Abstract:
Methods and systems for detecting and clearing battery power failure of an electric clutch actuator (ECA) include use of a capacitor connected to the ECA. The capacitor is connected to the ECA such that when the ECA and a battery configured to output a battery voltage are connected together a capacitor voltage matches the battery voltage and when the ECA and the battery are disconnected from one another the capacitor voltage differs from the battery voltage. A loss of battery connection is detected upon a difference between the capacitor voltage and the battery voltage exceeding a threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of: U.S. Provisional Application No. 61/980,066, filed Apr. 16, 2014; U.S. Provisional Application No. 62/008,087, filed Jun. 5, 2014; and U.S. Provisional Application No. 62/008,089, filed Jun. 5, 2014; the disclosures of which are hereby incorporated in their entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to detecting and clearing battery power failure of an electric clutch actuator. 
       BACKGROUND 
       [0003]    An electric clutch actuator (ECA) controls engagement and disengagement of a clutch. For instance, the clutch connects an engine to a transmission of a vehicle powertrain when engaged and disconnects the engine from the transmission when disengaged. The ECA receives power for controlling the clutch from a battery. At times, the level or amount of battery power to the ECA may be too low or too high. The battery power may become too low as a result of loss of battery connection while the ECA is in a motoring mode. Likewise, the battery power may become too high as a result of loss of battery connection while the ECA is in a regeneration mode. Timely detection of such battery power failure of the ECA in either case is desirable. 
       SUMMARY 
       [0004]    An object of the present invention includes detecting battery power failure of an electric clutch actuator (ECA) based on voltage at a capacitor connected between the ECA and a battery that is to provide the battery power. 
         [0005]    A further object of the present invention includes detecting re-establishment of proper battery power to the ECA, after battery power failure was detected, based on voltage at the capacitor. 
         [0006]    Another object of the present invention includes detecting the battery power of the ECA being too low based on voltage at the capacitor when the ECA is in a motoring mode. 
         [0007]    A further object of the present invention includes detecting re-establishment of proper battery power to the ECA, after the battery power was detected to be too low, based on voltage at the capacitor when the ECA is in the motoring mode. 
         [0008]    Another object of the present invention includes detecting the battery power to the ECA being too high based on voltage at the capacitor when the ECA is in a regeneration mode. 
         [0009]    A further object of the present invention includes detecting re-establishment of proper battery power to the ECA, after the battery power was detected to be too high, based on voltage at the capacitor when the ECA is in the regeneration mode. 
         [0010]    In carrying out at least one of the above and other objects, the present invention provides a method for an ECA. The method includes connecting a capacitor to the ECA such that when the ECA and a battery configured to output a battery voltage are connected together a capacitor voltage matches the battery voltage and when the ECA and the battery are disconnected from one another the capacitor voltage differs from the battery voltage. The method further includes detecting a loss of battery connection upon a difference between the capacitor voltage and the battery voltage exceeding a threshold. 
         [0011]    In an embodiment, the method further includes detecting re-establishment of the battery connection upon the difference between the capacitor voltage and the battery voltage being less than the threshold for a duration after a loss of battery connection was detected. 
         [0012]    In an embodiment, the method further includes detecting re-establishment of the battery connection upon the difference between the capacitor voltage and the battery voltage being less than the threshold and a rate of change of the capacitor voltage being less than a rate threshold for a duration after a loss of battery connection was detected. 
         [0013]    In an embodiment, the method further includes detecting re-establishment of the battery connection upon the difference between the capacitor voltage and the battery voltage being less than the threshold and a change of the capacitor voltage caused in response to motor excitation of the ECA being less than a change threshold after a loss of battery connection was detected. 
         [0014]    In an embodiment, the method further includes operating the ECA in a motoring mode in which the ECA consumes power such that during loss of battery connection the capacitor voltage falls and detecting a loss of battery connection upon the capacitor voltage falling lower than a low threshold. 
         [0015]    In an embodiment, the method further includes operating the ECA in a regeneration mode in which the ECA supplies power such that during loss of battery connection the capacitor voltage rises and detecting a loss of battery connection upon the capacitor voltage rising greater than a high threshold. 
