TRACTION BATTERY ASSEMBLY

Abstract

Traction battery assembly, comprising: a trough (20); adjacent cells (18) which are supported by the trough (20), each comprising a planar connection (13, 36, 38); and a busbar (1, 11, 22) which has a longitudinal center point (24) and defines a pair of curved sections (40, 42) which are connected at the center point, wherein an arc-shaped part along each of the sections (40, 42) is in contact with one of the terminals (13, 36, 38) when the terminals (13, 36, 38) have different heights relative to the trough (20) in order to provide increased contact between the busbar (1, 11, 22) and the terminals (13, 36, 38), characterized in that the busbar (1, 11, 22) comprises a rod which is attached at the midpoint (24) and is generally arranged perpendicular to a longitudinal axis of the busbar (1, 11, 22), or that the busbar (1, 11, 22) comprises first and second projections (94, 394, 98, 398) on opposite sides of the busbar (1, 11, 22), each originating near the midpoint (24) and extending away from the midpoint (24).

Description

TECHNICAL FIELD

[0001] This disclosure relates to busbars for vehicle traction battery assemblies. WO 2014 / 064 888 A1 discloses a power supply device, an electric vehicle with the power supply device, a rechargeable battery device, and a method for producing the power supply device. DE 102010 046 642 A1 discloses an electrical energy storage device and a conductor element for such an energy storage device. DE 102008 059 970 A1 discloses a vehicle battery. BACKGROUND

[0002] Vehicles, such as battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs), include a battery pack with a traction battery that acts as a power source for the vehicle. The battery pack may include components and systems to interact with the battery and assist in managing vehicle performance and operation. The battery pack may include one or more arrays of battery cells, with the cell terminals electrically connected to each other by bus bars. Independent claims 1, 7, and 12 represent an improvement on the prior art. Preferred embodiments thereof are specified in the further claims. SUMMARY

[0003] A bus bar having a pair of curved portions for increasing the contact area between the cell terminals and the curved portions when the cell terminals have different heights with respect to each other is provided.

[0004] In one embodiment, a traction battery assembly includes a tray and adjacent cells supported by the tray. Each of the adjacent cells includes a planar terminal. A planar terminal on each cell is electrically connected to a bus bar. The bus bar has a longitudinal center point and defines a pair of arcuate portions connected at the center point. An arcuate portion along each of the arcuate portions is in contact with one of the terminals when the terminals have different heights relative to the tray to provide increased contact between the bus bar and the terminals over a range of relative heights with respect to each other.

[0005] In another embodiment, a traction battery assembly includes a tray and adjacent cells supported by the tray. A casing is disposed on the cells opposite the tray and extends over the adjacent cells. The casing has a pair of opposing sidewalls that cooperate to define an enclosure. A bus bar is received within the enclosure. The bus bar has a longitudinal center point and a pair of bent portions connected at the center point. Each of the bent portions is in contact with one of the terminals when the terminals have different heights relative to the tray to provide increased contact between the bus bar and the terminals.

[0006] In yet another embodiment, a traction battery assembly includes adjacent cells supported by a tray. Each of the cells has a terminal. A bus bar electrically connects the cells. The bus bar has a longitudinal center point and defines a pair of rockers connected at the center point. Each of the rockers has a curved portion in contact with one of the terminals. The curved portions are configured to rock along the terminals to provide increased contact between the bus bar and the terminals when the bus bar has an angled orientation caused by a height difference between the terminals. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a busbar. Fig. 2 is a perspective view of a traction battery assembly. Fig. 3A and Fig. 3B are side views of prior art busbar and terminal assemblies. Fig. 4 is a perspective view of a busbar. Fig. 5A and Fig. 5B are side views of busbar and terminal arrangements. Fig. Figure 6 is a side view of another busbar and terminal arrangement. Fig. 7 is a perspective view of a pin-slot busbar module. Fig. Figure 8 is a perspective view of a rolled edge busbar module. Fig. 9 is a perspective view of another busbar. DETAILED DESCRIPTION

[0007] With reference to Fig. 1 shows a busbar. The busbar 1 comprises a body 3 with a first terminal 5 and a second terminal 7 at opposite ends. The busbar 1 has two semicircular recesses 9, which are sized and shaped for connection to a corresponding circular battery terminal.

