METHOD FOR OPERATING A HYBRID POWERTRAIN

Description

[0001] The present invention relates to a method for operating a hybrid powertrain. The invention particularly relates to a method for operating a hybrid powertrain with a hydrogen-powered internal combustion engine. The invention specifically relates to a method for operating a serial hybrid powertrain or a hybrid powertrain that can be operated at least temporarily as a serial hybrid powertrain.

[0002] Hybrid powertrains generally comprise two different energy converters for driving a mechanical load, such as a vehicle's wheels or hydraulic pumps. Typically, the first energy converter is an internal combustion engine, and the second is an electric motor. Alternatively, a fuel cell, for example, can be used instead of the internal combustion engine.

[0003] The interaction of the two energy converters is referred to as the powertrain topology. In serial hybrid powertrains, the first energy converter, or the internal combustion engine, drives a generator that supplies an on-board power system with electrical power. The second energy converter, or the electric machine, in turn converts the electrical power of the on-board power system into mechanical energy, which is used to drive the mechanical load. In addition to the serial topology of hybrid powertrains, parallel and power-split topologies for hybrid powertrains are also known. The first energy converter can be operated with various fuels, such as gasoline, diesel, and hydrogen. Depending on the fuel used, the first energy converter exhibits different emission characteristics depending on the operating state. High emission values ​​can occur briefly, particularly during dynamic load changes.

[0004] US 2008 / 236916 A1 discloses a method for operating a serial hybrid drive train for a motor vehicle with an internal combustion engine. The drive train comprises an output shaft that is non-rotatably connected to a first electric machine, a second electric machine that is mechanically connected to a drive wheel of the vehicle, and an electrical energy storage device that can be supplied with electrical energy from the first and second electric machines and that can supply the first and second electric machines with electrical energy. A control unit distributes electrical power between the electrical energy storage device and the second electric machine. The method comprises the step of controlling a rotational speed of the first electric machine and the power output of the internal combustion engine.

[0005] DE 10 2019 220 196 A1 discloses a method for operating a drive train with an energy storage system of a vehicle. The drive train has several drive units, at least one of which is embodied as an electric motor. An operating strategy for the drive train is determined using an artificial neural network. The operating strategy is determined with the aim of optimizing the energy efficiency of the drive train and energy storage system, which in particular also includes the lowest possible emissions of, for example, carbon dioxide and / or other pollutants.

[0006] DE 10 2007 019 989 A1 discloses a method for operating a hybrid drive with at least one electric motor and at least one internal combustion engine as prime movers. In this method, the hybrid drive generates a requested target drive torque while simultaneously maintaining a target power of the electric motor. The hybrid drive is controlled via characteristic maps generated "offline" under the constraint of minimizing fuel consumption and / or pollutant emissions.

[0007] The present invention is based on the object of providing a method for operating a hybrid drive train which allows dynamic operation with low emissions of pollutants.

[0008] To achieve the underlying problem, a method for operating a hybrid drive train is proposed, comprising the steps of: determining an actual state vector of an internal combustion engine of the hybrid drive train, wherein the actual state vector of the internal combustion engine (2) describes the state of the internal combustion engine (2) at a time (T) using one or more vector coordinates; determining a target power of the internal combustion engine; determining a target fuel mass flow for the internal combustion engine as a function of the target power of the internal combustion engine; determining a limit fuel mass flow of the internal combustion engine as a function of an emissions limit value, the target fuel mass flow and the actual state vector of the internal combustion engine; determining a target fuel mass flow by forming a minimum value as a function of the target fuel mass flow and the limit fuel mass flow;and setting the target fuel mass flow at the internal combustion engine.;

[0009] The method according to the invention has the advantage that the target mass flow can be determined and adjusted very quickly, ensuring highly dynamic operation while maintaining continuous compliance with emission limits. This eliminates the need for exhaust gas aftertreatment with an SCR system, for example. The commonly used nitrogen oxide sensors could also be dispensed with, if legal regulations permit.

[0010] Optional method steps may include determining a target discharge of the electrical energy storage device as a function of the difference between the target fuel mass flow and the target fuel mass flow, and setting the target discharge of the electrical energy storage device to drive an output arrangement of the hybrid powertrain. To determine a target discharge of the electrical energy storage device, a differential power to be provided by the electrical energy storage device can first be determined from the difference between the target fuel mass flow and the limit fuel mass flow. A desired charging power of the electrical energy storage device of the hybrid powertrain, which was previously determined to determine the target power of the combustion engine, can be subtracted from the differential power to determine the target discharge.

