Method and battery management system for operating a traction battery in a motor vehicle and motor vehicle having such a battery management system

Abstract

A method for operating a traction battery in a motor vehicle, wherein the traction battery is charged in a charging operating state with a fast-charging device. A quantity of energy to be recharged at the fast-charging device is specified. An anticipated heating of the traction battery is determined depending on a charging capacity, which, taking into consideration a predeterminable maximum charging time, is determined from the quantity of energy that is to be recharged. A starting temperature (T.sub.start) for the battery charging is determined in such a way that, after the charging operation has been carried out at the fast-charging device, a battery operating temperature (T.sub.batt) of the traction battery does not exceed an upper limit (T.sub.hi) for the battery operating temperature. The battery operating temperature (T.sub.batt) is recorded during a driving operating state of the motor vehicle.

Claims

1. A method for operating a traction battery in a motor vehicle, wherein the traction battery is charged in a charging operating state with a fast-charging device, comprising: specifying at the fast-charging device a quantity of energy that is to be recharged, determining a heating of the traction battery depending on a charging capacity, which, taking into consideration a predeterminable maximum charging time, is determined from the quantity of energy that is to be recharged, determining a starting temperature (T.sub.start) for the battery charging in such a way that, after the charging operation has been carried out at the fast-charging device, a battery operating temperature (T.sub.batt) of the traction battery does not exceed an upper limit (T.sub.hi) for the battery operating temperature, comparing the starting temperature (T.sub.start) for the battery charging to a lower limit (T.sub.lo) of the battery operating temperature, limiting the starting temperature (T.sub.start) for the battery charging to the lower limit (T.sub.lo) of the battery operating temperature when the comparison reveals a lower starting temperature (T.sub.start) for the battery charging than the lower limit (T.sub.lo) of the battery operating temperature, and recording the battery operating temperature (T.sub.batt) in a driving operating state of the motor vehicle, and in the case that the recorded battery operating temperature (T.sub.batt) is higher than the starting temperature (T.sub.start) for the battery charging: lowering the battery operating temperature (T.sub.batt) to the starting temperature (T.sub.start) for the battery charging during the driving operating state.

2. The method according to claim 1, further comprising: determining an excess cooling capacity availability in the driving operating state, determining a quantity of thermal energy that is to be dissipated from the traction battery depending on the recorded battery operating temperature (T.sub.batt) and the starting temperature (T.sub.start) for the battery charging as well as determining a required temperature lowering time, depending on the excess cooling capacity available and depending on the quantity of thermal energy that is to dissipated, determining an anticipated arrival time (t.sub.3) at the fast-charging device depending on a residual driving range remaining up to the fast-charging device, starting the lowering of the battery operating temperature (T.sub.batt) at the latest at a point in time (t.sub.2) that is determined from the anticipated arrival time minus the required temperature lowering time.

3. The method according to claim 1, further comprising: determining the quantity of energy that is to be recharged depending on a destination input into a navigation device of the motor vehicle.

4. The method according to claim 1, further comprising: determining a position of the fast-charging device, depending on a position of the motor vehicle and depending on an available remaining travel range of the motor vehicle.

5. The method according to claim 1, further comprising: specifying the quantity of energy that is to be recharged as a difference between the maximum quantity of energy that can be stored in a fully charged state of the traction battery and an anticipated residual quantity of energy remaining in the traction battery when the fast-charging device has been reached.

6. A battery management system for operating a traction battery in a motor vehicle, comprising: a control unit, configured to control the charging of the traction battery with a fast-charging device in a charging operating state, a state of charge regulator, configured to predetermine a quantity of energy to be recharged at the fast-charging device, a simulation computing unit configured to determine a heating of the traction battery that is to be anticipated depending on a charging capacity, which, taking into consideration a predeterminable maximum charging time, can be determined from the quantity of energy that is to be recharged, wherein the simulation computing unit is also configured to determine a starting temperature (T.sub.Start) for the battery charging in such a way that, after the charging operation has been carried out at the fast-charging device, a battery operating temperature (T.sub.batt) of the traction battery does not exceed an upper limit (T.sub.hi) for the battery operating temperature, a temperature sensor is configured to record the battery operating temperature (T.sub.batt) in a driving operating state of the motor vehicle, a battery cooling apparatus, configured to lower the battery operating temperature (T.sub.batt) to the starting temperature (T.sub.start) for the battery charging during the driving operating state in the case that the recorded battery operating temperature (T.sub.batt) is higher than the starting temperature (T.sub.start) for the battery charging; wherein the starting temperature (T.sub.start) for the battery charging is compared to a lower limit (T.sub.lo) of the battery operating temperature, and the starting temperature (T .sub.start) for the battery charging is limited to the lower limit (T.sub.lo) of the battery operating temperature when the comparison reveals a lower starting temperature (T.sub.start) for the battery charging than the lower limit (T.sub.lo) of the battery operating temperature.