[0008] With reference to Fig. 2, electric vehicles may include a power system with a traction battery assembly 10 having components such as one or more battery cell arrays 12, a battery electrical control module (BECM), and a direct current to direct current (DC / DC) converter unit. The battery cell arrays 12 provide power for the operation of the vehicle and its systems. The battery arrays 12 are in electrical communication with the BECM, the DC / DC converter unit, and other vehicle components. The BECM receives input signals from various systems, processes information contained in the input signals, and generates appropriate control signals in response. These control signals activate and / or deactivate the various components.The DC / DC converter unit converts high voltage from the battery cell arrays to low voltage for use by the components and other systems.

[0009] The battery assembly 10 includes a tray 20 for supporting the battery arrays 12. Each battery array 12 is supported on the tray 20 and includes a plurality of battery cells 18 connected in series or parallel. The battery cells 18, such as a prismatic cell, convert stored chemical energy into electrical energy. The cells 18 include a casing, a positive electrode (cathode), and a negative electrode (anode). An electrolyte allows ions to move between the anode and cathode during discharge and then return during recharging. Terminals allow current to flow from the cell for use by the vehicle. When arranged in an array with multiple battery cells, the terminals of each battery cell are oriented with opposite terminals (positive and negative) adjacent to each other to enable series connection between the multiple battery cells.Bus bars can be used to assist in completing the series connection between adjacent battery cells or groups of battery cells that are in close proximity to each other. Various battery pack configurations may be available to address individual vehicle variables, including packaging constraints and power requirements.

[0010] Battery cell dimensions may vary within a given tolerance due to manufacturing imperfections, so that adjacent cells may have slightly different dimensions. The arrangement of cells 18 in array 12 may also vary within a given tolerance due to manufacturing imperfections. Due to these imperfections, it is common for adjacent cells 18 to have slightly different heights relative to one another.

[0011] A height difference between adjacent cells can cause connection problems between the cell terminals and the busbar, since busbars are usually made of rigid, metallic materials. Two possible problems that can occur are described in Fig. 3A and Fig. 3B shown state of the art. In Fig. 3A, a straight busbar 11 is connected to two adjacent cell terminals 13 of different heights. The height difference between the terminals causes the busbar 11 to have an angled orientation with respect to the top of the terminals. The angled orientation of the busbar 11 provides a small busbar-terminal interface 15 and a gap 17 between the busbar 11 and the terminals 13. The contact area may be too small to provide a satisfactory weld, and thus the weld 19 must extend beyond the busbar-terminal interface 15 into the gap 17. Welding at the gap 17 requires additional welding materials and time.

[0012] In Fig. 3B, a straight bus bar 21 is connected between two adjacent cell terminals 23 of different heights. The bus bar 21 is pressed flush against each terminal 23. This eliminates the gap and increases the bus bar-to-terminal connection area, but also creates higher stress areas on the bus bar 21. When the bus bar 21 is pressed flush, the bus bar also bends, causing a deformation in the area 25 near the center of the bus bar 21. This deformation 25 cold-works the bus bar 21 and can degrade the electrical properties of the bus bar 21. The elasticity of the bus bar causes increased stress at the terminal-to-bus bar connection 27. This stress can fatigue the weld 29 over time, leading to connection problems. A stronger weld can be used to combat fatigue, but this can increase production costs.The process of pressing the power rail flush against each terminal can also have undesirable effects on the cells in the array if the compressive force is transmitted to the array.

[0013] With reference to Fig. 4, a bus bar 22 is shown. The bus bar 22 is a single strip of metal, such as copper or aluminum. The bus bar 22 has a longitudinal center point 24 and two longitudinal end points 26 distal to the center point 24. The bus bar 22 includes a pair of bent sections 28 defined between the center point 24 and a corresponding end point 26. The bent sections 28 are symmetrical about the center point 24. However, the bent sections 28 may be asymmetrical in certain applications. The bent sections 28 have a crescent-shaped curvature in the longitudinal direction 30 and are flat in the transverse direction 32.

