Abstract:
A battery management system for a vehicle includes a controller programmed to charge a battery at a predetermined charge current. The controller activates an electrical load to discharge the battery for a predetermined time in response to a charge current of the battery becoming less than the predetermined charge current at a predetermined voltage limit. After discharging for the predetermined time, the controller resumes charging at the predetermined charge current. A current magnitude during the discharge and the predetermined time may be based on factors including the predetermined charge rate, a battery temperature, and a charge current magnitude during charging.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 14/664,281 filed Mar. 20, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This application is generally related to charging lithium-ion based traction batteries. 
       BACKGROUND 
       [0003]    Batteries for electric and plug-in hybrid vehicles are charged between uses to restore energy to the battery for the next use cycle. A vehicle may be connected to a charger that is connected to a power source. The charger is controlled to provide voltage and current to the battery to restore energy to the battery. Different charging strategies are utilized to charge the battery in the vehicle. Present charging strategies may charge the battery at a constant current until a voltage limit is reached. When the voltage limit is reached, charging at a constant voltage may be initiated. During the constant voltage phase, the battery current decreases which results in a slower charge rate. 
       SUMMARY 
       [0004]    A battery management system includes a controller programmed to charge a battery at a predetermined charge current and, in response to a charge current of the battery becoming less than the predetermined charge current at a predetermined voltage limit, activate an electrical load to discharge the battery for a predetermined time and resume charging after the predetermined time at the predetermined charge current to reduce battery charge time. 
         [0005]    A vehicle includes an electrical load, a battery and at least one controller. The at least one controller is programmed to charge the battery at a predetermined charge current and, in response to a charge current of the battery becoming less than the predetermined charge current at a predetermined voltage limit, operate the electrical load to discharge the battery for a predetermined time and resume charging after the predetermined time at the predetermined charge current to reduce battery charge time. 
         [0006]    A method includes charging a battery at a predetermined charge current. The method further includes operating an electrical load to discharge the battery for a predetermined time in response to a charge current of the battery becoming less than the predetermined charge current at a predetermined voltage limit. The method further includes resuming charging the battery after the predetermined time at the predetermined charge current to reduce a battery charge time. The method may further include terminating the charging when a state of charge of the battery exceeds a predetermined state of charge indicative of a fully charged battery. 
         [0007]    The predetermined voltage limit may be a battery charge voltage limit at which constant voltage charging is initiated. The predetermined charge current may be based on one or more of a state of charge of the battery, a temperature of the battery, and an impedance of the battery. A discharge rate magnitude during the discharge may be less than a magnitude of the predetermined charge current. A current magnitude during the discharge and the predetermined time may be based one or more of a battery temperature, a battery state of charge, and a battery impedance. The current magnitude during the discharge and the predetermined time may be based on a charge current magnitude during the charge. 
         [0008]    The system and method described herein improves battery charging time. The battery charging time is improved by reducing or reversing battery cell polarization when a battery voltage limit is exceeded. Where prior systems are limited to a constant voltage phase with a decreasing current, the present strategy periodically adjusts the voltage and current so that a higher current flows to the battery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a diagram of a hybrid vehicle illustrating typical drivetrain and energy storage components; 
           [0010]      FIG. 2  is a diagram of a possible battery pack arrangement comprised of multiple cells, and monitored and controlled by a Battery Energy Control Module; 
           [0011]      FIG. 3  is a diagram of an example battery cell equivalent circuit; 
           [0012]      FIG. 4  is a plot of an exemplary battery voltage and current during a charge cycle using the disclosed strategy; 
           [0013]      FIG. 5  is a plot of battery voltage settling time after a period of charging with and without a discharge pulse; and 
           [0014]      FIG. 6  is a block diagram of a filter for generating a discharge pulse. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can 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 can 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. 
