Battery case

This application is a Section 371 National Stage Application of International Application No. PCT/JP2013/084863, filed Dec. 26, 2013, published as WO 2014/109243 A1 on Jul. 17, 2014, not in English, which is based on and claims the benefit of Japanese Patent Application No. 2013-003725, filed Jan. 11, 2013 in the Japan Patent Office, the contents of which are incorporated herein by reference in their entireties.

The present invention relates to a battery case.

An electric vehicle (EV), a plug-in hybrid vehicle (PHV), or the like includes, under its floor, a battery case to house a battery (see Patent Document 1).

Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-23230

Problems to be Solved by the Invention

The above-mentioned battery case involves a problem that its reinforcement structure against external impact tends to lead to weight increase.

In one aspect of the present invention, it is desirable to enhance weight reduction of a battery case.

Means for Solving the Problems

A battery case in one aspect of the present invention comprises a first casing member, a second casing member to form a closed space together with the first casing member, a foam material provided along an inner wall surface of the closed space, and a reinforcing member provided in the closed space so as to hold the foam material between the reinforcing member and the inner wall surface. According to such configuration, use of the foam material enables simplification of the reinforcing member, leading to achievement of weight reduction.

In the above configuration, the reinforcing member may be formed by hot stamping.

FIG. 1 is a perspective view of a battery case.

FIG. 2 is a sectional view taken along a line II-II of FIG. 1 .

FIG. 3 is a view showing an example of a mounting position of a battery case in an automobile.

FIG. 4 is a partial sectional view of a conventional battery case.

FIG. 5A is a diagram showing numerical examples of widths of reinforcing members.

FIG. 5B is a diagram showing numerical examples of battery mounting spaces.

FIG. 5C is a diagram showing numerical examples of full plastic moments.

FIG. 5D is a diagram showing numerical examples of masses.

FIG. 6 is a graph showing a relationship between a displacement amount and a load.

FIG. 7 is a sectional view of a modified example of the battery case.

1 . . . battery case, 2 . . . lower case, 3 . . . upper case, 4 . . . reinforcing member, 5 . . . resin foam material, 6 . . . sealing material, 7 . . . resin foam material, 9 . . . automobile, 21 . . . flange, 31 . . . flange, 41 . . . first plate portion, 42 . . . second plate portion, 43 . . . third plate portion, 44 . . . fourth plate portion

Hereinafter, a description will be given of an embodiment, to which the present invention is applied, with reference to the drawings.

FIG. 1 is a perspective view of a battery case 1 of the embodiment, FIG. 2 is a sectional view taken along a line II-II of FIG. 1 . As shown in FIG. 3 , for example, the battery case 1 is disposed under the floor of an automobile 9 , such as an electric vehicle (EV) and a plug-in hybrid vehicle (PHV). The battery case 1 comprises a lower case 2 , an upper case 3 , a reinforcing member 4 , and a resin foam material 5 .

Each of the lower case 2 and the upper case 3 is a member obtained by processing a metal material (a 270 material having a sheet thickness of 0.7 mm in this example), the member is formed in a container shape having a recessed portion in the center thereof and a generally rectangular bottom surface of the recessed portion. The lower case 2 and the upper case 3 are arranged such that their respective recessed sides face each other, to thereby form therein a generally rectangular parallelepiped housing space (a closed space) to house and seal a battery. The lower case 2 is shaped to have a depth larger than a depth of the upper case 3 , and the upper case 3 serves as a lid of the lower case 2 . The value “270” of the 270 material represents a tensile strength (a lower limit) of a material. The same is applicable to a later mentioned 590 material.

A flange 21 is formed at an outer periphery of the lower case 2 . In a similar manner, a flange 31 is formed at an outer periphery of the upper case 3 . The flanges 21 and 31 have corresponding shapes; the lower case 2 and the upper case 3 are assembled such that their respective flanges 21 and 31 overlap each other. A sealing material 6 is provided between the flanges 21 and 31 . The flanges 21 and 31 serve as a vehicle attachment portion to attach the battery case 1 to the automobile.

The reinforcing member 4 is formed by hot stamping of a metal material (an iron sheet having a thickness of 2.0 mm in this example). Hot stamping is a processing method of a combination of press molding and heat treatment (quenching and tempering) performed using a steel sheet. Through hot stamping, in which a steel sheet is first heated and then quickly cooled concurrently with molding using a die to form a desired shape, it is possible to quench the molded steel sheet to achieve improved strength.

The reinforcing member 4 is formed in a rectangular annular shape (a frame-like shape) so as to be located along an inner side surface of the lower case 2 . Specifically, the reinforcing member 4 comprises a first plate portion 41 , a second plate portion 42 , a third plate portion 43 , and a fourth plate portion 44 . The first plate portion 41 is welded to a bottom surface of the lower case 2 . The second plate portion 42 faces the inner side surface of the lower case 2 with a specified distance D 1 (for example, 30 mm) therebetween. The third plate portion 43 faces the bottom surface of the lower case 2 with a specified distance D 2 therebetween. The fourth plate portion 44 is welded to the inner side surface of the lower case 2 .

The resin foam material 5 , which is a high-rigidity foam filler to be filled in a closed space to thereby provide rigid foam, is filled in a space formed between the lower case 2 and the reinforcing member 4 . That is, the resin foam material 5 is formed in a rectangular annular shape (a frame-like shape) so as to be located along an inner wall surface (the bottom surface and the inner side surface) of the lower case 2 .

According to the embodiment detailed as above, the following effects can be obtained.

