Battery pack cooling structure

Abstract

To improve the air blow circulation efficiency inside a sealed battery pack, and thereby, to simplify the structure and achieve uniform temperature distribution and a cooling effect.SOLUTION: Provided is a cooling structure for a battery pack 1 that comprises a plurality of battery modules 32 in a battery case (an upper case 10 and a lower case 20). The lower case is formed as a heat radiation member using a thermoconductive material. The battery modules are fixedly arranged in the lower case with a gap between each other. The cooling structure comprises, in the lower case, a blower fan 5 arranged above in a vehicle height direction for the plurality of battery modules, and a blow duct 42 for sending air sent out from the blower fan while pressurizing the air into at least one air outlet 427 located at an intermediate part of the plurality of battery modules in a vehicle length direction and a vehicle width direction. The air Fa blown from the air outlet circulates to the blower fan through a gap between the plurality of battery modules and a gap between the plurality of battery modules and an inner surface of the battery case.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a cooling structure for a battery pack mounted in a vehicle. [Background technology]

[0002] In a battery pack mounted on a vehicle, for example, a battery pack for an electric vehicle, a plurality of modules each made up of a plurality of secondary batteries are arranged inside a flat case and placed on the floor of the vehicle or under the floor in order to increase the capacity while ensuring the space inside the vehicle and in the luggage compartment. Since the secondary batteries generate heat during charging and discharging, the battery pack is provided with a cooling structure.

[0003] Cooling structures for battery packs include an open type that introduces outside air and a sealed type that uses a heat pump; however, the former has issues with the intrusion of rainwater and dust, while the latter requires a compressor and radiator outside the battery pack (see Patent Document 1). As a result, the cooling system cannot be completed by the battery pack alone, making the system complicated and posing issues such as condensation water generated in the internal evaporator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-11632 A Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, a method is being reconsidered in which a blower fan is provided inside a sealed battery pack to make the temperature distribution inside the battery pack uniform while efficiently dissipating heat from the battery case, which serves as a heat dissipation member, to the outside.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to improve the efficiency of ventilation and circulation inside the battery pack, simplify the structure, uniformize the temperature distribution inside the battery pack, and achieve the desired cooling effect. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides A cooling structure for a battery pack to be mounted on a vehicle, the battery pack including a plurality of battery modules inside a substantially sealed battery case, The battery case is formed as a heat dissipation member using a thermally conductive material, the plurality of battery modules are fixedly disposed in the battery case with gaps between them; A battery case is provided inside the battery case, and the battery modules are disposed above the battery case in the vehicle height direction. , which opens into the internal space of the battery case a blower fan having an air intake and arranged to blow air from the blower fan to a center between the plurality of battery modules in a vehicle length direction and a vehicle width direction; And the height of the battery modules is intermediate and a blower duct for blowing the air under pressure to at least one blower outlet located at From the air outlet Front, back or left and right The cooling structure of the battery pack is configured so that the blown air passes through the gaps between the multiple battery modules and the gaps between the multiple battery modules and the inner surface of the battery case, and is circulated to the blower fan. Effect of the Invention

[0008] Since the cooling structure of the battery pack according to the present invention is configured as described above, the battery module is cooled by heat exchange between the air blown out to the middle part of the battery module and the battery module, and at the same time, the heated air moves upward and is circulated by the blower fan along the top surface (inner surface) of the battery case, thereby promoting heat dissipation to the outside through heat exchange with the top surface of the battery case and improving the air circulation efficiency inside the battery pack, thereby achieving a uniform temperature distribution and cooling effect for the battery module while avoiding a complicated structure. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a perspective view showing the appearance of the battery pack. [Diagram 2] FIG. 2 is a perspective view showing the inside of the battery pack. [Diagram 3] FIG. 2 is a plan view showing the inside of the battery pack. [Figure 4] 2 is a cross-sectional view taken along line AA in FIG. 1. [Diagram 5] FIG. 2 is a cross-sectional view of FIG. [Figure 6] FIG. 5 is an enlarged cross-sectional view of a main part of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] (Battery pack overview) 1, a battery pack 1 according to an embodiment of the present invention is designed to be mounted under the floor of a vehicle and has an overall flat shape except for a rear bulge 12. In the following description, unless otherwise specified, "front and rear" refers to the front and rear sides in the vehicle length direction FR, "left and right" refers to the left and right sides in the vehicle width direction W toward the forward vehicle length direction F, and "up and down" corresponds to the top and bottom sides in the vehicle height direction H.

