DE102012024454B4 - Method for testing the quality of a current-carrying connection of busbars to terminals of cells, in particular of lithium-ion cells, of a battery module - Google Patents

Abstract

A method for testing the quality of a current-carrying joint connection of busbars (5) to terminals of cells (2) of a battery module (1), wherein the cells (2) via the busbars (5) are interconnected, wherein the battery module (1) Current pulse, which leads to a current flow over the busbars (5), is applied, after which a thermographic image of the busbars (5), which provides information regarding the temperature distribution of the busbars (5), is taken, the thermographic image (11) automatically is evaluated by means of an evaluation device, characterized in that on the part of the evaluation device (8) an actual or abstracted busbars (5) performing analysis image (12) is created and output on a screen (9), are characterized in the quality of objectionable joints ,

Description

The invention relates to a method for testing the quality of a current-carrying connection of busbars to terminals of cells of a battery module, wherein the cells are connected to one another via the busbars, wherein a current pulse, which leads to a current flow over the busbars, is applied to the battery module, after which a thermographic image of the busbars, which provides information regarding the temperature distribution of the busbars, is recorded, wherein the thermographic image is evaluated automatically by means of an evaluation device.

Increasingly, electric or hybrid vehicles are enjoying great popularity. Electric vehicles drive purely electrically powered, while hybrid vehicles use a combination of internal combustion engine and electric motor, ie a partially electric operation. However, both types have in common that they need at least one battery module in order to provide the required electrical energy. Such a battery module consists of a plurality of individual, e.g. connected in series cells, preferably lithium-ion cells, wherein the number of interconnected cells varies depending on the voltage to be achieved. Also, the individual cells as well as several cell rows can be connected in parallel. The cells are usually interconnected via busbars, which are joined to the terminals of the individual cells, so that the desired cell series connection results. Usually connecting screws are used to connect the busbars with the cell terminals, but it is also known to weld busbars and connections together.

The goal of each connection is to minimize the contact resistance at the point of contact in the range of a few micro ohms, ideally of 0 ohms. Because too high a contact resistance at a joint connection leads to a higher voltage drop respectively a higher power loss.

In order to check the quality of the joints, the contact resistance at the individual joints is measured directly. This is very costly and difficult to integrate into a continuous, automated manufacturing process. This is particularly true when different battery configurations with different busbar tracks are to be manufactured depending on the application or scope of the battery module, so that there are also structural respectively with respect to the course of the busbars resulting differences.

A method of the type mentioned is out DE 10 2007 037 377 A1 known. There, a thermographic image is taken by means of an infrared camera in order to determine any defects in the conductor connection. The thermographic image is processed by means of a corresponding evaluation software and graphically displayed on an output unit for further analysis and evaluation.

The invention is therefore based on the problem of specifying a method which allows a simple test of the quality of current-carrying joint connections to battery modules.

To solve this problem, the invention provides that an analysis image representing the actual or abstracted busbars is created on the part of the evaluation device and displayed on a screen, in which the quality of the joints to be complained of is indicated.

According to the invention, a sufficiently high current pulse, for example a charging or discharging current pulse, is applied to the entire battery module. The battery module may e.g. be a high-voltage battery, but also a module with lower output voltage of e.g. <60 V. So there is a flow of current across the cells and thus inevitably on the busbars. This current flow ensures a certain heating of the busbars. It comes in places that have a higher contact resistance, so for example, at the joints in question, to a slightly stronger heating than at other locations along the busbars. According to the invention, a thermographic image of this "heated" busbar arrangement is now recorded, which provides information about the temperature or heat distribution over the busbars, thus providing locally exactly defined information about the actual temperature.

