Method for operating a motor vehicle, control unit for a drive system, and drive system

Abstract

A method for operating a hybrid drive system for a motor vehicle having an internal combustion engine and an electrical drive, which is supplied by an electrical energy store, the required powers of the internal combustion engine and/or of the electrical drive being set in accordance with a specified load distribution, including: regulating the load distribution between the electrical drive and the internal combustion engine based on a current setpoint state of charge of the electrical energy store; and determining the current setpoint state of charge from a specified linear setpoint state of charge curve between a current position of the motor vehicle and a destination.

Claims

1. A method for operating a hybrid drive system for a motor vehicle having an internal combustion engine and an electrical drive, the method comprising: regulating a load distribution between the electrical drive, which is supplied by an electrical energy store, and the internal combustion engine based on a current setpoint state of charge of the electrical energy store, wherein required power of the internal combustion engine and/or of the electrical drive is set in accordance with a specified load distribution; determining the current setpoint state of charge from a specified setpoint state of charge curve between a current position of the motor vehicle and a destination; ascertaining information about a current state of the motor vehicle, and updating the specified setpoint state of charge curve as a function of the ascertained information; wherein the specified setpoint state of charge curve is a linear setpoint state of charge curve, and wherein the linear setpoint state of charge curve is determined over a distance between the current position of the motor vehicle and the destination by calculating a linear curve of the setpoint state of charge with respect to the distance between the current position of the motor vehicle and the destination as a function of a state of charge at the current position of the motor vehicle and a specified discharge threshold value, which indicates a maximum admissible discharge; and wherein the updating of the specified setpoint state of change curve provides an updated linear setpoint state of change curve over a remaining distance to the destination of the motor vehicle, and wherein the method further comprises: after the updating, determining a new current setpoint state of charge from the updated linear setpoint state of charge curve based on a new current position of the vehicle; and further regulating the load distribution between the electrical drive and the internal combustion engine based on the new current setpoint state of change.

2. The method of claim 1, further comprising: ascertaining an energy differential of the motor vehicle between the current position of the motor vehicle and the destination from the ascertained information, calculating a correction value for a current setpoint state of charge based on the ascertained energy differential; and applying the correction value on the current setpoint state of charge.

3. The method of claim 2, further comprising: ascertaining a current driving speed and/or a current elevation coordinate of the vehicle and/or an absolute elevation at the destination, and ascertaining the energy differential from a kinetic energy of the vehicle and/or a potential energy of the vehicle with respect to the destination.

4. The method of claim 2, further comprising: calculating an expected recuperation energy based on an ascertained positive energy differential of the motor vehicle with respect to the destination, the expected recuperation power being converted into a reduction of a current setpoint state of charge, and/or calculating an additional energy requirement of the motor vehicle based on an ascertained negative energy differential of the motor vehicle with respect to the destination, the calculated additional energy requirement being converted into an increase of a current setpoint state of charge.

5. The method of claim 1, wherein an equivalent consumption minimization strategy (ECMS) process based on a current setpoint state of charge is used to regulate the state of charge.

6. The method of claim 1, wherein the method is repeated cyclically.

7. A control unit for operating a hybrid drive system for a motor vehicle having an internal combustion engine and an electrical drive, comprising: a control device configured to perform the following: regulating the load distribution between the electrical drive, which is supplied by an electrical energy store, and the internal combustion engine based on a current setpoint state of charge of the electrical energy store, wherein required powers of the internal combustion engine and/or of the electrical drive are set in accordance with a specified load distribution; determining the current setpoint state of charge from a specified setpoint state of charge curve between a current position of the motor vehicle and a destination; ascertaining information about a current state of the motor vehicle, and updating the specified setpoint state of charge curve as a function of the ascertained information; wherein the specified setpoint state of charge curve is a linear setpoint state of charge curve, and wherein the linear setpoint state of charge curve is determined over a distance between the current position of the motor vehicle and the destination by calculating a linear curve of the setpoint state of charge with respect to the distance between the current position of the motor vehicle and the destination as a function of a state of charge at the current position of the motor vehicle and a specified discharge threshold value, which indicates a maximum admissible discharge; and wherein the updating of the specified setpoint state of change curve provides an updated linear setpoint state of change curve over a remaining distance to the destination of the motor vehicle, and wherein the control device is further configured to perform the following: after the updating, determining a new current setpoint state of charge from the updated linear setpoint state of charge curve based on a new current position of the vehicle; and further regulating the load distribution between the electrical drive and the internal combustion engine based on the new current setpoint state of change.

