Battery mounting structure in vehicles

Abstract

The present invention provides a battery mounting structure for vehicles that facilitates increasing the energy density of a battery module having a case and battery group. [Solution] The battery stack 52 is formed by stacking a plurality of rectangular batteries 54, each having terminals on both longitudinal ends and forming a rectangular parallelepiped shape, in the thickness direction of the rectangular batteries; a lower case 24 having an opening 25 on its upper surface and housing the battery stack so that the thickness direction and the vertical direction coincide; an upper case 38 attached to the upper part of the lower case so as to close the opening and having an open bottom; fastening members 75, 76 that fasten the lower case and the upper case together so that a force in the thickness direction is exerted on the battery stack from the lower case and the upper case; and a cross member which is part of the vehicle frame member that supports the lower case and the upper case, extends in the vehicle width direction and whose lower surface exerts a force in the thickness direction on the upper surface of the upper case.

Description

Technical Field

[0001] The present invention relates to a battery mounting structure in a vehicle.

Background Art

[0002] In Patent Document 1 below, in order to suppress variations in the pressing force on a large number of secondary batteries constituting a battery stack, a battery module is disclosed in which a spacer is provided between a case for housing the battery stack and the battery stack.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, improving the energy density has been required for battery modules. However, in order to increase the energy density of a battery module, it is necessary to reduce the space occupied by members other than the battery stack in the case. That is, when a spacer is provided in the battery case as in Patent Document 1 above, it becomes difficult to improve the energy density of the battery module.

[0005] In consideration of the above facts, an object of the present invention is to obtain a battery mounting structure in a vehicle that is easy to increase the energy density of a battery module having a case and a battery group.

Means for Solving the Problems

[0006] The battery mounting structure in the vehicle according to the first embodiment comprises: a battery stack formed by stacking a plurality of rectangular batteries, each having terminals on both longitudinal ends and forming a rectangular parallelepiped shape, in the thickness direction of the rectangular batteries; a lower case having an opening on its upper surface and housing the battery stack so that the thickness direction and the vertical direction coincide; an upper case attached to the upper part of the lower case so as to close the opening and having an opening on its lower surface; fastening members that fasten the lower case and the upper case together so that a force in the thickness direction is exerted on the battery stack from the lower case and the upper case; and a cross member that is part of the vehicle frame member supporting the lower case and the upper case, extends in the vehicle width direction, and whose lower surface exerts a force in the thickness direction on the upper surface of the upper case.

[0007] The battery mounting structure in the first embodiment of the vehicle has a battery stack formed by stacking multiple rectangular batteries, each having terminals on both longitudinal ends and forming a rectangular parallelepiped shape, in the thickness direction of the rectangular batteries. Furthermore, the lower case houses the battery stack so that the thickness direction and the vertical direction coincide. Furthermore, when the lower case and the upper case are fastened together by fastening members, a force in the thickness direction of the rectangular batteries is exerted on the battery stack from the lower case and the upper case. Furthermore, the lower surface of the cross member extending in the vehicle width direction exerts a force in the thickness direction of the rectangular batteries on the upper surface of the upper case. As a result, the battery mounting structure in the first embodiment of the vehicle can exert pressure in the thickness direction of the rectangular batteries on each rectangular battery without providing spacers. Consequently, the battery mounting structure in the first embodiment of the vehicle makes it easier to increase the energy density of the battery module having the lower case, upper case and battery stack.

[0008] The battery mounting structure in the vehicle of the second embodiment, in the first embodiment, has a plurality of planar battery units formed by arranging a plurality of the prismatic batteries on a plane perpendicular to the thickness direction, and the plurality of planar battery units are arranged in the thickness direction, and a single cooler is provided in the gap formed between two adjacent planar battery units, in contact with each of the prismatic batteries constituting the planar battery unit.

[0009] According to the battery mounting structure in the vehicle of the second embodiment, a large number of prismatic batteries can be cooled by a small number of coolers.

[0010] In the battery mounting structure of the vehicle according to the third embodiment, the lower surface of the cross member and the upper surface of the upper case are in contact with each other, as in the first or second embodiment.