[0014] With reference to Fig. 5A und Fig. 5B is an elevational view looking down the long side of the battery array 12. The battery array 12 includes a tray 20 that supports a pair of adjacent cells 18. A first cell terminal 36 extends from one of the cells, and a second cell terminal 38 extends from the other cell. The terminals 36, 38 are planar terminals having a generally rectangular shape and a flat top. The first and second terminals 36, 38 are electrically connected by the bus bar 22. The bus bar 22 has a center point 24 and two end points 26. The center point 24 and the end points 26 define a first arcuate portion 40 and a second arcuate portion 42. The first arcuate portion 40 is connected to a first cell terminal 36 at a first arcuate portion 44, and the second arcuate portion 42 is connected to the second cell terminal 38 at a second arcuate portion 46.

[0015] With reference to Fig. 5A, the distal ends 48 of the first and second terminals 36, 38 have the same height relative to the trough 20. The bus bar 22 is disposed at the distal end 48 of the terminals 36, 38 at the first and second arcuate portions 44, 46. The bus bar 22 is generally horizontal, with the first and second arcuate portions 40, 42 having the same height relative to the trough 20. The bus bar-terminal connection surface 50a, 50b on each of the arcuate portions is symmetrical about the center point 24 and is centered on the terminals 36, 38. The arcuate portions 40, 42 have a weldable area 52a, 52b along a majority of the arcuate portion, beginning at a respective end point 26 and extending toward the center point 24.

[0016] With reference to Fig. 5B, the distal ends 48 of the first and second terminals 36, 38 have a different height relative to the trough 20. The first terminal 36 is, for example, 0.70 mm higher than the second terminal 38. The bus bar 22 is arranged at the distal end 48 of the terminals 36, 38, with the first curved portion 40 being higher than the second curved portion 42 relative to the trough 20. The height difference between the terminals 36, 38 causes the bus bar 22 to be pivotally mounted about the center point 24 and to have an angled orientation relative to the trough. The curvatures of the first and second bent portions 40, 42 cooperate to provide an enlarged busbar terminal connection area 50a, 50b and a weldable area 52a, 52b when the busbar 22 is in the angled orientation.

[0017] When comparing Fig. 5A and Fig. 5B, the busbar connection surface 50a has been bent along the first bent portion 40 in Fig. 5B toward the center point 24 because the bent portion 40 rocked at the terminal 36 due to the height difference between the terminals. Rocking of the first bent portion 40 has no effect on the size of the busbar-terminal connection surface 50a due to the curvature of the bent portion 40. The rocking increases the size of the weldable area 52a and shifts the weldable area 52a toward the center point 24.

[0018] The busbar connection surface 50b along the second bent portion 42 in Fig. 5B has shifted away from the center point 24 because the bent portion 42 rocked due to the height difference between the terminals at the terminal 38. The rocking of the second bent portion 42 has no effect on the size of the busbar-terminal connection surface 50b due to the curvature of the bent portion 40. The rocking reduces the size of the weldable area 52b and shifts the weldable area 52b toward the center point 24. Although the weldable area 52b in Fig. 5B is reduced in size, it is still large enough to provide a satisfactory connection.

[0019] With reference to Fig. 6 and Fig. 7, a bus bar module 54 is shown. The bus bar module 54 includes a housing 56 and a bus bar 22 supported by the housing 56. The bus bar housing 56 protects the bus bar 22 and serves as a locating device during installation of the bus bar 22 onto the battery array 12. The housing 56 has a first side wall 58 and a second side wall 60 connected by a pair of opposing end walls 62 to form a rectangular box. The first side wall 58 has a first slot 64 arranged perpendicular to a longitudinal axis 68 of the first side wall 58. The second side wall 60 has a similarly arranged second slot 66. The second side wall 60 has a notch 70 opening into the slot 66. The slots 64, 66 are centered at the midpoint of their respective side walls 58, 60.The housing 56 has a generally open bottom 72 with two partial bottom walls 80. The bottom walls 80 extend from a respective end wall 62 partially along the side walls 58, 60. The side walls 58, 60 and bottom walls 80 define the open bottom 72. The housing 56 has a generally open top 76. The top 76 has two ledges 84. Each of the ledges 84 extends into the housing 56 from the first side wall 58 and a respective end wall 62. The ledges 84 have an inner portion 86. The inner portion 86 has a straight portion 88 parallel to the end walls 62 and a tapered portion 90 extending from the straight portion 88 and terminating at a respective end wall 62. The strips 84 do not completely span the end wall 62, thereby providing a completely open top along the second side wall 60.Although the illustrated busbar module 54 includes a top and a bottom, the present disclosure contemplates a busbar module 54 with a completely open top and bottom. Alternatively, the busbar module 54 may have only a top and no bottom, or vice versa.