[0012] 1 to 5, the battery pack 1 includes a plurality of battery modules 31, 32 inside a battery case consisting of an upper case 10 and a lower case 20. Each battery module 31, 32 is modularized by holding a plurality of secondary battery cells (lithium ion secondary batteries, etc.) connected in series with each other in a stacked state inside a box-shaped or frame-shaped inner case.

[0013] The upper case 10 and the lower case 20 are formed into a shell or tray shape using press-molded parts made of metal with good thermal conductivity, such as steel, stainless steel, or an aluminum alloy, and they themselves function as heat dissipation members to the outside.

[0014] 1, the upper case 10 constituting the upper part of the battery pack 1 has a ridge 13 formed in the center in the vehicle width direction W on its top surface 11 extending in the vehicle length direction FR from the front to the rear in the vehicle length direction, and three small ridges 15 (beads 151, 152, 153) extending parallel to the vehicle length direction FR on each of the left and right sides. In addition, a meeting portion 14 between the ridge 13 and the front inclined surface 122 of the bulging portion 12 is formed in a funnel shape that rises and widens toward the bulging portion 12.

[0015] The above-mentioned ridge portion 13 and small ridge portion 15 are reinforcing structures (reinforcing bead portions) for improving the surface rigidity of the top surface 11 of the upper case 10, and at the same time, as described below, are also components of a cooling structure that forms a flow path (return flow path) for circulating air inside the upper case 10.

[0016] In addition, it is preferable that the ridge portion 13 is formed so that the protruding height is greater at the rear portion than at the front portion in the vehicle length direction FR, or that the protruding height of the ridge portion 13 increases toward the bulge portion 12.

[0017] The top surface 11 of the upper case 10 has the ridges 13 and small ridges 15, but is generally flat overall, whereas a bulge 12 that bulges upward is formed in the rear of the upper case 10 to be accommodated in the lower space of the kick-up section under the rear seat of the vehicle. The internal space expanded upward by this bulge 12 is an installation space for the ventilation duct 4 and ventilation fan 5 that constitute the cooling system, and is also a heat dissipation space separated from the battery modules 31 and 32, as described below.

[0018] The battery pack 1 is configured such that the battery modules 31, 32 and their control devices are housed in the lower case 20, and components such as the ventilation duct 4 and ventilation fan 5 that constitute the cooling system are arranged and the necessary wiring is completed. The flange portion 20f around the lower case 20 and the flange portion 10f of the upper case 10 are joined together with bolts or the like via sealing material 20c to ensure waterproofing and airtightness.

[0019] A support frame 25, which serves as a support frame for the battery pack 1, is fixed to the underside of the lower case 20. As shown in Fig. 4, the support frame 25 is configured in a ladder shape by a pair of left and right side frames 250 and a plurality of cross frames 251, 252, 253, 254, 255 extending between and rigidly connected to the pair of side frames 250 in the vehicle width direction W.

[0020] The battery pack 1 is provided with four mounting brackets 21, 22, 23, and 24 on each of the left and right sides as mounting portions to the vehicle body. Of these, the mounting brackets 22, 23, and 24 excluding the frontmost one are composed of an upper bracket joined to a flange portion 10f of the upper case 10 of the battery pack 1 and a lower bracket joined to a flange portion 20f of the lower case 20. The battery pack 1 is fixed to the vehicle body by fastening bolts inserted from below through bolt holes in each mounting bracket 21, 22, 23, and 24 to weld nuts of the mounting portions on the vehicle body side.

[0021] In the battery pack 1, a high-voltage connector 33 for inputting and outputting power to the vehicle drive motor is disposed on the front end surface of the lower case 20, and a high-voltage connector 36 for charging is disposed on the rear surface of the upper case 10 (bulge 12). Also, a service plug 34 for cutting off power to the battery modules 31, 32 during inspection or in an emergency is disposed on the top surface 11 of the upper case 10, and a control connector 35 is disposed on the top surface 121 of the bulge 12 of the upper case 10.

