Abstract:
A vehicle bus system includes a controller programmed to, after issuing a command to close a pair of contactors arranged to share a battery terminal and each configured to power a load when closed, initiate pre-charge of another terminal in response to voltages across the contactors exceeding corresponding closed-state thresholds, and generate a notification and preclude initiation of the pre-charge in response to one of the voltages being less than the corresponding closed-state threshold.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to systems and methods for performing fault detection in a multi-high voltage (HV) bus system. 
       BACKGROUND 
       [0002]    A hybrid or an electric vehicle may be equipped with at least one traction battery configured to provide energy for propulsion. The traction battery may also provide energy for other vehicle electrical systems. For example, the traction battery may transfer energy to high voltage loads, such as compressors and electric heaters. In another example, the traction battery may provide energy to low voltage loads, such as an auxiliary 12V battery. 
       SUMMARY 
       [0003]    A vehicle bus system includes a controller programmed to, after issuing a command to close a pair of contactors arranged to share a battery terminal and each configured to power a load when closed, initiate pre-charge of another terminal in response to voltages across the contactors exceeding corresponding closed-state thresholds, and generate a notification and preclude initiation of the pre-charge in response to one of the voltages being less than the corresponding closed-state threshold. 
         [0004]    A method includes, after issuing by a controller a command to close a pair of contactors arranged to share a battery terminal and each configured to power a load when closed, initiating pre-charge of another terminal in response to voltages across the contactors being greater than corresponding closed-state thresholds, and generating a notification and precluding initiation of the pre-charge in response to one of the voltages being less than the corresponding closed-state threshold. 
         [0005]    A vehicle bus controller includes input channels configured to receive signals indicative of voltages across a pair of contactors arranged to share a battery terminal and each configured to power a load when closed, output channels configured to provide a command to close the contactors, provide a command to initiate pre-charge of another traction battery terminal, and provide a notification, and control logic configured to, after issuance of the command to close the contactors, generate the command to initiate pre-charge of another terminal in response to the voltages being greater than corresponding closed-state thresholds and to generate the notification in response to one of the voltages being less than the corresponding closed-state threshold for a period longer than a closing delay of the corresponding contactor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a block diagram of a plug-in hybrid electric vehicle (PHEV) illustrating a typical drivetrain and energy storage components; 
           [0007]      FIG. 2A  is a block diagram illustrating a contactor arrangement for a single high voltage bus system; 
           [0008]      FIG. 2B  is a circuit diagram illustrating a contactor; 
           [0009]      FIG. 3  is a graph illustrating a sequence of commands for a single high voltage bus system; 
           [0010]      FIG. 4  is a block diagram illustrating a contactor arrangement for a multi-high voltage bus system; 
           [0011]      FIG. 5  is a graph illustrating a sequence of commands for a multi-high voltage bus system; and 
           [0012]      FIGS. 6A-6B  are flowcharts illustrating an algorithm for performing fault detection in a multi-high voltage bus system. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could 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. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0014]      FIG. 1  depicts an example plug-in hybrid-electric vehicle (PHEV) system  10 . A plug-in hybrid-electric vehicle  12 , hereinafter vehicle  12 , may comprise at least one traction battery or battery pack  14 . The battery pack  14  includes a battery controller  16  and may be configured to receive electric charge via a charging session at a charging station connected to a power grid. In one example, the power grid may include a device that harnesses renewable energy, such as a photovoltaic (PV) solar panel, or a wind turbine. 
         [0015]    The battery pack  14  may comprise one or more battery cells (not shown), e.g., electrochemical cells, capacitors, or other types of energy storage device implementations. The battery cells may be arranged in any suitable configuration and configured to receive and store electric energy for use in operation of the vehicle  12 . Each cell may provide a same or different nominal threshold of voltage. The battery cells may be further arranged into one or more arrays, sections, or modules further connected in series or in parallel. 
         [0016]    The battery pack  14  may further comprise a bussed electric center (BEC)  18  electrically connected to the battery cells, e.g., such as via a positive and a negative battery terminals  20 ,  21 . As will be described in further detail in reference to at least  FIGS. 2A-5 , the BEC  18  may be in communication with the battery controller  16  and may include a plurality of connectors and switches allowing the supply and withdrawal of electric energy to and from the battery pack  14 . 
