Battery case

Abstract

To provide a battery case which can improve an allowable limit value of a binding load on a battery.SOLUTION: A battery case comprises: a frame 20 which presses ends in a battery lamination direction; a cross member 200 disposed toward the battery lamination direction; and a cross bracket 100 coupling the frame 20 to the cross member 200. The cross bracket 100 has: a base part 110 bonded to the frame 20; and a pair of corner bracket parts 120, 120 which extends from the base part 110 so as to sandwich a wall part 210 of the cross member 200 from both sides, and which is bonded to the wall part 210. A cutout 130 is formed at a portion where a surface 122 on the wall part 210 side of each of the pair of corner bracket parts 120, 120 intersects a surface 112 on the wall part 210 side of the base part 110.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a battery case that houses a battery, and in particular to a battery case that is configured to restrain a battery in a stacking direction. [Background technology]

[0002] Vehicle batteries are mounted on a vehicle in a state where they are compressed in the stacking direction of the batteries and a high compressive force is applied to shorten their length. Since the batteries mounted on the vehicle tend to expand in the stacking direction, they need to be restrained in the stacking direction to prevent expansion. Patent Document 1 discloses a technology in which batteries stacked in the vehicle's length direction are housed between a pair of cross members spanning between a rocker panel and a floor panel, and the batteries are restrained by the pair of cross members.

[0003] In the technology described in Patent Document 1, the restraint load received by the cross member from the battery is input to the connection between the cross member and the rocker panel, and the connection between the cross member and the floor panel. The input of the restraint load generates stress at each connection, and depending on the structure of the connection, stress concentration may occur. However, Patent Document 1 does not disclose any ideas for dispersing the stress. If the stress generated by the battery restraint load cannot be effectively distributed, it is difficult to improve the allowable limit of the battery restraint load.

[0004] In addition to Patent Document 1, the following Patent Document 2 can be mentioned as an example of a document showing the state of the art in the technical field related to the present disclosure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-062933 A [Patent Document 2] JP 2008-004289 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a battery case that can improve the allowable limit value of the restraining load of a battery. [Means for solving the problem]

[0007] The battery case of the present disclosure includes a frame that holds down the ends of the batteries in the stacking direction, a cross member arranged in the stacking direction of the batteries, and a cross bracket that connects the frame and the cross member. The cross bracket includes a base portion joined to the frame, and a pair of corner bracket portions extending from the base portion to sandwich a wall portion of the cross member from both sides and joined to the wall portion of the cross member. A notch is provided at the location where the surface of each of the pair of corner bracket portions facing the wall portion of the cross member intersects with the surface of the base portion facing the wall portion of the cross member. The stress applied to the cross bracket by the restraining load of the battery is distributed by the notch.

[0008] In the battery case of the present disclosure, the end of the wall of the cross member may contact the base portion. Since there is no gap between the end of the wall and the base portion, the free running distance during a collision can be reduced.

[0009] In the battery case of the present disclosure, the base portion may have a rectangular shape with both upper ends rounded or a semi-elliptical shape when viewed from the side in the stacking direction of the batteries. The base portion may be welded to the frame by a single weld line connecting one lower end to the other lower end. This makes it possible to minimize the number of weld start ends and end ends when arc welding the cross bracket and the frame, and also makes it possible to perform arc welding by a robot.

[0010] In the battery case of the present disclosure, each of the pair of corner bracket parts may have a rectangular shape with a rounded upper end or a quarter ellipse shape when viewed from the side in a direction perpendicular to the stacking direction of the batteries. Also, each of the pair of corner bracket parts may be welded to the wall part of the cross member by a single weld line connecting the vicinity of the upper notch to the lower end of the tip. This makes it possible to minimize the number of weld start ends and end ends when arc welding the cross bracket and the cross member, and enables arc welding by a robot. Effect of the Invention