[0022] (Battery module placement) As shown in Figures 2 and 3, inside the battery pack 1, four battery modules 32 (32a, 32j) are arranged side by side at the front with their respective longitudinal directions aligned with the vehicle length direction FR and with gaps 320, 322 between them, and behind them in the middle of the battery pack 1, four battery modules 32 (32b) are arranged side by side in a similar arrangement with their respective longitudinal directions aligned with the vehicle length direction FR.

[0023] In the illustrated example, the second module 32j from the right at the front is a junction box equipped with a relay circuit that supplies / cuts off power to the high-voltage connector 33, but for example, this function can be consolidated into a junction box 38 in the bulge 12 to form a battery module, and for convenience it will be described as battery module 32.

[0024] At the rear inside the battery pack 1, four battery modules 31 (31c, 31d) are arranged side by side with their respective longitudinal directions aligned with the vehicle width direction W and with gaps 310, 312 between them, with a gap 330 between them and the intermediate battery module 32b, as shown by the dashed lines in Fig. 3. Of these, the two left-hand battery modules 31d have fewer sets of secondary battery cells than the other battery modules, and are half-size modules with shorter longitudinal lengths.

[0025] The battery modules 31, 32 are fixed to reinforcing frames 26, 27, 28 disposed on the inner bottom of the lower case 20, as shown in FIGS.

[0026] That is, the front and middle battery modules 32 are fixed with bolts at both front and rear ends in the longitudinal direction to reinforcing frames 26 extending in the vehicle width direction W and arranged at three locations spaced apart from each other from the front to the middle part of the inner bottom of the lower case 20, as shown in FIG. 4, and the four rear battery modules 31 are fixed with bolts at both left and right ends in the longitudinal direction to reinforcing frames 27, 28 extending in the vehicle length direction FR and arranged at a distance from each other on both sides and the middle part of the rear part of the inner bottom of the lower case 20, as shown in FIG. 5.

[0027] In the following description, the four battery modules 31 (31c, 31d) at the rear of the battery pack 1 may be collectively referred to as the first battery module group 31, and the eight battery modules 32 (32a, 32b) at the front and middle of the battery pack 1 described above may be collectively referred to as the second battery module group 32.

[0028] (Battery module cooling system) As shown in Figures 2 to 5, a support plate 17 for arranging the air duct 4 and the air fan 5 that constitute the cooling system is provided on the upper side of the four battery modules 31 arranged at the rear of the battery pack 1.

[0029] The support plate 17 is fixed to the reinforcing frame 27 on both sides in the vehicle width direction via legs 18. The legs 18 are formed of inverted U-shaped members formed by bending downward both ends of a frame material extending in the vehicle width direction W along the lower surface of the support plate 17, and each lower end (flange portion) is fixed to the reinforcing frame 27 with a bolt.

[0030] The support plate 17 is extended at a height approximately equal to the upper surface 11 of the upper case 10, with a gap between it and the upper surface of the battery module 31, and is arranged to partially separate the internal space of the bulge portion 12 of the upper case 10 from the lower battery module 31 side, except for the peripheral portion, and there is a gap between it and the side and rear surfaces of the bulge portion 12.

[0031] A blower fan 5 is disposed approximately in the center of the support plate 17 in the vehicle width direction W. A control device 37 for managing battery charge / discharge and cell balance control is disposed on the right side of the blower fan 5, and a junction box 38 for a high-voltage connector 36 is disposed on the left side of the blower fan 5. A blower duct 4 (second branch duct portion 42) is disposed along the front edge of the support plate 17 in front of them.

[0032] A centrifugal fan (sirocco fan or turbo fan) can be suitably used as the blower fan 5, and is fixed with bolts onto the support plate 17 so that the rotation axis direction coincides with the vehicle height direction H and the intake port 50 is located at the top of the fan case. In the illustrated example, a sirocco fan with a motor disposed inside the fan hub is used, so that the motor housing does not protrude downward and a sufficient air flow path is secured above the intake port 50.

[0033] The blower duct 4 includes a base 40 extending forward from the discharge port 54 of the blower fan 5, a first branch duct portion 41 extending downward from a communicating portion 410 at the bottom of approximately the middle portion of the base 40 through an opening 70 in the support plate 17, as shown in Figures 5 and 6, and a second branch duct portion 42 connected to the front end of the base 40, as shown in Figures 2 and 3.