[0011] In the battery mounting structure of the third embodiment of the vehicle, the lower surface of the cross member exerts pressure on the upper surface of the upper case in the thickness direction of the prismatic battery, and this pressure is transmitted from the upper case to the battery stack. Therefore, the battery mounting structure of the third embodiment of the vehicle can increase the energy density of the battery module while utilizing the cross member. [Effects of the Invention]

[0012] As described above, the battery mounting structure in a vehicle according to the present invention has the excellent effect of easily increasing the energy density of the battery module having a case and a battery group. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view of the battery mounting structure in a vehicle according to the embodiment. [Figure 2] This is a schematic cross-sectional view along the arrow 2-2 in Figure 1. [Figure 3] This is a perspective view of a battery cell. [Figure 4] This is a plan view of the lower case and the bottommost planar battery unit housed within the lower case. [Figure 5] This is a schematic cross-sectional view of the lower case, the upper case separated from the lower case, and the battery stack. [Figure 6] This is a cross-sectional view similar to Figure 5, showing the lower case and upper case fixed in place. [Modes for carrying out the invention]

[0014] The battery mounting structure in the vehicle according to the embodiment will be described below with reference to the attached drawings. The arrows UP, FR, and LH in each drawing indicate the upper side in the vertical direction of the vehicle, the front side in the longitudinal direction of the vehicle, and the left side in the lateral direction of the vehicle, respectively.

[0015] As shown in Figures 1 and 2, the vehicle 10 to which the battery mounting structure of this embodiment is applied comprises a pair of left and right rockers 12 that are part of the vehicle body frame member and extend in the longitudinal direction of the vehicle, and a cross member 17 that is part of the vehicle body frame member and extends in the vehicle width direction (left-right direction), with both ends fixed to the left and right rockers 12. The rockers 12 and the cross member 17 are made of metal. As shown in Figure 2, the cross-sectional shape of the rocker 12 is rectangular. Multiple through holes 14 are provided in the bottom plate portion 13 of the left and right rockers 12, arranged in a front-to-back direction (only one is shown in Figure 1). Furthermore, weld nuts 15 that are concentric with each through hole 14 are fixed at positions corresponding to each through hole 14 on the upper surface of the bottom plate portion 13.

[0016] The battery module 20 of this embodiment includes a battery case 22, a battery stack 52, a bolt 75, and a nut 76.

[0017] The battery case 22 has a lower case 24 and an upper case 38. The lower case 24 and the upper case 38 are integrally molded from metal.

[0018] As shown in FIGS. 1 and 4 to 6, the lower case 24 is a hollow body having an opening 25 formed in its upper surface. The lower case 24 has a bottom plate portion 26, a front plate portion 27, a rear plate portion 28, a pair of side plate portions 29, and a lower annular flange 30. The planar shape of the bottom plate portion 26 is a rectangle that is longer in the front-rear direction than in the left-right direction. The lower end portion of the front plate portion 27 is fixed to the front edge portion of the bottom plate portion 26, the lower end portion of the rear plate portion 28 is fixed to the rear edge portion of the bottom plate portion 26, and the lower end portions of the left and right side plate portions 29 are respectively fixed to the left and right side edge portions of the bottom plate portion 26. Further, the left and right side edge portions of the front plate portion 27 are respectively fixed to the front edge portions of the left and right side plate portions 29. Further, the left and right side edge portions of the rear plate portion 28 are respectively fixed to the rear edge portions of the left and right side plate portions 29. The left and right side plate portions 29 are substantially parallel to the vertical direction. On the other hand, in side view, the front plate portion 27 and the rear plate portion 28 are inclined with respect to the vertical direction. Further, as shown in FIGS. 1 and 2, a plurality of heat radiation holes 29S are formed as through holes in the front plate portion 27, the rear plate portion 28, and each side plate portion 29. The lower annular flange 30 having a square ring shape in plan view is fixed to the upper edge portions of the front plate portion 27, the rear plate portion 28, and the side plate portions 29. A plurality of first through holes 34 are formed side by side in the circumferential direction of the lower annular flange 30. Further, a plurality of second through holes 35 are formed side by side in the front-rear direction on both left and right sides of the lower annular flange 30. Further, a plurality of weld nuts 76 concentric with each first through hole 34 are fixed to the lower surface of the lower annular flange 30.

