Patent Publication Number: US-2023145674-A1

Title: Traction Battery for a Motor Vehicle, Motor Vehicle, and Method for Controlling Degassing Elements of a Traction Battery

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 from German Patent Application No. DE 10 2021 129 192.5, filed Nov. 10, 2021, the entire disclosure of which is herein expressly incorporated by reference. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to a traction battery with degassing elements which in the case of a cell outgassing are to be opened for the purpose of conducting the hot gases away, in order to conduct the stream of gas away out of the battery housing. In addition, the invention relates to a motor vehicle with such a traction battery, and also to a method for controlling the degassing elements in the case of a cell outgassing. 
     In case of a fault—for instance, a short circuit in a battery cell—there is the possibility that a battery cell will undergo thermal runaway. In this case, the battery cell may outgas, or emit gas—that is to say, hot gases emerge from the battery cell in question. In traction batteries, a plurality of battery cells are accommodated in a battery housing which separates the battery cells from the environment. In the event of a runaway of a battery cell, the hot stream of gas arising has to be conducted away to the outside (out of the battery housing), in order to prevent an uncontrolled rupturing of the battery housing or damage to further battery cells. For this purpose, degassing elements are known in the form of excess-pressure valves, bursting membranes or such like, which are integrated in various forms and numbers in the wall of the battery housing. In this connection, attention would have to be paid to ensuring that the hot streams of gas do not result in damage outside the battery housing by reason of excessive temperature when flowing out. 
     It is therefore an object of the present invention to obtain an improvement when routing gases away in the case of an outgassing of battery cells. This object is achieved by a traction battery, by a motor vehicle and also by a method according to the claimed invention. 
     According to one embodiment of the invention, a traction battery for a motor vehicle is provided, having a plurality of battery cells which are electrically connected to one another, having a battery housing which houses the battery cells, having several degassing elements for conducting gas away out of the battery housing in the case of a cell outgassing, having a sensing system for localizing the cell outgassing, having a control unit which in the case of a cell outgassing actuates the degassing elements in such a manner that the degassing element situated nearest the cell outgassing remains closed and one or more of the degassing elements that are farther away from the cell outgassing is/are opened. As a result, the stream of gas within the battery housing has to travel a certain distance before the stream of gas can escape to the environment. In this way, the interior of the battery housing serves as cooling path for the hot stream of gas, in turn lowering the risk of the stream of gas being too hot when it exits the battery housing. 
     According to a further embodiment of the invention, at least the degassing element that, of all the degassing elements in the battery housing in the case of outgassing, is farthest away from the cell outgassing is opened by the control unit. As a result, the cooling path within the battery housing is maximized, and the stream of gas is cooled as much as possible. 
     According to a further embodiment of the invention, the sensing system includes several temperature sensors. 
     According to a further embodiment of the invention, the sensing system includes a voltage-monitoring device with which a drop in voltage at one or more battery cells is capable of being detected, in order consequently to detect a cell outgassing. 
     According to a further embodiment of the invention, the sensing system includes an optical capture device. 
     In addition, the present invention provides a motor vehicle having such a traction battery. 
     Furthermore, the present invention provides a method for controlling degassing elements for conducting gas away out of a battery housing of a traction battery for a motor vehicle, with the following steps: identifying a cell outgassing, localizing the cell outgassing by way of a sensing system, actuating the degassing elements in such a manner in the case of a cell outgassing that the degassing element situated nearest the cell outgassing remains closed and one or more of the degassing elements that are farther away from the cell outgassing is/are opened. As already mentioned above, as a result the interior of the battery housing acts as cooling path. 
     According to a further embodiment of the method, at least the degassing element that, of all the degassing elements in the battery housing in the case of outgassing, is farthest away from the cell outgassing is opened by the control unit. As already mentioned, as a result the cooling path is maximized. 
     According to a further embodiment, the method further features the step of localizing the cell outgassing using temperature sensors. 
     According to a further embodiment, the method further features the step of localizing the cell outgassing using a voltage-monitoring device with which a drop in voltage at one or more battery cells is registered, in order to infer a cell outgassing therefrom. 
