On the other hand, in order to secure a cooling channel cross section, a method in which a battery is directly mounted on an assembled battery casing without using a module casing is cumbersome when mounting a plurality of batteries. End up.

[0006] Therefore, an object of the present invention is to provide a module housing and a battery pack housing that house a plurality of film-clad electrical devices that have high rigidity, good cooling characteristics, and light weight.

[0007] To achieve the above object, the module housing of the present invention accommodates and laminates a film-covered electrical device in which a chargeable / dischargeable electrical device element is covered with a film, thereby forming an electrical device element. In a module housing for holding a module formed by stacking a plurality of film-covered electrical device cases in which openings for supplying cooling air are formed in corresponding portions, and electrically connecting each film-covered electrical device,

A frame-shaped support portion that supports the module and a cooling duct that forms a cooling path communicating with the opening of each film-covered electrical device case are provided in a body.

[0008] The module housing of the present invention configured as described above has a configuration in which a cooling duct for cooling the film-covered electrical device is integrally provided on a frame-shaped support portion that holds the module. Therefore, the cooling duct can function not only as a cooling air flow path but also as a rigid member. As a result, the module casing of the present invention can ensure high rigidity as compared with a configuration in which the cooling duct and the support portion are provided separately from each other instead of the body. In the module housing of the present invention, the rigidity of the cooling duct itself is enhanced by providing the support portion integrally. In other words, the module housing of the present invention does not require ribs or the like to be provided on the duct wall surface, so that the ribs obstruct the flow of the cooling air in the duct without reducing the cross section of the flow path of the dirt. There is no such thing. Therefore, the module housing of the present invention can improve the cooling characteristics as compared with the structure in which the rib is provided on the inner wall of the duct and the rigidity is increased. Further, since the module housing of the present invention does not require a rib, it is not necessary to provide a current plate to cover the rib, and thus the weight is light. Furthermore, since the support portion has a frame shape and is not a box shape covering the entire module, it is lighter than a box shape. [0009] Further, in the module housing according to the present invention, the support portion has a holding surface for holding the module, and a frame-shaped side surface portion rising from the holding surface, and the cooling duct includes a duct bottom surface, a duct It has a duct side surface rising from the bottom surface and an opening for introducing cooling air into the film-clad electrical device, and is formed so that the duct side surface portion and the holding surface are continuously connected to each other. A cooling duct may be provided integrally.

[0010] The module housing of the present invention may have a force of one of the side portions of the support portion and a detachable L-shaped fixture force. In the module housing of the present invention, the end portion of the side surface portion other than the fixing device and the side surface portion facing the fixing device has a bent portion, and the bent portion is formed in the film-covered electrical device case. It may be configured to fit into the groove. By adopting a configuration in which the bent portion is fitted in the groove, it is possible to prevent the module from coming off from the module housing. In addition, since the module housing of the present invention is an L-shaped fixture that can be attached and detached at one of the side portions, the module is more tightly clamped by adjusting the mounting condition of the fixture. be able to.

[0011] The module housing of the present invention is a module formed by laminating a plurality of film-covered electrical device cases for storing film-covered electrical devices in which chargeable / dischargeable electrical device elements are covered with a film. In the module housing to hold,

A support portion having a holding surface for holding the module, a frame-shaped side portion rising from the holding surface, a duct bottom surface, a duct side surface rising from the duct bottom surface, and an opening for introducing cooling air are formed. A first casing in which the cooling duct is integrally provided on the support so that the duct side surface portion and the holding surface are continuously connected to each other, and the first casing The first housing and the second housing in a state where the module is sandwiched between the second housing having the same structure as the first housing and the holding surface of the first housing and the holding surface of the second housing. And a joining member that joins the body.

[0012] The module casing of the present invention having the above-described configuration is configured to sandwich the module by sandwiching the module between the first and second casings having the same shape and joining them with a joining member. The module housing of the present invention having such a structure is provided with the first casing and the second casing in addition to the high rigidity by the integrated cooling duct, light weight and improved cooling characteristics. Since the body is the same part, it is advantageous in terms of cost.

[0013] The assembled battery casing of the present invention is an assembled battery casing using the module casing of the present invention, and a plurality of module casings supporting the module are joined to the support portion. The duct arranged on the side facing the yule casing is joined by a joining member.

[0014] The module housing of the present invention can have high rigidity because the cooling duct functions as a rigid member by integrally providing the cooling duct on the frame-shaped support portion. In addition, the cooling duct of the module casing of the present invention is not configured to have a rib to increase rigidity, and therefore, good cooling characteristics can be obtained without impeding the flow of cooling air. Furthermore, since the cooling duct of the module housing of the present invention does not require a rib, the support portion that does not need to be provided with a rectifying plate that covers the rib has a frame shape and is not a box shape that covers the entire module. Light weight is possible.