[0011] A hybrid powertrain is understood to include, among other things, powertrains with two different energy converters, namely an internal combustion engine and an electric motor, and in particular at least one energy storage device, namely a fuel tank for the internal combustion engine. Specifically, the hybrid powertrain can have at least two energy storage devices, namely the fuel tank for the internal combustion engine and a battery.

[0012] The internal combustion engine can be designed as a hydrogen combustion engine. The internal combustion engine is then operated with an air-hydrogen mixture. The internal combustion engine can be designed as an ammonia combustion engine. The internal combustion engine is then operated with an air-ammonia mixture.

[0013] The output arrangement of the hybrid drive train can comprise one or more output units, in particular in the form of electric motors.

[0014] The hybrid powertrain may include a generator that is mechanically coupled to the internal combustion engine and electrically connected to an output arrangement of the hybrid powertrain and the electrical energy storage device via an electrical intermediate circuit of an on-board power system. A current converter may be provided between the generator and the electrical intermediate circuit of the on-board power system. This converter can convert the alternating current output of the generator into direct current and is particularly designed as a bidirectional current converter. The electrical energy storage device may include a DC / DC converter that can convert the battery's direct voltage to the desired direct voltage level of the electrical intermediate circuit.A current transformer arrangement can be provided between the electrical intermediate circuit of the on-board power system and the output arrangement, which can convert the direct current of the electrical intermediate circuit into an alternating current, which can drive the output arrangement. If the output arrangement of the hybrid powertrain has multiple output units, each output unit can be assigned a separate current transformer that is connected to the electrical intermediate circuit and can convert the direct current of the electrical intermediate circuit into an alternating current. The current transformer arrangement or the separate current transformers can also be designed, in particular, as bidirectional current transformers.

[0015] The actual state vector of the internal combustion engine describes the state of the internal combustion engine at time T using one or more vector coordinates. The actual state vector can include, as coordinates, at least one actual value of the engine speed, pressure in the injection system's distributor pipe, fuel mass flow, time of fuel injection in the combustion cycle, proportion of recirculated exhaust gas to fresh air mass, and air mass flow.

[0016] The target power of the internal combustion engine is the power that should ideally be generated by the internal combustion engine at a time T+1 following time T. The target power of the internal combustion engine can be determined depending on the power requirement of the output assembly of the hybrid powertrain and the desired charging power of the electrical energy storage device of the hybrid powertrain. The power requirement of the output assembly can be determined depending on the power requirements of several output units of the output assembly. The desired charging power of the energy storage device can be determined depending on the charge state of the energy storage device and / or the power requirement of the output assembly.

[0017] The target fuel mass flow is the fuel mass flow that is to be converted into mechanical energy in the internal combustion engine at a time T+1 following time T, so that the internal combustion engine can produce the target power at time T+1. The target fuel mass flow can also be determined depending on the actual state vector of the internal combustion engine. In particular, the target fuel mass flow can also be determined depending on at least a subset of the coordinates of the actual state vector of the internal combustion engine.

[0018] The emission limit value can be a limit emission vector for the limits of several emission types. The limit emission vector can comprise one or more coordinates, each defining the limit of a specific emission type. Examples of possible emission types include nitrogen oxides (NOx), carbon dioxide (CO2), or particulate matter. The emission limit value or the coordinates of the limit emission vector can depend on at least one of the actual state vector of an internal combustion engine, the target power of the internal combustion engine, and the target fuel mass flow for the internal combustion engine. For this purpose, characteristic curves and / or characteristic maps can be read out, for example.

[0019] The limit fuel mass flow is the maximum fuel mass flow that can be converted into mechanical energy in the internal combustion engine at a time T+1 following time T, such that defined boundary conditions, such as the emission limits or at least a subset of the emission limits of the limit emission vector, are met during operation of the internal combustion engine. The limit fuel mass flow of the internal combustion engine can also be determined based on a predicted emission value, which is modeled, in particular, by a data model. The predicted emission value is modeled for time T+1.

[0020] The limit fuel mass flow of the internal combustion engine can be determined using a data model, whereby an input fuel mass flow of the data model is iteratively reduced until a predicted emission value modeled by the data model for time T+1 is less than or equal to the emission limit. The data model can also be referred to as an emission prediction.

[0021] If the emission limit is implemented as a limit emission vector, the limit fuel mass flow of the internal combustion engine can be determined using the data model, whereby the input fuel mass flow of the data model is iteratively reduced until the coordinates of a predicted emission vector modeled by the data model are less than or equal to the corresponding emission limits of the limit emission vector. The predicted emission vector includes the emission values ​​modeled by the data model at time T+1 as coordinates.

