Abstract:
An exemplary battery charge monitoring method includes, among other things, calculating expected charge data for a battery using at least a capacity of the battery and a charge rate, and comparing actual charge data to the expected charge data to identify differences between the actual charge data and the expected charge data.

Description:
TECHNICAL FIELD 
     This disclosure relates generally to charging a battery and, more particularly, to preventing overcharging of the battery. 
     BACKGROUND 
     Electric vehicles and many other devices may rely on a battery to store electrical power. 
     Generally, electric vehicles differ from conventional motor vehicles because electric vehicles selectively drive the vehicle using one or more battery-powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine. Electric vehicles may use electric machines instead of, or in addition to, to the internal combustion engine. Example electric vehicles include hybrid electric vehicles (HEV&#39;s), plug in hybrid electric vehicles (PHEV&#39;s), and battery electric vehicles (BEV&#39;s). 
     Electric vehicles may be equipped with a battery configured to store electrical power for powering the electric machine. The batteries are charged prior to use, and recharged when the electric power in the battery becomes depleted. 
     A battery charger is typically used to charge batteries. In some electric vehicles, the electric machine may be used as a generator that is powered by the internal combustion engine in order to generate electrical power to charge the battery. Charging adds power to batteries. It can be difficult to determine when an appropriate amount of power has been added back to the battery during a charge. Adding too much power can cause the battery to become overcharged. 
     SUMMARY 
     A battery charge monitoring method according to an exemplary aspect of the present disclosure includes, among other things, calculating expected charge data for a battery using at least a capacity of the battery and a charge rate, and comparing actual charge data to the expected charge data to identify differences between the actual charge data and the expected charge data. 
     In a further non-limiting embodiment of the foregoing battery charge monitoring method, the method includes ending the charging in response to the comparing. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data comprises an expected charge time, and the actual charge data comprises an actual charge time. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the method includes ending the charge in response to the expected charge time exceeding the actual charge time. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data and the actual charge data comprise electric charge data, and charging of the battery is terminated in response to an actual amount of electrical charge exceeding an expected amount of electrical charge. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data and the actual charge data comprise voltage data, and charging of the battery is terminated in response to an actual voltage exceeding an expected amount of voltage. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data and the actual charge data comprise energy data, and charging of the battery is terminated in response to an actual energy to charge the battery exceeding an expected amount of energy required to charge the battery. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data comprises a substantially monotonic increase of the voltage such that a change in the voltage during the charging is substantially non-negative, and charging is terminated if the change in the voltage is negative. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the expected charge data comprises a substantially monotonic decreasing battery current such that a change in the battery current during the charging is less than or equal to zero, and charging is terminated if the change in the current is greater than zero. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the capacity of the battery comprises a maximum voltage for cells of the battery. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the capacity of the battery comprises a percentage of a maximum voltage for cells of the battery. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the capacity of the battery comprises an amp-hour capacity for cells of the battery. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the method includes using a battery charge controller for the calculating and the comparing. 
     In a further non-limiting embodiment of any the foregoing battery charge monitoring methods, the battery is a vehicle battery. 
     A battery charging system according to an exemplary aspect of the present disclosure includes a battery charger to charge a battery; and a controller configured to selectively end a charge of the battery in response to a comparison of an expected charge amount to an actual charge amount, the expected charge amount calculated using at least a capacity of the battery and a charge rate. 
     In a further non-limiting embodiment of the forgoing battery charging system, the actual charge amount comprises a measurement of time spent charging the battery with the battery charger. 
     In a further non-limiting embodiment of any of the forgoing battery charging systems, the controller selectively ends the charge in response to the expected charge amount exceeding the actual charge amount. 
     In a further non-limiting embodiment of any of the forgoing battery charging systems, the battery is an electric vehicle battery. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
         FIG. 1  schematically illustrates an electric vehicle powertrain having a battery. 
         FIG. 2  schematically illustrates an example battery charging system for charging the battery of  FIG. 1 . 
         FIG. 3  shows an example battery charge monitoring method. 
         FIG. 4  shows another example battery charge monitoring method. 
         FIG. 5  shows yet another example battery charge monitoring method. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a powertrain  10  for an electric vehicle  12 . Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electric vehicles, including but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s) and battery electric vehicles (BEV&#39;s). 
     In one embodiment, the powertrain  10  is a powersplit powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery  24 . In this example, the second drive system is considered an electric drive system  28  of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  32  of the electric vehicle  12 . 