Brief Description of Drawings

FIG. 1 is a perspective view showing an example of a conventional module.

FIG. 2 is a perspective view showing an example of a conventional assembled battery.

FIG. 3 is an external perspective view of an example of a film-clad battery according to the first embodiment of the present invention.

FIG. 4 is an external perspective view of an example of a module configured by stacking film-clad batteries housed in a cell case.

FIG. 5A is a perspective view of the module housing of the first exemplary embodiment of the present invention attached to the module.

FIG. 5B is a diagram showing a method of assembling the module housing to the module.

FIG. 6 is a view showing a state in which an upper cooling duct is further attached to each module attached to each module housing of the first embodiment of the present invention.

FIG. 7 is a diagram for explaining assembly of a module housing according to a second embodiment of the present invention.

FIG. 8 is an external perspective view showing a state in which the module housing of the second embodiment of the present invention is assembled to the module.

FIG. 9A is a perspective view illustrating joining of module housings.

FIG. 9B is an enlarged view of part A shown in FIG. 9A. BEST MODE FOR CARRYING OUT THE INVENTION

[0016] (First embodiment)

[Configuration of film-clad battery]

FIG. 3 shows an external perspective view of the film-clad battery of this embodiment.

[0017] The film-clad battery 1 of the present embodiment includes a power generation element 2 having a positive electrode side active electrode, a negative electrode side active electrode, and an electrolyte solution (not shown), a metal film such as aluminum, and a heat fusion resin. It has a structure in which a laminated film 7 formed by superimposing the film is heat-sealed on the four sides of the heat-sealing portion 7a and sealed.

[0018] The power generation element 2 of the film-clad battery 1 may be a laminated type composed of a positive electrode side active electrode and a negative electrode side active electrode laminated via a separator (not shown). Alternatively, in the power generation element 2, the belt-like positive electrode side active electrode and the negative electrode side active electrode are stacked via a separator, wound, and then compressed into a flat shape, whereby the positive electrode side active electrode and the negative electrode side active electrode are It may be a wound type with an alternately stacked structure.

[0019] Further, as the power generation element 2, any power generation element used in a normal battery can be applied as long as it includes a positive electrode, a negative electrode, and an electrolyte. A power generation element in a general lithium ion secondary battery is composed of a positive electrode plate coated with a positive electrode active material such as lithium manganese oxide and lithium cobaltate on both sides of an aluminum foil and the like, and doped with lithium. It is formed by facing a negative electrode plate, such as a copper foil, coated on both sides, such as a copper foil, through a separator, and impregnating it with an electrolyte containing a lithium salt. Examples of the power generation element 2 include power generation elements of other types of chemical batteries such as a nickel metal hydride battery, a nickel cadmium battery, a lithium metal primary battery or a secondary battery, and a lithium polymer battery. Furthermore, the present invention relates to an electric device capable of accumulating electric energy inside and generating gas by a chemical reaction or a physical reaction, such as a capacitor element exemplified by a capacitor such as an electric double layer capacitor or an electrolytic capacitor. It can also be applied to electrical devices in which the elements are sealed with an exterior film.

[0020] The film-clad battery 1 has a positive electrode terminal 3 connected to the positive active electrode and a negative electrode terminal 4 connected to the negative active electrode facing each other from the heat-sealing portion 7a in the short direction. It is extended. Aluminum is often used as the positive electrode terminal 3. Ma As the negative electrode terminal 4, copper or nickel is often used due to its electrical characteristics. Hereinafter, the positive electrode terminal 3 and the negative electrode terminal 4 may be collectively referred to as electrodes.

A plurality of film-clad batteries 1 are stacked and modularized while being housed in a cell case 10 shown in FIG.

The cell case 10 surrounding the film-clad battery 1 sandwiches the heat-sealing part 7a of the film-clad battery 1. The cell case 10 has a frame shape, and an opening 15 is formed at a location corresponding to the power generation element 2. A groove 11 is formed in the short direction of the cell case 10. By stacking the cell cases into the module 14, each groove 11 forms a positioning slit 12 extending in the stacking direction. The positioning slit 12 is for inserting a bent end 41 of a module housing 20 described later. Further, an opening 16 for allowing cooling air to cool the power generation element 2 is formed on the long surface 10a side of the cell case 10.

