Abstract:
A system for controlling battery charging in a vehicle includes a traction battery and a controller. The controller is configured to charge the traction battery to a SOC that is less than a maximum SOC based on an amount of charge predicted to be received from an anticipated regenerative braking event. The regenerative braking event is anticipated to occur during the next drive cycle. The target SOC may be set such that, upon occurrence of the anticipated regenerative braking event, the traction battery achieves the maximum SOC.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to increased efficiency charging strategies for traction batteries for plug in vehicles. 
       BACKGROUND 
       [0002]    Plug-in electric vehicles, including plug-in hybrid vehicles (PHEVs) and battery electric vehicles (BEVs) have increased in prevalence as advancements in vehicle propulsion and battery technology have occurred. Such vehicles may be connected to an external charger to recharge a vehicle traction battery while the vehicle is parked. They also are generally equipped with regenerative braking, which enables the vehicle to capture a portion of the kinetic energy of the vehicle while braking. 
       SUMMARY 
       [0003]    A system for controlling battery charging in a vehicle includes a traction battery and a controller. The controller is configured to charge the traction battery to a target state of charge that is less than a maximum charging state of charge. The difference between the target state of charge and the maximum charging state of charge is based on an amount of charge predicted to be received from an anticipated regenerative braking event. The regenerative braking event is anticipated to occur during the next drive cycle. The target state of charge is set such that, upon occurrence of the anticipated regenerative braking event, the traction battery achieves the maximum charging state of charge. 
         [0004]    In one embodiment, the amount of charge is equal to a difference between the target state of charge and the maximum charging state of charge. In another embodiment, the amount of charge is based on a learned vehicle regenerative charging pattern. In yet another embodiment, the amount of charge is based on a topological profile at a detected charging location. In one such embodiment, the topological profile at the detected charging location is a local maximum elevation at the detected charging location. 
         [0005]    A method for charging a battery in a hybrid electric vehicle includes charging the battery to a target state of charge that is less than a maximum state of charge by a predetermined charge quantity. The predetermined charge quantity corresponds with a predicted regenerative charge from an anticipated regenerative braking event for the next drive cycle. 
         [0006]    In one embodiment, the predetermined charge quantity is based on a learned vehicle regenerative charging pattern. In another embodiment, the predetermined charge quantity is based on a topographical profile at a detected charging location. 
         [0007]    A battery charger arrangement for a vehicle includes a battery charger. The battery charger is configured to charge a traction battery of the vehicle to a target state of charge in response to data indicative of an anticipated regenerative braking event for the next drive cycle. The target state of charge is less than a state of charge corresponding to a fully charged condition for the traction battery. 
         [0008]    In one embodiment, the battery charger is further configured to, in response to user input, charge the traction battery to the state of charge corresponding to the fully charged condition. In another embodiment, the target state of charge is less than the state of charge corresponding to the fully charged condition by a predetermined charge quantity. The predetermined charge quantity corresponds with an amount of charge predicted to be received from the anticipated regenerative braking event. In one such embodiment, the predetermined charge quantity is based on a learned vehicle regenerative charging pattern. In another such embodiment, the predetermined charge quantity is based on a topographical profile at a detected charging location. The topographical profile may be a local maximum elevation at the detected charging location. 
         [0009]    Embodiments according to the present disclosure provide a number of advantages. For example, systems and methods according to the present disclosure provide more efficient battery charging for plug in vehicles. In addition, such systems and methods recover regenerative energy that would otherwise be lost. 
         [0010]    The above advantage and other advantages and features of the present disclosure will be apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1A  is a schematic illustration of a plug in vehicle coupled with an external charger; 
           [0012]      FIG. 1B  is a schematic illustration of another embodiment of a vehicle coupled with an external charger; 
           [0013]      FIG. 2  illustrates a charge profile for charging a fraction battery in a plug in vehicle; 
           [0014]      FIG. 3  illustrates an increased efficiency charge profile for charging a traction battery in a plug in vehicle; 
           [0015]      FIG. 4  is a flow chart of an algorithm for selectively enabling an increased efficiency charge mode; 
           [0016]      FIG. 5  is a flow chart of an algorithm for charging a vehicle battery according to an increased efficiency mode; and 
           [0017]      FIG. 6  is a flow chart of another embodiment of an algorithm for charging a vehicle battery according to an increased efficiency mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0019]    Plug-in vehicles, including PHEVs and BEVs, include a vehicle traction battery configured to supply electric power to a traction motor. The traction battery, traction motor, and other components cooperate as an electric drive system. In a BEV the electric drive system may be the only source of propulsive power to vehicle traction wheels, while a PHEV may additionally be provided with an internal combustion engine. Such vehicles may be connected to an external power supply to recharge the traction battery. 