[0011] According to the battery case of the present disclosure, the stress applied to the cross bracket by the restraint load of the battery is dispersed by the notches provided at the intersection between the wall side surface of each of the pair of corner bracket parts and the wall side surface of the cross member of the base part, thereby mitigating the stress concentration occurring in the cross bracket and improving the allowable limit value of the restraint load of the battery. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a perspective view showing a battery case according to an embodiment of the present disclosure. [Diagram 2] FIG. 11 is a perspective view showing a connection structure between a side frame and an inner cross by a cross bracket according to an embodiment of the present disclosure. [Diagram 3] FIG. 11 is a plan view showing a connection structure between a side frame and an inner cross by a cross bracket according to an embodiment of the present disclosure. [Figure 4] FIG. 11 is a stress analysis diagram showing a comparison between stress distribution in a cross bracket according to an embodiment of the present disclosure and stress distribution in a cross bracket of a comparative example. [Diagram 5] 11A and 11B are plan views illustrating a cross bracket according to an embodiment of the present disclosure in comparison with a cross bracket of another comparative example. [Figure 6]1 is a plan view showing a welded structure between a cross bracket, a side frame, and an inner cross according to an embodiment of the present disclosure. FIG. [Figure 7] FIG. 2 is a perspective view showing a welded structure between the cross bracket, the side frame, and the inner cross according to the embodiment of the present disclosure. [Figure 8] FIG. 11 is a perspective view showing a welded structure between a side frame and an inner cross of a comparative example. [Figure 9] FIG. 11 is a perspective view showing a welded structure between a cross bracket, a side frame, and an inner cross in another comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. However, when the number, quantity, amount, range, etc. of each element is mentioned in the embodiments described below, the present invention is not limited to the mentioned number unless it is specifically stated or clearly specified in principle. Furthermore, the structures, etc. described in the embodiments described below are not necessarily essential to the present invention unless it is specifically stated or clearly specified in principle.

[0014] 1. Battery case structure FIG 1 is a perspective view showing a configuration of a battery case 10 according to an embodiment of the present disclosure. However, the upper cover of the battery case 10 shown in FIG 1 has been removed. When mounting the battery case 10 in a vehicle, the upper cover is attached with the battery housed inside the battery case 10. The housed battery is a battery stack formed by stacking a large number of battery cells. The battery cells are chargeable and dischargeable secondary batteries, for example, lithium ion secondary batteries.

[0015] The battery case 10 comprises a front frame 30 located at the front of the vehicle when mounted on the vehicle, a rear frame 40 located at the rear of the vehicle, and a pair of side frames 20 located on the sides of the vehicle. A plurality of inner cross members (cross members) 200 are installed within a framework consisting of these four frames. The inner cross members 200 are arranged at equal intervals in parallel with the front frame 30 and the rear frame 40. The frame and the inner cross members are die-cast products made of a light metal, specifically aluminum. A base plate 50 is joined to the underside of the rectangular frame formed by the frame.

[0016] The battery is mounted in the battery case 10 configured as described above with its stacking direction facing the vehicle width direction. The space surrounded by the side frames 20 on both sides and the two adjacent inner crosses 200, and the space surrounded by the side frames 20 on both sides, the rear frame 40, and the rearmost inner cross 200 are the mounting locations for the battery.

[0017] The battery is compressed in its stacking direction and is stored in the battery case 10 in a shortened state due to the application of a high compressive force. When mounted in the battery case 10, the battery attempts to expand in its stacking direction, but expansion of the battery in the stacking direction is prevented by the side frames 20 on both sides connected by multiple inner crosses 200. At this time, the battery restraint load received by the side frames 20 is borne by the front frame 30 and the rear frame 40 as well as the inner crosses 200 connecting the side frames 20 on both sides.

[0018] The restraining load acts on the joint between the side frame 20 and the inner cross 200. Since the battery expands in the stacking direction due to heat, the restraining load acting on the joint increases during operation. Therefore, if the joint strength is weak, the joint may not be able to withstand the restraining load of the battery. Therefore, the side frame 20 and the inner cross 200 are connected via the cross bracket 100. In the next chapter, the connection structure between the side frame 20 and the inner cross 200 by the cross bracket 100 will be explained.

[0019] 2. Cross bracket connects side frame and inner cross 2 is a perspective view showing the connection structure between the side frame 20 and the inner cross member 200 by the cross bracket 100. The cross bracket 100 includes a base portion 110 joined to the side frame 20, and a pair of corner bracket portions 120 extending from the base portion 110 and sandwiching a wall portion 210 of the inner cross member 200 from both sides. Each of the corner bracket portions 120 is joined to the wall portion 210 of the cross member 200.

[0020] 3 is a plan view showing the above-mentioned connection structure in more detail. The wall portion 210 of the cross member 200 is pressed against the base portion 110 of the cross bracket 100. In other words, the end face 212 of the wall portion 210 and the side surface (the surface on the wall portion 210 side) 112 of the base portion 110 are in contact with each other without any gaps. In this positional relationship, the side surface 214 of the wall portion 210 and the side surface (the surface on the wall portion 210 side) 122 of the corner bracket portion 120 are joined together.

[0021] When the battery restraint load is applied, a tensile force acts between the base portion 110 and the corner bracket portion 120. Stress caused by the tensile force is likely to occur in corners where the angle between two surfaces is small. Stress concentration can cause damage and lower the allowable limit of the battery restraint load. For this reason, the cross bracket 100 has a shape designed to make stress concentration less likely to occur.

