Method for operating a hybrid vehicle, control, drive arrangement and hybrid vehicle

Abstract

Method for operating a hybrid vehicle (1) with a drive arrangement (7) comprising: an internal combustion engine (2) with exhaust gas recirculation (11), an electric machine (3) and a traction battery (4) wherein the internal combustion engine (2) generates an engine torque and the engine torque a drive component (M A ) and a charging component (M L ) includes, if the state of charge (SOC) of the traction battery (4) is less than an upper limit state of charge (SOC) OG ) and the electric machine (3) by means of the charging component (M L ) is driven by a generator, so that a charging current is generated to charge the drive battery (4), where the charging component (M L ) corresponding to a minimum EGR charging rate assigned to the state of charge (SOC). L ) is determined and thus the setting is based on a minimum EGR charging rate (EGR) assigned to the state of charge (SOC).L ) is controllable so that the charging component (M L ) with regard to a minimized NO X -Emission is discontinued where the charging component (M L ) is achieved via an increase in the load point, wherein the load point increase occurs in accordance with a change in at least one operating condition influencing the state of charge (SOC), wherein the load point increase is carried out from an initial operating point (B1) to a charging operating point (B2; B3), wherein the charging operating point (B2; B3) is selected such that a minimum EGR charging rate (EGR) specified for the current state of charge (SOC) is achieved. L ) is adhered to and the load point increase is terminated or limited as soon as the EGR rate available at the charging operating point exceeds this minimum EGR charging rate (EGR). L ) would fall below.

Description

[0001] The present invention relates to a method for operating a hybrid vehicle with a drive arrangement comprising: an internal combustion engine with exhaust gas recirculation, an electric motor, and a traction battery. The invention further relates to a control system, a drive arrangement, and a hybrid vehicle, each configured to carry out such a method.

[0002] In light of future legal regulations regarding emission limits for motor vehicles, reducing raw exhaust emissions is becoming increasingly important, in addition to exhaust aftertreatment. This applies particularly to NOₓ. x -Limit values ​​which, despite highly efficient exhaust aftertreatment systems (ANB), can only be further minimized with comparatively high effort in vehicles with a diesel engine.

[0003] This problem also exists with the increasingly widespread hybrid vehicles, which are also increasingly equipped with a diesel combustion engine and additionally have an electric drive in order to offer additional potential in terms of optimizing fuel / energy consumption and emissions.

[0004] For the purposes of this application, the terms "hybrid vehicle" and "hybrid drive" shall be understood to mean all hybrid vehicle drive structures in which an internal combustion engine is combined with one or more electric motors. In particular, this shall include the three basic architectures known as "series hybrid," "parallel hybrid," and "power-split hybrid." Combinations and variants of these concepts, such as "series-parallel hybrid," "plug-in hybrid," and others, shall also be included.

[0005] The main advantages of such hybrid vehicles lie in the fact that these drive concepts can further reduce fuel consumption and thus CO2 emissions. This effect is achieved by allowing the combustion engine to operate within a narrower speed range with less variation in power demand and by relieving it of the burden during particularly fuel-intensive acceleration phases through the use of an additional electric drive.

[0006] Another advantage of hybrid drives and hybrid vehicles is that a second energy converter, the electric motor or electric machine, can briefly provide additional drive torque, thus delivering extra acceleration. This allows for high system performance without the need for high-performance, and therefore usually fuel-intensive and emission-intensive, combustion engines.

[0007] The additional electric machine can also act as a generator, recuperating energy during braking and feeding it into the drive battery.

[0008] In addition, another important component of hybrid vehicle drive strategies is to charge the drive battery, which powers the electric drive (usually an electric motor), while driving. A portion of the engine torque provided by the combustion engine – a charging component – ​​is used to drive the electric motor, which then – as with recuperation – operates as a generator and produces a corresponding charging current that can recharge the drive battery.

[0009] There are various concepts for adjusting this charging component during the operation of a hybrid vehicle. In most of these concepts, the control of the charging current is based solely on the current state of charge (SOC) of the traction battery. For example, DE 10 2013 104 433 A1 discloses a method for operating a modular hybrid vehicle powertrain. This method includes operating a traction motor (internal combustion engine) to charge a battery by generating a charging torque based on the battery's state of charge (SOC) and controlling a motor to respond to an increasing load by increasing the motor torque.

[0010] There are also approaches that take emission limits into account. For example, DE 10 2011 111 073 A1 specifies an energy management method for a hybrid drive system in which a torque-speed map is divided into map sections by intersecting torque curves, and the control of the internal combustion engine and the electric motor is carried out depending on the respective map section in which the current operating point is located. A torque curve indicates the course of a limit torque at which, for example, a maximum permissible exhaust emission of the hybrid drive system, in particular NOₓ, is reached. x and / or a soot emission is present.