[0034] (Ventilation duct; first branch duct section) As shown in Figures 3 and 5, the first branch duct portion 41 connects from the middle portions (310, 312) of the four battery modules 31c, 31d of the first battery module group 31 in the vehicle length direction FR and vehicle width direction W to a pair of first air outlets 417, 418 that open in both the left and right directions toward the gaps 310, 310 between each of the battery modules 31c, 31d.

[0035] 6, the first branch duct portion 41 is formed of a separate member from the base portion 40 and is not directly connected to the base portion 40. That is, the first branch duct portion 41 has a thick portion 41e at its lower end portion 41b, and with this lower end portion 41b (thick portion 41e) fitted into the gap 310 between the battery modules 31, 31, the upper end portion 41a facing the communication portion 410 abuts against the lower surface around the opening 70 of the support plate 17 via an elastic seal member, thereby being held between the support plate 17 and the reinforcing frame 28. The thick portion 41e may be a rib protruding from the lower end portion 41b of the first branch duct portion 41, or a spacer formed of a separate member from the lower end portion 41b.

[0036] This type of installation of the first branch duct portion 41 is performed after the installation and wiring of the four battery modules 31c, 31d below the support plate 17 is completed, by inserting the first branch duct portion 41 into the gap between the battery modules 31c, 31d from above, and temporarily fixing it by holding the lower end portion 41b (thick portion 41e) between the side surfaces of the battery modules 31, 31 and the upper surface of the reinforcing frame 28, and then attaching the support plate 17 above them and restraining them from both the top and bottom with the support plate 17 and the reinforcing frame 28 via an elastic sealing member.

[0037] Then, the base 40 of the air duct 4 together with the air fan 5 is fixed to the upper surface of the support plate 17, and the lower surface around the communicating portion 410 abuts against the upper surface around the opening 70 of the support plate 17 via an elastic sealing member, thereby forming an air flow path of the first branch duct 41 that runs from the base 40 through the communicating portion 410 to the first air outlets 417, 418.

[0038] (Ventilation duct; second branch duct section) As shown in Figures 2 and 3, the second branch duct portion 42 includes an upstream portion (first section) 421 extending from the front end of the base 40 to both sides in the vehicle width direction W along the front edge of the support plate 17, an upstream portion (second section) 422 reaching a first bend 423 adjacent to the side of the battery case 1, a downstream portion (first section) 424 extending downward and forward in the vehicle length direction from the first bend 423, and a downstream portion (second section) 426 bent at a second bend 425 in front of it and extending toward the center in the vehicle width direction W.

[0039] The downstream portion (second section) 426 is connected from the middle portions (320, 322) in the vehicle length direction FR and vehicle width direction W of the four battery modules 32a, 32b on each of the left and right sides of the second battery module group 32 to a pair of second air outlets 427, 428 that open forward and backward toward the gaps 320 between each battery module 32a, 32b.

[0040] The upstream portions 421, 422 of the second branch duct portion 42 are fixed to the support plate 17 by fastening members or the like at a front lower portion of the left and right second sections 422 and at other multiple mounting portions. The downstream portions 424, 426 of the second branch duct portion 42 are fixed to the inner bottom portion of the lower case 20 by fastening members or the like at a side portion of the first section 424 and at other multiple mounting portions.

[0041] (Air circulation and cooling effect inside the battery pack) In the cooling system configured as above, when the blower fan 5 is operated, air in the bulging portion 12 is sucked in through the intake port 50, (i) First cooling air Fc, Fd (FIGS. 3, 5, 6) that is pumped through the first branch duct portion 41 extending downward from the base portion 40 of the air supply duct 4 and is blown out to the left and right sides from the first air outlets 417, 418, and (ii) Second cooling air Fa, Fb (Figures 2 to 4) is generated, which is pressurized and sent from the base 40 of the blower duct 4 through the upstream sections 421, 422 and downstream sections 424, 426 of the second branch duct section 42, and blown out to the front and rear sides from the second air outlets 427, 428 on each of the left and right sides.

