System and method for quantifying battery usage

Methods and system are described for estimating an amount of battery usage for a traction battery of a vehicle. The traction battery usage estimate may be based on or a function of a distance per gallon of gasoline-equivalent so that the usage estimate may be more familiar to vehicle operators. In addition, the traction battery usage estimate may also be based on traction battery current and traction battery voltage.

FIELD

The present description relates generally to methods and systems for quantifying use of a battery. The battery usage may be applied to estimate battery degradation and expected remaining battery life.

A vehicle may include a traction or propulsion battery that supplies electric power to and receives electric power from an electric machine. The vehicle's manufacturer may warranty the battery for a prescribed amount of time or a prescribed vehicle travel distance. However, the amount of time that a battery is used and a distance that a vehicle is driven may not correlate well with battery degradation and remaining battery life. Therefore, it may be desirable to provide a metric for battery usage that more closely reflects the battery's operational status.

DETAILED DESCRIPTION

The following description relates to systems and methods for quantifying usage of a traction or propulsion battery of a vehicle. The battery usage metric is defined in a way that may make it seem more familiar to those that may not be as well versed in battery terminology. In particular, the battery usage metric may be described in terms of an aggregate distance that the battery has propelled the vehicle. The battery may be included in an electric vehicle as shown inFIG. 1or a hybrid vehicle. The battery usage metric may increase according to operating conditions as shown inFIG. 2. Example methods for determining a battery usage metric are shown inFIGS. 3 and 4. An example battery degradation map that is a function of vehicle usage and a total number of days a vehicle is driven is shown inFIG. 5.

A traction or propulsion battery may supply electric power to and receive electric power from an electric machine to propel a vehicle. The vehicle's manufacturer may warranty the battery for a prescribed amount of time or a prescribed vehicle travel distance. For example, the battery may be warrantied for 6 years or 160,000 kilometers (km). The warrantee may provide a level of comfort to the vehicle's owner, but the batteries life span may differ from what is provided by the warrantee because of the way the vehicle's owner has operated the vehicle. Consequently, the vehicle's owner may replace the battery when the end of the warrantee approaches, but the battery may have a significant amount of life left. Therefore, it may be desirable to provide a way of determining battery usage in a way that may allow a vehicle owner to have an improved estimate of expected battery life.

The inventors herein have recognized the above-mentioned issues and have developed a method for a battery, comprising: generating a battery usage estimate based on a distance per gallon of gasoline-equivalent, battery current, and battery voltage via a controller; and transferring the battery usage estimate from the controller to a device external to the controller.

By generating a battery usage estimate that is based on a distance per gallon of gasoline-equivalent, it may be possible to provide a technical result of generating a battery use metric that may be more intuitively understandable to some users. Further, the battery use metric may allow vehicle operators to make a more informed decision regarding whether or not a battery should be serviced.

The present description may provide several advantages. In particular, the approach may allow vehicle operators to have a better understanding of battery use and remaining battery life. Further, the approach may be implemented in different ways depending on the accuracy and sophistication level that is desired. Further still, the approach may be applied to electric only vehicles or hybrid vehicles.

FIG. 1illustrates an example vehicle propulsion system100for vehicle121. A front portion of vehicle121is indicated at110and a rear portion of vehicle121is indicated at111. Vehicle propulsion system100includes at two propulsion sources including front electric machine125and rear electric machine126. Electric machines125and126may consume or generate electrical power depending on their operating mode. Throughout the description ofFIG. 1, mechanical connections between various components are illustrated as solid lines, whereas electrical connections between various components are illustrated as dashed lines.

Vehicle propulsion system100has a front axle133and a rear axle122. In some examples, rear axle may comprise two half shafts, for example first half shaft122a, and second half shaft122b. Likewise, front axle133may comprise a first half shaft133aand a second half shaft133b. Vehicle propulsion system100further has front wheels130and rear wheels131. In this example, front wheels130may be selectively driven via electric machine125. Rear wheels131may be driven via electric machine126.