     The engine  14 , which is an internal combustion engine in this example, and the generator  18  may be connected through a power transfer unit  36 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  36  is a planetary gear set that includes a ring gear  40 , a sun gear  44 , and a carrier assembly  48 . 
     The generator  18  may be driven by engine  14  through the power transfer unit  36  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  52  connected to the power transfer unit  36 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
     The ring gear  40  of the power transfer unit  36  may be connected to a shaft  56 , which is connected to vehicle drive wheels  32  through a second power transfer unit  60 . The second power transfer unit  60  may include a gear set having a plurality of gears  64 . Other power transfer units may also be suitable. The gears  64  transfer torque from the engine  14  to a differential  68  to ultimately provide traction to the vehicle drive wheels  32 . The differential  68  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  32 . The second power transfer unit  60  is mechanically coupled to an axle  72  through the differential  68  to distribute torque to the vehicle drive wheels  32 . 
     The motor  22  (i.e., a second electric machine) can also be employed to drive the vehicle drive wheels  32  by outputting torque to a shaft  78  that is also connected to the second power transfer unit  60 . In one embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to a high voltage bus  82  and the battery  24 . The battery  24  may be a high voltage battery that is capable of outputting electrical power to operate the motor  22  and the generator  18 . Other types of energy storage devices and/or output devices can also be used with the electric vehicle  12 . 
     Referring now to  FIG. 2  with continuing reference to  FIG. 1 , a battery charging system  100  is used to recharge the battery  24  when charge in the battery  24  has been depleted due to operating the vehicle  12 . The battery charging system  100  could also be used to initially charge the battery  24  prior to use or prior to installation within the vehicle  12 . The battery  24  may stay in the vehicle  12  during a charge or may be removed from the vehicle. 
     The battery charging system  100  includes a battery charger  104  that selectively couples the battery  24  to a power source  108  to charge the battery  24  to a desired level. The battery charger  104  includes a processor  112  configured to control the selective coupling. The battery charging system  100  further includes a controller  116  configured to control the selective coupling to prevent overcharging the battery  24 . In this example, the processor  112  is part of the battery charger  104 . The controller  116  is a structure separate and distinct from the battery charger  104 . 
     When the battery charger  104  is coupled to the battery  24 , the battery charger  104  communicates charge to the battery  24  from the power source  108  to charge the battery  24  and specifically cells  120  of the battery  24 . Decoupling the battery charger  104  from the battery  24  ends the charge. 
     The battery charger  104  monitors the battery  24  to determine when to stop charging the battery  24 . Specifically, when the processor  112  determines that the battery  24  has received enough A-hr (Coulomb charge) and or kW-hr, the processor  112  stops the charge. The processor  112  selectively couples the battery charger  104  to the battery  24  to control charging of the battery  24 . The duration of the charge changes based on, an amount of charge required, a capacity of the battery  24 , a rate of charge, etc. In some examples, the processor  112  may incorrectly determine when to discontinue charging, which can result in undesirably charging the battery  24  beyond a desired level. 
     In this example, the controller  116  is used to inhibit charging the battery  24  beyond a desired level. The controller  116  monitors the charging of the battery  24  and compares expected charge data to actual charge data. The controller  116  may discontinue the charging, or take some other action in response to the comparison. For example, the controller  116  may discontinue the charging if the charging lasts longer than expected. Differences between expected charge data and actual charge data may, for example, indicate that the battery  24  requires repair or replacement. 
     Notably, in the example system  100 , both the controller  116  and the battery charger  104  (via the processor  112 ) are calculating the charge status of the battery  24 . In some examples, the controller  116  prevents the battery  24  from becoming overcharged. 
     The example controller  116  is shown separate from the battery  24  and the battery charger  104 . The controller  116  may be positioned elsewhere within the system, such as attached to the battery  24  or within the battery charger  104 . The processor  112  could also be positioned outside the battery charger  104 . 
     Referring now to  FIG. 3  with reference to  FIG. 2 , an example battery charge monitoring method  200  identifies discrepancies between actual charge data and expected charge data. The method  200  is utilized by the controller  116  to determine when to charge, and when not to charge, the battery  24 . 
     Expected charge data may include an expected time to complete the charge, the expected A-hrs carried by the battery  24  after completing the charge, etc. An example discrepancy may be the actual charge time lasting longer than the expected charge time. 
     In the method  200 , a step  204  utilizes a battery capacity and a charge rate to determine expected charge data for the battery  24 . 
