Abstract:
A battery testing system according to an exemplary aspect of the present disclosure includes, among other things, a penetrating device and an impedance meter electrically connected to the penetrating device.

Description:
TECHNICAL FIELD 
     This disclosure relates to electrified vehicles, and more particularly, but not exclusively, to a battery testing system and method for evaluating the response of a battery cell to an unintended puncture or other cell damage. 
     BACKGROUND 
     Hybrid electric vehicles (HEV&#39;s), plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEV&#39;s), fuel cell vehicles and other known electrified vehicles differ from conventional motor vehicles in that they are powered by one or more electric machines (i.e., electric motors and/or generators) instead of or in addition to an internal combustion engine. High voltage current is typically supplied to the electric machines by one or more batteries that store electrical power. 
     Electrified vehicle batteries may employ one or more battery cells, such as lithium-ion battery cells. Tests for evaluating the safety of such battery cells are known. One common evaluation test is referred to as the nail penetration test. During this test, a nail is driven through a battery cell to create a short circuit inside the battery cell. In response to the destructive test, battery temperatures and voltages are measured. One drawback to known battery penetration tests is that these tests reveal little to no detail concerning the internal response of the battery cell. 
     SUMMARY 
     A battery testing system according to an exemplary aspect of the present disclosure includes, among other things, a penetrating device and an impedance meter electrically connected to the penetrating device. 
     In a further non-limiting embodiment of the foregoing system, the penetrating device is a nail. 
     In a further non-limiting device of either of the foregoing systems, the penetrating device is movable between a first position and a second position to puncture and short circuit a battery cell. 
     In a further non-limiting device of any of the foregoing systems, the impedance meter is connected to a positive terminal or a negative terminal of the battery cell and is configured to measure impedance and voltage data between the penetrating device and a terminal of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, the impedance meter is connected to a positive terminal and a second impedance meter is connected to a negative terminal of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, a voltage meter is configured to measure a voltage across a positive terminal and a negative terminal of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, a temperature sensor is configured to measure a temperature of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, a tool moves the penetrating device between a first position and a second position to puncture a battery cell. 
     In a further non-limiting device of any of the foregoing systems, the penetrating device includes a first portion having a non-conductive coating and a second portion that excludes the non-conductive coating. 
     In a further non-limiting device of any of the foregoing systems, the second portion of the penetrating device includes a pointed tip. 
     A battery testing system according to another exemplary aspect of the present disclosure includes, among other things, a battery cell, a penetrating device configured to short circuit the battery cell and an impedance meter electrically connected to the battery cell and the penetrating device and configured to measure at least impedance data between the battery cell and the penetrating device. 
     In a further non-limiting embodiment of the foregoing system, the impedance meter is electrically connected between a positive terminal or a negative terminal of the battery cell and the penetrating device. 
     In a further non-limiting device of either of the foregoing systems, a second impedance meter is electrically connected to the penetrating device and a terminal of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, the impedance meter is connected to a positive terminal of the battery cell and the second impedance meter is connected to a negative terminal of the battery cell. 
     In a further non-limiting device of any of the foregoing systems, a data acquisition system is configured to collect and analyze the impedance data from the impedance meter. 
     A method according to another exemplary aspect of the present disclosure includes, among other things, creating a short circuit in a battery cell and measuring impedance data associated with the battery cell in response to the step of creating the short circuit. 
     In a further non-limiting embodiment of the foregoing method, the step of creating the short circuit includes penetrating the battery cell with a penetrating device. 
     In a further non-limiting embodiment of either of the foregoing methods, the method includes measuring voltage data associated with the battery cell. 
     In a further non-limiting embodiment of any of the foregoing methods, the method includes calculating a transient current through the short circuit using the impedance data and the voltage data. 
     In a further non-limiting embodiment of any of the foregoing methods, the method includes electrically connecting an impedance meter to a penetrating device and the battery cell. 
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
     The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
         FIG. 2  illustrates a first embodiment of a battery testing system. 
