METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE WITH AN EXHAUST TURBOCHARGER AND AN ELECTRICALLY DRIVED COMPRESSOR AND DEVICES THEREOF OF IT

Description

[0001] The invention relates to a method for operating an internal combustion engine, a control system, an internal combustion engine and a motor vehicle.

[0002] In general, turbocharging systems for internal combustion engines, particularly in the automotive sector, are known for supplying cylinders of the internal combustion engines with air at overpressure for the combustion of fuel.

[0003] Turbochargers and compressors, for example, are known for providing air at positive pressure. Turbochargers have a compressor and can be equipped with their own drive for the compressor, e.g., an electric motor, or they can be powered by exhaust gas from the combustion engine, for example, with the exhaust gas driving a turbine that is operatively connected / coupled to the compressor via a shaft. The latter are also referred to as exhaust gas turbochargers.

[0004] Furthermore, turbochargers with a bypass valve, also called a wastegate, and / or those with variable turbine geometry, which have adjustable, non-rotating guide vanes, are known. The gas throughput can be varied by adjusting the angle of attack of the guide vanes. Typically, the angle of attack of the guide vanes is set so that, at low gas throughput and high power demand, the turbocharger's power is increased by reducing the flow cross-section, and at high gas throughput and low power demand, it is increased by increasing the flow cross-section. However, it is known, for example, from DE 10 2014 210 026 A1, that a strong closing of the guide vanes typically also leads to high exhaust backpressure and thus to gas exchange losses, which in turn counteracts the effective torque buildup of an internal combustion engine.

[0005] Exhaust gas turbochargers with auxiliary drives are also known, such as from DE 10 2014 221 331 A1. Here, an auxiliary drive is provided on a shaft of the exhaust gas turbocharger and is controlled depending on the current turbine geometry. It is activated and operated as needed, for example, when the variable turbine geometry is set for optimized efficiency, but insufficient drive power is available for the compressor.

[0006] From DE 10 2016 121 287 A1 and DE 10 2014 208 092 A1, it is also known to provide an electrically operated compressor for supercharging an internal combustion engine in addition to an exhaust gas turbocharger. According to DE 10 2014 208 092 A1, the electrically operated compressor is primarily activated when sufficient or even excess electrical energy is available for its operation. As a result, charge air is primarily compressed by the electrically operated compressor, and a control device of the exhaust gas turbocharger, e.g., a variable turbine geometry or a wastegate, can be adjusted to reduce exhaust gas backpressure in the exhaust gas turbocharger. This enables less charge exchange work and, accordingly, lower fuel consumption of the internal combustion engine.

[0007] EP 1 816 326 A1 describes a method for controlling a turbocharging system capable of supplying intake air to an internal combustion engine with a first and a second pumping capacity, and comprising a turbine that receives exhaust gases from the engine through a flow resistance and generates the first pumping capacity. The method comprises reducing the flow resistance and increasing the second pumping capacity as the desired intake air flow of the engine increases.

[0008] As mentioned above, the use of a VTG can lead to high exhaust gas pressures, which impair charge exchange within the cylinders. Here, the scavenging gradient (difference between intake manifold pressure and pressure in the exhaust manifold) is a characteristic parameter for the degree of backflow of exhaust gas into the combustion chamber. If this scavenging gradient is negative, a certain proportion of exhaust gas flows back into the combustion chamber during charge exchange, thus reducing the available volume for fresh air. This can certainly be desirable under stationary partial load in order to dethrottle the fresh air side and thus increase engine efficiency. However, in positive engine dynamics, a maximum amount of air in the combustion chamber is necessary in order to achieve the fastest possible torque build-up.

[0009] Methods for controlling / operating internal combustion engines with turbocharging systems comprising an exhaust gas turbocharger and an electrically driven compressor are generally known. The object of the present invention is to provide an improved method for controlling / operating an internal combustion engine with such a turbocharging system, in which the known disadvantages can be at least partially eliminated.

[0010] This object is achieved by the method according to the invention according to claim 1, the control unit according to claim 8, the internal combustion engine according to claim 9 and the motor vehicle according to claim 10. Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

[0011] A first aspect of the present disclosure relates to a method for operating an internal combustion engine with a charging system having an exhaust gas turbocharger (ATL) and an electrically driven compressor, wherein a power of the ATL is adjustable via an adjusting device, the method comprising: Determining a target boost pressure to achieve an increased target engine torque; adjusting the charging system to build up an actual boost pressure according to the target boost pressure; and setting a positive scavenging gradient in a cylinder of the internal combustion engine as a primary reference variable for controlling the charging system.