7. A motor vehicle having a battery management system for operating a traction battery in the motor vehicle, comprising: a control unit, configured to control the charging of the traction battery with a fast-charging device in a charging operating state, a state of charge regulator, configured to predetermine a quantity of energy to be recharged at the fast-charging device, a simulation computing unit configured to determine a heating of the traction battery that is to be anticipated depending on a charging capacity, which, taking into consideration a predeterminable maximum charging time, can be determined from the quantity of energy that is to be recharged, wherein the simulation computing unit is also configured to determine a starting temperature (7.sub.Start) for the battery charging in such a way that, after the charging operation has been carried out at the fast-charging device, a battery operating temperature (T.sub.batt) of the traction battery does not exceed an upper limit (T.sub.hi) for the battery operating temperature, a temperature sensor is configured to record the battery operating temperature (T.sub.batt) in a driving operating state of the motor vehicle, a battery cooling apparatus, configured to lower the battery operating temperature (T.sub.batt) to the starting temperature (T.sub.start) for the battery charging during the driving operating state in the case that the recorded battery operating temperature (T.sub.batt) is higher than the starting temperature (T .sub.start) for the battery charging; wherein the starting temperature (T .sub.start) for the battery charging is compared to a lower limit(T.sub.lo) of the battery operating temperature, and the starting temperature (T.sub.start) for the battery charging is limited to the lower limit (T.sub.lo) of the battery operating temperature when the comparison reveals a lower starting temperature (T.sub.start) for the battery charging than the lower limit (T.sub.lo) of the battery operating temperature.

8. The method according to claim 4, further comprising: displaying the fast-charging device whose position has been determined to lie within the remaining travel range of the motor vehicle, to a user of the motor vehicle, confirming the intended use of the displayed fast-charging device by the user, starting the lowering of the battery operating temperature (T.sub.batt) to the starting temperature (T.sub.start) for the battery charging by a battery management system.

9. The method according to claim 1, further comprising one or more of: retrieving data on a state of the fast-charging device via a mobile network; and reserving a charging time window at the fast-charging device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are described below, Shown for this purpose are:

(2) FIG. 1 in simplified schematic illustration, a preferred embodiment of a method according to the invention;

(3) FIG. 2 in simplified schematic illustration, an exemplary course of a battery operating temperature in the application of the method according to the invention; and

(4) FIG. 3 in simplified schematic illustration, a preferred embodiment of a battery management system according to the invention.

DETAILED DESCRIPTION

(5) For the exemplary embodiments explained below, what is involved are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be regarded as being independent of one another, each of which the invention further develops independently of one another, and, accordingly, which are to be regarded, also individually or in a combination different from that shown, as belonging to the invention. Furthermore, the described embodiments can also be supplemented by additional ones of the already described features of the invention.

(6) In the figures, functionally equivalent elements are each furnished with the same reference numbers.

(7) In a preferred embodiment of the invention, a method 10 begins, as illustrated in FIG. 1, with a start 11. For better overview, reference numbers that are included only in FIG. 2 or FIG. 3 are introduced at this point. In a step 12, a destination is input by the user of the motor vehicle. The input of the destination here is made preferably by use of a navigation device 40 belonging to the vehicle.

(8) In a further step 13, the determination of the position of a fast-charging device 39 is made depending on the position of the motor vehicle and depending on an available remaining travel range of the motor vehicle. The determination of the position of the fast-charging device can be made by use of the navigation device 40 belonging to the vehicle; in addition, further data, such as, for example, data obtained using a mobile Internet connection, can be analyzed.