         [0016]      FIG. 1  depicts a typical plug-in hybrid-electric vehicle (PHEV). A typical plug-in hybrid-electric vehicle  12  may comprise one or more electric machines  14  mechanically coupled to a hybrid transmission  16 . The electric machines  14  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  16  is mechanically coupled to an engine  18 . The hybrid transmission  16  is also mechanically coupled to a drive shaft  20  that is mechanically coupled to the wheels  22 . The electric machines  14  can provide propulsion and deceleration capability when the engine  18  is turned on or off. The electric machines  14  also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in a friction braking system. The electric machines  14  may also reduce vehicle emissions by allowing the engine  18  to operate at more efficient speeds and allowing the hybrid-electric vehicle  12  to be operated in electric mode with the engine  18  off under certain conditions. 
         [0017]    A traction battery or battery pack  24  stores energy that can be used by the electric machines  14 . A vehicle battery pack  24  typically provides a high-voltage direct current (DC) output. The traction battery  24  is electrically coupled to one or more power electronics modules. One or more contactors  42  may isolate the traction battery  24  from other components when opened and connect the traction battery  24  to other components when closed. The power electronics module  26  is also electrically coupled to the electric machines  14  and provides the ability to bi-directionally transfer energy between the traction battery  24  and the electric machines  14 . For example, a traction battery  24  may provide a DC voltage while the electric machines  14  may operate with a three-phase alternating current (AC) to function. The power electronics module  26  may convert the DC voltage to a three-phase AC current to operate the electric machines  14 . In a regenerative mode, the power electronics module  26  may convert the three-phase AC current from the electric machines  14  acting as generators to the DC voltage compatible with the traction battery  24 . The description herein is equally applicable to a pure electric vehicle. For a pure electric vehicle, the hybrid transmission  16  may be a gear box connected to an electric machine  14  and the engine  18  may not be present. 
         [0018]    In addition to providing energy for propulsion, the traction battery  24  may provide energy for other vehicle electrical systems. A vehicle  12  may include a DC/DC converter module  28  that converts the high voltage DC output of the traction battery  24  to a low voltage DC supply that is compatible with low-voltage vehicle loads. An output of the DC/DC converter module  28  may be electrically coupled to an auxiliary battery  30  (e.g., 12V battery). The low-voltage systems may be electrically coupled to the auxiliary battery. Other high-voltage loads  46 , such as compressors and electric heaters, may be coupled to the high-voltage output of the traction battery  24 . 
         [0019]    The vehicle  12  may be an electric vehicle or a plug-in hybrid vehicle in which the traction battery  24  may be recharged by an external power source  36 . The external power source  36  may be a connection to an electrical outlet. The external power source  36  may be electrically coupled to a charger or electric vehicle supply equipment (EVSE)  38 . The external power source  36  may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE  38  may provide circuitry and controls to regulate and manage the transfer of energy between the power source  36  and the vehicle  12 . The external power source  36  may provide DC or AC electric power to the EVSE  38 . The EVSE  38  may have a charge connector  40  for plugging into a charge port  34  of the vehicle  12 . The charge port  34  may be any type of port configured to transfer power from the EVSE  38  to the vehicle  12 . The charge port  34  may be electrically coupled to a charger or on-board power conversion module  32 . The power conversion module  32  may condition the power supplied from the EVSE  38  to provide the proper voltage and current levels to the traction battery  24 . The power conversion module  32  may interface with the EVSE  38  to coordinate the delivery of power to the vehicle  12 . The EVSE connector  40  may have pins that mate with corresponding recesses of the charge port  34 . Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling. 
         [0020]    One or more wheel brakes  44  may be provided for decelerating the vehicle  12  and preventing motion of the vehicle  12 . The wheel brakes  44  may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes  44  may be a part of a brake system  50 . The brake system  50  may include other components to operate the wheel brakes  44 . For simplicity, the figure depicts a single connection between the brake system  50  and one of the wheel brakes  44 . A connection between the brake system  50  and the other wheel brakes  44  is implied. The brake system  50  may include a controller to monitor and coordinate the brake system  50 . The brake system  50  may monitor the brake components and control the wheel brakes  44  for vehicle deceleration. The brake system  50  may respond to driver commands via a brake pedal and may also operate autonomously to implement features such as stability control. The controller of the brake system  50  may implement a method of applying a requested brake force when requested by another controller or sub-function. 