[0019] As shown in Figures 1 and 4-6, the upper case 38 is a hollow body with an opening 39 formed on its lower surface. The upper case 38 has a top plate portion 40, a front plate portion 41, a rear plate portion 42, a pair of side plate portions 43, and an upper annular flange 44. The planar shape of the top plate portion 40 is a rectangle, with the front-to-back direction being longer than the left-to-right direction. As shown in Figures 5 and 6, the lower surface of the top plate portion 40 is provided with a plurality of pressing protrusions 40S extending in the front-to-back direction. The upper end of the front plate portion 41 is fixed to the front edge of the top plate portion 40, the upper end of the rear plate portion 42 is fixed to the rear edge of the top plate portion 40, and the upper ends of the left and right side plate portions 43 are fixed to the left and right side edges of the top plate portion 40, respectively. Furthermore, the left and right side edges of the front plate portion 41 are fixed to the front edges of the left and right side plate portions 43, respectively. Furthermore, the left and right side edges of the rear plate portion 42 are fixed to the rear edges of the left and right side plate portions 43, respectively. The left and right side plates 43 are substantially parallel to the vertical direction. On the other hand, in a side view, the front plate 41 and rear plate 42 are inclined with respect to the vertical direction. The upper annular flange 44, which forms a rectangular ring in a plan view, is fixed to the lower edges of the front plate 41, rear plate 42, and side plates 43. Multiple first through holes 48 are formed in the upper annular flange 44, arranged in the circumferential direction (only two first through holes 48 are shown in Figures 5 and 6). Furthermore, as shown in Figure 1, multiple second through holes 49 are formed on both the left and right sides of the upper annular flange 44, arranged in the front-to-back direction. The planar shape of the upper annular flange 44 is substantially the same as the planar shape of the lower annular flange 30. Furthermore, the number of first through holes 48 is the same as the number of first through holes 34, and the number of second through holes 49 is the same as the number of second through holes 35.

[0020] As shown in Figures 5 and 6, the battery stack 52 comprises a number of battery cells 54, a number of busbars (not shown), and two coolers 72.

[0021] As shown in FIG. 3, a battery cell 54 which is a secondary battery is a rectangular battery having a rectangular parallelepiped main body case 55, a pair of lid portions 58, a positive electrode terminal (terminal) 60, a negative electrode terminal (terminal) 62, and safety valves 64, 66. The metal main body case 55 is a hollow body with openings at both ends in its longitudinal direction (left - right direction). The main body case 55 includes a pair of upper and lower substrate portions 56 and a pair of side plate portions 57 that connect the front edge portions and the rear edge portions of the upper and lower substrate portions 56, respectively. The upper and lower substrate portions 56 are flat plates orthogonal to the vertical direction, and the left and right side plate portions 57 are flat plates orthogonal to the left - right direction.

[0022] Metal lid portions 58 are respectively fixed to the left and right openings of the substrate portion 56. A positive electrode terminal 60 is provided on one lid portion 58, and a negative electrode terminal 62 is provided on the other lid portion 58. Further, safety valves 64, 66 are respectively provided on each lid portion 58. Furthermore, an electrolytic solution or the like is stored in the internal space of the battery cell 54 formed by the main body case 55 and the pair of lid portions 58. The safety valves 64, 66 open when the pressure value in this internal space reaches a predetermined pressure, and discharge smoke or the like generated in the internal space to the outside of the battery cell 54.

[0023] As shown in Figures 4 to 6, multiple battery cells 54 are electrically connected to each other while arranged on a virtual plane perpendicular to the vertical direction. That is, multiple battery cells 54 are arranged on the virtual plane with one substrate portion 56 located below and a pair of cover portions 58 arranged in the left-right direction. The overall planar shape of the multiple battery cells 54 arranged on the virtual plane is a roughly rectangular shape, with the front-to-back direction being longer than the left-to-right direction. Hereinafter, the entire set of multiple battery cells 54 arranged on the virtual plane will be referred to as a planar battery unit 68. As shown in Figure 4, in this embodiment, four battery cells 54 are arranged in the left-to-right direction and ten battery cells 54 are arranged in the front-to-back direction. That is, the planar battery unit 68 comprises 40 battery cells 54. Furthermore, as shown in Figures 4 to 6, three linear gaps 69 extending in the front-to-back direction are formed between the cover portions 58 of the battery cells 54 arranged in the left-to-right direction. Furthermore, the front-to-back dimension of the planar battery unit 68 is slightly shorter than the front-to-back dimension of the pressing protrusion 40S. Furthermore, the positive terminal 60 and negative terminal 62 of battery cells 54 facing each other in the left-right direction are connected by a metal busbar (not shown). Additionally, the positive terminal 60 and negative terminal 62 located on the left edge of the planar battery unit 68 and adjacent to each other in the front-rear direction are connected by a metal busbar (not shown). Furthermore, the positive terminal 60 and negative terminal 62 located on the right edge of the planar battery unit 68 and adjacent to each other in the front-rear direction are connected by a metal busbar (not shown). In other words, all the battery cells 54 constituting one planar battery unit 68 are electrically connected to each other.