The rear axle122is coupled to electric machine126. Rear drive unit136may transfer power from electric machine126to axle122resulting in rotation of drive wheels131. Rear drive unit136may include a low gear set175and a high gear177that are coupled to electric machine126via output shaft126aof rear electric machine126. Low gear175may be engaged via fully closing low gear clutch176. High gear177may be engaged via fully closing high gear clutch178. High gear clutch178and low gear clutch176may be opened and closed via commands received by controller136cof rear drive unit136(e.g., rear drive unit controller136c) over controller area network (CAN)199. Alternatively, high gear clutch178and low gear clutch176may be opened and closed via digital outputs or pulse widths provided via control system14. Rear drive unit136may include differential128so that torque may be provided to axle122aand to axle122b. In some examples, an electrically controlled differential clutch (not shown) may be included in rear drive unit136.

The front axle133is coupled to electric machine125. Front drive unit137may transfer power from electric machine125to axle133resulting in rotation of drive wheels130. Front drive unit137may include a low gear set170and a high gear173that are coupled to electric machine125via output shaft125aof front electric machine125. Low gear170may be engaged via fully closing low gear clutch171. High gear173may be engaged via fully closing high gear clutch174. High gear clutch174and low gear clutch171may be opened and closed via commands received by controller133cover CAN199. Alternatively, high gear clutch174and low gear clutch171may be opened and closed via digital outputs or pulse widths provided via control system14. Front drive unit137may include differential127so that torque may be provided to axle133aand to axle133b. In some examples, an electrically controlled differential clutch (not shown) may be included in rear drive unit137.

Electric machines125and126may receive electrical power from onboard electrical energy storage device132(e.g., a traction or propulsion battery). Furthermore, electric machines125and126may provide a generator function to convert the vehicle's kinetic energy into electrical energy, where the electrical energy may be stored at electric energy storage device132for later use by the electric machine125and/or electric machine126. A first inverter system controller (ISC1)134may convert alternating current generated by rear electric machine126to direct current for storage at the electric energy storage device132and vice versa. A second inverter system controller (ISC2)147may convert alternating current generated by front electric machine125to direct current for storage at the electric energy storage device132and vice versa. Electric energy storage device132may be a battery, capacitor, inductor, or other electric energy storage device.

In some examples, electric energy storage device132may be configured to store electrical energy that may be supplied to other electrical loads residing on-board the vehicle (other than the motor), including cabin heating and air conditioning, engine starting, headlights, cabin audio and video systems, etc. Further, in some examples, only the front axle or only the rear axle includes an electric machine to propel the vehicle.

Control system14may communicate with one or more of electric machine125, electric machine126, energy storage device132, etc. via CAN199. Control system14may receive sensory feedback information from one or more of electric machine125, electric machine126, energy storage device132, etc. Further, control system14may send control signals to one or more of electric machine125, electric machine126, energy storage device132, etc., responsive to this sensory feedback. Control system14may receive an indication of an operator requested output of the vehicle propulsion system from a human operator102, or an autonomous controller. For example, control system14may receive sensory feedback from pedal position sensor194which communicates with pedal192. Pedal192may refer schematically to a propulsive effort pedal. Similarly, control system14may receive an indication of an operator requested vehicle braking via a human operator102, or an autonomous controller. For example, control system14may receive sensory feedback from pedal position sensor157which communicates with brake pedal156. Control system14may also communicate with other vehicles via vehicle to vehicle (V2V) communications system6. Control system14may also communicate with infrastructure8via vehicle to infrastructure (V2I) communications system7. Infrastructure8may include but is not limited to external computer servers, computer servers at vehicle service centers, and traffic control infrastructure computer servers.

Energy storage device132may periodically receive electrical energy from a power source such as a stationary power grid5residing external to the vehicle (e.g., not part of the vehicle). As a non-limiting example, vehicle propulsion system100may be configured as a plug-in electric vehicle (EV), whereby electrical energy may be supplied to energy storage device132via the power grid5.

Electric energy storage device132includes an electric energy storage device controller139and a power distribution module138. Electric energy storage device controller139may provide charge balancing between energy storage element (e.g., battery cells), battery usage estimates, and communication with other vehicle controllers (e.g., controller12). Electric energy storage device controller139may monitor battery current, battery voltage, and battery temperature via battery sensors10. Electric energy storage device controller139includes non-transitory (e.g., read only memory)139a, random access memory139b, digital inputs/outputs1139d, and a microcontroller139c. Power distribution module138controls flow of power into and out of electric energy storage device132.

