Abstract:
A method of determining a state-of-charge for a battery is provided. A startup state-of-charge of the battery is determined as a function of a present open circuit voltage measurement for a present ignition startup, at least one open circuit voltage observation of a previous ignition startup, and a current draw integration over a time period from a previous ignition startup event to a present ignition startup event. A run state-of-charge change of the battery is determined for an ignition key-on operation. The run state-of-charge change comprises a difference between the present open circuit voltage measurement and the at least one previous open circuit voltage observation, and is determined in response to of a current draw integration over a respective period of time. The state-of-charge of the battery is calculated based on a function of the startup state-of-charge and the run state-of-charge change of the battery.

Description:
BACKGROUND OF INVENTION 
       [0001]    An embodiment relates generally to determining a state of charge of a battery within a vehicle. 
         [0002]    Determining a state-of-charge (SOC) for a battery can be performed utilizing various techniques utilizing coulomb counting or parameter estimations techniques. Coulomb counting involves the use of one measurement (i.e., one open circuit voltage reading) to estimate the battery state-of-charge. The accuracy of the open circuit voltage is critical to determining a state of charge. If there is measurement error, then the state-of-charge estimation will be in error by basically the factor of the measurement error. 
         [0003]    Moreover, coulomb counting utilizing charge efficiency and battery capacity to determine state-of-charge often use the standard manufacturing specification values for a new battery values throughout the estimation process for the life of the battery. Over time the battery ages and charge efficiency and battery capacity changes as well thereby creating error in the state-of-charge estimation. 
         [0004]    Current parameter estimation techniques require excitations which are not necessarily available on conventional vehicles. 
       SUMMARY OF INVENTION 
       [0005]    An advantage of an embodiment is the determination of a state of charge of a battery where error in estimating the state of charge is reduced by utilizing the integration of both present and previous open circuit voltage measurements/estimations and current draws. Deficiencies of prior art techniques are overcome by not solely basing the determination of the battery capacity on a new battery. Since battery characteristics change over a life of the battery, utilizing both present and past battery characteristic measurements/estimations provide a more comprehensive analysis as to how the battery is changing over a course of time which reduces any anomalies that may occur in a single measurement/estimation. 
         [0006]    An embodiment contemplates a method of determining a state-of-charge for a battery. Open circuit voltages of a vehicle battery are measured during ignition startups. A startup state-of-charge of the battery is determined as a function of a present open circuit voltage measurement for a present ignition startup, at least one open circuit voltage observation of a previous ignition startup, and a current draw integration over a time period from a previous ignition startup event to a present ignition startup event. A run state-of-charge change of the battery is determined for an ignition key-on operation. The run state-of-charge change comprises a difference between the present open circuit voltage measurement and the at least one previous open circuit voltage observation, and is determined in response to of a current draw integration over a respective period of time. The state-of-charge of the battery is calculated based on a function of the startup state-of-charge and the run state-of-charge change of the battery. 
         [0007]    An embodiment contemplates a system for determining a state-of-charge of a battery. The system includes a battery, at least one component for drawing power from the battery, a voltmeter for measuring an open circuit voltage of the battery at ignition start sequences, a current sensor for sensing current drawn from the battery. The system further includes a control module for determining a state-of-charge of a battery as a function of the startup state-of-charge and the run state-of-charge change of the battery. The startup state-of-charge is determined at a time of an ignition startup event. The startup state-of-charge is further a function of a present open circuit voltage measurement for a present ignition startup, at least one previous open circuit voltage observation, and a current integration over time period from a previous ignition event to a present ignition event. The run state-of-charge change comprises at a time during an ignition on operation. The run state-of-charge change being estimated as a difference between the present open circuit voltage measurement and at least one previous open circuit voltage observation determined in response to current integration over a respective period of time* 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a block diagram system for estimating a state-of-charge (SOC) and battery capacity of a battery. 
           [0009]      FIG. 2  is a timeline schematic illustrating time instances for determining open circuit voltages. 
           [0010]      FIG. 3  a flowchart of a method for determining a state of charge (SOC) of a battery and battery capacity. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  illustrates a block diagram of an embodiment of a vehicle  10  incorporating a state-of-charge (SOC) and battery capacity estimation system. It should be understood that the vehicle may include, but is not limited to, hybrid vehicles, internal combustion vehicles, and electric vehicles or any machinery that utilizes batteries. The vehicle  10  includes a battery pack  12  having a single battery or a plurality of individual battery modules. For example, an embodiment may include a plurality of batteries connected in series to produce a high voltage nominal voltage or a vehicle may include a single 12 volt battery producing a 14 volt nominal voltage for an internal combustion vehicle. The state-of-charge and battery capacity estimation technique described herein may be applicable to variety of battery types, including but not limited to, nickel metal hydride (NiMH) batteries, lead acid batteries, or lithium ion batteries. 
         [0012]    The vehicle battery  12  is electrically coupled to a plurality of devices  14  which utilize the battery as a power source. The vehicle  10  may further include a current sensor  16 , and voltage meter  18 , and a control module  20 . 
         [0013]    The plurality of devices  14  include, but are not limited to, power outlets adapted to an external plug in device, accessories, components, subsystems, and systems of a vehicle. The current sensor  16  is used to monitor the current leaving the vehicle battery  12 . The voltmeter  18  measures a voltage so that an open circuit voltage may be determined. A control module  20 , or similar module, obtains, derives, monitors, and/or processes a set of parameters associated with vehicle battery  12 . These parameters may include, without limitation, current, voltage, state-of-charge (SOC), battery capacity, battery internal resistances, battery internal reactance, battery temperature, and power output of the vehicle battery. The control module  20  includes an algorithm, or like, for executing a vehicle state-of-charge and battery capacity estimation technique. In a hybrid vehicle or electric vehicle, it is typical that a current sensor is integral to the control module. 
         [0014]    To enhance battery charging control and vehicle power management, the open circuit voltage V oc  is used to estimate the SOC. The SOC of the battery is estimated utilizing a startup SOC and a run SOC change. The formula for the SOC of the battery is represented as follows: 
         [0000]        S   oc =SOC startup +SOC running   =f ( V   oc (0) ,T )+θ∫ Idt    (1)
 