         [0021]    One or more electrical loads  46  may be coupled to the high-voltage bus. The electrical loads  46  may have an associated controller that operates and controls the electrical loads  46  when appropriate. Examples of electrical loads  46  may be a heating module or an air-conditioning module. 
         [0022]    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. In addition, a system controller  48  may be present to coordinate the operation of the various components. 
         [0023]    A traction battery  24  may be constructed from a variety of chemical formulations. Typical battery pack chemistries may be lead acid, nickel-metal hydride (NIMH) or Lithium-Ion.  FIG. 2  shows a typical traction battery pack  24  in a simple series configuration of N battery cells  72 . Other battery packs  24 , however, may be composed of any number of individual battery cells connected in series or parallel or some combination thereof. A battery management system may have a one or more controllers, such as a Battery Energy Control Module (BECM)  76 , that monitor and control the performance of the traction battery  24 . The battery pack  24  may include sensors to measure various pack level characteristics. The battery pack  24  may include one or more pack current measurement sensors  78 , pack voltage measurement sensors  80 , and pack temperature measurement sensors  82 . The BECM  76  may include circuitry to interface with the pack current sensors  78 , the pack voltage sensors  80  and the pack temperature sensors  82 . The BECM  76  may have non-volatile memory such that data may be retained when the BECM  76  is in an off condition. Retained data may be available upon the next key cycle. 
         [0024]    In addition to the pack level characteristics, there may be battery cell  72  level characteristics that are measured and monitored. For example, the terminal voltage, current, and temperature of each cell  72  may be measured. A system may use a sensor module  74  to measure the battery cell  72  characteristics. Depending on the capabilities, the sensor module  74  may measure the characteristics of one or multiple of the battery cells  72 . The battery pack  24  may utilize up to N c  sensor modules  74  to measure the characteristics of all the battery cells  72 . Each sensor module  74  may transfer the measurements to the BECM  76  for further processing and coordination. The sensor module  74  may transfer signals in analog or digital form to the BECM  76 . In some configurations, the sensor module  74  functionality may be incorporated internally to the BECM  76 . That is, the sensor module  74  hardware may be integrated as part of the circuitry in the BECM  76  and the BECM  76  may handle the processing of raw signals. The BECM  76  may also include circuitry to interface with the one or more contactors  42  to open and close the contactors  42 . 
         [0025]    It may be useful to calculate various characteristics of the battery pack. Quantities such a battery power capability and battery state of charge may be useful for controlling the operation of the battery pack  24  as well as any electrical loads receiving power from the battery pack. Battery power capability is a measure of the maximum amount of power the battery  24  can provide or the maximum amount of power that the battery  24  can receive. Knowing the battery power capability allows the electrical loads to be managed such that the power requested is within limits that the battery  24  can handle. 
         [0026]    Battery pack state of charge (SOC) gives an indication of how much charge remains in the battery pack. The SOC may be expressed as a percentage of the total charge remaining in the battery pack. The battery pack SOC may be output to inform the driver of how much charge remains in the battery pack, similar to a fuel gauge. The battery pack SOC may also be used to control the mode of operation of the electric or hybrid-electric powertrain. Calculation of battery pack SOC can be accomplished by a variety of methods. One possible method of calculating battery SOC is to perform an integration of the battery pack current over time. This is well-known in the art as ampere-hour integration. 
         [0027]    The traction battery  24  may operate in a charging mode and a discharging mode. In the charging mode, the traction battery  24  accepts charge and the state of charge of the battery  24  may increase. Stated another way, in the charging mode, current flows into the traction battery  24  to increase the charge stored in the battery  24 . In the discharging mode, the traction battery  24  depletes charge and the state of charge of the battery  24  may decrease. Stated another way, in the discharging mode, current flows from the traction battery  24  to decrease the charge stored in the battery  24 . During operation of the vehicle, the traction battery  24  may be operated in alternating cycles of charging and discharging. 