         [0017]    The battery controller  16  is electrically connected with the BEC  18  and controls the energy flow between the BEC  18  and the battery cells. For example, the battery controller  16  may be configured to monitor and manage temperature and state of charge of each of the battery cells. The battery controller  16  may command the BEC  18  to open or close a plurality of switches in response to temperature or state of charge in a given battery cell reaching a predetermined threshold. 
         [0018]    The battery controller  16  may be in communication with one or more vehicle controllers  38 , such as, but not limited to, an engine controller (ECM) and transmission controller (TCM), and may command the BEC  18  to open or close a plurality of switches in response to a predetermined signal from the one or more vehicle controllers  38 . 
         [0019]    The vehicle  12  may further comprise one or more electric machines  22  mechanically connected to a hybrid transmission  24 . The electric machines  22  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  24  is mechanically connected to an engine  26 . The hybrid transmission  24  is also mechanically connected to a drive shaft  28  that is mechanically connected to the wheels  30 . 
         [0020]    The electric machines  22  can provide propulsion and deceleration capability when the engine  26  is turned on or off using energy stored in the battery pack  14 , such as via the BEC  18 . The electric machines  22  also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines  22  may also provide reduced pollutant emissions since the vehicle  12  may be operated in electric mode under certain conditions. 
         [0021]    The battery pack  14  typically provides a high voltage DC output. The BEC  18  of the battery pack  14  may be electrically connected to an inverter system controller (ISC)  32 . The ISC  32  is electrically connected to the electric machines  22  and provides the ability to bi-directionally transfer energy, such as via the BEC  18 , between the battery pack  14  and the electric machines  22 . In one example, the electric machines  22  and other components of the vehicle  12  supplying and/or receiving energy to and from the battery pack  14  may define a main load  34  of the battery pack  14 . 
         [0022]    In a motor mode, the ISC  32  may convert the DC output provided by the battery pack  14  to a three-phase alternating current as may be required for proper functionality of the electric machines  22 . In a regenerative mode, the ISC  32  may convert the three-phase AC output from the electric machines  22  acting as generators to the DC voltage required by the battery pack  14 . While  FIG. 1  depicts a typical plug-in hybrid electric vehicle, the description herein is equally applicable to a pure electric vehicle. For a pure electric vehicle, e.g., battery electric vehicle (BEV), the hybrid transmission  24  may be a gear box connected to the electric machines  22  and the engine  26  may not be present. In one example, the main load  34  of the battery pack  14  in the BEV may include the electric machines  22  and the gear box. 
         [0023]    In addition to providing energy for propulsion, the battery pack  14  may provide energy for other vehicle electrical systems (shown generally as auxiliary loads  36 ). For example, the battery pack  14  may transfer energy to high voltage loads, such as compressors and electric heaters. In another example, the battery pack  14  may provide energy to low voltage loads, such as an auxiliary 12V battery. In such an example the vehicle  12  may include a DC/DC converter module (not shown) that converts the high voltage DC output of the battery pack  14  to a low voltage DC supply that is compatible with the low voltage loads. The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. 
         [0024]    Referring now to  FIG. 2A , an example arrangement  40  of the BEC  18  for energy transfer to and from the main load  34  is shown. The arrangement  40  may include a main fuse  42  protecting the main load  34  from being exposed to excessive electric current. The BEC  18  may comprise a positive main contactor  44  electrically connected to the positive terminal  20  of the battery pack  14  and a negative main contactor  46  electrically connected to the negative terminal  21  of the battery pack  14 . 
         [0025]    As shown in  FIG. 2B , each of the positive and negative main contactors  44 ,  46  may define an electro-mechanical device  62  comprising an inductive coil  63  and a relay  64 , where energizing the inductive coil  63  causes the relay  64  to close and de-energizing the inductive coil  63  causes the relay  64  to open. In one example, a time delay may occur between a first time when the BEC  18  energizes terminals of the relay  64  and a second time when the relay  64  actually closes and connects the load to the source. The time delay may be, for example, between 10 ms and 50 ms or another threshold. The amount of delay a given contactor will experience may be affected by one or more characteristics, such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, testing, contactor age and/or cycling count, and so on. 