         [0000]    where f(V oc (0),T) is the startup SOC that is a function of the open circuit voltage and temperature, and θ∫Idt is the run SOC change that is a function of a battery parameter θ and previous current data integration. The battery parameter 
         [0000]    
       
         
           
             θ 
              
             
               ( 
               
                 = 
                 
                   c 
                   Q 
                 
               
               ) 
             
           
         
       
     
         [0000]    is a function of battery charge efficiency c and battery capacity Q. 
         [0015]    The open circuit voltage V oc  is a key element in determining the SOC. Therefore the following embodiment will focus on how V oc  is derived and utilized in determining SOC startup  and SOC running . 
         [0016]      FIG. 2  illustrates a timeline for estimating a plurality of open circuit voltages for SOC startup  which takes into consideration historical data. Historical data relates to previous instances of time at which an ignition off and ignition on event is detected and battery characteristics are observed. The term observed used herein refers to measured and/or estimated values based on measurements. A timing sequence of continuous ignition on I n  and ignition off I f  events is shown generally at  20 . Timeline  22  illustrates each of the time instances when the ignition transitions from an ignition-off to an ignition-on (e.g., t k-2 ,t k-1 ,t k ). Based on the different time instances, an open circuit voltage may be determined for each time instance taking into consideration not only the present open circuit voltage measurement, but also previous open circuit voltage measurements for estimating a more precise open circuit voltage value at the k th  ignition event. Formulas for the time instances t k-2 ,t k-1 ,t k  shown in  FIG. 2  are represented by the following formulas: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                     
                      
                     
                       ( 
                       
                         
                           t 
                           k 
                         
                         , 
                         
                           t 
                           k 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       V 
                       oc 
                     
                      
                     
                       ( 
                       
                         t 
                         k 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                     
                      
                     
                       ( 
                       
                         
                           t 
                           k 
                         
                         , 
                         
                           t 
                           
                             k 
                             - 
                             1 
                           
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         V 
                         oc 
                       
                        
                       
                         ( 
                         
                           t 
                           
                             k 
                             - 
                             1 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       θ 
                        
                       
                         
                           ∫ 
                           
                             t 
                             
                               k 
                               - 
                               1 
                             
                           
                           
                             t 
                             k 
                           
                         
                          