[0042] As shown in Figures 3 and 5, the first cooling air Fc, Fd flows from the middle of the four battery modules 31c, 31d of the first battery module group 31 to the left and right sides along the gaps 310, 310 in the vehicle width direction W of each battery module 31c, 31d, and in the process, each battery module 31c, 31d is cooled by heat exchange with each battery module 31c, 31d.

[0043] The air warmed by heat exchange with each battery module 31c, 31d rises from the gaps on both the left and right sides of the battery pack 1, as shown by arrows Fc1, Fd1 in Figure 5, and is collected into the upper bulge 12 of the support plate 17, which is under a slight negative pressure due to the suction of the blower fan 5. As the air flows from the side walls of the lower case 20 and the bulge 12 along the ceiling of the bulge 12, it dissipates heat through heat exchange with the lower case 20 and the upper case 10, and is drawn into the intake port 50 of the blower fan 5, as shown by arrows Fc2, Fd2.

[0044] As shown in Figures 2 to 4, the second cooling air Fa, Fb flows from the middle of the four battery modules 32a, 32b on each of the left and right sides of the second battery module group 32 along the gaps 320, 320 in the vehicle length direction FR of each battery module 32a, 32b to the front and rear sides, and in the process, each battery module 32a, 32b is cooled by heat exchange with each battery module 32a, 32b.

[0045] 4, the air heated by heat exchange with each battery module 32a at the forefront rises in the front part of the battery pack 1 and flows rearward along the ceiling part (11, 13) of the upper case 10 toward the bulging part 12 that is under a slight negative pressure due to the suction of the blower fan 5, while dissipating heat through heat exchange with the upper case 10. Meanwhile, the air heated by heat exchange with each battery module 32b at the middle part also flows rearward as shown by arrows Fb1 and Fb2, while dissipating heat through heat exchange with the upper case 10, is collected in the bulging part 12, and is sucked into the intake port 50 of the blower fan 5.

[0046] As described above, the inside (negative pressure area) of the bulge 12 of the battery pack 1 is separated from the lower side by the support plate 17 except for the peripheral portion, and a slight negative pressure is created by the arrangement of the blower fan 5 (air intake port 50), generating air flows Fb2, Fc2, and Fd2 that flow along the ceiling toward the air intake port 50.

[0047] On the other hand, the rear (first positive pressure area) of the battery pack 1 where the first battery module group 31 is arranged and cooling airs Fc, Fd are blown out to the left and right sides from the first air outlets 417, 418 of the air supply duct 4, and the front or middle (second positive pressure area) of the battery pack 1 where the second battery module group 32 is arranged and second cooling airs Fa, Fb are blown out to the front and rear sides from the second air outlets 427, 428 are slightly positive pressure.

[0048] Due to the pressure difference between the negative pressure area (12) and the first and second positive pressure areas (31, 32) as described above, and the rise in temperature of the cooling air due to heat exchange with the first and second battery module groups 31, 32, air circulation is promoted along the inner surface and inner ceiling surface of the upper case 10 to the bulge portion 12 which is relatively the highest. As a result, heat exchange is promoted on the top surface 11 of the upper case 10 and the top surface 121 of the bulge portion 12, resulting in a cooling effect for the first and second battery module groups 31, 32 and making the temperature distribution of the first and second battery module groups 31, 32 uniform.

[0049] Furthermore, the ridge portions 13 and small ridge portions 15 formed on the top surface 11 of the upper case 10 in the vehicle length direction FR ensure an air flow path cross-sectional area oriented in the vehicle length direction FR between the top surface of the second battery module group 32 and the inner ceiling surface of the upper case 10, promoting the formation of an air flow Fb1 that flows rearward along the inner ceiling portion of the upper case 10.

[0050] In addition, the ridge portion 13 is formed in approximately the center in the vehicle width direction W, and correspondingly, the blower fan 5 is arranged in approximately the center of the bulge portion 12 in the vehicle width direction W, which has the advantage of promoting air circulation from the ridge portion 13, which is the main air flow path with the largest air flow path cross section, to the air intake 50 of the blower fan 5.

[0051] Furthermore, the above-mentioned air circulation is further promoted by a configuration in which the protruding height of the ridge portion 13 increases toward the bulge portion 12, and by a configuration in which the meeting portion 14 between the ridge portion 13 and the front inclined surface 122 of the bulge portion 12 is formed into a funnel shape that rises and widens toward the bulge portion 12.