         [0026]    In reference to  FIG. 2A , voltage across the positive main contactor  44  may be measured at V POS  and V TOP  reference points  48 ,  50 , and voltage across the negative main contactor  46  may be measured at V NEG  and V BOT  reference points  52 ,  54 . In one example, closing the positive and negative main contactors  44 ,  46  allows the flow of electric energy to and from the battery cells of the battery pack  14 . In such an example, the battery controller  16  may command the BEC  18  to open or close the main contactors  44 ,  46  in response to receiving a signal from the one or more vehicle controllers  38 , e.g., ECM, TCM, and so on, indicative of a request to initiate or terminate transfer of electric energy between the main load  34  and the battery pack  14 . 
         [0027]    The BEC  18  may further comprise a pre-charge circuit  56  configured to control an energizing process of the positive terminal  20 . In one example, the pre-charge circuit  56  may include a pre-charge resistor  58  connected in series with a pre-charge contactor  60 . The pre-charge circuit  56  may be electrically connected in parallel with the positive main contactor  44 . When the pre-charge contactor  60  is closed, the positive main contactor  44  may be open and the negative main contactor  46  may be closed, allowing the electric energy to flow through the pre-charge circuit  56  and control an energizing process of the positive terminal  20 . 
         [0028]    In one example, the battery controller  16  may command BEC  18  to close the positive main contactor  44  and open the pre-charge contactor  60  in response to detecting that voltage across the positive and negative terminals  20 ,  21  reached a predetermined threshold. The transfer of electric energy between the main load  34  and the battery pack  14  may then continue via the positive and negative main contactors  44 ,  46 . For example, the BEC  18  may support electric energy transfer between the battery pack  14  and the ISC  32  during either a motor or a generator mode via a direct connection to conductors of the positive and negative main contactors  44 ,  46 . 
         [0029]    Shown in  FIG. 3  is an example graphical representation  66  of a plurality of commands issued by the battery controller  16  to the BEC  18  manipulating the positive and negative main contactors  44 ,  46  and the pre-charge contactor  60 . The graph  66  has x-axis  68  representing time measured in milliseconds and y-axis  70  representing bus voltage measured in volts. The battery controller  16  may command the BEC  18  at a time t 1    72 , e.g., t 1 =0 ms, to close the negative main contactor  46  and command the BEC  18  at a time t 2    74 , e.g., t 2 =10 ms to close the pre-charge contactor  60 . In one example, the BEC  18  may cause the one or more contactors to close by energizing their respective inductive coils. 
         [0030]    The negative main contactor  46  may close at a time t 3    76  and the pre-charge contactor  60  may close at a time t 4    78 . The battery controller  16  may determine that bus voltage changed from V 1 , e.g., V 1 =0V, at a time t 5  to V 2  at a time t 6  in response to the closing of both the negative main contactor  46  and the pre-charge contactor  60 . The battery controller  16 , in response to determining that bus voltage reached a predetermined threshold and/or at a time t 7    80 , may command the BEC  18  to close the positive main contactor  44 . In one example, the battery controller  16  may command the BEC  18  to close the positive main contactor  44  a predetermined period after determining that bus voltage reached a predetermined threshold. The positive main contactor  44  may close at a time t 8    82 . The battery controller  16  may determine that bus voltage changed from V 3  to V 4 , where |V 4 −V 3 |=δV, in response to the closing of the positive main contactor  44 . 
         [0031]    In another example, the battery controller  16  may enable energy transfer to the high voltage loads, such as compressors and electric heaters, via a direct connection to the positive and negative main contactors  44 ,  46 . In still another example, the battery controller  16  may command energy transfer to the low voltage loads, such as an auxiliary 12V battery, via a DC/DC converter (not shown) connected to the positive and negative main contactors  44 ,  46 . 
