Cell connection device comprising a spring element

Abstract

The invention relates to a cell connection device (1) for an electrical energy storage device for electrically connecting storage cells of the electrical energy storage device, the cell connection device comprising: • a connection element (2), designed to carry current, for electrical and mechanical connection to in each case one cell terminal of the storage cells, the connection element having at least one fuse (9) for interrupting current flow in the event of a fault, which fuse is designed as a cross-sectional constriction (4) that can be severed by the fault event, wherein a spring element (10), which is fastened to the connection element (2) and applies a load to the cross-sectional constriction (4), is designed to mechanically sever the cross-sectional constriction (4) in the event that the cross-sectional constriction (4) is only partially melted due to a fault event.

Description

[0001] Cell connection device with spring element

[0002] The invention relates to a cell connection device for an electrical energy storage device for electrically connecting the storage cells of the electrical energy storage device. The cell connection device has a connecting element designed for current conduction for electrical and mechanical connection to each cell terminal of the storage cells. The connecting element includes at least one fuse for interrupting the current flow in the event of a fault, which is designed as a cross-sectional reduction that can be separated by the fault. The invention also relates to an electrical energy storage device.

[0003] The focus here is on electrical energy storage devices, which can be used in particular as traction batteries for electrified motor vehicles, such as electric or hybrid vehicles. Such electrical energy storage devices are typically designed as high-voltage energy storage systems and comprise a large number of storage cells, for example, cylindrical or prismatic cells. Connecting elements or cell connectors are provided for interconnecting the storage cells, which can be electrically and mechanically connected to the cell terminals of the storage cells.

[0004] It is known from the prior art, for example DE 102022 124457 A1, to integrate a fusible link in the form of a cross-sectional reduction into the cell connectors. This reduction is designed to melt in the event of a fault current flowing through the cell connector, thereby interrupting the current flow. For this purpose, the fusible links typically require a fault current in the form of an overcurrent, which generates a sufficient heating effect not only to melt the cell connector material but also to produce further effects, such as movement of the melt, further heating of the liquid melt, vaporization of the melt, etc., which ultimately disconnect the cell connector. In certain fault conditions, however, the fault current is not high enough to produce these effects beyond the melting of the material.It is possible that current will continue to flow through the partially melted cell connector, releasing further heat into the electrical energy storage device. This can lead to safety-related consequential damage.

[0005] The object of the present invention is to provide a cell connector for electrically connecting storage cells of an electrical energy storage device, in which a current flow is safely and reliably interrupted in the event of a fault.

[0006] This problem is solved according to the invention by a cell connection device and an electrical energy storage device with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0007] A cell connection device according to the invention for an electrical energy storage device serves to connect the storage cells of the electrical energy storage device. The cell connection device comprises a connecting element designed for current conduction for electrical and mechanical connection to each cell terminal of the storage cells. The connecting element has at least one fuse for interrupting the current flow in the event of a fault, which is designed as a cross-sectional reduction that can be separated, in particular melted, by the fault. In addition, the cell connection device comprises a spring element attached to the connecting element, which loads the cross-sectional reduction, for mechanically cutting the cross-sectional reduction in the event that the cross-sectional reduction has only partially melted due to the fault.

[0008] The invention also relates to an electrical energy storage device for a motor vehicle. The electrical energy storage device comprises at least two storage cells and at least one cell connection device according to the invention, wherein the connection element is electrically and mechanically connected to the cell terminals of the storage cells. The electrical energy storage device is, in particular, a high-voltage energy storage device and serves as a traction battery for an electrified motor vehicle. The energy storage device comprises a plurality of storage cells, which are, in particular, designed as cylindrical cells. The cylindrical cells have a cylindrical cell housing in which a galvanic cell is arranged. The cell housing forms a negative cell terminal, which is electrically connected to a negative pole of the galvanic cell.Electrically insulated from the cell housing, a positive cell terminal is guided through a housing cover of the cell housing, which is electrically connected to a positive pole of the galvanic element.

[0009] To connect the storage cells, the electrical energy storage device has cell connection devices. Each cell connection device has a connecting element or cell connector, which is electrically and mechanically connected, for example by welding, to the cell terminals of two storage cells. To connect two storage cells in series, for example, the cell connector can be attached to the cell casing of one storage cell (forming the negative cell terminal) and to the positive cell terminal of the other battery cell. For this purpose, the cell connector has, for example, two contact points at its ends for electrical and mechanical connection to the cell terminals.