8. A non-transitory computer readable medium having a computer program, which is executable by a processor, comprising: a program code arrangement having program code for operating a hybrid drive system for a motor vehicle having an internal combustion engine and an electrical drive, by performing the following: regulating a load distribution between the electrical drive, which is supplied by an electrical energy store, and the internal combustion engine based on a current setpoint state of charge of the electrical energy store, wherein required power of the internal combustion engine and/or of the electrical drive is set in accordance with a specified load distribution; and determining the current setpoint state of charge from a specified setpoint state of charge curve between a current position of the motor vehicle and a destination; ascertaining information about a current state of the motor vehicle, and updating the specified setpoint state of charge curve as a function of the ascertained information; wherein the specified setpoint state of charge curve is a linear setpoint state of charge curve, and wherein the linear setpoint state of charge curve is determined over a distance between the current position of the motor vehicle and the destination by calculating a linear curve of the setpoint state of charge with respect to the distance between the current position of the motor vehicle and the destination as a function of a state of charge at the current position of the motor vehicle and a specified discharge threshold value, which indicates a maximum admissible discharge; and wherein the updating of the specified setpoint state of change curve provides an updated linear setpoint state of change curve over a remaining distance to the destination of the motor vehicle, and wherein the program code arrangement further performs the following: after the updating, determining a new current setpoint state of charge from the updated linear setpoint state of charge curve based on a new current position of the vehicle; and further regulating the load distribution between the electrical drive and the internal combustion engine based on the new current setpoint state of change.

9. The method as recited in claim 1, wherein the information about the current state of the motor vehicle includes a current driving speed of the motor vehicle, and a current absolute elevation at which the motor vehicle is located.

10. The method as recited in claim 1, wherein the ascertaining, the updating, the determining of the new current setpoint state of charge, and the further regulating, are performed repeatedly during travel of the motor vehicle from the current positon of the motor vehicle to the destination of the motor vehicle.

11. The method as recited in claim 1, wherein the linear setpoint state of charge curve linearly decreases over the entire distance from the current positon of the motor vehicle to the destination of the motor vehicle.

12. The method as recited in claim 11, wherein the hybrid drive system is operated in a blended mode over the entire distance from the current position of the motor vehicle to the destination of the motor vehicle, the blended mode being a mode in which the required power is provided partially by the internal combustion engine and partially by the electric drive.

13. A drive system, comprising: an internal combustion engine; an electrical drive, which is supplied by an electrical energy store; and a control unit for operating a hybrid drive system for a motor vehicle having an internal combustion engine and an electrical drive, including: a control device configured to perform the following: regulating the load distribution between the electrical drive, which is supplied by an electrical energy store, and the internal combustion engine based on a current setpoint state of charge of the electrical energy store, wherein required powers of the internal combustion engine and/or of the electrical drive are set in accordance with a specified load distribution; determining the current setpoint state of charge from a specified setpoint state of charge curve between a current position of the motor vehicle and a destination; ascertaining information about a current state of the motor vehicle, and updating the specified setpoint state of charge curve as a function of the ascertained information; wherein: the specified setpoint state of charge curve is a linear setpoint state of charge curve, and wherein the linear setpoint state of charge curve is determined over a distance between the current position of the motor vehicle and the destination by calculating a linear curve of the setpoint state of charge with respect to the distance between the current position of the motor vehicle and the destination as a function of a state of charge at the current position of the motor vehicle and a specified discharge threshold value, which indicates a maximum admissible discharge; the updating of the specified setpoint state of change curve provides an updated linear setpoint state of change curve over a remaining distance to the destination of the motor vehicle, and the control unit is further configured to perform: after the updating, determining a new current setpoint state of charge from the updated linear setpoint state of charge curve based on a new current position of the vehicle; and further regulating the load distribution between the electrical drive and the internal combustion engine based on the new current setpoint state of change.

14. The drive system as recited in claim 13, wherein the information about the current state of the motor vehicle includes a current driving speed of the motor vehicle, and a current absolute elevation at which the motor vehicle is located.

15. The drive system is recited in claim 13, wherein the ascertaining, the updating, the determining of the new current setpoint state of charge, and the further regulating, are performed repeatedly during travel of the motor vehicle from the current position of the motor vehicle to the destination of the motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a block diagram of a drive system for a plug-in hybrid electric vehicle (PHEV).

(2) FIG. 2 shows a diagram of a curve of a state of charge (SoC) of a battery of a drive system that is operated in a charge-depletion/charge-sustaining mode.

(3) FIG. 3 shows a diagram of a curve of an SoC of a battery of a drive system that is operated in a mixed mode (blended mode).

(4) FIG. 4 shows a flow chart of a method for operating a drive system.