         [0032]    Referring now to  FIG. 4 , an example arrangement  84  of the BEC  18  for energy transfer between the main load  34  and the battery pack  14  and between the auxiliary loads  36  and the battery pack  14  is shown. In addition to components described in reference to the example arrangement  40  of  FIG. 2A , the arrangement  84  may include an auxiliary fuse  86  protecting the auxiliary loads  36  from being exposed to excessive electric current. The BEC  18  may further comprise an auxiliary contactor  88  electrically connected to the negative terminal  21  of the battery pack  14 . In one example, the auxiliary contactor  88  may comprise the electro-mechanical device  62  described previously in reference to  FIG. 2B . 
         [0033]    Voltage across the auxiliary contactor  88  may be measured at V AUX  and V BOT  reference points  90 ,  54 . In one example, closing the positive main and auxiliary contactors  44 ,  88  allows the flow of electric energy between the auxiliary loads  36  and the battery pack  14 . In such an example, the battery controller  16  may command the BEC  18  to open or close the auxiliary contactor  88  in response to receiving a signal from the one or more vehicle controllers  38 , e.g., ECM, TCM, and so on, indicative of a request to initiate or terminate transfer of electric energy between the auxiliary loads  36  and the battery pack  14 . 
         [0034]    As described previously in reference to  FIG. 2B , a time delay may occur between a first time when the battery controller  16  commands the BEC  18  to close the conductor, e.g., by energizing an inductive coil of the contactor, and a second time when the conductor actually closes and connects the load to the source. The amount of delay associated with a given contactor may be affected by one or more characteristics, such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, testing, contactor age and/or cycling count, and so on. Moreover, in a high voltage system comprising multiple high voltage buses powering a plurality of electrical loads, such as, for example, the arrangement  84  of  FIG. 4 , time delays among the plurality of contactors may vary due to varying cycling counts and other variables. 
         [0035]    Shown in  FIG. 5  is an example graphical representation  92  of a plurality of commands issued by the battery controller  16  to the BEC  18  manipulating the negative main and auxiliary contactors  46 ,  88  and the pre-charge contactor  60 . The graph  92  has x-axis  94  representing time measured in milliseconds and y-axis  96  representing bus voltage measured in volts. The battery controller  16  may command the BEC  18  at a time t 9    98 , e.g., t 9 =0 ms, to close the negative main and the auxiliary contactors  46 ,  88  and command the BEC  18  at a time t 10    100 , e.g., t 10 =10 ms, to close the pre-charge contactor  60 . In one example, the BEC  18  may cause the one or more contactors to close by energizing their respective inductive coils. 
         [0036]    The negative main contactor  46  may close at a time t 11    102  and the pre-charge contactor  60  may close at a time t 12    104 . The battery controller  16  may determine that bus voltage changed from V 1  at a time t 13  in response to the closing of both the negative main contactor  46  and the pre-charge contactor  60 . In one example, the auxiliary contactor  88  may close at a time t 14    106  or a predetermined period after bus voltage began to change from V 1 . Thus, bus voltage may have reached a predetermined threshold V 3  when the auxiliary contactor  88  closed at a time t 14    106 . 
         [0037]    In reference to  FIGS. 6A and 6B , a diagnostic method  108  for performing a multi-high voltage bus system fault detection is shown. The method  108  may begin at block  110  where the battery controller  16  receives a signal indicative of a request to close the negative main and the auxiliary contactors  46 ,  88 . In one example, the battery controller  16  may receive a request to close the negative main and the auxiliary contactors  46 ,  88  from the one or more vehicle controllers  38  in response to a request to start the vehicle  12 . 
         [0038]    At block  112  the battery controller  16  determines whether the negative main contactor  46  is open. In one example, the battery controller  16  determines whether the negative main contactor  46  is open by determining whether an absolute value of a difference between V NEG  and V BOT  reference points  52 ,  54  is less than a predetermined threshold, e.g., 20V. The battery controller  16  determines at block  114  whether an elapsed time t 1     ELAPSED    is greater than a predetermined period in response to determining at block  112  that the negative main contactor  46  is closed, e.g., a difference (or an absolute value of a difference) between V NEG  and V BOT  reference points  52 ,  54  is greater than a predetermined threshold. 