[0011] US 2017 / 0057485A1 discloses a system and method for controlling the engine operation of an environmentally friendly vehicle to achieve optimal engine operating efficiency by modifying an engine operating point based on a battery state of charge (SOC) range and driver demand torque. The system and method meet driver demand torque, maintain battery state of charge (SOC), and achieve optimal engine operating efficiency by modifying an engine operating point based on the battery state of charge and driver demand torque to an operating point that minimizes battery discharge and maximizes battery charge.

[0012] However, the known methods have limitations regarding the flexible and dynamic consideration of NO, especially with regard to diesel engines increasingly used in hybrid systems.x -Emissions.

[0013] The task, therefore, is to provide an improved method for operating a hybrid vehicle, in which the NO x -Emissions in a charging operating condition via an internal combustion engine are easier to manage.

[0014] This problem is solved by the inventive method according to claim 1, the control system according to claim 6, the drive arrangement according to claim 7 and a hybrid vehicle according to claim 8.

[0015] A method according to the invention for operating a hybrid vehicle with a drive arrangement comprising an internal combustion engine with exhaust gas recirculation (EGR), an electric motor, and a traction battery. The internal combustion engine generates engine torque, and this engine torque includes a drive component and a charging component if the state of charge (SOC) of the traction battery is lower than an upper limit state of charge (SOC). OG), and the electric machine is driven by the charging component in a generator-like manner, so that a charging current is generated to charge the traction battery, the charging component being determined according to the state of charge (SOC) and thus controllable via the setting based on an EGR rate, so that the charging component is optimized with regard to minimized NO x -Emission can be optimized.

[0016] This approach is based on the principle that, particularly in diesel engines – but also in gasoline engines with direct injection – the emitted nitrogen oxides (NOx) are removed via exhaust gas recirculation. x ) can be effectively reduced.

[0017] Regardless of whether high-pressure or low-pressure exhaust gas recirculation is implemented, the NOₓ is successfully reduced. x-Reduction through a lowering of the peak temperature in the cylinder, which is achieved because the recirculated exhaust gas reduces the combustion rate and, due to its now higher heat capacity (mainly due to the CO2 content), the exhaust gas does not get as hot as the exhaust gas without exhaust gas recirculation for the same energy input, thus reducing NO x -Education is inhibited.

[0018] A distinction is made between high-pressure and low-pressure exhaust gas recirculation. In high-pressure exhaust gas recirculation, the exhaust gas cooler is positioned upstream of the turbocharger and returns the cooled exhaust gas to the fresh air intake.

[0019] In low-pressure exhaust gas recirculation (EGR), the exhaust gas is routed through the EGR cooler only after the turbine and mixed with the intake fresh air before the turbocharger compressor. With this method, the recirculated exhaust gas is already free of diesel particles, and the EGR cooler becomes less dirty, so that performance remains almost constant over its service life. Due to the lower cooler outlet temperature of the recirculated exhaust gases, the NOₓ emissions can be reduced. x -Reduction may already be sufficient without the need for further exhaust aftertreatment - for example by an SCR (Selective Catalytic Reduction) system.

[0020] The approach of the present invention is based on considering not only the charging requirement based on the state of charge of the traction battery when adjusting the charging component, but also the operating point at which the combustion engine is operated. In particular, the correlation between the exhaust gas recirculation rate profile in a torque-speed map and the specific NO curve is taken into account. x -Emissions utilized. Since exhaust gas recirculation rates correlate with nitrogen oxide emissions, they can be used as a criterion to adjust the charging component (especially by shifting the load point) so that only minimal NO emissions are produced. x -Increased emissions are caused.

[0021] In one version of the process, the combustion engine is designed as a diesel engine. This process is particularly effective and necessary here because of the NOₓ xEmissions are increased, particularly in diesel engines, due to the excess air in the combustion chamber that occurs during the diesel combustion process.

[0022] The principle also works for gasoline engines.

[0023] In a further development of the process, the charging component is implemented via a load point increase. This strategy is particularly suitable in partial load ranges, where high proportions of exhaust gas are recirculated, thus positively influencing nitrogen oxide emissions. As a result, despite the load point increase, only the minimum possible nitrogen oxide emissions are achieved.