         FIG. 3  illustrates a second embodiment of a battery testing system. 
         FIG. 4  illustrates a third embodiment of a battery testing system. 
         FIG. 5  illustrates a fourth embodiment of a battery testing system. 
         FIG. 6  illustrates an exemplary penetrating device that may be employed by a battery testing system. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to a battery testing system and method for evaluating the safety and design of a battery cell. The inventive battery testing system collects alternating current (AC) impedance data between a conductive penetrating device, such as a nail, and the battery cell. The impedance data may be collected using one or more impedance meters. The impedance data is collected and analyzed to calculate a transient current through a short circuit created in the battery cell by the penetrating device. The transient current calculations may then be used to improve the design and safety of the battery cell. 
       FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 , such as a HEV. Although depicted as a HEV, it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electrified vehicles, including but not limited to, PHEV&#39;s, BEV&#39;s, and fuel cell vehicles. 
     In one embodiment, the powertrain  10  is a power split system that employs a first drive system that includes a combination of an engine  14  and a generator  16  (i.e., a first electric machine) and a second drive system that includes at least a motor  36  (i.e., a second electric machine), the generator  16  and a battery  50 . For example, the motor  36 , the generator  16  and the battery  50  may make up an electric drive system  25  of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  30  of the electrified vehicle  12 . 
     The engine  14 , such as an internal combustion engine, and the generator  16  may be connected through a power transfer unit  18 . In one non-limiting embodiment, the power transfer unit  18  is a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  16 . The power transfer unit  18  may include a ring gear  20 , a sun gear  22  and a carrier assembly  24 . The generator  16  is driven by the power transfer unit  18  when acting as a generator to convert kinetic energy to electrical energy. The generator  16  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  26  connected to the carrier assembly  24  of the power transfer unit  18 . Because the generator  16  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  16 . 
     The ring gear  20  of the power transfer unit  18  may be connected to a shaft  28  that is connected to vehicle drive wheels  30  through a second power transfer unit  32 . The second power transfer unit  32  may include a gear set having a plurality of gears  34 A,  34 B,  34 C,  34 D,  34 E, and  34 F. Other power transfer units may also be suitable. The gears  34 A- 34 F transfer torque from the engine  14  to a differential  38  to provide traction to the vehicle drive wheels  30 . The differential  38  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  30 . The second power transfer unit  32  is mechanically coupled to an axle  40  through the differential  38  to distribute torque to the vehicle drive wheels  30 . 
     The motor  36  can also be employed to drive the vehicle drive wheels  30  by outputting torque to a shaft  46  that is also connected to the second power transfer unit  32 . In one embodiment, the motor  36  and the generator  16  are part of a regenerative braking system in which both the motor  36  and the generator  16  can be employed as motors to output torque. For example, the motor  36  and the generator  16  can each output electrical power to a high voltage bus  48  and the battery  50 . 
     The battery  50  may be a high voltage battery made up of one or more battery cells that are capable of outputting electrical power to operate the motor  36  and the generator  16 . Other types of energy storage devices and/or output devices can also be incorporated for use with the electrified vehicle  12 . 
     The motor  36 , the generator  16 , the power transfer unit  18 , and the power transfer unit  32  may generally be referred to as a transaxle  42 , or transmission, of the electrified vehicle  12 . Thus, when a driver selects a particular shift position, the transaxle  42  is appropriately controlled to provide the corresponding gear for advancing the electrified vehicle  12  by providing traction to the vehicle drive wheels  30 . 
     The powertrain  10  may additionally include a control system  44  for monitoring and/or controlling various aspects of the electrified vehicle  12 . For example, the control system  44  may communicate with the electric drive system  25 , the power transfer units  18 ,  32  or other components to monitor and/or control the electrified vehicle  12 . The control system  44  includes electronics and/or software to perform the necessary control functions for operating the electrified vehicle  12 . In one embodiment, the control system  44  is a combination vehicle system controller and powertrain control module (VSC/PCM). Although it is shown as a single hardware device, the control system  44  may include multiple controllers in the form of multiple hardware devices, or multiple software controllers within one or more hardware devices. 
