Abstract:
A method and apparatus for determining coolant leakage in a vehicular propulsion system battery. An AC isolation resistance test is used to determine whether an isolation fault has occurred within the battery, but can also determine the capacitance of the circuit or system, which can further determine the coolant leakage levels of the vehicular propulsion system battery. This eliminates having an additional device to measure the coolant leakage.

Description:
BACKGROUND 
       [0001]    The present application generally relates to an apparatus and method for monitoring a vehicular propulsion system battery and, specifically, to monitoring the vehicular propulsion system battery to determine the presence of coolant leakage. 
         [0002]    Hybrid and electric vehicles provide an alternative to conventional means of vehicular motive power by either supplementing (in the case of hybrids) or completely replacing (in the case of electric vehicles) the internal combustion engine (ICE). As such, at least a portion of the motive power in a hybrid or electric vehicle is provided by one or more battery packs that act as a direct current (DC) voltage source to a motor, generator or transmission that in turn can be used to provide the energy needed to rotate one or more of the vehicle&#39;s wheels. One form of battery that appears to be particularly promising for vehicular applications is known as a lithium-ion battery. 
         [0003]    Because such battery packs form a significant part of the vehicle&#39;s propulsion system, it is important to monitor parameters associated with battery operation to ensure proper vehicular performance. Examples of such parameters include cell temperature, voltage, state of charge and so forth. Another such parameter is the coolant leakage. 
         [0004]    Coolant leakage is an important parameter for a vehicular propulsion system battery, as it can lead to both a decrease in the efficiency of the battery thermal system as well as an increased likelihood that the system will overheat. Coolant leakage can also create a short circuit for the entire system. It can cause an isolation fault (voltage leaking from the main battery to the chassis) within the system. Finally, coolant leakage will limit the overall life of the battery. 
         [0005]    Conventionally, a separate device is needed within a vehicular system battery to measure coolant leakage; however, one form of test known as an AC isolation resistance test can be performed both to determine whether an isolation fault has occurred and to determine coolant leakage without the need for an extra device. The conventional AC isolation resistance test is performed by injecting an excitation signal into the system to generate a readback signal. The amplitude and phase of the readback signal is determined by the difference between the excitation signal and this readback signal. 
         [0006]    It can be difficult to ascertain the small changes between the amplitudes and phases of the original and readback signals of the conventional AC isolation resistance test, especially if the system experiences certain conditions. Even a slight difference in system conditions can lead to a large error in the isolation resistance measurement. Such a conventional method also uses a predefined range for a quantity known as Y capacitance. Y capacitors are used in high voltage systems in order to reduce interference. They are typically exposed to transients and overvoltages within a system, and are generally installed for line-to-ground or neutral-to-ground connections. Y capacitors are intended to be used where failure could lead to electric shock if proper ground connection is lost and they operate by discharging (shunting) current to the ground. The obtained value can lead to errors if the actual Y capacitance value is outside of the predefined range. The isolation resistance measurement will be inaccurate, which will lead to a false isolation detection. 
         [0007]    Accordingly, it is challenging and difficult to accurately determine whether an isolation fault has been detected. Likewise, it is challenging and difficult to perform an accurate AC isolation resistance measurement such that the obtained Y capacitance value can be related to a correct value for important system parameters such as coolant leakage for a vehicular battery. 
       SUMMARY 
       [0008]    According to one aspect of the invention, a method for monitoring a vehicular propulsion system battery to determine the presence of coolant leakage is disclosed. The method comprises receiving a first capacitance related to discharge current of the battery. Then, a second capacitance related to discharge current of the battery is received. The first capacitance is compared to the second capacitance and related to a coolant leakage. Finally, the related information is provided to indicate coolant leakage. 
         [0009]    Optionally, in this aspect, the first capacitance and the second capacitance are Y capacitances. The Y capacitances may be obtained from a plurality of waveforms, wherein the waveforms are filtered to generate a plurality of DC components. The DC components are then separated to receive an isolation resistance and the Y capacitances. The second capacitance may be continuously received. Additionally, providing the related information comprises conveying a sensory cue to the user. In one form, this may include using a gauge, audio alarm, warning light, or other means for alerting the user of a change in coolant leakage, i.e. a visual, light, sound or combinations thereof. 