         [0039]    In one example, an elapsed time t 1     ELAPSED    may be a period elapsed since the battery controller  16  received at block  110  a signal indicative of a request to close the negative main and the auxiliary contactors  46 ,  88 . In another example, the battery controller  16  may adjust a predetermined period using one or more factors affecting opening time of the negative main contactor  46 , such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, contactor life testing results, expected opening period for a given age and/or cycling count of the contactor. The battery controller  16  may return to block  112  in response to determining at block  114  that an elapsed time t 1     ELAPSED    is less than a predetermined period. 
         [0040]    The battery controller  16  reports a fault at block  116  in response to determining at block  114  that an elapsed time t 1     ELAPSED    is greater than a predetermined period. In one example, the battery controller  16  may transmit to the one or more vehicle controllers  38  a signal indicative of a diagnostic fault being detected at the negative main contactor  46 . In another example, the battery controller  16  and/or the one or more vehicle controllers  38  may set a diagnostic trouble code (DTC) indicative of a negative main contactor fault. The one or more vehicle controllers  38  may further display an indication to a user of the vehicle  12  that a contactor fault has been detected. The battery controller  16  may then exit the method  108  and preclude initiation of the pre-charge. 
         [0041]    At block  118  the battery controller  16  determines whether the auxiliary contactor  88  is open in response to determining at block  112  that the negative main contactor  46  is open. In one example, the battery controller  16  determines whether the auxiliary contactor  88  is open by determining whether a difference (or an absolute value of a difference) between V AUX  and V BOT  reference points  90 ,  54  is less than a predetermined threshold, e.g., 20V. The battery controller  16  determines at block  120  whether an elapsed time t 2     ELAPSED    is greater than a predetermined period in response to determining at block  118  that the auxiliary contactor  88  is closed, e.g., a difference between V AUX  and V BOT  reference points  90 ,  54  is greater than a predetermined threshold. 
         [0042]    In one example, an elapsed time t 2     ELAPSED    may be a period elapsed since the battery controller  16  received at block  110  a signal indicative of a request to close the negative main and the auxiliary contactors  46 ,  88 . In another example, the battery controller  16  may adjust a predetermined period using one or more factors affecting opening period of the auxiliary contactor  88 , such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, contactor life testing results, expected opening time for a given age and/or cycling count of the contactor. The battery controller  16  may return to block  118  in response to determining at block  120  that an elapsed time t 2     ELAPSED    is less than a predetermined period. 
         [0043]    The battery controller  16  reports a fault at block  122  in response to determining at block  120  that an elapsed time t 2     ELAPSED    is greater than a predetermined period. In one example, the battery controller  16  may transmit to the one or more vehicle controllers  38  a signal indicative of a diagnostic fault being detected at the auxiliary contactor  88 . In another example, the battery controller  16  and/or the one or more vehicle controllers  38  may set a DTC indicative of an auxiliary contactor fault. The one or more vehicle controllers  38  may further display an indication to a user of the vehicle  12  that a contactor fault has been detected. The battery controller  16  may then exit the method  108  and preclude initiation of the pre-charge. 
         [0044]    At block  124  the battery controller  16  transmits a signal to the BEC  18  indicative of a command to close the negative main and auxiliary contactors  46 ,  88  in response to determining at block  118  that the auxiliary contactor  88  is open, e.g., a difference between V AUX  and V BOT  reference points  90 ,  54  is less than a predetermined threshold. The battery controller  16  at block  126  determines whether the negative main contactor  46  is closed. In one example, the battery controller  16  determines whether the negative main contactor  46  is closed by determining whether a difference (or an absolute value of a difference) between V NEG  and V BOT  reference points  52 ,  54  is greater than a predetermined threshold, e.g., 20V. The battery controller  16  determines at block  128  whether an elapsed time t 3     ELAPSED    is greater than a predetermined period in response to determining at block  126  that the negative main contactor  46  is open, e.g., a difference between V NEG  and V BOT  reference points  52 ,  54  is less than a predetermined threshold. 
         [0045]    In one example, an elapsed time t 3     ELAPSED    may be a period elapsed since battery controller  16  transmitted at block  124  a signal indicative of a command to close the negative main and the auxiliary contactors  46 ,  88 . In another example, the battery controller  16  may adjust a predetermined period using one or more factors affecting closing time of the negative main contactor  46 , such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, contactor life testing results, expected closing time for a given age and/or cycling count of the contactor. The battery controller  16  may return to block  126  in response to determining at block  128  that an elapsed time t 3     ELAPSED    is less than a predetermined period. 