         [0028]    The battery cells  72  may be modeled in a variety of ways. For example, a battery cell may be modeled as an equivalent circuit.  FIG. 3  shows one possible battery cell equivalent circuit model (ECM) which may be referred to as a simplified Randles circuit model. The battery cell  72  may be modeled as a voltage source  100 , referred to as an open circuit voltage (V oc ), with associated impedance. The impedance may be comprised of one or more resistances ( 102  and  104 ) and a capacitance  106 . The open-circuit voltage (OCV)  100  of the battery may be expressed as a function of a battery SOC and temperature. The model may include an internal resistance, r 1    102 , a charge transfer resistance, r 2    104 , and a double layer capacitance, C  106 . The voltage V 1    112  is the voltage drop across the internal resistance  102  due to current  114  flowing from the voltage source  100 . The voltage V 2    110  is the voltage drop across the parallel combination of r 2    104  and C  106  due to current  114  flowing through the parallel combination. The terminal voltage (V t )  108  is the voltage across the terminals of the battery. The value of the parameters r 1    102 , r 2    104 , and C  106  may depend on the cell design, temperature, and the battery chemistry. The traction battery  24  may be modeled using a similar model with aggregate impedance values derived from the battery cells  72 . 
         [0029]    The open-circuit voltage  100  may be used to determine the SOC of the battery. A relationship between battery SOC and the open-circuit voltage  100  exists such that the battery SOC may be determined if the open-circuit voltage  100  is known (e.g., SOC=f(V oc )). The relationship may be expressed as a plot or a table that may be stored in controller memory. The relationship may be derived from battery testing or battery manufacturer data. 
         [0030]    During operation, the battery cells  72  may acquire a polarization caused by current flowing through the battery cells. The polarization effects may be modeled by the resistances  102 ,  104  and capacitance  106  of the equivalent circuit model. Because of the battery cell impedance, the terminal voltage, V t    108 , may not be the same as the open-circuit voltage  100 . The open-circuit voltage  100  is not readily measurable as only the terminal voltage  108  of the battery cell is accessible for measurement. When no current  114  is flowing for a sufficiently long period of time, the terminal voltage  108  may be the same as the open-circuit voltage  100 . The voltages may be equalized after a sufficiently long period of time to allow the internal dynamics of the battery to reach a steady state. Note that after a sufficient settling time with no current flowing through the battery, the terminal voltage  108  and the open-circuit voltage  100  may be nearly equal. One technique of estimating the open-circuit voltage  100  is to wait a sufficient period of time after a battery rest period before measuring the terminal voltage  108  to ensure that the voltages are close. 
         [0031]      FIG. 5  shows a plot  300  of representative voltage stabilization or relaxation times for a battery voltage after a relatively long period of charging and after a relatively short period of discharging. Curve  302  represents the response of the battery terminal voltage  108  after a relatively long charge cycle. That is, a charge voltage is applied to the battery for greater than a predetermined period of time prior to time zero and at time zero, charging is stopped (e.g., zero current). As shown in the plot, the post-charge settling time  306  is approximately fifty seconds. Curve  304  represents the battery terminal voltage  108  when applying a relatively short discharge pulse after the relatively long charge cycle. As shown in the plot, the post-discharge settling time  308 , is reduced to approximately five seconds. Similar curves may be obtained after a relatively long period of discharging except that a relatively short charge pulse is applied after a relatively long discharge cycle. The relevant observation is that the open-circuit voltage  100  and the terminal voltage  108  may equalize in less time by reversing the current flow through the battery for a relatively short time. That is, the polarization effects within the battery dissipate in a shorter time after reversing the current. The voltage stabilization time may be reduced by applying a current pulse with the opposite polarity. After a relatively long period of flowing current to the battery (e.g., charging), drawing a relatively short pulse of current from the battery (e.g., discharging) can reduce the voltage relaxation time. 