The battery case 1 comprises the lower case 2 , the upper case 3 to form a closed space together with the lower case 2 , the resin foam material 5 provided along the inner wall surface (the inner wall surface of the lower case 2 ), the reinforcing member 4 provided in the closed space so as to hold the resin foam material 5 between the reinforcing member 4 and the inner wall surface of the lower case 2 . According to the present embodiment, since a reinforcing structure using the resin foam material 5 can simplify the reinforcing member 4 , it is possible to achieve reduction in the number of components and size reduction of components, and thus to achieve weight reduction.

A description will be given of effects of the present embodiment in comparison with a conventional structure. A battery case 8 shown in FIG. 4 as a conventional example includes an upper case 81 and a lower case 82 made of the same material (a 270 material having a sheet thickness of 0.7 mm) as the material in the above-described embodiment, a plurality of reinforcing members 83 , 84 , and 85 made of a material (a 590 material having a sheet thickness of 2.0 mm) with higher strength than the material for these cases, and a reinforcing member 86 made of a material (a 590 material having a sheet thickness of 2.3 mm) with further higher strength. The reinforcing members 83 , 84 , 85 , and 86 are provided outside a housing space that is formed by the upper case 81 and the lower case 82 , and sealed with a plurality of sealing materials 87 (provided at four positions in this example). According to a structure to ensure strength only by reinforcing members of sheet metal, as described above, it is required to increase the sheet thicknesses of the reinforcing members and/or to increase the number of components, and thus the numbers of welding areas and sealing areas are more likely to be increased. Increase in the numbers of welding areas and sealing areas will lead to weight increase and/or deterioration in waterproof performance.

In contrast, according to the structure of the present embodiment, in which the reinforcing member 4 with high strength that is formed by hot stamping is provided in the housing space, it is possible to reduce the number of components to thereby reduce the number of sealing areas (for example, to only one area). Also, consideration on a filling shape of the resin foam material will lead to improved shape retainability of a sectional shape, which will further lead to improved load sharing ability of each of the components. As a result, size reduction and weight reduction may be achieved, and improved waterproof performance may be achieved. For example, a width D 3 of the reinforcing member needs to be 40 mm or more according to the conventional structure shown in FIG. 4 , in order to obtain a specified reinforcing effect in the battery case. On the other hand, according to the structure of the present embodiment shown in FIG. 2 , a width D 1 of the reinforcing member may be reduced to 30 mm ( FIG. 5A ). In a case where an outermost shape of the battery case is L1000 mm×<W900 mm, and the width of the flange 83 and the width of flange 31 are both 40 mm, a width dimension that can be used to mount a battery is 740 mm according to the conventional structure shown in FIG. 4 , whereas the width dimension may be 760 mm according to the structure of the present embodiment shown in FIG. 2 ( FIG. 5B ). That is, the structure of the present embodiment allows a larger housing space of the battery case than the conventional structure.

The lower case 2 , which is made of thin sheet metal, is weak against load; however, in the present embodiment, the resin foam material 5 is filled between the lower case 2 and the reinforcing member 4 to thereby increase the sectional strength by almost 50%, while controlling the filling amount to 40% by considering the filling shape ( FIG. 6 ). In this case, the full plastic moment was confirmed to be 3.8 [kN·m] in a state without filling; the full plastic moment will be 5.5 [kN·m] on an assumption of an improvement of 145% as compared with the state without filling of resin (the state where the resin foam material 5 is not filled), and thus it is expected that a strength almost equal to that of the conventional configuration can be obtained ( FIG. 5C ).

In particular, according to the present embodiment, substantial weight reduction can be achieved. For example, if it is configured such that an outermost shape is L1000 mm×W900 mm and a specified reinforcing effect is achieved in a battery case, the weight of the structure of the present embodiment can be reduced to 24.3 kg, whereas the weight of the conventional structure shown in FIG. 4 is 43.8 kg ( FIG. 5D ).

The lower case 2 corresponds to an example of a first casing member, the upper case 3 corresponds to an example of a second casing member, and the resin foam material 5 corresponds to an example of a foam material.

Although the embodiment of the present invention has been described as above, it is to be understood that the present invention should not be limited to the above-described embodiment, but may be practiced in various forms.

For example, although the resin foam material 5 is exemplified as the foam material in the above-described embodiment, other foam materials may be employed. Also, the shape, the number, or the like, of the foam materials is not particularly limited. Specifically, the foam material may be provided so as to fill the entirety of a fillable space (a space that is formed between the inner wall surface and the reinforcing member in the closed space formed by the first casing member and the second casing member), in which the foam material can be filled. Here, the expression “fill the entirety of a fillable space” is not limited to a strict meaning of leaving no gap, but means a state (for example, a state shown in FIG. 2 ) where the shape of the fillable space and the shape of the foam material correspond to each other, and a space without the foam material is not intentionally formed. On the other hand, the foam material may be provided so as to fill only part of the fillable space (in other words, such that a space without the foam material is formed) as shown in FIG. 7 , for example, or may be provided in plurality. In the example shown in FIG. 7 , a plurality of (three in this example) resin foam materials 7 , each having a circular section (i.e., each having a columnar shape in this example), are housed. Various shapes, such as a shape having a triangular section, a shape having a rectangular section, a shape having a trapezoidal section, etc., may be employed as the shape of the foam material.

Also, although the configuration including the reinforcing member 4 formed by hot stamping is exemplified in the above-described embodiment, this is not a limitation. For example, a configuration without a component formed by hot stamping may be employed, whereas a configuration in which a component formed by hot stamping is used also for the casing member may be employed.

Further, the present invention may be applied to other purposes than battery cases.