         [0046]    The battery controller  16  reports a fault at block  130  in response to determining at block  128  that an elapsed time t 3     ELAPSED    is greater than a predetermined period. In one example, the battery controller  16  may transmit to the one or more vehicle controllers  38  a signal indicative of a diagnostic fault being detected at the negative main contactor  46 . In another example, the battery controller  16  and/or the one or more vehicle controllers  38  may set a DTC indicative of a negative main contactor fault. The one or more vehicle controllers  38  may further display an indication to a user of the vehicle  12  that a contactor fault has been detected. The battery controller  16  may then exit the method  108  and preclude initiation of the pre-charge. 
         [0047]    At block  132  the battery controller  16  determines whether the auxiliary contactor  88  is closed in response to determining at block  126  that the negative main contactor  46  is closed. In one example, the battery controller  16  determines whether the auxiliary contactor  88  is closed by determining whether a difference (or an absolute value of a difference) between V AUX  and V BOT  reference points  90 ,  54  is greater than a predetermined threshold, e.g., 20V. The battery controller  16  determines at block  134  whether an elapsed time t 4     ELAPSED    is greater than a predetermined period in response to determining at block  132  that the auxiliary contactor  88  is open, e.g., a difference between V AUX  and V BOT  reference points  90 ,  54  is less than a predetermined threshold. 
         [0048]    In one example, an elapsed time t 4     ELAPSED    may be a period elapsed since the battery controller  16  transmitted at block  124  a signal indicative of a command to close the negative main and the auxiliary contactors  46 ,  88 . In another example, the battery controller  16  may adjust a predetermined period using one or more factors affecting closing time of the auxiliary contactor  88 , such as, but not limited to, design and manufacturer specifications, manufacturing methods and materials, contactor life testing results, expected closing time for a given age and/or cycling count of the contactor. The battery controller  16  may return to block  132  in response to determining at block  134  that an elapsed time t 4     ELAPSED    is less than a predetermined period. 
         [0049]    The battery controller  16  reports a fault at block  136  in response to determining at block  134  that an elapsed time t 4     ELAPSED    is greater than a predetermined period. In one example, the battery controller  16  may transmit to the one or more vehicle controllers  38  a signal indicative of a diagnostic fault being detected at the auxiliary contactor  88 . In another example, the battery controller  16  and/or the one or more vehicle controllers  38  may set a DTC indicative of an auxiliary contactor fault. The one or more vehicle controllers  38  may further display an indication to a user of the vehicle  12  that a contactor fault has been detected. The battery controller  16  may then exit the method  108  and preclude initiation of the pre-charge. 
         [0050]    At block  138  the battery controller  16  transmits a signal to the BEC  18  indicative of a command to close the pre-charge contactor  60  in response to determining at block  132  that the auxiliary contactor  88  is closed, e.g., a difference between V AUX  and V BOT  reference points  90 ,  54  is greater than a predetermined threshold. At this point the method  108  may end. In one example, the method  108  may be repeated in response to receiving a signal indicative of a request to close the negative main and the auxiliary contactors  46 ,  88  or in response to another notification or request. The method  108  contemplates that each of the elapsed times t 1     ELAPSED   , t 2     ELAPSED   , t 3     ELAPSED   , and t 4     ELAPSED    may be different or the same as the rest. Similarly, the method  108  contemplates that a predetermined period it takes for a relay of a given contactor to open may be different or the same as a predetermined period it takes for the relay to close. 
         [0051]    The battery controller  16  may transmit a signal to the BEC  18  indicative of a command to close the positive main contactor  44  a predetermined period after commanding the BEC  18  to close the pre-charge contactor  60 . In yet another example, the battery controller  16  may transmit a signal to the BEC  18  indicative of a command to close the positive main contactor  44  a predetermined period after determining that the pre-charge contactor  60  is closed. 
         [0052]    The processes, methods, or algorithms disclosed herein may be deliverable to or implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms may also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0053]    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 disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.