Battery pack

Abstract

To reduce variations in a distance between the bottom surface of a battery stack composed of a plurality of battery cells connected to each other and the bottom surface of a case for housing the battery stack in a battery pack including the battery stack and the case.SOLUTION: A battery stack 12 is fastened to a case 14 with a bolt 26. A regulating member that regulates the volume of a space formed between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 to a threshold value or less is used. The regulating member is a spring 30 mounted on the bolt 26. The battery stack 12 is fastened to the case 14 with the bolt 26 via the spring 30.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a battery pack including a plurality of battery cells connected to each other. [Background technology]

[0002] A known battery pack installed in vehicles such as hybrid vehicles and electric vehicles includes a battery stack made up of multiple battery cells connected to each other, a case that houses the battery stack, and a cooler that is installed on the bottom of the case and cools the battery cells. Patent Document 1 describes such a battery pack. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-067737 Summary of the Invention [Problem to be solved by the invention]

[0004] When multiple battery cells are connected to each other to form a battery stack, the arrangement of the multiple battery cells may be curved, causing the bottom surface of the battery stack to have a convex shape toward the top of the battery stack. If the degree of curvature differs among the battery packs, the distance between the bottom surface of the battery stack and the bottom surface of the case will vary among the battery packs, resulting in variations in the cooling effect of the cooler on the battery cells.

[0005] The object of the present disclosure is to reduce the variation in the distance between the bottom surface of a battery stack and the bottom surface of a case between battery packs that include a battery stack composed of multiple battery cells connected to each other and a case that houses the battery stack. [Means for solving the problem]

[0006] One aspect of the present disclosure is a battery pack comprising: a battery stack composed of a plurality of battery cells connected to each other; a case that houses the battery stack; and a regulating member that regulates the volume of a space formed between a bottom surface of the battery stack and a bottom surface of the case that faces the bottom surface of the battery stack to a threshold value or less.

[0007] The above configuration can reduce the variation in the distance between the bottom of the battery stack and the bottom of the case between battery packs. In battery packs in which a cooler that cools the battery cells is installed at the bottom of the case, variation in the distance can cause variation in the cooling effect on the battery cells between battery packs. By reducing the variation in the distance with the above configuration, it is possible to reduce the variation in the cooling effect on the battery cells between battery packs.

[0008] The battery pack may further include a fastening member that fastens the battery stack to the case, the regulating member being a spring installed in the fastening member, and the fastening member fastening the battery stack to the case via the spring.

[0009] The restricting member may be on the bottom surface of the case and have a convex shape facing the bottom surface of the battery stack. [Effects of the Invention]

[0010] According to the battery pack according to the present disclosure, it is possible to reduce the variation in the distance between the bottom surface of the battery stack and the bottom surface of the case between battery packs. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a view of the battery stack according to the first embodiment as viewed from the Z direction. [Figure 2] FIG. 2 is a view of the battery stack according to the first embodiment as viewed from the Y direction. [Figure 3] 1 is a cross-sectional view of a battery pack according to a first embodiment taken along an XZ plane. [Figure 4] FIG. 2 is a view of a portion of the battery stack according to the first embodiment, viewed from the Y direction. [Figure 5] 10 is a graph showing the relationship between a displacement amount A and a fastening torque. [Figure 6] 1 is a cross-sectional view of a battery pack according to a first embodiment taken along an XZ plane. [Figure 7] FIG. 10 is a cross-sectional view of the case according to the second embodiment when cut along the XZ plane. [Figure 8] 10 is a table showing the correspondence relationship between the amount of displacement A and the height of the bottom surface of the case. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment The battery pack according to the first embodiment will be described below with reference to the drawings. In the following description, the stacking direction of the battery cells 18 is referred to as the "X direction," the width direction of the battery cells 18 as the "Y direction," and the direction perpendicular to the X and Y directions as the "Z direction." FIG. 1 is a view of the battery stack 12 as seen from the Z direction. FIG. 2 is a view of the battery stack 12 as seen from the Y direction. FIG. 3 is a cross-sectional view of the battery pack 10 cut along the XZ plane. FIG. 4 is a view of a portion of the battery stack as seen from the Y direction.

[0013] The battery pack 10 is mounted on a vehicle such as an electric vehicle or a hybrid vehicle. The battery pack 10 includes a battery stack 12, a case 14 that houses the battery stack 12, and a bracket 16 that fixes the battery stack to the case 14.

[0014] The battery stack 12 includes a plurality of battery cells 18, a plurality of spacers 20, and end plates 22, 24. The battery cells 18 and the spacers 20 are alternately stacked, with the end plate 22 disposed on one side of the stacking direction (X direction) and the end plate 24 disposed on the other side. The plurality of battery cells 18 and the plurality of spacers 20 are constrained in a state where they are pressed in the stacking direction by a plurality of restraining members (not shown) that span between the end plates 22, 24.

