METHOD FOR DETERMINING A BASE CHARGE PRESSURE OF A GAS SYSTEM OF AN INTERNAL COMBUSTION ENGINE AND ENGINE CONTROL FOR EXECUTING SUCH A METHOD

Description

[0001] The invention relates to a method for determining a base boost pressure of a gas supply system of an internal combustion engine and an engine control unit for carrying out such a method. In particular, the invention relates to a method for determining a base boost pressure of a gas supply system of an internal combustion engine of a motor vehicle, for example a gasoline engine or a diesel engine of a motor vehicle, and an engine control unit for carrying out such a method.

[0002] In modern motor vehicle engines, cylinder filling plays a significant role, as it can considerably influence engine efficiency. Therefore, engines typically have actuators to regulate cylinder filling (cylinder filling devices). Examples of cylinder filling devices include a throttle valve and a turbocharger, preferably a turbocharger with a wastegate or a variable geometry turbocharger (VTG turbocharger).

[0003] The throttle valve and the turbocharger can be adjusted simultaneously, i.e., in parallel operation. This can mean that both actuators actively work against each other. For example, the turbocharger might increase the boost pressure while the throttle valve restricts it, thus working against it, leading to increased fuel consumption. This operating condition must be prevented.

[0004] However, if the two control mechanisms can be clearly distinguished from one another (deactivation and activation), the turbocharger only operates when the demand for increased boost pressure can no longer be met by further opening the throttle valve. This handover between the control mechanisms can occur at the base boost pressure threshold. Below this pressure threshold, the throttle valve operates; above it, the boost pressure control system, via the turbocharger, takes over.

[0005] It is therefore necessary to determine the current base boost pressure. This can be done, for example, by modeling the base boost pressure, as mentioned in DE 102 43 268 A1. DE 102 35 013 A1 describes a method for determining a target boost pressure using a speed-dependent base value.

[0006] US Patent 2011 / 0098876 A1 discloses a method for diagnosing the intake manifold of an internal combustion engine equipped with a compressor. The method verifies whether at least one predefined activation condition is met. A boost pressure downstream of the compressor is detected or determined. An adaptation curve or map is adjusted based on the engine speed and boost pressure if at least one activation condition is met. A gradient is determined that is representative of the slope of the adaptation curve or map. From the determined gradient, conclusions are drawn about a fault in the intake manifold of the internal combustion engine.

[0007] Furthermore, US 2015 / 0101578 A1 describes a method for estimating the boost pressure of a turbocharger. A throttle valve temperature is estimated as a function of engine operating parameters. An intake air mass flow rate and an exhaust gas mass flow rate are estimated as a function of the throttle valve temperature. A turbine inlet pressure and a turbine outlet pressure are estimated as a function of the engine operating parameters. The turbine speed is estimated as a function of the intake air mass flow rate, the exhaust gas mass flow rate, and the turbine inlet and outlet pressures. The boost pressure is estimated as a function of the turbine speed. A control signal for controlling the turbocharger is generated based on the estimated boost pressure.

[0008] However, the known base boost pressure models only possess moderate accuracy. Since the base boost pressure range introduces a degree of uncertainty, the software is calibrated to ensure good drivability, typically at the cost of both controllers operating in parallel, resulting in slightly increased fuel consumption. This compromise leads to problems, particularly with engines based on the Miller combustion process, as the base boost pressure significantly influences the engine design.

[0009] The object of the present invention is to provide a method and a motor control system that at least partially overcome the aforementioned disadvantages.

[0010] This problem is solved by the inventive method for determining the base boost pressure according to claim 1, the engine control according to claim 13, an internal combustion engine according to claim 14 and a motor vehicle with an internal combustion engine according to claim 15.