[0012] In the context of this invention, the terms control, adjustment, activation, control, and regulation encompass both control in the true sense (without feedback) and regulation (with one or more control loops). Therefore, the reference variable should also be understood as the target variable.

[0013] The combustion engine can, for example, be a gasoline engine and preferably a Miller engine.

[0014] The turbocharging system includes, among other things, an exhaust gas turbocharger (EGT) comprising a compressor and a turbine, the output of which can be adjusted via the control device. The control device can comprise a variable turbine geometry (VTG) as mentioned above, allowing the output of the EGT to be adjusted. Alternatively or additionally, the control device can comprise a wastegate.

[0015] In addition to the turbocharger, the turbocharging system features an electrically driven compressor. This can be driven, for example, by an electric motor. The electrically driven compressor is located downstream of the turbocharger's compressor (in an air supply line to the engine). Alternatively, the electrically driven compressor can also be located upstream of the turbocharger's compressor.

[0016] In a further alternative, the electrically driven compressor can be the compressor of the exhaust gas turbocharger, with the electric motor being coupled, in particular directly, to a shaft of the exhaust gas turbocharger. Thus, the power of the exhaust gas turbocharger, in particular the power of the exhaust gas turbocharger's compressor, is adjustable.

[0017] The increased target engine torque can, for example, be derived from a driver request expressed by a corresponding accelerator pedal operation. The increased target engine torque expresses that the driver's request is for acceleration.

[0018] Knowing the increased target engine torque allows a corresponding target boost pressure to be determined. The target boost pressure can, for example, be a function dependent on the engine torque and stored as a mathematical model and / or characteristic map or curve in a control system memory, e.g., an engine control unit.

[0019] To build up the target boost pressure, the turbocharging system is adjusted accordingly. This means, on the one hand, the output of the turbocharger is adjusted via the control device to build up the actual boost pressure, and, on the other hand, that the electrically driven compressor is operated at a corresponding output or at a corresponding target speed to build up the actual boost pressure so that the target boost pressure is achieved. For example, the electrically driven compressor can be operated via an electric motor, whereby the output of the electric motor and thus the compressor output can be adjusted.

[0020] When building up the actual boost pressure, a positive scavenging gradient is established in one cylinder of the combustion engine. The engine can have any number of cylinders, such as three, four, six, eight, twelve, or the like. The scavenging gradient for one cylinder of the engine is described here only as an example. "Scavenging gradient" refers to the pressure difference across the cylinder, i.e., the difference between the intake manifold pressure upstream of the cylinder and the pressure present within the engine's exhaust line downstream of the cylinder, upstream of the turbocharger's turbine. The latter is usually referred to as "exhaust backpressure."

[0021] As mentioned above, the purge gradient is adjusted to be positive. This means that the intake manifold pressure should be at least equal to, and usually greater than, the exhaust backpressure.

[0022] The positive purge gradient serves as the primary reference variable for controlling the boosting system. "Primary reference variable" here means that the boosting system is initially controlled / adjusted in such a way that the positive purge gradient is first set in the cylinder, and then the actual boost pressure is adjusted to the target boost pressure. The purge gradient within the cylinder is thus kept positive, while the actual boost pressure is adjusted to the target boost pressure. "Maintained positive" means that the purge gradient should be equal to or greater than 0 mbar.

[0023] By initially setting the positive scavenging gradient within the cylinder, it is possible to at least partially prevent exhaust gas from flowing back into the cylinder during a charge cycle. This allows for particularly effective engine torque buildup, as charge cycle losses due to exhaust gas flowing back (into the cylinder) are at least partially, if not completely, avoided by the positive scavenging gradient.

[0024] In one variant, the control device can include the variable turbine geometry mentioned above. This allows the turbocharger's performance to be particularly well adjusted.

[0025] Furthermore, the positive scavenging gradient can be achieved by operating the electrically driven compressor and the exhaust gas compressor, in particular its control device, in dependence on one another - i.e. in a coordinated manner.