[0024] As shown in Figures 5 and 6, the battery module 20 of this embodiment comprises three planar battery units 68 of the same structure. Each planar battery unit 68 is electrically connected to the others by busbars. The three planar battery units 68 are arranged side by side in the vertical direction, and a cooler 72 is provided in the gap 70 formed between two adjacent planar battery units 68. The cooler 72 is a hollow body whose planar shape is substantially the same as the planar shape of the planar battery unit 68, and is made of a metal such as aluminum. Furthermore, each cooler 72 is in contact with the substrate portion 56 of the main body case 55 of each battery cell 54 that constitutes the two planar battery units 68 located above and below it. One end of a pair of pipes (not shown) is connected to the cooler 72, and the other end of each pipe is connected to an electric pump and a heat exchanger, etc., on the outside of the battery case 22. In other words, the coolant inside the pair of pipes and the cooler 72 circulates through the electric pump, the heat exchanger, the pair of pipes, and the cooler 72 by the force generated by the electric pump.

[0025] As shown in Figure 5, the battery stack 52 with the configuration described above is placed in the internal space of the lower case 24, which is separated from the upper case 38, and rests on the underside of the bottom plate portion 26. Furthermore, as shown in Figure 4, the front end of the battery stack 52 is separated from the front plate portion 27 to the rear, and the rear end of the battery stack 52 is separated from the rear plate portion 28 to the front. Furthermore, as shown in Figures 4 to 6, the left end of the battery stack 52 is separated from the left side plate portion 29 to the right, and the right end of the battery stack 52 is separated from the right side plate portion 29 to the left. Furthermore, as shown in Figure 5, the upper end of the battery stack 52 is located above the upper end of the lower case 24.

[0026] Furthermore, as shown in Figure 5, the upper case 38 is placed over the lower case 24 which houses the battery stack 52. Although not shown in the illustration, this causes each pressing projection 40S of the upper case 38 to contact the upper surface of the main case 55 of each battery cell 54 that constitutes the uppermost planar battery unit 68 of the battery stack 52, and the upper annular flange 44 faces the lower annular flange 30 from above, forming a small gap between them.

[0027] Furthermore, as shown in Figure 6, a downward external force is applied to the upper case 38 to bring the upper annular flange 44 into contact with the lower annular flange 30 of the lower case 24. In this state, multiple bolts (fastening members) 75 are inserted into each first through hole 48 formed in the upper annular flange 44 and each first through hole 34 formed in the lower annular flange 30, and weld nuts (fastening members) 76 are screwed onto the lower part of each bolt 75 that protrudes downward from each first through hole 34, so that the heads of each bolt 75 are pressed against the upper surface of the upper annular flange 44. As a result, the pressing protrusions 40S are pressed against the upper surface of the main body case 55 of each battery cell 54 that constitutes the uppermost planar battery unit 68 of the battery stack 52. This completes the battery module 20.

[0028] As shown in Figures 1 and 2, the battery module 20 is fixed to the left and right rockers 12. Specifically, with the upper surface of the left edge of the upper annular flange 44 in contact with the lower surface of the bottom plate 13 of the left rocker 12, and the upper surface of the right edge of the upper annular flange 44 in contact with the lower surface of the bottom plate 13 of the right rocker 12, bolts 78 are inserted from below into the second through holes 35 and 49 of the lower annular flange 30 and the upper annular flange 44, respectively. Furthermore, the upper part of each bolt 78 is screwed into the corresponding weld nut 15, and the head of each bolt 78 is pressed against the lower surface of the bottom plate 13. When the battery module 20 is fixed to the left and right rockers 12 using multiple bolts 78 in this way, the upper surface of the upper case 38 is pressed against the lower surface of the cross member 17, as shown in Figure 6.