[0011] According to a first aspect, the invention relates to a method for determining a base boost pressure of a gas supply system of an internal combustion engine with a turbocharger comprising a compressor, a turbine, a shaft connecting the compressor and the turbine and a turbocharger actuator for varying a flow velocity through the turbine or a pressure ratio across the turbine, and wherein the gas supply system comprises a throttle valve arranged downstream of the compressor in the flow direction, comprising: Calculating an exhaust back pressure with the turbocharger actuator in the open position, wherein the flow velocity through or the pressure ratio across the turbine is minimal in the open turbocharger actuator position, and wherein the exhaust back pressure is a pressure upstream of the turbine; and determining the base boost pressure as a function of the calculated exhaust back pressure with the turbocharger actuator in the open position.

[0012] According to a second aspect, the invention relates to an engine control system for an internal combustion engine with a gas supply system comprising a turbocharger, which has a compressor, a turbine, a shaft connecting the compressor and the turbine, and a turbocharger actuator for varying a flow velocity through the turbine of the internal combustion engine or a pressure ratio across the turbine, and wherein the gas supply system comprises a throttle valve arranged downstream of the compressor in the flow direction, which is configured to perform a method for determining a base boost pressure of the gas supply system of the internal combustion engine according to the first aspect, comprising: Calculating an exhaust back pressure with the turbocharger actuator in the open position, wherein the flow velocity through or the pressure ratio across the turbine is minimal in the open turbocharger actuator position; and determining the base boost pressure as a function of the calculated exhaust back pressure with the turbocharger actuator in the open position.

[0013] According to a third aspect, the invention relates to an internal combustion engine with an engine control system according to the second aspect.

[0014] According to a fourth aspect, the invention relates to a motor vehicle with an internal combustion engine according to the third aspect.

[0015] Further advantageous embodiments of the invention will become apparent from the dependent claims and the following description of preferred embodiments of the present invention. The present invention relates to a method for determining a base boost pressure of a gas supply system of an internal combustion engine with a turbocharger comprising a compressor, a turbine, a shaft connecting the compressor and the turbine, and a turbocharger actuator for varying a flow velocity through the turbine or a pressure ratio across the turbine. The gas supply system further comprises a throttle valve, an intake manifold, an exhaust manifold, and other gas-carrying components.

[0016] The intake manifold can be connected to the internal combustion engine, for example, a gasoline engine, a Miller cycle engine, or a diesel engine, to supply it with fresh air. The intake manifold houses the turbocharger compressor and, downstream in the direction of airflow, the throttle valve. The pressure after the compressor and before the throttle valve is referred to as boost pressure. The exhaust manifold can be connected to the internal combustion engine to expel exhaust gases. The base boost pressure is the boost pressure present when the throttle valve is fully open and the turbocharger actuator is in the open position where the flow velocity through the turbine or the pressure ratio across the turbine is minimal.Accordingly, the base boost pressure can differ from the actual boost pressure if the turbine is in a different turbocharger actuator position than the fully open position. The base boost pressure can also depend on the turbine geometry of the turbocharger. In other words, the base boost pressure is defined as the pressure that exists before the throttle valve when the turbocharger is not being actuated. It therefore approximates a naturally aspirated engine operating at full load, with the caveat that the turbocharger also generates a certain amount of compression even without being actuated. This raises the base boost pressure, depending on the turbocharger geometry, to a greater or lesser extent above ambient pressure.

[0017] According to the inventive method, an exhaust backpressure is calculated, and in particular modeled, when the turbocharger actuator is in the open position, wherein the flow velocity through or the pressure ratio across the turbine is minimal in the open turbocharger actuator position. In the open actuator position, a boost pressure component attributable to the turbocharger can be minimized. For example, in the open actuator position, a flow cross-section through and / or around the turbine can be maximized, thereby minimizing the flow velocity and, if necessary, minimizing the boost pressure component of the turbocharger. The exhaust backpressure is the pressure upstream of the turbine.

[0018] According to the inventive method, the base boost pressure is then determined as a function of the calculated exhaust back pressure with the turbocharger actuator in the open position. The base boost pressure can also depend on the currently prevailing conditions of the gas flow system. The determination of the base boost pressure is explained in detail below.

[0019] The base boost pressure can be determined very reliably by measuring the exhaust back pressure when the turbocharger actuator is in the open position, which was determined for the open position of the turbocharger.