One or more wheel speed sensors (WSS)195may be coupled to one or more wheels of vehicle propulsion system100. The wheel speed sensors may detect rotational speed of each wheel. Such an example of a WSS may include a permanent magnet type of sensor.

Vehicle propulsion system100may further include a motor electronics coolant pump (MECP)146. MECP146may be used to circulate coolant to diffuse heat generated by at least electric machine120of vehicle propulsion system100, and the electronics system. MECP may receive electrical power from onboard energy storage device132, as an example.

Controller12may comprise a portion of a control system14. In some examples, controller12may be a single controller of the vehicle. Control system14is shown receiving information from a plurality of sensors16(various examples of which are described herein) and sending control signals to a plurality of actuators81(various examples of which are described herein). As one example, sensors16may include tire pressure sensor(s) (not shown), wheel speed sensor(s)195, etc. In some examples, sensors associated with electric machine125, electric machine126, wheel speed sensor195, etc., may communicate information to controller12, regarding various states of electric machine operation. Controller12includes non-transitory (e.g., read only memory)165, random access memory166, digital inputs/outputs168, and a microcontroller167. Controller12may also perform calculations and tasks that may be performed via electric energy storage device controller139.

Vehicle propulsion system100may also include an on-board navigation system17(for example, a Global Positioning System) on dashboard19that an operator of the vehicle may interact with. The navigation system17may include one or more location sensors for assisting in estimating a location (e.g., geographical coordinates) of the vehicle. For example, on-board navigation system17may receive signals from GPS satellites (not shown), and from the signal identify the geographical location of the vehicle. In some examples, the geographical location coordinates may be communicated to controller12.

Dashboard19may further include a display system18configured to display information to the vehicle operator. Display system18may comprise, as a non-limiting example, a touchscreen, or human machine interface (HMI), display which enables the vehicle operator to view graphical information as well as input commands. In some examples, display system18may be connected wirelessly to the internet (not shown) via controller (e.g.12). As such, in some examples, the vehicle operator may communicate via display system18with an internet site or software application (app).

Dashboard19may further include an operator interface15via which the vehicle operator may adjust the operating status of the vehicle. Specifically, the operator interface15may be configured to initiate and/or terminate operation of the vehicle driveline (e.g., electric machine125and electric machine126) based on an operator input. Various examples of the operator ignition interface15may include interfaces that require a physical apparatus, such as an active key, that may be inserted into the operator interface15to start the electric machines125and126and to turn on the vehicle, or may be removed to shut down the electric machines125and126to turn off the vehicle. Other examples may include a passive key that is communicatively coupled to the operator interface15. The passive key may be configured as an electronic key fob or a smart key that does not have to be inserted or removed from the interface15to operate the vehicle electric machines125and126. Rather, the passive key may need to be located inside or proximate to the vehicle (e.g., within a threshold distance of the vehicle). Still other examples may additionally or optionally use a start/stop button that is manually pressed by the operator to start or shut down the electric machines125and126to turn the vehicle on or off. In other examples, a remote electric machine start may be initiated remote computing device (not shown), for example a cellular telephone, or smartphone-based system where a user's cellular telephone sends data to a server and the server communicates with the vehicle controller12to start the engine. The devices included in dashboard19may communicate with controller12via CAN199.

The system ofFIG. 1provides for a vehicle system, comprising: a traction battery; and a controller including executable instructions stored in non-transitory memory that cause the controller to generate an estimate of battery usage based on a distance per gallon of gasoline-equivalent, traction battery current, traction battery voltage, and a weighting factor, the controller including additional instructions that cause the controller to transfer the estimate of battery usage to a device external to the controller. The vehicle system includes where the weighting factor is based on a traction battery state of charge, a traction battery current pulse duration, traction battery temperature, and traction battery current. The vehicle system includes where the device is a human/machine interface. The vehicle system includes where the device is a second controller. The vehicle system includes where the traction battery current is an electric discharge current. The vehicle system includes where the traction battery current is an electric charging current. The vehicle system further comprises additional executable instructions to integrate the traction battery current multiplied by the traction battery voltage.

