WO2008131994A2 - Method for operating a hybrid drive - Google Patents

Abstract

The invention relates to a method for operating a hybrid drive, especially a hybrid drive for a motor vehicle, comprising at least one electric engine and at least one internal combustion engine as driving engines. According to said method, the hybrid drive generates a required nominal drive torque and a nominal power of the electric engine is maintained. The method comprises the following steps: a plurality of characteristic diagrams are generated, in which a first driving torque of the electric engine and a second driving torque of the internal combustion engine are respectively allocated to a hybrid drive rotational speed and a hybrid driving torque, taking into account at least one selectable criterion; one of the characteristic diagrams is selected, in which the nominal power is at least maintained; and the hybrid drive is operated by means of the driving torques resulting from the selected characteristic diagram.

Description

 description

Title Procedure for operating a hybrid drive

The invention relates to a method for operating a hybrid drive, in particular a hybrid drive for a motor vehicle, with at least one electric machine and at least one internal combustion engine as drive machines, wherein the hybrid drive generates a requested desired drive torque while maintaining a desired output of the electric machine becomes.

State of the art

Such a method for operating a hybrid drive is known. In this case, the hybrid drive is designed in particular as a parallel hybrid drive, in which add the torques of the engine and the electric machines and act on a transmission input shaft. Here and in the following torques are to be referred to as shortcuts as moments. Depending on a driver's request, determined by an accelerator pedal, the desired drive torque and a target speed of the hybrid drive is formed. Target drive torque and target speed act on the transmission input shaft. In accordance with at least one predefinable operating strategy, for example a fuel-saving operating strategy, the desired drive torque is divided between a drive torque of the internal combustion engine and a drive torque of the electrical machine. In order to take into account a state of charge of an electrical energy store for supplying the electrical machine in this division, the desired torque of the electric machine is corrected. This correction results in a deviation from the

"Optimal" distribution of the desired drive torque according to the operating strategy.

Disclosure of the invention

The inventive method comprises the following steps: Generating a plurality of maps, in each case one hybrid drive speed and one hybrid drive torque, taking into account at least one selectable criterion, a first drive torque of the electric machine and a second

Drive torque is assigned to the internal combustion engine,

- Selection of one of the maps in which the target power is maintained or not fallen below and

- Operating the hybrid drive with the drive torque resulting from the selected map.

The hybrid drive is in particular a parallel Hybridantheb or operated as a parallel hybrid hybrid drive, in which the first drive torque of the electric machine and the second drive torque of the internal combustion engine together as a hybrid drive torque to a

Transmission input shaft of the hybrid drive associated gear acts. The hybrid drive torque is therefore also referred to as transmission input torque. Each of the characteristic maps assigns the parameters hybrid drive rotational speed and hybrid drive torque according to the criterion assigned to the characteristic map to a first drive torque of the electric machine and / or a second drive torque of the internal combustion engine. The map thus determines the torque distribution of the hybrid drive torque to the electric machine and the engine according to the criterion. After generating the maps, a selection of one of the maps is based on the electrical setpoint line. In this case, that of the maps is selected in which the setpoint line is maintained or not fallen below. Subsequently, the hybrid drive is operated with the torque distribution resulting from the selected characteristic map between the internal combustion engine and the electrical machine. The discrete values of the maps are supplemented by interpolation and / or extrapolation. The interpolation or extrapolation takes place on the basis of the nominal electrical power. In particular, a low-pass filtering of the maps is performed to change the ratio of first and second drive torque (map output) for small changes in hybrid drive speed and / or hybrid drive torque (map inputs) at the expense of Limit optimization potential. The maps are particularly designed so that for each combination of hybrid drive speed and hybrid drive torque, the first drive torque (for the electric machine) is created. The second drive torque (of the internal combustion engine) results from the difference between the hybrid drive torque and the first drive torque.