[0024] There are also methods where the load point increase corresponds to a change in at least one operating condition that influences the state of charge (SOC). This allows operating parameters other than the state of charge to be used to determine the load point increase. Several such operating condition variations can also be combined with each other and with the state of charge. This allows for very flexible adjustment of the load point increase.

[0025] Possible methods include at least one of the following changes: reducing driving speed; increasing the energy demand of an electrical consumer; selecting a driving program with increased charging requirements. Examples include sporty driving programs with boost requirements or so-called EV modes, which are designed to extend the electric driving range.

[0026] In a further development of the method, the load point increase is achieved from an initial operating point to a charging operating point, wherein the charging operating point is adjustable based on a state-of-charge-dependent EGR rate. In other words: The load point increase is adjustable from an operating point according to an inventive definition of a minimum permissible EGR rate for the current state of charge.

[0027] There are methods where the mapping between operating points and exhaust gas recirculation rates is based on a characteristic map. This makes the mapping to specific operating conditions and operating points particularly simple and repeatable. Typically, the EGR rates at the operating points are assigned in a torque-speed characteristic map and can be easily determined experimentally. Different characteristic maps can thus be used for different operating parameters or combinations thereof.

[0028] There are methods where the setting is performed between an upper and a lower charge limit of the traction battery. This establishes the basis for defining a charge range within which the charging component should be determined. Typically, a higher exhaust gas recirculation rate is targeted at a high charge limit to keep nitrogen oxide (NOx) levels low. Conversely, a relatively low exhaust gas recirculation rate is acceptable at a low charge level or at a lower charge limit, although this results in higher emissions and NOx levels. x Values ​​can occur. Since the load point increases are varied according to variable EGR rates, the higher the SOC, the higher the target EGR and the lower the load point increase. Conversely, the lower the SOC, the lower the acceptable EGR and the higher the load point increase to increase the charge component.

[0029] There are also methods where, when an upper limit or maximum state of charge is exceeded, no charging component is implemented via a load point increase, but rather the charging of the traction battery is solely achieved through recuperation. For this to work, the maximum state of charge must be selected such that the battery has a residual capacity available for recuperation operation.

[0030] A control unit, which may in particular be designed as an engine control unit for such a drive arrangement, and which is designed and configured to carry out the method according to the invention, makes it possible to implement the method in hybrid vehicles in a simple manner.

[0031] It may even be possible to retrofit the procedure into existing hybrid vehicles or their control units or engine control units. This allows for subsequent optimization of the charging component settings. The same applies to a drive system with a corresponding control unit or a hybrid vehicle with such a drive system.

[0032] Further advantageous embodiments of the invention will become apparent from the dependent claims and the following description of preferred embodiments of the present invention.

[0033] Exemplary embodiments of the invention will now be described by way of example and with reference to the accompanying drawing. The drawing shows: Fig. 1 a schematic representation of a vehicle with hybrid drive Fig. 2 a schematic representation of exhaust gas recirculation; Fig. 3 a schematic representation of a Mn map in which EGR rates are entered

[0034] Fig. Figure 1 shows a schematic representation of a hybrid vehicle 1 with an internal combustion engine 2, which, together with an electric motor 3, a drive battery 4, a drive shaft 5, and two drive wheels 6, forms a drive assembly 7. The internal combustion engine 2 is coupled to the drive shaft 5 via a clutch 8, which is also driven by the electric motor 3 and includes a transmission 9.

[0035] The electric machine 3 can operate as both a generator and a motor. The interaction of the components of the drive assembly 7 is controlled by a control unit 10, which includes elements for motor control of the internal combustion engine 2, as well as for controlling the electric machine 3 and for monitoring the state of charge of the traction battery 4. For this purpose, the control unit 10 is connected to the corresponding components via various signal and supply lines (not shown). The control unit 10 also serves to regulate the interaction between the internal combustion engine 2 and the electric drive components, namely the electric machine 3, the traction battery 4, and other electronic components required for control. To this end, the control unit 10 implements control processes, acquires and processes sensor data, executes algorithms, and utilizes characteristic maps.

[0036] The internal combustion engine 2 is equipped with an exhaust gas recirculation (EGR) system 11, which is located in Fig. Figure 2 shows the combustion engine 2, a diesel engine with a turbocharger 12. Incoming fresh air is compressed and passed through a fresh air cooler 13 before being fed into the combustion chambers of the individual cylinders, where diesel fuel is injected and the combustion process takes place. The exhaust gas drives the turbine of the turbocharger 12 and exits through an exhaust pipe 14. The exhaust pipe 14 is connected to the fresh air supply 13 via the exhaust gas recirculation system 11. The exhaust gas recirculation system 11 includes an exhaust gas cooler 15 and a control valve 16, which regulates the amount of exhaust gas recirculated. The control valve 16 is actuated by the control unit 10, which also controls the other drive components.