         [0010]    According to another aspect of the invention, an apparatus for monitoring a vehicular propulsion system battery to determine the presence of coolant leakage is described. The apparatus comprises a sensor for receiving a first and second capacitance related to discharge current of the battery, a processing component configured to compare the first and second capacitance, a relating mechanism for comparing capacitance to a coolant leakage, and an output source to a user to provide indicia of the coolant leakage. The processing component may be electrically connected to one or more sensors that may detect a coolant leakage. 
         [0011]    Optionally, in this aspect, the first capacitance and the second capacitance are Y capacitances. The Y capacitances may be obtained from a plurality of waveforms, wherein the waveforms are filtered to generate a plurality of DC components. The DC components are then separated to receive an isolation resistance and the Y capacitances. The second capacitance may be continuously received. Finally, an output source to a user may provide the related information to a user to indicate coolant leakage, wherein the providing comprises conveying a sensory cue to a user. In one form, this may include using a gauge, audio alarm, warning light, or other means for alerting the user of a change in coolant leakage, i.e. a visual, light, sound or combinations thereof. 
         [0012]    According to yet another aspect of the invention, a method for monitoring a fuel cell stack to determine the presence of coolant leakage is described. The method comprises receiving a first Y capacitance from a sensor coupled to the stack in such a way to measure the indicia of coolant leakage, receiving a second Y capacitance from a sensor coupled to the stack in such a way to measure the indicia of coolant leakage, comparing the first Y capacitance to the second Y capacitance, and providing a signal representative of the compared capacitances to a signal processing component. Optionally, the providing a signal representative of the compared capacitances comprises notifying a user of the coolant leakage. The signal processing component may be capable of responding, processing, receiving, transmitting or otherwise acting upon the capacitances to either maintain them or to convey indicia of a fuel cell leakage status to a user. The user may be an owner, operator or driver, or a person that may be assembling, servicing, or is otherwise responsible for overall fuel cell system well-being. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Preferred embodiments will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements and wherein: 
           [0014]      FIG. 1  is a flowchart of one embodiment of a method for monitoring a vehicular propulsion system battery to determine coolant leakage; and 
           [0015]      FIG. 2  is a block diagram showing an embodiment of a system capable of utilizing the method for monitoring a vehicular propulsion system battery to determine coolant leakage. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    It should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the drawings. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting. 
         [0017]    A possible way to detect coolant leakage is to obtain the Y capacitance values within the system. The present disclosure provides for an accurate AC isolation resistance test to be performed on a vehicular propulsion system battery. In one form, the present disclosure uses the AC isolation resistance test to specifically determine the Y capacitance, which can be related to coolant leakage. Such a configuration reduces the need for an additional or separate device within the system to measure coolant leakage. 
         [0018]    The present disclosure takes the readback signal from the isolation resistance test and multiplies it with a plurality of sinusoidal waveforms as a way to generate a plurality of DC components. One of the DC components determines the amplitude change. The other DC component determines the phase change. These DC components are more accurate and more readable than the previous method, because the previous method is highly sensitive to slight changes in system conditions. Thus, the DC components can be obtained with less noise from the system. The current method filters the DC components in order to determine both the isolation resistance and the Y capacitance. 
         [0019]    Once the first capacitance value is received, a second capacitance value can be continuously received. The timing of the second capacitance allows for an overall faster detection time of the system. A comparison of the two Y capacitance values is performed. In one form, the comparison can be done through a calculation, a look-up table, or other methods known in the art. The compared capacitances may then be used to relate to a coolant leakage value. The compared capacitances may be related to coolant leakage by conducting tests on the battery, by a look-up table, or by other methods known in the art. Finally, the compared capacitances may be provided to a user or to a signal processing component. 
         [0020]      FIG. 1  shows an illustration of one embodiment of a method for monitoring coolant leakage  18  in a vehicular propulsion system battery  10  in accordance with the present disclosure and shown generally at  200 . 
         [0021]    Method  200  begins when a vehicular propulsion system battery  10  is started  100 . The battery  10  may be started  100  by a user, an event, or any other method known in the art. A first capacitance  110  related to the discharge current is received. The first capacitance  110  may be received from a source or several sources. In one embodiment, the first capacitance  110  is received from a sensor  26 . In another embodiment, the first capacitance  110  is received from a processor. In yet another embodiment, the first capacitance  110  is received from a controller. The first capacitance  110  may include different types of capacitances. In one embodiment, the first capacitance  110  is a Y capacitance. In another embodiment, the first capacitance  110  is an X capacitance. In yet another embodiment, the first capacitance  110  may be any other type of capacitance received by the system. The first capacitance  110  may also be related to other system parameters, such as current, voltage, and so forth. 