         [0016]    Further, in carrying out at least one of the above and other objects, the present invention provides a system having an ECA operable to actuate a clutch. The system further includes a capacitor connected to the ECA such that when the ECA and a battery configured to output a battery voltage are connected together a capacitor voltage matches the battery voltage and when the ECA and the battery are disconnected from one another the capacitor voltage differs from the battery voltage. The system further includes a controller configured to detect a loss of battery connection upon a difference between the capacitor voltage and the battery voltage exceeding a threshold. 
         [0017]    In an embodiment, the system further includes a voltage bus configured to provide the battery voltage when the battery is connected to the voltage bus. In this case, the capacitor and the ECA are connected to the voltage bus. The capacitor and the ECA may be connected in parallel to one another to the voltage bus such that the capacitor is connected between the battery and the ECA when the battery is connected to the voltage bus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  illustrates a block diagram of an exemplary vehicle powertrain having an electric clutch actuator (ECA) powered by an auxiliary battery in accordance with an embodiment of the present invention; 
           [0019]      FIG. 2  illustrates a schematic diagram of the ECA, the auxiliary battery, and a capacitor connected together via a voltage bus with the capacitor being connected between the ECA and the auxiliary battery in accordance with an embodiment of the present invention; 
           [0020]      FIG. 3  illustrates plots depicting battery power failure scenarios upon loss of battery connection to the ECA; 
           [0021]      FIG. 4A  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in a motoring mode in accordance with a first embodiment of the present invention; 
           [0022]      FIG. 4B  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in a regeneration mode in accordance with the first embodiment of the present invention; 
           [0023]      FIG. 5A  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in the motoring mode in accordance with a first variation of the first embodiment of the present invention; 
           [0024]      FIG. 5B  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in the regeneration mode in accordance with the first variation of the first embodiment of the present invention; 
           [0025]      FIG. 6A  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in the motoring mode in accordance with a second variation of the first embodiment of the present invention; and 
           [0026]      FIG. 6B  illustrates a flowchart describing operation of detecting battery power failure of the ECA and detecting re-establishment of proper battery power to the ECA based on the capacitor voltage when the ECA is in the regeneration mode in accordance with the second variation of the first embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0028]    Referring now to  FIG. 1 , a block diagram of an exemplary vehicle powertrain  10  having an electric clutch actuator (ECA)  12  powered by an auxiliary battery  14  in accordance with an embodiment of the present invention is shown. Powertrain  10  is an electric hybrid powertrain further including an engine  16 , a motor  18 , and a transmission  20 . Motor  18  is connected to transmission  20  and receives power from a traction battery  22  for providing a motive force to the transmission. 
         [0029]    A clutch  24  is between engine  16  and motor  18 . ECA  12  controls the engagement (i.e., closing) and disengagement (i.e., opening) of clutch  24 . Clutch  24  connects engine  16  to motor  18  when engaged whereby engine  16  is connected to transmission  20  via motor  18 . ECA  12  operates in a motoring mode to cause clutch  24  to move from a starting position to a relatively more engaged position. On the other hand, clutch  24  disconnects engine  16  from motor  18  when disengaged whereby engine  16  is disconnected from both motor  18  and transmission  20 . ECA  12  operates in a regeneration mode when clutch  24  moves from a starting position to a relatively more disengaged position. 
         [0030]    Auxiliary battery  14  is a DC battery. ECA  12  receives DC battery power for controlling clutch  24  from battery  14 . In particular, battery  14  provides a battery voltage onto a voltage bus  26 . ECA  12  is connected to voltage bus  26  to receive the battery voltage and draw battery power therefrom. The battery voltage to ECA  12  may become too low as a result of loss of battery connection to the ECA while the ECA is in the motoring mode. Correspondingly, the battery voltage to ECA  12  may become too high as a result of loss of battery connection to the ECA while the ECA is in the regeneration mode. The loss of battery connection to ECA  12  occurs whenever ECA  12  or battery  14  becomes disconnected from voltage bus  26 . Such disconnection may occur during certain transient or longer term periods. Further, the battery voltage to ECA  12  may become too low as a result of battery  14  not providing sufficient battery power onto voltage bus  26  during certain transient periods, the demand for battery power from other units connected to voltage bus  26  being relatively too high during certain transient periods, etc. As further indicated above, timely detection of such battery power failure of ECA  12  is desirable. 