     The battery capacity, in this example, is a maximum total amount energy, A-hrs, or both that the battery  24  is capable of storing. The battery capacity may be based on design specifications for the vehicle  12  ( FIG. 1 ). In another example, the capacity of the battery  24  may be a desired percentage of the maximum total amount of battery capacity that the battery  24  is capable of storing. For example, it may be desirable to charge the battery  24  to ninety percent of its total battery capacity. In such an example, the battery capacity for the method  200  would be ninety percent of the total capacity of the battery  24 . 
     The charge rate is determined from the battery charger  104  and may utilize information from the battery  24 . The charge rate represents the rate at which the battery charger  104  delivers Amperes (A) or kW (kilowatts) from the power source  108  to the battery  24 . 
     After calculating the expected charge data at the step  204 , the method  200  begins monitoring a battery charge at a step  208 . This step monitors the A-hr and/or kW-hr charge rate to the battery  24  from the battery charger  104 . The monitoring may begin prior to, or at the same time as, the calculating step  204  in other examples. 
     At a step  212 , the controller  116  compares the actual charge data to the expected charge data from the step  204 . If the actual charge data is different than the expected charge data, the controller  116  responds, such as by tripping a warning flag at the step  216 . The controller  116  may also decouple the battery charger  104  from the battery  24  at the step  216 . 
     In one more specific example, the controller  116  compares the actual charge time to an expected charge time. If the actual charge time exceeds the expected charge time, the controller  116  initiates a flag that notifies a technician. This difference may indicate a failure within the system  100  or the vehicle  12 . An example failure may include degradation of the battery  24 . Severe degradation may require battery replacement. 
     Referring now to  FIG. 4 , another example battery charge monitoring method  300  identifies discrepancies between actual A-hrs and expected A-hrs used to charge the battery  24  to a desired voltage. The method  300  also identifies discrepancies between actual time and expected time used to charge the battery  24  to the desired voltage. 
     In the method  300 , a calculation at a step  304  utilizes the capacity of the battery  24  and the charge rate associated with the battery charger  104  to determine the expected capacity of the battery when charging the battery  24  to a desired level. At a step  308 , the method  300  calculates the expected time required to charge the battery  24  to the desired voltage. 
     The capacity of the battery  24  in the example method  300  is a maximum total capacity that the battery  24  is capable of storing. The capacity may be based on design specifications for the vehicle  12  ( FIG. 1 ). In another example, the capacity of the battery may be a desired percentage of the maximum total capacity that the battery  24  is capable of storing. For example, it may be desirable to charge the battery to sixty percent of its maximum total capacity. In such an example, the battery capacity for the method  300  would be sixty percent of the total maximum capacity of the battery  24 . 
     Next, at a step  312 , the method  300  recognizes that the battery  24  may already have a partial charge and then calculates the expected total capacity that the battery will contain after charging the battery  24  to its capacity. The method  300  realizes that there may be some energy lost during charging, limitations in sensor capabilities, etc. and adds an incremental capacity to the expected charge capacity. The method  300  begins charging the battery at a step  316 . 
     The method  300  calculates integrals of Pdt (kW-hr) and Idt (A-hrs) at a step  324 . In this example, these calculations are running calculations that update in real-time during the charging. The voltage rise on the cells  120  (or open circuit voltage) of the battery  24  is a function of the integral of Pdt and Idt. The method  300 , at a step  326  determines if the voltage is greater than or equal to a desired voltage. If so, the method ends the charge at a step  328 . 
     At a step  330 , an actual kW-hr and an actual A-hrs from the step  324  are compared real time to the expected charge rate values from the steps  312  and  316 . If one of the actual values is greater than the expected values, the method  300  trips a warning flag at a step  332 . If neither of the actual values is greater than the expected values, the method  300  takes no action and the battery charger  104  continues to monitor charging of the battery  24 . 
     The warning flag at the step  338  may take many forms. The warning flag could, for example, be an internal alert that notifies a technician of a discrepancy between an expected Pdt and Idt and an actual Pdt and Idt. 
     If, during successive charges, the method  300  continues trip the warning flag, the method may initiate another type of warning, such as a visual warning that is visible to the driver. For example, if the battery is charged ten times and each of those charges results in the warning flag, the method  300  may initiate the visual warning. 