[0020] The housing 56 defines an enclosure 92 for receiving the bus bar 22 therein. The bus bar 22 has a first projection 94 extending outwardly from a first side 96 of the bus bar 22 and a second projection 98 extending outwardly from a second side 100 of the bus bar 22. The first side 96 of the bus bar 22 is first inserted into the enclosure 92. The first side 96 is inserted through the open top 76 at the largest part of the opening near the second side wall 60. The first projection 94 is received within the first slot 64. The second projection 98 is received through the notch 70 and into the second slot 66. The slots 64, 66 and the projections 94, 98 cooperate to allow the busbar 22 to rotate about the projections 94, 98 and to move perpendicular, but not parallel, to the longitudinal axis 68 of the side walls 58, 60.The strips 84 and the bottom walls 80 cooperate to prevent rotation of the bus bar 22 beyond a desired range.

[0021] With reference to Fig. 6, the bus bar module 54 sits on the adjacent cells 18 and spans them transversely. The terminals 36, 38 are received through the opening 82 in the housing 56. The bus bar 22 is self-adjusting in height along the slots 64, 66 for correct alignment on the terminals 36, 38. The bus bar 22 is self-adjusting in rotation by pivoting in the slots about the projections 94, 98, allowing the bent portions 40, 42 to rock along the terminals and seat correctly. After the bus bar module 54 has positioned the bus bar 22, additional tooling may be used to weld the bus bar 22 to the terminals 36, 38. Additional tools could also be used to vibrate the bus bar module 54 to ensure that the bus bar 22 is properly seated on the terminals 36, 38.

[0022] With reference to Fig. 8, an alternative bus bar module 254 is shown. The bus bar module 254 includes a housing 256 and a bus bar 222 supported by the housing 256. The housing 256 has a first side wall 296 and a second side wall 200 connected by a pair of opposing end walls 262 to form a rectangular box and define an enclosure 206. The housing 256 has a generally open bottom 272 with two partial bottom walls 280. The bottom walls 280 extend from a respective end wall 262 partially along the side walls 200, 296. The side walls 200, 296 and bottom walls 280 define an opening. The housing 256 has a generally open top 202. The top includes two ledges 284. Each of the strips 284 extends into the housing 256 from the first side wall 296 and a corresponding end wall 262. The strips 284 have an inner side 286.The inner side 286 has a straight portion 288 parallel to the end walls 262 and a tapered portion 290 extending from the straight portion and terminating at a corresponding end wall 262. The ledges 284 do not completely span the end walls 262, thereby providing a complete opening along the second side wall 200.

[0023] The bus bar 222 has a center point and a pair of end points 226. Each of the end points 226 has a curled edge 204. The bus bar 222 is received through the open top 202 within the enclosure 206. The curled edges 204 engage the end walls 262 to align and locate the bus bar 222 within the housing 256. The curled edges 204 and the end wall 262 cooperate to allow movement perpendicular to the side walls 296, 200, but not longitudinally. The ledges 284 and the bottom walls 280 cooperate to prevent rotation of the bus bar 222 beyond a desired range.

[0024] Fig. Figure 9 illustrates a bus bar 322 of an alternative embodiment. In contrast to Fig.6, the first and second protrusions 394, 398 in this embodiment are integrally formed by deforming a portion of the main body 300 of the bus bar 322. The first protrusion 394 is formed by cutting the main body 300 at the surface 304. The first protrusion 394 is then bent away from the main body 300 to form a first projection 394 extending outward from the center point 324. The second protrusion 398 is formed in the same manner. This embodiment provides a smallest cross-sectional area along line 302. Line 302 also has work hardening stress due to the bending process. The smaller cross-sectional area and work hardening create a high resistance point along line 302, which is tunable to serve as a fuse.This can eliminate the need to provide additional fuses and can also be useful in meeting abuse test conditions for shipping lithium-ion batteries.