In particular, it is provided that the maps have been created and stored prior to selection and operation. Such a generation in advance enables a calculation time saving implementation of the torque distribution by the use of previously "offline", so regardless of the current operation, created maps, in particular using interpolation rules for adaptation to the current operating situation.The interpolation rule is preferably an extrapolation rule The selection of one of the maps and the subsequent operation of the hybrid drive is implemented, in particular, in a hybrid drive control unit can be obtained by off-line calculation, without the need for computation time in the control unit, and the selection and inter / extrapolation are based on few additions and multiplication reduced in the control unit. The interpolation or extrapolation takes place on the basis of the nominal electrical power.

According to a development of the invention, it is provided that the desired power of the electric machine is determined as a function of the state of charge of an electrical energy store, in particular a battery. By taking into account the state of charge in the target power, the selection of the map is made such that the current state of charge is adjusted to a desired state of charge.

In an advantageous embodiment of the invention, it is provided that the desired power of the electric machine is determined as a function of an electrical power requirement of aggregates of the hybrid drive and / or motor vehicle. Alternatively or in addition to the selection of the map in Depending on the state of charge of the energy storage, the electrical power requirement of units of the hybrid drive and / or motor vehicle is a. The sum of these aggregates is also referred to as vehicle electrical system.

Furthermore, it is advantageously provided that the criterion used is a minimization of the energy consumption of the hybrid drive. With the criterion of minimizing energy consumption, the energy consumption of the hybrid drive results from the electrical energy consumption of the electric machine and the fuel consumption of the internal combustion engine.

According to a development of the invention, it is provided that the criterion used is a minimization of the electrical energy consumption of the electrical machine.

Alternatively or additionally, it is advantageously provided that the criterion used is a minimization of the fuel consumption of the internal combustion engine.

In an advantageous embodiment of the invention, it is provided that the criterion used is a minimization of pollutant emissions of the hybrid drive and / or of the motor vehicle. In this criterion, the total pollutant emissions, so the pollutant emissions of the engine and the pollutant emissions to maintain the state of charge of the electrical energy storage is.

Furthermore, it is advantageously provided that the criterion used is a minimization of pollutant emissions such that an operation of the hybrid drive is performed only by means of the electric machine. In order to reduce the pollutant emissions of the current operation of the hybrid drive, the hybrid drive - if possible due to the target power - only performed by means of the electric machine.

According to a development of the invention, it is provided that one of the maps is selected on the basis of a selectable parameter in a possible use of multiple maps. If the selection results in one of the maps in which the target performance is maintained or not undershot an ambiguous result, so meet several maps this condition, so a selection is made on the basis of a selectable parameter. The selection based on the selectable parameter may be advanced or adjusted to the selection based on the desired power. The parameter may be, for example, minimum fuel consumption, minimum pollutant emissions or a weighted combination thereof.

Brief description of the drawings

The invention will be explained in more detail with reference to the accompanying drawings. It shows:

FIG. 1 shows a hybrid drive designed as a parallel hybrid drive;

Figure 2 is a block diagram of the input and output variables of a

Map and

FIG. 3 shows an exemplary embodiment of FIG. 2.

Embodiment (s) of the invention

1 shows a drive train topology of a designed as a parallel hybrid drive 1 hybrid drive 2 of a vehicle, not shown. The hybrid drive 2 has an internal combustion engine 3 and an electric machine 4 as drive machines 3, 4. The electric machine 4 is connected via a power electronics unit, not shown, with a trained as a rechargeable battery 5 electrical energy storage device 6. In this parallel hybrid drive 1, the internal combustion engine 3 and the electric machine 4 are arranged serially one after another on an axis 7. A along the axis 7 extending output train 8 of the