Referring now toFIG. 2, a prophetic vehicle operating sequence according to the method ofFIG. 4is shown. The vehicle and battery operating sequence shown inFIG. 2may be provided via the method ofFIG. 4in cooperation with the system shown inFIG. 1. The plots shown inFIG. 2occur at the same time and are aligned in time. The vertical lines at t0-t6 represent times of interest during the sequence.

The first plot from the top ofFIG. 2is a plot of traction battery current versus time. The vertical axis represents battery current and the battery current increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace202represents the battery current.

The second plot from the top ofFIG. 2is a plot of traction battery voltage versus time. The vertical axis represents the battery voltage and the battery voltage increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Line204represents the battery voltage.

The third plot from the top ofFIG. 2is a plot of a value of a weighting factor versus time. The vertical axis represents the value of the weighting factor and the weighting factor value increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace206represents the weighting factor value.

The fourth plot from the top ofFIG. 2is a plot of battery usage value (e.g., a value described in terms of an aggregate distance hypothetically traveled by a vehicle that is propelled via power from a battery, which may be referred to as electric mileage or E-mileage) versus time. The vertical axis represents the battery usage value and battery usage increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace208represents the battery usage value.

The fifth plot from the top ofFIG. 2is a plot of a distance per gallon of gasoline-equivalent value versus time. The vertical axis represents the distance per gallon of gasoline-equivalent and the distance per gallon of gasoline-equivalent value increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace210represents the distance per gallon of gasoline-equivalent value (e.g., miles per gallon of gasoline-equivalent MPGe).

At time t0, the battery current is zero and the battery voltage is at a higher level. The weighting factor is at a lower level and the battery usage value is not changing. The distance per gallon of gasoline-equivalent value is at a higher constant level.

At time t1, the battery current increases and the battery voltage remains at its previous level. The weighting factor remains at its previous level and the battery usage value begins to increase at a first rate. The distance per gallon of gasoline-equivalent value remains at its previous level.

At time t2, the battery current increases a second time and the battery voltage remains at its previous level. The weighting factor is unchanged and the battery usage value begins to increase at a second rate, the second rate being greater than the first rate. The battery usage amount increases as a function of the battery current. The distance per gallon of gasoline-equivalent value remains at its previous level.

At time t3, the battery current is reduced and the battery voltage remains at its previous level. The weighting factor is unchanged and the battery usage value changes at a third, the third rate less than the second rate and greater than the first rate. The distance per gallon of gasoline-equivalent value remains at its previous level.

At time t4, the battery current remains unchanged from its value at time t3 and the battery voltage is unchanged. The weighting factor increases, which in turn causes the battery usage value to increase at a fourth rate. The weighting factor may increase due to a battery temperature change or battery state of charge (SOC) change, for example. The distance per gallon of gasoline-equivalent value remains unchanged.

At time t5, the battery current increases a third time and the battery voltage remains at its previous level. The weighting factor is unchanged and the battery usage value begins to increase at a fifth rate, the fifth rate being greater than the second rate. The battery usage amount increases at a higher rate since the battery current has increased and since the weighting factor is at a larger value. The distance per gallon of gasoline-equivalent value remains at its previous level.

At time t6, the battery current decreases a second time and the battery voltage remains at its previous level. The weighting factor is unchanged and the battery usage value begins to increase at a lower rate since the battery current level is small. The distance per gallon of gasoline-equivalent value remains at its previous level.

In this way, the battery usage rate may change with battery operating conditions. The battery usage increases while the battery is supplying or receiving electric current. The battery usage may increase over the battery's life as the battery usage rate increases and decreases.

Referring now toFIG. 3, an example method for operating a vehicle that includes a traction battery is shown. The method ofFIG. 3may be incorporated into and may cooperate with the system ofFIG. 1. Further, at least portions of the method ofFIG. 3may be incorporated as executable instructions stored in non-transitory memory of a controller while other portions of the method may be performed via the controller transforming operating states of devices and actuators in the physical world.

At302, method300determines an actual total charging electric current (e.g., Ah (Ampere hours)) through the traction battery since the traction battery was installed in the vehicle. The actual total charging electric current may be determined via an electric current sensor that monitors electric current flow into and out of the traction battery. The charging electric current is current that enters the traction battery.