         [0022]    A second capacitance  120  related to the discharge current is received. The second capacitance  120  may be received from a source or several sources. In one embodiment, the second capacitance  120  is received from a sensor  26 . In another embodiment, the second capacitance  120  is received from a processor. In yet another embodiment, the second capacitance  120  is received from a controller. The second capacitance  120  may include different types of capacitances. In one embodiment, the second capacitance  120  is a Y capacitance. In another embodiment, the second capacitance  120  is an X capacitance. In yet another embodiment, the second capacitance  120  may be any other type of capacitance received by the system. The second capacitance  120  may also be related to other system parameters, such as current, voltage, and so forth. 
         [0023]    The second capacitance  120  may be continuously received by the system. In another embodiment, the second capacitance  120  may be stored within a memory component, a data repository, or any other storage device known in the art. Once the first capacitance  110  and the second capacitance  120  are received, a compared capacitance  130  is determined. The compared capacitance  130  may be stored within a memory component, a data repository, or any other storage device known in the art. 
         [0024]    After the compared capacitance  130  is determined, related information  140  between the compared capacitance  130  and the coolant leakage  18  is found. In one embodiment, the related information  140  is determined from empirical data and continuous testing of the battery. The test may compare the isolation resistance values to the physical measurements of the battery at different conditions, such as coolant leakage level. When the coolant leakage level changes, the Y-capacitance also changes, because of its sensitivity to the leakage level. In another embodiment, the related information  140  is determined from a processing component  20  that operates upon a table, index or any other method known in the art. If coolant leakage  18  is present  150 , then the related information  140  is provided  160  to a user  14  to indicate coolant leakage  18  with an output source  22 . The term “providing” may include outputting, displaying, conveying, transmitting, receiving or the like to a device, display, or any other component known in the art such that the user can be either directly or indirectly made known of the coolant leakage  18  status. 
         [0025]    In one embodiment, the output source  22  may provide a sensory cue that can be a visual, such as a picture, symbol, number, or display. In another embodiment, the output source  22  may provide a sensory cue that can be light, such as a dashboard light. In another embodiment, the output source  22  may provide a sensory cue that can be sound, such as a voice or beep. In yet another embodiment, the output source  22  may provide a sensory cue that is combinations of the preceding embodiments or any other sensory cue known in the art. 
         [0026]    Referring to  FIG. 2 , a block diagram showing an embodiment of a system capable of one embodiment of a method for determining coolant leakage  18  and its applicable use within a vehicular propulsion system battery  10  is shown. 
         [0027]    An example of a vehicular propulsion system battery  10  that is capable of the method for determining coolant leakage  18  discussed above is shown. The following paragraphs simply provide a brief overview of one such vehicular propulsion system battery  10 , however, other systems not shown could employ the disclosed method as well. 
         [0028]    A vehicle  12 , generally includes a user  14  and the vehicular propulsion system battery  10 . Vehicle  12  is preferably a mobile vehicle such as a motorcycle, car, truck, recreational vehicle (RV), boat, plane, moped, and so forth. Vehicle  12  is generally equipped with appropriate processing components  20  that allow it to perform various functions, including method  200 , which further comprises communication to the user  14 . A relating mechanism  24  for comparing the capacitances will also be present within the vehicle. If a coolant leakage is detected  150 , then an output source  22  provides indicia of the coolant leakage  18  to a user  14 . 
         [0029]    The related information may be conveyed to a user  14  by an onboard device  16  that provides a variety of mechanisms, such as an output source  22  that can provide a sensory cue. The output source  22  is linked to the vehicular system battery  10  and may provide indicia of the coolant leakage  18  to the user  14 . The output source  22  may provide a sensory cue that can be a visual, light, sound or combinations thereof or other known methods within the art. Such providing may also include an intermediate step, such as storing data related to the coolant leakage  18  in a storage repository that can be used to provide indicia of the leakage status to the output source  22 . 
         [0030]    While the present disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.