[0022] As a design innovation in the shape of the cross bracket 100, a notch 130 is provided in the area where the side surface 122 of the corner bracket portion 120 and the side surface 112 of the base portion 110 intersect, i.e., in the corner portion. By providing the notch 130 in the corner portion, the stress generated by the tensile force is dispersed and stress concentration is alleviated.

[0023] A method of applying R-machining to the corners is known as a common method of reducing stress concentration. However, compared to the case of making a notch 130, the effect of reducing stress concentration by applying R-machining is limited. FIG. 4(A) is a stress analysis diagram showing the stress distribution when a notch 130 is made in the corners, and FIG. 4(B) is a stress analysis diagram showing the stress distribution when a R-machining 132 is made in the corners. As can be seen from the comparison between the two, stress concentration occurs when the R-machining 132 is made, whereas the stress can be dispersed when the notch 130 is made. It was confirmed that the maximum stress can be reduced to approximately half when the notch 130 is made compared to the case of making the R-machining 132.

[0024] If the purpose is simply to relieve stress concentration, the R processing can also achieve the purpose. By performing R processing 134 with a small curvature on the corner portion as shown by the dotted line in FIG. 5, it is expected that the same effect of relieving stress concentration as that of inserting the notch 130 can be achieved. However, if such processing is performed on the corner portion, a large gap will be created between the end face 212 of the wall portion 210 of the cross member 200 and the side surface 112 of the base portion 110. This gap will increase the free running distance of the vehicle in a side collision. Therefore, it can be said that inserting the notch 130 is the most suitable method for obtaining the effect of relieving stress concentration while minimizing the free running distance in a side collision.

[0025] 3. Welded structure of cross bracket, side frame and inner cross Welding is used to join the cross bracket 100 and the side frame 20. Welding is also used to join the cross bracket 100 and the inner cross 200. The welding method used is arc welding by a robot.

[0026] 6 is a plan view showing the welded structure between the cross bracket 100, the side frame 20, and the inner cross 200. The base portion 110 and the side frame 20 of the cross bracket 100 are welded by a weld line L1 connecting point P11 and point P12. One of point P11 and point P12 is the start end of the weld line L1, and the other is the end end. Also, one corner bracket portion 120 and the wall portion 210 of the cross bracket 100 are welded by a weld line L2 connecting point P21 and point P22. One of point P21 and point P22 is the start end of the weld line L2, and the other is the end end. The other corner bracket portion 120 and the wall portion 210 of the cross bracket 100 are welded by a weld line L3 connecting point P31 and point P32. One of point P31 and point P32 is the start end of the weld line L3, and the other is the end end.

[0027] In arc welding, the start and end of a weld line are prone to become the starting point of destruction because the arc is unstable and the weld strength is relatively low. Therefore, it is desirable to reduce the number of start and end of a weld line as much as possible. In the example shown in Fig. 6, the total number of start and end of a weld line required to connect the side frame 20 and the inner cross 200 via the cross bracket 100 is limited to six. However, even if the number of start and end of a weld line is reduced, sufficient weld strength cannot be obtained if the total length of the weld line is short.

[0028] One method for making the weld line longer is to perform welding along the contour of the object to be welded. However, a robot that performs arc welding can only accurately draw a weld line by moving in a straight line or by moving in a gentle curve. In other words, depending on the external shape of the object to be welded, it may be difficult to adopt a long welding path. Therefore, the cross bracket 100 is designed with a shape that allows a long weld line to be obtained when arc welding by a robot.

[0029] FIG. 7 is a perspective view showing a welded structure between the cross bracket 100, the side frame 20, and the inner cross 200. The base portion 110 of the cross bracket 100 has a rectangular shape with both upper ends 116 rounded, so-called kamaboko shape, when viewed from the side from the stacking direction of the batteries. The radius of curvature of the upper end 116 is, for example, 15 mm or more. By forming the base portion 110 in such a shape, it is possible to take a point P11 at one lower end of the base portion 110 and a point P12 at the other lower end, and to take a long, gently curved weld line L1 connecting the points P11 and P21. This makes it possible to minimize the number of welding start ends and end ends when arc welding the cross bracket 100 and the side frame 20, and to enable efficient arc welding by a robot. The shape of the base portion 110 may be a semi-elliptical shape when viewed from the side from the stacking direction of the batteries.