         [0031]    Referring now to  FIG. 2 , with continual reference to  FIG. 1 , a schematic diagram of ECA  12 , auxiliary battery  14 , and a capacitor  28  connected together via voltage bus  26  with the capacitor connected between the ECA and the auxiliary battery in accordance with an embodiment of the present invention is shown. 
         [0032]    As shown in  FIG. 2 , ECA  12  includes an inverter  30  and a motor  32 . Motor  32  is operable in the motoring mode to cause clutch  24  to move from a starting position to a relatively more engaged position. Motor  32  is operable in the regeneration mode when clutch  24  moves from a starting position to a relatively more disengaged position. 
         [0033]    As further shown in  FIG. 2 , inverter  30  of ECA  12  is connected to voltage bus  26 . In the motoring mode, inverter  30  obtains the battery voltage from voltage bus  26 , converts the battery voltage into an AC voltage, and provides the AC voltage to motor  32  for the motor to move clutch  24  to a more engaged position. In the regeneration mode, motor  32  acts as a generator and generates an AC voltage from clutch  24  being moved to a more disengaged position. Motor  32  provides the generated AC voltage to inverter  30 . Inverter  30  converts the AC voltage to a DC voltage and provides the DC voltage onto voltage bus  26 . 
         [0034]    Capacitor  28  is connected to a link of voltage bus  26  adjacent to inverter  30  of ECA  12  and is in parallel with inverter  30 . As such, capacitor  28  and inverter  30  have the same battery voltage on voltage bus  26 . The voltage of capacitor  28  can be measured at a measurement location  34  of the link of voltage bus  26  using a resistor and an analog-to-digital (ADC) converter (not shown). 
         [0035]    As noted, the battery voltage provided by auxiliary battery  14  is a DC voltage. As such, voltage bus  26  is a DC voltage bus. Vehicle electronic control units typically run on 12 or 24 DC volt systems. ECA  12  is one such module which operates on 12/24 volt battery. ECA  12  operates to open and close clutch  24  such as in response to a request by a transmission control unit (not shown). As further noted, battery power failure scenarios include the battery voltage being too low or too high or loss of battery connection. Motor  32  of ECA  12  operates both in motoring and generating modes. Battery power failure is to be detected under either operating condition of motor  32 . 
         [0036]    Referring now to  FIG. 3 , with continual reference to  FIG. 2 , plots depicting battery power failure scenarios upon loss of connection of auxiliary battery  14  to ECA  12  are shown. A battery connection plot  36  depicts a sequence of loss of battery connection (i.e., loss of V batt  event). The loss of battery connection occurs at time t 0  as shown in plot  36 . A connection between ECA  12  and battery  14  is established prior to the time t 0  as indicated by plot line  38 . The connection between ECA  12  and battery  14  is disconnected after the time t 0  as indicated by plot line  40 . 
         [0037]    A first voltage plot  42  depicts the battery voltage at measurement location  34  prior to and after the loss of battery connection when ECA  12  is in the motoring mode. A second voltage plot  44  depicts the battery voltage at measurement location  34  prior to and after the loss of battery connection when ECA  12  is in the regeneration mode. The battery voltage at measurement location  34  is the voltage of capacitor  28 . Thus, first and second voltage plots  42  and  44  depict the voltage of capacitor  28  prior to and after the loss of battery connection when ECA  12  is in the motoring and regeneration modes, respectively. 
         [0038]    In general, when battery  14  is connected to inverter  30  of ECA  12 , which powers motor  32  of the ECA, capacitor  28  is at the battery voltage. In normal operation, when motor  32  draws battery power from battery  14  to actuate clutch  24 , capacitor  28  acts as a filter to absorb current/voltage transients induced by the switching action. In the motoring mode when motor  32  is powering clutch  24 , current is sourced from battery  14  to ECA  12  and the voltage of capacitor  28  is at the nominal battery voltage. On the other hand, when motor  32  is in the regeneration mode, current is fed back from ECA  12  to battery  14  and the voltage of capacitor  28  remains at the nominal battery voltage. 