[0020] In some embodiments, the turbocharger can be a variable-geometry turbocharger (VTG turbocharger) with adjustable guide vanes as actuators, and the guide vanes can be in their steepest position when the turbocharger actuator is open. Alternatively or additionally, the turbocharger can have a wastegate with a valve as an actuator that is fully open when the turbocharger actuator is open.

[0021] In some embodiments, the exhaust backpressure can be determined using an exhaust backpressure model with the turbine actuator in the open position or using a wastegate model with the turbine actuator in the open position. In particular, if the turbocharger is a variable geometry turbocharger with adjustable guide vanes as actuators, the exhaust backpressure can be determined using an exhaust backpressure model based on a turbine with guide vanes in the steepest possible position. If the turbocharger has a wastegate with a valve as the actuator, the exhaust backpressure can be determined using a wastegate model based on a turbocharger with the wastegate fully open.

[0022] In some embodiments, the method can further determine a turbine speed at an open turbocharger actuator position, depending on the modeled exhaust back pressure. The base boost pressure can then be determined as a function of the determined turbine speed at the open turbocharger actuator position.

[0023] In some embodiments, the turbine speed can be determined by determining a pressure ratio across the turbine at the open turbocharger actuator position, an exhaust gas mass flow rate (also called turbine mass flow rate) at the open turbocharger actuator position, and the turbine speed as a function of the determined pressure ratio and the determined exhaust gas mass flow rate. The pressure ratio is modeled, for example. The exhaust gas mass flow rate can also be modeled. Instead of the exhaust gas mass flow rate, a normalized exhaust gas mass flow rate can be determined and used to determine the turbine speed. To determine the normalized exhaust gas mass flow rate, an exhaust gas temperature at the open turbocharger actuator position can be determined, in particular modeled, and the normalized exhaust gas mass flow rate can be used. ṁ A,norm from the exhaust gas mass flow ṁ Aand the exhaust gas temperature TA based on proportionality m ˙ A , norm ≈ m ˙ A T A will be calculated.

[0024] In some embodiments, the turbine speed can be determined using a speed model, in particular a turbine map. The turbine map can be calculated from the pressure ratio at the open turbocharger actuator position and the exhaust gas mass flow rate. The output is then the turbine speed at the open turbocharger actuator position. Additionally, the inputs can be normalized to the exhaust gas temperature. The base boost pressure can be reliably determined from the modeled exhaust back pressure at the open turbocharger actuator position, which is part of the pressure ratio.

[0025] The turbine speed can therefore depend on exhaust back pressure when the turbocharger actuator is open, the pressure after the turbine, the exhaust mass flow, the exhaust temperature and the open turbocharger actuator position.

[0026] In some embodiments, the compressor speed when the turbocharger actuator is open can correspond to the turbine speed when the turbocharger actuator is open. This results from the fact that the compressor and the turbine are rigidly coupled via the shaft and therefore always rotate at the same speed. Thus, for example, using a speed model on the turbine side, and calculating an exhaust backpressure model when the turbocharger actuator is open, the following balance can be achieved for the compressor side: n T = n V , where n T the rotational speed of the turbine (turbine speed) and n VThe compressor speed is the speed of the compressor. A special feature here is that the turbine speed, and consequently the compressor speed, corresponds to the state of an open turbocharger and not necessarily to the current value of the turbine or compressor speed.

[0027] In some embodiments of the method, the compressor speed at the open turbocharger actuator position can be determined as a function of the modeled exhaust back pressure at the open turbocharger actuator position, particularly in a manner different from that described above, for example, via a suitable characteristic map. The base boost pressure can then be determined as a function of the determined compressor speed at the open turbocharger actuator position. Again, the use of the modeled exhaust back pressure enables a reliable determination of the base boost pressure.