         [0020]    With reference to  FIG. 1A , a vehicle charging system is illustrated according to an embodiment of the present disclosure. A vehicle  10  is provided with an electric drive system  12  including a traction battery  14  and a regenerative braking system  16 . The regenerative braking system  16  is configured to recover vehicle kinetic energy and convert it into electric energy to charge the traction battery  14 . In some embodiments, the regenerative braking system  16  may include a motor/generator configured to provide braking torque to vehicle wheels. 
         [0021]    The vehicle  10  is additionally provided with a vehicle controller  18 . The traction battery  14  and regenerative braking system  16  are in communication with or under the control of the vehicle controller  18 . Although illustrated as a single controller, the controller  18  may include multiple controllers that operate in conjunction to control various vehicle systems. For example, the vehicle controller  18  may be a vehicle system controller/powertrain control module (VSC/PCM). In this regard, the vehicle charging control portion of the VSC/PCM can be software embedded within the VSC/PCM, or it can be a separate hardware device. The vehicle controller  18  generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM and/or EEPROM) and software code to co-act with one another to perform a series of operations. The vehicle controller is in electrical communication with the vehicle battery, and receives signals that indicate the battery charge level. The vehicle controller  18  may further communicate with other controllers over a hardline vehicle connection using a common bus protocol (e.g., CAN), and may also employ wireless communication. 
         [0022]    The vehicle  10  is provided with a navigation system  19 . The navigation system  19  includes a positioning device such as a GPS system. The navigation system  19  may be equipped with a database including stored mapping data, with wireless communications to receive mapping data as needed, or a combination thereof. In some embodiments the navigation system  19  is installed in the vehicle  10 , while in other embodiments the navigation system  19  may be a separate device such as a cell phone or standalone GPS that is connected to the vehicle via a wireless or wired connection. The navigation system  19  is in communication with the vehicle controller  18 . 
         [0023]    The vehicle  10  is further provided with a user interface  20 . The user interface  20  may include a display monitor, touchscreen, mobile device interface, or other appropriate systems. The user interface  20  is in communication with the vehicle controller  18  and with the navigation system  19 . The user interface transmits various user inputs to the vehicle controller  18 , in response to which the vehicle controller  18  may adjust appropriate vehicle settings. The user interface also transmits various user inputs to the navigation system  19 , in response to which the navigation system may choose navigation routes, save geolocations, or other take other appropriate actions. 
         [0024]    An external charger  22  provides charging to the traction battery  14  via a charger interface  24 . In one embodiment, the external charger is physically connected to the vehicle, i.e. the charger interface  24  includes a receptacle on the vehicle into which the charger  22  is plugged to form a direct connection. In another embodiment, the charger interface  24  includes at least one induction plate and the external charger  22  includes at least one charging coil which cooperate to form an inductive charging system. Other charging systems known in the art may also be used. 
         [0025]    The charger interface  24  is in communication with and under the control of the vehicle controller  18 . The vehicle controller  18  may control the charger interface  24  to selectively enable or disable recharging of the traction battery  14 . 
         [0026]    Referring to  FIG. 1B , another embodiment is shown. In this embodiment, a vehicle  10 ′ is provided with an electric drive system  12 ′ having a traction battery  14 ′ and a regenerative braking system  16 ′, a vehicle controller  18 ′, a navigation system  19 ′, a user interface  20 ′, and a charger interface  24 ′. An external charger  22 ′ is configured to charge the traction battery  14 ′ via the charger interface  24 ′. The external charger  22 ′ is additionally provided with a charger controller  26 . The charger controller  26  is in communication with the vehicle controller  18 ′. The communication may occur over a communication bus if the charger physically connects with the vehicle. In embodiments having an inductive charger, the vehicle controller  18  may communicate with the charger controller  26  via a wireless communications system, such as RFID, NFC, Bluetooth, WiFi, or other methods known in the art. The charger controller  26  may control the external charger  22 ′ to selectively enable or disable recharging of the traction battery  14 ′. 