[0029] (Mechanism of action and effect) Next, the operation and effects of this embodiment will be described.

[0030] The battery mounting structure in the vehicle described above has a battery stack 52 formed by stacking multiple rectangular battery cells 54, each having a rectangular parallelepiped shape and equipped with positive terminals 60 and negative terminals 62 on both longitudinal ends, in the thickness direction. Furthermore, the lower case 24 houses the battery stack 52 so that the thickness direction and vertical direction of the battery cells 54 coincide. When the lower case 24 and the upper case 38 are fastened together by fastening members, bolts 75 and weld nuts 76, a vertical force (in the thickness direction of the battery cells 54) is exerted on the battery stack 52 from the bottom plate portion 26 of the lower case 24 and the pressing protrusions 40S of the upper case 38. Furthermore, the lower surface of the cross member 17 extending in the vehicle width direction exerts a downward force in the thickness direction of the battery cells 54 on the upper surface of the upper case 38. Thus, the battery mounting structure in the vehicle of this embodiment utilizes the cross member 17, the lower case 24, and the upper case 38 to apply pressure in the thickness direction to each battery cell 54 without the need for spacers. Therefore, it is easier to increase the energy density of the battery module 20 having the lower case 24, the upper case 38, and the battery stack 52.

[0031] When battery cells are stacked in the front-to-back direction to form a battery stack, and this battery stack is installed inside the lower case, spacers are inserted between both ends of the battery stack and the inner surfaces of the front and rear plates of the lower case. However, in order to increase the pressure exerted on the battery stack, it is necessary to increase the number of battery cells that make up the battery stack, so inserting this battery stack and spacers between the front and rear plates is not easy. In contrast, in the battery module 20 of this embodiment, the battery cells 54 are stacked in the vertical direction, and the battery stack 52 is sandwiched vertically between the lower case 24 and the upper case 38. Therefore, even if the number of stacked planar battery units 68 is increased in order to increase the pressure exerted on each battery cell 54, it is not difficult to assemble the battery module 20.

[0032] Furthermore, a single cooler 72 is inserted into each gap 70 formed between each planar battery unit 68, so that each cooler 72 is in contact with each battery cell 54 of the planar battery units 68 located above and below it. As a result, a large number of battery cells 54 can be cooled by a small number of coolers 72.

[0033] Furthermore, if the pressure in the internal space of at least one battery cell 54 reaches a predetermined pressure due to, for example, an internal short circuit, the safety valves 64 and 66 open, and the smoke generated in the internal space of the battery cell 54 is discharged to the outside of the battery cell 54. Note that, for example, a small foreign object on the outside of the battery cell 54 may enter the battery cell 54 through the gap between the main body case 55 and the lid 58, causing an internal short circuit. In this case, the internal short circuit occurs near the lid 58 inside the battery cell 54. Therefore, when such a short circuit occurs, the smoke generated near the lid 58 inside the battery cell 54 can be efficiently discharged to the outside of the battery cell 54 through the safety valves 64 and 66 provided on the lid 58.

[0034] Furthermore, since the battery case 22 of the battery module 20 is equipped with multiple heat dissipation holes 29S, smoke discharged from the safety valves 64 and 66 located on the left and right edges of the battery stack 52 (planar battery unit 68) can be discharged to the outside of the battery module 20 through the gap between the battery stack 52 and the side plate portion 29 via each heat dissipation hole 29S. In addition, the battery module 20 can discharge smoke discharged from the safety valves 64 and 66 located opposite each linear gap 69 to the outside of the battery module 20 through each linear gap 69 and the gap between the battery stack 52 and the front plate portion 27, rear plate portion 28 and side plate portion 29 via each heat dissipation hole 29S.

[0035] Furthermore, for example, when battery cells are stacked in the front-to-back direction to form a battery stack, spacers are inserted between both ends of the battery stack and the inner surfaces of the front plate portion 27 and the rear plate portion 28. Therefore, the front plate portion 27 and the rear plate portion 28 need to be approximately parallel to the vertical direction. However, in this embodiment, where such spacers are not provided, the front plate portion 27 and the rear plate portion 28 can be inclined with respect to the vertical direction. In other words, since the battery module 20 does not require such spacers, there is a high degree of design freedom for the lower case 24 (front plate portion 27, rear plate portion 28).