         [0039]    First voltage plot  42  depicts the voltage of capacitor  28  when ECA  12  is in the motoring mode. Prior to loss of battery connection, the voltage of capacitor  28  is at the nominal battery voltage as indicated by voltage plot line  46 . Upon loss of battery connection, motor current is sourced from capacitor  28  which quickly discharges as indicated by voltage plot line  48 . The voltage of capacitor  28  falls below the nominal battery voltage as a result of the discharging. When the voltage of capacitor  28  goes below a threshold voltage  50  (i.e., the battery voltage is too low), the loss of battery connection can be confirmed. 
         [0040]    Second voltage plot  44  depicts the voltage of capacitor  28  when ECA  12  is in the regeneration mode. Prior to loss of battery connection, the voltage of capacitor  28  is at the nominal battery voltage as indicated by voltage plot line  52 . Upon loss of battery connection, current flows from motor  32  to capacitor  28  which quickly charges as indicated by voltage plot line  54 . The voltage of capacitor  28  rises above the nominal battery voltage as a result of the charging. When the voltage of capacitor  28  rises above a threshold voltage  56  (i.e., the battery voltage is too high), the loss of battery connection can be confirmed. 
         [0041]    Threshold voltages  50  and  52  for the motoring and regeneration modes are determinable by characterizing the system under different temperature and initial battery voltage conditions to ensure timely detection. 
         [0042]    Detecting for battery power failure based on voltage at capacitor  28  in accordance with embodiments of the present invention generally include the following steps: sensing supply voltages; detecting battery voltage level—12 or 24 volts?; and detecting loss of battery connection (i.e., detecting loss of V batt ) based on the battery voltage level. The step of sensing supply voltages includes detecting ignition voltage and the battery voltage. The ignition is connected to a voltage bus powered by auxiliary battery  14 . The ignition voltage is measured directly from the ignition connection using a resistor divider and an ADC (not shown). As described above, the battery voltage is measured at measurement location  34  and therefore is the voltage of capacitor  28 . 
         [0043]    The step of detecting battery voltage level involves detecting whether the battery voltage level is 12 or 24 volts, in this example. As described, the battery voltage measurement is taken on the DC link of inverter  30  (i.e., at measurement location  34  connected to capacitor  28 ). The DC link voltage decreases in the motoring mode and increases in the regeneration mode. Thus, the battery voltage measurement cannot give the correct nominal battery voltage. Instead, the ignition voltage measurement is used for the battery voltage level detection. The ignition voltage measurement can be used as the ignition voltage is independent of the operating mode of motor  32  of ECA  12 . The ignition voltage to ECA  12  is directly derived from the battery voltage without level shifting and is representative of the battery voltage level. The detection is done as follows: (1) monitor the ignition voltage every 1 mSec, for example; (2A) if the measured ignition voltage is more than 18 volts consistently for 3 mSec, for example, then the vehicle battery level is set to 24 volts; and (2B) if the measured ignition voltage is less than 16 volts consistently for 3 mSec, for example, then the vehicle battery level is set to 12 volts. The (2A) case can take into account hysteresis with the ignition voltage increasing and the (2B) case can take into account hysteresis with the ignition voltage decreasing. 
         [0044]    The step of detecting loss of battery connection based on the battery voltage level is the subject of the flowcharts illustrated in  FIGS. 4A ,  4 B,  5 A,  5 B,  6 A, and  6 B. Another subject of the flowcharts is the step of detecting re-establishment of the battery connection based on the battery voltage level. In general, the flowcharts describe operation of detecting for battery power failure of ECA  12  and detecting for re-establishment of proper battery power to ECA  12  after the occurrence of battery power failure. The operation may be carried out by a controller in communication with ECA  12  and measurement location  34 . Such a controller may be external of ECA  12  or a component of the ECA. 