                         
                           I 
                            
                           
                              
                             t 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                     
                      
                     
                       ( 
                       
                         
                           t 
                           k 
                         
                         , 
                         
                           t 
                           
                             k 
                             - 
                             2 
                           
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         V 
                         oc 
                       
                        
                       
                         ( 
                         
                           t 
                           
                             k 
                             - 
                             2 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       θ 
                        
                       
                         
                           ∫ 
                           
                             t 
                             
                               k 
                               - 
                               1 
                             
                           
                           
                             t 
                             k 
                           
                         
                          
                         
                           I 
                            
                           
                              
                             t 
                           
                         
                       
                     
                     + 
                     
                       θ 
                        
                       
                         
                           ∫ 
                           
                             t 
                             
                               k 
                               - 
                               2 
                             
                           
                           
                             t 
                             
                               k 
                               - 
                               1 
                             
                           
                         
                          
                         
                           I 
                            
                           
                              
                             t 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0017]    When taking into consideration the past observations, a weighted average is obtained utilizing an adjustment factor λ. The adjustment factor λ weights the open circuit voltage estimation based on the duration of the key-off time or the key-on time. It should be understood that the technique described herein for determining the adjustment factor is only one embodiment of how the adjustment factor may be determined and that other techniques used to determine the adjustment factor may be applied herein without deviating from the scope of the invention. The formula for determining the open circuit voltage utilizing the adjustment factor is represented by the following formula: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                     
                      
                     
                       ( 
                       
                         t 
                         k 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       λ 
                        
                       
                         { 
                         
                           
                             
                               V 
                               ^ 
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           + 
                           
                             
                               θ 
                               ^ 
                             
                              
                             
                               
                                 ∫ 
                                 
                                   t 
                                   
                                     k 
                                     - 
                                     1 
                                   
                                 
                                 
                                   t 
                                   k 
                                 
                               
                                
                               
                                  
                                  
                                 
                                    
                                   t 
                                 
                               
                             
                           
                         
                         } 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           λ 
                         
                         ) 
                       
                        
                       
                         
                           
                             V 
                             oc 
                           
                            
                           
                             ( 
                             
                               t 
                               k 
                             
                             ) 
                           
                         
                         . 
                         
                           
 
                         
                          
                         where 
                       
                        
                       
                           
                       
                        
                       
                         { 
                         
                           
                             
                               V 
                               ^ 
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           + 
                           
                             
                               θ 
                               ^ 
                             
                              
                             
                               
                                 ∫ 
                                 
                                   t 
                                   
                                     k 
                                     - 
                                     1 
                                   
                                 
                                 
                                   t 
                                   k 
                                 
                               
                                
                               
                                  
                                  
                                 
                                    
                                   t 
                                 
                               
                             
                           
                         
                         } 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    represents the estimation based on previous observation (t k-n ), and (1−λ)V oc (t k ) represents a present observation (t k ). 
         [0018]    Therefore, if the key-off time is too short, then a greater emphasis is placed on the estimated value in which the adjustment factor would be preferably close to 1. If the key-off time is greater than a predetermined time value, then a greater emphasis is placed on the current observation, and the adjustment factor would be preferably close to 0. As a result, the following formula is used to determine the adjustment factor λ which is a function of the time off. The adjustment factor λ for the open circuit voltage is represented by the following formula: 
         [0000]      λ= e   −t     off     (t     k     )/τ   (6)
 
         [0000]    where t off  is a time from when the ignition key is turned off to a time the ignition is turned on, t k  is a time the ignition key is turned on at the k th  ignition interval, and τ is a time constant. 
         [0019]    The battery parameter θ is commonly determined by a ratio of the charge efficiency and the battery capacity. Charge efficiency and battery capacity values are typically nominal values based on a new battery. However, such parameters change as the battery ages, and as a result, are not robust factors for determining the battery parameter θ. Since these parameters change with age, the battery parameter θ should be estimated periodically. To estimate the battery parameter θ on a periodic basis (e.g., at least once a month), the battery parameter θ is solved for utilizing the open circuit voltage formula which is represented as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                     
                      
                     
                       ( 
                       
                         t 
                         k 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           V 
                           ^ 
                         
                         oc 
                       
                        
                       