[0028] In some embodiments, the method allows for the determination of a fresh air mass flow rate with the turbocharger actuator in the open position. Depending on the compressor speed with the turbocharger actuator in the open position and the fresh air mass flow rate, a pressure ratio across the compressor with the turbocharger actuator in the open position can then be determined. The base boost pressure can then be determined as a function of this pressure ratio. Alternatively, a normalized fresh air mass flow rate can be determined and used to determine the base boost pressure. To determine the normalized fresh air mass flow rate, a fresh air temperature can be determined with the turbocharger actuator in the open position, and the normalized fresh air mass flow rate can then be calculated. ṁ FL,norm from the fresh air mass flow ṁ FL and the fresh air temperature T FL based on proportionality m ˙ FL , norm ≈ m ˙ FL T FL will be calculated.

[0029] In some embodiments, the fresh air mass flow rate can be measured. For example, the fresh air mass flow rate can be measured with an air mass sensor, preferably a hot-film air mass meter (HFM). Alternatively, the fresh air mass flow rate can be modeled, for example, using pressure-based volumetric sensing.

[0030] In some embodiments, the pressure ratio can be determined using a compressor map. Using the calculated compressor speed and the fresh air mass flow rate, the pressure ratio across the compressor can be determined with the aid of the compressor map.

[0031] In some embodiments, the method allows for the determination of a pre-compressor pressure upstream of the compressor. The base boost pressure can then be determined as a function of the pressure ratio with the turbocharger actuator in the open position and the determined pre-compressor pressure. Specifically, the determined pressure ratio across the compressor is multiplied by the pre-compressor pressure to obtain the base boost pressure, i.e., the pressure downstream of the compressor with the turbocharger actuator not activated.

[0032] The pre-compressor pressure can be determined based on the ambient pressure. For example, the pressure before the compressor can be modeled using an ambient pressure-based model. A pressure loss corresponding to the passive flow resistance of an air filter in the intake duct can then be modeled and subtracted from this pressure.

[0033] The base boost pressure can therefore depend on the compressor speed with the turbocharger actuator in the open position, the pressure before the compressor, the fresh air mass flow rate, and the fresh air temperature.

[0034] By reliably determining the base boost pressure, the need for boost pressure control can be reduced, because the turbocharger is only engaged when the throttle valve can no longer provide sufficient torque. Consequently, less throttle is applied, which can reduce fuel consumption.

[0035] In summary, the procedure can be based on the following steps: First, the exhaust back pressure is determined with the turbocharger actuator in the open position. The turbine speed can then be determined. This can be calculated using the turbine map via the input variables: the pressure ratio (open) across the turbine with the turbocharger actuator in the open position and the exhaust mass flow rate. The pressure ratio used to determine the speed is therefore the pressure ratio in the case where the position of a variable turbine geometry (VTG) or the opening degree of a wastegate (bypass around the turbine), which are included in the pressure ratio calculation, are fixed at a fully open value. Therefore, it is preferable not to determine the current turbine speed, but rather the turbine speed (open) for the fully open state of the VTG (variable turbine geometry) or the wastegate. The exhaust mass flow rate and the pressure ratio across the turbine can be modeled.The turbine speed (open) can then be transferred to the compressor speed (open). The pressure ratio across the compressor can then be determined. This can be done using a compressor map that incorporates the fresh air mass flow (modeled or measured) and the compressor speed (open) at the open turbocharger actuator position. Finally, the base boost pressure is determined. This can be derived from the pressure upstream of the compressor (corrected ambient pressure) and the pressure ratio (open) across the compressor.

[0036] The present invention reliably models a boundary between the use of the turbocharger and the use of the throttle valve, and accurately reflects thermodynamic boundary conditions. This stabilizes the charge control during the transition period and reduces fuel consumption.