[0026] In a further variant, which is not part of the invention, the adjustment of the charging system in a first operating state can comprise operation of the electrically driven compressor at an optimized maximum power and operation of the actuating device in a first open position. The first open position of the actuating device can, for example, comprise a position that is as largely open as possible. Alternatively, the first open position can also comprise only a briefly closed position, which then transitions to a position that is as largely open as possible. The optimized maximum power depends on a capacity of an energy storage device (e.g. battery), wherein the energy storage device supplies the (electric) machine for driving the electrically driven compressor. Depending on the capacity (available power) of the energy storage device, the electrically driven compressor can have various optimized maximum powers.In other words, the optimized maximum performance of the electrically driven compressor depends on the capacity of the energy storage system.

[0027] Operating the actuator in the first open position means that the exhaust gas flowing out of the cylinder only partially drives the turbine. If, for example, the actuator has the VTG, the VTG is set in the first open position such that a flow cross-section of the turbine is at least partially, and preferably fully, open. If, on the other hand, the actuator has the wastegate, the wastegate is set such that the exhaust gas flowing out of the cylinder bypasses / flows through the turbine at least partially, and preferably completely, via the wastegate. The first open position of the actuator allows a particularly low exhaust backpressure to be set.By operating the electrically driven compressor at its optimized maximum power and the actuator in its first open position, the positive purge gradient can be achieved particularly quickly in this first operating state of the charging system, while taking into account the capacity of the energy storage device.

[0028] Furthermore, in the first operating state, upon reaching the positive purge gradient in a second operating state, the output of the exhaust gas turbocharger can be reduced to build up the actual boost pressure and, accordingly, the output of the electrically driven compressor. In other words, as soon as the positive purge gradient is set, the output of the electrically driven compressor is reduced accordingly (and gradually), while in parallel the output of the exhaust gas turbocharger is reduced by means of the actuating device in such a way that the actual boost pressure continues to be built up. In particular, the exhaust gas turbocharger is set / operated in such a way that its output (in particular turbine output) is as high as possible without the purge gradient becoming negative, i.e. the exhaust gas back pressure is greater than the intake manifold pressure. The second operating state of the turbocharging system therefore allows the actual boost pressure to be built up (gradually) by the exhaust gas turbocharger.Accordingly, by reducing the power of the electrically driven compressor, access to the capacity of the energy storage system is also reduced and the energy storage system is protected accordingly.

[0029] In one variant, the electrically driven compressor can be operated according to a first control variable, and the exhaust gas turbocharger according to a second control variable. For this purpose, setpoints for the control variables are generated via a control / regulation system to meet the requirements of the engine torque buildup.

[0030] The first manipulated variable can also be determined using a first reduction factor and the second manipulated variable using a reduction factor. The reduction factors represent a measure by how much the power of the electrically driven compressor and the actuating device is reduced / throttled. For the electrically driven compressor, a high first reduction factor corresponds to a (comparatively) lower power. For the actuating device, a high second reduction factor means that the power of the exhaust gas turbocharger is (comparatively) lower. Thus, a high reduction factor for the (second) manipulated variable of the VTG corresponds to the VTG having a larger flow cross-section. A high second reduction factor for the (second) manipulated variable of the wastegate means that more of the exhaust gas flowing out of the cylinder is routed around the turbine.

[0031] Thus, in the first operating state when adjusting the turbocharging system, the first reduction factor (for the electrically driven compressor) is initially set between 20% and 40%, preferably between 25% and 35%, and particularly preferably at 30% (particularly depending on the capacity of the energy storage device), which is why the electrically driven compressor operates at its optimized maximum power. In contrast, the second reduction factor (for the turbocharger or its control device) is adjusted or selected such that the positive purge gradient is adjusted quickly and taking the capacity of the energy storage device into account.

[0032] In the second operating state, the first reduction factor is increased (continuously) and the second reduction factor is increased (correspondingly). The first reduction factor is increased to such an extent that the electrically driven compressor's power is zero, meaning it can be shut down. The electrically driven compressor is shut down particularly when the actual boost pressure reaches the target boost pressure. At the same time, in the second operating state, the second reduction factor is increased to such an extent that the exhaust gas turbocharger primarily builds up the actual boost pressure without creating a negative scavenging gradient. This enables an energetically improved, if not optimal, charge exchange and torque buildup.

[0033] In process variants, the first and / or second reduction factor can be determined depending on a purge gradient, in particular an actual purge gradient, a valve overlap, the capacity of the energy storage device (i.e., an energy storage device coupled to the electrically driven compressor), and / or a firing angle. Using the valve overlap, the opening and closing times of the inlet and outlet valves of a cylinder can be determined at least indirectly.