                         ( 
                         
                           t 
                           
                             k 
                             - 
                             1 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       
                         
                           θ 
                           ^ 
                         
                         k 
                       
                        
                       
                         
                           ∫ 
                           
                             t 
                             
                               k 
                               - 
                               1 
                             
                           
                           
                             t 
                             k 
                           
                         
                          
                         
                           I 
                            
                           
                             
                                
                               t 
                             
                             . 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0000]    By modifying the open circuit voltage {circumflex over (V)} oc (t k ) to solve for θ, the resulting battery parameter θ is represented as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       θ 
                       ^ 
                     
                     k 
                   
                   = 
                   
                     
                       
                         
                           V 
                           oc 
                         
                          
                         
                           ( 
                           
                             t 
                             k 
                           
                           ) 
                         
                       
                       - 
                       
                         
                           
                             V 
                             ^ 
                           
                           oc 
                         
                          
                         
                           ( 
                           
                             t 
                             
                               k 
                               - 
                               1 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         ∫ 
                         
                           t 
                           
                             k 
                             - 
                             1 
                           
                         
                         
                           t 
                           k 
                         
                       
                        
                       
                         I 
                          
                         
                            
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0000]    To compensate for short ignition key-off times, an adjustment factor is incorporated in the battery parameter estimation formula. The adjustment factor for the battery parameter λ θ  is represented by the following formula: 
         [0000]      λ θ   =e   −t     off     (t     k     )/τ     θ     (9)
 
         [0000]    The resulting formula for the battery parameter is as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       θ 
                       ^ 
                     
                     k 
                   
                   = 
                   
                     
                       
                         λ 
                         θ 
                       
                        
                       
                         
                           θ 
                           ^ 
                         
                         
                           k 
                           - 
                           1 
                         
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             λ 
                             θ 
                           
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               V 
                               oc 
                             
                              
                             
                               ( 
                               
                                 t 
                                 k 
                               
                               ) 
                             
                           
                           - 
                           
                             
                               
                                 V 
                                 ^ 
                               
                               oc 
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                         
                           
                             ∫ 
                             
                               t 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             
                               t 
                               k 
                             
                           
                            
                           
                             I 
                              
                             
                                
                               t 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where θ k-1  is the previous battery parameter estimation and 
         [0000]    
       
         
           
             
               
                 
                   V 
                   oc 
                 
                  
                 
                   ( 
                   
                     t 
                     k 
                   
                   ) 
                 
               
               - 
               
                 
                   
                     V 
                     ^ 
                   
                   oc 
                 
                  
                 
                   ( 
                   
                     t 
                     
                       k 
                       - 
                       1 
                     
                   
                   ) 
                 
               
             
             
               
                 ∫ 
                 
                   t 
                   
                     k 
                     - 
                     1 
                   
                 
                 
                   t 
                   k 
                 
               
                
               
                 I 
                  
                 
                    
                   t 
                 
               
             
           
         
       
     
         [0000]    a present battery parameter estimation. 
         [0020]    Due to temperature differences when measurements for current and previous open circuit voltage are obtained, the estimation technique generated herein requires normalization between the open circuit voltage measurements. That is, each open circuit voltage (i.e., both present and previous), must be normalized at a standard temperature so that present observations and past observations can be cooperatively utilized. As a result, each open circuit voltage for a respective ignition event is converted to an open circuit voltage based on a normalized temperature. The conversion may be performed utilizing an algorithm, lookup table, or the like. For example, a normalized formula utilizing a standardized temperature, such as 25 degrees, is represented as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ^ 
                       
                       oc 
                       25 
                     
                      
                     
                       ( 
                       
                         t 
                         k 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       λ 
                        
                       
                         { 
                         
                           
                             
                               
                                 V 
                                 ^ 
                               
                               oc 
                               25 
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                           + 
                           
                             
                               
                                 θ 
                                 ^ 
                               
                               
                                 k 
                                 - 
                                 1 
                               
                               25 
                             
                              
                             
                               
                                 ∫ 
                                 
                                   t 
                                   
                                     k 
                                     - 
                                     1 
                                   
                                 
                                 
                                   t 
                                   k 
                                 
                               
                                
                               
                                  
                                  
                                 
                                    
                                   t 
                                 
                               
                             
                           
                         