         [0045]    The flowcharts of  FIGS. 4A ,  5 A, and  6 A involve the motoring mode of ECA  12 . The flowcharts of  FIGS. 4B ,  5 B, and  6 B involve the regeneration mode of ECA  12 . The operations depicted in the flowcharts include timing, voltage, and count variables/thresholds which are provided with specific numeric values. Such numeric values are exemplary and are provided to enable a fuller understanding of the operations. 
         [0046]    Referring now to  FIG. 4A , with continual reference to first voltage plot  42  in  FIG. 3 , a flowchart  40  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the motoring mode in accordance with a first embodiment is shown. The operation begins with measuring the battery voltage at capacitor  28  every 200 microseconds as indicated in block  42 . As such, the battery voltage is sampled with the sample size being 200 microseconds. Battery  14  is identified as being a 12 or 24 volt battery based on the measured battery voltage as indicated in block  44 . 
         [0047]    When battery  14  is identified as being a 12 volt battery in decision block  44 , the operation includes the following steps. If the measured battery voltage is less than 7.5 volts consistently for two samples (i.e., 400 microseconds) in decision block  46 , then the count is incremented twice by a count value of 750 to reach a limit value of 1500 as indicated in block  48 . When decision block  50  determines the count value to reach the limit value a battery power failure fault is set as indicated in block  52  (i.e., the battery voltage is too low). On the other hand, if the measured battery voltage is greater than 7.6 volts consistently for 1500 samples (i.e., 0.3 seconds) in decision block  54 , then the count is decremented by one for each sample until the count is zero as indicated in block  56 . When decision block  58  determines the count to have reached zero, the battery power failure fault is cleared as indicated in block  60 . Until the count reaches zero the battery power failure remains set as indicated in block  62 . The clearing of the battery power failure represents the detection of re-establishment of proper battery power to ECA  12 . Decision block  46  for detecting whether the battery voltage is too low can take into account hysteresis with the battery voltage decreasing. Likewise, decision block  54  for detecting whether the battery it too high can take into account hysteresis with the battery voltage increasing. 
         [0048]    When battery  14  is identified as being a 24 volt battery in decision block  44 , the operation includes the following steps. If the measured battery voltage is less than 13 volts consistently for two samples in decision block  64 , then the count is incremented twice and the battery power failure fault is set pursuant to blocks  48 ,  50 , and  52  (i.e., the battery voltage is too low). On the other hand, if the measured battery voltage is greater than 13.2 volts consistently for 1500 samples in decision block  66 , then the count is decremented by one for each sample until the count is zero as indicated in block  68 . When the count reaches zero the battery power failure fault is cleared pursuant to blocks  50 ,  58 , and  60 . Again, until the count reaches zero the battery power failure remains set as indicated in block  62 . Further, hysteresis of the measured battery voltage can be taken into account as described above. 
         [0049]    Referring now to  FIG. 4B , with continual reference to second voltage plot  44  in  FIG. 3 , a flowchart  70  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the regeneration mode in accordance with the first embodiment is shown. The operation begins with measuring the battery voltage at capacitor  28  every 200 microseconds as indicated in block  72 . Battery  14  is identified as being a 12 or 24 volt battery based on the measured battery voltage as indicated in block  74 . 
         [0050]    When battery  14  is identified as being a 12 volt battery in decision block  74 , the operation includes the following steps. If the measured battery voltage is greater than 21 volts consistently for two samples in decision block  76 , then the count is incremented twice and the battery power failure fault is set pursuant to blocks  78 ,  80 , and  82  (i.e., the battery voltage is too high). If the measured battery voltage is less than 20 volts consistently for 1500 samples in decision block  84 , then the count is decremented by one for each sample until the count is zero as indicated in block  86 . When the count reaches zero the battery power failure fault is cleared pursuant to blocks  80 ,  88 , and  90 . Until the count reaches zero the battery power failure remains set as indicated in block  92 . Again, the clearing of the battery power failure represents the detection of re-establishment of proper battery power to ECA  12  and hysteresis of the measured battery voltage can be taken into account. 