[0034] In other variants, the first or second reduction factor can be determined using characteristic maps and / or characteristic curves. These can be stored, for example, in an engine control unit and are therefore easily accessible and quickly retrievable.

[0035] Furthermore, the characteristic maps and / or characteristic curves can be determined empirically or created using, for example, mathematical models.

[0036] In an alternative, the second manipulated variable (for the actuating device) may be greater than a predetermined feedforward manipulated variable.

[0037] In one variant, the exhaust gas turbocharger's control device can include the wastegate described above. This allows for particularly good adjustment / adjustment of exhaust back pressure and the exhaust gas turbocharger's performance, similar to a VTG.

[0038] According to a second aspect, the present disclosure provides a controller for an internal combustion engine, the controller being configured to carry out the method according to any one of the preceding claims.

[0039] According to a third aspect, the present disclosure provides an internal combustion engine having a charging system as mentioned above and a controller according to the second aspect.

[0040] According to a fourth aspect, the present disclosure provides a motor vehicle having an internal combustion engine according to the third aspect.

[0041] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 schematically shows an embodiment of a motor vehicle with an internal combustion engine; Fig. 2 shows a determination of control variables for a charging system of the internal combustion engine according to a first variant; Fig. 3a shows a determination of control variables for the charging system of the internal combustion engine according to a second variant, which is not part of the invention; and Fig. 4 shows curves of operating parameters of the internal combustion engine and the charging system.

[0042] The Fig. 1 shows a motor vehicle 1 with an internal combustion engine 3 (combustion engine) and a charging system 8, which is controlled by a controller 21, which is embodied, for example, as an engine control unit. The charging system 8 comprises an exhaust gas turbocharger (ATL) 9 and an electrically driven compressor 11. An energy storage device 12 is coupled to the electrically driven compressor 11 to supply it with electrical energy for its operation.

[0043] The present invention is not limited to a specific type of motor, but is particularly designed as a Miller motor.

[0044] The engine 3 comprises one or more cylinders 4, one of which is shown here. The cylinder 4 is supplied with charged (combustion) air by the charging system 8. The exhaust gas turbine 9 comprises a compressor 13, which is driven or operated via a shaft 14 by a turbine (exhaust gas turbine) 15 with variable turbine geometry (VTG) 17. The turbine 15 is thus operatively connected / coupled to the compressor 13 via the shaft 14. The compressor 13 is arranged in an air line 5 to the engine 3, and the turbine 15 is arranged in an exhaust line 7, which discharges exhaust gas from the cylinder 4. The compressor 13 can thus be operated with the exhaust gas from the engine 3 by supplying the turbine 15 with the exhaust gas from the engine 3 and driving it thereby. Furthermore, the exhaust gas turbine 9 is coupled to the controller 21.

[0045] The VTG 17 is adjustable via an adjustment mechanism. A wastegate 19 can be provided as an alternative or in addition to the VTG 17. The exhaust gas supplied to the turbine 15 and, accordingly, the power of the compressor 13 can be adjusted via the adjustment mechanism (and / or the wastegate 19). Optionally, a multi-stage turbocharger unit can also be provided. In other words, multiple turbochargers 9 can also be provided.

[0046] In the example shown here, the electrically driven compressor 11 is arranged downstream of the compressor 13 and coupled to the controller 21. A supply line of the electrically driven compressor 11 branches off from the air line 5, and an outlet line of the electrically driven compressor 11 flows back into the air line 5 downstream of the electrically driven compressor 11. In other words, the electrically driven compressor 11 is arranged in a bypass line of the air line 5.

[0047] With the aid of an actuating arrangement (not shown) arranged accordingly in the air line 5, for example a 3-way control flap, the air supply to the electrically driven compressor 11 can be adjusted. Thus, downstream of the compressor 13, the air (supplied to the combustion engine 3) can be directed entirely through the electrically driven compressor 11. Furthermore, the actuating arrangement can be adjusted such that the air pre-compressed by the compressor 13 does not flow through the electrically driven compressor 11. The actuating arrangement can also (completely) prevent the air supply to the combustion engine 3, so that neither the air pre-compressed by the electrically driven compressor 11 nor by the compressor 13 can be supplied to the combustion engine 2. Finally, the actuating arrangement can be used to adjust the amount of air supplied to the combustion engine 3. The actuating arrangement can therefore perform a throttling function, as with a conventional throttle valve, for example.