                         } 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           λ 
                         
                         ) 
                       
                        
                       
                         
                           
                             V 
                             oc 
                             25 
                           
                            
                           
                             ( 
                             
                               t 
                               k 
                             
                             ) 
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0000]    The battery parameter using normalized temperatures is as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       θ 
                       ^ 
                     
                     k 
                     25 
                   
                   = 
                   
                     
                       
                         λ 
                         θ 
                       
                        
                       
                         
                           θ 
                           ^ 
                         
                         
                           k 
                           - 
                           1 
                         
                         25 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             λ 
                             θ 
                           
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               
                                 V 
                                 oc 
                                 25 
                               
                                
                               
                                 ( 
                                 
                                   t 
                                   k 
                                 
                                 ) 
                               
                             
                             - 
                             
                               
                                 
                                   V 
                                   ^ 
                                 
                                 oc 
                                 25 
                               
                                
                               
                                 ( 
                                 
                                   t 
                                   
                                     k 
                                     - 
                                     1 
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             
                               ∫ 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               
                                 t 
                                 k 
                               
                             
                              
                             
                               I 
                                
                               
                                  
                                 t 
                               
                             
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
         [0000]    As a result, the open circuit voltage for the SOC of the vehicle battery can be represented by the following formula: 
         [0000]        {circumflex over (V)}   oc   25 ( t,t   k )= {circumflex over (V)}   oc   25 ( t   k )+θ k   25 ∫ t     k     t   Idt.    (13)
 
         [0021]    Once the normalized open circuit voltage {circumflex over (V)} oc   25  (t, t k ) for the SOC of the battery is determined, the normalized open circuit voltage is converted back to the open circuit voltage at the current temperature and is represented by {circumflex over (V)} oc (t). 
         [0022]    The SOC charge of the battery is determined utilizing {circumflex over (V)} oc (t) that incorporates estimations of both current measurements and previous measurements. The other factors in determining SOC can be basically grouped as a linear mapping constant. As a result, the SOC of the vehicle battery at the present instance of time may be represented by the following formula: 
         [0000]      SOC( t )= f ( {circumflex over (V)}   oc ( t ) ,T )   (14)
 
         [0000]    where {circumflex over (V)} oc (t) is the estimated open circuit voltage of the battery using current measurements and previous measurements, and T is a respective temperature at the time of the measurement. 
         [0023]    The battery capacity Q is also determined utilizing current measurements and battery parameters. The battery capacity is derived utilizing the following formula represented by: 
         [0000]        Q   actual   25   =Q   new   25 (θ new   25 /θ k   25 )   (15)
 
         [0000]    where Q actual   25  is the normalized estimated battery capacity of the battery, Q new   25  is a normalized battery capacity of a new battery, θ new   25  is a normalized battery parameter of a new battery, and {circumflex over (θ)} k   25  is the normalized estimated battery parameter as a function of an adjustment factor. It should be understood that in deriving the battery capacity, estimations must be derived using a standard temperature (e.g., 25 degrees). The formula for determining the battery parameter at the k th  ignition start is represented by the following formula: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       θ 
                       ^ 
                     
                     k 
                     25 
                   
                   = 
                   
                     
                       
                         λ 
                         θ 
                       
                        
                       
                         
                           θ 
                           ^ 
                         
                         
                           k 
                           - 
                           1 
                         
                         25 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             λ 
                             θ 
                           
                         
                         ) 
                       
                        
                       
                         
                           
                             
                               V 
                               oc 
                               25 
                             
                              
                             
                               ( 
                               
                                 t 
                                 k 
                               
                               ) 
                             
                           
                           - 
                           
                             
                               
                                 V 
                                 ^ 
                               
                               oc 
                               25 
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   k 
                                   - 
                                   1 
                                 
                               
                               ) 
                             
                           
                         
                         
                           
                             ∫ 
                             
                               t 
                               
                                 k 
                                 - 
                                 1 
                               
                             
                             
                               t 
                               k 
                             
                           
                            
                           
                             I 
                              
                             
                                