[0015] The battery cells 18 are, for example, lithium ion secondary batteries having a rectangular parallelepiped shape. A substantially cylindrical positive electrode terminal 19p and a negative electrode terminal 19n protrude upward (Z direction) from the top surface of each battery cell 18. The positive electrode terminal 19p and the negative electrode terminal 19n are arranged with a gap in the width direction (Y direction). The positive electrode terminal 19p and the negative electrode terminal 19n adjacent to each other in the stacking direction are connected by a bus bar (not shown), thereby electrically connecting the multiple battery cells 18 in series.

[0016] Two brackets 16 are fixed to each of the end plates 22, 24. The brackets 16 are members that fix the battery stack 12 to the case 14. The brackets 16 are made of metal. The brackets 16 are fixed to the upper parts of the end plates 22, 24. The brackets 16 are fixed to the case 14 by bolts 26. The bolts 26 are an example of fastening members.

[0017] The case 14 is made of metal. As shown in FIG. 3 , support portions 28 are installed inside the case 14 at positions corresponding to the brackets 16. Threaded holes having shapes corresponding to the bolts 26 are formed in the support portions 28, and the brackets 16 are fastened to the support portions 28 by fitting the bolts 26 into the threaded holes. In this way, the battery stack 12 is fastened to the case 14. For example, four brackets 16 are used, and the battery stack 12 is fastened to the case 14 at four locations.

[0018] A cooler (not shown) is installed at the bottom of the case 14. The battery cells 18 are cooled by a cooling medium circulating inside the cooler.

[0019] In addition, viscous heat dissipation grease 31 is applied between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14. The heat dissipation grease 31 is made of, for example, a resin such as silicone. The same applies to the second embodiment described later.

[0020] When multiple battery cells 18 and multiple spacers 20 are stacked, as shown in FIG. 4, the bottom surface 12a of the battery stack 12 tends to curve upward (in the Z direction) and become convex upward. For example, a curve with a maximum displacement A occurs. If the displacement A differs between the battery packs 10, the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 varies between the battery packs 10. As a result, the cooling effect on the battery cells 18 by the cooler installed at the bottom of the case 14 varies between the battery packs 10.

[0021] To address this issue, a restricting member is used. The restricting member is a member that restricts the volume of the space formed between the bottom surface of the battery stack 12 and the bottom surface 14a of the case 14 that faces the bottom surface 12a of the battery stack 12 to a predetermined threshold value or less.

[0022] In the first embodiment, the restricting member is a spring 30. As shown in Fig. 3 , the spring 30 is installed around the bolt 26, and the bolt 26 fastens the battery stack 12 to the support portion 28 via the spring 30. Fastening the battery stack 12 to the support portion 28 by the bolt 26 via the spring 30 makes it possible to adjust the force fastening the battery stack 12 to the support portion 28 according to the degree of fastening by the bolt 26. The battery stack 12 is fixed to the case 14 in a state where the fastening force of the bolt 26 and the force of the spring 30 are balanced.

[0023] In the first embodiment, the fastening torque of the bolts 26 is adjusted according to the degree of curvature of the bottom surface 12a of the battery stack 12. Specifically, the fastening torque of the bolts 26 is adjusted according to the displacement amount A. For example, as shown in FIG. 5, the greater the displacement amount A, the greater the fastening torque of the bolts 26. Fastening with the bolts 26 presses the entire battery stack 12 against the bottom surface 14a of the case 14. The greater the fastening torque, the greater the pressing amount.

[0024] By increasing the fastening torque for battery packs 10 with a large displacement amount A and decreasing the fastening torque for battery packs 10 with a small displacement amount A, it is possible to reduce the variation in the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 between battery packs 10.

[0025] 6 shows an example of the displacement amount A. Reference numeral 32 indicates the bottom surface 12a of the battery stack 12 when the displacement amount A is 0.5 mm. Reference numeral 34 indicates the bottom surface 12a when the displacement amount A is 0.1 mm.

[0026] By making the fastening torque when the displacement A is 0.5 mm larger than the fastening torque when the displacement A is 0.1 mm, the entire battery stack 12 when the displacement A is 0.5 mm is pressed closer to the bottom surface 14a of the case 14 than the entire battery stack 12 when the displacement A is 0.1 mm. This reduces the difference between the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 when the displacement A is 0.5 mm and the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 when the displacement A is 0.1 mm. This reduces the variation in the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 among the battery packs 10. As a result, the variation in the cooling effect among the battery packs 10 can be reduced.