[0037] The present invention further relates to an engine control system for an internal combustion engine with a gas flow system comprising a turbocharger, a compressor, a turbine, a shaft connecting the compressor and the turbine, and a turbocharger actuator for varying a flow velocity through or a

[0038] The pressure ratio across the turbine is specified, and the gas supply system comprises a throttle valve arranged downstream of the compressor in the flow direction. The gas supply system can be configured as described above. The engine control unit is configured to perform a method for determining a base boost pressure of the gas supply system of the internal combustion engine, in which an exhaust back pressure is calculated when the turbocharger actuator is in the open position, wherein the flow velocity through or the pressure ratio across the turbine is minimal in the open turbocharger actuator position, and wherein the exhaust back pressure is a pressure upstream of the turbine, and the base boost pressure is determined as a function of the calculated exhaust back pressure when the turbocharger actuator is in the open position.The engine control unit is specifically designed to determine a turbine speed based on the exhaust back pressure, to transfer the turbine speed to a compressor speed, and to determine the base boost pressure based on the compressor speed. Preferably, the engine control unit can be configured to perform the above-described method for determining the base boost pressure.

[0039] The engine control unit may include a processor, in particular a microprocessor, for executing the above-described method for determining the base boost pressure. The control unit may also include a memory, for example a data memory, in which maps, models, and other parameters and information necessary for executing the above-described method for determining the base boost pressure can be stored. Furthermore, the engine control unit may have a data input for receiving measurement data or other parameters and a data output for outputting the determined base boost pressure or for controlling a throttle valve and the turbocharger.

[0040] The present invention further relates to an internal combustion engine with a gas flow system comprising a turbocharger, which includes a compressor, a turbine, a shaft connecting the compressor and the turbine, and a turbocharger actuator for varying a flow velocity through the turbine or a pressure ratio across the turbine, wherein the gas flow system comprises a throttle valve arranged downstream of the compressor in the flow direction, and wherein the internal combustion engine has the engine control described above. The internal combustion engine can be or include a gasoline engine, a Miller cycle engine, or a diesel engine.

[0041] The present invention further relates to a motor vehicle with the internal combustion engine described above.

[0042] Exemplary embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. These show: Fig. 1 shows a schematic diagram of an internal combustion engine and a gas supply system thereof with a turbocharger with wastegate; Fig. 2 shows a schematic flow diagram of a method for determining the base boost pressure of the gas supply system of the internal combustion engine. Fig. 1 Fig. 3 a schematic flowchart of a method for determining a turbine speed; Fig. 4 a schematic representation of a turbine characteristic map with the wastegate valve open; Fig. 5 a schematic flowchart of a method for determining a pressure ratio; Fig. 6 a schematic representation of a compressor characteristic map with the wastegate valve open; and Fig. 7 a schematic diagram of an internal combustion engine and a gas supply system thereof with a turbocharger with variable turbine geometry.

[0043] Fig. 1Figure 1 shows an internal combustion engine 1 and a first embodiment of a gas supply system 2 for the internal combustion engine 1. The gas supply system 2 comprises an exhaust gas turbocharger 20, a throttle valve 21, an intake port 22, and an exhaust port 23. The internal combustion engine 1 is connected to the intake port 21 and the exhaust port 23. The exhaust gas turbocharger 20, which is provided for regulating boost pressure in the intake port 22, comprises a turbine 200, a wastegate 201, and a compressor 202, which is connected to the turbine 200 via a shaft. The turbine 200 is arranged in the exhaust port 23 and is driven by exhaust gas flowing from the internal combustion engine 1. The wastegate 201 connects a section of the exhaust duct 23 upstream of the turbine 200 with a section of the exhaust duct 23 downstream of the turbine 200 to divert exhaust gas past the turbine 200.To regulate the exhaust gas bypassing the turbine 200, the wastegate 201 has a wastegate valve (not shown). The compressor 202 is located in the intake duct 22 and, driven by the turbine 200, compresses the fresh air in the intake duct 22. The throttle valve 21 is located downstream of the compressor 202 of the exhaust gas turbocharger 20 in the intake duct 22 in the direction of flow and is designed to control the boost pressure in the intake duct 22.

[0044] Fig. 1 Figure 3 further shows an engine control unit 3. The engine control unit 3 is connected to the internal combustion engine 1, the wastegate valve in wastegate 201, and the throttle valve 21. The engine control unit 3 is configured to control the internal combustion engine 1, the wastegate valve, and the throttle valve 21. For this purpose, the engine control unit 3 determines a base boost pressure of the gas supply system 2 according to the value shown in Figure 3. Figs. 2 to 6described method 4 for determining the base boost pressure and uses this for controlling the internal combustion engine 1 and the gas supply system 2, i.e. the wastegate valve and the throttle valve.