[0022] The input fuel mass flow of the data model can initially be equated with the previously determined target fuel mass flow both in the case of a single emission limit value and in the case of a limit emission vector.

[0023] The data model can also be used to model an actual emission vector that includes the emission values ​​modeled by the data model at time T as coordinates.

[0024] The limit fuel mass flow of the internal combustion engine can be determined alternatively or in combination using a data model comprising an artificial neural network. The artificial neural network can have, as neurons of an input layer, at least the actual state vector of the internal combustion engine or a subset of the coordinates of the actual state vector, the target fuel mass flow, and / or the emission limit value or the limit emission vector. The artificial neural network can have, as neurons of an output layer, the limit fuel mass flow, and / or the actual emission vector, and / or the predicted emission vector.

[0025] The artificial neural network can be trained at a time T0, which is prior to time T, based on internal combustion engine data obtained from a simulation or on measurement data from internal combustion engine test runs. Furthermore, the neural network can be trained based on a combination of internal combustion engine data obtained from a simulation and measurement data from internal combustion engine test runs. This process step can also be referred to as the basic calibration of the artificial neural network.

[0026] The target fuel mass flow is the fuel mass flow that is actually converted into mechanical energy in the internal combustion engine at a time T+1 following time T. The target fuel mass flow in the internal combustion engine is therefore set at a time T+1 following time T.

[0027] A target fuel mass flow is determined by calculating a minimum value as a function of the target fuel mass flow and the limit fuel mass flow. In other words, a target fuel mass flow is determined by calculating a minimum value, with the minimum value being a function of the target fuel mass flow and the limit fuel mass flow.

[0028] To determine the target fuel mass flow by calculating the minimum value based on the target fuel mass flow and the limit fuel mass flow, the minimum value of the target fuel mass flow and the limit fuel mass flow can be set as the target fuel mass flow. Alternatively, to determine the target fuel mass flow by calculating the minimum value based on the target fuel mass flow and the limit fuel mass flow, the target fuel mass flow can first be converted into a target torque and the limit fuel mass flow can then be converted into a limit torque. The minimum value can then be calculated from the target torque and the limit torque, with the resulting minimum value in turn being converted into a fuel mass flow, which is set as the target fuel mass flow.

[0029] In principle, one skilled in the art will recognize that the fuel mass flow is approximately proportional to the torque of the internal combustion engine. Thus, the method can include additional steps in which one of the target fuel mass flow, limit fuel mass flow, or desired fuel mass flow is converted into a corresponding torque, and vice versa.

[0030] Alternatively, or in combination, the target fuel mass flow can be determined depending on the available discharge power of the electrical energy storage device. For this purpose, the available discharge power of the electrical energy storage device can be determined, in particular depending on the state of charge of the electrical energy storage device.

[0031] An exemplary embodiment of the method is explained below using the figures. Figure 1 shows a schematic view of a hybrid powertrain with serial topology; and Figure 2 shows the method according to the invention in a flowchart.

[0032] In Figure 11 shows a hybrid drive train 1 with a serial topology that can be operated using the method according to the invention. The hybrid drive train 1 comprises an internal combustion engine 2, which is fixedly connected to a generator 4 via a motor shaft 3 and can drive the generator in rotation. The internal combustion engine 2 is operated here as a hydrogen combustion engine. The generator 4 is electrically connected to an electrical energy storage device 6 and an output arrangement 8 via an electrical intermediate circuit of an on-board power system. The electrical intermediate circuit 5 can be designed, for example, as a cable harness or busbar. The electrical intermediate circuit 5 is switchably connected to an external voltage source 15, for example, to the general low-voltage power grid, via a switch 16.The generator 4 and the voltage source 15 can thus apply a voltage to the electrical intermediate circuit 5 either selectively or in combination, so that the output arrangement 8 can be operated and / or the energy storage device 6 can be charged.

[0033] The electrical energy storage device 6 is configured here as a battery in the form of a lithium-ion accumulator. Alternatively, other accumulators or capacitors can also be used. The output arrangement 8 comprises a first output unit 7 and a second output unit 7', each configured as an electric motor. The first output unit 7 and the second output unit 7' each have an output shaft 9, 9' connected to a mechanical load (not shown). The mechanical loads in this case are hydraulic pumps, but are not limited thereto. It is understood that the output arrangement 8 can comprise any number of output units, each of which can be designed identically or differently.

[0034] The generator 4 comprises a generator control unit 10, which includes a condition monitoring system by means of which, for example, the generator speed and / or the current I_Gen introduced by the generator 4 into the electrical intermediate circuit 5 and / or the voltage U_Schiene applied to the electrical intermediate circuit 5 can be monitored. The generator control unit 10 also comprises power electronics in the form of a bidirectional AC / DC current converter. The AC / DC current converter can convert an alternating voltage provided by the generator 4 into a direct voltage, which is applied to the electrical intermediate circuit 5. The power electronics of the generator control unit 10 can also regulate the power fed into the electrical intermediate circuit 5 by the generator 4.