[0036] The battery module 20 in the vehicle according to the embodiment has been described above, but these can be modified as appropriate without departing from the spirit of the present invention.

[0037] For example, the number of battery cells 54 constituting each planar battery unit 68 may differ from the number mentioned above.

[0038] The battery stack 52 may comprise two or four or more planar battery units 68.

[0039] The pressing protrusion 40S may be omitted from the upper case 38, and the top plate portion 40 may be brought into contact with the upper end of the battery stack 52.

[0040] A safety valve 64 (66) may be provided on only one of the lid portions 58 of the battery cell 54.

[0041] The planar shape of each cooler 72 may differ from the planar shape of the planar battery unit 68. For example, the planar shape of each cooler 72 may be the same as the planar shape of all the battery cells 54 (10 battery cells 54 in this embodiment) arranged in the front-to-back direction. That is, four coolers may be provided in the gap 70. In this case, the smoke that flows out from the battery cells 54 (safety valves 64, 66) of each planar battery unit 68 into each linear gap 69 flows through the gaps between adjacent coolers in the left-to-right direction and between the vertically arranged linear gaps 69, so that the smoke can be efficiently discharged to the outside of the battery module 20 from each heat dissipation hole 29S.

[0042] Ribs extending linearly in the front-to-back direction and ribs extending linearly in the left-to-right direction may be provided on the bottom (top) surface of the bottom plate portion 26 of the lower case 24. The upper ends of these ribs are located below the lower ends of the positive terminal 60, negative terminal 62, and safety valves 64, 66 of the battery cells 54 placed on the bottom surface of the bottom plate portion 26. Furthermore, ribs extending in the front-to-back direction may be positioned in the linear gap 69 of the lowest planar battery unit 68, or ribs extending in the left-to-right direction may be positioned between adjacent battery cells 54 on the left and right sides of the lowest planar battery unit 68. In this way, the bottom plate portion 26 can be mechanically reinforced by each rib, and the battery stack 52 can be positioned in the front-to-back and left-to-right directions relative to the lower case 24 by each rib.

[0043] A different member may be interposed between the lower surface of the cross member 17 and the upper surface of the upper case 38. In this case, a downward force is exerted from the lower surface of the cross member 17 to the upper surface of the upper case 38 through this member. [Explanation of Symbols]

[0044] 12. Rocker (body frame component) 17 Cross member (body frame component) 20 Battery Modules 24 Lower case 25 Opening 38 Upper case 52 Battery Stack 54 Battery cells (prismatic batteries) 60 Positive terminal (terminal) 62 Negative terminal (terminal) 68-sided battery unit 70 gaps 72 Cooler 75 bolts (fastening members) 76. Weld nuts (fastening components)

Claims

1. A battery stack is formed by stacking multiple rectangular batteries, each having terminals on both ends in the longitudinal direction and forming a rectangular parallelepiped shape, in the thickness direction of the rectangular batteries. A lower case having an opening on its upper surface, which houses the battery stack such that the thickness direction and the vertical direction coincide, An upper case is attached to the upper part of the lower case so as to close the aforementioned opening, and the lower surface of the upper case is open, A fastening member fastens the lower case and the upper case together such that a force in the thickness direction is exerted on the battery stack from the lower case and the upper case, A cross member which is part of the vehicle body frame member supporting the lower case and the upper case, extending in the vehicle width direction and having its lower surface exert a force in the thickness direction on the upper surface of the upper case, Battery mounting structure in a vehicle equipped with the following.

2. The battery stack comprises a plurality of planar battery units formed by arranging a plurality of the prismatic batteries on a plane perpendicular to the thickness direction, Multiple of the planar battery units are arranged in the thickness direction, A battery mounting structure in a vehicle according to claim 1, wherein a single cooler is provided in the gap formed between two adjacent planar battery units, and contacts each of the rectangular batteries constituting the planar battery unit.

3. The battery mounting structure in a vehicle according to claim 1 or claim 2, wherein the lower surface of the cross member and the upper surface of the upper case are in contact.

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