[0010] Furthermore, the cell connector features an integrated fuse which, in the event of a fault current or overcurrent, can interrupt the current flow through the cell connector and thus the current flow between the two storage cells. The fuse is formed by a cross-sectional reduction within the cell connector. In other words, the cell connector has a reduced cross-section, for example, a reduced width, in the area of ​​the fuse. In this area of ​​cross-sectional reduction, the material of the cell connector is intended to largely melt due to the heating effect caused by the fault and be removed from the cross-section by further effects caused by the fault, so that the cell connector is severed in the area of ​​the cross-sectional reduction. The cross-sectional reduction is formed particularly adjacent to at least one of the contact points, especially the positive-side contact point.The fault condition is, in particular, a fault current flowing through the cell connector.

[0011] If the heating effect of the fault, for example due to an insufficient fault current, is not sufficient to completely separate the cell connector material, the cell connection device incorporates a spring element. The spring element is mechanically connected to the cell connector away from the cross-sectional reduction. For example, the spring element can form a snap-fit ​​connection with the cell connector or wrap around it. The spring element can also be designed as a U-shaped wire spring that rests against the connector away from the cross-sectional reduction. This spring element exerts a mechanical force on the cell connector in the area of ​​the cross-sectional reduction and severs the reduction if the cell connector material is only partially melted, i.e., merely liquefied.For this purpose, the spring element is pre-tensioned such that the holding force of the solid, unmelted cross-sectional constriction exceeds the restoring force of the spring element. As soon as the material begins to melt, the holding force of the cross-sectional constriction decreases, and the restoring force of the spring element predominates. This causes the spring element to relax again, mechanically cutting through the cross-sectional constriction. The spring element has a higher melting point than the melting point of the cell connector and is therefore thermally robust against failure. In particular, the spring element is made of steel, preferably spring steel.

[0012] Such a spring element ensures a safe and reliable separation of the cell connector in the event of partial melting of the cell connector resulting from a fault.

[0013] The connecting element may be composed of at least two materials with different melting points, with the spring element designed to cut through the cross-sectional reduction if a temperature caused by the fault current lies between the melting points of the two materials. For example, the materials are aluminum and aluminum oxide, with the connecting element being designed as an aluminum component surrounded by aluminum oxide and the spring element designed to cut through the aluminum oxide layer if the temperature caused by the fault current lies between the melting point of aluminum and the melting point of aluminum oxide.In the event of a fault current flowing through the cell connector, it can happen that the fault current melts one of the two materials, for example, the aluminum, but due to the aluminum component's encapsulation within the thermally very robust aluminum oxide layer, current continues to flow through the cell connector. The spring element is provided to cut through the material with the higher melting point, for example, the aluminum oxide layer, which holds together the molten aluminum that continues to carry the fault current.

[0014] In one embodiment of the invention, the connecting element has a plate-shaped central section, two cross-sectional tapers axially adjacent to the central section, and plate-shaped end sections adjacent to the cross-sectional tapers. The end sections form the contact points for electrical and mechanical connection to the cell terminals of the memory cells, and at least one of the cross-sectional tapers forms the at least one fuse. The central section can, for example, be rectangular. The end sections are designed as flat, plate-shaped elements that can be arranged adjacent to and attached to the respective cell terminal. The end sections forming the contact points can be shaped differently to accommodate the respective cell terminal.For example, the positive-side contact point can be circular to fit against the circular surface of the positive cell terminal, and the negative-side contact point can be ring-segment shaped to fit against the ring-shaped surface of the housing cover forming the negative cell terminal.

[0015] In particular, a first cross-sectional reduction, arranged between the central section and a first end section (which forms the positive-pole contact point for electrical and mechanical connection to the positive cell terminal), has a first cross-section, and a second cross-sectional reduction, arranged between the central section and a second end section (which forms the negative-pole contact point for electrical and mechanical connection to the negative cell terminal), has a larger cross-section compared to the first cross-section, with only the first, positive-pole-side reduction forming the fuse. This design is based on the understanding that, in the presence of a fault current, the cell connector typically melts from the positive-pole-side cell terminal. Therefore, the first cross-sectional reduction on the positive-pole side forms the fuse.The spring element is attached, in particular, at the central section in the direction of the thermally less stressed negative pole-side end section, so that stable support of the spring element can be ensured.