[Module enclosure]

FIG. 5A shows a perspective view of the module housing of this embodiment attached to the module, and FIG. 5B shows a method for assembling the module housing to the module. In FIG. 5, the cell case 10 and the film-clad battery 1 are shown in a simplified manner.

The module housing 20 includes a support portion 40 that supports the module 14 and a cooling duct 30 that flows cooling air that cools the module 14.

[0024] The support unit 40 includes a holding surface 42 that holds both ends of the cell case 10 in the longitudinal direction, a side surface 43 that also rises one end force of the holding surface 42, a bent end 41 that is a bent end portion of the side surface 43, The module has an abutting portion 44 for abutting and fixing the module 14 assembled in the module housing 20, and an L-shaped fixing bracket 45 for fixing the module 14 with a side force opposed to the abutting portion 44.

[0025] The holding surface 42, the side surface 43, and the bent end 41 are formed so as to face both sides of the abutting portion 44, and are formed into a frame shape by assembling the fixing bracket 45. That is, in the present embodiment, the support portion 40 includes two holding surfaces 42, three side surfaces 43, and a fixing bracket 45. It becomes a frame shape consisting of the side part including.

The cooling duct 30 is integrally provided at the lower part of the support portion 40. The cooling duct 30 is provided below the abutting portion 44, a duct side surface 31 continuously extending downward from the other end of each holding surface 42 of the support portion 40, a duct bottom surface 32 connecting each duct side surface 31, and the abutting portion 44. The duct end surface 33 has an opening 34 formed on the side facing the duct end surface 33. The width between the duct side surfaces 31 is narrower by the holding surface 42 than the width between the side surfaces 43 of the support portion 40. The duct side surface in the cooling duct 30 includes two duct side surfaces 31 and one duct end surface 33. The abutting portion 44 of the support portion 40 and the duct end surface 33 of the cooling duct 30 may be configured as a single continuous plate, but the holding surface 42 is provided between the abutting portion 44 and the duct end surface 33. It is possible to use a staircase shape that is formed, and a shape with increased rigidity!ヽ.

The module housing 20 has an opening on the side facing the duct bottom surface 32, and an opening 34 for introducing cooling air into the cooling duct 30 is formed. However, the module housing 20 of the present embodiment has a cross-sectional shape formed by bending the side surface 43, the holding surface 42, and the duct side surface 31, and each side surface 43 is connected to each other by the abutment portion 44. The side surface 31 has high rigidity by being connected to each other at the duct bottom surface 32 and the duct end surface 33. That is, the cooling duct 30 functions as a rigid member for increasing the rigidity of the support portion 40 in addition to the function of passing cooling air. Furthermore, the module housing 20 has a high rigidity because it has a frame shape with the fixing bracket 45 also functioning as a reinforcing member. The module housing 20 can be further enhanced in rigidity by adding a reinforcing member to each corner or the like, or bending the end.

Next, assembly of the module 14 to the module housing 20 will be described.

[0029] As shown in FIG. 5B, the module 14 is inserted so that the side force in which the opening 34 of the module housing 20 is formed also aligns the positioning slit 12 with the bending end 41 in the direction of arrow A.

[0030] The module 14 inserted into the module housing 20 is slid on the holding surface 42 of the support 40 and the longitudinal surface 10a of the cell case 10 until the first module end surface 14a hits the abutting portion 44. Make it.

[0031] With the abutting portion 44 abutting against the first module end surface 14a, the opening 34 side, that is, In other words, the fixing bracket 45 is pressed against the second module end surface 14b from the opposite side of the abutting portion 44 in the direction of arrow a. Finally, the screw hole 42a formed in the holding surface 42 and the screw hole 45a formed in the fixing bracket 45 are aligned, and the module 14 is fixed to the module housing 20 by screwing in the screw. Note that the bending end 41 is inserted into the positioning slit 12 so that the module 14 does not come out in the direction of arrow B in FIG. 5A.

[0032] The module 14 is fixed and held by a module housing 20 that has a longitudinal frame 10a side force frame shape and that uses the cooling duct 30 as a rigid member. That is, since the module housing 20 is not configured to cover the module 14 as a whole, it is lighter than a module case configured to cover the entire module. In addition, since the module housing 20 of the present embodiment has a frame shape in order to increase the rigidity as described above, the module 14 can be fixedly held firmly.