         [0032]    If the battery controller  76  is currently performing a charge cycle, the controller  76  may interrupt the charge cycle and command the discharge current pulse. Note that the battery controller  76  may coordinate with the engine  18  and the electric machines  14  to ensure that appropriate power is available for propulsion and other subsystems. In addition, the battery controller  76  may command external loads  46  to receive the discharge energy from the battery  24 . The discharge current pulse may be the result of command one or more of the external loads  46  to draw current from the traction battery  24 . For example, a heater may be activated to draw current from the battery  24  for a predetermined time. 
         [0033]      FIG. 4  depicts a plot of the battery terminal voltage  200 , battery SOC  202 , and battery current  206  during a possible charging cycle. During charging of the traction battery  24 , the terminal voltage  200  may approach a battery pack voltage limit  204  at which point, charging may be stopped or modified. Prior to the terminal voltage  200  reaching the battery voltage limit  204  the battery may be charging at a predetermined charge rate which may be at a predetermined current level  208 . The predetermined charge current  208  may be a maximum possible charge current. That is, the battery  24  may be charged at a constant current to yield the desired charge rate. During the constant current mode, the current may be controlled by adjusting the magnitude of the terminal voltage  200 . The predetermined charge rate may be selected to minimize battery charge time while respecting any maximum current limits of the battery system components. 
         [0034]    When charging at the predetermined charge current  208 , the difference between the terminal voltage  200  and the open-circuit voltage  100  may be the voltage drop (e.g, product of current and resistance) across the battery impedance. As the open-circuit voltage  100  increases, the terminal voltage  200  may also increase and reach the battery voltage limit  204 . This may typically occur at or about a predetermined battery SOC, since the battery SOC is a function of the open-circuit voltage  100 . Some systems may be configured to stop charging when the terminal voltage  200  exceeds the battery voltage limit  204 . In such a system, the battery  24  may not be fully charged at the end of the charge cycle. 
         [0035]    When the terminal voltage  200  meets or exceeds the battery pack voltage limit  204 , the current  206  flowing through the battery  24  may be decreased to prevent the terminal voltage  200  from increasing further. The decrease in current  206  causes the battery  24  to charge at a slower charge rate. The battery  24  may be charged in a constant voltage mode at this time. The constant voltage may be the battery pack charge voltage limit  204 . In this constant voltage mode, the current  206  may decrease as the open-circuit voltage  100  increases relative to the terminal voltage  200 . As the current  206  decreases, the time (e.g., charge time) to charge the battery  24  increases. During this constant voltage charging mode, the charge rate may decrease over time. For example, at a 3C charge rate, the controller may reduce the charge current when the battery SOC is greater than 80%. 
         [0036]    One technique to achieve higher currents during charging may be to apply a discharge current pulse  210  when the battery terminal voltage  200  is greater than or equal to the battery pack voltage limit  204 . The discharge current pulse  210  may be a discharge current that is applied for a period of time. The discharge current pulse  210  may be sufficient to reduce or reverse the cell polarization and decrease the cell voltage, making it possible to again charge at the predetermined charge current  208 . The discharge current pulse  210  may be of a predetermined magnitude and have a predetermined duration. The magnitude and duration of the discharge current pulse  210  may be based on the temperature of the battery  24 , the cell open-circuit voltage, and the charge current of the battery  24 . This process may be repeated until the battery  24  is fully charged. A magnitude of the discharge rate may be less than a magnitude of the charge rate. For example, for a 3C charge rate, a 1C discharge rate may be selected. The duration of the discharge pulse  210  may be selected to reduce or reverse the cell polarization and dissipate as little stored energy in the battery as possible. In some configurations, the magnitude of the discharge rate may be greater than the magnitude of the charge rate. 
         [0037]    As the battery SOC increases, the time between discharge pulses  210  may decrease. Each discharge current pulse  210  reduces the terminal voltage  200  to allow charging to be resumed at a higher current level. The terminal voltage  200  may then rise to the battery voltage limit  204  at which time another discharge pulse  210  may be applied. The controller  76  may monitor the battery SOC to determine when the battery pack  24  is fully charged (e.g., battery SOC approximately 100%). The result is that charging times may be reduced as higher charge currents are used for charging the battery  24 . Additionally, the method fully utilizes the battery capacity as charging does not have to end when the battery pack voltage limit  204  is reached. The methods disclosed may be adapted to existing battery management systems as the methods may be implemented in software on the controller  76 . 