[0045] Fig. 2 shows a flowchart of a procedure 4 for determining the base boost pressure in which in Fig. 1 Gas flow system 2 shown.

[0046] At 40, an exhaust back pressure in front of the turbine is modeled in a state where the wastegate valve is fully open and the flow velocity through the turbine and wastegate is minimal.

[0047] At 41, the turbine speed is determined as a function of the exhaust back pressure with the wastegate valve fully open. For example, the turbine speed can be determined using the value with reference to Fig. 3 and Fig. 4 The procedure described above can be determined using an example.

[0048] At 410 in Fig. 3A pressure in the exhaust gas channel downstream of the turbine is modeled. From the exhaust back pressure with the wastegate valve fully open and the modeled pressure downstream of the turbine, the pressure ratio across the turbine is calculated at step 411. This is done by dividing the exhaust back pressure with the wastegate valve fully open by the modeled pressure downstream of the turbine.

[0049] In step 412, the exhaust gas mass flow through the exhaust duct or turbine and the wastegate is modeled. In step 413, the exhaust gas temperature in the exhaust duct is determined. From the exhaust gas mass flow and the exhaust gas temperature, the normalized exhaust gas mass flow is then determined in step 414.

[0050] At 415, the turbine speed is determined from the pressure ratio with the wastegate valve fully open using a turbine map. The turbine map is plotted against the pressure ratio with the wastegate valve fully open and the standardized exhaust gas mass flow, allowing the turbine speed to be read. Fig. 4A schematic representation of a turbine characteristic map is shown as an example. The pressure ratio pvT / pnT is plotted on a horizontal axis (x-axis), and the normalized exhaust gas mass flow rate ṁA,norm is plotted on a vertical axis (y-axis). The turbine characteristic map shows the change in the normalized exhaust gas mass flow rate ṁA,norm as a function of the pressure ratio pvT / pnT for different turbine speeds nT. For each turbine speed nT, the exhaust gas mass flow rate ṁA,norm increases with decreasing slope as the pressure ratio pvT / pnT increases. The higher the turbine speed nT, the higher the exhaust gas mass flow rate ṁA,norm. The turbine speed nT can be determined from this turbine characteristic map.

[0051] At 42 in Fig. 2The turbine speed nT is transferred to the compressor speed nV when the wastegate valve is fully open. Since the turbocharger shaft rigidly connects the turbine and the compressor, the turbine speed nT always corresponds to the compressor speed nV, and the two speeds can be considered equivalent.

[0052] At 43, the base boost pressure is determined as a function of the compressor speed. For example, the base boost pressure can be determined using the formula with reference to Fig. 5 and Fig. 6 The procedure described above can be determined using an example.

[0053] At 430, the fresh air mass flow rate through the intake duct or compressor is measured. Alternatively, the fresh air mass flow rate can also be modeled. At 431, the fresh air temperature of the fresh air flowing through the intake duct or compressor is measured. From the fresh air mass flow rate and the fresh air temperature, the normalized fresh air mass flow rate is determined at 432.

[0054] In the 433, a compressor map is used to determine the pressure ratio across the compressor with the wastegate valve fully open, depending on the compressor speed and the standardized fresh air mass flow rate. The compressor map is plotted against the standardized fresh air mass flow rate and the pressure ratio across the compressor, allowing the pressure ratio to be read for different compressor speeds. Fig. 6A schematic representation of a compressor characteristic curve is shown as an example. The normalized fresh air mass flow rate ṁFL,norm is plotted on a horizontal axis (x-axis), and the pressure ratio pnV / pvV across the compressor is plotted on a vertical axis (y-axis). The characteristic curve shows the change in the pressure ratio as a function of the pressure ratio prV / pvV for different compressor speeds nV. For each compressor speed, the pressure ratio pnV / pvV decreases with increasing slope as the normalized fresh air mass flow rate ṁFL,norm increases. The higher the compressor speed nV, the higher the fresh air mass flow rate ṁFL,norm. From this compressor characteristic curve, the pressure ratio pnV / pvV for the compressor speed nV with the wastegate valve fully open can be determined.