[0037] Exhaust gas recirculation (EGR) is controlled based on the operating point – i.e., depending on the load. Corresponding EGR rates for specific operating points are stored in suitable maps or calculated in the control unit. EGR serves to reduce the NOₓ concentration. x -The proportion of the exhaust gas is reduced depending on the load point. For this purpose, a corresponding exhaust gas recirculation rate is set.

[0038] Fig. Figure 3 shows a torque-speed map under a full-load curve V, in which the corresponding exhaust gas recirculation rates in percent are plotted for the different operating ranges. Based on the Fig. In section 3, the basic idea of ​​the method according to the invention becomes clear.

[0039] The aim is to use a portion of the power or available engine torque during combustion engine operation to charge a traction battery 4, i.e., an electrical energy storage device. The traction battery 4 has a usable charge range that extends between a state of charge (SOC). max and a SOC min lies, each representing the minimum state of charge (SOC). min ) of the traction battery 4 and the maximum state of charge (SOC) max ) of the traction battery 4. A charging range lies between these values, within which combustion engine charging of the traction battery 4 is permitted. The highest state of charge up to which combustion engine charging is allowed is designated SOC. OG designated and the lower limit - the lowest state of charge for combustion engine charging with SOC UG SOC UG This is approximately 10-20% of the usable charging range and SOC. OGat 80-90% of the usable charging area.

[0040] If the state of charge is in a low range, i.e., close to SOC UG This indicates a high charging demand. If the charging range is in the upper charging range, i.e., close to the SOG state of charge, then the battery has a high charging demand. OG , so the charging area is small.

[0041] During combustion engine operation, the additional charging is achieved via the additional operation of the electric machine 3 by raising an initial operating or load point B1 at constant speed to a charging operating point B2. This means that the combustion engine 2 provides a higher load torque than would be required to drive the vehicle 1. The total engine torque then consists of a drive component (drive torque M). A ) and a charging component (charging torque M) L ), which corresponds to the moment contribution by which the load point B1 is raised to the load point B2.

[0042] To ensure the highest possible exhaust gas recirculation rate even during charging, a permissible EGR rate is assigned to each charging state within the charging limits. L This includes, for example, the SOC. UG an exhaust gas recirculation rate (EGR) UG ) assigned a minimum state of charge (SOC) that must not be undercut even when charging the traction battery. This is, for example, 35%; however, it can also be 25% or 30%. For a higher SOC, for example at 50%, a minimum exhaust gas recirculation (EGR) rate is used. SOC50 For example, a charge level of 45% is permitted, which must not be undercut at such a state of charge. Finally, the limit down to which charging via the internal combustion engine is permitted is called the State of Charge (SOC). OG a maximum exhaust gas recirculation rate (EGR) OG assigned a value of 50%, which must not fall below this level during charging and when such a charge level is present.

[0043] This establishes a charge-state-dependent relationship between operating-point-dependent exhaust gas recirculation rates. Minimum exhaust gas recirculation rates ensure that even at low charge states, no combustion engine charging occurs, which would result in excessively high NOₓ emissions. x Emissions may occur - this limits the engine's possible load increase.

[0044] In the present example, the initial operating point B1 can therefore be raised until it reaches the charging operating point B2, which corresponds to a charge-dependent exhaust gas recirculation rate. In the present figure, the dashed exhaust gas recirculation curve is EGR. 50 For example, it could be assigned a state of charge (SOC) of 50%. In this case, the operating point B1 could be raised to point B2 (as indicated by the dashed curve), thus creating a corresponding charging component M. LThe equation will be shown, which corresponds to the difference in moments between B1 and B2.

[0045] If the state of charge is lower than 50% and is, for example, at SOC UG In the diagram shown, the exhaust gas recirculation rate (EGR) corresponds to this state of charge. UG assigned. In this case, operating point B1 can be raised to point B3. For example, an exhaust gas recirculation rate of 35% is set, which corresponds to the state of charge (SOC). UG This corresponds to a correspondingly higher charging component M. L available. Nevertheless, it is ensured that a significant NO is still maintained. x -reducing exhaust gas recirculation rate is ensured.

[0046] Intermediate values ​​can be determined, for example, by linear interpolation between the characteristic map values. This ensures that, at a high state of charge close to the state of charge (SOC), the vehicle is correctly positioned. OGTurbocharging is only permissible if very high exhaust gas recirculation rates are achievable, i.e., a high NOₓ emission. x -Reduction remains ensured.