[0030] Each of the pair of corner bracket parts 120 has a rectangular shape with a rounded upper end 126 of the tip part when viewed from the side in a direction perpendicular to the stacking direction of the batteries, that is, a so-called half-fish cake shape. The radius of curvature of the upper end 126 is, for example, 15 mm or more. With such a shape, it is possible to take a point P21 near the upper notch 130 of one corner bracket part 120, a point P22 at the lower end of the tip part, and a long, gently curved weld line L2 connecting the two points P21 and P22. Also, it is possible to take a point P31 near the upper notch 130 of the other corner bracket part 120, a point P32 at the lower end of the tip part, and a long, gently curved weld line L3 connecting the two points P31 and P32. This makes it possible to minimize the number of welding start points and end points when arc welding the cross bracket 100 and the inner cross 200, and to enable efficient arc welding by a robot. The shape of the corner bracket portion 120 may be a quarter ellipse when viewed from the side in a direction perpendicular to the stacking direction of the batteries.

[0031] As described above, the shape of the cross bracket 100 has been designed to provide the advantage of enabling high-quality and highly efficient arc welding by a robot. This advantage can be made clearer by comparing with the two comparative examples described below.

[0032] 8, the inner cross 200 is butted against the side frame 20, and the side frame 20 and the inner cross 200 are directly welded together. In this case, both sides of the end of the wall portion 210 of the inner cross 200 are welded to the side frame 20 by welding lines L11 and L12. In addition, the bottom portions 220 on both sides of the inner cross 200 are welded to the side frame 20 by welding lines L13 and L14.

[0033] In the first comparative example, the number of start and end points of the weld lines is limited to a total of eight. However, the strength is insufficient because each weld line is short. In other words, the first comparative example is inferior in strength to the case where the cross bracket 100 is used, and the objective of improving the allowable limit value of the restraining load of the battery cannot be achieved.

[0034] In the second comparative example shown in Fig. 9, the side frame 20 and the inner cross 200 are connected via a cross bracket 300. Unlike the cross bracket 100, the cross bracket 300 has a simple shape with various points machined at right angles. The base portion 310 of the cross bracket 300 has a simple rectangular shape when viewed from the side in the stacking direction of the batteries. The corner bracket portion 320 has a simple rectangular shape when viewed from the side in a direction perpendicular to the stacking direction of the batteries.

[0035] Even if we try to set a weld line along a shape that is bent at a right angle as in the second comparative example, the robot cannot follow it. Therefore, we have no choice but to set a weld line for each side and weld it. When welding the side frame 20 and the base part 310, a total of three weld lines are required: a horizontal weld line L21 and two vertical weld lines L22, L23. When welding the wall part 210 of the inner cross 200 and the corner bracket part 320, a total of four weld lines are required: two horizontal weld lines L24, L26 and two vertical weld lines L25, L27.

[0036] As a result, when using the cross bracket 300, a total of seven weld lines are required, and the number of start and end points of the weld lines increases to a total of 14. Since the start and end points are likely to become the starting points of destruction, the second comparative example can be said to be inferior in quality to the case where the cross bracket 100 is used. In addition, since the number of processes increases as the number of weld lines increases, the second comparative example can be said to be inferior in efficiency to the case where the cross bracket 100 is used.

[0037] As is clear from the comparison with the above two comparative examples, the cross bracket 100 makes it possible to minimize the number of weld lines, thereby minimizing the number of start and end points that are likely to become the starting points of destruction, while making it possible to lengthen the length of each weld line. This makes it possible to achieve high quality and efficient arc welding by a robot while ensuring high weld strength. [Explanation of symbols]

[0038] 10 Battery case 20 Side frame (frame) 30 Front Frame 40 Rear frame 50 Base Plate 100 Cross bracket 110 Base 120 Corner bracket part 130 Cutout 200 Inner Cross (Cross Member) 210 Wall section L1, L2, L3 welding lines P11, P12, P21, P22, P31, P31 points (start or end)

Claims

1. A battery stack including a plurality of battery cells stacked in a vehicle width direction; a pair of side frames disposed on both ends of each of the plurality of battery stacks in a vehicle width direction and extending in a front-rear direction of the vehicle; a cross member disposed between the battery stacks in a vehicle front-rear direction and extending in a vehicle width direction between the pair of side frames; A battery mounting structure comprising: the cross member includes a first portion and a second portion that is disposed outboard of the first portion in a vehicle width direction and has an end portion that is on an upper side of the vehicle than the first portion and is disposed downward of the vehicle, The cross member is welded to the side frame at the second portion. Battery mounting structure for vehicle.

2. The cross member is linearly welded from at least the end portion on the upper side of the vehicle toward the lower side of the vehicle in the second portion, A vehicle mounting structure for a battery according to claim 1.

3. The cross member is linearly welded at least from the end on the upper side of the vehicle to a portion spaced apart from the end on the lower side of the vehicle in the second portion, A vehicle mounting structure for a battery according to claim 2.

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