(5) FIG. 5 shows a diagram of a curve of an SoC of a battery of a drive system that is operated in a blended mode.

(6) FIG. 6 shows a flow chart of a method for operating a drive system.

DETAILED DESCRIPTION

(7) FIG. 1 shows a block diagram of a hybrid drive system 1 of a motor vehicle, in particular of a plug-in hybrid electric vehicle (PHEV). Drive system 1 has an electric drive 2 and an internal combustion engine 3, which provide required power onto drive axle 5 of drive system 1 via drive shaft 4. Alternatively, it is also conceivable that drive system 1 has multiple electric drives 2 for driving multiple drive axles 5. Furthermore, it is also possible for drive system 1 to be equipped with a four-wheel drive.

(8) A first clutch 6 for opening and closing the drive train is situated between internal combustion engine 3 and electric drive 2. A first clutch 7 for opening and closing the drive train is situated between internal combustion engine 2 and electric drive 15. Electric drive 2 is supplied by an electrical energy store in the form of a battery 8, which is connected to electric drive 2 via a power electronics 9. The battery 8 may be a traction battery or a high-voltage battery for supplying electric drive 2 of drive system 1. Battery 8 is furthermore equipped with a charging terminal 10, to which an external current source 11 may be connected in order to charge battery 8.

(9) Power electronics 9 is connected to the engine control or control unit 12 of drive system 1. Control unit 12 controls internal combustion engine 3 and electric drive 2 for providing partial drive torques. Control unit 12 furthermore has a prediction module 13, which is able to calculate a setpoint state of charge curve (SoC). The setpoint state of charge curve corresponds to a desired or specified curve of a state of charge of battery 8. Prediction module 13 or control unit 12 is connected to sensor unit 14 for ascertaining vehicle information or surroundings information.

(10) Drive system 1 may be operated in different operating modes, in which respectively different portions of the total drive power are provided by electric drive 2 and by internal combustion engine 3 and the state of charge (SoC) of battery 8 is regulated in accordance with a specified strategy. The state of charge may be regulated by adapting an equivalence factor of a control strategy such as the ECMS (equivalent consumption minimization strategy).

(11) FIG. 2 shows a state of charge curve according to a charge-depleting/charge-sustaining (CD/CS) strategy. For this purpose, the aim is to achieve the curve of the state of charge of battery 8 shown in FIG. 2 over the distance x traveled. Drive system 1 begins the drive with a charged battery 8, the vehicle driving purely electrically for as long as possible or the entire required power being provided by electric drive 2. This phase corresponds to the charge-depleting mode (CD mode). Only when a specified lower SoC threshold of the state of charge is reached is internal combustion engine 3 activated and the state of charge of battery 8 is regulated by discharge and charge cycles (using electrical energy generated in the motor vehicle) about the lower SoC threshold. Such a drive system is able to regulate the state of charge of battery 8 to a low level over the entire remaining time span. This makes it possible to implement the CD/CS strategy shown.

(12) FIG. 3 shows a state of charge curve according to a strategy of a so-called blended mode over the distance x traveled. Drive system 1 is operated here in a blended mode, the required power during the entire operating time being provided partially by internal combustion engine 3 and partially by an electric drive 2 supplied from battery 8.

(13) Compared to the CD/CS strategy from FIG. 2, it is possible to achieve an improvement of the CO.sub.2 efficiency since the load distribution in the CD/CS strategy in real travel usually does not correspond to the optimal torque distribution of hybrid drive system 1. The blended-mode strategy approximates this optimal torque distribution much more closely.

(14) FIG. 4 shows a flow chart to illustrate a further method for operating a drive system:

(15) In step S1, the drive system is provided at the beginning of a drive with a completely charged battery 8.

(16) The method described below strives to discharge the battery as much as possible until the next charging opportunity is reached. In the process, battery 8 is discharged down to a specified discharge threshold value.

(17) In step S2, current information about the current state of the drive system 1 or the motor vehicle is ascertained and transmitted to prediction module 13.

(18) First, this information concerns the starting location as the current position of the motor vehicle and the location of the next possible charging opportunity as the destination, the length of the route between the starting location and the destination being determined in the process. Furthermore, the absolute elevation, especially the elevation above sea level, of the destination is determined and communicated to the prediction module 13. The necessary data may be provided for example by a navigation device used in the drive system 1, which is connected to the control unit of drive system 1.

(19) According to the specific embodiment shown here, the navigation device detects or knows the probably next charging location of the vehicle and passes this on to prediction module 13 as the destination and/or the resulting remaining travel distance. Otherwise, the remaining travel distance is calculated to the destination entered into the navigation device. Prediction module 13 is also able to take into account in the calculation the return drive to the starting location. This is expedient, for example, when the driver has no charging opportunity at the destination of the drive, but charges the motor vehicle at the starting location.