[0047] At low charge levels near SOC UG This ensures that, on the one hand, a sufficiently high charging component can be provided, but at the same time exhaust gas recirculation rates are achieved that significantly reduce NOₓ. x -Allow reduction.

[0048] For example, below an exhaust gas recirculation rate OG, which can be, for example, 50% and the SOC OG It is ensured that in the area below or beyond the limit of such a state of charge, only recuperative charging of the drive battery is permitted, i.e., no load increase is allowed that would mean a reduced exhaust gas recirculation rate and thus higher NOₓ. x -Emissions.

[0049] In addition to the method shown in the exemplary embodiment, the following also applies: There are also methods in which the load point increase occurs according to a change in at least one operating state Z that influences the state of charge (SOC), in Fig. 3 are labeled Z1 and Z2. This allows operating parameters other than the state of charge (SOC) to be used for determining the load point increase. Several such operating condition variations can also be combined with each other and with the state of charge. This allows for very flexible adjustment of the load point increase.

[0050] Possible methods include at least one of the following changes: Reduction of driving speed v F ; Increase in the energy demand of an electrical consumer; Selecting a driving program with increased charging requirements. This includes, for example, sporty driving programs with boost requirements or so-called EV modes, which are designed to extend the electric driving range. Reference symbol list 1 hybrid vehicle 2 Internal combustion engine 3 Electric machine 4 drive batteries 5 Drive shaft 6 drive wheels 7 Drive arrangement 8 Clutch 9 gearboxes 10 Control unit / control 11 EGR (Exhaust Gas Recirculation) 12 turbochargers 13 fresh air coolers 14 Exhaust system 15 exhaust gas coolers 16 Control valve V Full load curve M A Drive component, drive torque M L Charging component, charging torque EGR SOCUG Exhaust gas recirculation rate for lower limit state of charge EGR SOCOGExhaust gas recirculation rate for upper limit state of charge EGR SOC50 Exhaust gas recirculation rate for 50% state of charge EGR L Charge exhaust gas recirculation rate B1 Starting operating point B2, B3 Charging point SOC max maximum charge level SOC min minimum charge level SOC UG lower limit state of charge SOC OG upper limit charge state SOC 50 50% charge level v F Driving speed

Claims

[1] Method for operating a hybrid vehicle (1) with a drive arrangement (7) comprising: an internal combustion engine (2) with exhaust gas recirculation (11), an electric machine (3) and a traction battery (4) wherein the internal combustion engine (2) generates an engine torque and the engine torque a drive component (M A ) and a charging component (M L ) includes, if the state of charge (SOC) of the traction battery (4) is less than an upper limit state of charge (SOC) OG ) and the electric machine (3) by means of the charging component (M L ) is driven by a generator, so that a charging current is generated to charge the drive battery (4), where the charging component (M L ) corresponding to a minimum EGR charging rate assigned to the state of charge (SOC). L ) is determined and thus the setting is based on a minimum EGR charging rate (EGR) assigned to the state of charge (SOC).L ) is controllable so that the charging component (M L ) with regard to a minimized NO X -Emission is discontinued where the charging component (M L ) is achieved via an increase in the load point, wherein the load point increase occurs in accordance with a change in at least one operating condition influencing the state of charge (SOC), wherein the load point increase is carried out from an initial operating point (B1) to a charging operating point (B2; B3), wherein the charging operating point (B2; B3) is selected such that a minimum EGR charging rate (EGR) specified for the current state of charge (SOC) is achieved. L ) is adhered to and the load point increase is terminated or limited as soon as the EGR rate available at the charging operating point exceeds this minimum EGR charging rate (EGR). L ) would fall below. [2] Method according to claim 1, wherein the internal combustion engine (2) is designed as a diesel engine. [3] Method according to claim 1, wherein the change in the operating state comprises one of the following changes: - Reduction of driving speed; - Increase in the energy demand of an electrical consumer; - Selection of a driving program with increased recharging requirements. [4] Method according to claim 3, wherein the assignment between the charging operating point (B2; B3) and the charge-dependent exhaust gas recirculation rate (EGR) L ) via a characteristic map. [5] Method according to any one of the preceding claims, wherein the method is performed between the upper limit state of charge (SOC) OG ) and a lower limit state of charge (SOC) UG ) is executable. [6] Control (10) of a drive arrangement configured to perform the method according to any one of claims 1 to 5. [7] Drive arrangement (7) with a control unit (10) according to claim 6. [8] Hybrid vehicle (1) with a drive arrangement (7) according to claim 7.

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