[0016] It proves advantageous if the at least one cross-sectional reduction forming the fusible link has a deformation-absorbing bulge, whereby a restoring force of the spring element acts on an underside, particularly in the region of a vertex, of the bulge. The bulge allows a reversible change in length of the cell connector during vehicle operation, for example due to driving-related vibrations, and thereby prevents the cell connector from detaching, for example, tearing off, from the cell terminals. The spring element is arranged in the bulge and is supported in the region of the vertex of the bulge.For example, the spring element is designed as a wire loop which is supported on the connecting element away from the cross-sectional reduction forming the fusible link, passes through the bulge, and is pre-tensioned against the underside in the area of ​​the bulge's apex. The wire loop presses upwards against the apex of the bulge. Due to partial melting of the cell connector material in the area of ​​the cross-sectional reduction caused by a fault, the pre-tensioned wire loop can move further upwards and thereby sever the cross-sectional reduction.

[0017] The embodiments and advantages presented with reference to the cell connection device according to the invention apply accordingly to the electrical energy storage device according to the invention.

[0018] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own.

[0019] The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. The drawings show:

[0020] Fig. 1 shows a schematic representation of a cell interconnection device for an electrical energy storage device in an uninterrupted state; and

[0021] Fig. 2 shows a schematic representation of the cell connection device in a severed state.

[0022] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0023] Figures 1 and 2 show a cell connection device 1 for connecting storage cells or battery cells, in particular cylindrical cells, of an electrical energy storage device for a motor vehicle. The cell connection device 1 has a metallic, electrically conductive connecting element 2, which can, for example, be designed as an aluminum component encased in an aluminum oxide layer. The connecting element 2 has a plate-like, strip-shaped central section 3, two adjacent cross-sectional reductions 4, 5, and two end sections 6, 7 adjacent to the cross-sectional reductions 4, 5. A first end section 6 forms a first contact point on the positive terminal side and is designed for electrical and mechanical connection to a positive cell terminal of a storage cell.A second end section 7 forms a second contact point on the negative pole side and is designed for electrical and mechanical connection to a negative cell terminal of another storage cell. The cross-sectional reductions 4, 5 each have a bulge 8, which is designed to absorb deformations during vehicle travel. Furthermore, the contact points can be arranged at different heights by means of the bulges 8, since the cell terminals of cylindrical cells are located at different height levels.

[0024] Here, the cross-sectional reduction 4 on the positive pole side has the smallest cross-section of the connecting element 2, so that this cross-sectional reduction 4 forms a fuse 9 integrated into the connecting element 2. The fuse 9 is intended to disconnect the connecting element 2 in the event of a fault current flowing through the connecting element 2 by completely removing the material of the connecting element 2 in the area of ​​the cross-sectional reduction 4 by the fault current.

[0025] In the event of a fault current that does not completely separate the cross-sectional reduction 4, but, for example, only melts the aluminum but not the aluminum oxide, the fault current may continue to flow through the liquid aluminum held by the aluminum oxide layer. This fault current flow can release unwanted heat and lead to consequential damage to the electrical energy storage device.

[0026] To ensure an interruption of the current flow in such cases, the cell connection device 1 has a spring element 10 which, as shown in Fig. 1, loads the cross-sectional reduction 4 forming the fuse 9. The mechanical force exerted by the pre-tensioned spring element 10 on the cross-sectional reduction 4 is selected such that, under normal circumstances (without a fault current), the reduction 4 is not damaged and the current flow via the connection element 2 is not impaired. As soon as the connection element 2 heats up due to the fault current and partially melts in the area of ​​the cross-sectional reduction 4, the spring element 10 can relax, as shown in Fig. 2, and thereby sever the cross-sectional reduction 4.