(20) In step S3, a linear setpoint curve of the state of charge is determined from predictive information, the linear curve between the starting location or the current position of motor vehicle 1 and the destination, i.e. the location of the charging opportunity, being calculated, a state of charge of a maximum (maximally admissible) discharge being specified for the destination, which may correspond e.g. to a discharge threshold value. In other words, the linear curve results from a setpoint state of charge that decreases in a linear manner over the distance to the destination.

(21) The determined curve falls off in step S3 from a starting value, i.e. from the current state of charge down to a desired final state of charge or the specified discharge threshold value for the state of charge in a linear manner or in another manner that is simple to calculate. If the driver wishes to reach at the end of the drive a specific value for the state of charge of battery 8, it is possible for the prediction module 13 to set the setpoint state of charge in a linear manner to the desired target value and thus to apply an operating strategy that is lower in emissions and more comfortable or uniform than what is possible using strategies that change the setpoint state of charge immediately to the desired target value of the state of charge at the destination.

(22) The linear curve of the setpoint state of charge may be calculated over the remaining distance to be traveled. The linearity of the setpoint state of charge over the travel distance may be chosen because the determination of the predictive information is in this case particularly simple and precise, and it is typically possible to determine the remaining distance to the charging location more precisely than the remaining travel time. According to one variant, it is also possible, however, to plot the linearity over time.

(23) In step S4, the current values for additional predictive information, here: the current absolute elevation, at which the vehicle is located, and the driving speed, are ascertained and transmitted to prediction module 13.

(24) It is characteristic for prediction module 13 that the setpoint state of charge curve is determined, not at the beginning of travel, but during travel for the respective current point in time. It is thus no longer necessary to determine many items of information predictively.

(25) In step S5, the linear state of charge curve is modified by the additional predictive information determined in step S4.

(26) In the process, the linear setpoint state of charge curve is corrected by the remaining potential and kinetic energy of the vehicle with respect to the destination. Aside from the remaining travel distance, the absolute elevation at the destination is used as predictive information.

(27) For each point in time, the current driving speed and the current elevation of the vehicle are thus detected by vehicle sensors/navigation device and are transmitted to prediction module 13. There the potential and kinetic energy differential with respect to the destination is calculated. Furthermore, an expected recuperation energy to the destination is calculated with the aid of an estimated efficiency chain of the drive train and the battery system. This is converted into a reduction of the setpoint state of charge. A calculated negative potential energy (ascent) on the other hand is regarded as an additional energy requirement on battery 8, which, according to the present invention, also allows for an increase of the setpoint state of charge.

(28) In step S6, a current setpoint state of charge at each point in time is transmitted to control unit 12. Control unit 12 performs an operating strategy method in which a torque distribution or load distribution is determined as a function of the current setpoint state of charge, e.g. according to an ECMS (equivalent consumption minimization strategy) that is known per se. The operating strategy in the motor vehicle then regulates the state of charge to the desired setpoint state of charge as target value.

(29) FIG. 5 shows a diagram of a curve of a state of charge of a battery 8 of a drive system 1, which is operated in a blended mode and in accordance with the previously described method. In contrast to FIG. 3, in FIG. 5 updating the setpoint state of charge curve is additionally represented qualitatively. As shown in FIG. 5, the method initially begins with a linear curve, in which a linearly descending curve of the setpoint state of charge is assumed between starting location X.sub.0 and destination x.sub.f.

(30) At location x.sub.1, an exemplary updating of the linear curve is shown, in which the linear curve of control unit 12 is modified by a correction value SOC. In the following, the setpoint state of charge is regulated to the new setpoint state of charge value, the curve of the setpoint state of charge now descending in a more gently inclined slope than would have originally been the case without the modification. Such a modification or update may be performed repeatedly or cyclically during the method.

(31) FIG. 6 shows a method for operating a vehicle, in particular a plug-in hybrid electric vehicle. First, the state of charge is regulated in step S10 in accordance with a specified curve of the setpoint state of charge. This occurs on the basis of an operating strategy method that is implemented in control unit 12.

(32) In step S11, the at least one sensor unit ascertains information about a current state of the vehicle.

(33) Finally, in step S12, the specified setpoint state of charge curve is updated in that this setpoint state of charge curve is modified based on the ascertained information. This may be achieved by a correction value SOC, which is applied to the setpoint state of charge at location x.sub.1, at which the vehicle is currently located. Subsequently, the method returns to step S10 in order to continue to regulate the setpoint state of charge curve for example using an ECMS method.