[0048] In an alternative not shown, the electrically driven compressor 11 can also be arranged upstream of the compressor 13 in the air line 5.

[0049] In the air line 5, downstream of the compressor 13 and the electrically driven compressor 11, a charge air cooler (not shown) can be arranged, which cools the pre-compressed air supplied to the combustion engine 3.

[0050] In the Fig. 2 is shown schematically how a (target) manipulated variable u EV,opt for the electrically driven compressor 11 and a (target) manipulated variable u ATL,opt for the ATL 9 are determined. Thus, by means of a characteristic map 31, a reduction partial factor α p23 for the electrically driven compressor 11 and a second reduction partial factor β p23 for the ATL 9 are determined, which are dependent on an (actual) purge gradient p 23 and on a valve overlap vo. From a characteristic map 33, a reduction partial factor α KEV for the electrically driven compressor 11 and a reduction partial factor β KEV for the ATL 9 are determined, which are dependent on the capacity K ES of the energy storage device 12. Furthermore, a reduction factor α ia for the electrically driven compressor 11 and a reduction factor β ia for the ATL 9 are determined by means of a characteristic map 35, which are dependent on an ignition angle ia.

[0051] In block 37, the reduction subfactors α p23 and α KEV are offset against each other, in particular multiplied. The variable resulting from block 37 is then offset against the reduction subfactor α ia in block 39, in particular multiplied. This results in a reduction factor α for the electrically driven compressor 11 on the output side of block 39. This reduction factor α is converted / calculated into the manipulated variable u EV,opt by block 41. The manipulated variable u EV,opt is used to set the corresponding power of the electrically driven compressor 11, in particular its speed.

[0052] As described above for the reduction sub-factors α p23 , α KEV , α ia for the electrically driven compressor 11, the reduction sub-factors β p23 , β KEV , β ia for the ATL 9 are also calculated in corresponding blocks 43, 45, so that finally a reduction factor β is determined for the ATL 9. In block 51, the reduction factor β is converted / calculated into the reduction factor-dependent manipulated variable u lim,β for the ATL 9, i.e. for the VTG 17 and / or the wastegate 19.

[0053] Furthermore, in block 49, a pilot control variable u vs is determined or predetermined, which must at least reach and / or exceed the control variable u ATL,opt. For example, the pilot control variable u vs can be determined using the main turbocharger equation. To ensure that the control variable u ATL,opt reaches or exceeds the pilot control variable u vs, the reduction factor-dependent control variable u lim,β and the pilot control variable u vs are input to block 65 on the input side. In block 51, the larger of the two control variables u lim,β , u vs is selected, which then appears on the output side as the control variable u ATL. If the two control variables u lim,β , u vs are equal, u ATL,opt corresponds to their value. The corresponding power of the exhaust gas turbocharger 9, in particular its speed, is set using the control variable u ATL,opt. This means that the larger the manipulated variable u ATL,opt is, the higher the speed of the ATL 9.In other words, the larger the control variable u ATL,opt is, the smaller the flow cross-section of the VTG or the less exhaust gas flows through the wastegate 19.

[0054] From the characteristic maps 31, 33, 35, the reduction partial factors α p23 , α KEV , α ia for the electrically driven compressor 11 and the reduction partial factors β p23 , β KEV , β ia for the exhaust gas turbocharger 9 are stored together in the corresponding characteristic maps 31, 33, 35 in a dependent manner. The determined manipulated variables u EV,opt and u ATL,opt then adjust the electrically driven compressor 11 and the exhaust gas turbocharger 9, respectively, such that a positive purge gradient is initially achieved comparatively quickly, taking into account the capacity of the energy storage device. In the positive purge gradient range, the ATL 9 is then operated in such a way that its power (and therefore boost pressure build-up emanating from the ATL 9) is as high as possible without the purge gradient becoming negative, while at the same time the electrically driven compressor 11 is reduced in its power and thus also consumes less energy provided by the energy storage device.

[0055] In the Fig. 3a und 3b An alternative for determining the (target) control variables u EV,opt' for the electrically driven compressor 11 and u ALT,opt' for the ATL 9 is presented, which is not part of the invention. The difference to the approach from the Fig. 2 consists in that reduction sub-factors α p23' , α KEV' , α ia ', which correspond to the reduction sub-factors α p23' , α KEV' , α ia ', are determined from a characteristic map 61 or characteristic curves 63, 65, and the reduction sub-factors β p23 ', β KEV ', β ia' , which correspond to the reduction sub-factors β p23 , β KEV , β ia, from a characteristic map 81 or characteristic curves 83, 85.