(9) In a further step 14, the quantity of energy to be recharged is determined depending on the destination specified in the navigation device of the motor vehicle and depending on further data. Included are, in particular, also the position of the destination as well as the position of the motor vehicle at the present time, which can be utilized as a basis for estimating a residual quantity of energy in the traction battery 33 when the motor vehicle reaches the fast-charging device 39.

(10) In a further step 15, the quantity of energy to be recharged at the fast-charging device 39 is specified as a basis for further calculations.

(11) In a further step 16, a heating of the traction battery 33 that is to be anticipated depending on charging capacity is determined, said charging capacity being determined from the quantity of energy that is to be recharged taking into consideration a predeterminable maximum charging time.

(12) In a further step 17, a determination of a starting temperature T.sub.start for the battery charging follows in such a way that, after the charging operation has been carried out at the fast-charging device 39, a battery operating temperature T.sub.batt of the traction battery 33 does not exceed an upper limit T.sub.hi for the battery operating temperature.

(13) In a further step 18, the fast-charging device 39 whose position has been determined to lie within the remaining travel range of the motor vehicle is displayed to a user of the motor vehicle.

(14) In a further step 19, the user then has the possibility of confirming an intended use of the displayed fast-charging device 39. When the user does not wish to actuate the displayed fast-charging device 39, it is possible to go back to the method step 13 and to determine another fast-charging device 39. Branchings after a branch point, at which a check for a condition reveals that the condition is not met, are indicated by N in the flowchart in accordance with FIG. 1.

(15) When, in step 19, the user provides a confirmation, the lowering of the battery operating temperature T.sub.batt to the starting temperature T.sub.start for the battery charging is started by a battery management system 32 in the following step 20. In the scope of the display of the fast-charging station in step 18, it is also possible in a parallel step 18a to retrieve further data on the state of the fast-charging device 39. For this purpose, it is possible especially advantageously to use a mobile network, such as, for example, an Internet access provided via the mobile wireless network. Accordingly, in step 19, the confirmation by the user of the motor vehicle can be supplemented by another parallel step 19a in that a charging time window at the fast-charging device 39 is reserved.

(16) In a further step 21, the starting temperature T.sub.start for the battery charging is then compared with a lower limit T.sub.lo of the battery operating temperature, wherein, in a further step 22, the starting temperature T.sub.start for the battery charging is limited to the lower limit T.sub.lo of the battery operating temperature when the comparison reveals a lower starting temperature T.sub.start for the battery charging than the lower limit T.sub.lo battery operating temperature.

(17) In a further step 23, the actual temperature of the traction battery 33 is recorded in the form of the battery operating temperature T.sub.batt in a driving operating state 29 of the motor vehicle and, in a following step 24, it is checked whether the recorded battery operating temperature T.sub.batt is higher than the starting temperature T.sub.start for the battery charging. If this is the case, then, in a following step 25, the battery operating temperature T.sub.batt is lowered in the driving operating state 29 to the starting temperature T.sub.start for the battery charging.

(18) When, in a following step 26, the fast-charging device 39 is reached, the motor vehicle can be connected to it. Accordingly, the driving operating state 29 is ended (end 27) and a charging operating state 31 is initiated. In this charging operating state 31, as can be seen from the following statements, a fast charging of the traction battery 33 occurs with maximum available cooling capacity, with the battery operating temperature T.sub.batt rapidly rising during the fast-charging period.

(19) Illustrated in FIG. 2 for an explanation of the method is a graph 28, in which the temperature T is plotted over the time t and a plotted curve for the battery operating temperature T.sub.batt is illustrated by way of example. Between a first point in time t.sub.1 and a second point in time t.sub.2, a normal driving operation takes place in the driving operating state 29. Here, depending on the power requirements placed on the traction battery 33 and on the parameterization of the coolant circulating circuit (battery cooling apparatus 38) in the driving operation, a temperature curve that is freely variable in a certain range is established. At the second point in time t.sub.2, it is decided that it is necessary to drive toward the next fast-charging device 39 and a corresponding charging capacity is determined with which recharging should occur at the fast-charging device 39.