Alternatively, method300may determine an actual total discharging electric current through the traction battery since the traction battery was installed in the vehicle. The actual total discharging electric current may be determined via an electric current sensor that monitors electric current flow out of the traction battery. Method300proceeds to304.

At304, method300determines a nominal battery voltage. In one example, the nominal battery voltage may be determined by multiplying the total number of battery cells that are in series with the rated voltage of the battery cells (e.g., 3.7 volts). Alternatively, the nominal battery voltage may be measured via a volt meter or A/D converter in the battery controller when the battery is fully charged while current is not being supplied to or from the battery. Method300proceeds to306.

At306, method300determines a distance per gallon of gasoline equivalent for the vehicle. In one example, the distance per gallon of gasoline equivalent may be determined for a distance in miles, but other distances may be used. Thus, the distance per gallon of gasoline equivalent may be referred to as miles per gallon of gasoline equivalent. The miles per gallon of gasoline value for the vehicle may be stored in controller memory and retrieved from memory. The miles per gallon of gasoline equivalent may be determined according to 115,000 British thermal units produced by combusting a gallon of gasoline. It takes 33.7 kilowatts hours of electricity to generate the same amount of heat. Therefore, if the vehicle can travel 60 miles on 33.7 kilowatts, the vehicle would be rated at 60 miles per gallon of gasoline-equivalent. The equivalent is the electric power to travel the distance of 60 miles. Method300proceeds to308.

At308, method300determines the battery usage value. In one example, the battery usage value may be determined via the following equation:

E⁢-⁢mileage=Qd×Vnom1⁢0⁢0⁢03⁢3.7×MPGe
where E-mileage is the battery usage value, Qdis the actual total battery discharge current (Ah) since the battery was installed in the vehicle, Vnomis the nominal traction battery voltage, and MPGe is the miles per gallon gasoline equivalent. It should be noted that although miles, gallons, and gasoline are used in this example to determine the battery usage value, these units and type of fuel may be replaced by similar parameters. For example, liters may be substituted for gallons, diesel fuel may be substituted for gasoline, and kilometers may be substituted for miles.

Alternatively, the battery usage value may be determined via the following equation:

E⁢-⁢mileage=Qc×Vnom1⁢0⁢0⁢03⁢3.7×MPGe
where E-mileage is the battery usage value, Qcis the actual total battery charge current (Ah) since the battery was installed in the vehicle, Vnomis the nominal traction battery voltage, and MPGe is the miles per gallon gasoline equivalent. Again, although miles, gallons, and gasoline are used in this example to determine the battery usage value, these units and type of fuel may be replaced by similar parameters. Method300proceeds to310.

At310, method300judges whether or not the battery usage level or amount is greater than a threshold. If so, the answer is yes and method300proceeds to312. Otherwise, the answer is no and method300proceeds to313.

At313, method300makes the battery usage value available for battery degradation metrics, display to vehicle occupants, vehicle service scheduling, and infrastructure. In one example, a battery controller may transmit or transfer the battery usage value to other controllers on-board or off-board of the vehicle. For example, the battery controller may transfer the battery usage value to a controller that displays the value to vehicle occupants via a human/machine interface. Further, the battery controller may transfer the battery usage value to infrastructure so that the state of the vehicle may be determined. In addition, the battery controller may estimate battery degradation from a map that defines battery charge capacity retention percentage (e.g., a measure of battery degradation) as a function of battery usage and a total number of days a vehicle is driven as shown inFIG. 5and described further below. The battery controller may display the battery degradation value to vehicle occupants via transferring or transmitting the battery degradation value to another controller in the vehicle to display on a human/machine interface. In still other examples, the battery degradation value may be transmitted off-board the vehicle to a remote server so that vehicle service may be scheduled. Method300proceeds to exit.

At312, method300notifies the vehicle user (e.g., a human) that the battery usage exceeds a threshold value. The notification may be via displaying a message on a human/machine interface. In addition, method300may automatically schedule the vehicle for service of the battery via sending a vehicle service request to remote infrastructure. Method300proceeds to314.