[0056] This is how the Fig. 3a using the characteristic map 61, the reduction sub-factor α p23 ' for the electrically driven compressor 11 is determined, which depends on the (actual) purge gradient p 23 and on the valve overlap vo. The reduction sub-factor α KEV , which depends on the capacity K ES of the energy storage device 12, is determined from the characteristic curve 33. Furthermore, the reduction sub-factor α ia ', which depends on the ignition angle ia, is determined using the characteristic curve 65. In block 67, the reduction sub-factors α p23 ' and α KEV ' are offset against one another, in particular multiplied. The variable resulting from block 67 is then offset against the reduction sub-factor α ia ' in block 69, in particular multiplied. This results in a reduction factor α' for the electrically driven compressor 11 on the output side of block 69. This reduction factor α' is converted / calculated into the manipulated variable u EV,opt' by means of block 71.The control variable u EV,opt ' is used to set a corresponding power of the electrically driven compressor 11, in particular its speed.

[0057] The Fig. 3b schematically shows how the (setpoint) manipulated variable u ATL,opt ' for the ATL 9 is determined, whereby this manipulated variable u ATL,opt ' is determined in a similar way to the manipulated variable u EV,opt ' for the electrically driven compressor 11. Reduction partial factors β p23 ', β KEV ', β ia' are also determined, which depend on the (actual) scavenging gradient p 23 , the valve overlap vo, the capacity K ES and the ignition angle ia. A characteristic map 81 and characteristic curves 83, 85 have been set up accordingly for the determination of the reduction partial factors β p23 ', β KEV ', β ia '. As described above, the reduction sub-factors β p23 ', β KEV ', β ia' are also calculated, in particular multiplied, in corresponding blocks 87, 89, so that finally a reduction factor β' for the ATL 9 is determined.In block 91, the reduction factor β' is converted / calculated into the reduction-factor-dependent manipulated variable u lim,β ' for the exhaust gas turbocharger 9, i.e., for the VTG 17 and / or the wastegate 19. Block 49 is also used here to determine the pilot control variable u vs. As with block 51, block 95 ensures that of the manipulated variables u lim,β ' and u vs present on the input side of block 95, the larger one emerges as the output variable u ATL,opt '.

[0058] In the Fig. 3a und 3b the control variables u EV,opt' , u ATL,opt ' are determined without interdependence. This approach can indeed reduce the energy storage 12 compared to the approach from Fig. 2 comparatively higher load, but the control variables u EV,opt' , u ATL,opt' are determined particularly easily.

[0059] The Fig. 4shows qualitative and schematic curves for the scavenging gradient p 23 , for a speed n EV of the electrically driven compressor 11, for the manipulated variable u ATL for the ATL 9 and for the boost pressure p 2 . The speed n EV of the electrically driven compressor 11 can be adjusted via the manipulated variable u EV for the electrically driven compressor 11. The speed n EV therefore reflects the power of the electrically driven compressor 11. A target boost pressure curve p 2,Soll is shown, which is required to implement the driver command or the target engine torque, whereby the driver command is recorded at time t 0.

[0060] Furthermore, a curve for a scavenging gradient p 23,0 is shown in which the electrically driven compressor 11 is not operated. It can be seen that the scavenging gradient p 23,0 has a comparatively high deflection into the negative range and a minimum of the scavenging gradient p 23,0 occurs comparatively later in time. It can also be seen that the curve of the scavenging gradient P 23,0 only reaches the positive range at a comparatively late time t 3. This is because an actual boost pressure p 2,Ist,0 is only built up by the exhaust gas turbocharger 9 in this case. For this purpose, the actuating device 17, 19 (i.e. VTG 17 and / or wastegate 19) is adjusted via a corresponding manipulated variable u ATL,0 in order to temporarily increase the drive power of the turbine 15, in particular to maximize it, whereby the exhaust gas back pressure p 3 increases suddenly.In contrast, the actual boost pressure p 2,lst,0 is built up with a comparatively significant delay due to the high exhaust backpressure p 3 , since the exhaust backpressure p 3 reduces the fresh air charge in cylinder 4 by pushing back the exhaust gas. This results in the strong deflection of the scavenging gradient p 23,0 in the negative direction.