         [0027]    Referring now to  FIG. 2 , a charging profile for charging a vehicle traction battery is illustrated. In this illustrative example, the battery is fully discharged at time t=0. The battery is subsequently charged to a maximum state of charge (SOC max )  28 . The charging profile includes a high efficiency charging portion  30 . In this region, the battery is charged with a substantially constant current. The profile additionally includes a reduced efficiency charging region  32  as the battery SOC nears SOC max . In this region, the charging current is reduced. 
         [0028]    Thus it may be understood that the “top off” portion of charging is a less efficient portion of the charging profile. As an additional consideration, higher battery SOCs may contribute to battery life degradation, both in terms of life due to charge/discharge cycles and in terms of calendar life. Consequently a more efficient charging profile may be desirable. However, a countervailing consideration is that any alternate charging profile should also provide adequate battery charge for an upcoming vehicle drive cycle. 
         [0029]    Referring to  FIG. 3 , an increased efficiency or “eco charge” charging profile for a vehicle traction battery is illustrated. As in the previous example, the battery is fully discharged at time t=0. The battery is charged with a substantially constant current through high efficiency charging portion  30 ′. The battery is charged to a target state of charge (SOC target )  34  that is less than SOC max    28 ′. Preferably, SOC target  is an SOC within the high efficiency charging portion  30 ′ of the charging profile, as illustrated here. Although SOC target  may be set within a “top off” portion of the charging profile, such an embodiment would result in a less efficient charging cycle. SOC target  is less than SOC max  by a charge quantity (ΔSOC)  36 . 
         [0030]    Referring now to  FIG. 4 , a flow chart illustrates an algorithm for selectively enabling an increased efficiency charging profile. The algorithm begins at block  38 . A determination is made of whether the vehicle is charging, as illustrated at operation  40 . If no, the algorithm returns to block  38 . If yes, then a determination is made of whether an increased efficiency charging mode is active, as illustrated at operation  42 . Such a mode may be selected by a user, for example via a user interface  20  as illustrated in  FIG. 1A . If the increased efficiency charging mode is active, then the battery is charged to a state of charge equal to SOC target %, as illustrated at block  44 . If no, then the battery is charged to SOC max , as illustrated at block  46 . 
         [0031]    In some embodiments, this algorithm may be performed by a controller in a vehicle. For example, in the embodiment illustrated in  FIG. 1   a,  the vehicle controller  18  may determine whether the increased efficiency charging mode is active and control the charger interface  24  to discontinue charging once the traction battery  14  has charged to the appropriate SOC. In other embodiments, this algorithm may be performed by a controller in a vehicle in conjunction with a charger controller. For example, in the embodiment illustrated in  FIG. 1B , the vehicle controller  18 ′ may determine whether the increased efficiency charging mode is active and communicate the status of the increased efficiency charging mode to the charger controller  26 . The charger controller  26  may control the charger  22 ′ to discontinue charging once the traction battery  14 ′ has reached the appropriate SOC. Execution of the algorithm may involve various other controllers as well. 
         [0032]    The value of SOC target  for the increased efficiency charging mode may be set in various ways in different embodiment. In one embodiment, a driver may manually set SOC target . For example, if a PHEV has an SOC max  of 99% SOC, a driver could instead set SOC target  at 95% SOC. This selection could be made via a user interface, user interface  20  in  FIG. 1A . However, such an embodiment results in a decreased range while operating on battery power. Consequently, a user may need to manually vary SOC target  over time to optimize the charge limit for the user&#39;s driving situation. 