Internal combustion engine 3 is connected to a drive or output line 9 of the electric machine 4, which is arranged on the output line 8. The output line 8 of the internal combustion engine 3 is therefore at the same time the output train of the hybrid drive 2. In this drive train topology, the electric machine is a crankshaft electric machine 4, in which the internal combustion engine 3 is entrained undirected during electric driving. Alternatively, a non-illustrated controllable coupling is provided between the engine 3 and the electric machine 4. The power train 8 is connected to a transmission drive train 10 (transmission input train) with a transmission unit 11. The transmission unit 11 has a directly adjoining the transmission drive train 10 controllable clutch 12 and a subsequent to this clutch 12 transmission 13 with a transmission output line 14. At the transmission drive train 10 are a hybrid drive speed co and a hybrid drive torque M a rotation (arrow 15). The transmission unit 11 converts this hybrid drive speed ω and this hybrid drive torque M according to the ratio into a drive speed and a drive torque of a rotational movement (arrow 16), which are transmitted to drive wheels, not shown.

FIG. 2 shows a block diagram of the relationship between the hybrid drive speed co and the hybrid drive torque M applied to the transmission drive train 10 or the power train 8 of the hybrid drive via a selected (x-tes) map K _{x of} a multiplicity of characteristic maps Ki... K _N with a first Drive torque M _ED, soii- The selection of the selected

Characteristic map K _x via a desired power P _e , _SO ιι the electric machine 4. A second drive torque of the internal combustion engine 3 is obtained by forming the difference between the hybrid drive torque M and the first drive torque M _ED, soii the electric machine 4. Thus, there is a selected map K _x for the input variables hybrid drive speed co and hybrid drive torque M a first drive torque MED, soii and a second drive torque M _Eng , soii and thus a torque distribution of the hybrid drive torque M to the engine 3 and the electric machine 4 before.

FIG. 3 shows a particularly simple combination of the input and output variables of a characteristic diagram. In this map, only the hybrid drive speed co with the target power P _e , _S oiι linked, wherein the first drive torque M _ED, soii of the electric machine 4 results. This results in the following method for operating the hybrid drive 2, wherein the hybrid drive 2 generates a requested desired drive torque M _SO ιι and simultaneously a target power P _e , _SO ιι the electric machine 4 complies: In a first step, a set of Maps Ki, ..., K _N generated whose maps, taking into account a respective associated criterion G (quality criterion) of each combination of hybrid drive speed co and hybrid drive torque M a first drive torque M _ED, soii and a second drive torque M _Eng , soii assigns. The maps created in this way are subsequently stored and made available to a control device, not shown, which controls the drive machines 3, 4 of the hybrid drive 2. The control unit selects for a requested desired drive torque Msoii taking into account the desired power P _e , _S oiι the electric machine 4, in particular for maintaining a predetermined state of charge of the electrical energy storage 6, one of the maps Ki, ..., K _N and then controls the drive machines 3, 4 of the hybrid drive 2 in accordance with the drive torque MED, soii, M _Eng , soii resulting from the selected (x th) map K _x . Thus, in the method, a division of the drive torque from the first drive torque MED, soii and second drive torque M _Eng , soii for the realization of the requested desired drive torque M _SO ιι for pursuing a

Optimization goal (for example, minimum fuel consumption, minimum pollutant emissions or a combination thereof) achieved by means of an associated criterion G (optimal torque distribution). By means of the method using a number N of two-dimensional maps and an interpolation specification, an off-line, three-dimensional relationship between transmission input torque M, transmission input speed co and nominal electrical power P _e , _SO ιι in the control unit is displayed. By generating the maps in advance ("offline"), only the selection of one of the maps takes place in real time The interpolation rule is supplemented by an extrapolation rule which covers the case of input signals co, M outside predetermined limits electric driving turn N two-dimensional maps Ki, ..., K _N and an interpolation or extrapolation rule used that the used for the torque distribution interpolation or Extrapolation rule corresponds. Even so, a three-dimensional relationship between hybrid drive speed ω, hybrid drive torque M and electrical target power P _e , _S oiι mapped. The advantage here is that the total of 2 ^■ N required maps K can be obtained by an offline calculations, without the need for calculation time in the control unit. The evaluation of the three-dimensional relationships can be reduced to a few additions and / or multiplications in the control unit by using the 2 ^■ N maps K and the interpolation rule. The interpolation or extrapolation takes place on the basis of the nominal electrical power P _{e, so} ii. Furthermore, a low-pass filtering of the characteristic maps K can be carried out in order to limit the changes of the characteristic map outputs MED, SO, M _E ng, soiι for small changes in the characteristic field inputs ω, M at the expense of the optimization potential. The number N of characteristic maps K can be freely selected, with better utilization of the optimization potential for larger N without having to resort to a computing time of intensive online calculation in the control unit. In addition, the method described here shows a possibility of generating the decision on purely electric driving from the same optimization method as in torque distribution.