As described above, the module housing 20 of the present embodiment has a configuration in which the cooling duct 30 for cooling the film-clad battery 1 is integrally provided on the frame-shaped support portion 40 that holds the module 14. Therefore, the cooling duct 30 can function not only as a cooling air flow path but also as a rigid member. As a result, the cooling duct and the support portion can be made more rigid as compared to a configuration in which the cooling duct and the support portion are provided separately from each other. Further, the rigidity of the cooling duct 30 itself is enhanced by the provision of the support portion 40. That is, in the module housing 20 of the present embodiment, it is not necessary to provide ribs or the like on the duct wall surface, so that the ribs impede the flow of cooling air in the duct that does not narrow the cross section of the duct. There is nothing. Therefore, the module housing 20 of the present embodiment can improve the cooling characteristics as compared with the structure in which the rib is provided on the inner wall of the duct and the rigidity is increased. Furthermore, since the module housing 20 of the present embodiment does not require a rib, it is not necessary to provide a rectifying plate for covering the rib, and thus the weight is light. Further, since the support portion 40 has a frame shape and is not a box shape that covers the entire module 14, it is lighter than a box shape.

[Battery assembly and cooling method]

Next, an assembled battery configured by connecting a plurality of modules 14 and a method for cooling the assembled battery will be described with reference to FIG. FIG. 6 shows an example in which two modules 14 are connected to form an assembled battery. The module 14 on the left side of the figure is shown with the cell case 10 omitted, and for the module 14 on the right side of the figure, the cell case force extended electrode is connected to the electrode of the adjacent film-clad battery 1. It shows a state.

First, the modules 14 attached to the module housing 20 are arranged, and the module housings 20 are joined to each other. Details of the joining of the module casings 20 will be described later.

[0036] One end of the joint port 50 is attached to the periphery of the joined module case 20, that is, each corner and center. Attach the upper cooling duct 60 to the other end of the connecting rod 50. As a result, an assembled battery case is formed in which the lower side of each module case 20 formed into an assembled battery is covered with the module case 20 and the upper side is covered with the upper cooling duct 60. To join the upper cooling duct 60 and the module housing 20 with the joining rod 50, screw holes are provided at both ends of the joint port 50, and the upper cooling duct 60 and the module are screwed using these screw holes. The case 20 may be screwed.

[0037] The cooling air cooling path includes a cooling duct 30, an opening 16 between the cell cases 10, an adjacent power generation element 2, and an upper cooling duct 60. The cooling air is introduced from the opening 34, flows through the cooling duct 30, and flows into the opening 16 between the cell cases 10 as indicated by an arrow C in FIG. Cooling air flowing from the opening 16 between the cell cases 10 cools the power generating element 2 of the film-covered battery 1 and inside the upper cooling duct 60 as shown by the arrow D from the opening 16 on the opposite side of the cell case 10 Flows out. Cooling air that has flowed through the upper cooling duct 60 is discharged from a discharge portion 61 provided at an end of the upper cooling duct 60. With the above configuration, the cooling air can efficiently cool the portion of the power generating element 2 that generates the most heat.

[0038] As described above, the configuration in which the module housing 20 and the upper cooling duct 60 are joined by the joining rod 50 and the opening 16 between the cell cases 10 is used does not cover the entire module 14 and the cooling path. Can be configured. The assembled battery case with this configuration is lightweight and has good cooling characteristics.

(Second embodiment) In the embodiment described above, the module case 20 is prepared for each module 14, and the upper cooling duct 60 is prepared for one of the two modules 14. In contrast, in the present embodiment, as shown in FIGS. 7 and 8, a configuration example in which one module housing and one upper cooling duct are prepared for each module will be described.

[0039] The module housing 120 of the present embodiment also includes a support portion 140 that supports the module 14 and a cooling duct 130 that also functions as a rigid member. The configuration is basically the same as 20. However, the module housing 20 of the first embodiment is a system in which the module 14 is slid along the holding surface 42 and is finally fixed by the fixing bracket 45, whereas in the present embodiment, The difference is that the portion corresponding to the fixing bracket 45 of the first embodiment is already provided on the support portion 140 as one of the side surfaces 143. Therefore, the module 14 is attached to the module housing 120 by inserting it in the direction of arrow E in FIG.

[0040] In the first embodiment, the module housing 20 is attached to the lower part of each of the two modules 14, and the upper cooling duct 60 is covered with the two modules 14. On the other hand, in the present embodiment, one module housing 120 is attached to the lower part of one module 14, and one module housing 120 having the same shape as the module housing 120 attached to the lower part is attached to this module 14. It is set to cover. In other words, in the present embodiment, the module 14 is sandwiched between the module housings 120 having the same shape, and the corners of the two module housings 120 are joined by the joining rods 50.