Ideally, the busbars show a homogeneous temperature or heat distribution over their entire laying length, thus also in the area of the joining connections, ie the temperature is approximately the same everywhere. However, in places where a higher contact resistance is given, ie in particular in the region of the joint, the thermographic image shows a slightly higher temperature. Depending on how large the contact resistance is, the thermographic image provides the corresponding information. Based on this information can now be detected exactly and simultaneously for all joints, which quality are the individual joints. Because the information that can be detected from the image allows a relatively exact determination of the local contact resistance. The greater the local heating, the greater the contact resistance. If the local contact resistance that can be determined therefrom in the region of a joint exceeds a certain permissible threshold value, then the result is that the quality of this joint connection is not in order, and therefore must be reworked there or the battery module must accordingly be marked as not in order.

The method according to the invention is particularly simple and can be carried out very quickly and, with particular advantage, allows statements to be made about all joint connections by recording a single thermographic image. In addition to examining the extent to which the current flows evenly across the series-connected busbars, an evaluation can also be made as to whether parallel connection of cell rows also provides a uniform current distribution with regard to the series connected in parallel. The method can be readily integrated into an automatic manufacturing process, since ultimately only the taking of a thermographic image and its evaluation is required.

For taking the thermographic image, a thermal imaging camera is preferably used, which may be of any nature as long as it provides a sufficiently meaningful image. As an alternative to using a thermal imaging camera, it would also be conceivable to use a large-area array of IR sensors, which also provide heat-dependent signals.

The thermographic image may preferably be captured as a color image and output as such to a screen. This provides the opportunity to make a visual assessment. Warmer areas are z. B. brighter (or in a red color) than colder areas (darker or in a blue tone), so that it can be immediately recognized whether along the busbars in the region of any joints corresponding areas are given that have become too warm and therefore as qualitative not flawless joints are to be marked. This makes it possible to achieve a very simple visual evaluation. Alternatively, the thermographic image can also be output as a grayscale image, which can also be displayed on a screen and, although somewhat more difficult, can be optically evaluated.

An expedient development provides for the thermographic image to be evaluated automatically, if appropriate in addition to a purely optical evaluation, by means of an evaluation device. This evaluation device, that is, for example, a control device that also controls the image acquisition operation, has a corresponding evaluation or analysis algorithm to analyze the recorded thermographic image with respect to the heat distribution and to provide an evaluation result with respect to the individual joints. Such an evaluation result can also take place, for example, by comparing the recorded thermographic image with a comparison image which shows a recorded busbar distribution having qualitatively perfect joining connections. As an alternative to such an image or pattern comparison, it is of course also possible to carry out a purely mathematical evaluation on the basis of the individual signals resulting in the thermographic image.

If the evaluation is carried out by purely visual assessment of the image displayed on the screen, preferably the color image, it is of course here also possible to specify a comparison image showing a battery module respectively busbars with qualitatively perfect joints, which of course is equally a thermographic Picture acts.

However, if an automatic evaluation by means of an evaluation, so it is provided according to the invention that on the part of the evaluation an actual or abstracted busbars representing representing analysis image is created and output on the screen, are characterized in the quality of complaint to jointing. In other words, the evaluation device creates an analysis image in which the viewer is automatically marked with the one or more joints that have proved to be out of order on the basis of the analysis. This analysis image can be, for example, a real image of the busbar of the considered high-voltage cell, which was recorded, for example, by means of a parallel camera. It is also conceivable, however, that in the analysis image, a bus bar abstracted as a line drawing showing the course of the bus bars, is shown. The evaluation device is on the basis of the thermographic image readily able to determine the course of the busbars therefrom and to generate a corresponding abstracted representation. Even in this abstract representation, joints that are judged to be qualitatively imperfect can be easily represented.

• 1 eine Aufsicht auf ein erfindungsgemäßes Batteriemodul ohne aufgesetzte Stromschienen,
• 2 das Batteriemodul aus 1 mit aufgesetzten Stromschienen in einer Aufsicht,
• 3 eine Seitenansicht des Batteriemoduls 2 mit zugeordneter Qualitätsprüfungseinrichtung umfassend eine Wärmebildkamera,
• 4 eine Prinzipdarstellung eines mit der Wärmebildkamera aufgenommenen thermografischen Bildes zur Darstellung der Wärmeverteilung längs der Stromschienen, und
• 5 ein automatisch erstelltes Analysebild zur Darstellung der Stromschienen.