At314, method300makes the battery usage value available for battery degradation metrics, display to vehicle occupants, vehicle service scheduling, and infrastructure as described at313. Method300proceeds to316.

At316, method300judges whether or not the battery usage level or amount is greater than a second threshold. If so, the answer is yes and method300proceeds to318. Otherwise, the answer is no and method300exits.

At318, method300optionally adjusts vehicle operation. In one example, method300may adjust a relationship between propulsive pedal position and requested wheel torque such that greater application of the propulsive pedal may be required to generate middle level driver demand torques. In this way, the responsiveness of the electric machines may be reduced so that current may be drawn from the battery at a lower rate, thereby extending the life of the battery. Of course, full driver demand torque may be made available at the greatest application position of the propulsive effort pedal.

In another example, method300may reduce a rate of charging or electric current that may be accepted by the battery to extend battery life. In still other examples, selected vehicle modes may not be permitted or other modes that are not normally available may be made available. For example, only two wheel drive mode may be made available to further conserve battery charge capacity and to extend battery life. Method300proceeds to exit.

In this way, battery usage may be determined in a less sophisticated way as compared to the way described inFIG. 4. The battery usage metric may be the basis for indicating battery state to vehicle occupants and to schedule vehicle service.

Referring now toFIG. 4a second method for operating a vehicle that includes a traction battery is shown. The method ofFIG. 4may be incorporated into and may cooperate with the system ofFIG. 1. Further, at least portions of the method ofFIG. 4may be incorporated as executable instructions stored in non-transitory memory of a controller while other portions of the method may be performed via the controller transforming operating states of devices and actuators in the physical world.

At402, method400determines traction battery voltage and electric current. The traction battery voltage may be determined via an A/D converter within a controller. The traction battery current may be determined via a current sensor that is input to the controller. Method400proceeds to404.

At404, method400determines a value of a weighting factor. In one example, the weighting factor may be determined from a plurality of individual weights W1, W2, W3, and W4. For example, the weighting factor may be determined from the following equation:
W=W1×W2×W3×W4
where W is the weighting factor, W1 is a weight that is based on traction battery temperature (T(t)), W2 is a weight that is based on traction battery current (I(t)), W3 is a weight that is based on traction battery state of charge (SOC(t)), and W4 is a weight that is based on a duration of an electric current pulse P(t) duration. In one example, W1 may have a value of 1.2 if traction battery temperature is greater than 50° C. W2 may have a value of 2.0 when I(t) is ≥5 Amperes. Method400proceeds to406.

At406, method400determines a distance per gallon of gasoline equivalent for the vehicle. The distance per gallon of gasoline equivalent may be determined as described at306. Method400proceeds to408.

At408, method400determines the battery usage value. In one example, the battery usage value may be determined via the following equation:

E⁢-⁢mileage=⁢f⁡(I,T,SOC,MPGe,V,SOC,P)=⁢12⁢∫I⁡(t)·V⁡(t)⁢dt·W⁡(T⁡(t),I⁡(t),SOC⁡(t),P⁡(t))33.7×1000×MPGe
where E-mileage is the battery usage value, f is a function that returns the battery usage value, I is traction battery current, T is traction battery temperature, SOC is traction battery SOC, V is traction battery voltage, P is traction battery current pulse duration, t is time, and W is the weighting factor as previously described. Method400proceeds to410.

At410, method400judges whether or not the battery usage level or amount is greater than a threshold. If so, the answer is yes and method400proceeds to412. Otherwise, the answer is no and method400proceeds to413.

At413, method400makes the battery usage value available for battery degradation metrics, display to vehicle occupants, vehicle service scheduling, and infrastructure. In one example, a battery controller may transmit or transfer the battery usage value to other controllers on-board or off-board of the vehicle. For example, the battery controller may transfer the battery usage value to a controller that displays the value to vehicle occupants via a human/machine interface. Further, the battery controller may transfer the battery usage value to infrastructure so that the state of the vehicle may be determined. In addition, the battery controller may estimate battery degradation from a map that defines battery charge capacity retention percentage (e.g., a measure of battery degradation) as a function of battery usage and a total number of days a vehicle is driven as shown inFIG. 5and described further below. The battery controller may display the battery degradation value to vehicle occupants via transferring or transmitting the battery degradation value to another controller in the vehicle to display on a human/machine interface. In still other examples, the battery degradation value may be transmitted off-board the vehicle to a remote server so that vehicle service may be scheduled. Method300proceeds to exit.