(20) Starting from the second point in time t.sub.2, the battery operating temperature T.sub.batt is then continuously lowered to the value of the starting temperature T.sub.start for the battery charging, which is reached at a third point in time t.sub.3. Here, ideally at the same time, the arrival at the fast-charging device 39 and the beginning of the fast charging should occur. The time between the second point in time t.sub.2 and the third point in time t.sub.3, which is referred to as a preparation phase 30, thus serves for specific preparation of the traction battery 33 for the planned fast-charging operation with the maximum cooling capacity available in the motor vehicle. The preparation phase 30 in this case still belongs to the driving operating state 29 and, in the illustration in accordance with FIG. 2, ends at the same time as the point in time t.sub.3, at which the charging operating state 31 follows seamlessly.

(21) An initial temperature T.sub.0 is here the value of the battery operating temperature T.sub.batt at the second point in time t.sub.2. In particular, it can also be provided that the upper limit T.sub.hi of the battery operating temperature and the initial temperature T.sub.0 are chosen to be identical in value.

(22) The fast charging at the fast-charging device 39 is ended at a fourth point in time t.sub.4. At the end of the fast-charging operation, the value of the battery operating temperature T.sub.batt is specified, as predetermined, as being the very value that is specified as a parameter for the upper limit T.sub.hi of the battery operating temperature.

(23) For further explanation, several parameters with their typical values are included below. A targeted charging capacity for the fast-charging operation is 350 kilowatts. The maximum attained value of the battery operating temperature T.sub.batt after the fast charging should not lie higher than 40 degrees Celsius, because, immediately after the fast-charging operation, further driving should also still be possible with appropriate driving performance. Accordingly, for an expeditious further driving, the upper limit T.sub.hi of the battery operating temperature should ideally be 40 degrees Celsius. A typical degree of efficiency of a high-voltage battery using the currently available lithium ion technology is about 95 percent for fast charging. Accordingly, 5 percent of the supplied energy within the high-voltage battery is converted to lost heat. Typically, a lithium ion battery employed for a motor vehicle usually has a weight of about 650 kilograms. This value relates to an electric vehicle in the form of a passenger motor vehicle. The specific heat capacity of such a high-voltage battery (traction battery 33) is, on average over its various components, 1200 Joules per kilogram and Kelvin. As a maximum charging time for supplying 80 percent of the battery capacity, usually 15 minutes is assumed. As maximum available cooling capacity via a coolant circulation circuit (battery cooling apparatus 38) in the motor vehicle, 6 to 8 kilowatts is estimated.

(24) Accordingly, the method according to the invention can be illustrated on the basis of the following calculation by way of example. For fast charging with 350 kilowatts, the thermal dissipation power loss of the traction battery 33 is:
P.sub.loss=350 kilowatts×(1−95%)=17.5 kilowatts.

(25) The thermal capacity to be taken up by the thermal mass of the traction battery 33 in the case when, during fast charging, the battery is heated within 15 minutes from 25 degrees Celsius to a final temperature of 40 degrees Celsius is:

(26) $P_{\mathrm{therm}}=\frac{650\mathrm{kilograms}\times 1200\mathrm{Joules}}{\mathrm{kilogram}\mathrm{and}\mathrm{Kelvin}}\times \frac{40\mathrm{degrees}\mathrm{Celsius}-25\mathrm{degrees}\mathrm{Celsius})}{15\mathrm{minutes}\times 60\mathrm{seconds}\mathrm{per}\mathrm{minute}}=13\mathrm{kilowatts}$

(27) For this purpose, another 4.5 kilowatts are needed from the coolant circulation circuit of the vehicle during the fast charging, which lies within the maximum available cooling capacity (6-8 kilowatts).

(28) The charged quantity of energy within the 15-minute charging time with a charging capacity of 350 kilowatts is:

(29) $E_{\mathrm{charged}}=\frac{350\mathrm{kilowatts}\times 15\mathrm{minutes}}{60\mathrm{minutes}\mathrm{per}\mathrm{hour}}=87.5\mathrm{kilowatt}\mathrm{hours}$

(30) This quantity of energy is sufficient to drive further for about 350 kilometers. A time of 15 minutes for the charging operation is needed here only because the battery was nearly empty prior to the fast charging. When the traction battery 33 is driven only until half empty, it is necessary with the fast-charging operation to recharge only a quantity of energy of about 44 kilowatt hours, as a result of which the following charging time is obtained:

(31) $T_{\mathrm{charging}\mathrm{time}}=\frac{44\mathrm{kilowatt}\mathrm{hours}}{350\mathrm{kilowatts}}\times 60\mathrm{minutes}\mathrm{per}\mathrm{hour}=7.5\mathrm{minutes}.$

(32) The battery needs to be cooled only to 30 degrees Celsius during the driving operating state 29 in order not to exceed the targeted final temperature of 40 degrees Celsius after the fast charging.