Further advantages, features and details of the invention will become apparent from the embodiment described below and from the drawing. Showing:

• 1 a plan view of an inventive battery module without patch busbars,
• 2 the battery module off 1 with attached busbars in a plan,
• 3 a side view of the battery module 2 with assigned quality inspection device comprising a thermal imaging camera,
• 4 a schematic representation of a thermographic image taken with the thermal imaging camera for representing the heat distribution along the busbars, and
• 5 an automatically generated analysis image for displaying the busbars.

1 shows a battery module 1 , consisting of several, here a total of eight separate cells 2 For example, prismatic cells or pouch cells, primarily in the form of lithium-ion cells. Every cell 2 has a plus pole 3 and a negative pole 4 on. In the exemplary embodiment shown, a 1p cell arrangement is selected, ie, the individual cells 2 are arranged so that in each case a positive pole 3 and a negative pole 4 two adjacent cells 2 alternate, as in 1 shown. An alternative configuration would be a 2p configuration. In this case, two cells would be arranged in the same orientation, followed by again two cells in reverse, but in turn under the same arrangement. This would result in each pair being formed from two equal cells, with the respective pairs alternating in the reverse order. Because of this 2p arrangement, therefore, there are two positive poles 3 and two minus poles 4 each side by side, which would lead to a slightly different arrangement of the busbars as in the 1p arrangement.

To see the individual connections of the cells 2 So the positive poles 3 and the negative poles 4 , which are also shown geometrically different for the sake of clarity, to connect together, are busbars 5 provided, see 2 showing the arrangement of the busbars 5 for connecting the poles of the cells 2 according to 1 , ie in the 1p arrangement, shows. These are so-called two-busbars, ie, that the busbars 5 are relatively short. They obviously extend from one cell each 2 to the neighboring cell 2 and contacts the one port, for example the positive pole 3 , with the other connection, so the negative pole 4 the neighboring cell. Be seen by this arrangement of the busbars 5 the cells 2 all connected in series.

To connect each port, so each plus and minus pole 3 . 4 with the respective busbar 5 the busbar is firmly connected via a joint connection with the respective pole. This joint connection can be done for example by screwing, but preferably the busbar 5 with the respective pole 3 . 4 welded. For this purpose, for example, each busbar corresponding openings, which are interspersed by the respective pole. For a Montagecodierung it would even be conceivable that the poles 3 . 4 have different configuration, as shown in the figures, so that the busbars have corresponding, form-compatible openings. In the area of the transition from the busbar to the respective pole, a welded joint would then be applied to firmly connect the pole and busbar.

The goal here is the contact resistance of the busbar 5 to the respective pole 3 . 4 to be kept as low as possible. The higher the resistance, the higher the voltage that drops locally to this transition region, which adversely affects the performance of the battery module.

In order to check the quality of the respective joint connection, as in 3 shown a testing device 6 provided, comprising a thermal imaging camera 7 , a control device associated therewith 8th with a suitable evaluation and processing software and a screen 9 , The thermal imager is positioned so that it is on top of the battery module 1 is directed and therefore a top view of the busbar assembly, see 2 , picks up. In the side view are the individual cells 2 and on the top side the individual busbars 5 shown.

Shown is also a power source 10 , via which a current pulse to the busbar arrangement, here to the two outermost busbars 5 , which have corresponding contact areas, is placed. This current pulse leads to a brief current flow through the battery module 1 and thus on all busbars 5 which thereby warm, albeit small. The thermal imager 7 Immediately after the gift or termination of the current impulse, a thermal image is taken. The image data becomes the controller 8th depending on the process configuration and a picture on the screen 9 outputs.