[0027] The spring element 10 can, for example, have a wire loop 11 made of spring steel, which is supported on the central section 3 on the side of the negative, thermally less stressed end section 7. For example, the wire loop 11 can encircle the connecting element 2 in the region of the central section 3 or be clipped laterally to the central section 3. The wire loop 11 extends towards the positive, thermally more stressed end section 6 and passes through the bulge 8 of the cross-sectional reduction 4. The spring element 10 is pre-tensioned by the wire loop 11 being bent downwards and held in this downward-bent state by the rigid cross-sectional reduction 4. The wire loop 11 thereby exerts a mechanical force on an underside 12 of the cross-sectional reduction 4 in the region of a vertex of the cross-sectional reduction 4.As soon as the cross-sectional constriction 4 changes from a solid to a liquid state due to heat, it can no longer hold the wire clip 11, and the wire clip 11 can move upwards again to release the spring element 10. In doing so, the wire clip 11 cuts through the cross-sectional constriction 4.

Claims

Patent claims 1. Cell connection device (1) for an electrical energy storage device for electrically connecting storage cells of the electrical energy storage device, comprising: a connecting element (2) designed for current conduction for electrical and mechanical connection with each cell terminal of the storage cells, with at least one fuse (9) for interrupting the current conduction in the event of a fault, which is designed as a cross-sectional reduction (4) that can be separated by the fault, characterized by a spring element (10) attached to the connecting element (2) and bearing stress on the cross-sectional reduction (4) for mechanically cutting the cross-sectional reduction (4) in the event of a cross-sectional reduction (4) that is only partially melted by a fault.

2. Cell connection device (1) according to claim 1, characterized in that the fault condition is a fault current flowing via the connection element (2).

3. Cell connection device (1) according to claim 1 or 2, characterized in that the connecting element (2) consists of at least two materials with different melting temperatures, wherein the spring element (10) is designed to cut through the cross-sectional reduction (4) if a temperature caused by the fault condition lies between the melting temperatures of the two materials.

4. Cell connection device (1) according to claim 3, characterized in that the materials are aluminium and aluminium oxide, wherein the connecting element is designed as an aluminium component coated with aluminium oxide and the spring element (10) is designed to cut through the aluminium oxide layer if the temperature caused by the fault is between the melting temperature of aluminium and the melting temperature of aluminium oxide.

5. Cell connection device (1) according to one of the preceding claims, characterized in that the spring element (10) is made of steel, in particular spring steel.

6. Cell connection device (1) according to one of the preceding claims, characterized in that the spring element (10) is designed as a U-shaped wire spring.

7. Cell connection device (1) according to one of the preceding claims, characterized in that the connection element (2) has a plate-shaped central section (3), two cross-sectional reductions (4, 5) axially adjacent to the central section (3) and plate-shaped end sections (6, 7) adjacent to the cross-sectional reductions (4, 5), wherein the end sections (6, 7) form contact points for electrical and mechanical connection with the cell terminals of the storage cells and wherein at least one of the cross-sectional reductions (4) forms the at least one fuse (9).

8. Cell connection device (1) according to claim 7, characterized in that a first cross-sectional reduction (4), which is arranged between the central section (3) and a first end section (6), which forms a positive-pole contact point for electrical and mechanical connection with a positive-pole cell terminal, has a first cross-section and a second cross-sectional reduction (5), which is arranged between the central section (3) and a second end section (7), which forms a negative-pole contact point for electrical and mechanical connection with a negative-pole cell terminal, has a larger cross-section compared to the first cross-section has a cross-section, whereby only the first, positive pole-side cross-sectional reduction (4) forms the fuse (9).

9. Cell connection device (1) according to one of the preceding claims, characterized in that the at least one cross-sectional reduction forming the fuse (9) (4) has a deformation-absorbing bulge (8) wherein a restoring force of the spring element (10) acts on a bottom side (12) of the bulge (8).

10. Cell connection device (1) according to claim 9, characterized in that the spring element (10) has a wire loop (11) which is supported on the connecting element (2) away from the cross-sectional reduction (4) forming the fusible link (9), extends through the bulge (8) and is pre-tensioned against the underside (12) of the bulge (8).

11. Electrical energy storage device for a motor vehicle comprising at least two storage cells and at least one cell connection device (1) according to one of the preceding claims, wherein the connection element (2) is electrically and mechanically connected to cell terminals of the storage cells.

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