(33) $T_0=40\mathrm{degrees}\mathrm{Celsius}-\frac{17.5\mathrm{kilowatts}\times 7.5\mathrm{minutes}\times 60\mathrm{seconds}}{650\mathrm{kilograms}\times \frac{1200\mathrm{Joules}}{\mathrm{kilogram}\mathrm{and}\mathrm{Kelvin}}}=30\mathrm{degrees}\mathrm{Celsius}$

(34) For these initial conditions, no additional cooling capacity is required by the coolant circulation circuit during the fast charging. Accordingly, the air conditioning system can remained switched off, which is comfortable and energy-saving.

(35) Accordingly, for example, by use of a traction battery 33 for an electric vehicle with a weight of 650 kilograms, which corresponds to an average value obtained for current battery technology and travel range, and by starting from a battery operating temperature T.sub.batt that, at the beginning of charging, lies at 25 degrees Celsius and thus lies at the value chosen for the starting temperature T.sub.start for the battery charging, it is possible for a constant thermal dissipation power loss of 13 kilowatts to be taken up by the thermal mass of the high-voltage battery within 15 minutes. Accordingly, after a 15-minute charging operation, the battery operating temperature T.sub.batt settles at 40 degrees Celsius, which poses no problem for further driving. In addition, it is possible, using the cooling capacity of 6 to 8 kilowatts from the air conditioning system of the vehicle, to cover the entire thermal dissipation power loss of 17.5 kilowatts during fast charging without any problem.

(36) For a meaningful determination of the point in time starting from when the high-voltage battery needs to be cooled down specifically into the relatively low temperature range, it is appropriate to hook up the motor vehicle to the charging infrastructure via a network. Accordingly, the vehicle can use a corresponding operating strategy to obtain the necessary data as to when the battery will be depleted and as to when and in which charging station it can be recharged by means of fast charging, and also what time needs to be expended to be able to cool the traction battery 33 to the targeted temperature range with the use of the instantaneously available cooling capacity. This network connection with the charging infrastructure can be realized very simply through means that are already available at the present time.

(37) A preferred exemplary embodiment of a battery management system 32 according to the invention is illustrated in FIG. 3. The battery management system 32 in this case comprises a control unit 34, a state of charge regulator 35, a simulation computing unit 36, a temperature sensor 37, and a battery cooling apparatus 38.

(38) The battery cooling apparatus 38 is thermally coupled to a traction battery 33 in order to be able to lower the battery operating temperature T.sub.batt in the driving operating state 29 to the starting temperature T.sub.start for the battery charging. The temperature sensor 37 serves for recording the battery operating temperature T.sub.batt during a driving operating state 29 of the motor vehicle. The state of charge regulator 35 is coupled to a navigation device 40, via which it obtains data regarding the planned driving route as well as data that is further relevant to the driving itinerary, such as, for example, the distribution of charging devices. The control unit 34 serves for controlling the charging of the traction battery 33 with a fast-charging device 39 during the charging operating state 31, taking into consideration the quantity of energy that is to be recharged, as predetermined by the state of charge regulator 35. The simulation computing unit 36 serves for determining an anticipated heating of the traction battery 33 depending on charging capacity, which, taking into consideration a predeterminable maximum charging time, can be determined from the quantity of energy that is to be recharged. The starting temperature T.sub.start for the battery charging can be made available, as a target value, to the battery cooling apparatus 38 by the simulation computing unit 36, where it can be compared with the actual value in the form of the battery operating temperature T.sub.batt, which is indicated by the temperature sensor 37, and, in the case in which the actual value exceeds the target value, the battery temperature can be lowered.

(39) Overall, the examples show how the invention enables a concept for controlling the temperature of high-voltage batteries in electric vehicles during a fast charging to be realized at a smaller additional cost in comparison to a standard charging operation. Accordingly, it is possible to develop an optimized operating strategy for electric vehicles, for which, just prior to the fast charging, the high-voltage battery is cooled to and kept in a relatively low temperature range—for example, about 20 to 25 degrees Celsius—during the drive by using available cooling capacity through the air conditioning system of the vehicle.