         [0051]    When battery  14  is identified as being a 24 volt battery in decision block  74 , the operation includes the following steps. If the measured battery voltage is greater than 34 volts consistently for two samples in decision block  94 , then the count is incremented twice and the battery power failure fault is set pursuant to blocks  78 ,  80 , and  82  (i.e., the battery voltage is too high). If the measured battery voltage is less than 32 volts consistently for 1500 samples in decision block  96 , then the count is decremented by one for each sample until the count is zero as indicated in block  98 . When the count reaches zero the battery power failure fault is cleared pursuant to blocks  80 ,  88 , and  90 . Again, until the count reaches zero the battery power failure remains set as indicated in block  92  and hysteresis of the measured battery voltage can be taken into account as described above. 
         [0052]    As described, in addition to including steps for detecting a battery power failure fault, the operation depicted in flowcharts  40  and  70  of  FIGS. 4A and 4B  further include steps for clearing a battery power failure fault (i.e., steps for the detection of re-establishment of proper battery power to ECA  12  after a battery power failure was detected). In the case of the motoring mode described in  FIG. 4A , the criteria for clearing a battery power failure fault included the measured battery voltage being greater than a threshold voltage consistently for a time period such as 1500 samples. Correspondingly, in the case of the regeneration mode described in  FIG. 4B , the criteria for clearing a battery power failure fault included the measured battery voltage being less than a threshold voltage consistently for a time period such as 1500 samples. 
         [0053]    Other criteria for clearing a battery power failure fault are employed in accordance with embodiments of the present invention. As will be described, the operation described in  FIGS. 5A and 5B  include a strategy for clearing a battery power failure fault as a function of the rate of decay of the battery voltage. The operation described in  FIGS. 6A and 6B  include a strategy for clearing a battery power failure fault as a function of the change of battery voltage upon shorting the capacitor charge through the windings of motor  32  of ECA  12 . 
         [0054]    Clearing a battery power failure fault as a function of the rate of decay of the battery voltage pursuant to the operation described in  FIGS. 5A and 5B  overcomes an issue related to energizing the motor brake of ECA  12  when the threshold voltages come to within normal operating range after a battery power failure. Once a battery power failure (i.e., loss of V batt ) has taken place and clutch  24  is closing the voltage of capacitor  28  rises up sharply. In addition, if the motor brake is intended to be energized, then after the battery power failure detection has taken place the motor brake is de-energized. After the rotor of motor  32  stops moving, the voltage of capacitor  28  starts to bleed off. If the voltage comes within normal operating range, then the motor brake can be energized even though a physical loss of V batt  has taken place. 
         [0055]    In general, the operation for clearing a battery power failure fault as a function of the rate of decay of battery voltage includes measuring the rate of decay of battery voltage and if the decay is less than a threshold for a given duration for 12/24 volt systems then the fault is cleared. The rate of change of battery voltage is slow when the battery connection is present. The fault can therefore be cleared when the rate of change of battery voltage is slow as the slow rate of change is indicative of the battery connection being present. The steps will now be described in greater detail with respect to  FIGS. 5A and 5B . 
         [0056]    Referring now to  FIG. 5A , with continual reference to first voltage plot  42  in  FIG. 3  and  FIG. 4A , a flowchart  100  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the motoring mode in accordance with a first variation of the first embodiment is shown. The operation steps illustrated in flowchart  100  for setting a battery power failure fault (i.e., battery voltage too low in the motoring mode) have been described with reference to  FIG. 4A . As such, only the operation steps illustrated in flowchart  100  for clearing a battery power failure fault will be described in detail. 
         [0057]    When battery  14  is identified as being a 12 volt battery and a battery power failure fault is detected to be set in decision block  102 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is greater than 7.6 volts and the rate of change in the battery voltage is less than 1.5 volts/sec consistently for 800 mSec (for example) in decision block  104 , then the battery power failure fault is cleared pursuant to blocks  106 ,  108 ,  110 , and  112 . As the change in battery voltage cannot be reliably detected at 200 microsecond rate, in this example, due to ADC measurement resolution, the calculation is carried out every 200 mSec as indicated in block  114 . The described voltage change check condition is used only when the battery power failure fault is set. Further, decision block  104  can take into account hysteresis with the battery voltage increasing. 