Since, as described, current flows via the busbar arrangement, if locally different resistances are given, for example in the region of the joining connections of a busbar to the respective pole, local heat differences occur. The thermal imager 7 Now takes a thermographic image, so a thermal image, which ultimately shows exactly the heat distribution over the entire busbar train. The thermal image thus contains information regarding the temperature distribution of the current flow caused briefly heated busbars. Based on this temperature distribution can now by the controller 8th , Which automatically analyzes the thermal image based, for example, on suitable processing software, it is determined to what extent there is too high a local contact resistance due to the heat information extractable from the image. Because in the thermal image are places that are warmer than other places, shown in different colors.

Such a thermal image is exemplary in 4 it is shown on the monitor, for example 9 output. The thermal picture shown here 11 shows an example of the individual cells 2 as well as the individual busbars 5 but preferably color coded as a color image. That is, that all parts, so in particular the busbars 5 , not as rails as such, but just their heat information is shown. By way of example, the density of the puncturing is the respective temperature of the busbars 5 shown. Most busbars are largely homogeneously dotted, that is, they have largely the same temperature. Only the two busbars 5a and 5b are what the fixing of the busbar at the pole of the cell 2a (in the case of the busbar 5a) or the cell 2 B (in the case of the busbar 5b ), significantly dotted. This is intended to indicate that in this area the busbar 5a . 5b has a higher temperature. This in turn is a clear indication that the local joint of the busbar 5a . 5b to the respective pole 3 . 4 has a high, possibly also too high a resistance. Excessively high resistance can be achieved, for example, by means of a pattern or image comparison with a comparison image which shows a thermal image of a same busbar arrangement, but in which all contact resistances are correct. It is therefore a color comparison or an analysis of the respective temperature-encoding color distributions.

The control device 8th can make this comparison automatically and then output a corresponding analysis image, as exemplified in 5 is shown. There again is the monitor 9 the analysis picture 12 shown in which merely exemplifies and abstracts the individual busbars 5 are shown. At the power rail 5a and the busbar 5b is each a marker 13a . 13b representing the position where too high a contact resistance is given.

5 Thus, the possibility of automatic, control device side image analysis to evaluate the heat information and to decide whether a local, impermissible resistance distribution is given or not.

Alternatively, it is also conceivable, only in 4 displayed thermal image, so that the operator can decide for himself whether the joints are OK or not. If appropriate, the operator can be shown a comparison image parallel to the screen, which shows a busbar arrangement in which all contact resistances are in order, so that he can make the evaluation by comparing this comparison thermal image with the actual thermal image.

Although the 1 and 2 a battery module 1 in a 1p arrangement, of course, a battery with another busbar arrangement, for example a 2p arrangement, would also be analyzable in the same way. Not only can cells which are connected in series be analyzed here, but also cell blocks each consisting of several cells, the cell blocks being connected in parallel. Common to all applications, however, is that by means of a single thermographic image and its evaluation, an exact quality inspection of the individual joint connections takes place solely from the temperature coefficient or the heating behavior of the busbars.

Claims (5)

A method for testing the quality of a current-carrying joint connection of busbars (5) to terminals of cells (2) of a battery module (1), wherein the cells (2) via the busbars (5) are interconnected, wherein the battery module (1) Current pulse, which leads to a current flow over the busbars (5), is applied, after which a thermographic image of the busbars (5), which provides information regarding the temperature distribution of the busbars (5), is taken, the thermographic image (11) automatically is evaluated by means of an evaluation device, characterized in that on the part of the evaluation device (8) an actual or abstracted busbars (5) performing analysis image (12) is created and output on a screen (9), are characterized in the quality of objectionable joints , Method according to Claim 1 , characterized in that for receiving the thermographic image (11) a thermal imaging camera (7) is used. Method according to Claim 1 or 2 , characterized in that the thermographic image (11) is recorded as a color image. Method according to one of the preceding claims, characterized in that the thermographic image (11) is output on a screen (9). Method according to one of the preceding claims, characterized in that the current-carrying joints at terminals of lithium-ion cells are tested.

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