     A controller area network (CAN)  52  allows the control system  44  to communicate with the transaxle  42 . For example, the control system  44  may receive signals from the transaxle  42  to indicate whether a transition between shift positions is occurring. The control system  44  could also communicate with a battery control module of the battery  50 , or other control devices. 
     Additionally, the electric drive system  25  may include one or more controllers  54 , such as an inverter system controller (ISC). The controller  54  is configured to control specific components within the transaxle  42 , such as the generator  16  and/or the motor  36 , such as for supporting bidirectional power flow. In one embodiment, the controller  54  is an inverter system controller combined with a variable voltage converter (ISC/VVC). 
       FIG. 2  illustrates a battery testing system  60  for testing and evaluating a battery cell  62 . For example, as is discussed in greater detail below, the battery testing system  60  may be used to detect an internal short circuit (and associated short circuit current flow) of the battery cell  62  in order to evaluate the safety and design of the battery cell  62 . 
     The battery cell  62  could be part of the battery  50  of the electrified vehicle  12  described with respect to  FIG. 1 . However, the battery testing system  60  may be utilized to evaluate other battery cells, for any application, within the scope of this disclosure. 
     In one embodiment, the battery cell  62  includes a cell body  64  having opposing faces  65 . The opposing faces  65  extend between a positive terminal  66  and a negative terminal  68  of the battery cell  62 . Although shown as a prismatic cell, the battery cell  62  could be any type of cell including but not limited to laminate pouch, prismatic metal can or cylindrical can. 
     A penetrating device  70  of the battery testing system  60  may be used to penetrate the cell body  64  of the battery cell  62  in order to create a short circuit between the positive terminal  66  and the negative terminal  68 . In one embodiment, the penetrating device  70  is a nail. Other devices could potentially be used to penetrate the cell body  64  of the battery cell  62 , and these devices could include any size, shape, material and configuration. In one embodiment, the battery cell  62  is fully charged prior to performing a battery penetration test with the battery testing system  60 . However, the test can be performed at any state of charge, and can be used to explore changing abuse tolerance properties as a function of state of charge. 
     In one embodiment, the penetrating device  70  is configured to create a puncture  84  through one or both of the opposing faces  65  in order to simulate an internal shorting condition of the battery cell  62 . For example, the penetrating device  70  may include a pointed tip  89  for penetrating or puncturing the battery cell  62 . 
     The penetrating device  70  may be moved by a tool  72  between a first position X and a second position X′ (shown in phantom) in order to penetrate the battery cell  62 . For example, in the first position X the penetrating device  70  is spaced away from the battery cell  62 , and in the second position X′ the penetrating device  70  is moved to a position in which the penetrating device  70  has punctured through at least one of the opposing faces  65  of the battery cell  62 . 
     The tool  72  may move the penetrating device  70  linearly between the first position X and the second position X′, in one embodiment. The tool  72  can be actuated to control various parameters of the battery penetration test, including the speed at which the penetrating device  70  is moved to puncture the battery cell  62 . In one non-limiting embodiment, the tool  72  moves the penetrating device  70  at a speed of 80 mm/second during the battery penetration test. Other testing parameters are contemplated as within the scope of this disclosure, including other testing speeds. For example, slower testing speeds may provide higher quality data. 
     An impedance meter  74  may be electrically connected to the penetrating device  70  and one or both of the positive terminal  66  and negative terminal  68  of the battery cell  62 . The impedance meter  74  is a diagnostic tool operable to measure impedance and voltage data between the penetrating device  70  and the battery cell  62 . In one non-limiting embodiment, the impedance meter  74  is a commercially available product that operates at a certain frequency (i.e., 1 kHz, 10 kHz, etc.). However, other impedance measuring devices may also be utilized within the scope of this disclosure. 