         [0058]    Similarly, when battery  14  is identified as being a 24 volt battery and a battery power failure fault is detected to be set in decision block  116 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is greater than 13.2 volts and the rate of change in the battery voltage is less than 1.5 volts/sec consistently for 800 mSec in decision block  118 , then the battery power failure fault is cleared pursuant to blocks  120 ,  108 ,  110 , and  112 . Again, as the change in battery voltage cannot be reliably detected at 200 microsecond rate, the calculation is carried out every 200 mSec as indicated in block  122 . The described voltage change check condition is used only when the battery power failure fault is set and decision block  118  can take into account hysteresis with the battery voltage increasing. 
         [0059]    Referring now to  FIG. 5B , with continual reference to second voltage plot  44  in  FIG. 3  and  FIG. 4B , a flowchart  130  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the regeneration mode in accordance with a first variation of the first embodiment is shown. The operation steps illustrated in flowchart  130  for setting a battery power failure fault (i.e., battery voltage too high in the regeneration mode) have been described with reference to  FIG. 4B . As such, only the operation steps of illustrated in flowchart  130  for clearing a battery power failure fault will be described in detail. 
         [0060]    When battery  14  is identified as being a 12 volt battery and a battery power failure fault is detected to be set in decision block  132 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is less than 20 volts and the rate of change in the battery voltage is less than 1.5 volts/sec consistently for 800 mSec in decision block  134 , then the battery power failure fault is cleared pursuant to blocks  136 ,  138 ,  140 , and  142 . As the change in battery voltage cannot be reliably detected at 200 microsecond rate, the calculation is carried out every 200 mSec as indicated in block  144 . The described voltage change check condition is used only when the battery power failure fault is set and decision block  134  can take into account hysteresis with the battery voltage decreasing. 
         [0061]    Similarly, when battery  14  is identified as being a 24 volt battery and a battery power failure fault is detected to be set in decision block  145 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is less than 32 volts and the rate of change in the battery voltage is less than 1.5 volts/sec consistently for 800 mSec in decision block  146 , then the battery power failure fault is cleared pursuant to blocks  148 ,  138 ,  140 , and  142 . Again, as the change in battery voltage cannot be reliably detected at 200 microsecond rate, the calculation is carried out every 200 mSec as indicated in block  149 . The described voltage change check condition is used only when the battery power failure fault is set and decision block  145  can take into account hysteresis with the battery voltage decreasing. 
         [0062]    As such, the operation described in  FIGS. 5A and 5B  employ criteria for clearing a battery power failure fault based on the rate of decay of the battery voltage. As indicated above, the operation described in  FIGS. 6A and 6B  employ other criteria. In particular, the operation described in  FIGS. 6A and 6B  include clearing a battery power failure fault based on the change of battery voltage upon shorting the capacitor charge through the windings of motor  32  of ECA  12 . 
         [0063]    Clearing a battery power failure fault based on the change of battery voltage upon shorting the capacitor charge through the motor windings pursuant to the operation described in  FIGS. 6A and 6B  also overcomes the noted issue related to energizing the motor brake of ECA  12 . This issue comes into play when the threshold voltages come to within normal operating range after a battery power failure. Again, once a battery power failure (i.e., loss of V batt ) has taken place and clutch  24  is closing the voltage of capacitor  28  rises up sharply. In addition, if the motor brake is intended to be energized, then after the battery power failure detection has taken place the motor brake is de-energized. After the rotor of motor  32  stops moving, the voltage of capacitor  28  starts to bleed off. If the voltage comes within normal operating range, then the motor brake can be energized even though a physical loss of V batt  has taken place. 
         [0064]    In general, the operation for clearing a battery power failure fault based on the change of battery voltage upon shorting the capacitor charge through the motor windings includes measuring the change of battery voltage when motor  32  is energized and drawing current through the charged-up capacitor  28 . The change of battery voltage will be low when the battery connection is present. The fault can therefore be cleared when the change of battery voltage is low as the low change is indicative of the battery connection being present. The steps will now be described in greater detail with respect to  FIGS. 6A and 6B . 