At412, method400notifies the vehicle user (e.g., a human) that the battery usage exceeds a threshold value. The notification may be via displaying a message on a human/machine interface. In addition, method400may automatically schedule the vehicle for service of the battery via sending a vehicle service request to remote infrastructure. Method400proceeds to414.

At414, method300makes the battery usage value available for battery degradation metrics, display to vehicle occupants, vehicle service scheduling, and infrastructure as described at413. Method400proceeds to416.

At416, method400judges whether or not the battery usage level or amount is greater than a second threshold. If so, the answer is yes and method400proceeds to418. Otherwise, the answer is no and method400exits.

At418, method400optionally adjusts vehicle operation. In one example, method400may adjust a relationship between propulsive pedal position and requested wheel torque such that greater application of the propulsive pedal may be required to generate middle level driver demand torques. In this way, the responsiveness of the electric machines may be reduced so that current may be drawn from the battery at a lower rate, thereby extending the life of the battery. Of course, full driver demand torque may be made available at the greatest application position of the propulsive effort pedal.

In another example, method400may reduce a rate of charging or electric current that may be accepted by the battery to extend battery life. In still other examples, selected vehicle modes may not be permitted or other modes that are not normally available may be made available. For example, only two wheel drive mode may be made available to further conserve battery charge capacity and to extend battery life. Method400proceeds to exit.

In this way, battery usage may be determined in a more sophisticated way that may be more accurate than the method ofFIG. 3. The battery usage metric may be the basis for indicating battery state to vehicle occupants and to schedule vehicle service.

Thus, the methods ofFIGS. 3 and 4may provide a method for a battery, comprising: generating a battery usage estimate based on a distance per gallon of gasoline-equivalent, battery current, and battery voltage via a controller; and transferring the battery usage estimate from the controller to a device external to the controller. The method includes where the device is a display or user interface. The method includes where the device is a second controller. The method further comprises transferring the battery usage estimate to the second controller via a controller area network. The method includes where the battery current is multiplied by the voltage. The method includes where the battery current is a battery discharge current. The method includes where the battery current is a battery charging current. The method includes where the gallon of gasoline-equivalent is 33.7 kilowatt-hours of electric power.

The methods ofFIGS. 3 and 4also provide for a method for a battery, comprising: generating a battery usage estimate based on a distance per gallon of gasoline-equivalent, battery current, and battery voltage via a controller; generating a battery capacity retention value from the battery usage estimate and an actual total number of days of vehicle usage; and transferring the battery capacity retention value or a battery state of health value from the controller to a device external to the controller. The method includes where the battery state of health value is determined via the battery capacity retention value. The method includes where the battery capacity retention value is a function of an actual total distance a vehicle is driven. The method includes where the battery capacity retention value is a function of an actual total number of days a vehicle is driven. The method includes where the distance per gallon of gasoline-equivalent is based on 33.7 kilowatt-hours of electric power.

Referring now toFIG. 5, an example map for estimating degradation of a battery is shown. Map500includes eight rows as indicated and three columns as indicated. The first row represents an actual total number of days that the electric vehicle is operated to travel. The second row represents the battery usage, E-mileage in this example. The third column represents the battery's charge retention capacity relative to the battery's charge retention capacity when the battery is new.

The map may be referenced via the actual total number of days that the electric vehicle is operated or via the battery usage. For example, if the actual total number of days the vehicle is used is 500, the charge retention is expected to be 83%. If the battery usage is 35,548, then the charge capacity is expected to be 76%. The capacity retention may be determined via the following equation:
Charge_cap=min(f(miles),g(days))
where Charge capacity is the battery charge capacity, min is a function that returns the lesser value of argument f(miles) and g(days), f is a function that returns a traction battery charge capacity as a function of E-mileage, g is a function that returns a traction battery charge capacity as a function of an actual total number of days the vehicle is used. The functions f and g may access a map that is similar to map500. The battery's state of health may be determined via comparing the battery's present charge capacity to a worst case battery charge capacity.