[0055] In section 434, a model is used to determine the pressure in the intake duct upstream of the compressor. This pressure is modeled based on ambient pressure, from which a pressure loss is modeled and subtracted, corresponding to the passive flow resistance of an air filter in the intake duct.

[0056] At 435, the base boost pressure is calculated from the pressure ratio above the compressor and the pressure before the compressor. This is done by multiplying the pressure ratio above the compressor by the pressure before the compressor.

[0057] The specified base boost pressure can then be used to control the throttle valve, the turbocharger and the internal combustion engine.

[0058] Fig. 7 Figure 1 shows an internal combustion engine 1 and a second embodiment of a gas supply system 2' of the internal combustion engine 1. The gas supply system 2' has, instead of the one shown in Figure 1, a different gas supply system 2'. Fig. 1The turbocharger 20 with wastegate 201 shown is a VTG turbocharger 20' (variable turbine geometry turbocharger). The VTG turbocharger 20' is equipped with variable turbine geometry, so that the turbine blades (not shown) of the turbine 200' can be adjusted between a flattest possible setting and a steepest possible setting. In the flattest possible setting, the exhaust back pressure in front of the turbine 200 is at its maximum, while in the steepest possible setting, the exhaust back pressure in front of the turbine 200 is at its minimum.

[0059] The engine control unit 3' is configured to execute a procedure for determining the base boost pressure. This is done with reference to Figs. 2 to 6The described procedure is carried out analogously, whereby the exhaust back pressure is assumed to be at the steepest possible setting of the guide vanes instead of the exhaust back pressure with the wastegate valve fully open. Based on the determined base boost pressure, the engine control unit 3' then controls the turbine guide vanes, the throttle valve, and the internal combustion engine. Reference symbol list

[0060] 1 Internal combustion engine 2 Gas flow system 20, 20' Turbocharger 200, 200' Turbine 201 Wastegate 202, 202' Compressor 21 Throttle valve 22 Intake manifold 23 Exhaust manifold 24 Flow direction 3,3'Engine control 4Method for determining the base boost pressure 40Modeling the exhaust back pressure with the wastegate valve fully open 41Determining the turbine speed as a function of the exhaust back pressure 410Determining the pressure before the turbine 411Calculating the pressure ratio across the turbine 412Modeling the exhaust mass flow 413Determining the exhaust temperature 414Determining the normalized exhaust mass flow 415Determining the turbine speed using a turbine map 42Transferring the turbine speed to the compressor speed 43Determining the base boost pressure as a function of the compressor speed 430Measuring the fresh air mass flow 431Measuring the fresh air temperature 432Determining the normalized fresh air mass flow 433Determining a pressure ratio using a compressor map 434Determining the pressure before the compressor 435Calculating the base boost pressure,

Claims

1. Method for determining a base boost pressure of a gas conduction system (2) of an internal combustion engine (1) with a turbocharger (20) which has a compressor (202), a turbine (200), a shaft connecting the compressor (202) and the turbine (200), and a turbocharger control element for varying a flow velocity through the turbine (200) or a pressure ratio across the turbine (200), wherein the gas conduction system (2) comprises a throttle valve (21) arranged downstream of the compressor (202) in the flow direction, the method comprising: calculating (40) an exhaust gas back-pressure with the turbocharger control element in the open position, wherein the flow velocity through or the pressure ratio across the turbine (200) is minimal in the open turbocharger control element position, wherein the exhaust gas back-pressure is a pressure upstream of the turbine (200); and determining (43) the base boost pressure on the basis of the calculated exhaust gas back-pressure with the turbocharger control element in the open position, wherein the base boost pressure is a boost pressure that prevails when the throttle valve (21) of the gas conduction system (2) is maximally open and the turbocharger control element is in the open turbocharger control element position, and the boost pressure corresponds to a pressure downstream of the compressor (202) and upstream of the throttle valve (21), and wherein the method is performed by means of an engine control unit.