         [0065]    Referring now to  FIG. 6A , with continual reference to first voltage plot  42  in  FIG. 3  and  FIG. 4A , a flowchart  150  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the motoring mode in accordance with a second variation of the first embodiment is shown. The operation steps illustrated in flowchart  150  for setting a battery power failure fault (i.e., battery voltage too low in the motoring mode) have been described with reference to  FIG. 4A . As such, only the operation steps of illustrated in flowchart  150  for clearing a battery power failure fault will be described in detail. 
         [0066]    When battery  14  is identified as being a 12 volt battery and a battery power failure fault is detected to be set in decision block  152 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is greater than 7.6 volts for 800 mSec in decision block  154 , then motor  32  is run in two phase excitation with 1 amp current for 10 mSec (for example) as indicated in block  156 . If the change in voltage of the battery voltage before and after the two phase excitation is detected to be less than 0.5 volts in decision block  158 , then the battery power failure fault is cleared pursuant as indicated in block  160 . Decision block  154  can take into account hysteresis with the battery voltage increasing. 
         [0067]    Similarly, when battery  14  is identified as being a 24 volt battery and a battery power failure fault is detected to be set in decision block  152 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is greater than 13.2 volts for 800 mSec in decision block  162 , then motor  32  is run in two phase excitation with 1 amp current for 10 mSec (for example) as indicated in block  156 . If the change in voltage of the battery voltage before and after the two phase excitation is detected to be less than 0.5 volts in decision block  158 , then the battery power failure fault is cleared pursuant as indicated in block  160 . Decision block  162  can take into account hysteresis with the battery voltage increasing. 
         [0068]    Referring now to  FIG. 6B , with continual reference to second voltage plot  44  in  FIG. 3  and  FIG. 4B , a flowchart  170  describing operation of detecting battery power failure of ECA  12  and detecting re-establishment of proper battery power to the ECA based on voltage of capacitor  28  when the ECA is in the regeneration mode in accordance with a second variation of the first embodiment is shown. The operation steps illustrated in flowchart  170  for setting a battery power failure fault (i.e., battery voltage too high in the regeneration mode) have been described with reference to  FIG. 4B . As such, only the operation steps of illustrated in flowchart  170  for clearing a battery power failure fault will be described in detail. 
         [0069]    When battery  14  is identified as being a 12 volt battery and a battery power failure fault is detected to be set in decision block  172 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is less than 20 volts for 800 mSec in decision block  174 , then motor  32  is run in two phase excitation with 1 amp current for 10 mSec (for example) as indicated in block  176 . If the change in voltage of the battery voltage before and after the two phase excitation is detected to be less than 0.5 volts in decision block  178 , then the battery power failure fault is cleared pursuant as indicated in block  180 . Decision block  174  can take into account hysteresis with the battery voltage decreasing. 
         [0070]    Similarly, when battery  14  is identified as being a 24 volt battery and a battery power failure fault is detected to be set in decision block  172 , the operation for clearing the battery power failure fault includes the following steps. If the measured battery voltage is less than 32 volts for 800 mSec in decision block  182 , then motor  32  is run in two phase excitation with 1 amp current for 10 mSec (for example) as indicated in block  176 . If the change in voltage of the battery voltage before and after the two phase excitation is detected to be less than 0.5 volts in decision block  178 , then the battery power failure fault is cleared pursuant as indicated in block  180 . Decision block  182  can take into account hysteresis with the battery voltage decreasing. 
         [0071]    As described above, timely detection of loss of battery power to ECA  12  is desirable as the powertrain should be operated in a fall back mode for the vehicle to be brought to an acceptable and safe operating condition. In addition, the motor brake of ECA  12  is to be brought to a state depending on the “power fail mode” set by the system controller, which requires appropriate activation of power switches in a timely manner. Embodiments of the present invention eliminate the need for current sensors on DC voltage bus  26  and complex switching circuits, thereby helping realize potential cost savings. 
         [0072]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the present invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the present invention.