     Referring now to  FIG. 5 , another example battery charge monitoring method  400  is used to charge a battery (or cells of the battery). Depending on the information discovered during the monitoring, the method  400  may notify a user of a fault condition associated with the battery when ending the charge. Alternatively, the method  400  may simply end the charge (without identifying any fault condition). 
     In this example, the method  400 , at a step  410 , calculates the expected amp-hours (I-hr max) and energy (in kW-hrs) that are required to charge the battery. Factors that may be used to calculate these expected values include the battery&#39;s state-of-charge, capacity, temperature, age, maximum voltage, resistance, etc. Another factor may be a particular charge strategy for the battery. 
     The battery (and cells of the battery) typically have a known input resistance R. If the input resistance is not known, a person having skill in this art and the benefit of this disclosure would be able to determine the resistance R. 
     After calculating the expected values at the step  410 , the method  400  proceeds down a first path  420  or a second path  430 . The first path  420  is utilizes constant power charging (Pk) to charge the battery. The alternative second path  430  utilizes constant current charging (Ik) to charge the battery. A step  414  represents this selection. A user may make the selection at step  414  in some examples. 
     Referring to the first path  420 , the charge starts at a step  440 . The actual battery voltage (Vb) and actual battery current (Ib) are then monitored at a step  444  during the charge. With these actual values, the method  400  calculates actual power (P), actual energy (int(Pdt)), Amp-hr (int(Idt)), delta V, and delta I at a step  448 . As may be appreciated, energy (kW-hr) can be represented as int(V*Idt), and Amp-hr as int(Idt). 
     In this example, the increasing charge of the battery causes its voltage to increase monotonically, such that delta V is non-negative. Since a relatively constant power charge is utilized, and, because P=V*I, the voltage increasing monotonically indicates that the current during the charge decreases monotonically, such that delta I is less than or equal to zero. 
     Fluctuations from a substantially monotonic increase of the voltage, a substantially monotonic decrease of the current, or both are then detected at a step  452 . During the charging, if the actual voltage is decreasing or the actual current is increasing, there is an assumed error associated with the battery. The charge is then stopped, and an operator is notified of a fault condition at a step  456 . 
     If there are no such fluctuations, the method  400  proceeds to a step  460 . At the step  460 , if the actual battery voltage is greater than or equal to an expected voltage max, the charge is stopped at a step  466 . Also, at the step  460 , if the actual A-hr is greater than A-hr max similar to  FIG. 4  step  316 , the charge is stopped at the step  466 . Further, at the step  460 , if the energy to the battery (kW-hr−I 2 R loss) is greater than an estimated energy value required by the battery, the method  400  stops the charge at the step  466 . 
     Referring to the current controlled charge-based second path  430 , the charge starts at a step  470 . The actual battery voltage is then monitored at a step  474 . Ib is known, as the second path  430  represents current controlled charge. With the monitored value from the step  474 , the method  400  calculates power (P), energy (int(Pdt)), A-hr (int(Idt)), and delta V at a step  478 . 
     Since the example battery is charged at a relatively constant current, the voltage should always be increasing. If delta V is less than zero, which is detected at a step  482 , the method  400  assumes there is some error associated with the battery. The charge is then stopped, at the step  456 , and an operator is notified of a fault condition. 
     If delta V is greater than or equal to zero, the method  400  proceeds to a step  486 . At the step  486 , the method  400  determines if the voltage used for the charge is greater than or equal to an expected voltage max. If so, the charge ends at the step  466 . Also, at the step  486 , if the actual A-hr is greater than an expected A-hr, or if the energy to the battery (kW-hr−I 2 R loss) is greater than an estimated energy value required by the battery, the method  400  ends the charge at the step  466 . 
     In the some examples of this disclosure, charging may be automatically terminated in response to comparisons of actual measured data to expected (or calculated) data. In one more-specific example, actual Amp-hours required to charge exceeding calculated Amp-hours required to charge automatically terminates the charging. In another example, actual energy delivered to the cell exceeding calculated energy needed automatically terminates the charging. In other example, the charging is terminated if delta V of the battery is less than zero for power controlled or current controlled charges. In yet another example, the charging is terminated if delta I of the battery is positive for power controlled charges. Charging may also be terminated if the voltage of the battery is greater than a calculated maximum voltage for the battery. 
     A feature of this disclosure is real time monitoring of the battery for faults, plus determining a natural end of charge that may be based on maximum voltages, amp-hour maximums, and kilowatt-hour maximums. 
     Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. Further, unless otherwise specified, the steps may be performed in any order. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.