[0027] Note that thermal grease 31 is applied between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14, so that the bottom surface 12a of the battery stack 12 does not directly contact the bottom surface 14a of the case 14, but contacts the top surface of the layer of thermal grease 31. The amount by which the bottom surface 12a of the battery stack 12 sinks into the layer of thermal grease 31 changes depending on the magnitude of the fastening torque (i.e., the amount by which the bottom surface 12a of the battery stack 12 penetrates into the layer of thermal grease 31 changes), so the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 changes. The layer of thermal grease 31 has a thickness that is sufficient to eliminate variations in the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 among battery packs 10.

[0028] 6, the bottom surface 14a of the case 14 may have a convex shape facing the bottom surface 12a of the battery stack 12. For example, the bottom surface 12a is formed so that the apex of the convex shape is located at a position corresponding to the center of the stacking direction of the battery cells 18. As an example, the height of the apex is about 0.2 mm.

[0029] The following describes the procedure for housing the battery stack 12 in the case 14. For example, the height of each position on the bottom surface 12a of the battery stack 12 is measured by a measuring device. Specifically, the head of a laser displacement meter, which is an example of a measuring device, is scanned from end plate 22 to end plate 24 to measure the height of each position on the bottom surface 12a of the battery stack 12 and calculate the maximum displacement amount A. The measurement result (e.g., displacement amount A) is output from the laser displacement meter to a torque indicator. The torque indicator determines the value of the fastening torque corresponding to the displacement amount A by referring to the graph shown in FIG. 5 and outputs the value. The bolts 26 are fastened in accordance with the fastening torque value. This reduces the variation in the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 among the battery packs 10, thereby reducing the variation in the cooling effect among the battery packs 10.

[0030] Second Embodiment The second embodiment will be described below with reference to Fig. 7. Fig. 7 is a cross-sectional view showing a case 14 according to the second embodiment.

[0031] In the second embodiment, the restricting member is the bottom surface 14a of the case 14, and has a convex shape facing the bottom surface 12a of the battery stack 12.

[0032] A plurality of cases 14 having bottom surfaces 14a with different heights of the apex thereof are prepared in advance, and when the battery stack 12 is assembled to the cases 14, a case 14 having a bottom surface 14a with a height corresponding to the displacement amount A is selected, and the battery stack 12 is housed in the selected case 14.

[0033] 7, three levels (large upward convexity, medium upward convexity, and small upward convexity) are shown for the height of the apex of the bottom surface 14a, and one of the three levels is selected according to the displacement amount A. Reference numeral 36 indicates a bottom surface 14a with a large upward convexity, reference numeral 38 indicates a bottom surface 14a with a medium upward convexity, and reference numeral 40 indicates a bottom surface 14a with a small upward convexity.

[0034] 8 shows the correspondence relationship between the displacement amount A of the bottom surface 12a of the battery stack 12 and the level of the bottom surface 14a of the case 14. For example, if the displacement amount A is 0.4 mm or more and less than 0.8 mm, the case 14 having the bottom surface 14a with a peak height of 0.6 mm (case 14 of level 1) is selected. If the displacement amount A is 0.1 mm or more and less than 0.4 mm, the case 14 having the bottom surface 14a with a peak height of 0.25 mm (case 14 of level 2) is selected. If the displacement amount A is 0 mm or more and less than 0.1 mm, the case 14 having the bottom surface 14a with a peak height of 0.05 mm (case 14 of level 3) is selected.

[0035] As in the first embodiment, a measuring device such as a laser displacement meter measures the height of each position on the bottom surface 12a of the battery stack 12, and calculates the maximum displacement amount A. The measurement result is output from the laser displacement meter to a case level indicating device. The case level indicating device selects a level corresponding to the displacement amount A by referring to the correspondence shown in FIG. 7 and outputs that level. A case 14 having a bottom surface 14a with a height corresponding to that level is selected, and the battery stack 12 is housed in the selected case 14. This reduces the variation in the distance between the bottom surface 12a of the battery stack 12 and the bottom surface 14a of the case 14 among the battery packs 10, and as a result, the variation in the cooling effect among the battery packs 10 can be reduced. [Explanation of symbols]

[0036] 10 battery packs, 12 battery stacks, 14 cases, 18 battery cells, 30 springs.

Claims

1. a battery stack formed by a plurality of battery cells connected to each other; a case that houses the battery stack; a heat dissipation grease interposed between a bottom surface of the battery stack and a bottom surface of the case facing the bottom surface of the battery stack; a restricting member that restricts the volume of a space formed between a bottom surface of the battery stack and a bottom surface of the case facing the bottom surface of the battery stack to a threshold value or less; a fastening member that fastens the battery stack to the case; and the restricting member is a spring installed in the fastening member, the fastening member fastens the battery stack to the case via the spring; The amount of the battery stack that sinks into the thermal grease varies depending on the fastening torque of the fastening member. A battery pack characterized by:

2. The bottom surface of the battery stack is not in direct contact with the bottom surface of the case.

2. The battery pack according to claim 1, wherein the battery pack is a battery pack having a plurality of electrodes.

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