2. Method according to claim 1, wherein the turbocharger is a variable-geometry turbocharger (20') with adjustable guide vanes as control elements and the guide vanes are in the steepest position when the turbocharger control element is in the open position; and / or the turbocharger (20) has a wastegate (201) with a valve as a control element, which valve is fully open with the turbocharger control element in the open position.

3. Method according to claim 1 or 2, wherein the exhaust gas back-pressure is determined by means of an exhaust gas back-pressure model with the turbine control element in the open position or by means of a wastegate model with the turbine control element in the open position.

4. Method according to claim 3, further comprising: determining (41) a turbine speed with the turbocharger control element in the open position on the basis of the modeled exhaust gas back-pressure with the turbocharger control element in the open position, wherein the base boost pressure is determined on the basis of the determined turbine speed with the turbocharger control element in the open position.

5. Method according to claim 4, further comprising: determining (411) a pressure ratio across the turbine on the basis of the modeled exhaust gas back-pressure with the turbocharger control element in the open position; determining (412, 413, 414) an exhaust gas mass flow rate, in particular a normalized exhaust gas mass flow rate; and determining (415) the turbine speed on the basis of the pressure ratio and the exhaust gas mass flow rate.

6. Method according to either of claims 4 and 5, wherein the turbine speed is determined (415) by means of a speed model, in particular a turbine characteristic map.

7. Method according to any of claims 4 to 6, wherein a compressor speed with the turbocharger control element in the open position corresponds to a turbine speed with the turbocharger control element in the open position.

8. Method according to claim 3, comprising: determining a compressor speed with the turbocharger control element in the open position on the basis of the modeled exhaust gas back-pressure with the turbocharger control element in the open position, wherein the base boost pressure is determined on the basis of the determined compressor speed with the turbocharger control element in the open position.

9. Method according to either of claims 4 and 7, further comprising: obtaining (430, 431, 432) a fresh air mass flow rate, in particular determining a normalized fresh air mass flow rate; and determining (433) a pressure ratio across the compressor with the turbocharger control element in the open position on the basis of the compressor speed with the turbocharger control element in the open position and the fresh air mass flow rate, wherein the base boost pressure is determined on the basis of the pressure ratio across the compressor.

10. Method according to claim 9, wherein the fresh air mass flow rate is measured or modeled (430).

11. Method according to claim 9, wherein the pressure ratio across the compressor is determined (433) by means of a compressor characteristic map.

12. Method according to any of claims 9 to 11, further comprising: determining (434) a compressor-upstream pressure upstream of the compressor, wherein the base boost pressure is determined on the basis of the pressure ratio across the compressor with the turbocharger control element in the open position and the determined compressor-upstream pressure.

13. Engine control unit (3) for an internal combustion engine (1) comprising a gas conduction system (2) with a turbocharger (20) which has a compressor (202), a turbine (200), a shaft connecting the compressor (202) and the turbine (202), and a turbocharger control element for varying a flow velocity through the turbine (200) or a pressure ratio across the turbine (200), wherein the gas conduction system (2) comprises a throttle valve (21) arranged downstream of the compressor (202) in the flow direction, wherein the engine control unit (3) is designed to perform a method (4) for determining a base boost pressure of a gas conduction system of the internal combustion engine according to any of claims 1 to 12.

14. Internal combustion engine (1) comprising a gas conduction system (2) with a turbocharger (20) which has a compressor (202), a turbine (200), a shaft connecting the compressor (202) and the turbine (202), and a turbocharger control element for varying a flow velocity through the turbine (200) or a pressure ratio across the turbine (200), wherein the gas conduction system (2) comprises a throttle valve (21) arranged downstream of the compressor (202) in the flow direction, wherein the internal combustion engine has an engine control unit (3) according to claim 13.

15. Motor vehicle comprising an internal combustion engine (1) according to claim 14.