Claims

[1] Traction battery assembly comprising: a trough (20); adjacent cells (18) supported by the trough (20), each comprising a planar terminal (13, 36, 38); and a busbar (1, 11, 22) having a longitudinal center point (24) and defining a pair of bent sections (40, 42) connected at the center point, wherein an arcuate portion along each of the sections (40, 42) is in contact with one of the terminals (13, 36, 38) when the terminals (13, 36, 38) have different heights relative to the trough (20) to provide increased contact between the busbar (1, 11, 22) and the terminals (13, 36, 38), characterized bythat the busbar (1, 11, 22) comprises a rod which is attached to the center point (24) and is arranged generally perpendicular to a longitudinal axis of the busbar (1, 11, 22), or that the busbar (1, 11, 22) comprises first and second projections (94, 394, 98, 398) on opposite sides of the busbar (1, 11, 22), each originating near the center point (24) and extending away from the center point (24). [2] The assembly of claim 1, wherein an arcuate portion along each of the sections (40, 42) is in contact with one of the terminals (13, 36, 38) when the terminals (13, 36, 38) have the same height relative to the trough (20). [3] The assembly of claim 1, wherein the pair of bent portions (40, 42) are arranged symmetrically about the center point (24). [4] The assembly of claim 1, wherein each of the bent portions (40, 42) is crescent-shaped. [5] The assembly of claim 1, wherein a cross-sectional area of the center point (24) is smaller than a cross-sectional area of end portions of the bent sections (40, 42) such that the center point (24) has a resistance greater than a resistance of the end portions. [6] The assembly of claim 1, wherein a hardness of the center point (24) is greater than a hardness of end portions of the bent sections (40, 42) such that the center point (24) has a resistance greater than a resistance of the end portions. [7] Traction battery assembly comprising: a trough (20); adjacent cells (18) supported by the trough (20) and each comprising a terminal (13, 36, 38); a housing (256) disposed over the cells (18) opposite the trough (20) and spanning the adjacent cells (18), the housing (256) having a pair of opposed side walls cooperating to define an enclosure for the cells (18); and a busbar (222) received within the enclosure, the busbar (222) having a longitudinal center point (24) and a pair of bent portions (40, 42) connected at the center point (24), each of the bent portions (40, 42) being in contact with one of the terminals (13, 36, 38), if the connections (13, 36, 38) have different heights relative to the trough (20), to provide increased contact between the busbar (222) and the terminals (13, 36, 38), characterized bythat the busbar (222) comprises first and second projections (94, 394, 98, 398) on opposite sides of the busbar (222), each originating near the center point (24) and extending away from the center point (24), or that each of the bent sections (40, 42) has a rolled-up edge (204) which is arranged opposite the center point (24), the housing (256) further comprising a pair of end walls (262) which span between the opposite side walls, to form a rectangular box, and wherein each of the curled edges engages a corresponding end wall (262) to align the bus bar (222) within the housing (256). [8] The traction battery assembly of claim 7, wherein the housing (256) further defines an opening in each of the side walls configured to receive one of the projections (94, 98, 394, 398). [9] The traction battery assembly of claim 8, wherein each of the openings is a slot disposed perpendicular to a longitudinal axis of the respective sidewall and is configured to allow the bus bar (222) to move perpendicular, but not parallel, to the longitudinal axis of the respective sidewall. [10] The traction battery assembly of claim 7, wherein the first and second projections (94, 394, 98, 398) are opposite portions of a rod connected to the bus bar (222) at the midpoint (24). [11] The traction battery assembly of claim 7, wherein the center point (24) and the bent portions (40, 42) are configured such that a resistance of the center point (24) is greater than a resistance of the bent portions (40, 42). [12] Traction battery, comprising: adjacent cells (18) supported by a trough (20), each comprising a terminal (13, 36, 38); and a busbar (1, 11, 22) having a longitudinal center point (24) and defining a pair of rockers connected at the center point (24), each of the rockers having a curved portion in contact with one of the terminals (13, 36, 38), the curved portions being designed to rock along the terminals (13, 36, 38) to provide increased contact between the busbar (1, 11, 22) and the terminals (13, 36, 38) when the busbar (1, 11, 22) has an angled orientation caused by a height difference between the terminals (13, 36, 38), characterized bythat the busbar (1, 11, 22) comprises a rod which is attached to the center point (24) and is arranged generally perpendicular to a longitudinal axis of the busbar (1, 11, 22), or that the busbar (1, 11, 22) comprises first and second projections (94, 394, 98, 398) on opposite sides of the busbar (1, 11, 22), each originating near the center point (24) and extending away from the center point (24). [13] Traction battery according to claim 12, wherein the pair of rockers is arranged symmetrically around the center point (24).

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