[0052] In addition, the ridges 13 and small ridges 15 formed on the top surface 11 of the upper case 10 in the vehicle length direction FR increase the heat exchange area on the top surface 11 of the upper case 10, which is expected to improve heat exchange efficiency and heat dissipation efficiency.

[0053] In the above embodiment, the bulge portion 12 is described as being formed at the rear of the battery case 1 in the vehicle length direction, but it is also possible to implement a configuration in which the bulge portion 12 is provided at the front or middle of the vehicle length direction.

[0054] Although the embodiment of the present invention has been described above, it should be noted that the present invention is not limited to the above embodiment, and various modifications and variations are possible within the scope of the present invention. [Explanation of symbols]

[0055] 1 Battery pack 4. Air duct 5. Blower fan 10 Upper Case 11 Top side 12 Bulge 13 Ridge 14 Meeting part (funnel shaped part) 15 Small ridge 17 Support Plate 18 Legs 20 Lower case 26,27,28 Reinforcement frame 31, 31c, 31d Battery modules (first battery module group) 32, 32a, 32b Battery modules (second battery module group) 40 Base 41 First branch duct section 42 Second branch duct section 50 Air Intake 54 Discharge port 70 Opening 310,312,320,322,330 gap 410 Communication part 417,418 1st outlet 421,422 Upper reaches 424,426 downstream 427,428 2nd outlet

Claims

1. A cooling structure for a battery pack to be mounted on a vehicle, the battery pack including a plurality of battery modules inside a substantially sealed battery case, The battery case is formed as a heat dissipation member using a thermally conductive material, the plurality of battery modules are fixedly disposed in the battery case with gaps between them; a blower fan having an air intake opening opening into an internal space of the battery case and arranged above the battery modules in a vehicle height direction inside the battery case, and an air blower duct for pressurizing and sending air blown out from the blower fan to at least one air outlet located midway between the battery modules in the vehicle length direction and the vehicle width direction and midway between the battery modules in height, A cooling structure for a battery pack, wherein air blown out from the air outlet to the front and rear or to the left and right sides is configured to circulate to the blower fan through the gaps between the plurality of battery modules and the gaps between the plurality of battery modules and the inner surface of the battery case.

2. 2. The battery pack cooling structure according to claim 1, wherein the blower fan is a centrifugal fan whose rotation axis is oriented in a vehicle height direction and whose fan case has the intake port at an upper portion thereof.

3. 3. The cooling structure for a battery pack according to claim 1, wherein a bulge portion that bulges upward relative to an upper surface of the battery module is formed at a rear portion of the battery case in the vehicle length direction, and the blower fan is disposed at approximately the center in the vehicle width direction inside the bulge portion.

4. 4. The cooling structure for a battery pack as described in claim 3, wherein a support plate extending along an upper surface of the battery module is provided inside the bulge portion, and the support plate separates the central portion excluding the peripheral portion from the battery module side, and the blower fan is fixedly positioned on the support plate.

5. the plurality of battery modules include a first battery module group fixedly arranged at a rear portion of the battery case in a vehicle length direction with a gap therebetween, and a second battery module group fixedly arranged forward of the first battery module group in the vehicle length direction with a gap therebetween, 5. The battery pack cooling structure according to claim 4, wherein the blower duct includes a first branch duct portion for pressurizing and sending the air blown out from the blower fan to a first air outlet located midway between the first battery module group in the vehicle length direction and the vehicle width direction, and a second branch duct portion for pressurizing and sending the air to at least one second air outlet located midway between the second battery module group in the vehicle length direction and the vehicle width direction.

6. 6. The cooling structure for a battery pack according to claim 5, wherein the first branch duct portion extends downward from a base of the air blower duct that extends from an exhaust port of the blower fan to the second branch duct portion, through the support plate, and communicates with the first air outlet.

7. 6. The cooling structure for a battery pack as described in claim 5, wherein the second branch duct portion includes an upstream portion extending from a base of the air supply duct within the bulge portion to both sides in the vehicle width direction and reaching a first bend adjacent to a side of the battery case, and a downstream portion extending forward and downward in the vehicle length direction from the first bend, bending toward the center in the vehicle width direction at a second bend, extending along the gaps between the second battery module group, and reaching the second air outlet.

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