[0035] The first and second output units 7, 7' each comprise an output control unit 11, 11', which has a condition monitoring system by means of which, for example, the speed, the output torque and / or the output power of the output shafts 9, 9' and / or the voltage U_rail applied to the electrical intermediate circuit 5 can be monitored. The output control units 11, 11' each comprise power electronics in the form of a bidirectional AC / DC current converter for regulating the output torque applied to the output shafts 9, 9'. The AC / DC current converter can convert a DC voltage provided by the electrical intermediate circuit 5 into an AC voltage, which is applied to the output units 7, 7'. The AC / DC current converter can also be used to regulate the frequency of the alternating current.

[0036] The electrical energy storage device 6 comprises an energy storage control unit 12, which includes a state monitor, by means of which, for example, the charge state of the energy storage device 6 and the charging or discharging current I_Bat can be monitored. If the energy storage device 6 is charged, I_Bat has a negative sign. If the energy storage device 6 is discharged, I_Bat has a positive sign.

[0037] The current I_An flowing into the output arrangement 8 results from the sum of the current I_Gen introduced by the generator 4 into the electrical intermediate circuit 5 and the charging or discharging current I_Bat.

[0038] The internal combustion engine 2 comprises an engine control unit 14, which has a condition monitoring system by means of which an actual state vector of the internal combustion engine 2 can be determined. The actual state vector of the internal combustion engine 2 describes the state of the internal combustion engine 2 at a defined time T using vector coordinates. In this case, the actual state vector includes, without limitation, the actual values ​​of the engine speed, pressure in the distributor pipe of the injection system, fuel mass flow, time of fuel injection in the combustion cycle, proportion of recirculated exhaust gas to fresh air mass, and air mass flow. The engine control unit 14 can also regulate the parameters necessary for the operation of the internal combustion engine 2.

[0039] A higher-level control unit 13 is designed to communicate with the generator control unit 10, the output control units 11, 11', the energy storage control unit 12 and the engine control unit 14 and to control the switch 16. The control unit 13 is designed to control the hybrid drive train 1 according to the Figure 2 to operate the procedures shown.

[0040] In a method step V10, the control unit 13 determines the actual state vector of the internal combustion engine 2 of the hybrid drive train 1 at time T. For this purpose, the actual state vector is transmitted from the engine control unit 14 to the control unit 13.

[0041] In a subsequent method step V20, the control unit 13 determines a target power of the internal combustion engine 2. The target power of the internal combustion engine 2 is determined as a function of a power requirement of the output arrangement 8 and a desired charging power of the electrical energy storage device 6. For this purpose, the speed and output torque of the output shafts 9, 9' of the drive units 7, 7' are transmitted from the output control units 11, 11' to the control unit 13. The control unit 13 calculates an output power for each drive unit 7, 7' from the respective speed and output torque. Alternatively, the output power can be determined in the output control units 11, 11' and communicated directly to the control unit 13. The power requirement of the output arrangement 8 results from the sum of the output powers of the drive units 7, 7'.

[0042] The desired charging power of the electrical energy storage device 6 can be determined by the energy storage control unit 12 or the control unit 13 depending on the state of charge of the energy storage device 6 and / or depending on the power requirements of the output arrangement 8.

[0043] In a further method step V30, the control unit 13 determines the target fuel mass flow for the internal combustion engine 2 as a function of the target power of the internal combustion engine 2 and as a function of the actual state vector of the internal combustion engine 2. The target fuel mass flow for the internal combustion engine 2 can be determined using data models or characteristic maps.

[0044] In a further method step V40, the control unit 13 determines the limit fuel mass flow of the internal combustion engine 2. In the present case, this occurs as a function of a limit emission vector, the previously determined target fuel mass flow, and the previously determined actual state vector of the internal combustion engine 2 using a data model. The data model used here is an artificial neural network, which has the limit emission vector, the target fuel mass flow, and the actual state vector of the internal combustion engine 2 as neurons of an input layer. The output layer of the artificial neural network comprises the limit fuel mass flow and the actual emission vector as neurons. The output layer of the artificial neural network additionally or optionally comprises a predicted emission vector as a further neuron.

[0045] In a subsequent method step V50, the target fuel mass flow is determined by the control unit 13. The target fuel mass flow is set equal to the smaller of the target fuel mass flow and the limit fuel mass flow.