                               t 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
         [0024]      FIG. 3  illustrates a flowchart for a technique for estimating the SOC and battery capacity utilizing V oc  data. In step  30 , a first key-on event is initiated. The first key-on represents a time when the vehicle ignition is first started and data is collected. The first key-on event may also represent a time when the vehicle ignition is started directly after the vehicle battery is replaced and data is obtained for the new battery. In this manner, previous data relating to past battery operating conditions and parameters would no longer be valid since the new battery would have different charging and efficiency characteristics (e.g., charge efficiency values and battery capacity values). 
         [0025]    In step  31 , the measurable parameters and estimated parameters are initialized. That is, at the initiation of a new vehicle startup or when the battery is replaced, all variables for the each of the formulas described above are re-set to their initial conditions. For example, k=0, λ=0, λ θ =1, θ 0   25 =θ new   25   , {circumflex over (V)}   oc   25 (0)=13V, Δ Q=Q   new   25 . 
         [0026]    In step  32 , the present open circuit voltage V oc (t k ) and the battery temperature T are measured. 
         [0027]    In step  33 , the open circuit voltage V oc (t k ) is converted to an open circuit voltage at a standard temperature V oc   25 (t k ). The conversion may be performed using an algorithm or a lookup table. 
         [0028]    In step  34 , the startup voltage is updated using the formula set forth in equation (11). 
         [0029]    In step  35 , the battery parameter is updated using the formula set forth in equation (12). 
         [0030]    In step  36 , the battery capacity is updated using the formula set forth in equation (15). 
         [0031]    In step  37 , the current integration ∫Idt is reset to zero. 
         [0032]    In step  38 , a determination is made whether the ignition key is in the key-off position. If the ignition is in the key-off position, then the routine proceeds to step  39 ; otherwise the routine proceeds to step  47 . 
         [0033]    In step  39 , the key-off time is reset to zero (t off =0). This initiates a counter for determining how long the ignition is in the key-off position. 
         [0034]    In step  40 , a determination is made whether the ignition key is in the key-on position. If the ignition key is not in the key-on position, then the routine proceeds to step  41 . 
         [0035]    In step  41 , the routine waits for a period of time before updating the key-off time. 
         [0036]    In step  42 , the key-off time is updated. The key-off time is represented by the following formula: 
         [0000]    
       
      
       t 
       off 
       =t 
       off 
       +Δt 
       off  
      
     
         [0000]    where t off  is a summation of the key-off time since the resetting the key-off time, and Δt off  is the additive time period elapsed in step  41 . 
         [0037]    In step  43 , the current measurement (I) of the battery is measured. 
         [0038]    In step  44 , the current integration is updated which incorporates the present current measurement with the past current measurements. The routine proceeds back to step  40 . 
         [0039]    In step  40 , if the determination is made that the ignition key is on, then the routine proceeds to step  45 , otherwise, the routine proceeds to step  41 . 
         [0040]    In step  45 , a key-on cycle count is updated. The key-on cycle count is the number of times the ignition key has been turned on since system initialization in step  31 . Each time the ignition key is turned on, the count is increased by 1. 
         [0041]    In step  46 , the adjustment factor is determined for the open circuit voltage as set forth in equation (6) and the adjustment factor is determined for the battery parameter as set forth in equation (8). Thereafter, a return is made to step  32  to execute steps  32 - 38  as described above. 
         [0042]    In step  38 , if the determination is made that the ignition key is not in the key-off position, then the routine proceeds to step  47 . 
         [0043]    In step  47 , the current (I) leaving the battery and the temperature (T) is measured. 
         [0044]    In step  48 , the current integration is updated based on the past to present measurements. 
         [0045]    In step  49 , the running open circuit voltage {circumflex over (V)} oc   25 (t) at the standard temperature is updated using the formula set forth in equation (13). 
         [0046]    In step  50 , the running open circuit voltage {circumflex over (V)} oc   25 (t) is converted back to a running open circuit voltage {circumflex over (V)} oc (t) at the present temperature using an algorithm or a lookup table. 
         [0047]    In step  51 , the SOC for the battery at the present temperature is determined using the formula set forth in equation (14). 
         [0048]    In step  52 , a predetermined period of time elapses before returning to step  38 . 
         [0049]    The battery capacity derived in step  36  and the SOC derived step  51  are either displayed to the driver of the vehicle identifying the condition of the battery or may be represented in some other capacity for indicating the SOC and battery capacity. 
         [0050]    While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.