         [0038]    The battery charge rate may be decreased as the battery SOC approaches a target SOC level (e.g., 100%). That is, the predetermined charge current  208  may be adjusted for each charge cycle as the battery SOC approaches a fully charged level. The decreased battery charge rate may compensate for the fact that the battery terminal voltage is the sum of the open-circuit voltage and the product of the charge current and battery resistance. As the battery SOC approaches the target SOC level, the open-circuit voltage approaches the maximum charge voltage. The battery charge rate may be decreased to prevent the terminal voltage from exceeding the maximum charge voltage before cell polarization occurs. 
         [0039]    After a discharge current pulse  210 , the charge current may be restored to the predetermined charge current  208 . As the battery SOC approaches the full-charge level, the predetermined charge current  208  may be decreased. The predetermined charge current  208  may be based on the battery SOC, the battery temperature, and the battery impedance. The predetermined charge current  208  may be selected to maintain the battery terminal voltage within the charge voltage limit. In some configurations, the discharge pulse  210  may be initiated when the charge current begins to decrease from the predetermined charge current  208 . In some configurations, the battery voltage limit  204  may correspond to the voltage level at which the charge current decreases. 
         [0040]    The discharge current pulse  210  has a magnitude and an associated duration. The magnitude and duration may be based on the magnitude of the charge current and the battery temperature. The magnitude and duration may be based on the battery SOC and the battery impedance. In some configurations, the magnitude of the discharge current pulse  210  may have a smaller magnitude than the charge current. The magnitude and duration of the discharge current pulse  210  may be selected to be a current that is sufficient to reverse cell polarization. The magnitude and duration of the discharge current pulse  210  may be selected to minimize an amount of energy discharged from the battery  24 . The magnitude and duration selection may be implemented in a controller as a lookup table. The lookup table may have predetermined values of the discharge current pulse magnitude and duration and be indexed by the charge current and the pack temperature. 
         [0041]      FIG. 6  depicts a block diagram of one possible configuration for determining the magnitude of the discharge pulse. A filter  400  may be utilized such that the magnitude of the discharge pulse  410  is based on a filtered version of the battery current  404 . The filter  400  may be a first-order low-pass filter having a filter-time constant (e.g., tau) that may be based on a first input  406  and a second input  408 . The first input  406  may be the battery pack SOC. The second input may be the battery pack temperature. The filter-time constant may be derived from a lookup table  402  that inputs the first input  406  and the second input  408  and outputs the filter-time constant. The filter  400  may be configured such that over a period of time that is based on the filter-time constant, the output (e.g., discharge current pulse magnitude  410 ) of the filter  400  approaches the input (e.g., battery current  404 ). The filter  400  may operate such that a longer duration of a constant battery current will produce a larger magnitude of the discharge current pulse magnitude  410 . The magnitude of the discharge pulse may approach the constant battery current magnitude if the duration is equivalent to several filter-time constants. 
         [0042]    The principle of the filter operation is that the discharge current pulse magnitude  410  is a function of a battery current  404  magnitude and duration. A large battery current magnitude applied for a long duration will result in a greater discharge pulse magnitude  410  than the same large battery current applied for a short duration. 
         [0043]    The duration of the discharge pulse may be a fixed value. For example, the discharge pulse may be set to a predetermined time of one second. In some configurations, the discharge pulse duration may be a variable amount of time based on other parameters. The predetermined time may be based on battery parameters. The magnitude and duration of the discharge current pulse may be sufficient to fully or partially reverse the cell polarization of the battery  24  so that the terminal voltage  108  will be less than the maximum charge voltage limit. 
         [0044]    The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can 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 can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can 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. 
         [0045]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can 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 can 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 can be desirable for particular applications.