     In one embodiment, the impedance meter  74  is connected to the positive terminal  66  of the battery cell  62  via a first electrode  86  and to the penetrating device  70  via a second electrode  88  (see  FIG. 2 ). In another embodiment, the impedance meter  74  is connected to the negative terminal  68  of the battery cell  62  (see  FIG. 3 ) with the first electrode  86  and to the penetrating device  70  via the second electrode  88 . In other words, the impedance data may be collected between the penetrating device  70  and either the positive terminal  66  or the negative terminal  68  of the battery cell  62 . 
     The battery testing system  60  may also employ a voltage meter  76 . The voltage meter  76  may be utilized to measure voltage data across the positive terminal  66  and the negative terminal  68  of the battery cell  62 . 
     Optionally, the battery testing system  60  may also include a temperature sensor  78  for measuring a temperature associated with the battery cell  62 . In one non-limiting embodiment, the temperature sensor  78  is positioned near the puncture  84  of the battery cell  62 . However, the temperature sensor  78  may be positioned at other locations within the scope of this disclosure. 
     In response to the penetrating device  70  creating a short circuit in the battery cells  62 , the battery testing system  60  measures the impedance data, voltage data and/or temperature data using the impedance meter  74 , the voltage meter  76  and, optionally, the temperature sensor  78 , respectively. This data may be communicated to a data acquisition system  82  of the battery testing system  60 . The data acquisition system  82  is configured to receive, store and analyze the impedance data, voltage data and/or temperature data in order to evaluate the design and safety of the battery cell  62 . The data acquisition system  82  may include the necessary hardware and software for converting the impedance data, voltage data and/or temperature data into digital numeric values that can be manipulated by a computer. 
     For example, in one non-limiting embodiment, the data acquisition system  82  may be utilized to analyze this data in order to calculate the transient current and heat associated with a short circuit of the battery cell  62  responsive to a battery penetration test. This information can then be used by a battery designer to improve the design and safety of the battery cell  62 . 
       FIG. 4  illustrates another exemplary battery testing system  160 . In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of 100 or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements. 
     In this embodiment, the battery testing system  160  includes a first impedance meter  74 A and a second impedance meter  74 B. The first impedance meter  74 A is electrically connected to the positive terminal  66  of a battery cell  62 , and the second impedance meter  74 B is electrically connected to the negative terminal  68  of the battery cell  62 . In this way, two sets of impedance data may be collected simultaneously in response to creating a short circuit in the battery cell  62  with a penetrating device  70 . 
       FIG. 5  illustrates yet another battery testing system  260 . In this embodiment, the battery testing system  260  incorporates a third impedance meter  74 C in addition to the first impedance meter  74 A and the second impedance meter  74 B. In one embodiment, the third impedance meter  74 C measures impedance data across the positive terminal  66  and negative terminal  68  of the battery cell  62 . In this way, three sets of impedance data may be collected simultaneously (i.e., positive terminal, negative terminal, whole cell). In general, a more accurate analysis of the safety and design of the battery cell  62  may be completed by collecting a greater amount of impedance data. 
       FIG. 6  illustrates a penetrating device  170  that may be used with any of the battery testing systems  60 ,  160 ,  260  described above. In this embodiment, the penetrating device  170  includes a first portion  90  and a second portion  92 . The second portion  92  includes a pointed tip  189 , in one embodiment. The pointed tip  189  enables the penetrating device  170  to more easily penetrate a battery cell during a battery penetration test. The pointed tip  189  may be sharp or rounded within the scope of this disclosure. 
     In one embodiment, the first portion  90  may be coated with an anti-conductive coating  94 . In one non-limiting embodiment, the anti-conductive coating  94  includes plastic, although other non-conductive materials are also contemplated herein. In contrast, the second portion  92  excludes any anti-conductive coating. In other words, the first portion  90  is coated or otherwise modified to restrict the conductive portion of the penetrating device  170  to only those portions that are not coated by the anti-conductive coating  94 . This significantly minimizes any non-idealities associated with introducing a conductive path from a battery cell and is expected to more closely approximate cell behavior during a true internal short circuit. 
     Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
     The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.