[0041] Due to such a configuration, in the present embodiment, a cooling path can be formed for each module 14, and the module 14 has a strong force in the module casing 120 whose rigidity is increased in the vertical direction. The module 14 is easy to handle.

In addition, this embodiment is advantageous in terms of cost because the two module housings 120 are parts having the same shape.

[0043] The module housing 120 of the present embodiment also has high rigidity, light weight, and good cooling characteristics, like the module housing 20 of the first embodiment. [Bonding module housings]

Next, joining of module housings will be described with reference to FIGS. 9A and 9B. In addition, the code | symbol used for description uses the code | symbol used in 1st Embodiment.

In FIG. 9A, two module housings 20a and 20b are joined. The module casing 20b is provided with a duct end face 30. The module casing 20a is not provided with a duct end face 30 and is open. That is, the module housing 20a has an opening 34 and an opening formed on the side facing the opening 34. Due to such a configuration, the module casings 20a and 20b are joined, whereby the cooling duct 30 of the module casing 20a and the cooling duct 30 of the module casing 20b communicate with each other.

A joint flange 20c is formed in each of the opening 34 of the module casing 20b and the opening facing the opening 34 of the module casing 20a. Referring to FIG. 9B, which is an enlarged view of the portion indicated by A in FIG. 9A, the module housings 20a and 20b are joined to each other by screws or rivets facing each other between the joining flanges 20c.

Furthermore, when the module casings 20a and 20b on which the module 14 is mounted are covered with the canopy 70, the cover 70 and the module casings 20a and 20b are joined with screws or rivets. That is, a plurality of joint holes 71 are formed at the lower end of the cover 70, and the joint holes 43a are also formed on the side surfaces 43 of the module housings 20a and 20b at positions corresponding to the joint holes 71 of the cover 70. After these are aligned, the cover 70 and the module casings 20a and 20b are joined by passing through screws or rivets.

[0047] As described above, not only the module casings 20a and 20b are directly bonded to each other, but also the cover 70 is bonded to ensure more reliable bonding.

[0048] When the cover 70 is not used, the upper cooling duct 60 is used instead of the cover 70.

[0049] At both end portions of the upper cooling duct 60, flanges 6 Oa having a plurality of joint holes 60b are provided. Also, holes corresponding to the joint holes 60b are provided in the module housings 20a and 20b (not shown). By joining the joint hole 60b of the upper cooling duct 60 and the hole of the module housing 20a, 20b with the joint rod 50, the module housing 20a, 20b The coupling between the two can be made more reliable.

Claims

The scope of the claims

[1] Film in which an opening capable of supplying cooling air is formed in a portion corresponding to the electric device element by storing and laminating a film-covered electric device in which a chargeable / dischargeable electric device element is covered with a film In a module housing for holding a module in which a plurality of cases for exterior electrical devices are stacked and each film exterior electrical device is electrically connected,

A module comprising: a frame-shaped support portion that supports the module; and a cooling duct that forms a cooling path that communicates with the opening of each film-covered electrical device case. Enclosure.

[2] The support portion includes a holding surface for holding the module, and a frame-shaped side portion that stands up from the holding surface,

The cooling duct has a duct bottom surface, a duct side surface portion rising from the duct bottom surface, and an opening for introducing cooling air into the film-covered electrical device,

The module casing according to claim 1, wherein the cooling duct is integrally provided in the support portion by forming the duct side surface portion and the holding surface so as to be continuously connected. .

[3] The module housing according to [2], wherein one of the side surface portions of the support portion includes a detachable L-shaped fixture.

[4] An end of the side surface portion other than the side surface portion at a position facing the fixing device and the fixing device has a bending portion, and the bending portion is formed in the film-covered electrical device case. The module housing according to claim 3, which fits into the housing.

[5] In a module housing for holding a module formed by stacking a plurality of cases for film-covered electrical devices that store film-covered electrical devices in which chargeable / dischargeable electrical device elements are covered with a film,

A supporting portion having a holding surface for holding the module; a frame-shaped side portion rising from the holding surface; a duct bottom surface; a duct side surface rising from the duct bottom surface; and an opening for introducing cooling air. A cooling duct formed on the support portion, the duct side surface portion and the holding surface being continuously connected to each other. A first housing integrally provided with a duct;

A second housing having the same structure as the first housing;

In a state where the module is sandwiched between the holding surface of the first housing and the holding surface of the second housing, the first housing and the second housing are A module housing having a joining member to be joined.

A battery pack case using the module case according to claim 1,

An assembled battery housing in which a plurality of module housings supporting the module are joined to the support portion, and a duct arranged on the side facing each module housing is joined by a joining member.