For simplicity, in the embodiment, both the speed co of the engine 3, the speed co of the electric machine 4 and the hybrid drive speed ω (transmission input speed) are equal. The basis of the torque distribution is the minimization of the criterion G referred to as the quality criterion, in which the desired operating point of the internal combustion engine 3, the desired operating point of the electric machine 4, the fuel consumption and the electrical power consumption as a function of the desired operating points, and a conversion factor λ between fuel consumption and electrical Take power. The criterion G can take the following form, for example:

G = 1 lv [ _Eng (M _{Eng soll} , ω) ^■ M _{Eng should} ^■ ω + λ ^■ 1 / η _Z3 (M _{ED soll} , ω) ^■ M _{ED should be} ^■ ω

In the minimization, it is assumed that the hybrid drive torque M is the sum of the first and the second drive torque MED, so, M _Eng , soii composed. For given hybrid drive speeds co and hybrid drive torques M, the following minimization problem is solved in each case:

MEngMl * ™ ^{1 G}

The result of this minimization is on the one hand a map K _op t, which contains an optimal setpoint torque M _ED, soii, o _P t of the electric machine and thus also the optimal torque distribution as a function of the hybrid drive speed co and the hybrid drive torque M, on the other hand _{Characteristic} map K _∞s t, which contains the value of the criterion G at the optimal moment distribution as a function of M and ω.

For purely electric driving, at each operating point (characterized by M, co) in the modified criterion G *

G * = 1 IT \ _ED ( ^M _ED , _SOU , ω) ^■ M _{ED should} ^■ co

and a corresponding second drive torque (M _E ng, soi = 0 for the decoupled internal combustion engine and with the second drive torque M _Eng , soii equal to an effective drag torque M _Eng , drag of the internal combustion engine 3) a comparison value cost _E D for the corresponding entry in the map cost _H D = Kcost (M, co) are calculated. The modified criterion G ^* corresponds to the original criterion G without consideration of the internal combustion engine component.

Thus, a separate map K _ED for electric driving is generated, in which for each operating point the query cost _ED <cost _H D is performed. It is thus decided for each operating point (M, co) whether the optimum torque distribution or the electric driving represents the best solution of the specified optimization criterion. It then applies:

K _ED = 1 for cost _ED <cost _HD and K _ED = 0 otherwise Whenever 1 is in the K _ED map, electric driving is the optimum operating mode for the respective operating point.

Variations within the criterion G and thus also in G ^* can be used to generate many characteristic field triples K _op t, K _e and K _cos t. Each of these characteristic field triples is assigned an electric power P _e , _K , which corresponds to an average electric power when using the characteristic triplet on a selection of operating points (M, ω), which are respectively set for a time t:

The selection of operating points is carried out so that the operating points relevant in driving operation are sufficiently represented. In particular, the operating points occurring during a certification cycle can be used here.

By a map from the map triplet and the electrical power P _e , _K is a three-dimensional relationship between hybrid drive speed, ω, hybrid drive torque M and electrical target power P _e , _S oiι given, for example, for optimal torque distribution or optimal decision for electric driving is used.