[0046] In a further method step V60, the target fuel mass flow at the internal combustion engine 2 is set at time T+1. For this purpose, the control unit 13 communicates the target fuel mass flow to the engine control unit 14. The engine control unit 14 controls the fuel mass flow provided by a fuel injection arrangement in accordance with the target fuel mass flow.

[0047] It is understood that the determination of the target fuel mass flow, the limit fuel mass flow and the desired fuel mass flow for the internal combustion engine 2 can alternatively take place in the engine control unit 14 and these values ​​can be communicated from the engine control unit 14 to the control unit 13.

[0048] In a further optional method step V70, after method step V50 and in particular parallel to method step V60, control unit 13 can determine a target discharge of the electrical energy storage device 6. In this case, this is done depending on the difference between the target fuel mass flow and the target fuel mass flow. Alternatively or in combination, the target discharge of the electrical energy storage device 6 can also be determined depending on the state of charge of the electrical energy storage device 6.

[0049] Subsequently, in a likewise optional method step V80, the control unit 13 sets the target discharge of the electrical energy storage device 6 for driving the output arrangement 8 of the hybrid drive train 1 at time T+1. List of reference symbols

[0050] 1Hybrid powertrain 2Internal combustion engine 3Motor shaft 4Generator 5Electrical intermediate circuit 6Electrical energy storage 7, 7`Output unit 8Output arrangement 9, 9`Output shaft 10Generator control unit 11, 11`Output control unit 12Energy storage control unit 13Control unit 14Engine control unit 15External voltage source 16Switch

Claims

1. Method for operating a hybrid drive train, comprising the steps: (V10) determining a current state vector of an internal combustion engine (2) of the hybrid drive train (1), wherein the current state vector of the internal combustion engine (2) describes the state of the internal combustion engine (2) at a time (T) by using one or more vector coordinates; (V20) determining a target output of the internal combustion engine (2); (V30) determining a target fuel mass flow for the internal combustion engine (2) as a function of the target output of the internal combustion engine (2); (V40) determining a limiting fuel mass flow of the internal combustion engine (2) as a function of an emission limiting value, of the target fuel mass flow and of the current state vector of the internal combustion engine (2); (V50) determining a desired fuel mass flow by forming a minimum value as a function of the target fuel mass flow and the limiting fuel mass flow; and (V60) adjusting the desired fuel mass flow on the internal combustion engine (2).

2. Method according to Claim 1, characterized in that the current state vector of the internal combustion engine (2) comprises at least one current value of the rotational speed, the pressure in the manifold of the injection system, the fuel mass flow, the time of the fuel injection in the working cycle, the proportion of the exhaust gas fed back to the fresh air mass and the air mass flow.

3. Method according to either of Claims 1 and 2, characterized in that the target output of the internal combustion engine (2) is determined as a function of the power required by an output drive arrangement (8) of the hybrid drive train (1) and a desired charge output of an electrical energy store (6) of the hybrid drive train (1).

4. Method according to Claim 3, characterized in that the power required by the output drive arrangement (8) is determined as a function of the power demand of a plurality of output drive units (7, 7') of the output drive arrangement (8).

5. Method according to either of Claims 3 and 4, characterized in that the desired charge output of the energy store (6) is determined as a function of the state of charge of the energy store (6).

6. Method according to one of Claims 1 to 5, characterized in that the limiting fuel mass flow of the internal combustion engine (2) is additionally determined as a function of a predicted emission value.

7. Method according to Claim 6, characterized in that the limiting fuel mass flow of the internal combustion engine (2) is determined by means of a data model, wherein an input fuel mass flow of the data model is reduced iteratively until the predicted emission value of the data model is less than or equal to the emission limiting value.

8. Method according to Claim 7, characterized in that the input fuel mass flow of the data model is initially set equal to the previously determined target fuel mass flow.

9. Method according to one of Claims 1 to 8, characterized in that the limiting fuel mass flow of the internal combustion engine (2) is determined by means of an artificial neural network.

10. Method according to Claim 9, characterized in that the artificial neural network has at least the current state vector of the internal combustion engine (2), the target fuel mass flow and the emission limiting value as neurons of an input layer.

11. Method according to either of Claims 9 and 10, characterized in that the artificial neural network has the limiting fuel mass flow and / or a current emission vector as neurons of an output layer.

12. Method according to one of Claims 1 to 11, characterized by (V70) determining a desired discharge rate of the electrical energy store (6) as a function of the difference between the target fuel mass flow and the desired fuel mass flow, and (V80) adjusting the desired discharge rate of the electrical energy store (6) for driving an output drive arrangement (8) of the hybrid drive train (1).