[0061] Furthermore, a non-optimized curve p 23,max is shown, in which the electrically driven compressor 11 is not operated optimally, i.e. at a non-optimized speed n EV,max, as a result of which it temporarily runs at its non-optimized maximum (speed) power. In other words, the electrically driven compressor 11 is operated at its component-dependent maximum speed. Furthermore, the exhaust gas turbocharger 9 is operated with a non-optimized manipulated variable u ATL,max, with which the exhaust gas turbocharger 9 is temporarily set to a maximum possible target speed. The non-optimized manipulated variable u ATL,max follows the same pattern as the manipulated variable u ATL,0 up to time t 1. As a result of the non-optimized manipulated variable u ATL,max, the exhaust gas turbocharger 9 or the actuating device 17 is temporarily set to its actuator limit - as was the case with the manipulated variable u ATL,0.As a result, a non-optimized boost pressure p 2,actual,max and, accordingly, the positive purge gradient p 23 are built up comparatively quickly at time t 1, while the curve for the non-optimized purge gradient p 23,max before time t 1 exhibits a comparatively small deflection into the negative range. Since the electrically driven compressor 11 is temporarily operated at non-optimized maximum power, the energy stored by the energy storage device (for the operation of the electrically driven compressor 2) is also consumed correspondingly faster.

[0062] An optimized (or, in other words, ideal) purge gradient p 23,opt is set by operating the electrically driven compressor 11 at an optimized speed n EV,opt.

[0063] This optimized speed n EV,opt is set according to the reduction factor α or the (reduction factor-dependent) manipulated variable u EV,opt. Meanwhile, the actuating device 17, 19 is operated with an optimized (possibly reduction factor-dependent) manipulated variable u ATL,opt, whereby the manipulated variable u ATL,opt is greater than the pre-control manipulated variable u vs at time t 0. The manipulated variable u ATL,opt follows the same pattern as the manipulated variable u ATL,0 up to time t 0. Compared to the pattern p 23,0, the optimized pattern for the purge gradient p 23,opt has a smaller deflection into a negative purge gradient range. Furthermore, the optimized purge gradient p 23,opt becomes positive at an earlier time t 2 and the purge gradient p 23,0 only at a later time t 3 .

[0064] It can also be seen that the speed n EV of the electrically driven compressor 11 is lower due to the optimized operation n EV,opt (or due to the faster adjustment of the positive purge gradient) compared to the non-optimized operation n EV,max. This means that in optimized operation, the optimized actual boost pressure p 2,Ist,opt tracks the target boost pressure p 2,Soll more slowly than the non-optimized actual boost pressure p 2,Ist,max. However, the optimized operation of the electrically driven compressor 11 takes the capacity of the energy storage device into account.

[0065] In all cases, the speed n EV of the electrically driven compressor 11 and the control variable u ATL for the ATL 9 are reduced as soon as the purge gradient p 23 reaches the positive range until the actual boost pressure p 2,actual, in particular essentially reaches the target boost pressure p 2,target. Subsequently, the control variable u ATL for the ATL 9 is set to a corresponding value for steady-state operation of the combustion engine 3 and, if necessary, the electrically driven compressor 11 is deactivated, i.e., its speed n EV is set to zero. List of reference symbols

[0066] 1 Motor vehicle 3 Combustion engine / combustion machine 4 Cylinder 5 Air line 7 Exhaust line 8 Charging system 9 Exhaust turbocharger 11 Electrically driven compressor 12 Energy storage device 13 Compressor 15 Turbine 17 VTG (adjustment mechanism) 19 Wastegate 21 Control unit 31, 33, 35 37, 39, 41, 43 Characteristic map 45, 47, 49, 51 Block 61 Characteristic map 63, 65 Characteristic curve 67, 69, 71 Block 81 Characteristic map 83, 83 87, 89, 91, Characteristic curve 95 Block α, α'first reduction factor α ia , α ia 'Partial reduction factor (ignition angle) α KEV , α KEV 'Partial reduction factor (capacity of electrically driven compressor) α p23 , α p23 'partial reduction factor (purge gradient) β, β'first reduction factor β ia , β ia 'partial reduction factor (ignition angle) β KEV , β KEV 'partial reduction factor (depending on the capacity of the energy storage) β p23 , β p23 'partial reduction factor (purge gradient) K ES capacity of the energy storage n EV,opt optimized speed of the electrically driven compressor n EV,max non-optimized speed of the electrically driven compressor p 2,setpoint target boost pressure P 2,actual,opt optimized actual boost pressure P 23,actual,max non-optimized actual boost pressure P 23,opt optimized purge gradient P 23,max non-optimized purge gradient u ATL,opt , U ATL,opt 'optimized (second) control variable for ATL U EV,opt , u EV,opt' optimized control variable for electrically driven compressor u ATL,max non-optimized (second) control variable for ATL,