In the next method step, a number of N pairs (K _op t, _K , K _ED, n with associated P _e , _{K, n} ) are selected with N = 3 from the existing map triplets and stored in the control unit. In addition, low pass filtering of the maps may be performed to limit the change of the map outputs for small changes in the map inputs at the expense of the optimization potential.

The electrical power P _e , _S oiι is a quantity which, on the one hand, includes the power of the electrical consumers and, on the other hand, comprises a term which, depending on the current state of charge SOC of the electrical energy store 6 and a desired state of charge SOC _SO ιι, is a target value. Charging power for the electrical energy storage 6 describes. It follows: ^{M = M} En _g , _S oU + ^M ED, _S oü

JFor any request of hybrid lifting torque M, hybrid drive speed ω and electrical target power P _e , _SO ιι can from the maps, the torque distribution to the first and second Aufhebungsoment MEng, soii, M _E D, soii by interpolation between the individual maps K _op t , _{n be determined} with the independent variable of the target power P _e , _SO ιι. It is possible to use here either a linear interpolation or a "nearest neighbor" interpolation of the desired power P _{e, SO} ιι between the individual electrical powers P _e , _K, n. The interpolation factor obtained therefrom interpolates between the individual characteristic diagrams K _op t, _n -. If the values of the target power P _{e, SO} ιι outside the range of the individual electric powers P _{e, k,} n, a corresponding extrapolation method can be applied in, the simplest case is the value from the map K _op t, _n used, whose associated electrical power P _e , _K, n is closest to the desired electrical power P _e , _SO ιι, in addition there is the possibility of this value depending on the desired electrical power P _{e, So} iι With the same interpolation or extrapolation method _, the decision for electric driving becomes dependent on the individual characteristic diagrams K _{e, n} speed of the hybrid drive torque M, the hybrid drive speed ω and the electrical target power P _e , _S oiι generated. This results in a change in the desired power P _{e, So} iι to a change in the torque distribution. However, the new moment distribution is an optimal solution to the original optimization problem when

J

The decision for electric driving follows the same procedure. This ensures that the operating mode is always requested, which is optimal according to the specified criterion G or G ^* .

Claims

claims 1. A method for operating a hybrid drive, in particular a hybrid drive for a motor vehicle, with at least one electric machine and with at least one internal combustion engine as drive machines, wherein the hybrid drive generates a requested desired drive torque while maintaining a desired output of the electric machine, with the following steps: Generating a plurality of characteristic maps, in each of which a hybrid drive rotational speed and a hybrid drive torque, taking into account at least one selectable criterion, a first drive torque of the electric machine and a second drive torque of the internal combustion engine, selection of one of the maps in which the target power is maintained or not is fallen below and - Operating the hybrid drive with the drive torque resulting from the selected map. 2. The method according to claim 1, characterized in that the maps have been created and stored prior to operation. 3. The method according to any one of the preceding claims, characterized in that the desired power of the electric machine in dependence on the state of charge of an electrical energy storage device, in particular a battery is determined. 4. The method according to any one of the preceding claims, characterized in that the desired power of the electric machine in dependence on an electrical power requirement of aggregates of the hybrid drive and / or motor vehicle is determined. 5. The method according to any one of the preceding claims, characterized in that as a criterion to minimize the energy consumption of the hybrid drive is used. 6. The method according to any one of the preceding claims, characterized in that as a criterion minimizing the electrical energy consumption of the electric machine is used. 7. The method according to any one of the preceding claims, characterized in that as a criterion to minimize the fuel consumption of the internal combustion engine is used. 8. The method according to any one of the preceding claims, characterized in that as a criterion minimizing pollutant emissions of the hybrid drive and / or the motor vehicle is used. 9. The method according to any one of the preceding claims, characterized in that as a criterion minimizing the emission of pollutants is used such that an operation of the hybrid drive is performed only by means of the electric machine. 10. The method according to any one of the preceding claims, characterized in that is selected in a possible use of multiple maps one of the maps on the basis of a selectable parameter.