         [0033]    In another embodiment, a driver may set a desired electric driving range for an upcoming drive cycle. In response to the desired range, a controller may calculate a corresponding SOC target  to provide electric driving operation range. As an example, the SOC target  may be calculated based on an average watt-hour per mile usage rate for the vehicle and a known watt-hour per unit SOC usage rate. This calculation may be done using the formula: 
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         [0034]    Referring now to  FIG. 5 , a flow chart illustrates another embodiment for setting SOC target . The algorithm begins at block  48 . A determination is then made of whether the vehicle is charging, as illustrated at block  50 . This determination may be performed, for example, by a vehicle controller such as vehicle controller  18  illustrated in  FIG. 1A . If the vehicle is not charging, then operation returns to the start at block  48 . If the vehicle is charging, then the charging location is learned and the vehicle is charged to SOC max , as illustrated at block  52 . On a subsequent drive cycle from the learned charging location, so-called “lost” regenerative charging capacity is monitored. Lost regenerative charging refers to regenerative braking opportunities that are unused because the traction battery is fully charged. In one embodiment, the monitoring is performed over a time interval or distance interval of the drive cycle commencing when the vehicle leaves the charging location. In another embodiment, once the SOC has depleted to a calibratable level (e.g. to 90% SOC), a comparison is made between regenerative energy produced and regenerative energy collected. A determination is made of whether the lost regenerative energy exceeds an associated threshold, as illustrated at block  56 . As an example, the associated threshold may be 40 Wh. If no, then the operation returns to start at block  48 . If yes, then a charge amount ΔSOC is determined based on the lost regenerative capacity and SOC target  at the learned location is set based on ΔSOC, as illustrated at block  58 . This may be performed using the formula: SOC target =SOC max −ΔSOC. 
         [0035]    The above algorithm may be repeated at multiple charging locations, each of which may be associated with a charge amount corresponding to a lost regenerative capacity at that respective charging location. 
         [0036]    According to various embodiments, ΔSOC may be set equal to the lost regenerative capacity, or greater or less than the lost regenerative capacity to provide a margin to account for variability in regenerative charging opportunities. 
         [0037]    In some embodiments, a calibratable lost regenerative capacity threshold may be provided, and SOC target  is lowered only when the lost regenerative capacity during the drive cycle exceeds the associated threshold. In an exemplary embodiment, the calibratable threshold is 0.5% SOC. 
         [0038]    In some embodiments, lost regenerative charging opportunities may be monitored over multiple drive cycles. In such embodiments, SOC target  is lowered only when regenerative capacity is lost over each of multiple drive cycles. In an exemplary embodiment, SOC target  is lowered when regenerative capacity is lost over each of three drive cycles. 
         [0039]    Referring to  FIG. 6 , a flow chart illustrates another embodiment for setting SOC target . The algorithm begins at block  60 . A determination is then made of whether the vehicle is charging, as illustrated at block  62 . This determination may be performed, for example, by a vehicle controller such as vehicle controller  18  illustrated in  FIG. 1A . If the vehicle is not charging, then operation returns to the start at block  60 . If the vehicle is charging, then the charging location is detected, as illustrated at block  64 . This determination may be performed, for example, via manual user entry or use of an on-board GPS system. Local topographical data is then looked up, as illustrated at block  66 . This may be performed via accessing locally stored mapping data, accessing remote mapping data using wireless communications, or other methods known in the art. A determination is then made of whether the detected charging location is at a local topographical maximum, e.g. a hill, as illustrated at block  68 . At such locations, surrounding roads are at lower altitudes than the charging location. Drivers generally apply vehicle brakes while driving downhill, and thus if a vehicle is charged at the top of a hill, it may be anticipated that regenerative brakes will be applied as the vehicle descends. If the vehicle is not at a local topographical maximum, then the operation returns to start at block  60 . If yes, then a charge amount ΔSOC is determined based on the regenerative charging potential and SOC target  is set based on ΔSOC, as illustrated at block  70 . The regenerative charging potential may be based on topographical factors including local gradient and elevation change. 
         [0040]    As can be seen from the various embodiments, the present invention provides systems and methods for more efficiently charging a traction battery in a plug in vehicle. In addition, such systems and methods enable regenerative energy to be stored that would otherwise be lost. 
         [0041]    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. 
         [0042]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.