     In the following, a preferred embodiment of the present invention will be described with reference to the drawing. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG.  1    shows schematically a traction battery  1  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWING 
     The traction battery  1  has been installed in a motor vehicle which is not represented. The motor vehicle is an electrified motor vehicle which, at least at times, is propelled purely electrically. In particular, it may be a passenger car. 
     The traction battery  1  includes a plurality of battery cells  2  which are electrically connected to one another. For instance, the battery cells  2  may have been electrically connected in series and/or in parallel. The battery cells  2  are electrochemically-based cells for storing and providing electrical energy at least for the drive of the motor vehicle—that is to say, for supplying one or more drive motors. The battery cells  2  may be cylindrical cells or (as shown by way of example) rectangular-cuboid cells. In case of a fault, particularly in the event of a thermal runaway of the battery cell  2 , a battery cell  2  might outgas—that is to say, hot gases might emerge from the battery cell, that is to say, a cell outgassing  3  is present. 
     The battery cells  2  are housed in a battery housing  4  which separates the battery cells  2  from the environment of the battery housing  4  in a fluid-tight manner or hermetically. 
     Degassing elements  5  (at least two, for instance also three, four or more) are arranged in or on one or more walls of the battery housing  4 . In normal operation—that is to say, when a cell outgassing  3  of a battery cell  2  is not present—the degassing elements  5  are closed in fluid-tight manner. In the case of a cell outgassing  3  of at least one battery cell  2 , at least one of the degassing elements  5  is opened, so that the hot gases emerging from the outgassing battery cell  2  can escape from the battery housing  4  to the environment via the opened degassing element(s)  5 —that is to say, outside the battery housing  4 —in particular to a region surrounding the motor vehicle. The degassing elements  5  are valves, flaps or such like which are capable of being actuated. 
     In addition, the traction battery  1  includes a control unit  6  which has been adapted to actuate the degassing elements  5 . The control unit  6  may have been arranged in, on or outside the battery housing  4 . 
     Furthermore, a sensing system  7  is provided which communicates detection signals to the control unit  6 . The control unit  6  may have been connected to the degassing elements  5  and to the sensing system  7  via wires, cables, or in wireless manner. The sensing system  7  may include several temperature sensors, pressure sensors and/or temperature/pressure sensors spaced from one another. In  FIG.  1   , temperature sensors are indicated as an example of the sensing system  7 . Additionally or alternatively, the sensing system  7  may include a voltage-monitoring device which monitors a voltage of the individual battery cells  2  and, in the event of a drop in voltage occurring, determines that a cell outgassing  3  of a particular battery cell  2  is present, and can infer the position of the cell outgassing  3  with the aid of stored positions of the individual battery cells  2 . In addition, the sensing system  7  may include an optical capture device, for example an optical camera or a thermal-imaging camera, by way of which a cell outgassing  3  is capable of being identified and localized. 
     In the case of a detected cell outgassing  3  and the localization of the cell outgassing  3 , the control unit  6  controls the degassing elements  5  in such a manner that at least the degassing element  5  that has the shortest spacing from the cell outgassing  3  remains closed. The degassing elements  5  are to be configured structurally in such a way that they are not opened unintentionally even by a pressure surge possibly arising as a result of the cell outgassing  3 . Of the remaining degassing elements  5 , one or more is/are opened. At least a single degassing element  5  is opened, specifically that one which has the largest spacing from the cell outgassing  3 . 
     As a result, the stream of gas within the battery housing  4  has to travel a certain distance before the stream of gas escapes to the environment, so the interior of the battery housing serves as cooling path for the hot stream of gas. 
     Whilst the invention has been illustrated and described in detail in the drawing and in the foregoing description, this illustration and description is to be understood as being exemplary and not restrictive, and it is not the intention to restrict the invention to the disclosed embodiment. The mere fact that certain features have been mentioned in various dependent claims is not intended to suggest that a combination of these features might not also be utilized advantageously. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.