Claims

1. Method for operating an internal combustion engine (3) having a supercharging system (8) that has an exhaust-gas turbocharger (ATL) (9) and an electrically driven compressor (11), wherein an output of the exhaust-gas turbocharger (9) can be adjusted by means of an actuating device (17, 19), the opening and closing times of input and output valves of a cylinder (4) of the internal combustion engine exhibit a valve overlap (vo) and wherein the actuating device (17, 19) comprises a variable turbine geometry (17) and / or a wastegate (19), wherein the method comprises the following steps: - determining a setpoint boost pressure (p2,set) for achieving an increased engine setpoint torque; - operating the electrically driven compressor (11) and the actuating device (17, 19) depending on each other in order to build up an actual boost pressure (P2,act) in accordance with the setpoint boost pressure (P2, set) and a positive scavenging gradient (p23) to be achieved; characterized in that the method further comprises the following steps: - determining a capacity (KES) of the power-supplying battery (12); - determining an optimized actuating variable (UATL,opt) for the actuating device (17, 19) in a first operating state depending on at least the positive scavenging gradient (p23) to be achieved and the capacity (KES) of the power-supplying battery (12); and - determining an optimized actuating variable (UEV,opt) for the electrically driven compressor (11) in the first operating state depending on at least the positive scavenging gradient (p23) to be achieved and the determined capacity (KES) of the power-supplying battery (12), wherein the optimized actuating variable (UATL,opt) for the actuating device (17, 19) and the optimized actuating variable (UEV,opt) for the electrically driven compressor (11) are determined based on common characteristic maps and / or characteristic curves (31, 33) in order to operate the electrically driven compressor (11) and the actuating device (17, 19) depending on each other.

2. Method according to Claim 1, wherein, in the first operating state when the positive scavenging gradient (p23) is achieved, in a second operating state an output of the exhaust-gas turbocharger (9) for building up the actual boost pressure (p2,act) and accordingly the output of the electrically driven compressor (11) are reduced.

3. Method according to Claim 1, wherein the optimized actuating variable (UEV,opt) for the electrically driven compressor (11) can be determined on the basis of a first reduction factor (α) and the optimized actuating variable (UATL, opt, UATL,opt') for the actuating device (17, 19) can be determined on the basis of a second reduction factor (β).

4. Method according to Claim 3, wherein the first and / or the second reduction factor (α, β) are / is determined depending on the scavenging gradient (p23) to be achieved, the valve overlap (vo), the capacity (KEV) of the power-supplying battery (12) and an optional ignition angle (ia).

5. Method according to Claim 4, wherein the first and the second reduction factor (α, β) are determined by means of characteristic maps and / or characteristic curves.

6. Method according to Claim 5, wherein the characteristic maps and / or characteristic curves can be empirically determined or created by means of models.

7. Method according to any of Claims 1 to 6, wherein the optimized actuating variable (UATL,opt, UATL,opt') for the actuating device (17, 19) is greater than a predetermined pilot control actuating variable (uVS).

8. Engine controller for an internal combustion engine (3), wherein the engine controller is configured to execute the method according to any of the preceding claims.

9. Internal combustion engine (3) having a supercharging system (8) that has an exhaust-gas turbocharger, ATL, (9) and an electrically driven compressor (11), wherein an output of the exhaust-gas turbocharger (9) can be adjusted by means of an actuating device (17, 19), the opening and closing times of input and output valves of a cylinder (4) of the internal combustion engine (3) exhibit a valve overlap (vo), the actuating device (17, 19) comprises a variable turbine geometry (17) and / or a wastegate (19), and the internal combustion engine (3) is supplied with power by a battery (12), and an engine controller according to Claim 8.

10. Motor vehicle (1) having an internal combustion engine (3) according to Claim 9 and a battery (12) supplying power to the internal combustion engine (3).